Cold machining and annealing treatment method for small-diameter FeCrAl thin-wall pipe fitting

Abstract

The invention provides a cold machining and annealing treatment method for a small-diameter FeCrAl thin-wall pipe fitting, and relates to the technical field of nuclear fusion reactor thin-wall pipe fittings. The small-diameter FeCrAl thin-wall pipe fitting is prepared from the following chemical components in percentage by mass: 11 to 16 percent of Cr, 4 to 6 percent of Al, 0.2 to 0.8 percent of Si, 0.2 to 0.6 percent of Mn, 1.0 to 2.2 percent of W, 0.01 to 0.1 percent of Y and the balance of Fe and inevitable impurities. The method comprises the steps of raw material weighing, smelting and casting, forging and machining, through hole and hot extrusion, cold rolling and inter-pass annealing. According to the preparation method, the small-diameter FeCrAl thin-wall pipe fitting with the mechanical property and the hydrogen permeation resistance synergistically improved is prepared through raw material weighing, smelting and refining, hot forging and machining, through hole forming and hot extrusion and cold rolling and inter-pass annealing; the preparation method is simple and easy to operate, green and environment-friendly, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The invention relates to the technical field of thin-walled pipe fittings for nuclear fusion reactors, in particular to a cold working and annealing treatment method for small-diameter FeCrAl thin-walled pipe fittings. Background Art

[0002] Existing FeCrAl pipes are primarily designed for use in nuclear fission reactors, where active elements such as Mo and Ni are present in their composition. However, fusion reactor structural materials require very low levels of active elements, placing higher demands on FeCrAl pipes for their hydrogen permeation resistance. Therefore, research is needed on methods for mass-producing FeCrAl pipes and their high hydrogen permeation resistance.

[0003] In the prior art, Chinese patent CN110004367A discloses a method for preparing oxide-dispersion-strengthened FeCrAl alloy pipes, which belongs to the field of nuclear fission technology. The FeCrAl alloy pipes have a composition of 14-22% Cr, 3-5% Al, 0.15-0.5% Y, and the balance Fe. The method involves first preparing powder by mechanical alloying, then hot isostatic pressing to prepare ODS steel, which is then forged into bars at 1100-1250°C, followed by heat treatment at 800-1000°C for 40-80 minutes and piercing, and finally cold rolling followed by vacuum annealing at 700-1050°C for 30-90 minutes between passes.

[0004] Chinese patent CN115161564A discloses a FeCrAl stainless steel cladding tube and its preparation method, which belongs to the field of nuclear fusion technology. The composition of the FeCrAl stainless steel cladding tube is Cr 8-14%, Al 3-6%, Mo 0.5-2%, Y The method comprises the following steps: firstly, vacuum induction melting and die casting are performed to form an ingot, followed by holding at 1100-1250°C for 1 hour and forging, with a final forging temperature greater than 750°C and a forging ratio greater than 3, to obtain a rod; secondly, the forged rod is subjected to hot isostatic pressing sintering at 1050-1250°C for 1-3 hours, followed by holding at 700-900°C for 1-2 hours and hot extrusion with an extrusion ratio of 8-20:1; thirdly, annealing is performed at 700-950°C for 0.5-2 hours; and finally, warm rolling is performed at 500-750°C for 25-50%, followed by cold rolling at 15-40% and inter-pass annealing at 700-850°C.

[0005] It can be seen from the above two existing technologies that the preparation technology of FeCrAl pipe fittings mainly has the following technical defects:

[0006] (1) FeCrAl alloy thin-walled pipes developed with existing technology are mainly used in nuclear fission reactors. The Cr and Al elements added to the composition can form a dense Cr-rich and Al-rich oxide film in a high-temperature and high-pressure water environment, thereby improving the corrosion resistance of the material. However, in addition to good corrosion resistance, thin-walled pipes for fusion reactor blankets must also have higher hydrogen permeation resistance requirements. Adding a certain amount of Si to FeCrAl alloy can significantly improve its hydrogen permeation resistance.

[0007] (2) Since the addition of Cr, Al, and Si elements to FeCrAl alloys easily produces a solid solution strengthening effect, FeCrAl alloys still maintain high strength and deformation resistance at high temperatures (such as 1000-1200°C). If the temperature is not properly controlled during hot working, it may cause cracking of the ingot. At the same time, the solid solution strengthening effect of Cr, Al, and Si elements reduces the ductility of the FeCrAl alloy, causing the pipe to harden rapidly during cold deformation (high work hardening index), making it easy to crack.

