FeCrAl alloy and method for producing the same

Abstract

The application discloses an FeCrAl alloy, and has the following alloy components and mass percentages: C<=0.02%, Si<=0.3%, Mn<=0.3%, P<=0.01%, S<=0.008%, Cr 23-25%, Al 7-8%, W 1-3%, Nb 0.03-0.05%, V 0.08-0.12%, Y 0.1-0.2%, Ce 0.05-0.15%, N<=0.008%, and the balance of Fe and inevitable impurities. The FeCrAl electric heating alloy has excellent mechanical and electrical properties, and the production process is relatively simple and easy to be applied on a large scale.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and further belongs to a FeCrAl electrothermal alloy. BACKGROUND

[0002] An electrothermal alloy is a functional alloy material that generates Joule heat to convert electrical energy into heat energy by using the resistance characteristics of a substance, and can be divided into two categories of Ni-Cr-(Fe) system with austenitic structure and Fe-Cr-Al system with ferritic structure according to the organizational structure.

[0003] The Fe-Cr-Al electrothermal alloy has a service temperature of 1000-1400℃, and is widely used due to its low price, good high-temperature oxidation resistance, and high resistivity. However, the alloy also has some disadvantages. First, as the temperature increases, the plasticity of the material increases, and the material may creep. Second, the material is prone to brittle fracture after long-term use at high temperature.

[0004] In order to overcome the high-temperature plastic deformation and toughness reduction of the Fe-Cr-Al alloy, the composition and process are often optimized during processing design: first, the content of chromium and aluminum is optimized to ensure low resistivity and good oxidation resistance, and to avoid the precipitation of brittle phases; second, the heat treatment process is optimized to avoid the precipitation of chromium-rich and iron-rich brittle alpha' phases and to avoid the 475℃ medium-temperature brittleness; third, a small amount of rare earth elements is added to reduce the grain coarsening speed at high temperature and to avoid high-temperature brittleness.

[0005] However, even with the above considerations, under some harsh conditions, the Ni-Cr electrothermal alloy with higher cost is still selected, and the main reason is that the high-temperature strength and hardness of the Fe-Cr-Al alloy are poor.

[0006] Publication No. CN115198205A discloses an electrothermal alloy and a preparation method thereof. The alloy contains 0.01-0.02% S to improve the processing performance, but S is easy to form large particle sulfide inclusions with rare earth, which increases the risk of brittle fracture and deprives the rare earth of part of the high-temperature oxidation resistance.

[0007] Publication No. CN114250425A discloses a high-temperature iron-chromium alloy containing niobium and a preparation method thereof. The alloy contains 1.5-3% of the precious metal Re, which attempts to apply the "Re effect" to improve the high-temperature performance of the alloy. However, Re is a strategic material (the price is about 1 / 3 of gold), and is only used in the production of single-crystal high-temperature alloys for second-generation and third-generation engine blades. Using it in iron-based materials is too costly and is not conducive to large-scale application.

[0008] In addition, the alloys of different components of iron-chromium-aluminum disclosed in CN114196890A, CN113802052A, CN113122778A and the like are also disclosed, but either the cost is too high or the process is relatively complex, which is not desirable.

[0009] Therefore, the present application provides an electric heating alloy with lower cost and higher production efficiency and a preparation method thereof. SUMMARY

[0010] The present application aims to provide an Fe-Cr-Al alloy containing W by reasonable component design, improve its mechanical properties such as strength and hardness, and provide a relatively simple production method to ensure the electric heating performance of the material at room temperature and high temperature.

[0011] To solve the above technical problems, the technical scheme of the present application is as follows: an FeCrAl alloy, the alloy components and their mass percentages are as follows: C≤0.02%, Si≤0.3%, Mn≤0.3%, P≤0.01%, S≤0.008%, Cr 23-25%, Al 7-8%, W 1-3%, Nb 0.03-0.05%, V 0.08-0.12%, Y 0.1-0.2%, Ce 0.05-0.15%, N≤0.008%, and the balance is Fe and unavoidable impurities.

[0012] A preparation method of the above-mentioned FeCrAl alloy, the alloy ingot forging process adopts the following steps:

[0013] 1) Heating: first heat the alloy ingot to 650±10℃ and keep for 1-2h, then heat to 1200-1250℃ and keep for 8-12h.

