JP3367455B2 - Method for producing hot-dip coated steel sheet with uniform crystal pattern - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip Al-Zn alloy plated steel sheet and a method for producing a surface-treated steel sheet which is surface-treated.

[0002]

2. Description of the Related Art Hot dip galvanized steel sheet containing Al, especially 55
The% Al- (1.5% Si) -Zn alloy hot-dip galvanized steel sheet has a beautiful spangled appearance after plating and is excellent in corrosion resistance. Therefore, it is widely used as a roof / wall material after being plated or subjected to one or two treatments of chromate treatment or resin coating treatment without applying a colored coating after plating.

Generally, a continuous hot-dip Al-Zn alloy coated steel sheet is annealed in a continuous annealing furnace attached to the steel sheet after hot rolling → pickling or hot rolling → pickling → cold rolling, and then a snout. And is immersed in a plating bath. After that, the amount of plating adhered is controlled by the wiping nozzle, and then natural cooling, cooling by liquid spraying or air cooling is performed to complete solidification. (See, for example, Japanese Patent Application Laid-Open No. 51-81743). The hot-dip Al-Zn alloy-plated steel sheet thus produced has a spangle pattern peculiar to the solidification structure.

[0004]

In the hot-dip plated steel sheet produced in this manner, the size of the spangle pattern between the coils and within the coil and the uniformity of the size are directly related to the commercial value.

However, in practice, even if the components are manufactured under the same composition, the same plate thickness, and the same manufacturing conditions, the spangle size after plating causes a visible difference between the coils or within the coils. There are many. It is considered that this is largely due to the surface condition of the steel sheet before being immersed in the plating bath.

[0006] That is, uncontrolled delicate changes in the base material composition, manufacturing before plating such as hot rolling, pickling, cold rolling, and annealing, and processing conditions are reduced and cleaned in the reduction annealing furnace. It is presumed that there is a difference in the surface condition of the steel sheet, and as a result, a difference in reactivity between the plating and the base steel sheet occurs, resulting in a difference in the spangle pattern after plating.

In the conventional manufacturing method, it is impossible to control delicate parts even if the manufacturing conditions before plating are controlled, and as a result, spangle unevenness is inevitably generated. .

As a means for solving such a drawback, Japanese Patent Laid-Open No. 9-235661 discloses a plating base material having a thickness of 0.
Although a manufacturing method for ensuring the uniformity of spangles by grinding at least 05 μm (0.4 g / m ² ) (Examples 0 to 1.34 μm) has been described, as a result of subsequent research, it is possible to use only the grinding method. , The base metal additive element is concentrated in the surface layer after grinding,
It is difficult to ensure the uniformity of spangles because the degree of concentration is uncontrollable, and there are many variations among base materials with different components. Then, it was found that it is difficult to suppress the subtle component variation in the surface layer.

Therefore, an object of the present invention is to produce a hot-dip Al-Zn alloy-plated steel sheet capable of removing the difference in surface condition before plating as much as possible and allowing spangles to be uniformly and clearly expressed in a certain size or more. Is to provide a method.

[0010]

Here, the present inventors
In order to achieve such an object, various studies were repeated, and it was found that a combination of surface grinding of a plating base material and reduction pretreatment under predetermined conditions was effective, and the present invention was completed.

Therefore, the present invention provides a hot dip coating containing 20 to 95% of Al, for example, Al: 20 to 95% by weight, an appropriate amount of an alloying element such as Si, the balance Zn and unavoidable impurities. When a steel sheet with a Zn alloy plating film is manufactured in a continuous hot dip plating facility, the base material surface layer is removed by grinding or acid dipping at least 1 g / m ² before plating, and then, if not necessary, After performing non-oxidative heating or oxidative heating by, the dew point of the atmosphere gas in the reduction annealing furnace is set to -40 ℃ to + 20 ℃, annealing is performed, and then hot dipping is performed to make the spangle on the plating surface uniform.
A method for producing a molten Al-Zn alloy coated steel sheet characterized thereby Hirakihana.

