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锻造过程中钢锭内部孔洞型缺陷闭合规律研究 总被引:5,自引:0,他引:5
对可能影响锻造过程中大型钢锭内部孔洞型缺陷闭合的各种因素进行了系统研究.结果表明,变形温度、应变速率、摩擦系数、试样尺寸和孔洞尺寸对锻造过程中孔洞的闭合基本没有影响,而试样高径比、孔洞位置和孔洞形状对孔洞的闭合有较大影响.其中试样高径比和孔洞位置通过影响孔洞周围的应变条件来影响孔洞闭合,是间接因素.孔洞所在位置的应变越大,孔洞越容易闭合.孔洞形状是影响孔洞闭合的直接因素,也是最本质的因素.为了描述这种现象,提出了孔洞高径比的概念.模拟结果显示,沿变形方向孔洞的高径比越大,孔洞越难闭合.基于以上研究和大钢锭的实际解剖结果,提出了全新的宽砧径向压实工艺(WRF法).该工艺可使应变集中于钢锭中心区域,并满足孔洞闭合所需的最佳高径比条件,因此,可高效愈合钢锭的中心缩孔、疏松.工业实验验证了该工艺的有效性和实用性. 相似文献
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根据压力容器整体顶盖的终成形工艺,设置不同位置、不同尺寸的孔洞缺陷,采用Super Form模拟软件分析拉胀成形过程中孔洞的变形行为,确定了顶盖终成形前毛坯内部孔洞体积、尺寸变化最大的位置及终成形前毛坯内部孔洞所允许的最大体积和尺寸。同时对原始205 t钢锭中的孔洞闭合进行了解析计算,制定了合理的预锻工艺。 相似文献
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本文运用高温密栅云纹法试验模拟技术,结合常温密栅云纹法模拟技术和临界压合技术,系统地研究了中心压实法(JTS)锻造时锻件内部应力、应变分布及变化规律和锻合锻件内部孔洞性缺陷的作用、机理,给出了工艺参数的影响和合理选择范围.用铸态轧辊材料为试件,研究了该工艺对锻件内部组织和机械性能的影响. 相似文献
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本文是作者一篇论文的详细摘要。作者对锻件内部孔洞消除机制作了实验研究,对锻造过程孔洞压合和应变分布用塑性有限元法进行数值模拟,并对锻造坯料内部应变分布作了试验量测。研究结果表明:大锻件内部孔洞的锻合过程由变形、压合、焊合三个阶段组成,孔洞只有在高温下才能焊合;孔洞闭合度λ与最大压应变ε_1呈线性关系,孔洞的几何因素和工具接触表面摩擦不改变这种规律,但可使应变向坯料心部集中,有利于闭合心部孔洞;用平砧拔长时,砧宽比应取0. 51以上,而用FM 法时,砧宽比应大于0. 4。作者建议制定大钢锭锻造工艺时,要注意:1) 尽量使最大压应变ε_1的方向同内部孔洞的短轴相一致;2) 拔长时应使用合理的砧宽比;3) 压合内部孔洞要在较高温度下进行。 相似文献
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25Cr2Ni4MoV钢锻造过程孔洞缺陷愈合规律研究 总被引:1,自引:0,他引:1
实测了核电转子用25Cr2Ni4MoV钢的高温应力应变曲线和热物性参数,基于ABAQUS软件建立了锻造过程孔洞闭合的有限元模型,模拟了不同温度和变形量下的孔洞闭合行为.研究发现,典型的孔洞闭合过程分为3个阶段,即闭合速率减小-增加-再次减小.模拟结果表明,900—1200℃时孔洞几乎在同一压下率(约25%)下闭合,即孔洞闭合对变形温度不敏感.在模拟结果的基础上,进一步设计了孔洞闭合后焊合过程的物理模拟实验,研究了恒应变速率(0.01s~(-1))下压下率(25%-45%)和变形温度(900-1200℃)对闭合孔洞焊合过程的影响.焊合界面的拉伸实验结果表明,较高的温度和闭合后持续的塑性变形能极大地促进闭合界面的焊合,当变形温度大于1000℃,压下率为35%时,闭合界面结合强度可达基体强度,孔洞实现完全焊合;当温度降至900℃时,孔洞需45%的压下率才能完全焊合.最后,基于拉伸断口的形貌,对影响孔洞焊合的因素进行了讨论. 相似文献
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Internal void closure during the forging of large cast ingots using a simulation approach 总被引:1,自引:0,他引:1
Y.S. LeeS.U. Lee C.J. Van TyneB.D. Joo Y.H. Moon 《Journal of Materials Processing Technology》2011,211(6):1136-1145
Large cast ingots often contain defects or undesirable microstructural features, such as voids and zones related to casting. Some of these features can remain after hot open die forging, which is an important process for converting large cast ingots into wrought components. During the initial cogging and deformation steps prior to the detailed open-die-forging operations, any internal voids should be eliminated. The present work focuses on the closure of internal voids during open die forging so as to produce a sound component. Hot compression tests were conducted to obtain the flow strength of the cast microstructure at different temperatures and strain rates. The measured flow strength data together with other appropriate material properties were used to simulate the forging steps for a large cast ingot. The numerical simulations for the forging deformation and for the internal void behavior were performed using DEFORM-3D™. Actual defects were measured in commercial ingots with an X-ray scanner. The simulation results for the void deformation behavior are compared with voids measured before and after forging. Through the comparison of experimental results and numerical simulation, a criterion for void closure is proposed. The criterion is that a local effective strain value of 0.6 or greater must be achieved for void closure during forging. Such a criterion can be used in conjunction with simulations to insure that a sound component is produced during the hot open die forging of large cast ingots. 相似文献
