THIN COLD-ROLLED SHEET HAVING HIGH STRENGTH AND FORMABILITY AND METHOD FOR MANUFACTURING THE COLD-ROLLED SHEET

摘要

PURPOSE: An extremely thin cold-milled plate with high strength and moldability is provided to obtain predetermined strength and moldability without second rolling by promoting bainitic transformation at continuous annealing without increasing initial strength by using alloys like Mn, B, etc. CONSTITUTION: An extremely thin cold-milled plate with high strength and moldability comprises 0.15-0.25 weight% of carbon, 1.5-2.5 weight% of manganese, 0.1-1.0 weight% of silicon, 0.01-0.05 weight% of titanium, 5-30 ppm of boron, and residual Fe and unavoidable impurities. The structure of extremely thin cold-milled plate comprises 70-100 vol% of bainite and 0-30 vol% of ferrite. The thickness of cold rolled steel is 0.5 mm or less. The number of visible cracks are 2 per unit meter or less at r=0 L-bending test.