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Abstract The reason for fracture of steam turbine regulating valve stem is analyzed by macroscopic examination, fracture analysis, component examination, hardness testing and metallographic observation. The results show that chemical composition of the invalid stem is in accordance with the requirements of the GB/T 8732-2014 standard. The microstructure of the invalid stem is martensite. The hardness value of the stem is in accordance with the GB/T 8732-2014 standard. Machining marks exist in the retreating slot position of the stem and the larger surface roughness is the reasons for fracture. The valve stem bears the cyclic tensile stress for a long time during the operation of the unit, of which fatigue cracks produced in the root chamfering position with greater stress concentration, leading to the fracture of valve stem.
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Published: 25 May 2018
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