Dynamic Recrystallization Kinetics and Microstructural Evolution for LZ50 Steel During Hot Deformation

The dynamic recrystallization (DRX) behavior of LZ50 steel was investigated using hot compression tests at a deformation temperature of 870-1170 °C and a strain rate of 0.05-3 s^?1. The effects of deformation temperature, strain, strain rate, and initial austenite grain size on the microstructural evolution during DRX were studied in detail. The austenite grain size of DRX was refined with increasing strain rate and decreasing temperature, whereas the initial grain size had no influence on DRX grain size. A model based on the Avrami equation was proposed to estimate the kinetics of the DRX under different deformation conditions. A DRX map, which was derived from the DRX kinetics, the recrystallized microstructure, and the flow stress analysis, can be used to identify optimal deformation conditions. The initiation of DRX was lower than Z _c (critical Zener-Hollomon parameter) and higher than ε_c (critical strain). The relationship between the DRX microstructure and the Z parameter was analyzed. Fine DRX grain sizes can be achieved with a moderate Z value, which can be used to identify suitable deformation parameters.     

35CrMo结构钢的热变形行为

通过对奥氏体再结晶行为的研究得到35CrMo钢发生动态再结晶的形变条件为:形变温度T>1000℃,应变速率ε≤1/s.描述动态再结晶动力学方程f=1-exp(-b(Z)tn(Z))中的系数b和n与变形参数Z有关.计算值与实测值较为吻合.通过非线性回归得到35CrMo钢的动态再结晶晶粒尺寸的关系式为:DDRX=2.25 × 104Z-0.22.通过双道次压缩和单道次压缩保温实验,得出35CrMo钢静态再结晶激活能和动力学方程.     

一种铌微合金钢热变形过程中的动态再结晶

通过一种铌微合金钢高温下(900～1100℃)不同应变速率(0.01～10s<'-1>)的热模拟单道次压缩试验,结合组织观察,研究了热变形参数对动态再结晶过程的影响,求出动态再结晶形变激活能及相关参数,建立了该钢的热变形本构方程.实验结果表明,合金元素的添加,由于固溶原子拖曳及析出物的钉扎作用,增加了动态再结晶激活能,显著抑制了该钢的动态再结晶及晶粒长大过程.原始奥氏体晶粒尺寸增大、变形温度降低及应变速率增大将抑制动态再结晶过程.     

Dynamic Recrystallization Behavior and Processing Map Development of 25CrMo4 Mirror Plate Steel During Hot Deformation

The dynamic recrystallization behavior of 25 CrMo4 steel was systematically investigated by compression deformation at different temperatures and strain rates on a Gleeble 1500 thermal mechanical simulation tester. The flow curves under different deformation conditions were obtained, and the effects of deformation temperature and strain rate on the appearance of the flow curves were discussed. Based on the experimental flow curves, the activation energy determined by regression analysis was Q = 337 k J/mol, and the constitutive model was constructed. All the characteristic points of the flow curves were identified from the work hardening rate curves(θ=dó/dεvs ó), which were derived from the flow curves. Then, the kinetics model of dynamic recrystallization was determined by combining the Avrami equation with the stress loss resulted from the dynamic recrystallization. With the aid of the kinetics model, the effect of strain on the efficiency of power dissipation was discussed. Furthermore, the optimum parameters for the forging process were determined based on the processing maps.     

Modeling Deformation Flow Curves and Dynamic Recrystallization of BA-160 Steel During Hot Compression

The hot deformation behavior of a high strength low carbon steel was investigated using hot compression test at the temperature range of 850–1100 °C and under strain rates varying from 0.001 to 1 s^?1. It was found that the flow curves of the steel were typical of dynamic recrystallization at the temperature of 950 °C and above; at tested strain rates lower than 1 s^?1. A very good correlation between the flow stress and Zener–Hollomon parameter was obtained using a hyperbolic sine function. The activation energy of deformation was found to be around 390 kJ mol^?1. The kinetics of dynamic recrystallization of the steel was studied by comparing it with a hypothetical dynamic recovery curve, and the dynamically fraction recrystallized was modeled by the Kolmogorov–Johnson–Mehl–Avrami relation. The Avrami exponent was approximately constant around 1.8, which suggested that the type of nucleation was one of site saturation on grain boundaries and edges.     

