奥氏体不锈钢凝固组织中残留铁素体特征研究

 采用化学侵蚀、彩色金相和电子探针（EPMA）等方法对AISI304奥氏体不锈钢连铸方坯凝固组织及其残留铁素体的形貌、化学组成等特征进行了分析，并采用DICTRA软件对铁素体向奥氏体的扩散转变进行了模拟研究，结果表明AISI304不锈钢铸坯表层树枝晶区的二次枝晶间距为12~20μm，富Cr贫Ni的残留铁素体呈骨骼状分布；铸坯中心等轴晶区的残留铁素体为蠕虫状分布，中心等轴晶区的残留铁素体富Cr贫Ni的同时富Si贫Mn，且其富Cr贫Ni的程度比柱状晶区的残留铁素体轻。钢液成分和先析铁素体向奥氏体扩散转变时间、距离是影响残留铁素体化学组成的主要因素。

Characteristics of Residual Ferrite in Solidification Microstructures of Austenitic Stainless Steel

The morphology,composition of residual ferrite in continuous casting AISI304 stainless steel billet was studied by chemical etching,color metallography and electron probe micro-analysis(EPMA) method.The transformation of ferrite to austenite was simulated by DICTRA software,too.The results show that the spacing between secondary branched dendrites is about 12-20 μm in dendritic crystal zone of AISI304 stainless steel;the solidification mode in columnar dendrite zone is the FA mode;the morphology of residual ferrite enriched in Cr and depleted in Ni is skeletal.The morphology of residual ferrite enriched in Cr,Si and depleted in Ni,Mn is vermicular in center equiaxed grain zone.The chemical composition of molten steel,transformation time and distance of ferrite to austenite are the key factors for composite of retained ferrite.