改善连铸重轨钢中心偏析的技术探讨

综述了重轨钢连铸方坯中心偏析的形成机理改善措施，分析了电磁搅拌，低过热浇铸以及适当的宽厚比和轻压下技术对消除或改善重轨钢连铸方坯中心偏析的作用和效果。指出组合式电磁搅拌和低过热度浇铸是改善重轨钢连铸方坯中心偏析的有效途径。     

高碳钢连铸坯中心偏析的控制与改善

分析钢水过热度、拉速、二冷强度等连铸工艺参数对高碳钢连铸坯中心偏析的影响,认为采取提高钢水洁净度、低过热度浇注、电磁搅拌、轻压下和优化二冷技术等措施是减轻高碳钢连铸方坯中心偏析的有效途径.     

改善82B小方坯碳偏析的连铸工艺研究

文章阐述了控制82B小方坯连铸坯碳偏析的连铸方法。综合考虑了结晶器电磁搅拌及末端电磁搅拌技术的应用、调整二冷强度、降低过热度。选择合适的控制参数与之相匹配,制定的生产工艺有效抑制了高碳钢的中心碳偏析。     

结晶器电磁搅拌对高碳钢连铸坯质量的影响

通过在八钢四流方坯连铸机上500多炉的工业试验,系统地研究了结晶器电磁搅拌对连铸坯缩孔、中心偏析和纯净度的影响。试验结果表明,结晶器电磁搅拌可有效改善连铸坯的中心缩孔,在高过热度浇铸条件下(大于30℃),改善缩孔的效果明显。结晶器电磁搅拌能有效改善高碳钢的中心偏析,降低铸坯中全氧,电磁搅拌电流强度的增加对去除钢水中的氧化物夹杂有利。     

40Cr连铸坯元素偏析金属原位分析研究

应用金属原位统计分布分析技术研究了40Cr连铸方坯中C、S、P、Si、Mh和Al的宏观偏析规律.研究表明在较高的等轴晶率下中间包钢水过热度对C的宏观偏析不产生影响.但对S和P的宏观偏析仍然产生明显影响.具有强烈偏析倾向的S和P呈现完全不同的偏析规律;接近液相线温度浇铸时并不能减轻S和P的偏析程度.Si基本不产生偏析,而Mn在常规浇钢过热度下呈中心正偏析;元素Al的中心正偏析主要是因Al2O3夹杂向连铸坯中心聚集引起.     

改善弹簧钢连铸方坯中心碳偏析的试验

为改善弹簧钢(55SiMnVB)连铸方坯中心碳偏析,制定了合理的钢水过热度范围和电磁搅拌参数。     

GCr15轴承钢连铸坯冶金质量的分析

分析了结晶器电磁搅拌、钢水过热度和轧钢工艺对连铸GCr15轴承钢180方坯轧材中心疏松、碳偏析、碳化物液析等缺陷的影响，结果得出连铸时采用电磁搅拌和降低钢水过热度可减轻铸坯碳偏析，铸坯在1210℃均热60min可减轻甚至消除钢中碳化物液析。     

高碳钢连铸钢液过热度的控制

阐述了在武钢第一炼钢厂条件下生产高碳钢时浇铸温度的控制措施。通过改善钢包、中包的保温效果，并采用合理的LF炉温度控制模式，可以使得高碳钢在进行低拉速浇铸时获得稳定且较低的过热度．从而有效降低铸坯碳偏析。     

利用电磁搅拌改善连铸坯的中心偏析

在连续铸钢生产中,尤其对高碳钢,中心偏析是一种常见的有害缺陷。本文对二冷区位置电磁搅拌改善连铸方坯的中心偏析进行了实验研究。结果表明,搅拌工艺选择适当可较好地改善连铸坯中心偏析;反之则会导致中心偏析无变化或更严重。     

过热度对高碳钢小方坯宏观偏析影响研究

基于国内某厂高碳钢小方坯连铸生产过程,首先利用ProCAST软件进行过热度对连铸坯宏观偏析影响的模拟研究,然后对过热度分别为44、39和28℃的连铸坯横断面和纵截面进行宏观偏析和疏松缩孔的研究。模拟结果表明:连铸坯横断面中心碳偏析随着过热度的增加不断增大,过热度超过25℃时,连铸坯横断面中心碳偏析度更加严重;试验结果表明,过热度分别为44、39和28℃的连铸坯横断面中心碳最大偏析度分别为1.39、1.32和1.06。结合模拟结果能够有效指导实际生产过程中连铸参数的调整,过热度越高,连铸坯中心碳偏析、条带状疏松缩孔越严重,为了降低连铸坯宏观偏析,建议将过热度控制在25～30℃。     

