Effect of Silicon Content on the Microstructure and Mechanical Properties of Dual-Phase Steels

Abstract

An experimental investigation was conducted using laboratory-processed, low carbon 0.08C–2.0Mn–0.2Cr–0.15Mo steels with different Si contents to evaluate the influence of Si additions on the mechanical properties and microstructure of dual-phase steels. The heat treatment was carried out in a salt bath furnace to heat the samples between 720 and 860 °C; samples were held isothermally for 60 s, followed by air cooling or water quenching. This was accomplished by evaluating the formation of austenite at various intercritical temperatures during annealing and its decomposition during subsequent cooling. It was found that Si addition accelerates the recrystallization of ferrite during heating in the intercritical temperature range, which in turn promotes the formation of austenite through the nucleation process, followed by grain growth. Addition of Si favors the formation of a homogeneous austenite of higher hardenability resulting in a higher volume of martensite in the final structure. Thus, a silicon-bearing steel has been demonstrated to possess a higher strength in comparison with Si-free steel.