JPH0224551A - Detecting method of degree of embrittlement of test specimen and detecting apparatus therefor - Google Patents

Abstract

PURPOSE:To judge the degree of embrittlement of low-alloy steel or the like due to thermal hysteresis efficiently and with high precision and high sensitivity by a method wherein an electrolytic solution made up of a mixed water solution of an aromatic compound and inorganic salt is brought into contact with a test specimen and a spontaneous potential generated thereby is measured. CONSTITUTION:A mixed water solution of an aromatic compound and inorganic salt being used as an electrolytic solution 15; this electrolytic solution 15 is brought into contact with a test specimen 11, which is low-alloy steel or the like; a spontaneous potential generated thereby is measured by an electrometer 21; and the degree of embrittlement of the test specimen 11 due to thermal hysteresis is detected from said spontaneous potential. The electrolytic solution 15 is the mixed water solution of the aromatic compound, such as a picric acid, and the inorganic salt, such as sodium hydroxide containing a hydroxyl group, for instance, and the aromatic compound has at least either the hydroxyl group or a caboxyl group and a nitro group in a molecule. According to this method, a time for measurement can be shortened to about a half of the one required in a conventional testing method of dielectric polarization.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a method and apparatus for detecting the degree of embrittlement of a measured object such as low alloy steel, and particularly relates to an electrical The present invention relates to a method and apparatus for detecting the degree of embrittlement of objects to be measured such as low alloy steel, which non-destructively measures aging embrittlement from changes in chemical properties.

(Conventional technology) Low alloy steel used at high temperatures is chemically stable at high temperatures,
It is required to have sufficient mechanical strength and have a stable metal structure at high temperatures. These low-alloy steels are used in equipment such as steam turbines, but in equipment such as steam turbines that are used in high-temperature conditions for long periods of time, structural changes occur within the low-alloy steel, and low-alloy steel deteriorates over time. Deterioration tends to be noticeable.

A particular problem in material deterioration is so-called tempering embrittlement. This temper embrittlement is caused by p contained in low alloy steel,
It is thought that this is caused by impurity elements, especially phosphorus (P) from 3n, AS, 3b, etc., which segregate at grain boundaries and weaken the grain boundary strength.

On the other hand, when tempering embrittlement occurs in low alloy steel, the toughness of low alloy #1 equipment decreases, increasing the risk of causing a breakage accident. Therefore, from the viewpoint of quality evaluation of low alloy steel and accident prevention, various embrittlement degree detection techniques have been developed to measure the aging tempering embrittlement of low alloy steel.

A conventional and widely used method for detecting the degree of embrittlement of low-alloy steel is the Charvi impact test. This detection method detects the degree of decrease in the absorbed energy value when the sample is subjected to impact fracture, or the shift to the high temperature side of the impact value-test temperature curve, that is, the transition temperature of the impact value. The ductile fracture ratio is determined by measuring the ratio of the ductile fracture surface area of one fracture surface to the non-fracture surface area, and from this temperature dependence, the fracture surface transition temperature is defined as the temperature corresponding to the ductile fracture ratio of 50%. The degree of embrittlement is detected by ΔFATT.

However, this test method
This is a destructive test in which a measurement test piece is cut out from a single manufactured product. For this reason, after the embrittlement test for low alloy steel has been completed, the product made of low alloy steel cannot be reused, and the inspection method based on the Charvy impact test cannot be repeatedly used for periodic inspections for the purpose of maintenance.

How to use: A method for non-destructively testing the degree of embrittlement of low-alloy steel.
It is disclosed in Japanese Patent Application Laid-Open No. 14155/1983. This nondestructive testing method measures the temper embrittlement of low alloy steel by applying an electrochemical method, and is configured as shown in FIG. 7.

The low alloy steel embrittlement testing device shown in FIG. Soak 4. 5 is a reference electrode, 6 is a salt bridge, and 7 is a reference electrode.
and 8 are a voltmeter and an ammeter.

So-C1 This inspection device measures the magnitude of the repassivation current obtained in the process of measuring the polarization curve by immersing the low alloy steel 3 as an anode with an ammeter 8. The degree of embrittlement, that is, the degree of embrittlement, is evaluated.

The polarization curve at this time is expressed as shown in Fig. 8, and the sweep starts from the self-potential a, and this sweep continues until the maximum active current point A reaches the passive region.
The sweep is stopped once at the fM reversal point C of the region.

Next, when the sweep direction is reversed and a reverse sweep is started, the current (intensity) decreases rapidly and reaches minimum parts d and e. The current defined by this minimum part is the repassivation current. When temper embrittlement has not occurred in the low alloy steel to be inspected, the repassivation current i6 becomes zero or a value close to it, as shown in the minimum part d.

