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概要

Modified 9Cr-Mo steel is a candidate structural steel for demonstration fast breeder reactors (FBR's). Due to low thermal activation, the steel can maintain steady-state deformation during long-term creep. The creep strength of its weldment is lower than that of the base metal. Because of different creep strain rate in the solidified weld metal and heat-affected zone (HAZ), creep deformation in HAZ can be lowered but maximum principal stress augmented in fine-grained HAZ to cause detrimental Type IV cra cks in this zone.In this study, FEM analyses were made on long-term creep of over 60 years in double U groove welded Modified 9Cr-Mo steel with typical microstructures in the welded region of the steel taken into consideration. The typical welded region of the steel consists of solidified weld, coarse grain HAZ, fine grain HAZ, interfacial HAZ and base metal. These microstructures were modeled as polycrystal structures having slip systems approximated by rectilinearly anisotropic deformation properties.

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