| 摘要 |
PROBLEM TO BE SOLVED: To provide a manufacturing method of steels for cold forging excellent in cold forgeability, by heating a steel material with a Cr content lower than that of high carbon chromium bearing steels in general use as material for various parts as specified in JIS G4805 (specifically, steel material with a Cr content less than 0.9%) for spheroidizing annealing, capable of forming excellent spheroidized structure in any of a high-temperature portion and a low-temperature portion generated due to temperature distribution caused during heating for spheroidizing annealing.SOLUTION: The manufacturing method of steels for cold forging includes heating a steel material containing 0.7 to 1.5% of C and less than 0.9% (excluding 0%) of Cr, with an average lamellar spacing of pearlite structure of 130 nm or less, for spheroidizing annealing. A first spheroidizing annealing is performed such that a portion heated at the lowest temperature in the steel material due to temperature distribution caused during heating for spheroidizing annealing is subject to predetermined conditions for spheroidizing annealing, and a portion heated at the highest temperature is heated at a heating temperature of higher than point A+25°C. Subsequently a second spheroidizing annealing is performed such that the portion heated at the highest temperature in the first spheroidizing annealing is subject to predetermined conditions for spheroidizing anneal. |
