| 摘要 |
PROBLEM TO BE SOLVED: To obtain a steel pipe having high strength and high resistance to corrision, that is, the steel pipe of a heavy-load bearing material, after obtaining a hollow pipe stock by piercing a material to be rolled whose hot ductility is lowered at a temp. not less than a specified temp. at a temp. less than the hot ductility lowering temp., by assistantly heating this pipe stock before a mandrel bar is inserted and rolling this hollow pipe stock which is assistantly heated with a mandrel mill. SOLUTION: A round billet which is heated with a heating furnace 1 so that the temp. of the material to be rolled after piercing is less than the temp. (>=1000 deg.C) where the hot ductility is rapidly lowered is pierced with a piercer 2 at the temp. less than the hot ductility lowering temp. and the hollow pipe stock is conveyed to a shape straightening machine 3 and, moreover, heated before inserting a mandrel bar with a solenoid type induction heating device 4 for assistantly heating. By inserting the mandrel bar into the hollow pipe stock which is heated to a degree that the rolling capacity of the mandrel mill 5 is satisfied, the pipe stock is rolled to a prescribed thickness with the mandrel mill 5, the mandrel bar is pulled out and the pipe stock is conveyed to the reheating furnace in the next stage.
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