7075模锻件心部裂纹原因分析

7075模锻件横截面断口上有白色带状缺陷，表现形式为紊流状和小裂纹，这是心部强烈变形区组织薄弱点被拉断所致。产生裂纹与锻造温度不当和两次锻造变形量分配不合理有关。为了消除锻件心部裂纹，应控制好铸锭加热温度，合理分配两次锻造变形量。     

铌微合金钢形变诱导相变的上限温度

在Gleeble 1500热模拟实验机上进行单道次压缩实验,通过改变变形量以及变形后立即淬火的方法,研究了应变量对微合金钢形变诱导相变上限温度Ad3的影响.还通过不同温度的奥氏体化,研究了铌对微合金钢形变诱导相变上限温度Ad3的影响.结果表明,Ad3随应变量的增大而升高,并且当应变量较大时,Ad3趋于不变;铌对形变诱导相变有强烈的促进作用.     

锻造变形量对TC4-DT钛合金锻件组织与力学性能的影响

TC4-DT钛合金是一种高强高韧损伤容限型钛合金,常被用于新型飞机制造中,而变形量会对该合金的组织产生重要影响,并最终决定其力学性能。为此,本实验以300 mm×180 mm的TC4-DT钛合金棒材为原料,进行3种不同变形量的锻造变形,研究锻造变形量对锻件组织和力学性能的影响。结果表明:变形量太大或太小均会引起锻件内部显微组织不均匀,同时引起锻件不同部位力学性能存在较大的偏差,经综合分析确定TC4-DT钛合金合理的锻造变形量为35%左右。     

锻造对铝合金冶金缺陷的影响

通过锻造模拟实验，研究了锻造过程中的应力应变状态对铝合金飞机锻件中冶金缺陷的影响。结果表明，在挤压开坯中无法焊合的冶金缺陷，在锻造过程中将发生形状和尺寸的变化，当这些缺陷处于剪切变形区和附加拉应力作用区域内时，其当量尺寸将明显扩大。     

复合包套模锻新工艺研究

复合包套由金属套和隔热层组成，用复合包套模锻可获得理想的模锻温度，降低模锻时的变形抗力，细化锻件的晶粒，消除锻造裂纹，改善锻件性能，提高模具寿命等效果。本研究是应用复合包套模锻的方法，在３００ＭＮ水压机上成功地生产出需５００ＭＮ水压机才能生产的难变形合金的大型精密模锻件。     

大型扁平状锻件的变形方法探索

常规锻造大型碳素或低合金类模具钢扁平状锻件的方法是在进行拔长时采用上下平砧进行锻造变形。由于大型扁平状锻件的尺寸特征,上下平砧的锻造方法无法满足足够的砧宽比以减少塑性变形过程中钢锭内部出现拉应力的条件,因而在锻造过程中,其钢锭原有疏松、夹杂或晶界等的薄弱处容易形成新的裂纹源,最终造成超声波检验探伤报废的情况。为了克服大型碳素或低合金类模具钢扁平状锻件的锻造变形缺点,根据锻造理论及经验,对此类钢种大型扁平状锻件的变形方法进行探索,提出大型碳素或低合金类模具钢扁平状锻件的变形方法,可有效增加砧宽比,防止在锻件内产生形成裂纹的条件,最终大幅度提高大型扁平状锻件的探伤合格率。     

20MnMo管板件锻造缺陷分析及工艺改进

管板件产量在我厂锻件总量中占有很大的比例,但该产品内部质量极不稳定,探伤废品量大,经济损失惊人.改善20MnMo管板件的内部质量,提高产品合格率的重要性就不言而喻.通过分析认为缺陷属于塑性夹杂性裂纹,根据缺陷形成原因,结合现有设备能力及工蓑的情况,提出了一个适合本厂的锻造工艺方法.经过生产实践证明通过此锻造方法来进行改进锻造工艺、优化工艺参数对改善20MnMo管板件内部质量是切实可行的.     

