Microstructural evolution of Cr–Mn–N austenitic steels during cold work hardening

The cold work behaviour and the evolution of the microstructure of a new high nitrogen alloyed CrMn austenitic steel were investigated in order to clarify, whether existing models can be used to explain the behaviour of this alloy. Tensile tests and detailed light-optical and transmission electron microscopy investigations were performed on the new alloy, Cr21Mn23N0.9 (mass%), and a standard alloy, Cr14Mn20N0.3. Samples were subjected to plastic strains up to 30% applied by uniaxial tensile tests. Despite presumed high stacking fault energy, dislocation slip in Cr21Mn23N0.9 was found to be strictly planar. Short range order phenomena are suggested to be the leading mechanisms for planar glide. The fraction of deformation induced constituents in the microstructure (mechanical twins and ɛ-martensite) was low with the exception of twins in alloy Cr14Mn20N0.3. The planarity of dislocation slip was identified as crucial importance with regard to the work hardening rate.