包晶钢连铸板坯表面质量的控制

包晶钢凝固时处于包晶区(L δ→γ)，发生δFe→γFe转变，有较大的体积收缩，导致初生坯壳不均匀，在薄弱处应力集中而产生裂纹。通过提高钢水的洁净度、稳定结晶器钢液面控制、优化结晶器、保护渣、二次冷却等工艺参数可以有效控制包晶钢连铸板坯表面缺陷的发生。     

合金元素对钢亚包晶转变与连铸纵裂倾向的影响

 亚包晶钢连铸过程中常出现表面纵裂质量问题,与其在结晶器内较大高温相变收缩引起的初生坯壳不均匀生长密切相关,其纵裂纹敏感性可由包晶特征点计算出的包晶转变率判定。利用Factsage热力学计算软件研究钢种常见合金元素对Fe-C二元平衡相图中包晶特征点的影响,回归得到包晶特征点的预测公式。基于预测公式,可准确判断一定成分钢种的亚包晶范围,从而指导实际连铸生产中保护渣的选择。研究表明,通过合理的成分微调可有效降低包晶转变率,降低亚包晶钢高温相变收缩程度,甚至改变凝固模式变为过包晶模式,从而大大降低连铸坯纵裂纹敏感性。     

包晶钢铸坯裂纹形成机理的实验研究

针对包晶钢在连铸生产中铸坯裂纹出现较严重,选用具有相似收缩特征的Ag-Zn合金作为研究对象,开展定向凝固实验.研究得出,包晶钢包晶相变过程中包晶转变(δ→γ)阶段引起的收缩是导致铸坯裂纹的主要原因.与过包晶钢相比,亚包晶钢因在包晶相变过程中有较多的δ铁生成量和较少富余液相的补缩,铸坯更容易出现裂纹.亚包晶钢铸坯裂纹较低碳钢严重,是因为低碳钢发生包晶转变的温度低,避开了钢的零强度和零塑性温度区.     

连铸生产Mn13板坯表面纵裂控制

针对Mn13钢种在板坯连铸生产时发生表面纵裂纹缺陷的问题,结合Mn13材料凝固的特点,在工业生产中对浇铸过热度、拉速、水口对中、水口插入深度等工艺参数进行摸索,优化了保护渣化渣条件,保证了液渣在弯月面的均匀流入,改善了结晶器润滑与铸坯传热,控制了初生坯壳生长的均匀性,从而解决了Mn13板坯的表面纵裂纹缺陷,实现了Mn13的板坯多炉连铸生产,提高了铸坯合格率,由50％以下提高到96％.     

钢种初始凝固模式对连铸坯表面质量的影响

连铸过程中铸坯表面常产生各种质量问题，严重影响铸坯质量和生产顺行，然而，钢种初始凝固模式的差异对铸坯表面质量缺陷的影响规律尚不够明确。选用一系列代表性钢种，利用JmatPro软件进行了热力学平衡相图和高温力学性能的计算，结合Fe-C-X多元伪平衡相图特征点的理论计算公式，综合研究不同钢种的初始凝固模式及其对铸坯表面质量的影响规律。结果表明，对4种不同凝固模式的钢种而言，低碳、亚包晶凝固模式的钢种铸坯的主要表面质量缺陷分别是皮下夹杂、表面纵裂，其主要原因是高温阶段的相变引起的极限屈服强度和相变应变的变化；过包晶与高碳凝固模式的钢种铸坯很少出现表面质量问题。因此，表面缺陷的发生概率由钢发生高温相变(L+δ→γ/δ→γ)时δ相的比例、温度区间及坯壳的相变应变程度共同决定。基于钢种凝固模式及其对铸坯表面质量的影响，预测可能出现的铸坯表面质量缺陷，并采取相关措施降低表面缺陷发生率，对提高连铸坯质量具有重要意义。     

薄板坯耐候钢表面纵裂成因分析和控制

本钢薄板坯连铸在生产集装箱耐候钢时集中批量出现表面纵裂纹缺陷。本文研究了结晶器冷却、二冷水制度、钢水成分对保护渣影响等因素,对结晶器内初生坯壳生长采取弱冷,修改二次冷却喷淋方式,优化保护渣性能等控制铸坯表面纵裂纹的技术措施,进而改善了薄板坯耐候钢的表面质量。     

