Creep-fatigue tests on the heat-affected zone(HAZ) simulated materials, base metal, weld metal and weld joint of 2.25Cr-1Mo steel, and elastic-plastic and creep FEM analysis for the weld joint were conducted. It was found from the comparison between experimental evidences and the analytical results that “Type IV” cracking was caused by two major reasons. One is accumulation of creep strain during strain hold in the fine-grain region is larger than that in other regions, suggesting progress of creep damage in the fine-grain region prior to other regions. The other is existence of triaxial tensile stress field within the fine-grain region caused reduction of failure ductility. Crack initiation portion and failure life under the creep-fatigue test could be well predicted by the nonlinear damage accumulation model based on the FEM analysis results.

Issue Section:
Technical Papers
Keywords:
boilers, pressure vessels, creep testing, fatigue testing, steel, alloy steel, molybdenum alloys, chromium alloys, elasticity, plasticity, tensile strength
Topics:
Creep, Damage, Fatigue, Boilers
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