Spallation analysis of oxide scale on low carbon steel

Abstract

Failure at the interface between a steel substrate and the oxide scale was analyzed by finite element simulations. Two major stress components along the interface, i.e., tensile normal stress at the peak and shear stress at the inflection point of the undulated interface geometry, were calculated and used for the analysis. The mechanical properties of the oxide scale and steel substrate were experimentally measured by indentation and by uniaxial tensile tests, respectively. The simulations consist of cooling from 1000°C to room temperature to predict residual stresses accumulated during cooling, followed by additional four-point bending to represent the uncoiling process. The two major stress components were amplified by the roughness of the interface and by the residual stress generated by thermal mismatch between the oxide and the steel substrate during cooling. In addition, the shear stress was proved to be a significant factor for the spallation behavior; this fact had not been well recognized in the previous literature. The finite element simulation showed that the severity of the fracture-inducing stress components increases as the oxide thickness and the period of the idealized undulation decrease; the severity also increases as the amplitude of the roughness increases.