Mechanical properties of sintered austenitic stainless steel—effect of silicon addition

Abstract

The effect of the addition of elemental silicon to austenitic stainless steel powder on the mechanical properties of sintered specimens was investigated. It was recognized that the addition of silicon powder to sintered stainless steel affects the pore morphology, microstructure, mechanical properties and corrosion behaviour. Second phase, ferrite, formation within the austenite matrix was not observed up to a silicon content of 4 wt.% when sintering in dissociated ammonia at 1120 °C. At a higher sintering temperature of 1280 °C, ferrite started to form at a content of 2.5 wt.% silicon. The ferrite fraction rises sharply at a silicon content of 4 wt.%, increasing the hardness of the specimens, while a decrease in the elongation values was observed. The pore morphology improved owing to the formation of a transient liquid phase, yet the residual porosity exhibited large rounded pores. The established ultimate tensile strength (UTS) and yield point (YP) values are lower than in austenitic stainless steel sintered without any additive, owing to the basic mechanical properties of the ferritic (b.c.c.) phase. Although the specimens exhibited a transient liquid phase mechanism, an overall detrimental effect was observed on the mechanical properties. The addition of coarse grain silicon powder degrades the mechanical properties and the corrosion resistance of the specimens but increases the hardness of the individual grains. The addition of fine grain silicon powder leads to better properties, mainly corrosion resistance.