Metallographic Investigation of the Iron, Iron-Carbide, Iron-Boride System Citation Clark, Donald Sherman (1934) Metallographic Investigation of the Iron, Iron-Carbide, Iron-Boride System. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/KKRD-7J80. https://resolver.caltech.edu/CaltechETD:etd-05132003-154630 Abstract No abstract. Item Type: Thesis (Dissertation (Ph.D.)) Subject Keywords: Mechanical Engineering Degree Grantor: California Institute of Technology Division: Engineering and Applied Science Major Option: Mechanical Engineering Thesis Availability: Public (worldwide access) Research Advisor(s): Unknown, Unknown Thesis Committee: Unknown, Unknown Defense Date: 1 January 1934 Record Number: CaltechETD:etd-05132003-154630 Persistent URL: https://resolver.caltech.edu/CaltechETD:etd-05132003-154630 DOI: 10.7907/KKRD-7J80 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 1766 Collection: CaltechTHESIS Deposited By: Imported from ETD-db Deposited On: 14 May 2003 Last Modified: 03 Oct 2019 23:11 Thesis Files Preview PDF (Clark_ds_1934.pdf) - Final Version See Usage Policy. 83MB Repository Staff Only: item control page

METALLOGRAPHIC INVESTIGATION oF THE THON, TRON-CaAnBIDE, TRON-BORIDE SYSTEM Thesis by Donald S. Clark In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology, Pasadena, California, i034. Acknowledgments Intreduction References Part I. - Theoretical Considerations Part II. ~ Experimental Considerations Pari Lxperimental Melts Table I. - Experimental alloys Structures of Experivental Alloys Structures of Commercial Alloys Table IIT. - Conmereial Alloys Figure 106 - Concentration Triangle cera) affect of Annealing on the Structures of Commercial Alloys Color Paotomicrograph of Structure Iii. - Paysical. Properties Tffest of Composition on Transverse Sorength and Hardness Table III. - Summary of Tests Figure £16 ~ Strength-Hardness Curves Tavle IV. - Test Data Heat Teeatuen’ Table V, ras) on a Table VI. - Tensile Tests Table VIL. - Compression Tests Table. Vill. - Transverse Toasts Sable Ik. - Stress Strain Relations Thermal Conductivity Pacle X. Figure £17 - Thermal Conductivity Curve Summary Bibliograpiy R04 ACKNOWLEDGMENTS The writer desires. to express his appreciation to The Industrial Research Laboratories of Los Angeles, California, for furnishing all.materials ond much of the equipment used in carrying out this research and for bearing the entire financial burden of the work. Appreciation is expecially extended to hin, Walter #. Hirsch, Chief Metallurzist of the. Industrial Research Laboratories, for his untiring efforts in assisting in the preparation and analysis of alloys for this research. Appreciation is also extended to the other members of the staff of the Industrial Research Laboratories who have made this investigation possible. Deep appreciation is extended to Professor William Howard Clapp of the California Institute of Technology for his helpful eriticisu in tuis work and to «ll otuers who have contributed in auy way to this investigation. The writer also wisnas to extend his appreciation to Professor G, Tammann of Gottingen, Germany, for suggestions in connection with the Literature snd to Professor Franz viever of Dusseldorf, Germany, for his assistance in the review of the Litereture, METALLOGRAPHIC INVESTIGATION or THE TRON, IRON-~CARBIDE, IRON-BORIDE SYSTEM INTRODUCTION This thesis presents the results of certain investigations which the author has carried out during. the last three years on alloys of the ternary system iron, iron-carbide, iron-boride. The report deals largely with metallographic features but there is also given a discussion of certain: physical properties of a group of these alloys which is commercially important. The system, iron-carbon,has been investigated and discussed more fully than any other binary alloy. The system, iron-voron, has also been reported upon by a number of investigators, With one exception, no work has been done upon the ternary systen. This is probably due to a feeling that these alloys are of no commercial importance. Within the last three years, sowever, it has. been shown that a certain group of these alloys is extrenely hard and wear-resistant and that they also possess other valuable properties. Some of these properties are a low melting temperature, an ability to form a strong metallic pond with steel and other alloys, and low thermal conductivity. This combination of proper- ties has made it possible to flow the metal onto a backing surface GY e of steel to form a thin wear-resistant welded overlay, suitable for liners and other applications requiring wear resistance. Because of its relatively low cost, it competes with other pro- cesses such as nitriding, carburizing and chrome plating. An investigation of the ternary system, iron, carbon, boron was made in 1922 at Gottingen dy R. Vgel and G. Tammann. Cooling eurves of numerous alloys were determined and used to establish equilibrium relations of the phases. The authors did not discuss the mechanical oroperties, except for those alloys having a very low boron. and carbon content. The work on the equilibrium rela- tions was carefully performed and the present author has been guided by it in his investigation of micro-structure and phase relations. Sous vork appears in tha literature on the dron-boron system, the most important of which is that by Vagel and Tammann!, and Wever and Miller®. The work of Vigel and. Tammann was in connection with their investigation of the ternary system, which has been discussed briefly above. Other work was done on this system by G. Hannesen®, and N. Tscheachewsky and A. Herdt*. In general, Vdgel and Tammann, Hannesen, and Tscheschewsky and Herdt agree on. the phase relations, with some minor exceptions with regard to trans- formation temperatures.. Wever and Miller at Disseldorf, however, show. some disagreenent with the other investigators in the increasing ee * solubility of boron in gamma iron. They attribute this difference to the imowrity of the melts used by the first mentiomed. investi- getors in that carbon, Silicon, and particularly aluminum being present effected this difference, yielding false results. ‘However, Vever and Miller,in their investigation to determine the effect of these elements on the squilibrium relations of iron and boron, considered only small amounts of carbon, Hence, little information can be obtained from their research with regard to the ternary system as concerns the phase relations and none with regard to the properties of such ternary alloya. The effect. of impurities such as silicon and aluminum will be considered in the theoretical considerations in the next section, based on the investigation of Wever and Miller, In general it can be said, from the existing information, that the effect of boron on iron-carbon alleys low in carbon is to increase hardness and brittleness, resulting in a relatively useless vroduct. No mention has been made of the effect with higher carbon contents, ther than the assumption that the same effect is carried to higher carbon alloys. The writer has found by expericnce that iron-carbon alloys with high earbon contents containing boron have commercial applications because of their resistance to wear, Henee- forth lu this thesls emphasis will be placed on the alloys with relatively high carbon content. References: = 1. Végel and Tammann - Zeit. f. An. und Alge. Chemie 121-123, 225-275. 2. Wever and Mtller - Mitl. K. NW. Inst. f. Eisenfors chung zu. Dusseldorf Band XI L. 12 (1929), 3. Hannesen ~ 2. anorg. Chem. €9:(1915) 8. 257. 4. Tscheschewsky and Herdt -~ J. Russ. Met. Ges, 1915 Ref. Iron age 98 (1918) S. 394, cars e PART I. THEORETICAL CONSIDERARTON In order to give a clear understanding of the experimental results of this research it is necessary to present the phase relations existing in the iron-iron-carhide-iron=horide system. The equilibrium relations of this ternary system are represented in the usual way by a. three-dimensional figure with a triangular base representing the composition and the vertical direction representing teuperature. One side of the triangular prism represents the binary system iron-iron carbide, the second side represents the binary systen iron-iron boride, and the third side represents the binary system iron carbide~iron boride. The various transforaations are repre- sented by surfaces ln the space figure. The phase relations of the binary system iron-iron carbide are represented as shown in Figure 1 with composition plotted as the abscissae and temperature as ordinates. Pure iron is represented at the extrene left of the diagram. and pure iron carbide containing €.67% carbon at the extreme right. This systen exhibits a eutectic composed of 4.2% carbon with a melting point of 1150°C., a eutectoid at 0.9% carbon having a transformation temperature of 730°C. The phase fields of this binary system are indicated in the figure. The delta and beta transform. ations are intentionally omitted because of complications involved in an already complicated system and because of thelr minor importance in the ternary system which is to be considered. D C' 825°C. A IRON ~ IRON CARBIDE SYSTEM H40%C 730°C. (egO 6.67 PER CENT CARBON 4.2 17 0.9 ° (Fe) The phase relations of the binary system iron-iron boride are represented as shown in Figure 2 With compositions plotted as abscissae and temperature as ordinates. Considerable argument exists as to the true form of the equilibrium diagram of this binary system. Figure 2 is the diagram proposed by Vogel and Tammann which shows a. sutscetic with 3.8% boron with a melting point of 1165°C. This diagram also shows that the solubility of boron in gamma iron increases with decreasing tenper- ature to about 780°C. with a maximum of 3.2% boron. It also shows a soluvility of boron in alpha iron up to 0.08% boron. The phase fields of this system are indicated in the figure. Figure 3 shows the diagram proposed. by Hannesen which is. similar to that of Vogel and Tammann with the exception of the compositions and transformation temperatures. The results of Tschewsky and Herdt are shown in Figure 4, which is more nearly like that of Vogel and Tammann differing somewhat in com- positions and transformation temperatures. Wever and Miller propose the diagram given in Figure 5 in which they show no increasing solubility of boron in gamma fron. Their sontention is that the method of melting the alloys employod in the previous work introduced carbon and silicon which falsified the results of the previous workers. Further, the ferro-boron used in preparing the melts contained about 4.5% aluminum thus leaving the final melts containing about 1% aluminum, which they feel alters considerably the equilibrium couditions of the binary system. Heneeforth in their a) * A 1530° C. oN E> a J ° 165°C. < K ON | N\ | NN | | | U eo°c. | | 760°C. 2 | iQ _ H I | | ; 1 { | i Alle PE Ee (Fe) 0000 PER CENT BORON 32.38 68 (Fe.8) FIG. 2 IRON-!IRON BORIDE SYSTEM TAMMANN if 1335 sre Ann rset sme ses sete, saute ty emma ste iss spelt, nee san kay Se mn ee me ee ee lt lhe tr cee met, etme an tof mn Simm aim, _ 4.0 PER CENT BORON 7.3 8.0 S15 i420 "> $3aH930 NI 850 750Ki 2UN Lvs ada L 710 00.2 0.7 3 FIG. IRON-IRON BORIDE SYSTEM HANNESEN i540 nN af tard aot’ 1330 —4 |050 5235 PER CENT BORON °* TSCHISCHEWSKY AND HERDT 120 TEMPERATURE IN DEGREES C. iB. T i428 1385 R 1174 p 37 Q | i G l 915 H l i | ea KK i | i i I | 0 0.2 38 2.0 16.2 PER CENT BORON FIG. § IRON- BORON SYSTEM WEVER AND MULLER * 2 win ad research they have attempted to determine the effect of these three elements, carbon, silicon, and aluminum, on: the equilibrium diagram of the binary system iron-boron. To do this they studied the effect of each element on the transformation points of iron and assumed an extrapolation of the results in order to obtain their. diagram of the binary system. The work of Wever and Maller can hardly be questioned with regard to accuracy and technique and undoubtedly their diagram is the most correct of the several proposed. According to Wever and Miller the increased solubility of boron in gamma iron is due primarily to very amall amounts.of carbon. If this is the case, it would be apparent that this condition of increased solubility would occur if not in the oure iron boron alloys, then at a very short distance from the plane of the binary iron boron system. Hence I feel that in the research work for this thesia it ils sufficiently accurate to consider that. the diagr according to Vogel and Tammann approaches the conditions more closely than that of Wever and Miller. In other words, the surface of the upper limit of solubility of boron in gamaa iron, line JPp of Figure 2, . would turn sharply from the binary plane of iron boron system following the surface as indicated by Tammann and Vogel in their ternary diagram, which will be discussed later. The phase relations of the binary system iron carbide and iron boride are shown in Figure 6 as proposed by Tamnann and Vogel. In this system a evteotie is formed with about 3.2% boron-and 1.3% sarbon é fot 4h + 1300" C. 150 ec B ‘(Fe.B) © PER CENT CARBON Fe, y 6.8 PER CENT BORON Cc ‘ 887(FeC) IRON BORIDE -IRON CARBIDE SYSTEM TAMMANN having a melting point at 1150°C. The system shows a solubility of iron ' poride in iron carbide with 6 maxircun of about.1.7% boron and 5.