Method of producing carburizing forging steel material

A method of producing forging material for a carburizing treatment wherein the forging material is a steel material comprising:

• C:
• 0.20 to 0.30 mass %,
• Si:
• 0.03 to 1.50 mass %,
• Mn:
• 0.30 to 1.00 mass %,
• Cr:
• 0.30 to 2.50 mass %,
• Al:
• 0.025 to 0.100 mass %,
• N:
• 0.0120 to 0.0180 mass %,
• Nb:
• 0.05 to 0.10 mass %, and
• Mo:
• 0 to 0.80 mass %, and
• a balance:
• Fe and inevitable impurities,
• the method comprising:
• heating the steel material at 1300° C. or higher and forming Nb in a solid solution state in the steel material;
• rolling the steel material at the temperature of 1300° C. or higher;
• heating the rolled steel material in a range of 950 to 1050° C.;
• hot forging the steel material obtained by the heating at 950 to 1050° C. under a heating condition in a range of 950 to 1040° C.;
• adjusting the temperature of the forged steel material to 950 to 970° C. and maintaining that temperature for 1 minute or more to precipitate a Nb carbonitride in the hot forged steel material;
• cooling the Nb carbonitride precipitated steel material to a temperature range of 730 to 870° C. and maintaining that temperature for 10 minutes or longer to precipitate a ferrite phase in the Nb carbonitride precipitated steel material;
• and
• cooling the Nb carbonitride and ferrite precipitated steel material to room temperature.