| 摘要 |
PROBLEM TO BE SOLVED: To improve the life and the quality of the plug without supplying lubricant specially to the piercing of an alloy by constructing a part including at least the tip of the plug by a graphite-crystallized cast iron material with a lubrication effect and the remainder by a low allot steel respectively, and performing the scale treatment of a part constructed by at least the low alloy steel for the purpose of heat resistance and wear resistance. SOLUTION: The heat input of the plug during piercing a press roll is largest at the tip of the plug and it reaches 1300 deg.C on its surface layer. Therefore, if a cast iron material with a low melting point is used in this part, the case iron material is melted at this temperature. A load can be reduced by the lubrication performance of contained graphite, and since an iron-component is supplied, it has an effect quickening the generation of scale on the surface layer of the plug. In this case, it is preferable that a diameter part C' corresponding to 20 to 90% of the diameter C of the plug from its tip, is manufactured with graphite-crystallized case iron 1. A rear end part is used by generating the scale 100 to 300μm in thickness on the surface layer of a Cr-Ni base low alloy steel part 2 being used usually.
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