Metallographic detection method for stainless steel-carbon steel dissimilar metal welded joint

Abstract

The invention belongs to the technical field of macroscopic metallographic detection, and discloses a stainless steel-carbon steel dissimilar metal welded joint metallographic detection method, which comprises the following steps: grinding a metallographic sample by using abrasive paper to ensure the roughness; corroding the metallographic specimen to determine the contour of a fusion line on one side of the carbon steel; according to the determined contour of the fusion line on one side of the carbon steel, the surface of the carbon steel structure is completely coated with an anti-corrosion coating; then the stainless steel structure and the welding seam are corroded, so that the stainless steel structure and the welding seam are clearly developed; the anti-corrosion coating is removed, and the metallographic specimen is corroded, so that the carbon steel structure is clearly developed; and then detecting and analyzing the treated metallographic specimen. By adopting the method, the problems of difficulty in macroscopic metallographic detection of the stainless steel-carbon steel dissimilar metal welded joint and poor display effect of a metallographic photo are effectively solved, and the method has the advantages of simplicity in operation, good corrosion effect, low detection cost and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of macroscopic metallographic detection, and in particular relates to a metallographic detection method for a stainless steel-carbon steel dissimilar metal weld joint. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In the car body underframe structure of stainless steel subways, stainless steel-carbon steel dissimilar metal welded joints are relatively common. The welding wire of this type of welded joint is made of stainless steel to ensure that the composition of the weld is close to that of stainless steel and has good corrosion resistance. Metallographic testing of welded joints is a crucial quality control and failure analysis method.

[0004] Metallographic testing generally involves sampling, polishing, etching, and analysis. When sampling welded joints, the sample must include the fusion line, weld metal, heat-affected zones on both sides, and the parent metal. Common etching methods include chemical etching, electrolytic etching, or thermal etching. Chemical etching methods include immersion, wiping, or spray etching.

[0005] When performing metallographic testing on stainless steel-carbon steel dissimilar metal welded joints, conventional metallographic corrosion methods cannot corrode both stainless steel and carbon steel to a moderate state simultaneously due to the significant difference in corrosion resistance between stainless steel and carbon steel. If the etching method is used, the metallographic specimen is immersed in the corrosive agent, and the entire test surface is affected by the corrosive agent. Since carbon steel has significantly weaker corrosion resistance than stainless steel, the degree of corrosion on carbon steel will be significantly heavier than that on stainless steel and the weld, resulting in a large color difference. Abrasion generally involves using absorbent cotton dipped in corrosive agent to smear on the metallographic test surface. This method can corrode a local area of ​​the test surface, but this method cannot accurately corrode only one side of the stainless steel and weld, or only one side of the carbon steel. Firstly, the fusion line of the weld is an irregular curve. Secondly, the cotton ball is relatively thick compared to the metallographic specimen, especially compared to the fusion line of the weld. Thirdly, the corrosive agent is a liquid with good fluidity, making it difficult to accurately control.

[0006] When the corrosion degree of the two materials in a welded joint differs greatly, it will not only interfere with the identification of welding defects and weld morphology, but will also directly lead to excessive color difference on both sides of the joint when taking pictures, affecting the display effect of the metallographic photos and having an adverse impact on the joint quality assessment and defect analysis. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints, which solves the problems of difficult macroscopic metallographic detection of stainless steel-carbon steel dissimilar metal weld joints and poor metallographic photograph display effect.

[0008] In order to achieve the above object, the present invention is implemented through the following technical solutions: A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: polishing a metallographic sample with sandpaper to ensure roughness; The metallographic specimens were etched to determine the fusion line profile on the carbon steel side; According to the determined fusion line profile on one side of the carbon steel, an anti-corrosion coating is applied to the entire surface of the carbon steel; Then the stainless steel structure and weld are corroded to make the stainless steel structure and weld clearly visible; Remove the anti-corrosion coating and corrode the metallographic specimen to make the carbon steel structure clearly visible; The processed metallographic samples are then tested and analyzed.

