US2696450A

US2696450A - Austenitic alloy steel and procedure for making same

Info

Publication number: US2696450A
Application number: US300227A
Authority: US
Inventors: Walter R Breeler
Original assignee: Allegheny Ludlum Steel Corp
Current assignee: Allegheny Ludlum Steel Corp
Priority date: 1952-07-22
Filing date: 1952-07-22
Publication date: 1954-12-07
Anticipated expiration: 1971-12-07

Description

Dec. 7, 1954 w. R. BREELER ,4 9

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 'Filed July 22 1952 7 Sheets-Sheet l 45. 3% Reduction IO Gcu L in I000 Lbs.

Stress IOO I Room Temperature .L.= Propoflioncl Limii Y= Yield Strenqih .002 .004 .006 .008 .0l0, .012 .0l4 .0l6 .0l8 .020

Strum m lnches/ Wa'lfer R. Bree/er JM, 7%: W #Mv HIS ATTORNEYS Dec. 7, 1954 Filed July 22, 1952 in I000 Lbs.

Stre s s w. R. BREELER 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 7 Sheets-Sheet 2 .230 J70 rd 45.3% Reduction l0" Gou a Room Temperpruro P. L.= Proportional Limii Y Yield Strenqih U.S. e

.002 .004 .006 .008 .0l0 .0l2 .0I4 .Ol 6 .0l8 .020

Strum m Inches/ INVENTOR. Walter R. Bree/er HIS ATTORNE Y3 Dec. 7, 954

Filed July 22, 1952 in I000 Lbs.

Stress w. R. BREELER 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 7 Sheets-Sheet 3 IBO Room Temperature P.L.= Proportional Limit Y Yield Strong":

.002 .004 .006 .008 .0l0 .0l2 .0l4 .OI6 .OIB .020

Strain in lnch es/ R g. 5 INVENTOR.

Walter R. Bree/er jzm/filcw HIS ATTORNEYS Dec. 7, 1954 Filed July 22, 1952 in I000 Lbs.

Stress w. R. BREELER 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 7 Sheets-Sheet. 4

lsq

Room Temperature -|Ol.3 F

P.L.=Proportionol Limit Y Yield Strength US.= Ulti .002 .004 .006 .008 .010 .0l2 .0l4 .Ol6 .OIB .020

Strum m Inches I N V EN TOR. Walter R. Brag/er HIS A 7' TORNEYS Dec. 7, 1954 Filed July 22, 1952 w. R. BREELER 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 7 Sheets-Sheet 5 .230 J67 rd 47.5% Reduction l0" Gauge IS Room Temperature *ls -9o.4 F

P.L.=Proporfionul Limit Y =Yield Strength $.=U e St nqih .002 .004 .006 .008 .0l0 .012 .0l4 .016 .0l8 .020

Strain in Inches /lnch w INVENTOR. Waller R. Bree/er HIS ATTORNEYS Dec. 7, i954 w. R. BREELER 0 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME Filed July 22, 1952 7 Sheets-Sheet 6 .230 .l45'rd 60.5% Reducti in I000 Lbs.

Stress Room Tomporoturo Proportional Limit Yield Sirongth .002 .004 .006 .008 .OI0 .012 .0l4 .0l6 .0l8 .020

Strum |n lnchies/ I 6 v INVENTOR.

Walter R. Bree/er Bvgw hm My HIS r romvsrs Dec. 7, 1954 Filed July 22, 1952 in I000 Lbs.

Stress w. R. BREELER 2,696,450

AUSTENITIC ALLOY STEEL AND PROCEDURE FOR MAKING SAME 7 SheetsPSheet 7 .230 J25 rd 70.5% Reduction IO" Go "I9 Room Tomporoturo P.L. Proportional Limit Y Yield Strength .002 .004 .006 .008 .0l0 .0l2 .0I4 .0I6 .0l8 .020 strain in Inches/ Inch Fig.7

IN VEN TOR. Walter R. Breqler HIS 1 ATTORNEYS United States PatentQ ilfii ik USTEH IIGZAELQ {S L BQCEDUBE Walter R. Breel er, Fredonia, N. Y., assignor to Allegheny- Ludlum Steel Cbrpol'afioil; Brackenridge, 151., afc orporationf Pennsylvianih: Y

