JPH05171408A - Manufacture of vapor deposition al-plated steel - Google Patents

Abstract

PURPOSE:To obtain a vapor deposition Al-plated steel excellent in corrosion resistance even if the thickness of plating is thin. CONSTITUTION:The surface roughness of a steel to be plated is regulated to <=1.5mum Ra, and the steel heated to 200 to 400 deg.C surface temp. is subjected to vapor deposition Al plating. At the time of regulating the surface roughness to <=1.5mum Ra, the generation of pin holes piercing the formed vapor deposition Al-plated layer is suppressed to improve the corrosion resistance of the plated steel. Moreover, because the surface temp. is held to 200 to 400 deg.C, the adhesion of the plated layer to the base steel is made excellent, and the workability of the plated steel is also made good.

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 vapor-deposited Al-plated steel material having excellent adhesion and corrosion resistance without changing the characteristics of the base steel such as strips and sheets.

[0002]

2. Description of the Related Art The corrosion resistance can be improved by plating the surface of steel with Zn, Al or the like. Recently, a similar plating layer has been formed on stainless steel to improve the corrosion resistance.

As a means for forming a plating layer, electroplating, hot dipping, etc. have been used for a long time. However, in the case of the electroplating method, the hot dipping method, etc., the metal that can be plated is restricted. Particularly in hot dip plating, since the steel material is heated to a high temperature, a brittle Al-Fe-based intermetallic compound or the like is likely to occur between the base steel and the plating layer. Therefore, when the plated steel material is subjected to processing such as press forming, cracks are likely to occur in the plated layer, which causes drawbacks such as powdering and flaking.

The steel substrate is exposed where the plating layer is peeled off or cracks are formed in the plating layer. Therefore, corrosion progresses mainly in the defective portion of the plating layer. Further, when the base steel is exposed to a wet atmosphere in an exposed state, a local battery is formed between the plating metal, which is a dissimilar metal, and the base steel, and the plating layer is consumed and red rust is generated in the base steel.

Therefore, a vacuum vapor deposition method, which has little influence on the base steel, is considered promising. When using the vacuum deposition method, there is no restriction on the plating metal that can be used, and it is possible to plate many kinds of metals. The formed plating layer does not form an alloy layer with the base steel, and thus has excellent workability. Further, when different kinds of metals are vapor-deposited from different evaporation sources, an alloy plating layer having a desired composition can be easily obtained.

[0006]

When an Al plating layer is formed on the surface of a steel material by vacuum vapor deposition, electron beam heating,
After activating the steel material surface by gas reduction or the like, Al is vapor-deposited on the steel material surface. The thicker the Al plating layer is, the more the protective action against the base steel is improved, and the corrosion resistance of the product is improved. However, considering the productivity, the thickness of the Al plating layer is usually set to 1
It is suppressed to 0 μm or less.

Therefore, various methods have been proposed so far in order to improve the adhesion of the plating layer to the base steel in order to form a vapor-deposited Al plating layer exhibiting a good anticorrosion effect under the condition that the plating thickness is limited. There is. For example, the present inventors have also developed a method of performing vapor deposition plating after activating the surface of a steel material by irradiation with an ion beam, and disclosed in JP-A-64-5.
It was introduced in Japanese Patent No. 6862. Ion beam irradiation utilizes an etching action that occurs when accelerated ions collide with the surface of the steel material, unlike the method of thermally activating the surface of the steel material by electron beam heating. Therefore, the surface of the steel material that has been irradiated with the ion beam becomes a base suitable for forming a vapor-deposited plating layer that has an excellent activated state and good adhesion.

The activation treatment improves the adhesion of the vapor-deposited Al plating layer to the steel surface. However, it is still impossible to eliminate defects such as pinholes.
This is because vapor deposition plating itself is easier to form a porous plating layer than other plating methods. Especially when the plating layer is thin, continuous pinholes from the surface of the plating layer to the base steel are likely to occur. If there is a defect such as a pinhole penetrating the plating layer, the base steel is exposed to the atmosphere through the pinhole, and the corrosion of the base steel proceeds around the defective part of the plating layer.

