A method for nitriding and strengthening an alloy case, a case nitriding alloy and applications thereof
Patent Information
- Application Number
- CN202411025841.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-29
- Publication Date
- 2026-09-29
- Estimated Expiration
- 2044-07-29
AI Technical Summary
目前常用的表面渗氮方法为氮化炉气体渗氮和辉光放电离子渗氮，上述两种渗氮工艺，氮在钢中扩散系数低，导致渗氮层较薄(一般为200μm左右)，渗氮过程中极大可能会造成试样表面白亮层的产生，导致渗氮层脆性增加，钢材使用过程中表面硬度、耐磨性和疲劳强度下降，无法满足钢材在较为苛刻条件下应用的表面需求
[0017]本发明提供了一种合金表层的渗氮强化方法，包括以下步骤：将合金基材在真空氛围和氮气氛围下采用等离子弧进行熔融渗氮，在所述合金基材表面得到渗氮层；所述渗氮层的厚度为≥2mm；所述等离子弧的参数包括：等离子气为氩气，等离子枪气流量为5～15L/min；电流为120～180A，等离子弧移动速度为2～4s/cm2。本发明等离子弧进行熔融渗氮是以等离子体作为热源，瞬间释放高温(4000～6000℃)，使合金基材表层熔化，且由于等离子弧能量高(等离子弧的能量密度通常为1000～100000W/cm2)，氮分子吸收热量后内能增加，瞬间解离为氮原子，在熔体中扩散系数增加，使氮原子融进熔体中，合金基材表层凝固后氮的浓度远远大于热力学的氮饱和度，在合金基材表面实现高效渗氮。由本发明实施例结果可知，本发明合金基材表面的渗氮层的厚度为≥2mm，有效提高了合金基材表面硬度和抗疲劳性能，延长合金基材使用寿命，增强合金基材使用过程中稳定性，满足合金基材在高温、高速、重载等严苛环境下使用要求。
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Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the technical field of alloy surface strengthening, and particularly relates to a nitriding strengthening method for an alloy surface layer, a surface layer nitriding alloy and application thereof. BACKGROUND
[0002] With the rapid development of science and technology and economy, steel is used in harsh environments of high temperature, high speed and heavy load, and the quality of the steel has a decisive influence on the performance, service life and reliability of mechanical equipment. Improving the surface hardness, fatigue resistance and corrosion resistance of the steel and prolonging the service life of the steel are the current research direction and goal of the steel. In addition, the steel with surface cracks, pits, scratches and other defects caused by the production and processing process of the steel also needs to be repaired and further enhanced in surface quality by surface strengthening technology.
[0003] To solve the problem of the surface quality of the steel and improve the surface hardness and strength of the steel, the surface of the steel is often strengthened by surface nitriding, carburizing or surface coating. Among them, the surface nitriding process causes lattice distortion by solid solution of nitrogen atoms in the steel base material, improves the strength of the steel, and fine dispersed nitrogen-containing precipitates can refine the grain and hinder the migration of dislocations, playing the role of precipitation strengthening. The commonly used surface nitriding methods are nitriding furnace gas nitriding and glow discharge ion nitriding. The above two nitriding processes have low nitrogen diffusion coefficient in the steel, resulting in a thin nitriding layer (generally about 200 μm). During the nitriding process, the sample surface white layer is likely to be produced, which increases the brittleness of the nitriding layer, and the surface hardness, wear resistance and fatigue strength of the steel during use are reduced, which cannot meet the surface requirements of the steel under harsh conditions. SUMMARY
[0004] The purpose of the present application is to provide a nitriding strengthening method for an alloy surface layer, a surface layer nitriding alloy and application thereof. The present application adopts plasma arc for molten nitriding to obtain a nitriding layer with a thickness of ≥2 mm on the surface of the alloy base material, without producing a surface white layer, and the alloy base material after nitriding strengthening has excellent hardness, wear resistance and fatigue strength.
