Effect of annealing process on microstructure and mechanical property of medium-manganese TRIP steel

For studying the feasibility of the production of automobile steel of medium-manganese containing nitrogen TRIP steel with the continuous annealing process, effect of annealing temperatures at 630°C to 700°C for 180 s on the microstructure and properties were investigated. SEM, TEM, EDS, XRD and tensile tests were used to characterise the composition and mechanical properties of the annealed steel. It shows that, when the annealing temperature is low, the (Fe, Mn)3C composite carbide precipitates along the grain boundary. As the temperature increases, it coarsens first and then dissolves; the volume fraction of retained austenite increases as the temperature increases. When the temperature is kept at 675°C for 180 s, C, Mn and N elements work together to maintain the stability of austenite, the elongation (18.9%) and strong plastic product (20 GPa*%) of the test steel reach the maximum, and the tensile strength reaches 1,050 MPa, the mechanical performance reaches the best.