Fracture mechanism in coarse grained HAZ of HSLA steel welds

Abstract 1. 1. The effects of M-A constituent on the micromechanism of fracture processes in the coarse grained HAZ of HSLA steel welds were investigated by examining the initiation of voids and microcracks in sectioned tensile specimens. 2. 2. The coarse grained HAZ includes two locally brittle microstructures, whose toughness values are strongly affected by the amount of M-A constituents. 3. 3. Voids and microcracks are observed to initiate at the M-A constituents by the shear cracking process, i.e. , cracking or decohesion of the M-A constituents at the orientation of 40– 50 degree to the tensile axis when the M-A constituents are approximately parallel to the tensile axis. 4. 4. The void initiation strain in the coarse grained HAZ are very low because of premature void nucleation or brittle fracture at M-A constituents, confirming that the M-A constituents is the main metallurgical factor which governs the toughness of the coarse grained HAZ.