US2291842A - Production of steel - Google Patents

Description

with the steel-making practice.

Patented tag. 4, 1942 PRODUCTION OF STEEL Jerome Strauss, New York, N. Y., assignor to Vanadium Corporation of America, New York, N. Y., a corporation of Delaware No Drawing. Application July 18, 1940,

Serial No. 346,141 1 18 Claims.

This application is a continuation in part of my .co-pending applications, Serial No. 192,325, filed February 24, 1938, and Serial No. 296,422, filed September 25, 1939.

This invention relates to the production of steels having properties not residing in the steels known to and made by the methods of the prior art which possess the same essential or nominal chemical composition, as ordinarily understood, as the steels described in this specification. It provides for a novel treatment whereby acombination of properties not hitherto associated with carbon and very low alloy steels may be assured thus producingin these steels an ability to satisfy uses from which they individually have heretofore been excluded. The properties and the steels in which they maybe produced as well as the sphere 'of utility of these steels will be apparent to those acquainted with the art, from the description and explanation following.

In the manufacture anduse of carbon and alloy steels and the adjustment or control of their compositions and methods of manufacture, with the objective of properly fitting the mechanical and other properties of the finished render, it is recognized that the behavior of any ments added 60 carbon steels to produce alloy steels important, but also those elements added to both typesof. steels to at least in part effect steel when cooling it from some elevated temperature at a rate tending to produce hardening afiords most valuable indications of its numerous mechanical and metallurgical characteristics. This behavior is influenced by many factors. Important among them is the carbon or carbide content and the size and number of the carbide particles prior to heating for hardening; equally important is the rate of solution of these carbides in the iron matrix at. any temperature from which some hardening can be efiected and, after solution, the rate and manner of their separation from the matrix on cooling at variousrates; this functioning of the carbide is closely associated with the remainder of the steel composition and In respect to the influence of the steel-making process, important effects are caused by the nature of the raw materials used, the type of slag covering employed for the purpose of effecting the refining operations performed on the-moltemmetal, the

changes in the composition and temperature 'of the slag during the course of the steel'refining and duringthe adjustment of the steel composition, and principally by thefinal conditioning of the molten metal as, for example, thecontrol of the content of oxygen or oxides and the materials and technique employed for this purpose. In recontrol overthe residual oxygen content. Theoretically, carbon steels are alloys of iron and carbon; practically, they contain in addition manganese or silicon or manganese and silicon to secure desired fabricating qualities, and sulphur, phosphorus, oxygen, nitrogen, non-metallic particles, and other impurities incident to the raw materials and manufacturing processes employed. Alloy steels contain in addition one or more other elements such as nickel, chromium, vanadium, molybdenum, copper, cobalt, 'etc.,

and/or increased quantities of manganese or silicon or of some of the elements regarded as impurities;

Other factors exert their influence, as will be referred to later, such as mechanical-thermal history of the steel, and the grain size of the matrix after partial or complete carbide solution; the latter in turn is the result of the conditions of heating for hardening combined with all of the phases of the steel-making and subsequent treatment. .When hardening these carbon or alloy'steels by heating and then cooling at a suitable rate, it is observed that the extent to which they harden is affected greatly by the mass of the article being hardened and further that the hardening characteristics as influenced by composition and manufacturing method, as noted above, determine whether a heated and quenched steel article of a given size or mass will harden throughout or only at and near the surface or not even harden fully at the'surface. In many machine parts deep hardening is important from the standpoint of having uniform strength throughout the section. To measure the performance of steels in hardening, it is customary to use one of two methods. The older practice is to heat bars of any steel, of suitable length and of different diameters (as for example 1, 2, 3 and 4 inches) to the temperatures employed for hardening, cool them in the desired quenching medium and, either when they have cooled to toas the Jominy method, is to heat a bar approximately 1 inch diameter and 3 inches long, to a suitable temperature and then transfer it to a simple fixture in which it is rapidly cooled by a stream of quenching fluid (usually water) at one end only, while the remainder is exposed only-to the atmosphere. A longitudinal flat surface is obtained by grinding away just a small amount of the cylindrical surface and the measured hardness along this strip is plotted against the distance from the quenched end.

As the temperature of carbon and low alloy steels isfincreased, for the purpose of hardening them, above a certain temperature range characteristic of each steel, the carbon (or carbides) present enters into solution in the iron or ironalloy matrix to form the phase designated as austenite. On cooling the steel from this condition, at a rate tending to produce hardening, it may according to its mass, the composition and characteristics of the steel and the characteristics of the cooling medium, be retained in the austen- 'For the purpose of this presentation it is not necessary to define these constituents by their microscopic or other characteristics or to refer to the different variations in which they occur. It is sufficient to point out that for any selected carbon or low alloy steel, retention on quenching (from' a state of partial or complete solution of carbon) of some austenite with martensite results in somewhat lessthan the maximum hardness of which the particular steel is capable, whereas all martensite retained on cooling gives the maximum of hardness; the occurrence of some or all troostite also means less than maximum hardness. The result in any instance depends on the actual cooling rate in the quenching operation. It has been observed that the time at constant temperature required for initiation of the decomposition of the austenite is at a minimum at about 900 to 1000 F. and that transformation is completed in minimum time at this temperature. Actually time and rate vary little over the range of about 1100 to 850 F. and experimental rates are measured over this approximate range. Hence for full hardening the cooling rate must be suflicient to prevent transformation in (or above) this temperature range (with the formation of troostite or softer constituents), and thereby enforce transformation of the cooled austenite at a lower temperature (probably not over 800 F.) resulting in a predominantly martensitic structure. The minimum rate necessary to attain this end is known as the critical cooling rate." This critical rate is fixed by the composition and by the physicalmetallurgical character of the steel as influenced by its mode of manufacture; for a given chemical composition as ordinarily determined it may vary widely according to its production history. Two major manufacturing'factors are involvedone the conditionsimposed up to the completion of solidification and the other the thermalmechanical treatment in the solid state; of these the former is of primary importance, although the end results depend also on the latter.

Each melt of steel, therefore, reacts in accordance with its molten-state history and solidification conditions, quite independent of its ordinary chemical composition, which behavior is ex- .pressed in part in carbon-diffusion characterissize in relation to temperature and time at temperature. Its critical cooling speed is quite closely associated with the actual grain size existing at the te'mperature from which cooling for hardening takes place. Fine grain size (such as A. S. T. M. standard of 7 or smaller) has been observed to be accompanied by rapid transformation of the austenite on cooling and coarse grain size (such as A. S. T. M. standard of 4 or larger) by slower transformation. Thus for full hardening throughout of a fine-grained steel of some given composition and section, the actual cooling rate must be high to equal or exceed the critical rate (since the critical rate is high), whereas for a coarse-grained steel of the same composition and section the actual rate for full hardening need not be so high since the critical rate is lower. Or, in the case of a fixed cooling rate, the fine-grained steel will fully harden to a lesser depth than will the coarse-grained steel in the same section size.

It has also been observed that for the same ordinary chemical composition fine-grained steels possess to a much greater extent than do coarsegrained steels those attributesso much in demand in many structural and machine parts; namely, ductility, toughness, and resistance to impact stresses. It has further been observed that certain elements added to steels, influence the grain size. For example, small amounts of vanadium (such as 0.15%) or aluminum (such as 0.05%), or titanium, (such as 0.05%) added, in the form of high carbon ferro-titanium for example, to a carefully made 0.40% carbon steel tend to produce fine grain size and hence shallow hardening. On the other hand, relatively large amounts of nickel or molybdenum or chromium, for example, by their effect upon the rate of carbide diffusion and not any relatively great infiuence on grain size, 'so vastly alter the critical cooling rate that they produce deeper hardening steels. These latter elements greatly improve the properties of the steels since they produce deep hardening by a means other than promoting coarse grain size; however, they do not enhance the toughness and impact strength of the steels to nearly so great a degree as if they were accompanied by fine grain size obtained in the manner previously noted. If toughness and impact strength combined with full hardening in medium to large sections is required, it has been necessary to combine the two groups of elements and to use rather large amounts of the lastmentioned group as, for example, 5% of nickel, or 2% nickel with 1% chromium and 0.3% molybdenum, or 3% chromium, molybdenum and vanadium. Manganese and silicon in practicable amounts greater than those present in commercial carbon steels also contribute to deep hardening (although not to the extent of the nickel or nickel-chromium-molybdenum or chromium molybdenum vanadium steels just noted) Manganese and silicon, however, tend to produce coarse grain size and hence require the grain refining elements to secure some degree of toughness and impact strength. But whenever the combination of deep hardening, toughness and impact strength has been required in high degree in manganese or silicon steels, these two elements alone plus the grain refining elements were not quite adequate so that other elements have had to be added as wellnickel, for example.

