High-temperature low-expansion alloy forge piece and manufacturing method thereof

Abstract

The invention provides a high-temperature low-expansion alloy forge piece and a manufacturing method thereof. The high-temperature low-expansion alloy forge piece comprises, by mass, 31.0%-33.5% of Ni, 7.0%-9.0% of Co, smaller than or equal to 0.20% of Nb, smaller than or equal to 0.04% of C, smaller than or equal to 0.20% of Si, smaller than or equal to 0.25% of Mn, smaller than or equal to 0.02% of P, smaller than or equal to 0.02% of S, smaller than or equal to 0.20% of Cr, smaller than or equal to 0.20% of Mo, smaller than or equal to 0.1% of Al, smaller than or equal to 0.1% of Ti, smaller than or equal to 0.1% of Zr, smaller than or equal to 100 ppm of N, smaller than or equal to 50 ppm of O and the balance Fe and inevitable impurities. The alloy forge piece prepared through the method is large in section, the average linear expansion coefficient in the wide temperature range of 20-500 DEG C is low, the martensite phase transformation temperature is smaller than or equal to-60 DEG C, and the excellent high-temperature low-expansion performance is achieved.

Description

Technical Field

[0001] This invention relates to the field of high-temperature low-expansion alloy technology, and more specifically, to a high-temperature low-expansion alloy forging and its manufacturing method. Background Technology

[0002] High-temperature low-expansion alloys refer to a class of functional structural alloys that maintain an extremely low average coefficient of linear expansion and possess excellent dimensional stability within a relatively high temperature range (typically 20℃ to 500℃). Within the service temperature range, the coefficient of linear expansion of this alloy does not increase significantly with increasing temperature, effectively preventing deformation, warping, or structural failure caused by temperature fluctuations, thus ensuring the precise operation of equipment. The low-expansion performance of this type of alloy places extremely high demands on the accuracy of component proportioning, metallurgical purity, and the matching of hot working process parameters; even slight deviations can lead to significant performance deviations from design standards. With the rapid development of industrial society, equipment in aerospace, marine engineering, and other fields is upgrading towards high-end and precision, placing higher performance and structural stability requirements on high-temperature low-expansion alloy forgings under various operating conditions.

[0003] Currently, commonly used low-expansion alloys in the industrial field are mainly Invar series alloys such as 4J36, 4J32, 4J32A, and 4J40. However, ordinary Invar series low-expansion alloys such as 4J36, 4J32, 4J32A, and 4J40 are mainly small-area / small-section alloys. Large-section workpieces, under high-temperature conditions or heat treatment, have uneven internal temperature distribution, which can easily lead to dimensional accuracy failure due to fluctuations in the expansion coefficient, failing to meet the requirements of precision scenarios. Patent application number 202311738671.3 discloses a low-expansion high-temperature alloy and its manufacturing method, meeting the requirements of high-temperature service environments, but does not mention large-section workpieces. Patent application number 202410576761.5 discloses a smelting and forging process of 4J36 low-expansion alloy, which uses scrap steel to reduce costs, eliminates the need for vacuum induction / remelting treatment, and produces a low-expansion alloy at low cost.

[0004] Therefore, there is an urgent need for a high-temperature, low-expansion alloy forging with better thermal stability that can stably produce products with large cross-sections. Summary of the Invention

[0005] The problem solved by this invention is that existing high-temperature, low-expansion alloy forgings have small cross-sections and low dimensional stability, which cannot meet the needs of existing technologies for large-size, precision structural parts.

[0006] To address the aforementioned problems, this invention provides a high-temperature, low-expansion alloy forging, comprising, by mass percentage: Ni: 31.0~33.5%, Co: 7.0~9.0%, Nb≤0.20%, C≤0.04%, Si≤0.20%, Mn≤0.25%, P≤0.02%, S≤0.02%, Cr≤0.20%, Mo≤0.20%, Al≤0.1%, Ti≤0.1%, Zr≤0.1%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities.

[0007] This invention partially replaces Ni in existing alloys such as 4J36 / 4J32 / 4J40 with Co, utilizing the stronger Invar anomalous effect of Co to shift the temperature corresponding to the minimum expansion coefficient to a higher temperature, raising the Curie temperature to 400℃, thereby obtaining high-temperature and low-expansion characteristics. At the same time, trace amounts of Nb are added for microalloying, using Nb to fix C and N in the alloy and form dispersed Nb-rich microparticle precipitates with Ni, Co, etc., further reducing the expansion coefficient and lowering the martensitic transformation temperature. In addition, residual elements such as C, Si, Mn, Cr, and Mo are strictly controlled to ensure the stability of alloy performance.

