Ageing Susceptibility of Continuously Annealed Low-Carbon-Steel Strips

Abstract

The continuously annealed low-carbon-steel strips from industrial production showed an average aging index of about 30 N/mm². This increase in yield strength caused by the continuous-annealing process was strongly dependent on the soaking temperature and the soaking time. Whilst the optimization of the overaging parameters and the use of a higher annealing temperature would reduce the ageing susceptibility of low-carbon-steel strips, it was considered unlikely that its magnitude could be reduced to a comparable level to that of the batch-annealed one. Within the limit of low-carbon-strip specifications, there was very little effect of the C content on the ageing. The aging index of the temper-rolled materials decreased with the increase in the temper-rolling reductions, and a maximum increase in yield strength was achieved at a temper-rolling reduction of about 1%. In this work, the effect of C content, Al content, continuous-annealing cycles, and temper-rolling reduction on the ageing susceptibility of the continuously annealed low-carbon-steel strips was examined. SEM/EBSD technique was developed to characterize the temper-rolling strain bands and to assess the effect of temper-rolling reduction on the yield strength of the low-carbon-steel strips.