A method of improving the plasticity of a large ingot of hastelloy steel by forging and a hastelloy alloy

Abstract

The application discloses a forging method for improving plasticity of large-size Invar alloy ingot and an Invar alloy. The method comprises the following steps: smelting molten steel by using an electric furnace, and obtaining a large-size Invar alloy ingot with a weight of 15-25 t after casting; heating the cold Invar alloy ingot to 1000-1200 DEG C and keeping the temperature, and controlling the keeping time to be greater than or equal to 10 h; performing three times of upsetting and elongating on the heated Invar alloy ingot, and performing upsetting according to 15-50% of the total height of the Invar alloy ingot in each time, then elongating to the original height of the Invar alloy ingot after the upsetting, and returning to the heating furnace for heating and keeping after the upsetting and elongating in each time; the final upsetting temperature is greater than or equal to 750 DEG C; the Invar alloy ingot after the heating and keeping in the last time is forged to a specified size, and then slowly cooled to room temperature in air to obtain an Invar alloy forging blank. The application improves the hot plasticity of the large-size Invar alloy ingot, and solves the technical problems of easy cracking of the large-size Invar alloy ingot during forging.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal materials, in particular to a forging method for improving the plasticity of large Invar alloy ingots and an Invar alloy. BACKGROUND

[0002] Invar alloy is a binary system austenitic Fe-Ni alloy, which belongs to precision alloy with abnormal thermal expansion characteristics or controllable thermal expansion characteristics, and is widely used in fields with high requirements for material expansion performance such as electronic components. The expansion coefficient of the Invar alloy is relatively low, and its expansion coefficient at 20-100℃ is ≤1.5×10 -6 / ℃, which is only 1 / 5-1 / 10 of ordinary steel. Currently, the Invar alloy with commercial application is mainly Fe-Ni alloy, such as 4J36 Invar alloy for aircraft composite mold, Ni36 Invar alloy for thin film type LNG ship, and high-strength H36 Invar alloy for high-voltage capacity conductors. In addition to Fe-Ni Invar alloy, Fe-Ni-Co super Invar alloy is widely used in aerospace field due to its excellent ultra-low expansion performance, and its composition mainly includes C≤0.04%, Si≤0.25%, 0.2%≤Mn≤0.4%, S≤0.0015%, P≤0.008%, 35%≤Ni≤36.5%, 3%≤Co≤4%, and the rest is Fe. The expansion performance requirement of the alloy in the temperature range of-180-0℃ is 1-2×10 -6 / ℃. In recent years, the demand for Invar alloy cold-rolled strips has increased in many application fields, and traditional small-size Invar alloy ingots cannot meet the production and processing requirements, so it is urgent to develop a large-size Invar alloy ingot smelting and forging process. However, due to the solidification structure characteristics of Invar alloy, the larger the size of the ingot, the worse the hot working plasticity, and the risk of forging cracking is high, which brings great economic loss to enterprises, so it is urgent to develop a forging method for improving the plasticity of large Invar alloy ingots.

[0003] Chinese patent publication No. CN118854142A proposes a preparation method of Invar alloy thick plate with δ≥70mm for aviation mold, which adopts non-vacuum induction furnace melting, vacuum self-consumption melting, large deformation ratio forging, and hot treatment to make the grain grow again, reduce the grain size difference between the edge and the core; the preparation method can prepare 200×1000mm width Invar alloy plate, but the steel ingot size involved in the technology is small, and the risk of forging cracking is small;

[0004] Chinese patent publication No. CN119456694A proposes a production method of Invar alloy 4J36 hot-rolled coil, which discloses the rolling method of Invar alloy hot-rolled coil, but the technical parameters related to the hot rolling process are disclosed, and the steel ingot forging process is not involved.

[0005] Chinese patent publication No. CN117548519A proposes a low-expansion coefficient iron-nickel-based silicon steel forging and rolling hybrid forming process. The method is a forging blank and hot rolling hybrid forming process, mainly for small electroslag ingots. It does not involve the forging process of large Invar alloy steel ingots.

[0006] In summary, there is an urgent need to develop a forging method to improve the plasticity of large Invar alloy steel ingots, which can solve the technical problems such as cracking of large Invar alloy steel ingots during forging. SUMMARY

[0007] In view of the defects in the prior art, the purpose of the present application is to provide a forging method for improving the plasticity of large Invar alloy steel ingots and an Invar alloy, which effectively improves the hot plasticity of large Invar alloy steel ingots, solves the technical problems such as cracking of large Invar alloy steel ingots during forging, and improves the yield of Invar alloy forgings.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The first aspect of the present application provides a forging method for improving the plasticity of large Invar alloy steel ingots, comprising the following steps:

[0010] S1, melting process, using an electric furnace to smelt a molten steel that meets the internal control composition requirements of Invar alloy, and obtaining a large Invar alloy steel ingot with a weight of 15-25t after casting;

