Defect healing in the axial zone of continuous-cast billet

Minimization of the metal consumption in components imposes ever-increasing structural requirements on steel. Accordingly, it is important to study the behavior of structural defects in continuous-cast billet (shrinkage pores, gas bubbles, axial porosity) during deformation. The use of laminar physical models to study the pressure treatment of metals is further developed in the present work. The influence of the strain on defect healing may be assessed by using laminar models together with defect application to the surface of layer n and the analysis of information regarding its distortion. The proposed method is applied to the deformation of continuous- cast bar billet in the first three rectangular grooves of the reduction cell in the 500/370 linear rolling mill at PAO Donetskii Metalloprokatnyi Zavod. On the basis of the experimental data, the existing healing mechanism for axial metal defects may be refined in terms of the total extension and the applied deforming forces.     

Strain Effect on the Microstructure,Mechanical Properties and Fracture Characteristics of a TWIP Steel Sheet

Twinning-induced plasticity (TWIP) steels are a highly promising group of steels for the production of complex structural components in cold forming operations for car body manufacturing. In this work, the effect of cold rolling strain on the microstructure, mechanical properties and fracture characteristics of a TWIP steel sheet used for automobile body structure was studied by means of optical microscopy, scanning electron microscopy, electron back-scattered diffraction technique, microhardness measurement, tensile test and fractography. TWIP steel sheets were cold rolled with reductions of 0, 15 and 30%. An increase of the cold rolling strain led to an increase of deformation twinning activity in certain favourably oriented grains and resulted in significant increase in ultimate tensile strength and hardness of TWIP steel. However, the ductility of TWIP steel significantly decreased with increasing degree of cold rolling strain. The increase in the ultimate tensile strength was almost linear with the increase in cold rolling strain. After cold rolling reduction of 30%, the ultimate tensile strength increased by approximately 50%, whereas the elongation decreased by approximately 85%. The size and depth of the dimples in the fracture surface decreased with the increase of the twin boundaries at 30% cold rolling strain, leading to highly limited plasticity through the tensile testing.     

不锈钢-碳钢复合带肋钢筋的制备工艺研究

使用金属熔覆和热轧的方法成功制备了覆层为Cr13不锈钢的复合钢筋.通过有限元数值模拟发现,在粗轧区域的高温变形过程,塑性应变主要集中在轧件表层和1/4位置,芯部的变形较表层偏小,随着变形的不断进行,塑性应变不断向碳钢芯部渗透.复合钢筋在成品机架K1变形时,不锈钢全部包裹在碳钢上,但是在横断面的不锈钢覆层厚度分布不均匀,...     

Capture of an H-beam blank by the rollers in the reduction stand of a 1300 universal beam mill

The capture conditions for an H-beam blank by the grooved rollers in the 1300 reduction stand of a universal beam mill at Nizhny Tagil metallurgical works are considered. The stress–strain state of the metal in the deformation regions on rolling the beam in the roller grooves of the reduction stand is investigated. The calculation results are presented as the distribution of the contact normal and tangential stress in the deformation regions as the H-beam blank is captured by the rollers. The normal tensile stress in the wall of the Hbeam blank is no more than 52 MPa. In the deformation regions of the crosspieces and at their junction with the wall, the normal contact stress is compressive. That indicates a stress state favorable in terms of H-beam quality, with high compressive stress. A method is developed for calculating the dynamic loads in the drive line of the 1300 reduction stand, with allowance for the gaps in the spindle joints.     

Surface-crack formation in the manufacture of microalloyed steel pipe

Deform-3D software is used to model surface-crack formation in the rolling of thick sheet on a 5000 mill. The calculations show that the temperature field and stress state are relatively uniform over the width of the sheet, except at the edges. The minimum temperature of the surface layers of metal hardly depends on the sheet thickness and the relative reduction per pass. The Cockroft–Latham criterion is used to analyze the probability of steel failure in rolling. Analysis shows that metal failure may occur at points where ferrite appears, especially at the instant that the metal leaves the deformation region. Considerable tensile stress acts at those points.     

Surface-crack formation in the two-phase region when rolling thick microalloyed-steel sheet

The formation of a surface defect (a lobed scab) in the final stage of large-diameter pipe production is analyzed. Surface microcracks are assumed to form in the rolling of thick sheet on account of problems in the two-phase region on rolling, with localization of the plastic strain, as well as the action of tensile stress in the surface layer and the attainment of limiting stress values. Physical modeling in the Gleeble system permits determination of the limiting stress (rupture strength) in rolling in the two-phase region, which depends on the temperature and is structure-sensitive. The limiting stress is determined by ferritic and bainitic transformation in the steel.     

Rolling of profiles with a rhombic cross section

Selection of the optimal blank in the rolling of profiles with a rhombic cross section may be based not only on the consumption of metal and the rolling force but also on the utilization of the material’s margin of plasticity and the profile’s margin of stability in rolling. Calculations of four groove configurations permit the identification of the rectangle-rhombus configuration as optimal. The performance of the product is more stable in that case.     

