JP3406448B2 - Plating method for ultra-high strength steel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating treatment method for reducing brittleness caused by hydrogen generated during pretreatment of ultra high strength steel.

[0002]

2. Description of the Related Art Ultrahigh-strength steel has been widely used in aircraft parts and electronic equipment parts for aircraft. Further, in recent years, this super high strength steel has been widely used for automobiles as well in order to reduce its weight and size. This is because the strength of this ultra- high-strength steel is significantly higher than that of ordinary steel.

[0003] The ultra-high-tensile steel carbon content High Strength Steel
It is known that hydrogen is more brittle than that of low carbon steel and low carbon steel, and hydrogen embrittlement is prominent due to absorption of hydrogen in the pretreatment process of plating. This hydrogen embrittlement is a phenomenon in which hydrogen atoms generated on the surface of ultra- high strength steel during pretreatment are absorbed by iron to make it brittle, and it is hardly a problem for high-strength steel and low-carbon steel. However, it becomes a problem for more than hard steel containing a lot of carbon.

FIG. 7 is a diagram showing a conventional plating process, and shows four kinds of methods (1) to (4). In the method (1), first, in order to remove oils and fats attached to the surface of the material (material to be plated) and contamination, alkali immersion degreasing treatment 100 is performed in a heated alkaline liquid. Next, an acid electrolysis treatment 102 for electrolytically washing the surface of the material in an acid solution is performed, and then a baking treatment 104 is performed. The original plating process 106 is performed after such pretreatment.

Here, sulfuric acid is usually used for the acid electrolysis treatment 102. When an electric current is passed through this acid solution, oxygen is produced at the anode and hydrogen is produced at the cathode. Therefore, in the cathode treatment using the material as a cathode, hydrogen gas is attached to the material, and there is a great concern about hydrogen embrittlement. The baking treatment 104 is to accelerate dehydrogenation by placing the material in an electric heating furnace and performing heat treatment at about 430 ° C. for 2 to 4 hours.

The method (1) uses a pickling treatment 108 instead of the acid electrolysis treatment 102. When the raw material is steel, industrial sulfuric acid or hydrochloric acid is generally used for this pickling treatment 108. Usually, the acid concentration is set to 2 to 15% and the temperature is raised to shorten the acid treatment time. This is because hydrogen embrittlement is reduced by shortening the treatment time.

In the method (1), after the pickling treatment 108, an electrolytic degreasing treatment 110 is performed, and then an acid immersion treatment 112 is performed. The electrolytic degreasing treatment 110 usually electrolyzes in an alkaline solution to make cleaning even more complete. The acid immersion treatment 112 is to activate the surface by immersing it in a 5 to 10% solution of hydrochloric acid or sulfuric acid immediately before the plating treatment 106.

The method (1) is performed by acid electrolysis 102 or pickling 108.
Instead of chemical treatment such as, the mechanical treatment 114 by shot blasting or honing is performed. The surface is mechanically cleaned by this treatment 114, and electrolytic degreasing 1
After performing 10, the main plating process 106 is performed.

After performing the plating treatment 106, a baking treatment 1 is further performed to remove hydrogen on the surface of the material.
16 is carried out to obtain a product. The baking treatment 116 is performed by heating in an electric heating furnace at about 200 ° C. for about 24 hours.

When the plating process 106 is inappropriate, a peeling process 118 is performed on the inappropriate plating layer, and then the re-plating process 120 is performed. Here, the peeling treatment 118 is to remove the plating layer by immersing the material in an acid solution to dissolve the plating layer.

In the above conventional method, the cause of hydrogen embrittlement is considered to be "acid" such as hydrochloric acid or sulfuric acid.
Is the next four processes. That is, it is a pickling treatment 108, an acid immersion treatment 112, an acid electrolysis treatment 102, and a peeling treatment 118.

[0012] atomic hydrogen to the material surface of the ultra-high tensile steel in these processes is produced, ultra-high-tensile steel occludes hydrogen atom, hydrogen embrittlement occurs. In particular, when re-plating is performed, a strong acid is used for the peeling treatment, so that the risk of product destruction due to hydrogen embrittlement is particularly high.

