Investigating the microstructure and mechanical properties of vanadium bearing Delta-Trip Steel

Many researchers have investigated the effect of alloying elements on the properties of high-strength steels. Vanadium is of great importance due to its positive effect on solid solution strengthening, precipitation hardening, and grain boundary refinement, but the effect of this element on the properties of delta-trip steel has not been investigated independently, therefore, in this reserch, the effect of adding 0.12 and 0.25 wt.% vanadium on the microstructure and mechanical properties of a Delta-TRIP steel has been studied.  The structure of the three steels before applying the heat treatment cycle consisted of delta-ferrite, allotriomorphic ferrite, martensite, and pearlite. The heat treatment cycle led to the stability of the austenite phase. The addition of 0.12 wt.% V resulted in the enhancement of the mechanical properties so that the best combination of strength (866 MPa) and elongation percentage (41%) was achieved in this steel. Nonetheless, the addition of 0.25 wt.% V deteriorated the mechanical properties since the increase in the vanadium content promoted the formation of martensite, decreased the percentage of the retained austenite, and weakened the mechanical properties. However, adding 0.12 wt.% V improved the mechanical properties since it increased the strength through solid-solution strengthening and precipitation hardening; no brittle martensite was formed, and lamellar δ-ferrite was achieved. The steel containing 0.12 wt.% V, exhibiting a formability index of 35700 MPa%, is in the range of third-generation advanced high-strength steels.