| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot-dip galvannealed steel sheet which suppresses the formation of an untransformed structure, has superior adhesiveness between a steel sheet and a galvanizing layer, and also has high strength and superior workability (particularly extensibility). SOLUTION: The galvannealed steel sheet employs a steel sheet composed of, 0.10-0.30% C (which means mass% hereafter for a chemical componential composition), 1.0-3.0% Si, 1.0-5.0% Mn, 0.1% or less P (excluding 0%), 0.01% or less S (excluding 0%), 0.01-0.5% Al, and the balance iron with unavoidable impurities. The manufacturing method includes holding the steel sheet at the austenitizing temperature (Ac3 point) or higher, cooling the steel sheet to a temperature range of (Ms point - 50°C) to the Bs point, holding the steel sheet at the same temperature range for 300 seconds or longer, and then subjecting the steel sheet to hot-dip galvanizing and alloying treatment, sequentially in a hot-dip galvanizing line. COPYRIGHT: (C)2010,JPO&INPIT
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