Ultra-high specific strength ultra-high strength steel and preparation method thereof

Abstract

The present application relates to the technical field of alloy steel, and specifically discloses an ultra-high specific strength ultra-high strength steel and a preparation method thereof. The ultra-high specific strength ultra-high strength steel provided in the present application, in terms of weight percentage, has an elemental composition of: C: 0.25-0.40%, Cr: 1-3%, Mo: 2-4%, Ni: 10-16%, Co: 6-12%, Al: 0-3%, and the remainder is Fe and unavoidable impurities. The present application also provides a preparation method for the above-mentioned ultra-high specific strength ultra-high strength steel. The technical solution provided in the present application can be used to obtain ultra-high specific strength ultra-high strength steel with a tensile strength of more than 3000MPa.

Description

Technical Field

[0001] The present application relates to the technical field of alloy steel, and in particular to an ultra-high specific strength ultra-high strength steel and a preparation method thereof. Background Art

[0002] Ultra-high strength steel is widely used in key load-bearing components such as aerospace, energy and transportation, and mechanical equipment, such as engine shafts, aircraft landing gear, and space station manipulators, which are often subjected to cyclic loads during service. As the core of the engine, the aerospace power shaft is subjected to strong strain fatigue during service, and studies have shown that its strain fatigue cracking is more related to the strength and plasticity of the material. Since 2000, secondary hardening ultra-high strength steels represented by GE1014 and ML340 have shown high strength, high toughness, high plasticity and excellent strain fatigue performance, and have become the main selection materials for advanced aerospace engine power shafts, such as the British Rolls-Royce Trent 1000 engine and the French LEAP-1 engine low-pressure turbine shaft. However, the strength of existing power shaft materials is around 2GPa. Further improving the strength is the future development trend of aerospace power shaft materials, which is of great significance for the integration of engine power shaft-tooth-key and the miniaturization and lightweighting of engines. From the perspective of strengthening and toughening methods, compared with secondary hardening type ultra-high strength steel, the strengthening method of maraging steel is more direct, and maraging steel with strength above 3GPa has also been reported. However, its excessive reliance on precipitation strengthening is bound to affect its fatigue performance. Therefore, it is urgent to develop 3GPa-level secondary hardening type ultra-high strength steel. Summary of the invention

[0003] In view of the problem that the existing secondary hardening ultra-high strength steel is insufficient in strength and cannot meet the future development trend of aerospace power shaft materials, the present application provides an ultra-high specific strength ultra-high strength steel and a preparation method thereof.

[0004] The present application provides an ultra-high specific strength and ultra-high strength steel. The element composition of the ultra-high specific strength and ultra-high strength steel is, by weight percentage, C: 0.25-0.40%, Cr: 1-3%, Mo: 1-4%, Ni: 10-18%, Co: 6-12%, Al: 0-3%, and the balance is Fe and unavoidable impurities.

[0005] Measured in percentage by weight, the C content in the ultra-high specific strength ultra-high strength steel provided in this application is 0.25-0.40%. C is the most important strengthening element, and the C content directly determines the strength of martensite. For secondary hardening ultra-high strength steel, the M2C carbide formed during the aging process provides a significant strengthening effect. Therefore, a C content higher than 0.25% is the key to ensuring the strength of the material, and a C content that is too low will result in insufficient material strength. However, a high C content (>0.40%) will significantly deteriorate the toughness and plasticity of the material, so this application controls the C content to 0.25-0.40%.

[0006] According to the weight percentage, the Cr content in the ultra-high specific strength ultra-high strength steel provided by the present application is 1-3%. Cr can effectively improve the hardenability, and as a strong carbide forming element, it replaces the Mo element in M2C, promotes the secondary hardening reaction, and improves the strength of the material. However, if the Cr content is too high, the volume fraction of the precipitated phase will be too high, and high Cr is prone to cause the transformation of the carbide type. Therefore, the present application controls the Cr content to 1-3%.

[0007] According to the weight percentage, the Mo content in the ultra-high specific strength ultra-high strength steel provided by the present application is 1-4%. Mo is the main forming element of M2C carbide, providing a strong secondary hardening effect. The higher the Mo content, the higher the secondary hardening peak value. Through the mutual cooperation of Mo, Cr and C elements, a fine and dispersed nano-precipitate phase can be obtained. If the Mo content is too high, it is easy to cause too much volume fraction of the precipitate phase, which damages the toughness and plasticity of the material. Therefore, the present application controls the Mo content to 1-4%.