Prediction of Velocity and Deformation Fields During Multipass Plate Hot Rolling by Novel Mixed Analytical-Numerical Method

 An integrated mathematical model is proposed to predict the velocity field and strain distribution during multi-pass plate hot rolling. This model is a part of the mixed analytical-numerical method (ANM) aiming at prediction of deformation variables, temperature and microstructure evolution for plate hot rolling. First a velocity field with undetermined coefficients is developed according to the principle of volume constancy and characteristics of metal flow during rolling, and then it is solved by minimizing the total energy consumption rate. Meanwhile a thermal model coupling with the plastic deformation is exploited through series function solution to determine temperature distribution and calculate the flow stress. After that, strain rate field is calculated through geometric equations and strain field is derived by means of difference method. This model is employed in simulation of an industrial seven-pass plate hot rolling process. The velocity field result and strain field result are in good agreement with that from FEM simulation. Furthermore, the rolling force and temperature agree well with the measured ones. The comparisons verify the validity of the presented method. The calculation of temperature, strain and strain rate are helpful in predicting microstructure. Above all, the greatest advantage of the presented method is the high efficiency, it only takes 12 s to simulate a seven-pass schedule, so it is more efficient than other numerical methods such as FEM.     

Ø75 mm GCr15圆棒材孔型工艺优化及数值模拟

西宁特钢精品小棒线在生产Ø75 mm的GCr15热轧圆钢时,发现轧后棒材内部存在中心疏松缺陷,导致棒材精整后超声探伤合格率低。通过修改孔型参数,结合数值模拟研究测试棒材芯部应力及等效应变的变化情况,再经现场生产验证,结合成品棒材超声探伤合格率的分析,来验证优化后的孔型参数是否可行,指导现场生产实践,提高轴承钢棒材的产品质量水平。参数的确定中,对各道次压下量的重新分配,主要是增加了第2道次的压下量,从58增加到86 mm,减小了第4道次的压下量,从58减小到30 mm。优化后的工艺直接从11架出Ø75 mm成品,节约了后2架轧机的能源消耗与轧辊磨损消耗。模拟结果显示第1道次的棒材内部应力由之前的拉应力变为压应力,结合轧制速度的降低,有利于提高棒材芯部质量。实际生产证明工艺优化后低倍质量显著提升,探伤合格率为96.37%,较之前提高3.63%。     

摩擦系数不等的非对称轧制条件下变形区内的变形分析

采用三维大变形热一力耦合有限元法分析了摩擦系数不等的非对称热轧板带变形区内轧件的变形情况，得到了不同摩擦系数条件下变形区内应力、应变和应变能量密度的分布规律。结果表明：在摩擦系数比不同的非对称轧制条件下，会产生不同于普通压缩变形的附加剪切变形，而且这种附加剪切变形为组织细化提供了有利条件。     

轧辊直径不等的非对称轧制条件下变形区内的变形分析

为了研究非对称轧制条件下变形区内金属的变形情况,采用三维大变形热-力耦合有限元法,分析了轧辊半径不等的非对称热轧板带变形区内轧件变形的情况,得到了在不同异径比条件下,变形区内应力、应变和应变能量密度的分布规律。结果表明：在非对称轧制条件下会产生不同于普通压缩变形的附加剪切变形,而且异径比越大,产生的附加剪切变形也越大。     

辊速不等的非对称轧制条件下变形区内的变形分析

采用三维大变形热-力耦合有限元法分析了辊速不等的非对称热轧板带变形区内轧件的变形情况,得到了不同辊速比条件下变形区内应力、应变和应变能量密度的分布规律。结果表明：在辊速比不同的非对称轧制条件下,会产生不同于普通压缩变形的附加剪切变形,而且这种附加剪切变形为组织细化提供了有利条件。     

GCr15 轴承钢 250 mm x 280 mm 铸坯至 138 mm x 150 mm坯粗轧数值模拟及工艺优化

生产Φ50～75 mm的GCr15轴承钢时,轧后棒材存在中心疏松缺陷。通过数值模拟研究,观察棒材心部等效应变的渗透情况,并对粗轧孔型工艺进行优化,将优化前一二道次的压下量从21 mm、58 mm分别增加到51 mm、85 mm,第三道次的压下量从60 mm减小到34 mm。等效应变值随着道次的增加,呈逐渐增大趋势,棒材中的拉应力在经工艺优化后变为压应力,变形均匀度也得到提升,促进了铸坯心部的变形,有利于中心孔洞的压合。工艺优化后轴承钢的探伤合格率由原93.25%提高到96.06%。     

热连轧低合金钢边部横裂形成原因分析

通过采集现场过程数据,从温度、成分、相变、晶粒形貌、轧制变形应力等方面对低合金钢Q355B宽规格钢板在热连轧过程中产生边部横向裂纹缺陷的原因进行机理分析.结果 表明,宽规格低合金钢边部横向裂纹产生原因与板坯宽度方向温度均匀性相关,边部局部温度过低导致两相区和非再结晶区域轧制,边裂区晶粒度尺寸和形貌与正常区有明显差异,从...     

