Influence of the machined surface roughness on the pitting behavior of 304 stainless steel

The relationship between specimens with different machined surface roughness and pitting resistance was explored using the critical pitting temperature (CPT), critical pitting potential (E-p), and FeCl3 pitting immersion tests. Compared with the arithmetic mean deviation of the surface contour (Ra), the depth-width ratio could characterize the mathematical relationship between the machined surface roughness and pitting parameters more simply. With an increase in the depth-width ratio, the CPT and E-p of 304 stainless steel decreased, the average corrosion rate increased, the number of pits decreased, and the pit sizes increased. A larger depth-width ratio led to a larger effective diffusion length of metal cations in the pits, thus, the critical pitting criteria could be reached easily, which resulted in the reduction of the pitting resistance of 304 stainless steel.