| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength alloyed-galvanized steel sheet excellent in the energy-absorbing characteristics with which as the alloyed-galvanized steel sheet by using the ultra-high strength steel sheet having 980 MPa class or higher as the base material, even at colliding time of car, a brittle fracture is difficult to generate. SOLUTION: To a steel billet having a component composition comprising, by mass, 0.05-0.20% C, 0.3-1.5% Si, 1.0-2.5% Mn,≤0.1% P and the balance Fe with inevitable impurities, after applying a hot-rolling, pickling and cold-rolling, in the galvanizing line, the annealing, in which after holding at 750-900°C, the cooling is performed at≥2°C/s average cooling speed, and thereafter, the galvanizing is applied. After galvanizing treatment, immediately, the alloying treatment is applied in the temperature zone of 460-530°C, the micro-structure of the base material steel sheet is made to be composed of 25-50 vol% in the total of one or two kinds of martensite and retained austenite and the balance is ferrite and bainite. COPYRIGHT: (C)2009,JPO&INPIT
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