A method and application of vanadium diffusion in salt bath for low-carbon steel

Abstract

This invention discloses a method and application for vanadium infiltration in a salt bath on low-carbon steel, belonging to the field of coating technology. The invention first nitrids the low-carbon steel to obtain a nitrided layer of a certain thickness. Then, a molten salt is prepared using NaCl, CaCl2, NaF, V2O5, and Al powder. The substitution reaction between Al and V2O5 yields vanadium active atoms. Finally, the nitrided low-carbon steel is immersed in the molten salt for vanadium infiltration, obtaining a vanadium infiltrated layer of a certain thickness, thereby significantly improving the hardness and wear resistance of the low-carbon steel. Furthermore, the nitrided and vanadium-infiltrated low-carbon steel prepared by this invention has a hardness between 2700 and 3360 HV and a wear rate between 0.1 and 1.5 × 10⁻⁶ HV. ‑15 m 3 / Nm, which is far higher than the hardness and wear resistance of low carbon steel with vanadium-dipped layers produced by traditional vanadium-dipped processes.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and particularly relates to a method and application of vanadium diffusion into low-carbon steel using a salt bath. Background Technology

[0002] Low-carbon steel, due to its excellent mechanical properties, has been widely used in various shafts, gears, sliders, and other products. However, its low hardness leads to severe wear during service, easily causing premature failure. Nitriding and carburizing are the mainstream methods to improve the wear resistance of low-carbon steel surfaces, but the hardness of nitrided and carburized layers prepared by existing processes is still very low, making it difficult to meet the friction and wear performance requirements under heavy loads, greatly limiting the industrial application of low-carbon steel. In addition, coatings prepared by physical vapor deposition have high hardness and advantages in wear and corrosion resistance, but the significant difference in hardness between the coating and the low-carbon steel substrate results in low coating adhesion and poor industrial application value.

[0003] Furthermore, although existing vanadium infiltration technology has been widely used to improve the surface hardness and wear resistance of cold work die steels, traditional vanadium infiltration processes require the steel to have a carbon content greater than 0.6 wt.%, such as the SKD11, DC53, and Cr12MoV series of cold work die steels, whose carbon content is typically 1.0–1.3 wt.%. There are currently no reports on how to utilize vanadium infiltration technology to improve the surface hardness and wear resistance of low-carbon steels.

[0004] Therefore, there is an urgent need for a vanadium infiltration technology that can improve the surface hardness and wear resistance of low-carbon steel in order to expand the industrial application value of low-carbon steel. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method and application for vanadium diffusion into low-carbon steel using a salt bath.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for vanadium diffusion into low-carbon steel using a salt bath, comprising the following steps:

[0008] S1. Nitriding treatment is performed on low carbon steel to obtain nitrided low carbon steel;

[0009] S2. Mix NaCl and CaCl2 and heat to obtain a basic salt; then add NaF to the basic salt, let it stand, and then add V2O5 and Al powder to obtain a molten salt;

[0010] S3. Immerse the nitrided low-carbon steel obtained in step S1 into the molten salt obtained in step S2 for vanadium diffusion treatment to obtain nitrided and vanadium-dipped low-carbon steel.

[0011] Steps S1 and S2 are not in any particular order.

[0012] Preferably, in step S1, the carbon content of the low-carbon steel is <0.5 wt.%.

[0013] Preferably, in step S1, the nitriding treatment temperature is 400–700°C, the nitriding treatment time is 1–20 h, and the gas flow rate is 200–600 sccm.

[0014] Preferably, in step S2, the NaCl content in the base salt is 20-80% by mass.

[0015] Preferably, in step S2, the heating temperature is 500-1000℃, and the heating holding time is 1-20h.

[0016] Preferably, in step S2, the amount of NaF added is 1 to 10% of the mass of the base salt.

[0017] Preferably, in step S2, the amount of V2O5 added is 10-30% of the mass of the base salt, the amount of Al powder added is 30-100% of the mass of the base salt, and the atomic ratio of V in V2O5 to Al in Al powder is (0.1-0.8):1.

[0018] Preferably, in step S3, the temperature of the vanadium infiltration treatment is 500-1000℃, the holding time of the vanadium infiltration treatment is 1-20h, and the cooling method of the vanadium infiltration treatment is water cooling.

[0019] The present invention provides a vanadium-diffused layer obtained by the vanadium-diffusion method for low-carbon steel in the salt bath described in the above technical solution.

[0020] The present invention also provides the application of the vanadium infiltration layer described above in molds, fuel cell bipolar plates or medical devices.