[0011] S2, heating process, heating the cold Invar alloy steel ingot to 1000-1200℃ and maintaining the temperature, and controlling the maintaining time to be greater than or equal to 10h;

[0012] S3, upsetting and elongating process, the heated Invar alloy steel ingot is upset and elongated three times, each time the upsetting amount is 15-50% of the total height of the Invar alloy steel ingot, and after upsetting, the Invar alloy steel ingot is elongated to the original height, after each time of upsetting and elongating, the Invar alloy steel ingot is returned to the heating furnace for heating and maintaining, and the final forging temperature of each time of upsetting and elongating is greater than or equal to 750℃;

[0013] S4, forging and forming, the Invar alloy steel ingot after the last heating and maintaining in step S3 is forged to a specified size, and then slowly cooled to room temperature in air to obtain an Invar alloy steel forging blank.

[0014] Preferably, in step S1, pure nickel plates and pure iron are used as raw materials in the melting process, the content of Ni element in the pure nickel plate is greater than 99.5%, and the total content of impurity elements is less than or equal to 0.05%, these impurity elements include Zr, Ti, Cr, Nb, V, etc.

[0015] Preferably, in step S1, the molten steel satisfies the following Invar alloy internal control composition requirements: C≤0.08%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the balance being iron and unavoidable impurities, in terms of percentage by weight.

[0016] Preferably, in step S2, the holding time satisfies the following formula:

[0017] t≥8d+1.5

[0018] wherein t is time, in units of h; and d is the diameter of the Invar alloy ingot, in units of m.

[0019] If the holding time in step S2 does not satisfy the above formula requirements, the ingot cannot be thoroughly held, and there is a risk of cracking during subsequent forging; if the holding time is too long, the ingot is at risk of overburning. The holding temperature is 1100-1200℃

[0020] Preferably, in step S2, during the heating process, the heating rate is 20-100℃ / h.

[0021] Preferably, the upsetting and drawing process of step S3 specifically includes the following processes:

[0022] S31, first fire upsetting and drawing, the heated Invar alloy ingot is upset by an amount of 30-50% of the total height of the Invar alloy ingot, and then drawn to the original height of the Invar alloy ingot, with a single pass reduction of 5-10mm, a final forging temperature of ≥750℃, and then returned to the heating furnace for heating and holding at a temperature of 1100-1200℃ for 1-3h;

[0023] S32, second fire upsetting and drawing, the upsetting amount is controlled to be 20-40% of the total height of the Invar alloy ingot, with a single pass reduction of 10-15mm, a final forging temperature of ≥750℃, and after upsetting and drawing, returned to the heating furnace for heating and holding at a temperature of 1100-1200℃ for 1-3h; since the grain structure is refined after the first fire upsetting and drawing, the single pass reduction is increased compared to the previous fire, to ensure that the internal grains of the ingot are fully recrystallized and refined;

[0024] S33, third fire upsetting and drawing, the upsetting amount is controlled to be 15-35% of the total height of the Invar alloy ingot, with a single pass reduction of 15-20mm, a final forging temperature of ≥750℃, and after upsetting and drawing, returned to the heating furnace for heating and holding at a temperature of 1100-1200℃ for 1-3h.

[0025] In the three times of upsetting and elongating in step S3: the first time of upsetting and elongating is to increase the cross-sectional area by axial compression of the metal blank, reduce the height of the ingot, provide a material distribution basis for subsequent elongation, and then elongate the wide surface of the subsequent light tap ingot to the original height of the ingot. The elongation process breaks the surface coarse columnar crystal size grains of the ingot and optimizes the material flow distribution. The single pass reduction amount cannot exceed 10 mm to prevent excessive deformation from causing cracks. In the first time of upsetting and elongating process, if the upsetting amount is too small (less than 30% of the total height of the ingot), the reduction ratio is small, which leads to insufficient breaking of the ingot columnar crystal, and if the upsetting amount exceeds 50% of the total height of the ingot, the ingot has a risk of cracking during forging. Therefore, according to the production experience of the ingot, the upsetting amount of the first time of upsetting and elongating process is set to 30-50% of the total height of the ingot. Similarly, the upsetting amount of the second time of upsetting and elongating process and the third time of upsetting and elongating process is set to 20-40% and 15-35% of the total height of the ingot, respectively. The single pass reduction amount of the first time of upsetting and elongating is controlled to be 5-10 mm. If the single pass reduction amount is ≤5 mm, the ingot has small reduction deformation, and the grain deformation energy is low, so the ingot cannot fully complete the breaking of the ingot columnar crystal organization and recrystallization. If the single pass reduction amount is ≥10 mm, the deformation is too large, which easily leads to cracks. Therefore, when the single pass deformation reduction amount is controlled to be 5-10 mm, the ingot can ensure sufficient deformation for breaking the columnar crystal organization and recrystallization, and can also avoid the risk of cracks caused by excessive deformation. With the increase of the number of times of upsetting and elongating, the columnar crystal organization is gradually broken, the grain size is gradually reduced, and the single pass reduction amount is gradually increased. In this way, the refined grain organization can fully undergo the recrystallization process. In the above-mentioned upsetting and elongating process, the reduction rate and the elongation rate are controlled to be 0.1-10 / s (such as 1-10 / s). If the reduction rate and the elongation rate are too large, the columnar crystal organization in the ingot cannot fully recrystallize and refine, and the grain organization cannot be fully refined.