[0008] Furthermore, the high-temperature low-expansion alloy forging comprises, by mass percentage: Ni: 31.0~33.5%, Co: 7.0~9.0%, Nb≤0.20%, C≤0.04%, Si≤0.20%, Mn≤0.25%, P≤0.02%, S≤0.02%, Cr≤0.20%, Mo≤0.20%, Al≤0.1%, Ti≤0.1%, Zr≤0.1%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities, and the mass content of Nb is not 0.

[0009] Furthermore, the high-temperature, low-expansion alloy forging is composed of the following components by mass percentage: Ni: 31.5~33.0%, Co: 7.0~8.5%, Nb≤0.20%, C≤0.03%, Si≤0.15%, Mn≤0.20%, P≤0.02%, S≤0.02%, Cr≤0.10%, Mo≤0.10%, Al≤0.06%, Ti≤0.06%, Zr≤0.05%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities.

[0010] Furthermore, taking the sum of the mass percentages of Ni and Co as 100%, Co / (Ni+Co) is 17.5%~22.5%, of which the [Ni] equivalent is 31~34 ([Ni]=Ni%+2.5(Mn%)+18(C%)).

[0011] Chemical composition control is crucial to alloy performance. Deviations in composition during production can lead to frequent fluctuations in the alloy's coefficient of thermal expansion and may even trigger a transformation from austenite (γ) to martensite (α), increasing the alloy's coefficient of thermal expansion. This invention precisely controls the Co / (Ni+Co) ratio, allowing some Ni to be replaced by Co, thereby obtaining an alloy with high-temperature, low-expansion characteristics.

[0012] In this invention, the sum of the mass percentages of Ni and Co is taken as 100%, and Co / (Ni+Co) is preferably 18%~20%, wherein the [Ni] equivalent is 31~34 ([Ni]=Ni%+2.5(Mn%)+18(C%)).

[0013] Furthermore, the high-temperature low-expansion alloy forging is a bar or a ring forging; the bar has a cross-sectional diameter ≥180mm, and the ring forging has an outer diameter ≥400mm, a height ≥130mm, and a heat-treated cross-section exceeding 50mm.

[0014] Existing Invar series alloys have low Curie temperatures, a rapidly increasing coefficient of thermal expansion at high temperatures, and can only produce small-section products, failing to meet the growing industrial demands. This invention, through rational chemical composition design, overcomes the limitations of low-expansion alloy wires, strips, tubes, and small-diameter bars in terms of small cross-sections, obtaining ring forgings with an outer diameter ≥400mm, a height ≥130mm, and a heat-treated cross-section exceeding 50mm, and bars with a diameter ≥180mm. Simultaneously, the forgings exhibit a low average coefficient of linear expansion (average coefficient of linear expansion α (20℃~300℃) ≤2.0×10⁻⁶). -6 / ℃, α (20℃~400℃) ≤ 4.5×10 -6 / ℃, α (20℃~500℃) ≤ 6.5×10 -6 / ℃), with a martensitic phase transformation temperature of ≤-60℃, meeting the needs of aerospace and marine engineering fields such as satellite communication, electronic countermeasures, infrared guidance, and airborne fire control.

[0015] In one specific embodiment of the present invention, the cross-sectional diameter of the bar is 200 mm, and the outer diameter of the ring forging is 400 mm, the inner diameter is 250 mm, and the height is 130 mm.

[0016] The present invention also provides a method for manufacturing the high-temperature, low-expansion alloy forgings described in the above technical solution, comprising the following steps:

[0017] S1, Vacuum Induction Melting

[0018] Raw materials are added and melted in a vacuum environment using a vacuum induction furnace. After the raw materials are completely melted, they are refined and the steel is tapped to obtain consumable electrodes.

[0019] S2, Electroslag Remelting / Vacuum Arsenic Remelting

[0020] The consumable electrode is subjected to electroslag remelting / vacuum consumable remelting to obtain steel ingot;

[0021] S3, Forging

[0022] After heating the steel ingot, it undergoes forging and secondary forging processes, and is immediately air-cooled after forging to obtain the forged billet.

[0023] S4, heat treatment and aging treatment

[0024] The forging billet is subjected to solution treatment at a temperature of 700~900℃ for a holding time of ≥2h, and then cooled immediately after the holding time is completed. After cooling, it is subjected to aging treatment at a temperature of 300~350℃ for a holding time of ≥120min to obtain the high-temperature low-expansion alloy forging.

