JP3158192B2 - How to make artificial pits - Google Patents

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 an artificial pit on a metal in order to perform a strength evaluation, a durability / strength test, a corrosion test, and the like of a metal artificial defect material.

[0002]

2. Description of the Related Art Generally, when various machines and devices are used for a long period of time, pitting may occur under various conditions. Inspection of the metal material used in the apparatus and the apparatus is performed. Pitting is localized spot-like corrosion that occurs from defects in the coating under the conditions of a protective film in which the metal is stable, and artificial pitting similar to this pitting is performed using a test piece. The test piece is manufactured and subjected to a fatigue test, a corrosion test, and the like, and the life prediction and the like are evaluated.

Heretofore, a method for producing this artificial pit has been performed by a mechanical method using a drill or the like, a method utilizing electric discharge machining, an anodic polarization method, or the like.

A mechanical method using a drill or the like has been performed by mounting a test piece on a drilling machine and making a pit on the test piece with a tool such as a drill. Since this method can be performed by an easy operation, the operation can be performed in a short time.

[0005] In the method of producing artificial pits by electric discharge machining, a test piece is placed in a machining fluid of an electric discharge machine, a discharge is generated between an electrode tool and the test piece, and sparks are repeated to produce pits. This makes it possible to perform an accurate inspection with good surface accuracy of the pits produced on the test piece.

An artificial pitting method using the anodic polarization method is an electrochemical method for generating pitting corrosion by setting conditions from an obtained anodic component curve and directly polarizing a pitting expected area of a test piece. One, as shown in FIG.
The reference electrode 21 and the sample electrode 22 are connected to the potentiostat 23 and immersed in the sample solution 24,
The voltage is raised by a potential sweeping device 25 for a predetermined time, and when the voltage reaches a predetermined potential, the current value rises sharply, causing pitting corrosion on a test piece arranged on the sample electrode 22. With this method, accurate pitting can be produced in a short time with respect to minute holes.

[0007]

However, the above-mentioned respective methods for producing artificial pitting have the following problems. For example, with a mechanical method using a drill or the like, it is difficult to process when minute pitting is formed, and the surface becomes dirty with oil, unnecessary scratches on the test piece surface due to cutting chips, etc., and furthermore, In addition, a compositionally deformed layer may be formed on the surface metal of the hole by machining to prevent accurate pitting corrosion from being produced.

Further, in the method for producing pitting corrosion by electric discharge machining,
Since the electric discharge machine itself is a large-scale device, installation space is required, and the heat associated with electric discharge is applied to the machining surface, so that the metal melts partially and the metal composition differs from the other parts. May come.

Further, in the method of producing pitting corrosion by the anodic polarization method, it takes a considerable amount of time to form deep and large pitting corrosion, and corrosion is likely to occur in unnecessary portions.

The present invention has been made to solve the above-mentioned problem, and has a high precision of a pitting surface even when a deep and large pit is formed without unnecessary damage, and is accurate in a short time. An object of the present invention is to provide a method for producing an artificial pit which can produce pits.

[0011]

The method for producing an artificial pitting corrosion according to the present invention is based on the following method to solve the above-mentioned problems. That is, in order to perform a test / inspection of a metal material, an artificial pit making method for making an artificial pit on a surface of a test piece of the metal, wherein anodic electrolysis is performed on the surface of the metal. is there.

[0012] Further, the artificial pit making method is an artificial pit making method for making an artificial pit on the surface of a metal test piece in order to test and inspect a metal material. In addition, an electrically insulating protective film is formed, a pinhole is formed in the protective film, an anodic electrolysis is performed by bringing an electrolytic penetrated with an electrolytic solution into contact with the pinhole portion, and then performing a anodic electrolysis with a solvent. It is characterized in that pitting corrosion is produced by removing the protective film.

Further, the protective film has a thin film formed on the metal surface, and an insulating tape stuck around a pinhole formed on the thin film. It is preferable that the holes are formed so as to have a diameter equal to or larger than the hole diameter.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an electrolytic artificial pitting production apparatus M, which is performed to investigate the influence of the shape and depth of the pitting on the break life in a corrosion fatigue test of a turbine rotor. is there. The test piece 1 is formed of an iron-chromium-nickel alloy, and the center portion of a male screw is formed of a round bar at both ends. An electrically insulating coating film (hereinafter, referred to as a protective film) 2 is attached to the surface of the test piece 1, and an electric pen 3 is disposed on the protective film 2. The electric pen 3 is filled with glass wool 5 that has been impregnated with an electrolyte 4. The electric pen 3 is connected to the (−) side of the DC power supply 6, and the (+) side of the DC power supply 6 is connected to the test piece 1.

