Evaluation of stress corrosion cracking susceptibility of stainless steel 304L with surface nanocrystallization by small punch test

In this study, the small punch test (SPT) was conducted to evaluate the stress corrosion cracking (SCC) susceptibility of stainless steel (SS) 304L with surface nanocrystallization (SNC) in 1 mol/L NaCl+0.5 mol/L HCl aq. The surface mechanical attrition treatment (SMAT) was applied to realize the SNC. The mechanical property and micro-structural evolutions of SS 304L induced by SMAT were investigated through optical microscope (OM), X-ray diffraction (XRD), micro-Vickers hardness and transmission electron microscopy (TEM). The grain size on the surface of the material was reduced to 30-100 nm. The SPT was conducted in both ambient air and corrosive solution. The results were investigated by OM and scanning electron microscopy (SEM), showing that in ambient air, the specimen with 30 min SMAT performed a higher yield strength and lower ductility than the solution annealed (SA) counterpart. The SS 304L without SMAT presented a transgranular SCC (TGSCC) mode in chloride solution. In contrast, the SNC 304L SS showed a higher SCC susceptibility with a typical intergranular SCC (IGSCC).