EGR cooler based on corrosion-resistant material

Abstract

The invention discloses an EGR (Exhaust Gas Recirculation) cooler based on a corrosion-resistant material, the EGR cooler adopts the corrosion-resistant material, and the corrosion-resistant material comprises the following components in percentage by mass: 17.0 to 20.0 percent of Cr, 0 to 0.8 percent of Nb, 0 to 0.8 percent of Ti, 0 to 0.8 percent of W, 1.75 to 5.0 percent of Mo and 0 to 0.025 percent of N. The corrosion-resistant material which is excellent in corrosion resistance and relatively low in price is applied to the EGR cooler, the corrosion resistance of the EGR cooler is improved, and compared with 300-series stainless steel, the Ni content is greatly reduced, so that the cost is reduced, and the problems that the corrosion-resistant material adopted by an existing EGR cooler is insufficient in corrosion resistance and high in price are solved; and by adding transfer elements Nb, Ti, W, Mo and N, the corrosion resistance of the corrosion-resistant material is improved.

Description

Technical Field

[0001] The present invention relates to the field of coolants, and more particularly to an EGR cooler based on corrosion-resistant materials. Background Art

[0002] An EGR (Exhaust Gas Re-circulation) cooler, that is, an exhaust gas recirculation cooler, allows a part of the engine exhaust gas to recombine with the filtered fresh air and enter the cylinder, and re-introduces a small amount of exhaust gas into the intake valve, which can reduce the temperature of the exhaust gas entering the cylinder. The lower the temperature of the exhaust gas, the better the inhibitory effect on NOx of the engine. In this way, it is possible to avoid the problem that the direct entry of the exhaust gas into the cylinder at too high a temperature will cause very poor combustion, resulting in problems such as insufficient power and black smoke.

[0003] During the operation of the EGR cooler, corrosion problems are likely to occur. Therefore, corrosion-resistant materials are often used in the existing EGR coolers. The existing corrosion-resistant materials are mainly stainless steel materials, including the 300 series and the 400 series. Among them, the corrosion resistance of the 300 series is better than that of the 400 series, but the 300 series has a high Ni content. Since nickel is a precious metal with large price fluctuations, its price is expensive.

[0004] Therefore, it is of great significance to use a corrosion-resistant material with excellent corrosion resistance and price competitiveness for the EGR cooler. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides an EGR cooler based on corrosion-resistant materials, which uses a corrosion-resistant material with excellent corrosion resistance and relatively low price, and solves the problems of insufficient corrosion resistance and high price of the corrosion-resistant materials used in the existing EGR coolers.

[0006] To solve the above technical problems, the present invention provides an EGR cooler based on corrosion-resistant materials. The EGR cooler uses the corrosion-resistant material, and the corrosion-resistant material includes the following components in mass percentage: Cr 17.0 - 20.0%, Nb 0 - 0.8%, Ti 0 - 0.8%, W 1.0 - 5.0%, Mo 1.75 - 5.0%, N 0 - 0.025%.

[0007] Further, the corrosion-resistant material further includes the following components in mass percentage: Ni 0 - 1.0%, C 0 - 0.025%, Si 0 - 1.0%, Mn 0 - 1.0%, P 0 - 0.04%, S 0 - 0.03%.

[0008] Furthermore, the mass percentages of the components of the corrosion-resistant material are as follows: Cr 18.0 - 19.0%, Nb 0.5 - 0.6%, Ti 0.2 - 0.3%, W 1.0 - 2.0%, Mo 2.0 - 3.0%, N 0.005 - 0.01%.

[0009] Furthermore, the mass percentages of the components of the corrosion-resistant material are as follows: Ni 0.1 - 0.2%, C 0.005 - 0.01%, Si 0.4 - 0.5%, Mn 0.8 - 0.9%, P 0.02 - 0.03%, S 0.003 - 0.004%.

[0010] Furthermore, the sum of the mass percentages of Nb and Ti is 0.8%.

[0011] Furthermore, the balance of the corrosion-resistant material is Fe.

[0012] Furthermore, the corrosion-resistant material stabilizes the C element by preferentially combining Nb and Ti with C to form carbides.

[0013] Furthermore, the corrosion-resistant material stabilizes the Cr oxide film through W, Mo, and N in a corrosive environment.

