US2171391A - Process of producing hard materials - Google Patents

Description

Patent A PROCESS OF PDU ker, Bielerhoi, Biel, Switzerland, as- -.,.r S, A, Biol, switzfir- Alfred signer land No-Drag. Application March. 19, 1937, Serial No. 131,959. in Switaerland March 25, 1936 3 Claims.

This invention relates to a process for the production of a so-called hard metal.

According to the process of this invention at least two metals of groups No, Va and VB: of the periodic system of elements or compounds thereof are mixed in a finely divided state with at least one metalloid, which is capable of forming a hard material with at least one of the metals and the mixture is thereafter heated at a temperature of from 1500 to 2000" o.

The hard metals or materials hitherto known are as a rule produced from one or more very hard but in themselves extremely brittle metal carbides, silicides, borides and the like, as primary substances. The carbides and the like are for'this purpose produced individually and are then mixed in the desired proportions with the addition of an auidliary metal as cementing agent, shaped and sintered at a temperature slightly above the melting point of the auxiliary metal. Hard metals as aforesaid, which it is attempted to make as tough as possible, have hitherto not been nearly tough enough to enable the industry concerned to employ them for all existing operations. Thus they are still to be regarded as being extremely brittle as compared with high speed steels and for this reason the latter have hitherto still been employed for operations, in which the metals are subjected to powerful impacts, as in planing, milling, etc. The aforementioned undesirable properties which are still possessed by the hard metal hitherto produced are to be sought for in their synthesis. The known hard metalsconsist of extremely fine carbide etc. dust, which has a high melting point and is combined to a solid mass with as small a quantity as possible of another very finely divided metal, for example a metal of the iron group, particularly nickel or cobalt, which has and auxiliary metal can of course only be heated to the temperature at which this binding or auxiliary metal .melts. The molten auxiliary metal, provided that it has been well distributed when using known additions of 5 to 6%, in this process to a certain extent constitutes the binding mass, which cements these extremely fine carbide particles together. If it were possible to dissolve out the hard fine carbide particles from this whole mass, a fine skeleton .-of this auxiliary metal would remain, somewhat resembling the honeycomb from abeehive. It is accordingly abundantly clear that the auxiliary meta do s a considerably lower melting point than carbide etc. The moulded mixture consisting of carbide not play the part of a component which becomes alloyed with the actual hard metal materials, but only constitutes one component of a mixture so that the hard metal produced always retains the brittleness of the original starting materials. 5

The process of the present invention may be carried into effect by first weighing the desired proportions of the substances, which are to be used for synthesising the hard metal, pouring 10 them together and thoroughly mixing. The resulting mixture, if desired after shaping and pressing, may then be introduced into an electrical furnace and be heated therein, if desired in an atmosphere rich in oxygen, to-a tempera- 15 ture of from 1500 to 2000 0., depending upon the composition of the mixture. By heating to these temperatures for a suitable time, which may amount up to 10 hours, hard materials are formed consisting of carbides, borides, silicides 2 etc. depending upon the nature of the substances selected. The reaction mass may thereafter be very finely comminuted and finally shaped into small pieces, the size and shape of the latter depending on the tools or instruments to be 25 manufactured therefrom. These shaped bodies are then again heated within the above temperature range and can then be further worked up in known manner into tools or instruments.

The following are examples of suitable starting 80 mixtures:

Tungsten, vanadium and carbon,

Tungsten; titanium and carbon,

Tungsten, titanium, vanadium and carbon,

Tungsten, tantalum, titanium and carbon, 35

Tungsten, tantalum, niobium and carbon.

The mixtures may contain silicon or boron, in place of carbon, in which event hard silicides or borides are formed.

The quantity of metalloids to be added is as a rule the theoretical quantity for any given case. An excess, particularly of carbon, would easily give rise to free carbon (graphite) in the end product, which would in turn considerably reduce the strength of the carbides and conse- 5 quently the strength of the hard metal. It could even be unquestionably proved that a'smaller" quantity of carbon in the carbide than corresponds to the theoretical quantity would cause the formation of a still tougher carbide.

