Microstructure and mechanical behaviour of single pressed and vacuum sintered gas and water atomised 316L stainless steel powders

The present study concerns the microstructure and mechanical behaviour of 316L PM steels produced from gas and water atomised powders by single pressing and vacuum sintering. The gas atomised powder was agglomerated with an organic binder to allow pressing. After sintering at 1250 degrees C, the densification of the two materials is similar. Increasing the sintering temperature to 1350 degrees C results in a pronounced densification of the gas atomised powder caused by the formation of ferrite, resulting in improved mechanical properties. Sintering the water atomised powder at 1350 degrees C leads to limited densification and thereby less improvement of the mechanical properties. Prior particle boundaries with their oxides have a stiffening effect on the materials in the water atomised conditions with relatively sharp elastic/plastic transition. The gas atomised powder materials instead have a more diffuse yielding behaviour. The effective strain hardening, normalised by the relative density, was found to be virtually independent of porosity level, pore morphology, virgin powder, and prior particle boundaries. All materials studied continuously strain harden until final fracture and necking preceding fracture is weak.