[0026] Preferably, in step S4, the Invar alloy steel forging blank has a thickness of 150-300 mm, a length of 4-7 m, and straight angles at the corners.

[0027] Preferably, in step S4, the Invar alloy steel forging blank has a grain size of ≥4 levels, an elongation of ≥40%, and an expansion performance a -180～0℃ 1×10 -6 / ℃-2×10 -6 / ℃.

[0028] In the forging method of the application, the heating furnace used in the heating process of steps S2 and S3 can be a bogie type heating furnace.

[0029] The second aspect of the present application provides a wrought Invar alloy prepared by the forging method for improving plasticity of a large Invar alloy ingot according to the first aspect of the present application, and the Invar alloy has the following components in terms of percentage by weight: C≤0.08%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the balance being iron and inevitable impurities.

[0030] Preferably, the grain size is≥4 levels, the elongation is≥40% (such as 40%-80%), the expansion performance a at the temperature of-180-0 ℃ is -180～0℃ 1×10 -6 / ℃-2×10 -6 / ℃.

[0031] In the prepared Invar alloy, the following conditions are met:

[0032] Mn: Mn is an austenite forming element, which has very strong ability to stabilize austenite phase and can effectively control the low-temperature phase change of martensite. Therefore, the content of Mn in the present application is required to be≤0.5%.

[0033] Si: Si is a deoxidizing agent for molten steel, which can strengthen the matrix and improve the high-temperature oxidation resistance of steel. Appropriate Si can improve the ability of the steel to resist strong acid corrosion, but too high Si will reduce the hot working performance and toughness of the steel and affect the magnetic permeability of the steel. Therefore, the content of Si in the present application is controlled to be≤0.8%.

[0034] Ni: Ni is an austenite forming element, which can improve the strength and corrosion resistance of the steel. However, too high Ni content will reduce the solubility of nitrogen in the steel, inhibit the precipitation of strengthening phase carbon and nitride, affect the strength, and increase the cost. The influence law of Ni content on the expansion performance of Invar alloy in the low-temperature service temperature range and the high-temperature service temperature range is different. With the decrease of Ni content, the Curie temperature point decreases and is closer to the low-temperature service temperature range. When the content of Ni is less than 28% or more than 35%, the expansion performance does not meet the user standard requirements. Therefore, the content of Ni in the present application is controlled to be 28%≤Ni≤35%.

[0035] C: C is an austenite strengthening element, and increasing the content of C can effectively reduce the saturation solubility of nitrogen in the molten steel. In terms of mechanical properties, C increases the strength of the alloy while reducing the toughness of the alloy and the low-temperature expansion performance of the alloy. Therefore, in order to ensure the strength and toughness of the alloy, the content of C in the present application is controlled to be C≤0.08%.

[0036] Mg, Al elements can further remove oxygen elements in invar alloy, improve the hot plasticity of the ingot, but both of them should not be too high. At the same time, the addition of Mg element in invar alloy can refine austenite grains, pin austenite grains in the hot working process, and inhibit the growth of austenite grains; therefore, in the application, Mg is controlled to be less than or equal to 0.1%, and Al is controlled to be less than or equal to 0.20%.

[0037] P, S: as harmful elements, the two types of elements are easy to segregate near the columnar grain boundary of the ingot, and easily have adverse effects on the welding performance of the material, therefore, P and S elements are controlled in a lower range, combined with the P and S content level of the raw material, P is required to be less than or equal to 0.020%, and S is required to be less than or equal to 0.06%.

[0038] Compared with the prior art, the application has the following beneficial effects:

[0039] 1. The application can effectively improve the technical difficulties such as poor hot plasticity of large invar alloy ingot and easy cracking in forging, prepare invar alloy ingot with uniform and fine structure and grain size reaching grade 4 and above, reduce the rejection rate of unqualified products in ingot forging, and further reduce the production cost of products;

[0040] 2. The application adjusts the composition of invar alloy, and controls the parameters of heating process and forging process, so as to improve the hot plasticity of large invar alloy ingot, and solve the technical difficulties such as easy cracking in forging of large invar alloy ingot;

[0041] 3. The invar alloy prepared by the application can be widely applied in the fields of aerospace, national defense and military industry, energy transportation and the like. Due to the excellent hot working performance and excellent expansion performance, the elongation of the forging blank in the high temperature section can reach 80%, the expansion performance a -180～0℃ of the forging blank in the temperature range of-180-0 DEG C can reach 1*10 -6 / ℃-2*10 -6 / ℃; the successful design and development of invar alloy will bring wide economic benefits and wide market application. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is the microstructure morphology diagram of the invar alloy prepared in example 1 of the application;

[0043] Figure 2 It is the microstructure morphology diagram of the forging blank prepared in comparative example 1. DETAILED DESCRIPTION

[0044] The application will be described in detail below in combination with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form.