V-5Cr-5Ti合金热压缩模拟实验分析

在Gleeble1500热模拟材料试验机上对铸态V-5Cr-5Ti合金进行恒定应变速率热压缩模拟实验。研究了在1100～1250℃温度范围、应变速率为10.s-1和应变量分别为20%,30%,40%和50%条件下,铸态合金热压缩过程中的变形规律和热压缩后宏观形貌与组织的变化。通过分析不同压缩工艺条件下合金的应力-应变曲线和热压缩变形后的宏观形貌与微观组织,确定V-5Cr-5Ti合金的热压缩变形温度和变形量,进而制定出合金合理的锻造工艺,并通过生产实践验证了该锻造工艺。结果表明:V-5Cr-5Ti合金热锻造温度在1150～1250℃范围内,变形量控制在30%以内,可以得到性能满足需要的合金材料。     

高温变形对含钼钢显微组织的影响

 为了寻求变形温度、变形量对含钼钢显微组织、先共析铁素体量及其晶粒度的影响规律，利用Gleeble 1500热模拟实验机、光学显微镜、XL 30扫描电镜和IA32图像分析仪，分析了不同变形量、不同变形温度下含钼钢的组织。结果表明：在一定条件下，随着变形量的增加，显微组织由铁素体+贝氏体转变为铁素体+贝氏体+珠光体；同时先共析铁素体含量及其晶粒度级别均呈现出提高的趋势。     

影响大锻件内部孔隙性缺陷扩散焊合的因素

 针对大型锻件内部孔隙性缺陷的扩散焊合物理过程及其焊合机理，建立了孔隙性缺陷扩散焊合的物理模拟模型，在Gleeble 3500热模拟机上对影响焊合质量的压力、温度和保温时间等因素进行了研究。分析了焊合界面剪应力对孔隙性缺陷修复过程的作用机理，首次建立了考虑剪应力作用的扩散焊合模型，为研究宏观剪切变形工艺对内部孔隙性缺陷的修复过程奠定了基础。     

Crack Healing in a Low-Carbon Steel Under Hot Plastic Deformation

The behavior of internal crack healing in low-carbon steel samples undergoing hot plastic deformation was investigated using the MMS 200 thermo-mechanical simulator. The characterization of cracks after plastic deformation was analyzed using scanning electron microscopy under different heating temperatures, reduction ratios, numbers of deformation passes, strain rates, and holding time durations. It was found that the degree of crack healing increases with increasing heating temperature, reduction ratio, and holding time duration, and with decreasing number of deformation passes and strain rate.     

FEM Analysis of Void Closure Behaviour during Open Die Forging of Rectangular Billets

Finite element analysis of open die forging to make rectangular billets has been performed in this study. Three‐dimensional rigid‐plastic finite element method (FEM) was used to analyse the effects of process variables, forging pass design and die configurations on the void closure phenomena. The major objective was to control the internal deformation for better structural homogeneity and centreline consolidation of the rectangular billet. The effect of die width ratio, die feed rate, die shape, and number of passes on the void closure ratio has been examined. Although it is difficult to optimize process parameters in industrial environments, favourable process conditions are recommended to achieve better product quality.     

影响TC4合金大规格锻棒表面质量和力学性能因素分析及工艺改进

针对TC4合金大规格锻棒生产表面出现大量裂纹,且力学性能不能达到国标要求的问题,分析了影响锻棒表面质量和力学性能的主要因素,提出了通过制定合理的加热工艺并尽量采用电加热炉加热、控制合金的终锻温度≥780℃及控制合金初锻单边压下量≤25 mm来提高棒材的表面质量;通过控制合金的配料为Al 6.4％左右、V4.2％左右、00.1％左右,方坯加热温度在相变点以下10℃至相变点以上5℃,方坯到棒材的变形量在30％以上来改善锻棒的力学性能.采取这些措施后,生产出的大规格TC4合金锻棒表面质量得到了较大改善,且力学性能可达到国标要求.     

Effect of deformation conditions on the transformation of micro-alloyed medium-carbon forging steels

The CCT diagrams of three medium-carbon steels without and with microalloying by vanadium and titanium were constructed by applying direct cooling of as-deformed austenite. Deformation parameters corresponding to those of industrial forging were varied with a laboratory simulation technique by using the plane strain hot compression test. The effect of microalloying, deformation, and deformation temperature on the amount of structural substituents was quantified. For practical application of the study the as-forged controlled cooling conditions were determined to achieve the desired bainite-free ferritic-pearlitic microstructure with beneficial mechanical properties.     

