Tensile strain hardening behaviours of nitrogen strengthening high manganese austenitic cryogenic steel

The strain hardening behavior of 32Mn-7Cr-1Mo-0.3N austenitic steels was investigated and characterized. The results show that Hollomon relationship is inapplicable. The value of n increases with increasing true strain e. However, after the value of true strain is larger than 0.2, the value of dn/de at 77 K is obviously higher than that at other temperatures, and the value of d2σ/de2 at 77 K becomes positive, which results in the high strain hardening rate and elongation increasing at 77 K. The micro mechanisms are proposed to be the coordination of the forming rates of twins and the interactions between twins and dislocations with strain hardening rates. Subsequently, the necking is delayed and the ability of uniform deformation is obtained.