JPH05287508A - Local corrosion-resistant al/ti double-layer plated steel sheet - Google Patents

Abstract

PURPOSE:To improve the local corrosion resistance by controlling the bias voltage of a substrate and film thickness in Ti ion plating to suppress the formation of an Al-Ti intermetallic compd. and forming an Al layer on a Ti layer on the surface of a steel sheet without interposing the compd. CONSTITUTION:The surface of a steel sheet is ion-plated with Ti to form a Ti film on the surface. In this case, the Ti film and substrate minus bias voltage are allowed to lie in the area enclosed by (10mum, -50V), (10mum, -600V), (6mum, -100V), (0.1mum, -1000V) and (0.1mum, -50V), as shown in the figure. An Al layer is then formed on the Ti layer by vacuum deposition or ion plating.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a local corrosion-resistant Al / Ti two-layer plating suitable as a thin plate material used particularly in a high temperature, high chlorine ion concentration and acidic wet corrosive environment such as a material for automobile exhaust. TECHNICAL FIELD The present invention relates to a steel plate and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a hot-dip Al-plated steel sheet or a hot-dip Al-Si alloy-plated steel sheet has been used as a material for which high temperature oxidation resistance and corrosion resistance have been required, for example, a material for automobile exhaust which undergoes severe internal corrosion due to exhaust condensed water. It was used. However, in the former case, if a pure Al bath is used for hot dip Al plating, a brittle Fe—Al alloy layer grows between the steel plate and the Al layer, so that the plating layer peels off during processing. In the latter case, the Al-Si alloy layer causes Fe to
-Since the formation of the Al alloy layer is suppressed, the workability is improved as compared with the hot-dip Al-plated steel sheet, and excellent high-temperature oxidation resistance at 600 ° C or lower, while 700 to 800
There is a problem that when the temperature rises to 0 ° C., oxidation rapidly progresses and heat resistance deteriorates (Japanese Patent Laid-Open Nos. 62-80261 and 62-62).
80262).

Further, as a base steel sheet, ultra low carbon Cr--Ti
A method of improving high temperature oxidation resistance at 700 to 800 ° C. by using a killed steel sheet has also been attempted. However, this method has a drawback that the workability is deteriorated because an alloy layer is formed between the plating layer and the steel sheet (see JP-A-62-80261 and JP-A-62-80262).

On the other hand, it is known that when a steel sheet is subjected to Al plating by vacuum vapor deposition, no alloy layer is formed between the formed Al film and the steel sheet, and the adhesion and workability are excellent. However, the vacuum-deposited Al-plated steel sheet has many pinholes in the Al film, and a corrosion current flows between the Al layer near the pinholes and Fe in the base steel sheet, so that Al is rapidly dissolved and sufficient corrosion resistance is obtained. Is not obtained (Japanese Patent Laid-Open No. 62-
80261, JP-A-62-80262). In addition, since Al and Fe alloy with each other in a high temperature atmosphere, oxidation of the base steel sheet proceeds from the peeled portion of the alloy layer, and sufficient heat resistance cannot be obtained.

