Method for improving corrosion resistance of precipitation-hardening stainless steel material after heat treatment

Abstract

The invention belongs to the technical field of corrosion prevention of parts, and particularly relates to a method for improving corrosion resistance of a precipitation-hardening stainless steel material after heat treatment, which comprises the following steps: carrying out primary sand blasting treatment on a part, and removing oxidation color and oxide skin on the surface of the material after heat treatment; the part is subjected to acid pickling treatment, and a pollution layer on the surface layer of the sand-blasted material is removed; secondary sand blasting treatment is conducted on the part, and dust on the surface of the material subjected to acid pickling is removed; the turning and / or milling part of the part is machined, so that a surface pollution layer is thoroughly removed, and the surface roughness of the product is reduced; carrying out passivating treatment on the part, removing oil stains on the surface of the material after machining, and forming a layer of passivating film; and the part is sealed, so that a protective film layer is formed on the surface of the passivated material. According to the method, the corrosion resistance of the part is improved, the part can meet the dry-wet alternate salt spray experiment and is not rusted for a long time, and the safety and reliability of the part in the working process are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of part anti-corrosion, and particularly relates to a method for improving the corrosion resistance of precipitation hardening stainless steel materials after heat treatment. Background Art

[0002] Precipitation hardening stainless steel materials such as 0Cr13Ni8Mo2Al, 0Cr17Ni7Al, etc. obtain the best mechanical properties through heat treatment. When not heat-treated, their salt spray corrosion resistance is good. However, after heat treatment of this material, a contamination layer (carburized layer or chromium-depleted layer) often appears on the surface, affecting the corrosion resistance of the material. It is necessary to perform corrosion-resistant modification on the surface of the parts after heat treatment. The commonly used method is to remove the contamination layer by turning or milling. However, the corrosion-resistant time of the parts is limited. Moreover, for parts directly formed by methods such as upsetting after heat treatment, such as hexagon head bolts, gear groove bolts, etc., the parts after upsetting and heat treatment cannot be completely turned, and the contamination layer (carburized layer or chromium-depleted layer) on the surface is not easy to remove, resulting in the risk of rust still existing in the parts after heat treatment. Summary of the Invention

[0003] To overcome the above defects, the purpose of the present invention is to provide a method for improving the corrosion resistance of precipitation hardening stainless steel materials after heat treatment.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A method for improving the corrosion resistance of precipitation hardening stainless steel materials after heat treatment, comprising the following steps:

[0006] S1. Perform primary sandblasting on the parts to remove the oxide color and oxide scale on the surface of the material after heat treatment;

[0007] S2. Perform pickling treatment on the parts to remove the contamination layer on the surface layer of the material after sandblasting;

[0008] S3. Perform secondary sandblasting on the parts to remove the ash adhering to the surface of the material after pickling;

[0009] S4. Perform machining on the turnable and / or millable parts of the parts to completely remove the surface contamination layer and reduce the surface roughness of the product;

[0010] S5. Perform passivation treatment on the parts to remove the oil stain on the surface of the material after machining and form a passivation film;

[0011] S6. Perform sealing treatment on the parts to form a protective film layer on the surface of the passivated material.

[0012] Preferably, in step S1, the primary sandblasting or in step S3, the secondary sandblasting is carried out by blowing sand with white corundum material, and the blowing sand time is 5 - 7 min.

[0013] Preferably, the pickling solution used in the pickling treatment in step S2 is made of the following raw materials: 80-100 g of sulfuric acid, 60-90 g of nitric acid, 30-45 mL of hydrofluoric acid with a mass concentration of 40%, 1-1.5 g of urotropine, and deionized water is added to 1000 mL.

[0014] Preferably, the pickling treatment time in step S2 is 30 to 40 minutes.

[0015] Preferably, the machining removal amount in step S4 is ≥ 0.015 mm.

[0016] Preferably, the passivation treatment of the parts in step S5 includes chemical and / or electrochemical degreasing.

[0017] Preferably, the sealing process in step S6 comprises the following steps:

[0018] Apply the sealing liquid to the surface of the part and cure it at 240-260℃ for 1.5-2.5h to form a protective film layer on the surface of the material.

[0019] Preferably, the protective film layer has a thickness of 5 to 15 μm.

[0020] Preferably, the sealing liquid is made of the following raw materials in parts by weight: 10-15 parts of epoxy resin, 5-10 parts of rutile nano-TiO2, 2-5 parts of phthalic anhydride, 5-10 parts of cyclohexanol and 30-45 parts of acetone.

[0021] Preferably, the method for preparing the blocking solution comprises the following steps:

[0022] Put rutile nano-TiO2, epoxy resin and phthalic anhydride into a beaker, then pour in cyclohexanol and acetone, and stir thoroughly until the phthalic anhydride is completely dissolved.

