AUSTENITIC STEEL HAVING EXCELLENT MACHINABILITY AND ULTRA-LOW TEMPERATURE TOUGHNESS IN WELD HEAT-AFFECTED ZONE, AND METHOD OF MANUFACTURING THE SAME

摘要

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≧28 and 33.5C−Mn≦23, 5 wt % or less (excluding 0 wt %) of copper (Cu), chromium (Cr) satisfying 28.5C+4.4Cr≦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 −196° 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.