微合金钢高温变形及动态再结晶行为的研究

本文主要采用高温压缩和高温扭转变形方法,研究了0.04％V低碳钢和Ti处理16Mn钢的高温变形行为和动态再结晶规律。 研究工作主要有:1)金属材料高温变形与动态再结晶(DRX)行为。2)绘制热形变奥氏体的组织状态图。3)形变参数对热形变奥氏体动态再结晶晶粒尺寸的影响。结果表明,应变速率,形变量ε,形变温度T和原始晶粒尺寸D_0对(σ-ε)曲线和DRX行为有很大的影响。热形变奥氏体DRX晶粒尺寸dr不仅与Z[Z=·exp(Q/RT)]参数有关,而且在完全DRX区的一定形变量范围内还与形变量ε有关。dr随ε增大而减小。当形变量达到一临界值时,趋向一恒定值。超过此临界值,DRX晶粒尺寸dr不再与形变量ε有关,而仅决定于Z参数。     

热变形对奥氏体晶粒尺寸的影响

本文研究了热变形对12CrNi3A钢和18Ni马氏体时效钢再结晶行为和奥氏体组织状态的影响,并着重讨论了不同状态奥氏体的晶粒大小与热变形参数间的关系。文中还探讨了热变形对细化奥氏体晶粒的极限值,续动态再结晶的晶粒长大和形变量对动态再结晶晶粒尺寸的影响等问题。     

ULCB钢的奥氏体形变组织研究

采用单道次压缩实验方法,用THERMECHMASTOR-Z热模拟试验机在1 100～850℃、变形速率2 s-1和变形量10%～50%的应变条件下,对900 Mpa级ULCB钢进行应力-应变曲线和奥氏体形变组织的试验.结果表明,在950℃以下的低温变形中不发牛形变再结晶,随着变形量增大,先出现晶内形变带直到晶粒拉长变形.在1 000℃以上的高温变形中,当变形量大于临界变形量时发生形变再结晶.随着变形量增大,奥氏体再结晶晶粒面积百分数依次增加,形变组织为部分或完全再结晶奥氏体,奥氏体晶粒平均截距的大小取决于形变再结晶奥氏体的晶粒尺寸和面积百分数.     

超声振动影响低碳钢热压缩过程的分析和试验

为研究超声振动对低碳钢热变形中奥氏体再结晶过程的影响,基于Gleeble-1500热模拟试验和对变形后淬火试样原始奥氏体晶界观测,构建Q235钢热压缩变形抗力和奥氏体平均晶粒尺寸数学模型,对超声振动和常规压缩变形条件下低碳钢圆柱试样的热压缩过程进行仿真分析。结果表明,超声振动导致试样一端变形如倒置的伞状,发生奥氏体动态再结晶所需临界变形程度明显降低;奥氏体动态再结晶首先从试样超振激励端开始,变形后试样内最小奥氏体晶粒尺寸约为20μm;超声振动变形试验表明,试样表层组织纳米化,内部晶粒尺寸相比常规压缩明显细化。     

高温合金800H的动态再结晶及其模型的建立

采用单道次热压缩实验分析了变形参数对高温高强合金800H热变形的影响。结果表明:初始晶粒尺寸越小、变形温度越高、变形速率越小,越容易出现动态再结晶现象;同样,在能够发生动态再结晶的情况下,变形量的增大促使动态再结晶充分进行;利用拟合得到了800H合金的动态再结晶激活能、临界变形量模型、再结晶动力学模型、再结晶运动学模型和再结晶晶粒尺寸模型。采用Deform-2D进行晶粒度模拟,仿真模拟结果与金相统计出的再结晶晶粒尺寸变化趋势一致,平均误差为4.5μm。极小的平均误差表明所建模型与实际情况相符合,可以用于预测800H合金热变形过程中再结晶的晶粒尺寸。     

高强度低合金钢热轧变形再结晶与动态再结晶的相关性研究

本文采用热压缩方法(Gleeble试验机)和定量金相方法,研究了原始奥氏体晶粒尺寸和形变速率对动态应力一应变曲线的影响,以及原始奥氏体晶粒尺寸、形变量和形变速率等工艺参数对再结晶晶粒尺寸的影响,据此解释了高强度低合金钢热轧变形再结晶与热压缩动态再结晶的研究方面,存在的一些矛盾和问题。     

