Preparation method of GH4169RE rare earth heat-resistant alloy strip for corrugated pipe

Abstract

The invention relates to the technical field of strip preparation, and discloses a preparation method of a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe, which comprises the following steps: step A, designing chemical components; step B, smelting; c, forging and cogging; d, hot rolling and cold rolling; e, heat treatment; and F, inspecting a finished product. The alloy strip which can still keep high tensile strength and yield strength at the high temperature is prepared through precisely designed chemical components, particularly adding a proper amount of rare earth element Y (yttrium) and combining optimized smelting, forging, hot rolling, cold rolling and heat treatment processes, compared with a traditional GH4169 alloy, the tensile strength of the alloy strip is improved to 1180MPa at the temperature of 650 DEG C, and the yield strength of the alloy strip is improved to 1180MPa at the temperature of 650 DEG C. The yield strength is improved to 1020 MPa, and the use requirements of aerospace, chemical engineering, petrifaction and other high-temperature and high-pressure environments are remarkably met.

Description

Technical Field

[0001] The invention relates to the technical field of strip preparation, in particular to a method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe. Background Art

[0002] In modern industry and aerospace, high-temperature alloys are widely used due to their excellent high-temperature performance, high strength and good corrosion resistance. GH4169, also known as Inconel 718, is a precipitation-hardened deformable high-temperature alloy based on nickel-chromium-iron. It is copied from the American Inconel 718 alloy and has been widely used in aerospace, energy, chemical industry and other fields in the following decades due to its excellent high-temperature strength and good comprehensive performance, especially in the temperature range of -253 to 700°C. GH4169 alloy has high strength and good fatigue resistance, radiation resistance, oxidation resistance, corrosion resistance and other characteristics below 650°C. The yield strength below 650°C ranks first among deformable high-temperature alloys. It can be manufactured into various complex-shaped parts and has been widely used.

[0003] The patent with publication number CN109097631A discloses a method for preparing GH4169 alloy, which belongs to the technical field of alloy material preparation, and includes the following steps: Step 1: Prepare GH4169 alloy by selective laser melting 3D printing technology; Step 2: Solution treat GH4169 alloy at 950℃-1200℃ for 0.5h. The present invention adopts selective laser melting 3D printing technology, and then undergoes solution treatment. On the basis of greatly shortening the solution treatment time, the hardness of the obtained GH4169 alloy can be increased by more than 14% compared with the hardness of the GH4169 alloy obtained in the prior art.

[0004] The patent with publication number CN102825189A discloses a method for manufacturing a GH4169 alloy tube. The fatigue resistance of all GH4169 alloys that have undergone longitudinal magnetic field heat treatment has been improved to varying degrees, up to 16%, and air cooling after heating at T1 temperature is better than water quenching. This shows that the magnetic field heat treatment of the GH4169 alloy has produced a preferential arrangement of martensitic twin variants in the alloy. The invention refines the grains and increases the grain size by making the original cast or forged billet into a forging billet through an upsetting and rolling process and then forming it through near-isothermal forging. It does not rely on the use of consolidated powder billets to refine the grains and increase the strength of the forgings, thereby greatly reducing the forging cost.

[0005] The tensile property of GH4169 alloy is one of its most important mechanical properties. At room temperature, the tensile strength of GH4169 alloy is usually between 1200-1400MPa, and the yield strength is about 900-1100MPa. As the temperature rises, although the tensile strength and yield strength will decrease, GH4169 alloy can still maintain a high strength level at high temperature due to its fine microstructure and precipitation phase strengthening. However, in some special environmental use fields, such as the aerospace field and the chemical and petrochemical industries, extremely high temperatures and pressures will be experienced during use. At 650°C, the tensile strength of GH4169 alloy is about 800MPa and the yield strength is about 600MPa, which can no longer meet the use requirements. Based on this, the present invention proposes a preparation method of GH4169RE rare earth heat-resistant alloy strip for corrugated pipes to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe, which solves the problem in the background technology that the strength cannot meet the requirements due to environmental changes.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe comprises the following steps:

[0009] Step A, chemical composition design, the chemical composition of the alloy strip includes, by weight percentage, C: 0.015-0.060%, Si: ≤0.35%, Mn: ≤0.35%, P: ≤0.015%, S: ≤0.010%, Cr: 17.00-21.00%, Ni: 50.00-55.00%, Mo: 2.85-3.50%, Nb: 5.00-5.60%, a composition containing rare earth element Y (yttrium): 0.03-0.06% (in terms of Y), Al: 0.30-0.80%, Ti: 0.85-1.15%, Cu≤0.30%, Ca: ≤0.05%, Mg: ≤0.005%, B: 0.006%, [H]≤1.5PPM, [O]≤25PPM, [N]≤50PPM, and the balance is Fe and other residual elements;

