Preparation method of high-strength beryllium-aluminum composite material by breaking continuous beryllium oxide layer of beryllium particle reinforcement through matrix alloying

Abstract

The invention relates to a preparation method of a high-strength beryllium-aluminum composite material, in particular to a preparation method of a high-strength beryllium-aluminum composite material by breaking a continuous beryllium oxide layer of a beryllium particle reinforcement through matrix alloying. In order to solve the problems that beryllium oxide on the surfaces of beryllium particles has a hindering effect on diffusion of alloy elements, and existence of the beryllium oxide is not beneficial to regulation and control of a Be-BeO-Al interface and improvement of a beryllium-aluminum interface. The Fe element is introduced to react with the beryllium oxide layer wrapping the beryllium particles, BeFe2O4 is generated, the oxide layer on the surfaces of the beryllium particles is destroyed, molten aluminum can immerse the beryllium particles conveniently, a BeAl2O4-BeFe2O4 solid solution is formed, an interface structure which is connected through chemical bonds and has relation is obtained, the interface bonding strength is improved, AlFeBe4 and FeBe11 strengthening phases can also be obtained, and then the strength of an aluminum matrix is improved. In addition, no protective atmosphere is used in the preparation process, the material preparation cost is reduced, the bad effect of the beryllium oxide layer can be improved, the production period is short, and the high-density beryllium-aluminum composite material can be obtained.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-strength beryllium aluminum composite material. Background Art

[0002] The aerospace industry is constantly seeking lightweight, high-strength materials that can meet complex work requirements. Most of these materials are low-density alloys or composite materials. Among them, beryllium aluminum composite materials are composed of two lightweight alloys, which have the advantages of high specific strength and high specific stiffness of beryllium and the machinability of aluminum, and have attracted much attention from R&D personnel. At present, the AlBecast and AlBeMet series produced by Materion in the United States and the Beralcast series produced by IBC Advanced Alloys Corp have been widely used in the aerospace industry. However, the interface problem is a key factor limiting the improvement of beryllium aluminum composite materials.

[0003] There is a close connection between the interface and the mechanical properties. Optimizing the interface structure can achieve strong interface bonding, improve the load transfer capacity of the material, and thus improve the mechanical properties of the material; good interface bonding can achieve effective strengthening of beryllium particles, carry more loads, and maximize the strengthening effect of beryllium particles on the aluminum matrix. However, there is no intermediate compound between beryllium and aluminum, and the interface bonding is poor. In order to improve the beryllium-aluminum interface, the beryllium and aluminum interfaces can be effectively combined by adding alloying elements. However, beryllium is very easy to oxidize, and its oxidation ability is higher than that of aluminum. A thin layer of beryllium oxide is produced on the surface of the beryllium particles, forming a Be-BeO-Al interface structure, and the particle size of the beryllium powder is reduced, the specific surface area is increased, and the degree of oxidation of the particles is increased. Beryllium oxide hinders the diffusion of alloying elements, which is not conducive to the beryllium-aluminum interface bonding, and the added alloying elements cannot play a role in improving the beryllium-aluminum interface. In order to avoid the generation of beryllium oxide, it is often carried out in a protective atmosphere or vacuum environment. This method makes the preparation cost high. Therefore, there is an urgent need for a low-cost, tunable preparation method for the Be-BeO-Al interface to improve the bonding strength of the Be-Aluminum interface. Summary of the invention

[0004] In order to solve the problem that beryllium oxide on the surface of beryllium particles hinders the diffusion of alloy elements and the existence of beryllium oxide is not conducive to regulating the Be-BeO-Al interface and improving the beryllium-aluminum interface, the present invention provides a method for preparing a high-strength beryllium aluminum composite material by utilizing matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement. The beryllium oxide layer is destroyed by the added alloy element, the beryllium-aluminum interface bonding is promoted, and the high-strength beryllium aluminum composite material is prepared at a low cost.

