奥氏体不锈钢热变形晶粒演变规律

对初始晶粒度为6.5级的321奥氏体不锈钢进行不同温度及保温时间的热处理试验,利用金相显微镜观察并统计材料内部的晶粒演变趋势,建立材料的晶粒长大模型。利用Gleeble-3500热模拟实验机对321奥氏体不锈钢在不同变形温度和应变速率条件下进行等温热压缩实验,通过分析应力-应变曲线及再结晶晶粒尺寸建立材料的动态再结晶模型。再利用所建立的模型对实际生产锻件进行模拟,得出合理的锻造工艺。经检测,不锈钢锻件取样位置晶粒度为7级,与模拟结果一致,表明所建立微观组织模型能够准确预测321奥氏体不锈钢锻件实际生产过程中的晶粒演变过程。     

F45MnVS非调质钢动态再结晶模型与晶粒尺寸数值模拟

在变形温度950～1050℃、应变速率0.01～5 s-1下对F45MnVS非调质钢进行不同变形量(5％～56％)的单道次压缩试验,研究了变形温度、应变速率和变形量对该钢变形行为和晶粒尺寸的影响;基于试验数据建立动态再结晶临界应变模型和平均晶粒尺寸模型,嵌入Deform软件中模拟了试验钢的动态再结晶平均晶粒尺寸.结果表明:随着变形量或应变速率的增大,或者变形温度的降低,试验钢的平均晶粒尺寸减小;较高应变速率下加工软化导致的应力下降不明显,动态再结晶程度较小,较低应变速率下则相反;模拟得到的再结晶平均晶粒尺寸与试验结果较吻合,且平均晶粒尺寸随变形温度、应变速率和变形量的变化规律与试验结果相符.     

大型环形件用2219铝合金的动态再结晶行为

选用Gleeble-3500型热模拟试验机在变形温度330～450℃、应变速率10-2～10 s-1、压缩变形量60％条件下对2219铝合金进行热压缩试验,研究了其在热变形过程中的动态再结晶行为;通过对试验数据进行分析拟合,建立了以Z参数表示的热变形特征参数模型,基于改进Avrami方程的动态再结晶动力学模型以及以变形温度、应变速率表示的再结晶晶粒尺寸模型.结果表明:在低应变速率和高变形温度下,2219铝合金更易于发生动态再结晶;根据动态再结晶动力学模型,最佳热加工条件为应变速率0.1 s-1、温度360℃,此时2219铝合金的动态再结晶程度最高;动态再结晶晶粒尺寸模型预测精度较高,线性相关系数达0.95.     

18CrNiMo7-6齿轮钢的热压缩变形行为及显微组织演变

采用热模拟方法研究了18CrNiMo7-6齿轮钢在变形温度900～1 150℃、应变速率0.01～5 s^-1条件下的热压缩变形行为;建立了基于Arrhenius模型的全应变本构方程,采用该方程对流变应力曲线进行预测;根据动态材料模型绘制热加工图,并结合热加工图系统地研究显微组织演变特征。结果表明：试验钢的峰值应力随应变速率的增加或变形温度的降低而增大,动态回复和动态再结晶是热变形过程中的主要软化机制;采用建立的全应变本构方程预测得到流变应力曲线与试验结果基本吻合,预测真应力与试验结果的相对误差小于4.715%,说明该模型可以精确地模拟18CrNiMo7-6齿轮钢的热压缩变形行为。试验钢的适合热加工工艺参数为变形温度1 050～1 150℃、应变速率0.1～1 s^-1,此时组织为均匀细小的再结晶晶粒,晶粒尺寸在5～15μm。随着变形温度的升高或应变速率的降低,原始奥氏体晶粒不断被动态再结晶晶粒取代,且动态再结晶程度和再结晶晶粒尺寸增大。     

