Relationship between work hardening behaviour and deformation structure in Ni-free high nitrogen austenitic stainless steels

The work hardening behaviour of high nitrogen austenitic steel (HNS) depends not only on the nitrogen content but also on the addition of substitutional alloying elements such as Mn and Ni, although the effect of nitrogen content has been considered to be a main factor controlling the work hardening rate in HNS. In this study, two kinds of high nitrogen austenitic steels containing nearly 1 mass-% of nitrogen with and without Mn (Fe-25%Cr-1.1%N and Fe-21%Cr-0.9%N-23%Mn alloys) were tensile-tested and their work hardening behaviour was investigated for the purpose of clarifying the effect of Mn on the work hardening behaviour. Then the results were related to the change in deformation substructure. In the Fe-25Cr-1.1N alloy, the work hardening rate kept high until fracture occurred, while in the Fe-21Cr-0.9N-23Mn alloy it tended to decrease gradually with tensile deformation in the high strain region. It was concluded that the difference in work hardening behaviour between both alloys is attributed to the change in dislocation substructure from planar dislocation array to dislocation cell by the addition of Mn.