Effect of Tempering Temperature on Carbide Evolution and Mechanical Response of Deep Cryogenically Treated Martensitic Stainless Steel

Deep cryogenic treatment (DC) is widely applied to martensitic stainless steels to suppress the presence of metastable retained austenite (RA), which may otherwise transform into brittle martensite under deformation and degrade mechanical performance. In this study, a low-carbon 13Cr-2Ni-2Mo martensitic stainless steel was subjected to deep cryogenic treatment for 2 h, followed by tempering at 200–600 °C to investigate carbide evolution and its correlation with mechanical response. At 200 °C, undissolved M23C6 was observed, accompanied by an RA volume fraction of 8.43% which exhibited a hardness of 543.3 ± 5.1 Hv. When tempered at 400 °C, M3C became predominant, corresponding to a hardness of 524.5 ± 5.1 Hv. At 500 °C, the simultaneous precipitation of M3C, M7C3, and M23C6 carbides induced pronounced secondary hardening, which promoted the peak hardness of 559 ± 5.6 Hv. Further tempering at 600 °C resulted in carbide spheroidization M23C6, which resulted in a hardness reduction to 392.2 ± 3.9 Hv while enhancing ductility. These findings reveal that the tempering temperature plays a decisive role in controlling the carbide precipitation sequence and the stability of retained austenite, thereby enabling the design of an optimal strength–ductility balance in deep cryogenically treated martensitic stainless steels.