Hydrogen embrittlement-resistant high-entropy alloy based on carbide precipitated phase strengthening and preparation method of hydrogen embrittlement-resistant high-entropy alloy

Abstract

The invention discloses a hydrogen embrittlement-resistant high-entropy alloy based on carbide precipitated phase strengthening. The hydrogen embrittlement-resistant high-entropy alloy is composed of Co, Cr, Fe, Mn, Ni, M and C elements. The chemical general formula of the material is (CoCrFeMnNi) (1-x-y) MxCy, the preparation method comprises the following steps: preparing raw materials; smelting in a vacuum furnace; performing homogenizing annealing; air cooling; hot rolling; cold rolling to the product thickness; annealing is conducted; and water-cooling to room temperature. The composite material is composed of an FCC face-centered cubic phase and an MC type carbide precipitated phase. The tensile strength before hydrogen filling is 650-740 MPa, the elongation percentage is 35.2-40.4%, the tensile strength after hydrogen filling is 620-700 MPa, the elongation percentage is 34.6-38.8%, the hydrogen-induced plasticity loss rate is 1.70-3.96%, the production process is simple and convenient, and large-scale industrial production can be achieved conveniently.

Description

Technical Field

[0001] The invention belongs to the field of high entropy alloy materials, and specifically refers to a high entropy alloy resistant to hydrogen embrittlement based on carbide precipitation phase strengthening and a preparation method thereof. Background Art

[0002] Hydrogen embrittlement refers to the phenomenon that hydrogen atoms that penetrate into the metal interact with the matrix, resulting in a decrease in the mechanical properties of the material, such as strength and elongation, or causing stress concentration inside the material, resulting in cracks and hydrogen-induced fracture. With the rapid development of science and technology, the performance requirements for engineering equipment materials are becoming higher and higher, especially in the fields of aviation, ocean, petroleum, chemical industry, nuclear energy, etc. Since the working environment in the above-mentioned fields is usually high-pressure hydrogen, high-temperature water-salt solution, etc., the engineering equipment materials will be exposed to hydrogen-containing environments for a long time, posing a major threat to the safety and reliability of the parts, and increasing the risk of hydrogen embrittlement. Therefore, the materials are required to have excellent hydrogen embrittlement resistance.

[0003] The earliest definition of high entropy alloy is a multi-principal alloy composed of 5 or more main elements in equal or nearly equal molar ratios, and the proportion of each element in the total alloy composition (atomic fraction) is between 5% and 35%. Studies have found that high entropy alloys also have outstanding hydrogen embrittlement resistance, and the tensile mechanical properties hardly change after hydrogen charging. Therefore, high entropy alloys are regarded as highly potential hydrogen embrittlement-resistant materials.

[0004] The patent document with publication number CN117845117A discloses a method for preparing a corrosion-resistant and hydrogen-embrittlement-resistant high-entropy alloy. Six elements Al, Co, Cr, Fe, Ni, and Cu with large melting point differences are used. The hydrogen embrittlement resistance is improved through composition design and heat treatment process. The hydrogen-induced plasticity loss rate is 2.02-4.76%, which needs to be further improved. The patent document with publication number CN117418174A discloses a method for preparing a high-strength and tough, hydrogen-embrittlement-resistant Nb microalloyed high-entropy alloy. Through Nb microalloying and organizational regulation, the strength change before and after hydrogen charging is small, but the plasticity loss is more serious, and its hydrogen-induced plasticity loss rate is 56.9-72.7%. Summary of the invention

[0005] The invention aims to provide a high entropy alloy resistant to hydrogen embrittlement based on carbide precipitation phase strengthening and a preparation method thereof. By controlling the heat treatment process, the carbide precipitation phase is located inside the grain, and the quantity and size are moderate, so as to achieve the purpose of strengthening the hydrogen embrittlement resistance of the high entropy alloy; and the tensile strength before hydrogen charging is 650-740MPa, the elongation is 35.2-40.4%, the tensile strength after hydrogen charging is 620-700MPa, the elongation is 34.6-38.8%, and the hydrogen-induced plasticity loss rate is 1.70-3.96%.

