粉末冶金排气门座圈在出厂检验时发现其密封面存在缺肉现象。通过化学成分分析、硬度检测、密度检测及金相分析发现，失效座圈的化学成分、硬度、密度及显微组织均与正常座圈的非常接近，且均在控制要求范围内。利用Nano CT成像扫描系统和扫描电子显微镜（SEM）观察发现，零件内部无明显缺陷和气孔，但缺陷处有磕碰痕迹，同时该部位未形成有效的烧结联结。通过对生产工序的检查发现，传送导轨上的海绵缓冲垫破损，使座圈生坯在压制工序后的出料过程中与传送导轨发生磕碰，产生损伤，烧结后座圈密封面出现缺肉现象。

Incomplete phenomenon was found on the sealing surface of the powder metallurgy exhaust valve seat inserts in the factory inspection before delivery. Through chemical composition analysis, hardness testing, density testing and metallographic analysis, it was found that the chemical compositions, hardness, density and microstructure of the failure seat inserts were all very close to those of the normal seat inserts and they were all in the range of control requirements. By observation with Nano CT imaging scanning system and scanning electron microscopy (SEM), no obvious internal defects and pores were found, but bump marks were found near the surface defect position, and effective sintered junction did not form at this position. Through the inspection of the production process, it was found that the sponge cushion on the transmission rail damaged, so the green compact of the seat inserts bumped with the transmission rail in the discharge process after pressing, which resulted in the damage. So incomplete phenomenon appeared on the sealing surface of the seat inserts after sintering.