JP3427691B2 - Appearance method and apparatus of metal material grain boundary fracture surface - 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 of revealing a grain boundary fracture surface of a metal, a steel material or the like when performing analysis of grain boundary segregation elements by Auger electron analysis, and to efficiently obtain a grain boundary fracture surface. And a method and device for displaying the same.

[0002]

2. Description of the Related Art The brittleness of steel and metal materials is localized in the grain boundaries.
It is affected by the concentrations of P, C, S, etc. that are analyzed. High in low alloy steel
Hot temper brittleness is one example. Quantifying grain boundary segregation elements
As an analysis method, for example, Auger electronic analysis method
(Hereinafter, abbreviated as AES). At AES,
The analysis depth is a few nm, which is extremely shallow from the material surface
Highly sensitive separation of segregated elements such as P and S in several atomic layers
Can be analyzed. In order to take advantage of this advantage,
The material is fractured in ultra-high vacuum to reveal grain boundary fracture surfaces.
And are required. The reason is that the material is broken in the atmosphere
Also on the grain boundary surface ₂, O₂, H₂O, CO₂In the atmosphere
Thickly adsorb the gas molecules of the
This is because it becomes impossible to analyze.

Generally, as a grain boundary breaking method in an AES apparatus, for example, "Practical Auger electron spectroscopy for users" edited by Ryuichi Shimizu and Kazuhiro Yoshihara (Kyoritsu Shuppan, Chapter 8, p.
153-155) and Transaction of the ASM 62 (3) (19
69) There is a cooling fracture method known on p.776. This is A
This is a method in which the material attached to the ES device is cooled to around −100 ° C., and the low-temperature brittleness of steel is used to utilize a mechanism in which a material test piece is broken at a grain boundary by an external impact.

Like tough metal and low alloy steel, -10
For materials that do not break at grain boundaries when cooled to about 0 ° C,
As disclosed in Japanese Patent Laid-Open No. 59-138936, there is one
A method is known in which high pressure hydrogen of 0 to 7600 Torr (10 atm) is introduced and a repetitive stress having a low strain rate is applied to a sample in an apparatus to facilitate breakage at a grain boundary. This method attempts to expose a large number of grain boundaries by absorbing hydrogen into the grain boundaries through the strain generated in the material.

On the other hand, as a treatment method for accelerating the grain boundary rupture outside the apparatus, a constant load at 500 ° C. is applied (creep) until just before rupture, as in JP-A-63-115041. Then, a method of applying a low strain rate tensile force to damage the crystal grain boundaries to selectively expose the grain boundaries is known.

In the breaking method in which the material is cooled to about -100 ° C. with liquid nitrogen and subjected to an impact, the toughness is excellent and the low temperature embrittlement resistance is good in many cases, and the ductility or the intragranular fracture surface is caused in the metal material. It is extremely difficult to reveal grain boundaries. Further, in the method of introducing high-pressure hydrogen into the analyzer and breaking it, a special container for introducing high-pressure hydrogen, a gas introduction system and a mechanism for applying stress to the material are required,
The structure of the device is complicated and large, and there is a problem in operability and economy.

In addition, in the method of giving tensile damage at a low strain rate to damage the grain boundaries subsequent to creep application, since creep application is performed at a high temperature of 500 ° C., thermal diffusion causes
There is a problem that the element moves from the grain boundary into the grain, the grain boundary element concentration changes before and after the creep is applied, and an accurate analysis cannot be performed. Further, in this breaking method, although the strain rate is low, tensile stress is applied to the material, so that the material is damaged and many cracks occur in the material. When this cracking unit, was introduced for N ₂ in the air, O _2, H ₂ O, gases such as CO ₂ from entering the processed material specimens in a predetermined shape in ultra-high vacuum apparatus, There is a problem in that the degree of vacuum in the device is lowered due to the generation of gas from the test piece, and the gas molecules released into the device are adsorbed by the grain boundaries exposed after the material is broken, which lowers the analysis accuracy.

