异形坯表面纵裂纹产生原因及控制措施

利用金相和扫描电镜对异形坯表面纵裂纹进行分析,裂纹内表面覆盖了一层氧化铁,在距离表面0.67 mm以内区域有保护渣成分,再往内部除氧化铁外,未见有保护渣成分,说明裂纹是在结晶器内产生的、二冷段里扩展的。通过对钢水成分、结晶器冷却水、结晶器液面波动、保护渣成分、钢水过热度、拉速、二次冷却水等工艺参数的优化调整,异形坯表面纵裂纹的发生率明显降低,纵裂纹指数由80 mm/m降至≤5 mm/m。     

超高强钢铸坯裂纹观察及成因分析

采用金相显微镜和扫描电镜观察与分析了980MPa级超高强钢铸坯裂纹断口形貌及组织,并利用Gleeble-2000D研究了铸坯高温热塑性。结果表明:裂纹铸坯原始奥氏体晶界处有大量的铁素体析出,并在晶界处连接成片形成膜状铁素体带,膜状铁素体上分布着白色链状的Nb、Ti碳氮化物。980 MPa级超高强钢铸坯的第Ⅲ脆性区为650℃-950℃,其断面收缩率均低于40%,而在775℃时热塑性最差,断面收缩率仅为12%。处于低塑性温度区间的铸坯在热应力和机械应力在强度较低的奥氏体晶界上的膜状铁素体集中促进裂纹萌生和扩展。     

高拉速情况下容易出现的铸坯缺陷

连铸机拉坯速度与铸坯质量有着非常复杂的关系。由于拉速提高，钢水在结晶器中的流动状态更加激烈，传热及凝固过程易于波动，高拉速时容易出现偏角纵裂纹漏钢、铸坯表面纵裂纹。拉速提高，钢水中夹杂物上浮困难，二次冷却区液心长度增长，受各种应力的作用，铸流在此区间的湍流影响范围较大，易于产生内裂和偏析。     

沟槽内壁结晶器坯壳初期凝固过程模拟研究

以锡液水冷铜板浸渍实验模拟钢连铸过程,研究结晶器内壁划分沟槽对坯壳初期凝固过程的影响,结果表明,沟槽内壁结晶器可改善铸坯传热效果和初期凝固坯壳不均匀程度,减少铸坯表面纵裂纹的产生。     

大方坯连铸过程中铸坯传热及凝固行为的研究

结晶器和二冷区传热对大方坯产品质量和铸机的生产率有重要影响，本文讨论了包钢引进的全国最大的方坯连铸机在拉坯时结晶器和二冷区传热情况以及坯壳凝固生长，铸坯温度的变化规律。着重讨论了电磁搅拌，过热度和拉速对坯壳凝固和生长规律的影响，指出控制铸坯凝固的主要因素是凝固潜热，影响凝固未端的最主要因素是拉速，而电磁搅拌对其影响区内的传热和坯壳生长和铸坯温度亦有重大影响。     

减少铸坯裂纹是提高管线钢质量的有力措施

常看到石油管线钢用X65、X75、X120等表示等级,这是美国石油学会（API）规定的以管线钢屈服强度（σ8）的高低表示的,X95表示其屈服强度极限达到95000磅／平方英寸（约667MPa）．X120管线钢的屈服极限应达到120000磅／平方英寸（约827MPa）．屈服强度越高,表明管线钢的性能越好．目前,日本森美孚化工（ExxonMobil）公司和新日铁正在共同进行超高强度X120管线钢的开发,以大幅度提高强度来达到降低管线钢成本的目的．     

PSO-LM-BP神经网络在板坯表面纵裂纹诊断中的应用

板坯连铸生产过程中,表面纵裂纹是最常见的缺陷之一,其准确在线诊断对板坯热送热装来说至关重要。针对传统BP神经网络存在训练过程中收敛速度慢及易收敛于局部最小点的缺点,引入粒子群算法与LM算法优化BP神经网络,通过对板坯生产过程形成表面纵裂纹的多种因素的综合分析,建立诊断模型,最后利用采集到的历史数据样本训练及测试模型。与其他诊断模型比较表明,PSO-LM-BP神经网络建立的模型具有诊断精度高、收敛速度快等优点,对表面纵裂纹在线诊断具有较好的指导作用。     

大规格Q345E连铸圆坯表面裂纹原因分析及控制措施

以大规格Q345E系列连铸圆坯为研究对象,对铸坯表面裂纹现状及形成原因进行研究.结果表明,适当降低结晶器保护渣粘度,降低结晶器水冷却强度约20％,拉速提升约10％,同时矫直压力下调15％左右时,可显著改善连铸坯表面裂纹.     

Longitudinal surface cracks on continuous casting slabs of P and Cu containing container steel

The fact that the amount of the mold flux components differs at different locations on the cracking surface indicates that the longitudinal surface cracks are initially formed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductility measurement of two typical container used steels, it is known that the steels are in severe embrittlement state in the temperature range of 825-775℃. By means of increasing Cr/Ni plating thickness on the upper part of the mold, reducing mold heat flux, adopting new secondary cooling pattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuous casting) slabs has been significantly reduced.     

Research on mold flux for hypo-peritectic steel at high casting speed

Mold fluxes having adaptable properties were developed in the laboratory to solve quality defects, such as depressions and longitudinal cracks when casting hypo-peritectic steel at high casting speed. Firstly, the effect of components on the high basicity mold flux properties was first studied using the orthogonal method. In the scope of the studied content, Li2O has the largest effect on the melting temperature, and the least effect on the viscosity; CaF2 has the largest effect on the viscosity, and the least effect on the melting temperature; Na2O and CaO/SiO2 have no obvious influence on the melting temperature and viscosity. Secondly, two powders (Z1 and Z6) have reasonable viscosity-temperature curves, higher solidification temperatures, and porous structure after solidification, but the crystal property of Z6 is worse than that of Z1, and thus Z1 is more suitable for continuous casting hypo-peritectic steel at high casting speed. Thirdly, a higher basicity of powder, a less free enthalpy of crystal compound, and a lower baffle energy are good for a higher tendentiousness of crystal.     

