Recrystallization Behavior of IF Steel Sheets Immediately after Hot-rolling in Ferrite Region

摘要

It is known that high r-value hot-rolled steel sheets can be produced by hot rolling in the ferrite region with lubrication, whereas dynamic recovery easily occurs during ferritic rolling, in which texture formation is quite different from that in cold rolling, when the quantity of recovery increases. In this study, one pass hot rolling in the ferrite region was conducted at higher temperatures, using various rolling temperatures and rolling reductions, with two types of ULC steels, 0.016% Nb and 0.023% Ti, and their recrystallization behaviors immediately after hot rolling were investigated. The Ti-bearing steel easily recrystallized; recrystallization occurred even at 1 323 K with a low rolling reduction of 30%. The γ-fiber strength reached its maximum at around 50% rolling reduction at 1 273 K with the Nb-bearing steel and 1 323 K with the Ti-bearing steel. On the other hand, in high temperature rolling of the Ti-bearing steel, the γ-fiber did not develop, independent of rolling reduction. These changes corresponded to the recrystallized fraction, in that the strength of the γ-fiber decreased when recrystallization occurred immediately after rolling. The deformation microstructures were different in each grain and even in each part of the same grain. New recrystallized-like grains were produced in the domain where distortions were particularly concentrated. Recrystallization seemed to be the result of various mechanisms, as some recrystallized grains were formed by a bulging mechanism, whilst others were surrounded by high angle grain boundaries.