超高压气瓶钢34CrMo4H热压缩流変应力行为

采用Gleeble-3800型热模拟机试验研究了34CrMo4H钢在900～1200℃、应变速率0.1～10s^-1时的高温热压缩行为,分析了热压缩变形时材料的流变应力与变形温度、应变速率之间的关系,确定了该钢的流变应力本构方程。结果表明,34CrMo4H钢在热压缩时流变应力随形变温度的升高而减小,随应变速率的增加而增大。应变速率小于0.1 s^-1时,该钢应力-应变曲线表现出明显的动态再结晶特征。34CrMo4H级钢的变形激活能为395.45kJ/mol。     

Hot Deformation Behavior of GCr15 Steel

 Hot deformation behavior of GCr15 (ASTM 52100) steel was investigated using single-hit compression tests on Gleeble-1500 simulator at the temperature range of 850-1100 ℃ and strain rate range of 0. 1-10 s-1. The flow stress constitutive equation of GCr15 steel during hot deformation was determined by stress-strain curves analysis on the basis of the hyperbolic sine equation. And the models of dynamic recrystallization fraction and dynamic recrystallization grain size of GCr15 steel were established by the measured curves and microstructure observation in different experimental conditions. The mean activation energy and the time exponent of dynamic recrystallization kinetics equation in the range of experimental conditions were determined to be 356. 2 kJ/mol and 2. 12, respectively. Meanwhile, the flow stress model was also established by the method of allocating flow stress curve with three main stress values, the saturation stress, the steady state stress and the stress when strain is 0. 1. The flow stress curves predicted by the developed models under different deformation conditions are in good agreements with the measured ones.     

Hot deformation behavior of 07Cr25Ni21NbN austenitic heat resistant steel modified using 0. 3% vanadium

Hot deformation behavior and processing maps of test steel were investigated at temperature range of 930-1230?? and the strain rate range of 0. 005-5s-1using isothermal hot compression tests by Gleeble3800 thermal- mechanical simulators. The change of microstructure of test steel with different deformation conditions was observed by means of metallographic microscope. The flow stress curve of the test steel was analyzed and its activation energy for thermal deformation was 571kJ/mol. The processing maps of the test steel were established when the true strain were 0. 4 and 0. 8, respectively. It is found that there are three boundaries of the peak area of dissipation power in processing map with the true strain of 0. 8. When the deformation temperature is 1230?? and the deformation rate is from 0. 005 to 5s-1, the microstructure of the test steel transitions from coarse serrated grains to finer equiaxed grains. When the deformation rate is 0. 5s-1 and the deformation temperature is increased from 930?? to 1230??, the microstructure changes from equiaxed structure and partially dynamic recrystallization structure to flow instability structure.     

CL70车轮钢热压缩流变应力行为

用Gleeble-3800热模拟机研究了CL70车轮钢在应变速率0. 01～10s^-1、900～1300 ℃时的高温热压缩行为,分析了热压缩变形时该钢的流变应力、变形温度及应变速率之间的关系,通过线性回归确定该钢流变应力本构方程。结果表明,CL70钢在高温压缩时流变应力随变形温度的减小而增大,随应变速率升高而增大。当应变速率≤1 s^-1时,CL70钢的流变应力曲线表现为动态再结晶特征。CL70钢的热变形激活能为401.06 kJ/mol。     

一种含铁Ni_3Al基合金的热变形行为

采用Gleeble-1500D热模拟试验机对一种含铁Ni3Al基合金进行了高温压缩试验,试验温度为1 050~1 150℃,应变速率为0.1~1.0s-1,工程应变量为50%。获得了不同变形条件下的真应力-真应变曲线,并分析了合金微观组织的变化。结果表明:合金的流变应力随着变形程度的增加先达到峰值应力,之后逐渐降低,趋于稳态流变。提高变形温度及减小应变速率能有效促进动态再结晶过程。在变形温度1 100℃以上,工程应变为50%时,能够获得完全再结晶的锻态组织。基体中的γ′相粒子对合金动态再结晶有抑制作用,β相的存在促进了相界处动态再结晶形核但抑制了完全动态再结晶晶粒的长大。高温下β相的软化效应和γ′相的回溶转变都有效提高了Ni3Al基合金热加工性能。     

Q345E钢奥氏体动态再结晶行为研究及数学模型的建立

利用Gleeble-3800热模拟试验机对低合金高强度结构钢Q345E在1150~800℃之间的奥氏体动态再结晶及动态相变行为进行研究。确定了试验钢Q345E奥氏体动态再结晶的临界应变条件;研究了变形温度、应变速率等变形条件对试验钢奥氏体动态再结晶的影响,通过高温热力学模拟试验得到了Q345E钢在不同变形条件下的流动应力曲线,得出了动态再结晶激活能为467.767kJ/mol,通过对实验数据的拟合回归分析,建立了动态再结晶热变形模型和峰值应力、峰值应变与Z因子的关系,为控制该钢的组织和性能提供了基本依据。     

