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针对18CrMnB齿轮钢棒材局部硬度异常、加工性能较差的问题，对其硬质点区域的夹杂物和基体进行了成分与组织研究，探讨了棒材中硬质点相的性质，分析了影响硬质点形成及分布的工艺因素。结果表明，大块与分散型夹杂物分别为顶渣带入的复合氧化物以及其轧制破碎的小型夹杂物。这些氧化物熔点高硬度大，构成棒材加工过程中的硬质相。基体微观组织均为铁素体和珠光体，尽管自表面至中心有大小差异，但不是棒材加工局部硬度大的成因。“,”For the problem of partial abnormal hardness and poor machinability with the hot-rolled bars of 18CrMnB gear steel,the related inclusions and base microstructure were analyzed.The properties of the hard phases were dis-cussed,and the process factors resulting in the defect were investigated.The results show that the bigger and scat-tered inclusions were ladle flux induced combined oxides and their crushed ones due to rolling operation,respective-ly.The high melting point oxides led to the appearance of the hard phases in the steel bars.The basic microstruc-ture of the steel,however,was confirmed to be composed of ferrite plus pearlite,which shew different sizes from surface to inward but should not be the cause of the hard phases.