Accounting for shear deformation in fast models for plate rolling

For on-line prediction of roll force and torque, fast models have been available for a long time, which are mainly based on the slab method or other solution methods that allow for computing times in the range of seconds. Such fast models typically treat the rolling process as a plane strain problem and neglect shear deformation, which is always present in real processes. The shear deformation results in inhomogeneous strain profiles and thus might lead to inhomogeneity in microstructure over plate thickness. In this paper, a novel method is presented that allows for superposition of shear strain onto the strain state obtained from the slab method. The shear strains are interpolated from an extensive finite element (FE) parameter study of rolling processes that covers the entire parameter range of today’s plate rolling. For the regimes of very thick and thin plates different interpolation functions are introduced. It is shown that when the proposed shear strain model is combined with the slab method, similar results are obtained as with a full-scale FE calculation of the rolling problem but with a calculation time in the range of seconds.     

Investigation of rolls size effects on hot ring rolling process by coupled thermo-mechanical 3D-FEA

Hot ring rolling is a significant branch of ring rolling characterized by high nonlinearity, 3D deformation, continuously progressive forming, unsteady-state, asymmetry, etc. with coupled thermo-mechanical behaviors which have significant effects on the deformation behavior, microstructure and mechanical properties of the ring. Changing the sizes of forming rolls including mandrel and driver rolls will considerably affect the roll gap deformation zone which is in close relation to the feed amount of both forming rolls and thus affects forming quality of the ring as well as power parameters. In this study, a reliable coupled thermo-mechanical and 3D rigid-plastic finite-element (FE) model for hot rolling of large rings is established. Then, based on the stable forming condition of the ring rolling process and comprehensive numerical simulations, the size effects of forming rolls on strain and temperature distributions and their uniformity, stress distribution, side spread and power parameters were investigated by 3D coupled thermo-mechanical FE simulation. The results show that there are optimum sizes of mandrel and driver rolls under which the strain and temperature distributions of ring and thus its microstructure are the most uniform where fishtail coefficient and power parameters have reasonable values. The achievements obtained can not only serve as a guide to the design of rolls sizes, optimization and quality control of the hot ring rolling process, but also clarify the plastic deformation and heat transferring of hot rolling of large rectangular-section rings.     

中厚板轧制过程的数值模拟

以L245级管线钢材料的热物性参数(密度、泊松比、杨氏模量、热膨胀系数、热导率和比热)和热模拟压缩实验获得的高温变形时应力—应变曲线等试验数据为基础,在MSC.Marc软件中建立了该钢种材料数据库,并建立了中厚板多道次轧制过程的二维有限元模型。以铸坯厚度为220mm、成品厚度为25.4mm的热轧过程为例,通过对轧件与轧辊接触面间换热系数采用取不同常数值的方法,并依据其生产时所采集的各道次相关工艺参数,对该轧件全道次热轧过程进行了数值模拟,将各道次的轧制力计算值与实测值进行了分析比较,确定了轧件与轧辊间接触面换热系数的最佳值。利用本文模型对厚度为180mm的轧件单道次轧制过程进行了数值模拟,研究了不同变形工艺参数(轧制温度、道次压下率和轧制速度)对变形区等效应变和等效应力的影响。结果表明,在轧机设备能力及生产现场条件允许时,高温粗轧阶段纵轧道次可采用低速大压下率进行轧制成形,使变形较充分地向轧件芯部渗透,从而使钢板获得细小均匀的晶粒组织,有效改善钢板的强韧性能。     

硅钢片轧制过程的有限元数值模拟

利用体积成形软件DEFORM对硅钢片的轧制变形过程进行有限元数值模拟．其中包括对轧件不同厚度层应力及应变分布、整个轧制过程的扭矩分布的数值模拟。结果表明,其模拟结果与传统理论所述结果基本一致。     

楔横轧轴类件热变形时奥氏体微观组织演变的预测

运用Gleeble-3500热模拟实验机对轴类件用钢40Cr高温热变形的组织形态进行研究,并由金相分析数据回归得出高温奥氏体组织演变数学模型．然后利用非线性有限元法建立了金属成形过程中热、应力、组织相互耦合的刚塑性有限元模型．采用该模型对二辊楔横轧成形工艺进行仿真计算,得出了轧后工件的温度场、变形场、高温奥氏体晶粒尺寸分布等．对比轧后工件奥氏体组织分布的计算结果与实测值可知,两者吻合良好．     

热带粗轧机组立轧非稳定轧制阶段变形规律的实验研究

采用铅作为模拟材料，模拟比１∶１０，对热带粗轧机组平辊立轧时非稳定轧制阶段变形规律进行了模拟实验研究。分析和比较了头、尾部最大狗骨高度非稳定行为、失宽行为、鱼尾长度与立辊直径、侧压量、板坯来料厚度及宽度之间的关系，并建立了新的数学模型。     

Void closure prediction in cold rolling using finite element analysis and neural network

Cold rolling is used to eliminate void defects in cast materials thus improving the material performance during service. A comprehensive procedure is developed using finite element analysis and neural network to predict the degree of void closure. A three-dimensional nonlinear dynamic finite element model was used to study the mechanism of void deformation. Experiments were conducted to investigate void closure during the cold flat rolling process. Experimental results are compared to the three-dimensional finite element predictions to validate the model. The void reduction predictions from finite element analysis are in good agreement with experimental findings. Plastic strain, principal stress distribution around the void and void reduction ratio are presented for various case studies. As finite element simulation is time-consuming, a back-propagation neural network model is also developed to predict void closure behavior. Based on the correlation analysis, the reduction in sheet thickness, the dimension of the void and the size of the rollers were selected as the inputs for the neural network. The neural network model was trained based on results obtained from finite element analysis for various simulation cases. The trained neural network model provides an accurate and efficient procedure to predict void closure behavior in cold rolling.     

