US2395687A - Alloy steel - Google Patents

Description

Patented Feb. 26, 1946 i ALLOY STEEL- Luciano o. Selmi, Detroit, and 01mm L. Altenburger,'Deai-born, Mich. assignors to National Steel Corporation, a corporation of Delaware No Drawing. Application September 30, 1942.

Serial No. 460,273

2- Claims. .(Cl. Fit-'12s) This invention relates to improvementsin low alloy steels. More particularly, the invention relates to steels of the type disclosed and claimed in applicants Patent No. 2,250,505 issued July 29, 1941.

In the steels described in the foregoing patent. zirconium is incorporated as a constituent to deoxidize the steel and attain an inherently fine grain. In the present invention, by substituting vanadium for the zirconium in similar steels the many advantages of the steels of the patent have been retained while eliminating certain disadvantages inherent in the use of zirconium. These disadvantagesin the use of zirconium in no way affect the characteristics of the patented steels but appear only during the manufacture. By the present invention a similar steel incorporating the same characteristics as those of the patented steels can be more easily produced, the substitution of vanadium for the zirconium eliminating many of the pouring and casting troubles encountered with the use of zirconium. On the render a steel of this general nature highly re- I treatment.

other hand we have found that the incorporation of the vanadium in place of the zirconium does not deleteriously affect the physical characteristics of the specific steel-involved. Thus the steel of the present invention has substantially the same physical characteristics as the, steels disclosed in Patent No. 2,250,505.

The general object of the present invention is to provide a steel which may be easily and economically manufactured and which shall have important characteristics heretofore obtained only in steels using larger quantities of alloying metals.

More specifically, steels heretofore manufactured which have the properties of high degree Steels now on the market having characteristics 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 Molybdenum .35 Chromium .75 Carbon .40 Manganese .70 Silicon v .20 Phosphorus, maximum .03 Sulphur, maximum .03 Aluminum lb. per ton 1 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 attainthe essential characteristics of such a steel as will hereinafter appear or high levels of hardness, variable hardenability,

' purposes.

Further pecific objects therefore are to obtainin an alloy steel certain herein described characteristics with the use of a low percentage of alloy elements.

Further specific objects include the 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 thepresent invention is to with comparatively low percentages of such alloying elements as nickel and thus effect 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 by relatively small variations in the elements. [Likee wise we are able to provide a steel in which the hardenability may be varied by small changes of the quenching temperatures.

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 diflicult to obtain with anything comparable to our small percentages of the alloying elements.

Steels according to the present invention will.

have compositions within the following ranges:

Below is given-a specific example of a steel similar to the steel of the present invention to from the 2 which no molybdenum has been added and an. example of the steels oi the present invention:

SteslA Swan Trace .14

Steel A has a hardness in excess of 50 Rockwell 0, along a net end quench bar up to 1 inch quenching end when quenched from 1500'1'. v

Steel B has a hardness in excess of 50 Rockwell along 2 inches or more from the, quenched end when quenched from 1500' l".

In these examples, both steels are held at 1500" l". 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' r. to harden above so Rockwell C, whereas in the example given for the steel B,- cooling may be as slow as about 23 I. per second through the temperature or 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 or 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 ExampleB, molybdenum is given at 0.14%. Varying this range or 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 is, through thicknesses of six inches or more.

It willalso be noted that the relative hardenability between our steels A and B is accompanied with but slight changes in the other alloying elemanta which are all maintained within comparative low percentages. The carbon in Example B is slightly less than Example A; the manganese is slightly higher; the silicon is raised in the Example B from .75 to 39%; chromium is preferably slightly increased; the molybdenum shows the marked change, being raised from a trac up too. substantial, but still low amount. I

As will be seen from the example given of a steel heretotoreused in which a comparatively highpercentage oi a notably expensive element, such as nickel is used, such higher percentage, namely 1.75% seems to have been heretofore'considered essential to attain the characteristics which we attain.

In particular reference to hardenability, widely assess? ature, with shapes having comparatively thin or narrow crow-sections. The steel A may thus Practically be treated to attain desired hardness levels throughout by variations of quenching tem-' I v peraturesthrough narrow ranges.

Examples of the eiiects obtained by variati in cooling rates and quenching temperatures in the treating or steelB are tabulated below as illustrative. From these tables the increased hardenability eilected by change in temperature and the resulting levels .01 hai-dness' which we have found are clearly apparent.

The left-hand column lists the dii'lerences from the quenched end of the depth or distance to which the hardness reaches. The second column 1 gives the cooling rate passing through the temperature oi 1250 F. The third and fourth columns list Rockwell C hardness when quenched, using temperatures 01' 1475 F. and 1500 F., and after seventy-five minutes. 7

Steel B, in which more molybdenum is used, a

as for instance in the example given, is likewise responsive to slight changes in, th quench temperature but its hardenability throughout is governed more by the presence oi molybdenum.

Examples of uses of alloy steels made in accord-,

ance 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 or the alloys for steels now used for agiven weight or part may be several 7 times that of steels made in accordance with our used steels such as having the first-given formula,

may have their quality of hardness varied only comparatively slightly by widely varying th quenching temperatures.

With our present steel we may vary the levels or 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 1''. for corresponding 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 temperpresent invention and having like or in some respects superior characteristics.

By the present invention, we have produced, as aboveindicated, an inherently fine grained, clean steel. It is substantially deoxidized and it is sub- Ject to controlling the degree and depth 01- its hardness.

A steel, such as Example B, above-described, is highly resistant to quench cracking. It will withstand a drastic quench treatment such as that of live 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 the other elements, have surprisingly critical characteristics accomplishing the objects as above set forth.

The oxidizing 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 propertiesbut which, as. heretofore indicated, must have higher percentages of other elements, such, for example,

as nickel. v

. ,We' have found that in using the steel of the certain optimum percentages of the constituents exist inaccordance with the. thickness or the plate. The following table shows some of these preferred compositions:

Pietethinlmmininehes I Upto 1 2andup 0.3-0.8!) are-ea amen .50- .15 .85- .co-un .50- .90 .50- .90 .m- .00 .50 .75 .00 .eo- .lo- .20 .10- .10- .01- .10 .01- .Ql- JO present invention 'for heat treated plates that We claim:

1. A low alloy steel having inherently fine grain with hardenability variable through wide ranges, consisting of carbon .26 to 310%; manganese .74 to 1.00%; silicon .50 to- .90%; chromium .50 to 115%; molybdenum .05- to 25%; vanadium .01 to .l.0%; the balance being iron and incidental imp s- I 2. A low alloy steel having inherently flne grain with hardenability variable through wide ranges, consisting of carbon .26 to 50%; manganese .85

,to 1.00%;silicon .50 to .90%; chromium .60 to 310%: molybdenum .10 to 20%; vanadium .01 to 10%: the balance being iron and incidental impurities. v

- LUCIANO G. SELMI. v CLARENCE L. ALTENBURGER.