球化剂稀土含量对大断面球铁石墨组织及低温冲击韧性的影响

选用3种具有不同Ce含量的球化剂FeSiMg6RE2、FeSiMg8RE3和FeSiMg8RE5对铁液进行盖包法处理,球化处理后浇注成180mm×180mm×200mm的球铁试块。通过室温拉伸、光学显微镜(OM)、扫描电子显微镜(SEM)、能谱分析仪(EDS)和低温冲击试验机等分析手段,研究了稀土元素Ce对大断面低温球铁的石墨组织、力学性能和低温冲击韧性的影响。结果表明:用稀土含量低的球化剂FeSiMg6RE2进行处理,试样的石墨组织细小均匀,石墨形态好,低温冲击韧性高,冲击功平均值约为14.5J;用稀土含量高的球化剂FeSiMg8RE3和FeSiMg8RE5分别进行处理,试样中出现了大面积碎块状石墨等变异组织,低温冲击韧性差,冲击功平均值分别约为6.5和5.1J。能谱分析结果表明:高稀土含量球化剂处理的球铁试样,石墨组织晶界上发生了稀土元素Ce的富集,其质量分数分别约为0.36%和0.42%,这是造成铸件中碎块状石墨等变异组织产生的根本原因,严重恶化了铸件的力学性能。

Effect of Re content in nodulizer on graphite microstructure and low-temperature impact toughness of heavy section ductile cast iron

Molten iron was treated in tundish-cover spheroidizing process by adopting three kinds of nodulizer (FeSi-Mg6RE2 ,FeSiMg8RE3 and FeSiMg8RE5) with different Ce contents and ductile iron test blocks with the dimen-sions of 180 mm × 180 mm × 200 mm were poured .The influences of RE content in nodulizer on graphite micro-structures and low-temperature impact toughness of heavy section ductile cast iron were investigated by room tem-perature tensile test ,metallographic microscope(OM ) ,scanning electron microscope (SEM ) ,energy dispersive spectrometer (EDS) and impact testing machine .The results show that the sample can get fine graphite grain , better graphite morphology ,and obtain high low-temperature impact toughness ,and the average impact power is about 14.5 J by nodularizing treatment adopting FeSiMg6RE2 ;by adopting FeSi-Mg8RE3 and FeSiMg8RE5 ,a great deal of chunky graphite appears in the castings ,the low-temperature impact toughness becomes bad ,the av-erage impact energy is only 6.5 and 5.1J ,respectively .And energy spectrum analysis shows that Ce is enriched at the grain boundary around the nodular graphite and the mass fraction is about 0.36 mass% and 0.42 mass% ,re-spectively ,which is the fundamental cause of the variation of the microstructure of the fragmented graphite ,seri-ously deteriorating the mechanical properties of castings .