The impact of silicon on the solidification of duplex lightweight steels

Abstract

Efforts are being made worldwide to transform road transport to minimise its contribution to greenhouse gas emissions, with a focus on reducing vehicle mass. Lightweight manganese–aluminium steels have gained popularity for this purpose due to their low density and combination of strength and plasticity. In this particular study, the solidification process of five lightweight manganese–aluminium steels with different silicon content was investigated. The steels were fabricated by inductive melting in a vacuum and remelted during further thermal analysis. A reference steel composition (Fe-14Mn-10Al-0.2Si-0.8C) was used, and the remaining four steels contained different amounts of silicon (0.5, 1.0, 2.0 and 4.0 mass%). The impact of silicon on solidification was analysed by thermodynamic calculations (CALPHAD method), differential thermal analysis and optical microscopy. The thermodynamic calculations gave good estimates for the liquidus and austenite liquidus temperatures, but higher solidus temperatures than the experimental results. The presence of silicon decreases the density and lowers the solidus and liquidus temperatures, resulting in a prolonged solidification interval. In addition, the spacing of the secondary dendrite arms decreases, except at a silicon concentration of 0.5 mass%, where an increase was observed compared to the reference steel.