A method for preparing high-performance Inconel 718 alloy strip based on thin strip continuous casting

Abstract

The application discloses a high-performance Inconel 718 alloy strip preparation method based on thin strip continuous casting, which comprises the following steps: smelting alloy liquid according to a set component; the alloy liquid is subjected to rapid solidification forming to obtain a cast strip with a thickness of 1.5-2.5 mm; the cast strip is directly subjected to pre-rolling treatment at room temperature, and short-time solid solution treatment is combined to accurately control the size, distribution and morphology of a Laves phase; the solid solution strip is subjected to secondary cold rolling and recrystallization treatment; and finally, two-stage aging treatment is carried out to obtain an Inconel 718 alloy strip with high strength and high plasticity. The Inconel 718 alloy strip is directly prepared by using the thin strip continuous casting near-net-shape forming technology, and the production process of the Inconel 718 alloy strip is significantly simplified. In addition, the sub-rapid solidification can significantly inhibit solidification segregation, refine the solidification structure and simplify the homogenization process, and finally realize the efficient preparation of the Inconel 718 alloy strip.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials and relates to a method for preparing high-performance Inconel 718 alloy plates and strips based on thin strip continuous casting. Background Technology

[0002] Inconel 718 alloy is the most widely used nickel-based wrought superalloy. Inconel 718 alloy sheets and strips are widely used in aerospace, nuclear energy, and petrochemical industries, and are crucial alloy materials for manufacturing key components such as honeycomb seals, guide vanes, casings, heating grids, and baffles. Developing efficient, high-quality, and low-energy-consumption production processes for superalloy sheets is of great significance for promoting the development of my country's industrial sector.

[0003] The current manufacturing process for Inconel 718 alloy sheet and strip involves: duplex or triple melting to produce alloy ingots, high-temperature, long-duration homogenization treatment to eliminate the Laves phase, forging, hot rolling, cold rolling, heat treatment, and straightening. This process is highly complex, with a long production line, and it is difficult to guarantee the stability of alloy quality. Furthermore, Inconel 718 alloy contains a large amount of refractory alloying elements such as Nb and Mo, resulting in a high degree of alloying. Conventional duplex or triple melting processes have low cooling rates, approximately 0.01–0.33 °C / s. This high degree of alloying combined with a low cooling rate leads to severe solidification segregation in the ingots, even producing defects such as "black spots" and "white spots," significantly deteriorating ingot quality. Additionally, at the end of solidification, Nb atoms aggregate in the dendrites to form large-sized brittle Laves phases, reducing the alloy's ductile processing properties. Inconel 718 alloy ingots typically require a two-stage high-temperature, long-duration homogenization treatment to eliminate elemental segregation before subsequent processing and deformation. Therefore, simplifying the production process of Inconel 718 alloy sheet and strip, suppressing element segregation, and refining the Laves phase are key to achieving stable mass production of high-temperature alloy sheet and strip.

[0004] Chinese Patent 202111604538 describes a method for controlling the microstructure and shape of high-temperature alloy plates for aerospace applications. This method utilizes a three-stage melting process to prepare alloy ingots, followed by a series of processes including homogenization annealing, forging, multi-pass hot rolling, heat treatment, grinding, and polishing to obtain high-temperature alloy plates and strips. The production process is extremely complex. Chinese Patent Application 202311477815 describes a method for preparing nickel-based high-temperature alloy plates and strips, which involves pressing nickel-based high-temperature alloy powder into slabs. This method requires prior powder preparation and subsequent sintering and densification treatment. Furthermore, the powder melting temperature is high, and the sintering time is long, making it difficult to achieve efficient and short-process preparation of high-temperature alloy plates and strips. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting.

