US2978320A - Method for producing a high strength ferrous metal - Google Patents

Description

United States METHOD FOR PRODUCING A HIGH STRENGTH FERROUS METAL William B. Larson, Birmingham, Robert F. Thamson, Grosse Pointe Woods, and Fred J. Wehhere, @rchard Lake, Mich, assignors to General Motors (Iorporation, Detroit, Mich., a corporation of Delaware No Drawing. Filed Dec. 29, 1958, Ser. No. 783,144

'8. Claims. (Cl. 75-130) present invention, describes and claims an improved ferrous metal composition which provides castings having outstanding mechanical properties. These properties result from the fact that substantially all of the hypereutectoid carbon is present as free graphite in a compacted or roughly spheroidal form with practically no hypereutectoid carbide being present. In order to obtain this desirable microstructure, specified small amounts of carbon, silicon, and boron must be present in the metal, and the melt is preferably also inoculated with tellurium and/or bismuth.

The cast ferrous product described and claimed in the aforementioned White et al. patent application possesses outstanding mechanical properties in both the as-cast and heat treated conditions. For example, castings formed from this material have, in the as-cast condition, a modulus of elasticity of at least 27.5 p.s.i., a minimum tensile strength of 80,000 p.s.i., and a yield strength of at least 60,000 psi. at 0.2% ofiset. In some instances the modulus of elasticity is as high as 29x10 p.s.i., while the tensile strength ranges up to about 90,000 psi.

However, we have found that even the preferred composition disclosed in the White et al. patent application without the aforementioned inoculations may solidify in .a wide range of microstructures.

These microstructures vary from all gray iron containing flake graphite and some isolated compacted graphite in one extreme to all white iron with no free graphite on the other. This variation is believed to be the primary cause of the different amounts of residual iron carbide observed after inoculation.

Accordingly, it is a principal object of the, present invention to eliminate any inconsistency in the microstructure of this type of ferrous metal. A further object of this invention is to provide a method of producing a ferrous metal product which always possesses the aforementioned desirable mechanical properties and micro- .structure without the necessity of inoculating the melt with tellurium and/or bismuth. A still further object of our invention is to provide a simple and inexpensive process for forming such a ferrous metal alloy in which the desired microstructure may be consistently produced,

thereby insuring that all castings have the same outstanding mechanical properties.

These and other objects are attained :in accordance with this invention by a process in which the boroncontainingmoltenferrous metal in .eachheat is brought line to the same metallurgical condition. This is done prior to inoculation with tellurium, if tellurium is .to be added. Specifically, the desirable microstructure and mechanical properties of the ferrous metal are obtained by superheating the base metal at a temperature of approximately 2900 F. to 3100 F. for a short period of time prior to tapping and inoculation, if the latter is employed. A superheat temperature of 2950 F. to 3000 F. is generally preferred. Also, desirable agitation can be provided by lancing or flushing the melt, which is preferably also superheated, with a dry gas to produce turbulence. The latter procedure considerably reduces the necessary holding time at superheat to produce the desired microstructure.

Superheating the melt to the foregoing temperature in accordance with our invention eliminates the necessity of inoculating the melt with tellurium and/or bismuth in most instances and still provides castings which consistently contain free graphite in compacted form without the presence of any appreciable amount of iron carbide or flake graphite. Moreover, we have now found that a preferred microstructure can be obtained with the process described herein at a lower silicon content than was heretofore possible. For example, excellent results are provided with a ferrous metal of this type which contains only about 1.5% silicon. The resultant castings have improved as-cast strength and ductility.

As indicated above, this new steel-like material, which has a substantial amount of graphite in the as-cast condition, contains a controlled amount of boron as well as silicon and carbon. The composition is such that the metal normally would solidify as a white cast iron if no boron were present; that is, in the absence of boron the carbon will be present in the combined form rather than as free carbon. On occasion, it may be desirable to include a small amount of tellurium and/or bismuth in the melt. At the present time tellurium is preferred over bismuth as an inoculant because it appears to produce superior results.

