淬火过程初应变项对淬火残余应力的影响

淬火过程是温度、组织和应力应变3方面交互作用的复杂过程。文章考虑了淬火过程中各项热物性参数、力学性能参数等随温度的变化情况,建立了温度、组织和应力的耦合分析结构图,自行开发了淬火过程有限元模拟软件,选择平面问题为研究对象,建立相应的有限元分析模型,分析和讨论了由温度引起的初应变、相变引起的初应变及相变塑性对淬火残余应力的影响。根据有限元分析的结果,得到了淬火过程各项初应变对淬火残余应力的影响规律。     

Modeling and Analysis of Deformation for Spiral Bevel Gear in Die Quenching Based on the Hardenability Variation

Spiral bevel gears are widely used to transmit energy between intersecting axes. The strength and fatigue life of the gears are improved by carburizing and quenching. A die quenching process is used to control the deformation of the gear. The deformation is determined by the variations in the hardenability for a certain die quenching process. The relationship between hardenability, phase transformation and deformation needs to be studied to minimize deformation during the adjustment of the die quenching process parameters. In this paper, material properties for 22CrMoH steel are determined by the results of Jominy tests, dilatometry experiments and static mechanical property tests. The material models were built based on testing results under the consideration of hardenability variation. An finite element analysis model was developed to couple the phase transformation and deformation history of the complete carburizing and die quenching process for the spiral bevel gears. The final microstructures in the gear were bainite for low hardenability steel and a mixture of bainite and ferrite for high hardenability steel. The largest buckling deformation at the gear bottom surface is 0.375 mm at the outer circle for the low hardenability gear and 0.091 mm at the inner circle for the high hardenability gear.     

Microstructural evolution and localized corrosion resistance of an aged superduplex stainless steel

The present investigation was undertaken to analyze the effects of isothermal ageing treatments, carried out between 700 and 900 °C for a variety of times up to two weeks and followed by water quenching, on the microstructure and on the localized corrosion resistance of a superduplex stainless steel, SAF 2507.The quantitative metallography coupled with X-ray diffraction techniques was adopted to follow the microstructural evolution, together with SEM microscopy.Electrochemical potentiodynamic tests, as cyclic polarization curves recorded in sodium chloride solutions, together with weight loss measurements were employed to evaluate the susceptibility of the aged specimens to pitting corrosion.The influence of the transformation of ferrite into secondary austenite and sigma phase and of other microstructural variations, as chromium nitrides precipitation, on the stability of the passive film is shown. The susceptibility of the aged alloy to pitting corrosion phenomena, is related to sigma phase precipitation in association to the secondary austenite formation, which lead to a noticeable Cr depletion at grain boundaries.     

分级淬火对高铬铸铁轧辊组织的影响

采用LINSEIS L78膨胀仪模拟了高铬铸铁轧辊的分级淬火冷却过程,采用膨胀法、光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)等方法研究了分级淬火温度对Ms点及室温组织和硬度的影响。结果表明,分级淬火对淬火冷却过程发生的相变影响不大;与直接淬火相比,分级淬火降低了Ms点,而且Ms点随分级淬火温度的降低而降低;当分级温度为560 ℃时,Ms点降低程度不大,淬火后硬度升高到62.1 HRC,而且经450~500 ℃回火后,硬度进一步升高到64.5 HRC。     

由“冷却模型”到“冷却工程”的演进

冷却方式决定热处理工艺的类型。淬火是金属热处理中具有标志性的核心技术,其中最关键的操作环节是冷却。通过冷却曲线分析提出了钢探头在有物态变化介质中冷却时的主、辅界面模型。分析了钢在奥氏体化后冷却转变的物理冶金学现象与工程实际所能提供的冷却环境之间的联系。概述了淬火介质与冷却技术的研究现状与发展动态,特别指出了新的冷却技术及其装备开发的重要性。总之,从单纯的冷却模型研究到冷却工程的实现将是一大跨越。     

