JP2000273605A - Production of hot dip plated steel sheet uniform in crystal pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow spangles to uniformly and clearly exhibit at the size equal to or above the certain one by removing the surface layer of a base material by a specified amt. by grinding, acid dipping or the like before plating, executing annealing treatment in such a manner that the dew point of atmospheric gas in a reducing annealing furnace is controlled to a specified temp. range and then executing hot dip plating. SOLUTION: The amt. of the surface layer of a base material to be removed is controlled to >=1 g/m2. By controlling the dew point in a reducing annealing furnace to -40 to +20 deg.C, preferably to -40 to +10 deg.C, the reactivity of the surface of the steel sheet is uniformized and controlled, concretely, the element to be added easy to oxidize more than the case of Fe, e.g. P is oxidized, and the reactivity between those elements and the plating bath is controlled. Aneealing treatment is executed, and then, a hot dip plating film contg. 20 to 95 wt.% Al is formed. The surface of the hot dip Al-Zn alloy plated steel sheet may be subjected to chromate treatment, or it may be coated with a resin after the application of chromate treatment. Or, it may be subjected to chromate treatment with a chromate treating soln. incorporated with a resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 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 has been subjected to a surface treatment.

[0002]

2. Description of the Related Art Al-containing hot-dip galvanized steel sheets, especially 55
% Al- (1.5% Si) -Zn alloy hot-dip coated steel sheet has a beautiful spangle pattern after plating and has excellent corrosion resistance. Therefore, it is widely used as a roof or wall material without color coating after plating, as it is, or after one or two types of chromate treatment or resin coating treatment, and then roll forming.

[0003] Generally, a continuous hot-dip Al-Zn alloy-plated 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 subjected to snout. And then immersed in the plating bath. Then, after controlling the amount of plating applied by the wiping nozzle, natural cooling, cooling by liquid spraying, or air cooling is performed to complete the solidification. (See, for example, JP-A-51-81743.) A spangle pattern peculiar to the solidification structure is generated in the hot-dip Al-Zn alloy-plated steel sheet manufactured as described above.

[0004]

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

[0005] However, in practice, even when manufactured under the same composition, the same plate thickness, and the same manufacturing conditions, the size of the spangle after plating causes a visually noticeable difference between or within the coils. There are many. It is considered that the cause largely depends on the surface condition of the steel sheet before immersion in the plating bath.

[0006] That is, uncontrollable subtle changes in conditions such as base material components, production before plating such as hot rolling, pickling, cold rolling, and annealing, and processing conditions are reduced and cleaned in a reduction annealing furnace. It is presumed that a considerable difference is caused in the surface condition of the plated steel sheet, and as a result, a difference in reactivity between the plating and the base material steel sheet occurs, resulting in a difference in spangle pattern after plating.

In the conventional manufacturing method, no matter how the manufacturing conditions are controlled before plating, it is impossible to control to delicate points, and as a result, spangle non-uniformity inevitably occurs. .

As a means for solving such a drawback, Japanese Patent Application Laid-Open No. 9-235661 discloses a method in which a plating base material is previously coated with a thickness of 0.1 mm.
A manufacturing method that ensures uniformity of spangles by grinding at least 05 μm (0.4 g / m ² ) (Examples 0 to 1.34 μm) is described. , The base material additive element concentrates on the surface layer after grinding,
It is difficult to maintain spangle uniformity due to the uncontrollable degree of concentration, and there are many variations in base materials with different components. It was found that it was difficult to suppress subtle component variations in the surface layer.

Accordingly, an object of the present invention is to manufacture a hot-dip Al-Zn alloy-coated steel sheet capable of removing a difference in the surface state before plating as much as possible and allowing spangles to be uniformly and sharply expressed in a certain size or more. Is to provide a way.

[0010]

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

Accordingly, the present invention provides a hot-dip coating containing 20 to 95% of Al, for example, Al: 20 to 95% by weight, if necessary, an appropriate amount of an alloy element such as Si, a balance of Zn and unavoidable impurities. When manufacturing a steel sheet with a Zn alloy plating film in a continuous hot-dip plating facility, remove 1 g / m ² or more of the base material surface by grinding or acid immersion before plating, and then, although not necessary, After performing non-oxidizing heating or oxidizing heating, the dew point of the atmospheric gas in the reduction annealing furnace is set to −40 ° C. to + 20 ° C., and then annealing treatment is performed, and then hot-dip plating is performed. This is a method for producing a hot-dip Al-Zn alloy-plated steel sheet having excellent design properties, in which sublimation is uniform.

In a preferred embodiment of the present invention, the adjustment of the dew point of the atmosphere gas in the annealing furnace may be performed 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 also affected accordingly, but in a further preferred aspect of the present invention,
The dew point of the snout atmosphere gas is adjusted to −60 ° C. to −10 ° C.

