JP6963745B2 - Laves phase detection method for high Cr steel - Google Patents

Description

The present invention relates to a method for detecting the Laves phase of high Cr steel by an electrochemical polarization method. The present invention specifically relates to a method capable of selective detection of the Laves phase.

Since the parts of the steam turbine used in thermal power generation equipment are used for a long time at high temperature and high stress, the materials used deteriorate over time. In order to stably supply the electric power of the thermal power generation equipment, it is necessary to prevent the steam turbine from being damaged. For that purpose, the degree of deterioration of the steam turbine parts is measured non-destructively and the remaining life of the parts is predicted. Diagnostic technology is important. This makes it possible to repair and replace steam turbine parts at an appropriate timing.

Deterioration of steam turbine parts mainly includes fatigue damage, creep damage, and brittleness, and these material deteriorations are caused by solid solution strengthening by additive elements in the material, and heat-resistant alloy steel with high strength due to fine precipitation and dislocation structure. When used for a long period of time under high temperature and high stress, the solid solution strengthening element precipitates as an intermetallic compound or carbon nitride and coagulates and coarsens, and the dislocation structure is restored, resulting in close contact with material changes. Related to. Due to heating aging, a new Laves phase, which is an intermetallic compound, is precipitated in the material, and the carbonitride is aggregated and coarsened. Especially for embrittlement and creep damage, the coarse Laves phase or the coagulation coarse part of the carbonitride is the starting point of the damage. Therefore, measuring the amount of precipitates such as the Laves phase and the carbonitride predicts the degree of deterioration of the material. It is effective for.

The electrochemical polarization method is known as a method for non-destructively measuring the amount of precipitates of the Laves phase and carbonitrides (for example, Non-Patent Document 1). In the electrochemical polarization method, the solution is brought into contact with the material under test and the potential is swept between the material under test and the electrolytic solution to obtain an anode current polarization waveform, and the amount of the precipitate contained in the material under test is measured. The method. The electrochemical method described in Non-Patent Document 1 uses a 1 mol / L potassium hydroxide aqueous solution having a pH of 14 to obtain a potential sweep rate of 0.5 mV / sec. Sweep the potential with and measure the anode current polarization waveform. In the measured anode current polarization waveform, the anode peak current density Ip observed at -100 to 400 mV (vs. SCE) is observed, and it is said that there is a correlation between this anode peak current density Ip and the Laves phase amount.

In addition, an electrochemical polarization method using an acidic electrolyte is also known (for example, Patent Document 1). In the electrochemical polarization method described in Patent Document 1, only the Raves phase of high chromium steel is obtained by obtaining the maximum value of the anode current density in the anodic polarization curve using an electrolytic solution having a pH value greater than 0 and less than 5. Discloses that the parameters produced by dissolution are obtained. Then, it is disclosed that the toughness can be easily evaluated by this method.

Japanese Unexamined Patent Publication No. 2010-38553

J.Soc.Mat.Sci., Japan, Vol.49, No.8, pp.919-926, Aug.2000

In the method disclosed in Non-Patent Document 1, since the anode peak current density observed at -100 to 400 mV includes not only the Laves phase but also the current value due to the dissolution of the carbonitride, only the Laves phase is selectively detected. It's not done. On the other hand, in the method of Patent Document 1, the Laves phase containing tungsten (W) could not be dissolved, and there was a problem that the undetectable Laves phase remained in the high Cr steel containing W.

In order to accurately predict the brittleness of the material to be measured, it is necessary to selectively detect only the Laves phase, which is a brittle factor, and the material to be measured contains a plurality of precipitates such as the Laves phase and carbon nitride. In this case, a method capable of dissolving the Laves phase and the carbon nitride separately is required.

