An etchant for revealing the microstructure of a butt joint between carbon steel and austenitic stainless steel and a method of using the same

Abstract

The application discloses an etchant for displaying the metallurgical structure of a butt joint of carbon steel and austenitic stainless steel, which is prepared by mixing raw materials with the following mass percentages: sodium nitrate 9-15%, ferric chloride 3-7%, oxalic acid 0.5-4%, phosphoric acid 18-26%, hydrochloric acid 4-8%, distilled water 40-60% and hydrogen peroxide 0.1-0.6%. The etchant is composed of sodium nitrate, ferric chloride, oxalic acid, phosphoric acid, hydrochloric acid, distilled water and hydrogen peroxide, and has the advantages of simple composition, convenient preparation and use, clear, real, complete and non-illusory display of the microstructure of each region of the butt joint of carbon steel and austenitic stainless steel, complete display of the structure details, no special requirement for the observation equipment, and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallographic corrosion, and particularly relates to an etchant for displaying the metallographic structure of a butt joint of carbon steel and austenitic stainless steel and a use method thereof. BACKGROUND

[0002] Since the welding between dissimilar materials can make full use of the performance of various materials, in the case of meeting various performance requirements, various valuable materials can be saved, and the cost can be reduced. Therefore, the dissimilar material composite parts manufactured by using dissimilar steel welding are more and more widely valued by people. It has been widely used in mechanical equipment and components in power station boilers, petrochemical industry, transportation, mechanical and electronic, and aerospace industries. Since the austenitic stainless steel has excellent corrosion resistance, and the carbon steel has high hardness and high strength, people manufacture the composite plate by welding the austenitic stainless steel and the carbon steel, and use the composite plate in the power station boiler, so that the boiler or the composite plate has the excellent performance of the austenitic stainless steel and the carbon steel. Especially in the power station boiler, the butt joint of the carbon steel 20G and the austenitic stainless steel 12Cr18Ni9, 06Cr19Ni10 and 06Cr18Ni11Nb has the largest difference in the aspects of base material chemical composition, microstructure, physical and mechanical properties and the like, and is the most dissimilar steel joint. The welding joint quality has been the focus of the power plant and the power enterprise for a long time. The metallographic examination as an important quality control means is widely used in the quality control of the joint, the optimization of the welding process, the life assessment of the in-service parts and the failure analysis. The preparation of a good metallographic sample is the premise of ensuring the detection quality. Therefore, the etching display of the metallographic structure of the dissimilar steel joint becomes the key to the metallographic examination and analysis of the butt joint of the carbon steel and the austenitic stainless steel.

[0003] However, the corrosion of carbon steel is faster, and the corrosion of stainless steel is slower, and the display method of the metallographic structure of such dissimilar steel joint mainly adopts step-by-step etching method, for example, a Chinese invention patent with publication number CN110261207A discloses a metallographic etching method for the electron beam welded joint part of duplex stainless steel and carbon steel composite plate, three kinds of etchants are used for step-by-step etching, which are 20% oxalic acid electrolytic etching, 20% sodium hydroxide solution electrolytic etching, and three kinds of etchants of hydrochloric acid, picric acid, ferric chloride, alcohol and acetone for step-by-step etching. However, due to the step-by-step etching method, each time only the local etching display of the sample can be carried out, which causes the incompleteness of the structure display of each region of the joint (including the weld, the two sides of the base material and the heat affected zone), the discontinuity of the analysis and observation, and the repeatability of the sample preparation, which seriously restricts the overall observation and analysis and photography of the sample, and greatly affects the detection analysis quality and work efficiency. Especially when the boiler in-service parts are supervised and inspected on site, the step-by-step etching method often brings great inconvenience. Therefore, it is urgent to find a simple and safe etchant which can clearly, truly, completely and without false image display the structure of each region of the carbon steel and austenitic stainless steel butt joint at the same time, so as to improve the metallographic detection quality and efficiency of such dissimilar steel joint, ensure the accuracy of the detection result, and provide excellent and reliable detection means for the quality control and rapid detection of such dissimilar steel butt joint. SUMMARY

[0004] The technical problem to be solved by the present application is to provide an etchant for displaying the metallographic structure of carbon steel and austenitic stainless steel butt joint, which can clearly, truly, completely and without false image display the structure of each region of the carbon steel and austenitic stainless steel butt joint at the same time.

