电渣重熔工艺对GCr15轴承钢凝固组织的影响

基于CAFE法(元胞自动机-有限元模型),采用ProCAST对电渣重熔方法生产的GCr15轴承钢钢锭的微观组织进行数值模拟,得到了电渣钢锭的晶粒生长过程、熔池形状变化和晶区分布情况,并分析了不同的工艺参数对熔池形状以及凝固组织的影响.熔池深度随着钢锭固相区的扩展而变得越来越深,当钢锭长到一定高度,熔池深度和晶粒生长方向均不再变化.研究结果表明:结晶器冷却强度越大,熔池温度越低,熔池深度与钢锭半径之比h/R越小,而晶粒平均尺寸增大且柱状晶越多;渣池温度越高,h/R越大,晶粒平均尺寸增大;重熔速度是最显著的影响因素,熔速增大,h/R显著增大,柱状晶尺寸增大且数量增多.经过对电渣锭的凝固组织观察试验发现,模拟结果与试验结果有较好的一致性.     

非均匀温度场Fe-0.06%C合金焊接接头凝固过程模拟分析

利用元胞自动机和有限差分(CA-FD)法,采用宏-微观两种尺度,将宏观温度场与微观枝晶生长过程耦合在一起,再现了Fe-0.06%C二元合金焊接熔池的凝固过程.同时,探讨了边界散热速率对焊接熔池中枝晶生长形貌及晶粒尺寸的影响;分析了形核基底数与枝晶生长间的关系;并用实验对模拟结果进行了验证.结果表明,在熔池凝固过程中,温度梯度沿散热边界向绝热边界方向不断减小,等温线弧度不断增大;熔池散热边界附近的液相中溶质浓度远远高于绝热边附近和模拟区域中心的液相溶质浓度;模拟区域内的温度梯度随着边界散热速率的增大而升高.此外,随着形核基底的增加,柱状晶数量基本不变;而等轴晶数量不断增多,分布范围逐渐扩大,但尺寸有所减小.模拟结果反映了焊接熔池的凝固过程,并与实验结果吻合,为实际焊接工艺的选取提供了一定的参考.     

不同焊接条件下TIG焊接紫铜厚板的热效应研究

为改善紫铜厚板的焊接性,采用商业有限元软件Marc对钨极气体保护焊接紫铜厚板的温度场进行模拟,并详细讨论了焊接电流以及预热温度对熔池和热影响区的影响.结果表明,熔池和热影响区均随着预热温度和焊接电流的增加而增加,因此,在采用不同的预热温度和焊接电流的组合可以得到相同尺寸的熔池,但热影响区尺寸差别很大;在20℃时采用He或N2气保护焊得到的熔池尺寸与Ar气保护预热400℃时得到的熔池尺寸基本一致,但热影响区的尺寸窄于Ar气保护预热400℃时得到的热影响区尺寸.     

Ti-6Al-4V三元合金焊接熔池凝固组织模拟

将二元合金元胞自动机模型与热力学相平衡求解软件相结合,提出了一种三元合金元胞自动机模型.对模型的稳定性进行了验证,模拟了Ti-6Al-4V三元合金焊接熔池凝固过程中枝晶的生长形貌、溶质浓度的分布以及扰动振幅对枝晶生长的影响,并进行了金相实验验证.结果表明,模型稳定性良好,能够实现三元合金焊接熔池凝固过程的数值模拟;熔池中枝晶择优生长显著,且存在晶界偏析现象;Al元素与V元素在液相中的浓度分布规律大致相同;随着扰动振幅的增大,熔池中的枝晶数量逐渐增加,枝晶臂间距减小,竞争生长进一步加强;模拟结果与实验结果基本吻合.     