% carbon with decreasing solubility with decreasing temperature. In view of the above discussion the results of Tammann and Vogel Will be used to form the three component equilibrium diagram. Hence, Figures 1, 2, and 6 will form the sides: of the triangular prism, Figure 7. In Figure 7? is shown the concentration triangle of the ternary system (iron-iron curblde-ivun vorlde) iu which the bDiuary equiliprium Giagrams are unflapped. In this figure the projection of the liquid surface is shown bounded by the three eutectic curves E,'R', Ee'R', and Eg'R' end by the binary liquid curves. The point R' ia the projection of the ternary eutectic point onto the concentration triangle. In the discussion to follow, points on the surfaces will be indicated by letters without primes while projected points will be indicated by the corresponding letters with primes. The melting point of this ternary eutectic is 1100°C. In addition to the liquid surfaces, also is shown the boundary of the surfaces of limiting solubility of boron and carbon in gamma iron which terminate in V' along the dotted lines to the level or the ternary eutectic. According to the diagram there are three types of crystals formed at the liquid surfaces depending upon the region in which the alloy exists. ie may cull this surface the erystallization surface, 1.e., the surface at which crystallization commences. In the field A'E|'R'Eg! the first erystals to form will be a ternary solid solution composed of gamma iron, earbon and voran, which we may designate with the letter "T". LG. A A -(Fe) \ | L _ |e | Y p . E, L/Vvi Ss Ri-\E2 M- Ww H (FesC) C’ \ ES B' (FepB) fo) Jp cle FIG. 7 IRON-IRON CARBIDE-IRON BORIDE SYSTEM In the field 3'Eg'R'Es' the compound iron boride (FeoB) will crystallize upon solidification at the crystallization surface over the field referred to. In the field C'E]'R'Eg' a solid solution composed of iron carbide and iroa boride will form upon erystallization of the melt. The ternary solid solution I which forms in the field A'EL'R'Ea! changes in composition with decreasing temperature according to the surface A'L'V'S' which we may call a melt surface, since with rising temperature molting will begin when the temperature of the alloy reaches thie surface. This surface is bounded by the curve AL on the iron-iron carbide diagrem, the curve AJ on the iron-iron boride diagram, the space curve LV, and the space curve IV. Along the curve LV the erystalse. vill be saturated in carbon and along the curve JV they will be saturated in boron, while at V the crystals will be saturated in both carbon and boron. Upon solidification of alloys in the region L'V'R'E,' the composi- tion of the melt will move along the surface HLREA toward the eutectic ‘suive EVR in some curve until the eutectic curve is reached, whereupon Secondary crystallization commences. Alloys in the field I'V'R'Ee' upon solidifying will move along the same surface as mentioned above toward the eutectic curve EgR in some curve until the eutectic curve is reached, whereupon secondary crystallization will begin. In the region Ee'BIRt the melts will move toward the eutectic curve EgR on the surface BEeREg in the same way as in the above case. In the fiela BIR 4st the melt will move along the surface BEgREg toward the eutectic curve EgR in a menner similar to those mentioned above. In the region N'RtEg' the melt will ~move along the surface CELRES toward the eutectie curve EgR along some curve until the eutectic curve is reached, whereupon secondary crystal- ligation takes place. In the field Cth, 'R'N' the melt moves toward the eutectic curve £)R along some curve until it reaches the eutectic curve, whereupon secondary crystallization takes place, By secondary crystallization is meant crystallization from the melt in which the separation of two types of crystals takes place at the same time and are in equilibrium with the melt. At the end of primary erystallization the composition of the melts will lie along the eutectic eurves,as indicated above. Melts lying along the cutvelic curve EV|R will be in equilibrium with solid solutions corresponding to the curve LY and with solid solutions corresponding to the curve MN. Melts on the curve EpgR will be in equilibrium with solid solutians corresponding to the curve JV and with the compound iron boride. Melts on EgR will be in equilibriwa with the solid solution N and the iron voride. A tertiary crystallization will occur for all alloys lying in the composition range V'N'3', since the melts of alloys in this field ena in the ternary eutectic point R. The melts ending with this composi- tion precipitate the ternary solid solution saturated in iron, carbon, and boron; iron boride; and the solid solution N of iron earbide end izon boride, Since there are four phases in equilibrium at this point, the transformation or precipitation will take place at constant temperature forming a eutectic structure. id. To summarize the foregoing material it might be well to explain what. occurs during the crystallization of alloys in the various fields and thereby clarify the wxuception of the various surfaces existing in the ternary system. Consider an alloy ,G in the region L'V'R'E,' of Figure 8, When the temperature of the liquid alloy has reached the erystallization surface at t) it will be in equilibriua with a solid of the com- position ,o' which is on the surface ALVT at the temperature tis Tails solid will be a solid solution of gamma iron, iron carbide and iron boride. As the tempereture decreases the composition of the solid will change according to sone eurve such as drawn between 2' and x". The composition of the liquid will change from that of 79 to that of Y in some curve. The line joining the solid and licuid at any temperature must be straight and must also pass through the vertical through ,@. The points fand j* can easily be located if the isotherms are kuown because only one straight horizontal line can be drawn through /G between the curves LV and HjR at one given temperature. At temperature to the melt y will be in equilibriwn with the ternary solid solution y' and the binary solid solution y''. As the temperature lJecreases secondary crystallization takes place. ue composition of the melt changes according to the curve ER and the solid solutions seeording to their respective curves, CjN and LV. When the temperature has reached tg the line (Fe A + LIQUID-SOLID SURFACES connecting delta prime and delta double: prime will intersect the vertical through Qwhich indicates that. solidification has been completed. The lest melt to exist in equilibriws: with the solid will be at delta. The triangles formed by the three phases are designated as three phase triangles. Another way of considering the salidification from the point y¥' is to consider the composition of the solid as whole rether than to break it wo into its two ohases. In this case we would consider the line «'r to rotate around the vertical throuch “4, avproaching delta,and y¥' approaching 3 in a curved path which can be easily deternined from knowing the vosition of the isotherms. In this way the lever arm principle can be applied very easily to determine the anownts of phases in equilibrium at any instant. Sow consider an alloy Gin the region Btig'R' of Figure 9. When the termperature of the liquid alloy has reached the erystal- lization surface at t,. the melt will be in equilibrium with eryetals of tren boride represented et Bt. As the temperature continues to decrease more crystels of iron boride will form and the composition of the Liquid will follow over the horizontal line YB! until the point Y is reached. at temperature te where the primary crystallization will be completed. At this point the melt _¥ must be in equilibrium with iron boride and the solid solution Nt. With further cooling the composition of the melt will change y FIG. 9 LIQUID-SOLID SURFACES Pe tx * according to the curve EsR and more iron boride will we precini«#= tated and, in addition, solid solution N' will be precipiteted, When tie temperature tg is reached the melt will be of the com- position of the ternary eutectic and hence will solidify at constant ‘temperature and will be composed of iron boride, ternary solid solution, und binary solid solution N. According to the second method of consitering the soliditi- cation as used in the previous case, when the connoesition of the melt reaches ¥ and proceeds along the eutectic curve ,thse line connecting Y and Bt can be considered to turn about the vertical through @ thus intersecting the £3'3' and LgiR!, 3y this method the relstive amounts of each phase can be found by the usual lever arm law. in the region Ep'R'V'J' the crystallization will be very eimilar to the process that took place in the region L'V'RtE,' of Figure 8 except that instead of two solid solutions deing: in equilibrium with the liquid during the Secondery crystallization, there will be an equilibrium between the ternary solid solution represented by the composition along the curve JV and iron borides as represented in Figure 10. In this figure the three phase triangles are given as in the previous eases. The method of analysis is the same as in the previous cases and, hence, will not be taken up again, (Fesc)C N Ey B' (Fe2B) LIQUID-SOLID SURFACES 25. Any alloys falling in the region L'V'J'a’ will be completely solic at the end of the primary erystallization and will be composed entirely of a ternary solid solution of gemma iron, carbon and boron as represented by its position in the field. An alloy of composi- tion V will end its solidification in a solid solution of gamma iron saturated in both carbon and boron. The above completes the discussion of the process of crystel- lization from the melts and it now remains to diseuss the trans- formations in the solid state. In Figure 11 is shown the concentration triangle on which surfaces of transformation in the solid state are projected. One of the limiting surfaces of the ternary solid solution is given by the projection J'Po'SV'J' intersecting the iron-iron boride binary system in the curve JPp. In this case the solubility of boron in gamma iron increases with decreasing temperature. Another of the Limiting surfaces of the bernary solid solution is given by the projection L'V'SP ,'L' intersecting the iron-iron