Properties of High Basicity Mold Fluxes for Peritectic Steel Slab Casting

 In high speed continuous casting of peritectic steel slabs, mold fluxes with high basicity are required for less surface defect product. However, the basicity of remaining liquid slag film tends to decrease in casting process because of the crystallization of 3CaO·2SiO2·CaF2. Thus, a way is put forward to improve mold fluxes′ properties by raising the original basicity. In order to confirm the possibility of this method, the effect of rising original basicity on the properties of mold fluxes is discussed. Properties of high fluorine based mold fluxes with different basicities and contents of CaF2, Na2O, and MgO were measured, respectively. Then, properties of higher basicity mold fluxes were discussed and compared with traditional ones. The results show that increasing the basicity index can improve the melting and flow property of mold fluxes. With the increasing basicity, crystallization rate of mold fluxes increases obviously and crystallization temperature tends to decrease when the basicity exceeds 1.35. The method presented before is proved as a potential way to resolve the contradiction between horizontal heat transfer controlling and solidified shell lubricating for peritectic steel slab casting. But further study on improving the flow property of liquid slag is needed. This work can be used to guide mold fluxes design for high speed continuous casting of peritectic steel slabs.     

Mould Powder Requirements for High‐speed Casting

Mould powders play an important role in the stability of the continuous casting process of steel. The main functions of mould slag (i.e. molten powder) are to provide sufficient lubrication and to control the heat transfer between the developing steel shell and the mould. Sufficient lubrication requires an undisturbed melting of mould powders and uniform infiltration of mould slag. Based on the casting practice in IJmuiden, it is found that these demands become even more important for the applied high casting speeds in thin slab casting at 5 to 6 m/min. At Corus RD&T, mould powders were characterised by X‐ray diffraction and subsequent fully quantitative Rietveld analysis. Additionally, the melting of mould powders has been studied in‐situ using high‐temperature X‐ray diffraction, to gain crucial knowledge about melting relations. Slag rims obtained from the thin slab caster mould were characterised using extended microscopic techniques in order to describe the mechanisms of rim formation and growth. Finally, slag films obtained after casting were characterised. As a result, not only the melting process of mould powder, but also the mechanism of formation and growth of slag rims is much better understood. This knowledge will be applied to define the demands on the composition and properties of mould powder for even higher casting speeds.     

助熔剂对保护渣熔化温度的影响

通过对不同助熔剂加入量下连铸保护渣熔化温度的研究，得出助熔剂对保护渣熔化温度的影响规律，对其机理也进行了深入的讨论。     

保护渣对含硫易切钢连铸坯表面质量的影响

含硫易切钢中硫含量高达 0 .2 5 %～ 0 .35 % ,氧含量高达 (15 0～ 30 0 )× 10 - 6 ,结晶器内钢水弯月面处硫、氧含量更高 ,使得保护渣容易形成熔化不良的“絮状”渣团 ,导致铸坯出现严重的夹渣、横裂纹、皮下裂纹和气孔缺陷。针对该问题 ,研究了保护渣对增大结晶器弯月面处钢渣界面张力的作用途径和效果。工业化试验表明 ,在保护渣中添加金属还原剂和提高粗石墨含量 ,可有效抑制“絮状”渣团及其引起的铸坯缺陷 ,以获得表面质量优良的铸坯。工业化生产中含硫易切钢铸坯合格率达到 99.87%     

马氏体不锈钢板坯连铸保护渣研制与应用

 由于钢种特点,连铸马氏体不锈钢板坯容易产生裂纹缺陷,影响生产节奏和修磨效率;同时,由于采用通用型保护渣,也无法针对马氏体不锈钢板坯质量问题做出进一步改进。因此,尝试马氏体不锈钢板坯连铸保护渣的国产化研制和使用,通过保护渣碱度、CaF等的不同范围与保护渣结晶、黏度性能的关系研究,确定采用高碱度、低黏度、高结晶性的保护渣设计原则,并由此得出了适应马氏体不锈钢板坯连铸的保护渣设计方案。实际使用过程中,板坯纵裂率下降幅度达到30%,证明了马氏体不锈钢连铸板坯保护渣设计和研制的合理性和可行性。     

