| 摘要 |
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%. |
