| 摘要 |
PROBLEM TO BE SOLVED: To provide an innovative rapid spheroidizing annealing treatment capable of conducting a spheroidizing annealing treatment for steel in a short time, which conventionally required 6 to 11 hours treatment time.SOLUTION: A heat pattern has a fist cooling period for cooling from the soaking temperature (e.g. AC1+20°C) to the transformation start temperature (AC1) at a first cooling speed (e.g. 100°C/hour), a second cooling period for cooling from the transformation start temperature (AC1) to the transformation complete temperature (e.g. AC1-15°C) at a second cooling speed (e.g. 15°C/hour), and a third cooling period for cooling from the transformation complete temperature (e.g. AC1-15°C) to the pre-determined cooling start temperature (e.g. AC1-40°C) at a third cooling speed (e.g. 40°C/hour), and slow cooling periods for the three cooling periods. The transformation complete temperature is an estimated temperature at which complete transformation is estimated and both promoting of secure transformation completion and shortening of slow cooling periods are achieved by setting a relatively moderate third cooling speed. |
