Corrosion behavior of cold-rolled and post heat-treated 316L stainless steel in 0.9wt% NaCl solution

The effect of cold rolling and post-rolling heat treatment on the microstructural and electrochemical properties of the 316L stainless steel was investigated. Two-pass and four-pass cold-rolled stainless steel specimens were heat-treated by annealing at 900°C followed by quenching in water. During the cold rolling, the microstructure of the as-received specimen transformed from austenite to strain-induced α′-martensite due to significant plastic deformation that also resulted in significant grain elongation (i.e., ~33% and 223% increases in the grain elongation after two and four rolling passes, respectively). The hardness of the heat-treated as-received specimen decreased from HV 190 to 146 due to the recovery and recrystallization of the austenite grain structure. The cyclic polarization scans of the as-rolled and heat-treated specimens were obtained in 0.9wt% NaCl solution. The pitting potential of the four-pass rolled specimen was significantly increased from 322.3 to 930.5 mV after post-rolling heat treatment. The beneficial effect of the heat treatment process was evident from ~10-times-lower corrosion current density and two-orders-of-magnitude-lower passive current density of the heat-treated specimens compared with those of the as-rolled specimens. Similarly, appreciably lower corrosion rate (3.302 × 10⁻⁴ mm/a) and higher pitting resistance (1115.5 mV) were exhibited by the post-rolled heat-treated specimens compared with the as-rolled 316L stainless steel specimens.