Salt-spray-resistant steel, preparation method and application of salt-spray-resistant steel

Abstract

The invention provides salt-spray-resistant steel, a preparation method and application of the salt-spray-resistant steel. The salt-spray-resistant steel sequentially comprises an alloy matrix, a permeable layer and an anti-corrosion coating from inside to outside. The alloy matrix comprises an Fe element; the permeable layer comprises Fe, N and O elements; the anticorrosive coating covers at least the surface of the permeable layer. The steel has the characteristics of high strength and salt spray resistance, the binding force of the coating and a matrix is good, the thickness of the anti-corrosion coating is greatly reduced under the condition that the anti-corrosion requirement of the CX grade is met, the machinable performance of a workpiece is effectively improved, and the adverse effects that the workpiece meshing force is poor, and the surface is not uniform due to the thick coating are avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of metal building materials, and in particular to a salt spray resistant steel material, a preparation method and application thereof. Background Art

[0002] Steel has become the preferred material for national infrastructure and machinery production due to its advantages such as abundant raw materials, good processability, diverse performance, high strength, and economic benefits. However, the service environment of large steel structures and steel components often has corrosion factors, which can easily cause corrosion damage, leading to huge economic losses and personal safety accidents. Therefore, it is extremely necessary to provide long-term, stable and efficient anti-corrosion measures for steel.

[0003] At present, in extreme environments with high humidity and high salinity such as coastal areas and offshore platforms, the national standard generally requires C5 or CX anti-corrosion grades. The neutral salt spray of C5 grade is not less than 2000h, while the neutral salt spray of CX grade is not less than 4000h. Common steel anti-corrosion treatment uses alloy coating spraying to prevent steel corrosion, so that the coating provides protection for steel in highly corrosive application environments such as seawater and soil. Among them, Zn-Al binary alloy coating has a wide range of applications and has good corrosion resistance. However, to meet the C5 grade anti-corrosion requirements, the thickness of the zinc-aluminum coating must range from 80 to 120 microns; to meet the CX grade anti-corrosion requirements, the thickness of the zinc-aluminum coating ranges up to 150 microns. However, due to the thick coating thickness, it will bring about adverse effects such as easy peeling of the coating and the substrate, poor bite force of the workpiece, and uneven coating surface. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a salt spray resistant steel, a preparation method and an application thereof. The steel of the present invention has high-strength salt spray resistance, good bonding strength between the coating and the substrate, and can greatly reduce the thickness of the anti-corrosion coating while meeting the CX grade anti-corrosion requirements, thereby effectively improving the machinability of the workpiece and avoiding adverse effects such as poor bite force of the workpiece and uneven surface caused by a thicker coating.

[0005] To this end, a first object of the present invention is to provide a salt spray resistant steel.

[0006] The second object of the present invention is to provide a method for preparing salt spray resistant steel.

[0007] The third object of the present invention is to provide an application of salt spray resistant steel.

[0008] To achieve the first objective of the present invention, the technical solution of the present invention provides a salt spray resistant steel, which comprises, from the inside to the outside, an alloy matrix, a permeation layer and an anti-corrosion coating; the alloy matrix comprises Fe elements; the permeation layer comprises Fe, N and O elements; and the anti-corrosion coating covers at least the surface of the permeation layer.

[0009] Compared with the prior art, the technical effect achieved by adopting this technical scheme is as follows: the salt spray resistant steel of the present invention has a composite layered structure of an alloy matrix, a permeation layer and an anti-corrosion coating; the surface of the alloy matrix absorbs N elements and O oxygen elements to form a dense permeation layer with excellent corrosion resistance and wear resistance; the anti-corrosion coating and the permeation layer work synergistically to further enhance the anti-corrosion performance and interlayer bonding strength of the steel.

[0010] In one technical solution of the present invention, the alloy matrix includes, by mass percentage, the following: C: 0.30%-0.35%; Si: 0.60%-0.80%; Mn: 1.00%-1.20%; S: ≤0.03%; P: ≤0.03%; Ni: 0.3%-0.5%; Mo: 0.05%-0.10%; V: 0.03%-0.05%; O: ≤20ppm; N: ≤30ppm; the remainder is Fe and unavoidable impurities.

