Improved strength of a medium -Mn steel by V addition without sacrificing ductility

Here, we investigated the effects of adding a micro-alloying element to medium-Mn steel and explored why a resulting sample containing precipitates exhibited higher strength than one without precipitates, without sacrificing ductility. The model alloys comprised steels of Fe-8Mn-0.2C-3Al-(0, 0.2)V (wt.%); they were cold-rolled and intercritically annealed at identical temperatures between 670 and 730 degrees C for 30 min. These annealed steels exhibited two-phase microstructures consisting of ferrite (alpha) and retained austenite (gamma(R)), with a nanoscale globular morphology. Smaller grain sizes and lower volume fractions of gamma(R) were observed in the V-containing specimen, relative to the V-free specimen, owing to the formation of VC precipitates. The latter were mostly formed in the alpha phase, rather than in the gamma(R) phase. These VC precipitates meant that the V-containing steel showed a lower C concentration in gamma(R) and a higher C concentration in alpha than the V-free steel. We propose that such phase compositions enhanced the strain hardening rate during the later stage of mechanical loading due to more active twinning-induced plasticity and dynamic strain aging. These effects resulted in the observed higher tensile strength in the V-containing steel, without sacrificing ductility.

Automated summary

By adding a micro-alloying element and forming precipitates, the steel exhibits higher strength without sacrificing ductility compared to steel without precipitates. The formation of precipitates changes the microstructure of the steel and enhances the strain hardening rate, leading to higher tensile strength.