薄板坯合金钢窄面凹陷的控制实践

鞍钢股份有限公司炼钢总厂四分厂3#板坯连铸机生产过程中,合金钢铸坯窄面经常出现纵向凹陷,影响连铸坯的表面质量,并造成轧材缺陷。分析了连铸板坯窄面纵向凹陷的形成原因,结合生产试验,通过采取优化结晶器足辊冷却水流量、结晶器锥度、结晶器窄边足辊布置及铸机拉速等措施,提高了连铸板坯的表面质量,有效地控制了铸坯窄面的纵向凹陷。     

Study on fluid flow in the mold with electromagnetic braking

Multiphase flow control w ith electromagnetic braking( EMBr) is w idely used in the continuous casting of steel slabs. The basic aim of the flow control system of the process is to deliver molten steel from the ladle through the tundish,upper tundish nozzle,slide gate,and submerged entry nozzle into the mold region w ith minimal defects. This requires the optimization of turbulence levels at a meniscus to avoid both an excessively fast flow( which creates high fluctuations of the meniscus level in addition to slag entrapment,surface nonuniformities,and surface defects) and insufficient slow flow( w hich leads to meniscus solidification,inadequate flux infiltration,and surface defects). In this study,a Eulerian-Lagrangian approach is used to investigate the effects of EM Br and Ar bubble injection on the surface flow velocity. The results show that high Ar injection rates can lead to an increase in surface velocity.     

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.     

坯壳鼓肚对铸机矫直区内铸坯变形的影响

 在连铸机辊列矫直段,带液芯铸坯的坯壳同时受钢水静压力与矫直力的作用,坯壳固液交界面处的矫直应变与鼓肚应变发生叠加。如果总应变超过临界值,就会发生内裂。确定矫直区坯壳固液交界面处的应变与应变速率,对铸机辊列设计与工艺参数的设定有重要的意义。基于高温坯壳力学特性,建立了连续矫直理论中铸坯坯壳变形的数学模型。利用该模型计算坯壳鼓肚变形,并与实测数据进行对比,验证了模型的有效性。根据某厂由奥钢联设计的工业板坯连铸机的辊列参数,利用该模型计算铸坯横截面的应变与应变速率。最后分析了不同辊间距与不同拉坯速度情况下矫直区内铸坯坯壳固液交界面处的应变速率变化规律,结合不同钢种的临界应变速率得到铸机矫直段辊间距的取值范围。     

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。     

A mold simulator for the continuous casting of steel: Part I. The development of a simulator

Surface defects, such as oscillation marks, ripples, and cracks that can be found on the surface of continuously cast steel, originate in the continuous casting mold. Therefore, a detailed knowledge of initial solidification behavior of steel in a continuous casting mold is necessary because it determines the surface quality of continuously cast slabs. In order to develop an understanding of the initial solidification of continuous cast steels, a “mold simulator” was designed and constructed to investigate heat-transfer phenomena during the initial phase of strand solidification. The mold simulator was used to obtain solidified steel shells of different grades of steel under conditions similar to those found in industrial casting operations. The resulting cast surface morphologies were compared with industrial slabs and were found to be in good agreement, indicating that it is possible to simulate the continuous casting process by a laboratory scale simulator.     

304不锈钢连铸过程中结晶器渣圈形成机制

 在连铸过程中,结晶器易结渣圈是造成铸坯产生缺陷的主要原因之一。对304不锈钢板坯连铸过程中结晶器保护渣原渣、距开浇60 min时的液渣和渣圈的化学组成、理化性能、结晶矿相以及渣圈形貌结构进行对比分析。结果表明,连铸过程中TiO2和Cr2O3从钢液进入液渣生成高熔点氧化物,使液渣和渣圈的完全熔化温度和黏度显著增大,碱度、转折温度降低。液渣与渣圈的物相以枪晶石和钙铝黄长石为主。高熔点相钙铝黄长石的大量析出以及TiO2和Cr2O3进入液渣使液渣黏度增大是渣圈形成并长大的重要原因。     