[0025] This invention successfully produces alloy forgings with excellent high-temperature and low-expansion properties by optimizing the design of a reasonable smelting process route and metallurgical methods, precisely controlling the narrow target component ratio, and optimizing the hot working process windows such as forging and stabilization heat treatment. At the same time, the products have large diameters, which are suitable for modern development needs.

[0026] Furthermore, in step S1, the melting temperature is 1500~1550℃; the refining temperature is 1580~1610℃; the holding time is 50~70min; and the vacuum degree is maintained at ≤5Pa during the vacuum induction melting process.

[0027] In this invention, before tapping the steel after refining, it is preferable to add deoxidizers Ni-Mg alloy, rare earth Ce, and sponge Zr to deoxidize and purify the molten steel.

[0028] Furthermore, in step S2, when electroslag remelting is used for processing, the consumable electrode is immersed in the molten slag, and the remelting rate is controlled at 300~400 kg / h to obtain a steel ingot; the slag is a mixture of raw materials with a mass percentage of CaF2:CaO:Al2O3:MgO = 55~65%:15~20%:15~20%:2~5%.

[0029] When vacuum arc remelting is used, the remelting speed is controlled at 300~450 kg / h and the arc length is 8~10 mm.

[0030] This invention employs a dual-melting and refining process combining vacuum induction melting (VIM) and electroslag remelting (ESR) / vacuum arc remelting (VAR) to obtain steel ingots with uniform elemental composition, low segregation, low sulfur content and inclusion levels, dense and uniform microstructure, smooth surface, and high purity. ESR is a secondary refining process that allows for precise control of the alloy composition through refining operations and optimization of the alloy's microstructure during solidification. Vacuum arc remelting, in a high-vacuum, slag-free environment, utilizes a low-voltage DC arc to generate high-temperature melting of the alloy electrodes. The molten metal forms droplets at the electrode tips, which then drip into a water-cooled copper crystallizer after passing through the arc region, where they solidify sequentially to form the final ingot.

[0031] This invention achieves the goals of removing gas, reducing oxygen content, eliminating harmful impurities, and optimizing the morphology and distribution of inclusions through a dual melting process of vacuum induction and electroslag remelting / vacuum consumable remelting, thereby significantly improving the purity and performance stability of the alloy. At the same time, it can also improve the microstructure of the alloy, enhance its hot working performance, and make the alloy more suitable for engineering applications in high-temperature environments.

[0032] In this invention, the remelting rate of the electroslag remelting is preferably 300~360 kg / h; the slag material is preferably a mixture of raw materials with a mass percentage of CaF2:CaO:Al2O3:MgO=60%:17%:20%:3%; and the remelting rate of the vacuum consumable remelting is preferably 350~400 kg / h.

[0033] Furthermore, in step S3, the heating temperature of the forging billet is 1050~1200℃, the final forging temperature is ≥850℃, the steel ingot upsetting ratio is ≥2.0, the total forging ratio is ≥5.0, and the deformation amount of the last forging is ≥20%.

[0034] This invention prevents the alloy from being scrapped due to cracking during the forging process by setting the forging process parameters to ensure that the heating temperature is not too high or too low.

[0035] Furthermore, the heating temperature for the secondary forging is 1100℃±20℃, the final forging temperature is 850~950℃, and the deformation amount in the last forging is 25~35%.

[0036] Furthermore, the solution treatment temperature is 850~900℃, and the holding time is ≥2h; the aging treatment temperature is 300~320℃, and the holding time is ≥180min.

[0037] A stable heat treatment process is crucial for ensuring the average coefficient of linear expansion and long-term stability of alloys. The average coefficient of linear expansion and its stability over time are highly sensitive to heat treatment conditions. Simple annealing leads to an increase in the coefficient of linear expansion, while extending the stabilization treatment time or increasing the stabilization treatment temperature also increases the average coefficient of linear expansion. To obtain the lowest possible average coefficient of linear expansion, this invention employs a synergistic heat treatment scheme of solution treatment and aging, which reduces the average coefficient of linear expansion of the alloy and ensures its long-term stability, thus meeting the service requirements of high-temperature, low-expansion alloys.

[0038] In this invention, the solution treatment temperature is preferably 860°C, and the holding time is 3 hours to ensure that the workpiece is thoroughly heated and then rapidly cooled; the aging treatment temperature is 315°C, and the holding time is 180 minutes; water cooling is used to ensure the uniformity of composition and the stability of the structure.

