A Bainite/Ferrite Dual-Phase Low-carbon Microalloying Steel with High Strength and Ductility

A ferrite/bainite dual-phase low-carbon microalloying steel has been obtained by special microal-loying design and optimum thermo-mechanical control process(TMCP). The microstructure shows that there are some amounts of ferrite/quasi-polygonal ferrite on the prior-austenite boundary and/or within the grains, and the rest of matrix is ultra-fine lath-like bainitic ferrite. The ferrite grain size is also very fine (about several microns). The mechanical properties of this kind of dual-phase steel show that the yield strength do not decrease obviously comparing with the ultra-fine bainitic steel, but the elongation increases. For a 700 MPa grade dual-phase steel (tempering at 680C for 1h), the elongation is more than 25%. This kind of dual-phase low-carbon microalloying steel has the advantages of more than 700 MPa grade strength and good ductility.