| 摘要 |
PROBLEM TO BE SOLVED: To provide a low yield ratio steel for low temperature use which is excellent in low-temperature toughness, and is suitable as the steel for a multi-purpose tank. SOLUTION: The steel for low temperature use contains C, Si, Mn, P, S, Nb, Ti, sol.Al, N, contains two or more elements of Cu, Ni, Cr, Mo and the balance Fe with inevitable impurities, and satisfies the following formula, SP1=Cr/5+Mo/3+(Cu+Ni)/15 is 0.06-0.12%. At the position of t/4 where (t) is the thickness of the steel sheet, the texture is diplophase texture of ferrite structure and hard texture structure. The hardened structure satisfies the following formula Hvh/Hvm≥3.0, and contains≥15 pieces in the range of 100μm square, and the average grain diameter corresponding to the circle average grain diameter corresponding to the circle of the hardened structure is 2-5μm. The same of the ferrite structure is 7.5-20μm, and the aspect ratio thereof is≤2.0. Wherein, the Hvh and the Hvm express the Vickers hardness of the hardened structure and the perrite structure respectively. COPYRIGHT: (C)2010,JPO&INPIT
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