Abstract
A novel straining process characterized by multidirectional deformation was proposed to fabricate large scale, ultrafine-grained (UFG) steel for a thick plate. To impose a large strain into the whole area of material, free forging technology was applied. The principles of grain refinement in basic experiments using small-scale samples were directly applied to test production of large-scale samples. Three-dimensional finite element simulation (FE simulation) was utilized in developing the new process from the viewpoints of the prediction of press load, microstructure, and plate shape. The proposed UFG process was tried using a practical manufacturing press having maximum press load of 3500 ton. The microstructure and hardness of the plate were made as predicted. As a result, it is possible to fabricate UFG steel plates with 25 mm or more thickness by free forging at warm working temperatures.
