US3376780A - Stainless steel, products and method - Google Patents

Description

April 9, 1968 H. TANczYN STAINLESS STEEL, PRODUCTS AND METHOD Filed Sept. 19, 1966 5 Sheets-Sheet l.

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INVENTOR ULTIMATE TENSILE STRENGTH PSI x IOOO Harry anczyn J4 749ML H. TANCZYN April 9, 1968 STAINLESS STEEL, PRODUCTS AND METHOD 5 Sheets-Sheet Filed Sept. 19, 1966 QNO Omo

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ROCKWELL HARDNESS HIS ATTORNEY April 9, 1968 H. TANCZYN 3,376,780

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INVENTOR Harry 727/7 zyn 67E M. A

H/S ATTORNEY United States Patent O 3,376,780 STAINLESS STEEL, PRODUCTS AND METHOD Harry Tanczyn, Baltimore, Md., assignor to Amico Steel Corporation, Middletown, hio, a corporation of Ghio Continuation-impart of application Ser. No. 249,506, Ian. 4, 1963, This application Sept. 19, 1966, Ser. No. 580,305

17 Claims. (Cl. 85-4S) ABSTRACT OF THE DISCLOSURE Chromium-nickel-copper-aluminum stainless steel of such composition balance that in the annealed condition it is fully austenitic and readily lends itself to drastic coldreduction and which, moreover, following cold-reduction, is readily hardened by ageing at moderate ageing tempera tures. Such steel consists essentially of about to 25% chromium-molybdenum with the actual chromium content being at least 10% and molybdenum up to 5% being substituted for chromium on a 1 to l basis; about 5% to nickel-manganese with the actual nickel content being at least 4% and manganese upto 15% substituted for nickel on a 2 to 1 basis, with the relationship between the two groups being:

about 1%to 5% copper; about .25% to 2.50% aluminum; and remainder substantially all iron. In one specific embodiment the steel is of such particular composition balance that in the final age-hardened condition the metal remains austenitic and essentially non-magnetic. In a further embodiment the composition balance is such that the steel becomes magnetic in the age-hardened condition.

Cross-reference to related application My application for patent is a continuation-impart of my co-pending application Ser. No. 249,506 led Jan. 4,'

1963, now abandoned, and entitled Stainless Steel, Products and Method.

Introduction The present invention is concerned with the austenitic chromium-nickel stainless steels, more particularly with such steels as are hardenable by heat-treatment. Concern also is with a method of hardening the same and with a' variety of hardened articles and products fashioned of the steel.

One of the objects of my invention is the provision of a chromium-nickel stainless steel which works well in the mill as by rolling, drawing, and the like, in the production of sheet, strip, plate, bars, rods, wire and special shapes, which steel then is readily formed through coldworking operations such as drawing, upsetting, rolling, spinning and the like, as in the production of wire, springs,

Ispun shapes and articles, rolled shapes and articles such "ice mium-nickel stainless steel which is cold-formed easily into desired shapes with minimum wear on the forming equipment and which steel is then age-hardenable by heattreatment at moderate temperatures and which in 'the work-hardened and age-hardened condition possesses the surprising combination of toughness and strength together with high surface hardness, abrasion-resistance and wearability.

A further object of my invention is the provision of a wide variety of radio antenna wire, instrument springs, industrial springs and the like, the provision of rolled shapes such as threaded fastening devices such as screws, bolts, etc., wherein the threaded portions thereof are rolledon to give fastening devices which are tough, strong and present hard and abrasion-resistant threaded surfaces, which antenna wire, shapes, springs, fastening devices and the like are well adapted to withstand corrosion, wear and the stresses generally encountered in actual use.

An additional vobject is t-he provision of self-tapping screws, screws of such vexternal or surface hardness and abrasion-resistance in the threaded portions thereof, and of such internal toughness and strength, as to serve in the tapping of metal parts such as sheet metal roofing, sidings and the like, and sheet metal housings for refxige rators, washing machines and other appliances, and then secure and fasten the same together.

Other objects of my invention in part will lbe obvious and in part particularly pointed to in the description which follows.

Accordingly, my invention resides inthe combination of elements, in the mixture of ingredients and in the relation between the same, as well as in thel various coldworking or cold-forming steps, in the various heat-treating steps and in the relation between composition, forming and heat-treatment, all as described herein, the scopev of application of which is indicated in the claims at the end of this specification.

Background of the invention Many of these are work-hardening, that is, they vharden during cold-working and cold-forming operations. For example, the American Iron and Steel Institute Type 305 comprising about 18% chromium, 11% nickel, and re-` maiuder ir-on, has a relatively low work-hardening rate,V

but with a 60% reduction in area a hardness on the order of Rockwell C 50 may -be obtained. Nevertheless, in anyI substantial working or forming operations intermediate and costly annealing treatments are required. Moreover,

this steel cannot be significantly hardened by an ageing treatment.

The straight-chromium grades of stainless steel, for example Type 430, comprising about 17% chromium and remainder iron, as well as the Type 410 comprising about 12% chromium and remainder iron, although not inclined to harden as a result of cold-working operations, are not disposed to harden by ageing treatment either, that is, treatment at rather modest temperatures. Hardening of these steels is had by heating to high temperatures, that is, temperatures on the order of some 1800" F. and

quenching, the high temperature causing scaling, which: scaling must be removed at some expenditure of time and money. The structure is martensitic.

The more complex chromium-nickel stainless steels, for

example, the chromium-nickel-copper-aluminum stainless steels made the subject of the Tanczyn U.S. Patent 2,694,-

626 of Nov. 16, 1954, although age-hardenable, are characterized by an vobjectionably high work-hardening rate.v

3 This steel, like Athe others, is not suited to drastic colddeformation and subsequent ageing to develop great hardness.

