A method for preparing high-strength, high-plasticity, low-expansion invar alloy rod

Abstract

The application belongs to the technical field of preparation of inconel alloy rod, and particularly relates to a preparation method of high-strength, high-plasticity and low-expansion inconel alloy rod, which comprises the following steps: according to the chemical composition requirements of the target inconel alloy rod, raw materials are weighed and proportioned, a first part of deoxidizing materials is used to heat smelting materials in a vacuum environment to obtain molten steel, a second part of the deoxidizing materials is used to refine the molten steel to obtain purified molten steel, alloying materials are added into the purified molten steel to obtain a steel ingot, and the steel ingot is heated, forged and cooled to obtain the inconel alloy rod. Through three times of molten steel purification, the oxygen content and the inclusion content in the alloy are effectively reduced, the rare earth Ce is used to form stable compounds with oxygen, sulfur and other elements by virtue of the strong affinity, and the stable compounds are removed by floating, and the as-cast grain growth is effectively inhibited, so that the strength and the plasticity are simultaneously improved on the basis of maintaining the low expansion coefficient.

Description

Technical Field

[0001] This invention belongs to the field of Invar alloy rod preparation technology, specifically relating to a method for preparing high-strength, high-plasticity, and low-expansion Invar alloy rods. Background Technology

[0002] Invar alloys are primarily used as low-expansion functional materials in aerospace, electronic instruments, and optical equipment. With a nickel content of approximately 36%, Invar alloys exhibit an extremely low coefficient of thermal expansion at room temperature. As science and technology continue to advance, the global demand for such low-expansion alloys is constantly increasing, making the development of high-performance Invar alloys a focus of worldwide attention. However, the high Ni content in Invar alloys causes them to maintain a single-phase austenitic structure over a wide temperature range, resulting in relatively low room-temperature strength.

[0003] Extensive research has been conducted on the strengthening and toughening mechanisms of Invar alloys. The main strengthening methods include deformation strengthening, second-phase strengthening, and solid solution strengthening. Deformation strengthening primarily involves applying external force to gradually increase the strength of the alloy through work hardening; however, this increase in strength leads to a decrease in plasticity. Second-phase strengthening mainly involves adding elements that can form stable compounds (such as Cr, Mo, and V), which precipitate uniformly distributed strengthening phases in the matrix to improve strength without disrupting the matrix's plasticity or structural continuity. However, the precipitated phases consume matrix elements, altering the Invar alloy matrix composition and causing abnormal expansion coefficients. Solid solution strengthening works by adding alloying elements with atomic radii larger than the matrix atoms, causing lattice distortion in the matrix to increase strength; however, the increase in solid solution atoms also leads to a deterioration in the expansion coefficient. Summary of the Invention

[0004] (a) Purpose of the invention The purpose of this invention is to provide a method for preparing high-strength, high-plasticity, and low-expansion Invar alloy rods, which solves the problems of unstable expansion coefficient and poor plasticity in Invar alloys using deformation strengthening, second-phase strengthening, and solid solution strengthening methods, and achieves simultaneous improvement in strength and plasticity while maintaining a low expansion coefficient.

[0005] (II) Technical Solution To address the above problems, this invention provides a method for preparing high-strength, high-plasticity, low-expansion Invar alloy rods, comprising: According to the chemical composition requirements of the target Invar alloy bar, the raw materials are weighed and proportioned. The raw materials include smelting materials, alloying materials and deoxidizing materials. The deoxidizing materials include a first part and a second part. The first part of the smelting material and the deoxidizing material are heated in a vacuum environment to obtain molten steel; The molten steel is refined using the second part of the deoxidizing material to obtain purified molten steel; The alloying material is added to the purified molten steel to obtain a steel ingot; The steel ingot is heated, forged, and cooled to obtain Invar alloy bars.

[0006] In another aspect of the present invention, preferably, the chemical composition of the Invar alloy rod comprises, by mass percentage: C ≤ 0.03%, Mn: 0.30–1.20%, Si ≤ 0.5%, Ni: 35.0–38.0%, Ti: 0.03–0.15%, Ce: 0.003–0.025%, with the remainder being Fe and unavoidable impurities; The ratio of the first part to the second part is 1:2~3.

[0007] In another aspect of the present invention, preferably, the smelting material includes Fe and Ni, the alloying material includes Mn, Si, Ti and Ce, and the deoxidizing material includes C.

