Abstract��A spark plug was failed with brittle crack from the swollen slot. It was analyzed in detail by optical microscope�� scanning microscope and microhardness tester as well as thermal desorption spectroscopy. There were red rust spots on the inner surface with rough tool marks. The origin of crack was at the sub-surface of inner layer and intergranular fractures were all over the cross section. It was equi-axial ferrite and martensite with carbide particles at deformation place�� and coarse grain in the interior inwall with duplex grain size. There were galvanized nickel layer on the surface of the samples�� and it was thin in the inner layer. It could be found that retained rust under the layer along the inner wall. The micro-hardness on the cross section of swollen slot was different. It was lower than 150 HV in the coarse grain zone while it was 230 HV before heated. The mass concentration of diffusible hydrogen was 0.042 mg/m3 in the failure sample. The conclusion could be drawn that the failure sample with delayed brittle crack caused by hydrogen added by galvanization coupled with retained stress result from heat-riveting.
�����գ���ǿ�������� Ρ. �������Ͳ۴��Կ���ʧЧ����[J]. �й������ڿ���, 2015, 33(5): 35-39.
WANG Jun-yi��GAO Jia-qiang��SHEN Jian-hua��SHEN Wei. Failure analysis of brittle crack in the swollen slot of a spark plug. Chinese Journal of Iron and Steel, 2015, 33(5): 35-39.
2015, Vol. 33 
