Microstructural characteristics and toughness of the simulated coarse grained heat affected zone of high strength low carbon bainitic steel

► Total toughness can be separated into crack initiation energy and crack propagation energy. ► Small effective grain size of lath martensite can improve the crack propagation energy. ► MA constituent is mainly responsible for the low toughness of coarse bainite specimens. ► High angle packet boundary in coarser bainite has few contributions to improving crack propagation energy.