Microhardness Homogeneity and Microstructure of High-Nitrogen Austenitic Steel Processed by High-Pressure Torsion

The authors investigate microhardness homogeneity and microstructure of the high-nitrogen austenitic steel Fe-23Cr-19Mn-0.2C-0.5N (wt %) subjected to high-pressure torsion. High-pressure torsion causes a significant increase in the microhardness of steel from 300 HV in the initial state up to 600 HV after torsion for one full revolution. Experimental results reveal a homogeneous distribution of microhardness values across the discs after deformation for N = 1/4 revolution. The control of the top and bottom surfaces of steel specimens shows that microhardness radial distributions are independent of the side of the specimens (position of a moving plunger during plastic deformation). Under high-pressure torsion, the spacings between twin boundaries decrease, while the dislocation density increases. The formation of a twin net in high-nitrogen steel in high-pressure torsion for N = 1/4-1 revolutions provides a homogeneous distribution of microhardness across the discs under torsion.