Posco

Hyun-Kwan Cho

Hak-Cheol Lee

Jong-Kyo Choi

Hee-Goon Noh

In-Gyu Park

Hong-Ju Lee

In-Shik Suh

Soon-Gi Lee

Kyung-Keun Um

Woo-Kil Jang

Young-Hwan Park

Provided are an austenitic steel having excellent machinability and ultra-low temperature toughness in a weld heat-affected zone including 15 wt % to 35 wt % of manganese (Mn), carbon (C) satisfying 23.6C+Mn&#x2265;28 and 33.5C&#x2212;Mn&#x2264;23, 5 wt % or less (excluding 0 wt %) of copper (Cu), chromium (Cr) satisfying 28.5C+4.4Cr&#x2264;57 (excluding 0 wt %), and iron (Fe) as well as other unavoidable impurities as a remainder, wherein a Charpy impact value of a weld heat-affected zone at &#x2212;196&#xb0; C. is 41 J or more, and a method of manufacturing the steel. According to the present invention, a low-cost ultra-low temperature steel may be obtained, a stable austenite phase may be formed at low temperature, carbide formation may be effectively suppressed, and a structural steel having excellent machinability and ultra-low temperature toughness in a weld heat-affected zone may be provided.

Austenitic steel having excellent machinability and ultra-low temperature toughness in weld heat-affected zone, and method of manufacturing the same

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&#xb0; 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&#xb0; C. or less at a rolling reduction rate of 40% or more. The rolled steel is cooled to a temperature of 400&#xb0; C. or less at a cooling rate of 2&#xb0; C./s or more. Thereafter, the steel is tempered for 0.5-4 hours to a temperature within a range of 550 to 650&#xb0; C. after the cooling.

High-strength steel material having outstanding ultra-low-temperature toughness and a production method therefor

Growing community of inventors

Pohang-si, South Korea

Hyun-Kwan Cho