オーステナイト系ステンレス鋼溶接金属の溶接条件と長時間加熱による材質変化について

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Effect of welding conditions and a long term heat-treatment at 650℃ on metallurgical changes in austenitic stainless steels (SUS 304 and SUS 316) weld metals have been investigated. Results were as follows ; 1) The solidifying structure at center parts of weld metals tend to grow parallel to the direction of plate thickness of the 1 pass 1 layer welded joint. 2) δ-ferrite forms in the order to the solidifying directions. 3) δ-ferrite changes those morphologies from granular and rod-like shape to net-like shape with increase of the amount of δ-ferrite. In the case of large amount δ-ferrite, this net-like δ-ferrite takes the form into densely three-dimentional network in the inner part of each pass. 4) There is no δ-ferrite network in the boundary zone between pass and the following pass, because δ-ferrite in these boundary zone are mixed granular and rod-like shape. 5) Networks of δ-ferrite in high heat input weld metals are larger than that in low heat input weld metals. 6) Carbides and σ phase precipitate in δ-ferrite subjected to heating for a long term at 650℃. 7) Carbides and σ phase take the form of network with a long term heating at 650℃ in the weld metal containing a large volume of δ-ferrite. From above results and the correlated research results of creep test and notch toughness of austenitic stainless steel weld metals subjected to a long term heat-treatment, it is considered that the following processes are advisable for the prevention measure of material worse at high temperature ; 1) Selecting of the weld metals in which have the amount of δ-ferrite under about 5%, for the reason of dispertion of δ-ferrite and for destruction of δ-ferrite networks. 2) Making use of 2 pass 1 layer welding sequence to disperse the solidifying direction and applying the low heat input welding process to destroy δ-ferrite networks.
1979-12-01

オーステナイト系ステンレス鋼溶接金属の溶接条件と長時間加熱による材質変化について

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