[0008] In another aspect of the present invention, preferably, the step of heating the first portion of the smelting material and the deoxidizing material in a vacuum environment to obtain molten steel includes: The first part of the smelting material and the deoxidizing material are loaded into the vacuum induction furnace; The vacuum induction furnace is evacuated to below a first vacuum level and preheated with a first power until the material inside the furnace turns red. The vacuum induction furnace is continuously evacuated to below the second vacuum level and heated with the second power to obtain molten steel; Adjust the heating power to maintain the temperature of the molten steel at the first temperature.

[0009] In another aspect of the present invention, preferably, the first vacuum degree is 2.5 to 3.5 Pa, the first power is 50 to 120 kW, the second vacuum degree is 1.0 to 1.2 Pa, the second power is 140 to 180 kW, and the first temperature is 1550 to 1600 °C.

[0010] In another aspect of the present invention, preferably, the refining of the molten steel using the second portion of the deoxidizing material to obtain purified molten steel includes: The molten steel is heated to a second temperature for refining, and the refining time is the first time. During the refining process, the second portion of the deoxidizing material is added to the molten steel in multiple batches, with the time interval between two adjacent additions being the second time interval.

[0011] In another aspect of the present invention, preferably, the step of adding the alloying material to the purified molten steel to obtain a steel ingot includes: Argon gas is introduced into the purified molten steel, and Mn, Si and Ti are added for alloying treatment to obtain the first molten steel. The first molten steel is stirred for a third time to obtain the stirred first molten steel. Ce is added to the first molten steel after the stirring is completed to obtain the second molten steel; The second molten steel is poured, and after pouring is completed, the vacuum is broken and the steel is cooled for a time greater than or equal to the fourth time to obtain a steel ingot.

[0012] In another aspect of the present invention, preferably, the second temperature is 1580-1620°C, the first time is 40-50 min, the multiple batches are 2-3 batches, the second time is 12-18 min, the third time is 3-8 min, and the fourth time is 12 h.

[0013] In another aspect of the present invention, preferably, the heating, forging, and cooling of the steel ingot to obtain Invar alloy bars includes: The steel ingot is heated under first and second conditions to obtain a first steel ingot; The first steel ingot is forged under the third condition to obtain the first intermediate billet; The intermediate billet is heated under the fourth and fifth conditions to obtain a second intermediate billet; The second intermediate billet is forged under the sixth condition to obtain the third intermediate billet; The third intermediate billet is cooled to obtain Invar alloy rods.

[0014] In another aspect of the present invention, preferably, the first conditions include: a heating temperature of 750–880°C, a heating rate of 70–120°C / min, and a heat preservation coefficient of 0.6 min / mm; The second condition includes: a heating temperature of 950–1070°C, a heating rate of 60–100°C / min, and a heat preservation coefficient of 0.4 min / mm; The third condition includes: forging ratio ≥4, remelting when the temperature is below 800℃, remelting temperature of 980~1030℃, remelting heating and heat preservation coefficient of 0.3min / mm, and water cooling or air cooling after forging. The fourth condition includes: a heating temperature of 730–830°C, a heating rate of 80–130°C / min, and a heat preservation coefficient of 0.6 min / mm; The fifth condition includes: a heating temperature of 900–1000℃, a heating rate of 80–120℃ / min, and a heat preservation coefficient of 0.4min / mm; The sixth condition includes: forging ratio ≥2, remelting when the temperature is below 800℃, remelting temperature of 930~980℃, and remelting heating and heat preservation coefficient of 0.3min / mm.

[0015] (III) Beneficial Effects The above-described technical solution of the present invention has the following beneficial technical effects: This invention effectively reduces the oxygen content and inclusion content in the alloy by implementing three purification processes in the molten steel stages of smelting, refining, and tapping. During the vacuum furnace charging stage, some graphite carbon is charged into the furnace along with the raw materials, allowing free oxygen overflowing during Fe and Ni melting to react with the graphite carbon in a timely manner to generate carbon monoxide, which is then removed by the vacuum pump, thus inhibiting the accumulation of oxygen content at the source. In the refining stage, continuous deoxidation is achieved by adding graphite carbon in batches, maintaining a low carbon content in the molten steel while meeting deoxidation requirements. During the tapping stage, rare earth element Ce is added, utilizing its strong affinity for elements such as oxygen and sulfur to form stable compounds that float to the surface and are removed, effectively inhibiting grain growth in the as-cast state. Furthermore, this invention employs a two-forging process, avoiding cracking caused by a large forging ratio while significantly improving the uniformity of the microstructure and mechanical properties through two deformation processes. The first forging is followed by water cooling, effectively preventing grain coarsening caused by residual heat in the intermediate billet. Compared with products prepared by traditional processes, the Invar alloy rods prepared using the method of this invention have a tensile strength that is increased by more than 8%, a yield strength that is increased by more than 13.8%, and an elongation that is increased by more than 16%, resulting in a significant improvement in overall performance. Attached Figure Description