The various constituents in the cast ferrous metal, of this invention are so balanced that free carbon separates out of the cast product in compacted form, generally similar to the temper carbon of conventional malleable iron, rather than in flake form as in ordinary gray cast iron. In general, the ingredients of the new cast material are present in amounts to provide a ferrous base metal comprising approximately 1% to 2.5% carbon, 1.5% to 3.2% silicon, manganese not in excess of 1.15%, 0.001% to 0.02% boron and the balance substantially all iron. For optimum results, the carbon content should be between 1.5% and 1.9% and the silicon content approximately 2% to 2.6%. V

When tellurium is employed, it should not be present in an amount greater than about 0.01%, a tellurium addition of about 0.003% to 0.008% being preferred. A tellurium content exceeding 0.008% results in a tendency to produce chill in thin sections. This result of using higher tellurium contents is of particular interest since the preferred composition set forth above is not highly section sensitive in that there is only a slightly greater tendency for hypereutectoid carbide formation in thin sections than in heavy sections. If bismuth rather than tellurium is used, as much as 0.02% of this material may be used. Although both tellurium and bismuth may be present at the same time, the total amount of these constituents should not exceed approximately 0.02%.

Of course, sulfur is normally always present in cast iron and steel, and this constituent is not detrimental to the resultant product in quantities even as large as 0.5%, provided the metal also contains a sufiicient amount of manganese. Usually, however, about 0.3% is the maxi.-

mum amount of sulfur normally found in such ferrous metals. The manganese counteracts the detrimental effects of sulfur by combining with it to form manganese sulfide.

Accordingly, it is desirable to have a sufficient amount of manganese present to combine with the sulfur, but an excess of either of these constituents is detrimental since it results in undesirable carbide stabilization. The preferred manganese content should satisfy the equation Mn=1.7 (percent sulfur)+0.2. In practice, sulfur will always be present, and the sulfur content usually is at least 0.02% unless a special procedure is employed for reducing the amount of sulfur. However, manganese sulfide functions as a chip breaker in machining operations and thereby improves the machineability of the resultant castings. It also appears that the presence of sulfur may somewhat improve the fluidity of the molten cast metal. From the standpoint of the present invention, manganese does not appear to be necessary if no sulfur is present.

A cast ferrous base metal having the following composition appears to possess optimum physical properties: 1.5% to 1.9% carbon, 2% to 2.6% silicon, 0.3% to 0.8% manganese, 0.05% to 0.2% sulfur, 0.005% to 0.015% boron and the balance iron. However, for some applications it may be desirable to include as much as 0.05% boron and to use tellurium in an amount as small as 0.001% or as large as 0.01%. If bismuth is substituted for tellurium, the preferred range is between 0.005% and 0.01%. tained using an as-cast malleable iron consisting essentially of 1.7% carbon, 2.25% silicon, 0.4% manganese, 0.1% sulfur, 0.01% boron, 0.05% phosphorus and the balance iron.

Of course, the impurities normally found in cast iron may be present in the usual small amounts. In addition to the elements listed above, the ferrous base product of the present invention also may contain one or more of the various elements which are frequently present in cast iron either as impurities in small quantities or as intentional additives in larger, controlled amounts when particular properties are desired. These elements include chromium, nickel, copper, titanium, aluminum, vanadium, molybdenum, tin, etc.

It should be noted that the high silicon content and the low carbon content of this new ferrous base material are just the reverse of the proportions of these elements normally used in cast irons. tion, in conjunction with the presence of boron and the application of superheat. which imparts to the resultant product its high modulus of elasticity and outstanding versatility.