相变对22CrMo钢淬火应力影响的数值模拟

利用有限元法和热弹塑性理论,结合马氏体相变动力学方程,对22CrMo钢圆柱体试样在淬火过程中的温度场、组织场和应力场进行数值模拟分析,重点模拟分析了试样表面和心部在淬火过程中应力的变化及马氏体相变对淬火应力的影响。模拟发现,相变对淬火应力影响比较明显。在一定条件下,在油中淬火,组织应力对淬火应力分布的影响要远大于热应力的影响,最终试样的淬火残余应力将以表层为拉应力而心部为压应力的组织应力形式存在。通过对残余应力的测量结果表明,计算结果与实测值相吻合。     

基于温差结晶法的盐浴等温淬火介质回收技术

为避免金属制件在淬火后淬火介质随废水直接排放造成硝盐的浪费及环境污染,利用温差结晶法对淬火介质进行结晶回收,采用三级水洗的方法对淬火后的工件进行清洗,并利用旋风除尘装置对淬火时的介质浮粉进行回收。结果表明,利用该技术可以最大限度地实现节水和淬火剂溶质的循环利用,使整个生产过程做到不排放废水、溶质得到90%以上回收,水的用量也减少到原来的近1/20。     

粘结相Co的切变机制及微观结构的研究

本文以工业纯钻粉、钴基合金、硬质合金作为研究对象,分别运用X射线衍射、金相、扫面电镜能谱、EBSD等分析技术,并结合晶体学的相关知识研究了钴的基本特性、微观结构及其切变机制。通过研磨工业纯钴粉,比较分析研磨前后X射线衍射分析结果,定性描述了钻粉的α-Co向ε-Co的转变过程;实验制备了不同固溶W含量的Co基合金,并对合金金相组织及相结构进行了分析;对淬火后的WC-10％Co硬质合金,研究了在不同回火温度、时间工艺参数条件下合金粘结相Co的微观组织结构变化规律及其主要影响因素;通过离子束抛光制样,运用背散射电子衍射（EBSD）技术研究了WC-20％Co硬质合金中的α-Co与ε-Co形貌特征及其分布状态。实验结果表明：α-Co结构的稳定性较差,α-Co向ε-Co的转变的相变驱动力仅几J/mol;固溶W含量对钴基合金中晶粒的孪晶组织有重要的影响,Co基合金中固溶的W含量越多其孪晶组织越少,且α-Co含量越多;硬质合金淬火后回火实验说明硬质合金粘结相Co的8马氏体相变过程既可在较高温度、短时间内形成变温马氏体ε-Co,也可在较低温度、长时间下形成恒温马氏体ε-Co,合金内部组织内应力的释放会引起α-Co向ε-Co的转变;EBSD分析发现硬质合金中粘结相大部分是以α-Co结构存在,ε-Co呈条带状,厚度在2μm以下,长度在6μm左右,主要分布在粘结相与WC相的界面处或较厚钴层的中间部位。文中重点论述了硬质合金ε-Co马氏体的基本特征及其切变机制。     

空心圆柱体GCr15钢淬火过程的计算机模拟

用有限元法研究了GCr1 5钢圆柱体在油淬过程中的温度、组织及应力变化。在实测了淬火油换热系数的基础上 ,对轴对称空心圆柱体淬火时的温度场和组织场进行了模拟。同时运用热弹塑性理论 ,对圆柱体内外表面点及中心点应力的演化过程进行了模拟。模拟结果表明 :圆柱体内表面的冷速小于外表面。在淬火初期 ,由于热应力的作用使工件表面受拉而心部受压 ,在发生应力反向前 ,发生了组织转变 ,并使表面应力迅速转向 ,在应力达到最低点后又逐渐回升 ,最后表面形成了拉应力。心部的应力变化正好相反 ,最终形成了组织应力型的内应力分布。     

Effect of quenching temperature on structure and properties of titanium alloy: Structure and phase composition

X-ray diffraction analysis and transmission and scanning electron microscopy have been used to study regularities of the formation of structure and phase composition of a VT16 alloy during its quenching. The formation of an athermal ω phase in the VT16 alloy with the initial (α + β) structure during quenching of the alloy from 800°C was found to be possible. Quenching temperatures (T _q) at which various metastable phase compositions, such as the metastable β solid solution, β + α″ + ω, β + α″, and α″ martensite, are formed have been determined to be 750, 800, 750–850, and ≤850°C, respectively. Dependences of variations in the volume fractions of phases were plotted. It has been shown that, at quenching temperatures close to the β-transus, the active growth of β-phase grains takes place at the expense of a decrease in the α-phase volume fraction.     