Effects of Temperature and Strain Rate on Flow Behavior and Microstructural Evolution of Super Duplex Stainless Steel under Hot Deformation

Hot compression tests were carried out in the temperature range of 1 223-1 473 Kand strain rate range of0.01-30s-1 to investigate the flow behavior and microstructural evolution of super duplex stainless steel 2507(SDSS2507).It is found that most of the flow curves exhibit a characteristic of dynamic recrystallization(DRX)and the flow stress increases with the decrease of temperature and the increase of strain rate.The apparent activation energy Qof SDSS2507 with varying true strain and strain rate is determined.As the strain increases,the value of Qdeclines in different ways with varying strain rate.The microstructural evolution characteristics and the strain partition between the two constituent phases are significantly affected by the Zener-Hollomon parameter(Z).At a lower lnZ,dynamic recovery(DRV)and continuous dynamic recrystallization(CDRX)of the ferrite dominate the softening mechanism during the compression.At this time,steady state deformation takes place at the last stage of deformation.In contrast,a higher lnZ will facilitate the plastic deformation of the austenite and then activate the discontinuous dynamic recrystallization(DDRX)of the austenite,which leads to a continuous decline of the flow stress even at the last deformation stage together with CDRX of the ferrite.     

中温中压容器用钢13MnNiMoR的热变形行为研究

为制定中温中压容器用钢13MnNiMoR的热加工工艺提供理论依据并实现其工业化生产,利用单道次热压缩模拟实验研究了变形温度(900~1150℃)和应变速率(0.01~1s~(-1))对其热变形行为的影响.结果表明:当应变速率低于0.1s~(-1)时,新晶粒有足够的时间进行形核和长大,奥氏体容易发生动态再结晶;当变形温度降低或应变速率增加时,实验钢在变形过程中主要发生动态回复,流变应力也随之提高.基于测定的流变应力曲线,通过拟合得到实验钢在热变形时的应力指数为4.29,动态再结晶激活能为319kJ/mol,据此建立了13MnNiMoR钢在高温变形时的热加工方程.     

T91钢的高温塑性变形及动态再结晶行为

采用Gleeble-1500热模拟试验机进行了T91钢的压缩试验,研究了变形温度为1100~1250℃、应变速率为0.01~1 s-1时该钢的变形行为,分析了流变应力与应变速率和变形温度之间的关系,计算了高温变形时应力指数和变形激活能,并采用Zener-Hollomon参数法构建该钢高温塑性变形的本构关系,绘制了动态再结晶图和热加工图.结果表明:在试验变形条件范围内,其真应力-真应变曲线呈双峰特征;钢中发生了明显的动态再结晶,且再结晶类型属于连续动态再结晶.T91钢的热变形激活能为484 kJ.mol-1,利用加工图确定了热变形的流变失稳区,结合力学性能,可以优先选择的变形温度为1200~1 250℃,应变速率不高于0.1 s-1.      

铸造TiAl基合金的热变形行为及加工图

通过高温压缩模拟试验结果建立TiAl基合金的热加工图,结合扫描电镜、透射电镜等试验手段,研究铸造TiAl基合金在温度为1 000~1 150℃、应变速率为0.001~1 s 1范围内的热变形行为。结果表明:铸造TiAl基合金是温度、应变速率敏感材料,其流变应力随温度升高和应变速率降低而降低。铸造TiAl基合金的高温变形机制以层片晶团的扭折、弯曲及动态再结晶过程为主。在高温(1 150℃),低应变速率(≤0.01 s 1)下变形后,铸态组织中β相含量明显减少直至消除。在变形温度1 150℃、应变速率0.001 s 1下变形时,铸造TiAl基合金未发生超塑性变形;此时由于动态再结晶晶粒异常长大导致加工图上该区域功率耗散值未达到最大,而是有减小的趋势。     

High Temperature Deformation Behavior of 4340 Steel: Activation Energy Calculation and Modeling of Flow Response

The 4340 steel is extensively utilized in several industries including automotive and aerospace for manufacturing a large number of structural components. Due to the importance of thermo-mechanical processing in the production of steels, the dynamic recrystallization (DRX) characteristics of 4340 steel were investigated. Namely, hot compression tests on 4340 steel have been performed in a temperature range of 900–1200 °C and a strain rate range of 0. 01–1 s^?1 and the strain of up to 0. 9. The resulting flow stress curves show the occurrence of dynamic recrystallization. The flow stress values decrease with the increase of deformation temperature and the decrease of strain rate. The microstructure of 4340 steel after deformation has been studied and it is suggested that the evolution of DRX grain structures can be accompanied by considerable migration of grain boundaries. The constitutive equations were developed to model the hot deformation behavior. Finally based on the classical stress-dislocation relations and the kinematics of the dynamic recrystallization; the flow stress constitutive equations for the dynamic recovery period and dynamic recrystallization period were derived for 4340 steel, respectively. The validity of the model was demonstrated by demonstrating the experimental data with the numerical results with reasonable agreement.     

