A microstructure evolution model for numerical prediction of austenite grain size distribution

In this study, a mathematical model has been developed to predict austenite grain size (AGS) of hot rolled steel. Using the compression test, the static (SRX) and metadynamic (MDRX) recrystallization characteristics of medium carbon steel were studied. Compression tests were carried out at various temperatures in the range 900-1100 °C with strain rates ranging from 0.1 to 10 s⁻¹. The time required for 50% recrystallization for the SRX and MDRX was determined by carrying out double compression tests, respectively. Grain growth equation after full recrystallization was also derived by compression tests with various interpass times. The currently determined microstructure model has been integrated with a three-dimensional non-isothermal finite element program. The predicted results based on the model proposed in the present investigation for hot bar rolling processes were compared with the experimental data available in the literature. It was found that the proposed model was beneficial to understand the effect of recrystallization behavior and control the microstructure evolution during the hot bar rolling.     

热轧过程微观组织演变的数值预报与试验研究

对于热力耦合大变形问题 ,构造了同时求解变形和温度的热弹塑性变分原理和相应有限元法 ,并与金属微观组织演变数学模型相结合 ,提出了热变形过程微观组织的数值预报方法。针对再结晶动力学方程和晶粒长大方程对时间和温度的高度非线性 ,定义了一个经温度补偿的适用于变温过程的等效时间 ,解决了变温状态下对时间的叠加问题。作为应用 ,模拟了H型钢热轧过程的微观组织演变 ,并相应地进行了试验研究。预报值与实测值吻合良好 ,表明该方法已能成功预报热变形后的金属微观组织     

热带钢连轧多场耦合演变过程有限元分析

根据物理冶金组织演变规律和经验公式，开发了金属热变形过程耦合组织演变的计算模块。结合某厂2050热带钢连轧工艺过程，利用非线性刚塑性有限元法，建立热连轧过程热、力、组织的多参量耦合仿真模型。运用该模型对2050现场实际轧制过程进行模拟计算，分析了轧制过程轧件变形场、温度场及显微组织的演变规律。模拟得到的轧制力能参数、温度、组织分布与实测数据基本一致。     

环件辗扩成形过程微观组织及性能控制研究进展

高性能大型环件精确辗扩控形控性一体化制造是大型运载火箭仓体、风电法兰、核电反应堆及石油化工容器等高端装备向着安全、轻量、高效和长寿命方面发展的迫切需求。综述环件辗扩成形过程微观组织及性能研究现状,分析单、双道次简单热模拟压缩试验和显微组织演变数值模拟技术在环件辗扩过程组织演变研究中的应用,探讨环件组织与性能控制中存在的问题,并指出目前的研究已无法满足上述高性能环件制造要求。提出复杂多道次物理模拟及内变量组织建模用于环件辗扩组织演化分析的必要性,探明环件宏观/微观织构定量表征和晶体塑性有限元法(Crystal plasticity finite element method,CPFEM)揭示组织演变机理的可行性。阐述今后高性能环件辗扩成形组织演变及性能控制的研究方向与重点,未来必须构建辗扩过程环件组织、织构和力学性能之间及其与工艺参数的定量关系。     

Metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during hot compression

The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the metadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.     

Influence of strain distribution on microstructure evolution during rod-rolling

A thermo-viscoplastic constitutive model is used in an explicit finite element analysis to determine the strain distribution that develops during rod rolling. The computed strains are then used to predict the resulting grain size of the material microstructure. Predictions are compared to experiments conducted on rolling of square billets. There is good agreement between the measured and predicted roll loads and torques as well as on the deformed geometry. The ability of the analysis to predict the resulting heterogeneous microstructure is also demonstrated.     

Effect of Extreme Pressure Additives on the Deformation Behavior of Oxide Scale during the Hot Rolling of Ferritic Stainless Steel Strips

High-speed steel (HSS) materials are universally used as work rolls for the hot rolling of stainless steels. Their use has increased the output of the rolling mill and decreased roll material consumption and grinding. Sticking defects often occur, however, during the hot rolling process. In this article, extreme pressure (EP) additives were dropped on the HSS samples at high temperature. Zinc dialkyl dithiophosphate (ZDDP) was chosen as the most effective EP additive by scratch tests on the HSS samples. In order to determine the optimum proportion of ZDDP in the lubricant, two reduction rates were tested on a Hille 100 experimental rolling mill by hot rolling ferritic stainless steel 445J1M at five different concentrations of ZDDP. The mechanism of EP additive action during the hot rolling process was also investigated. By analyzing the deformation behavior of the oxide scale of samples after hot rolling using different proportions of ZDDP, it was found that 20% ZDDP in the lubricant is the preferred concentration for industrial application.     