The method of charging the material with hydrogen by the electrolytic method allows hydrogen to be introduced into the material relatively easily, and the metallic material selectively forms grain boundaries due to the embrittlement effect of the introduced hydrogen. Since it is embrittled, it breaks along the grain boundaries. Therefore, as a grain boundary expression method for analyzing grain boundary segregation elements by AES, the grain boundary segregation elements are changed for steel and metal materials that do not show low temperature brittleness when cooled at around -100 ° C. This is an effective method for the material to be processed.

In a sensitizing material of stainless steel, the ductility of the steel is lowered by charging the cathode with hydrogen.
The Japan Institute of Metals, Vol. 46, No. 9, (1982),
p. 877-886, and as a method of exposing the grain boundaries of the sensitizing material of the austenitic Fe-Ni-Cr alloy by utilizing this phenomenon, Japanese Patent Laid-Open No. 04-285.
As in No. 187, the alloy was charged with hydrogen by an electrolysis method, then the material was heated at 100 ° C., dehydrogenation treatment (discharge) was performed, and this hydrogen charge / discharge was repeated multiple times, and then the material was broken. Then, a method of creating a crystal grain boundary is known.

However, in the method of discharging after the hydrogen is charged by the electrolytic method, hydrogen is charged into the material, so that the hydrogen diffuses from the metal surface to the inside and further to the crystal grain boundary, and the grain boundary is embrittled. Due to the subsequent dehydrogenation treatment, hydrogen is diffused into the material, and at the same time, hydrogen is released from the material surface. Therefore, depending on the temperature and time of the dehydrogenation process, the embrittlement layer at the grain boundaries generated by hydrogen charging disappears, the hydrogen-free state is restored, and the grain boundary fracture surface created when the material is fractured. Area ratio is reduced. Even when the discharge process is not performed, hydrogen has a high diffusion rate and is easily released from the material into the atmosphere at room temperature. Therefore, most of the charged hydrogen is released from the material, and hydrogen is fragile at grain boundaries. There is a problem that the area ratio of the grain boundary fracture surface created when the chemical layer disappears and breaks decreases.

As a device for charging hydrogen to a metal material by an electrolysis method, as known from JP-A-04-285187, a 1N-sulfuric acid solution at 50 ° C. (with addition of NaAsO ₃ ) is used.
Among them, the cathodic hydrogen charging method based on the constant current method is known. In this method, a platinum electrode is arranged as a counter electrode (anode) on the entire surface of the test piece as a cathode, and a potential change is recorded by a reference electrode. When the platinum electrode is confronted so as to cover the surface of the test piece, hydrogen invades the entire test piece, which requires a long charging time. However, there was a problem that the amount of charged hydrogen fluctuates greatly due to the change in the liquid concentration due to the evaporation of the electrolytic solution due to the hydrogen charge. Furthermore, when electrolytic hydrogen charging is performed in an apparatus in which the amount of hydrogen charge changes in this way, the concentration of hydrogen introduced into the material changes significantly, and the area ratio of grain boundary fracture surfaces due to hydrogen embrittlement changes. There was a problem of change.

[0012]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, and for the analysis of grain boundary segregation elements of steel and metal materials,
An attempt is made to provide a technique for efficiently revealing more grain boundary fracture surfaces.

[0013]

That is, in order to solve the above problems, the present invention uses an electrolytic hydrogen charging method to selectively introduce hydrogen into the vicinity of a notch in a metallic steel material, and A method for revealing a grain boundary fracture surface of a metal material, characterized in that a hydrogen concentration is set to 3 ppm or more, the surface of the material is subjected to Ni electroplating, the material is stored in liquid nitrogen, and then the material is broken. provide. Furthermore, the present invention is an electrolytic hydrogen charging device for charging a metal steel piece having a cutout portion with hydrogen as a negative electrode, wherein the cutout portion contains 0.5 to 3N sulfuric acid containing a small amount of sodium arsenite. Electrolyzer containing solution electrolyte, temperature control means to keep the temperature of the electrolyte constant, automatic fixed amount feeding means to keep the amount of electrolyte constant, near the notch of metal steel material as the negative electrode There is provided an electrolytic hydrogen charging device comprising a positive electrode placed opposite to each other and a power source for applying an electrolytic voltage to the negative electrode and the positive electrode.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. As described above, the method of the present invention is an electrolytic hydrogen charging method, in which hydrogen is selectively introduced in the vicinity of the notch of a metallic steel material so that the hydrogen concentration in the material is 3 ppm or more, and then Ni electrolytic plating is performed on the surface of the material. Then, the material is stored in liquid nitrogen, and then the material is broken. Here, the electrolytic charging method is a method in which hydrogen is infiltrated into a cathode as a reference material by a constant current method in an electrolytic solution at a constant temperature. In this method, a platinum electrode is arranged as a counter electrode (anode) on the surface of the test piece at the cathode. The present invention is characterized in that hydrogen is selectively charged not in the entire material but in the vicinity of the notch.

