新型铝奥氏体耐热合金的高温塑性变形行为和热力工性能

新型含铝奥氏体耐热合金(AFA)进行压缩热模拟试验,使用OM和EBSD等手段研究了这种合金在950~1150℃和0.01~5 s^-1条件下的微观组织演变、建立了基于动态材料模型热加工图、分析了变形参数对合金加工性能的影响并按照不同区域组织变形的特征构建了合金的热变形机理图。结果表明：新型AFA合金的高温流变应力受到变形温度和应变速率的显著影响。在变形温度为950~1150℃和应变速率为0.18~10 s^-1条件下,这种合金易发生流变失稳。在变形温度为1050~1120℃、应变速率0.01~0.1 s^-1和变形温度1120~1150℃、应变速率10^-0.5~10^-1.5 s^-1这两个区间,这种合金发生完全动态再结晶行为且其再结晶晶粒均匀细小,功率耗散因子η达到峰值45%。新型AFA合金的热加工艺,应该优先选择再结晶区域。     

TA12钛合金热变形微观组织演变及变形参数优化

在应变速率为0.01~10 s-1,变形温度为870~1 070℃,最大变形量为80%的条件下,利用Gleeble-3800热模拟机对TA12合金高温压缩变形行为进行研究。依据实验结果绘制真应力-应变曲线,分析变形参数与组织的关系。同时把应力-应变曲线作为计算应变速率敏感指数m、功率耗散因子η、失稳判据ξ的底层数据,研究应变速率、变形温度、变形量共同存在对应变速率敏感指数m、功率耗散因子η的影响,绘制失稳图对失稳区域进行识别,并将功率耗散图和失稳图叠加构建热加工图。结果表明,在变形温度较低时,温度的影响主要表现为α相形态和数量的变化,在变形温度较高时,主要表现为β晶粒粗化;应变速率的影响主要表现在变形时间上;较高的η和ξ区域为良好加工区域,较低的η和ξ的失稳变形参数区域为加工避免区域。本批次合金适宜加工参数为温度910~970℃,应变速率0.01~0.3 s-1。     

挤压态Mg-Gd-Y-Zn-Zr合金本构方程及加工图

目的 通过热模拟实验研究挤压态Mg-8.5Gd-4.5Y-0.7Zn-0.4Zr合金的本构方程及加工图.方法 在Gleeble热模拟机上开展应变速率为0.001～1 s?1,变形温度为300～450℃条件下的单轴热压缩实验.根据动态材料模型,建立合金的热加工图,分析功率耗散因子随变形温度、应变速率和应变的变化规律.结果 合金的流变应力在不同的变形温度和应变速率下表现出不同的特征,流变应力与变形温度和应变速率的关系可用双曲正弦本构关系来描述,其平均激活能为209.223 kJ/mol,应力指数为3.442.合金的失稳区出现在变形温度为420～450℃,应变速率为0.1～1 s?1的范围内.结论 得到了挤压态合金的本构方程,合金最佳热加工工艺参数为变形温度为400℃,应变速率为1 s?1.     

反应堆压力容器用SA508Gr.4N钢的热变形行为

利用Gleeble-1500D热模拟试验机,在温度为1050~1250℃、应变速率为0.001~0.1s-1、真应变量0.16的条件下,研究和分析SA508Gr.4N钢高温塑性变形及动态再结晶行为。结果表明:SA508Gr.4N钢的高温真应力-应变曲线主要以动态再结晶为特征,峰值应力随变形温度的降低或应变速率的升高而增加,属于温度和应变速率敏感材料;在真应力-应变曲线的基础上,建立材料热变形本构方程,较好地表征了材料高温流变特征,其热激活能为383.862kJ/mol;其硬化率-应力(θ-σ)曲线均呈现拐点且-dθ/dσ-σ曲线出现极小值;临界应变随应变速率的增大与变形温度的降低而增加,且临界应变(εc)与峰值应变(εp)之间具有一定相关性,即εc/εp=0.517;临界应变与Z参数之间的函数关系为εc=8.57×10-4 Z0.148。     

新型高强Al-Zn-Mg-Cu合金的热变形行为和热加工图

采用热力模拟实验方法进行热压缩变形实验,研究了一种新型Al-Zn-Mg-Cu高强铝合金铸态组织在变形温度为300～450℃,应变速率为10-3～10s-1,压缩变形量为50%条件下的热变形行为,建立了该合金的热加工图。变形温度和应变速率对该合金流变应力的影响显著;实验参数条件下,该合金流变应力曲线呈现稳态动态回复型曲线特征。热加工图和组织分析表明:当应变较小时(ε=0.1),合金具备铸态组织特征,合适的热加工参数:350～450℃,应变速率10-3～10-2s-1;当应变较大时(ε=0.5),合金具备锻态组织特征,较佳的热加工参数:300～450℃,应变速率10-3～10-1s-1。     

