US2384567A - Alloy steel method and products - Google Patents

Description

Patented Sept. 11, 1945.

ALLOY STEEL METHOD AND-PRODUCTS Henry S. Schaui'us, Baltimore, Md assignor to Rustless Iron and Steel Corporation, a corporation of Delaware No Drawing. Application December 13, 1940, Serial No. 370,074,

7 Claims. (Cl. 14831) My invention relates to products fashioned of a high chromium alloy steel, especially a freemachining steel as disclosed in my co-pendlng application Serial No. 370,072 filed of even date herewith and entitled Alloy steel and articles and to an art or method of producing the same.

Among the objects of my invention is the provision of a simple, direct and economical art for uniformly obtaining high chromium alloy steel products, such as bars, rods, wire, plate, sheet, tubes, forgings, drop-forgings and the like (especially to such products having good machining characteristics by virtue of substantial sulphur content), of high impact strength in spite of temperature variations in the working operations and in the various finishing temperatures encountered in actual practical use, and to the semiconverted products themselves as produced in accordance with my method.

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

The invention accordingly consists in the com position of ingredients, combination 01 elements and mixture of materials and in the several operational steps and the relation of each of the same to one or more of the others as described herein, the scope ofthe application or which is indicated in the claims.

A better appreciation of my invention perhaps best may be gained through a general preliminary consideration of certain of the heretofore known and used high chromium alloy steels, commonly referred to as stainless steel. One ot the most common types is the 12% to 14% chromium grade. The steel is readily workable into bars, rods, wire, plate, sheet, strip and tubes through conventional not or hot and cold methods. It may be heat-treated to give a wide range of hardness, strength and impact resistance. Moreover, the products readily may be fashioned through riveting, welding or soldering methods into a host of articles of ultimate use. i reasonably strong and tough and possesses an excellent impact strength. Even the free-machining grades of this steel are high in impact strength. The 12% to 14% chromium grade, however, is severely limited in its corrosion xesisting properties; it is recommended only where the most mild form of corrosive agents are encountered.

Where rather severe corrosive conditions are to be encountered the austenitic grades of chromium-nickel stainless steel, that is, stainless steel having about 18% chromium and 8% nickel, commonly are used. This steel likewise may This steel it free-machining qualities.

heat treatment and moreover it is quite expen-- sive largely because of .its high nickel content.

While it might be expected that a reasonably inexpensive stainless steel of desired physical and corrosion resisting properties could be had in ome higher chromium grade, for example, a 17% chromium grade, I find that this is by no 'means the case, especially where the steel contains a substantial amount of sulphur to give The 17% chromium grade, particularly of the free-machining type, although possessed of good working properties and good corrosion resisting characteristics, seriously suffers in impact strength. For this reason it is not recommended in applicaticns where shock, vibration, or other active stresses are commonly met with in use. This is particularly true of the sulphur-bearing steel which is so low in impact strength as to be virtually worthless for engineering applications.

Now in my co-pending application for patent identified above, I have described and claimed a stainless steel having good impact strength in combiration with good corrosion resistance, and good machineability, which at the srme time is hardenable by heat treatment and comparatively inexpensive. Also in my co-pending application, Serial No. 370,073, filed of even date herewith and entitled Method of working alloy steel and products thereof, I have described and claimed One of the outstanding objects of my present invention accordingly is the provision of an economical method for uniformly and consistently obtaining high chromium stainless steel converted products especially of the freemachining grade, or high impact strength, in spite of temperature variations in the working operations metal.

and in spite of a variance in the finishing temperatures.

Turning now to the practice of my invention, stainless steel containing 14.5% to 18.0% chromium, .5% to 2.0% nickel and .06% to .30% nitrogen, with a maximum of 20% carbon and the remainder principally iron (together with a sulphur content of 20% to .50% for the freemachining grade), is produced according to any one of several well-known melting processes such, for example, as those generally described in the United States Letters Patent 1,925,182, issued to Alexander L Delhi on Septembe 5, 1933, and entitled Process for 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. The nitrogen addition is conveniently made as described in the co-pending application of William B. Arness, Serial No. 113,256, filed November 28, 1936, and entitled Production of rustless iron.

The'sulphur addition conveniently is made in the .7

conventional manner through the addition of lump sulphur to the ladle in tapping the heat of 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. Similarly, where desired, certain of the converted or semiconverted forms may be forged or drop-forged in the production of semi-finished articles. The products are reheated to a temperature of 1000 F. to 1450 F. and air-cooled.

These various converted products are made into a wide variety of articles of ultimate use. Converted articles of the free-machining grade are fashioned into various machine parts such as gears, worms, spindles, shafts, sleeves, bushings, rings, and discs, as well as' threaded bolts. pins, studs, nuts, valve parts and the like wherein assess? for the surprising combination of good impact strength and good corrosion resistance in products converted according to my invention, in spite of variations in the working temperatures 6 employed, this nevertheless is an accomplished ffl mially is this so in connection with the free-machining grade of steel where the comblnation or good impact strength, good machineability and good corrosion resistance is realized 10 in converted products even where the temperatures of conversion widely vary. For some reason unknown to me the presence of nitrogen directly contributes to the realization of this result.