Effect of Titanium Addition on As Cast Structure and Macrosegregation of High‐Carbon High‐Chromium Steel

In casting heavy ingots of high‐chromium high‐carbon cold work steels, macrosegregation develops in the center of the ingot, causing difficulties during subsequent hot working. Heat transfer and solidification of an industrial scale high‐carbon high‐chromium steel ingot was simulated and thereafter a laboratory scale representative ingot was designed to model the solidification of the industrial scale ingot. Titanium in the range of 0.3–1% was added to the high‐chromium high‐carbon (12%Cr–2%C) steel during melting process. Microstructures, macrosegregation and phase formations were studied using optical microscopy, scanning electron microscopy, energy dispersive X‐ray spectrometry, wave dispersive X‐ray spectrometry, optical emission spectroscopy, and X‐ray diffraction. Addition of 0.3% titanium was sufficient to diminish the macrosegregation; however it did not have a significant effect on the grain size. Addition of 0.7 and 1% titanium had a substantial effect on grain size in the longitudinal direction and refined the primary carbides structure. The formation of small TiC carbides that precipitated before solidification of liquid iron acted as nuclei for primary pro‐eutectic austenite grains.     

板坯连铸结晶器内吹入气体对钢液行为的影响

采用水力学模拟方法研究板坯连铸结晶器内流场，分析塞棒吹Ａｒ时，浸入式水口琢拉速等工艺参数对连铸结晶器内钢液行为的影响。     

Development of Mould Flux for High Speed Thin Slab Casting

Mould powders impact the stability of the continuous casting process for steel at all casting speeds. The main functions of mould powder are to provide sufficient lubrication and to control the mould heat transfer between the solidifying steel shell and the copper mould. At higher casting speeds associated with thin slab casting, the role of the mould powder is even more important. Actual casting speeds for the thin slab caster at Corus IJmuiden are between 5.4 and 6 m/min; the production level is around 1.3 Mt/year (coils). It has been decided to increase the production of this caster to a level of 1.8 Mt/year (coils). In order to meet this demand, the steel in mould time has to be increased to approximately 85% and the maximum casting speed will be increased to 8 m/min. A collaborative project between Sumitomo Metal Industries (SMI) and Corus IJmuiden was initiated to develop mould powders which facilitate casting speeds up to 8 m/min at the thin slab caster. Main subjects of this project are: mould powder design, characterisation of mould powder and mould slag, trials at the pilot caster of Sumitomo and finally plant trials at the thin slab caster of Corus. A special point of attention is the condition to use mould powder as a granulated material at the thin slab caster. As a consequence, the characterisation work focussed on the choice of raw materials and on the corresponding phase relations at elevated temperatures. Typical of the developed mould powders are so‐called mild cooling properties which will result in a controlled mould heat transfer during casting. In this paper, several aspects of this joint project between Sumitomo and Corus will be described.     

连铸中碳钢用CK—2保护渣的研制

中碳钢亦称裂纹敏感性钢,在加铸过程中容易产生铸坯表面纵裂纹等缺陷,使用性能合适的保护渣可以改善结晶器内初始坯壳的传热条件,控制表面裂纹的产生,介绍了研制武钢三炼钢厂中碳钢用保护渣的过程及裂纹控制效果,分析了保护渣使用过程的性能变化和渣膜微观结构。     

不锈钢分公司不锈钢板坯连铸三电控制系统的结晶器液位控制系统

介绍不锈钢工程板坯连铸三电控制系统中,控制功能核心之一的结晶器液位控制系统的控制结构和控制实现方法,以及带模糊控制PID控制策略投入后的控制效果比较.     

