Bearing steel material with excellent rolling fatigue property and bearing part

Abstract

A bearing steel material which contains 0.8-1.1 mass % C, 0.15-0.8 mass % Si, 0.1-1.0 mass % Mn, 1.3-1.8 mass % Cr, up to 0.05 mass % P (0 mass % is excluded), up to 0.015 mass % S (0 mass % excluded), 0.0002-0.005 mass % Al, 0.0002-0.0020 mass % Ca, 0.0005-0.010 mass % Ti, up to 0.0080 mass % N (0 mass % is excluded), and up to 0.0025 mass % O (0 mass % is excluded). The steel material contains oxide inclusions which have an average composition that comprises, in terms of mass %, 20-50% CaO, 20-50% Al 2 O 3 , 20-70% SiO 2 , and 3-10% TiO 2 .

1 . A bearing steel material, comprising:
 iron,   from 0.8 to 1.1 mass % of C,   from 0.15 to 0.8 mass % of Si,   from 0.1 to 1.0 mass % of Mn,   from 1.3 to 1.8 mass % of Cr,   more than 0 mass % and 0.05 mass % or less of P,   more than 0 mass % and 0.015 mass or less of S,   from 0.0002 to 0.005 mass % of Al,   from 0.0002 to 0.0020 mass % of Ca,   from 0.0005 to 0.0050 mass % of Ti,   more than 0 mass % and 0.0080 mass % or less of N, and   more than 0 mass % and 0.0025 mass % or less of O,   wherein the steel material comprises oxide inclusions, and the oxide inclusions comprise, on the mass % basis,   from 20 to 50% of CaO,   from 20 to 50% of Al 2 O 3 ,   from 20 to 70% of SiO 2 , and   from 3 to 10% of TiO 2 .   
     
     
         2 . The bearing steel material according to  claim 1 , wherein an aspect ratio, which is major diameter/minor diameter, of the oxide inclusions present on a surface cross sectioned in parallel to the longitudinal direction of the steel material is restricted to 3.0 or less in average. 
     
     
         3 . The bearing steel material according to  claim 2 , wherein the aspect ratio is 1.0 or more in average. 
     
     
         4 . A bearing part comprising the bearing steel material according to  claim 1 . 
     
     
         5 . A bearing part comprising the bearing steel material according to  claim 2 . 
     
     
         6 . A bearing part comprising the bearing steel material according to  claim 3 . 
     
     
         7 . The bearing steel material according to  claim 1 , which comprises Ti of from 0.0008 to 0.0050 mass %. 
     
     
         8 . The bearing steel material according to  claim 1 , which comprises Ti of from 0.0011 to 0.0050 mass %. 
     
     
         9 . The bearing steel material according to  claim 1 , which comprises Ti of from 0.0005 to 0.0030 mass %.