Spark plasma sintering of nitrogen-containing nickel-free stainless steel powders and effect of sintering temperature

Abstract

Nitrogen-containing nickel-free austenitic stainless steels were fabricated by spark plasma sintering technique at the various temperatures of 1073 K, 1173 K and 1273 K in vacuum for 480 s under the pressure of 40 MPa. Two kinds of stainless steel powders, with a mean particle size of 55 μm (powder A) and 27 μm (powder B), respectively, were employed in this work. The density of the sintered specimens was measured by the Archimedes method, and nitrogen content in the materials was also analyzed. The phase identification was investigated by X-ray diffractometer, and the fractographies were performed by scanning electron microscopy. The mechanical properties such as hardness, tensile strength were also investigated. The results indicated that the density of SPS sintered stainless steels increased with the rise of sintering temperature, and relative density of 98.99% for A-series specimens and 99.78% for B-series specimens sintered at 1273 K were obtained. SPS sintered specimens showed relatively high nitrogen content owing to the connection of the role of Mn on austenitic steels with the quick cooling capability of SPS system. Nitrides and ferrites were completely disappeared and fully austenitic structures were obtained at the suitable sintering temperature of 1073–1273 K. Both series specimens showed maximal ultimate tensile strength and the yield strength at 1173 K, and maximal Vickers hardness at 1273 K.