Austenitic steel material having excellent hydrogen-embrittlement resistance

Abstract

Disclosed is an austenitic material having excellent hydrogen-embrittlement resistance, comprising, by weight, 0.1-0.5% of C, 5% or less (0% exclusive) of Cu, 1% or less (0% exclusive) of N, a content of Mn satisfying Mn≥−10.7C+24.5, 10% or less of Cr, 5% or less of Ni, 5% or less of Mo, 4% or less of Si, 5% or less of Al, and a balance amount of Fe and inevitable impurities, with a T-El 2 /T-El 1 ratio of 0.5 or higher, wherein T-El 1 is an elongation at break according to a tensile test at 25° C. under an atmospheric condition of 1 atm and T-El 2 is an elongation at break according to a tensile test at 25° C. under a hydrogen condition of 70 MPa.

1 . An austenitic steel material having high hydrogen-embrittlement resistance, the austenitic steel material comprising, by wt %, carbon (C): 0.1% to 0.5%, copper (Cu): 5% or less (excluding 0%), nitrogen (N): 1% or less (excluding 0%), manganese (Mn): [Mn]≥−10.7[C]+24.5 where each of [Mn] and [C] refers to a weight percent (wt %) of a corresponding element, chromium (Cr): 10% or less, nickel (Ni): 5% or less, molybdenum (Mo): 5% or less, silicon (Si): 4% or less, aluminum (Al): 5% or less, and a balance of iron (Fe) and inevitable impurities,
 wherein the austenitic steel material has a T-El 2 /T-El 1  ratio of 0.5 or greater, where T-El 2  is an elongation at break in a tensile test performed under hydrogen conditions of 25° C. and 70 MPa, and T-El 1  is an elongation at break in a tensile test performed under atmospheric conditions of 25° C. and 1 atm. 
 
     
     
         2 . The austenitic steel material of  claim 1 , wherein the austenitic steel material has stacking fault energy (SFE) defined by Formula 1 below within a range of 30 mJ/m 2  or greater,
     SFE (mJ/m 2 )=1.6[Ni]−1.3[Mn]+0.06[Mn] 2 −1.7[Cr]+0.01[Cr] 2 +15[Mo]−5.6[Si]+1.6[Cu]+5.5[Al]−60([C]+1.2[N]) 1/2 +26.3([C]+1.2[N])([Cr][Mn]+[Mo]) 1/2 +0.6{[Ni]([Cr]+[Mn])} 1/2   [Formula 1]
   where each of [Ni], [Mn], [Cr], [Mo], [Si], [Cu], [Al], [C], and [N] refers to a content (wt %) of a corresponding element.   
     
     
         3 . The austenitic steel material of  claim 1 , wherein the austenitic steel material has a strain hardening rate of 14000 N/mm 2  or less in the tensile test performed under the atmospheric conditions of 25° C. and 1 atm. 
     
     
         4 . The austenitic steel material of  claim 1 , wherein the austenitic steel material has a tensile strength of 800 MPa or less in the tensile test performed under the atmospheric conditions of 25° C. and 1 atm. 
     
     
         5 . The austenitic steel material of  claim 1 , wherein the austenitic steel material has a microstructure comprising austenite in an area fraction of 95% or greater (including 100%). 
     
     
         6 . The austenitic steel material of  claim 1 , wherein after the tensile test performed under the atmospheric conditions of 25° C. and 1 atm, the austenitic steel material has a microstructure formed of austenite, or formed of s-martensite and austenite.