[0008] (3) Cast FeCrAl has coarse grains, and the number of grain boundaries in the alloy is significantly reduced, resulting in a decrease in the resistance to crack propagation. Once a crack is formed during deformation, it is more likely to propagate along the grain boundary or through the grain, leading to brittle fracture. Summary of the Invention

[0009] To address the existing technical problems of FeCrAl, such as the single hydrogen-blocking element in the composition, easy cracking during cold working, high production cost, and low production efficiency, the present invention proposes a cold working and annealing method for small-diameter FeCrAl thin-walled pipes that can solve the aforementioned technical problems. The technical solution is as follows:

[0010] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0011] S1. Raw material weighing: The chemical composition of small-diameter FeCrAl thin-walled pipe fittings is as follows by mass percentage: Cr 11-16%, Al 4-6%, Si 0.2-0.8%, Mn 0.2-0.6%, W 1.0-2.2%, Y 0.01-0.1%, and the balance is Fe and unavoidable impurities; weigh the raw materials according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fittings described above;

[0012] S2, melting and casting: The weighed raw materials of S1 are melted multiple times by vacuum melting process, and then cooled to room temperature with the furnace after casting to obtain alloy ingots;

[0013] S3, forging and machining: the alloy ingot of S2 is hot forged at high temperature to obtain φ220×900+M mm, where M is greater than 0, and then air-cooled to room temperature, and the forged rod is processed into a Φ204mm×900mm smooth rod;

[0014] S4, through-hole and hot extrusion: The light rod of S3 is drilled axially in the center of the rod using a through-hole machine, and the corners are rounded at both ends. The hollow billet after chamfering is heated by induction in a ring heating furnace for a step-by-step increase. The temperature is then continuously increased and the central through-hole is enlarged. After a second induction heating, the hot extrusion tube is completed under the joint action of the core rod and the extrusion barrel of the hot extruder to obtain a rough tube;

[0015] S5, cold rolling and inter-pass annealing: The S4 rough pipe is subjected to multiple passes of cold rolling and inter-pass annealing. As the rolling passes and deformation resistance increase, the pass deformation is reduced by 10% compared with before, and the inter-pass annealing temperature is increased by 50°C compared with before, finally obtaining a small-diameter FeCrAl thin-walled pipe fitting.

[0016] Optionally, the small diameter FeCrAl thin-walled pipe fitting of S1 has an outer diameter of 5-11 mm, a wall thickness of 0.3-1.3 mm, and a length of 2200-3500 mm.

[0017] Optionally, in the vacuum melting process of S2, 130-180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of the vacuum induction furnace before melting.

[0018] Optionally, in the vacuum melting process of S2, when the vacuum degree in the induction furnace reaches 50-1000 Pa, the power is adjusted to start induction heating of the alloy raw material in the crucible.

[0019] Optionally, in the vacuum melting process of S2, the raw materials are completely melted within 30-120 minutes, and the molten steel is kept at 1550-1600°C for 10-60 minutes for refining; after refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 0.5-2 minutes to allow the molten steel to cool rapidly.

[0020] Optionally, in the high-temperature hot forging of S3, the alloy ingot of S2 needs to be kept at 1100-1200°C for 1-3 hours before hot forging, and the final forging temperature is not lower than 950°C; the microstructure of the light rod is a single ferrite phase, the grain size is ≤200μm, the room temperature tensile strength is ≥550MPa, the yield strength is ≥450MPa, and the elongation is ≥15%.

[0021] Optionally, the through hole diameter of S4 is Φ20-40mm, the heating rate of the first induction heating step heating is 1-5℃ / min, the holding temperature is 700-900℃, and the holding time is 1-5h; the heating rate of continued heating before hole expansion is 50-150℃ / min, the holding temperature is 900-1100℃, and the holding time is 2-10min.

[0022] Optionally, the central through hole of S4 is enlarged by 200-400%, the heating rate of the secondary induction heating is 50-150°C / min, the holding temperature is 1100-1150°C, and the holding time is 2-10min; the extrusion ratio of the hot extrusion tube is 20-40:1; the size of the rough tube is Φ50×5-80mm×8mm, the microstructure of the rough tube is a single ferrite phase, the grain size is ≤100μm, the room temperature tensile strength is ≥600MPa, the yield strength is ≥500MPa, and the elongation is ≥18%.

[0023] Optionally, the S5 multi-pass cold rolling is 10-16 passes with a total reduction of 60-95%; before 3-5 cold rolling passes, the increase in rolling passes and deformation resistance is not large, the reduction in each pass is 20-40%, and the annealing temperature between passes is 750-850°C; after 5-7 cold rolling passes, as the rolling passes and deformation resistance increase, the reduction in each pass is 10-30%, and the annealing temperature between passes is 800-850°C.

[0024] Optionally, the tensile strength of the small-diameter FeCrAl thin-walled pipe fittings of S5 at room temperature is not less than 630 MPa, the yield strength is not less than 550 MPa, the yield strength ratio is not less than 0.8, the elongation is not less than 25%, and the strength-ductility product is not less than 15 GPa·%; the tensile strength at 600°C is not less than 280 MPa, the yield strength is not less than 190 MPa, the yield strength ratio is not less than 0.6, the elongation is not less than 17%, and the strength-ductility product is not less than 4.5 GPa·%; and the hydrogen permeability resistance factor PRF value at 500°C is not less than 10,000.

[0025] Optionally, the grain size of the S5 small-diameter FeCrAl thin-walled pipe is not less than grade 5.

[0026] Optionally, after the S5 small diameter FeCrAl thin-walled pipe is expanded by 30%, no cracks or splits may appear; after the pipe is pressed to close, no cracks or splits may appear.