According to another aspect of the present invention, a resin may be applied to the hot-dip Al-Zn-based alloy-plated steel sheet produced as described above, or may be subjected to a chromate treatment, or after the chromate treatment. You may.

[0014] According to still another embodiment, the resin is applied to the hot-dip Al-Zn-based alloy-plated steel sheet produced as described above, or the chromate treatment is carried out with a chromate treatment liquid containing the resin. May be applied.

[0015]

Next, the configuration of the present invention will be described together with its operational effects. With respect to the base steel sheet, the type of steel is not particularly limited. For example, Al-killed steel, T
Ultra-low carbon steel to which i, Nb and the like are added, and high-strength steel of 410 N class or more to which C, P, Si, Mn and the like are added can be used. There are no restrictions on the hot rolling conditions or cold rolling conditions for these rolling conditions.

Preferred examples of the composition are as follows. Al-killed steel: C: 0.02-0.08%, Si: 0.02% or less, Mn:
0.10 to 0.30%, P: 0.03% or less, Al: 0.1% or less, S:
0.03% or less Ultra-low carbon steel: C: 0.005% or less, Si: 0.02% or less, Mn:
0.1-0.2%, 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.
03% or less Before entering the continuous annealing furnace, the surface of the base steel sheet is removed by 1 g / m ² or more by grinding, immersion, or acid coating, etc., because it is an additional element such as oxide film P, Mn, and S on the steel sheet surface. This is for removing the concentrated layer of and further reducing the reactivity of the steel sheet surface during annealing reduction. There is no upper limit on the amount of removal at this time, but it is 10 g / m ² or less in consideration of economy.

Here, there is no particular problem whether the method of removing the surface layer is either mechanical means or chemical means. Normally, in continuous hot-dip plating equipment, the surface of the steel sheet to be treated is cleaned by heating the steel sheet in an oxidation furnace or a non-oxidation furnace, and once the steel sheet surface is oxidized, annealing is performed 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 prior art, and at the stage of reduction annealing, components that are easily reduced such as Fe are reduced. Elements that are easily oxidized such as Si and P are oxidized.

Therefore, according to the present invention, removal of the base material surface layer alone is not sufficient as described above, and reduction annealing is performed prior to hot-dip plating under the following conditions. 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 via the soaking zone.

In the method of the present invention, by controlling the dew point in the annealing furnace at this time to -40 ° C to + 20 ° C, preferably -40 ° C to + 10 ° C, the reactivity of the steel sheet surface is controlled to be uniform,
Specifically, additional elements that are more easily oxidized than Fe (for example, P)
And oxidizes the components to suppress the reactivity of these components with the plating bath. This makes it possible to produce a plated steel sheet having excellent design properties without making the size non-uniform.

The dew point of the atmospheric gas in the conventional annealing furnace is not particularly controlled, and is generally considered to be around -50.degree. Therefore, the aforementioned Japanese Patent Application Laid-Open No. 9-235661
The dew point of the atmosphere gas in the reduction annealing furnace is -45 to
It is thought that it should be as low as -60 ° C, and since it is supplied to such a reduction annealing furnace immediately after surface grinding, its surface properties are heterogeneous, and the present invention It is different.

If the dew point is too high, the reduction of the steel sheet surface is insufficient, the growth of the alloy layer growing on 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, non-uniformity occurs in the reactivity of the steel sheet surface,
Spangles also become uneven in size.

The details of the mechanism of such spangle non-uniformity are unknown, but the present inventors presume that the reduction of the steel sheet surface 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 performed on the atmosphere gas in the annealing furnace, and it is particularly important to adjust the dew point of the atmosphere gas in the heating zone and the solitary zone. After the annealing treatment, the steel sheet that has exited the reduction annealing furnace through the cooling zone is sent to the hot metal plating equipment as it is, at which time the base material is lowered to a predetermined temperature in the snout, and then immersed in the plating bath. Plating. 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 is likely to occur. On the other hand, if the dew point is too low,
Zn evaporates easily, 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 easily caused.

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 the plating adhesion and the 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, since the system from the annealing furnace to the snout is not a completely closed system, 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 point in the annealing furnace and the dew point in the snout, facilities 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 injection pipe, in addition to the usual equipment for charging hydrogen, nitrogen, etc., while the snout has:
Separately controls the dew points in the annealing furnace and snout by providing pipes that can be charged with dry nitrogen, hydrogen, etc., allowing spangles to open uniformly and melting without problems of adhesion and non-plating. A Zn-Al- (Si) -based alloy-plated steel sheet can be obtained.

[0027] The base material steel sheet that has left the snout in this way is immersed in a hot-dip plating bath and hot-dip plating is performed. At this time, the composition of the hot-dip bath is as follows: Regarding Al, if the content is too high or too low, a beautiful spangle pattern on the surface does not appear, and if it is too low, the spangle pattern does not develop if it is too low, and if it is too high, non-plating surface defects occur It will be easier. The preferred composition range of the plating bath is Al = 45 to 65%, Si = 1.0 to 2.0%.
More preferably, Al is 50 to 60%.

