热轧带钢在冷却过程中的内应力解析

针对热轧带钢的冷却过程,开发了温度、相变的内应力的耦合解析模型,该模型采用有限元法,同时考虑了相变的温度依存性、相变潜热、相变膨胀。通过该数值解析模型,能够模拟热轧带钢在冷却过程中温度一组织内应力的演变过程,计算结果与实测值符合良好。     

层流冷却过程中带钢温度场的数值模拟

建立了温度与相变耦合的二维有限差分预测模型,并对带钢轧后冷却过程带钢厚度和宽度方向的温度场进行了模拟计算.根据连续等温转变实验曲线,采用Avrami方程和Seheil的可加性法则来计算带钢相变潜热,实现温度和相变耦合求解,计算结果和现场实测结果吻合.     

带钢层流冷却过程数值模拟及卷取温度预测分析

结合宝钢2050热连轧层流冷却生产线,建立了带钢层流冷却过程传热数学模型,同时考虑相变潜热对带钢温度的贡献。采用实测的卷取温度,修正了带钢表面换热系数模型,模拟研究了冷却模式、速度、厚度等对卷取温度的影响。结果表明:卷取温度计算值与实测值的标准差小于14℃;相变潜热对卷取温度的贡献为28℃;冷却模式、速度、厚度是影响卷取温度的重要因素;该模型能够满足宝钢2050热连轧层流冷却卷取温度的预报精度,对实际生产具有较好的指导性作用。     

稀土管线钢轧制工艺的模型研究

为了研究稀土对变形奥氏体晶粒的影响,建立了稀土管线钢的轧制模型,实验验证表明,模型可以精确预测稀土管线钢轧制过程中奥氏体晶粒的长大行为.研究发现,稀土改变了X80管线钢的奥氏体变形行为,原有的TMCP工艺不适合稀土管线钢.对于稀土管线钢而言,通过适当的调整轧制工艺,稀土的微合金作用可以得到充分发挥,相变之前的奥氏体组织明显细化.     

齿轮钢淬火过程多场耦合分析

利用有限元分析软件MSC.Marc,结合热弹塑性模型和编写的用户子程序,对(%)0.21C-1.03Cr- 0.20Mo0.03Nb齿轮钢圆柱体淬火过程的温度、组织和应力场进行了多场耦合分析。结果表明,淬火过程产生的内 应力促进马氏体相变,在马氏体相变的情况下,组织应力强于热应力,使淬火后工件的残余应力呈组织应力分布。 测量值和计算值对比表明,淬火过程应力场数值模拟中,考虑应力与相变的相互作用,使计算结果更为精确。     

Nb微合金钢连续冷却过程中铁素体晶粒尺寸的预测

基于相变动力学和热力学原理,讨论了合金元素Nb对铁素体相变的影响,建立了连续冷却过程中Nb微合金钢铁素体晶粒尺寸预测模型,模拟了应变量、轧制温度、冷却速度和固溶Nb含量对铁素体晶粒尺寸的影响,并将模型计算结果和试验结果进行比较,两者吻合良好,表明该模型能够用来预测Nb微合金钢连续冷却过程中铁素体晶粒尺寸。     

DQ+ACC快冷工艺下X70M级管线钢板形质量提升及系统优化

钢板冷却过程中存在温度-相变二者耦合形成的内应力。通过建立温度场和相变耦合有限元模型,分析X70M级管线钢中厚板厚度方向上温度和相变分布规律。结果表明:在DQ+ACC冷却过程中,钢板宽度和厚度方向均存在温度分布不均现象,导致相变行为差异性。经过有限元计算分析得出,终冷温度为500℃,钢板边部和中部的温差为60℃,边部相变达到80%,中部相变达到40%,中部应力趋于0,边部存在很小的拉应力;终冷温度为550℃,边部相变达到40%,中部相变未开始,中部和边部均受压应力,最大值分别为-34 MPa和-170 MPa。通过采取DQ、ACC上部集管横向不均匀的水流量分布模式、优化DQ+ACC上下水比、降低终冷温度等措施,使X70M级管线钢中厚板在快冷工艺下的板形平直度得到明显改善。     

中厚板生产过程中组织性能的预报

建立了C-Mn钢在控制轧制和控制冷却生产中微观组织演变和力学性能预测的物理冶金模型。模型包括加热、再结晶、相变和力学性能四部分，分别描述了中厚板热轧及冷却过程中的物理冶金现象。根据现场数据，计算了轧制过程奥氏体晶粒尺寸和再结晶分数的演变，预测了在不同工艺条件下连续冷却转变各相的体积分数和铁素体的晶粒尺寸等显微组织参数和相关的力学性能，预测结果和实测值吻合较好。     

高碳钢线材轧制组织和性能模型的应用

开发了用于模拟高碳钢高速线材生产过程中断面温度分布,奥氏体组织演变和产品性能的系统数学模型组。由实验确定的临界应变、奥氏体再结晶、斯太尔摩冷却线上奥氏体相变、组织和力学性能关系子模型耦合轧件温度场,构建了一个组织性能预报系统。该系统所计算出的轧制线上关键点钢材温度,奥氏体晶粒度和力学性能与实测值吻合较好。     

