US2126748A - Alloy - Google Patents

Description

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August 16, 1938 UNITED STATES PATENT OFFICE No Drawing. Application May 18, 1937, Serial No. 143,299

3 Claims.

The present invention relates to a new and useful alloy containing boron, zirconium, tungsten, and cobalt, which is characterized by being responsive to thermal treatment for the improvement of physical properties. This application is a continuation in part of my copending application Serial No. 721,771 filed April 21, 1934.

An object of the present invention is to provide an alloy especially adapted for use as metal cutting tools, the cutting efilciency of which is superior to that of heretofore known high speed tools and other alloys. A further object is to provide an alloy which is free from, or substantially free from, carbon, and which is readily amenable to thermal treatment by means of which the hardness, cutting efiiciency and other physical properties and characteristics can be accurately controlled over a comparatively wide range.

I have found through experiment that by alloying or otherwise intimately combining boron, zirconium, tungsten and cobalt within the range of boron 0.50% to 4%, zirconium 0.25% to 5%, tungsten 5% to 25% and cobalt substantially the balance, that I obtain metallic compositions which are readily responsive to thermal treatment by means of which the physical properties and characteristics can be developed and controlled.

Alloys of this invention may be used in the cast condition for certain purposes, but approximate maximum values of hardness, resistance to impact and certain other important physical properties can be developed only through thermal treatment, or through mechanical working and thermal treatment. Bodies of the alloy which have been subjected to such treatment are particularly valuable for use as tools, dies, and the like, for the cutting or mechanical working of metals, as well as for many other industrial uses.

Numerous metallic compositions have heretofore been proposed as improvements on known types of high speed tool steel, but all of such proposed compositions have disadvantages which render them unsuitable for general application as metal cutting or forming tools. One disadvantage of such compositions is that none of them are amenable to thermal treatment for regulation of physical properties, and consequently physical properties and characteristics are governed entirely by the chemical compositions of the alloy.

My alloy is particularly responsive to thermal treatment for the development of precipitation hardening, often referred to as age hardening. I generally prefer to subject the alloy to thermal treatment before using it for metal cutting tools, dies, etc. I have found that both the cast and forged material are responsive to thermal treatment. As an illustration, cast bodies of this alloy may have a hardness of from 50 to 60 on the Rockwell C scale and by subjecting the material to suitable thermal treatment, such as heating to a temperature higher than approximately 1,000 C., followed by rapid quenching, the hardness may be lowered to an approximate range of from 36 to 44 Rockwell C. The alloy can subsequently be subjected to a second thermal treatment, such as heating to a temperature lower than 1,000 C. for a period of one hour or more, followed by cooling at a normal rate, by which the hardness can be increased to from approvimately 58 to 67 Rockwell C. In the latter condition the alloy is especially valuable for use in the cutting or mechanical working of a large number of metals and alloys, as well as numerous nonmetallic materials.

An important property of the alloy is that virtually all of the maximum hardness, developed by thermal treatment, is retained when the alloy is subjected to elevated temperatures; e. g., such as are generated in the tip of a tool cutting metal.

The alloy has a relatively high degree of hardness and resistance to abrasion by hot metal chips, and it is also remarkably resistant to failure from sudden or repeated shock. Consequently, tools made of the present alloy retain an efiicient cutting edge longer than similar equipment composed of other alloys.

The more important distinctive advantages are apparently due to the presence of appreciable amounts of boron in the composition, in conjunction with the other components within the percentages specified herein.

I have found that molybdenum may be used to supplant all or a portion of the tungsten of the alloy. Likewise, uranium may be used in place of either tungsten or molybdenum.

Specific examples of compositions within the scope of the present invention which I have found well adapted for metal cutting tools, dies, and other industrial purposes, are the following: boron 1.65%, zirconium 0.75%, tungsten 7.50%, cobalt substantially the balance; boron 2.10%, zirconium 2.35%, tungsten 17%, cobalt substantially the balance; boron 2.35%, zirconium 4.10%, molybdenum 12%, cobalt substantially the balance.

An objective of the present invention is to provide an alloy having high hardness, advantageous metal cutting properties, etc., which is free from, or substantially free from, carbon, and thus eliminate all of the serious disadvantages associated with carbon containing alloys or composition intended for metal cutting tools, etc. Although I prefer to have the alloy of this invention entirely free from carbon, in many instances I have found carbon present in the nature of an impurity incidental to manufacture. It is important, however, to restrict the carbon content to a maximum of about 0.15%, as I have found that the presence of higher percentages of this element not only embrittle the alloy, but also inhibit or retard the desired or necessary reactions during thermal treatment. The presence of appreciable amounts of carbon decreases the red hardness of the alloy; i. e., hardness at temperatures of approximately 550 C. and higher.

My investigations indicate that the preferred structure of a body of the present alloy, particularly after thermal treatment, comprises at least two principal constituents; one, a relatively hard intermetallic compound of boron with one or more of the other essential components; and, two, a solid solution of two or more of the essential components which has a lower degree of hardness and functions as a matrix. The ratio of the constituents, as well as the ratio of particle size in any particular body of the alloy may be accurately controlled and fixed over a wide range of means of thermal treatment or mechanical working and thermal treatment.

By reason of the combined advantageous physical properties and characteristics possessed by the alloy of the present invention tools and other articles composed of this alloy may be operated efficiently and economically under conditions which are impossible or uneconomical with tools, etc., composed of heretofore known alloys or metallic compositions.

By the term the balance substantially cobalt or the balance cobalt in the foregoing and in the following claims, I intend that the alloy of the present invention comprises boron, zirconium, and tungsten within the percentage limits specified, with the remainder cobalt, except for ineffectual amounts of impurities which may be present incidental to manufacture.

I claim:

1. An alloy, characterized by responsiveness to thermal treatment containing boron 0.50%, zirconium 0.25% to 5%, metal selected from the group tungsten, molybdenum and uranium 5% to 25%, the balance cobalt. .7

ANTHONY G. DE GOLYER.