| 摘要 |
PROBLEM TO BE SOLVED: To provide a high carbon steel material suited for friction pressure welding with less increase in hardness at friction pressure welded joints, and provide its production method. SOLUTION: A steel slab containing, by mass, 0.2-0.9% C, C 0.5% or less Si, 1.5% or less Mn, 2.0% or less Cr and 0.03-0.30% Nb, and according to needs, further containing 1.0% or less Mo is hot rolled with the temperature at the end of its finish rolling controlled between [Ar3 transformation point -10 deg.C] and [Ar3 transformation point +30 deg.C], and is cooled immediately after the end of rolling, followed by winding at the temperature of 500 deg.C or less. Such a production method makes it possible to maintain 0.005% or more Nb in the material in a solid solution state, to achieve 9 or more in the austenite grain-size number measured after heat treating at 800 deg.C for 5 minutes under the oxidation process based on the specification of the JIS G 0551, and to enable the control of increase in hardness at the joint areas when friction pressure welding is performed.
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