Gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer, preparation method thereof and connection fitting

Abstract

The invention relates to the technical field of structural materials, in particular to a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer, a preparation method thereof and a connecting fitting. By adopting a specific carbonitriding process and controlling the iron content in the gradient Zn-Fe plating layer, the problem that a carbonitriding layer, the gradient Zn-Fe plating layer and a passivation layer are difficult to form a stable and effective structure is solved; the prepared composite layer not only can improve the strength, wear resistance and corrosion resistance of the surface of the matrix, but also is stable in performance.

Description

Technical Field

[0001] The invention relates to the technical field of structural materials, and in particular to a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer and a preparation method and connecting hardware thereof. Background Art

[0002] As the most important basic material, carbon steel is widely used in industries such as electricity, communications, chemicals, automobiles, and national defense. Taking U-shaped rings, ball head hanging rings and other power fittings as examples, line fittings are exposed to various meteorological conditions all year round, and corrosion occurs all the time. Breeze vibration, dancing, icing, sub-span vibration, wire de-icing and jumping will all cause wear of line fittings to varying degrees, which requires power fittings to have both corrosion and wear conditions. Traditional overhead line connection fittings are generally made of low-alloy steel materials, and the surface is treated with hot-dip galvanizing for corrosion protection. The galvanized layer acts as a sacrificial anode and realizes cathodic protection through its own consumption. Coastal areas are characterized by high temperature, high humidity, high salt and strong winds. Connecting hardware is subjected to the combined effects of high stress, sliding wear and dirty corrosion. The galvanized layer will accelerate degradation. After the galvanized layer is consumed, steel-to-steel wear will form and the body will be directly exposed to a heavy corrosion environment, further aggravating the wear and corrosion of the hardware, causing the hardware to fail and break in a short period of time. Cases of abrasion failure of power hardware in coastal areas are common. On the other hand, with the development of society, people have also put forward higher requirements for the environmental protection and cost of anti-abrasion materials. Therefore, the development of environmentally friendly and low-cost anti-abrasion layers has significant practical significance.

[0003] To improve the corrosion resistance of carbon steel components, zinc-based alloy coatings such as Zn-Ni, Zn-Co, and Zn-Fe have been developed currently. Among them, the Zn-Fe alloy coating has the lowest cost and is more environmentally friendly. However, the alloy structure varies with the Fe content, resulting in significant differences in the performance of the Zn-Fe alloy coating. When the Fe content ≤ 1 wt%, its corrosion resistance can be greatly improved by passivation. For example, Li Xueyuan et al. passivated the Zn-Fe deposition layer with an Fe content of 0.3 wt% - 0.9 wt%. After 1488 hours of neutral salt spray test, no red rust was observed (Li Xueyuan et al., Electrodeposition and Corrosion Resistance of Zn-Fe Alloy Coatings, Acta Aeronautica et Astronautica Sinica, 2000, 21: S58 - S61). At this time, Zn-Fe is in the η phase (Yang Fangzu et al., Relationship between Iron Content and Performance of Zinc-Iron Alloy Coatings, Electroplating & Finishing, 1992, 11(1): 11 - 14), and the hardness value is only 120 - 130 HV (Zeng Xiangde, 20-Year Application Practice of Environmentally Friendly High-Corrosion-Resistant Zinc-Iron Alloy Electroplating Process, Surface Engineering Information, 2010, 5: 10 - 13). Obviously, the Zn-Fe alloy coating with an Fe content ≤ 1 wt% has good corrosion resistance but poor tribological properties. When 23 wt% ≤ Fe content ≤ 28 wt%, it is in the γ phase, and the hardness value can reach 450 - 550 HV (Zhang Sifang, Influence of Fe Content in Zinc-Iron Coating on Coating Structure and Performance of Products, 2013 National Cold Rolled Sheet and Strip Production Technology Exchange Conference, 2013: 125 - 128). However, due to the high iron content, it cannot be passivated conventionally, which affects its corrosion resistance (Cui Ping et al., Study on Electroplating Zinc-Iron Alloy with Low Iron Content in Alkaline Solution, Materials Protection, 2008, 41(9): 31 - 33, 51). Therefore, although the Zn-Fe alloy coating at this time has certain tribological properties, its corrosion resistance is poor. Chen Jie et al. studied a surface coating process for electric power fittings (CN117845164A). After ion plating treatment on the cleaned electric power fittings, nitriding treatment was carried out after etching. Through heat treatment, the coating undergoes phase transformation or changes in crystal structure, and an organic or inorganic coating is applied on the surface. Although this method improves the wear resistance of electric power fittings, its corrosion resistance is poor.

[0004] It can be seen from this that the current single Zn-Fe alloy coating is obviously difficult to meet the requirements of carbon steel components such as electric power fittings in abrasive working conditions. Therefore, the research on composite coatings is extremely necessary. However, there are generally problems with unstable bonding between coatings in composite coatings. Therefore, it is of great significance to develop a new composite layer with wear resistance, fatigue resistance, corrosion resistance, and stable bonding between coatings. Summary of the Invention

[0005] Based on this, the present invention provides a preparation method for a gradient carbonitride zinc-iron corrosion-resistant composite layer. The composite layer prepared by this method can not only improve the strength, wear resistance, and corrosion resistance of the substrate surface but also has stable performance.

