Surface treatment and heat treatment combined process of a hub adapter

Abstract

This invention proposes a composite surface treatment and heat treatment process for a wheel hub adapter, belonging to the technical field, and includes the following steps: Step 1, workpiece pretreatment; Step 2, multi-stage temperature-controlled tempering heat treatment; Step 3, laser shock peening pretreatment; Step 4, graded controllable gas nitriding treatment; Step 5, preparation of a surface nano-protective layer. This invention proposes a composite surface treatment and heat treatment process for a wheel hub adapter, forming a gradient structure of "high toughness in the core, high hardness in the surface layer, and corrosion resistance" through multi-stage tempering heat treatment, laser shock peening, graded nitriding, and nano-coating. The core hardness reaches 34-38 HRC, and the impact energy is ≥65 J; the residual compressive stress depth of the surface layer reaches 1.2 mm, with a peak value of -700 MPa; the nitrided layer depth is 0.35 mm, and the hardness reaches 850 HV. 0.3 The nano-coating has a friction coefficient ≤0.12 and withstands a 600-hour salt spray test. The synergistic effect of each process significantly improves overall service performance.

Description

Technical Field

[0001] This invention relates to the field of wheel hub adapter processing technology, and more particularly to a composite process of surface treatment and heat treatment for wheel hub adapters. Background Technology

[0002] Wheel adapters (also known as wheel flanges) are key connecting components in automotive wheel systems, used to connect the wheel hub to the axle half-shaft, enabling power transmission and load support. During use, wheel adapters are subjected to cyclic bending loads, torsional moments, and impact loads, resulting in complex stress states that place high demands on the strength, toughness, fatigue life, and surface wear resistance of the materials used. Simultaneously, wheel adapters are exposed to corrosive road environments (salt spray, moisture, mud, etc.), and their surface corrosion resistance directly affects the service life of the components and driving safety.

[0003] Currently, wheel hub adapters are typically manufactured using medium-carbon alloy steels such as 42CrMo and 40Cr, which undergo quenching and tempering heat treatment to achieve good comprehensive mechanical properties. 42CrMo steel, with the addition of approximately 0.15% to 0.25% molybdenum (Mo) to the composition of 40Cr, exhibits significantly better hardenability and toughness than 40Cr, with a tensile strength exceeding 1080 MPa. However, the surface hardness of quenched and tempered wheel hub adapters is usually between 30 and 38 HRC, resulting in limited surface wear resistance and fatigue resistance. Under high-cycle loading, fatigue crack initiation and propagation are prone to occur, especially in stress concentration areas such as threaded holes and flange roots.

[0004] In existing industrial production, to improve the surface performance of wheel hub adapters, single surface strengthening methods such as induction hardening, shot peening, or gas nitriding are often used. For induction hardening, for example, due to the complex geometry of wheel hub adapters (including flange planes, steps, threaded holes, and arc transition areas), it is difficult to ensure the uniformity of heating of irregular surfaces by the induction coil, easily leading to uneven distribution of the hardened layer depth. This can easily result in soft bands or localized overheating at the transition fillet at the flange root, affecting the overall load-bearing capacity. Furthermore, induction hardening usually requires a separate tempering treatment, making the process lengthy. Shot peening introduces a relatively shallow residual compressive stress layer, typically within the range of 0.10–0.20 mm, with a significant increase in surface roughness. Its effect on improving fatigue life is limited by the depth and integrity of the compressive stress layer. Under high-cycle fatigue conditions, when cracks initiate at deeper locations, the shallow residual compressive stress is insufficient to effectively inhibit crack propagation. While traditional gas nitriding can significantly improve surface hardness (up to 600–800 HV), conventional nitriding temperatures are usually in the range of 500℃–550℃, with holding times as long as 20–50 hours. Prolonged holding at these temperatures leads to further tempering and softening of the pre-tempered matrix, causing a decrease in core hardness of 3–6 HRC, thus weakening the overall strength and load-bearing capacity of the part. Simultaneously, the steep hardness gradient between the nitrided layer and the matrix easily leads to stress concentration at the interface under alternating loads, causing nitrided layer spalling failure.

