Model control technologies of dynamic secondary cooling and soft reduction for slab continuous casting

Dynamic model control technologies of secondary cooling and soft reduction of Baosteel are introduced. Model principle and control system architecture are summarized, as well as functions and features. Finally, applications of model technologies are discussed. The self-developed dynamic secondary cooling model and the dynamic soft reduction model have been applied on several casting machines inside and outside Baosteel, desired control effects were achieved with good stability and reliability. Temperature measurement results verified the correctness of model.

Effect of cooling structure on thermal behavior of copper plates of slab continuous casting mold

A three-dimensional finite-element model of slab continuous casting mold was conducted to clarify the effect of cooling structure on thermal behavior of copper plates. The results show that temperature distribution of hot surface is mainly governed by cooling structure and heat-transfer conditions. For hot surface centricity, maximum surface temperature promotions are 30 ℃and 15 ℃ with thickness increments of copper plates of 5 mm and nickel layers of 1 ram, respectively. The surface temperature without nickel layers is depressed by 10 ℃ when the depth increment of water slots is 2 mm and that with nickel layers adjacent to and away from mold outlet is depressed by 7℃ and 5 ℃, respectively. The specific trend of temperature distribution of transverse sections of copper plates is nearly free of cooling structure, but temperature is changed and its law is similar to the corresponding surface temperature.

Numerical Analysis of Secondary Cooling in Continuous Slab Casting

In the present study, a numerical optimization program has been developed for predicting the optimal secondary cooling patterns in a continuous slab caster. Optimization strategy using Broydon-Fletcher-Goldfarb-Shanno （13FGS） method is carried out by determining the constant heat transfer coefficients in each spray zone, which could satisfy the casting conditions and metallurgical criteria specified by the engineer. From the present results, it is found that even a slight variation in the pouring temperature, allowable surface temperature, and casting speed could give rise to the changes in the cooling pattern throughout the spray zones.

Numerical Simulation of Linear Electromagnetic Stirring in Secondary Cooling Region of Slab Caster

According to the theory of alternating magnetohydrodynamics and magnetic boundary renewal method,mathematical models were proposed for electromagnetic stirring in secondary cooling region( SEMS) of slab caster. The magnetic fields and flow fields of melt were simulated with SEMS. It's shown that the electromagnetic forces with inward and sidelong components produced by travel magnetic field at the wide faces of slab make the melt whirling in horizontal section,and the convection of the melt is strengthened obviously there. In addition,magnetic flux density attenuates from the edge to the center of slab,and the profile of the melt velocity along slab thickness in the center of the horizontal section takes a two-opposite-peak configuration. Ultimately,the stirring intensity and features are determined by the electromagnetic parameters,coil arrangement and stirring types.

Application and Numerical Simulation of Electromagnetic Stirring in Secondary Cooling Zone During Continuous Casting of Ultra-Thick Slab

The segregation of solute elements at solidification front could be greatly improved by application of electromagnetic stirring(SEM)in secondary cooling zone.The location of SEM in secondary cooling zone affects the operational effect.In the present study,based on the application of SEM in Ultra-thick slab continuous casting,the shell thickness was calculated by self-programming code and the results were verified by nail-shooting test.A numerical model was established to calculate the fluid flow of molten steel under shell to determine the suitable SEM location in secondary cooling zone.The results shows that the velocity of molten steel increases with increase of stirring current which enhance the circulatory flow of unset steel at solidification front.Whereas,in order to fully develop ability of SEM it is necessary to select suitable stirring current and mode for ultra-thick slab casting.This calculation provides theoretical base for application of SEM in secondary cooling zone during ultra-thick slab casting process.

Design and Simulation Test of Advanced Secondary Cooling Control System of Continuous Casting Based on Fuzzy Self-Adaptive PID

To improve billet quality and the trackability and stability of secondary cooling water during continuous casting, the superheat is introduced into the water distribution for secondary cooling to design the relevant control system, based on the water distribution model, superheat and fuzzy self-adaptive PID （process identity） . A spray cooling system is set up for simulation test in laboratory to test the step signal from the conventional, integral sepa rated and fuzzy self-adaptive PID controllers and the simulation casting. And the on-site test is done in some steel plant. The test results show that the fuzzy self-adaptive PID controller＇s performance is better than that of the other two controllers, which provides a basis for further study and application.

