Densification behavior is investigated by means of dilatometry for powder-injection-molded (PIM) and die-compacted 17-4 PH stainless steel during sintering in pure H 2 and H 2 ϩ N 2 . The corresponding microstructural evolution is examined by quenching in a vertical furnace at various stages of sintering. The results show that in comparison with pure H 2 , the H 2 ϩ N 2 atmosphere retards densification and produces a lower shrinkage rate above 1220 ЊC. The X-ray diffraction (XRD) analysis reveals the presence of a stabilized austenitic microstructure during H 2 ϩ N 2 sintering. In pure H 2 , however, ␦ ferrite forms and grows above 1220 ЊC, producing a higher shrinkage rate. In terms of the atomic diffusivity, ␦ -ferrite formation is beneficial to pore shrinkage and densification.

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