水口结构对连铸中低碳钢流场和温度场的影响

 为研究水口结构形状对连铸中低碳钢结晶器内流场和温度场分布的影响,采用有限容积法建立连铸圆坯三维数学模型,模拟了不同水口形状下圆铸坯的流场和温度场。结果表明,在水口浸入深度为80 mm、其他参数不变时,与直水口相比,旋流水口使钢水冲击深度降低,结晶器内涡流增强,弯月面温度和二冷区凝固率提高,且随着水口数量的增加,弯月面波高和结晶器出口温度降低;采用旋流水口并施加结晶器电磁搅拌(M EMS)时,结晶器中钢液温度升高,弯月面有卷渣行为,结晶器出口未形成凝固坯壳。在实际应用中,应避免同时使用M EMS和旋流水口,或使用旋流水口时采用低强度的M EMS。     

薄板坯连铸结晶器内流动传热行为的研究

基于珠钢CSP薄板坯连铸机设备工艺条件和所采用扁平浸入式水口结构,结合铜板测温导出的热流密度分布进行了漏斗形结晶器内钢水流动、自由液面以及传热凝固等冶金现象的综合描述和数值分析.结晶器熔池中以两个上旋涡为主的钢水循环流动局限在漏斗形结晶器内,上旋涡流股冲击和离开熔池液面分别对液面起伏波动有所贡献,弯月面下距窄边100 mm范围内有二次涡形成.除水口下方两侧存在两个具有明显过热的高温区外,熔池中绝大部分钢水的温度在液相线附近保持恒定,铸坯表面温度分布和坯壳发育过程均反映出水口高温射流的影响,铸坯表面最高温区位于熔池液面下方靠近结晶器窄边的地方.     

钢的软接触电磁连铸技术的研究进展

钢的软接触电磁连铸技术(SoftContactElectromagneticContinuousCasting)是利用高频交变电磁场在结晶器内铸坯初始凝固区施加电磁压力来减少钢液与结晶器壁的接触压力,从而减小结晶器振动对铸坯表面质量的影响,降低拉坯阻力和减弱初始凝固点的传热来提高铸坯表面质量。分析了实现钢的软接触电磁连铸在结晶器结构、材质以及电磁场参数等方面需要解决的问题,并介绍了该技术的最新研究成果:高频调幅磁场及无结晶器振动的电磁连铸技术。     

特大圆坯连铸用新型浸入式水口的设计与研究

 针对特大截面圆坯连续浇铸的特点,基于依靠浸入式水口自身结构减小钢流冲击深度,同时保证流动与传热沿周向分布均匀的思想,首次提出了新型浸入式伞形水口设计方案,并建立了结晶器内钢水的流-热-固耦合模型,对钢水的流动、传热和凝固行为进行了数值耦合模拟分析,验证了此水口的优越性与合理性：伞形水口的射流在结晶器内形成上下两个回流区,不仅有利于夹杂物、气体等的上浮分离,还能有效降低钢流冲击深度,使过热钢液均匀分布在结晶器上部,可提高弯月面温度和化渣效果;沿周向凝壳生长均匀,减轻了纵裂纹的萌生概率;在0.35m/min拉速下,出结晶器凝壳厚度达到31.2mm,满足安全生产要求。     

Multiphase Flow and Thermo-Mechanical Behaviors of Solidifying Shell in Continuous Casting Mold

 The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product. The multiphase flow phenomena of molten steel, steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation, and the effect of electromagnetic brake (EMBR) and argon gas blowing on the process were investigated. The relationship between wavy fluctuation height near meniscus and the level fluctuation index F, which reflects the situation of mold flux entrapment, was clarified. Moreover, based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification, the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux, temperature and stress of shell in slab continuous casting mold were described.     

A 3D Mathematical Modeling on Meniscus Solidification and Heat Transfer in Continuous Casting Chamfered Mold of Slab

Herein, a 3D mathematical model is established to elucidate the meniscus solidification and heat transfer in the chamfered mold. The fluid flow, heat transfer, the solidification of steel, the oscillation of the mold, and the steel–slag interfacial tension are considered, and the meniscus behavior on different longitudinal sections and cross sections is discussed. Under the influence of the upper roll flow, the height of the steel level increases from submerged entry nozzle to narrow face, which affects the distribution of the oscillation mark on the surface of the shell. With the mold chamfer and two new corners, the thickness of the slag film at the corner 1 with angle of 123.7° is the largest, and the shell thickness is the smallest, which is related to the 3D profile of the meniscus near the corner. The largest heat flux is located at 10–14 mm below the initial level of liquid steel and is below 3.0 MW m⁻². The heat flux at the corner 1 with small obtuse angle is the smallest on the same cross section, indicating that small obtuse angle near the corner resulted in the low heat transfer.     