To summarize; fine grain is accompanied by toughness but shallow hardening, coarse grain is accompanied by deep hardening but low tough- ,trol, also costly.

ness, so that in the prior art to secure'full-hardcued-throughout, impact-resistantmediumto large sections it has been necessary to usev the grain refining elements plus large totalamounts of usually more than one element of-the deephardening type. The higher the actual hardness required in any specified. machine part the more necessary has been this combination of elements; moreover, to secure this high hardness along with very high toughness, especially in medium to large sections has demandedlarge amounts of these elements with their attendant cost, along with exceptionally careful manufacturing con- I have now discovered thatthe hitherto diametrically opposed fine grain size (with its ac-' and impact companying high toughness. strength) and deep hardening capacitymay be secured simultaneously, without the use of largeand costly amounts of the elements heretofore recognized as contributing. to deep hardening, by the addition to steel in a late stage of-its manufacture of very small amounts of an element heretofore regarded as contributing to fine grain size only and because of, or along with this contribution, to shallow hardening. This unexpected result is achieved by the addition of titanium provided that the element isin a certain state of restricted association with other ele-' ments.

I- have further discovered that the. addition of vanadium achieves certain advantages which are not imparted by the use of titanium alone. Still further advantages result from the incorporation of aluminum along with the vanadium and titanium under certain operating conditions so that the preferred addition is one comprising titanium,.vanadium and aluminum.

It has long been known to deoxidize molten steels by the addition to them of titaninm. alloys.

. Titanium for this purpose has been available in or 2.00% or more, but when not used for such purposes the addition has been-made in small amounts for the mere purpose of deoxidation, scavenging or other purification.

High carbon ferro-titanium, containing about 7.5% carbon'and 15 to 20% titanium has supplied the greatest tonnage of titanium for the metallurgical industry. In the deoxidation of killed steels of both carbon and low alloy types, it is in use in steel castings and alsoin ingot steels for railroad tires and wheels, rails, springs, heavy and light forgings' and numerous other classes of articles. In the partial deoxidation of steels for sheets subjected in fabrication to drawing and forming operations and for reinforcing bars, piling and other products in this category, it has been used in considerable quantity. For sheets, however, a lower carbon grade described as medium-carbon ferro-titanium has been recently preferred. With its 4% carbon and 15 to 20% titanium, it presents advantages due to the growing use of very low carbon steels for this purpose, namely 0.06% carbon and less, and the necessity for restricting the addition of carbon to the steel bath from all possible sources; this is important incontrolling the uniformity of the product at'minimum cost. Additions to these rimming steels are usually not over about three pounds of alloy per ton of steel or 0.006% carbon added but this is importent and is preferably notexceeded. Lower carbon aIIQYS would offer further advantage in this respect buttheir cost or the presence of. other elements in them is highly objectionable gin these rimmed sheet steels. In the killed steels previouslymentioned, grain size is often an important specification requirement. This is usually secured by aluminum additions; high-carbon and medium-carbon term-titanium have been tried to simultaneously deoxidize andproduce fine grain but even with amounts up to about 20 pounds per ton- .(about 0.18% titanium) they have not been successful and required simultaneuos use of some'aluminum. Fine grain size produced 5 by these. practices has always been accompanied by shallow hardening unless, of course, large amounts of alloying metals such as nickel, molybdenum or chromium are present. If the additions are small and the steel coarse grained, it

hardens somewhat more deeply but is then of lower toughness, especially when quenched and temperedto high hardness.

Numerous low-carbon titanium .alloyshave been available but their cost, due to necessarily costly production methods such as reduction by aluminum, has restricted their application to products of high value such as tool andelectric furnace steels. to the producerof tonnage steels of the carbon or low alloy class purely on the grounds of economy and there was, therefore, no stimulus to try to apply them or study them. Aside from a small tonnage entering into the production of nonferrous alloys, the ferro-titaniums of less than 0.20% carbon and 20 to titanium havefound four major uses. Additions of to 1 %of titanium in the form of these alloys are made to austenitic nickel-chromium steels, in order to improve their resistance to corrosive attack under certain conditions of fabrication and use. The titanium combines with the carbon of the steel, removing it from solution in the austenitic matrix, thus preventing precipitation of intergranular carbides (detrimental to corrosion preferably-does not exceed 15% of the titanium content. Another application of low-carbon ferro-titanium depends on this same association of titanium and carbon, namely, the use in medium to high chromium steels of from about 2 to' about 10 times as much titanium as there is carbon present. in the steel in order to combine with this carbon, remove it from the steel matrix and .thus prevent hardening on rapid cooling from heat treatment temperatures. This use, it will be observed, is'directly opposed to that of the present invention. In both of the uses just mentioned the stated proportions of titanium to carbon are those in the finished steel; actual addltions are higher, due to the losses sustained on adding, this loss usually being about 40%. For some time, these low-carbon ferro-titaniums were used in the manufacture of non-aging sheet steels; the use was confined to steels of low sili- They have been of no interest Forthis purpose, it

con and manganese content as well as low carbon content (not over about 0.06% and usually 0.01 to 0.03%) which obviouslyhave very low hardness, of the order of 100 Brinell. In this instance also restraint of hardening is sought; this refers to hardening by means other than quenching from above the A3 transformation (for example, quenching from below A1 followed by aging) since the steel compositions are such that they are beyond the limits of appreciable martensitization by rapid cooling from above A3. This use has been discontinued, due to cost considerations." Another limited application of low carbon ferro-titanium is for deoxidation only- (as contrasted with carbon-fixation of the first two uses) of special highly alloyed steels, especially castings, such as those used for heat resistance and corrosion resistancef Thus these low-carbon titanium alloys, in which the titanium content costs three to four times that of the medium and high-carbon alloys, have been used entirely in non-hardening steels or steels of high value such as those containing five per cent or moreof alloying elements.

Other commercial ferro-titanium alloys have also been available. For example, an alloy containing about 13% titanium, 20% aluminum, 3% silicon, 4% carbon, balance principally iron has been suggested for carbon steels to deoxidize and produce fine grain. Another group of titanium alloys comprises term-titanium of about 20% titanium, 20% silicon, 0.3% carbon, and 0.3% aluminum, remainder principally iron, and silicotitaniums of about 35% silicon, 03% carbon,

0.3% aluminum, 35 to 55% titanium, balance principally iron; these alloys have been restricted in their commercial use to the addition of titanium to cast iron, since they are easily dissolved in iron alloys but add considerable silicon to the molten metal. Another class of alloys have been made containing manganese in large proportions; with about 30% titanium, 8% aluminum, 3% silicon and 35 or 55% manganese, balance principally iron and low carbon content, they have because of cost been restricted in use to non-ferrous alloys and to highly-alloyed steels of high value.

