The effect of carbon diffusion on creep behaviours for a dissimilar joint between P91 and 12Cr1MoV steels

Yanping Zhao, Jianming Gong, Yong Jiang

科研成果: 书/报告/会议事项章节会议稿件同行评审

摘要

Dissimilar joints have been widely used in many applications, especially for steam piping in the superheater and reheater of power plants. However, these dissimilar metal welds tend to fail less than half of their design life, and carbon diffusion is the main cause of the premature failure. Dissimilar joints operated at high temperature or after post-weld heat treatment (PWHT) exhibit carbon-enriched zone (CEZ) in the high alloy part and carbon-depleted zone (CDZ) in the low alloy part, causing by the chemical potential gradients across the weld interface. The carbides dissolute in the low alloy part while precipitate in the high alloy part. At the same time, a consequent of strength gradients are generated between the CEZ and CDE. The CDZ results in a loss of creep strength due to the carbides dissolution while an increase of strength due to the carbides precipitation. In this work, welding consumable of GTR-2CM was used to join P91 and 12Cr1MoV metals together. The stable phases and carbon activities of these metals are calculated by THERMO-CALC software. Carbon diffusion between P91/GTR-2CM/12Cr1MoV dissimilar joint after aging at 550°C for varying time are predicted by employing dispersed multiphase model in DICTRA software. Volume fractions of carbides varying with distance from both sides of the weld interfaces were also investigated, showing that the formation of CDZs and CEZs is related to the dissolution and precipitation of M23C6 and M7C3 carbides. The dissolution and coarsening of M7C3 and M23C6 particles in the CDZ and CEZ were also modelled by DICTRA software. The creep properties of base metals, weld metal and the dissimilar joint were investigated at 550°C. The stress dependence of minimum creep rate and rupture life obeyed the Norton's power law, and the stress exponents can be used to identify the creep mechanism. Monkman-Grant (MG) relations were also used to study the creep rupture data. The simulation results of carbon diffusion can be used to study the creep properties of CDZ and CEZ for the P91/GTR-2CM/12Cr1MoV dissimilar joint. The threshold stress concept can be incorporated into the analysis of creep power law. The magnitudes of threshold stress within CEZ and CDZ can be calculated according to the volume fraction and average diameter of carbides from carbon diffusion.

源语言英语
主期刊名High-Pressure Technology; Rudy Scavuzzo Student Paper Symposium and 24th Annual Student Paper Competition; ASME Nondestructive Evaluation, Diagnosis and Prognosis Division (NDPD); Electric Power Research Institute (EPRI) Creep Fatigue Workshop
出版商American Society of Mechanical Engineers (ASME)
ISBN(电子版)9780791850411
DOI
出版状态已出版 - 2016
活动ASME 2016 Pressure Vessels and Piping Conference, PVP 2016 - Vancouver, 加拿大
期限: 17 7月 201621 7月 2016

出版系列

姓名American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP
5
ISSN(印刷版)0277-027X

会议

会议ASME 2016 Pressure Vessels and Piping Conference, PVP 2016
国家/地区加拿大
Vancouver
时期17/07/1621/07/16

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