Application of Hot Strength and Ductility Test to Optimization of Secondary Cooling System in Billet Continuous Casting Process

By means of Gleeble-1500 dynamic thermomechanical simulator, the continuous casting process for HRB335C steel was simulated using solidifying method and hot ductility and strength of the steel were determined. The test results indicate that there are three temperature regions of brittleness for HRB335C billet in the temperature range from 700 ℃ to solidification point; the first temperature region of brittleness is 1 300 ℃ to solidification point of the billet, the second temperature region of brittleness is 1 200-- 1 000 ℃, and the third temperature region of brittleness is 700-850 ℃ ; the steel is plastic at 850--1 000 ℃. The cracking sensitivity was studied in the different temperature zones of the brittleness for steel HRB335C and the target surface temperature curve for the secondary cooling is determined. With optimized process, the mathematical model of the steady temperature field with two-dimensional heat transfer for 150 mm×150 mm HRB335C steel billet was established to optimize the secondary cooling process. The conic relation of water distribution between secondary cooling water flux and casting speed is regressed. Keeping the surface temperature of billet before the straightening point above 1 000 ℃, the results of billet test indicate that there is free central shrinkage cavity. The billet defect is decreased greatly, and the quality of billet is obviously improved.

Formation mechanism of internal cracks in continuously cast slab

In order to make clear the formation mechanism of centerline cracks incontinuously cast slabs, the form, distribution and other characteristics of the cracks wereanalyzed. The final solidification point, surface temperature of the slabs and strain in solidifyingshell were investigated. The results were that: (1) Five relatively low temperature zones exist onslab surface below the three water spraying nozzles and near the two edges, respectively, whichcorresponds to the places of centerline cracks and triangle-zone cracks. (2) Centerline cracks andtriangle-zone cracks occur because of weak secondary cooling, uneven cooling along slab width, andlarge variation of roll gap. (3) After minimizing the variation of roll gap and applying the newsecondary cooling pattern, the occurring frequency of centerline and triangle-zone cracks minimizesto zero.

Mechanism of broadening of slab in continuous casting

The mechanism of broadening of slab in continuous casting was studied by numerical simulations and experimental measurements in factories. The mechanism is derived by gradual exclusion of various factors related to the broadening of slab. It is concluded that the slab exposes to no constraint at the direction of narrow face. Because of the static pressure of molten steel, the slab deforms creepily in the direction that consequently results in the broadening of slab. The broadening of slab increases with casting speed and static pressure of molten steel. The decrease of secondary cooling intensity and strength of steel at high temperature also contribute to the broadening of slab. The micro-alloying plays an important role in improving the strength of steel and in reducing the broadening of slab.

Secondary cooling technology for high-efficiency continuous billet-casting

The mathematical model of high-efficiency continuous billet casting was developed, incorporating the effective spraying water coefficient and the effective specific spraying water flowrate of secondary cooling. To realize uniform cooling in secondary cooling zones, the spraying cooling structure and the arrangement of nozzles were redesigned and optimized, and an additional spraying cooling zone was used. A new secondary cooling model of spraying water was built. It was found that the required spraying water flowrate of a cooling zone was related with the casting speed, the casting temperature, the compositions of liquid steel and the cooling water temperature of secondary cooling. The operation of the reformed caster proved that the spraying cooling structure and the new secondary cooling model were suitable, and the casting speed was greatly enhanced. The highest casting speed was （3.8 to 4.0） m/min for billet with a section of 150× 150 mm^2. The quality And the outout of the billet were imoroved, andthe economical benefit was heightened.

Effect of Cooling Intensity and Position on Solidification in Semi-Continuous Casting of Copper

Cooling heat flux effect in both primary and secondary cooling zone has been studied in semi-continuous casting of copper billet. Sufficient cooling is essential to reduce casting defects and to get high productivity, however low rate of solidification is aimed in order to get coarser grain size and softer metal for less losses in extrusion. A three-dimensional numerical model has been developed including solidification behavior of copper through mushy zone. At steady state and constant casting speed, solid shell thickness is monitored during the reduction of cooling rate at mould region to avoid breaking out. Heat flux intensity at mould plays important role not only in the formation of solid shell thickness. But, pool length and mushy zone thickness can be significantly increased by decreasing primary cooling intensity. Increase intensity of secondary cooling zone for two particular cases of primary cooling is tested. First case is tested at mould inlet water temperature of 38°C, and second case at water temperature of 63°C. Results showed that the combination of increasing secondary cooling intensity and reduction of primary cooling intensity can increase pool length and mushy zone thickness. Also, it is shown that, secondary cooling intensity can be magnified by up to 1.5 times for cooling water temperature of 63°C to get pool length close to that of water temperature of 38°C.

Dynamic Water Modeling and Application of Billet Continuous Casting

The continuous casting process is used for solidifying molten steel into semi-finished steel.The technology of secondary cooling is extremely important for output of the casting machine and billet quality.A dynamic water model was introduced,including solidification model in the secondary cooling,feedforward control strategy based on continuous temperature measurement in tundish,and feedback control strategy based on surface temperature measurement.The mathematical model of solidification process was developed according to the principle of solidification,and the solidification model was validated by measuring billet shell thickness through shooting nail and sulfur print.Primary water distribution was calculated by the solidification model according to procedure parameters,and it was adjusted by the other two control strategies online.The model was applied on some caster and billet quality was obviously improved,indicating that the dynamic water model is better than conventional ones.

