Clogging behavior of submerged entry nozzles for Ti-bearing IF steel

The nozzle clogging behavior of Ti-bearing IF steel was studied by metallographic analysis,scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）,and X-ray diffraction（XRD）.According to the experimental results,nozzle clogging primarily appears three layers.There are a lot of large-sized iron particles in the inner layer and mainly slag phase in the middle and outer layers.The principal clog constituents of the inner layer are loose alumina cluster inclusions and granular shaped alumina inclusions,containing iron particles. The clog constituents of the middle layer are mainly dendrite alumina inclusions.The primary phases existing in nozzle clogging are FeO·TiO2 and FeO·Al2O3 besidesα-Al2O3 and a-Fe.The FeO·TiO2 phases among the deposits adhere the deposits together firmly enough to lead to the inferior castability of Ti-bearing ultra low carbon steel compared with that of Ti-free low carbon Al-killed steel.

Influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds

The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozzle port not only increases the velocity of molten steel, but also enhances the wall shear stress, F number and heat flux. This clogging has the greatest effect on the behavior of molten steel. However, clogging at the top 1/3 of the nozzle only increases the velocity of molten steel and has little influence. Clogging at the bottom of the nozzle almost has no influence.

Effect of electromagnetic stirring on flow field in mold under submerged entry nozzle clogging

A physical model with mercury as analog was developed to investigate the influences of electromagnetic stirring（EMS） on flow field in slab continuous casting when the submerged entry nozzle（SEN） was clogged with different clogging rates（0,10% ,25% ,and 50% ）. The flow field in mold under different EMS currents（0, 40 A, and 60 A） was measured by an ultrasonic Doppler velocimeter. The results proved that the flow field in the mold was a typical double roll structure under non-clogging SEN. As the SEN clogging rate increased, the flow field structure was transformed from a double roll to asymmetry flow. When the clogging rate reached 50%, the up circulation disappeared on the clogged side. The zone under the meniscus near the narrow face was a non-flowing area. EMS could correct bias flow caused by SEN clogging and improve the symmetry of the flow field during SEN clogging.

Research Progress on Anti-clogging Technology of Submerged Entry Nozzles for Continuous Casting

The causes, the formation process, and the prevention of submerged entry nozzle(SEN) clogging were introduced. The influence of electric field on the SEN clogging was focused on, including the basic theory and measurement of SEN charging,the preliminary research on SEN charging, the influence of molten steel on the wetting behavior of refractory materials in electric field, and the influence of electric field on the oxide inclusions in molten steel. Based on the influence of the hydrodynamics, chemistry and other factors on refractory materials, structure, inclusion particle transfer and adhesion, many anti-clogging researches have been carried out, such as optimizing process conditions, compositing anti-clogging inner lining materials, innovating SEN structure and applying physical fields, which solve the problem of SEN clogging to a certain extent.However, the problems of weak adaptability and superficial study on clogging mechanism are still prominent. The electric field control is a new technology to prevent clogging. Although it has achieved certain results in on-site continuous casting trials,some problems such as the method of applying electric field, the electric field parameters and the equipment still need to be gradually improved, and the surface characteristics of inclusions and SEN materials at high temperatures need to be further studied. It was pointed out that the combination of materials and applied electric field will become an important direction for SEN anti-clogging technology.

Anchor-Shaped Design of a Submerged Entry Nozzle for the Continuous Casting of Steel

An anchor-shaped geometrical design for a Submerged Entry Nozzle for the slab continuous casting of steel is presented in this work. To evaluate its performance, transient 3D multiphase numerical simulations were carried out using the Computational Fluid Dynamics technique. The performance of the proposed nozzle is numerically compared with that of a conventional cylindrical nozzle. Computer results show that the chance of formation of Karman’s vortexes and powder entrapment becomes small for the anchor-shaped SEN.

