【作者】 贾斌；

【导师】 彭艳；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2012， 博士

【摘要】 随着社会对钢铁质量要求的不断提高，用户对钢材强度、韧性、可焊性、耐磨性和热稳定性等各项性能都有了更高要求。铌与钒、钛的微合金化相比，铌是最有效的细化晶粒的微合金化元素，通过控制轧制可在相当低的成本下提高钢的强度又改善钢的韧性，达到良好的强度、韧性、成型性及焊接性相结合的综合使用性能，因而在全世界范围内得到了充分利用；广泛应用于轿车、桥梁、建筑、船舶、车辆、压力容器、采油平台、输油管道等各种工程结构。特别在低碳经济和绿色冶金发展前提下，控制轧制工艺消除了昂贵的热处理工序，提高了生产效率，并实现减碳节能的目标。铌微合金钢板带材产品性能是由轧制过程铌微合金钢组织形态决定的，而组织形态又是由合金成分和轧制工艺来决定的。轧件的金属变形、传热、位错密度演变和微观组织演变过程(包括基体微观组织演变和第二相析出)之间存在着复杂的交互作用，变形过程主要通过内热源改变轧件内的热量和应变状态，从而改变组织演变的条件，来影响传热过程和组织演变过程；传热过程主要通过本构关系影响流变应力和改变轧件内的温度分布，以影响变形过程和组织演变过程；组织演变过程则主要通过本构关系改变流变应力，以影响变形过程和传热过程。论文基于固体与分子经验电子理论(EET)建立了微合金钢三元合金系价电子结构模型，在Fe-C-M(Nb, V, Ti)合金系价电子结构计算结果的基础上，将EET与离散点阵平面/最近邻断键(DLP/NNBB)模型相结合建立微合金钢界面能的价电子结构理论计算模型，对析出第二相与铁基体界面能进行理论计算与分析。考虑微观组织演变、析出相和晶粒尺寸对位错密度演变的影响，将微观组织演变和介观尺度的位错密度相结合，建立了铌微合金钢热轧过程微观组织演变模型、位错密度演变模型、第二相析出模型和晶粒尺寸模型的耦合计算模型。为进一步建立基于微观组织演变的材料非线性本构模型奠定了基础，并为最终实现热轧过程多尺度耦合有限元数值模拟提供材料组织演变的计算模型。通过对铌微合金钢Q345B进行热压缩实验，获得了一系列的流变曲线。基于实验结果，充分考虑热加工工艺参数(应变速率和变形温度)和动态软化机制(动态回复和动态再结晶)对高温流变应力的影响，将产生加工硬化的硬化阶段与发生动态回复或动态再结晶的软化阶段的流变应力通过位错密度看成是应变、应变速率及温度的函数，通过弹塑性力学理论，将流变应力模型与原有材料硬化函数等效，引入硬化-软化函数，将动态软化机制与弹塑性力学理论实现了统一；并给出了硬化-软化函数求解的方法，确定了函数关系式中与工艺参数相关的主要参数的定量关系式。最后对硬化-软化函数关系式进行了有效性分析，验证了硬化-软化函数是有效可行的，能够较准确地描述材料在发生动态再结晶的软化过程和进入稳定流变时的应力－应变关系。最后推导了用于有限元分析的弹塑性矩阵，为进一步进行有限元模拟分析提供本构关系模型。最后，在建立的多尺度模型基础上，通过MARC提供的开放接口和相应子程序系统，寻求到一种多尺度耦合分析的实现方法，将多尺度的计算模块集成在MARC2010和FORTRON10.1平台并实现了对某钢厂中厚板热轧生产线多道次轧制过程的多尺度耦合有限元数值模拟计算。对模拟结果中各场变量(温度场、应力应变场、微观组织演变和轧制力)在不同轧制道次的变化规律，进行了详细分析；并对本文模型和其他模型的流变应力计算值与实验值，及相应轧制力计算值与现场实测值进行了对比分析，和其他模型相比，证明了本文模型更接近实测值。更多还原