There are two conceivable routes for infiltration of hydrogen into ultra-high strength steel. First path, pickling, electrolytic cleaning, hydrogen atom generated on the surface of the ultra-high tensile steel during electroplating, ultrasonic
It is absorbed by high-strength steel and diffuses inside. The second route is that hydrogen atoms generated when the ultra-high-strength steel itself or the plating layer attached thereto reacts with water and corrodes, are absorbed by the ultra-high-strength steel and diffuse inside. The second route is very rare and the first route is usually a problem.

The hydrogen atoms that have penetrated into the ultra-high strength steel can contain one hydrogen atom for each one of the body-centered cubic lattices of iron, and can freely move and diffuse.
However, since two hydrogen atoms cannot enter the crystal lattice at one time, two hydrogen atoms cannot combine to form a hydrogen molecule, and it is said that the hydrogen atom always exists in an atomic state. This hydrogen atom has the property of diffusing and moving to the place where the tensile stress is concentrated, and if a lattice defect occurs at the place where the stress is concentrated, hydrogen atoms penetrate into the gap and bond with each other. Form a molecule. It is considered that this gradually accumulates and an extremely high pressure is generated, which destroys the structure of the ultra-high-strength steel and causes cracks, which leads to brittle fracture.

In order to eliminate the cause of the hydrogen embrittlement thus generated, it is sufficient to prevent hydrogen from being generated in the pretreatment step of plating or to surely remove even if hydrogen is generated. it is conceivable that.

Therefore, conventionally, the following method has been adopted for the material of ultra- high strength steel. As shown in FIG. 7, mechanical treatment 114 such as shot blasting or honing is used instead of pickling (108) with hydrochloric acid or sulfuric acid. The acid immersion time in pickling (108) is shortened. After pickling (108) and plating treatment (106)
Bake at about 430 ° C for 2-4 hours before baking (10
4). After the plating process (106), it is baked (116) at about 200 ° C. for about 24 hours.

[0017]

However, each of these methods has the following problems. In the method using the mechanical treatment (114), the processed surface becomes rough, and in the method of shortening the acid immersion time, the cleaned surface becomes insufficient. For this reason, the adhesion of the plating in the plating process (106) deteriorates, which adversely affects the plating characteristics.

Baking treatment before plating (104)
Causes a new scale on the surface of the material immediately after baking. Therefore, it is difficult to obtain a uniform plating finish. In the baking treatment (116) after plating, it is difficult to sufficiently remove the hydrogen occluded in the material due to the plating film being an obstacle, and this baking causes blistering, peeling, discoloration, etc. of the plating film. It is easy to occur.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a good adhesion of plating, a uniform finish is obtained, and hydrogen embrittlement is reduced without causing defects such as blistering in the plating film. It is an object of the present invention to provide a plating treatment method for ultra- high-strength steel that can be used.

[0020]

According to the present invention, an object of the present invention is to provide a plating treatment method for reducing hydrogen embrittlement caused by plating treatment of ultra- high strength steel. It is achieved by a plating method for ultra high strength steel, which is characterized in that it is carried out.

When there is a pickling treatment in the middle of the pretreatment step, it is desirable to put the alkaline anodic electrolytic treatment at two places, the end of the pretreatment and immediately after this pickling treatment. In this case, it is preferable to perform pickling while vibrating with ultrasonic waves. When the pretreatment step includes an acid electrolysis treatment, the alkaline anodic electrolysis treatment is performed after the acid electrolysis treatment. The ultrasonic vibration may be applied to other treatments as well as pickling.
Also in this case, the effect of accelerating the treatment and removing hydrogen from the material can be obtained.

The composition of the electrolytic solution (processing solution) used in the alkaline anodic electrolytic treatment is sodium hydroxide (NaOH) 100
g / L, sodium cyanide (NaCN) 50 g / L,
Ethylenediaminetetraacetic acid (EDTA) is preferably 30 g / L. Here, L means liter. In this case, electrolyte temperature 60 ° C, current density 15 A / dm ² , treatment time 1
It is desirable to set it to 0 minutes. The oscillator used for ultrasonic excitation has a high-frequency output of about 3 for a pickling solution of about 15 L.
00W, may be a piezoelectric vibrator comprising a bimorph barium titanate having an output frequency approximately 40kH _Z.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a plating treatment step which is one embodiment of the present invention, FIG. 2 is a diagram showing a pickling treatment tank, FIG. 3 is a diagram showing effects of one embodiment, and FIG. 4 is a peeling treatment. FIG. 5 is a diagram showing an effect when applied later, FIG. 5 is an external view of a hydrogen embrittlement tester, and FIG. 6 is an explanatory diagram of hydrogen embrittlement rate.

