37Mn5钢管内壁鼓包缺陷分析

37Mn5钢管热轧矫直后在内管壁出现鼓包缺陷,为了查找鼓包产生原因,采用显微镜和扫描电子显微镜等设备对鼓包的形貌、微观组织、化学成分及鼓包区域的形貌等内容进行了分析。结果表明:钢管化学成分和组织正常,钢管基体和鼓包区域含有较多相同的夹杂物,夹杂物均含有Ca、O、Fe、Na、K、Mg 等元素,这些元素组成含有多种氧化物和结晶器保护渣的大尺寸复合型夹杂物。进而得知钢管的鼓包缺陷产生原因:由于钢管内存在大量此类复合夹杂物在穿管过程中和钢管基体间的接触层面脱离并逐渐萌生裂纹,裂纹在比较大的周向压力作用下向内壁凸起并形成鼓包。

The bulging defect analysis of inner wall of 37Mn5 steel pipe

The bulging defects were observed in inner wall of 37Mn5 steel pipe after hot rolling and straightening. In order to find out the causes of bulging, the morphology of bulge, microstructure, chemical composition, and morphology of bulge area were analyzed by means of microscope and scanning electron microscope. The results showed that the chemical composition and microstructure of the steel pipe were normal. There were many same inclusions in the steel pipe matrix and the bulging area. All inclusions contained Ca, O, Fe, Na, K, Mg and other elements, and these elements formed large-scale composite inclusions containing a variety of oxides and mold flux. It was found that the cause of the bulging defect of the steel pipe was as follows: many such compound inclusions were separated from the contact plane among and the steel pipe matrix and gradually initiated cracks in the process of pipe threading. The cracks bulged to the inner wall and formed bulging under the action of relatively high circumferential pressure.