[0027] Technical principle of the present invention:

[0028] FeCrAl thin-walled pipes prepared using existing technology usually do not contain Si. We added 0.2-0.8% Si to the FeCrAl alloy composition. The prepared thin-walled pipes can form an oxide film rich in Cr, Al and Si in the high-temperature environment of a fusion reactor. The Si-rich oxide film has good thermal stability and hydrogen permeation resistance at high temperatures. The addition of these three strong oxide-forming elements can synergistically achieve the goals of corrosion resistance and high hydrogen resistance.

[0029] The FeCrAl pipe design of the present invention replaces Mo with the low-activating element W (1.0-2.2%) for solid solution strengthening. Furthermore, the addition of 0.2-0.8 wt.% Si to FeCrAl promotes the formation of a protective oxide film in high-temperature, high-pressure water environments, further improving the FeCrAl alloy's resistance to hydrogen permeation.

[0030] Vacuum induction melting can produce FeCrAl alloys in large quantities, but there is a problem of coarse cast grains, which makes subsequent plastic processing difficult. The main methods to solve the coarse grains of FeCrAl ingots are: (i) Adding heterogeneous nucleating agents: Appropriate addition of rare earth element Y (<0.1%), the Y-containing oxides precipitated in the molten steel act as heterogeneous nucleation cores to inhibit grain boundary migration, thereby refining the grain size. (ii) Controlling the tapping temperature: Before tapping, the pouring temperature is lowered to 50-100°C above the liquidus (the pouring temperature is controlled at 1550-1600°C) to reduce the melting of the nucleation points by the superheated melt. (iii) Rapid solidification: Using a flat steel ingot mold can make the molten steel solidify rapidly in the ingot mold, thereby inhibiting the growth of the ingot grains.

[0031] Due to the solid solution strengthening effect of the high Cr, Al and Si content in FeCrAl alloy, FeCrAl alloy still maintains high strength and deformation resistance at high temperatures (such as 1000-1200℃). If the temperature is not properly controlled during hot working, it may cause cracking of the ingot. At the same time, the solid solution strengthening effect of Cr, Al and Si elements reduces the ductility of FeCrAl alloy, causing the pipe to harden rapidly during cold deformation (high work hardening index).

[0032] The key technology to address the difficulty in machining FeCrAl alloys due to their high deformation resistance is to produce rough tubes through high-deformation hot extrusion, utilizing triaxial compressive stress to suppress cracking during forging. Hot extrusion refines the grain size of the cast FeCrAl alloy, further optimizing its cold working properties.

[0033] The key technology to address work hardening during cold working of FeCrAl pipe fittings is to use multiple passes of cold rolling with small deformations, combined with intermediate annealing to eliminate the hardening. When annealing at temperatures above 850°C, FeCrAl alloys experience rapid grain growth, so the annealing temperature between cold working passes must be kept below 850°C.

[0034] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0035] The above scheme, the present invention proposes a cold working and annealing treatment method for small diameter FeCrAl thin-walled pipe fittings, which can solve the technical problems of the prior art such as the single hydrogen-blocking element in the FeCrAl composition, easy cracking during cold working, high preparation cost and low production efficiency.

[0036] The invention can obtain FeCrAl alloy ingots with uniform composition by weighing, smelting and refining raw materials.

[0037] The invention can refine the coarse grains in the ingot after vacuum induction melting, eliminate casting defects, improve the mechanical properties of the material, prevent cracking in the subsequent hot extrusion process, and obtain the light rod size required for hot extrusion through hot forging and machining.

[0038] The present invention uses through-holes and hot extrusion to suppress cracking during continuous forging using triaxial compressive stress, so that the FeCrAl alloy with large deformation resistance undergoes plastic deformation at high temperature to obtain finer grains, thereby avoiding cracking during subsequent cold rolling.

[0039] The present invention can cause the FeCrAl alloy to recrystallize during the diameter reduction and wall reduction process through appropriate cold rolling deformation and inter-pass annealing temperature, eliminate hardening in time to avoid cracking, and avoid rapid grain growth caused by excessively high annealing temperature.

[0040] In summary, compared with other traditional methods, the method of the present invention can prepare small-diameter FeCrAl thin-walled pipe fittings with synergistically improved mechanical properties and hydrogen permeation resistance through weighing, smelting and refining, hot forging and machining, through-hole and hot extrusion, and cold rolling and inter-pass annealing of raw materials. The preparation method is simple and easy to operate, green and environmentally friendly, low in cost, short in process, and high in efficiency, which is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 1 of the present invention;

[0043] Figure 2 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 2 of the present invention;

[0044] Figure 3 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 3 of the present invention;

[0045] Figure 4 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 4 of the present invention;

[0046] Figure 5 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 5 of the present invention;

[0047] Figure 6 This is a stress-strain curve diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 6 of the present invention;

[0048] Figure 7 This is a microstructure diagram of a small-diameter FeCrAl thin-walled pipe obtained by a cold working and annealing method for a small-diameter FeCrAl thin-walled pipe according to Example 6 of the present invention;

[0049] Figure 8 This is a physical picture of FeCrAl alloy thin-walled tubes of different sizes obtained by the cold working and annealing treatment method of a small-diameter FeCrAl thin-walled tube fitting of the present invention. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0051] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0052] In the embodiments of the present invention, “image” and “picture” may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are the same.