[0014] In the corrosion-resistant material, based on the property that Cr is prone to combine with C and its characteristic of becoming more active when heated, Cr 23 C6 (chromium carbide) will be formed, resulting in the shedding of Cr grains. In the present invention, transfer elements Nb and Ti (Nb + Ti = 0.8%) are added to the corrosion-resistant material. First, Ti and Nb react with C to form NbTi / C composite carbides, and the formation of this composite carbide can improve the binding property between C and the iron matrix. Second, Ti and Nb can also combine with C to form stable carbides, prevent C from combining with Cr to form a sensitization phenomenon, consume free carbon, prevent the formation of harmful phases, and at the same time refine the structure by pinning the grain boundaries, significantly improving the high-temperature performance, mechanical properties, and corrosion resistance of the material, thereby ensuring the mechanical properties and corrosion resistance of the material.

[0015] The exhaust gas treated by the EGR cooler is corrosive. Among them, halogens in Group 17 of the periodic table such as chloride ions will damage the Cr2O3 chromium oxide film on the surface of the EGR cooler components and gradually corrode inward, resulting in local pitting corrosion and affecting the life of the cooler. In the present invention, transfer elements W, Mo, and N are added. Through multiple mechanisms such as solid solution strengthening, inhibiting Cr depletion, forming a composite oxide film, and enhancing the passivation ability, the integrity of the Cr2O3 film is synergistically protected. This effect is particularly significant in high-temperature oxidation, sulfidation, or halogen ion environments, enabling the material to maintain excellent corrosion resistance and oxidation resistance under harsh conditions. The specific principle is as follows:

[0016] (1) Inhibit the diffusion of harmful elements and densify the oxide film: W and Mo dissolve in the matrix, delay the destruction of the oxide film (Cr2O3) by reducing the diffusion rate of harmful elements such as oxygen, sulfur, and chlorine. At the same time, their high-melting-point oxides (such as WO3, MoO2) are embedded in the Cr2O3 film, filling the lattice defects, enhancing the denseness of the film, and reducing the penetration of oxidation media (O2, S, etc.). N forms interstitial solid solutions or nitrides (such as Cr2N) in steel, which can refine the grains and inhibit the grain boundary depletion of Cr. This effect can maintain the surface Cr concentration, ensuring the continuity and rapid repair ability of the oxide film.

[0017] (2) Inhibit the depletion of Cr and maintain the regeneration of the oxide film: In high-temperature or corrosive environments, Cr will preferentially oxidize to form a Cr2O3 protective film. W and Mo regulate the diffusion of Cr, avoid the depletion of Cr in the matrix, ensure that there is enough Cr in the matrix to continuously supplement the oxide film, and maintain its integrity. N combines with Cr to form chromium nitride (Cr2N), inhibits the excessive oxidation consumption of Cr, and at the same time stabilizes the austenite structure, reducing the Cr depletion at the grain boundaries, thus avoiding the preferential rupture of the oxide film at the grain boundaries.

[0018] (3) Form composite oxides or nitrides to enhance protection: Oxides of W and Mo (such as WO3, MoO2) can form a composite oxide layer with Cr2O3, improving the adhesion and high-temperature stability of the film. For example, Mo can generate MoS2 or Mo-O-S complexes in a sulfur-containing environment, inhibiting the destruction of the Cr2O3 film by sulfidation corrosion. N participates in the formation of nitrogen oxides (such as Cr-O-N) at high temperatures. These compounds are denser than pure Cr2O3 and have higher chemical inertness, effectively resisting the erosion of acidic or sulfide environments. In addition, in an environment containing halogen ions such as chloride ions, Mo can promote the repassivation ability of the passive film and inhibit the expansion of pitting corrosion. Its oxidation products (such as MoO4 2- ) can be adsorbed at the defects of the oxide film, blocking the progress of the corrosion reaction. N improves the pitting corrosion and crevice corrosion resistance of the material by enhancing the stability of the passive film.

[0019] Furthermore, the heat exchange component of the EGR cooler uses the corrosion-resistant material.

[0020] Furthermore, in the EGR cooler, the components using the corrosion-resistant material include the gas pipe, corrugated fins, and matrix plate.