[0023] The positive beneficial effects of the present invention are:

[0024] 1. The present invention discloses a method for improving the corrosion resistance of precipitation hardened stainless steel materials after heat treatment, wherein the surface of a part after heat treatment by direct forming methods such as pier forming is subjected to a primary sandblasting, pickling, secondary sandblasting, mechanical processing, and passivation treatment to remove the contamination layer (carburized layer or chromium-depleted layer) generated after the heat treatment, and then a sealing liquid is coated on the surface of the part and then cured to form a protective film layer. The protective film layer can improve the corrosion resistance of the surface where the contamination layer is not completely cleaned due to mechanical processing or pickling, perform secondary protection on the entire surface of the part, improve the corrosion resistance of the part, enable the part to meet the dry-wet alternating salt spray test and not generate rust for a long time, ensure the safety and reliability of the part during operation, and avoid the risk of rusting of the part during use.

[0025] 2. The dissolving ability of a single acid for metal oxides is weak, and it is difficult to completely remove the surface contamination layer, so the brightening purpose cannot be achieved. In the pickling solution of the present invention, sulfuric acid, nitric acid, and hydrofluoric acid are used in combination. At the same time, to prevent and reduce the over-corrosion and hydrogen penetration of steel parts during the etching process, hexamine is added as a pickling inhibitor to inhibit the over-corrosion of stainless steel. After the etched surface of the parts is treated with the pickling solution of the present invention, the color is uniform, white, and bright, without over-corrosion phenomenon, and the pickling solution has a long service life.

[0026] 3. Rutile nano-TiO₂ in the sealing liquid of the present invention has excellent ultraviolet shielding ability and chemical stability, can effectively block the invasion of ultraviolet rays on the material, and slow down the material aging process. The addition of rutile nano-TiO₂ can also improve the weather resistance and durability of the coating, so that it can still maintain good performance under harsh environments; epoxy resin, as a film-forming substance, has good adhesiveness and mechanical strength, and can firmly fix rutile nano-TiO₂ on the material surface to form a dense protective layer; phthalic anhydride, as a curing agent, undergoes a cross-linking reaction with epoxy resin to form a three-dimensional network structure polymer. This structure makes the coating have higher hardness and wear resistance. At the same time, the addition of phthalic anhydride can also improve the heat resistance and corrosion resistance of the coating, and improve the overall performance of the coating. Cyclohexanol and acetone, as solvents, can adjust the viscosity and drying speed of the coating, making the coating easier to apply and level during the construction process, improving the uniformity and gloss of the coating. At the same time, the volatilization of the solvent can also take away the moisture and impurities in the coating, further improving the quality of the coating. The sealing liquid of the present invention is coated on the surface of the parts to form a protective film layer on the material surface, greatly improving the corrosion resistance of the parts. Brief Description of the Drawings

[0027] Figure 1 The part drawing obtained by the method of Example 1 of the present invention;

[0028] Figure 2 The part drawing obtained by the method of Example 2 of the present invention;

[0029] Figure 3 The part drawing obtained by the method of Comparative Example 1;

[0030] Figure 4 One of the part drawings obtained by the method of Comparative Example 2;

[0031] Figure 5 The other part drawing obtained by the method of Comparative Example 2;

[0032] Figure 6 The part drawing obtained by the method of Comparative Example 3;

[0033] Figure 7 It is the part drawing obtained after processing by the method of Comparative Example 4. Specific Embodiments

[0034] The present invention will be further described below in conjunction with some specific embodiments.

[0035] Embodiment 1

[0036] A method for improving the corrosion resistance of precipitation hardening stainless steel materials after heat treatment. The material is a 0Cr13Ni8Mo2Al gear groove bolt, and the method includes the following steps:

[0037] S1. Perform primary sandblasting on the parts to remove the oxidation color and scale on the surface of the material after heat treatment;

[0038] S2. Perform pickling on the parts to remove the contaminated layer on the surface of the material after sandblasting;

[0039] S3. Perform secondary sandblasting on the parts to remove the ash hanging on the surface of the material after pickling;

[0040] S4. Perform machining on the machinable parts of the parts to completely remove the surface contaminated layer, reduce the surface roughness of the product, and then roll the threads;

[0041] S5. Perform passivation on the parts to remove the oil stain on the surface of the material after machining and form a passivation film;

[0042] S6. Perform sealing on the parts to form a protective film layer on the surface of the passivated material.

[0043] Further, the primary sandblasting in step S1 or the secondary sandblasting in step S3 is carried out by blowing sand with white fused alumina material, and the blowing sand time is 5 min.

