Bearing part, heat treatment method thereof, and rolling bearing

Abstract

A bearing part having long life against rolling contact fatigue, excellent in anti-crack strength and restricted in an increase of aged dimensional change, a heat treatment method thereof, and a rolling bearing including the bearing part are obtained. Steel for a bearing part is subjected to carbonitriding at a carbonitriding temperature exceeding the A 1 transformation temperature, and cooled to a temperature lower than the A 1 transformation temperature. The steel is reheated to a temperature for quenching that is not lower than the A 1 transformation temperature but lower than the carbonitriding temperature, and then quenched.

What is claimed is: 
     
         1 . A heat treatment method of a bearing part, comprising the steps of:
 carbonitriding steel for a bearing part at a carbonitriding temperature exceeding A 1  transformation temperature;   cooling the steel to a temperature lower than the A 1  transformation temperature;   reheating the steel to a temperature for quenching that is not lower than said A 1  transformation temperature but lower than said carbonitriding temperature; and   quenching the steel.   
     
     
         2 . The heat treatment method of a bearing part according to  claim 1 , wherein said temperature for quenching is in a temperature range from 790° C. to 830° C. 
     
     
         3 . A bearing part subjected to the heat treatment method of a bearing part according to  claim 2 , having austenite grains of a mean grain size of not greater than 8 μm. 
     
     
         4 . A rolling bearing, including the bearing part according to  claim 3 . 
     
     
         5 . A bearing part formed of steel for a bearing part, including a carbonitrided layer, and having austenite grains of a mean grain size of not greater than 8 μm in either one of quenched microstructure and quenched and tempered microstructure. 
     
     
         6 . The bearing part according to  claim 5 , wherein said steel for the bearing part includes, in a portion other than a carbonitrided surface layer, 0.6-1.2 wt. % of carbon, 0.15-1.1 wt. % of silicon and 0.3-1.5 wt. % of manganese. 
     
     
         7 . The bearing part according to  claim 6 , wherein said steel for the bearing part further includes chromium of not greater than 2.0 wt. %. 
     
     
         8 . The bearing part according to  claim 5 , wherein said bearing part is at least one of rolling bearing ring and rolling element of a rolling bearing. 
     
     
         9 . A rolling bearing, including the bearing part according to  claim 5 . 
     
     
         10 . A bearing part incorporated into a rolling bearing, including a carbonitrided layer, and having austenite grains of a grain size exceeding a JIS grain size number 10. 
     
     
         11 . A rolling bearing having an inner ring, an outer ring and a plurality of rolling elements,
 at least one member of said inner ring, outer ring and rolling elements being formed with the bearing part according to  claim 10 .   
     
     
         12 . A bearing part incorporated into a rolling bearing, including steel having a carbonitrided layer, and having fracture stress of not lower than 2650 MPa. 
     
     
         13 . A rolling bearing having an inner ring, an outer ring and a plurality of rolling elements,
 at least one member of said inner ring, outer ring and rolling elements being formed with the bearing part according to  claim 12 .   
     
     
         14 . A bearing part incorporated into a rolling bearing, having a carbonitrided layer, and having hydrogen content of not greater than 0.5 ppm. 
     
     
         15 . The bearing part according to  claim 14 , having austenite grains of a grain size exceeding a JIS grain size number 10. 
     
     
         16 . A rolling bearing having an inner ring, an outer ring and a plurality of rolling elements,
 at least one member of said inner ring, outer ring and rolling elements being formed with the bearing part according to  claim 14 .   
     
     
         17 . The rolling bearing according to  claim 16 , wherein austenite grains of said member have a grain size exceeding a JIS grain size number 10.