High-temperature-lead-bismuth-corrosion-resistant high-silicon-content ferrite / martensite steel ladle tube and preparation method thereof

Abstract

The invention belongs to the technical field of research and development of fast neutron reactor jackets and structural materials, and particularly relates to a high-temperature-lead-bismuth-corrosion-resistant high-silicon-content ferrite / martensite steel ladle tube and a preparation method thereof. According to the mass percentage, the composition mainly comprises the following components: 0.16-0.24% of C; 0.4 to 0.8 percent of Mn; cr: 11.6% to 12.4%; 1.2 to 1.8 percent of W; 0.1 to 0.4 percent of Ta; 0.2 to 0.4 percent of V; 1.0%-1.8% of Si and Fe. The preparation method comprises the steps of vacuum induction and vacuum arc remelting. Carrying out homogenization treatment and forging; extruding and annealing; cold rolling and annealing; and performing normalizing and tempering treatment. Through an efficient short-flow process route and reasonable smelting, pipe machining deformation and heat treatment processes, the microscopic structure of the material is remarkably improved, then the mechanical property and high-temperature lead and bismuth corrosion resistance of the finished pipe are improved, and the use requirement of the lead and bismuth cooling fast reactor fuel assembly cladding material under the high-temperature working condition is met.

Description

Technical Field

[0001] This invention belongs to the field of fast neutron reactor cladding and structural material research and development technology, specifically involving a high-silicon-content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion and its preparation method. Background Technology

[0002] Ferritic / martensitic stainless steel (FMS) possesses excellent resistance to radiation swelling, a good balance of strength and toughness, stable thermophysical properties, and relatively good resistance to high-temperature oxidation and corrosion, making it one of the most promising candidate materials for fuel cladding and other structural materials in lead-cooled fast neutron reactors. However, current lead-cooled fast reactors are designed to operate at temperatures of 500-650℃ (and will likely be higher in the future), with a lead-bismuth eutectic liquid coolant and an operating radiation dose of approximately 50-150 dPa (currently reaching a maximum of 200 dPa), producing 10-500 appm He (currently reaching a maximum of 1000 appm). This harsh service environment places extremely high performance requirements on the cladding materials. Because the coolant in lead-cooled fast neutron reactors is highly corrosive lead-bismuth liquid metal, the high-temperature flowing lead-bismuth liquid metal causes a series of physicochemical reactions on the cladding materials, including scouring, dissolution, and oxidation, leading to corrosion of the structural materials and structural failure, severely impacting the safe operation of the reactor.

[0003] The corrosion of structural materials in liquid metal mainly includes two aspects: First, dissolution corrosion. Most elements in F / M steel (such as Fe and Ni) have a certain solubility in lead-bismuth alloys, and the solubility increases with increasing temperature, causing compositional failure on the material surface. Simultaneously, lead-bismuth metal atoms in the coolant diffuse to the alloy surface and penetrate into the inner layers, causing structural instability. The other aspect is oxidation corrosion. Under high-temperature conditions, alloying elements in F / M steel also undergo oxidation reactions with dissolved oxygen in the coolant, forming an oxide film on the surface. The density and thickness of this oxide film determine the subsequent oxidation reaction and also the penetration of lead-bismuth alloy elements into the F / M steel. The density and thickness of the oxide film depend on its structure and composition. Furthermore, when F / M steel is exposed to liquid metal for a long period, the alloy undergoes sudden brittle fracture, a phenomenon known as liquid metal embrittlement (LME). The prerequisite for LME is contact between the structural material and the liquid metal, and the oxide layer of high-Cr steel has a significant inhibitory effect on LME.

[0004] Studies have shown that silicon (Si) readily reacts with oxygen (O) to form a dense SiO2 oxide film. Furthermore, the addition of Si effectively improves the stability of the Cr2O3 oxide film in F / M steel, significantly enhancing the oxidation resistance of 9-12% Cr steel. Simultaneously, the addition of Si also improves the resistance of ferritic / martensitic steel to liquid metal corrosion.