鞍钢8m弧半径小方坯连铸机提速实践

针对8 m弧半径小方坯铸机拉速低不能满足生产要求的问题,分析了影响铸机提速的主要原因,采取了增加结晶器长度,更新结晶器供水泵,更新二冷水嘴,增大二冷管径以及优化系统温度等措施,铸机拉速由2.8 m/min提高到3.5 m/min,铸坯质量合格率达到99.95%,实现了小方坯铸机高速稳定生产。

Effect of droplet characteristics on liquid-phase distribution in spray zone of internal mixing air-mist nozzle

In continuous casting production,droplet characteristics are important parameters for evaluating the nozzle atomization quality,and have a significant impact on the secondary cooling effect and the slab quality.In order to study the behavior of atomized droplets after reaching the slab surface and to optimize the spray cooling effect,the influence of droplet diameter and droplet velocity on the migration behavior of droplets in the secondary cooling zone was analyzed by FLUENT software.Results show that the droplets in the spray zone and on the slab surface are mainly concentrated in the center,thus,the liquid volume fraction in the center is higher than that of either side.As the droplet diameter increases,the region of high liquid volume fraction on the slab surface becomes wider,and the liquid phase distribution in the slab width direction becomes uneven.Although increasing the droplet velocity at the nozzle exit has little effect on droplet diffusion in the spray zone,the distribution becomes more uneven due to more liquid reaches the slab surface per unit time.A prediction formula of the maximum water flow rate on the slab surface for specific droplet characteristics was proposed based on dimensionless analysis and validated by simulated data.A nozzle spacing of 210 mm was recommended under the working conditions in this study,which ensures effective coverage of the spray water over the slab surface and enhances the distribution uniformity of water flow rate in the transverse direction.

基于ABAQUS的X70管线钢连铸板坯空冷的热力耦合分析

随着管线钢连铸板坯热送热装占比的升高,切割后的连铸板坯在相变、热应力以及温度的耦合作用下易形成质量缺陷,造成巨大的经济损失。以X70管线钢为研究对象,通过综合考虑材料热物性参数随温度的非线性变化及边界条件的设定,利用ABAQUS有限元分析软件对X70管线钢4 500 mm×2 300 mm×300 mm连铸板坯的单坯冷却过程进行热力耦合数值模拟分析。结果表明,铸坯重心平均散热速率为0.076℃/s,表面中心为0.084℃/s,表面与心部温差区间为100~210℃,并随着时间逐步减小。铸坯边部应力值为25 MPa,边部300 mm以内热应力大致相同,在200 MPa以内。结合温度场变化情况应尽量缩短切割到加热炉的时间,或增加保温措施以防止因热应力过大形成质量缺陷。

基于凝固过程应力控制的板坯内部质量控制方法研究与应用

为了提高板坯内部质量控制水平,从铸坯凝固过程所受应力对内部质量的影响角度,阐述了铸坯内部缺陷的形成机理,提出铸坯在扇形段内综合受力状态是影响内部质量关键因素的理论。通过开发极限工况下二冷水控制模型,减少铸坯凝固过程中所受应力,最大拉坯阻力由2 500 kN降低至1 850 kN,铸坯低倍中间裂纹问题得到明显改善,低倍检测B类0.5级~C类1.0级中心偏析占比98%,0.5级以下中间裂纹占比85%,铸坯内部质量控制水平得到明显提升。

宝钢1930板坯铸机二冷喷嘴布置方式对铸坯质量的影响

在对宝钢 193 0铸机铸坯质量缺陷类型和形成位置分析的基础上 ,通过喷嘴性能测试和数值模拟计算 ,重点研究了 193 0铸机六、七冷却区喷嘴布置方式对铸坯的冷却均匀性和铸坯质量的影响 ,从解决铸坯角部横裂纹和内部三角区裂纹角度出发 ,提出了宝钢 193

高效板坯连铸铸机的二冷技术

在进行了高效板坯连铸二冷技术相关基础研究的基础上，通过优化二冷配水制度，保证了１－８ｍ／ｍｉｎ 拉速的实现。

板坯连铸二冷区凝固传热过程与控制

依据安钢板坯连铸机的具体条件，建立了连铸板坯凝固传热数学模型，实现了随铸坯钢种、断面尺寸及拉速变化对各回路水量连续实时控制．经现场应用表明，利用配水模型所制定的二冷配水制度是合理的，效果良好．

汽车用钢连铸坯的高温力学性能

运用经典热模拟的方法研究石钢电炉生产汽车用钢的连铸坯高温力学性能,获得了五个钢种热塑性曲线和强度曲线．针对不同方向铸坯取样的结果与其他研究结果作了对比．运用扫描电镜对试样拉断后的断口形貌进行观察,得出了相应钢在各温度区域的断裂机理．讨论了连铸坯质量与高温力学性能的关系．