[0005] The method for preparing a high-strength beryllium aluminum composite material by using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement is carried out in the following steps:

[0006] 1. Raw materials for preparing beryllium aluminum composite materials:

[0007] Weigh beryllium powder in a sealed glove box; weigh Al-Fe master alloy block and pure aluminum block at the same time;

[0008] The ratio of the mass of the beryllium powder to the total mass of the Al-Fe master alloy block and the pure aluminum block is 1:10-25;

[0009] 2. Pressing of Metal Beryllium Powder Preform

[0010] The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform;

[0011] 3. Preparation of Beryllium Aluminum Composite Materials

[0012] The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification;

[0013] The pressure during the pressure infiltration is 70-140 MPa;

[0014] 4. Heat treatment of beryllium aluminum composite materials

[0015] The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment;

[0016] The high temperature treatment process is: heating to 350°C-450°C in the furnace, keeping warm for 0.5-1h, rapidly heating to 550°C-620°C at a heating rate of 5°C / s and keeping warm for 10-60s, then rapidly cooling to 350°C-450°C at a cooling rate of 10°C / s and keeping warm for 0.5-1h.

[0017] Principle and beneficial effects of the invention:

[0018] 1. The present invention adopts a solid + liquid (metal beryllium powder + liquid aluminum alloy) combination method to prepare a beryllium aluminum composite material, rather than the currently commonly used solid + solid (metal beryllium powder + pure aluminum powder or beryllium aluminum pre-alloyed powder) combination and liquid-liquid (molten beryllium, aluminum) combination method. In the present invention, the alloying elements diffuse from liquid to solid, and the diffusion rate of the alloying elements is higher than the diffusion rate from solid to solid. Compared with the solid-solid combination method of melting pure beryllium and pure aluminum and then atomizing to form beryllium aluminum pre-alloyed powder, the present invention can effectively introduce alloying elements, regulate the interface structure of the material, and obtain a beryllium aluminum composite material with high interface bonding strength; compared with the liquid-liquid combination method, the present invention combines the molten aluminum alloy with the solid beryllium powder, avoiding the need to reach above 1287°C in the liquid-liquid combination, and the mutual solubility of beryllium and aluminum is low, avoiding the formation of coarse beryllium dendrites during the solidification process, and avoiding casting defects caused by the large difference in the melting point temperature of beryllium and aluminum.

[0019] 2. The present invention selects Al-Fe master alloy as the matrix alloy and introduces Fe element. Fe element diffuses to the interface and reacts with the beryllium oxide layer covering the beryllium particles to produce BeFe 2 O 4 , destroying the oxide layer on the surface of the beryllium particles, facilitating the aluminum liquid to penetrate into the beryllium particles and form BeAl 2 O 4 -BeFe 2 O 4 Solid solution, transforming the existing direct contact "sandwich" interface structure (Be-BeO-Al structure) into a connected interface structure connected by chemical bonds, improving the interface bonding strength, and also obtaining AlFeBe 4 、FeBe 11 Strengthening phase, thereby improving the strength of the aluminum matrix.

[0020] 3. The present invention improves the diffusion capacity of Fe element by subjecting the beryllium / aluminum composite material to high temperature treatment. The subsequent heat preservation in the low temperature stage can reduce the thermal stress of the material and also avoid overburning of the aluminum alloy due to high temperature, thereby reducing the performance of the material.

[0021] 4. The present invention does not use a protective atmosphere in the preparation process, which reduces the material preparation cost, improves the adverse effects of the beryllium oxide layer, shortens the production cycle, and can obtain a high-density beryllium aluminum composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The SEM and element distribution diagram of the beryllium aluminum composite material obtained in Example 1. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any reasonable combination of the specific implementation modes.

[0024] Specific implementation method 1: In this implementation method, the preparation method of the high-strength beryllium aluminum composite material using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement is carried out in the following steps:

[0025] 1. Raw materials for preparing beryllium aluminum composite materials:

[0026] Weigh beryllium powder in a sealed glove box; weigh Al-Fe master alloy block and pure aluminum block at the same time;

[0027] The ratio of the mass of the beryllium powder to the total mass of the Al-Fe master alloy block and the pure aluminum block is 1:10-25;

[0028] 2. Pressing of Metal Beryllium Powder Preform

[0029] The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform;

[0030] 3. Preparation of Beryllium Aluminum Composite Materials

[0031] The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification;

[0032] The pressure during the pressure infiltration is 70-140 MPa;

[0033] 4. Heat treatment of beryllium aluminum composite materials

[0034] The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment;

[0035] The high temperature treatment process is: heating to 350°C-450°C in the furnace, keeping warm for 0.5-1h, rapidly heating to 550°C-620°C at a heating rate of 5°C / s and keeping warm for 10-60s, then rapidly cooling to 350°C-450°C at a cooling rate of 10°C / s and keeping warm for 0.5-1h.

