PURPOSE: To reduce internal scab generated at the time of rolling martensitic stainless steel or duplex stainless steel with an elongator.
CONSTITUTION: When a tube stock 4 made of martensitic stainless steel (or duplex stainless steel) which is represented by SUS 420 J1 steel of the JIS standard (or SUS 329 J1 steel) having ≤0.25 wall thickness/outside diameter ratio is drawn and rolled with the elongator 5, the draft Rd of outside diameter in a plug contact starting position is taken as 0.04<Rd<-0.83N +15.15 (or 0.04<Rd<-0.8N+14.0). Where, Rd=(Din Dp)/Din. (N: the number of working with a pair of rolls from the roll contact starting position of a rolled stock to the plug contact starting position in a outside diameter rolling-down process, Din: the outside diameter of the tube stock on the inlet side, Dp: the roll gap in the plug contact starting position.) In this way, the generation of internal flaws is drastically reduced and the quality and yield are improved.
SOGO YASUO
NARASAKI KOJI
BITO AKIKAGE
SAKAMOTO TOSHIHARU
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