Constitutive Modeling and Dynamic Recrystallization Mechanisms of an Ultralow-carbon Microalloyed Steel During Hot Compression Tests

The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1 073-1 373 K and strain rate range of 0.01-10 s~(-1).The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate.The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test.Furthermore,a new constitutive model based on the Z-parameter was proposed for this steel.The predictive ability of two constitutive models was compared with statistical measures.The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation.The dynamic recrystallization (DRX) nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy (TEM),and strain-induced grain boundary migration was observed at 1 373 K/0.01 s~(-1).     

Determination of the dynamic recrystallization kinetics model for SCM435 steel

The flow stress behavior of SCM435 steel was studied by using a MMS-200 thermal simulation machine, under the conditions with deformation temperatures of 1023–1323 K and strain rate of 0.01–10 s^?1. The experimental results indicated that the critical strain would get smaller with the increment in temperature and the decrement in strain rate, leaving the dynamic recrystallization easier to occur. The peak stress constitutive equation of SCM435 steel under high temperatures was established by the form of hyperbolic sine, and the activation energy of deformation under high temperature was obtained by regression equation. The critical strain ? _c for dynamic recrystallization was accurately derived from the θ-σ curve containing strain hardening rate θ and flow stress σ. Then the correlation between peak stress, peak strain, critical stress, critical strain and the parameter Z was further obtained. The Avrami kinetic equation of dynamic recrystallization for SCM435 steel was developed from stress-strain curve, and the Avrami exponent m was abstracted. Observations also indicated that the Avrami constants would decrease with increments in temperature, but increase with increments in strain rate. The Avrami constant took small influence from the deforming temperature, but significant influence from strain rate, and the correlation between Avrami constant and the strain rate was obtained by regression equation.     

Mg-9Gd-3Y合金热变形行为与本构关系

为了解决Mg-9Gd-3Y合金在热塑性变形过程中的本构关系问题,对Mg-9Gd-3Y合金进行了不同变形温度（653～753K）下采用不同应变速率（0.01～10s-1）的热压缩试验,利用载荷/位移数据建立真应力/真应变曲线和本构方程.结果表明：动态再结晶在晶界处较易发生,流变曲线显示出典型的动态再结晶特征,以及应力水平与变形温度和应变速率的关系.本构方程预测出的流变应力数据与相应的试验结果较一致.     

82B高碳钢热变形行为研究

采用单道次热压缩实验方法,在Thermomaster-Z型热模拟试验机上模拟高碳钢高速线材热轧变形过程动态再结晶行为,测定82B高碳钢在变形温度为800～1 100℃、变形速率为0.1～50 s-1、变形程度为0～0.60条件下的真应力-应变曲线,利用曲线特征值确定高应变速率下的变形激活能,根据实验结果分析动态再结晶变形条件,建立动态再结晶状态图。     

AZ81E镁合金的高温流变应力模型及热加工图研究

在应变速率为0．003—3．0s^-1、温度为340～430℃的变形条件下,采用Gleeble-1500热模拟机对AZ81E镁合金进行高温热压缩变形特性研究。结果表明：流变应力随变形温度的升高和应变速率的降低而减小,峰值应力随温度的降低和应变速率的升高向应变较大处转移,进入稳态阶段的临界应变明显增大。结合Arrhenius方程并引入Zener-Hollomon参数,构建AZ81E镁合金的高温流变应力模型,其平均变形激活能为166．15kJ／mol。根据材料动态模型,计算并分析AZ81E镁合金的热加工图。利用热加工图确定热变形的流变失稳区,获得试验参数范围内的热变形过程最佳工艺参数：热加工温度范围为380～420℃,应变速率范围为0．01～0．03S^-1.     

Flow stress behavior and processing map of Al-Cu-Mg-Ag alloy during hot compression

The hot deformation behavior of Al-Cu-Mg-Ag was studied by isothermal hot compression tests in the temperature range of 573-773 K and strain rate range of 0.001-1 s^-1 on a Gleeble 1500 D thermal mechanical simulator. The results show the flow stress of Al-Cu-Mg-Ag alloy increases with strain rate and decreases after a peak value, indicating dynamic recovery and recrystallization. A hyperbolic sine relationship is found to correlate well the flow stress with the strain rate and temperature, the flow stress equation is estimated to illustrate the relation of strain rate and stress and temperature during high temperature deformation process. The processing maps exhibit two domains as optimum fields for hot deformation at different strains, including the high strain rate domain in 623-773 K and the low strain rate domain in 573-673 K.     

