Cu-P-Cr-Ni-Mo耐候钢高温变形奥氏体的动态再结晶

用Gleeble-3500热模拟试验机研究了Cu-P-Cr-Ni-Mo耐候钢(%:0.10C、0.075P、0.65Cr、0.22Ni、0.43Mo、0.28Cu)在应变速率0.01～1 s-1、温度850～1150℃时的动态再结晶行为,得出该钢奥氏体区的真应力-真应变曲线和动态再结晶图,分析了变形参数对峰值应力的影响和不同热变形时耐候钢的动态再结晶体积分数与真应变的关系,建立了该钢的奥氏体热变形方程、动态再结晶临界条件回归方程和奥氏体动态再结晶体积分数数学模型。结果表明,随变形温度升高,峰值应力下降;随变形速率增大,峰值应力升高;随Z参数增大即变形温度降低,应变速率增加,发生再结晶的临界应变εc和发生完全再结晶的应变εs均呈线性增加。     

Ti-25Al-14Nb-2Mo-1Fe合金热压缩变形流变应力行为与微观组织演变的研究

在Gleeble-3500热模拟试验机上对Ti-25Al-14Nb-2Mo-1Fe合金进行了等温恒应变速率压缩试验,研究了在变形温度为950~1 100℃,应变速率为0.001~1 s-1,最大变形程度为50%的条件下合金的热压缩变形流变应力行为与微观组织演变。结果表明:Ti-25Al-14Nb-2Mo-1Fe合金的流变应力对变形温度和应变速率均较为敏感,其流变应力曲线具有应力峰值、流变软化和稳态流变的特征。在变形温度为950℃,应变速率为0.001~0.1 s-1的条件下,Ti-25Al-14Nb-2Mo-1Fe合金的热变形特性为片层组织球化,其热变形机制可用晶界分离球化模型进行解释说明;在变形温度为1 000~1 100℃,应变速率为1 s-1的条件下,材料只发生了动态回复现象;在变形温度为1 050~1 100℃,应变速率为0.001~0.1 s-1的条件下,材料发生了动态再结晶现象。     

Cu-Cr-Zr合金的热变形行为

采用Gleeble-3500热模拟实验机对Cu-Cr-Zr合金进行了压缩变形实验,分析了在变形温度为25~700℃、应变速率为0.0001~0.1000s-1的条件下流变应力的变化规律,利用扫描电镜及透射电镜分析合金在热压缩过程中的组织演变及动态再结晶机制。结果表明:Cu-Cr-Zr合金在热变形过程中发生了动态再结晶,且变形温度和应变速率均对流变应力有显著的影响,流变应力随着变形温度的升高而降低,随着应变速率的增加而升高,说明该合金属于正应变速率敏感材料;当变形温度为400~500℃时,低应变速率(0.0001~0.0010 s-1)的真应力-真应变曲线呈现动态再结晶曲线特征,高应变速率(0.01~0.10 s-1)的真应力-真应变曲线呈现动态回复特征;在真应力-真应变曲线的基础上,采用双曲正弦模型能较好地描述Cu-Cr-Zr合金高温变形时的流变行为,建立了完整描述合金热变形过程中流变应力与应变速率和变形温度关系的本构方程,确定了合金的变形激活能为311.43 kJ·mol-1。     

热变形对40CrMnMo钢的晶粒尺寸影响规律研究

采用了MMS-200热力模拟机以40CrMnMo钢为实验对象进行了热压缩试验,研究了变形温度850℃～1150℃,变形量0.8,应变速率在0.01～10s~(-1)条件下实验钢的热变形行为。通过分析高温下变形参数对流变应力和奥氏体晶粒尺寸的影响,建立40CrMnMo钢的稳态动态再结晶晶粒尺寸模型。结果表明:变形温度为850℃～1150℃,实验钢在应变速率0.01～0.1s~(-1)下发生连续动态再结晶,应变速率1～10s~(-1)下发生动态回复。通过引入Zener-Hollomon(Z)参数表征变形参数对稳态动态再结晶晶粒尺寸的影响,建立了稳态再结晶晶粒尺寸的数学模型,得出提高应变速率或变形温度较低能使Z参数增大,峰值应力升高且动态再结晶晶粒减小。     

