1994 年 34 巻 1 号 p. 108-114
The effect of adding Nb on the Lankford value (r-value) and of the continuous annealing conditions on hardness has been investigated for extra-low-carbon steel sheet used as tin mill black plate (TMBP).
When hot rolling was finished in the ferrite region, adding a small amount of Nb markedly improved both the average r-value and its planar anisotropy. The reason for this improvement is considered to be that, by finishing hot rolling in the ferrite region, a texture like that from cold rolling appeared in the hot band when Nb had been added. By using such hot bands, the cold-rolled texture was more strongly developed in as-cold-rolled steel sheet than was the case when using steel without added Nb. This stronger cold-rolled texture created a strong {554}<225> orientation after continuous annealing and improved the r-value.
The hardness of TMBP is influenced by whether complete recrystallization is achieved or not, the degree of recrystallization depending on the heating rate, annealing temperature and soaking time during the continuous annealing process. However, by soaking for about 10 sec, the effect of heating rate become small. After complete recrystallization, the effect of cooling rate and the other annealing conditions on the hardness is very small. The insensitivity of this steel toward the annealing conditions is favorable for increasing the speed and efficiency of the continuous annealing process.