[0010] Step B, smelting, using vacuum + electroslag smelting technology to prepare alloy ingots to ensure low segregation, high purity, uniform and dense structure of the alloy ingots;

[0011] Step C, forging and blanking, using a forging method to blank the alloy ingot, and using a repeated upsetting process during the forging process;

[0012] Step D, hot rolling and cold rolling, hot rolling and cold rolling the forged alloy billet in sequence to ensure the surface quality and internal structural uniformity of the steel;

[0013] Step E, heat treatment, heat treatment of the cold-rolled steel strip for a certain period of time to promote the solid solution of alloy elements; then air cooling or faster cooling is used to form an austenite structure to ensure fine and uniform grains;

[0014] Step F, finished product inspection, conduct finished product inspection on the heat-treated steel strip to ensure that the yield strength of the steel strip is ≥1100MPa, the tensile strength is ≥1300MPa, and the elongation is ≥15% to meet the requirements of the corrugated pipe material for high temperature strength, corrosion resistance and formability.

[0015] Preferably, in step A, a composition containing the rare earth element Y (yttrium) is added to the chemical composition to significantly improve the grain refinement and structural uniformity of the steel, enhance the deoxidation effect of the steel and reduce the inclusion content in the steel.

[0016] Preferably, in the step B, during the smelting process, after the molten steel is melted, the temperature is controlled between 1450 and 1460°C, and a composition containing the rare earth element Y (yttrium) is added to ensure sufficient dissolution, dispersion and uniform distribution of the rare earth element; through this smelting process, the S content in the alloy is reduced, the number of large-sized inclusions is reduced, the average size of the inclusions is reduced, and the purity and comprehensive performance of the alloy are improved.

[0017] The specific smelting method is vacuum + electroslag smelting, wherein the vacuum furnace smelting steps are as follows: 1. Charging: The materials are loaded into different parts of the crucible according to the melting point, specific gravity, activity and volatility of the raw materials. The charging process requires tightness at the bottom and looseness at the top to prevent the "bridging" phenomenon of the charge. The crucible filled with the charge is placed in a vacuum chamber, and power is supplied to evacuate the vacuum. The vacuum degree during the melting period is ≤4Pa. 2. Melting: The induction coil on the crucible wall generates an alternating magnetic field under the action of alternating current. The induced current excited by the alternating magnetic field flows in the material to generate heat, and the heat melts the material. When the material is completely cleared, the temperature is measured and controlled between 1580-1600℃, and samples are taken for analysis. 3. Refining: The vacuum degree during the refining period is ≤4Pa. After refining for 30 minutes (low vacuum must not be switched during this period), samples are taken in the furnace for component analysis, and the chemical composition is adjusted according to the analysis results in the furnace. Rare earth elements are gradually added to the molten steel in small doses. During this process, electromagnetic stirring technology is used, and the stirring time should be controlled within 5-10 minutes to ensure that the rare earth alloy is evenly dispersed and fully dissolved in the molten steel. 4. Pouring: Pour the alloy liquid into the launder, and then pass through the launder into the ingot mold for solidification.

[0018] The steps of electroslag remelting are as follows: 1. Electrode preparation: Grind and shot blast the surface of the vacuum smelted electrode blank, weld the dummy electrode head, and install it on the arm of the electroslag furnace. 2. Slag: All slag (except titanium dioxide powder) must be heated before use, the heating temperature is greater than 800℃, the time is not less than 5h, and it must be hung in front of the furnace within 5 minutes before starting arcing. Slag system ratio: CaF2: CaO: Al2O3 = 70: 15: 15. 3. Remelting period: After slag making is completed, adjust the current and voltage, keep the current constant, reduce fluctuations (the fluctuation value is less than 300A), and maintain constant melting speed remelting. 4. Cooling of electroslag ingot: The mold cooling time should ensure that the slag and molten steel are fully solidified. During the whole process of mold cooling, it is strictly forbidden to take liquid slag out of the slag pool or use electrodes and other objects to dip slag outwards. It is forbidden to use air ducts to blow directly into the slag pool for rapid cooling. 5. Homogenization treatment of electroslag ingot: Place the electroslag ingot in a heat treatment furnace and perform homogenization treatment of the electroslag ingot according to the heat treatment system of "1130℃×24h+1160℃×24h+1190℃×48h".

[0019] Preferably, in step C, the total deformation ratio is greater than 10 to ensure uniform distribution and microstructure refinement of the rare earth element Y (yttrium) in the steel and to improve the mechanical properties and corrosion resistance of the steel.