In the prior art self-tapping stainless steel screws are known. These customarily are made of the 12% chromium grade of stainless steel. The screws are hardened by heating at about 1800 F. and quenching. Following this they are relieved of quenching stresses by reheating at a ternperature of about 400 F. to 600 F. The hardening treatment, however, leaves a heat-scale on the metal as noted above, with the result that the metal must be cleansed before use, Often to obtain a higher level of corrosionresistance they are chromium-plated.

The self-tapping screws of the prior art are hardened throughout and for this reason are somewhat brittle.

One of the objects of my invention is the provision of a chromium-nickel-copper-aluminum stainless steel of such composition balance as to overcome the deficiencies of the steels of the prior art and be but moderately hardenable or greatly hardenable as desired, as a result of colddeformation through cold-working and cold-forming operations; which cold worked or cold-formed steel then lends itself to age-hardening or precipitation-hardening by heat-treatment at moderate temperatures, i.e., temperatures not sufficiently high to cause formation of objectionable heat-scale; which steel and articles fashioned thereof are possessed of great surface hardness and abrasionresistance, yet interiorly thereof are tough, ductile and adapted to withstand the stresses encountered in use; and which steel in the cold-worked and age-hardened condition is peculiarly adapted to withstand corrosive elfects encountered in use, including those of galvanic origin.

Summary of the invention Referring now more particularly to the practice of my invention, I provide a chromium-nickel-copper-aluminum stainless steel which consistsessentially of a chromiumlike metal in the amount of 10%-25%, a nickel-like metal in the amount of 5%20%, copper in the amount of 1%-5%, aluminum in the amount of .25 %-2.50%, with remainder substantially all iron. Now the chromium-like metal is chromium with or without the further ingredient molybdenum. In every instance the amount of chromium itself must be-at least And the amount of molybdenum which may be included as a part of the chromiumlike metal must not exceed 5%. Where molybdenum is` employed along with chromium, replacement of molybdenum for chromium is on the basis of 1-1.

The nickel-like metal consists of nickel with or without the further ingredient manganese. The amount of nickel itself must be at least 4%. And where manganese is employed as a partial substitute for nickel, the substitution is on the basis of 2 for 1, with the total manganese content not exceeding In the steel of my invention, carbon, of course, is present, this in amounts up to 0.20%, although I find that best results are had where the carbon content does not exceed 0.10%, particularly where it does not exceed 0.05%.-

Nitrogen also is present in small amounts, that is, amounts up to .25%, although here again, best result are achieved where the nitrogen content does not exceed 0.10%, and particularly where it does not exceed 0.05%.

In my steel the sum of the carbon and nitrogen contents ordinarily does not exceed 0.10%. Best results, asv previously indicated, are had where both carbon and nitrogen are maintained at a minimum; particularly where the sum of the two does not exceed 0.05%, for I find that both of these ingredients increase the hardness of the steel in the annealed condition. And this necessitates additional working and forming to achieve a desired amount of plastic deformation. Any substantial carbon content, for example, carbon in excess of the 0.20% max. permissible ligure, additionally would require objectionably high annealing temperatures in order to take the carbon into solution. And an excess of nitrogen additionally would run the risk of gas evolution on freezing of the ingot with consequent unsoundness in the final product.

Silicon, likewise is present, this in amounts up to 2%. So, too, manganese in amounts up to 1% even Where there is no purposeful manganese addition. Phosphorus and sulphur are present, each up to a maximum of about 0.05

The steel of my invention additionally may contain purposeful additions of boron in amounts up to 0.009% for improved hot-Working properties in the presence of the high total alloy content. Titanium, zirconium and columbium also may be included where desired in amounts up to about 1%, to obtain an improvement in age-hardenability. These additions have no significant effect on workhardening. The ingredients selenium, lead, bismuth, tellurium and silver, as well as phosphorus and sulphur, may be present in sum total up to 0.50% as a maximum, to lend improved machinability to the metal where required in certain applications. These additions are not included in the steel of my invention where cold-heading operations or other cold-upsetting operations are resorted to, or where significant bending stresses are contemplated. In general, my steel is free of these additions.

Brief description of the drawings In the accompanying drawings:

FIGURE 1 presents in graphic form the tensile properties of wire according to my invention Which has been annealed and then cold-drawn differing amounts and wire which, subsequent to the cold drawing has been agehardened,

FIGURE 2 illustrates the hardness of the wire of FIG- URE 1 for differing cold-reductions, and

FIGURE 3 illustrates on greatly enlarged scale, a ground and polished section of a self-tapping Phillips head screw according to my invention.

Description of the preferred embodiments Now in the steel of my invention I employ a particular balance or relationship between the chromium-like component, on the one hand, and the nickel-like component, on the other. I find that where there is a high ratio between the chromium-like content and the nickel-like content, substantially uniform elongation is achieved in working, but that the work-hardening rate is unduly high; such a steel has a high work-hardening factor.1 Where, however, the ratio between the chromium-like and the nickel-like ingredients is low, that is, less than l, the el-ongation of the metal is not uniform; it tends to neck down. And even though the rate of work-hardening is acceptable, the steel is not satisfactory.

In the steel of my invention the work-hardening factor amounts to about 85, this falling well below the 162 work-hardening factor of the Type 301 steel (17% chromium, 7% nickel, and remainder iron), a steel of objectionably high work-hardening rate. It falls very close to the very low work-hardening factor of which is had in a 16-18 steel (16% chromium, 18% nickel, and remainder iron). This latter steel, however, is subject to objectionable localized elongation.

While the balance between the chromium-like and the nickel-like components of my steel is generally such that the steel in the annealed condition is non-magnetic, a balance substantially exceeding 2 is inclined to give a duplex structure, wherein the metal does not work well in the hot mill. It is inclined to break and tear through the ferrite constituent.

