【作者】 王成全；

【导师】 李廷举； 方园； 于艳；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2005， 硕士

【摘要】 薄带连铸工艺是将金属液直接浇铸到旋转的结晶辊中间的熔池中,在结晶辊的激冷作用下凝固并受到结晶辊的轧制后成带,是当前冶金界的前沿技术。 本文采用自行研制的界面传热模拟实验装置在实验室中模拟研究不锈钢的亚快速凝固过程,随着浸入时间的增加,试样的凝固组织粗化,凝固由枝晶生长变为胞晶生长,二次枝晶臂间距增大,通过与薄带连铸工艺比较发现,两者的界面传热类型、凝固方式以及冷却速度相当;在Confocal高温成像仪下,实时观察薄带连铸不锈钢铸带在高温下的组织变化过程,在600～900℃晶内首先析出碳化物,随后晶界也开始析出,析出的碳化物在1000℃开始溶入基体内;在熔化时,连铸薄带以晶内熔化为主,传统工艺不锈钢以晶界熔化为主。 对薄带连铸不锈钢铸带组织分析发现,夹杂物直径粗大,大部分呈球形弥散均匀分布,没有产生偏聚;碳化物主要在铁素体奧氏体相界和晶界处产生,呈点状或线条状不连续分布;不锈钢中铁素体分布主要以条状或短条状为主,含量受到合金成分,凝固冷却速度等的影响。铁素体数量与不锈钢的铬镍当量比率成正比关系,快速的冷却速度容易在奧素体枝晶间形成长条状铁素体,对不锈钢组织和性能产生不利影响;在带厚方向发现存在Ni、Mn等元素的偏析现象,这与薄带连铸工艺有很大的关系,受到凝固扩散和液相流动的双重影响。更多还原

【Abstract】 Twin-roll strip cast process is a advanced technology in the fields of current metallurgy, that the metal melt is directly cast into a pool made of two rotating rolls, solidified under chill cooling of the rolls and formed a strip with the rolls.An interfacial heat transfer simulation apparatus is used to study the austenitic stainless steel microstructure under near-rapid solidification. The samples have larger secondary dendnte arm space and take place morphology transition from dendrite growth to cell growth with the increasing of immerging time. Similar to the twin-roll strip cast process, they have same kind of interfacial heat transfer ,solidification type and also the same cooling rate. The microstructure transition of stainless steel cast strip is observed dynamically at real time with the Lasertech Confocal Scanning Laser Microscope. During 600-900 ℃,the carbides are precipitated first in grains inside, then grains interfaces. However, the precipitated carbides is dissolved slowly into substrate when the strip is heated higher than 1000℃.While stainless steel is melt, the strip produced by strip cast process is melt first mainly in grains inside, but stainless steel produced by conventional processes first mainly in grains interface.Through stainless steel strip microstructure analysis, it can be found that the inclusions have bigger diameter size and most distributing equably as spheres, no inclusions gathering has been found. The carbides precipitate in grains interface and phases boundary between ferrite and austenite, uncontinuously distributing as spot or line. The ferrite in stainless steel mainly distributes as acicula or cosh, the counts are effected by alloy components, solidification cooling rate and so on, it’s a linearity relation with alloy’s Cr/Ni ratio. Under rapid cooling rate, lathy ferrite will be formed among the austenite dendrite branches, badly effect on the stainless steel microstructure and properties. A Ni, Mn elements segregation is found in strip thickness direction, related to the strip cast process due to the effect of solidification diffusion and meltflow.更多还原