[0045] Example 1

[0046] The forging method for improving plasticity of the large Invar alloy ingot of the embodiment comprises the following steps:

[0047] Step one: smelting process: pure nickel plate and pure iron are used as Invar alloy raw materials, the content of Ni element in the pure nickel plate is greater than 99.5%, and the total content of impurity elements (Zr, Ti, Cr, Nb, V, etc.) is less than or equal to 0.05%. A 100t electric furnace is used to smelt the molten steel (the composition is shown in Table 1) meeting the internal control composition requirements of Invar alloy, and a 20t Invar alloy ingot mold is used for pouring, which needs to be completed within 22 minutes. After cooling for 30 hours, the Invar alloy ingot is demolded to prepare a 20t Invar alloy ingot with a diameter of 1.1 meters.

[0048] Step two: ingot heating process: the Invar alloy ingot after solidification and cooling is placed in a trolley type heating furnace and heated to 1200℃ at a heating rate of 20℃ / h for heat preservation, and the heat preservation time is controlled to be 12h (satisfying t≥8d+1.5=10.3).

[0049] Step three: upsetting and elongating process: the Invar alloy ingot meeting the heating requirements is taken out for three times of upsetting and elongating; in the first time of upsetting and elongating process, the upsetting amount is 30% of the total height of the ingot, and after the upsetting is completed, the ingot is elongated to the original length of the ingot in three passes, and the reduction amount of each pass is controlled to be 5mm, and the reduction rate is 1 / s. After the above process is completed, the ingot is returned to the heating furnace and heated at 1100℃ for heat preservation, and the heat preservation time is 3h; in the second time of upsetting and elongating process, the upsetting amount is 20% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original length of the ingot, and the elongation is performed in three passes, and the reduction amount of each pass is controlled to be 10mm, and the reduction rate is 1 / s, and the final forging temperature is required to be greater than 800℃. After the above process is completed, the ingot is returned to the heating furnace and heated at 1100℃ for heat preservation, and the heat preservation time is 3h; in the third time of upsetting and elongating process, the upsetting amount is 15% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original length of the ingot, and the elongation is performed in three passes, and the reduction amount of each pass is controlled to be 15mm, and the reduction rate is 1 / s, and the final forging temperature is required to be greater than 750℃. After the above process is completed, the ingot is returned to the trolley type heating furnace and heated at 1100℃ for heat preservation, and the heat preservation time is 3h.

[0050] Step four: forging forming process, the Invar alloy ingot after the third time of heating and heat preservation in step three is forged to a thickness of 300mm and a length of 4m, and the corner of the forging blank must be forged into a right angle, and then the Invar alloy forging blank is obtained after slow cooling to room temperature in air.

[0051] Example 2

[0052] The forging method for improving plasticity of the large Invar alloy ingot of the embodiment comprises the following steps:

[0053] Step one: smelting process: pure nickel plate and pure iron as the raw material of invar alloy, the content of Ni element in pure nickel plate is greater than 99.5%, the total content of impurity elements (Zr, Ti, Cr, Nb, V, etc.) is less than or equal to 0.05%. A 100t electric furnace is used to smelt the liquid steel (the composition is shown in Table 1) meeting the internal composition requirements of invar alloy, and a 20t invar alloy ingot mold is used for pouring, which needs to be completed within 22min, and the ingot is demolded after cooling for 30h to prepare a 20t invar alloy ingot with a diameter of 1.2m.

[0054] Step two: ingot heating process: the invar alloy ingot after solidification and cooling is placed in a trolley type heating furnace and heated to 1100℃ at a heating rate of 40℃ / h for heat preservation, and the heat preservation time is controlled within 13h (satisfying t≥8d+1.5=11.1).

