PRODUCTION OF COLD ROLLED STEEL SHEET HAVING EXCELLENT CORROSION RESISTANCE AND CHEMICAL CONVERSION TREATABILITY

摘要

PURPOSE:To produce a cold-rolled steel sheet having excellent phosphate treatability and corrosion resistance after painting with less stages in a continuous annealing stage for the cold rolled steel sheet by introducing directly the steel sheet after an aging treatment into a surface conditioning device without subjecting the same to a pickling treatment. CONSTITUTION:The cold-rolled steel sheet S which is annealed by being passed through the inside of a continuous annealing furnace consisting of a heating furnace 5 and a holding furnace 6 of aging treatment furnace 8 and is then introduced directly into a cathodic electrolysis treatment vessel 93 of the surface conditioning device 9 without being subjected to pickling and subsequent rinsing treatment so that Ni is slightly deposited thereon at 1-50mg/m<2> by the cathodic electrolysis treatment of the transition metal such as Ni except Fe. Such steel sheet is thoroughly rinsed in a rinsing tank 94 and is then temper-rolled. The cold-rolled steel sheet having the excellent chemical conversion film formability by phosphate and the corrosion resistance after painting is thus obtd. with a stage simpler than heretofore.