[0005] There are already numerous reports on high-Si content cladding materials for ironworks and their preparation methods. Russia has developed a high-Si content F / M steel—EP823 alloy—with a composition of 11.7Cr, 1.1Si, 0.73Mo, 0.63W, 0.65Ni, 0.54Mn, 0.34V, 0.26Nb, 0.17C, and Fe (reference: Maloy SA, Romero T, James MR, et al, Tensile testing of EP-823 and HT-9 after irradiation in STIP II, Journal of Nuclear Materials, 2006, 356: 56–61, doi:10.1016 / j.jnucmat. 2006.05.003). While this high-Si ironworks significantly improves corrosion resistance, it also increases the alloy's brittleness. Document CN116695003A discloses a ferritic / martensitic steel resistant to liquid lead-bismuth corrosion and its preparation method. The material's composition system is 7~12Cr, 0.5~3.0Si, 0.01~2.0Mo, 0.01~2.0W, 0.01~5.0Ni, 0.01~2.0Mn, 0.01~1.0V, 0.1~1.0Nb, 0.01~0.5Ti, 0.05~0.2C, 0.01~1.0Y, and Fe. Its microstructure is characterized by a phase area ratio of α-Fe to martensite of 1:(5-20). The preparation of its plates is mainly accomplished through steps such as smelting, casting, forging, controlled rolling and cooling, and heat treatment. However, after corrosion in liquid lead-bismuth at 500℃ for 2000 hours, the oxide layer thickness of this material reaches a maximum of 19.4μm. CN117431370A discloses a high-temperature, high-strength, and ductile ferritic / martensitic steel and its preparation method. The material's composition system is 8~12Cr, 0~1.5Si, 1.0~2.0W, 0.3~0.8Mn, 0.01~0.3V, 0.1~0.3Ta, 0.08~0.14C, 0~0.03Zr, and Fe. The preparation is mainly completed through hot working (forging + rolling + heat treatment), cold plastic deformation (one or more of rotary forging, rolling, forging, or extrusion), and annealing. Its main purpose is to improve the high-temperature, high-strength, and ductile properties of ferritic / martensitic steel, but it does not explain the effect on improving its resistance to lead and bismuth corrosion. In addition, the composition ranges proposed in the aforementioned documents CN116695003A and CN117431370A are relatively wide (with some elements having an order of magnitude difference between the upper and lower limits), and the composition has a significant impact on the material processing window. However, the documents have not yet proposed specific process requirements for different compositions.Document CN112695255B discloses a method for preparing ferritic martensitic steel clad pipes. The material's composition system is 10.5~12.5Cr, 0.4~1.2Si, 1.0~2.5W, 0.3~0.8Mn, 0.1~0.4V, 0.1~0.4Ta, 0.005~0.08Zr, 0.15~0.25C, 0.005~0.05La, 0.008~0.04N, and Fe. The main process steps are: determining the alloy composition, smelting, casting, forging, extrusion, billet processing and heat treatment, multi-pass cold rolling and intermediate heat treatment of the alloy, and final heat treatment of the pipe. This invention improves the material's microstructure and refines the grains through innovative composition design, optimized pipe processing deformation technology, and heat treatment techniques, thereby enhancing the alloy's overall performance. However, this paper uses Zr, La, and N elements. Zr and La are reactive, while N is a gaseous element, making it difficult to control their content during the smelting process. Summary of the Invention

[0006] The purpose of this invention is to solve the aforementioned problems. Addressing the challenge of high-temperature liquid lead-bismuth corrosion resistance in existing ferritic / martensitic steel cladding materials for lead-bismuth coolers, this invention proposes a high-silicon content ferritic / martensitic steel cladding tube with excellent high-temperature lead-bismuth corrosion resistance and its preparation method. Through innovative compositional design and the addition of trace alloying elements, the composition and structure of the oxide film in the high-temperature liquid lead-bismuth environment of the ferritic / martensitic steel are optimized. Based on the influence of composition on the evolution of material microstructure, specific process parameters for hot working, cold working, and heat treatment of cladding tubes with different compositions are proposed, achieving fine and uniform microstructure control of the finished tube, ultimately obtaining a high-silicon content ferritic / martensitic steel cladding tube with excellent high-temperature lead-bismuth corrosion resistance.

[0007] Therefore, a first aspect of the present invention provides a high-silicon content ferritic / martensitic steel cladding pipe resistant to high-temperature lead-bismuth corrosion, wherein the chemical composition, by mass percentage, contains: C: 0.16~0.24%; Mn: 0.4~0.8%; Cr: 11.6~12.4%; W: 1.2~1.8%; Ta: 0.1~0.4%; V: 0.2~0.4%; Si: 1.0~1.8%; P < 0.01%; S < 0.01%; O ≤ 0.002%; H < 0.001%; ​​the balance is Fe and unavoidable impurities; and satisfies: Grain size not less than grade 8; The content of high-temperature δ-ferrite is no more than 10%; Tensile strength at 550℃ ≥450MPa, elongation ≥20%; At 550℃ / 10 -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness is no greater than 5.0 μm.

[0008] Among the aforementioned chemical compositions, silicon can form a dense SiO2 oxide film, effectively improving the stability of the Cr2O3 oxide film in the steel; the nickel-free design can significantly slow down the dissolution corrosion of ferritic / martensitic steel in lead-bismuth environments. The combination of these two factors effectively enhances the oxidation resistance and liquid metal corrosion resistance of ferritic / martensitic steel.

[0009] According to the present invention, in several specific embodiments, the grain size of the high-silicon-content ferritic / martensitic steel cladding tube is 8.5 to 10.

[0010] According to the present invention, in several specific embodiments, the high-temperature δ-ferrite content of the high-silicon ferritic / martensitic steel cladding tube is 3~10%.

[0011] According to the present invention, in several specific embodiments, the high-silicon-content ferritic / martensitic steel cladding tube has a tensile strength of 455~490MPa and an elongation of 20~26% when stretched at 550℃.

[0012] According to the present invention, in several specific embodiments, high-silicon content ferritic / martensitic steel cladding tubes are subjected to 550°C / 10 -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the thickness of the oxide film is 2.6~5.0 μm.

