Large deformation for a common C-Mn steel at the temperatures around Ar₃ results in an ultrafine-grained ferrite structure. This is due to dynamic transformation and recrystallization of ferrite during deformation. To apply the new finding to an actual plant rolling, multi-pass deformations which substitute for a single pass heavy deformation have been studied.
It was realized that when the interpass time during successive deformations is shorter than 2s, the effect of accumulative strain can make ferrite grains fine.
A trial of strip rolling in plant provided a mean ferrite grain size of ASTM No. 13.5.