Metallographic corrosion method for core-spun wire with Hastelloy alloy core

Abstract

The invention discloses a metallographic corrosion method of a Hastelloy core cored wire, which comprises the following steps of: 1, machining the Hastelloy core cored wire to form a microstructure observation plane on the Hastelloy core cored wire; 2, grinding the microscopic structure observation plane of the core-spun wire, and then mechanically polishing the microscopic structure observation plane; and 3, etching the microscopic structure observation plane of the core-spun wire after mechanical polishing in the step 2 by using an etchant solution to obtain the microscopic structure observation plane of the core-spun wire to be observed. By controlling the composition ratio of the etchant solution, adopting sulfuric acid as the etchant solution component and additionally adding the hydrogen peroxide catalyst, the etchant solution has more active corrosion performance, the electrochemical reaction is effectively prevented, and the metallographic structure of the Hastelloy as the core material is rapidly and clearly presented; the accuracy of metallographic detection results and the detection efficiency are improved, the corrosion time is greatly shortened, and the method is suitable for the field of metallographic sample preparation of metal core-spun wires.

Description

Technical Field

[0001] This invention belongs to the field of metallographic sample preparation technology of metallic materials, and specifically relates to a metallographic etching method for cored wire with Hastelloy core. Background Technology

[0002] Metal-core wire with an outer layer of 316L and an inner layer of Hastelloy alloy is a composite special metal material. By combining the advantages of both alloys, complementary performance is achieved: the toughness of 316L compensates for the potential brittleness of Hastelloy, while the high strength of Hastelloy enhances the overall compressive strength, making it suitable for manufacturing components such as springs and seals that require both elasticity and corrosion resistance. The selection of the metallographic etchant is crucial for accurately displaying the microstructure of the metal material. For this metal-core wire, the focus is primarily on detecting the microscopic characteristics of the core metal. However, because the outer metal layer is more susceptible to corrosion than the core metal, and both the inner and outer layers are corroded by HCl in the corresponding metallographic etchant, an electrochemical reaction occurs during the metallographic etching process. This leads to a faster corrosion rate for the outer metal, while the core metal remains uncorroded, making it impossible to observe the microstructure of the core metal after metallographic etching.

[0003] The currently disclosed detection methods include: (1) Aqua regia (1 nitric acid + 3 hydrochloric acid) etching method, which can slightly corrode the metallographic structure of the core material Hastelloy, but the whole etching process is very long, generally requiring at least 30 minutes, and the etching process is unstable and has low repeatability. At the same time, after a long time of etching with aqua regia, the outer metal material is severely corroded, and may even fall off. The core metal material Hastelloy will also be etched, resulting in an uneven surface for microstructure observation, which affects the results of metallographic microscopy. (2) Copper sulfate hydrochloric acid alcohol solution, by wiping the sample surface, cannot corrode the microstructure of the core metal material. Only the outer metal will be gradually over-etched over time.

[0004] Therefore, there is a need to develop a metallographic etching method that can rapidly etch out the metallographic structure of Hastelloy core material. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a metallographic etching method for Hastelloy cored wire. This method, by controlling the composition ratio of the etching solution, uses sulfuric acid as a component and adds hydrogen peroxide as a catalyst, making the etching solution more reactive and effectively preventing electrochemical reactions. This ensures the rapid and clear visualization of the Hastelloy core material's metallographic structure, improving the accuracy and efficiency of metallographic detection results, and significantly shortening the etching time. It solves the problem that the inconsistent corrosion rates of the inner and outer metal layers in existing cored wire materials prevent the observation of the Hastelloy core's microstructure.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a metallographic etching method for a Hastelloy core-coated wire, characterized in that the method includes the following steps: Step 1: Machining the core-coated wire of the Hastelloy core to form a microstructure observation plane on the core-coated wire; Step 2: Grind the microstructure observation plane of the core-spun wire formed in Step 1 on a metallographic pre-grinding machine, and then place it in a polishing machine for mechanical polishing; Step 3: The microstructure observation plane of the core-spun wire after mechanical polishing in Step 2 is etched with an etching solution to obtain the microstructure observation plane of the core-spun wire to be observed; the ratio of the etching solution by volume is HCl:H2SO4:H2O2=2~3:1:1, wherein the mass fraction of HCl is 95%~98%, the mass fraction of H2SO4 is 36%~38%, and the mass fraction of H2O2 is above 30%.

[0007] The above-mentioned metallographic etching method for a Hastelloy core-coated wire is characterized in that the grinding in step two is as follows: the microstructure observation plane of the core-coated wire is ground with metallographic wet sandpaper of different mesh sizes; wherein, each time the metallographic wet sandpaper is changed, the grinding direction is rotated by 90°.

[0008] The above-mentioned metallographic etching method for a Hastelloy core-coated wire is characterized in that, in step two, 120#, 800# and 1200# metallographic wet sandpaper are used sequentially to grind the microstructure observation plane of the core-coated wire.

[0009] The above-mentioned metallographic etching method for a Hastelloy core-coated wire is characterized in that the polishing agent used in step two is a diamond spray polishing agent with a particle size ranging from 5μm to 2.5μm, and the polishing cloth is a metallographic velvet polishing cloth.

