US2250505A - Alloy steel - Google Patents

Description

Patented July 29, 1941 armor srcnr.

' Luciano G. Selmi, Detroit, and Clarence L. Altenlmrger, Deal-born, Mich, assignors to Great Lakes Steel Corporation, Ecorse, Mich, a corporation of Delaware No Drawing.

Application March 3, 1941,

Serial No. 381,560

4Claims.

The present invention relates to an alloy steel of the general nature of that set forth in our copending application, Serial No. 345,227, filed July 12, 1940 for Alloy steel.v The steel the said application is of the low alloy type in that it comprises but small quantities-of alloying metals, or alloy elements, and yet has properties of high tensile strength, deep drawing characteristics, high fatigue resistance and other important properties necessary for many uses of steels of this character.

The general object of the present invention is to provide a steel which may be cheaply manufactured and which shall have some of the same characteristics as the steel of the aforementioned application and which shall have, in addition, im-

- portant characteristics heretofore-obtained only in steels using larger quantities of alloying metals.

Such steels may thus be produced by the present invention at much lower cost than steels now on the market which have like characteristics.

More specifically steels heretofore manufactured, which have the properties of high degree or high levels of hardness and capable of variable hardenability and also having important characteristics such as ductility and machinability, have been made by including in the steel comparatively large quantities of alloying elements. These elements are, by their very nature, expensive, and at the present time are becoming increasingly diiiicult toobtain for commercial purposes.

Further specific objects therefore are to attain in an alloy steel certain herein described desirable characteristics with the use of a low percentage of alloy elements.

As we have stated, a low alloy steel having many valuable characteristics i described and claimed in our above designated copending application. We have found that by maintaining certain relationships between alloying elements, such an alloy steel may be given unexpectedly difierent and highly desirable characteristics with only minor changes in the percentages of the alloy elements. I

Further specific objects include a provision of a steel which shall be resistant to a very high velocity impact, resistant to shock and fragmentation, and which shall have permanent high cohesive strength. It is desirable that the steel of the present invention shall have this high cohesive strength with a high ratio of such cohesive strength to its shear strength. Thus the steel is resistant to growth of and propagation of cracks. Another object of the present invention is to Steels'now on the market having characteristic and properties such as are attained by our present invention, include alloying metals in substantially high percentages-such for example as follows:

Nickel 1.75 Molyb n Chromium 75 Carbon 40 Manganese [70 Silicon 20 Phosphorus, maximum .03 Sulphur, maximum .03 Aluminum lb. per ton 1 /2 It will be seen that in the foregoing example of commercial steel comparatively high percentages of these variable alloying elements have been heretofore considered essential to attain certain characteristics; We attain the essential characteristics of such a steel as will hereinafter appear with comparatively low percentages of such render a steel of this general nature highly resistant to quench alloying. elements as nickel and thus efiect marked economies.

With the low alloy metals of the percentages such as herein given, we-are enabled to provide a steel having an inherently fine grain and in which hardenability may be varied as desired through heretofore unexpectedly wide ranges byrelatively small variations in the elements. Likewise we are able to provide a steel in which the hardenability may be varied by small changes ofthe quenching temperatures. I

All of the above purposes and characteristics are attained within ranges of very much lower cost per ton.

Furthermore, we are enabled to maintain uniformity of product heretofore difficult to obtain with anything comparable to our small percent-. ages of the alloying elements. S

As examples of steels made in accordance with the present invention and which have a wide variety of practical commercial uses which illustrates the wide range in hardenability with small changes in the contained chemistry, that is, th alloyformula, we give the following: a

Steel A Steel B Steel A has a hardness in excess of 50 Rockwell C, along a flat end quench bar up to V inch from the quenching endwhen quenched from 1500" F.

Steel 3 has a hardness in excess of 50 Rockasasggaa well C along 2% inches or more from the quenched end when quenched from 1500 F.

In these examples, both steels are held at 1500 F. for one hour prior to quenching. Both are one inch round bars.

Steel A must be cooled at a rate in excess of 21 F. per second at 1250 F. to harden above 50 Rockwell C, whereas in the example given for the steel B, cooling may be as slow as about 2.7" F. per second through the temperature of 1250 F. and still it will harden above the level of 50 Rockwell C.

From the foregoing examples, it will be noted that the marked increased depth of hardenability of the steel B over the steel A accompanies the increase of molybdenum. In the Example A, the molybdenum given is but a trace. In the Example B, molybdenum is given at 0.16%. Varying this range of molybdenum, while still maintaining it in within comparatively small quantity range, we have found our steels are hardenable through great depths, and it is entirely practical within the range, say, of up to 0.35% molybdenum to harden locomotive or car axles throughout, that V is, through thicknesses of six inches or more.

