ASME Grade 91鋼溶接継手のクリープ強度に対する母材熱処理の影響評価

抄録

In this work, the effect of prior PWHT conditions on creep strength of ASME Grade 91 steel welded joint was experimentally examined. By connecting Grade 91 steel subjected to the PWHT condition (740C, 6h) and the same steel without the PWHT, the material was welded to have two HAZ regions which have different heat treatments before welding. Regarding microstructure, hardness, tensile properties and creep strength, there were not distinct differences between welded joints of the steel with and without the prior PWHT condition. To examine on the effect of the prior heat treatment under general PWHT conditions, various aging tests were conducted on Grade 91 steel base metal, and the aged base metals were subjected to a heat treatment to make simulated fine grain HAZ materials. Creep test results on the prior aged HAZ simulated materials indicated that the effect of the prior PWHT on creep strength of the material is negligible if temperatures at PWHT are controlled within the standard condition and PWHT duration is less than 100h.