粉末冶金气门座圈裂纹成因分析

Failure Analysis of Powder Metallurgy Valve Seat

采用力学、物理性能测试,金相、扫描电镜、能谱和X衍射分析研究了气门座圈产品失效的主要原因。研究结果表明,失效座圈合金的密度(7.26 g/cm3 ),洛氏硬度(40. 0)和压溃强度(740 MPa)均稍低于正常产品的密度(7.38 g/cm3)、洛氏硬度(46.0)和压溃强度(760 MPa);样品上部平行于表面有细微的分层断面,断面上有大量疏松颗粒、二次裂纹和少量夹杂物;密实工艺不当,造成微观疏松,是座圈失效的直接原因;合金中断口处K和Ca的含量分别达到1.37%,1.61%,导致液态金属脆化,是座圈失效的另一原因。

The failure of the powder metallurgy valve seat was analyzed by optical microscopy, scanning electronic microscopy, X-ray energy spectrum and X-ray diffraction. The results show that the density (7.26 g/cm3), Rockwell hardness (40.0) and compressing strength (740 MPa) of the failure valve are lower than those of the normal products (7.38 g/cm3, 46.5 and 760 MPa, respectively). There are a lot of incompact particles, secondary microcracks and impurities on the fracture surface that parallels to top surface of valve seat. Unsuitable compaction procedure is a direct reason for the failure of the valve seat. A high content of K(1.37%), Ca(1.61%) in the valve seat causes liquid metal embrittlement, which is another reason for the failure.