[0013] As a preferred option, in the aforementioned high-silicon content ferritic / martensitic steel cladding pipe resistant to high-temperature lead-bismuth corrosion, the total amount of Si and W is 2.4~3.0%, and the total amount of unavoidable impurities is ≤0.05%. Excessive silicon and tungsten elements will form in the steel. x Brittle phases such as laves can be present. When the total amount of Si and W is 2.4% to 3.0%, the formation of excessive brittle phases can be avoided, which would significantly deteriorate the machinability of the steel and the mechanical properties of the finished pipe. Unavoidable impurities include, but are not limited to, Co, Cu, and Pb.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned high-temperature lead-bismuth corrosion-resistant high-silicon content ferritic / martensitic steel cladding tube, the method comprising: S1: The ingredients are prepared according to the design composition and then undergo vacuum induction melting and vacuum arc remelting to obtain a vacuum arc remelted ingot. S2: The vacuum consumable arc remelting ingot of S1 is homogenized and hot forged to obtain a forged bar; S3: The forged bar of S2 is hot-extruded, annealed, and machined to obtain a round tube blank; S4: The round tube blank of S3 is cold rolled in 4 to 6 passes, and degreasing and annealing are performed between cold rolling passes to obtain cold rolled round tube. S5: The cold-rolled round tube of S4 is normalized and tempered, straightened and finished to obtain the finished clad tube.

[0015] As a preferred embodiment, in step S2 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the homogenization treatment temperature is [temperature value missing]. T 1. The temperature of hot forging is T 2; In step S3, the temperature of hot extrusion is T 3; Satisfies: 1050℃≤ T 1≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 2≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 3≤[1150℃+250(%C)-20(%W)-40(%Si)].

[0016] Since the content of carbon, silicon, and tungsten elements has a significant impact on the temperature range of high-temperature δ-ferrite in materials, the temperature ranges for homogenization, forging, and hot extrusion are specified. This not only ensures the yield of high-silicon ferritic / martensitic steel pipes but also avoids the formation of excessive high-temperature δ-ferrite, which would deteriorate the pipe performance.

[0017] As a preferred embodiment, in step S2 of the above-mentioned method for preparing high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the final forging temperature of the forging bar is not lower than 850°C. If the forging bar is lower than this temperature during the forging process, it is returned to the furnace for heat preservation, and the temperature is controlled according to the temperature of the homogenization treatment.

[0018] As a preferred embodiment, in steps S2, S3, and S4 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the forging ratio is not less than 3.0.

[0019] As a preferred embodiment, in step S3 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the deformation amount of hot extrusion is not less than 85%.

[0020] As a preferred embodiment, in step S4 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the deformation amount of the tube in a single cold rolling pass is not less than 40%, and the total deformation amount in cold rolling is not less than 90%.

[0021] As a preferred embodiment, in step S3 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the annealing temperature after hot extrusion is 700~850℃.

[0022] As a preferred embodiment, in step S4 of the above-mentioned method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion, the annealing temperature between cold rolling passes is 700~850℃.

[0023] As a preferred embodiment, step S5 of the above-described method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion satisfies at least one of the following characteristics: The vacuum degree during normalizing and tempering processes is <1.0×10⁻⁶. -2 Pa; The normalizing temperature is 950~1100℃, and the normalizing holding time is 15~30min; The tempering temperature is 600~800℃, and the tempering holding time is 30~60min; The cooling process uses high-purity inert gas to cool the temperature to below 200°C.

[0024] According to the present invention, the diameter of the cladding tube obtained by the above-described method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion is [missing information]. F 7.0~15.0mm, diameter tolerance is ±0.02mm, wall thickness is 0.4~1.0mm.

[0025] According to one specific embodiment of the present invention, the method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion includes: (1) Vacuum induction melting + vacuum consumable arc remelting Alloying elements are batched according to the designed composition. The materials are melted and refined through vacuum induction melting, and high-silicon content ferritic / martensitic steel vacuum induction ingots are produced by die casting. After removing solidification defects from the head and tail areas of the high-silicon content ferritic / martensitic steel vacuum induction ingot and completing surface machining, it is placed on the cathode of a vacuum arc remelting furnace. Using a disc with the same composition as the high-silicon content ferritic / martensitic steel vacuum induction ingot as the arc ignition plate, remelting is carried out under a vacuum degree <0.1 Pa to obtain a high-silicon content ferritic / martensitic steel arc remelted ingot with the required composition.

[0026] (2) Homogenization treatment + forging The high-silicon content ferritic / martensitic steel arc remelting ingot obtained in step (1) is heated to... TThe material is held at 1℃ for at least 12 hours to complete the homogenization process before forging (the final forging temperature is not lower than 850℃; if the billet temperature is lower than this during forging, it is returned to the furnace for holding for at least 1 hour, with the holding temperature controlled according to the homogenization temperature). The homogenization temperature is... T 1. The temperature of hot forging is T 2. Obtain high-silicon-content ferritic / martensitic steel forging bars.

[0027] The formula used to calculate the homogenization temperature is as follows: 1050℃≤ T 1≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 2≤[1150℃+250(%C)-20(%W)-40(%Si)]; %C, %W, and %Si represent the mass percentages of carbon, tungsten, and silicon in an arc-remelted ingot of high-silicon ferritic / martensitic steel, respectively, in units of %.