SS400钢板表面纵裂纹分析及实验研究

针对SS40钢板在生产过程中产生的表面纵向裂纹现象进行研究与分析.结果表明,钢板表面纵向裂纹大部分分布在钢板宽度方向的2个1/4区域内,裂纹的长度一般在0.5~2 m,宽度均小于1 mm,深度为0.1~0.2mm.进一步分析后认为,该种表面缺陷产生于连铸结晶器内,在随后二冷区的强冷和加热炉的加热过程中,裂纹得到了进一步的扩展.     

闭口型压型钢板-混凝土组合楼板纵向抗剪性能试验研究

对18块YXB65-185-555闭口型压型钢板-混凝土组合楼板进行了纵向抗剪性能试验研究,考察了楼板厚度、压型钢板厚度以及剪跨等因素对组合楼板纵向抗剪性能的影响.得到了组合板的极限承载力、变形和破坏形态以及压型钢板与混凝土之间的滑移.试验结果表明:随着组合板和压型钢板厚度的增大,组合板的纵向抗剪承载力越大;剪跨越大,纵向抗剪承载力越小;剪跨比较小的试件主要发生纵向剪切粘结破坏,剪跨比较大的组合板主要发生弯曲破坏和弯曲剪切粘结破坏.基于欧洲规范4的建议公式,对试验结果进行线性回归得到了适用于该板型的压型钢板-混凝土组合楼板的纵向剪力粘结系数m、k,可为该种楼板的工程设计提供参考.     

Longitudinal crack on slab surface at straightening stage during continuous casting using finite element method

Deformation behavior of slab at the straightening stage during continuous casting was simulated by the explicit dynamic finite element method, and the stress distribution along the width direction of the slab and its change regularity at slab center during continuous casting were obtained. The influence of distribution and change of stress on the propagation of longitudinal cracks on slab surface was discussed. The results show that the tensional stress appears on slab surface at the inner arc side and the compressive stress appears on slab surface at the outer arc side at stages 6-8 in straightening zone during continuous casting. Longitudinal cracks generally appear on slab top surface and do not appear on slab bottom surface, which are also observed in industry.     

Formation mechanism of internal cracks in continuously cast slab

In order to make clear the formation mechanism of centerline cracks in continuously cast slabs, the form, distribution and other characteristics of the cracks were analyzed. The final solidification point, surface temperature of the slabs and strain in solidifying shell were investigated. The results were that: (1) Five relatively low temperature zones exist on slab surface below the three water spraying nozzles and near the two edges, respectively, which corresponds to the places of centerline cracks and triangle-zone cracks. (2) Centerline cracks and triangle-zone cracks occur because of weak secondary cooling, uneven cooling along slab width, and large variation of roll gap. (3) After minimizing the variation of roll gap and applying the new secondary cooling pattern, the occurring frequency of centerline and triangle-zone cracks minimizes to zero.     

新型双向钢筋桁架叠合板底板受力性能试验研究

装配式建筑中,钢筋桁架叠合板作为主要受力构件应用广泛,然而,其底板在工地安装前经常出现开裂现象,导致叠合板无法使用.提出一种新型双向钢筋桁架叠合板,即在传统钢筋桁架叠合板上安装横向附加钢筋支架,从而提高叠合板的抗弯承载力.为了考察安装的横向钢筋支架对叠合板底板开裂状态和受力特性发挥的作用,分别对双向钢筋桁架叠合板底板和...     

低碳钢头坯洁净度研究

采用氧氮分析、金相分析、大样电解分析、扫描电镜及能谱分析等,研究LD—Ar站—CC生产的低碳钢头坯不同浇铸长度处的洁净度变化规律,并与正常坯洁净度水平进行对比分析。结果表明,头坯中T[O]和氮含量均随着浇铸长度的增加呈明显的下降趋势;头坯中显微夹杂物数量和大型夹杂物数量随着浇铸长度的增加大体都呈减少趋势;头坯中显微夹杂物主要来源于脱氧产物和二次氧化,大型夹杂物来源于二次氧化、结晶器卷渣、中间包卷渣和钢包引流砂;与正常坯洁净度相比较,头坯洁净度在浇铸长度大于3m以后与正常坯水平相一致。     

先张预应力混凝土板最小板长及钢绞线折算强度计算方法

首先分析了高强钢绞线在先张预应力构件中的粘结锚固性能,将预应力传递长度与弯曲粘结长度之和定义之延伸长度,给出了延伸长度的计算公式。其次为使构件破坏时充分发挥预应力钢绞线的强度,防止弯曲裂缝出现在延伸长度之内,提出了先张预应力混凝土板在均布荷载作用下的最小板长。最后针对预应力混凝土板长小于最小板长时会在延伸长度内出现弯曲裂缝,需将钢绞线强度进行折减,并提出了钢绞线折算强度的计算方法。     

Longitudinal surface cracks of thin slabs

Based on the production practice of medium carbon thin slabs in the CSP plant,the reasons and influencing factors for the formation of longitudinal cracks were investigated,and some industrial measures were taken to eliminate the cracks.The results show that the efficient solutions to reduce longitudinal cracks are improving the performance of the mold powder,stabilizing the mold heat flux,and maintaining a proper taper of the mold during casting.Proper pouring temperature and secondary cooling also play...