400 MPa级C-Mn钢控轧控冷生产过程组织-性能的预测

建立了C－Mn钢在控制轧制和控制冷却生产中微观组织演变和力学性能预测的物理冶金模型，模型包括加热、再结晶、相变和力学性能四部分，分别描述了带热轧及冷却过程中的物理冶金现象，根据现场数据，计算了轧制过程奥氏体晶粒尺寸和再结晶分数的演变，预测了在不同工艺条件下连续冷却转变各相的体积分数和铁素体的晶粒尺寸等显微组织参数和相关的力学性能，预测结果和实测值吻合较好。     

Comparison of Austenite Decomposition Models During Finite Element Simulation of Water Quenching and Air Cooling of AISI 4140 Steel

An indigenous, non-linear, and coupled finite element (FE) program has been developed to predict the temperature field and phase evolution during heat treatment of steels. The diffusional transformations during continuous cooling of steels were modeled using Johnson–Mehl–Avrami–Komogorov equation, and the non-diffusion transformation was modeled using Koistinen–Marburger equation. Cylindrical quench probes made of AISI 4140 steel of 20-mm diameter and 50-mm long were heated to 1123 K (850 °C), quenched in water, and cooled in air. The temperature history during continuous cooling was recorded at the selected interior locations of the quench probes. The probes were then sectioned at the mid plane and resultant microstructures were observed. The process of water quenching and air cooling of AISI 4140 steel probes was simulated with the heat flux boundary condition in the FE program. The heat flux for air cooling process was calculated through the inverse heat conduction method using the cooling curve measured during air cooling of a stainless steel 304L probe as an input. The heat flux for the water quenching process was calculated from a surface heat flux model proposed for quenching simulations. The isothermal transformation start and finish times of different phases were taken from the published TTT data and were also calculated using Kirkaldy model and Li model and used in the FE program. The simulated cooling curves and phases using the published TTT data had a good agreement with the experimentally measured values. The computation results revealed that the use of published TTT data was more reliable in predicting the phase transformation during heat treatment of low alloy steels than the use of the Kirkaldy or Li model.     

相变潜热对ф160mm GCr15轴承钢棒材控冷工艺的影响

利用MSC.Marc软件,对直径ф160mm GCr15轴承钢喷水冷却过程的温度场进行模拟分析。利用编写的ufilm和flux子程序,将相变潜热以内热源的方式添加到温度场。通过分析棒材在不同相变潜热取值下沿径向的温度变化情况,理论探讨了相变潜热对控冷工艺的影响。结果表明:相变潜热显著减缓了棒材的冷却速度,且越接近棒材芯部相变潜热引起的温升越大。考虑相变潜热时,原来的控冷方案不满足工艺要求。因此,在模拟研究控冷时,就本文理论探讨的GCr15轴承钢棒材的控冷工艺来看,相变潜热不应忽略。     

Modeling of γ→α Transformation Temperature Ar3 for High-Nb Pipeline Steel During Cooling Process

 According to the research on the deformation resistance and the ferrite transformation behavior of X80 pipeline steel by using Gleeble-3500 thermal simulator, a mathematical model of the α-phase start transformation temperature for high-Nb pipeline steel was established, based on the transformation kinetics and thermodynamics. The influence of deformation and cooling rate as well as Nb content on the α-phase starting temperature was thoroughly investigated. The results given by the model were in good agreement with the experimental results, which showed that the model could predict the α-phase starting temperature for high-Nb pipeline steel during cooling process.     

钢液凝固与冷却过程及固体钢加热过程钢中非金属夹杂物成分动力学转变的几个概念和特征曲线

利用钢中非金属夹杂物成分变化的集成模型,介绍了夹杂物成分随时间和冷却速率的变化,提出了夹杂物成分转变分数的概念,然后介绍了夹杂物成分转变的等温转变曲线（TTT）、连续冷却转变曲线（CCT）和等径转变曲线（TDT）的概念及应用.该集成模型考虑了钢液流动、传热、凝固和元素偏析,也考虑了钢与夹杂物反应的热力学和动力学.然后以管线钢、重轨钢和轴承钢为例,进一步分析讨论了钢液凝固与冷却过程中的冷却速率、固体钢加热过程中的加热温度和加热时间、钢成分以及夹杂物尺寸等参数对夹杂物成分转变的影响.这些概念和特征曲线能够直观展示在钢液凝固冷却过程及固体钢加热过程钢中非金属夹杂物的成分转变,将钢中夹杂物的控制方略从钢液拓展到固体钢中.     