[0021] Compared with the prior art, the present invention has the following advantages and technical effects:

[0022] This invention first nitrids low-carbon steel to obtain a nitrided layer of a certain thickness. Then, molten salt is prepared using NaCl, CaCl2, NaF, V2O5, and Al powder. The substitution reaction between Al and V2O5 is used to obtain vanadium active atoms. Finally, the nitrided low-carbon steel is immersed in the molten salt for vanadium diffusion treatment to obtain a vanadium diffusion layer of a certain thickness, thereby significantly improving the hardness and wear resistance of the low-carbon steel.

[0023] The nitrided and vanadium-dipped low-carbon steel prepared by this invention has a hardness between 2700 and 3360 HV and a wear rate between 0.1 and 1.5 × 10⁻⁶ HV. -15 m 3 / Nm, which is far higher than the hardness and wear resistance of low carbon steel with vanadium-dipped layers produced by traditional vanadium-dipped processes. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a SEM image of the transverse interface structure of the vanadium-diffused layer of the nitrided and vanadium-diffused low-carbon steel prepared in Example 1 of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] This invention provides a method for vanadium diffusion into low-carbon steel using a salt bath, comprising the following steps:

[0029] S1. Nitriding treatment is performed on low carbon steel to obtain nitrided low carbon steel;

[0030] S2. Mix NaCl and CaCl2 and heat to obtain a basic salt; then add NaF to the basic salt, let it stand, and then add V2O5 and Al powder to obtain a molten salt;

[0031] S3. Immerse the nitrided low-carbon steel obtained in step S1 into the molten salt obtained in step S2 for vanadium diffusion treatment to obtain nitrided and vanadium-dipped low-carbon steel.

[0032] Steps S1 and S2 are not in any particular order.

[0033] This invention first nitrids low-carbon steel to obtain a nitrided layer of a certain thickness. Then, molten salt is prepared using NaCl, CaCl2, NaF, V2O5, and Al powder. The substitution reaction between Al and V2O5 is used to obtain vanadium active atoms. Finally, the nitrided low-carbon steel is immersed in the molten salt for vanadium diffusion treatment to obtain a vanadium diffusion layer of a certain thickness, thereby significantly improving the hardness and wear resistance of the low-carbon steel.

[0034] In a preferred embodiment, in step S1, the carbon content of the low-carbon steel is <0.5 wt.%, preferably ≤0.45 wt.%.

[0035] In a preferred embodiment, in step S1, the nitriding temperature is 400–700°C, preferably 450–600°C; the nitriding time is 1–20 h, preferably 2–10 h; and the gas flow rate is 200–600 sccm. This invention generates a nitrided layer on the surface of low-carbon steel through nitriding, and the presence of this nitrided layer is beneficial for improving the hardness and wear resistance of the low-carbon steel. By controlling the nitriding process parameters within the above-mentioned ranges, this invention facilitates the acquisition of a dense nitrided layer.

[0036] In a preferred embodiment, in step S1, the pressure of the nitriding treatment is 20-300 Pa, the matrix bias voltage is -300 to -600 V, and the duty cycle is 50-80%; the gas introduced during the nitriding treatment is nitrogen and argon, and the flow ratio of nitrogen to argon is (3-4):1.

[0037] In a preferred embodiment, the thickness of the nitrided layer in the nitrided low-carbon steel obtained in step S1 is approximately 2–40 μm.

[0038] In a preferred embodiment, in step S2, the NaCl content in the base salt is 20-80% by mass. In this invention, NaCl and CaCl2 serve as base salts and act as fluxes.

[0039] In a preferred embodiment, in step S2, the heating temperature is 500–1000°C, preferably 600–1000°C, and the heating holding time is 1–20 h, preferably 2–20 h.

[0040] In a preferred embodiment, in step S2, the amount of NaF added is 1-10% of the mass of the base salt. In this invention, NaF plays a role in improving melt flowability.

[0041] In a preferred embodiment, in step S2, the settling time is 10 to 60 minutes.

[0042] In a preferred embodiment, in step S2, the amount of V2O5 added is 10-30% of the mass of the base salt, and the amount of Al powder added is 30-100% of the mass of the base salt. The atomic ratio of V in V2O5 to Al in Al powder is (0.1-0.8):1, preferably (0.2-0.5):1. This invention controls the amount of V2O5 and Al powder added, as well as the atomic ratio of V2O5 to Al powder, within the above ranges, which is beneficial for obtaining a dense vanadium-infiltrated layer, thereby significantly improving the hardness and wear resistance of low-carbon steel.

