Microstructure Evolution of Different Forging Processes for 12％Cr Steel During Hot Deformation

Five forging experiments were designed and conducted to investigate the effect of process parameters on microstructure evolution during hot deformation for X12CrMoWVNbN10-1-1 steel.The experimental results indicated that average grain size became finer with the increasing number of upsetting and stretching.Especially,the size of stretching three times with upsetting twice had the most remarkable effect on refinement,and the size was only 27.36%of the original one.Moreover,the stress model was integrated into the software and finite element models were established.Simulation results demonstrated that the strain at center point of workpiece was far larger than critical strain value in each process,so that dynamic recrystallization(DRX) occurred in each workpiece,which implied DRX could occur for several times with the increasing number of upsetting and stretching,and uniform finer microstructure would be obtained.However,the results also showed that higher temperature was an unfavorable factor for grain refinement,so the times of heating should be limited for workpiece,and as many forging processes as possible should be finished in once heating.     

Investigation on Zener-Hollomon Parameter in the Warm-Hot Deformation Behavior of CF53

The warm-hot deformation behavior of CF53 steel was studied with hot compression tests at temperature of 1 123 ~1 273 K and strain rate of 0.1~20 s -1 . The activation energy for warm-hot deformation is 274.816 kJ/mol. The influences of Zener-Hollomon parameter, strain and grain size imposing on the flow stress were analyzed in the temperature range of warm-hot forging. Based on the creep theory and mathematic theory of statistics, mathematical models of flow stress were obtained. The results provide a scientific basis for controlling microstructure of forging process through Zener-Hollomon parameter.     

Simulation and analysis of microstructure evolution of IN718 in rotary forgings by FEM

A numerical analysis was performed to study the in?uence of process parameters on the microstruc-ture evolution of IN718 alloy in rotary forging using the finite element method(FEM).For this purpose, a constitutive equation considering the effects of strain hardening and dynamic softening of IN718 alloy was built.The constitutive equation and microstructure models were implemented into the finite element code to investigate the microstructure evolution during rotary forging subject to large deformations.The simulations were carried out in the ratio of initial height to diameter range 0.2-0.8, the angle of the rocker 3°-7° and the relative feed per revolution range 0.01-0.1 r-1.The research results revealed the deformation mechanism and the correlation of process parameters with the grain size evolution of IN718 alloy during rotary forging.These provide evidence for the selection of rotary forging parameters.     

LZ50车轴钢中的混晶组织

对具有不同原始组织的三个炉号的LZ50车轴钢进行了不同工艺的热处理,用金相方法分析了晶粒度的变化规律,比较了钢中微量元素Al、Ti含量与晶粒度的关系,结果表明：具有混晶组织的LZ50车轴钢加热到Ac1~Ac3之间时晶粒细化,但超过Ac3温度后即出现混晶,且不同钢中混晶倾向与原始状态的相同;钢中微量元素Al、Ti含量越高,混晶倾向越严重;高温固溶、低温析出预备热处理可以改变晶粒长大倾向,消除混晶组织.在此基础上对LZ50车轴钢的混晶原因进行了讨论.     

大直径曲轴自由锻成形工艺探讨

曲轴是各种内燃机中不可缺少的关键部件,它的寿命常常代表该内燃机的使用寿命。单纯从成形的角度考虑,用铸造的方法生产曲轴毛坯是最容易不过的事情。但由于铸造是一个金属冶炼且在砂型中凝固的过程,难以避免会出现夹渣、气空、白点等铸造缺陷而无法满足性能要求。工业上多采用各种压力加工方法来生产曲轴毛坯。小型内燃机上使用的尺寸和重量不大的曲轴一般采用模锻来大批量生产,尺寸较大特别是很大尺寸的曲轴就必需用其它的压力加工方法了。这里仅对特大尺寸的曲轴的自由锻成形工艺进行一些探讨。     

稀土元素对精密铸钢裂纹形成的影响

设计了精密铸件裂纹敏感试样,通过在铸件成分中添加不同比例的稀土元素,探讨稀土元素对铸件产生裂纹倾向的影响.试验结果表明:合适的稀土添加量的增加,铸件裂纹率显著降低:金相组织分析表明,稀土元素添加能较好地细化晶粒,并有效改善夹杂物的数量、尺寸和分布,从而降低了铸钢的裂纹倾向.     

