High-strength and high-plasticity 3GPa-grade maraging steel and preparation method thereof

Abstract

The invention relates to the technical field of alloy steel, and particularly discloses high-strength and high-plasticity 3GPa-grade maraging steel and a preparation method thereof. The invention discloses high-strength and high-plasticity 3GPa-grade maraging steel, which is prepared from the following elements in percentage by weight: 15 to 20 percent of Ni, 0.1 to 2 percent of Al, 3 to 7 percent of Mo, 1.0 to 2.0 percent of Ti, 12 to 16 percent of Co and the balance of Fe and inevitable impurities. According to the maraging type ultrahigh-strength steel, by reasonably adding the elements and the proportion thereof and combining the forging process that the forging ratio and the forging temperature are reasonably adjusted and controlled, the maraging type ultrahigh-strength steel with the tensile strength of 3 GPa or above and the excellent plasticity is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of alloy steel, and in particular to a high-strength and plastic 3GPa grade martensitic aging steel and a preparation method thereof. Background Art

[0002] At present, ultra-high strength steel is widely used in major aerospace engineering load-bearing components such as landing gears of civil airliners and military aircraft, strategic missile engine casings, space station robotic arms, and spacecraft power shafts. In view of the particularity of the aerospace field, the strength and specific strength of materials have always been important indicators for design and material selection in this field. At present, the strength grade of aerospace ultra-high strength steel with practical engineering applications as a structural material is about 2.2-2.5GPa, such as ML340, C350, etc. Further improvement of strength faces the problem of insufficient plasticity. At present, ultra-high strength steel with a strength grade of 3GPa has been reported, but the elongation is mostly less than 5%, and the cross-sectional shrinkage is also low. The poor plasticity limits its application in load-bearing components. It is urgent to develop a 3GPa ultra-high strength steel with excellent plasticity. Summary of the invention

[0003] In order to solve the above technical problems, the present application provides a high-strength and plastic 3GPa grade martensitic aged steel and a preparation method thereof.

[0004] The present application provides a high-strength and plastic 3GPa grade maraging steel. The element composition of the high-strength and plastic 3GPa grade maraging steel is, by weight percentage, Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the remainder is Fe and unavoidable impurities.

[0005] In terms of weight percentage, the ultra-high strength steel of the present application includes Ni: 15-20%. Ni is an important component element in maraging steel. Ni can inhibit the decomposition of screw dislocations in maraging steel to ensure the progress of cross slip, and the Fe-Ni-based martensite formed has good plasticity and toughness. In addition, in the present application, Ni is combined with Al, Ti, Mo, etc. to form a nanoscale second phase to exert precipitation strengthening. The Ni element will lower the Ms point. Too much Ni will make it difficult for the material to obtain a full martensitic structure, resulting in insufficient material strength. Lower Ni will make the material less plastic and tough. Therefore, the Ni content in the present application is controlled to 15-20%.

[0006] In terms of weight percentage, the ultra-high strength steel of the present application includes Al: 0.1-2%. In the present application, Al is an important strengthening element, and the coherent nano NiAl phase formed by Al and Ni is the key to ensuring the strength of the material, but too high Al content will greatly damage the plasticity of the material, so the Al content of the present application is controlled to 0.1-2%.

[0007] In terms of weight percentage, the ultra-high strength steel of the present application includes 3-7% Mo. Mo can form Ni3Mo intermetallic compounds with Ni to strengthen the matrix, but too high a Mo content will form large-sized Fe2Mo in the steel, so the Mo content of the present application is controlled to 3-7%.

[0008] In terms of weight percentage, the ultra-high strength steel of the present application includes Ti: 1.0-2.0%. Ti is the most important strengthening element in maraging steel, and the formed Ni3Ti has a strong precipitation strengthening effect. However, Ti easily forms large-sized harmful inclusions with impurity elements C and N in steel, so the present application controls the Ti content to 1.0-2.0%.

[0009] In terms of weight percentage, the ultra-high strength steel of the present application includes Co: 12-16%. Co does not form a precipitation phase in the steel, and can promote the fine and uniform precipitation of the precipitation phase by inhibiting dislocation recovery during the aging process, thereby improving the precipitation strengthening effect. Too high a Co content will damage the plasticity and toughness of the steel, so the Co content is controlled to 12-16% in the present application.

[0010] Preferably, the element composition of the high-strength and plastic 3 GPa grade maraging steel is, by weight percentage, Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, and the remainder is Fe and unavoidable impurities.

[0011] Preferably, the element composition of the high-strength and plastic 3GPa grade maraging steel is, by weight percentage, Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, S≤0.003%, P≤0.005%, O≤0.003%, N≤0.003%, H≤0.0002%, C≤0.02%, and the balance is Fe.

