Microstructure Characteristics of TIG Welding Joint of 740H Pipe for Ultra-Supercritical Power Plant Boilers

Abstract:

Microstructure and mechanical property of tungsten inert gas (TIG) welding joint of 740H pipe were studied by optical microscope, scanning electron microscope and HV tester in this paper. The principal segregated elements in fusion zone of 740H weldment were Nb and Ti. The discontinuous MC-type phase with irregular shape and γ′ phase were distributed in the interdendritic region. The γ′, M₂₃C₆ and MC phases on grain boundary in heat affected zone (HAZ) dissolved into matrix. Hardness of weld metal and HAZ were apparantly lower than that of base metal. The previous weld bead was the heat affected zone of the subsequent weld metal, thus hardness was different in different area of the fusion zone (FZ). After the postweld heat treatment of 800°C/4h followed by air cooling, the volume fraction of γ′ in the interdendritic region was larger than that in the dendrite arm. The hardness of HAZ and FZ were approximately equal to that of base metal (BM).

• Periodical: Materials Science Forum (Volume 816)
• Pages: 662-668
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.816.662
• Online since: April 2015
• Authors: Jian Shui Ye*, Jian Xin Dong, Mai Cang Zhang, Zhi Hao Yao, Lei Zheng
• Keywords: 740H, Microstructure, Tungsten Inert Gas (TIG)

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