[0005] Furthermore, in existing conventional processes, heat treatment and surface strengthening are usually performed as independent steps, resulting in insufficient process integration. The transfer and waiting of workpieces between different processes leads to extended production cycles and increased energy consumption. Moreover, there is a lack of systematic composite strengthening solutions specifically addressing the characteristics of multiple stress concentration areas in wheel hub adapters. For example, after traditional quenching and tempering heat treatment, the surface hardness and wear resistance of wheel hub adapters are insufficient to meet the requirements of long-term service under high load conditions, especially in stress concentration areas such as the flange root and threaded hole edges, where early fatigue cracks are prone to occur. Existing single surface strengthening methods (such as induction hardening, shot peening, and gas quenching) are also problematic. When applied to complex-shaped wheel hub adapters, bulk nitriding presents challenges such as uneven hardened layer distribution, limited residual compressive stress depth, or matrix softening, making it difficult to achieve synergistic optimization of surface strengthening and core toughness. Furthermore, the temperature range of traditional gas nitriding overlaps with the tempering temperature range of quenched and tempered steel, leading to matrix softening and decreased core hardness over extended periods, thus limiting the simultaneous achievement of surface hardness enhancement and core strength maintenance. Existing processes separate heat treatment and surface treatment steps, resulting in long production flows, high energy consumption, and a lack of integrated strengthening methods, hindering the full realization of material potential. Summary of the Invention

[0006] Based on the technical problems existing in the background art, the present invention proposes a composite process of surface treatment and heat treatment for wheel hub adapters.

[0007] The present invention proposes a composite process of surface treatment and heat treatment for a wheel hub adapter, comprising the following steps:

[0008] Step 1: Workpiece Pretreatment

[0009] Take 42CrMo steel wheel hub adapter workpieces that have been forged and rough machined, with an outer diameter of 150-300mm and a thickness of 25-35mm; clean them with an alkaline cleaning solution in an ultrasonic cleaning device at a cleaning temperature of 50℃-70℃ for 15-30 minutes to remove surface oil and impurities; rinse with deionized water after cleaning and dry at 80℃-100℃ for 20-40 minutes.

[0010] Step 2: Multi-stage temperature-controlled tempering heat treatment

[0011] The pre-treated wheel adapter workpiece from step one is placed in an atmosphere-protected heat treatment furnace and subjected to multi-stage temperature-controlled tempering heat treatment under a nitrogen protective atmosphere, including:

[0012] 1. Preheating stage: Raise the furnace temperature to 550℃~600℃ at a heating rate of 5~8℃ / min, and hold for 30~45min;

[0013] 2. Austenitizing stage: Raise the furnace temperature to 860℃~890℃ at a heating rate of 8~12℃ / min, and hold for 60~90min to fully austenitize the workpiece;

[0014] 3. Stage quenching: The workpiece is quickly transferred to a nitrate isothermal quenching medium at a temperature of 180℃~220℃ and held isothermally for 15~25min to obtain a multiphase structure of lower bainite and martensite; then the workpiece is removed and cooled to room temperature in air.

[0015] 4. Tempering stage: The quenched workpiece is subjected to high-temperature tempering treatment at a temperature of 520℃~560℃ for 90~150min. After the holding time is completed, the workpiece is cooled to room temperature in air.

[0016] Step 3: Laser Shock Enhancement Pretreatment

[0017] The surface of the wheel adapter workpiece after the tempering and heat treatment in step two is subjected to laser shock peening treatment, including: coating the workpiece surface with a black absorption layer (using graphite suspension or black paint) with a thickness of 0.08-0.12 mm, and then applying a transparent constraint layer (using deionized water flowing film) with a thickness of 1.0-1.5 mm on the surface of the absorption layer; using a Nd:YAG pulsed laser with a wavelength of 1064 nm for laser shock peening, with a laser energy of 4-8 J, a spot diameter of 2.5-3.5 mm, an overlap rate of 40%-60%, and a spot scanning speed of 2-4 mm / s, to perform a full-coverage scan of the flange surface, the area around the threaded hole, and the transition area at the flange root of the wheel adapter workpiece.

