Large-size ultralow-expansion alloy forged rod with uniform structure and production method thereof

Abstract

The invention discloses a large-size ultralow-expansion alloy forged rod with a uniform structure and a production method thereof. The large-size ultralow-expansion alloy forged rod comprises the following chemical components in percentage by weight: 0.01-0.05% of C, less than or equal to 0.15% of Si, less than or equal to 0.5% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 32.5-35.0% of Ni, 3.5-4.5% of Co, 0.04-0.20% of V and the balance of Fe and inevitable impurities. The total amount of impurity elements is less than 0.05 wt%. On the basis of the 4J32 alloy, by designing alloy components and reasonably controlling the smelting process, the heating process, the forging process and the heat treatment process, it is guaranteed that the large-specification forged rod with the uniform structure is obtained, and the phenomenon that mixed crystals are likely to be generated in the hot working process of the existing 4J32 alloy is overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of expanded alloy, in particular to a large-size ultra-low expansion alloy forged bar with uniform structure and a production method thereof. BACKGROUND

[0002] In the field of aerospace, the ultra-low expansion alloy 4J32 is mainly used for manufacturing radar antenna, missile guidance system and fire control system, etc., and the market demand is huge. Compared with 4J36, the expansion coefficient of 4J32 is lower (≤1.0×10-6 / ℃) at 20-100℃, so the alloy has more advantages in precise guidance; but when used as a high-performance missile guidance system component, the uniformity of the structure of the 4J32 forged bar is required to be higher. Generally, the ultra-low expansion alloy is mainly used in the instrument and meter industry, and there is no clear requirement for the uniformity of the structure in the national standard under the condition of meeting the physical performance requirements. Since the 4J32 alloy is a single-phase austenitic alloy, there is no precipitated phase in the alloy to pin the grain boundary movement, and the recrystallization temperature of the alloy is low, so the grains are easily grown and mixed crystal structure is easily appeared during the hot working and heat treatment, so it is difficult to prepare a large-size ultra-low expansion alloy forged bar with uniform structure.

[0003] In order to overcome the above-mentioned deficiencies of the prior art, the present application develops a large-size ultra-low expansion alloy forged bar with uniform structure and a production method thereof, and through novelty search, two patents similar to the present application are found in the ultra-low expansion alloy.

[0004] The Chinese patent publication No. CN104862585A discloses an ultra-low expansion alloy material and a preparation method thereof, and the main chemical components are: C 0-0.05%, Ni 36-38%, Y 0.6%; the ultra-low expansion alloy material has the advantages of low expansion, high elastic modulus, good processing performance, etc.; but the alloy of the technology has high Ni content, and adds element Y, which is obviously different from the composition of the alloy of the present application, and the alloy adopts a conventional forging process, which is different from the forging process of the alloy of the present application.

[0005] The Chinese patent publication No. CN1114366A discloses a high-strength super-invar alloy and a production method thereof, and the main chemical components are: C 0.03-0.50%, Mn ≤0.6%, Ni 31.0-32.5%, Co 3-5%, Nb 0.1-0.5%; the alloy of the technology has high C content and low Ni content, and adds Nb element, which is different from the composition of the present application; in addition, the alloy of the technology is smelted by a vacuum induction furnace and a non-vacuum induction furnace, after hot working, light cold deformation and pickling, and then cold working into a strip or wire, the production method thereof is obviously different from the present application.

[0006] The composition comparison of the above-mentioned patents and the present application is shown in Table 1.

[0007] SUMMARY

[0008] In order to overcome the defects in the prior art, the present application aims to provide a large-size ultra-low expansion alloy forged bar with uniform structure and a production method thereof. On the basis of 4J32 alloy, by designing alloy composition and reasonably controlling smelting process, heating process, forging process and heat treatment process, a large-size forged bar with uniform structure is ensured, and the phenomenon of mixed crystal easily produced in the process of hot working of the existing 4J32 alloy is overcome.