On the other hand, when tempering embrittlement exists, the repassivation current I becomes a small current value, as shown in the minimum part e.

The conventional method for detecting the degree of embrittlement of low alloy steel evaluates the degree of embrittlement, that is, the degree of embrittlement, of low alloy steel by detecting the magnitude of the repassivation current.

(Problem to be solved by the invention) In the conventional method for detecting the degree of embrittlement of Iba alloy steel,
Before measuring the II state current, the anode polarization curve is measured from the natural potential a through the active region, so the total measurement time is longer, and when there are many objects to be inspected during periodic inspections, the inspection efficiency may be reduced. The problem was that it was bad.

Also, low alloy steel 3 is active! Dissolution occurs on the test surface at the time of passing through the five regions. Dissolution of the inspection surface occurs non-uniformly in accordance with its metallographic structure, resulting in fine irregularities on the inspection surface, and these irregularities make the thickness of the passive film formed non-uniform.

The conventional method for detecting the degree of embrittlement of low-alloy steel is that it is difficult to detect embrittlement due to the action of phosphorus (P), an impurity element segregated at grain boundaries. The state of P segregation and the degree of embrittlement associated with this segregation are detected by the magnitude of the current flowing through the portion where the formation of the ll-state film is inhibited. Therefore, it is conceivable that the technology for detecting the degree of embrittlement of low-alloy steel may deteriorate due to factors other than the segregation of P that affect the formation of the passive film.

In addition, equipment for non-destructively detecting the degree of embrittlement of low-alloy steel includes:
An electrolytic cell 1 is used to store an electrolyte 12 in the cell 1, but the electrolytic cell 1 cannot store a large amount of electrolyte due to its structure. For this reason, there have been problems such as the characteristics of the electrolyte being deteriorated by corrosion products such as iron ions eluted in the active region, and the accuracy of detecting the degree of embrittlement being lowered.

The present invention has been made in consideration of the above-mentioned circumstances, and the degree of embrittlement of the object to be measured, such as low alloy steel, can be determined within a short period of time by measuring the natural potential while immersed in an electrolytic solution. An object of the present invention is to provide a method for detecting the degree of embrittlement of a measured object such as low alloy steel, which can be measured with high accuracy and sensitivity, and a detection device therefor.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above-mentioned problems, the method for detecting the degree of embrittlement of a measured object according to the present invention uses a mixed aqueous solution of an aromatic compound and an inorganic salt as an electrolytic solution. This method is characterized by bringing an electrolytic solution into contact with an object to be measured such as low alloy steel, measuring the natural potential, and detecting the degree of embrittlement due to the thermal history of the object from this natural potential.

In addition, in order to solve the above-mentioned problems, the device for detecting the degree of embrittlement of a measured object according to the present invention has an electrolytic cell provided in a liquid-tight manner on the measured object such as low alloy steel, and the electrolytic cell is filled with liquid. The electrolytic solution is brought into contact with the object to be measured through the opening of the electrolytic cell, and a reference electrode is placed in the electrolytic solution of the electrolytic cell.
A potential detector is provided for measuring the potential between the reference electrode and the object to be measured as a natural potential.

(Function) In the present invention, when an object to be measured such as low-alloy steel is brought into contact with an electrolytic solution formed of a mixed aqueous solution of an aromatic compound and an inorganic salt, the natural potential of the object to be measured such as low-alloy T14 is This method focuses on the point that changes depending on the degree of embrittlement, and by measuring this self-potential, it is possible to repeatedly measure the degree of embrittlement of low-alloy steel with high precision and sensitivity.

In this case, the measurement time of the object to be measured such as low alloy steel can be reduced to about half compared to the conventional polarization test method, and =tm efficiency can be improved. Furthermore, in the present invention, since it is not necessary to measure the polarization current, there is no need for a counter electrode in the potentiostat or the electrolytic cell, and the measuring device can be simplified.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a principle diagram showing an apparatus for detecting the degree of embrittlement of objects to be measured such as low alloy #f according to the present invention. This embrittlement degree detection device 10
is a measurement object 1 made of low alloy steel such as CrMO steel and CrMoV steel.
1, an electrolytic cell 12 is provided in a liquid-tight manner via a sealing material 13 such as packing. The electrolytic cell 12 includes an opening 14 that opens toward the inspection surface of the object 11 to be measured.

The interior of the electrolytic cell 12 is filled with a snowmelt solution 75, and this electrolytic solution 15 is in contact with the inspection surface of the object to be measured 11 through the opening 14 of the electrolytic cell 12. The electrolytic solution 15 is a mixed aqueous solution of a hexa-aromatic compound of picric acid and an inorganic salt such as sodium hydroxide containing a hydroxyl group. It is something that you have. Examples of such aromatic compounds include O-nitrophenol, m-nitrophenol, P-nitrophenol, 2゜4-dinitrobenzoic acid, 2.5-dinitrobenzoic acid, 3.4-dinitrobenzoic acid, 0- Examples include dinitrobenzoic acid, m-nitrobenzoic acid, and p-nitrobenzoic acid. In addition, examples of inorganic salts containing hydroxyl groups include potassium hydroxide, sodium hydroxide,
Examples include ammonium hydroxide.

