Effect of surface nanocrystallization induced by mechanical grinding treatment on stress corrosion cracking behavior of 316 L austenitic stainless steel in boiling MgCl2 solution

The effect of surface nanocrystallization prepared by surface mechanical grinding treatment (SMGT) on stress corrosion cracking (SCC) behavior of 316 L austenitic stainless steel was studied in boiling MgCl₂ solutions at 155 °C and 130 °C, respectively. The refined-grain structures of different morphologies produced by three different SMGT penetration depths were employed to assess how different microstructures and corrosive environments affected the SCC behavior of nanocrystallized surfaces. Results showed that in the 155 °C boiling MgCl₂ solution, the refinement of grains resulted in an increase in the critical stress for SCC initiation and progressively enhanced the ability to inhibit crack propagation with the SMGT penetration depth increasing from 20 μm to 60 μm. In the 130 °C MgCl₂ solution, the grain refinement still contributed to resisting crack propagation, but the threshold stress for SCC initiation on the surface with the deepest SMGT penetration depth of 60 μm was lower than that in the 155 °C MgCl₂ solution. This behavior was attributed to the significant martensitic phase transformation formed in SMGT with penetration depth of 60 μm, resulting in the mechanism of SCC transforming from anodic dissolution in MgCl₂ solution at 155 °C to hydrogen embrittlement at 130 °C.