Sumitomo Metal Industries, Inc.

Naruhito Shouji

Kunio Kondo

Kazuo Okamura

Michiharu Hariki

A method of cooling a martensitic steel pipe by cooling the inner and outer surface substantially equally while rotating the pipe around the axis, wherein the cooling rate is 8.degree. C./s or higher. The inner surface is preferably cooled by passing water without completely filling the inside of pipe. The maximum cooling rate at the both surfaces is 35.degree. C./s or lower for a martensitic stainless steel pipe. The 2-step cooling method of a martensitic stainless steel pipe, comprising the 1st air cooling where the pipe is cooled from 30.degree. C. lower than Ms(martensitic transformation start temp.) to the average of Ms and Mf(martensitic transformation finish temp.) and 2nd intensive water cooling where the the pipe is cooled down below Mf. The 3-step cooling method comprising 1st intensive cooling where the pipe is cooled from Ms+400.degree. C. to Ms, 2nd mild cooling where the pipe is cooled from Ms to the average of Ms and Mf, and 3rd intensive cooling to the Mf.

Growing community of inventors

Tonosho-machi, Japan

Naruhito Shouji