| 摘要 |
PROBLEM TO BE SOLVED: To prevent generation of defects such as crack in the end part of a tube stock and the like due toδferrite at the time of piercing rolling of cast billet for seamless tube with a piercer by rolling billet under satisfying specified condition so as not to allowδferrite to appear in the metallic structure of tube stock. SOLUTION: Billet of high chrome alloy containing >=9wt.% Cr is rolled under a constitution satisfying the inequalities 0.1<=EA<=1.6, EA<=0.075T-89.9, EA<=-0.03T+39.1, and 1200<=T<=1300. In these inequalities, EA: average strain velocity of billet=(dE/dt) (sec<-1> ), E: strain of billet=1n (So/S) (-), So: sectional area of billet at the inlet of piercer(cm<2> ), S: sectional area of billet at the outlet of piercer(cm<2> ), t: time (sec), and T: temperature of billet at the heating furnace ( deg.C). The strain velocity EA is set at a suitable value by adjusting sectional size of tube stock billet, inclination angle of roll of piecer, opening of roll and number of revolution of roll.
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