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采用金相显微镜、扫描电镜、能谱仪、直读光谱仪等手段对09CrCuSb无缝钢管外表面出现的典型缺陷问题进行了系统性分析。分析结果表明,钢管外表面缺陷产生的原因是铸坯存在皮下气泡,在加热炉加热过程中铸坯近表面气泡被烧暴露,轧制后在圆钢表面形成纵向短裂纹,穿管后在钢管外表面产生缺陷。通过优化炼钢及连铸工艺,成功解决了此类质量问题。 相似文献
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运用金相显微镜、扫描电镜等手段,对存在质量缺陷的Q235B钢板进行了显微组织分析。结果表明,孔洞缺陷的原因是铸机浇铸过程中氩气流量过高;裂纹周边有轻微脱碳现象及在裂纹内部发现存在Si、Ca、M g的氧化物,由于同时存在脱碳和氧化质点,可推断该类裂纹来源于连铸坯表面纵向裂纹及铸坯气孔,在轧制过程中进一步扩展。同时对连铸生产提出了优化措施。 相似文献
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通过对高碳钢的检验,分析了高碳钢连轧坯表面缺陷的类型和产生原因,主要有表面划伤和皮下气孔轧后缺陷两种类型。研究发现,连轧过程导板或导辊等设备有“挂腊”现象、连轧辊存在表面磨损等缺陷是造成连轧坯表面划伤的原因,连轧坯的皮下气孔轧后缺陷是由于连铸坯的皮下气孔缺陷引起的。在高碳钢钢坯连轧前必须对连轧设备的工作状态进行检查,防止连轧坯表面划伤的产生。减轻连铸过程水口吹氩流量是减轻连铸坯皮下气孔缺陷的一种措施,但减少吹氩量对连铸过程活跃保护渣层是不利的。建议在连铸过程进行结晶器电磁搅拌,以减轻连轧大方坯皮下气孔缺陷,提高连轧坯表面质量。 相似文献
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摘要:通过数值模拟的方法研究了典型大方坯(325mm×280mm)连铸过程中温度场和应力场分布,分析了铸坯皮下裂纹产生的原因和主要影响因素,制定了控制铸坯皮下裂纹的具体措施。结果表明:在连铸过程中铸坯的最大回温为121℃,二冷一区最高回热速率达到217.48℃/m,二冷二区最高回热速率达到131.95℃/m,其他各区回热速率都较低。温度回升后铸坯横断面距铸坯表面15~30mm处的最大应力应变值已经超过了钢的极限应力应变值,因此,二冷一区和二区温度回升是铸坯产生皮下裂纹的主要原因。增加二冷一区水量,将此水量在二冷三区和四区相应地减小,可以降低二冷一区回热速率,降低最大回热温度到88℃,控制铸坯皮下裂纹的产生。 相似文献
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《钢铁研究学报》2021,(3)
通过数值模拟的方法研究了典型大方坯(325 mm×280 mm)连铸过程中温度场和应力场分布,分析了铸坯皮下裂纹产生的原因和主要影响因素,制定了控制铸坯皮下裂纹的具体措施。结果表明:在连铸过程中铸坯的最大回温为121℃,二冷一区最高回热速率达到217.48℃/m,二冷二区最高回热速率达到131.95℃/m,其他各区回热速率都较低。温度回升后铸坯横断面距铸坯表面15~30 mm处的最大应力应变值已经超过了钢的极限应力应变值,因此,二冷一区和二区温度回升是铸坯产生皮下裂纹的主要原因。增加二冷一区水量,将此水量在二冷三区和四区相应地减小,可以降低二冷一区回热速率,降低最大回热温度到88℃,控制铸坯皮下裂纹的产生。 相似文献
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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。 相似文献
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钢材产品实行负偏差轧制是企业提高经济效益的有效措施。莱钢锻压厂为实现负偏差轧制,除改进工艺技术、改造生产线外,还加强管理,提高操作技术水平,严格计量,严格岗位责任制,从而保证了负差材产品质量稳定,年多创经济效益1000 多万元。 相似文献
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建立温度计算模型针对22 mm和28 mm规格20MnSi棒材热连轧及控制冷却过程温度场进行了计算机模拟分析,获得了棒材精轧及轧后分级控冷过程的温度变化规律。对轧制圆钢和螺纹钢筋不同条件下成品道次温度变化特点进行了研究。研究结果是,轧制22 mm和28 mm规格20MnSi螺纹钢筋时的终轧温度比轧制相同规格圆钢时显著升高。轧制螺纹钢筋时精轧末道次轧材表层形成螺纹出现较大的局部应变量和应变速率,由此产生大量变形热是终轧钢筋表层急速升温的根本原因。与轧制圆钢相比,为完成同等控冷效果及有效控制轧后组织性能,20MnSi螺纹钢筋精轧后第1水冷段的换热系数明显较高,因此需要相应采用较大的冷却水量。 相似文献
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通过大生产跟踪试验和金相分析表明,由13.3吨扁锭轧成的中厚钢板上的裂纹与初轧板坯上的拉裂、纵裂有关。而发状裂纹、结疤缺陷则是初轧板坯上的气泡经轧制演变而成。 相似文献
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Maria Rita Ridolfi Stefano Fraschetti Andrea de Vito Luis A. Ferro 《Metallurgical and Materials Transactions B》2010,41(6):1293-1309
Billets produced by continuous casting sometimes show the presence of subsurface cracks that can compromise the quality of
the final product. The presence of these cracks is revealed by Baumann prints of billet cross sections in which the chill
zone is visible and the short radial cracks are located only where the chill zone thickness is thinner. This experimental
finding induces the hypothesis that cracks are formed as a result of the presence of unevenness in the mold heat extraction
around the billet perimeter. Cracks start to open in the dendritic front in regions where the shell growth in the mold is