To summarize the foregoing, low-carbon titanium alloys have found their sphere of usefulness in non-ferrous alloys, special steels of restricted hardening capacity and highly alloyed steels of relatively high value. In the tonnage carbon and low-alloy steels such as automotive and other repetitive-manufacturing uses, titanium has been employed in the form of alloys of r relatively high carbon content; in such use, when either small or large amounts have been added, the steels produced have either not shown a tendency toward fine grain or, if fine grained, due to the use of other grain-refining practices, have tended strongly toward shallow hardening on quenching. To get deep-hardening steels of fine grain size using the titanium-treated carbon and low-alloy steelsof the prior art, substantial increase in the alloy-metal content of the steels has been required, such for example as adding or increasing the percentages of nickel, molybdenum, chromium, etc., in addition to the conditioning by titanium and aluminum. I have discovered that these results are obtainable, namely deep-hardening in the presence of fine grain size with the known high toughness due to the latter, without the addition of elements heretofore known to contribute greatly to deep hardening on quenching if, to the carbon or lowresult.

alloy steel, titanium is added in suflicient but not excessive amount and in the form of compounds or alloys in which it is present in certain restricted combination. To titanium in this form or condition I have applied the designation reactive. 7 1

Titanium which has been combined with carbon or nitrogen or oxygen in sufficient proportion to form completely or even in large part the known stable compounds with these non-metallic elements, is not reactive and is not suited to the present purpose.- For example, high-carbon or medium-carbon ferro-titanium, both suited for deoxidation of steels, as previously explained, will not produce deep-hardening of fine-grained carbon or low alloy steels; in these titanium alloys there is from almost-suflicient up to morethan sufiicient carbon to satisfy the formation of the chemical compound TiC. Likewise titanium nitride or cyanonitrideor dioxide or mixtures or solid solutions rich in these compounds do not produce the novel efiects. -On the other hand low-carbon,. low-nitrogen, low-oxygen alloys with iron, manganese, nickel, copper, cobalt or chromium, alone or together, do producethis Silicon may be present in the alloy but should be less than'the titanium content; when equal to or more than the titanium the desirable effects are secured in considerably reduced degree and the properties of the steels are greatly inferior to those herein described. Effects in the direction indicated are obtained by the introduction of titanium only when in combination with carbon, nitrogen or, oxygen in minor proportions. In other words,-the metal titanium, or its alloys with, for example, the metals just enumerated may contain limited amounts of carbon, nitrogen or oxygen to function in this desired manner, but they must not containsufiicient to completely or in large measure satisfy the combining power of the titanium for these elements; to some degree, the amount of metal or alloy added to the steel bath may be increased when carbon, nitrogen or oxygen are present, over, that required when they are virtually absent, to produce a given effect upon a given steel, whereby there would be added to the steel a suificient quantity of reactive titanium, but of course not to such an extent as to chill the steel and/or prevent efiective solution of the added alloy. However, in any case the titanium content should exceed about 8 times the carbon content plus about 15 times the nitrogen content plus about 10 times the oxygen content.

In the alloy as added to the steel bath, there may also be present elements which protect the titanium from loss during the process of addition (as for example by combination with oxygen or oxides) such as aluminum, zirconium and magnesium. In general, it is not necessary that they be present to an extent of more than 50% of the titanium content and in no case is it desirable that they total more than three times the titanium content. Further, in the case of aluminum, the addition via this alloy plus any aluminum added separately to the steel bath should not in most instances exceed about 0.15%.

Other elements may be present in the alloy, provided that they are not subversive of the characteristics herein described as imparted by the alloy to steels. While-this statement applies to all elements, it may be specifically mentioned, by way of example, that vanadium, columbium, tantalum, molybdenum or tungsten may be present in the alloy in amounts up to about 5% each nickel, copper, cobalt or chromium, contains reactive titanium" ifthe titanium content of the alloy exceeds about 8 times the carbon present plus about 15 times the nitrogen present plus about 10 times the oxygen present and in which the titanium content also exceeds individually the aluminum content and the silicon content;

alkali or alkaline earth elements may be present in appreciable quantities and up to twice the titanium content and if in total they exceed about 10% of the titanium content, the silicon need not be restricted and may be regarded as one of the carrier metals; zirconium or magnesium may be presentup to about equal the titanium content; elements not subversive of the properties imparted by the titanium to carbon and low-alloy steels may also be present. In the appended claims the term reactive titanium is used with these limitations.

Obviously this invention relates to steels of the ferritic type in which hardness is raised by martensitization on rapid cooling from an elevated temperature and not to austenitic steels which are hardenable only by cold working or by precipitation of highly dispersed micro-constituents. In the former it is known, as heretofore mentioned, to add titanium in suflicient amount to combine with and remove the carbon from the steel matrix and thus largely prevent hardening. The amount required for this purposeis 2% or more times, usually 6 times, the carbon content (exclusive of the usual 40% loss in making .the addition). The present invention, however, consists in the discovery of an approximately opposite efiect, not heretofore recognized, resulting from the addition of much smaller amounts of titanium, approximately to of the carbon content and in no case greater than twice the carbon content. Insome cases, an effective amount may be exceedingly small. I have discovered that the large amounts of the prior art are not required and are actually detrimental to the objective sought, and on the other hand, the small deoxidizing additions of high-carbon alloys are equally ineffective. made due to the fact that the mechanism by which the titanium produces the observed effects describedherein, is not fully understood. These effects may or may not, for example, bear some relation to the content of, and changes in, those elements present in small amounts in steels which are not determined by the conventional methods of chemical analysis. The effects may equally as well result from the removal of, or prevention on solidification of g the formation of, intergranularfilms of non-metallic material or inclusions of particular nature or size, that when present serve as precipitation nuclei during rapid cooling of the steel from above the transformation range. Or it may be that reactive titanium in restricted amounts when present in austenite is extremely efiective in restraining decomposi--v tion of the solid solution on cooling and that above these restricted amounts it forms easily precipitated carbide that by removing carbon These statements are from solid solution reacts in the opposite manner anddecreases hardenability.

As illustrative of the eflects produced, there are given in Table I the properties of a 40% carbon medium-manganese steel as influenc adding various amountsof a low-carbon termtitanium alloy containing a small amount ofv aluminum. These steels were made. in an electric induction furnace, cast into 3% inch square ingots, forged to 1 inch round bars, normalized, oil quenched and then tempered at 450 F.

Hardenability was determined by the' Jominy method on previously normalized bars and recorded as the distance from the hardened end of the quenched bar to the last point at which a. hardness of 50 Rockwell "C" or higher was obtained; this measures fairly closely the depth of martensitizsition.

Steel No. 1 with'no grain-refining addition is moderately deep-hardening but has low impact resistance and only moderately good reduction of area in tension. Steel No. 2, rendered fine grained by the customary aluminum addition made for this purpose, has far greater impact strength along with comparable reduction of area but very low hardenability. Steel No. 3 with only a very small amount of reactive titanium added shows very little change in properties except for a small increase in hardenability. The next larger addition of reactive titanium (steel No. 4) causes a further increase in hardenability and a large increase in impact resistance. With 0.10% reactive titanium (steel No. 5) there is an increase simultaneously in elongation, reduction of area, impact strength and hardenability. Further increase in the addition of titanium results in a slow decrease in these several properties although even with the largest addition made (steel No. 7) the impact strength and hardenability are substantially greater than those of the coarse grained or fine grained steels to which no low-carbon ferrotitanium has been added (steels Nos. 1 and 2).

TABLEI 'Efiect of titanium on medium manganese steels Composition ofsteel I C Heat Titanium ompgsltign otauoy No. added 0 s1 M11 Ti o '81 Al Ti 1 .42 .24 1.80 None(a)' .2 .3: -i .None'(b) ""1:

(a) Coarse grained. (b) Fine grainedml added).

. Mechanical properties Harden- H... $5 y -1 No Yield Tensile Elong. gg s ig I I! point strength m2 9 pact uucrr g In Table II are shown the properties of steels of similar composition to-which have been added 0.10 titanium in the form of various other titanium alloys. The processing of the steels is i the same as in the case of those of Table I.

Heats 10, i3, and 12 show that with low carbon alloys, silicon in moderate amount is not detrimental but in amount approximating the titaniuih content prevents the development of the desired properties in the steel to which it is added,-unless an alkali or alkaline earth metal is also present in the alloy in significant amount. Heats 14 and 1'7, compared with 15, 16 and 18 show the striking efiect in the alloy of high carbon as distinct from relatively low carbon in preventing the attainment of the desired steel properties; heat 10, of course, with very low carbon, functions better-than any of the higher carbon alloys.

TABLE II Efiect of composition of titanium alloy Composition of steel Composition of alloy Titanium added Heat No.

C Si Ti Si (a) Briquet of aluminum plus high carbon ferro-titanium (average analysis quoted).

