| Summary: | 碩士 === 國立中興大學 === 機械工程學系 === 92 === This study is proposed to develop a multi-forging process, which can be served as an alternative thermomechanical process by accumulating strain to achieve the effect of grain refinement. In this study a medium carbon steel AISI-1045 is used as a sample material to demonstrate the potential of the multi-forging process, in which the medium steel is porcessed repeatedly by stacking, forging, cutting, and heat treating. A commercial finite element code DEFORM 2D is applied to simulate the grain refinement process of multi-forging in this study. The experiments performed in this study have verified the simulation results. A procedure is successfully established in this study to optimize the process parameters in order to achieve a uniform grain distribution and a minimum size in the multi-forged workpiece. For the first forging step, the material is heated in a environment of 1000℃ for 15 min of material. However, the grain growth in material is so severe at such high temperature, that the heating temperature and the heating time on the material for the subsequent forging step must be regulated. Therefore, the material must be heated in a 900℃ environment for 12 min before the second forging step, and in 850℃ for 15 min before the third forging step. As a result, after three forging steps under a constant forging rate 7.2 mm/min, an average grain size of 7.6 μm can be found uniformly distributed in the forged medium carbon steel, which has initially 24 mm in thickness and an average grain size of 100 μm. The results will be served as a reference to apply the multi-forging process for grain refinement.
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