[0028] (3) Extrusion and annealing The high-silicon content ferritic / martensitic steel forging rods obtained in step (2) are cut to a fixed length, and their outer surfaces are machined (the amount removed from the outer surface of each forging rod is not less than 1.5 mm). The blanks are then bored in the center area of ​​the blanks to obtain extruded billets. The outer diameter of the extruded billets matches the size of the extrusion cylinder, and the diameter of the central hole matches the size of the extrusion needle.

[0029] To avoid excessive stress differences in various regions during deformation due to uneven temperature distribution in the extruded billet, the extruded billet is first preheated to 750-900℃ and held at that temperature for at least 1 hour. It is then transferred to an induction heating furnace and heated to a uniform heating temperature. T 3. After hot extrusion (the deformation amount of hot extrusion is not less than 85%, and the cooling method is air cooling), high-silicon content ferritic / martensitic steel extruded tubes are obtained. The high-silicon content ferritic / martensitic steel extruded tubes are then annealed at 700~850℃ to obtain extruded annealed tubes.

[0030] 1050℃≤ T 3≤[1150℃+250(%C)-20(%W)-40(%Si)], where %C, %W, and %Si are the mass percentages of carbon, tungsten, and silicon in high-silicon ferritic / martensitic steel arc remelted ingots, respectively, in units of %.

[0031] (4) Cold rolling and annealing The high-silicon content ferritic / martensitic steel extruded and annealed tubes obtained in step (3) are machined to remove the oxide scale on their inner and outer surfaces, and then subjected to 4 to 6 passes of cold rolling deformation. The deformation amount of each pass of cold rolling is not less than 40%, and the total deformation amount of cold rolling is not less than 90%. Annealing treatment is required between the cold rolling deformation passes of the tubes, and the annealing temperature is 700 to 850℃ to obtain high-silicon content ferritic / martensitic steel cold-rolled round tubes.

[0032] (5) Normalizing + Tempering The high-silicon content ferritic / martensitic steel cold-rolled round tubes obtained in step (4) are subjected to "normalizing + tempering" treatment, with the vacuum degree during the normalizing and tempering processes being <1.0×10⁻⁶. -2 The normalizing temperature is 950~1100℃, the normalizing holding time is 15~30min, the tempering temperature is 600~800℃, the tempering holding time is 30~60min, and high-purity inert gas is used to cool the steel to below 200℃ during the cooling process. Finally, through straightening and internal and external surface treatment, high-silicon content ferritic / martensitic steel finished round tubes are obtained.

[0033] According to one specific embodiment of the present invention, the high-silicon content ferritic / martensitic steel forging bar prepared by the present invention is a crack-free forging bar.

[0034] According to one specific embodiment of the present invention, the high-silicon-content ferritic / martensitic steel extruded tube prepared by the present invention is a crack-free round tube.

[0035] According to one specific embodiment of the present invention, the high-silicon content ferritic / martensitic steel finished pipe prepared by the present invention is a crack-free seamless round pipe.

[0036] Compared with the prior art, the main principles and advantages of the present invention are as follows: 1. This invention adopts a high-silicon, nickel-free composition design concept. On the one hand, by increasing the silicon content in ferritic / martensitic steel, a dense SiO2 oxide film is formed, effectively improving the stability of the Cr2O3 oxide film in the steel. On the other hand, by adopting a nickel-free design, the degree of dissolution corrosion of ferritic / martensitic steel in a lead-bismuth environment can be significantly slowed down. Therefore, it can effectively improve the oxidation resistance and liquid metal corrosion resistance of ferritic / martensitic steel. Furthermore, because excessive silicon and tungsten elements will form in the steel... x The presence of brittle phases such as laves is a concern. Therefore, this invention imposes additional limits on the total content of silicon and tungsten to avoid the formation of excessive brittle phases that could significantly deteriorate the machinability of the steel and the mechanical properties of the finished pipe.

[0037] 2. Since the contents of carbon, silicon, and tungsten significantly affect the temperature range of high-temperature δ-ferrite in materials, the temperature ranges for homogenization, forging, and hot extrusion are specified for the specific contents of different elements in the material. This not only ensures the yield of high-silicon ferritic / martensitic steel pipes but also avoids the formation of excessive high-temperature δ-ferrite, which would deteriorate the pipe performance. The ferritic / martensitic steel involved in this invention does not contain Zr, La, or N elements, making its composition more refined and reducing the difficulty of smelting and manufacturing costs. This invention, through the synergistic effect of large deformation extrusion and rolling, and normal tempering processes, fully refines the grains, increases the substructure in the material microstructure, and allows carbides to precipitate diffusely, achieving the effect of microalloying of the three elements.

[0038] 3. High-silicon ferritic / martensitic steel is a high-strength alloy. This invention addresses the processing and usage requirements of process billets / tubes and finished tubes by designing different heat treatment schemes. For billets / process tubes after large deformation hot extrusion and cold rolling, high-temperature annealing is used to obtain a microstructure dominated by granular pearlite (the microstructure was observed using an Olympus CX71 metallographic microscope and a FEI Nova / Nano 400 field emission scanning electron microscope), effectively eliminating residual stress inside the hot-extruded billets and cold-rolled tubes, giving them good cold working performance. For finished cold-rolled round tubes, normalizing is first used to induce a martensitic phase transformation in the material matrix, initially achieving ultra-high strength, followed by tempering to promote the formation of finer microstructures. 23 The C6 and MX precipitates disperse and relieve some of the stress, ultimately resulting in finished pipes that possess both high plasticity and excellent resistance to high-temperature lead-bismuth corrosion.

