JPS6133068B2 - - Google Patents

Description

[Detailed description of the invention] The present invention has excellent corrosion resistance and does not cause "kinks" on the plating surface.
The present invention relates to a method for producing hot-dip galvanized steel sheets that are free from "hair" and have good gloss.

Hot-dip galvanized steel sheets have rapidly grown due to their excellent anti-corrosion properties, and are used as corrosion-resistant materials in a wide range of fields such as building materials, home appliance materials, and automobile body materials.
It has reached 6 million tons, accounting for approximately 30% of cold-rolled steel sheets.

Zinc is an inexpensive and chemically active metal, and at the same time, the compound produced by the reaction is dense, so that a moderate corrosion rate can be obtained, making it a metal suitable for corrosion protection of steel materials. Generally, the sacrificial anticorrosion ability of zinc against steel materials in a neutral environment is in an overly protective state, and even if the corrosion rate of zinc is further suppressed, sufficient sacrificial anticorrosion ability can be exhibited. For example, when measured in 3% saline, sacrificial corrosion protection against steel is effective even if the corrosion rate of pure zinc is suppressed to 1/20 to 1/50. Therefore, in a neutral environment, if the corrosion rate of zinc can be suppressed to 1/20 to 1/50 by some means, a life of 20 to 50 times longer than that of pure zinc with the same basis weight can be achieved, and the current It is possible to lower the basis weight to 1/20 to 1/50 to obtain the same performance.

The present invention focuses on this point and is a method for manufacturing a plated steel strip, which is as follows.

(1) A method for producing a hot-dip galvanized steel strip, which includes a step of plating at least one side in a zinc bath and controlling the amount of plating, comprising 0.1 to 2.0% Mg and 0.1 to 0.8% Sn.
%, the remainder consisting of zinc and unavoidable impurities, and at least part of the time during which the plating metal adhering to the steel strip surface solidifies from the bath surface is surrounded by a seal box, and the bath surface side including the wiping nozzle is At the same time, the oxygen concentration on the solidification zone side of the plating metal above it is not controlled if the plating weight is less than 50 g/ ^m2 , and the plating weight is 50 g/m2. ² or more 200
The feature is that the unsolidified plating metal on the surface of the steel strip is solidified by controlling the plating weight to 100 ppm or more when the plating weight is less than 200 g/ ^{m2 ,} and from 100 ppm to less than the atmospheric concentration when the plating weight is 200 g/m2 or more. A method for manufacturing a matte steel strip.

(2) The method for producing a plated steel strip according to item 1 above, characterized in that the bath surface side is a space of 1 m at most above the wiping nozzle from the plated bath surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The mode of carrying out the present invention will be described below in detail with reference to the drawings.

Figure 1 shows electrolytic zinc (99.97% purity) and its
The corrosion resistance of a steel plate hot-dipped using a Sendzimer pilot line was tested for 3 days in accordance with the salt spray test method stipulated in Japanese Industrial Standards (JIS) Z2371 using a mixed zinc bath containing Mg as shown in Figure 1. This is a record of the corrosion loss measured using a straight line.
N ₁ indicates the level of corrosion rate of electrolytic zinc without Mg addition, and curve A ₁ is the result of electrolytic zinc bath with Mg addition. Figure 1 shows that the corrosion resistance of hot-dip galvanized steel sheets in an electrolytic zinc bath is significantly improved by the addition of Mg.
Compared to no additive, Mg0.5% reduces weight by 1/10, Mg1.0%
Then, the weight will be reduced by 1/14. However, adding a large amount of Mg is meaningless; adding 1.5% Mg provides only a slight improvement over adding 1.0%, and even adding 2.0% Mg causes almost no change and the performance is saturated. Therefore, for the purpose of improving corrosion resistance, the effective amount of Mg added is 0.1 to 2.0%.

A hot-dip galvanized steel sheet composition characterized by containing 0.1 to 2.0% Mg as an alloying element and having an Al content of 0.01% or less was filed by the applicant in a patent application filed on April 25, 1980. Although a patent application has been filed in No. 55152/1980, the present invention relates to a manufacturing method characterized by controlling the oxygen concentration of the atmosphere in the unsolidified region and solidified region of the Mg-containing Zn plating metal.

Steel plates plated with a zinc bath containing Mg are extremely effective in improving corrosion resistance, but are also effective in improving topcoatability. In particular, with regard to phosphate treatment performed as a painting treatment, a stable phosphate film can be formed under the same conditions as conventional galvanized steel sheets. Top coats have excellent performance for almost all types of coatings, including electrodeposition coatings (cationic and anionic) and baking coatings used in the automobile industry, primer coatings for color steel plates, baking coatings for home appliances, etc. demonstrate.

As mentioned above, the addition of Mg to the zinc bath is very effective in improving corrosion resistance, but there are many problems in terms of manufacturing and quality. In terms of manufacturing, the increase in dross,
There are problems such as uncontrollable basis weight and poor appearance due to skin covering, etc., and quality problems such as discoloration such as blackening, unevenness, spangle-free, etc. occur. That is, simply using the current production method with a bath containing Mg does not allow production, and in terms of quality, it can only be applied to extremely limited fields. In the meantime, the inventors conducted many pilot line experiments and were able to complete a galvanized steel sheet containing Mg that solved the above-mentioned problems.

In particular, regarding blackening, steel strips treated with plating baths containing Mg may develop blackening over time. Blackening is a phenomenon in which Mg and plating metal oxidize over time, causing the surface to turn black. In order to prevent such blackening phenomenon, it has been found through experiments conducted in the present invention that it is extremely effective to further add Sn to the zinc bath to which Mg has been added. Figure 2 is 38℃
This is a diagram arranging the timing of blackening when each sheet is exposed and stored in a constant temperature room in terms of Mg% and Sn%. The time of occurrence of black discoloration is marked with ● (within 1 month)○†a double

Claims (1)

[Claims] 1. A method for producing a hot-dip galvanized steel strip, which includes plating at least one side in a zinc bath and controlling the amount of plating, comprising 0.1 to 2.0% Mg, 0.1 to 0.8% Sn, and the remainder. uses a bath consisting of zinc and unavoidable impurities,
enclosing at least a portion of the plated metal adhering to the steel strip surface from the bath surface with a seal box during solidification;
The oxygen concentration on the bath surface side including the wiping nozzle is 100%.
~1000ppm, and the oxygen concentration on the solidification zone side of the plating metal above it is set to 50g/
If the plating weight is less than 50 g/m ² or ^more and less than 200 g/m ² , there is no control.
A method for producing a plated steel strip, which comprises solidifying the unsolidified plated metal on the surface of the steel strip by controlling the concentration to 100 ppm or more and, if the plated surface adhesion is 200 g/m ² or more, to less than 100 ppm to the atmospheric concentration. 2. Claim 1, in which the bath surface side is a space of 1 m at most above the wiping nozzle from the plating bath surface.
A method for producing a plated steel strip as described in Section 1.