CHROMIUM-MOLYBDENUM STEEL PLATE HAVING EXCELLENT CREEP STRENGTH AND METHOD FOR MANUFACTURING SAME
Provided are a chromium-molybdenum steel plate having excellent creep strength and a method for manufacturing same. The chromium-molybdenum steel plate of the present invention comprises, by weight %, 0.11-0.15% of C, 0.10% or less of Si (exclusive of 0%), 0.3-0.6% of Mn, 0.010% or less of S (exclusive of 0%), 0.015% or less of P (exclusive of 0%), 2.0-2.5% of Cr, 0.9-1.1% of Mo, 0.65-1.0% of V, 0.25% or less of Ni (exclusive of 0%), 0.20% or less of Cu (exclusive of 0%), 0.07% or less of Nb (exclusive of 0%), 0.03% or less of Ti (exclusive of 0%), 0.015% or less of N (exclusive of 0%), 0.025% or less of Al (exclusive of 0%), 0.002% or less of B (exclusive of 0%), and the remainder of Fe and unavoidable impurities.
1 . A chromium-molybdenum steel plate having excellent creep strength comprising, by weight: 0.11 to 0.15% of C, 0.10% or less (exclusive of 0%) of Si, 0.3 to 0.6% of Mn, 0.010% or less (exclusive of 0%) of S, 0.015% or less (exclusive of 0%) of P, 2.0 to 2.5% of Cr, 0.9 to 1.1% of Mo, 0.65 to 1.0% of V, 0.25% or less (exclusive of 0%) of Ni, 0.20% or less (exclusive of 0%) of Cu, 0.07% or less (exclusive of 0%) of Nb, 0.03% or less (exclusive of 0%) of Ti, 0.015% or less (exclusive of 0%) of N, 0.025% or less (exclusive of 0%) of Al, and 0.002% or less (exclusive of 0%) of B, with a balance of Fe and unavoidable impurities.
2 . The chromium-molybdenum steel plate having excellent creep strength of claim 1 , wherein the steel plate has a microstructure including tempered martensite.
3 . The chromium-molybdenum steel plate having excellent creep strength of claim 2 , wherein the number of precipitates having a diameter of 200 nm or more including (Fe,Cr) 23 C 6 is in a range of one/μm 2 or less in the microstructure of the steel plate.
4 . The chromium-molybdenum steel plate having excellent creep strength of claim 2 , wherein the number of precipitates having a diameter of 20 nm or less is in a range of 20/μm 2 or more in the microstructure of the steel plate.
5 . The chromium-molybdenum steel plate having excellent creep strength of claim 4 , wherein the precipitates having a diameter of 20 nm or less are (V,Mo,Nb,Ti) (C,N).
6 . A method for manufacturing a chromium-molybdenum steel plate having excellent creep strength, the method comprising:
hot-rolling a steel slab including, by weight: 0.11 to 0.15% of C, 0.10% or less (exclusive of 0%) of Si, 0.3 to 0.6% of Mn, 0.010% or less (exclusive of 0%) of S, 0.015% or less (exclusive of 0%) of P, 2.0 to 2.5% of Cr, 0.9 to 1.1% of Mo, 0.65 to 1.0% of V, 0.25% or less (exclusive of 0%) of Ni, 0.20% or less (exclusive of 0%) of Cu, 0.07% or less (exclusive of 0%) of Nb, 0.03% or less (exclusive of 0%) of Ti, 0.015% or less (exclusive of 0%) of N, 0.025% or less (exclusive of 0%) of Al, and 0.002% or less (exclusive of 0%) of B, with a balance of Fe and unavoidable impurities so that a finish rolling temperature is equivalent to or higher than Ar3 to manufacture a hot rolled steel plate, and then cooling the hot rolled steel plate;
reheating the cooled hot rolled steel plate in a temperature range of 900° C. to 1200° C. for 1 t to 3 t minutes [t (mm) is a thickness of the hot rolled steel plate] to austenitize the steel plate;
quenching the austenitized hot rolled steel plate to room temperature; and
tempering the quenched hot rolled steel plate in a temperature range of 675 to 800° C. for 30 minutes to 120 minutes.
7 . The method for manufacturing a chromium-molybdenum steel plate having excellent creep strength of claim 6 , wherein the steel plate has a microstructure including tempered martensite and the number of precipitates having a diameter of 200 nm or more including (Fe,Cr) 23 C 6 is in a range of one/μm 2 or less in the microstructure of the steel plate.
8 . The method for manufacturing a chromium-molybdenum steel plate having excellent creep strength of claim 6 , wherein the steel plate has a microstructure including tempered martensite and the number of precipitates having a diameter of 20 nm or less is in a range of 20/μm 2 or more in the microstructure of the steel plate.
9 . The method for manufacturing a chromium-molybdenum steel plate having excellent creep strength of claim 8 , wherein the precipitates having a diameter of 20 nm or less are (V,Mo,Nb,Ti) (C,N).