PRODUCTION OF HIGH STRENGTH COLD ROLLED STEEL SHEET FOR AUTOMOBILE EXCELLENT IN FORMABILITY, HAVING BAKING HARDENABILITY IN COATING AND REDUCED VARIATION THEREOF IN WIDTH DIRECTION

• Main Authors: ASANO HIROHIDE, TEFUN MAKOTO, ITAMI ATSUSHI
• Format: Patent
• Language: English
• Published: 24.10.1995
• Edition: 6
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PURPOSE:To impart excellent formability, facial strain resistance, dent resis tance, baking performance for coating by passing the extra low carbon steel, which is added with a specified trace element and solid solution strengthening element, in the hot rolling through continuous annealing line having the specified condition. CONSTITUTION:The steel has a composition consisting of, by weight, 0.0010-0.0030% C, <=0.0030% N, <=0.5% Si, 0.3-1.5% Mn, 0.03-0.08% P, <=0.03% S, 0.005-0.7% acid soluble Al, <=0.03% Nb, Nb/C value in atomic weight 0.7-1.3, 24/14N(%)-72/14N Ti and the balance Fe. The steel is hot rolled at the finish temp. higher than Ar3 point, rapidly cooled within two sec and wound up at 650-770 deg.C. After it is cold rolled at 72-92% draft, subjected to annealing at 830-880 deg.C for >=20sec, cooled down to >670 deg.C at 3-15 deg.C/sec cooling rate and <=670 deg.C at 30 deg.C/sec cooling speed. Successively, it is subjected to a skin pass of 0.8-1.5% elongation rate. By this method, the steel sheet excellent in baking hardenability in coating is obtained.