Method for improving corrosion resistance of steel for railway vehicle

Abstract

The invention discloses a method for improving corrosion resistance of steel for railway vehicles. The method comprises the steps of steelmaking, continuous casting, heating, hot rolling and slow cooling. After finish rolling, the steel is slowly cooled to 650-700 DEG C and then slowly cooled to the room temperature in controlled cooling equipment, enrichment of key elements in a rust layer is promoted, and a compact protection layer is formed; the steel comprises the following chemical components in percentage by mass: 0.03%-0.05% of C, 0.15%-0.20% of Si, 0.40%-0.50% of Mn, less than or equal to 0.015% of P, less than or equal to 0.010% of S, 3.0%-3.5% of Cr, 0.25%-0.35% of Ni, 0.25%-0.35% of Cu, 0.010%-0.020% of Ti, 0.010%-0.020% of Nb and the balance of iron and impurities. The compactness and stability of a steel rust layer are enhanced by optimizing chemical components and a production process, and corrosion of corrosive liquid to a matrix is prevented.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a method for improving the corrosion resistance of steel for railway vehicles. Background Art

[0002] With the rapid development of railway transportation technology, railway vehicles are developing towards high speed, heavy load and long life, which puts higher requirements on the performance of steel materials. Corrosion is one of the main forms of damage to steel materials. Especially when railway vehicles are exposed to the atmospheric environment for a long time, due to factors such as dry-wet alternation, temperature changes and industrial pollution, it is easy to cause local corrosion and rust layer shedding, thereby shortening the service life of the material. The traditional Q345B steel has limited corrosion resistance and can no longer meet the use requirements of modern railway vehicles in highly corrosive environments.

[0003] In recent years, high weathering steels such as Q450NQR1 steel have been gradually applied to the field of railway vehicles due to their excellent corrosion resistance in atmospheric environments. However, the rust layer formed by Q450NQR1 steel in the early stage of corrosion is still loose and not dense enough, and cannot completely prevent the corrosive liquid from invading the matrix. In addition, the distribution of key corrosion-resistant elements such as Cr, Cu, and Ni is uneven, and the role of alloy elements in protecting the rust layer cannot be effectively played.

[0004] In order to solve the above problems, it is urgent to develop a steel with better corrosion resistance. By adjusting the chemical composition and optimizing the production process, the corrosion rate can be further reduced, the density and stability of the rust layer can be improved, so as to extend the service life of the steel and reduce the maintenance cost. In response to this demand, the present invention proposes a new type of high weathering steel and its preparation method, which provides a new solution for the development of steel for railway vehicles. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the corrosion resistance of railway vehicle steel, and a new type of steel with excellent weather resistance is prepared by optimizing the chemical composition and production process. The present invention enhances the compactness and stability of the steel rust layer by accurately adjusting the proportions of elements such as C, Si, Mn, Cr, Ni, Cu, Ti and Nb; at the same time, by using optimized hot rolling and slow cooling processes, the key corrosion-resistant elements (such as Cr and Cu) in the rust layer are enriched in the pores, further preventing the corrosion of the substrate by the corrosive liquid.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for improving the corrosion resistance of steel for railway vehicles, comprising: steelmaking, continuous casting, heating, hot rolling, and slow cooling; the method is characterized in that:

[0008] After desulfurization, the molten iron is used for steelmaking in a converter, and undergoes LF refining and RH vacuum degassing to reduce impurity content and ensure accurate composition;

[0009] The molten steel is formed into ingots through continuous casting process. The ingots must be free of cracks, looseness and inclusion defects.

[0010] The ingot is heated to 1200°C to ensure uniform heating to reduce structural defects;

[0011] The multi-pass rolling process is adopted, the rough rolling and final rolling temperatures are controlled at 1050℃~1100℃, and the finishing rolling and final rolling temperatures are controlled at 850℃~890℃ to ensure the refinement of the microstructure;

[0012] After final rolling, the steel is slowly cooled to 650℃~700℃, and then slowly cooled to room temperature in a controlled cooling device to promote the enrichment of key elements in the rust layer and form a dense protective layer;

[0013] The chemical composition of the railway vehicle steel includes by weight percentage: C 0.03%-0.05%, Si 0.15%-0.20%, Mn 0.40%-0.50%, P≤0.015%, S≤0.010%, Cr 3.0-3.5%, Ni 0.25-0.35%, Cu 0.25-0.35%, Ti 0.010-0.020%, Nb 0.010-0.020%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%.

