US2108797A - Method of producing hard cemented carbide composites - Google Patents

Description

and lapping thereof in much the same manner as hardened and overtempered steel. By increasing the hardness and strength f the presiritered material, the diillculties which have previously precluded its satisfactory grinding into ne razor edges is removed and advantage can be taken of a condition of the material which permits of its being worked into these shapes very much as steel iscustomarily fabricated into the usual razor blade.

. Accordingly, objects of my invention are to provide: a novel hard cemented carbide; a novel process for making a hard cemented carbide; a

Y novel hard cemented carbide razor blade; novel of control of the composite in the pre-sintered several hours.

and/or final sintered stage; the step in the process which comprises increasing the compacting pressure applied to the comxninuted composite previous to sintering; the step of oxidizing the binding metal during mixing; the step of producing an oxide coating of the cementing mate-A rial around the hard carbide particles; and the employment of an auxiliary binding metal'in the process to provide temporary hardness, or any combination of these steps in the process.

Ihere are other objects of my invention which, together with the foregoing, will appear in the detailed description which is to.follow.

In practising my invention, I mix the hard f metal carbide and cementing metal or metals in powdered form in Aa metal rolling barrel filled with metal balls or rods. This is completed in Heretofore, it has been the prac.- tice during this operation to prevent oxidation of the powdered cementing metal by illling the barrel with water or a neutral or reducing gas. In accordance with my invention, I, quite the contrary, contemplate a slight oxidation of the cementing metal. Accordingly, during this mix-` ing, I heat the barrel slightly and introduce oxygen in order to slightly oxidizethe binding metal which thus forms an oxide illm around. the car-- bide particles.

Subsequently, on the application of further heat with a reducing agent as will be described hereinafter, the oxide illm will be re` duced after compacting and during the pre-sintering treatment will cement the carbide producing a considerable increase in the hardness and strength of the material. L Y

The degree of heat employed and the duration of this oxidizing treatment will vary with the materials used. I have found, however, that using tungsten carbide, for example, as a hard carbide constituent and 10% by weight of metallic cobalt in powdered form as a cementing material that a barrel temperature of from 200 to 400 F. and

an oxidizing period of about an hour with theintroduction of three liters of oxygen' at atmospheric pressure is sufilcient to produce satisfactory results.

economy although rectangular billets or other. forms can be used. I employ apressure 0f fr0!!! 60,000 to 200,000 pounds per square inch or even A greater pressures, depending upon the materials used and the type of blade which is to be made. In the usual practice, pressures of from 10,000 to 60,000 pounds per square inch are used. As a means of furthering the even application of these high pressures, I have found it advisable to employ a lubricant such as parailln or c amphor,- treating the powders with these materials in such carrying mediums as carbon tetrachloride or benzene as is the common practice.

I may, if desired, employ an auxiliarymetal of lower melting point than the cementing metal or metals, although this is not always necessary as the other steps of my process are sufilcient'for the production .of blades of some types. vIn that use, I generally introduce the auxiliary metal in A powdered form atthe same time as the cementing metal, but it can be added either before or after the oxidizing process just described depending upon the type of the auxiliary metal which is used. The function of this auxiliary metal is to cement the particles of hard carbide and the rparticles or pelliclesof the cementing metal or be used, In selecting them, care must be exeri cised to combine them suitably with the true cementing metals if they are to remain as an alloy of the ultimate metal matrix. Copper can be used satisfactorily with nickel or cobalt as an auxiliary metal in a cemented tungsten carbide composition for example. In making a composition of this kind I would, for example, mix the following powdered components in the manner which has been described, adding the copper powder after the oxidizing period: tungsten carbide, by weight; cobalt or nickel, 7% by weight; copper. 3% by weight. v

I may, on the other hand, employ an auxiliary metal such as silver in conjunction with a true cementing metal such as nickel with which it doesnot alloy. Or under some circumstances, I may use zinc which melts at al low temperature and is volatile before the melting point of 'such metals as cobaltor nickel.