连铸方坯中心线凝固行为波动现象及变化规律

连铸坯中心线区域钢液的凝固行为与中心偏析缺陷的形成及控制密切相关。基于中碳钢连铸方坯纵断面的实际凝固组织,以中心偏析点内部二次枝晶间距计算局部冷却速率,揭示了铸坯中心线局部冷却速率的波动特征。结合连铸三维凝固模型,研究了铸坯中心线固相率波动引起局部冷却速率波动并最终影响铸坯中心组织和性能的均匀性的机理;对不同工况铸坯中心线固相率和局部冷却速率波动的周期性进行了分析对比,提出了连铸坯凝固终点位置的周期性波动机理并得到了不同拉速下凝固终点波动距离的判断方程,对于所选连铸方坯,凝固终点波动距离为25.0～27.5 mm;在此基础之上,研究了拉速对中心线固相率波动程度的影响规律,并分析了凝固终点波动距离变化对末端电磁搅拌(final electromagnetic stirring, F-EMS)和轻压下(mechanical soft reduction, MSR)作用均匀性的影响。结果表明,拉速由1.8 m/min提高至2.4 m/min后,虽然液相穴长度增加可能增加整体偏析程度,但铸坯中心线固相率波动程度降低了20%,这有利于减轻中心线偏析沿拉坯方向的波动性,提高铸坯中心质量的均匀性。并...     

Some effects of electromagnetically induced fluid flow on macrosegregation in continuously cast steel

Electromagnetically induced and controlled flow of the molten metal inside the solid shell has been found to be a technique for controlling solidification structures and centerline segregation in continuously cast steel billets. Measurements of centerline segregation in steel billets solidified under induced flow indicate a reduction of centerline segregation by a factor of two for carbon, phosphorus, sulfur, chromium, and nickel, and somewhat smaller improvements for other elements. The type of induction stirring technique applied was found to have a substantial effect on the macrosegregation patterns found in the billets solidified under induced flow.     

连铸板坯三维二冷动态配水与精准压下研究与应用

在现有工艺条件下,校验和完善二冷区铸坯凝固传热计算数学模型,开发三维二冷配水模型,解决目前设备状况下冷却水分布不均匀对铸坯温度的影响,从而控制铸坯表面质量,特别是铸坯的角部裂纹,同时对板坯连铸二冷配水制度进行改进和优化,使之满足高效连铸生产条件和改善铸坯质量的需要。提出压下参数计算公式,结合所开发三维二冷配水模型,优化现有压下工艺,提出并应用精准可控单段压下、非稳态压下控制,集中解决连铸板坯中心偏析、中心疏松和缩孔等内部质量问题。同时优化模型数据库,使之数据更加完备,模型计算更加准确,同时模型具备异钢种混浇过程二冷及压下控制功能,能够进行凝固终点W形预测与控制,可进一步提高模型适用性和准确性。模型开发并成功在多家钢厂现场应用,有效改善了铸坯裂纹和偏析等铸坯表面和内部的质量问题。      

连铸工艺参数对高碳钢小方坯内部质量的影响

研究了连铸工艺参数对于高碳钢小方坯内部质量的影响,结果表明,结晶器电磁搅拌强度增加,高碳钢小方坯中心碳偏析减小,但坯壳内的负偏析加重。在结晶器电磁搅拌条件下,随着二冷比水量增大,中心碳偏析减小;随拉速、中间包钢水过热度和钢中碳含量增加,中心碳偏析加重。     

GCr15轴承钢大方坯凝固过程微观偏析模型及应用研究

建立了考虑δ/γ相变的GCr15轴承钢大方坯连铸凝固两相区溶质微观偏析模型,并应用于220 mm ×260 mm铸坯的凝固传热。结果表明:通过模型可以获得高碳钢精确的固液相线温度,以及温度与固相率的关系;GCr15轴承钢大方坯凝固过程仅析出γ相,凝固末期S、P和C元素的偏析严重;固相率越大,冷却速率对偏析度的影响更明显;S和P元素含量以及冷却速率对零塑性温度（ZDT）影响较大;采用基于凝固传热模型优化的连铸工艺后,铸坯中心碳偏析指数控制在0.961.05,且铸坯未产生内裂纹。     