连铸结晶器内钢液流动、凝固和夹杂物的分布

 建立并求解动量、热量和质量传输耦合模型,研究了连铸结晶器内钢液流动、传热、凝固、溶质输送和夹杂碰撞长大行为。数值结果表明,受钢液流动的影响,在连铸机内钢液温度、碳浓度和夹杂物的空间分布与钢水流动特征相似,也可分为上下两个循环区。但是其分布具有各自的特点。在涡心处,钢液温度较低,碳浓度较高,夹杂物体积浓度和数量密度较低。在弯月面处,钢液温度较低,碳浓度较高,夹杂物的体积浓度和数量密度较低。在结晶器出口处的凝固坯壳内,夹杂物的浓度和数量密度分布极不均匀,存在阶跃现象,这与冲击点处凝固坯壳的重熔有关。     

大方坯连铸过程凝固规律

通过建立425mm×320mm连铸大方坯二维凝固传热数学模型,模拟了凝固坯壳的长大过程,并通过窄面射钉实验对数学模型进行了验证,精确得到了任意位置处大方坯凝固坯壳的厚度分布情况及最终凝固终点的位置,发现经典的凝固平方根定律对于连铸大方坯的凝壳长大进程不再适用.回归宽面中心坯壳厚度与凝固时间平方根的关系式发现,结晶器弯月面至二冷区出口,近似为线性关系,符合平方根定律,二冷区出口至凝固终点,二者为非线性关系,不再符合平方根定律.      

IF钢连铸坯凝固钩数学模拟与试验

 根据IF钢连铸坯凝固钩的形成机理,通过建立二维纵向切片传热模型,模拟了凝固钩的演变行为;结合金相试验结果分析了连铸工艺参数对凝固钩深度的影响。结果表明,在初始凝固过程中,凝固钩中经历了形成、熔化及生长等阶段,在数学模拟条件下,当结晶器内由浸入式水口流出的钢液温度为1 555 ℃、拉速为1.3 m/min时,在距离弯月面55.12 mm处,即凝固钩生长达到稳定状态,其深度为2.368 mm。当拉坯速度、结晶器内钢水温度、振动频率增加时,凝固钩深度均减小。凝固钩数学模拟结果符合实际生产。     

电磁搅拌对大圆坯结晶器冶金行为影响的探讨

 为了探究结晶器电磁搅拌(M EMS)对大圆坯结晶器内综合冶金行为的影响。以大断面圆坯连铸结晶器冶金行为为研究对象,基于电磁热流体与凝固传输理论建立三维耦合数值模型。揭示大圆坯连铸常用五孔水口浇注条件下结晶器内电磁场、流场、传热与凝固等综合冶金行为,提出电磁搅拌对结晶器冶金性能影响的多参量评价方法。以中碳铬钼齿轮钢650 mm大圆坯连铸为例,指出结晶器电磁搅拌存在最佳搅拌电流,可获得相对较好的综合冶金效果。具体表现为弯月面保持一定的切向速度和过热度,有利于保护渣的熔化和夹杂物的上浮去除;液面波动幅度在控制范围内,可避免卷渣、改善表面质量;结晶器内钢液过热得到有效耗散,有利于等轴晶形核改善铸坯内部质量;侧孔出流钢液速度得到有效控制,可抑制注流对初凝坯壳的冲刷,提高了初生坯壳生长的均匀性。此外,电磁搅拌产生的水平旋流强度也可得到有效控制,有利于避免常见的皮下白亮带现象。     

水口类型对大方坯结晶器内钢水流动与凝固行为的影响

采用数值计算方法对比研究了直通式、4分径向以及新型4分切向水口对大方坯连铸结晶器内钢水流动与凝固行为的影响.结果表明,当前常用的直通式水口对坯壳无冲击,利于坯壳均匀生长,但钢水冲击深度大,易在弯月面处形成死区,不利于大方坯内部及表面质量的提高;改用4分水口浇铸时,结晶器宽、窄面冲击区附近都会出现不同程度的坯壳厚度零增长...     