Therefore, the present invention has been devised to solve such a problem, and by defining the surface roughness and surface temperature of the steel material to be plated, a relatively small plating thickness can be achieved. Also aims to prevent the generation of pinholes penetrating the plating layer and improve the corrosion resistance of the vapor-deposited Al-plated steel material.

[0010]

In order to achieve the object, the method for producing a vapor-deposited Al-plated steel material according to the present invention has a surface temperature of 200 to 40 for a steel material having a surface roughness Ra of 1.5 μm or less.
It is characterized by heating to 0 ° C. and depositing aluminum or aluminum alloy on the surface of the steel material.

[0011]

The function of the deposited Al plating layer formed on the surface of the steel material is affected by the surface roughness of the base steel. Figure 1
It is the figure which represented typically the influence which surface roughness gives to compactness. Al as plating metal 2 on uneven base steel 1
When vapor-depositing, the surface unevenness causes a shadowed portion in the flight direction of the plated metal 2. In the shaded area, the plating metal 2 does not fly, and the plating layer 4 is formed on the void 3 with the void 3 still existing. Therefore, when the plating layer 4 is formed thin, a pinhole extending from the void 3 opens on the surface of the plating layer 4. As a result, a pinhole penetrating the plating layer 4 is formed.

Therefore, in the present invention, by setting the surface roughness to be low, the shadow portion where the plating metal 2 does not come in is reduced as much as possible. As a result, the generation of the voids 3 and thus the penetration pinholes is suppressed, and a vapor-deposited Al plating layer having an excellent density is formed.

The extremely low surface roughness requires a special pretreatment such as polishing for the steel material to be plated, which causes an increase in manufacturing cost. In this regard, Ra1.
It was found that the generation of pinholes can be sufficiently suppressed as long as the surface roughness of 5 μm or less is maintained.

Further, when the surface roughness is Ra 1.5 μm or less, the unevenness on the surface of the steel material becomes extremely fine. Since the plating metal is vapor-deposited on the fine irregularities, many growth points of the plating layer can be obtained. That is, since the plating layer grows from many growth points, the plating layer itself becomes dense. As a result, even if the plating thickness is 10 μm or less, the formed plating layer has a sufficiently dense structure and exhibits an excellent protective effect on the base steel.

The steel material on which the plating layer is formed needs to be maintained at a surface temperature of 200 to 400 ° C. in order to improve the adhesion of the plating layer. If the surface temperature is less than 200 ° C., the force of the flying plating metal to adhere to the surface of the steel material becomes weak, and a gap is likely to be formed between the deposit and the surface of the steel material. On the other hand, when the surface temperature exceeds 400 ° C., an alloying reaction occurs between the plating layer and the base steel, and brittle intermetallic compounds and the like are easily generated.

[0016]

EXAMPLES Next, the present invention will be described in detail with reference to examples. In this example, the electron beam vapor deposition apparatus shown in FIG. 2 was used. That is, the substrate 11 is placed inside the vacuum chamber 10.
And the electron beam evaporation source 12 was opposed to the substrate 11. The electron beam evaporation source 12 contains Al as evaporation metal 14 in a water-cooled copper hearth 13. Evaporated metal 14
Are heated and evaporated by the electron beam 16 from the electron gun 15 and fly to the substrate 11. The substrate 11 is heated to a predetermined temperature by an electron beam 18 from a heating electron gun 17 arranged on the back side.

As the substrate 11, a 70 mm × 150 mm test piece was cut from a Ti-added steel plate cold-rolled to a plate thickness of 0.6 mm and subjected to alkaline electrolytic degreasing. At this time, the surface roughness of the test piece was adjusted to various levels in the final step of cold rolling and the electrolytic degreasing step. Also, evaporating metal 14
For this, granular Al having a purity of 99.99% was used.