[0014] 2) Rough forging: three-die three-drawing is performed, the interval temperature is 950-1050℃; the first time, the deformation of each die-drawing is not less than 30%. After the first die-drawing is completed, continue to keep in the furnace for 2.5-3h, and the furnace temperature is set to 1200±10℃; the second time, the deformation of each die-drawing is not less than 40%, after the die-drawing is completed, continue to keep in the furnace for 2-2.5h, and the furnace temperature is set to 1200±10℃; the third time, the deformation of each die-drawing is not less than 50%, after the die-drawing is completed, continue to keep in the furnace for 1.5-2h, and the furnace temperature is set to 1200±10℃;

[0015] 3) Precision forging: length-drawing operation is performed, the interval temperature is 970-1030℃, the deformation of each time is 28-43%, after the drawing is completed, keep in the furnace for 1-1.5h, the furnace temperature is set to 1200±10℃, and the final forging deformation is 14-20%;

[0016] 4) Air cooling: the alloy blank obtained by forging is placed on a cooling bed for air cooling.

[0017] Further, the alloy ingot has a diameter of 300mm, and the alloy blank has a diameter of 25-30mm.

[0018] Further, the alloy ingot is obtained by primary refining and electroslag remelting, and the electroslag remelting process uses a slag system with the following components and mass percentage: 15%-20% CaO, 15%-18% Al2O3, 2%-3% MgO, 2%-3% Y2O3, 1%-2% Ce2O3, and the balance CaF2.

[0019] The components of the present application have the following effects in the alloy:

[0020] (1) The addition of 1-3% W in the alloy can greatly increase the strength and hardness of the alloy; 0.03-0.05% Nb can play a role in carbon fixation, and the formed NbC can inhibit the growth of ferrite grains at high temperature and prevent high-temperature brittleness; 0.08-0.12% V and N form VN to refine ferrite grains and improve the strength and toughness of the matrix.

[0021] (2) The addition of 0.15-0.35% Y+Ce in the alloy can improve the oxidation resistance of the alloy by changing the composition structure and oxygen binding capacity of the alloy oxide film. Pure addition of rare earth Ce forms a CeO2 inner layer in the oxide film, and the molar ratio of rare earth to oxygen is 1:2. When Y is added, the oxide film inner layer is Al2Y4O9+CeO2 complex phase, and the molar ratio of rare earth to oxygen is greater than 1:2, indicating that the oxygen binding capacity is significantly improved, greatly delaying the oxygen permeation effect; another advantage of adding Y is that the atomic mass of rare earth Y is 88, which is the rare earth with the smallest density, while the atomic masses of rare earth Ce and La are 140 and 139 respectively. With the same mass, the amount of substance of Y is 1.59 times that of Ce and La, and the oxygen binding capacity is also 1.59 times.

[0022] Compared with the traditional FeCrAl alloy forging process, the forging method of the present application adopts a cross forging method with gradually increasing deformation, which effectively breaks up the coarse primary structure and forms fine grains; at the same time, the forging temperature is controlled to be in the temperature range of NbC and VN precipitation, which hinders the growth of grains at high temperature; air cooling after forging inhibits the aggregation and growth of C and N compounds, ensuring the fine dispersion of the precipitation strengthening phase.

[0023] The beneficial effects of the above technical solution are as follows:

[0024] The FeCrAl electric heating alloy of the present application has excellent mechanical and electrical properties, and the production process is relatively simple and easy to scale up. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0026] Examples 1-13

[0027] Example 1

[0028] An iron-chromium-aluminum alloy was prepared by using a 500 kg vacuum induction furnace, a Φ300x1300 mm crystallizer electroslag furnace, a power 150 kw heating furnace and an 800 t hydraulic forging machine. The processes of each working procedure are as follows:

[0029] 1) Vacuum induction furnace smelting

[0030] Furnace charging: 200 kg pure iron rods were laid at the bottom of the crucible, 115 kg of metal chromium, 21.4 kg of tungsten iron (the mass percentage of tungsten in the tungsten iron WW=70%) were placed in the middle, and 127 kg of pure iron rods were placed at the upper part; the second material bin was loaded with 0.42 kg of niobium iron (the mass percentage of niobium in the niobium iron WNb=60%), 1.2 kg of vanadium iron (the mass percentage of vanadium in the vanadium iron WV=50%), 1 kg of single crystal silicon, 0.5 kg of metal manganese, 35 kg of aluminum particles, 1 kg of metal Y and 0.5 kg of metal Ce;

