Influence of Hot Deformation Conditions on the Annealing Behaviour of Cold Rolled Ultra Low Carbon Steel

抄録

An ultra low carbon (ULC) steel has been deformed in plane strain compression (PSC) using a Gleeble 3500 thermal and mechanical simulator followed by cold rolling and annealing (CRA). Multiple-pass deformation was used to simulate conditions encountered during hot rolling and to study the effect of finish deformation temperature (FDT) on microstructural development during CRA. It was found that a range of ferrite microstructures were produced when FDT decreased from 920 to 600°C, a temperature range which encompasses both austenite (γ) and ferrite (α) deformation. For FDT>870°C, fine equiaxed ferrite was produced, whereas FDT 850°C produced a coarse-grained microstructure. As FDT was decreased below 850°C, as-deformed ferrite remained with a decreasing propensity for the formation of statically recrystallized grains. At higher FDT, the γ-to-α transformation produced a hot-band texture consisting mainly of {001}<110>, and at FDT below the critical transformation temperature the typical body centred cubic rolling texture also developed. Sections of the as-hot-deformed samples were cold rolled to 80% reduction and annealed at 650°C. It was found that the hot deformation microstructure has a strong influence both on the kinetics of recrystallization and texture development during CRA. In particular, a warm-deformed ferrite microstructure (lower FDT) recrystallized most rapidly to produce a strong <111>//ND recrystallization texture (γ-fibre), whereas an initial coarse-grained ferrite microstructure recrystallized most sluggishly to produce a strong {001}<110> texture. The implications of these results in the production of formable sheet steels is outlined.