| 摘要 |
<p>A high carbon steel sheet having excellent impact toughness is provided to perform remelting of cementite completely even in a short quenching heat treatment process, and a manufacturing method of the high carbon steel sheet is provided. A manufacturing method of a high carbon steel sheet having improved impact toughness comprises the steps of: manufacturing a steel slab comprising, by weight percent, 0.2 to 0.5% of C, 0.1 to 1.2% of Mn, 0.4% or less of Si, 0.5% or less of Cr,0.01 to 0.1% of Al, 0.012% or less of S, 0.5x48/14x[N] to 0.03% of Ti, 0.0005 to 0.0080% of B, and 0.006% of N with the balance of Fe and other inevitable impurities, or manufacturing a steel slab comprising, by weight percent, 0.2 to 0.5% of C, 0.1 to 1.2% of Mn, 0.4% or less of Si, 0.5% or less of Cr,0.01 to 0.1% of Al, 0.012% or less of S, less than 0.5x48/14x[N]% of Ti, 0.0005 to 0.0080% of B, and 0.006% of N, a condition of B(at.%)/N(at.%)>1 being satisfied, with the balance of Fe and other inevitable impurities; reheating the steel slab, and hot rolling the steel slab at a finishing temperature of at least an Ar3 transformation temperature to manufacture a hot rolled steel sheet; cooling the hot rolled steel sheet in a cooling rate range of 20 to 100 deg.C/sec; and coiling the cooled hot rolled steel sheet in a temperature range of Ma to 530 deg.C to manufacture a hot rolled coil, wherein the manufacturing method further comprises performing a reheat treatment process of a steel sheet having a principal phase of bainite with an average carbide size of not more than 1 mum at 900 deg.C for 10 seconds to 30 minutes, the bainite containing 5% or less of a fraction of saltpeter ferrite in which carbides are not present and 5% or less of a fraction of pearlite with a lamellar carbide structure.</p> |
