论文部分内容阅读
某冷挤压成形的火花塞铁壳热铆组装之后于膨胀槽处横向脆性开裂。为了探讨失效原因,采用光学显微镜、扫描电镜和显微硬度计以及氢热分析仪等对其进行了全面地显微分析。结果表明:铁壳内壁机加工痕迹明显,并有少量点状锈蚀。人工打开失效样品发现起裂源位于靠近内壁的次表面,整个横截面上均为沿晶开裂形貌,并存有大量二次裂纹。失效样品的热铆变形处显微组织为等轴铁素体+马氏体及碳化物颗粒,铁素体为双重晶粒。失效样品的电镀镍层厚度相对较薄,内壁局部厚度不足1μm,镀层内还残留少量氧化铁。膨胀槽纵截面的显微硬度波动较大,粗晶区域的显微硬度低于150 HV,而热铆前约为230 HV。失效样品的氢扩散质量浓度为0.042 mg/m3。由此认为样品失效原因系电镀增氢与热铆产生的残余应力耦合导致铁壳中最薄弱的膨胀槽处发生脆性延迟开裂。
A cold extrusion of the spark plug after hot riveting assembly expansion slot at the transverse brittle cracking. In order to investigate the cause of failure, a comprehensive microscopic analysis was conducted using optical microscope, scanning electron microscope and microhardness tester as well as hydrothermal analyzer. The results show that the machining marks on the inner wall of the iron shell are obvious and there is a small amount of pitting corrosion. Manually open the failure samples found that the source of cracking is located near the inner wall of the sub-surface, the entire cross-section are along the crystal cracking morphology, and there are a large number of secondary cracks. The failure of the sample hot riveting deformation microstructure of equiaxed ferrite + martensite and carbide particles, ferrite double grain. The thickness of the electroplated nickel layer of the failure samples is relatively thin, and the local thickness of the inner wall is less than 1 μm, and a small amount of iron oxide remains in the plating layer. The microhardness of the longitudinal section of the expansion tank fluctuates greatly. The microhardness of the coarse grain region is less than 150 HV and about 230 HV before the hot riveting. The hydrogen diffusion mass concentration of the failed sample was 0.042 mg / m3. Therefore, it is considered that the cause of sample failure is the coupling of residual stress caused by electroplating, hydrogenation and hot riveting, leading to brittle delayed cracking at the weakest expansion tank in the steel shell.