【摘要】 采用宏观断口分析、化学成分分析及金相检验等方法,对发动机排气门杆断裂原因进行了分析。结果表明,气门杆断口附近的近表面基体内存在大量非金属夹杂,同时气门杆表面碳氮共渗层存在黑色组织,这些均是气门杆疲劳强度降低的原因,其中较大尺寸的脆性夹杂物在次表面首先产生微细裂纹,最终导致了疲劳断裂。更多还原

【Abstract】 By means of macroscopic analysis, chemical composition analysis and microstructure examination, the cracking reason of engine exhaust valve stem has been studied. The results show that a lot of non-metallic inclusions consisting in the valve stem matrix around the fracture and the black microstructure in the gas nitrocarburized layer reduced the fatigue strength of the valve. The relatively high brittle inclusions initiate the microcrack in the sub-surface at first, and the microcrack caused the fatigue fracture at last.更多还原