In the preferred embodiment of the present invention, the dew point of the atmosphere gas in the annealing furnace may be adjusted at least in the soaking zone of the annealing furnace. If the dew point of the atmosphere gas of the annealing furnace is adjusted, the dew point of the atmosphere gas of the snout is affected accordingly, but in a further preferred aspect of the present invention,
The dew point of the atmosphere gas of the snout is adjusted to -60 ° C to -10 ° C.

According to another aspect of the present invention, the resin is applied after the chromate treatment or after the chromate treatment on the molten Al--Zn alloy plated steel sheet manufactured as described above. May be.

According to still another embodiment, the resin is applied onto the molten Al--Zn alloy plated steel sheet produced as described above, or chromate treatment is performed with a chromate treatment liquid containing resin. May be given.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the structure of the present invention will be described together with its function and effect. Regarding the base steel sheet, the steel type is not particularly limited. For example, Al killed steel, T
Ultra-low carbon steel containing i, Nb, etc., high-strength steel of 410 N grade or more containing C, P, Si, Mn, etc. can be used. Regarding the rolling conditions, there are no restrictions on hot rolling conditions and cold rolling conditions.

A preferred composition example is as follows. Al killed steel: C: 0.02 to 0.08%, Si: 0.02% or less, Mn:
0.10 to 0.30%, P: 0.03% or less, Al: 0.1% or less, S:
Ultra low carbon steel 0.03% or less: C: 0.005% or less, Si: 0.02% or less, Mn:
0.1 to 0.2%, P: 0.02% or less, Al: 0.08% or less, S:
0.01% or less High tensile steel: C: 0.07 to 0.20%, Si: 0.05% or less, Mn: 0.
3 to 0.8%, P: 0.05% or less, Al: 0.1% or less, S: 0.
Before entering the continuous annealing furnace of less than 03%, the surface of the base material steel sheet is removed by 1 g / m ² or more by grinding, acid dipping or acid coating. This is because the concentrated layer of is removed and the reactivity of the steel sheet surface is further homogenized during annealing reduction. There is no upper limit on the removal amount at this time, but considering economic efficiency, it is set to 10 g / m ² or less.

Here, the method of removing the surface layer may be either mechanical means or chemical means, and there is no particular problem. Normally, in continuous hot dip coating equipment, the surface of the steel sheet to be treated is cleaned by heating it in an oxidation furnace or a non-oxidation furnace for the steel sheet, and the steel sheet surface is once made into an oxidized state, and then annealed in a reducing atmosphere. However, in the case of the present invention, it is not actively oxidized by heating in an oxidation furnace as in the conventional case, and at the stage of reduction annealing, components such as Fe that are easily reduced are reduced, Elements that are easily oxidized, such as Si and P, are oxidized.

Therefore, according to the present invention, the removal of the base material surface layer is not sufficient as described above, and reduction annealing is performed under the following conditions prior to hot dipping. In the present invention, the inside of the annealing furnace for adjusting the dew point of the atmospheric gas is a period from the heating zone of the continuous annealing furnace to the cooling zone through soaking.

In the method of the present invention, at this time, the dew point in the annealing furnace is controlled to -40 ° C to + 20 ° C, preferably -40 ° C to + 10 ° C to uniformly control the reactivity of the steel sheet surface,
Specifically, an additive element (for example, P) that is more easily oxidized than Fe
To suppress the reactivity of those components with the plating bath, and to increase the adhesion with the plating film by controlling the reaction with the plating bath exclusively by the Fe content of the base metal, and at the same time, to improve the spangle of plating. Therefore, it is possible to manufacture a plated steel sheet having an excellent design property without making the sizes uneven.

The dew point of the atmospheric gas in the conventional annealing furnace is not particularly controlled, and is usually considered to be about -50 ° C. Therefore, the above-mentioned JP-A-9-235661 is used.
In the case of the publication, the dew point of the atmosphere gas in the reduction annealing furnace is -45 to
It is considered that the temperature should be as low as possible at about -60 ° C, and since it is supplied to such a reduction annealing furnace immediately after the surface grinding, its surface properties are non-uniformly active. It's different.