carbide binary system in the curve LP,,. This surface shows a decrease in solu- bility of carbon in gamma iron with decreasing temperature. Another limiting surface of the ternary solid solution exists in the projection U'Pe'sSPl'u' (Uteoincides with At in the eoncen- tration triengle) intersecting the iron-iron horide hinary diacram in the curve UPp and the iron-iron carbide diagram in the curve UPl. This surface is the limit of the existence of garma iron and the 264 Cc “— FIG. 11 SOLID TRANSFORMATIONS a “J beginning of the formation of alpha iron. Tn order to make these surfaces clear, let us consider them separately with respect to an alloy within the region of each, Tn Figure 12 is shown the projection of the surfaces J'Po'SV'I' and A'I't*v'L'at, The cooling of alloys within the region A'J'V'Ltat was considered in erystallization from the licuid state and henee will not be repeated here. Consider an alloy “/in the region 3'V'SPo'T', upon completion of crystallization the alloy consisted of ternary solic solution of the composition corresponding ta A! and erystals of iron boride. With further cooling the point <' Will move toward ,g over the straight line 4’ 938° on the surface under consideration. When the point 9 is reached the alloy will consist entirely of ternary solid solution of the composition fe ‘ 4ny alloy within the region P2'SB' would transform in much the same way except that in this case ,g' would meet the curve Pes and further transformation would teke place along this curve which will be explained later. Now considering the two surfaces which intersect in PS, Figure ig. Take an alloy 3 in the region Pe'SQ’. Above this surface the alloy will be composed entirely of ternary solid solution as noted from the previcus example in Figure 12. When the temperature has docreased sufficiently gueh that the point /3 touches the plane PeSP1U a solid solution of alpha iron and boron will begin to ore- 28. FIG. {2 SOLID TRANSFORMATIONS SOLID FIG. 13 TRANSFORMATIONS oO. eipitate out at f' Guring further cooling the composition of the alpha solid solution will move on the curve UQ toward Q. At the same time the composition of the ternary solid solution will move on the surface under consideration in some curve from /3 te Yr. When this condition has been reached the ternary solid solution Will be in equilibrium with 9' and B'. With farther cooling the ternary solid solution moves along the curve PoS to S passing through the point delta. At S the ternary solid solution of compos- ition corresponding to S is in equilibrium with iron boride (B') and the binary solid solution Q’ of iron boride and alpha iron, With further eooling tho romaining tornary eolid solution transforms into a ternary pearlite composed of iron boride (B'), solid solution of iron boride in alpha iron (Q'), and solid solution of iron boride in iron carbide (Z'). Hence, the resulting alloy will consist of an exeess of solid solution Q' and the ternary pearlite. Alloys in the region Poe’B'S will cool in much the same way except that iron boride will continue to precipitate until the curve Pes is reached. This will produce an alloy with an excess of iron boride with the ternary pearlite. Consider now an alloy @ in the region P,'SQ' of Figure 14 which will be composed entirely of ternary solid selution above the surface in question, When the temperature has decreased such that @ touches the surface under consideration, solid solution of FIG. 14 SOLID TRANSFORMATIONS B26 alpha irom and boron Will be precipitated at /3'. With further cooling the composition of the alpha solid solution will change according to the curve UQ and the composition of the ternary solid solution will change along the surface in quootion moving toward and ending in the point Yon the curve PS. At the point y the ternary solid solution will be in equilibrium with alphe iron boron solid solution and the solid solution of iron boride in iron carbide of composition ¥'. With further cooling the com- position of the ternary solid solution changes along the curve P1S. At the temperature at which the line joining 9' and y' intersects the vertical through fo, the ternary solid solution will be con pletely decomposed, the resulting produet being an exeess of alpha solid solution with a eutectoid composed of delta prime and 9°. The last composition of the ternary solid solution was that of peint delta. If the point had been within the region 9'Z'Bt some ternary pearlite would have been formed. Alloys lying in the region Py *SL'will transform in much the same way as in the previous case exeept when the point ,9 correspond~ ing to the composition in this range touches the surface in question solid solution of iron boride in iron carbide-will be precipitated from the ternary solid solution. When B reaches the curve PiS the transformation will take place as outlined above. Boe An alloy lying in the region B'SY', in Figure 15, on the sur- face BVT will consist of iron boride and ternary solid solution @'. Ag the temperature is decreased the composition of the ternary solid solution will move on the surface PeVI over the straight line ~'SB" to yt. At this point the ternary solid solution fr' will be in ecuilibrium with iron boride and the solid solution ¢'', With éecreasing temperature the composition of the ternary solid solution will change according to the curve VS moving toward S. The composi- tion of the binary solid solution yx'* will change according to the wurve NZ moving toward Z'. When the temperature of S is reached the remaining ternary solid solutian will transform to ternary pearlite consisting of 9', B', and Z'. Therefore the resulting alloy shoulé be composed of ternary pearlite, solid solution Z', and iron boride. Alloys lying in the region N'x'y'Bt of Figure 15 will consist of ternary sulid solution V’, binary solid solution N*, and iron boride in the plane of NtV'B'. With decreasing temperature the composition of the ternary solid solution moves down the curve V'S as in the previous case, The composition of the binary solid solu- tion will move down NZ as previously. The end product will consist then of the same phases as in the previous case; namely, ternary pearlite 8, iron boride, and binary solid solution 2’. Alloys in the other portions of this three phase triangle will Boe FIG. 15 SOLID. TRANSFORMATIONS £2 on e éecompose in similar manner to the previous ease. In these cases just cited it should be noted thet the surface N'x'V'SX'Z' has a serew shape. The phases or constituents in equilibrium in the various areas are shown on the concentration triangle, Higure 16, at room temperature. és ca Z+B'+ S FIG. 6 CONCENTRATION TRIANGLE PART II. EXPERIMENTAL CONSIDERATIONS The experimental pert of this rescarch problem may be divided tuto three parts. First, the investigation of relatively pure alloys of iron, boron, and carbon in order to determine the more nearly perfect structures of the system for comparison with the commercial melts. Second, the investigation of the structure of commercial alloys to study the comparison between the relatively pure melts end their relation to physical properties. Third, the investigation of the physiesl properties of some of the most important and useful alloys existing in this system. Experimental Melts For the first part, seventeer alloys were made up in induction furnace in which Armco iron, carbon, and Perro~boron were used as the components. The Ferro-boron was obtained from the Electro Metallurgical Company of New York. It was composed of 48% Boron, 1,55% Silicon, 1.54% Aluminum, 6.14% Carbon, and the balance mostly iron. These alloys were melted in Mullite crucibles in smell amounts, sufficient for metallographic exeminations. The chemical analysis of the alloys produced is given in Table I. The positions of these alloys are viotted in the concentration triangle of Figure 104. TABLE I, EXPERIMENTAL ALLOYS Spec. % C. %B, %Si. SAL. PY Figure Number Number As Cast Annealed 1 9,45 3404 25, 24, 25, 26 27, 28 EA] 0.23 8.52 0.68 0.37 9.01 17, 18,19, 20 281, 22 3 1.19 5.86 C.41 6.31 6.0L 29, 30, 2 BL, 3S 4 1,2. 4.34 34, 35, 36 37, 38 5 28,89 S.86 0.90 0,08 0.01 43, 44 45, 46 6 2.71 4.20 39, 40 41, 42 8 1.84 5.35 47, 48, 49 50, SL 9 2.18 2egd 62, 65, 84 65, 66 10 3.23 1.16 93, 74, 75 76, 77 11 2.83 2.91 52, 53, 54 55, 56 12 l.2l 2.60 0.17 0.09 0.01 83, 84, 85 . g6, 87 1S 2.21 © 2.31 67, 68, 69, 70 71, 72 14 8.99 2.81 67, Se, 59 60, 61 15 1.22 1.28 0.07 78, 79, 80 B1, 82 16 2.14 i.el 88, 89, 90 91, 92 17 «2.41 1.le 93, 94, 95 96, 97 12 3.80 0.96 0.04 5.07 0.01 98, 99, 100 ici, 102 Trees alleys were preduced by firet making on iren searbon alloy frera Armeo iron ané pure earbon in the induction furnace. The proper anount of this iron carbon alloy, Armco iron, and Ferro-boron to mke the desired composition was placed in the crucible and covered with berax. ‘The ervucible was then placed in the furnace. when the alloy was completely melted it was stirred and then poured into a metal mold. After being cast the alloys were analysed as shown by the table. After the alloys were cast a portion of each was packed in carbon and ennealed at 1800° F. for one hour and allowed to escol slowly from this temperature. In the metallographic description which follows each alloy is given a number. These numbers are shown underlined in Figure 105 from which their composition and position.in the ternary system may de seen. Structures of Experimental Alloys Let us now consider the structures of these alloys in conjunetion with the equilibrium diagram... All specimens were first ground in the autometie polishing machine designed hy Professor W. H. Clapp and the author which insured flat surfaces and not too fast but efficient polishing. The specimens were then finished with 600 alundum powder and six hour settlement alumina suspended in water, Most of the specimens were etched five minutes in bolling Murakami's reagent, cousisting of LO% sedium hydroxide, 10% potessium Ferricyanide, and 40. 80% distilled water. A fracture surfaces of specinuen number 2 containing $,.52% doron anc 0.22% carbon is shown in Figure 17, The metal itself is very dense, but the ingot showed considerable amount of sHrinkage holes. Figure 18 shows the microstructure at a magnification of 100 dia~- meters, Figure 19 at 500 diameters, and Figure 20 at 2000 diameters shows the detail strueture. Figures 21 and 22 show the strueture after annealing at 1800° F. In this alloy one should expsct to find a very large amount of iron carbide and a very small amount of ternary pearlite, The cast structure does not show just this arrangement. Figure 1¢ shows a ground mass consisting of primary iron boride which separated out during the primary crystallization; the darker stringy strueture is composed or the iron boride precipitated Trom the ternary solution, and the light spots the binary lLron earbide-iron boride solid solution precipitated in the ternary pearlite transformation, The stxuature does not take on the expected appearance because of rapid cooling in the mold. After annealing the two constituents. thrown out of solution have agglomerated somewhat although not as completely as shown in Figures 21 and 22. Figure 83 shows the fracture of specimen number 1 containing 3.64% poron and 0.45% carbon. The fracture shows definite fine needies in a very dense metal, The porosity was not very great, one or two good sized shrinkage holes were observed. Figures 24 to 26, S . _ ZS oe _ Bee _ Sy . . . S — : es me a | . . oo. . _ xe oe . ok inclusive, show the microstructure of this alloy as cast and Figures 27 and 28, the structure after annealing at 1800° F. These photo- micrographs would tudicate that supercooling had again taken place in the cooling of this alloy which effect was not removed by annealing, We would normally expect a structure similar to that