[0055] Step three: upsetting and elongating process: the invar alloy ingot meeting the heating requirements is taken out for three-fire upsetting and elongating; in the first-fire upsetting and elongating process, the upsetting amount is 30% of the total height of the ingot, and after the upsetting is completed, the ingot is elongated to the original height of the ingot in three passes, and the reduction amount of each pass is controlled to be 7mm, and the reduction rate is 3.0 / s, after the above process, the ingot is returned to the heating furnace for heating and heat preservation at 1100℃, and the heat preservation time is 2h; in the second-fire upsetting and elongating process, the upsetting amount is 25% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original length of the ingot in three passes, and the reduction amount of each pass is controlled to be 12mm, and the reduction rate is 1 / s, and the final forging temperature is required to be greater than 850℃, after the above process, the ingot is returned to the heating furnace for heating and heat preservation at 1120℃, and the heat preservation time is 2.5h; in the third-fire upsetting and elongating process, the upsetting amount is 25% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original length of the ingot in three passes, and the reduction amount of each pass is controlled to be 17mm, and the reduction rate is 3 / s, and the final forging temperature is required to be greater than 750℃; after the above process, the ingot is returned to the trolley type heating furnace for heating and heat preservation at 1120℃, and the heat preservation time is 2.5h.

[0056] Step four: forging forming process, the invar alloy ingot after the third-fire heat preservation in step three is forged to a thickness of 250mm and a length of 5m, and the corner of the forging blank must be forged into a right angle, and then air cooling to room temperature to obtain an invar alloy forging blank.

[0057] Example 3

[0058] The forging method for improving the plasticity of large invar alloy ingots of the present embodiment includes the following steps:

[0059] Step one: smelting process: pure nickel plate and pure iron as the raw material of invar alloy, the content of Ni element in pure nickel plate is greater than 99.5%, the total content of impurity elements (Zr, Ti, Cr, Nb, V, etc.) is less than or equal to 0.05%. The 100t electric furnace is used to smelt the liquid steel (the composition is shown in Table 1) meeting the internal control composition requirements of invar alloy, and the 20t invar alloy ingot mold is used for pouring, and the pouring needs to be completed within 22min, and the ingot is demolded after cooling for 30h to prepare a 20t large-size invar alloy ingot with a diameter of 1.1m.

[0060] Step two: ingot heating process: the invar alloy ingot after solidification and cooling is put into a trolley type heating furnace and heated to 1130℃ at a heating rate of 50℃ / h for heat preservation, and the heat preservation time is controlled to be 12h (satisfying t≥8d+1.5=10.3).

[0061] Step three: upsetting and elongating process: the invar alloy ingot meeting the heating requirements is taken out for three-fire upsetting and elongating; in the first-fire upsetting and elongating process, the upsetting amount is 30% of the total height of the ingot, and after the upsetting is completed, the ingot is elongated to the original ingot height, and the elongation is divided into three passes, and the reduction amount of each pass is controlled to be 8mm, and the reduction rate is 5.0 / s, after the above process is completed, the ingot is returned to the heating furnace and heated at 1140℃ for heat preservation, and the heat preservation time is 2.2h; in the second-fire upsetting and elongating process, the upsetting amount is 30% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original ingot length, and the elongation is divided into three passes, and the reduction amount of each pass is controlled to be 13mm, and the reduction rate is 1 / s, and the final forging temperature is required to be greater than 850℃, after the above process is completed, the ingot is returned to the heating furnace and heated at 1140℃ for heat preservation, and the heat preservation time is 2.2h; in the third-fire upsetting and elongating process, the upsetting amount is 30% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original ingot length, and the elongation is divided into three passes, and the reduction amount of each pass is controlled to be 18mm, and the reduction rate is 10 / s, and the final forging temperature is required to be greater than 750℃; after the above process is completed, the ingot is returned to the trolley type heating furnace and heated at 1140℃ for heat preservation, and the heat preservation time is 2.2h.

[0062] Step four: forging forming process, the invar alloy ingot after the third-fire heat preservation in step three is forged to a thickness of 220mm and a length of 5.5m, and the corner of the forging blank must be forged into a right angle, and then the invar alloy forging blank is obtained after slow cooling to room temperature in air.

[0063] Example 4

[0064] The forging method for improving the plasticity of large invar alloy ingot of the embodiment includes the following steps:

[0065] Step one: smelting process: pure nickel plate and pure iron as the raw material of invar alloy, the content of Ni element in pure nickel plate is greater than 99.5%, the total content of impurity elements (Zr, Ti, Cr, Nb, V, etc.) is less than or equal to 0.05%. A 100t electric furnace is used to smelt the liquid steel (the composition is shown in Table 1) meeting the internal composition requirements of invar alloy, and a 15t invar alloy ingot mold is used for pouring. The pouring needs to be completed within 22min, and the ingot is demolded after cooling for 30h to prepare a 15t large-size invar alloy ingot with a diameter of 1.1m.

[0066] Step two: ingot heating process: the invar alloy ingot after solidification and cooling is placed in a trolley type heating furnace and heated to 1150℃ at a heating rate of 60℃ / h for heat preservation. The heat preservation time is controlled to be 12h (satisfying t≥8d+1.5=10.3).