B对X100/X120高强度管线钢连续冷却相变组织的影响

 利用热模拟技术（DIL805A热膨胀仪）和显微分析方法,对不同成分体系X100/X120高强度管线钢在连续冷却转变下的显微组织的变化规律进行了研究。研究结果表明,对于无B钢,随冷速增加,组织中依次出现多边形铁素体(PF)、粒状贝氏体(GB)、贝氏体铁素体(BF)和马氏体(M)。B元素的添加使得管线钢相变开始温度降低到500℃左右,抑制了多边形铁素体的形成,促进了贝氏体的形成。为了获得高级别管线钢X100的复相组织,无B钢的冷却速度应控制在20~30℃/s,而含B钢的冷速只需控制在5~15℃/s,简化了冷却工艺。     

Consideration of Phase Transformations in Numerical Simulation of Press Hardening

The importance of high‐strength steel concepts for car bodies has increased in the last years due to the need of reduction in weight and enhanced crash safety. It is possible to produce components with a much higher strength, e.g. a tensile strength of about R_m = 1500 MPa, compared to cold forming processes when using press hardening of boron alloyed heat‐treatable steels. Moreover, parts with complex shapes can be realized. Numerical simulation by means of Finite‐Element Method has become an indispensable tool for process design and construction. But for a more realistic prediction of the resulting component properties, for instance residual stresses and distortion, it is essential to consider the complex effects of phase transformation within the simulation. Because it is not a standard task currently, a material model was implemented in the commercial FE‐Code LS‐Dyna. The diffusion‐controlled phase transformation is modelled with Johnson‐Mehl‐Avrami equation for isothermal transformation. The formation of martensite is described by Koistinen‐Marburger equation for diffusionless transformation. The latent heat caused by austenite decomposition is also considered by implementation of a thermal model via a user subroutine. The needed isotherm time‐temperature‐transformation diagram is approximated by a diagram of related steel. These approaches are applied to a simple model process. In this process a round sheet metal is formed and subsequently quenched by cooled tools, therefore a thermal‐mechanical sequential coupled simulation of a model process is implemented. The transport from furnace to the press and the closing of the tools are simulated in order to get a realistic temperature distribution in the sheet metal at the beginning of the forming process. The tools are modelled as deformable bodies and heat‐transfer is taken into account. The simulation results show that nearly the whole austenite is transformed into martensite after the cooling phase.     

珠江钢厂CSP热连轧层流冷却热过程模拟研究

分析了带钢层流冷却的传热过程，将相变潜热引入到层流冷却热过程数学模型，用过程模拟的方法研究了珠江钢厂CSP热连轧层流冷却系统。讨论了喷水方式、喷嘴位置、板速和板厚对带钢温度场分布的影响。结果表明建立的模型对于珠钢CSP热连轧层流冷却系统有较好的适应性，能够对实际生产起到较好的指导性作用。     

Calculation of solidification-related thermophysical properties for steels

Special algorithms have been developed to calculate important solidification-related thermophysical properties: enthalpy and enthalpy-related data (i.e., specific and latent heat), density, and thermal conductivity for low-alloyed and stainless steels. The algorithms are heavily based on the use of earlier developed phase transformation models, an interdendritic solidification model (IDS), and an austenite decomposition model (ADC), which solve, as a function of temperature, the phase fractions and compositions needed in these calculations. As a result, the thermophysical properties can be calculated at any temperature, from 1600 °C to 25 °C, taking into account the discontinuities caused by special phase transformations (i.e., ferritic, austenitic and peritectic solidification, ferrite/austenite transformation, and austenite decomposition to various structures) influenced by the steel grade and the cooling conditions.     

Three-dimensional finite-element analysis of the quenching process of plain-carbon steel with phase transformation

In this study, three-dimensional finite-element (FE) analyses were carried out to predict the volume fractions of various phases generated during the quenching process of plain-carbon steel and the temperature history, considering the latent heat generated due to phase transformation. Diffusional phase transformation for a nonisothermal process was described by discretizing the cooling curve into various small isothermal steps and using a time-temperature-transformation (TTT) diagram for carbon steel. For this, Sheil’s additive rule was adopted to predict the incubation time which indicates the onset of phase nucleation, and, also, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was used to model the phase growth. For handling diffusionless transformation, Koistinen and Marburger’s equation was employed to model the austenite-martensite transformation during the rapid quenching process. Finally, temperature variations obtained from the FE simulation were compared to the experimental data available in the literature to validate the reliability of the numerical solution, and its application was made to simulate the three-dimensional forming process of a bevel gear and cam lobe.     

核岛用P280GH钢的冷却相变过程及数值模拟

 为了研究核岛用P280GH钢管热轧成形后的冷却过程组织演变,采用物理模拟方法建立了CCT和TTT相变动力学曲线。结果表明,低冷速会形成粗大铁素体和珠光体,增大冷速可细化低温相组织,当冷速超过10 ℃/s时即开始出现贝氏体组织。运用叠加原理,基于有限元法,建立了试验钢冷却过程数值模型,分析了[?]219.1 mm×18.26 mm规格P280GH钢管在空冷和水冷两种冷却过程沿壁厚方向温度场、组织演变规律。结果显示,空冷条件相变组织为均匀的珠光体、无贝氏体和残余奥氏体;水冷条件获得相变组织为马氏体组织,管内外表面体积分数相差3.6%,计算结果与实际热处理工况基本一致。研究结果可为热轧P280GH钢管生产的控冷工艺提供指导。