[0012] The ultra-high strength steel of the present application also includes inevitable impurity elements. The impurity elements mainly include S, P, O, N, H, C, etc. In terms of weight percentage, S≤0.003%, P≤0.005%, O≤0.003%, N≤0.003%, H≤0.00002%, C≤0.02%. The present application controls the impurity elements within the above range to ensure the strong plasticity of the material.

[0013] Preferably, the element composition of the high-strength and plastic 3GPa grade maraging steel is, by weight percentage, Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, S≤0.0015%, P≤0.004%, O≤0.001%, N≤0.001%, H≤0.0002%, C≤0.01%, and the balance is Fe.

[0014] In a specific embodiment, the element composition of the high-strength and plastic 3GPa grade maraging steel is, by weight percentage, Ni: 18.16%, Al: 0.98%, Mo: 4.31%, Ti: 1.49%, Co: 15.20%, S: 0.0010%, P: 0.0010%, O: 0.0008%, N: 0.0005%, H: 0.0001%, and C: 0.0089%.

[0015] Preferably, the room temperature tensile strength of the high-strength and plastic 3 GPa grade maraging steel is ≥3000 MPa, the elongation after fracture is ≥5%, and the cross-sectional shrinkage is ≥30%.

[0016] In a second aspect, the present application provides a method for preparing the above-mentioned high-strength and plastic 3GPa grade martensitic aging steel, which specifically comprises the following steps in sequence: smelting, forging, deep cooling, and aging treatment.

[0017] Preferably, the smelting process is: smelting is carried out using one method or a combination of multiple methods including but not limited to a converter, an electric furnace, a vacuum induction furnace, an LF furnace, and a vacuum consumable furnace; the element composition of the shell ingot prepared by smelting is, in terms of weight percentage, Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the balance is Fe and unavoidable impurities.

[0018] Preferably, the forging process comprises: The heating temperature for forging is 1180-1250℃, the holding time is 3-15h, and the billet is forged by at least three times of forging. After forging, the blank is reheated at 980-1100℃, the holding time is 3-10h, the number of upsetting and drawing is not less than three times, and the forging ratio is 2-6; Heating at 850-1050℃, holding time 3-10h, one-time forging to obtain the final bar, forging ratio ≥6.

[0019] In some specific embodiments, the forging process includes: The heating temperature for forging is 1200-1230℃, the holding time is 6-10h, and the billet is forged by at least three times; After forging, the blank is reheated at a temperature of 1000-1080°C, with a holding time of 3-5 hours, and the number of upsetting and drawing is not less than three times, with a forging ratio of 2-6; Heating at 880-1020℃, holding time 5-7h, one-time forging to obtain the final bar, forging ratio ≥6.

[0020] Preferably, the cryogenic treatment process includes: cryogenic treatment in the range of -196--73°C, and heat preservation for 0.5-3h.

[0021] In a specific embodiment, the cryogenic treatment process includes: cryogenic treatment at -73°C and keeping warm for 2 hours.

[0022] Preferably, the aging treatment process comprises: heating the rod to 460-540° C. and keeping the temperature for 4-30 hours.

[0023] In a specific embodiment, the aging treatment process includes: heating the rod to 480° C. and keeping the temperature for 4-6 hours.

[0024] In summary, the technical solution of this application has the following effects: The maraging ultra-high strength steel of the present application reasonably adds elements and their proportions, and reasonably regulates the forging process in combination with the forging ratio and forging temperature, thereby obtaining a maraging steel with an ultra-high strength of more than 3GPa in tensile strength and excellent strength and plasticity. DETAILED DESCRIPTION

[0025] 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. Example

[0026] Example 1 Example 1 provides a high-strength and plastic 3 GPa grade maraging steel and a preparation method thereof.

[0027] The specific steps of the preparation method of high-strength and high-ductility 3GPa grade maraging steel in this embodiment are as follows: 1) Melting: Melting is performed in a 25kg vacuum induction furnace and cast into a shell ingot; when the steel is tapped, the element composition of the steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the remainder is Fe and unavoidable impurities, as shown in Table 1.

[0028] 2) Forging: After smelting, the billet is forged. The heating temperature of the billet forging is 1220℃ and the holding time is 8h to ensure that the steel ingot is burned through. After that, it is forged into a square billet of 60mm×60mm×L through three forgings and three drawing, and then air-cooled to room temperature. After forging, the billet is reheated to 1050℃, kept at this temperature for 4 hours, and drawn 4 times before being forged into a 35mm×35mm square billet; it is placed in a 950℃ heating furnace to ensure that the sample is heated through, kept at this temperature for 6 hours, and forged into a final bar in one fire, forged into a Φ12mm round bar; 3) Deep cooling: Place the Φ12mm round bar in -73℃ for 2 hours, then air cool it to room temperature; 4) Aging treatment: The round bar is subjected to aging treatment at an aging temperature of 480°C for 5 hours.

