INJECTION-MOLDING OF GAS AND WATER-ATOMIZED STAINLESS-STEEL POWDERS

Gas- and water-atomized stainless steel powders of small particle diam eter 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, respective ly. The binder removal rate was established by measuring the weight de crease during heating of the components. Binder removal was performed in nitrogen gas at either 400 degrees C or 500 degrees C for times var ying from 4h to 23h. After debinding the specimens were vacuum sintere d at 1200 degrees C or 1250 degrees C for times ranging from 4h to 8h. Maximum tensile strength was obtained for the gas-atomized powder sin tered at 1250 degrees C. The tensile strength of the water-atomized po wder sintered at the same temperature was lower due to higher porosity Gas-atomized powder sintered to the same high porosity level as the w ater-atomized showed the same tensile strength values as the latter If was also shown that binder removal at the lower temperature (400 degr ees C), resulted in higher strength, due probably to a more effective reduction of the oxide by binder residuals during sintering.