In order to solve these problems, in JP-A-52-123343 and JP-A-62-80262, T
An Al / Ti double-layer plated steel sheet in which an i film and an Al film are sequentially formed has been proposed. The invention of Japanese Patent Laid-Open No. 52-123343 is a composite vapor deposition treatment method in which Ti is first deposited on the surface of the object to be treated and then Al is deposited. Also, JP-A-62-8
In the invention of No. 0261, a Ti film and an Al film having a thickness of 0.02 to 5 μm are quasi-formed on the surface of the steel sheet, and the total film thickness is 0.5 to 20 μm and the thickness of the Ti film is the total film thickness. It is a plated steel sheet with 60% or less. However, such an Al / Ti double-layer plated steel sheet still has a problem to be solved. That is, the material for automobile exhaust contains acidic and high concentration chlorine ions required,
Further, in a severe corrosive environment exposed to a high temperature humid environment of 100 ° C. or higher, the surface Al layer is wholly or partially dissolved. Then, if an Al—Ti intermetallic compound such as Al ₃ Ti is present microscopically at the boundary between the Al layer and the Ti layer, there is a problem that local corrosion progresses to the Ti layer starting from this portion. That is, the present inventors
_A corrosion test was performed on an Al / Ti double-layer plated steel sheet (substrate: SUS41OL, plate thickness: 0.8 mm) in which ₃ Ti intermetallic compound was present, and the surface after the test was observed by a scanning electron microscope. As a result, as shown in FIG. 3, it was found that pitting corrosion occurred in the portion where the intermetallic compound was generated and the local corrosion resistance was poor.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent local corrosion from occurring even in an acidic wet corrosive environment at high temperature and high chlorine ion concentration. / Ti double-layer plated steel sheet and a method for manufacturing the same.

[0007]

A local corrosion resistant Al / Ti double-layer plated steel sheet according to the present invention is a steel sheet, a Ti layer formed on the steel sheet surface, and an Al-Ti intermetallic compound on the surface of the Ti layer. And an Al layer formed directly without interposing a layer.

[0008] The method for producing the Al / Ti bilayer plated steel sheet having such a structure is to define the Ti film thickness and the substrate bias voltage at the time of Ti ion plating within the shaded FIG 1, Al ₃ Ti, intermetallic compounds Al-Ti-based, such as TiAl or Ti ₃ Al is prevented from generating even microscopically the boundary of the Al layer and the Ti layer.

Specifically, the present invention is a process of performing Ti ion plating on the surface of a steel sheet to form a Ti layer on the surface of the steel sheet, and performing Al vacuum deposition or Al ion plating on the surface of the Ti layer. In the method for producing an Al / Ti double-layer plated steel sheet, which continuously performs the step of forming a layer, the substrate negative bias voltage and the film thickness in Ti ion plating are set to (-50 V, 10 μm).
m), (-600V, 10 μm), (-1000V, 6
μm), (−1000V, 0.1 μm), (−50V,
0.1 μm) and (−50 V, 10 μm), preferably (−50 V, 10 μm) and (−1000).
V, 0.1 μm), (-50 V, 0.1 μm), (-5
Within the range surrounded by 0 V, 10 μm (that is, 0 μm
≤ Ti film thickness ≤ 10 µm, -1000 V ≤ bias voltage ≤
-50 V, and Ti film thickness ≤ 0.01 x bias voltage +1
As a condition of 6), a local corrosion resistance of forming a Ti layer Al /
It is a method for manufacturing a Ti double-layer plated steel sheet.

Another method of the present invention is that T
A step of forming a Ti layer on the surface of the steel sheet by performing i ion plating, and Al vacuum deposition or A on the surface of the Ti layer.
In the method for producing an Al / Ti double-layer plated steel sheet, which comprises the step of performing an ion plating to form an Al layer, the substrate negative bias voltage and the film thickness in the Ti ion plating are set to (-50 V, 10 μm).
m), (-600V, 10 μm), (-1000V, 6
μm), (−1000V, 0.1 μm), (−50V,
0.1 μm) and (−50 V, 10 μm), preferably, the substrate negative bias voltage and film thickness in Ti ion plating are (−50 V, 10 μm).
m), (-1000V, 0.1 μm), (-50V,
0.1 μm), (-50 V, 10 μm) Local corrosion resistance Al / T for forming a Ti layer under the condition of being surrounded by (-50 V, 10 μm)
i It is a method for manufacturing a double-layer plated steel sheet.

[0011]

In order to facilitate the understanding of the present invention, it will be described specifically and in detail below.