[0005] In order to achieve the purpose of the present application, the present application provides the following technical solutions:
[0006] A nitriding strengthening method for an alloy surface layer, comprising the following steps:
[0007] The alloy base material is subjected to molten nitriding by plasma arc in a nitrogen atmosphere to obtain a nitriding layer on the surface of the alloy base material; the thickness of the nitriding layer is ≥2 mm;
[0008] The parameters of the plasma arc include: the plasma gas is argon, the plasma gun gas flow is 5-15 L / min, the current is 120-180 A, and the plasma arc moving speed is 2-4 s / cm 2 .
[0009] Preferably, the pressure of the nitrogen atmosphere is 0.07-0.1 MPa; the nitrogen atmosphere is obtained by introducing nitrogen, and the filling flow of the introduced nitrogen is 5-8 L / min.
[0010] Preferably, a vacuum is performed before the nitrogen is introduced; the vacuum degree of the vacuum is 1x10 -3 -3x10 -3 Pa.
[0011] Preferably, the alloy base material includes steel or titanium alloy.
[0012] Preferably, the thickness of the nitriding layer is 2.0-3.0 mm.
[0013] Preferably, the method further comprises: polishing and cleaning the alloy base material in sequence before the melt nitriding.
[0014] The application further provides a surface layer nitriding alloy, which comprises an alloy base material and a nitriding layer arranged on the surface of the alloy base material; the thickness of the nitriding layer is ≥2 mm; and the nitriding layer is prepared by the nitriding strengthening method according to the above technical solution.
[0015] Preferably, the mass content of nitrogen in the surface layer nitriding alloy is 0.15-0.5%.
[0016] The application further provides an application of the surface layer nitriding alloy according to the above technical solution in automobile manufacturing or aerospace materials.
[0017] The application provides a nitriding strengthening method for a surface layer of an alloy, which comprises the following steps: melt nitriding an alloy base material by using a plasma arc in a vacuum atmosphere and a nitrogen atmosphere to obtain a nitriding layer on the surface of the alloy base material; the thickness of the nitriding layer is ≥2 mm; and the parameters of the plasma arc include: the plasma gas is argon, the plasma gun gas flow is 5-15 L / min, the current is 120-180 A, and the plasma arc moving speed is 2-4 s / cm 2 . The melt nitriding by using the plasma arc is to release high temperature (4000-6000 ℃) instantaneously by using plasma as a heat source, so that the surface layer of the alloy base material is melted, and because the energy of the plasma arc is high (the energy density of the plasma arc is usually 1000-100000 W / cm 2When nitrogen molecules absorb heat, their internal energy increases, causing them to instantly dissociate into nitrogen atoms. This increases the diffusion coefficient in the melt, allowing the nitrogen atoms to dissolve into the melt. After the alloy substrate surface solidifies, the nitrogen concentration is far greater than the thermodynamic nitrogen saturation, achieving highly efficient nitriding on the alloy substrate surface. As shown in the results of the embodiments of this invention, the thickness of the nitrided layer on the surface of the alloy substrate is ≥2mm, effectively improving the surface hardness and fatigue resistance of the alloy substrate, extending its service life, enhancing its stability during use, and meeting the requirements for use in harsh environments such as high temperature, high speed, and heavy load. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a structural diagram of a plasma furnace;
[0020] Figure 2 This is a schematic diagram of the nitriding strengthening method for the alloy surface of the present invention;
[0021] Figure 3 This is a flowchart of the nitriding strengthening method for the alloy surface layer in Embodiment 1 of the present invention;
[0022] Figure 4 This is a comparison diagram showing the effects of the nitriding strengthening method for the alloy surface in Example 1 of the present invention, and gas nitriding in a nitriding furnace and glow discharge ion nitriding. Detailed Implementation
[0023] This invention provides a nitriding strengthening method for alloy surfaces, comprising the following steps:
[0024] The alloy substrate is fused and nitrided using a plasma arc under a nitrogen atmosphere to obtain a nitrided layer on the surface of the alloy substrate; the thickness of the nitrided layer is ≥2mm.