While it is possible to produce compacted graphite in castings having compositions within the broader ranges recited above, the narrower ranges are preferred in order to produce optimum results. The low carbon, high silicon composition, such as one containing 1.80% carbon and 2.25% silicon, has been found to be peculiarly susceptible to the formation of compacted graphite when processed according to the present invention. Deviations from the preferred analysis may result in useful but less favorable structures. For example, in some instances section sensitivity is encountered with compositions outside the narrow ranges listed above. Moreover, the higher carbon or lower silicon levels which approach those of conventional malleable iron produce a corresponding increase in hypereutectoid iron carbide. Although this carbide may be substantially eliminated by raising the silicon content or by inoculation with various graphitizers, such procedures frequently produce some flake graphite, particularly in heavy sections of the casting. As is true with conventional pearlitic malleable iron and so-called ductile cast iron or nodular iron, the presence of flake graphite or hypereutectoid iron carbide reduces the strength and ductility of the metal. Tensile tests indicate, however, that the presence of Excellent results have been obu It is this unique combinasome small hypereutectoid carbide particles randomly distributed throughout the metal is much less detrimental to mechanical properties than the presence of flake graphite. Acceptable strength and ductility can be obtained with this improved ferrous metal in both the as-cast condition and in the heat-treated condition even when some carbide is present in this form. While we have found that the presence of approximately 5% by volume of Type D graphite may lower tensile strength by 20,000 psi. and reduce the ductility drastically, we have also found that the presence of stubby flakes or quasi-flake graphite in small amounts generally has no appreciable effect on either tensile strength or ductility. It appears that if the base iron melt having the preferred composition is a type which would solidify as only white iron with no free carbon being present, the inclusion of boron alone would produce a structure having of the free carbon in the form of compacted graphite and which contains no residual hypereutectoid iron carbide. Superheating the melt at a temperature of 2900" F. to 3050 F., however, insures such a structure regardless of the structure of the base iron without boron.

If the retained boron is present in a quantity greater than approximately 0.02%, some stabilized hypereutectoid carbide will be produced. Consequently, the addition of excess boron does not compensate for the deleterious effects produced by too high a carbon content. Chemical analysis has indicated that when the preferred compacted graphite structure is obtained, more than twothirds of the total boron is present as acid-insoluble boron, while an increased amount of Type D flake graphite with less compacted graphite is associated with an increase in acid-soluble boron. It therefore appears that the formation of compacted graphite is correlated with the presence of an acid-insoluble boron compound. The acid solubility of the boron in the metal was deter mined by standard analyses using a solution of 20% sulfuric acid or phophoric acid.

Although boron is the essential ingredient which produces compacted graphite in the composition described herein, the use of superheat insures against the formation of flake graphite. Regarding hypereutectoid iron carbide, it is generally desirable to reduce the amount of this compound to less than 1% of the volume of the metal, although for some applications the carbide content may range up to 5% or higher. However, it is much more diflicult to machine the cast product when it contains more than about 2% hypereutectoid iron carbide. Nevertheless, the presence of this carbide contributes measurably to the wear resistance of the metal, and consequently a hypereutectoid carbide content as high as even 10% by volume may be desirable in applications where high wear resistance is an important factor. As indicated above, the present process applied to the preferred composition consistently produces a cast ferrous base metal which contains less than 1% hypereutectoid carbide.

This metal may be prepared by various melting processes employed in making conventional iron castings. Direct arc melting and high-frequency induction melting are among the specific procedures which have been successfully used. Likewise, either batch-type or continuous cupola-direct arc duplcxing operation may be employed. The process for producing the ferrous base metal appears to be independent of the furnace lining used. Heats have been successfully melted in furnaces lined with SiO (acid), MgO (basic) and zirconium silicate (neutral). Tapping and pouring temperatures of 2750 F. to 2850 F. and 2600 F. to 2700 F, respectively, provide satisfactory results. These temperatures are consistent with current malleable iron practice. However, the tapping temperature may range from about 2700 F. to 3000 F. under particular conditions, and the pouring temperature may be as high as approximately 2750 F.

Apparently because of the low carbon content of the oxidize the metal.

metal, melting .in direct arc furnaces frequentlyresults in some porosity due to occluded gas. This condition can be avoided by melting the metal under a protective slag.

The optimum carbon content of approximately 1.8% may be obtained by a mixture of plain carbon steel and conventional white iron, such as an iron containing 2.6% carbon, 1.4% silicon, 0.35% manganese and 0.1% sulfur. When melting in induction furnaces, it is convenient to mix white iron scrap with the steel and to melt these two metals together. On the other hand, when a direct arc furnace is used, it appears desirable to transfer the molten iron from the cupola to a direct arc furnace and to subsequently add an appropriate amount of slag. The molten steel, which has previously been melted in a second direct arc furnace, is then mixed with the cupola metal. Such a procedure provides consistent chemistry control due to minimum oxidation loss and also constitutes a convenient means of preventing gas pickup.

