US2297686A - Chromium-vanadium-iron alloy cutting tool - Google Patents

Description

Patented Oct. 6, 1942 I CHROMIUM-VANADIUM-IRON ALLUY- CUTTING TOOL Charles 0. Burgess and William D. Forgeng, Niagara Falls, N. Y., assignors to Haynes Stellite Company, a corporation of Indiana No Drawing. Application July 30, 1940, Serial No. MBAM 2 Claims.

ment, it has been possible to vary the hardness.

toughness, and strength of the alloys over wide ranges. But hardness of a very high degree such as is required of a metal-cutting tool has heretofore been accompanied by an undue degree of brittleness. Cutting tool high speed" steels have been basically tungsten-iron compositions rather than chromium-iron, and have typically contained 18% tungsten, 4% chromium, and 1% vanadium (so-called 18-4l) sometimes modihad by the addition of one or more of the metals cobalt, nickel and molybdenum.

It is a primary object of the invention to provide an abrasion resistant chromium iron alloy cutting tool which will cut metals at high speeds at least as well as 18-4-1 high speed steel.

We have discovered that the properties of a hard chromium-iron alloy containing between 25% and 60% chromium are considerably enhanced by the addition of carbon, preferably in a percentage between 1% and 3%, and of at least 5% vanadium, the sum of the percentages of chromium and vanadium being between 35% and 70%. For some purposes, the carbon content may be somewhat below or abov the range of 1% to 3%. We have further found that such an alloy may be heat treated to improve its properties as a cutting tool or other a rasion-reslstant article. We have also found tha the toughness and general suitability of such an alloy for use as a cutting tool and other abrasion-resisting articles may be still further enhanced by the addition of one or more of the following elements: cobalt, nickel, boron, silicon tungsten, columbium, tantalum, and molybdenum, in certain pro portions hereinafter described.

Mor specifically, according to the invention abrasion-resistant cutting tools comprise chromium between 25% and 60%, at least 5% vanadium (the sum of the chromium andvanaclium being between 35% and 70%), at least 15% iron, and carbon, the carbon preferably being between 1 and 3%.

In addition to the chromium, vanadium, iron, and carbon, the alloy may contain up to 5% silicon or up to 5% boron, or both in an aggregate proportion not exceeding 5%; up to nickel; up to 10% cobalt; and a total of up to 10% of one or more of the elements tungsten, molybdenum, columbium, tantalum, titanium, and zirconium. Small fractional percentages of the common impurities, such as sulfur, phosphorus, and nitrogen, may also be present. Preferably, the carbon does not exceed 2.5%

The tools are heated at temperatures within the range of 550 C. and 850 C. for a time be-- tween about 5 minutes at the higher temperatures within said range and about twenty hours at the lower temperatures. The described heat treatment markedly improves the utility of the composition throughout the range described.

Although this invention does not depend for its successful application on any theory, we believe that the improvement is at least partly brought about by the formation of a constituent known as the sigma phase, a phase described in the literature variously as an intermetallic compound and as a highly saturated solid solution in an unusual allotropic form of iron.

A limited amount of hot forging may be done on most of the alloy compositions of the invention if they are not previously given a prolonged'exposure to elevated temperatures below 900 C. Preferably, forging is commenced before the cast metal has cooled from the casting step to below 900 C.

Depending chiefly upon the composition and the heat treating conditions, the hardness of the alloy tool of invention varies between'the approximate limits or' to Rockwell C. The transverse strength of the as-cast alloy is upwards of 700 pounds (loading applied centrally to a section 0.5 inch by 0.5 inch square, supported in a a inch span), and usually attains i pounds and sometimes more.

Cutting tests indicate that the alloy tool of the invention compares favorably with standard high speed steel tools of the 18-14-1 type. In accelerated life tests cutting steel billets and semi-steel billets, using surface speeds, feeds, and cuts considerably greater than normal, tools of this invention cut from two to eight times as far as standard Rex AAA, a widely used high speed steel of high quality.

We claim:

l. A cutting tool having substantially the composition: between 25%and 60% chromium, at

least 5% vanadium, the sum of the chromium and vanadium being between 35% and 70%,

within the range of 550 C. to 850 C. for a time between five minutes and twenty hours.

2. A cutting tool having substantially the composition: between 2 5% and 60% chromium, at least 5% vanadium, the sum 01' the chromium and vanadium being between 35% and 70%, be-

tween 1% and 2.5% carbon, remainder iron;

which tool is in the improved condition resulting from subjection to heating within the range 0! 550 C. to 850 C. for a time between five minutes and twenty hours.

CHARLES O. BURGESS. WILLIAM D. FORGENG.