[0031] Melting: vacuum extraction to 5 Pa, start power supply, melt clean after 3 h;

[0032] Refining: adjust the vacuum degree to below 0.1 Pa, heat to 1600 ℃, and refine for 40 min;

[0033] Alloying: turn off the vacuum pump, fill in 40000 Pa of argon, add niobium iron, vanadium iron, single crystal silicon, metal manganese and aluminum particles; after melting, take a sample for composition detection and fine adjustment; after passing, stop power supply and film forming, add Y and Ce, and power supply large stirring for 3 min;

[0034] Casting: electric steel tapping, and casting into a Φ220x1800 mm round ingot;

[0035] Demoulding and annealing: demoulding after 100 min, and then stress relief annealing at a heating temperature of 650 ℃ for 2 h.

[0036] 2) Electroslag remelting

[0037] Preparation: baking 30 kg of slag material in a 600 ℃ furnace for 6 h, and the slag composition is 60% CaF2, 20% CaO, 15% Al2O3, 2% MgO, 2% Y2O3 and 1% Ce2O3; the vacuum ingot is polished and welded to the dummy electrode;

[0038] Melting: Ignition arc, add slag, 25 min after slag is clear, quickly increase slag temperature to 1600-1700°C; enter remelting period, maintain melting rate of 180-240 kg / h; start to supplement when the electrode remains 50 kg, gradually reduce input power, end after 30 min of supplement; continuously input argon as protective gas during the whole melting period;

[0039] Melting: Ignition arc, add slag, 25 min after slag is clear, quickly increase slag temperature to 1600-1700°C; enter remelting period, maintain melting rate of 180-240 kg / h; start to supplement when the electrode remains 50 kg, gradually reduce input power, end after 30 min of supplement; continuously input argon as protective gas during the whole melting period;

[0040] Melting: Ignition arc, add slag, 25 min after slag is clear, quickly increase slag temperature to 1600-1700°C; enter remelting period, maintain melting rate of 180-240 kg / h; start to supplement when the electrode remains 50 kg, gradually reduce input power, end after 30 min of supplement; continuously input argon as protective gas during the whole melting period;

[0041] 3)Forging

[0042] Homogenization: Put the electroslag ingot into the furnace, first increase the temperature to 640°C for 1 h, then increase the temperature to 1200°C for 8 h;

[0043] Rough forging: After the electroslag ingot is taken out of the furnace, forge at a temperature of 950-1050°C; first upset and draw, the Φ300 mm electroslag ingot is first upset to Φ400 mm, then drawn to 240×240 mm 2 square billet, cut into 2 sections and return to the furnace for 2.5 h; second time of upsetting and drawing, the 240×240 mm 2 square billet is upset to 300×300 mm 2 square billet, then drawn to 160×160 mm 2 square billet, each section is cut again and returned to the furnace for 2 h; third time of upsetting and drawing, the 160×160 mm 2 square billet is upset to 240×240 mm 2 , then drawn to 120×120 mm 2 , each section is cut again and returned to the furnace for 1.5 h; the furnace temperature during the rough forging process is set to 1200±10°C.

[0044] Fine forging: the forging temperature is 970-1030°C, the 120×120 mm 2 square billet is forged into Φ25 mm rod through the following process, (120 mm) 2 square billet→(95 mm) 2 square billet→(75 mm) 2 square billet→(60 mm) 2 square billet→(50 mm) 2 square billet→(40 mm) 2 square billet→(32 mm) 2 square billet→(27 mm) 2 square billet→Φ25 mm round rod; the furnace temperature during the fine forging process is set to 1200±10°C.

[0045] Air cooling: place Φ25mm round bar on the cooling bed, air cool to room temperature.

[0046] The FeCrAl alloy of the present application is produced according to the above process, and the components and mass percentage of the FeCrAl alloy are shown in Table 1. The 0Cr27Al7Mo2 alloy produced according to the above process is used as a comparative material, and the properties of the two materials are detected, and the results are shown in Table 2.

