二相ステンレス鋼の超塑性現象を利用した固相接合

抄録

Solid state bonding of superplastic δ/γ duplex stainless steels with similar and dissimilar ferrous materials has been studied by means of hot compressive bonding test at temperatures ranging from 1073 to 1573 K in the N₂ atmosphere. By using the superplasticity of duplex stainless steels, good bonding, in which the specimen is fractured in the base metal by room temperature tensile test, can be obtained in significantly short time, e.g., the critical time for the bonding at 1373 K under a compressive stress of 19.6 MPa was 120 s in the case of similar bonding of as-hot rolled 25%Cr-7%Ni-3%Mo duplex stainless steels.In the vicinity of the bonding interface, fine microstructure is observed, indicating dynamic recrystallization due to superplastic deformation. The bonding ability is hardly deteriorated by increasing the surface roughness up to 100 μm or by mixing O₂ up to 0.5% in the N₂ atmosphere, because of the easy adhesion or of easy breakage of the oxide film formed on the bonding interface. Bonding of the duplex stainless steels with other non-superplastic materials such as austenitic, ferritic stainless and low carbon steels can also be obtained. By using the superplastic duplex stainless steel sheets as insert materials, non-superplastic steels can easily be joined. The critical bonding time largely depends on the superplasticity of the insert materials such as the kind of steel or the prior treatment.