Analysis on clogging of submerged entry nozzle in continuous casting of high strength steel with rare earth

The type of inclusions in tundish steel and the formation mechanism of the submerged entry nozzle(SEN)clogging in the continuous casting of the rare earth(RE)high strength steel without calcium treatment were studied based on the plant trials and thermodynamic calculation.It was found that Ce_(2)O_(3) and CeAlO_(3) in tundish molten steel were transformed into Ce_(2)O_(2)S+CaO-Al_(2)O_(3) with the size of 2-3 lm during cooling.When the flow velocity of molten steel on surface of the SEN was slow due to the boundary layer effect,Ce_(2)O_(3) inclusion in molten steel reacted with Al_(2)O_(3) in the SEN refractory to form CeAlO3.With the continuous erosion of molten steel and reaction,the compositions of CeAlO_(3),Al_(2)O_(3) and CaO were aggregated,and the clogging layers with different zones were formed on surface of the SEN.Meanwhile,a small amount of molten steel remaining in the arc zone and corner zone of the SEN formed solidified steel.When calcium treatment is canceled,the reaction probability between inclusions in molten steel and refractory should be reduced by improving the material and shape of the SEN.

Formation of Dense Inclusion Buildup on Submerged Entry Nozzle by Electric Current Pulse

In this work, low-density electric current pulse （ECP） has been applied to submerged entry nozzle （SEN） and its effect on the morphology of the inclusion buildup and the distribution of the inclusions in slab has been explored. The results reveal that under the unique effects of ECP, part of small inclusions less than 10 μm is expelled through the boundary layer along the current direction to form dense inclusion buildup. This method is of great potential to prolong the service life of SEN and improve the quality of the steel product.

INFLUENCES OF CASTING SPEED AND SEN DEPTH ON FLUID FLOW IN THE FUNNEL TYPE MOLD OF A THIN SLAB CASTER

In recent years, thin slab continuous casting technology has been widely used to improve the quality of the product and to reduce the cost. One of the challenges faced by this technology is to design reasonable flow patterns, which strongly affect the surface and inner properties of the final slab in the mold. With the fixed scales and complex geometrical structures of nozzle and funnel type mold, a series of numerical simulations are made to analyze the flow patterns in melt steel using finite volume method based on structured body fitted coordinate grids. The CFD （computational fluid dynamics） package is validated first using one typical case described in previously published studies, and then it is developed to study the effect of operational parameters on fluid flow in thin slab caster. Two operational parameters, casting speed and SEN （submerged entry nozzle） depth, are mainly considered for numerical analysis. On the basis of present simulations, the reasonable SEN submergence depths corresponding to different casting speeds are suggested according to fluid flow characteristics like, flow jet impingement on the narrow side of the mold, flow speed of the melt steel beneath the meniscus and the recirculation region. This is the first stage of study on the numerical analysis of the whole thin slab casting process with electromagnetic brake.

Al_(2)O_(3)夹杂物在浸入式水口内衬材料上的成核与反应性研究

浸入式水口复合无硅无碳内衬材料是减缓结瘤堵塞的重要措施。为深化研究Al_(2)O_(3)夹杂物在浸入式水口内衬表面的结瘤现象,采用晶格失配计算及高温模拟试验验证的方法研究了钢液中Al_(2)O_(3)夹杂物在氧化锆质、尖晶石质、刚玉质、莫来石质内衬材料上的成核趋势及反应;基于显微结构观察分析了异质形核机理和沉积过程。结果表明:Al_(2)O_(3)夹杂物与刚玉质、氧化锆质、尖晶石质、莫来石质内衬材料的二维失配度分别为0%,30.97%、8.43%、11.14%,表明Al_(2)O_(3)夹杂物易于在刚玉质内衬上成核,难以在氧化锆质内衬上成核,氧化锆基材料适宜作为浸入式水口防堵内衬材质。高温模拟试验结果与二维失配计算结果相一致,氧化锆基内衬不易与钢液发生反应且表面Al_(2)O_(3)结瘤程度较轻,仅为刚玉质、尖晶石质、莫来石质内衬上Al_(2)O_(3)结瘤厚度的1/2。本工作基于晶格失配理论提出了一种抗Al_(2)O_(3)结瘤内衬材料优选策略,可为开发高性能功能耐火材料提供科学指导。

浸入式水口结瘤机制及优化措施

在钢铁实际生产过程中,浸入式水口结瘤会对结晶器流场的稳定性产生严重影响。这种现象不仅影响了连铸过程的顺利进行,还可能导致结瘤物剥落,从而降低铸坯质量。阐述了浸入式水口结瘤机制的研究现状,从优化水口结构、优化水口材质、提高钢液洁净度以及施加外部电场共4个方面总结了防止浸入式水口结瘤的措施,并对浸入式水口防结瘤未来的研究方向进行了展望。

