JP2602621B2 - Electropolishing method for stainless steel members - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to corrosion resistance, heat resistance,
The present invention relates to a method for producing an electrolytic surface treatment or a polished surface of a stainless steel member used as a constituent member requiring various functional surfaces.

[0002]

2. Description of the Related Art Electrochemical processing is a processing method utilizing an electrochemical reaction. Since the electrochemical reaction involves electric energy, it is easier to control the reaction than in the case of a chemical reaction. Processing speed is fast.

[0003] This electrolytic processing, like other special processing,
Developed to deal with difficult-to-machine materials, the advantage of electrolytic machining is that most metals can be processed regardless of the hardness of the material, and complex shapes can be processed in one step. That it can be machined, that there is no wear of the tool, and that no damaged layer is left. The disadvantages, however, are that the device is large and expensive, and that a corrosive electrolyte must be handled.

In this electrolytic machining method, a tool electrode and a workpiece are brought close to each other, and an electrolytic solution (NaC
1, NaNO ₃ aqueous solution) at a high speed, and a DC current is applied with the tool electrode as the cathode and the workpiece as the anode.
The part of the workpiece facing the tool electrode begins to elute due to the electrolytic action. By feeding the tool electrode in accordance with the elution amount of the workpiece, a female shape having the male tool electrode is processed into the workpiece. The eluted metal ions are oxidized in the electrolytic solution to form colloidal oxides or hydroxides, which are removed as sludge.

[0005] In electrolytic machining, usually, the machining voltage is set to a constant voltage (power supply voltage: 5 to 20 V), and the machining of the tool electrode is performed by constant speed feed. In normal machining, a self-adjusting action is applied to the machining interval, and the machining interval is kept almost constant.The elution speed of the workpiece in the steady state is equal to the feed speed of the tool electrode, and the elution speed is the Faraday It is proportional to the machining current density according to the law. Actually, since the elution valence of the eluting component metal is unknown, the electrochemical equivalent cannot be determined in many cases. Conversely, the elution valence of the alloy component metal is estimated from the elution speed.

[0006] By the way, the conditions required as an electrolytic machining liquid are that the workpiece has an appropriate specific conductivity, can work a workpiece with high current efficiency without causing electrodeposition on a tool electrode, and has good surface properties. Is obtained.

For example, as an electrolytic processing liquid for an iron-based material, an aqueous solution of sodium chloride (NaCl), sodium nitrate (NaNO ₃ ), sodium chlorate (NaClO ₃ ) or the like is known.

[0008]

The above-mentioned sodium chloride electrolyte has a strong corrosive action and is inferior in processing accuracy, but can obtain a high processing speed and can be used even when processing alloy steel (stainless steel) having a high chromium content. Since chromium is eluted as trivalent chromium which is easy to handle, it is partially used in a field where the surface roughness is not so problematic, but a mirror surface cannot be obtained.

In order to obtain a mirror surface, it is necessary to suppress corrosion. As a method of preventing corrosion of a metal to a chloride aqueous solution, it is conceivable to add various rust inhibitors (inhibitors). Can be

As a representative of the inorganic type, chromic acid, which forms an anticorrosive oxide film on a metal as an oxidizing agent, is ineffective in a neutral solution and has a problem of harmful hexavalent chromium. In addition, organic materials form an anticorrosive film by adsorption, but have a problem that current efficiency is reduced due to an insulating action.

The sodium nitrate electrolyte is most frequently used because it has a weaker corrosive action than the sodium chloride electrolyte and can provide good processing accuracy. Further, although sodium chlorate electrolyte has excellent processing characteristics, it has a high risk of fire and is hardly used at present.

As a result of examining the elution valence when stainless steel was processed with sodium nitrate and sodium chlorate electrolytes, when an alloy steel having a high chromium content was processed,
Hexavalent chromium which is harmful to the human body may remain in the sludge, and therefore, there is a problem in treatment such as disposal.

When the current efficiency (elution amount per unit amount of electricity) of the electrolytic solution is examined by a function of the current density, the current efficiency of the sodium chloride electrolytic solution does not depend on the current density, and iron is in a divalent state. Thus, a high efficiency value close to the theoretical electrochemical equivalent at which chromium is eluted in a trivalent state is obtained.

On the other hand, in the sodium nitrate and sodium chlorate electrolytes, the stainless steel is passivated in the low current density region, so that current is consumed for oxygen generation, and the current efficiency of metal elution decreases. . However, at a high current density, the effect of a strong electric field destroys the passive film and increases the current efficiency, so that the efficiency is about the same as that of sodium chloride. However, there is a problem that a strong electric field oxidizes chromium eluted in a trivalent state and converts it into harmful hexavalent chromium.