[0053] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0054] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0055] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0056] S1. Raw material weighing: The chemical composition of small-diameter FeCrAl thin-walled pipe fittings is as follows by mass percentage: Cr 11-16%, Al 4-6%, Si 0.2-0.8%, Mn 0.2-0.6%, W 1.0-2.2%, Y 0.01-0.1%, and the balance is Fe and unavoidable impurities; weigh the raw materials according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fittings described above;

[0057] S2, melting and casting: The weighed raw materials of S1 are melted multiple times by vacuum melting process, and then cooled to room temperature with the furnace after casting to obtain alloy ingots;

[0058] S3, forging and machining: the alloy ingot of S2 is hot forged at high temperature to obtain φ220×900+M mm, where M is greater than 0, and then air-cooled to room temperature, and the forged rod is processed into a Φ204mm×900mm smooth rod;

[0059] S4, through-hole and hot extrusion: The light rod of S3 is drilled axially in the center of the rod using a through-hole machine, and the corners are rounded at both ends. The hollow billet after chamfering is heated by induction in a ring heating furnace for a step-by-step increase. The temperature is then continuously increased and the central through-hole is enlarged. After a second induction heating, the hot extrusion tube is completed under the joint action of the core rod and the extrusion barrel of the hot extruder to obtain a rough tube;

[0060] S5, cold rolling and inter-pass annealing: The S4 rough pipe is subjected to multiple passes of cold rolling and inter-pass annealing. As the rolling passes and deformation resistance increase, the pass deformation is reduced by 10% compared with before, and the inter-pass annealing temperature is increased by 50°C compared with before, finally obtaining a small-diameter FeCrAl thin-walled pipe fitting.

[0061] In particular, the dimensions of S1's small-diameter FeCrAl thin-walled pipe fittings are 5-11mm outer diameter, 0.3-1.3mm wall thickness, and 2200-3500mm length.

[0062] In particular, in the vacuum melting process of S2, 130-180 kg of industrial pure Fe and other raw materials calculated according to the composition of FeCrAl alloy are added to the crucible of the vacuum induction furnace before melting.

[0063] In particular, in the vacuum melting process of S2, when the vacuum degree in the induction furnace reaches 50-1000Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible.

[0064] In particular, in the vacuum melting process of S2, the raw materials are completely melted within 30-120 minutes, and the molten steel is kept at 1550-1600℃ for 10-60 minutes for refining; after refining, the molten steel is cast into a flat steel ingot mold with a length of 40cm, a width of 10cm and a height of 60cm within 0.5-2 minutes to allow the molten steel to cool rapidly.

[0065] In particular, during the high-temperature hot forging of S3, the alloy ingot of S2 needs to be kept at 1100-1200°C for 1-3 hours before hot forging, and the final forging temperature is not lower than 950°C; the microstructure of the light rod is a single ferrite phase, the grain size is ≤200μm, the room temperature tensile strength is ≥550MPa, the yield strength is ≥450MPa, and the elongation is ≥15%.

[0066] In particular, the through-hole diameter of S4 is Φ20-40mm, the heating rate of the first induction heating step heating is 1-5℃ / min, the holding temperature is 700-900℃, and the holding time is 1-5h; the heating rate of the continued heating before hole expansion is 50-150℃ / min, the holding temperature is 900-1100℃, and the holding time is 2-10min.

[0067] In particular, the central through hole of S4 is enlarged by 200-400%, the heating rate of the secondary induction heating is 50-150℃ / min, the holding temperature is 1100-1150℃, and the holding time is 2-10min; the extrusion ratio of the hot extrusion tube is 20-40:1; the microstructure of the rough tube is a single ferrite phase, the grain size is ≤100μm, the room temperature tensile strength is ≥600MPa, the yield strength is ≥500MPa, and the elongation is ≥18%.

[0068] In particular, the S5 multi-pass cold rolling is 10-16 passes with a total reduction of 60-95%; before 3-5 passes of cold rolling, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 20-40%, and the annealing temperature between passes is 750-850°C; after 5-7 passes of cold rolling, as the rolling passes and deformation resistance increase, the reduction per pass is 10-30%, and the annealing temperature between passes is 800-850°C.

[0069] In particular, the tensile strength of S5's small-diameter FeCrAl thin-walled pipe fittings at room temperature shall not be less than 630MPa, the yield strength shall not be less than 550MPa, the yield strength ratio shall not be less than 0.8, the elongation shall not be less than 25%, and the strength-ductility product shall not be less than 15GPa·%; the tensile strength at 600°C shall not be less than 280MPa, the yield strength shall not be less than 190MPa, the yield strength ratio shall not be less than 0.6, the elongation shall not be less than 17%, and the strength-ductility product shall not be less than 4.5GPa·%; and the hydrogen permeability resistance factor PRF value at 500°C shall not be less than 10,000.

[0070] In particular, the grain size of S5's small-diameter FeCrAl thin-walled pipes is not less than grade 5.

[0071] In particular, S5's small-diameter FeCrAl thin-walled pipes must not exhibit cracks or splits after being expanded 30%; and must not exhibit cracks or splits after the pipes are pressed closed.