[0009] The beneficial effects achieved by one or more embodiments of the present invention are as follows: In the present invention, the metallographic sample is first pre-corroded to determine the fusion line profile on the carbon steel side, and then the carbon steel structure is effectively protected by applying an anti-corrosion coating. When the stainless steel structure and weld (stainless steel welding wire is used for welding) are subsequently corroded, the carbon steel structure is isolated from the corrosive liquid to prevent the carbon steel structure from being corroded preferentially.

[0010] After the stainless steel structure and welds are corroded moderately, the anti-corrosion coating is removed and the metallographic specimen is corroded. At this time, the corrosion degree of the carbon steel can be made close to that of the stainless steel by controlling the corrosion time, thereby preventing excessive corrosion of the carbon steel structure.

[0011] This method effectively solves the problems of difficult macroscopic metallographic detection of stainless steel-carbon steel dissimilar metal weld joints and poor metallographic photograph display effects. It has the advantages of simple operation, good corrosion effect, and low detection cost. It can meet the needs of stainless steel-carbon steel dissimilar metal weld joint evaluation and help promote the research and development of stainless steel body welding technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0013] Figure 1 This is a metallographic photograph of a local area of ​​the fusion line on one side of the carbon steel after abrasion in Example 1 of the present invention; Figure 2 This is a metallographic photograph of the carbon steel structure after the anti-corrosion coating is applied to all of the carbon steel structure in Example 1 of the present invention; Figure 3This is a metallographic photograph of the metallographic sample after three etchings in Example 1 of the present invention; Figure 4 This is a metallographic photograph of the metallographic sample after corrosion in Comparative Example 1 of the present invention; Figure 5 This is a metallographic photograph of the metallographic sample after corrosion in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0014] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0015] A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: polishing a metallographic sample with sandpaper to ensure roughness; The metallographic specimens were etched to determine the fusion line profile on the carbon steel side; According to the determined fusion line profile on one side of the carbon steel, an anti-corrosion coating is applied to the entire surface of the carbon steel structure; Then the stainless steel structure and weld are corroded to make the stainless steel structure and weld clearly visible; Remove the anti-corrosion coating and corrode the metallographic specimen to make the carbon steel structure clearly visible; The processed metallographic samples are then tested and analyzed.

[0016] Polishing is a fundamental step in metallographic specimen preparation. Its primary purpose is to remove surface processing marks (such as scratches from cutting or machining), oxide layers, and contaminants using sandpaper, resulting in a smooth and uniform surface roughness. This process provides excellent surface conditions for subsequent etching and low-magnification microstructure observation: a flat surface ensures uniform action of the etchant, preventing localized over- or under-etching due to surface unevenness; and an appropriate degree of roughness (non-mirror finish) facilitates clear visualization of low-magnification microstructures after etching (an overly smooth surface may interfere with observation due to reflections).

[0017] In some embodiments, the metallographic specimen is polished using 320# and 600# sandpapers in sequence.

[0018] During cutting or sampling, the surface of a metallographic specimen may produce deep scratches, metal deformation layers, and oxidized contamination layers due to mechanical action. 320# sandpaper has coarser grit and stronger cutting force, which can quickly grind away deep scratches and deformation layers on the surface, initially smoothing the rough original surface. 600# sandpaper has finer grit and can cover and eliminate coarse scratches left by sanding the surface of the previous sandpaper, thus ensuring the observation accuracy of the metallographic specimen.

[0019] Preferably, the roughness of the inspection surface of the metallographic sample after sandpaper polishing is Ra0.1-0.2 μm.

[0020] Before metallographic etching, the surface roughness of the test is required to reach Ra0.1~0.2μm (i.e., the surface is highly uniform and has no obvious scratches or bumps). This is to provide a uniform, undisturbed substrate for etching, avoid uneven corrosion caused by physical defects (scratches, pits), and ensure that the true microstructure of the sample is observed under the stereo microscope.

[0021] In some embodiments, the etchant used in the third etching is a mixture of hydrochloric acid, nitric acid, and FeCl3, wherein the volume ratio of HCl, HNO3, and H2O is 2-4:4-6:10-15, and FeCl3 is 0.08-0.12 g / mL.