First, after cleaning the surface of a steel plate or a steel plate containing 5% or more of Cr such as a stainless steel plate or a heat-resistant steel plate, a Ti film is formed by plating. There is no limitation on the film forming method for forming the Ti film. That is, any of dry plating such as ion plating in a high vacuum, vacuum deposition, ion beam deposition or sputtering may be used, but ion plating is preferable in terms of workability and productivity (Hiroshi Kagechika, Tomoaki Hyodo, Hiroshi Kibe, Yoshihiko Yasue: N
KK Technical Report, No.135 (1991), page 23). In the case of ion plating, it is possible to form a Ti film on ion plating in a low or medium vacuum using an introduced gas, such as DC discharge ion plating or high frequency discharge ion plating, but in this case the film adhesion Therefore, ion plating in a high vacuum of 1 × 10 ⁻⁵ Torr or less, such as arc discharge type ion plating, is desirable because it may impair the property and the density and increase the pinhole generation rate.

The Ti film thickness range is from 0.1 μm to 10 μm.
Below. This is because if the coating thickness is less than 0.1 μm, the corrosion resistance effect cannot be obtained, and if it exceeds 10 μm, the workability deteriorates.

The negative bias voltage applied to the substrate during Ti ion plating is set to -1000V or more and -50V or less. When the bias voltage exceeds -50V, the crystal grains become small and the workability is impaired. Further, when the bias voltage is less than -1000V, the Ti film has a thickness of 0.1.
This is because even when the thickness is as thin as μm, the kinetic energy when Ti ions collide with the steel sheet becomes high and the substrate temperature becomes 600 ° C. or higher, so that an Al—Ti intermetallic compound is generated and the local corrosion resistance deteriorates.

Further, even in the Ti film thickness range and the bias voltage range, under the coating conditions in which the Ti film thickness is 6 μm to 10 μm and the substrate bias voltage is −1000 V to −600 V, the substrate temperature is likely to rise due to the synergistic action of both. .. Therefore, the Al-Ti intermetallic compound (Al ₃ Ti, T
iAl and Ti ₃ Al) are generated, and the local corrosion resistance is likely to deteriorate. Therefore, when the Ti film thickness is large, it is necessary to increase the negative bias voltage applied to the substrate (decrease the absolute value) accordingly. That is, (-60 in FIG.
0 V, 10 μm), (−1000 V, 6 μm), that is, a Ti film thickness range and a bias voltage range satisfying the condition of Ti film thickness (μm) ≦ 0.01 × bias voltage (V) +16. To set.

When both sides of an Al / Ti double-layer plated steel sheet are applied, the substrate temperature rises depending on the Ti film thickness and the substrate bias voltage when performing Ti ion plating on the back surface. For this reason, if the Ti film thickness range and the bias voltage range are not set appropriately, Al and Ti on the front surface already coated are alloyed to form an Al-Ti intermetallic compound, so that Ti and Al are continuously plated. Similarly, the local corrosion resistance is impaired. In this case also, the setting conditions are the same as above.

In summary, the range of the film thickness and the bias voltage in Ti ion plating is (-50 V, 10 μm) and (-600 V, 10 μm) as shown in FIG.
m), (-1000V, 6 μm), (-1000V,
0.1 μm), (-50 V, 0.1 μm), (-50
V, 10 μm) and particularly (−50 V,
10 μm), (−1000 V, 0.1 μm), (−50
V, 0.1 μm) and (−50 V, 10 μm) are preferable.

Next, an Al film is formed on the Ti film.
Ion plating or vacuum deposition is desirable as a forming method from the viewpoint of workability and productivity. Al plays a role in protecting the base steel sheet by a sacrificial anticorrosive action in this corrosive environment.
Furthermore, even after Al is completely dissolved,
If the ions remain, it has the effect of suppressing the dissolution of Ti and the base steel sheet. The thickness of the Al film is 0.1 μm or more and 20 μm
Is preferred. That is, if it is less than 0.1 μm, the anticorrosive effect cannot be obtained, and if it exceeds 20 μm, the workability is deteriorated.

