Technology and experiments of 42CrMo bearing ring forming based on casting ring blank

Bearing ring is the crucial component of bearing. With regard to such problems as material waste, low efficiency and high energy consumption in current process of producing large bearing ring, a new process named ＂casting-rolling compound forming technology＂ is researched by taking the typical 42CrMo slew bearing as object. Through theoretical analysis, the design criteria of the main casting-rolling forming parameters are put forward at first. Then the constitutive relationship model of as-cast 42CrMo steel and its mathematical model of dynamic recrystallization are obtained according to the results of the hot compression experiment. By a coupled thermal-mechanical finite element model for radial-axial rolling of bearing ring, the fraction of dynamic recrystallization is calculated and recrystallized grains size are predicated. Meanwhile, the effects of the initial rolling temperature and feed rate of idle roll on material microstructure evolution are analyzed. Finally, the industrial rolling experiment is designed and performed, based on the simulation results. In addition, mechanical and metallographic tests are conducted on rolled bearing ring to get the mechanical parameters and metallographic structure. The experimental data and results show that the mechanical properties of bearing ring produced by casting-rolling compound forming technology are up to industrial standard, and a qualified bearing ring can be successfully formed by employing this new technology. Through the study, a process of forming large bearing ring directly by using casting ring blank is obtained, which could provide an effective theoretical guidance for manufacturing large ring parts. It also has an edge in saving material, lowering energy and improving efficiency.     

Combined Cellular Automaton Model for Dynamic Recrystallization Evolution of 42CrMo Cast Steel

The dynamic recrystallization (DRX) simulation performance largely depends on simulated grain topological structures. However, currently solutions used different models for describing two-dimensional (2D) and three-dimensional (3D) grain size distributions. Therefore, it is necessary to develop a more universal simulation technique. A cellular automaton (CA) model combined with an optimized topology deformation technology is proposed to simulate the microstructural evolution of 42CrMo cast steel during DRX. In order to obtain values of material constants adopted in the CA model, hot deformation characteristics of 42CrMo cast steel are investigated by hot compression metallographic testing. The proposed CA model deviates in two important aspects from the regular CA model. First, an optimized grain topology deformation technology is utilized for studying the hot compression effect on the topology of grain deformation. Second, the overlapping grain topological structures are optimized by using an independent component analysis method, and the influence of various thermomechanical parameters on the nucleation process, grain growth kinetics, and mean grain sizes observed during DRX are explored. Experimental study shows that the average relative root mean square error (RRMSE) of the mean grain diameter obtained by the regular CA model is equal to 0.173, while the magnitude calculated using the proposed optimized CA model is only 0.11. This paper proposes a novel combined CA model for simulating the microstructural evolution of 42CrMo cast steel, which notably uses a ICA-based grain topology deformation method to optimize the overlapping grain topological structures in simulation.     

Combined Cellular Automaton Model for Dynamic Recrystallization Evolution of 42CrMo Cast Steel

The dynamic recrystallization(DRX) simulation performance largely depends on simulated grain topological struc?tures. However, currently solutions used di erent models for describing two?dimensional(2 D) and three?dimensional(3 D) grain size distributions. Therefore, it is necessary to develop a more universal simulation technique. A cellular automaton(CA) model combined with an optimized topology deformation technology is proposed to simulate the microstructural evolution of 42 CrMo cast steel during DRX. In order to obtain values of material constants adopted in the CA model, hot deformation characteristics of 42 CrMo cast steel are investigated by hot compression metal?lographic testing. The proposed CA model deviates in two important aspects from the regular CA model. First, an optimized grain topology deformation technology is utilized for studying the hot compression e ect on the topology of grain deformation. Second, the overlapping grain topological structures are optimized by using an independent component analysis method, and the influence of various thermomechanical parameters on the nucleation process, grain growth kinetics, and mean grain sizes observed during DRX are explored. Experimental study shows that the average relative root mean square error(RRMSE) of the mean grain diameter obtained by the regular CA model is equal to 0.173, while the magnitude calculated using the proposed optimized CA model is only 0.11. This paper pro?poses a novel combined CA model for simulating the microstructural evolution of 42 CrMo cast steel, which notably uses a ICA?based grain topology deformation method to optimize the overlapping grain topological structures in simulation.     

