热加工参数对GH738合金动态再结晶行为的影响

采用Gleeble-1500D热加工模拟试验机及微观组织分析系统研究了热加工参数对GH738合金动态再结晶组织分布的影响规律。结果表明:影响GH738合金动态再结晶晶粒分布均匀性的主要因素是变形量,当变形量大于50%且接近70%时更易获得较均匀的再结晶组织。变形速度及温度对动态再结晶也有一定的影响:变形速率减小,变形温度升高,再结晶体积分数提高;变形速率增大,变形温度降低都导致再结晶晶粒的体积分数减小。进一步的电镜分析表明,GH738合金动态再结晶的形核机制以应变诱发形核为主。     

Effects of Hydrogen on the Critical Conditions for Dynamic Recrystallization of Titanium Alloy During Hot Deformation

Hot deformation tests were performed to study the flow behavior and microstructural evolution of a Ti600 titanium alloy with different hydrogen contents. The effects of hydrogen on the critical conditions for the initiation of dynamic recrystallization (DRX) were investigated. The DRX kinetics models of hydrogenated Ti600 alloy were developed, and the DRX volume fractions were quantified under different deformation conditions. The results indicate that the addition of proper hydrogen (no greater than 0.3 pct) benefits the decrease of both the critical stress and critical strain for the initiation of DRX. The critical stress and critical strain are dependent linearly on the peak stress and the strain to peak stress, respectively. The strain range from the initiation to the completion of DRX increases gradually with hydrogen in the hydrogen range of 0 to 0.3 pct, and a slightly decreased strain range is observed at the hydrogen content of 0.5 pct relative to that of 0.3 pct. The addition of large amounts of hydrogen (0.3 pct or greater) in Ti600 alloy induces incomplete DRX during hot deformation.     

Microscopically-Determined Static Recrystallization of Copper During Holding Without Stress or with Stress Relaxation After Hot Working

Abstract

After deformation to 0.15 in the range 450–540°C and 1.8 × 10^?3 to 1.8 s^?l in compression or torsion, the recrystallization of ETP Cu determined microscopically is compared to the restoration measured mechanically during intervals of holding at the deformation temperature under both stress-free and stress-relaxation conditions. Recrystallization is initially much slower than softening, the difference being due to recovery, but finally they become equal at about 85%. TEM substructures sharpen considerably during intervals up to 100 s. Recovery and recrystallization occur more rapidly as strain rate and temperature rise in both modes of holding, but in stress relaxation the former is slowed down and as a result the latter is speeded up.     

含动态再结晶粘塑性模型的参数识别

针对含动态再结晶粘塑性模型中的材料参数应用传统的测试方法很难准确测定的问题,吸收了遗传算法、增广高斯-牛顿算法、Levenberg-Marquardt算法和可变多面体算法的优点,构造了一套混合的全局优化算法.以26Cr2Ni4MoV为例,以镦粗实验提供的实验数据和刚塑性有限元模拟提供的数值解差值的l₂范数的平方作为目标函数,应用构造的算法识别了该模型中的材料参数,计算结果和实验结果符合良好.     

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant.These pipes are manufactured by hot forging,during which dynamic recrystallization acts as the most important microstructural evolution mechanism.A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes.In this model,the coupled effects of dislocation density change,dynamic recovery,dynamic recrystallization and grain orientation function were con-sidered.Besides,physically based simulation experiments were conducted on a Gleeble-3500 thermo-mechanical sim-ulator,and the specimens after deformation were observed by optical metallography (OM)and electron back-scat-tered diffraction (EBSD)method.The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate.The grains become much finer after full dynamic recrystallization.The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress-strain curves,grain size,and recrystallization kinetics.Besides,this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.     

碳锰钢热变形行为及动态再结晶模型

 采用单道次热模拟实验分析了各变形参数(初始晶粒尺寸、变形速率、变形温度和变形量)对碳锰钢动态再结晶的影响。结果表明,当初始晶粒越细小、变形温度越高、变形速率越小时,越易发生动态再结晶,同时在能够发生动态再结晶的条件下,变形量越大,动态再结晶越充分。得到了发生动态再结晶时的形变激活能Qdef、临界变形量模型、动态再结晶百分数模型及动态再结晶晶粒尺寸模型。计算得出ε05模型的平均误差为395%,模型预测值与实验数据计算值符合较好。     

Description of Austenite Recrystallization Kinetics During Low-Alloy Steel Hot Deformation

Metallurgist - Mathematical analysis of experimental data for low-alloy steel 09G2S austenite recrystallization after hot rolling is provided. An original mathematical model is proposed that...     