大板坯连铸结晶器内流场实验研究

文中通过大板坯连帮结晶器的水模实验，研究了结晶器宽度、拉速、浸入式水口出口角、水口浸入深度及水口吹气量等工艺参数分别变化结晶器内流场的特性。认为，以水口吹气的影响最大；得出了不同工艺条件下的临界吹气量值。     

Optimization of Oscillation Model for Slab Continuous Casting Mould Based on Mould Friction Measurements in Plant Trial

Lubrication and friction between the mould and strand are strongly influenced by mould oscillation, and play an important role in slab quality and operating safety during continuous casting processes. Investigation of mould oscillation is therefore essential for getting a better online control of the mould processes. A feasible approach for the development and optimization of mould oscillation was put forward, which combined online measurement of mould friction, design of negative oscillating parameters and evaluation for powder consumption. Three different control models including sinusoidal and non-sinusoidal oscillation for mould oscillations were developed to investigate and evaluate the effects of oscillation on mould friction and powder lubrication. For the purpose of investigating mould friction between mould and strand, online measurement was carried out on a slab continuous caster equipped with a hydraulic oscillator. Also the comparison of the mould friction in sinusoidal and non-sinusoidal mould oscillation was made for subsequent analysis. The industrial experiment result shows that the combination of inverse control model and non-sinusoidal oscillation mode will contribute to the proper powder consumption, leading to a suitable effect of friction force on strand surface, especially for high speed continuous casting. The proposed method provides reliable basis for guiding and optimizing mould oscillation among control models, sinusoidal oscillation and non-sinusoidal oscillation.     

Prediction of Local Heat Flux and Temperature Distribution in a Mould Copper Plate for Flexible Thin Slab Casting Based on In‐plant Temperature Measurements

A three‐dimensional (3D) numerical model has been employed to predict the local temperature and heat flux distribution on the funnel‐shaped Flexible Thin Slab Casting (FTSC) H2 mould plate®. The modelling was combined with in‐plant temperature measurements from thermocouples installed in the mould. For the measurements the thermocouples are arranged to be adapted to the funnel‐curved shape of the mould such that the spatial locations of measured temperature data sets from the thermocouples can be regarded to form a plane. The method divides the geometry of the mould plate into two computational domains along the measured temperature plane in order to utilize the data as the boundary condition by interpolation. The measured data are compared with those obtained by the average heat flux and one‐dimensional (1D) heat conductivity model in the thermal analysis of the mould plate. It is found that the assumption of average heat flux only along the longitudinal direction, used in conventional billet or slab moulds, is not satisfactory to describe the heat transfer of the complex funnel‐shaped mould in the longitudinal and transverse direction. The heat flux values and hot face temperature in funnel‐shaped mould plates obtained by the 3D model are lower in comparison to the 1D model. The structure of cooling water channels has a significant influence on the uniformity of the heat flux. Some fluctuations of heat flux and temperature occur in the junction between the parallel‐curved and funnel‐curved zone along the longitudinal and transverse direction for the present case. It is expected that by utilizing the measured temperature data, the present model can be helpful to understand the thermal behaviour and define the thermal boundary condition of the funnel‐type mould plate.     

耐候钢异型坯连铸结晶器保护渣性能优化研究

由于异型坯形状复杂,在浇注耐候钢的过程中,铸坯表面质量较差,并经常发生粘结漏钢事故。通过实验室研究和工业性试验相结合的方法,根据异型坯连铸耐候钢的特点,分析了耐候钢异型坯表面质量差和浇注过程中发生粘结性漏钢的原因,提出了异型坯连铸耐候钢保护渣优化设计思路,重点研究了协调保护渣润滑和传热性能的影响因素。根据研究结果配制的异型坯连铸耐候钢专用保护渣,大生产应用结果表明,连浇炉数达到10炉以上,未发生粘结漏钢事故,耐候钢异型坯表面质量也有了明显提高。     

武钢三炼钢连铸低碳钢用结晶器保护渣的研制

介绍用于武钢三炼钢厂板坯连铸低碳钢器保护渣的研制过程，包括实验室保护渣配方的确定，保护渣造粒，以及现场试验。叙述了保护渣使用情况，应用效果，分析了保护渣使用前后的性能变化。