JP2687014B2 - High corrosion resistance chrome plated stainless steel product and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a highly corrosion-resistant chrome-plated stainless steel product and a method for producing the same.

[Conventional technology]

In general, decorative chromium plating on stainless steel products is generally performed by nickel strike plating or bright nickel plating on the base, and then chromium plating having a thickness of 0.1 to 0.3 μm. Further, in order to further improve the corrosion resistance, a method of setting the nickel plating thickness to 20 μm or more, and to prevent galvanic corrosion with the chromium plating layer,
A method of adjusting the sulfur content derived from the brightening agent contained in each layer by using two or three nickel plating layers has been carried out.

However, the conventional decorative chrome plating on stainless steel products is a multi-layer plating with nickel plating on the underlayer, so internal stress and cracks due to processing occurred in the chrome plating layer and reached the underlayer nickel plating layer. In cases where the pinholes of the nickel plating layer could not be covered due to poor throwing power of the chromium plating,
Galvanic corrosion occurs at the boundary between the chrome plating layer and the nickel plating layer, and the corrosion resistance of the plating layer is extremely deteriorated. In recent years, in order to prevent this carbanic corrosion, a nickel plating layer has been added as described above.
A method of adjusting the sulfur content derived from the brightening agent in layers and 3 layers is performed. However, this method has a drawback that the number of steps is increased.

[Problems to be solved by the invention]

Therefore, an object of the present invention is to provide a chrome-plated stainless steel product having excellent corrosion resistance and a method for producing the same.

[Means for solving the problem]

The present invention has a thickness of 0.1 to 1.0 μm on the surface of stainless steel products.
Chromium plating is directly applied and 0.25 normal hydrochloric acid (50 ℃)
To provide a highly corrosion-resistant chrome-plated stainless steel product having a potential V _{100, tp} corresponding to a current density of 100 μA / cm ² of a positive polarization curve of 0.5 V (Ag / AgCl) or more. .

The present invention also provides a stainless steel product surface with a thickness of 0.1 to
It is intended to provide a method for producing the above-described highly corrosion-resistant chrome-plated stainless steel product by directly applying 1.0 μm chrome plating and heat-treating in the atmosphere to release hydrogen stored in the plating layer.

The present invention further provides a mirror-finished product obtained by further buffing the above-mentioned highly corrosion-resistant chrome-plated stainless steel product.

 Hereinafter, the present invention will be described in detail.

The stainless steel used in the present invention is not particularly limited, but is generally austenitic and ferritic stainless steel. First, if necessary, these stainless steel products are degreased with an organic solvent or an alkaline agent, then the surface of the stainless steel is activated, and then chromium plating is directly applied.

Examples of the method for activating the surface of stainless steel include immersion in acid, anodic or cathodic electrolysis in acid, and anodic electrolysis treatment in a plating solution.

Chromium plating, in a general chrome plating solution,
It is performed by performing cathodic electrolysis treatment.

The thickness of the plating layer is appropriately 0.1 μm to 1.0 μm, and typically, a plating layer having a thickness of about 0.3 μm is provided.
Even if the thickness is more than 1.0 μm, the effect of improving the corrosion resistance is not further improved, and if it is less than 0.1 μm, the corrosion resistance may be lowered when the buffing is performed.

After washing and drying the chromium-plated product as soon as possible, preferably within 48 hours, more preferably immediately after plating at 100 ° C to 300 ° C in the atmosphere for 0.5 to 24 hours, preferably 150.
Atmosphere heat treatment is performed for 1 to 10 hours at ℃ to 250 ℃.

The heat treatment is generally performed on a chromium-plated product for industrial use and removes hydrogen embrittlement and adjusts the hardness of the plating layer at the same time. In the conventional decorative chromium plating, the plating layer is thin (0.1 to 0.3 μm thick) and the hydrogen storage amount is small, so that the heat treatment is not performed and the corrosion resistance is not sufficient. However, since chrome plating has a very high hydrogen overvoltage, a large amount of hydrogen is stored in the generated plating layer (about 10 cc / g as hydrogen gas), and hydrogen immediately after plating exists as protons. These protonic hydrogens are
It has a very strong reducing property, and it is considered that it reduces the passive film at the time of diffusion and release, and becomes an obstacle to the formation of a corrosion-resistant passive film. Proton-like hydrogen bonds with other protons over time and becomes present as hydrogen gas in the plating layer. Therefore, it is more effective to perform heat treatment immediately after plating, and leave it for 3 weeks after plating. After that, even if heat treatment is performed, there is almost no effect of improving the corrosion resistance.

In the present invention, by heat treatment, hydrogen in a proton state immediately after plating is released from the plating layer in a short time, the hydrogen is completely removed, and a passivation film having excellent corrosion resistance is formed on the surface of the plating layer.

When gloss is required for the final product, wet or dry buffing treatment and mirror finishing treatment may be performed before or after the heat treatment. The wet buffing treatment is preferably performed before the heat treatment. Even if the buffing treatment is performed before the heat treatment, the effect of improving the corrosion resistance can be obtained by the heat treatment as long as the heat treatment is performed within a short time after the chrome plating is completed.

The buffing treatment may be a batch type or a continuous type, and particularly when the final product is a band-shaped one, the chrome plating treatment, the heat treatment and the buffing treatment can be continuously performed. More specifically, plating treatment → wet buffing treatment → heat treatment; plating treatment → dry buffing treatment → heat treatment; plating treatment → heating treatment → dry buffing treatment can be continuously performed.

