US2686743A - Heat-treated ferrous alloy castings and method of heat treating the same - Google Patents

Description

7, 1954 R; A. FLINN ET AL 2,686,743

HEAT-TREATED FERROUS ALLOY CASTINGS AND METHOD OF HEAT TREATING THE SAME Filed June 3, 1953 I5 Sheets-Sheet l Aug. 17, 1954 R. A. FLINN ET AL 2,686,743

HEAT-TREATED FERROUS ALLOY CASTINGS AND METHOD OF HEAT TREATING THE SAME Filed June 3, 1955 :5 Sheets-Sheet 2 777a TTORNEYS 3 Sheets-Sheet 3 Aug. 17, 1954 R. A. FLINN ET AL HEAT-TREATED FERROUS ALLOY CASTINGS AND METHOD OF HEAT TREATING THE SAME 'lled June 3, 1953 0 0 0 wmmmmww.

21M i a him i 1 Patented Aug. 1?, 1954 HEA'r 'rREATED FERROUSALLOYCASTINGS AND METHOD OF HEAT TREATING THE SAME Richard A. Flinn, Ann Arbor, Mich and Raymond H. Schaefer, Mahwah, N. J assignors to American Brake Shoe Company, New York, N. Y., a corporation of Delaware Application June a, 1953, s same. 359,312

This application is a continuationein-part of our application, Serial No. 96,120, filed May 28, 1949, now abandoned, entitled Heat Treated Ferrous Alloy Castings and Method of Heat- Treating the Same. 1

This invention relates to heat-treated ferrous alloy castings and to a method ofheat-treating thesame. l l

More particularly, this invention relates to ferrous alloy. castings containing not substantially less than 1.30 and not substantially more than 1.65 per cent carbon, which are substantially free fromgra'phite, and which possess excellent Wear resistance, high tensile strength, appreciable ductility, excellent resistance to :both impact and thermal shocks, and to a method for heat ,treating such ferrous alloy castings. i i, v

lt iswknown that white cast iron containing from 2.5 to 3.5 per cent carbon, has excellent wear resistance, but itis extremely brittle due to the presence therein of a hard carbide network which cannot be completely dispersed or converted into a spheroidized, a non-continuous form of carbide by heat treatment alone.

However, in the practice of the present invention we have found that if the carbon content of ferrous alloy castings is maintained between 1.30 and 1.65 per cent, a brittle carbide network is formed in the castings but that this brittle carbide network can be dispersed into a spheroidized form by the heat treatment process of the presentinvention and without the necessity for forging the castings and without the formation of graphite which reduces the wear resistance of snchcastings. t t it The use of ferrous metal castings containing 1 s Claimsu (c1. its-21.55

carbon within the range of 1.30 to 1.65 per cent such prior ferrous alloy castings have, in general,

been unsatisfactoryheretofore in that either (a) they have contained appreciable amounts of ob J'ectionable graphite or (b) it has been necessary toforge such castingsto break up the objectionable carbide network formed in the cast articles.

Accordingly, an object of the present invert son is to provide a new and improved cast ferrous alloy casting containing ,not substantially I less than 1.30 nor substantially more;than,1.65

1.65 per cent carbon and which possesses excellent wear resistance, high tensile strength, ap-

- preciable ductility, as indicatedby its per cent elongation upon being tested for tensile strength, and excellent resistance to boththermal shock and mechanical impact.

Another object of the invention is to provide a new and improved ferrousalloy casting containing from 1.30 to 1.65 per cent carbon and which is particularly adapted for use in the manufacture of railway car wheel castings and the like.

An additional object of the present invention to provide a new and improved ferrous alloy casting containing from 1.30 to 1.65 per cent carbon which, beingsubstantially free of, objectionable grain boundary carbide network, does not require forging as has been required heretofore to break up the harmful grain boundary iron carbide network in prior ferrous alloy castings containing approximately 1.5 per cent carbon.

