Modeling bainitic transformations during press hardening

模拟热压硬化过程中的贝氏体转变

• 批准号: 257471754
• 负责人: Dr.-Ing. Martin Hunkel
• 金额: --
• 依托单位: Institut für Metallformung
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/257471754?language=en
• 关键词: Modeling; bainitic; transformations; during; press

Press hardening is an important processing technology for the production of safety relevant components for automotive applications. The parts are hot formed in the austenitic state in a tool with defined tool temperature below 550 °C and afterwards quenched under load inside this tool. This technology allows forming of complex shaped parts made of ultrahigh strength steels. Depending on quenching conditions martensitic or bainitic microstructures form, with a strong coupling between mechanical load, internal stresses, chemical composition and phase transformation kinetics. In this project, we focus on the austenite-to-bainite transformation during a partial or bainitic press hardening process, using tools of about 400 to 500 °C. Due to processing conditions, the bainite forms from a pre-strained austenite under high stresses. In this scale-bridging project we aim for a fundamental understanding of the underlying bainitic transformations in a bottom-up approach. We start from the theoretical description of bainitic platelets and sheaves on the smallest scales using phase field methods. The outcome from these phase front growth predictions is connected to an intermediate modeling step on the mesoscale level, which pursues the prediction of transformation kinetics and material properties in representative volume elements, involving plastic deformations. Phase fractions are predicted using coarser grained phase field models combined with a crystal plasticity approach. Handshaking with macroscopic descriptions based on a mean field concept combined with kinetic models allow for a theory-guided prediction of transformation kinetics and the mechanical behavior under the influence of mechanical load. Here, finite element based models allow to predict the mechanical behavior of entire work pieces during processing. The trilogy of thermo-chemo-mechanically coupled modeling levels is compared to experimental investigations of bainite formation during press hardening. Advanced electron microscopy using EBSD+EDX, HR-EPMA and TEM are applied within this project for quantitative microstructure kinetics evaluation. This allows to directly validate the simulation predictions on different scales and allows for improvements of the theoretical descriptions, as well as to link experimental setups and conditions to the multi-scale modeling approach. The main goal of the project is to develop a bottom-up understanding of bainitic transformations in particular under the influence of applied stresses, and to set the path for a theory-guided improvement of processing steps during advanced press hardening of high strength steel sheet components. A focus will be on the role of alloying elements (C, Si, Cr), the influence of plastic effects on interface kinetics and precipitation, and the link to thermodynamically consistent models.

压制硬化是生产汽车应用安全相关部件的重要加工技术。零件在奥氏体状态下在工具中热成型，工具温度低于550 °C，然后在该工具内的负载下淬火。该技术允许形成由高强度钢制成的复杂形状的部件。取决于淬火条件，马氏体或贝氏体显微组织形成，机械载荷、内应力、化学成分和相变动力学之间存在强耦合。在这个项目中，我们专注于在部分或贝氏体压制硬化过程中，使用约400至500 °C的工具进行贝氏体到贝氏体的转变。由于加工条件，贝氏体在高应力下由预应变奥氏体形成。在这个规模桥接项目中，我们的目标是从根本上了解贝氏体转变的自下而上的方法。我们从理论描述贝氏体片层和层的最小尺度上使用相场方法。从这些相前沿增长预测的结果连接到中间建模步骤的中尺度水平，追求的转化动力学和材料性能的预测，在代表性的体积元素，涉及塑性变形。相分数预测使用粗粒相场模型结合晶体塑性方法。基于平均场概念与动力学模型相结合的宏观描述的握手允许在理论指导下预测转变动力学和机械负载影响下的机械行为。在这里，基于有限元的模型允许预测整个工件在加工过程中的机械行为。热-化学-机械耦合建模水平的三部曲相比，在压制硬化过程中贝氏体形成的实验研究。先进的电子显微镜，EBSD+EDX，HR-EPMA和TEM应用于本项目的定量微观结构动力学评价。这允许直接验证不同尺度上的模拟预测，并允许改进理论描述，以及将实验设置和条件与多尺度建模方法联系起来。该项目的主要目标是开发一个自下而上的贝氏体转变的理解，特别是在施加的应力的影响下，并设置路径的理论指导的工艺步骤的改进，在先进的压力淬火高强度钢板部件。一个重点将是合金元素（C，Si，Cr）的作用，界面动力学和沉淀的塑性效应的影响，并链接到物理一致的模型。