[0006] This invention provides a method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting, comprising:

[0007] (1) The alloy liquid is smelted according to the set composition, which contains, by weight percentage, Ni 50-55%, Cr 17-21%, Mo 2.8-3.3%, Nb 4.75-5.5%, Al 0.2-0.8%, Ti 0.65-1.15%, Co≤1%, C≤0.8%, Si≤0.35%, P≤0.015%, B≤0.006%, with the balance being Fe and unavoidable impurities;

[0008] (2) Thin strip continuous casting process: The alloy liquid is poured into the tundish, and then the alloy liquid is poured into the triangular molten pool composed of two counter-rotating casting rolls and side sealing plates. After casting and rolling, a casting strip with a thickness of 1.5 to 2.5 mm is obtained. After the casting strip exits the rolls, it is water cooled to room temperature.

[0009] (3) Pre-cooling rolling: The cast strip is pre-cooled directly at room temperature;

[0010] (4) Solution treatment: The pre-cooled rolled strip is solution treated at 1050-1150℃ for 1-30 minutes;

[0011] (5) Secondary cold rolling: The solution-treated strip is subjected to secondary cold rolling;

[0012] (6) Recrystallization treatment: The secondary cold-rolled strip is held at 1010℃ for 3 minutes for recrystallization treatment, and then air-cooled to room temperature;

[0013] (7) Two-stage aging treatment: The recrystallized strip is kept at 720°C for 8 hours, then furnace cooled to 620°C at a rate of 50-55°C / h, kept at 720°C for 8 hours, and then air cooled to room temperature to obtain Inconel 718 alloy strip with high strength and high plasticity.

[0014] Furthermore, the superheat of the intermediate ladle in step (2) is controlled at 40-60°C.

[0015] Furthermore, the reduction in the pre-cooling rolling in step (3) is 25-40%.

[0016] Furthermore, the total reduction in the secondary cold rolling in step (5) is 60-80%.

[0017] Furthermore, the Inconel 718 alloy sheet and strip have a tensile strength of over 1400 MPa and an elongation of over 15% under room temperature tensile conditions; and a tensile strength of over 1150 MPa and an elongation of over 18% under 650°C tensile conditions.

[0018] The present invention provides a method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting, which has the following beneficial effects:

[0019] 1. The alloy sheet and strip preparation method of the present invention omits the forging, hot rolling and reheating processes in the conventional preparation process, and directly obtains Inconel 718 alloy sheet and strip.

[0020] 2. The sub-rapid solidification characteristics of thin strip continuous casting can significantly suppress the segregation of alloying elements, inhibit the growth of harmful Laves phases, and refine the solidification structure.

[0021] 3. The alloy strip preparation method of the present invention can directly perform cold rolling deformation treatment on Inconel 718 alloy casting strip without high temperature and long time homogenization treatment.

[0022] 4. In the alloy plate and strip preparation method of the present invention, the pre-cooled rolled plate and strip only needs to be solution treated at 1150℃ / 10min to achieve uniform distribution of alloy elements, which significantly simplifies the homogenization process.

[0023] 5. The invented method for preparing alloy plates and strips can effectively regulate the characteristic parameters of the Laves phase, control the morphology and size of the Laves phase precipitation, and transform the traditional harmful large-size irregular Laves phase into a beneficial submicron-sized granular Laves phase.

[0024] 6. The Inconel 718 alloy sheet and strip prepared by the method of the present invention have a tensile strength of more than 1400 MPa and an elongation of more than 15% under room temperature tensile conditions; and a tensile strength of more than 1150 MPa and an elongation of more than 18% under 650℃ tensile conditions. Attached Figure Description

[0025] Figure 1 A flowchart of a method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting according to the present invention;

[0026] Figure 2(a) shows the Laves phase morphology of the pre-cooled rolled strip;

[0027] Figure 2(b) shows the Laves phase morphology after 1 min of solid solution treatment;

[0028] Figure 2(c) shows the Laves phase morphology after 5 min of solid solution treatment;

[0029] Figure 2(d) shows the morphology of the Laves phase after 10 min of solid solution treatment;

[0030] Figure 3(a) shows the effect of Laves on the distribution of major elements in the Inconel 718 alloy after 1 min of solution treatment;

[0031] Figure 3(b) shows the effect of Laves on the distribution of major elements in the Inconel 718 alloy after 5 min of solution treatment;