55SiMnMo贝氏体钢高温流变应力本构方程

 采用Gleeble-3500热模拟试验机对55SiMnMo贝氏体钢进行了热压缩试验,得到了其在变形温度为950~1150℃和应变速率为0.01~10s-1条件下的高温流变应力行为。试验结果表明,峰值应力随变形温度的降低和应变率的提高而增大;当应变速率为0.01和0.1s-1,变形温度t ≥1000℃时,发生动态再结晶。基于试验结果,充分考虑了热变形工艺参数（应变、应变速率和变形温度）对流变应力的影响,建立了一种考虑应变速率补偿的高温流变应力本构方程。通过对该本构方程预测得到的流变应力值和试验值对比,验证了模型的准确性。     

Custom 450高强度不锈钢的动态再结晶行为

摘要：为了探究Custom 450钢的动态再结晶行为,采用Gleeble 3800热模拟试验机,在变形温度为1050~1200℃和应变速率为0.01~10s-1的变形条件下开展了单道次等温压缩试验。研究结果显示,在变形温度为1050~1200℃和应变速率为1.0~10s-1的变形范围内,钢虽发生了完全的动态再结晶,但应力应变曲线未表现出明显的应力峰值;钢的动态再结晶的晶粒尺寸随着变形温度的升高和应变速率的降低逐渐增大,当应变速率为001s-1时,动态再结晶晶粒发生长大。采用双曲正弦函数构建了Cutom 450钢的热变形方程,并建立了钢的动态再结晶动力学、临界应变、峰值应变及动态再结晶晶粒尺寸与Zener Holloman参数的定量关系。     

SCM435钢热变形动态再结晶动力学模型参数的确定

通过分析冷镦钢SCM435在温度为950～1150℃、应变速率为0.1～1s-1范围内发生动态再结晶的热/力模拟试验数据,利用其应变硬化速率θ与流变应力σ的θ-σ曲线,准确确定了其发生动态再结晶的临界应变εc、峰值应变εp、临界应力σc和峰值应力σp,用应力-应变(σ-ε)曲线方法计算SCM435钢的动态再结晶Avrami动力学曲线和时间指数n.结果表明:SCM435钢发生动态再结晶的临界应变与峰值应变的平均比值εc/εp=0.73,动态再结晶Avrami时间指数平均值n=1.91;在温度950～1150℃,应变速率0.1～1s-1范围内,应变速率是SCM435钢的动态再结晶动力学敏感因素,温度对其影响不大;动态再结晶率50%的时间t50与应变速率成反比.     

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℃)。     

电热合金Cr20 Ni80的热变形行为及热加工图

为了解决Cr20Ni80电热合金锻造开裂的问题,在Gleeb-1500D热模拟试验机上对该合金进行热压缩试验,研究变形温度为900~1220℃,应变速率为0.001~10 s-1条件下的热变形行为,并根据动态材料模型建立合金的热加工图.合金的真应力-真应变曲线呈现稳态流变特征,峰值应力随变形温度的降低或应变速率的升高而增加;热变形过程中稳态流变应力可用双曲正弦本构方程来描述,其激活能为371.29 k J·mol-1.根据热加工图确定了热变形流变失稳区及热变形过程的最佳工艺参数,其加工温度为1050~1200℃,应变速率为0.03~0.08 s-1.优化的热加工工艺在生产中得到验证.     

700℃超超临界锅炉材料GH4700合金热压缩行为

利用变形温度为1120~1210℃、应变速率为0.1~20 s-1以及变形量为15%~60%的等温热压缩实验研究了GH4700合金的热变形行为.通过对低温和高应变速率条件下的形变热效应进行修正,得到准确的流变曲线,推导出描述峰值应力与温度和应变速率等变形参数的本构方程,并得到GH4700合金热变形表观激活能为322 kJ.组织分析表明,动态再结晶是热变形过程中最主要的软化方式,再结晶形核方式为应变诱发晶界迁移,变形温度升高和应变速率增大均有利于再结晶形核.再结晶发展阶段,随着变形量的增大和变形温度的升高,动态再结晶比例增加,在应变速率-温度坐标中,再结晶比例等值线呈反"C"形式.采用分段函数描述了不同应变速率下GH4700合金动态再结晶晶粒尺寸与变形参数的关系.      

