Spindle speed in friction surfacing of 316L stainless steel - How it affects the microstructure, hardness and pitting corrosion resistance

Using friction surfacing (FS), stainless steel 316L coatings were successfully fabricated on 304 substrates. The spindle speed employed in FS was found to have a more significant effect on the microstructure of the coating surface than that in the cross-section. Compared with the as-received 316L consumable rod, hardness improvement was observed in FSed coatings owing to dynamic recrystallization (DRX) during FS. Moreover, the pitting corrosion resistance of the FSed coatings was enhanced by the severe plastic deformation (SPD), which fragmented the micro-sized MnS inclusions in the consumable rod into inconspicuous size after FS. From the immersion test, pits were gathered in {111} grains of the coatings, and the inferior pitting resistance of the {111} grains could be attributed to their lower stacking fault energy. They sustained considerable elastic strain during FS, and generated a higher residual tensile stress that led to pitting. For the coatings fabricated at a moderate spindle speed (1500 rpm), discontinuous DRX became dominant and the recrystallized random orientated grains weakened the {111} texture, resulting in the highest pitting resistance. However, the pitting corrosion resistance improvement induced by the crystallographic effect of different spindle speeds was less prominent comparing with that caused by MnS inclusion fragmentation. Moreover, the advancing side of the FSed coatings was plastically deformed severely, leading to a stronger {111} texture than in other places, which restricted the pitting corrosion resistance enhancement of entire FSed coating.