Fracture toughness behavior of ex-service 2-1/4Cr-1Mo steels from a 22-year-old fossil power plant |
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| Authors: | P K Liaw M G Burke A Saxena J D Landes |
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| Affiliation: | (1) Department of Materials Evaluation, Westinghouse Science and Technology Center, 15235 Pittsburgh, PA;(2) School of Materials Engineering, Georgia Institute of Technology, 30332 Atlanta, GA;(3) Department of Engineering Science and Mechanics, The University of Tennessee, 37996-2030 Knoxville, TN |
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| Abstract: | Elevated-temperature fracture toughness properties were developed on ex-service 2-l/4Cr-1Mo steel weldments. Fracture toughness
was measured on both base and heat-affected zone (HAZ) metals. A composite specimen consisting of base, HAZ, and weld metals
was used to develop fracture toughness properties in the HAZ area. It was observed that the J-R curve of the HAZ was significantly
lower than that of the base metal. Increasing crack extension increased the difference between theJ-R curves of the base metal and the HAZ. Dimpled fracture was the prime fracture mode in the base metal specimen, and a mixed-mode
(ductile and “granular”) fracture was found in the HAZ specimens. Scanning transmission electron microscopy (STEM) examination
revealed significant intergranular carbide precipitation and agglomeration within the HAZ. The lower fracture toughness of
the HAZ, as compared to the base metal, was attributed to the large accumulation of carbides in the grain boundaries of the
HAZ, which weakened the grain boundaries and caused “granular” fracture. |
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