板坯夹渣原因分析及预防

通过分析热轧卷夹渣缺陷的形貌及成分,结果显示:夹渣主要是结晶器保护渣卷入钢液中形成的。基于理论分析,得出结晶器窄边翻,水口结瘤以及液面波动是板卷夹渣缺陷的主要影响因素。最后,通过优化浸入式水口插入深度和吹氩流量,及时更换浸入式水口,以及稳定结晶器液面波动和拉坯速度等措施,显著地改善了铸坯质量,热轧归户降级率改进56.7%。     

舞钢连铸板坯皮下气泡缺陷的成因分析与控制

对舞钢生产连铸板坯的皮下气泡缺陷进行分析,发现气泡形状、位置以及产生原因与钢液气体含量、过热度、辅料含水量、浸入式水口形状及插入深度等因素有关.通过一系列工艺优化措施,例如提高过热度达标率、控制辅料含水量、优化浸入式水口形状和插入深度、改善结晶器保护渣透气性,将铸坯皮下气泡缺陷发生率降低30％以上.     

住友金属低成本浇注板坯的技术措施

介绍了日本住友金属工业公司低成本浇注板坯的技术措施,包括保温性能优良的结晶器保护渣的开发,合理控制超低碳钢浇铸用保护渣的碱度和粘度以减少板坯表面夹杂物、提高铸坯的质量,中间包底部供气以促进夹杂物上浮去除.在浸入式水口的设计方面,指出了优化设计水口内部耐火材料成分能减少夹杂物Al2O3黏结堵塞水口内壁,重点叙述了新型涡流浸入式水口的开发及在和歌山厂和鹿岛厂的应用情况:涡流浸入式水口减缓了钢水对结晶器液面的冲击,液面波动减小,板坯表面针孔和条状缺陷减少,水口使用寿命延长.     

20Cr钢曲轴锻件翘皮成因分析和工艺改进

20Cr钢的生产流程为120 t BOF-LF-200 mm×200 mm坯CC-轧制。对Φ35 mm 20Cr圆钢锻造的小型机械曲轴的结疤翘皮进行了成分检测、金相分析和电镜扫描能谱分析。结果表明,连铸过程结晶器液面波动超过±5 mm,造成保护渣卷入弯月面,引起铸坯表面夹渣和增碳,轧制过程形成结疤翘皮缺陷。通过浸入式水口深度由80～120 mm增加至90～130 mm,强化中间包水口和塞棒管控以及优化保护渣操作与性能使熔渣层厚度为10～15 mm,保证结晶器液面波动稳定在±3 mm内,避免了铸坯卷渣和锻件翘皮。     

大圆坯低碳钢表面裂纹的改善

大圆坯连铸机生产的低碳钢有时会出现铸坯表面裂纹缺陷,通过对浸入式水口插入深度、保护渣的使用、结晶器系统以及二次冷却强度等各项指标的优化,降低了低碳钢表面裂纹的缺陷。     

窄带钢边部缺陷成因及对策

分析了窄带钢烂边的主要原因及对策。认为结晶器卷渣是窄带钢烂边的主要原因,非稳态浇注是造成结晶器卷渣的主要因素。形成非稳态的主要因素有:中间包液面波动过大;浸入式水口插入深度不足;浸入式水口不对中;浸入式水口管壁穿透;拉速过快;开浇及浇注结束时间短;保护渣性能不匹配等。其中任何一个因素出现问题都会造成严重的铸坯表面夹渣。结合企业实际情况,通过提高渣系碱度,规范换包操作,调整浸入式水口深度等措施控制结晶器卷渣后,窄带钢边部缺陷已基本消失。     

25CrMnMo钢表面缺陷成因分析及控制

通过宏观形貌观察、微观组织(SEM)和能谱分析(EDS)等手段,分析了25CrMnMo钢管生产过程中表面缺陷产生的原因,并进行了系统优化。通过对25CrMnMo钢的理化性能分析,发现钢管表面宏观缺陷存在结晶器保护渣剥落现象,而微观分析发现钢管皮下含有许多大尺寸FeO-Na₂O-Al₂O₃-CaO不规则夹杂物。同时,将钢管表面缺陷处夹杂物成分与长水口、浸入式水口以及炉渣成分、结晶器内保护渣进行对比分析,发现钢内夹杂物中Na、Al为结晶器保护渣的代表元素,推断原工艺条件下,卷入且来不及上浮的结晶器保护渣在凝固前沿时被凝固坯壳捕获,并形成表面及皮下夹杂缺陷是25CrMnMo钢管出现缺陷的主要原因。通过将浸入式水口的插入深度由80～130 mm改为90～130 mm,电磁搅拌电流由300 A降为200 A,频率3.0 Hz不变等降低卷渣指数的措施,有效改善了25CrMnMo钢结晶器卷渣问题,提高了铸坯质量。     