[0018] Step 4: Staged Controlled Gas Nitriding Treatment

[0019] The wheel adapter workpiece after the laser shock hardening treatment in step three is placed in a gas nitriding furnace for graded and controllable gas nitriding treatment, including:

[0020] 1. First stage of nitriding: Raise the furnace temperature to 480℃~510℃, introduce ammonia gas, control the ammonia decomposition rate at 20%~30%, and nitriding time is 6~12h to form a nitrogen-rich diffusion layer on the surface of the workpiece.

[0021] 2. Second stage of nitriding: The furnace temperature is raised to 520℃~540℃, the ammonia decomposition rate is controlled at 35%~45%, and the nitriding time is 8~16h, which promotes the diffusion of nitrogen atoms into the deeper layers and forms a dense ε-Fe2₋3N compound layer.

[0022] 3. Third stage of nitriding: The furnace temperature is reduced to 460℃~490℃, the ammonia decomposition rate is controlled at 15%~25%, the nitriding time is 3~6h, the nitrided layer structure is stabilized, and the brittleness of the white bright layer is reduced.

[0023] 4. After nitriding is completed, the workpiece is slowly cooled in the furnace to below 150°C, and then removed and cooled to room temperature in the air.

[0024] Step 5: Preparation of Surface Nanoprotective Layer

[0025] The preparation of a nanocomposite protective layer on the surface of the hub adapter workpiece after nitriding treatment in step four includes: immersing the workpiece in an organic-inorganic hybrid coating containing nano-molybdenum disulfide (MoS2) particles and nano-silica (SiO2) particles, with a coating viscosity of 25–35 mPa·s (measured at 25℃), an immersion time of 5–15 min, and a lifting speed of 50–100 mm / min; after immersion and lifting, curing at 100℃–120℃ for 20–40 min, and then curing at 150℃–180℃ for 30–60 min, forming a nanocomposite protective layer with a thickness of 8–15 μm on the surface of the nitrided layer.

[0026] Preferably, the austenitizing temperature in step two is 870℃~880℃, and the holding time is 70~80min.

[0027] Preferably, the nitrate isothermal quenching medium in step two is a mixture of sodium nitrate (NaNO3) and sodium nitrite (NaNO2) in a mass ratio of 1:1, and the isothermal temperature is 190℃~210℃.

[0028] Preferably, the laser energy used in step three for laser shock strengthening is 5-7 J, and the overlap rate is 50%.

[0029] Preferably, in step four, the first-stage nitriding temperature is 490℃~500℃, the ammonia decomposition rate is 25%, and the nitriding time is 8~10h.

[0030] Preferably, in step four, the second-stage nitriding temperature is 530℃~535℃, the ammonia decomposition rate is 40%, and the nitriding time is 12~14h.

[0031] Preferably, in step five, the average particle size of the nano-molybdenum disulfide (MoS2) particles is 50-100 nm, the average particle size of the nano-silica (SiO2) particles is 20-40 nm, and the total mass fraction of the two in the organic-inorganic hybrid coating is 5%-8%.

[0032] Preferably, the nitrogen purity in the atmosphere-protected heat treatment furnace in step two is not less than 99.9%, and the gas flow rate is 2-4 L / min.

[0033] Preferably, the laser shock strengthening coverage area in step three includes the upper and lower surfaces of the flange, the inner walls of all threaded holes and the edge areas of the holes, and the arc transition area at the flange root.

[0034] The surface treatment and heat treatment composite process for a wheel hub adapter proposed in this invention has the following beneficial effects: By organically combining multi-stage temperature-controlled tempering heat treatment with laser shock strengthening, graded controllable nitriding treatment, and the preparation of a surface nano-protective layer, a gradient performance structure of "high toughness in the core, high hardness in the surface layer, and corrosion resistance" is achieved in the wheel hub adapter; the multi-stage temperature-controlled tempering heat treatment enables the workpiece to obtain a dual-phase structure of lower bainite and martensite, with a core hardness of 34-38 HRC, a tensile strength of 1100-1250 MPa, and a Charpy V-notch impact energy of not less than 65 J; laser shock strengthening introduces a residual compressive stress field with a depth of 0.8-1.2 mm on the surface and near the surface layer, with a residual compressive stress peak of -550 MPa to -700 MPa, effectively inhibiting the initiation and propagation of fatigue cracks.

