POSCO Holdings Inc.
ULTRA-THICK STRUCTURAL STEEL HAVING EXCELLENT BRITTLE CRACK INITIATION RESISTANCE, AND MANUFACTURING METHOD THEREFOR

Abstract:

One embodiment of the present invention provides an ultra-thick structural steel having excellent brittle crack initiation resistance, and a manufacturing method therefor, the ultra-thick structural steel comprising, by wt %, 0.03-0.08% of C, 1.6-2.2% of Mn, 0.6-1.3% of Ni, 0.005-0.03% of Nb, 0.005-0.02% of Ti, 0.1-0.4% of Cu, 100 ppm or less of P, 40 ppm or less of S, 1.5 ppm or less of H, and the balance of Fe and other inevitable impurities, wherein the sum of acicular ferrite and granular bainite in the microstructure is 80% or more by area fraction, the sum of the total length of cracks having a size of 30 .mu.m or more per unit area of 1 mm2 in a .+-.1 mm region on the basis of the thickness center of the steel is 130 .mu.m or less, and the yield strength is 500 MPa or more.