Computer simulation of microscopic stress distribution in complex microstructure using a phase field model

Microscopic stress distribution in a metallic material which has complex microstructure is simulated using a phase field model. The fundamental equations which take into account the coupling effects among phase transformation, temperature and stress/strain are used, while thermal effects are neglected to focus on the volumetric change due to phase transformation in this paper. A two-dimensional square region is considered, and the evolution of microscopic stress and the resultant residual stress distribution are calculated using the finite element method. As the phase transformation progresses and grains grow larger, stress is generated around the growing interface. When a grain collides with another one, specifically large stress is observed. Residual stress is finally distributed in the microstructure formed, and apparently large stresses are retained along the grain boundaries. Subsequently, dependency of the stress distribution on microstructure pattern is investigated. First, variously sized square grains are tested, and it reveals that the maximum stress tends to decrease as the grain size becomes smaller. Next, the shapes of the grains are varied. As a result, the stress distribution is remarkably affected, while the maximum stress value does not change so much. More complicated grain arrangement is finally tested with eight or nine grain models. Then, it is revealed as a common feature that large stress is generated along the grain boundaries and that the stress distribution is dependent on the grain arrangement.     

蠕变抗力恢复热处理对21/4Cr-1Mo钢焊接接头蠕变空洞形态及其分布的影响

本文用光镜(OLM)、扫描电镜(SEM)分析了一段已服役约210000h 的电厂再热蒸汽管道焊接接头蠕变空洞的分布形态;分析了两种恢复热处理工艺(亚临界温度热处理和正回火热处理)对蠕变空洞形态及其分布的影响.试验结果表明,两种恢复热处理工艺都能减少蠕变空洞的数量,改善蠕变空洞的形态及其分布,使蠕变空洞由原来不规则的形状变成球形,使原来主要分布在晶界处的蠕变空洞部分“迁移”到晶内,从而改善了晶界处的应力状态,提高了蠕变抗力.比较两种恢复热处理工艺对减少蠕变空洞的数量,以及对改善螭变空洞的形态及其分布的作用后发现,正回火工艺优于亚临界温度热处理工艺.     

Forging penetration efficiency of steel H13 stepped shaft radial forging with GFM forging machine

The numerical thermal mechanical simulation of radial forging process of steel H13 stepped shaft with GFM (Gesellschaft fur Fertigungstechnik und Maschinenbau) forging machine was carried out by three-dimensional finite element code DEFORM 3D. According to the effective plastic strain, the mean stress and the mean plastic strain distribution of the radial forging, the forging penetration efficiency (FPE) was studied throughout each operation. The results show that the effective plastic strain in the center of the forging is always greater than zero for the desirable larger axial drawing velocity. The mean stress in the center of the workpiece is proposed to describe hydrostatic pressure in this paper. There is compressive strain layer beneath the surface of the workpiece to be found, while there is tensile strain core in the center of the workpiece. These results could be a valuable reference for designing the similar forging operations.     

焊接修复对铁素体不锈钢焊接接头组织和性能的影响

通过拉伸、弯曲、冲击、硬度、金相组织分析等试验,对不同焊修次数T4003铁素体不锈钢焊接接头的组织和性能进行研究.试验结果表明:焊修一、二次对T4003铁素体不锈钢焊接接头的抗拉、弯曲和冲击性能均影响不大;不同焊修次数T4003铁素体不锈钢焊缝的显微组织为奥氏体+δ铁素体;熔合区的显微组织为铁素体+马氏体,晶粒粗大;母材的显微组织为块状铁素体,沿轧制方向成条状分布.焊接修复对T4003铁素体不锈钢焊接接头的粗晶区宽度、晶粒度与马氏体含量的影响不大.不同焊修次数T4003铁素体不锈钢焊接接头焊缝的显微硬度相近,母材显微硬度大致相同,热影响区显微硬度的变化不大.     

电液锤改造的难点与解决办法

换头节能改造是对模锻锤和空气锤进行改造的有效方法，可以取得显著的经济效益和社会效益。主要介绍了电液锤换头改造模锻锤和空气锤过程中遇到的突出问题及解决的办法。     

消失模液锻中气隙压力和气流速度的计算分析

通过计算分析了消失模液锻制备颗粒增强金属基复合材料中，附带的增强颗粒泡沫载体与金属液作用后产生的气隙压力和气流速度，然后在消失模液锻TiC／ZG270-500实验中测量气隙压力和气流速度值，并探讨液锻工艺参数对气隙压力和气流速度的影响规律．实验结果表明：气隙压力和气流速度随充型速度、浇注温度、内浇口与排气孔横截面积比呈递增趋势，但均不随成形压力变化．此外，气流速度还随排气孔与型腔横截面积比增大而增大，气流速度随工艺参数变化趋势较平缓．     

Computer Simulation of Thermal-Mechanical Processing

AlterationIntroductionThereisastrongini6ractionamongtemPetalrefield,strCssfield,andmicrosttuctutulaltOrationinm8terialsduringtheirhotworking[l'2].Especiallyduringthecoolingprocess,inwhichtemPeratorechangnsgreatly,intendionsbecomemorecomplexbecauseoftransformationoccurmnce.Duringthehotdeformation,thingswillaPpearsuchas:a.hotdeformation,relatedtostressfieId,changesessentiallytheshaPeofmaterialsandcausesthevariationofthecontactstatebetWeenthedieandsample,resultinginchangeofthethermalboundnyco…     