, If, in place of one oii the metals, a metal compound, for examplean oxygen compound, is employed, a hard material of particularly great hardness and toughness is obtained. Thus in a mixture of tungsten, vanadium and carbon, the

vanadium may for example be replaced by vanadic acid. In this case however the quantity of carbon added must be increased, since the vanadic acid would first be reduced by carbon to vanadiumwith the formation of carbon dioxide. Since metallic tungsten is present in this case there is formed immediately after the reduction of the vanadic acid to vanadium, a tungsten vanadide, which with increasing temperature in the electric furnace is then carburised. When employing titanic 'acid instead of titanium a tungsten titanide is formed with the tungsten and in this way a number of further mixtures can be produced.

The common thermal treatment of several metals with hard material-forming metalloids renders possible the formation of alloys between the initial materials and/ or the end materials before, during or after the formation of the hard materials, whereby hard metals are formed, which possess special valuable properties with regard to toughness and hardness over the hitherto known hard metals. cases, where the amount of metalloid, for example carbon, added is below thetheoretical quantity, or oxygen compounds are co-employed, hard metals result, which owing to their content of complex compounds possess a toughness hitherto not obtained together with great hardness.

The production of 'hard metal according to the process. of the present invention may accordingly be effected in one single operation, whereas hitherto the hard materials were as a rule first prepared individually, comminuted and the individual particles cemented together by an auxiliary metal.

The process according to this invention enables much more uniform distribution of the individual substances to be effected, then in the hitherto known processes.

Since according to the process of this invention the mixing possibilities are very great and all metals of groups I Va, Va and Wu of the periodic system may-be successfully employed for the synthesis of the hard metal, gradations between relatively great and relatively slight toughness can be very easily produced. Such gradations are desirable for working up corresponding materials of great hardness and strength down to tough and soft materials, which, 'as is known, can never be as satisfactorily'worked up as hard metals.

The economy of the process of this invention deserves to be particularly emphasized. For the production for example of tungsten carbides, tem

peratures of from 1400" to 1800 C. are required, for the production of titanium carbidestemperatures of about 2300 C. and for the production of vanadium carbides temperatures of from- 2300 to 2500 C. If however such carbides are produced in admixture according to the process of this invention the operation can be conveniently Particularly i carried out below 2000 C. The production of temperatures above 2000 C.-subjects electric furnaces and the heating elements thereof to great strain. These heating elements are very costly and very frequently burn out and must therefore be interchanged, whereas at temperatures below 2000 C. at least ten times greater security of working for these heating elementsis ensured.

The following are a few analyses of hard metals produced by the process according to this invention:

The carbon contents of both products are slightly less than the theoretical quantities.

- What I claim is:

1. Process of manufacturing a hard metal consisting of the steps of mixing pulverized tungsten and an acid selected from the group consisting of vanadic and titanic acids,'with a quantity of carbon below that theoretically required to form the carbides of the metal components and in an amount of from about 8% to 13%, heating the mixture at 1500 to 2000 C. to form a compound of tungsten selected from the group consisting of tungsten vanadide and tungsten titanide respectively, and to carburlze said tungsten compound, finely pulverizing the product. forming shaped bodies thereof, and heating the shaped bodies at 1500 to 2000 C.

2. Process of manufacturing a hard metal consisting of the steps of mixing pulverized tungten, and vanadic acid with a quantity of carbon below that theoretically required to form carbides of the metal components and in an amount of from about 8% to 13%, heating the mixture at 1500 to 2000 C, to form tungsten vanadide and to carburlze said tungsten vanadide finely pulve g the product, forming shaped bodies thereo and heating the shaped bodies at 1500 to 2000 C.

pulverizing the product, forming shaped bodies thereof, and heating the shaped bodies'at' 1500 to 2000 C. K