[0011] Furthermore, the alloy matrix includes, by mass percentage, the following: C: 0.30%-0.32%; Si: 0.60%-0.70%; Mn: 1.00%-1.10%; S: ≤0.02%; P: ≤0.02%; Ni: 0.3%-0.4%; Mo: 0.05%-0.10%; V: 0.03%-0.04%; O: ≤20ppm; N: ≤30ppm; the remainder is Fe and unavoidable impurities.

[0012] Compared with the existing technology, the technical effect achieved by adopting this technical solution is as follows: the alloy matrix formula design of the present invention aims to achieve excellent mechanical properties, corrosion resistance and processing performance by precisely controlling the chemical composition and impurity levels, while taking into account the cost and production feasibility. The anti-corrosion coating further improves the surface performance of salt spray resistant steel. The carbon content is between 0.30% and 0.35%, which can ensure that the steel has sufficient strength and hardness while maintaining a certain toughness; the silicon content is between 0.60% and 0.80%, which helps to improve the elasticity and wear resistance of the steel; the manganese content is between 1.00% and 1.20%, which helps to improve the strength, hardness and hardenability of the steel; the addition of appropriate amounts of Ni and Mo elements can significantly improve the corrosion resistance, weather resistance and stability of the steel; the addition of a small amount of V element helps to refine the grains and further improve the strength and corrosion resistance of the material; the sulfur and phosphorus contents are strictly controlled to ≤0.03%, which helps to reduce material embrittlement and improve the overall quality of the steel; the oxygen and nitrogen contents are controlled below 20ppm and 30ppm respectively, which helps to avoid the formation of bubbles and inclusions and ensure the cleanliness and consistency of the material; the formula design of the alloy matrix takes into account the convenience of processing, ensuring that the material can be processed by conventional metal processing technology without losing its performance, and providing optimal performance under the premise of controllable costs.

[0013] In one technical solution of the present invention, the anti-corrosion coating is Cu(OH) 2 , SiC composite materials and Zn-Al anti-corrosion coatings.

[0014] Compared with the prior art, the technical effects achieved by adopting the technical scheme are as follows: the copper hydroxide in the anti-corrosion coating of the present invention can effectively inhibit the attachment and growth of organisms by continuously releasing copper ions, thereby slowing down the corrosion of these organisms on the material; the SiC composite material has excellent mechanical properties and chemical stability, which can not only improve the hardness and wear resistance of the coating, but also significantly improve the corrosion resistance of the substrate; zinc has a lower electrode potential and can sacrifice anode protection, that is, zinc will corrode first before the steel substrate, thereby protecting the substrate from corrosion, and aluminum forms a dense aluminum oxide film on its surface, which can effectively isolate the corrosive medium and extend the service life of the coating. The dense accumulation layer formed by the Zn-Al coating on the surface of the alloy substrate can effectively block the direct contact between the corrosive medium such as moisture and oxygen and the substrate, thereby slowing down the corrosion process.

[0015] In one technical solution of the present invention, the thickness of the anti-corrosion coating is 3 μm-5 μm.

[0016] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the thickness of the anti-corrosion coating is controlled by the present invention to achieve the best anti-corrosion effect and economy. When the coating thickness is less than 3 μm, the anti-corrosion effect is poor; when the coating thickness is greater than 5 μm, the coating is easy to peel off and the cost is high. The appropriate coating thickness can ensure that the coating provides sufficient isolation and protection in a corrosive environment, thereby extending the service life of the metal substrate.

[0017] To achieve the second purpose of the present invention, the technical solution of the present invention provides a method for preparing salt spray resistant steel, comprising: S100, subjecting an alloy substrate to a nitrogen-oxygen co-diffusion treatment to obtain a steel blank; S200, applying an anti-corrosion coating on any surface of the steel blank to obtain salt spray resistant steel; wherein the steel blank is an alloy structure in which a permeation layer covers at least the surface of the alloy substrate.

