【作者】 张锐；

【导师】 姜周华；

【作者基本信息】 东北大学 ， 冶金工程， 2021， 硕士

【摘要】 节能环保、海洋工程、石油化工等高端装备制造业的迅猛发展,必然对关键材料的质量提出更高要求。超级奥氏体不锈钢具有十分优秀的强度及耐腐蚀性能,在腐蚀性严重的领域应用广泛,是高端装备制造业急需的关键材料之一。超级奥氏体不锈钢的开发和应用主要集中在国外,目前我国仅实现了第一代超级奥氏体不锈钢904L和第二代超级奥氏体不锈钢254SMO的国产化,并且254SMO的生产过程中还有很多瓶颈问题急需解决,第三代超级奥氏体不锈钢654SMO正处于研发阶段。超级奥氏体不锈钢654SMO在制备与热加工阶段存在许多问题:(1)654SMO铸坯在连铸制备过程中体积收缩十分严重,铸坯表面易开裂;(2)654SMO合金元素含量高,中心元素偏析及二次相析出严重;(3)铸坯均质化过程中晶粒粗化与高温氧化严重,且热连轧过程中极易开裂。基于以上问题,本文提出应用结晶器喂带技术,即通过不锈钢带熔化吸热快速降低钢液中心过热度并增加形核质点,提高等轴晶率并细化等轴晶。本文利用商业软件Fluent,耦合Launder-Sharma低雷诺数湍流模型、焓多孔介质模型、VOF多相流模型,建立了喂带前后立式板坯连铸过程的三维凝固模型,详细分析了单侧喂带、双侧喂带工艺下流场、温度场及凝固坯壳的分布并分析了单侧喂带工艺下喂带速度及喂带温度的影响,同时研究了固态钢带在过热钢液中的生长过程及熔融钢带的流动方向和空间分布。计算结果表明,向结晶器中喂入钢带后钢液流场依旧维持经典的“双辊式”结构。钢带一开始喂入钢液时生长很快;喂到水口侧口附近时生长极慢;喂过侧口时生长速度突然增大,且钢带在喂入熔池过程中生长速度逐渐减小。在钢带能喂过侧口的工况中,熔融钢带主要向中心流动替代喂带前中心过热钢液的位置,板坯中心过热度因此得到显著降低。在钢带不能喂过侧口的工况,熔融钢带向板坯窄面流动并促进坯壳生长。在单侧喂带工艺中,随着喂带速度增加或喂带温度减小,喂带深度将增加,更多钢液的过热得到降低。向结晶器中喂入钢带可以促进结晶器内坯壳的生长且双侧喂带工艺的促进效果更明显。双侧喂带工艺可以解决单侧喂带造成的流场、温度场不对称问题,且双侧喂带工艺对温度场的改善效果比单侧喂带更好。基于建立的数学模型,研究了单侧喂入振荡钢带对钢液流场、温度场分布及坯壳分布的影响。研究结果表明,向结晶器中喂入振荡钢带后,流场依旧维持着经典的“双辊式”结构,钢带附近一部分钢液被振动钢带带动向钢带两侧流动,只有一小部分钢液在绕过钢带后拥有足够的动能再次绕过钢带形成完整回流,大部分钢液在绕过钢带或撞击结晶器窄面后会沿着铸造方向向下流动。单侧喂入不振荡钢带可以使中心过热度下降2～4K,喂入振荡钢带可使中心过热度在此基础上再下降约5 K。单侧喂入振荡钢带对坯壳生长的促进效果比喂入不振荡钢带明显得多,由于过热钢液冲刷形成的未凝固区域基本上完全消失。更多还原

【Abstract】 The rapid development of advanced equipment manufacturing industry such as energy-saving environmental protection,ocean engineering,petrochemical engineering will inevitably put forward higher requirements for the quality of key materials.Super austenitic stainless steel has excellent strength and corrosion resistance,is one of the key materials urgently needed by advanced equipment manufacturing industry when it is used in areas with serious material corrosion.The development and application of super austenitic stainless steel are mainly concentrated in foreign countries.At present,China has only realized the localization of he first generation of super austenitic stainless steel 904L and the second generation of super austenitic stainless steel 254SMO,but in the production process of which there are still many bottleneck problems.The third generation of super austenitic stainless steel 654SMO is in the research and development stage.There are many problems in the production process of super austenitic stainless steel 654SMO:(1)The volume shrinkage of 654SMO slab is very serious during continuous casting process,which leads to easy cracking on the surface of slab;(2)The content of alloy elements is high for 654SMO,which leads to the serious central element segregation and secondary phase precipitation;(3)Grain coarsening and high temperature oxidation are serious during homogenization process of slab,and cracking is easy during hot continuous rolling.Based on above problems,the application of feeding strip technology has been proposed in this paper,which is,decreasing central superheat rapidly and increasing nucleation particles through the feeding strip technology,so that the equiaxed crystal rate is improved and the equiaxed crystal is refined.This paper has used the commercial software Fluent,coupled Launder-Sharma low Reynolds turbulence model,the enthalpy-porosity technology,VOF multiphase model,built a 3D solidification model during vertical slab continuous casting process with or without strip feeding.The flow field,temperature field and solidified shell distribution have been simulated,the effects of strip feeding speed and temperature during unilateral strip feeding process have been analyzed in detail,and the growth process of solid strip in superheated melt and the flow direction and spatial distribution of molten strip have been studied at the same time.Simulation results show,the flow field still maintains "double roll" pattern after strip feeding into the mold.Strip grows quickly when starts to be fed;strip grows slowly when strip is fed around SEN port;at the time that strip is fed beyond SEN port,its growth speed increases suddenly,as strip is fed into melt,the speed of strip growth gradually decreases.Under the condition that strip can be fed through the SEN port,molten strip mainly flows toward center and replaces superheated liquid steel,central temperature thus decreases significantly.Under the condition that strip can’t be fed through the SEN port,molten strip flows toward side of slab and solidification trend of solidified shell in the mold becomes more obvious.In the unilateral strip feeding situation,as strip feeding speed increases or feeding temperature decreases,the depth of strip feeding will be larger,and the superheat of more central melt will decrease.Strip feeding can promote solidification trend of solidified shell in the mold,the improvement effect of bilateral strip feeding is better.Bilateral strip feeding can improve symmetry of flow and temperature field compared to unilateral strip feeding,and the improvement effect of bilateral strip feeding on temperature field is better compared to unilateral strip feeding.Based on the established mathematical model,the influence of feeding vibrating strip unilaterally on the flow field,temperature field and solidified shell distribution of liquid steel has been studied.Simulation results show,the flow field still maintains"double roll" pattern after feeding vibrating strip unilaterally.A part of liquid steel around strip is carried by strip and flows toward two sides of strip.Only a little part of liquid steel has enough momentum to bypass strip again to form a complete backflow after bypassing the steel strip,most flows down along the casting direction after bypassing the steel strip or hitting the narrow face of the mold.Feeding non-vibrating strip unilaterally can reduce the central superheat by 2～6 K,and feeding vibrating strip can reduce the central superheat by about 5 K on this basis.The effect of feeding vibrating strip unilaterally on the growth of solidified shell is much more obvious than that of feeding non-vibrating strip,and the no solidified shell formation due to the wash of superheated liquid steel almost completely disappears.更多还原