A further object of the invention is to provide a new and relatively simple but efficient method of eliminating, harmful grain boundary carbide network in ferrous alloy castings containing from 1.30 to 1.65 per cent carbon by heat treatment alone and without the necessity fora, forging operation as hasbeenrequired heretofore in the art and, Without the formation of graphite in the resulting heat treated ferrous alloy casting. Still another object of the invention. is to provide a new and improved method of making a heat-treated ferrous alloy casting, and a new andimproved heat treatment therefor, which will assure that the resulting ferrous alloy casting is freefrom objectionable graphitic carbon injexcess of 0.12 per cent, by weight.

" A still further object of the present invention isto provide a new and improved method and formula for, determining and assuring such a balanced relationship between or among the carbide-stabilizing or metallic-carbide forming agentsnainellbsulphur and/or chromium, and

the graphitizingfdeoxidizing agents, namely, silicon and aluminum,'present in the ferrous a1- loys which maybe employed in the practice of the present invention as will assure that the t resulting heat-treatedferrous alloy casting of per, cent carbon, which is free from objectionable 1 i graphite, and which is also free from. the :harmful grain boundary carbide network present in comparable prioriart ferrous alloy castings.

Anotherobject of the invention is to provide a ferrous alloy casting containing from 1.30 to the present invention will not contain an excess of 0.12 per-cent, by weight, of graphitic carbon.

Other objects willappear hereinafter. Inthe drawings; l l 9 Fig. 1 is. a photomicrograph (magnification 1000) (2 per centNital etch) illustrating the grain boundary carbide network present in a ferrous alloy casting containing an optimum of 1.5 percent carbon; 1 -FigJ-2 is a photomicrograph (1000K) illus- 3 trating the structure of a specimen of ferrous alloy castings having the same composition as the specimen to which Fig. 1 relates but which has been heated at a temperature of 1850 F. for a period of five hours and then oil quenched;

Fig. 3 is a photomicrograph (1000X) of a specimen of the same ferrous alloy casting as that to which Figs. 1 and 2 relate after the specimen has been heated at a temperature of 1850 F. for a period of one hour, then oil quenched, then heated at a temperature of1450 F. for a period of five hours for spheroidization, and finally cooled in the spheroidizing furnace in accordance with the practice of the present invention;

Fig. 4 is a photomicrograph (1000K) illustrating the structure of a specimen of the same ferrous alloy casting as that to which Fig. 1 relates which has been treated at a temperature of 1450 F. for a period of five hours and then air quenched and then reheated at 1450 F. for a period of five hours and cooled in the spheroidizing furnace but which had not previously been heated to a temperature above the temperature range favoring the formation of the carbide network, that is, from about 1700 to about 1850", as was done in the case of the specimen having the structure illustrated in Fig. 3;

Fig. 5 is a photomicrograph (100021) of a specimen of the same ferrous alloy castin as that to which Fig. 1 relates but which has been subjected to the heat treatment process of the present invention, and in which the specimen has been cooled rapidly by air cooling, after having been treated at 1450 F., instead of by gradual cooling in the spheroidizing furnace, as in the case of the specimen having the structure illustrated in Fig. 3;

Fig. 6 is a photomicrograph (1000K) illustrating the effect of employing a relatively fast cooling rate after spheroidizing, by means of Water quenching, in the heat treatment process of the present invention; and

Fig. 7 is a graphical illustration showin the effect of the presence of graphitic carbon in a ferrous alloy, as shown by wear tests made upon a railway freight car wheel comprised of a ferrous alloy casting containing 1.5 per cent carbon which contains 0.50 per cent graphitic carbon (graph "7), and wear tests made upon a comparable railway car wheel comprised of a ferrous alloy casting containing 1.5 per cent carbon which had been heat-treated in accordance with the practice of the present invention and, as a result thereof, contained only 0.04 per cent graphitic carbon (graph 8).

In the practice of the present invention typical specimens of ferrous alloy castings employed were prepared in a conventional manner by pouring the castings and cooling to a temperature of 1200" F.,'"or below, the specimens having the composition illustrated in the followin examples in which all parts indicated are in terms of per cent by Weight:

EXAMPLE NO. 1

,Per cent by weight In the foregoing Example No. 2 the chromium content may be varied from 0.45 to 0.50 per cent and within these limits will assure that the resulting ferrous alloy casting has the desired low raphitic carbon level of not in excess of 0.12 per cent by weight.