[0020] The specific hot forging method is: placing the steel ingot obtained by smelting in a heating furnace for heating, in a single-phase temperature zone of 1020-1120°C, adopting a step-by-step cooling method, and repeatedly upsetting and drawing to break up grains and carbides; in the final firing stage, performing low-temperature large deformation at 980-1020°C, and making full use of the pinning effect after the precipitation of the δ phase to achieve grain refinement of the forging blank.

[0021] Preferably, the step D comprises the following steps:

[0022] Step d1, hot rolling the forged alloy billet to obtain a hot-rolled strip;

[0023] Step d2, performing a solution pickling treatment on the hot-rolled strip to remove surface oxides and contaminants;

[0024] Step d3, cold rolling treatment is performed to ensure the surface quality and internal structural uniformity of the steel material to meet the strict requirements of the corrugated pipe on the material surface quality and mechanical properties.

[0025] The specific method of hot rolling is as follows: the steel billet obtained by forging is placed in a step-beam heating furnace for heating, and kept at 1220-1260°C for 10-15h to make the alloy elements basically dissolved; after the steel billet is removed from the furnace, it is subjected to high-pressure water descaling treatment, and then enters the rough rolling mill for billet rolling, and the rolling temperature is 1100-1180°C; after rough rolling, the temperature of the intermediate billet is ≥900°C, and the billet is air-cooled and ground offline. Then it is reheated to 1180-1200 and enters the finishing mill for 10 passes of rolling, and the final rolling temperature is 840-900°C; after rolling, it is air-cooled online to ensure the recovery and recrystallization of the steel structure. The collection temperature is 200-300°C, and finally a 4-5mm steel strip billet is obtained.

[0026] The specific method of cold-rolling the steel strip is as follows: the hot-rolled strip is subjected to solutionizing and pickling to remove surface defects and then cold-rolled, with a single-pass reduction rate of ≥20% and repeated rolling, with a total deformation ratio greater than 6, to ensure uniform distribution of rare earth in the steel and refined structure.

[0027] Preferably, the step E comprises the following steps:

[0028] Step e1, heat treating the cold-rolled steel strip, including heating to 940° C. to 995° C. and maintaining for a certain period of time to promote the solid solution of alloy elements;

[0029] Step e2, using air cooling or faster cooling to form an austenite structure to ensure fine and uniform grains;

[0030] Step e3, perform aging treatment, heat to 720°C, keep warm for 8 hours, cool to 620°C at a rate of (50±10)°C / h, keep warm for 8 hours, then take out of the furnace and air cool, so that the steel strip is fully precipitated and strengthened to improve the high temperature strength and corrosion resistance of the steel strip.

[0031] The specific method of the heat treatment is as follows: the steel strip is heated to 940℃~995℃, maintained for a certain period of time to promote the solid solution of alloy elements, and the cooling method is air cooling or faster cooling to form an austenite structure to ensure fine and uniform grains. Then, an aging treatment is performed, heating to 720℃, keeping the temperature for 8h, cooling to 620℃ at a rate of (50±10)℃ / h, keeping the temperature for 8h, and then air cooling out of the furnace to fully precipitate and strengthen the steel strip to improve the high temperature performance of the steel strip.

[0032] Preferably, in step A, the design of the chemical composition refers to the typical composition range of the GH4169 alloy, and is optimized in combination with the special requirements of the bellows material, by precisely controlling the content of each element to control the interaction between the elements and their influence on the alloy properties; the software is used to simulate the grain refinement effect under different rare earth element Y (yttrium) contents, and the optimal addition range of 0.045% to 0.055% is determined to achieve the best balance between grain size distribution and mechanical properties.

[0033] Preferably, in step C, a large hydraulic forging machine is used to perform multiple upsetting and drawing, and after each upsetting and drawing, ultrasonic testing (UT) technology is used to check internal defects to ensure that there are no cracks and inclusion defects. At the same time, a metallographic microscope and a scanning electron microscope (SEM) are used to analyze the microstructure after forging to ensure the uniform distribution of the rare earth element Y (yttrium) and the grain refinement effect.

[0034] Preferably, in step D, the hot rolling temperature is set to 1100°C to 1150°C, and the final rolling temperature is not less than 850°C to ensure good thermoplasticity; before cold rolling, a pickling line (HCl+H2SO4 mixed pickling) is used to remove the oxide scale on the surface of the hot-rolled strip, and the surface roughness Ra after pickling is ≤0.8μm; the total cold rolling reduction rate is controlled between 60% and 70%, and a tension control system is used to maintain a stable rolling tension to further optimize the plate shape and straightness of the strip.

[0035] Preferably, in step F, electron backscatter diffraction (EBSD) technology is used to analyze the grain orientation and texture, and transmission electron microscopy (TEM) is used to observe the morphology and distribution of the precipitated phase to ensure that the alloy strip meets the strict requirements of high temperature strength, corrosion resistance, formability and long-term service stability in bellows applications.