药芯焊丝电弧焊(FCAW)的焊接电流对Fe-Cr-C合金堆焊金属组织与耐磨性的影响

采用自制药芯焊丝在3种焊接电流条件下堆焊获得了相应堆焊试样,对其显微组织进行了观察,并对相结构进行了分析。在此基础上,分析了焊接电流对堆焊金属硬度及耐磨性的影响。然后采用数值模拟方法对不同焊接电流的堆焊熔池温度进行了计算,并采用热力学软件对不同焊接电流堆焊金属在冷却过程中的CCT曲线进行了预测。结果表明,随着焊接电流的增加,堆焊熔池温度显著升高,堆焊金属的淬透性增加,从而使冷却后的堆焊金属中的马氏体含量增加,而残余奥氏体含量降低,导致堆焊金属的硬度和耐磨性均显著提升。     

高性能轴承钢真空自耗熔炼过程组织演变规律与控制研究

通过Pro-CAST有限元软件模拟了高性能轴承钢真空自耗熔炼过程的温度场、熔池形貌和微观组织,研究了真空自耗铸锭组织演变规律,探究了温度场、熔池形貌对组织生长的影响。熔炼结束后,对真空自耗铸锭进行解剖酸洗以验证模拟结果。研究表明:模拟结果与实验结果吻合,铸锭组织形貌为贯穿铸锭中心的细长柱状晶,真空自耗铸锭的底部、边部和凝固末端有小面积等轴晶。柱状晶的生长带有明显的择优取向,底部柱状晶取向为垂直向上,中上部为斜向上。熔池深度越大,斜向上角度越小;熔池形貌对铸锭组织形貌影响显著,通过控制熔炼参数控制好熔池形貌能有效提高铸锭质量。     

AgSnO_2触头材料电弧侵蚀特征的分子动力学模拟

研究电接触材料电弧侵蚀作用过程中灭弧过程的微观机理,采用分子动力学和实验的方法对反应合成的AgSnO2电接触材料的熔池行为进行模拟。结果表明:根据起弧时的物相所构建的模型,能够准确地模拟熔池特征,熔池内部物质运动和存在状态是决定耐电弧侵蚀的关键因素。可通过增加反应合成AgSnO2电接触材料与基体浸润的氧化物组分,以及氧化物发生物态变化、化学分解过程来达到熄弧的目的。     

熔池高度对双辊薄带凝固组织影响的模拟预测

在已建立的理论数学模型的基础上,以1Cr18Ni9Ti不锈钢为研究对象,模拟预测了薄带厚度保持不变条件下熔池高度对薄带凝固组织的影响.研究结果表明:随着熔池高度增加,1Cr18Ni9Ti不锈钢双辊薄带凝固组织中柱状晶区比例首先增大,然后又逐渐减小.而柱状枝晶取向度和枝晶间距则随着熔池高度的增加而增大,但在较低的熔池高度条件下,柱状枝晶间距在凝固结束时有突然增大的趋势.     

激光熔化沉积成形过程数值模拟研究现状

激光熔化沉积(Laser melting deposition,LMD)技术具有效率高、成本低、成形件性能优异等优点,成为零件修复和大尺寸构件制造的有效方法.然而,金属LMD成形是金属粉末、激光束和基体三者相互作用的一个多因素耦合过程,涉及流动熔池、快速非平衡凝固、固态相变以及复杂的温度和热应力演变.预测熔池流动情况、凝固规律以及温度应力的演变规律,对于成形试样的气孔、裂纹等缺陷控制,微观组织、力学性能和应力变形调控具有重要意义.数值模拟是一种经济、快捷的工具,对于LMD成形过程的粉末流动预测、熔池变化预测、组织预测、温度观测以及冷却后的残余应力和变形预测具有重要意义.近几年,LMD数值模拟研究已经涉及以上几个方面,但研究深度各不相同.针对温度场的研究,主要集中于建立不同的热源模型,探讨沉积过程的温度演变及工艺方案的影响规律.针对应力场的研究,以探索工艺方案的影响规律和应力消除方法为主.研究流场则以熔池流动和粉末流动为主.微观组织模拟考虑熔池流动对宏观温度场及熔池形状的影响,采用定向凝固的生长条件,可以确定枝晶一次间距等凝固信息.本文主要从温度场、应力场、流场、微观组织等几个方面总结了金属激光熔化沉积数值模拟的研究现状,并提出了其存在的问题和预发展的方向.     