predicted for the previous alloy; i.e., primary iron boride with ternary pearlite. These figures show some primary iron boride, the dark fairly regular prisms. in Figures £4 to 26, inclusive, and white in Figures £7 and 28. Also, secondarily separated iron boride is shown as the inner gray struéture and last the pearlite structure surrounded by the mixture of binary solid solution iron boride in iron ecerbide and the solid solution of iron boride in iron, shoym by the white matrix material, This ternary pearlite is shown in Figures 24 and 27 as gark clusters because of the fineness of the stnucture. Figure 29 shows the fracture of specimen number 3 containing 5.60% buruu aud 1.19% carvon, The fructure shows a very asnse material which sparkles, probably due to the iron boride crystals embedded in its matrix. No porosity was evident in this material. The structure expected here shown consist of primary arains of iron voride in rather large amounts together with a relatively large amount of binary solid solution of iron boride in iron cerbide with a very small amount of ternary pearlite,. Figures 30 and Sl show the structure obtained on casting and Figures 32 and 33 the atructure efter annealing at 1800° ¥. The ee primary iron boride is very evident as regular white prisms surrounded by a rather lerge amount of the iron carbide solid solwtion in which is embedded the ternary pearlite. In Figure 31 considerable coring is noticeable in the ternary pearlite due to lack of equilibrium eonditions. In the case of the annealed structure the binary alpha iron iron berids solid solution has probably mixod with the iron carbide solid solution and hence is not distinguishable. The white finer structure in Figure 34 is probably the iron boride of the ternary pearlite. Figure 34 shows the fracture of specimen mamber 4 containing 4,62% boron and 1.21% carbon, This Yraecture snows quite a dense material with sparkling needles undoubtedly due to the primary iron boride. Some slight porosity is observable. In this ease a structure similar to the previous alloy should be expected except with a smaller proportion of iron voride (primary) and iron carbide solid solution: with a greater proportion of ternary pearlite., Figures 35 and 36. show the structure efter casting and Figures 37 and 38 after annealing at 1800° F, Very considerable coring is observed in this structure around the primary iron boride. This is probably due to the separation of the ternary euteetic in which the iron boride that separates collects around the crystals existing at that temperature, The remaining material will be con-~ posed of the iron-iron boride solid solution and iron earbide solid solution, This lest approaches more nearly a binary pearlite. Figure 29 shows the fracture of specimen number 6 containing 4,2% boron and 2.71% earbon. The fracture shows a dense structure tending to be granular with some cleavage. No porosity was ob- served in this specimen. Figure 40 shows the structure of this alloy as cast and Figures 41 and 42 show thé structure after annealing at 1800° F. In this ease we should expect considerably more iron carbide solid solution with less primary iron boride than was found in specimen munber 3 which lies in the same concentration region, We should also expect a small amount of ternary pearlite. The structure actually shows these constituents to be present. In Figure 40 the primary iron boride is evident as the white regular prisms, the ivou carblds sblid solution as the gray ground mass in which is embedded the smail amount of ternary pearlite. After annealing the primary iron boride appears to be the same es before, but the ternary pearlite has been broken up so that the iron iron-boride solid solution has blended with the iron carbide solid solution leaving only the secondarily separated iron boride in small segregations es shown in Figures 41 and 42, Figure 42 shows the fracture of specimen number 5 containing 3,88% borgn aud £,83% carbon, The fracbure shows a deuse structure with some cleavage about as shown in Figure 6 and no porosity is observed. Figure 44 shows the structure after casting and Figures 45 and 46 show the structure after annealing at 1800° F. In comparing this alloy with the structure found in number 6, we find less primary iron boride as predicted by the diagram with somewhat more ternery pearlite. Figure 47 shows the fracture of specimen number 8 containing %,35% boron and 1.84% carbon. ‘The fracture shovs a very dense structure which is very granular, Neo peresity was observed in this alloy. Figures 46 and 49 show the structure after casting and Figures 50 and 51 show the atructure after annealing at 1800° F. Some primary iron boride should be expected in this structure in view oP its position in the concentration triangle. ‘Some ternary eutectic would be expected which dissociates into ths three types of crystals. The photoulcrographs do not show any primary iron boride, but show what might be considered to be either primary or secondary iron earbide solid solution precipitated during primary erystallization or during secondary erystallization. Probably the actual case in this alloy was that super-cooling took place preventing the primary separation of iron boride and brought about. the separation of the tron carbide solid solution during secondary erystallization, The ternary eutectic dissociates into the iron boride, iron earbide solid solution, and the iron iron-boride solid solution which may be represented by the fine eutectic appearing structure. This sompletes the study of these alleys in the region ean= taining primary iron »oride. According to the concentration tri- angle specimen number 11. should lie on the eutectic curve Esk, Fisure 103, or possibly a little on the side which would produce primary iron carbide solid solution. Let us see what the atructure Figure 52 shows the fracture of specimen number 11 containing 2.91% boron and 2.83% carbon. The fracture shows a very dense materlal,whieh cleaves readily along plates. Figures 523 and 54 show the structure after casting and Wigures 55 ana 56, arter annealing at 1600° F. The structure appears to lie about on the eutectic curve referred to, in that the photomicrographs show a large masa probably of iron boride and imon earbide solid solution. This is substantiated by the apnear- ance of Figure 54 showing a very fine net work structure: within the large rounded gray areas. The remaining material should te ternary pearlite, which, as has been seen before, breaks up into its constituents,as particularly shown in the annealed specimen, Figure 5¢, tnwhieh only iron boride is shown in the ground mass. Figure 57 shows the fracture of specimen number 14 containing ¢ boron and 2.97% carbon. ‘The fracture showa very dense structure having a granular form. Figures 58 and 59 show the structure after casting and Figures 2 ee re ae ae ue oe Se cae oe es i a ke ol G 4 69 and 61 sho es) < y the structure after annesling at 1800° F, The structure expected here should be primary iron carbide solld solu- tion with the ternary pearlite. This is showm to be the case in the photomicrographs. In Figure 58 the white constituent is the {ron carbide solid solution while the finer interlacing structure is then ternary pearlite. Figure 50 shows this structure to be relatively homogeneous and hence might be the ternary solid solution whieh hes been too rapidly cooled ta allow disseciation inte its three components. In Figure 60 is shown about the same structure, except that the colors are reversed and the mtrix material has vecome eularged. This ls undoubtedly due to very slow cooling dur- ing the pearlitic transformation which.allowed complete separation of the two types of solid solutions leaving the iron boride as the white constituent,as we have seen in some of the previous alloys. Figure 62 shows the fracture of specimen 9 containing 2.58% boron and 2.18% carbon. The structure shows a very dense granular structure with no porosity. From the position of this alloy in the system we should expect about the same structure as we found in the previous alloy, except that less iron carbide solid solution should be present with more ternary pearlite. Also, in view of its position in the system, we might expect to find more of the ternary eutectic structure which may explein the eutectic-appearing portion of the structure, as FO. shown in Figures 65 and 64, The white constituent is the primary and seconcery iron carbide solid solution. In this case, aiso, it is apparent that insufficient time has been given to allow the dissociation of the ternary pearlite of which the ternary sutectic will consist. In Megures 65 and 66 is shown the structure after annealing at 1800° F. This shows the same condition as existed in the previous ailoy, that after annealing the ternary pearlite was dissociated into its components leaving the iron boride white and the mialure of iron carculde svllid solution end iron, ireucboride solid solution dark. Figure 67 shows the fracture of specimen number 1t containing 2.81% boron and 2,21% carbon. The fracture shows a very porous easting which is mostly due to shrinkage,as is epparent fron the white bright surfaces of the holes, The metal itself is dense and granular, Since the composition of this alloy lies very close to that of the previous alloy, one would expect. to obtain a simller struc- ture with somewhat less primary iron carbide solid solution, if any. The composition lies so near to the eutectic curve, EAR, that it should consist of possibly more ternary solid solution and iron eerbide solid solution. In Figures 68, 69, and 70 is shown the structure of this alloy in which there is apparently some primary ipon carbide solid solution surrounded by a very large amount of 73, materiel of ternary eutectic orligin,.as might be expected. igures at 71.and 72 show the structure efter annealing at 1600° F. in which no extremely large primary solid solution is observed, indicating that the condition shown in the cast state is false, The structure of the ternary eutectic has been obliterated and the usual dis- sociation has occurred, as indicated above. Figure 73 shows the fracture of specimen number 10 conteining 1.16% boron and 3.23% carbon. The fracture shovs a very dense structure with plates which show cleavage and no porosity. According to the concentration triangle, this alloy should oomtaln ternary pearlite with considerable iron carbide saolid solution and a very small amount of iron boride. The structure, as shown in Figures 74 and 75 for the cast condition, present plates of a primerily separeted crystal which can only be interpreted to be the iron carbide solid solution which could separate along the C4 curve. The fine sutectic~appearing structure has the appearance 4 of a binary eutectic. Such a structure would indicate thet the curve NY was shifted to the right of where it has seen placed by Temmean and Vogel,in that such a structure would be expected in the region between C and Hy, and N, in whieh we have the binary eutectic f iron, iron-boride solid solution and iron earbide solid solution. This conception is further borne out by the structure exhibited by ie) Re a) o Sq rs iz + cae er 18, Figure 98, In Figures 76 ané. 77 is shown the same a Bo. alley after annealing at 1800° F. Nothing wnusual has occurred in this structure by annealing, except a coarsening of the fine eutectic structure by more thorough separetion of the solid solution constituent. ie) Figure 78 shovs the frecture of specimen number 15 containing 1.29% boron po né 1.22% carbon. The fracture shows an extremely éense structure with very fine erain. s far from wheat he The photomlcregraphs snow a structure whick oh would be expected; viz., a large amount of ternary pearlite with some 0] excess of iron carbide solid solution ané