JPH04221097A - Treatment of stainless steel material before plating - Google Patents

Abstract

PURPOSE:To form a plating excellent in adhesion and corrosion resistance by previously electroplating a stainless steel material with a metal contg. specified concns. of Fe, Co and Ni as the third element before the steel material is plated. CONSTITUTION:A stainless steel material is degreased, pickled and/or electrolytically activated, and the surface is previously electroplated with the iron-group metal such as Fe, Co and Ni alone or their alloy before plating so that the atomic concn. M3 of the third element fulfils the inequality (MFe, MCo and MNi are respectively the atomic concn. of Fe, Co and Ni). A brightener is not incorporated in this previous plating, and the current efficiency is controlled to <= about 50%. The steel material is then normally plated, and various metallic layers are formed on the stainless steel surface with excellent adhesion.

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 plated stainless steel materials with excellent plating adhesion and corrosion resistance.

0002

2. Description of the Related Art Stainless steel has excellent corrosion resistance and a clean surface, so it is used in its pure state for various purposes. However, depending on the application, corrosion resistance may be insufficient. In addition, design is considered important, and special functions such as solderability are sometimes provided so that various processing can be performed. For example, gold,
Solderability is imparted by plating the surface of stainless steel with silver, copper, nickel, chromium, etc.

[0003] A strong passive film is formed on the surface of this stainless steel. This passive film has an effective effect in maintaining the corrosion resistance of stainless steel, but
When plating stainless steel, it acts as a harmful layer, making it extremely difficult to form a plating layer with excellent adhesion. Therefore, methods such as electrolytic activation have been developed to obtain a highly active stainless steel surface from which the passive film has been removed. It is also known to form a protective film with excellent oxidation resistance on the stainless steel surface after the passive film has been removed in order to prevent the passive film from forming again on the stainless steel surface.

0004

[Problems to be Solved by the Invention] Due to the passive film present on the surface of stainless steel, it is very difficult to obtain good plating adhesion. This passive film also needs to be removed when plating gold, silver, copper, etc. However, the passive film cannot be completely removed by pickling, and a method using electrolytic activation in a sulfuric acid or hydrochloric acid bath, that is, cathodic electrolysis, is used. On the other hand, the stainless steel surface after the passive film has been removed is in a very active state, and when this surface comes into contact with the atmosphere, it is immediately oxidized and the passive film is re-formed.

[0005] In order to remove the passive film from the surface of stainless steel, conventional techniques have been used to avoid contact with the atmosphere and to apply electroplating to the stainless steel with the acid solution still attached. However, when stainless steel with an acid solution attached to it is introduced into a plating tank, the acid solution is brought into the plating solution, making the plating conditions unstable. Further, even in this case, contact between the activated stainless steel surface and the atmosphere cannot be completely prevented, and a passive film is still formed. In order to completely suppress contact with the atmosphere, it is necessary to place the plating line in a completely sealed protective atmosphere, which is not practical.

Therefore, as a means to prevent the electrolytically activated stainless steel from coming into contact with the atmosphere, a metal source that can be electrolytically deposited is added to an electrolytically activated bath such as sulfuric acid or hydrochloric acid. A possible method is to coat the surface with an added metal. For example, when ions such as copper and nickel are added to sulfuric acid, hydrochloric acid, etc., the surface of stainless steel is coated with copper and nickel that are precipitated during electrolytic activation. As a result, the formation of a passive film on the surface of the activated stainless steel is suppressed.

However, conventional pretreatments have been developed depending on the type of metal to be plated, and cannot be applied to different types of plating layers. For example, pretreatment for gold plating cannot be used as pretreatment for chrome plating. Furthermore, conventional pretreatments are often applied to cut plates, processed products, etc., and cannot be applied to continuous plating of stainless steel strips and the like. Moreover, the type of plating metal varies depending on the application, and the plating method itself is diverse, such as electroplating, hot-dip plating, and vapor deposition.

[0008] In this respect, conventional plating pretreatments lack versatility and cannot quickly respond to changes in demand. For example, when plating stainless steel strips, productivity can be improved if different types of plating layers can be formed on the same production line. For this purpose, a base treatment that can be used commonly for various plating layers is required.

The present invention was developed to meet these demands, and is designed to form a high-quality plating layer with excellent adhesion on stainless steel materials, regardless of the type of plating metal or plating method. The purpose is to modify the surface of

0010

[Means for Solving the Problems] In order to achieve the object, the plating pretreatment method of the present invention includes applying Fe to the surface of the stainless steel material before plating the stainless steel material.
, Co, and Ni or their alloys are electrolytically preplated.