[0019]

EXAMPLES Next, examples of the present invention will be described. (Example 1) Continuous plating method Cold-rolled steel sheet (cold-rolled steel sheet) defined by JIS G3141, a cold-rolled stainless steel sheet defined by JIS G4305, and JIS G4312 having a plate thickness of 0.6 to 1.5 mm.
After preheating the heat-resistant steel plate specified in 1. to 100 to 300 ° C., pretreatment with Ar bombardment was performed in vacuum. In this method, a high frequency discharge is generated in an Ar gas atmosphere of 1.0 × 10 ⁻³ Torr, and at the same time, a negative voltage of −1 kV is applied to the steel sheet to cause Ar ions to collide with the steel sheet and remove oxides on the surface of the steel sheet. It is a method of obtaining a clean steel plate surface.

Then, the steel sheet was plated with Ti while being heated at 100 to 300 ° C. Plating condition is 1.0 × 10 ^-5
Pure Ti is heated and evaporated by an electron beam at an atmospheric pressure of Torr or lower, and the evaporated Ti particles are ionized,
It carried out on the conditions which plate the steel plate to which the negative voltage of -1000V was applied. Further, in the comparative example, the coating was performed even under the conditions that deviate from the bias voltage range and the Ti film thickness range of the present invention. Similarly, pure Al is heated and evaporated by an electron beam under the same atmospheric pressure to perform plating. A plated steel sheet having a Ti film and an Al film formed by such a plating treatment was manufactured by changing the film thickness of each film.

These steel sheets were examined for adhesion, corrosion resistance and heat resistance. The results are shown in Table 1.

The adhesion was evaluated by a bending tape peel test. This test was evaluated by performing a tape peeling test each time it was bent once at 0 ° at 180 °, repeating the peeling test until the base material was broken, and examining the presence or absence of peeling of the plating film.

Corrosion resistance in a high temperature acidic wet corrosive environment is
It was evaluated by a 5% salt spray test. Also, as a simulated corrosion environment for the inner surface of an automobile muffler, whether the test piece is immersed in a corrosive solution of carbonate ion, sulfate ion and chlorine ion and heated at 130 ° C for 48 hours five times to cause red rust to reach the base steel plate It was evaluated by.

[0024]

[Table 1] Note 1) Evaluation criteria (Adhesion) ○: No peeling of plating layer, ×: Peeling of plating layer (Workability) ○: No crack on the sample surface after bending,
×: Crack generation (salt spray test) ○: No local corrosion, ×: Local corrosion (muffler test) ○: No local corrosion, ×: Local corrosion Note 2) Muffler test: Carbon ion concentration = 500ppm with ammonium salt, Prepare a test solution containing sulfate ion concentration = 100 ppm and chloride ion concentration = 500 ppm, immerse the test piece, and then heat at 130 ° C for 48 hours. The solution evaporates in about 20 hours, but the corrosion products are not removed, and the test solution is injected again, and
Heating at 130 ° C for 48 hours is repeated 5 times in total. Note 3) Coating order: Substrate preheating (100 to 300)
° C) → Ar ion bombardment → Ti ion plating → Al vacuum deposition (Ti and Al plating is continuously treated) (Example 2) Double-sided plating method The surface is plated with Ti and Al under the same conditions as in Example 1. After that, the back surface was plated with Ti and Al under the same conditions as in Example 1. Table 2 shows the manufacturing conditions and test results of the obtained double-layer plated steel sheet.

