Austenite Grain Size Evolution in Railway Wheel During Multi-Stage Forging Processes

 The knowledge of microstructure evolution of railway wheel during hot forming process is the prerequisite of improving mechanical properties of the final product. In order to investigate the austenite grain size evolution of railway wheel during multi-stage forging process, mathematical models of recrystallization and austenite grain growth were derived firstly by hot compression tests for railway wheel steel CL50D, which then were integrated with a thermal-mechanical finite element model by the developed subroutines. The information about kinetics of recrystallization and grain size distribution during the forging process was obtained by simulation. The predicted results were validated by experiments in an industrial scale, and the average error between the predicted grain sizes and the measured ones is about 5%. The result shows that, under the current railway wheel forging process, the grain size distribution after final forging is inhomogeneous extremely. There is a narrow coarse grain zone between the external part and center of the hub caused by static recrystallization after final forging. With cooling of 60 s after final forging, the grain size is about 85 μm for the areas near the web surface and 175 μm for center areas of the hub and rim.     

车轮轧制成形过程有限元分析

使用MSC.SuperForm对840火车轮轧制成形过程建立三维热力耦合有限元分析模型,研究分析了车轮立式轧制成形过程的金属变形规律.得出车轮轧制成形过程最大变形分布在辐板与轮辋连接处及轮辋外端靠近踏面处,轮辋外端变形明显大于轮辋内端变形,轮辋中心变形较难深透;车轮轧制中,辐板靠近轮辋端的金属周向流动明显,周向流动主要发生在轧制中后期;研究还得出车轮轧制过程各轧辊的受力及其变化情况,为制定车轮轧制工艺提供了参考.     

60kg/m重轨轧制全道次的有限元模拟和试验研究

对60kg/m U71Mn重轨轧制全道次进行了三维热力耦合有限元模拟。轧辊建模时分别通过翻转和平移轧辊来实现轧件翻钢和侧向推钢过程;轧件的建模采用抽取中间截面网格拉伸的建模方法,既消除网格畸变的影响又使得前后数据得到继承。模拟结果表明:重轨轧制过程中存在严重的不均匀变形,铸坯横断面金属质点在轧制过程中沿轧制方向不同步;轨底部位金属沿轧制方向和轨底高度方向流动;轨腰部位金属沿轧制方向和宽度方向流动,其中心向轨底部位偏移;轨头金属沿轧制方向被延伸。人工打孔制造缺陷坯轧制试验的特征点位置变化与模拟结果吻合良好,验证了轧件在各道次的金属流变规律。所建立的金属在轧制过程中的位置对应关系可以为生产过程中轧制缺陷的溯源分析提供便利。     

两辊楔横轧等内径空心轴产生椭圆原因的数值模拟研究

针对两辊楔横轧等内径空心轴轧件易产生椭圆的问题,采用有限元数值模拟方法,研究了两辊楔横轧等内径空心轴的轧制成形过程及应力应变情况.结果表明成形过程中轧件的径向压缩和轴向流动不匹配,造成金属切向流动显著、圆周长大,这是椭圆形成的主要原因.      

方坯直轧工艺中头尾温差消除过程数值模拟

方坯直轧工艺有一个难以避免的问题，即钢坯头尾温差问题，当头尾温差过大时，会对产品长度方向上组织性能均匀性产生不利影响。针对方坯直轧工艺下钢坯“头低尾高”的温度特点，提出采用在精轧前进行“头弱尾强”的变水量冷却策略，或在粗轧前进行“头强尾弱”的变功率感应补热策略，并利用有限元法分别对上述两种过程进行数值模拟，根据计算结果对关键工艺参数进行优化设计，为实际应用提供参考。模拟计算结果表明，对于变水量冷却方式，为消除纵向上线性分布的头尾温差，所需水流密度与轧件长度基本呈抛物线关系；对于变功率感应补热方式，所需补热功率与钢坯长度基本呈线性关系。     

热轧U型钢板桩精轧过程金属流动行为的有限元分析

针对热轧U型钢板桩(SY390BZ/%:0.23C、1.60Mn、0.44Si、0.18V,0.18Ti、0.05Nb)轧制过程中产生翘曲缺陷,采用有限元分析软件ABAQUS显式动力学算法,结合实验室试验测量参数,对钢板桩的精轧过程进行了仿真计算。在仿真计算的基础上,根据轧制平面内节点位移矢量分布情况,分析了轧件横向和纵向断面内金属流动规律。模拟结果显示轧件断面在孔型轧制的压下方向上存在零位移线,表明U型钢板桩轧制中坯料翼缘和锁口处在轧制压力方向上轧件内金属流动存在位移中性面,并伴有轧件锁口凸缘处金属流动过快,腹板处金属流动较慢而产生翘曲的现象。     

