US3333987A - Carbon-stabilized steel products and method of making the same - Google Patents

Description

United States Patent 3,333,987 CARBON-STABILIZED STEEL PRODUCTS AND METHOD OF MAKING THE SAME Carlton F. Schrader, Chesterton, Ind., and Michael C. Kopchak, Olympia Fields, Ill., assignors to Inland Steel Company, Chicago, Ill., a corporation of Delaware No Drawing. Filed Dec. 2, 1964, Ser. No. 415,474 11 Claims. (Cl. 148-2) This invention relates to improvements in the manufacture of carbon-stabilized steel. Steels made in accordance withthe present invention are particularly useful as enameling steel but are also useful for other purposes where nonaging or retarded aging properties are advantageous, e.g. as steel bases for the application of hot dip zinc and aluminum coatings ora diffusion coating of chromium.

For the most part, the material known as enameling iron (a low carbon, low manganese rimmed steel) has heretofore been the major ferrous base material supplied to the enameling trade because of its enamel adherence properties and its acceptable sag or warpage resistance in the usual enamel firing temperature range, viz. 1400- 1600 F. However, enameling iron is subject to certain surface defects during enameling, and numerous proposals have been made for the elimination of defects in the enamelsurface caused by such well-known phenomena as boiling, reboiling, blistering, and fish scaling.

Certain of these defects have been attributed to the evolution, at the enamel firing temperature, of carbonaceous gases resulting from the reaction between iron oxide and carbon in the ferrous metal base. To overcome this problem, it is customary to use a two-coat enameling procedure, i.e. a ground coat and a cover coat, in order to obtain a satisfactory enameled article. Consequently, much effort has been devoted to the problem of overcoming such gas evolution by suitable modifications of the composition of the ferrous metal base so that a single coat of enamel can be used without a ground coat.

It is well known that certain strong carbide-forming elements can be added to steel in the quantities necessary to combine chemically with the carbon and thereby obtain a carbonstabilized steel having superior enameling characteristics such that it is possible to use only a single light colored enamel coat without the usual dark colored ground coat. For example, U.S. Patents Nos. 2,495,762, 2,495,835, 2,495,836, and 2,495,837 disclosed the'addition of titanium, vanadium, columbium, and zirconium for this purpose. However, such steels require the addition of appreciable amounts of stabilizing or carbide-forming elements (i.e. at least the stoichiometric quantities and preferably more) and are therefore relatively expensive so that they have enjoyed somewhat limited commercial use.

Instead of stabilizing the carbon content of enameling steel by' the addition of carbide-forming elements, it has also been proposed to obtain improved enameling properties by decarburizing steel sheet material to relatively low carbon levels (e.g. .01 wt. percent or less). See U.S. Patent No. 2,956,906. However, decarburized steel of this type undergoes a serious loss in yield strength under certain conditions and cannot be used satisfactorily for many applications involving drawing and subsequent enameling. Thus, when such steel is subjected to a critical degree of strain (namely, from about 3% to about 20% elongation) during drawing or fabrication and is thereafter subjected to an elevated temperature (such as in an enamel firing step at 1400-1600" F.), a coarse recrystallized grain structure develops resulting in a substantial loss of yield strength. A steel exhibiting this phenomenon is referred to herein as having poor strain-anneal characteristics.

Prior to the present invention, n0 completely satisice factory solution has been known to the problem of making a carbon-stabilized or decarburized steel without the aforementioned disadvantages.

Accordingly, a primary object of the present invention is to provide a novel and improved method of making carbon-stabilized steels, particularly enameling steels and steels having non-aging or retarded aging characteristics.

A further object of the invention is to provide novel and improved means for minimizing the amount of expensive carbide-forming element required to obtain a carbon-stabilized steel.

An additional object of the invention is to provide a novel and improved decarburized steel which possesses favorable strain-anneal characteristics as reflected by the retention of yield strength after a critical degree of straining or forming and a subsequent high temperature enamel firing step.