[0006] Measures to achieve the above objectives:

[0007] A high entropy alloy based on carbide precipitation phase strengthening and anti-hydrogen embrittlement, which is composed of Co, Cr, Fe, Mn, Ni, M, and C elements; its general chemical formula is: (CoCrFeMnNi) 1-x-y M x C y ,

[0008] Where: x—represents the mass percentage of the M element, and its value range is 0<x≤5;

[0009] y—represents the mass percentage of C element, and its value range is 0<y≤0.5;

[0010] M—represents the general term for auxiliary elements, including one or a combination of elements Mo, Nb, V, and Ti, in mass percentage %;

[0011] C—is carbon element, the unit is mass percentage %;

[0012] Note: The mass percentage of each element Co, Cr, Fe, Mn, Ni, M, and C is the same;

[0013] Preferably, the value range of x is: 2≤x≤5.

[0014] Preferably, the value range of y is: 0.2≤y≤0.5.

[0015] A method for preparing a hydrogen embrittlement resistant high entropy alloy based on carbide precipitation phase strengthening, the steps are:

[0016] 1) Raw materials configuration

[0017] Co, Cr, Fe, Mn, Ni, and M metal particles with purities higher than 99.9% are weighed according to their respective value ranges, wherein the C element is added in the form of FeC alloy. Since the C element is added in the form of FeC alloy, this part should be subtracted when calculating the mass of the corresponding pure Fe metal particles, and the Fe content is also not less than 99.9%;

[0018] 2) Melting in a vacuum furnace

[0019] Put the above-prepared raw materials into a vacuum furnace for smelting. During this period: close the vacuum cover and wait until the vacuum degree is ≤5×

[0020] 10 -3 Pa, introduce argon gas for stirring and melting; and control the whole process to repeat the melting 4 to 5 times; then cast into ingots, and the thickness of the ingots is controlled to be 40 to 45 mm;

[0021] 3) Perform homogenization annealing, control the annealing temperature at 1230-1270°C, and keep it at this temperature for 50-70 minutes;

[0022] 4) Air cooling to 150-200°C;

[0023] 5) hot rolling, controlling the initial rolling temperature at 980-1020° C., the final rolling temperature at 890-910° C., the rolling passes at 3-4 times, and the total deformation at 40-50%;

[0024] 6) Cold rolling to product thickness, controlling the rolling passes to 5-6 times, and the total deformation to 85-90%;

[0025] 7) Annealing is performed, the annealing temperature is controlled at 890-910°C, and the temperature is kept at this temperature for 25-35 minutes;

[0026] 8) Cool with water to room temperature at a cooling rate of 25 to 32°C / s.

[0027] The functions and mechanisms of the components and main processes in the present invention.

[0028] Co: The Co element helps to stabilize the FCC phase and reduce the diffusion rate of hydrogen, thereby reducing the risk of hydrogen aggregation in the alloy and inducing hydrogen embrittlement, and improving the alloy's resistance to hydrogen embrittlement. However, excessive Co may cause brittle phases or element segregation in the alloy, thereby reducing the resistance to hydrogen embrittlement.

[0029] Cr: The Cr element mainly affects the diffusion and capture of hydrogen in high entropy alloys. The Cr-H system can capture hydrogen atoms more effectively, and the hydrogen diffusion coefficient decreases significantly with the increase of Cr concentration. However, excessive Cr content will gradually precipitate BCC or B2 phase in the alloy, making the alloy hard and brittle.

[0030] Fe: The Fe element mainly affects the phase structure of high entropy alloys, and thus affects their resistance to hydrogen embrittlement. An appropriate amount of Fe can improve the structural stability of the FCC phase, reduce the number of hard and brittle BCC phases, and improve the resistance to hydrogen embrittlement. Too low Fe content will lead to an increase in the proportion of BCC phases and an increase in the hydrogen embrittlement sensitivity of the alloy. Too high Fe content will make the alloy brittle and reduce ductility.

[0031] Mn: Mn element will increase the stacking fault energy of high entropy alloys. An appropriate amount of Mn element can activate mechanisms such as solid solution strengthening and precipitation strengthening, which helps to improve the overall strength of the alloy, thereby enhancing its resistance to hydrogen embrittlement to a certain extent. Excessive Mn element will promote intergranular fracture, thereby reducing the alloy's resistance to hydrogen embrittlement.