[0005] The technical solution adopted by the present application to solve the technical problem is that an etchant for displaying the metallographic structure of carbon steel and austenitic stainless steel butt joint is prepared by mixing the following raw materials in the following mass percentages: sodium nitrate 9-15%, ferric chloride 3-7%, oxalic acid 0.5-4%, phosphoric acid 18-26%, hydrochloric acid 4-8%, distilled water 40-60%, and hydrogen peroxide 0.1-0.6%.

[0006] Further, an etchant for displaying the metallographic structure of carbon steel and austenitic stainless steel butt joint is prepared by mixing the following raw materials in the following mass percentages: sodium nitrate 10-12%, ferric chloride 4-6%, oxalic acid 2-3%, phosphoric acid 20-24%, hydrochloric acid 6-7%, distilled water 48-55%, and hydrogen peroxide 0.2-0.5%.

[0007] Further, the carbon steel is 20G carbon steel, and the austenitic stainless steel is 12Cr18Ni9, 06Cr19Ni10 or 06Cr18Ni11Nb.

[0008] Further, the purity grade of the sodium nitrate, ferric chloride, oxalic acid, phosphoric acid, hydrochloric acid is analytical pure.

[0009] A method for using an etchant for displaying the microstructure of a carbon steel and austenitic stainless steel butt joint, comprising the following steps:

[0010] (1) Etchant preparation: place the formula amount of distilled water in a container, then add sodium nitrate, ferric chloride and oxalic acid, stir and dissolve, then add phosphoric acid, hydrochloric acid and hydrogen peroxide, stir until uniform to obtain the etchant;

[0011] (2) Etching: after polishing the sample to be etched, immerse it in the etchant obtained in step (1), wipe the sample with absorbent cotton for 10-15s, then rinse with water and then with anhydrous ethanol, then dry with hot air or oven dry, and then observe and analyze the microstructure.

[0012] Further, the etchant in step (2) is 2-3mm higher than the polished surface of the sample.

[0013] The beneficial effects of the present application are: the etchant composed of sodium nitrate, ferric chloride, oxalic acid, phosphoric acid, hydrochloric acid, distilled water and hydrogen peroxide can clearly, truly, completely and without false image display the microstructure morphology of each region of the carbon steel and austenitic stainless steel butt joint, and the detailed structure is complete, and there is no special requirement for the observation equipment.

[0014] The etchant reagent composition of the present application is simple, convenient to prepare and use, and has good reproducibility, and there is no special requirement for the optical microscope for observation, which is an ideal new method for displaying the microstructure morphology of the carbon steel and austenitic stainless steel butt joint. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the weld microstructure morphology observed under an optical microscope after etching of the 20G and 06Cr18Ni11Nb dissimilar steel welded joint sample of Example 1;

[0016] Figure 2 is the 20G side fusion line microstructure morphology observed under an optical microscope after etching of the 20G and 06Cr18Ni11Nb dissimilar steel welded joint sample of Example 1;

[0017] Figure 3 is the 06Cr18Ni11Nb side fusion line microstructure morphology observed under an optical microscope after etching of the 20G and 06Cr18Ni11Nb dissimilar steel welded joint sample of Example 1;

[0018] Figure 4is the microstructure morphology of the 20G side base metal of the 20G and 06Cr18Ni11Nb dissimilar steel welded joint sample of Example 1 observed under an optical microscope after etching;

[0019] Figure 5 is the microstructure morphology of the 06Cr18Ni11Nb side base metal of the 20G and 06Cr18Ni11Nb dissimilar steel welded joint sample of Example 1 observed under an optical microscope after etching.