211Z.X耐热高强韧铝合金热变形行为及加工图研究

在Gleeble-3500热模拟试验机上对211Z.X耐热高强韧铝合金进行了等温热压缩实验,实验的应变温度为350~500℃、应变速率为0.01~10s~(-1)。研究了不同变形条件下的流变特征,并分析该合金高温变形时流变应力的规律,构建了材料流变应力本构模型;同时基于动态材料模型建立了加工图,确立了该合金在实验条件的最佳工艺参数。结果显示:功率耗散图与失稳图随应变量的增加而变化,功率耗散峰区由3个逐渐减为1个,失稳区域随应变而移动并逐渐增大;在加工图中,随着应变的增大,安全加工区域逐渐减小。综合加工图与微观组织的分析结果,211Z.X铝合金最佳的加工工艺区间为:变形温度485~500℃、应变速率0.03~10s~(-1)。     

基于位错密度理论的超高强双相钢DP1000热变形本构模型

对超高强双相钢DP1000进行单道次热模拟压缩实验,研究了其在950~1150℃和0.05~10 s~(-1)条件下的热变形行为,分析了变形温度和变形速率对流变应力的影响,建立了基于位错密度理论的热力学本构模型,确定了可表征微观硬化和软化机制的材料特征参数,量化了加工硬化、动态回复和动态再结晶对宏观力学行为的影响。结果表明:超高强双相钢DP1000的热变形应变速率ε?≤0.05 s~(-1)时以动态再结晶软化机制为主,应变速率ε?0.1 s~(-1)时以动态回复软化机制为主,应变速率0.05 s~(-1)ε?≤0.1 s~(-1)时由这两种软化机制共同作用。这个本构模型的预测值与实验值具有较高的一致性,能准确预测超高强双相钢DP1000在高温变形条件下的流变应力。     

Ti−6Mo−5V−3Al−2Fe−2Zr合金热变形行为及热加工图

目的 建立近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr(质量分数)的热变形本构方程,绘制热加工图,确定该合金的流变失稳区和适宜加工区,为其在工业生产中热加工工艺参数的制定提供指导。方法 在变形温度700~ 850 ℃、应变速率0.000 5~0.5 s⁻¹、真应变0.7的条件下,对近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr进行热压缩实验;基于Arrhenius方程建立该合金的热变形本构方程,并对方程进行验证;根据Prasad失稳准则,构建该合金的热加工图。结果 该合金的流变应力随着变形温度的升高而减小,随着应变速率的增大而增大;其热变形激活能为226.29 kJ/mol,本构方程为;通过热变形本构方程得到的峰值应力计算值与实验值平均误差为4.21%。结论 建立的热变形本构方程预测了流变应力,描述了该合金的热变形行为;通过叠加合金的能量耗散图和流变失稳图,获得了该合金的热加工图。基于热加工图确定该合金的流变失稳区为变形温度700~755 ℃与784~850 ℃、应变速率0.5~0.05 s⁻¹,最佳加工区为变形温度836~850 ℃、应变速率0.000 5~0.005 s⁻¹。     

18Cr-3Mn-1Ni-0.22N节镍型双相不锈钢热压缩再结晶行为研究

采用物理模拟方法研究了18Cr-3Mn-1Ni-0.22N节镍型双相不锈钢在1123～1423 K/0.01～10 s-1、变形量为70％条件下的热压缩变形行为.不锈钢的流变曲线在1223～1423 K/0.01～1 s-1条件下发生了流变软化和二次硬化现象,且二次硬化随应变速率增至10 s-1而减缓.动态再结晶组织演变主要受温度和变形量的影响,在1123 K/0.01～10 s-1变形时主要发生在铁素体相,而在1323 K/0.01～10 s-1变形时主要发生在奥氏体相.不同应变速率条件下,1123 K变形时不锈钢发生动态软化的程度最大,并随温度升至1223 K时应力降幅较快.不同温度下1 s-1变形时不锈钢的软化程度最差,0.1 s-1且高于1223 K变形时不锈钢的软化程度最好.当应变速率一定时,再结晶临界应变随温度升高呈先增加后下降趋势.建立了0.2～1.2真应变条件下功率耗散系数η与失稳因子ξ的3D热加工图.随应变的增大,η>0.3的区域逐渐从1300～1400 K/0.01 s-1向1300～1400 K/10 s-1扩大,ξ>0的安全区域集中在高温区.预测热加工的最佳参数范围为T=1280～1423 K,ε·=0.033～0.326 s-1,功率耗散系数η=0.39～0.44.     