[0039] This invention avoids an increase in the coefficient of thermal expansion due to parameter deviations by precisely controlling heat treatment parameters.

[0040] The present invention provides a high-temperature, low-expansion alloy forging and its manufacturing method, which has the following beneficial effects:

[0041] (1) The present invention uses Co to replace part of Ni and adds a small amount of Nb to raise the Curie temperature of the alloy to 400℃, which is far higher than the Curie temperature of the existing Invar series alloys (200℃), achieving low expansion performance in a wide temperature range of 20℃~500℃; at the same time, the martensitic phase transformation temperature is ≤-60℃, ensuring that the twinned austenitic structure is always maintained in the service temperature range of the alloy, and no martensite is detected, avoiding the drastic change in expansion coefficient and volume change caused by the austenite to martensite phase transformation, and ensuring dimensional stability and performance consistency during long-term service.

[0042] (2) By optimizing the smelting process route and metallurgical means, accurately designing and controlling the target composition with a narrow window, and accurately optimizing the hot working process window such as forging and stabilization heat treatment, the present invention has prepared bars with a cross-sectional diameter ≥180mm and ring forgings with an outer diameter ≥400mm, a height ≥130mm, and a heat treatment cross-section exceeding 50mm. Attached Figure Description

[0043] Figure 1 The image shows the metallographic structure of the high-temperature, low-expansion alloy forging described in Embodiment 1 of this invention.

[0044] Figure 2 This is a curve showing the average linear expansion coefficient of the high-temperature, low-expansion alloy forging described in Embodiment 1 of the present invention.

[0045] Figure 3 The image shows the metallographic structure of the high-temperature, low-expansion alloy forging described in Example 2 of this invention.

[0046] Figure 4 This is a curve showing the average linear expansion coefficient of the high-temperature, low-expansion alloy forging described in Embodiment 2 of the present invention.

[0047] Figure 5 The image shows the metallographic structure of the alloy forging described in Comparative Example 2 of this invention.

[0048] Figure 6 This is a curve showing the average linear expansion coefficient of the alloy forging described in Comparative Example 2 of the present invention.

[0049] Figure 7 This is a curve showing the average linear expansion coefficient of the alloy forging described in Comparative Example 3 of the present invention. Detailed Implementation

[0050] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] Example 1

[0052] The manufacturing method of the high-temperature, low-expansion alloy forging described in Embodiment 1 of the present invention includes the following steps:

[0053] (1) Vacuum induction smelting

[0054] The raw materials were prepared according to the following chemical composition by mass percentage:

[0055] Chemical composition by mass percentage: C: 0.015%, Si: 0.12%, Mn: 0.15%, P: 0.009%, S: 0.008%, Ni: 33.4%, Co: 8.2%, Nb: 0.08%, Cr: 0.10%, Mo: 0.10%, Al < 0.05%, Ti < 0.05%, Zr < 0.05%, N: 100ppm, O: 50ppm, with the remainder being Fe and unavoidable impurities; among which, (Ni+Co)%: 41.6%; Co / (Ni+Co)%: 19.7%; [Ni] equivalent: 34.045 ([Ni] = Ni% + 2.5 (Mn%) + 18 (C%)).

[0056] The raw materials are loaded into a 1.5T vacuum induction furnace with an ultimate vacuum of <0.5Pa; melting is carried out at 1500~1550℃ until the raw materials are completely melted; then refining is carried out at 1580~1610℃ and a vacuum of ≤5Pa for 60 minutes; after refining, the resulting alloy molten metal is cast into consumable electrode rods at 1560~1610℃, with argon gas filling the casting process for protection at a pressure of 4000~6000Pa; before casting, 0.05% Ni-Mg alloy, 0.05% rare earth Ce, and 0.05% sponge Zr are added in a mass ratio of 0.05% to the raw materials for deoxidation; after casting, the oxide scale on the electrode surface is cleaned until the surface is completely white.

[0057] (2) Electroslag remelting refining

[0058] Slag was prepared with a mass ratio of CaF2:CaO:Al2O3:MgO = 60%:17%:20%:3%, with a total slag weight of 70 kg. The electrode obtained by vacuum induction smelting was placed into the electroslag remelting furnace, and the slag was added to the crystallizer. The power was turned on to carry out electroslag remelting, and the remelting rate was controlled at 300~360 kg / h. At the same time, argon gas was introduced as a protective atmosphere to prevent oxidation of the molten pool and the surface of the ingot. After remelting, argon gas was continued to be introduced to protect the ingot from cooling. The ingot was then demolded to obtain an ingot with a diameter of 460 mm.

