Steel material

Abstract

A steel material that achieves both high strength and excellent fracture toughness is provided. A steel material according to the present disclosure contains C: 0.10 to 0.45%, Si: 1.00% or less, Mn: 0.01 to 1.00%, Al: 0.001 to 0.100%, Cr: 0.1 to 2.0%, and Mo: 0.20 to 2.00%, contains any one or more elements among Ca: 0.0005 to 0.0200% and Mg: 0.0005 to 0.0200%, contains any one or more elements among Ti: 0.001 to 0.300%, Nb: 0.001 to 0.300%, and V: 0.01 to 0.50%, with the balance being Fe and impurities, and satisfies Formulae (1) and (2) described in the description. The yield strength is 758 to less than 862 MPa. A number density of MX-type precipitates which have an equivalent circular diameter of 100 nm or less and in which, when the total content of Mo, Nb, V, and Ti is defined as 100% by mass, the content of Mo is more than 50% by mass is 20/μm 2 or more.

1 . A steel material consisting of, in mass %,
 C: 0.10 to 0.45%,   Si: 1.00% or less,   Mn: 0.01 to 1.00%,   P: 0.050% or less,   S: 0.0050% or less,   Al: 0.001 to 0.100%,   Cr: 0.1 to 2.0%,   Mo: 0.20 to 2.00%,   N: 0.010% or less,   W: 0 to 0.50%,   Co: 0 to 0.50%,   Ni: 0 to 0.50%,   rare earth metal: 0 to 0.020%,   Cu: 0 to 0.50%, and   B: 0 to 0.0100%,   further containing one or more elements selected from a group consisting of:   Ca: 0.0005 to 0.0200%, and   Mg: 0.0005 to 0.0200%,   further containing one or more elements selected from a group consisting of:   Ti: 0.001 to 0.300%,   Nb: 0.001 to 0.300%, and   V: 0.01 to 0.50%,   with the balance being Fe and impurities, and   satisfying Formula (1) and Formula (2),   wherein:   a yield strength is 758 to less than 862 MPa; and   in the steel material,   a number density of MX-type precipitates which have an equivalent circular diameter of 100 nm or less and in which, when a total content of Mo, Nb, V, and Ti is defined as 100% by mass, a content of Mo is more than 50% by mass is 20/μm 2  or more:   
       
         
           
             
               
                 
                   
                     
                       Mn 
                       × 
                       Sp 
                     
                     ≤ 
                     12. 
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         
           
             
               
                 
                   
                     0.05 
                     ≤ 
                     
                       
                         7 
                         × 
                         Ti 
                       
                       + 
                       
                         2 
                         × 
                         Nb 
                       
                       + 
                       
                         3 
                         × 
                         V 
                       
                     
                     ≤ 
                     0.8 
                   
                 
                 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
         where, in Formula (1), a content of Mn in percent by mass is substituted for “Mn”, and a content of S in ppm is substituted for “Sp”; a content of a corresponding element in percent by mass is substituted for each symbol of an element in Formula (2); note that, when a corresponding element is not contained, “0” is substituted for the symbol of the relevant element. 
       
     
     
         2 . The steel material according to  claim 1 , containing one or more elements selected from a group consisting of:
 W: 0.01 to 0.50%,   Co: 0.01 to 0.50%,   Ni: 0.01 to 0.50%,   rare earth metal: 0.001 to 0.020%,   Cu: 0.01 to 0.50%, and   B: 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.