[0032] Ni: The effect of Ni on the hydrogen embrittlement resistance of high entropy alloys is similar to that of Fe. Ni is also an element that improves the stability of the FCC phase. Too low Ni content will lead to an increase in the BCC phase ratio and an increase in the hydrogen embrittlement sensitivity of the alloy. Too high Ni content will lead to a decrease in the plasticity of the alloy.

[0033] Mo, Nb, V, Ti, C: Mo, Nb, V, Ti, and C elements mainly generate precipitates as hydrogen trap capture sites, reduce the diffusion and aggregation of hydrogen, and improve the material's resistance to hydrogen embrittlement. However, the more precipitates there are, the more hydrogen is trapped, which will cause serious hydrogen-induced local plastic deformation. Therefore, in the present invention, the content of Mo, Nb, V, and Ti is controlled to no more than 5%, and the content of C is controlled to no more than 0.5%.

[0034] The reason why the present invention closes the vacuum cover during vacuum smelting and introduces argon gas for stirring and smelting when the vacuum degree is ≤5×10-3Pa is to prevent the metal from reacting with oxygen at high temperature, thereby preventing the metal from being oxidized or producing other unnecessary compounds.

[0035] The reason why the present invention controls the homogenization annealing temperature at 1230-1270°C and keeps it at this temperature for 50-70 minutes is to promote the diffusion of alloy elements, make the chemical composition inside the alloy more uniform, eliminate element segregation, and avoid melting of alloy grain boundaries and burning of main elements due to excessively high temperature or excessively long time, thereby reducing the performance of the alloy.

[0036] The reason why the present invention controls the initial rolling temperature at 980-1020° C., the final rolling temperature at 890-910° C., and the total deformation at 40-50% is to refine the grains and improve the internal organizational structure.

[0037] The reason why the cumulative deformation of cold rolling is controlled within 80-90% in the present invention is to further refine the grains and introduce a large number of dislocations and grain boundaries.

[0038] The reason why the present invention controls the annealing temperature at 890-910° C. and keeps the temperature at 890-910° C. for 25-35 minutes is to promote the recrystallization of deformed grains in the alloy and the precipitation of carbides and other precipitates.

[0039] The reason why the cooling rate of the present invention is 25-32°C / s is to eliminate the internal stress generated in the alloy during the rolling process.

[0040] Compared with the prior art, the present invention consists of an FCC face-centered cubic phase and an MC type carbide precipitation phase; the tensile strength before hydrogen charging is 650-740 MPa, the elongation is 35.2-40.4%, the tensile strength after hydrogen charging is 620-700 MPa, the elongation is 34.6-38.8%, the hydrogen-induced plasticity loss rate is 1.70-3.96%, and the production process is simple, which is convenient for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the SEM organization diagram of the present invention. DETAILED DESCRIPTION

[0042] The present invention is described in detail below:

[0043] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0044] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0045] Table 3 is a table of performance test results of various embodiments and comparative examples of the present invention.

[0046] Each embodiment of the present invention is produced according to the following steps

[0047] 1) Raw materials configuration

[0048] Co, Cr, Fe, Mn, Ni, and M metal particles with purities higher than 99.9% are weighed according to their respective value ranges, wherein the C element is added in the form of FeC alloy. Since the C element is added in the form of FeC alloy, this part should be subtracted when calculating the mass of the corresponding pure Fe metal particles, and the Fe content is also not less than 99.9%;

[0049] 2) Melting in a vacuum furnace

[0050] The prepared raw materials are placed in a vacuum furnace for smelting. During this period, the vacuum cover is closed and the vacuum degree is ≤5×10 -3 Pa, introduce argon gas for stirring and melting; and control the whole process to repeat the melting 4 to 5 times; then cast into ingots, and the thickness of the ingots is controlled to be 40 to 45 mm;

[0051] 3) Perform homogenization annealing, control the annealing temperature at 1230-1270°C, and keep it at this temperature for 50-70 minutes;

[0052] 4) Air cooling to 150-200°C;

[0053] 5) hot rolling, controlling the initial rolling temperature at 980-1020° C., the final rolling temperature at 890-910° C., the rolling passes at 3-4 times, and the total deformation at 40-50%;

[0054] 6) Cold rolling to product thickness, controlling the rolling passes to 5-6 times, and the total deformation to 85-90%;

[0055] 7) Annealing is performed, and the annealing temperature is controlled at 890-910°C, and kept at this temperature for 25-35 minutes.