[0008] According to the percentage by weight, the Ni content in the ultra-high specific strength ultra-high strength steel provided in the present application is 10-18%. Ni is an austenite stabilizing element and is also the main toughening element in the present application. Ni can toughen the martensite matrix, improve the resistance of martensite to cleavage, and thus improve toughness. During the aging process of the secondary hardened steel, good toughness is also guaranteed by forming a Ni-rich film-like austenite between the martensite laths. In addition, Ni and Al can be combined to form intermetallic compounds in the present application to improve the strength of the material. In general, if the Ni content is too low, it is easy to cause the material strength to be too high and the toughness and plasticity to be poor. If the Ni content is too high, it is easy to form too much austenite, resulting in insufficient material strength. Therefore, the present application controls the Ni content to 10-18%.

[0009] According to the weight percentage, the Co content in the ultra-high specific strength ultra-high strength steel provided in the present application is 6-12%. Co does not form a precipitate phase in the steel, and improves the strength of the steel through solid solution strengthening. Co can delay the dislocation recovery of the martensitic matrix during the tempering process, and strongly promote the secondary hardening effect. However, too high a Co content will damage the toughness and plasticity, so the present application controls the Co content to 6-12%.

[0010] According to the weight percentage, the Al content in the ultra-high specific strength ultra-high strength steel provided in the present application is 0-3%. Al is a strong deoxidizer, and the addition of a certain amount of Al can significantly reduce the O content in the molten steel. In the present invention, Al is also a strengthening element, which forms an intermetallic compound by combining with Ni and forms a composite precipitation strengthening with M2C, but if the Al content is too high, the toughness and plasticity of the material will deteriorate sharply, so the Al content in the present application is controlled to be 0-3%.

[0011] Preferably, the element composition of the ultra-high specific strength and ultra-high strength steel is, by weight percentage, C: 0.29-0.35%, Cr: 1.5-2.5%, Mo: 1.5-3.5%, Ni: 12-15%, Co: 8-11%, Al: 1-2.5%, and the remainder is Fe and unavoidable impurities.

[0012] In a specific embodiment, the element composition of the ultra-high specific strength and ultra-high strength steel can be: C: 0.29%, Cr: 2.00%, Mo: 2.18%, Ni: 14.36%, Co: 9.99%, Al: 2.25%, and the remainder is Fe and unavoidable impurities.

[0013] In a specific embodiment, the element composition of the ultra-high specific strength and ultra-high strength steel can be: C: 0.30%, Cr: 2.20%, Mo: 2.00%, Ni: 12.37%, Co: 8.02%, Al: 2.26%, and the remainder is Fe and unavoidable impurities.

[0014] In a specific embodiment, the element composition of the ultra-high specific strength and ultra-high strength steel can be: C: 0.32%, Cr: 1.80%, Mo: 2.15%, Ni: 15.63%, Co: 11.05%, Al: 1.80%, and the remainder is Fe and unavoidable impurities.

[0015] Preferably, the element composition of the ultra-high specific strength and ultra-high strength steel is, by weight percentage, C: 0.30-0.35%, Cr: 1.5-2.5%, Mo: 2.5-3.5%, Ni: 12-14%, Co: 8-11%, Al: 1-2.5%, S≤0.003%, P≤0.005%, O≤0.003%, N≤0.003%, H≤0.0002%, Ti≤0.01%, Si≤0.05%, Mn≤0.05%, and the balance is Fe.

[0016] The ultra-high specific strength and ultra-high strength steel of the present application also includes inevitable impurity elements. The impurity elements are controlled within the above range in order to ensure the toughness and fatigue performance of the ultra-high specific strength and ultra-high strength steel material.

[0017] In a second aspect, the present application provides a method for preparing the above-mentioned ultra-high specific strength ultra-high strength steel, which specifically comprises the following steps in sequence: smelting, forging, deep cooling, cold deformation, and aging treatment;

[0018] The specific steps of forging are: heating temperature of billet forging is ≤1200°C, holding time is 3-15h, and forging into a square billet through not less than three times of upsetting and drawing forging; reheating after billet forging, heating temperature is ≤1100°C, holding time is 3-10h, and forging ratio is ≥4; air cooling after forging, waiting for the sample to cool to 500-800°C before further forging, forging ratio is ≥5, and water cooling after forging.

