热轧H型钢的高应变低周疲劳性能研究

 对热轧H型钢的高应变低周疲劳性能进行了研究。采用轴向应变控制的方法，在Instron-1342型电液伺服疲劳试验机上测定了热轧H型钢的低周疲劳性能数据，研究了在循环载荷下材料的循环应力响应特征、循环应力与应变关系，并用Coffin-Manson公式拟合得到热轧H型钢的疲劳寿命计算公式，据此计算了 =100时的 值。通过断口扫描发现，裂纹不仅在试样表面处形核，同时也在试样内部杂质处形核，然后通过不断的扩展形成微裂纹，许多微裂纹通过扩展连接形成宏观裂纹，最终导致材料断裂。     

连铸结晶器内含钛无氟保护渣固态渣膜再结晶研究

将Kissinger方程引入到保护渣研究领域,研究了含钛无氟保护渣玻璃体升温结晶(升温速率5～30K/min)、液态降温结晶(降温速率5～30 K/min)的激活能。实验结果表明,保护渣玻璃体的结晶激活能E约为52.75 kJ/mol,保护渣液态降温结晶的激活能E约为61.15 kJ/mol,实验研究的保护渣玻璃体结晶峰温度915～940K,急速冷却形成的玻璃态渣膜在结晶器内存在再结晶,衡量保护渣结晶性能应综合考虑液态降温结晶行为和渣膜在结晶器内再结晶的行为。     

亚包晶钢板坯连铸保护渣凝固结晶行为的研究

对≤1.3 m/min常规拉速(TCaO/SiO₂=1.19)和≥1.5 m/min高拉速(TCaO/SiO₂=1.40)0.07～0.10C亚包晶钢板坯用两种保护渣(%:2.54～3.0Al₂O₃、7.34～8.35Na₂O、8.83～8.87F、0.79～3.00Li₂O)降温凝固过程中结晶特性以及结晶对熔渣粘度的影响进行了研究,得出高拉速保护渣在凝固之前有明显的结晶行为,结晶矿相主要为枪晶石(3CaO·2SiO2·CaF₂);常规拉速保护渣在凝固温度以上时,没有明显的结晶现象。与常规拉速保护渣相比,高拉速保护渣完全凝固后晶粒粗大,组织中有大量空隙,有利于增加渣膜热阻,减缓结晶器传热。TCaO/SiO₂=1.40保护渣在结晶温度以上时,具有较低的粘度,有利于结晶器润滑;结晶温度以下时,粘度迅速增加,有利于增加固渣膜厚度,减缓结晶器传热。     

Nonisothermal Crystallization Kinetics of Glassy Mold Fluxes

Crystallization of the solid glassy mold flux film occurring in the gap between the initial shell and mold wall is important, as it determines the in-mold heat transfer and mold lubrication during the process of continuous casting. In order to study the nonisothermal crystallization behavior of the glassy mold flux film in the continuous casting mold, the continuous heating transformation diagram, crystallization mechanism, and precipitate phases were investigated using the single hot thermocouple technique, kinetic models, a scanning electron microscope, and an energy-dispersive spectrometer (EDS). The results show that the initial crystallization temperature for CaO-SiO₂ based flux A ranges from [1086 K to 1147 K (813 °C to 874 °C)], which is lower than the case of CaO-Al₂O₃ based flux B ranging from [1205 K to 1245 K (932 °C to 972 °C)]. The crystallization kinetics for flux A are constant nucleation rate, two-dimensional growth, and control by diffusion. For flux B, they are constant nucleation rate, three-dimensional growth, and control by interface reaction. Besides, the EDS results indicate that the precipitate crystals in fluxes A and B are CaSiO₃ and Ca₂AlSiO₄, respectively.     

连铸结晶器内渣膜形成及传热的研究现状

介绍了模拟结晶器内渣膜形成的实验方法, 综述了国内外学者在保护渣传热方面所做的研究工作, 包括固态渣膜的界面热阻、保护渣的导热系数、辐射传热以及渣膜的光学性质, 并提出了今后在渣膜形成及传热研究中有待进一步完善的内容和方向.现有的研究结果表明利用热丝法可以对渣膜的形成过程进行原位观察, 采用水冷铜探头法可以获取用于研究渣膜微观组织的固态渣膜样品.渣膜的界面热阻在0.0002~0.002 m2·K·W-1之间.在800℃以下, 保护渣的导热系数在1.0~2.0 W·m-1·K-1范围内, 且随温度的升高而逐渐增加.渣膜中的晶体一方面可以增加渣膜的界面热阻, 另一方面可以提高固态渣膜的反射率, 起到降低辐射热流的作用.此外, 过渡族金属氧化物的加入以及固态渣膜中弥散分布的微小颗粒也能改变渣膜的光学性质, 从而影响通过渣膜的辐射传热.      

