The mechanical properties of Ni-containing PM steels are always inferior to those of their wrought counterparts due to the non-uniform Ni distribution and the porosity. To improve the microstructure and mechanical properties, the mechanism of the formation of Ni-rich areas was investigated, and a method to resolve this problem is proposed in this study. The results indicated that the poor Ni distribution was caused mainly by the strong repulsion between Ni and C, in addition to the slow diffusion rate of Ni in Fe. The addition of Cr, either by using Cr-containing prealloyed base powders or by adding stainless steel powder into iron powders, was found to successfully alleviate this repulsion effect. With a more uniform Ni and C distribution, the Ni-rich ferrite, which was weak and was prone to fracture during mechanical testing, was replaced by Ni-rich martensite. Thus, the mechanical properties of the Ni-containing PM steels were much improved.
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