1990 Volume 76 Issue 9 Pages 1536-1543
Metallurgical factors realizing low temperature coiling of hot-rolled bands for producing deep-drawable continuous-annealed Al-killed sheet steels have been investigated in order to improve yield and productivity. The following proposal is given: the control of chemical composition such as i) C ≤0.02%, ii) Mn≤0.15%, and iii) Al ≥0.05%, and the choice of iv) low slab reheating temperature below 1150°C. The conditions i) and ii) contribute to the coarsening of cementite particles in hot-rolled bands and to the reduced amount of Mn-C complex during annealing, while the condition iii) contributes to the promotion of AIN precipitation in hot-rolled bands. These are considered to play a significant role in ameliorating r-value of the final products. Furthermore the condition iv) not only has an effect of improving formability, but also contributes to the prevention of hot-shortness caused by S. The effective mechanisms are discussed concerning the influence of C and Mn contents on the cementite coarsening in hot-rolled bands.
On the basis of the knowledge obtained by the laboratory investigation, a mill test was carried out and it was confirmed that the proposal ensures a high and uniform r-value through the whole length of a coil employing the low temperature coiling.
