Effect of Silicon on AHSS As-Cast Microstructure Development and Properties

Abstract

This work linked properties and performance in as-cast condition for 3rd generation advanced high strength steel (AHSS) by examining the effects of chemical composition and microstructure on mechanical properties. Elevated levels of carbon, manganese, and silicon in new AHSS grades lead to a complex evolution of microstructure during solidification that can lead to castability problems. Three lab cast ingots with 0.2 wt% C, 3 wt% Mn, and 0.5, 1.5, and 3 wt% Si were characterized by their microstructure and mechanical properties. Light optical microscopy (LOM) and Scanning Electron Microscopy (SEM) confirmed that the microstructure of steels was mostly granular bainite, with some proeutectoid ferrite allotriomorphs at 3 wt% Si. Tensile testing showed Si increased strength and that ductility of all samples was low. Higher silicon levels were found to promote formation of proeutectoid ferrite allotriomorphs and changed the cracking propagation behavior. Some comparisons between the observed microstructures and those expected in continuously cast slabs were also discussed.