Effect of surface nanocrystallization on the sensitization and desensitization behavior of Super304H stainless steel

• Nano-crystallization accompanied by stress-induced α′-martensite during shot peening was analyzed by TEM.
• Classical and martensite-induced sensitizations were distinguished by DL-EPR test.
• Martensite was blamed to have increased the degree of sensitization (DOS) at 600 °C.
• Shot peening treatment could shorten the finishing time of sensitization.
• The self-healing of shot-peened Super304H happened in a much shorter time of 2 h at 700 °C.

An attempt has been made to understand the sensitization and desensitization behavior of the shot-peened Super304H during aging around service temperature. The results show that strain-induced α′-martensite was blamed mainly for the significant increase of the degree of sensitization (DOS) of shot-peened Super304H when aged at 600 °C. However, the DOS decreased greatly when aged at 650 °C for 24 h or 700 °C for 2 h, indicating a faster self-healing process of chromium depletion zones due to long range Cr diffusion enhancement by surface nanocrystallization and also the reverse transformation of α′-martensite to austenite at the same time.

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