[0016] Figure 1 This is an overall flowchart of one embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0018] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0019] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] The invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0022] Example A method for preparing high-strength, high-plasticity, low-expansion Invar alloy rods. Figure 1 An overall flowchart of one embodiment of the present invention is shown, as follows: Figure 1 As shown, it includes: According to the chemical composition requirements of the target Invar alloy bar, the raw materials are weighed and proportioned. The raw materials include smelting materials, alloying materials, and deoxidizing materials. The deoxidizing materials are divided into a first part and a second part. The smelting materials include iron and nickel. The alloying materials are used to control the microstructure and properties of the alloy in subsequent stages. The deoxidizing materials are used to reduce the oxygen content in the molten steel and are divided into a first part and a second part to adapt to the deoxidation requirements of different processes. Further, in this embodiment, the chemical composition of the Invar alloy bar, by mass percentage, includes: C ≤ 0.03%, Mn: 0.30~1.20%, Si ≤ 0.5%, Ni: 35.0~38.0%, Ti: 0.03~0.15%, Ce: 0.003~0.025%, with the remainder being Fe and unavoidable impurities. The smelting materials include Fe and Ni, the alloying materials include Mn, Si, Ti, and Ce, and the deoxidizing materials include C. Ti plays a crucial role in improving the strength of the Invar alloy. Ti combines with C to form TiC particles in situ. These particles, ranging in size from tens to hundreds of nanometers, are spherical or ellipsoidal and bond well with the matrix. TiC particles hinder dislocation movement through the Orowan strengthening mechanism, thereby significantly improving the tensile strength and yield strength of the alloy, while maintaining good plasticity and expansion properties of the matrix. The addition of Ti also enhances the Vickers hardness of the alloy, making a positive contribution to its mechanical properties.

[0023] Rare earth element Ce primarily improves the plasticity of Invar alloys. On the one hand, Ce can inhibit grain growth in the as-cast state, maintaining a more uniform grain morphology in the ingot. On the other hand, during hot working, it can change the morphology of sulfide inclusions from elongated strips to elliptical shapes distributed along the deformation direction, which helps to improve the transverse impact toughness of the alloy and improve anisotropy. Especially during plastic deformation, it can prevent cracking caused by uneven deformation due to sulfide inclusions.

[0024] Furthermore, the ratio of the first part to the second part is not limited here. Optionally, in this embodiment, the ratio of the first part to the second part is 1:2~3. Before loading, the alloying materials are pretreated. The pretreatment includes: for Mn, Si, and Ti, they need to be baked at 200~300℃ for ≥12h before loading into the furnace to remove moisture; rare earth Ce is extracted with TBP (tributyl phosphate) for 40~50min in advance.

[0025] The smelting material and the first part of the deoxidizing material are heated in a vacuum environment to obtain molten steel. The smelting material and the first part of the deoxidizing material are then loaded together into a vacuum melting equipment. During loading, Fe and Ni raw materials are loaded alternately and heated and melted in a vacuum environment. By controlling the vacuum level and heating power, the smelting material is gradually melted to form molten steel. During this process, the first part of the deoxidizing material reacts with the free oxygen released from the smelting material, and the generated gas is promptly extracted, thereby achieving preliminary deoxidation during the material preparation stage and reducing the oxygen content in the molten steel. Further, in this embodiment, heating the smelting material and the first part of the deoxidizing material in a vacuum environment to obtain molten steel includes: The first part of the molten material and the first part of the deoxidizing material are loaded into the vacuum induction furnace. The molten material and the first part of the deoxidizing material are loaded together into the crucible of the vacuum induction furnace so that the deoxidizing material can participate in the reaction in the early stage of material processing.

[0026] The vacuum induction furnace is evacuated to a vacuum level below a first degree and preheated at a first power until the material inside the furnace turns red. The first vacuum level is 2.5–3.5 Pa, and the first power is 50–120 kW. This preheating process treats the raw materials inside the furnace. During this preheating stage, the material inside the furnace gradually heats up and turns red, thereby reducing the thermal shock in the subsequent melting stage and improving the melting stability.