INFLUENCES OF EDGING ROLL SHAPE ON THE PLASTIC STRAIN DISTRIBUTION OF SLAB DURING MULTI-PASS V-H ROLLING PROCESS

Multi-pass slab vertical-horizontal （V-H） rolling process with variable edging roll shape have been simulated with explicit dynamic finite element method and updating geometric method. The distributions of plastic strain contour in slab daring rolling process with different edging roll and under different rolling stage have been obtained. The results show that there exist two thin strain assembling zones in slab when the flat edging roll is used, and there just exist one strain assembling zone in slab when the edging roll with groove is used. And compared the deformation equality between flat edging roll and edging roll with groove, the lateris better than the former, which supplies the theory prove to the slab deformation distribution during V-H rolling process and is helpful for predicting the slab texture.     

A study of pore closure and welding in hot rolling process

The design of processing conditions to eliminate porosity in steel during hot rolling has become more critical with the advent of continuously cast feed stock. To predict appropriate process parameters, experiments were performed in which holes were drilled in steel slabs, at different depth below the surface perpendicular to the rolling direction. After hot rolling, the state of the deformed holes was examined by optical microscopy. The fracture surfaces of tensile specimens notched in the plane of the closed holes were examined under a scanning electron microscope to investigate the bonding ( welding ) between the surfaces of the closed holes because this bonding is the most important factor indetermining the transverse mechanical properties of the rolled product. The deformation of such holes in the roll gap was modelled as an clastic / plastic plane strain problem using the FE software ABAQUS to investigate the strain and stress around holes and to analyze the conditions required to promote pore closure and welding between the closed surfaces.

Experiment results showed that the rate of pore closure was affected by the parameters of rolling process and the position of holes relative to the rolling contact surfaces. FE simulation of pore closure showed a good agreement with experimental results and showed that a certain level of hydrostatic pressure resulted in the closure of pore and that the holding period of the pressure in the compressive state determined the degree of welding of surface of pores; shear is favourable to this welding.     

大型厚壁深槽环件卧式复合轧制新方法理论与模拟(一)

由于大型厚壁深槽环件特殊的几何特征,需要采用自由锻与切削的工艺,导致能源材料消耗高、效率低、产品性能差。该文提出一种用于成形大型厚壁深槽环件的卧式复合轧制新方法,基于环件卧式复合轧制成形原理,提出了主要成形参数的设计方法;利用ABAQUS有限元软件进行三维热力耦合有限元建模与模拟分析,验证了环件卧式复合轧制技术可行性,揭示了轧制过程中环件几何尺寸、应变、温度以及力能参数分布演变规律。研究成果为深入研究大型厚壁深槽环件卧式复合轧制成形机理和工艺设计方法奠定了重要基础。     

GH4169异型材单轧槽轧制工艺

采用轧制工艺生产GH4169合金异型材,结合实验条件,基于有限元模拟软件建立了单轧槽少道次轧制过程的三维刚塑性有限元模型。采用异型坯作为坯料,分析了轧制过程中孔型充满度、变形温度、等效应变和等效应力的分布情况。模拟结果表明,采用Φ160 mm×200 mm轧机时,初轧温度为1070℃,断面收缩率为45%,单轧槽两道次轧制成形,孔型充满度良好,等效应变约为0.3~1.4。结合模拟结果,在轧机上进行了热轧实验,轧件厚度满足尺寸要求,宽度比成品小2 mm,没有发生晶粒细化。这主要是由于多火次、多次数轧制,使得加热引起的晶粒长大程度大于小变形量引起的晶粒细化程度,使得晶粒未细化,宽度不够。     

钢坯高温抗氧化涂料应用效果试验研究

由于钢坯在加热过程中温度高、时间长,其表面氧化烧损严重,不仅降低了热连轧过程金属收得率,而且影响轧制过程中高压水的除鳞效果,产生带钢表面质量缺陷,为此出现了高温抗氧化涂料的研究和应用.在某常规热连轧生产线针对低碳钢、微合金钢、耐侯钢,试验研究了一种钢坯高温抗氧化涂料的高温防氧化效果及使用性能.结果表明,试验应用的高温抗...     