[0018] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the salt spray resistant steel of the present invention is processed by nitrogen-oxygen co-diffusion of the alloy matrix, and N and O oxygen elements are absorbed on the surface of the alloy matrix to form a dense penetration layer, which significantly improves the hardness and surface strength of the material, and the penetration layer can also effectively isolate moisture and salt; then an anti-corrosion coating is applied to any surface of the steel blank to form a salt spray resistant steel with a composite layered structure of an alloy matrix, a penetration layer and an anti-corrosion coating. The preparation method of the salt spray resistant steel of the present invention is simple in process, saves anti-corrosion coating resources, effectively reduces the production cost of high-corrosion-resistant workpieces, and is of great significance for the wide application of steel.

[0019] In a technical solution of the present invention, S100 specifically includes: S110, quenching the alloy raw material under a protective atmosphere to obtain an alloy blank; S120, tempering the alloy blank under a controlled atmosphere to obtain an alloy matrix; S130, nitrogen-oxygen co-diffusion treatment of the alloy matrix under a controlled atmosphere to obtain a steel blank.

[0020] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the preparation of the alloy raw material of the present invention is smelted, cast and preliminarily formed according to the alloy matrix raw material ratio of the technical solution of the present invention. In the preparation process of salt spray resistant steel, there is a phenomenon of hydrogen absorption during quenching and heating. The preparation method of the salt spray resistant steel of the present invention can effectively dehydrogenate through the tempering process, basically maintain the hydrogen content level of the blank, and effectively avoid hydrogen embrittlement; the controlled atmosphere nitrogen and oxygen co-diffusion treatment uses gaseous reactants to react chemically on the solid surface as the temperature rises, generating solid deposits to form a dense permeation layer, which helps to increase the strength, hardness and salt spray resistance of the alloy, and effectively isolates moisture and salt, which is of great significance for the corrosion protection of marine steel.

[0021] In a technical solution of the present invention, in S110, the temperature of the quenching treatment is 850°C-870°C; and / or in S110, the holding time of the quenching treatment is 20min-30min.

[0022] Furthermore, the protective atmosphere is at least one of inert gases.

[0023] Compared with the prior art, the technical effect achieved by adopting the technical solution is as follows: the present invention controls the protective atmosphere, temperature and time of quenching treatment, which can effectively improve the overall performance of the steel after quenching. The temperature of quenching treatment changes the microstructure of the steel, so that the steel reaches the ideal hardness and uniform structure. Too high heating temperature may cause coarse grains, thereby reducing the toughness and impact strength of the material. Too low heating temperature affects the formation degree and composition uniformity of the metallographic structure; the protective atmosphere of quenching treatment can prevent oxidation and decarburization, maintain the surface quality of the steel, and reduce the evaporation of alloy elements to ensure the stability of the chemical composition and performance of the steel; the length of quenching treatment time determines the distribution uniformity of carbon and other alloy elements in the metallographic structure. Insufficient heat preservation time will lead to uneven distribution of components, affecting the subsequent quenching effect. Too long heat preservation time may cause surface decarburization, which will reduce the hardness and wear resistance of the steel surface. Long-term heat preservation may also cause the growth of metallographic grains, affecting the performance of the steel after quenching.

[0024] In one technical solution of the present invention, in S120, the controllable atmosphere is water vapor, air and ammonia, and the volume ratio of water vapor, air and ammonia is (1-2): (3-7): (2-3); and / or in S120, the tempering treatment temperature is 550°C-600°C; and / or in S120, the tempering treatment time is 40min-80min.

[0025] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the present invention prevents oxidation of the alloy matrix and effectively dehydrogenates by precisely controlling the controllable atmosphere, temperature and time of the tempering treatment, thereby significantly improving the toughness and mechanical properties of the material; reducing internal stress, thereby ensuring the reliability and stability of salt spray resistant steel in harsh environments.

[0026] In a technical solution of the present invention, in S130, the temperature of the nitriding treatment is 600°C-650°C; and / or in S130, the time of the nitriding treatment is 40min-80min.

[0027] Compared with the prior art, the technical effect achieved by adopting this technical solution is as follows: the present invention controls the amount of N and O oxygen elements absorbed by the surface of the alloy matrix through the controllable atmosphere, temperature and time of nitrogen-oxygen co-diffusion treatment to form a moderate penetration layer thickness and surface quality, thereby improving the hardness, wear resistance and corrosion resistance of the material, as well as the bonding strength with the anti-corrosion coating.

