US2215459A - Carbon-free alloy - Google Patents

Description

Patented Sept. 24, 1940 PATENT- OFFICE CARBON-FREE ALLOY Robert H. Canfield and Herman F. Kaiser, Washington, D. 0., Roy A. Gezelius, Somerville, N. J., and Henry S. Jerabek, Minneapolis, Minn.

No Drawing.

Application October 6, 1938, Serial No. 233,594

2 Claims.- (Cl. 75 170) (Granted under the act of March 5, 1883, as amended April 30, 1928; 370 0. G. 757)- This invention relates to carbon-free alloys and to methods of heat treating and preparing them for various uses:

It is an object of this invention to provide hard 5 alloys which are substantially free from carbon and which owe their hardness to the presence of other metals. v

It is a further object of this invention to provide alloys which can be softened and subsequently in hardened to the range of hardness of tool-steels without deformation or cracking.

It is a further object of this invention to provide alloys which possess the red-hardness of stellite and the 18-4-1 tool steels while at the same time possessing enough ductility and toughness to allow bending without breaking.

It is a still further object of our invention to provide methods of heat treating and preparing these alloys which will allow working of them in 20 a softened state and subsequent development of the quality of hardness to the extent desired. Further objects of this invention will become apparent from a reading of the following description:

.25 In the art of tool making, as at present practiced, the metal of the tool derives its hardness mainly from the presence of carbon inthe form of metallic carbides. In simple steel it is cementite or iron carbide which -supplies the hardness; but in other steels it may be, in addition, the carbides of chromium, tungsten, molybdenum or other metals. In the case of metals which are not strictly steels, such as stellite and carbolloy, there are nevertheless carbides of f chromium, tungsten or other metals present, and it is to these substances that the alloys largely owe their hardness.

We have discovered that it is possible to make alloys of iron and cobalt which are substantially free from carbon, and owe their hardness to the presence of small amounts of another metal or metals. Furthermore, the method of developing this hardness is quite different from that used with steel, since our metal is softened by being quenched from a high temperature, and subsequently hardened by an annealing treatment at a temperature somewhat lower than the one from which it was quenched. As a result of the nature of this process it is possible to make articles of intricate shape using ordinary machine-shop methods and later harden them uniformly without internal strain, without deformation or cracking and without exposing them to destructive atmospheres. Also, tools made out of our metal may be used for cutting at temperatures nearly up to that at which they have received their hardening anneal, without losing their usefulness as cutting tools at this elevated temperature. Thus this alloy shares the property of red-hardness with such materials as stellite and the 18-4-1 5 tool steels. Our alloy, even in the hardened condition possesses considerable toughness and ductility, so that it is still possible to bend it without. breaking it.

Our alloy can be prepared within a certain. 10 range of compositions and still possess its distinctive qualities; but its typical analysis consists of a base alloy of cobalt and iron 35% to which may be added several other elements to a total amount of generally less than 5%. How- I ever, we have made useful alloys where the base composition varied between 62% cobalt, 38%.iron, and 68% cobalt, 32% iron, with additions up to over six percent of other elements. The added elements (to the presence of which the alloy owes 20 its distinctive hardening properties) are manganese and one or both of the elements chromium and molybdenum. The presence of manganese is not essential to the alloy and it may be omitted, if desired. The manganese is. added in amounts 25 up to 1.5%, the chromium up to 3%, the molybdenum up to 5%; but all these elements cannot be present at the same time in their maximum amounts without entirely altering the nature of the alloy. This is illustrated in the 30 following table:

Total composition-Rockwell C -hardness Alloy No. 00 Fe Mn Cr M05 Max. Min.

It will be seen that while alloys 1 and'3, containing 2.3% chromium and 5.4 molybdenum respectively, are both highly hardenable, alloy 5 containing 2.2% chromium and 4.0% molybdenum, is even in its hardest condition inferior to the others in their softest condition; it is in fact an entirely difierent alloy metallographically. As for carbon, we have. found that its efiect is detrimental; it does not enhance the hardness of the alloys'in their hardest state, while it tends to make them too hard in their softest state. We keep it below 0.05%.

As already mentioned, these alloys can be in the original form ofcastings, forgings; or rolled sections. The first step in preparing the metal for further work is to quench it from a high temperature. This temperature varies according to the composition but is always above 1650 F.

We preferably quench the metal in water or brine since even air-cooling may be slow enough to permit some of the changes which produce hardening. After this quenching operation the article will'be soft enough (usually Rockwell -39) to permit any kind of machining operation, including milling, turning, drilling, cold-rolling and others. If necessary to re-soften the metal, it can be quenched again. When the article is finally ready for hardening, we preferably pack it with steel wool in an annealing box, but any kind of suitable container can be used, and heat it in a furnace to a temperature and for a time dependent'somewhat on the composition and on the ultimate properties desired; but generally the temperature-is above 800 F. and it is always below 1200 FL; and the time is between one and twenty hours. For example, we took a piece of the alloy listed as No. 1 in the foregoing table, and forged it into a bar square. We then quenched it in brine from 2000 F. After it had been sawed and milled to the form of a lathe tool at Rockwell 0-39, we packed it in steel wool in a closed iron pipe and heated it to 1000 R; we kept it there for one hour and then removed it from the furnace. On cooling and unpacking, the

tool had a hardnesspf Rockwell (1-63 and was used in heavy turning of ,machinery steel on a lathe, the out being so deep and fast that the condition our alloy No. 1 already described after being'magnetized'possessed a residual induction of 9000'8auss and a coercive force of 65 oersteds, and yet was soft enough to machine, and could be cold bent or rolled without aifecting its magnetic properties. It was now heated to 1150 F. and cooled again, having remained permanently magnetized during the whole operation and re taining afterwards a large proportion of its orginal residual induction.

Although we have mentioned only tools and permanent magnets as applications of our alloy, there are other applications which will suggest themselves to one versed in metallurgy and physics, and we include all'such applications in our specification. I

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment -of any royalties thereon or therefor.

- Having thus set forth and disclosed the nature of this invention, what is claimed is:

1. An age hardenable alloy consisting of 58 to 68% cobalt, 28 to 38% iron and .4 to 3.0% chromium, with less than .05% carbon.

2. An age'hardenable alloy consisting of 58 to 68% cobalt, 28 to 38% iron and 1.0 to 6% molybdenum, with less than .05% carbon.

ROBERT H. CANFIELD. HERMAN F. KAISER. ROY A. GEZELIUS. I'ENRY S. JERABFK.