Effect of Reducing Nickel and Increasing Nitrogen on Microstructure and Thermoplasticity of 18Cr-5Ni Stainless Steel

Thermodynamic balance calculation of 18Cr-5Ni stainless steel was performed by using Thermal-Calc2020a thermodynamic software,and hot compression test of 18Cr-5Ni stainless steel added with 0.24wt% N was tested by Gleeble-1500D thermal simulator. The stress-strain curves of hot compression in the range of deformation temperature of 1273-1473 K and strain rate of 0.01-10 s^-1 were measured. The constitutive equation of high temperature plastic deformation was constructed by the Zener-Hollomon parameter method.The metallographic structure of hot compression deformation was studied. The results show that nitrogen promotes the formation of single austenite structure of 18Cr-5Ni stainless steel; nitrogen has a strengthening effect on the tested steel.Dynamic recrystallization characteristics exist in the stress-strain curves.The activation energy of thermal deformation after adding nitrogen is 475.24 kJ/mol. Nitrogen addition promotes carbon nitride precipitation, and nitrogen delays the dynamic recrystallization process of the steel.Dynamic recrystallization is easy to occur at high temperature and low strain rate.