[0039] 4. This invention, through large deformation forging, hot extrusion and cold rolling, not only significantly refines the microstructure, but also makes the process flow compact and facilitates industrial production. Furthermore, through targeted control of process parameters, it significantly improves the yield of the product, thereby reducing production energy consumption and costs.

[0040] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0042] In this embodiment of the invention, the method for determining the size and properties of high-temperature tensile specimens is based on GB / T228.2, and the equipment used is a WDW-100C electronic universal testing machine.

[0043] In this embodiment of the invention, the equipment used for high-temperature lead-bismuth corrosion is a static lead-bismuth corrosion device.

[0044] In the embodiments and comparative examples of this invention, the raw materials are commercially available.

[0045] In this embodiment of the invention, the homogenization temperature is T 1. The temperature of hot forging is T 2. The temperature of hot extrusion is T 3; Satisfies: 1050℃≤ T 1≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 2≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 3≤[1150℃+250(%C)-20(%W)-40(%Si)].

[0046] Example 1 According to the designed composition, the alloying elements are prepared by loading the prepared raw materials, such as high-purity iron, pure chromium, pure silicon, pure tantalum, and pure tungsten, into a crucible and then heating it under a vacuum of 7.63~9.50×10⁻⁶. -2 Under the condition of Pa, the steel is heated and smelted until a molten pool is formed and there is no other unmelted metal in the pool. Then, the vacuum is turned off and pure vanadium and ferromanganese alloy, which were placed in the vacuum induction furnace feeder in advance, are added to the crucible in sequence for alloying under the protection of high-purity argon. The temperature of the molten steel is adjusted to the casting temperature by power adjustment and high-silicon ferritic / martensitic steel vacuum induction ingot is produced by die casting.

[0047] Solidification defects in the head and tail regions of a high-silicon content ferritic / martensitic steel vacuum induction ingot are removed, and surface oxide scale is removed by machining. The ingot is then mounted on the cathode of a vacuum arc remelting furnace. A circular plate with the same composition as the high-silicon content ferritic / martensitic steel vacuum induction ingot is used as the arc-starting plate, and the furnace operates at a vacuum degree of 5.84~8.90×10⁻⁶. -2 Remelting was carried out under Pa conditions to obtain high-silicon content ferritic / martensitic steel arc-remelted ingots. The composition of the arc-remelted ingots was: C 0.16%; Mn 0.8%; Cr 11.6%; W 1.2%; Ta 0.4%; V 0.4%; Si 1.8%; P < 0.01%; S < 0.01%; O ≤ 0.002%; H < 0.001%. The total amount of Si and W was 3.0%, and the total amount of impurity elements such as Co, Cu, and Pb was 0.04%.

[0048] After heating the high-silicon content ferritic / martensitic steel ingot to 1070℃ and holding it for 12.5h, it was forged multiple times at 1070℃, and the final forging temperature was controlled at 860℃ to obtain a high-silicon content ferritic / martensitic steel forged bar with a forging ratio of 3.5.

[0049] High-silicon ferritic / martensitic steel forging bars are cut to a fixed length, and their outer surfaces are machined and then bored in the central area of ​​the billet to obtain extruded tube blanks.

[0050] The extruded billet is preheated to 755°C in a ring furnace and then transferred to an induction heating furnace to be heated to 1050°C. After sufficient lubrication, it is extruded to obtain a high-silicon content ferritic / martensitic steel extruded round tube. The extrusion deformation of the round tube is 86%, and it is air-cooled.

[0051] High-silicon-content ferritic / martensitic steel extruded round tubes were annealed at 850℃ for 60 minutes and then air-cooled to obtain annealed high-silicon-content ferritic / martensitic steel round tubes.

[0052] After removing the oxide scale from the inner and outer surfaces of the high-silicon content ferritic / martensitic steel extruded and annealed tube, it undergoes a 6-pass cold rolling deformation process. The minimum single-pass deformation is 41%, and the total cold rolling deformation is 92%. The annealing temperature between the cold rolling deformation passes is 700℃. The holding time for the first 4 passes is 1 hour, and the holding time for the 5th pass is 30 minutes, resulting in a high-silicon content ferritic / martensitic steel cold-rolled round tube.

[0053] High-silicon content ferritic / martensitic steel cold-rolled round tubes are subjected to a "normalizing + tempering" treatment, with a vacuum degree of 9.5 × 10⁻⁶ during the normalizing and tempering processes. -3 The normalizing temperature was 950℃, the normalizing holding time was 30 min, the tempering temperature was 800℃, the tempering holding time was 60 min, and high-purity inert gas was used to cool the steel to room temperature during the cooling process. Finally, high-silicon content ferritic / martensitic steel finished round tubes were obtained through straightening and internal and external surface treatment.