[0019] Preferably, the smelting process is to prepare ultra-high specific strength and ultra-high strength steel of corresponding chemical composition by a converter method, an electric furnace method, a vacuum induction furnace method, an LF furnace method, a vacuum consumable method or a combination of multiple methods.

[0020] Preferably, the specific steps of the forging process are: the heating temperature for billet forging is 1100-1200°C, the holding time is 3-15h, and the billet is forged into a square billet by no less than three upsetting and drawing forgings; reheating after billet forging, the heating temperature is 1000-1100°C, the holding time is 3-10h, and the forging ratio is ≥4; air cooling after forging, waiting for the sample to cool to 500-800°C before further forging, the forging ratio is ≥5, and water cooling after forging.

[0021] Furthermore, the specific steps of the forging process are: the heating temperature for billet forging is 1130~1170℃, the holding time is 6~10h, and it is forged into a square billet through no less than three upsetting and drawing forgings; reheating after billet forging, the heating temperature is 1020~1080℃, the holding time is 5~7h, and the forging ratio is ≥4; air cooling after forging, waiting for the sample to cool to 600~700℃ before further forging, the forging ratio is ≥5, and water cooling after forging.

[0022] Preferably, the specific steps of the cryogenic treatment are: cryogenic treatment in the range of -196 to -73°C, keeping warm for 0.5 to 3 hours, and air cooling to room temperature.

[0023] Furthermore, the specific steps of the cryogenic treatment are: cryogenic treatment in the range of -126~-93°C, keeping warm for 1-2h, and air cooling to room temperature.

[0024] Preferably, the specific steps of the cold deformation process are: cold deformation after cryogenic treatment, and the cold deformation process requires a total compression rate of ≤5%.

[0025] Preferably, the specific steps of the aging treatment are: heating the rod to 460-540°C, keeping it warm for 4-8 hours, and air cooling it to room temperature.

[0026] Furthermore, the specific steps of the aging treatment are: heating the rod to 480-520°C, keeping it warm for 5-7 hours, and air cooling it to room temperature.

[0027] The ultra-high specific strength and ultra-high strength steel obtained by using the technical solution provided in this application has a tensile strength of ≥3000MPa and an elongation after fracture of ≥5%.

[0028] In summary, the technical solution of this application has the following effects:

[0029] This application optimizes the design of smelting, forging, deep cooling, cold deformation and aging treatment processes by accurately designing the chemical composition elements, so that the chemical composition elements and various process parameters are well matched, and the steel produced has higher strength and higher elongation. DETAILED DESCRIPTION

[0030] The present application is further described in detail below in conjunction with examples, comparative examples and performance testing experiments. These examples should not be construed as limiting the scope of protection claimed in the present application.

[0031] Example

[0032] Examples 1-3

[0033] Embodiments 1-3 respectively provide an ultra-high specific strength and ultra-high strength steel.

[0034] The difference between the above embodiments is that the contents of the main elements are different, as shown in Table 1.

[0035] The specific steps of the method for preparing ultra-high specific strength and ultra-high strength steel in the above embodiment are:

[0036] 1) Add pure materials according to the element contents shown in Table 1, melt the raw materials in a 25kg vacuum induction furnace, and cast them into artillery shell ingots;

[0037] 2) After smelting, the billet is forged at a heating temperature of 1200°C and a holding time of 8 hours to ensure that the ingot is burned through. After that, it is forged into a square billet of 60mm×60mm×L through three forgings and three drawing forgings, and then air-cooled to room temperature;

[0038] 3) Reheat to 1100℃, keep warm for 4h, then forge into Φ30mm round billet, forging ratio is 5.1, air-cool after forging, and further forge into Φ12mm round bar after cooling to 600℃, forging ratio is 6.25, and water-cooling after forging;

[0039] 4) Place the Φ12mm round bar in -73℃ for 2 hours, then air cool it to room temperature;

[0040] 5) The round bar is slightly cold deformed, with a total cross-sectional reduction of 2%;

[0041] 6) The drawn round bar is subjected to aging treatment at a temperature of 490°C for 5 hours.

[0042] Table 1 Main element composition content in Examples 1-3 and Comparative Examples 1-2

[0043] Example 4

[0044] Example 4 provides an ultra-high specific strength and ultra-high strength steel.

[0045] The element content composition of the ultra-high specific strength and ultra-high strength steel in this embodiment is the same as that in Example 2.