slower. The study presented in this article focused on steels with a sulfur content of about 300 ppm. The Baumann prints taken
from billet samples of numerous different heats allowed detecting the presence of subsurface cracks and their location nearby
visible chill zone thinning areas. To understand the mechanisms of crack formation and to define the possible corrections,
a modeling activity has been carried out using the finite element technique on 148-mm diameter billets continuously cast at
TenarisDalmine (Dalmine, Italy). The model performs a two-dimensional thermomechanical analysis of the solidification in the
mold and within about 4 cm below the mold exit, along which the shell surface is cooled only by radiation to the environment,
before the sprays of the first ring impact on the strand. The model includes the contact of the shell with the mold inner
surface, which moves according to taper and distortion (this last part is calculated by means of a separate mold model); the
steel creep behavior; the calculation of the heat transfer through the gap depending on the local mutual distance between
the two surfaces; the effect of the liquid steel fluid dynamics on the solidification growth as a result of the temperature
distribution; and the calculation of a hot tearing indicator represented by the porosity fraction caused by mechanical strains
applied at the dendrite roots. From the simulation results, it is concluded that subsurface cracks are generated in the space
between the mold exit and the first cooling ring; the involved mechanisms of formation also are withdrawn. Nucleation of MnS
precipitates of large dimensions is an additional cause of defectiveness in controlled sulfur steels. As a final conclusion
of this work, the most important actions to eliminate subsurface cracks are derived. 相似文献
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The surface quality of continuously cast material is strongly depending on the initial solidification of the steel. Oscillation marks are formed at the very early stages of the strand shell growing process, thus influencing the microstructure and cracking behaviour of the surface and subsurface region. An industrial study of the oscillation mark morphology and the surface structure of peritectic medium carbon steel slabs was performed. The formation of oscillation marks and their effect on the surface quality was examined by metallographic investigations of slab samples. Although constant casting and oscillation conditions were applied, a variation of oscillation mark geometry along the narrow faces of the slabs was measured. A relation between the depth of the oscillation marks and the thickness of a layer of segregated melt situated inside the bottom of the marks was found. Measuring the distribution and length of surface and subsurface segregated cracks in the vicinity of the marks, existing theories of oscillation mark formation could be confirmed. The austenite grain size was found to increase with increasing oscillation mark depth. There was no clear correlation between the austenite and the δ‐ferrite grain size. 相似文献
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