Cold melting by direct arc is also possible, but the higher carbon content white iron should be melted and a fluid slag obtained prior to adding steel. In either direct are or induction melting, silicon and manganese may be added to the metal at any stage.

We have also found that the desirable low carbon content may be produced by employing an oxygen jet converter type of arrangement to reduce the carbon content of conventional cupola melt malleable iron. A refractory-lined vessel and a water-cooled copper lance maybe used. By carefully controlling the chemistry and quantity of the hot charge and metering the oxygen, it is possible to accurately predict thecarbon content of the melt at any time during the blow, Silicon and manganese can be added to the receiving ladle upon tapping of the melt in order to compensate for losses which occur during the blow and to maintain proper amounts of these elements in the melt. These additions also serve to de- If the melt is to be inoculated with boron and/ or tellurium, this may be .done while tapping the metal from the receiving ladle to a transfer ladle. However, such a practice .does .not appear to be as economical as .a normal cupola .direct arc duplexing operation.

The importance of a microstructure which is substantially free of hypereutectoid iron carbide and flake graphite is well recognized in the nodular iron and malleable iron industries. To produce such a microstructure inaccordance with the present invention, it is necessary to use the aforementioned amount of boron. However, it is generally found that the base metal will have some boron present and, by superheating the boron-containing rmelt as described herein, it frequently is unnecessary to inoculate it with additional boron. A residual boron content of approximately 0.001% to 0.003% normally can be obtained from white iron scrap used in the base charge. 1

Ladle additions of boron and tellurium land/or bismuth, if employed, areadjusted according to the composition of a base iron, melting conditions, .etc. A boron inoculation may be made with a number of boroncontaining compounds. Among the inoculants which can be employed are ferroboron, boron carbide, calcium boride, nickel-boron, pure boron metal and anhydrous borax. Tellurium also may be added in various forms,

such as pure tellurium, ferrotellurium or copper-tellurium, for example; and bismuth can be introduced as .sub-

t6 However, in large production quantities where considerable turbulence is generated, the additive or additives may be placed in the bottom of the receiving ladle or introduced into the stream.

When the ferrous metal having the aforementioned composition is heated to a conventional melting and pouring temperature of about 2700 F. to 2800 F. and thereafter cast, the microstructure of the resultant castings frequently will not show the desired spheroidal or compacted graphite. On the other hand, when such a metal is superheated to a temperature between approximately 2900 F. and 3050 F., and held at this temperature for at least 10 minutes, the castings produced have a microstructure which contains considerably less massive or hypereutectoid carbide. Furthermore, the free graphite has a roughly spheroidal or compacted configuration quite similar to the obtained by annealing white iron.

It should be noted that superheating the melt at. the aforementioned temperature results in less retained carbide in the cast structure than heating an identical melt to only 2800 F. This result is contrary to the .normal concept that superheating cast iron has a de-graphitizing effect because it destroys centers of nucleation.

in general, a superheat temperature between 2950 VP. and 3000 F. is preferred. With a melt which has been induction heated to such a temperature, a holding time at superheat of about 15 to 25 minutes is highly satisfactory. can be obtained with superheat times as short as 10 minutes in an induction furnace, a period of 15 to 20 minutes is preferable to insure complete compacting of the free graphite. If a direct arc furnace is employed, the time the melt must be held at superheat to produce the proper microstructure can be reduced to approximately 2 to 5 minutes.

As hereinbefore stated, this microstructure can be pro duced at a somewhat lower melt temperature in an induction furnace by agitating the molten metal with dry gas introduced below the surface of the melt. Such lancing or flushing of the melt to produce turbulence also considerably reduces the necessary holding time at superheat. Thus it is possible to combine the superheating and gas treatment to produce a compacted graphite structure in 2 to 5 minutes at superheat. The result evidently is not dependent upon chemical reaction with the gas and may be accomplished with an inert or reducing gas as well as with an oxidizing gas. However, the gas should be in a dry condition. Examples of dry gases which have proved to be satisfactory are air, oxygen, nitrogen, argon, helium, carbon dioxide and ammonia gas, although other dry gases may be employed. Gas lancing of the melt appears to be considerably more effective in an induction furnace than in adirect arc furnace or the ladle. The typical long, narrow induction furnace permits more thorough agitation of the melt by the gas.