【Abstract】 As industry develops so rapidly, the integrated service performance such as materialstrength, toughness, compactibility and weldability is eager to be called for. Nbmicroalloyed steel can obtain the performance, so we making use of it all over the world.In contrast to Ti, V, the grain refining effect of Nb is better. By control rolling Nbmicroalloyed steel can obtain the higher strength, toughness and the integrated serviceperformance at a low cost., so it can apply to different kinds of engineering structures suchas bridge, architecture, shipping, car, pressure reservoir, oil production platform, pipelineand so on. At the same time, control rolling technology can dispel the expensive heattreatment procedure, improve the production efficiency, reduce cost and achieve the targetfor energy saving.The product performance of Nb microalloyed steel is determined by themicrostructure morphology, alloying component and rolling process. The metaldeformation, heat transfer, dislocation density evolution and microstructure evolution(including matrix microstructure evolution and second-phase precipitates) of rolled piecehave a complex mutual effect. Deformation process can change the heat quantity by theinternal heat source in rolled piece and state of strain, then the condition of microstructureevolution is changed to effect the heat transfer and microstructure evolution. Heat transfercan change the flow stress and temperature distribution by the constitutive relationship asto effect deformation process and microstructure evolution. Microstructure evolution canchange the flow stress by the constitutive relationship as to effect deformation process andheat transfer. Because of all above, it is necessary to coupling calculate the metaldeformation, heat transfer, dislocation density evolution and microstructure evolution.The valence electron structures of crystal cells in Fe-M-C alloy system (M=Nb, Ti orV) were calculated using the Empirical Electron Theory in Solid and Molecules(EET).Based on the calculational results, the coherent interfacial energy between second phaseand iron matrix in Fe-M-C alloy system (M=Nb, Ti or V) was calculated by intergratingEET into discrete lattice plane, nearest neighbor broken bond(DLP/NNBB) methodthrough covalence bond energy. Considering the effect of microstructure evolution, second phase precipitates andgrain size on dislocation density evolution, the way to calculate the microstructureevolution, second phase precipitates and grain size is proposed during Nb microalloyedsteel hot rolling. The microstructure evolution are integrated with mesoscopic dislocationdensity evolution in order to establish the nonlinear constitutive model based on themicrostructure evolution next chapter and provide the microstructure evolution model formulti-scale finite element numerical simulation during hot rolling.The flow stress curves of Nb microalloyed steel Q345B during hot compressiondeformation were obtained on Gleeble-3500thermo-simulation machine. Based on theexperimental results, the constitutive model of Nb microalloyed steel during hightemperature deformation was established to describe the stress-strain relationship duringdynamic softening (dynamic recovery and dynamic recrystallization) and in the steadyflow state, in which the influences of the thermal deformation parameters (strain rate anddeformation temperature) and dynamic softening mechanism (dynamic recovery anddynamic recrystallization) on the flow stress were considered. Through elasto plasticitymechanics theory, the original work-hardening function is considered as flow stress curvesequivalently. The work-hardening and softening function is propounded. A method wasprovided to solve the work-hardening and softening function and establish the mathematicexpressions of the correlation coefficients. It is shown that the calculated results by themodel are in good agreement with the experimental results, and can represent accuratelythe flow stress during dynamic softening (dynamic recovery and dynamic recrystallization)and in the steady flow state. At last, the elastic-plastic matrix is derived as to calculate theconstitutive relationship during finite element numerical simulation during hot rollingnext.Finally, based on the multi-scale models established above, an approach to realize thecoupling analysis is found. The multi-scale computer modules are integrated on theplatform of MARC2010and FORTRON10.1. The case of Ansteel3450medium plateproduction line is analyzed on the platform. Based on the simulated results, thedistribution of the fields, such as the strain, the strain rate and temperature and the changesof austenite grain size and recrystallization volume fraction in muti-pass hot rolling process is precited and anlyzed. Finally, the calculated flow stress curves and rolling forceby paper’s model and others’ model are compared with the experimental flow stresscurves and rolling force. it is shown that the calculated results by the paper’s model are inbetter agreement with the experimental results than other’s model.更多还原