Analysis of the Local Plastic Deformation of the Surface Oxide Layer formed on Low-Alloy High-strength Steel

The microstructure of the tertiary oxide scale formed on the surface of low-alloy steel and local strains in three different regions were characterized by electron backscatter diffraction. Local strains of four different phase grains of hematite, magnetite, wustite, and ferrite in these three regions were systematically evaluated. A higher strength misorientation was detected around cracks of the oxide scale. On the surface of the oxide scale and the interface seam layer, Fe3O4 had a lower average local orientation difference than Fe2O3. Small spherical Fe3O4 crystal grains accumulated at the interface between the oxide layer and the steel matrix, resulting in a sharp increase in local strain, and it could be attributed to the phase transformation of magnetite during nucleation and growth processes. During high-temperature deformation, the stress released at the interface caused a different misorientation distribution at the joint seam layer. The quantification of the spatial distribution of local plastic strain in the microstructure of the tertiary oxide scale provided a good insight into the nature and distribution of crystal defects in the oxide scale, helping in controlling the formation of oxide scales during high-temperature hot rolling.