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采用热旋压工艺将30Cr Mo无缝钢管成形为气瓶后,在气瓶封头底部熔合处出现裂纹,严重影响了气瓶质量。本文通过金相、扫描电镜、能谱分析等方法,对气瓶裂纹部位进行了金相组织观察及夹杂物分析。结果发现,裂纹周边出现大量脱碳铁素体,强度较低,且铁素体晶粒粗大,组织中伴有混晶,形变时受晶界影响的区域相对缩小,大尺寸晶粒间易造成应力集中,导致裂纹产生。裂纹周围还存在大量氧化夹杂物,破坏了母体金属的连续性,降低了材料塑性,如果这时局部塑变过大,超过微区塑变极限,就会形成微裂纹,并进一步扩展为宏观裂纹。
After the hot-rolled 30Cr Mo seamless steel tube is formed into a cylinder by hot spinning, a crack occurs at the fusion spot of the bottom of the cylinder head, which seriously affects the quality of the cylinder. In this paper, microstructure, scanning electron microscopy, energy spectrum analysis and other methods, the microstructure of the cylinder cracks were observed and inclusions analysis. The results show that a large amount of decarburized ferrite appears at the periphery of the crack, the strength is low, the ferrite grains are coarse, the mixed crystal is formed in the structure, the area influenced by the grain boundary during the deformation is relatively narrowed, and large- Stress concentration, resulting in cracks. There are also a large number of oxidized inclusions around the cracks, which destroy the continuity of the parent metal and reduce the plasticity of the material. If the local plastic deformation is too large at this time, the micro-cracks will be formed beyond the plastic deformation limit of the micro-zone and the macro-cracks will be further expanded .