Journal
INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING
Volume 86, Issue 9, Pages 585-592Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ijpvp.2009.04.008
Keywords
Mod.9Cr-1Mo steel; Welded joint; Creep; Creep voids; Type IV cracking; FEM analysis
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Mod.9Cr-1Mo steel has been used for boiler components in ultra-supercritical (USC) thermal power plants. The creep strength of welded joint of this steel decreases due to the formation of Type IV cracking in heat affected zone (HAZ) at higher temperatures. The present paper aims to clarify the damage processes and mechanisms of the welded joint for Mod.9Cr-1Mo steel. Long-term creep tests of base metal, welded joint and simulated fine- grained HAZ were conducted at 550, 600 and 650 degrees C. Creep tests using thick plate welded joint specimen were interrupted at several time steps, and evolutions and distributions of creep damages were measured quantitatively using laser microscope. it is found that creep voids initiate at early stage of creep life (0.2 of life), the number of creep voids increases until 0.7 of and then voids coalesced into the macro crack at the later stage of life (0.8 of life). Creep damages life, concentrate mostly at a quarter depths of the plate thickness within the fine-grained HAZ of the present welded joint. The experimental creep damage distributions were compared with the computed results by using the FEM analysis. Both creep strain concentration and high stress triaxiality in fine-grained HAZ of welded joint are considered to accelerate the creep void formation and growth. (C) 2009 Elsevier Ltd. All rights reserved.
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