Mechanical properties Hgirlden- Heat tufts. 9 33- Yield Tensile 15.10115. 55%? 53? g f g size point strength in 2 area pact well 0" l0 2%, 350 265, 000 12. 0 43. 6 l6. 5 0. 85 8 11. 220,050 259, 150 11. 5 46. 6 13.3 0. 42 8 12 215,)0 269, 900 10. 5 40. 0 ll. 8 0.41 7 to 8 13.--. 212, 800 9. 5 33. 1 5. 5 0. 24 7 to 8 14---. 222, 800 265, 500 10. 5 42. 2 ll. 8 0. 48 7 to 8 15---- 206, 300 249, 250 7.0 26. l 6. 3 0.23 8 16.--- 191, 800 256, 250 5. 5 14.8 6. 5 0. 26 7 to 8 17-.-- 2%, 250 266, 000 8.0 34. 7 l0. 5 0. 43 8 18---- 191,800 244, 500 4.0 17.7 8.8 0.22 8

As noted above, the optimum titanium addition to steels made in the described manner is about 0.10%. This optimum amount may vary with the steel type or composition, the steel-making,

pouring and teeming methods and the conditions under which the additions are made. It may vary from about 0.01 to 0.20% titanium but in any case is an amount required to increase the hardenability over that secured from the same steel without the addition and an amount below that resulting in loss of hardenability to below that of the untreated steel caused by combination of the titanium with the carbon of the steel, preventing in part or in whole their engaging in the hardening reaction.

From the foregoing description, it will be clear that ferro-titanium in which the titanium is reactive, that is, either uncombined or only partly combined with elements with which it produces compounds of high heats of formation, specifically carbon, oxygen and nitrogen and to a lesser degree silicon, will produce in carbon and low-alloy steels, even in the presence of fine grain size, hardenability and toughness at high hardness so greatly above these properties in the untreated steels as to set them apart from the latter due to the possession of distinctive properties rendering them serviceable in uses and under stresses for which the untreated steels1 are unfitted. As indicated, these results are not secured with titanium alloys of all compositions, The titanium content of the added alloy should preferably be within the range of 5 to 50% and more particularly 10 to 35%. The carbon content of the added alloy should be low, preferably under 0.25%, although moderately good results are secured with the carbon up to about one-eighth of the titanium content. Nitrogen and oxygen in the alloy should be below about one-fifteenth and one-tenth of the titanium content, respectively. Silicon may be present in the alloy up to about the titanium content unless alkali or alkaline earth elements are present in amounts above about 10% of the titanium content, in which case the silicon may appreciably exceed the titanium content. Aluminum may be present up to an amount about equal to that of the titanium content. The remainder of the alloy may be iron or manganese or nickel or cobalt or copper or chromium or any combination of them or other element or combination of elements not subversive to the attainment of the desired properties in the treated steels.. This is largely included in the above noted definition of "reactive titanium."

Additionally I have discovered that the simultaneous introduction into the steel of vanadium with the reactive titanium confers further benefits upon the steel. When vanadium is associated with the titanium thev amount of the latter necessary to insure continuously under commercial conditions the properties heretofore described is materially reduced and the characteristics of the steel improved. The use of vanadium along with smaller titanium additions is productive of greater cleanliness, which is a desired property in the finished steels especially so when the articles to be made of the steel are subjected to stresses in the direction transverse to rolling or forging and ductility in this direction must approach as nearly as possible to the ductility in the longitudinal direction. Machining and hot working characteristics are also benefited. Vanadium also is desirable in maintaining a uniform and consistent fine grain size and when it is used with reduced amounts of titanium or reduced amounts of titanium and aluminum, this objective is attained. simultaneously with the above-mentioned improvement in cleanliness.

Furthermore, the yield ratio when vanadium is used is higher than when it is not present. Thus a means is afforded whereby through the use of very small amounts of vanadium there are obtained in the steel not only the properties that have heretofore resulted from the so-called full vanadium content but in addition the deep hardenability and toughness at high hardness referred to above. It should be observed that this dual benefit is secured with very low amounts .of vanadium, which if used alone in the form of an addition of ferro-vanadium would not produce either of these desired groups of properties.

The preferred form of the addition containing vanadium with titanium is a ferro-alloy of these two elements or a ferro-alloy containing vanadium, titanium and aluminum with the customary accompanying impurities common to such ferro-alloys. In these alloys the iron serves as a carrier metal and may be replaced in whole or in part by other carrier metals which are not subversive of the properties of the alloy from the standpoint of its effective introduction into the steel or of the properties of the steel to which the ferro-alloy is added. Such other carrier metals may be, for example, manganese,

copper, cobalt, nickel, chromium, molybdenum, tungsten, etc. Preferably the silicon is low although it may be present to any extent that is necessary to an economic method of manufacture of the alloy, or may be intentionally added to replace part of one of the carrier metals. The silicon is usually less than 5% and preferably should not exceed or although it may under some circumstances be as high as of the alloy. The silicon is preferably less 10 than 60% of the combined vanadium .and titanium.

Alloys of the following ultimate compositions have been successfully used:

15 V Ti A1 Si Mn Remainder in each case is iron plus impurities.

Although the above are illustrative of the preferred materials used in practicing this form of the invention, other variations also may be employed. Nanadium may be substituted in part 30 or in whole by one or more of columbium, tantalum and uranium. Titanium may be substituted in part or in whole by one or more of beryllium; boron and thorium, which are "reactive" under the conditions which render the titanium reactive. As heretofore pointed out, protection againstbxidation, which may be at least in part the function of the aluminum where used, may also be attained by substituting for all or part of the aluminum one or more of zirconium and magnesium. Other carrier metals may of course replace iron in this alloy in whole or in part, as heretofore indicated. For example, half or three-quarters of the iron may be replaced by nickel; or manganese may be introduced in place of like amounts of iron to the extent of about 5 to 15%, or may replace it entirely.

In the group comprising titanium, beryllium, boron and thorium, titanium is preferred because it is the most satisfactory from the combination of ease of addition, effectiveness, cost, and absence of any undesirable properties in the finished steel. Likewise vanadium is'preferred in the group comprising v'anadium, columbium, tantalum and uranium and for similar reasons. In the group of protective elements again as a matter of effectiveness and ease and economy of use the preferred element is aluminum.

Among the alloys containing these several elesired results are:

The'remainder in each case is iron plus impurities.

When vanadium and titanium or their substitutes are added with little or no aluminum or its substitutes, they must .be added in'intimate mean a very close association of the several metals or elements ranging between the atomic or molecular association of a single-phase alloy through the relatively uniform fine mechanical mixture in fixed position of a multiple-phase alloy, through the coarser mechanical mixture of a briquet of intermixed 20 mesh or finer particles of alloys of the several metals or of the metals themselves, to the mixture in a container or the like of somewhat coarser particles of the several metals or their (for example) ferro-alloys, as contrasted with adding lumps of the metals or ferro-alloys at succeeding short inter vals during pouring of the steel or mixing on a shovel or other implement metals or alloys in -some standard size such as 2 inches by down.

and adding them together. Likewise when the titanium is used without vanadium as described.

earlier in this specification, the titanium is preferably added to the steel in the form of a ferroalloy which in addition to the iron contains the other alloying elements to be added to the steel with the titanium; and if not in the form of a ferro-alloy, then the several elements are pref-' erably added in intimate association. The line of demarcation between successful and unsuc cessful methods cannot be sharp, depending as it does upon the metals used and the steel-making procedure in a specific case; the desired result is obtained when the metals added are dissolved in the iron or steel bath in their entirety in sufliciently close proximity in respect to both space and timethat they may begin to react simultaneously upon any minute volume of the steel at their respective natural rates and not one or more of them reach this minute volume after the other or'others have completed their reaction at this point (and perhaps theproducts of the reaction coalesced alone or with other substances and become relatively unreactive).

Aluminum may be absent in some cases or,

loys containing 10 to 35% vanadium, 10 to 35% titanium, with either about 4% or less alumi- Alloy V U Cb Ta Mo W T1 21' Al Ca Si Mn Not determined.

num or about 20% aluminum have been very effective; these alloys have been added in amounts corresponding to 0.03 to 0.10% vanadium and titanium taken together. An alloy containing 20% vanadium, titanium, silicon, and not over 2% aluminum, also produces the desired properties when added to molten steels in amounts corresponding to approximately 0.02 to 0.10% vanadium; similar results obtain if this alloy composition also includes 10%. manganese.

The range of composition of the alloys productive of these results is from 6 or 7 to 50% of an element or elements of the group comprising vanadium, columbium, tantalum and uranium and 6 or 7 to 50% of an element or elements of the group comprising titanium, beryllium, boron and thorium. To these may be added up to 35% of an element or elements of the group comprising aluminum, zirconium and magnesium and up to silicon. The remainder of the composition is iron or other carrier metal containing the usual impurities resulting from raw materials used or the process of manufacture.

