High-strength corrosion-resistant automobile hinge lug and preparation method thereof

Abstract

The invention discloses a high-strength corrosion-resistant automobile hinge lug and a preparation method thereof, and relates to the technical field of automobile part manufacturing, and the automobile hinge lug is prepared from the following raw materials: 0.25%-0.35% of C, 0.20%-0.45% of Si, 1.20%-1.60% of Mn, 0.80%-1.20% of Cr, 0.30%-0.60% of Ni, 0.15%-0.25% of Mo, 0.05%-0.15% of mixed rare earth elements, and the balance of Fe and inevitable impurities. By accurately controlling the adding proportion and proportion of the mixed rare earth elements, deep purification of molten steel and grain refinement are cooperatively achieved, and the tensile strength of a hinge lug base body breaks through 850 MPa and is improved by 25% or above compared with a conventional alloy steel hinge lug.

Description

Technical Field

[0001] The invention relates to the technical field of automobile parts manufacturing, in particular to a high-strength, corrosion-resistant automobile hinge ear and a preparation method thereof. Background Art

[0002] In recent years, with the increasing demand for lightweight and long-life vehicles, automotive hinge lugs, as the core load-bearing components of door hinge systems, have faced increasingly severe challenges in terms of mechanical strength and corrosion resistance. Traditional carbon steel or low-alloy steel hinge lugs are prone to corrosion fatigue fracture in humid and salty environments, and their tensile strength is generally below 600 MPa, making them unable to meet the reliability requirements under high-load conditions.

[0003] Although the industry has tried to use aluminum alloy to reduce weight or galvanized coating for corrosion protection, the former causes the lugs to deform and fail due to insufficient strength, and the latter is prone to peeling at dynamic friction sites, accelerating the electrochemical corrosion process.

[0004] Patent CN106222575B discloses a corrosion-resistant hinge, which has good corrosion resistance and mechanical properties.

[0005] The corrosion-resistant hinge of the above-mentioned patent is made of alloy steel, the constituent elements of which and their mass percentages are: C: 0.10-0.15%, Cr: 1.4-1.6%, Si: 0.14-0.20%, Mn: 0.8-1.15%, Al: 0.03-0.05%, N: 0.008-0.015%, Ti: 0.12-0.22%, S: 0.005-0.022%, V: 0.08-0.15%, P≤0.015%, and the remainder is Fe and unavoidable impurities. It is processed through raw material steelmaking, deep cold treatment, electroplating, passivation, and sealing treatment. The hinge has good corrosion resistance and mechanical properties, but the above-mentioned patent does not solve the inherent corrosion resistance of the material and relies on the surface electroplating layer.

[0006] To this end, the present application proposes a high-strength and corrosion-resistant automobile hinge ear with corrosion resistance and a preparation method thereof. Summary of the Invention

[0007] The object of the present invention is to provide a high-strength, corrosion-resistant automobile hinge ear and a preparation method thereof, so as to solve the technical problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for preparing a high-strength, corrosion-resistant automobile hinge lug, comprising the following steps:

[0009] S1. Molten steel smelting and rare earth addition: weigh the raw materials according to mass percentage, and after refining and deoxidation in an LF furnace, feed rare earth ferrosilicon alloy into molten steel at 1600-1650°C at a feed speed of 80-120m / min. Let it stand for ≥15min before continuous casting into billets;

[0010] S2, controlled rolling and controlled cold forming: heat the billet to 1150-1200℃ and keep it warm for 1-2 hours, and adopt three-stage controlled rolling:

[0011] Rough rolling stage: rolling temperature 1050-1100℃, single pass deformation 15-20%;

[0012] Finishing rolling stage: final rolling temperature 880-920℃, cumulative deformation 40-50%;

[0013] Relaxation stage: air cooling to 700-750℃ after rolling and keeping warm for 10-15min;

[0014] S3. Heat treatment strengthening: quenching and tempering of rolled pieces:

[0015] Oil quenching temperature 850-880℃, holding time 0.5-1h, cooling rate 80-100℃ / s;

[0016] Tempering temperature 550-600℃, keep warm for 1.5-2.5h and then air cool;

[0017] S4. Surface rare earth passivation: immerse the hinged lug in a solution containing 15-25g / L cerium nitrate, 30-50ml / L hydrogen peroxide, 3-5g / L citric acid, and 0.5-1g / L sodium dodecyl sulfate at 40-60°C for 10-20min.