[0028] To achieve the third purpose of the present invention, the technical solution of the present invention provides an application of a salt spray resistant steel material, wherein the salt spray resistant steel material obtained by any of the above-mentioned salt spray resistant steel materials or preparation methods is used in scaffolding structural members.

[0029] Compared with the prior art, the technical effect achieved by adopting this technical scheme is as follows: the scaffolding structural member of this technical scheme includes the salt spray resistant steel or the preparation method of any technical scheme of the present invention, and thus has all the beneficial effects of the salt spray resistant steel or the preparation method of any technical scheme of the present invention, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The metallographic structure diagram of the salt spray resistant steel provided in the first embodiment of the present invention; Description of reference numerals: 100-alloy substrate; 200-penetration layer; 300-anti-corrosion coating. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0032] Refer to the following Figure 1 The technical solutions of some embodiments of the present invention are described.

[0033] Reference Figure 1 As shown, an embodiment of the present invention provides a salt spray resistant steel, which includes, from the inside to the outside, an alloy matrix 100, a permeation layer 200 and an anti-corrosion coating 300; the alloy matrix 100 includes Fe elements; the permeation layer 200 includes Fe, N and O elements; the anti-corrosion coating 300 covers at least the surface of the permeation layer.

[0034] Figure 1This is a metallographic structure diagram of the salt spray resistant steel provided in Example 1 of the present invention, in which the dark portion at the top of the figure is the anti-corrosion coating 100; the transition layer in the middle is the penetration layer 200; the uniform portion at the bottom of the figure is the alloy matrix 300; wherein, the side of the penetration layer 200 close to the anti-corrosion coating 300 is the Fe-NO compound, and the side of the penetration layer 200 close to the alloy matrix 100 is the diffusion product of Fe (N, O).

[0035] An embodiment of the present invention provides a method for preparing salt spray resistant steel, comprising: S100, subjecting an alloy substrate to a nitrogen-oxygen co-diffusion treatment to obtain a steel blank; S200, applying an anti-corrosion coating on any surface of the steel blank to obtain salt spray resistant steel; wherein the steel blank is an alloy structure in which a permeation layer covers at least the surface of the alloy substrate.

[0036] In one embodiment of the present invention, S100 specifically includes: S110, quenching the alloy raw material under a protective atmosphere to obtain an alloy blank; S120, tempering the alloy blank under a controlled atmosphere to obtain an alloy matrix; S130, nitriding the alloy matrix under a controlled atmosphere to obtain a steel blank.

[0037] By way of example, the temperature of the controlled atmosphere is 400°C.

[0038] In one embodiment of the present invention, when the anti-corrosion coating of the salt spray resistant steel includes a SiC composite material, in S200, the coating preparation method includes: mixing SiC, a silane coupling agent and a silicone resin evenly, treating at 800°C-900°C for 15min-30min under an inert gas atmosphere to obtain the SiC composite material.

[0039] For example, the silane coupling agent is a modified aminosilane coupling agent, and the silicone resin is a polymethyl silicone resin.

[0040] For example, the added amounts of SiC, silane coupling agent and silicone resin are 1 g-5 g SiC: 5 mL-25 mL silane coupling agent: 1.25 mol silicone resin.

[0041] The SiC composite material coating of the present invention not only has the protective function of ordinary organic coatings, but also, due to the high stability and corrosion resistance of SiC, the entire salt spray resistant steel can maintain its performance for a long time in harsh environments. SiC itself has excellent wear resistance, high temperature resistance and corrosion resistance. In the anti-corrosion coating of salt spray resistant steel, SiC provides a solid protective layer that can effectively block the invasion of external corrosive media; the silane coupling agent improves the bonding force between SiC and the silicone resin, and enhances the overall stability and adhesion of the coating; the silicone resin, as a binder of the coating, provides the basic molding characteristics of the coating and gives the coating good elasticity and chemical resistance.