The preferred composition contains about 10 to 30% of an element or elements of the above vanadium group and about 8 to 30% of an element or elements of the above titanium group, and less than 10 or 15% silicon. When an element or elements of the aluminum group is added it may be present in one of several preferred ranges depending upon the type of steel to which the addition is made; these preferred ranges are not over 4%, '7 to 12%, and 18 to Manganese when used in substantial quantities is preferably in the range of 5 to 15%. When silicon is not intentionally added it is generally not over 3% and manganese similarly not over Similar to the requirements when using the reactive titanium without vanadium, the addition alloy or mixture when employing vanadium with titanium must not contain such amounts of carbon as will prevent their proper functioning. In the case of the vanadium-titanium-aluminum a1 loy in the preferred ranges of compositionit is steel, silicon up to 0.18%, and manganese up to 0.25%. The preferred amounts are in the following ranges:

Per cent Vanadium 0.01 to 0.10 Titanium 0.01 to 0.08 Aluminum 0.005 to 0.10 Silicon Trace to 0.10 Manganese Trace to 0.05

The vanadium usually is 0.01 to 0.06% and the titanium 0.01 to 0.06%. The amount of aluminum usually varies more widely depending upon the type of steel. Where aluminum is objectionable in certain restricted amounts, as in some cast steels, the amount added, if any, is under 0.01% or about 0.06 to 0.10%. In steels to be hot or cold rolled, the amount of aluminum is often about 0.01% but may be and is frequently 0.03 to 0.08%. In some steels, certain amounts of aluminum are objectionable; for example, in cast steels of about 0.035 to 0.050 sulphur content, it is preferred to add either less than 0.01% aluminum or about 0.06 to 0.10%.

On adding the alloy or intimate mixture of this invention to steels, a large part appears to be retained in the steel, the amount, in proportion to the addition, depending on the condition of the steel bath, the technique of adding the alloy or mixture, and other factors. It is possible that the amount retained is entirely in the form of metal or (on cooling) associated with carbon either alone or with iron, manganese, etc., as carbide, but this is not a known fact due to the extreme difliculty of precisely distinguishing by analytical methods between metal as such or as carbide and metal in the form of compounds with oxygen, nitrogen, etc. Analyses for total residual metals from the addition have been made, without positive determination of the'form or forms in which the metals exist. While these residual amounts may preferable that the carbon content be under I% and more particularly not over 0.25%. In no case should the carbon content exceed about one-tenth of the vanadium content plus about one-eighth of the titanium content. The nitrogen and oxygen contents also should be limited, the former not exceeding about one-fifteenth the titanium and the latter not exceeding about onetenth the titanium content.

In adding the vanadium-titanium alloy 9. combined addition of as little as 0.02% vanadium and 0.01% titanium is productive of the desired result in a large degree, the extent depending, of course, on the composition and manufacturing history of the steel. In the treatment of carbon steels of 0.40% carbon and manganese steels of 0.40% carbon and 1.75% manganese, additions of 0.03% vanadium, 0.02% titanium and 0.01% aluminum, following (if required by the steel-making practice) a prior addition of 0.03 to 0.08% aluminum, has yielded steels possessing the desired qualities, as illustrated hereafter. In general the range of amounts added to the steel needed to secure these properties are about 0.01 Y

to 0.15% of vanadium or its substitute, and about 0.01 to 0.15% of titanium or its substitute. It indicated by the requirements in any particular case, aluminum or its substitute may be present completely account for the novel combination of properties found in the steels of the invention, this cannot be stated with certainty and the invention is, therefore, not limited in this manner. The results of these analyses have, however, been within the following limits:

Per cent Vanadium 0.01 to 0.15 Titanium 0.002 to 0.08 Aluminum 0.002 to 0.08

The vanadium appears to be substantially all recovered. The titanium and aluminum are only partially recovered, the contentas indicated by analysis being usually one-half to three-quarters of the original metallic addition. When the preferred amounts of titanium, vanadium and aluminum are added as indicated above, the residual contents of these elements in the finished steel will be approximately 0.01 to 0.10% vanadium, 0.005 to 0.05% titanium, and 0.002 to 0.05% aluminum.

Silicon and manganese, not being essential to the invention'and being in practically every instance, added in further amount other than through the medium of the alloy herein described, no efi'ort been made to evaluate the amounts remaining from this addition.

Example I in the addition up to 0.15% of the weight of the 1600 R, quenching in oil from 1550 F. (after machining to 0.525 inch diameter), then tempered at 450 F. and subsequently machined to 0.505 inch diameter. The test data follow:

Hardenability Austenite grain size (Jominy) (A. S. T. M. standard) at Rockwell Steel 0 Mn Si hardness 1700 F 1550 F. if; a M

A 0.391.890.23 7(fcw6dr8).-. 9(fow 8) 62 50 36 32 B 0.41 1.74 0.21 6 (few 5, 6, 8)-- 9(iew 8) 03 56 52 48 Elonga- Reduc- Yield Tensile Izod Rockwell Steel point, strength, g gh gr impact, 0"

1 p. s. i. p. s. i. in per ceilt it.lb. hardness Steel B was made similarly to steel A except for a final addition of 3% pounds per ton of steel of an alloy of vanadium, 15% titanium, 10% aluminum, 2% silicon, .5% manganese, balance iron.and impurities. Note the increase due to the alloy in impact strength and hardness penetration with other properties practically identical.

A number of other tests of steels of the T-1340 type have been made, especially to note the factor of hardenability. With approximately equal yield point and tensile strength, the hardenability of the untreated steel has been such that with a Rockwell C" hardness at the quenched end of the Jominy type test bar, of 60 to 63, a hardness not less than extended along the bar for only to inch; with steels of 0.40 to 0.41% carbon and about 1.70% manganese, application of the process of the invention yielded this value at 1 to 1%, inch, whereas with steels of 0.43 to 0.44% carbon and about 1.85% manganese, this high hardness extended along the bar to 1% or 2 inches. These properties have long been sought in inexpensive steels wherewith to produce hardened parts in medium sections and of very high quality, capable of sustaining very severe service loads.

Example II Two heats of basic open hearth steel, made in the same plant, but not the plant of Example I, with no difierence in procedure except for the addition of 3 pounds per ton of steel of an alloy similar to that used in Example I. The composition is S. A. E. 1040 with manganese at the upper limit of the range. The steels are compared after rolling, normalizing at 1600 F., quenching in oil or water from 1550 F. as inch rounds, tempering at 600 F. and machining as it does in water and that when both steels are hardened in water, steel B is superior in both strength and ductility.

Example III Two heats of silico-manganese spring steel (S. A. E. 9255) were made in a small electric induction furnace using the same procedure in making both except for-the addition to one of 0.30% vanadium in the form of a ferro-alloy of 23% vanadium, 17 titanium, 13% aluminum, and 3 silicon. The ingots were forged from 3 -inch square to zla-inch and 1 inch rounds and normalized at 1625 F. The 2%-inch bars were machined to 12-inch diameter, oil quenched from 1575 F., and cut transversely for hardness measurement. The 1 inch rounds were oil quenched from 1575 F., a similar section cut for hardness penetration measurements, and the remainder tempered at 800 F., then machined for tension-and impact testing.

Hardenability, Rockwell "0 hardness I Grain size Heat 0 Si Mn (Mfiggsiid- L 2" Surl'. Cent. Surf. Mid. Cent.

A. 0. 57 2.02 0.78 4 (lew3 & 5) 61. 5 56 46. 5 36 34 B 0.581.94 0.84 6(tew4&7)- 63.5 62 58.0 41.5 34

. Elonga- Reduc- Yield Tensile Izod tion tion 01 Brinell Heat point, strength impact p. s. i. p. s. i. gzzh it.-lb. hardness The improvement in all properties of steel B. the one to which the alloy was added, should be noted.