[0014] Furthermore, the chemical composition of the railway vehicle steel includes, by weight percentage, C 0.05%, Si 0.20%, Mn 0.47%, P 0.010%, S 0.005%, Cr 3.5%, Ni 0.3%, Cu 0.3%, Ti 0.01%, Nb 0.01%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%.

[0015] Furthermore, hot rolling parameters are: heating temperature 1200°C, rough rolling and final rolling temperature 1100°C.

[0016] Furthermore, the finishing rolling temperature is 890°C.

[0017] Furthermore, the final cooling temperature is 650°C.

[0018] Further, slow cooling method: slowly cooling to room temperature in a controlled cooling device.

[0019] Furthermore, compared with traditional steel, the corrosion weight loss rate is reduced by more than 30%.

[0020] The design ideas of chemical composition are as follows:

[0021] C: controlled at 0.03% to 0.05% to reduce the effect of carbon on grain boundary embrittlement while ensuring good plasticity and toughness;

[0022] Si: The content is controlled at 0.15% to 0.20%. As a deoxidizing element, it can promote the formation of oxide film, but too high a content will reduce the toughness of the steel, so the content is limited;

[0023] Mn: The content is controlled at 0.40% to 0.50%, mainly used to improve the strength of steel and ensure the deoxidation effect;

[0024] Cr: designed to be 3.0% to 3.5%. Cr is the core element of weathering steel and can be enriched in the pores of the rust layer to form a dense protective layer, effectively improving corrosion resistance;

[0025] Cu: The content is controlled at 0.25% to 0.35%. Cu can slow down the dissolution rate of iron, reduce the electronic conductivity of the rust layer, and inhibit the intrusion of Cl- in the marine atmosphere;

[0026] Ni: Add 0.25% to 0.35%. Ni can be enriched in the stable rust layer, further improving the corrosion resistance of steel in dry-wet alternation and industrial pollution environments;

[0027] P and S: strictly control P≤0.015%, S≤0.010% to reduce the damage of impurities to the integrity of the rust layer structure;

[0028] Ti and Nb: Add 0.01% to 0.02%. Trace amounts of Ti and Nb can refine the grains, improve the strength of steel, and promote the uniform formation of the rust layer in the early stages of corrosion.

[0029] Compared with the prior art, the beneficial technical effects of the present invention are:

[0030] Through the above design, the chemical composition of the present invention can quickly form a uniform and dense protective rust layer in a corrosive environment, significantly improving the corrosion resistance while taking into account the mechanical properties and economy.

[0031] The present invention discloses a method for improving the corrosion resistance of steel for railway vehicles, and successfully prepares a Q450EWR1 steel with significantly improved corrosion resistance by optimizing the chemical composition design and production process. By strictly controlling the proportions of alloying elements such as C, Si, Mn, Cr, Ni, Cu, Ti and Nb, the compactness and stability of the rust layer of the steel are improved; combined with the optimized steelmaking, hot rolling and slow cooling processes, the enrichment of key corrosion-resistant elements in the rust layer is ensured, and the corrosion of the substrate by the corrosive liquid is further prevented. According to performance tests, the steel of the present invention is superior to existing comparative steel grades in terms of corrosion weight loss rate and rust layer morphology, and is particularly suitable for the demand for high corrosion resistance in the long-term service environment of railway vehicles, providing an innovative technical solution for the promotion and application of high-weathering steel for railway vehicles.

[0032] (1) The present invention optimizes the chemical composition and adopts a slow cooling process, so that the steel can form a dense rust layer in a corrosive environment, and promotes the enrichment of key elements (such as Cr, Cu, and Ni) in the rust layer, effectively preventing the corrosive liquid from further corroding the matrix. Compared with traditional steel, the corrosion weight loss rate is reduced by more than 30%. (2) The prepared Q450EWR1 steel has excellent weather resistance and high stability, which can reduce the occurrence of rust layer shedding and steel corrosion in the long-term service environment of railway vehicles, significantly extend the service life, and reduce the frequency and cost of vehicle inspection and maintenance. (3) The method of the present invention is based on the existing steelmaking and hot rolling production lines, and can be achieved by optimizing process parameters. It has small equipment modification requirements and low cost investment. It has good prospects for industrial application, can meet large-scale production needs and improve the economic benefits of enterprises.