[0011] Here, the pre-plating layer formed by electro-plating can contain a third element having an atomic concentration M3 or less specified by the following formula. However, MFe, MCo and MNi in the following formula represent the atomic concentrations of Fe, Co and Ni, respectively. M3≦(2.22×MFe+1.72×
MCo+0. 61×MNi)/(MFe+M
Co+MNi+2. 22×MFe+1. 72 x MC
o+0. 61×MNi)

[0012] Furthermore, electrolytic pre-plating may be applied to the stainless steel material after it has been degreased, pickled and/or electrolytically activated. Various plating methods such as hot-dip plating, electroplating, and vapor deposition can be used to plate the stainless steel after the electroplating layer has been formed.

[0013]

[Operation] The present inventors investigated and studied the process by which the surface of stainless steel is activated by removing the passive film by electrolytic activation. As a result, we found that the surface of stainless steel is not activated by the simple process of reducing the passive film with hydrogen gas, as previously thought. The present invention was completed based on this clarification.

[0014] When copper ions are added to sulfuric acid or hydrochloric acid and electrolytically activated, copper, which is a noble metal, is pre-plated on the surface of stainless steel. If the current efficiency of the copper is reduced by further adding acid to the electrolytic activation bath, hydrogen generation becomes active and the electrodeposited copper peels off from the stainless steel surface. This shows that although the passive film is certainly reduced to some extent by the hydrogen generated by electrolysis, the passive film is not removed only by reduction by hydrogen.

Therefore, the present inventors considered the reduction mechanism of the passive film on the surface of stainless steel as follows. In an electrolytic bath of sulfuric acid, hydrochloric acid, or the like to which metal ions are added, hydrogen ions are generated and metal ions are reduced simultaneously according to the following reaction. However, in the formula, M represents an electrode metal or an electrodeposited metal. H+ + e- (-M) → H-MH-M
+ H-M → H2 + M or H-M
+ H+ + e- (-M) → H2 +
M

[0016] When hydrogen ions are reduced, they instantaneously exist as atomic hydrogen. Since charge transfer occurs at the interface between the cathode and the solution, the generated atomic hydrogen bonds with the metal at the cathode. This atomic hydrogen is in an extremely unstable state, and becomes hydrogen gas by immediately bonding with each other or by generating electric discharge on the spot. At this time, some metal species of the cathode have a strong bonding force with atomic hydrogen, and in this case, atomic hydrogen exists on the cathode surface for a relatively long time. The atomic hydrogen present on the surface of the cathode has an extremely large reducing power compared to gaseous hydrogen, and is thought to have the effect of reducing the passive film on the surface of stainless steel.

[0017] Therefore, in order to efficiently reduce the passive film, it is necessary to store a large amount of atomic hydrogen on the cathode surface. Therefore, generating a large amount of hydrogen and using a metal with a high hydrogen overvoltage or a metal with a strong bonding force with atomic hydrogen as a cathode material are considered effective means for reducing the passive film.

[0018] In order to generate a large amount of hydrogen, cathodic electrolytic treatment in an acid solution is appropriate. From this point of view, it is considered that electrolytic activation in an acid solution has been conventionally employed as a means for reducing and removing the passive film of stainless steel. However, if the stainless steel is simply electrolytically activated in an acid solution, a passive film will be formed again on the surface of the activated stainless steel as described above.

Metals with high hydrogen overvoltage include zinc, mercury, and the like. However, pre-plating these metals on the surface of stainless steel may cause problems with the subsequent product properties, which limits the applications.

[0020] Examples of metals that have a high bonding force with atomic hydrogen include iron group metals such as Fe, Co, and Ni. The reason why these iron group metals exhibit a large binding force to atomic hydrogen is as follows. That is, atomic hydrogen consists of one proton and one electron, and forms a covalent bond with the metal. On the other hand, iron group metals have electron vacancies, that is, unpaired 3d electrons, in the 3d band in the solid metal state. Because of these unpaired 3d electrons, iron group metals easily form covalent bonds with atomic hydrogen. Therefore, the presence of unpaired 3d electrons is considered to have an important influence on the plating adhesion of stainless steel.

The number of unpaired electrons corresponds to the number of Bohr magnetons per atom. For example, the effective magneton number nB given by Kittel is shown in Table 1.

[0022]

[Table 1]

[0023]

As shown in Table 1, Fe, Co
and Ni are each 2.0% per atom. 22,1. 7
2 and 0. It has 61 unpaired atoms. Note that the reason why the number of unpaired atoms is not an integer is due to the asymmetry between the 3d subbands. It can be seen from Table 1 that for the same reason, Gd and Dy can also be used as elements that form bonds with atomic hydrogen. However, these elements Gd and Dy are not suitable as metals to be pre-plated because the chemicals for dissolving them are not common and are expensive.

