GB575343A - Improvements in powder metallurgy - Google Patents

Abstract

575,343. Making coherent masses from metal powder. HARDY METALLURGICAL CO. March 10, 1944, No. 4521. Convention date, July 16, 1943. [Class 82 (i)] A process for producing steel powder for use in powder metallurgy comprises fritting a mixture of fine soft iron particles with fine ferrous alloy particles containing substantial proportion of combined carbon and then subjecting the fritted mixture to mild comminution to produce a powder that is substantially coarser than the original mixture. The soft iron powder may be produced electrolytically and the ferrous alloy powder may comprise cast iron powder or high carbon ferrochrome, all screened through 325 mesh. In one example, two parts by weight of soft iron powder and one part of crushed white cast iron powder containing 3.3 per cent carbon in the form of iron carbide all screened through 325 mesh are mixed for two hours and heated in an atmosphere of commercial hydrogen for five minutes at 800‹ C. and then cooled. The resulting fritted powder is screened through 100 mesh. For the production of steel objects from this powder, the powder is compressed in a die at 50 tons per square inch to form a compact mass which is sintered for one hour at 1200‹ C. in commercial hydrogen, cooled to room temperature, hardened by being heated to 1420‹ F. in a neutral salt bath and quenched in water. In a second example, 15 per cent crushed white cast iron powder containing 3.3 per cent carbon and 85 per cent electrolytic iron powder, all passing 325 mesh are mixed as before and heated in a hydrogen atmosphere for twenty-seven minutes at 750‹ C., cooled and screened through 100 mesh. Powders screened originally through 200 mesh instead of 325 mesh may be used.