[0025]

[Table 2] Note 1) Evaluation criteria (Adhesion) ○: No peeling of plating layer, ×: Peeling of plating layer (Workability) ○: No crack on the sample surface after bending,
×: Crack generation (salt spray test) ○: No local corrosion, ×: Local corrosion (muffler test) ○: No local corrosion, ×: Local corrosion Note 2) Muffler test: Carbon ion concentration = 500ppm with ammonium salt, Prepare a test solution containing sulfate ion concentration = 100 ppm and chloride ion concentration = 500 ppm, immerse the test piece, and then heat at 130 ° C for 48 hours. The solution evaporates in about 20 hours, but the corrosion products are not removed, and the test solution is injected again, and
Heating at 130 ° C for 48 hours is repeated 5 times in total. Note 3) Coating order: Substrate preheating (100 to 300)
℃) → Ar ion bombardment → Ti ion plating → Al vacuum deposition → Steel plate inversion → Ti ion plating → Al vacuum deposition (double-sided plating)

[0026]

As described above, according to the present invention, the Ti film thickness and the substrate bias voltage are regulated, and the Al--Ti based intermetallic compound such as Al ₃ Ti, TiAl or Ti ₃ Al is A.
It is particularly useful as a thin plate material for automobile exhaust because it does not generate microscopically at the boundary between the 1-layer and the Ti layer, and local corrosion does not occur even when used in an acidic wet corrosive environment at high temperature and high chlorine ion concentration. Is.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a substrate negative bias voltage and a Ti film thickness in a Ti ion plating specified in the present invention.

FIG. 2 is a schematic sectional view of an Al / Ti double-layer plated steel sheet according to the present invention.

FIG. 3 is a micrograph showing an example of localized corrosion (pitting corrosion) observed in an Al3Ti intermetallic compound layer in which an Al layer and a Ti layer are alloyed.

[Explanation of symbols]

 1 ... Steel plate, 2 ... Ti layer, 3 ... Al layer

Claims (5)

[Claims] 1. A local corrosion resistant Al comprising a steel sheet, a Ti layer formed on the surface of the steel sheet, and an Al layer formed directly on the surface of the Ti layer without interposing an Al--Ti intermetallic compound layer. / Ti double-layer plated steel sheet. 2. A step of forming a Ti layer on the surface of a steel sheet by performing Ti ion plating on the surface of the steel sheet, and a step of performing Al vacuum deposition or Al ion plating on the surface of the Ti layer to form an Al layer. In a method for continuously producing an Al / Ti double-layer plated steel sheet, the substrate negative bias voltage and the film thickness in Ti ion plating are (-50 V, 10 μm), (-60
0 V, 10 μm), (-1000 V, 6 μm), (-1
000V, 0.1 μm), (−50V, 0.1 μm),
A method for producing a locally corroded Al / Ti double-layer plated steel sheet, wherein a Ti layer is formed under a condition surrounded by (-50 V, 10 μm). 3. The substrate negative bias voltage and film thickness in Ti ion plating are set to (-50 V, 10 μm).
m), (-1000V, 0.1 μm), (-50V,
0.1 μm), (−50 V, 10 μm) The Ti layer is formed as a condition within a range surrounded by (−50 V, 10 μm). 4. A step of forming a Ti layer on the surface of a steel plate by performing Ti ion plating on both surfaces of the steel plate,
And / or Al vacuum deposition or Al ion plating on the surface of the layer to form an Al layer.
In the method for producing a Ti double-layer plated steel sheet, the substrate negative bias voltage and the film thickness in Ti ion plating are (-50 V, 10 μm), (-60
0 V, 10 μm), (-1000 V, 6 μm), (-1
000V, 0.1 μm), (−50V, 0.1 μm),
A method for producing a locally corroded Al / Ti double-layer plated steel sheet, wherein a Ti layer is formed under a condition surrounded by (-50 V, 10 μm). 5. The substrate negative bias voltage and the film thickness in Ti ion plating are set to (-50 V, 10 μm).
m), (-1000V, 0.1 μm), (-50V,
0.1 μm), (−50 V, 10 μm) The method for producing a locally corroded Al / Ti double-layer plated steel sheet according to claim 4, wherein the Ti layer is formed under the condition of a range.