Dynamic Recrystallization during Hot Deformation of 304 Austenitic Stainless Steel

The kinetics of dynamic recrystallization (DRX) during hot compression of 304 austenitic stainless steel was studied over the temperature range of 900-1200 °C and strain rate range of 0.002-0.1 s^?1. The initiation and evolution of DRX were investigated using the process variables derived from flow curves. By the regression analysis for conventional hyperbolic sine equation, the activation energy for DRX was determined as Q = 475 kJ mol^?1. The temperature and strain rate domain where DRX occurred were identified from the strain rate sensitivity contour map. The critical stress (and strain) for the initiation of DRX was determined from the inflection point on the work hardening rate (θ = dσ/dε) versus flow stress (σ) curve. The saturation stress of the dynamic recovery (DRV) curve was calculated from the θ-σ plot at the same condition at which DRX occurred. Progress of fraction recrystallization was determined from the difference between the generated DRV curve and the experimental DRX curve. In addition, the microstructural evolution at different strain levels during DRX was characterized and compared with the calculated fraction recrystallization.     

压下量对铸态42CrMo钢动态再结晶的影响研究

运用刚粘塑性有限元Deform软件和热力耦合方法对铸态42CrMo钢热压缩过程中动态再结晶行为进行了研究,得到了热压缩过程中动态再结晶百分数分布规律.模拟发现再结晶晶粒细化区主要分布在心部大变形区和接触边缘区域,鼓部外圈仍为粗晶区.通过金相观察法验证了模拟的正确性.     

低碳钢热变形过程中奥氏体动态再结晶问题分析

以Q235低碳钢为研究对象,研究其在不同温度和应变速率热变形过程中的膨胀曲线改变,揭示低碳钢在动态再结晶过程的临界条件和晶粒尺寸。结果表明,当变形温度大于850℃,应变速率在0.1~60.0 s-1之间,应力应变曲线上对应峰值为动态再结晶过程。奥氏体动态再结晶发生的前提条件是εc=3.628×10-4DA0.21Z0.17,且可以通过控制钢的冷却速度获得较小尺寸的铁素体晶粒。     

Hot Deformation and Dynamic Recrystallization Behavior of Austenite-Based Low-Density Fe–Mn–Al–C Steel

The hot deformation and dynamic recrystallization(DRX) behavior of austenite-based Fe–27Mn–11.5Al–0.95 C steel with a density of 6.55 g cm-3were investigated by compressive deformation at the temperature range of900–1150 °C and strain rate of 0.01–10 s-1. Typical DRX behavior was observed under chosen deformation conditions and yield-point-elongation-like effect caused by DRX of d-ferrite. The flow stress characteristics were determined by DRX of the d-ferrite at early stage and the austenite at later stage, respectively. On the basis of hyperbolic sine function and linear fitting, the calculated thermal activation energy for the experimental steel was 294.204 k J mol-1. The occurrence of DRX for both the austenite and the d-ferrite was estimated and plotted by related Zener–Hollomon equations. A DRX kinetic model of the steel was established by flow stress and peak strain without considering dynamic recovery and d-ferrite DRX. The effects of deformation temperature and strain rate on DRX volume fraction were discussed in detail. Increasing deformation temperature or strain rate contributes to DRX of both the austenite and the d-ferrite, whereas a lower strain rate leads to the austenite grains growth and the d-ferrite evolution, from banded to island-like structure.     

