连铸厚板坯轻压下技术的应用

 对首秦2号板坯连铸机轻压下工艺进行了细致的研究。通过连铸坯射钉试验对首秦2号连铸机二级冷却模型进行了校验;通过不同轻压下率试验条件下连铸坯中心偏析的程度确定了合理的、能够有效改善连铸坯中心偏析的轻压下率;通过连铸坯厚度方向不同部位碳硫元素的分析对轻压下工艺改善前后连铸坯中心偏析度进行了对比。结果表明：首秦2号连铸机二级冷却模型能够准确反映连铸坯凝固末端的位置。在拉速为0.70m/min的连铸工艺条件下,320mm厚连铸坯轻压下段为第9和第10段,合理的轻压下率应该保持在0.85～1.0mm/m之间。采用合理的轻压下工艺后,连铸坯中心偏析得到了明显改善,满足了首秦高品质中厚板对连铸坯内部质量的严格要求。     

1650板坯压下过程热/力学行为及压下工艺优化

为了控制梅钢1 650板坯连铸包晶钢过程铸坯内裂纹发生,基于梅钢1 650板坯连铸机生产实际,建立了1 560mm×230mm断面包晶钢铸坯凝固过程三维热/力耦合有限元模型,揭示了铸坯凝固过程各冷却区内的温度场分布规律和铸坯压下过程应力与变形行为演变规律。结果表明,铸坯在结晶器及零段内冷却强度大,沿拉坯及其垂直方向的温度分布梯度大;在实施铸坯凝固末端压下过程中,铸坯宽面中心与宽向1/4处的表面变形及应力变化较为同步,且靠近铸坯内弧侧凝固前沿的塑性应变最大,铸坯应力最大值集中在角部区域;目前梅钢包晶钢连铸压下区间设置不当,易引发铸坯产生内部裂纹。     

连铸特厚板坯内部质量控制的关键技术

 采用连铸工艺流程生产特厚钢板具有低能耗、低排放和高效率的显著优势。然而，连铸坯中心偏析与疏松、内部大尺寸夹杂物未能得到较好的控制，是导致厚度不小于100 mm特厚板探伤不合格的主要原因。鉴于此，研发了特厚板连铸坯内部夹杂物去除技术与中心偏析、疏松控制技术，给出了利于夹杂物充分上浮去除的铸机最佳垂直段高度，以及改善铸坯中心偏析与疏松缺陷的凝固末端压下率参数。应用结果表明，上述技术措施取得了明显效果，生产的特厚板坯质量良好，采用连铸特厚板坯轧制出了优质特厚板。     

微合金钢薄板坯连铸边角裂纹控制

微合金钢薄板坯连铸过程高发边角部裂纹,致使热轧卷板边部产生翘皮、烂边等质量缺陷,是钢铁行业的共性技术难题。本文立足于某钢厂QStE380TM低碳含铌钛微合金钢薄板坯连铸生产,检测分析了铸坯角部组织金相结构与碳氮化物析出特点、不同冷却与变形速率条件下钢的断面收缩率,并数值仿真研究了不同结构结晶器和二冷区铸坯温度与应力的演变规律。结果表明:微合金钢薄板坯连铸过程存在明显的第三脆性区,且变形速率越大,第三脆性区越显著。传统薄板坯连铸工艺条件下,结晶器的中上部及其出口至液芯压下段的二冷高温区,铸坯角部冷速较低,致使其组织晶界含铌钛微合金碳氮化物呈链状析出。铸坯在液芯压下过程,低塑性角部因受较大变形与应力作用而引发裂纹缺陷。实施沿高度方向有效补偿坯壳凝固收缩的窄面高斯凹型曲面结晶器及其足辊区超强冷工艺,可分别提升铸坯角部冷速至10和20 ℃·s?1以上,从而促使铸坯角部组织碳氮化物弥散析出,并促进铸坯窄面在液芯压下过程金属宽展流动而降低角部压下应力,大幅降低了微合金钢薄板坯边角部裂纹发生率。      