方矩形管端部成型机制

 利用非线性有限元方法,结合实际生产中方矩形管辊压成形过程,建立了有限元仿真模型。基于该模型对7机架实际辊压成型过程进行了模拟运算,得到了成形过程中稳定段处节点位移矢量、应力和应变的分布情况。通过对仿真计算结果的分析,得到管头端面上在角部和边部的过渡区存在着“位移中性面”,在端面上角部和边部的中心处伴有明显的金属“外翻”和“内翻”的情况,仿真结果与现场轧制结果相符。     

数值模拟在极限规格H型钢工艺优化中的应用

针对HW150mm×150mm极限规格H型钢产品偏心问题,采用有限元方法对粗轧阶段孔型系统进行三维热力耦合数值模拟。基于模拟结果分析金属流动、塑性应变及温度变化,以此为基础,根据变形特点及各孔型轧件尺寸分析偏心产生的原因,优化孔型并进行验证,最后进行现场实践,排除缺陷。结果表明,有限元模拟有助于分析轧制过程中的金属成形,尤其对于型钢轧制过程中的变形规律及缺陷分析具有较高的参考价值和指导意义。     

厚壁无缝钢管张减过程横向壁厚不均研究

为解决热轧厚壁无缝钢管横向壁厚分布不均的问题,建立三维热力耦合有限元模型,对张力减径轧制过程进行了动态模拟,并结合工业试验验证仿真模型.根据仿真结果分析了轧制过程中温度、应变和摩擦力的分布,研究了单道次轧制时金属的径向和周向流动规律,并结合整个轧制过程对金属的横向流动及壁厚不均的形成过程进行了分析,研究了轧制过程中温度对金属流动行为的影响,从而总结出横向壁厚分布不均的原因.结果表明:(1)在经过单道次轧制时,金属的周向流动为从孔型顶部流向辊缝,对应孔型角±30°位置处金属的周向流动最活跃,靠近孔型顶部和辊缝位置的金属周向流动性较差.但从整个轧制过程来看,金属总的周向流动为从孔型顶部和辊缝向孔型角±30°位置处流动,从而导致孔型角±30°位置处的壁厚比孔型顶部和辊缝位置要厚.(2)温度分布对金属横向流动有重大影响.由于塑性功换热的原因,孔型角±30°位置处金属的温度比辊缝和孔型顶部处高,此处金属较软,阻力较小,孔型顶部和辊缝处金属向此处的流动性增强,导致钢管截面呈内边方形.      

齿廓间相对滑动对滚轧齿轮齿廓金属流动的影响

基于范成挤压原理,采用梯形面积近似代替轧件长高齿形面积,对齿廓间的相对滑动进行了理论求解分析;从齿廓的相对滑动状况分析了其对轧件齿廓所受剪切摩擦方向的影响.通过仿真和实验相结合的方法验证了齿廓间相对滑动对齿廓金属流动方向的影响,证实了齿廓金属拉起和所受摩擦方向的一致性.      

Structural changes in a railway wheel rim during operation

The structural changes in the near-surface layers of a railway wheel rim are studied during operation in rolling stock. The standard operating conditions of rail transport are shown to be characterized by alternating impact loading; regular braking; and, hence, periods of rapid heating of the surface layers in wheels that are replaced by intense heat removal after the end of braking of rolling stock. In this case, the heating of wheels is sufficient for the beginning of phase transformations, which result in softening, embrittlement, and strain aging of the near-surface layer metal.     

Cross-Wedge Rolling of Shafts With an Eccentric Step

 A new concept for forming eccentric shafts on the basis of the cross wedge rolling (CWR) process was presented. This concept was based on the application of special guides, which, by acting on a billet, lead to its controlled movement in the vertical direction. This movement made possible eccentric cutting of tools into the billet. FEM calculations and experimental rolling tests clearly confirmed the effectiveness of the proposed forming method.     

楔横轧小断面收缩率轧件螺旋组织缺陷研究

轧件发生局部变形是楔横轧的主要工艺特征,尤其小断面收缩率轧件轴向流动能力弱,内外变形差异显著导致楔横轧成形困难.除了容易产生心部破坏缺陷,在轧件表层一定范围内出现的螺旋组织缺陷,也会降低产品的机械性能.本文通过轧制实验,展示出轧件螺旋组织缺陷宏观上呈现为车削后在表层一定深度范围内沿展宽螺旋线分布的亮带,微观上由轧件表面折叠向内部延伸呈带状分布的组织形态.结合有限元数值模拟方法研究了缺陷产生的主要原因,发现由于成形区的金属发生沿展宽负向的金属流动,导致轧件形成沿展宽螺旋线分布的表面折叠和小轴向应变带.同时,螺旋带附近较大的径向压缩使轧件由表面向内部沿折叠裂纹方向组织具有方向性.采用对模具楔尖倒圆角局部改善金属沿负展宽方向的轴向流动,可以既消除表层螺旋组织缺陷,又避免轧件心部损伤风险,使成形质量满足使用要求.经实验验证,确定了模具楔尖圆角的最优取值.      