[0009] In order to achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0010] The first aspect of the present application provides a large-size ultra-low expansion alloy forged bar with uniform structure, and the chemical composition is as follows: C: 0.01-0.05%, Si: ≤0.15%, Mn: ≤0.5%, P ≤0.010%, S ≤0.005%, Ni: 32.5-35.0%, Co: 3.5-4.5%, V: 0.04-0.20%, and the rest is Fe and inevitable impurities.

[0011] The total amount of impurity elements is less than 0.05wt%.

[0012] Preferably, V and C satisfy: 3.5 ≤ V / C ≤ 4.5.

[0013] Preferably, Si: 0.09-0.15%, Mn: 0.25-0.5%.

[0014] The second aspect of the present application provides a production method of the large-size ultra-low expansion alloy forged bar with uniform structure according to the first aspect of the present application, comprising the following steps:

[0015] S1, smelting to obtain an ingot;

[0016] S2, heating the ingot, the ingot is loaded into the furnace after being cooled, the ingot loading temperature is ≤800℃, the temperature is increased to 1180℃±20℃ and kept for 4-6 hours;

[0017] S3, first fire forging, the open forging temperature is ≥1080℃, the final forging temperature is ≥800℃, the forged blank after forging is reheated, and the heating temperature is 1160℃±20℃;

[0018] S4, second fire forging, the open forging temperature is ≥1080℃, the final forging temperature is ≥800℃, the forged blank after forging is reheated, and the heating temperature is 1140℃±20℃;

[0019] S5, third fire forging, the forged blank after the second fire forging is forged to the finished product size, the last fire deformation is controlled to be more than 30%, and the forged blank is air-cooled after forging;

[0020] S6, heat treatment, annealing the third forged bar at high temperature, and obtaining the large-size ultra-low expansion alloy forged bar after air cooling.

[0021] Preferably, in the step S1, the smelting is performed by vacuum induction + electroslag, or electric furnace + secondary refining + electroslag, or electric furnace + secondary refining + mold casting.

[0022] Preferably, in the step S2, the heating speed of the ingot is ≤80℃ / h.

[0023] Preferably, in the steps S3 and S4, the holding time of the reheating is ≥60 minutes.

[0024] Preferably, in the step S5, the third forging is performed at a starting forging temperature ≥1080℃ and a final forging temperature ≥800℃.

[0025] Preferably, in the step S6, the heat treatment temperature is 900±10℃ and the holding time is ≥2 hours.

[0026] Preferably, the large-size ultra-low expansion alloy forged bar has a grain size finer than 5 and an expansion coefficient ≤1.0×10 -6 / ℃.

[0027] The alloy composition design has the following features: the alloy is based on the 4J32 alloy, V and C are added to the alloy to precipitate carbides, so as to prevent the grain growth during the hot working process of the alloy and achieve the purpose of refining the grains. In order to avoid the increase of the expansion coefficient of the alloy due to the excessive V and C in the alloy, the ratio of V and C in the alloy is controlled to be 3.5≤V / C≤4.5. At the same time, in order to overcome the phenomenon of the increase of the expansion coefficient of the alloy due to the addition of V, and to ensure that the alloy still has an ultra-low expansion coefficient, the content of Ni and Co in the alloy is appropriately increased to ensure that a lower expansion coefficient is obtained.

[0028] The reasons for selecting the chemical composition range of the alloy are as follows:

[0029] C: the addition of C is mainly to form carbides, to prevent the grain growth during the hot working process, and to achieve the purpose of refining the grains. However, too high C content will rapidly increase the expansion coefficient of the material. Preferably, the C content in the alloy is 0.01-0.05%.

[0030] Si: Si is added to the alloy to play a deoxidizing role. With the increase of the Si content in the alloy, the expansion coefficient increases. Therefore, under the condition of ensuring good deoxidization of the molten steel, the Si content in the alloy is as low as possible. Preferably, Si≤0.15%.

[0031] Mn: Mn is added to the alloy to deoxidize. In order to ensure good deoxidization of the alloy, a certain amount of Mn needs to be added to the alloy, but when the content exceeds 0.5%, the expansion coefficient will increase sharply. Therefore, the content of Mn is preferably ≤0.5%.

