Effects of Compression Deformation in Austenite Zone on Phase Transformation of Bainite in Low-carbon Bainitic Steel

The static supercooled austenite continuous cooling transition curve of Si-Mn-Mo-Cr-V low-carbon bainitic steel was drawn by thermal expanding curve obtained with thermal expansion phase change meter combined with microstructure and hardness test results. The test steel was subjected to compression deformation in austenite zone with different deformation, and then was cooled to different temperatures for 150 s and air cooled to room temperature by thermal simulation testing machine; the effect of compression deformation in austenite zone on bainite phase transformation and microstructure were studied. The results show that the initial temperatures of bainite phase transformation of test steel without compression deformation in austenite zone, with single-pass compression deformation by 40% in austenite zone and with double-pass compression deformation by 58% in austenite zone were 400, 385, 300℃, respectively. The bainite phase transformation of test steel during cooling process was delayed after compression deformation in austenite zone; the initial phase transformation temperature decreased, and the greater the deformation in austenite zone, the lower the initial temperature of the bainite phase transformation. Compared with the test steel without compression deformation in austenite zone, the bainite of the test steel with compression deformation in austenite zone became finer, the grain orientation increased, and the hardness were obviously improved.