| 摘要 |
Provided are a thick steel sheet and a UOE steel pipe, which have high strength of X60 grade or greater and excellent HIC-resistance characteristics and have a chemical composition by mass% of C: 0,02 to 0,07%, Si : 0,05 to 0,50%, Mn : 1,1 to 1,6%, P : 0,015% or less, S : 0,002% or less, Nb : 0,005 to 0,060%, Ti : 0,005 to 0,030%, Al : 0,005 to 0,06%, Ca : de 0,0005 to 0,0060%, N : 0,0015 to 0,007%, at least one of Cu, Ni, Cr, and Mo such that the total exceeds 0.1% but is less than 1.5%, and Fe and impurities as the balance, with the degree of segregation of the Nb and the degree of segregation of the Ti each being 2.0 or less and the ratio of the degree of segregation of Nb/the degree of segregation of Mn and the ratio of the degree of segregation of Ti/the degree of segregation of Mn each being between 1.0 and 1.5.
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