Effect of microstructure and microtexture evolution of oxide layer over J82B steel on mechanical descaling properties

Abstract

The oxide layer covering a high-carbon steel wire rod must be efficiently removed to form ‘a well-adhered yet easy-to-remove oxide scale’ during the mechanical descaling process. In this study, the relationship between the microstructural characteristics of the oxides and the efficiency of mechanical descaling was investigated. An electron backscatter diffraction analysis was conducted prior to bending and microscratch testing to clarify the microstructural discrepancies, namely, the phase distribution and texture orientation of the oxide constituents within the oxide scale system over the steel wire rod. The oxide scale system exhibits a double-scale layered structure, primarily consisting of FeO and Fe3O4. The low-angle and low-Σ coincident site lattice (CSL) boundaries in the Fe3O4 grains inhibit crack propagation without diffusion interactions, supporting oxide spallation in the large flake state during descaling. However, if the Fe3O4 grains were distributed along the boundary between the oxide scale and the iron substrate and had a high orientation consistency with the α-Fe grains, the grown oxide scale spalled into fine fragments, and a considerable amount of oxide scale residue firmly adhered to the descaled steel specimen. Stress relief and ion vacancy diffusion mechanisms govern the growth of Fe3O4 grains near the surface and at the interface of the matrix. These results provide guidelines for adjusting the oxide scale heterogeneity of high-carbon steels to improve their descaling performance.