Evaluation of stress corrosion cracking susceptibility of nanocrystallized stainless steel 304L welded joint by small punch test

A small punch test (SPT) was carried out to evaluate the stress corrosion cracking (SCC) susceptibility of nanocrystallized stainless steel (SS) 304L welded joint in 1 mol/L NaCl + 0.5 mol/L HCl aq. The surface mechanical attrition treatment (SMAT) was applied to realize the surface naocrystallization (SNC). Mechanical properties and micro-structural evolutions of S nanocrystallized SS 304L welded joint were investigated through optical microscopy (OM), X-ray diffraction (XRD), micro-Vickers hardness test and transmission electron microscopy (TEM). The SPT was conducted in both ambient air and corrosive solution at the loading rate 3 × 10−3 mm/min, and SNC phenomena were observed at the welded seam (WS) and heat affected zone (HAZ) after SMAT. The results show that for both HAZ and WS materials, specimens with 30 min SMAT have higher hardness, higher yield strength, and lower ductility than the as-received counterparts in ambient air. After SPT in the corrosive solution, the as-received HAZ specimen showed a mixed type of both the intergranular SCC (IGSCC) and transgranular cleavage fracture; The SMAT sample shows a typical intergranular stress corrosion cracking (IGSCC) mode with a higher SCC susceptibility. Neither the as-received nor the SMAT WS specimen showed significant SCC susceptibility, they had the similar fractures with their counterparts in ambient air.