The present invention provides steel containing
manganese and
nickel that is used as a
structural material for a cryogenic storage container for
liquefied natural gas (LNG) or the like, and a manufacturing method thereof; and more particularly, to steel having good
cryogenic temperature toughness and also high strength by adding low-cost Mn instead of relatively expensive Ni at an optimized ratio, refining a
microstructure through controlled rolling and cooling, and precipitating retained
austenite through
tempering, and a manufacturing method of the steel. To achieve the object, the technical feature of the present invention is a method of manufacturing high-strength steel with
cryogenic temperature toughness. In the method, a steel slab is heated to a temperature within a range of 1,000 to 1,250° C., wherein the steel slab includes, by weight: 0.01-0.06% of carbon (C), 2.0-8.0% of
manganese (Mn), 0.01-6.0% of
nickel (Ni), 0.02-0.6% of
molybdenum (Mo), 0.03-0.5% of
silicon (Si), 0.003-0.05% of aluminum (Al), 0.0015-0.01% of
nitrogen (N), 0.02% or less of phosphorous (P), 0.01% or less of
sulfur (S), with a remainder of iron (Fe) and other unavoidable impurities. Then, the heated slab is finish-rolled at a temperature of 950° C. or less at a rolling
reduction rate of 40% or more. The rolled steel is cooled to a temperature of 400° C. or less at a
cooling rate of 2° C. / s or more. Thereafter, the steel is tempered for 0.5-4 hours to a temperature within a range of 550 to 650° C. after the cooling.