铸铁合金凝固过程中石墨演化过程研究

Microstructure Evolution of Cast Iron Alloys during Solidification

以柴油机缸盖用铸铁材料(HT300、RuT300、QT600)为研究对象,采用液淬的方法制备不同凝固阶段的试样,并分析其凝固过程。研究铸铁的显微组织、相组成,分析显微组织演变机理,特别对石墨的生长过程进行了研究。结果表明,共晶反应阶段蠕墨铸铁释放的热量较多,球墨铸铁次之,灰口铸铁释放的热量最少。铸铁合金石墨初始形貌均为球状,且石墨球独立生长,在共晶反应阶段发生变异形成片状、球状或蠕虫状。石墨内部和外部元素差异较大,石墨内部碳含量很高,四周出现O、S、Si、Mg等合金元素的富集现象。石墨核心碳元素的原子百分比为91.72%;石墨靠外部分的碳原子百分比降至77.95%,S元素原子百分增加4.74%,Mg元素原子百分比增加5.09%。

Cast iron(HT300,Rut300,QT600)for diesel engine cylinder head was used as the research object.The solidification process of cast iron samples in different solidification stages was analyzed by liquid quenching.The microstructure and phase composition of cast iron were studied,and the evolution mechanism of microstructure was analyzed.The growth process of graphite was also studied.The results show that the heat release of vermicular cast iron is more during the eutectic reaction stage,followed by nodular cast iron and gray cast iron.The graphite of cast iron alloy is spheroidal in its initial morphology,and the graphite spheroidal grows independently.During the eutectic reaction stage,the graphite spheroidal or vermicular shape changes.The internal and external elements of graphite are very different,the internal carbon content is very high,and the enrichment phenomenon of O,S,Si,Mg and other alloying elements appears around the graphite.The atomic percentage of carbon element in graphite core is 91.72%.The percentage of carbon atom in the outer part of graphite decreases to 77.95%,the percentage of S element atom increases by 4.74%,and the percentage of Mg element atom increases by 5.09%.