[0035] A staged, controllable gas nitriding process was employed, with three stages of nitriding temperature and ammonia decomposition rate synergistically controlled. The first stage of nitriding (480℃~510℃) formed the initial nitriding layer at a relatively low temperature, preventing excessive softening of the matrix. The second stage of nitriding (520℃~540℃) promoted deep diffusion of nitrogen atoms at an appropriately increased temperature, achieving an effective nitrided layer depth of 0.25~0.35mm. The third stage of nitriding (460℃~490℃) stabilized the nitrided layer structure at a low temperature, effectively controlling the thickness of the white gloss layer within the range of 5~10μm and reducing brittleness. The surface hardness reached 750~850HV. 0.3 Its wear resistance is 2 to 3 times higher than that of traditional quenching and tempering treatment.

[0036] Laser shock peening pretreatment is introduced before nitriding. The dislocation multiplication and grain refinement effect generated by laser shock on the surface and near-surface layer provides more diffusion channels for nitrogen atoms to diffuse during the subsequent nitriding process, which improves the nitriding efficiency by 15% to 25%. At the same time, the hardness gradient of the nitrided layer is more gradual, the interfacial bonding force is increased by more than 20%, and the nitrided layer peeling failure is avoided.

[0037] An organic-inorganic hybrid protective layer containing nano-MoS2 and nano-SiO2 was prepared on the surface of the nitrided layer. Nano-MoS2 endowed the surface with excellent self-lubricating properties (the coefficient of friction was reduced to 0.06-0.12), while nano-SiO2 improved the density and corrosion resistance of the coating. After testing in a neutral salt spray test (ISO9227 standard), the salt spray corrosion resistance time reached 480-600h, which is 3-4 times longer than that of the uncoated workpiece.

[0038] There is a good synergistic effect between the various process steps: the high-density dislocations introduced by laser shock strengthening promote the improvement of nitriding efficiency; the hardened layer formed by nitriding provides a hard bearing foundation for the surface nano-protective layer; the nano-protective layer seals the micro-pores on the surface of the nitrided layer, further improving corrosion resistance. It can be implemented industrially and is suitable for the production of wheel hub adapters made of various medium carbon alloy steels such as 42CrMo, 40Cr, and 40CrNiMo. Attached Figure Description

[0039] Figure 1 This is a flowchart of a composite process for surface treatment and heat treatment of a wheel hub adapter proposed in this invention. Detailed Implementation

[0040] Example 1

[0041] Reference Figure 1 This invention proposes a composite process of surface treatment and heat treatment for a wheel hub adapter. The workpiece material is 42CrMo steel, the outer diameter of the workpiece is 200mm, and the thickness is 30mm. The specific steps are as follows:

[0042] Step 1: Workpiece Pretreatment

[0043] Forged and rough-machined 42CrMo steel wheel hub adapter workpieces were cleaned in an ultrasonic cleaning device using an alkaline cleaning solution (a mixed aqueous solution mainly composed of sodium hydroxide and sodium carbonate) with a pH of 9-10. The cleaning temperature was 60℃ and the cleaning time was 20 minutes. After cleaning, the surface was rinsed with deionized water and dried in a hot air drying oven at 90℃ for 30 minutes.

[0044] Step 2: Multi-stage temperature-controlled tempering heat treatment

[0045] The pretreated workpiece from step one is placed in an atmosphere-protected heat treatment furnace, and nitrogen gas with a purity of 99.99% is introduced at a flow rate of 3L / min.

[0046] Preheating stage: The furnace temperature is raised to 580℃ at a heating rate of 6℃ / min and held for 40min to eliminate residual stress from processing and to homogenize the temperature of the workpiece.

[0047] Austenitizing stage: The furnace temperature is raised to 875℃ at a heating rate of 10℃ / min and held for 80min to fully austenitize the workpiece and dissolve the carbides.