Simulation on Effect of Divergent Angle of Submerged Entry Nozzle on Flow and Temperature Fields in Round Billet Mold in Electromagnetic Swirling Continuous Casting Process简

A new process for swirling flow generation in the submerged entry nozzle （SEN） in continuous casting process of steel was proposed. A rotating electromagnetic field was set up around the SEN to induce swirling flow by Lorentz force. The flow and temperature fields in the SEN and round billet mold with electromagnetic swirling were numerically simulated and then verified by the electromagnetic swirling model experiment of low melting point alloy. The effects of divergent angle of the SEN on the flow and temperature fields in mold with electromagnetic swirling were investigated. The electromagnetic swirling flow generator （EMSFG） could effectively induce swirling flow of molten steel in the SEN, which consequently improved greatly the flow and temperature fields in the mold. Below the nozzle outlet in mold, with the increase of divergent angle, the stream of bulk flow diverged more widely, the high temperature zone shifted up, and the temperature field became more uniform. Above the nozzle outlet in mold, with 350 A electromagnetic swirling, when the divergent angle of the SEN increased, the upward flow velocity and the meniscus temperature first increased and then decreased. With a divergent angle of 60~, the upward flow velocity and meniscus temperature reaced the largest value.     

Analysis on Initial Defects Based on Mechanical State of Meniscus Shell

The meniscus shell plays an important role in slab quality and process operation for continuously cast steel.One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscillation and liquid steel flow to generate disturbance of casting.The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects.The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending.The formed crack may also expand and propagate due to the following secondary cooling and straightening behavior.The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell.The inter-dendrite bridging is also likely to be formed to produce other internal defects,such as air hole and solute enrichment in the residual molten steel located in the bridging area.     

Effect of Induction Heat on Initial Solidification During Electromagnetic Continuous Casting of Steel

 Aiming at the process of electromagnetic continuous casting (EMCC), a three dimensional finite element model on electromagnetic field and temperature field was developed through the commercial software ANSYS to investigate the effects of induction heat of high frequency electromagnetic field on the early solidification process of molten steel in soft contact mold under various conditions of exciting current parameters. The results show that the induction heat has significant effects on the early solidification process, which appear as increasing the billet surface temperature, thinning the initial solidified shell and lowering the starting point of the initial solidification. The increases of exciting current frequency and density make the effects of induction heat on solidification process increased remarkably. Especially, with the increase of exciting current frequency, the early solidification process and shell growth become non-uniform in billet circumferential direction. Morever, if the exciting current density exceeds a certain value, there occurs a high temperature region in the top of molten steel column, and then the initial solidification rate is decreased greatly.     

A Study for Initial Solidification of Sn-Pb Alloy During Continuous Casting: Part II. Effects of Casting Parameters on Initial Solidification and Shell Surface

The initial shell solidification of liquid steel in the mold has significant influence on both surface and internal quality of the final slab, and it is mainly determined by the high transient high temperature thermodynamics occurring in the mold. This study investigated the effects of casting parameters like casting temperature, mold oscillation frequency, and stroke on the initial solidification of a Sn-Pb alloy through the use of a mold simulator to allow the clear understanding of the inter-relationship between irregular shell solidification, heat transfer, negative strip time (NST), and casting conditions. Results suggested that the shell surface oscillation marks (OMs) are strongly depending upon the fluctuations of meniscus responding temperatures and heat flux. An abrupt sudden fluctuation of high frequency temperature and heat flux at the meniscus during the NST would deteriorate the shell surface and leads to deep OMs. The fluctuations of responding temperature and heat flux are determined by the NST, meniscus solidification, and oil infiltration, which in turn are influenced by casting conditions, like casting temperature, oscillation frequency, stroke, etc.     

The formation of oscillation marks in the continuous casting of steel slabs

The formation of oscillation marks on the surface of continuously cast slabs has been studied by metallographically examining slab samples and by performing a set of mathematical analyses of heat flow, lubrication, and meniscus shape in the meniscus region of the mold. The metallographic study has revealed that, in agreement with previous work, the oscillation marks can be classified principally according to the presence or absence of a small “hook” in the subsurface structure at the base of individual oscillation marks. The depth of the oscillation marks exhibiting subsurface hooks varies with the carbon content, reaching a maximum at about 0.1 pct carbon, while the oscillation marks without hooks show no carbon dependence. The analysis of heat flow at the meniscus, which is based on a measured mold heat-flux distribution, indicates that depending on the level of superheat, the meniscus may partially freeze within the period of a typical mold oscillation cycle. Lubrication theory has shown that, owing to the geometry of the mold flux channel between the solidifying shell at the meniscus and the straight mold wall, significant pressure gradients capable of deforming the meniscus can be generated in the flux by the reciprocating motion of the mold relative to the shell. A force balance on the interface between the steel and the mold flux has been applied to compute the shape of the meniscus as a function of the pressure developed in the lubricating flux at different stages in the mold oscillation cycle. This has demonstrated that the “contact” point between the meniscus and mold moves out of phase with (by π/2), and has a greater amplitude than, the mold displacement so that just at, or near, the end of the negative strip time molten steel can overflow at the meniscus. From these studies a reasonable mechanism of oscillation-mark formation emerges which involves interaction between the oscillating mold and the meniscusvia pressure gradients in the mold flux, meniscus solidification, and overflow. The mechanism is consistent with industrial observations. E. TAKEUCHI, on study leave from Nippon Steel Corporation     