The metallic steel material to be subjected to the method of the present invention is
It is not particularly limited as long as it is a steel material, but it can also be applied to austenitic stainless steel, low alloy steel, carbon steel and the like. A notch having a depth of about 0.5 mm, which is a breaking point, is formed in the metal steel material used as the test piece.

The hydrogen concentration of the notch in the material is 3 ppm or more, preferably 4-5 ppm, particularly preferably 4 p.
pm. When hydrogen is charged by the electrolysis method so that the hydrogen concentration in the material becomes 3 ppm or more, the area ratio of the grain boundary fracture surface increases remarkably, the observation range increases, and the analysis accuracy improves.

Ni electrolytic plating is preferably NiSO ₄
Plating solution composition of 150 g / l and ammonia chloride 15 g / l, 20 to 25 ° C., preferably 20 ° C. plating bath temperature,
0.2 to 2.0 A / dm ² , preferably 0.5 to 1 A /
dm ² current density, ² to 10 min, preferably 4 to 6
It is performed under electrolysis conditions with a plating time of min. The pH is adjusted by adding dilute sulfuric acid and Ni carbonate. A Ni plating having a thickness of 0.5 μm or more, preferably 1 μm or more is deposited on the surface of the metallic steel material by Ni electrolytic plating. Immediately after the introduction of hydrogen, Ni with high solubility of hydrogen on the surface of the material test piece
By plating, it becomes difficult for hydrogen in the material to permeate to the outside, and the release of hydrogen from the material can be reduced.

The liquid nitrogen is stored for 5 minutes or longer, preferably about 30 minutes, and stored in liquid nitrogen. Thereby, the diffusion of hydrogen in the metallic steel material can be suppressed, and the release from the material can be reduced.

The fracture is caused by N ₂ , O ₂ , H ₂ O and C on the grain boundary surface.
In order to prevent the gas molecules in the atmosphere such as O _{2 from} being thickly adsorbed and obscuring the segregated elements, the process is performed in an ultra-high vacuum in the AES apparatus. Examples of the grain boundary fracture method in the AES apparatus include “Practical Auger electron spectroscopy for users” edited by Ryuichi Shimizu and Kazuhiro Yoshihara (Kyoritsu Shuppan, Chapter 8, pp. 153-1).
55) and Transaction of the ASM 62 (3) (1969) p.776.
A general method such as the cooling rupture method known in the above can be used.

The electrolytic charging method used in the method of the present invention can be preferably carried out by using the apparatus of the present invention, and by using the apparatus of the present invention, the hydrogen concentration in the metallic steel material can be easily controlled to 3 ppm or more. The device of the present invention will be described below with reference to FIG. 2, which illustrates a preferred example of the device of the present invention. The device of the present invention is not limited to the illustrated example. The apparatus of the present invention shown in FIG. 2 uses a metal steel piece 2 having a notch 1 as a negative electrode and a platinum electrode 8 as an anode in an electrolytic cell 7 filled with an electrolytic solution 6 to electrolyze hydrogen into the notch 1. Infiltrate.
If the metal steel piece 3 having another notch 4 is similarly used as the negative electrode and the other platinum electrode 9 is opposed to this cathode, a plurality of steel pieces can be simultaneously charged with hydrogen.