Dynamic recrystallization behavior and microstructural evolution in SPHC steel

The dynamic recrystallization(DRX) behaviors in SPHC steel were investigated with hot compression tests at deformation temperatures of 950-1 150,strain rates of 0.1-15 s-1,and initial austenite grain sizes of 86-232 μm.The effects of deformation temperature,strain,strain rate and the initial austenite grain size on the microstructural evolution during DRX were studied in detail.The results show that DRX is observed under the condition of the Zener-Hollomon parameter being less than 1.07×10 13 s-1.The deformation activation energy for SPHC steel is calculated to be 299.4 kJ/mol by regression analysis.Austenite grain size of DRX is refined with decreasing temperature and increasing strain rate under steady state conditions,but it is not influenced by the initial grain size.The mathematical equation of DRX grain size of SPHC steel is obtained.     

考虑初始空隙压密的岩石变形全过程本构模型

为了建立能够准确模拟岩石变形全过程的本构模型,深入分析了现有统计损伤模型难以描述岩石初始非线性变形阶段的局限性.综合考虑岩石的变形机理,将岩石抽象为由空隙和骨架组成的材料,分析了岩石变形及空隙与骨架两部分变形之间的关系,提出了空隙应变比K的概念;利用岩石三轴试验结果,提出了岩石骨架和空隙两部分应变的计算方法,推导了K的...     

Numerical analysis of unconventional forging process of hollowed shaft from Ti-6Al-4V alloy

This paper presents theoretical analysis of unconventional forging process of hollowed shaft from Ti-6Al-4V alloy in a three-slide forging press. This method in comparison with other metal forming methods allows for obtaining of hollowed products. The designed process is verified theoretically by means of numerical simulations based on finite element method with assumption of 3D state of strain. The following factors are considered in the analysis: material flow kinematics, strain distribution, temperature distribution and force of process. On the basis of results, it is stated that the application of designed technology allows for obtaining of a product of assumed quality. A comparison is made between material consumption in analyzed process and material consumption in typical metal forming methods, also in used at present technology of shaft manufacturing by machining only. It is stated that the application of forging in the three-slide forging press allows for a considerable decrease of manufacturing costs due to material savings and decrease of labor consumption of operations at finishing.     

钢衬里壁板预拉伸成形装备设计及分析

钢采用顶升模架对钢衬里预拉伸,顶升拉力使壁板的拉伸应力接近其屈服强度,同时对壁板外侧实施周向和轴向加劲角钢焊接,保持壁板的曲率半径不变.为确保成形质量,对预拉伸成形装备进行参数化建模,并利用Ansys有限元软件对顶升模架进行静力学分析.结果表明,预拉伸成形装备结构模型及其参数设置合理,为优化设计和钢衬里壁板的建造质量提供了数据保证.钢衬里预拉伸成形理念的提出和实施,打破了传统的制造工艺,为核岛钢衬里建造工艺的新突破.     

公路工程真空灌浆施工技术分析

在水泥混凝土路面工程中应用真空灌浆技术,能够有效预防脱空、裂缝以及接缝多等问题.对真空灌浆技术的原理进行介绍,并对该技术的具体工艺方法进行研究.     

稀土对5CrMnMo钢奥氏体晶粒度的影响

用电子探针分析了稀土在5crMnMo钢中的分布,研究了不同稀土含量对奥氏体晶粒度的影响,实施结果表明,稀土分布于奥氏体晶界,使5CrMnMo钢的奥氏体晶粒度显著细化。     

滚动方向对CL60车轮材料接触疲劳损伤的影响

为研究车轮滚动方向对车轮材料接触疲劳损伤的影响机制，利用WR-1滚动磨损试验机进行了车轮单向和双向运行滚滑磨损试验，使用光镜和扫描电镜分析了试验后车轮试样的表面磨损形貌、剖面疲劳裂纹形貌及磨屑尺寸，探究了换向运行工况下车轮表面损伤、裂纹扩展、磨屑尺寸随反向循环次数的演变规律. 研究结果表明:车轮表面损伤以起皮剥落为主，反向循环次数从1万次增加到12万次时，初始剥落逐渐消失，继而形成与原滚动方向相反的新剥落，相同循环次数下改变车轮滚动方向有利于减轻车轮材料疲劳损伤；车轮换向改变了表面微裂纹的扩展方向，形成4°～8° 的反向疲劳裂纹，并出现了裂纹扭曲和分支现象；单向滚动时，随循环次数增加，磨屑尺寸先增大后减小，反向后磨屑厚度先增大后减小，反向1万次时，磨屑厚度增大到10～12 μm，为单向时的两倍.