高镍316L不锈钢连铸方坯凝固模式及残留铁素体特征  

Solidification mode and residual ferrite characteristics of high nickel 316L stainless steel continuous casting billet

作　　者：王洋 陈蕾 牟望重 张政睿 王剑[1] 陈超[1] WANG Yang;CHEN Lei;MU Wangzhong;ZHANG Zhengrui;WANG Jian;CHEN Chao(College of Materials Science and Engineering,Taiyuan University of Technology,Taiyuan 030024,Shanxi,China;College of Mechanical and Vehicle Engineering,Taiyuan University of Technology,Taiyuan 030024,Shanxi,China;Department of Materials Science and Engineering,KTH Royal Institute of Technology,Stockholm SE-10044,Sweden;Key Laboratory of Electromagnetic Processing of Materials(Ministry of Education),Northeastern University,Shenyang 110819,Liaoning,China)

机构地区：[1]太原理工大学材料科学与工程学院,山西太原030024 [2]太原理工大学机械与运载工程学院,山西太原030024 [3]瑞典皇家工学院材料科学与工程系,瑞典斯德哥尔摩SE10044 [4]东北大学材料电磁过程研究教育部重点实验室,辽宁沈阳110819

出　　处：《钢铁》2024年第5期80-91,共12页Iron and Steel

基　　金：国家自然科学基金资助项目(52104338);教育部“春晖计划”合作科研资助项目(HZKY20220507);山西省回国留学人员科研资助项目(2022-040);山西省应用基础研究计划面上资助项目(202303021221036)。

摘　　要：奥氏体不锈钢中的残留铁素体对其使用性能有着重要影响,而残留铁素体特征主要与成分、冷却速率和凝固模式有关。研究了高镍含量316L奥氏体不锈钢连铸方坯,其成分位于共晶点附近,凝固模式容易发生改变。采用金相显微镜(OM)、image-pro-plus软件计算等方法,探究316L奥氏体不锈钢连铸方坯沿厚度方向残留铁素体特征及分布规律。结果表明,残留铁素体沿厚度方向呈现短棒状、颗粒状、骨骼状和网状结构,其铁素体分布情况与板坯中“M”形分布相似。铸坯表面到距铸坯表面55 mm处,铁素体体积分数在2%左右波动,在距铸坯65 mm处,铁素体体积分数增加到最高值(4.77%),随后75 mm处铁素体体积分数又突然降低,从75 mm到中心铁素体体积分数有增加趋势。使用电子探针(EPMA)分析发现,Cr、Ni、Mo、Si、Mn等元素都出现了不同程度的微观偏析现象,同时发现由铁素体通过固态相变形成的二次奥氏体还保留部分铁素体的成分特征。使用热力学计算软件(Thermo-Calc)计算了Fe-Cr-Ni三元相图以及铸坯边部和中心的平衡凝固过程,计算结果表明,铸坯边部以FA模式凝固,铸坯中心以AF模式凝固。通过残留铁素体形貌判断的凝固模式与热力学计算结果不同,铸坯在边部和中心以AF模式凝固,在柱状晶区出现了以FA模式凝固的骨骼状铁素体。最后分析了残留铁素体分布的形成机理,表面细晶区铁素体体积分数较少,这是由于表面凝固模式为AF模式;在距铸坯表面65 mm处铁素体体积分数增加到最高值,这是由于凝固模式发生了由AF模式向AF+FA模式的转变;75 mm处铁素体体积分数降低,这是由于凝固模式又转变为了AF模式;从75 mm处到铸坯中心,等轴晶结构和冷却速率降低使得固态相变所需的扩散距离增加,导致铁素体体积分数增加。The presence of residual ferrite in austenitic stainless steel significantly influences its performance.The characteristics of residual ferrite is related to composition,cooling rate,and solidification mode.This study focuses on a 316L austenitic stainless steel continuous casting billet,which possesses a high nickel content and is in the eutectic point of composition.Moreover,its solidification mode exhibits susceptibility to alteration.The characteristics and distribution of residual ferrite in the thickness direction of 316L austenitic stainless steel billet were investigated using optical microscopy(OM)and image-pro-plus software.The results reveal that the residual ferrite exhibits a morphology characterized by short rods,granules,skeletal structures,and network formations along the thickness direction.Furthermore,the distribution pattern of ferrite resembles an"M"type distribution which is similar to that observed in slabs.The ferrite content(volume fraction)exhibits a fluctuation around 2%from the billet surface to a depth of 55mm,reaching its highest value(4.77%)at a distance of 65mm from the surface before abruptly decreasing at 75mm.Subsequently,there is an increase in ferrite content towards the center.Electron probe microanalysis(EPMA)was employed to investigate Cr,Ni,Mo,Si,Mn and other elements,revealing that the secondary austenite formed through solid phase transformation retains certain compositional characteristics inherited from ferrite.The ternary phase diagram of Fe-Cr-Ni and the equilibrium solidification process of the edge and center of the billet were calculated using a thermodynamic calculation software(Thermo-Calc).The results indicate that FA mode is observed at the edge while AF mode is observed at the center of the billet.Notably,the solidification mode determined by residual ferrite morphology differs from the thermodynamic calculation results.The casting billet solidifies in the AF mode at both the edge and center,while a skeleton-like ferrite forms which indicate the FA mode within

关 键 词：316L奥氏体不锈钢 铁素体形貌 铁素体体积分数 热力学计算 凝固模式 

分 类 号：TF777.2[冶金工程—钢铁冶金]