JP3367456B2 - Method for producing hot-dip coated steel sheet with spangle pattern - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a hot-dip Al—Zn alloy plated steel sheet.

[0002]

2. Description of the Related Art Conventionally, hot-dip Zn-plated steel sheets have been used for building materials and home appliances, but in recent years, the amount of hot-dip Al-Zn alloy-plated steel sheets with higher corrosion resistance and durability has increased. ing. Of these, about 55% Al in the plating film,
The hot-dip Zn-Al-Si alloy-plated steel sheet containing 1 to 2% of Si has a beautiful spangle pattern on the surface, and therefore has a design property.

However, such molten Zn-Al-Si
When manufacturing hot-dip Al-Zn alloy plated steel sheet such as alloy plated steel sheet, spangle pattern on the surface at every manufacturing opportunity,
Between the coils, and further in the longitudinal direction and width direction of the coil,
Usually, there are variations in size. For example, when the base material coil is changed, the spangles often have different sizes even when plated under the same plating conditions. Sometimes very fine spangles are formed,
Such products cannot normally be used in applications where appearance is important from the viewpoint of design.

Conventionally, the following method has been proposed as a technique for suppressing such variations in spangles. (1) Japanese Patent Laid-Open No. 9-235661: The surface of a steel plate is ground by 0.05 μm or more. (2) Japanese Patent Laid-Open Nos. 1018009 and 10-18013: Control the roughness and waviness of the steel plate surface. (3) Japanese Patent Application Laid-Open Nos. 10-18010 and 10-18012: Control the texture and crystal grain size of the steel sheet surface. (4) Japanese Patent Laid-Open No. 9-241814: The immersion time in the plating bath is set to 2 seconds or more. (5) JP-A-9-25550: Control the dew point, hydrogen concentration, and bath temperature in the snout of the plating equipment.

[0005]

However, the above-mentioned conventional techniques have the following problems, respectively. Above (1)
In spite of the fact that the non-uniformity of the surface layer is slightly eliminated by grinding, the additive elements such as Si, P, and Mn may be non-uniformly concentrated on the surface, which may promote the variation of the spangle size. is there.

In the above methods (2) and (3), the effect is very small in spite of restricting the process before plating, such as rolling process, and the effect of spangle size due to variations in other manufacturing conditions is large. Cannot be suppressed.

Regarding the above (4), it is effective in that the size of the spangle can be controlled only by adjusting the plating conditions, but it is necessary to newly install equipment such as an elevating device for the in-bath roll, which is a cost disadvantage. Is. In addition, if the immersion time is set too long, the spangles become finer overall and the molten Zn
-The original design of the Al-Si alloy plated steel sheet is impaired.

The above method (5) is a method of suppressing the evaporation of Zn from the plating bath by controlling the atmosphere in the snout.
Here, evaporated Zn induces plating defects or spangle unevenness. Therefore, the method (5) does not make the unevenness of the spangle size worse than the level (for example, due to the plating base metal) obtained by the usual method. It is not suitable for suppressing.

An object of the present invention is to provide a hot-dip Al-Zn alloy-plated steel sheet which has a large spangle pattern having a spangle diameter of 0.6 mm or more and which can be stably obtained with little variation and which has good adhesion of the plating film. It is to provide a manufacturing method.

[0010]

[Means for Solving the Problems] The spangle of Al-containing hot-dip galvanized steel sheet is determined by the morphology of the solidification structure of primary Al. Therefore, it is generally considered that post-plating conditions such as cooling after plating and plating thickness have an influence. However, at present, even if the conditions after plating are the same, variations occur between the coils and within the coils. It is considered that this is because the operating conditions before plating or the properties of the steel sheet before plating are slightly different between the coils or within the coils. Differences due to the operating conditions of the steel sheet before plating (e.g. steel composition, hot rolling, cold rolling, pickling, annealing) cause a non-negligible difference when reducing the surface of the steel sheet. It is considered that this is because a remarkable change occurs during the reaction in the inside, which affects the solidification process after plating.