高压气淬过程的数值模拟

应用有限体积法建立了数学模型,对高压气淬过程中气体的速度场、气体和工件的温度场以及工件内部的组织场进行了耦合计算,针对一组小棒料高压气淬的模拟结果,分析了气体流动、工件温度与相变各自的影响因素以及它们之间的相互影响,指出几何模型准确建立的重要性.另外通过模拟结果与实测冷却曲线的比较,该模型基本反映了高压气淬过程,其中加入相变计算能更符合实际,并且还能预测出工件的最终组织.应用本文中的相变计算模型,相变的计算结果与工件金相照片中的实测结果基本吻合.     

Phase transformation of metastable beta Ti alloys with tweed structure

This paper presents the finding of a microstructural abnormality generated in the metastable phase of a supersaturated state, and compares the results with ordering behavior such as premartensitic transformation. A tweed structure consisting of the metastable phase was observed by transmission electron microscopy, and spot satellites inflicted by streaks were also observed in lattice diffraction. The present report also reviews a new phase transformation from the metastable phase caused by the processes of aging, sub-zero quenching, and induced strain or stress.     

三维点式感应淬火电磁热耦合场数值模拟

针对45钢三维点式感应淬火工艺进行参数设计,建立点式感应淬火过程的电磁场及温度场的非线性偏微分方程组,在有限元软件ANSYS中使用耦合场分析的方法实现了对加热功率为36 kW,电流频率为50 kHz的感应热处理工艺的数值模拟.结果表明,在综合考虑表面组织完全奥氏体化及感应加热效率的情况下,该工艺的最佳加热时间约为2 s.通过模拟分别得到使用冷却水和冷却油作为冷却介质时的感应淬火过程中的温度变化规律,结合45钢的连续冷却转变曲线,以马氏体转变临界冷却速度为判断依据,对淬火后工件表面组织进行预测,结果表明两种淬火条件均可以实现表面组织马氏体转变,实现工件的表面强化,且淬硬深度均约为1.0 mm.     

Nb元素对含Ti低碳微合金钢连续冷却转变及析出行为的影响

采用热模拟试验机研究了Nb元素对含Ti低碳微合金钢的动态连续冷却转变行为的影响,利用OM和TEM对等温淬火工艺处理后实验钢的显微组织和析出行为进行观察和分析。结果表明：Nb元素使得含Ti低碳微合金钢的动态CCT曲线整体向右下方移动,大大减小了先共析铁素体和珠光体相变区,同时扩大了针状铁素体和贝氏体相变区,在较低冷速时能得到较多的针状铁素体;含Nb- Ti和含Ti两种实验钢经等温淬火工艺处理后的显微组织均由铁素体和马氏体两相组成,铁素体相中析出物平均尺寸分别为6.8、4.2 nm,利用Orowan机制对析出强化量进行计算得出析出强化量分别为90.6、142.3 MPa。     

淬火后的逆相变退火温度对5%Mn冷轧中锰钢组织与性能的影响

对5%Mn冷轧中锰钢进行930 ℃×20 min淬火后再进行660、665、675、685 ℃保温30 min的逆相变退火处理,并用光学显微镜、扫描电镜、X射线衍射仪等研究退火温度对中锰钢组织和力学性能的影响。结果表明:5%Mn冷轧中锰钢经过高温淬火和逆相变退火后的组织为超细晶铁素体、板条马氏体和奥氏体。随着逆相变退火温度由660 ℃增加至685 ℃,奥氏体含量先增加后降低并在665 ℃逆相变退火后达到最大值,抗拉强度持续增加,屈服强度先升高后降低并在675 ℃退火时达到最大,伸长率先升高后降低并在665 ℃时达到最大值。综合来看,5%Mn中锰钢冷轧板经过930 ℃×20 min淬火和665 ℃×30 min逆相变退火后的综合力学性能最佳,此时奥氏体体积分数为24.24%,抗拉强度为980 MPa,伸长率为23.68%,强塑积达到了23.21GPa·%。     

