Hot deformation behavior and microstructural evolution of as-cast Co-containing maraging stainless steels

A new type of maraging stainless steel (MSS) was developed by cobalt alloying technology to improve the strength and ductility of maraging precipitation hardening stainless steel. However, the effect of cobalt addition on the hot deformation behavior and the mechanism of microstructural evolution are still unclear. In this paper, therefore, hot uniaxial compression tests of two as-cast Co-free and Co-containing MSSs were carried out at temperatures of 950 °C–1150 °C and strain rates of 0.01–10 s −1 . A comparative study on hot deformation behaviors of Co-free and Co-containing steels had been conducted. The constitutive relations of flow stress, temperature and strain rate were established respectively, and the average deformation activation energy of the two steels under the present deformation region was identified (Co-free: 458.371 ± 27 kJ mol −1 and Co-containing: 379.024 ± 11 kJ mol −1 ). The processing maps for the two steels based on dynamic material model were generated to reveal the correlation between microstructural evolution and processing parameters. The regions of deformation stability and instability of the two steels were characterized respectively. In most working conditions, the power consumption of Co-containing steel was higher than that of Co-free steel. The dynamic recrystallization occurred in both steels under most conditions. The addition of cobalt promoted the dynamic recrystallization during hot deformation due to the reduction of the stacking fault energy of the matrix and to the suppression of dislocation climb and cross-slip.