As a result of an investigation to solve such a problem, the present inventors have made the reactivity of the steel sheet as uniform as possible,
Moreover, it has been found that when the pretreatment is carried out under an operating condition that does not hinder the reactivity but suppresses it somewhat, the spangle tends to have a uniform size as a whole and the adhesion of the plating film can be secured.

For example, after annealing a steel sheet in an air atmosphere,
When immersed in a molten Zn-Al-Si alloy plating bath, a beautiful spangle can be stably obtained. However, on the other hand, in such a method of simply annealing in the air atmosphere, the surface of the steel sheet is excessively oxidized and the surface of the steel sheet hardly reacts with the plating bath, so that plating adhesion cannot be obtained at all. Also, non-plating is likely to occur.

Therefore, conditions are required to appropriately suppress the reactivity of the steel sheet surface. As a result of further studies by the present inventors, the steel plate surface roughness of the base material before plating, waviness, grain size, texture, or steel composition is controlled in an appropriate range, and the dew point in the annealing furnace is −40 ° C. The present invention has been completed by finding that controlling the temperature to + 10 ° C. makes it possible to control the spangle size uniformly and easily without damaging the adhesion.

The present invention is as follows. (1) By using continuous hot dip galvanizing equipment with an annealing furnace, for example, for steel sheets with a surface average roughness Ra of 0.3 μm or more and 1.2 μm or less, the dew point of atmospheric gas in the annealing furnace is −40 ° C. or more + 10 ° C.
℃ after the annealing in the following, to the formation of a plating film containing 20 to 95% of Al is immersed in a molten plating bath
Method for producing a soluble <br/> melting Al-Zn alloy coated steel sheet you characterized by uniformizing more spangle pattern.

(2) Surface average waviness Wca is 0.2 μm or more.
For steel plates of 8 μm or less, for example, by using a continuous hot dip galvanizing equipment attached to an annealing furnace, the dew point of the atmospheric gas in the annealing furnace is set to -40 ° C to + 10 ° C and then annealed. The spangle pattern can be made uniform by dipping it to form a plating film containing 20 to 95% Al.
Method for producing a molten Al-Zn alloy coated steel sheet shall be the features and.

(3) For a steel plate with a surface grain size of 9.5 or less,
For example, using a continuous hot-dip galvanizing equipment attached to an annealing furnace, annealing is performed by setting the dew point of the atmospheric gas in the annealing furnace to -40 ° C or higher and + 10 ° C or lower, and then dipping it in a hot dip bath to add Al
Span by forming a plating film containing 95%
Method for producing a molten Al-Zn alloy coated steel sheet you characterized by uniformizing the guru pattern.

(4) The crystal plane strength ratio of the surface texture is (110) /
(200) One or more steel sheets are annealed, for example, using a continuous hot dip galvanizing equipment attached to an annealing furnace, and the dew point of the atmosphere gas in the annealing furnace is -40 ° C to + 10 ° C. manufacturing method of dipping it molten Al-Zn alloy coated steel sheet you characterized by uniformizing the spangle pattern by forming a plating film containing 20 to 95% of Al to.

(5) Si: 0.03% or less, Mn: 0.50% or less,
P: 0.05% or less of steel sheet is annealed by using a continuous hot dip galvanizing equipment attached to an annealing furnace, for example, by setting the dew point of the atmosphere gas in the annealing furnace to -40 ° C to + 10 ° C or less, and then performing a hot dipping bath. manufacturing method of dipping it molten Al-Zn alloy coated steel sheet you characterized by uniformizing the spangle pattern by forming a plating film containing 20 to 95% of Al to.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below together with their effects. In the present invention, the base material steel sheet is heat-treated in an oxidation furnace and then in an annealing furnace, and then the base material steel sheet is subjected to hot dip plating treatment by using a continuous hot dip plating facility attached to the annealing furnace. After the hot dip coating, the spun may be adjusted by cooling the plating film at a predetermined cooling rate.