[0006] The gradient carbonitride zinc-iron corrosion-resistant composite layer provided by the present invention has excellent, stable and effective wear and corrosion resistance.

[0007] The connecting fitting provided by the present invention has excellent wear and corrosion resistance and a long service life.

[0008] The present invention realizes the above technical purpose through the following technical solutions:

[0009] A preparation method of a gradient carbonitride zinc-iron corrosion-resistant composite layer includes the following steps:

[0010] Step 1, performing quenching and tempering heat treatment on the substrate;

[0011] Step 2, shot peening the substrate after quenching and tempering heat treatment, then performing carbonitriding treatment to form a carbonitriding layer on its surface and then performing cooling treatment; wherein, the process of carbonitriding treatment is: under vacuum conditions, heating to 480 - 560 °C, introducing a nitriding agent and a carburizing agent, controlling the flow ratio of the gaseous nitriding agent to be 90 - 95%, the first stage: controlling the nitrogen potential to be 0.8 - 1.2, the flow rate of the gaseous nitriding agent to be 0.6 - 1.2 m 3 / h, holding for 2 - 4 hours; the second stage: controlling the nitrogen potential to be 0.4 - 0.8, the flow rate of the gaseous nitriding agent to be 0.3 - 0.6 m 3 / h, holding for 4 - 8 h;

[0012] Step 3; after cleaning the substrate after carbonitriding treatment, depositing a gradient Zn-Fe coating with the iron content gradually decreasing from 8 - 30 wt% to 0.03 - 1.0 wt%;

[0013] Step 4: Performing passivation treatment to form a passivation layer on its surface and then trimming to obtain the gradient carbonitride zinc-iron corrosion-resistant composite layer.

[0014] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the cooling treatment is to first cool in an atmosphere environment of argon or a gaseous nitriding agent until the substrate temperature is below 100 °C and then take it out of the furnace and cool to room temperature.

[0015] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the gaseous nitriding agent is ammonia gas, and the gaseous carburizing agent is carbon dioxide.

[0016] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the gradient Zn-Fe coating includes a high-iron Zn-Fe coating and a low-iron Zn-Fe coating, the iron content in the high-iron Zn-Fe coating is 8 - 30 wt%, and the iron content in the low-iron Zn-Fe coating is 0.03 - 1.0 wt%.

[0017] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the thickness of the high-iron Zn-Fe coating is 6-15 μm, and the thickness of the low-iron Zn-Fe coating is 6-15 μm.

[0018] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the thickness of the carbonitriding layer is 100-250 μm.

[0019] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, in step 1, the substrate is modulated and heat-treated to a hardness of 300-360 HBW.

[0020] According to the preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer described above, the substrate is a carbon steel or medium-low alloy steel component.

[0021] A gradient carbonitride zinc-iron corrosion-resistant composite layer, which successively includes a carbonitriding layer formed on a substrate, a gradient Zn-Fe coating with an iron content gradually decreasing from 8-30 wt% to 0.03-1.0 wt%, and a passivation layer.

[0022] The gradient carbonitride zinc-iron corrosion-resistant composite layer described above is prepared by the above method.

[0023] The gradient carbonitride zinc-iron corrosion-resistant composite layer described above successively includes a carbonitriding layer formed on a substrate, a high-iron Zn-Fe coating with an iron content of 8-30 wt%, a low-iron Zn-Fe coating with an iron content of 0.03-1.0 wt%, and a passivation layer.

[0024] A connecting fitting, the surface of which is the above-mentioned gradient carbonitride zinc-iron corrosion-resistant composite layer.

[0025] The preparation method of the gradient carbonitride zinc-iron corrosion-resistant composite layer provided by the present invention solves the problem that it is difficult to form a stable and effective structure for the carbonitriding layer, the gradient Zn-Fe coating, and the passivation layer, and can ensure the stable and effective performance of the prepared composite layer.

[0026] The gradient carbonitride zinc-iron corrosion-resistant composite layer provided by the present invention improves the surface strength, wear resistance, and corrosion resistance of the substrate through the synergistic effect of the carbonitriding layer, the gradient Zn-Fe coating, and the passivation layer. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the gradient carbonitride zinc-iron corrosion-resistant composite layer described in an embodiment of the present invention;

[0028] Figure 2 It is a schematic diagram of the measurement sites of the hardness and thickness of the carbonitriding layer in Example 1 of the present invention;

[0029] Figure 3 Hardness measurement results of the carbonitriding layer with different thicknesses in Example 1 of the present invention;

[0030] Figure 4 Metallographic inspection result diagram after carbonitriding in Example 1 of the present invention;

[0031] Figure 5 Surface morphology diagram of the connecting fitting prepared in Example 1 of the present invention after neutral salt spray corrosion for 3600 h.