The present invention has been made in order to solve such technical problems, and has as its object the purpose of the present invention is to improve the surface smoothness and corrosion resistance, and to make chromium a trivalent harmless component among the stainless steel components which are electrolytically eluted. It is an object of the present invention to provide an electrolytic combined polishing method which can be eluted in a stable state and can be processed with higher current efficiency and excellent in workability.

[0016]

In order to solve the above-mentioned problems, an electropolishing method for a stainless steel member according to the present invention is characterized in that 1% by weight or more of one or more of sodium chloride, potassium chloride and ammonium chloride is combined. To
Using an electrolytic solution to which 0.03 to 0.5% by weight of BTA (C ₆ H ₄ NHN ₂ : benzotriazole) is added, a stainless steel member as a material to be treated is used as an anode and between the cathode and the cathode. This is a polishing method in which electrolytic rubbing is performed while flowing the above-mentioned electrolytic solution through a water-permeable nonwoven fabric containing abrasive grains.

More specifically, chromium ions eluted from stainless steel during electrolytic processing can be combined with the composition of the electrolytic solution and the organic rust inhibitor (BTA) and abrasive particles to remove rubbing of the adsorbed organic rust inhibitor. Is dissolved in a harmless trivalent state, and a method for electrolytically complexing or polishing a stainless steel member having high current efficiency and excellent corrosion resistance, smoothness and surface cleanliness is provided.

[0018]

The present invention is constituted as described above. In short, a non-polluting neutral salt solution prepared by adding an organic rust inhibitor to a non-oxidizing neutral salt having excellent current efficiency in an electropolishing liquid is used. This removes the adsorbed organic insulating film formed on the surface by abrasive grains so that the current efficiency is high due to the anodic polarization current-potential characteristics of the electrolyte and stainless steel, and the eluted trivalent chromium is not excessively oxidized to hexavalent. Polishing while polishing.

The electrolytic combined polishing method applied in the present invention is to electrolytically elute a metal to be polished to be an anode by electrolysis and to remove the passive oxide film formed on the surface convex portion of the metal to be polished by abrasive grains. Is a method of polishing and removing the polishing surface by the rubbing action of the abrasive grain to process the mirror surface. At the same time, the polishing surface is rubbed by giving a certain speed or more to the abrasive grains, and at the same time, several A / cm ² or less through the passivation type electrolytic solution. This is a polishing method that generates an anodic reaction of elution and oxidation on a polished surface at an electrolytic current density.

One example of polishing is as follows: # 120- # 1
500 SiC-based abrasives with an initial surface roughness of 5-10 μm
When polishing a SUS316L member of (Rmax), a 20 wt% aqueous solution of NaNO ₃ was used as a passive electrolyte and the electrolytic current density was changed in the range of 0 to 5 A / cm ² , resulting in rough polishing. A member surface having a thickness of 1 μm (Rmax) or less was obtained.

According to this electrolytic combined polishing method, in addition to smoothing of the member and removal of local defects, electrolytic elution and anodic oxidation occur in an oxidizing neutral electrolytic solution, and a specific atom (C
r) is concentrated on the surface and changes the composition of the formed passive film;
The structure stability, density, and film thickness are excellent in corrosion resistance, and are different from the surface obtained by conventional electrolytic polishing mainly using phosphoric acid and sulfuric acid.

Meanwhile, the sodium nitrate electrolyte used for electrolytic combined polishing is one in which the generation of harmful hexavalent chromium is unavoidable due to the anodic polarization current-potential characteristics of the electrolyte and stainless steel. When used alone, hexavalent chromium was not generated, but the polished surface properties were poor and it was difficult to use. The use of these solutions alone cannot be solved by the anodic polarization properties of stainless steel alone, but combines the development of a new electrolyte with the removal of abrasive particles by abrasive grains for the formation and destruction of passive films and the formation of hexavalent chromium. There is a need.

Therefore, the present invention relates to a composition containing one or more of 1% by weight or more of sodium chloride, potassium chloride and ammonium chloride in an amount of 0.03 to 0.5%.
Using an electrolyte solution containing BTA (C ₆ H ₄ NHN ₂ : benzotriazole) in a weight percentage, a stainless steel member as a material to be treated is used as an anode, and water-permeable containing abrasive grains between the cathode and the cathode. This is performed by electrolytic rubbing while flowing the above-mentioned electrolytic solution through the nonwoven fabric.

As will be apparent from the examples described later, when the chloride concentration is less than 1% by weight, the electric conductivity becomes insufficient,
An increase in electric resistance, a decrease in polishing characteristics due to excessive voltage, and a decrease in quality are observed. The upper limit of the concentration is the saturation concentration. However, in practice, the workability is degraded due to the removal of salt and the precipitation of the salt, so that the concentration is preferably in the range of 5 to 20% by weight.