In particular, according to the present invention, a hot-dip Al-Zn alloy-plated steel sheet which can improve the plating adhesion and can suppress the variation of the spangle diameter can be manufactured with a high yield without requiring expensive equipment.

The steel type of the base steel sheet is not particularly limited, and a normal cold-rolled steel sheet can be used, but in a preferred embodiment of the present invention, Si: 0.03% or less, Mn: 0.50% or less, P: Contains 0.05% or less. Si: 0.03%
In case of over, Mn: more than 0.50%, or P: more than 0.05%,
Is that the plating adhesion may not be sufficient.

The definition of the amount of such additional elements in steel is as follows.
This is because in order to make the spangle uniform and beautiful, the amount of elements that tend to be concentrated in the surface layer of the steel sheet in the pre-plating step is suppressed. Commonly added to low and ultra low carbon steels
The ranges of Si, Mn and P are defined in the above ranges, and more preferably Si ≦ 0.02%, Mn ≦ 0.4% and P ≦ 0.04%.

In the present invention, other additive elements are not restricted in the steel composition. For example, Al killed steel and ultra low carbon steel to which Ti, Nb, etc. are added can also be used. In the present invention, the average surface roughness Ra of the base material is 0.3 μm ≦ Ra ≦ 1.
The reason for limiting the thickness to 2 μm is to control the true surface area that reacts with the hot dip plating bath and to uniformly generate the alloy layer at the plating film-steel plate interface. The base material surface roughness (Ra) is preferably in the range of 0.5 to 1.0 μm. The surface roughness (Ra) is an indication of the surface roughness specified in JIS B0601.

According to another aspect of the present invention, the surface average waviness (Wca) of the plating base material is specified to be 0.2 μm or more and 0.8 μm or less. The reason for the limitation is also the above-mentioned base material surface roughness. This is the same as in the case, in order to uniformly generate the alloy layer at the plating film-steel plate interface. The average surface waviness (Wca) of the steel plate surface is a surface waviness standard defined in JIS B 0610.

According to yet another aspect of the present invention, the surface grain size of the steel sheet surface of the plating base material is limited to 9.5 or less. This grain size is also defined in order to uniformly generate the alloy layer at the plating film-steel plate interface. The reactivity between the grain boundary and the inside of the grain is different, and the grain boundary is higher in reactivity. Therefore, it is desirable that the ratio of grain boundaries to the total surface area is as small as possible, and the grain size is No. ≤ 9.5. Preferably, the grain size No. ≦ 9.0. The "surface layer grain size" on the surface of the steel sheet is limited to JIS G 0552, and in the present invention, it is measured and evaluated according to it.

According to still another aspect of the present invention, the crystal plane strength ratio of the surface texture of the steel sheet which is the plating base material is (1
10) / (200) specifies 1 or more. Although the cause of the texture of the surface layer is unknown, it is considered that the orientation of the steel sheet is related to the solidification of the plating. When (110) / (200) ≧ 1, a uniform and beautiful spangle is exhibited. Preferably 2.
0 ≧ (110) / (200) ≧ 1.2.

In the present invention, further, in order to make the spangle uniform and beautiful, the conditions of the annealing furnace are controlled as follows after the steel plate state is specified as described above. In addition,
In the present invention, the inside of the annealing furnace in which the dew point of the atmospheric gas is controlled is between the heating zone and the cooling zone of the continuous annealing furnace.