[0018] S5. Composite sealing treatment: Place the passivated parts in a sealing liquid containing 50-65 parts of water-based acrylic resin, 10-15 parts of nano-silicon dioxide, 5-8 parts of silane coupling agent KH-550, 3-6 parts of sodium molybdate, and 100-120 parts of deionized water. Immerse at 70-80°C for 30-45 minutes and cure at 180-200°C for 1-1.5 hours.

[0019] Preferably, in the mixed rare earth elements, Ce accounts for 50-60% of the total rare earth content, La accounts for 30-35%, and Y accounts for 10-15%.

[0020] Preferably, the rare earth element content in the rare earth ferrosilicon alloy is ≥30%, and the Si content is 35-40%.

[0021] Preferably, in step S1, the ladle is left to stand for 15-20 minutes after wire feeding.

[0022] Preferably, the quenching and holding time is 40-50 minutes.

[0023] Preferably, the pH value of the passivation solution is 3.0-3.5.

[0024] Preferably, the nano-silicon dioxide particle size is 20-50 nm.

[0025] Preferably, the final hinge ear performance satisfies:

[0026] Tensile strength ≥850MPa, yield strength ≥650MPa, elongation ≥15%, neutral salt spray corrosion resistance ≥1000h.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention achieves deep purification of molten steel and grain refinement by precisely controlling the addition ratio and proportion of mixed rare earth elements, resulting in a hinge lug base with a tensile strength exceeding 850 MPa, which is more than 25% higher than that of conventional alloy steel hinge lugs.

[0029] 2. This invention uses a three-stage controlled rolling + relaxation and heat preservation process to effectively eliminate the deformation stress of rare earth steel, suppress mixed crystal defects, solve the problem of delayed recrystallization caused by rare earths, and increase the fatigue life of the product by three times;

[0030] 3. This invention uses surface rare earth-molybdenum synergistic passivation and sealing technology to construct a nano-scale dense protective layer on the surface of the hinge lug. Its charge transfer resistance is five times that of conventional galvanized layers, and its salt spray corrosion life exceeds 1000 hours, far exceeding industry standards.

[0031] 4. The present invention optimizes the quenching-tempering window, avoids the brittle temperature zone of rare earth steel, promotes uniform spheroidization of carbides, and achieves a yield strength of 650 MPa while maintaining an elongation of 15%, achieving both high strength and toughness and stress corrosion resistance. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," "the other end," and the like, which indicate positions or relationships, are used solely to facilitate description and simplify the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "provided with," "connected," etc., should be understood in a broad sense. For example, "connected" may refer to a fixed connection, a detachable connection, or an integral connection; it may refer to a mechanical connection or an electrical connection; it may refer to a direct connection or an indirect connection through an intermediate medium; it may refer to internal communication between two components. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] Example 1:

[0036] A high-strength, corrosion-resistant automobile hinge lug and a preparation method thereof, comprising the following contents:

[0037] Material ratio: C 0.28%, Si 0.25%, Mn 1.35%, Cr 0.95%, Ni 0.45%, Mo 0.18%, mixed rare earth elements 0.08%, including Ce 0.048%, La 0.024%, Y 0.008%, and the balance Fe and inevitable impurities;

[0038] Unavoidable impurities include: S≤0.015%, P≤0.020%, O≤0.002%, N≤0.008%, Cu≤0.15%, Sn≤0.03%, As≤0.02%, Pb≤0.002%, and the total amount of impurity elements ≤0.10%.