[0067] Step three: upsetting and elongating process: the invar alloy ingot meeting the heating requirements is taken out for three-fire upsetting and elongating; in the first-fire upsetting and elongating process, the upsetting amount is 30% of the total height of the ingot, and after the upsetting is completed, the ingot is elongated to the original ingot height. The elongation is divided into three passes, and the reduction amount of each pass is controlled to be 10mm, and the reduction rate is 8.0 / s. After the above process is completed, the ingot is returned to the heating furnace and heated at 1160℃ for heat preservation, and the heat preservation time is 2h. In the second-fire upsetting and elongating process, the upsetting amount is 40% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original ingot length. The elongation is divided into three passes, and the reduction amount of each pass is controlled to be 14mm, and the reduction rate is 1 / s. The final forging temperature is required to be greater than 850℃. After the above process is completed, the ingot is returned to the heating furnace and heated at 1160℃ for heat preservation, and the heat preservation time is 2h. In the third-fire upsetting and elongating process, the upsetting amount is 30% of the original height of the ingot, and after the upsetting step is completed, the ingot is elongated to the original ingot length. The elongation is divided into three passes, and the reduction amount of each pass is controlled to be 15mm, and the reduction rate is 3 / s. The final forging temperature is required to be greater than 750℃. After the above process is completed, the ingot is returned to the trolley type heating furnace and heated at 1160℃ for heat preservation, and the heat preservation time is 2h.

[0068] Step four: forging forming process, the invar alloy ingot after the third-fire heat preservation in step three is forged to a thickness of 200mm and a length of 6m. The corner of the forging blank must be forged into a right angle. Then, after slow cooling to room temperature in air, an invar alloy forging blank is obtained.

[0069] Example 5

[0070] The forging method for improving the plasticity of large invar alloy ingot of the present embodiment includes the following steps:

[0071] Step one: smelting process: pure nickel plate and pure iron as the raw material of invar alloy, the content of Ni element in pure nickel plate is greater than 99.5%, the total content of impurity elements (Zr, Ti, Cr, Nb, V, etc.) is less than or equal to 0.05%. The 100t electric furnace is used to smelt the liquid steel (the composition is shown in Table 1) meeting the internal composition requirements of invar alloy, and the 25t invar alloy ingot mold is used for pouring, and the pouring needs to be completed within 22min, and the ingot is demolded after cooling for 30h to prepare a 25t large-size invar alloy ingot with a diameter of 1.1m.

[0072] Step two: ingot heating process: the invar alloy ingot after solidification and cooling is placed in a trolley type heating furnace and heated to 1200℃ at a heating rate of 100℃ / h for heat preservation, and the heat preservation time is controlled to be 12h.

[0073] Step three: upsetting and drawing process: the invar alloy ingot meeting the heating requirements is taken out for three-fire upsetting and drawing; in the first-fire upsetting and drawing process, the upsetting amount is 50% of the total height of the ingot, and after the upsetting is completed, the ingot is drawn to the original ingot height, and the drawing is divided into three passes, and the reduction amount of each pass is controlled to be 10mm, and the reduction rate is 10 / s; after the above process is completed, the ingot is returned to the heating furnace and heated at 1100℃ for heat preservation, and the heat preservation time is 3h; in the second-fire upsetting and drawing process, the upsetting amount is 40% of the original height of the ingot, and after the upsetting step is completed, the ingot is drawn to the original ingot length, and the drawing is divided into three passes, and the reduction amount of each pass is controlled to be 15mm, and the reduction rate is 1 / s, and the final forging temperature is required to be greater than 850℃; after the above process is completed, the ingot is returned to the heating furnace and heated at 1200℃ for heat preservation, and the heat preservation time is 2h; in the third-fire upsetting and drawing process, the upsetting amount is 30% of the original height of the ingot, and after the upsetting step is completed, the ingot is drawn to the original ingot length, and the drawing is divided into three passes, and the reduction amount of each pass is controlled to be 15mm, and the reduction rate is 3 / s, and the final forging temperature is required to be greater than 750℃; after the above process is completed, the ingot is returned to the trolley type heating furnace and heated at 1200℃ for heat preservation, and the heat preservation time is 1h.

[0074] Step four: forging forming process, the invar alloy ingot after heat preservation in step three is forged to a thickness of 150mm and a length of 7m, and the corner of the forging blank must be forged into a right angle, and then slowly cooled to room temperature in air to obtain an invar alloy forging blank.

[0075] Comparative Example 1

[0076] The forging method of the invar alloy of the comparative example is as follows:

[0077] Step one: smelting process: pure nickel plate and pure iron as the raw material of the invar alloy, using 100t electric furnace smelting liquid steel (composition see table 1) to meet the standard internal control composition requirements, and using 20t invar alloy ingot mold for pouring, the pouring needs to be completed within 25min, and the ingot is demoulded after cooling for 30h to prepare large-size invar alloy ingot.