消除合金结构钢连铸过程中夹渣的研究

采用先进的测试技术,并结合现场生产试验,查清了连铸坯产生夹渣的主要原因是浸入式水口穿裂、插入深度浅、结晶器电磁搅拌强度过大,造成结晶器卷渣.其次是钢包下渣卷入钢水中,钢中氢含量高与大颗粒夹杂形成渣气孔,钙处理加入Si-Ca量大,钙侵蚀耐火材料形成mCaO·nAl2O3未上浮留在钢中.为此,采用提高耐火材料质量及合理烘烤制度,降低结晶器搅拌电流,增加浸入式水口插入深度≥120 mm,提高钢的纯净度,降低氢含量,钙处理加入Si-Ca量控制在0.25～0.35 kg/t,使合金结构钢连铸坯低倍夹渣完全消除,确保了合金结构钢铸坯的内部质量.     

改善铸坯角部质量工艺优化研究

承钢提钒钢轧二厂连铸车间为提高铸坯质量,减少角部裂纹缺陷的产生,围绕结晶器流场与二冷比水量大小对铸坯质量的影响,从结晶器流场人手,重点分析了振动、浸入水口、塞棒吹氩、保护渣、结晶器液面波动对结晶器流场的影响,二冷比水量对铸坯冷却效果的影响,制定可行性方案,减少铸坯在结晶器内形成缺陷造成质量缺陷,改造后纵裂纹明显减少,降低了成本。     

热轧板夹渣缺陷成因及控制

利用SEM及EDS对河钢唐钢1700线热轧板夹渣缺陷的产生原因进行了分析。研究结果表明,夹渣缺陷主要为黑线和翘皮,两者成分中均含有一定量Na元素,主要为连铸过程中结晶器卷渣带入。从夹渣缺陷的产生机理入手,通过选择合适的氩气流量、水口结构、水口板面尺寸精度、水口浸入深度、保护渣,减少结晶器液位波动,稳定控制塞棒动作,减少拉速波动,优化捞渣、启渣线操作等措施,夹渣缺陷减少了至少60%,板卷夹渣率由4.9%降至1.5%,控制效果良好,产品质量得到有效提升。     

Three-dimensional analysis of molten steel flow in slab continuous casting mould with rotated ports in submerged entry nozzle

Abstract

The purpose of this study is to develop a three-dimensional (3D) analysis system capable of analysing the flow field of molten steel in the slab continuous casting mould with rotated ports in the submerged entry nozzle. The ultimate goal is to obtain the optimal design for the entry ports of the submerged nozzle, which can introduce favourable flow patterns to remove non-metallic inclusions and avoid entrapment of molten slag and casting powder to produce steel slab of high cleanliness. In this study, a computational fluid dynamics technique, Sola-Surf, is employed to conduct the 3D fluid flow analysis. The technique has the capability of treating fluid flow problems with a free surface that slightly vibrates. The slightly vibrating free surface presents fairly accurately the behaviour of the molten slag–casting powder layer in the continuous casting mould. The developed simulation system is then tested on a slab continuous casting mould to analyse the fluid flow behaviour of molten steel under various nozzle designs. The design conditions include submerged depth of the nozzle, tilted angle of the nozzle port, and rotated angle of the nozzle port. The results of the simulations show that of the various design factors rotation of the nozzle entry ports has the greatest effect on the flow pattern. It can prolong the residence time of the molten steel and stabilise the molten slag–casting powder layer, which is very favourable for obtaining continuous casting slag of high cleanliness.     

双渣线操作提高结晶器浸入式水口使用寿命的工艺实践

基于保护渣对6流140mm×140mm坯连铸结晶器铝锆质浸入式水口侵蚀机理的分析,通过控制结晶器钢液面为折线形周期性波动（振幅为5 mm,周期为2 h）浇铸5 h后升高中间包高度20~40 mm更换水口的渣线位置,扩大了水口被侵蚀的面积,减轻浸入式水口侵蚀深度。生产结果表明,在使用8 h的条件下,水口的侵蚀深度由工艺优化前的15 mm减小到优化后的5.5mm,提高了水口的强度,避免了因更换水口断裂而发生停浇事故。浸入式水口的使用寿命由8 h提高到10~12 h。     

Study on mechanism of mould powder entrapment in funnel type mould of flexible thin slab casting machine

Abstract

A physical model was established to study the mechanism of mould powder entrapment in the funnel type mould of a flexible thin slab casting machine, and the effects of operational parameters on the powder entrapment were investigated. The results show that there are three mechanisms of mould powder entrapment, vis-à-vis entrapment caused by shear stress, entrapment caused by vortex and entrapment caused by shear stress and vortex. Three different modes of the entrapment caused by the shear stress, between the mould powder and the molten steel flow produced by the flow from the upper ports of a four-port submerged entry nozzle, were observed. The entrapment caused by vortex occurs at the lowest position of the metal/slag interface. The entrapment caused by shear stress and vortex is a new mechanism, in which the powder is firstly drawn downward by shear stress and then pulls the powder layers above under the common action of shear stress and vortex.     