[0036] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0037] 1. The present invention, through the precise design of chemical composition, especially the addition of an appropriate amount of rare earth element Y (yttrium), combined with optimized smelting, forging, hot rolling, cold rolling and heat treatment processes, prepares an alloy strip that can still maintain high tensile strength and yield strength at high temperatures. Compared with the traditional GH4169 alloy, the tensile strength of the alloy strip of the present invention at 650°C is increased to 1180MPa, and the yield strength is increased to 1020MPa, which significantly meets the use requirements in high temperature and high pressure environments such as aerospace, chemical industry and petrochemical industry.

[0038] 2. In the present invention, the addition of rare earth element Y (yttrium) not only realizes grain refinement, but also improves the structural uniformity of the alloy, reduces the inclusion content, and improves the purity and comprehensive performance of the alloy. Through advanced microstructure analysis techniques such as electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), the alloy strip of the present invention exhibits excellent grain orientation and texture, as well as reasonable precipitation phase morphology and distribution, thereby ensuring its long-term service stability under high temperature, high pressure and corrosive environment.

[0039] 3. The optimized chemical composition and preparation process of the present invention not only improve the high temperature strength of the alloy, but also enhance its corrosion resistance. The alloy strip of the present invention exhibits good corrosion resistance in a variety of corrosive media; by precisely controlling the temperature, reduction rate and heat treatment process of hot rolling and cold rolling, the present invention has good plasticity and forming properties, which enables the bellows to easily meet the processing requirements of various complex shapes during the manufacturing process, thereby improving production efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of a method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe of the present invention;

[0041] Figure 2 This is a specific step diagram of a method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe of the present invention;

[0042] Figure 3 This is a diagram showing the actual dissection results of the ingot structure of the homogenized GH4169RE alloy of the present invention;

[0043] Figure 4 The typical inclusion morphology and EDS surface scanning element distribution diagram of the GH4169RE alloy of the present invention;

[0044] Figure 5 These are SEM images of the second phase of the GH4169RE alloy of the present invention after being heated at different temperatures for 60 minutes. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] See also Figure 1-Figure 5 In an embodiment of the present invention, a method for preparing a GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe comprises the following steps:

[0047] Step A, chemical composition design, the chemical composition of the alloy strip includes, by weight percentage, C: 0.015-0.060%, Si: ≤0.35%, Mn: ≤0.35%, P: ≤0.015%, S: ≤0.010%, Cr: 17.00-21.00%, Ni: 50.00-55.00%, Mo: 2.85-3.50%, Nb: 5.00-5.60%, a composition containing rare earth element Y (yttrium): 0.03-0.06% (in terms of Y), Al: 0.30-0.80%, Ti: 0.85-1.15%, Cu≤0.30%, Ca: ≤0.05%, Mg: ≤0.005%, B: 0.006%, [H]≤1.5PPM, [O]≤25PPM, [N]≤50PPM, and the balance is Fe and other residual elements;

[0048] Step B, smelting, using vacuum + electroslag smelting technology to prepare alloy ingots to ensure low segregation, high purity, uniform and dense structure of the alloy ingots;

[0049] Step C, forging and blanking, using a forging method to blank the alloy ingot, and using a repeated upsetting process during the forging process;

[0050] Step D, hot rolling and cold rolling, hot rolling and cold rolling the forged alloy billet in sequence to ensure the surface quality and internal structural uniformity of the steel;

[0051] Step E, heat treatment, heat treatment of the cold-rolled steel strip for a certain period of time to promote the solid solution of alloy elements; then air cooling or faster cooling is used to form an austenite structure to ensure fine and uniform grains;

[0052] Step F, finished product inspection, conduct finished product inspection on the heat-treated steel strip to ensure that the yield strength of the steel strip is ≥1100MPa, the tensile strength is ≥1300MPa, and the elongation is ≥15% to meet the requirements of the corrugated pipe material for high temperature strength, corrosion resistance and formability.

[0053] In step A, a composition containing the rare earth element Y (yttrium) is added to the chemical composition to significantly improve the grain refinement and structural uniformity of the steel, enhance the deoxidation effect of the steel and reduce the inclusion content in the steel.

[0054] In step B, during the smelting process, after the molten steel is melted, the temperature is controlled between 1450 and 1460° C., and a composition containing a rare earth element Y (yttrium) is added to ensure that the rare earth element is fully dissolved, dispersed, and evenly distributed; through this smelting process, the S content in the alloy is reduced, the number of large-sized inclusions is reduced, the average size of the inclusions is reduced, and the purity and comprehensive performance of the alloy are improved.

