Method of streamer corrosion of a martensitic stainless steel forging

Abstract

The application provides a method for showing the flow lines of a martensitic stainless steel forging. The method comprises the following steps: step 1, sampling the martensitic stainless steel forging, and the thickness of the sample is between 15 mm and 25 mm; step 2, polishing the surface of the sample so that the roughness of the sample surface is less than or equal to Ra0.8 μm; step 3, removing oil on the surface of the sample; step 4, preparing a corrosion agent by using 450 g-650 g of copper chloride, 180 ml-250 ml of analytical pure hydrochloric acid, 100 ml-150 ml of analytical pure sulfuric acid, 20 g-50 g of lecithin and 2000 ml of water, and corroding the sample in the corrosion agent for 12 h-24 h; and step 5, taking out the sample from the corrosion agent, removing the corrosion products on the surface of the sample, rinsing the sample with water, and then observing the flow lines of the sample.

Description

Technical Field

[0001] This invention relates to the field of stainless steel forging sample preparation technology, specifically a method for flowline corrosion of martensitic stainless steel forgings. Background Technology

[0002] Forging streamlines impart anisotropy to the forging metal, manifested in superior mechanical properties such as strength, plasticity, and toughness along the deformation direction compared to those perpendicular to the deformation direction. Streamlines perpendicular to the deformation direction exhibit stronger resistance to shear stress. When designing and manufacturing parts, streamlines should be aligned with the direction of tensile stress and perpendicular to the external shear stress. Undesirable streamlines such as interrupted flow, eddies, through-flow, and turbulent flow should be avoided to prevent impacting the actual use of the workpiece.

[0003] Streamline detection is mostly performed at low magnification. The stainless steel used in power components is often smelted via electroslag remelting, resulting in low levels of non-metallic inclusions and weak segregation. Its excellent uniformity makes it difficult to visualize flowlines in forgings using conventional methods at low magnification, thus posing challenges to flowline detection.

[0004] Existing methods for preparing stainless steel forging specimens can refer to standard GB / T226-2015. Specifically, the No. 9 etching solution (copper sulfate, hydrochloric acid, and water) listed in Table 2 is used to etch Cr13 type martensitic stainless steel to prepare specimens. The resulting specimen photographs are shown below. Figure 1 As shown, it can only display low-magnification microstructure and cannot display the flow lines of the forging. Summary of the Invention

[0005] To address the problem that low-magnification samples of martensitic stainless steel prepared using existing methods cannot display flow lines, this invention provides a flow line corrosion method for martensitic stainless steel forgings. This corrosion method can clearly display the flow lines of forgings on martensitic stainless steel materials.

[0006] The technical solution is as follows: A method for flow line corrosion of martensitic stainless steel forgings, characterized by the following steps: Step 1, sampling the martensitic stainless steel forgings, with the obtained sample thickness between 15mm and 25mm. Step 2: Polish the sample surface to make the surface roughness less than or equal to Ra0.8μm; Step 3: Degrease the sample surface; Step 4: Prepare an etchant by mixing 450g-650g copper chloride, 180ml-250ml analytical grade hydrochloric acid, 100ml-150ml analytical grade sulfuric acid, 20g-50g lecithin and 2000ml water. Place the sample in the etchant for etching for 12h-24h. Step 5: Remove the sample from the etchant and remove the corrosion products on the surface. Rinse with water, dry and observe the flow lines of the sample.

[0007] Its further features are: The sample surface was degreased using alcohol.

[0008] The beneficial effects of this invention are: the martensitic stainless steel forging samples obtained by this method can clearly show the flow lines, and the etchant is inexpensive, readily available, convenient to use and prepare. Attached Figure Description

[0009] Figure 1 Photographs of the surface of a martensitic stainless steel specimen, showing corrosion using the corrosion methods exemplified in the standard; Figure 2 This is a photograph of the surface of the martensitic stainless steel sample prepared in Example 1. Detailed Implementation

[0010] A method for streamline corrosion of martensitic stainless steel forgings includes the following steps: Step 1, sampling the martensitic stainless steel forgings using methods such as wire cutting / sawing, with a sample thickness between 15mm and 25mm; Step 2, polishing the sample surface to achieve a surface roughness less than or equal to Ra 0.8μm; Step 3, degreasing the sample surface; Step 4, preparing a corrosive agent using 450g-650g copper chloride, 180ml-250ml analytical grade hydrochloric acid, 100ml-150ml analytical grade sulfuric acid, 20g-50g lecithin, and 2000ml water. The corrosive agent primarily utilizes chloride ions to destroy the passivation film on the stainless steel surface during the corrosion reaction, hydrogen ions to uniformly corrode the sample surface, copper ions to reveal material inhomogeneities, and lecithin as a corrosion inhibitor to significantly slow down the metal corrosion rate, ensuring sufficient contact between the corrosive agent and the sample surface. Through Cu… 2+ cl - H + The appropriate ratio of corrosion inhibitor and corrosion inhibitor can realize the corrosion display of stainless steel flow lines at low magnification. After preparing the corrosion inhibitor, place the sample in the corrosion inhibitor for corrosion, and the corrosion time is 12h-24h. Step 5: Take the sample out of the corrosion inhibitor and remove the corrosion products on the surface. After rinsing with water and drying, observe the flow lines of the sample.

[0011] Specifically, Example 1 demonstrates that the sample prepared using the above method can display clear flow lines.

[0012] Step 1: Take a sample from the Cr13 type martensitic stainless steel forging, and obtain a sample thickness of 20mm.

[0013] Step 2: Polish the sample surface to make the sample surface roughness Ra0.8μm.

[0014] Step 3: Use alcohol to degrease the sample surface.

[0015] Step 4: Prepare an etchant using 500g copper chloride, 220ml analytical grade hydrochloric acid, 130ml analytical grade sulfuric acid, 35g lecithin, and 2000ml water. Place the sample in the etchant for etching for 20 hours.

[0016] Step 5: Remove the sample from the etchant and remove the corrosion products on the surface. Rinse with water, dry, and observe the flow lines of the sample under good light.

[0017] Samples such as Figure 2 As shown, it has clearly visible streamlines.

[0018] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for flowline corrosion of martensitic stainless steel forgings, characterized in that, It includes the following steps: Step 1: Take samples from the martensitic stainless steel forgings, and obtain samples with a thickness between 15mm and 25mm. Step 2: Polish the sample surface to make the surface roughness less than or equal to Ra0.8μm; Step 3: Degrease the sample surface; Step 4: Prepare an etchant using 450g-650g copper chloride, 180ml-250ml analytical grade hydrochloric acid, 100ml-150ml analytical grade sulfuric acid, 20g-50g lecithin, and 2000ml water. Place the sample in the etchant for etching for 12h-24h. Step 5: Remove the sample from the etchant and remove the corrosion products on the surface. Rinse with water, dry and observe the flow lines of the sample. The corrosive agent primarily destroys the passivation film on the stainless steel surface through chloride ions in the corrosion reaction, hydrogen ions uniformly corrode the sample surface, copper ions reveal the non-uniformity in the material, and lecithin, as a corrosion inhibitor, significantly slows down the metal corrosion rate, allowing the corrosive agent to fully contact the sample surface.

2. The method for flowline corrosion of martensitic stainless steel forgings according to claim 1, characterized in that: The sample surface was degreased using alcohol.

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