[0078] Step two: ingot heating process: the solidified and cooled invar alloy ingot is placed in a trolley type heating furnace and heated to 1100℃ at a heating rate of 120℃ / h for heat preservation, and the heat preservation time is controlled within 15h.

[0079] Step three: upsetting and elongation process: the invar alloy ingot meeting the heating requirements is taken out, the first upsetting is performed according to the upsetting amount of 60% of the total height of the ingot, after the upsetting step is completed, the ingot is elongated to the original ingot length, and the elongation is divided into three passes, and the pass reduction amount is controlled to be 10mm, and the reduction rate is 1 / s.

[0080] Step four: return to furnace and heat preservation process: the ingot elongated by upsetting in step three is returned to the trolley type heating furnace and heated and preserved at 1100℃, and the heat preservation time is 3h.

[0081] Step five: forging forming process: after the heat preservation in step four reaches the specified time, the ingot is taken out of the furnace and forged to a thickness of 150-300mm, a length of 4-7m, and the corner of the ingot must be forged into a right angle.

[0082] Step six: the finished product ingot is cooled by air cooling.

[0083] Comparative example 2

[0084] The method of this comparative example adopts the method of example 1, the difference is that the upsetting amount in the three-pass upsetting and elongation process of step three is 26%, 17%, and 12% of the total height of the ingot, respectively.

[0085] Comparative example 3

[0086] The method of this comparative example adopts the method of example 1, the difference is that the upsetting amount in the three-pass upsetting and elongation process of step three is 53%, 43%, and 40% of the total height of the ingot, respectively.

[0087] Comparative example 4

[0088] The method of this comparative example adopts the method of example 1, the difference is that the pass reduction amount in the three-pass upsetting and elongation process of step three is 12mm, 18mm, and 25mm, respectively.

[0089] Comparative example 5

[0090] The method of the present comparative example adopts the method of Example 1, except that the pass reduction in the three-pass upsetting and elongating process of Step Three is 4 mm, 8 mm, and 12 mm, respectively.

[0091] Comparative Example 6

[0092] The method of the present comparative example adopts the method of Example 1, except that in the melting process of Step One, the molten steel meets the Inconel alloy internal control composition requirements shown in Table 1.

[0093] Comparative Example 7

[0094] The method of the present comparative example adopts the method of Example 1, except that in the melting process of Step One, the molten steel meets the Inconel alloy internal control composition requirements shown in Table 1.

[0095] Table 1 Chemical composition of molten steel and Inconel alloy forging billets (wt%)

[0096]

[0097] Table 2 Performance indicators of Inconel alloy forging billets

[0098]

[0099] Figure 1 The grain structure morphology of the Inconel alloy forging billet prepared in Example 1 can be seen from the figure, which is more refined and uniform, and cracking is less likely to occur during forging, and the hot working plasticity is good. The grain size of the Inconel alloy forging billet reaches Grade 4, and there is no mixed crystal and abnormally grown grain. The elongation of the forging billet sample at room temperature is 40%.

[0100] Figure 2 The microstructure morphology of the forging billet prepared in Comparative Example 1 can be seen from the figure, which is coarse, and cracking is likely to occur during forging. The grain size of the Inconel alloy forging billet is Grade 2, and part of the grain size is Grade 1. The elongation of the mechanical properties of the forging billet sample at room temperature is 20%.

[0101] The Inconel alloy forging billets forged in Examples 1-5 and Comparative Examples 1-7 are tested for grain size and elongation. The specific performance is shown in Table 2. The Inconel alloy forging billets prepared in Examples 1-5 have a grain size of Grade 4-6 and an elongation of 40%-60%. The forged slabs are all formed without cracking and other quality problems, and the expansion performance is a -180～0℃ 1.2 x 10 -6 / ℃-1.6 x 10 -6 / ℃, which meets the use requirements -180～0℃ ≤2 x 10 -6℃. The grain refinement grade and elongation of the invar alloy forging blank prepared in the example are obviously better than those of the comparative example 1, because the upsetting and elongating process is performed three times in the example, and the process parameters are more in line with the hot working characteristics of the invar alloy. In the full upsetting and elongating process, the forging blank structure grains are fully refined, and the hot working plasticity is greatly improved.

[0102] It can be known from the example 1 and the comparative examples 2 and 3 that the upsetting amount of the comparative example 2 is obviously less than the range specified in the application, resulting in that the internal structure of the ingot is not fully broken, and the final ingot does not crack, but the grain size of the forging blank structure is poor, the coarse grains are obvious, and the core grain structure reaches level 2. The upsetting amount of each fire of the comparative example 3 exceeds the range specified in the application, and the forging blank cracks in the second deformation due to the excessive deformation, and cannot continue to deform.

