Heat-treated roller bearing ring

An inner ring or outer ring for a roller bearing,

• wherein at least a core of the inner or outer ring is composed of a steel composition comprising:
• 0.39-0.45 wt. % carbon;
• 0.2-0.4 wt. % silicon;
• 0.7-0.8 wt. % manganese;
• 1.0-1.1 wt. % chromium;
• 0.15-0.3 wt. % molybdenum;
• 0-0.7 wt. % nickel;
• 0-0.02 wt. % phosphorus;
• and
• 0-0.02 wt. % sulfur;
• the balance being iron and unavoidable impurities;
• wherein:
• the core has a microstructure that comprises bainite;
• and
• a carbonitrided case layer is provided on a surface of the inner ring or the outer ring adjacent to the core.

A method for heat treating an inner ring or an outer ring for a roller bearing, the method comprising:

• providing a ring formed from a steel composition comprising:
• 0.30-0.45 wt. % carbon;
• 0.1-0.7 wt. % silicon;
• 0.6-0.9 wt. % manganese;
• 0.9-1.2 wt. % chromium;
• 0.15-0.7 wt. % molybdenum;
• 0-2.0 wt. % nickel;
• 0-0.02 wt. % phosphorus;
• and
• 0-0.02 wt. % sulfur;
• the balance being iron and unavoidable impurities;
• (ii) subjecting the ring to a carbonitriding process to obtain a carbonitrided ring having a carbonitrided case layer provided on a surface of the carbonitrided ring;
• and
• (iii) after step (ii), holding the carbonitrided ring at a temperature of 210° C. to 250° C. for 4-7 hours to obtain a heat-treated ring having a microstructure that comprises bainite.