Microstructural evolution on streamlines during hot strip rolling using internal state variables

In this work, a numerical-based model has been proposed to calculate distributions of temperature, strain and strain rate during hot rolling as well as the subsequent microstructural changes after hot rolling of an aluminum alloy. For doing so, a transient finite difference analysis together with a stream function method have been coupled to calculate temperature distribution and velocity field within the rolling metal. A new approach considering internal state variables method has been employed to predict the kinetics of static recrystallization after hot rolling. The predicted results were then compared with the experimental ones and a good consistency was observed between the two sets of data.     

Finite Element Analysis for Microstructure Evolution in Hot Finishing Rolling of Steel Strips

A computer model that describes the evolution of microstructures during the hot finishing rolling of SS400 steel has been proposed. It has been found that the microstructure strongly depends on processing of materials and on their parameters,which affected the history of the thermomechanical variables,such as temperature,strain,and strain rate. To investigate the microstructural evolutions during the hot finishing rolling process,the rigid-thermoviscoplastic finite element method(FEM) has been combined with dynamic recrystallization,static recrystallization,and grain growth models. The simulation results show a good agreement with those from the prediction software online.     

Temperature field analysis and its application in hot continuous rolling of Inconel 718 superalloy

A coupled thermo-mechanical model containing metal flow and temperature field for calculating temperature variation has been developed on fourteen-pass hot continu-ous rolling of round rod for Inconel 718 alloy using 3D elastic-plastic finite element method(FEM).The temperature of characteristic analysis points in the intermedi-ate cross-section of the workpiece has been simulated at initial temperature ranging from 960 to 1000 °C and initial velocity in range of 0.15-0.55 m·s-1.Based on fi-nite element ana...     

基于Deform高线粗轧奥氏体晶粒细化研究

本文结合GCr15再结晶模型, 根据轧线实际孔型参数、轧线布置与轧制程序, 采用刚塑性有限元法, 利用模拟软件Deform对轴承钢线材GCr15粗轧进行了三维有限元模拟, 分析总结了粗轧过程中轧件温度场、等效应变和应变速率的变化规律, 得出粗轧过程动态、亚动态和静态再结晶的百分数和对应晶粒尺寸, 揭示了轧件在粗轧过程中再结晶规律及奥氏体晶粒细化规律, 并且证实了初始晶粒尺寸对粗轧过程奥氏体晶粒细化的影响规律。     

Flow stress modeling and warm rolling simulation behavior of two Ti–Nb interstitial-free steels in the ferrite region

Axisymmetric compression tests and compact strip production (CSP) warm rolling simulations were carried out on two commercial Ti–Nb stabilized interstitial-free (IF) steels to investigate their flow behavior in the ferrite region. The comparison between the measured and predicted stress curves indicated that dynamic recovery was the dominant softening mechanism during axisymmetric compression deformation. The flow stress curves during CSP-warm rolling simulations indicated that static and dynamic recovery dominated the softening process for early passes and an apparent dynamic recrystallization contributed to the flow stress reductions for the last two passes. The microstructural evolution during the simulation confirmed that the very fine quasi-equiaxed ferrite grains obtained could be explained by apparent dynamic recrystallization, which was assisted by dynamic recovery at high temperature and a reduced Nb solute drag.     

Microstructural development during warm rolling of an IF steel

Wedge-shaped slab rolling was employed to investigate the microstructural evolution of an interstitial-free (IF) steel during warm working in the temperature range 500–800°C. Mean flow stress-strain curves calculated from load-time data of rolling tests reasonably correspond to work hardening and dynamic recovery behaviour. The development of substructures in the deformed material was investigated using optical and electron microscopy. A close correlation was observed between mechanical behaviour and microstructural development during deformation. Microbands in directions of ± 35° with respect to the rolling direction, independent of strain, temperature and initial grain orientations are the most noticeable features in the microstructural observations. The sequences of substructural changes from the appearance of early microbands at very low strains, their development with strain, to the formation of equiaxed subgrains at higher strains and temperatures were followed by TEM.     

A new approach to predicting partial recrystallization in the multi-pass hot rolling process

An exploratory approach to handling partial recrystallization in multi-pass hot rolling where the heterogeneity of steel microstructures is inherent is presented. The proposed model is based on a modification of the conventional model in which the microstructure of deformed austenite at each pass is simply taken as homogeneous during the multi-pass rolling. The usefulness of the modified model is demonstrated by applying it to a four-pass oval-round (or round-oval) rod rolling sequence. The pass-by-pass recrystallized fraction and austenite grain size (AGS) computed from the modified model are compared with those from the conventional model. The result showed that in multi-pass rolling at higher rolling speed, the recrystallization behavior and evolution of the austenite grain size at a given pass was strongly influenced by the modeling method of the partial recrystallization attributed to microstructural heterogeneity.     

