| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a production method of a mandrel bar capable of extending tool life of the mandrel bar without deterioration of profitability or a large amount of investment.SOLUTION: Provided is the production method of a mandrel bar forming a mandrel bar 1 by performing final heat treatment to a bar material which is a half-finished product having a mandrel-bar shape. During the final heat treatment, the bar material is heated to tempering temperature, and then the bar material is subjected to accelerated cooling in which cooling speed CR from the tempering temperature to 100°C is 10.0°C/minute or more and 35°C/minute or less.</p> |
