低碳钢热连轧过程中工艺参数及组织演变的预测

采用二维有限元法对热连轧生产过程中沿带钢厚度方向的温度场分布进行了预测，建立了描述低碳钢软化行为的再结晶模型，并利用此模型对奥氏体再结晶动力学及微观组织演变进行了模拟计算，建立了计算精轧过程应力-应变曲线的流变应力模型，根据现场数据，对400MPa级超级钢细晶工业轧制实验的轧制力、轧制力矩和轧制功率进行了预测，结果与实测值吻合较好，反映了工业生产实际。     

X46级管线钢热连轧过程中温度场及平均流变应力的预测

采用有限元计算模型和实测轧件温度以及精轧各道次的轧制压力值，对不同边界条件下的传热系数和塑性功转热率进行了优化计算，得到了轧件断面温度场。在此基础上考虑了再结晶等因素，建立了计算精轧过程中应力一应变曲线的流变应力模型，并利用该模型对X46级管线钢精轧各道次的流变应力进行了预测。结果表明：该模型的计算结果与用Sims法计算的结果吻合较好，能真实反映工业生产的实际情况。     

Mathematical modeling of the hot strip rolling of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels

Industrial mill logs from seven different hot strip mills (HSMs) were analyzed in order to calculate the mean flow stresses (MFSs) developed in each stand. The schedules were typical of the processing of microalloyed Nb, multiply-alloyed Cr-Mo, and plain C-Mn steels. The calculations, based on the Sims analysis, take into account work roll flattening, redundant strain, and the forward slip ratio. The measured stresses are then compared to the predictions of a model based on an improved Misaka MFS equation, in which solute effects, strain accumulation, and the kinetics of static recrystallization (SRX) and metadynamic recrystallization (MDRX) are fully accounted for. Good agreement between the measured and predicted MFSs is obtained over the whole range of rolling temperatures. The evolution of grain size and the fractional softening are also predicted by the model during all stages of strip rolling. Special attention was paid to the Nb steels, in which the occurrence of Nb(C, N) precipitation strongly influences the rolling behavior, preventing softening between passes. The present study leads to the conclusion that Mn addition retards the strain-induced precipitation of Nb; by contrast, Si addition has an accelerating effect. The critical strain for the onset of dynamic recrystallization (DRX) in Nb steels is derived, and it is shown that the critical strain/peak strain ratio decreases with increasing Nb content; furthermore, Mn and Si have marginal but opposite effects. It is demonstrated that DRX followed by MDRX occurs under most conditions of hot strip rolling; during the initial passes, it is due to high strains, low strain rates, and high temperatures, and, in the final passes, it is a consequence of strain accumulation.     

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.     

400 MPa超级钢热连轧过程中再结晶及流变应力的预测

开发了描述低碳钢软化行为的再结晶模型，并对奥氏体再结晶动力学和微观组织演变进行了模拟计算。在此基础上建立了计算机精轧过程应力-应变模型，根据现场数据预测了400MPa级超级钢细晶化轧制的轧制力，预测结果与实验值吻合，这项研究可广泛用于钢种开发，轧制规程设定和优化以及轧制过程的在线控制。     

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.     

热轧带钢组织性能预报模型及应用

 基于物理冶金理论,研究了热轧带钢过程中的奥氏体晶粒长大模型、奥氏体再结晶模型、奥氏体相变模型以及力学性能模型。奥氏体再结晶模型中,通过研究位错密度的变化来描述由于再结晶不完全造成的变形抗力的变化。奥氏体相变模型中,通过碳扩散理论描述了奥氏体-铁素体相界面随冷却过程的变化规律。基于热轧带钢过程中的冶金物理模型,开发热轧带钢组织性能预报系统。系统包括4个模块,分别用于计算板坯在加热炉、粗轧精轧、层流冷却和卷取完成各阶段的组织和力学性能参数,生产工艺是该系统的重要输入参数。利用该系统对某钢厂实际生产过程的组织性能进行预报,预报的力学性能和现场实测值有较好的一致性。     

Recrystallization Behavior Design for Controlling Grain Size in Strip Rolling Process

To promote effectively dynamic recrystallization and obtain a homogeneous distribution of ultrafine grain size in strip finish rolling process,the behavior of static and dynamic recrystallization must be appropriately designed to provide an ultrafine austenite microstructure without mixed grain size.The design of rolling schedule was analyzed based on the control of the recrystallization behavior to achieve ultrafine grain size in the strip rolling process of niobium microalloyed steel.The experimental simulations were presented to validate the twice dynamic recrystallization design to achieve ultrafine grain size control.     