Example IV s. to 0 505 mch standard bar Hardembmty (Jominy) Grain size Rockwell O hardness Grain 51 3 Heat 0 Mn 81 Steel 0 Mn Si Me uai I E311) Surface Mo" $6" Me" A 0.38 0.91 0.24 6 to 8 0. 0.66 0.14 8 (few 5, 6, 7)- Notmeasured 54 40 26 B 0.38 0.91 0.24 6 to8 B---- 0420.62 0.22 7&8 (iew6) do 56 55 41 Elon a- Reduc- Elonga- Reduc- Steel Quenched 32 5}? 523 53 1:105 t tion of 3 2: 55 H t Tem Yield 'tlzensilitla1 tion tion of mllzod2 liringll rcen area ea pere porn s reng per area pac nr m i in 2" per celit ness F. p. s. i. p. s. 1 cent per ft.-lb. ness in 2" cent A 011 87,830 116,000 25.0 69.2 217 B Oi1 205, 300 238, 500 11. 5 44. 0 444 A. 800 98, 530 125, 850 20. 0 59. 5 78. 4 259 A"..- Water 155,820 183, 030 11.5 44.3 387 13.--- 800 123, 154,350 18.0 63.4 50.8 339 B Water.-. 186, 800 500 14. 5 58. 2 430 B. 950 105, 330 127, 730 20. 3 64. 9 84. 8 273 Heat 13 is the one to which thealloy of this invention .was added. The hardening capacity is higher as shown not onlyby the hardenability tests but by the test bars tempered at 800 F., yet with the higher strength, toughness as measured in part by=reduction vof area, is also higher in steel B. When tempered to equal hardness and strength, steel B has higher yield point, higher reduction of area and higher impact strength.

The so-called full-vanadium steels, of 0.15 to 0.25% vanadium content, possess in a measure the desirable properties of the steels of my invention. Vanadium contributes to shallow hardening through its definite and uniform effect upon grain size (thus also providing toughness) but it further contributes to deep hardening through its direct alloying effect in decreasing the critical cooling speed. Thus full-vanadium steels have long been esteemed and widely used for this desirable combination of properties. When fine grained, tough and exceptionally deep hardening steel has been necessitated by en'- gineering requirements, especially in moderate to very large sections, low-alloy full-vanadium steels have not, however, been entirely adequate; these needs have been met by nickel-vanadium, nickelmolybdenum-vanadium, nickel-chromium mo lybdenum-vanadium and chromium-molybdenum-vanadium steels of high total alloy content. These are today the important steels of ve y large sections in the principal members of heavy machinery but they are too costly for common use in the manufacture of mass-production articles. Steels of 0.10% vanadium have been used but the combined grain-refining and deep hardening efiects have been somewhat less and the needed content of other alloying. elements correspondingly higher. To illustrate these properties of the full-vanadium steels, two examples may be cited. (1) Carbon-vanadium tool steelhardens to a medium depth and is highly uniform in this performance, the hardened zone after quenching from'the usual quenching temperature range of 1450 to 1600 F. being on a 1 inch round bar about 0.15 to 0.20 inch. The core is uniformly of high toughness. Carbon tool steel rendered fine grained by the addition of aluminum hardens fully to a lesser depth and successive heats show a wide variation in this depth as well as variable toughness in the metal beneath the fully hardened outer layer. Increasing the vanadium content .of carbon-vanadium tool steel to about Steel 0 Mn Si Cr v Hardness alter oil quenching Bars 3 inches diameter quenched in oil flowing at feet per minute.

The steels to which my alloy is added possess these desirable properties of the full-vanadium steels but to an enhanced degree (corresponding to the complex heavily-alloyed full-vanadiumsteels) and as a result of only a very small total addition of elements, as heretofore described.

Grain-refining additions may be made to the steel other than those added for the specific purposes described herein in a manner depending upon other features of the steel-making practice and upon the article to be produced from the steel. Thus wrought steels such as a 0.40% carbon steel may have a small or a large addition of aluminum (0.25 or 2.00 pounds per ton of steel) prior to the addition of my material. A zirconium-silicon alloy or aluminum-silicon-iron or aluminum-silicon-titanium-iron or ferro-vanadium, as examples, may *be employed in customary amounts. Other additions common in existing methods of steelmaking and known to those familiar with the art, may be employed without departing from the spirit of this invention.

Reactive titanium or the alloys or mixtures forming this invention may be added to the molten steel in the furnace, or in the ladle to the bath of metal partly formed therein, or into the metal stream as it issues from the furnace, or it may be added in the ingot molds if the ingot weight and cross-section are not so small as to prevent the alloy from entering and reacting with the molten metal. Surprisingly by the application to a number of steels of this latter method, no visibly harmful inclusions have been introduced to detract from the salutary effects of the alloy addition.

As set forth in the several examples given above, the steels to which my alloy additions are made are killed steels. The alloy is, therefore, not added merely for purposes of deoxidation, degasification, scavenging or other purification, for which purposes additions of titanium or the like have customarily been made.

In the foregoing, there has been described the method of improving the hardenability of steels that consists in the addition to them in a late stage in their manufacture of a titanium alloy in which this metal is in a reactive condition.

The description has been given with reference to fine-grained steels because in the prior art titanium additions have assisted in producing fine-grain size (although not alone capable of producing very fine grain such as 7 to 8 on the McQuaid-Ehn scale) but fine grain size has been accompanied by shallow hardening except in steels containing rather large amounts of alloying elements. Coarse grained steels of any composition are more deeply hardenable than fine grained ones of like composition. However, my reactive titanium may be used to further increase the hardenability of these coarse grained steels. The resultant steels will obviously not be as tough, especially at high hardnesses, as steels of elements to secure deep hardening there is usu-' ally only a slight contribution toward fine grain size, not necessarily production of very fine grain (A. S. T. M. standard 7 or smaller). Sometimes no appreciable change is observed. The extent to which grain size is decreased, if any, over that size that would result in a given heat ofsteel without these additions, depends upon the condition of the molten bathof metal at the time the addition is made, upon the remainder of the steel composition, upon other grain-refining additions made,;and upon the total amount and the protions of the constituent elements in the specific alloy or mixture of this invention, that is employed. Thus while the grain size will not be coarse (such as A. S. T. M. standard 2 or larger), it may not in every case be very fine but rather medium in size, usually not larger than A. S. T. M. 5. For example a steel which as'ordinarily produced will show a grain size of 4. may by the addition of this alloy have its hardenability considerably increased and yet the average grain size may be decreased only to 5 or not altered at all. Steels which are ordinarily'made to 7 to 8 grain size may after the addition of these elements still be 7 to 8 grain size but their hardenability will be considerably increased. As previously explained, a nickel steel may have a grain size of 6 and on the addition of this alloy will have its hardenability increased, while its toughness likewise will be increased; the average grain size may be unchanged or decreased only to 7. Increase in carbon also tends to decrease grain size under like conditions of manufacture and therefore to decrease the critical cooling speed; thus in carbon steels while in creased hardenability will be conferred upon compositions of different carboncontent, the likelihood of decrease in grain size due to the addition will be less when the carbon content is higher. It should be understood that the invention is applicable to steels of all grain sizes, but is of most interest in connection with medium and fine grained steels, since under these conditions the best combination of properties is imparted.

Another feature of the inventionis the obtention of the desired properties of the steel without resort to effective large amounts of alloying elements such as vanadium, nickel, chromium, molybdenum, cobalt, copper, etc. and also the two usual elements in carbon steelsmanganese and siliconabove the limits common to commercial carbon steels,- namely, 1.05% and 0.35% respectively. Whenever the term alloying elements" is used in the specification or claims, or where low alloy steels are referred to, it is the intention that manganese is to be considered as an alloying element only to the extent to which it exceeds this limit of 1.05%, and silicon is to be considered as an alloying element only to the extent to which it exceeds 0.35%. To secure the full benefits of this invention, namely, complete hardening or nearly complete hardening throughout medium and heavy sections along with medium'to fine grain size, it is not necessary to exceed about 5% of alloying elements and in most cases not to exceed about 3% of alloying elements. It has been observed that'the critical cooling rate is decreased and hence the hardening capacity of steels is increased not only by the addition of certain alloying elements but also,

ments but in the temperatures within certain limits, by increase in carbon content. This limit of 3% of alloying. elements is, therefore, not absolute but varies somewhat with the carbon content of the steels. Therefore, to produce tough steels capable of hardening throughout in medium to large sections there will generally not be over about 3.5% of total alloying elements when the carbon content is less than 0.25%, not more than about 3% of these alloying elements when the carbon content is in the range of 0.25% to 0.50% and not more than about 2.5% of these alloying elements when the carbon content exceeds 0.50%. It has been shown in the prior art that tough deep-hardening steels can be produced by large amounts of alloying elepractice of this invention, these largeadditions are not usually required. Typical low alloy steels to which the invention is applicable have the following amounts of these alloying elements:

Ni Cr Low alloy steels are those intermediatejzbetween the plain carbon steels and the so-called high alloy steels, such for example, the stainless steels and high speed steels. Low alloy steels have a limited alloy content of usually not more than 5 or 6%. The alloying elements that are included upto this limit of 5 or 6% are manganese and silicon above the limits common, to ordinary carbon steels, nickel, cobalt, copper, chromium, tungsten, molybdenum, vanadium, and at times small amounts usually not ovenon'ehalf percent of some other rare metal.

