US2646352A - Alloy steel products - Google Patents

Description

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HARRY TANozYN fw W "5 www atented July-:21, i

UNITED STATES PATENT OFFICE Y x v o Y f 2,646,352 u,

i` ALLOY STEEL Pnoiiicirs vHarry 'Tanczym Baltimore', assigner t Armco Steel Corporation, a corporation ofOhio' rApplication April 8, l947, Serial No. 740,120

This invention relates to stainless steel and more especially to manufactures produced from the steel. l nAmong the-,objects Aof my invention is` the provision, with savings in material, of stainless steels which are substantially free of detrimental inclusions that ordinarily impair the general surface appearance, and which steels are amenable to working and fabricating into a lhost of c orrosion-resistant products all having substantial freedom from surface imperfections such as 'black spots, blisters, pits and inclusion lines.

Other objects vin part will be obviousr and'in part pointed out hereinafter.

The invention accordinglyconsists in the combination of elements, composition of ingredients and mixture of materials, and in the articles,"

products and manufactures thereof, as described herein, the scope'of the applicationA of which is indicated in the vfollowing claims.Y Y y In the single figure of the accompanying drawing is 'la diagram showing curves for certain specific values of chromium in my stainless steels and products, and the amounts of manganese and minimum amounts of silicon which are useful alongV with the specic chromium vcontents for the prevention of detrimental silicate inclusions.

As conducive to a clearer understanding of certain .features of my invention, it may be noted at this point that stainless steel is recognized as ybeing carbon steelwhich contains aboutrl0% to 35% chromium, with or without nickel the nickel in so-called straight chromium grades of the steel being even so high as about 3% or entirely omitted) and with or without supplemental Y' amounts of such elements as cobalt, copper,

metallurgical basis when applied `to stainless steel,despite being valid for plainecarb'on steels. It follows then that the most reliable approach highly'specialized field. Y Y Y y In connection with. the above, it, is interesting to observe that vfor many years, the use of manganese in certain quantities in plain carbon steels has beenv accepted as imperative forsecuring desiredproperties, as forexample amounts:

s claims. (o1. 'i5-12s) 'to the solution of problems in the stainless steel art, involves thinking in terms of the rrelated Yat rolling'temperatures and accordingly between about'0.3% and 0.5% for the prevention of hot shortness in rolling and forging operations. rShe common explanation of the value of manganes'e in the elimination of hot shortness in ordi- Y nary carbon Vsteels is that this element combines with sulphur, thereby forming manganese sulphides.Y Where manganese is not present in ap preciable quantities, other sulphides, namely iron sulphides, having a'relatively low melting point arezformed, these becoming liquid or semi-liquid ing .the hot rolling properties.

, Manganese also is of benefit in preventing hot shortness, in plain carbon steeis lbecause it forms a solid solution with iron oxide. This voxide is dispersed freely throughplain carbon steels, and its effect is deleterious in hot working operations unless controlled by such elements as manganese. The" solid solution promoted by manganese has a higher melting point than pure ferrous oxide; thus the melting of low temperature constituents isravoided and hot shortness prevented. Among other functions of manganese in the plain carbon steels is that of promoting deep-hardening prop-A erties if used kin amounts around 1%. Still greater quantities o f this element tend to increase wear resistance. f Y

, The practiceof usingb manganese in the plain v carbon steels, for thepurposes described, has

carried over'the manufacture of stainless steels.

In fact, the belief in the importance of manganese in stainless steels has become so entrenched that buyers of straight chromium steels, for example,v

require substantial amounts ofthe element to be present according to specifications, and even the manufacturers of these steels have set up definite manganese requirements. In many instances, however, lit seems that lno serious investigation has been made as to whether this element is wholly beneficialv and desirable.

TheV straight chromium stainless steels are highly susceptible to the development of black spot defects and similar unsightly blemishes which mar the metal surface, these vspots often being observed on the surface of sheet, strip, wire Y or other products following such operations as products as knives, spoons andthe like Vby constituting a series of streaks, pits and lines which are difficult if not impossible to remove by further polishing.