[0042] In one embodiment of the present invention, S110 specifically includes: quenching the alloy body, water cooling to 300° C., and then air cooling to room temperature, and then sequentially performing shot peening, tempering in a controlled atmosphere, and air cooling to room temperature.

[0043] Water cooling is a key step in the quenching process. By rapidly cooling the high-temperature alloy blank, the effect of solid solution treatment is achieved, that is, the strengthening phase in the alloy is fully dissolved to form a supersaturated solid solution, which is ready for subsequent aging precipitation hardening. The process of water cooling to 300°C can effectively control the cooling rate of the alloy, prevent deformation or cracking of the alloy caused by too fast cooling, and also ensure the mechanical properties and hardness of the alloy. After water cooling to 300°C, the alloy blank needs to be slowly cooled to room temperature by air cooling. This step is aimed at reducing the thermal stress inside the alloy, avoiding the residual stress caused by rapid cooling, and promoting the precipitation and transformation of certain phases in the alloy. The air cooling process helps to stabilize the microstructure of the alloy, reduce internal defects, and improve the toughness and fatigue life of the alloy. Shot peening is a surface strengthening process. By high-speed jetting of shot to impact the alloy surface, the surface is plastically deformed to form a compressive stress layer, which can effectively improve the hardness and fatigue strength of the alloy surface, remove the oxide scale and tiny defects on the surface, and at the same time, the introduced compressive stress helps to offset the tensile stress caused by external loads, thereby improving the fatigue resistance of the alloy.

[0044] An embodiment of the present invention provides an application of a salt spray resistant steel material. The salt spray resistant steel material obtained by using any of the above-mentioned salt spray resistant steel materials or preparation methods is used in scaffolding structural members.

[0045] For example, the salt spray resistant steel material may be specifically in the shape of a scaffolding structure, including at least one of a steel plate, a nut, a screw, a connector, a steel pipe, and a plug.

[0046] For example, salt spray resistant steel can also be used in fasteners, auto parts and highway guardrail accessories.

[0047] The scaffolding structure of this embodiment includes the salt spray resistant steel or the preparation method of any embodiment of the present invention, and thus has all the beneficial effects of the salt spray resistant steel or the preparation method of any embodiment of the present invention, which will not be repeated here.

[0048] [Example 1] This embodiment provides a salt spray resistant steel material, and a method for preparing the salt spray resistant steel material, comprising: S100, preparing an alloy body from the alloy matrix raw materials including, by mass percentage, carbon: 0.30%; silicon: 0.60%; manganese: 1.00%; sulfur: 0.03%; phosphorus: 0.03%; Ni: 0.3%; Mo: 0.05%; V: 0.05%; O: 20ppm; N: 30ppm; the remainder being Fe and unavoidable impurities, quenching the alloy body under a protective atmosphere, and sequentially performing a tempering treatment and a nitrox-oxygen co-diffusion treatment under a controlled atmosphere, wherein the thickness of the penetration layer is 2μm, to obtain a steel body; S200, coating a coating of copper hydroxide and SiC composite material mixed in a mass ratio of 1:1 on any surface of the alloy substrate, the thickness of the anti-corrosion coating is controlled at 3 μm, and after coating, drying is carried out at 300°C for 30 minutes, and salt spray resistant steel is obtained after drying; Among them, the quenching heating temperature is 850℃, the holding time is 20min, water cooling to 300℃, air cooling to room temperature, and then the surface is shot peening and tempering. The tempering temperature is 600℃, the tempering time is 60min, and the controlled atmosphere is water vapor: air: ammonia = 1:3:2 in volume ratio; the temperature of nitroxyzolysis treatment is 600℃, and the holding time is 40min.

[0049] [Example 2] The present embodiment provides a salt spray resistant steel, which specifically refers to Example 1. The difference from Example 1 is that in S100, the alloy matrix raw materials include, by mass percentage: carbon: 0.32%; silicon: 0.70%; manganese: 1.10%; sulfur: 0.02%; phosphorus: 0.03%; Ni: 0.4%; Mo: 0.08%; V: 0.04%; O: 20ppm; N: 30ppm; the remainder is Fe and unavoidable impurities; the controlled atmosphere of the nitriding treatment is water vapor: air: ammonia = 1:7:3 in the volume ratio; the temperature of the nitriding treatment is 600°C, the holding time is 80min, and the thickness of the penetration layer is 60μm.

