Austenitic steel having excellent ultra-low temperature toughness in weld heat-affected zone, and manufacturing method therefor

Abstract

According to one aspect of the present invention, an austenitic high-manganese steel having excellent ultra-low temperature toughness in a weld heat-affected cone, and a manufacturing method therefor can be provided.

1 . An austenitic steel, comprising:
 by wt %, manganese (Mn): 10 to 45%, carbon (C): range satisfying 24*[C]+ [Mn]≥25 and 33.5*[C]—[Mn]≤18, chromium (Cr): 10% or less (excluding 0%), and the balance of iron (Fe) and inevitable impurities,   wherein, when a Charpy impact test is performed at −253° C. on a weld heat-affected zone, a lateral expansion in the weld heat-affected zone is 0.32 mm or more, and   the [C] and [Mn] in the above equation mean a content (wt %) of the carbon (C) and manganese (Mn) contained in the steel.   
     
     
         2 . The austenitic steel of  claim 1 , wherein a room temperature yield strength of the steel is 245 MPa or more and less than 400 MPa. 
     
     
         3 . The austenitic steel of  claim 1 , wherein the weld heat-affected zone includes, as a microstructure, 95 area % or more (including 100 area %) of austenite and 5 area % or less (including 0 area %) of grain boundary carbides. 
     
     
         4 . The austenitic steel of  claim 1 , wherein an average grain size of the weld heat-affected zone is 5 to 200 μm. 
     
     
         5 . The austenitic steel of  claim 1 , wherein an average grain aspect ratio of the weld heat-affected zone is 1.0 to 5.0. 
     
     
         6 . The austenitic steel of  claim 1 , wherein a dislocation density of the steel is 2.3*10 15  to 3.3*10 15 /mm 2 . 
     
     
         7 . A manufacturing method for an austenitic steel, comprising:
 preparing a slab including, by wt %, manganese (Mn): 10 to 45%, carbon (C): range satisfying 24*[C]+ [Mn]≥25 and 33.5*[C]—[Mn]≤18, chromium (Cr): 10% or less (excluding 0%), and the balance of iron (Fe) and inevitable impurities;   providing a hot-rolled steel sheet by heating the slab and then hot-rolling the heated slab; and   performing heat treatment that heats the hot-rolled steel sheet to a temperature range of 500 to 1000° C. and maintains the heated hot-rolled steel sheet in the temperature range for 1.3t (hot-rolled steel sheet thickness, mm)+5 minutes or more,   wherein the [C] and [Mn] in the above equation mean a content (wt) of the carbon (C) and manganese (Mn) contained in the steel.