US2384565A - Alloy steel and articles - Google Patents

Description

atented Sept. 11, 1945 ALLOY STEEL AND ARTICLES Henry S. Schaufus, Baltimore, Md., assignor to Rustless Iron and Steel Corporation, a corporation of Delaware No Drawing. Application December 13, 19M),

Serial No. 370,072

8 Claims.

This invention relates to an alloy steel, and to articles of use fashioned of the same.

One of the objects of my invention is the provision of an alloy steel which not only is corrosion resistant, but which combines high impact strength with good machinability.

Another object is the provision of such a steel which readily may be worked hot or cold without tearing, cracking or splitting, and which readily lends itself to various cutting, drilling, tapping, threading and other machining operations, in the production of spindles, gears, worms, shafts, threaded bolts, pins, nuts, studs, discs, bushings, sleeves, rings, valve seats and the like.

A further object of my invention is the provision of machined articles of the character described, which in spite of sharp notches and sections, nevertheless are strong, tough Wear-resistant and are of high impact strength under the many conditions of heat, vibration, shock and the like encountered in actual practical use.

Other objects of my invention will be obvious in part and in part pointed out hereinafter.

The invention consists in the combination of elements, mixture of materials, and composition of ingredients .and in the relation of each of the same to one or more of the others as described herein. the scope of the useful application of which is indicated in the claims.

As conducive to a clear understanding of certain features of my invention, it may be noted at this point that many types f alloy steels are known and used at the present time. In the field of corrosion resisting steels which commonly are referred to as stainless steels, types are available for a wide variety of service requirements. At the present time there are some forty or fifty standard types available on the market.

Several of the types of stainless steel now on the market find use as machine parts or like applications where good machining qualities are necessary. For example, the 12% to 14% chromium grade of stainless steel containing suflicient sulphur to lend the desired free machining qualities to the steel, is useful in a variety of applications where mild corrosive conditions are encountered. This steel is readily workable into bars, rods, wire, plate, sheet and strip through conventional hot or hot and cold methods. The steel is ferritic or martensitic, largely depending upon its carbon content, and may be heat treated to give agood range of hardness, strength, and impact resistance. The steel, however, is not qualified for applications in which a wide variety of corrosiveconditions are encountered, nor even where severe corrosive conditions of a limited character are met with.

In applications where rather severe corrosive conditions are found, machine parts commonly are fashioned, for example, of the austenitic chromium-nickel stainless steel of the 18% chromium-8% nickel grade, including suflicient sulphur to give the desired free-machining qualities. Such a steel is strong, ductile, tough and of good impact strength. On the other hand, however, it is not hardenable by heat treatment and it is quite expensive.

It ordinarily might be expected that desired corrosion resisting properties could be obtained in ferritic and martensitic stainless alloy steels of chromium contents substantially greater than the 12% to 14% chromium grade mentioned above. For example, it might be expected that the 17% chromium grade of free-machining stainless steel would be suited for machined parts and articles where reasonably severe corrosive conditions are encountered. I find, however, that such a steel, although of good corrosion resistance and good machinability, is virtually worthless for such applications under the conditions of service encountered in actual practical use. Such articles and products fashioned of v this steel are found to possess an exceedingly low impact resistance. The products are inclined to fail, particularly at the notched, grooved or otherwise constricted sections.

One of the principal objects of my invention, therefore, is the provision of a comparatively inexpensive stainiess alloy steel which is of good corrison resistance and good machinability, which may be hardened by heat treatment and which is strong and tough, and which possesses a good impact strength, and which readily may be fashioned into various articles and products having machined or otherwise constricted portions and yet which are adapted to withstand the various conditions of shock, vibration and impact encountered in actual, practical use.

Referring now more particularly to the practice of my invention, I prepare a stainless steel containing 14.5% to 18.0% chromium, 20% to 50% sulphur, .5% to 2.0% nickel, with a maximum carbon content of .20% and with the remainder principally iron and the usual impurities. This steel is made by any one of several known steel melting processes sucn, for example, as that generally described in the United States Letters Patent 1.925,182, issued to Alexander L.

Feild on September 5, 1933, and entitled Process to the manufacture of rustless iron; or United States Letters Patent 2,056,162 issued to William B. Arness on October 6, 1936, and entitled Production of rustless iron, from which it is obtained in ingot form. The sulphur addition is made in conventional manner as through the addition of lump sulphur to the ladle in tapping the melting furnace.

The steel is worked from ingots to billets or blooms, and thence to bars, rods and wire in the one case, or plate and sheet in the other through conventional hot-working methods, although best results are had where the working is conducted in the manner more particularly described and claimed in my co-pending application, Serial No. 870,073, died of even date herewith and entitled Method of working alloy steel and products thereof. Where desired these converted products may be further fashioned into cold-rolled or colddrawn bars, rods and wire, or cold-rolled plate and sheet. Also, where desired certain of the converted products may be forged or drop-forged to approximate specifications of size and shape.