Infiltration of Slag Film into the Grooves on a Continuous Casting Mold

An analytical model is developed to clarify the slag film infiltration into grooves on a copper mold during the continuous casting of steel slabs. A grooved-type casting mold was applied to investigate the infiltration of slag film into the grooves of a pitch of 0.8 mm, width of 0.7 mm, and depth of 0.6 mm at the vicinity of a meniscus. The plant trial tests were carried out at a casting speed of 5.5 m min^?1. The slag film captured at a commercial thin slab casting plant showed that both the overall and the liquid film thickness were decreased exponentially as the distance from the meniscus increases. In contrast, the infiltration of slag film into the grooves had been increased with increasing distance from the meniscus. A theoretic model has been derived based on the measured profile of slag film thickness to calculate the infiltration of slag film into the grooves. It successfully reproduces the empirical observation that infiltration ratio increased sharply along casting direction, about 80 pct at 50 mm and 95 pct at 150 mm below the meniscus. In the model calculation, the infiltration of slag film increases with increasing groove width and/or surface tension of the slag. The effect of groove depth is negligible when the width to depth ratio of the groove is larger than unity. It is expected that the developed model for slag film infiltration in this study will be widely utilized to optimize the design of groove dimensions in continuous casting molds.     

高拉速薄板坯连铸保护渣剪切变稀性质

 针对高拉速薄板坯连铸保护渣现场使用过程中卷渣风险加剧、黏结报警频发等问题,通过使保护渣产生非牛顿流体行为,从而有效解决上述问题。该种新型保护渣具有剪切变稀的特性,即在较低剪切速率下具有较高黏度、在较高剪切速率下具有较低黏度。基于现场数据,计算出高拉速薄板坯结晶器钢液面表面区域的剪切速率为10~90 s-1,结晶器弯月面及以下区域的剪切速率可达120~1 600 s-1。采用旋转圆筒法研究了Al₂O₃对保护渣剪切变稀性质的影响。采用Oswald-De Waele幂律模型对剪切变稀行为进行了定量分析。结果表明,随着Al₂O₃含量的增加,保护渣剪切变稀性质先增强后减弱,Al₂O₃质量分数为8.61%的试样剪切变稀性质最强,其流动性指数最低达到0.764 4。研究发现,非牛顿流体保护渣具有的剪切变稀性质能够满足在结晶器钢液面表面区域和弯月面及以下区域内对保护渣黏度的要求。基于高拉速薄板坯连铸的具体工艺参数,建立结晶器内多相耦合模型,通过模型计算发现,保护渣的剪切变稀性质增强不仅会明显降低剪切卷渣的风险,提高结晶器弯月面区域液渣流入的均匀性,而且在结晶器弯月面及以下区域具有更厚的液态渣膜,更容易实现全程液态润滑,同时提高了渣耗量,进一步剖析了保护渣剪切变稀性质的作用效果。本研究为开发非牛顿流体高拉速薄板坯连铸保护渣提供了理论依据。     

不锈钢(304HC)浇铸过程保护渣成分变化及其对渣性能影响

通过不锈钢(304HC)连铸过程中对结晶器内液渣现场取样、分析,探索了结晶器内渣-钢界面化学反应及钢中杂夹的吸收造成渣成分的变化,及其对熔渣性能的影响.研究表明,渣中Al2O3、Cr2O3含量有所增长,F减少,碱度下降,并造成保护渣使用性能发生变化,粘度有波动、凝固温度升高及结晶率下降.研究结果为更合理地设计不锈钢连铸保护渣配方,进一步降低不锈钢铸坯表面缺陷提供了依据.     

