POSCO Holdings Inc.
LOW-TEMPERATURE STEEL MATERIAL HAVING EXCELLENT TOUGHNESS IN WELDING PORTION THEREOF AND MANUFACTURING METHOD THEREFOR

Abstract:

Provided according to a preferable aspect of the present invention are a low-temperature steel material having excellent toughness in a welding portion thereof and a manufacturing method therefor, the low-temperature steel material comprising, by weight %, 0.02-0.06% of C, 6.0-7.5% of Ni, 0.4-1.0% of Mn, 0.02-0.15% of Si, 0.02-0.3% of Mo, 0.02-0.3% of Cr, 50 ppm or less of P, 10 ppm or less of S, 0.005-0.015% of Ti, 60 ppm or less of N, with a Ti/N weight % ratio of 2.5 of 4, and the balance of iron (Fe) and other inevitable impurities; and having: an effective grain size of 50 micrometers or less, with a boundary angle found to be 15 degrees or greater as measured by EBSD in an area of a fusion line (FL)-FL+1 mm in a weld heat-affected zone of a weld portion welded at a heat input of 5-50 kJ/cm; and an impact toughness of 70 J or higher at -196.degree. C. as measured in an area of fusion line (FL)-FL+1 mm.