新型优质GH738合金热变形过程动态再结晶模型的建立

采用MTS810-25T低周疲劳试验机对新型优质GH738合金进行热压缩试验,分析该合金在不同初始晶粒尺寸(42～340μm)、变形温度(1 020～1 100℃)、应变速率(0.01～1 s-1)和应变量(0.15～0.70)条件下的动态再结晶(Dynamic recrystallization,DRX)组织演化规律,并利用Avrami方程构建了该合金的动态再结晶模型,进而结合DEFORM软件及热压缩试验进行验证。结果表明,随着初始晶粒尺寸的减小,应变速率的降低,变形温度升高,应变量增加,动态再结晶的体积分数增加;有限元结果及验证试验均表明,建立的新型优质GH738合金的动态再结晶临界应变模型、体积分数模型以及晶粒尺寸模型,具有良好的预测精度。     

热轧A36钢静态再结晶动力学模型

为了模拟A36钢轧制过程的微观结构演变,在Gleeble 1500热模拟试验机上进行了双道次热压缩实验。通过在不同变形工艺下的软化行为研究,建立了A36钢在轧制情况下的静态再结晶动力学模型。该模型综合考虑了不同变形温度、应变率、应变及初始奥氏体晶粒尺寸等参数对静态再结晶行为的影响,仿真结果和实验结果比较吻合。     

不同条件高温压缩变形后35CrMo钢的显微组织

采用Gleeble-3810型热模拟试验机在变形温度为8501 150℃、应变速率为0.01{50 s~(-1)的条件下对35CrMo钢铸坯进行了变形量为60%的热压缩变形试验,结合真应力-真应变曲线特征,研究了应变速率和变形温度对其压缩后显微组织的影响。结果表明:在不同条件下压缩变形后,试验钢的显微组织均具有动态再结晶特征;同一应变速率下,随着变形温度的升高,压缩后的动态再结晶晶粒逐渐变大;同一变形温度下,随应变速率的增大,动态再结晶晶粒逐渐变小;热压缩变形后,试验钢不同位置处的晶粒尺寸不同,中心区域大变形区的晶粒最为细小,随着距中心区域垂直距离和水平距离的增大,晶粒尺寸逐渐变大。     

高铁螺纹道钉用TD16钢的动态再结晶行为

在变形温度为850~1 150℃、应变速率为0.01~10s-1下,利用Gleeble-3500型热模拟试验机对高铁螺纹道钉用TD16钢进行了高温压缩试验,研究了其动态再结晶行为,建立了动态再结晶模型并进行了试验验证。结果表明:TD16钢在试验条件下变形过程中存在动态再结晶行为,温度越低、应变速率越大,动态再结晶越不容易发生,动态再结晶晶粒越细;由动态再结晶模型预测得到的峰值应变/临界应变,ε0.5,晶粒尺寸与试验值的最大相对误差分别为7.08%,11.06%,21.3%,均吻合较好,建立的动态再结晶模型可用于预测TD16钢的动态再结晶行为。     

不同变形量下20CrNi2Mo钢的热压缩变形行为

在相变仪上对20CrNi2Mo钢进行热模拟压缩试验,研究了其在840℃时不同变形量(0~50%)下的热压缩变形行为,并分析了它的显微组织和硬度。结果表明:20CrNi2Mo钢流变应力曲线呈现出明显的动态再结晶特征;当变形量达到10%时,会发生动态再结晶;随着变形量增加,晶粒逐渐细化,之后尺寸基本保持稳定,当变形量达到50%时,进入完全再结晶状态;随着变形量逐渐增大,马氏体板条束逐渐细化,残余奥氏体含量降低;当变形量由10%增至20%时,硬度显著增大,而后趋于稳定。     