Another object of the invention is to provide a novel and improved enameled article formed from the abovedescribed carbon-stabilized steel.

Still another object of the invention is to provide other novel and improved coated steel products wherein the above-described carbon-stabilized steel has a hot dip zinc or aluminum coating or a diflYusion coating of chromium.

Our invention is based on the discovery that if substantially less than the stoichiometric amount of carbideforming element is included in the steel, it is then possible to remove the excess or unstabilized carbon by decarburization without any appreciable loss of the carbide-forming element. As hereinafter explained in greater detail, by this means it becomes feasible to make a carbon-stabilized steel from either killed or semi-killed steel without the necessity of using excessive additions of the expensive carbide-forming elements and without the development of unfavorable strain-anneal characteristics in the final product.

In accordance with the present invention, a killed or semi-killed steel is produced by conventional methods (using either aluminum or silicon deoxidizers) which has a relatively low carbon content of from about .04 wt. percent to about .10 wt. percent, a manganese content of from about .10 wt. percent to about .60 wt. percent, and the balance iron with the usual amounts of phosphorus, sulfur, and silicon or aluminum encountered in a low carbon killed or semi-killed deep-drawing steel. At the time of tapping, a predetermined amount of titanium, columbium, or zirconium, or mixtures thereof, is added to the steel either in the ingot molds or in the ladle, preferably the latter. Such additions may be in the form of the free metal or suitable alloys such as ferroalloys or the like.

It will be understood that for complete stabilization of the carbon content of the steel by carbide formation it would be necessary to add to the steel at least the stoichiometric quantity of the selected stabilizing element and, inmost cases, it would be necessary to add appreciably more than the stoichiometric amount in order to compensate for the usual losses incident to such reactions. Thus, in the case of titanium, the minimum weight ratio of stabilizing'element to carbon to achieve complete stabilization of the carbon is approximately 4:1, and in the case of columbium and zirconium, the minimum weight ratio is somewhat in excess of 7: 1. In actual practice it is usually necessary to use a minimum Ti:C ratio of 6:1, and a minimum Cb:C or Zr:C ratio of 10:1.

However, in accordance with the present invention, the amount of stabilizing element added to the steel is appreciably less than the stoichiometric quantity necessary to combine with all of the carbon in the steel. Consequently, at this stage of the process the steel may contain from about .04 wt. percent to about .10 wt. percent carbon of which only a portion is stabilized as titanium carbide, columbium carbide, zirconium carbide, or mixtures thereof, and the remainder is present in the usual form as iron carbide. Thereafter, the steel ingots are processed in the usual sequence of slabbing, hot rolling, pickling, and cold rolling to the desired gauge.

In accordance with the present invention, the steel strip is then decarburized to the extent necessary to eliminate all of the excess or unstabilized carbon. After the decarburization step, the weight ratio of stabilizing element to carbon in the steel is approximately the stoichiometric ratio required for complete stabilization and possibly slightly higher. Decarburization is effected by contacting the steel strip with a gaseous decarburizing atmosphere at an elevated temperature and for a time sufficient to effect the desired extent of carbon removal by selective oxidation. This decarburization step may be carried out by any suitable technique, but at the present time open coil decarburization has been found to be the most practical and convenient way of accomplishing the desired result. As in open coil annealing, the strip is first coiled with a wire spacer interposed between each lap to provide an open or expanded coil, i.e. one with spaces between adjacent laps. The open coil is then heat treated in a suitable decarburizing atmosphere which is blown axially through the open coil whereby the entire surface area of the strip is contacted by the flowing gas so as to obtain rapid and uniform heat transfer and chemical reaction. Subsequently, the wire spacer is removed during winding of the decarburized strip into a tight coil.