[0032] Figure 3(c) shows the effect of Laves on the distribution of major elements in the Inconel 718 alloy after 10 min of solution treatment;

[0033] Figure 4(a) shows the room temperature tensile curve;

[0034] Figure 4(b) shows the high-temperature tensile curve. Detailed Implementation

[0035] The preparation method of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0036] Example 1

[0037] like Figure 1 The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting in this embodiment is carried out according to the following steps:

[0038] (1) The steel is smelted according to the set composition, which contains, by weight percentage, Ni 50%, Cr 18%, Mo 3.1%, Nb 5.2%, Al 0.3%, Ti 0.75%, Co 0.9%, C 0.6%, Si 0.31%, P 0.012%, B 0.005%, with the balance being Fe and unavoidable impurities.

[0039] (2) Thin strip continuous casting process: The alloy liquid is poured into the tundish and the superheat is controlled at +50℃. Then the alloy liquid is poured into a triangular molten pool composed of two counter-rotating casting rolls and side sealing plates. After casting and rolling, a casting strip with a thickness of 1.8mm is obtained. After the casting strip exits the rolls, it is water cooled to room temperature.

[0040] (3) Pre-cooling rolling: The cast strip is pre-cooled directly at room temperature, with a reduction of 40%.

[0041] (4) Solution treatment: The pre-cooled rolled strip was solution treated at 1150℃ for 1 min, 5 min and 10 min respectively; the Laves phase precipitation was as follows Figures 2(a)-2(d) As shown.

[0042] Figure 2(a) shows the Laves phase morphology of the pre-cooled rolled strip, where a large number of elongated Laves phases are still retained. Figure 2(b) shows the Laves phase morphology after 1 min of solution treatment; after 1 min of holding, the Laves phase is still mainly elongated. Figure 2(c) shows the Laves phase morphology after 5 min of solution treatment; after 5 min of holding, the Laves phase evolves into granular form. Figure 2(d) shows the Laves phase morphology after 10 min of solution treatment; after 10 min of holding, the Laves phase completely disappears, leaving a small amount of carbides.

[0043] (5) Secondary cold rolling: The solution-treated strip undergoes secondary cold rolling with a total reduction of 60% and a final thickness of 0.8 mm;

[0044] (6) Recrystallization treatment: The secondary cold-rolled strip is held at 1010℃ for 3 minutes for recrystallization treatment, and then air-cooled to room temperature;

[0045] (7) Two-stage aging treatment: The recrystallized strip is held at 720℃ for 8 hours, then furnace cooled to 620℃ at a rate of 50-55℃ / h, and held for another 8 hours before being air-cooled to room temperature. This yields Inconel 718 alloy strip with both high strength and high plasticity.

[0046] Figure 3(a) shows the effect of Laves on the distribution of major elements in Inconel 718 alloy after 1 min of solution treatment; Figure 3(b) shows the effect of Laves on the distribution of major elements in Inconel 718 alloy after 5 min of solution treatment; Figure 3(c) shows the effect of Laves on the distribution of major elements in Inconel 718 alloy after 10 min of solution treatment.

[0047] Under room temperature tensile conditions, the tensile strength of the specimen was 1543 MPa, corresponding to an elongation of 19%. Under tensile conditions at 650℃, the tensile strength of the specimen was 1276 MPa, corresponding to an elongation of 22%. The corresponding tensile curves are shown below. Figures 4(a)-4(b) As shown in Figure 4(a), the room temperature tensile curve is shown; Figure 4(b) is the high temperature tensile curve. Specific Implementation Example 2

[0049] The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting in this embodiment is carried out according to the following steps:

[0050] (1) The molten steel is smelted according to the set composition, which contains, by weight percentage, Ni 52%, Cr 19%, Mo 2.9%, Nb 4.9%, Al 0.4%, Ti 0.98%, Co 0.7%, C 0.5%, Si 0.29%, P 0.011%, B 0.003%, with the balance being Fe and unavoidable impurities;

[0051] (2) Thin strip continuous casting process: The alloy liquid is poured into the tundish and the superheat is controlled at +40℃. Then the alloy liquid is poured into a triangular molten pool composed of two counter-rotating casting rolls and side sealing plates. After casting and rolling, a casting strip with a thickness of 1.9mm is obtained. After the casting strip exits the rolls, it is water cooled to room temperature.