In hot rolled stainless steel strip and sheet,

`diflculty also is encountered with fblisters which are caused by imbedded masses of incluimpairsions; these blisters are unsightly and destroy the usefulness of the metal on which they occur. A further dinculty encountered with many of the straight'chromium grade stainless steels is the tendency of the alloy metal toward pitting to an objectionable extent` when exposed to passivation treatment in such acids as nitric acid. Under these conditions, the metal suers' flash attack, during which an evolution or gas `occurs for a few seconds before achieving "passivatiorr This attack, While not long'"`in"duration, "frequently causes rough surfaces and hurtiuliy a'ffects the appearance of the finished stainless..

steel or even, in severe cases, renders themsteel useless for certain purposes, particularly for uses Where reasonably smooth nnishes are of irnportance.' 'An outstanding object of my invention accordingly isthe provision of wrought and'passivated straight chromium stainless steel articles and products, a's'for example, Wire, sheet, s tripQor the like, which whether 'in the polished or unpclished condition' are substantially Without detrimental silicate inclusions of the character indicated and are' substantially `free of attack from passivation.

I 4ln'd that the` poor surface conditionof straight chromium stainless' steels is'traceable to the? character of noneinetallic' inclusionsy present and theirsise frequency 'of o currence in the steels."`There are inr ract'several diierent general classes of non-metallic inclusions in these steels, 'among which 'are relativelyl simple noneo'mplexinclusions suchY as or silica-type; also, loivm'elting point'ma'lleable 'complex inclusions whicliu'sually are much 'elongated informing or rolling or'other'wo'rking and are the source of such evils as black spots' and similar unsightly blemishes in polished sheets. The larger size complex inclusions upon being deformed at Workin'g'temperatur'es, as' vin rolling the metal, are elongated or extended to produce darlrareas and black spots. The simple'nonwomplex silica inclusions usually'o'ccur insmualler'forrn, are relatively h'ard, and do not elongate as readily as the complexones" at' hot'iyorking temperatures, are much" less visible on'polish'ed stainless steel article's and products, "and 'are generally" not troublesome.

' My explorations into the causes of compl x sili'cate'inclusion's have revealed that manganese promotes the'development'of these'inclusions in the 'straight 'chromium steels, depending upon the' amount' of' chr 'nium" and silicon present. lvl'ang'anese, chrom'iu and/ironv tend to reduce the free silica of fireb'ricl; in runners, protective sleevesand ladle lining to'w produce ferrous oxide, manganous' oxide, chromium' oxide and `silicon'. The'silic'on is' absorbed'by'the metal while the ferrousofride, manganous oxide' and 'chromium oxide flux additional quantities of silica to form the undesirable complex silicate inclusions. Since iron and chromium possess very weak reducing powers with regard to silica whereas Inanganese is very powerful in this respect, the'elincination of manganese from stainless steels will forestall the aforementioned reactions with the flrebrick and 'result in the presence of small, widely-scattered silica inclusions.

The complexv silicates may be changed to harmless silica by a proper manganese-to-silicon ratio; the simple silica'inclusions are small and non-deformable at hot Working temperatures and not readily visible to the naked eye. Of still iurther irnportance, Where the manganese content is extremely low or substantially absent, the

4 chromium in these steels in many respects tends t0 function as a substitute for manganese, such as in producing sulphides, deep-hardening eiiects where the" steelsare hardenable, resistance to abrasion, and freedom from hot shortness.

Rete ring noW more particularly to Ithe -p r'acs tice of invention, I provide 10% to 35% straight chromium stainless steels and products or Ythe st'els (as for example wire, sheet, strip and the like, in the' Wrought and unpolished or polished 'cndi'tionl in which manganese and silicon" are' consistent With amounts indicated ben th the appropriate curve in the accom'ar pan n'g diagram, vthe curve corresponding to the speciiic amount of chromium used. rThe cloro` mium curves define highly critical upper limits onwthe maximum'perm'issible 'quantity of Inanganese in the steel, for any specific vsilicon and chromium contents'in achieving `simple silica in-` clusionslas' distinguishedfrom complex silicate inclusions. Other chromium curves and upper limits 'on manganese in rny steels, of course, may be arriyed 'at' in the' diagraml by interpolation. The steels are of'h,ardeningY v'or 'nonhardening que' ty, as desired, depending uponmthe speci/nc composition "a its response" toV heat treatment.