Φ16 mm GCr15轴承钢棒材KOCKS轧机热连轧工艺数值模拟和分析

采用DEFORM-3D三维大变形热力耦合弹塑性有限元软件对Ф21.5 mm GCr15轴承钢坯料在四架KOCKS轧机连轧成Φ16 mm棒材工艺过程进行了数值模拟。分析了棒材在KOCKS轧机孔型中轧制时的等效应力、等效应变、温度场以及轧制力等轧制工艺参数。结果表明,棒材在KOCKS机组中的变形主要发生在延伸孔型,精轧孔型的变形量较小,尤其在最后一道次;棒材在KOCKS机组中的宽展是不均匀,在靠近轧辊的区域宽展较小,在辊缝处宽展较大并产生鼓形;棒材在KOCKS机组中等效应变已达到芯部渗透,这对保证组织致密度和成品内部质量是非常有利的,现场各道次轧制力的实测值与模拟值的相对误差＜2%。     

轧制同轴复合棒材的芯材变形规律

棒材同轴复合时芯材与加工工具不接触，其横截面形状及尺寸精度控制难度大，采用方-椭圆孔型轧制时芯材圆度严重超公差。在建立覆材和芯材变形抗力模型的基础上，利用三维弹塑性热力耦合有限元方法对同轴复合棒材热轧变形过程进行数值模拟。分析了轧制孔型、覆材及芯材外形对轧制后芯材变形和形状的影响，用工业试验对模拟计算结果进行验证。结果表明：轧辊孔型设计对芯材不圆度的影响最明显，覆材及芯材外形是次要影响因素。这是因为方-椭圆孔型系统会导致最终轧件在横截面上的非对称等效累积应变分布，以及导致轧后芯材严重不圆。减少K4孔的轧件压下量，增加K3孔轧件压下量，可以改善方-椭圆孔型中轧件变形的对称性，减少芯材不圆度。     

HRB400E细晶粒热轧钢筋生产工艺及品种开发

 细晶钢筋轧制技术可以充分发挥钢铁材料的性能,减少国家稀缺合金金属的耗用,达到节约资源的目的。抚顺新钢铁有限责任公司以20MnSi钢坯成分为基础,通过化学成分调整,利用公司现有的全连轧生产线工艺装备,采用控轧控冷工艺技术,通过控制变形量、变形温度、变形速度和冷却速度,成功生产出[?16 mm]和[?20 mm]规格的铁素体晶粒度不大于9级的HRB400E细晶粒钢筋。试验结果表明,通过控轧控冷工艺,可以生产出HRB400E级热轧细晶粒钢筋,并确定了工业化生产HRB400E细晶粒钢筋的各项工艺制度。     

Analysis of stress and strain fields in upset forged forgings

Theoretical investigation of influence of degree of deformation, slenderness ratio of a billet and shape of anvils upon distribution of stress and strain in upset forged material are presented in this paper. The deformation of a material was determined by the variational method and the stress field was determined from equations of equilibrium. Results of calculations indicate that formation of tensile stress in layers of a material at the free surface is connected with surface convexity. Factors which cause the increase of barrelling are also responsible for an increase of tensile stresses at the free surface of upset forged material.     

不同加热轧制AZ91镁合金带材数值模拟及试验验证

利用有限元法研究了热辊热带(HSR-HR)、热辊冷带(NSR-HR)和冷辊热带(HSR-NR)3种不同加热方式下AZ91镁合金轧制过程热-力行为,并进行了大压下率热辊冷带工艺试验和组织性能分析.结果表明,HSR-HR、NSR-HR及HSR-NR 3种加热轧制方式的应力三轴度依次增大,中性点附近应力状态软性系数依次减小....     

不锈钢/碳钢耐蚀海水带肋钢筋轧制复合工艺

摘要：海洋工程用带肋钢筋要求有耐氯离子腐蚀能力，但选用双相不锈钢生产成本过高，不锈钢 碳钢轧制复合钢筋则可兼顾耐蚀性和低成本。覆层采用2205不锈钢，基材为低合金钢20MnSi，用有限元方法模拟钢筋的热轧复合过程，分析轧制过程尤其是成品孔中轧件的变形规律。有限元仿真发现，矩形组合坯料无孔型轧制时，其角部复合困难，而成品孔轧制时，钢筋横肋根部的应变最大，覆层在此位置减薄显著，应选择合适的复合坯覆层厚度。在实验室采用焊接、真空处理和热轧方法制备了直径为16mm的复合钢筋，屈服强度为485MPa，抗拉强度为701MPa，断后伸长率约为37.1%，复合界面剪切强度为317.5MPa。复合钢筋呈良好的冶金结合，Fe和Cr的扩散层厚度约为40μm。该工艺生产的复合带肋钢筋成本较不锈钢降低50%以上。