iron boride, These are § not apparcnut Prom Figures 79 end 80 in the cast condition and from Figures 81 and O£ which have been annealed at 1800° F, One explan- ation which aight be offered for this structure, is that the tron carbide solid sulution has been theroughly divorced from the ternary pearlite producing the typical large rounded white structure vhich is surrounded by a binary~appearing pearlite. Such a condition is quite reasoneble in view of the fact that equilibrium conditions undoubteély did not exist and are hard to attain in this alloy. Figure 86 shows the fracture of specimen number 12 containing 2.6% boron and 1.21% carbon. The fracture shows a very dense granular structure with considerable porosity in the casting. In this ease, we should expect considersble ternary eutectic with some excess of the ternary solid solution which, upon slow 88, cooling under equilibrium conditions: would disintegrate to the ternary pearlite. This condition is actually shown in Figures 84 and 85. The white dendritie structure is the primary ternary solid solution while the ground mass is the ternary eutectic. This structure 1s almost completely removed by annealing at 1e00° Fey as shown by Figures 86 and 87, which should and does show this ternary eutetti¢ as transformed to the ternary pearlite with some excess of iron carbide solic solution. Figure 88 shows the fracture of the specimen mumber 16 contain- ing 1.21% boron and 2.14% carbon. The fracture shows ¢ very dense fine grain structure that has a tendeney to cleave, The structure in the ease of this allov should consist of an excess of ternary sclid solution with ternary eutectic. This is shown in Figures 89 anc 90, in which the white structure ia the ternary solid solution and is surrounded by the ternary eutectic. Upon annealing this exeess solid-solution is not obliterated, but apparently does transform into the ternary pearlite, as indicated by Figures 91 and particularly 92, In Figure 92 some pearlite is eistinguishable in Lhe white structure. This termary pearlite is very difficult to bring out with etching, and, hence, may in most cases be obscured. The ternary sutectic after annesling has been pretty well disintegreted into its constituents. Figure 96 shows the fracture of specimen number 17 containing 1,18% voron and 2.41% carbon. The fracture shows a cense structure containing Tine needles, According ta the eoncentration triangle, this alloy shaula consist of ternary pea Lite with some excess iron carbide solid solution. Figures 94 and 95 show this strueture in which we have some iron carbide solid solution as the gray material surrounded by material probably formed from the eutectic, consisting initi- ally of iron carbide solld sulubignu aud Lernury sulld solution, Figures 96 and 97 show the structure after annealing at 1eco0° F, The eutectic structure has been broken up completely, leaving the unresolved ternary pearlite (white) and the iron carbide solid solution. Figure 96 shows the fracture of specimen number 18 containing 0.96% boron and 3.80% carbon. The fracture shows a dense material containing plates, The microstructure of this alloy is shown in Figures 99 and 100 as cast showing primary separation of the iron carbide solid CO] olution which has the form usually taken by pure iron carbide in a hyper-eutectic iron carbon alloy. This. is surrounded by the eutectic which separated along the curve E,R which presents more nearly the structure of a binary pearlite., Figures, 101 and 102 show the structure after annealing at 1800° F. This shows that the eutectic structure has been very thoroughly disintegrated, leaving only the mixture of binary peerlite, consisting of Lrou, iron~bubide solid solution (white) and iron carbide solid solution dark. ~ ‘ . ve aS s AoE Lol. The results of this part of the investigation check very well with the equilibrium diagram. ‘The microscopic investigation of alioys for checking a complicated system, such as this, is very difficult, beeause absolute equilibrium or even conditions which approach equilibrium are very difficult to obtain. However, the results show, for all practical purposes, the structures obtained in this system follow the diagram proposed by Tammann and Vogel insofar as the liquid-solid transformations are concerned. Structures of Commercial Alloys As pointed out in the introduction, the most. useful alloys have been found to lie in a relatively restricted composition range, For the remainder of this thesis, the structures and properties of alloys will be considered which, with a few exceptions, have proven to be of considerable value commercially in their resistance to wear. Wo attemot will be made here to discuss the relative merits or the various alloys from the standpoint of wear resistance since this thesis is concerned with the metallographic investigation. Hence, the remainder of the discussion of the experimental work will be devoted to the metallographic structure of the alloys in this region and their physical properties. The compositions of repre- sentative alloys used in this part of the research are listed in Table II. and plotted on the ternary concentration triangle shown in Figure 105. The specimen numbers underlined in this dtagrem refer to the alloys used in investigating the equilibrium diagram, as discussed in the previous section of the experimental work. io TABLE IT. COMMERCIAL ALLOYS Spec, % Carbon % % Figures No. Graphitic TotdBoron Silicon As Cast Annealed 6258 0.088 2.71 0.80 0.58 104,105,175 171,172,173,174 135 3.19 0.12 0.49 113,114,178,179 176,179 i189 2,85 0.97 0.49 129,130 199 ,200 221 3.07 0.87 126 184,185 225 2.45 1,81 0.85 141,142 201 ,202 228 2.76 1,04 194,195,196 ,197 245 1.78 2.82 0.53 156,157,158,159 246 2.53 2.94 0.51 160,161,162 247 3.16 1.24 0.78 134,135 248 0.83 3.84 2.88 0.30 152,153,154,155 212,213 249 0.12 5.00 0.49 167,168,169,170 214,215 255 5.05 1.40 1.61 136 261 2.52 0.65 1.14 106,107 262 3.73 1.20 1.21 127,128 267 2.54 1.51 1.30 138,139 186 ,187,188,189, 190,191,192,193 268 2.90 5.42 0 1.44 116,117 270 6.18 3.50 0.22 1.13 118,119 180,181 271 0.18 3.45 0.49 1.16 122,125 182,183 272 0.18 5.26 1.02 0.80 162,183 276 0.22 3.03 1.706 1.36 143,144 20% to 211 incl. TABLE II. COMMERCIAL ALLOYS, Continued Spec. % Carbon % % Figures No. Graphitic Total Boron Silicon As Cast Annealed erence 279° 80.53 3.05 2.57 1.10 150,151 278 0.52 2.76 2.14 2,14 145,146 279 0.80 28.34 2.57 4.25 147,148,149 289 0 0 6.33 165,166 291 0.41 6.33 163,164 292 3.00 0 108,109 293 3.00 0.10 1.50 110 294 3.00 0.25 1.50 111 295 3.00 0.50 1.50 112 296 3.00 1.00 1.50 131 297 2.50 0 1.50 115 298 2.50 0.10 1.50 120 299 2.50 0.25 1.50 121 400 2.50 0.60 1.50 184 401 2.50 1.00 1,50 125 405 2.72 1.69 0.15 137 406 2.29 1.63 0.91 140 PER CENT CARBON FIG. 103 CONCENTRATION TRIANGLE The structures of these commercial melts will be investigated aeearding to the different ecaneentration fields. First consider specimen 62-2 having a structure consisting, first, of primary ternary solid solution, which breaks up into the ternary pearlite, and, second, a eutectic between the ternary solid solution and the iron carbide solid solution. In Figures 104 and 105 is shown this atructure in which the white material ic the iron cerbide solid solution, the larger dark portions are pearlite, the very fine dark spotted groupings are from the eutectic between the ternary solid solution and the iron carbide solid solution. Specimen 261, Figures 106 and 107, shows the same type of structure as the previous alloy. it is apparent that this alloy does lie within the region being considered, since this structure does persist and no excess of iron earbide solid solution is apparent. Figures 108 and 109 show the structure of specimen 292 which is not justified according to the chemical analysis. The structure presented here would indicate that its composition should be of less carbon content, since a very definite pearlitic structure is eoboerved for practically the entire arca of the photomicrograph. This ‘alloy contains about 1.5% silicon which might partially account for this effect, but certainly not completely. ed? co fe gy Sted ilo. Figures 110, 111, and 112 show the structures obtained in specimens 293, 294, and 295, respectively. These specimens contain the same amounts of carbon with increasing amounts of boron as in- dicated in the table. The structures are similar to those discussed above and are about as would be expected from a study of the equi- iibprium diagram. Figures 113 and 114 show the structure of specimen 135, reveal- ing a rather large amount of primary ternary solid solution which has disintegrated, as in the previous specimens,into pearlite. Tho surrounding white constituent is the iron carbide solid solution. The difference between the structure of this alloy containing only 0.49% silicon and the structure of specimen 293 (Figure 110) which contains 1.5% silicon should be particularly noted. This is very iudicative of the influence of silicon on the structure of the alloys in this region. The effect seems to be to alter the trans- formation compositions so that a structure somewhat different. from what would be exnected is ohtained. Figure 115 shows the structure of specimen 297 which also has 1.5% silicon and compares favorably with the other structures in this region, in that it contains more material originating from the primery solid solution. Figures 116 and 117 show the slructure of specimen 268 in whicn there is no boron present. Due to the relatively high silicon ils. content the iron carbide has been caused to dissociate to graphite and ferrite, as shown by the photomicrograph. The previous alloys seem to indicate that the iron carbide is rendered considerably more stable by the addition of boron in that some of the previously mentioned alloys contained almost as much silicon as did this particular alloy and no graphite separation. was observed. Figures 118 and 119 show the structure of specimen £70. In this case a small amount of disintegrated primary solid solution and a rather large proportion. of eutectic are present. In Figure 118 the pearlitic materiel is the gray structure shown at higher magnification in Figure 119. Figures 120 and 121 show the structures of two other alloys, 298 and 299, in this region which should show some eutectic. Figure 1¢<0 contains some eutectic, but only a very Little, while Figure 121 shows none at all. These two specimens also contain 1.5% silicon which undoubtedly causes considerable alteration of the structure. Figures 122 and 123 show the structure of specimen 271 in which the lightest constituent is the pearlite and the dark the iron carbide solid solution. Here we see considerable eutectic. Figure 124 shows the structure of specimen 400 which contains 1,5% silicon and takes on the appearance, as discussed for some of the previous alloys. Some eutectic is apparent, though not as much whan hat ba ali L2l. as indicated by the diagram. This difference is undoubtedly due to the silicon present. In Figure 125 is shown the structure of specimen 221 which, according to the chemical analysis, lies well below the eutectic curve and, hence, no primary iron carbide solid solution. should be expected. However, the photomicrograph shows very definitely thet primary iron carbide solid solution is present and is surrounded by eutectic. No reason for this discrepancy has been found other than thet the chemical analysis is in error. Figures 126.and 127 show the structure of specimen 262 which ehould show somo primary iron carbide solic solution with the eutectic. ‘he photomicrographs check this prediction very well. However, it is evident that no ternary pearlite of constant com- position exists, which confirms the location of this field as shown on the composition triangle. Now let us consider the alloys in the region