Superhe'ating accompanied by gas lancing produces a predominance of compacted graphite without adding tel- .lurium and without the necessity of boron inoculation, provided the base metal contains a sutficient amount of boron. As indicated above, however, a tellurium inoculation further helps to eliminate any small amount of flake graphicwh-ich might otherwise be present and provides for more compact graphite nodules. In the absence of superheating, it is quite frequently found that residual flake graphite is present in the solidified boron-containing castings.

When the melt is superheated to the proper temperature, the reaction time required with gas flushing is very constant, requiring two to fourminutes for pounds of molten metal at a gas flow rate of 20 cubic feet per hour. This flow rate is equivalent to approximately 0.0145 cubic foot of gas per pound of metal. In general, we have found that a lancing rate of about 0.01 to 0.03 cubic foot of ,gas per pound of metal provides satisfactory results.

While the desired microstructure frequently Of course, higher gas lancing rates may be employed, but normally no additional benefits are provided by gas rates in excess of those hereinbefore listed. Likewise, it is obvious that lower flow rates for the gases may be used when superheating is employed in conjunction with gas lancing.

As hereinbefore mentioned, the influence of gas flushing is not due to chemical reaction of the molten metal with the gas, but instead evidently results fro-m the turbulence created by the gas stream. The eflect of flushing on induction melts is reduced at lower temperatures because of the decreased fluidity of the melt. Accordingly, a considerably longer lancing time is required to provide any beneficial results at temperatures in the order of 2750 F. to 2800 F. than at the superheat temperature of 2900 F. to 3000 F. At the former relatively low temperatures, a lancing rate of approximately 0.025 cubic foot of oxygen per pound of melt was required to produce any benefits, while excellent results were obtained with lancing a melt superheated to 2900 F. with an oxygen flow rate of only about 0.0145 cubic of oxygen per pound of melt.

Unlike purging with the other gases mentioned, an ammonia or ammonium chloride flush in an induction heated melt appears to result in a more porous casting. The gaseous condition produced by NH CI and NH evidently is largely attributable to nitrogen because we have found that the addition of about 0.03% aluminum or titanium following a NH lance completely eliminates the porosity otherwise produced in the castings. The titanium addition resulted in the formation of titanium nitrides in the microstructure. Additions of approximately 0.1% aluminum or titanium were highly successful in eliminating porosity in castings poured from direct arc melts.

If gas lancing is employed, the gas may be introduced by means of a steel tube coated with a suitable refractory, such as an oxide wash. Such a tube can be used in the uncoated condition, but a fired ceramic coating, for example, reduces any tendency for the tube to melt. A refractory tube or a graphite tube coated with a refractory also may be employed, but any ceramic should be preheated before insertion into the melt to prevent cracking from thermal shock. In general, the outlet end of the tube should extend at least six inches below the surface of the molten metal. A tube having an internal diameter of A inch to /2 inch is satisfactory, but the tube may be larger or smaller depending upon the flow rate and the size of the melt. If the flow rate is maintained constant, the larger diameter tube is more inclined to become clogged with semi-molten metal. Of course, too high a flow rate would actually tend to blow the metal out of the furnace.

Extreme preferred orientation of compacted graphite can be produced when pouring temperatures are excessively high due to pouring too soon after tapping of the superheated melt. High pouring temperatures tend to produce larger primary austentite dendrites and magnify the segregation of these dendrites and graphite, the last constituent to solidify; and we have found that a relatively low pouring temperature substantially eliminates this condition of preferred orientation of compacted graphite. Hence it is highly desirable to pour the molten ferrous metal from the ladle into the mold at a temperature below 2800 F. In general, pouring temperatures of 2650" F. to 2700 F. are preferred.

Various tests were conducted to determine the mech anism involved in the graphitizirig eflect produced by superheating. For example, one heat had a composition of about 1.83% carbon, 2.6% silicon, 0.4% manganese, 0.01% boron, 0.09% sulfur and the balance iron. This melt was melted at approximately 3000" F. in a magnesia crucible, transferred to a ceramic lined ladle, and subsequently poured into a sand mold. Almost all the graphite was of the compacted type. The iron carbide was about completely eliminated, even in casting sections having a thickness of only inch, by a twenty-four minuteholding time at superheat temperature.

