Effect of hot rolled grain size on the nitride precipitation and recrystallisation in cold rolled aluminium-killed steel casting production

摘要

In this paper the effect of hot roiled grain size on the nitride precipitation and recrystallisation has been analysed in cold rolled aluminium-killed low carbon steel.The hot rolled sheet used for experiments showed layered grain structure: the grain size was quite different within the thickness of the sheet.In the near surface regions (on both sides) larger grain size was present than in the centre of the sheet.The three regions (two near surface, large grain size regions and a central small grain size region) are markedly separated.The hot rolled sheet cold rolled with 75％ thickness reduction and the effect of initial (hot rolled) grain size on the nitride precipitation and recrystallization has been analysed on continuously heated specimens.According to the experimental investigations and computer simulations,the hot rolled grain size strongly influences the recrystallisation process, but has not significant effect on the nitride precipitation.Beside the initial grain size, the effect of heating rate on the nitride precipitation during industrial annealing has been also investigated.According to the simulation results, if the nitride precipitation reaches approx.45 ～ 60％ before the beginning of the recrystallisation, then a good deep drawable microstructure forms during the annealing process.