[0052] (3) Pre-cooling rolling: The cast strip is pre-cooled directly at room temperature, with a reduction of 25%;

[0053] (4) Solution treatment: The pre-cooled rolled strip was solution treated at 1100℃ for 1 min, 5 min and 30 min respectively;

[0054] (5) Secondary cold rolling: The solution-treated strip undergoes secondary cold rolling with a total reduction of 70% and a final thickness of 0.6 mm;

[0055] (6) Recrystallization treatment: The secondary cold-rolled strip is held at 1010℃ for 3 minutes for recrystallization treatment, and then air-cooled to room temperature;

[0056] (7) Two-stage aging treatment: The recrystallized strip is kept at 720°C for 8 hours, then furnace cooled to 620°C at a rate of 50-55°C / h, kept at 720°C for 8 hours, and then air cooled to room temperature to obtain Inconel 718 alloy strip with high strength and high plasticity.

[0057] Under room temperature tensile conditions, the tensile strength of the specimen is 1450 MPa, and the elongation is over 18%. Under 650℃ tensile conditions, the tensile strength of the specimen is 1200 MPa, and the elongation is over 21%. Specific Implementation Example 3

[0059] The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting in this embodiment is carried out according to the following steps:

[0060] (1) The molten steel is smelted according to the set composition, which contains, by weight percentage, Ni 54%, Cr 20%, Mo 3.1%, Nb 5.1%, Al 0.7%, Ti 0.91%, Co 0.5%, C 0.4%, Si 0.21%, P 0.011%, B 0.005%, with the balance being Fe and unavoidable impurities;

[0061] (2) Thin strip continuous casting process: The alloy liquid is poured into the tundish and the superheat is controlled at +40℃. Then the alloy liquid is poured into a triangular molten pool composed of two counter-rotating casting rolls and side sealing plates. After casting and rolling, a casting strip with a thickness of 2mm is obtained. After the casting strip exits the rolls, it is water cooled to room temperature.

[0062] (3) Pre-cooling rolling: The cast strip is pre-cooled and rolled directly at room temperature, with a reduction of 30%;

[0063] (4) Solution treatment: The pre-cooled rolled strip was solution treated at 1050℃ for 1 min, 5 min and 30 min respectively;

[0064] (5) Secondary cold rolling: The solution-treated strip undergoes secondary cold rolling with a total reduction of 80% and a final thickness of 0.4 mm;

[0065] (6) Recrystallization treatment: The secondary cold-rolled strip is held at 1010℃ for 3 minutes for recrystallization treatment, and then air-cooled to room temperature;

[0066] (7) Two-stage aging treatment: The recrystallized strip is kept at 720°C for 8 hours, then furnace cooled to 620°C at a rate of 50-55°C / h, kept at 720°C for 8 hours, and then air cooled to room temperature to obtain Inconel 718 alloy strip with high strength and high plasticity.

[0067] Under room temperature tensile conditions, the tensile strength of the specimen is 1600 MPa, and the elongation is over 15%. Under 650℃ tensile conditions, the tensile strength of the specimen is 1250 MPa, and the elongation is over 18%.

[0068] This invention discloses a method for preparing high-performance Inconel 718 alloy sheet and strip based on thin-strip continuous casting, characterized by sub-rapid solidification and a short process. Molten metal is directly poured into a triangular molten pool consisting of a pair of counter-rotating water-cooled casting rolls and side sealing plates, rapidly solidifying within 0.1 seconds to form an alloy casting strip with a thickness of 1.5–2.5 mm. The alloy casting strip can then be subjected to only one small deformation step to obtain the desired thickness of alloy material, significantly simplifying the preparation process of Inconel 718 alloy sheet and strip using traditional methods. Furthermore, the solidification rate of the thin-strip continuous casting Inconel 718 alloy is much higher than that of traditional processes. The sub-rapid solidification characteristic significantly suppresses elemental segregation and refines the secondary dendrite spacing, thereby reducing the size of the harmful Laves phase. The alloy casting strip can then undergo cold deformation directly without homogenization treatment.