Now in the cold-worked and age-hardened condition my steel may become magnetic or it may remain nonmagnetic, depending upon the particular balance of ingredients. For the magnetic steel I employ a nickel-like content of about 13% to 16% for a chromium-like con- 1Tl1e Cold-Work-Hardening Properties of Stainless Steel in Compression by Bloom, Goller and Mabus: 1947 Transactions A.S.H., volume 39, page 843.

tent of a nickel-like content of 8%-14% for a chromium-like content of about 12%, -a nickel-like content of 7%-13% for a chromium-like content of 16%, a nickel-like content of 6.5%-9.5% for a chromium-like content of 19%, and a nickel-like content of 5%6% for a chromium-like content of 22%. In these steels the copper content amounts to about 3% and the aluminum content about 1%, although in general some latitude is desirable; the copper ranging from 3%4%, permissibly from 1%-5%`, and the aluminum from .75%-1.50%, although permissible from .25% to 2.50%.

While all the above steels are essentially austenitic in the annealed condition, the steel of 22% chromium content does contain some ferrite. But when subjected to drastic cold-deformation al1 of the steels become martensitic and magnetic. This condition obtains even in the steel of 10% chromiumcontent with :a nickel content of 13% to 16% where the cold-deformation amounts to as much as 70%. These steels, of course, remain martensitio and magnetic even after a subsequent age-hardening treatment.

'In the magnetic steels manganese may be partially substituted for nickel, this on a 2 to 1 basis, as noted above. Where the chromium content of the particular steel is below 16%, the manganese content may be as much as 12%, this being substituted for 6% nickel. But where the chromium content is above 16%, no more than about 8% manganese may be employed, this as a substitute for 4% nickel. In these steels it will be understood, as previously indicated, that the actual nickel content must -be at least 4% in order to enjoy the desired combination of work-hardening and age-hardening properties.

Now in the non-magnetic steel, i.e. the steel which is non-magnetic in the annealed condition, non-magnetic in the work-hardened condition and non-magnetic in the agehardened condition, I employ a nickel-like content of 15%-20% for a chromium-like content of 10%, a nickellike content of 14%-20% for a chromium-like content of 12%, a nickel-like content of 12%-20% `for a chromium-like content of 16%, a nickel-like content of 11%- 20% for a chromium-like content of 19%, a nickel-like content of l4%-20% for a chromium-like content of 22%, and a nickel-like content of 15%-20% for a chromium-like content of 25%. In each of these steels the copper content amounts to about 3% and the alumi-l num content about 1%, although the copper may range from about 1%-5%, preferably 2%-4%, and the aluminum from .25%-2.50%, preferably .75%-l.50%.

In the non-magnetic steel manganese may be partially substituted for nickel up to about 15% of manganese, this for 7.5% nickel. The actual nickel content, as previously indicated, must be at least 4% In the steel of my invention the amounts of the ingredients chromium, nickel, copper and aluminum, as well as the amounts of the ingredients molybdenum, and

unstably austenitic and the desired combination of work-v hardening and age-hardening is not had. The manganese substituent may not exceed 15%; actually, it may not exceed 12% for the magnetic steels of chromium contents below 16% and may not exceed 8% for the steels of chromium content above 16%, as previously noted, for I nd that higher manganese contents as well as higher nickel contents disturb the composition balance necessary to achieve the combination of initial work-hardening and subsequent age-hardening treatments.

In the steels of my invention both copper and aluminum serve to lower the work-hardening rate, that is, lower it to an acceptable figure. The copper content, while permissibly ranging from 1%-5%, preferably does not exceed 4% because I find that amounts significantly above the 4% figure are inclined to adversely affect the hot-rolling properties of the metal; apparently the limit of solubility for copper is about 4%, and any excess appears as free copper, introducing a liquid phase with resulting breaking in the mill unless the hot-rolling operation is conducted at an undesirably lowered temperature. A copper content below the 1% figure has no benelicial effect; excessive amounts of aluminum would be required and this, in turn, would require an excessive amount of nickel, for the reason that aluminum apparently lowers the activity of the nickel present in the steel. Best results are had with a copper content of 2%-4%, as previously noted.

The aluminum content of my steel permissibly ranges from .25%-2.50%. Below the .25% ligure there is no beneficial eifect, and above a figure of 2.50%, the nickel requirement again becomes excessive. I nd that best results are had where the aluminum content ranges from about .75% t-o 1.50%.

The steel of my invention conveniently is melted in the electric arc furnace or by other means known to those skilled in the art to which the invention relates. On this further comment is believed unnecessary, save to remark that the steel handles well in the furnace, teems well and the ingot mold strips from the ingot with ease.

Ingots, blooms, billets, and the like, work well in the hot mill at conventional rolling temperatures, as in the production of plate, sheet, strip, bars, rods, wire, and special shapes. The hardness of the metal in the hot-rolled condition and in the annealed condition is on the order of Rockwell B -80. And upon cleaning, it is suited to a variety of cold-working and cold-forming operations, such as upsetting, rolling, drawing, spinning, and the like,'in the production of screws, bolts and other headed and threaded fasteners, instrument springs and industrial springs, washmanganese, whichl were partially substituted for chromium, and nickel, respectively, are in every sense critical. So, too, is the relation between the several ingredients.' As noted above, the chromium-like component ranges from 10% to- 25%, with the actual chromium content being at least 10%. Where the actual chromium content-is less than the 10% ligure, and more par-` ticularly where it is less than Y12%, the required corroers, and various machine parts.