[0032] In the figure, 1 is the substrate, 2 is the carbonitriding layer, 3 is the high-iron Zn-Fe coating, 4 is the low-iron Zn-Fe coating, and 5 is the passivation layer. Detailed implementation manners

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Based on the problem that the current single Zn-Fe alloy coating is difficult to meet the usage requirements of carbon steel components such as electric power fittings in abrasion working conditions, and the composite coating is unstable. The present invention manufactures a carbonitriding layer on the substrate through a specific carbonitriding process, and further manufactures a gradient zinc-iron coating with a specific iron content on the carbonitriding layer, solving the problem of unstable composite coating, and through the synergistic effect of the carbonitriding layer, gradient zinc-iron coating, and passivation layer, improving the wear resistance, fatigue resistance, and corrosion resistance of the substrate carbon steel components (such as connecting fittings).

[0035] The present invention provides a preparation method for a gradient carbonitriding zinc-iron corrosion-resistant composite layer, including the following steps:

[0036] Step 1, performing quenching and tempering heat treatment on the substrate;

[0037] Step 2, shot peening the substrate after quenching and tempering heat treatment, and then performing carbonitriding treatment to form a carbonitriding layer on its surface and then performing cooling treatment; wherein, the process of carbonitriding treatment is: under vacuum conditions, heating to 480-560 °C, introducing a nitriding agent and a carburizing agent, controlling the flow ratio of the gaseous nitriding agent to be 90-95%, the first stage: controlling the nitrogen potential to be 0.8-1.2, the flow rate of the gaseous nitriding agent to be 0.6-1.2 m 3 / h, and holding for 2-4 hours; the second stage: controlling the nitrogen potential to be 0.4-0.8, the flow rate of the gaseous nitriding agent to be 0.3-0.6 m 3 / h, and holding for 4-8 h;

[0038] Step 3: After cleaning the matrix after carbonitriding treatment, deposit a gradient Zn-Fe coating with the iron content gradually decreasing from 8-30 wt% to 0.3-1.0 wt%.

[0039] Step 4: After passivation treatment to form a passivation layer on its surface, trim it to obtain a gradient carbonitrided zinc-iron corrosion-resistant composite layer.

[0040] By adopting a specific carbonitriding process and controlling the iron content in the gradient Zn-Fe coating, the present invention solves the problem that it is difficult to form a stable and effective structure for the carbonitrided layer, the gradient Zn-Fe coating and the passivation layer. The prepared composite layer can not only improve the surface strength, wear resistance and corrosion resistance of the matrix, but also has stable performance. First, through the carbonitriding process, without changing the appearance size of the matrix, C and N elements are diffused into the matrix to obtain a carbonitrided layer, which improves the surface strength and wear resistance of the matrix, increases the tensile strength of the matrix, and prevents deformation and fracture. Further, through the gradient Zn-Fe coating, the corrosion resistance and wear resistance are improved. Finally, through the passivation layer, its corrosion resistance is further greatly improved.

[0041] It should be noted that the present invention not only needs to strictly control the carbonitriding process, but also needs to strictly control the iron content in the gradient Zn-Fe coating. The carbonitriding process and the iron content will seriously affect the stability of the combination of the carbonitrided layer, the gradient Zn-Fe coating and the passivation layer, and thus affect the performance of the finally obtained composite layer.

[0042] In some specific embodiments of the present invention, the cooling treatment is to first cool the matrix temperature to below 100 °C in an atmosphere environment of argon or gaseous nitriding agent and then take it out of the furnace and cool it to room temperature.

[0043] In some specific embodiments of the present invention, the gaseous nitriding agent used is ammonia, and the gaseous carburizing agent is carbon dioxide.

[0044] In some specific embodiments of the present invention, refer to Figure 1 , the gradient Zn-Fe coating includes a high-iron Zn-Fe coating 3 and a low-iron Zn-Fe coating 4. Among them, the iron content in the high-iron Zn-Fe coating 3 is 8-30 wt%, such as 8 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt% and the range between any two of the above values; the iron content in the low-iron Zn-Fe coating 4 is 0.03-1.0 wt%, such as 0.03 wt%, 0.05 wt%, 0.07 wt%, 0.09 wt%, 1.0 wt% and the range between any two of the above values.

[0045] In some specific embodiments of the present invention, the thickness of the high-iron Zn-Fe coating 3 is 6-15 μm, for example, it can be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, and the range between any two of the above values; the thickness of the low-iron Zn-Fe coating 4 is 6-15 μm, for example, it can be 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, and the range between any two of the above values.

[0046] In some other specific embodiments of the present invention, the thickness of the carbonitriding layer 2 is 100-250 μm, for example, it can be 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, 200 μm, 220 μm, 240 μm, 250 μm, and the range between any two of the above values.

[0047] Before the carbonitriding treatment, it is first heat-treated to obtain the required mechanical properties and a better combination of strength and toughness through quenching and tempering treatment, improve the mechanical properties of the base material, eliminate the internal stress generated by forging or other deformation processes of the base material, and regulate the internal microstructure. In some specific embodiments of the present invention, the base material is tempered heat-treated to a hardness of 300-360 HBW.

[0048] The gradient carbonitriding zinc-iron corrosion-resistant composite layer described in the present invention can be applied to components such as carbon steel, carbon structural steel, medium and low alloy steel, alloy structural steel, etc., that is, the base body 1 can be a carbon steel or medium and low alloy steel component.

[0049] It can also be understood that during the processing of the above various steps, the base body (component) can be ensured to be clean and burr-free through conventional pickling, water washing and other methods.