[0027] The vacuum induction furnace is continuously evacuated to below the second vacuum level and heated with the second power to obtain molten steel. The second vacuum level is 1.0 to 1.2 Pa and the second power is 140 to 180 kW. During the melting process, the first part of the deoxidizing material reacts with the free oxygen released from the molten material, and the generated gas is discharged in time under vacuum conditions, effectively reducing the oxygen content in the molten steel.

[0028] The heating power is adjusted to maintain the temperature of the molten steel at a first temperature, which is 1550–1600°C. Once the molten steel has fully formed, the temperature is precisely controlled by adjusting the heating power to keep it stable within the range of 1550–1600°C, thus providing uniform composition and stable temperature conditions for subsequent refining and alloying processes.

[0029] The molten steel is refined using the second part of the deoxidizing material to obtain purified molten steel. By controlling the refining temperature, refining time, and the method of adding the deoxidizing material, residual oxygen and some impurities in the molten steel are further removed, resulting in purified molten steel with uniform composition and high purity. In this embodiment, refining the molten steel using the second part of the deoxidizing material to obtain purified molten steel includes: The molten steel is heated to a second temperature for refining. The refining time is the same as the first time, the second temperature is 1580–1620°C, and the first time is 40–50 minutes. Specifically, the molten steel in the vacuum induction furnace is further heated to raise and stabilize the temperature within the range of 1580–1620°C, and the molten steel is refined within this temperature range for 40–50 minutes. Maintaining a certain refining time at a higher temperature helps to promote the full homogenization of the internal composition of the molten steel, while enhancing the deoxidation reaction and the impurity flotation process.

[0030] During the refining process, the second portion of the deoxidizing material is added to the molten steel in multiple batches. The time interval between two consecutive additions is called the second time interval. There are 2-3 batches, and the second time interval is 12-18 minutes. This batch-addition method allows the deoxidation reaction to continue throughout the refining process, avoiding excessively vigorous local reactions or large fluctuations in the steel composition caused by adding the deoxidizing material all at once. This ensures effective deoxidation while facilitating stable control of the steel's chemical composition. Under the aforementioned refining conditions, the second portion of the deoxidizing material continuously reacts with residual oxygen in the molten steel. The resulting reaction products gradually aggregate and float to the surface at high temperatures, effectively removing them and further reducing the oxygen content and inclusions in the molten steel. Through coordinated control of refining temperature, refining time, and the method of adding the deoxidizing material, a purified molten steel with uniform composition and low impurity content is ultimately obtained.

[0031] The alloying material is added to the purified molten steel to obtain a steel ingot. After refining, the alloying material is added to the purified molten steel for alloying treatment, so that the alloying elements are fully dissolved and uniformly distributed. The alloyed molten steel is then cast to obtain a dense steel ingot structure. In this embodiment, adding the alloying material to the purified molten steel to obtain a steel ingot includes: Argon gas is introduced into the purified molten steel, and Mn, Si and Ti are added for alloying treatment to obtain the first molten steel. By introducing argon gas, the outside air can be effectively isolated, the secondary oxidation of the molten steel during the alloying process can be inhibited, and the alloying elements can be fully dissolved and uniformly dispersed.

[0032] The first molten steel is stirred for a third time, and the stirred first molten steel is obtained. The third time is 3 to 8 minutes. Stirring can promote the rapid diffusion and homogenization of alloying elements such as Mn, Si and Ti in the molten steel, avoid compositional segregation, improve the compositional consistency of the molten steel, and thus obtain the stirred first molten steel with stable structure and properties.

[0033] Ce is added to the first molten steel after stirring to obtain a second molten steel. This allows it to further react with residual oxygen, sulfur, and other impurities in the molten steel to generate stable compounds. These compounds easily aggregate and float in the molten steel, which is beneficial for the removal of inclusions. At the same time, rare earth Ce can also inhibit the growth of as-cast grains and improve the initial microstructure of the steel ingot, thereby obtaining the second molten steel.

[0034] The second molten steel is poured, and after pouring, the vacuum is broken, and the mixture is cooled for a cooling time greater than or equal to a fourth time, which is 12 hours, to obtain a steel ingot. The crucible is tilted to pour the second molten steel into an intermediate ladle, and then poured into an alloy ingot mold. The vacuum is broken, and the mixture is cooled in place for more than 12 hours before being transferred and demolded to obtain the finished steel ingot.

