Microstructural evolution and mechanical properties of V-containing medium-Mn steel manufactured via cold rolling and intercritical annealing

Abstract

V was added into a cold-rolled medium-Mn steel for optimizing comprehensive mechanical properties by the V-carbide precipitation. After annealing, the V-carbide particles in austenite grains easily coarsen than that in ferrite. The contributed yield strength increment of V-carbide precipitation strengthening in ferrite is in a range of 200–250 MPa. With increasing annealing temperature, the morphology of ferrite and austenite gradually transforms from lamellar to equiaxed. The sample after intercritical annealing at 650 °C shows 1450 MPa ultimate tensile strength, 1210 MPa yield strength, and 18% tensile elongation. In addition, samples with lamellar and equiaxed structures display larger Lüders plateaus than samples with a single equiaxed/lamellar structure. Partial martensitic transformation and continuous interactions between dislocation and twin are responsible for the Lüders plateau propagation. Therein, the number fraction of coarse austenite grains should be responsible for the propagation of Lüders plateau.

Keywords

• Austenite stability
• Precipitation strengthening
• Dislocation strengthening
• TRIP and TWIP effect
• Lüders plateau