On the Two-Stage Annealing of Aluminium-Killed Steel Sheet

Abstract

Recrystallizaticn textures of Al-killed steel sheets cold-rolled to 60, 70 and 80% reductions in thickness and finally heat-treated by various combinations of 1st-stage and 2nd-stage annealings were examined by X-ray diffraction method and optical microscopy.
The time of the 1st-stage annealing was kept to 40 min, and the pole densities of (222), (110) and (200) parallel to the sheet plane after the 2nd-stage annealing were measured as functions of the 1 st-stage annealing temperature. The maximum densities of (222) after the 2nd-stage annealing.at 650°C for 1 hr could be obtained in the 70% rolled sheet by the 1 st-stage annealing at about 480°C and 575°C. These two maxima were termed as 1st-peak and 2nd-peak respectively. The 1st-peak temperature (480°C) was independent on the cold-rolling reduction in the range between 60 and 80%, but shifted to a higher temperature when a higher 2nd-stage annealing temperature was adopted.
The maximum elongation ratio of the recrystallized grains after final annealing could be related to the maximum density of (222), whereas the maximum size of the recrystallized grains was found to correspond to the minimum in the (222) pole density.
These results were discussed by relating the recrystallization process with the process of clustering of Al and N which inhibits the nucleation of recrystallized grains with some ranges of orientation.