42CrMo铸坯环件热辗扩有限元模拟与分析

基于ABAQUS软件平台,建立了42CrMo大型环形铸坯热辗扩三维热力耦合有限元模型,模拟了铸坯热辗扩过程中应变场和温度场,研究了初始辗扩温度对辗扩力的影响规律.模拟结果表明在环形铸坯热辗扩过程中：①铸坯等效应变呈阶梯状上升,内外表面应变大于中间层应变;在稳定成形阶段,沿环件径向方向,由于导向辊与芯辊直径差异,导致环件最大平均等效应变可能出现在环件内表面也可能出现在环件外表面;②初始阶段,变形区与成形辊接触处温度降低较快,非变形区温度变化不是很明显;随着辗扩的进行,芯部温度逐渐上升,边缘温度低,温度分布不均匀;③随着铸坯初始辗扩温度升高,平均辗扩力明显下降,但随时间变化趋势保持一致.     

环形铸坯热辗扩成形微观组织演变规律研究

建立了铸态42CrMo钢的微观组织演变模型和环件热辗扩三维刚塑性有限元模型.基于DEFORM-3D软件平台,对微观组织演变和宏观热力学行为进行了耦合模拟,研究了环形铸坯热辗扩成形过程中芯辊进给速度对动态再结晶晶粒尺寸和体积分数分布的影响规律.结果表明,在变形量比较大的环件外层和内层容易发生动态再结晶,晶粒尺寸细化明显;...     

基于铸坯的42CrMo环件辗扩成形工艺热力耦合分析

以42CrMo钢为研究对象,对铸态坯料的环形零件辗扩成形过程进行了热力耦合分析。通过铸态42CrMo材料的热压缩实验,建立了两段式流变应力模型;对环形铸坯热辗扩成形过程进行了数值模拟,得出了基于铸坯的环件热辗扩成形过程等效应变、温度场及载荷的分布情况与演变规律,分析了辗扩工艺参数对成形过程中应力、应变和温度变化的影响。结合工业性铸坯环件辗扩成形试验,对改善和提高辗扩成形零件的组织和性能提出了建议和措施。所得结果对于完善环形零件铸辗复合成形新工艺具有指导意义。     

基于铸坯的环件热辗扩过程微观组织演变研究

根据建立的环形铸坯热辗扩成形刚塑性有限元模型和铸态42CrMo钢动态再结晶数学模型,基于DEFORM-3D软件平台,综合考虑了变形、传热和微观组织演变等因素,对辗扩过程中的变形和动态再结晶行为进行宏微观耦合模拟.结果表明:在环形铸坯热辗扩成形过程中,动态再结晶程度较低,等效应变和晶粒尺寸呈现环带状分布,环件的内外层等效...     

基于铸坯的25Mn钢环件热辗扩成形力学性能分析

环形铸坯辗扩成形是一个多场耦合、局部加载和连续成形过程,与传统辗扩工艺相比,缩短工艺流程,减少加热次数,节材、降能耗,具有重要的研究价值与推广应用前景。辗扩过程中,不仅要控制环形铸坯辗扩后的成形精度,还应通过高温塑性变形获得所需微观组织,提高综合力学性能,实现成形/成性一体化调控。根据环件轧制技术及基于铸坯的辗扩成形基础理论,通过对25Mn钢环形铸坯进行辗扩,分析辗扩成形环件不同部位微观组织的变化及力学性能,并借助扫描电镜观察,揭示其拉伸与冲击断口的断裂机理。结果表明:辗扩后环件的外形好,宽展小,椭圆度为0.4;组织内部平均晶粒尺寸小,环件各个区域的力学性能均较高,且中层的略低于内层和外层;拉伸与冲击断裂形式主要为准解理,并伴有韧窝断裂。可见,基于铸坯的25Mn钢环件热辗扩"成形"/"成性"质量较高,为其进一步研究以及实际生产提供了理论指导价值。     

大型内沟槽环件热辗扩数值模拟

环件热辗扩工艺是利用轧环机上旋转着的型辊对环坯局部连续加压．使环坯在回转过程中产生径向收缩、周向伸长从而使直径扩大、壁厚减薄、截面轮廓成形的连续局部回转塑性成形，是无缝环形零件的先进制造技术之一。由于该工艺具有节能、节材、优质、高效和低噪等优点而被广泛应用于汽车、航空航天等工业领域。大型内沟槽环件辗扩属于异形截面环件轧...     

基于锻坯的大型内台阶环件双件轧制

利用Gleeble-3500D热模拟实验机对Q345E钢进行单道次热压缩实验,建立起环件用钢的流变应力模型,在有限元模拟软件SIMUFACT中建立起大型锻坯内台阶环件双件轧制三维数值仿真模型,对大型内台阶环件一个生产周期内的环件轧制过程进行了数值模拟,并对其可靠性进行了实验验证,研究了环件热轧过程中环件不同部位的等效应变场、温度场、辗扩力以及金属流动特性的规律。结果表明:轧制过程中环件的应变分布规律为,驱动辊、芯辊与环件台阶高度的应变、环件的棱角区的应变要明显大于环件其他部位的应变,且越靠近这些部位的应变越大,反映出整个环件轧制过程中变形区由成形辊与环件接触面部位和棱角处向环件内部逐渐扩展;环件的高温区域越来越来窄,且向环件内部集中,环件内部的温度要远远高于驱动辊和芯辊与环件接触部位的温度;轧制力与轧制力矩的变化规律为先增大后保持在一定范围内波动,最后逐渐下降。     

驱动辊转速对铸态42CrMo钢环件热辗轧微观组织的影响规律

环形铸柸微观组织的演变规律及合理控制是环类零件铸辗复合成形新技术发展面临的主要瓶颈问题.驱动辊转速是影响铸坯材料再结晶行为及组织状态的关键因素之一.本文基于ABAQUS平台,建立了42CrMo铸坯环件热辗轧的宏微观有限元模型,模拟揭示了环形铸坯材料的动态再结晶行为,阐明了驱动辊转速对再结晶晶粒尺寸及其分布的影响规律与机制.结果表明:铸坯材料动态再结晶百分数在环件内、外层高而使晶粒细化,而在环件中间层低导致粗品;驱动辊转速增大,铸坯材料动态再结晶百分数增加,轧制环件的平均晶粒尺寸减小;驱动辊转速对平均晶粒尺寸分布的均匀性影响不大.     

环形毛坯冷辗扩微元体变形及受力分析

针对环件冷辗扩的现状和特点,研究了多芯辊辗扩的成形原理.对环件多芯辊辗扩进行了运动学及力学分析,对环形毛坯冷辗扩微元体进行了变形分析,对多芯辊辗扩环形毛坯厚度方向的变形规律及芯辊的移动值应满足的切向应变与径向应变的关系进行了分析,推导出了最小瞬时压下量等所需工艺参数的数学表达式.研究结果可作为设计环件多芯辊辗扩工艺的理论依据.     

芯辊进给方式对辗环成形的影响

芯辊进给速度是径轴向环形辗扩成形的重要工艺参数。本文根据热辗扩的成形特点,用锻造软件Forge对芯辊三种不同进给方式(恒定进给速度、恒定每转进给量、恒定外半径增长速度)时径轴向辗环过程进行了数值模拟,分析了三种不同的芯辊进给方式对辗环成形的影响。结果表明,芯辊以恒定外半径增长速度进给时,轧件温差为88.738℃,是三种进给方式中温差最大的。这不利于控制轧制过程中温度的稳定性。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。