EXAMPLE NO. 3

Per cent by weight C 1.30 Mn 0.60 P 0.04 S 0.03 Si 1 0. 0 Al v 0.04

CI Fe Balance In the foregoing Example No. 3 the chromium content may be varied from 0.10 to,0.15 per cent, by weight, and when so varied within these limits will assure that the resulting ferrous alloy casting has the desired low graphitic carbon level of not in excess of 0.12 per cent, by weight.

EXAMPLE N0. 4

Per cent by weight C 1.60 Mn 0.60 P 0.04 S 0.12 Si 0.50 A1 0.04 Cr 0.05 Fe -1 Balance In the foregoin Example No. 4 the chromium content may be varied from 0.05 to 0.10, per cent, by weight, and when so varied Within these limits will assure that the resulting ferrous alloy casting has the desired low graphitic carbon level of not in excess of 0.12 per cent, by weight.

Fe Balance In the foregoing Example No. 5 no chromium is required to assure that the resulting ferrous alloy casting will have the desired low 'graphitic carbon level of not in excess of 0.12 per cent, by weight.

In general, however, the composition of the i new heat-treated ferrous alloy casting may be 0 -1 1-. 1.50 Mn 0.60 P 0.07 S 0.07 S1 0.20 A1 0.04 Cr 0.30 Fe Balance varied within the limits indicated inthe follow-v It should be noted in connection with the fore going Example No. 2 that while theranges of sulphur andphosphorous are as indicated it is notcommercially practical to produce heats containing no sulphur or phosphorususing commercilallyavailable melting stocks.

a In the manufactureof the new heat-treated carbon ferrous alloy castings of the present invention the arbide-stabilizing or metallic car bide formingagents, namely, sulphur and chromium, and the graphitizing-deoxidizing agents,

at the same time producing a ferrous alloycasting having, the desired lowgraphitic carbon level of notin excess of 0.12 per cent, by weight, some threehundred (300) heats or heat tests were run on batches of metal containing the various elements called for in Examples Nos. 1 to 6,inelusive, and ,upon the basis of thesethree hun- 'dred"heatsf or heat tests the following formula has been established and evolved for determining the desired balancedrelationship between the ,carbide-stabilizing 1 or metallic-carbide forming agents, namely, sulphur and/or chromium, and the graphitizing .deoxidizing (agents, namely, silicon and aluminumfas will assure against the formation of graphitic, carbon in excess of 0.12 per cent, by weight, in a ferrous alloy casting prep red in accordance withthe practice of the presentinvention:

" FormulcNoJ Per cent C+0.2 (per cent Si plus per cent Al)+ (per cent Mn0.70)--1.5 per cent Cr-5 (per -cent S0.04)1.14 per 'cent graphitic carbon in resulting heat-treated ferrous alloy casting; 0

- It-is to be noted, however, that in the foregoing Formula No. I the Mn factor is to be included therein only when theMn content of theferrous alloy employed exceeds 0.70 per cent and the S factor is to be includedin theformula only when theScontent of the ferrous alloy exceeds 0.04 percent, byweight.

- Itwill thus be notedthat it is possible by the application of the foregoing" Formula No. 1 to determine, among other thingsthe amount or percentage of metallic-carbide forming or carbide-stabilizing agents namely, chromium and/or sulphurrequired to assure the desired lowgra phitic carbon contact of not in excess of 0.12 per cent, by weight, in the resulting heat-treated ferrous alloy casting provided the composition of the ferrous alloy employed is maintained within the ranges specified in the foregoing Example 6.9.

It will be noted that phosphorous has not been recitedin the foregoing Formula No. 1 because it has an insignificant effect in the quantities usually present in ferrous alloys of the characteremployed in the practice of the present invention and the permissible maximum percentage of phosphorous which may be employed is limited by the tendency of this element to produce hot tears or casting cracks upon mold cooling.