The various converted products are made into a host of articles or parts of articles of ultimate use where various cutting, drilling, tapping, threading or other machine operations are resorted to. For example, my stainless alloy steel is particularly suited to the manufacture of spindles, gears, worms, shafts, threaded bolts, pins, nuts, studs. discs, bushings, sleeves, rings, valve seats and like articles or part of articles. I find that such articles are strong and tough. They are resistant to a wide variety of corrosive agents. Of particular importance these articles possess great impact strength, a result which is indeed surprising in view of their threaded. notched or otherwise sharply restricted sections. In a particular case, for example, where a bar of steel according to my invention is found to possess an impact strength of 25 to 100 foot-pounds Izod, this inversely depending upon the carbon content, a like bar of free-machining stainless steel of identical chromium, sulphur and carbon contents, without the nickel content however, possesses an impact strength of only 1 to 5 foot-pounds Izod. The various articles and parts fashioned of my stainless steel are well calculated to withstand the bending, torsion and impact stresses en-- countered in actual use.

The particular correlation of the ingredients chromium, nickel, sulphur and carbon according to my invention is pecially important in achieving the desired combination of physical properties. I find that where the proportions given are substantially departed from, one or more of the desiredproperties are lost. For example, with an increase in chromium above the limiting figure given the impact strength is lost; and with a decrease beyond its limit, the corrosion resistance accordingly decreases. Similarly, for a decrease in nickel below its lower limit impact suffers while for an increase above its upper limit thesteel is inclined to air-harden and crack. Likewise, there is a loss of machinability with a substantial lowering of the sulphur content below its limiting .value and an attendant hot shortness and loss of impact strength where it above .the limiting value.

Many of the desirable characteristics of my high impact, free-machining stainless steel are achieved in the non-hardening or ferritic grades (these lncllldlni; those which harden to some slight extent) while further desirable characteristics are had in the hardening or martensitic grades. I find, for example, that excellent imis appreciably increased assases pact strength in combination with machinability and good corrosion resistance are obtained in the non-hardening steel comprising 14.5% to 16.5% chromium, 20% to .50% sulphur, .5% to 2.0% nickel, with a maximum carbon content of .1296 and the principal part of the remainder iron. Similarly, I find that desirably good impact strength, good corrosion resistance and desired hardness are achieved in what I call the hardening grade comprising 14.5% to 18.0% chromium, 20% to .50% sulphur, .5% to 2.0% nickel, with .12% to .20% carbon and the remainder principally iron.

In my high impact, free-machining stainless steel, best results are achieved where the silicon content is no more than about .35% although where the nickel is on the high side and the chromium is on the low side, the silicon content may amount to as much as .60%.

Also, in my sainless steel it frequently is desirable to employ a high manganese content. I find that best results in impact strength, machinabllity and workability in the hot and cold conditions are realized where the manganese content is used in amounts up to 1.5%, the range preferably being .5% to 1.5%. This quantity of manganese also assures a certain desired fluidity in the melting, tapping and teeming of the steel.

My high impact free-machining stainless steel also is benefited through the addition of the ingredient nitrogen in the amount of .06% to 30%. This ingredient readily may be introduced into the metal during its melting as described, for example. in the eo-pending application of William B. Amess, Serial No. 113,258, flied November 28, 1936, and entitled Production of rustless iron. Such a steel, in accordance with my invention, then analyzes 14.5% to 18.0% chromium, .20% to .50% sulphur, .5% to 2.0% nickel, .08% to .30% nitrogen, with a maximum carbon content of .20% and the remainder of the metal principally iron. It will be understood that the silicon and manganese contents preferably are at a maximum of .60% for the silicon and up to 1.5% for the manganese. While in the hardening grade of my steel the nitrogen content may range from .06% to .30%, I prefer to maintain this ingredient at avalue of .06% to 20% in the non-hardening grade. One of the advantages of including in my steel the prescribed amount of nitrogen is to assure a uniformly high impact strength in spite of vagaries in the hot-working temperatures employed, as is more particularly described and claimed in my co-pending application, Serial No. 370,074, entitled alloy steel method and products,

filed of even date herewith.

A further improvement in strength, toughness and general corrosion resistance is had in my alloy steel by including in its composition a small amount of molybdenum. For the hardening grade molybdenum is employed in the amount of .2% to 2.0%. In the non-hardening grade the molybdenum content preferably is preserved beflow in grinding and tween .2% and 1.0%,, Molybdenum imparts a certain denseness to the metal and moreover renders the steel peculiarly wear-resistant, a result which is particularly important in the machine parts fashioned according to my invention. Molybdenum also assures a good surface in machined articles and products apparently giving these products a certain resistance to surface polishing operations. This ingredient is gainfully employed in my steel both where one or more of the ingredients silicon, manganese and nitrogen are as specified above,

stantially all iron.

and where they are at values other than as specifled, it being noted however that best results are had in my steel and in the various articles and machine parts fashioned of the same where all of the ingredients are present in the amounts indicated.