The present inventors have sought a method for selectively detecting only the Laves phase in the electrochemical polarization method, which is a non-destructive analytical method. Then, they have found that only the Laves phase can be selectively dissolved under predetermined conditions, and have completed the present invention. That is, according to one embodiment, the present invention is a method for detecting a Raves phase of a high Cr steel, in which an electrolytic solution having a pH higher than 14.3 is brought into contact with a material to be measured made of the high Cr steel to be subjected to the above-mentioned anode. A step of obtaining an anodic current polarization waveform by sweeping the potential between the measuring material and the electrolytic solution from the low potential side to the high potential side, and when there are three or more anodic peak currents in the anodic current polarization waveform, 2 It includes a step of detecting the Raves phase based on the next anode peak current.

In the Laves phase detection method for high Cr steel, the sweep rate of the potential is 100 mV / min. The following is preferable.

In the Laves phase detection method for high Cr steel, the step of detecting the Laves phase is an index value of the Laves phase precipitation amount based on the maximum value of the secondary anode peak current density or the integrated value of the secondary anode peak current density. Including getting.

In the Laves phase detection method for the high Cr steel, the Cr content of the high Cr steel is preferably 8 to 14% by weight.

In the Laves phase detection method for high Cr steel, it is preferable that the high Cr steel contains iron (Fe) and molybdenum (Mo).

In the Laves phase detection method for high Cr steel, it is preferable that the high Cr steel contains iron (Fe), tungsten (W), and molybdenum (Mo).

In the Laves phase detection method for high Cr steel, the high Cr steel is a constituent member of the turbine.

According to another embodiment, the present invention is a method for measuring a change over time in the amount of Raves phase precipitated in a high Cr steel. the obtaining a anode current polarization wave by sweeping the potential between the measured material electrolyte from the low potential side to the high potential side, b) based on the anode current polarization wave, three or more anodic peak current In the presence of, the step of obtaining the maximum value of the secondary anode peak current density or the integrated value of the secondary anode peak current density, and c) the same material to be measured, the steps a) and b) over time. This includes a step of obtaining a change over time in the amount of the Raves phase precipitated in the high Cr steel.

According to the method according to the present invention, it is possible to selectively detect the Laves phase, which is an intermetallic compound precipitated with the deterioration of high Cr steel, and to obtain an index value of the Laves phase precipitation amount. .. This makes it possible to non-destructively inspect the degree of deterioration of actual equipment for various parts of the steam turbine.

FIG. 1 is a diagram conceptually showing an example of an electropolarizing cell used in an electrochemical polarization method. FIG. 2 is a diagram conceptually showing an example of an anode current polarization waveform obtained by the method according to the present invention. FIG. 3 is a graph conceptually showing the correlation between the maximum value of the secondary anode peak current density or the integrated value Q of the secondary anode peak current density and the deterioration parameters of temperature and time. FIG. 4 is a diagram showing an anode current polarization waveform obtained in Example 1. FIG. 5 is a photograph of the surface of a high Cr steel sample in the initial state (a) and after heating aging (b) observed by a backscattered electron image of a scanning electron microscope, respectively. In FIG. 6, a potassium hydroxide solution having a pH of 12.9 to 14.2 is used as an electrolytic solution for a material to be measured made of high Cr steel, and is held at a constant potential of 0.2 V before (a) and after (a). b) is a photograph of the surface of the material to be measured observed by a backscattered electron image of a scanning electron microscope. In FIG. 7, for the material to be measured made of high Cr steel, a potassium hydroxide solution having a pH of 14.7 was used as an electrolytic solution, and the sweep test from the corrosion potential to −0.56 V was performed before (a) and after (b). It is a photograph of the surface of the material to be measured observed by the reflected electron image of each scanning electron microscope. FIG. 8 is a diagram showing an anode current polarization waveform obtained in Example 2.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below.

[First Embodiment]
According to the first embodiment, the present invention relates to a method for detecting the Laves phase. The method for detecting the Raves phase is to bring an electrolytic solution having a pH higher than 14.3 into contact with an object to be measured made of high Cr steel, and sweep the potential between the object to be measured and the electrolytic solution from the low potential side to the high potential side. This includes a step of obtaining an anode current polarization waveform and a step of detecting a Raves phase based on the secondary anode peak current when three or more anode peak currents are present in the anode current polarization waveform.