As the electrolytic solution 6, a 0.5 to 3 N sulfuric acid solution containing a small amount of sodium arsenite is used. The amount of arsenous acid contained in the electrolytic solution is very small, but preferably 0.5 g /
1 to 1 g / l. By adding a small amount of sodium arsenite, generation and adhesion of hydrogen gas due to rapid reaction progress at the cathode can be suppressed, and the cathode reaction can be continued. The sulfuric acid concentration of the electrolytic solution is 0.5 to 3N, preferably 1 to 2N. This is because it is possible to set the electrolysis conditions (current, temperature, time) for making the hydrogen concentration of the material 3 ppm or more by this sulfuric acid concentration.

The device of the present invention is provided with temperature control means.
The temperature control means is composed of a controller 10, a temperature sensor 11 and a heater 12 for keeping the temperature of the electrolytic solution constant.
The temperature sensor 11 is preferably a thermometer such as a thermocouple provided in the electrolytic solution 6, and the heater 12 is a heating device such as a heating wire provided at the bottom 17 of the electrolytic bath 7. The temperature sensor 11 and the heater 12 are each a controller 10
Electrically connected to. When the temperature of the electrolytic solution 6 is detected by the temperature sensor 11 and the temperature of the electrolytic solution 6 is lower than the desired temperature, the heater 12 is activated by the command from the controller 10 to heat the electrolytic solution 6. In this way, the temperature of the electrolytic solution 6 can always be kept constant. The temperature is kept constant because the amount of hydrogen charged by electrolysis varies depending on the temperature of the electrolytic solution. By keeping the temperature of the electrolytic solution constant, the hydrogen concentration in the material can be controlled to 3 ppm or more with good reproducibility.

The automatic fixed amount liquid feeding means has a liquid level sensor 13, a pump 14, and a distilled water tank 15. When the liquid level sensor 13 detects the amount of the electrolytic solution 6 and the amount of the electrolytic solution 6 does not reach the desired amount, that is, the desired concentration due to the evaporation of water, the pump 14 causes the distilled water tank 15 to move to the electrolytic tank 7.
Supply distilled water to. As a result, the concentration and pH of the electrolytic solution 6
This is to keep constant. The amount of hydrogen charged by electrolysis varies depending on the electrolyte concentration and pH value. According to the present invention, the concentration and pH of the electrolytic solution can be kept constant by providing an automatic fixed amount liquid feeding means for automatically replenishing distilled water by detecting a decrease in the electrolytic solution 6 that evaporates during long-term hydrogen charging. Therefore, the hydrogen concentration in the material can be controlled to 3 ppm or more with good reproducibility.

The negative electrode of the electrode is a metallic steel material 2, and a notch 1 to be a breaking point is provided in the negative electrode. The positive electrode is a platinum electrode 8 and the positive electrode is arranged so as to face the notch 1 of the material. The shape of the platinum electrode 8 is a ring provided apart from the linear shape when the notch 1 is a substantially horizontal linear shape provided in the metallic steel material, and its width is slightly larger than the width of the notch 1. It is preferable to widen it. That is, it is preferable that the anodes 8 are opposed to each other so as to surround the shape of the notch 1 at a position separated from the notch 1. With such an arrangement, the introduction of hydrogen can be limited to the vicinity of the notch 1, and hydrogen can be introduced directly to the fracture portion where the fracture occurs to reveal the grain boundary fracture surface. It becomes possible to promote embrittlement. Further, since hydrogen is charged only in a specific place, the charging time can be shortened. Further, a potentiostat 16 as a power source is connected to the electrodes, and the negative electrode and the positive electrode are connected to the negative terminal and the positive terminal of the potentiostat, respectively. The potentiostat 16 automatically keeps the electric potential of the current flowing through the electrodes constant. Since the amount of hydrogen charged by electrolysis varies depending on the electrolysis current, by installing a potentiostat, the hydrogen concentration in the material can be controlled to 3 ppm or more with good reproducibility.