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Xiao-Xun Zhang Zhen-Shan Cui Wen Chen Yan Li 《Journal of Materials Processing Technology》2009,209(4):1950-1959
A quantitative investigation of the mesomechanism of void closure in large ingots during hot forging is undertaken in the present study. The constitutive relation of the void-free matrix is assumed to obey the Norton power law. A cell model which includes matrix and void is employed and a Ritz procedure is developed to study the volumetric strain-rate of the void. On the basis of a large number of numerical computations, a criterion for void closure in large ingots during hot forging is proposed. In addition, the significant effects of the Norton exponent, the remote stress triaxiality and the remote effective strain on void closure are revealed: (1) the volumetric strain-rate of the void increases monotonically as the stress triaxiality level and the Norton exponent of the material increase, (2) the remote effective strain required for void closure decreases as the stress triaxiality level and the Norton exponent increase and (3) the void becomes unstable and the collapse rate decreases at the final stages of void closure. With the criterion for void closure, process design and optimization in terms of elimination of voids in large ingots will be convenient since the criterion can be easily applied in CAE analysis. 相似文献
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Jong-Jin Park 《Metals and Materials International》2013,19(2):259-265
Closure of a spherical voids in a steel slab under plane-strain deformation was investigated using the rigidplastic finite-element method. Variations in the major and minor axes of a void from finite element analysis of a void model were related to the minimum principal strain and hydrostatic stress from finite element analysis of a non-void model. The correlation curves were obtained and a method using these curves to predict the void closure progress was proposed. The method was successfully applied to deformation processes such as simple compression, forging and rolling. Since hydrostatic stress also influenced void closure, the effective strain by itself was not sufficiently capable of predicting void closure. However, the effective strain was used to predict void closure for a specific process because it reached about 0.7 in compression or forging and about 0.78 during rolling as the void completely closed. 相似文献
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Hideki Kakimoto Takefumi Arikawa Yoichi Takahashi Tatsuya Tanaka Yutaka Imaida 《Journal of Materials Processing Technology》2010,210(3):415-422