[0055] In step C, the total deformation ratio is greater than 10 to ensure uniform distribution and microstructure refinement of the rare earth element Y (yttrium) in the steel and to improve the mechanical properties and corrosion resistance of the steel.

[0056] Step D includes the following steps:

[0057] Step d1, hot rolling the forged alloy billet to obtain a hot-rolled strip;

[0058] Step d2, performing a solution pickling treatment on the hot-rolled strip to remove surface oxides and contaminants;

[0059] Step d3, cold rolling treatment is performed to ensure the surface quality and internal structural uniformity of the steel material to meet the strict requirements of the corrugated pipe on the material surface quality and mechanical properties.

[0060] Step E includes the following steps:

[0061] Step e1, heat treating the cold-rolled steel strip, including heating to 940° C. to 995° C. and maintaining for a certain period of time to promote the solid solution of alloy elements;

[0062] Step e2, using air cooling or faster cooling to form an austenite structure to ensure fine and uniform grains;

[0063] Step e3, perform aging treatment, heat to 720°C, keep warm for 8 hours, cool to 620°C at a rate of (50±10)°C / h, keep warm for 8 hours, then take out of the furnace and air cool, so that the steel strip is fully precipitated and strengthened to improve the high temperature strength and corrosion resistance of the steel strip.

[0064] The working principle of the embodiment of the present invention is: vacuum smelting + electroslag remelting: place the crucible containing the charge in a vacuum chamber, power on and evacuate, and the vacuum degree during the melting period is ≤4Pa. When the material is completely clear, the temperature is controlled between 1580-1600°C, and sampling is performed for analysis. The vacuum degree during the refining period is ≤4Pa, and after refining for 30 minutes (low vacuum must not be switched during this period), samples are taken from the furnace for component analysis, and the chemical composition is adjusted according to the analysis results in the furnace. Rare earth elements are gradually added to the molten steel in small doses. In this process, electromagnetic stirring technology is used, and the stirring time should be controlled within 5-10 minutes to ensure that the rare earth alloy is evenly dispersed and fully dissolved in the molten steel. After the composition of the molten steel is qualified, the alloy liquid is poured into the launder, and then enters the ingot mold through the launder for solidification. The surface of the vacuum-smelted electrode blank is ground and shot peened, and after welding the dummy electrode head, it is installed on the arm of the electroslag furnace. The slag used in the electroslag furnace (except titanium dioxide powder) must be heated before use, the heating temperature is greater than 800℃, the time is not less than 5h, and it must be hoisted to the front of the furnace within 5 minutes before the arc is started. Slag system ratio: CaF2: CaO: Al2O3 = 70:15:15. After slag making is completed, adjust the current and voltage, keep the current constant, reduce fluctuations (fluctuation value is less than 300A), and maintain constant melting rate remelting. The electroslag ingot mold cooling time should ensure that the slag and molten steel are fully solidified. During the entire mold cooling process, it is strictly forbidden to take liquid slag out of the slag pool or use electrodes and other objects to dip slag outwards. It is forbidden to use a duct to blow directly into the slag pool for rapid cooling. Electroslag ingot homogenization treatment: Place the electroslag ingot in a heat treatment furnace and perform electroslag ingot homogenization treatment according to the heat treatment system of "1130℃×24h+1160℃×24h+1190℃×48h".

[0065] Forging: The steel ingot obtained by smelting is placed in a heating furnace for heating. In the single-phase temperature zone of 1020-1120℃, the temperature is gradually reduced, and the grains and carbides are broken by repeated upsetting and drawing. In the final firing stage, low-temperature large deformation is carried out at 980-1020℃, and the pinning effect after the precipitation of δ phase is fully utilized to achieve grain refinement of the forging blank.

[0066] Hot rolling: The forged steel billet is placed in a step-beam heating furnace for heating, and kept at 1220-1260℃ for 10-15h to make the alloy elements basically dissolved; after the steel billet is removed from the furnace, it is descaled by high-pressure water and then enters the rough rolling mill for billet rolling, with the starting rolling temperature of 1100-1180℃; after rough rolling, the temperature of the intermediate billet is ≥900℃, and the billet is air-cooled and ground offline. Then it is reheated to 1180-1200 and enters the finishing mill for 10 passes of rolling, with the final rolling temperature of 840-900℃; after rolling, it is air-cooled online to ensure the recovery and recrystallization of the steel structure. The collection temperature is 200-300℃, and finally a 4-5mm steel strip billet is obtained.

[0067] Cold rolling: After the hot-rolled strip is subjected to solution treatment and pickling to remove surface defects, it is cold rolled, with a single-pass reduction rate of ≥20%, and repeated rolling is performed, with a total deformation ratio greater than 6 to ensure uniform distribution of rare earth in the steel and refined structure.

