| 摘要 |
<p>PURPOSE:To prevent the extensional deformation of a mandrel bar by the repeated use and to improve the service life. CONSTITUTION:In the mandrel bar constituted of tool steel represented by SKD61, the difference in hardness between the central part and a hardened surface layer is regulated within 15 based on Shore hardness. When the extensional deformation of the bar is caused, reduction of its outside diameter is accelerated thereby and the service life of the bar is shortened. This problem is improved particularly and the service life of the bar is extended more than doubling according to this invention method. This effect is especially remarkable in rolling alloy steel such as 13% Cr.</p> |
