【作者】 曹娜；

【导师】 朱苗勇；

【作者基本信息】 东北大学 ， 钢铁冶金， 2008， 博士

【摘要】 高拉速条件下结晶器内的卷渣是困扰连铸生产的一个技术难题,尤其是浸入式水口吹氩时结晶器内的流动与钢/渣界面行为变得更为复杂,对其的控制也更加困难。因此,揭示并把握高拉速与吹氩条件下结晶器内的钢/渣界面行为特征以及操作参数的影响规律就显得尤为重要。针对目前关于钢/渣界面和卷渣研究工作中很少同时涉及高拉速和吹氩条件下的情况以及保持结晶器内双循环流型的条件仍不清晰的现状,本文采用数学和物理模拟相结合的研究方法对高拉速和吹氩条件下板坯结晶器内钢/渣界面和流动行为进行了研究,主要研究内容和获得的结果如下：(1)按照相似原理建立了结晶器物理模型研究体系,观察有、无吹气条件下结晶器内水/油界面运动和卷混现象；根据不同的工艺条件确定结晶器水模型内的临界吹气量(即保持双循环流型)。为数学模型的验证和完善提供基础。(2)利用连续性方程、动量方程、湍流模型、Lagrange多相流模型和界面波动模型VOF(Volume of Fluid)方法建立了描述结晶器内钢/渣界面行为的数学模型,并采用CSF (Continuum Surface Force)模型考虑钢/渣界面张力作用。在用水模型验证的基础上,描述了高拉速与吹氩条件下钢/渣界面瞬态行为特征,揭示了操作参数与界面行为之间的定量关系,并提出了抑制界面波动和防止熔渣层乳化的措施。结果表明：①提高拉速明显加剧钢/渣界面的波动和增加界面速度,且最大界面速度位于距离窄面1/3附近处。拉速由1.4 m/min升至2.2 m/min过程中,最大波高的增幅达8.5mm,最大界面速度增加了0.087m/s；增大结晶器宽度对降低最大波高和界面速度的影响并不大；增加水口浸入深度和下倾角度能有效抑制钢/渣界面波动和降低界面速度,浸入深度由120 mm增至220 mm,最大波高降低了5.2mm,最大界面速度减少了0.052 m/s,水口出口角度每向下增加5°,以上两值分别降低约3.7 mm和0.05 m/s；熔渣黏度对钢/渣界面形状几乎没有影响,而适当增加熔渣黏度可降低最大界面速度,熔渣黏度由0.02 kg/(m·s)增至0.50 kg/(m·s),该值的降幅达0.059 m/s。②吹氩使气泡上浮区域内的钢/渣界面速度降低,同时也导致波高显著上升。当钢流量为3.20 ton/min(所对应的拉速为1.8 m/min),吹氩量为4.5 L/min时,结晶器内的上循环区明显缩小；增至9.0 L/min时,钢液流型已转为单循环且界面波动剧烈。吹氩量由0增至9.0 L/min过程中,最大波高升高了7.7 mm,而最大界面速度降低了0.111 m/s。当吹氩量为4.5 L/min,钢流量由2.13 ton/min(所对应的拉速1.2 m/min)增至3.91 ton/min(所对应的拉速2.2 m/min),上循环流重新出现,且界面卷混减弱,最大波高降低了2.4 mm。钢液流动特征和界面行为受钢流量(拉速×结晶器宽度)和吹氩量的影响,两者的合理匹配对获得双循环流和平稳的钢／渣界面至关重要。③增加水口浸入深度对抑制吹氩下钢/渣界面波动的作用较明显,当浸入深度由120 mm增至220 mm,最大波高和界面波动范围均降低了3.5 mm;气泡尺寸也显著影响钢/渣界面行为。(3)利用Lagrange多相流模型定量研究了吹氩结晶器内双循环流形成条件,确定实际操作参数下的临界吹氩量,并提出保持此流型的控制手段。在本研究条件中,当钢流量为2.84 ton/min(所对应的拉速1.6 m/min),吹氩量为6.0 L/min时,钢液流型已从双循环转为单循环。选择与其他工艺参数匹配的吹氩量是保证双循环流型的重要条件,临界吹氩量范围随钢流量的增加而扩大。当钢流量较大(>2.5ton/min)时,减小结晶器宽度和增加水口浸入深度均有助于扩大临界吹氩量范围,适当减少水口下倾角度使上循环流的趋势略有增强；当钢流量较小ton/min)时,以上操作参数的影响均不显著。更多还原

