JPH036392A - Manufacture of chromium plated stainless steel having excellent gloss - Google Patents

Abstract

PURPOSE:To form a Cr plated layer having an excellent gloss with tight adhesion at the time of applying Cr plating onto a stainless steel by degreasing the surface of the stainless steel, activating it, thereafter immersing the steel into a nonoxidizing acid water soln., immersing it into a Cr plating soln. in the state where the surface is coated with the above soln. as voltage is applied and executing plating. CONSTITUTION:The surface of a stainless steel is cleaned by degreasing and an oxidized film is thereafter removed by activating treatment; without water- washed, the steel is successively immersed into a nonoxidizing acid water soln. constituted of sulfuric acid or hydrochloric acid having 0.5 to 15wt.% concn. In the state where the surface is coated with the nonoxidizing acid water soln., the steel is immersed into a Cr plating soln. as negative voltage is applied to execute Cr electroplating. A Cr plating layer having excellent glossiness is formed on the surface of the stainless steel with close adhesion.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing chromium-plated stainless steel with excellent gloss, particularly for automobiles, home appliances, etc., which require materials with excellent corrosion resistance and gloss. Our objective is to provide ROM-plated stainless steel suitable for kitchen use, building materials, etc.

[Conventional technology] Stainless steel has traditionally been used as a corrosion-resistant material for automobiles, home appliances, kitchens, building materials, etc. Stainless steel is also made of ordinary steel with a thick base plating of copper and nickel. materials are also widely used.

Recently, weight reduction has become an issue, and cold-rolled stainless steel sheets plated with chromium are required as materials that retain their corrosion resistance and luster even in harsh corrosive environments.

[Problems to be Solved by the Present Invention] However, when directly plating stainless steel with chromium, it is difficult to obtain a high shine, so the chrome plating surface is usually polished to make it shiny or It is known that chrome is plated on top of bright nickel plating.

The need for such a complicated process inevitably leads to a rise in product costs.
Moreover, a method must be developed that can obtain excellent gloss without polishing.

In view of the above circumstances, the present inventors conducted various studies, and as a result, confirmed the following facts.

That is, in general, when plating stainless steel, a plating with good adhesion cannot be obtained unless the oxide film on the surface is removed by activation treatment.

For this reason, Ni strike plating is usually performed as a sub-baking treatment to ensure that no oxide film is re-formed on the stainless steel substrate, and then various metal platings are applied. In the case of chrome plating, a chrome plating with excellent gloss can be obtained by applying it on top of Ni strike plating, but Ni
It is known that corrosion resistance is poor when the layer is extremely thin, such as 1 μm or less.

Therefore, as mentioned above, in order to produce products with corrosion resistance, excellent gloss, and low cost, it is necessary to remove the oxide film on the stainless steel base directly by activation treatment without applying Ni strike plating. It has been found that by applying chrome plating while preventing regeneration, a product with excellent gloss can be obtained.

[Means for Solving the Problems] The present invention has been made based on the above findings, and includes:
The gist of this is that in the process of chromium plating stainless steel, the stainless steel is immediately immersed in a non-oxidizing acid aqueous solution with a concentration of 0.5 to 15% by weight following pretreatment of degreasing and activation. The structure is such that chromium plating is applied by immersing the material coated with a liquid film in a plating bath while applying voltage.

[Function] Prior to the present invention, the inventors conducted repeated studies on the pretreatment and plating conditions, since when chromium plating is applied to stainless steel, the gloss differs significantly depending on the plating conditions, and as a result, as described below. It was discovered that the gloss of chrome plating is largely controlled by the chromium oxide film.

In other words, stainless steel is coated with a stable passive film, and even if the oxide film is removed through activation treatment, when it comes into contact with air or water, chromium and oxygen react immediately and the chromium oxide film, which is a passive film, is removed. A working film is formed.

