基于热连轧生产实绩的变形抗力模型应用研究

分析了攀钢1450精轧变形抗力模型结构和相关的回归系数.根据现场的实测数据,发现模型中的问题与不足,提出了优化方法,完善变形抗力模型公式,满足了产品精度的需要;优化后的变形抗力预测精度得到了更高的精度.     

基于热轧工艺参数的冷轧变形抗力预报建模研究

变形抗力作为冷轧工艺设定中重要的材料和控制参数，计算精度直接影响到轧制力设定精度，继而影响带钢平坦度等质量指标的控制精度。针对变形抗力机制模型设定精度低、无法考虑热轧过程参数遗传影响等问题，采用鲸鱼优化算法(WOA)优化BP神经网络建立预测模型(WOA-BP),并通过现场收集的热、冷轧历史过程工艺参数对模型进行训练。WOA-BP模型预测结果表明，平均绝对值误差为10.42,平均绝对百分比误差为1.22,平均均方根误差为13.13,均优于BP神经网络模型，弥补了BP神经网络处理复杂的非线性问题训练时间长、预测精度低等缺点。与传统依托冷轧单工序建立的机制模型相比，考虑热轧工艺参数后，变形抗力预测误差由±15%降低至±6%,应用于L2级系统模型设定后，轧制力精度平均提高了2.09%。     

基于RBF的轴承钢变形抗力的预测

以凸轮式高速形变试验机得到的试验数据为基础,利用Matlab人工神经网络工具箱,建立了轴承钢的变形抗力与其化学成分、变形温度、变形速率及变形程度对应关系的RBF神经网络预测模型.分析了变形温度和变形速率对轧制压力网络模型精度的影响.得出随着变形温度的增加,网络的预测误差逐渐增大;随着变形速率的增大,网络的预测误差逐渐减...     

轧制变形抗力数学模型的发展与研究动态

建立变形抗力数学模型对变形抗力预测和电子计算机在线控制生产的普及具有重要意义。从传统解析法和人工神经网络法两个角度,系统介绍了国内外建立变形抗力模型的发展应用与研究动态,结合建模中存在的问题,针对性地提出了一些建议。     

变形抗力模型对中厚板轧制压力预报精度影响的研究

中厚板轧制压力分别采用凸轮试验和热模拟试验两种变形抗力模型进行预报,变形抗力模型对中厚板轧制压力预报精度的影响显得尤为重要。相关分析研究结果表明:在中厚板轧制过程中,凸轮试验变形抗力模型对轧制压力的预报精度较为稳定;热模拟试验变形抗力模型对轧制压力的预报精度波动较大,但在中间轧制道次,热模拟试验变形抗力模型对轧制压力的预报精度高于凸轮试验变形抗力模型。     

基于Gleeble-1500热/力模拟实验机的轧机轧制力研究

在Gleeble-1500热/力模拟实验机的基础上,用QuikSim管理软件配套记录实验数据,测定Q345钢材的应力-应变曲线,并以Rp0.2作为材料的屈服极限值,得到不同条件下的变形抗力值.通过分析变形速度、变形温度对变形抗力的影响,表明随变形速度的增加,变形抗力提高;随变形温度的升高,变形抗力降低.根据实验所得变形抗力而计算的轧制力能很好的预测粗轧机的轧制力.     

热带轧机高精度轧制负荷预测模型的开发

为了提高精轧机轧制负荷的预测精度 ,提出一种在轧制负荷模型的结构中考虑相变和累计应变对轧制坯料变形抗力的影响和厚度方向的温度分布的新方法。采用本文所述的方法 ,预测精度优于旧模型。预测结果的相对误差限制在± 5 %以内。     

冷轧变形抗力模型研究

冷轧轧制力计算模型是过程控制的核心和基础,而轧制力计算的基础为变形抗力,因此提高变形抗力计算精度是提高轧制力计算精度的一条有效途径。为此,笔者首先通过实际轧制力数据反算变形抗力,然后使用数据分析软件对变形抗力进行曲线拟合。由于根据曲线拟合公式计算出的轧制力与实际轧制力存在差距,因此为了提高轧制力的设定精度,根据带钢压下率对轧制力进行了补偿。现场实际应用证明,这种方法能有效提高轧制力设定精度。     

0.47C-0.36Si-0.67Mn钢连铸板坯低温轧制过程变形抗力模型

用Gleeble-3500热模拟试验机对0.47C-0.36Si-0.67Mn中碳钢150 mm连铸板坯在650 ～920℃、变形量0.1～0.6、变形速率10～20 s-1单道次轴向压缩时的变形抗力进行试验和研究,并建立了实验钢在低温下的变形抗力数学模型.结果表明,随温度降低,变形速率和变形量增加,试验钢变形抗力增加;在700℃以下变形时,由于发生动态铁素体相变,当加工硬化同动态相变软化达到平衡时曲线出现变形抗力极值,而后随形变诱导铁素体量的增加,变形抗力下降.预报值与实测值相符,变形抗力的预报精度为±13.76 MPa.     