CSP热轧TRIP钢动态再结晶行为研究

摘要：采用Gleeble-3500热模拟试验机,在温度为950~1150℃、应变速率为0.1~10s-1和变形量为65%的条件下研究了CSP热轧TRIP钢的动态再结晶行为,探讨了初始奥氏体晶粒尺寸对TRIP钢动态再结晶行为的影响。研究结果表明,初始奥氏体晶粒尺寸越小,变形温度越高,应变速率越慢时,TRIP钢中奥氏体越易发生动态再结晶。其中,粗晶试样（初始奥氏体晶粒尺寸为767.54μm）在1050~1150℃内变形时,将发生动态再结晶。其热变形激活能为361539.17J/mol,确定了Zener-Holloman参数与应变速率和温度的关系式,建立了动态再结晶临界应变模型、高温奥氏体流动应力模型和动态再结晶晶粒尺寸模型,理论模拟结果与试验结果吻合较好。     

低碳钢Q235形变奥氏体的静态再结晶

在Thermecmastor-Z热模拟试验机上进行了低碳钢Q235的双道次压缩试验,确定了该钢静态再结晶的动力学方程.结果表明,在大变形量下,即使变形温度较低(850～800℃),应变速率较高时,静态再结晶的速度仍然很快.通过静态再结晶可以将奥氏体晶粒尺寸细化至10～20μm.     

Custom 450高强度不锈钢的动态再结晶行为

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1 050～1 200℃和应变速率为0.01～10 s~(-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1 050～1 200℃和应变速率为1.0～10 s~(-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0.01 s~(-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。     

新型二次硬化渗碳钢的高温塑性及热加工图

 利用Gleeble-3800热模拟试验机,对一种新型二次硬化渗碳钢C61进行了高温轴向压缩试验,测得其高温流变曲线,观察了高温变形后的显微组织,获得了该钢的热变形激活能[Q]为414.84 kJ/mol,建立了试验钢的热变形本构方程,并绘制了其热加工图。结合高温变形后的显微组织和热加工图,确定最优热变形工艺参数为变形温度范围为1 050～1 100 ℃,应变速率范围为0.1～1.0 s－1,此时试验钢组织发生了完全动态再结晶,晶粒明显细化,且对应的能量耗散效率达到峰值。     

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To explore the hot compression recrystallization behaviours of low carbon CrNiMo carburized bearing steel, isothermal compression simulation experiment was carried out by the Gleeble 1500D thermal-mechanical simulator at temperatures between 900 and 1050??, strain rates between 0??1, 1 and 10s-1 and deformations among 10%, 30%, 50%. Thermal deformation dynamic recrystallization process was analyzed by grain sizes and true strain-true stress curves in different conditions. Material??s deformation activation energy and hot deformation equation was regressed, the hot working map of material was calculated, and the critical time of static recrystallization was experimented. The results show that, high deformation temperature, low strain rate and large deformation are conducive to the occurrence of dynamic recrystallization. The fine recrystallized grains were abtained at 1050??, 50% deformation and strain rate 1s-1 in this experiment, and the average grain size is 14??97??m; The activation energy of low carbon CrNiMo carburized bearing steel decreases slowly when deformation larger than 30%. It is deduced to 436??016kJ/mol in 50% deformation, and the experimental results are also matched to the hot working map. The material has reached to the dynamic recrystallization thermodynamic condition in 900??, 1s-1, 50% deformation ,and the critical static recrystallization time is 5min after continue heated.     

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The effect of deformation parameters on hot deformation of superalloy 800H was studied by means of single-pass compression test. It was found that smaller initial grain size, higher deformation temperature and lower strain rate are more easily to cause dynamic recrystallization. And when dynamic recrystallization can take place during deformation, the fraction of dynamic recrystallization increases with increasing of strain. The models of dynamic recrystallization activation energy, critical strain, dynamic recrystallization kinetics, dynamic recrystallization kinematics and grain size of dynamic recrystallization for 800H were obtained through the analysis of data obtained by single-pass compression. The variation tendency for grain size simulated by Deform-2D is consistent with metallographic statistics, and the average error is 4. 5??m. Very small average error shows that the model is consistent with practical situation and can be used to predict recrystallized grain size for 800H during thermal deformation.     