In FIG. 1, the same processes as those in FIG. 7 are designated by the same reference numerals, and the description thereof will not be repeated.
The processing method shown in FIG. 1 differs from that in FIG. 7 in that there is no baking processing (104 and 116 in FIG. 7) and ultrasonic pickling processing 200 instead of pickling (108).
And the use of alkaline anodic electrolytic treatment 202, 204,
The point 206 is added.

In the ultrasonic pickling treatment 200, the treatment liquid or the material to be treated is vibrated by ultrasonic vibration during the pickling treatment. FIG. 2 shows an example of the structure of the processing tank.
In FIG. 2, 10 is a processing tank, 12 is a processing liquid,
In this case, it is about 15 liters (L). Reference numeral 14 is a piezoelectric vibrator attached to the inner bottom surface of the processing tank 10. The vibrator 14 may be made of barium titanate bimorph. This vibrator 14 has a high frequency output of about 300 W and a frequency of about 4 by an exciting device 16.
Driven to a 0kH _Z. The material 18, which is the material to be treated, is immersed in the treatment liquid 12 for a certain period of time (about 1 minute) and pickled.

The method shown in FIG.
Immediately after 2, the alkaline anode electrolytic treatment 202 is performed. In this alkaline anodic electrolytic treatment 202, a material serving as an anode and a cathode are immersed in an alkaline electrolytic solution having the following composition for electrolytic treatment.

The composition of this electrolytic solution is, for example, 100 g / L of sodium hydroxide (NaOH), 50 g / L of sodium cyanide (NaCN), ethylenediaminetetraacetic acid (E).
DTA) 30 g / L. Treatment conditions are electrolyte temperature 6
The temperature is 0 ° C., the current density is 15 A / dm ² , and the processing time is about 10 minutes. Copper, lead, etc. are used for the cathode. When the temperature of the electrolytic solution is 60 ° C. or higher, the etching of the surface of the material is likely to proceed, and the adhesion of the plating film during the plating process deteriorates. Further, even if the treatment is performed for 10 minutes or longer, the effect of removing hydrogen does not increase. This point will be described later.

The alkaline anodic electrolysis treatment 202 is to neutralize the acid by the acid electrolysis treatment 102 performed immediately before and to remove hydrogen occluded in the raw material by using the raw material as an anode. As a result, hydrogen can be removed from the material to reduce hydrogen embrittlement. Immediately after performing the alkaline anode electrolytic treatment 202 in this way, the plating treatment 10
Perform 6 to obtain the product.

The method shown in FIG.
Before step 6, acid immersion treatment 1 to activate the plated surface
12 is put. In this case, immediately after the acid immersion treatment 112, the alkaline anode electrolytic treatment 204 is added, and then the plating treatment 106 is performed. Alkali anode electrolytic treatment 20
4 is the same as the above-mentioned alkaline anode electrolytic treatment 202. By this alkaline anodic electrolysis treatment 204, the acid (hydrochloric acid, sulfuric acid) used in the acid immersion treatment 112 immediately before that is neutralized, and hydrogen can be removed from the treated surface.

When the plating film formed by the plating process 106 is inappropriate, a peeling process 118 is performed and a re-plating process 120 is performed. At this time, an acid solution is used in the peeling process 118.
Therefore, by performing the alkaline anode electrolytic treatment 206 immediately after the stripping treatment 118, the acid used in the stripping treatment 118 can be neutralized and hydrogen can be removed from the treated surface. The alkaline anode electrolysis treatment 206 used here is the same as the above-mentioned treatments 202 and 204.

FIG. 3 is a diagram showing the effect of the method of FIG. 1 according to the experimental results. The test piece used here is not an ultra high strength steel, but its composition ratio is extremely high.
Carbon tool steel SK5 with Rockwell hardness HRC52 , which is easily available, has a thickness of 0.8 mm and 100 mm x 10
It is processed into a dimension of mm. Alkaline immersion degreasing treatment 100 was performed using a treatment liquid widely used for this test piece (trade name "Escreen A220" manufactured by Okuno Chemical Industries Co., Ltd.).