[0048] Graded quenching stage: The workpiece is quickly transferred to a nitrate isothermal quenching medium at a temperature of 200℃ (sodium nitrate and sodium nitrite in a mass ratio of 1:1), and isothermally held for 20 minutes to obtain a dual structure of lower bainite and martensite; then the workpiece is removed and cooled to room temperature in still air.

[0049] Tempering stage: Place the quenched workpiece in a tempering furnace and perform high-temperature tempering treatment at 540℃ for 120 minutes. After the holding time is completed, remove the workpiece and cool it to room temperature in still air.

[0050] Step 3: Laser Shock Enhancement Pretreatment

[0051] Laser shock peening was applied to the surface of the wheel adapter workpiece after the heat treatment in step two. First, a black graphite suspension with a thickness of approximately 0.10 mm was coated onto the workpiece surface as an absorption layer. Then, a flowing deionized water film with a thickness of approximately 1.2 mm was applied to the surface of the absorption layer as a transparent constraint layer. Laser shock peening was performed using a 1064 nm Nd:YAG pulsed laser with a laser energy of 6 J, a spot diameter of 3.0 mm, an overlap rate of 50%, and a spot scanning speed of 3 mm / s. A full-coverage scan was performed on the upper and lower surfaces of the flange, the inner walls and edge areas of all six threaded holes, and the arc transition area at the flange root of the wheel adapter workpiece.

[0052] Step 4: Staged Controlled Gas Nitriding Treatment

[0053] The workpiece after laser shock hardening in step three is placed in a gas nitriding furnace for graded and controlled gas nitriding treatment:

[0054] First stage of nitriding: Raise the furnace temperature to 500℃, introduce ammonia gas, control the ammonia decomposition rate to 25%, and nitriding time to 9 hours;

[0055] Second stage of nitriding: Raise the furnace temperature to 530℃, control the ammonia decomposition rate to 40%, and nitriding time to 12h;

[0056] The third nitriding stage: the furnace temperature is reduced to 480℃, the ammonia decomposition rate is controlled at 20%, and the nitriding time is 4 hours.

[0057] After nitriding is completed, the workpiece is slowly cooled in the furnace to below 150°C, and then taken out and cooled to room temperature in the air.

[0058] Step 5: Preparation of Surface Nanoprotective Layer

[0059] A nanocomposite protective layer was prepared on the surface of the workpiece after nitriding treatment in step four. The workpiece was immersed in an organic-inorganic hybrid coating containing nano-MoS2 particles (average particle size 80 nm) and nano-SiO2 particles (average particle size 30 nm), with a total mass fraction of 6% nanoparticles and a coating viscosity of 30 mPa·s (measured at 25 °C). The immersion time was 10 min, and the pull-out speed was 80 mm / min. After immersion and pull-out, the coating was cured at 110 °C for 30 min, and then cured at 160 °C for 45 min, forming a nanocomposite protective layer with a thickness of approximately 10 μm on the surface of the nitrided layer.

[0060] Performance test results:

[0061] The performance of the wheel hub adapter workpiece processed in Example 1 was tested, and the results are as follows:

[0062] Core hardness: 36.5 HRC;

[0063] Surface hardness: 798 HV 0.3 (Equivalent to 63.5 HRC);

[0064] Effective nitriding layer depth: 0.31mm (with a hardness 50HV higher than the substrate hardness) 0.3 (as a boundary)

[0065] White gloss layer thickness: approximately 7μm;

[0066] Tensile strength: 1180 MPa;

[0067] Surface residual compressive stress: -635MPa;

[0068] Rotational bending fatigue limit (R=-1): increased from 385MPa before treatment to 526MPa, an increase of 36.6%;

[0069] Neutral salt spray test (ISO 9227 standard): 580h, no obvious red rust;

[0070] Coefficient of friction (under dry friction conditions): 0.08~0.10.

[0071] Example 2

[0072] This embodiment provides another composite process for surface treatment and heat treatment of wheel hub adapters. The workpiece material is 42CrMo steel, the workpiece outer diameter is 150mm, and the thickness is 25mm. The specific steps are as follows:

[0073] Step 1: Workpiece Pretreatment

[0074] The same cleaning and drying process as in Example 1 was used, with a cleaning temperature of 50°C, a cleaning time of 30 min, a drying temperature of 80°C, and a drying time of 40 min.

