Characteristics of Austenite Grain Refinement by High-Speed Large-Reduction Forging —Production Technology for Fine Grained Steel by Large Deformation Forging III—

Abstract

To obtain fine and uniform microstructures, appropriate forging conditions were examined using high-speed large-reduction forging. Swing-type forging equipment was employed in hot-forging experiments using low-carbon steel (0.14%C–0.64%Mn). Also, a microstructure analytical system was developed by combining thermomechanical FE analysis with microstructural analysis to discuss the metallurgical phenomena occurring during forging. It was observed that coarse austenite grains can be refined to 20–30 µm uniformly using the proposed forging technology in the case of 59% reduction in thickness at 1273 K. In this case, dynamic recrystallization is a dominant factor for obtaining fine and uniform austenite grains. In the case of 43% reduction in thickness, the recrystallization is inhomogeneous, resulting in an inhomogeneous microstructure. Thus, about 60% reduction in thickness is necessary to obtain fine and uniform microstructures using the proposed technology when applied to the roughing of hot strip mills.