[0054] The diameter of the finished round tube is F 7.0mm diameter, with a diameter tolerance of ±0.015mm and a wall thickness of 1.0mm. The pipe has a grain size of grade 10 and a high-temperature δ-ferrite content of 9.25%. The pipe has a tensile strength of 455MPa and an elongation of 26% at 550℃. The pipe is tested at 550℃ / 10... -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness was 2.6 μm.

[0055] Example 2 The method is the same as in Example 1, except that: (1) The mass percentage of the chemical composition of the vacuum arc remelted ingot is C 0.24%; Mn 0.4%; Cr 12.4%; W 1.8%; Ta 0.1%; V 0.2%; Si 1.0%; P < 0.01%; S < 0.01%; O ≤ 0.002%; H < 0.001%. The total amount of Si and W is 2.8%, and the total amount of impurity elements such as Co, Cu, and Pb is 0.02%.

[0056] (2) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1050℃ and held for 14h, it is forged multiple times at 1050℃, and the forging ratio of the forging bar is 4.8.

[0057] (3) The extruded tube blank is preheated to 900°C in a ring furnace and then transferred to an induction heating furnace to be heated to 1120°C. After sufficient lubrication, it is extruded to obtain a high silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 700°C and the holding time is 60 min.

[0058] (4) After the high silicon content ferritic / martensitic steel extrusion annealed tube is machined, it is subjected to 4 passes of cold rolling deformation, with a total cold rolling deformation of 94%. The annealing temperature between the cold rolling deformation passes of the tube is 850℃, the holding time of the first 3 passes is 30min, and the holding time of the 4th pass is 15min.

[0059] (5) The normalizing temperature of cold-rolled round tubes of high silicon content ferritic / martensitic steel is 1100℃, the normalizing holding time is 15min, the tempering temperature is 600℃, and the tempering holding time is 30min.

[0060] (6) The diameter of the finished round tube is F The tube has a diameter of 15mm, a diameter tolerance of ±0.02mm, and a wall thickness of 0.7mm. The tube's grain size is grade 8.5, and the high-temperature δ-ferrite content is 3.33% (significantly superior to Examples 1 and 3 due to lower silicon content, higher carbon content, and reduced chromium-to-nickel equivalent, which inhibits ferrite formation). The tube exhibits a tensile strength of 490MPa and an elongation of 23% at 550℃. The tube is also suitable for applications involving 550℃ / 10... -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness was 4.9 μm.

[0061] Example 3 The method is the same as in Example 1, except that: (1) The mass percentage of the chemical composition of the vacuum arc remelted ingot is C 0.20%; Mn 0.4%; Cr 12.0%; W 1.4%; Ta 0.25%; V 0.3%; Si 1.4%; P < 0.01%; S < 0.01%; O ≤ 0.002%; H < 0.001%. The total amount of Si and W is 2.8%.

[0062] (2) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1115℃ and held for 20h, it is forged in multiple passes at 1115℃.

[0063] (3) The extruded tube blank is preheated to 900°C in a ring furnace and then transferred to an induction heating furnace to be heated to 1060°C. After sufficient lubrication, it is extruded to obtain a high silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 800°C.

[0064] (4) After the high silicon content ferritic / martensitic steel extruded and annealed tube is machined, it is subjected to 5 passes of cold rolling deformation, with a total cold rolling deformation of 95.2%. The annealing temperature between the cold rolling deformation passes of the tube is 800℃, the holding time for the first 4 passes is 60min, and the holding time for the 5th pass is 45min.

[0065] (5) The normalizing temperature of high silicon content ferritic / martensitic steel cold-rolled round tube is 1000℃, the normalizing holding time is 20min, the tempering temperature is 700℃, and the tempering holding time is 45min.

[0066] (6) The diameter of the finished round tube is F The pipe has a diameter tolerance of ±0.017 mm and a wall thickness of 1.0 mm. The grain size is grade 9.0, and the high-temperature δ-ferrite content is 7.15%. The pipe has a tensile strength of 475 MPa and an elongation of 25% at 550℃. The pipe is also suitable for applications involving 550℃ / 10... -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness was 3.9 μm.

[0067] Comparative Example 1 The difference from Example 1 is as follows: (1) The mass percentage of the chemical composition of the vacuum arc remelting ingot is Cr 11.5%; W 1.0%; Si 0.8%, and other chemical compositions are the same as in Example 1.

[0068] (2) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1130℃ and held for 20h, it is forged in multiple firings.

[0069] (3) The extruded billet is preheated to 850°C in a ring furnace and then transferred to an induction heating furnace to be heated to 1180°C (>[1150°C+250(%C)-20(%W)-40(%Si)]=1116°C). After sufficient lubrication, it is extruded to obtain a high silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 750°C.

[0070] (4) The normalizing temperature of the cold-rolled round tube of high silicon content ferritic / martensitic steel is 950℃, the normalizing holding time is 20min, the tempering temperature is 800℃, and the tempering holding time is 45min.

