Method of forming bearing ring resistant to season cracking

Abstract

A method sets a retained austenite amount of an edge of a bearing ring of a bearing to between 3% or more and 20% or less. The method includes exposing the bearing ring to an environment having a temperature in the range of 850° C. to 930° C., an ammonia concentration, and a carbon concentration C·P in a range of 0.9 to 1.1%, for a period of not more than 5 hours. The ammonia concentration of the environment is in a range of 4 to 7 CFH. The temperature of the environment is then reduced to a temperature in a range of 800° C. to 830° C. for a second period of at least 30 minutes. The bearing ring is next quenched in oil and then heat treated in an environment set to a temperature of 160° C. to 200° C. and then air cooled.

1 . A method of producing a bearing ring with a retained austenite concentration of 3% to 20% in an edge surface, comprising: 
 forming a bearing ring of carbon steel; and    exposing the bearing ring to an environment having a temperature in the range of 850° C. to 930° C. an ammonia concentration, and a carbon concentration C·P in a range of 0.9 to less than 1.1%, for a period of not more than 5 hours.    
     
     
         2 . The method of  claim 1  further comprising setting the ammonia concentration of the environment in a range of 4 to 7 CFH.  
     
     
         3 . The method of  claim 2  further comprising reducing the temperature of the environment to a temperature in a range of 800° C. to 830° C. for a second period of at least 30 minutes after the period of not more than 5 hours is expired.  
     
     
         4 . The method of  claim 3  further comprising removing the bearing ring from the environment at the end of the second period and quenching the bearing ring in oil at a temperature in a range of 60° C. to 100° C.  
     
     
         5 . The method of  claim 4  further comprising tempering the bearing ring after the quenching in an environment set to a temperature of 160° C. to 200° C.  
     
     
         6 . The method of  claim 5  further comprising air cooling the bearing ring after the quenching.  
     
     
         7 . The method of  claim 6  wherein the carbon steel is high carbon chromium steel corresponding to Japanese Industrial Standards SUJ2.  
     
     
         8 . The method of  claim 6  wherein the carbon steel is machine structural use steel corresponding to Japanese Industrial Standards S55C.  
     
     
         9 . The method of  claim 1  further comprising setting an ammonia concentration of the environment is in the range of 4 to less than 7 CFH.  
     
     
         10 . The method of  claim 9  further comprising reducing the temperature of the environment to a temperature in a range of 800° C. to 830° C. for a second period of at least 30 minutes after the period of not more than 5 hours is expired.  
     
     
         11 . The method of  claim 10  further comprising removing the bearing ring from the environment at the end of the second period and quenching the bearing ring in oil at a temperature in a range of 60° C. to 100° C.  
     
     
         12 . The method of  claim 11  further comprising tempering the bearing ring after the quenching in an environment set to a temperature in a range of 160° C. to 200° C.  
     
     
         13 . The method of  claim 12  further comprising air cooling the bearing ring after the quenching.  
     
     
         14 . The method of  claim 13  wherein the carbon steel is high carbon chromium steel corresponding to Japanese Industrial Standards SUJ2.  
     
     
         15 . The method of  claim 13  wherein the carbon steel is machine structural use steel corresponding to Japanese Industrial Standards S55C.  
     
     
         16 . A method of producing a bearing ring with a retained austenite concentration of 3% to 20% in an edge surface, comprising: 
 forming a bearing ring of carbon steel; and    exposing the bearing ring to an environment having a temperature in the range of 850° C. to 930° C., an ammonia concentration of the environment in the range of 4 to less than 7 CFH, and a carbon concentration for a period of not more than 5 hours.    
     
     
         17 . The method of  claim 16  further comprising setting the carbon concentration C·P in a range of 0.9 to less than 1.1%,  
     
     
         18 . The method of  claim 17  further comprising reducing the temperature of the environment to a temperature in a range of 800° C. to 830° C. for a second period of at least 30 minutes after the period of not more than 5 hours is expired.  
     
     
         19 . The method of  claim 18  further comprising removing the bearing ring from the environment at the end of the second period and quenching the bearing ring in oil at a temperature in a range of 60° C. to 100° C.  
     
     
         20 . The method of  claim 19  further comprising tempering the bearing ring after the quenching in an environment set to a temperature in a range of 160° C. to 200° C.  
     
     
         21 . The method of  claim 20  further comprising air cooling the bearing ring after the quenching.  
     
     
         22 . The method of  claim 21  wherein the carbon steel is high carbon chromium steel corresponding to Japanese Industrial Standards SUJ2.  
     
     
         23 . The method of  claim 21  wherein the carbon steel is machine structural use steel corresponding to Japanese Industrial Standards S55C.