Simulation of corrosion of a dual phase alloy steel based on its constituent phase polarization properties

Abstract

In this study, the corrosion of dual phase alloy steel namely super duplex stainless steel (SDSS) is simulated by taking into consideration the presence of two distinct phases that are austenite and ferrite. A simulation algorithm is developed by the authors for simulating micro galvanic corrosion by random assignment of anode and cathode zones assuming non-linear polarization curves. The governing equation for electric potential in the electrolyte is Laplace equation owing to charge neutrality implying diffusion limited corrosion rate. The metal-electrolyte interface is allowed to dissolve as a moving boundary problem approach in a computer simulation by assigning ferrite property to anode and austenite property to cathode randomly. To validate this proposition, the true non-linear polarization data and its fluctuations in the form of fitted Butler–Volmer expressions of individual phases of the SDSS alloy are used as the boundary condition on anode and cathode zones corresponding to ferrite and austenite phases. This modeling approach is applied to pure austenite as SS304 and pure ferrite as SS430 and 50–50 austenite-ferrite as SDSS. The obtained simulation results of corrosion rate of the SDSS and its constituent pure phases compared well with the direct polarization prediction of corrosion rate for various concentrations of NaCl in water. The simulation prediction is found to be a good fit than by weighted average method.