In the cold-working and cold-forming operations the steel of my invention acquires significant hardness; the hardness customarily increases up to about Rockwell C 37 for theV steels of such composition balance as to be martensitic and magnetic, and up to aboutRc 26 for the steels which are of such composition balance `as to be fully austenitic and non-magnetic. These maximum hardness gures represent cold-reductions on the order of some 60%-70%. Even greater hardnesses are had where drastic cold-reductions are employed, Athat is, reductions approaching as more particularly discussed hereinafter. It will be seen that in the martensitic and magnetic steels such hardnesses amount to some Rockwell C 46 for a reduction of 87% Y Following the cold-working and cold forming operation the steel is age-hardened, the ageing temperature employed being dependent upon the composition. For the steel and articles of magnetic composition balance, for example, 15%-18% chromium, 7%10% nickel, 2%- 5% copper, .75%-1.50% aluminum, and remainder substantially all iron, hardening is achieved by heating the 7 8 same at` a temperature of about 700 F.-900 F. and coolthe chemical analyses of several specilic examples are ing in any one of air, oil or water. I find that the coldgiven in Table I below; those being martensitic and magworking operation has sufficiently strained the metal to netic in the final age-hardened condition are given under induce age-hardening by the comparatively low-tempera- I(a) and those remaining austenitic and non-magnetic in ture ageing treatment. My steel and articles are free of the aged condition are given under I(b):

TABLE L-CHEMICAL ANALYSES OF TYPICAL CR-NI-CU-AL STAINLESS STEELS OF THE INVENTION [I(a) Magnetic as age-hardened1 C Mn Si Cr N 1 Cu Al N Mo High Manganese Variation Low Carbon Variation Molybdenum Variation [I(b) Non-magnetic as age-hardened] scale, or other objectionable surface effect. In the aged y The hardness of the steels of Table I in the annealed condition the hardness had amounts up to about Rockcondition, as well as the Work-hardening factor for the well C 52 for reductions on the order of 60% and up to same, the hardness had when reduced 40% and when about Rockwell C 57 for reductions approaching 90%. reduced 60%, and the final hardness in the age-hardened Similarly, for the steel and articles of such composition condition -both for the reduced steels and the 60% balance as to be fully austenitic in the aged condition and reduced steels are given in Table II below. Here again free of magnetic eifects, that is, the steel analyzing about 40 the steels which are magnetic in the age-hardened condi- 15%-18% chromium, 11% to 13% nickel, 2% to 5% tion are given under II(a) and those remaining noncopper, .75%-1.50% aluminum, and remainder substanmagnetic after ageing are given under II(b). In cach tially all iron, ageing is achieved by heating the metal at instance the hardness data was developed on wire of a temperature of about 1050 F.-1250 F. and then analysis specified initially of B1" diameter by 1S length.

TABLE L-HARDNESS AND WORK-HARDENING FACTORS OF THE CBNI-CU-AL STAINLESS STEELS OF TABLE I (a) Magnetic as Age-Hardcned11' Heat No. Cold Work Annealed 2 Cold Drawn 40% Cold Drawn 60% Cold drawn 40% Cold Drawn 60% Hardenlng Factor Hardness Rockwell Hard. Rockwell Hard. Rockwell and Aged Rockwell and Aged Rockwell R3609 B82 C34 C44 C48 C53 B66 C29 C42 C43 C51 109. 5 B 76 C31 C35 C39 C50 100. 8 B78 C31 C35 C39 C42 85.7 B 75 C32 C36 C47 C51 87. 7 B 79 91. 8 B78 C29 C36 C34 C46 85, 4 B80 C24 C31 92. 9 B80 C30 C36 C33 C41 86.3 B68 C31 C36 C44 C48 High Manganese Variation H3473 84.7 B75 C26 C35 C36 C48 Low Carbon Variation H3969 80. 2 B63 C23 C30 C29 C4() 13,3970 81.8 B C26 C36 C40 C49 Molybdenum Variation R3893 102. 2 B 78 C31 C36 C37 C48 R3894 104. 5 B80 C31 C35 C36 C48 [II(b) Non-magnetic as age-hardenedP 78. 5 B72 C24 C28 C37 C41 77. 1 B 73 C26 C30 C35 C38 79.0 B72 C25 C31 C35 C39 1 Anneal, 850 F. for 1 hr. and air-cool. 2 Annea11,900 to 1,950 F., 20 min., water-quench. 3 Anneal, 1,100 F. for 5 hrs. and air-cool.

quenching in air, oil or Water. The hardness had there It will be seen from the test data presented above that comes up to about Rockwell C 40 for reductions of about in the annealed condition both the magnetic and non- 60% anda hardness of about Rockwell C 44 for a reducmagnetic steels of my invention have a hardness on the tion approaching 90%. order of Rockwell B 63-82. No particular difference in As generally illustrative of the steels of my invention, 75 hardness between the two steels is apparent in either the annealed condition or in the hotrolled condition. In the cold-worked condition, however, the martensitic and magnetic steel with about 40% reduction, had a hardness of some Rockwell C 23-34 and with a 60% coldpreaching 90%) and in the cold-drawn and age-hardened condition. The chemical composition of the specific example and the mechanical properties are reported in Table III below:

TABLE III.CHEMICAL COMPOSITION AND MECHANICAL PROPERTIES OF ANNEALED, COLD-DRAWN AND COLD-DRAWN-AGE-HARDENED WIRE SECTIONS Heat No. C Mn P S Si Cr Ni Cu Al Wire Dia. Condition Ult.'1ens Str., 0.2% Yld. Str., Percent Elong. Percent Red. Rockwell (inches) p.s.i. 2 p.s.i. 2 Area Hardness 89/92 26]28 46/47 65/66 B68 103/103 (i2/62 43/40 67/68 B80 99/100 62/68 41/41 67/67 B81 109/110 71/74 33/37 62,"63 B96 105/106 80/81 33/37 65/66 B98 122/123 75/78 32/33 61/61 C23 125/126 10D/102 33/34 60/61 C24 140/140 110/111 24/16 59/61 C28 165/165 141/141 18/18 59/59 C35 170/172 162/168 14/14 56/56 C35 234/235 200/204 14/14 51/51 C46 189/190 180/182 13/15 52/53 C39 284/288 250/255 11/12 47/48 C51 217/222 209/219 11/11 48/49 C44 310/314 279/284 11/11 40/43 C56 229/233 204/210 10,/10 41/47 C45 328/330 (3) 0/10 40/42 C57 235/238 210/215 6/9 41/41 C46 335/336 11/11 40/40 C57 l Aluminum content checked 4 billet section, H-900=900 F. 1 hr., -air cool.