Thus, it will'be seen that there has been provided in this invention an alloy steel and certain manufactures or articles fashioned of the same, in which the various objects hereinbefore noted, together with many thoroughly practical advan= tages, are successfully achieved. It will be seen that my alloy steel is strong, tough and corrosion resistant. Moreover, it will be seen that my steel possesses good impact strength in combination with good machinability. "Furthermore, it will be seen that these various properties are had at minimum expense and that this combination of ,useful properties is particularly important in various machined products and articles, especially machine parts, having grooved, slotted, notched or other constricted portions, which nor:

mally give rise to high impact stresses under the conditions of shock and vibration encountered in use.

As many possible embodiments may be made of my invention and as many changes may be made in the embodimentshereinbefore set forth, it is to be understood that all matter described herein is to be interpreted as being illustrative and not as a limitation.

I claim as my invention:

1. In compositions of matter of the c de= scribed, an alloy steel or good corrosion resisting properties, good machining characteristics d good resistanceto impact, said alloy steel comprisin 14.5% to 18.0% chromium, 20% to .50% sulphur, .5% to 2.0% nickel, .06% to 30% nitrogen, with a. maximum carbon content of 20%. and the remainder substantially all iron.

2. In compositions of matter of the class described, an alloy steel of good corrosion resisting properties, good machining characteristicsand good resistance to impact, said alloy steel comprising 14.5% to 18.0% chromium. .20% to .50% sulphur, up to 1.5% manganese, .5% to 2.0% nickel, 06% to .30% nitrogen, with a maximum carbon content or 20%,

3. In compositions of matter of the class described, an alloy steel of good corrosion resisting properties, good machining characteristics and good resistance to impact, said alloy steel comprising 14.5% to 18.0% chromium, 20% to .50% sulphur, .5%

gen, 9, maximum or 35% silicon, with a maximum to 2.0% nickel, .06% to 30% nitroand the remainder subn 3 carbon content of 20%, and the remainder substantially all iron.

4. In compositions of matter of the class described, an alloy steel of good corrosion resisting properties, good machining characteristics and good resistance to impact, said alloy steel comprising 14'.5% to 18.0% chromium, 20% to .50% sulphur, .5% to 2.0% nickel, .2% to 2.0% molybdenum, 06% to 30% nitrogen, a maximum of 20% carbon, and the remainder substantially all iron.

5. In manufactures of the class described, machined articles, such as spindles, gears, worms, shafts, axles, threaded bolts, pins, nuts and the like, having threaded or notched portions, which articles ar strong, tough, corrosion resisting and of good impact strength, consisting of alloy steel comprising 14.5% to 18.0% chromium, 20% to .50% sulphur, .5% to 2.0% nickel, 06% to 00% nitrogen, a maximum of 20% carbon, and the remainder substantially all iron.

6. In manufactures of the class described, machined articles, such as spindles, gears, worms, shafts, axles, threaded bolts, pins, nuts and the like, having threaded or notched portions; which articles are strong, tough, corrosion resisting and of good impact strength, consisting oi an alloy steel comprising 14.5% to 18.0% chromium, -20% to .50% sulphur, .2% to 2.0% molybdenum, .5% to 2.0% nickel, .06% to 30% nitrogen, a maximum of 35% silicon, a maximum of 20% carbon, and the remainder substantially all iron.

7. In manufactures of the class described, machined articles, such as spindles, gears, worms, shafts, axles, threaded bolts, pins, nuts and the like, having threaded or notched portions, which articles are strong, tough, corrosion resisting and of good impact strength, consisting of an alloy steel comprising 14.5% to 18.0% chromium, 20% to .50% sulphur, 2% :to 2.0% molybdenum, .5% to 2.0% nickel, 06% to .30% nitrogen, up to 1.5%

manganese, a maximum of .60% silicon, a' inaxi- 7 mum of .20% carbon, and the remainder substantially alliron.

8. In compositions of matter oi the class described, an alloy steel of good corrosion-resisting properties, good machining characteristics, good workability in the hot and cold conditions and good resistance to impact, said alloy steel com- I prising 14.5% to 18.0% chromium, 20% to .50%

sulphur, .5% to 1.5% manganese, .5% to 2.0% nickel, 06% to 30% nitrogen, at maximum of .60% silicon, with a maximum carbon content 5 or 30%;, and the remainder substantially all iron.

ma a. scnaonns.