Flow Stress and Critical Dynamic Recrystallization Behavior of Cu–Fe16Mn0.6C High Manganese TWIP Steel

The true stress–strain curve of Cu–Fe16Mn0.6C twinning induced plasticity (TWIP) steel was studied with a compression test on Thermecmastor‐Z thermal simulator at a temperature range of 850–1150°C and strain rate range of 0.03–30 s^?1. The influence of deformation temperature and strain rate on high‐temperature flow stress and critical recrystallization behavior of the TWIP steel was investigated. It is concluded that the peak flow stress of Cu–Fe16Mn0.6C under high‐temperature deformation decreases as the temperature increases but increases with the strain rate. Meanwhile at strain rate of 0.03 and 30 s^?1 obvious peak stresses are observed which demonstrates the dynamic recrystallization. The constitutive equation of Cu–Fe16Mn0.6C under high temperature deformation is calculated by linear regression method. The activation energy is 505 kJ mol^?1. The relationship between critical strain of dynamic revrystallization and Zener–Hollomon parameter is determined by the curve between strain‐hardening rate and flow stress.     

Application of a Dislocation Density-Based Constitutive Model to Al-Alloyed TWIP Steel

High Mn steels exhibit an exceptional combination of high strength and large ductility owing to their high strain-hardening rate during deformation. The addition of Al is needed to improve the mechanical performance of TWIP steel by means of the control of the stacking fault energy. In this study, a constitutive modeling approach, which can describe the strain-hardening behavior and the effect of Al on the mechanical properties, was used. In order to understand the deformation behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels, a comparative study of the microstructural evolution was conducted by means of transmission electron microscopy and electron backscatter diffraction. The microstructure analysis focused on dislocations, stacking faults, and mechanical twins as these are the defects controlling the strain-hardening behavior of TWIP steels. A comparison of the strain-hardening behavior of Fe18Mn0.6C and Fe18Mn0.6C1.5Al TWIP steels was made in terms of a dislocation density-based constitutive model that goes back to the Kubin–Estrin model. The densities of mobile and forest dislocations are coupled in order to account for the interaction between the two dislocation populations during straining. The model was used to estimate the contribution of dynamic strain aging to the flow stress. As deformation twinning occurred only in a subset of the grains, the grain population was subdivided into twinned grains and twin-free grains. Different constitutive equations were used for the two families of grains. The analysis revealed that (i) the grain size and dynamic recovery effects determine the strain-hardening behavior of the twin-free grains, (ii) the deformation twins, which act as effective barriers to dislocation motion, are the predominant elements of the microstructure that governs the strain hardening of the twinned grains, and (iii) the DSA contribution to strain hardening of TWIP steel is only minor.     

Mechanical Properties and Microstructure Evolution During Deformation of Fe–Mn–C TWIP Steel

The mechanical and deformation microstructure properties of the Fe–Mn–C TWIP steel was investigated by means of tensile experiment, in situ scanning electron microscope (SEM) and transmission electron microscope (TEM).The results showed that the sample has excellent mechanical with tensile strength of the steel is about 1140 MPa and the yield strength is higher than 480 MPa, while the elongation is above 57%, the true stress–strain curve from tension tests exhibited repeated serrations and its strain‐hardening rate is constantly changing. It is found that there were different deformation mechanisms at different deformation stages result in the unique true stress–strain curve. Dislocation slip dominated the initial deformation and with the accumulation of deformation stress concentration reached the twin shear stress resulting in twin shear, which lead to TWIP effect. As the strain capacity increased continually, the parallel twins can no longer rotate and shear deformation occurred, which lead to the forming of shear bands. The intercoordination of slip deformation, twin deformation, and shear deformation mechanism make the TWIP steel show high strength and high plasticity.     

高锰奥氏体TRIP/TWIP钢的组织和力学性能

研究了两种不同锰含量的高锰奥氏体钢在室温拉伸变形过程中力学性能和组织的变化.结果表明,随着钢中锰含量的变化,实验钢在流变应力的作用下出现相变诱导塑性的TRIP效应和孪晶诱导塑性的TWIP效应.在1×10-3 s-1的初始应变速率条件下,锰的质量分数为23.8%的实验钢可达到666 MPa的抗拉强度和67%的伸长率,而锰的质量分数为33%的实验钢可达到540 MPa的抗拉强度和97%的伸长率.并且在10-3～10-1 s-1的初始应变速率范围内,实验钢的抗拉强度对于流变应力不敏感,而实验钢的塑性则表现出一定的应变速率敏感性.由于该钢具有较好的综合力学性能,有望作为新一代高强度、高塑性汽车用钢.     

