A heat-resistant steel with excellent high-temperature strength-ductility based on a combination of solid-solution strengthening and precipitation hardening

Precipitation hardening and solid-solution strengthening are the most two effective strengthening mechanisms in the heat resistant martensite steel. However, it is difficult to maximize both mechanisms simultaneously because alloying elements may affect both mechanisms in different ways. Based on this challenge, a high-throughput CALPHAD method was used to design a steel with maximum strengthening effect by adjusting some elements in the steel, and then a heat resistant steel with the composition of 0.07C-0.09N-11Cr-4Ni-2.5Al-0.3Nb-10Co-0.17Ti was chosen. After normalizing and tempering treatment, the microstructure is composed of tempered martensite and ferrite, and high-density NiAl precipitates with ordered BCC structure and nano-sized MX (M, N; X C and N) precipitates are distributed uniformly. After aging at 650 °C for 500 h, the hardness of the alloy seldom decreases and stabilizes at 300 HV for the low coarsening rate of the precipitates. The designed steel has excellent high temperature tensile properties at 650 °C (yield strength 365 MPa, fracture elongation 98 %). The high yield strength can be attributed to the high precipitation strengthening and solid strengthening. While the good ductility is attribute to the excellent deformation coordination ability between ferrite and martensite matrix for the similar hardness.