Characterisation of Dispersed Nano‐Sulphides Precipitated in Low Carbon Steel Solidified under High Rate of Cooling

Abstract

The aim of this study was to investigate size distribution, chemistry, thermal stability and deformability of nano‐sulphides finer than about 100 nm formed in low carbon steel solidified under high rate of cooling and to assess the effect of the nano‐sulphides on the properties of steel. Laboratory mini‐ingots of low carbon steel containing various amounts of Mn, Cu and S, solidified under conditions simulating the direct strip casting process, were used as experimental material. Nano‐sulphides of MnS, (Mn,Cu)S, CuS, Cu2‐xS and CuS2‐x were identified in substantial quantities (volume fraction up to 3 ·10−4) using TEM techniques. It was shown that interaction between the nano‐sulphides and migrating grain boundaries of austenite occurred during annealing and in the course of thermomechanical processing resulting in grain refinement. Nano‐sulphides of MnS and (Mn,Cu)S type were also identified in significant quantities (volume fraction up to 6 ·10−4) in the shell and corner areas of commercial continuously cast billet.