[0022] Preferably, in the corrosive agent, the volume ratio of HCl, HNO3 and H2O is 2~4:4~6:10~13, and FeCl3 is 0.09~0.11 g / mL.

[0023] Further preferably, the etchant comprises a volume ratio of HCl, HNO3, and H2O of 3:5:12, and FeCl3 of 0.10 g / mL. The carbon steel-side fusion line is the boundary between the carbon steel base metal and the weld metal in a stainless steel-carbon steel dissimilar metal weld joint. Determining the carbon steel-side fusion line profile serves the following key purposes: According to the fusion line profile on the carbon steel side, the weld joint is accurately divided into two parts: stainless steel structure and weld and carbon steel structure, providing a basis for the subsequent coating of anti-corrosion coating on the entire surface of the carbon steel structure to protect the carbon steel structure.

[0024] If the position of the fusion line in carbon steel is misjudged, it may result in: The anti-corrosion coating is insufficient, the carbon steel base material or the heat-affected zone is partially unprotected, and the stainless steel corrosive liquid penetrates into the carbon steel area, causing excessive corrosion of the carbon steel structure, destroying its structural characteristics and making it impossible to observe accurately.

[0025] If the anti-corrosion coating covers too wide, it may cover part of the weld or the stainless steel side, resulting in insufficient corrosion of the area when the stainless steel corrodes, and its structure is not clearly displayed, affecting the analysis.

[0026] Therefore, in order to ensure the accuracy of metallographic testing, it is crucial to accurately determine the location of the carbon steel fusion line.

[0027] In some embodiments, the etching method for etching the metallographic specimen to determine the fusion line profile on one side of the carbon steel is abrasion etching, immersion etching, or spray etching.

[0028] Preferably, the etching method for corroding the metallographic specimen to determine the fusion line profile on the carbon steel side is abrasion. This is because, on the one hand, the time taken to etch the carbon steel fusion line is short, and abrasion is more flexible and suitable for a short-time etching method. On the other hand, abrasion can observe the corrosion effect in real time, which is conducive to controlling the degree of corrosion (spray etching is not suitable for highly volatile corrosive agents).

[0029] More preferably, the abrasion time is 5-15 s, and the abrasion temperature is 15-35° C.

[0030] In some embodiments, the coating material of the anti-corrosion coating is paint, acrylic resin, paraffin, beeswax or silicone sealant.

[0031] Preferably, the coating material of the anti-corrosion coating is paint or paraffin.

[0032] Preferably, the tool for applying the anti-corrosion coating is a pointed flexible pen.

[0033] The material of the pointed flexible pen can be selected according to the specific type of paint.

[0034] Further preferably, the coating method of the anti-corrosion coating is: using a pointed flexible pen to finely trace the fusion line on one side of the carbon steel, and then coating the entire surface of the carbon steel structure with the coating by roughly tracing.

[0035] The dimensions of metallographic specimens for weld joints are typically 30-40 mm long and 4-10 mm short; therefore, the cross-sectional area is relatively small. Furthermore, the fusion line is typically an irregular arc, making it difficult to coat the entire surface of carbon steel with an anti-corrosion coating using traditional dip coating methods.

[0036] Therefore, use a pointed flexible pen to apply the anti-corrosion paint. First, draw the fusion line on one side of the carbon steel in detail to accurately divide the coating area, and then roughly paint all the remaining areas. This can ensure that the entire surface area of ​​the carbon steel tissue is coated with anti-corrosion paint.

[0037] More preferably, the method further includes the step of allowing the applied paint to stand and dry.

[0038] In some embodiments, the method for corroding the stainless steel structure and welds is abrasion, immersion or spray corrosion, and immersion corrosion is preferred. The reasons are, on the one hand, that the corrosion time is longer, and on the other hand, that the paint is prevented from falling off at weak points due to abrasion (spray corrosion is not suitable for highly volatile corrosive agents).

[0039] Preferably, the immersion corrosion time is 30 to 100 seconds, preferably 40 to 90 seconds, more preferably 50 to 70 seconds, and even more preferably 50 to 60 seconds.

