27CrMoTi钢套管螺纹表面裂纹成因分析

摘要

某厂生产的27CrMoTi钢套管经车削加工后,在螺纹表面发现有裂纹缺陷.采用化学成分分析、宏观观察、扫描电镜及能谱分析、金相检验等方法,分析了裂纹的产生原因.结果表明:27CrMoTi钢套管螺纹表面裂纹内部存在大量夹杂物,为连铸结晶器保护渣卷渣造成的;在热轧穿管时,应力集中致使套管萌生裂纹,且扩展成为表面裂纹.%Crack defects were found on surface of thread of 27CrMoTi steel casing pipes produced by one plant after turning process.Causes for cracks were analyzed by methods of chemical composition analysis, macroscopic observation,analysis of scanning electron microscope and energy spectrum,metallographic inspection and so on.The results show that:there were a great amount of inclusions in the interior of surface cracks of thread of 27CrMoTi steel casing pipes,and the inclusions were caused by slag entrapment of mould powder for continuous casting crystallizer;the cracks initiated and propagated to be surface cracks as a result of stress concentration during hot-rolling.