To effect decarburization of the steel as required by the present invention, the decarburizing atmosphere must contain a reducing gas, such as CO or H and a controlled amount of water vapor. The relative amounts of reducing gas and water vapor are regulated so that the atmosphere is oxidizing with respect to carbon but is non-oxidizing to iron at the elevated temperature of the decarburizing step, and the time, temperature, and atmosphere composition are correlated to achieve the desired degree of carbon removal. The interdependence of the foregoing factors is well understood in the art, and for the sake of convenience the following literature references may be consulted for a discussion of the principles involved:

Ienkins, IvorControlled atmospheres for the Heat Treatment of Metals, Chapman and Hill, Ltd., 1951, p. 266 ff.

Hotchkiss, A.G.-Webber, H. M.; Protective Atmospheres, Wiley and Sons, Inc., New York, 1953, p. 9 ff.

Low, J. R., Ir.Gensamer, J.; Aging and the Yield Point in Steel, Trans. A.I.M.E., Iron and Steel Division, vol. 158, 1944, p. 207 ff.

Suitable decarburizing atmospheres which may be used in practicing the invention include such commercially available atmospheres as DX gas (comprising C0, C H and N or HNX gas comprising 614% H the balance N with added water vapor in either case. Other examples include a straight hydrogen atmosphere or a mixture of hydrogen and nitrogen with added water vapor in either case.

The steel strip is contacted with the decarburizing atmosphere at a temperature of from about 1100 F. to about 1500 F. (preferably from about 1275 F. to about 1350 F.) for the required period of time to reduce the carbon content of the steel to the desired extent, prefer ably to about .025 wt. percent max. and in some cases as low as about .005 wt. percent. The time may range from a minimum of about 4 hours to as long as about 40 hours depending upon the initial carbon content of the steel, the temperature, and the composition of the decarburizing atmosphere. In general, increasing the hydrogen content of the decarburizing atmosphere allows an increase in the permissible amount of water vapor without rendering the atmosphere oxidizing to iron and thereby increases the reaction rate and decreases the time required to attain the desired low carbon level.

From thermodynamic considerations, it might have been expected that the decarburizing atmosphere, which is oxidizing to carbon but not to iron, would also cause oxidation of the titanium or other stabilizing element previously added to the steel. However, our experimental work has shown that the excess or unstabilized carbon can be preferentially oxidized without any detrimental effect on the previously formed titanium carbide or other stable carbide. In particular, by restricting the maximum temperature during the decarburizing step to not more than about 1350 R, we have found that the desired stoichiometric ratio of stabilizing element to carbon can readily be achieved without loss of the stabilizing element.

The resultant product after decarburization has all of the desirable properties of a carbon-stabilized steel but does not possess the undesirable strain-anneal characteristics commonly associated with decarburized steel. Thus, the product has good ductility and is suitable for deep drawing in its as-shipped or temper-rolled condition and also has acceptable enameling characteristics, namely, good enamel adherence, freedom from enamel surface defects, good sag or warpage resistance, and normal pickle-loss characteristics. In addition, the product is resistant to grain growth after critical straining by drawing or cold working and subsequent enamel firing and, consequently, there is no undesirable loss of structural strength. Moreover, the product of the present process has retarded aging characteristics and in many instances is essentially non-aging, i.e. it does not show a return of yield point after skin rolling and one year of natural aging or four hours of aging in boiling water. As previously mentioned, the carbon-stabilized steel produced by the process described above is also well adapted as a steel base for various metallic coatings. For example, soft, ductile, non-aging coated products are obtained by hot dip coating the carbon-stabilized steel with zinc or aluminum according to the well known Sendzimir technique or by applying a diffused chromium coating according to well known chromium diffusion techniques.

As will readily be understood, in the practice of the present invention substantially less titanium or other stabilizing element is required than would be required to effect carbon stabilization in a steel having the same initial carbon content but without the subsequent decarburization step. For example, Table I below shows in the first two columns the theoretical and actual amounts of the respective carbide forming elements which are required to stabilize a steel having a carbon content of .05 wt. percent max. The last two columns of Table I show the substantially decreased amounts of stabilizing elements which will suffice when the steel is subsequently decarburized to a carbon content of .025 wt. percent in accordance with the present invention.