[0050] The present invention also provides a gradient carbonitriding zinc-iron corrosion-resistant composite layer, which sequentially includes a carbonitriding layer, a gradient Zn-Fe coating with an iron content gradually decreasing from 8-30 wt% to 0.03-1.0 wt%, and a passivation layer made on the base body.

[0051] In some specific embodiments of the present invention, as Figure 1 shown, this composite layer sequentially includes a carbonitriding layer 2 made on the base body 1, a high-iron Zn-Fe coating 3 with an iron content of 8-30%, a low-iron Zn-Fe coating 4 with an iron content of 0.03-1.0 wt%, and a passivation layer 5.

[0052] Furthermore, this composite layer is prepared by the above method. Through the synergistic effect of the carbonitriding layer, the gradient Zn-Fe coating and the passivation layer, the surface strength, wear resistance and corrosion resistance of the base body are improved and the performance is stable.

[0053] The present invention also provides a connecting fitting, the surface of which is the above-mentioned gradient carbonitride zinc iron corrosion-resistant composite layer or the gradient carbonitride zinc iron corrosion-resistant composite layer prepared by the above method.

[0054] The following describes in detail the preparation method of the gradient carbonitride zinc iron corrosion-resistant composite layer, the obtained composite layer and the connecting fitting according to the present invention in combination with specific embodiments.

[0055] Method for measuring the hardness of the heat-treated workpiece: Use a Brinell hardness tester to measure the hardness of the heat-treated workpiece, and the measurement standard is "GB / T 231.1 Metallic materials - Brinell hardness test - Part 1: Test method".

[0056] Method for measuring the hardness of the nitrided workpiece: Use a Vickers hardness tester to measure the surface hardness of the nitrided workpiece, and the measurement standard is "GB / T 4340.1 Metallic materials - Vickers hardness test - Part 1: Test method".

[0057] Example 1

[0058] This example provides a gradient carbonitride zinc iron corrosion-resistant composite layer, a workpiece connecting fitting and a preparation method thereof, and the specific steps are as follows:

[0059] (1) Quench and temper the substrate to a hardness of 300 - 360 HBW.

[0060] Stock cutting: Select the required 35CrMo round steel for stock cutting according to the drawing and process requirements, check its material and specification, saw cut the required stock cutting size and quantity to obtain the substrate blank, where the specification of the blank is D20*190mm;

[0061] Heating: Heat the substrate blank using an oven or a mesh belt furnace, raise the temperature to 1150°C and hold for 0.5 hours;

[0062] Die forging: Forge the blank directly for die forging forming. When die forging forming, use a die forging forming die to perform die forging forming on a friction press to obtain the workpiece connecting fitting;

[0063] Machining: Use machining equipment such as lathes, milling machines, sawing machines and grinding machines to machine the workpiece obtained after forging;

[0064] Quenching heat treatment: Perform quenching heat treatment on the workpiece, raise the temperature of the workpiece to 880°C, hold for 1.5 hours, and after the holding ends, quench in oil to room temperature, and take out the workpiece from the oil quenching furnace;

[0065] Tempering heat treatment: Temper the workpiece after cryogenic treatment at 560°C and hold for 4h;

[0066] Inspection: After heat treatment, the workpiece is inspected for hardness, dimensions, internal and external defects, etc. The hardness after inspection is 320 HBW.

[0067] (2) After shot peening the workpiece after quenching and tempering heat treatment, carbonitriding treatment is carried out to form a carbonitriding layer on its surface.

[0068] Shot peening: The workpiece after the above treatment is put into a shot peening machine to remove defects such as scale and burrs on the surface, and the shot-peened workpiece is dried for standby;

[0069] Carbonitriding: After evacuating to below 20 Pa, the temperature is raised to 540 °C, and gaseous nitriding agent ammonia gas and gaseous carburizing agent carbon dioxide are introduced. The flow rate ratio of the gaseous nitriding agent is controlled at 95%, and the flow rate ratio of the gaseous carburizing agent is controlled at 5%; In the first stage, the nitrogen potential is controlled at 0.8, and the flow rate of the gaseous nitriding agent is 0.8 m 3 / h, and the workpiece is subjected to carbonitriding treatment for 4 h; In the second stage: the flow rate of ammonia gas is reduced to 0.4 m 3 / h, the nitrogen potential is controlled at 0.6, and the holding treatment is continued for 6 h. After the holding is completed, argon gas is introduced, and the flow rate of argon gas is 0.1 m 3 / h, and it is cooled in an argon gas atmosphere until the workpiece temperature is lower than 100 °C;

[0070] Air cooling: The workpiece cooled to below 100 °C is taken out of the furnace and air-cooled to room temperature;

[0071] Inspection: The workpiece after nitriding is inspected for the surface hardness and nitriding layer thickness of the workpiece. The results are as Figure 2 、 3 shown, where the surface hardness is about 1230 HV and the nitriding layer thickness is about 140 μm. The metallographic inspection is as Figure 4 shown.

[0072] (3) After cleaning the workpiece after carbonitriding treatment, a gradient Zn-Fe coating with gradually decreasing iron content is deposited.

