| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacturing alloyed hot dip galvanized steel sheet capable of suppressing defective plating and delay of a galvannealing time even when the content of Si is 0.2 mass% or more. SOLUTION: The method of manufacturing alloyed hot dip galvanized steel sheet includes: an annealing process of drying a steel belt washed with the washing liquid for hot dip galvanization containing 0.01 mass% or more of dicarboxylic acids which are represented by a general formula HOCO-(CH<SB>2</SB>)<SB>n</SB>-COOH (n is an integer of 8 or less) and annealing the steel belt in the temperature range of 700 to 900°C for 30 to 60 sec; a cooling process of cooling the steel belt to the temperature range of 350 to 550°C with a cooling speed of 3 to 200°C/s; a retention process of retaining the steel belt in the temperature range of 350 to 550°C for 10 to 90 sec; a plating process of immersing the steel belt into a hot dip galvanization bath of which the total Al concentration is adjusted to be 0.08 to 0.5 mass%; and, further as necessary, an alloying process in the temperature range of 450 to 580°C. Therein, a hydrogen concentration in an environment from the annealing process to the retention process is 2 to 40 volume% and a dew point DM of the environment in the annealing process and a dew point DL of the environment in the retention process satisfy the following relation: DL≤-30°C and DM-DL≥10°C. COPYRIGHT: (C)2010,JPO&INPIT |
