POSCO Holdings Inc.
ULTRA-THICK STEEL MATERIAL HAVING EXCELLENT SURFACE PART NRL-DWT PROPERTIES AND METHOD FOR MANUFACTURING SAME

Abstract:

Disclosed are a high-strength ultra-thick steel material and a method for manufacturing same. The high-strength ultra-thick steel material comprises in weight % 0.04-0.1% of C, 0.05-0.5% of Si, 0.01-0.05% of Al, 1.6-2.2% of Mn, 0.5-1.2% of Ni, 0.005-0.050% of Nb, 0.005-0.03% of Ti and 0.2-0.6% of Cu, 100 ppm or less of P and 40 ppm or less of S with a balance of Fe, and inevitable impurities, and comprises, in a subsurface area up to t/10 (t hereafter being referred to as the thickness of the steel material), bainite of 90 area % or greater (including 100 area %) as microstructures. And the particle size of crysta1lites having a high inclination angle boundary of 15.degree. or higher measured by EBSD is 10 .mu.m or less (not including 0 .mu.m).