Fe-11Mn-10Al-0.9C低密度钢的变形抗力模型和热加工图

以一种具有潜力的汽车用低密度钢(Fe-11Mn-10Al-0. 9C)为研究材料,在Gleeble-1500热模拟试验机上进行单道次压缩实验.在真应力-应变曲线的基础上,分析了变形程度、变形温度和应变速率对Fe-11Mn-10Al-0. 9C低密度钢变形抗力的影响,建立了实验钢的变形抗力模型.预测值与实验值的平均相对误差仅为4. 12%,证实了本文建立的变形抗力模型具有较好的拟合特性和预测精度.基于动态材料模型,建立热加工图,结合热变形组织进行分析.结果表明:当变形温度为950～1 100℃、应变速率0. 01～1s-1时,再结晶过程充分发展,为Fe-11Mn-10Al-0. 9C低密度钢的最佳热加工工艺区间.     

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.     

Micromechanical Formulation of Stress Dilatancy as a Flow Rule in Plasticity of Granular Materials

The paper presents micromechanical formulations of stress dilatancy and their connection to a flow rule in classical elastoplasticity. Dilatancy is inarguably the manifestation of an internal kinematic constraint involving both particle shape and connectivity (texture or fabric) with operative interparticle friction against applied stresses. However, this notion of microstructural dependence is nonexistent in most stress-dilatancy formulations in the literature. We present two different micromechanical approaches that arrive at stress-dilatancy expressions with embedded micromechanical information in the form of a second-order fabric tensor. In connection to stress dilatancy, the underlying nature of the flow rule is next discussed with respect to the dependence of the plastic strain increment vector on the direction of loading (stress increment). It is demonstrated analytically that the flow rule is singular in three-dimensional stress and strain conditions. Finally, the dependencies of dilatancy on fabric are illustrated through various numerical simulations using the micromechanically enriched stress-dilatancy models and a discrete element method.     

轧制过程分析工具—热连轧轧制力模型校正软件

在分析影响轧制力计算精度的诸因素基础上，提出一种模拟方法来校正热连轧精轧机组轧制力数学模型组，并利用实测数据结合操作经验增加了修正因子，提高了模型组的计算精度。采用该模拟软件，可对流动应力模型影响轧制力的程度进行分析，也可对传热模型影响轧制力的程度进行分析。     

Turbulence Modeling of Flows over Circular Spillways

To predict the characteristics of flows over circular spillways, a turbulence model based on the Reynolds stress model (RSM) is presented. Circular spillways are used to regulate water levels in reservoirs. The flow over the spillway is rapidly varied with highly curvilinear streamlines. The isotropic eddy-viscosity models such as k-ε models are based on the Boussinesq eddy viscosity approximation that assumes the components of the turbulence Reynolds stress tensor linearly vary with the mean rate of strain tensor. Hence, they cannot very precisely predict the characteristics of flows over the spillway. On the other hand, the non-isotropic turbulence models such as the turbulence Reynolds stress models (RSM) that calculate all the components of the Reynolds stress tensor can accurately predict the characteristics of these flows. The k-ε models and RSM were applied in the present study to obtain the flow parameters such as the pressure and velocity distributions as well as water surface profiles. The previously published experimental results were used to validate the simulation predictions. For flow over a circular spillway, RSM appears to properly validate the characteristics of the flow under various conditions in the field, without recourse to expensive experimental procedures.     

