Abstract: A continuous annealing line for annealing a cold-rolled strip of a ultra-low-carbon steel comprising a heating furnace for heating the strip which is fed continuously, with or without a soaking furnace following the heating furnace, a cooling furnace in which the heated steel strip is cooled, and a carburizing/nitriding furnace disposed between the heating furnace or the soaking furnace and the cooling furnace. The carburizing/nitriding furnace may be divided into a plurality of zones, each of which is provided with control means for controlling the carburizing/nitriding atmosphere and carburizing/nitriding temperature in the zone. The continuous annealing line may further comprise a plurality of carburizing/nitriding furnaces and have an arrangement for conducting a switching between a mode in which the carburizing/nitriding furnace is used for carburizing/nitriding the steel strip and a mode in which the carburizing/cooling furnace is used for cooling the steel strip.

Abstract: In a method of continuously annealing and pickling steel strips successively transferred through a continuous annealing apparatus including heating and cooling zones and a pickling apparatus, annealing the steel strips is effected in reducing atmosphere and thereafter pickling is effected at least by nitric acid electrolytic treatment. In an apparatus for continuously annealing and pickling steel strips, including a continuous annealing furnace and a pickling apparatus, the continuous annealing furnace consists of vertical furnaces capable of advancing a steel strip in a manner substantially repeating upward and downward movements alternately in substantially vertical directions and the pickling apparatus comprises at least a nitric acid electrolytic cell.