Steel material and expandable oil country tubular goods

Abstract

There is provided a steel material having a chemical composition consisting, by mass percent, of C: 0.6-1.8%, Si: 0.05-1.00%, Mn: >25.0-45.0%, Al: 0.003-0.06%, P: ≦0.03%, S: ≦0.03%, Cu: 0.5-3.0%, N: ≦0.10%, V: 0-2.0%, Cr: 0-3.0%, Mo: 0-3.0%, Ni: 0-1.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: 0-0.005%, Mg: 0-0.005%, REM: 0-0.01%, B: 0-0.015%, the balance: Fe and impurities, and satisfying [0.6<C−0.18V<1.44], wherein a metal micro-structure is consisting of an austenite single phase, a yield strength is 241 MPa or higher, and a uniform elongation is 40% or higher.

1 . A steel material having a chemical composition consisting, by mass percent, of
 C: 0.6 to 1.8%,   Si: 0.05 to 1.00%,   Mn: more than 25.0% and 45.0% or less,   Al: 0.003 to 0.06%,   P: 0.03% or less,   S: 0.03% or less,   Cu: 0.5 to 3.0%,   N: 0.10% or less,   V: 0 to 2.0%,   Cr: 0 to 3.0%,   Mo: 0 to 3.0%,   Ni: 0 to 1.5%,   Nb: 0 to 0.5%,   Ta: 0 to 0.5%,   Ti: 0 to 0.5%,   Zr: 0 to 0.5%,   Ca: 0 to 0.005%,   Mg: 0 to 0.005%,   REM: 0 to 0.01%,   B: 0 to 0.015%,   the balance: Fe and impurities, and   satisfying the following formula (i),   wherein a metal micro-structure is consisting of an austenite single phase,   a yield strength is 241 MPa or higher, and a uniform elongation is 40% or higher;
   0.6<C−0.18V<1.44  (i)
 
   where, the symbol of an element in the formula represents the content (mass %) of the element contained in the steel material, and is made zero in the case where the element is not contained.   
     
     
         2 . The steel material according to  claim 1 ,
 wherein the chemical composition contains, by mass percent,   V: 0.03 to 2.0%.   
     
     
         3 . The steel material according to  claim 1 ,
 wherein the chemical composition contains, by mass percent,   one or more elements selected from   Cr: 0.1 to 3.0%,   Mo: 0.1 to 3.0% and   Ni: 0.1 to 1.5%.   
     
     
         4 . The steel material according to  claim 1 ,
 wherein the chemical composition contains, by mass percent,   one or more elements selected from   Nb: 0.005 to 0.5%,   Ta: 0.005 to 0.5%,   Ti: 0.005 to 0.5%,   Zr: 0.005 to 0.5%,   Ca: 0.0003 to 0.005%,   Mg: 0.0003 to 0.005%,   REM: 0.001 to 0.01% and   B: 0.0001 to 0.015%.   
     
     
         5 . Expandable oil country tubular goods, which are comprised of the steel material according to  claim 1 . 
     
     
         6 . The expandable oil country tubular goods according to  claim 5 , which are seamless oil country tubular goods. 
     
     
         7 . Expandable oil country tubular goods, which are comprised of the steel material according to  claim 2 . 
     
     
         8 . Expandable oil country tubular goods, which are comprised of the steel material according to  claim 3 . 
     
     
         9 . Expandable oil country tubular goods, which are comprised of the steel material according to  claim 4 . 
     
     
         10 . The expandable oil country tubular goods according to  claim 7 , which are seamless oil country tubular goods. 
     
     
         11 . The expandable oil country tubular goods according to  claim 8 , which are seamless oil country tubular goods. 
     
     
         12 . The expandable oil country tubular goods according to  claim 9 , which are seamless oil country tubular goods.