The carbon content of such low alloy steels may range from 0.10 to 0.75 or 1.0% or even higher, but, is preferably from 0.20 to 0.65%."

The invention is equally applicable to plain carbon steels and has been successfully applied to steels containing from 0.10 to 1.00%.carbon with manganese and silicon contents normal for the particular steels and their applications. In

general, the invention shows greatest utility when applied to steels of 0.10 to 0.75% carbon and more particularly in the range of 0.20 to 0.65% carbon. 5

i The iron is at least about. 98% in the case of plain carbon steels and at least 94 to 95% in the case of the low alloy steels to which the invention is applicable.

' Although great benefits are conferred upon steels that are quenched to a very hard state and subsequently tempered, and although the maximum benefits are conferred upon steel articles tempered at relatively low temperatures so that their hardness is above 250 Brinell and preferably 350 Brinell or higher, steel processed in accordance with thisinvention may be ad-. vantageously used for parts tempered at higher or as rolled, or as normalized or normalized and tempered. 'In some cases the hardening phenomena will be such thatit is best to lower the carbon or alloy content or both, so that the steel articles will have strength equal to that procurable with the original composition. if the alloy of the invention were not used but will, with equal strength, possess greatly enhanced toughness. v Hot rolled or forged bars or billets made from steel ingots produced in accordance with this invention maybe converted into various finished or semi-finished parts by the usual forging, machining and heat treating practices.

subjected to either normalizing and tempering or annealing by the practices common to secure the desired machining qualities, then heated. for quenching in a temperature range characteristic of the steel and the size of the gear made'fro'm' it, namely, 1400 to 1700 F., and after cooling "in the quenching medium to a temperature, suit- Gears, T for example, may be drop forged or upset, then able to effect hardening of the steel, reheated to a proper temperature in the range of 350m 600 followed either by slow or rapid cooling. Theproper temperature for this reheating or tempering operation may be confined to the lower side of this range. In steels of the prior art, tempering in thislower part of the range often. produced such high hardness that thegears or other similar parts made from the steel did not. possess adequate toughness, and tempering in the higher part of the range caused the small amount of austenite retained on quenching to be converted to martensite with consequent e'mbrittlement- Steels made in accordance with my invention may be tempered safely in the lower part of the range and the benefits obtained thereby of the higher hardness and wear resistance, because of the added toughness resulting from the practice of the invention. In the range of tempering-temperatures used for springs. spline shafts and. other similar parts, namely, 800-to 1000 F., the

practice of this invention is also-beneficial and an improved combination of averagehardness throughout the section and of toughness is secured. The hardness. of such parts (for both tempering ranges) is usually from ahout 350 to 500 Brinell or somewhat higher. In the case of articles such as drill pipe and sucker rods, used in the oil producing "industry and which are' usually marketed in the normalized or normal- :'-zed and. tempered condition, the invention is practiced to best advantageby 'not adding the elements toa steel of the composition heretofore used but to one having a somewhat-smaller content of thosejelements that produce harde'ning. Forexample, a steel of 0. 35 190.40% carbon and 1.60 to 1. 90% man'ganesewou1 d be replaced when practicing this, invention hy a steel of 0.30 to 0.35% carbon with 1.40.to l.'75%;mangan ese,' v

plus the additions as. described herein; In 'cerj tain plate 'steels used because olf-their ready weld ability and ductility after welding without being subjected to heat treatment (at least in] sections not over 1' inch in thickness) ,1 substitution. of Ta steel of 0.15% carbon, 1.25% manganese and "0.10% vvanandiun'i would be madelj llowerins themanganese to 1.00% and a'ddinggthe vanadium either in whole orin part as a vanadiumtitaninm .or vanadium-titanium-alummum';alloy,

Steels made in accordance wit 'thisinverition are not limitedto those heat treated by the meth-'- ods outlinedabove, but may also-be steels "to be. subjected to the more specialized methods-of heat lorby adding reactive titanium in.=-necessary' -a.moun t,-.aII aspreviously described., c

-in accordance with these teachings.

bility' ofthe anstempenng process in that larger sizes of a given composition may be effectively treated; or in a given size, smaller amounts of alloying elements are necessitated.

In the above examples and elsewhere in this speciiication it has been pointed out that the practice of this invention results in steels of greatly improved toughness and possessing the hitherto unrealized combination of properties. namely, fine grain size and its accompanying toughness, along with deep hardenability, in carbon steels or steels containing small amounts of alloying elements. However, the practice of this invention results in additional advantages. The steels made appear to be freer ,from detrimental 1 non-metallic inclusions than are steels not treated in accordance with this invention, and the mechanicalproperties as well as the machining characteristics, as noted below, are improved thereby. With, for example, the customary pre-' stances which improve machinability such as sulphur, phosphorus, lead, selenium, etc., and compoundscontaining them do not detract from the properties imparted to the steel by the addi--' tion alloy herein described. The substances may be added separately ormaybe includedin the composition of the alloy. I

As previously indicated, I do not know whether the element or elements described herein, when added to molten steel, are obtained inthe solidifled steel in the metallic. form or whether they are present in simple or complex carbides or in the form of other compounds, such as oxides, nitrides, etc. Some part-of theadded elements remain and. are determinable by chemical analysis but the form or combination in which they exist is not precisely determinable with assurance of correctness. The history of the steel melt and its condition at the time the alloy or mixture is added probably-are determinative and these will vary and may necessitate variation in the amount or composition added, or both. .The important facts are the results secured even though they be due only to the residue from the addition in whatever form itmay exist, or to the removal of unrecognized substances normally interfering with the-development of the very highest proper- .ties.

)M additionalloy ay contain the impurities usua.l'in ferro-alloys and also may contain minor amountsof alloying metals or' metalloids which it maybe-desired to'introduce into the steel, and therefore when Ispeak 'of the ferro-alloy as being substantially all iron Idonot mean to exclude such minor amountsof other substances.

: While-II have 's'peciflcally' described the preferred-embodiment of my invention and the best modes now known tome for practicing it, it is' [to be understood. that the invention is not so limited but may be otherwise embodied and prac-I 'ticed withinthe scope of the following claims.

treatment such'as carburizing',-nitriding, austenrpering,.etc. Theuse of the alloys and procg'asses.

described herein greatly" enhances the applica- '75 'I'claim: 1. The process of treating steel containing from 0.20 to 0.65% carbon andof the class consisting ofplain carbon steel and low alloy steels containing less than alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from 0.01 to 0.20%01 reactive titanium and in an parting to the steel deep hardenability concomitant with great toughness.

2. The process of treating a steel containing from 0.20 to 0.65% carbon and of the class consisting oi. plain carbon steel and low alloy steels containing less than 5% alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.20 of reactive titanium and in an amount suilicient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without said a titanium addition, and in the form of a ferroalloy in which carbon is less than about oneeighth of the titanium, nitrogen less than about one-fifteenth of the titanium, oxygen less than about one-tenth of the titanium and silicon less than the titanium, the remainder being substantially iron, an amount of aluminum as a protective agent for the titanium but not more than three times the titanium and metal which is not subversive of the action of the titanium in imparting to the steel deep hardenability concomitant with great toughness.

3. The process of treating a steel containing from 0.10 to 1.00% carbon and of the class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.20% of reactive titanium and in an amount sufficient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without said titanium addition, said titanium being added to the steel in the form of an alloy containing carbon not over one-eighth of the titanium, the remainder being metal which is not subversive of the action of the titanium in imparting to the steel deep hardenability concomitant with great toughness.

4. The process of treating a steel containing from 0.10 to 1.00% carbon and of the class consisting of a plain carbon steel and low alloy steels containing less than five percent alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.20% of reactive metal of the class consisting of titanium, beryllium, boron and thorium and in an amount sufiicient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without said reactive metal addition, said reactive metal being added to the steel in alloy form containing carbon not over one-eighth of the reactive metal, the remainder being metal which is not subversive of the action or the reactive metal in impartingto the steel deep hardenability concomitant with great toughness.

