通过真空感应炉试验,研究不同Mg含量处理所获得的不同MgO-Al2 O3-SiO2复合夹杂物对凝固组织的影响.试验结果表明,随着钢中Mg含量的增加,铸锭等轴晶率呈现先升高后下降的趋势,而等轴晶尺寸和柱状晶宽度呈现先降低后升高趋势,存在一个最佳的Mg的质量分数范围(5～13)×101,铸锭的等轴晶率在70％以上.夹杂物观测并结合热力学计算发现,随着钢中Mg含量的增加,MgO-Al2O3-SiO2复合夹杂物外层逐步析出MgO·Al2O3相;然而,Mg的质量分数高于13×10-6时,夹杂物外层开始析出2MgO·SiO2相.晶面错配度计算表明,MgO·Al2O3与δ-Fe的错配度为1.2％,2MgO·SiO2与δ-Fe的错配度为13％.可以判断,MgO·Al2O3相可促进等轴晶形成,抑制品粒长大,2MgO· SiO2相则起不到促进形核作用.从而解释了铸锭等轴晶率、晶粒尺寸随Mg含量的变化规律.
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