The occurrence of shear bands in nonisothermal,hot forging of Ti-6AI-2Sn-4Zr-2Mo-0.1Si

The occurrence of shear bands in nonisothermal, hot forging of Ti-6Al-2Sn-4Zr-2Mo-0. ISi (Ti-6242) was investigated in order to establish the material properties and process parameters which generally lead to shear bands and shear cracks in conventional hot forging of metals. Upset compression tests on cylindrical samples and lateral sidepressing tests on long, round bars were performed to determine the modes by which flow localizes in deformation states ranging from axisymmetric to plane strain. In axisymmetric deformation, it was found that nonisothermal, hot compression leads to chill zones and bands of intense deformation separating the chill zones from the deforming bulk. For plane strain deformation, shear bands were found to initiate along zero extension directions and subsequently localize flow in a manner analogous to the formation and propagation of shear bands in isothermal, hot forging. For both deformation states, it was found that material properties, such as the flow stress dependence on temperature, and process parameters, such as forging speed and die temperature which strongly influence the amount of heat transfer, play critical roles in the flow localization process. A simple model quantifying these effects was developed to predict the occurrence and severity of the shear bands observed in the Ti-6242 alloy hot forged at various temperatures and rates. In addition, the occurrence of shear cracking under certain forging conditions was rationalized in terms of the chilling brought about by nonisothermal, hot forging conditions and the inferior workability of Ti-6242 at temperatures far below the transus temperature.     

Healing Behavior of Micropores in Powder Metallurgy 316L Stainless Steel during Hot Forging and Heat Treatment

The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a re- sult of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense mate rials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelera- ting the reerystallization according to the difference of deformation temperatures.     

Gatorized Waspaloy 合金等温锻造过程中的本构方程

详细分析了应变、应变速率、变形温度等变形工艺参数对GatorizedWaspaloy合金低应变速率镦饼中应力-应变曲线的影响。建立了反映该变形过程金属流动规律的本构方程。实现了对该变形过程的数值模拟。     

Influence of Controlled Rolling and Cooling Process on the Mechanical Properties of Low Carbon Cold Forging Steel

In the present paper,controlled rolling and cooling processing was conducted by using a laboratory hot rolling mill.The influence of different processing parameters on the mechanical properties of low carbon cold forging steel was investigated.The results show that the faster cooling after the deformation (especially in low temperature rolling conditions) leads to the refinement of the ferrite grain.The specimen exhibits very good mechanical properties owing to the finer ferrite grains.The pearlite morphologies can also affect the mechanical properties of low carbon cold forging steel.The mechanical properties increase with decreasing final cooling temperature within the range from 650℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony.The mechanical properties of the specimens with fast cooling after the conventional rolling are not only better than those of the specimens with slow cooling after low temperature rolling,but also almost similar to those of the specimens with fast cooling after low temperature rolling.It is suggested that fast cooling after high temperature rolling (the conventional rolling) process would be of important industrial value.     

大型船用曲轴曲拐弯锻过程的计算机模拟与工艺优化研究

采用计算机模拟和试验手段研究了传统工艺曲拐弯锻的过程,指出了传统工艺的不足和锻造过程容易出现的各种典型缺陷。采用逆推法确定了改进工艺后预成形毛坯形状,优化了毛坯的形状因子,有针对性地提出了解决各种缺陷的措施。在此基础上对改进的工艺进行了计算机模拟,模拟结果表明,改进后的工艺能够消除喇叭口、裂纹、“细腰”、减薄等缺陷;毛坯变形抗力为传统工艺的72％;毛坯截面积减小,可节省原材料约15％。最后对改进的工艺进行了试验,得到了合格的曲拐毛坯锻件,验证了模拟的准确性。所建立的模型和研究方法为进一步优化锻压工艺和今后开发其它型号的大型曲轴曲拐产品提供理论指导和技术保障。     

TiAl基合金方坯可锻性数值模拟

利用有限元模拟软件Deform-3D对TiAl基合金方坯高温锻造过程进行数值模拟。分析坯料的不同圆角半径R和不同高宽比值H/a等参数对等效应变和变形均匀性系数的影响。结果表明,随R增大,方坯变形均匀性系数降低,变形更加均匀;随着H/a值增大,等效应力减小,变形均匀性系数增大,且当H/a≥2.1时,锻坯呈现双鼓形。实际锻造实验结果显示,通过选取合适的坯料圆角R和H/a值,能够得到表面光滑、组织均匀的锻坯。