Preparation method of FeCrAl / molten iron bimetal composite cladding pipe

Abstract

The invention provides a preparation method of a FeCrAl / ferrocene bimetal composite cladding pipe. The preparation method comprises the following steps: preparing and screening FeCrAl alloy powder; the FeCrAl alloy powder is deposited on the surface of the molten iron forging rod through a selective laser melting method; the composite bar blank is subjected to annealing heat treatment and machined to the proper length and outer diameter, and a hole is drilled in the center of the bar blank; carrying out hot extrusion deformation on the composite extrusion billet, annealing after deformation, and carrying out inner and outer surface machining treatment on the tube blank; and carrying out multi-pass rolling and process annealing on the composite pipe blank, and carrying out normalizing and tempering vacuum heat treatment on the pipe with the finished size to obtain the FeCrAl / molten iron bimetal composite cladding pipe. According to the preparation method, metallurgical bonding of FeCrAl and the ferrierite is achieved through a high-energy beam melting technology, the microstructure and the comprehensive performance of the pipe are regulated and controlled through hot and cold machining, the bimetal composite cladding pipe with the high-temperature mechanical performance of the ferrierite and the high-temperature lead and bismuth corrosion resistance of FeCrAl is prepared, and the harsh service condition requirement of a fourth-generation fast reactor is met.

Description

Technical Field

[0001] This invention belongs to the field of fourth-generation fast reactor technology, specifically relating to a method for preparing FeCrAl / Iron-Maintenance bimetallic composite cladding tubes. Background Technology

[0002] Iron-clad steel (ICS) possesses excellent high-temperature strength, radiation resistance, and significant resistance to high-temperature liquid metal corrosion, making it a highly promising candidate material, primarily used in key components of fast reactors in Generation IV advanced nuclear energy systems. However, with the continuous increase in reactor fuel cooling temperatures, higher demands are placed on the corrosion resistance of cladding materials under high-temperature conditions, and single ICS cladding materials are insufficient to meet design requirements. Therefore, the industry has proposed external coating technology as one of the technical directions to solve this problem. This approach mainly involves preparing a coating such as aluminum or alumina on the metal cladding through chemical or physical methods to improve the cladding material's resistance to lead and bismuth corrosion under high-temperature environments. This process has drawbacks such as high cost, low bonding strength between the coating and the cladding substrate, and failure due to differences in the physical properties of the substrate and coating during application.

[0003] Based on the above, to avoid failures caused by non-metallurgical bonding between dissimilar materials, while fully utilizing the excellent high-temperature mechanical properties of iron and steel and improving the high-temperature corrosion resistance of the outer cladding layer, some studies have proposed methods for preparing metallurgically bonded composite pipes. A common method for preparing composite pipes is to first prepare pipes of two different materials, then nest the two pipes together, and finally achieve a metallurgical bond through heat treatment. However, problems such as poor bonding effect and poor material co-deformation ability still exist. Summary of the Invention

[0004] This invention addresses the problems of insufficient high-temperature corrosion resistance of single materials, inadequate bonding strength between coatings and traditional composite tube fabrication techniques leading to application failures, high manufacturing costs, and insufficient material performance stability in existing processes. It proposes a method for preparing FeCrAl / Iron-Mountain Steel bimetallic composite cladding tubes: FeCrAl and Iron-Mountain Steel are metallurgically bonded through a high-energy beam melting process. Subsequent hot and cold processing controls the microstructure and overall tube properties, resulting in a bimetallic composite cladding tube that combines the high-temperature mechanical properties of Iron-Mountain Steel with the high-temperature lead-bismuth corrosion resistance of FeCrAl, meeting the stringent service requirements of Generation IV fast reactors.

[0005] The technical solution adopted in this invention is as follows:

[0006] A FeCrAl / TiMa Steel bimetallic composite cladding tube preparation technology includes the following steps:

[0007] Step 1: Prepare and screen FeCrAl alloy powder;

[0008] Step 2: The FeCrAl alloy powder is deposited on the surface of the forged bar of Tiema Steel using a laser selective melting method to obtain FeCrAl / Tiema Steel bimetallic composite bar billet;

[0009] Step 3: Anneal the FeCrAl / Tiema Steel bimetallic composite billet and machine it to a suitable length and outer diameter. Drill a hole in the center of the billet to obtain the FeCrAl / Tiema Steel bimetallic composite extruded billet.

