Toshiki Hiruta

Effect of Accumulative Bending Conditions on Grain Refinement on Hot-rolled Sheet

As a technology to manufacture fine-grained steel, accumulative bending process after hot rolling was proposed, and multi-bending equipment of laboratory scale were established. The effects of accumulative bending on microstructure and ferrite grain size by changing the thermo-mechanical conditions were investigated. As the results, a microstructure with the grain size of 2.2 μm was obtained at specimen surface by accumulative bending after hot rolling in the optimized thermal condition. By the results of FE analysis, it was cleared that equivalent strain was accumulated on not only surface but also center of thickness.

Experimental Analysis of Thickness Reduction Limits in Ultra Thin Stainless Steel Foil Rolling

In rolling of ultra thin stainless steel foil, there are two rolling limits. One is owing to elastic deformation of work rolls, and the other is owing to edge crack of rolled foil. In this paper, fundamental investigation was conducted about the basic characteristic of the rolling limits of ultra thin stainless steel foil. The influence of several rolling conditions on minimum thickness and behavior of edge crack were investigated experimentally. This paper provides new formula to predict the minimum thickness in ultra thin foil rolling. The relation between the edge crack depth and the rolling conditions is also discussed. The edge crack expands with rolling passes. However, the degree of the edge crack at same foil thickness shows different behavior depending on rolling conditions. The depth of edge crack rolled by small diameter work rolls is shallower than that of same thickness foil rolled by large diameter work rolls. Moreover, when Youngs modulus of work rolls is high, it turns out that the edge crack is small. Based on detailed observation of the foil edge phenomenon, good correlation between edge crack depth and foil thickness at extreme edge portion is found. From those experimental results, it is suggested that the rolling conditions advantageous to control edge drop are effective to suppress edge crack expansion.