[0025]

[Function] When hydrogen is added to a metal or steel material, the material becomes brittle (hydrogen embrittlement). This is because hydrogen in the material is mainly distributed along the crystal grain boundaries and the grain boundaries become brittle. The present invention is an application of the above phenomenon to a method of revealing a grain boundary fracture surface for grain boundary segregation element analysis of AES. According to the present invention, for example, a material having a round bar of 3.5 mmφ × 17.5 mm is used. And a notch having a depth of about 0.5 mm, which becomes a breaking point of the test piece, is formed along the circumference at substantially the center in the major axis direction.
A positive electrode having a width substantially the same as or slightly larger than the notch is arranged so as to face the notch 1 of the ES breaking test piece, and hydrogen is charged by electrolysis. As a result, the introduction of hydrogen is
It will be limited to the vicinity of the notch, it will be possible to directly introduce hydrogen to the fracture portion which later fractures and the grain boundary fracture surface appears, and it is possible to promote grain boundary embrittlement only in the vicinity of the fracture portion Become.

Further, according to the present invention, the surface of the material test piece is plated with Ni immediately after the introduction of hydrogen, and the material test piece is stored in liquid nitrogen to make it difficult for hydrogen in the material to permeate to the outside and to It is possible to suppress the diffusion of hydrogen at, and reduce the release of hydrogen from the material.

FIG. 1 shows the hydrogen concentration (ppm) in the carbon steel charged by the electrolysis method and the grain boundaries after breaking the carbon steel test piece in the AES analyzer, which were observed by SEM (scanning electron microscope). At this time, the relationship of the area ratio (%) of the grain boundary fracture surface to the entire area is shown. Regarding the amount of hydrogen in carbon steel, a test piece (3.5 mmφ × 17.5 mm round bar) was introduced into a furnace at 1000 ° C. for 2 to 3 seconds, and the generated H ₂ gas was detected by the built-in thermal conductivity. It measured using the hydrogen analyzer which analyzes by the instrument. According to FIG. 1, the hydrogen concentration of carbon steel not charged with hydrogen is 0.3 to 0.5 ppm, and the grain boundary fracture surface ratio is 0.
%, That is, almost all ductile fracture surfaces (or all intragranular fracture surfaces), the hydrogen concentration in the steel is 3 ppm when charged with hydrogen.
It can be seen that the grain boundary fracture rate is about 50%, which is remarkably increased, and the grain boundary fracture rate tends to be saturated when the hydrogen concentration in the steel is 4 ppm or more. In the present invention, by charging hydrogen by an electrolysis method so that the hydrogen concentration in the material becomes 3 ppm or more, the area ratio of the grain boundary fracture surface is significantly increased, the observation range is increased, and the analysis accuracy is improved. .

In order to set the hydrogen concentration in the material to 3 ppm or more, it is necessary to set the conditions for electrolytic hydrogen charging. According to the present invention, by using a 0.5 to 3N sulfuric acid solution containing a trace amount of sodium arsenite as an electrolytic solution, electrolytic conditions (current, temperature, time) for setting the hydrogen concentration of the material to 3 ppm are set. It becomes possible. Here, a small amount of sodium arsenite suppresses the generation and adhesion of hydrogen gas due to the rapid reaction progress at the cathode, and continues the cathode reaction. The amount of hydrogen charged by the electrolysis method varies depending on the temperature of the electrolytic solution, electrolytic current, electrolytic solution concentration, and pH value. By using the device of the present invention, a potentiostat for maintaining a constant electrolysis current and a temperature control means for maintaining a constant temperature are attached to detect a decrease in the electrolytic solution that evaporates during hydrogen charging for a long time. Since it has an automatic fixed-quantity liquid feed pump that automatically replenishes distilled water, the temperature, concentration and pH of the electrolyte can be kept constant, and the hydrogen concentration in the material can be easily controlled to 3 ppm or more. .