330mm厚度连铸坯技术的开发与应用

舞钢第二炼钢厂通过对3鹕每机进行技术改造,成功实现了330mm厚规格铸坯的生产和板坯轻压下、结晶器液压振动、浸入式水口快速更换、小辊密排、电磁搅拌等多项连铸新技术的应用。新技术的应用提高板坯的内部质量,减少偏析、疏松以及中心裂纹的产生。高拉速又提高了2#、3#板坯连铸机的产能。既满足了产量的需求,又为内部及表面质量提供了重要保证。     

薄板坯连铸带液芯轻压下过程的力学计算

为了给实际薄板坯连铸带液芯轻压下的设备设计和工艺设计提供依据，对薄板坯连铸带液芯轻压下过程中的铸坯变形抗力、拉坯阻力及其变化特性进行了理论计算。分析比较了不同轻压下设备(二冷支撑段辊列)条件下，连铸及轻压下过程的工艺参数对它们的影响。结果表明，在二冷支撑段辊列运动挤压铸坯阶段，最后一对支撑辊的移动量、挤压速度、拉坯速度、支撑辊间距离、辊径和对数以及坯壳温度对铸坯变形抗力和拉坯阻力有很大影响；而在二冷支撑段辊列稳定挤压铸坯阶段，只有总轻压下变形量及坯壳厚度影响较大。     

0.23mm厚度高磁感取向硅钢片生产中的技术改进

0．23mm厚度高磁感取向硅钢片生产中存在的问题有：板坯加热温度太高，热轧板偏厚，边裂太多，需要多次常化、冷轧，表面质量不稳定。采取的措施是：研制低温板坯加热用钢，在钢中添加Cr，减薄热轧板的厚度，调整热轧、冷轧工艺，在MgO中添加适宜的添加剂，优化酸洗工艺等。     

轻压下参数对75Cr1高碳钢230 mm连铸板坯冶金质量的影响

基于有限元法,利用ANSYS软件模拟计算了高碳钢（0.73%~0.77%C）连铸板坯轻压下过程中热-机械塑性应变分布,分析了给定扇形段的压下量2 mm+2 mm,3 mm+3 mm和2 mm+2 mm+2 mm对压下区间和位置的塑性应变的影响,并通过现场试验对模拟结果进行了验证。结果表明,塑性应变模型模拟值与实测值吻合;热变形过程中,铸坯心部的等效应变最大,表面节点次之,1/4位置等效应变最小;热-机械塑性应变随着压下量和压下速率的增加而增加,3 mm+3 mm压下模式具有较好的压下效果。生产试验结果表明,采用2个扇形段（6^#和7^#或7^#和8^#）进行2.2 mm+2.3 mm轻压下铸坯较优化前3个扇形段（6^#,7^#和8^#）1.5 mm+1.5 mm+1.5 mm轻压下铸坯中心偏析2.0级和中心疏松2.0级提高中心偏析0.5级和中心疏松0.5级,显著改善了连铸板坯的低倍质量。     

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。     

首钢板坯连铸技术进步

回顾了近十年来首钢为生产优质冷轧钢板和特厚钢板而开发的板坯连铸新技术。为了降低优质冷轧钢板表面冶金缺陷,开发了浸入式水口防堵塞技术、结晶器内钢液流动综合控制技术和中高拉速FC结晶器技术等。综合应用这些技术后,水口堵塞率降低60%以上,结晶器液面波动±3 mm比例提高至98%以上,冷轧钢板表面卷渣缺陷指数降低50%以上。为了提升特厚钢板的冶金质量,开发了特厚板坯窄面鼓肚控制技术、倒角结晶器连铸技术、半干法连铸技术和二冷间歇式喷淋等技术,400 mm厚板坯窄面鼓肚量降低至5 mm以下,含铌微合金化钢板坯表面裂纹发生率大大降低。开发了特厚板坯连铸轻压下技术,中心偏析C类1.0级及以下比例达到100%,确保了150 mm特厚钢板的心部韧性达到100 J以上。     