5. The process of treating a steel containing from 0.10 to 1.00% carbon and of th class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.20% of reactive metal of the class consisting of titanium, beryllium, boron and thorium and in an amount suflicient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without said reactive metal addition, said reactive metal being added to the steel in alloy form containing carbon not over one-eighth of the reactive metal, and also containing a substantial amount but not more than three times the reactive metal of protective metal of the class consisting of aluminum, zirconium and magnesium, the remainder of the allo being metal which is not subversive of the action of the reactive metal in imparting to the steel deep hardenability concomitant with great toughness.

6. A deep hardenable ferritic steel containing from 0.10 to 1.00% carbon and of the class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents together with titanium in the amount and form which results from adding to a killed steel while in a molten state 0.01 to 0.20% of reactive titanium and in an amount suilicient to increase the depth hardening capacity of the steelover that of a steel of identical composition but without said titanium addition, said titanium being added to the steel in the form of an alloy containing carbon not over one-eighth of the titanium, the remainder being metal which is not subversive of the action of the titanium in imparting to the steel deep hardenability concomitant with great toughness, said steel being characterized by a deeper hardenability and greater toughness after heating and quenching than that of a steel of otherwise identical composition but to which such reactive titanium has not been added.

'7. A deep hardening ferritic steel containing 0.10 to 1.00% carbon and containing titanium in the amount and form resulting from adding to the steel after it'is killed and while it is in a molten state from 0.01 to 0.20% of reactive titanium and in an amount sufficient to increase the depth hardening capacity of the steel over that of steel of identical composition but without the titanium addition, said titanium being added to the steel in the form of a ferro-alloy containing carbon not over one-eighth of the titanium, the remainder of said ferro-alloy being substantially iron and metal which is not subversive of the action of the titanium in imparting to the steel deep hardenability concomitant with great toughness, the remainder of the steel being iron with not more than-3.5% of alloying elements when the carbon is below 0.25%; not more than three percent of alloying elements when the carbon is between 0.25 and 0.50%, and not more than 2.5% of alloying elements when the carbon is above 0.50 said steel being characterized by a deeper hardenability toughness after heating and quenching than that of a steel of otherwise identical composition but to which such reactive titanium has not been added.

and greater t i -8. The process of treating a steel containing about 0.01 to-0.15% of titanium, and silicon less than'sixty percent of the vanadium and titanium, in the iorm'of a ferroalloy in which the carbon is less than about one-tenth of the vanadium plus one-eighth of the titanium, the remainder being substantially iron and metal which is not subversive of the action of the vanadium and titanium in imparting to the steel deep hardenability concomitant with great toughness, and in amount sufficient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without the vanadium and titanium additions.

9. The process of treating a steel containing 0.10% to 1.00% carbon and of the class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents to impart. deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it'is in a molten state from about 0.010 to 0.15% of vanadium, about 0.01 to 0.15% of titanium, about 0.005 to 0.15% aluminum, and silicon less than sixty percent of the combined metals of the first two groups, in the form of a ferro-alloy in which the carbon is less than about one-tenth of the vanadium plus about one-eighth of the titanium, the remainder being substantially iron and metal which is not subversive of the action of the vanadium and titanium in imparting to the steel deep hardenability concomitant with great toughness, and in amount suiilcient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without the vanadium, titanium and aluminum additions.

10. The process of treating a steel containing from 0.10 to 1.00% carbon and of the class con sisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents to impart deep hardenability combined with great toughness, which comprises adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.20% of a metal or metals of the group consisting of vanadium, columbium, tantalum and uranium, about 0.01 to 0.15% of a metal or metals of the group consisting of titanium,beryllium, boron and thorium, and silicon less than sixty percent of the combined metals of said groups, in the form of an intimate association and containing carbon not over about one-tenth of vanadium group metal plus about one-eighth of titanium group metal, the remainder being metal which is not subversive of the action of the metals of the vanadium and titanium groups in imparting to the steel deep hardenability concomitant with great toughness, and in amount sufiicient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without the vanadium and titanium group metal additions.

11. The process of treating a steel containing 0.10 to 1.00% carbon and of the class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituand thorium, about 0.005 to 0.15% ofa metal or. metals of the group consisting of aluminum, zir-.

conium and magnesium, and silicon less than sixty percent of the combined metals of the first two groupsfin the form of an intimate association and containing carbon less than about onetenth the vanadium group metal plus about one- -eighth the titanium group metal, the remainder being metal which is not subversive of the action of said intimate association in imparting to the steel deep hardenability concomitant with great toughness, and in amount suflicient to increase the depth hardening capacity of the steel over that of a steel of identical composition but without the vanadium, titanium, and aluminum group metal additions. I

12. A deep hardenable ierritic steel containing from 0.10 to 1.00% carbon and of the class consisting of plain carbon steels and low alloy steels containing less than five percent alloying constituents together with vanadium and titanium in the amount and form which results from adding to the steel after it has been killed and while in a molten state from 0.01 to 0.20% vanadium, 0.01 to 0.15% titanium and silicon less than sixty percent of the vanadium and titanium, in the form of an alloy in which the carbon is less than about one-tenth of the vanadium plus about one-eighth the titanium, the remainder being metal which is not subversive of the action of the vanadium and titanium in imparting to the steel deep hardenability concomitant with great toughness, said steel being characterized by a deeper hardenability and greater toughness after heating and quenching than that of a steel otherwise identical in'composition but to which such alloy has not been added.

13. A deep hardenable ierritic steel containing 0.10 to 1.00% carbon and of the class consisting of plain carbon steel and low alloy steels containing less than five percent alloying constituents together with vanadium and titanium in the amount and form which results from adding to the steel after it has been killed and while it is in a molten state from about 0.01 to 0.15% vanadium, 0.01 to 0.15% titanium, 0.005 to 0.15% aluminum, and silicon less than sixty percent of the vanadium and titanium, in the form 0! a ferro-alloy in which the carbon is less than about one-tenth the vanadium plus about one-eighth the titanium, the remainder being substantially iron and metal which is not subversive of the action of the alloy in imparting to the steel deep hardenability concomitant with great toughness, said steel being characterized by a deeper hardenability and greater toughness after heating and quenching than that of a steel of otherwise identical composition but to which such alloy has not been added.

14. A ferro-alloyfor the treatment of steel containing about 10 to 30% vanadium, about 8 to 30% titanium, and less than 15% silicon, and capable of imparting deep hardenability conmitant with great toughness to steels oi the class consisting of plain carbon steel and low alloy steels containing less than 5% of alloying constituents. ents to impart deep hardenability combined with 15. A Ierro-alloy for the treatment or steel to 30% titanium, about 2 to 25% aluminum, and

less than 20% silicon, and capable of imparting deep hardenability concomitant with great toughnessto steels of the class consisting of plain carbon steel and low alloy steels containing less than 5% of alloying constituents.

16. A ferro-alloy for the treatment of steel containing about 7 to 50% vanadium, about 7 to 50% titanium, and'7 to 25% aluminum, and less than 20% silicon, and capable of imparting deep hardenability concomitant with great toughness to steels of the class consisting of plain carbon steel and low alloy steels containing less than 5% 01 alloying constituents.

1'7. A ferro-alloy for the treatment or steel containing 5 to 50% titanium together with aluminum and zirconium in amount to serve as effective protective elements for the titanium but not more than three times the titanium, and silicon less than 20%, said ferro-alloy being capable of imparting deep hardenability concomitant with great toughness to steels of the'class consisting of plain carbon steel and low alloy steels containing less than 5% of alloying constituents.

18. A ferro-alloy for the treatment of steel containing 5 to of reactive metal of the class consisting of titanium, beryllium, boron and thorium together with aluminum and zirconium in amount to serve as efiective protective elements for said reactive metal but not more than three times said reactive metal, and silicon less than 20%, the remainder being metal which is not subversive of the reaction of said reactive metal in imparting to the steel deep hardenability concomitant with great toughness, said ferroalloy being capable of imparting deep hardenability concomitant with great toughness to steels of the class consisting of plain carbon steel and low alloy steels containing less than 5% of alloying constituents.

' JEROME STRAUSS.