[0036] This implementation has the following beneficial effects:

[0037] 1. This embodiment adopts a solid + liquid (metal beryllium powder + liquid aluminum alloy) combination method to prepare a beryllium aluminum composite material, rather than the currently commonly used solid + solid (metal beryllium powder + pure aluminum powder or beryllium aluminum pre-alloyed powder) combination and liquid-liquid (molten beryllium, aluminum) combination method. In this embodiment, the alloying elements diffuse from liquid to solid, and the diffusion rate of the alloying elements is higher than the diffusion rate from solid to solid. Compared with the solid-solid combination method of melting pure beryllium and pure aluminum and then atomizing to form beryllium aluminum pre-alloyed powder, this embodiment can effectively introduce alloying elements, regulate the interface structure of the material, and obtain a beryllium aluminum composite material with high interface bonding strength; compared with the liquid-liquid combination method, this embodiment combines the molten aluminum alloy with the solid beryllium powder, avoiding the need to reach above 1287°C in the liquid-liquid combination, and the mutual solubility of beryllium and aluminum is low, avoiding the formation of coarse beryllium dendrites during the solidification process, and avoiding casting defects caused by the large difference in the melting point temperature of beryllium and aluminum.

[0038] 2. In this embodiment, Al-Fe master alloy is selected as the matrix alloy, and Fe element is introduced. Fe element diffuses to the interface and reacts with the beryllium oxide layer covering the beryllium particles to produce BeFe 2 O 4 , destroying the oxide layer on the surface of the beryllium particles, facilitating the aluminum liquid to penetrate into the beryllium particles and form BeAl 2 O 4 -BeFe 2 O 4Solid solution, transforming the existing direct contact "sandwich" interface structure (Be-BeO-Al structure) into a connected interface structure connected by chemical bonds, improving the interface bonding strength, and also obtaining AlFeBe 4 、FeBe 11 Strengthening phase, thereby improving the strength of the aluminum matrix.

[0039] 3. This embodiment improves the diffusion capacity of Fe element by subjecting beryllium / aluminum composite material to high temperature treatment. The subsequent low temperature insulation can reduce the thermal stress of the material and also avoid overburning of aluminum alloy due to high temperature, thereby reducing the performance of the material.

[0040] 4. In the preparation process of this embodiment, no protective atmosphere is used, which reduces the material preparation cost, improves the adverse effects of the beryllium oxide layer, shortens the production cycle, and obtains a high-density beryllium aluminum composite material.

[0041] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that: the average particle size of the beryllium powder in step 1 is 15-60 μm, and the purity is 99%.

[0042] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that: the purity of the Al-Fe intermediate alloy block and the pure aluminum block in step one is 99.99%.

[0043] Specific implementation method 4: This implementation method is different from any one of specific implementation methods 1 to 3 in that: the particles of the beryllium powder in step 1 are spherical or strip-shaped.

[0044] Specific implementation method five: This implementation method is different from any one of specific implementation methods one to four in that: the cold pressing mold in step two is cylindrical, with an outer diameter of 80 mm and an inner diameter of 40 mm.

[0045] Specific implementation method 6: This implementation method is different from any one of specific implementation methods 1 to 5 in that: the pressing process in step 2 is: maintaining a pressure of 60 to 100 MPa for 5 to 15 minutes.

[0046] Specific implementation method seven: This implementation method is different from any one of specific implementation methods one to six in that: the pressing process described in step two is: pressurizing to 120 MPa and then releasing the pressure.

[0047] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that: the smelting temperature in step three is 800-1000°C.

[0048] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that: the pressure during the pressure infiltration in step 3 is 105 MPa.

[0049] Specific embodiment ten: The difference between this embodiment and any one of specific embodiments one to nine is that the high temperature treatment process described in step four is: heating with the furnace to 450°C, keeping warm for 1 hour, rapidly heating to 600°C at a heating rate of 5°C / s and keeping warm for 30 seconds, then rapidly cooling to 450°C at a cooling rate of 10°C / s and keeping warm for 1 hour.