In the embodiment, the high Cr steel as the material to be measured is not particularly limited as long as it is a highly heat-resistant steel member containing Cr, but preferably contains 8 to 14% by weight of Cr, and Fe, W, and others. It may contain Mo and the like. In a certain embodiment, the material to be measured may be a high Cr steel containing 8 to 14% by weight of Cr and also containing Fe and Mo as main components. In another embodiment, the material to be measured may be a high Cr steel containing 8 to 14% by weight of Cr and also containing Fe, W, and Mo as main components. Further, the material to be measured may be a member exposed to high temperature or stress, and examples thereof include, but are not limited to, steam turbines and gas turbines for thermal power plants. Further, the measurement portion of the material to be measured is not particularly limited, and may be a desired portion of a member made of high Cr steel. For example, when a steam turbine is evaluated, it can be a part that is easily exposed to high temperature and high pressure and has a high degree of embrittlement, and is a part that is predicted to have a high degree of embrittlement by simulation calculation or the like. However, it is not limited to these. According to the method of the present invention, the Laves phase can be detected nondestructively at a desired portion of a member made of high Cr steel by using an electric polarization cell described later.

The step of obtaining the anode current polarization waveform is performed using an electrochemical polarization method. FIG. 1 is a diagram conceptually showing an example of an electropolarizing cell used in an electrochemical polarization method. The electric polarization cell 1 is roughly divided into an upper reference electrode portion and a lower electrolyte portion, and is separated by, for example, an acrylic resin partition plate 2. The cell may be made of a resin such as acrylic. The electrolytic solution portion is divided so that each internal component can be easily attached, and the divided portion is adhered by a rubber ring 3 by an adhesive or a screw structure. The opening of the reference electrode portion at the upper part of the cell is sealed with a rubber stopper 4, the reference electrode portion is filled with the saturated potassium chloride solution 5, and the reference electrode 6 is installed at the center portion of the cell so as to penetrate the rubber stopper. The electrolytic solution 7 is injected into the electrolytic solution portion from a glass tube 11 penetrating the rubber stopper and the partition plate made of acrylic resin. The bottom of the cell is formed by a rubber plate 9 having a through hole 8 in the center, and the material 10 to be measured is set on the rubber plate 9 surface opposite to the electrolytic solution portion. As a result, only the surface of the material to be measured 10 exposed in the through hole in the center of the rubber plate comes into contact with the electrolytic solution. The counter electrode 14 is attached so as to penetrate the rubber stopper and the acrylic plate and be immersed in the electrolytic solution, and the conductor wire 13 connected to the material to be measured and the conductor wire 15 connected to the counter electrode are connected to the constant potential generator 16. At the time of measurement, nitrogen gas flows in from the glass tube 12 penetrating the rubber stopper and the partition plate, the nitrogen gas is stopped when the potential becomes constant, the glass tubes 11 and 12 are sealed with the rubber stopper, and the material to be measured and the counter electrode are used. Apply a potential between. When an electric potential is applied, an anode current is generated between the salt bridge 17 arranged in the cell and the material to be measured due to an electrochemical reaction on the surface of the material to be measured. This anode current can be measured by the constant potential generator 16 via the reference electrode 6. The obtained anode current changes depending on the surface properties of the material to be measured and the electrochemical reaction. By recording this anode current using the recording device 18, an anode current polarization waveform can be obtained. By using such an electric polarization cell 1, if the material to be measured has a surface of, for example, ^{about 1 cm 2} , the measurement according to the present embodiment becomes possible. The above-mentioned configuration of the electric polarization cell and its material are examples, and an apparatus composed of an alternative configuration or material that can obtain similar measurement results can also be used.

