J55热轧板卷边部裂纹成因及控制分析

 利用金相、扫描电镜等对J55边部裂纹进行了观察,并对边部裂纹的产生原因进行了分析,研究表明：连铸坯表面的角横裂纹是热轧板卷边部裂纹产生的主要根源,连铸坯角部过冷导致奥氏体晶界细小的AlN、Nb(N,C)析出,加剧了连铸坯对裂纹的敏感性,连铸坯经过轧制后,连铸坯表面的角横裂纹扩展成为热轧板卷的边部裂纹。     

连铸工艺对板坯裂纹的影响及防止措施

连铸坯的裂纹是造成连铸坯报废的主要原因，针对连铸板坯的宽面纵裂和角部横裂问题进行了金相组织检验和热模拟试验，对铸坯裂纹产生的原因和机理进行分析，提出了防止铸坯产生裂纹的具体措施。     

连铸坯表面裂纹的控制

生产无缺陷的连铸坯是连铸坯热送、热装的前提条件.铸坯表面裂纹可能导致最终轧制产品出现缺陷.简要评述了影响连铸坯表面纵裂纹、横裂纹和星形裂纹形成的原因,及防止表面裂纹产生的技术措施.     

铜连铸坯中裂纹和孔洞的形成机理和工艺控制研究

分析了SCR连铸连轧生产线铜连铸坯中常见的裂纹和孔洞缺陷类型,探讨了在连铸过程中铜铸坯中裂纹和孔洞缺陷的形成机理和可能原因,并提出了减少裂纹和孔洞缺陷的工艺控制措施。研究认为,铜连铸坯中裂纹的形成与铸坯的高温力学性能、铸坯的应变行为、凝固冶金行为和铸造机设备运行状态有关;孔洞的形成主要与熔铸过程中的水蒸汽、浇铸速度、涂炭层不均匀以及浇铸温度不稳定有关;通过对铜原料的处理和熔炼气氛、涂炭工艺和铸造轮干燥工艺的控制以及铜液的过热度、浇铸速度和冷却效果的控制,可以有效减少铜连铸坯中孔洞和裂纹缺陷的出现。     

42CrMo表面裂纹的分析与改进

针对采用矩形坯轧制棒材42CrMo生产中出现的表面裂纹缺陷,通过对棒材表面裂纹和棒材质量的分析,认为是铸坯表面裂纹导致棒材表面裂纹缺陷的产生,并且裂纹的产生是由于连铸工艺参数的不合理引起的。通过对连铸工艺的改进,合理优化结晶器电磁搅拌参数、二冷配水和拉坯速度,消除了铸坯表面裂纹,从而解决了棒材表面裂纹的缺陷。     

压下对重轨钢大方坯内裂纹敏感性的影响

为研究压下对连铸坯内部裂纹产生的影响,利用ABAQUS有限元软件建立了230 mm×280 mm断面大方坯压下数学模型。通过压下模型对重轨钢连铸坯压下过程进行热力耦合模拟计算,对压下过程中产生的内部裂纹进行了预测。首先,对连铸坯不同中心固相率为0.3～0.7的温度场进行计算;然后,利用压下模型计算了连铸坯中心固相率0.3～0.7时凝固前沿的等效塑性应变。研究结果表明,在连铸坯中心固相率为0.3～0.7的位置处分别施加7 mm压下量进行压下,连铸坯凝固前沿等效塑性应变未超过临界等效塑性应变（0.4%）,连铸坯未出现内裂纹;同时,对连铸坯在中心固相率为0.6位置处进行了不同压下量的研究,研究结果表明,当连铸坯压下量超过7 mm时,凝固前沿的等效塑性应变超过临界塑性应变（0.4%）,连铸坯出现内裂纹,并且压下量越大,连铸坯内裂纹越严重。同时,工业试验结果与模型计算结果基本吻合,验证了模型计算的准确性。      

加硼钢连铸坯中间裂纹缺陷的改善

通过对添加硼前后A36钢连铸坯中间裂纹分布特征及其高温力学性能的调查研究,分析了其中间裂纹的形成原因.结果表明,硼的加入降低了钢的零塑性温度是铸坯产生中间裂纹的内因,而铸坯在连铸过程中受弯曲应变、矫直应变以及辊缝不对中引起的过大应变是裂纹产生和扩展的外因.据此提出了相应的改进措施,有效地减轻了A36-B钢连铸坯中间裂纹.     

