Steel plate for pressure vessel with excellent cryogenic toughness, and method of manufacturing same

Abstract

The present invention relates to a method of manufacturing a cryogenic steel plate for a pressure vessel and a cryogenic steel plate for a pressure vessel manufactured thereby, the method comprising the steps of: reheating a slab containing, in weight %, C: 0.05-0.15%, Si: 0.20-0.35%, Mn: 0.5-1.5%, P: 0.012% or less, S: 0.015% or less, Al: 0.02-0.10%, Ni: 6.01-6.49%, Mo: 0.2-0.4%, Cr: and the balance being Fe and inevitable impurities; hot-rolling the reheated steel plate, followed by air cooling; subjecting the air-cooled steel plate to primary heat treatment at 800-880° C. for (2.4×t+(10−40)) minutes (t: slab thickness (mm)), followed by primary water cooling: subjecting the primarily water-cooled steel plate to secondary heat treatment at 700-780° C. for (2.4×t+(10−40)) minutes (t: slab thickness (mm)), followed by secondary water cooling: and tempering the secondarily water-cooled steel plate.