Viscosity of casting fluxes used during continuous casting of steel

Molten flux viscosity of eighteen commercially available casting fluxes has been measured as a function of temperature in the range of 1223 to 1723 K. Results show that, at a constant temperature, the flux viscosity is primarily dependent on the mole fractions of SiO₂ and A1₂O₃. The calculated activation energy for viscous flow at 1573 K varies from 59 to 215 kJ/mol depending on the flux viscosity and the flux basicity ratio. The observed “breakpoints” in the viscosity vs temperature plots are explained in terms of precipitation of crystalline phases. The tendency for crystal precipitation is related to the relative viscosity and the basicity of the flux. Using X-ray diffraction techniques the precipitating crystal phases have been identified. Metallographic structures of quenched and air-solidified casting fluxes are reported.     

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.     

Modeling superheat removal during continuous casting of steel slabs

To investigate superheat dissipation in a continuous slab casting machine, mathematical models have been developed to compute fluid flow velocities, temperature distribution within the liquid pool, heat transfer to the inside of the solidifying shell, and its effect on growth of the shell. Three-dimensional (3-D) velocity and heat-transfer predictions compare reasonably with pre-vious experimental measurements and two-dimensional (2-D) calculations. The results indicate that the maximum heat input to the shell occurs near the impingement point on the narrow face and confirm that most of the superheat is dissipated in or just below the mold. Superheat tem-perature and casting speed have the most important and direct influence on heat flux. The effects of other variables, including mold width, nozzle jet angle, and submergence depth, are also investigated. Calculated heat flux profiles are then input to a one-dimensional (1-D) solidifi-cation model to calculate growth of the shell. Shell thickness profiles down the wide and narrow faces are compared with the predictions of conventional heat conduction models and available measurements.     

连铸二冷模式对微合金钢板坯角部表层组织的影响

为减少和预防攀枝花钢钒有限公司P510L微合金钢连铸坯角部裂纹的发生,进行了二冷区不同冷却模式对铸坯角部表层组织及表面横裂纹的影响研究。结果表明:传统弱冷模式下,大量膜状先共析铁素体连成网状,阻碍了奥氏体基体的连续性,降低了铸坯角部的热塑性。在优化冷却模式下,在铸坯角部表层2~3 mm的组织细小、分布均匀,没有出现先共析铁素体膜,有利于控制铸坯表面横裂纹的发生。相对于传统弱冷模式,优化冷却模式可将铸坯角部表面横裂纹指数由3.2降至0.4,裂纹发生率得到了控制。     

Horizontal continuous casting of steel

The history of horizontal casting of steel is considered. Some features of horizontal machines are noted: low height; no ingot deformation in casting; no secondary oxidation of the metal; the ability to cast small cross sections. The basic characteristics of Russian systems are described, along with operational experience. The prospects for horizontal machines in metallurgical micro mills and in the reconstruction of existing mills are discussed.     

Factors affecting the reoxydation of molten steel during continuous casting

Abstract

When molten steel is teemed through air, oxygen picked up by the metal from the atmosphere reacts with other elements dissolved in the steel to form products of reoxidation. Unless removed from the steel prior to solidification, this nonmetallic material will form a major source of inclusions in the final product. In this paper, factors governing the reoxidation of molten steel during continuous casting operations are examined on the basis of information obtained from plant observations, water-model studies and levitation experiments conducted with molten steel droplets.

Résumé

Lorsque le jet de coulée de l'acier passe dans l'air, des éléments de l'acier sont susceptibles de s'oxyder. Les produits d'oxydation donneraient lieu à des inclusions. Les auteurs ont étudié, à partir de la pratique et de lévitation de gouttelettes, les facteurs qui influent sur l'oxydation qui se fait au moment de la coulée continue.     

