Manufacturing method of hot-dip galvanized steel sheet

Abstract

The present invention provides a method for producing a hot-dip galvanized steel sheet that has high coating adhesion and can obtain a good coating appearance even when hot-dip galvanizing is performed on a steel strip containing 0.2% by mass or more of Si. In the present invention, within the annealing furnace, the steel strip is conveyed in the order of a heating zone, a soaking zone, and a cooling zone, the steel strip is annealed, and then the steel strip discharged from the cooling zone is subjected to hot-dip galvanizing. The reducing gas or non-oxidizing gas supplied to the soaking zone is humidified gas and dry gas. While the width of the steel strip passing through the soaking zone and the passing speed are constant, fluctuations in the pressure in the annealing furnace are suppressed by adjusting the flow rate of the drying gas, and on the other hand, the moisture supplied to the soaking zone is controlled by the humidified gas. The fluctuation range of the quantity is controlled below 20%.

Description

technical field [0001] The invention relates to a method for manufacturing hot-dip galvanized steel sheets, which uses a continuous hot-dip galvanizing device with an annealing furnace and hot-dip galvanizing equipment. The above-mentioned annealing furnace is arranged in sequence with a heating zone, a soaking zone and a cooling zone. A hot-dip galvanizing plant adjoins the aforementioned cooling zone. Background technique [0002] In recent years, demand for high-tensile steel sheets (high-strength steel sheets) that contribute to weight reduction of structures has been increasing in the fields of automobiles, home appliances, and building materials. As a high-strength steel material, for example, it is known that a steel sheet with good hole expandability can be produced by including Si in the steel, and a steel sheet with good ductility can be produced by easily forming residual γ by containing Si and Al. [0003] However, when a galvannealed steel sheet is manufactured...

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Problems solved by technology

In addition, even if it is not serious enough to cause non-plating, there is a problem of poor plating adhesion

Furthermore, if Si in the steel is selectively oxidized and enriched on the surface of the steel sheet, a significant alloying delay occurs in the alloying process after hot-dip galvanizing, and there is a problem that the productivity is significantly hindered.

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