STRENGTH-MISMATCH EFFECT ON STEEL WELD HAZ-TOUGHNESS IN CTOD AND CHARPY TESTS

The effects of strength-mismatch between the base and weld metal in welded joints on CTOD and Charpy impact toughness of heat-affected zone (HAZ) are investigated in this study. Both toughness properties are compared, in consideration of the effect of the local brittle zone (LBZ) in HAZ, and strength-mismatch effects are discussed analytically. Two types of welded joints for 490 MPa strength class structural steel with the same thickness of 25 mm, which were strength-matched and overmatched joints, are prepared under the same welded conditions (heat input = 4 KJ/mm) with different welding consumables. The critical CTOD of the HAZ for the overmatched joint exhibits the lower values in wide temperature range of ductile-to-brittle fracture transition than that for the matched joint, whereas microstructures and total LBZ size along crack-tip are consistent with each other. On the contrary, significant difference between the matched and overmatched joints in the lower temperature range cannot be observed in the Charpy impact toughness. The reason why the strength-mismatch effects on the fracture toughness are different between the CTOD and Charpy impact tests is discussed.