超宽板坯包晶钢连铸初生坯壳应力的数值模拟

利用商业软件计算了超宽包晶钢连铸过程中初生坯壳所受应力.研究结果表明,由于包晶反应引起的体积收缩,包晶成分钢种的凝固坯壳表面应力显著大于非包晶钢成分钢种,在距铸坯中心约200～400 mm处应力出现极大值;随板坯宽度的增加,坯壳表面应力增大,应力极值点向坯壳中心方向移动;连铸工艺参数直接影响包晶钢表面应力大小,随过热度减小,拉速增加,结晶器冷却强度减弱,坯壳表面应力减小,铸坯表面裂纹发生概率降低.在本研究条件下,对断面为3 200 mm×150 mm的铸坯,适宜的过热度为15～25℃,拉速为1.2 m/min,结晶器宽面冷却强度为5 500 L/min.     

连铸方坯动态轻压下位置

为准确确定铸坯凝固末端的位置,合理选择压下区域,为实施动态轻压下提供有效技术手段,利用数值模拟方法计算某炼钢厂2#铸机连铸方坯中温度场,用传热模型分析了45#钢在某工艺下的铸坯温度分布图。固相率0.3为轻压下初始点,压下区间总长度为10 m且拉速0.76 m/min时的压下量为0.7 mm/m。     

Q345D板坯连铸凝固传热过程数值模拟

基于凝固传热学理论,以300 mm厚Q345D板坯连铸过程为研究对象,建立了板坯二维凝固传热数学模型。利用等效比热法对凝固潜热进行处理,分析了拉速、过热度、二冷区喷水量以及二冷区长度变化对出结晶器坯壳厚度、铸坯表面温度等凝固参数的影响。结果表明,适当提高拉速、降低过热度和增加二冷段长度,可以促进连铸坯凝固,降低板坯缺陷,提高生产效率。     

优化二冷制度实现宽板坯角部复热的研究

根据国内某厂宽板坯连铸工艺条件,利用二维非稳态传热模型及喷嘴冷却特性,分析不同因素对铸坯角部复热的影响规律。结果表明,铸坯断面宽度为1800 mm时,喷嘴间距选为450 mm,铸坯宽面表面温差小,有利于实现铸坯的角部复热;喷嘴间距一定,随二冷区比水量的减小及铸坯宽面外侧两喷嘴冷却水量的降低,铸坯角部复热效果更好;较小的角部凝固坯壳厚度有利于减小内部高温钢液蓄含的热量向铸坯角部传递的阻力,改善角部复热效果。     

不锈钢板坯连铸温度场及凝固末端位置的研究

采用有限元法计算了不锈钢板坯在连铸时凝固过程中温度场及坯壳的生长随时间的变化，讨论了过热度，拉速及二冷配水量对温度场及凝固末端位置的影响。结果表明，影响铸坯温度场和凝固末端位置的主要因素是拉速和二冷配水，而过热度影响较小。     

工艺因素对SCM435钢大方坯凝固组织的影响

为了模拟不同工艺条件下的连铸坯的凝固组织,采用有限元法模拟了SCM435钢的连铸凝固过程,获得了325 mm×280 mm连铸坯的温度场,在此基础上与元胞自动机(Cell automaton,CA)耦合模拟凝固组织.结果表明,随浇注温度的降低,柱状晶区逐步减少,表面细晶区及中心等轴晶扩大,晶粒密度逐步增加,最大晶粒面积及平均半径大大减少;但中心凝固所需要的时间反而有所增加,中心处的晶粒的平均半径先降低后升高;拉速对凝固位置的影响较为显著,随拉速的增加,晶粒密度逐步减少,柱状晶宽度与中心处的等轴晶半径略有增加.     