Furthermore, when stainless steel is brought into contact with a chromium plating bath containing chromic acid as a main component without electricity, it is oxidized by the chromic acid, which is a strong oxidizing agent, and an oxide film, which is a passive film, is immediately formed.

Even if such an oxide film is formed, if it is very thin, chromium will break through it and electrodeposit directly onto the stainless steel base, forming a chromium plating layer with good adhesion, but Since it precipitates in granular form regardless of crystal orientation, gloss deteriorates due to diffuse reflection.

Therefore, as in a normal plating process, after the activation treatment, the material is washed with water, immersed in a chromium plating bath, and then energized to plate chromium, resulting in matte finish. As a result, in order to improve gloss, it is necessary to prevent the formation of an oxidized film on chromium, and after activation treatment, the surface should be immediately immersed in a non-oxidizing acid aqueous solution without rinsing with water to prevent surface oxidation. is required.

When moving from such a pretreatment state to the chromium plating process, if a voltage is applied to the plating bath in advance so that electricity can be applied at the same time as immersion, the chromium will not be affected by the oxidation effect of chromic acid and the crystal orientation of the plating base plate will be adjusted. A plated surface with the same gloss as the substrate is obtained. As the non-oxidizing acid aqueous solution, an aqueous solution of sulfuric acid, hydrochloric acid, etc. can be used. In this case, the acid concentration is between 0.5 and 15% by weight. This is because if the amount is less than 0.5% by weight, the effect will decrease, and if it is more than 15% by weight, the surface of the substrate will become rough and the gloss will deteriorate.

The temperature of the non-oxidizing acid aqueous solution and the time during which it is coated with the aqueous solution are not particularly limited, but in order to prevent the formation of an oxide film, it is preferable to keep the temperature at room temperature for a short time.

[Effects of the present invention] As described above, the present invention enables chromium plating to be applied to stainless steel by applying a voltage load in a non-oxidizing acid aqueous solution after activation treatment without using the conventional water washing process. Since a liquid film of the aqueous solution is formed, there is no need for the conventional polishing process, and there is no need for base treatment for Ni strike plating, so the gloss finishing process can be significantly shortened. This material can easily meet the demands of automobile and building materials, which demand materials with low cost and excellent corrosion resistance, and provides excellent industrial effects.

[Example] Next, the present invention will be specifically described with reference to Examples.

SUS 430 series stainless steel plate (0.4mm+thickness) with bright annealing finish is immersed in degreasing (alkaline degreasing liquid, 55℃)
, immersion for 1 minute), electrolytic degreasing during water washing (alkaline degreasing solution, room temperature, anodic electrolysis IA/dm' for 1 minute) φ water washing φ electrolytic activation treatment (solid acid aqueous solution, room temperature, cathodic electrolysis IA/dm')
After passing through a plating pretreatment process in the order of 1 minute), chrome plating was applied by the method of the present invention and the comparative example shown below, respectively, and the chrome plating surface was measured with a glossy needle.

In addition, chrome plating is carried out at 50℃ in a Sargent bath at 40A/
Electricity was applied for dm2.30 seconds, and the plating thickness was 0.3μ. In addition, a reflective gloss needle with a silver mirror surface of 100% was used for gloss evaluation. The results are shown in Table 1.

Table 1 (Gloss of plating original Fi base = 64%) As shown in Table 1, after activation treatment, without washing with water, at room temperature, 0
．． It is clear that if the plate is immersed in a 5 to 15% by weight aqueous sulfuric acid solution, then immersed in a chrome plating bath with the liquid film covered, and the voltage is applied before immersion, the same gloss as the original plating plate can be obtained. It is.

Claims (1)

[Claims] In the process of chromium plating stainless steel, the stainless steel is immediately immersed in a non-oxidizing acid aqueous solution with a concentration of 0.5 to 15% by weight following pretreatment of degreasing and activation. A method for producing chrome-plated stainless steel with excellent luster, which is characterized by applying chromium plating by immersing the coated state in a film in a plating bath under voltage load.