[0050] Embodiment 1:

[0051] The preparation method of the high-strength beryllium aluminum composite material of this embodiment using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement is carried out in the following steps:

[0052] 1. Raw materials for preparing beryllium aluminum composite materials:

[0053] In a sealed glove box, 40 g of beryllium powder was weighed; 250 g of Al-Fe20 master alloy block and 750 g of pure aluminum block were weighed at the same time; the mass fraction of Fe in the Al-Fe20 master alloy block was 20%;

[0054] The beryllium powder has an average particle size of 20 μm and a purity of 99%;

[0055] The purity of the Al-Fe20 master alloy block and the pure aluminum block is 99.99%;

[0056] The particles of the beryllium powder are spherical;

[0057] 2. Pressing of Metal Beryllium Powder Preform

[0058] The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform;

[0059] The pressing process is as follows: maintaining the pressure at 80 MPa for 10 minutes; the cold pressing mold is cylindrical with an outer diameter of 80 mm and an inner diameter of 40 mm;

[0060] 3. Preparation of Beryllium Aluminum Composite Materials

[0061] The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification;

[0062] The smelting temperature is 900°C;

[0063] The pressure during the pressure infiltration is 105MPa;

[0064] 4. Heat treatment of beryllium aluminum composite materials

[0065] The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment;

[0066] The high temperature treatment process is as follows: after heating to 450°C in the furnace, keeping the temperature for 1 hour, rapidly heating to 600°C at a heating rate of 5°C / s and keeping the temperature for 30 seconds, and then rapidly cooling to 450°C at a cooling rate of 10°C / s and keeping the temperature for 1 hour.

[0067] Figure 1 The SEM and element distribution diagram of the beryllium aluminum composite material obtained in Example 1 are shown in FIG. Figure 1 The Fe element is mostly superimposed with the O element distribution area at the beryllium-aluminum interface and in the aluminum matrix, indicating that the Fe element is beneficial to the beryllium-aluminum interface. The high-strength beryllium aluminum composite material prepared in Example 1 has a density of 99%, an elastic modulus of 191 GPa, a tensile strength of 350 MPa, and an elongation of 4%.

[0068] Embodiment 2:

[0069] The preparation method of the high-strength beryllium aluminum composite material of this embodiment using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement is carried out in the following steps:

[0070] 1. Raw materials for preparing beryllium aluminum composite materials:

[0071] In a sealed glove box, 40 g of beryllium powder was weighed; at the same time, 500 g of Al-Fe20 master alloy block and 500 g of pure aluminum block were weighed; the mass fraction of Fe in the Al-Fe20 master alloy block was 20%;

[0072] The beryllium powder has an average particle size of 20 μm and a purity of 99%;

[0073] The purity of the Al-Fe20 master alloy block and the pure aluminum block is 99.99%;

[0074] The particles of the beryllium powder are spherical;

[0075] 2. Pressing of Metal Beryllium Powder Preform

[0076] The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform;

[0077] The pressing process is as follows: maintaining the pressure at 80 MPa for 10 minutes; the cold pressing mold is cylindrical with an outer diameter of 80 mm and an inner diameter of 40 mm;

[0078] 3. Preparation of Beryllium Aluminum Composite Materials

[0079] The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification;

[0080] The smelting temperature is 900°C;

[0081] The pressure during the pressure infiltration is 105MPa;

[0082] 4. Heat treatment of beryllium aluminum composite materials

[0083] The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment;

[0084] The high temperature treatment process is as follows: heating to 450°C in the furnace, keeping the temperature for 1 hour, rapidly heating to 600°C at a heating rate of 5°C / s and keeping the temperature for 30 seconds, and then rapidly cooling to 450°C at a cooling rate of 10°C / s and keeping the temperature for 1 hour.

[0085] The high-strength beryllium aluminum composite material prepared in Example 2 has a density of 99%, an elastic modulus of 200 GPa, a tensile strength of 400 MPa, and an elongation of 3.5%.