[0059] (3) Forging

[0060] The ingot is subjected to a forging process. Before forging, the ingot is heated to 1100℃±20℃. During forging, it is upsetting with an upsetting ratio of 2.0 and a drawing ratio of 4.0. The deformation amount in the last forging is 30%, and the final forging temperature is ≥900℃. After forging, the forging billet is air-cooled to room temperature.

[0061] After forging, the billet is subjected to a secondary forging process. Before forging, the ingot is heated to 1100℃±20℃, the final forging temperature is 900℃, the deformation amount of the last forging is 30%, the wall thickness is ≥60mm, and after forging, the billet is air-cooled to room temperature to obtain a billet with a specification of φ200mm.

[0062] (4) Heat treatment

[0063] The forged billet after secondary forging is heated to 860℃ and held for 3 hours for solution treatment. After the holding period, it is immediately removed and rapidly water-cooled to obtain the forging. After cooling, the forging is heated to 315℃ and held for 4 hours for aging treatment to obtain the high-temperature low-expansion alloy forging.

[0064] Example 2

[0065] The manufacturing method of the high-temperature, low-expansion alloy forging described in Embodiment 2 of the present invention includes the following steps:

[0066] (1) Vacuum induction smelting:

[0067] The raw materials were prepared according to the following chemical composition by mass percentage:

[0068] Chemical composition by mass percentage: C≤0.03%, Si≤0.15%, Mn≤0.25%, P≤0.02%, S≤0.02%, Ni: 31.5~33.5%, Co: 7.0~8.5%, Nb≤0.25%, Cr≤0.2%, Mo≤0.2%, Al≤0.1%, Ti≤0.1%, Zr≤0.1%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities; among which, (Ni+Co)%: 38.5%~42%; Co / (Ni+Co)%: 17.3%~21.3%; [Ni] equivalent ≥32 ([Ni]=Ni%+2.5(Mn%)+18(C%)).

[0069] The raw materials are loaded into a 1.5T vacuum induction furnace with an ultimate vacuum of <0.5Pa; melting is carried out at 1500~1550℃ until the raw materials are completely melted; then refining is carried out at 1580~1610℃ with a vacuum of ≤5Pa for 60 minutes; after refining, the resulting alloy molten metal is cast into consumable electrode rods at 1560~1610℃, with argon gas filling the casting process for protection at a pressure of 4000~6000Pa; before casting, 0.05% Ni-Mg alloy, 0.05% rare earth Ce, and 0.05% sponge Zr are added for deoxidation; after casting, the oxide scale on the electrode surface is cleaned until the surface is completely white.

[0070] (2) Vacuum consumable remelting refining

[0071] The electrode obtained by vacuum induction smelting is placed in a vacuum consumable remelting furnace. The vacuum system is activated to evacuate the furnace to a vacuum level of 0.3 Pa. Simultaneously, the cooling water circulation system is activated, and the cooling water temperature is adjusted to 30°C. The helium supply system is turned on, and a small amount of helium is pre-charged into the furnace to replace the residual air. The power supply is then turned on for vacuum consumable remelting refining, controlling the remelting rate at 350~400 kg / h and maintaining a stable short arc length of 8~10 mm. At the same time, the helium charging pressure is maintained at 300 Pa to prevent oxidation of the molten pool and ingot surface. The vacuum level in the furnace is monitored in real time and kept stable at 0.3 Pa to avoid arc instability caused by vacuum fluctuations. After remelting, helium is continued to be introduced to protect the ingot from cooling. The ingot is then demolded to obtain an ingot with a diameter of 480 mm.

[0072] (3) Forging

[0073] The ingot is subjected to a forging process, including heating the ingot to 1100℃±20℃ before forging, upsetting and drawing during forging, wherein the upsetting ratio of the steel ingot is ≥2, the drawing ratio is ≥4, and the final forging temperature is 900℃, resulting in a φ200*L round bar. After forging, the forging billet is air-cooled to room temperature.

[0074] The forged billet after forging is subjected to a secondary forging process. It is heated to 1100℃±20℃ before forging, punched and expanded during forging, and the deformation amount of the last forging is 30%. The final forging temperature is ≥900℃. After forging, the forged billet is air-cooled to room temperature to obtain a forged billet with an outer diameter of φ400mm, an inner diameter of φ250mm, and a height of 130mm.