In this study, the closing behavior of internal voids was examined by a deformation analysis involving the 2-D finite element method (FEM), which simulates voids in steel ingots in the compression process (upset process). In the compression process, a model experiment that uses internal voids was carried out to confirm the accuracy of the deformation analysis. By comparing the model experiment with the analytical results, it was confirmed to simulate the internal void behavior by this analysis. The relationship between the reduction ratio and the void shape/void position was investigated by the analysis. In the forging process, the closing evaluation value of internal voids (Q value) was calculated by a model experiment and 3-D FEM. Using the analysis results, a limit value of the closing behavior of voids was quantified, and it is now understood that the voids close at more than Q = 0.21. In addition, the forging process of filling the above-mentioned value was designed by the Taguchi method. The predicted Q value in the case of using the Taguchi method almost corresponds to the value calculated by the deformation analysis. It was clarified that the process is capable of being designed simply. 相似文献
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通过对CoCrMoW合金电渣锭在两种不同的保温制度下保温后进行两种不同的锻造变形方式开坯锻造,研究了CoCrMoW电渣锭锻造保温温度及锻造变形方式对可锻性的影响。试验研究结果表明:CoCrMoW合金电渣锭在1220℃保温1 h后采用整体锻造,锻件的表面质量与内部质量良好;1200℃保温2 h后,采用整体锻造,锻件的表面质量良好,但是内部有缺陷产生;CoCrMoW合金电渣锭在1220℃保温1 h后锻造变形,电渣锭采用分段锻造时表面出现开裂,采用整体锻造时表面质量与内部质量良好;经过开坯后的小规格坯料再继续开坯或锻成品时,分段锻造与整体锻造均可采用。该合金合理的锻造保温温度为1220~1240℃,电渣锭锻造变形方式必须采用整体锻造;小规格锻造方坯变形方式宜采用整体锻造,但也可采用分段锻造。 相似文献
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7A52合金铸锭粗大化合物研究 总被引:1,自引:0,他引:1
以7A52合金生产过程中出现的铸造供流漏斗底结物、铸锭粗大化合物、锻件偏析、板材点条状缺陷为研究对象,采用化学成分分析、显微组织观察、显微硬度测试、X射线衍射、扫描电镜及能谱分析、热分析等手段,揭示了合金锻件偏析、板材点条状缺陷与铸锭中粗大化合物之间的联系.研究表明,粗大化合物是由Mn、Cr、Ti等元素偏聚形成的MnAl6、CrAl7、TiAl3等组成的混合组织.液穴温度、中间合金及原料、熔炼工艺等是形成粗大化合物的主要影响因素.提出了Mn、Cr、Ti按标准下限控制、延长熔炼时间、适当提高熔体温度、废料预处理重熔及减小中间合金化合物尺寸等措施,经西南铝业集团公司熔铸厂实践证明,避免了7A52圆铸锭中产生粗大化合物. 相似文献
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Void closure studies have been conducted numerically and experimentally for open-die forging processes. The plane-strain FEM analysis was compared with bite forging experiments in order to determine how well the plane-strain approximation predicted the material flow in open-die forging. In addition physical modeling with plasticine was used to compare the measured and calculated deformation of the internal defect. The FEM analysis was in good agreement with the experimental results. Correlations for the computed effective strain and hydrostatic stress to the void closure were then calculated. Simulations of a solid cylinder side pressed with flat dies, V-shaped dies, and FML dies were done to determine the effectiveness of these dies at consolidating internal porosity based on the calculated strain and hydrostatic stress at the center of the billet. The V-shaped dies were found to be the most effective among those investigated. However, the press load for the V-shaped dies was also the highest. 相似文献
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1INTRODUCTIONNew alloys have been developed for variousdemands[1].Advanced titanium alloy with highstrength and toughness is one of the i mportant de-velopment directions in the related area[2].TC21titaniumalloy is a new(α+β)high strength andtoughness alloy that belongs to Ti-Al-Sn-Zr-Mo-Cr-Nb-Si system.This alloy was patented inChina[3],and quite promising for the structuralparts of advanced aircraft.Several papers describedits characteristics recently[46].Though forgingtechniques… 相似文献