It will be understood that the quantity of stabilizing element added to the steel will vary and that the extent of decarburizaion will likewise vary and will be correlated with the amount of stabilizing element added to achieve the desired result of a carbon-stabilized steel. Dependent upon the cost of the stabilizing element being used and upon other factors, it will be found that in most cases the cost of decarburizing will be more than compensated for by the savings realized through the smaller required amounts of expensive carbide-forming element. In most cases, carbon-stabilized steel must be given a special heat treatment to develop maximum ductility, in which event only slight additional cost is entailed by using a decarburizing atmosphere.

In general, for steels having an initial carbon content of from about .04 wt. percent to about .10 wt. percent, the decarburizing step is preferably conducted so as to obtain a final carbon content of .025 wt. percent max., and the amount of carbide-forming element added is such as to provide in the final decarburized steel product from about .10 wt. percent to about .20 wt. percent in the case of titanium and from about .15 wt. percent to about .25 wt. percent in the case of columbium and zirconium.

Previous attempts to manufacture non-aging steel or improved enameling steel by decarburization have resulted in the unfavorable strain-anneal characteristics explained above so that the resultant product was not suitable for use in any application requiring deep drawing or extensive cold working followed by exposure to an elevated temperature. However, in the process of the present invention, it has been discovered that the presence of titanium carbide, or other carbide of the stabilizing elements herein disclosed, apparently acts as a strengthener and inhibits grain growth during the subsequent decarburization step. As a result, the product of the present invention has superior sag resistance and does not exhibit the loss of structural strength which is ordinarily encountered upon critical straining and subsequent heating of decarburized steel. This totally unexpected grain stabilizing effect of the relatively small amounts of titanium carbide or the like makes it possible to obtain important advantages which cannot be realized either by carbon stabilization alone or by decarburization alone.

Because of the relatively smaller amounts of titanium, columbium, or zirconium which'are added to the steel in accordance with the present invention, it is possible to use semi-killed steel as well as fully killed steel, thereby obtaining the benefit of the superior-- surface characteristics of semi-killed steel. However, there is also a further reason why the present invention alfords a product having better surface qualities than heretofore known. As is Well known, when titanium or other strong carbide-forming element is added to steel, there is a tendency for a certain amount of the titanium or the like to combine with oxygen in the steel to form a refractory oxide which is distributed throughout the steel and tends to impair the surface quality of the sheets or strip material ultimately produced.- However, the present invention requires substantially smaller amounts of titanium or other stabilizing element and at the low levels of addition of these elements there is considerably less tendency for the stabilizing element ness and is conveniently incorporated in the steel in the form of ferr-otitanium. As the subsequent experimental data will show, for a steel having'from about .04 to about .10 wt. percent carbon, the titanium content in the final decarburized product should be from about .10 wt. percent to about .20 wt. percent, preferably from about .15 wt. percent to about .20 wt. percent. This is appreciably less than the -.30-.35 wt. percent titanium content which is typical of the titanium-stabilized enameling steels heretofore known. For maximum ductility of the titaniumstabilized decarburized product it is desirable to subject the steel product to a normalizing heat treatment at a temperature of from about 1670 F. to about 1690' F. for one hour or more.

For purposes of further illustrating the invention, but not by way of limitation, the following specific examples are presented.

Example I A series of test specimens were prepared for the purpose of simulating the cold working and enamel firing conditions experienced in various end uses of enameling steel. Each test specimen was a rectangular section 9" by '%s" with a thickness of about 20 gauge. For each material a plurality of specimens were strained to various degrees of elongation between 5% and 20% in a standard tensile machine. The strained specimens were then heated for about 5 minutes at 1500 to 1550 F., cooled, machined to standard size, and subjected to tensile testing to determine the change in yield strength and grain size for the various degrees of elongation.