In the present embodiment, a solution having a pH greater than 14.3 is used as the electrolytic solution to be used by filling the electric polarization cell. The preferable pH of the electrolytic solution is generally larger than 14.3 and about 15.2 or less, and may be, for example, 14.6 or more and about 15.0 or less. As long as the aqueous solution has a pH higher than 14.3, it may be, for example, a potassium hydroxide (KOH) solution or another alkaline solution. When a Laves phase is present on the electrolytic solution contact surface of the material to be measured by using an electrolytic solution having a pH higher than 14.3, a predetermined potential is applied between the material to be measured and the electrolytic solution to obtain a Laves phase. It can be selectively dissolved. The temperature of the electrolytic solution may be about room temperature, and can be, for example, about 20 to 25 ° C.

In the step of obtaining the anodic current polarization waveform, the anodic current polarization waveform is obtained by sweeping the potential between the material to be measured and the electrolytic solution from the low potential side to the high potential side. The applied potential is preferably swept from the corrosion potential of about -1.2 to -1.0 V to about 0.2 to 0.4 V, but the starting potential and the sweep are terminated depending on the composition of the material to be measured. The potential may be changed as appropriate. The potential sweep rate is 100 mV / min. It is preferably the following, and is approximately 5 to 50 mV / min. It is preferably about. This is because the peak corresponding to the dissolution of the Laves phase is sufficiently separated from the peak corresponding to the dissolution of other precipitates.

FIG. 2 is a conceptual diagram of the anode current polarization waveform of the material to be measured, which is obtained by using the above-mentioned device and method. The horizontal axis of FIG. 2 shows the potential, and the vertical axis shows the current density. In the waveform shown in FIG. 2, there are three anode peaks, that is, the primary anode peak Ip1, the secondary anode peak Ip2, and the tertiary anode peak Ip3 in order from the low potential side. The primary anode peak is derived from the anode current due to activation of the metal surface, the secondary anode peak is derived from the anode current due to Raves phase dissolution, and the tertiary anode peak is derived from the anode current due to carbon nitride. In the present specification, each of one or more peaks obtained by one sweep is referred to as "nth-order anode peak (n is an integer)", and when the potential is swept from the low potential side to the high potential side. , The nth peak to appear.

When the Laves phase is present in the material to be measured, three anode peaks mainly appear, and the secondary anode peak Ip2 corresponds to the dissolution of the Laves phase. The secondary anode peak Ip2 is observed at a potential of -0.8 to -0.4 V, for example, depending on the composition of the material to be measured and the measurement conditions. On the other hand, the primary anode peak Ip1 is generally observed at 1-1 to −0.9 V. The primary anode peak Ip1 may be difficult to identify, but when the current density on the vertical axis is displayed in logarithm, the peak appears prominently, and the existence of the peak can be confirmed. The tertiary anode peak Ip3 is observed at a potential of approximately −0.3 to 0.45 V, although it depends on the composition of the material to be measured. Regarding the potential at which the primary anode peak Ip1, the secondary anode peak Ip2, and the tertiary anode peak Ip3 appear, the Laves phase and the presence of carbon nitride have been confirmed in advance by other analytical methods, etc. The measurement material can be confirmed by conducting a preliminary experiment to obtain an anode current polarization waveform under the same conditions of the composition (pH) of the electrolytic solution and the sweep rate.

The amount of Laves phase precipitation _{correlates with the maximum value Ip2 max of} the secondary anode peak current density or the integrated value Q of the secondary anode peak current density. The integrated value Q of the secondary anode peak current density is the area of the portion surrounded by the baseline and the peak (hatched portion in FIG. 2) obtained by drawing the baseline L with respect to the secondary anode peak in the anode current polarization waveform. Can be represented. Therefore, the Ip2 _max value or the Q value can be used as an index value of the Laves phase precipitation amount.

By obtaining a quantifiable index value in this way, for example, for a material to be measured in which the amount of Laves phase precipitation is quantified by another method in advance, the Ip2 _max value or Q value and the amount of Laves phase precipitation are obtained. The Laves phase can be quantified from the measured values of _{Ip2 max} or Q value by obtaining the correlation with. Furthermore, since the amount of Laves phase precipitation has a large correlation with the deterioration of high Cr steel, it is possible to _{obtain a correlation equation between the deterioration parameters of temperature and time and the Ip2 max} value or the Q value. FIG. 3 conceptually shows such a correlation. Examples of the deterioration parameter of temperature and time include, but are not limited to, aging heating time at a predetermined temperature, Larson mirror parameter consisting of temperature and time, and the like.