Here, if the dew point is too high, the reduction of the steel sheet surface is insufficient, the growth of the alloy layer growing at the steel sheet-plating interface is uneven, and the adhesion of the plating is poor. On the other hand, if the dew point is too low, the reactivity of the steel sheet surface will be non-uniform,
The spangle size will also be uneven.

Although details of the mechanism of such spangle unevenness are unknown, the present inventors presume that the reduction of the surface of the steel sheet proceeds and the reactivity with the plating bath becomes too high. Considering operating conditions and measurement variations, it is more preferable that the dew point is manufactured in the range of -20 ° C to 0 ° C.

Such dew point adjustment is carried out with respect to the atmosphere gas of the annealing furnace, but it is particularly important to adjust the dew point of the atmosphere gas in the heating zone and the soaking zone. After the annealing treatment, through the cooling zone, the steel sheet exiting the reduction annealing furnace is sent to the hot metal plating equipment as it is, at that time, the base material is lowered to a predetermined temperature in a snout, and then immersed in a plating bath. Plate. At this time, if the dew point in the snout is too high,
Since a thick oxide film is formed on the surface of the base steel sheet, poor adhesion tends to occur. On the other hand, if the dew point is too low,
Zn easily evaporates, and Zn powder is deposited on the snout. When the deposit falls on the surface of the steel sheet, the reaction with the plating bath during plating is locally inhibited, and a plating defect called non-plating is likely to occur.

According to the preferred embodiment of the present invention, by controlling the dew point of the atmospheric gas in the snout within the range of -60 ° C to -10 ° C, both plating adhesion and suppression of non-plating can be achieved. A more preferable range of the dew point of the atmospheric gas in the snout is -20 ° C to -50 ° C.

By the way, normally, since the annealing furnace to the snout are not completely closed systems, if the dew point in the annealing furnace is controlled for the purpose of optimizing the spangle, the dew point in the snout also changes accordingly. Therefore, in order to optimize the dew points in the annealing furnace and snout, equipments that are independent of each other are required.

Therefore, in a preferred embodiment of the present invention, the annealing furnace is provided with equipment for raising the dew point such as a steam introduction pipe in addition to usual equipment for introducing hydrogen, nitrogen and the like, while the snout is provided with
In addition to this, by installing piping that can be charged with dry nitrogen, hydrogen, etc., the dew point in the annealing furnace and the snout can be controlled separately, and the spangle can be evenly spread, and there is no problem of adhesion or non-plating. A Zn-Al- (Si) -based alloy plated steel sheet can be obtained.

The base material steel sheet thus out of the snout is immersed in a hot dip plating bath to carry out hot dip plating. The composition of the hot dip bath at this time is such that in the case of hot dip Al-Si-Zn alloy plating, For Al, if the content is too high or too low, a beautiful spangle pattern on the surface does not develop.For Si, too low a spangle pattern does not develop, and if it is high, unplated surface defects occur. It will be easier. The composition range of the preferable plating bath is Al = 45-65%, Si = 1.0-2.0%
And more preferably Al = 50-60%.

Other plating conditions are not particularly limited as long as they do not affect the surface quality, performance and operation, and may be ordinary conditions. Thus, according to the present invention, a molten Al—Zn alloy plated steel sheet having a spangle diameter of 0.4 mm or more and having a small variation in size can be efficiently manufactured.

[0029]

[Example] As a plating base material, a low carbon composition as shown in Table 1
A cold-rolled strip of Al-killed steel (thickness 0.6 mm × width 920 mm) was used.

These plating base materials were subjected to pretreatment, annealing treatment and hot dip plating treatment under the conditions shown in Table 2 using a continuous hot dip plating equipment to produce an Al-containing hot dip plated steel sheet. In the annealing furnace, H ₂ , N ₂ , and steam piping systems were installed independently, and the gas atmosphere and dew point in the furnace were controlled by adjusting the flow rate while measuring with a hydrogen concentration meter and dew point meter. did.