Another heat consisting of about 1.76% carbon, 2.6% silicon, 0.42% manganese, 0.01% boron, 0.1% sulfur and the balance iron was heated to 2900 F. It was then lanced with oxygen for one to four minutes with a flow rate of approximately 13 cubic feet per hour. The resultant castings exhibited a good compacted graphite structure. Optimum graphite density and complete elimination of excess iron carbide were obtained with only a two minute lancing period.

Other specimens of generally similar composition, which were superheated at 2900 F. and lanced with argon, were completely free of iron carbide and contained compacted graphite. Similar results were obtained with nitrogen lancing at 2900 F. Hydrogen also was successfully employed, but the graphite was somewhat less dense than in heats lanced with oxygen, nitrogen or argon.

Tests also show that this ferrous metal composition contains excess carbide if it is superheated much above 3050 F. For example, one heat consisting of about 1.6% carbon, 2.6% silicon, 0.35% manganese, 0.01% boron, 0.1% sulfur and the balance iron was superheated for eighteen minutes at 3100 F. with no gas lancing being employed. A relatively large amount of carbide was present in the resultant castings, indicating that superheating above about 3000 F. provides no additional advantages and superheating at a temperature higher than approximately 3050 F. appears to be detrimental.

The steel-like ferrous metal produced by the foregoing process consistently possesses a tensile strength of 80,000 to 100,000 p.s.i. at 2% to 3% elongation at rupture without the benefit of heat treatment. Its modulus of elasticity of 27.5 to 28.5 million p.s.i. is superior to that of any other known cast iron type of material, including gray cast iron, malleable iron, and ductile iron produced with magnesium or rare earth inoculations. These desirable mechanical properties make this material particularly advantageous for applications requiring stiffness and high strength, such as for crankshafts of gasoline and diesel engines.

The feeding characteristics of the cast ferrous base metal processed in accordance with this invention are only very slightly inferior to those of white cast iron of the compositions commonly used in making conventional malleable iron. The relatively high silicon content of this material undoubtedly measurably contributes to these satisfactory feeding characteristics. As a result, sound castings of various shapes and sizes can be readily formed. In casting many articles the cast-to-clean ratio can be made equal to that of conventional malleable iron by the addition of small quantities of an exothermic riser compound.

Castings of this ferrous base metal can be successfully produced in green sand molds, dry sand molds and shell molds with no apparent variation in results. Unlike white cast iron, the metal exhibits no tendency to mottle when poured into shell molds. Also, the prevention of flake graphite formation is not a serious problem as is true with nodular iron. Another very important consideration is the fact that the condition of cope side segregation of graphite nodules, which frequently is present in nodular iron castings, does not occur in the ferrous metal described herein. Homogeneous microstructures are obtained in castings of all sizes.

When this metal was made into test castings having section thicknesses ranging from A1. inch to several inches, there was no greater tendency for carbide to form in the thin sections than in the larger sections, even though the size of the graphite nodules was somewhat reduced.

Moreover, the machineability of this ferrous metal, either in the as-cast condition or after heat treatment, appears to be entirely satisfactory. When compared with pearlitic malleable iron, it was found that identical turning speeds and feed rates may be used, while drilling cast metal is somewhat less than in pearlitic malleable Since the'cast metal produced by our process may be annealed at temperatures in the order of 1350 F. to provide a ferritic matrix, it .is possible for a single foundry using the same base iron to produce all of the parts currently formed from both ferritic and ,pearlitic malleable iron. Moreover, the increased strength resulting from normalizing and quenching and tempering treatments, as well as the high elastic modulus of the metal, permits it to be used in forming articles which are conventionally forged from plain carbon steel.

It should 'be noted that this cast ferrous metal requires no costly or explosive addition agents, injection apparatus, or extensive heat treatment. Of course, there is no problem with regard to clogging of injection-tubes or controlling feed rates of injected material. Also, since an injection operation is not used, there is no reduction in temperature caused by such a procedure, and speed in the preparation of the metal is not an important factor. Late ferrosilicon additions are not required to reduce the chill of the metal. Furthermore, unlike some of the upgraded cast irons heretofore made, a dry, granular slag is not formed during production of the metal and hence does not present any removal problems Likewise, it is unnecessary to de-sulfurize the metal or to use a base metal having a very low sulfur content. It is also not necessary to employ a basic or neutral-lined ladle. Despite these facts, however, the outstanding mechanical properties of the new metal may be varied appreciably by short and inexpensive heat treating procedures to provide a diversity of useful products.

