Effect of grain ultra-refinement on corrosion behavior of ultra-high strength high nitrogen stainless steel

[Display omitted] •Strength and corrosion resistance of cold-rolled stainless steel were improved.•Uniform ultrafine-grained microstructure (∼300 nm) was achieved by water-cooled FSP.•Grain ultra-refinement significantly improved repassivation ability.•Increased element content of passive film improved pitting corrosion resistance. High-performance high nitrogen stainless steel (HNS) with ultra-high strength up to ∼1.7 GPa and excellent corrosion resistance was successfully obtained by friction stir processing. The simultaneous enhancement in strength and corrosion resistance was mainly attributed to the grain ultra-refinement. Uniform ultrafine-grained microstructure (∼225 nm) significantly improved the repassivation behavior of HNS. With significantly increased element diffusion rate and element content, the passive film formed on the ultrafine-grained HNS showed high resistance to the nucleation and growth of pits. Grain ultra-refinement was confirmed to be an effectual method for improving corrosion resistance of HNS without sacrificing strength.