Method for heat treating a steel component

Abstract

A method for heat treating a steel component includes heating the component to a temperature at or above the austenitizing temperature and holding the component at or above the austenitizing temperature for a time sufficient to at least partially austenitize the steel, cooling the component to a first temperature in a temperature range of 200° C. to 270° C. and holding the component in the temperature range for at most 6 hours, thereby transforming at least a portion of the austenite into bainite, cooling the component to a temperature of from −30° C. to 30° C., thereby forming martensite; and reheating the component to a second temperature in the temperature range, holding the component in the temperature range for at most 6 hours and then cooling the component to a temperature of from −30° C. to 30° C., thereby transforming a further portion of the austenite into bainite and forming tempered martensite.

What is claimed is: 
     
         1 . A method for heat treating a steel component, the method comprising:
 (i) providing a steel component formed of a high-carbon bearing steel having an austenitizing temperature;   (ii) heating the component to a temperature at or above the austenitizing temperature and holding the component at or above the austenitizing temperature for a time sufficient to at least partially austenitize the steel;   (iii) after step (ii), cooling the component to a first temperature in a first temperature range of 200° C. to 270° C. and holding the component in the first temperature range for at most 6 hours, thereby transforming at least a portion of the austenite into bainite;   (iv) after step (iii), cooling and/or quenching the component to a temperature of from −30° C. to 30° C., thereby forming martensite; and   (v) after step (iv) reheating the component to a second temperature in the first temperature range, holding the component in the first temperature range for at most 6 hours and then cooling and/or quenching the component to a temperature of from −30° C. to 30° C., thereby transforming a further portion of the austenite into bainite and forming tempered martensite.   
     
     
         2 . The method according to  claim 1 ,
 wherein holding the component in the first temperature range for at most 6 hours in step (iii) comprises holding the component in the first temperature range for at most 4 hours.   
     
     
         3 . The method according to  claim 1 , further comprising, after step (v), reheating the component to a third temperature in the first temperature range, holding the component in the first temperature range for at most 6 hours and then cooling and/or quenching the component to a temperature of from −30° C. to 30° C., thereby transforming a further portion of the austenite into bainite. 
     
     
         4 . The method according to  claim 1 , wherein the reheating the component is performed in a tempering furnace. 
     
     
         5 . The method according to any  claim 1 , wherein steps (ii)— (v) are completed within 24 hours. 
     
     
         6 . The method according to  claim 1 , wherein steps (ii)— (v) are completed within 22 hours. 
     
     
         7 . The method according to  claim 1 ,
 wherein, in step (iii), the component is cooled to a temperature of from 220° C. to 240° C.   
     
     
         8 . The method according to  claim 1 ,
 wherein in step (v) the second temperature is greater than the first temperature.   
     
     
         9 . The method according to  claim 1 ,
 wherein, in step (iii), the first temperature is from 220° C. to 240° C. and in step (v) the second temperature is greater than the first temperature.   
     
     
         10 . The method according to  claim 1 ,
 wherein cooling and/or quenching the component comprises cooling the component at a rate of from 0.5° C. to 1.0° C. per minute to a temperature in a second temperature range of 80° C. to 120° C. and then quenching the component.   
     
     
         11 . The method according to  claim 1 ,
 wherein the steel component is a tapered inner bearing ring or a tapered outer bearing ring.   
     
     
         12 . An inner bearing ring or an outer bearing ring formed by the method of  claim 1 . 
     
     
         13 . A method for heat treating a steel component, the method comprising:
 (i) providing a steel component formed of a high-carbon bearing steel having an austenitizing temperature;   (ii) heating the component to a temperature at or above the austenitizing temperature and holding the component at or above the austenitizing temperature for a time sufficient to at least partially austenitize the steel;   (iii) after step (ii), cooling the component to a first temperature in a first temperature range of 220° C. to 240° C. and holding the component in the first temperature range for at most 4 hours, thereby transforming at least a portion of the austenite into bainite;   (iv) after step (iii), cooling the component at a rate of from 0.5° C. to 1.0° C. per minute to a temperature in a second temperature range of 80° C. to 120° C. and then quenching the component to a temperature of from −30° C. to 30° C., thereby forming martensite; and   (v) after step (iv) reheating the component to a second temperature in the first temperature range, holding the component in the first temperature range for at most 6 hours and then cooling the component at a rate of from 0.5° C. to 1.0° C. per minute to a second temperature in the second temperature range and then quenching the component to a temperature of from −30° C. to 30° C., thereby transforming a further portion of the austenite into bainite and forming tempered martensite,   wherein the second temperature is greater than the first temperature, and   wherein steps (ii)-(v) are completed within 22 hours.   
     
     
         14 . A bearing ring having a raceway track and being formed of a high-carbon bearing steel;
 wherein a microstructure of the bearing steel forming the raceway track comprises at least 60 vol. % bainite; and   wherein a microstructure of the bearing steel away from the raceway track comprises at most 5 vol. % retained austenite.   
     
     
         15 . The bearing ring according to  claim 14 , wherein the ring has a bore diameter of at least 0.5 m. 
     
     
         16 . The bearing ring according to  claim 14 , wherein the ring has a bore diameter of at least 1.5 m.