Transient fluid flow and superheat transport in continuous casting of steel slabs

The turbulent flow of molten steel and the superheat transport in the mold region of a continuous caster of thin steel slabs are investigated with transient large-eddy simulations and plant experiments. The predicted fluid velocities matched measurements taken from dye-injection experiments on full-scale water models of the process. The corresponding predicted temperatures matched measurements by thermocouples lowered into the molten steel during continuous casting. The classic double-roll flow pattern is confirmed for this 132×984 mm slab caster at a 1.52 m/min casting speed, with about 85 pct of the single-phase flow leaving the two side ports of the three-port nozzle. The temperature in the top portion of the molten pool dropped to about 30 pct of the superheat-temperature difference entering the mold of 58 °C. About 12 pct of the superheat is extracted at the narrow face, where the peak heat flux averages almost 750 kW/m² and the instantaneous peaks exceed 1500 kW/m². Two-thirds of the superheat is removed in the mold. The jets exiting the nozzle ports exhibit chaotic variations, producing temperature fluctuations in the upper liquid pool of ±4 °C and peak heat-flux variations of±350 kW/m². Employing a static-k subgrid-scale (SGS) model into the three-dimensional (3-D) finite-volume code had little effect on the solution.     

攀钢板坯连铸高效化技术研究

简述了攀钢板坯连铸高效化生产技术及其应用效果.通过研究开发适应高拉速要求的连铸保护渣、结晶器冷却制度和钢水温度控制制度,连铸拉速达到1.30～1.80 m/min;通过应用钢包渣改性、精炼工艺优化和高粘度连铸保护渣,IF钢冷轧板卷条痕缺陷率由10.97%降至1%以内;通过合理分配两台板坯铸机功能,推广应用中包快换水口,减少LF工序钢水加热时间和提高RH连续处理能力等技术,铸机作业率由平均89.39%增至92.96%.为攀钢2008年上半年板坯产量达154万t提供了重要的技术支撑.     

板坯连铸机浸入式水口结构优化的水模研究

通过水力模型实验,研究了水口结构对南钢板坯连铸机结晶器内钢水流动特性的影响.研究结果表明:使用现有水口结晶器内液面波动大且存在明显裸露并有严重的卷渣现象,适当增加浸入式水口出口面积,在不改变水口其它结构参数和插入深度条件下,能够获得液面波动小,保护渣覆盖良好且没有卷渣的钢水流动特性,不仅能够实现提高拉速的要求,还能提高铸坯质量.     

稀土钢连铸板坯纵裂研究

研究分析了影响稀土钢连铸板坯纵裂的多种工艺因素，包括钢中化学成分、结晶器保护渣、结晶器拔热量、二冷水、拉速和中间包过热度等。据此采取了有效措施，彻底消除了稀土钢板坯纵裂。     

酒钢连铸板坯表面纵裂的成因分析及改进措施

连铸板坯表面纵裂起因于结晶器弯月面初生凝固坯壳厚度的不均匀性.针对酒泉钢铁公司4号连铸机的实际生产情况,分析了影响板坯表面纵裂的因素,发现连铸板坯纵裂与结晶器冷却强度、钢水成分、夹杂含量、拉坯速度、钢水过热度等诸因素密切相关.通过采取相应的措施,可使连铸板坯纵裂指数有一定改善.     

含钛型连铸保护渣性能及应用研究进展

 随着钢铁技术的进步和社会发展需求,钢铁企业正在研发和生产强度高、韧性好、抗腐蚀性强等各种类型的高质量特殊钢种。如何有效控制特殊钢种连铸生产工艺的稳定性是当前保护渣开发面临的共性难题。设计研发合理的保护渣化学成分、稳定其物化性能,以保证特殊钢种良好的铸坯质量是钢铁冶金领域科研人员关注的热点问题。为此,有关科研人员开展了大量的保护渣基础理论及应用研究,取得了一定的成效。大多数学者研究认为,在传统保护渣中添加一定量的TiO₂可以改善保护渣物化性能、提高吸附夹杂物的能力、阻止钢-渣界面反应、减少铸坯质量问题的发生。保护渣中TiO₂质量分数为4%~8%、碱度为1.1~1.3时,可以有效改善保护渣的熔化温度、黏度以及热流密度等物化性能,对渣膜结晶也可以起到促进作用,能基本满足高钛钢、高铝钢等特殊钢种的要求;含钛保护渣渣膜中的钙钛矿可以代替传统保护渣渣膜中的枪晶石,对保护渣的传热起着决定性的作用;含钛保护渣吸收钢水中夹杂物后,保护渣的物理性能保持稳定,并可以防止特殊钢水中的钛与保护渣发生界面反应而引起的铸坯表面“结鱼”等问题的发生;含钛型保护渣在某些特殊钢种中已进行初步探索应用并取得阶段性成果。关于渣膜中钙钛矿及其他矿物对含钛型保护渣传热的影响机理,如何更好地协调保护渣的基础性能与润滑传热机制之间的矛盾,实现含钛型保护渣在连铸工艺中的广泛应用,以满足连铸工艺优质高效稳定的生产需要,仍是冶金工作者进一步研究的主要课题。     