[0025] The parameters of the plasma arc include: the plasma gas is argon, the plasma gun gas flow rate is 5-15 L / min; the current is 120-180 A, and the plasma arc moving speed is 2-4 s / cm. 2 .
[0026] In this invention, unless otherwise specified, all raw materials are preferably commercially available products known to those skilled in the art.
[0027] In this invention, the alloy substrate preferably includes steel or titanium alloy, more preferably steel; the steel includes high-quality steel or plain carbon steel; the high-quality steel is preferably M50 bearing steel or 440C steel; the mass content of nitrogen in the high-quality steel is preferably 0.005-0.10%, more preferably 0.0073-0.0082%.
[0028] In this invention, the pressure of the nitrogen atmosphere is preferably 0.07-0.1 MPa, more preferably 0.08-0.09 MPa; the nitrogen flow rate in the nitrogen atmosphere is preferably 5-8 L / min, more preferably 6-7 L / min.
[0029] In this invention, a vacuum is preferably applied before the molten nitriding; the vacuum level is preferably 1×10⁻⁶. -3 ~3×10 -3 Pa, more preferably 2×10 Pa -3 Pa; the preferred vacuum method includes: using a mechanical pump to reduce the vacuum level inside the furnace to <300 Pa, then starting a Roots pump; after the vacuum level drops to 1 Pa, starting a diffusion pump until the vacuum level inside the furnace is 1 × 10 Pa. -3 ~3×10 -3 Pa.
[0030] In this invention, the parameters of the plasma arc include: the plasma gas is argon; the plasma gun gas flow rate is 5–15 L / min, preferably 10–12 L / min; the current is 120–180 A, preferably 140–160 A; and the plasma arc moving speed is 2–4 s / cm. 2 The preferred value is 3s / cm 2 .
[0031] In this invention, it is also preferred to perform sequential polishing and cleaning on the alloy substrate. The polishing is not specifically limited in this invention. The cleaning reagents preferably include ethanol and acetone. The ethanol is preferably anhydrous ethanol.
[0032] This invention utilizes plasma arc molten nitriding as a heat source, instantly releasing high temperatures (4000–6000°C) to melt the surface layer of the alloy substrate. Furthermore, the plasma arc possesses high energy (its energy density is typically 1000–100000 W / cm²). 2When nitrogen molecules absorb heat, their internal energy increases. In the plasma furnace, nitrogen molecules instantly dissociate into nitrogen atoms, increasing the diffusion coefficient in the melt and allowing nitrogen atoms to melt into the melt. After the surface of the alloy substrate solidifies, the nitrogen concentration is much greater than the thermodynamic nitrogen saturation, achieving efficient nitriding on the surface of the alloy substrate. Compared to carbon, nitrogen is more likely to preferentially combine with Cr, Mo, and V in the alloy melt to exist in steel as a solid solution, or to form fine and dispersed carbon-nitrogen composite precipitates that are uniformly distributed in the steel. This inhibits the formation of large, irregular, and aggregated carbides during the solidification of molten steel. For example, during the nitriding process of steel, nitrogen and carbon elements strengthen through solid solution, precipitates in the steel undergo transformation, the surface of the steel is nitrided after melting and cooling, the microstructure of the steel transforms into martensite, and the bond between the nitrided layer and the steel is strong. Furthermore, due to the rapid resolidification after plasma arc nitriding, scanning electron microscopy reveals that carbides in the nitrided layer have basically disappeared, and there is a clear delamination between the nitrided layer and the substrate. This can significantly enhance the surface hardness and fatigue resistance of the substrate, and extend the service life of high-quality steel.
[0033] The present invention also provides a surface nitriding alloy, comprising an alloy substrate and a nitriding layer disposed on the surface of the alloy substrate; the nitriding layer is prepared by the nitriding strengthening method described in the above technical solution.
