Surface nanocrystallization induced by shot peening and its effect on corrosion resistance of 1Cr18Ni9Ti stainless steel

The nanocrystalline microstructure in the surface of 1Cr18Ni9Ti stainless steel induced by high-energy shot peening has been characterized by means of X-ray diffractometry and transmission electron microscopy. The effects of shot peening on corrosion resistance of the steel have been investigated by polarization curves and pit corrosion tests, and the surface morphologies of the corrosion samples have been characterized by scanning electron microscopy. The results show that shot peening can cause surface nanocrystallization; that is, a nanocrystalline microstructure with an average grain size of ∼ 18 nm forms in the surface layer of the sample, and furthermore, can induce α-martensite of about 15% in volume fraction. With increasing depth from the shot-peened surface, the grain size increases, but the volume fraction of the α-martensite decreases. The surface nanocrystallization can improve the potentiodynamic polarization behavior of 1Cr18Ni9Ti stainless steel in 3.5% NaCl solution. Comparing to the as-received coarse crystalline counterpart, the passive film on the surface of the shot-peened sample is easier to form and more stable. Shot-peening-induced surface nanocrystallization can markedly enhance the corrosion resistance of 1Cr18Ni9Ti stainless steel in the chlorine–ion-contained solution.