The corrosion resistance of the final product thus obtained is evaluated as follows.

Electrochemical evaluation of corrosion resistance The measured sample was washed with alcohol and JIS G 0579
Put it together with the Viton spacer (fluorine rubber plate) in the acrylic holder shown in Fig. 3a, and press it with an acrylic screw from the back side to make an electrode with a liquid contact area of 1.0 cm ² .

The test solution is 0.25N hydrochloric acid, and the specific conductivity is 2 μS · cm.
^{It is} prepared by a dilution method using ion-exchanged water of ^-1 or less and 1N hydrochloric acid for volumetric analysis (manufactured by Wako Pure Chemical Industries, Ltd.).

The measurement procedure is as follows: The sample electrode is immersed in a test solution set to 50 ± 1 ° C under open air, and after the natural electrode potential stabilizes, the silver / silver chloride electrode is used as a reference electrode from that potential and the potentiostat (Hokuto Potential sweep speed 50min. ・ V ^-1 with potentiogalvanostat HA-501 type manufactured by Denko Co., Ltd.
The anodic polarization is started at, and the measurement is ended at the potential (V _{100, tp} ) at which the current density becomes 100 μA · cm ⁻² .

In the present invention, V _{100, tp} is 0.5 V or more, preferably 0.6 V or more, more preferably 0.8 V or more, still more preferably 1.0 V or more.

〔The invention's effect〕

Since the chrome-plated stainless steel product according to the present invention has extremely excellent corrosion resistance, it can be used in a severe corrosive environment, and is particularly suitable for exterior moldings for automobiles and exterior materials for construction. Because of its excellent pitting corrosion resistance and crevice corrosion resistance,
It is also suitable for use in food facilities, interior materials for construction, household appliances, home appliances parts, etc. where local corrosion is likely to occur. Furthermore, since it has better corrosion resistance than ordinary stainless steel, it is also suitable for chemical equipment and nuclear power.

Example 1 Specimen 430MA ・ BA (19Cr, 0.6Nb, 0.4Cu, LC) (0.4mm
(Thickness) was subjected to immersion boiling for 10 minutes in a commercially available alkaline degreasing solution to degrease it.

After washing with water, plating solution (Sergant solution 300g / l CrO ₃ + 3g / l
Anodic electrolysis (55 ° C, 30A / dm ² , 1 minute) in H ₂ SO ₄ ), immediately followed by cathodic electrolysis (55 ° C, 40A / dm ² , 1.5 minutes) to determine the plating thickness. It was around 0.3 μm.

After washing with water and drying, heat treatment was performed in the air at 300 ° C. for 1 hour.

V _{100, tp} of the material processed by the above method is 0.95V
Met.

Comparative Example The same operation as in Example 1 was repeated except that the heat treatment was not performed at 300 ° C. for 1 hour. V of the obtained material
_{100, tp} was 0.3V.

Example 2 The test material of Example 1 was similarly plated, then subjected to dry buffing with a blue rod as an abrasive, and then in air for 30 days.
Heat treatment was performed at 0 ° C. for 1 hour. The plating treatment, buffing treatment, and heat treatment were continuously performed. The reduction in the plating thickness after the buffing treatment was 0.01 to 0.02 μm, and a mirror finished product having excellent corrosion resistance was obtained. V100 _{, tp} was 0.95V.

Example 3 The sample of Example 1 was similarly plated, then wet-buffed with alumina, washed with water, dried, and then heat-treated in the air at 300 ° C. for 1 hour. Similar to Example 2, these treatments were continuously performed using a strip-shaped sample. A mirror finished product with excellent corrosion resistance was obtained. V
_{100, tp} was 0.95V.

Example 4 In Example 1, after the plating process, the plate was left in the atmosphere for a predetermined time and then heat-treated. As shown in the table below, it is understood that the value of V _{100, tp} decreases as the standing time increases.

Example 5 In Example 1, samples having various V _{100, tp} values were prepared by changing the standing time after plating treatment and before heat treatment, and the corrosion resistance of each sample was examined according to CASS JIS D 0201. The rusting situation after 240 hours is shown in the table below.

The sample of the present invention having V _{100, tp} of 0.5 V or more has a rating No. of 9.5 or more after the CASS test, which shows that it has extremely excellent corrosion resistance.

Claims (4)

(57) [Claims] 1. A thickness of 0.1 to 1.0 μm on the surface of a stainless steel product.
chrome plating is applied directly to 0.25 normal hydrochloric acid (50
High corrosion-resistant chrome-plated stainless steel product characterized by a potential V _{100, tp} corresponding to a current density of 100 μA / cm ^{2 of a} anodic polarization curve at ℃) of 0.5 V (Ag / AgCl) or more. 2. The highly corrosion-resistant chrome-plated stainless steel product according to claim 1, which is further mirror-finished. 3. A stainless steel product surface having a thickness of 0.1 to 1.0 μm.
The method for producing a highly corrosion-resistant chrome-plated stainless steel product according to claim 1, wherein the chrome-plated m steel is directly applied and heat-treated in the atmosphere to release hydrogen stored in the plating layer. 4. The method for producing a highly corrosion-resistant chrome-plated stainless steel product according to claim 2, wherein buffing is performed before or after the heat treatment.