[0072] Example 1

[0073] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0074] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.2%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0075] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0076] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a microstructure of a single ferrite phase, a grain size of 180 μm, a room temperature tensile strength of 564 MPa, a yield strength of 480 MPa, and an elongation of 17%.

[0077] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is expanded. The maximum amplitude is 300%. After that, secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the mandrel and extrusion barrel of the hot extruder. The extrusion ratio of the hot extrusion through the tube is 20:1, and a rough tube with a size of Φ78mm×7mm is obtained. The microstructure of the rough tube is a single ferrite phase with a grain size of 90μm, a room temperature tensile strength of 616MPa, a yield strength of 537MPa, and an elongation of 20%.

[0078] S5, cold rolling and annealing between passes: The S4 rough pipe is subjected to 10 cold rolling passes and annealing between passes, with a total reduction of 84%; before 4 cold rolling passes, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 23%, and the annealing temperature between passes is 750°C; after 4 cold rolling passes, as the rolling passes and deformation resistance increase, the reduction per pass is 10%, and the annealing temperature between passes is 800°C, finally obtaining an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0079] like Figure 1As shown, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 637 MPa, a yield strength of 565 MPa, a yield strength ratio of 0.89, an elongation of 30.5%, and a strength-ductility product of 19.4 GPa·% at room temperature; a tensile strength of 292 MPa, a yield strength of 202 MPa, a yield strength ratio of 0.69, an elongation of 23.5%, and a strength-ductility product of 6.9 GPa·% at 600°C; and a hydrogen permeability resistance factor (PRF) value of 10325 at 500°C.

[0080] The grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is level 5.

[0081] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0082] Example 2 (Increasing the Si content in the FeCrAl component from 0.2% to 0.6%, the hydrogen barrier factor can be increased by about 30%, and the other process parameters are the same as in Example 1)

[0083] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0084] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.6%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0085] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0086] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a single ferrite phase microstructure, a grain size of 192 μm, a room temperature tensile strength of 583 MPa, a yield strength of 498 MPa, and an elongation of 16%.

[0087] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is enlarged and the center through hole is The expansion is 300%; then secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the mandrel and extrusion barrel of the hot extruder, with an extrusion ratio of 20:1, resulting in a rough tube with a size of Φ78×7mm. The rough tube has a single ferrite phase, a grain size of 87μm, a room temperature tensile strength of 619MPa, a yield strength of 541MPa, and an elongation of 19%.

[0088] S5, cold rolling and annealing between passes: The S4 rough pipe is subjected to 10 cold rolling passes and annealing between passes, with a total reduction of 84%; before 4 cold rolling passes, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 23%, and the annealing temperature between passes is 750°C; after 4 cold rolling passes, as the rolling passes and deformation resistance increase, the reduction per pass is 10%, and the annealing temperature between passes is 800°C, finally obtaining an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0089] like Figure 2 As shown, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 638 MPa, a yield strength of 567 MPa, a yield strength ratio of 0.89, an elongation of 33.0%, and a strength-ductility product of 21.1 GPa·% at room temperature; the tensile strength at 600°C is 286 MPa, the yield strength is 213 MPa, the yield strength ratio is 0.74, the elongation is 21.5%, and the strength-ductility product is 6.1 GPa·%; and the hydrogen permeability factor PRF value at 500°C is 13964.

[0090] The grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is level 5.

[0091] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0092] Example 3 (Increasing the extrusion ratio from 20:1 to 30:1 can improve the mechanical properties of the extruded rough tube and the final thin-walled tube. The rough tube size is reduced, and the corresponding cold working deformation is also adjusted. Other aspects are the same as in Example 2)

[0093] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0094] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.6%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0095] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0096] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a single ferrite phase microstructure, a grain size of 192 μm, a room temperature tensile strength of 583 MPa, a yield strength of 498 MPa, and an elongation of 16%.

[0097] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is expanded. The maximum amplitude is 300%. After that, secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the core rod and extrusion barrel of the hot extruder. The extrusion ratio of the hot extrusion through the tube is 30:1, and a rough tube with a size of Φ62mm×6mm is obtained. The microstructure of the rough tube is a single ferrite phase with a grain size of 79μm, a room temperature tensile strength of 655MPa, a yield strength of 583MPa, and an elongation of 20%.

[0098] S5, cold rolling and annealing between passes: The S4 rough pipe is subjected to 10 cold rolling passes and annealing between passes, with a total reduction of 78%; before 3 cold rolling passes, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 25%, and the annealing temperature between passes is 750°C; after 3 cold rolling passes, as the rolling passes and deformation resistance increase, the reduction per pass is 11%, and the annealing temperature between passes is 800°C, finally obtaining an outer diameter of 10.1 mm, a wall thickness of 1.3 mm, and a length of 2200 mm.

[0099] like Figure 3 As shown, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 680 MPa, a yield strength of 636 MPa, a yield strength ratio of 0.94, an elongation of 27.0%, and a strength-ductility product of 18.4 GPa·% at room temperature; a tensile strength of 286 MPa, a yield strength of 198 MPa, a yield strength ratio of 0.69, an elongation of 17.0%, and a strength-ductility product of 4.9 GPa·% at 600°C; and a hydrogen permeability resistance factor (PRF) value of 14028 at 500°C.

[0100] The grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is level 5.