The waveform shown in FIG. 2 is an example, and the size and shape of a plurality of peaks and their relative sizes may differ depending on the amount of precipitation of the Laves phase or other carbonitrides. Alternatively, a peak exceeding 3 may be confirmed. Although not shown, when an electrolytic solution having a pH of less than 14.3 was used, there was no peak corresponding to the secondary peak in FIG. 2, and the pH was approximately 1.1 to −0.9 V. A peak appears at a potential of approximately -0.3 to 0.3 V. The former is derived from the anodic current due to activation of the metal surface, and the latter is derived from the anodic current due to carbonitride.

According to the method according to the present embodiment, the presence or absence of the Laves phase can be determined based on the waveform (number and position of peaks) by the step of obtaining the anode current polarization waveform under predetermined conditions. Further, based on the anode current polarization waveform, a quantifiable index value such as a maximum value of the secondary anode peak current density or an integrated value of the secondary anode peak current density can be obtained. These index values reflect the amount of precipitates only in the Laves phase, which has been difficult in the past, and are very useful in predicting the deterioration and life of high Cr steel.

[Second Embodiment]
According to the second embodiment, the present invention relates to a method for measuring a change over time in the amount of Laves phase precipitation of high Cr steel. The method of measuring the change over time is
a) A step of bringing an electrolytic solution having a pH higher than 14.3 into contact with the material to be measured and sweeping the potential between the material to be measured and the electrolytic solution from the low potential side to the high potential side to obtain an anode current polarization waveform. When,
Based on b) the anode current polarization wave, and obtaining when three or more anodic peak current is present, the maximum value of the secondary anodic peak current density, or the integrated value of the secondary anodic peak current densities,
c) Includes a step of obtaining a change over time in the amount of Laves phase precipitation of high Cr steel by performing the steps a) and b) for the same material to be measured over time.

In the present embodiment, steps a) and b) may be the same as those described in detail in the first embodiment, and description thereof will be omitted here. In the present embodiment, by carrying out step c), for example, the precipitation state of the Laves phase can be compared, and a change with time can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples do not limit the present invention.

[Example 1. Detection of precipitates]
The Laves phase of high Cr steel was detected by the electrochemical polarization method. In this embodiment, a high Cr steel containing 10% Cr and other main components Fe, W, and Mo used for steam turbine parts, and the precipitation of the Laves phase and carbon nitride was confirmed. The sample used was used as the material to be measured. As a device for obtaining the anode current polarization waveform, a device simpler than that in FIG. 1 was used. Specifically, it was composed of a reference electrode 6 in FIG. 1, an electrolytic solution 7, a small piece of the material to be measured 10, a glass tube 11, a lead wire 15, a constant potential generator 16, a salt bridge 17, a recorder 18, and a thermometer. A simple device was used. It has been confirmed that a similar polarization waveform can be obtained by using a simple device. As the electrolytic solution, a potassium hydroxide solution of 0.086, 0.86, 1.72, 4.25 mol / L (pH 12.9, 13.9, 14.2, 14.6) was used as the electrolytic solution. The temperature was 25 ° C., and the potential was swept from the corrosion potential (around −1.1 V) to the high potential side at a sweep speed of 10 mV / min. The obtained anode current polarization waveform is shown in FIG.

As a preliminary experiment of this example, for a high Cr steel having the same composition as the material to be measured in Example 1, a sample in an initial state in which the Laves phase is not precipitated and a sample after heating at 630 ° C. for 15,000 hours are used. Observed. FIG. 5A is a photograph of the surface of the sample in the initial state, and FIG. 5B is a photograph of the surface of the sample after heating and aging, which are observed by a backscattered electron image of a scanning electron microscope. Comparing FIG. 5 (a) and FIG. 5 (b), in the sample after heating aging, white granules 21 which were not present in the sample in the initial state are observed, and gray granules 22 are also observed. .. Elemental analysis of the white granules 21 revealed that Cr was about 13.9%, Fe was about 60.9%, Mo was 14.6%, and W was about 8.9% (all units were). At%), it was estimated that the white precipitate 21 was in the Laves phase.