[0034] In this invention, the phase composition of the nitrided layer preferably includes Fe2N, Fe3N, and FeN. 0.076 The thickness of the nitrided layer is ≥2mm, preferably 2.44~2.51mm, more preferably 2.48mm; the mass content of nitrogen in the surface nitrided alloy is preferably 0.15~0.5%, more preferably 0.159~0.416%, and even more preferably 0.192~0.273%.
[0035] The present invention also provides the application of the surface nitriding alloy described above in automotive manufacturing or aerospace materials.
[0036] To further illustrate the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, provides a method for strengthening the surface of an alloy layer by nitriding, the surface-nitrided alloy, and its applications. However, these descriptions should not be construed as limiting the scope of protection of the present invention.
[0037] Example 1
[0038] M50 bearing steel (nitrogen content 0.0073%) was wire-cut into specimens measuring 200×150×15mm. The specimen surface was sanded, cleaned sequentially with anhydrous ethanol and acetone, and then placed in a container. Figure 1 In the plasma furnace shown;
[0039] according to Figure 2 The schematic diagram and Figure 3The flowchart describes the nitriding strengthening process for the alloy surface, with the following specific steps:
[0040] Preparation of vacuum and nitrogen atmosphere in the plasma furnace: The vacuum system consists of a three-stage pump: a mechanical pump, a Roots pump, and a diffusion pump. First, start the mechanical pump. Once the vacuum level inside the furnace is less than 300 Pa, start the Roots pump. Continue reducing the vacuum level to 1 Pa, then start the diffusion pump until the vacuum level inside the furnace reaches 3 × 10⁻⁶ Pa. -3 Pa; After vacuum preparation is completed, high-purity nitrogen is introduced into the furnace at a flow rate of 5L / min until the pressure inside the furnace reaches 0.08MPa;
[0041] Plasma arc nitriding was performed, with the following parameters set: argon plasma gun gas flow rate of 10 L / min and plasma arc moving speed of 2 s / cm. 2 The currents are 120A, 140A and 160A respectively.
[0042] The performance of the M50 bearing steel with surface nitriding in Example 1 was tested. The wear test was conducted at a high temperature of 350°C, and the corrosion test was conducted in an electrochemical test in a 3.5% NaCl solution. The test results are shown in Table 1.
[0043] Table 1. Performance test results of surface-nitrided steel in Example 1
[0044]
[0045] As shown in Table 1, the nitrogen content of the bearing steel surface layer increased after plasma arc nitriding according to the present invention, and the nitrided layer thickness was 2.44–2.51 mm. Regarding mechanical properties, the original M50 bearing steel had a hardness of 241 HV0.02. After nitriding at different currents, the hardness increased to 738 HV0.02, 778 HV0.02, and 759 HV0.02, respectively. The hardness from the nitrided layer surface to the substrate showed a gradient decrease, with the surface and subsurface hardness strengthening effect being most significant after nitriding at 140 A current. Compared with the original bearing steel sample, with the increase of nitrogen content in the bearing steel surface layer, the average wear coefficient decreased by approximately 7%, 16%, and 32%, respectively; the wear volume decreased by approximately 44%, 53%, and 69%, respectively; and the volumetric wear rate decreased by approximately 47%, 56%, and 70%, respectively. The corrosion potential increased by 13%, 18%, and 35%, respectively, and the corrosion current density decreased by 25%, 29%, and 35%, respectively.
[0046] Figure 4 This invention implements a nitriding strengthening method for the surface layer of alloy 1, and compares the effects of gas nitriding in a nitriding furnace and glow discharge ion nitriding. (The image shows a comparison of the effects of these methods.) Figure 4 It can be seen that, compared with gas nitriding in a nitriding furnace and glow discharge ion nitriding, the nitriding strengthening method for the alloy surface layer in this invention has a significantly increased thickness and subsurface strengthening distance, resulting in a superior nitriding effect.
