Preparation method of HR3C precipitation phase after service

Abstract

The present invention discloses a method for preparing a precipitated phase of HR3C after service, comprising the following steps: preparing a corrosive solution, immersing a sample to be tested and a counter electrode in the corrosive solution, the sample to be tested and the counter electrode are respectively connected to the positive electrode and the negative electrode of a power supply for electrolysis, and when the remaining amount of the sample to be tested is less than 50%, filtering the corrosive solution with electrolytic residue, and the obtained solid is the precipitated phase; the sample to be tested is HR3C after service. The benefit of the present invention is that the method for preparing the precipitated phase of HR3C after service solves the problem that the traditional method requires more highly corrosive liquids, and can quickly obtain a large amount of precipitated phases in HR3C after service under room temperature conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of sample preparation, and in particular relates to a method for preparing a precipitated phase of austenitic heat-resistant steel HR3C after service aging. Background Art

[0002] Thermal power generation will remain the main source of electricity in my country for some time to come. In order to further rationally utilize fossil fuels such as coal and improve the power generation efficiency of units while reducing greenhouse gas emissions, more and more ultra-supercritical units have been developed in my country. HR3C austenitic heat-resistant steel has the advantages of good organizational stability, oxidation resistance and high corrosion resistance under high temperature conditions, and is widely used in key parts such as high-temperature reheaters and superheaters of ultra-supercritical thermal power units.

[0003] Austenitic heat-resistant steel HR3C is different from martensitic heat-resistant steel, which has a large number of lath and other dislocation structures. Under high temperature conditions, the strengthening mechanism of austenitic heat-resistant steel HR3C is generally dominated by solid solution strengthening and precipitation phase strengthening. The main strengthening method in HR3C heat-resistant steel is precipitation phase strengthening. Under the condition of high-temperature service of HR3C, due to the addition of a large number of alloy elements in HR3C, second phases of various sizes and morphologies will precipitate inside the material during service, especially nano-scale precipitation phases. These fine and dispersed second phase particles generate stress fields around them, hindering dislocation movement, thereby improving the strength of the material. Precipitation phase strengthening is very common in steel materials and is also one of the main strengthening methods in austenitic heat-resistant steel. Therefore, the study of precipitation phases plays a key role in the study of the high-temperature performance of austenitic heat-resistant steel HR3C.

[0004] HR3C heat-resistant steel is a heat-resistant steel containing 25% Cr and 20% Ni by mass. Due to the high content of Cr and Ni, the material is difficult to corrode in conventional solutions. In the prior art, the precipitate extraction method for austenitic heat-resistant steel HR3C generally adopts the method of preparing a corrosion solution with concentrated HCl (Zhang Caili, Taiyuan University of Technology, a method for rapid extraction of austenitic stainless steel composite precipitate phase at room temperature), but it has disadvantages such as being unfriendly to the environment; or the process is complicated, requiring the operator to operate delicately and formulate a directional method to obtain a specific precipitate (Cai Linling, Shanghai University, a sample preparation method for studying the Cu precipitate phase of steel using extraction replica). Summary of the invention

[0005] In view of this, in order to overcome the defects of the prior art and achieve the above-mentioned purpose, the purpose of the present invention is to provide an improved method for preparing a HR3C precipitate phase after service, which can quickly prepare the precipitate phase at room temperature and the process is pollution-free.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a HR3C precipitate phase after service, comprising the following steps:

[0008] Prepare a corrosive solution, immerse the sample to be tested and the counter electrode in the corrosive solution, connect the sample to be tested and the counter electrode to the positive electrode and the negative electrode of the power supply respectively for electrolysis, and when the remaining amount of the sample to be tested is less than 50%, filter the corrosive solution with electrolysis residue, and the obtained solid is the precipitated phase; the sample to be tested is HR3C after service;

