Effect of heat treatment temperature on microstructure of long-term serviced T23 steel weld

doi:10.13251/j.issn.0254-6051.2023.05.035

Abstract

Abstract: Butt joints of T23 steel water-cooled wall pipes with a service time of more than 60 000 h were taken as the research object. The welded joints were subjected to heat treatment at different temperatures. The microstructure evolution of the weld zone after heat treatment at different temperatures was deeply studied by means of microhardness analysis, metallographic analysis, scanning electron microscope and energy spectrum analysis. The distribution law of alloy carbides on grain boundaries was analyzed, and the forming mechanism of reheat cracks in weld zone of the T23 steel welded joints was revealed. The results show that the weld structure of the welded specimen of T23 steel is a mixture of coarse lath martensite and bainite, with obvious prior austenite grain boundaries, the maximum grain size exceeding 300 μm, and size of most grains being 150-200 μm. After heat treatment at 580 ℃, the weld zone has obvious secondary hardening phenomenon, and grain refinement and dispersion strengthening are the main reasons for secondary hardening. When heat treated at 720 ℃ and 760 ℃, holes and precipitates appear on the grain boundaries of the T23 steel cap weld zone, and the precipitates are mainly M₂₃C₆ and MC. There are two main modes of the positional relationship between precipitates and pores. One is that the pores grow along the grain boundary in the front of the precipitates, and the other is that the pores grow on the side of the precipitates near the inner grain. The formation mechanism needs to be further studied.

Key words: T23 steel water-cooled wall, weld zone, heat treatment, reheat crack

CLC Number:

TG441.8

Zhang Zhenhua, Yin Shaohua, Sun Zhiqiang, Wang Chuandong, Zhu Wanjin. Effect of heat treatment temperature on microstructure of long-term serviced T23 steel weld[J]. Heat Treatment of Metals, 2023, 48(5): 229-235.

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