[0032] Ni: is a necessary element to ensure that the alloy has a low expansion coefficient. Due to the addition of C and V in the alloy, the expansion coefficient of the alloy will increase. In order to obtain a lower expansion coefficient, the content of Ni in the alloy should be appropriately increased. The content of Ni in the alloy is preferably controlled in the range of 32.5-35.0%.

[0033] Co: Co and Ni are used in combination to reduce the expansion coefficient, but adding a large amount of Co will increase the cost of the alloy, therefore, the content of Co should be controlled below 5.0%. Since both Co and Ni have the effect of reducing the expansion coefficient, but Co is more obvious than Ni in reducing the expansion coefficient. Therefore, when the alloy contains a certain amount of Co, the content of Ni should be correspondingly reduced. According to the content of Ni in the alloy of the present application, the content of Co in the alloy is preferably controlled in the range of 3.5-4.5%.

[0034] V: The addition of V is mainly to form VC, refine the grain and the structure. In order to ensure that the expansion coefficient meets the requirements and at the same time achieve the purpose of refining and uniformizing the structure, it is required that the content of V in the alloy meets the requirement of 3.5≤V / C≤4.5, therefore, according to the content of C in the alloy of the present application, the content of V is preferably controlled in the range of 0.04-0.20%.

[0035] P: With the increase of the content of P, the expansion coefficient of the alloy increases; at the same time, P is a harmful substance which can cause cold brittleness of the alloy, resulting in a significant decrease in plasticity and toughness. Therefore, the content of P should be controlled as low as possible. The present application controls P≤0.010%.

[0036] S: With the increase of the content of S, the expansion coefficient of the alloy increases; at the same time, S is also a harmful substance which can cause hot brittleness of the alloy, resulting in a decrease in various mechanical properties. Therefore, the lower the content of S in the alloy, the better. The present application controls S≤0.005%.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] 1. The present application is based on the 4J32 alloy, by adding C and V elements, and controlling 3.5≤V / C≤4.5, through the precipitation of VC to prevent the growth of grains in the alloy, and then applying the large deformation stepwise cooling forging process and heat treatment process to ensure obtaining a uniform structure; in order to overcome the phenomenon that the addition of V in the alloy leads to an increase in the expansion coefficient, and to ensure that the alloy still has an ultra-low expansion coefficient, the content of Ni+Co in the alloy is appropriately increased to ensure that a lower expansion coefficient is obtained.

[0039] 2、The present application adopts stepwise temperature reduction large deformation forging process in the aspect of hot working, avoids coarse grains in the alloy, and then adopts high temperature annealing heat treatment to regulate and control the uniformity of grains in the alloy, so that a large size super low expansion alloy forging rod with uniform structure is obtained;

[0040] 3、The designed super low expansion alloy of the present application overcomes the phenomenon that the existing 4J32 alloy is prone to mixed grains in the hot working process, and is very suitable for the fields with high requirements for alloy structure uniformity such as aerospace. BRIEF DESCRIPTION OF DRAWINGS

[0041] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0042] Figure 1 is a flow chart of the production method of the large size super low expansion alloy forging rod with uniform structure of the present application;

[0043] Figure 2 is a edge structure diagram of the large size super low expansion alloy forging rod prepared in Example 1 of the present application;

[0044] Figure 3 is a structure diagram at 1 / 2 radius of the large size super low expansion alloy forging rod prepared in Example 1 of the present application;

[0045] Figure 4 is a core structure diagram of the large size super low expansion alloy forging rod prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0046] The present application will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form.

[0047] The present application is based on 4J32 alloy, and a certain amount of C and V are added to form VC, which prevents grain growth during hot working and avoids mixed grain structure, so as to refine and uniformize the structure. The addition of C and V increases the expansion coefficient of the alloy. In order to ensure that the expansion coefficient meets the requirements and achieve the purpose of refining and uniformizing the structure, the content of C and V in the alloy is required to meet the requirement of 3.5≤V / C≤4.5, and the content of Ni+Co in the alloy is appropriately increased. In the aspect of hot working, stepwise temperature reduction large deformation forging process is adopted to avoid coarse grains in the alloy, and then high temperature annealing heat treatment is adopted to regulate and control the uniformity of grains in the alloy, so that a large size super low expansion alloy forging rod with uniform structure is obtained. The alloy of the present application is widely applicable to the fields of aerospace, high-precision instruments and meters, tracks and rail connecting parts of high-speed trains, high-temperature thermoelectric generators and the like, and has a wide application prospect.