[0031]

[Table 1]

[0032]

[Table 2]

A method for evaluating spangles will be described.
First, nine standard samples with apparently different spangles were prepared and classified from 0 (very fine) to 8 (very coarse), respectively. Hereinafter, this value is referred to as a spangle code.

On the other hand, by taking a magnified photograph of the surface of the standard sample and counting the number of spangle boundary lines that cross the line segment corresponding to the actual length of 30 mm, the spangle diameter = 30 mm ÷ boundary The number of lines. Further, this measurement was repeated 5 times for each standard sample, and the average value was defined as "spangle diameter". Table 3 shows the correspondence between the spangle diameter and the spangle code.

The spangle uniformity was evaluated by spherical approximation of each spangle crossing a line segment corresponding to a length of 30 mm and the standard deviation value of the diameter. Rating is from 0 (very small variation) to 5
The grade of 2 or less was a pass level in 6 grades up to (very large variation). Table 4 shows the correspondence between the spangle variation and the spangle variation code.

[0036]

[Table 3]

[0037]

[Table 4]

The size of the spangle in the examples was visually compared and compared with the standard sample, and evaluated by the spangle code of the standard sample having the closest spangle size.

Next, regarding the adhesion of the plating, the obtained sample was subjected to close bending using a lock former, and all three types of samples passed only those in which peeling did not occur over the entire width in the plate width direction. And

The non-plating was visually evaluated, and the non-plating (about
Those that were not recognized (0.1 mm or more) were accepted. Table 5 and Table 6 collectively show these results for the test material 1.

Similarly, in FIG. 1, for the test materials 1 and 2, the spangle diameter evaluation code is 1.5 or more, the spangle variation evaluation code is 2 or more, and non-plating and plating adhesion are good. , ●, and x in other cases are shown in a graph against the dew point in the annealing furnace and the amount of base material surface layer removed.

[0042]

[Table 5]

[0043]

[Table 6]

As can be seen from these results, the surface layer is removed and annealed under the conditions specified in the present invention, and then hot dip plating is performed, so that the adhesion is not impaired and the spangle is almost uniformly opened. You can

On the other hand, if annealing is performed under conditions deviating from the conditions specified in the present invention to the high dew point side, poor adhesion will occur. On the contrary, when annealing is performed under the condition deviated from the condition defined in the present invention to the low dew point side, spangle unevenness may occur.

[0046]

EFFECTS OF THE INVENTION According to the present invention, it is possible to uniformly distribute spangles of approximately the same size, and a hot-dip Al-Zn alloy plated steel sheet excellent in designability can be produced by a simple means. In particular, it is suitable for home electric appliances for which demand has recently been expanding, and its significance is significant from a practical point of view.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a dew point of an atmospheric gas in an annealing furnace and a surface layer removal amount of a plating base material.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-7-97670 (JP, A) JP-A-9-235661 (JP, A) JP-A-9-25550 (JP, A) JP-A-9- 59753 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (5)

(57) [Claims] 1. After removing 1 g / m ² or more per surface of the steel sheet, the dew point of the atmosphere gas in the annealing furnace is −40 ° C. or higher +20.
℃ after performing annealing treatment in the following, by forming a molten plating film containing Al 20 to 95%, the plating table
A method for producing a hot dip aluminum-zinc alloy plated steel sheet, which comprises uniformly spreading the surface spangles . 2. A method for producing a surface-treated steel sheet, which comprises subjecting the hot dip aluminum-zinc alloy plated steel sheet produced by the method of claim 1 to chromate treatment. 3. A method for producing a surface-treated steel sheet, which comprises applying a resin after performing a chromate treatment on the hot-dip aluminum-zinc alloy plated steel sheet produced by the method according to claim 1. 4. A method for producing a surface-treated steel sheet, which comprises applying a resin onto the hot dip aluminum-zinc alloy plated steel sheet produced by the method according to claim 1. 5. The production of a surface-treated steel sheet, which comprises subjecting the hot dip aluminum-zinc alloy plated steel sheet produced by the method of claim 1 to a chromate treatment with a resin-containing chromate treatment solution. Method.