Pitting corrosion behavior of friction-surfaced 17-4PH stainless steel coatings with and without subsequent heat treatment

Improvement in pitting corrosion resistance of the friction-surfaced (FSed) 17-4PH stainless steel coatings was mainly attributed to fragmentation of sulfide inclusions during friction surfacing (FS). Formation of vermicular δ-ferrite and grain refinement of martensitic matrix around the δ-ferrite affected the distribution of pits. FS parameters had a negligible effect on the pitting corrosion resistance of the FSed 17-4PH coatings. However, the decrease in pitting corrosion resistance of the FSed coatings after aging (H900) was due to the higher dislocation density for facilitating the metastable pit initiation and promoting the transition of metastable pits to the stable ones.