Application of high-basicity mould fluxes for continuous casting of large steel slabs

Controlling the formation of longitudinal cracks on hypo-peritectic steel slab surfaces is one of the key challenges in continuous casting worldwide. Based on the production in Chongqing Iron & Steel Co., mould fluxes with high basicity ranging from 1.7 to 1.8 were put forward and the effects of compositions on the basic properties of mould flux were studied in the present paper. After laboratory experiments, a high-basicity mould flux with an increased crystallisation speed to abate the heat-transfer capability in the meniscus area was fully applied in the first steelmaking plant of Chongqing Iron & Steel Co. Using the high-basicity mould flux, for more than 3 million tonnes of slab production, the large longitudinal crack was eliminated and the rate of formation of small longitudinal cracks decreased greatly. During the production process, sticking that impedes the smooth running of continuous casting was infrequent, and the spot check for longitudinal cracks on micro alloy steel surface was simplified in the slab finishing process. Furthermore, since the application effect of mass production is remarkable, the hot charging process is better implemented, and the contract can be accomplished in time. In summary, the problem of longitudinal cracks on hypo-peritectic steel slab surfaces is finally resolved and the high-basicity mould fluxes have become indispensable auxiliary materials during continuous casting of hypo-peritectic steel.     

连铸与模铸高铁车轴钢的高周疲劳破坏行为

连铸车轴钢能否达到模铸车轴钢的性能水平是其能否应用的一个关键。对此,采用旋转弯曲疲劳试验及疲劳裂纹扩展速率试验对比研究了连铸与模铸工艺生产的高铁车轴钢的高周疲劳破坏行为。结果表明,工业试制的连铸车轴钢的强度和疲劳极限均低于模铸车轴钢,且前者的疲劳裂纹扩展速率略高于后者。疲劳断口分析表明,疲劳断裂大部分起源于试样表面基体。微观组织分析表明,尽管两者的微观组织均为高温回火马氏体,但连铸车轴钢中原奥氏体晶粒尺寸及碳化物均略大于模铸车轴钢。金相评级法及夹杂物极值统计法的结果均表明,连铸车轴钢中的夹杂物尺寸明显大于模铸车轴钢。因此,为了以连铸工艺取代模铸工艺,还需要进一步优化连铸车轴钢的成分、冶金生产和热处理等工艺,以获得优良的冶金质量和组织性能。     

Three-dimensional analysis and design of petal-like mould for continuous casting of steels

Abstract

Understanding the shrinkage behaviour of a steel billet is very important for designing the continuous casting mould, and conversely, a well designed mould is beneficial when matching the shrinkage behaviour of the billet. The shrinkage behaviour of a billet is hard to measure in situ during continuous casting but can be calculated by numerical simulation. A three-dimensional finite element model has been built to simulate the thermal and stress fields of the billet in the mould. The dynamic thermal boundary condition, the effect of ferrostatic pressure and the temperature dependent thermophysical parameters have been considered in the model. The shrinkage of billet when considering ferrostatic pressure is on average 0·08 mm smaller than when not considering ferrostatic pressure. The temperature and stress distributions are analysed in the present paper, and based on this analysis, a novel petal-like mould was designed and its taper determined. The designed mould has been tested in industrial practice showing better lifetime and billet quality.     

Looking into continuous casting mould

Abstract

When you look into the continuous casting mould you can see very little. Consequently, steelmakers have had to rely on plant trials, simulation experiments and physical property measurements on fluxes and steels to gain an understanding of the mechanisms responsible for process problems and product defects. However, in recent years, mathematical modelling has advanced to the stage where they can provide us with great insight into these mechanisms. As a non-mathematical modeller, I was initially sceptical of some of the predictions of the mathematical models. However, I have been completely won over by the ability of these models to simulate accurately the mechanisms responsible for various defects, such as slag entrapment, oscillation mark formation, etc. Mathematical modelling literally allows us to ‘see’ what is happening in the mould. It is a remarkable tool.     