, Specimens of the ferrous alloy casting having the typical composition illustrated in Example No. 1 were cut from a three inch section of a casting in the form of a railway car wheel rim. These specimens possessed the carbide network structure illustrated in Fig. 1 and which is commonly associated with high carbon (1.5 per cent) steel alloys and which, while imparting wear resistance to such alloys, also renders them extremely brittle. In this condition the specimen possessed the characteristics illustrated in the following Table 1: a

TABLE 1 Tensile strength (p. s. i.) 65,900 Ductility in terms of per cent elongation (2" gage length) Brinell hardness As may be seen by reference to Fig. 1 the specimen ferrous alloy 1.5 per cent carbon casting having the composition illustrated in the foregoing Example 1,.prior to being. subjected to the heattreatment of the present invention, which will be described presently, possessed the objectionable grain boundary. iron carbide. net? work I which is associated with conventional high carbon (1.5 per cent) steel alloys and which renders such alloys brittle. Suchconventional high carbon (1.5 per cent) steel alloys are further characterized bylow ductility, in terms ,of per cent elongation, low tensile strength, low resistance to thermal and impact shocks, and good wear resistance.

By reference to Fig. 1 it will be noted that the objectionable grain boundary iron carbide network I may be readily seen accompaniedby the pearlite structure 2; particles of manganese sul-. phide being indicated at 3. I 1 i Fig. 2 illustrates the structure of a specimen of the same ferrous meta11.5 per cent carbon alloy having the composition set forth in Example 1 after. the specimen had been heated at a temperature of 1850 F. for a period of five hours and then oil quenched. Afterthisheat treatment the specimen exhibited the characteristics set forth in the following Table 2:

TABLE 2 Tensile strength (p. s. i.) Relatively high.

Ductility in terms of percent elongation (2" gage length)- Very low. Brinell hardness 450. i I

As shown in Fig. 2, the objectionable grain boundary iron carbide network pattern is 'still present in the casting after this treatment but is somewhat finer, as indicated at I, and is accompanied by the pearlite], but is somewhat less pronounced than in Fig. 1. However, by this opq eration the casting has been conditioned for the next step in the heat treatment process of the present invention, which will now be described.

Aspecimen of the new heat-treated ferrous alloy casting having the characteristics illustrated in Fig. 1, and having the composition illustrated in the foregoing Example No. 1, was heated to a temperature of 1850 F., which is above the temperature maintained at this temperature for a period of 2 hours, and then cooled rapidly by oil quenching to avoid the formation of a heavy carbide network. Cooling was interrupted at a temperature of 1200 F. and the specimen was then transferred to the spheroidizing furnace and reheated to a temperature of 1450 F. and maintained at this temperature for a period of hours and then furnace cooled. The specimen thus heat-treated by the heat treatment process of the present invention exhibited the completely spheroidized grain structure illustrated in Fig. 3 and possessed the characteristics illustrated in the following Table 3:

TABLE 3 Tensile strength (p. s. i.) 102,000 Ductility in terms of per cent elongation (2" gage length) Brinell hardness By reference to Fig.3 the completely spheroidized carbide is indicated by the fact that all of the carbide present is in the form of a myriad of small balls 5 in the ferrite background 4.

tained at this temperature for a period of 5 hours and then furnace cooled. In this instance the specimen Was not first subjected to the essential step of the heat treatment process of the present invention which resides in first heating the specimen to a temperature (1850 F.) above the temperature range favoring the formation of the iron carbide network and then cooling rapidly (to avoid the formation of a heavy carbide network) to a temperature of 1200 F. before transferring the specimen to the spheroidizing furnace.

The specimen having the structure illustrated in Fig. 4 still possessed the harmful grain boundary iron carbide network I, though less marked, and possessed the properties shown in the following Table 4:

TABLE 4 Tensile strength (p. s. i.) 90,400 Ductility in terms of per cent elongation (2" gage length) 2.34 Brinell hardness 229 The toughness of the completely spheroidized graphite free high carbon ferrous alloy casting of the present invention may be seen by comparing the ductility in terms of per cent of elongation exhibited in testing for tensile strength in the as-rcastalloy (Table 1) and in the specimen heat treated in accordance with the practice of the present invention (Table 3).