[0009] The etching solution includes the following components: methanol, zinc chloride, concentrated hydrochloric acid and citric acid, and the volume ratio of each substance is: methanol: zinc chloride: concentrated hydrochloric acid: citric acid = 40-45: 4-6: 3-5: 1. In some embodiments of the present invention, the preferred volume ratio is: methanol: zinc chloride: concentrated hydrochloric acid: citric acid = 125: 15: 12: 3. Methanol is used as a dissolving liquid, which can make the electrolyte solutes such as concentrated hydrochloric acid and citric acid mix evenly, and zinc chloride is an accelerator in the electrolysis process, which can accelerate the speed of electrolytic dissolution of stainless steel. Concentrated hydrochloric acid is a key solvent for corroding stainless steel. The application of zinc ions, especially the addition of an appropriate amount of concentrated hydrochloric acid, can avoid the electrolysis rate of zinc chloride being greatly reduced due to the formation of colloids during the electrolysis process. The role of citric acid prevents metal deposition on the electrode during the electrolysis process, which leads to other reactions.

[0010] According to some preferred implementation aspects of the present invention, the preparation method of the corrosive liquid is as follows:

[0011] Under stirring, zinc chloride aqueous solution, concentrated hydrochloric acid and citric acid are added to methanol, and mixed evenly to obtain the etching solution, wherein the mass concentration of citric acid is 3%.

[0012] In some embodiments of the present invention, the method for preparing the corrosive liquid specifically comprises the following steps:

[0013] Add 100g ZnCl2 to 100ml deionized water to prepare ZnCl2 aqueous solution, stir evenly for standby use, and prepare 3% citric acid for standby use; take another beaker with a capacity of 500mL, add 250mL methanol to the beaker, and add a magnetic stirring rotor to the beaker, place the beaker on a stirring table and rotate at 2-3 gear speed (speed is about 5r / s), add 30mL ZnCl2 solution, 24mL concentrated HCL and 6mL citric acid, stir evenly to obtain a corrosion solution, and place the prepared corrosion solution in a fume hood for standby use. There is no restriction on the order of adding zinc chloride aqueous solution, concentrated hydrochloric acid and citric acid.

[0014] According to some preferred implementation aspects of the present invention, the counter electrode is made of copper, and the size of the counter electrode is the same as the size of the sample to be tested.

[0015] According to some preferred implementation aspects of the present invention, during the electrolysis, the electrolysis temperature is 20±5°C, the electrolysis current is ≤1A, the stirring speed of the corrosive solution is 0.5-1r / s, and the electrolysis time is 2-3h. The above-mentioned electrolyte formula and corresponding method enable the electrolysis to be carried out at room temperature. Compared with high temperature or low temperature conditions, the present invention can solve the requirements for ambient temperature during the electrolysis process on the one hand, and can reduce the toxicity of the electrolyte on the other hand, which is beneficial to the subsequent waste liquid recovery process.

[0016] According to some preferred implementation aspects of the present invention, the remaining sample to be tested is rinsed with a 10 g / L citric acid ethanol solution, and the rinse solution with the precipitate and the corrosion solution with the electrolytic residue are filtered together.

[0017] After most of the sample rod immersed in the methanol solution is dissolved, the undissolved anode sample rod and attached precipitation are brushed into a beaker with a 10g / L citric acid ethanol solution and a brush, and the electrolytic residue in the beaker and the residue in the anode test solution are filtered out with a microporous filter membrane with a pore size range of 0.2-0.3μm. The citric acid ethanol solution has low toxicity and good solubility, which can dissolve the excess sample residue.

[0018] According to some preferred embodiments of the present invention, the filtered solid is washed and dried.

[0019] According to some preferred implementation aspects of the present invention, the cleaning is performed using 10 g / L citric acid ethanol solution, 10 g / L citric acid solution, 10 g / L sodium hydroxide solution and distilled water in sequence.

[0020] According to some preferred embodiments of the present invention, the filtration is performed using a microporous filter membrane with a pore size ranging from 0.2 to 0.3 μm.

[0021] According to some preferred implementation aspects of the present invention, the preparation of the sample to be tested includes grinding and ultrasonic cleaning steps, and the grinding is: cross-grinding and polishing with 400 mesh, 800 mesh and 1200 mesh sandpaper in sequence to completely remove the uneven relief on the surface of the HR3C material after service, and finally fine grinding with 2000 mesh sandpaper until the scratches introduced by the 1200 mesh sandpaper completely disappear.

