阅读说明：本技术 一种检测钢中Laves相含量的方法 (Method for detecting Laves phase content in steel ) 是由 郭琦 袁随 梁峰瑞 徐健 任潞 于 2021-07-20 设计创作，主要内容包括：本发明属于电化学检测技术领域,公开了一种检测钢中Laves相含量的方法。该方法中使用的检测溶液中的氢氧根浓度大于6mol/L,且采用的动电位极化扫描的扫描速率为8-10.5mV/min。检测所用检测溶液的氢氧根浓度大于6mol/L,使得待测样品中仅有Laves相发生溶解而其他物质不受影响,采用的动电位极化扫描的扫描速率为8-10.5mV/min,从而使得本发明所述的电化学检测方法检测的准确度高。与现有技术中的微观组织分析法的相对误差不超过6％。本发明的方法是一种电化学方法,操作简单,快速有效,可实现Laves相现场检测。(The invention belongs to the technical field of electrochemical detection, and discloses a method for detecting the content of Laves phases in steel. The concentration of hydroxyl in the detection solution used in the method is more than 6mol/L, and the scanning rate of the potentiodynamic polarization scanning is 8-10.5 mV/min. The hydroxide concentration of the detection solution used for detection is more than 6mol/L, so that only the Laves phase in the sample to be detected is dissolved, and other substances are not influenced, and the scanning rate of the zeta potential polarization scanning is 8-10.5mV/min, so that the electrochemical detection method disclosed by the invention is high in detection accuracy. The relative error with the prior art microstructure analysis method is not more than 6%. The method is an electrochemical method, is simple to operate, is quick and effective, and can realize Laves phase field detection.)

1. A method for detecting the Laves phase content in steel is characterized in that the hydroxide concentration of a detection solution used in the method is more than 6mol/L, and the scanning rate of potentiodynamic polarization scanning is 8-10.5 mV/min.

2. The method of claim 1, comprising the steps of:

(1) preparation of a working electrode: taking steel as a sample to be detected, and preparing the sample to be detected, resin, a curing agent and a lead into a working electrode;

(2) forming an electrochemical testing device by using the working electrode, the counter electrode, the reference electrode, an electrolytic cell, a salt bridge and an electrochemical working station prepared in the step (1), wherein the electrolytic cell contains a detection solution, the concentration of hydroxyl in the detection solution is more than 6mol/L, carrying out one-time potentiodynamic polarization scanning on a sample to be tested, the scanning speed is 8-10.5mV/min, and the scanning potential interval is from open circuit potential to-400 mV Ag/AgCl to obtain a polarization curve of current density to electrode potential;

(3) making a current density-time curve: and (3) corresponding a current peak at-900 to-500 mV Ag/AgCl on the polarization curve of the current density to the electrode potential obtained in the step (2) to a Laves phase solution peak, integrating the current density to the polarization time, and deducting the passivation current background of the substrate by using data processing software to obtain the dissolved charge amount of the Laves phase, thereby calculating and obtaining the Laves phase content in the sample to be detected.

3. The method according to claim 2, wherein in step (1), the sample to be tested has a size of (0.5-1) cm x (0.1-0.5) cm.

4. The method according to claim 2, wherein the specific process of step (1) is as follows: taking steel as a sample to be detected, welding the sample to be detected on a lead, putting the welded sample to be detected into a cold-inlaid die, and then adding resin and a curing agent according to the proportion of (1-2): 1 to obtain a mixture, stirring the mixture until the mixture is in a transparent state, pouring the mixture into a cold-inlaid die, covering the welding point of a sample to be tested and a lead with the mixture, standing for 1-2 hours, and curing resin to obtain the working electrode.

5. The method according to claim 2, wherein in the step (1), the steel is a martensitic heat-resistant steel or a heat-resistant steel having a Cr content of 8 to 15% by mass.

6. The method of claim 1 or 2, wherein the detection solution is selected from a NaOH solution or a KOH solution.

7. The method according to claim 2, wherein in the step (2), the detection solution is subjected to oxygen removal treatment with an inert gas.

8. The method according to claim 2, wherein in step (2), the scanning speed is 9.5-10 mV/min.

9. Use of the method of any one of claims 1-8 for detecting device security.

10. Use according to claim 9, wherein the device is a metal support, a metal pipe or a chemical metal container.

Technical Field

The invention belongs to the technical field of electrochemical detection, and particularly relates to a method for detecting the content of Laves phases in steel.