In addition to measuring the tensile properties of the strained and heated materials, duplicate unstrained test specimens were also evaluated for pickling characteristics and enameling properties. The test for pickling characteristics comprised immersing the specimen for 15 minutes in 9 wt. percent sulfuric acid at 170 F. and determining the total weight lossin gm./sq. ft. The pickled specimens were then spray coated with a single coat of white enamel and fired for 5 minutes at 1550 F. The appearance of the enameled specimens was noted and the enamel adherence was evaluated by the standard impact test.

The comparative strain characteristics and enameling properties of several titanium-containing decarburized steels made in accordance with the present invention (specimens III, IV, and V) were determined along with the corresponding properties for a normal-grade of decarburized rimmed steel (specimen 1) and a typical titanium-containing non-decarburized enameling steel (specimen II). The analyses of the various specimens were as follows (wt. percent);

Specimen Description o Mn P s Si 5 Al Ti Ti/C v Ratio Decarburized rimmed steal I 02 35 009 023 002 Ti-conta'ining enameling steel (not 045 30 010 i 019 03 018 34 7. 6 Ti-eontaining and decarburized steel 022 47 012 026 04 003 .11 ,5. 0 d0. 045 46 012' .026 04 004 19 4.2 110...- 062 .46 010 024 04 006 26 4. 2

to combine with oxygen. Consequently, the final steel product has a much greater freedom from refractory oxides than would otherwise be the case.

Although the other stabilizing elements disclosed above are operable in the present invention,titanium is the preferredmaterial from the viewpoints of cost and effective- The steel for specimens III, IV, and V originated from v a heat of .07-.08 wt. percent carbon semi-killed steel following standard open hearth practice. Titanium additions were made to series of ingots at the varying titanium levels set forth in Table 2. Hot mill coils (.093" x 36") were produced having the following physical properties:

TABLE 3 Yield Strength Ultimate Elongation, Grain Specimen Hardness, (0.2% offset), Strength, Percent in Size Rb p.s.l. x 1,000 p.s.i. x 1,000 2 in. AS'IM Decarburization and heat treatment of the cold rolled (18 gauge) coils were carried out using the open coil technique. For decarburization an HNX gas was used containing 8% H with added steam to provide an entry characteristics can be noted as compared with specimen I, and athigher titanium level (specimens IV and V) yield strength values above 20,000 p.s.i. are achieved at all levels of prestraining. Consequently, a significant re- P9 of 115 to 1350 For heat treatment 9 5 duction in the amount of titanium has been achieved and mall-2mg the steam was tmned off i to Provlde dry properties comparable to or better than the normal grade E R The decarbunzmg'normahzmg cycle was as of titanium stabilized steel have been developed.

ows:

(1) Decarburization at 1280-1300 F. for time sufficient to achieve a Ti:C wt. percent ratio of about :1, Example 11 (2) Heat at 16201640 F. for 1 hour, and (3) Normahzc at 1670-16900 for 1 hour- Two steel coils from. the same ingots as specimens III b As :vlll bef rtlgtecl tfrorn Tablet: 2, the extlent( of d and IV above were given an extended normalizing time, urlza ion 0 e lanlum-con alnlng s ees speclmens the modified decarburor I III, IV, and V) decreased as the titanium level increased. lows, 121 g n m lzmg cycle being as f Thus, it is evident that the added titanium combined with o all of the carbon required to reach equilibrium and the R ZE SJ ZE EFP 3280-1100 g g i excess or uncombined carbon was then removed to estab- 61 61620 3 g g 0 u lish the desired Ti:C ratio corresponding to complete eat at o or an stabilization of the carbon or slightly in excess thereof. (3) heat 1670469? for 2 The enameling tests on specimens III, IV, and V The analysls Physlcal P PQ of P T- P showed acceptable adherence and surface appearance. mans VI and from these C0115 are Shown n Ta l s The physical properties and strain-anneal chracteristics 5 3 (16- of the various specimens are shown in the following table:

TABLE 4 Value after straining and heating Specimen Property Initial PickieLoss, Hardness, Qlsen Pue- Value 5% 8% 12% 15% 20% (gm/it?) Rb tllity (ln.)

