Steel plate with excellent sour resistance, haz toughness and haz hardness, and steel pipe for line pipe

Abstract

The present invention relates to a steel plate with excellent sour resistance, HAZ toughness and HAZ hardness, including, in terms of mass %, C: 0.02-0.20%, Si: 0.02-0.50%, Mn: 0.6-2.0%, P: over 0% and 0.030% or less, S: over 0% and 0.004% or less, Al: 0.010-0.08%, N: 0.001-0.01%, Nb: 0.002% or more and less than 0.05%, O: over 0% and 0.0040% or less, REM: 0.0002-0.05%, and Zr: 0.0003-0.020% with the remainder consisting of iron and inevitable impurities, in which an expression 10,000×[Nb]+31×Di−82≧0 (where Di =([C]/10) 0.5 ×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×1.115) is satisfied, and, in the composition of inclusions with 1 μm or more width contained in steel, Zr amount is 1-40%, REM amount is 5-50%, Al amount is 3-30%, and S amount is over 0% and less than 20%.

1 . A steel plate with excellent sour resistance, HAZ toughness and HAZ hardness, comprising in terms of mass %:
 C: 0.02-0.20%;   Si: 0.02-0.50%;   Mn: 0.6-2.0%;   P: over 0% and 0.030% or less;   S: over 0% and 0.004% or less;   Al: 0.010-0.08%;   N: 0.001-0.01%;   Nb: 0.002% or more and less than 0.05%;   O: over 0% and 0.0040% or less;   REM: 0.0002-0.05%; and   Zr: 0.0003-0.020%   with the remainder consisting of iron and inevitable impurities; wherein   an expression 10,000×[Nb]+31×Di−82≧0,   wherein Di=([C]/10) 0.5 ×(1+0.7×[Si])×(1+3.33×[Mn])×(1+0.35×[Cu])×(1+0.36×[Ni])×(1+2.16×[Cr])×(1+3×[Mo])×(1+1.75×[V])×1.115 is satisfied, and   in the composition of inclusions with 1 μm or more width contained in steel a   Zr amount is 1-40%,   REM amount is 5-50%,   Al amount is 3-30%, and a   S amount is over 0% and less than 20%.   
     
     
         2 . The steel plate according to  claim 1 , further comprising at least one element selected from a group consisting of:
 Ca: 0.0003-0.0060%; and   Mg: 0.0003-0.005%.   
     
     
         3 . The steel plate according to  claim 2 , wherein in the composition of the inclusions with 1 μm or more width contained in steel a
 Zr amount is 1-40%, 
 REM amount is 5-50%, 
 Al amount is 3-30%, 
 Ca amount is 5-60%, and a 
 S amount is over 0% and less than 20%. 
 
     
     
         4 . The steel plate according to  claim 1 , further comprising at least one element selected from a group consisting of:
 Ti: 0.003-0.03%,   B: 0.0002-0.005%,   V: 0.003-0.1%,   Cu: 0.01-1.5%,   Ni: 0.01-3.5%,   Cr: 0.01-1.5%, and   Mo: 0.01-1.5%.   
     
     
         5 . A steel pipe manufactured using the steel plate according to  claim 1 . 
     
     
         6 . A line pipe manufactured using the steel pipe according to  claim 6 . 
     
     
         7 . A steel pipe for a line pipe manufactured using the steel plate according to  claim 1 . 
     
     
         8 . A line pipe manufactured using the steel pipe according to  claim 7  steel plate according to  claim 4 .