Hic-resistant thick steel plate and uoe steel pipe

Abstract

A thick steel plate and a UOE steel pipe having a high strength of at least X60 grade and improved resistance to HIC have a chemical composition consisting essentially of, in mass percent, C: 0.02-0.07%, Si: 0.05-0.50%, Mn: 1.1-1.6%, P: at most 0.015%, S: at most 0.002%, Nb: 0.005-0.060%, Ti: 0.005-0.030%, Al: 0.005-0.06%, Ca: 0.0005-0.0060%, N: 0.0015-0.007%, at least one of Cu, Ni, Cr, and Mo in a total amount of greater than 0.1% and less than 1.5%, and a remainder of Fe and impurities, wherein the degrees of segregation of Nb and Ti are both at most 2.0, and the ratio of (the degree of Nb segregation)/(the degree of Mn segregation) and the ratio of (the degree of Ti segregation)/(the degree of Mn segregation) are both at least 1.0 and at most 1.5.

1 . A thick steel plate having improved resistance to HIC characterized by
 having a chemical composition consisting essentially of, in mass percent, C: 0.02-0.07%, Si: 0.05-0.50%, Mn: 1.1-1.6%, P: at most 0.015%, S: at most 0.002%, Nb: 0.005-0.060%, Ti: 0.005-0.030%, Al: 0.005-0.06%, Ca: 0.0005-0.0060%, N: 0.0015-0.007%), at least one of Cu, Ni, Cr, and Mo in amounts which satisfy Equation (1), V: 0-0.10%, and a remainder of Fe and impurities, wherein the degree of Nb segregation is at most 2.0, the ratio α of the degree of Nb segregation to the degree of Mn segregation (α=the degree of Nb segregation/the degree of Mn segregation) is at least 1.0 and at most 1.5, the degree of Ti segregation is at most 2.0, and the ratio β of the degree of Ti segregation to the degree of Mn segregation (β=the degree of Ti segregation/the degree of Mn segregation) is at least 1.0 and at most 1.5:
   0.1%<(Cu+Ni+Cr+Mo)<1.5%  Equation (1)
 
 wherein the symbols for elements in the equation indicate the content (mass percent) of each element. 
   
     
     
         2 . A thick steel plate as set forth in  claim 1  wherein the chemical composition contains 0.01-0.10% of V. 
     
     
         3 . A UOE steel pipe characterized by being formed from a thick steel plate as set forth in  claim 1 .