Constitutive Modeling of the Tensile Behavior of Al-TWIP Steel

High Mn steels demonstrate an exceptional combination of high strength and large ductility as a result of their high strain-hardening rate during deformation. The microstructure evolution and strain-hardening behavior of Fe18Mn0.6C1.5Al TWIP steel in uniaxial tension were examined. The purpose of this study was to determine the contribution of all the relevant deformation mechanisms—slip, twinning, and dynamic strain aging. Constitutive modeling was carried out based on the Kubin–Estrin model, in which the densities of mobile and forest dislocations are coupled to account for the interaction between the two dislocation populations during straining. These coupled dislocation densities were used to simulate the contribution of dynamic strain aging to the flow stress. The model was modified to include the effect of twinning. To ascertain the validity of the model, the microstructural evolution was characterized in detail by means of transmission electron microscopy and electron back-scatter diffraction.     

Serrated Flow and Dynamic Strain Aging in Fe-Mn-C TWIP Steel

The tensile behavior, serrated flow, and dynamic strain aging of Fe-(20 to 24)Mn-(0.4 to 0.6)C twinning-induced plasticity (TWIP) steel have been investigated. A mathematical approach to analyze the DSA and PLC band parameters has been developed. For Fe-(20 to 24)Mn-(0.4 to 0.6)C TWIP steel with a theoretical ordering index (TOI) between 0.1 and 0.3, DSA can occur at the very beginning of plastic deformation and provide serrations during work hardening, while for TOI less than 0.1 the occurrence of DSA is delayed and twinning-dominant work hardening remains relatively smooth. The critical strain for the onset of DSA and PLC bands in Fe-Mn-C TWIP steels decreases as C content increases, while the numbers of serrations and bands increase. As Mn content increases, the critical strain for DSA and PLC band varies irregularly, but the numbers of serrations and bands increase. For Fe-(20 to 24)Mn-(0.4 to 0.6)C TWIP steel with grain size of about 10 to 20 μm, the twinning-induced work hardening rate is about 2.5 to 3.0 GPa, while the DSA-dominant hardening rate is about 2.0 GPa on average. With increasing engineering strain from 0.01 to 0.55 at an applied strain rate of 0.001s^?1, the cycle time for PLC bands in Fe-Mn-C TWIP steel increases from 6.5 to 162 seconds, while the band velocity decreases from 4.5 to 0.5 mm s^?1, and the band strain increases from 0.005 to 0.08. Increasing applied strain rate leads to a linear increase of band velocity despite composition differences. In addition, the influence of the Mn and C content on the tensile properties of Fe-Mn-C TWIP steel has been also studied. As C content increases, the yield strength and tensile strength of Fe-Mn-C TWIP steel increase, but the total elongation variation against C content is dependent on Mn content. As Mn content increases, the yield strength and tensile strength decrease, while the total elongation increases, despite C content. Taking both tensile properties and serrated flow behavior into consideration, Fe-22Mn-0.4C TWIP steel shows excellent mechanical performance with a high product of tensile strength and total elongation and a slightly serrated stress–strain response. To suppress the negative effect of DSA in Fe-Mn-C TWIP steels on the stability of tensile behavior, a TOI lower than 0.1 is strongly suggested.     

B30MnSi钢的动态再结晶行为

采用Gleeble1500热模拟试验机对B30MnSi钢(%:0.32C,1.04Mn,0.85Si,0.019P,0.009S)进行变形温度为850～1000℃,应变速度为0.1～101/s的压缩变形试验,以研究该钢的动态再结晶规律。并通过回归分析得出峰值应力σm,应变εp,动态再结晶临界应变εc与温度补偿变形速率因子Z之间关系式为σm=16.689Ln(Z)-347.41;εp=0.0474Ln(Z)-1.1023;εc≈0.0393Ln(Z)-0.915。     

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。     

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.