EFFECT OF STRAIN-INDUCED BY HEARTH ROLLS AND TENSION ON DUCTILITY OF STRIP PROCESSED ON CONTINUOUS ANNEALING AND PROCESSING LINE

Unlike the steel strip annealed in the laboratory, the strip processed on continuous annealing and processing line (C.A.P.L.) contains consi derable dislocation. Such dislocation, or plastic strain, is considere d to deteriorate the ductility of continuously annealed material. Sinc e the strip near the soaking furnace is softened, the effect oi strip tension is considerably large. Therefore, assuming that C.A.P.L. also functions as a tension leveler, the relationship is obtained between t he amount oi plastic strain, which is imparted to the strip, and the s trip tension with respect to roll diameters. As a result, the strip is stretched each time it passes between rolls. The experiment shows tha t the amount of strain imparted to the strip is proportional to the de gree oi deterioration in the total elongation. In order to improve the mechanical properties oi continuously annealed material, it is effect ive to reduce strip tension and increase roll diameters, In particular , if the strip tension: sigma(t) is maintained below the certain value obtainable by the next equation, sigma(t) less than or equal to D sig ma(e)(2)/2hE, where D: roll diameter, sigma(e): yield stress, h: thick ness of strip and E: modulus of elasticity, there exists a condition w hich practically enables no-strain annealing where strain does not acc umulate even when the strip passes between rolls.