C-Mn钢高温变形过程再结晶及位错密度的研究

利用Gleeble 15 0 0热力模拟机 ,通过双道次压缩试验 ,计算了C -Mn钢SS4 0 0的热变形激活能 ,建立了静态再结晶模型。模拟计算了因热力学行为的演变引起的静态、动态再结晶以及位错密度等物理冶金现象的变化。研究结果表明 :动态再结晶易在温度较高、应变速率较低的条件下发生 ;静态再结晶在前几道次发生的比较充分 ;粗轧阶段细化晶粒的效果比精轧阶段明显。     

Recrystallization behavior of twin roll cast low carbon steel strip

The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investigate dynamic recrystallization behavior,as cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure.Tensile test was used and the deformation temperature is in the range of 900℃to 1 100℃and strain rates are 0.01 s^-1,0.1 s^-1,1 s^-1.The activation energy and stress exponent were determined as 306kJ/mol and 4.69 respectively.The ratio of critical strain to the peak strain is 0.65,and that of critical stress to the peak stress is 0.92.The dependence of the peak strain on the initial grain size and Zener - Hollomon parameters Z isε_p =9.1×10^-4×D₀^0.48Z^0.13.The kinetics of the dynamic recrystallization and recrystallized grain size was predicted using models published.The as cast coarse austenite were dramatically refined after complete dynamic recrystallization.For static recrystallization,the tensile test was carried out on Gleeble -3500 thermo - mechanical simulator.The deformation temperature is in the range of 800℃to 1 200℃with strain rate 0.01 s^-1 to 1s^-1.The pre strain is fixed at 0.04 to 0.12 and the inter-hit delay time varies from 1 s to 3 000 s.The activation energy and Avrami exponent of static recrystallization were determined as 241 kJ/mol and 0.54 respectively.A kinetics model was proposed to describe the static recrystallization kinetics.The predicted results were in good agreement with the experimental results.     

FGH4102粉末高温合金等温热模拟压缩试验及动态再结晶组织研究

本文研究了新型第四代粉末高温合金FGH4102在等温热模拟压缩过程中的组织演变,对γ′相在动态再结晶过程中的作用进行了探讨。结果表明,热等静压态合金在1060~1120℃温度范围变形时,热加工性能较好。1140℃变形后试样容易发生开裂,合金热加工性能较差。合金在γ+γ′两相区变形时均发生了不同程度的动态再结晶,再结晶晶粒尺寸远小于热等静压态的晶粒尺寸。变形过程中,尺寸较大的γ′相起到促进动态再结晶的作用。变形参数对动态再结晶的影响非常显著。低温高应变速率变形时,γ′相促进动态再结晶形核占主导地位,再结晶晶粒比较细小;高温低应变速率变形时,晶粒长大逐渐占据主导地位,再结晶晶粒尺寸较大。     

含铌微合金带钢精轧过程中的再结晶行为

介绍了含铌微合金带钢在精轧过程中的再结晶行为。在不同条件下，含铌钢将发生静态再结晶、动态再结晶和亚动态再结晶，而且沉淀的析出对再结晶有不同程度的影响。     

Ti对低碳Mn-V钢奥氏体动态再结晶的影响

采用Gleeble热模拟试验机和透射电镜、扫描电镜及定量金相等分析技术,就钛对低碳Mn-V钢奥氏体晶粒长大行为、奥氏体动态再结晶行为等进行了研究.结果表明,含钛钢中形成稳定的碳氮化钛,对阻止再加热奥氏体晶粒长大有利.含钛钢变形抗力比不含钛钢要高,其动态再结晶开始的临界变形量比不加钛钢的小,易于发生再结晶,且含钛钢的再结晶晶粒尺寸相对较细,再结晶晶粒长大速度也更慢.     

L360管线钢热轧过程静态再结晶行为的研究

奥氏体再结晶行为是影响热轧钢带组织和力学性能的1个主要因素。在热模拟试验的基础上,采用应力松弛法和显微组织观察法,对含Nb和Ti的L360管线钢热轧过程奥氏体静态再结晶行为进行了研究,分析了应变、变形温度、应变速率、原始奥氏体晶粒尺寸对奥氏体静态再结晶的影响。利用线性回归分析,计算出试验钢静态再结晶激活能为203kJ;同时通过回归,得出试验钢热轧过程静态再结晶动力学方程。     

