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 plating adhesion and can obtain good plating even when hot-dip galvanized a steel sheet having a Si content of 0.2% by mass or more appearance without deteriorating tensile strength. In the present disclosure, the steel sheet is conveyed in the order of the heating zone, the soaking zone, and the cooling zone inside the annealing furnace, the steel sheet is annealed, and then hot-dip galvanized is applied to the steel sheet discharged from the cooling zone. Reducing or non-oxidizing humidified gas and reducing or non-oxidizing drying gas are supplied to the soaking zone. At this time, a CO gas concentration meter is installed at the exhaust part of the soaking zone to measure the CO gas concentration, and the decarburized layer thickness of the steel sheet is calculated from the measured CO concentration, so that the calculated decarburized layer thickness is equal to or less than the preset thickness. At least one of the above-mentioned flow rate and dew point of the humidified gas is controlled in a manner.

Description

Technical field [0001] The present invention relates to a method for producing a hot dip galvanized steel sheet using a continuous hot dip galvanizing device, and the continuous hot dip galvanizing device has an annealing furnace sequentially and has a heating tape, a homogeneous trip, and a cooling belt and a cooling strip. The downstream hot dip galvanizing equipment. Background technique [0002] In recent years, in the fields of automobiles, home appliances, building materials, the demand for high-strength steel plates (high-strength steel sheets) that contribute to the lightweight of the constructor is increasing. It can be seen that a steel sheet having a good residual gamma and a good delay can be easily formed, for example, a steel sheet having a good replenishing property, for example by containing Si in the steel, by containing Si, Al. [0003] However, when a high tension steel sheet containing (especially 0.2% by mass or more) Si is used as a base material, the follow...

AI Technical Summary

Problems solved by technology

Therefore, as the concentration of Si in the steel increases, the wettability decreases sharply, and missing plating often occurs.

In addition, even when missing plating is not achieved, 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, there is also a problem that a significant delay in alloying occurs in the alloying process after hot-dip galvanizing, which significantly hinders productivity.

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