[0010] The aforementioned method for metallographic etching of Hastelloy cored wire is characterized in that, in step three, the microstructure observation plane of the mechanically polished cored wire is immersed in the etching solution using an inverted suspension method. Unlike conventional methods that immerse the entire metallographic sample in the etching solution, this invention uses an inverted suspension method, ensuring that the surface of the microstructure observation plane of the mechanically polished cored wire is suspended at the interface with the etching solution. This means that only the observation surface is in complete contact with the etching solution, without other interference, thus guaranteeing rapid and clear exposure of the Hastelloy core material's metallographic structure.

[0011] The aforementioned method for metallographic etching of Hastelloy cored wire is characterized in that the immersion depth of the microstructure observation plane of the mechanically polished cored wire into the etching solution is less than 2 mm. By controlling the immersion depth, it is ensured that only the surface of the microstructure observation plane of the mechanically polished cored wire comes into contact with the etching solution and is thus etched, avoiding excessive immersion that could introduce corrosion interference from other parts and prevent the acquisition of a good metallographic structure of the Hastelloy core material.

[0012] The metallographic etching method for a Hastelloy core-coated wire described above is characterized in that the etching time is 5s to 10s.

[0013] The aforementioned method for metallographic etching of Hastelloy cored wire is characterized in that the etching solution in step three is prepared by adding HCl, H2SO4, and H2O2 sequentially. In this invention, H2O2 is added as a catalyst after HCl and H2SO4 in the etching solution. Its catalytic effect enhances the activity of the etching solution, strengthens its etching effect, and accelerates the etching rate, thereby preventing electrochemical reactions in the etching solution and allowing the metallographic structure of the Hastelloy core material to be rapidly and clearly revealed.

[0014] The metallographic etching method for a Hastelloy cored wire described above is characterized in that the HCl and H2SO4 are analytical grade reagents.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The present invention first processes the core wire of the Hastelloy core to form a microstructure observation plane, and then grinds, mechanically polishes and etches the microstructure observation plane in sequence. By controlling the composition ratio of the etching solution, the clear and uniform metallographic structure of the core material Hastelloy is etched out very quickly, which greatly improves the accuracy and efficiency of metallographic detection results.

[0016] 2. In existing technologies, the corrosion solutions using hydrochloric acid and nitric acid, as well as the conventional corrosion solution for Hastelloy (1.5g copper sulfate + 20mL hydrochloric acid + 20mL anhydrous ethanol), all undergo electrochemical reactions, resulting in the failure to reveal the metallographic structure of the Hastelloy core material or requiring at least 30 minutes of etching time. This invention not only uses sulfuric acid, which is stronger than nitric acid, as a component of the corrosion solution, but also adds hydrogen peroxide, making the corrosion solution more reactive and effectively preventing electrochemical reactions. This ensures that the metallographic structure of the Hastelloy core material is revealed quickly and clearly, and significantly shortens the etching time.

[0017] 3. The method of the present invention is simple to operate and requires no special equipment, which greatly reduces the corrosion difficulty and investment cost of Hastelloy core wire. Moreover, the corrosion effect is stable, highly repeatable, and widely applicable. It can be applied to the metallographic corrosion of core wire where the outer metal material is more susceptible to corrosion than the core metal material, and both the inner and outer metals are corroded by the same acid in the corresponding metallographic etchant.

[0018] 4. Compared with the disadvantages of existing methods that require longer etching time and cannot obtain good Hastelloy metallographic structure in the core, the method of the present invention shortens the etching time from at least 30 minutes to 5 seconds and has excellent etching effect, which has obvious advantages.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in Embodiment 1 of the present invention.

[0021] Figure 2 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in Embodiment 2 of the present invention.

[0022] Figure 3 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in Embodiment 3 of the present invention.

[0023] Figure 4 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in Comparative Example 1 of the present invention.

[0024] Figure 5 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0025] Example 1 This embodiment includes the following steps: Step 1: Machining the core wire of the Hastelloy alloy core to form a microstructure observation plane on the core wire; the outer metal of the core wire is 316L stainless steel, and the grade of the Hastelloy alloy core is Alloy 59. Step 2: On a metallographic pre-grinding machine, use 120#, 800# and 1200# metallographic wet sandpaper in sequence to grind the microstructure observation plane of the core-spun wire formed in Step 1. Each time the metallographic wet sandpaper is changed, the grinding direction is rotated 90°. Then, place it in a polishing machine and use diamond spray with a particle size of 5μm and 2.5μm and metallographic velvet polishing cloth for mechanical polishing. Step 3: Using an inverted suspension method, immerse the mechanically polished core-spun filament microstructure observation plane from Step 2 into the etching solution until the immersion depth is less than 2 mm for 5 seconds to obtain the observation plane of the core-spun filament microstructure. The etching solution is prepared by volume ratio of HCl:H2SO4:H2O2=2:1:1, wherein the mass fraction of HCl is 95%~98%, the mass fraction of H2SO4 is 36%~38%, and the mass fraction of H2O2 is above 30%. The etching solution is prepared by adding HCl, H2SO4, and H2O2 in sequence. HCl and H2SO4 are analytical grade reagents.

