Fracture failure analysis of high-temperature fastening bolt for turbine control valve

doi:10.13251/j.issn.0254-6051.2023.03.049

Abstract

Abstract: High temperature fastening bolt of the steam turbine IP governing valve was broken and failed during the unit maintenance in A thermal power plant. In order to determine the cause of failure and avoid the recurrence of similar events, macro morphology, fracture micro morphology, chemical composition, microstructure and mechanical properties of the fractured bolt were tested and analyzed by direct reading spectrometer, optical microscope, scanning electron microscope and pendulum impact tester. The results show that the main reason for the fracture of high temperature fastening bolt made of 20Cr1Mo1VTiB steel is that the forging temperature of the bolt in the manufacturing stage is too high or the quenching temperature is too high, which results in the coarse grain structure and the impact property of the material is reduced. Under the impact load generated by the frequent action of the turbine control valve, the bolt cracks along the coarse grain region and extends in the form of brittle cleavage fracture until the bolt is completely broken.

Key words: high-temperature fastening bolt, 20Cr1Mo1VTiB steel, fracture, coarse grain, hot working

CLC Number:

TF146

Sun Yunfei, Shi Xianda, Zhang Zhihao, Chen Hao, Lü Lei, Yun feng. Fracture failure analysis of high-temperature fastening bolt for turbine control valve[J]. Heat Treatment of Metals, 2023, 48(3): 292-295.

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