Application; July: 22st LQSZQQzighNQk $0,221: 1

' ,tcls' k 21,

This invention relates to; ansteni'tieferrous .a lloysofj v v a no 1nd? i 't l f ce'd'ure is "at least;-' in v "partibase'd upon novel d ppvenes made connection with critical? lbw: tempera 'r'e-sensi tive characteristics of: the steel It is w'ell known in the 'ait'that steels change their inherent structure when; heated up to a emperatur above a normal room; temperature and wn em thereafterbrought down to a ngrmal ro m temperature: 'lhsuch teel at normal'room at ease, the ultimate str-uct-nreof temperatures may be determine y treatnien involved} Fo'n exam'ple, it relatively high temperature, theie is:

temperatnre to; form 'a; solid soluti'on' w; and provide 'austenit-ip' ehara'eteristiqs. 3 that steelsrnay be made; austenitic-La room tempera-t bya proper; propQrt-ioning "oi their; chemical compo tions alfId P aItICHI aI IY, by "the utilization ofif-an 6S Sfit'ial -4 0 anstenitic'jor-mers such as: manganese, the; propqr tion-in'g-f ofaustem'tie-enhaneers eachas: copper; manganese, ear

anstenitic 'formenT snch-"asriick'elg' the; use of -other" bran and nit-rogen-- with nickel; and lirnit ing 'the" "amountof-fernteformers-such molyhdehn lumbitgm, etc,

approach each other, and if tin-attempt made to' fullyplastically deform the st ee1, thag the ultimate strength may be exceeded with resultanthreakage. Thus, a definite problem is presented in endeavoring to, as aminiimum, at, leastnstabilize anvnimprovement in; properties that is present at such-,subzeriotemperatures. and. tor do.

sQ,-Without damagingjhe stee1;;and to provide a usable n blem, presentednto e steel-as to at least.

I have-found the product. three foldzz (-1) to sonclon not d c s the stai t! b tw en i s, yisli aamij tens le strengths andat zero temperature p @1011? nstnitu qalsi (2)"tofurther andfully deto. develop uniformfind the best possible improvement it-p1 a fi'lpi hfi teel-a Q s ssetseh at i 68-:

, v v n w en-sir strength of the 'steel at such tempera-times tend toiplpsel y-f San-1e preliminarilyfix its subshe. steel andf tfl i iz i thii d'sr'a slmzsd sttn tnte tho'ut e ineate stee s; (.3) and t shszehl st stst el 2 2 epseststn sstee fisrss rt iljfiql q s d has eserh t l treating it at 500 to; loose-1 is. (05m F. optimum), an;

to. provide itwith anrinereased hardness, Although, surface: working; an such temperatures appears: tozproh. vijdeasurface hardness, which is; retainedwhen'the: steell is' returned: .tQJa room tempexzatnregand which is stated to;

be; further impnOved; ,byg, theaging;heat:v treatment; aif'ullzj and unifprm impnosernent jot." itsbphy' icals is laekingi and anysin provement'is limitcdtto its, hardened surface: There; is; a definite necdjjforiai piracticah procedure which:

will enable the steel, after amini tial' subz oatemperas ture..treatn1ent, to ibe v fullyv plastically' deiormed through its fullr thickness section! to; fiullyn develo its; Subzero;

physicalswithont, at; the: sametime; setting; up a danger:-. ps: brittleness aspe s, d: m'genereh; thout? introduce.

ing l-imi-tinsrt etors incident: o an; attemptito; so: detormt,

sz teel a ubzemi emperature-t It has thus been'an object of my invention to provide a solutionit c the; problem; presented; and toijdeyiset a, commerci'ally; practical procedure, ut' ing: subzewizoiatenanv Pera ute eat dau tenit e teek:

A ot r; object h sh lenam: prov de. a new and: 11 12:

proved austenitic; steel from: the; standpoint; o f-:'its physical:

A further objeot" has; be nie: develop, a, procedure: for.

