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1. (WO2011151995) METHOD FOR SUPPRESSING SURFACE INDENTATION FLAW IN ELEMENT TUBE FOR SEAMLESS STEEL TUBE

Pub. No.:    WO/2011/151995    International Application No.:    PCT/JP2011/002907
Publication Date: Dec 8, 2011 International Filing Date: May 25, 2011
IPC: B21D 3/02
B21D 3/00
Applicants: SUMITOMO METAL INDUSTRIES, LTD.
住友金属工業株式会社
INUZUKA, Ryohei
犬塚 僚平
KOCHI, Yasuhiro
神地 康弘
Inventors: INUZUKA, Ryohei
犬塚 僚平
KOCHI, Yasuhiro
神地 康弘
Title: METHOD FOR SUPPRESSING SURFACE INDENTATION FLAW IN ELEMENT TUBE FOR SEAMLESS STEEL TUBE
Abstract:
An element tube (an element tube for a seamless steel tube) to which straightening by a straightener is applied after heat-transferred and tube-made, and which is then submitted to cold working, wherein, during the straightening by the straightener, cooling water is sprayed all over the surfaces of rolls (1a, 1b) constituting the straightener, and soft reduction is applied to the element tube with the loads added to the straightener rolls (1a, 1b) as 550 kN or less, thereby making it possible to effectively suppress surface indentation flaws occurring in the element tube for the seamless steel tube. It is effective as a means for the soft reduction to use a hot straightener for adding straightening such as bend removal to the element tube in a temperature range of 500-550˚C inclusive after heat-transferred and tube-made. It is desirable to perform the spraying of the cooling water all over the surfaces of the rolls (1a, 1b) by one or more means of the increased wide angle of the tip shape of cooling water nozzles, the proper arrangement of the cooling water nozzles, and an increase in the water volume of cooling water to be sprayed.