Hard-metal body
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 method of making a hard-metal body, the method including the steps of:
pre-sintering an unsintered green body at a temperature in the range from 1,000 degrees centigrade 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, to form a pre-sintered body having open porosity within the surface region of the pre-sintered body, wherein the unsintered green body comprises 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;
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 percent 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 to form the hard-metal body.
2. The method according to claim 1 , wherein the method is carried out in the absence of a grain-growth inhibitor or precursor thereof being applied to a surface of the green body or the pre-sintered body prior to the liquid-phase sintering step.
3. The method according to claim 1 wherein the hard-metal body comprises a hard-metal, the hard-metal comprising tungsten carbide grains and metal binder comprising cobalt having a concentration of tungsten dissolved therein, and the body comprises 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.