[0075] (4) Heat treatment

[0076] The forged billet after secondary forging is heated to 860℃ and held for 3 hours for solution treatment. After the holding period, it is immediately removed and rapidly water-cooled to obtain the forging. After cooling, the forging is heated to 315℃ and held for 4 hours for aging treatment to obtain the high-temperature low-expansion alloy forging.

[0077] Test case

[0078] Metallographic examination was performed on samples taken from the high-temperature, low-expansion alloy forgings obtained in Examples 1 and 2. The results are as follows: Figure 1 and Figure 3 As shown.

[0079] from Figure 1 and Figure 3 As can be seen from the above, the high-temperature low-expansion alloy of the present invention has a metallographic structure of twinned austenite with no detected martensite; the twinned austenite has a uniform and dense face-centered cubic structure with fine grains and few grain boundary defects, which can effectively suppress lattice distortion when the temperature changes.

[0080] Samples were taken from the high-temperature, low-expansion alloy forgings obtained in Examples 1 and 2, and the average linear expansion coefficient was tested according to GB / T4339 standard. The test results are as follows: Figure 2 , Figure 3 As shown in Table 1 below; the martensitic phase transformation temperature was tested according to GB / T14985 standard, and the martensitic phase transformation temperature is ≤-60℃.

[0081] Table 1. Average linear expansion coefficients of the alloys obtained in Examples 1-2

[0082] sample α（20℃~300℃） α（20℃~400℃） α（20℃~500℃） Example 1 <![CDATA[1.99×10 -6 / ℃]]> <![CDATA[4.20×10 -6 / ℃]]> <![CDATA[6.40×10 -6 / ℃]]> Example 2 <![CDATA[1.90×10 -6 / ℃]]> <![CDATA[4.17×10 -6 / ℃]]> <![CDATA[6.49×10 -6 / ℃]]>

[0083] As can be seen from Table 1, the average linear expansion coefficient α (20℃~300℃) of the high-temperature low-expansion alloy obtained by this invention is ≤2.0×10⁻⁶. -6 / ℃, α (20℃~400℃) ≤ 4.5×10-6 / ℃, α (20℃~500℃) ≤ 6.5×10 -6 It exhibits excellent stability at / ℃.

[0084] Comparative Example 1

[0085] Table 2 below shows the average linear expansion coefficient of existing Invar series alloys.

[0086] Table 2 Average linear expansion coefficient of existing Invar series alloys

[0087] sample α（20℃~300℃） α（20℃~400℃） α（20℃~500℃） 4J32 <![CDATA[4.3×10 -6 / ℃]]> <![CDATA[7.2×10 -6 / ℃]]> <![CDATA[9.3×10 -6 / ℃]]> 4J36 <![CDATA[5.1×10 -6 / ℃]]> <![CDATA[8.0×10 -6 / ℃]]> <![CDATA[10.0×10 -6 / ℃]]> 4J32A <![CDATA[3.6×10 -6 / ℃]]> / / 4J40 <![CDATA[2.5×10 -6 / ℃]]> <![CDATA[5.5×10 -6 / ℃]]> <![CDATA[7.9×10 -6 / ℃]]>

[0088] As can be seen from Table 2, compared with the low average linear expansion coefficient of existing Invar series alloys, the high-temperature low-expansion alloy obtained by the present invention has an even lower average linear expansion coefficient and excellent thermal stability.

[0089] Comparative Example 2

[0090] The preparation method is the same as in Example 2, except that the chemical composition (mass percentage) is different.

[0091] (1) Vacuum induction smelting:

[0092] The raw materials were prepared according to the following chemical composition by mass percentage:

[0093] Chemical composition by mass percentage: C: 0.05%, Si: 0.20%, Mn: 0.40%, P≤0.02%, S≤0.02%, Ni: 34%, Co: 8.8%, Al: 0.05%, with the remainder being Fe and unavoidable impurities; among which, (Ni+Co)%: 42.2%; Co / (Ni+Co)%: 20.8%.

[0094] The raw materials are loaded into a 1.5T vacuum induction furnace with an ultimate vacuum of <0.5Pa; they are melted at 1500~1550℃ until they are completely melted; then they are refined at 1580~1610℃ with a vacuum of ≤5Pa for 60 minutes; after refining, the resulting alloy molten metal is cast into consumable electrode rods at 1560~1610℃, with argon gas filling the casting process for protection at a pressure of 4000~6000Pa; after casting, the oxide scale on the electrode surface is cleaned until the surface is completely white.

