窒素を含むステンレス鋼溶接部における低温靱性の異方性

抄録

Anisotropic fracture toghness (E_v) of austenitic stainless steel weld metal containing various levels of nitrogen has been investigated. In the case of high nitrogen content, E_v values indicated an anisotropic property in weld metal, while in the case of low nitrogen content, E_v was isotropic. When the weld metal contained 1606 ppm nitrogen, the value of E_v of the specimen which was parallel to the columnar structure was 1.4 times that of the one which was vertical to the columnar structure. The origin of anisotropy was related to the change in microstructure. The nitrogen promoted the formation of a columnar structure vertical to the weld center. The cleavage readily occurred parallel to the residual ferrite existing boundary of the columnar structure ; therefore, the fracture toughness indicated anisotropy. The ferrite volume fraction (A), the morphology factor (S) and the anisotropic factor (R_θ) were measured by a computr-aided image analyzer. The anisotropic fracture toughness values (E) were estimated by the equation E = (A·S·R_θ)^-0.187.