[0046] The specific steps of the method for preparing ultra-high specific strength and ultra-high strength steel in this embodiment are:

[0047] 1) Melting in a 100kg vacuum induction furnace and casting into shell ingots;

[0048] 2) After smelting, the billet is forged at a heating temperature of 1200°C and a holding time of 8 hours to ensure that the ingot is burned through. After that, it is forged into a square billet of 120mm×120mm×L through three forgings and three drawing forgings, and then air-cooled to room temperature;

[0049] 3) Reheat to 1100℃, keep warm for 4h, then forge into Φ60mm round billet, forging ratio is 5.1, air-cool after forging, and further forge into Φ26mm round bar after cooling to 600℃, forging ratio is 5.3, and water-cooling after forging;

[0050] 4) Place the Φ26mm round bar in -73℃ for 2 hours, then air cool it to room temperature;

[0051] 5) The round bar is slightly cold deformed, with a total cross-sectional reduction of 2.8%;

[0052] 6) The drawn round bar is subjected to aging treatment at an aging temperature of 510°C for 5 hours. Comparative Example

[0053] Comparative Example 1-2

[0054] Comparative Examples 1-2 each provide a type of steel.

[0055] The difference between the comparative example and Example 2 is that the contents of the main elements are different, as shown in Table 1.

[0056] The preparation method of the steel in the above comparative example is the same as that in Example 2. Comparative Example 3

[0057] Comparative Example 3 provides a steel.

[0058] The element content composition of the ultra-high specific strength and ultra-high strength steel in this comparative example is the same as that in Example 2, except that no cold deformation treatment is performed.

[0059] The specific steps of the method for preparing steel in this comparative example are:

[0060] 1) Melting in a 25kg vacuum induction furnace and casting into shell ingots;

[0061] 2) After smelting, the billet is forged at a heating temperature of 1200°C and a holding time of 8 hours to ensure that the ingot is burned through. After that, it is forged into a square billet of 60mm×60mm×L through three forgings and three drawing forgings, and then air-cooled to room temperature;

[0062] 3) Reheat to 1100℃, keep warm for 4h, then forge into Φ30mm round billet, forging ratio is 5.1, air-cool after forging, and further forge into Φ12mm round bar after cooling to 600℃, forging ratio is 6.25, and water-cooling after forging;

[0063] 4) Place the Φ12mm round bar in -73℃ for 2 hours, then air cool it to room temperature;

[0064] 5) The drawn round bar is subjected to aging treatment at an aging temperature of 490°C for 5 hours. Comparative Example 4

[0065] Comparative Example 4 provides a steel.

[0066] The element content composition of the steel in this comparative example is the same as that in Example 4, except that no cold deformation treatment is performed.

[0067] The specific steps of the method for preparing steel in this comparative example are:

[0068] 1) Melting in a 100kg vacuum induction furnace and casting into shell ingots;

[0069] 2) After smelting, the billet is forged at a heating temperature of 1200°C and a holding time of 8 hours to ensure that the ingot is burned through. After that, it is forged into a square billet of 120mm×120mm×L through three forgings and three drawing forgings, and then air-cooled to room temperature;

[0070] 3) Reheat to 1100℃, keep warm for 4h, then forge into Φ60mm round billet, forging ratio is 5.1, air-cool after forging, and further forge into Φ26mm round bar after cooling to 600℃, forging ratio is 5.3, and water-cooling after forging;

[0071] 4) Place the Φ26mm round bar in -73℃ for 2 hours, then air cool it to room temperature;

[0072] 5) The drawn round bar is subjected to aging treatment at an aging temperature of 510°C for 5 hours.

[0073] Performance testing

[0074] The steels in Examples 1-4 and Comparative Examples 1-4 were subjected to chemical composition analysis and mechanical properties, inclusion rating, and fatigue performance testing.

[0075] Among them, the detection method of S shall refer to GB / T 20123-2006; the detection method of P shall refer to GB / T 223.59-2008; the detection method of O shall refer to GB / T 11261-2006; the detection method of N shall refer to GB / T 20124-2006; the detection method of H shall refer to GB / T 20124-2006; the detection method of Ti shall refer to GB / T223.17-1989; the detection method of Si shall refer to GB / T 20125-2006; the detection method of Mn shall refer to GB / T 223.64-2008; the detection method of Rm shall refer to GB / T 228.1-2021; the detection method of Rp0.2 shall refer to GB / T 228.1-2021; the detection method of A shall refer to GB / T 228.1-2021.