铸辗复合成形法兰坯高温变形行为及加工图

环件铸辗复合成形工艺具有缩短工艺流程、高效和节能节材等优点,研究铸态环坯在铸辗复合成形工艺下的高温变形行为,揭示其组织演变机理,是实现材料在该成形工艺中成形与成性的关键。在不同变形条件下对砂型铸造和离心铸造Q235B法兰坯进行高温压缩试验,分析其流变应力的变化,推导出二者的本构方程。综合变形温度和应变速率对材料微观结构与性能的影响,建立基于动态材料模型的加工图。试验结果表明:二者的流变应力随着应变速率的增加和变形温度的降低而增大。离心铸造法兰坯的流变应力较低,动态再结晶易于发生,且功耗效率值及其变化幅度都要大于砂型铸造,表明了其显微组织变化剧烈,演变更加充分。结合二者的热加工图及其识别出的典型区域显微组织,获得了适合该法兰坯辗扩工艺的热力参数范围,离心铸造可为法兰坯铸辗复合成形工艺提供高质量的铸坯。     

铸态42CrMo钢热压缩变形时的动态再结晶行为

基于Gleeble-1500型热模拟试验机进行热压缩试验,通过对试验数据进行线性回归分析推导出了铸态42CrMo钢热压缩变形的本构方程,同时探讨了热压缩变形参数对显微组织的影响。结果表明:在相同的变形温度(850～1 150℃)下,该钢变形后的显微组织随着应变速率的增大逐渐变细,在5s-1时达到最细;在相同的应变速率(0.1～5s-1)下,显微组织随着变形温度的升高逐渐变细后再粗化,在1 050℃时马氏体板条最细;在相同的应变速率(1～5s-1)和变形温度(900～1 050℃)下,随着变形量的增加,再结晶晶粒尺寸均得到了显著细化;在温度为1 050℃、应变速率为5s-1、应变为0.6时热压缩后晶粒的细化效果最为显著。     

A microstructure evolution model for numerical prediction of austenite grain size distribution

In this study, a mathematical model has been developed to predict austenite grain size (AGS) of hot rolled steel. Using the compression test, the static (SRX) and metadynamic (MDRX) recrystallization characteristics of medium carbon steel were studied. Compression tests were carried out at various temperatures in the range 900-1100 °C with strain rates ranging from 0.1 to 10 s⁻¹. The time required for 50% recrystallization for the SRX and MDRX was determined by carrying out double compression tests, respectively. Grain growth equation after full recrystallization was also derived by compression tests with various interpass times. The currently determined microstructure model has been integrated with a three-dimensional non-isothermal finite element program. The predicted results based on the model proposed in the present investigation for hot bar rolling processes were compared with the experimental data available in the literature. It was found that the proposed model was beneficial to understand the effect of recrystallization behavior and control the microstructure evolution during the hot bar rolling.     

Processing map for the hot working of Ti-8Ta-3Nb

This paper considers the deformation behavior during hot forging in as-cast and forged specimens of Ti-8Ta-3Nb. The experimental specimens are as-cast and forged specimens of Ti-8Ta-3Nb. The deformation behavior of Ti-8Ta-3Nb alloy has been characterized on the basis of its flow stress variation obtained by true strain rate compression testing in the temperature range 650-900°C and strain rate range 0.001–10s⁻¹ P. The present study aims at assessing the hot workability of as-cast and forged Ti-8Ta-3Nb using the approach of processing maps and comparing specimens of Ti-8Ta-3Nb. The maps are an explicit representation of the various processes that occur in the different temperature and strain rate conditions. The construction of the maps is based on the experimentally determined changes of strain rate sensitivity coefficient. Processing maps were obtained at strains of 0.2, 0.3, 0.4 and 0.5 in both as-cast and forged specimens.     

10B06冷镦钢连铸坯的热压缩流变行为

利用MMS-200型热力模拟试验机研究了10B06冷镦钢连铸坯在750～1 100℃、应变速率为0.01～20s-1条件下的热压缩流变行为,并且通过线性回归确定了该钢的应变硬化指数以及热激活能,获得了其在变形条件下的流变应力本构方程。结果表明:该钢在热压缩变形时的流变软化行为是动态再结晶、动态回复与加工硬化联合作用的结果;当变形温度较低、应变速率较小时,软化效应以动态再结晶为主;而当变形温度较高、应变速率较大时,软化效应是动态再结晶和动态回复共同作用的结果;该钢的流变应力可采用Zener-Hollomon参数的函数来描述,其热激活能为220.132 3kJ.mol-1。     

0Cr19Ni9N奥氏体不锈钢锻件的再结晶

从工业化生产的 0Cr19Ni9N奥氏体不锈钢大锻件实物中取样 ,研究了粗大原始组织的高温再结晶。结果表明 ,通过再结晶可得到细小的均匀组织 ,形变储存能越高 ,再结晶温度越低 ,原始组织晶粒越细 ,再结晶温度也越低。而且 ,提高再结晶温度可显著加速再结晶 ,完全再结晶后 ,其强度下降 ,塑性增加     