[0101] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0102] Example 4 (Adjusting the number of cold working passes and deformation amount to prepare a pipe with an outer diameter of 6 mm, a wall thickness of 0.8 mm, and a length of 3000 mm. Other conditions are the same as those in Example 3)

[0103] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0104] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.6%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 6 mm, a wall thickness of 0.8 mm, and a length of 3000 mm.

[0105] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0106] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a single ferrite phase microstructure, a grain size of 192 μm, a room temperature tensile strength of 583 MPa, a yield strength of 498 MPa, and an elongation of 16%.

[0107] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is expanded. The maximum amplitude is 300%. After that, secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the core rod and extrusion barrel of the hot extruder. The extrusion ratio of the hot extrusion through the tube is 30:1, and a rough tube with a size of Φ62mm×6mm is obtained. The microstructure of the rough tube is a single ferrite phase with a grain size of 79μm, a room temperature tensile strength of 655MPa, a yield strength of 583MPa, and an elongation of 20%.

[0108] S5, cold rolling and annealing between passes: The S4 rough pipe is subjected to 14 cold rolling passes and annealing between passes, with a total reduction of 87%; before 3 cold rolling passes, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 25%, and the annealing temperature between passes is 750°C; after 3 cold rolling passes, as the rolling passes and deformation resistance increase, the reduction per pass is 11%, and the annealing temperature between passes is 800°C, finally obtaining an outer diameter of 6 mm, a wall thickness of 0.8 mm, and a length of 3000 mm.

[0109] like Figure 4 As shown, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 692 MPa, a yield strength of 646 MPa, a yield strength ratio of 0.93, an elongation of 27.0%, and a strength-ductility product of 18.7 GPa·% at room temperature; the tensile strength at 600°C is 290 MPa, the yield strength is 208 MPa, the yield strength ratio is 0.72, the elongation is 23.5%, and the strength-ductility product is 6.8 GPa·%; and the hydrogen permeability resistance factor PRF value at 500°C is 13673.

[0110] The grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is level 5.

[0111] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0112] Example 5 (Adjusting the number of cold working passes and deformation amount to prepare a pipe with an outer diameter of 5 mm, a wall thickness of 0.5 mm, and a length of 3500 mm. Other conditions are the same as those in Example 4)

[0113] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0114] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.6%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 5 mm, a wall thickness of 0.5 mm, and a length of 3500 mm.

[0115] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0116] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a single ferrite phase microstructure, a grain size of 192 μm, a room temperature tensile strength of 583 MPa, a yield strength of 498 MPa, and an elongation of 16%.

[0117] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is expanded. The maximum amplitude is 300%. After that, secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the core rod and extrusion barrel of the hot extruder. The extrusion ratio of the hot extrusion through the tube is 30:1, and a rough tube with a size of Φ62mm×6mm is obtained. The microstructure of the rough tube is a single ferrite phase with a grain size of 79μm, a room temperature tensile strength of 655MPa, a yield strength of 583MPa, and an elongation of 20%.

[0118] S5, cold rolling and inter-pass annealing: The S4 rough pipe is subjected to 16 cold rolling passes and inter-pass annealing, with a total reduction of 92%; before the third cold rolling pass, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 25%, and the inter-pass annealing temperature is 750°C; during the 4-13 cold rolling passes, the reduction per pass is 14%, and the inter-pass annealing temperature is 800°C; during the last three cold rolling passes, the reduction per pass is 10%, and the inter-pass annealing temperature is 800°C, and the final outer diameter is 5 mm, the wall thickness is 0.5 mm, and the length is 3500 mm.

[0119] like Figure 5 As shown in the figure, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 723 MPa, a yield strength of 687 MPa, a yield strength ratio of 0.95, an elongation of 26.5%, and a strength-ductility product of 19.2 GPa·% at room temperature; a tensile strength of 293 MPa, a yield strength of 215 MPa, a yield strength ratio of 0.73, an elongation of 18.0%, and a strength-ductility product of 5.3 GPa·% at 600°C; and a hydrogen permeability resistance factor (PRF) value of 14419 at 500°C.

[0120] The grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is 5.5.

[0121] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0122] Example 6 (annealing temperature after cold working is increased by 50°C, grain size and mechanical properties of thin-walled tube slightly decrease, other conditions are the same as Example 5)

[0123] A cold working and annealing method for a small-diameter FeCrAl thin-walled pipe fitting comprises the following steps:

[0124] S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass: Cr 13%, Al 5%, Si 0.6%, Mn 0.4%, W 1.6%, Y 0.02%, with the balance being Fe and unavoidable impurities. The raw materials are weighed according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting described above. The dimensions of the small-diameter FeCrAl thin-walled pipe fitting are an outer diameter of 5 mm, a wall thickness of 0.5 mm, and a length of 3500 mm.

[0125] S2. Melting and Casting: The weighed raw materials of S1 are melted multiple times using a vacuum melting process. Before melting, 180 kg of industrial pure Fe and other raw materials calculated according to the composition of the FeCrAl alloy are added to the crucible of a vacuum induction furnace. When the vacuum degree in the induction furnace reaches 100 Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible. The raw materials are completely melted within 60 minutes. The melted molten steel is kept at 1560° C. for 20 minutes for refining. After refining, the molten steel is cast into a flat steel ingot mold of 40 cm long × 10 cm wide × 60 cm high within 1 minute, and the molten steel is rapidly cooled to obtain an alloy ingot.