[0010] Step 4: The FeCrAl / Tiema Steel bimetallic composite extrusion billet is hot-extruded and deformed, then annealed, and the inner and outer surfaces of the billet are machined to obtain the FeCrAl / Tiema Steel bimetallic composite billet.

[0011] Step 5: The FeCrAl / TiMaSteel bimetallic composite tube blank is subjected to multi-pass rolling and process annealing, and the finished tube is subjected to normalizing and tempering vacuum heat treatment to obtain FeCrAl / TiMaSteel bimetallic composite cladding tube.

[0012] The FeCrAl alloy powder has the following composition by mass percentage: Cr 10.5–13.5%, Al 2.0–6.0%, Mo 0.10–3.00%, Si 0.05–2.00%, Nb 0.03–1.50%, Y 0.005–0.08%, with the remainder being Fe and unavoidable impurities. The composition contains gaseous impurities by mass percentage: O ≤ 0.002%, N ≤ 0.02%, H ≤ 0.001%. The powder particle size is controlled within the range of 10 μm to 53 μm; the powder flowability is required to be ≤ 25 s / 50 g; and the loose packing density is required to be > 4.0 g / cm³. 3 .

[0013] The laser selective melting method uses a laser power of 300–350 W, a scanning rate of 700–900 mm / s, a spot diameter of 70–90 μm, a substrate preheating temperature of 150–200 °C, and a powder layer thickness of 30–40 μm. The deposited FeCrAl material has a thickness of 20–25 mm.

[0014] The hot extrusion deformation temperature is 1020℃~1100℃, and the extrusion deformation process is to extrude a round ingot with a diameter of Φ170mm~Φ200mm into a tube blank with an outer diameter of Φ57mm~Φ62mm and a wall thickness of 6mm~9mm.

[0015] The rolling and annealing process involves 5 to 8 rolling passes, with each pass having a deformation of more than 25% and less than 45%. After each rolling pass, a vacuum intermediate annealing heat treatment is performed at a temperature of 750℃ to 850℃ and a holding time of 0.5 to 1 hour. After the holding time is completed, the mixture is rapidly cooled with argon gas.

[0016] The normalizing and tempering vacuum heat treatment is performed at a normalizing temperature of 1050℃~1150℃ for a holding time of 10~60min, followed by rapid cooling with argon gas after the holding time is completed; and at a tempering temperature of 650℃~850℃ for a holding time of 10~60min, followed by rapid cooling with argon gas after the holding time is completed.

[0017] The FeCrAl / Tiema Steel bimetallic composite cladding tube has an outer diameter of 8–10 mm and a wall thickness of 0.5–0.8 mm; the FeCrAl layer thickness is 0.1–0.2 mm.

[0018] The FeCrAl / TiMaSteel bimetallic composite cladding pipe consists of a TiMaSteel matrix layer, a transition layer, and a surface FeCrAl layer. The TiMaSteel matrix layer has a tempered martensite microstructure with an average grain size not exceeding 5μm. The transition layer has a ferrite / martensite dual-phase microstructure with an average grain size not exceeding 5μm. The surface FeCrAl layer has a ferrite microstructure with an average grain size not exceeding 5μm.

[0019] The room temperature performance of FeCrAl / Tiema Steel bimetallic composite cladding tubes is as follows: yield strength > 500 MPa, tensile strength > 650 MPa, and elongation ≥ 18%.

[0020] The beneficial effects of this invention are:

[0021] (1) The present invention provides a method for preparing FeCrAl / TiMa Steel bimetallic composite cladding tube, which uses laser selective melting or electron beam melting to deposit FeCrAl powder on the surface of the IronMa Steel forging bar, enabling the outer layer material and the base material to achieve metallurgical bonding with high bonding strength.

[0022] (2) The present invention provides a method for preparing FeCrAl / Iron Horse Steel bimetallic composite cladding tube. During the hot extrusion and cold rolling deformation process, the FeCrAl / Iron Horse Steel bimetallic tube is deformed in synergy by controlling the process temperature and deformation speed, thereby further improving the bonding strength and achieving high-precision dimensional control of the prepared tube. The interface bonding strength is increased by 1 times compared with the composite cladding tube prepared by coating.

[0023] (3) The present invention provides a method for preparing FeCrAl / Iron Horse Steel bimetallic composite cladding tube, wherein the microstructure evolution process of FeCrAl / Iron Horse Steel bimetallic is coordinated, that is, by controlling process parameters such as heat treatment temperature and time, the optimal microstructure of the two metals under the same heat treatment process is obtained, thereby improving the high-temperature microstructure stability of the cladding.