[0040] In some embodiments, the method for removing the anti-corrosion coating is cleaning with an organic solvent.

[0041] Preferably, the organic solvent is alcohol. In some embodiments, when removing the anti-corrosion coating and corroding the metallographic specimen, the corroding method is abrasion, immersion or spray corrosion.

[0042] Preferably, when removing the anti-corrosion coating and corroding the metallographic sample, the corrosion method is abrasion. The reason is that on the one hand, the corrosion time of carbon steel structure is short, and abrasion is more flexible and suitable for a short-time corrosion method. On the other hand, abrasion can observe the corrosion effect in real time, which is conducive to controlling the degree of corrosion.

[0043] More preferably, the abrasion time is 5 to 20 seconds, preferably 10 to 20 seconds, and more preferably 10 to 15 seconds.

[0044] The present invention will be further described below with reference to the embodiments.

[0045] The stainless steel test plates used in the following examples and comparative examples are all of SUS304, the carbon steel test plates are all of Q345C, the welding wires are all of 308LSi, and the welding method is MAG welding.

[0046] Example 1 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the metallographic specimen in turn, so that the roughness of the test surface is Ra 0.2μm; (2) The metallographic specimen was etched at room temperature (25°C) for 10 s using a etchant consisting of a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3, and 60 mL H2O. (3) After the corrosion is completed, the metallographic specimen is cleaned and dried; (4) Use a pointed paint pen to draw a fine line on the fusion line on one side of the carbon steel, and then use a rough drawing to coat the entire surface of the carbon steel structure with paint to obtain an anti-corrosion coating; (5) Let the anti-corrosion coating stand and dry for 10 minutes to allow the anti-corrosion coating to solidify; (6) The stainless steel structure and weld of the metallographic specimen after protection in step (5) are etched in an etchant at room temperature for 50 seconds to make the stainless steel structure and weld clearly visible; the etchant is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (7) After etching, clean the metallographic specimen and use alcohol to clean the anti-corrosion coating on the surface of the carbon steel structure; (8) Use a corrosive agent to abrade the carbon steel structure area of ​​the test surface at room temperature for 15 seconds, so that the carbon steel structure is clearly imaged and the corrosion is completed; the corrosive agent is a mixture of 15mLHCl, 25mLHNO3, 10gFeCl3 and 60mLH2O; (9) After the corrosion is completed, clean and dry the metallographic specimen. Use a stereo microscope to observe the low-magnification structure of the weld joint.

[0047] Metallographic photograph of the local area of ​​the fusion line on the carbon steel side after abrasion, such as Figure 1 As shown, it can be seen that after abrasion, the fusion line on the carbon steel side is clearly visible, and at the same time the carbon steel body and the stainless steel body are not excessively corroded, which is convenient for subsequent operations; Metallographic photos after the carbon steel structure is fully coated with anti-corrosion coating, such as Figure 2 As shown, since the fusion line on the carbon steel side is clearly shown, the carbon steel surface can be completely coated with anti-corrosion coating; The metallographic photograph of the metallographic sample after three corrosions is as follows: Figure 3 As shown, it can be seen that the carbon steel side fusion line, carbon steel structure, weld structure, stainless steel side fusion line and stainless steel structure of the metallographic specimen after corrosion are all well imaged, and the welding quality of the welded joint can be accurately evaluated.

[0048] Example 2 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the metallographic specimen in turn, so that the roughness of the test surface is Ra 0.1μm; (2) The metallographic specimen was etched at 20°C for 15 s using a etchant consisting of a mixture of 15 mL HCl, 25 mL HNO₃, 10 g FeCl₃, and 60 mL H₂O. (3) After the corrosion is completed, the metallographic specimen is cleaned and dried; (4) Use a pointed flexible pen dipped in molten paraffin oil to draw a fine line on the fusion line on one side of the carbon steel, and then use a rough line to coat the entire surface of the carbon steel tissue with molten paraffin oil to obtain an anti-corrosion coating; (5) Allow the anti-corrosion coating to stand and cure for 10 minutes to allow the anti-corrosion coating to solidify; (6) The stainless steel structure and weld of the metallographic specimen after protection in step (5) are etched in an etchant at 20°C for 60 seconds to make the stainless steel structure and weld clearly visible; the etchant is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (7) After etching, clean the metallographic specimen and remove the anti-corrosion coating on the surface of the carbon steel structure; (8) Use a corrosive agent to erode the carbon steel structure area of ​​the test surface at 20°C for 20 seconds until the carbon steel structure is clearly imaged and the etching is complete; the corrosive agent is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (9) After the corrosion is completed, clean and dry the metallographic specimen. Use a stereo microscope to observe the low-magnification structure of the weld joint.