[0020] Figure 6 is the microstructure morphology of the weld of the 20G and 12Cr18Ni9 dissimilar steel welded joint sample of Example 2 observed under an optical microscope after etching;

[0021] Figure 7 is the microstructure morphology of the 20G side fusion line of the 20G and 12Cr18Ni9 dissimilar steel welded joint sample of Example 2 observed under an optical microscope after etching;

[0022] Figure 8 is the microstructure morphology of the 12Cr18Ni9 side fusion line of the 20G and 12Cr18Ni9 dissimilar steel welded joint sample of Example 2 observed under an optical microscope after etching;

[0023] Figure 9 is the microstructure morphology of the 20G side base metal of the 20G and 12Cr18Ni9 dissimilar steel welded joint sample of Example 2 observed under an optical microscope after etching;

[0024] Figure 10 is the microstructure morphology of the 12Cr18Ni9 side base metal of the 20G and 12Cr18Ni9 dissimilar steel welded joint sample of Example 2 observed under an optical microscope after etching.

[0025] Figure 11 is the microstructure morphology of the weld of the 20G and 06Cr19Ni10 dissimilar steel welded joint sample of Example 3 observed under an optical microscope after etching;

[0026] Figure 12 is the microstructure morphology of the 20G side fusion line of the 20G and 06Cr19Ni10 dissimilar steel welded joint sample of Example 3 observed under an optical microscope after etching;

[0027] Figure 13 is the microstructure morphology of the 06Cr19Ni10 side fusion line of the 20G and 06Cr19Ni10 dissimilar steel welded joint sample of Example 3 observed under an optical microscope after etching;

[0028] Figure 14is the 20G side base metal microstructure morphology of the 20G and 06Cr19Ni10 dissimilar steel welded joint sample observed under an optical microscope after etching in Example 3;

[0029] Figure 15 is the 06Cr19Ni10 side base metal microstructure morphology of the 20G and 06Cr19Ni10 dissimilar steel welded joint sample observed under an optical microscope after etching in Example 3. DETAILED DESCRIPTION

[0030] The application is further described below in combination with the drawings and examples.

[0031] Example 1:

[0032] (1) Preparation of etchant: analytical pure sodium nitrate, ferric chloride, oxalic acid, phosphoric acid, and hydrochloric acid were prepared, distilled water was placed in a container, sodium nitrate, ferric chloride, and oxalic acid were added and stirred to dissolve, then phosphoric acid, hydrochloric acid, and hydrogen peroxide were added and stirred until uniform to obtain the etchant, the mass percentage content of each component in the etchant was sodium nitrate 14.8%, ferric chloride 6.5%, oxalic acid 3.6%, phosphoric acid 18.9%, hydrochloric acid 7.6%, distilled water 48%, and hydrogen peroxide 0.6%;

[0033] (2) Etching: the welded joint of 20G carbon steel and austenitic stainless steel 06Cr18Ni11Nb was used as a sample, after the etching sample was ground and polished, it was immersed in the above obtained etchant, the etchant was 2mm higher than the polished surface of the sample, the sample was wiped with degreasing cotton for 15s, then washed with water and then washed with anhydrous ethanol, and then dried with hot air for microscopic observation and analysis of the metallographic structure.

[0034] (3) The dried sample was observed under the bright field illumination of an optical microscope, and the results are shown in Figures 1-5 .