2 Psi. 1,000. 3 N o oiset shown.

reduction, a hardness of Rc 30-44. The austenitic and nommagnetic steel when subjected to a reduction of 60% has a hardness of Rc 28-31 for the examples given.

When aged, following work-hardening, the martensitic and magnetic steels (heating at 850 F. and air-cooled) 4 have a hardness of some Rockwell C 29-48 for the steels with 40% cold-reduction and a hardness of some Re 40- .'13 for those with 60% cold-reduction. The non-magne tic steels when aged (1100o F. and air-cooled) following the 40% cold-reduction, have a hardness of some Rc 35- '.57 for the examples given, and following the 60% Coldreduction have a hardness of Rc 34-41. Greatest hardening is had with the magnetic or martensitic steels.

' As more particularly illustrated of the great strength had in the martensitic and magnetic steels of my invention when cold-drawn up to about 90% reduction, a specie example iu the form of wire analyzing about chromium, about 7%-8% nickel, about 3% copper, about 1% aluminum, and remainder substantially all iron, Was tested in the annealed condition, in the colddrawn condition (for various amounts of drawn ap- The ultimate tensile strength, the percentage elongation in 2 and the percentage reduction in area for the examples of cold-drawn, and cold-drawn and age-hardened steel Wire of Table III, are graphically illustrated in FIG- URE 1 of the accompanying drawings for differing percentages of cold reduction. The hardnesses had for the differing cold-reductions is illustrated in the FIGUREZ. It is to be especially noted that while there is an increase in tensile strength and hardness with an increase in the cold reductions, the ductility of the metal, as exemplified by the reduction of area and the elongation figures, is well retained. These fall but little until reductions of V% or especially reductions of and more are made. It is the subsequent age-hardening treatment, however, which imparts the great strength and hardness whichl characterize the steel.

Note that with the age-hardening treatment these severely cold-reduced steels enjoy an increase in tensile strength of some 90,000 to 100,000 p.s.i. to reach tensile strengths exceeding 300,000 p.s.i. for the more severely reduced steels (from about 190,000 to 285,000p.s.i., an

TABLE IV.-HARDNESS AND ROOM TEMPERATURE TENSILE PROPERTIES OF NON- MAGNETIC PRECIIITATION-HARDENABLE STAINLESS STEELS C Mu Si Cr Ni Cu A1 N Condition Heat Ult. Tens. 0.2% Yld. Percent Rockwell No. Str., psi. Str., p.s.i. Elong. Hardness Annealed, 1925 F., 20 mins. water H3644 74,000 29, 000 56 B72 quench. R3801 76,000 28, 700 57 B73 R3804 74, 0 28, 500 57 B72 Annealed plus cold-drawn 40% H3644 132,000 98,000 40 C24 R3801 134, 00 101, 000 41 C26 R3804 135, 000 99,000 39 C25 Annealed, cold-drawn 40%+1,100 F., H3644 165,000 138, 000 28 C37 5 hrs., air cool. H3801 161,000 130,000 C35 R3804 159, 000 125, 000 32 C35 Annealed, cold-drawn 60% R3644 145, 000 120,000 32 C28 H3801 147, 000 115, 000 30 R30 R3804 148, 000 119, 000 31 R31 Annealed, cold-drawn 60%-I-l,100 F., H3644 178,000 147, 000 21 C41 5 hrs., air cool. R380l 170,000 140,000 23 C38 :H3804 172, 000 145, 000 20 C39 Annealed, cold-drawn 80% H3644 170, 000 150 000 22 C37 R3801 171, 000 158, 000 20 C38 R3804 168, 000 159, 000 20 C38 Annealed, Cold-drawn 80%-{1,100 F., H3644 197,000 183,000 17 C44 5 hrs., air cool. H3801 195,000 180, 000 16 C42 R3804 192, 000 178, 000 C43 Annealed, cold-drawn 90% R3644 179, 000 165, 000 18 C30 R3801 181, 000 167, 000 17 C40 R3804 182, 000 169, 000 17 C41 Armealed, Cold-drawn 90%-l-1,100 F., R3644 205, 000 191,000 15 C45 5 hrs., air C001. R3801 198, 000 186,000 14 C44 R3804 195, 000 187, 000 14 C44 l l increase of 95,000 p.s.i., for the 70% cold-reduced steel; from about 220,000 to about 310,000 p.s.i., an increase of 90,000 p.s.i., for the 80% cold-reduced steel; and from about 235,000 to 335,000 p.s.i., an increase of 100,000 p.s.i., for the 87% cold-reduced steel). Yet the great hardness and strength of the severely cold drawn wire (some Rockwell C 57 and a tensile strength of 335,000 p.s.i. for the 87% cold-drawn and aged sample of Table III) are had without sacrifice of ductility, the elongation amounting to some 11% and the reduction in area being some 40%; there is little vchange in the elongation andA reduction in area figures as a result of the ageing treatment. The combination of great strength and hardness along with good retained ductility permits the drastically cold-reduced and age-hardened steel wire to be wound into a variety of springs.

