| 摘要 |
PURPOSE: To manufacture hot rolled steel sheets for high strength line pipe having yield strength of 100ksi(API-x100), molybdenum and vanadium are added to steel. Also, direct quenching process and tempering process are adopted. CONSTITUTION: The hot rolled steel sheet is manufactured by heating a steel slab comprising C 0.05-0.07wt.%, Mn 1.8-2.0wt.%, Si 0.3wt.% or less, Cu 0.2-0.3wt.%, Ni 0.3-0.5wt.%, Mo 0.2-0.3wt.%, V 0.04-0.05wt.%, Ti 0.01-0.02wt.%, P 0.015wt.% or less, S 0.010wt.%, N 0.0050wt.% or less, a balance of Fe, and other inevitable impurities in the temperature range of 1150 to 1250deg.C; hot rolling the steel slab at 900deg.C; directly quenching it the hot rolled steel sheet to ambient temperature in a cooling rate of at least 20°C/sec; tempering it to 600-650deg.C.
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