practically; and "effectively; deformingi subzero temper as turertreated; ranstenitie', $115313); obtain highly, improved physicals;

A stiilfurtherobj eethas been to develop eniteriaivfon.

processingzanstenitic; steels from; an mit-iaL subzeroj tem- P a ure sa en r;

These-rand; many other, objeets of; invention; will ape p art' h Q- k 1 a l1 h art rom the de a l dvd s rin tion..the1:eof-. and:the'datehcre nflfitersq forthil,

he d awin s ur s. 1 o n1i1siv r present. strain-stress curves. plotted for; austenitic gsteels; of differ? ntm' alv mp iti m, diff r n pe s n a es; ofi vfull plasticwork, deformation; (-rednetion);, and at .difierent initiatingtemperatures; In; the; cur-Yves; of1.eaeh-, ,figune, B,

hav c mp red the t iaimst essf ha act risti s. ff. ne ventionally .eold. (roomtemperature) deform'fid steels.

e io :v ha he sam .ch mitzal commsi ma dl uh ject loathes-ame amount of work ldefomnat-ion butthe treatment of which is; initiatedat a; specified; subzeros temperature Morev speoifically', Eigurqli shows; comparative; curves: for", a. somewhat unstableallstenitie steel; when given bou -45 defimmatimwnth tee men sy Figure .2 hows-,1compflrative cusvesofz asteelof: inten ediatestahili w ubjeqtedto1abon 45-2 .deformaiti 2n5 work, treatment;

Figure shows eomparative cutzvesztfor; the steehof u e ut ject d; o bcmt-v 5% 5 e ms! tiontandaEigure t for, thezsame steel as subjected; to about 7 0.5% worktdeformation;

Figure; 5; showsicomparative; curves of a; still more stable .steele subj'ectedxtoahbbut: 47.6%. work n deformation, Figure 6tshowss curves for the same steel assu-lajctedt. to about-f16Ql-5 treatment, and Figure? shows curves-for Forf'the purpose of fiirther refe'renlce the alloyof Figalloy of Figures 2; 3.

Although {have determihed that austenitig, steelsnin,

Patented. Dec. 7, 1954 worked austenitic steels. For example, I have started with an austenitic steel as reduced by hot working and then applied my intermediate treatment instead of a conventional cold rolling, forging, upsetting, or drawmg process.

Briefly stated, in carrying out my invention, I, (1) condition the austenite of an austenitic steel at a subzero temperature; (2) heat fix the conditioned austenite; (3) and finally, develop the conditioned structure of the steel to provide it with highly improved physicals. That is, I first cool the steel down to a temperature of not greater that F., that may be as low as 320 F. and as an optimum, is within a range of about 30 F. and l20 F. After the steel (which may be in the form of bars, wire, strips, or sheets, for example) has been fully brought down to such a subzero temperature, it is then quickly (approaching instantaneously) brought up, by what may be termed a heat fix, to a higher temperature that as a minimum is 2 or 3 degrees agove 0 F. and as a maximum, up to about 350 F. (well below its ageing temperature). I have discovered that is hi hly essential that the steel be brought up at least slightly above 0 F. before it is plastically deformed or pres sure reduced. This second step lowers the compression resistance of the steel to deformation or working and tends to slightly increase the spread between its tensile strength and yield strength without a further development of and without an appreciable change in its subzero physicals.

I have found that it is also essential that the steel be provided with a tem erature by the second step of my process which will allow for any heating up of the steel incident to its essential subsequent deformation in accordance with a third step of my process. That is, if for example, a number of subsequent draw reductions the employed. the steel should not reach a temperature higher than 350 F. in the first reduction. If, on the other hand, the subzero temperature-treated steel is permitted to very slowly come back or heat up to a normal or room tem erature, it will return to its previous, substantially stable austenitic room temperature state, such that any improvement of its physicals from the preliminary subzero treatment is impossible of attainment.

