980 MPa Grade Low-Alloy Carbide-Free Bainitic Steel Obtained by Dynamic Continuous Cooling Transformation

The addition of high-content alloying elements and the unbefitting process make carbide-free bainite steel difficult in industrial production. Thus, we adopted a dynamic continuous cooling process for developing the high-strength cold-rolled low-alloy carbide-free bainitic steels in this study. The influence of cooling rates on the microstructure and mechanical properties was investigated by dilatometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and tensile tests. The results show that the bainitic ferrite plates were refined by decreasing the cooling rate, and more austenite was retained in the steel with a medium cooling rate. Both the TRIP effect and the refined bainitic ferrite plate contribute to the good strength–ductility match. Consequently, the propitious microstructure adjustment is critical for developing 980 MPa carbide-free bainitic steel.