Hot Deformation and Recrystallization of 3 % Silicon Steel: Part 3: Effect of Hot Deformation Variables on Static Recrystallization

Abstract

The static recrystallization kinetics and the recrystallized grain size of 3 % Si steel after hot rolling at temperatures of 900 to 1 100°C to equivalent strains of 0.25 to 1.24 applied in a single pass or by two pass rolling have been investigated. When the annealing temperature was changed for a constant rolling temperature, an apparent activation energy of 230 kJ/mol, and a small increase in recrystallized grain size with increase in annealing temperature were found. Rolling at different temperatures had a surprisingly small effect. The growth rate of recrystallizing regions showed a rapid decrease with annealing time, being inversely proportional to time initially, but decreasing more rapidly at longer times. For conditions leading to long recrstallization times, growth rate fell to zero, resulting in plateaux in fraction recrystallized. Increase in equivalent strain accelerated recrystallization, but the effect after two pass rolling is complicated by a change in rolling direction between the passes. The majority of results can be interpreted by a simple model based on site saturated nucleation and negligible coarsening of recrystallized grains, but smaller strains in single pass rolling, or in the second pass of two pass rolling give large discrepancies with the model.

Hot Deformation and Recrystallization of 3% Silicon: Steel Part 2: Effect of Microstructural Variables on Static Recrystallization

“…Rolling temperatures quoted are slab centre temperatures at entry to the first pass. As discussed elsewhere, 9) there was no detectable recrystallization in the coarse grained materials rolled by a single pass of 30 % reduction on annealing for at least an order of magnitude longer time that the 15 s interpass time, even at 1 100°C. For the smallest grain sizes, recrystallization may have started in the interpass time.…”

“…This is also true for a strain of 0.25 (when P gb ϭ0), as observed experimentally, whereas after higher strains, (when P gb is real) the lines fall below the power law at long times, again as indicated by the experimental results for G. This predicted fall in net driving pressure to zero is consistent with the observation of plateaux in the recrystallization curves for some experimental conditions. This is discussed in detail elsewhere, 9) but the effects of initial grain size, Fig. 9, and the presence of austenite particles during rolling, Fig.…”

Hot Deformation and Recrystallization of 3% Silicon Steel: Part 4: Effect of Recovery and Partial Recrystallization between Passes on Subsequent Recrystallization Behaviour

“…As noted previously when discussing the effect of strain on recrystallization kinetics, 3) rolling to the same equivalent strain in two passes leads to significant retardation of recrystallization compared with rolling in a single pass. This is illustrated in Fig.…”

“…3. It is also possible, from the measured kinetics after single pass rolling 3) that the large retardation in Fig. 3, particularly for the centre of the slab where the temperature remains higher, had a contribution from the onset of interpass recrystallization, even though no grains of type 2, Fig.…”

“…In recently published papers [1][2][3] on the effects of grain size and austenite content, and on the effects of the rolling variables of strain, strain rate and temperature on the static recrystallization behaviour of 3 % Si steel, it was noted that, when high strains were given by two pass rolling, recrystallization after the second pass was retarded compared with rolling to the same total reduction in a single pass, even when there was no static recrystallization between the passes in the two pass rolling. The role of static recovery between two passes on the recrystallization behaviour after the second pass has received surprisingly little systematic study, and the results of the few studies are somewhat conflicting.…”