Study on the development of cold rolled grain oriented steel

Abstract

Cold rolled grain oriented (CRGO) steel is a Fe-Si alloy which is commercially produced for the application in transformer cores. A thin sheet of CRGO steel is manufactured by following hot rolling, cold rolling, and various intermediate annealing steps. In the final steps, primary and secondary recrystallization annealing is carried out where coarse Goss ({110}<001>) oriented grains are deliberately grown via abnormal grain growth phenomenon. However, the development of Goss orientation is still not completely understood. Furthermore, higher silicon concentration in electrical steel is beneficial in reducing magnetostriction and eddy current losses, but cracks can develop during cold rolling of Fe-Si alloy having more than 3 wt. % Si. In the present investigation, three Fe-Si alloys with 3.78 wt.%, 3.23 wt.% and 2.98 wt.% Si have been prepared in vacuum induction furnace. The microstructure and crystallographic texture after different stages of processing have been characterized using various experimental techniques such as Electron Backscatter Diffraction (EBSD), X-Ray Diffraction (XRD) etc. Analytical stress and crystallographic texture have been predicted using Finite Element Method (FEM) and crystal plasticity based analysis, respectively. Edge crack and alligator crack have been found to develop during cold rolling of Fe-3.78 wt.% Si. The FEM based stress analysis suggests that tensile stress along normal and rolling direction may evolve during cold rolling, which could be sufficient to develop such cracks. Also, the possibility of crack formation during cold rolling increases with increasing Si content. Hot band annealing and intermediate annealing treatment between cold rolling passes were found to be helpful in eliminating these cracks.