| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for producing a galvannealed steel sheet excellent in coat-baking hardenability provided with strength and workability and further, BH (Baking Hardenability) and a slow-aging property at the ordinary temperature. Ž<P>SOLUTION: In the producing process for galvannealed steel sheet, a steel slab having extra-low carbon content of 0.0014-0.0025 mass% is subjected to hot-rolling, cold-rolling and continuous annealing, is once subjected to skin pass rolling, is thereafter galvanized in a continuous hot-dip galvanizing line, is further subjected to alloying heating treatment, and is again subjected to skin pass rolling. The relation between two kinds of the skin pass rolling ratios before and after galvannealing satisfies the following formula; SP1+SP2≤SP0≤0.75×SP1+1.5×SP2 (wherein, SP0:the minimum skin pass rolling ratio(%) for securing the slow aging property of the steel sheet at the time of producing the cold-rolled steel sheet with only annealing line after cold-rolling, SP1 and SP2: the respective skin pass rolling ratios(%) before and after galvannealing in the galvannealing line after the annealing line). Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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