Referring to FIG. 4, in the anodic current polarization waveform using a 0.086 to 1.72 mol / L potassium hydroxide solution having a pH of 12.9 to 14.2 as the electrolytic solution, 1-1 to −0.9 V ( Only the primary anode peak current density Ip1 was observed at vs. Ag / AgCl) and the tertiary anode peak current density Ip3 was observed at −0.1 to 0.45 V (vs. Ag / AgCl). FIG. 6A is a photograph of the surface of the material to be measured before applying the potential, which is observed by a reflected electron image of a scanning electron microscope. In FIG. 6B, the electrolytic solution is brought into contact with the material to be measured, held at a constant potential of 0.2 V (vs. Ag / AgCl) for a predetermined time, and then the surface of the contacted electrolytic solution is subjected to a scanning electron microscope. It is a photograph observed by a backscattered electron image. It was confirmed by elemental analysis that the white granules 21 seen in FIG. 6 (a) had substantially the same composition as the white granules in FIG. 5 (b). Therefore, the white granules 21 are presumed to be in the Laves phase. In FIG. 6 (b), the white granules 21 remained, and in FIG. 6 (a), black dissolution marks 23 which were hardly present were observed. From this, the tertiary anode peak current density Ip3 obtained at −0.1 to 0.45 V (vs. Ag / AgCl) when an electrolytic solution having a pH of 12.9 to 14.2 is used is mainly a carbonitride. It is considered to be the peak current density due to the dissolution of.

In the anode current polarization waveform using a 4.25 mol / L potassium hydroxide aqueous solution having a pH of 14.6 as an electrolytic solution, the primary anode peak current density Ip1 was 1-1 to −0.9 V (vs. Ag / AgCl). , A tertiary anode peak current density was observed at -0.3 to 0.3 V (vs. Ag / AgCl), and a secondary anode peak at -0.8 to -0.4 V (vs. Ag / AgCl). The current density Ip2 was observed. FIG. 7A is a photograph of the surface of the material to be measured before the potential sweep, which is observed by a reflected electron image of a scanning electron microscope. In FIG. 7 (b), a 5 mol / L potassium hydroxide solution having a pH of 14.6 was used as the electrolytic solution, and after a sweep test from the corrosion potential to −0.56 V (vs. Ag / AgCl), the electrolytic solution was brought into contact with the electrolytic solution. It is a photograph which observed the surface with the reflected electron image of the scanning electron microscope. It was confirmed by elemental analysis that the white granules 21 seen in FIG. 7 (a) had substantially the same composition as the white granules in FIG. 5 (b). Therefore, the white granules 21 are presumed to be in the Laves phase. In FIG. 7B, the white granules 21 are not observed, and the dissolution marks 23 are observed at the locations where the white particles were present. From this, it is observed at −0.8 to −0.4 V (vs. Ag / AgCl) in the anodic current polarization waveform using a 4.25 mol / L potassium hydroxide solution having a pH of 14.6 as the electrolytic solution. The secondary anode peak current density Ip2 is considered to be the peak current density in which the Raves phase is almost dissolved.

In addition to the above experiment, an anodic current polarization waveform was obtained under the same conditions as above except that potassium hydroxide aqueous solutions having pH 14.3, 14.4, 14.5 and pH 14.7 were used as the electrolytic solution. As a result, under the conditions of pH 14.4, 14.5 and pH 14.7, the secondary anode peak current density was observed in the vicinity of −0.8 to −0.4 V (vs. Ag / AgCl). On the other hand, no secondary anode peak was observed at pH 14.3 (waveform not shown). In particular, at pH 14.7, a waveform having a secondary anode peak having a magnitude similar to that obtained under the condition of pH 14.6 in FIG. 4 was obtained. In the measured pH range of 14.4 to 14.7, both the maximum value of the secondary anode peak current density and the integrated value of the secondary anode peak current density tended to increase as the pH increased.

