Analysis of the causes of cracking in valve stem keyways

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Analysis of the Causes of Cracking in the Valve Stem Keyway Abstract: In S42 series 36″ hard-sealed valves, the valve stem fractured at the root of the keyway during valve opening after the sealing test. This paper disassembles the valve and analyzes the causes of its cracking from various aspects, including the design parameters of the valve, the production process, and the raw materials of the fractured valve stem. The results show that the improper heat treatment process of the valve stem’s raw material led to the presence of a large amount of σ-phase and precipitated phases in its microstructure, which is the main cause of the brittle fracture of the valve stem ； Secondly, there is a right angle at the root of the keyway, which easily leads to stress concentration during the machining process, accelerating the cracking of the keyway. Keywords: duplex stainless steel ； Heat treatment ； Microstructure ； Tensile strength ； elongation at break ； brittle fracture