Background

The power generation technology adopting the ultra-supercritical unit has the remarkable effects of saving energy and improving the environment, wherein the martensite heat-resistant steel is one of the best candidate materials for the thick-wall part of the ultra-supercritical unit due to excellent structure stability and good high-temperature strength. Creep is one of the main reasons for the failure of structural materials in service in high-temperature environment, and the martensite heat-resistant steel is usually added with Mo and W elements to improve the creep life of the materials, but the existence of the Mo and the W elements can promote the materials to separate out a Laves phase in the high-temperature service process. The precipitation of Laves phase (Laves phase is a close-packed cubic or hexagonal structure intermetallic compound with a chemical formula mainly AB2 type) affects the strength and fracture sensitivity of the material, thereby reducing the service life of the material. Therefore, the detection of the Laves phase content of the martensite heat-resistant steel in the high-temperature service process is beneficial to the prediction of the service life of the material, and has important significance for reasonably arranging the running time of pipelines and ensuring the long-term safe running of industrial equipment.

Common Laves phase content detection methods include an electrolytic extraction method, a microstructure analysis method and the like, but the existing detection methods have the defects of long evaluation time, complicated experimental device and unsuitability for field detection of industrial materials. Therefore, a rapid method suitable for detecting the Laves phase content on site needs to be developed.

Disclosure of Invention

The present invention is directed to solving at least one of the problems of the prior art described above. Therefore, the method for detecting the content of the Laves phase in the steel is an electrochemical method, is simple to operate, is quick and effective, and can realize the field detection of the Laves phase.

The invention conception of the invention is as follows: according to Faraday's law, the electric quantity corresponding to the dissolution current in the electrochemical test has a one-to-one correspondence relationship with the dissolved Laves phase content, so that the Laves phase content in the sample can be obtained through an electrochemical curve. According to the invention, through specific electrochemical detection conditions, the hydroxide concentration of the detection solution is more than 6mol/L, so that only the Laves phase is dissolved, and other substances are not influenced, and the scanning rate of the zeta potential polarization scanning is 8-10.5mV/min, so that the electrochemical detection method has high detection accuracy.

The first aspect of the invention provides a method for detecting the content of Laves phases in steel.

Specifically, the method for detecting the Laves phase content in the steel uses a detection solution with a hydroxyl concentration of more than 6mol/L and a zeta potential polarization scanning scan rate of 8-10.5 mV/min.

Preferably, the method for detecting the content of the Laves phase in the steel comprises the following steps:

(1) preparation of a working electrode: taking steel as a sample to be detected, and preparing the sample to be detected, resin, a curing agent and a lead into a working electrode;

(2) forming an electrochemical testing device by using the working electrode, the counter electrode, the reference electrode, an electrolytic cell, a salt bridge and an electrochemical working station prepared in the step (1), wherein the electrolytic cell contains a detection solution, the concentration of hydroxyl in the detection solution is more than 6mol/L, carrying out one-time potentiodynamic polarization scanning on a sample to be tested, the scanning speed is 8-10.5mV/min, and the scanning potential interval is from open circuit potential to-400 mV Ag/AgCl to obtain a polarization curve of current density to electrode potential;

(3) making a current density-time curve: and (3) corresponding a current peak at-900 to-500 mV Ag/AgCl on the polarization curve of the current density to the electrode potential obtained in the step (2) to a Laves phase solution peak, integrating the current density to the polarization time, and deducting the passivation current background of the substrate by using data processing software to obtain the dissolved charge amount of the Laves phase, thereby calculating and obtaining the Laves phase content in the sample to be detected.

Preferably, the specific process of step (1) is as follows: firstly, taking steel as a sample to be detected, wherein the size of the sample to be detected is (0.5-1) cm multiplied by (0.1-0.5) cm (length multiplied by width multiplied by height), welding the sample to be detected on a copper wire, and measuring the resistance after welding by using an universal meter to ensure that the copper wire is conducted with the sample to be detected; placing a welded sample to be tested into a cold-insert die (the cold-insert die can be provided by Kao-Mitsu instrument metallographical test instrument Co., Ltd., product model is phi 25), bending a copper wire to ensure that the surface to be tested of the sample to be tested is attached to the bottom of the die and can be kept stable, and placing a resin (such as epoxy resin) and a curing agent (such as an epoxy resin curing agent, wherein the epoxy resin and the epoxy resin curing agent are conventional technologies and commercially available) according to the proportion of (1-2): 1 to obtain a mixture, slowly stirring the mixture to avoid generating bubbles until the mixture is in a transparent state, and quickly pouring the mixture into a cold-inlaid die to enable the mixture to cover a welding point of a sample to be detected and a copper wire; standing for 1-2 hours until the resin is completely cured (the resin can be cured at normal temperature), and preparing the working electrode.