[0022] According to some preferred implementation aspects of the present invention, the ultrasonic cleaning is: placing the polished sample into a container containing ethanol, with the ethanol liquid level exceeding the top of the sample by more than 1 cm; sealing the container and placing it in an ultrasonic cleaning instrument for cleaning, and the cleaning time is 30-60 minutes.

[0023] In some embodiments of the present invention, preparing the HR3C heat-resistant steel material after service into the sample to be tested preferably includes a cutting step before fine grinding: the HR3C heat-resistant steel material after service is cut into a flat sample with a shape of 10mm*3mm*60mm by using an electric spark wire cutting process, which is the size of the sample to be tested.

[0024] Due to the adoption of the above technical scheme, compared with the prior art, the advantages of the present invention are: the preparation method of the post-service HR3C precipitation phase of the present invention solves the problem that the traditional method requires more highly corrosive liquids, and at the same time, a large amount of precipitation phase in the post-service HR3C can be quickly obtained under room temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a transmission electron microscope morphology picture of the precipitated phase of HR3C obtained by the present invention in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0028] Example 1

[0029] The preparation method of the post-service HR3C precipitation phase of this embodiment specifically comprises the following steps:

[0030] 1) Prepare the sample to be tested

[0031] 1.1) Cutting

[0032] The HR3C heat-resistant steel material after service was cut into flat plate samples with a shape of 10mm*3mm*60mm using the electric spark wire cutting process.

[0033] 1.2) Polishing

[0034] The flat sample obtained in step 1.1) was cross-grinded and polished (the grinding direction of the sandpaper was cross-grinded or vertical) with 400-grit, 800-grit and 1200-grit sandpapers in sequence to completely remove the uneven surface relief introduced by the wire cutting method on the surface of the flat sample. Finally, fine grinding was performed with 2000-grit sandpaper until the scratches introduced by the 1200-grit sandpaper completely disappeared.

[0035] 1.3) Ultrasonic cleaning

[0036] Place the polished flat sample into a beaker containing ethanol. The flat sample is completely immersed in the ethanol and the ethanol liquid level is more than 1 cm above the top of the flat sample.

[0037] Seal the container with plastic wrap and tighten it with a rubber band. Then put the beaker into an ultrasonic cleaning tank for cleaning for 30 minutes. The cleaned sample is the sample to be tested.

[0038] 2) Prepare the corrosive solution

[0039] The etching solution includes the following components: methanol, zinc chloride, concentrated hydrochloric acid and citric acid.

[0040] Add 100g ZnCl2 to 100ml deionized water to prepare a ZnCl2 aqueous solution, stir well for use, and prepare 3% citric acid for use; take another beaker with a capacity of 500mL, add 250mL of methanol to the beaker, and add a magnetic stirring rotor to the beaker, place the beaker on a stirring table and rotate at 2-3 gear speed (speed is about 5r / s), add 30ml ZnCl2 solution, 24ml concentrated HCL and 6mL citric acid in turn, stir well and place the prepared corrosion solution in a fume hood for use.

[0041] 3) Electrolysis

[0042] The sample to be tested and the counter electrode are immersed in the beaker containing the corrosive solution in step 2), and the sample to be tested and the counter electrode are respectively connected to the positive and negative electrodes of the power supply for electrolysis. The sample to be tested is HR3C after service, and the counter electrode is a copper sheet or a copper rod, and the size of the counter electrode is the same as that of the sample to be tested.

[0043] The electrolysis temperature during electrolysis is 25°C, the electrolysis current is 1A, the stirring speed of the etching solution is 1r / s, and the electrolysis time is 2h. In this embodiment, the beaker containing the etching solution is placed in a constant temperature water bath with a magnetic stirring function, and the temperature of the water bath is controlled to control the temperature during electrolysis.

[0044] 4) Collection

[0045] When the remaining amount of the sample to be tested is about 80%, the etching solution with electrolytic residue is filtered. At the same time, the remaining sample to be tested is rinsed with 10g / L citric acid ethanol solution, the rinse solution with precipitation and the etching solution with electrolytic residue are filtered together, and the filtered solid is washed and dried.

[0046] During cleaning, use 10g / L citric acid ethanol solution, 10g / L citric acid solution, and 10g / L sodium hydroxide solution for three times respectively, and finally use distilled water for cleaning.