[0095] (2) Vacuum consumable remelting refining

[0096] The electrode obtained by vacuum induction smelting is placed in a vacuum consumable remelting furnace. The vacuum system is activated to evacuate the furnace to a vacuum level of 0.3 Pa. Simultaneously, the cooling water circulation system is activated, and the cooling water temperature is adjusted to 30°C. The helium supply system is turned on, and a small amount of helium is pre-charged into the furnace to replace the residual air. The power supply is then turned on for vacuum consumable remelting refining, controlling the remelting rate at 350~400 kg / h and maintaining a stable short arc length of 8~10 mm. At the same time, the helium charging pressure is maintained at 300 Pa to prevent oxidation of the molten pool and ingot surface. The vacuum level in the furnace is monitored in real time and kept stable at 0.3 Pa to avoid arc instability caused by vacuum fluctuations. After remelting, helium is continued to be introduced to protect the ingot from cooling. The ingot is then demolded to obtain an ingot with a diameter of 480 mm.

[0097] (3) Forging

[0098] The ingot is subjected to a forging process, including heating the ingot to 1200℃±20℃ before forging, upsetting and drawing during forging, with an upsetting ratio ≥2 and a drawing ratio ≥4. The final forging temperature is 950℃, and the specification is φ200*L round bar. After forging, the forging billet is air-cooled to room temperature.

[0099] The forging billet after forging is subjected to a secondary forging process. It is heated to 1200℃±20℃ before forging, punched and expanded during forging, and the deformation amount of the last forging is 10%. The final forging temperature is ≥950℃. After forging, the forging billet is air-cooled to room temperature to obtain a forging billet with an outer diameter of φ348mm, an inner diameter of φ290mm, and a height of 90mm.

[0100] (4) Heat treatment

[0101] The forged billet after secondary forging is heated to 840℃ and held for 3 hours for solution treatment. After the holding period, it is immediately taken out and rapidly water-cooled to obtain the alloy forging.

[0102] Comparative Example 3

[0103] The preparation method is the same as in Example 1, except that the chemical composition (mass percentage) is different.

[0104] The chemical composition (mass percentage) of the alloy forging in Comparative Example 3 is as follows: C: 0.04%, Si: 0.15%, Mn: 0.35%, P≤0.02%, S≤0.02%, Ni: 35%, Co: 7%, Al: 0.04%, Ti: 0.04%, Zr: 0.04%, with the remainder being Fe and unavoidable impurities; among which, (Ni+Co)%: 32%; Co / (Ni+Co)%: 21.9%.

[0105] Test case

[0106] Metallographic examination was performed on samples taken from the alloy forgings obtained in Comparative Example 2, and the results are as follows: Figure 5 As shown.

[0107] from Figure 5 As can be seen, the alloy obtained in Comparative Example 2 exhibits significant mixed crystal structure. The microstructure consists of a fine-grained matrix of approximately 85% with a grain size of 3.5 and a coarse-grained matrix of approximately 15% with a grain size of 1.5. The coarse-grained particles are randomly distributed on the fine-grained matrix and vary considerably in size. The overall average grain size is rated as 3.0.

[0108] Samples were taken from the alloy forgings obtained in Comparative Examples 2 and 3, and the average linear expansion coefficient was tested according to GB / T4339 standard. The test results are as follows: Figure 5 , Figure 6 As shown in Table 3 below.

[0109] Table 3. Average linear expansion coefficients of alloys obtained from Comparative Examples 2 and 3

[0110] sample α（20℃~300℃） α（20℃~400℃） α（20℃~500℃） Comparative Example 2 <![CDATA[2.21×10 -6 / ℃]]> <![CDATA[4.61×10 -6 / ℃]]> <![CDATA[6.94×10 -6 / ℃]]> Comparative Example 3 <![CDATA[2.26×10 -6 / ℃]]> <![CDATA[4.67×10 -6 / ℃]]> <![CDATA[7.01×10 -6 / ℃]]>

[0111] As can be seen from Table 3, the percentage of Ni+Co mass content in the alloy forgings obtained in Comparative Example 2 and Comparative Example 3 changed, and the average coefficient of linear expansion decreased, which does not meet the requirement of α (20℃~300℃) ≤ 2.0×10 -6 / ℃, α (20℃~400℃) ≤ 4.5×10 -6 / ℃, α (20℃~500℃) ≤ 6.5×10 -6 / ℃ requirement.

[0112] This invention successfully produces high-temperature, low-expansion alloy forgings by optimizing process routes and metallurgical control methods, precisely designing and controlling target compositions within a narrow range, and optimizing hot working process windows such as forging and stabilization heat treatment. This meets the application needs of aerospace and marine engineering fields such as satellite communication, electronic countermeasures, infrared guidance, and airborne fire control, and provides reliable data support for subsequent large-scale stable production.

