高張力鋼溶接継手の熱影響部微視組織と破壊靱性

抄録

The fracture toughness in a low alloy welded steel has been examined with particular reference to HAZ microstructures. It is shown that a wide variety of structure in the HAZ adjacent to fusion boundary through thickness is produced by virtue of the different thermal histories experienced by each part in a multi-pass welded low alloy steel. The HAZ microstructures can be classified into seven distinct kinds (named A, B, C, D, E, F and G) according to the microscopic constituent and grain size. Fracture toughness dependence on the HAZ microstructures is demonstrated by instrumented Charpy dynamic Kd and static COD test on small specimens taken from the full thickness welded plate. The slit tip is carefully located in the HAZ adjacent to fusion boundary. The results make it clear that static COD test is more available for assessing fracture toughness dependence on the HAZ microstructures than instrumented Charpy impact test. The martensitic-bainitic HAZ microstructures (A, B and C) which are localized in the vicinity of the weld toe fusion boundary impair most significantly of all the HAZ microstructures. Furthermore, the emphasis must be placed upon the fact that martensitic-bainitic HAZ microstructure G tempered at relative high temperature during following welding process has excellent toughness, although .the microstructure G seems to be similar to the microstructure of weld toe HAZ.