Electrochemical potentiokinetic reactivation study of laser-surface-melted 3CR12 steel

Laser surface melting (LSM) of ferritic/martensitic 3CR12 steel, using a 3 kW CW Nd:YAG laser with a line beam profile, provides improvement in the resistance to pitting corrosion in chloride-containing solutions to an extent dependent upon the final microstructure. In particular, LSM parameters that transform the dual-phase banded microstructure of the hot-rolled and annealed steel to a mainly ferritic structure generate relatively large increases in pitting potential. Under conditions of slower cooling, associated with smaller improvements of pitting potential, significant amounts of martensite, which is re-formed at ferrite grain boundaries, remain in the melted layer. Such regions, with reduced chromium content, are preferred sites for initiation of pits. The present study employs electrochemical potentiokinetic reactivation (EPR), using 0.1 M H2SO4 solution, to detect the presence of martensite in the laser-melted steel, and also chromium-depleted regions along the grain boundaries. Thus, the techniq...