Principles in cast rolling with liquid core of thin slab continuous casting

Dynamic rolling deformation behavior of continuously cast slabs with liquid core is studied with the aid of the thermomechanically coupled finite element method (FEM) of elastic-plasticity. The effects of shell thickness and related height reduction on the longitudinal tensile strain of strand are analyzed from a simplified three-dimensional (3-D) model. The results show that the longitudinal tensile deformation can be omitted for strands with thin shell, but it cannot be neglected for those with thick shell. A new concept of inward pushing or pushing into the liquid core is put forward based on the analysis, which leads to a reasonable explanation and better understanding of the liquid core cast-rolling processes in the present Inline Strip Production (ISP) thin slab casting.     

Flexure of Two-Way Slabs Strengthened with Prestressed or Nonprestressed CFRP Sheets

This paper presents a study on the flexural behavior of two-way reinforced concrete slabs externally strengthened with prestressed or nonprestressed carbon fiber-reinforced polymer (CFRP) sheets. Four large-scale flat plate slabs (3,000?mm×3,000?mm×90?mm) are tested and a nonlinear three-dimensional finite-element analysis is conducted to predict the flexural behaviors of the tested slabs, including the load-deflection response, strain distribution, crack propagation, and crack mouth opening displacement. An increase in the load-carrying capacity of 25 and 72% is achieved for the slabs strengthened with nonprestressed and prestressed CFRP sheets, respectively, in comparison to the unstrengthened slab. A reduction of the deflections up to 32% in service is noted for the strengthened slabs. The unstrengthened slab shows very ductile behavior, whereas, progressive failure is observed for the strengthened slabs, exhibiting pseudoductility in postpeak behavior. Stress redistribution between the internal and external reinforcement is significant in the slab strengthened with prestressed CFRP sheets.     

薄板坯连铸连轧的液芯压下技术

介绍了国内外薄板坯连铸连轧流程中液芯压下技术的发展与应用情况,分析了液芯压下过程中铸坯的凝固机理以及变形的应变特点,并根据铸坯的凝固机理和坯壳凝固前沿的应变条件,提出了确定单辊压下量、压下量分配和总压下量的基本方法。     

板坯连铸轻压下扇形段变形计算与研究

轻压下技术是减轻铸坯中心偏析,提高内部质量最为有效的方法。以三明钢厂220×1600mm板坯连铸机轻压下技术的实施为背景,对轻压下涉及的扇形段及铸坯的变形进行研究,合理设计了辊缝补偿量并在实际生产中采用,取得了很好的压下效果。     

预防中间包尾坯浇注过程中钢液卷渣的数学模拟和工艺优化效果

为降低中间包尾坯判废率,预防中间包尾坯降拉速过程钢液卷渣,应用流体力学软件FLUENT,对尾坯降拉速过程进行优化,研究尾坯拉坯过程的拉速变化对钢厂3^#板坯连铸机80 t中间包钢液紊流卷渣的影响。通过每次降拉速后的停留时间历程的湍动能时间跟踪曲线分析,确定了中间包尾坯降拉速优化方案。该方案在原方案基础上,将8 t铸余增加到10 t,缩短了各拉速下的持续拉坯时间,并将封顶操作从0.1 m/min提高到0.2 m/min,可减小尾坯卷渣的可能性和降低了生产成本,节约中间包尾坯降拉速总时间266.8 s和节约钢水量5.08 t。300mm×2000 mm 3^#板坯连铸机采用优化操作后,每月尾坯废品总量从576.4 t降低到139.1t。     

The“state of the art”slab caster for stainless steel in ThyssenKrupp Acciai Speciali Terni

On April 23,2009,a new single strand slab caster at ThyssenKrupp Acciai Speciali Terni(TKAST) was successfully started up with the first cast of AISI 304 grade in Terni plant,central Italy.TKAST is the Italian company of ThyssenKrupp Stainless group. The new caster is designed for a total capacity of approx.900.000 tpy of stainless steel slabs covering the complete range of stainless grades,including AISI 300 and 400 families(austenitic,ferritic and martensitic grades).This state of the art caster for the production of 215 mm thick slabs replaced an existing thin slab caster. This paper resumes the reasons of the installation of the new plant designed,manufactured erected and commissioned by Danieli and describes the technological solution,main features as well as the excellent results of this state of the art caster.     