Ti–43Al合金薄板连铸过程的数值模拟及微观组织预测

目的 研究真空条件下Ti–43Al合金在连铸过程中的传热特性及其微观组织特点。方法 通过ProCAST铸造仿真软件,基于非稳态连铸计算模型建立了连铸过程的温度场模型,获得了连铸板材在凝固过程中的温度场及其固相率的分布规律,并采用CAFE计算模块对连铸板材的微观组织结果进行了预测。结果 连铸坯表面与结晶器接触的位置温度下降速度较快,熔池的深度在整个连铸过程中处在较为合理的水平上;连铸板材两侧表面的细晶区非常狭窄,并形成了由板材表面向板材心部生长的柱状晶区,在靠近铸件心部的位置发生了CET转变。结论 越靠近铸坯心部,温度梯度和过冷度越小,越有利于发生CET转变,使铸坯由外生长转变为内生长。数值模拟预测所得的结果与验证实验结果吻合得较好。     

激光功率对钛合金双侧同步焊接温度场的影响

为研究激光功率对TC4钛合金T型结构双激光束双侧同步焊接温度场的影响,针对TC4钛合金T型结构的双激光束双侧同步焊接过程,建立了相应的有限元模型,利用有限元分析软件进行了焊接过程温度场的计算,研究了激光功率对熔池形状的影响规律,并对不同激光功率下的温度场进行了分析.结果表明:随着激光功率的增加,熔池的熔深、熔宽均有所增...     

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.

Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.

In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.

Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

Modelling and simulation of the electric slag remelting guide vane casting (ESRC) process and its application

Modelling and experiment work is carried out for a large stainless steel casting with variable cross-section and a curved surface which is produced by the electric slag remelting casting process. The casting is part of a hydraulic runner generator at a power station of a big river.Mathematical models of the heat transfer and melted rate from an expendable metallic electrode were established. The melted rate is related to some important parameters, such as electric current and voltage, temperature and the flow rate of the cooling water in a crystallizer. Electrode melting, the moving pattern of the melted pool and the slag pool and the melt solidification in the metal pool were simulated.In order to make the enmeshment of the variable curved surface of the casting, a co-operation method of extended constructive solid geometry (CSG) from 9 to 21 uniform geometry with B-Spline surface functions is developed. By this method the guide vane casting is enmeshed. The boundary condition between the steel casting and the crystallizer cooled by water was measured.Based on the above new content the solidification simulation software ESRC3D is developed. Using it to simulate the whole process of ESRC with different parameters, instead of exploring the technological parameters of casting production by the trail-and-error method, the optimized parameters from the simulation for production of the large stainless steel castings with variable cross-section and a curved surface, such as the guide vane castings, have been used to produce them. Economic benefit and good quality of castings are obtained. Guide vane castings are widely applied to the hydraulic runner generator at numerous river power stations.     

22 MnB5 钢板热冲压工艺数值模拟及试验

目的研究热冲压过程中板料的温度变化及相变情况。方法采用Abaqus软件建立了热力耦合模型,对U形件热冲压成形及冷却淬火过程进行了数值模拟,分析了板料及模具的温度分布变化,并研究了板料不同区域的冷却速率,最后进行了热冲压试验。结果研究结果表明,板料经冷却淬火后,温度分布均匀,且冷却速率均大于临界冷却速率,板料可以发生完全马氏体相变。结论板料的底部冷却速率最快,淬火后为分布均匀的、细小的马氏体组织,最终通过热冲压试验验证了模拟结果的准确性。     