Among thesteels and''productsl which I vprovide are those including ab"V4 "t 10% tolgq'chromium, up to about`""1'.5f"7 carbon, manganese below about 0.2%; i and "silicfn'Y frofm incid 'ntal ameunts up to"`l% r'rfno the manganes also eing'v consistent with amounts rthe accomf( pany'ing diagram fallingbenea'th the appropri chromium curve', therenain ercf'the composi-v tion being substantially irnfV In' 4the latter group; are' steels'containmg over 0fi5 7`a`carbon and 12% to 14% chr rn, and'those contai ci ing 0.66% to 1.20% carbon'aiid 14% 'te 18% ehm; mium asY in the form of cutlery products and surgical' instrunients,A respectively. U *Along* with chreniiumf"manganese 'and ilicon, my steels sometimes inc'ludenickel upto'about and/or quantities of some other element or elements such" 'as ni'olybder'iurnfa coniur'n, titaniumfvanaeine, colombiani, "slup' u 1`-,'fpl1js`pl' n.5, "or seleni'un,V for'specialpurposos,V vettiniestlie manerations'iny roduetion allovv,Y Quite often, my steels and' products'are'madeto havea very lorv inan"`an`es`e content yrangingy up to Yabout0,1%, this'co'ntent lfurther beil in `Ikeeping with the lovlf' side ofthe speciil'e chromium curve in theA accompanying'diagram and nctmexlceeding the maximum'ai'nount permitted bythe specific` sili;Y

con contentaccor'ding'to' the'diagrar'n-V I iind that not only is an important saving in material effected in my stainless'steels' and predu'cts', Where the 'manganese centent is duits" low or virtually eliminated, but valuable improve? ments, in certain properties are had, amongv thesev being improved. resistance to corrosion and im pact, andv the substantial freedom from silicate inclusions which ordinarilycause elongated black spots and the like inrwrought corrosion-resistant steels. Y

As illustrative offthe practiceof my invention, in the production ofahstraight chromium stainless steel from available'and inexpensive raw materials, Iprepa're a bath of ferrous metal in.A a suitable furnace, for example, an,l electric arc furnace, using inthe charge` suchmaterials as rustless iron scrapand/or ordinary, low-carbonv steel scrap, and an oxidizing agent such as iron ore, roll scale or the like. The scrap materials entering thecharge are forexampleof .0.30% to Where practical consid-.

avoided in the furnace. -metal resulting from the charge has an oxidizing slag or covering which forms during the melting operation. I bring thebath to a uniformly high temperature.

- 0.60% manganese gradefor'simplifying the elimination of manganese during the Process to the amount desired in my stainlessA steels. Any other substantial sources of manganese also are The bath of Y ferrous Chromium additions are made either along with the initial melt down ingredichrome or chrome ore, or these additions may be made to the bath and slag formed as indicated above, as throughthe use Vof chrome ore.'v

- Under the action of thestrongly oxidizing slag vents,y using, for example, high carbon ferro-` and the high temperatures employed, carbon y coming from the furnace electrodes and furnace atmosphere, as Well as from the raw materials, is effectively excluded and/ or removed from the bath of. ferrous metal. A portion ofthe manganese in the charge passes to the slag and is not fully reduced to metal again. The use of oxidizing :agents such as supplemental amounts 0f the iron ore or roll scale, furthers the elimination of manganese to the' slag. Along with the oxidation of carbon and manganese there is an incigferrochrome, and silicon at least in amounts Ycalled for in the accompanying diagram by the speciiic amounts of chromium and manganese for ensuring the substantial absence of complex silicates in thersteel. Other elements asfor spe- -c ial purposes are added if desired. I then teem the melt into ingot molds and thus form ingots of the straight chromium steel.

Thegsteels Which vI provide, whether produced in the' electric arc furnace or inA any other suitable manner, `and Whether of ferritic non-hardening quality or of martensitic hardening quality, suffer no appreciable detriment to hot working properties, ultimate tensile strength, reduction Vv in area, elongation, machinability, and the like, which might be traced to the control over manganese and silicon in re- Y lation to chromium.

dental oxidation of chromium from the metal; f

silicon contents of the bath, I -usually introducek basic slag-forming materials,` such as burnt lime, in amounts sufcient to assure basic conditions during Athe reduction of the'oxides in the slag. Thebasic slag prevents silicon contamination of the bath and allows for adjustment of the silicon contents after the reducing period should ad,

justment be needed over and above the incidental'amounts present'.

Under the reducing conditions vonly apartia recovery of manganese is had, which element passes back tothe bath along with the iron and chromium recovered. Byv careful control overV manganese contents ofthe kbath as derived from the furnace charge and the like, however, the re.-

.covery of'manganese from the slag is not, excessive and the manganese content of the bath remains at say for example some value belo'vv0.l%. I draw off the slag and substitute a suitable finishing slag on the surface of the steel.