[0035] Example 2:

[0036] (1) Preparation of etchant: analytical pure sodium nitrate, ferric chloride, oxalic acid, phosphoric acid, and hydrochloric acid were prepared, distilled water was placed in a container, sodium nitrate, ferric chloride, and oxalic acid were added and stirred to dissolve, then phosphoric acid, hydrochloric acid, and hydrogen peroxide were added and stirred until uniform to obtain the etchant, the mass percentage content of each component in the etchant was sodium nitrate 10.5%, ferric chloride 5.6%, oxalic acid 2.3%, phosphoric acid 20.8%, hydrochloric acid 6.6%, distilled water 53.7%, and hydrogen peroxide 0.5%;

[0037] (2) Etching: the welded joint of 20G carbon steel and austenitic stainless steel 12Cr18Ni9 is used as a sample, after the etching sample is ground and polished, it is immersed in the etching agent obtained above, the etching agent is 2mm higher than the polished surface of the sample, after the sample is wiped for 10s with degreasing cotton, it is washed with clean water and then washed with anhydrous ethanol, and then dried with hot air, so that the metallographic structure can be observed and analyzed.

[0038] (3) The dried sample is placed under the bright field illumination of an optical microscope for observation, and the results are shown in Figures 6-10 .

[0039] Example 3

[0040] (1) Preparation of etchant: analytical pure sodium nitrate, ferric chloride, oxalic acid, phosphoric acid and hydrochloric acid are prepared, distilled water is placed in a container, sodium nitrate, ferric chloride and oxalic acid are added and stirred to dissolve, then phosphoric acid, hydrochloric acid and hydrogen peroxide are added and stirred uniformly to obtain the etchant, the mass percentage content of each component in the etchant is sodium nitrate 9.6%, ferric chloride 3.2%, oxalic acid 0.8%, phosphoric acid 24.8%, hydrochloric acid 4.5%, distilled water 57%, and hydrogen peroxide 0.1%;

[0041] (2) Etching: the welded joint of 20G carbon steel and austenitic stainless steel 06Cr19Ni10 is used as a sample, after the etching sample is ground and polished, it is immersed in the etching agent obtained above, the etching agent is 3mm higher than the polished surface of the sample, after the sample is wiped for 12s with degreasing cotton, it is washed with clean water and then washed with anhydrous ethanol, and then dried with hot air, so that the metallographic structure can be observed and analyzed.

[0042] (3) The dried sample is placed under the bright field illumination of an optical microscope for observation, and the results are shown in Figures 11-15 .

Claims

1. An etching agent for revealing the metallographic structure of a butt joint between carbon steel and austenitic stainless steel, characterized in that, The carbon steel is 20G carbon steel, and the austenitic stainless steel is 12Cr18Ni9, 06Cr19Ni10 or 06Cr18Ni11Nb.

2. The etchant for revealing the microstructure of a butt joint between carbon steel and austenitic stainless steel according to claim 1, characterized by, The carbon steel is 20G carbon steel, and the austenitic stainless steel is 12Cr18Ni9, 06Cr19Ni10 or 06Cr18Ni11Nb.

3. The etchant for revealing microstructure of carbon steel to austenitic stainless steel butt joint according to claim 1, characterized in that, The purity grade of the sodium nitrate, the ferric chloride, the oxalic acid, the phosphoric acid and the hydrochloric acid is analytically pure.

4. The use of an etchant for revealing the microstructure of a butt joint between carbon steel and austenitic stainless steel according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: (1) Preparation of the etchant: the formula amount of distilled water is placed in a container, then the sodium nitrate, the ferric chloride and the oxalic acid are added and stirred to dissolve, and then the phosphoric acid, the hydrochloric acid and the hydrogen peroxide are added and stirred to be uniform, so that the etchant is obtained; (2) Etching: after the sample to be etched is ground and polished, the sample is immersed in the etchant obtained in the step (1), the sample is wiped for 10-15 s by using the absorbent cotton, then the sample is washed by using the clean water and then washed by using the anhydrous ethanol, and then the sample is dried by using the hot air or dried by using the oven, so that the metallographic structure can be observed and analyzed.

5. The method of using the etchant for revealing microstructure of carbon steel to austenitic stainless steel butt joint according to claim 4, characterized in that, In the step (2), the etchant is 2-3 mm higher than the polished surface of the sample.

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