In carrying out the third step of my procedure. I fully plasticallv deform or compression reduce the steel from its subzero fixed state to both further increase or improve its physicals and to stabilize such improvement. From a practical standpoint, I prefer (if the resultant temperature of the steel after the second step is lower than room temperature) to substantially immediately effect the full plastic deformation of the steel throughout its cross section. Any subsequent work reductions or deformations may be carried out in a conventional manner with ut destroying the improved physicals of the steel. In this connection, I have found that the improvement in physicals is highly stable and that such improvement is not adversely affected by subseouent temperature applications in the neighborhood of 1000 F. or higher.

With reference to the composition of the steel, I find that austenite appears to be conditioned by the sub-zero temperature and fixed bv the seco d step in such a manner that a subsequent full and uniform deformation (reduction or upset) can be effected without embrittlement. I stress the steel in the third step and attain hi her physicals for a given reduction. In accordance with my invention. T attain a hi her tensile level without a sacrifice of ductility. as compared to results obtained by conventional procedure. The amount of stressing is governed by the stability of the austenite content and surprisingly, may be controlled on the same basis as austenitic steels processed in a conventional manner. For example, I have found that types A, B and C alloys (as treated in accordance with

steps

1 and 2 of my invention) can be deformed (reduced, drawn or upset) about as much as the same steels processed by a conventional procedure involving their direct (not subiected to

steps

1 and 2 of my procedure) cold deformation from a room temperature.

The steel should initially, in its room temperature state, be at least 50% austenitic. As finally processed, it should have less than 50% ferrite and an optimum. less than 40% and above an essentially austenitic steel must be utilized which has some austenite capable of being converted to ferrite dur ing the third step of my procedure.

It is thus apparent that Although it is difficult to determine exactly what occurs, my inventigations indicate that the sub-zero treatment produces a mixed structure in the steel, that the heat fix substantially retains such sub-zero structure (with a slight but favorable modification), so that the steel is amenable to a full development of its physicals by a full plastic or compression deformation without developing brittleness. By way of example, an austenitic steel (type B) had a tensile strength of 157,000 p. s. i. and 330 Vickers when cooled to about -7S F. in accordance with the first step of my procedure, had a tensile strength of 147,000 p. s. i. and a 310 Vickers at +2 F. after the second step was effected, and developed a tensile strength of 290,000 p. s. i. and 600 Vickers after about 70.5% deformation or reduction in accordance with the third step of my procedure. On the other hand, such a steel initially cooled to about +2 F. and tested, had a tensile strength of about 127,000 p. s. i. and a 265 Vickers.

I have also determined that less work is necessary upon an alloy processed in accordance with my inven tion and that the size or thickness of the alloy can be reduced to obtain physicals as good or better than those of a larger size alloy piece as processed in accordance with normal procedure. Thus, from this standpoint, an increase in ductility may be provided for a given desired tensile strength and a greater ductility can be provided in a steel shape of a required tensile strength processed in accordance with my invention, as compared to a normally processed steel of the same initial chemical composition. Another advantage of my procedure is that less deformation is required for obtaining desired physicals. For a given required tensile strength, I may employ a lesser total number of reductions, starting, of course, with an initially lesser gauge than otherwise possible. That is, lesser percentage reductions and a lesser number of passes are needed.

Austenitic steels may be processed in accordance with my invention to provide a marked improvement in physicalswithout breakage and without a substantial impairment of their corrosion resistance. In fact, the improvement of the physicals made possible has been sufiicient to cause the usage of these more expansive steels in entirely new fields. For example, my invention makes possible, for the first time, the practical utilization of austenitic stainless wire for spring wire utilization to provide a much better spring. Heretofore, music wire which has had little corrosion resistance has been used because of its high physicals. It will be noted that the physicals obtained by my procedure run well over the minimum required for spring wire. In addition to fine wire and spring wire usefulness (a proportional yield point gain of 50% or more can be obtained in accordance with my invention), an alloy produced in accordance with my invention is particularly useful in connection with airplane requirements, since stressed parts with a minimum of weight are required.

The following Table I shows a comparison of permeability of steels A, B and C where they are processed in accordance with normal room temperature cold workprocedure as compared to where they are processed in accordance with my invention (starting from the indi cated, initial sub-zero temperature treatment). In this Table I, the data is based on equal percentages of deformation (reduction). It should be noted that permeability in austenitic steels is a measure of the stress to which they are subjected.