Modeling of metadynamic recrystallization kinetics after hot deformation of low-alloy steel Q345B

Based on the steady-state strain measured by single-pass hot compression tests, the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics. The metadynamic recrystallization behavior of low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000–1 100 °C, the strain rate range of 0.01–0.10 s⁻¹ and the interpass time range of 0.5–50 s on a Gleeble-3500 thermo-simulation machine. The results show that metadynamic recrystallization during the interpass time can be observed. As the deformation temperature and strain rate increase, softening caused by metadynamic recrystallization is obvious. According to the data of thermo-simulation, the metadynamic recrystallization activation energy is obtained to be Q _md=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up. Finally, the error analysis of metadynamic recrystallization kinetics model proves that the model has high accuracy (correlation coefficient R=0.988 6).     

Hot deformation behavior and constitutive relationship of Q420qE steel

Isothermal compression tests at temperatures from 1 273 to 1 423 K and strain rates from 0.1 to 10 s-1 were carried out to investigate the flow behaviors of Q420qE steel.Stress-strain data collected from the tests were employed to establish the constitutive equation,in which the influence of strain was incorporated by considering the effect of strain on material constants Q,n,α,and ln A.The results show that the flow stress curves are dependent on the strain,strain rate and deformation temperature.They disp...     

TC11钛合金高温塑性本构方程研究

有限元数值模拟技术的重大发展使得其在锻造加工研究领域中得到了越来越广泛的应用。本文通过实验,研究了TC11钛合金在高温条件下的塑性本构方程,本构方程是描述材料的基本信息和有限元模拟中不可缺少的数学模型,它反映了流动应力与应变、应变速率以及温度之间的依赖关系。为了建立本构方程,必须测量一定温度、应变速率范围内的流动应力值,这通常是由压缩试验来完成的。有限元模拟结果的有效性首先取决于本构方程的精确程度,所以,如何获取精确的本构方程成为锻造成形过程计算机模拟技术中的首要问题     

含稀土的23Cr型双相不锈钢的高温变形行为

利用Gleeble-3500热力模拟试验机在950-1200℃,应变速率为0.1-10s-1条件下进行了含稀土的23Cr型双相不锈钢的热压缩变形,获得了流变曲线,建立了热变形方程,分析了变形组织。结果表明：在流变曲线上既存在峰值应力也有稳态应力;在高温低应变速率条件下,峰值应变减小。上述变形条件下,试验钢的热变形激活能Q=436kJ/mol,表观应力指数n=3.91,热变形方程为：ε=2.41×1016[sinh（0.012σs）]3.91exp （-436000/RT）。奥氏体的动态再结晶在试验钢的动态软化机制中起主导作用且随着温度的升高和应变速率的降低越来越充分;而大应变下,铁素体的软化主要表现为较充分的动态回复。稀土元素影响了热变形时两相中Mo元素的再分配是稀土改善双相不锈钢高温塑性的重要原因之一。稀土使Mo在铁素体中浓度较低温度下降低,高温下升高;而奥氏体相中,使得Mo浓度在较低温度下升高而高温下降低。     

Hot deformation behavior of Super304H austenitic heat resistant steel

The hot compression tests of Super304H austenitic heat resistant steel were carried out at 800-1200℃and 0.005-5 s~(-1) using a Gleeble 3500 thermal-mechanical simulator,and its deformation behavior was analyzed.The results show that the flow stress of Super304H steel decreases with the decrease of strain rate and the increase of deformation temperature;the hot deformation activation energy of the steel is 485 kJ/mol.The hot deformation equation and the relationship between the peak stress and the deforma...     

Hot deformation behavior and flow stress model of F40MnV steel

Single hit compression tests were performed at 1 223-1 473 K and strain rate of 0.1-10 s-1 to study hot deformation behavior and flow stress model of F40MnV steel. The dependence of the peak stress, initial stress, saturation stress, steady state stress and peak stain on Zener-Hollomon parameter were obtained. The mathematical models of dynamic recrystallization fraction and grain size were also obtained. Based on the tested data, the flow stress model of F40MnV steel was established in dynamic recovery region and dynamic recrystallization region, respectively. The results show that the activation energy for dynamic recrystallization is 278.6 kJ/mol by regression analysis. The flow stress model of F40MnV steel is proved to approximate the tested data and suitable for numerical simulation of hot forging.     

