凝固坯壳对高拉速板坯连铸结晶器液面特征的影响

采用1：1的水模型研究了高拉速条件下凝固坯壳对结晶器内的流场与液面特征的影响.结果表明：考虑凝固坯壳时结晶器内的流场出现了轻微的不对称现象,在高拉速条件下（2.4 m·min^-1）,有坯壳时结晶器液面最大平均波高与表面流速比没有坯壳时分别大31%和35%.对比有/无坯壳条件下自由液面形状可知：考虑凝固坯壳之后的液面变形程度比没有考虑时更大,更易导致卷渣的发生.液面波动的功傅里叶变换分析表明：考虑坯壳之后结晶器液面的高频率波动的振幅大于无坯壳的情形,所以考虑坯壳之后由于结晶器下部内腔变小,更多的流股能量集中在上回流区,使得上回流的湍流程度比无坯壳时要大,进而导致了液面波动与表面流速的增大.因此,为了缩小与实际连铸过程的差别,在高拉速的物理模拟中有必要考虑凝固坯壳的影响.     

凝固坯壳对高拉速板坯连铸结晶器钢水流动特征的影响

 采用全比例的水力学模型,利用刺激-响应法、波高传感器、流速仪研究了考虑凝固坯壳时高拉速板坯连铸结晶器内的钢水流动、液面特征与卷渣特征。结果表明：考虑凝固坯壳后钢液到达液面的时间缩短;在高拉速条件下(2.4 m/min), 有坯壳时结晶器液面最大平均波高与表面流速比没有坯壳时分别大31 % 和17.5 %,使卷渣更容易发生。其主要原因在于考虑坯壳后结晶器下部钢液的自由流动空间变小,下回流的钢液流动受到抑制,上回流的能量变大。所以在高拉速结晶器水模拟试验过程中,有必要考虑凝固坯壳的影响。     

高拉速连铸过程传输行为特征及关键技术探析

高拉速连铸是实现直轧、铸轧的前提保障,是实现钢铁生产流程高效化、绿色化的具体体现,是发展新一代高效连铸的主题.高拉速连铸面临最大挑战是漏钢与裂纹频发,凝固坯壳均匀生长控制应是其实现的核心内涵,重点在于结晶器技术集成,包括结晶器流动控制、保护渣类型、结晶器润滑、结晶器内腔结构、结晶器冷却结构与制度等,关键在于结晶器液位的...     

连铸坯凝固过程热力耦合有限元模拟

 以铸坯和结晶器之间的间隙热阻为纽带,考虑保护渣凝固对接触热阻和渣膜热阻的影响,建立了连铸结晶器与铸坯热力耦合模型并编写了相应的有限元仿真程序。模型预测的坯壳厚度和实验结果吻合良好,两者差值≤2 mm。应用模型分析了大方坯连铸结晶器内的传热过程和坯壳的应力分布。结果表明,随着拉速提高,凝固坯壳厚度减薄,铸坯产生角部裂纹的趋势增加。     

包晶钢结晶器液面周期性波动原因及控制

针对鞍钢股份有限公司鲅鱼圈钢铁分公司板坯连铸在生产包晶系列钢种时．连铸结晶器钢液面周期性剧烈波动的原因进行了分析。包晶钢液在凝固过程的包晶相变造成初生坯壳的不均匀生长是导致结晶器出现液面周期性剧烈波动的主要原因。通过调整结晶器冷却水强度和控制保护渣传热性能,有效地控制了结晶器液面周期性波动,提高了铸坯质量。     

连续铸钢结晶器与保护渣渣膜间的界面热阻

结晶器弯月面附近凝固坯壳与结晶器间的传递在连铸产品表面裂纹的形成中起着重要作用,保护渣膜与铜结晶器壁间的界面热阻对热传递影响很大,因此,建立一个由坯壳、保护渣膜和铜壁组成的模型模拟连铸中结晶器弯月面附近的热传递。通过测量模拟器铜模内的梯度确定热阻,以前的研究认为,界面热阻与渣膜厚度无关,而经研究发现,界面热阻随潭膜厚度增加而增加,界面热阻点热传递总热阻的５０％,对于相同潭膜厚度的保护渣,当浇注结晶     

高拉速条件下中碳钢连铸用保护渣的性能研究

高拉速连铸技术因其高效生产的优点而备受人们关注,其中典型的紧凑型带钢连铸技术的连铸速度普遍提高至3～6 m/min,甚至达9 m/min。因高拉速连铸技术的拉坯速度提高,导致结晶器内部许多参数发生了改变,使得该工艺对保护渣的要求也变得颇为严苛。针对紧凑型带钢连铸连轧生产中碳钢所用保护渣开展了研究,并与传统低拉速连铸保护渣的理化性能进行对比。研究结果表明:中碳钢高拉速连铸用保护渣相比低拉速连铸用保护渣需要有更好的润滑性能,1 300℃时的黏度应低于0.086 Pa·s(拉速3.5 m/min);因高速拉坯,结晶器内壁与初始钢坯之间的热流大大增加,为避免过快的传热导致铸坯缺陷则需采用控热能力更均匀更强的保护渣。     