[0035] The steel ingot is heated, forged, and cooled to obtain Invar alloy bars. By rationally controlling the heating regime and forging process parameters, the internal structure of the steel ingot is fully broken down and homogenized, casting defects are eliminated, and the grain structure is improved, ultimately obtaining Invar alloy bars with high strength, high plasticity, and low thermal expansion characteristics. In this embodiment, heating, forging, and cooling the steel ingot to obtain Invar alloy bars includes: The steel ingot is heated under first and second conditions to obtain a first steel ingot. The steel ingot undergoes a two-stage heating treatment. Under the first condition, the steel ingot is heated to 750–880°C at a heating rate controlled at 70–120°C / min, and held at a holding coefficient of 0.6 min / mm to ensure uniform heating of the entire ingot, reduce the internal and external temperature difference, and lower thermal stress. After the first stage of heating, under the second condition, the temperature is further increased to 950–1070°C at a heating rate of 60–100°C / min, with a holding coefficient of 0.4 min / mm, bringing the steel ingot to a temperature range suitable for plastic deformation, thus obtaining the first steel ingot.

[0036] The first steel ingot is forged under third conditions to obtain a first intermediate billet. These third conditions include: a forging ratio ≥ 4; remelting when the temperature is below 800℃; a remelting temperature of 980–1030℃; a remelting holding coefficient of 0.3 min / mm; and water or air cooling after forging. The forging ratio is not less than 4 to fully break up the as-cast grains and improve the density of the internal structure. During forging, when the material temperature is below 800℃, it is immediately remelted, with the remelting temperature controlled at 980–1030℃, and held at a holding coefficient of 0.3 min / mm to restore the material's plasticity and prevent cracking. After the first forging, the forging is water-cooled to quickly fix the grain morphology and microstructure formed after forging, obtaining the first intermediate billet.

[0037] The intermediate billet is heated under fourth and fifth conditions to obtain a second intermediate billet. The fourth condition includes a heating temperature of 730–830°C, a heating rate of 80–130°C / min, and a holding coefficient of 0.6 min / mm. The fifth condition includes a heating temperature of 900–1000°C, a heating rate of 80–120°C / min, and a holding coefficient of 0.4 min / mm. The first intermediate billet is then subjected to a second two-stage heating process. Under the fourth condition, the intermediate billet is heated to 730–830°C at a heating rate of 80–130°C / min and a holding coefficient of 0.6 min / mm to achieve uniform preheating of the billet. Subsequently, under the fifth condition, the temperature is further increased to 900–1000°C at a heating rate of 80–120°C / min and a holding coefficient of 0.4 min / mm to bring the intermediate billet to the temperature required for the second forging, thus obtaining the second intermediate billet.

[0038] The second intermediate billet is forged under a sixth condition to obtain the third intermediate billet. The sixth condition includes: a forging ratio ≥ 2, reheating at a temperature below 800℃ to a reheating temperature of 930–980℃, a reheating holding coefficient of 0.3 min / mm, and a forging ratio not less than 2, to complete the final deformation and further refine the grains and improve the overall mechanical properties of the material. During the forging process, when the alloy temperature is below 800℃, it is reheated to 930–980℃ and held at a holding coefficient of 0.3 min / mm to ensure the continuity and stability of the forging process.

[0039] The third intermediate billet is cooled to obtain Invar alloy rods.

[0040] This embodiment effectively reduces the oxygen content and inclusion content in the alloy by implementing three purification processes in the molten steel stages of smelting, refining, and tapping. During the vacuum furnace charging stage, some graphite carbon is charged into the furnace along with the raw materials, allowing free oxygen overflowing during Fe and Ni melting to react with the graphite carbon in a timely manner to generate carbon monoxide, which is then removed by the vacuum pump, thus suppressing the accumulation of oxygen content at the source. In the refining stage, continuous deoxidation is achieved by adding graphite carbon in batches, maintaining a low carbon content in the molten steel while meeting deoxidation requirements. Adding an appropriate amount of rare earth element Ce inhibits grain growth and refines the as-cast microstructure. This is because rare earth element Ce has a larger atomic radius, making it more prone to segregation at grain boundaries, thus limiting the straightening of grain boundaries. Furthermore, rare earth element Ce may also act as a heterogeneous nucleation core, promoting the nucleation process. Rare earth element Ce has a strong affinity for elements such as oxygen and sulfur. Adding it to molten steel can significantly deoxidize and desulfurize, reducing the types and numbers of non-metallic inclusions in the alloy and making residual inclusions finer. In Invar alloys, the addition of rare earth element Ce significantly refines the grain size of the forged microstructure. This is because rare earth element Ce is mainly enriched at austenite grain boundaries, reducing the grain boundary free energy and thus decreasing the driving force for recrystallization grain growth, thereby delaying the recrystallization process. Secondly, rare earth element Ce easily adsorbs on the surface of grain nuclei, inhibiting grain growth. Adding an appropriate amount of rare earth element Ce can also significantly control the morphology, quantity, and type of sulfide inclusions, thus improving the transverse toughness and plasticity of the steel.