I Yield St Ultimate St Elongation. Grain size.

II Yield St Ultimate St-.. Elongation Grain size Ultimate S Elongation.-. Grain size.

IV Yield St Ultimate St Eiongati0n Grain size.

Yield St Ultimate St-.. Elongation.

Grain size 1 Yield strength (0.2% 0fiset),p.s.i. x 1,000; ultimate strength, p.s.i. x 1,000; elongation, percentin 2 in.; ASTM grain size.

From the foregoing data it will be seen that specimen 11 containing the normal amount of titanium (34%) TABLE 5 exhibits strain-anneal characteristics that are far superior Specimen Ti (wt, percent) 0 wt. percent) Ti:C Ratio to decarburized rimmed steel of specimen I. This is evidenced by the retention of yield strength values above v1 Q 20,000 p.s.i. at all levels of prestraining. At .11% titanium (specimen 111) an improvement in strain-anneal TABLE 6 Value after straining and Initial heating Pickle Hardness, Olsen Specimen Property 1 Value Loss, Rb Ductllity v1 Yield St Ultimate St.-- Elongation... Grain size.

vrr... Yield st Ultimate St--. Elongation. Grain size grain size.

p.s.i. x 1,000; elongation, percent in 2 in.; ASTM The results are generally similar to those of Example 1.

Example III In another series of experimental semi-killed steel ingots the procedure described above in Example I was followed to obtain the following hot rolled properties:

TABLE 7 Weight percent C .09 Weight percent Ti .21 Hardness, Rb 95 Yield strength, p.s.i 90,000

Ultimate strength, p.s.i 100,000 Elongation, percent 15 After decarburization to .04 wt. percent carbon, the following properties were obtained along with good enameling characteristics:

TABLE 8 Hardness, Rb 50 Olsen ductility, .390 Yield strength, p.s. 29,000 Ultimate strength, p.s.i. 51, 000 Elongation, percent. 36 Grain size (ASTM)-.. 9 Strain-anneal properti Percent strain 8 12 20 Yield strength, p.s.i. x 1,000 46 47 20 22 Pickle loss, gin/ft. 7-8

Example IV The procedure of Example III was repeated on an aluminum killed grade of steel to obtain a decarburized product having the following analysis (wt, percent): .04 C, .36 Mn, .010 P, .016 S, .002 Si, .053 Al, .19 Ti. The physical properties were as follows:

Example V A semi-killed columbium containing steel was prepared with the following hot rolled properties:

TABLE 10 Weight percent C .08.09 Weight, percent Cb .10 Hardness, Rb 90 Yield strength, p.s.i 80,000 Ultimate strength, p.s.i 90,000 Elongation, percent After decarburization to 018-024 wt. percent carbon, the following properties were obtained as well as acceptable enameling characteristics:

TABLE 11 Hardness, Rb 48 Olsen ductility, in .395 Yield strength, p.s 29,000 Ultimate strength, p. 50, 000 Elongation, percent" 35 Grain size (ASTM) 9-10 Strain-anneal properties:

Percent strain Yield strength, p.s.i. x 1,000 Pickle loss, gm/ftfl Although the invention has been described above with particular emphasis on the production of deep drawing enameling steel, it should be understood that the invention is not so limited inasmuch as steels which are non-aging or which possess retarded aging characteristics have numerous other uses well known to those skilled in the art. For example, non-aging steels do not exhibit yield point elongation and can therefore be subjected to drawing, bending or other forming operations without the development of stretcher strains or surface disfiguration characteristic of sheets made from an aging steel. Moreover, the carbon-stabilized steels herein described are useful for the production of galvanized, aluminum coated, and diffusion chromized steel.