Effect of V on Hot Deformation Characteristics of TWIP Steels

Twinning induced plasticity (TWIP) steels, which rely on high Mn contents to promote twinning as the deformation mechanism, exhibit high ultimate strengths together with outstanding combinations of ultimate strength and ductility. In terms of mechanical properties, one of the most important microstructural features is grain size. The knowledge of the kinetics of recrystallization mechanisms, i.e., dynamic recrystallization (DRX) and static recrystallization (SRX), can be used in order to control the grain size of the final product by a proper rolling schedule design. The focus of this work is the characterization of the DRX kinetics of two TWIP steels. The basic composition of the steels is Fe–21Mn–0.4C–1.5Al–1.5Si, and one of them is further alloyed with 0.12% V. With this objective, compression tests were carried out at 900, 1000, and 1100°C and strain rates ranging from 1 × 10^?1 s^?1 to 1 × 10^?4 s^?1. Furthermore, metallographic observation by optical microscopy (OM) was done to assess the evolution of grain size for the different deformation conditions. According to the results, the existence of V in the composition does not affect the hot flow behavior of the steel, although recrystallization fraction and recrystallized grain size decrease for the V‐containing steel.     

薄板坯连铸连轧流程钛微合金钢控制轧制技术

 重点阐述了薄板坯连铸连轧流程钛微合金钢的控制轧制模式及其机理。基于应力松弛试验和双道次压缩热模拟试验,研究分析了薄板坯连铸连轧钛微合金钢的奥氏体再结晶动力学。研究结果表明,轧前铸态粗大奥氏体组织经F1高温大压下后可实现完全静态再结晶;铸坯中固析TiN粒子可以有效阻止奥氏体再结晶晶粒的长大,实现再结晶区控轧。固溶钛的溶质拖曳作用以及形变诱导析出的TiC粒子对奥氏体再结晶具有抑制作用,可以阻止奥氏体再结晶的发生,实现未再结晶区控轧。     

Study on dynamic recrystallization behavior of hot rolled TRIP steel produced by CSP process

The dynamic recrystallization behavior of hot rolled TRIP steel produced by CSP process was studied by means of Gleeble-3500 thermal simulation testing machine in the temperature range of 950-1150℃ with the strain rate of 0.1-10s-1 and the strain of 65%. And the effect of initial austenite grain size on the dynamic recrystallization behavior of TRIP steel was explored. The results show that the finer initial austenite grain size, the higher deformation temperature and the lower strain rate, the more positive austenite dynamic recrystallization of TRIP steel. Moreover, it is found that when the coarse grained samples (initial austenite grain size is 767.54μm) deform in the range of 1050℃ to 1150℃, the austenite dynamic recrystallization will take place, and the dynamic recrystallization activation energy of TRIP steel is deduced as 361539.17J/mol. The Zener-Hollomon parameter equation as a function of strain rate and temperature is determined. And the model of critical strain for dynamic recrystallization, the flow stress model of austenite at high temperature and the grain size model for dynamic recrystallization are also established. The calculation results are coincided well with the experimental results.     

FTSR轧制含铌钢的再结晶行为

 结合某钢厂FTSR薄板坯连铸连轧生产线轧制X46含Nb钢的工艺参数,在Gleeble 2000热/力模拟实验机上模拟了粗轧阶段该钢的组织演变,并研究了Nb含量对未再结晶温度的影响。研究结果表明：①粗轧阶段,粗大的铸态组织发生了充分的动态再结晶,有效地细化了奥氏体晶粒。②随着钢中Nb含量的增加,未再结晶温度逐渐升高,该生产线可有效进行控制轧制,避免轧制含Nb钢时混晶现象的发生。     

铌、钒对高强钢筋再结晶影响及轧制工艺设计

 为了研究和设计高强钢筋添加铌、钒后轧制过程中对奥氏体区再结晶行为的量化管控,采用Gleeble-3500热模拟机对铌、钒微合金化高强螺纹钢进行单轴热压缩试验,基于再结晶临界条件的热力学原理,通过对不同形变条件下应力-应变曲线分析,采用Avrami方程得到了不同变形条件下的再结晶动力学曲线,并根据再结晶动力学曲线,量化对比分析了铌、钒微合金化对高强螺纹钢再结晶开始、转变及终了过程的影响。结果表明,铌、钒微合金化螺纹钢的热压缩过程均呈现了明显的动态再结晶特征,由于微合金元素Nb/Nb+V的添加,阻碍了20MnSi钢的动态再结晶,变形温度的提高或应变速率的增加可促进再结晶。针对生产中利用动态再结晶而组织调控进行了工艺设计,精轧机组中成品机架前进行冷却和回复,确保830 ℃左右有利再结晶分数达到95%。     

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。     

H型钢粗轧微观组织演化的数值分析

在ABAQUS软件的基础上,利用基于稳态判断的数值分析流程,构建了对H型材任意轧制道次进行微观组织演化模拟的分析平台。以某中型H型钢11道次热轧过程为研究对象,详细分析了粗轧过程轧件内奥氏体晶粒直径、温度、动态再结晶区域、动态再结晶奥氏体体积分数,以及道次间隙期间晶粒的长大和温度分布情况。     