S355圆管坯表面裂纹成因及解决对策

采用金相显微镜和电子透射显微镜检验了某批次S355圆管坯的表面裂纹。分析认为，S355钢在连铸过程中，由于结晶器液位制动系统故障引起液面波动大，导致振痕加深，并且凝固过程中发生包晶转变，凝固坯壳体积收缩大，应力集中在坯壳薄弱区即振痕底部，则产生裂纹。通过调整工艺和设备后，有效地控制了S355圆管坯表面裂纹的产生。     

包晶钢结晶器液面周期性波动原因及控制

针对鞍钢股份有限公司鲅鱼圈钢铁分公司板坯连铸在生产包晶系列钢种时．连铸结晶器钢液面周期性剧烈波动的原因进行了分析。包晶钢液在凝固过程的包晶相变造成初生坯壳的不均匀生长是导致结晶器出现液面周期性剧烈波动的主要原因。通过调整结晶器冷却水强度和控制保护渣传热性能,有效地控制了结晶器液面周期性波动,提高了铸坯质量。     

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。     

A105连铸坯表面横裂纹形成原因分析

<正>连铸坯表面缺陷可分为纵裂纹、横裂纹、网状裂纹、皮下针孔和宏观夹杂,但主要缺陷是表面裂纹。表面裂纹形成的一个主要原因是在结晶器弯月面区域钢水—结晶器壁—保护渣—坯壳之间不均衡凝固,它取决于钢水在结晶器中的凝固过程。在二冷区,铸坯表面裂纹会继续扩展,它会导致轧材表面的微细裂纹,影响产品质量。连铸坯裂纹的形成是一个非常复杂的过程,是传热、传质和应力相互作用的结果。北京科技大学的学者应用配     

高速连铸结晶器内凝固传热行为及其均匀性控制

从分析高拉速包晶钢板坯连铸结晶器内凝固传热行为特征入手,首先阐明拉速对结晶器内的界面热阻、凝固坯壳的温度与应力分布的影响规律,研究发现拉速超过1.6 m·min?1时,界面热阻明显增加,拉速由1.4 m·min?1提升至1.6 m·min?1和1.8m·min?1时,出结晶器坯壳厚度相应减少约10%,其发生漏钢的危险不断增加;在此基础上,阐述了结晶器的内腔结构、保护渣、振动与液面控制等控制结晶器内坯壳凝固均匀性的相关技术。要实现高速连铸,首要应考虑结晶器内腔结构的优化设计,使其能更好地迎合凝固坯壳的生长,研制适合包晶钢等凝固特点的专用连铸保护渣至关重要,铸坯鼓肚控制也是保障高拉速液面稳定的关键。      

Simulation of thermal behavior during peritectic steel solidification in slab continuous casting mold

Thermal behavior of the solidifying shell in continuous casting mold is very important to final steel products.In the present work,one two-dimension transient thermal-mechanical finite element model was developed to simulate the thermal behavior of peritectic steel solidifying in slab continuous casting mold by using the sequential coupling method.In this model,the steel physical properties at high temperature was gotten from the micro-segregation model withδ/γtransformation in mushy zone,and the heat flux was obtained according to the displacement between the surface of solidifying shell and the hot face of mold as solidification contraction,the liquid-solid structure and distribution of mold flux,and the temperature distribution of slab surface and mold hot face,in addition,the rate-dependent elastic-viscoplastic constitutive equation was applied to account for the evolution of shell stress in the mold.With this model,the variation characteristics of surface temperature,heat flux, and growth of the solidifying shell corner,as well as the thickness distribution of the liquid flux,solidified flux,air gap and the corresponding thermal resistance were described.     