基于热加工图的锻造斗齿用钢热加工工艺参数

目的制定一种锻造斗齿用新型低合金耐磨钢的热加工工艺参数。方法采用Gleeble-1500D热模拟试验机对实验钢进行高温压缩,在变形温度为1173~1473 K,应变速率为0.01~10 s~(-1)条件下,压缩变形60%,得到其真应力-真应变曲线。依据压缩实验数据,基于动态材料模型,建立材料的热加工图,分析实验钢在不同热变形条件下的变形特点。结果该锻造斗齿用低合金耐磨钢在不同应变下的热加工图呈现相近特征,能量耗散系数η随变形温度的升高而增大,随着应变速率的减小而减小;当应变值大于等于0.3时,在变形温度为1173~1440 K,应变速率为0.32~10 s~(-1)范围内,热加工失稳区域随着变形温度的升高而减小,随着应变速率的减小而减小。结论该锻造斗齿用低合金耐磨钢适宜的热加工工艺参数范围:变形温度为1185~1373K,应变速率为0.01~2 s~(-1);最优参数范围:变形温度为1330~1340 K,应变速率为0.2~0.5 s~(-1)。     

Characterization of hot deformation behavior of a new Ni–Cr–Co based P/M superalloy

The hot deformation behavior of a new Ni–Cr–Co based P/M superalloy was studied in the temperature range of 950–1150 °C and strain rate range of 0.0003–1 s^? 1 using hot compression tests. It was characterized by true stress–true strain curves, constitutive equation, strain rate sensitivity m contour maps, power dissipation η maps and hot processing maps. The microstructural validation of processing maps was also done. The results show that the flow stress decreases with increasing temperature and decreasing strain rate. The hot deformation apparent activation energy of the Ni–Cr–Co based P/M superalloy at peak stress is 805 kJ/mol. The m and η contour maps are similar, and the values of m and η in the peak zones increase with increasing strain. When the strain is 0.5, a domain with its peak η of 40% and peak m of 25% occurs at 1050 °C and 0.0003 s^? 1, which corresponds to dynamic recrystallization and can be as an optimum condition for good workability.     

一种新型近β型Ti-5.5Mo-6V-7Cr-4Al-2Sn-1Fe合金热变形行为

采用Gleeble-3800型热模拟试验机对一种新型近β型Ti-5.5Mo-6V-7Cr-4Al-2Sn-1Fe(质量分数/%)钛合金进行等温恒应变速率压缩实验。变形温度范围为:655~855℃,应变速率范围为:0.001~10s^-1 ,最大真应变为0.8。根据实验数据,建立了该合金的高温流变应力模型,计算出热变形激活能约为255kJ/mol,并绘制出热加工图。结合热加工图与材料的显微组织分析可知,在高应变速率(1~10s^-1 )条件下变形时,在热加工图上表现为材料的功率耗散值(η)低,为失稳区域,易产生绝热剪切带与局部塑性流动、开裂等现象。在应变速率小于0.01s^-1 和相变点( T β)温度以下(655~755℃)进行热变形时,组织变化主要以动态回复为主;在应变速率小于0.01s^-1 和 T β以上(755~855℃)进行热变形时,组织发生动态再结晶,且随着温度的升高,新产生的再结晶晶粒逐渐长大。在相变点附近(755~770℃),变形速率为0.001~0.003s^-1 区域内变形时,功率耗散值达到最大值,组织发生动态再结晶,该区域为合金热变形的“安全区”。     

Development of processing maps for a Ni-based superalloy

The hot deformation characteristics of a Ni-based superalloy were studied in the temperature range 1050–1180 °C and strain rate range 0.01–10 s^− 1 using hot compression tests. Processing maps for hot working were developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate, interpreted using a dynamic materials model. A hot deformation equation is given to characterize the dependence of peak stress on the temperature and strain rate. A hot deformation apparent activation energy of the Ni-based superalloy is about 496 kJ/mol. The processing maps of the Ni-based superalloy obtained in a strain range of 0.1–0.7 are essentially similar, which indicates that strain does not have a significant influence. The maps exhibit a clear domain with its peak efficiency at about 1140 °C and 0.01 s^− 1; the domain has its peak efficiency of about 36–41% for different strains. On the basis of hot deformation microstructural observations, the full recrystallization region can be identified in the processing map at a strain of 0.7.     

Effects of strain on the workability of a high strength low alloy steel in hot compression

Based on the experimental results from the hot compression tests of 42CrMo steel, the efficiencies of power dissipation and instability parameter were evaluated. The effects of strain on the efficiency of power dissipation and instability parameter of 42CrMo steel have been discussed in detail. Processing maps were constructed by superimposition of the instability map over the power dissipation map. The dynamic recrystallization domains and instable zones were identified in the processing map. The effects of strain on microstructural evolutions were correlated with the processing maps. According to the 3D processing maps, the optimum domain of hot deformation is in the temperature range of 1050–1150 °C and strain rate range of 0.01–3 s⁻¹, with its peak efficiency of 32% at about 1140 °C and 0.23 s⁻¹, which are the optimum hot working parameters.     

