1. Key Laboratory of Iron and Steel Metallurgy and Resource Utilization,Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China; 2. Department of Structural Steels, Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China; 3. Wuchuan Heavy Engineering Co., Ltd., Wuhan 430415, China
Abstract：In view of the uneven cross-sectional properties of bulb flat steel caused by the expansion of size, the properties of V-N microalloying large size bulb flat steel were predicted by the combination of static undercooled austenite continuous cooling transformation curve (CCT) and ANSYS finite element multi field coupling simulation.At the same time, the strengthening mechanism of bulb and flat was studied by means of transmission electron microscope and phase analysis. The results show that the full section structure of 18# asymmetric bulb flat steel designed by V-N microalloying was ferrite + pearlite + bainite. The cooling speed of the ball was about 2 ℃/s slower than that of the flat during the cooling process, and the maximum temperature difference reached 104.6 ℃ in 170 s. The grain size and hardness difference between the ball and the flat was 2.7 μm and 20 HV5, respectively. The longer high temperature residence time of the bulb made the precipitation amount of V(C, N) more than that of the flat, and the precipitation size was smaller. Compared with the comparative bulb flat steel, the yield strength of the test bulb flat steel designed by V-N microalloying increased by 55-78 MPa, and the difference between the bulb and the flat was reduced from 22 MPa to 1 MPa, which significantly improved the section uniformity of the bulb flat steel.
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