Influences of Nb-microalloying on microstructure and mechanical properties of Fe–25Mn–3Si–3Al TWIP steel

Highlights: • The yield strength of Fe–25Mn–3Si–3Al steel is greatly improved by Nb microalloying. • The strength is improved with the help of grain refinement and precipitation strengthening. • Precipitation is controlled in the nanoscale by heat treatments. • The occurrence of TWIP effect ensures a satisfactory ductility to the modified steel. - Abstract: The Fe–25Mn–3Si–3Al TWIP steel was microalloyed by niobium in this paper, and the appropriate heat treatment and cold rolling processes were drafted in order to improve the poor yield strength of the steel. The results show that the yield strength of the steel increases from 320 MPa to 445 MPa, and the tensile strength increases from 680 MPa to 795 MPa, but the uniform elongation decreases from 65% to 55%. Nb addition can strongly hinder the growth of recrystallized grains, moreover Nb atoms react with C atoms to form nanoscale NbC precipitations, and these precipitations can block the dislocation motion, and then the yield strength and initial work hardening ability of Fe–25Mn–3Si–3Al steel is clearly improved. Furthermore, the strain-induced twinning is still a major deformation mechanism for the Nb-microalloying TWIP steel, and the twinning induced plasticity (TWIP) effect ensures a satisfactory ductility for the steel. Finally, the modified TWIP steel obtains a better match between the strength and plasticity by the joint action of precipitation strengthening and TWIP effect.