2524铝合金的热压缩变形行为

利用Gleeble-1500热模拟实验机,对2524铝合金进行高温等温压缩试验,实验变形温度为300～500℃,应变速率为0.01～10 s-1的条件下,研究了2524铝合金的流变变形行为。结果表明:合金流变应力的大小跟变形温度和应变速率有很大关联,2524铝合金真应力-应变曲线中,流变应力开始随应变增加而增大,达到峰值后趋于平稳,表现出动态回复特征,而峰值流变应力随变形温度的降低和应变速率的升高而增大;在流变速率ε为10 s-1,变形温度300℃以上时,应力出现锯齿波动,合金表现出动态再结晶特征。采用温度补偿应变速率Zener-Hollomon参数值来描述2524铝合金在高温塑性变形流变行为时,其变形激活能Q为216.647 kJ/mol。在等温热压缩形变中,合金可加工条件为:高应变速率(>0.5 s-1)或低应变速率(0.01 s-1～0.02 s-1)、高应变温度(440℃～500℃)。     

Hot Deformation Behavior of P92 Steel Used for Ultra-Super-Critical Power Plants

 Hot compression tests of P92 steel at temperatures in the range of 1173 to 1523 K and at strain rates in the range of 0.1 to 10 s-1 were carried out on a Gleeble-3500 thermal-mechanical simulator, and the corresponding flow curves were measured. The results showed that the flow stress and the peak strain increase with decreasing deformation temperature and increasing strain rate. The critical Z value, below which the complete dynamic recrystallization may occur, was determined to have 4.61×1018. The hot deformation activation energy of the steel was about 437 kJ/mol. The hot deformation equation and the microstructure diagram of P92 steel were obtained. For the convenience of the practical application, the empirical equation for the peak stress can be described as σP=17.17ln+902499T-524.1.     

Hot Deformation Behavior of As-cast AISI M2 High-speed Steel Containing Mischmetal

The hot deformation behavior of as-cast AISI M2high-speed steel containing mischmetal(RE)has been investigated on a Gleeble-3500simulator in the temperature range of 1 000-1 150℃and strain rate range of 0.01-10 s-1 at true strain of 1.0.The mechanical behavior has been characterized using stress-strain curve analysis,kinetic analysis,processing maps,etc.Metallographic investigation was performed to evaluate the mechanism of flow instability.The results show that the deformation activation energy decreases with increasing deformation temperature; the efficiency of power dissipation increases with decreasing strain rate and increasing temperature;flow instability is observed at low-to-medium temperature and higher strain rate region when the strain is smaller,but extends to lower strain rate and high temperature regions with the increment of strain,in which it is manifested as flow localization near the grain boundary.Hot deformation equations and processing maps are obtained.The optimal processing window is suggested and the deformation mechanism is dynamic recrystallization(DRX).     

7085铝合金的高温压缩流变应力及软化行为

对均匀化炉冷态7085铝合金进行高温压缩实验,研究该合金在变形温度为350~450℃、变形速率为0.001~0.1 s 1和应变量为0~0.6条件下的流变应力及软化行为。结果表明:流变应力在变形初期随着应变的增加而迅速增大,出现峰值后逐渐软化进入稳态流变;随着变形温度的升高和应变速率的降低,峰值流变应力降低。采用包含Zener-Hollomon参数的Arrhenius双曲正弦关系描述合金的流变行为。分析和建立了应变量与本构方程参数(激活能、应力指数和结构因子)的关系,研究发现本构方程参数随应变量的增加而减少。合金的流变行为差异与动态回复再结晶和第二相粒子相关。     

一种非调质连杆用高碳微合金钢的热变形行为

用Gleeble-3500热力模拟试验机在温度为1 223～1 323 K,应变速率为0.2～10 s-1的条件下对一种非调质连杆用高碳微合金钢进行了热压缩变形试验,测得了其流变曲线,并观察了变形后的组织.试验结果表明,流变应力和峰值应变随变形温度的降低和应变速率的提高而增大.试验用钢在真应变为0.8,温度为1 223～1 323 K,应变速率为0.2～10 s-1的条件下,发生完全动态再结晶.测得试验用钢的热变形激活能为289.9 kJ/mol,并得出了其热变形方程,以及动态再结晶晶粒尺寸与Zener-Hollomon参数之间的关系和动态再结晶状态图.     

