On the Hot Deformation Behavior of a Ni-Free Austenitic Stainless Steel Interstitially Alloyed with Low Nitrogen Content

Hot deformation behavior of a Ni-free, Fe-17Cr-12Mn-0.28N-0.06C (wt.%) austenitic stainless steel, hereinafter coded as FeCrMnN, was investigated using hot compression tests conducted under different deformation conditions comprising temperature and strain rate ranges of 800-1200 degrees C and 0.01-10s(-1), respectively. While the hot deformation at high strain rate and low temperatures (e.g., 10s(-1) and 800 or 900 degrees C) showed essentially dynamic recovery, resulting in a pancake-shaped microstructure, most of the other conditions exhibited occurrence of dynamic recrystallization (DRX). Increasing deformation temperature and decreasing strain rate showed a decrease in the critical stress and strain for initiating DRX. In general, DRX resulted in extensive microstructural reconstitution and grain refinement. For instance, hot deformation at 1000 degrees C/0.01s(-1) resulted in a fully recrystallized fine-grained microstructure with an average grain size of about 15m in comparison with the initial grain size of 60 mu m. Increasing the temperature enhanced grain growth, but an increase in strain rate resulted in a finer grain structure. The amount of delta ferrite in the present steel varied under different conditions of deformation such that the lowest amount of delta ferrite (about 4.5%) was observed at 1000 degrees C. The activation energy of deformation (Q(def)) for the present FeCrMnN steel with the initial grain size of 60 mu m was estimated to be about 502kJ/mol, which is higher than that of the conventional austenitic stainless steels.