微合金超高强度钢的热变形行为及流变应力模型

采用Gleeble-3500热模拟试验机研究微合金超高强度复相钢(CP钢)在变形温度为900～1150℃、应变速率为0.1～10 s-1条件下的热变形行为,观察了不同变形条件下的晶粒组织。根据实验结果,建立了CP钢在热变形过程中的本构方程及动态再结晶过程的物理模型。实验结果表明,微合金元素钛的存在,明显抑制了动态再结晶的发生,提高了变形激活能,其值为439.09 kJ/mol。另外,热变形参数对最终的晶粒大小具有重要影响,随着再结晶变形温度的降低及应变速率的提高,晶粒尺寸明显减小。本构方程、动态再结晶模型能为科学设计和有效控制CP钢的热加工工艺提供依据。     

Hot Deformation Behavior and Dynamic Recrystallization Characteristics in a Low-Alloy High-Strength Ni–Cr–Mo–V Steel

This study presented a quantitative investigation of deformation behavior and dynamic recrystallization of low-alloy highstrength Ni–Cr–Mo–V steels during hot deformation.A series of isothermal compression experiments were performed at temperatures ranging from 800 to 1200°C and strain rates from 0.01 to 10 s~(-1)with a height reduction of 60%.A complete Arrhenius constitutive model and processing maps were developed.The results showed that the constitutive model had the ability to predict the flow stress with an average absolute relative error of\5.7%.The processing maps constructed at strains of 0.2,0.4,and 0.8 showed that flow instability was prone to occur at higher strain.Dynamic recrystallization tended to take place at higher temperatures(900–1200°C)and lower strain rates(0.01–1 s~(-1)).The critical strain for the onset of dynamic recrystallization was determined,and a kinetics model was developed.The predicted results for recrystallization volume fraction and flow stress were compared with the experimental data,which indicated that the model was accurate and reliable.     

304L不锈钢高温变形组织的演化

采用Gleeble-1500D热/力学模拟试验机对304 L不锈钢铸态及锻态试样进行了热压缩试验研究,工艺参数为：变形温度950℃～1 150℃、变形量0.7,变形速率0.1s-1。结果表明：铸态的峰值应力低于锻态的峰值应力,铸态组织的动态再结晶明显迟于锻态组织;铸态及锻态304L不锈钢流变应力随着温度的升高而降低;随着变形温度的升高,动态再结晶百分数增加,再结晶组织增多并趋于完全。     

82B高碳钢热变形奥氏体再结晶行为研究

用Gleeble2000热模拟试验机对82B钢奥氏体再结晶进行了研究。结果表明，82B钢以0．5s^-1的应变速率在950℃及其以上温度进行变形时将发生动态再结晶，950℃以下发生动态回复；以2s^-1的应变速率在1000℃以上进行变形时发生动态再结晶．1000℃及其以下仅发生动态回复；在所有试验温度以10s^-1和30s^-1的应变速率变形时．均仅发生动态回复。恒温双道次压缩时，在3-200s的间隔时间内均发生了静态再结晶。     

82B高碳钢热变形奥氏体再结晶行为研究

用Gleeble2000热模拟试验机对82B钢奥氏体再结晶进行了研究。结果表明,82B钢以0.5s-1的应变速率在950℃及其以上温度进行变形时将发生动态再结晶,950℃以下发生动态回复;以2s-1的应变速率在1000℃以上进行变形时发生动态再结晶,1000℃及其以下仅发生动态回复;在所有试验温度以10s-1和30s-1的应变速率变形时,均仅发生动态回复。恒温双道次压缩时,在3￣200s的间隔时间内均发生了静态再结晶。     

35CrMo钢热变形机制的模拟研究

以弯曲镦锻 3 5 Cr Mo钢火车曲轴为例 ,通过将该钢以 90 0℃～ 1 2 5 0℃变形温度 ;0 .0 5 s-1、0 .5s-1、1 .0 s-1的应变速率 ;在 Greeble-1 5 0 0试验机上进行压缩 1 5 %～ 80 %的热变形实验 ,和随后进行的微观组织分析得出了 :材料热变形屈服应力变化模型 ;材料热变形本构关系 ;动态与静态再结晶模型和热加工参数与微观组织变化的相关性资料。描绘了在 1 2 5 0℃ ,应变速率为 1 .0 s-1时 ,3 5 Cr Mo钢热变形应力应变曲线和相应的再结晶组织。通过对 3 5 Cr Mo钢在高温大变形条件下 ,试件内部各区域晶粒尺寸的回归计算 ,验证了该钢热变形晶粒计算模型。所得出的实验结果和计算模型为热成形工艺分析和质量控制提供了科学的依据     