If the amount of BTA added is less than 0.03% by weight, there is no effect.
This is not preferable because it is not dissolved in the electrolytic solution and becomes turbid due to the possibility of clogging a filter or the like. However, by adding an appropriate amount of BTA, an adsorbed organic rust-preventive film is formed on the metal surface, and corrosion by chloride is suppressed.

Further, rubbing while flowing an electrolytic solution through a water-permeable nonwoven fabric containing abrasive grains is also a means for obtaining a mirror surface, but it is possible to remove an excessively adsorbed organic rust preventive film on the surface convex portion.
This has the effect of suppressing an increase in the anodic polarization potential due to film formation, and can reduce a decrease in current efficiency.

Hereinafter, embodiments will be described.

[0028]

【Example】

Example 1 As shown in FIG.
An aqueous solution consisting of 0.2% by weight of BTA, 0.2% by weight of BTA, and the balance of water is used as an electrolytic solution 1. A commercially available SUS3 is used as a material to be polished.
04 (JIS standard) A pickled stainless steel plate (which has been subjected to mild cold working with a bright roll after pickling and has been given a luster) 2 is used as an anode, and is provided with a # 600 alumina abrasive grain adhering. 70 with the aqueous nonwoven fabric 12 attached
Using a φ rotating buffing polishing head (rotational speed 800 RPM, moving speed 0.4 mm / sec) 11, the electrolytic solution 1 was rubbed at a current density of 1 A / cm ² while flowing the electrolytic solution 1 at a rate of 1 liter / min. % And a mirror surface having a surface roughness of 1 μm (Rmax) or less was obtained. Also,
Elution of hexavalent chromium into the electrolyte was not detected. In FIG. 1, reference numeral 3 denotes a passive film, and FIG. 2 shows the relationship between current density and current efficiency in various electrolytes.

As Comparative Example 1, sodium chloride 2
When stainless steel was polished in the same manner as in Example 1 using an aqueous solution consisting of 0% by weight, 0.2% by weight of sodium chromate and the balance of water as an electrolyte, pitting occurred on the stainless steel. In the polarization characteristics shown in FIG. 2, although the addition of sodium chromate has the effect of suppressing metal elution, pitting corrosion due to local corrosion occurred. Also, the addition of chromium is undesirable.

As Comparative Example 2, sodium chloride 2
When an aqueous solution consisting of 0% by weight, sodium molybdate 0.02% by weight and the balance water was used as an electrolytic solution and stainless steel was polished in the same manner as in Example 1, hexavalent chromium was not detected. As such, it did not exhibit significant corrosion inhibition and mirror effects.

Example 2 Stainless steel was polished in the same manner as in Example 1 using an aqueous solution consisting of 10% by weight of ammonium chloride, 0.04% by weight of BTA and the balance water as an electrolytic solution. Was. The use of ammonium chloride eliminates the problem of residual sodium contamination on the polished surface, so that, for example, electrolytic polishing suitable for surface polishing of components in semiconductor manufacturing equipment can be performed. In this case as well, no elution of hexavalent chromium into the electrolytic solution was detected.

According to the above-mentioned electrolytic polishing method, the drawback is that chromium eluted from trivalent to hexavalent by the potential when the passivation film of the stainless steel member is destroyed by anodic overvoltage in the oxidizing liquid and electrolytically eluted. With an electrolytic solution containing a non-oxidizing liquid and a corrosion inhibitor, and processing with high current efficiency by rubbing the excessively adsorbed organic insulating film on the surface protrusions with a water-permeable nonwoven fabric containing abrasive grains. it can.

[0033]

As described above, according to the electrolytic polishing method of the present invention, the chromium eluted by the potential when the passive film of the stainless steel member breaks down in the oxidizing liquid due to the anode overvoltage and electrolytically elutes is trivalent. Can be solved by the non-oxidizing liquid and the electrolytic solution added with the corrosion inhibitor, and the excessively adsorbed organic insulating film on the surface convex portion is formed by a water-permeable nonwoven fabric containing abrasive grains. By rubbing, there is an advantage that processing can be performed with high current efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic side view illustrating an electrolytic polishing method according to an embodiment of the present invention.

FIG. 2 is a graph showing current density and elution current efficiency in various electrolytic solutions.

FIG. 3 is a graph showing the anodic polarization characteristics of stainless steel with various rust preventive additives.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte 2 Finish plate 11 Buffing head 12 Water-permeable nonwoven fabric

Claims (1)

(57) [Claims] 1. One or more of 1% by weight or more of sodium chloride, potassium chloride and ammonium chloride are combined with 0.03 to 0.5% by weight of BTA (C ₆
H ₄ NHN ₂ : Benzotriazole) was added to the electrolyte, and the stainless steel member as the material to be treated was used as the anode, and the electrolyte was passed through a water-permeable nonwoven fabric containing abrasive grains between the cathode and the cathode. A method for electrolytic polishing a stainless steel member, wherein the material is subjected to electrolytic rubbing.