Effect of Vanadium-Alloying on Microstructural Evolution and Strengthening Mechanisms of High-Nitrogen Steel Processed by High-Pressure Torsion

Abstract We study the effect of high-pressure torsion on the microstructure, phase composition, microhardness, and strengthening mechanisms of high-nitrogen austenitic steels with different vanadium content: Fe-23Cr-19Mn-0.2C-0.5N, Fe-19Cr-21Mn-1.3V-0.3C-0.8N, and Fe-18Cr-23Mn-2.6V-0.3C-0.8N, wt %. Regardless of the chemical composition of the steels, high-pressure torsion (HPT) causes the refinement of their microstructure due to a high density of dislocations, twin boundaries, and shear bands. Vanadium alloying decreases the stacking fault probability in the structure of the steels and changes their dominating deformation mechanism under high-pressure torsion: from planar dislocation slip and twinning in the vanadium-free steel to dislocation slip with a tendency to shear band formation in the vanadium-alloyed steels. An increase in the vanadium content forces precipitation hardening. Thus, after HPT, the V-alloyed steels have a higher microhardness as compared to the vanadium-free one. Different strengthening factors (strain hardening, solid solution hardening, and precipitation strengthening) govern the value and kinetics of growth of microhardness of the steels processed by high-pressure torsion. Vanadium alloying and increasing its content result in the growth of the contribution of precipitation hardening and decreases strain hardening of high-nitrogen steels.