初始晶粒尺寸对2024铝合金热变形行为和组织的影响

利用永磁搅拌近液相线铸造和普通铸造方法制备不同晶粒尺寸的2024铝合金铸锭,利用Gleeble-1500热模拟试验机研究初始晶粒尺寸对不同压缩变形条件下2024铝合金的热变形行为和变形后显微组织的影响。研究表明:2024铝合金的热变形行为依赖于变形条件和初始组织。初始晶粒尺寸对流变应力的影响是:当应变速率小于0.1 s~(-1)时,流变应力随晶粒尺寸减小而减少;当应变速率为10 s~(-1)时,流变应力随晶粒尺寸减小而增大。降低变形温度会弱化晶粒尺寸对流变应力的影响。热压缩流变应力随应变速率增大而增大,随变形温度升高而减小。应变速率为10 s~(-1)时,热压缩应力应变曲线呈现周期性波动;只在粗晶2024铝合金中发现变形剪切带。     

Locating Discharge Trajectories in Still and Moving Ambient Fluids

The angular momentum principle is employed to locate the trajectories of wastewater plumes. This momentum-based method differs from the traditional approach where a perturbation analysis, based on the centerline velocities, is employed for locating discharges. Evidence of the latter can be found in existing Eulerian-integral and length-scale models. The momentum-based method is incorporated into the hybrid model SD3D, where the regional flow solutions are modified to incorporate the influences of relatively small components of momentum on the discharge trajectory. This method provides a clear understanding of the factors that influence the location of the discharge. The momentum-based approach yields analytical trajectory solutions in many cases, and it eliminates the need to arbitrarily select the appropriate characteristic velocity for locating the flow. Comparisons are made with available experimental data, and they show that the momentum-based method provides accurate predictions of the flow trajectories under a variety of discharge conditions. Comparisons are also made with predictions from the CORMIX1 and JETLAG models. In general the predictions are consistent, but some important discrepancies are highlighted. The use of the momentum-based method for locating discharges is discussed in light of recent experimental studies.     

Strengthening by ordered precipitates in a Ni−Ni4Mo system

The strength characteristics and microstructures of aged Ni−Mo alloys containing ordered (Ni₄Mo) precipitates were studied as a function of aging time and temperature. It was found that 17 at. pct Mo alloy aged at 750°C produced a uniform dispersion of cuboidal β precipitates which coarsened with time producing a gradual increase in flow stress. The flow stress increment was found to vary in qualitative agreement with both order strengthening and coherency strain models. Both these models give over-estimates of the strengthening increment. A negative dependence of flow stress on temperature is attributed to coherency strain contributions.     

Heat transfer-solidification kinetics modeling of solidification of castings

A close examination of the recent developments in the field of computer simulation of solidification process reveals that a combination of both macroscopic and microscopic models is necessary in order to accurately describe the solidification of castings. Currently available macroscopic models include models that describe heat transfer from metal to mold, fluid flow of liquid metal during mold filling, and stress field in the casting. At the microscopic level, the models should include more intricate issues such as solidification kinetics and fluid flow in the mushy zone. Although significant progress has been accomplished over the years in each field, the task of including all of these models into a comprehensive package is far from being complete. This paper describes the state of the art on coupling the macroscopic heat transfer (HT) and microscopic solidification kinetics (SK) models and introduces thelatent heat method as a more accurate method for solving the heat source term in the heat conduction equation. A new method for calculation of fraction of solid evolved during solidification based on computer-aided cooling curve analysis (CA-CCA), as well as a method based on nucleation and growth kinetics laws, is discussed. A new nucleation model based on the concept of instantaneous nucleation, which is used to describe equiaxed eutectic solidification of commercial alloys, has been introduced. It is demonstrated that the instantaneous nucleation model agrees well with the experimental results in terms of cooling curves and of evolution of the fraction of solid during solidification. Validation results are also shown for SK models that are based on CA-CCA coupled with HT models for eutectic Al-Si and gray cast iron alloys.     

Evaluation on some important force models for cold strip rolling

To improve the accuracy of rolling force prediction, some important force models were evaluated through applied computation for cold rolling of low carbon steel and aluminum alloy according to measured data on lab mill. The effects of model structure and three important variables ‐ flow stress, contact length and friction coefficient ‐ on the precision of computed force were quantitatively studied. Flow stress was measured with plane‐strain compression test, contact length was based on elastic flattening of work‐roll by Hitchcock, and friction‐coefficient was determined by rolling strain and numerical iteration. In steel rolling Bland & Ford integration model and Bryant & Osborn algebraic equation are better in accuracy than Ekelund and Parkins. In aluminum rolling all the models produce large deviations ΔF_R = 10–20% if flow stress, contact length and friction coefficient are determined with the same method as steel rolling. The elastic deformation of aluminum strip is now taken into account for its low elastic modulus. An effective method to determine plastic and elastic contact has been developed in this investigation. The accuracy of force computation is obviously improved for aluminum rolling.