A suitable composition entailing the use of silver would be: tungsten carbide, 87% by weight; nickel, 1% by weight; silver, 6% by weight. If zinc is usedl aisuitable composition `would be: titanium carbide, 87%; nickel, 9%;

zine, 4%. n should be understood 'that these examples are given for illustration purposes only and that the scope of my invention is not -limited to beused depends upon the character of the blade which is to be produced, the composition of the hard cemented carbide material which has been selected and the auxiliary metal, if any, which is employed in the production of a suitable pre-sintered state of hardness, strength and cohesion.

As the suitable metals have a wide variety of melting points, I prefer an upper limit of just below the melting point of the true cementing metal or alloy. For example, with a cobalt ce- 50 f' pounlds per square inch depending upon the in the composite.

to 200,000. pounds per square inch depending upon the material used, and applying a presintering temperature just below the melting point of the cementlng metal and reducing the oxides formed 10. In the presintering process 'for producing hard cemented carbides, the steps of controlling the hardness of the presintered composite which comprises mixing tungsten carbide and powdered metallic cobalt, heating the composite in an oxidizing atmosphere, -compacting the. composite at a pressure above 60,000 pounds per square -inch depending upon the metals used, and applying' a presintering temperature just vbelow the melting point of the metallic cobalt and reducing' the oxides formed in the composite.

11. In the presinteri'ng process for producing Vhard cemented carbides, the steps of controlling the hardness of the presintered composite which comprises mixing a, hard metal carbide and a cementing metal in powdered form, heating the I'. composite to a temperature of 200 to 400 F. in an lso oxidizing atmosphere, compacting the composite at a pressure above 60,000 pounds per square inch, and applying a presintering temperature just below the melting point of the cementing metal .and reducing the oxides formed in the composite.

l2.` In the presintering process for producing hard cemented carbides, the-steps of controlling the hardness of the presintered composite whichcomprises mixing a hard metal carbide and a rst cementing metal in powdered form, heating the composite in an oxidizing atmosphere, compacting the composite at a, pressure above 60,000

pounds per square inch depending upon the metals used, cementing the metals with a powdered metal added with the rst cementing metal and having a lower melting point than the rst cementing metal for transient binding before working the composite, and applying a presintering temperature just below the melting point of the rst cementing metal and reducing the oxides formed in the composite.

13. In the presntering process for producingV hard cemented carbides, the steps of controlling the hardness of the presintered composite which comprises mixing a hard metal carbide and a rst cementing metal in powdered form, heating the composite in an oxidizing atmosphere, compacting the composite at a pressure above 60,000

metals used, adding together with the iirst cementing metal a metal which alloys withlthe first cementng metal and melts atjf'a-lower temperature to bind the composite forworking, and applying a presintering temperature just below the melting point of the ilrst cementlng metal and reducing the oxides formed'jin ythe composite.

14. In.the presintering process for producing hard cemented carbides, the steps of controlling' the hardness of the'presintered composite which comprises mixing a hard metal carbide and a rst cementing metal in powdered form, heating the composite in an oxidizing atmosphere, compacting the composite at a pressure above 60,000 pounds persquare inch depending upon the metals used, adding together with the rst cementing metal a cementing metal whichA volatilizes below the melting point of the rst cementing metal, and applying a presintering tempera-y ture just below the' melting point ofthe first cementing metal and reducing the oxidesrformed in the composite.

15. In the prcsintering process .foi-1; producingy hard cemented carbides, the steps offontrolling the hardness of the presintered composite which comprises mixing a hard metalk Acarbide as tungsten carbide 94% and a first cementing metal in powdered form as cobalt 6%, heatingthe composite in an oxidizing atmosphere, compacting they f composite at a pressure above 60,00054 pounds per square inch depending upon the. metals used, cemcnting the metals with a powdered metal added with the iirst eementing metal and having a.y

lower melting point than the rst cenienting metal for transient binding before'working the pounds per square inch, and applying a presintering temperature just below the melting point of the cementing metal and reducing the `oxides formed in the composite.

GREGORY J. COMSTOCK.