Steel Material and Method for Producing Steel Material

Abstract

The steel material according to the present disclosure contains a chemical composition consisting of, in mass %, C: more than 0.50 to 0.80%, Si: 0.05 to 1.00%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.20 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010% and O: 0.0100% or less, with the balance being Fe and impurities. The steel material contains an amount of dissolved C within a range of 0.010 to 0.060 mass %. The steel material also has a yield strength within a range of 965 to 1069 MPa, and a yield ratio of the steel material is 90% or more.

1 . A steel material comprising:
 a chemical composition consisting of, in mass %,   C: more than 0.50 to 0.80%,   Si: 0.05 to 1.00%,   Mn: 0.05 to 1.00%,   P: 0.025% or less,   S: 0.0100% or less,   Al: 0.005 to 0.100%,   Cr: 0.20 to 1.50%,   Mo: 0.25 to 1.50%,   Ti: 0.002 to 0.050%,   B: 0.0001 to 0.0050%,   N: 0.002 to 0.010%,   O: 0.0100% or less,   V: 0 to 0.30%,   Nb: 0 to 0.100%,   Ca: 0 to 0.0100%,   Mg: 0 to 0.0100%,   Zr: 0 to 0.0100%,   Co: 0 to 0.50%,   W: 0 to 0.50%,   Ni: 0 to 0.50%, and   Cu: 0 to 0.50%   with the balance being Fe and impurities,   an amount of dissolved C within a range of 0.010 to 0.060 mass %,   a yield strength within a range of 965 to 1069 MPa, and   a yield ratio of 90% or more.   
     
     
         2 . The steel material according to  claim 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 V: 0.01 to 0.30%, and   Nb: 0.002 to 0.100%.   
     
     
         3 . The steel material according to  claim 1 , 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%, and   Zr: 0.0001 to 0.0100%.   
     
     
         4 - 8 . (canceled) 
     
     
         9 . The steel material according to  claim 2 , 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%, and   Zr: 0.0001 to 0.0100%.   
     
     
         10 . The steel material according to  claim 1 , 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%.   
     
     
         11 . The steel material according to  claim 2 , 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 3 , 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 1 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         15 . The steel material according to  claim 2 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         16 . The steel material according to  claim 3 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         17 . The steel material according to  claim 9 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         18 . The steel material according to  claim 10 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         19 . The steel material according to  claim 11 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         20 . The steel material according to  claim 12 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         21 . The steel material according to  claim 13 , wherein the chemical composition contains one or more types of element selected from the group consisting of:
 Ni: 0.02 to 0.50%, and   Cu: 0.01 to 0.50%.   
     
     
         22 . The steel material according to  claim 1 , wherein the steel material is an oil-well steel pipe. 
     
     
         23 . A method for producing a steel material, comprising:
 a preparation process of preparing an intermediate steel material containing a chemical composition according to  claim 1 ,   a quenching process of, after the preparation process, cooling the intermediate steel material that is at a temperature in a range of 800 to 1000° C. at a cooling rate of 50° C./min; and   a tempering process of holding the intermediate steel material after quenching at a temperature in a range of 660° C. to an A c1  point for 10 to 90 minutes, and thereafter cooling the intermediate steel material at an average cooling rate in a temperature region from 600° C. to 200° C. of 5 to 300° C./sec.   
     
     
         24 . The method for producing a steel material according to  claim 23 , wherein the preparation process includes:
 a starting material preparation process of preparing a starting material containing a chemical composition according to  claim 1 , and   a hot working process of subjecting the starting material to hot working to produce an intermediate steel material.