The concentration of the electrolytic solution 15 is preferably adjusted so that pf-1 is 3.5 or less. If the pH exceeds 3.5, when the electrolytic solution 15 is brought into contact with the measured object 11 made of low-alloy steel, a precipitated film of oxides, hydroxides, etc. is likely to be formed on the surface of the measured object 11, and the degree of embrittlement may be reduced. This is because reproducible judgment becomes difficult.

The electrolytic solution 15 is supplied to the electrolytic cell 1 through an injection port (supply/discharge port) 16.
During this injection, the fluid in the electrolytic cell 12 is discharged from the outlet 17 and overflows. Reference numeral 18 indicates a valve provided at the inlet 16 and the outlet 17.

Further, a reference electrode +4i20 is inserted into the electrolytic solution 15 stored in the electrolytic cell 12, and this reference electrode 20 is connected together with the object to be measured 11 to a potential detector such as an electrometer 21. The natural potential was measured at 21. The output from the electrometer 21 is ]-
It is recorded on a recorder 22 such as a front recorder.

Next, a method for measuring the degree of embrittlement of low alloy steel will be explained.

The object 11 to be measured is made of 06M071m steel or the like as a low alloy steel. The surface of the object to be measured 11 is mechanically polished using, for example, a #600 emery vapor and washed with pure water.
Install the electrolytic cell 12 in a liquid-tight manner. Electrolytic solution 15 is injected into electrolytic cell 12 through injection port 16, and when electrolytic solution 15 overflows from discharge port 17, valve 18 is closed.

Then, by measuring the potential between the object to be measured 11 and the reference electrode 20 with the electrometer 21, the natural potential Em of the object to be measured 11 is measured, and the output thereof is recorded by the recorder 22.

FIG. 2 shows the temporal change in the natural potential Em of the object to be measured 11 measured by the embrittlement degree measuring device 10 for low alloy steel. In the figure, the symbol a indicates the time-varying curve of the natural potential Em when a embrittleable material is used as the object to be measured, and the symbol s indicates the time-varying curve of the natural potential [m] when a non-embrittleable material is used. .

From Fig. 2, the potential rises in the noble direction for the first few minutes, and then gradually decreases in the base direction, regardless of whether an embrittleable material or a non-embrittleable material is used for the measured object 11. Then, for example, after 15 minutes have elapsed, the value becomes approximately constant. From this relationship, it is desirable to measure the potential after 15 minutes as the natural potential Fm.

FIG. 3 is a graph showing the results of measuring the natural potential of several types of embrittlement materials, for example, seven types of embrittlement materials with different degrees of embrittlement.

In this figure, the vertical axis shows the self-potential Em after 15 minutes, and the horizontal axis shows the increase in fracture surface transition temperature ΔFATT based on the non-embrittlement material, which is an index and does not represent the degree of embrittlement. From Figure 3, the natural potential Em changes linearly in accordance with the degree of embrittlement,
The higher the degree of embrittlement, the more the natural potential Em shifts toward the nobler direction. Therefore, it can be seen that the degree of embrittlement of low alloy steel can be measured by measuring the natural potential Em. The measurement time at that time is 15 minutes for injecting the electrolyte 15, compared to about 30 minutes for the conventional polarization measurement method.
It was found that the time could be reduced to about 1/2.

- On the other hand, when various types of low-alloy steel undergo thermal history, metallographic changes occur and mechanical properties deteriorate.
It is known that natural molecules change in various electrolytes. This change in self-potential is thought to be due to changes in anode polarization behavior and cathode polarization behavior in the electrolyte due to changes in the structure of the low alloy steel.

This change phenomenon will be explained using FIG. Figure 4 is a schematic representation of the polarization behavior of low alloy steel.
). In a non-embrittling material (object to be measured) that undergoes deterioration due to thermal history, the anodic polarization curve and the cathodic polarization curve are represented by curves A and B, and the natural potential is an enhanced potential indicated by EITI.

As the non-embrittling material deteriorates, its corrosivity changes due to the segregation of impurities, resulting in changes in the anodic polarization curve and the cathodic polarization curve B.
move to A' and B', respectively.

At this time, the natural potential (mixed potential) Em also shifts to Em'. Whether the natural potential Ern shifts to the true direction or to the base direction depends on changes in the anode curve A and cathode curve B.