[0047] During filtration, a microporous filter membrane with a pore size range of 0.2-0.3 μm is used for suction filtration.

[0048] The obtained solid is dried to obtain the precipitated phase of HR3C after service.

[0049] The collected precipitated phases are the strengthening phases such as M23C6 phase, NbCrN phase, and MX phase precipitated during the aging process of HR3C heat-resistant steel. XRD or TEM can be used for qualitative or quantitative analysis to study scientific issues such as the aging law of HR3C. Figure 1 As shown, Figure 1 This is the morphology picture of the HR3C precipitate phase obtained under a transmission electron microscope.

[0050] The preparation method of the HR3C precipitation phase after service of the present invention is aimed at the process of using a large amount of HCL, HNO3 and the like in the extraction process of the precipitation phase of key heat-resistant steel for typical thermal power ultra-supercritical units such as HR3C after long-term service, which may cause serious environmental pollution. Through a special corrosive liquid formula, the HR3C heat-resistant steel after service can be electrolytically extracted under room temperature and in a magnetic field stirring process. The preparation method of the HR3C precipitation phase after service of the present invention solves the problem that the traditional method requires more highly corrosive liquids, is environmentally friendly, and is simple and convenient. It can quickly extract the M23C6 phase, NbCrN and MX phase generated during the service process of HR3C.

[0051] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing HR3C precipitated phase after service, characterized in that: The steps include: Prepare a corrosive solution, immerse the sample to be tested and the counter electrode in the corrosive solution, respectively connect the sample to be tested and the counter electrode to the positive electrode and the negative electrode of the power supply for electrolysis, and when the remaining amount of the sample to be tested is less than 50%, filter the corrosive solution with electrolytic residue, and the obtained solid is the precipitated phase; the sample to be tested is HR3C after service; the collected precipitated phase is the strengthening phase precipitated during the aging process of HR3C heat-resistant steel, which can be qualitatively analyzed or quantitatively analyzed later; The remaining sample to be tested is rinsed with ethanol solution of citric acid, and the rinse solution with precipitate and the corrosion solution with electrolytic residue are filtered together; The etching solution includes the following components: methanol, zinc chloride, concentrated hydrochloric acid and citric acid, and the volume ratio of each substance is: methanol: zinc chloride: concentrated hydrochloric acid: citric acid = 250:30:24:6; the concentration of the zinc chloride is 1000g / L; Under stirring, adding zinc chloride aqueous solution, concentrated hydrochloric acid and citric acid to methanol, and mixing them evenly to obtain the etching solution, wherein the mass concentration of citric acid is 3%; During the electrolysis, the electrolysis temperature is 20±5° C., the electrolysis current is ≤1A, the stirring speed of the corrosive liquid is 0.5-1r / s, and the electrolysis time is 2-3h; the filtered solid is washed and dried; the washing is carried out by sequentially using citric acid ethanol solution, citric acid solution, sodium hydroxide solution and distilled water.

2. The method for preparing the post-service HR3C precipitate phase according to claim 1, characterized in that: The material of the counter electrode is copper, and the size of the counter electrode is the same as the size of the sample to be tested.

3. The method for preparing the post-service HR3C precipitate phase according to claim 1, characterized in that: The filtration is performed using a microporous filter membrane with a pore size range of 0.2-0.3 μm.

4. The method for preparing the post-service HR3C precipitate phase according to any one of claims 1 to 3, characterized in that: The preparation of the sample to be tested includes grinding and ultrasonic cleaning steps. The grinding is: cross-grinding and polishing with 400 mesh, 800 mesh and 1200 mesh sandpaper in sequence to completely remove the uneven relief on the surface of the HR3C material after service, and finally fine grinding with 2000 mesh sandpaper until the scratches introduced by the 1200 mesh sandpaper completely disappear.

5. The method for preparing the post-service HR3C precipitate phase according to claim 4, characterized in that: The ultrasonic cleaning is as follows: the polished sample is placed in a container containing ethanol, with the ethanol liquid level exceeding the top of the sample by more than 1 cm; the container is sealed and placed in an ultrasonic cleaning chamber for 30-60 minutes.

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