[0024] (4) The present invention provides a method for preparing FeCrAl / Iron Horse Steel bimetallic composite cladding tube. The obtained FeCrAl / Iron Horse Steel bimetallic composite cladding tube has both the high temperature mechanical properties of Iron Horse Steel and the high temperature resistance to lead bismuth corrosion of FeCrAl, and the high temperature resistance to corrosion of Iron Horse Steel is increased by 100℃ compared with that of Iron Horse Steel alone. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0026] The present invention provides a method for preparing a FeCrAl / TiMa Steel bimetallic composite cladding tube, comprising the following steps:

[0027] S1. Screening suitable FeCrAl powder, wherein the FeCrAl powder has the following characteristics: particle size control range of 10μm to 53μm; powder flowability ≤25s / 50g; and loose packing density >4.0g / cm³. 3 The chemical composition requirements for the powder are: oxygen content ≤ 0.002 wt.%, nitrogen content ≤ 0.02 wt.%, and hydrogen content ≤ 0.001 wt.%; the particle size distribution requirements are shown in Table 1.

[0028] Table 1 Requirements for Particle Size Distribution of FeCrAl Powder

[0029] D10 D50 D90 ≤10μm 30~40μm ≤53μm

[0030] S2. A layer of FeCrAl material is deposited on the surface of the iron and steel forging bar using laser or electron beam. The interface has no obvious pores, looseness, or inclusions, and the interface is completely metallurgically bonded. The FeCrAl alloy has a Cr content greater than 12 wt.% and an Al content greater than 5 wt.%.

[0031] Process parameters: laser power 325W; scanning rate 800mm / s; spot diameter 80μm; substrate preheating temperature 180℃; powder layer thickness 30μm. The thickness of the deposited FeCrAl material is 20-25mm.

[0032] S3, billet heat treatment

[0033] The composite round ingots obtained in step 2 are cut into billets with a length of 400mm to 600mm and an outer diameter of 180mm by a saw. The billets are then subjected to annealing heat treatment at a temperature of 750℃ to 850℃ and a holding time of 2 to 6 hours. After furnace cooling to below 500℃, the billets are then air-cooled.

[0034] S4. Co-extrude the heat-treated billet.

[0035] S401. A through hole is drilled in the center of the billet by machining to obtain the extruded billet; the diameter of the central hole matches the needle size of the extrusion die.

[0036] S402. The extruded billet is preheated to the set temperature using a ring furnace; the extruded billet is then transferred to an induction furnace and heated to the extrusion temperature, which is 1020℃~1100℃.

[0037] S403. The heated extruded billet is subjected to co-extrusion deformation of the composite pipe with an extrusion ratio greater than or equal to 12; it is extruded into a pipe billet with an outer diameter of 57 mm and a wall thickness of 6 mm.

[0038] S404. Anneal the tube blank obtained in step 4; annealing temperature 750℃~850℃, holding time 1~2h, furnace cooling to below 500℃ and air cooling. Honing the inner surface and polishing the outer surface of the tube blank after furnace cooling.

[0039] S5. Roll and heat treat the tube blank obtained in step 4.

[0040] S501. The billet is rolled in 6 passes, with each pass having a deformation of more than 25% and less than 45%. After each pass, a vacuum intermediate annealing process is performed at a temperature of 750℃~850℃ and a holding time of 0.5~1h. After the holding time is completed, the billet is rapidly cooled with argon gas.

[0041] S502. After degreasing and cleaning, the finished composite cladding tubes are normalized and tempered. The normalizing temperature is 1100℃ and the holding time is 1 hour. After the holding time is completed, the tubes are purged with argon gas and cooled quickly. The tempering temperature is 750℃ and the holding time is 1 hour. After the holding time is completed, the tubes are purged with argon gas and cooled quickly.

[0042] The FeCrAl / Tiema Steel bimetallic composite cladding tube prepared by this embodiment has an outer diameter of 9 mm and a wall thickness of 0.6 mm; the FeCrAl layer thickness of the finished composite cladding tube is approximately 0.1 mm.

[0043] Based on its microstructure, the iron-manganese steel can be divided into a matrix layer, a transition layer, and a surface FeCrAl layer. The matrix layer is composed of tempered martensite with an average grain size of 3.5 μm. The transition layer is a ferrite / martensite dual-phase structure with an average grain size of 3.3 μm. The surface FeCrAl layer is a ferrite structure with an average grain size of 3.8 μm.