Preferably, the surface to be tested of the sample to be tested in the working electrode is polished, washed and dried step by step, and then the surface to be tested can be directly used for testing.

Preferably, in the step (1), the steel is martensite heat-resistant steel or heat-resistant steel with 8-15% of Cr by mass; further preferably, the heat-resistant steel has a Cr content of 9 to 12% by mass.

Preferably, in step (2), the detection solution is selected from a NaOH solution or a KOH solution.

Preferably, in the step (2), the detection solution is subjected to oxygen removal treatment with an inert gas.

Preferably, in step (2), the scanning speed is 9.5-10 mV/min.

In the step (3), the current background is deducted when the integral area is obtained, so that the interference of the matrix passivation current is reduced. The accuracy of detection is further improved.

The second aspect of the invention provides an application of the method for detecting the Laves phase content in the steel.

The method for detecting the Laves phase content in the steel is applied to detecting equipment safety.

Preferably, the device can be various metal supports, metal pipelines or chemical metal containers.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the electrochemical detection method, through specific electrochemical detection conditions, specifically, the hydroxide concentration of a detection solution used for detection is more than 6mol/L, only a Laves phase in a sample to be detected is dissolved, other substances are not affected, and the scanning rate of the zeta potential polarization scanning is 8-10.5mV/min, so that the electrochemical detection method has high detection accuracy. The relative error with the prior art microstructure analysis method is not more than 6%.

(2) The experimental device is portable and simple and convenient to operate, and can be used for on-site on-line detection.

(3) The invention has short experimental test time and simple data processing, and can realize high-efficiency and quick test and result analysis of the sample to be tested.

(4) The method adopts an electrochemical method to detect the Laves phase content in the steel, and has small damage to a sample to be detected.

(5) According to the invention, the background current is deducted in the calculation, the interference of the passivation current of the matrix is reduced, and the reliability of the test result is ensured.

Drawings

FIG. 1 is an SEM (scanning Electron microscope) image of a tempered P92 heat-resistant steel;

FIG. 2 is an SEM image of P92 heat resistant steel that has not been subjected to tempering treatment;

FIG. 3 is a schematic view of an electrochemical test apparatus used in example 1;

FIG. 4 is a polarization plot of current density versus electrode potential measured in example 1;

FIG. 5 is a polarization plot of current density versus electrode potential for P92 heat resistant steel without the Laves phase;

FIG. 6 is a graph of current density versus time as measured in example 1;

FIG. 7 is a schematic of peak area integral minus background current;

FIG. 8 is a graph of the correlation between electrochemical methods and microstructural analysis;

FIG. 9 is a statistical plot of the particle size of the Laves phase by microstructural analysis.

Detailed Description

In order to make the technical solutions of the present invention more apparent to those skilled in the art, the following examples are given for illustration. It should be noted that the following examples are not intended to limit the scope of the claimed invention.

The starting materials, reagents or apparatuses used in the following examples are conventionally commercially available or can be obtained by conventionally known methods, unless otherwise specified.

The electrochemical workstation used below is available from Gamry electrochemical instruments, Inc. of U.S. under the product designation Interface 1010E.

Example 1

The supplier of the P92 heat-resistant steel is Bao Steel products Co., Ltd, and the composition of the P92 heat-resistant steel is shown in Table 1.

Table 1: p92 Heat-resistant steel component (unit: mass%)

FIG. 1 is an SEM image of a tempered P92 heat-resistant steel (sample to be tested); fig. 2 is an SEM image of P92 heat resistant steel that has not been subjected to tempering treatment. As can be seen from fig. 1-2, the SEM image (or referred to as microstructure morphology image) of the P92 heat-resistant steel after being tempered at 650 ℃ for 2500 hours is different from the microstructure morphology image of the P92 heat-resistant steel without being tempered, the P92 heat-resistant steel with being tempered contains Laves phase, and the P92 heat-resistant steel without being tempered does not contain Laves phase.

A method for detecting the content of Laves phases in steel comprises the following steps:

(1) preparation of a working electrode: firstly, taking P92 heat-resistant steel subjected to tempering treatment as a sample to be detected, polishing the sample to be detected by using 2000-mesh sand paper, wherein the size of the sample to be detected is 1cm multiplied by 0.5cm (length multiplied by width multiplied by height), welding the sample to be detected on a copper wire, and measuring the resistance after welding by using an multimeter to ensure that the copper wire is conducted with the sample to be detected; put the good await measuring sample of welding cold inlay mould (cold inlay mould can be provided by guangzhou yu appearance metallographic test instrument limited company, and the product model is phi 25), the copper line of buckling guarantees that the await measuring face of await measuring sample and the laminating of mould bottom and can keep steady, presses 2 with resin and curing agent: 1 to obtain a mixture, slowly stirring the mixture to avoid generating bubbles until the mixture is in a transparent state, and quickly pouring the mixture into a cold-inlaid die to enable the mixture to cover a welding point of a sample to be detected and a copper wire; standing for 2 hours, and preparing a working electrode after the resin is completely cured (the resin can be cured at normal temperature);