ZK60和ZK60-1.0Er镁合金热压缩变形和加工图

采用Gleeble-1500D热模拟试验机对ZK60和ZK60-1.0Er镁合金进行了热压缩实验,分析了合金在温度为160~420℃,应变速率为0.0001~1.0s-1条件下的流变应力变化特征。结果表明:两种镁合金在热压缩过程中的流变应力随变形温度的降低和应变速率的升高而增加,在流变应力达到峰值后随即进入稳态流变;稀土Er的加入使得平均变形激活能珚Q值由183kJ/mol降到153kJ/mol,应力指数n值由6提高到8;发生动态再结晶的临界应力σc值随变形温度升高和应变速率降低而降低,在420℃/1.0s-1高温高应变速率时,稀土Er的加入使得ZK60镁合金发生动态再结晶的临界应力值σc由76MPa降到50MPa。通过动态模型构建热加工图并结合金相组织观察可知:稀土Er的加入缩小了ZK60镁合金的热加工失稳区,增加了热加工安全区的功率耗散效率峰值η_(max),由35%增大到45%,促进了动态再结晶晶粒的形核,但抑制了再结晶晶粒的长大。     

Hot deformation and processing maps of X-750 nickel-based superalloy

The deformation behavior of X-750 superalloy was investigated using the hot compression test in the temperature range of 850–1050 °C, and strain rate of 0.1–50 s⁻¹. The experimental results show that the flow stress of superalloy is significantly sensitive to the strain, the strain rate and the deformation temperature. Using dynamic materials model the processing maps of X-750 superalloy at strain of 0.1, 0.3 and 0.5 were established respectively. Microstructure observations reveal that the grain size as well as the volume fraction of the recrystallized grains increased at higher deformation temperature or lower strain rate. At strain of 0.5, the flow instability domain mainly located at lower temperature which is associated with shear band formation and flow localization. The optimum parameters for hot working of the alloy are deformation temperature of 1000–1050 °C and strain rate of 0.1–1 s⁻¹ according to the processing map and microstructure at true strain of 0.5.     

2519A铝合金热压缩流变行为和显微组织分析

在Gleeble-1500D热模拟仪上进行热压缩实验,研究温度从300℃～450℃、应变速率为0．001～10s^-1时2519A铝合金热压塑行为,并用金相显微镜分析在不同热压缩条件下的组织形貌特征。结果表明,流变应力开始随着应变的增大而增大,出现峰值之后慢慢减小并慢慢趋于平稳。应力峰值随温度的增加而减小,随应变增大而增大,其热变形行为可用包含Zener-Hollomon参数的双弦本构关系来描述,得到平均激活能Q=223．11706kj／mol。合金在0．001s^-1～1s^-1。应变速率条件下软化机制主要为动态回复,而当应变速率上升到10s^-1后,合金微观组织出现局部动态再结晶。     

Application of neural networks to predict the elevated temperature flow behavior of a low alloy steel

In order to study the workability and establish the optimum hot forming processing parameters for 42CrMo steel, the compressive deformation behavior of 42CrMo steel was investigated at the temperatures from 850 °C to 1150 °C and strain rates from 0.01 s⁻¹ to 50 s⁻¹ on Gleeble-1500 thermo-simulation machine. Based on these experimental results, an artificial neural network (ANN) model is developed to predict the constitutive flow behaviors of 42CrMo steel during hot deformation. The inputs of the neural network are deformation temperature, log strain rate and strain whereas flow stress is the output. A three layer feed forward network with 12 neurons in a single hidden layer and back propagation (BP) learning algorithm has been employed. The effect of deformation temperature, strain rate and strain on the flow behavior of 42CrMo steel has been investigated by comparing the experimental and predicted results using the developed ANN model. A very good correlation between experimental and predicted result has been obtained, and the predicted results are consistent with what is expected from fundamental theory of hot compression deformation, which indicates that the excellent capability of the developed ANN model to predict the flow stress level, the strain hardening and flow softening stages is well evidenced.     

Hot Deformation and Modeling of Flow Stress for a Ti-containing HSLA Steel

Single-stage and double-stage interrupted hot compression tests for simulating hot rolling have been carried out for a Ti-containing HSLA steel (10Ti). Physical simulation of hot rolling was in progress utilizing a Thermecmastor-Z simulator in 850~1150℃ and strain rate of 0.1~60 s-1.A model for residual strain ratio λ was designed, and a model of flow stress considering residual strain has been obtained. The hot deformation behaviour at various strain rates has been studied.