热轧卷板表面夹渣缺陷来源分析及控制现状

热轧卷板的表面夹渣缺陷对热轧板的质量及产品性能会产生极其恶劣的影响,会导致产品品级的下降乃至报废等问题,并对产品的服役期限及性能造成一定影响.随着冶炼过程中钢液洁净度的不断提高,夹渣缺陷所造成的质量问题显得尤为严重.而不同生产工艺下表面夹渣缺陷的来源方式略有差异,缺陷的来源主要有精炼过程中钢包渣的卷渣、非稳态浇注时期的...     

Measurements and Calculation of Interfacial Tension between Commercial Steels and Mould Flux Slags

Surface quality of continuously cast is strongly influenced by the interfacial tension between steel and mould flux slag. The meniscus shape and the inclusion entrapment are directly determined by interfacial tension. To achieve a better understanding of the continuous casting process, the interface between four commercial steels and the mould fluxes used at the continuous casting of each steel grade have been investigated. The situation at this interface is determined by the surface tension of steel and slag respectively and also by the mass transfer occurring across the interface. The surface tensions of the mould flux slags have been measured by sessile drop method. The results indicate that the surface tension of mould flux slags decreases with increasing temperature but does not vary so much within the present composition range. Interfacial tensions between steel samples and mould flux slags have been measured in the same way with the aid of X‐ray unit. Estimation of interfacial tension from the steel and slag composition was done by applying empirical models. The measured and the calculated values were in agreement. The interfacial tension was lower for higher alloyed steel grades according to both experiments and calculations though the influence of surface active elements is significant.     

Q355R连铸坯表面微裂纹研究

摘要：裂纹是影响连铸坯质量的主要缺陷,其成因和影响因素复杂众多。针对Q355R连铸坯表面微裂纹,在铸坯典型裂纹处采用金相观察、扫描电镜、能谱进行表征,进一步分析其形成机制,进而对连铸工艺进行优化改进。结果表明,铸坯表面的微小裂纹,其形貌不同于传统的网状星形裂纹和横裂纹,裂纹端主要为钝口且无延伸端,个别裂纹上端存在微裂纹细线,裂纹端呈“针”状且有延伸段。微裂纹主要成因是由结晶器卷渣、钢水二次氧化、钢水过热度大以及在连铸机弯曲和矫直区域外部应力共同作用所导致。通过对水口结构优化,改善结晶器流场,减弱结晶器卷渣,以及对连铸工艺优化,使铸坯表面微裂纹得到了有效控制。     

Study of the Effects of the Mold Surface and Solid Mold Flux Crystallization on Radiative Heat Transfer Rates in Continuous Casting

Radiative heat transfer plays a crucial role in the meniscus area of a steel continuous casting machine. However, the study of radiation across the mold flux and copper molds is very difficult due to the harsh environment and highly transient nature of the phenomena in continuous casting molds. By using an infrared radiation emitter, a radiative heat flux was able to be applied to a copper mold with different top surfaces to observe their effects on the radiative heat transfer. The mold surface was covered with solid slag disk subjected to the radiative heat flux to simulate the radiative heat transfer phenomena in continuous casting. The solid slag disk could either be glass or a mixture of glass and precipitated crystals. The effect of full crystallization of a slag disk was to reduce the heat transfer rate by 20.5%, as compared with a completely glassy sample.