Injection molding of gas and water-atomized stainless steel powders

Gas- and water-atomized stainless steel powders of small particle diameter were injection molded with a binder consisting of polyolefins and low melting waxes. The critical powder loadings for injection molding were 65 and 56v/o for the gas- and water-atomized powders, respectively. The binder removal rate was established by measuring the weight decrease during heating of the components. Binder removal was performed in nitrogen gas at either 400°C or 500°C for times varying from 4h to 23h. After debinding the specimens were vacuum sintered at 1200°C or 1250°C for times ranging from 4h to 8h. Maximum tensile strength was obtained for the gas-atomized powder sintered at 1250°C. The tensile strength of the water-atomized powder sintered at the same temperature was lower due to higher porosity. Gas-atomized powder sintered to the same high porosity level as the water-atomized showed the same tensile strength values as the latter. It was also shown that binder removal at the lower temperature (400°C), resulted in higher strength, due probably to a more effective reduction of the oxide by binder residuals during sintering.