Evolution of Precipitates During Rolling and Annealing Process in Non-Oriented Electrical Steel

Precipitates in slabs, hot-rolled plates, cold-rolled plates, and annealed plates of a non-oriented electrical steel were investigated by automatic scanning electron microscope (ASPEX) and field-emission scanning electron microscope. The composition, size, and number density of precipitates were analyzed. Thermodynamic analysis was performed by FactSage^@7.1. The calculated precipitation temperature of MnS and AlN were 1218.5 °C and 1186.7 °C, respectively. Due to their similar precipitation temperatures, AlN and MnS always co-precipitated and formed complex precipitates. The analysis results by ASPEX also revealed that precipitates increased sharply in hot-rolled plates. In slabs, co-precipitates of AlN-MnS were relatively less and larger, for the cooling rate during continuous casting was very low. It is deemed that part of precipitates would re-dissolve during reheating process and tended to precipitate along the dislocation line during the hot-rolling process. After the cold-rolling process, AlN tended to be broken, while MnS particles showed plastic deformation along the rolling direction.