[0073] Degreasing treatment: The oil and paint on the surface of the workpiece are removed by alkali washing, and the residual alkaline liquid on the surface of the workpiece is removed by water washing;

[0074] Pickling: Pickling is carried out with 20% hydrochloric acid. When the workpiece is put into the hydrochloric acid tank, it should be put in slowly to prevent acid spraying and hurting people. The pickling time is 5 minutes. During pickling, the material frame should be vibrated frequently to ensure uniform pickling. After pickling, check the appearance of the workpiece, and it is required that the surface is smooth and consistent, without residual oxide scale and oil stain pollution;

[0075] Water washing: Wash the workpiece in a flowing clean water tank, ensuring that the workpiece is completely immersed in water during washing to clean the residual hydrochloric acid from the pickling process. The iron salt content standard in the washing water shall not exceed the limit, and there shall be no other impurities. After washing, the surface moisture of the product shall be drained and it shall be quickly immersed into the flux;

[0076] Depositing high-iron Zn-Fe coating: Take the workpiece after water washing as the cathode and immerse it into the zinc-iron bath solution with high iron content under electrification. The anode is a nickel plate. The composition of the zinc-iron bath solution with high iron content is as follows: zinc oxide 10 g / L, sodium hydroxide 100 g / L, ammonium ferrous sulfate hexahydrate 30 g / L, polycomplex system: sodium gluconate 20 g / L, triethanolamine 20 mL / L, ammonium citrate 20 g / L, sodium salicylate 2 g / L. For the combined brightener, take benzylpyridinium carboxylate 0.1 mL / L, vanillin 80 mg / L, polyethylene glycol 60 mg / L. For the leveling agent, take sodium vinyl sulfonate 10 mg / L, sodium hippurate 8 mg / L. For the stabilizer, take sodium potassium tartrate 15 g / L, sodium bisulfite 50 mg / L, manganese dichloride 3 g / L. For the rare earth salt, take cerium sulfate 0.004 mol / L. The cathode current density is 3 A / dm 2 , the water bath temperature is 25 °C. After 30 minutes, a bright and flat coating can be obtained on the surface of the workpiece. The EDS semi-quantitative analysis results show that the zinc content in the obtained coating is 73.2 wt%, the iron content is 25.7 wt%, the balance is other substances, the thickness is 9 μm, and the hardness value measured by a microhardness tester is 532 HV;

[0077] Depositing low-iron Zn-Fe coating: Further take the workpiece as the cathode and immerse it into the zinc-iron bath solution with low iron content under electrification. The anode is a nickel plate. The composition of the zinc-iron bath solution with low iron content is as follows: zinc oxide 10 g / L, sodium hydroxide 100 g / L, ammonium ferrous sulfate hexahydrate 4 g / L, polycomplex system: sodium gluconate 15 g / L, triethanolamine 10 mL / L, tetraethylenepentamine 15 mL / L, ethylenediamine 5 mL / L. For the combined brightener, take benzylpyridinium carboxylate 0.1 mL / L, piperonal 70 mg / L, butynediol 60 mg / L. For the leveling agent, take sodium vinyl sulfonate 10 mg / L, sodium hippurate 8 mg / L. For the stabilizer, take sodium potassium tartrate 12 g / L, sodium bisulfite 8 mg / L, manganese dichloride 1 g / L. For the rare earth salt, take cerium sulfate 0.004 mol / L. The cathode current density is 3 A / dm 2 , the water bath temperature is 25 °C. After 30 minutes, a bright and flat coating can be obtained on the surface of the workpiece. The EDS semi-quantitative analysis results show that the zinc content in the obtained coating is 98.2 wt%, the iron content is 0.7 wt%, the balance is other substances, and the thickness is 8 μm.

[0078] (4) After deposition, carry out passivation treatment to form a passivation layer on its surface, and then carry out finishing to obtain the gradient carbonitride zinc-iron corrosion-resistant composite layer and the connecting fitting including this composite layer.

[0079] Passivation: After taking out the workpiece, through post-treatment processes such as brightening - passivation - water washing - sealing - drying, the composite layer is obtained. The passivation process is as follows: chromium nitrate nonahydrate 60 g / L, sodium nitrate 15 g / L, sodium oxalate 10 g / L, sodium malonate 10 g / L, maleic anhydride 2 g / L, cobalt nitrate hexahydrate 6 g / L, amino silicone 4 mL / L. The pH value is adjusted to 2 with nitric acid or sodium hydroxide, the temperature is 30 °C, and the time is 40 s.

[0080] Water washing: The passivated workpiece is rinsed with running water to wash away the passivation water marks, and self-inspection can be carried out only after the water has drained completely.

[0081] Trimming: Burrs, drips, and excess lumps generated after galvanizing are carefully ground off, taking care not to over-grind.

[0082] Neutral salt spray corrosion test: In accordance with the requirements of the standard "GB / T 10125 Artificial Atmosphere Corrosion Tests - Salt Spray Tests", after continuously corroding for 3600 h using a neutral salt spray corrosion test machine, observe its surface morphology. The results are as Figure 5 shown, and there is no obvious red rust on the surface.