While the present invention has been described by means of certain specific examples, it will be understood that the scope of the invention is not to be limited thereby except as defined in the following claims.

We claim:

1. A method of producing a ferrous metal casting having a high modulus of elasticity, tensile strength and yield strength in the as-cast condition, said method com prising forming a melt which would solidify with an essentially White iron microstructure in the absence of boron, said melt comprising 1% to 2.5% carbon, 1.5%

to 3.2% silicon, manganese not in excess of 1.15%,

0.001% to 0.05% boron and the balance substantially all iron, superheating said melt to a temperature of about 2900 F. to 3100 F. for a period of time sufficient to insure that castings produced therefrom have a microstructure substantially free of flake graphite with free carbon predominantly in the form of compacted graphite, and subsequently pouring said melt at a temperature of about 2600 F. to 2800 F. into a mold.

2. A method of producing a ferrous metal casting having a high modulus of elasticity, tensile strength and yield strength in the as-c-ast condition, said method comprising forming a melt which would solidify with an essentially white iron microstructure in the absence of boron, said melt comprising approximately 1% to 2.5 carbon, 1.5% to 3.2% silicon, manganese not in excess of 1.15%, and the balance substantially all iron, superheating said meltto a temperature of about 2900 F. to 3100" F. for a short period of time suflicient to insure that castings formed from said melt have an as-cast microstructure substantially free of flake graphite with free carbon predominantly in the form of compacted graphite, thereafter tapping said melt into a ladle at a temperature of 2700 F. to 3000 F., inoculating the melt with boron in an amount suflicient to provide the melt with a boron content of about 0.001% to 0.05%, and subsequently pouring said inoculated melt at a temperature of about 2600 F. to 2800 F. into a mold.

3. A method of producing a ferrous metal casting 1 0 having a modulus of elasticity of ,at least 27.5- 010 p.s.i., said method comprising melting together a mixture of plain low carbon steel and white cast iron in a pro of about 2750 F. to 3000 F. and subsequently pouring said melt at a temperature of about 2600 F. to 2800 F. from said ladle into a mold.

4. A method of producing a ferrous metal casting having a modulus of elasticity of at least 27.5 X 10 .;p.s.i., said method comprising melting together a mixture of plain low carbon steel and white cast iron in a proportion such that the resultant melt comprises about, 1% to to 2.5% carbon, 1.5% to 2.8% silicon, manganese not in excess of 1.15 sulfur not in excess of 0.5% and the balance substantially all iron, superheating said melt to a temperature of about 2900 F. to 3100 F. for a short period of time sufficient to insure that castings formed from said melt have an as-cast microstructure substantially free of flake graphite with free carbon predominantly in the form of compacted graphite, inoculating said melt with boron in an amount suflicient to constitute approximately 0.001% to 0.02% of the melt, and subsequently pouring said melt at a temperature of about 2600 F. to 2700 F. into a mold.

5. A method of producing a ferrous metal casting having a modulus of elasticity of at least 27.5)(10 p.s.i., said method comprising forming a melt which would solidify with an essentially white iron microstructure in the absence of boron, said melt consisting essentially of about 1.5% to 1.9% carbon, 2% to 2.6% silicon, 0.3% to 1.15% manganese, 0.001% to 0.02% boron, 0.05% to 0.15% sulfur and the balance substantially all iron, superheating said melt to a temperature of about 2900 F. to 3000 F. for a period of time suflicient to insure that castings produced therefrom have an as-cast microstructure substantially free of flake graphite with free carbon predominantly in the form of compacted graphite, tapping said melt into a ladle, and subsequently pouring said melt at a temperature of about 2600 F. to 2700 F. from said ladle into a mold.