Tables II to V, inclusive, show test data on alloys A to C, inclusive, as well as on a straight chromium (nonaustenitic) alloy D. The lack of improvement in alloy D is evident from Table V.

.230 Rd., 45% Work Ten. Size, .166 Rd. Ult. Strength, 222,000 p. s. i. Elong. in 227 Red. of Area, 57%;;

.230" Rd., 60.5% Work Ten. Siz, .143 Rd. Ult. Strength, 254,000 p. 5.1.

Elong. in 11%. Red. of Area, 48%

8 TABLE Grade C Drawn to .167 Rd. from .230 Rd., 47.5% Work Ten. Size, .167 Rd.

Ult. Strength, 173,000 p. s. i. Elong. in

Drawn to .145" Rd. from .280 Rd., 60.5% Work Ten. Size, .142 Rd.

Ult. Strength. 208,000 p. s. i.

Elong. in V 20% Red. of Area, 58% Red. of Area, 49}% Load P. s 1 Strain .001 P. s 1 Strain .001"

P. s 1 Strain .001 P. s 1 Strain .001 4, 600 23,000 46, 000 4, 550 2 6, 300 2% 69, 000 22, 750 10 31. 500 12% 000 45, 500 10% 63,000 26% 115, 000 08, 250 29% 94, 500 41% 138,000 91,000 40 126. 000 57 161,000 113, 750 51% 157.500 79% 174, 800 136, 500 67 189,000 1173 184, 000 159, 250 92% 207, 000 172, 900 113 Drawn to .125" Rd. from. 230" Drawn to .125 Rd. from .230

Rd., 70.5% Work Rd., 70.5 Work Ten. Size, .121" Rd. Ten. Size, .122 Rd. Ult. Strength, 284,000 p. s. i. 30 Ult. Strength, 227.000 p. s. i. Elong. 1n 6% Elong. in 12%% Red. of Area, 46% Red. of Area, 42%

Load P. s 1 Strain .001 Load P. s 1 Strain .001

TABLE IIId TABLE Iva Grade B o .00 Cr 18.84 N18.46Drawn after Subzero treatment at -90.4 FJ Grade C (1) (2) [C .07 Ni 10.99 Cr 18.84Drawn after subzero treatment at -101.3 F.]

Drawn to .170 Rd. from Drawn to .145 Rd. from .230 Ed, 45% Work Ten. Size, .169 Rd. Ult. Strength, 232,000 p. s. i. Elong. in 25% Red. of Area, 57%% .230 Rd., 60.5% Work Ten. Size, .140 Rd. Ult. Strength, 278,000 p. s. i. Elong. in 18%% Red. of Area, 51%

Drawn to .167 Rd. from .230 Rd., 47.5% Work Ten. Size, .166 Rd.

Ult. Strength, 197,000 p. s. i.

Elong. in 20% Red. of Area, 58%

Drawn to .145 Rd. from .230" Rd., 60.5% Work Ten. Size, .139 Rd.

U117. Strength, 236,000 p. S. i.

Elong. in 12%% Red. of Area, 44%

Strain .001

Drawn to .125 Rd. from .230

Rd., 70.5% Work Ten. Size, .122 Rd.

Ult. Strength, 263,000 p. s. i.

Elong. in 14", 12%

Red. of Area, 41%

P. s. i. Strain .001

Drawn after Subzero -Treatment at 101.3: F. to .1895 ag n 2% "1 45% Drawn at Room Temp. to .1895 .Rd.,from .244. Rd.,. 145%Work '1 Ten. ,size, .1895 .Rd.

i zneq. of Area, 05.5% Areafssjzf y 1., ,r- 1%.. Lea @P-s 1 s ra 4 -.s-:- strew 3,550" 2 a, 000 .2 17, 750 1 18, 000 as, 500 10 30, 000 as p 43,250 .2754 54, 000 .2795