[0049] Example 3 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the metallographic specimen in turn, so that the roughness of the test surface is Ra 0.2μm; (2) The metallographic specimen was etched at 30°C for 10 s using a etchant, and the etchant area was a local area including the fusion line on the carbon steel side. The etchant was a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3, and 60 mL H2O. (3) After the corrosion is completed, the metallographic specimen is cleaned and dried; (4) Use a pointed flexible pen dipped in hot-melt acrylic resin to draw a fine line on the fusion line on one side of the carbon steel, and then use a rough line to coat the entire surface of the carbon steel tissue with hot-melt acrylic resin to obtain an anti-corrosion coating; (5) Allow the anti-corrosion coating to stand and cure for 10 minutes to allow the anti-corrosion coating to solidify; (6) The stainless steel structure and weld of the metallographic specimen after protection in step (5) are etched in an etchant at 30°C for 45 seconds to make the stainless steel structure and weld clearly visible; the etchant is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (7) After etching, clean the metallographic specimen and remove the anti-corrosion coating on the surface of the carbon steel structure; (8) Use a corrosive agent to erode the carbon steel structure area of ​​the test surface at 30°C for 15 seconds until the carbon steel structure is clearly imaged and the etching is complete; the corrosive agent is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (9) After the corrosion is completed, clean and dry the metallographic specimen. Use a stereo microscope to observe the low-magnification structure of the weld joint.

[0050] Example 4 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the metallographic specimen in turn, so that the roughness of the test surface is Ra 0.2μm; (2) The metallographic specimen was etched at 32°C for 15 seconds using an etchant consisting of a mixture of 5 g FeCl3 (anhydrous ferric chloride), 50 mL concentrated hydrochloric acid (HCl), and 50 mL deionized water. (3) After the corrosion is completed, the metallographic specimen is cleaned and dried; (4) Use a pointed flexible pen dipped in molten paraffin oil to draw a fine line on the fusion line on one side of the carbon steel, and then use a rough line to coat the entire surface of the carbon steel tissue with molten paraffin oil to obtain an anti-corrosion coating; (5) Allow the anti-corrosion coating to stand and cure for 10 minutes to allow the anti-corrosion coating to solidify; (6) The stainless steel structure and weld of the metallographic specimen after protection in step (5) are etched in an etchant at 20°C for 70 seconds to make the stainless steel structure and weld clearly visible; the etchant composition is a mixture of 5g FeCl3 (anhydrous ferric chloride), 50mL concentrated hydrochloric acid (HCl) and 50mL deionized water; (7) After etching, clean the metallographic specimen and remove the anti-corrosion coating on the surface of the carbon steel structure; (8) Use an etchant to etch the carbon steel tissue area on the surface to be tested at 27°C for 15 seconds until the carbon steel tissue is clearly visible and the etching is complete; the etchant composition is a mixture of 5g FeCl3 (anhydrous ferric chloride), 50mL concentrated hydrochloric acid (HCl) and 50mL deionized water; (9) After the corrosion is completed, clean and dry the metallographic specimen. Use a stereo microscope to observe the low-magnification structure of the weld joint.

[0051] Comparative Example 1 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the metallographic specimen in turn to make its surface roughness Ra0.2μm; (2) Use an etchant to etch the surface of the metallographic specimen to be tested at room temperature (25°C) for 75 seconds; the etchant is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (3) After etching, take out the metallographic sample, clean it and blow it dry.