After setting the substrate 11 in the vacuum chamber 10, the vacuum chamber 10 was evacuated to 1 × 10 ⁻³ Pa. Then, the temperature of the substrate 11 is set to 200 to 400 by the heating electron gun 17.
Various changes were made in the range of ° C. Under this condition, Al was evaporated from the electron beam evaporation source 12 on the surface of the substrate 11 to form an Al plating layer having a thickness of 1 to 8 μm.

After sealing the back surface and the end surface of the substrate 11 on which the vapor-deposited Al plating layer was formed, a wetting test according to JIS K2246 was performed on the surface on the side where the vapor-deposited Al plating layer was formed. The test conditions were (1) rotation speed of the test piece frame: about 1/3 times / minute, (2) temperature of the test piece suspension position: 49 ± 1 ° C, (3) relative humidity: 95% or more , (4)
Water: Pure water was used.

The wet test was continued under these conditions, and the time until the ratio of the red rust generation area to the total surface area of the test piece reached 5% was measured. This time was classified into three stages, and the corrosion resistance of each test piece was judged. The results are shown in Table 1. In addition,
In Table 1, ∘ indicates a 5% red rust occurrence time of 500 hours or more, Δ indicates a 5% red rust occurrence time of 200 to 500 hours or more, and x indicates a 5% red rust occurrence time of less than 200 hours.

The density of the plated layer was examined by SEM observation, and the results of the examination are also shown in Table 1.

[0022]

[Table 1]

As is apparent from Table 1, the surface roughness Ra is
The test pieces of Test Nos. 1 to 11 maintained at 1.5 μm or less show good corrosion resistance in all cases. And, the pinhole penetrating the plating layer is tested N
It was not detected at all except the test piece of o.4. Even in the test piece of Test No. 4, the number of pinholes detected was very small, and the corrosion resistance was also good.

On the other hand, in the test pieces of Test Nos. 12 and 13 in which the surface roughness was Ra 1.8 μm and 2.0 μm, many pinholes were detected in the plating layer. Then, the red rust generated on the test piece after the wet test was generated from the base steel portion exposed to the atmosphere through the pinhole as a starting point.

As is clear from this comparison, when the surface roughness of the steel material to be vapor-deposited Al-plated is Ra 1.5 μm or less and the surface temperature is kept at 200 to 400 ° C., a vapor-deposited Al-plated layer excellent in corrosion resistance is formed. I understand that it will be done. Further, in any of Test Nos. 1 to 11, no alloying reaction between the plating layer and the base steel was observed, and the plating layer having excellent adhesion was formed.

[0026]

As described above, in the present invention, the vapor-deposited Al plating excellent in corrosion resistance is obtained by setting the surface roughness of the steel material to be plated to Ra 1.5 μm or less and the surface temperature to 200 to 400 ° C. A layer is formed. Even if the vapor-deposited Al-plated layer is as thin as 10 μm or less, there are substantially no pinholes reaching the base steel, so that the vapor-deposited Al-plated steel material exhibiting excellent corrosion resistance can be produced with good productivity. Moreover, since there is no alloying reaction between the plated layer and the base steel and the deposited Al plated layer is formed with excellent adhesion, the deposited Al plated steel sheet obtained is free from defects such as powdering and flaking. A material that can be processed into a product shape without being generated.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating the effect of surface roughness on the density of a plated layer.

FIG. 2 is an electron beam evaporation apparatus used in an embodiment of the present invention.

[Explanation of symbols]

10 vacuum tank 11 substrate (material to be plated) 14 evaporated metal (plating metal) 16 electron beam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Saito 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd.

Claims (1)

[Claims] 1. A vapor-deposited Al-plated steel material, characterized in that a steel material having a surface roughness Ra of 1.5 μm or less is heated to a surface temperature of 200 to 400 ° C., and aluminum or an aluminum alloy is vapor-deposited on the surface of the steel material. Method.