While the completely spheroidized structure illustrated in Fig. 3 possesses maximum toughness it offers somewhat less resistance to flow than a harder and more wear-resistant structure and, in certain instances, such, for example, as when the new ferrous alloy casting is to be used 'in'railway' car wheels, such additional wear ro sistance maybe desirable. Thus inthe practice of the present invention such additional hardness and wear resistance may be imparted to the ferrous alloy casting by employing a faster cooling ratio, as by air cooling or water quenching, in place of cooling in the spheroidizing furnace as in the case of the specimen having the structure illustrated in Fig. 3.

Thus, Fig. 5 illustrates a specimen of the high carbon (1.5 per cent) ferrous alloy casting having the composition set forth in Example No. 1 which was heated to a temperature above the tempera ture range favorable for the formation of the iron carbide network. I

The temperature employed in this instance was 1700 F., and the specimen was maintainedat this temperature for a period of 2 hours, after which it was air cooled to a temperature of 1200 F., transferred to the spheroidizing furnace and reheated to a temperature of 1450 F. and maintained at this temperature for a period of 5 hours and then air cooled. The specimen so treated possessed the properties shown in the followingTable 5:

TABLE 5 Tensile strength (p. s. i.) 112,000 Ductility in terms of per cent elongation (2" gage length) 4.0 Brinell hardness 255 It will be noted by reference to Fig. 5 that While some of the carbide is present in the structure in a finely dispersed spheroidized form, as indicated by the small balls 5 scattered throughout the relatively fine pearlite structure 2, none of the carbide has reverted to the harmful grain boundary carbide network type. The resulting specimen exhibited good elongation and its tensile strength was considerably higher than that of the completely spheroidized structure illustrated in Fig. 3, due to its higher hardness, as may be seen by comparing Tables 5 and 3.

Fig. 6 is a photomicrograph (1000K) illustrating the effect of employing a relatively fast cooling rate in the heat treatment process of the present invention. In this instance the 1.5 per cent carbon ferrous alloy casting was heated to 1700 F. and maintained at this temperature for a period of 2 hours and then air cooled, then reheated to a temperature of 1450 F. and maintained at this temperature for a period of 5 hours and then furnace cooled, and then reheated to a temperature of 1500 F. and maintained at this temperature for a period Of 1 hour and finally water quenched for a period of one minute. The resulting structure contains spheroidized carbide 5 in a matrix 6 of hard martensite.

The graphs shown in Fig. 7 illustrate the effect of graphitic carbon in a 1.5 per cent carbon ferrous alloy casting. Thus in Fig. 7 the ordinates are in terms of radial wear in inches upon a railway freight car wheel and the abscissae are in terms of the number of thousands of miles which the car traveled during 10,000 miles of a test with a constant load per wheel of 10.5 tons.

Thus in Fig. '7, graph '7 shows the effect of the test upon a railway freight car wheel comprised of a 1.5 per cent carbon ferrous alloy (steel) casting, in which the carbon was largely in the form of spherodizecl carbide except for 0.50 per cent'of graphitic carbon, and graph 8 shows the results of the same test upon another wheel on the same railway freight car but which .was

(steel) casting which had been heat-treated in whereas under identical conditions in the same test the railway freight car wheel composed of a 1.5 per cent carbon 'spheroidized steel casting containing only 0.04 per cent of graphitic carbon exhibited a total radial wear of only 0032" after a total radial wear of 0.085 after 10,000 miles 10,000 miles under a constant wheel load of 10.5

tons.

In the practice of the present invention some latitude may be allowed in the heat treatment employed but, in general, the 1.30 to 1.65 per cent carbon ferrous alloy is heated to a temperature of from 1600 F. to 1900 E, which is above the temperature range favoring the formation of the iron carbide network, and the said ferrous alloy is maintained at this temperature for a period of at least 2 hours and preferably 5 hours. then cooled to atemperature below the austenite transformation temperature, (about 1325 F.) depending upon the cooling rate, then reheated to a temperature of from not substan: tially less than 1350 F. to not substantially more than 1500 F. and maintained at this temperature for a period of at least 2 hours, but preferably 5 hours, and then cooled at a controlled rate depending upon the hardness desired in the resulting heat-treated and cooled spherodized carbon ferrous alloy casting. Thus air cooling affords greater hardness and furnace cooling a softer structure.

