Influence of Si content on the microstructure and mechanical properties of silicon stainless steel

The influence of Si addition on the microstructure and mechanical behavior of cast silicon stainless steel alloys was investigated. It was recognized that after incorporation of Si in the range of - 2-6 wt%, microstructure changes significantly. It transforms from single-phase austenitic to duplex microstructure containing ferrite and austenite. In addition, TiC precipitates with angular and spherical morphology were observed in all the sample conditions. Uniaxial tensile tests suggested that the incorporation of Si improved the strength and ductility as long as the microstructure remains primarily austenitic. However, at much higher silicon content (-6 wt%), microstructure transformed to duplex structure, followed by the drastic reduction in ductility and toughness. Overall, the alloy with -4 wt% Si exhibited comparatively better strength, ductility as well as toughness. The mechanical properties of the individual phases, characterized using nanoindentation, indicated that the hardness and modulus of the austenite phase improved significantly after Si incorporation up to -6 wt%. Concomitantly correlation between the mechanical properties and crystallographic orientation of grains was also established by performing post-nanoindentation EBSD analysis. The results indicated that the average hardness and modulus of each phase are significantly related to the crystallographic orientation of grains, i.e., it is highly anisotropic. Finally, the nanomechanical properties of the individual phases were utilized to predict and compare the bulk mechanical properties using the ECM model. A reliable quantitative comparison between nanomechanical and bulk mechanical properties of alloys with single-phase microstructure was obtained, whereas a more refined ECMs are required for envisaging the bulk characteristics of the materials with duplex microstructure.