[0126] S3. Forging and machining: The alloy ingot of S2 was held at 1200°C for 3 hours and then hot forged to obtain a φ220×900+M mm bar, where M is greater than 0 and the final forging temperature is not less than 950°C. The forged bar was air-cooled to room temperature and processed into a Φ204 mm×900 mm polished bar. The polished bar had a single ferrite phase microstructure, a grain size of 192 μm, a room temperature tensile strength of 583 MPa, a yield strength of 498 MPa, and an elongation of 16%.

[0127] S4, through hole and hot extrusion: Use a through hole machine to drill a through hole with a diameter of Φ30mm in the center of the S3 light rod along the axial direction, and chamfer the corners at both ends. The hollow billet after chamfering is heated by induction heating in a ring heating furnace. The heating rate of the induction heating step is 3℃ / min, the holding temperature is 800℃, and the holding time is 4h. The heating rate of the continuous heating before hole expansion is 100℃ / min, the holding temperature is 1100℃, and the holding time is 3min. The center through hole is expanded. The maximum amplitude is 300%. After that, secondary induction heating is performed at a heating rate of 100°C / min, a holding temperature of 1150°C, and a holding time of 3 minutes. Hot extrusion through the tube is completed under the combined action of the core rod and extrusion barrel of the hot extruder. The extrusion ratio of the hot extrusion through the tube is 30:1, and a rough tube with a size of Φ62mm×6mm is obtained. The microstructure of the rough tube is a single ferrite phase with a grain size of 79μm, a room temperature tensile strength of 655MPa, a yield strength of 583MPa, and an elongation of 20%.

[0128] S5, cold rolling and inter-pass annealing: The S4 rough pipe is subjected to 16 cold rolling passes and inter-pass annealing, with a total reduction of 92%; before the third cold rolling pass, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 25%, and the inter-pass annealing temperature is 800°C; during the 4-13 cold rolling passes, the reduction per pass is 14%, and the inter-pass annealing temperature is 850°C; during the last three cold rolling passes, the reduction per pass is 10%, and the inter-pass annealing temperature is 850°C, finally obtaining an outer diameter of 5 mm, a wall thickness of 0.5 mm, and a length of 3500 mm.

[0129] like Figure 6 As shown, the small-diameter FeCrAl thin-walled pipe prepared in this embodiment has a tensile strength of 696 MPa, a yield strength of 681 MPa, a yield strength ratio of 0.98, an elongation of 25.5%, and a strength-ductility product of 17.7 GPa·% at room temperature; the tensile strength at 600°C is 286 MPa, the yield strength is 206 MPa, the yield strength ratio is 0.72, the elongation is 18.0%, and the strength-ductility product is 5.1 GPa·%; and the hydrogen permeability factor PRF value at 500°C is 14675.

[0130] like Figure 7 As shown, the grain size of the small-diameter FeCrAl thin-walled pipe prepared in this embodiment is level 5.

[0131] The small-diameter FeCrAl thin-walled pipe prepared in this embodiment did not show any cracks or fissures after the pipe was expanded by 30%; and did not show any cracks or fissures after the pipe was pressed closed.

[0132] Physical comparison of FeCrAl alloy thin-walled tubes of different sizes Figure 8 shown.

[0133] The above scheme, the present invention proposes a cold working and annealing treatment method for small diameter FeCrAl thin-walled pipe fittings, which can solve the technical problems of the prior art such as the single hydrogen-blocking element in the FeCrAl composition, easy cracking during cold working, high preparation cost and low production efficiency.

[0134] The invention can obtain FeCrAl alloy ingots with uniform composition by weighing, smelting and refining raw materials.

[0135] The invention can refine the coarse grains in the ingot after vacuum induction melting, eliminate casting defects, improve the mechanical properties of the material, prevent cracking in the subsequent hot extrusion process, and obtain the light rod size required for hot extrusion through hot forging and machining.

[0136] The present invention uses through-holes and hot extrusion to suppress cracking during continuous forging using triaxial compressive stress, so that the FeCrAl alloy with large deformation resistance undergoes plastic deformation at high temperature to obtain finer grains, thereby avoiding cracking during subsequent cold rolling.

[0137] The present invention can cause the FeCrAl alloy to recrystallize during the diameter reduction and wall reduction process through appropriate cold rolling deformation and inter-pass annealing temperature, eliminate hardening in time to avoid cracking, and avoid rapid grain growth caused by excessively high annealing temperature.

[0138] In summary, compared with other traditional methods, the method of the present invention can prepare small-diameter FeCrAl thin-walled pipe fittings with synergistically improved mechanical properties and hydrogen permeation resistance through weighing, smelting and refining, hot forging and machining, through-hole and hot extrusion, and cold rolling and inter-pass annealing of raw materials. The preparation method is simple and easy to operate, green and environmentally friendly, low in cost, short in process, and high in efficiency, which is conducive to large-scale industrial production and promotion.