We claim:

1. A process for making a carbon-stabilized steel which comprises adding to a molten steel containing from about .04 Wt. percent to about .10 Wt. percent carbon the amount of said element added of a carbide-forming element selected from the group consisting of titanium, columbium, zirconium, and mixtures thereof, said predetermined amount being less than the stoichiometric amount required to combine with said carbon, and thereafter decarburizing said steel to remove the carbon which is not combined with said element.

2. The process of claim 1 further characterized in that said steel is decarburized to about .025 wt. percent max. carbon.

3. The process of claim 1 further characterized in that said steel is decarburized by open coil decarburization using a moisture-containing reducing gas at a temperature of from about 1100 F. to about 1500 F.

4. The process of claim 1 further characterized in that the amount of said element added to said steel is sufficient toprovide in the final steel product from about .10 Wt. percent to about .20 wt. percent in the case of titanium and from about .15 wt. percent to about .25 wt. percent in the case of columbium and zirconium.

5. A process for making a carbon-stabilized steel which comprises adding to a molten steel containing from about .04 wt. percent to about .10 wt. percent carbon a predetermined amount of titanium, said predetermined amount being less than the stoichiometric amount required to combine with said carbon but suflicient to provide from about .10 Wt. percent to about .20 wt. percent titanium in the final steel product, and thereafter decarburizing said steel to remove the carbon which is not combined with titanium.

6. The process of claim 5 further characterized in that said steel is decarburized to about .025 wt. percent max. carbon.

7. The process of claim 5 further characterized in that the amount of titanium added to said steel is sufficient to provide from about .15 wt. percent to about .20 wt. percent titanium in the final steel product.

8. The process of claim 5 further characterized in that said steel is normalized after the decarburizing step by heating at a temperature of from about 1670 F. to about 1690 F.

9. The process of claim 3 further characterized in that said temperature is from about 1275 F. to about 1350 F.

10. The process of claim 5 further characterized in that said steel is decarburized by open coil decarburization using a moisture-containing reducing gas at a temperature of from about 1100" F. to about 1500 F.

11. The process of claim 10 further characterized in that said temperature is from about 1275 F. to about 1350 F.

References Cited UNITED STATES PATENTS 2,455,331 11/1948, Eckel et al. 148'12.1 2,459,836 1/1950 Comstock 117129 2,755,210 7/1956 Sutphen et al 14816 3,055,779 9/1962 Chu et al. 148--16 X 3,193,417 7/1965 Kopchak 117-129 3,228,810 1/1966 Coburn 148-l6 HYLAND BIZOT, Primary Examiner. CHARLES N. LOVELL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,333,987 August 1, 1967 Carlton F. Schrader et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1, line 47, for "disclosed" read disclose column 6, line 37, after "percent" insert aqueous column 8, line 17, for "of", first occurrence, read a column 10, lines 13 and 14, strike out "the amount of said element added of"; lines 16 and 17, for "said predetermined amount" read the amount of said element added Signed and sealed this 20th day of August 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS FOR MAKING A CARBON-STABILIZED STEEL WHICH COMPRISES ADDING TO A MOLTEN STEEL CONTAINING FROM ABOUT .04 WT. PERCENT TO ABOUT .10 WT. PERCENT CARBON THE AMOUNT OF SAID ELEMENT ADDED OF A CARBIDE-FORMING ELEMENT SELECTED FROM THE GROUP CONSISTING OF TITANIUM, COLUMBIUM, ZIRCONIUM, AND MIXTURES THEREOF, SAID PREDETERMINED AMOUNT BEING LESS THAN THE STOICHIOMETRIC AMOUNT REQUIRED TO COMBINE WITH SAID CARBON, AND THEREAFTER DECARBURIZING SAID STEEL TO REMOVE THE CARBON WHICH IS NOT COMBINED WITH SAID ELEMENT.