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.The SEN deposit profile was characterized as occurring in three major layers:(1)an eroded refractory layer;(2)an initial adhesive layer comprised an Al_(2)O_(3)-ZrO_(2) composite sub-layer and a dense Al_(2)O_(3)-based deposit sub-layer;and(3)a porous multiphase deposit layer mainly consisting of MgO·Al_(2)O_(3),CaO-Al_(2)O_(3),and CaO-TiOx.The MgO·Al_(2)O_(3)-rich inclusions did not adhere directly to the eroded refractory but were entrapped during the deposit growth.Results of inclusion characterization in the tundish revealed that the MgO·Al2O3-rich particles present in the tundish served as the primary source of clogging deposits.Furthermore,a novel cavity-induced adhesion model by circular approximation was established to explain the effects of complex inclusion characteristics and refractory material type on adhesion force.A high number of small MgO·Al_(2)O_(3) inclusions were expected to accelerate the buildup of clogging deposits.Improving the modification of MgO·Al_(2)O_(3)-rich inclusions in the size range of 2-4μm by Ca treatment was crucial to minimizing the risk of SEN clogging during the continuous casting of Ti-UPFS steels.

含钛不锈钢连铸浸入式水口结瘤的研究

为了解决含钛不锈钢连铸过程中浸入式水口的结瘤问题,采用扫描电镜和 X射线微区衍射等方法分析了AISI 321不锈钢连铸水口结瘤物的物相,探讨了浸入式水口的结瘤机理。结果表明:水口结瘤物中的物相主要有CaO·TiO2 -MgO·Al2O3 和金属,其中CaO·TiO2- MgO·Al2O3 主要来自于钢液中的夹杂物。喂钛线后吹氩搅拌过强使钢液面裸露和浇铸时的二次氧化会显著增加钢中CaO·TiO2- MgO·Al2O3 双相夹杂物的数量,导致结瘤层明显变厚。冶炼过程中采用低铝硅铁(ωAl=0 05%)还原,且不加铝、Ca- Si脱氧,或者在加 Ca Si后通过喂钛线前的吹氩弱搅拌尽可能排除钢中CaO- SiO2、CaO- SiO2 Al2O3 等夹杂物,严格控制二次氧化,可使喂入钛线后钢中CaO·TiO ·Al O 双相夹杂物数量明显减少,从而改善水口结瘤现象。

CSP连铸浸入式水口结瘤案例研究

研究了CSP连铸浸入式水口结瘤两种案例。案例曲线表明,塞棒开度和结晶器液面波动是钢水浇铸过程中最重要的特征参数。薄板坯连铸铝镇静钢中间包水口结瘤是高熔点夹杂在水口内壁的聚集。生产不稳,积压钢水在LF多次处理,产生细小的高熔点夹杂难以去除;软吹钢水“露眼”和开浇烧氧再生高熔点夹杂来不及去除都会导致水口结瘤。钙处理主要是球化夹杂,改善钢水可浇性。即使Ca/Als(钙/酸溶铝)和Ca/Alin(钙/酸不溶铝)都合适,夹杂物绝对量大,钢水可浇性仍较差,水口容易结瘤。

304和321不锈钢连铸水口结瘤的不同机理

分析了304和321不锈钢连铸水口结瘤物的物相,探讨了结瘤机理.结果表明,304水口结瘤物主要由Al2O3,MgO·Al2O3和少量细小的金属颗粒构成,结瘤层较薄,对正常浇铸的影响不显著,控制钢中Al<0.01％,可改善其结瘤.321连铸水口结瘤有TiN和CaO·TiO2两种类型:TiN型结瘤物主要由TiN和少量金属组成,控制措施是保持钢中钛氮积小于3.5,Al<0.01％;CaO·TiO2型结瘤物由CaO·TiO2-MgO·Al2O3和大量金属构成,尽可能减少钢中CaO·TiO2-MgO·Al2O3双相夹杂物的数量和避免二次氧化,可改善CaO·TiO2型结瘤,适当提高浇铸温度可缓解CaO·TiO2型结瘤.