[0024] When alloy plating is performed on iron group metals, unpaired 3d electrons are not filled. Therefore, atomic hydrogen is stored on the cathode surface regardless of the composition. However, this tendency is different when pre-plating an iron group metal alone or as an alloy with a third element. For example, the Bohr magneton numbers of iron group metals and their binary alloys are shown in Figure 1, and as the concentration of the third element in the precipitated alloy increases,
The vacant d-electron orbital is filled, and the unpaired 3d orbital that should finally store atomic hydrogen disappears. With such a precipitated alloy composition, the passive film on the stainless steel surface cannot be reduced and removed, and plating adhesion cannot be improved.

In this regard, when the atomic concentration of the third element is M3, the concentration in the precipitated alloy composition is specified by the following equation. However, MFe, MCo and MNi are Fe, MCo and MNi, respectively.
The atomic concentrations of Co and Ni are shown. M3≦(2.22×MFe+1.72×
MCo+0. 61×MNi)/(MFe+M
Co+MNi+2. 22×MFe+1. 72 x MC
o+0. 61×MNi)

The present invention will be explained in detail below.

In the present invention, when plating stainless steel, after degreasing, pickling, etc., iron group metals or alloys thereof, or tertiary metals are added to the extent that the unpaired 3d electrons are not satisfied.
Pretreatment is performed by electroplating an alloy of iron group metals to which elements have been added.

The type of stainless steel used as the plating material is selected depending on the purpose of use. However, since a pre-plating layer is formed, the plating properties do not vary depending on the type of stainless steel. Further, since pre-plating is performed by electroplating, it is preferable to finish the surface of the stainless steel by pickling. However, the present invention can also be applied to materials that have been subjected to a bright annealing finish, a polishing finish, or the like.

The plating process for stainless steel according to the present invention includes the steps of degreasing, pickling and/or electrolytic activation, pre-electroplating and main plating.

[0030] Degreasing is necessary to remove oils remaining on the surface of stainless steel and to ensure that subsequent processes can be carried out evenly. As the degreasing method, a method used in a normal plating process can be adopted, such as immersion degreasing or electrolytic degreasing. In addition, for materials such as ordinary stainless steel strips that have little oil adhesion, the stainless steel surface can be cleaned only by the usual electrolytic degreasing using sodium orthosilicate.

Pickling is performed to activate the stainless steel surface. Acids used for pickling include non-oxidizing acids such as hydrochloric acid and low concentration sulfuric acid. Nitric acid cannot be used as it re-passivates the stainless steel. The pickling bath has an acid concentration of about 5 to 10% and may be at a temperature of about room temperature. Note that pickling is employed when the surface of stainless steel is particularly oxidized and colored, and there is no need to pickle for stainless steel with a normal surface condition.

[0032] Electrolytic activation is also performed to activate the stainless steel surface, and even if the surface is not completely activated, it makes the action of pre-plating more effective. This electrolytic activation is carried out using a sulfuric or hydrochloric acid bath. However, when considering that an insoluble anode is used as a counter electrode, a sulfuric acid bath is preferable to a hydrochloric acid bath in which chlorine gas is generated from the counter electrode. This electrolytic activation bath may be maintained at a temperature of about room temperature. The higher the current density during electrolysis, the more hydrogen will be generated and the treatment time will be shortened. However, when considering practicality, it is preferable to maintain the upper limit of the current density at about 100 A/dm2.

The pickled or electrolytically activated stainless steel is pre-plated. The metal or alloy for pre-plating is appropriately selected depending on the use of the stainless steel to be plated. However, as long as the alloy is within the range specified by the present invention, there will be no functional problem considering that the base is stainless steel.

The conditions for pre-plating cannot be determined unconditionally because the bath composition, electrolytic conditions, etc. vary depending on the alloy forming the pre-plating layer, but specific conditions will be explained in Examples. However, compounds containing sulfur, nitrogen, etc. that are used as brighteners in ordinary electroplating are
Because it binds preferentially to electrons, less atomic hydrogen accumulates. Therefore, the pre-plating bath needs to be free of these brighteners.

[0035] In pre-plating, it is preferable to set the current efficiency to 50% or less. More than half of the current efficiency is used for hydrogen reduction, increasing the amount of atomic hydrogen stored. As a result, the passive film is efficiently reduced and removed from the stainless steel surface.

[0036] When the main plating subsequent to the pre-plating is performed by electroplating, the pre-plated stainless steel is washed with water and then the main plating step is carried out as it is. When the main plating is performed by a hot-dip plating method, the hot-dip plating process is started after a water washing and drying process.

[0037]

[Example] Examples will be explained below.