[0029]

EXAMPLE FIG. 2 is a configuration diagram of a cathode electrolytic hydrogen charging device by constant current control using a potentiostat 16. The illustrated apparatus is an electrolytic cell 7 containing an electrolytic solution 6 which is a 0.5 to 1 N sulfuric acid solution containing a small amount of sodium arsenite, and two material test pieces 2 processed into a predetermined shape as a cathode. 3 (carbon steel), the anode is provided with platinum electrodes 8 and 9 facing the notch 1 at the substantially central portion of each material test piece, and the negative and positive terminals of the potentiostat 16 are respectively arranged. It is connected. In this electrolytic cell 7,
A heater 12 for detecting the temperature of the electrolytic solution with a temperature sensor 11 and keeping the liquid temperature constant through a temperature controller 10 is attached. Therefore, when the electrolyte temperature rises, the current flowing through the heater 12 is reduced to lower the liquid temperature. Conversely, when the liquid temperature falls,
The controller 10 acts to increase the current flowing through the heater 12 and lower the liquid temperature. Further, a liquid level sensor 1 for detecting a decrease in the electrolytic solution due to evaporation of water.
3 and a liquid delivery pump 14 for automatically replenishing evaporated water from the distilled water tank 15. When the liquid level sensor 13 detects a decrease in the electrolytic solution 6, the liquid feed pump 14 operates and acts to replenish the electrolytic solution 6 with distilled water.

Table 1 shows that the current value of the potentiostat is 25 mA, the electrolytic solution concentration is 1 N, and the temperature of the solution is set to 50 by the heater.
The fluctuation range of the hydrogen concentration in steel at the time of carrying out hydrogen charge of 86.4ks at ° C is shown. As shown in Table 1, in the device of the present invention using both the temperature sensor and the liquid level sensor, the fluctuation range of the hydrogen concentration introduced into the steel is small, and in this fluctuation range, the grain boundary fracture surface area ratio The result was that the hydrogen concentration in the steel of 3 ppm or more required to achieve 50% or more could be achieved. Figure 1 shows the anode
Rupture the relationship between the grain boundary fracture surface ratio and hydrogen concentration in steel when hydrogen is charged on the entire test piece without placing the platinum electrode so as to face the notch in the center of the material test piece. This is shown in comparison with the method of the present invention in which the platinum electrode is arranged so as to face the notch. In the method of the present invention in which the notch is charged with hydrogen, hydrogen is introduced only in the vicinity of the portion to be observed and analyzed for embrittlement to cause embrittlement, so that the grain boundary is exposed at a remarkably high grain boundary fracture rate. The result is that it is possible.

[0031]

FIG. 3 is a diagram showing the relationship between the hydrogen concentration in steel and the temperature of the electrolytic solution, the electrolytic solution concentration, and the electrolysis time. This allows
The electrolysis conditions for hydrogen charging using the device of the present invention could be determined. The electrolytic current for hydrogen charging is 10 to 100.
As a result of conducting the experiment in the range of mA, the hydrogen concentration in the steel became the highest at 25 mA, so it was set to 25 mA. From FIG. 3, it becomes clear that the hydrogen concentration in the steel becomes highest when the electrolyte concentration is 1 N and the liquid temperature is 50 ° C., and the hydrogen concentration in the steel decreases when either the electrolyte concentration or the liquid temperature deviates from this condition. . Further, it was found that the hydrogen concentration in the steel increased with the increase of the electrolysis time, but became almost constant at 180 ks or more. Therefore, when the electrolyte concentration is 0.5 to 3 N, it is necessary to set the liquid temperature to 50 to 70 ° C. and the electrolysis time to 86.4 ks or more to obtain the grain boundary fracture surface ratio of 50% or more. It was found that a high hydrogen concentration of 3 ppm or more in steel can be achieved.

In order to suppress the release of hydrogen introduced into the steel to the outside, the material test piece after electrolytic hydrogen charging was replaced with Ni.
After electroplating, it was stored in liquid nitrogen (-170 ° C). Ni electrolytic plating is NiSO ₄ : 150 g /
1, ammonia chloride: 15 g / l, boric acid: 15 g /
1, the electrolytic solution has a hydrogen ion concentration of pH 5.8 to 6.2, the composition of the plating solution is 20 ° C., and the current density is 0.
The electrolysis was performed under the electrolytic conditions of 5 to 1 A / dm ² and plating time of 4 to 6 min. The pH value of the electrolytic solution was adjusted by adding dilute sulfuric acid when the pH was high and by adding Ni carbonate when the pH was low. Under these plating conditions, the thickness is approximately 1 μm (applied amount approximately 9 g
/ M ² ) or more of Ni plating adhered to the surface of the material test piece.