[0103] It can be known from the example 1 and the comparative examples 4 and 5 that the deformation amount of the comparative example 4 obviously exceeds the range specified in the application, resulting in that the ingot cracks in the second forging, and cannot continue to deform; the deformation amount of the comparative example 5 does not exceed the range specified in the application, but the grain structure reaches level 2, and there is part of mixed grains.

[0104] It can be known from the example 1 and the comparative examples 6 and 7 that the chemical compositions of the comparative examples 6 and 7 both exceed the range specified in the application, resulting in that the expansion performance of the alloy is obviously deteriorated, and cannot meet the performance index requirement of a -180～0℃ ≤2×10 -6 / ℃.

[0105] In summary, the invar alloy prepared in the application can be widely used in the fields of aerospace, national defense and military industry, energy transportation and the like. Due to the excellent hot working performance and excellent expansion performance, the successful design and development of the alloy will bring extensive economic benefits, and the market application is wide.

[0106] It should be noted that the above examples are only used to illustrate the technical solutions of the application but not limit the application. Although the application is 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 the claims of the application.

Claims

1. A forging method for improving the plasticity of a large-sized Invar alloy ingot, characterized by, The method comprises the following steps: S1, a smelting process, using an electric furnace to smelt a molten steel meeting the internal control component requirements of Invar alloy, and casting to obtain a large Invar alloy steel ingot with a weight of 15-25 t; The molten steel meets the following internal control component requirements of Invar alloy: C≤0.08%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the balance being iron and inevitable impurities, in terms of percentage by weight; S2, a heating process, heating the cold Invar alloy steel ingot to 1000-1200 ℃ and keeping the temperature for more than or equal to 10 h; The keeping time meets the following formula: t≥8d+1.5 Wherein, t is time, in units of h; and d is the diameter of the Invar alloy steel ingot, in units of m; S3, a upsetting and drawing process, upsetting and drawing the heated Invar alloy steel ingot for three times, each time upsetting by 15-50% of the total height of the Invar alloy steel ingot, and then drawing to the original height of the Invar alloy steel ingot, and each time returning to the heating furnace for heating and keeping, and the final forging temperature of each time of upsetting and drawing is greater than or equal to 750 ℃; In the three times of upsetting and drawing, the upsetting amount of the first, second and third times is 30-50%, 20-40% and 15-35% of the total height of the Invar alloy steel ingot, respectively. Step S3 comprises the following processes: S31, first time upsetting and drawing, upsetting the heated Invar alloy steel ingot, and then drawing to the original height of the Invar alloy steel ingot, the single pass reduction is 5-10 mm, the final forging temperature is greater than or equal to 750 ℃, and then returning to the heating furnace for heating and keeping at 1100-1200 ℃ for 2-3 h; S32, second time upsetting and drawing, the single pass reduction is 10-15 mm, the final forging temperature is greater than or equal to 750 ℃, and after upsetting and drawing, returning to the heating furnace for heating and keeping at 1100-1200 ℃ for 1-2 h; S33, third time upsetting and drawing, the single pass reduction is 15-20 mm, the final forging temperature is greater than or equal to 750 ℃, and after upsetting and drawing, returning to the heating furnace for heating and keeping at 1100-1200 ℃ for 1-2 h; S4, forging forming, forging the Invar alloy steel ingot after the last time of heating and keeping in step S3 to the specified size, and then slowly cooling to room temperature in air to obtain an Invar alloy steel forging blank; The invar alloy steel forging billet has a grain size of ≥4 levels, an elongation of ≥40%, and expansion performance a at -180-0 ℃ of 1×10 -180～0℃ -2 -6 / ℃. -6 / ℃.

2. The forging method for improving the plasticity of a large-sized Hadfield steel ingot according to claim 1, characterized by, In step S1, in the smelting process, pure nickel plates and pure iron are used as raw materials, the content of Ni element in the pure nickel plates is greater than 99.5%, and the total content of impurity elements is less than or equal to 0.05%.

3. The forging method for improving the plasticity of large Invar alloy steel ingots as described in claim 1, characterized in that, In step S2, in the heating process, the heating rate is 20-100 ℃ / h.

4. The forging method for improving the plasticity of large Invar alloy steel ingots as described in claim 1, characterized in that, In step S4, the thickness of the Invar alloy steel forging blank is 150-300 mm, the length is 4-7 m, and the corner of the forging blank is a right angle.

5. An Invar alloy prepared by a forging method for improving the plasticity of large Invar alloy steel ingots as described in any one of claims 1 to 4, characterized in that, The components of the Invar alloy are as follows in terms of percentage by weight: C≤0.08%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the balance being iron and inevitable impurities.

6. The inconel alloy as claimed in claim 5, wherein, Its performance is as follows: grain size ≥ 4 levels, elongation ≥ 40%, expansion performance a at -180~0 ℃ temperature -180～0℃ 1 x 10 -6 / ℃~2 x 10 -6 / ℃.

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