NVB.on the con- centration triangle which have an excess of the ternary solid. solution VY. Figure 122 shows the structure of specimen 401, which should contain some ternary eutectic, as indicated by the diagram. Figures 129 and 130 show the structure of specimen 199 which shoulé consist of some excess ternary solid solution, but actually shows primary iron carbide solid solution. It is difficult to see how such a structure could be obtained with the analysis shown. It is conceivable that such a structure might be brought about by super-cooling, in which the composition of the remaining liquid would indicate a precipitation of primary iron earbide solid solu- tion. This particular alloy is one which does not fit the equili- brium diagram. Figure 181 shows the structure of specimen £96 in which we see primary separated pearlite drived from the ternary solid solu- tion surrounded with a eutectic. From the structure of this alloy, it is certain that it lies very close, if not directly on the curve NV, since there is no indication of the formation of ternary eutectic which has a characteristic structure as will be seen in some of the photomicrographs later. Figures 152 and 153 show the structure of specimen 272 in which we have nearly all eutectic as is indicated. there should be from the diagram. No ternary eutectic is visible in this structure and hence its composition lies either directly on or very close to the curve NV. Figures 154 and 135 show the structure of specimen 247 in which there is some primary iron carbide solid solution present. This would indicate that the alloy actually lies on the other side of EL'R', that is on the side of higher iron carbide solid solution. Furthermore, no ternary eutectic is observed, only the binary eutectic of iron carbide solid solution and ternary solid solution, The structure of this alloy is further confirmed by that of specimen 10, shown in Figure 73, which is of approximately the same comnosi- tion. , Figure 156 shows the structure of specimen 255, which still shows no ternery eutectic, but the structure of an alloy lying on the curve NV.. No primary iron carbide solid solution is observed, indicating that it is very close to the eutectic curve. Figure 137 shows the structure of specimen 405 in which there is a very slight indication of a ternary eutectic being formed in the interstices of the larger grains of transformed ternary solid eolution. Figures 158 and 139 show the structure of specimen 267, which shows an abundance of ternary eutectie with some excess of the ternary solid solution. This is the usual form of the ternary eutectic, as can be seen by comparison with Figures 68 and 69, which show the structure of specimen 13, Figure 140 shows the structure of specimen 406 in which: there is orimary ternary solid solution disintegrated into pearlite with Some very small amount of ternary eutectic. ‘his does not fully agree with the structure of specimen £67, but this can be accounted for by the difference in silicon content. Specimen 267 contains 13d. more silicon than specimen 406 and, hence, as has been seen before, the structure is much finer and the transformation compositions are shifted considerably. Figures 141 and 142 show the structure of specimen 225 in which we find the primary solid solution with considerable ternary eutectic. This structure agrees very well with the diagram. Now consider the alloys in the region in which there is an excess of the Lron carbide solid solution. figures 146 and 144 show the. structure of specimen 276 in which is found an excess of the iron carbide solic solution surrounded py the ternary eutectic. | Figures 145 and 146 sow the structure of specimen 278 in which there 1s an excess of the iron carbide solid solution surrounded by the ternary eutectic. Figures 147, 148, and 149 show the structure of specimen 279 in which there is considerable primary iron boride surrounded by ternary eutectic. ‘this structure does not check the equilibrium diagram and, in fact, should not since the alloy contains, accord- ing to chemical analysis, 4.25% silicon, which disturbs the condi- tions very markedly. Undoubtedly, the effect of silicon in this ease is to shift the eutectic curve EsR to higher carbon contents anc, henee, puts this alloy in position to precipitate primsry iron boride. fare fous ye 7D Ae pn taxa fe Figures 150 and 151 show the structure of specimen 277 in which there is an abundance of iron carbide solid solution surrounded by a small amount of ternary eutectic. The black spots are shrinkage holes found in the castings. Figures 152, 153, 154, and 155 show the structure of specimen 248 which is very close to the eutectic of iron carbide solid solu- tion and iron boride and shows this in the photomicrographs. Figure 152 and 153 are at the same magnification, the difference being that 152 was taken with a Wratten B (Green) filter, while 153 was taken with a Wratten A filter (Red), hence, changing the contrast of the structure. This effect indicates the general outlines of the primary iron carbide solid solution that was formed and which later changed its composition during the transformation from the curve NV to 2S, the original position of disposition remains in the final structure. The ternary eutectic is also observed: in this structure, as shown by Figure 154, and the pearlite structure is shown in Figure 155, Figures 156, 157, 158, and 159 show the structure of specimen 245 which shows a very large amount of iron carbide solid solution which is derived from the eutectic and surrounded by some ternary eutectic. Also, there are some erystals of primary iron boride seattered through the structure, as shown in Figures 158 and 159. This alloy checks very closely the equilibrium diagram, exeept that @ larger amount of iron carbide solid solution is: present than would Boe pe pe indicated Irom the diagram. This may be due to the etrect of super-cooling. Figures 160, 161, and 162 show the structure of specimen 246, which is very similar to that of the nreceding alloy except that no primary crystals of iron boride were observed. his indicates that the composition is on the curve EgR or else just to the left of it. The structure shows a large amount of iron carbide solid solution with some ternary eutectic. Figures 160 and 161 differ in thet the firet is taken with the Wratten B filter while the second is with the A (Red) filter showing a little better contrast and definition. Figures 163 and 164 show the structure of specimen 291, which, from the chemical analysis, should be in the field BVJ. The photo- micrographs indicate that a very fine structure, in which we have mostly a eutectic, has formed. Considering its position in the concentration triangle, we should expect some primary iron boride which does not appear in the photomicrographs. It is possible that, due to super~cooling, the eutectic between iron boride and a ternary solid solution is formed presenting the structure shown. This is about the only way the observed structure can be justified. Figures 165 and 166 show the structure of specimen 289 which does not compare at all with the concontration diagram in that a 150. primary constituent which takes.on the appearance of the iron carbide solid solution is presant. This primary constituent is surrounded by a eutectic materidl. In this research the primary iron boride has never been observed to precipitate in the form shown by. this structure and hence impurities must be the source of trouble in this particular structure. Figures 167, 168, 169, and 170 show the structure of specimen 249, The photomicrographs show the structure to consist of primary iron carbide crystals surrounded by a eutectic. This eutectic is between Lron boride and the ternary solid solution. Figure 169 shows the structure of the primary iron boride surrounded by the eutectic and Figure 170 shows the structure of the eutectic. In conclusion to this survey of the structures of the commercial alloys, we can say that the structures in general check very closely the equilibrium diagram. Discrepancies in the correlation are primarily due to non-equilibrium conditions or to the presence of impurities, particularly silicon. the effect of silicon has been pointed out in the description of the various atructures. ‘The principal effect seems to be to cause considerable refinement and a shifting of the transformation compositions toward the eutectic compositions. Effect of Annealing on the Structures of Conmorical Alloyo The previous section dealt altogether with melts that were cast in sand molds for commercial work. In cooling such as takes place in sand castings the transitions that take place may differ very greatly from transitions under equilibrium conditions or the alloy may be one in which diffusion takes place very readily anc, henee, the relatively rapid. cooling has little or no effect upon the structure. Therefore, it is desirable to determine the effect of ennesling on the structures of these alloys. In the discussion to follow an attempt will be made to point out that annealing does change the structures of most of the alloys in that it allows con- Gitions more nearly like those of equilibrium to exist, at least in the solid transformations. Most of the applications of these alloys are in the cast form and are not subjected to an annealing treatment, therefore, the only interest in the investigation of the effect of annealing is to determine the effect of such treatment on the structures in order to learn more of the equilibrium condi- tions. First consider the alloys in the region CNVP]1. Figures 171, 172, 173, and 174 show the structure of alloy 62-2 which has been annealed at 1800° F. for ten hours. This structure should: be com- pared with Figures 104 and 105. which show the structure in the as L5é. east condition. In comparing these figures one must bear in mind that Figures 104 and 105 were prepared by etching the specimen in 5% picrol while the photomicrographs of the annealed sample were prepared by etching in alkaline potasium ferricyanide. Figure 175 is inserted here to show the fine structure of the as cast alloy etched with the ferricyanide reagent. The larger grain such as that in the center is composed of the iron carbide solid solution and the surrounding material is the pearlite.. Between two of these two solid solution crystals can te seen another constituent, In Figure 172 this matrix material is very. definitely shown to be well coagulated. When the sample is etched with 5% picrol this matrix structure is not revealed, but. some crystals, which have a tendency to be prismatic, are brought out in the pearlite grains. These figures seem to indicate that the iron boride has a tendency to coagulate in the pearlite, forming these crystals. The pearlite should consist of a fine mixture of iron boride in alpha iron and the iron carbide soiid solution which contains iron boride in solution. It would appear that some iron boride has come out of solution in both cases, producing the structures observed. Figures 176 ané 177 show the structure of alloy 155 annealed at 1800° F. for ten hours. This structure should be compared with Figures 113 and 114. In addition to these last photomicrographs, Figures 178 and 179 show the structure of the as cast alloy etched i. | Fig. 179 (B135-C) As cast Magnification 1000X% Sten Murakami with the ferricyanide reagent, These last two figures show defin- itely that a constituent is being thrown out of solution forming envelopes around the pearlite grains. In the annealed alloy these envelopes seem to have been broken up somewhat and coagulated. ‘This series of photomicrographs also seems to substantiate the idea that iron boride is thrown out of solution. One distinguishing feature is the color of this constituent when etched with the . ferricyanide