6. A method of producing a ferrous metal casting having a modulus of elasticity of at least 27.5 10 p.s.i., said method comprising forming a melt which would solidify with an essentially white cast iron microstructure in the absence of boron, said melt consisting essentially of about 1.5% to 1.9% carbon, 2% to 2.6% silicon, 0.001% to 0.015% boron, manganese not in excess of 1.15 sulfur not in excess of 0.5% and the balance substantially all iron, superheating said melt to a temperature of about 2900 F. to 3000 F. for a short period of time sufficient to insure that castings formed from said melt have an as-cast microstructure substantially free of flake graphite with free carbon predominantly in the form of compacted graphite, lancing said melt, thereafter tapping said melt into a ladle and subsequently pouring said lanced melt at a temperature of about 2600 F. to 2700 F. from said ladle into a mold.

7. A method of producing a ferrous metal casting having a modulus of elasticity of at least 27.5 10 p.s.i., said method comprising melting together a mixture of plain carbon steel and boron-containing white cast iron, the ratio of said steel to said white cast iron being such as to provide a melt consisting of about 1.5 to 1.9% carbon, 2% to 2.6% silicon, 0.005% to 0.02% boron, 0.3% to 1.15 manganese, sulfur not in excess of 0.03% and the balance substantially all iron, lancing said melt;

with a dry gas to produce turbulence of said melt, superheating the melt at a temperature of about 2900 F. to 3000 F. for a period of time sufiicient to insure that castings formed from said melt have an as-cast microstructure substantially free of hypereutectoid iron carbide and Type D flake graphite with free carbon predominantly in compacted form, tapping said lanced melt into a ladle at a temperature of 2750 F. to 3000 F., subsequently pouring said melt from said ladle at a temperature of about 2600 F. to 2700 F. into a mold.

8. A method of producing a ferrous metal casting having a modulus of elasticity of at least 27.5 10 p.s.i., said method comprising melting together in a furnace a mixture of plain carbon steel and boron-containing white cast iron, the ratio of said steel to said white cast iron being such as to provide a melt consisting of about 1.5% to 1.9% carbon, 2% to 2.6% silicon, 0.005% to 0.015% boron, 0.3% to 0.8% manganese, sulfur not in excess of 0.03% and the balance substantially all iron, lancing said melt while in said furnace with a dry gas to produce turbulence of said melt, superheating the melt at a temperature of about 2900" F. to 3000 F. for a short period of time sufiicient to insure that castings formed from said melt are substantially free of hypereutectoid iron carbide and Type D flake graphite with free carbon predominantly in compacted form, tapping said lanced melt into a ladle at a temperature of 2750" F. to 3000 F., inoculating the tapped melt with tellurium in an amount equal to approximately 0.001% to 0.01% of the weight of the melt, and subsequently pouring said inoculated melt from said ladle at a temperature of about 2600 F. to 2700 F. into a mold.

References Cited in the file of this patent UNITED STATES PATENTS Ihrig June 12, 1956

Claims (1)

1. A METHOD OF PRODUCING A FERROUS METAL CASTING HAVING A HIGH MODULUS OF ELASTICITY, TENSILE STRENGTH AND YIELD STRENGTH IN THE AS-CAST CONDITION, SAID METHOD COMPRISING FORMING A MELT WHICH WOULD SOLIDIFY WITH AN ESSENTIALLY WHITE IRON MICROSTRUCTURE IN THE ABSENCE OF BORON, SAID MELT COMPRISING 1% TO 2.5% CARBON, 1.5% TO 3.2% SILICON, MANGANESE NOT IN EXCESS OF 1.15%, 0.001% TO 0.05% BORON AND THE BALANCE SUBSTANTIALLY ALL IRON, SUPERHEATING SAID MELT TO A TEMPERATURE OF ABOUT 2900*F. TO 3100*F. FOR A PERIOD OF TIME SUFFICIENT TO INSURE THAT CASTINGS PRODUCED THEREFROM HAVE A MICROSTRUCTURE SUBSTANTIALLY FREE OF FLAKE GRAPHITE WITH FREE CARBON PREDOMINANTLY IN THE FORM OF COMPACTED GRAPHITE, AND SUBSEQUENTLY POURING SAID MELT AT A TEMPERATURE OF ABOUT 2600*F. TO 2800*F. INTO A MOLD.