[0075] Step 2: Multi-stage temperature-controlled tempering heat treatment

[0076] Preheating stage: Raise the furnace temperature to 550℃ at a heating rate of 5℃ / min and hold for 45min;

[0077] Austenitizing stage: The furnace temperature is raised to 860℃ at a heating rate of 8℃ / min and held for 90min;

[0078] Stage quenching: isothermal temperature is 180℃, isothermal holding time is 25min;

[0079] Tempering stage: Tempering temperature is 520℃, and holding time is 150min;

[0080] Other conditions are the same as in Example 1.

[0081] Step 3: Laser Shock Enhancement Pretreatment

[0082] The laser energy was 4J, the spot diameter was 2.5mm, the overlap rate was 40%, and the scanning speed was 2mm / s. The coverage area was the same as in Example 1.

[0083] Step 4: Staged Controlled Gas Nitriding Treatment

[0084] First-stage nitriding: temperature 480℃, ammonia decomposition rate 20%, nitriding time 12h;

[0085] Second-stage nitriding: temperature 520℃, ammonia decomposition rate 35%, nitriding time 16h;

[0086] Third-stage nitriding: temperature 460℃, ammonia decomposition rate 15%, nitriding time 6h.

[0087] Step 5: Preparation of Surface Nanoprotective Layer

[0088] The coating viscosity was 25 mPa·s, the impregnation time was 15 min, the lifting speed was 50 mm / min, and the curing conditions were the same as in Example 1.

[0089] Performance test results:

[0090] Cardiac hardness: 34.2 HRC;

[0091] Surface hardness: 755HV 0.3 ;

[0092] Effective nitriding layer depth: 0.27 mm;

[0093] White gloss layer thickness: approximately 5μm;

[0094] Surface residual compressive stress: -558 MPa;

[0095] Rotational bending fatigue limit: increased from 385 MPa before treatment to 498 MPa, an increase of 29.4%;

[0096] Neutral salt spray test: No obvious red rust after 490 hours.

[0097] Example 3

[0098] This embodiment provides another composite process for surface treatment and heat treatment of wheel hub adapters. The workpiece material is 42CrMo steel, the workpiece outer diameter is 300mm, and the thickness is 35mm. The specific steps are as follows:

[0099] Step 1: Workpiece Pretreatment

[0100] The cleaning temperature is 70℃ and the cleaning time is 15 minutes. The drying temperature is 100℃ and the drying time is 20 minutes.

[0101] Step 2: Multi-stage temperature-controlled tempering heat treatment

[0102] Preheating stage: Raise the furnace temperature to 600℃ at a heating rate of 8℃ / min and hold for 30min;

[0103] Austenitizing stage: The furnace temperature is raised to 890℃ at a heating rate of 12℃ / min and held for 60min;

[0104] Stage quenching: isothermal temperature is 220℃, isothermal holding time is 15min;

[0105] Tempering stage: Tempering temperature is 560℃, and holding time is 90 minutes;

[0106] Other conditions are the same as in Example 1.

[0107] Step 3: Laser Shock Enhancement Pretreatment

[0108] The laser energy was 8J, the spot diameter was 3.5mm, the overlap rate was 60%, and the scanning speed was 4mm / s. The coverage area was the same as in Example 1.

[0109] Step 4: Staged Controlled Gas Nitriding Treatment

[0110] First-stage nitriding: temperature 510℃, ammonia decomposition rate 30%, nitriding time 6h;

[0111] Second-stage nitriding: temperature 540℃, ammonia decomposition rate 45%, nitriding time 8h;

[0112] Third-stage nitriding: temperature 490℃, ammonia decomposition rate 25%, nitriding time 3h.

[0113] Step 5: Preparation of Surface Nanoprotective Layer

[0114] The coating viscosity was 35 mPa·s, the impregnation time was 5 min, the lifting speed was 100 mm / min, and the curing conditions were the same as in Example 1.