[0048] The application provides a large-size ultra-low expansion alloy forged bar with uniform structure, and the chemical composition of the large-size ultra-low expansion alloy forged bar is as follows: C: 0.01-0.05%, Si: ≤0.15%, Mn: ≤0.5%, P: ≤0.010%, S: ≤0.005%, Ni: 32.5-35.0%, Co: 3.5-4.5%, V: 0.04-0.20%, and the rest is Fe and inevitable impurities; and the total amount of the impurity elements is less than 0.05 wt%.

[0049] In the preferred embodiment, V and C satisfy: 3.5≤V / C≤4.5.

[0050] In the preferred embodiment, Si: 0.09-0.15%, and Mn: 0.25-0.5%.

[0051] In combination Figure 1 As shown, the application also provides a production method of the large-size ultra-low expansion alloy forged bar with uniform structure, and the method comprises the following steps: obtaining a required steel ingot by using a vacuum induction+electroslag, an electric furnace+secondary refining+electroslag, or an electric furnace+secondary refining+die casting method, and then obtaining the forged bar with uniform structure by using a special forging process and a heat treatment process.

[0052] S1, smelting to obtain a steel ingot;

[0053] The smelting process comprises the following steps: obtaining a required steel ingot by using a vacuum induction+electroslag, an electric furnace+secondary refining+electroslag, or an electric furnace+secondary refining+die casting method, and the steel ingot has a specification of Φ510, Φ660 or 5.8t, and other specifications can also be used.

[0054] S2, heating the steel ingot, and loading the steel ingot into a furnace at a temperature of ≤800℃, and then increasing the temperature to 1180℃±20℃ and maintaining for 4-6 hours;

[0055] The steel ingot heating process comprises the following steps: loading the steel ingot into a furnace at a temperature of ≤800℃, and then increasing the temperature to 1180℃±20℃ at a speed of ≤80℃ / hour and maintaining for 4-6 hours.

[0056] S3, first fire forging, the forging temperature is ≥1080℃, the final forging temperature is ≥800℃, the forged blank after forging is reheated, and the reheating temperature is 1160℃±20℃;

[0057] The first fire forging process comprises the following steps: using a 12t forging hammer to forge, first placing the steel ingot on a flat anvil, if the steel ingot is a die casting steel ingot, the cap is downward, the steel ingot is vertically placed on the flat anvil, the steel ingot is hammered quickly, when the steel ingot is upset to 1 / 2 of the original height, the steel ingot is elongated, and the elongation is to the original length of the steel ingot, the forging temperature is ≥1080℃, and the final forging temperature is ≥800℃.

[0058] Reheating process: the forging blank is reheated, the heating temperature is reduced to 1160℃±20℃, and the holding time is ≥60 minutes.

[0059] S4, second fire forging, the open forging temperature is ≥1080℃, the final forging temperature is ≥800℃, the forging blank after forging is reheated, the heating temperature is 1140℃±20℃;

[0060] Second fire forging process: the blank is upset to a height of 1 / 2, and then the upset blank is drawn to a square chamfer of 450-500mm, the open forging temperature is ≥1080℃, and the final forging temperature is ≥800℃.

[0061] Reheating process: the forging blank is reheated, the heating temperature is reduced to 1140℃±20℃, and the holding time is ≥60 minutes.

[0062] S5, third fire forging, the forging blank after the second fire forging is forged to the finished product specification, and the last fire deformation is controlled to be more than 30%, and the forging is air cooled;

[0063] Third fire forging process: the blank after the square chamfer of 450-500mm is directly drawn to the finished product specification (such as Φ350mm), and the last fire deformation is ensured to be more than 30%, the open forging temperature is ≥1080℃, and the final forging temperature is ≥800℃. The forging is air cooled.