[0050] [Example 3] The present embodiment provides a salt spray resistant steel, which specifically refers to Example 1. The difference from Example 1 is that in S100, the alloy matrix raw materials include, by mass percentage: carbon: 0.35%; silicon: 0.80%; manganese: 1.20%; sulfur: 0.03%; phosphorus: 0.03%; Ni: 0.5%; Mo: 0.10%; V: 0.05%; O: 10ppm; N: 20ppm; the remainder is Fe and unavoidable impurities; the controlled atmosphere of the nitriding treatment is water vapor: air: ammonia = 2:4:2 in a volume ratio; the temperature of the nitriding treatment is 550°C, the holding time is 60min, and the thickness of the penetration layer is 30μm.

[0051] [Example 4] This embodiment provides a salt spray resistant steel, which specifically refers to Example 1. The difference from Example 1 is that the volume ratio of the controlled atmosphere is water vapor: air: ammonia = 2:5:2; in S200, copper hydroxide and SiC composite material are mixed in a mass ratio of 1:2.

[0052] [Example 5] This embodiment provides a salt spray resistant steel, which specifically refers to Example 1. The difference from Example 1 is that the volume ratio of the controlled atmosphere is water vapor: air: ammonia = 1:5:2; in S200, copper hydroxide and SiC composite materials are mixed in a mass ratio of 1:2, and the thickness of the anti-corrosion coating is controlled at 4 μm.

[0053] [Example 6] This embodiment provides a salt spray resistant steel, which specifically refers to Example 1. The difference from Example 1 is that the volume ratio of the controlled atmosphere is water vapor: air: ammonia = 2:7:2; in S200, copper hydroxide and SiC composite materials are mixed in a mass ratio of 1:2, and the thickness of the anti-corrosion coating is controlled at 5μm.

[0054] [Example 7] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 1. The difference from Embodiment 1 is that in S200, the coating is a Zn-Al coating.

[0055] [Example 8] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 7. The difference from Embodiment 7 is that in S100, the alloy matrix is ​​35CrMo steel.

[0056] [Example 9] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 7. The difference from Embodiment 7 is that in S100, the alloy matrix is ​​42CrMo steel.

[0057] [Example 10] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 7. The difference from Embodiment 7 is that in S100, the alloy matrix is ​​40Cr steel.

[0058] [Example 11] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 1. The difference from Embodiment 1 is that step S200 is not performed.

[0059] [Comparative Example 1] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 1. The difference from Embodiment 1 is that in S100, no oxynitriding treatment is performed.

[0060] [Comparative Example 2] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 8. The difference from Embodiment 8 is that in S100, no oxynitriding treatment is performed.

[0061] [Comparative Example 3] This embodiment provides a salt spray resistant steel material, with specific reference to Comparative Example 2. The difference from Comparative Example 2 is that in S100, no nitriding treatment is performed, and in S200, the thickness of the anti-corrosion coating is 100 μm.

[0062] [Comparative Example 4] This embodiment provides a salt spray resistant steel material, with specific reference to Comparative Example 2. The difference from Comparative Example 2 is that in S200, the thickness of the anti-corrosion coating is 150 μm.

[0063] [Comparative Example 5] This embodiment provides a salt spray resistant steel material, which specifically refers to Embodiment 3. The difference from Embodiment 3 is that the thickness of the penetration layer is 61 μm.

[0064] [Comparative Example 6] This embodiment provides a salt spray resistant steel material, which specifically refers to Example 3. The difference from Example 3 is that the thickness of the anti-corrosion coating is 6 μm.

[0065] Performance test, detection method reference: GB / T10125-2012 Artificial gas corrosion test-Salt spray test; GB / T6461-2002 Metal and other inorganic coatings on metal substrates-Rating of specimens and test pieces after corrosion tests.