[0083] Wear test: In accordance with the requirements of the standard "DL / T 1693 Test Method for Wear of Transmission Line Hardware", measure the weight before and after wear. The wear mass loss is 2.866 g, and the wear weight loss is not more than 0.1 cm 3 / 100 g, while the wear loss of galvanized steel is 22.641 g.

[0084] Example 2

[0085] This example provides a gradient carbonitrided zinc-iron corrosion-resistant composite layer, a workpiece connecting fitting, and a preparation method thereof. The difference between this example and Example 1 lies in the carbonitriding process, the iron content in the high-iron Zn-Fe coating, and the iron content in the low-iron Zn-Fe coating. The specific steps are as follows:

[0086] (1) Quench and temper the substrate heat treatment to a hardness of 300 - 360 HBW.

[0087] Blanking: Select 35CrMo round steel for blanking according to the drawing and process requirements, check its material and specifications, saw cut to obtain the required blanking size and quantity to obtain the substrate blank, where the specification of the blank is D20*190 mm;

[0088] Heating: Heat the substrate blank using an oven or a mesh belt furnace, raise the temperature to 1150 °C and hold for 0.5 hours;

[0089] Die forging: Forge the blank directly for die forging. When die forging, use a die forging die on a friction press for die forging to obtain the workpiece connecting fitting;

[0090] Machining: The machined parts obtained after forging are machined using machining equipment such as lathes, milling machines, sawing machines and grinding machines;

[0091] Quenching heat treatment: The workpieces are subjected to quenching heat treatment. The workpieces are heated to 880 °C and held for 1.5 hours. After the holding is completed, they are quenched in oil to room temperature, and the workpieces are taken out of the oil quenching furnace;

[0092] Tempering heat treatment: The workpieces after cryogenic treatment are tempered at 560 °C and held for 4 h;

[0093] Inspection: The heat-treated workpieces are inspected for hardness, dimensions, internal and external defects, etc. The hardness after inspection is 320 HBW.

[0094] (2) The workpieces after quenching and tempering heat treatment are subjected to shot peening and then carbonitriding treatment to form a carbonitriding layer on their surfaces.

[0095] Shot peening: The workpieces after the above treatment are put into a shot peening machine to remove defects such as scale and burrs on the surface, and the workpieces after shot peening are dried for standby;

[0096] Carbonitriding: After evacuating to below 20 Pa, the temperature is raised to 500 °C, gaseous nitriding agent ammonia gas and gaseous carburizing agent carbon dioxide are introduced, and the flow ratio of the gaseous nitriding agent is controlled at 92%, and the flow ratio of the gaseous carburizing agent is 8%; First stage: Control the nitrogen potential to 1.0, and the flow rate of the gaseous nitriding agent is 1.0 m 3 / h, and start carbonitriding the workpieces for 3 h; Second stage, reduce the flow rate of ammonia gas to 0.6 m 3 / h, control the nitrogen potential to 0.4, and continue the holding treatment for 8 h. After the holding is completed, argon gas is introduced, and the flow rate of argon gas is 0.1 m 3 / h, and cool in an argon gas atmosphere until the workpiece temperature is lower than 100 °C;

[0097] Air cooling: The workpieces cooled to below 100 °C are taken out of the furnace and air-cooled to room temperature;

[0098] Inspection: The nitrided workpieces are inspected for the surface hardness and nitrided layer thickness of the workpieces. The results are as Figure 2 、 3 shown, where the surface hardness is about 1025 HV and the nitrided layer thickness is about 123 μm.

[0099] (3) The workpieces after carbonitriding treatment are cleaned and deposited with a gradient Zn-Fe coating with gradually decreasing iron content.

[0100] Degreasing treatment: Alkaline washing is used to remove the oil and paint on the surface of the workpieces, and water washing is used to remove the residual alkaline liquid on the surface of the workpieces;

[0101] Pickling: Use 20% hydrochloric acid for pickling. When the workpiece is put into the hydrochloric acid tank, it should be put in slowly to prevent acid spraying and hurting people. The pickling time is 5 minutes. During pickling, the material basket should be vibrated frequently to ensure uniform pickling. After pickling, check the appearance of the workpiece, requiring the surface to be smooth and consistent, without residual oxide scale and oil stain pollution;

[0102] Water washing: Wash the workpiece in a flowing clean water tank. Ensure that the workpiece is completely immersed in water during water washing to clean the residual hydrochloric acid in the pickling process. The iron salt content standard in the cleaning water shall not exceed the standard and there shall be no other sundries. After cleaning, the surface moisture of the product should be drained and it should enter the flux as soon as possible;

[0103] Plating high-iron Zn-Fe coating: Take the water-washed workpiece as the cathode and put it into the zinc-iron bath with high iron content under electrification. The anode is a nickel plate. The composition of the zinc-iron bath with high iron content is: zinc oxide 10 g / L, sodium hydroxide 100 g / L, ammonium ferrous sulfate hexahydrate 20 g / L, polycomplex system sodium gluconate 20 g / L, triethanolamine 20 mL / L, ammonium citrate 20 g / L, sodium salicylate 2 g / L. The combined brightener takes benzylpyridinium carboxylate 0.1 mL / L, vanillin 80 mg / L, polyethylene glycol 60 mg / L. The leveling agent takes sodium vinylsulfonate 10 mg / L, sodium hippurate 8 mg / L. The stabilizer takes sodium potassium tartrate 15 g / L, sodium bisulfite 50 mg / L, manganese dichloride 3 g / L. The rare earth salt takes cerium sulfate 0.004 mol / L. The cathode current density is 3 A / dm 2 , the water bath temperature is 25 °C. After 35 minutes, a bright and smooth coating can be obtained on the surface of the workpiece. The EDS semi-quantitative analysis results show that the zinc content in the obtained coating is 77.8 wt%, the iron content is 20.1 wt%, the balance is others, the thickness is 12 μm, and the hardness value measured by a microhardness tester is 558 HV;