Experimental and mathematical modeling of metal spray forming process

The metal spray forming process was examined using mathematical simulation and verified through the prototyping evaluation at Baosteel’s test and development facilities.The mathematical model comprised of four sections,including jet gas flow in the deposition chamber;single droplet behavior along its trajectory path;probability and statistical analysis of droplet mass behavior,and forecast of the shape and temperature distribution of the billet during the spray forming process.     

Void Closure Behavior in Large Diameter Steel Rodduring H-V Rolling Process

In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontalvertical(H-V)groove rolling process,a three-dimensional thermomechanically coupled finite element model was established for 9-stand H-V groove rolling process aiming at a150mm steel rod production line.A spherical hole with diameter from 2to 10mm was preset into the center of continuous casting billet with a rectangle cross section of300mm×360mm in this model to simulate the void defect,and then finite element analyses were carried out to observe and quantify the void shape evolution in each pass on the three orthogonal coordinate plane sections.The results showed that the void was formed roughly in the reduction and extension directions,and crushed gradually from spherical shape to an approximate ellipsoid,micro-crack and finally to be closed.A quantitative analysis was carried out by using elliptic radii and closure ratio to describe this evolution process;it indicated that the longest axis of the ellipsoid coincided with the rolling line,and the second and third axes were alternatively horizontal and vertical on the exit cross section according to change of the reduction direction in H-V groove.The void closure behavior during HV rolling was more complicated than that of common horizontal rolling,and the influence of groove type and the extension coefficient on the void closure ratio was presented.Finally,apilot rolling experiment was performed on a 5-stand H-V experimental mill to verify the numerical simulation results,and the experimental results are in good agreement with the numerical simulation results.     

Numerical simulation of tube profile growth during spray forming process

Spray forming is a new type of metal material forming process,which can produce metal blanks such as billet,tube,plate etc.A mathematical model has been developed to forecast the shape evolution of tube billets during the spray forming process.The atomizer mass flux as,radial distribution coefficient bs,draw velocity and diameter of mandrel were considered in this model and the influence of different parameters such as metal flowrate,draw velocity of mandrel,diameter of mandrel on the tube’s shape change were simulated and analyzed in this paper.The simulation results obtained from this model can be provided to engineers as reference.     

异型扁坯轧制过程横变形规律的研究

通过异型扁坯热轧成型过程的模拟实验，研究了轧件的宽展、孔型充满度的变化规律，提出了孔型高向充满程度和合理压下量的概念，得到了既定异型扁坯的成型方法及合理成型条件。     

钢球斜轧成形的金属流动规律

基于钢球斜轧成形原理,采用DEFORM-3D有限元软件建立了钢球斜轧成形的有限元模型.相应的实验结果表明有限元模型是可信的.利用有限元结果研究了钢球斜轧成形过程的金属径向和轴向变形规律.研究表明:坯料的金属以周期振荡方式累积变形.在轴线方向上,球体间的连接颈是变形最剧烈的位置,离连接颈越近,金属的径向变形和轴向变形越大.在横截面方向上,球体前半球的金属,离轴线中心越近,径向压缩量越小,轴向位移越大;球体后半球的金属,离轴线中心越近,径向压缩量越小,轴向位移越小.      

高强韧铝合金轮毂的轻量化铸旋新工艺

综述了铸造铝合金的强韧化研究现状和最新进展,介绍了铝合金轮毂的铸旋成形新技术,分析了铸旋工艺在铝合金轮毂轻量化中的作用。分析表明热塑性形变韧化可成为A356合金强韧化的新途径,以此为基础发展的铸旋成形工艺可满足汽车轮毂进一步轻量化的要求。采用铸旋工艺成形的铝合金车轮轮辋部位的各项性能指标比低压铸造车轮有大幅提高,轮辋壁厚也可大幅度减薄,相同规格的车轮,采用铸旋工艺生产可减重5%～15%,实现了产品的高强度、轻量化要求,具有更轻的竞争力。之后重点介绍了铝合金轮毂铸坯热旋压工艺原理、A356合金的可旋性、工艺参数的选择及有限元分析在热旋压工艺设计中的应用,并指出存在的问题和所需做的进一步研究。结果表明铸造A356合金的热旋压可加工窗口较窄,成形温度控制是关键,为了促进铝合金轮毂铸旋工艺的广泛应用与发展,在铸造铝合金的热旋压变形性能、热旋压时金属的变形机理和流动行为,以及热旋工艺数值模拟和参数优化等方面还需要做大量的、深入系统的研究工作。     

基于Deform-3D软件对AISI4340钢Φ600mm铸坯开坯工艺参数的模拟数值

利用Deform-3D软件对AISI4340钢Φ600 mm铸坯至300 mm × 300 mm坯的开坯过程工艺参数进行了数值模拟.通过对加热温度、轧制速度、压下率、2道次压下对铸坯心部变形和材料流动影响的研究,分析了开坯成形过程中心部等效应力和材料变形特点,获得了Φ600圆连铸坯开坯成300 mm方坯的成形规律.结果...