Steel material suitable for use in sour environment

Abstract

A steel material according to the present disclosure consists of, in mass %, C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.05 to 0.30%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.10%, Mo: 0.40 to 2.00%, Ti: 0.002 to 0.020%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, N: 0.0100% or less, and O: less than 0.0040%, with the balance being Fe and impurities, and has a yield strength of 862 MPa or more. In the steel material, a number density of Si oxides which have a major axis of 5.0 μm or more is 5/100 mm 2 or less, and in a case where the yield strength is 931 MPa or more, the number density of the Si oxides is 5/200 mm 2 or less.

1 . A steel material consisting of, in mass %,
 C: 0.15 to 0.45%,   Si: 0.05 to 1.00%,   Mn: 0.05 to 0.30%,   P: 0.030% or less,   S: 0.0050% or less,   Al: 0.005 to 0.100%,   Cr: 0.30 to 1.10%,   Mo: 0.40 to 2.00%,   Ti: 0.002 to 0.020%,   Nb: 0.002 to 0.100%,   B: 0.0005 to 0.0040%,   N: 0.0100% or less,   O: less than 0.0040%,   V: 0 to 0.30%,   Cu: 0 to 0.50%,   Ni: 0 to 0.50%,   W: 0 to 1.50%,   Ca: 0 to 0.0100%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0100%, and   rare earth metal: 0 to 0.0100%,   with the balance being Fe and impurities,   wherein:   a yield strength is 862 MPa or more, and   in the steel material,   a number density of Si oxides in which, in mass %, a content of Si is 20% or more and a content of O is 10% or more, and which have a major axis of 5.0 μm or more is 5/100 mm 2  or less, and   in a case where the yield strength is 931 MPa or more, a number density of the Si oxides is 5/200 mm 2  or less.   
     
     
         2 . The steel material according to  claim 1 , containing one or more elements selected from a group consisting of:
 V: 0.01 to 0.30%,   Cu: 0.01 to 0.50%,   Ni: 0.01 to 0.50%,   W: 0.01 to 1.50%,   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%.   
     
     
         3 . The steel material according to  claim 1 , wherein:
 the steel material is an oil-well steel pipe.   
     
     
         4 . The steel material according to  claim 2 , wherein:
 the steel material is an oil-well steel pipe.