A certain auto engine exhaust valve,made of an austenitic heat-resistant steel,has broken when subjected to durability test up to 334 h.The broken exhaust valve was subjected to visual inspection and microscopic analysis of the fracture,chemical composition analysis and hardness test to reveal the reason for its breaking.The results show that machining defects such as fold and groove where stress concentration is easy to happen and crack is easy to initiate is present in the exhaust valve.In addition,the exhaust valve undergoes high temperature oxidation corrosion.The foregoing two factors cause the exhaust valve to break during the durability test.%某汽车发动机排气阀，材料为奥氏体耐热钢，在耐久试验至334 h时发生断裂。对断裂的排气阀进行了宏观及微观断口分析、化学成分分析和硬度测定，以揭示其断裂的原因。结果表明，该排气阀存在易产生应力集中和萌生裂纹的折叠、沟槽等机加工缺陷，加上高温氧化腐蚀作用，最终导致其在耐久试验时发生断裂。
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