[0064] S6, heat treatment, the forging rod after the third fire forging is subjected to high-temperature annealing treatment, and a large-specification ultra-low expansion alloy forging rod is obtained after air cooling.

[0065] Heat treatment process: in order to refine the grain of the steel and ensure that the forging rod is fully recrystallized, high-temperature annealing treatment is adopted, the heat treatment temperature is 900℃±10℃, the holding time is ≥2 hours, and the air cooling is performed.

[0066] After the above method, the grain size of the large-specification ultra-low expansion alloy forging rod with uniform structure of the application is finer than 5 levels, and the expansion coefficient is ≤1.0×10 -6 / ℃.

[0067] The large-specification ultra-low expansion alloy forging rod with uniform structure and the production method thereof will be further introduced below in combination with specific examples.

[0068] Five batches of alloys are produced according to the designed chemical composition and the production method of the application, and the specific composition of the alloy in the example is shown in Table 2. The structure of the alloy in Example 1 is shown in the figure, and it can be seen from the figure that the structure uniformity is very good from the edge to the center of the forging rod. Figures 2 to 4

[0069] Example 1

[0070] ​The Φ510 steel ingot is obtained by vacuum induction + electroslag method. The cold ingot is charged into the furnace at 800℃. The ingot is heated at a speed of 80℃ / h, and the temperature is raised to 1180℃ for 4h. The 12t forging hammer is used for forging. The ingot is first placed on a flat anvil, and the ingot is vertically hit with fast force when the ingot is perpendicular to the flat anvil. When the ingot is upset to 1 / 2 of the original height, the forging blank is elongated to the original ingot length. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The forging blank is reheated, and the heating temperature is 1160℃ for 60min. When the blank is upset to 1 / 2 of the height, the upset blank is elongated to 500mm square chamfer. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The blank is reheated, and the heating temperature is 1140℃ for 60min. The 500mm square chamfered blank is directly elongated to the finished product Φ350mm. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The blank is air cooled after forging. The forged bar is subjected to high temperature annealing treatment. The heat treatment temperature is 900℃, the holding time is 2h, and the blank is air cooled.

[0071] The grain size of the large-size ultra-low expansion alloy forged bar prepared in this embodiment is 5, and the expansion coefficient is 0.62×10 -6 / ℃.

[0072] Example 2

[0073] The Φ510 steel ingot is obtained by vacuum induction + electroslag method. The cold ingot is charged into the furnace at 800℃. The ingot is heated at a speed of 80℃ / h, and the temperature is raised to 1180℃ for 4h. The 12t forging hammer is used for forging. The ingot is first placed on a flat anvil, and the ingot is vertically hit with fast force when the ingot is perpendicular to the flat anvil. When the ingot is upset to 1 / 2 of the original height, the forging blank is elongated to the original ingot length. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The forging blank is reheated, and the heating temperature is 1160℃ for 60min. When the blank is upset to 1 / 2 of the height, the upset blank is elongated to 500mm square chamfer. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The blank is reheated, and the heating temperature is 1140℃ for 60min. The 500mm square chamfered blank is directly elongated to the finished product Φ350mm. The open forging temperature is 1080℃, and the final forging temperature is 800℃. The blank is air cooled after forging. The forged bar is subjected to high temperature annealing treatment. The heat treatment temperature is 900℃, the holding time is 2h, and the blank is air cooled.

[0074] The grain size of the large-size ultra-low expansion alloy forged bar prepared in this embodiment is 5, and the expansion coefficient is 0.62×10 -6 / ℃.

