Setting an ultrafine grain at forged preforms by using cross wedge rolling

通过楔横轧生产的预锻件被锻造工业用于各种零件。它们的特点是剩余材料的数量很少。与ECAE相比，楔横轧已经在工业上得到了实现和建立。与粗晶材料相比，超细晶具有更高的屈服强度和缺口冲击强度等力学性能。因此，具有超细晶粒的零件可以制造得更轻，从而降低了材料的消耗。通过这种方式节省的材料降低了生产过程中和运动部件的能耗，例如内燃机在使用过程中。楔横轧与超细晶粒零件力学性能的改善相结合，可以大大提高工艺设计和材料效率。因此，本研究项目的目的是开发一种楔横轧工艺，可用于调整锻造预锻件的超细增益，并可在工业中实施。目标晶粒尺寸与仅在ECAE等研究项目中使用的工艺生产的晶粒尺寸相同。最后，晶粒的力学性能，如平均晶粒直径，应与楔横轧的几何形状和工艺参数相关联。三个子目标中的第一个目标是开发一种合适的楔横轧工艺，可以成功地形成圆柱形零件。这些工具应该能够系统地变化。在第二个子目标中，必须研究楔横轧过程与成形速度和坯料温度等工艺参数的关系。在第三个子目标中，应检查楔横轧后与冷却条件的关系。在楔横轧过程中，冷却条件决定了最终晶粒尺寸。因此，必须研究不同的冷却速度和流体。

Preforms produced by cross wedge rolling are used for a variety of parts by the forging industry. They are characterized by a low amount of surplus material. Compared with ECAE cross wedge rolling is implemented and established in industry. In comparison, an ultrafine grain has better mechanical properties as a higher yield strength and notch impact strength than materials with a coarse grain. Therefore parts with ultrafine grain can be constructed more light-weighted which lowers the material consumption. The material that is saved through this lowers the energy consumption during the production and regarding moving parts, e.g. in combustion engines while usage, too. With the combination of cross wedge rolling and the improved mechanical properties of parts with ultrafine grain the design of processes and material efficiency can be both improved dramatically. The aim of this research project therefore is to develop a cross wedge rolling process that can be used to adjust an ultrafine gain for forging preforms and can be implemented in industry. The target grain size is the same as those producible with processes that are used only in research projects like ECAE. In the end the mechanical properties of the grain like the average grain diameter should be associated with geometry and process parameters at cross wedge rolling. The first of three sub-aims is to develop a suitable cross wedge rolling process that can successfully form cylindrical parts. The tools should be able to be varied systematically. Within the second sub-aim a dependency of the cross wedge rolling process from process parameters like forming velocity and billet temperature has to be investigated. Within the third sub-aim a dependency from cooling conditions after the cross wedge rolling should be examined. The cooling conditions determine the final grain size based on the nuclei grown at cross wedge rolling. Therefore different cooling velocities and fluid have to be investigated.