板带粗轧过程热、力、组织耦合三维有限元模拟

根据某厂2050热带钢粗轧机组轧制工艺，借助物理冶金组织演变模型，利用非线性有限元法开发了热连轧过程热、力、组织耦合三维刚塑性有限元模型。运用该模型对低碳钢SS400的现场实际轧制情况进行仿真计算，得到轧件三维变形场、温度场及显微组织的分布规律。模拟得到的轧制力能参数、粗轧出口温度与现场实测结果吻合很好。     

[成形质量的闭环与自适应控制技术]热轧带钢出口凸度数据驱动建模及智能化预测分析

提出一种基于热轧现场生产数据和智能算法的新型带钢出口凸度预测模型，该模型采用差分进化算法对支持向量机的惩罚因子和核函数宽度进行优化。确定了支持向量回归模型的最佳参数组合，采用大量实际生产数据对模型进行训练并将其用于带钢出口凸度预测。该模型结构简单、容易实现，其整体性能用平均绝对误差（MAE）、平均绝对百分误差（MAPE）、均方根误差（RMSE）和决定系数R2来评价。预测值和实际值的比较验证了所提出模型的可行性。     

Texture evolution in grain-oriented electrical steel during hot band annealing and cold rolling

The optimization of magnetic and physical properties of electrical steel is imperative for many engineering applications. The key factors to improve magnetic properties are the steel composition as well as control of the crystallographic orientation and microstructure of the steel during processing. However, this requires careful control of processing at all stages of production. Under certain conditions of deformation and annealing, electrical steel can be produced to have favourable texture components. For grain‐oriented (GO) electrical steels that are used in most transformer cores, a pronounced {110}〈001〉 Goss texture plays a vital role to achieve low power losses and high permeability. Essentially, Goss texture develops during secondary re‐crystallization in GO electrical steels; however, the mechanism of the abnormal Goss grain growth is still disputed in the literature. In the current study, the influence of the annealing conditions on the development of annealing, cold rolling and re‐crystallization textures of hot‐rolled GO electrical steel were investigated in detail following each processing step. Furthermore, the orientation data from electron backscatter diffraction were used to evaluate the orientation‐dependent stored energy of deformed grains after hot rolling. In the light of new findings in the present study, annealing and deformation texture development mechanisms were critically reviewed.     

Investigation of closure of internal cracks during rolling by FE model considering crack surface roughness

Internal cracks often appear in cast slabs, and their evolution during hot deformation directly affects the product quality. In this paper, the authors investigate the closure behavior of internal cracks during plate rolling using a finite element (FE) model that takes into account the roughness of the crack surface. Influences of the roughness and reduction ratio on the closure of cracks are analyzed. The simulated results show that the models with consideration of the initial crack roughness can be used to investigate the formation of residual voids around the crack after rolling. The simulation results are validated by experimental observations. Finally, we propose an explanation of the crack closure mechanism during rolling.     

Study on the oxidation of stainless steels 304 and 304L in humid air and the friction during hot rolling

In rolling process, the contact friction is of crucial importance for accurate modeling, optimum design and control of industrial rolling processes. It is important to characterize the features of the oxide scale of stainless steel in hot strip rolling because the scale on the strip surface affects friction coefficient and thermal conductivity coefficient. To some extent, the rolling force and friction condition depend on the thickness and the microstructure of the oxide scale. Oxidation tests of stainless steels 304 and 304L were carried out in a high temperature electric resistance furnace. The humid air in which the water vapour content can be controlled was generated and remained to flow into the chamber of the furnace in 2.5 × 10⁻⁴ m³/s to study the effect of humidity on the oxidation of stainless steels. The microstructure and thickness of oxide scale layer of stainless steels were obtained and two or three oxide layers can be found. The humid air has a significant effect on the growth of oxide scale. Hot rolling tests were carried out on Hille 100 rolling mill. The friction condition at the roll–strip interface during hot rolling of stainless steel was determined and the transfer of surface roughness was discussed.     

Microstructure evolution modeling of titanium alloy large ring in hot ring rolling

Exploration of microstructure evolution is of significance for manufacturing the large ring with high performance and high reliability in hot ring rolling. In the study, the microstructure evolution model and the rate-/temperature-/microstructure-dependent constitutive model of titanium alloy are implemented in ABAQUS/Explicit through the user material subroutine VUMAT. The developed subroutine is validated by single-element models and isothermal upsetting experiments of Ti–6Al–4V cylinder. The subroutine is imbedded into a coupled thermomechanical three-dimensional finite element (3D-FE) model for hot rolling of Ti–6Al–4V large ring. The evolution characteristics of β phase volume fraction and grain size of Ti–6Al–4V during the process are revealed, and the final microstructures of the large ring under different processing conditions are explored. The results obtained show that (1) microstructure evolution follows the trend with the process progressing: the fine grain zone transfers from the surface layer (SL) to the middle layer (ML) of the ring; the poor β zone extends from the outside of the SL to the end-plane of the ML, and the rich β zone always locates at the SL. (2) decreasing the rotational velocity of the driver roll n ₁, or increasing the feed rate of the idle roll v or the initial temperature of the ring T ₀ contributes to more uniform distributions of β phase and its grain size, but results in the increase of the β phase volume fraction and grain size.     