[0056] 8) Cool with water to room temperature at a cooling rate of 25 to 32°C / s.

[0057] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0058]

[0059] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0060]

[0061] Table 2

[0062]

[0063]

[0064] Table 3 List of mechanical properties test results of various embodiments of the present invention and comparative examples

[0065]

[0066] From the results in Table 3, it can be seen that the high entropy alloy using the composition design and production process of the present invention has excellent hydrogen embrittlement resistance, with a tensile strength of 650-740MPa before hydrogen charging, an elongation of 35.2-40.4%, a tensile strength of 620-700MPa after hydrogen charging, an elongation of 34.6-38.8%, and a hydrogen-induced plasticity loss rate of 1.70-3.96%. However, the performance indicators of Comparative Examples 1 and 2, which are not within the design range, are not as good as those of the embodiments, and the hydrogen embrittlement resistance is poor, and the hydrogen-induced plasticity loss rate is 11.16-19.34%. It can be seen that MC precipitates have a positive effect on the hydrogen embrittlement resistance of high entropy alloys, and the degree of influence thereof increases first and then decreases with the type and quantity of MC precipitates.

[0067] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A high entropy alloy based on carbide precipitation phase strengthening and anti-hydrogen embrittlement, which is composed of Co, Cr, Fe, Mn, Ni, M, and C elements; its general chemical formula is: (CoCrFeMnNi) 1-x-y M x C y , Where: x—represents the mass percentage of the M element, and its value range is 0<x≤5; y—represents the mass percentage of C element, and its value range is 0<y≤0.5; M—represents the general term for auxiliary elements, including one or a combination of elements Mo, Nb, V, and Ti, in mass percentage %; C—is carbon element, the unit is mass percentage %; Note: The mass percentage of each element Co, Cr, Fe, Mn, Ni, M, and C is the same.

2. A high entropy alloy based on carbide precipitation phase strengthening and hydrogen embrittlement resistance as claimed in claim 1, characterized in that: The value range of x is: 2≤x≤5.

3. A high entropy alloy based on carbide precipitation phase strengthening and hydrogen embrittlement resistance as claimed in claim 1, characterized in that: The value range of y is: 0.2≤y≤0.

5.

4. A method for preparing a high entropy alloy resistant to hydrogen embrittlement based on carbide precipitation phase strengthening as claimed in claim 1, comprising the steps of: 1) Raw materials configuration Co, Cr, Fe, Mn, Ni, and M metal particles with purities higher than 99.9% are weighed according to their respective value ranges, wherein the C element is added in the form of FeC alloy. Since the C element is added in the form of FeC alloy, this part should be subtracted when calculating the mass of the corresponding pure Fe metal particles, and the Fe content is also not less than 99.9%; 2) Melting in a vacuum furnace The prepared raw materials are placed in a vacuum furnace for smelting. During this period, the vacuum cover is closed and the vacuum degree is ≤5×10 -3 Pa, introduce argon gas for stirring and melting; and control the whole process to repeat the melting 4 to 5 times; then cast into ingots, and the thickness of the ingots is controlled to be 40 to 45 mm; 3) Perform homogenization annealing, control the annealing temperature at 1230-1270°C, and keep it at this temperature for 50-70 minutes; 4) Air cooling to 150-200°C; 5) hot rolling, controlling the initial rolling temperature at 980-1020° C., the final rolling temperature at 890-910° C., the rolling passes at 3-4 times, and the total deformation at 40-50%; 6) Cold rolling to product thickness, controlling the rolling passes to 5-6 times, and the total deformation to 85-90%; 7) Annealing is performed, and the annealing temperature is controlled at 890-910°C, and kept at this temperature for 25-35 minutes. 8) Cool with water to room temperature at a cooling rate of 25 to 32°C / s.

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