【作者】 王丽君；

【导师】 关小军；

【作者基本信息】 山东大学 ， 材料加工工程， 2011， 博士

【摘要】 随着控冷控轧技术与合金化的综合应用,性能更加优越的各种新型钢种不断得到开发和应用。其中,奥氏体区再结晶轧制发挥了重要作用。为了确定最佳的热轧工艺参数以实现合理的再结晶控轧,深入研究钢的热变形期间动态再结晶行为十分必要,特别是采用计算机模拟方法进行的动态再结晶研究更具有重要的理论和实际意义。由于形成机制复杂、影响因素众多、过程较快、组织变化模型难以构建等,桥梁钢动态再结晶模拟的研究相对较晚,且基于物理或实验模拟的有限元-宏观组织模拟与有限元—介观组织模拟相结合的双尺度动态再结晶模拟的相关研究更是鲜见。为此,本文以新型桥梁钢特别是HPS485wf钢为研究对象,在结合了热模拟实验、定量金相分析技术、有限元分析技术和动态再结晶组织模拟技术的基础上,以MARC软件作为数值模拟的支撑平台、基于唯象模型或MC模型所开发的应用程序作为动态再结晶组织模拟的工具,对该钢单道次热压缩变形过程中动态再结晶行为进行了物理模拟—有限元模拟—双尺度组织模拟(宏观与介观)的全面研究。首先,对HPS485wf和Q420qE两种典型的桥梁钢进行了系统的热模拟等温压缩实验,揭示了变形参数对它们的热变形力学行为和动态再结晶组织演变的影响规律及其形成机理,获得了发生动态再结晶的特征参数值,为后序的唯象模型和MC模型的建立、检验以及它们的宏观和介观组织模拟奠定了实验基础。其次,根据变形条件对形变和动态再结晶行为存在影响进行的热模拟实验研究,建立了能够描述HPS485wf钢流变行为的通用本构关系模型和简化本构关系模型。基于Najafizadeh和Jonas提出的简化0-σ模型以及Cingara和McQueen提出的流变应力模型,得到了该钢热压缩变形动态再结晶临界参数模型以及对应的动态再结晶唯象模型,使得后续有限元—动态再结晶唯象模型的宏观组织模拟得以进行。随后,采用热/力耦合刚塑性有限元—动态再结晶唯象模型,以通用的大型商业分析软件MSC. MARC与二次开发的子程序为软件支撑,成功模拟了HPS485wf(?)冈在不同热压缩变形条件下其内部的等效应变、动态再结晶状态的演化过程,验证了所建临界参数模型、动态再结晶唯象模型的合理性；研究了变形条件对其力学行为、组织演化及其动态再结晶行为的影响,全面揭示了该钢内部的宏观动态再结晶规律,为有限元—介观动态再结晶组织模拟的研究提供了对比素材。然后,基于MC法建立了包括能量模型、形核模型、实时转换模型等的介观动态再结晶模型,成功模拟了不同热压缩条件下HPS485wf(?)冈的微观组织、动态再结晶体积分数、平均晶粒尺寸演变的介观尺度特征,实现了多轮次动态再结晶共存现象的介观模拟,揭示了该钢内部介观组织动态再结晶规律,为有限元—介观动态再结晶组织模拟提供了有效模型。最后,采用热/力耦合有限元—动态再结晶MC模型,完成了选定变形条件下HPS485wf钢内部微区的动态再结晶行为的介观组织模拟,并与相应的热/力耦合有限元—动态再结晶唯象模型的宏观组织模拟进行了对比,证实了两种尺度模拟结果的相互关联,实现了该钢动态再结晶宏观—介观的双尺度模拟。综上所述,本文实现了热压缩变形的HPS485wf钢动态再结晶的双尺度模拟；创建了该钢的本构关系模型、临界参数模型、动态再结晶唯象模型、动态再结晶MC模型,开发了相关应用程序,成功地模拟了它的多轮次共存动态再结晶现象；完成了该钢热压缩变形的物理模拟—有限元数值模拟—动态再结晶组织模拟的系统研究,从宏观和介观层次上全面揭示了变形条件对其形变和动态再结晶行为的影响规律及其物理本质,实现了它的动态再结晶行为及其组织演变的全面仿真和预报。更多还原