Ti对超低碳钢浸入水口堵塞的影响

针对鞍钢股份有限公司炼钢总厂2150 ASP中薄板坯铸机在浇注含Ti超低碳钢时水口堵塞严重的问题,分析了超低碳钢中Ti含量对水口堵塞的影响,通过优化RH工艺、顶渣改质、保护浇铸及提高耐材烘烤温度等措施,铸流换水口的频率由原来的平均1.7次/浇次降低到1.2次/浇次,单支浸入式水口的使用寿命由原来的平均88 min延长到119 min。     

圆坯结晶器水口优化的模拟研究

以大圆坯结晶器为原型,采用数值模拟与物理模拟相结合的方法,分别研究了使用直通式水口和4孔旋转水口时该圆坯结晶器内钢液流场和温度场的分布情况,对比分析了2种水口的优劣。数值模拟和物理模拟结果表明,使用目前常用的直通型水口时钢水冲击深度大,易在弯月面处形成死区,不利于圆坯内部及表面质量的提高;4孔旋转水口比直通水口的钢液冲击深度浅,回旋区位置明显比直通水口更靠近自由液面,这将有利于夹杂物的上浮去除和热区中心的上移。温度场模拟结果显示,使用旋转水口时自由液面温度比直通型水口高14℃,更有利于结晶器内钢水过热耗散及保护渣的熔化,可防止液面结壳。     

结晶器保护渣试验条件探讨

介绍了影响结晶器保护渣试验效果的主要浇注工艺因素,对结晶器保护渣试验条件进行了探讨。试验时必须考虑钢水质量和温度、浇注液面的稳定性、水口插入深度及对中精度、保护浇注效果、氩气大小以及保护渣操作等各方面因素的影响。通过保护渣反复试验,不断调整保护渣理化指标和连铸机浇注工艺条件,保护渣性能才能不断满足工艺质量的要求。     

宽板坯连铸结晶器内钢液流动的数值模拟

结合水模型实验,应用商业软件Phoenies模拟230 mm×2 000 mm连铸坯结晶器内钢液流场。研究了浸入式水口底型、插入深度、出口倾角等工艺参数对钢液面波动及流股对结晶器窄面冲击力的影响,并用水模型实验进行验证。结果表明,合理的浸入式水口结构尺寸和工艺参数为:凹底结构、插入深度120 mm、倾角15°。     

水口扩张角对230mm x 1300 mm板坯结晶器流场及氩气泡行为的影响

利用离散相模型研究水口扩张角（0~12°）对230mm×1300 mm板坯结晶器流场及氩气泡行为影响。并用水模型实验进行了验证。结果表明,扩张角增大,能显著减小注流冲击深度及氩气泡在自由液面上浮区域;尤其当扩张角为9°时,结晶器流场较好,自由液面波动较小,有利于夹杂物去除及减轻界面卷渣几率。双流230mm板坯连铸工业性试验表明,安装扩张角9°的水口一流铸坯较安装无扩张角水口的另一流铸坯表面夹渣发生率降低了5.9%~14.8%。     

Carbon Pickup in Continuous Casting Processes

The quality of the as‐cast strand is influenced by a recarburization reaction since mould powder contains carbon particles necessary for a controlled melting behaviour. Intensive testing reveals a carbon pickup in the surface of the as‐cast strand depending on content and type of the carbon in the mould powder. Using the combination of laboratory trials and numerical simulations the effect of carbon pickup from mould powder to the strand shell was investigated. Laboratory experiments show that the recarburization of the liquid steel through the mould powder can be explained by Marangoni convection. This can happen in the slag rim when the carbon is entrapped by the solidifying steel and starts to diffuse inwards the strand.     

Effects of several casting parameters on slag entrapment in mould (part B:numerical modeling)

Based on the effects of several casting parameters on slag entrapment in the mould (water modeling),the numerical modeling was researched. The results show that the flow field with a submerged nozzle section dimension of 65 mm×80 mm is better than that with a submerged nozzle section dimension of 40 mm×40 mm and is favorable for avoiding slag entrapment. In this paper,low surface velocity,small level fluctuation and proper impact depth can be achieved with a nozzle of an outlet angle of 25° and an immersion depth of 150 mm,or with a prototype nozzle of an outlet angle of 15° angle and an immersion depth of 150 mm.