X80热连轧管线钢的成分、工艺对组织及性能的影响

对三种不同成分设计的Mn-Mo-Nb+钢的精轧轧程、轧制温度以及C、Mo含量对热轧板卷屈服强度和DWTT撕裂面积等性能的影响进行了研究,所得到的结论对提高强度,细化奥氏体晶粒,避免混晶具有指导性。采用含Mo低碳、高Nb设计,控制精轧轧程,可以获得具有优良强度和韧性的X80热连轧管线钢产品。     

X70管线钢热连轧过程奥氏体再结晶、晶粒尺寸和平均流变应力的预测

在考虑动态、亚动态再结晶及静态再结晶的基础上,建立了X70管线钢的物理冶金模型,并应用于板带钢热连轧过程奥氏体再结晶、晶粒尺寸和流变应力的预测.结果表明,在合理的温度和压下条件下,应变累积可导致在精轧过程出现动态 亚动态再结晶行为,促进奥氏体晶粒的进一步细化.终轧温度的降低可引起奥氏体晶粒的粗化和残余应变的显著提高.建立了考虑晶粒尺寸和残余应变影响的平均流变应力(MFS)的人工神经网络预测模型,大大提高了热连轧过程MFS预测精度.     

Prediction of Rolling Load, Recrystallization Kinetics, and Microstructure During Hot Strip Rolling

 The recrystallization kinetics and grain size models were developed for the C Mn and niobium containing steels to describe the metallurgical phenomenon such as softening, grain growth, and strain accumulation. Based on the recrystallization kinetics equations, the mean flow stress and the rolling load of each pass were predicted and the optimum rolling schedule was proposed for hot strip rolling. The austenite grain refinement is associated with the addition of niobium, the decrease of starting temperature of finish rolling, and the reduction of finished thickness. The mean flow stress curve with a continuous rising characteristic can be usually observed in the finish rolling of niobium containing steel, which is formed as a result of the heavy incomplete softening and strain accumulation. The predicted rolling loads are in good agreement with the measured ones.     

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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.     

60Si2Mn钢动态再结晶数学模型的实验研究

利用计算机技术对轧制过程进行组织性能预报在工业生产中有着广泛的应用前景，而开发合理的数学模型就成为组织性能预报的关键：轧制过程中发生的动态再结晶行为直接影响着预报结果的可靠性。作者在实验室条件下采用单、双道次压缩实验对60Si2Mn钢的轧制过程进行了研究，得到了该钢种动态再结晶的计算模型：     

直接轧制工艺对中厚板组织与性能的影响

 连铸坯直接轧制技术作为一种变革性的绿色钢铁生产流程,目前主要用于超薄带和线棒材生产,近年来国内外逐步开始了中厚板直接轧制工艺的探索性工作。直接轧制工艺与常规热轧工艺相比,具有不同的温度履历和物理冶金学过程。选取Nb-Ti微合金钢为研究对象,从产品组织与性能的角度,探讨中厚板直接轧制工艺的可行性。采用炼钢-连铸-轧制中试试验,对比研究了直接轧制工艺及常规热轧工艺下中厚板产品的组织和性能,并基于动态再结晶模型,探讨了直接轧制工艺下试验钢的组织细化机制。研究结果表明,直接轧制工艺下,虽然连铸坯轧前未经过γ-α-γ相变过程,仍保留铸态粗大的奥氏体晶粒,但轧制过程中较大的芯表温差有利于变形向芯部渗透,芯部再结晶进行得更加充分,可以用形变再结晶机制代替常规热轧工艺的相变机制细化成品芯部组织,获得与常规热轧工艺相近甚至更优的显微组织与力学性能。     

热变形对轴承钢G80T晶粒细化行为的影响

利用Gleeble-3800热模拟变形试验机,对高温轴承钢G80T的动态再结晶行为及相关力学性能进行了研究。通过对该钢在1 050℃下以10s-1的变形速率进行0%~70%的不同形变量的单道次压缩,研究了不同形变量下热变形钢的微观组织结构及硬度。结果表明:当形变量在20%时,无动态再结晶发生;当形变量达到40%时,热变形组织出现了部分的再结晶晶粒;随着形变量的进一步加大,再结晶晶粒数目增多,形变量达到60%后,形变组织形成了平均晶粒尺寸为2.8μm的完全再结晶组织。同时由于形变和晶粒尺寸大幅度细化,钢中的碳化物也随着形变量的增加而逐步减少。通过对压缩应力-应变曲线软化行为的分析,认为该钢的再结晶属于动态再结晶;在1 050℃进行60%的形变可以实现该钢的完全动态再结晶,将平均晶粒尺寸从原始的22μm细化到2.8μm,同时将钢的硬度从820 HV提高到895 HV。研究结果表明,动态再结晶是细化高温轴承钢G80T晶粒尺寸和提高性能的一种有效措施。