This test piece was washed thoroughly with water and then washed with 10% hydrochloric acid (H
It was immersed in a Cl) concentration solution (normal temperature), and ultrasonic vibration was applied for 1 minute as described above. Excitation by ultrasonic is a high frequency output 300 W, frequency 40KH _Z To a solution of the street about 15L.

Next, this test piece was washed with spray water and immediately subjected to alkaline anodic electrolytic treatment 202. The bath composition was a mixed aqueous solution of sodium hydroxide 100 g / L, sodium cyanide 50 g / L, and EDTA 30 g / L as described above, and the temperature was kept at 60 ° C. The test piece is used as an anode in this,
Electric current was supplied for 10 minutes at a current density of 15 A / dm ² . Thereafter, the treated surface is activated by an acid immersion treatment 112 which is a conventional method,
After the alkaline anode electrolysis treatment 204 was performed again, zinc plating (106) was performed immediately.

The test pieces plated as described above were tested with a hydrogen embrittlement tester Digital Gauge (manufactured by Delta Research) shown in FIG. This test piece is a long plate having a predetermined size (0.8 mm × 100 mm × 10 mm). The test piece 50 is sandwiched between a fixed stopper 52 and a movable vice 54, and the vice 54 is moved toward the stopper 52 to compress in the longitudinal direction,
The test piece 50 is curved as shown in FIG. The moving distance L ₀ of the vise 54 until the test piece 50 breaks.
Is to measure.

Here, the amount of movement of the vise 54 until the untreated test piece 50 breaks is L. The moving amount of the vise 54 until the processed test piece 50 breaks is L ₀ . The hydrogen embrittlement ratio A (%) at this time is defined as follows.

[0036]

## EQU1 ## A = {(L ₀ −L) / L ₀ } × 100

The results of this test are shown in FIG. The test piece 50 treated here is plated by the method in FIG. The X mark in FIG. 3 represents the test result of the treated test piece 50, and the hydrogen embrittlement rate A was about 50% as the alkaline anode electrolytic treatment time t (min) increased.
It was found that the value decreased from about 5% to about 5%, and became constant at about 5% after 10 minutes.

Incidentally, in this figure, the star marks show the test results for the test pieces which were processed by the conventional method explained in FIG. In this case, the hydrogen embrittlement ratio A was about 81%. As a result, it was revealed that the hydrogen embrittlement ratio A can be significantly reduced by performing the treatment according to the present invention.

Next, the effect obtained when the stripping treatment (118) is performed on the zinc-plated test piece in the plating treatment (106) will be described with reference to FIG. In this test, the galvanized (106) test piece was immersed in a 12% hydrochloric acid bath for peeling treatment (118), and immediately after that, the test piece was just washed with water, and after being washed with water, an alkali was further applied under the above conditions. A test piece subjected to anodic electrolytic treatment (206, see FIG. 1) was used.

The hydrogen embrittlement rate A (%) of each of these test pieces was determined by the method described with reference to FIGS. In FIG. 4, the horizontal axis represents the immersion time t (minutes) in the stripping solution. The alkaline anodic electrolytic treatment time was 10 minutes in all.

In FIG. 4, curve a shows the result of the test piece only washed with water, and curve b shows the result of the test piece to which the alkaline anodic electrolytic treatment was added. From this figure, it was found that the effect of reducing the hydrogen embrittlement rate according to the present invention is extremely remarkable.

The alkaline anodic electrolytic treatment performed in the present invention is not limited to the above-mentioned embodiment. For example, the following processing liquids A and B may be used under the following conditions. Treatment liquid A Sodium hydroxide (NaOH) 75 g / L Trisodium phosphate (Na ₃ PO ₄ ) 10 g / L Sodium carbonate (NaCO ₃ ) 14 g / L Surfactant 1 g / L Treatment conditions Liquid temperature 80-90 ° C Current density 7.5-10 A / dm ² Treatment time 10 minutes Treatment liquid B Sodium hydroxide (NaOH) 30 g / L Sodium carbonate (NaCO ₃ ) 30-50 g / L Surfactant 2 g / L Treatment condition Liquid temperature 80-90 ° C Current Density 5-7 A / dm ² Treatment time 15 minutes

[0043]

As described above, according to the invention of claim 1, the alkaline anodic electrolytic treatment is performed at the end of the plating pretreatment step.
Hydrogen attached to the surface of the material can be removed to reduce the hydrogen embrittlement rate of ultra high strength steel. Here, the alkaline anodic electrolytic treatment includes that performed immediately before the re-plating treatment.