[0041] Furthermore, this embodiment employs a two-forging process, which avoids cracking caused by a large forging ratio while significantly improving the uniformity of the microstructure and mechanical properties through two deformations. Water cooling is used after the first forging to effectively prevent grain coarsening caused by residual heat in the intermediate billet.

[0042] Example 1 The chemical composition of the target Invar alloy bar, by mass percentage, includes: C: 0.02%, Mn: 0.60%, Si: 0.16%, Ni: 37%, Ti: 0.10%, Ce: 0.008%, with the remainder being Fe and unavoidable impurities.

[0043] Before loading the furnace, weigh out 1 / 3 of the deoxidizing material C as the first part, and the remaining deoxidizing material C as the second part; Mn and Ti need to be baked at 200℃ for ≥12h before loading the furnace to remove moisture; Ce should be extracted with alcohol for more than 40min in advance.

[0044] The smelting material and the first part are loaded into the crucible of the vacuum induction furnace, with Fe and Ni added alternately. The vacuum is evacuated to below 3 Pa, and then the crucible is preheated at 80 kW until the material inside the furnace glows red. The vacuum is then continued to be evacuated to <0.8 Pa, and the power is increased to 160 kW, melting the material inside the crucible into molten steel. The power is adjusted until the temperature of the molten steel reaches 1570~1580℃. During this process, the deoxidizing material continuously reacts with the oxygen overflowing from the material inside the crucible, and the generated carbon monoxide is removed, ensuring an oxygen-free environment in the vacuum furnace.

[0045] The molten steel is heated to 1590~1600℃ and refined for 45 minutes. The second part is divided into 3 batches, with deoxidation added every 15 minutes.

[0046] After refining, argon gas is introduced, and Mn, Si, and Ti are added through the feeding hopper for alloying. After adding the materials, the mixture is stirred for 5 minutes. Rare earth Ce is added 2 minutes before tapping. The crucible is tilted to inject the alloy steel liquid into the tundish for secondary purification, and then injected into the alloy ingot mold. The vacuum is broken and the mixture is cooled in place for more than 12 hours before being transferred and demolded to obtain the finished steel ingot.

[0047] The steel ingot is heated in two stages using an electric furnace under first and second conditions. The first condition is a heating temperature of 800℃, a heating rate of 80℃ / min, and a holding coefficient of 0.6min / mm. The second condition is a heating temperature of 1020℃, a heating rate of 100℃ / min, and a holding coefficient of 0.4min / mm.

[0048] After heating, the steel ingot is forged under a third condition: a forging ratio ≥4. The purpose of this third condition is to break up the as-cast grains and homogenize the as-cast microstructure. If the alloy temperature is below 800℃, it is immediately returned to the furnace at a temperature of 1000℃, with a holding coefficient of 0.3 min / mm. After forging, it is water-cooled to obtain a first intermediate billet of 50+5mm.

[0049] The first intermediate billet is heated in two stages under the fourth and fifth conditions to obtain the second intermediate billet. The fourth condition is a heating temperature of 780℃, a heating rate of 90℃ / min, and a holding coefficient of 0.6min / mm. The fifth condition is a heating temperature of 980℃, a heating rate of 120℃ / min, and a holding coefficient of 0.4min / mm.

[0050] After the second intermediate billet exits the furnace, it undergoes a second forging under condition six, which is a forging ratio ≥ 2. The purpose of this condition is to further improve the billet's properties and complete the final deformation. The billet is immediately returned to the furnace if the alloy temperature is below 800℃, with a return temperature of 960℃ and a reheating holding coefficient of 0.3 min / mm. After forging, it is cooled to obtain a finished Invar alloy bar with a diameter of φ35±1mm.