[0139] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0140] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0141] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0142] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A cold working and annealing method for small diameter FeCrAl thin-walled pipe fittings, characterized in that: The cold working and annealing method of the small diameter FeCrAl thin-walled pipe fitting is as follows: S1. Raw material weighing: The chemical composition of the small-diameter FeCrAl thin-walled pipe fitting is as follows by mass percentage: Cr 11-16%, Al 4-6%, Si 0.2-0.8%, Mn 0.2-0.6%, W 1.0-2.2%, Y 0.01-0.1%, and the balance is Fe and unavoidable impurities; weigh the raw materials according to the chemical composition of the small-diameter FeCrAl thin-walled pipe fitting; S2, melting and casting: The weighed raw materials of S1 are melted multiple times by vacuum melting process, and then cooled to room temperature with the furnace after casting to obtain alloy ingots; S3, forging and machining: The alloy ingot of S2 is subjected to high temperature hot forging to obtain M is greater than 0, air-cooled to room temperature, and the forged rod is processed into a Φ204mm×900mm smooth rod; S4, through-hole and hot extrusion: The light rod of S3 is drilled axially in the center of the rod using a through-hole machine, and the corners are rounded at both ends. The hollow billet after chamfering is heated by induction in a ring heating furnace for a step-by-step increase. The temperature is then continuously increased and the central through-hole is enlarged. After a second induction heating, the hot extrusion tube is completed under the joint action of the core rod and the extrusion barrel of the hot extruder to obtain a rough tube; S5, cold rolling and inter-pass annealing: The S4 rough pipe is subjected to multiple passes of cold rolling and inter-pass annealing. As the rolling passes and deformation resistance increase, the pass deformation is reduced by 10% compared with before, and the inter-pass annealing temperature is increased by 50°C compared with before, finally obtaining a small-diameter FeCrAl thin-walled pipe fitting.

2. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: The dimensions of S1's small diameter FeCrAl thin-walled pipe fittings are 5-11mm outer diameter, 0.3-1.3mm wall thickness, and 2200-3500mm length.

3. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: In the vacuum melting process of S2, 130-180 kg of industrial pure Fe and other raw materials calculated according to the composition of FeCrAl alloy are added to the crucible of the vacuum induction furnace before melting.

4. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: In the vacuum melting process of S2, when the vacuum degree in the induction furnace reaches 50-1000Pa, the power is adjusted to start induction heating of the alloy raw materials in the crucible.

5. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: In the vacuum melting process of S2, the raw materials are completely melted within 30-120 minutes, and the molten steel is kept at 1550-1600℃ for 10-60 minutes for refining; after refining, the molten steel is cast into a flat steel ingot mold with a length of 40cm, a width of 10cm and a height of 60cm within 0.5-2 minutes to allow the molten steel to cool rapidly.

6. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: During the high-temperature hot forging of S3, the alloy ingot of S2 needs to be kept at 1100-1200°C for 1-3 hours before hot forging, and the final forging temperature is not less than 950°C; the microstructure of the light rod is a single ferrite phase, the grain size is ≤200μm, the room temperature tensile strength is ≥550MPa, the yield strength is ≥450MPa, and the elongation is ≥15%.

7. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: The through-hole diameter of S4 is Φ20-40mm, the heating rate of the first induction heating step heating is 1-5℃ / min, the holding temperature is 700-900℃, and the holding time is 1-5h; the heating rate of the continued heating before hole expansion is 50-150℃ / min, the holding temperature is 900-1100℃, and the holding time is 2-10min.

8. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: The expansion amplitude of the central through hole of S4 is 200-400%, the heating rate of the secondary induction heating is 50-150℃ / min, the holding temperature is 1100-1150℃, and the holding time is 2-10min; the extrusion ratio of the hot extrusion tube is 20-40:1; the size of the rough tube is Φ50×5-80mm×8mm, the microstructure of the rough tube is a single ferrite phase, the grain size is ≤100μm, the room temperature tensile strength is ≥600MPa, the yield strength is ≥500MPa, and the elongation is ≥18%.

9. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: S5 multi-pass cold rolling is 10-16 passes with a total reduction of 60-95%; before 3-5 passes of cold rolling, the increase in rolling passes and deformation resistance is not large, the reduction per pass is 20-40%, and the annealing temperature between passes is 750-850°C; after 5-7 passes of cold rolling, as the rolling passes and deformation resistance increase, the reduction per pass is 10-30%, and the annealing temperature between passes is 800-850°C.

10. The cold working and annealing method for a small diameter FeCrAl thin-walled pipe according to claim 1, characterized in that: The tensile strength of S5 small-diameter FeCrAl thin-walled pipe fittings at room temperature shall not be less than 630MPa, the yield strength shall not be less than 550MPa, the yield strength ratio shall not be less than 0.8, the elongation shall not be less than 25%, and the strength-ductility product shall not be less than 15GPa·%; the tensile strength at 600℃ shall not be less than 280MPa, the yield strength shall not be less than 190MPa, the yield strength ratio shall not be less than 0.6, the elongation shall not be less than 17%, and the strength-ductility product shall not be less than 4.5GPa·%; the hydrogen permeability resistance factor PRF value at 500℃ shall not be less than 10000.

Images