冷轧双相钢在退火过程中的组织和织构演变

通过模拟双相钢的热镀锌退火处理,研究了钢的组织和织构演变。结果表明:冷轧后试验钢加热到630℃时,在变形铁素体晶界附近出现少量再结晶晶核,当加热温度升高至690℃时,变形组织已基本消失,再结晶过程基本完成;在再结晶过程中析出的细小弥散TiC、NbC相对{111}织构的形核具有促进作用,阻碍了不利织构的形核,从而使得γ织构密度增强,α取向线上的{001}〈110〉至{112}〈110〉范围内的织构密度减弱,甚至消失;在再结晶晶核长大阶段,TiC、NbC相对{111}织构的长大具有阻碍作用,使得{001}〈110〉织构密度升高。     

[成形过程仿真优化与集成计算材料工程]钛合金热成形工艺形变与组织演变耦合多尺度仿真研究进展

讨论了钛合金高温变形晶体塑性有限元模拟的研究进展,并分析了晶体塑性模型在钛合金细观尺度不均匀变形和组织演化方面的应用;围绕钛合金热成形过程变形与组织演变耦合模拟需求,讨论了钛合金高温成形统一黏塑性本构模型的发展过程,并介绍了统一黏塑性本构模型在钛合金热成形工艺的应用实例。统一黏塑性本构模型考虑了钛合金高温变形过程中回复、再结晶、相变、损伤等组织演变行为与宏观应力应变之间的耦合作用,为实现钛合金构件形状尺寸和组织性能的精确预测和成形工艺优化提供了有效的手段。最后分析了钛合金热成形工艺多尺度建模仍存在的问题,并展望了多尺度建模的发展趋势。     

A theoretical and experimental investigation into asymmetrical hot rolling

A simple slip-line field solution for asymmetrical hot rolling is investigated and used to predict the sign and magnitude of the curvature of the rolled strip. These predictions are compared with measurements from a two high model rolling mill.     

Occurrence of surface defects on strips during hot rolling process by FEM

During a hot rolling process, surface defects on strips can severely affect the quality of the rolled product, particularly for two conditions: (1) there are initial defects on continuous casting slabs that propagate and/or are inherited from those on the surface of rolled steels from upstream rolling processes; and (2) there are no initial defects on continuous casting slabs, and they consequently appear on the surface of rolled steels due to improper rolling technologies. In this paper, the authors present a new 3D finite element model coupled with constrained node failure to understand better the initiation and growth of surface defects on strips during the hot rolling process for case 2. The strip deformation processes were simulated for various rolling reduction ratios and friction coefficients between the roll and the strip. The occurrence of surface defects on strips was modeled under some rolling conditions. The plastic strain distribution in strips and the rolling forces were obtained. The risk of occurrence of surface defects on strips increases as the friction between the roll and strip increases for the same reduction ratio.     

Ni/Al多层板的复合法制备及放热性能

在纯铝箔上化学镀镍得到微米级厚度的镍层,再将该镀镍铝箔堆垛热压后进行累积叠轧(1~7道次),得到Ni/Al多层板,研究了该多层板的组织结构及放热性能。结果表明:化学镀镍层为非晶态,在热压过程中发生晶化;随着叠轧道次的增加,镍层逐渐发生颈缩和断裂,其碎片镶嵌在铝中,增加了镍和铝的接触面积,从而提高了Ni/Al多层板的放热性能,其能量密度由1道次的520.27J·g^-1增大到7道次的1203.4J·g^-1,达到理论值的87.15%;不同道次叠轧Ni/Al多层板的起始反应温度均高于475℃,说明该多层板具有良好的室温稳定性。     

基于改进GTN损伤模型的镁合金镦粗成形损伤及裂纹预测研究

镁合金在成形过程中极易产生开裂，精准的损伤预测可以为塑性成形工艺提供理论支撑。为此，基于含连续介质剪切损伤因子的Gurson-Tvergarrd-Needleman(GTN)损伤模型被应用于预测镁合金成形时的损伤演化，通过压缩试样的力-位移曲线标定了AZ31B镁合金的流动应力和剪切损伤参数，预测并验证了AZ31B镁合金在镦粗工艺下的表面损伤及开裂，扩展了模型对低应力三轴度下的成形工艺损伤预测的适用性。在此基础上，对AZ31B镁合金在受压条件下损伤成因、裂纹扩展进行了分析。结果表明，随着压缩位移的增加，镁合金侧面中心区域的切应力不断增加，在此作用下基体内部孔洞沿非垂直压缩方向伸长、聚合，最终形成宏观裂纹；镦粗后的试样侧面裂纹走向与垂直压缩方向所成角度范围为34°～46°，改进的GTN模型模拟结果为44°～54°，原始GTN模型模拟结果均呈90°；改进后的GTN模型可应用于预测镁合金在轧制、热冲压等工艺下的损伤演化行为，为后续工艺优化奠定基础。     

大型船用曲轴弯锻成形过程仿真和组织模拟研究

采用DEFORM-3D软件对船用大功率低速柴油机曲轴曲拐弯锻成形过程进行三维数值热模拟试验研究，获得应力、应变、应变速率、温度分布等信息。在DEFORM-3D软件基础上开发了组织模拟用户子程序，可以预测曲轴平均晶粒度的变化。结合仿真数据，并基于元胞自动机法，研究了曲拐弯锻成形动态再结晶过程，分析了应变、应变速率等参数对微观结构演化的影响。