热轧A36钢静态再结晶动力学模型

为了模拟A36钢轧制过程的微观结构演变,在Gleeble 1500热模拟试验机上进行了双道次热压缩实验。通过在不同变形工艺下的软化行为研究,建立了A36钢在轧制情况下的静态再结晶动力学模型。该模型综合考虑了不同变形温度、应变率、应变及初始奥氏体晶粒尺寸等参数对静态再结晶行为的影响,仿真结果和实验结果比较吻合。     

45钢微铸轧增材成形件的组织性能研究

利用华中科技大学材料科学与工程学院研制的微铸轧增材成形技术和装置,在电弧熔积和微铸轧2种工艺条件下进行试验,分析测试了增材成形的45钢试样的组织特征和力学性能。试验结果表明:与电弧熔积成形相比,微铸轧工艺将晶粒粒度由3.0级提升至9.0级,抗拉强度提高了31.3%,屈服强度提高了68.8%,平均硬度提高了10.9%;与熔模铸造相比,抗拉强度提高了58.4%,屈服强度提高了107.7%。因此,微铸轧增材成形技术将为低成本制造高强度钢零件提供一条有效途径。     

The role of dynamic recrystallization in dry sliding wear

In dry sliding wear dynamic recrystallization gives a better understanding than grain boundary sliding and fatigue of the process near the contact zone. The process explains the low value of the deformation measured by grain thickness reduction and the absence of visible deformation marks in the case of low melting materials. Dynamic recrystallization explains the almost total consumption of the friction energy by the plastic process. It is also possible to compute the geometry of the worn material in a wear test. This phenomenon is proved experimentally using a copper pin sliding against an SAE 1045 steel ring. Pins of both single crystal and polycrystalline copper were used. The structure was observed by examining thin foils of the material taken from near the contact zone in an electron microscope.     

BT25钛合金动态再结晶行为的元胞自动机模拟

为研究热加工工艺参数对钛合金塑性成形过程中微观组织的影响,利用Gleeble-3500型热模拟试验机对BT25钛合金进行单道次等温恒应变压缩试验。分析真应力-应变曲线,建立JMAK动态再结晶动力学方程;通过对热变形行为的分析,推导出钛合金的位错密度模型、再结晶形核和晶粒长大模型;结合元胞自动机的算法,建立元胞自动机(Cellular automata, CA)模型并利用该模型模拟和验证了BT25钛合金热变形过程中动态再结晶行为。结果表明,BT25钛合金的流动应力对应变速率和变形温度非常敏感;提高变形温度或降低应变速率均有利于材料发生动态再结晶;CA模型模拟晶粒尺寸误差约为3%,预测DRX体积分数误差在10%以内。该模型具有良好的预测精度,为合金材料在塑性加工过程中优化工艺参数和控制锻件微观组织演变提供了可靠性依据。     

特大型零件热态成形制造技术基础研究

在中国国家自然科学基金重点项目《特大件成形制造技术基础研究》、国家科技支撑计划课题《大型轧机共性技术》、国家重点基础研究发展计划(973计划)前期研究专项《大型零件热态成形制造虚拟技术基础研究》,以及中国河北省科技攻关项目《大型轧机共性技术》和《特大件成形制造技术基础研究》共同资助下,以大型锻钢轧辊(辊身直径超过1 000 mm或质量大于100 t)为对象,通过宏观 微观强耦合建模,解决铸造缺陷信息遗传、孔洞锻合条件、形变焊合条件、材料断裂准则构建,以及热 力 微观组织耦合建模等关键技术问题,建立以淬硬层深度数值预测技术为核心的热处理工艺分析与优化系统,提出基于非均质轧辊辊间接触力学模型的轧辊强度设计方法,构建起大型锻钢轧辊热态成形制造与服役评估的多学科耦合决策支持理论体系,提出理论研究报告。针对缩孔和气孔等大型铸钢锭铸造中的孔洞缺陷控制,以大锻件内部孔洞锻造闭合过程为科学问题,以大锻件内部有效锻合区域数值预测为目标,将有限元方法与人工神经网络技术相结合,利用神经网络的非线性映射能力,描述材料变形抗力、温度、应力应变与孔洞闭合程度之间的复杂关系,将孔洞锻合过程有限元模拟结果作为神经网络训练样本,建立起温度、应力和变形等多场耦合作用下的孔洞锻合条件模型(VCCM)。针对孔洞形变焊合机理与物理模拟模型一致性问题,以消除大锻件心部残留微孔隙,实现物理闭合状态下的锻合孔洞缺陷的真正冶金结合为目标,基于临界闭合孔洞界面接触力学原型和原子高温扩散理论,以界面接触应变和高温环境作为孔洞焊合的驱动力,利用高温和大变形对闭合孔洞界面扩散焊合的有利影响,提出适用于大锻件在锻造成形阶段的内部孔洞缺陷形变的形变焊合方法,通过物理模拟实     