[0115] Performance test results:

[0116] Cardiac hardness: 37.8 HRC;

[0117] Surface hardness: 842HV 0.3 ;

[0118] Effective nitriding layer depth: 0.34 mm;

[0119] White gloss layer thickness: approximately 9μm;

[0120] Surface residual compressive stress: -689MPa;

[0121] Rotational bending fatigue limit: increased from 385 MPa before treatment to 540 MPa, an increase of 40.3%;

[0122] Neutral salt spray test: No obvious red rust after 610 hours.

[0123] Comparative Example 1 (Traditional Conditioning Process)

[0124] The same 42CrMo steel wheel hub adapter workpiece as in Example 1 was used, and only conventional quenching and tempering heat treatment was performed: austenitizing temperature 860℃, holding for 80 min, oil quenching, tempering at 560℃ for 120 min. Performance test results: core hardness 32.5 HRC, surface hardness 34.2 HRC, surface residual compressive stress approximately -80 MPa, rotational bending fatigue limit 385 MPa, obvious red rust appeared after 120 h of neutral salt spray test, and the coefficient of friction was 0.45~0.55.

[0125] Comparative Example 2 (Temperature treatment and single-gas nitriding)

[0126] Using the same workpiece as in Example 1, conventional quenching and tempering heat treatment was first performed (same as Comparative Example 1), followed by single-gas nitriding: nitriding temperature 530℃, ammonia decomposition rate 35%, and nitriding time 21 hours. Performance test results: surface hardness 742 HV. 0.3 The effective nitriding layer depth is 0.22 mm, the core hardness is reduced to 28.5 HRC (4 HRC lower than before treatment), the surface residual compressive stress is about -310 MPa, the rotational bending fatigue limit is 428 MPa, and red rust appears after 280 h of neutral salt spray test.

[0127] Performance comparison of each embodiment with the comparative example:

[0128] Performance indicators Comparative Example 1 (Traditional Conditioning) Comparative Example 2 (Tempering and single nitriding) Example 1 Example 2 Example 3 Heart hardness (HRC) 32.5 28.5 36.5 34.2 37.8 <![CDATA[Surface hardness (HV 0.3 )]]> Approximately 340 742 798 755 842 Effective nitriding layer depth (mm) - 0.22 0.31 0.27 0.34 Surface residual compressive stress (MPa) -80 -310 -635 -558 -689 Rotational bending fatigue limit (MPa) 385 428 526 498 540 Salt spray test duration (h) 120 280 580 490 610 dry friction coefficient 0.45～0.55 0.35～0.45 0.08～0.10 0.09～0.12 0.06～0.09

[0129] The comparative data shows that the composite process provided by this invention is significantly superior to the traditional single processing process in all aspects of performance indicators, especially in terms of maintaining core hardness, improving surface residual compressive stress, extending fatigue life and improving corrosion resistance.

[0130] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite process for surface treatment and heat treatment of a wheel hub adapter, characterized in that, Includes the following steps: Step 1: Workpiece pretreatment: Clean and dry the forged and rough-machined wheel hub adapter workpieces; Step 2, Multi-stage temperature-controlled tempering heat treatment: The pre-treated wheel hub adapter workpiece is subjected to preheating, austenitization, staged quenching and tempering treatment in sequence under a protective atmosphere; Step 3, Laser Shock Enhancement Pretreatment: The surface of the hub adapter workpiece after heat treatment is subjected to laser shock enhancement treatment to form a residual compressive stress field on the workpiece surface; Step 4: Staged Controlled Gas Nitriding Treatment: The wheel adapter workpiece after laser shock strengthening is placed in a nitriding furnace and subjected to staged gas nitriding treatment with at least two stages of nitriding temperature and ammonia decomposition rate control. Step 5: Preparation of surface nano-protective layer: Coating the surface of the nitrided wheel adapter workpiece with a coating containing nanoparticles, and curing it to form a nano-composite protective layer.

