Effects of heat treatment on microstructure, mechanical properties and corrosion resistance 13Cr-2Ni-2Mo martensitic stainless steel

Abstract

The effects of varying austenitizing and tempering temperatures on the microstructure, mechanical properties, and corrosion resistance of newly developed 13Cr-2Ni-2Mo martensitic stainless steel for marine and coastal applications were systematically investigated. The findings indicate that the highest hardness and optimal corrosion resistance are achieved with austenitizing at 1150 °C. This is due to the dissolution of carbides back into the matrix, which results in solid solution strengthening and an elevated chromium content within the matrix. The steel exhibits the highest hardness when subjected to tempering at 150 °C. As the tempering temperature increases, the dislocation density in the matrix decreases, and different carbides precipitate in the order of M₃C, M₇C₃, and M₂₃C₆. During the tempering process, reverse austenite forms along the boundaries of martensite laths, exhibiting the phenomenon known as the “austenite memory effect.” A competitive relationship between reverse austenite and carbides with regard to carbon has been observed. The precipitation of carbides at tempering temperatures of 450–500 °C results in secondary hardening. The 13Cr-2Ni-2Mo steel exhibits the most favorable corrosion resistance when tempered at 150 °C, with a corrosion current density of 5.50 × 10⁻⁷ A/cm² and a pitting potential of 0.307 V in a 3.5 % NaCl solution. As the tempering temperature increases, the precipitation of M₇C₃ and M₂₃C₆ carbides results in a decrease in the chromium content of the matrix. This leads to the formation of chromium-depleted zones and a looser passivation film structure, which in turn reduces the pitting resistance and corrosion resistance. This study systematically correlates heat treatment, microstructural evolution, mechanical performance, and corrosion behavior of 13Cr-2Ni-2Mo stainless steel, providing insights for optimizing its performance in marine and coastal applications.