Precipitation and Strengthening Behavior of M23C6 Carbides in Tempered G115 Steel

High-Cr martensitic heat-resistant steel has been widely used in high-parameter thermal power units because of its excellent mechanical properties and oxidation resistance. Microstructure evolution and mechanical properties of G115 steel after different tempering were investigated. Meanwhile, the precipitation and strengthening behavior of M23C6 carbides is also systematically discussed. The results show that the precipitation of M23C6 carbides during tempering causes obvious precipitation strengthening, and that the contribution of M23C6 carbides to yield strength first increases and then decreases with the increase in tempering temperature, which is consistent with the variation of actual yield strength. From this point of view, M23C6 carbides are the major factor that governs the yield strength of tempered samples. The maximum precipitation of M23C6 carbides and the maximum degree of precipitation strengthening occur with tempering at 740 °C, and the corresponding size of M23C6 carbides is 0.106 μm.