Orientation gradient on surface of non oriented electrical steel annealed by g a transformation
The microstructures and textures of the non oriented electrical steel sheets under various annealing conditions were investigated. The orientation gradient in the interior of grains appeared on the surface of steel sheets after a g a transformation in various atmospheres. The orientation gradient that appeared on the surface was inherited into the center of the steel sheet in H 2 atmosphere, while that appeared only in the grains of the surface layer during g a transformation with N 2 atmosphere. The thin oxide scale was generated in various atmospheres containing traces of O 2 and H 2 O. The formation mechanism of orientation gradient is related to the thermal stress caused by the difference of thermal expansion coefficients between the oxide scale and the thin ferrite on the surface. The combined effect of phase transformation stress and thermal stress caused the plastic deformation of the thin ferrite grains on the surface in the initial stage of g a transformation, and then the orientations of the thin ferrite grains gradually rotated and caused the orientation gradient in the interior of grains.
Journal of Iron and Steel Research International