结晶器振动双机互备份控制系统

介绍连铸生产中结晶器振动控制系统的组成原理，提出双机互备份并行工作方案，以确保连铸核心装置部分的连续性与稳定性。实际运行表明，该系统工作稳定，有效地提高了连铸生产的可靠性。     

薄板坯连铸低碳铝镇静钢结晶器液位波动的控制

针对薄板坯连铸低碳铝镇静钢结晶器液位波动的问题,从现场操作、工艺优化、设备维护等方面对造成液位波动的原因及影响因素进行了分析。在此基础上采取了相应的措施,使浇铸过程中结晶器液位波动到了很好的控制,满足了生产需求。     

板坯连铸结晶器内钢液流动的数值模拟

利用Fluent软件对1650mm×220mm板坯结晶器建立了三维稳态数学模型,对三种方案条件下结晶器内钢液流动进行模拟.结果表明,结晶器的宽度对结晶器表面速度分布影响显著,随着结晶器宽度的增加,结晶器表面的速度分布越来越不均匀.表面的最大速度受到多种参数的影响,包括浸入式水口入口钢液的速度、水口出口角度和水口浸入深度等,其中入口钢液的速度影响最为显著.最优方案为：铸坯宽度1100mm,底部结构为山形和出口角度向下30°的水口,水口浸入深度120mm,流量为11.6m³·h^-1,入口速度为0.8384m·s^-1.     

Analysis of non-uniform thermal behaviour of special steel during slab continuous casting

A full-scale finite-element model of a slab and its mould was developed to reveal the complex thermal behaviour of special steel in a vertical caster during slab continuous casting. An inverse algorithm was applied to calculate the heat flux and combined with the temperatures measured using thermocouples that were buried in different positions of the mould. The model was validated by comparing the calculated temperature with the measured ones. The temperature distribution of the slab is not symmetric, reflecting the non-uniform nature of heat transfer and hence the necessity of formulating a full-scale model. It will provide a helpful tool for further improving the casting parameters and operations for special steel.     

方坯连铸结晶器凝固传热的有限元数值模拟

根据方坯结晶器的传热特点,研究了方坯连铸机结晶器二维非稳态凝固传热的有限元模型,应用ANSYS软件预测在浇注过程中结晶器的温度分布和凝固状态,分析了拉速、浇注温度及结晶器圆角半径对铸坯温度和坯壳厚度的影响.结果表明,经模型计算得出坯壳厚度值与现场测定拉漏数据基本相符.     

连续铸钢结晶器钢水液位自动控制及其实践

介绍连续铸钢结晶器钢水液位自动控制技术的国内外状况,包括液位检测技术、控制算法和执行器等在实际生产过程中的应用情况及存在的问题。针对上述状况进行了评估并提出解决问题的建议。     

热型连铸单晶铜工艺设备关键材质的选择

热型连铸是一项近净成形（near-net-shape）技术,它是将定向凝固和连铸技术结合在一起的新型工艺.通过对有关文献的综述介绍了热型连铸技术的特点和技术要点.在热型连铸技术应用于单晶铜生产工艺过程中,基于温度场直接影响热型连铸技术的关键———固液界面的位置和形状,重点介绍了影响温度场分布的熔体、铸型及引锭等关键部件的材质选用,为进一步改善热型连铸单晶铜生产工艺提供一定的参考依据.     

Understanding mould powders for high-speed casting

The development and application of mould powder for high-speed continuous casting of steel is described. For thin slab casting, the main requirements are proper powder melting, undisturbed slag infiltration, adequate strand lubrication and the control of mould heat transfer. For increased casting speeds i.e. up to 8?m/min, slag infiltration and in particular the control of mould heat transfer via crystallisation of the slag film becomes even more important. It was found that a low powder consumption and hence a thin slag film is no restriction for an undisturbed thin slab casting process. Given a stable casting process and machine condition, the mould powder properties are not as critical as widely assumed.     