Samples of three non-magnetic stainless steels were cold-drawn from diameter wire in differing amounts up to 90% and then age-hardened. The chemical composition of these steels and their mechanical properties in the cold-drawn and in the cold-drawn and age-hardened condition are given in Table IV.

It is to be noted that the drastically cold-reduced samples of 80% and 90% reductions in the annealed conditions have tensile strengths of some l68,000-l7l,000 p.s.i. for the 80% reductions and some 179,000-182,000 p.s.i. forthe 90% reductions. In the age-hardened condition these strengths rise to some 192,000197,000 p.s.i. for the lesser reductions and to some l95,000-205,000 p.s.i. for the greater reductions. The increase in strength with the ageing treatment amounts to some 24,000-27,000 p.s.i. for the 80% reductions and some 13,000-26,000 p.s.i. for those reduced 90%. The ductility of the steel, as reected by the elongation figures, is well retained with the ageing treatment,the elongation falling only from 20- 22% down to l6-l8% for the samples reduced 80% and only from l7-l8% down to 14-15 for those reduced 90%.

In the work-hardened and age-hardened condition, the steels of my invention possess a combination of high surface or external hardness together with internal toughness and ductility; the internal hardness is substantially lower than the surface hardness. And of particular consequence, the hardness of the finished metal is` greatest at the points where the greatest cold-working has been had and least where the least amount of cold-working results. In every case, however, the final hardness achieved is not that of the cold-working operation, but it is that of the combination of cold-working and age-hardening. Particularly great strength in combination with significant ductility is had with the martensitic steels reduced in the amount of some 70%-90% and especially about 80%- 90%. Note that with the age-hardening these severely cold-reduced steels enjoy an increase in tensile strength of some 90,000 to 100,000 p.s.i. as a result of the ageing treatment to reach tensile strengths exceeding 300,000 p.s.i. for the more severely reduced steels (from 190,000 to 285,000 p.s.i., an increase of 95,000 p.s.i., for the 70% cold-reduced steel; from 220,000 to 310,000 p.s.i., an increase of 90,000 p.s.i., for the 80% cold-reduced steel; and from 235,000 to 335,000 p.s.i., an increase of 100,000 p.s.i., for the 87% cold-reduced steel). And it is noted even the most severely cold-reduced steel, following the age-hardening treatment, enjoys substantial ductility, this on the order of 11% elongation in 2 and a reduction in area of about 40%.

As particularly illustrative of the practice of lmy invention, reference is made to the production of self-tapping drive screws, this by way of automatic machinery, the screws being produced at the rate of about 300 a minute. In this operation wire stock, typically 0.132 diameter, is upset in forming the screw head. The head then may be provided with .a milled slot or it may be recessed to provide a Phillips head. The required thread is lrolled on. In this cold-rolling operation, as well as in the cold- The cold-formed screws are subjected to age-hardening .A treatment with a resultant increase in hardness approaching Rockwell C 52 for the screws with a cold-worked hardness approaching Rockwell C 37 (magnetic, with ageing at 700-900 F.) and a hardness approaching Rockwell C 40 for those having a cold-Work hardness approaching Rockwell C 26 (non-magnetic, with ageing at 1050"- 1250 E).

All of the screws in the age-hardened condition are possessed of a surprising combination of great surface hardness, particularly :at the extreme edges of the threads, together with much reduced hardness and great toughness and ductility throughout the core of the screw. The surface of the sunken head likewise is hard and is admirably adapted to accommodate a driving tool, that is, power screwdriver or manual screwdriver. The threads of high surface hardness are abrasion-resistant and cut into metal siding, sheathing, and the like, as a self-tapping operation. And the screws are well suited to secure metal pieces together, holding them firmly without thread breakage.

Screws of the particular composition balance resulting in an austenitic and non-magnetic structure are peculiarly adapted to the securing of aluminum siding, roofing, and the like, as well as refrigerator, washing-machine and other aluminum housings, in that they are free of the hydrogen-embrittling effect resulting from galvanic action found in certain screws of the prior art, notably those of martensitic structure.

With regard to the self-tapping drive screw of my invention, attention is directed to the FIGURE 3 of the accompanying drawing showing, on much enlarged scale, one-half of a Phillips screw, the other half of which has been removed by grinding operation, lthe screw being fashioned of .132" diameter wire of the Heat R39l9 of chemical analysis reported in Table I above and aged at 850 F. for 5 hours and air-cooled following fabrication. Hardness determinations made along the central core of the screw as well as those made along the roots of the threads and the extreme tips of the threads are .given in Rockwell C figures. So, too, the hardness had along the head of the screw is given. It is noted that while the core of the screw has a hardness of some Rock-well C 22-25 (the hardness determinations were made at the particular points indicated adjacent the hardness numbers), the hardness along the root of the threads amounts to some Rockwell C 30-39. Further along the threads the hardening is about Rc 39-42. At the extreme outer edges of the Itnreads the hardness is some Rc 50-52. The tip of the screw has a hardness of about Rc 47 and the head is v seen to-have a hardness of some Rc 35-39 except at the recess. There the hardness amounts to Rc 42-46. On the basis of hardness tests made on cold-drawn and aged sections of wire for Heat R39l9 it is estimated that local reduction in area on the self-tapping screw ranges up to 70%, this at the extreme outer edges of the threads.

The self-tapping screw of my invention is well suited to tapping and then securing of sheet metal sections of iron, aluminum, copper, brass and the like, the particular composition balance being selected to avoid galvanic effects in connection with aluminum sections. The screws for aluminum sections preferably are fully austenitic :and non-magnetic. The austenitic, and non-magnetic, steel also is suited to the production of instrument springs, instrument panels, dials, pointers and the like.