As illustrative of one of the features of my invention, a comparison is given between converted products of a low nitrogen steel and a high nitrogen steel which in other respects are of like analyses. The compositions of the two steels are given in Table I, as follows:

Table I Low High Ingredients nitrogen nitrogen Chromium i6. 25 is. 05 Sulphur 31 .23 Nickel. .76 .73 Nitrogen" 02 06 fiolybdenum 3:11 anganese Silicon .30 .40 Carbon .07 .09 Iron Remainder Remainder Two sample ingots of each analysis were rolled down, one at a higher working temperature than the other. Although all four ingots rolled well, it is significant that in the low nitrogen samples there is a wide dliierence in the impact strengths realized. In the case of the high nitrogen 0 samples. however, it is noted that the impact strengths are virtually the same in spite of the temperature differences in the two rolling operacutting. drilling. tapping, threading orother mations. A comparison for the four samples is chine operations are required. given in Table 11 below:

Table II Rolling Impact mums Izod, mple um Structure Grain ioot lbs.

Start Finhh healed) F. 1''. 2,210 1,700 ierrligleuremaindcr decomposed Slightly elongated"... 6-12 marte Low nitrogen 1, 925 1,000 60% iizreriteuremalndel' decomposed Greatly elongated.-. 41-46 mar ns ah nitrogen 2.210 1,700 30% letgisieulemallldel' decomposed Slightly eiongaied..... 28-35 2 mar 811 nitrogen-"0.. 1,915. 1, M95 ierritismremsinder decomposed Slightly elongsted 31-38 marten:

In accordance with my invention I find that the converted products as well as the products of ultimate use iashioned thereof are strong and tough. Those of the higher carbon grade, .1296 to 20% carbon, lend'themselves to considerable hardening by heat-treatment. In all grades, this From the comparison given above it will be observed not only that the presence of nitrogen assures uniform high impact strength in'splte oi vagaries in the working temperatures, but also that the presence of nitrogen substantially reduces the directional eflects in the products. This is particularly important in the converted products which subsequently are to be made into various machine parts where it is readily understood-that the various bending, torsion, impact and other stresses encountered in actual practical use may be applied in an infinite number of directions.

While as more particularly indicated above my novel method of lending good impact strength to high chromium stainless steel converted products 75 is illustrated in connection with a high chromium low nickel steel, certain further advantages are had by introducing a manganese content in excess of that normally present, the manganese content ranging then up to 1.5% and desirably being between .5% and 1.5%.

The ingredient silicon, which, like manganese is commonly present in stainless steel, preferably should be maintained at a low value, that 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 proportionately may be higher, up to about .60%.

Certain further advantages are had in the converted products produced in accordance with my invention where the ingredient molybdenum in the amount of .2% to 2.0% is included in their composition. This ingredient preferably is preserved in amounts of .2% to 1.0% in the nonhardening grades of my steel. I find that molybdenum lends a certain denseness to the metal and imparts peculiar wear-resisting qualities to the articles of use into which the converted products are fashioned, as more particularly indicated in my co-pending application referred to above and entitled Alloy steel and articles.

Thus it will be seen. that there has been provided in my invention an art of uniformly obfree of directional effects and which lend them-- selves to fabrication into a host of articles of ultimate use. j

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

I claim as my invention:

1. In the production of hot-worked alloy steel semi-converted products, of good machining characteristics, comprising 14.5% to 18.0% chromium, .20% to .50% sulphur, .5% to 2.0% nickel. with a maximum of .20% carbon and the remainder substantially all iron, the art which include assuring improved impact strength in such products in spite of irregularities in the hot-working operations, by including in the composition of the alloy steel the ingredient nitrogen in the amount of .06% to .30%, and air-cooling the steel from a temperature of 1000 F. to 1450 F.

2. In the production of hot-worked alloy steel semi-converted products, of good machining characteristics, comprising 14.5% to 18.0% chromium, .20% to .50% sulphur, with a maximum of .20% carbon and the remainder substantially all iron, the art which includes assuring high impact strength in such products in spite of irregularities in the hot-working operations, by including in the composition of th alloy steel the ingredients nickel, in the amount of .5% to 2.0% and nitrogen in the amount-of .06% to 30%. 3. Inmanufactures of the class described, semiconverted hot-worked alloy steel products of good machining qualities and of uniformly improved impact strength, such products comprising 14.5% to 13.0% chromium, .20% to sulphur, 5% to 2.0% nickel, .06% to .30% nitrogen, a maximum of. .20% carbon and the balance substantially iron.

4. In manufactures of the class described, semiconverted hot-worked alloy steel products of good machining qualities and of uniformly improved impact strength, such products comprising 14.5% to 18.0% chromium, .20% to .50% sulphur, .5% to 2.0% nickel, .06% to .30% nitrogen, .2% to 2.0% molybdenum, a maximum of .20% carbon and the balance substantially all iron.

5. In manufactures of the class described, hot.- worked alloy steel bars, rods and wire of good machining properties and high impact strength, comprising 14.5% to 18.0% chromium, .20% to 50% sulphur, .5%' to 2.0% nickel, .06% to 30% nitrogen, a maximum of .20% carbon and the balance substantially alliron.

6. In manufactures of the class described, hotworked alloy steel plate and sheet of good machining characteristics and high impact strength such alloy steel plate and sheet comprising 14.5% to 18.0% chromium, .20% to .50% sulphur, .5% to 2.0% nickel. .08% to .30% nitrogen, with a maxi- 'mum of .20% carbon and the remainder substantially all of iron.

7. In manufactures of the class described, alloy steel drop-forgings of good machining character istics and high impact strength, comprising 14.5% to 18.0% chromium, .20% to 50% sulphur, .5% to 2.0% nickel, .06% to 30% nitrogen, with a maximum oi .20% carbon and the remainder substantially all of iron;

HENRY S. SCHAUFUS.