As described above, in continuous hot dip coating equipment, the steel sheet is usually heated in an oxidizing furnace or a non-oxidizing furnace to clean the surface and once make the steel sheet surface in an oxidized state, and then reduce it. Anneal in an atmosphere. In the present invention, at this time, for example, (N ₂ + H ₂ ) in the annealing furnace is used.
Dew point of ambient gas is -40 ℃ to + 10 ℃ by adding steam
By controlling to make the reactivity of the surface of the steel sheet uniform, and specifically, preferentially oxidize an additive element (for example, P) that is more easily oxidized than Fe, and react with the plating bath. Is suppressed and the reaction with the plating bath is dominated by the Fe content of the base material, so that the spangle size of the plating film does not become non-uniform, but it is coarse and excellent in design. To produce coated steel sheets.

If the dew point is higher than the above range, 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, when the dew point is lower than the above range, the reactivity of the steel sheet surface becomes non-uniform and the spangle size becomes non-uniform.

Although the 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, the dew point is −
It is preferable to anneal by adjusting the temperature in the range of 30 ° C to 0 ° C.

Subsequent to the annealing treatment under such conditions, the base material steel plate is lowered to a predetermined temperature in the snout through a cooling zone, and then immersed in a plating bath for plating. At this time, if the dew point in the snout is too high, a thick oxide film is formed on the surface of the base steel sheet, so that poor adhesion tends to occur. On the other hand, if the dew point is too low, Zn easily evaporates from the plating bath, and Zn powder is deposited on the snout. When the deposits fall on the surface of the steel sheet, the reaction with the plating bath during plating is locally hindered, and plating defects called non-plating are likely to occur.

Therefore, according to a further preferred embodiment of the present invention, by controlling the dew point in the snout in the range of −60 ° C. to −10 ° C., it is possible to more reliably achieve both plating adhesion and suppression of non-plating. Good. A more preferable range of the dew point 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 the above-described aspect of the present invention, the annealing furnace is provided with equipment for increasing the dew point such as a steam feeding pipe in addition to the usual feeding equipment for hydrogen, nitrogen, etc., while the snout is dried separately. By providing a pipe into which nitrogen and hydrogen can be introduced, the dew point in the annealing furnace and the snout can be controlled separately, the spangles can be evenly spread, and there is no problem of adhesion or non-plating, for example, molten Zn-Al- We were able to obtain molten Al-Zn alloy plated steel sheets such as Si alloy plated steel sheets.

The composition of the hot dip bath is, for example, Al-
In the case of Si-Zn plating bath, for Al, if the composition is too high or too low, a beautiful spangle pattern on the surface does not appear,
If Si is too low, the spangle pattern does not appear, and if it is high, unplated surface defects are likely to occur. The preferred ranges are Al = 45 to 65%, Si = 1.0 to 2.0%, and more preferably Al = 50 to 60%. Other plating conditions are not particularly limited as long as they do not affect surface quality, performance, and operation, and may be ordinary conditions.

The steel sheet immersed in the hot dip plating bath is pulled up after the immersion and cooled at a predetermined cooling rate. Also in the present invention, although not particularly limited, the cooling rate after hot dip plating is preferably 10 to 30 ° C./sec.

[0036]

EXAMPLES In this example, cold-rolled steel strips of low-carbon and ultra-low-carbon Al-killed steels having the steel compositions shown in Table 1 (sheet thickness 0.6 mm × width 920 m
m) was used as the base material for plating. As the test materials, those having different surface roughness, those having different surface waviness, those having different grain size, and those having different texture morphology were prepared.

These test materials were hot-dip-plated under the conditions shown in Table 2 using continuous hot-dip plating equipment.
In the annealing furnace, H ₂ , N ₂ and water vapor piping systems were installed independently, and the gas atmosphere and dew point in the furnace were measured by a hydrogen concentration meter and a dew point meter while adjusting the respective flow rates. , Controlled.

[0038]

[Table 1]

[0039]

[Table 2]

In this example, spangles were evaluated according to the following procedure. First, 9 standard samples with apparently different spangle diameters were prepared, and each was set to 0 (very fine).
It was classified into 8 (very coarse). Hereinafter, this value is referred to as a spangle code. On the other hand, by taking a magnified photo of the surface of a standard sample and counting the number of spangle boundary lines that cross a line segment corresponding to the actual length of 30 mm on the photo, the spangle diameter = 30 mm / number of boundary lines The spangle diameter was calculated from the equation.