Dynamic Recrystallization of Hot Deformed 3Cr2NiMnMo Steel: Modeling and Numerical Simulation

Hot compression tests of 3Cr2NiMnMo steel were performed at temperatures in the range of 850 to 1100 °C and with strain rates of 10^?2s^?1 to 1s^?1. Both the constitutive equations and the hot deformation activation energy were derived from the correlativity of flow stress, strain rate and temperature. The mathematical models of the dynamic recrystallization of 3Cr2NiMnMo steel, which include the dynamic recrystallization kinetics model and the crystallization grain size model, are based on Avrami's law and the results of thermosimulation experiments. By integrating derived dynamic recrystallization models with the thermal-mechanical coupled finite element method, the microstructure evolution in hot compressive deformation was simulated. The distribution of dynamic recrystallization grains and grain sizes were determined through a comparison of the simulation results with the experimental results. The distribution of strain and dynamic recrystallization grain is also discussed. The similarity between the experimental results and the simulated results indicates that the derived dynamic recrystallization models can be applied effectively to predict and analyze the microstructure evolution in hot deformed 3Cr2NiMnMo steel.     

Optimization of Hot Workability in Superaustenitic Stainless Steel 654SMO

Hot compression tests were conducted on a Gleeble-3800 machine in a temperature range of 950 to 1200 ℃ and a strain rate range of 0. 001 to 10 s-1 in order to study the hot deformation behaviour of superaustenitic stainless steel 654SMO. The results show that peak stress increases with decreasing temperature and increasing strain rate, and the apparent activation energy of this alloy was determined to be about 494 kJ/mol. The constitutive equation which can be used to relate the peak stress to the absolute temperature and strain rate was obtained. The processing maps for hot working developed on the basis of flow stress data and the dynamic materials model were adopted to op- timize the hot workability. It is found that the features of the maps obtained in the strain range of 0.2 to 1.0 are fun- damentally similar, indicating that the strain does not have a substantial influence on processing map. The combina- tion of processing map and mierostructural observations indicates that the favorable hot deformation conditions are located in two domains of processing map. The first domain occurs in the temperature range of 980 to 1035 ℃ and strain rate range of 0. 001 to 0.01 s-1 with a peak efficiency of 55%. The second domain appears in the temperature range of 1 120 to 1 180 ℃ and strain rate range of 0.3 to 3 s-1 with peak efficiency of 35%. Compared to other stable domains, the specimens deformed in these two domains exhibit full dynamic recrystallization grains with finer and more uniform sizes. An instability domain occurs at temperatures below 1 100 ℃ and strain rate above 0.1 s-1 , and flow instability is manifested in the form of flow localization.     

Physical simulation of hot deformation, and microstructural evolution for 42CrMo4 steel prior to direct quenching

 Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot-rolling plays a major role on the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as to predict the microstructure and the properties of the components. These models were mostly applied to predict austenite grain size (AGS), dynamic, meta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. In this paper the hot compression tests were carried on 42CrMo4 steel in the temperature range of 900 - 1100°C and the strain rate range of 0.05 - 1 s- 1 in order to study the high temperature softening behavior of the steel. For the exact prediction of flow stress, the effective stress - effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in a good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.     

RAFM钢应变补偿本构关系及热加工图

低活化铁素体/马氏体(RAFM)钢具有较低的辐照肿胀率和优异的力学性能,被认为是聚变堆首选的结构材料。然而,低活化钢强度高、冷塑性变形抗力大的特点,使其难以通过冷加工或低温加工实现大规模生产。使用MMS-200型热模拟试验机,在变形温度为950～1 200℃、应变速率为0.1～5 s^-1和最大变形量为50%条件下,进行了低活化铁素体/马氏体钢(0.11C-9.4Cr-1.35W-0.22V-0.05Si-0.11Ta-0.50Mn)单道次热压缩试验,研究其热变形行为。基于动态材料模型构建了不同应变量下的低活化钢变形本构方程和热加工图,确定了最优热加工参数,结合金相结果分析了材料变形过程中微观组织演化规律,为低活化钢的热加工成形工艺及组织优化提供理论参考。结果表明,在相同应变速率下,随着变形温度升高,流变应力逐渐降低,在一定变形温度下,流变应力随应变速率增大而增大;温度和应变速率对组织的影响主要取决于变形过程中材料内部发生的动态回复和再结晶等机制的交互作用。使用六阶多项式拟合进行应变补偿建立的低活化钢变形本构方程具有较高的预测精度,平方相关系数为0.972。显微组织...