Simulation of the Kinetics of Dynamic Recrystallization of Alloy KhN55MBYu-VD During Hot Deformation

Metal Science and Heat Treatment - A facility for physical simulation is used to plot dependences of flow stress on the degree of deformation in the temperature range from 1000 to 1230°C at...     

GCr15钢高速热变形与再结晶的研究

利用Ｆｏｒｍａｓｔｏｒ－Ｐｒｅｓｓ热模拟试验机对ＧＣｒ１５钢高速热变形及再结晶过程进行了研究，着重探讨了形变速率及间隔时间对变形与再结晶过程的影响。结果表明：Ｌ在高速变形条件下，随着变形速率的增加，形变享晶数量逐渐增加，同时，形变速率的增加促进了动再结晶过程的进行，改善了再结晶后组织的均匀性。在高形变速率、小变形量、多次变形时，当各道次各间隔时间很短时（＜ｌｓ），真应力－真应变曲线接近于平滑。     

GH625合金的动态再结晶行为研究

采用Gleeble-3800热模拟试验机研究了GH625合金在变形温度为950～1150℃,应变速率为0.001～5s-1条件下的热变形特性,并用OM和TEM分析了变形条件对微观结构的影响。结果表明:当应变量很小时,该合金没有发生再结晶,直到应变量达到0.1时才开始有再结晶晶粒析出。随着变形温度的升高,再结晶晶粒尺寸增大,位错密度降低;当温度较低时显微结构中可以观察到孪晶。当变形温度一定时,随应变速率的增大,再结晶的形核率增大且晶粒变小,位错密度变大;而当应变速率较低时,再结晶进行得比较充分,晶粒尺寸较大。根据实测的应力-应变曲线,获得了该合金发生动态再结晶的临界应变εc和峰值应变εp与Z参数之间的关系:εc=2.0×10-3.Z0.12385,lnεp=-6.02285+0.12385lnZ。此外,还采用定量金相法计算出了合金的动态再结晶体积分数,并建立了该合金动态再结晶的动力学模型:Xd=1-exp[-0.5634(ε/εp-0.79)1.313]。     

海面建筑用高Cr-N钢在热腐蚀过程中的动态再结晶行为分析

研究了中铬钢和高铬钢在不同冷却速率下的显微结构和动态再结晶行为。结果表明,高铬钢在冷却速度不低于0.5℃/s,中铬钢冷却速率不低于10.0℃/s时,可以使板条马氏体比例不低于95%。冷却速度为10℃/s时,中铬钢中有将近3.5%的介于板条马氏体之间的薄膜状残留奥氏体。     

Zr-1.0Sn-1.0Nb-0.1Fe合金热变形行为及动态再结晶模型建立

热轧过程中的动态再结晶影响锆合金板材的组织、织构演化以及最终力学性能。在本研究中,利用Gleeble 3800热模拟实验研究了Zr-1.0Sn-1.0Nb-0.1Fe合金在应变速率为0.01～10 s-1范围下,变形温度在550～700℃的动态再结晶行为。通过对实测应力-应变结果的加工硬化速率分析,确定了动态再结晶开始发生的临界应变和峰值应变。动态再结晶是通过塑性变形过程中流变应力的软化来判断的,并量化为计算的动态回复曲线和实测的应力-应变曲线之间的差异。采用计算的临界应变、峰值应变和动态再结晶体积分数对动态再结晶过程进行建模,最终利用EBSD统计所得的再结晶体积分数验证了Zr-1.0Sn-1.0Nb-0.1Fe合金的动态再结晶模型。