Computational Fluid Dynamics Modeling of Macrosegregation and Shrinkage in Large-Diameter Steel Roll Castings

Minimizing macrosegregation and shrinkage in large cast steel mill rolls challenges the limits of commercial foundry technology. Processing improvements have been achieved by balancing the total heat input of casting with the rate of heat extraction from the surface of the roll in the mold. A submerged entry nozzle (SEN) technique that injects a dilute alloy addition through a nozzle into the partially solidified net-shaped roll ingot can mitigate both centerline segregation and midradius channel segregate conditions. The objective of this study is to optimize the melt chemistry, solidification, and SEN conditions to minimize centerline and midradius segregation, and then to improve the quality of the transition region between the outer shell and the diluted interior region. To accomplish this objective, a multiphase, multicomponent computational fluid dynamics (CFD) code was developed for studying the macrosegregation and shrinkage under various casting conditions for a 65-ton, 1.6-m-diameter steel roll. The developed CFD framework consists of solving for the volume fraction of phases (air and steel mixture), temperature, flow, and solute balance in multicomponent alloy systems. Thermal boundary conditions were determined by measuring the temperature in the mold at several radial depths and height locations. The thermophysical properties including viscosity of steel alloy used in the simulations are functions of temperature. The steel mixture in the species-transfer model consists of the following elements: Fe, Mn, Si, S, P, C, Cr, Mo, and V. Density and liquidus temperature of the steel mixture are locally affected by the segregation of these elements. The model predictions were validated against macrosegregation measured from pieces cut from the 65-ton roll. The effect of key processing parameters such as melt composition and superheat of both the shell and the dilute interior alloy are addressed. The influence of mold type and thickness on macrosegregation and shrinkage also are discussed.     

Experimental and computational study of nozzle electromagnetic stirring and its effects on solidification structure

Abstract

Centreline shrinkage and segregation in continuously cast billets have an adverse effect on cast product quality. Nozzle electromagnetic stirring (N-EMS) is an effective method to refine the solidification structure of continuously cast billets and thereby improve the cast product quality. The effect of N-EMS on the solidification structure of continuously cast Sn-3·5Pb alloy has been investigated by means of experiments and numerical analysis. The results show that, upon imposing N-EMS, crystal grains within the billets are refined and continuous casting can be conducted at a lower pouring temperature; the solidification structure of the resulting obtained billets is much finer than without N-EMS. The mechanism by which the solidification structure of the billets is improved is considered to be a change in the flow and temperature distribution of molten metal in the nozzle.     

On the formation of pipes and centerline segregates in continuously cast billets

Centerline macrosegregation in continuously cast steel billets, blooms, and slabs is a significant problem. Thermal contraction of the solidified shell at the final end of the liquid pool causes a separation in the central portion of the strand and formation of a pore. When this pore fills with liquid, centerline macrosegregation results. Segregation formation is influenced by the cooling and casting conditions. The effects of those parameters are discussed in this article. Thermal contraction also causes formation of a large pipe in the very last portion of the strand. The casting parameters that control the centerline macrosegregation also control the size of the pipe.     

汽车用高锰TWIP钢的研究现状

高锰TWIP钢的塑性机制与其堆垛层错能有关。采用试验法和热力学计算法确定TWIP钢层错能的研究结果存在差异,TWIP效应与层错能的对应关系也未达成一致。高锰TWIP钢凝固温区宽,凝固时容易形成疏松、偏析等铸态缺陷。铸态TWIP钢高温时的断面收缩率均低于40%,可能导致连铸弯矫时开裂。水平连铸和双辊薄带连铸在TWIP钢生产上具有突出优势。TWIP钢的热轧温度区间窄,与其固相线温度低和高温塑性差有关。冷轧后连续退火温度和退火时间也尚在摸索之中。Fe-Mn-Si-Al系TWIP钢的强化机制以孪晶形成动态细化晶粒为主,而Fe-Mn-C-(-Al)系TWIP钢中动态应变时效可能是主导作用。TWIP钢的延迟断裂敏感性可通过Al合金化来改善,其主要机制是在试样表层下形成的α-Al2O3层阻止氢的渗入。