[0075] Example 3

[0076] The Φ510 steel ingot is obtained by vacuum induction + electroslag method. The cold ingot is charged into the furnace at 735℃. The ingot is heated at a speed of 80℃ / h, and the temperature is raised to 1200℃ for 4h. The 12t forging hammer is used for forging. First, the ingot is placed on a flat anvil, and the ingot is vertically hit with fast force when the ingot is perpendicular to the flat anvil. When the ingot is upset to 1 / 2 of the original height, the forging blank is elongated to the original ingot length. The open forging temperature is 1095℃, and the finish forging temperature is 850℃. The forging blank is reheated, and the heating temperature is 1170℃ for 65min. When the blank is upset to 1 / 2 of the height, the upset blank is elongated to 450mm square chamfer. The open forging temperature is 1085℃, and the finish forging temperature is 850℃. The blank is reheated, and the heating temperature is 1130℃ for 70min. The 450mm square chamfered blank is directly elongated to the finished product Φ350mm. The open forging temperature is 1081℃, and the finish forging temperature is 800℃. The blank is air cooled after forging. The forged bar is annealed at a high temperature, the heat treatment temperature is 910℃, the holding time is 2.5h, and the blank is air cooled.

[0077] The grain size of the large-size ultra-low expansion alloy forged bar prepared in this embodiment is 5.5, and the expansion coefficient is 0.68×10 -6 / ℃.

[0078] Example 4

[0079] The Φ510 steel ingot is obtained by vacuum induction + electroslag method. The cold ingot is charged into the furnace at 735℃. The ingot is heated at a speed of 80℃ / h, and the temperature is raised to 1200℃ for 4h. The 12t forging hammer is used for forging. First, the ingot is placed on a flat anvil, and the ingot is vertically hit with fast force when the ingot is perpendicular to the flat anvil. When the ingot is upset to 1 / 2 of the original height, the forging blank is elongated to the original ingot length. The open forging temperature is 1095℃, and the finish forging temperature is 850℃. The forging blank is reheated, and the heating temperature is 1170℃ for 65min. When the blank is upset to 1 / 2 of the height, the upset blank is elongated to 450mm square chamfer. The open forging temperature is 1085℃, and the finish forging temperature is 850℃. The blank is reheated, and the heating temperature is 1130℃ for 70min. The 450mm square chamfered blank is directly elongated to the finished product Φ350mm. The open forging temperature is 1081℃, and the finish forging temperature is 800℃. The blank is air cooled after forging. The forged bar is annealed at a high temperature, the heat treatment temperature is 910℃, the holding time is 2.5h, and the blank is air cooled.

[0080] The grain size of the large-size ultra-low expansion alloy forged bar prepared in this embodiment is 5.5, and the expansion coefficient is 0.68×10 -6 / ℃.

[0081] Example 5

[0082] The embodiment adopts vacuum induction + electroslag to obtain Φ510 steel ingot. The steel ingot is cold ingot loaded into furnace, the loading temperature is 800℃; the steel ingot heating speed is 80℃ / h, and the temperature is raised to 1170℃ and kept for 5h. The 12t forging hammer is used for forging, first, the steel ingot is placed on a flat anvil, when the steel ingot is perpendicular to the flat anvil, the steel ingot is quickly hammered, when the steel ingot is upset to 1 / 2 of the original height, the forging blank is elongated, and the elongation is to the original steel ingot length. The open forging temperature is 1085℃, and the final forging temperature is 830℃. The forging blank is reheated, the heating temperature is 1150℃ and kept for 60min. When the out-of-furnace forging blank is upset to 1 / 2 of the height, the upset forging blank is elongated to 450mm square chamfer, the open forging temperature is 1090℃, and the final forging temperature is 850℃. The forging blank is reheated, the heating temperature is 1140℃ and kept for 65min. The 450mm square chamfered forging blank is directly elongated to the finished product Φ350mm, the open forging temperature is 1085℃, and the final forging temperature is 810℃. The forging is air cooled. The forging rod is subjected to high temperature annealing treatment, the heat treatment temperature is 900℃, the keeping time is 2h, and the air cooling is performed.

[0083] The grain size of the large-size ultra-low expansion alloy forging rod prepared in the embodiment is 5.5, and the expansion coefficient is 0.63×10 -6 / ℃.