This alkaline anodic electrolytic treatment may be appropriately added in the middle of the plating pretreatment step, and in particular, treatment using an acid, such as pickling treatment, acid electrolysis treatment, plating film peeling treatment at the time of re-plating, etc. It is better to add it immediately (claims 2, 3, and 4). During the pickling treatment, it is preferable to vibrate the treatment liquid or the material to be plated by ultrasonic vibration (claim 5). This vibration can forcibly remove the hydrogen gas attached to the surface of the material, which is more suitable for reducing the hydrogen embrittlement rate. The ultrasonic vibration may be added to a treatment other than pickling, and in this case, the treatment can be accelerated.

The electrolytic solution used for the alkaline anodic electrolytic treatment is
Sodium hydroxide 100g / L, sodium cyanide 5
It has a composition of 0 g / L, ethylenediaminetetraacetic acid 30 g / L, processing liquid temperature of about 60 ° C, current density of about 15 A / c.
It is desirable that m ² and the processing time be about 10 minutes (claim 6).

For ultrasonic excitation, a piezoelectric element such as barium titanate can be fixed to the inner surface of the processing tank. In this case, for example, with respect to 15L of the treatment liquid, a high frequency power of about 300 W, preferably set to a frequency of about 40kH _Z (claim 7).

[Brief description of drawings]

FIG. 1 is a diagram showing a plating treatment step which is an embodiment of the present invention.

FIG. 2 shows a pickling tank

FIG. 3 is a diagram showing an effect of one embodiment.

FIG. 4 is a diagram showing the effect of the present invention applied after the peeling process.

FIG. 5: External view of hydrogen embrittlement tester

FIG. 6 is an explanatory diagram of hydrogen embrittlement rate.

FIG. 7 is a diagram showing a conventional plating process.

[Explanation of symbols]

10 treatment tanks 12 Treatment liquid 14 Piezoelectric element 18 material

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-216524 (JP, A) JP-A-6-272008 (JP, A) Plating Technology Handbook Editorial Committee, “Plating Technology Handbook”, first edition, daily publication Kogyo Shimbun, P 120-123, P 139-140, July 1983, Japan Institute of Metals, Japan Iron and Steel Institute, "Handbook of Steel Materials", 2nd edition, Maruzen Co., Ltd., P 595-598, July 1995 Zaio Zaimitsu, "Metallic Materials", First Edition, Asakura Shoten, P94, March 1980 (58) Fields investigated (Int.Cl. ⁷ , DB name) C25F 1/00-7/02 C25D 5/36

Claims (7)

(57) [Claims] 1. A plating method for reducing hydrogen embrittlement that occurs in association with the plating of ultra-high tensile steel, the end of the pretreatment step, ultra-high tension and performing alkali anodic electrolysis treatment Steel plating method. 2. A pickling treatment is provided during the pretreatment process,
The plating treatment method for ultra- high strength steel according to claim 1, wherein the alkaline anodic electrolytic treatment is performed at the end of the pretreatment step and after the pickling treatment. 3. The method for plating an ultrahigh- strength steel according to claim 1, wherein the alkaline anodic electrolytic treatment is performed after the acid electrolytic treatment. 4. The plating treatment method for ultra- high strength steel according to claim 1, wherein the alkaline anodic electrolytic treatment is performed after the plating film peeling treatment during re-plating. 5. The plating treatment method for ultra- high tensile steel, wherein the pickling treatment according to claim 2 is performed while vibrating the treatment liquid or the material to be plated by ultrasonic vibration. 6. The composition of the electrolytic solution used in the alkaline anodic electrolysis treatment is sodium hydroxide 100 g / L, sodium cyanide 50 g / L, ethylenediamine tetraacetic acid 30 g / L, and the treatment conditions are a treatment liquid temperature of about 60 ° C. and an electric current. Density about 15
The plating treatment method for ultra- high strength steel according to claim 1, wherein A / dm ² and treatment time are about 10 minutes. 7. The method of claim 5, pickling liquid high-frequency output of about 300W to about 15L, frequency about 40KH _Z plating method ultra-high strength steel pickling while vibrating a piezoelectric vibrator having an output of .