reagent. When the specimen is etched for five minutes in a boiling solution, these precipitations are colored a blue green. It has been observed that in alloys containing vrimary iron boride, the boride crystals also take on this characteristic color when etched with this reagent. ‘this is further proof that this constituent is iron boride which has been thrown out of solu- tion. More eases will be cited to substantiate this statement. Figures 180 end 181 show the structure of alloy 270 annealed at 1800° F. for eight hours, When these are compared with Figures 118 and 119 very little difference is observed except that somewhat “more coagulation has occurred in the primary pearlite. However, at higher magnification none of the previously mentioned boride has come out of solution. This alloy contains about 1.13% silicon, whereas the others contained about 0.5%. This retention of the iron boride in solution may be attributed to the silicon content. figures 182. and 185 show the structure of alloy 271 annesled at 1800° F. for eight hours. Comparing these with Figures 122 and Lé4, 123 we see very little difference, except possibly a little more uniform structure. Such a difference can be attributed to the heterogeneity found lo such castings. figures 184 and 185 show the structure of alloy 221 annealed at 1800° F. for ten hours. In comparing these figures with Figure 125, it may be seen that the effect of annealing has been to re- move some of the typical casting structure and to increase the grain size. Furthermore, as in some of the previous cases, a constituent which remains between the pearlite grains has been thrown out of solution. This interstitial material carries the characteristic blue green color, indicating the presence of iron borice. This completes the study of the effect of annealing on alloys in this region. The prineipal point sained from this part of the research is thet with long annealing iron boride is precipitated from solution, which may indicate that the solubility of iron boride is not as great as indicated by Tammann. Alloys in which the silicon was relatively high did not show this precipitation, which would indicate that Tammann's results were affected by the silicon, as indicated by Wever and Muller. Now let us consider the region NVB for alloys containing the ternary solid solution V in excess of the ternary eutectic. In order to determine the effect of the temperature at which alloys in this group are annealed, a group of specimens was cut 168, ‘from alloy 247 and heated at different temperatures for a period of eight hours, One specimen was heated at 600° f., another at eooe F., another at 1000° F., another at 1200° ., another at 1400° F., another at 1600° ¥., and the last at 1800° +. No change in structure was observed until heating at 1400° #, Figures 138 and 159 show the structure in tne as cast condition. figures 146 and 187 show the structure after annealing at 1200° #. for eight hours. Comparing this structure with thet in the as cast condition, no ehange ean he ohserved. s'igures 188, 189, 190, 191, lee, 196% show the structures obtained with higher annealing temperatures. the structure shown after casting consists of ternary eutectic and excess of the pearlitic constituent. However, at some temper- ature between 1200° F. and 1400° +. this ternary eutectic structure is nearly obliterated, probably due to complete ciffusion at this temperature. The figures show a progressive coarsening, coagula- tion of the constituents, and finally the complete removal of. the ternary eutectic structure. No noticeable precipitation of iron boride is observed, as in the previous discussion. Alloy 228 containing 2.76% carbon and 1.04% boron, falling very close to the SZ curve, was given a special series of treatments. in this series, four specimens were used, of which one was heated for tires hours, one for six hours, one for eight hours, and the last for ten hours at 1800° F. The structures obtained with such Lvl, treatment are shown in Figures 194 to 197, inelusive, in order of increasing time. After anneal ine for three hours the structure is about as would be expected after casting. However, after six hours the blue green constituent, which we have previously observed, appears joined to a network surrounding the pearlite grains. With further annealing, this network structure dlsaappears and the sub- stance seems to coagulate considerably. Another alloy which is very close to the one considered above is alloy 189, whose structure was shown in the as east eondition in Figures 129 and 130. These photomicrographs were prepared by etching the specimen in 5% picrol. Figure 198 shows the structure when the as cast specimen was etched with the ferricyanide reagent. This shows a segregation of material in the pearlite. Figures 199 and 200 show the structure of this alloy after annealing at 1800° F. for ten hours. Here we see a complete coagulation of this consti- tuent which takes on the blue green appearance of the iron boride. This alloy contains a small amount of silicon, whieh further sub- stantiates the statement of the solubility of iron boride. Figures 201 and 202 show the structure of alloy 225 annealed at 1800° F. for ten hours. If this is compared with the structure of the alloy in the as cast condition, shown in Figures 141 and 142, it will de noted that the annealing has eliminated the eutectic structure, bringing about almost complete diffusion. It should be noted that those alloys which lie approximately L?7. on the ZS curve have the property of displacing the boride con- stituent from solution, while those lying definitely in the tri- angle do not have this property, but merely an elimination of the eutectic structure occurs on annealing. A few alloys within the triangle NVB in the region of primary iren carbide solid solution will uow be cousidered. In Figures 205 to 211 is shown the effect of different annealing temperatures on alloy 276, Figures 143 and 144. The effect on this alloy is found between 1200° F. and 1400° F., as in the previous ease, where the ternary eutectic is partially obliterated and, as the temper- ature is inereased, the pearlitic structure agglomerates to the fullest extent and the ternary eutectic finally disappears. Alloy 248,which has been annealed at 1800° F. for eight hours, also lies in this region and is shovn in: figures 212 and 215. ‘he as cast structure appears in Figures 152 and 153. ‘he effect of the annealing is very noticeable in this case in that the ternary eutectic has entirely disappeared and all that remaina is the ternary pearlite, which is readily brought out in Figure 213. It is very noticeable in all the alloys lying in this field that the Gistinction between the iron carbide solid solution and the iron boride is not resolved, due undoubtedly to the close similarity of their properties. In Figure 213 the structure enclosed by bound- aries is not a homogeneous solution, as the photomicrograph would indicate, but is the ternary pearlite. 13d. Figures 214 and 215 show the structure of alloy 249, which has been annealed at 1800° F. for eight hours, Compsring this structure with that of Figures.167 to 170, inclusive, about the only change that ioe noticeable is the loss in the eutectic structure which existed before annealing. In conclusion to this part of the research, it ean be said that upon annealing alloys in the range CNVL the pearlitic struec- ture is oroken up and that iron boride is precipitated from solu- tion provided the silicon is low. Im the triangular region NVB a loss of the ternary eutectic structure occurs, accompanied by an aggregation of the pearlite and a coarsening of the general structure. In the field BVI vetwoon Ez and B there ccoure a lose of the eutectic structure and a general coagulation of the iron boride contained therein and a generel coarsening. PART III. PHYSICAL PROPERTIES The most important considerations in the study of any metal or alloy are those concerning its physical properties. The metallographic structure is important chiefly because of the assist- ance it gives in explaining why certain properties exist. lt is limited in its scope because of the fineness of the metal structure and the limitations of the optical method. Alloys in this system, containing about three percent carbon and from one or twe-tenths to two percent boron, have been found commercially valuable in their resistance to wear, Those alloys waich exhibit the quality to resist wear have considerable hardness, of the order of 500 to 800 Brinell. Consequently, in this research some of the alloys in the useful range have been investigated for hardness and transverse strength, in order to have some basis for comparison with other materials. One series has been carried out to determine tensile and compressive strength and modulus of elasticity; another to determine the effect of boron on the thermal conductivity of these alloys. The alloys used for determining the transverse and hardness properties were cast in sand molds in the form of the standard arbi- tration bar, thirteen inches long and one and one-quarter inches in diameter. The bars were allowed to cool in the mold. ALL Specimens were tested by placing them between fulerums twelve inches apart and applying a load at the center of the bar in the 50,000 pound Universal testing machine. ‘the modulus of rupture referred to as transverse strength was computed from the relation 32 Mot, where S is the modulus of rupture in pounds per square inch, Mis the maximum moment at the center (P1/4) in inch pounds, o is the distance from the neutral axis to the extreme fiber in inches, Assuming the neutral exis at the center, C has beon taken as ecusl to the radius. I is the moment of inertia of the section in (inehes)#, P the load at the center, and 1 the length of the specimen in inches. Substitution of the specific values in the general expression gives the relation S = 30.5 P/a5, affect of Composition on Transverse Strength and Hardness Table TIT. gives the composition and average results for the alloys used in this work. These results are plotted on a composition diagrem shown in Figure 216, on which contours of transverse strength and hardness have been drawn. The values given are the averages of two tests made on each alloy. ‘lable IV. gives the values for each of these tests. In reading this graph, it should be remembered that these alloys are commercial melts and, hence, there is some variation in silicon content which may cause some variation in the results. TABLE ITT. SUMMARY OF TESTS Average Hardness Modulus of Deflection Sclero- Diamond Spec. Rupture inches in scope Brinell No. 2G. &B. Si. lbs/sq.in. 12 inches 247 3.16 1.24 0.78 18,400 0.038 63 255 3.05 1.40 1.61 21,010 0.020 62 262 3.73 1.20 1.21 6,245 0.017 21 268 3.42 0.00 1.44 52,300 0.109 32 235 269 3.67 6.09 1.48 47 ,500 ©.080 43 oLS 270 3.50 0.22 1.18 52,600 0.041 57 523 271 3.43 0.49 1.16 30, 525 0.024 68 649 272 3.26 1.08 0.80 25,100 0.019 BB 705 276 3.03 1.70 1.36 32,675 0.025 95 800 292 3.00 0.00 1.50 75,400 0.117 38 286 295 3.00 O1c - 75,450 0.057 49 496 294 3.00 0.25 = 69,800 0.056 51 479 295 3.00 0.50 - 62,850 0,047 53 556 296 3.00 1.00 - 45,600 0.034 8? 