[0044] Further, the pickling solution used in the pickling treatment in step S2 is made of raw materials with the following weights: 90 g of sulfuric acid, 70 g of nitric acid, 30 mL of hydrofluoric acid with a mass concentration of 40%, 1 g of hexamethylenetetramine, and deionized water is added to make up to 1000 mL.

[0045] Further, the pickling treatment time in step S2 is 30 min.

[0046] Further, the machining removal amount in step S4 is 0.015 mm.

[0047] Further, the passivation treatment of the parts in step S5 includes removing oil stains by chemical means.

[0048] Further, the sealing treatment in step S6 includes the following steps:

[0049] The sealing liquid is applied to the surface of the part by air spraying and cured at 250°C for 2 hours to form a protective film layer on the surface of the passivated material.

[0050] Furthermore, the protective film layer has a thickness of 10 μm.

[0051] Furthermore, the sealing liquid is made of the following raw materials in parts by weight: 12 parts of epoxy resin, 5 parts of rutile nano-TiO2, 3 parts of phthalic anhydride, 8 parts of cyclohexanol and 40 parts of acetone.

[0052] Furthermore, the method for preparing the blocking solution comprises the following steps:

[0053] Before use, heat the cyclohexanol to 60°C in a water bath to melt it; put rutile nano-TiO2, epoxy resin, and phthalic anhydride into a beaker, then pour in cyclohexanol and acetone, and stir thoroughly until the phthalic anhydride is completely dissolved.

[0054] like Figure 1 The following is the status of the product after 720 hours of dry-wet alternating salt spray test. Figure 1 It can be seen that the parts treated by the embodiment of the present invention did not rust after 720 hours of dry-wet alternating salt spray test, indicating that the method of the present invention can greatly improve the corrosion resistance of the product.

[0055] Example 2

[0056] This embodiment is basically the same as Embodiment 1, and the similarities are not repeated here. Some differences are as follows:

[0057] A method for improving the corrosion resistance of precipitation hardened stainless steel material after heat treatment, the material is 0Cr13Ni8Mo2Al bar, comprising the following steps:

[0058] S1. Perform sandblasting on the parts to remove the oxidation color and oxide scale on the surface of the material after heat treatment;

[0059] S2. Pickling the parts to remove the contamination layer on the surface of the material after sandblasting;

[0060] S3. Perform secondary sandblasting on the parts to remove dust on the surface of the material after pickling;

[0061] S4. Machining the parts that can be turned to completely remove the surface contamination layer and reduce the surface roughness of the product;

[0062] S5. Passivate the parts to remove oil stains on the surface of the materials after machining and form a passivation film;

[0063] S6. Perform sealing treatment on the parts to form a protective film layer on the surface of the passivated material.

[0064] Further, the pickling solution used in the pickling treatment in step S2 is made of raw materials with the following weights: 90 g of sulfuric acid, 60 g of nitric acid, 40 mL of hydrofluoric acid with a mass concentration of 40%, 1.5 g of hexamine, and deionized water is added to make up to 1000 mL.

[0065] Further, the sealing liquid is made of raw materials with the following parts by weight: 15 parts of epoxy resin, 10 parts of rutile-type nano-TiO₂, 5 parts of phthalic anhydride, 10 parts of cyclohexanol, and 45 parts of acetone.

[0066] As Figure 2 shown is the product state after 720 h of the wet-dry alternate salt spray test. From Figure 2 it can be seen that the machinable parts of the parts are machined, the removal amount is 0.015 mm, the surface contamination layer is completely removed, and no rust appears on the product matrix after 720 h of the wet-dry alternate salt spray test.

[0067] Comparative Example 1

[0068] This example is basically the same as Example 1, and the same parts will not be repeated. The differences are as follows: The sealing treatment in step S6 is not carried out, and no protective film layer is formed on the material surface.

[0069] The product state after 720 h of the wet-dry alternate salt spray test is as Figure 3 shown. From Figure 3 it can be seen that rust appears in the gear groove of the product after 720 h of the wet-dry alternate salt spray test without the sealing treatment.

[0070] Comparative Example 2

[0071] This example is basically the same as Example 1, and the same parts will not be repeated. The differences are as follows: The machinable parts of the parts are not machined, the sealing treatment in step S6 is not carried out, and no protective film layer is formed on the material surface.

[0072] The product states after 192 h and 336 h of the wet-dry alternate salt spray test are respectively as Figure 4 and Figure 5 shown. From Figure 4 、 5 it can be seen that the product that is not machined at the machinable parts of the parts and is not sealed can meet the 192 h wet-dry alternate salt spray test, but rust appears in the gear groove at 336 h, and slight rust also appears on the end face of the product head, and it cannot meet the 336 h wet-dry alternate salt spray test without rusting.