[0052] Use a stereo microscope to observe the low-magnification structure of the welded joint. Figure 4 As shown, it can be seen that when the same corrosion time as in Example 1 is adopted, the entire metallographic specimen is easily etched to cause excessive corrosion of the carbon steel structure, causing serious damage to its metallographic structure, making it impossible to observe, and thus making it difficult to accurately evaluate the welding quality of the welded joint.

[0053] Comparative Example 2 A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints comprises the following steps: (1) Use 320# and 600# sandpaper to polish the surface of the metallographic specimen to be tested in turn, so that its surface roughness is Ra 0.2μm; (2) Use an etchant to etch the surface of the metallographic specimen to be tested at room temperature (25°C) for 25 seconds; the etchant is a mixture of 15 mL HCl, 25 mL HNO3, 10 g FeCl3 and 60 mL H2O; (3) After etching, take out the metallographic sample, clean it and blow it dry.

[0054] Use stereo microscope to observe the low-magnification structure of the welded joint. Figure 5 As shown, it can be seen that when the overall etching time of the metallographic specimen is short, the stainless steel structure and weld structure cannot be effectively corroded, making it difficult to accurately observe their metallographic structures and thus difficult to evaluate the welding quality of the welded joints.

[0055] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints, characterized by: The method comprises the following steps: grinding the metallographic sample with sandpaper to ensure the roughness; The metallographic specimens were etched to determine the fusion line profile on the carbon steel side; According to the determined fusion line profile on one side of the carbon steel, an anti-corrosion coating is applied to the entire surface of the carbon steel structure; Corrosion of stainless steel structure and welds to make the stainless steel structure and welds clearly visible; Remove the anti-corrosion coating and corrode the metallographic specimen to make the carbon steel structure clearly visible; The processed metallographic samples are then tested and analyzed.

2. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: When etching metallographic specimens to determine the fusion line profile on one side of carbon steel, the etching method is abrasion, immersion or spray etching; Preferably, the etching method for etching the metallographic specimen to determine the fusion line profile on one side of the carbon steel is abrasion; Preferably, the abrasion time is 5-15 s, and the abrasion temperature is 15-35°C.

3. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: Use 320# and 600# sandpaper to polish the metallographic specimens in turn; Preferably, the roughness of the inspection surface of the metallographic sample after sandpaper polishing is Ra0.1-0.2 μm.

4. The metallographic inspection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: The etchant used in the third etching was a mixture of hydrochloric acid, nitric acid, and FeCl3, where the volume ratio of HCl, HNO3, and H2O was 2-4:4-6:10-15, and FeCl3 was 0.08-0.12 g / mL; Preferably, in the corrosive agent, the volume ratio of HCl, HNO3 and H2O is 3:5:12, and FeCl3 is 0.10 g / mL.

5. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: The coating material of the anti-corrosion coating is paint, thermoplastic acrylic resin, paraffin, beeswax or silicone sealant; Preferably, the coating material of the anti-corrosion coating is paint or paraffin.

6. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 5, characterized in that: a pointed flexible pen coated with the anti-corrosion coating; Preferably, the coating method of the anti-corrosion coating is: using a pointed flexible pen to finely trace the fusion line on one side of the carbon steel, and then coating the entire surface of the carbon steel structure with the coating by roughly tracing.

7. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: The method of corroding the stainless steel structure and weld is abrasion, immersion or spray corrosion, preferably immersion corrosion; Preferably, the immersion corrosion time is 30 to 100 seconds, preferably 40 to 90 seconds, more preferably 50 to 70 seconds, and even more preferably 50 to 60 seconds.

8. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: When the anti-corrosion coating is removed and the metallographic specimen is corroded, the corrosion method is abrasion, immersion or spray corrosion.

9. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 8, characterized in that: When removing the anti-corrosion coating and corroding the metallographic specimen, the corrosion method is abrasion; Preferably, the abrasion time is 5 to 20 seconds, preferably 10 to 20 seconds, and more preferably 10 to 15 seconds.

10. The metallographic detection method for stainless steel-carbon steel dissimilar metal weld joints according to claim 1, characterized in that: The method for removing the anti-corrosion coating is to clean it with an organic solvent; Preferably, the organic solvent is alcohol.

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