Experimental study of oscillation mark depth in continuous casting of steel

Abstract

Mould oscillation is needed to reduce friction and thus prevent sticking and breakout of the liquid metal during casting. However, this oscillation is known to cause surface defects in the solidified steel slabs, so called oscillation marks. In this paper, the depth and the depth variation of these oscillation marks were studied using a two-level full factorial experiment (2) with four additional centre point runs. Four factors were studied: stroke length of the mould, oscillation frequency, motion pattern (strip factor) and casting speed. The stroke length affected the depth of the marks the most, where larger strokes created deeper marks. The interaction between the oscillation frequency and the strip factor of the mould also affected the oscillation mark depth. The oscillation mark depth variation was also increased by increased stroke lengths and at higher oscillation frequencies. The largest effect on the oscillation depth variation was found for the interaction between the stroke length and the oscillation frequency.     

保护渣对连铸二冷水中氟含量的影响

调查了使用不同氟含量保护渣时连铸二冷水中F^-质量浓度的变化,并在实验室研究了保护渣组分及保护渣在水中的浸泡时间对水浸液中F^-质量浓度的影响．研究结果表明,A厂使用低氟保护渣,二冷水中F^-质量浓度增幅为1．2～24．3mg·L^-1水样呈中性;B厂使用高氟保护渣,二冷水中F^-质量浓度增幅为57．9mg·L^-1,水样呈酸性．保护渣中氟含量越高,保护渣在水中的浸泡时间越长,渣中氟向水中的转移量就越多．控制保护渣中氟不超过2％,有利于减弱保护渣氟的浸出对二冷水的危害．在研究的组成范围内,碱度CaO／SiO₂和Li₂O对渣中氟的浸出无明显影响．增加保护渣中B₂O3含量,有利于降低保护渣中氟在二冷水中的浸出．     

论连铸设备在连铸生产中的地位和作用

本文对连铸设备对提高连铸生产效率、质量和效益的作用，连铸设备组成与连铸设备管理中几个主要问题，连铸装备水平的优化与提高，连铸工艺与设备的结合，抓好连铸设备人员培训等问题进行了论述。     

FTSR连铸耐蚀钢保护渣优化及铸坯角横裂控制

通化钢铁股份公司采用FTSR工艺在试生产的采暖散热器片用耐蚀钢的过程中,易出现角横裂缺陷和粘结事故.为了提高结晶器内初生凝固壳生长的均匀性,在保证优良的润滑性前提下,对保护渣的成分、性能进行了优化,从而实现了结晶器弯月面处坯壳的弱冷.在此基础上,对结晶器和二冷段的冷却工艺进行了优化,提出了防止铸坯角横裂的技术措施,改善...     

连铸结晶器内凝固坯壳粘结行为研究现状

预防和监控结晶器内凝固坯壳与铜板的粘结对保证连铸生产顺行、生产高质量铸坯和优化连铸工艺都具有重要意义,粘结是制约高拉速连铸和宽厚板连铸技术发展的关键因素之一。在回顾前人对结晶器内凝固坯壳粘结行为研究的基础上,全面概述了其形成、传播和修复机制,并对结晶器内坯壳粘结行为的检测和判定方法研究现状进行了介绍,同时指出了进一步研究结晶器内坯壳粘结行为的方向。     

连铸准沸腾钢生产技术的发展

介绍了连铸准沸腾钢生产技术的发展现状,提出了我国钢厂连铸生产中采用准沸腾钢生产技术的有关建议     

Inclusion behaviour in aluminium-killed steel during continuous casting

The inclusion behaviour during continuous casting were investigated in ultra low carbon (ULC) and high strength low alloy (HSLA) steels. From tundish to cast slabs, the total oxygen (T.O) content decreased from 19 to 12?ppm, 12 to 11?ppm in ULC steel and HSLA steel, respectively. The number density of inclusions in ULC decreased by about 40%, while it kept almost constant in HSLA steel during casting. A simple calculation on the T.O removal agreed well with the measured value, which showed that T.O removal was much larger through mould flux absorption than nozzle attachment. The T.O removal in ULC steel is substantially higher than that of HSLA steel due to the fact that alumina particles in ULC steel tend to agglomerate easier than calcium aluminates in HSLA steel, which facilitates inclusion removal to the mould powder.