[0068] Heat treatment: heat the steel strip to 940℃~995℃, keep it for a certain time to promote the solid solution of alloy elements, and cool it in air or faster to form an austenite structure to ensure fine and uniform grains. Then carry out aging treatment, heat it to 720℃, keep it for 8h, cool it to 620℃ at a rate of (50±10)℃ / h, keep it for 8h, take it out of the furnace and air cool it, so that the steel strip is fully precipitated and strengthened to improve the high temperature performance of the steel strip.

[0069] See also Figure 1-Figure 5 In the embodiment of the present invention, in step A, the design of the chemical composition refers to the typical composition range of the GH4169 alloy, and is optimized in combination with the special requirements of the bellows material. The content of each element is precisely controlled to control the interaction between the elements and their influence on the alloy properties. The software is used to simulate the grain refinement effect under different rare earth element Y (yttrium) contents, and the optimal addition range of 0.045% to 0.055% is determined to achieve the best balance between grain size distribution and mechanical properties.

[0070] In step C, a large hydraulic forging machine is used to perform multiple upsetting and drawing passes, and ultrasonic testing (UT) technology is used to check internal defects after each upsetting and drawing to ensure that there are no cracks and inclusion defects. At the same time, a metallographic microscope and a scanning electron microscope (SEM) are used to analyze the microstructure after forging to ensure the uniform distribution of the rare earth element Y (yttrium) and the grain refinement effect.

[0071] In step D, the hot rolling temperature is set to 1100°C to 1150°C, and the final rolling temperature is not less than 850°C to ensure good thermoplasticity; before cold rolling, a pickling line (HCl+H2SO4 mixed pickling) is used to remove the oxide scale on the surface of the hot-rolled strip, and the surface roughness Ra after pickling is ≤0.8μm; the total cold rolling reduction rate is controlled between 60% and 70%, and a tension control system is used to maintain a stable rolling tension to further optimize the plate shape and straightness of the strip.

[0072] In step F, electron backscatter diffraction (EBSD) technology is also used to analyze the grain orientation and texture, and transmission electron microscopy (TEM) is used to observe the morphology and distribution of the precipitated phase to ensure that the alloy strip meets the strict requirements of high temperature strength, corrosion resistance, formability and long-term service stability in bellows applications.

[0073] The working principle of the embodiment of the present invention is: in the process of preparing GH4169RE rare earth heat-resistant alloy strip for bellows, the design of chemical composition is a crucial step. This step refers to the typical composition range of GH4169 alloy and is optimized in combination with the special requirements of bellows materials. By accurately controlling the content of each element, such as main alloying elements such as C, Si, Mn, P, S, Cr, Ni, Mo, Nb and trace elements such as Al, Ti, Cu, Ca, Mg, etc., it is ensured that the alloy has excellent high temperature strength, corrosion resistance and forming performance. In particular, a composition containing rare earth element Y (yttrium) is added, and its addition amount is determined after software simulation of the grain refinement effect under different contents, and the optimal addition range is 0.045% to 0.055%. This addition amount not only achieves the best grain size distribution, but also balances the mechanical properties of the alloy, such as yield strength, tensile strength and elongation, thereby meeting the high performance requirements of the bellows material.

[0074] The use of a large hydraulic forging machine for multiple upsetting passes can ensure that the alloy ingot is fully deformed during the forging process, thereby achieving uniform distribution and microstructure refinement of the rare earth element Y (yttrium) in the steel. After each upsetting, ultrasonic testing (UT) technology is used to check internal defects to ensure that there are no cracks and inclusion defects, which is an important measure to ensure the quality of the alloy strip; at the same time, the metallographic microscope and scanning electron microscope (SEM) are used to analyze the microstructure after forging, and the uniform distribution of the rare earth element Y (yttrium) and the grain refinement effect can be intuitively observed.

[0075] During the hot rolling process, the hot rolling temperature range is set to 1100℃ to 1150℃, and the final rolling temperature is not less than 850℃ to ensure good thermoplasticity and deformation ability; at the same time, the pickling line (HCl+H2SO4 mixed pickling) is used to remove the oxide scale on the surface of the hot-rolled strip, and the surface roughness after pickling is Ra≤0.8μm, providing a high-quality surface for subsequent cold rolling. During the cold rolling process, the total reduction rate is controlled between 60% and 70%, and a tension control system is used to maintain a stable rolling tension, which helps to further optimize the strip shape and straightness. By accurately controlling the temperature and reduction rate of hot rolling and cold rolling, it can ensure that the alloy strip has excellent mechanical properties and surface quality.

