Steel material

Abstract

Provided is a steel material which can achieve excellent fatigue strength even when a carburized steel component is produced by welding before carburizing treatment. The steel material has a chemical composition containing: in mass %, C: 0.09 to 0.16%, Si: 0.01 to 0.50%, Mn: 0.40 to 0.60%, P: 0.030% or less, S: 0.025% or less, Cr: 0.90 to 2.00%, Mo: 0.10 to 0.40%, Al: 0.005 to 0.030%, Ti: 0.010 to less than 0.050%, Nb: 0.010 to 0.030%, N: 0.0080% or less, O: 0.0030% or less, B: 0.0003 to 0.0030%, Ca: 0.0005 to 0.0050%, and the balance: Fe and impurities, and satisfying Formula (1) to Formula (3) according to the description. In a cross section parallel to an axial direction of the steel material, an amount of Mn sulfide is 70.0 pieces/mm2 or less, and an amount of oxide is 25.0 pieces/mm2 or less.

1 . A steel material consisting of: in mass %,
 C: 0.09 to 0.16%,   Si: 0.01 to 0.50%,   Mn: 0.40 to 0.60%,   P: 0.030% or less,   S: 0.025% or less,   Cr: 0.90 to 2.00%,   Mo: 0.10 to 0.40%,   Al: 0.005 to 0.030%,   Ti: 0.010 to less than 0.050%,   Nb: 0.010 to 0.030%,   N: 0.0080% or less,   O: 0.0030% or less,   B: 0.0003 to 0.0030%,   Ca: 0.0005 to 0.0050%,   Cu: 0 to 0.50%,   Ni: 0 to 0.30%, and   V: 0 to 0.10%,   with the balance being Fe and impurities, and   the steel material satisfying Formula (1) to Formula (3), wherein   in a cross section parallel to an axial direction of the steel material, an amount of Mn sulfide having, in mass %, a Mn content of 10.0% or more, a S content of 10.0% or more, and an O content of less than 10.0% is 70.0 pieces/mm 2  or less, and an amount of oxide having an O content of 10.0% or more is 25.0 pieces/mm 2  or less:
   0.140<C+0.194×Si+0.065×Mn+0.012×Cr+0.033×Mo+0.067×Ni+0.097×Cu+0.078×Al<0.235  (1)
 
   13.0<(0.70×Si+1)×(5.1×Mn+1)×(2.2×Cr+1)×(3.0×Mo+1)×(0.36×Ni+1)<45.0   (2)
 
   0.004<Ti—N×(48114)<0.030  (3)
 
   where, each element symbol of the Formulae (1) to (3) is substituted by the content (mass %) of the corresponding element, and if the corresponding element is not contained, the element symbol is substituted by “0”.   
     
     
         2 . The steel material according to  claim 1 , wherein
 when a radius in a cross section perpendicular to an axial direction of the steel material is defined as R (mm), in a microstructure in the cross section perpendicular to the axial direction of the steel material, an area fraction of bainite in at least an outer layer region from a surface to 0.1R depth is 95.0% or more.   
     
     
         3 . The steel material according to  claim 1 , wherein
 when a radius in a cross section perpendicular to an axial direction of the steel material is defined as R (mm), in a microstructure in the cross section perpendicular to the axial direction of the steel material, at least an outer layer region from the surface to 0.1R depth is composed of ferrite and cementite, and a spheroidization ratio of the cementite in the outer layer region is 90.0% or more.   
     
     
         4 . The steel material according to  claim 1 , containing,
 one or more elements selected from the group consisting of: in mass %,   Cu: 0.01 to 0.50%,   Ni: 0.01 to 0.30%, and   V: 0.01 to 0.10%.   
     
     
         5 . The steel material according to  claim 2 , containing,
 one or more elements selected from the group consisting of: in mass %,   Cu: 0.01 to 0.50%,   Ni: 0.01 to 0.30%, and   V: 0.01 to 0.10%.   
     
     
         6 . The steel material according to  claim 3 , containing,
 one or more elements selected from the group consisting of: in mass %,   Cu: 0.01 to 0.50%,   Ni: 0.01 to 0.30%, and   V: 0.01 to 0.10%.