[0029] Table 1 Main element composition of shell ingots prepared by smelting in Example 1-3 and Comparative Example 1-2 Example 2 Example 2 provides a high-strength and plastic 3 GPa grade maraging steel and a preparation method thereof.

[0030] The specific steps of the preparation method of high-strength and high-ductility 3GPa grade maraging steel in this embodiment are as follows: 1) Melting: Melting is performed in a 25kg vacuum induction furnace and cast into a shell ingot; when the steel is tapped, the element composition of the steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the remainder is Fe and unavoidable impurities, as shown in Table 1.

[0031] 2) Forging: After smelting, the billet is forged. The heating temperature of the billet forging is 1230℃ and the holding time is 8h to ensure that the steel ingot is burned through. After that, it is forged into a square billet of 60mm×60mm×L through three forgings and three drawing, and then air-cooled to room temperature; After forging, the billet is reheated to 1050°C, kept at this temperature for 4 hours, and then forged into a 35mm×35mm square billet; Put it into a 920℃ heating furnace to ensure that the sample is heated through, and forged into a Φ10mm round bar; 3) Deep cooling: Place the Φ10 mm round bar in -73°C for 2 hours, then air cool it to room temperature; 4) Aging treatment: The round bar is subjected to aging treatment at an aging temperature of 490°C for 5 hours.

[0032] Example 3 Example 3 provides a high-strength and plastic 3 GPa grade martensitic aged steel and a preparation method thereof.

[0033] The specific steps of the preparation method of high-strength and high-ductility 3GPa grade maraging steel in this embodiment are as follows: 1) Melting: Melting is performed in a 25kg vacuum induction furnace and cast into a shell ingot; when the steel is tapped, the element composition of the steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the remainder is Fe and unavoidable impurities, as shown in Table 1.

[0034] 2) Forging: After smelting, the billet is forged. The heating temperature of the billet forging is 1220℃ and the holding time is 8h to ensure that the steel ingot is burned through. After that, it is forged into a square billet of 60mm×60mm×L through three forgings and three drawing, and then air-cooled to room temperature. After forging, the billet is reheated to 1030°C, kept at this temperature for 4 hours, and then forged into a 35mm×35mm square billet; Put it into a 920℃ heating furnace to ensure that the sample is heated through, and forged into a Φ12mm round bar; 3) Deep cooling: Place the Φ12mm round bar in -73℃ for 2h, then air cool it to room temperature; 4) Aging treatment: The round bar is subjected to aging treatment at an aging temperature of 480°C for 5 hours.

[0035] Comparative Example Comparative Example 1 Comparative Example 1 provides a maraging steel and a preparation method thereof.

[0036] The specific steps of the preparation method of maraging steel in Comparative Example 1 are: 1) Melting in a 25kg vacuum induction furnace and casting into a shell ingot; when tapping, the element composition of the steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the balance is Fe and unavoidable impurities, as shown in Table 1.

[0037] 2) After smelting, the billet is forged at a heating temperature of 1220°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; Reheat to 1050℃, keep warm for 4h, and then forge into 35mm×35mm square billet; Put it into a 950℃ heating furnace to ensure that the sample is heated through, and forged into a Φ12mm round bar; 3) Place the Φ12mm round bar in -73℃ for 2 hours, then air cool it to room temperature; 4) The round bar is subjected to aging treatment at a temperature of 480°C for 5 hours.

[0038] Comparative Example 2 Comparative Example 2 provides a maraging steel and a preparation method thereof.

[0039] The specific steps of the preparation method of maraging steel in Comparative Example 2 are: 1) Melting in a 25kg vacuum induction furnace and casting into a shell ingot; when tapping, the element composition of the steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the balance is Fe and unavoidable impurities, as shown in Table 1.

[0040] 2) After smelting, the billet is forged at a heating temperature of 1220°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; Reheat to 1050℃, keep warm for 4h, and then forge into 35mm×35mm square billet; Put it into a 950℃ heating furnace to ensure that the sample is heated through, and forged into a Φ12mm round bar; 3) Place the Φ12mm round bar in -196℃ for 2 hours, then air cool it to room temperature; 4) The round bar is subjected to aging treatment at a temperature of 480°C for 5 hours.

[0041] Performance testing The finished maraging steel products in Examples 1-3 and Comparative Examples 1-2 were subjected to chemical composition analysis and tested for mechanical properties, inclusion rating, and fatigue properties.