Identification of Defect Prone Peritectic Steel Grades by Analyzing High-Temperature Phase Transformations

Continuous casting of peritectic steels is often difficult and critical; bad surface quality, cracks, and even breakouts may occur. The initial solidification of peritectic steels within the mold leads to formation of surface depressions and uneven shell growth. As commercial steels are always multicomponent alloys, the influence also of the alloying elements besides carbon on the peritectic phase transition needs to be taken into account. Information on the solidification sequence and phase diagrams for initial solidification are lacking especially for new steel grades, like high-alloyed TRIP-steels with high Mn, Si, and particularly high Al contents. Based on a comprehensive method development, the current study shows that differential scanning calorimeter measurements allow a clear prediction if an alloy is peritectic (i.e., critical to cast). In order to confirm these results, thermo-optical analyses with a high-temperature laser-scanning-confocal-microscope are performed to observe the phase transformations in situ up to the melting point.     

Heat Transfer and Deformation Behavior of Shell Solidification in Wide and Thick Slab Continuous Casting Mold

With the considerations of the behaviors of shell deformation, mold flux film and air gap dynamic distribution in shell/mold gap, a two dimensional slice-travel transient thermo-mechanical coupled model of simulation shell solidification in wide and thick slab continuous casting mold was developed by using the commercial program ANSYS. The evolutions of strand-mold system thermal behaviors, including the air gap formation and the mold flux film dynamical distribution in shell/mold gap and shell temperature field, and the evolutions of shell deformation and stress distribution of peritectic steel solidified in a 2120 mm wide and 266 mm thick slab continuous casting mold were analyzed. The results show that the air gap formation and the thick mold flux film distribution mainly concentrate in the regions 0–21 mm and 0–7 mm, 0–120 mm and 0–100 mm off the shell wide and narrow faces corners, and thus the hot spots are given rise to form in the regions 15–55 mm and 15–50 mm off the shell wide and narrow face corners. The shell server deformation occurs in the off-corners in the middle and lower parts of the mold. The stress evolution in shell surface is tensile stress, while that in shell solidification front is compressive stress.     

包晶钢连铸坯表面纵裂与保护渣性能选择

 某钢厂宽厚板250 mm×1 820 mm连铸机使用包晶钢类型MB-59型保护渣生产[w(C)]为0.120%～0.150%钢种时,连铸坯表面出现大量纵向裂纹与皮下裂纹缺陷。通过提高保护渣碱度,降低保护渣黏度,改善铸坯坯壳与结晶器壁之间渣膜传热等技术措施,使铸坯的表面裂纹与皮下裂纹缺陷得到了有效控制。同时,对浇注[w(C)]为0.090%～0.120%钢种时采用MB-59型保护渣连铸坯表面无裂纹的原因进行了探讨分析,认为由于选分结晶,优先凝固的坯壳中碳质量分数低于钢液原始碳质量分数,使优先凝固的坯壳中[w(C)]实际已经小于0.090%,不再属于裂纹敏感性强的包晶钢范围,因此表面质量较好。     

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.     

包晶相变对连铸坯初生坯壳凝固收缩的影响

基于Ｆｅ－Ｃ合金的微观组织结构,建立了碳钢线性热膨胀系数计算模型,计算出不同碳含量的钢各在不同温度下的瞬时线性热膨胀系数,并将计算相应用于铸坯热－弹－塑性应力模型,研究了包晶相变对连铸坯初生坯壳凝固收缩的影响,模拟结果表明：浇铸碳含量在０．１％附近的包晶钢时,初生坯壳在靠近弯月面区域和角部区域的收缩很不规划,容易诱发表面缺陷。     

A mold simulator for the continuous casting of steel: Part I. The development of a simulator

Surface defects, such as oscillation marks, ripples, and cracks that can be found on the surface of continuously cast steel, originate in the continuous casting mold. Therefore, a detailed knowledge of initial solidification behavior of steel in a continuous casting mold is necessary because it determines the surface quality of continuously cast slabs. In order to develop an understanding of the initial solidification of continuous cast steels, a “mold simulator” was designed and constructed to investigate heat-transfer phenomena during the initial phase of strand solidification. The mold simulator was used to obtain solidified steel shells of different grades of steel under conditions similar to those found in industrial casting operations. The resulting cast surface morphologies were compared with industrial slabs and were found to be in good agreement, indicating that it is possible to simulate the continuous casting process by a laboratory scale simulator.