采用薄板坯连铸生产高表面质量冷轧钢板的可行性分析

薄板坯连铸由于拉速高,结晶器容量小,结晶器钢水液面波动高度和表面流速显著高于传统连铸,因此容易造成保护渣卷渣,这是薄板坯连铸生产高表面质量冷轧钢板钢种的主要困难所在。NUCOR、蒂森一克鲁伯等企业采用薄板坯连铸连轧工艺生产冷轧钢板的实践也表明,在表面质量方面与传统工艺产品尚有较大的差距。采用薄板坯连铸工艺生产优质冷轧钢种,应适当增加铸坯厚度,以降低拉速和增加结晶器对钢水流的缓冲作用,可采用120mm厚铸坯(结晶器出口),3m／min左右拉速。为了减少结晶器保护渣卷渣,应对中等厚度薄板坯连铸结晶器内钢水流动控制(SEN结构参数、SEN浸入深度、拉速等)、电磁制动、保护渣等开展深入的试验研究。     

H型坯连铸结晶器内钢液传递特性的数值模拟

以950 kg/m H型连铸坯结晶器为研究对象,采用FLUENT软件建立三维几何模型,模拟研究了水口浸入深度125 mm和175 mm时拉速（0.6~1.2 m/s）对结晶器内钢液传递特性的影响。结果表明,不同拉速条件下H型坯结晶器内钢液流态相似,但随着拉速的增大,结晶器内钢液流股冲击深度增大和结晶器自由表面流速增大,保护渣熔化状况有改善趋势,同时结晶器液面波动和钢水对凝固坯壳的冲刷有增大趋势。而各粒径夹杂物上浮去除率随拉速的增大而降低,其中大颗粒夹杂物去除率降低显著,当拉速由0.6 m/min增至1.2 m/min时,100μm夹杂物的去除率由16%降至10%。该模拟条件下,20~100μm夹杂物去除率在4%~16%。     

薄板坯连铸漏斗形结晶器内卷渣行为物理模拟

针对高拉速下薄板坯连铸结晶器内的液面卷渣问题，建立了1∶1水力学模型，采用水/真空泵油模拟钢/保护渣介质，研究了连铸拉速、水口插入深度、保护渣黏度对漏斗形结晶器内液渣层变化及卷渣行为的影响。结果表明，随着拉速提高，结晶器内液面波高升高，液面高度自窄边向水口方向逐渐降低，液渣层厚度相应由薄变厚，导致结晶器窄边附近钢液裸露；结晶器内窄边至水口之间1/2处波高变化较大、液面流速最大、易发生剪切卷渣。在试验条件下，采用增加水口插入深度、降低最高拉速、适当提高保护渣黏度等方法，使液面速度小于0.486 m/s的临界流速、液面波动指数F数小于5.45,可防止结晶器内产生剪切卷渣。然而，这些手段不能避免结晶器内水口附近的旋涡卷渣，这是因为薄板坯连铸钢通量大以及漏斗形结晶器和鸭嘴形水口容易形成负压旋涡造成的。     

Simulation of thermal behavior during peritectic steel solidification in slab continuous casting mold

Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products.In the present work,one two-dimension transient thermal-mechanical finite element model was developed to simulate the thermal behavior of peritectic steel solidifying in slab continuous casting mold by using the sequential coupling method.In this model,the steel physical properties at high temperature was gotten from the micro-segregation model withδ/γtransformation in mushy zone,and the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction,the liquid-solid structure and distribution of mold flux,and the temperature distribution of slab surface and mold hot face,in addition,the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.With this model,the variation characteristics of surface temperature,heat flux, and growth of the solidifying shell corner,as well as the thickness distribution of the liquid flux,solidified flux,air gap and the corresponding thermal resistance were described.     

亚包晶钢板坯连铸保护渣凝固结晶行为的研究

对≤1.3 m/min常规拉速(TCaO/SiO₂=1.19)和≥1.5 m/min高拉速(TCaO/SiO₂=1.40)0.07～0.10C亚包晶钢板坯用两种保护渣(%:2.54～3.0Al₂O₃、7.34～8.35Na₂O、8.83～8.87F、0.79～3.00Li₂O)降温凝固过程中结晶特性以及结晶对熔渣粘度的影响进行了研究,得出高拉速保护渣在凝固之前有明显的结晶行为,结晶矿相主要为枪晶石(3CaO·2SiO2·CaF₂);常规拉速保护渣在凝固温度以上时,没有明显的结晶现象。与常规拉速保护渣相比,高拉速保护渣完全凝固后晶粒粗大,组织中有大量空隙,有利于增加渣膜热阻,减缓结晶器传热。TCaO/SiO₂=1.40保护渣在结晶温度以上时,具有较低的粘度,有利于结晶器润滑;结晶温度以下时,粘度迅速增加,有利于增加固渣膜厚度,减缓结晶器传热。     