[0043] In a preferred embodiment, in step S3, the temperature of the vanadium infiltration treatment is 500–1000°C, preferably 600–1000°C; the holding time of the vanadium infiltration treatment is 1–20 h, preferably 2–10 h; and the cooling method of the vanadium infiltration treatment is water cooling. In this invention, if the vanadium infiltration treatment temperature is too high, the vanadium infiltrated layer will have a loose structure and low hardness; if the holding time is too long, the growth rate of the infiltrated layer will be slow, and energy consumption will be high.

[0044] In a preferred embodiment, the thickness of the vanadium-diffused layer in the nitrided and vanadium-diffused low-carbon steel obtained in step S3 is approximately 5–52 μm.

[0045] The present invention provides a vanadium-diffused layer obtained by the vanadium-diffusion method for low-carbon steel in the salt bath described in the above technical solution.

[0046] The present invention also provides the application of the vanadium infiltration layer described above in molds, fuel cell bipolar plates or medical devices.

[0047] In this embodiment of the invention, room temperature refers to "25±2℃".

[0048] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0049] Example 1

[0050] A method for vanadium diffusion into low-carbon steel using a salt bath, comprising the following specific steps:

[0051] S1. Polish 20CrMnTi steel with a carbon content of about 0.2wt.% to a roughness of ≤0.1μm, then ultrasonically clean it with acetone and anhydrous ethanol for 30min in sequence, and blow it dry with an air gun. Then place it in a plasma nitriding furnace, set the furnace temperature to 550℃, evacuate the vacuum to 20Pa, introduce nitrogen and argon gas at a flow rate of 300sccm, control the nitrogen to argon flow rate ratio at 3:1, set the substrate bias voltage to -500V, the duty cycle to 70%, and nitrid for 5h to obtain nitrided low carbon steel.

[0052] S2. Add NaCl and CaCl2 to a crucible at a mass ratio of 1:2, heat to 600℃, and hold for 2 hours to obtain a basic salt (the basic salt contains 33.3% NaCl and 66.7% CaCl2 by mass). Then add 5% NaF by mass of the basic salt, let stand for 10 minutes, and then add 20% V2O5 by mass of the basic salt and 60% Al powder by mass of the basic salt. The atomic ratio of V in V2O5 to Al in Al powder is 0.33:1. Adjust the temperature to 700℃ to obtain a molten salt.

[0053] S3. Immerse the nitrided low-carbon steel obtained in step S1 into molten salt at a temperature of 700℃ obtained in step S2, keep it at that temperature for 5 hours, take it out and quench it in water to obtain nitrided and vanadium-doped low-carbon steel.

[0054] Figure 1 This is a SEM image of the transverse interface microstructure of the vanadium-diffused layer in the nitrided and vanadium-diffused low-carbon steel prepared in Example 1. Figure 1 It can be seen that a vanadium-infiltrated layer of a certain thickness is formed on the steel surface, with a thickness of about 20μm.

[0055] Examples 2-8

[0056] The difference from Example 1 is that the nitriding temperature, nitriding time, mass ratio of V2O5 to Al powder, vanadium diffusion temperature or vanadium diffusion time are different. Other process parameters and steps are the same as in Example 1. The differences from Example 1 are shown in Table 1.

[0057] Example 9

[0058] The difference from Example 1 is that the 20CrMnTi steel in step S1 is replaced with 08F steel, and the carbon content of 08F steel is 0.08wt.%. Other steps and process parameters are the same as in Example 1.

[0059] Example 10

[0060] The difference from Example 1 is that the 20CrMnTi steel in step S1 is replaced with 45 steel, and the carbon content of 45 steel is 0.45 wt.%. Other steps and process parameters are the same as in Example 1.

[0061] Table 1. Process parameters for nitriding and vanadium diffusion treatments in Examples 1-10

[0062]

[0063] Comparative Examples 1-3

[0064] A method for preparing vanadium-impregnated low-carbon steel, the specific steps of which are as follows:

[0065] S1. 20CrMnTi (Comparative Example 1) with a carbon content of about 0.2 wt.%, 08F steel (Comparative Example 2) with a carbon content of 0.08 wt.%, and 45 steel (Comparative Example 3) with a carbon content of 0.45 wt.% were polished to a roughness of ≤0.1 μm, then ultrasonically cleaned with acetone and anhydrous ethanol for 30 min in sequence, and dried with an air gun to obtain pretreated low carbon steel;

[0066] S2. Add NaCl and CaCl2 to a crucible in a mass ratio of 1:2, heat to 600℃, and hold for 2 hours to obtain the basic salt; then add 5% NaF by mass of the basic salt, let stand for 10 minutes, then add 20% V2O5 by mass of the basic salt and 60% Al powder by mass of the basic salt, with the atomic ratio of V in V2O5 to Al in Al powder being 0.33:1, and adjust the temperature to 700℃ to obtain the molten salt;

[0067] S3. Immerse the pretreated low-carbon steel obtained in step S1 into molten salt at a temperature of 950℃ obtained in step S2, keep it at that temperature for 5 hours, take it out and quench it in water to obtain vanadium-impregnated low-carbon steel.