[0104] Plating low-iron Zn-Fe coating: Further take the workpiece as the cathode and put it into the zinc-iron bath with low iron content under electrification. The anode is a nickel plate. The composition of the zinc-iron bath with low iron content is: zinc oxide 10 g / L, sodium hydroxide 100 g / L, ammonium ferrous sulfate hexahydrate 6 g / L, polycomplex system sodium gluconate 15 g / L, triethanolamine 10 mL / L, tetraethylenepentamine 15 mL / L, ethylenediamine 5 mL / L. The combined brightener takes benzylpyridinium carboxylate 0.1 mL / L, piperonal 70 mg / L, butynediol 60 mg / L. The leveling agent takes sodium vinylsulfonate 10 mg / L, sodium hippurate 8 mg / L. The stabilizer takes sodium potassium tartrate 12 g / L, sodium bisulfite 8 mg / L, manganese dichloride 1 g / L. The rare earth salt takes cerium sulfate 0.004 mol / L. The cathode current density is 3 A / dm 2, with the water bath temperature at 25 °C, a bright and smooth coating can be obtained on the surface of the workpiece after 30 minutes. The results of EDS semi-quantitative analysis show that the zinc content in the obtained coating is 99.8 wt.%, the iron content is 0.05 wt%, the balance is other substances, and the thickness is 8 μm.

[0105] (4) After deposition, passivation treatment is carried out to form a passivation layer on its surface, and then finishing is carried out to obtain the gradient carbonitride zinc-iron corrosion-resistant composite layer and the connecting fitting including this composite layer.

[0106] Passivation: After taking out the workpiece, it undergoes post-treatment processes such as brightening - passivation - water washing - sealing - drying, etc., to obtain the said composite layer. The passivation process is as follows: chromium nitrate nonahydrate 60 g / L, sodium nitrate 15 g / L, sodium oxalate 10 g / L, sodium malonate 10 g / L, maleic anhydride 2 g / L, cobalt nitrate hexahydrate 6 g / L, amino silicone 4 mL / L. The pH value is adjusted to 2 with nitric acid or sodium hydroxide, the temperature is 30 °C, and the time is 40 s.

[0107] Water washing: The passivated workpiece is rinsed with running water to wash away the passivation water marks, and self-inspection can be carried out only after the water has drained completely.

[0108] Finishing: Burrs, drips, and excess lumps generated after galvanizing are carefully ground off, taking care not to grind too much.

[0109] Neutral salt spray corrosion test: In accordance with the requirements of the standard "GB / T 10125 Artificial Atmosphere Corrosion Tests - Salt Spray Tests", after continuously corroding for 3600 h using a neutral salt spray corrosion testing machine, observe its surface morphology, and there is no obvious red rust on the surface.

[0110] Wear test: In accordance with the requirements of the standard "DL / T 1693 Test Method for Wear of Transmission Line Fittings", measure the weight before and after wear, and the wear mass loss is 2.799 g, and the wear weight loss is not more than 0.1 cm 3 / 100 g.

[0111] Example 3

[0112] This example provides a gradient carbonitride zinc-iron corrosion-resistant composite layer, a connecting fitting, and its preparation method. The difference between this example and Example 1 is:

[0113] The process of carbonitriding treatment is as follows: After evacuating to below 20 Pa, heat up to 530 °C, and introduce gaseous nitriding agent ammonia gas and gaseous carburizing agent carbon dioxide. Control the flow rate ratio of the gaseous nitriding agent to be 91% and the flow rate ratio of the gaseous carburizing agent to be 9%; First stage: Control the nitrogen potential to be 1.2, and the flow rate of the gaseous nitriding agent is 1.0 m 3 / h, and start carbonitriding the workpiece for 2 h; Second stage, reduce the flow rate of ammonia gas to 0.5 m 3 / h, control the nitrogen potential to 0.8, and continue the heat preservation treatment for 4 h. After the heat preservation is completed, introduce argon, and the flow rate of argon is 0.1 m 3 / h, cool in an argon atmosphere until the workpiece temperature is lower than 100 °C;

[0114] The iron content in the high-iron Zn-Fe coating is 12 wt%, and the iron content in the low-iron Zn-Fe coating is 1.0 wt%.

[0115] Neutral salt spray corrosion test: According to the requirements of the standard "GB / T 10125 Artificial Atmosphere Corrosion Test Salt Spray Test", after continuously corroding for 3600 h with a neutral salt spray corrosion test machine, observe its surface morphology, and there is no obvious red rust on the surface.