Criteria for evaluating the cooling capacity of quenching media

Numerous criteria have been suggested for evaluating the cooling capacity of quenching media. Although the cooling capacity of a medium can hardly be evaluated by a single number, such data can be helpful in the initial stage of choosing the medium for quenching a specific part. Various criteria for evaluating the cooling capacity of polymer quenching media have been analyzed within the developed international standard based on ISO 9950 (for industrial quenchants). Those that can be calculated from results of tests of a medium by means of a Wolfson gauge, recommended by the ISO 9950 standard, have been chosen. The aim of the present work consists in determining the correlation between the criteria suggested by various researchers for various domestic and foreign quenching liquids on a polymer base. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 18–21, October, 1998.     

Phase transformations in the B2 phase of Co-rich Co-Al binary alloys

Phase transformations in the β (B2) phase of Co-21 and -23 at.% Al alloys were examined using transmission electron microscopy, energy dispersive X-ray spectroscopy and differential scanning calorimetry. The microstructures obtained from as-quenched specimens were found to be strongly affected by the quenching condition. While relatively thick sheet-specimens with a lower quenching rate showed bainitic plate precipitates with a fcc structure, a martensite-like structure was observed by optical microscopy in relatively thin specimens with a higher quenching rate. Regardless of the quenching condition, a spinodal-like microstructure composed of A2 and B2 phases was also detected and the A2 phase changed to a metastable hcp phase during further aging.     

基于ANSYS软件的T8钢淬火过程三维温度场的模拟

用有限元软件ANSYS模拟计算了T8钢圆柱体水淬过程中三维温度场的变化.计算时综合考虑了非线性的材料热物性参数、界面换热系数及相变潜热的影响.通过对计算硬度与实测淬火试样硬度分布的比较,表明模拟结果与实际情况较为符合.     

Optimization of Process Parameters for the Axial Distortion and Distortion Range During Die Quenching of a Spiral Bevel Gear

The strength of high-duty gears can be improved by carburizing and quenching processes. Quenching distortion is inevitable during the process, and it has direct effects on the precision of the gear. For spiral bevel gear with big diameter and small thickness, die quenching process is applied in the manufacturing to control the distortion in axial direction. Die quenching parameters must be optimized to minimize the distortion while considering non-uniformity of chemical compositions and loads. In this paper, material models of gear material (22CrMoH) built based on the phase transformation kinetics, static mechanical properties and phase transformation plasticity equations. Finite element analysis (FEA) models are conducted to study the whole die quenching process based on the production process. Die quenching experiments and testing of microstructures and distortions are conducted to verify the accuracy of the FEA models. The effects of loads and bottom die obliquity on the final distortion are studied to set the appropriate range and control distortion. The distortion was very sensitive to the bottom die obliquity and some part of load ranges. The distortion changes little when the load of inner die was in the range of 1.38-2.07 MPa and the load of outer die was in the range of 2.07-2.76 MPa. The distortion range is fitted the production requirements by setting the inclination angle of bottom die between 0.12° and 0.29°.     

温度和相变影响的弹塑性本构关系及应用

通过考虑温度和相变对等效物性参数的影响,建立了包含附加应力和应变的弹塑性增量本构关系,并采用该本构关系和ABAQUS软件构建了淬火过程的数值模拟平台.该本构模型引入的附加应力和应变分别由温度变化和相演化引起的.具有明确的物理意义.通过对26Cr2Ni4MoV钢的圆筒零件水淬过程的模拟表明,该模型能够正确地分析残余应力沿半径方向的分布规律.并且在截面中间部位残余应力值和靠近外表面的应力峰值与实测值更加接近,说明全面考虑温度和相变影响的弹塑性增量本构关系可改善模拟计算的精度.