[0021] Advantages of the present invention:

[0022] The present invention uses a corrosion-resistant material with excellent corrosion resistance and relatively low price in the EGR cooler to improve the corrosion resistance of the EGR cooler. Compared with the 300 series, the Ni content is greatly reduced, thus reducing the cost and solving the problems of insufficient corrosion resistance and high price of the corrosion-resistant materials used in the existing EGR coolers.

[0023] In the present invention, the elements Nb and Ti preferentially combine with C to form carbides instead of Cr, avoiding the problem of Cr grain shedding caused by the combination of Cr and C to form carbides; in a corrosive environment, the Cr oxide film is stabilized by W, Mo, and N, avoiding the problem of local pitting corrosion caused by the destruction of the Cr oxide film. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 is a schematic diagram of the corrosion of the grain boundary where Cr combines with C;

[0026] Figure 2 is a metallographic photograph of the corrosion-resistant material before the corrosion experiment in Example 1 of the present invention;

[0027] Figure 3 is a metallographic photograph of the corrosion-resistant material after the corrosion test in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0029] This embodiment provides an EGR cooler based on a corrosion-resistant material. The EGR cooler uses the corrosion-resistant material, and the corrosion-resistant material includes the following components by mass percentage: Cr 17.0 - 20.0%, Nb 0 - 0.8%, Ti 0 - 0.8%, W 1.0 - 5.0%, Mo 1.75 - 5.0%, N 0 - 0.025%, Ni 0 - 1.0%, C 0 - 0.025%, Si 0 - 1.0%, Mn 0 - 1.0%, P 0 - 0.04%, S 0 - 0.03%.

[0030] As a preferred embodiment, the mass percentages of the components of the corrosion-resistant material are as follows: Cr 18.0 - 19.0%, Nb 0.5 - 0.6%, Ti 0.2 - 0.3%, W 1.0 - 2.0%, Mo 2.0 - 3.0%, N 0.005 - 0.01%, Ni 0.1 - 0.2%, C 0.005 - 0.01%, Si 0.4 - 0.5%, Mn 0.8 - 0.9%, P 0.02 - 0.03%, S 0.003 - 0.004%, and the balance is Fe. More preferably, the sum of the mass percentages of Nb and Ti is 0.8%.

[0031] Specifically, in the corrosion-resistant material, Nb and Ti preferentially combine with C to form carbides to stabilize the C element, and W, Mo, and N stabilize the Cr oxide film in the corrosion environment.

[0032] In this embodiment, referring to Figure 1 , in the corrosion-resistant material, based on the property that Cr is prone to combine with C and its characteristic of being more active when heated, Cr 23 C6 (chromium carbide) will be formed at this time, resulting in the shedding of Cr grains. In the present invention, the transfer elements Nb and Ti (Nb + Ti = 0.8%) are added to the corrosion-resistant material. First, Ti and Nb react with C to form NbTi / C composite carbides, and the formation of this composite carbide can improve the binding property between C and the iron matrix. Secondly, Ti and Nb can also combine with C to form stable carbides, prevent C from combining with Cr to form a sensitization phenomenon, consume free carbon, prevent the formation of harmful phases, and at the same time refine the structure by pinning grain boundaries, significantly improving the high-temperature performance, mechanical properties, and corrosion resistance of the material, thereby ensuring the mechanical properties and corrosion resistance of the material. The exhaust gas treated by the EGR cooler is corrosive. Among them, halogens in Group 17 of the periodic table such as chloride ions will damage the Cr2O3 chromium oxide film on the surface of the EGR cooler components and gradually corrode inward, resulting in local pitting corrosion and affecting the life of the cooler. In the present invention, the transfer elements W, Mo, and N are added, and through multiple mechanisms such as solid solution strengthening, inhibiting Cr depletion, forming a composite oxide film, and enhancing passivation ability, the integrity of the Cr2O3 film is synergistically protected. This effect is particularly significant in high-temperature oxidation, sulfidation, or halogen ion environments, enabling the material to maintain excellent corrosion resistance and oxidation resistance under harsh conditions.

[0033] Specifically, the heat exchange components of the EGR cooler are made of the corrosion-resistant material, and specifically include a gas pipe, corrugated fins, and a base plate.

[0034] Example 1

[0035] This embodiment relates to a corrosion-resistant material for an EGR cooler. The mass percentages of the components of the corrosion-resistant material are as follows: Cr 18.576%, Nb 0.553%, Ti 0.247%, W 1.12%, Mo 2.418%, N 0.0088%, Ni 0.102%, C 0.0089%, Si 0.427%, Mn 0.859%, P 0.0255%, S 0.0038%, and the balance is Fe.