包晶钢矩形连铸坯中间裂纹的分析与控制

针对包晶钢矩形连铸坯出现的中间裂纹,通过低倍酸洗对中间裂纹特征进行检验分析,找出了连铸坯柱状晶发达、晶间偏析是中间裂纹产生的主要原因。通过控制钢水Mn/S、氧含量,优化温度制度、拉速制度、冷却制度、夹辊辊缝,解决了连铸坯中间裂纹问题。     

莱钢包晶钢矩形连铸坯的中间裂纹分析与控制

针对包晶钢矩形连铸坯出现的中间裂纹,通过低倍酸洗对中间裂纹宏特征进行检验分析,找出了连铸坯柱状晶发达、晶间偏析是中间裂纹产生的主要原因.通过控制钢水Mn/S、氧含量,优化温度制度、拉速制度、冷却制度、夹辊辊缝,解决了连铸坯中间裂纹.     

40Cr热轧圆钢表面裂纹的金相检验和分析

针对轧制40Cr圆钢表面发现裂纹的现象,对存在裂纹的圆钢进行了化学成分分析和金相分析,发现裂纹中存在脱碳,氧化圆点等缺陷,推断连铸坯表面及皮下存在缺陷。对连铸坯进行低倍检验和金相组织分析,发现铸坯存在表面裂纹、皮下裂纹以及树枝晶裂纹。追溯了连铸生产数据,对铸坯缺陷产生原因进行分析确认,并提出工艺优化建议。     

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.     

连铸板坯网状裂纹成因及影响因素的研究

采用金相显微镜、SEM、TEM和EDS等方法,分析了因连铸板坯表面冷却不均匀引起γ→α反复相变导致碳氮化物在晶界析出,并在外力(热应力、弯曲矫直应力等)作用下产生沿晶界开裂的网状裂纹的形成机理,以及钢中[C]、Mn/S、[Al]、[V]、连铸冷却强度等对连铸板坯网状裂纹的形成和扩展的影响.     

宝钢厚板边裂成因分析和改善

边裂是影响宝钢厚板质量的一个重要因素.对厚板边部的非连续弧形裂纹缺陷取样,进行金相分析,并对连铸板坯进行对比轧制试验,证实钢板边裂是由连铸板坯角部横向裂纹引起.分析了影响板坯角部横裂的结晶器保护渣、二冷水、结晶器、浇注速度等工艺因素.在此基础上,提出了改善板坯角部横裂的有效措施,即改进保护渣性能、优化二冷水水量分配、弱化结晶器冷却、稳定结晶器锥度和采用合适的浇注速度等等.实施以上措施后,钢板边部裂纹大幅度减少.     

Prediction of cracks in continuously cast steel beam blank through fully coupled analysis of fluid flow, heat transfer, and deformation behavior of a solidifying shell

A mathematical model has been developed for the prediction of cracks in the continuously cast steel beam blank through the fully coupled analysis of fluid flow, heat transfer, and deformation behavior of a solidifying shell. Fluid flow and heat transfer in the strand mold were analyzed with a three-dimensional (3-D) finite-volume method (FVM). For the complex geometry of the beam blank, a body-fitted coordinate (BFC) system was employed. Thermo-elastic-plastic deformation behavior in the strand was analyzed using the finite-element method (FEM) based on the two-dimensional (2-D) slice model. The thermal fields of the strand calculated with the FVM were used in the analysis of the deformation behavior of the strand. Through the iterative analysis of the fluid flow, heat-transfer, and deformation behavior, the coupling parameter of the heat-transfer coefficient between the strand and the mold was obtained. In order to describe the thermophysical properties and thermomechanical behavior of steel in the mushy zone, the microsegregation of solute elements was assessed. Consequently, some characteristic temperatures of steel as well as variations of phase fractions with temperature were determined. The probability of cracking in the strand, originating from an interdendritic liquid film, was quantified as a crack susceptibility coefficient. Recirculating flows were developed in the web and flange-tip regions. The development of a solidifying shell in the flange-center region was retarded by the inlet flow from a submerged entry nozzle (SEN). An air gap was formed mainly near the flange-tip corner. Surface cracks in the web and fillet regions and internal cracks in the flange-tip region were predicted.     

