US2076366A - Hard carbide composition - Google Patents

Description

Patented Apr. 6, 1937 I IUNITEDISTATES PATENT, OFFICE HARD CARBIDE COMPOSITION Hugh S. Cooper; Cleveland, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Application September 28, 1935. Serial No. 42.711

' 2 Claims. (01. 75-136) In the making of tool bi ts, forming dies, draw- ,carbide melts well below the melting point of ing dies, and the like, hard carbides are extensiveeither constituent. This mixture is thoroughly 1y used, especially the carbides of tungsten and liquid at a. temperature of about 2475 C. while tantalum. These carbides are extremely diflicult its constituents melt at considerably higher 5 to melt, and when solidified from the melted state points, vanadium carbide at 2750 C., and 5 they are porous, coarsely crystalline, and lack molybdenum carbide at 2960 C. strength. For these reasons they are usually fab- Besides providing a very liquid melt at a temr'icated' by mixing the powdered carbidewith a perature that is comparatively low for carbides, powdered metal of ,comparatively low melting this mixture has other properties desirable in a point, such as cobalt, nickel, or iron, and then substance of this kind. The cast material is 10 pressing into the required shape and heating solid, dense, and strong, and shows no segregauntil the metal fuses and cements the carbide tion. Its hardness, as nearly as can be deter particles together. The shapes that can be promined is at least equal to, and probably greater duced by this process are somewhat limited and than that of tungsten carbide. It produces castthe process is not at all as simple as a casting ings having a sharp definition of outline. It can 15 process. I be cast in the pure state, or if desired additions Attempts have also been made to cast mixtures of cobalt or'the metals of the iron group can be of carbide with cementing metal, such as cobalt, made. If such additions are made there is no nickel or iron, but unless the carbide content is segregation, as with tungsten carbide, apparently made prohibitively small the casting temperature because the specific gravities of the carbides and 20 of the mixture is so high (well above 2500 C.) the added metal are very nearly equal.

as to render the process commercially imprac- In the practice of this process the two carbides ticable. Furthermore the great difference in are prepared in finely powdered form. The respecific gravity between cobalt and the tungsten quired vanadium carbide has a carbon content carbide, which usually are employed, is so great of about 18% while the molybdenum carbide conthat segregation and lack of uniformity occur in tains about 6% of carbon. The two powders are the resulting composition. thoroughly blended in a ball mill, and then sifted An object of the present invention is to overthrough bolting cloth. To facilitate handling, the come the foregoing difliculties by providing a carsifted powder can then be pressed into briquettes bide composition that has a melting point within of any convenient shape. The pressed briquettes 30 practicable limits. are then placed in a crucible of carbon or graphite Another object of the invention is to provide and heated in a furnace having a reducing atmosa carbide composition which is strong, dense, and phere. An electrical resistance furnace having a hard, in the cast condition. tubular carbon or graphite resistor serves quite Still another objector the invention is to prowell, and a reducing atmosphere can be main- '35 vide a carbide composition which can be fabritained by thepassage of either carbon monoxide cated directly into useful shapes by a process of or hydrogen, preferably the latter, through the casting. faumace. .If a binding metal is desired it can be The metallic carbides as a class are among the added to the melt. Castings can be made in car- 40 most'refra'ctory of materials and therefore canbon or graphite molds. 40

not be conveniently melted for casting. This is What I claim as new and desire to secure by especially true of the very hard carbides used in Letters Patent of the United States, is:

the manufacture of metal cutting tools. While 1. A cast alloy consisting hiefly f molybdemetals may be combined to form alloys which Illlm Carbide and Vanadium carbide, d carhave melting points lower than their constituents, bides being present in said alloy in substantially 45 this is not generally true of carbides. Thus, acequal parts by weight, the remainder of said cording to the scientific literature, mixtures of alloy consisting of metal of the iron group. tantalum carbide with zirconium carbide or haf- 2. A cast alloy consisting of substantially equal nium carbide both melt above the melting point parts by weight of molybdenum carbide and 5 01' either constituent. I have discovered howvanadium carbide.

ever, that a mixture of approximately equal parts HUGH S. COOPER. by weight of vanadium carbide and molybdenum