Research on the Multiscale Correlation Between Dynamic Temperature Field and Microstructure of High‐Strength Corrosion‐Resistant Steel by Initial Electrode Distance in Flash Butt Welding

The study systematically elucidates the mechanism by which the initial electrode distance affects the thermal–mechanical coupling effect and microstructural properties of flash butt welded joints of 600 MPa grade high‐strength corrosion‐resistant steel. A dynamic temperature field flash butt welding is constructed based on real‐time thermocouple measurement data at multiple locations, combined with testing, to establish a quantitative correlation mechanism among the initial electrode distance parameter, phase transformation behavior, and mechanical properties. The experimental results indicated that increasing the initial electrode distance reduces the peak weld temperature, effectively suppressing abnormal grain growth in the coarse‐grained heat‐affected zone (CGHAZ). Microstructural evolution analysis reveals similarly that the weld zone primarily consists of acicular ferrite and bainite, the CGHAZ exhibits a mixed structure of lath bainite and granular bainite, while the fine‐grained heat‐affected zone comprises a composite structure of polygonal ferrite and granular bainite. Fractographic analysis shows that the fracture surfaces of joints with an initial electrode distance of 14 mm exhibit tough‐brittle mixed fractures and the minimum impact energy. In contrast, the initial electrode distance increases 16 mm, and the impact toughness enhances to over 60 J, which is an increase of 21%, exhibiting superior mechanical properties.