Investigation of the effects of shallow and deep cryogenic treatment on the mechanical and microstructural properties of AISI 431 martensitic stainless steel

This study aimed to determine the effects of cryogenic treatment to increase the hardness, wear resistance, and tensile strength of AISI 431 martensitic stainless steel. After austenitizing, quenching, and tempering, the steel samples were subjected to shallow cryogenic treatment at −80 °C and deep cryogenic treatment at −180 °C. Samples were cryopreserved for 12 and 24 h in each case. Following these processes, a tempering heat treatment was applied at 200 °C for 120 min. Experimental results revealed that cryogenic treatment positively affected the mechanical properties of AISI 431 steel. Samples that underwent a 24-h deep cryogenic treatment, however, yielded the best mechanical characteristics. Wear resistance was most significantly affected by cryogenic treatment. Compared to the sample with only conventional hardening, the wear rate of the sample with deep cryogenic treatment for 24 h was 82% lower. Between shallow and deep cryogenic treatment types, samples treated with deep cryogenic treatment exhibited superior properties. In both species, longer cryogenic treatment holding time resulted in greater improvement in mechanical properties. Deep cryogenic treatment for 24 h provided approximately 5.61%, 7.49% and 1.75% increase in hardness, yield strength and tensile strength, respectively. In addition, cryogenic treatment has been shown to effectively reduce residual austenite, providing more homogeneous carbide distribution and new carbide precipitation.