Steel plate for pipeline, having excellent hydrogen induced crack resistance, and preparation method thereof

Abstract

Disclosed are a steel plate for a line pipe having excellent hydrogen induced crack resistance with a tensile strength of 450 MPa or more, and a preparation method thereof. According to the present invention, the steel plate for a line pipe, having excellent hydrogen induced crack resistance comprises: 0.03-0.05 wt % of carbon (C); 0.2-0.3 wt % of silicon (Si); 0.5-1.3 wt % of manganese (Mn); 0.010 wt % or less of phosphorus (P); 0.005 wt % or less of sulfur (S); 0.02-0.05 wt % of aluminum (Al); 0.2-0.5 wt % of nickel (Ni); 0.2-0.3 wt % of chromium (Cr); 0.03-0.05 wt % of niobium (Nb); 0.02-0.05 wt % of vanadium (V); 0.01-0.02 wt % of titanium (Ti); 0.001-0.004 wt % of calcium (Ca); and a balance of iron (Fe) and inevitable impurities, and has a tensile strength of 450 MPa or more.

1 . A steel plate comprising:
 carbon (C), 0.03˜0.05 wt %; silicon (Si), 0.2˜0.3 wt %; manganese (Mn), 0.5˜1.3 wt %; phosphorous (P), 0.010 wt % or less; sulfur (S), 0.005 wt % or less; aluminum (Al), 0.02˜0.05 wt %; nickel (Ni), 0.2˜0.5 wt %; chromium (Cr), 0.2˜0.3 wt %; niobium (Nb), 0.03˜0.05 wt %; vanadium (V), 0.02˜0.05 wt %; titanium (Ti), 0.01˜0.02 wt %; calcium (Ca), 0.001˜0.004 wt %; and the balance of iron (Fe) and other unavoidable impurities,   the steel plate having a tensile strength of 450 MPa or more.   
     
     
         2 . The steel plate according to  claim 1 , wherein the steel plate has a yield ratio (yield strength/tensile strength) of 80% or less. 
     
     
         3 . The steel plate according to  claim 1 , wherein microstructure of the steel plate is a composite structure including acicular ferrite and bainite structures. 
     
     
         4 . The steel plate according to  claim 3 , wherein the composite structure including acicular ferrite and bainite structures occupies 30% or more of the entirety of the microstructure in terms of cross-sectional area ratio. 
     
     
         5 . The steel plate according to  claim 4 , wherein a composite structure including ferrite and pearlite structures occupies 70% or less of the entirety of the microstructure in terms of cross-sectional area ratio. 
     
     
         6 . A method of manufacturing a steel plate, comprising:
 (A) reheating a steel slab including: carbon (C), 0.03˜0.05 wt %; silicon (Si), 0.2˜0.3 wt %; manganese (Mn), 0.5˜1.3 wt %; phosphorous (P), 0.010 wt % or less; sulfur (S), 0.005 wt % or less; aluminum (Al), 0.02˜0.05 wt %; nickel (Ni), 0.2˜0.5 wt %; chromium (Cr), 0.2˜0.3 wt %; niobium (Nb), 0.03˜0.05 wt %; vanadium (V), 0.02˜0.05 wt %; titanium (Ti), 0.01˜0.02 wt %; calcium (Ca), 0.001˜0.004 wt %; and the balance of iron (Fe) and other unavoidable impurities;   (B) hot rolling the reheated steel slab; and   (C) cooling the hot-rolled steel plate.   
     
     
         7 . The method according to  claim 6 , wherein the reheating (A) is performed at a temperature of 1100˜1250° C. 
     
     
         8 . The method according to  claim 6 , wherein the hot rolling (B) is performed at a reduction rate of 50% to 70% based on the whole reduction rate of 100 at an Ar 3  temperature or less. 
     
     
         9 . The method according to  claim 6 , wherein the hot rolling (B) has a rolling finishing temperature of 750˜850° C. 
     
     
         10 . The method according to  claim 6 , wherein the cooling (C) has a cooling finishing temperature of 300˜450° C. 
     
     
         11 . The method according to  claim 6 , wherein the cooling (C) is performed at a cooling rate of 15˜25° C./sec.