The heat treatment of the present invention rous alloy castings having a carbon content of 1.30 to 1.65 per cent, by weight.

In another aspect of the invention it has been found that when a high carbon ferrous alloy casting of the character hereinbefore described is subjected to liquid quenching in oil or water, rather than to air cooling, after having been reheated to a temperature of from 1350 F. to 1450 F. for a period of at least two hours, a martensitic-bainitic structure is provided which, upon subsequent tempering possesses the same. desirable characteristics as the pearlitic structure hereinbefore described for use in and as railway car wheels, and thelike.

It will thus be seen from the foregoing description, considered in conjunction with the accompanying drawings, that the present invention provides a new and improved method for spheroidizing high carbon (1.30 to 1.65 per cent) ferrous metal alloys by heat treatment alone and without graphitization (and the resulting decrease in wear resistance), and without the necessity for forging to break up the carbide network in the alloy, and that the invention thus provides a new and improved high carbon (1.30.

to 1.65 per cent) ferrous alloy casting having the desirable properties and characteristics which are inherent therein and which have been referred to hereinbefore including good wear resistance, high tensile strength, appreciable ductibility,

and high resistance to both thermal and impact shocks.

hereinbefore pointed outand others which are inherent therein.

We claim: y 1

l. A method of-spheroidizing while avoiding graphitization in a high carbon ferrous alloy casting which, as cast, embodies a grain boundary carbide network and which contains not less than 1.30 per cent nor more than 1.65; per cent carbon, 0.40 to 1.00 per cent manganese, metallic carbide forming agents in the form of from 0.00 to 0.60 per cent chromium, and 0.00 to 0.12 per cent sulphur, graphitizing-deoxidizing agents in the form of from 0.15 to 0.50 per cent silicon and from 0.02 to 0.10 per cent aluminum, in terms of per cent, by weight, with the balance being substantially all iron, so as to eliminate said grain boundary carbide network therefrom and to provide a ferrous alloy casting which contains not more than 0.12 per cent of graphitic carbon, by Weight, said method comprising the steps of heating said ferrous alloy casting to a temperature of from 1650 F. to 1900 F. and maintaining said alloy casting at this temperature for at least one hour, cooling the thus heated ferrous alloy casting to a temperature below the austenite transformation temperature and reheating the thus cooled ferrous alloy casting to a temperature of from 1350 F. to 1500 F. and maintaining it at thistemperature for a period of at least two hours, whereby the metal carbides present in said carbide network are completely spheroidized and said carbide network thus eliminated, and then cooling the thus heat-treated ferrous alloy casting at a controlled rate depending upon the hardness desired in the resulting heat-treated and cooled spheroidized alloy casting, the relationship between the said metalliccarbide forming agents and the said graphitizing-deoxidizing agents necessary to assure that the resulting ferrous alloy casting will contain not more than 0.12 per cent, by weight, of graphitic carbon being indicated by the following formula in which all parts indicated are in terms of per cent, by weight:

Per cent C+0.2 (per cent Si plus percentAD-I- (per cent Mn0.'70)'1.5 per cent Cr5 (per cent S0.04) 1.14=per cent graphitic carbon in resulting heat-treated ferrous alloy casting and which is less than 0.12 per cent, of graphitic carbon, by weight.

2. The method defined in claim 1 in which the final cooling of the heat-treated ferrous alloy casting is done by air cooling.

3. The method defined in claim 1 in which the final cooling of the heat-treated ferrous alloy casting is effected by liquid quenching.

4. A high carbon ferrous alloy casting which is the product of the method defined in claim 1.

5. A high carbon ferrous alloy casting which is the product of the method defined in claim 2 and which is characterized by the absence of grain boundary carbide network and by the presence therein of not in excess of 0.12 per cent, by weight, of graphitic carbon, and which when air cooled after having been subjected to the reheating treatment at a temperature of from 1350 F. to 1500 F. forms a pearlitic structure containing spheroidized carbides and possessing high wear resistance, high tensile strength, appreciable ductility and high resistance to both thermal and impact shocks.

