Steel material suitable for use in sour environment

Abstract

A steel material according to the present disclosure has a chemical composition consisting of, in mass %: C: 0.20 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.60 to 1.50%, Mo: more than 1.00 to 2.00%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.005 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, O: less than 0.0020%, and the balance being Fe and impurities, and satisfying Formula (1) described in the specification. A grain diameter of a prior-austenite grain is 11.0 μm or less, and an average area of precipitate which is precipitated in a prior-austenite grain boundary is 10.0×10 −3 μm 2 or less. A yield strength is 758 to 862 MPa.

1 .- 6 . (canceled) 
     
     
         7 . A steel material comprising:
 a chemical composition consisting of, in mass %:   C: 0.20 to 0.45%,   Si: 0.05 to 1.00%,   Mn: 0.01 to 1.00%,   P: 0.030% or less,   S: 0.0050% or less,   Al: 0.005 to 0.100%,   Cr: 0.60 to 1.50%,   Mo: more than 1.00 to 2.00%,   Ti: 0.002 to 0.020%,   V: 0.05 to 0.30%,   Nb: 0.005 to 0.100%,   B: 0.0005 to 0.0040%,   N: 0.0100% or less,   O: less than 0.0020%,   Ca: 0 to 0.0100%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0100%,   rare earth metal: 0 to 0.0100%,   Cu: 0 to 0.50%,   Ni: 0 to 0.50%,   Co: 0 to 0.50%, and   W: 0 to 0.50%,   with the balance being Fe and impurities,   and satisfying Formula (1),   wherein   in the steel material, a grain diameter of a prior-austenite grain is 11.0 μm or less,   an average area of precipitate which is precipitated in a prior-austenite grain boundary is 10.0×10 −3  μm 2  or less, and   a yield strength is 758 to 862 MPa:
   2.7×C+0.4×Si+Mn+0.45×Ni+0.45×Cu+0.8×Cr+2×Mo≥3.90  (1)
 
   where, content in mass % of a corresponding element is substituted for each symbol of an element in Formula (1), and if a corresponding element is not contained, “0” is substituted for the element symbol of the relevant element.   
     
     
         8 . The steel material according to  claim 7 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Ca: 0.0001 to 0.0100%,   Mg: 0.0001 to 0.0100%,   Zr: 0.0001 to 0.0100%, and   rare earth metal: 0.0001 to 0.0100%.   
     
     
         9 . The steel material according to  claim 7 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Cu: 0.02 to 0.50%, and   Ni: 0.02 to 0.50%.   
     
     
         10 . The steel material according to  claim 8 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Cu: 0.02 to 0.50%, and   Ni: 0.02 to 0.50%.   
     
     
         11 . The steel material according to  claim 7 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Co: 0.02 to 0.50%, and   W: 0.02 to 0.50%.   
     
     
         12 . The steel material according to  claim 8 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Co: 0.02 to 0.50%, and   W: 0.02 to 0.50%.   
     
     
         13 . The steel material according to  claim 9 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Co: 0.02 to 0.50%, and   W: 0.02 to 0.50%.   
     
     
         14 . The steel material according to  claim 10 , wherein
 the chemical composition contains one or more types of element selected from the group consisting of:   Co: 0.02 to 0.50%, and   W: 0.02 to 0.50%.   
     
     
         15 . The steel material according to  claim 7 , wherein
 the steel material is an oil-well steel pipe.   
     
     
         16 . The steel material according to  claim 7 , wherein
 the steel material is a seamless steel pipe.