[0042] The detection methods for the main element content are: the detection method for Ni is GB / T223.23-2008; the detection method for Al is GB / T223.8-2000; the detection method for Mo is GB / T223.26-2008; the detection method for Ti is GB / T223.11-2008; The detection method for Co is GB / T223.26-2008; The detection methods for impurity element content are: S detection method: GB / T20123-2006; P detection method: GB / T223.59-2008; O detection method: GB / T11261-2006; N detection method: GB / T20124-2006; H detection method: GB / T20124-2006; C detection method: GB / T11261-2006.

[0043] The test method for room temperature tensile strength Rm / MPa is: GB / T 228.1-2021; yield strength R p0.2 / MPa testing method is: GB / T 228.1-2021; the testing method of elongation after fracture A / % is: GB / T 228.1-2021; the testing method of cross-sectional shrinkage Z / % is: GB / T 228.1-2021.

[0044] Test results: as shown in Table 2.

[0045] Table 2 Chemical composition analysis and performance test results of maraging steel products in Examples 1-3 and Comparative Examples 1-2 Combined with Table 2, by comparing the test results of the embodiment and the comparative example, it can be seen that the maraging type ultra-high strength steel of the present application reasonably adds Ni, Al, Mo, Ti, Co elements and their proportions, and reasonably controls the forging process in combination with the forging ratio and forging temperature to obtain a tensile strength of more than 3GPa, an elongation after fracture ≥5%, a cross-sectional shrinkage rate ≥30%, and a maraging steel with excellent strength and plasticity.

[0046] 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. A high strength and plasticity 3GPa grade maraging steel, characterized in that: Measured by weight percentage, the element composition of the high-strength and plastic 3GPa grade maraging steel is: Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the balance is Fe and unavoidable impurities.

2. The high-strength and plastic 3GPa grade maraging steel according to claim 1, characterized in that: Calculated by weight percentage, the element composition of the high-strength and plastic 3GPa grade maraging steel is: Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, and the balance is Fe and unavoidable impurities.

3. The high strength and plasticity 3GPa grade maraging steel according to claim 1, characterized in that: Measured in percentage by weight, the element composition of the high-strength and plastic 3GPa grade maraging steel is: Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, S≤0.003%, P≤0.005%, O≤0.003%, N≤0.003%, H≤0.0002%, C≤0.02%, and the balance is Fe.

4. The high-strength and plastic 3 GPa grade maraging steel according to claim 3, characterized in that: Measured in percentage by weight, the element composition of the high-strength and plastic 3GPa grade maraging steel is: Ni: 16-19%, Al: 0.5-1.5%, Mo: 4-6%, Ti: 1.3-1.6%, Co: 13-15.5%, S≤0.0015%, P≤0.004%, O≤0.001%, N≤0.001%, H≤0.0002%, C≤0.01%, and the balance is Fe.

5. The high strength and plasticity 3 GPa grade maraging steel according to any one of claims 1 to 4, characterized in that: The room temperature tensile strength of the high-strength and plastic 3GPa grade martensitic aging steel is ≥3000MPa, the elongation after fracture is ≥5%, and the cross-sectional shrinkage is ≥30%.

6. The method for preparing high-strength and high-plasticity 3 GPa grade maraging steel according to any one of claims 1 to 5, characterized in that: Specifically, the following steps are performed in sequence: smelting, forging, deep cooling, and aging treatment.

7. The method for preparing high-strength and high-plasticity 3GPa grade maraging steel according to claim 6, characterized in that: The smelting process is: smelting is carried out using one method or a combination of multiple methods including but not limited to a converter, an electric furnace, a vacuum induction furnace, an LF furnace, and a vacuum consumable furnace; the element composition of the shell ingot prepared by smelting is, in terms of weight percentage, Ni: 15-20%, Al: 0.1-2%, Mo: 3-7%, Ti: 1.0-2.0%, Co: 12-16%, and the balance is Fe and unavoidable impurities.

8. The method for preparing high-strength and high-plasticity 3GPa grade maraging steel according to claim 6, characterized in that: The forging process comprises: The heating temperature for forging is 1180-1250℃, the holding time is 3-15h, and the billet is forged by at least three times of forging. After forging, the blank is reheated at 980-1100℃, the holding time is 3-10h, the number of upsetting and drawing is not less than three times, and the forging ratio is 2-6; Heating at 850-1050℃, holding time 3-10h, one-time forging to obtain the final bar, forging ratio ≥6.

9. The method for preparing high-strength and high-plasticity 3GPa grade maraging steel according to claim 6, characterized in that: The cryogenic treatment process includes: cryogenic treatment in the range of -196--73°C, and heat preservation for 0.5-3h.

10. The method for preparing high-strength and high-plasticity 3GPa grade maraging steel according to claim 6, characterized in that: The aging treatment process includes: heating the rod to 460-540° C. and keeping the temperature for 4-30 hours.

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