[0069] The innovations of this invention are as follows: 1) High-temperature alloy thin strips are directly prepared using near-net-shape thin-strip casting technology, which is significantly different from traditional duplex or triple smelting or powder metallurgy methods for preparing high-temperature alloys. 2) The solidification rate of thin-strip continuous casting technology can reach 300-1000℃ / s. Sub-rapid solidification can significantly suppress element segregation, refine the solidification structure, and ultimately shorten the homogenization process. In this invention, the Inconel 718 alloy strip can be directly cold-rolled without homogenization treatment. 3) The precipitation state of the Laves phase can be precisely controlled by combining pre-deformation with solution treatment. Long, large-sized Laves phases can severely damage the mechanical properties of materials and reduce the plasticity of alloys. By transforming the brittle, long, thin-strip Laves phase into beneficial submicron-sized granular Laves phases through subsequent treatment, the damaging effect of Laves phases on plasticity can be significantly weakened. 4) Based on grain refinement, solid solution strengthening, and precipitation strengthening, pre-cold rolling combined with short-time solid solution treatment enables thin-strip continuously cast Inconel 718 alloy plates to possess both high strength and high plasticity. In this invention, the room temperature tensile strength and elongation of the thin-strip continuously cast Inconel 718 alloy can reach 1543 MPa and 19%, respectively, and the high temperature tensile strength can reach 1280 MPa, while maintaining excellent elongation of approximately 21%.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the ideas of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting, characterized in that, include: (1) The alloy liquid is smelted according to the set composition, which contains, by weight percentage, Ni 50-55%, Cr 17-21%, Mo 2.8-3.3%, Nb 4.75-5.5%, Al 0.2-0.8%, Ti 0.65-1.15%, Co≤1%, C≤0.8%, Si≤0.35%, P≤0.015%, B≤0.006%, with the balance being Fe and unavoidable impurities; (2) Thin strip continuous casting process: The alloy liquid is poured into the tundish, and then the alloy liquid is poured into the triangular molten pool composed of two counter-rotating casting rolls and side sealing plates. After casting and rolling, a casting strip with a thickness of 1.5 to 2.5 mm is obtained. After the casting strip exits the rolls, it is water cooled to room temperature. (3) Pre-cooling rolling: The cast strip is pre-cooled directly at room temperature; (4) Solution treatment: The pre-cooled rolled strip is solution treated at 1050-1150℃ for 1-30 minutes; (5) Secondary cold rolling: The solution-treated strip is subjected to secondary cold rolling; (6) Recrystallization treatment: The secondary cold-rolled strip is held at 1010℃ for 3 minutes for recrystallization treatment, and then air-cooled to room temperature; (7) Two-stage aging treatment: The recrystallized strip is kept at 720°C for 8 hours, then furnace cooled to 620°C at a rate of 50-55°C / h, kept at 720°C for 8 hours, and then air cooled to room temperature to obtain Inconel 718 alloy strip with high strength and high plasticity.

2. The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting as described in claim 1, characterized in that, The superheat of the intermediate ladle in step (2) is controlled at 40-60°C.

3. The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting as described in claim 1, characterized in that, The reduction in the pre-cooling rolling in step (3) is 25-40%.

4. The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting as described in claim 1, characterized in that, The total reduction in the secondary cold rolling in step (5) is 60-80%.

5. The method for preparing high-performance Inconel 718 alloy sheet and strip based on thin strip continuous casting as described in claim 1, characterized in that, The Inconel 718 alloy sheet and strip have a tensile strength of over 1400 MPa and an elongation of over 15% under room temperature tensile conditions; and a tensile strength of over 1150 MPa and an elongation of over 18% under 650°C tensile conditions.

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