Effect of post-forging heat treatment on stress corrosion cracking of nuclear grade 316LN stainless steel in boiling MgCl₂solution

Effect of post solution- and stress relief- treatment on the stress corrosion cracking (SCC) resistance via U-bend specimens test in 42% boiling MgCl₂solution, as well as the microstructure, residual strain and mechanical properties of the forged 316LN stainless steel was studied. Results showed that the yield stress was reduced and the residual strain was eliminated through post solution-treatment for the forged steel. After immersion in boiling MgCl₂solution for 24, 48 and 72 h, respectively, all the U-bend specimens of either the solution-treated or the stress relief-treated steels suffered from clearly transgranular stress corrosion cracking (TGSCC). Furthermore, of which all the stress relief-treated specimens were entirly cracked, while the solution-treated specimens were only locally cracked after immersion for 72 h, suggesting higher SCC resistance for the forged steel after a proper post solution-treatment. Finally, the mechanism of the effect of post-heat vtreatments on the SCC resistance was discussed in terms of the residual strain and yield stress of the forged steel.