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球墨铸铁件异常灰斑组织的研究
Research on Abnormal Grey-speckle Structure of Ductile Iron
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- DOI:
- 作者:
- 邓晗 杨志刚 王瑞 陈璐
DENG Han;YANG Zhigang;WANG Rui;CHEN Lu
- 作者单位:
- 中车戚墅堰机车车辆工艺研究所有限公司
CRCC Qishuyan locomotive&rolling stock technology research institute Co.,Ltd.,Changzhou 213011,China
- 关键词:
- 球墨铸铁 灰斑 偏析
ductile iron black spot segregation
- 摘要:
- 球墨铸铁件厚大部位在特定情况下易产生一种条带状灰斑缺陷,该缺陷会显著降低材料的硬度。通过扫描电镜(SEM)和能谱分析(EDS)等方法对异常灰斑的金相组织和微区成分进行了分析。结果表明:低于4.3%的碳当量、成分偏析和厚大且相对封闭的铸件结构是形成这一缺陷的主要原因。在这些条件下易形成缓冷枝晶,Si元素在缓慢冷却的奥氏体支晶内部偏析并富集,促进形成铁素体;而Mn元素和Cu元素在枝晶附近及外部偏析并富集,促进珠光体形成。两种基体组织的硬度差使加工后出现很大的色差,形成宏观的灰斑形貌。Under certain conditions,most of the thickness of nodular cast iron was prone to strip gray spot defects,which would significantly reduce the hardness of the material.The microstructure and microregion composition of abnormal gray spots were analyzed by SEM and EDS.The results show that carbon equivalent of less than 4.3%,composition segregation and thick and relatively closed casting structure are the main causes of this defect.Under these conditions,slow-cooling dendrites are easy to form.Si elements are isolated and enriched in the slow-cooling austenite branchlets to promote the formation of ferrite.Mn and Cu are separated and enriched near and outside the dendrite to promote the formation of pearlite.The hardness difference of the two kinds of matrix makes great color difference after processing and forms the macroscopic gray spot morphology.