[0036] Comparative Example 1

[0037] This comparative example is commercially available SUS444.

[0038] Test Example

[0039] The samples of Example 1 and Comparative Example 1 were divided into three groups for corrosion resistance tests. The samples were placed in a 6% by mass FeCl3 solution and soaked at 22 ± 1°C for 72 h. The corrosion rate was calculated as (weight of the sample before the test - weight of the sample after the test) / sample area / test time. The results are shown in Table 1.

[0040] Table 1

[0041]

[0042] As can be seen from Table 1, under the same corrosion conditions, the corrosion resistance of the corrosion-resistant material in Example 1 was significantly improved compared to SUS444, and the corrosion was reduced by 41.6%. Among them, Figure 2 and Figure 3 are the metallographic photos before and after the corrosion test of the example respectively. It can be seen that after the test, corresponding corrosion appears at the grain boundaries. However, due to the stable addition of the transition elements Nb, Ti, W, Mo, and N, the grains are ensured to be stable, avoiding the problem of grain shedding.

[0043] In summary, the present invention uses a corrosion-resistant material with excellent corrosion resistance and relatively low price in the EGR cooler, improving the corrosion resistance of the EGR cooler and reducing costs, solving the problems of insufficient corrosion resistance and high price of the corrosion-resistant materials used in the existing EGR coolers; by the transition elements Nb and Ti preferentially combining with C to form carbides, avoiding the problem of Cr grain shedding caused by the combination of Cr and C to form carbides; in the corrosion environment, stabilizing the Cr oxide film by W, Mo, and N, avoiding the problem of local pitting corrosion caused by the destruction of the Cr oxide film.

[0044] The present invention has been described in detail above in connection with specific embodiments and exemplary examples. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and all of these fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. An EGR cooler based on corrosion-resistant materials, characterized in that, The EGR cooler adopts the corrosion-resistant material, and the corrosion-resistant material comprises components with the following mass percentages: Cr 17.0 - 20.0%, Nb 0 - 0.8%, Ti 0 - 0.8%, W 1.0 - 5.0%, Mo 1.75 - 5.0%, N 0 - 0.025%.

2. The EGR cooler based on a corrosion-resistant material according to claim 1, wherein The corrosion-resistant material further comprises components with the following mass percentages: Ni 0 - 1.0%, C 0 - 0.025%, Si 0 - 1.0%, Mn 0 - 1.0%, P 0 - 0.04%, S 0 - 0.03%.

3. The EGR cooler based on a corrosion-resistant material according to claim 2, wherein The mass percentages of the components of the corrosion-resistant material are: Cr 18.0 - 19.0%, Nb 0.5 - 0.6%, Ti 0.2 - 0.3%, W 1.0 - 2.0%, Mo 2.0 - 3.0%, N 0.005 - 0.01%.

4. The EGR cooler based on a corrosion-resistant material according to claim 3, characterized in that, The mass percentages of the components of the corrosion-resistant material are: Ni 0.1 - 0.2%, C 0.005 - 0.01%, Si 0.4 - 0.5%, Mn 0.8 - 0.9%, P 0.02 - 0.03%, S 0.003 - 0.004%.

5. The EGR cooler based on a corrosion-resistant material according to claim 4, characterized in that, The balance of the corrosion-resistant material is Fe.

6. The EGR cooler based on a corrosion-resistant material according to claim 4, wherein The sum of the mass percentages of Nb and Ti is 0.8%.

7. The EGR cooler based on a corrosion-resistant material according to claim 2, wherein In the corrosion-resistant material, C element is stabilized by forming carbides with Nb and Ti prior to Cr combining with C.

8. The EGR cooler based on a corrosion-resistant material according to claim 2, characterized in that, In the corrosion environment, the Cr oxide film is stabilized by W, Mo, and N in the corrosion-resistant material.

9. The EGR cooler based on a corrosion-resistant material according to claim 1, wherein The heat exchange component of the EGR cooler adopts the corrosion-resistant material.

10. The EGR cooler based on corrosion-resistant materials according to claim 1, characterized in that, In the EGR cooler, the components adopting the corrosion-resistant material include an air pipe, corrugated fins, and a base plate.

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