[0116] Wear test: According to the requirements of the standard "DL / T 1693 Test Method for Wear of Transmission Line Hardware", measure the weight before and after wear. The wear mass loss is 2.831 g, and the wear weight loss is not more than 0.1 cm 3 / 100 g.

[0117] Comparative Example 1

[0118] This comparative example provides a gradient carbonitrided zinc-iron corrosion-resistant composite layer, a connecting fitting and its preparation method. The difference from Example 1 is that the iron content in the high-iron Zn-Fe coating is 11.4 wt%, and the iron content in the low-iron Zn-Fe coating is 5.1%. The obtained product has poor bonding strength of the transition layer, and the surface Zn-Fe layer is easy to fall off.

[0119] Comparative Example 2

[0120] This comparative example provides a gradient carbonitrided zinc-iron corrosion-resistant composite layer, a connecting fitting and its preparation method. The difference from Example 1 is that

[0121] The process of carbonitriding treatment is as follows: After evacuating to below 20 Pa, heat up to 540 °C, introduce gaseous nitriding agent ammonia gas and gaseous carburizing agent carbon dioxide, control the flow rate ratio of the gaseous nitriding agent to be 95%, and the flow rate ratio of the gaseous carburizing agent to be 5%; In the first stage, control the nitrogen potential to 1.2, and the flow rate of the gaseous nitriding agent is 0.8 m 3 / h, carry out carbonitriding treatment on the workpiece for 4 h; In the second stage: reduce the flow rate of ammonia gas to 0.5 m 3 / h, control the nitrogen potential to 1.0, and continue the heat preservation treatment for 6 h. After the heat preservation is completed, introduce argon, and the flow rate of argon is 0.1 m 3 / h, cool in an argon atmosphere until the workpiece temperature is lower than 100 °C;

[0122] It is detected that a bright white layer is formed on the surface of the carbonitriding layer. The formation of the bright white layer affects the bonding strength between the carbonitriding layer and the Zn-Fe coating, making the bonding of the final composite coating unstable.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer, characterized in that: The following steps are involved: Step 1, subjecting the substrate to a tempering heat treatment; Step 2, shot blasting the substrate after quenching and tempering heat treatment, and then carbonitriding treatment to form a carbonitriding layer on its surface and then cooling treatment; wherein the carbonitriding process is: under vacuum conditions, heating to 480-560 ° C, introducing nitriding agent and carburizing agent, controlling the flow rate ratio of gaseous nitriding agent to 90-95%, the first stage: controlling the nitrogen potential to 0.8-1.2, the flow rate of gaseous nitriding agent to 0.6-1.2m 3 / h, keep warm for 2-4 hours; the second stage: control the nitrogen potential to 0.4-0.8, and the flow rate of the gaseous nitriding agent to 0.3-0.6m 3 / h, keep warm for 4-8h; Step 3: After cleaning the substrate after carbonitriding treatment, a gradient Zn-Fe coating with an iron content gradually reduced from 8-30wt% to 0.03-1.0wt% is deposited; Step 4: Passivation treatment forms a passivation layer on its surface and then trims it to obtain a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer.

2. The method for preparing the gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to claim 1, characterized in that: The cooling treatment is to first cool the substrate in an argon or gaseous nitriding agent atmosphere until the substrate temperature is below 100° C. and then cool the substrate out of the furnace to room temperature.

3. The method for preparing the gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to claim 1, characterized in that: The gaseous nitriding agent is ammonia, and the gaseous carburizing agent is carbon dioxide.

4. The method for preparing the gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to claim 1, characterized in that: The gradient Zn-Fe coating includes a high-iron Zn-Fe coating and a low-iron Zn-Fe coating, wherein the iron content of the high-iron Zn-Fe coating is 8-30 wt %, and the iron content of the low-iron Zn-Fe coating is 0.03-1.0 wt %.

5. The method for preparing the gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to claim 4, characterized in that: The thickness of the high iron Zn-Fe coating is 6-15 μm, and the thickness of the low iron Zn-Fe coating is 6-15 μm; and / or The thickness of the carbonitriding layer is 100-250 μm.

6. The method for preparing a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to any one of claims 1 to 4, characterized in that: In step 1, the substrate is subjected to a conditioning heat treatment until its hardness is 300-360 HBW.

7. The method for preparing a gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to any one of claims 1 to 4, characterized in that: The substrate is a carbon steel or medium or low alloy steel component.

8. A gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer, characterized in that: The composite layer sequentially comprises a carbonitriding layer formed on a substrate, a gradient Zn-Fe coating layer whose iron content gradually decreases from 8-30 wt % to 0.03-1.0 wt % and a passivation layer; and / or The composite layer is prepared by the method according to any one of claims 1 to 7.

9. The gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer according to claim 8, characterized in that: The composite layer sequentially comprises a carbonitriding layer made on a substrate, a high-iron Zn-Fe coating layer with an iron content of 8-30 wt%, a low-iron Zn-Fe coating layer with an iron content of 0.03-1.0 wt% and a passivation layer.

10. A connection fitting, characterized in that: The surface of the connecting hardware is the gradient carbon-nitrogen-zinc-iron corrosion-resistant composite layer as described in claim 8 or 9.

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