【Abstract】 Mold powder entrapment with high casting speed is a technical problem in the continuous casting of steel. The fluid steel flow and steel/slag interface behavior become more complex and the control on them are also more difficult, especially blowing argon gas from the SEN (Submerged Entry Nozzle). Therefore, it is highly emphasized to reveal steel/slag interfacial behavior and the influences of operating parameters on it. On account of the present research on the steel/slag interface and powder entrapment phenomena in the mold rarely involving high casting speed and blowing argon gas simultaneously, as well as the conditions of maintaining a double-recirculation flow pattern (DRFP) in the mold is still inexplicit, the fluid steel flow pattern and interfacial behavior of fluid steel and molten slag in a slab continuous casting mold with both high casting speed and blowing argon gas were investigated by mathematical and physical simulations in this paper. The main contents and results obtained are as follows:(1) The physical model for the mold has been established according to similarity principle. Water/oil interfacial movement and entrainment phenomena with and without blowing gas have been observed and the critical air flowrate (to maintain DRFP) have been achieved under the different casting conditions in mold model. The results of physical model are greatly essential to validate and perfect the numerical model.(2) The mathematical model to simulate the interfacial behavior between fluid steel and molten slag layer in a slab continuous casting mold with blowing argon gas has been developed by the conservation equations for mass continuity and momentum, turbulence model, Lagrange multi-phase model, VOF (Volume of Fluid) method, and CSF (Continuum Surface Force) model considering the steel/slag interfacial tension. Steel/slag interfacial transient behavior with high casting speed and blowing argon gas and the quantitative relationship between operating parameters and interfacial behavior have been described and revealed basing on the prediction results validated by the water model. In addition, the countermeasures to restrain the interface fluctuation and avoid the emulsification phenomena of the molten slag have been presented. The results show that: ①Steel/slag interface fluctuates strongly and the interface velocity increases significantly along with raising the casting speed, moreover, the maximum interface velocity is found about 1/3 of the mold width to the narrow face. Within the range of casting speed from 1.2 m/min to 2.2 m/min, the maximum wave height and the largest interface velocity increase by 8.5 mm and 0.087 m/s, respectively. Mold width has a little impact on the maximum wave height and interface velocity; nevertheless, increasing the penetration depth and downward port degree of SEN can effectively restrain interfacial oscillations and decrease the whole interface velocity. The maximum wave height and interface velocity decrease by 5.2 mm and 0.052 m/s, respectively, with the submergence depth added from 120 mm to 220 mm. Furthermore, the downward port degree increasing every 5°, the above two values approximately reduce by 3.7 mm and 0.05m/s, respectively. Molten slag viscosity has hardly influence on interfacial profile of steel and slag, however, the maximum steel/slag interface velocity decreases with increasing molten slag viscosity, and it reduces by 0.059 m/s with molten slag viscosity increasing from 0.02 kg/(m·s) to 0.50 kg/(m·s).②Blowing argon gas can reduce the steel/slag interface velocity of the region with the bubbles floating up, it also lead to wave height increasing remarkably at the same time. For a giving fluid steel mass flowrate of 3.20 ton/min (corresponding to the casting speed of 1.8 m/min), the upper circulation region is significantly suppressed with argon gas flowrate of 4.5 L/min, while the flow pattern of fluid steel changes to single recirculation, and the steel/slag interface fluctuates evidently with argon gas flowrate increasing to 9.0 L/min. The maximum wave height increases by 7.7 mm, nevertheless, the maxim interface velocity decreases by 0.111 m/s from the mold without argon gas to the flowrate of 9.0 L/min. In the process of the fluid steel mass flowrate increasing from 2.13 ton/min (corresponding to the casting speed of 1.2 m/min) to 3.91 ton/min (corresponding to the casting speed of 2.2 m/min) with the argon gas flowrate of 4.5 L/min, the upper recirculation appears again, and steel/slag interface entrainment are weakened, moreover, the maximum wave height is lowered by 2.4 mm. Fluid steel flow pattern and interfacial behavior of steel and slag strongly depend on the fluid steel mass flowrate (casting speed×mold width) and the argon gas flowrate, so it is very important that the argon gas flowrate matches the fluid steel mass flowrate for ensuring the DRFP and the even steel/slag interface.③Increasing the submergence depth of SEN is useful to reduce interfacial oscillations in the mold. The maximum wave height and fluctuation range of steel/slag interface both reduce by 3.5 mm when the submergence depth increasing from 120 mm to 220mm, moreover, bubble size also has a remarkable influence on the interfacial behavior of fluid steel and molten slag.(3) The condition for the formation of the DRFP in a slab continuous casting mold with blowing argon gas has been quantitively described using the Lagrange multi-phase flow model, and the operating parameters for maintaining the DRFP have been presented. The flow pattern of fluid steel changes from double recirculation to single recirculation with the fluid steel mass flowrate of 2.84 ton/min (corresponding to the casting speed of 1.6 m/min) and argon gas flowrate of 6.0 L/min in this study condition. The critical argon gas flowrate increases with the increasing fluid steel mass flowrate, and the range of argon gas flowrate for keeping the DRFP will be enlarged by decreasing the mold width and increasing the submergence depth of SEN as the fluid steel mass flowrate is more than 2.5 ton/min, nevertheless, the port downward angle of SEN has little effect on it. However, the operation parameters have no significant influence on it as the fluid steel mass flowrate is below 2.5 ton/min.更多还原