TYPE IV CREEP RUPTURE CHARACTERISTICS OF P92 STEEL WELDMENT
WANG Xue1, PAN Qiangang2, TAO Yongshun2, ZHANG Yinglin1,ZENG Huiqiang2,LIU Hong2
1. School of Power and Mechanics, Wuhan University, Wuhan 430072
2. Dongfang Electric Corporation, Dongfang Boiler Group Co Ltd., Zigong 643001
Cite this article:
WANG Xue1, PAN Qiangang2, TAO Yongshun2, ZHANG Yinglin1,ZENG Huiqiang2,LIU Hong2. TYPE IV CREEP RUPTURE CHARACTERISTICS OF P92 STEEL WELDMENT. Acta Metall Sin, 2012, 48(4): 427-434.
Abstract Creep tests at 600～650℃ with applied stresses in the range 100～240MPa and microstructural observations by means of OM, SEM, TEM were conducted on weld joints of P92 steel prepared by SAW process to investigated its characteristics of Type Ⅳ creep rupture. The results showed that Type Ⅳ failure took place at higher temperature and lower stress and tend to have a critical condition expressed by Larson-Miller parameter（L.M.P.）or stress level which values are 35.5 and 120MPa respectively. Type Ⅳ failure showed a lack of ductility and located in the fine grained HAZ（heated to just above AC3）close to intercritical HAZ, where microstructural changes are obviously different from those in the base metal, including formation of equiaxed sub-grain structure, mass precipitation and rapid growth of Laves phases on the grain boundaries during creep exposure, which lead to the Type Ⅳ failure. The size of M23C6 carbide in the AC3 FGHAZ was almost the same as that in the base metal, which has little effect on the failure. Type Ⅳ rupture is a brittle intergranular fracture due to cavity coalescence, which were nucleated at coarse precipitates of Laves phase. The void area ratio of f or AA is employed to quantify grain boundary damage and evaluate Type Ⅳ failure of P92 steel weld joints, and when their values were above 1～1.2% or 0.5%, Type Ⅳ failure would occur.
