Steel material excellent in rolling fatigue property

Abstract

A steel material excellent in rolling fatigue property, the steel material including, in mass %: C: 0.10% to 1.50%, Si: 0.01% to 0.80%, Mn: 0.10% to 1.50%, Cr: 0.02% to 2.50%, Al: 0.002% to less than 0.010%, Ce+La+Nd: 0.0001% to 0.0025%, Mg: 0.0005% to 0.0050%, O: 0.0001% to 0.0020%, Ti: 0.000% to less than 0.005%, N: 0.0180% or less, P: 0.030% or less, S: 0.005% or less, Ca: 0.0000% to 0.0010%, V: 0.00 to 0.40%, Mo: 0.00 to 0.60%, Cu: 0.00 to 0.50%, Nb: 0.000 to less than 0.050%, Ni: 0.00 to 2.50%, Pb: 0.00 to 0.10%, Bi: 0.00 to 0.10%, B: 0.0000 to 0.0050%, and the balance being Fe and an impurity, wherein a fatigue-initiating inclusion detected by an ultrasonic fatigue test contains one or more of Ce, La, and Nd, and Mg, Al, and O, and a composition ratio in the fatigue-initiating inclusion satisfies Formula (1).

What is claimed is: 
     
         1 . A steel material excellent in rolling fatigue property, the steel material comprising, in mass %:
 C: 0.10% to 1.50%,   Si: 0.01% to 0.80%,   Mn: 0.10% to 1.50%,   Cr: 0.02% to 2.50%,   Al: 0.002% to less than 0.010%,   Ce+La+Nd: 0.0001% to 0.0025%,   Mg: 0.0005% to 0.0050%,   O: 0.0001% to 0.0020%,   Ti: 0.000% to less than 0.005%,   N: 0.0180% or less,   P: 0.030% or less,   S: 0.005% or less,   Ca: 0.0000% to 0.0010%,   V: 0.00 to 0.40%,   Mo: 0.00 to 0.60%,   Cu: 0.00 to 0.50%,   Nb: 0.000 to less than 0.050%,   Ni: 0.00 to 2.50%,   Pb: 0.00 to 0.10%,   Bi: 0.00 to 0.10%,   B: 0.0000 to 0.0050%, and   the balance being Fe and an impurity,   wherein a fatigue-initiating inclusion detected by an ultrasonic fatigue test contains Mg, Al, and O, and one or more of Ce, La, and Nd, and a composition ratio in the fatigue-initiating inclusion satisfies Formula (1),
   (Ce %+La %+Nd %+Mg %)/Al %≥0.20  Formula (1),
 
   
       where Ce %, La %, Nd %, Mg %, and Al % are atomic (at) % of respective Ce, La, Nd, Mg, and Al contained in the fatigue-initiating inclusion. 
     
     
         2 . The steel material excellent in rolling fatigue property according to  claim 1 , wherein, in mass %, C: 0.10% to less than 0.45%, and Cr: 0.02 to 1.50%. 
     
     
         3 . The steel material excellent in rolling fatigue property according to  claim 1 , wherein, in mass %, C: 0.45% to less than 0.90%, and Cr: 0.70 to 2.50%. 
     
     
         4 . The steel material excellent in rolling fatigue property according to  claim 1 , wherein, in mass %, C: 0.90% to 1.50%, and Cr: 0.70 to 2.50%.