[0033] Compared with traditional Q450NQR1 steel and Q345B steel, the Q450EWR1 steel of the present invention can form a more uniform and dense block rust layer during the corrosion process, significantly reducing the corrosion rate and meeting the high corrosion resistance requirements of railway vehicles in a long-term service environment. The preparation method of the present invention is simple and easy to implement, and can be used in large-scale industrial production in existing production lines, providing technical guarantees for increasing the service life of railway vehicles and reducing maintenance costs, and has significant economic and social value. DETAILED DESCRIPTION

[0034] The following is a further detailed description of a method for improving the corrosion resistance of railway vehicle steel according to the present invention.

[0035] Embodiment: This embodiment is a preferred embodiment among various implementation modes of the present invention.

[0036] The present embodiment provides a method for improving the corrosion resistance of railway vehicle steel, the railway vehicle steel grade is Q450EWR1. The mass percentage of its chemical composition includes: C 0.03% to 0.05%, Si 0.15% to 0.20%, Mn 0.40% to 0.50%, P ≤ 0.015%, S ≤ 0.010%, Cr 3.0 to 3.5%, Ni 0.25 to 0.35%, Cu 0.25 to 0.35%, Ti 0.010 to 0.020%, Nb 0.010 to 0.020%, and the rest is Fe and unavoidable trace impurities, with a total mass fraction of 100%.

[0037] A method of improving the corrosion resistance of railway vehicle steel in this embodiment is: steelmaking, continuous casting, heating, hot rolling, and slow cooling.

[0038] After desulfurization, the molten iron is used for steelmaking in a converter, and undergoes LF refining and RH vacuum degassing to reduce impurity content and ensure accurate composition;

[0039] The molten steel is formed into ingots through continuous casting process. The ingots must be free of cracks, looseness and inclusion defects.

[0040] The ingot is heated to 1200°C to ensure uniform heating to reduce structural defects;

[0041] The multi-pass rolling process is adopted, the rough rolling and final rolling temperatures are controlled at 1050℃~1100℃, and the finishing rolling and final rolling temperatures are controlled at 850℃~890℃ to ensure the refinement of the microstructure;

[0042] After final rolling, the steel is slowly cooled to 650℃~700℃, and then slowly cooled to room temperature in a controlled cooling device to promote the enrichment of key elements in the rust layer and form a dense protective layer.

[0043] Embodiment 1:

[0044] The steel grade is Q450EWR1 steel with chemical composition of C 0.05%, Si 0.20%, Mn 0.47%, P 0.010%, S0.005%, Cr 3.5%, Ni 0.3%, Cu 0.3%, Ti 0.01%, Nb 0.01%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0045] Production process: molten iron desulfurization → converter steelmaking → LF refining → RH → continuous casting → hot rolling → slow cooling.

[0046] Hot rolling parameters: heating temperature 1200℃, rough rolling final rolling temperature 1100℃, finishing rolling final rolling temperature 890℃, final cooling temperature 650℃.

[0047] Slow cooling method: Slowly cool to room temperature in a controlled cooling device.

[0048] Experimental testing: Corrosion tests were carried out in accordance with GB / T 19746-2005 standard to measure the corrosion rate and rust layer density.

[0049] Comparative Example 1:

[0050] The steel grade is Q450NQR1 steel with chemical composition of C 0.11%, Si 0.25%, Mn 1.15%, P 0.012%, S0.007%, Cr 1.5%, Ni 0.25%, Cu 0.20%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0051] Traditional hot rolling process, without slow cooling treatment.

[0052] Comparative Example 2:

[0053] The steel grade is Q355B steel with the chemical composition of C 0.17%, Si 0.45%, Mn 1.55%, P 0.015%, S0.010%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0054] Traditional hot rolling process.

[0055] Comparative Example 3:

[0056] The steel type is silicon-containing weathering steel (experimental steel) with a chemical composition of C 0.13%, Si 0.45%, Mn 0.85%, P0.015%, S 0.010%, Cr 1.0%, Ni 0.15%, Cu 0.15%, Ti 0.01%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0057] Traditional hot rolling process.

[0058] Comparison of experimental results:

[0059] Corrosion weight loss rate: The relative weight loss rate of the Q450EWR1 steel in Example 1 was less than 30% in five cycles, while the relative weight loss rates of all comparative steel grades were higher than 30%, see Table 1.

[0060] Table 1 Weight loss rate and relative weight loss rate of the embodiments and comparative examples

[0061]

[0062] Rust layer morphology: The rust layer of Q450EWR1 steel gradually changes from loose cotton-like to a uniform and dense block structure, which effectively prevents the invasion of corrosive liquid; the rust layer of other steel types is loose and porous, lacks sufficient density, and corrosive liquid can easily penetrate the rust layer.

