Low alloy steel for oil country tubular goods having excellent sulfide stress cracking resistance and manufacturing method therefor

Abstract

The low alloy steel for oil country tubular goods according to the present invention has a chemical composition containing, by mass percent, C: 0.56 to 1.00%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: at most 0.025%, 5: at most 0.010%, Al: 0.005 to 0.100%, Mo: 0.40 to 1.00%, V: 0.05 to 0.30%, and O: at most 0.010%, the balance being Fe and impurities, wherein the yield stress thereof is at least 862 MPa, and the half-value width of a [211] crystal surface obtained by X-ray diffraction is at most 0.50°.

1 - 15 . (canceled) 
     
     
         16 . A low alloy steel for oil country tubular goods having a chemical composition containing, by mass percent,
 C: 0.56 to 1.00%,   Si: 0.05 to 0.50%,   Mn: 0.05 to 1.00%,   P: at most 0.025%,   S: at most 0.010%,   Al: 0.005 to 0.100%,   Mo: 0.40 to 1.00%,   V: 0.07 to 0.30%,   O: at most 0.010%, and   N: at most 0.0300%,   the balance being Fe and impurities, wherein   the yield stress thereof is at least 862 MPa; and   the half-value width of a [211] crystal surface obtained by X-ray diffraction is at most 0.50°.   
     
     
         17 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the chemical composition contains Cr: at most 2.00% in place of some of Fe. 
     
     
         18 . The low alloy steel for oil country tubular goods according to claim 
     
     
         16 , wherein the chemical composition contains, in place of some of Fe,
 one or more selected from a group consisting of   Nb: at most 0.100%,   Ti: at most 0.100%, and   Zr: at most 0.100%.   
     
     
         19 . The low alloy steel for oil country tubular goods according to  claim 17 , wherein the chemical composition contains, in place of some of Fe,
 one or more selected from a group consisting of   Nb: at most 0.100%,   Ti: at most 0.100%, and   Zr: at most 0.100%.   
     
     
         20 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the chemical composition contains Ca: at most 0.0100% in place of some of Fe. 
     
     
         21 . The low alloy steel for oil country tubular goods according to  claim 17 , wherein the chemical composition contains Ca: at most 0.0100% in place of some of Fe. 
     
     
         22 . The low alloy steel for oil country tubular goods according to  claim 18 , wherein the chemical composition contains Ca: at most 0.0100% in place of some of Fe. 
     
     
         23 . The low alloy steel for oil country tubular goods according to  claim 19 , wherein the chemical composition contains Ca: at most 0.0100% in place of some of Fe. 
     
     
         24 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         25 . The low alloy steel for oil country tubular goods according to  claim 17 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         26 . The low alloy steel for oil country tubular goods according to  claim 18 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         27 . The low alloy steel for oil country tubular goods according to  claim 19 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         28 . The low alloy steel for oil country tubular goods according to  claim 20 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         29 . The low alloy steel for oil country tubular goods according to  claim 21 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         30 . The low alloy steel for oil country tubular goods according to  claim 22 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         31 . The low alloy steel for oil country tubular goods according to  claim 23 , wherein the chemical composition contains B: at most 0.0030% in place of some of Fe. 
     
     
         32 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the low alloy steel for oil country tubular goods has a retained austenite percentage of lower than 5%. 
     
     
         33 . An oil country tubular good produced from the low alloy steel for oil country tubular goods according to  claim 16 , having an outer diameter of 100 to 450 mm and a wall thickness of 5 to 100 mm and having no quenching crack. 
     
     
         34 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the aspect ratio of carbide of the low alloy steel is 0.45 or above. 
     
     
         35 . The low alloy steel for oil country tubular goods according to  claim 16 , wherein the C content of the chemical composition is 0.61 to 1.00%.