圆坯钢电磁软接触连铸的实验研究

为确定工业实验基本参数,对电磁软接触连铸结晶器进行了优化设计计算,设计制作了φ100 mm圆坯电磁软接触连铸结晶器,利用Sn-Pb-Bi合金实验研究了结晶器内的弯月面行为,并进行了w(C)为0.22%钢坯的电磁软接触连铸实验。结果表明,电磁软接触连铸结晶器内磁场和弯月面变形具有不均匀性,切缝数为12时,磁场周向分布和弯月面变形较均匀。输入功率增加,弯月面高度增高,液面波动加剧。对于100 mm圆坯电磁软接触连铸系统,功率可控制在50~60 kW左右。实际应用中,浇注液面应控制在线圈中心偏上位置。较低的电源频率可获得较高的弯月面,频率应控制在20 kHz左右,可获得较高的周向均匀的磁场。获得了表面质量改善的电磁软接触连铸钢坯。随功率增加,铸坯表面依次会出现环状振痕、无振痕和波纹状振痕等3种振痕形态。     

电磁搅拌对特大方坯结晶器内流场及温度场影响

以某厂断面为410 mm × 530 mm的特大方坯结晶器为原型,利用ANSYS有限元软件建立三维数值模型,研究电磁搅拌对结晶器流场及温度场的影响。施加电磁搅拌后,钢液受到径向电磁力,液面呈现旋转流动趋势。结晶器内钢液最大切向速度随着电流的增加而增大,随着频率的增加而减小。电磁搅拌的电流大小由0 增加到500 A时,液面波动由1.21 mm增加到4.35 mm。电磁搅拌能够使钢水的高温区局限于连铸结晶器上部,钢水温度更加均匀。同时钢液的水平旋流能够抑制初生坯壳的生长,降低坯壳的生长速度,使结晶器出口处坯壳厚度变薄。综合分析,该厂在实际生产时合理的电磁搅拌的电流大小应为400 A,频率为1.5 Hz,此时钢渣液面波动约为2.73 mm,温度场较为均匀。      

X80管线钢238 mm x 1 650 mm连铸坯温度场及凝固末端位置的数学模拟

用二维切片跟踪铸坯凝固传热的方法建立了X80管线钢（/%:0.04C,1.85Mn,0.25Si,0.006P,0.003S,0.30Ni,0.21Mo,0.06Nb,0.02V）238 mm×1650 mm板坯连铸过程中垂直拉坯方向传热的数学模型,通过ANSYS对X80管线钢连铸过程中温度场及坯壳厚度的渐变进行计算,得出拉速1.2mm/min时,出结晶器坯壳厚为18.14 mm,铸坯液芯长22.58 m。凝固壳厚度计算值射钉测试结果的相对误差≤2.5%,凝固末端位置的相对误差为0.68%。分析了过热度（25~55℃）,拉速（1.2~1.3m/min）和二冷水量（79.2~96.8 m³/h）对切片各点温度和凝固末端位置的影响。结果表明,增大拉速、减小二冷配水量,连铸坯表面温降变慢,凝固末端位置距离结晶器液面越远,凝固时间变长;该X80管线钢板坯连铸最佳工艺参数为钢水过热度35℃,拉速1.2 m/min和二冷配水量88m³/h。     

大圆坯连铸二冷配水设计模型的开发

根据钢厂新建Φ600 mm圆坯连铸机的主要技术参数,建立柱坐标一维非稳态连铸坯凝固传热数学模型,运用有限差分法求解并编制相关程序,分析拉速、过热度、冷却强度对铸坯温度的影响,实现在给定水量下连铸坯温度场的计算。浇铸Φ500 mm轴承钢GCr15SiMn计算得出拉速每提高0.1 m/min,出结晶器处凝固坯壳厚度减薄约7.9 mm,凝固终点延长6.7 m。