-Example 1- A commercially available nitric-hydrofluoric acid pickled plate with a thickness of 0. After electrolytically degreasing a 4 mm stainless steel strip SUS430, it was pre-plated under the conditions shown in Table 2. Further, Table 3 shows the composition of the plating bath used at this time. Note that the alloy compositions in Table 2 are expressed in weight %. In addition, the basis weight for pre-plated stainless steel is 3. Copper plating was performed at 5 g/m2.

A 2t bending test was performed on copper-plated stainless steel to determine whether the plating layer had peeled off or not, and to evaluate the adhesion. The evaluation results are also shown in Table 2. At this time, peeling of the plating layer occurred between the pre-plating layer and the underlying stainless steel. (Hereafter, the margins of this page)

[0040]

[Table 2]

[0041]

[Table 3]

From Table 2, for stainless steel pre-plated by electroplating with an iron group metal alone or an alloy thereof and an alloy of an iron group metal to which a third element is added within a range that does not satisfy the unpaired 3d electrons, It can be seen that a copper plating layer with excellent adhesion was formed. On the other hand, in the case of the pre-plated stainless steel of the comparative example, the copper plating layer formed by the main plating completely peeled off.

-Example 2- A commercially available nitric-hydrofluoric acid pickled plate with a thickness of 0. A 4 mm stainless steel strip SUS304 was electrolytically degreased, pickled with 5% sulfuric acid, and then pre-plated under the conditions shown in Table 5. As this bath, a plating bath having the same composition as shown in Table 3 was used.

[0044] Nickel plating was applied to pre-plated stainless steel to a plating thickness of 2 μm per side under the following conditions.
It was applied at m. D
Conditions for plating Plating bath composition: NiSO4
7H2O 240g/l
NiCl2 ・6H2
O 45g/l
H3 BO3
30g/l current
Density: 1~10A/dm2
Bath temperature: 50℃

0
[045] A 2t bending test was conducted on nickel-plated stainless steel in the same manner as in Example 1 to investigate the adhesion of the plating layer. The survey results are also shown in Table 4. Table 5 shows that when pre-plating was performed according to the present invention, a nickel plating layer with excellent adhesion was formed.

[0046]

[Table 4]

-Example 3- A commercially available nitric-hydrofluoric acid pickled plate with a thickness of 0. 4 mm stainless steel strips SUS304 and SUS430 were electrolytically degreased, pickled with 5% sulfuric acid, and then pre-plated under the conditions shown in Table 5.

[0048]

[Table 5]

Pre-plated stainless steel with a dew point of -6
3 at 700°C in a reducing atmosphere of 50% H2-N2 at 0°C.
Zn held at 450-460 °C after heating for 0 seconds
-0. The sample was introduced into a hot-dip zinc bath having a composition of 4Al, and hot-dip galvanizing was performed at a zinc coating weight of 100 to 150 g/m2. The plating adhesion of the plated stainless steel was investigated in the same manner as in Examples 1 and 2. The survey results are also shown in Table 5. As is clear from Table 5, the effect of pre-plating was also exhibited in hot-dip plating, and the adhesiveness of the formed hot-dip galvanized layer was excellent.

[0050] In the above embodiments, electrolytic copper plating, electrolytic nickel plating, and hot-dip galvanizing using stainless steel as a base were explained. However, the present invention is not limited thereto, and can be applied to electroplating such as chromium plating, gold plating, silver plating, hot-dip plating such as zinc alloy plating, aluminum, aluminum alloy plating, etc., as well as base materials such as vapor deposition and ion plating. It can also be used as a treatment.

[0051]

As explained above, when pre-plating is performed according to the present invention, plating layers of various metals can be formed on the surface of stainless steel with excellent adhesion. Further, this pre-plating is not limited to stainless steel, but can be similarly applied to other materials such as ordinary steel and special steel, and a plated layer with excellent adhesion and surface properties is formed.

[Brief explanation of the drawing]

[Figure 1] A graph showing the relationship between electron concentration and atomic moment in a binary alloy of iron group elements.

Claims (2)

[Claims] 1. Prior to plating the stainless steel material, Fe, Co, and Ni are applied to the surface of the stainless steel material so that the atomic concentration M3 of the third element in the pre-plating layer to be formed satisfies the following formula. A method for pre-plating stainless steel material, characterized by electrolytic pre-plating of iron group metals or their alloys. M3≦(2.22×MFe+1.72×
MCo+0. 61×MNi)/(MFe+M
Co+MNi+2. 22×MFe+1. 72 x MC
o+0. 61×MNi) (However, MFe, MCo and MNi are each Fe
, Co and Ni atomic concentrations. ) 2. A pre-plating method for stainless steel material, characterized in that the electrolytic pre-plating according to claim 1 or 2 is applied to the stainless steel material after it has been degreased, pickled and/or electrolytically activated.