567 297 2.5 0.00 - 82,300 0.082 Be 356 298 2.5 0.10 - 25,750 0.074 AG 425 299 2.5 0.25 - 80,600 0.066 48 462 400 2.5 0.50 - 70,100 0.051 47 506 401 2.5 1,00 - 55, 300 0,046 SL S28 ~wnee mee il NO¥O@ .LN3D wad 071 20 91 a Zz Toy es om ei to ote . ¢ vBZo. CBZ ZOU My, we i © el NO@uvY> IN3D Yad | S4ANND SS3NQYVH TaNINe | Ny _ HLONBULS =«ASUBAGNVUL ee ao) Fe gg Lae, TABLE IV. TEST DATA Modulus of Deflection Specimen Diameter Load Rupture inches in Number _ Inches Pounds __lbs/sg.in. ig inches 247 1.261 820 13,460 0.038 255—1 1.281 1,450 21,020 0.018 255-2 1.305 1,530 21,000 0.023 262-1 1,275 410 6,030 6,012 262-2 1.278 450 6,560 0.021 268 A L274 3,510 51,800 9.107 268 B 1.233 3,240 52 ,800 O,111 269 A 1.259 5,120 47,800 0.078 269 B 1.231 2,880 47 ,200 0,083 270 A 1.257 3,060 47,100 0.037 270 B 1.232 3,540 58,100 6.046 BVL A 1.261 1,370 Z8 400 0.025 271 B 1.2350 1,860 52,650 0.023 272 A 1.256 1,440 25,100 0.019 272 8B 1.25 1,190 19,540 0.016 276 A 1.271 2,190 32,650 0.025 276 B 1,284 2,010 52,700 0.026 292 A 1.28 4,000 61,000 0.090 292 B 1.25 4,860 76,000 0.115 292 C6 1.25 4,790 74,800 0.120 293 A 1.24 4,970 79,600 0.059 293 B 1.24 4,460 71,300 3.055 294 A 1,23 4,720 77,300 0,063 294 B 1.24 3,900 62,400 0.050 295 A 1.24 5,890 62,200 0.051 295 B 1.228 3,780 63,500 0.044 296 A 1.24 2,780 44,400 0.082 296 B 1.24 2,930 46 ,800 0,056 207 A 1.22 4,540 76 ,500 0,086 297 B 1.24 5,520 88, 506 0.074 209 A 1.24 &,820 93,300 0,075 298 B 1.24 6 ,140 98,200 0,072 299 A 1.22 4,440 74,8600 0,054 299 B 1.22 5,150 B86 , 600 0.070 400 4 1.238 4,130 67,700 0.049 400 B 1.23 4,420 72,500 0.054 401 A 1.26 3,380 51,600 0.041 401 B 1.24 3,690 59 , 000 0.052 From the trend of the transverse strength curves, it is indicated that tue highest strength and lowest. hardness will occur at about the point V, Figure 100, and also that the hardness increases as we go into the region of excess or primary iron carbide solid solution. This is ih-agreement with the equilibrium diagrem, in that we know a material with larger amounts of iron carbide solid solution possesses inherent hardness. An examole of this characteristic hardness is found in lron-carbon alloys containing excess iron carbide. The hardness determinations were made with a Monotrone hard- ness testing machine with which several readings were taken and the average values entered in the table. Heat Treatment 4& series of tests was made to determine the general physical properties of the alloys.in the region CNVL, Figure 103. for this test alloy 62 was usec, More tests were not made because of the expense of grinding the specimens. It was felt that the tests made on this particular alloy would be indicative of the properties of alloys in this region. Another interesting result observed in these tests is the effect of silicon on the physical properties. This particular alloy (62) contains only 0,55% silicon, while the alloys used in the transverse and hardness tests previously men- tioned, contained about 1% or more of silicon. iol. Tests were made of this material in the as cast, annealed, and normalized conditions. Some specimens were quenched in various media, but the data is not included here, since unsatisfactory results were obtained. The specimens to be heat treated were placed in the furnace at 1650° F. for one hour and then cooled, as indicated in Table VI. The summary of average results of these tests are listed in Table V. Specimens for the tension tests were cast in black-washed sand molds and were allowed to cool to room temperature. The test Specimens were ground to a uniform diameter in the working section and given large fillets at the ends to accommodate their support in special grips. The supporting grips were suspended from spherical seats, insuring against eccentric loading. The results of these tests are shown in Table VI. Specimens for the compression tests were ground to a one inch diameter and a height of one and one-eighth inch. The specimens were placed on spherical heads in the testing machine. The results are given in Table VII. The specimens for the transverse tests were rough castings of the same dimensions as those previously described. Results are given in Table VIII. The averages of several Scleroscope hardness determinations on these specimens are reported in the Tables mentioned above. be © wo TABLE V. Condition Tensile Compressive Modulus of Strength Strength of Specimen Material #/sq.in. #/sq.in. Rupture Hardness Number sgein. Scleroscope eam meneame tenn hore npanartaaarmerl D-12 As Cast 19,635 227 ,000 26,100 64 ~ 80 D-13 Cooled in 24,530 224,000 31,000 57 -61 Furnace from 1650° F, Da14 Cooled in 22,450 247 500 27 ,180 69 ~76 Air from 1650° F, The Modulus of Elasticity = 34,000,000 lbs. per sq. in. Se Se ecre ae eereeeenee rsemannemnaneaieeenneetaness TABLE VI. TENSILE TESTS Total Ultimate Seclero- Spec. Diameter area Load at Strength | scope Condition No. Tnehes Sq. in. Break lbs. lbs./in.* Hardness 1 0.579 0.205 4,830 18,350 65 As Cast 2 0.574 0.259 5,110 19,770 64 As Cast 3 0.568 0,253 4,790 18,920 61 As Cast 4 0.573 0.260 5,600 21,500 66 As Cast 9 0.560 0.246 6,490 26 , 400 59 Cooled in furnace from 1650° F, LO 0,565 0,251 5,680 22,650 59 Cooled in Furnace fron L650" ¥F, ? 0.568 0.255 5,896 23,900 69. Cooled in Alr frou 16560° F. 8 0.581 0.265 5,720 £1,600 69 Cooled in Air from 1650° F. L194. TABLE VII. COMPRESSION TESTS Specs. Diem, Area Losd at Ultimate Length L/D Selero~ Condition No, in. ag..;Break Strength {1} scope in, los. #/sq.in, inches Hardness 1 06.970 0.789 177,440 240,000 1.694 1.13 75.4 As Cast 0.974 0,745 159,460 224,000 1.101 1.15 77.5 As Cast ta] gn 0.970 0.739 164,620 222,000 0.959 0.99 56.9 Cooled in Furnace from 1650° F, 4 0.970 0.739 167,808 226,000 1.110 1.14 61.2 Cooled in Furnace from 1650° F. 5 0.974 0.745 179,700 841,000 1.10 1.14 7568 Cooled in Air from 1650° ¥F. 6 0.970 0.769 187,720 254,000 1.119 1.15 76.3 Cooled in Air from 1650° F. TABLE VIII. TRANSVERSE TEST Lead at Deflec. Modulus of Spee. Diameter Area Center in 12 Rupture Condition No. inches sq.in. lbs. inches 1b./sq.in. 1 1.224 41,179 1695 0.02 28,200 As Cast Pa 1.223 1.178 1440 0.081 24,000 As Cast o- 2.21? came Rone L600 0,081 RF LOO Cooled in Furnace from 6 1650° F,. 4 1.205 1.141 2000 0.080 24,900 Cooled in Furnace from 1é650° FF. 8 1.225 1,180 1940 0.028 Of , 200 Cooled in Air from 1650° F. 6 1.215 1.160 13500 6.020 22,100 Cooled in Air from 1650° F,. Oue of the tension specimens in the as cast condition was used for the determination of modulus of elasticity. The method was to determine deflections for equal increments of applied load aver a two inch gauge length. The deflections were determined with a Huggenberger Tensometer which allowed the determination of deflections to 0.0000299 inches in the gauge length. The results of this test will be found in Table IX. The value wes found to be thirty-four million pounds per square inch. This is somewhat higher than is found for white cast iron with a value of obout thirty- two million pounds per square inch as a maximum. From this set of tests, it can be concluded that annealing inereages the tensile strangth and modulus of rupture and decreases the hardness of these alloys. Cooling in air decreases the tensile and transverse strengths over the annealed material, but increases over the as cast condition. The effect of annealing and air cool- ing is primarily due to the reheating of the cast material thereby obtaining a more uniform structure. Other specimens were used to determine the effect of quenching on the alloy. Quenching in any media is very detrimental to these alloys, in that large cracks are developed rendering them worth- less. The hardness is inereased to some extent by quenching, due to the existence of partially decomposed ternary solid solution. The data obtained on these quenching tests is omitted here. Lo?, TABLE IX. STRESS STRAIN DETERMINATION FOR COMPUTATION OF MODULUS OF ELASTICITY Unit Total Total True Total Load Load Deflection Deflection Deformation lbs. los.sq.in. Readi Difference in./in. 000 0.62 ) ) 500 LOO 0.64 0.02 0.0000800 L000 BB06 0.88 0,06 0.0000900 L560 5200 0.72 C.10 0.0001500 2000 7600 0.75 0,18 00001950 2500 8500 0479 0.17 0.0002545 3000 1i400s«w 0.22 0.0008145 3500 13300 0.86 0.84 0.0005590 4000 15200 C.90 0.28 0.0004190 D.# 0.579 inches A = 0.263 sq. in. Thermal Conductivity The thermal conductivity of alloys in the iron, iron-carbide, iron-boride system has proven to be of considerable interest, because of the particularly low value obtained. A series of alloys, listed in Table X., was used for determinations of thermal conductivity. The coefficients of thermal conductivity were determined by 5. H. Sage and Earl S,. Hill of the California Institute of Technology by measuring the flow of heat through bars similar in dimension to those used for the transverse tests. In this case all test bars were finished ground. Heat was supplied by an electrically heated brass block soldered to one end of the bar. The quantity of heat flowing through the bar was determined ‘by the rise in temperature of a known stream of water flowing through a similar brass block soldered to the other end of the bar. The rise in temperature of the water was determined by two short range thermometers placed in insulated wells. The rate of flow of water was determined by weighing. The temperature gradient was measured by thermometers inserted at the ends of the bar. Water temperatures were read to 0.02° F, The entire apparatus was heavily legged and was ealibrated by means of a bar of low carbon steel, from which it was found that no correction for heat loss was necessary. The results of these tests are tabulated in Table X. and the values plotted against boron content in Figure 217. TABLE X. Spec. Total Graphitic Silicon Boron Thermal Conductivity No. Carbon Carbon B.t.u./hr./sq./tt./ g, gt, t oF. /ft. 288 2.42 2.30 1.44 0.00 27.5 269 5.67 2.08 1.42 0.09 20.2 270 5.50 0.18 1.13 0.22 7.5 271 3.45 0.18 1.16 0.49 6.0 272 5.28 0.18 0.08 1.02 548 276 O05 Ueez 1.56 1.70 &,6 % i NOYOE LN|aS 01 20 | | | ' ; “ ; rm —~ gis ot. a 4 a wpe te nie tae amt cp > : vocpenen when fb eer ace etd ram ath ~ _ a Ee Ss Se en NEN As Snes Se Cen Oy . nee oO ~ : | : re ere eee z | : er ee : 4 ' i the bod < ie i berate nets nabeenin nonin cea nan scape nee ne ny fee - bee le bel : aol iz | L . . ch cab . eg : eoupds DB cqeeceeees feserwnaein nese oe . 5 See an SE _— , wa i ts ALIAILONGNOD WANYAHL | iS a oobi ehh £12 Ol , seed : ° oe . a a ee ee : : g rr ™ : detec — eee , : two oe cob. i. 7 - 4 ‘ ; 1, ; pom £ - caw ont 4. ot a ae) > Fo The effect of boron is very noticeable on the thermal conducti- vity. It may be noticed that the therml conductivity decreases very sharply and that the amount of graphitic carbon decreases in about the same way. This fact may account in some way for the drop in thermal conductivity, but the drop in graphitic carbon content can be attributed to the presence of boron. SUMMARY (1) As a result of this research the equilibrium relations of the iron, lron-carbide, iron-boride system, as proposed by Vogel and Tammann, have been checked metallographieslly for the liquid solid transformations throughout the composition range. (2) The equilibrium relations of the iron, iron-carbide, iron-boride system, as proposed by Vogel and Tammann for the transformations in the solid state, have been ehecked metallo- — graphically in all regions of the system with the exception of that region containing less than about one percent boron. In this case discrepancies were found in the commercial alloys in that the solubility of iron boride in alpha iron wae not as great as suggested by Vogel and Tammann. Such solubility was found in alloys containing silicon in exeess of one percent. (3) The solubility of iron boride in alpha iron has been found to be increased by the presence of silicon. (4) The hardness of alloys in this system has been found to increase with increase of carbon and boron content. (5) The transverse strength of alloys in this system has been found to decrease with increase in carbon and boron content to a very low value, (6) Annealing of the alloys in the iron, iron-carbide, iron-boride system has been found to cause coagulation of iton ZOOS « boride in the metallographic structure. (7) Annealing of alloys in this system hes been found to inerease slightly the transverse strength and tensile strength without great loss in hardnees. 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