[0051] Example 2 The rare earth element Ce content was adjusted to 0.012%, the first vacuum degree was 2.5 Pa, the first power was 65 kW, the second vacuum degree was 1.0 Pa, the second power was 140 kW, the first temperature was 1560~1570℃, the second temperature was 1580~1590℃, the first time was 40 min (for multiple batches, it was 2 batches), the second time was 12 min, the third time was 3 min, and the fourth time was 12 h. The first condition is that the heating temperature is 780℃, the heating rate is 95℃ / min, and the heat preservation coefficient is 0.6min / mm; The second condition is that the heating temperature is 980℃, the heating rate is 90℃ / min, and the heat preservation coefficient is 0.4min / mm; The third condition is that the forging ratio is 5, the temperature is below 800℃, the remelting temperature is 980℃, the remelting heating and heat preservation coefficient is 0.3min / mm, and water cooling is performed after forging. The fourth condition is a heating temperature of 760℃, a heating rate of 110℃ / min, and a heat preservation coefficient of 0.6min / mm; The fifth condition is that the heating temperature is 960℃, the heating rate is 95℃ / min, and the heat preservation coefficient is 0.4min / mm; The sixth condition is a forging ratio of 3, and the furnace is returned to the furnace when the temperature is below 800°C. The furnace return temperature is 960°C, and the furnace heating and holding coefficient is 0.3 min / mm. Other operations are the same as in Example 1.

[0052] Example 3 The processing parameters were changed to: first vacuum degree 3.5Pa, first power 120kW, second vacuum degree 1.2Pa, second power 180kW, first temperature 1600℃, second temperature 1620℃, first time 50min, multiple batches 3 batches, second time 18min, third time 8min, and fourth time 12h. The first condition is that the heating temperature is 880℃, the heating rate is 120℃ / min, and the heat preservation coefficient is 0.6min / mm; The second condition is that the heating temperature is 1070℃, the heating rate is 100℃ / min, and the heat preservation coefficient is 0.4min / mm; The third condition is a forging ratio of 4, the furnace is returned when the temperature is below 800℃, the furnace return temperature is 1030℃, the furnace return heating and holding coefficient is 0.3min / mm, and air cooling is performed after forging. The fourth condition is a heating temperature of 830℃, a heating rate of 130℃ / min, and a heat preservation coefficient of 0.6min / mm; The fifth condition is that the heating temperature is 1000℃, the heating rate is 120℃ / min, and the heat preservation coefficient is 0.4min / mm; The sixth condition is that the forging ratio is 2, the temperature is below 800°C, the furnace is returned to the furnace at a temperature of 980°C, and the furnace heating holding coefficient is 0.3 min / mm. Other operations are the same as in Example 1.

[0053] Example 4 The two-stage forging process was changed to a single-stage forging process, and the other operations were the same as in Example 1.

[0054] Comparative Example 1 Ti and rare earth Ce are not added to the molten steel, and other operations are the same as in Example 1.

[0055] Table 1 shows the chemical composition of Examples 1-4 and Comparative Example 1; Table 2 shows the mechanical properties and grain size of Examples 1-4 and Comparative Example 1; Table 3 shows the coefficient of thermal expansion of Examples 1-4 and Comparative Example 1; and Table 4 shows the inclusion detection results of Examples 1-4 and Comparative Example 1. As shown in Tables 1, 2, 3, and 4, the Invar alloy bars prepared according to Examples 1, 2, 3, and 4, compared with Comparative Example 1, showed an increase in tensile strength of 9.4%~15.8%, an increase in yield strength of 8.6%~22.5%, and an increase in elongation of 10.9%~16.8%, and the coefficient of thermal expansion could be stably maintained at 0.9~1.1*10. -6 / ℃, all inclusions are of D fineness grade 0.5, and all grain size is greater than 5.0.

[0056] Table 1 Chemical composition (%) of Examples 1-4 and Comparative Example 1 Table 2 Mechanical properties and grain size of Examples 1-4 and Comparative Example 1 Table 3. Expansion coefficients of Examples 1-4 and Comparative Example 1 Table 4. Inclusion detection results of Examples 1-4 and Comparative Example 1 In summary, this embodiment can significantly improve the overall mechanical properties and microstructure quality of Invar alloy bars while ensuring low expansion characteristics, and has good process stability and engineering application value.

[0057] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

[0058] The present invention has been described above with reference to embodiments thereof. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

[0059] Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and modifications can be made to the embodiments of the present invention without departing from the spirit and scope of the invention.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a high-strength, high-plasticity, low-expansion Invar alloy rod, characterized in that, include: According to the chemical composition requirements of the target Invar alloy bar, the raw materials are weighed and proportioned. The raw materials include smelting materials, alloying materials and deoxidizing materials. The deoxidizing materials include a first part and a second part. The first part of the smelting material and the deoxidizing material are heated in a vacuum environment to obtain molten steel; The molten steel is refined using the second part of the deoxidizing material to obtain purified molten steel; The alloying material is added to the purified molten steel to obtain a steel ingot; The steel ingot is heated, forged, and cooled to obtain Invar alloy bars.

