Process Simulation and Microstructure Analysis of Low Carbon Si-Mn Quenched and Partitioned Steel

The quenching and partitioning (Q&P) process was experimentally investigated on the thermomechanical simulator (Gleeble3800). The microstructure and fracture mechanism of the sheets were investigated by means of TEM. It was found that the microstructure of quenched and partitioned steel consists of fine lath martensite and thin inter-lath austenite films. The optimum quenching temperature of producing the maximum amount of retained austenite after final quenching at room temperature was predicted by Matlab software package. It was found that the calculations by Matlab software can provide guidance for experimental processing design reliably. The volume fraction of retained austenite at room temperature was approximately 8%, which was measured easily by the software VC6.0++ programming. The results verified that quenched and partitioned steel possesses a good combination of strength and plasticity due to its fine microstructure. This steel exhibited high ultimate tensile strength (exceeding 1 000 MPa) and good elongation of 25%. The results showed that the fracture mechanism of the sheets is typical tough fracture under the condition of tensile failure.