40CrNiMo钢的热变形特征及变形抗力模型

采用Gleeble-3500型热模拟试验机对40CrNiMo钢进行了单道次热压缩试验,得到了其在应变速率0.1~50s~(-1)、变形温度800~1 100℃下的应力-应变曲线,观察了变形后的显微组织并分析了热变形特征;建立了该钢的变形抗力模型并进行了试验验证。结果表明:较高的变形温度或较低的应变速率更有利于40CrNiMo钢的完全动态再结晶;变形温度为800℃时,应变速率增大使动态再结晶晶粒增多;应变速率为10s~(-1)条件下,当变形温度由800℃升至900℃时,动态再结晶晶粒增多,变形温度为1 000℃时,40CrNiMo钢发生了完全动态再结晶,变形温度为1 100℃时,动态再结晶晶粒长大;计算得到40CrNiMo钢的动态再结晶激活能为322.53kJ·mol~(-1);由周纪华-管克智模型计算得到的变形抗力与试验值的平均相对误差为4.82%,模拟精度较高。     

Numerical modeling of dynamic recrystallization during nonisothermal hot compression by cellular automata and finite element analysis

In this study, dynamic recrystallization during nonisothermal hot compression was numerically simulated by cellular automata and finite element analysis. A modified cellular automata model was developed by introducing a new parameter for considering solute drag effect. The isothermal hot compression tests of pure copper were carried out to verify the modified cellular automata model by comparing material behavior and average grain size. The effect of solute drag was numerically considered and compared to the experimental data and the numerical data obtained by conventional cellular automata without solute drag effect. Then, the modified cellular automata model was applied to a nonisothermal hot compression by combining with a finite element analysis. The finite element analysis was conducted to acquire local parameters such as strain, strain rate, and temperature. These values were provided to the cellular automata model as input. The local changes of microstructure and average grain size were simulated by cellular automata and compared with nonisothermal hot compression results. The simulation results were in reasonably good agreement with experimentally determined microstructures by electron backscattering diffraction. The developed model was further applied to simulate a hot gear blank forging process to check its applicability. With the current approach, local microstructures can be determined for better understanding microstructural changes during the nonisothermal process.     

GCr15钢奥氏体晶粒长大的有限元模拟

用Gleeble-3800型热模拟试验机研究了不同加热温度和保温时间对GCr15钢奥氏体晶粒的长大影响,得到了描述GCr15钢奥氏体晶粒长大规律的数学模型;并将该模型写入Marc的子程序,利用大型商业有限元软件Marc模拟了加热保温过程中GCr15钢奥氏体晶粒的长大过程。结果表明:晶粒长大的模拟结果与试验结果基本吻合。     

A microstructure evolution model for numerical prediction of austenite grain size distribution

In this study, a mathematical model has been developed to predict austenite grain size (AGS) of hot rolled steel. Using the compression test, the static (SRX) and metadynamic (MDRX) recrystallization characteristics of medium carbon steel were studied. Compression tests were carried out at various temperatures in the range 900-1100 °C with strain rates ranging from 0.1 to 10 s⁻¹. The time required for 50% recrystallization for the SRX and MDRX was determined by carrying out double compression tests, respectively. Grain growth equation after full recrystallization was also derived by compression tests with various interpass times. The currently determined microstructure model has been integrated with a three-dimensional non-isothermal finite element program. The predicted results based on the model proposed in the present investigation for hot bar rolling processes were compared with the experimental data available in the literature. It was found that the proposed model was beneficial to understand the effect of recrystallization behavior and control the microstructure evolution during the hot bar rolling.     

20CrMnSiNi2MoA凿岩用钢等温自由锻模拟及试验研究

针对凿岩钻头用钢20CrMnSiNi2MoA,基于JMatPro软件模拟计算材料的应力应变曲线,并线性回归出材料的流变应力方程;基于DEFORM-3D有限元软件对材料进行了不对称V型砧锻造法等温自由锻造压缩,并预测了微观组织变化趋势。研究结果表明：原始奥氏体晶粒随着压缩量的变大,发生了动态再结晶,晶粒尺寸得到细化;温度一定时,随着变形速率的提高,晶粒平均尺寸变小。将通过不对称V型砧锻造法等温自由锻及热处理得到的钻头成品的机械性能与国外同类产品的机械性能进行了对比。     

