US2375954A - Alloy steel - Google Patents

Description

Patented May 15, 1945 ALLOY STEEL Luciano G- Selmi, Detroit, and Clarence L. Alteribnrger, Dcarborn, Mich, assignors to National Steel Corporation, a corporation of Delaware No Drawing. Application September 30, 1942, Serial No. 460,275

4 Claims.

This invention relates to improvements in 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 steel described in the foregoing patent, zirconium is incorporated as a constituent to deoxidize the steel and attain an inherently flne grain. In the present invention, by substituting titanium 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 disadvantages in 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 titanium for the zirconium eliminating many of the pouring and casting troubles encountered with the use of zirconium. n the other hand we have found that the incorporation of the titanium in place of the zirconium does not deleteriously afi'ect 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 or high levels of hardness, variable hardenability, ductility and machinability, have been made by including in the steel comparatively large quantitles of alloying elements. These elements are expensive and at the present time are becoming increasingly difiicult to obtain for commercial purposes;

Further specific objects therefore are to obtain in 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 the present invention is to render a steel of this general nature highly resistant to quench cracking even under drastic treatment.

Steels now on the market having character-- istics and properties such as are attained by our present invention, include alloying metals in substantially high percentages-such for example as follows:

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 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 by relatively small variations in the elements. likewise 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 difiicult to obtain with anything comparable to our small percentages of the alloying elements.

Steels according to the present invention ml! have compositions within the following ranges:

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

SteelA StedB Trace .16

Steel Amust 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 13, cooling may be as slow as about 2. F. per second through the temperature of 1250 F. and still it will harden above the level of 50 Rockwell C. 1

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 iound Ollr steels are hardenable through great depths, and it is entirely practical within the range, say -oj pp to 0.35% molybdenum to harden locomotive or oar-axles throughout, that 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 elements which are all maintained within comparative low percentages. The carbon in Example B is slightly less than Example A; the manganese is slightly lower; the silicon is nearly the same; chromium is slightly increased; the molybdenum shows the marked change, being raised from a trace up to a substantial, but still low amount.

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

In particular reference to hardenability, widely used steels such as having the first-given formula, may have their quality of hardness varied only comparatively slightly by widel 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 temperature of as high as 200 F. 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 degrees in quenching temperatxxrawithshapesinvingeomparatlvelythinor narrow ems- The steel A may thus practically be treated to attain desired hardness levelsthroughoutbynriaflonsotquenchingtemperaturs throughnarrowranges.

Examples of the eifects obtained by variation in cooling rates and temperatures in theireating ofsteelBare tabulatedbelowas illustrative. From these tables the increased hardenability dlected by change in temperature and the resulting levels of hardnw which we haveioundamciearly apparent.

Timleft-handoolumnlists the diiIerences from thequmchedendotthedepthordistanceto which the hardnes reaches. The second column gives the cooling rate posing through the temperatureof 1250' F. The third and fourth columns list Rockwell C hardnw when quenched. using tem 01' 1175' F. and 1500' F., and

Steel B,inwhichmotennlybdenumisused, as forinstanceinfliee'xnmplegivmislikewiseresponsive to slight changes in the quench temperature 'but its throughout is governed more by the prance at molybdenum.

Examplesofnsesofalloysteelsmadeinaccordance with our resent invention and which maybefurnishedatluwcostcomparedtopresent alloys used for like are: automobile axles, gears, automolile springs, airplane propellers, airplane engine shark and many other partswhere exoepticmnlbdeephardening isrequired such as, for example, large axles for railway uses.

Theexpenseoroostoftheailoysforsteels now used for a given weight or part may be several times that of steels made inaccordance with our present invention and having like or in some respects superior charaeteristiis.

By the present invenfion, we have produced, as above indicated, an inherently iine grained, clean steel. It is snlshnfially dioxidized and it is subject to controlling the degree and depth of its hardness.

Asteel, suchasExlmpleB, above-described, is highly nsistant to qumch cracking. It will withstand a drastic quench treatment such as that o! five percent caustic solution from above critical temperatures; for example, 1480' F. down to 32 F.

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

The elements present in the steel aresuchastoproducelowdegreesoidistortion 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.

We have found that in using the steel of the present invention for heat treated plates that certain optimum percentages of the constituents existin accordance with the thickness of the plate. The following table shows some of these preferred compositions:

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

We claim:

1. A low alloy steel having inherently fine grain with hardenability variable through wide ranges, consisting of carbon .26 to 370%; manganese .50 to 1.00%; silicon .50 to .90%; chromium .25 to 75%;, molybdenum .05 to 25% titanium .015 to .20%; the balance being iron and incidental impurities.

2. A low allow steel having inherently fine grain with hardenability variable through wide ranges, consisting of carbon .26 to .'70%; manganese .50 to 1.00%; silicon .50 to .90%; chromium .25 to .75%; molybdenum .10 to 20%; titanium .015 to .10%; the balance being iron and incidental impurities.

3. A low alloy steel having inherently fine grain with hardenability variable through wide ranges, consisting of carbon .26 to manganese .50 to 1.00%; silicon .50 to 90%; chromium .25 to .75%; molybdenum .10 to .20%; titanium .015 to .10%; the balance being iron and incidental im purities.

4. A low alloy steel having inherently fine 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 molybdenum .10 to 20%; titanium .015 to .10%; the balance being iron and incidental impurities.

LUCIANO G. SELMI.

CLARENCE L. ALTENBURGER.