(2) forming an electrochemical testing device (shown in figure 3) by using the working electrode, the counter electrode (Pt electrode), the reference electrode (Ag/AgCl reference electrode), the electrolytic cell, the salt bridge, the lead, the air inlet pipe, the air outlet pipe and the electrochemical workstation which are prepared in the step (1), wherein the working electrode, the counter electrode and the reference electrode are immersed in NaOH solution (the NaOH solution is connected to the electrochemical workstation through the lead on the liquid level), the concentration of hydroxyl in the NaOH solution is 7mol/L, one-time potentiodynamic polarization scanning is carried out on a sample to be tested, the scanning speed is 10mV/min, the scanning potential interval is open circuit potential to 400mV Ag/AgCl, and a polarization curve of current density to electrode potential is obtained, and is shown in figure 4; the current peaks at-900 to-500 mV Ag/AgCl on the polarization curve in FIG. 4 correspond to the Laves phase dissolution peaks; in order to show that the matrix does not dissolve under the polarization condition, namely, no dissolution peak appears on the polarization curve, the polarization curve of P92 heat-resistant steel without Laves phase is shown in FIG. 5, and no dissolution peak of Laves phase appears on the polarization curve from-900 mV to-500 mV Ag/AgCl in FIG. 5;

(3) making a current density-time curve: integrating the current density in the polarization curve (shown in figure 4) of the current density to the electrode potential obtained in the step (2) with respect to the polarization time to obtain a current density-time curve (shown in figure 6), wherein the peak integration area on the curve corresponding to about 1590s to 3480s in figure 7 represents the content of the Laves phase in the P92 heat-resistant steel, integrating the peak area on the curve (firstly subtracting the background current by using data processing software (Origin), the background is divided into two parts, the background at the start of the peak is the current density of the passivation area, and the background at the tail of the peak is the current density of the current reduced to the platform area), and calculating the dissolved charge amount of the Laves phase so as to calculate the Laves phase content in the sample to be measured.

FIG. 3 is a schematic view of an electrochemical test apparatus used in example 1; in fig. 3, "1" represents a working electrode, "2" represents a reference electrode, "3" represents a counter electrode, "4" represents a salt bridge, "5" represents an electrolytic cell, "6" represents a KOH solution, "7" represents a lead, 8 "represents an electrochemical workstation," 9 "represents an air inlet pipe, and" 10 "represents an air outlet pipe.

FIG. 4 is a polarization plot of current density versus electrode potential measured in example 1. The abscissa "Current density" in FIG. 4 represents the Current density and the ordinate "Potential" represents the electrode Potential relative to Ag/AgCl.

Fig. 5 is a polarization plot of current density versus electrode potential for P92 heat resistant steel without Laves phase. As can be seen from FIGS. 4 and 5, the current peaks at-900 to-500 mV Ag/AgCl on the polarization curve correspond to the Laves phase dissolution peaks.

FIG. 6 is a graph of current density versus time measured in example 1. In fig. 6, the ordinate "Current density" represents the Current density, and the abscissa "Time" represents the Time.

FIG. 7 is a graph of peak area integration minus background current. In fig. 7, the ordinate "Current density" represents the Current density, and the abscissa "Time" represents the Time.

The Laves phase content in the sample to be detected is calculated by the following formula (1):

m ═ M × q × S)/(F × z) formula (1);

in the formula (1), m represents the content of the Laves phase and is expressed in g;

m represents the molar mass of the Laves phase and is expressed in g/mol;

q represents the dissolved electric quantity of the Laves phase per unit area, and the unit is C/cm²；

S represents the area of the sample to be measured in cm²；

z represents the number of electrons transferred by dissolution of 1mol of the Laves phase;

f represents a Faraday constant, and 96500C/mol is taken;

and (3) carrying out analytical characterization (the characterization method is a conventional technology, and specifically, carrying out energy spectrum point analysis by using an SEM-EDS scanning electron microscope to obtain the main components of the dissolved Laves phase), wherein the main components of the dissolved Laves phase are shown in Table 2.

