Effect of Heat Treatment on Microstructure and Mechanical Properties of 800MPa Grade Ultra Low Carbon Bainite Steel

摘要

A new kind of bainite steel with ultra-low carbon content and Nb, Ti alloys has been developed. By applying thermo-mechanical control process, water quenching and tempering at different temperature, excellent properties have been obtained when tempered at 450°C, with the yield strength of 813MPa and elongation of 16.2%. The morphology observed by SEM shows that the microstructure consists of fine lath-shaped bainite, polygonal ferrite, quasi-polygonal ferrite and a small fraction of residual austenite or martensite-austenite constituents. In a TEM study plenty of precipitates with the size about 5-10nm were observed interacting with the dislocations, which is very significant for the optimization of strength and ductility.