[0073] Comparative Example 3

[0074] This embodiment is basically the same as Embodiment 1, and the same parts will not be repeated. The differences are as follows: the pickling treatment time is 12 min, step S4 of machining the machinable parts of the parts is not carried out, step S6 of sealing treatment is not carried out, and a protective film layer is not formed on the material surface.

[0075] As Figure 6 shown is the product state after 2 h of the wet-dry alternate salt spray test. The above test results show that the pickling time of 12 min < 30 min, step S4 of machining the machinable parts of the parts is not carried out, step S6 of sealing treatment is not carried out, and rust appears on the product matrix in a short time, and the rust phenomenon is more serious than that of the product in Comparative Example 2. Therefore, different pickling times have a great influence on the corrosion resistance of the product. It is verified that the pickling time needs to be ≥30 min. However, since this material belongs to high-strength stainless steel, in order to avoid increasing the hydrogen embrittlement risk of the material in the pickling process, the upper limit time of pickling needs to be controlled. Finally, through tests, the pickling treatment time is obtained as 30 - 40 min.

[0076] Comparative Example 4

[0077] This embodiment is basically the same as Embodiment 2, and the same parts will not be repeated. The differences are as follows: the machining removal amount in step S4 is 0.005 mm, step S6 of sealing treatment is not carried out, and a protective film layer is not formed on the material surface.

[0078] As Figure 7 shown is the product state after 1 h of the wet-dry alternate salt spray test. The above test results show that a layer of non-corrosion-resistant pollution layer is generated on the surface layer of the product during the heat treatment process. When the removal amount is small, the pollution layer is not completely removed, and the corrosion resistance is relatively poor. Only after the pollution layer is removed can the corrosion resistance of the material be increased. It is verified that the thickness of the pollution layer is 0.010 - 0.015 mm. Therefore, the machining removal amount for the machinable or millable parts of the parts is ≥0.015 mm. If the removal amount is too low, it will not meet the requirements of the wet-dry alternate salt spray test standard and rust problems will occur.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving the corrosion resistance of precipitation hardening stainless steel materials after heat treatment, characterized in that The steps include: S1. Perform sandblasting on the parts to remove the oxidation color and oxide scale on the surface of the material after heat treatment; S2. Pickling the parts to remove the contamination layer on the surface of the material after sandblasting; S3. Perform secondary sandblasting on the parts to remove dust on the surface of the material after pickling; S4. Perform machining on parts that can be turned and / or milled to completely remove the surface contamination layer and reduce the surface roughness of the product; S5. Passivate the parts to remove oil stains on the surface of the materials after machining and form a passivation film; S6. Perform sealing treatment on the parts to form a protective film layer on the surface of the passivated material.

2. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 1, wherein The primary sandblasting in step S1 or the secondary sandblasting in step S3 uses white corundum material for sandblasting, and the sandblasting time is 5 to 7 minutes.

3. The method for improving the corrosion resistance after heat treatment of a precipitation-hardening stainless steel material according to claim 1, wherein, The pickling solution used in the pickling treatment in step S2 is made of the following raw materials: 80-100 g of sulfuric acid, 60-90 g of nitric acid, 30-45 mL of hydrofluoric acid with a mass concentration of 40%, 1-1.5 g of urotropine, and deionized water is added to 1000 mL.

4. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 3, characterized in that, The pickling treatment time in step S2 is 30 to 40 minutes.

5. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 1, wherein, The machining removal amount in step S4 is ≥ 0.015 mm.

6. The method for improving the corrosion resistance of a precipitation hardening stainless steel material after heat treatment according to claim 1, wherein, The passivation treatment of the parts in step S5 includes chemical and / or electrochemical degreasing.

7. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 1, wherein, The sealing process in step S6 includes the following steps: Apply the sealing liquid to the surface of the part and cure it at 240-260℃ for 1.5-2.5h to form a protective film layer on the surface of the material.

8. The method for improving the corrosion resistance of a precipitation hardening stainless steel material after heat treatment according to claim 7, wherein, The protective film layer has a thickness of 5 to 15 μm.

9. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 7 or 8, characterized in that, The sealing liquid is prepared from the following raw materials in parts by weight: 10-15 parts of epoxy resin, 5-10 parts of rutile nano-TiO2, 2-5 parts of phthalic anhydride, 5-10 parts of cyclohexanol and 30-45 parts of acetone.

10. The method for improving the corrosion resistance of a precipitation-hardening stainless steel material after heat treatment according to claim 9, characterized in that, The method for preparing the blocking solution comprises the following steps: Put rutile nano-TiO2, epoxy resin and phthalic anhydride into a beaker, then pour in cyclohexanol and acetone, and stir thoroughly until the phthalic anhydride is completely dissolved.

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