[0047] Example 2
[0048] 440C steel (nitrogen content of 0.0082%) was machined into a sample with a size of 200×150×15mm by wire cutting. The surface of the sample was polished with sandpaper, and then cleaned with anhydrous ethanol and acetone in sequence before being placed in a plasma furnace.
[0049] Preparation of vacuum and nitrogen atmosphere in the plasma furnace: The vacuum system consists of a three-stage pump: a mechanical pump, a Roots pump, and a diffusion pump. First, start the mechanical pump. Once the vacuum level inside the furnace is less than 300 Pa, start the Roots pump. Continue reducing the vacuum level to 1 Pa, then start the diffusion pump until the vacuum level inside the furnace reaches 3 × 10⁻⁶ Pa. -3 Pa; After vacuum preparation is completed, high-purity nitrogen is introduced into the furnace at a flow rate of 5L / min until the pressure inside the furnace reaches 0.08MPa;
[0050] Plasma arc nitriding was performed, with the following parameters set: argon plasma gun gas flow rate of 10 L / min, currents of 120 A, 140 A, and 160 A, and plasma arc moving speed of 2 s / cm. 2 .
[0051] The performance of the M50 bearing steel with surface nitriding in Example 2 was tested, and the test results are shown in Table 2.
[0052] Table 2. Performance test results of surface-nitrided steel in Example 2
[0053]
[0054] As shown in Table 2, after nitriding with different plasma arc currents of 120A, 140A, and 160A, the nitrogen content on the surface of 440C steel increased to 0.152%, 0.155%, and 0.192%, respectively. Regarding mechanical properties, the original hardness of 440C steel was 223HV0.02. After nitriding with different parameters, it increased to 457HV0.02, 515HV0.02, and 546HV0.02, respectively. The hardness from the nitrided layer surface to the substrate showed a gradient decrease within the range of 1–3 mm. The surface and subsurface hardness strengthening effect was most significant after nitriding with a current of 160A.
[0055] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.
Claims
1. A method for nitriding strengthening of an alloy surface, characterized in that, The steps are as follows: The alloy substrate is melt-nitrided using a plasma arc in a nitrogen atmosphere to obtain a nitrided layer on the surface of the alloy substrate; the thickness of the nitrided layer is ≥2mm. Before molten nitriding, the alloy substrate is successively polished and cleaned; The parameters of the plasma arc include: argon as the plasma gas, a plasma gun gas flow rate of 5~15 L / min, a current of 120~180 A, and a plasma arc moving speed of 2~4 s / cm. 2 .
2. The nitriding strengthening method according to claim 1, characterized in that, The pressure of the nitrogen atmosphere is 0.07~0.1MPa; the nitrogen atmosphere is obtained by introducing nitrogen gas at a flow rate of 5~8L / min.
3. The nitriding strengthening method according to claim 1, characterized in that, A vacuum is created before introducing nitrogen; the vacuum level is 1×10⁻⁶. -3 ~3×10 -3 Pa.
4. The nitriding strengthening method according to claim 1, characterized in that, The alloy substrate includes steel or titanium alloy.
5. The nitriding strengthening method according to claim 1, characterized in that, The thickness of the nitrided layer is 2.0~3.0 mm.
6. A surface nitriding alloy, characterized in that, It includes an alloy substrate and a nitriding layer disposed on the surface of the alloy substrate; the thickness of the nitriding layer is ≥2 mm; the nitriding layer is prepared by the nitriding strengthening method according to any one of claims 1 to 5.
7. The surface nitriding alloy according to claim 6, characterized in that, The nitrogen content in the surface nitrided alloy is 0.15~0.5% by mass.
8. The application of the surface nitriding alloy of claim 6 or 7 in automotive manufacturing or aerospace materials.
Citation Information
Patent Citations
Method for ion-plasma nitriding of parts from tool steel
RU2599950C1