[0076] In addition to conventional mechanical property tests (such as yield strength, tensile strength and elongation), electron backscatter diffraction (EBSD) technology is used to analyze grain orientation and texture, and transmission electron microscopy (TEM) is used to observe the morphology and distribution of precipitated phases. These advanced microstructure analysis technologies can reveal the microstructure characteristics inside the alloy strip, thereby evaluating its high temperature strength, corrosion resistance, forming performance and long-term service stability. Through the comprehensive application of these analysis technologies and performance testing methods, it can be ensured that the alloy strip meets the strict requirements of bellows applications and provides high-quality material guarantees for the manufacture of bellows.

[0077] See also Figure 1-Figure 5 In the embodiment of the present invention, the alloy strip processed as above is tested, and the test results are as follows:

[0078] At room temperature, the tensile strength is 1420MPa; the yield strength is 1280MPa, and the elongation after break is 18%.

[0079] At 650℃, the tensile strength is 1180MPa; the yield strength is 1020MPa; and the elongation after fracture is 12%.

[0080] Figure 3-Figure 5 This is the inspection and testing picture during the manufacturing process of GH4169RE.

[0081] The working principle of the embodiment of the present invention is: the tensile strength indicates the maximum tensile force that a material can withstand in a tensile test, and is one of the important indicators for evaluating the mechanical properties of a material. In this embodiment, the tensile strength at room temperature reaches 1420MPa, which is much higher than the conventional requirement (≥1300MPa), indicating that the alloy strip has extremely high tensile properties and can withstand large external forces without breaking.

[0082] The yield strength indicates the minimum stress value at which the material begins to undergo plastic deformation during the stretching process. The yield strength at room temperature is 1280MPa, which is also much higher than the conventional requirement (≥1100MPa), indicating that the alloy strip can maintain high rigidity and stability when subjected to stress.

[0083] The elongation after fracture indicates the relative increase in the length of the sample after the material is stretched and fractured, and is an important indicator for evaluating the plastic deformation capacity of the material. The elongation after fracture at room temperature is 18%, indicating that the alloy strip has good plastic deformation capacity and can undergo a certain degree of plastic deformation without immediate fracture when subjected to stress.

[0084] As for the high temperature mechanical properties of the alloy strip, at 650°C, the tensile strength and yield strength are maintained at 1180MPa and 1020MPa respectively, and the elongation after fracture is 12%, indicating that the alloy strip can still maintain high mechanical properties in a high temperature environment and meet the use requirements of the bellows under high temperature conditions.

[0085] Working principle: The core of the working principle of the embodiment of the present invention is to prepare high-performance GH4169RE rare earth heat-resistant alloy strip for bellows through precisely designed chemical composition and optimized preparation process. First of all, chemical composition design is the key. Referring to the GH4169 alloy composition and combining with the special needs of the bellows, the content of each element is accurately controlled, especially adding an appropriate amount of rare earth element Y (yttrium) to optimize the grain refinement effect and improve the high temperature strength, corrosion resistance and forming performance of the alloy.

[0086] During the preparation process, vacuum + electroslag smelting technology is used to ensure the low segregation, high purity and uniformity of the alloy ingot; then it is subjected to multiple upsetting and drawing processes using a large hydraulic forging machine, combined with ultrasonic detection technology to ensure that there are no internal defects, and a microscope is used to analyze the microstructure to ensure the uniform distribution of the rare earth element Y (yttrium) and grain refinement; the temperature and reduction rate are precisely controlled during the hot rolling and cold rolling processes to provide a high-quality surface and excellent mechanical properties; finally, heat treatment is used to promote the solid solution of alloy elements to form a fine and uniform austenite structure, and aging treatment is used to further precipitate and strengthen the structure to improve the high-temperature performance of the alloy strip.

[0087] In addition, the present invention also uses advanced microstructure analysis techniques, such as electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), to reveal the microstructure characteristics inside the alloy strip and evaluate its high temperature strength, corrosion resistance, forming performance and long-term service stability. These comprehensive measures ensure that the alloy strip meets the strict requirements in the application of bellows and provide material guarantee for the manufacture of bellows.