[0076] Determination method and test results: as shown in Table 2.

[0077] Table 2 Chemical composition analysis and performance test results of the finished steel products in Examples 1-4 and Comparative Examples 1-4

[0078]

[0079] Combined with the test results in Table 2, it can be seen that the present application has a high strength and high elongation by accurately designing the chemical composition elements, optimizing the smelting, forging, deep cooling, cold deformation, and aging treatment processes, so that the chemical composition elements and the various process parameters are well matched. In addition, the ultra-high specific strength and ultra-high strength steel of the present application controls the impurity elements within the above range, ensuring the toughness and fatigue performance of the steel.

[0080] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. An ultra-high specific strength and ultra-high strength steel, characterized in that: The element composition of the ultra-high specific strength and ultra-high strength steel is, by weight percentage, C: 0.25-0.40%, Cr: 1-3%, Mo: 1-4%, Ni: 12.37-18%, Co: 6-12%, Al: 0-3% and the content of Al is not 0, and the balance is Fe and unavoidable impurities; The method for preparing the ultra-high specific strength ultra-high strength steel specifically comprises the following steps in sequence: smelting, forging, deep cooling, cold deformation, and aging treatment; The specific steps of forging are: heating the billet forging at a temperature of 1100-1200° C., holding time of 3-15 hours, and forging into a square billet by forging for not less than three times; reheating after billet forging, heating temperature of 1000-1100° C., holding time of 3-10 hours, forging ratio ≥4; air cooling after forging, waiting for the sample to cool to 400-700° C. before further forging, forging ratio ≥5, and water cooling after forging; The specific steps of the cold deformation process are: cold deformation after cryogenic treatment, and the cold deformation process requires a total compression rate of ≤5%; The tensile strength of the ultra-high specific strength and ultra-high strength steel is ≥3000MPa, and the elongation after fracture is ≥5%.

2. The ultra-high specific strength and ultra-high strength steel according to claim 1, characterized in that: Measured in percentage by weight, the element composition of the ultra-high specific strength and ultra-high strength steel is: C: 0.29-0.35%, Cr: 1.5-2.5%, Mo: 1.5-3.5%, Ni: 12.37-15%, Co: 8-11%, Al: 1-2.5%, and the remainder is Fe and unavoidable impurities.

3. The ultra-high specific strength and ultra-high strength steel according to claim 1, characterized in that: Measured in percentage by weight, the element composition of the ultra-high specific strength and ultra-high strength steel is: C: 0.30-0.35%, Cr: 1.5-2.5%, Mo: 2.5-3.5%, Ni: 12.37-14%, Co: 8-11%, Al: 1-2.5%, S≤0.003%, P≤0.005%, O≤0.003%, N≤0.003%, H≤0.0002%, Ti≤0.01%, Si≤0.05%, Mn≤0.05%, and the balance is Fe.

4. The method for preparing ultra-high specific strength and ultra-high strength steel according to any one of claims 1 to 3, characterized in that: Specifically, the following steps are carried out in sequence: smelting, forging, deep cooling, cold deformation, and aging treatment; The specific steps of forging are: heating the billet forging at a temperature of 1100-1200°C, holding time of 3-15h, and forging into a square billet by forging for not less than three times; reheating after billet forging, heating temperature of 1000-1100°C, holding time of 3-10h, forging ratio ≥4; air cooling after forging, waiting for the sample to cool to 400-700°C before further forging, forging ratio ≥5, water cooling after forging The specific steps of the cold deformation process are: cold deformation after deep cryogenic treatment, and the cold deformation process requires a total compression rate of ≤5%.

5. The method for preparing ultra-high specific strength and ultra-high strength steel according to claim 4, characterized in that: The smelting process is to prepare ultra-high specific strength and ultra-high strength steel of corresponding chemical composition by a converter method, an electric furnace method, a vacuum induction furnace method, an LF furnace method, a vacuum consumable method or a combination of multiple methods.

6. The method for preparing ultra-high specific strength and ultra-high strength steel according to claim 4, characterized in that: The specific steps of the cryogenic treatment are: cryogenic treatment in the range of -196 to -73°C, keeping warm for 0.5 to 3 hours, and air cooling to room temperature.

7. The method for preparing ultra-high specific strength and ultra-high strength steel according to claim 4, characterized in that: The specific steps of the aging treatment are: heating the rod to 460-540° C., keeping the temperature for 4-8 hours, and air cooling to room temperature.

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