Effect of grain size on the corrosion resistance of low carbon steel

Systematic works on the effect of grain size on the corrosion resistance of low carbon steel are scant. In the present work, a spectrum of grain sizes was obtained by simple heat treatment routes in a typical low-carbon steel. It was revealed that two distinct stages for the dependency of corrosion current density (i(corr)) on the grain size exist. Above a limiting average grain size of similar to 22 mu m, i(corr) decreased slowly with increasing grain size. However, below this limiting value, i(corr) increased rapidly, which was related to the increased density of grain boundaries as interpreted by theoretical calculation of number of grains per unit area. Conclusively, a grain size of similar to 22 mu m (ASTM grain-size number of 8) was considered to be an optimum value according to the mechanical and corrosion standpoints.