[0039] Preparation steps:

[0040] S1. The raw materials are smelted in an LF furnace. After refining and deoxidation, rare earth ferrosilicon alloy is fed into 1620°C molten steel at a speed of 100m / min. The high temperature is used to improve the rare earth yield, with 32% rare earth elements and 38% Si. The reducibility of silicon is used to reduce rare earth oxidation and burning, and the Fe carrier is used to promote the uniform diffusion of rare earth in the molten steel. The steel is allowed to stand for 18 minutes to complete the deoxidation and desulfurization reaction of the rare earth, and then continuously cast into billets.

[0041] S2. The billet is heated to 1180°C and held for 1.5 hours to achieve complete austenitization, followed by three-stage controlled rolling: a single-pass 18% deformation is used to break the original cast structure in the 1080°C rough rolling stage; a cumulative deformation of 45% is used in the 900°C finishing rolling stage to induce recrystallization and refine the grains; and after rolling, the billet is air-cooled to 730°C and held for 12 minutes for relaxation treatment to promote the release of deformation energy through static recrystallization and avoid mixed crystal defects caused by rare earth elements.

[0042] S3. Heat treatment strengthening is performed on the rolled piece. The rolled piece is oil quenched and held at 860°C for 45 minutes to compensate for the increased Ac3 point of the rare earth, inhibit the precipitation of rare earth carbides, ensure the dissolution of carbides, and suppress the segregation of rare earth at a cooling rate of 90°C / s. The rolled piece is then tempered at 580°C for 2 hours to avoid the brittle zone of 400-500°C of rare earth steel. The Mo element is used to stabilize the tempered structure, promote the spheroidization of carbides and eliminate quenching stress. The tempered bainite structure is obtained after air cooling.

[0043] S4. Immerse the hinged ear in a passivation solution containing 20g / L cerium nitrate, 40ml / L hydrogen peroxide, 4g / L citric acid, 0.8g / L sodium dodecyl sulfate, pH=3.2, and treat it at 50℃ for 15min. The hydrogen peroxide will remove the Ce 3+ Oxidized to Ce 4+ CeO2 crystal nuclei are formed, and at the same time, they are partially reduced to generate amorphous Ce2O3 under the fluctuation of interface pH, finally forming a core-shell structure composite membrane with CeO2 as the core and Ce2O3 as the shell. Ce2O provides self-healing function, citric acid complexation controls the deposition rate, sodium dodecyl sulfate eliminates bubbles and improves the density of the film layer. After passivation, it is placed in a sealing liquid containing 55 parts of water-based acrylic resin, 12 parts of nano-silica with a particle size of 30nm, 6 parts of silane coupling agent KH-550, 4 parts of sodium molybdate, and 110 parts of deionized water. It is immersed at 75℃ for 40 minutes to allow the nano-silica to fill the micropores of the passivation film. The silane coupling agent KH-550 bridges the resin and the matrix. It is then cured at 190℃ for 1.2 hours to form an organic-inorganic interpenetrating network structure, in which sodium molybdate and CeO2 construct a pn junction semiconductor layer to block electrochemical corrosion.

[0044] Example 2:

[0045] A high-strength, corrosion-resistant automobile hinge lug and a preparation method thereof, comprising the following contents:

[0046] Material ratio: C: 0.32%, Si: 0.40%, Mn: 1.55%, Cr: 1.15%, Ni: 0.55%, Mo: 0.22%, mixed rare earth 0.12%, of which Ce: 0.072%, La: 0.036%, Y: 0.012%, balance Fe and impurities;

[0047] Preparation steps: Repeat the steps of Example 1, adjusting the following parameters:

[0048] Melting: 1650℃ wire feeding, speed 120m / min, standing for 15min and continuous casting;

[0049] Hot rolling and relaxation: rough rolling: 1100℃, deformation 20%, finishing rolling: 920℃, final rolling, deformation 50%, relaxation: 750℃, holding for 10min;

[0050] Heat treatment: oil quenching: 880℃ for 30min, cooling rate 100℃ / s, tempering: 550℃ for 2.5h;

[0051] Surface treatment: Passivation solution: cerium nitrate 25g / L, hydrogen peroxide 50ml / L, citric acid 5g / L, sodium lauryl sulfate 1g / L, pH=3.0;

[0052] Sealing liquid: 65 parts of water-based acrylic resin, 15 parts of nano-silica, 8 parts of silane coupling agent KH-550, 6 parts of sodium molybdate, 120 parts of deionized water;

[0053] Sealing: immersion at 80℃ for 30min, curing at 200℃ for 1h.

