Relationship between Ductility and Microstructure for Heat Affected Zone of Steel for Building Structure

This paper deals with ductility of weld heat affected zone of steel for building structure.The test materials which were applied thermal cycle simulating the heat affected zone of the multilayer CO 2 gas shielded arc weld joint were prepared.The heat affected zone subjected to single thermal cycle and the one subjected to reheat in the two-phase region were tested.Tensile tests for smooth round-bar specimens and circumferentially notched round-bar specimens and FEM analysis simulating the tests were carried out to confirm the ductility of base metal and each heat affected zone.As a result, it was confirmed that the ductility of the coarse-grained heat affected zone and that of the coarse-grained heat affected zone subjected to two-phase zone reheating were lower than those of base metal and the other heat affected zone.The microstructure observation was carried out, and it was confirmed that the coarse-grained heat affected zone has a coarse-grained bainitic microstructure and that the coarse-grained heat affected zone subjected to two-phase zone reheating has the microstructure in which the acicular cementite disappeared partly by the reheating in the coarse-grained bainite microstructure.It was also confirmed that there was a difference in ductile fracture behavior by the fracture section observation, and it was clarified that the difference in ductile fracture behavior caused by the difference in microstructure of the material caused the difference in ductility of the material.