FIG. 5 shows an example in which an aqueous solution of an aromatic compound having at least one of a water group and a carboxyl group and a 21.0 group in the molecule is used as the electrolyte. In this case, the degraded material anode polarization curve A changes to A', and the cathode polarization plane 1
! JB remains almost unchanged.

Therefore, the natural potential of the non-embrittling material moves in the true direction from Em to Em'.

In this case, the change in the seven-node decentralization curve A is considered to be mainly due to the coarsening of the agglomeration of carbides. This type of electrolyte is sensitive to carbide changes, but grain boundary segregation of impurities cannot be detected.

FIG. 6 is a schematic diagram of a mixed aqueous solution obtained by adding an inorganic salt containing a water R group to the electrolytic solution shown in FIG. 5.

The addition of the inorganic salt reduces the change in the anode polarization plane GA, and instead increases the change in the cathode polarization curve B.

This is due to the effect of phosphorus (P), an impurity element segregated at grain boundaries due to tempering embrittlement of low alloy steel, which reduces the hydrogen overvoltage at grain boundaries and activates the hydrogen reduction reaction. Conceivable. In this case, the natural potential Em changes in the upward direction from Em to Em' due to embrittlement, so the degree of embrittlement of the low alloy steel can be determined by measuring the change in this natural potential Em.

In one embodiment of the present invention, a mixed aqueous solution of an aromatic compound such as 2.4.6-dolinitrophenol and an inorganic salt such as sodium hydroxide was used as the electrolyte. In order to improve wettability between the electrolyte and the electrolyte, alcohols such as ethyl alcohol are added to the electrolyte, and sodium trimethylbenzenesulfone and alkylbenzenesulfonic acid are used as surfactants.
You may also add lium etc.

Further, in one embodiment, an example was shown in which low-alloy steel was used as the material to be measured, but the material to be measured is not necessarily limited to low-alloy steel.

〔Effect of the invention〕

As described above, in the present invention, the self-potential generated by bringing an electrolytic solution made of a mixed aqueous solution of an aromatic compound and an inorganic salt into contact with an object to be measured, such as low-alloy steel, is used to reduce the The degree of embrittlement due to thermal history of alloy steel, etc. can be efficiently determined with high accuracy and sensitivity, and the measurement time can be reduced to about half that of conventional polarization testing methods, improving measurement efficiency. Can be done.

Further, in the present invention, it is only necessary to measure the natural potential, and there is no need to measure the polarization current. There is no need for a counter electrode, an ammeter, etc. in the electrolytic cell, and the measurement device can be certainly simplified.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the embrittlement degree detection device for a measured object according to the present invention, FIG. 2 is a diagram illustrating the time change of the natural potential in the embrittlement degree detection device, and FIG. 3 is the above-mentioned A diagram showing the relationship between the self-potential and the degree of embrittlement ΔFATT in a embrittlement degree detection device, Figure 4 is an Evans diagram schematically representing the decentralization behavior of low alloy steel, and Figure 5 is an electrolytic solution with hydroxyl groups and Evans diagram when an aqueous solution of an aromatic compound having at least one carboxyl group and a nitro group is used, and Figure 6 shows the case when an electrolyte solution prepared by adding an inorganic salt containing water R1) to the aqueous solution in Figure 5 is used. 7 is a diagram showing a conventional embrittlement degree detection device for low alloy steel, and FIG. 8 is a diagram showing a polarization curve for measuring the current density for re-11Il transformation. DESCRIPTION OF SYMBOLS 10... Embrittlement degree detection device, 11... Measured object (low alloy steel), 12... Electrolytic cell, 13... Sealing material, 1
4... Opening, 15... Electrolyte, 16... Inlet, 17... Outlet, 20... Reference electrode, 21...
Elec] - meter (potential detector), 22... recorder. Representative Patent Attorney Nori Chika Ken Kanshu Daiko Maru Ken Figure 1 Figure oo t- Degree of view ΔFATT+'C) Figure 5 flow log + i Figure 5 Current log Figure Figure Figure Figure Figure

Claims (1)

[Claims] 1. A mixed aqueous solution of an aromatic compound and an inorganic salt is used as an electrolyte, and the electrolyte is brought into contact with an object to be measured such as low alloy steel to measure the natural potential. A method for detecting the degree of embrittlement of a measured object, characterized by detecting the degree of embrittlement due to the thermal history of the measured object. 2. An electrolytic cell is liquid-tightly provided on an object to be measured such as low alloy steel, and the electrolytic solution filled in the electrolytic cell is brought into contact with the object to be measured through the opening of the electrolytic cell. A device for detecting the degree of embrittlement of an object to be measured, characterized in that a reference electrode is inserted into an electrolytic solution, and a potential detector is provided for measuring the potential between the reference electrode and the object as a natural potential. .