Effect of crystallographic features on low-temperature fatigue ductile-to-brittle transition for simulated coarse-grained heat-affected zone of bainite steel weld

The coarse-grained heat-affected zone (CGHAZ) of bainite steel welds is prone to lose toughness due to welding thermal history. This study aims to reveal the correlation between crystallographic characteristics and fatigue ductile-to-brittle transition (FDBT) for typical microstructures (lath bainite and granular bainite) in the CGHAZ at low temperatures. Compared to the granular bainite, the lath bainite presents retarded growth of fatigue cracking and significantly lowered FDBT temperature (-20 degrees C vs-40 degrees C). The superior low-temperature fatigue performances of lath bainite are ascribed to the high-fraction high-angle grain boundary formed by its unique variant selection.