Li2O对CaO-Al2O3基保护渣结晶性能的影响

摘要：高铝钢用新型CaO-Al2O3基连铸结晶器保护渣结晶性能较强，在连续浇铸过程中易出现润滑与传热功能协调不均的问题。基于此，针对新型CaO-Al2O3基保护渣，考察了典型助熔剂Li2O对保护渣析晶温度、析晶物相等性能的影响，并进行了相关结晶动力学分析。结果表明，提高Li2O含量可使保护渣的临界冷却速率和初始结晶温度呈现先降低后升高的趋势，当Li2O质量分数为4%时，保护渣结晶倾向最弱。随Li2O质量分数从0增至6%，保护渣的结晶孕育时间先延长后缩短。析晶物相由CaAl4O7+CaF2转变为CaAl4O7+CaF2+LiAlO2，Li2O的加入及其含量的提高促进了LiAlO2的析出。此外，随Li2O质量分数从0增至6%，保护渣结晶活化能先增大后减小，析晶过程受到的阻力先增强后减弱，与结晶性能的变化规律相吻合。     

连铸保护渣中CaF_2含量对脱玻化性能的影响

通过运用SHTTⅡ型熔化结晶温度测试仪构建了TTT曲线,计算出不同CaF_2下保护渣脱玻化活化能;再通过X射线衍射仪并结合JADE软件计算出结晶率和分析结晶矿相;最后利用金相显微镜,观察多种回温处理下不同CaF_2含量的保护渣渣膜的表面形貌,探究CaF_2对保护渣脱玻化的影响。试验结果表明:随着CaF_2含量增加保护渣脱玻化的温度和活化能不断降低,渣膜表面粗糙度增大;随着玻璃体渣膜处理温度的升高,保护渣析出矿相种类单一化。     

CSP结晶器保护渣固态渣膜结构和矿相的分析

通过光学显微镜、扫描电镜及X射线衍射分析,研究了1537 mm×67 mm CSP连铸结晶器保护(%:34.6CaO,28.6SiO₂,8.8C,8.5F,8.6Na₂O)固态渣膜的结构、矿相组成和析晶率,分析结果表明,绝大多数固 态渣膜厚0.6~1.3mm, 呈三层结构：结晶层-玻璃层-结晶层,靠结晶器壁侧为0.10～0.14mm 厚的结晶层;CSP 固态渣膜的析晶率为40%～80%,结晶矿相主要为枪晶石(3CaO ·2SiO₂ ·CaF₂)和矿物Na₂O ·Al₂O₃ ·SiQ₂。通过 调整固态渣膜的厚度及枪晶石等矿物的析晶率,可达到控制渣膜传热,提高连铸坯表面质量的目的     

The Effect of Basicity on the Radiative Heat Transfer and Interfacial Thermal Resistance in Continuous Casting

The basicity of mold flux has been recognized to have a significant influence on the mold flux crystallization in continuous casting, which would in turn affect the heat-transfer rate between the solidified shell and mold. The research regarding the mold flux crystallization as well as its effect on the heat transfer has been conducted intensively. However, few studies have been developed to specify the effect of basicity introduced mold flux crystallization on the radiative heat transfer and interfacial thermal resistance in continuous casting. By using an infrared radiation emitter, a radiative heat flux was applied to a copper mold covered with a solid mold flux disk to simulate the heat-transfer phenomena in continuous casting. The crystallization behaviors of mold fluxes with different basicities and their impact on the radiative heat transfer were investigated dynamically. The interfacial thermal resistance between the solid mold flux and copper mold was also studied in this article. The results suggested that the basicity tends to enhance the mold flux crystallization, leading to the reduction of radiative heat-transfer rate and enlargement of interfacial thermal resistance.     

唐钢中厚板厂连铸保护渣结晶器渣膜矿相分析

为改善唐钢中厚板厂船板钢的浇铸条件以及铸坯质量,将现场所用保护渣A进行调整形成保护渣B。基于相图平衡计算,采用光学显微镜对保护渣A和B在结晶器内的渣膜进行观察,研究渣膜结构对保护渣润滑和传热的影响机制。结果表明,保护渣A析晶温度和析晶率较高,析晶矿相主要为导热系数大的黄长石,渣膜中存在不均匀分布的气孔,使得铸坯向结晶器传热较快且不均匀,并恶化铸坯润滑,导致发生黏结漏钢,且铸坯出现裂纹,轧材合格率为98.73%。而保护渣B析晶温度和析晶率相应有所降低,渣膜结构分层明显,存在玻璃层,析晶矿相有适量导热系数小的枪晶石,有少量气孔,能有效控制铸坯向结晶器壁的均匀传热,并保证润滑铸坯,避免了黏结漏钢,且显著减少了铸坯裂纹率,轧材合格率为99.65%。     

Effect of Titania Absorption into a Mold Flux on the Heat Transfer Between the Mold and the Slab in the Continuous Casting of Titanium-Stabilized Stainless Steel

The heat transfer behavior between mold and slab changes when titania is absorbed into the mold flux during the continuous casting of titanium-stabilized stainless steel. The trend and the extent of this effect were investigated in the laboratory. Furthermore, to investigate the effect of titania on heat transfer, the effect of titania on the crystallization properties of the mold flux was studied. The results showed that with an increasing titania content of mold fluxes, the heat transfer coefficient and the heat flux of the slag film increases, whereas the heat transfer resistance decreases; the effect is that the growth and crystallization temperature of the cuspidine crystallites in the slag are suppressed by the absorption of titania.