Although thin slab-direct hot rolling process is expected as a future process of steel sheet production, its metallurgy has not been investigated thoroughly. In this paper, the metallurgy of mild steel in thin slab-direct hot rolling process has been discussed with special attention to the precipitation behavior of MnS and its influence on the hot-cracking at the edge of hot bands and the mechanical properties of cold rolled low carbon steel sheets. The following results are obtained :
1. The hot-cracking resistance and mechanical properties of cold rolled sheets produced through thin slab-direct hot rolling process are not inferior to those produced through a conventional process, if S content is reduced and/or proper heat treatment prior hot rolling is carried out.
2. The experimental findings indicate that MnS precipitates under a condition of the local equilibrium at the MnS/γ interface.
3. The hot-cracking is probably caused by the remelting reaction of austenite at grain boundaries occupied by sulfur. For explaining the experimental findings, not only the equilibrium but also the kinetics of the diffusional reaction must be considered for the remelting process.