[0113] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A high-temperature, low-expansion alloy forging, characterized in that, The high-temperature, low-expansion alloy forgings comprise, by mass percentage: Ni: 31.0~33.5%, Co: 7.0~9.0%, Nb≤0.20%, C≤0.04%, Si≤0.20%, Mn≤0.25%, P≤0.02%, S≤0.02%, Cr≤0.20%, Mo≤0.20%, Al≤0.1%, Ti≤0.1%, Zr≤0.1%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities.

2. The high-temperature, low-expansion alloy forging according to claim 1, characterized in that, The high-temperature, low-expansion alloy forging is composed of the following components by mass percentage. Composition: Ni: 31.5~33.0%, Co: 7.0~8.5%, Nb≤0.20%, C≤0.03%, Si≤0.15%, Mn≤0.20%, P≤0.02%, S≤0.02%, Cr≤0.10%, Mo≤0.10%, Al≤0.06%, Ti≤0.06%, Zr≤0.05%, N≤100ppm, O≤50ppm, with the remainder being Fe and unavoidable impurities.

3. The high-temperature, low-expansion alloy forging according to claim 1, characterized in that, Taking the sum of the mass percentages of Ni and Co as 100%, Co / (Ni+Co) is 17.5%~22.5%, of which the [Ni] equivalent is 31~34 ([Ni]=Ni%+2.5(Mn%)+18(C%)).

4. The high-temperature, low-expansion alloy forging according to claim 1, characterized in that, The high-temperature, low-expansion alloy forging is a bar or a ring forging; the bar has a cross-sectional diameter ≥180mm, and the ring forging has an outer diameter ≥400mm, a height ≥130mm, and a heat-treated cross-section exceeding 50mm.

5. The method for manufacturing the high-temperature, low-expansion alloy forging according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1, Vacuum Induction Melting Raw materials are added and melted in a vacuum environment using a vacuum induction furnace. After the raw materials are completely melted, they are refined and the steel is tapped to obtain consumable electrodes. S2, Electroslag Remelting / Vacuum Arsenic Remelting The consumable electrode is subjected to electroslag remelting / vacuum consumable remelting to obtain steel ingot; S3, Forging After heating the steel ingot, it undergoes forging and secondary forging processes, and is immediately air-cooled after forging to obtain the forged billet. S4, heat treatment and aging treatment The forging billet is subjected to solution treatment at a temperature of 700~900℃ for a holding time of ≥2h, and then cooled immediately after the holding time is completed. After cooling, an aging treatment is performed at a temperature of 300~350℃ and a holding time of ≥120min to obtain the high-temperature low-expansion alloy forging.

6. The method for manufacturing high-temperature, low-expansion alloy forgings according to claim 5, characterized in that, In step S1, the melting temperature is 1500~1550℃; the refining temperature is 1580~1610℃; the holding time is 50~70min; and the vacuum degree is maintained at ≤5Pa during the vacuum induction melting process.

7. The method for manufacturing high-temperature, low-expansion alloy forgings according to claim 5, characterized in that, In step S2, when electroslag remelting is used for processing, the consumable electrode is immersed in the molten slag, and the remelting rate is controlled at 300~400 kg / h to obtain steel ingots; the slag is a mixture of raw materials with a mass percentage of CaF2:CaO:Al2O3:MgO = 55~65%:15~20%:15~20%:2~5%; When vacuum arc remelting is used, the remelting speed is controlled at 300~450 kg / h and the arc length is 8~10 mm.

8. The method for manufacturing high-temperature, low-expansion alloy forgings according to claim 5, characterized in that, In step S3, the heating temperature of the forging billet is 1050~1200℃, the final forging temperature is ≥850℃, the steel ingot upsetting ratio is ≥2.0, the total forging ratio is ≥5.0, and the deformation amount of the last forging is ≥20%.

9. The method for manufacturing high-temperature, low-expansion alloy forgings according to claim 8, characterized in that, In step S3, The heating temperature for the secondary forging is 1100℃±20℃, the final forging temperature is 850~950℃, and the deformation amount in the last forging is 25~35%.

10. The method for manufacturing high-temperature, low-expansion alloy forgings according to claim 5, characterized in that, The solution treatment temperature is 850~900℃, and the holding time is ≥2h; the aging treatment temperature is 300~320℃, and the holding time is ≥180min.

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