[0054] Example 3:

[0055] A high-strength, corrosion-resistant automobile hinge lug and a preparation method thereof, comprising the following contents:

[0056] Material ratio: C: 0.25%, Si: 0.20%, Mn: 1.20%, Cr: 0.80%, Ni: 0.30%, Mo: 0.15%, mixed rare earth elements: 0.05%, including Ce 0.03%, La 0.015%, Y 0.005%, and the balance Fe;

[0057] Preparation steps: Repeat the steps of Example 1, adjusting the following parameters:

[0058] Melting: molten steel temperature 1600℃, feeding speed 80m / min, standing time 20min;

[0059] Hot rolling: rough rolling: starting rolling temperature 1050℃, single pass deformation 15%, finishing rolling: final rolling temperature 880℃, cumulative deformation 40%, relaxation: 700℃ holding time 15min;

[0060] Heat treatment: oil quenching: 850℃ for 60min, cooling rate 80℃ / s, tempering: 600℃ for 1.5h;

[0061] Surface treatment: Passivation solution: cerium nitrate 15g / L, hydrogen peroxide 30ml / L, citric acid 3g / L, sodium lauryl sulfate 0.5g / L;

[0062] Sealing liquid: 50 parts of water-based acrylic resin, 10 parts of nano-silica, 5 parts of silane coupling agent KH-550, 3 parts of sodium molybdate, and 100 parts of deionized water.

[0063] Example 4:

[0064] A high-strength, corrosion-resistant automobile hinge lug and a preparation method thereof, comprising the following contents:

[0065] Material ratio: C: 0.35%, Si: 0.45%, Mn: 1.60%, Cr: 1.20%, Ni: 0.60%, Mo: 0.25%, mixed rare earth elements: 0.15%, including Ce 0.08%, La 0.05%, Y 0.02%, and the balance Fe;

[0066] Preparation steps: Repeat the steps of Example 1, adjusting the following parameters:

[0067] Hot rolling: Finishing rolling stage final rolling temperature 910℃, cumulative deformation 48%;

[0068] Heat treatment: Tempering temperature 570℃ for 2h;

[0069] Sealing treatment: curing temperature 195℃ and heat preservation for 1.3h.

[0070] Example 5:

[0071] A high-strength, corrosion-resistant automobile hinge lug and a preparation method thereof, comprising the following contents:

[0072] Material ratio: C: 0.30%, Si: 0.35%, Mn: 1.45%, Cr: 1.00%, Ni: 0.50%, Mo: 0.20%, mixed rare earth elements: 0.10%, including Ce 0.06%, La 0.03%, Y 0.01%, and the balance Fe.

[0073] Comparative Example 1:

[0074] The difference from Example 1 is that no rare earth element is added, mixed rare earth is removed from the composition, and the other steps are the same.

[0075] Comparative Example 2:

[0076] The difference from Example 1 is that the mixed rare earth is changed to single Ce, with a total amount of 0.08%. The other steps are the same.

[0077] Comparative Example 3:

[0078] Difference from Example 1: Surface treatment is changed to traditional galvanizing:

[0079] Plating solution: Zn 2+ 20g / L, Ni2+ 2g / L, NaOH150g / L;

[0080] Electroplating conditions: 40°C, current density 3A / dm 2 , time 30 minutes;

[0081] Chromate passivation replaces rare earth passivation, and the other steps are the same.

[0082] Comparative Example 4:

[0083] The difference from Example 1 is that the passivation solution removes citric acid, and the other steps are the same.

[0084] The high-strength, corrosion-resistant automobile hinge lugs prepared in Examples 1-5 and Comparative Examples 1-4 were tested according to GB / T228.1, GB / T 10125, and GB / T 6394 standards. Detailed results are shown in Table 1.

