Study on microstructure evolution and toughening of coarse grain heat affected zone of 690 MPa grade bridge steel Online publication date: Thu, 09-Jun-2022
by Xuming Wang; Aimin Zhao; Yishun Zhang; Yue Zhang; Zhiyi Bao
International Journal of Microstructure and Materials Properties (IJMMP), Vol. 16, No. 1, 2022
Abstract: Using Gleeble-3500 to simulate the coarse-grain heat affected zone (CGHAZ) under different heat inputs (HIs) (15~50 kJ/cm), the welding performance of 690 MPa bridge steel was investigated. Optical microscope (OM), scanning electron microscope (SEM) and electron back-scattering diffraction (EBSD) were used to analyse the microstructure. The mechanical properties were researched by Charpy V-notch test and microhardness test. The results indicate that under different HIs conditions, the microstructure of CGHAZ obtained by simulation is mainly composed of granular bainite (GB), lath bainite (LB) and slight of martensite. As the HIs increases, the martensite content in the microstructure decreases, the content of granular bainite increases. When the HIs is 30 kJ/cm, the obtained microstructure of simulated CGHAZ is mainly LB, with the highest density of large-angle grain boundaries (orientation difference greater than 45°), resulting the highest impact absorbed energy.
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