The details of this apparatus and the procedure for making pitting corrosion are shown in FIGS. First, as shown in FIG. 2, a coating material such as nail polish formed mainly of nitrocellulose or acrylic resin is applied on the surface of a round bar of a test piece 1 to form an electrically insulating protective film 2. To form

Next, as shown in FIG. 3, a plastic film plate 8 having holes 8a formed at predetermined positions in advance is placed on the protective film 2. As shown in FIG. 4, the film plate 8 has a thickness of 0.1 to 0.2 mm, and is formed in an H shape, and a plurality of minute holes 8a are formed in a central transition portion. Since the film plate 8 is used as a jig, its material is not limited to plastic. Along the hole 8a formed in the film plate 8, the protective film 2 formed on the surface of the test piece 1 is removed by shaving with a needle 7 or the like.
When the film plate 8 is removed, the test piece 1 contains the film plate 8
A plurality of holes (hereinafter referred to as pinholes) 2a having the same shape as the holes 8a formed in the protective film 2 are formed. Therefore, the surface of the test piece 1 appears in the pinhole 2a. The hole diameter of the pinhole 2a is correlated with the hole depth, and the details will be described later.

Subsequently, as shown in FIGS.
Insulating vinyl tape 9 with m 9 holes 9a
Is adhered on the protective film 2 so as to cover the surface of the round bar of the test piece 1 around the pinhole 2a. Vinyl tape 9
Serves as a protective film and is particularly adhered to prevent the electrolytic solution 3 from flowing from the round test piece 1 to the outside. The test piece 1 is formed in a planar shape. Some of them are not attached.

Then, an electric pen 3 containing glass wool 5 impregnated with the electrolyte 4 is connected to the cathode (−) side of the DC power supply 6, and the test piece 1 is connected to the anode (+) of the DC power supply 6. 7, the electric pen 3 is placed so that the electrolyte 4 comes into contact with the surface of the test piece 1 exposed in the pinhole 2a as shown in FIG.

As the electrolytic solution 4, one adapted to the material of the test piece is used. In the case of the iron type as in this embodiment, mainly ammonia chloride (about 12%), glycerin (about 37%), water (About 51%) is used. In the case of this embodiment, it may be composed of phosphoric acid (about 63%), sulfuric acid (about 15%), chromic anhydride (about 10%), and water (about 12%).

When the test piece is made of aluminum or aluminum alloy, an electrolytic solution composed of sodium carbonate (about 15%), trisodium phosphate (about 5%) and water (about 80%) may be used. , Phosphoric acid (about 75%), sulfuric acid (about 4.7%)
%), Chromic anhydride (about 6.5%), AL & Cr (about 6%).
%) And water (about 7.8%).
Further, a test piece formed of copper, a copper alloy, nickel, a nickel alloy, or the like also uses an appropriate electrolytic solution.

The glass wool 5 impregnated with the electrolytic solution 4 is formed into a fine mesh and is filled at the tip of the electric pen 3. However, as long as the electrolytic solution 4 can be directly filled into the electric pen 3, glass cotton is not particularly required.

The diameter of the pits produced by the present apparatus M is from 50 μm or less to 500 μm or more, and the pit depth is 500 μm or more. In this embodiment, the pit depth is set to 250 μm. Pitting depth increases with electric field time,
The pit diameter increases as the pit depth increases. This relationship is illustrated by the graphs in FIGS. In this graph, the voltage is set to 20 V, and the pitting depth becomes 250 μm when the electric field time is about 72 seconds. When the pitting depth is 250 μm, the pitting diameter is expanded by 300 μm. Therefore,
The diameter of the pinhole 2a formed in the protective film 2 is formed so as to be 300 μm smaller than the pitting diameter to be produced, and when the aspect ratio (pitting depth / pitting radius) is set to 0.7, the diameter of the pit is reduced. The diameter of the eclipse is 714 μm and the diameter of the pinhole is 4
14 μm.

