Effects of C and N on high-temperature deformation behavior of 15Cr-15Mn-4Ni austenitic stainless steels

The effect of interstitial C and N atoms on high-temperature deformation behavior was investigated in 15Cr-15Mn-4Ni austenitic stainless steels containing 0.1-0.3 wt% of either C or N. Single-hit compression tests were performed in the deformation temperature range 800-1100 degrees C and the strain rate range 0.01-1 s- 1. In both C-added (+C) and N-added (+N) steels, the high-temperature strength, i.e. mean flow stress, increased as the concentration of C or N increased. At the same level of C or N concentration, the mean flow stress, activation energy for high-temperature deformation, and degree of lattice expansion were larger in +N-steels than in +Csteels, whereas the dynamically recrystallized grain size and grain growth rate were larger and faster in +C-steels than in +N-steels. The higher strength of +N-steels over +C-steels at a wide range of temperatures was attributed to the stronger solid solution hardening effect of N atoms compared to C atoms. Dynamic recrystallization was relatively retarded in the +N-steels, because N atoms interacted strongly with grain boundaries.