TABLE 2

	Fe	Cr	W	Mo
					Mole fraction	0.544	0.116	0.302	0.030

Thus, M is 94.90 g/mol; in this example 1, the amount of dissolved charge in the Laves phase in the sample to be measured was 6.4X 10-3C/cm as measured by electrochemical method²(ii) a The number of electrons dissolved and transferred in 1mol of Laves phase is obtained by calculation, and z is 4; in this example 1, the area of the sample to be measured was 0.231cm²Finally, the Laves phase content on the surface of the sample to be detected is calculated to be 3.62 multiplied by 10^{- 7}g。

In order to illustrate the accuracy of the detection method, the content of Laves phase on the surface of the sample to be detected (tempered P92 heat-resistant steel) in example 1 was theoretically calculated by using a microstructure analysis method commonly used in the prior art.

20 SEM pictures are taken in a visual field range of 56 microns multiplied by 40 microns and used for counting the quantity and the grain size of carbides on the surface of a sample to be measured, and the SEM pictures can be seen in figure 1. The formula for calculating the Laves phase content by the microstructure analysis method can be seen in formula (2).

m ═ n × ρ × V/k formula (2);

in the formula (2), m represents the content of the Laves phase and is expressed in g;

n is the number of Laves phases on the SEM picture, and the number is 224 counted by software image J.

ρ represents the density of the Laves phase in g/cm²Since the density of the Laves phase could not be measured in this example, ρ was estimated to be 14.58g/cm based on the composition³；

V is the volume of individual Laves phase particles in cm³Since the Laves phase is irregular in shape, its volume needs to be calculated by the correction of equation (3):

F_v＝(nπD²) 6 formula (3);

in the formula (3), F_vRepresents the volume fraction of Laves phases;

d represents the average particle diameter of the Laves phase.

The average equivalent circular diameter of the Laves phase is calculated by equation (4):

D＝2(Aπ)^1/2formula (4);

in the formula (4), A represents the area of the Laves phase particles.

The average particle diameter can be calculated by image J software to obtain A of 8.98 × 10^-5cm²So D is 3.36X 10^-5cm, the volume of the Laves phase was finally determined to be 1.02X 10^-12cm³；

k is the area fraction of the sample to be measured in the SEM analysis, and is 0.0097 in the present embodiment.

Finally, calculating by a microstructure analysis method that the surface Laves phase mass of the sample to be detected is 3.44 multiplied by 10^-7g。

The electrochemical method adopted by the invention and the microstructure analysis method have the relative error (3.62 multiplied by 10) of the test result of the same sample to be tested^-7g-3.44×10^-7g)/3.44×10^-7It is found that the electrochemical method of the present invention has high reliability because g × 100% is 5.23%.

Example 2

To further illustrate the accuracy of the electrochemical method of the present invention, the microstructure analysis data of P92 heat resistant steel treated at different tempering times were compared with the electrochemical data, as shown in fig. 8. The abscissa is electrochemical data, the abscissa "Charge density" represents the Charge density, the Charge density represents the volume of the Laves phase in a unit Area of the sample to be measured, the ordinate is microstructure analysis data, the "Area fraction" represents the Area fraction, and the Area fraction represents the Area of the Laves phase in a unit Area of the sample to be measured. It can be seen that the slope of the curve becomes progressively smaller, this trend being related to the particle size of the Laves phase. The Laves phase is generally considered to be spherical, the ratio of the area to the volume of the Laves phase (i.e. the slope in fig. 8, fig. 8 is a correlation graph of the electrochemical method and the microstructure analysis method) is inversely proportional to the particle size, and the slope is gradually decreased, i.e. the particle size is continuously increased, as shown in fig. 8, which is consistent with the Laves phase particle size data obtained by the microstructure analysis method (as shown in fig. 9, fig. 9 is a Laves phase particle size statistical graph of the microstructure analysis method, the abscissa "aging time" in fig. 9 represents the aging time, the unit "hrs" represents the hour, the aging time can also be referred to as the tempering time, and the ordinate "diameter of the Laves phase" represents the Laves phase particle size).

In addition, in the technical scheme of the invention, for example, the hydroxide radical concentration in the detection solution is changed to be more than 6mol/L, the scanning rate of the potentiodynamic polarization scanning is 8-10.5mV/min, and the relative error of the detection result with the prior microstructure analysis method is not more than 6%. However, if the hydroxide concentration in the detection solution is less than or equal to 6mol/L, partial dissolution of the Laves phase may result, resulting in a relative error of more than 6% from the detection result of the prior art microstructure analysis method. If the scanning speed of the potentiodynamic polarization scanning is more than or less than 8-10.5mV/min, the relative error of the detection result of the microstructure analysis method in the prior art is more than 6.5 percent.