The artificial pitting apparatus M connects the DC power supply 6 to the test piece 1 and the electric pen 3 so that
The electrolytic solution 4 immersed in the sample enters the test piece 1 through the pinhole 2a of the protective film 2, and is electrolyzed in the electrolytic solution 4, chloride ions move to the test piece 1 side, and ammonium The ions move to the electric pen 3 and a current flows, and pitting is created on the test piece 1. When anodic electrolysis is performed for an electric field time of 1 to 2 minutes as described above, a pit having a depth of 250 μm and an outer diameter of about 714 μm is produced. Note that a ring-shaped rubber packing 10 is inserted between the electric pen 3 and the vinyl tape 9 in FIG. 7 to prevent the electrolyte 4 from leaking to the outside. Then, the anode electrode is similarly formed on other portions where the pinholes 2a are formed, and then the vinyl tape 9 is completely removed, and the protective film 2 is removed with a solvent such as acetone.

The pit 12 thus produced is shown in FIG.
As shown in (a) and (b), it is shown in an enlarged cross section taken by a micrograph. (A) is 100 times enlarged and (b) is 880 times enlarged the bottom central portion 12b of the pit 12. According to this, the produced pitting surface 12a is very clearly shown, and its composition shows almost the same state as the other part of the test piece which is not pitted. Therefore, scratches and the like that occur when machining by a conventional drill do not occur, and melting around the pitting surface that occurs during electric discharge machining does not occur. Nearly suitable as a standard for pitting corrosion models.

[0025]

According to the artificial pitting method of the present invention, pits are formed on a test piece by anodic electrolysis, so that the prepared pitting surface is formed with high accuracy, and the pits having a diameter of 50 μm or less are produced. To pits having a diameter of 500 μm or more. Moreover, since the test piece is not changed by other factors during the test, it is extremely suitable as a standard model of pitting corrosion.

Further, at the time of anodic electrolysis, an electrically insulating protective film is formed on the surface of the test piece, a pinhole is formed in the protective film, and an electrolytic penetrated with an electrolytic solution is placed in the pinhole portion. After performing the anodic electrolysis by contacting with, the method is performed by removing the protective film with a solvent, so that it is possible to produce pitting corrosion in an extremely easy procedure and in a very short time without requiring a large apparatus. it can.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an apparatus according to one embodiment of an artificial pitting production method of the present invention.

FIG. 2 is a view showing a procedure for producing pitting corrosion by the apparatus of FIG. 1;

FIG. 3 is a diagram showing the next procedure of FIG. 2;

FIG. 4 is a perspective view showing a film plate used in FIG. 3;

FIG. 5 is a diagram showing a procedure following the procedure shown in FIG. 3;

FIG. 6 is a perspective view of FIG. 5;

FIG. 7 is a diagram showing the next procedure of FIG. 5;

FIG. 8 is a graph showing the relationship between pit depth and electric field time.

FIG. 9 is a graph showing the relationship between the depth of pitting and the spread of pore diameter.

FIG. 10 is a photomicrograph of the prepared pit (FIG.
0x, (b) is a 880x magnification micrograph)

FIG. 11 is a schematic view showing a conventional anode electrode method.

[Explanation of Signs] 1 ... Test piece 2 ... Protective film 2a ... Pin hole 3 ... Electric pen 4 ... Electrolyte 5 ... Glass surface 6 ... DC power supply 8 ... Film plate 9 ... Vinyl tape M ... Electrolytic artificial pitting method

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 1/32 G01N 1/28

Claims (1)

(57) [Claims] (1) In order to test and inspect metal materials,
How to make artificial pits on metal test piece surface
A law, the test piece surface to form an electrically insulating protective layer, wherein the pinhole is formed in the protective film, the contact of the electrolyte pen electrolytic solution is penetrated into the pin hole
After performing anodic electrolysis, a pit is formed by removing the protective film with a solvent, and the protective film is formed on the surface of the test piece by a thin film.
Attached around the pinhole formed on the thin film
An edge tape, and the insulating tape is set to a diameter equal to or larger than the hole diameter of the pinhole.
Method for making artificial pits, characterized by the formation of pits
Law.