Steel material

Abstract

A steel material of the present disclosure has the chemical composition described in the specification, Fn defined by formula (1) is 0.45 to 1.05, at a depth of 0.08R from a surface of the steel material (R is a radius), a number density of fine Bi particles, which are Bi particles having an equivalent circular diameter of 0.1 to 1.0 μm, is 15.00 pieces/mm 2 or more and a number density of coarse Bi particles, which are Bi particles having an equivalent circular diameter of 10.0 μm or more, is 0.25 pieces/mm 2 or less, and at a depth of 0.65R from the surface of the steel material, the number density of the fine Bi particles is less than 15.00 pieces/mm 2 and the number density of the coarse Bi particles is more than 0.25 pieces/mm 2 .

1 . A steel material whose cross section perpendicular to an axial direction thereof is circular, consisting of, by mass %,
 C: more than 0.30 to 0.60%,   Si: 0.01 to 0.90%,   Mn: 0.50 to 1.70%,   P: 0.030% or less,   S: 0.200% or less,   Bi: 0.0051 to 0.2500%,   Al: 0.001 to 0.100%,   N: 0.0250% or less,   O: 0.0050% or less,   Cr: 0 to 1.30%,   V: 0 to 0.200%,   Sn: 0 to 0.1000%,   Sb: 0 to 0.0500%,   As: 0 to 0.0500%,   Pb: 0 to 0.09%,   Mg: 0 to 0.0100%,   Ti: 0 to 0.0400%,   Nb: 0 to 0.0500%,   W: 0 to 0.4000%,   Zr: 0 to 0.2000%,   Ca: 0 to 0.0100%,   Te: 0 to 0.0100%,   B: 0 to 0.0050%,   rare earth metal: 0 to 0.0100%,   Co: 0 to 0.0100%,   Se: 0 to 0.0100%,   In: 0 to 0.0100%,   Mo: 0 to 0.30%,   Cu: 0 to 0.50%,   Ni:0 to 0.50%, and   with the balance being Fe and impurities,   and Fn defined by formula (1) is 0.45 to 1.05,   wherein:   at a depth of 0.08R from a surface of the steel material, where R defines a radius of the steel material,
 a number density of fine Bi particles having an equivalent circular diameter of 0.1 to 1.0 μm, is 15.00 pieces/mm 2  or more, and 
 a number density of coarse Bi particles having an equivalent circular diameter of 10.0 μm or more, is 0.25 pieces/mm 2  or less, 
   at a depth of 0.65R from the surface of the steel material,
 the number density of the fine Bi particles is less than 15.00 pieces/mm 2 , and 
 the number density of the coarse Bi particles is more than 0.25 pieces/mm 2 , and 
   
       
         
           
             
               
                 
                   
                     
                       Fn 
                       = 
                       
                         C 
                         + 
                         
                           ( 
                           
                             Si 
                             / 
                             10 
                           
                           ) 
                         
                         + 
                         
                           ( 
                           
                             Mn 
                             / 
                             5 
                           
                           ) 
                         
                         - 
                         
                           ( 
                           
                             5 
                             ⁢ 
                             S 
                             / 
                             7 
                           
                           ) 
                         
                         + 
                         
                           ( 
                           
                             5 
                             ⁢ 
                             Cr 
                             / 
                             22 
                           
                           ) 
                         
                         + 
                         
                           1.65 
                           V 
                         
                       
                     
                     , 
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         where, a content in percent by mass of a corresponding element is substituted for each symbol of an element in the formula (1), and if an element is not contained, “0” is substituted for the corresponding symbol of an element. 
       
     
     
         2 . The steel material according to  claim 1 , comprising one or more elements selected from a group consisting of:
 Cr: 0.01 to 1.30%,   V: 0.001 to 0.200%,   Sn: 0.0001 to 0.1000%,   Sb: 0.0001 to 0.0500%,   As: 0.0001 to 0.0500%,   Pb: 0.01 to 0.09%,   Mg: 0.0001 to 0.0100%,   Ti: 0.0001 to 0.0400%,   Nb: 0.0001 to 0.0500%,   W: 0.0001 to 0.4000%,   Zr: 0.0001 to 0.2000%,   Ca: 0.0001 to 0.0100%,   Te: 0.0001 to 0.010000,   B: 0.0001 to 0.0050%,   rare earth metal: 0.0001 to 0.0100%,   Co: 0.0001 to 0.0100%,   Se: 0.0001 to 0.0100%,   In: 0.0001 to 0.0100%,   Mo: 0.01 to 0.30%,   Cu: 0.01 to 0.50%, and   Ni: 0.01 to 0.50%.