POSCO Holdings Inc.
ULTRA-THICK STEEL EXCELLENT IN BRITTLE CRACK ARRESTABILITY AND MANUFACTURING METHOD THEREFOR

Abstract:

An ultra-thick steel excellent in brittle crack arrestability according to an aspect of the present invention comprises, by weight, C: 0.02-0.07%, Mn: 1.8-2.2%, Ni: 0.7-1.2%, Nb: 0.005-0.02%, Ti: 0.005-0.02%, Cu: 0.1-0.4%, P: 0.01% or less, S: 0.004% or less, and the balance of Fe and inevitable impurities, wherein crystal grains that have a high angle grain boundary of 15 degrees or more, as measured by EBSD, may have an average grain size of 15 .mu.m or less in the t/4-(3*t)/8 region (wherein t represents a thickness of the steel, the same below).