热带粗轧机组调宽工艺中数学模型的建立

采用铅作为模拟材料，对热带粗轧机组平辊立轧－－平轧调宽的变形规律进行了实验研究，简要分析了立轧时的“狗骨”行为和随后平轧时宽度变化行为与来料厚度，宽度、轧辊直径和压下量的关系，并建立了新的数学模型。     

立辊辊槽磨损对板坯断面形状的影响

针对热连轧粗轧段板坯在线调宽生产中立辊辊槽的磨损对轧制后板坯截面“狗骨”形状的影响,本文基于弹塑性有限元理论,利用有限元软件MSC．Marc,对在不同侧压量下,采用新立辊、磨损中、磨损后立辊和磨损的理想极限平立辊四种轧制条件下对应的板坯截面形状变化进行了仿真分析。得出了立辊辊槽磨损对“狗骨”形状的影响规律,随着磨损加深,立辊辊槽宽度增大,“狗骨”形状明显。     

镁合金有限元与三维加工图相结合的材料驱动的可加工性模拟

基于PRASAD提出的传统的二维加工图理论,建立考虑应变的三维加工图,描述功率耗散系数和流变失稳区域随应变速率、温度和应变的变化。三维加工图说明了材料的内禀可加工性,而有限元分析方法可得到材料在特定工艺条件下应力、应变、应变速率及金属流动情况,说明了由模具形状和工艺条件决定的应力状态可加工性。基于此,提出一个新的由材料驱动的热变形可加工分析方法,联合考虑有限元和三维加工图,可以说明整个热加工过程的材料可加工性（包括应力状态可加工性和内禀的可加工性）。通过此方法,研究难变形金属镁合金的热锻过程,包括复杂热锻直齿锥齿轮的三维热力耦合有限元和三维加工图的集成模式。基于得到的研究结果,成功进行了热锻试验。试验表明新的方法用于确定最佳工艺参数是合理的。     

Deformation behaviors and conditions in L-section profile cold ring rolling

Three-dimensional FE model of plastic penetration in L-section profile cold ring rolling is established under ABAQUS software. Based on this model, the expanding rules of plastic zone in roll gap are revealed by FE simulation, and three deformation behaviors of L-section ring that exist in the rolling process are exposited. Conditions for three deformation behaviors are studied and verified by rolling simulation and experiment. The deformation behavior, which is needed for normal rolling of L-section ring, and its conditions are determined at last.     

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实验室模拟了不同热送热装温度的Ti微合金化连铸坯热送热装和加热过程,并采用光学显微分析、扫描电镜分析和透射电镜分析等方法,观察了生产条件下连铸坯和粗轧中间坯试样的显微组织,以及实验室条件下不同热履历铸坯试样的显微组织,分析了热送热装连铸坯在粗轧过程中表面裂纹的生成原因。结果表明,经热送热装的连铸坯表面金属中奥氏体晶界处的先共析铁素体膜及沿奥氏体晶界的碳氮析出物可能是导致粗轧过程表面裂纹形成的主要原因。     

42CrMo铸坯环件热辗扩有限元模拟与分析

基于ABAQUS软件平台,建立了42CrMo大型环形铸坯热辗扩三维热力耦合有限元模型,模拟了铸坯热辗扩过程中应变场和温度场,研究了初始辗扩温度对辗扩力的影响规律.模拟结果表明在环形铸坯热辗扩过程中：①铸坯等效应变呈阶梯状上升,内外表面应变大于中间层应变;在稳定成形阶段,沿环件径向方向,由于导向辊与芯辊直径差异,导致环件最大平均等效应变可能出现在环件内表面也可能出现在环件外表面;②初始阶段,变形区与成形辊接触处温度降低较快,非变形区温度变化不是很明显;随着辗扩的进行,芯部温度逐渐上升,边缘温度低,温度分布不均匀;③随着铸坯初始辗扩温度升高,平均辗扩力明显下降,但随时间变化趋势保持一致.     

A study of the effect of the deformation parameters on recrystallization behavior in the rod rolling process

Rod rolling is a process in which the deformation of the workpiece between the work rolls is quite different from the rod drawing process, but the area strains (natural logarithm of area reduction ratio) multiplied by a constant have been used in the calculation of the pass-by-pass evolution of austenite grain size in rod (or bar) rolling without any verification. Considering that the deformation parameters (strain and strain rate) at a given pass play a crucial role in determining recrystallization behavior, the calculation method for the deformation parameters associated with rod rolling should be examined. In this study, a series of numerical simulations has been carried out using an area strain model [5] and an analytic model [6] which calculate the pass-by-pass strain in the rod rolling process, focusing on the effect of the calculation method for the pass-by-pass strain on the recrystallization behavior and evolution of AGS (austenite grain size) during a given pass. These have been investigated for a six-pass rolling sequence (oval-round or round-oval) designed for this study by incorporating the recrystallization and AGS evolution model being widely used in hot rolling. It was found that the recrystallization behavior and evolution of AGS during a given pass were significantly influenced by the calculation methods for deformation parameters. The area strain model lacks mathematical grounds to be used as input to the equations for recrystallization and AGS evolution.     

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 分析了薄板坯连铸连轧工艺流程的热态模拟要点，为薄板坯连铸连轧工艺流程的工艺优化和产品开发提供了合理的模拟方法。该方法与现场生产具有良好的相关性，具有精确控制钢水成分、轧制方案选择多样化等优点。