US2246166A - Sintered hard-metal alloy for implements and tools - Google Patents

Description

Patented June 17, 1941 SINTERED HARD-METAL ALLOY FOR DHPLEMENTS AND TOOLS Walther DawihL- Berlin-Kohlhasenbruck, and Karl Schriiter, Berlin, Germany, assignors to General Electric Company, a corporation of New York No Drawing. Application March 30, 1940, Serial No. 326,972. In Germany February 2, 1939' 2 Claims.

' Hard metal alloys or cemented carbides heretofore produced generally have consisted of one or more hard metal carbides with a high melting point such as tungsten carbide, molybdenum carbide, titanium carbide or tantalum carbide and a metallic addition, the so-called auxiliary metal which has a relatively low melting point and and may constitute up to about 25% of the weight of the hard metal alloy. Cobalt, nickel or iron either individually or in suitable mixture preferably are used for such metallic additions and these metals are very soft as compared to the hard metal carbides. As a result of this great difference in hardness it sometimes happens that in the use of hard metal alloy tools of the abovenoted character, the auxiliary metal wears away relatively quickly thereby exposing the hard carbide grains which thereafter break away from the tool and shorten its life.

According to the present invention, this property of hard-metal composition which reduces the life of the tool or implement, is improved when a mixture, preferably vpre-heated and crushed again, consisting of a metal with a lower melting point or several such metals, as cobalt, nickel, iron, manganese or chromium and a tungsten or molybdenum carbon alloy with a carbon content between 1 and 5% is used as the addition to the carbide or carbides of metals with a high melting point-which forms the basic mass. The portion of the admixture of more readily melting metals lies in that case between and 80%; consequently the portion of the tungsten or molybdenum carbon alloy is from 90' to Such mixtures have melting points which lie between 1400" and'1600 irrespective'of which of the more readily ,melting auxiliary metal is used and irrespective of whether the carbon content of the tungsten or molybdenum carbon alloy present in the mixture is only'1% or up to 5%. Because of the relatively low melting temperature of the added mixture, it is possible to retain the sintering temperatures customary in the hardmetal industry when using the' new admixture, and to obtain thereby all advantages which are included in the application of auxiliary metals with a lower melting point. On the other hand, it has, however, been found that the admixtures that are to be used according to the invention within the indicated range of composition have much higher hardness values than the pure auxiliary metals generally used heretofore. The hardness values of the indicated mixtures'of adclltion are sometimes so high that, if desired, they maybe utilized independently as hard alloys.

Their inherent hardness closely approaches the inherent hardness of the carbides that form the basic compound of the entire composition so that the wearing away phenomena hereinbefore described is avoided.

To obtain the highest hardness values, it is particularly advantageous to employ composition of the added mixture which lie within the range of composition indicated by the formulas COsWzC and COaWaC. I

In the production of the added mixture, it is desirable to mix about 35 parts by weight of cobalt with about parts by weight of a tungsten carbon alloy having a 3% carbon content. The mixture is heated to approximately 1300 C. togive the alloy an opportunity to form and is then pulverized. Of this pulverized alloy there are then mixed 10 parts by weight with parts by weight of tungsten carbide having a carbon content of 6.12%. Molded bodies are produced from the mixture and these are then sintered in a known manner at a temperature of approximately 1500" C.

The sintered bodies obtained are distinguished by a hardness which is distributed very uniformly over the entire cross section; their strength is somewhat less than that of hard metal alloys produced with pure alloy metals so that they may be used to advantage whenever a uniformly high hardness is required without too high strength requirements. The alloy formation between the carbide or carbides that constitute the basic mass and the added mixture is favored considerably when the latter, prior to the mixing with the basic mass, is preheated and crushed a'gain. The

more ready alloy formation in conjunction with the uniform distribution of the particles of the added mixture in the basic carbide mass results in finished sintered bodies which have an extremely low degree of porosity.

It previously has been suggested to add to the initial materials of hard metal alloys, metals with a high melting point like, for instance} metallic tungsten. However, it has been found that the conversions which occur during the sintering, lead to alloys whose distribution in the sintered body is very irregular so that in the 'structure of the finished sintered body, a pronolmced concentration in this alloy can be found at indie vidual points, while it is completely lacking at other points. This irregular distribution naturally results in irregular hardness and porosity of the finished sintered body.

As a result of its uniform hardness and low porosity, the hard metal alloys according to the furthermore as the material used as the tips on measuring gauges or other parts subjected to much wear on machines and apparatus. The higher acid resistance of these alloys is also frequently advantageous. I

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. The method or making a sintered hard met-'- al composition which comprises mixing metal of the iron group with a compound which consists of about 1 to 5% carbon with the remainder metal from the group tungsten and molybdenum, heating said mixture to a temperature in the neighborhood of 1300" 0., crushing the resulting product and thereafter employing such product as a binder material for pulverized carbide particles, pressing the resulting mixture into a desired form and sintering it to thereby form a cemented carbide.

2. A sintered hard metal alloy. which consists of one or several carbides of metals with a high melting point and a metallic addition constituting at most 25% of the total alloy, said addi- WALTHER DAWIHL. KARL SCHRbTER.