37Mn5钢高温变形抗力模型及动态再结晶动力学模型研究

通过Gleeble热模拟试验获得不同变形条件下37Mn5钢的应力应变试验数据,采用不同模型对试验数据进行回归,找到适合37Mn5钢高温变形时的变形抗力模型。同时,通过计算得到了该钢的动态再结晶动力学方程和动态再结晶体积分数表达式。将以上模型的计算值与实测值进行比较,结果表明,计算值与实测值非常接近。     

37Mn5钢热变形行为与流变应力模型研究

利用Gleeble-1500热模拟实验机研究37Mn5钢在变形温度为800～1150℃、变形速率为0．1～10s^-1条件下的热压缩变形行为。采用应变硬化率-应力曲线图较精确地获得峰值应力,并用双曲正弦方程描述37Mn5钢热压缩变形过程中的峰值应力与Zener—Hollomon参数的关系。回归分析得到方程中变形激活能及各材料常数的值,获得37Mn5钢在高温条件下的流变应力本构方程。结果表明,采用该本构方程计算出的流变应力值与实验所得应力值非常接近。     

Al-Mg-Si合金热压缩变形的流变应力方程

为了给制定和优化热加工工艺参数提供理论依据,采用Gleeble-1500热模拟机研究了含锆Al-Mg-Si合金在变形温度为653~803 K、变形速率为0.01~10s^-1条件下的热压缩变形的流变应力行为,并通过回归法建立材料变形的流变应力数学模型.结果表明：该合金为正应变速率敏感材料,真应力-真应变曲线存在明显的稳态流变特征;流变应力随着变形速率的增加以及变形温度的降低而增加;在较低变形温度条件下,真应力〖CDF*3〗真应变曲线为动态回复曲线;在较高变形温度条件下真应力-真应变曲线为动态再结晶曲线.该合金流变应力σ可用包含Arrhenius项的Zener Hollomon参数的函数来描述,式中A、α和n的值分别为1.89×10¹⁰s^-1、0.024MPa^-1和7.46,热变形激活能Q为166.85kJ/mol.     

Deformation Behavior of 6063 Aluminum Alloy During High-Speed Compression

The deformation behavior characteristics of 6063 aluminum alloy were studied experimentally by isothermal compression tests on a Gleeble- 1500 thermal-mechanical simulator. Cylindrical specimens of 14mm in height and 10mm in diameter were compressed dynamically at temperatures ranging from 473 to 723K and at higher strain rntes from 5 to 30s^-1. It is fouud that the flow curves not only depend on the strain rate and temperature but nlso on the dynamic recovery aud recrystallization behavior. The results show that the flow stress decreased with the increase of temperature, while increased with the increase of strain rate. The discontinuous dynamic recrystallization （DDRX） may take place at a high strain rate of 20s^-1 under the tested conditions. At 30s^-1 , the flow curve can exhibit,flow softening due to the effect of temperature rise that raised the temperature by aboat 32K in less than 0.05s.     

温度、应变率和晶粒对Mn18Cr18N钢高温塑性的影响

通过拉伸热模拟试验研究了温度、应变率和晶粒尺寸对Mn18Cr18N高氮奥氏体不锈钢高温塑性的影响。结果表明：在800℃~1 200℃温度范围内,Mn18Cr18N高氮奥氏体不锈钢的塑性随温度升高而升高,1 200℃时达到最好,然后开始下降;应变率通过再结晶的作用而影响塑性;当温度低于1100℃时,细晶粒尺寸材料的塑性优于粗晶粒尺寸,而温度高于1 100℃时中等晶粒尺寸材料塑性最好。     

Research on flow stress in ferrite deformation of a Ti-IF steel

The experiments of the ferrite warm deformation of ultra-low carbon （ULC） Ti-IF steel were carded out on a hot simulator and the influences of deformation temperature, strain, and strain rate on the flow stress were analyzed. New flow stress models suitable to ferrite warm forming of Ti-IF steel were given on the basis of analyzing the influence of deformation technology parameters on the flow stress.     

Effect of twinning on flow stress during initial stage of hot compression of twin roll cast Mg-5.51Zn-0.49Zr alloy

A Thermecmastor-Z hot deformation simulator,optical microscopy,XRD and TEM were employed to characterize the flow stress behavior and microstructure of twin roll cast ZK60 magnesium alloy during initial stage of hot compression at elevated temperature of 300 ℃ and 400 ℃ and a given strain rate of 10-2s-1.The results suggest that flow stress drop during initial stage of hot compression at 300℃,generally led by dynamic recrystallization,is attributed to twinning,correspondingly to dynamic recrystallization as...     

Hot deformation behaviors and flow stress model of GCr15 bearing steel

The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950℃ and 1150℃ and strain rates between 0.1 and 10 s^-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150℃ and strain rate range of 0.1-10 s^-1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization （DRX） grain size were also established. The model predictions show good agreement with experimental results.