含钛铁素体不锈钢连铸浸入式水口结瘤机理研究

采用光学显微镜和扫描电镜,对00Cr18Ti铁素体不锈钢钢样中夹杂物类型和浸入式水口结瘤物的物相进行分析,研究水口结瘤机理。结果表明,钢液中存在大量TiO2夹杂物,并不断附着沉积在水口内壁,造成浸入式水口氧化钛型结瘤;通过控制钢中w[Al]-w[Ti]值在铝钛竞争氧化反应平衡曲线之下,使w[Ti]/w[Al]4/3<273.55,能够防止大量TiO2夹杂物的生成,避免氧化钛型水口结瘤。

409L不锈钢连铸浸入式水口结瘤分析和改进措施

采用扫描电镜和X射线衍射法,分析了EAF-AOD-VOD精炼409L不锈钢(%:0.009～0.011C、11.36～11.63Cr、0.15～0.22Ti、0.0074～0.0112N)连铸水口结瘤的物相。结果表明:水口结瘤中的物相主要有TiO2和金属。喂钛线后吹氩搅拌过强时,由于钢水的二次氧化会显著增加钢中TiO2夹杂物的数量,导致结瘤层明显变厚。喂钛线后采用吹氩弱搅拌,能尽可能排除钢中TiO2夹杂物;同时应避免连铸时铸流二次氧化,从而减少水口结瘤的发生。

薄板坯连铸机新型浸入式水口

基于相似原理，采用１：１的水模型，模拟了薄板坯连铸结晶器内钢液的流场．采用ＳＧ８００水工数据采集系统对结晶器内液面波动和注流冲击深度进行了定量测量．针对薄板坯连铸高拉速的需要，开发了一种新型的耗散型浸入式水口．通过研究耗散水日上下出口面积比、出口角度以及拉坯速度对结晶器液面波动和对结晶器窄边冲击情况的影响，找出了其中的变化规律，为优化耗散式水口的结构和工艺参数提供了理论依据．通过与普通双侧孔水口的试验比较，证明耗散型水口是一种适合薄板坯连铸高拉速生产的新型水口．

连铸用浸入式水口防结瘤研究进展

介绍了水口结瘤产生的原因、结瘤物的形成过程、防止水口结瘤的方法,重点综述了电场对浸入式水口结瘤的影响,包括浸入式水口荷电的基础理论和测量、浸入式水口荷电初步研究、电场条件下钢液对耐火材料润湿行为的影响、电场对熔融金属中的氧化物夹杂的影响。基于流体力学、化学等因素对耐火材料材质、结构及夹杂物颗粒传递、黏附的影响规律,通过优化工艺条件、内壁复合防堵塞材料、创新浸入式水口结构、施加物理场等开展了较多的研究,使水口结瘤问题得到了一定程度的解决,但适用性不强、结瘤机制研究不深入等问题仍然很突出;利用电场调控防止浸入式水口结瘤堵塞作为一种新兴的防堵技术,虽然已在连铸现场试验中取得了一定的效果,但施加电场方式、电场参数及设备等工艺问题还需逐步完善,对夹杂物、浸入式水口材料在高温下的表面特性还需进一步深入研究。最后指出材料与外加电场结合将成为浸入式水口防堵塞技术的重要方向。

薄板坯连铸结晶器水模试验研究

以兰州钢厂薄板坯连铸机为原型，通过流场显示、波高测量及冲击力测量，研究了高拉速条件下．浸入式水口类型、插入深度、出口角度及出口形状对结晶器内流场变化的影响及变化规律。

板坯连铸结晶器浸入式水口结构研究

在实验室条件下,基于某厂实际水口结构及生产状况重新设计了4种不同结构的浸入式水口,然后采用1∶1的水模型对该厂600 mm×170 mm断面板坯连铸结晶器的流场特征进行试验,通过对比分析不同拉速下采用不同结构浸入式水口时结晶器内钢液的流场特征的变化情况,从而优选出适合该厂的浸入式水口结构。研究表明,在拉速≤1.6 m/min时,采用底部形状为凸底、出口倾角18°、侧出孔尺寸为40 mm×60 mm的椭圆形水口,结晶器内流场最为理想,即为最优水口结构。