Grain size distribution effects on the corrosion behaviour of materials

► Effect of grain size distribution on corrosion current has been studied. ► Mathematical relationship to understand this effect has been established. ► Broader grain size distribution leads to higher corrosion resistance in active environment. ► Broader grain size distribution leads to lower corrosion resistance in passivating environment. ► Effect of grain size distribution on corrosion behaviour of bimodal microstructure is discussed. While the effect of grain size refinement on the corrosion behaviour of materials is well studied, the effect of grain size distribution has not been explored. By utilising existing correlations between corrosion current and grain size, we derive relationships for corrosion current and grain size distribution. These relationships suggest that for the same average grain size, a broader grain size distribution leads to increased corrosion resistance in a non-passivating environment and vice versa in a passivating environment. These relationships are also used to predict the corrosion behaviour of bimodal microstructures.