JPH0627316B2 - Method for producing steel sheet with alloyed molten zinc plating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet, and more specifically, an alloyed hot-dip galvanized sheet capable of promoting alloying after plating. The present invention relates to a method for manufacturing a steel plate.

[Prior Art] Alloyed hot-dip galvanized steel sheet whose coating layer is Zn-Fe alloy layer is widely used for automobiles, household electric appliances, etc. due to its excellent paintability and weldability. It is used.

This alloyed hot-dip galvanized steel sheet is reheated immediately after hot-dip galvanizing, so that Zn in the hot-dip galvanized layer and Fe in the base iron diffuse and the entire galvanized layer changes to a Zn-Fe alloy layer. is there.

And, in order to produce the alloyed hot-dip galvanized steel sheet with high productivity, it is necessary to increase the alloying rate of Zn and Fe, but this alloying rate is the Al concentration usually added to the plating bath. The alloying rate becomes slower as the Al concentration increases. This is clear from what is shown in FIG.

Then, the addition of Al to the plating bath, that is, the types of hot dip galvanized steel sheets include zero spangle materials and regular spangle materials that do not undergo alloying treatment other than alloying hot dip galvanized steel sheets, In many cases, these three types of plated steel sheets are made separately on the same line. To produce zero spangle material and regular spangle material, Al is added to the plating bath to secure the adhesion of the plating layer. If not, the brittle Zn-Fe alloy layer is thickly formed and the adhesion of the plating layer is reduced. This means that Al added to the plating bath reacts with the base iron more preferentially as compared with Zn to form a thin Fe-Al alloy layer, and the above Zn-
The adhesion is improved because the growth of the Fe alloy layer is suppressed. For that purpose, 0.05 to 0.5 wt% of Al is usually added to the plating bath.

However, in the production of galvannealed steel sheet,
In order to develop the Fe-Zn alloy layer to the plating layer surface,
It is necessary to promote alloying by diffusion of Fe of the base iron and Zn of the plating layer, and therefore lower the Al concentration in the plating bath to reduce the growth inhibitory effect of the Zn-Fe alloy layer by the Fe-Al alloy layer. There must be.

Then, when producing an alloyed hot-dip galvanized steel sheet after producing a zero spangle material or a regular spangle material, as a method of reducing the Al concentration in the plating bath, (1) after drawing a part of the plating bath , A method of producing an alloyed hot-dip galvanized steel sheet by introducing pure zinc metal not containing Al to reduce Al in the bath.

(2) Manufacture zero spangle material or regular spangle material while introducing pure zinc metal not containing Al, and gradually
A method for producing an alloyed hot-dip galvanized steel sheet after reducing the Al concentration to a predetermined concentration.

Is being carried out.

However, in the method (1), the pumping out of the bath,
Non-alloying melting occurs because the plating operation is interrupted by the injection of metal and the constant bath temperature is secured, and in the method (2), the Al concentration in the plating bath gradually decreases. There is a problem that the plating adhesion of the galvanized steel sheet decreases.

As another method, there is a method of plating Cu or Ni prior to hot dip galvanizing to promote the alloying reaction.
Although proposed by Japanese Patent Publication No. 8-120771, this method adds a step for plating Cu and Ni to increase the cost, and further, plated Cu and Ni are dissolved in a molten zinc bath to form a bath. There is a problem that is polluted.

Therefore, a method of increasing the alloying rate without lowering the Al concentration in the plating bath is desired.

[Problems to be Solved by the Invention] In view of various problems in the production of a conventional alloyed hot-dip galvanized steel sheet as described above, the present invention has been earnestly studied by the present inventors, and as a result, plating In the bath
It was found that the alloying rate can be significantly increased by adding a small amount of Ti to the plating bath in order to increase the alloying rate without reducing the Al concentration, and the alloying-treated hot dip galvanized steel sheet according to the present invention. Was developed.

[Means for Solving Problems] A feature of the method for producing an alloyed hot-dip galvanized steel sheet according to the present invention is that it contains Al 0.05 to 0.5 wt% and inevitable impurities, and further contains Ti of 0.001 The purpose is to immerse a steel sheet in a hot dip galvanizing bath containing ~ 0.5 wt% to perform plating, and then perform alloying treatment.

The method for producing the galvannealed steel sheet according to the present invention will be described in detail below.

First, the contained components and component ratios of the hot dip galvanizing bath used in the method for producing an alloyed hot-dip galvanized steel sheet according to the present invention will be described.