[0068] Comparative Example 4

[0069] A method for preparing vanadium-infiltrated low-carbon steel using a traditional vanadium infiltration process, the specific steps of which are as follows:

[0070] S1. Polish 20CrMnTi steel with a carbon content of about 0.2wt.% to a roughness of ≤0.1μm, then ultrasonically clean it with acetone and anhydrous ethanol for 30min in sequence, and blow it dry with an air gun.

[0071] S2. Immerse the 20CrMnTi steel treated in step S1 into a traditional vanadium-diffusion molten salt, hold it at 950℃ for 5 hours, remove it and quench it in water to obtain vanadium-diffusion low-carbon steel; wherein, the composition of the traditional vanadium-diffusion molten salt is: 75.6 wt.% borax, 8.4 wt.% BaCl2, 10 wt.% V2O5 and 6 wt.% Al powder.

[0072] Performance testing

[0073] Microhardness test: The coating hardness of the vanadium-infiltrated low-carbon steel prepared in the examples and comparative examples was tested using a microhardness tester with a test load of 100g.

[0074] Wear resistance test: The wear rate of the vanadium-infiltrated low-carbon steel coatings prepared in the examples and comparative examples was tested using a room temperature friction and wear tester. The lower the wear rate, the better the wear resistance.

[0075] The coating hardness and coating wear rate of Examples 1-10 and Comparative Examples 1-4 are shown in Table 2.

[0076] Table 2. Coating performance of Examples 1-10 and Comparative Examples 1-4

[0077]

[0078]

[0079] As shown in Table 2, the hardness of the nitrided and vanadium-dipped low-carbon steels prepared in Examples 1-10 ranges from 2700 to 3360 HV, and the wear rate ranges from 0.1 to 1.5 × 10⁻⁶. -15 m 3 / Nm, its hardness and wear resistance are far higher than those of low carbon steel with vanadium-dipped layers produced by traditional vanadium-dipped processes, and vanadium-dipped treatment of low carbon steel has been successfully achieved.

[0080] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for vanadium diffusion into low-carbon steel using a salt bath, characterized in that, Includes the following steps: S1. Nitriding treatment is performed on low carbon steel to obtain nitrided low carbon steel; the nitriding treatment temperature is 550-600℃, the nitriding treatment time is 1-20h, and the gas flow rate is 200-600sccm. S2. NaCl and CaCl2 are mixed and heated to obtain a basic salt; then NaF is added to the basic salt, and after standing, V2O5 and Al powder are added to obtain a molten salt; the amount of V2O5 added is 10-30% of the mass of the basic salt, the amount of Al powder added is 30-100% of the mass of the basic salt, and the atomic ratio of V in V2O5 to Al in Al powder is (0.2-0.5):1; S3. Immerse the nitrided low-carbon steel obtained in step S1 into the molten salt obtained in step S2 for vanadium diffusion treatment to obtain nitrided and vanadium-dipped low-carbon steel; the temperature of the vanadium diffusion treatment is 600-1000℃, the holding time of the vanadium diffusion treatment is 2-10h, and the cooling method of the vanadium diffusion treatment is water cooling. Steps S1 and S2 are not in any particular order.

2. The method for vanadium diffusion into low-carbon steel using a salt bath according to claim 1, characterized in that, In step S1, the carbon content of the low-carbon steel is <0.5 wt.%.

3. The method for vanadium diffusion into low-carbon steel using a salt bath according to claim 1, characterized in that, In step S2, the NaCl content in the base salt is 20-80% by mass.

4. The method for vanadium diffusion into low-carbon steel using a salt bath according to claim 1, characterized in that, In step S2, the heating temperature is 500-1000℃, and the heating holding time is 1-20h.

5. The method for vanadium diffusion into low-carbon steel using a salt bath according to claim 1, characterized in that, In step S2, the amount of NaF added is 1 to 10% of the mass of the base salt.

6. The vanadium-diffused layer obtained by the salt bath vanadium-diffusion method for low-carbon steel according to any one of claims 1 to 5.

7. The application of the vanadium-impregnated layer according to claim 6 in molds, fuel cell bipolar plates, or medical devices.

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