Effect of prestrain and deformation temperature on the recrystallization behavior of steels microalloyed with niobium

The evolution of microstructure during the hot working of steels microalloyed with Nb is governed by the recrystallization kinetics of austenite and the recrystallization-precipitation interaction. The present study focuses on the effects of prestrain and deformation temperature on the rectrystallization behavior in these steels. The extent of recrystallization is characterized by a softening parameter calculated from a series of interrupted plane strain compression tests carried out at different deformation temperatures and strain levels. The results indicate that at low temperatures, softening is caused by static recovery, while at higher temperatures, static recrystallization is the predominant mechanism. The recrystallization-stop temperature (T _5pct) and the recrystallization-limit temperature (T _95pct), marking the beginning and end of recrystallization, respectively, are determined as a function of strain. In order to achieve a homogeneous microstructure, finish rolling should be carried out outside the window of partial recrystallization (T _5pct<T<T _95pct), as determined in this study. The Nb(CN) precipitation kinetics have been calculated using a model proposed in an earlier work, and these results are used to estimate the precipitate pinning force under the given processing conditions. Based on these estimations, a criterion has been proposed to predict the onset of recrystallization. The predicted results are found to be in reasonably good agreement with the experimental measurements.     

A Physical Analysis of the Stress Relaxation Kinetics of Deformed Austenite in C‐Mn Steel

The softening kinetics following hot deformation of austenite have been characterised using the stress relaxation technique. Samples were deformed in compression for a variety of temperatures, strains and strain rates. At low strains where recovery was the only softening mechanism, the stress relaxation kinetics have been analysed using a recovery model previously proposed in the literature, the main parameters being activation energy and activation volume. The activation energy for recovery was found to be 314 kJ/mol, whilst the activation volume was inversely proportional to the internal stress. At higher strains where austenite recrystallization occurred as well, the stress relaxation kinetics were modelled using the recovery model combined with a single grain model for recrystallization. Reasonable agreement was obtained between model and experiment for a variety of deformation conditions. Analysis of the model parameters and experimental data indicated that the nucleation density for recrystallization depended only on the applied strain for the range of deformation conditions imposed. In addition the mobility of recrystallizing boundaries was best explained by solute drag due to manganese atoms.     

Effect of Austenite Recrystallization on Microstructure and Properties of Q345 Steel

The Q345 plate steel austenite recrystallization behavior and strain accumulation during rolling were investigated through thermal simulation and rolling. The effect of the recrystallization behavior on the microstructure and properties of the steel was discussed and analyzed. The control principles of the pass reduction in the austenite recrystallization region and partial recrystallization region were established. It is found that to increase the thickness of intermediate billet in the finish temperature interval of 880-820℃ is favorable to grain refinement. The result has been applied to the industrial production of the 3 500 mm plate mill of Shougang Group. The average grain size of the steel plate conforms to ASTM No. 10-12, and the grade of band structure has been reduced to below 1.5.     

再结晶软化程度对C-Mn钢变形抗力的影响

利用带钢热连轧的实测条件研究了再结晶软化程度对C-Mn钢变形抗力的影响。结果表明，根据金属的再结晶规律得到的实质应变，比计算“残留应变率”法不但与实测更为接近，而且更符合理论结果；考虑再结晶软化程度对变形抗力的影响后使轧机负荷的预报精度得到明显提高；给出的C-Mn钢静态再结晶模型所得结果与实测符合得较好，从而为控制产品的组织性能提供了奥氏体再结晶的定量化依据。     

17Cr2Ni2Mo齿轮用钢热变形动态再结晶行为

 为了探索材料热塑性变形工艺理论,针对热轧态17Cr2Ni2Mo齿轮用钢进行热力模拟试验,研究材料在应变速率=0.01～10 s-1、热变形温度t=1 050～1 150 ℃条件下的动态再结晶行为。结果表明,在较高应变速率下,应力在峰值后,出现动态回复或持续性动态再结晶软化,在较低应变速率下,应力呈现波浪多峰值状,出现多次动态再结晶软化。通过加工硬化率随应变变化曲线(θ ε),确定了动态再结晶临界特征应变量εc,结合峰值应变量εp统计得到εc/εp比值为0.629～0.854,并可知当应变速率一定时,εc随着温度升高而减小,当温度一定时,εc随应变速率的增大而增大。同时建立了流变应力本构方程,数据验证平均相对误差为1.705%。最后建立了动态再结晶动力学模型。     