低Ni型LNG钢的热变形行为及力学性能

通过单道次、双道次压缩试验,研究了低Ni型LNG钢的高温奥氏体动态再结晶及静态再结晶行为,并采用两阶段控制轧制及超快速冷却技术进行不同轧制工艺下的热轧试验,通过热模拟及热轧试验研究了低Ni型LNG钢的热变形行为及力学性能。结果表明,在高温(1000~1050 ℃)、低应变速率(0.1~0.5 s^-1)下奥氏体容易发生动态再结晶,确定了发生再结晶的临界条件,并建立了动态再结晶动力学模型。试验钢在较高温度(800~1050 ℃)、较长道次间隔时间(60 s)下静态软化现象明显,容易发生静态再结晶。依据热模拟试验结果制定热轧试验工艺,通过控制精轧开轧温度和终轧温度调控高温奥氏体再结晶行为,从而细化晶粒,改善低Ni钢的冲击性能。精轧开轧温度920 ℃、终轧温度770 ℃时,低Ni钢的低温冲击吸收能量为180.1 J,屈服强度为595.1 MPa,抗拉强度为717.8 MPa。     

Mathematical model to simulate thermo-mechanical controlled processing in rod (or bar) rolling

This study presents a mathematical model for computing the thermo-mechanical parameters such as the strain and strain rate at a given pass and the temperature variation during rolling and cooling between inter-stands (pass), to assess the potential for developing “Thermo-Mechanical Controlled Process” technology in rod (or bar) rolling, which has been a well-known technical terminology in strip (or plate) rolling since the 1970s. The model has then been applied to a four-pass (oval-round or round-oval) bar rolling sequence for predicting the pass-by-pass AGS, by incorporating the equation for recrystallization behavior and AGS evolution being widely used in strip rolling. The predicted AGS was compared with those obtained from the hot torsion experiment. Results revealed the proposed model, coupled with the recrystallization behavior and AGS evolution model developed for strip (or plate) rolling, might be applied directly to rod (or bar) rolling. We also found that the recrystallization behavior during rod rolling was significantly influenced by the method for calculating the thermo-mechanical parameters, especially the strain.     

Spread Model for TC4 Alloy Rod during the Three-Roll Tandem Rolling Process

为了保证三辊连轧过程中棒材的成型精度,研究了TC4钛合金棒材的宽展。采用正交试验优化设计方法设计数值模拟方案,在Marc有限元平台上,研究轧制工艺参数(轧制温度、轧制速度、孔型内切圆直径、轧辊直径、摩擦系数)对宽展的影响,并分析了各参数的影响显著性顺序。在此基础上,建立了三辊轧制TC4棒材的宽展模型。试验在自行研制的8机架Y型连轧机上进行,孔型系统为平三角-圆。宽展测量结果和模型计算结果吻合较好。     

热轧终轧条件对ELC—BH钢板Ar3的影响

研究表明,随着ELC—BH钢板终轧变形量和终轧变形速度增加以及终轧温度降低,A_(r3)升高,这些规律归因于高温变形期间加工硬化和热激活软化两种因素竞争引起的微观组织结构的变化。     

A Model to Predict Recrystallization Kinetics in Hot Strip Rolling Using Combined Artificial Neural Network and Finite Elements

A thermo-mechanical model has been developed to establish a coupled heat conduction and plastic flow analysis in hot-rolling process. This model is capable of predicting temperature, strain, and strain rate distributions during hot rolling as well as the subsequent static recrystallization fraction and grain size changes after hot deformation. Finite element and neural network models are coupled to assess recrystallization kinetics after hot rolling. A new algorithm has been suggested to create differential data sets to train the neural network. The model is then used to predict histories of various deformation variables and recrystallization kinetics in hot rolling of AA5083. Comparison between the theoretical and the experimental data shows the validity of the model.     