[0071] (6) The pipe grain size is grade 8.5. However, due to the high hot extrusion temperature, the extrusion process temperature range is in the high-temperature δ-ferrite region. Therefore, the high-temperature δ-ferrite content of the finished pipe is 14.36%. Consequently, the tensile strength of the finished pipe at 550℃ is only 434 MPa, and the elongation is only 17.5%. In addition, due to the reduction in chromium and silicon content, the pipe's resistance to high-temperature lead-bismuth corrosion is significantly reduced. -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness is about 12 μm.

[0072] Comparative Example 2 The difference from Example 1 is as follows: (1) The mass percentage of the chemical composition of the vacuum arc remelted ingot is C 0.14%; W 2.2%; Si 2.0%; V 0.55%; Ta 0.5%, and other chemical compositions are the same as in Example 1.

[0073] (2) After the high-silicon content ferritic / martensitic steel arc remelting ingot was homogenized at 1030℃ (<1050℃) and held for 20h, it was forged in multiple passes. The final forging temperature of the forged bar was 815℃. Due to the low homogenization and final forging temperatures, the surface of the forged bar showed obvious folding and cracking. After removing the folding and cracking defects on the surface of the forged bar by machining, it was further subjected to hot extrusion deformation.

[0074] (3) The extruded billet is preheated in a ring furnace and then transferred to an induction heating furnace to be heated to 1050°C. After being fully lubricated, it is extruded to obtain a high-silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 800°C.

[0075] (4) The normalizing temperature of cold-rolled round tubes of high silicon content ferritic / martensitic steel is 1000℃, the normalizing holding time is 30min, the tempering temperature is 700℃, and the tempering holding time is 60min.

[0076] (6) The pipe has a grain size of grade 9. Due to the low carbon content and high tungsten and silicon content, the finished pipe contains up to 27.15% high-temperature δ-ferrite, and also precipitates about 2.0% of ferrite. x It contains brittle phases such as laves. The tensile strength of the pipe at 550℃ is only 468MPa, but the elongation is only 10.5%.

[0077] Comparative Example 3 The difference from Example 1 is as follows: (1) The mass percentage of the chemical composition of the vacuum arc remelted ingot is C 0.26%; Cr 12.5%; V 0.1%; Ta 0.08%, and other chemical compositions are the same as in Example 1.

[0078] (2) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1100℃ and held for 15h, it is forged in multiple forging cycles with a forging ratio of 2.8.

[0079] (3) The extruded billet is preheated in a ring furnace and then transferred to an induction heating furnace to be heated to 1060°C. After being fully lubricated, it is extruded with an extrusion deformation of 85% to obtain a high silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 820°C.

[0080] (4) After removing the oxide scale from the inner and outer surfaces of the high-silicon content ferritic / martensitic steel extruded annealed tube by machining, it is subjected to 7 passes of cold rolling deformation. The minimum deformation per pass of the tube is 38%, and the total deformation is 87%. The annealing temperature between the cold rolling deformation passes is 700℃. The holding time for the first 5 passes is 1h, and the holding time for the 5th pass is 30min, thus obtaining a high-silicon content ferritic / martensitic steel cold-rolled round tube.

[0081] (5) The normalizing temperature of the cold-rolled round tube of high silicon content ferritic / martensitic steel is 960℃, the normalizing holding time is 30min, the tempering temperature is 780℃, and the tempering holding time is 50min.

[0082] (6) Due to the low forging ratio, extrusion deformation, single-pass cold rolling deformation, and total cold rolling deformation, the pipe grain size is grade 6.0, and the high-temperature δ-ferrite content is 4.94%. Because the pipe grain is coarse, the tensile strength of the pipe at 550℃ is only 398 MPa. Furthermore, due to the high carbon and chromium content but low vanadium and tantalum content, a large amount of Mg2+ precipitates in the finished pipe. 23 C6, therefore the pipe elongation is only 15.7%.

[0083] Comparative Example 4 The difference from Example 1 is as follows: (1) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1100℃ and held for 20h, it is forged in multiple heats.

[0084] (2) The extruded tube blank is preheated to 850°C in a ring furnace and then transferred to an induction heating furnace to be heated to 1125°C. After sufficient lubrication, it is extruded to obtain a high silicon content ferritic / martensitic steel extruded round tube. The annealing temperature of the extruded round tube is 750°C.

[0085] (3) The grain size of the pipe is grade 7. However, due to the high homogenization temperature of the arc remelting ingot and the high hot extrusion temperature of the pipe, the temperature range of the extrusion process is the high temperature δ ferrite region. Therefore, the high temperature δ ferrite content of the finished pipe is 12%, and the elongation of the finished pipe at 550℃ is only 18.5%.

[0086] Comparative Example 5 The difference from Example 3 is that: (1) The chemical composition of the vacuum arc remelted ingot by mass percentage is: C 0.20%; Mn 0.4%; Cr 12.0%; W 1.7%; Ta 0.25%; V 0.3%; Si 1.4%; P < 0.01%; S < 0.01%; O ≤ 0.002%; H < 0.001%. The total amount of Si and W is 3.1%.

[0087] (2) After the high silicon content ferritic / martensitic steel arc remelting ingot is homogenized at 1115℃ and held for 20h, it is forged multiple times at 1115℃, and the temperature is higher than: [1150℃+250(%C)-20(%W)-40(%Si)]=1100℃.

