HIGH STRENGTH COLD ROLLED STEEL SHEET AND GALVANNEALED STEEL SHEET HAVING EXCELLENT BURRING PROPERTY, AND MANUFACTURING METHOD THEREFOR

• Main Authors: KWAK, Jai-Hyun, CHO, Hang-Sik
• Format: Patent
• Language: English; French; German
• Published: 27.10.2021
• 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

A high strength cold rolled steel sheet having excellent burring properties according to an aspect of the present invention comprises: by weight%, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon(Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al) + chrome (Cr) + molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01 % or less of nitrogen (N) , and the balance of Fe and inevitable impurities; and, by area fraction, 3-25% of ferrite, 20-40% of martensite, 5-20% of residual austenite, wherein the ferrite has an average grain size of 2µm or less at the reference point of 4/t (wherein t refers to a steel sheet thickness), with the average ratio between lengths in the thickness direction and in the rolling direction being 1.5 or less.