[0086] Embodiment 3:

[0087] The preparation method of the high-strength beryllium aluminum composite material of this embodiment using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement is carried out in the following steps:

[0088] 1. Raw materials for preparing beryllium aluminum composite materials:

[0089] In a sealed glove box, 40 g of beryllium powder was weighed; 750 g of Al-Fe20 master alloy block and 250 g of pure aluminum block were weighed at the same time; the mass fraction of Fe in the Al-Fe20 master alloy block was 20%;

[0090] The beryllium powder has an average particle size of 20 μm and a purity of 99%;

[0091] The purity of the Al-Fe20 master alloy block and the pure aluminum block is 99.99%;

[0092] The particles of the beryllium powder are spherical;

[0093] 2. Pressing of Metal Beryllium Powder Preform

[0094] The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform;

[0095] The pressing process is as follows: maintaining the pressure at 80 MPa for 10 minutes; the cold pressing mold is cylindrical with an outer diameter of 80 mm and an inner diameter of 40 mm;

[0096] 3. Preparation of Beryllium Aluminum Composite Materials

[0097] The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification;

[0098] The smelting temperature is 900°C;

[0099] The pressure during the pressure infiltration is 105MPa;

[0100] 4. Heat treatment of beryllium aluminum composite materials

[0101] The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment;

[0102] The high temperature treatment process is as follows: heating to 450°C in the furnace, keeping the temperature for 1 hour, rapidly heating to 600°C at a heating rate of 5°C / s and keeping the temperature for 30 seconds, and then rapidly cooling to 450°C at a cooling rate of 10°C / s and keeping the temperature for 1 hour.

[0103] The high-strength beryllium aluminum composite material prepared in Example 3 has a density of 99%, an elastic modulus of 202 GPa, a tensile strength of 460 MPa, and an elongation of 2%.

Claims

1. A method for preparing a high-strength beryllium aluminum composite material by using matrix alloying to destroy the continuous beryllium oxide layer of the beryllium particle reinforcement, characterized in that: The preparation method of the high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying is carried out in the following steps:

1. Raw materials for preparing beryllium aluminum composite materials: Weigh beryllium powder in a sealed glove box; weigh Al-Fe master alloy block and pure aluminum block at the same time; The ratio of the mass of the beryllium powder to the total mass of the Al-Fe master alloy block and the pure aluminum block is 1:10-25; 2. Pressing of Metal Beryllium Powder Preform The beryllium powder weighed in step 1 is placed in a cold pressing mold and pressed at room temperature to obtain a preform; 3. Preparation of Beryllium Aluminum Composite Materials The Al-Fe master alloy block and the pure aluminum block weighed in step 1 are melted to obtain a liquid alloy, and the liquid alloy is poured into a mold containing a preform for pressure infiltration, and a beryllium aluminum composite material is obtained after solidification; The pressure during the pressure infiltration is 70-140 MPa; 4. Heat treatment of beryllium aluminum composite materials The beryllium aluminum composite material obtained in step 3 is subjected to high temperature treatment; The high temperature treatment process is: heating to 350°C-450°C in the furnace, keeping warm for 0.5-1h, rapidly heating to 550°C-620°C at a heating rate of 5°C / s and keeping warm for 10-60s, then rapidly cooling to 350°C-450°C at a cooling rate of 10°C / s and keeping warm for 0.5-1h.

2. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The beryllium powder in step 1 has an average particle size of 15 to 60 μm and a purity of 99%.

3. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The purity of the Al-Fe intermediate alloy block and the pure aluminum block in step 1 is 99.99%.

4. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The beryllium powder particles in step 1 are spherical or strip-shaped.

5. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The cold pressing mold in step 2 is cylindrical with an outer diameter of 80 mm and an inner diameter of 40 mm.

6. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The pressing process in step 2 is: maintaining the pressure at 60-100 MPa for 5-15 minutes.

7. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The pressing process in step 2 is: pressurizing to 120 MPa and then releasing the pressure.

8. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The smelting temperature in step 3 is 800-1000°C.

9. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The pressure during the pressure infiltration in step 3 is 105 MPa.

10. The method for preparing a high-strength beryllium aluminum composite material by destroying the continuous beryllium oxide layer of the beryllium particle reinforcement by matrix alloying according to claim 1, characterized in that: The high temperature treatment process described in step 4 is: heat up to 450°C with the furnace, keep warm for 1 hour, quickly heat up to 600°C at a heating rate of 5°C / s and keep warm for 30 seconds, then quickly cool down to 450°C at a cooling rate of 10°C / s and keep warm for 1 hour.

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