船用柴油机排气阀的断裂失效分析

对船用4Cr9Si2钢断裂柴油机排气阀进行了金相组织、扫描电镜、金属流线及断口分析和硬度检测.结果表明,阀体材料的化学成分、断裂阀杆表面硬度符合产品的技术要求.断裂过程的形成是由中阀杆圆柱表面上的氧化皮向基体扩展作用不均匀,首先在阀杆表面形成浅沟形开裂,逐渐发展成较深的裂纹,最终导致阀杆的疲劳断裂.材料的断裂方式为高温腐蚀疲劳,断裂原因为材料的高温腐蚀疲劳性能不能满足排气阀高温腐蚀运行工况的要求.

Rupture Failure Analysis of Marine Diesel Exhaust Valve

The rupture failures of the marine diesel exhaust valve spindle 4Cr9Si2 steel were analyzed by metallographic, SEM, metal flow line and fracture analysis as well as hardness testing. The results show that the valve material and surface hardness of the spindle meet the technical requirements of the product. The rupture process is caused by uneven expansion of oxide layer from the cylindrical surface to the substrate, firstly forming shallow ditch shape cracks on the surface, then developing gradually into the deeper cracks, and finally leading to the fatigue fracture. The material fracture is defined as high temperature corrosion fatigue, and the high temperature corruption of material can not sufficiently meet the requirements of the ooerating condition of exhaust valve.