[Example 2. Detection of changes in precipitates over time in artificially deteriorated materials]
Precipitates were detected in the artificially deteriorated material produced by heating aging according to the second embodiment of the present invention. As the artificial deterioration material, high Cr steel having the same composition as that of Example 1 is heated at a temperature of 630 ° C. for 1400 hours, 2800 hours, 5600 hours, 10000 hours, 15000 hours, and 20000 hours, respectively. A heat-aged sample under a total of 6 conditions and an initial material having a heat-age treatment time of 0 hours were used. The heat aging treatment temperature is, for example, 610 ° C. to 650 ° C. In FIG. 8, the sample represented by “As sintered” is a sample obtained by subjecting the material (initial material) to the re-quenching treatment as it is received. The quenching treatment temperature is a temperature higher than the heating aging treatment temperature. As an apparatus for obtaining the anode current polarization waveform, the same apparatus as in Example 1 was used. Potassium hydroxide having a pH of 14.6 was used as the electrolytic solution. The potential was changed from the initial state (around -1.2 to -1.0 V) to 0.4 V at 10 mV / min. The electric polarization waveform was swept at a constant speed, and the obtained electric polarization waveform was output to a recorder. The results are shown in FIG. The secondary anode peak current increased as the heating aging time increased. On the other hand, the initial material (0h) and the sample represented by "As quenched" did not have a secondary anode peak. When the correlation between the secondary anode peak current value of each artificially deteriorated material obtained in FIG. 8 and the deterioration parameters of temperature and time is roughly shown, a curve substantially the same as the curve in FIG. 3 was obtained. By obtaining such correlations for multiple parameters in advance, it is possible to quantify changes in the amount of intermetallic compounds due to deterioration, and it is possible to inspect the degree of deterioration of actual equipment in a non-destructive manner. It is considered to be.

The method for detecting precipitates by the method of the present invention evaluates the degree of deterioration of a member made of high Cr steel used as a member of a machine used at a high temperature, for example, a steam turbine component for a thermal power plant, for example, embrittlement. It can be useful in evaluation of embrittlement and calculation of remaining life.

Claims (8)

Anode current polarization waveform by bringing an electrolytic solution having a pH higher than 14.3 into contact with a material under test made of high Cr steel and sweeping the potential between the material under test and the electrolytic solution from the low potential side to the high potential side. And the process of obtaining
A method for detecting a Laves phase of high Cr steel, which comprises a step of detecting a Laves phase based on a secondary anode peak current when three or more anode peak currents are present in the anode current polarization waveform. The sweep rate of the potential is 100 mV / min. The method according to claim 1, which is as follows. The step of detecting the Laves phase includes obtaining an index value of the Laves phase precipitation amount based on the maximum value of the secondary anode peak current density or the integrated value of the secondary anode peak current density, according to claim 1 or 2. The method described in. The method according to any one of claims 1 to 3, wherein the high Cr steel has a Cr content of 8 to 14% by weight. The method according to any one of claims 1 to 4, wherein the high Cr steel contains Fe and Mo. The method according to any one of claims 1 to 4, wherein the high Cr steel contains Fe, W, and Mo. The method according to any one of claims 1 to 6, wherein the high Cr steel is a constituent member of the turbine. This is a method for measuring the change over time in the amount of Laves phase precipitation of high Cr steel.
a) A step of bringing an electrolytic solution having a higher pH of 14.3 into contact with the material to be measured and sweeping the potential between the material to be measured and the electrolytic solution from the low potential side to the high potential side to obtain an anode current polarization waveform. ,
Based on b) the anode current polarization wave, and obtaining when three or more anodic peak current is present, the maximum value of the secondary anodic peak current density, or the integrated value of the secondary anodic peak current densities,
c) A method including a step of obtaining a change over time in the amount of Laves phase precipitation of high Cr steel by performing the above steps a) and b) on the same material to be measured over time.

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