中厚板轧制多参量耦合的数值模拟(Ⅰ)

基于物理冶金组织演变经验模型,采用三维刚塑性有限元法建立中厚板轧制过程多参量耦合数值仿真模型.运用该模型对16Mn钢典型工艺下中厚板轧制过程进行模拟计算,分析了变形场、温度场、组织等场变量的演变规律以及冷却过程铁素体晶粒转变.实测得到的铁素体晶粒尺寸,与计算结果基本吻合.     

宝钢2050热轧带钢组织性能的预测

建立了热轧C-Mn钢奥氏体再结晶、流变应力、晶粒尺寸和相变的预测模型,并利用对宝钢2050热连轧及层冷卷取过程温度场的模拟结果定量分析了不同C、Mn含量对组织演变的影响。结果表明,预测值与实测值符合得较好,该模型可用于热轧带钢生产线的预测和控制。     

宝钢2050热轧带钢组织性能的预测

建立了热轧C-Mn钢奥氏体再结晶、流变应力、晶粒尺寸和相变的预测模型．并利用对宝钢2050热连轧及层冷卷取过程温度场的模拟结果定量分析了不同C、Mn含量对组织演变的影响。结果表明，预测值与实测值符合得较好，该模型可用于热轧带钢生产线的预测和控制。     

Microstructure and temperature monitoring during the hot rolling of AZ31

This study details the microstructural evolution during hot rolling of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to understand the deformation mechanisms leading to grain refinement under industrial processing conditions and to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400, and 450°C, and two rolling speeds, 20 and 50 rpm. A total thickness reduction of 67% was obtained using multiple passes, with reductions of either 15% or 30% per pass. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e., strain) per pass and the rolling speed (i.e., strain rate). The results show that the large cast grain structure is broken down by segmentation of the cast grain through localized deformation in twin bands, where dynamic recrystallization occurs in these bands as well as at the grain boundaries (necklacing).     

多道次立-平轧制热力耦合有限元分析

结合显式动力学有限元方法、几何模型更新方法、隐式静力有限元方法对立-平辊轧制过程三道次三维热、力场进行了分析。通过模拟计算的结果,分析了各道次轧件在轧制过程中的温度变化及其原因,并给出了轧件等效应变的分布、各方向应力场的分布。研究结果可以用来分析轧制过程中轧件缺陷变形行为,同时为研究多道次轧制过程和复杂断面轧件轧后冷却过程变形行为提供了新的方法。     

中厚板轧制多参量耦合的数值模拟(Ⅱ)

在采用三维刚塑性有限元法和金属热变形组织演变规律,建立中厚板轧制过程多参量耦合数值仿真模型。在数值模拟(Ⅰ)分析典型工艺下16Mn中厚板显微组织演变规律之后[10],运用该模型对16Mn钢中厚板轧制过程进行了各种工况的有限元模拟,分析了压下量、变形温度及轧制速度对轧件热机械性、组织变化的影响规律。     

The application of EBSD to the study of substructural development in a cold rolled single-phase aluminium alloy

Scanning electron microscopy and high resolution electron backscatter diffraction (EBSD) have been used to study substructural development during cold rolling of a single-phase Al–0.1 Mg alloy, the use of EBSD enabling more detailed quantitative measurements to be made than are possible with the transmission electron microscope (TEM). At low strains, bands of elongated cells, aligned at approximately 35° to rolling direction are formed. As the applied strain was increased, intersecting thinner and more widely spaced bands form within many grains, flow becomes localised within these new bands and they develop into microshear bands, which shear the original elongated cell structures. The changes in the scale of the microstructural features, the development of misorientations of the various types of low angle boundary and the alignment of the features to the rolling plane have been measured as a function of strain. The results are compared with previous TEM investigations of deformed aluminium, and a qualitative model of the microstructural evolution is proposed.     

Development of Texture and Microstructure During Cold Rolling and Annealing of a Fe-Based Shape Memory Alloy

Texture evolution and microstructural changes during cold rolling and annealing of Fe-14Mn-6Si-9Cr-5Ni shape memory alloy have been investigated. The starting solution-annealed material has a nearly random texture with microstructure composed of equiaxed austenite grains with ε martensite plates inside. Cold rolling induces a strong alloy type texture with Brass {011}〈211〉 and Goss {011}〈100〉 as major components. Annealing of the cold-deformed material produces a nearly random texture. The microstructural investigation reveals that with increase in cold deformation, the amount of stress-induced ε and α′ martensite volumes increase. The electron back-scattered diffraction (EBSD) phase mapping shows that reversion of the ε martensite begins only after recrystallization sets in at a temperature of 1073 K.