FIG. 4 is a diagram comparing the relationship between the hydrogen concentration in steel and the hydrogen charging time when the above Ni plating is carried out after electrolytic hydrogen charging, as compared with the case where Ni plating is not carried out. The hydrogen concentration in steel increases as the electrolytic hydrogen charging time increases, but tends to saturate at 180 ks.
In the test piece which was kept in liquid nitrogen without plating Ni, the hydrogen concentration in the steel was considerably lower than that of the test piece which was kept in liquid nitrogen after being charged with hydrogen for the same time and subjected to Ni plating. Even in the charging time of, the hydrogen concentration in the steel did not reach 3 ppm. Therefore, in the present invention, since the Ni plating is made to adhere to the surface of the hydrogen-charged test piece by electrolytically about 1 μm, it is possible to suppress the release of 3 ppm or more of hydrogen introduced into the material to the outside. The result is that crystal grain boundaries can be revealed with a high grain boundary fracture surface ratio of 50% or more. In the above examples, as the target material, the case of carbon steel has been described, but the present invention is not limited to this, and a steel material such as a thin steel plate, an electromagnetic steel plate, a thick steel plate, and a swab steel. Alternatively, an alloy having a crystal grain boundary or a metal material may be used.

[0035]

According to the present invention, by selectively charging the notch portion of the sample material with hydrogen, the grains essential for the analysis sample when the grain boundary segregation element is analyzed by Auger electron analysis It becomes possible to expose a large number of cross-sections with high efficiency and reproducibility. as a result,
It is possible to easily obtain a test piece having a high grain boundary fracture surface area ratio of 50% or more for a material that has excellent toughness and does not exhibit low temperature brittleness at -100 ° C or a material that does not easily break at grain boundaries. As a result, the number of crystal grain boundaries to be analyzed during Auger analysis increases, and the accuracy of quantitative analysis of grain boundary segregation elements can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between hydrogen concentration in steel and grain boundary fracture surface ratio.

FIG. 2 is a side view showing the configuration of an electrolytic hydrogen charging device.

FIG. 3 is a diagram showing electrolysis conditions for carrying out hydrogen charging with an electrolytic hydrogen charging device, and is a relationship diagram of hydrogen concentration in steel, electrolyte concentration, liquid temperature, and electrolysis time.

FIG. 4 is a diagram showing the relationship between the presence or absence of Ni plating after hydrogen charging, the hydrogen concentration in steel, and the hydrogen charging time.

[Explanation of symbols]

1 notch 2 Metal steel pieces 3 Metal steel pieces 4 notches 5 Electrolytic hydrogen charging device 6 Electrolyte 7 Electrolyzer 8 Platinum electrode 9 Platinum electrode 10 controller 11 Temperature sensor 12 heater 13 Liquid level sensor 14 Liquid feed pump 15 distilled water tank 16 potentiostat 17 bottom

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 1/28 G01N 23/227 G01N 33/20 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. An electrolytic hydrogen charging method, in which hydrogen is selectively introduced in the vicinity of a cutout portion of a metallic steel material so that the hydrogen concentration in the material is 3 ppm or more, and then Ni electrolytic plating is performed on the surface of the material. A method for revealing a grain boundary fracture surface of a metal material, which comprises storing the material in liquid nitrogen and then breaking the material. 2. An electrolytic hydrogen charging device for charging a metal steel piece having a cutout portion with hydrogen as a negative electrode, wherein the cutout portion contains 0.5 to 5% of sodium arsenite.
An electrolytic cell containing an electrolytic solution which is a 3N sulfuric acid solution, a temperature control means for keeping the temperature of the electrolytic solution constant, an automatic fixed amount feeding means for keeping the amount of the electrolytic solution constant, and a metal steel material which is a negative electrode An electrolytic hydrogen charging device comprising: a positive electrode, which is installed in the vicinity of the cutout portion so as to face each other; and a power source for applying an electrolytic voltage to the negative electrode and the positive electrode.