HOT ROLLED STEEL SHEET HAVING EXCELLENT CHEMICAL CONVERTIBILITY, AND ITS PRODUCTION METHOD

• Main Authors: HAYASHIDA TERUKI, OBARA MASAHIRO
• Format: Patent
• Language: English
• Published: 28.07.2005
• Edition: 7
• 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

PROBLEM TO BE SOLVED: To homogeneously form a chemical film on the whole face of a high strength hot rolled steel sheet comprising Si, Ti and Nb, to apply it to the conventional production line, and to facilitate operational control and quality control as well. SOLUTION: The hot rolled steel sheet has a composition comprising, by mass, 0.01 to 0.1% C, ≤1.5% Si, 0.5 to 3.0% Mn, ≤0.07% P, ≤0.01% S, 0.015 to 0.1% Al, 0.001 to 0.008% N and either or both of Ti and Nb by 0.02 to 0.4% in total, and satisfying C-(Ti/4)-(Nb/6)>0.002% and A.I. (Aging Index)≥1.5 MPa. In the hot rolling stage, after the completion of finish rolling, the steel sheet is cooled to a coiling temperature at the average cooling rate of ≥50°C/s, and is coiled in the temperature range of 400 to 600°C so as to control the A.I. to ≥1.5 MPa. COPYRIGHT: (C)2005,JPO&NCIPI