Influence of hydrogen-charging on microstructure and microhardness of high-nitrogen austenitic steel processed by high-pressure torsion

The influence of hydrogen-charging on microstructure and microhardness of a high-nitrogen austenitic Fe– 19Cr–21Mn–1.5V–0.3C–0.8N (wt. %) steel processed by high-pressure torsion (HPT) was investigated. X-rays diffraction data indicate that hydrogenation of HPT-deformed specimens leads to an additional broadening of X-rays lines and their shifting, which testify to the formation of the stacking-faults and high residual stresses. Hydrogen-charging of HPT-processed steel promotes to γ–e martensitic transformation. Due to hydrogen-induced phase hardening, the microhardness of HPT-deformed specimens increases up to 6.8 GPa in hydrogen-charged condition (6.5 GPa in hydrogen-free one). After following exposure of hydrogen-charged specimens for 170 h at air condition, the release of hydrogen atoms occurs, and the X-rays lines shift back to positions corresponded to hydrogen-free HPT-processed specimens.