沉积铜箔用阴极辊钛环轧制驱动辊转速研究

基于有限元模拟软件Deform-3D和三维造型软件建立有限元模型进行模拟。选取不同的驱动辊转速(1.75 rad/s、2.25 rad/s、2.75 rad/s、3.25 rad/s)针对模拟结果考虑不同的驱动辊转速对环坯温度场、等效应变、环件表面微观组织以及成形性能的影响。综合分析得出环坯轧制过程中驱动辊的最佳转速为1.75 rad/s,并进行了实际生产验证,验证结果与模拟结果吻合。     

Effect of reheat temperature on continuous cooling bainite transformation behavior in low carbon microalloyed steel

The effect of reheat temperature on continuous cooling bainite transformation in a low carbon microalloyed steel was investigated using a dilatometer based on welding thermal simulation process. The variation of microstructure was analyzed in detail by means of optical microscope and transmission electron microscope (TEM). The results showed that the morphology of the main microstructure changes from polygonal ferrite to granular bainite with increasing reheat temperature at a given lower cooling rate. For the higher cooling rate, the microstructure is predominantly lath bainite irrespective of the reheat temperature. The specimens with the relatively fine austenite grain size have the lowest bainite start and finish temperatures among the simulated sub-zones of heat affected zone, which is consistent with the result of the bainite lath width size observed using the TEM. Meanwhile, although the prevailing type of impingement mode of transformation is anisotropic growth impingement for all heat treatment processes, the reheat temperature has some influence on the maximum transformation rate and effective activation energy of bainite transformation.     

金属热成形过程的综合数值模拟

金属在热成形过程中的微观组织演变是影响产品力学性能的关键因素,该演变过程取决于温度、应变和应变速率。本文基于有限变形理论和微观组织演变的数学模型,建立了能够模拟变形过程、温度变化过程和微观组织演变过程的有限元法,研制了通用的三维有限元计算软件,并在H型钢三维热轧模拟方面进行了深入开发,给出了原材料为C-Mn钢的H型钢热轧过程综合模拟结果。综合对比了8组不同工艺下的热轧实验结果和计算机模拟结果,二者均吻合良好,表明本文方法能够较好地预报金属热成形过程。     

304不锈钢冷却管束加工缺陷产生原因分析

通过化学成分分析、金相检验和断口分析等方法检测分析了在某一批次加工304不锈钢冷却管束过程中产生缺陷的原因。结果表明:缺陷主要有清理焊缝后出现的凹坑和焊后出现的裂纹两种;由于材料中存在微量氧和锡等有害元素以及分布不均的铜和铈元素,导致在管子焊接过程中,钨极氩弧焊接过程中熔池中产生氧化物熔渣,有的残留在焊缝金属表面被去除后产生凹坑;焊管在弯曲过程中,由于Cu-Sn合金产生铜脆而在钢管的受拉应力的一侧产生局部裂纹。因此,这些缺陷是由此批次不锈钢的纯净度较差引起的。     

Fluid flow behavior and solidification process of welding pool under rapid cooling condition based on cellular automata-lattice Boltzmann method (CA-LBM) couple model

Based on the basic principle of lattice Boltzmann method (LBM), this paper first establishes a numerical model for simulating the evolution process of flow field, temperature field and concentration field. Then the cellular automata-lattice Boltzmann method (CA-LBM) coupling model is established to simulate the solidification process of welding pool. Finally, the solidification process of the welding pool under different rapid cooling powers is analyzed. It is found that the solidification process of the welding pool is significantly correlated with the magnitude of the rapid cooling power. As the rapid cooling power increases, the maximum temperature, the temperature interval and the size of the welding pool decrease, which lead to the Marangoni convection effect in the welding pool increases obviously and the unevenness of the concentration field is reduced. Meanwhile, due to the increase in the degree of supercooling, the nucleation rate increases. Finally, under the combined action, the microstructure of the weld is refined. The results of the coupling model accurately reflect the complex changes of the physical fields in the solidification process of welding pool under different cooling power. It lays a foundation for solving practical engineering problems in large calculation area.