11,000 as 72,000 as 88,750 40 00, 000 54 00, 400 as 100, 800 10 In, for example processing wire to carry out the first step, I have placed an annealed austenitic steel coil in a large insulated tank having a removable cover, a slght glass and a coil-temper-ature-reading thermometer. 'the tank has an exit cut in it above the cooling solution level. A solution of alcohol (methyl) and Dry Ice has been used as the cooling agent or solution to produce a temperature of down to about -l12 F. For temperatures down to about 320 F., liquid nitrogen may be used and a commercial freezing unit will provide a temperature of down to about -l F. The wire may be coiled on a rotating swift or spindle in the tank and its end threaded through the exit and introduced into a contact die having a draw bore of the same diameter as the wire and a relatively large metal mass. In this die, the temperature of the wire is quickly raised to above 0 F. and the wire may then be drawn from such die into a reduction die of a smaller bore diameter at which point its physicals arefully developed and stabilized. A wiper of soft material is positioned to wipe off moisture from the wire as it leaves the tank so as to prevent the formation of frost.

In this manner, wire increments are progressively heat fixed from their subzero temperature by the first contact die and are then plastically deformed or compressionreduced in the second die to carry out the third step of my procedure. The first'die has a contact bore of a conductive material such as tool steel and a sufficient mass to quickly and effectively generate heat in the wire increments passing therethrough in frictional engagement therewith. A copper coating or dry soap has been found helpful as a lubricant. Of course, it will be apparent to those skilled in the art that any suitable apparatus may be employed and that the above arrangement is merely exemplary.

This is a continuation-in-part of my application, Serial No. 241,085, filed August 9, 1951, now abandoned, and entitled Austenitic Alloy Steel and Procedure for Making Same.

The heat fixing (highly critical second step) of my procedure involves approaching instantaneously (maximum period of less than about 5 minutes) and as quickly as possible (optimum), bringing the fully cooled austenitic steel up from its subzero temperature to a temperature above 0 F. (to a minimum of about 2 or 3 above 0 F. and as a maximum up to about 350 F.). This accomplishes several highly important results: (a) it is at a rate that is sutficiently fast to effect a substantial retention of the subzero-temperature-developed subzero austenitic-ferritic structure; (b) the steel substantially retains its unstable (subzero) austenitic condition but its (subzero) compress-ion and tension resistance to defiormation is lowered, so that it can be fully worked; (0) the small spread between its tensile and yield strengths which is characteristic of its subzero condition is slightly increased to an amount that is sufficient to permit fully working or plastically deforming it without developing brittleness (it has a retained favorably modified subzero structure); and (d) the substantial instantaneous fixing of the subzero steel makes it not only fully amenable to a full work development and o tac ie for wlre, o a. I through.,whichtheslieet, s'trrpor wire imrnediat'ely after leaving the cooling agency or unit. The m v s i o he uni n z vrssily a ju te da .1 3??? g 'thdteni turepf the steel :(suchasby a thermometer se ney a i eers th 'ilisa 's s fli tin -shutt e); s itswans out l 1 t a my .PP$.$ uhis s a, h swea s gr ast ss st min a Wor ts s g n? a a r asm ss slo m ts ph s als 14 mrl-qrts tt t m d f bz stt tli" e 1 om o ra swans nallope. tron); ithout raising the temperaeazabpve' a o 50 Kn intain'it. 2- s'tahtially or'w'e'll below' its'age'i'ng temperature). Thus, the steel is brought down to its final gauge, shape or form after the subzero treatment and in such a manner as to develop and stabilize its highly improved physicals. It will thus be apparent that it is advantageous to effect the heat fixing step at a raised temperature that is closely above about 2 F. to provide a wider working range for the operation or operations of the subsequent plastic deforming step.

What I claim is:

l. A method of imparting improved physicals to a steel that is essentially austenitic at room temperature and that has austenite capable of being converted to ferrite under the treatment herein set forth which comprises, developing its subzero austenitic-ferritic structure by initially fully cooling the steel to a subzero temperature of below 0 F., making the steel workable and developing and retaining a favorably modified subzero structure by substantially instantaneously raising it from the subzero temperature to a temperature of at least about 2 F. and substantially below its aging temperature, and developing stabilized and highly improved physicals in the steel by them fully plastically work-stressing it throughout its section and at least initially, while retaining the steel at a temperature below about 350 F.