[0084] Table 2 Chemical composition (wt%) of large-size ultra-low expansion alloy forging rod in embodiments 1-5 of the application

[0085] C Si Mn P S Ni Co V Fe Example 1 0.05 0.09 0.35 0.008 0.005 35.0 3.50 0.20 remainder Example 2 0.03 0.11 0.44 0.009 0.002 33.5 3.62 0.11 remainder Example 3 0.02 0.12 0.29 0.008 0.003 33.4 3.78 0.07 remainder Example 4 0.04 0.10 0.46 0.010 0.003 32.5 4.50 0.18 remainder Example 5 0.01 0.12 0.50 0.007 0.004 34.5 4.12 0.04 remainder

[0086] It can be known from the embodiments that the large-size ultra-low expansion alloy forging rod developed by the application has good uniformity (the grain size is finer than 5), and the expansion coefficient is low (the expansion coefficient is ≤1.0×10 -6 / ℃), and is very suitable for the field of aerospace which has high requirements on uniformity. In addition, the alloy of the application is also suitable for manufacturing high-precision instruments and meters, track and rail connecting parts of high-speed trains, high-temperature thermoelectric generators and other fields, and has wide application prospect.

[0087] It should be noted that the above embodiments are only used to illustrate the technical solutions of the application but not limit the application. Although the application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the application can be modified or replaced equivalently without departing from the purpose and scope of the application, and all should be covered in the scope of claims of the application.

Claims

1. A large-size ultra-low expansion alloy forged bar with uniform microstructure, characterized in that, Its chemical composition by weight percentage is as follows: C: 0.01~0.05%, Si: ≤0.15%, Mn: ≤0.5%, P≤0.010%, S≤0.005%, Ni: 32.5~35.0%, Co: 3.5~4.5%, V: 0.04~0.20%, with the remainder being Fe and unavoidable impurities; The total amount of impurity elements is less than 0.05 wt%.

2. The large-size ultra-low expansion alloy forging bar with uniform microstructure as described in claim 1, characterized in that: V and C satisfy: 3.5≤V / C≤4.

5.

3. The large-size ultra-low expansion alloy forging bar with uniform microstructure as described in claim 1, characterized in that: Si: 0.09 to 0.15%, Mn: 0.25 to 0.5%.

4. A method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure according to claims 1-3, characterized in that: Includes the following steps: S1, smelting to obtain steel ingots; S2, steel ingot heating, cold steel ingot loading into the furnace, steel ingot loading temperature ≤800℃, temperature rises to 1180℃±20℃ and holds for 4~6 hours; S3, first forging, initial forging temperature ≥1080℃, final forging temperature ≥800℃, the forged billet is reheated in the furnace at a temperature of 1160℃±20℃; S4, second forging, initial forging temperature ≥1080℃, final forging temperature ≥800℃, the forged billet is reheated in the furnace at a temperature of 1140℃±20℃; S5, the third forging, forges the billet after the second forging to the finished product specifications. The deformation amount of the last forging is controlled to be more than 30%, and the billet is air-cooled after forging. S6, heat treatment, the forged bar after the third fire forging is subjected to high temperature annealing treatment, and after air cooling, a large-size ultra-low expansion alloy forged bar is obtained.

5. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, In step S1, the smelting process uses vacuum induction + electroslag refining, or electric furnace + ladle refining + electroslag refining, or electric furnace + ladle refining + die casting to obtain steel ingots.

6. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, In step S2, during the heating process of the steel ingot, the heating rate of the steel ingot is ≤80℃ / h.

7. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, In steps S3 and S4, the holding time for reheating in the furnace is ≥60 minutes.

8. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, In step S5, during the third forging process, the initial forging temperature is ≥1080℃ and the final forging temperature is ≥800℃.

9. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, In step S6, during the high-temperature annealing process, the heat treatment temperature is 900±10℃ and the holding time is ≥2 hours.

10. The method for producing large-size ultra-low expansion alloy forging bars with uniform microstructure as described in claim 4, characterized in that, The uniformly structured, large-size, ultra-low expansion alloy forged bar has a grain size finer than grade 5 and an expansion coefficient ≤1.0×10⁻⁶. -6 / ℃.

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