Although the content of Al is defined as 0.05 to 0.5 wt%, this is because the adhesion at the time of manufacturing zero spangle material or regular spangle material cannot be ensured if the Al content is less than 0.05 wt%, and 0.5 wt% If it is contained in excess of%, the effect of improving the adhesiveness will be saturated. Therefore, the Al content is 0.05 ~
0.5 wt% In addition, Al is added to give high corrosion resistance.
It is also effective for promoting alloying treatment of Zn-Al alloy plated steel sheet containing 0.5 to 55 wt%.

Ti is an element that affects the alloying rate, and the effect of Ti addition is shown in FIG. This Fig. 2 shows that Al in the plating bath was 0.
2wt%, coating weight 70g / m ² (one side), alloying furnace temperature 60
At 0 ° C., the relationship between the alloying heating time, which is one of the indicators of the alloying rate, and the Fe concentration in the alloyed plating layer was determined by measuring the Ti in the plating bath.
The added amount is shown as a parameter.

That is, as the alloying reaction progresses, the Zn-Fe alloy layer develops from the base iron side toward the plating layer surface, and the Fe concentration in the plating layer increases. The Fe concentration in the alloyed plating layer of the galvannealed steel sheet is approximately 9 to 13 wt%.
Is in the range.

In Fig. 2, the amount of Ti added to the plating bath increases, and the Fe concentration in the plating layer increases rapidly with the alloying time. Thus, the addition of Ti markedly increases the alloying rate. However, if the Ti addition amount is less than 0.001 wt%, the alloying promotion effect is small, and if the Ti addition amount exceeds 0.5 wt%, the alloying promotion effect is saturated. Therefore, the amount of Ti added is 0.
Specified as 001 to 0.5 wt%.

[Examples] Examples of a method for producing an alloyed hot-dip galvanized steel sheet according to the present invention will be described.

Example 1 Using a hot dip coating line, the Al concentration in the plating bath was 0.2 w
Two levels of t% and 0.1 wt% were prepared, and alloyed hot-dip galvanized steel sheets were manufactured with and without addition of Ti, and the Fe concentration in the alloyed plating layer was measured.

The results are shown in Table 1.

In Table 1, Al concentration in the plating bath is 0.2w without Ti addition.
At t%, the Fe concentration is 3.5 wt%, which is 9 to 13 wt% as described above.
%, The alloying is insufficient, and when the Al concentration in the plating bath is reduced to 0.1 wt%, the Fe concentration becomes 10.3 wt% and the alloying reaction is promoted to fall within the proper range.

Further, when the Ti addition is applied to a plating bath having an Al concentration of 0.2 wt%, which is a method for producing an alloyed hot-dip galvanized steel sheet according to the present invention, the Fe concentration in the alloyed plating layer becomes 10.6 wt% and the proper Fe content is obtained. An alloyed plating layer having a concentration is obtained. That is, almost the same alloying promotion effect as when the Al concentration was easily halved by adding a small amount of Ti to the plating bath was obtained without reducing the Al concentration in the plating bath.

Example 2 In order to confirm the energy-saving effect of adding Ti to the plating bath, various alloying furnace preset temperatures were used to produce alloyed hot-dip galvanized steel sheets, and
The Fe concentration was measured.

The results are shown in Table 2.

In Table 2, proper Fe without adding Ti in the plating bath
To obtain the concentration, the alloying furnace temperature needs to be 900 ° C.

However, in order to obtain a proper Fe concentration range by adding Ti to the plating bath by the method for producing an alloyed hot-dip galvanized steel sheet according to the present invention, the alloying furnace temperature is 600 ° C.
Is sufficient and has a great energy saving effect.

The alloying furnace temperature was set at 750 by adding Ti to the plating bath.
When the temperature is 900 ° C. or 900 ° C., the Fe concentration in the plating layer exceeds the proper range, but this suggests that the line speed can be further increased, and the productivity can be improved.

[Effects of the Invention] As described above, since the method for producing an alloyed hot-dip galvanized steel sheet according to the present invention has the above-described configuration, a small amount of Ti is added to the plating bath to reduce the Al content. It has an excellent effect that the Fe concentration can be adjusted to an appropriate concentration in the alloy plating layer without performing the above, and further, alloying after plating can be promoted.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the alloying time due to the addition of Ti and the Fe concentration in the plating layer, and FIG. 2 is a diagram showing the relationship between the Al concentration in the plating bath and the alloying treatment time.

Claims (1)

[Claims] 1. A steel sheet is immersed in a hot dip galvanizing bath containing Al of 0.05 to 0.5 wt% and unavoidable impurities and further containing 0.001 to 0.5 wt% of Ti to perform plating, and then an alloying treatment. A method for producing an alloyed hot-dip galvanized steel sheet, the method comprising: