JP2003129205A - Plated steel with high corrosion resistance and excellent workability and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a zinc-alloy-plated steel having a high corrosion resistance and an excellent workability. SOLUTION: The plate steel, having a high corrosion resistance and an excellent workability, has a plating layer comprising 18-25 mass% Al and the balance Zn. At the interface of the plating layer and base iron, an Fe-Zn intermetallic compound layer is present. The thickness of the intermetallic compound layer is 20 μm or lower. The plating layer may further contain 5 wt.% or lower Mg.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plated steel material in which the corrosion resistance of the steel material subjected to rolling and drawing after plating is improved, and a method for producing the same.

[0002]

2. Description of the Related Art As a galvanized steel material, a galvanized steel material or a zinc-aluminum alloy plated steel material having better corrosion resistance than that is used. This zinc-aluminum alloy-plated steel material is generally treated by cleaning the steel material by cleaning, degreasing, etc., then performing flux treatment, followed by hot-dip galvanizing mainly as zinc as the first step, and then as the second step. It is prepared by hot-dip plating in a Zn-Al alloy bath with an Al addition amount of 10%, or by directly plating with a Zn-Al alloy bath with an Al addition amount of 10%, pulling up from the plating bath and cooling.

Regarding this zinc-aluminum alloy plated steel material, there is a method of increasing the plating thickness in order to further improve the corrosion resistance. To ensure the desired plating thickness,
There is a method of increasing the amount of plating alloy adhered to the steel material due to the viscosity of the hot-dip galvanized alloy by pulling the steel material out of the plating bath at high speed. However, due to the increase in speed, unevenness of the plating thickness is likely to occur in the cross section of the plated steel material at right angles to the longitudinal direction, which causes a limitation in production equipment. Therefore, the zinc plating by the current manufacturing equipment and the hot dip coating by Zn-Al alloy do not have sufficient corrosion resistance, and today there is a strong demand for longer life of the plated steel material. there were. A Zn-Al-Mg alloy-based plating composition with high corrosion resistance in which Mg is added to the plating bath is disclosed in Japanese Patent Laid-Open No. 07-207
No. 421, the method is disclosed in Zn--Al.
This is a method of applying a thick Mg-Mg alloy plating, and if this method is applied as it is, there is a problem that the Fe-Zn alloy layer becomes thick and the alloy layer cracks and peels during processing of the steel material.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a steel material which is subjected to processing such as rolling and drawing after plating on a plated steel material, in particular, a plated steel material having improved corrosion resistance of a wire and a method for producing the same.

[0005]

The present invention is excellent for solving the above problems, and its gist is as follows. (1) In plated steel, the composition of the plated layer is mass%
Then, a plated steel material having high corrosion resistance and excellent workability, which is characterized by comprising Al: 18 to 25% and the balance Zn. (2) In the plated steel material, at the interface between the plated layer and the base steel
Fe-Zn intermetallic compound layer (1)
The listed plated steel material. (3) The plated steel material having high corrosion resistance and excellent workability according to (2), wherein the alloy layer has a thickness of 20 μm or less. (4) In addition to the composition of the plating layer, further in mass%, M
g: containing 5% or less (1) to
A plated steel material according to any one of (3), which has high corrosion resistance and excellent workability. (5) In addition to the composition of the plating layer, in addition, in mass%, S
i: 0.01 to 1.0% is contained, The plated steel material having high corrosion resistance and excellent workability according to any one of (1) to (4). (6) In addition to the composition of the plating layer, L
It is characterized by containing 0.01 to 0.1% of one or more of a, Se, or B (1).
~ A plated steel material having high corrosion resistance and excellent workability according to any one of (5). (7) The plated steel material having high corrosion resistance and excellent workability according to any one of (2) to (6), characterized in that the alloy layer contains 4% or more of Al in mass%. . (8) The plated steel material is a steel wire, the composition of the steel wire is% by mass, C: 0.02 to 1.02%, Si: 1% or less, Mn: 0.6% or less, P: 0. 0.04%, S: 0.0
4% or less, balance Fe and unavoidable impurities, The plated steel material having high corrosion resistance and excellent workability according to any one of (1) to (7). (9) In the method for producing a plated steel material in which plating is performed in a two-step treatment, the first step is plating with a plating bath containing zinc as a main component, and the second step is plating bath (1) or (4). To (6), plating is performed in a plating bath having a composition range of the plating layer according to any one of (1) to (8), which has high corrosion resistance and is processed. Method for producing plated steel with excellent properties. (10) In the method for producing a plated steel material in which plating is performed in a two-step treatment, electroplating mainly using zinc is performed as the first step, and then the plating bath is (1) or (4) to (6) as the second step. (1) characterized in that plating is performed in a plating bath having a composition range of the plating layer described in any one of (1).
~ A method for producing a plated steel material having high corrosion resistance and excellent workability according to any one of (8). (11) When the plated steel material is pulled up from the second-stage plating bath, the plated steel material is purged with an inert gas to prevent oxidation of the plating bath surface and the plated steel material (9) or ( 10) The method for producing a plated steel material having high corrosion resistance and excellent workability as described above. (12) The immersion time in the first-stage plating bath is 20 seconds or less, and then the immersion time in the second-stage plating bath is 2 seconds.
The method for producing a plated steel material having high corrosion resistance and excellent workability according to (9), which is performed for 0 second or less. (13) Any one of (9) to (12), characterized in that the plating alloy is solidified by water spray, steam spray, or direct water cooling by water flow immediately after pulling the plated steel material from the second-stage plating bath. The method for producing a plated steel material having high corrosion resistance and excellent workability according to the above item.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a plated steel material,
The composition of the plating layer is mass% Al: 18 to 25%, the balance Z
It is a plated steel material having high corrosion resistance and excellent workability, which is characterized by comprising n. Zn-22% Al alloy is known to exhibit superplasticity, and is disclosed in JP-A-4-99803, "Zn-22
There is a method of manufacturing a superplastic composite magnetic material using Al powder ”. However, there is no example of using this alloy as plating. The present invention is a plated steel material that utilizes good corrosion resistance and superplasticity as a Zn alloy. As a result of various investigations, Zn-10Al shows relatively good workability, but when the Al concentration is less than 18%, the structure mainly composed of Zn becomes coarse,
When performing large processing such that the surface reduction rate exceeds 20%, Z
n The main part is cracked. Also, the Al concentration is 2
If it exceeds 5%, the structure mainly composed of Al becomes coarse and A
A film-like Zn layer is formed between the structures mainly composed of l, and cracks are formed at the base point, which cannot withstand heavy working. 18 to 2 Al
It has been found that by setting the content to 5%, it is possible to form a fine structure in which both phases are uniformly present and to secure strong workability.

An alloy layer mainly composed of Fe-Zn is formed at the interface of the plated base metal. When the alloy layer is thick, the alloy layer is cracked, or the interface between the alloy layer and the base iron or the interface between the alloy layer and the plated layer. Is easily cracked. If the thickness of this alloy layer exceeds 20 μm, cracks increase and it is not practical for plating. Since the upper limit that does not impair workability is 20 μm, F
The thickness of the e-Zn alloy layer is 20 μm or less.

Further, it is also effective to add Mg to the plated layer in order to further improve the corrosion resistance. Although Mg improves the corrosion resistance, it hardens the plating layer, so the limit of maintaining workability was set to 5% or less.

It is also effective to add Si in order to improve the corrosion resistance. When Si is added in a large amount, the addition of Si has a function of forming an intermetallic compound and enhancing the anticorrosion effect, and thus it is more effective to add Si. In the present invention, when the maximum amount of addition of Mg is 5%, the maximum amount of the effect of Si is 1.0%.
Therefore, the range of Si was set to 0.01 to 1.0%.

Further, by containing 0.01 to 0.1% of each of La, Se, and B, one kind or two kinds or more, an effect of improving the surface property of plating can be obtained. These effects can be obtained by adding a very small amount, and the required amount is 0.01-0.1%.
Is. In addition to these, the addition of antimony, misch metal, etc., can improve the surface quality of the plating.

In the plated steel material according to the present invention, A in mass% in the Fe--Zn alloy layer existing at the interface of the plated base iron
1: Corrosion resistance is improved by containing 4% or more.
If the Al content in the alloy layer is less than 4%, the effect of improving the corrosion resistance cannot be obtained, so the Al content is set to 4% or more.

As a method for obtaining the plated steel material of the present invention, there is a two-step plating method. By performing hot dip plating mainly containing zinc as a first step to form an Fe-Zn alloy layer, and then making the average composition of the hot dip zinc alloy within the range of the present invention as a second step, the above-mentioned plated steel material can be efficiently prepared. can get. First
The molten zinc alloy in the second stage may contain Al: 3% or less by mass%. When Al is included in the first stage,
It becomes difficult for the Fe-Zn alloy layer to grow, and Al is contained in the alloy layer.
Has the effect of easily entering.

To produce the plated steel material of the present invention, the portion pulled up from the plating alloy is purged with nitrogen gas,
Workability can be improved by preventing oxidation of the bath surface and the plated steel material. If oxides are formed on the plating surface or formed on the bath surface immediately after plating,
The plating may crack with the oxide as a nucleus during processing.
Therefore, it is important to prevent oxidation of the takeout part. In addition to nitrogen, an inert gas such as argon or helium can be used for preventing oxidation, but nitrogen is the best in terms of cost.

When the plated wire of the present invention is obtained by two-step plating, in order to reduce the thickness of the Fe-Zn alloy layer to 20 μm or less, hot-dip plating mainly containing zinc as the first step is immersed in the plating bath for 20 seconds. It is necessary to perform the following, and then, as the second step, perform hot dip zinc alloy plating with a plating bath immersion time of 20 seconds or less. As a result, when plating is performed for a long time, the thickness of the alloy layer becomes thicker and exceeds 20 microns. Therefore, as the first step, hot dip plating mainly consisting of zinc is performed with a plating bath immersion time of 20 seconds or less, then Hot-dip zinc alloy plating is performed in two steps with a plating bath immersion time of 20 seconds or less.

When the plated wire of the present invention is obtained by two-step plating, in order to further thin the Fe-Zn alloy layer, electroplating mainly containing zinc is applied as the first step, The Fe-Zn alloy layer can have a thickness of 1 μm or less. Then, as a second step, hot dip zinc alloy plating is performed for 20 seconds or less in a plating bath so that the thickness can be 20 μm or less. If plating is performed for a longer time than this, the thickness of the alloy layer becomes thicker and exceeds 20 microns. Therefore, as the second step, hot dip zinc alloy plating is performed with a plating bath immersion time of 20 seconds or less.

Since the plating alloy of the plated steel material after plating is rapidly cooled from the molten state, each phase is solidified without growing, so that the plating structure can be made fine. As the method, immediately after the plated steel material is pulled up from the plated alloy, the plated alloy is solidified by water spray or steam spray or direct water cooling with a water flow. When cooling the plated steel material, cooling is started while the plating is in a molten state, so that the plated layer on the surface is rapidly cooled to form a fine structure.

The steel composition of the plated steel product is C:
0.02 to 1.02%, Si: 1% or less, Mn: 0.6
% Or less, P: 0.04%, S: 0.04% or less for the following reasons.

C is an element that determines the strength of steel, and is required to be 0.02% or more in order to realize the strength of ordinary plated steel. On the other hand, if it exceeds 1.02%, C becomes too high, and during plating, C diffuses into the plated alloy and deteriorates the workability, so the content is made 1.02% or less. Si has the effect of improving plating adhesion and at the same time having the effect of increasing strength. If Si exceeds 1%, the strength increases too much, so the upper limit is made 1%. Mn has the effect of increasing the toughness of steel and at the same time the effect of increasing the strength. Mn
Exists in excess of 0.6%, the strength increases too much, so the upper limit is made 0.6%. P and S cause embrittlement of the steel, so the upper limit is made 0.04%.

[0019]

[Example] 4 mm diameter JIS G 3505 SW with pure Zn plating on the surface
The plated wire of RM6 was subjected to the zinc alloy plating of the present invention under the conditions shown in Table 1 and evaluated.

For the corrosion resistance, the amount of corrosion of the plating per unit area was determined as the corrosion weight loss due to the weight difference before and after the test by continuous salt water spray for 250 hours. In this test, pass / fail was determined by passing 20 g / m ² or less.

In the evaluation of workability, the plated wire thus produced was drawn with a die having a surface reduction rate of 20% by 3 dies, and the surface thereof was visually observed to determine the presence or absence of cracks. Further, after the cellophane tape was attached to the sample after the judgment of cracking, the presence or absence of peeling of the plating was observed when peeled off, and the condition of passing was that neither cracking nor peeling occurred.

Table 1 shows the plating composition, plating layer hardness and Fe.
-The relationship between the thickness of the Zn alloy layer and the corrosion resistance and workability is shown.

[0023]

[Table 1]

The examples of the present invention all exhibit good corrosion resistance and workability. In Comparative Examples 1 to 5, the plating alloy composition is outside the scope of the present invention. In Comparative Examples 1 to 3, the amount of Al added is lower than the lower limit and the workability is poor. In Comparative Examples 4 to 6, the amount of Al added is higher than the upper limit and the workability is poor. Comparative Examples 7 to 10 are cases where the components other than Al or the thickness and components of the alloy layer are out of the range of the present invention, resulting in poor workability.

[0025]

According to the present invention, a zinc alloy plated steel material having high corrosion resistance and excellent workability can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C23C 2/38 C23C 2/38 28/02 28/02 (72) Inventor Nishida Century 1 Kimitsu, Kimitsu-shi, Chiba Address Nippon Steel Co., Ltd. Kimitsu Works (72) Inventor Akira Takahashi 1 Kimitsu, Kimitsu, Chiba Pref. AE03 AE23 4K044 AA02 AB04 BA06 BA10 BB03 BC02 BC05 CA11 CA18 CA62

Claims (13)

[Claims] 1. A plated steel material having high corrosion resistance and excellent workability, characterized in that the composition of the plated layer in the plated steel material is, by mass%, Al: 18 to 25% and the balance Zn. 2. The plated steel material according to claim 1, wherein the plated steel material has an Fe—Zn intermetallic compound layer at the interface between the plated layer and the base iron. 3. The plated steel material having high corrosion resistance and excellent workability according to claim 2, wherein the alloy layer has a thickness of 20 μm or less. 4. In addition to the composition of the plating layer, further mass%
And, the plated steel material having high corrosion resistance and excellent workability according to any one of claims 1 to 3, which contains Mg: 5% or less. 5. In addition to the composition of the plating layer, further mass%
In addition, Si: 0.01 to 1.0% is contained, The plated steel material having high corrosion resistance and excellent workability according to any one of claims 1 to 4. 6. In addition to the composition of the plating layer, further mass%
And 0.01 to 0.1% of one or more of La, Se, and B, respectively, are included, and the high corrosion resistance according to any one of claims 1 to 5 is provided. Plated steel with excellent workability. 7. A plated steel material having high corrosion resistance and excellent workability according to claim 2, wherein the alloy layer contains 4% or more of Al in mass%. . 8. The plated steel material is a steel wire, the composition of the steel wire is mass%, C: 0.02 to 1.02%, Si:
1% or less, Mn: 0.6% or less, P: 0.04%, S:
The plated steel material having high corrosion resistance and excellent workability according to any one of claims 1 to 7, wherein the balance is 0.04% or less and the balance is Fe and inevitable impurities. 9. A method for producing a plated steel material which is plated in a two-step process, wherein the first step is plating with a plating bath containing a zinc-based component, and the second step is a plating bath. Item 9. The plating is performed in a plating bath having a composition range of the plating layer according to any one of items 4 to 6, which has high corrosion resistance and workability according to any one of items 1 to 8. An excellent method for producing plated steel. 10. A method for producing a plated steel material in which plating is performed in a two-step process, wherein electroplating mainly containing zinc is performed as the first stage, and then a plating bath is used as the second stage. 9. A plated steel material having high corrosion resistance and excellent workability according to any one of claims 1 to 8, characterized in that plating is performed with a plating bath having a composition range of the plating layer according to any one of claims 1 to 8. Manufacturing method. 11. The method according to claim 9, wherein when the plated steel material is pulled up from the second-stage plating bath, the plated steel material is purged with an inert gas to prevent oxidation of the plating bath surface and the plated steel material. Alternatively, the method for producing a plated steel material having high corrosion resistance as described in 10 and excellent in workability. 12. The immersion time in the first stage plating bath is 20 seconds or less, and then the immersion time in the second stage plating bath is 20 seconds or less. The method for producing a plated steel material having high corrosion resistance and excellent workability. 13. The plating alloy is solidified by water spray, steam spray, or direct water cooling with a water stream immediately after pulling the plated steel material from the second-stage plating bath. The method for producing a plated steel material having high corrosion resistance and excellent workability according to the above item.