高拉速下凝固进程的试验测量与模型预测

 根据京唐高拉速试验特点,结合板坯连铸机设备和洁净钢连铸工艺特点和要求,建立连铸板坯凝固传热模型并结合射钉法测量综合预测了1.9～2.4 m/min高拉速条件下铸坯的凝固坯壳厚度和凝固终点位置。综合研究表明,结合射钉试验和数值模拟能更精确跟踪铸坯的凝固进程,为高拉速试验提供准确的凝固信息,并能为评价连铸机综合冷却能力、优化二冷制度和轻压下工艺提供合理的参考信息。     

Control of the secondary cooling in continuous casting during nozzle replacement

The cooling and solidification of a continuous-cast ingot in transient casting conditions are studied by simulation. The influence of the method of controlling the secondary cooling on the thermal state of the ingot is shown. Different approaches to the control of the coolant flow rates in various operations are compared.     

Recovery mechanism of the sticking-type breakout during continuous casting of steel

Sticking-type breakout is one of key factors which restrict the development of high-speed or wide-heavy plate continuous casting technology. In order to better heal and control the sticking-type breakout, this paper presents a comprehensive study for its recovery mechanism. First, according to force characteristics of solidified shell at mold exit, calculation method of safe shell thickness is proposed. Then, considering sticker propagation behaviour and safe shell thickness, a more practical recovery model of sticking-type breakout is established and verified by actual examples. The result shows the proposed recovery strategies avoid casting speed to be decreased too low or cast stop, thus save unnecessary operating time, and are better than original strategies. Furthermore, influencing factors of recovery behaviour are analyzed. The result shows hot spot location, operating casting speed, and mold oscillation frequency have a significant effect on minimum speed for the recovery and oscillation stoke has little influence on it.     

连铸大方坯气瓶钢白点缺陷的防止

介绍电炉—大方坯连铸生产气瓶钢防止白点缺陷的改进措施。连铸大方坯轧制后的气瓶钢坯上经常发现轻微白点缺陷,在连铸中间包的开浇炉上更为明显。白点缺陷存在安全隐患,是气瓶钢中不允许存在的缺陷,为此加强对炼钢原辅材的防潮、VD真空过程以及中间包烘烤时间的管理,同时通过不同缓冷方式的试验,确定最合适的缓冷工艺,有效避免了轧制后钢坯白点现象的发生。在低倍组织检验时这种细小白点缺陷容易漏判,采用超声波探伤检查．对防止白点误判非常重要。     

SWRH82B方坯连铸的二次冷却研究

文中测量了SWRH82B钢高温力学性能参数,找出了SWRH82B钢的脆性温度区间,确定了二次冷却目标表面温度曲线;然后根据铸机参数和热物性参数,利用编制的仿真软件仿真计算出具体铸机的二冷水量,开发了方坯连铸SWRH82B钢的二冷制度,并取得了比较好的效果。     

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.     

Minimisation of melt spitting during continuous billet casting of low carbon steel

Abstract

Less critical grades of steel for long products are commonly produced from open cast billets. However, melt spitting from the mould is one of the potential safety hazards and may adversely affect the cast steel quality besides upsetting the caster productivity. In the present work, investigations have been carried out in an attempt to minimise the spitting problem during open pour casting. A typical fairly low carbon steel grade has been chosen for the study, as the problem of spitting was more severe for this steel grade as compared with other grades of steel. Influences of some of the relevant operating parameters were considered for investigation, and extent of spitting was quantified by determining the spitting for each case. Among the various variables considered, electromagnetic stirrer position in the mould was found to have the dominating influence. In addition, several other counter measures were adopted, and the spitting problem was minimised significantly.     

2205双相不锈钢连铸过程中夹杂物的形成机制

摘要：为了研究2205双相不锈钢连铸过程中夹杂物的特征及形成机制，从2205双相不锈钢连铸中间包和板坯上分别取试样，利用扫描电镜分析夹杂物的类型及形貌特征，并结合热力学计算探讨夹杂物的演变规律及其形成原因。结果表明，2205双相不锈钢中间包中存在大于10μm的夹杂物，中间包中夹杂物类型主要为CaO Al2O3和CaO Al2O3 MgO球形夹杂物，板坯中夹杂物尺寸都小于10μm，板坯中CaO Al2O3和CaO Al2O3 MgO球形夹杂物外面包裹了一层TiN。错配度和热力学计算表明凝固过程中CaO Al2O3和CaO Al2O3 MgO球形夹杂物为TiN的析出提供了形核质点。