[0026] Figure 1 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in this embodiment. Figure 1 It can be seen that the Hastelloy wire in the core is slightly corroded, the grain boundaries are visible, and no corrosion is observed at the boundaries between the wires.

[0027] Example 2 The difference between this embodiment and Embodiment 1 is that the etching time in step three is 10 seconds.

[0028] Figure 2 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in this embodiment. Figure 2 It can be seen that the core Hastelloy wire was corroded, and the grain boundaries of the structure were clearly visible, achieving the expected corrosion effect. Furthermore, no corrosion was observed at the boundaries between the wires.

[0029] Example 3 The difference between this embodiment and Embodiment 2 is that the ratio of the corrosion solution is HCl:H2SO4:H2O2=3:1:1.

[0030] Figure 3 This is a metallographic image of the observation plane of the microstructure of the core-spun wire obtained in this embodiment. Figure 3 It can be seen that the core Hastelloy wire was subjected to corrosion, and the grain boundaries of the structure were clearly visible without any interference, achieving the expected corrosion effect. Furthermore, no corrosion was observed at the boundaries between the wires.

[0031] Comparative Example 1 The difference between this comparative example and Example 2 is that this comparative example uses a conventional Hastelloy etching solution prepared by 1.5g copper sulfate, 20mL hydrochloric acid with a mass fraction of 95%~98% and 20mL anhydrous ethanol for etching.

[0032] Figure 4 This is a metallographic image of the observation plane of the core-spun wire microstructure obtained in this comparative example. Figure 4 It can be seen that the grains in the core Hastelloy wire were not visible after being corroded.

[0033] Comparative Example 2 The difference between this comparative example and Example 2 is that a corrosion solution prepared by hydrochloric acid and nitric acid in a volume ratio of HCl:HNO3 = 3:1 was used for immersion for 30 minutes, and then the process was extended to 60 minutes. The mass fraction of HCl was 95%~98%, and the mass fraction of HNO3 was 68%.

[0034] Figure 5 This is a metallographic image of the observation plane of the core-spun wire microstructure obtained in this comparative example. Figure 5 It can be seen that the outline of the Hastelloy core wire in the core-coated wire gradually appears. Even if the etching time is extended from 30 min to 60 min, its grains still cannot be observed. Moreover, the excessive etching time has caused the outer metal material to be severely over-corroded, with corrosion pits or even detachment.

[0035] Comparing Example 2 with Comparative Examples 1 and 2, it can be seen that, compared with the corrosion solutions using hydrochloric acid and nitric acid and the conventional corrosion solutions for Hastelloy, the corrosion solution of the present invention has more active corrosion properties, achieving the effect of preventing electrochemical reactions, ensuring that the metallographic structure of the core material Hastelloy is rapidly and clearly revealed, and significantly shortening the corrosion time.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for metallographic etching of a Hastelloy cored wire, characterized in that, The method includes the following steps: Step 1: Machining the core-coated wire of the Hastelloy core to form a microstructure observation plane on the core-coated wire; Step 2: Grind the microstructure observation plane of the core-spun wire formed in Step 1 on a metallographic pre-grinding machine, and then place it in a polishing machine for mechanical polishing; Step 3: The microstructure observation plane of the core-spun wire after mechanical polishing in Step 2 is etched with an etching solution to obtain the microstructure observation plane of the core-spun wire to be observed; the ratio of the etching solution by volume is HCl:H2SO4:H2O2=2~3:1:1, wherein the mass fraction of HCl is 95%~98%, the mass fraction of H2SO4 is 36%~38%, and the mass fraction of H2O2 is above 30%.

2. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, The grinding described in step two involves grinding the microstructure observation plane of the core-spun wire material using metallographic wet sandpaper of different mesh sizes; wherein, each time the metallographic wet sandpaper is changed, the grinding direction is rotated by 90°.

3. The metallographic etching method for a Hastelloy cored wire according to claim 2, characterized in that, In step two, 120#, 800# and 1200# metallographic wet sandpaper were used in sequence to grind the microstructure observation plane of the core-spun wire.

4. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, The polishing agent used in step two is a diamond spray polishing agent with a particle size ranging from 5μm to 2.5μm, and the polishing cloth is a metallographic velvet polishing cloth.

5. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, In step three, the microstructure observation plane of the mechanically polished core-spun wire is immersed in the etching solution using an inverted suspension method.

6. The metallographic etching method for a Hastelloy cored wire according to claim 5, characterized in that, The immersion depth of the microstructure observation plane of the mechanically polished core-spun wire in the corrosion solution is less than 2 mm.

7. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, The etching time is 5s to 10s.

8. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, The order of preparation of the corrosion solution in step three is to add HCl, H2SO4, and H2O2 in sequence.

9. The metallographic etching method for a Hastelloy cored wire according to claim 1, characterized in that, The HCl and H2SO4 were analytical grade reagents.

Images