An asymptotic model of the mold region in a continuous steel caster

A model is developed to simulate the solidification of the steel shell in the mold region of the continuous casting process. Conduction-dominated temperature fields in the mold, mold flux, steel shell, and molten steel regions are determined through the development of an evolution equation for the solidifying front. This equation is derived in the limit of small aspect ratio, mold width to height, using asymptotic methods. These results are coupled with a lubrication-theory model for the mold flux region. This model assumes a temperature-dependent viscosity for the mold flux and allows for solidification of the flux at temperatures below a critical value. System response to changing casting speeds, superheat, mold wall temperatures, and mold flux properties is investigated.     

碳含量及连铸工艺参数对宽厚板坯结晶器热流的影响

对钢厂0.07%~0.18%C钢220~320 mm×1 800~2700 mm宽厚板的连铸过程进行了一年的在线检测与统计,研究了不同碳含量的钢种的拉速(0.65~1.2 m/min),钢水过热度(13~35℃),结晶器进水温度(27~35℃)和结晶器液位(775~810 mm)等工艺参数对结晶器铜板热流的影响。结果表明,浇铸220 mm板坯的结晶器热流随拉速增加而上升,但拉速>1.05 m/min时热流不再增大;对具有包晶反应的钢种,宽面与窄面热流随钢液过热度的增加而增大,但进水温度升高,热流降低;受包晶相变收缩的影响,浇铸0.13%C钢时结晶器热流最低。     

15CrMoG钢棒材表面缺陷机理分析和工艺改进

分析得出,棒材表面细小纵裂纹和表面裂口缺陷产生于铸坯加热之前,且与结晶器弯月面保护渣有关。利用Thermo-Calc热力学软件计算15CrMoG钢凝固相变过程,结合亚包晶钢连铸凝固特点综合分析15CrMoG钢棒材表面缺陷的产生原因和产生机理。结果表明:15CrMoG钢在固相线温度附近发生包晶反应L+δ→γ和包晶转变δ→γ,不仅导致初生坯壳生长不均匀,而且加剧P、S元素在凝固前沿的偏析。而初生坯壳不均匀是导致棒材表面缺陷根本原因。棒材表面细小纵裂纹产生于结晶器内坯壳薄弱处,经过二冷和轧制工序在夹杂物和硫偏聚处扩展长大。棒材表面裂口缺陷是初生坯壳不均匀导致结晶器内液面波动大,造成铸坯夹渣所致。通过控制[C]0.16%～0.17%、[S]≤0.005%、保护渣碱度1.2、熔点≥1200℃、粘度≥1.0Pa·s,260 mm×30mm铸坯水量150 m³/h,拉速0.5 m/min等措施,裂纹合格探伤合格率由原45%提高至98%。     

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.     

Effects of Mold Powder Chemistry on Shell Growth,Momentum and Heat Transfer in a Billet Mold

Effects of mold powder chemistry on shell growth and thinning have been studied using Computer Fluid Dynamic techniques under conditions of constant casting speed and steel superheat for a peritectic steel in a billet caster. Two mold powders were considered; a basic powder suitable for peritectic steels and an acid powder not recommendable for this steel in order to emphasize the importance of chemistry on shell stability. Numerical results indicate a strong interaction between powder composition and steel flow‐heat transfer phenomena. The acid powder creates recirculating flows at both sides of the entry jet that transport sensible heat to the shell inducing its remelting and thinning leading, eventually, to a strand breakout. Meanwhile, the basic powder induces a single recirculating flow in the internal radius side of the mold without severe shell thinning. A colder meniscus is predicted using the acid powder which is in agreement with the casting practice experience. Powder infiltration of the basic powder in between the mold hot wall and the strand provides a powder shell with a macroscopically smooth surface while the acid powder yields irregular infiltration. Buoyancy forces along the mold working height and mold curvature play a fundamental role on the generation of the recirculating flows. Interaction between powder chemistry and fluid flow‐heat transfer are two‐way coupled phenomena that must be considered for powder design purposes.     

宝钢圆坯连铸提高拉速生产实践

介绍了圆坯连铸提速的生产实践和取得的效果.对于包晶钢,尝试通过提高拉速来改善结晶器壁与坯壳间换热的均匀性,从而降低这类钢种的漏钢率.对于石油套管、钻杆类钢种,经过3个阶段的工作,成功将平均拉速提高到2.6 m/min,而且产品的内部质量有所提高.连铸拉速提高后,有了降低中间包过热度的可能,平均过热度下降达5 K.随着拉速的提高,VD成为产线生产的瓶颈.经试验,即使VD高真空时间缩短5 min,VD后的[H]仍可达到1.5×10-4%,同时发现,VD脱氮率与高真空保持时间无相关关系.于是VD处理时间成功缩短5 min,满足产线的节奏要求.     

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。