2. The method for preparing Invar alloy rods according to claim 1, characterized in that, The chemical composition of the Invar alloy rod, by mass percentage, includes: C≤0.03%, Mn: 0.30~1.20%, Si≤0.5%, Ni: 35.0~38.0%, Ti: 0.03~0.15%, Ce: 0.003~0.025%, with the remainder being Fe and unavoidable impurities; The ratio of the first part to the second part is 1:2~3.

3. The method for preparing Invar alloy rods according to claim 2, characterized in that, The smelting materials include Fe and Ni, the alloying materials include Mn, Si, Ti and Ce, and the deoxidizing materials include C.

4. The method for preparing Invar alloy rods according to claim 3, characterized in that: The step of heating the first portion of the smelting material and the deoxidizing material in a vacuum environment to obtain molten steel includes: The first part of the smelting material and the deoxidizing material are loaded into the vacuum induction furnace; The vacuum induction furnace is evacuated to below a first vacuum level and preheated with a first power until the material inside the furnace turns red. The vacuum induction furnace is continuously evacuated to below the second vacuum level and heated with the second power to obtain molten steel; Adjust the heating power to maintain the temperature of the molten steel at the first temperature.

5. The method for preparing Invar alloy rods according to claim 4, characterized in that: The first vacuum degree is 2.5 to 3.5 Pa, the first power is 50 to 120 kW, the second vacuum degree is 1.0 to 1.2 Pa, the second power is 140 to 180 kW, and the first temperature is 1550 to 1600 °C.

6. The method for preparing Invar alloy rods according to claim 5, characterized in that: The refining of the molten steel using the second part of the deoxidizing material to obtain purified molten steel includes: The molten steel is heated to a second temperature for refining, and the refining time is the first time. During the refining process, the second portion of the deoxidizing material is added to the molten steel in multiple batches, with the time interval between two adjacent additions being the second time interval.

7. The method for preparing Invar alloy rods according to claim 6, characterized in that: The step of adding the alloying material to the purified molten steel to obtain a steel ingot includes: Argon gas is introduced into the purified molten steel, and Mn, Si and Ti are added for alloying treatment to obtain the first molten steel. The first molten steel is stirred for a third time to obtain the stirred first molten steel. Ce is added to the first molten steel after the stirring is completed to obtain the second molten steel; The second molten steel is poured, and after pouring is completed, the vacuum is broken and the steel is cooled for a time greater than or equal to the fourth time to obtain a steel ingot.

8. The method for preparing Invar alloy rods according to claim 7, characterized in that: The second temperature is 1580-1620℃, the first time is 40-50 min, the multiple batches are 2-3 batches, the second time is 12-18 min, the third time is 3-8 min, and the fourth time is 12 h.

9. The method for preparing Invar alloy rods according to claim 8, characterized in that: The process of heating, forging, and cooling the steel ingot to obtain Invar alloy bars includes: The steel ingot is heated under first and second conditions to obtain a first steel ingot; The first steel ingot is forged under the third condition to obtain the first intermediate billet; The intermediate billet is heated under the fourth and fifth conditions to obtain a second intermediate billet; The second intermediate billet is forged under the sixth condition to obtain the third intermediate billet; The third intermediate billet is cooled to obtain Invar alloy rods.

10. The method for preparing Invar alloy rods according to claim 9, characterized in that: The first condition includes: a heating temperature of 750–880°C, a heating rate of 70–120°C / min, and a heat preservation coefficient of 0.6 min / mm; The second condition includes: a heating temperature of 950–1070°C, a heating rate of 60–100°C / min, and a heat preservation coefficient of 0.4 min / mm; The third condition includes: forging ratio ≥4, remelting when the temperature is below 800℃, remelting temperature of 980~1030℃, remelting heating and heat preservation coefficient of 0.3min / mm, and water cooling or air cooling after forging. The fourth condition includes: a heating temperature of 730–830°C, a heating rate of 80–130°C / min, and a heat preservation coefficient of 0.6 min / mm; The fifth condition includes: a heating temperature of 900–1000℃, a heating rate of 80–120℃ / min, and a heat preservation coefficient of 0.4min / mm; The sixth condition includes: forging ratio ≥2, remelting when the temperature is below 800℃, remelting temperature of 930~980℃, and remelting heating and heat preservation coefficient of 0.3min / mm.

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