Dynamic Recrystallization and Processing Map of Pb-30Mg-9Al-1B Alloy During Hot Compression

Metallurgical and Materials Transactions A - The dynamic recrystallization (DRX) behavior of Pb-30Mg-9Al-1B alloy was investigated during hot compression at temperatures ranging from 513 K...     

Predicting Critical Conditions and Stress-Strain Curves for Dynamic Recrystallization in SPHC Steel

The hot compression tests on an SPHC steel were carried out in the temperature range of 900-1150 ℃ and strain rate range of 0.1-10 s-1,in which the maximum true strain is 0.8.The activation energy of test steel was calculated,to be 299.4 kJ/mol.The critical stresses and strains for initiation of dynamic recrystallization were determined based on changes of the work hardening rate(θ)as a function of the flow stress(σ)or strain(ε),respectively.The dependence of the peak strain(εp),the peak stress(σp),and the steady state stress(σs)were determined based on the Zener-Hollomen parameter.The mathematical models of the flow stress evolution were established in the hardening and dynamic recovery region and dynamic recrystallization region,respectively.The average error between experimental curves and predicted ones was around 3.26%.     

Influences of Interfaces on Dynamic Recrystallization and Texture Evolution During Hot Rolling of Graphene Nanoribbon/Cu Composite

Metallurgical and Materials Transactions A - The influences of rigid heterointerfaces on the dynamic recrystallization (DRX) process and texture evolution during hot rolling of a graphene...     

Dynamic Recrystallization Behavior of Medium Carbon Cr-Ni-Mo-Nb Steel during Hot Deformation

Hot compression deformation behaviors of medium carbon Cr-Ni-Mo-Nb steel were investigated at deformation temperatures ranging from 1223 to 1423 Kand strain rates of 0.1,1and 5s^-1.Dynamic recovery（DRV）and dynamic recrystallization（DRX）were observed during the hot compression deformation.For all of the samples,DRX occurred at deformation temperatures above 1323 Kat different strain rates,while below 1223 K,no DRX was observed.The activation energy of the tested steel was determined as 386.06kJ/mol.The ratio of critical stress to peak stress and the ratio of critical strain to peak strain were 0.835 and 0.37,respectively.Kinetic equations interpreting the DRX behavior of the tested steel were proposed,and the corresponding parameters including the volume fraction and the average grain size were determined.Moreover,the microstructures induced under different deformation conditions were analyzed.     

Textural Evolution During Dynamic Recovery and Static Recrystallization of Molybdenum

In the current investigation, sintered molybdenum specimens with random textures were deformed in compression in a deformation dilatometer over a range of temperatures from 0.44T _M [K] to 0.61T _M [K] and true strains between ???=?0.3 and 0.92. Subsequent annealing treatments were carried out in the dilatometer in order to study static recrystallization phenomena. Electron backscatter diffraction scans of deformed and recrystallized specimens revealed that the microstructure after hot deformation is a recovered structure with two remarkably strong orientation components, ??111?? parallel to the loading direction exhibiting a high Taylor factor and ??100?? parallel to the loading direction with a low one. The fraction of the first component increases with lowering the deformation temperature, while static recrystallization leads to a higher fraction of the second component. The late-stage recrystallization behavior is sluggish due to a high amount of recovery. The results are discussed employing models for textural evolution in body-centered cubic (bcc) metals on the one hand and recrystallization of high-stacking-fault energy materials on the other.     

403Nb叶片钢高温热压缩静态再结晶研究

利用Gleeble-3500热模拟试验机对403Nb马氏体叶片钢进行二道次高温热压缩试验,对不同温度、应变速率、道次间隔下发生的静态再结晶进行了研究和计算,得到403Nb静态再结晶、静态再结晶激活能和静态再结晶晶粒尺寸模型。     

Plastic Flow During Hot Working of Ti-7Al

Metallurgical and Materials Transactions A - Plastic flow during hot working of Ti-7Al with an equiaxed-α (fully-recrystallized) starting microstructure was quantified and interpreted via hot...