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

[0029]

EXAMPLES As a plating base material, a low carbon material having the composition shown in Table 1 was used.
An Al-killed steel cold-rolled steel strip (sheet thickness 0.6 mm x width 920 mm) was used.

These plated base materials were subjected to a pretreatment, an annealing treatment, and a hot-dip plating process under the conditions shown in Table 2 using a continuous hot-dip plating apparatus, thereby producing an Al-containing hot-dip coated steel sheet. The annealing furnace, placed H _2, N _2, steam piping system to independently atmosphere and dew point in the furnace, while measuring hydrogen concentration meter and dew, controlled by respectively regulating the flow rate did.

[0031]

[Table 1]

[0032]

[Table 2]

A method for evaluating spangles will be described.
Initially, nine grades of standard samples with apparently different spangles were prepared, each of which was rated from 0 (very fine) to 8 (very coarse). Hereinafter, this numerical value is referred to as a spangle code.

On the other hand, an enlarged photograph of the surface of the standard sample is taken, and the number of spangle boundary lines crossing a line segment corresponding to an actual length of 30 mm is counted on the photograph. Number of lines. Further, this measurement was repeated five times per standard sample, and the average value was defined as “spangle diameter”. Table 3 shows the correspondence between the spangle diameter and the spangle cord.

The uniformity of the spangle was evaluated by spherical approximation of each spangle across all the line segments corresponding to the length of 30 mm, and evaluated by the standard deviation value of the diameter. Rating is from 0 (very small variation) to 5
(Very large variation), and the evaluation level of 2 or less was judged to be acceptable level in 6 steps. 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 evaluated by the spangle code of the standard sample having the closest spangle size, by visual comparison with the standard sample.

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

The non-plating was evaluated by visual inspection, and the
(0.1 mm or more) was not accepted. Table 5 and Table 6 collectively show these results for the test sample 1.

Similarly, FIG. 1 shows that the test pieces 1 and 2 have a spangle diameter evaluation code of 1.5 or more and a spangle variation evaluation code of 2 or more, and show good results in the case of non-plating and good plating adhesion. , ●, and in the other cases, x, the dew point in the annealing furnace and the removal amount of the base material surface layer are graphically shown.

[0042]

[Table 5]

[0043]

[Table 6]

As can be seen from these results, by removing the surface layer and annealing under the conditions specified in the present invention, and then performing hot-dip plating, the adhesion is not impaired, and the spangle is almost uniformly sublimated. Can be.

On the other hand, when annealing is performed under the conditions deviated from the conditions specified in the present invention to the high dew point side, poor adhesion occurs. Conversely, if annealing is performed under conditions deviating from the conditions specified in the present invention to the low dew point side, spangle variation failure occurs.

[0046]

According to the present invention, spangles of substantially the same size can be uniformly distributed, and a hot-dip Al-Zn-based alloy-plated steel sheet excellent in design can be produced by simple means. Particularly, it is suitable for home electric appliances whose demand is increasing recently, and its significance is great from a practical viewpoint.

[Brief description of the drawings]

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

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D075 BB02X BB74X BB87X BB93X CB11 DA06 DB02 DB05 DB07 DC01 DC02 EB31 4K026 AA02 AA07 AA09 AA13 AA22 BA06 BB01 CA19 CA20 EA01 EA06 EB08 EB11 AC02 AB02 AC02 AC82 AD10 AE03 AE25 AE33 AE34 AE37

Claims (5)

[Claims] After the steel sheet surface is removed by 1 g / m ² or more per one side, the dew point of the atmospheric gas in the annealing furnace is set to −40 ° C. or more and + 20 ° C.
A method for producing a hot-dip aluminum-zinc alloy-coated steel sheet, comprising forming a hot-dip coating containing 20 to 95% of Al after performing an annealing treatment at a temperature of not more than ℃. 2. A method for producing a surface-treated steel sheet, comprising subjecting a hot-dip aluminum-zinc alloy-plated steel sheet produced by the method according to claim 1 to a chromate treatment. 3. A method for producing a surface-treated steel sheet, which comprises applying a resin after performing a chromate treatment on the molten aluminum-zinc alloy-plated steel sheet produced by the method according to claim 1. 4. A method for producing a surface-treated steel sheet, comprising applying a resin onto the hot-dip aluminum-zinc alloy-plated steel sheet produced by the method according to claim 1. 5. A method for producing a surface-treated steel sheet, comprising subjecting a hot-dip aluminum-zinc alloy-plated steel sheet produced by the method according to claim 1 to a chromate treatment with a chromate treatment liquid containing a resin. Method.