[0047] Table 1

[0048] C / ％ Si / % Mn / % P / ％ S / ％ Cr / ％ Al / ％ W / ％ Nb / % V / ％ Y / ％ Ce / % N / ％ 0.01 0.18 0.1 0.006 0.005 23.1 7 2.9 0.05 0.11 0.13 0.07 0.006

[0049] Table 2

[0050]

[0051] It can be seen that the component control of the FeCrAl alloy of Example 1 is relatively easy, and the processing technology is also relatively simple. The properties such as room temperature tensile property, resistivity, hardness, fast life value and absolute wear amount of the FeCrAl alloy are all better than those of the 0Cr27Al7Mo2 alloy produced by the same process, and meet the use requirements of the electrothermal alloy.

[0052] Examples 2-8

[0053] The iron-chromium-aluminum electrothermal alloy is produced by using a 1000kg vacuum induction furnace, a Φ400x1300mm crystallizer electroslag furnace and an 800t hydraulic forging machine, and the finished product is Φ30mm bar. The components and mass percentage of the alloy are shown in Table 3. The alloy bar is sampled and compared with the properties of five electrothermal alloys with similar components, i.e. GB / T1234-0Cr21Al6Nb, ASTMB603-I, JISC2520-FCH(R)W1, DIN17470-CrAl25 5 and ГOCT10994-OX23Ю5A, and the property detection results are shown in Table 4.

[0054] Table 3

[0055]

[0056] Table 4

[0057] Examples 9-13

[0058] The remelted ingot obtained by remelting the ingot of Example 1 is forged in Examples 9-13, and the forging process is shown in Tables 5 and 6. The round bar obtained by forging is detected for properties, and the properties are shown in Tables 6 and 7.

[0059] Table 5

[0060]

[0061] Table 6

[0062]

[0063] Table 7

[0064] The above examples are only used to illustrate but not to limit the technical solutions of the present application. Although the present application is described in detail with reference to the above examples, those skilled in the art should understand that the present application can still be modified or equivalently replaced without departing from the spirit and scope of the present application, and any modification or partial replacement should be covered in the scope of claims of the present application.

Claims

1. A FeCrAl alloy, characterized in that, The alloy composition and its mass percentage are as follows: C ≤0.02%, Si ≤0.3%, Mn ≤0.3%, P ≤0.01%, S ≤0.008%, Cr 23~25%, Al 7~8%, W 1~3%, Nb 0.03~0.05%, V 0.08~0.12%, Y 0.1~0.2%, Ce 0.05~0.15%, N≤0.008%, with the balance being Fe and unavoidable impurities; the alloy ingot forging process adopts the following steps: 1) Heating: First heat the alloy ingot to 650±10℃ and hold for 1 to 2 hours, then heat to 1200 to 1250℃ and hold for 8 to 12 hours; 2) Rough forging: Three upsetting and three drawing processes are performed, with a temperature range of 950-1050℃. For the first upsetting and three drawing processes, the deformation should be no less than 30%. After upsetting, the material is returned to the furnace and held at the same temperature for 2.5-3 hours, with the furnace temperature set at 1200±10℃. For the second upsetting and drawing processes, the deformation should be no less than 40%. After upsetting, the material is returned to the furnace and held at the same temperature for 2-2.5 hours, with the furnace temperature set at 1200±10℃. For the third upsetting and drawing processes, the deformation should be no less than 50%. After upsetting, the material is returned to the furnace and held at the same temperature for 1.5-2 hours, with the furnace temperature set at 1200±10℃. 3) Precision forging: Perform drawing operation, with a temperature range of 970~1030℃, and a deformation amount of 28~43% each time. After drawing, return to the furnace and hold for 1~1.5h. The furnace temperature is set at 1200±10℃, and the final forging deformation amount is 14~20%. 4) Air cooling: The forged alloy billet is placed on a cooling bed for air cooling.

2. The method for preparing a FeCrAl alloy according to claim 1, characterized in that, The alloy ingot has a diameter of 300 mm, and the alloy billet has a diameter of 25-30 mm.

3. The method for preparing a FeCrAl alloy according to claim 1, characterized in that, The alloy ingot is obtained by electroslag remelting of primary casting ingot. The slag system used in the electroslag remelting process has the following composition and mass percentage: 15%–20% CaO, 15%–18% Al2O3, 2%–3% MgO, 2%–3% Y2O3, 1%–2% Ce2O3, and the balance is CaF2.

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