| 摘要 |
PURPOSE: A method is provided, which manufactures a steel product for line pipe having 50 Kgf/mm2 level of yield strength and superior hydrogen induced cracking resistance and sulfide stress corrosion cracking resistance by adding Ca during the vacuum degassing (RH) treatment not adding Cu and Ni during the steelmaking process, thereby composing the steel constituents in the appropriate range, and properly controlling conditions of hot rolling and cooling of the steel. CONSTITUTION: The method comprises the steps of preparing a composition comprising 0.05 to 0.12 wt.% of C, 0.5 wt.% or less of Si, 0.6 to 1.5 wt.% of Mn, 0.01 to 0.1 wt.% of Al, 0.005 to 0.03 wt.% of Ti, 0.01 to 0.05 wt.% of Nb, 0.01 to 0.1 wt.% of V, 0.002 wt.% or less of S, 0.02 wt.% or less of P, 10 to 100 ppm of N, 0.01 to 0.05 wt.% of O, 10 to 100 ppm of Ca and a balance of Fe and other inevitable impurities; hot rolling the heated steel slab in the recrystallization range after heating a steel slab having the above composition in the temperature range of 1050 to 1300 deg.C, wherein the hot rolling is performed to a reduction ratio ranging from 60 to 80% in a temperature ranging from non-recrystallization zone below the recrystallization temperature to Ar3±30 deg.C; and air cooling the water cooled steel plate to an ordinary temperature after water cooling the hot rolled plate to a temperature of 400 to 600 deg.C in a cooling rate of 10 to 20 deg.C/sec.
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