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。     

20CrNi2Mo钢高温变形的本构方程与动态再结晶行为

 在DIL805A/T热模拟机上对低碳合金钢20CrNi2Mo进行等温单向热压缩试验,研究了该钢在温度为900～1 050 ℃、应变速率为0.001～1 s－1条件下的应变补偿本构方程及动态再结晶行为,为探索塑性变形行为和组织控制提供理论指导。对应变补偿本构方程进行验证发现,考虑应变补偿后得到的应力值与试验值的线性相关系数[R＝0.992 1,]平均相对误差[AARE]为3.019 2%;采用对[θ-σ]曲线进行3次多项式拟和求解拐点的方法,建立了临界动态再结晶模型,并结合微观组织分析了不同变形条件下动态再结晶进行的难易程度。结果表明,20CrNi2Mo钢在试验条件范围内全部发生了动态再结晶,且变形温度越高,应变速率越小,动态再结晶进行得越充分,并建立了[Z]参数动态再结晶临界应力模型和临界应变模型。     

Recrystallization kinetics of an austenitic high-manganese steel subjected to severe plastic deformation

The evolution of the microstructure and the properties of an austenitic high-manganese steel subjected to severe deformation by cold rolling and subsequent recrystallization annealing is investigated. Cold rolling is accompanied by mechanical structural twinning and shear banding. The microhardness and microstructural analysis of annealed samples are used to study the recrystallization kinetics of the high-manganese steel. It is shown that large plastic deformation and subsequent annealing result in rapid development of recrystallization processes and the formation of an ultrafine-grained structure. A completely recrystallized structure with an average grain size of 0.64 μm forms after 30-min annealing at a temperature of 550°C. No significant structural changes are observed when the annealing time increases to 18 h, which indicates stability of the recrystallized microstructure. The steel cold rolled to 90% and annealed at 550°C for 30 min demonstrates very high strength properties: the yield strength and the tensile strength achieve 650 and 850MPa, respectively. The dependence of the strength properties of the steel on the grain size formed after rolling and recrystallization annealing is described by the Hall–Petch relation.     

Hot Deformation Behavior of Nickel-Based Superalloy GH4720Li

 The hot deformation characteristics of GH4720Li alloy were studied at the temperature of 1100-1170 ℃ and strain rate of 001-1 s-1 using Gleeble hot compression tests. True stress-true strain curves and deformation microstructures were investigated. Constitutive equation was established using the hyperbolic law. Processing map for hot working was also developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate. The results show that dynamic recrystallization is the dominant softening mechanism during hot deformation. Fully recrystallized grain is obtained at strain of 07 above 1130 ℃, and coarsening occurs above 1150 ℃. The mean deformation activation energy is determined to be 512 kJ/mol. According to the low activation energy value, high dissipation efficiency parameter and fine recrystallized microstructure, 1130 ℃ is chosen as the hot working temperature for GH4720Li alloy.     

60Si2MnA弹簧钢的热变形行为

通过热模拟压缩试验，研究了60Si2MnA弹簧钢高温变形时的力学行为和动态再结晶行为。由实验数据求得了60Si2MnA弹簧钢的热变形激活能，峰值应力，峰值应变以及动态再结晶晶粒尺寸与Zener-Hollomon参数之间的关系。结果表明，通过动态再结晶能获得细小的晶粒。     

Recrystailization Behavior of Deformed Austenite in High Strength Microalloyed Pipeline Steel

Using methods of single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator,the curves of flow stress and stress relaxation,the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied,and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated.It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning.The deformation conditions such as deformation temperature,strain,and strain rate influenced the recrystallization kinetics and the microstructure respectively.Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.     

Recrystallization Behavior of Deformed Austenite in High Strength Microailoyed Pipeline Steel

Using methods of single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxation, the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied, and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated. It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning. The deformation conditions such as deformation temperature, strain, and strain rate influenced the recrystallization kinetics and the microstructure respectively. Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.     

Recrystallization Behavior of Deformed Austenite in High Strength Microalloyed Pipeline Steel

 Using methods of single hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxation, the microstructure and the recrystallization behavior of Nb V Ti high strength microalloyed low carbon pipeline steel were studied, and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated. It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning. The deformation conditions such as deformation temperature, strain, and strain rate influenced the recrystallization kinetics and the microstructure respectively. Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.