Abstract
A caliber-rolling process with new type groove characterized by multidirectional deformation was proposed to fabricate ultrafine-grained (UFG) steel bars efficiently. To impose a large strain into center of cross-section, the groove configuration of foval (flat-like-oval) type was designed. Three-dimensional finite element simulation (FE simulation) was utilized for this purpose, and the caliber-rolling process of square/foval pass was investigated from the viewpoints of a large strain accumulation and cross-sectional shape variation in a bar. The UFG steel bars were fabricated by using the commercial caliber-rolling with the grooves designed from FE simulation. The cross-sectional shape predicted from FE simulation was in excellent agreement with the shape of the rolled bars. The strain imposed in the rolled bars has a distribution with maximum at the center. The giant strain of 5.2 is accumulative in center regardless of reduction in area of 79%. The good correlation between the strain imposed and the hardness of the rolled bars was confirmed.
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