6. A-high carbon ferrous alloy casting which is the product of the method defined in claim 3. and which is characterized by the absence of grain boundary carbide network and by the presence therein of not in excess of 0.12 per cent, by weight, of graphitic carbon, and. which when liquid quenched after having been subjected to the reheating treatment at a temperature of from 1350 F. to 1500 F. forms a martensiticbainitic structure containing spheroidized carbides and possessing high wear resistance, high tensile strength, appreciable ductility and-high resistance to both thermal and impact, shocks.

Number Name Date Bonte July 20; 1937 McCarro1 Feb. 27, I945 Bonte fi Dec. 3'1, 1946

Claims (1)

1. A METHOD OF SPHEROIDIZING WHILE AVOIDING GRAPHITIZATION IN A HIGH CARBON FERROUS ALLOY CASTING WHICH, AS CAST, EMBODIES A GRAIN BOUNDARY CARBIDE NETWORK AND WHICH CONTAINS NOT LESS THAN 1.30 PER CENT NOR MORE THAN 1.65 PER CENT CARBON, 0.40 TO 1.00 PER CENT MANGANESE, METALLIC CARBIDE FORMING AGENTS IN THE FORM OF FROM 0.00 TO 0.60 PER CENT CHROMIUM, AND 0.00 TO 0.12 PER CENT SULPHUR, GRAPHITIZING-DEOXIDIZING AGENTS IN THE FORM OF FROM 0.15 TO 0.50 PER CENT SILICON AND FROM 0.02 TO 0.10 PER CENT ALUMINUM, IN TERMS OF PER CENT, BY WEIGHT, WITH THE BALANCE BEING SUBSTANTIALLY ALL IRON, SO AS TO ELIMINATE SAID GRAIN BOUNDARY CARBIDE NETWORK THEREFROM AND TO PROVIDE A FERROUS ALLOY CASTING WHICH CONTAINS NOT MORE THAN 0.12 PER CENT OF GRAPHITIC CARBON, BY WEIGHT, SAID METHOD COMPRISING THE STEPS OF HEATING SAID FERROUS ALLOY CASTING TO A TEMPERATURE OF FROM 1650* F. TO 1900* F. AND MAINTAINING SAID ALLOY CASTING AT THIS TEMPERATURE FOR AT LEAST ONE HOUR, COOLING THE THUS HEATED FERROUS ALLOY CASTING TO A TEMPERATURE BELOW THE AUSTENITE TRANSFORMATION TEMPERATURE AND REHEATING THE THUS COOLED FERROUS ALLOY CASTING TO A TEMPERATURE OF FROM 1350* F. TO 1500* F. AND MAINTAINING IT AT THIS TEMPERATURE FOR A PERIOD OF AT LEAST TWO HOURS, WHEREBY THE METAL CARBIDES PRESENT IN SAID CARBIDE NETWORK ARE COMPLETELY SPHEROIDIZED AND SAID CARBIDE NETWORK THUS ELIMINATED, AND THEN COOLING THE THUS HEAT-TREATED FERROUS ALLOY CASTING AT A CONTROLLED RATE DEPENDING UPON THE HARDNESS DESIRED IN THE RESULTING HEAT-TREATED AND COOLED SPEROIDIZED ALLOY CASTING, THE RELATIONSHIP BETWEEN THE SAID METALLICCARBIDE FORMING AGENTS AND THE SAID GRAPHITIZING-DEOXIDIZING AGENTS NECESSARY TO ASSURE THAT THE RESULTING FERROUS ALLOY CASTING WILL CONTAIN NOT MORE THAN 0.12 PER CENT, BY WEIGHT, OF GRAPHITIC CARBON BEING INDICATED BY THE FOLLOWING FORMULA IN WHICH ALL PARTS INDICATED ARE IN TERMS OF PER CENT, BY WEIGHT: PER CENT C+0.2 (PER CENT SI PLUS PERCENT AL)+ (PER CENT MN-0.70)-1.5 PER CENT CR-5 (PER CENT S-0.04)-1.14=PER CENT GRAPHITIC CARBON IN RESULTING HEAT-TREATED FERROUS ALLOY CASTING AND WHICH IS LESS THAN 0.12 PER CENT, OF GRAPHITIC CARBON, BY WEIGHT.

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