拉坯速度对连铸大方坯凝固的影响

结合现场研究,利用显式有限差分法计算出不同工艺条件下的铸坯凝固情况;进行了拉坯速度对出结晶器坯壳厚度、铸坯表面温度、铸坯凝固终点位置和铸坯质量影响的模拟分析研究.模拟结果表明,拉速对铸坯表面温度和凝固终点的影响较大,随拉速的增大,表面温度升高,出结晶器坯壳厚度减薄,铸坯液相穴拉长.     

320mm×480mm断面矩形坯连铸轻压下过程热力耦合分析

针对断面为320 mm×480 mm矩形连铸坯存在的中心偏析和中心疏松等缺陷,结合某厂矩形坯连铸工艺条件,建立矩形坯连铸轻压下过程热力耦合三维数学模型,模拟分析连铸压下量和压下区间对矩形坯压下效果的影响规律,据此提出优化轻压下工艺建议。结果表明：铸坯的塑性应变主要分布在纵向心部±30 mm位置,与压下时刻的固相率关系较大;其他条件一定时,压下量越大心部的等效塑性应变越大,压下量为11 mm时等效塑性应变为0.035;压下量越大,铸坯中心纵向位移越大,铸坯心部变形量越大;压下区间固相率为0.3～0.9和0.7～1.0时铸坯心部等效塑性应变为0.024～0.026,压下区间固相率为0.1～0.8时铸坯心部等效塑性应变几乎为零,因此压下区间固相率不能小于0.1～0.8。建议在铸坯轻压下过程中,除考虑压下量及压下区间等工艺参数对铸坯应变及位移的影响外,还应考虑过热度、拉速等生产过程参数对铸坯质量的影响,多角度优化轻压下工艺。     

薄板坯在二冷区传热现象的研究

研究了薄板坯连铸二冷区不同的工艺参数对传热现象的影响.计算中采用二维传热模型对温度分布进行计算.计算了不同拉速、不同水量下铸坯的温度分布和坯壳生长.分析了不同工艺对铸坯温度和坯壳生长的影响.得到了不同工艺下,铸坯温度分布规律和坯壳生长规律:拉速的变化对铸坯温度分布和坯壳生长有很明显的影响;而水量变化20%对铸坯温度分布和坯壳生长没有明显的影响.     

连铸板坯二冷区的应力分析

以某钢厂二号板坯连铸机结晶器至二冷区的35钢连铸坯为研究对象,采用有限元软件MSC.MARC建立沿拉坯方向上铸坯的二维纵断面弹塑性应力模型,对连铸坯的连铸过程进行数值模拟,研究不同拉速下铸坯表面应力和裂纹指数的变化规律。仿真结果表明,铸坯表面应力和裂纹指数随着拉坯速度的提升而增大,连铸坯的拉速控制在1.2m/min以内时,表面裂纹可得到较好的控制。     

CSP结晶器内钢液流动及凝固的数值模拟

应用数值模拟方法,建立CSP漏斗型结晶器内钢液流动及凝固传热耦合模型。针对结晶器内铸坯角部受到强冷的特点,对结晶器内热流密度采用修正方程进行计算,分析热流密度修正系数对铸坯凝固坯壳表面温度计算精度的影响。通过比较不同拉坯速率下结晶器内钢液凝固的特点,研究凝固坯壳对结晶器内钢液流动行为的影响。结果表明,采用热流密度修正系数后,铸坯凝固坯壳角部温度的计算值与实际情况更相符;提高拉坯速率可使铸坯凝固坯壳厚度减小;拉坯速率较大时凝固坯壳厚度随铸坯距弯月面距离的增大基本呈线性增长,拉坯速率为3m/min时,凝固坯壳在生长过程中厚度的增长有短暂的停滞现象;凝固坯壳对钢液流动的影响较大,主要是由钢液有效流动区域减少及两相区额外动量阻损造成的。     

Q235小方坯连铸过程中凝固特性的研究

分析了Q235凝固时的结晶特性,柱状晶容易生长.数值计算了小方坯连铸机在2.6 m/min拉速、不同二冷配水下铸坯的温度场和凝固前沿温度梯度.在弱水冷却时,铸坯坯壳凝固前沿温度梯度比较小,得到细小的柱状晶和少量等轴晶.连铸坯中间裂纹主要与二冷水相关,合适的二冷配水可降低或消除中间裂纹.     

