Gradient microstructure–mechanical property correlation in medium Mn steel fabricated by a novel high-ratio differential speed rolling: the impact of intercritical annealing time
摘要
The gradient microstructure and mechanical properties of medium Mn steel (MMS) processed by high-ratio differential speed rolling (HRDSR) treated at different intercritical annealing (IA) times at 740 ℃ were investigated. The samples exhibit a duplex phase gradient microstructure of ultrafine austenite and ferrite. With the IA time increasing from 5 to 120 min, the grain size in the edge region of the sample increases from 0.75 to 0.97 μm, and in the core region of the sample increases from 0.79 to 1.29 μm. Additionally, the hardness value in the edge decreases from 320(± 5) to 270(± 5) HV and the hardness value in the core decreases from 290(± 5) to 230(± 5) HV, as the IA time increases from 5 to 120 min. The product of strength and elongation is 25GPa·% at 5 min, then increases up to 51GPa·% at 60 min, and finally decreases to 42GPa·% at 120 min. It should be noted that the elongation of the experimental steel can reach 64%, which is higher than those in similar chemical components reported in others works. During the tensile process, the gradient microstructure of the sample makes the austenitic transformation behaviors of the surface and the core different, and fine grain of edge hinders the crack propagation and finally presents good tensile properties.