【Abstract】 With the comprehensive application of controlled rolling and controlled cooling technology and alloying, various new steels with superior performance get to be developed and applied, in which controlled recrystallization rolling at the austenitic area plays an important role. In order to determine the optimum parameters to achieve reasonable controlled recrystallization rolling, it is necessary to intensively investigate the dynamic recrystallization (DRX) behavior during hot rolling, especially, the research on DRX by computer simulation methods is of theoretical and practical significance.Due to the complex deformation mechanism, a number of influence factors, fast deformation process and the difficulty of establishing microstructure models, the study on simulation of DRX for bridge steel started relatively late, and little attention has been paid on physical or experimental modelling based finite element method (FEM) microstructure simulation in macro scale, and FEM-mesoscopic microstructure modelling combined dual-scale simulation of DRX. Therefore, novel high performance bridge steels, especially advanced HPS485wf steel, were selected as object of this study. Combined with thermo-mechanical simulation experiment, quantitative metallographic analysis, FEM analysis technology, and DRX microstructure simulation technology, choosing MARC software as the FEM modelling support platform, and using the application programs based on phenomenological model or MC model as tools for simulation of DRX microstructure evolutions, physical-FEM modeling-dual scale (macro scale and meso scale) simulation of the DRX behavior during single pass hot compressive deformation for HPS485wf steel was carried out.To start with, systemic isothermal compressive tests of HPS485wf steel and Q420qE steel were conducted. The effects of deformation parameters on mechanical behavior of hot deformation and microstructure evolutions of DRX were investigated. The values of characteristic parameters of DRX were obtained, which could provide experimental foundation not only for establishment and verification of phenomenological model and MC model, but also for macroscopic and mesoscopic microstructure simulation.Secondly, according the true stress-true strain data collected from hot compressive tests, a general constitutive relationship model and a simplified one, which can describe the flow behavior of HPS485wf steel, were established. The critical parameters model of DRX for HPS485wf steel were obtained by using both simplifiedθ—σmodel proposed by Najafizadeh and Jonas and flow stress model proposed by Cingara and McQueen, respectively. These models made it possible to simulate microstructure evolutions by FEM-DRX phenomenological model in macro scale.Thirdly, based on the large commercial finite element software MSC.MARC, necessarily secondary development using the MARC platform, and the thermo-mechanical coupled rigid-plastic FEM-DRX phenomenological model, the evolutions of equivalent effective strain and state of DRX during hot compressive deformation in HPS485wf steel were successfully simulated, which verified the phenomenological model and the critical parameters model. The impacts of deformation conditions on mechanical behavior and microstructure evolutions were analyzed and the macroscopic law of DRX in the steel was totally revealed. These results provide raw data for FEM-mesoscopic microstructure simulation of DRX.In the next place, a mesoscopic DRX MC model, including energy model, nucleation model, R-grain growth model and real time model, was developed. The mesoscopic characteristics of evolutions of microstructure, volume fraction and mean grain size under different deformation conditions for HPS485wf steel were investigated. The phenomenon of coexistence of multi-circles DRX was successfully simulated. Thus, the mesoscopic law of DRX in the steel was displayed. Meanwhile, an effective mesoscopic model was prepared for FEM-mesoscopic simulation for DRX.Finally, mesoscopic DRX behavior of different deformation zones in HPS485wf steel at a certain deformation condition was studied by using the thermal-mechanical coupled FEM—DRX MC model, and the simulation results were compared with those obtained from thermal-mechanical coupled FEM-DRX phenomenological model. The macroscopic and mesoscopic simulation results were well interrelated, indicating the proposed model for macro-meso dual-scale simulation of DRX was reasonable.To conclude, in this study, dual scale simulation of DRX during hot compressive deformation for HPS485wf steel has been realized. The constitutive relationship model, the critical parameter model and the DRX phenomenological model for HPS485wf steel were established. The DRX MC model and corresponding application program was developed, which well simulated the phenomenon of coexistence of multi-circles DRX of this steel. Systemic studies on physical simulation-FEM modeling-mesoscopic DRX microstructure simulation of HPS485wf steel were carried out. The effects of deformation conditions on DRX behavior and involved physical essence were revealed in both macro and meso scale. As a result, it is achievable to simulate and predict DRX behavior and microstructure evolutions of HPS485wf steel.更多还原