[0063] Key element distribution:

[0064] In the examples, key elements such as Cr, Ni, and Cu are significantly enriched in the pores of the rust layer; no obvious enrichment phenomenon is detected in the comparative examples.

[0065] The present invention prepares Q450EWR1 steel with significantly better corrosion resistance than traditional Q450NQR1 steel by optimizing chemical composition and process route. Its novelty is reflected in the compactness of rust layer and efficient enrichment of key elements, which significantly improves the practical application value of steel in railway vehicles.

[0066] It can be seen from the above examples and comparative examples that (1) the relative weight loss rate of Q450EWR1 steel in five corrosion cycles is always less than 30%, showing extremely excellent corrosion resistance. This is due to its optimized chemical composition design (especially the addition of corrosion-resistant elements such as Cr, Cu, and Ni) and slow cooling process, which makes the rust layer more compact and stable, effectively preventing the corrosion of the substrate by the corrosive liquid; (2) Compared with traditional Q355B steel, Q450NQR1 steel significantly reduces the relative weight loss rate by adding a certain amount of corrosion-resistant elements (such as Cr and Cu). However, due to the insufficient density of the rust layer and the uniformity of element distribution, its corrosion resistance is still inferior to that of Q450EWR1 steel; (3) The relative weight loss rate of Q355B steel reached 100% in all cycles, indicating that its rust layer structure in a corrosive environment is loose and its protective effect on the matrix is ​​extremely limited, which cannot meet the high corrosion resistance requirements of railway vehicles; (4) From the experimental results, it can be seen that the reasonable addition of corrosion-resistant elements such as Cr, Cu, and Ni, as well as the use of final rolling and slow cooling process, are crucial to significantly improve the corrosion resistance of steel. With scientific design, Q450EWR1 steel has achieved a perfect balance between performance and economy, showing broad application prospects; (5) Q450EWR1 steel has significant technical advantages and can effectively meet the requirements of railway vehicle steel for high corrosion resistance and long life, providing important reference and application value for technological progress in this field.

[0067] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the corrosion resistance of railway vehicle steel, comprising: Steelmaking, continuous casting, heating, hot rolling, slow cooling; its characteristics are: After desulfurization, the molten iron is used for steelmaking in a converter, and then undergoes LF refining and RH vacuum degassing to reduce impurity content and ensure accurate composition; The molten steel is formed into ingots through continuous casting process. The ingots must be free of cracks, looseness and inclusion defects. The ingot is heated to 1200°C to ensure uniform heating to reduce structural defects; The multi-pass rolling process is adopted, the rough rolling and final rolling temperatures are controlled at 1050℃~1100℃, and the finishing rolling and final rolling temperatures are controlled at 850℃~890℃ to ensure the refinement of the microstructure; After final rolling, the steel is slowly cooled to 650℃~700℃, and then slowly cooled to room temperature in a controlled cooling device to promote the enrichment of key elements in the rust layer and form a dense protective layer; The chemical composition of the railway vehicle steel includes by weight percentage: C 0.03%-0.05%, Si 0.15%-0.20%, Mn 0.40%-0.50%, P≤0.015%, S≤0.010%, Cr 3.0-3.5%, Ni 0.25-0.35%, Cu 0.25-0.35%, Ti 0.010-0.020%, Nb 0.010-0.020%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%.

2. The method for improving the corrosion resistance of railway vehicle steel according to claim 1, characterized in that: The chemical composition of the railway vehicle steel includes, by weight percentage, C 0.05%, Si 0.20%, Mn 0.47%, P 0.010%, S 0.005%, Cr 3.5%, Ni 0.3%, Cu 0.3%, Ti 0.01%, Nb 0.01%, and the rest is Fe and unavoidable trace impurities, with a total weight fraction of 100%.

3. The method for improving the corrosion resistance of railway vehicle steel according to claim 2, characterized in that: Hot rolling parameters: heating temperature 1200℃, rough rolling and final rolling temperature 1100℃.

4. The method for improving the corrosion resistance of railway vehicle steel according to claim 3, characterized in that: The final rolling temperature is 890℃.

5. The method for improving the corrosion resistance of railway vehicle steel according to claim 4, characterized in that: Final cooling temperature is 650℃.

6. The method for improving the corrosion resistance of railway vehicle steel according to claim 5, characterized in that: Slow cooling method: Slowly cool to room temperature in a controlled cooling device.

7. The method for improving the corrosion resistance of railway vehicle steel according to claim 1, characterized in that: Compared with traditional steel, the corrosion weight loss rate is reduced by more than 30%.

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