オーバル孔型とスクエア孔型を用いた多方向大ひずみ圧延によって生成する微細粒組織と力学的性質の関係

Abstract

Multidirectional warm caliber rolling process using oval grooves and square grooves was developed. Microstructure and mechanical properties obtained by this process in a low carbon steel were investigated. Ultrafine grains with high angle grain boundaries were generated in the center region in a material by just 2-pass oval-square caliber rolling. The region having ultrafine ferrite grains expanded along with rolling and almost all of region was occupied with ultrafine ferrite grains with high angle grain boundaries by 6-pass oval-square caliber rolling. Although apparent rolling reduction in this 6-pass oval-square process is 71%, large plastic strain larger than 3 can be introduced into materials due to the effect of multidirectional deformation. Comparing with square-square caliber rolling in which 21-pass is required to obtain fully ultrafine grained structure, oval-square caliber rolling is very efficient process to create ultrafine microstructure.