[0088] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations may be made to the embodiments without departing from the principles and spirit thereof, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing GH4169RE rare earth heat-resistant alloy strip for corrugated pipe, characterized in that: The following steps are involved: Step A, chemical composition design, the chemical composition of the alloy strip includes, by weight percentage, C: 0.015-0.060%, Si: ≤0.35%, Mn: ≤0.35%, P: ≤0.015%, S: ≤0.010%, Cr: 17.00-21.00%, Ni: 50.00-55.00%, Mo: 2.85-3.50%, Nb: 5.00-5.60%, a composition containing rare earth element Y (yttrium): 0.03-0.06% (in terms of Y), Al: 0.30-0.80%, Ti: 0.85-1.15%, Cu≤0.30%, Ca: ≤0.05%, Mg: ≤0.005%, B: 0.006%, [H]≤1.5PPM, [O]≤25PPM, [N]≤50PPM, and the balance is Fe and other residual elements; Step B, smelting, using vacuum + electroslag smelting technology to prepare alloy ingots to ensure low segregation, high purity, uniform and dense structure of the alloy ingots; Step C, forging and blanking, using a forging method to blank the alloy ingot, and using a repeated upsetting process during the forging process; Step D, hot rolling and cold rolling, hot rolling and cold rolling the forged alloy billet in sequence to ensure the surface quality and internal structural uniformity of the steel; Step E, heat treatment, heat treatment of the cold-rolled steel strip for a certain period of time to promote the solid solution of alloy elements; then air cooling or faster cooling is used to form an austenite structure to ensure fine and uniform grains; Step F, finished product inspection, conduct finished product inspection on the heat-treated steel strip to ensure that the yield strength of the steel strip is ≥1100MPa, the tensile strength is ≥1300MPa, and the elongation is ≥15% to meet the requirements of the corrugated pipe material for high temperature strength, corrosion resistance and formability.

2. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In the step A, a composition containing the rare earth element Y (yttrium) is added to the chemical composition to significantly improve the grain refinement and structural uniformity of the steel, enhance the deoxidation effect of the steel and reduce the inclusion content in the steel.

3. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In the step B, during the smelting process, after the molten steel is melted, the temperature is controlled between 1450 and 1460° C., and a composition containing the rare earth element Y (yttrium) is added to ensure sufficient dissolution, dispersion and uniform distribution of the rare earth element; through this smelting process, the S content in the alloy is reduced, the number of large-sized inclusions is reduced, the average size of the inclusions is reduced, and the purity and comprehensive performance of the alloy are improved.

4. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In the step C, the total deformation ratio is greater than 10 to ensure the uniform distribution and microstructure refinement of the rare earth element Y (yttrium) in the steel and to improve the mechanical properties and corrosion resistance of the steel.

5. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: The step D comprises the following steps: Step d1, hot rolling the forged alloy billet to obtain a hot-rolled strip; Step d2, performing a solution pickling treatment on the hot-rolled strip to remove surface oxides and contaminants; Step d3, cold rolling treatment is performed to ensure the surface quality and internal structural uniformity of the steel material to meet the strict requirements of the corrugated pipe on the material surface quality and mechanical properties.

6. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: The step E comprises the following steps: Step e1, heat treating the cold-rolled steel strip, including heating to 940° C. to 995° C. and maintaining for a certain period of time to promote the solid solution of alloy elements; Step e2, using air cooling or faster cooling to form an austenite structure to ensure fine and uniform grains; Step e3, perform aging treatment, heat to 720°C, keep warm for 8 hours, cool to 620°C at a rate of (50±10)°C / h, keep warm for 8 hours, then take out of the furnace and air cool, so that the steel strip is fully precipitated and strengthened to improve the high temperature strength and corrosion resistance of the steel strip.

7. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In step A, the design of the chemical composition refers to the typical composition range of the GH4169 alloy and is optimized in combination with the special requirements of the bellows material. The content of each element is precisely controlled to control the interaction between the elements and their influence on the alloy properties. The software is used to simulate the grain refinement effect under different rare earth element Y (yttrium) contents, and the optimal addition range of 0.045% to 0.055% is determined to achieve the best balance between grain size distribution and mechanical properties.

8. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In the step C, a large hydraulic forging machine is used to perform multiple upsetting and drawing, and after each upsetting and drawing, ultrasonic testing (UT) technology is used to check internal defects to ensure that there are no cracks and inclusion defects. At the same time, a metallographic microscope and a scanning electron microscope (SEM) are used to analyze the microstructure after forging to ensure the uniform distribution of the rare earth element Y (yttrium) and the grain refinement effect.

9. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In the step D, the hot rolling temperature is set to 1100°C to 1150°C, and the final rolling temperature is not less than 850°C to ensure good thermoplasticity; before cold rolling, a pickling line (HCl+H2SO4 mixed pickling) is used to remove the oxide scale on the surface of the hot-rolled strip, and the surface roughness Ra after pickling is ≤0.8μm; the total cold rolling reduction rate is controlled between 60% and 70%, and a tension control system is used to maintain a stable rolling tension to further optimize the plate shape and straightness of the strip.

10. The method for preparing the GH4169RE rare earth heat-resistant alloy strip for a corrugated pipe according to claim 1, characterized in that: In step F, electron backscatter diffraction (EBSD) technology is used to analyze the grain orientation and texture, and transmission electron microscopy (TEM) is used to observe the morphology and distribution of the precipitated phase to ensure that the alloy strip meets the strict requirements for high temperature strength, corrosion resistance, formability and long-term service stability in the application of corrugated pipes.

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