晶粒相对尺寸对FCC多晶体板材单向拉伸流动应力的影响

采用动力显式有限元方法和速率相关的多晶体弹性-粘塑性有限元分析模型模拟退火FCC多晶体和6111-T4铝板的单向拉伸过程。考察了板厚与晶粒尺寸之比变化时由于晶界约束变化而导致板材流动应力变化的规律，得出的结论表明，晶粒的相对尺寸增大时，相邻晶粒之间晶界的约束作用也随之增大，从而导致多晶体材料流动应力增大，该结论与实验结果相吻合。     

Deformation behaviour of the hot upsetting cylindrical specimen with dynamic recrystallization

Based on the homogeneous deformation assumption, the hot upsetting of the small cylindrical specimen is usually used for generating the material parameters of metals under hot working condition. However, the homogeneous deformation is impossible due to friction. This paper first summarizes the viscoplastic model considering dynamic recrystallization, and then compiles the axisymmetrical finite element software to simulate the upsetting processing of the cylindrical specimen, at last applies the complied software to study the deformation behaviour of the upsetting cylindrical specimen with dynamic recrystallization and assesses the suitability of the assumption for the generation of the material parameters based on the simulated result, taking the model considering dynamic recrystallization as an example. For the model in question, the study shows that the reliability of the stress–strain curve is very high; however, the reliability of most of the microstructures is relatively low.     

DYNAMIC SIMULATION OF MICROSTRUCTURE EVOLUTION DURING HOT FORGING FOR ENGINE STIGMATA

0 INTRODUCTIONMetal foeing is a main industrial process for manufacturing workpieces with high strength. Alongwilh increasing standwh of qUality reqUired by people, it is neeessap that the process should beunderstood Perfectly and controlled correctly. However, during hot forming process, microstructurechanges in the material occurred decisively ialluence the mechanical properties of the final pIDduct, in themeantime, the ndcrostructure changes also affect the forming p~ess itself, since…     

挤压式楔横轧小料头轧制的微观组织演变分析

针对目前楔横轧技术料头较大,导致材料利用率低的问题,创新性地提出了挤压式楔横轧工艺以实现小料头轧制。通过在DEFORM-3D有限元软件中建立42CrMo钢的动态再结晶模型,模拟分析了挤压式楔横轧的动态再结晶体积分数及奥氏体平均晶粒尺寸大小的分布规律。最后结合挤压式楔横轧轧制油泵轴试验及金相分析试验,验证了挤压式楔横轧小料头轧制的可行性。研究表明,挤压式楔横轧产生的料头体积相较于传统楔横轧产生的料头体积减小了75%左右,其材料利用率可以提高到95%左右,同时该轧制方法还可以细化晶粒,提高金属综合力学性能。     

铁素体与碳化物双相组织低温变形对低碳钢显微组织的影响

用Gleeble1500热模拟机对宝钢SS400钢的铁素体与碳化物双相组织在600℃进行了变形,用光镜、扫描电镜、透射电镜进行组织观察。结果表明：铁素体发生动态回复与动态再结晶,变形后加热到800℃铁素体发生静态回复与静态再结晶,加热到900℃,保温30s获得平均直径大约10μm的细小奥氏体晶粒。     

考虑晶粒变形动态再结晶过程模拟的元胞自动机法

结合金属塑性成形过程的冶金学原理,给出了一种考虑动态再结晶过程晶粒变形的元胞自动机模型.考虑了晶粒变形对再结晶形核的影响,给出了一种与基元形状有关的形核概率计算方法.根据动态再结晶晶粒生长速度和与其相邻基元形状确定转变概率.采用元胞自动机模型对动态再结晶组织的演变进行了模拟,模拟结果与不考虑晶粒变形的结果进行了比较.