2. A method of imparting improved physicals to a steel that is essentially austenitic at room temperature and that has austenite capable of being converted to ferrite under the treatment herein set forth which comprises, developing its subzero austenitic-ferritic structure by initially fully cooling the steel to a subzero temperature of below 0 F., making the steel workable and developing and retaining a favorably modified subzero structure by substantially instantaneously raising it from the subzero temperature to a temperature of at least about 2 F. and up to about 350 F., and developing stabilized and highly improved physicals in the steel by then fully plastically work-deforming its favorably modified subzero structure throughout its section and at least initially, while retaining the steel at a temperature below about 350 F.

3. A method as defined in claim 2 wherein, the steel is maintained below about 350 F. while it is both initially and subsequently plastically work-deformed.

4. A method as defined in claim 2 wherein, the substantially instantaneous raising of the steel from the subzero temperature is effected within a maximum period of about five minutes.

5. A method as defined in claim 2 wherein, the steel as processed, contains not less than about 10% and not more than about 40% ferrite.

6. An austenitic steel as processed in accordance with claim 5 as characterized by its highly improved and uniform physicals throughout its section from the standpoint of ultimate strength, tensile strength, yield strength, proportional limits, and relative ductility.

7. A method of imparting improved physicals to a nickel-containing steel that contains at least 50% autenite at room temperature and that has austenite capable of being converted to ferrite under the treatment herein set forth which comprises, developing its subzero austenitic-ferritic structure by fully cooling the steel to a subzero temperature within a range of below 0 F. to 320 F.; making the steel workable and developing and retaining a favorably modified subzero structure by substantially instantaneously, and within a maximum perlod of about five minutes, raising it from a subzero temperature of the defined range to a temperature of at least about 2 F. and up to about 350 F.; developing stabilized and highly improved physicals in the steel by then fully plastically reducing the steel throughout its section, while maintaining it at a temperature below about 350 F.; and effecting a maximum conversion of austenite to ferrite in the steel of 40% of its above-mentioned initial content.

8. A method of imparting improved physicals to a chromium-nickel steel that is essentially austenitic at room temperature and that has austenite capable of being converted to ferrite under the treatment herein set forth which comprises, developing its sub-zero austenitic ferritic structure by initially fully cooling the steel to a subzero temperature within the range of below F. to 320 F., making the steel workable and developing and retaining a favorably modified sub-zero structure by substantially instantaneously and within a maximum period of about five minutes, raising it from the sub-zero temperature to a temperature of at least about 2 F. and up to about 350 F., developing stabilized and highly improved physicals in the steel by then fully plastically reducing the steel throughout its section while maintaining it at a temperature of below about 350 F. and effecting a conversion of austenite to ferrite in the steel of less than about and of above about 10% of its initial room temperature content.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A METHOD OF IMPARTING IMPROVED PHYSICALS TO A STEEL THAT IS ESSENTIALLY AUSTENITIC AT ROOM TEMPERATURE AND THAT HAS AUSTENITE CAPABLE OF BEING CONVERTED TO FERRITE UNDER THE TREATMENT HEREIN SET FORTH WHICH COMPRISES, DEVELOPING ITS SUBZERO AUSTENITIC-FERRITIC STRUCTURE BY INITIALLY FULLY COOLING THE STEEL TO A SUBZERO TEMPERATURE OF BELOW 0* F., MAKING THE STEEL WORKABLE AND DEVELOPING AND RETAINING A FAVORABLY MODIFIED SUBZERO STRUCTURE BY SUBSTANTIALLY INSTANTANEOUSLY RAISING IT FROM THE SUBZERO TEMPERATURE TO A TEMPERATURE OF AT LEAST ABOUT 2* F. AND SUBSTANTIALLY BELOW ITS AGING TEMPERATURE, AND DEVELOPING STABILIZED AND HIGHLY IMPROVED PHYSICALS IN THE STEEL BY THEN FULLY PLASTICALLY WORK-STRESSING IT THROUGHOUT ITS SETION AND AT LEAST INITIALLY, WHILE RETAINING THE STEEL AT A TEMPERATURE BELOW ABOUT 350* F.