Simulation of Static Recrystallization Behavior of 58SiMn Steel

58SiMn steel can be used as a kind of material for projectile-like barrel parts.During producing barrel parts,the microstructure of the barrel parts will be changed due to its hot deformation at certain high temperature,which resulted in the variety of the part’s mechanical properties.It is necessary to optimize the parameters for recrystallization process by prediction and simulation.The double-pass hot compression tests were conducted using Gleeble 1500 System at different deformation temperature,strain rate and pre-strain.Effect of pre-strain,deformation temperature on the curve of stress-strain has been analyzed.The static recrystallization fraction of double-pass hot deformation was computed and analyzed using compensation test.The actual grain size was measured by metallographic method using oxidation process,which overcomes the difficulty in revealing grain size of 58SiMn steel.The oxidation process was the method of heating the martensite in very fast speed and use of its microstructure inherent characteristic and regarding the size of austenite grain as the maximum of martensite plate.Using regression of the experimental data,the mathematical model of static recrystallization is set up.The average grain size of 58SiMn steel during hot deformation was calculated by deform-3D software and verified by experiment.The results show that the rate of static recrystallization was in direct proportional to the pre-strain of the steel.The grain size decreased with the increase of holding time at low deformation temperature 1 173 K and pre-strain 0.10.The mathematical model proposed could be used for predicting the static recrystallization behaviors of 58SiMn steel.     

Q345钢热变形奥氏体晶粒尺寸的数值模拟

用Gleeble1500型热模拟机进行了单道次压缩变形试验，分析了不同变形工艺参数对Q345钢奥氏体晶粒尺寸的影响规律，根据试验结果，建立了动态再结晶数学模型及其材料数据库，并写入Marc用户子程序，利用有限元软件Marc和热力耦合弹塑性有限元法模拟了试样的压缩过程，分析计算了采用不同再结晶模型得到的再结晶晶粒尺寸。结果表明：新建立的动态再结晶模型计算的奥氏体晶粒尺寸与实测值吻合很好。     

铸态和锻造态钛-硫易切削钢中硫化物形态及力学性能对比

熔炼了2种钛含量(质量分数分别为0.09%,0.21%)的钛-硫易切削钢,并在1200℃进行锻造,对比研究了铸态和锻造态试验钢组织中硫化物形貌、尺寸、数量以及试验钢的力学性能。结果表明:在铸态试验钢中,硫化锰大多为近似短棒状和球状,沿晶界呈链状或网状分布,锻造后硫化锰沿着锻造方向伸长,统计得到的长宽比增大,单位面积内数量减少;钛含量的提高使单位面积内硫化锰数量增多;铸态试验钢拉伸断口主要特征为解理台阶与河流状花样,断裂方式为脆性断裂,锻后的拉伸断口为解理和韧窝混合型形貌,断裂方式为韧性断裂;锻造态试验钢的拉伸性能和冲击韧性与铸态相比均有明显改善,锻造有助于提高钛-硫易切削钢的力学性能。     

Deformation behavior and microstructure evolution of wrought magnesium alloys

There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250-400 ℃ and 0.001-1 s-1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 oC/0.1 s-1 for TRC and 350 oC/1 s-1 for conventional casting (CC), while AZ41M alloy is 300 oC/0.01 s-1 for TRC and 350 oC/0.1 s-1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.     

20CrMnSiNi2MoA凿岩用钢等温自由锻模拟及试验研究

针对凿岩钻头用钢20CrMnSiNi2MoA,基于JMatPro软件模拟计算材料的应力应变曲线,并线性回归出材料的流变应力方程;基于DEFORM-3D有限元软件对材料进行了不对称V型砧锻造法等温自由锻造压缩,并预测了微观组织变化趋势。研究结果表明：原始奥氏体晶粒随着压缩量的变大,发生了动态再结晶,晶粒尺寸得到细化;温度一定时,随着变形速率的提高,晶粒平均尺寸变小。将通过不对称V型砧锻造法等温自由锻及热处理得到的钻头成品的机械性能与国外同类产品的机械性能进行了对比。     

基于铸辗复合成形的42CrMo钢环坯铸造工艺与试验研究

针对目前环形零件生产工艺流程长,加热次数多,浪费材料和能源等问题,提出和研究环形零件短流程铸辗复合成形新工艺。该工艺采用铸造环坯直接辗扩成形,具有节能、节材和缩短工艺流程等优点。在这种新工艺中,环坯的铸造质量、组织和力学性能对后续的辗扩工艺和环形零件组织、性能具有重要的影响。以轴承环件常用的42CrMo钢为研究对象,通过理论分析和模拟研究,提出高质量环形铸坯铸造工艺;并进行实际工业试验。通过试验研究和性能测试,表明该铸造工艺生产的环形铸坯具有良好的质量、组织和力学性能,可以为轴承环件铸辗复合成形提供高质量的铸坯。