Y After this, I adjust the contentsA of the bath to ther desired alloycontents as by the addition of low-carbon For illustrating certain properties of my lowmanganese hardening steels, as compared with those of several steelscontaining an excessive amount of manganese forv the silicon and chromium present, referV to specic compositions noted in Table I. It Will be seen that Steel A in this table contains a quite small quantity of manganese as permitted by the accompanying diagram. The Steel B, however, has a relatively high manganese content in view of Vthe siliconV and Achromium contents and Vis objectionably susceptible to the formation of complex silicates as would be expected in View of the diagram.

Table I.-Hardem'ng steelsV steel o for Mn s1` N1 P s Y A 0.091 12.13 0.00 0.20v 0.00 0.013 0.013 B1 0.090 12.20 0.52 0.20 0.02 0.000 0.012

1 Prior art.

' v It is to be observed in Table II that many of the beneficial properties of the Steels A and B remain substantially unchanged despite the differences in manganese contents, and therelation of the latter vto silicon and chromium. The hardening characteristics of these steels are not materially altered Whether the materials are airlcooled or oil quenched from the hardening temperature, such as by heating at 1750 F. for onehalf hour, following with an oil quenched andl tempering, or by heating at 1150 F. for four hours, thereaftercooling in air and tempering (see Table Il) A very surprising feature, however, notable in the table, is that the Steel A, has a higher impact value than the Steel B Where both steels are in the hardened and tempered condition. This improved impact resistance is attributed to the manganese content with relation to the silicon and chromium and is a general characteristic of my hardened and tempered steels. Y

`Table IIe-Mechanical properties of steels in Table I 111mg; Red. o1 Brineu Ult. Tens. 0.2? Yld. Izod 1 Steel Heat Treatment 0 Percent Area Hard- Str., p. s. 1. Str., p. s. 1. 2 Percet. Impact ness n n-.- 1,150 F. (4 hrs.) air cooled and 115, 700 es, 35,0 l 20. 0 es. 7 99 251 Tempered. B l,l50 F. (4 hrs.) air Cooled and 113, 500 99, 000 20.0 68. 9 85-86. 5 248 Tempered. Y'

strength, yield r sired limits.

Table III-.Non-ha'rdening steels Steel v C Cr Mn Si Ni P S 1 Prior art.

lt will be seen in Table IV, that after like heat treatment, lebanon-hardening Steel C has superior impact resistance as compared with the excessively high-manganese Steel Dvwhich also is of non-hardening quality.

ments-my stainless steels are often made to'function as needles, spring, nttings, gimbals and indicators. E also make cutlery including such products as scissors, knives, ice picks, and other culinary items. On other occasions the steels are fabricated into dairy equipment, trim and hardware for house, ofiice or restaurant use, or into chemical plant equipment, particularly for nitric acid plants and illustratively including pipes, towers, tanks, heat exchangers and the like. Still other products of the steel fall into a miscellaneous group comprising such articles as propellers for vmotor boats and outboard engines used in salt Water, solenoidl magnet cores, pneumatic toolsv where exposure to weather and shock are encountered, turbine blades, seeming rolls for can-filling machinery, surgical instruments, dental instruments, and a variety of tools such as wrenches,` screw drivers and saws as Where toughness and corrosion resi-stance are desirable. While many further products of my stainless steels could be speciiicaliy identified, it is believed that the above will suiiice or purposes of illus-- tration.

l Table I.V.- Mecham`cal. properties of steels in Table III v Percent v l Ult. Tens. 0.2% Yld. Percent Izod Brinell Steel Amealmg 'hammam' Str., p. s. i. Str., p. s. i. Red. area m021?? m Impact Hardness C 1,{l450 Fhto l ,47,5 F. (4 hrs.) aldwater G9, 500 37, 650 72. 0 37. 5 37-5() B-78 queue D l,450 I". to 1,475u F. (4 hrs.) and Water 66, 900 37, 600 68. 9 35. 5 ll-9 B-82 quench. l

My stainless steels, whether hardening or nonhardening'v are highly resistant to corrosion in various acids such as nitric, acetic, sulphuric` or hydrochloric acid, and under a wide variety of f other conditions, 'as for example those involving corrosivegases, heat, moisture or the like. A furt'herlvaluable asset of my stainless steels is that they displayoutstanding resistance to khash attack aspwhen immersed for passivation in a nitric acid solution, Where desired, therefore, I'subjject the-steels to passivation treatment, and with highlyy satisfactory results. The treated metal'is4 substantially free of pits, blemishes, and jother results; ci: rlash attack.