As further illustrative of the practice of my invention reference is made to the manufacture of radio antenna wire. The chemical composition of the wire, the sequence of operational. steps employed (for Hot-rolled .and then C-old-drawn, Line-Up No. 1 and for Annealed and Cold- 13 Drawn, Line-up No. 2) and the resulting mechanical properties are given in Table V below:

14 and manganese, with an actual nickel content of at least 4% and manganese up to 15% being substituted for nickel TABLE V.-MANUFACTURE OF .200ll DIAMETER RADIO ANTENNA WIRE FROM HOT-ROLLED WIRE l Lineup No. 1 Lineup No. 2 Condition U.T.S.,A 0.2% YS, Percent Percent U.T.S., 0.2% YS, Percent Percent p.s.i. 2 p.s.i. 2 long. R.A. p.s.i. 2 p.s.i. 2 Elong. R.A Hot-rolled Rd 98/102 48/55 45/46 58/59 Annealed. 88/90 26/28 45/50 67/68 CD 70%, .206" Rd 212/213 203/205 8/9 42/44 20G/206 20G/201 10/11 44/45 CD 70%-straightened .206" Rd 208/210 205/205 11/11 47/48 203/204 201/201 11/13 44/47 CD 70%-straightened, hardened 900 F.

1 hr., centerless ground, .200" Rd. 289/290 286/288 12/13 42/44 285/290 274/277 12/13 43/44 l Chemical composition: C, .042; Mn, 1.00; P, .020; S, .010; Si, .40; Cr, 14 2 P.s.i. 1,0oo. Y Aluminum analysis made on 1 sq. billet section.

Here it is to be noted that for the 70% cold-drawn wire there is had a gain in strength of about 80,000 p.s.i. as a result of the age-hardening treatment (for some 208,000-210,000 p.s.i. for the `drawn material to some 289,000-290,000 for the drawn :and aged material). And that with the ageing there is retained good ductility (some l2-13% elongation and some 4244% reduction in area for the aged wire as compared to some 11% elongation and some"47-48% reduction in area for the cold drawn and straightened material).

Conclusion Thus it will be seen that I provide in my invention a chromium-miekel-copper-aluminum stainless steel and a method of treating the same in which the various objects hereinbefore set forth, together with many practical advantages are successfully achieved.

' The steel of my invention by reason of particular chromium-nickel-copper-aluminum composition and a particular balancing of the same, readily lends itself to cold-working and cold-forming as by upsetting, rolling,

spinning and the like, to effect a certain hardening of the metal. In addition, the steel lends itself to further hardening, i.e.-hardening by heat-treatment at moderate ternperatures, to achieve an ageing or precipitation hardening elect.

I also provide in my invention a Variety of converted forms such as bar, rod, wire, sheet, strip, special shapes, and the like, readily suited to moderate hardening as a result of the cold-.working and cold-forming operations noted, as in the production of a Variety of articles and products which then lend themselves to age-hardening, giving a combination of high surface hardness, abrasionresistance and wearability, together with internal toughness and ductility. y v

Since many embodiments may be made of my invention and since numerous changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter'described herein or shown in the accompanying drawing, is to be interpreted as illustrative and not by way of limitation. l

I claim as my invention:

1. A.chromium-nickel-copper-aluminum stainless steel which is but moderately hardenable by cold-Work and which thereafter is substantially hardenable by ageing heat-treatment, said steel consisting essentially of about to 25 metal of the group consisting of chromium and molybdenum with# an actual chromium content of at least 10% and molybdenum up to 5%, the molybdenum being substituted for chromium on a 1 to 1 basis; about 5% to 20% metal of the group consisting of nickel Ni, 7.65; Cu, 3.19; A1, 1.16.

on a 2 to l basis with the relation between the two groups being:

Chromium-molybdenum, Nickel-manganese,

percent: percent 10 13 to 20 12 8 to 20 16 7 to 20 19 6.5 to 20 22 5 t0 20 25 5 to 20 about 1% to 5% copper; about .25% to 2.50% aluminum; and remainder substantially all iron.

2. A chromium-nickelcopper-aluminum stainless steel which is but moderately hardenable by cold-work and age-hardened, which cold-worked and aged steel is essentially non-magnetic and consists essentially of about 10% to 25% metal of the group consisting of chromium and molybdenum, with an actual chromium content of at least 10% and molybdenum up to 5% as a substitute for chromium on a 1 to 1 basis; about 11% to 20% metal of the group consisting of nickel and manganese, with an actual nickel content of at least 4% and manganese up to 15 substituted for nickel on a 2 to 1 basis; about 1% to 4% copper; about .25% to 2.50% aluminum; and remainder substantially all iron.

3. A chromium-nickel-copper-aluminum stainless steel which is but moderately hardenable by cold-Work and which thereafter is substantially hardened by ageing heattreatment, said steel in the cold-worked and aged condition being substantially magnetic and consisting essentially of about 10% to 22% chromium; about 5% to 16% nickel, with the relation between the chromium and the nickel within the broad ran-ges being:

Chromium, percent: Nickel, percent 10 13 to 16 12 8 to 14 16 7 t0 13 19 6.5 to 9.5 22 5 to 6 1 5 10% to 25% chromium; about 11% to 20% nickel, with the relation between the two being:

Chromium, percent: Nickel, percent 10 '15 tO 20 12 14 t0 20 16 l2 t0 2O 19 ll to 20 22 14 to 20 25 l5 t0 20 about 1% to 4% copper; about .25% to 2.5% aluminum;

carbon not exceeding 0.10%; and remainder substantially all iron.