Formation of internal cracks in steel billets during soft reduction

To investigate the formation of internal cracks in steel billets during soft reduction, fully coupled thermo-mechanical finite element models were developed using the commercial software ABAQUS, also casting and soft reduction tests were carried out in a laboratory strand casting machine. With the finite element models, the temperature distribution, the stress and strain states in the bil-let were calculated. The relation between internal cracks and equivalent plastic strain, as well as maximal principal stress was ana-lyzed. The results indicate that tensile stresses can develop in the mushy zone during soft reduction and the equivalent strain nearby the zero ductility temperature (ZDT) increases with decreasing solid fraction. Internal cracks can be initiated when the accumulated strain exceeds the critical strain or the applied tensile stress exceeds the critical fracture stress during solidification.     

Mathematical model of solidification for round CC billets

A coupled mathematical model was established to simulate the whole solidification process of round billet continuous casting for wheel steel using piecewise linear functions of heat flux density in the mold, the secondary cooling zone and the withdrawing-straightening zone. The calculated results were consistent with the measured data showing that the model accords with the practice. The surface temperature and the solidified shell thickness of round billets are more strongly influenced by casting speed than by casting temperature. The holding zones have effect on surface temperature, which is more obvious for the 450 mm round billet. The relation between casting temperature/speed and solidification end is expressed as a linear function. The solidification end is located after straightening machine.     

Simulation of inside-grooved mould improving heat transfer of original shell of casting slab

The dipping experiment was carried out by putting the water-cooled copper plate into the stannum-lead alloy to simulate the process of initial solidification of steel, and the result that the heat transfer of original shell improved by grooving on the surface of the water-cooled copper plate was investigated. A mathematical model of heat transfer was set up and the temperature field of casting slab 1000 mm×200 mm was calculated. The experimentation and simulation results indicate that the inside-grooved mould could improve the heat transfer of original shell, decrease the non-uniformity of original shell thickness and reduce the longitudinal surface cracks of casting slab.     

Effect of ultrasonic power and casting speed on solidification structure of 7050 aluminum alloy ingot in ultrasonic field

With the experiment and finite element simulation, the influences of power ultrasonic on the solidification structure of 7050 aluminum alloy ingot in semi-continuous casting were researched, and the effects of casting speed on solidification structure in ultrasonic field were also analyzed. The experiment and simulation results show that the solidification structure of the ingot is homogeneously distributed, and its grain size is obviously refined at ultrasonic power of 240 W. The average grain sizes, which can be seen from the Leica microscope, are less than 100 μm. When the casting speed is 45-50 mm/min, the best grain refinement is obtained.     

小方坯连铸二冷配水对凝固与传热的影响

研究小方坯连铸在二次冷却过程中的坯壳凝固情况,建立了传热过程的二维非稳态数学模型,计算出在整个连铸过程中温度变化和温度场分布,并得出在二冷区铸坯凝固速度与换热系数的关系.     

大方坯连铸过程中铸坯传热及凝固行为的研究

结晶器和二冷区传热对大方坯产品质量和铸机的生产率有重要影响，本文讨论了包钢引进的全国最大的方坯连铸机在拉坯时结晶器和二冷区传热情况以及坯壳凝固生长，铸坯温度的变化规律。着重讨论了电磁搅拌，过热度和拉速对坯壳凝固和生长规律的影响，指出控制铸坯凝固的主要因素是凝固潜热，影响凝固未端的最主要因素是拉速，而电磁搅拌对其影响区内的传热和坯壳生长和铸坯温度亦有重大影响。