Friction Forces between Mould and Strand Shell during Billet Casting

During continuous casting processes lubrication between mould and strand shell is very important for reaching and maintaining a good surface quality of both the as‐cast strand and the finished product. The lubrication is influenced by the properties of the mould powder but also by the friction forces caused by the periodic movements of mould and the descending strand shell. In the present research measurements were carried out to investigate the friction forces during 150 mm sq. billet casting of different steel grades using mould powder or granules and submerged entry nozzles. The friction forces reached values up to 6 kN. Since friction forces are depending on upward and downward movements within the mould‐strand‐system, the evaluation of a rheogram shows the typical change of pressure and tension. Maximum friction forces arise during the positive strip time of the rising mould, introducing tensions and cracks in the as‐cast strand. On the other hand lowest frictions forces are generated by the descending mould within the negative strip time leading to the healing of faults in the as‐cast strand. These industrial experiments indicate a correlation between friction forces and surface quality of as‐cast strands.     

连铸板坯表面横裂纹成因分析

本文通过对铸坯裂纹产生机理的分析,指出了连铸板坯表面横裂纹产生的原因,讨论了影响连铸板坯表面横裂纹产生的因素。     

Quality Control for Continuously Cast Slab of High Strength Weathering Steel Q450NQR1

In order to reduce the transverse corner cracks of high strength weathering steel Q450NQR1,the factors influencing transverse corner cracks on continuously cast slab,such as level fluctuation of molten steel in mold,mold taper,primary cooling,mold powder,secondary cooling,nitrogen content in steel,spray nozzle structure,processing parameters and equipment of CC,etc.,were analyzed.Based on this,a series of comprehensive countermeasures have been proposed.The operation shows by the use of key technologies,including stabilizing steel level,optimizing the mold taper,weakening the primary cooling and the secondary cooling,reforming the mold powder,and adjusting spray nozzle structure,the transverse corner cracks on continuously cast slab have been significantly reduced,and the edge cracks on hot rolled sheet have been eliminated due to the transverse corner cracks.The qualified slabs are delivered to produce weathering cold forming sectional steel,whose yield strength is greater than 450MPa.     

中厚板表面微裂纹成因及影响因素研究

对重钢连铸板坯轧制中厚板出现的表面微裂纹进行取样,经低倍检验发现,微裂纹有3种类型;与之对应的连铸板坯酸洗后发现,微裂纹也有3种类型,采用镀层结晶器铜板前以网状裂纹为主,尔后以横裂纹为主;对裂纹量最多的网状裂纹进行高倍和能谱检验,发现网状裂纹主要是铜裂纹.分析产生裂纹炉次的对应工艺,找出其主要影响因素是结晶器铜板、结晶器保护渣、二次冷却制度、钢中的w(N)等,针对性地采取预防措施,使中厚板表面微裂纹大幅度减少.     

HRB335热轧带肋钢筋表面纵向裂纹原因分析

采用铸坯低倍酸浸检验、金相检验、扫描电镜及能谱分析等方法对HRB335热轧带肋钢筋的冷弯表面纵向裂纹进行了综合分析,结果表明:产生表面纵向裂纹的主要原因是铸坯存在严重的皮下气孔和内部裂纹,在后期的热加工过程中与表面贯通,气孔或裂纹表面被氧化,造成轧制过程无法焊合。讨论了生产过程中铸坯皮下气孔及裂纹产生的原因,对其生产工艺的改进提出建议。     

Control of transverse cracking in special quality slabs

Abstract

Rolled plates from continuously cast slabs at Bhilai Steel Plant have been frequently rejected due to the formation of irregular shaped fine surface cracks. These cracks originate from fine transverse cracks located below oscillation marks/surface depressions of the cast slabs. The random occurrence of this defect from heat to heat was of major concern to Bhilai Steel Plant where slabs are cast of special grades such as boiler, microalloying, and high tensile quality. The mechanism of formation of this defect was identified through a detailed metallographic study of defect bearing slabs and plates and analysis of rejection patterns with respect to various important process parameters. The crack formation mechanism was verified through a process perturbation trial. A defect potential index was developed to explain the random occurrence of these cracks. The index incorporated parameters which influence crack formation in the Bhilai casters. A significant reduction in this type of cracking was observed, based on the recommendations made in this study