Effect of Rolling Pre-deformation and Austenitizing Temperature on Microstructure and Tensile Properties of Bainitic Steel

Fe-0.9C-1.4Si-1.6Mn-0.8Cr-0.2Mo-0.25Al steel ingot was subjected to cold rolling and hot rolling deformation, respectively, and then was treated by austenitizing at 850-1 100 ℃ and isothermal treatment at 300 ℃. The effects of the rolling pre-deformation and austenitizing temperature on the microstructure and tensile properties were studied. The results show that the cold rolled pre-deformed steel was mainly composed of bainite ferrite and retained austenite after austenitizing at 950 ℃, while the hot rolled pre-deformed steel was composed of bainite and retained austenite. Compared with that of the non-pre-deformed steel, the retained austenite content decreased. Cold rolling deformation could improve both tensile strength and percentage elongation after fracture of the steel, while hot rolling deformation could reduce the percentage elongation after fracture. The content of retained austenite in cold rolled pre-deformed steel did not change much at austenitizing temperatures of 850-1 050 ℃, but decreased at 1 100 ℃. At the austenitizing temperature of 1 100 ℃, flake Widmanstatten ferrite appeared. With the increase of austenitizing temperature, the tensile strength and percentage elongation after fracture of cold rolled pre-deformed steel first increased slightly and then decreased, and reached the maximum at the austenitizing temperature of 950 ℃.