[0066] Table 1 Conclusion: In the performance test of Table 1, it can be seen from Examples 1-10 compared with Comparative Examples 1-2 that the surface hardness, hardened layer depth, salt spray resistance time and corrosion resistance grade of the steel after the nitrogen-oxygen co-diffusion treatment of the present invention are significantly improved; Example 11 shows that the salt spray resistant steel of the present invention with a permeable layer has a good corrosion resistance grade even without anti-corrosion treatment. Similarly, if the anti-corrosion coating of the salt spray resistant steel of the present invention is damaged, it also has a certain anti-corrosion effect to protect the alloy matrix and reduce losses; In Comparative Examples 3-4, by increasing the thickness of the anti-corrosion coating, a salt spray resistance time of 4000 hours and a certain corrosion resistance grade can be achieved, but due to its thicker anti-corrosion coating, the mechanical properties are poor; By comparing the test data of Examples 1-3 and Comparative Examples 5-6, it can be seen that appropriately increasing the thickness of the permeable layer and the anti-corrosion coating has a positive effect on the surface hardness, the depth of the hardened layer, the salt spray resistance time and the corrosion resistance grade, but when the thickness of the permeable layer and the anti-corrosion coating is too high, the bonding force between the two is affected, which has an adverse effect on the mechanical properties.

[0067] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "specific embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0068] The writing method of "S100" and "S200" etc. in this specification is to facilitate the description of the embodiments of the present invention. The present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the order of the specific embodiments of the above writing method.

[0069] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A salt spray resistant steel material, characterized in that: The steel material includes, from the inside to the outside, an alloy matrix, a permeation layer and an anti-corrosion coating; The alloy matrix includes Fe element; The permeation layer includes Fe, N and O elements; The anti-corrosion coating covers at least the surface of the permeable layer.

2. The steel material according to claim 1, characterized in that: The alloy matrix includes, by mass percentage, the following: C: 0.30%-0.35%; Si: 0.60%-0.80%; Mn: 1.00%-1.20%; S: ≤0.03%; P: ≤0.03%; Ni: 0.3%-0.5%; Mo: 0.05%-0.10%; V: 0.03%-0.05%; O: ≤20ppm; N: ≤30ppm; the remainder is Fe and unavoidable impurities.

3. The steel material according to claim 1, characterized in that: The anti-corrosion coating is at least one of Cu(OH)2, SiC composite material and Zn-Al anti-corrosion coating.

4. The steel material according to claim 1, characterized in that: The thickness of the anti-corrosion coating is 3 μm-5 μm; and / or The thickness of the permeation layer is 1 μm-60 μm.

5. A method for preparing a salt spray resistant steel material, used for preparing the steel material as claimed in any one of claims 1 to 4, characterized in that: include: S100, subjecting the alloy substrate to oxynitriding treatment to obtain a steel blank; S200, applying an anti-corrosion coating on any surface of the steel blank to obtain the salt spray resistant steel; The steel blank is an alloy structure in which the infiltration layer covers at least the surface of the alloy matrix.

6. The method for preparing steel according to claim 5, characterized in that: The S100 specifically includes: S110, quenching the alloy raw material under a protective atmosphere to obtain an alloy blank; S120, tempering the alloy blank in a controlled atmosphere to obtain the alloy matrix; S130, subjecting the alloy substrate to oxynitriding treatment in the controlled atmosphere to obtain the steel blank.

7. The method for preparing steel according to claim 6, characterized in that: In S110, the temperature of the quenching treatment is 850° C.-870° C.; and / or In S110, the holding time of the quenching treatment is 20 min-30 min.

8. The method for preparing steel according to claim 6, characterized in that: In S120, the controllable atmosphere is water vapor, air and ammonia, and the volume ratio of the water vapor, air and ammonia is (1-2): (3-7): (2-3); and / or In S120, the tempering treatment temperature is 550° C.-600° C.; and / or In S120, the tempering treatment time is 40 min-80 min.

9. The method for preparing steel according to claim 6, characterized in that: In S130, the temperature of the nitriding treatment is 600° C.-650° C.; and / or In S130, the nitriding treatment time is 40 min-80 min.

10. An application of salt spray resistant steel, characterized in that: The salt spray resistant steel obtained by using the steel according to any one of claims 1 to 4 or the preparation method according to any one of claims 5 to 9 is used in scaffolding structural parts.

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