Bearing part and rolling bearing

Abstract

Each of an outer race, an inner race and a ball as a bearing part is a bearing part made of JIS standard SUJ2 and having a carbonitrided layer formed in a surface thereof, wherein, after heat treatment at a heating temperature of 500° C. for a retention time of one hour is performed, a Vickers hardness at a position with a depth of 0.02×T+0.175 (mm) from the surface is higher than a Vickers hardness at a core portion, which is a region where the carbonitrided layer is not formed in a thickness direction of the bearing part, by not less than 80 HV, where T represents the time of carbonitriding treatment for forming the carbonitrided layer.

1 . A bearing part made of JIS standard SUJ2 and having a carbonitrided layer formed in a surface thereof, manufactured by a process including the step of:
 carbonitriding treatment for a time of T hours to form said carbonitrided layer;   heat treatment at a heating temperature of approximately 500° C. for a retention time of approximately one hour;   after the heat treatment, measuring a first Vickers hardness, at a position with a depth of approximately 0.02×T+0.175+t (mm) from the surface, and a second Vickers hardness, at a core portion where said carbonitrided layer is not formed in a thickness direction of said bearing part; and   after the measuring, if the first Vickers hardness is measured to be higher than the second Vickers hardness by not less than 80 HV, grinding the surface of the bearing part to remove a thickness of t mm of the surface of the bearing part.   
     
     
         2 . The bearing part according to  claim 1 , wherein
 the time of said carbonitriding treatment is not less than 4 hours and not more than 10 hours.   
     
     
         3 . The bearing part according to  claim 1 , wherein
 the time of said carbonitriding treatment is not less than 6 hours and not more than 8 hours.   
     
     
         4 . The bearing part according to  claim 1 , wherein
 said carbonitriding treatment is performed in a temperature range of not less than 840° C. and not more than 860° C.   
     
     
         5 . The bearing part according  claim 1 , wherein
 a prior austenite crystal grain size is within a range of JIS standard No. 9 to No. 11.   
     
     
         6 . A rolling bearing comprising the bearing part as recited in  claim 1 . 
     
     
         7 . The rolling bearing according to  claim 6 , wherein
 the rolling bearing is any one of a deep groove ball bearing, a conical roller bearing, a cylindrical roller bearing, and a needle roller bearing.   
     
     
         8 . A bearing part made of JIS standard SUJ2 and having a carbonitrided layer formed in a surface thereof, manufactured by a process including the step of:
 carbonitriding treatment for a time T to form said carbonitrided layer;   heat treatment at a heating temperature not less than 300° C. and not more than 700° C.;   after the heat treatment, measuring a first Vickers hardness, at a position with a depth of approximately 0.02×T+0.175+t (mm) from the surface, and a second Vickers hardness, at a core portion where said carbonitrided layer is not formed in a thickness direction of said bearing part;   after the measuring, if the first Vickers hardness is measured to be higher than the second Vickers hardness by not less than 80 HV, grinding the surface of the bearing part to remove a thickness oft mm of the surface of the bearing part.   
     
     
         9 . A bearing part made of JIS standard SUJ2 and having a carbonitrided layer formed in a surface thereof, manufactured by a process including the step of:
 carbonitriding treatment for a time T to form said carbonitrided layer;   heat treatment at a heating temperature not less than 300° C. and not more than 700° C.;   grinding a surface of the bearing part to remove a thickness of the surface of the bearing part; and   determining whether a first Vickers hardness, at a position with a depth of approximately 0.02×T+0.175 (mm) from the ground surface, is higher than a second Vickers hardness, at a core portion where said carbonitrided layer is not formed in a thickness direction of said bearing part by not less than 80 HV.   
     
     
         10 . A method of manufacturing a bearing part made of JIS standard SUJ2 and having a carbonitrided layer formed in a surface thereof, including the step of:
 carbonitriding treatment for a time T to form said carbonitrided layer;   heat treatment at a heating temperature not less than 300° C. and not more than 700° C.;   after the heat treatment, measuring a first Vickers hardness, at a position with a depth of approximately 0.02×T+0.175+t (mm) from said surface, and a second Vickers hardness, at a core portion where said carbonitrided layer is not formed in a thickness direction of said bearing part;   after the measuring, if the first Vickers hardness is measured to be higher than the second Vickers hardness by not less than 80 HV, grinding a surface of the bearing part to remove a thickness of t mm of the surface of the bearing part.