5. A chromiumnickelcopperaluminum stainless steel which is but moderately hardenable by cold-work and which thereafter is substantially hardenable by ageing heat-treatment; said steel consisting essentially of about 14% to 19% chromium; about 7% to 13% nickel, with the nickel being at least about 8% for a chromium content of 14% and at least about 7% for a chromium content of 19%; about 1% to 5% copper; about .5% to 2% aluminum; a carbon content not exceeding 0.10%; a nitrogen content not exceeding 0.10%; and remainder substantially all iron.

6. A chromium-nickel-copper-aluminum stainless steel which is but moderately hardenable by cold-work and which thereafter is substantially hardenable by ageing heat-treatment, said steel consisting essentially of about 14% to 19% chromium; about 7% to 13% nickel, with nickel being at least about 8% for a chromium content of 14% and at least about 7% for a chromium content of 19%; about 1% to 4% copper; about .5% to 2% aluminum; with carbon and nitrogen taken together not exceeding 0.10%; and remainder substantially all iron.

7. A chromium-nickelcopper-aluminum stainless steel which is but moderately hardenable `by cold-work and age-hardened, which cold-worked and `aged steel is essentially non-magnetic and consists essentially of about 15% to 18% chromium; about 11% to 13% nickel; about 2% to 4% copper; about .75% t-o 1.50% aluminum; and remainder substantially all iron.

8. Stainless steel product cold-reduced 70% to 90% and age-hardenable to great strength and hardness with significant ductility, said product essentially consisting of about 15% to 18% chromium; about 7% to 10% nickel; about 2% Ito 5% copper, about .75% to 1.50% aluminum; and remainder substantially all iron.

9. Stainless steel product cold-reduced 70% to 90% and age-hardenable t great strength and hardness along with signiticant ductility, said product essentially consisting of about 15% to 18% chromium; Vabout 11% to 13% nickel; about 2% to 5% copper; about .75% to 1.50% aluminum; and remainder substantially all iron.

10. Cold-formed stainless steel threaded fastener comprising a cold-reduced rolled-on threaded portion and a tough ductile core portion, sa-id threaded portion being in age-hardened con-dition and the tough duotile core portion being not substantially age-hardened, said fastener consisting essentially of about 10% t-o 25% metal of the group chromium -an-d molybdenum, with an actual chromium content of atleast and molybdenum up to 5% being substituted yfor chromium on a 1 to 1 basis; about 5% .to 20% metal of the group nickel and manganese, with an actual nickel content of at least 4% and manganese up to being substituted for nickel on a 2 to 1 basis; Iabout 1% to 5% copper; -about .25% to 2.50% aluminum; and remainder substantially all iron.

11. Cold-formed stainless steel threaded fastener which is essentially non-magnetic comprising a cold-reduced rolled-on threaded portion and a tough ductile core portion, said threaded portion being yin ageahardened condition and the tough -ductile core portion ybeing not substantially age-hardened, which fastener consists essentially Iof about 10% to 25% metal of the group chromium and molybdenum, with an -actual chromium content of atl least 10% and molybdenum up t-o 5% as a substitute for chromium on a 1 to 1 basis; about 11% to 20% metal of the group nickel and manganese, with an actual nickel content of at least 4% and manganese up to 15% substituted for nickel on a 2 to 1 basis; about 1% to 4% copper; about .25% to 2.50% aluminum; and remainder substantially all iron.

12. Age-.hardened stainless steel self-tapping drive screw comprising a Irolled-on threaded portion of hard surface; and a tough -duotile core portion, which screw is substantially magnetic and consists essentially of about 15 to 18% chromium; about 7% to 10% nickel; about 2% to 5% copper; about .75% t-o 1.50% aluminum; and remainder substantially all iron.

13. Age-hardene-d stainless steel self-tapping drive screw comprising a rolled-on threaded portion of hard surface; and a tough ductile core portion; which screw is essentially non-magnetic and consists essentially of about 15 to 18% chromium; about 11% to 13% nickel; about 2% to 5% copper; about .75% to 1.50% aluminum; and remainder substantially all iron.

14. Stainless steel spring cold-reduced at least and subsequently age-hardened, said spring consisting essentially of about 10% to 25% metal ofthe group chromium and molybdenum with an actual chromium content of at least 10% and molybdenum up to 5% being substituted for chromium on a 1 to 1 basis; about 5% to 20% metal of the group nickel and manganese with an actual nickel content of at least 4% and manganese up to 15 being substituted -for nickel on a 2 to 1 basis with the relation Vbetween Athe two groups being:

Chromium-molybdenum, Nickel-manganese,

percent: percent: 10 13 to 20 12 8 to 2O 16 7 to 20 19 6.5 to 2O 22 5 to 20 25 5 to 20 about 1% to 5% copper; about .25% t-o 2.50% aluminum; and vremainder substantially all iron.

15. Magnetic stainless steel spring essentially consisting of .about 15% to 18% chromium; 7% to 10% nickel; about 2% to 5% copper; about .75% to 1.50% aluminum; and remainder substantially all iron.

16. Non-magnetic stainless steel spring essentially consisting of about 15% to 18% chromium; about 11% to 13% nickel; about 2% to 5% copper; about .75% to 1.50% aluminum; and remainder substantially all iron.

17. Radio antenna wire essentially consisting of about 15% chromium, about 8% nickel, about 3% copper, about 1% aluminum, and remainder substantially all iron.

References Cited UNITED STATES PATENTS 2,505,763 5/1950 Goller 75-124 2,553,706 5/1951 Goller l48-121.3X 2,553,707 5/1951 Goller 148-1232( 2,614,921 10/1952 Tanczyn 75--124 2,694,626 11/1954 Tanczyn 75-124 3,069,961 12/1962 Baubles 10-152 3,152,934 10/1964 Lula et al. 75-124 HY'LAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

P. WEINSTEIN, AsSistant'Exa/niner.

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