My straight chromium steels are successfully worked, formed and fabricated and by such operations as lforging, rolling, drawing,- stamping, machining, welding, or any other or' a'host of permissible operations, lprovide products of the steels. rljhese products by reason ofthe substantial f-reedom of the` metal from complexsilicate inclusions take-on a highly satisfactory sur-race nnish suchas where the surface is polished or finished without a. polish. l sometimes subject my steel products to an electrolyticv polishing treatment, as of any conventional type used in the polishing of stainless steels. The polished surface is substantially free of blisters, black-` spots and hair-line defects which so frequently occur from inclusions in excessively high-manganese, straight chromium stainless-steels.

Apart from such products as Wire, sheet, strip, andl the .like whichV I make from my stainless sj;ee l s, theY metalmis fabricated when desired" into ahcst of. other products, among these being valve parts including stems, shafts, valve balls, valve trim, seats or rocker arms. of my products includes carburetor parts which handle corrosive gasolines. In precision instru- A further category the steels themselves are substantially free of black spots. It will' also be appreciated that the steels are workable and capable of being iinished by polishing and passivation treatment with highly satisfactory results and are well suited for resisting corrosion in use.

While considerable emphasis has been placed upon the accompanying diagram and the relation of manganese, silicon and chromium there prescribed,y it will be appreciated that the chromium to some extent may be replaced by partial Y substitution inactual practice withinthe scope of the invention.

As many possible embodiments may be made A of my invention andasfmany changes may be made in the'- embodiment hereinbefore setforth, it will be understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

l' claim:

l. In manufactures of the class described, wrought and polished straight chromium stainless steel sheet, strip, Wire, and like products containing large amounts of chromium and small amountsotmanganese and silicon which products` are substantially free of surface-defacing complex silicate inclusions and comprise 10% to 27% chromium, up to about 0.2% manganese and from incidental amounts up to about 1% silicon with said manganese content restricted to amounts beneath the curve in the accom@ panying diagram corresponding to the specific amountof said chromium, and the remainder substantially all iron.V Y

2. In manufactures of the class described,

' wrought and polished straight chromium stainless steel products containing substantial amounts of chromium and small amounts of manganese and silicon which products are substantially free of surface-defacing complex silicate inclusionsand comprise at least 0.15% carbon, 12% to 14% chromium, less than 0.2% manganese and from incidental amounts up to '1% silicon with saidmanganese and silicon contents falling beneath the curveinthe accompanying diagram corresponding'toV the 'specic amount of said chromium, andthe remainder substantially all iron.

3. In manufactures of' the class described, wrought and polished straight chromium stainless steel products containing s u b s t-a n ti al amountsl ofl chromium and small amounts of manganese'and silicon which products are substantially free of surface-defacing complex silicate inclusions and comprise 0.60% to 1.20% carbon, 16% to"18% chromium, less than 0.2% manganese and from incidental amounts up to 1% silicon with said silicon and manganese con- Y tents fallingvbeneath they curve in the accom'- 10 panying diagram corresponding to the specific amount' of said chromium, and the remainder substantially all iron.

HARRY TANCZYN.

References cited in the me of this patent UNITED STATES PATENTS OTHER REFERENCES Chemical and Metallurgical Engineering, July, 1927, .pages 417, 418, 4'19.

' Stainless Iron and Steel, 2nd edition, pages 103, 107, 109, 129, 141, 218, 306, 416,V 439,467, 496 to 504, 520, 543. Edited by Monypenny.l

Publishedin 19731 by Chapman andfHall, London, England.

Book of Stainless Steel, 2nd edition, pages A.14:9 to 156. Edited by Thum. Published in 1935 by the American Society for Metals, Cleveland,

Ohio. Y

Claims (1)

1. IN MANUFACTURES OF THE CLASS DESCRIBED, WROUGHT AND POLISHED STRAIGHT CHROMIUM STAINLESS STEEL SHEET, STRIP, WIRE AND LIKE PRODUCTS CONTAINING LARGE AMOUNTS OF CHROMIUM AND SMALL AMOUNTS OF MANGANESE AND SILICON WHICH PRODUCTS ARE SUBSTANTIALLY FREE OF SURFACE-DEFACING COMPLEX SILICATE INCLUSIONS AND COMPRISE 10% TO 27% CHROMIUM, UP TO ABOUT 0.2% MANGANESE AND FROM INCIDENTAL AMOUNTS UP TO ABOUT 1% SILICON WITH SAID MANGANESE CONTENT RESTRICTED TO AMOUNTS BENEATH THE CURVE IN THE ACCOMPANYING DIAGRAM CORRESPONDING TO THE SPECIFIC AMOUNT OF SAID CHROMIUM, AND THE REMAINDER SUBSTANTIALLY ALL IRON.

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