Production of areas with reduced strength in press-hardened components by means of a tempering station

转移项目应在单个成型步骤之前或之间采用局部温度控制的方法，以在实际应用中使用压制硬化为例，具体设定所需的微观结构。应通过与项目合作伙伴大众汽车公司合作，采用两相喷雾冷却工艺技术，在基于局部适应微观结构的压制硬化部件中获得定制的材料性能B。局部强度降低区域的冲压硬化部件显示出更高的连接性能并便于修剪。在拟议的转移项目中，微观结构调整应通过在实际压制硬化过程之前对局部部件区域进行有针对性的预冷却来进行。必须开发合适的热控制单元，以通过两相喷射和部件区域的同时温度控制来设计这样的预冷却，部件区域不应冷却并且必须保持在高于Ac3的温度。为此目的，应应用正在进行的前期项目（“开发适合曲轴的微观结构锻造技术”）的数值模拟模型和经验。在预冷却区域中，首先应调节贝氏体或珠光体转变范围内的温度，以在随后的压制硬化工具中的均匀冷却期间实现贝氏体显微组织转变。从高于Ac3的温度水平淬火的区域由于在压制硬化工具中的冷却而经历马氏体转变。该工艺的优点是不需要局部回火的压制硬化工具，并且可以在热冲压期间使用短的保持时间。最后，应验证回火站是否实际上可用于通过局部冷却同时保持板的局部结晶化状态来局部形成不同的微观结构。在汉诺威莱布尼茨大学，回火站和热冲压的设计在成型技术和机械研究所进行，预冷装置的开发和微观结构表征在材料科学研究所进行。

The transfer project shall adapt the methodology of a local temperature control of austenitized materials before or in between individual forming steps for the specific setting of a desired microstructure in a practical application using the example of press hardening. Tailored material properties shall b obtained in the press-hardened components based on locally adapted microstructures by employing the technology of a two-phase spray cooling process in collaboration with the project partner, Volkswagen AG. Press-hardened components that feature regions with locally reduced strength show increased joining properties and facilitate trimming. In the proposed transfer project, the microstructural adjustment shall take place through a targeted pre-cooling on localized component areas before the actual press hardening process. A suitable heat control unit must be developed to design such a pre-cooling by means of two-phase spray and simultaneous temperature control of component regions, which should not cool down and must be kept at a temperature above Ac3. For this purpose, numerical simulation models and experiences from the ongoing precedigng project ("Development of a microstructural suited forging technology for crank shafts") shall be applied. In the pre-cooled areas at first a temperature in the range of bainite or pearlite transformation should be adjusted to achieve a bainitic microstructural transformation during the subsequent and uniform cooling in the press-hardening tool. Areas quenched from a temperature level above Ac3 undergo a martensitic transformation due to cooling in the press-hardening tool. The advantage of this procedure is that no locally tempered press-hardening tools are required and short holding times during hot stamping can be used. Ultimately, it should be verified whether the tempering station is practically useful for the local formation of different microstructures by means of local cooling and maintaining the local austenitized state of the sheets at the same time. At Leibniz Universität Hannover, the design of the tempering station and the hot stamping is carried out at the Institute of Forming Technology and Machines, and the development of the pre-cooling device and the microstructure characterization is carried out at the Institut für Werkstoffkunde (Materials Science).