Hard-metal body

Abstract

The invention relates to hard-metal body comprising a hard-metal, the hard-metal comprising tungsten carbide grains and metal binder comprising cobalt having a concentration of tungsten dissolved therein, the body comprising a surface region adjacent a surface and a core region remote from the surface, the surface region and the core region being contiguous with each other; the mean binder fraction of the core region being greater than that of the surface region; the mean carbon concentration within the binder being higher in the surface region than in the core region; to tools comprising same and methods of making same.

1 . A hard-metal body comprising a hard-metal, the hard-metal comprising tungsten carbide grains and metal binder comprising cobalt having a concentration of tungsten dissolved therein, the body comprising a surface region adjacent a surface and a core region remote from the surface, the surface region and the core region being contiguous with each other; the mean binder fraction of the core region being greater than that of the surface region; the mean carbon concentration within the binder being higher in the surface region than in the core region; and the mean magnetic moment of the hard-metal in the surface region being greater than that in the core region; the hard-metal body being substantially devoid of eta-phase and free carbon; and the concentration in weight percent of tungsten dissolved in the binder in the surface region being less than that in the core region, the concentration in weight percent of tungsten dissolved in the binder being determined as (16.1−σ B )/0.275; σ B  being the magnetic moment of the hard-metal within a region of the hard-metal body divided by the binder weight fraction in the region. 
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . A hard-metal body as claimed in  claim 1 , in which the surface region is a layer or stratum integrally formed with the core region, the surface region having a thickness of at most 10 mm and at least 0.5 mm. 
     
     
         5 . (canceled) 
     
     
         6 . (canceled) 
     
     
         7 . A hard-metal body as claimed in  claim 1 , in which the mean binder fraction within the surface region is lower than that within the core region by a factor of at least 0.05 at most 0.90. 
     
     
         8 . (canceled) 
     
     
         9 . A hard-metal body as claimed in  claim 1 , in which the surface region is substantially devoid of chromium or vanadium or their carbides. 
     
     
         10 . (canceled) 
     
     
         11 . A tool insert for cutting, machining, drilling or otherwise forming or degrading a workpiece or other body, the tool insert comprising a hard-metal body as claimed in  claim 1 . 
     
     
         12 . A tool insert as claimed in  claim 11 , comprising polycrystalline diamond (PCD) or a polycrystalline cubic boron nitride (PCBN) structure joined to the hard-metal body. 
     
     
         13 . A tool comprising a tool insert as claimed in  claim 12 . 
     
     
         14 . A method of making a hard-metal body as claimed in  claim 1 , the method including providing an unsintered green body comprising grains of metal carbide dispersed within a metal binder, and a carbon content in the range from 95 percent to 99 percent of the stoichiometric content of carbon in the presence of the hard-metal in the metal binder; pre-sintering the green body at a temperature in the range from 1,000 to 1,280 degrees centigrade for a period of time in the range from 1 hour to 3 hours in a vacuum or inert atmosphere to form a pre-sintered body, the temperature being sufficiently low to avoid substantial melting of the metal binder and the temperature and time being sufficient to maintain open porosity within the surface region of green body; heat-treating the pre-sintered body in a carbon-containing atmosphere to form a carburised surface region having a carbon content in the range from 101 percent to 105 of the stoichiometric content; and liquid-phase sintering the pre-sintered body at a temperature in the range from 1,320 degrees centigrade to 1,400 degrees centigrade.