[0044] The room temperature properties of the finished clad tube are: yield strength 620MPa, tensile strength 802MPa, and elongation 20%.

[0045] While those skilled in the art will recognize that the invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention, the embodiments should be considered illustrative and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and therefore all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the invention.

[0046] Furthermore, it should be understood that although the present invention is described according to embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a FeCrAl / TiMa Steel bimetallic composite cladding tube, characterized in that, Includes the following steps: Step 1: Prepare and screen FeCrAl alloy powder; Step 2: The FeCrAl alloy powder is deposited on the surface of the forged bar of Tiema Steel using a laser selective melting method to obtain FeCrAl / Tiema Steel bimetallic composite bar billet; Step 3: Anneal the FeCrAl / Tiema Steel bimetallic composite billet and machine it to a suitable length and outer diameter. Drill a hole in the center of the billet to obtain the FeCrAl / Tiema Steel bimetallic composite extruded billet. Step 4: The FeCrAl / Tiema Steel bimetallic composite extrusion billet is subjected to hot extrusion deformation and annealing heat treatment, and the inner and outer surfaces of the billet are machined to obtain the FeCrAl / Tiema Steel bimetallic composite billet. Step 5: Roll and process anneal the FeCrAl / TiMaSteel bimetallic composite tube blank, and perform normalizing and tempering vacuum heat treatment on the finished tube to obtain FeCrAl / TiMaSteel bimetallic composite cladding tube.

2. The method for preparing FeCrAl / Tiema Steel bimetallic composite cladding tube according to claim 1, characterized in that, The FeCrAl alloy powder has the following composition by mass percentage: Cr 10.5-13.5%, Al 2.0-6.0%, Mo 0.10-3.00%, Si 0.05-2.00%, Nb 0.03-1.50%, Y 0.005-0.08%, with the remainder being Fe and unavoidable impurities. The gaseous impurity elements in the composition can be controlled by mass percentage as follows: O ≤ 0.002%, N ≤ 0.02%, H ≤ 0.001%. The powder particle size is required to be between 10μm and 53μm. The powder flowability is required to be ≤ 25s / 50g. The loose packing density of the powder is required to be > 4.0g / cm3.

3. The laser selective melting method according to claim 2 has the following characteristics: laser power of 300–350 W; scanning rate of 700–900 mm / s; spot diameter of 70–90 μm; substrate preheating temperature of 150–200 °C; powder layer thickness of 30–40 μm; and deposited FeCrAl material thickness of 20–25 mm.

4. The hot extrusion deformation temperature according to claim 3 is 1020℃~1100℃, and the extrusion deformation process is to extrude a round ingot with a diameter of Φ170mm~Φ200mm into a tube blank with an outer diameter of Φ57mm~Φ62mm and a wall thickness of 6mm~9mm.

5. The rolling and annealing of the pipe according to claim 4 involves 5 to 8 rolling passes, with each pass having a deformation of more than 25% and less than 45%; after each rolling pass, a vacuum intermediate annealing heat treatment is performed at a temperature of 750℃ to 850℃ and a holding time of 0.5 to 1 hour, followed by rapid cooling with argon gas after the holding time is completed.

6. The finished size pipe according to claim 5 is subjected to normalizing and tempering vacuum heat treatment, wherein the normalizing temperature is 1050℃~1150℃, the holding time is 10~60min, and argon gas is purged and rapidly cooled after the holding time is completed; the tempering temperature is 650℃~850℃, the holding time is 10~60min, and argon gas is purged and rapidly cooled after the holding time is completed.

7. The FeCrAl / Iron Horse Steel bimetallic composite cladding tube according to claim 6 has an outer diameter of 8-10 mm and a wall thickness of 0.5-0.8 mm; wherein, The FeCrAl layer thickness is 0.1–0.2 mm.

8. The FeCrAl / Iron-Maintenance bimetallic composite cladding tube according to claim 7 is divided into an Iron-Maintenance matrix layer, a transition layer and a surface FeCrAl layer. The Iron-Maintenance matrix layer has a tempered martensite microstructure with an average grain size not exceeding 5 μm. The transition layer has a ferrite / martensite dual-phase microstructure with an average grain size not exceeding 5 μm. The surface FeCrAl layer has a ferrite microstructure with an average grain size not exceeding 5 μm.

9. The room temperature performance of the FeCrAl / Tiema Steel bimetallic composite cladding tube according to claim 8 is as follows: yield strength > 500 MPa, tensile strength > 650 MPa, and elongation ≥ 18%.