大断面球铁件电炉熔炼工艺及石墨畸变机理研究

探讨了大断面QT600-3球铁件电炉熔炼生产工艺的技术要点,检测了试生产条件下球铁单铸试块与本体试块的化学成分、金相组织与力学性能,基于石墨结晶核心和石墨形态的分析,探讨了石墨畸变机理。生产试验结果表明:炉外增Si预处理增加铁液成核,轻、重稀土混合使用作为球化剂,侧重后期孕育,适当降低浇注温度,合理使用Cu元素,是电炉熔炼工艺生产大断面球铁件的重要环节;采用电炉熔炼工艺生产大断面球铁件,球化等级与化学成分稳定控制有关,抗拉强度、伸长率等力学性能与化学成分、基体组织有关;Y在铁液中形成高熔点Y2O3作为石墨析出的核心,可获得良好石墨形态;大断面球铁件中,Ti、Cu元素的偏析和球化元素Mg或稀土(Y、La、Ce)的氧化,破坏了奥氏体壳的稳定性,是造成石墨畸变的主要原因。

Study on Electrosmelting Process of Large Section Ductile Iron and the Mechanism of Graphite Distortion

Electrosmelting process of large section QT600-3 ductile iron was discussed,the chemical composition,microstructure and mechanical properties are detected under the conditions of the pre-production,and the mechanism of graphite distortion was analyzed on the basis of graphite core and form.The results show that the important part of large section casting produced by the electrosmelting process may be as follows: the pretreatment by Si addition,light and heavy rare earth mixed use for nodularizer,focusing on post-inoculation,reducing the pouring temperature,the rational use of Cu element.Using furnace process to produce large section ductile iron parts,nodularizing grade is related to stability of the chemical composition,tensile strength,elongation and other mechanical properties is related to chemical composition and the matrix organization.Better graphite morphology is obtained because the graphite core is mainly composed of high melting-point precipitation Y2O3 from Y element in the molten iron,the graphite distortion is caused by Ti,Cu elements segregation and nodularizing elements Mg or rare earth(Y,La,Ce) oxidation,which destroy the austenite shell stability.