[0088] (3) The grain size of the pipe is grade 9.0, and the high-temperature δ-ferrite content is 14.5%. The tensile elongation of the pipe at 550℃ is only 10.5%.

[0089] Comparative Example 6 The difference from Example 2 is that: (1) The extrusion deformation of the extruded tube blank is 82%, and a high silicon content ferritic / martensitic steel extruded round tube is obtained.

[0090] (2) After the oxide scale on the inner and outer surfaces of the high silicon content ferritic / martensitic steel extrusion annealed tube is removed by machining, it is subjected to 4 passes of cold rolling deformation, with a total cold rolling deformation of 87%.

[0091] (3) Due to the low amount of extrusion deformation and total deformation during cold rolling, the grain breakage during the deformation process of the pipe is insufficient. After normalizing and tempering heat treatment, the average grain size of the pipe is grade 5.5, and mixed grains appear. Due to the coarse grains of the pipe, the tensile strength of the pipe at 550℃ is only 382 MPa.

[0092] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-silicon content ferritic / martensitic steel cladding pipe resistant to high-temperature lead-bismuth corrosion, characterized in that, The chemical composition, by mass percentage, contains: C: 0.16~0.24%; Mn: 0.4~0.8%; Cr：11.6~12.4%； W：1.2~1.8%； Ta: 0.1~0.4%; V：0.2~0.4%； Si: 1.0~1.8%; P＜0.01%； S < 0.01%; O ≤ 0.002%; H < 0.001%; ​​the balance is Fe and unavoidable impurities; and it satisfies: Grain size not less than grade 8; The content of high-temperature δ-ferrite is no more than 10%; Tensile strength at 550℃ ≥450MPa, elongation ≥20%; At 550℃ / 10 -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the oxide film thickness is no greater than 5.0 μm.

2. The high-silicon content ferritic / martensitic steel cladding pipe resistant to high-temperature lead-bismuth corrosion according to claim 1, characterized in that, High-silicon-content ferritic / martensitic steel cladding pipes satisfy at least one of the following characteristics: The grain size is 8.5~10. The high-temperature δ-ferrite content is 3~10%; The tensile strength at 550℃ is 455~490MPa, and the elongation is 20~26%. At 550℃ / 10 -6 After corrosion in wt% lead-bismuth molten metal for 3000 hours, the thickness of the oxide film is 2.6~5.0 μm.

3. The high-silicon content ferritic / martensitic steel cladding pipe resistant to high-temperature lead-bismuth corrosion according to claim 1, characterized in that, The total amount of Si and W is 2.4~3.0%, and the total amount of unavoidable impurities is ≤0.05%.

4. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion as described in any one of claims 1-3, characterized in that, The preparation method includes: S1: The ingredients are prepared according to the design composition and then undergo vacuum induction melting and vacuum arc remelting to obtain a vacuum arc remelted ingot. S2: The vacuum consumable arc remelting ingot of S1 is homogenized and hot forged to obtain a forged bar; S3: The forged bar of S2 is hot-extruded, annealed, and machined to obtain a round tube blank; S4: The round tube blank of S3 is cold rolled in 4 to 6 passes, and degreasing and annealing are performed between cold rolling passes to obtain cold rolled round tube. S5: The cold-rolled round tube of S4 is normalized and tempered, straightened and finished to obtain the finished clad tube.

5. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, In step S2, the homogenization temperature is T 1. The temperature of hot forging is T 2; In step S3, the temperature of hot extrusion is T 3; Satisfies: 1050℃≤ T 1≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 2≤[1150℃+250(%C)-20(%W)-40(%Si)]; 1050℃≤ T 3≤[1150℃+250(%C)-20(%W)-40(%Si)]。 6. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, In step S2, the final forging temperature of the forging bar shall not be lower than 850℃. If the forging bar is lower than this temperature during the forging process, it shall be returned to the furnace for heat preservation, and the temperature shall be controlled according to the temperature of the homogenization treatment.

7. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, Satisfy at least one of the following characteristics: In steps S2, S3, and S4, the forging ratio is not less than 3.0; In step S3, the deformation amount of hot extrusion is not less than 85%; In step S4, the deformation amount of the pipe in a single cold rolling pass shall not be less than 40%, and the total deformation amount in cold rolling shall not be less than 90%.

8. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, Satisfy at least one of the following characteristics: In step S3, the annealing temperature after hot extrusion is 700~850℃; In step S4, the annealing temperature between cold rolling passes is 700~850℃.

9. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, Step S5 satisfies at least one of the following characteristics: The vacuum degree during normalizing and tempering processes is <1.0×10⁻⁶. -2 Pa; The normalizing temperature is 950~1100℃, and the normalizing holding time is 15~30min; The tempering temperature is 600~800℃, and the tempering holding time is 30~60min; The cooling process uses high-purity inert gas to cool the temperature to below 200°C.

10. The method for preparing a high-silicon content ferritic / martensitic steel cladding tube resistant to high-temperature lead-bismuth corrosion according to claim 4, characterized in that, The diameter of the resulting cladding tube is Φ 7.0~15.0mm, diameter tolerance is ±0.02mm, wall thickness is 0.4~1.0mm.