Phase-Field Simulation of Stress Corrosion Cracking in Stainless Steel

Abstract

Stress corrosion cracking (SCC) sometimes occurs in stainless steels, which are used for steam turbines of geothermal power plants. In order to prevent SCC that causes serious accidents in the plants, understanding the SCC behavior through experiments and numerical simulations is essential. Phase-field (PF) method is one of the widely used numerical simulation methods to analyze various microscale-material phenomena including electrochemical reactions such as corrosion. In this study, we have developed a new PF model for simulating a SCC behavior in a stainless steel, which includes the stress concentration at the propagating crack tip, diffusion and electrophoresis of ions in the liquid solution. The PF model is based on the PF model for general and pitting corrosion in a pure iron [C. Tsuyuki et al., Scientific Reports, Vol. 8 (2018), 12777.], which incorporates the Butler-Volmer equation. The stress evolution during the SCC is calculated by solving the mechanical equilibrium equation by means of fast Fourier transform. The diffusion and electrophoresis of ions are analyzed by solving the Nernst-Planck equation. Through the numerical simulations of SCC in a polycrystalline stainless steel which have a notch, we revealed that the crack growth rate increase in accordance with the stress intensity factor. The results have proved the crack proceeds through the grain when the elastic strain energy at the crack tip is high, and it propagate through the grain boundary when the low energy.