Laser surface melting for improving intergranular corrosion resistance of cold‐worked and sensitised type 316 stainless steel

This study used laser melting techniques to improve the intergranular corrosion resistance of cold worked and sensitised stainless steel surfaces. Type 316 stainless steel specimens, cold worked to 5 per cent, 10 per cent and 20 per cent reductions in thickness values, were sensitised at 923K for 25 hours. These specimens were laser‐surface‐melted by using a 300W Nd:YAG pulsed laser, and tested according to ASTM A262 practice A and practice E tests. The results of the practice A test showed that a cellular‐dendritic structure was present in the laser‐melted region in contrast to a typical ditch microstructure observed for sensitised unmelted specimens and a ditch structure was not present in the melt‐affected zone (MAZ). The hardness measurements across the melted, MAZ, and unmelted zones showed significant variations in their values. The results of the practice E tests showed no intergranular cracks for laser‐melted specimens while the unmelted specimens (5 and 10 per cent cold working) failed the test through significant cracking. The improvement in IGC resistance is attributed to the dissolution of M₂₃C₆ carbides and the homogenisation of chromium‐depleted regions.