An Innovative Experimental Thermomechanical Simulator of Ring-Rolling Process on Screw Press
摘要
IN718 nickel-based superalloy is widely used in the aeroturbine industry, because of well-balanced mechanical properties at high temperatures. The final microstructure of the parts, strongly influenced by the thermomechanical path applied during forging, mainly governs the mechanical properties such as tensile, creep, and fatigue properties. Understanding the relation between this forging route and the resulting microstructure is challenging, particularly for the ring rolling, which is an industrial incremental forming process with alternating direction of the forming direction. Grain coarsening can occur during the heating or solution treatment following ring rolling. Establishing how the process parameters contribute to this grain coarsening is therefore essential for controlling the final microstructure. The thermomechanical path experienced by the part is difficult to reproduce with conventional laboratory tests (like compression or torsion tests). In the present work, an innovative experimental forging test was developed to reproduce the key features of this thermomechanical loading. This test involves incremental deformations at high strain rate (> 1 s−1), alternating forming direction, and short dwell times (< 5 seconds) between two successive strokes. The metallurgical characterization focuses primarily on the grain size distribution of both the as-forged structure and the material after the subsequent solution heat treatment. The results show an increase of the minimum cumulative strain and a broadening of the cumulative strain range leading to the formation of large grains after the heat treatment, this being probably due to the recovery during the dwell time between two successive paths.