Effect of sintering atmosphere on structure and properties of austeno-ferritic stainless steels

Prealloyed 316L and 430L stainless steel powders along with Cu, Cr, Mo and Ni have been used to produce different austeno-ferritic stainless steels through powder metallurgy route. Cylindrical green compacts of 30 mm diameter and 12 mm height have been made at three different compaction pressures and sintered in nitrogen and argon atmospheres at 1350 °C for 4 h, to study the effect of sintering on densification behaviour and mechanical properties. Stainless steels sintered in argon atmosphere exhibited better densification rate than the nitrogen atmosphere sintering. The microstructure of stainless steel sintered in nitrogen atmosphere revealed lamellar constituents with grain boundary Cr2N in ferritic matrix. Composition A (50 wt% 316L + 50 wt% 430L) of austeno-ferritic stainless steel sintered in argon atmosphere showed bi-phase structure with high strength and better elongation. The XRD patterns are in line with the microstructure. The ferrite content was measured by ferrite scope and is coherent with the strength and structures.