Comparative study on effects of annealing temperature on microstructures and mechanical properties of high-Al low-Si steel

Abstract

We elucidate here profound effects of quenching and partitioning process after partial (IQP) or full austenitization (FQP) on the microstructure and mechanical properties of high strength hot-dip galvanized steel with high Al and low Si content. The results showed that the FQP steel contains 3.38% vol.% retained austenite with mainly film-like morphology, while the IQP steel mainly consists of 6.44–8.13 vol.% retained austenite with block shape. Additionally, retained austenite in the IQP sample transforms into martensite more easily duo to higher nucleation rate, which means lower austenite stability. A combination of various austenite grain size and morphology make the TRIP effect throughout the whole deformation process and increased the elongation for IQP sample. When the steel was treated by annealing temperature of 967 °C, partitioning temperature and time of 460 °C and 100 s respectively, the steel exhibited excellent mechanical properties with tensile strength of 754 MPa, total elongation of 27% and the product of strength and ductility exceeds 20 GPa%. The proposed content in the present study demonstrates compatibility with the continuous hot-dip galvanizing process.