High productivity and technological developments at Corus DSP thin slab caster

Abstract

The Corus IJmuiden Direct Sheet Plant focuses on production of thin gauged material through a single casting strand and an (semi-) endless rolling process. The caster has a 90 mm thick funnel shaped mould and is equipped with liquid core reduction, allowing a slab thickness of 70 mm. To reach casting speeds up to 5·4 mm min^?1, steel is fed into the mould using a specially designed submerged entry nozzle and an adjustable multi-pole electromagnetic braking system is installed. Although still increasing, productivity is now at the design level of 1·3 Mt/year. Average casting speed (including start and stop procedures) is >5·0 m min^?1 with sequence lengths up to nine 300 t ladles, representing a maximum planned casting time of 12 h. Significant growth has occurred in the production of (thin gauged) high strength steels. Breakouts have been a constant threat but stabilisation of the casting process has resulted in significant reduction in these events, allowing steady growth to productivity targets. Developments to improve mould fluid flow, mould level control, mould heat transfer and strand lubrication are described.     

Types of Continuous Casters and the Quality of Continuous-Cast Slabs for Obtaining Rolled Products for Crucial Applications

This article examines the production of continuous-cast slabs for the production of thick (thicker than 20 mm) plates used in critical applications. It is shown that the melt needs to be carefully prepared for casting on a continuous caster. When the steel is made in a converter, the pig iron must be desulfurized beforehand and the steel tapped from the furnace must subsequently be treated on ladle-furnace and vacuum-degassing units. It was established that production of high-quality slabs suitable for obtaining critical rolled products can be consistently achieved only through the use of a vertical continuous caster. The bending and unbending which slabs undergo on curvilinear casters and the curved axis of such casters make it very difficult or even impossible to obtain slabs and thick plates that do not have asymmetrically distributed nonmetallic inclusions, axial segregation, and internal and external cracks. The article analyzes the success that the company Severstal' had in rebuilding its vertical slab caster. The project, carried out by TsNIIchermet and the companies ORMET-YuUMZ and Korad, shows that Russian metallurgical science, the metallurgical industry, and the machine-building sector have competitive engineering solutions to offer.     

Laboratory simulation of thin slab casting

Abstract

Near net shape casting processes have been studied and applied by the steelmaking industry since the 1980s. Laboratory and numerical simulation have been used, along with pilot plants, to develop this new technology. The present paper describes equipment designed and built to simulate the conditions of thin slab casting and experiments carried out using it. The influence of liquid core reduction, one of the parameters used to obtain improved microstructure of thin slabs, has been analysed. The instrumented simulator consists of a water cooled mould with a movable side wall driven by a hydraulic piston. Experiments have been conducted using V-Nb microalloyed steel, with and without liquid core reduction, to assess the influence of solidification parameters on microstructure formation. Specimens from as cast slabs have been examined after polishing and etching to characterise the microstructure. Both macro- and microstructures of slabs obtained under various solidification conditions are described. Finally, chemical composition analysis by X-ray fluorescence has been used to investigate manganese segregation.     

辊子错位对铸坯鼓肚变形的影响

 由于加工、安装、变形与磨损等原因,连铸机辊列中的辊子会偏离设计位置而产生错位,这对铸坯鼓肚变形产生较大影响。基于高温铸坯黏弹塑性本构方程,建立两辊间距内的铸坯坯壳动态鼓肚数学模型,并利用模型计算试验铸机的铸坯坯壳鼓肚曲线,依照实测数据验证了模型的有效性。根据奥钢联工业连铸机的设备及工艺参数,计算铸机不同扇形段内铸坯坯壳在不同辊子错位量情况下的鼓肚变形,并讨论在辊子发生错位的情况下辊间距对铸坯坯壳固液交界面处最大应变的影响,并给出铸机辊间距的确定方法。