Further, this measurement was repeated 5 times for each standard sample, and the average value was defined as the "spangle diameter". Table 3 shows the correspondence between the spangle diameter and the spangle code.

To evaluate the uniformity of spangles, each spangle crossing a line segment corresponding to a length of 30 mm was approximated to a sphere, and the standard deviation of the diameter was evaluated. The evaluation was carried out in 6 grades from 0 (very small variation) to 5 (very large variation), and a rating of 2 or less was a passing level.
See Table 4.

[0043]

[Table 3]

[0044]

[Table 4]

The size of the spangle in the examples was visually 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 plating, the obtained sample was subjected to close bending using a lock former, and in all three types of samples, only those in which peeling did not occur over the entire width in the plate width direction were passed. did.

The non-plating was visually evaluated, and the non-plating (about
Those that were not recognized were judged to be acceptable. The results are summarized in Table 5 to Table 9.

[0048]

[Table 5]

[0049]

[Table 6]

[0050]

[Table 7]

[0051]

[Table 8]

[0052]

[Table 9]

[0053]

As described above, according to the present invention, a relatively large spangle of 0.6 mm or more can be stably obtained, and the adhesion of the plating film is good. The present invention has great practical significance in a situation where it is required to inexpensively manufacture a highly corrosion-resistant plated steel sheet having an excellent design property.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-97670 (JP, A) JP-A-10-18013 (JP, A) JP-A-10-18009 (JP, A) JP-A-10- 18012 (JP, A) JP 10-18010 (JP, A) JP 8-81748 (JP, A) JP 10-152765 (JP, A) JP 9-25550 (JP, A) JP, 9-59753 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (5)

(57) [Claims] 1. The average surface roughness Ra is 0.3 μm or more and 1.2 μm.
Annealing the following steel sheets with the dew point of the atmospheric gas in the annealing furnace at -40 ° C to + 10 ° C, and then immersing it in a hot dip bath to form a plating film containing 20 to 95% Al. method for producing a molten Al-Zn alloy coated steel sheet you <br/> characterized by uniformizing the spangle pattern by. 2. The surface average waviness Wca is 0.2 μm or more and 0.8.
The dew point of the atmosphere gas in the annealing furnace is -40
° C. after performing annealing above + 10 ° C. and below, molten Al you characterized by uniformizing the spangle pattern by forming a plating film containing 20 to 95% of Al is immersed in a molten plating bath -A method for manufacturing a Zn-based alloy-plated steel sheet. 3. A steel plate having a surface grain size of 9.5 or less,
Annealing is performed by setting the dew point of the atmosphere gas in the annealing furnace to -40 ° C or more and + 10 ° C or less, and then dipping it in a hot dip bath to remove Al
Spa by forming a plating film containing 95%
It characterized by uniformizing the Single pattern molten Al-Zn
Method for producing base alloy plated steel sheet. 4. The crystal plane strength ratio of the surface texture is (110) /
(200) One or more steel sheets are annealed by setting the dew point of the atmosphere gas in the annealing furnace to -40 ° C or higher and + 10 ° C or lower, and then immersed in a hot dip bath to contain Al containing 20 to 95% Al. A uniform film can be formed by forming a film.
Method for producing a molten Al-Zn alloy coated steel sheet shall be the features and. 5. Si: 0.03% or less, Mn: 0.50% or less, P:
A steel plate containing 0.05% or less is annealed by setting the dew point of the atmosphere gas in the annealing furnace to -40 ° C to + 10 ° C or less, and then immersed in a hot dip plating bath to form a plating film containing 20 to 95% Al. To make the spangle pattern uniform
Method for producing a molten Al-Zn alloy coated steel sheet you wherein a.