Tooth flanks used in gear rim applications of iron ore pelletizing plant get failed frequently, and the failures are also likely to take place in other suspected flanks. The objective of the study is to identify crack through nondestructive inspection and ascertain the probable cause and causes of failure to occur in the part based on examination and by studying its chemical, metallurgical, and mechanical properties. Ultrasonic inspection has been carried out on many tooth flanks fitted in the gear rim at plant site and found the presence of a subsurface crack in the core region at 40 mm depth from the side surface of the tooth flank. The inspected and identified tooth flank was used for failure analysis. Liquid penetrant test was carried out and it was found that a longitudinal centerline crack existed which propagated from core to the surface toward the trailing edge. Samples identified near the cracked region and surface were cut by machining, and metallographic characterization was carried out through optical, field emission scanning electron microscope, and electron probe microanalyzer. The microstructural features show the presence of many isolated micro-cracks and their orientation and inclusions. The presence of the martensitic phase at subsurfaces and pro-eutectoid cementite at isolated regions with the presence of high carbon concentration, amount to an increase in hardness in comparison with tempered martensite phase at core region. It was observed that micro-crack nucleated at nonmetallic inclusions. The nonmetallic inclusions, i.e., MnS, the difference in microstructures, a variation of hardness and nucleation of the void, void growth, and void coalescence, were found in the grain interface leading to propagation of crack and caused the rupture of the part during service.

铁矿石造粒厂齿轮轮缘应用中使用的齿面经常出现故障，并且其他怀疑的齿面也可能发生故障。本研究的目的是通过无损检查确定裂纹，并通过检查并研究其化学，冶金和机械性能，确定零件发生故障的可能原因。在工厂现场对安装在齿轮轮辋上的许多齿面进行了超声波检查，发现在距齿面侧面40 mm深度的核心区域存在亚表面裂纹。经检查和确定的齿面用于故障分析。进行了液体渗透测试，发现存在纵向中心线裂纹，该裂纹从芯部向表面向后缘扩展。通过加工切割在裂纹区域和表面附近识别出的样品，并通过光学，场发射扫描电子显微镜和电子探针显微分析仪进行金相表征。微观结构特征表明存在许多孤立的微裂纹及其取向和夹杂物。与核心区域的回火马氏体相相比，在地下区域存在马氏体相，在孤立区域存在高碳浓度的前共析渗碳体，等于增加了硬度。观察到微裂纹在非金属夹杂物中成核。非金属夹杂物，即