[0085] Table 1 Data comparison table

[0086] sample Tensile strength (MPa) Yield strength (MPa) Elongation (%) Salt spray time (h) Example 1 827 668 16 1024 Example 2 891 685 15 1050 Example 3 855 652 17 1005 Example 4 905 698 15 1076 Example 5 880 670 16 1035 Comparative Example 1 735 520 20 420 Comparative Example 2 850 645 15 920 Comparative Example 3 865 655 16 580 Comparative Example 4 865 660 16 780

[0087] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A high-strength, corrosion-resistant automobile hinge lug, characterized by: The automobile hinge lug is made of the following raw materials: C: 0.25-0.35%, Si: 0.20-0.45%, Mn: 1.20-1.60%, Cr: 0.80-1.20%, Ni: 0.30-0.60%, Mo: 0.15-0.25%, mixed rare earth elements: 0.05-0.15%, and the balance is Fe and unavoidable impurities; In the mixed rare earth elements, Ce accounts for 50-60% of the total rare earth content, La accounts for 30-35%, and Y accounts for 10-15%. The specific mass percentages are: Ce: 0.03%–0.08%; La: 0.02%–0.05%; Y: 0.005%–0.02%。 2. A method for preparing a high-strength, corrosion-resistant automobile hinge lug, applicable to the high-strength, corrosion-resistant automobile hinge lug according to claim 1, characterized in that: The preparation method comprises the following steps: S1, smelting molten steel according to the above ratio, adding rare earth ferrosilicon alloy to the molten steel at 1600-1650°C after deoxidation, stirring and continuously casting into billets; S2. Heat the steel billet to 1150-1200℃ and keep it for 1-2h, then hot roll it at 880-920℃, with the rolling deformation ≥60%; S3. Quench and temper the rolled piece at an oil quenching temperature of 850-880°C and a holding time of 0.5-1h; tempering at a temperature of 550-600°C and a holding time of 1.5-2.5h; S4. Perform rare earth passivation treatment on the surface of the hinge lug by immersing it in a solution containing 15-25 g / L cerium nitrate and 30-50 ml / L hydrogen peroxide at a temperature of 40-60° C. for 10-20 minutes; S5. Place the passivated hinged ear in a sealing liquid for sealing.

3. The method for preparing a high-strength, corrosion-resistant automobile hinge lug according to claim 2, characterized in that: The hot rolling adopts three-stage controlled rolling: Rough rolling stage: starting rolling temperature 1050-1100℃, single pass deformation 15-20%; Finishing rolling stage: final rolling temperature 880-920℃, cumulative deformation 40-50%; Relaxation stage: After rolling, air cool to 700-750℃ and keep warm for 10-15 minutes.

4. The method for preparing a high-strength, corrosion-resistant automobile hinge lug according to claim 2, characterized in that: The quenching cooling rate is 80-100°C / s, and the quenching is performed after tempering and air cooling to room temperature.

5. The method for preparing a high-strength, corrosion-resistant automobile hinge lug according to claim 2, characterized in that: The passivation solution also contains 3-5 g / L of citric acid and 0.5-1 g / L of sodium lauryl sulfate.

6. The method for preparing a high-strength, corrosion-resistant automobile hinge lug according to claim 2, characterized in that: The sealing liquid is composed of the following components: 50-65 parts of water-based acrylic resin, 10-15 parts of nano-silicon dioxide, 5-8 parts of silane coupling agent KH-550, 3-6 parts of sodium molybdate, and 100-120 parts of deionized water.

7. The method for preparing a high-strength, corrosion-resistant automobile hinge lug according to claim 2, characterized in that: The sealing treatment conditions are: The temperature is 70-80℃, the time is 30-45min, and the curing conditions are 180-200℃ and insulation for 1-1.5h.

8. The high-strength, corrosion-resistant automobile hinge lug according to claim 1, characterized in that: The mechanical properties of the hinge ear meet the following requirements: tensile strength ≥850MPa, yield strength ≥650MPa, elongation ≥15%, and salt spray corrosion resistance time ≥1000h.