2. The composite process of surface treatment and heat treatment for a wheel hub adapter according to claim 1, characterized in that, In step one, the workpiece material is selected from 42CrMo steel, 40Cr steel, and 40CrNiMo steel, and the outer diameter of the workpiece is 150-300mm and the thickness is 25-35mm. The cleaning is carried out in an ultrasonic cleaning device using an alkaline cleaning solution at a temperature of 50℃~70℃ for 15~30 minutes. The drying temperature is 80℃~100℃, and the drying time is 20~40min.

3. The composite process of surface treatment and heat treatment for a wheel hub adapter according to claim 1, characterized in that, In step two, the preheating stage raises the furnace temperature to 550℃ to 600℃ at a heating rate of 5 to 8℃ / min and holds it for 30 to 45 minutes. During the austenitization stage, the furnace temperature is raised to 860℃~890℃ at a heating rate of 8~12℃ / min and held for 60~90min. During the graded quenching stage, the workpiece is quickly transferred to a nitrate isothermal quenching medium at a temperature of 180℃~220℃, held isothermally for 15~25 minutes, and then air-cooled to room temperature. During the tempering stage, the temperature is maintained at 520℃~560℃ for 90~150 minutes and then air-cooled to room temperature.

4. The surface treatment and heat treatment composite process for a wheel hub adapter according to claim 3, characterized in that, The nitrate isothermal quenching medium in the graded quenching stage is a mixture of sodium nitrate and sodium nitrite in a mass ratio of 1:1, and the isothermal temperature is 190℃~210℃.

5. The surface treatment and heat treatment composite process for a wheel hub adapter according to claim 1, characterized in that, The laser shock strengthening process in step three includes: coating a black absorption layer with a thickness of 0.08 to 0.12 mm onto the surface of the workpiece, and then applying a transparent constraint layer with a thickness of 1.0 to 1.5 mm onto the surface of the absorption layer; A 1064nm Nd:YAG pulsed laser was used for laser shock, with a laser energy of 4–8J, a spot diameter of 2.5–3.5mm, an overlap rate of 40%–60%, and a spot scanning speed of 2–4mm / s. The laser shock coverage area includes the flange surface, the area around the threaded holes, and the transition area at the flange root.

6. The surface treatment and heat treatment composite process for a wheel hub adapter according to claim 5, characterized in that, The laser energy is 5-7J, and the overlap rate is 50%.

7. The composite process of surface treatment and heat treatment for a wheel hub adapter according to claim 1, characterized in that, The graded controllable gas nitriding treatment in step four includes: the first stage of nitriding: furnace temperature 480℃~510℃, ammonia decomposition rate 20%~30%, and nitriding time 6~12h. Second stage of nitriding: furnace temperature 520℃~540℃, ammonia decomposition rate 35%~45%, nitriding time 8~16h; The third nitriding stage: furnace temperature 460℃~490℃, ammonia decomposition rate 15%~25%, nitriding time 3~6h; After nitriding, the workpiece is slowly cooled in the furnace to below 150°C before being removed and air-cooled.

8. The surface treatment and heat treatment composite process for a wheel hub adapter according to claim 7, characterized in that, The first-stage nitriding temperature is 490℃~500℃, the ammonia decomposition rate is 25%, and the nitriding time is 8~10h; The second-stage nitriding temperature is 530℃~535℃, the ammonia decomposition rate is 40%, and the nitriding time is 12~14h.

9. The composite process of surface treatment and heat treatment for a wheel hub adapter according to claim 1, characterized in that, In step five, the workpiece is immersed in an organic-inorganic hybrid coating containing nano-molybdenum disulfide particles and nano-silica particles. The coating viscosity is 25-35 mPa·s, the immersion time is 5-15 min, and the lifting speed is 50-100 mm / min. After impregnation and lifting, the material is cured at 100℃~120℃ for 20~40 min, and then cured at 150℃~180℃ for 30~60 min to form a nanocomposite protective layer with a thickness of 8~15μm.

10. The composite process of surface treatment and heat treatment for a wheel hub adapter according to claim 9, characterized in that, The average particle size of the nano-molybdenum disulfide particles is 50-100 nm, and the average particle size of the nano-silica particles is 20-40 nm. The total mass fraction of the two in the organic-inorganic hybrid coating is 5%-8%.

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