It will also be noted that the relative hardenability between our steels A and B is accompanied with but slight changes in the other alloying 'ele-- is slightly less than Example A; the manganese is slightly higher; the silicon is raised in the Ex- In particular reference to hardenability, widely I used steels such as having the first-given formula, may have their quality of hardness varied only comparatively slightly by widely varying the quenching temperatures.

With our present steel we may vary the levels of hardness through marked ranges by slight variations in temperatures.

Steels, such as the example given, and others heretofore used, require variations in quenching temperatures of as high as 200 F. for correspond- 'ing results.

A steel such as steel A- may have its degree or levels of hardness varied materially by changes of as little as 20 degrees in quenching temperature, with shapes having comparatively thin or narrow cross-sections. The steel A may thus practically be treatedto attain desired hardness levels throughout by variations of quenching temperatures through narrow ranges.

Examples of the efl'ects obtained by variation in cooling rates and quenching temperatures in the treating of steel 13 are tabulated below as illustratlve. From these tables the increaseed hardenability effected by change in temperatures and the resulting levels of hardness which we have found are clearly apparent.

The left-hand column lists the diil'erences from the quenched end of the depth or distance to which the hardness reaches. The second column gives thecooling rate of passing through the temperature of 1250 1". The third and fourth columns list Rockwell C hardness when quenched, using temperatures of 1475 F. and 1500 F, and after seventy-five minutes.

Rockwell 0 Distance Cooling rate mm F /sec at quenched quenched iz? 1250 r. 1476" F. 15oo r.

after after min. 75 min.

Me 700 60 0034 it 450 60 60 9% 100 60% 60% ii 75 61 60 it 21 58% 58 ii 14 58 56% l 8. 7 64 56% 1% 6 669i 1% 4 48 66 1% 3. 5 45% 56 2 3 45% 65 2 l4 2. 7 44% 2% 2. 6 44% 53% 2% 2. 5 48 Steel B, in which more molybdenum is used, as for instance in the example given, is likewise responsive to slight changes in the quench temperature but its hardenability throughout is governed more by the presence 0! molybdenum.

Examples of uses of alloy steels made in accordance with our present invention and which may be furnished at low cost compared to present alloys used for like purposes are: automobile axles, gears, automobile springs, airplane propellers, airplane engine shafts and many other parts where exceptionally deep hardening is required such as, for example, large axles for railway uses..

The expense or cost of the alloys for steels now used for a given weight or part may be several times that of steels made in accordance with our present invention and having like win some respects superior characteristics.

By the present invention, we have produced, as above indicated, an inherently fine grained, clean steel. It is substantially deoxidized and it is subject to controlling the degree and depth of its hardness.

A steel, suchas Example B, above-described, is highly resistant to quench cracking. It will withstand a drastic quench treatment such as that of five percent caustic solution from above critical temperatures; for example, 1480 F. down to 32 F.

The steel has a balanced alloy composition and the relationship between the molybdenum, when used, and theother elements, have surprisingly critical characteristics accomplishing the objects as above set forth.

The oxydizing elements present in the steel are such as to produce low degrees of distortion during high heat treatment. The steel, unlike other steels having comparable degrees of hardenability, has inherent properties which result in a steel suitable for convenient and practical fabrication such as forging and otherwise working. Our present steel has characteristics of weldability, that compare with alloys having like properties but which, as heretofore indicated. must have higher percentages of other elements, such, for example, as nickel.

The example of the previous steels and examples of the two formulas of our present alloy steel are given as illustrative, but it is understood that variation within reasonable elements may be made without departing from the scope of the present invention as defined in the appended claims.

We claim:

1. A steel having inherently fine grain and containing comparatively small quantities of alloy elements with hardenability variable through wide ranges by relatively small variations of the alloy elements capable of being welded by commercial processes, and consisting of carbon .25-

..50 to 315%; silicon .70 to .90%; zirconium, .05

to .35%; molybdenum .05 to .25% and the balance iron. I

3. A steel having inherently fine grain and containing comparatively small quantities of aly elements in balanced ratios with hardenability variable, ductile at high degree of hardness; resistant to quench cracking, and consisting of carbon .40 to 55%; manganese .50 to .75%;

chromium .50 to 375%; silicon .70 to .90%; zirconium -.05 to 25%; molybdenum .05 to 20 and the remainder being iron.

4. A steel having a -hardness in excess of Rockwell C, having inherently fine grain and containing comparatively small quantities of alloy elements consisting of carbon .45%; manganese chromium 370%; silicon 30%; zirconium .l5%; phosphorus .03% maximum; sulphur .03%

maximum; molybdenum about .15%, and the balance being iron, with hardenability variable through wide ranges by small variation of quenching temperature.

' LUCIANO G. SELMI. I CLARENCE L. ALTENBURGER.