Hot Deformation Behavior of GCr15 Steel

 Hot deformation behavior of GCr15 (ASTM 52100) steel was investigated using single-hit compression tests on Gleeble-1500 simulator at the temperature range of 850-1100 ℃ and strain rate range of 0. 1-10 s-1. The flow stress constitutive equation of GCr15 steel during hot deformation was determined by stress-strain curves analysis on the basis of the hyperbolic sine equation. And the models of dynamic recrystallization fraction and dynamic recrystallization grain size of GCr15 steel were established by the measured curves and microstructure observation in different experimental conditions. The mean activation energy and the time exponent of dynamic recrystallization kinetics equation in the range of experimental conditions were determined to be 356. 2 kJ/mol and 2. 12, respectively. Meanwhile, the flow stress model was also established by the method of allocating flow stress curve with three main stress values, the saturation stress, the steady state stress and the stress when strain is 0. 1. The flow stress curves predicted by the developed models under different deformation conditions are in good agreements with the measured ones.     

开轧温度对42CrMo4钢轧制动态组织变化影响的有限元模拟

应用LARSTRAN/SHAPE有限元模拟软件对42CrMo4合金钢箱形孔型轧制过程进行三维热力耦合有限元模拟.用粘塑性有限元理论模拟轧制过程各时间离散步的局部量包括等效应力、等效应变、等效应变速率、温度分布等,由此计算动态再结晶和晶粒大小的变化.通过模拟研究得出开轧温度≥1 050℃时,42CrMo4钢动态再结晶显著增加,生产42CrMo4钢棒材的合适开轧温度为1 050～1 100℃.     

Role of Cerium on the Intricacies of Deformed State and Softening Mechanisms of Low-Carbon Steels

The present study investigates the softening kinetics of two cerium (Ce)-modified steels after 60% cold rolling and annealing at 600 °C for 2–16 h. Cold rolling accumulates substantial strain in the ferritic matrix of low Ce (LCe) steel (0.03 wt% Ce) compared to high Ce (HCe) steel (0.6 wt% Ce). The acicular ferrite and Fe₃C partition the imposed strain preferentially inside the ferrite matrix of LCe sample. Contrarily, a homogenous strain distribution in HCe sample is promoted by soft Ce₂O₃ particles embedded in ferrite. Both the steels achieve partial recovery and recrystallization even after 16 h of annealing. LCe steel experiences a softening fraction of ≈28 vol% after 16 h, inferior to HCe steel (≈34 vol%). During initial stage of annealing, nucleation of strain-free grains are observed in LCe sample due to availability of grain and interphase boundaries. Subsequently, recrystallization kinetics get delayed because of the pinning effect exerted by fine CeO₂ and Fe₃C particles. In HCe samples, the early stage of ferrite nucleation is hindered by the segregation of Ce at grain boundaries. However, at a later stage, the recrystallization kinetics are accelerated owing to the ineffective pinning of dislocations and boundaries by coarse Ce₂Fe₁₇ and Ce₂C₃ particles.     

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。     

Physical simulation of hot deformation, and microstructural evolution for 42CrMo4 steel prior to direct quenching

 Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot-rolling plays a major role on the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as to predict the microstructure and the properties of the components. These models were mostly applied to predict austenite grain size (AGS), dynamic, meta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. In this paper the hot compression tests were carried on 42CrMo4 steel in the temperature range of 900 - 1100°C and the strain rate range of 0.05 - 1 s- 1 in order to study the high temperature softening behavior of the steel. For the exact prediction of flow stress, the effective stress - effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in a good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.     

Si-Mn系相变诱导塑性钢热轧过程中组织演变的预测

 建立了热轧相变诱导塑性(TRIP)钢奥氏体动态和静态再结晶、晶粒尺寸和流变应力预测模型,定量分析了不同硅含量对其再结晶的影响。结果表明,预测值与实测值符合较好;硅含量增加可抑制、减缓动态和静态再结晶发生,抑制奥氏体晶粒长大,提高流变应力、残余应变和位错密度,从而有利于铁素体相变的发生。