Anti-fatigue low-alloy ultrahigh-strength steel as well as preparation method and application thereof
By controlling the alloy composition and heat treatment process, fatigue-resistant low alloy ultra-high strength steel was developed, which solved the problem of insufficient landing gear material strength, achieved a balance of high strength and economy, and met the needs of large passenger aircraft.
Patent Information
- Application Number
- CN202510325684.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-19
- Publication Date
- 2025-07-04
AI Technical Summary
The strength level of the landing gear trunk material in service cannot meet the development needs of large passenger aircraft in the future, and the economic and fatigue performance of existing materials are difficult to take into account.
A low-alloy ultra-high strength steel with chemical compositions including C 0.46-0.56%, Si 0.5-2%, Mn 0.5-1.8%, Cr 0.1-0.7%, Mo 0.5-2%, Ni 0.5-1.4%, fine crystalline elements V and Nb are added, tempered martensite matrix and nano-scale ε precipitation phase are formed by quenching and tempering treatment, and the Cr+Mo+Ni content is controlled ≤3%, preferably ≤2.5%.
The tensile strength of 2200MPa grade, the yield strength of 1700MPa grade, 8% elongation and 30% cross-section shrinkage are achieved, which significantly improves the economic and fatigue properties of the material and extends the service life.
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Abstract
Description
Technical Field
[0001] This application relates to the technical field of alloy steel, and particularly relates to an anti-fatigue low-alloy ultra-high strength steel and its preparation method and application. Background Art
[0002] The landing gear is a core load-bearing component of an aircraft. During service, it bears strong fatigue loads. The anti-fatigue performance of the landing gear material is crucial for the overall safety and reliability of the aircraft. In the 1950s, International Nickel Company of the United States developed 300M steel based on 4340 steel. Due to its low alloying cost, high strength and high toughness, 300M steel has become the current main material for landing gears.
[0003] However, with the continuous increase in the takeoff weight and load of aircraft, it is necessary to further increase the strength grade of the steel for landing gears from 1900 MPa to 2200 MPa. The ultra-high strength of the steel for landing gears is beneficial to reducing the design size of the landing gear system, which is of great significance for weight reduction and range extension of civil airliners, as well as energy conservation, emission reduction, cost reduction and efficiency improvement throughout the life cycle. However, the difficulty in developing this material lies not only in the reasonable matching of the strength, toughness and fatigue performance of ultra-high strength steel, but also in fully considering the economic characteristics of the civil aviation field.
[0004] Therefore, there is an urgent need to develop a new generation of ultra-high strength steel for landing gears with a strength grade of 2200 MPa, better comprehensive performance than 300M steel, and a cost equivalent to or lower than that of 300M steel. Summary of the Invention
[0005] This application provides an anti-fatigue low-alloy ultra-high strength steel and its preparation method and application.
[0006] This application aims at the problem that the strength grade of the current main material for landing gears cannot meet the development of future large airliners, and develops a 2200 MPa grade ultra-high strength steel with anti-fatigue and low cost.
[0007] In the first aspect, this application provides an anti-fatigue low-alloy ultra-high strength steel, adopting the following technical solution:
[0008] An anti-fatigue low-alloy ultra-high strength steel, the chemical composition of the anti-fatigue low-alloy ultra-high strength steel is in mass percentage: C 0.46 - 0.56%, Si 0.5 - 2%, Mn 0.5 - 1.8%, Cr 0.1 - 0.7%, Mo 0.5 - 2%, Ni 0.5 - 1.4%, and the balance is Fe and unavoidable impurities.
[0009] Optionally, the grain size of the anti-fatigue low-alloy ultra-high strength steel is ≥ grade 6.
[0010] Optionally, the anti-fatigue low-alloy ultra-high strength steel further includes fine grain elements.
[0011] Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the fine grain elements include, but are not limited to, any one or more of V and Nb.
[0012] Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the V content is 0.01-0.2%.
[0013] Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the Nb content is 0.01-0.10%.
[0014] In the composition of the anti-fatigue low-alloy ultra-high strength steel provided by this application, fine grain elements can be added as appropriate. The purpose is to ensure the grain size requirement of the material (≥ grade 6), so as to ensure the final performance of the material. The fine grain elements include, but are not limited to, V 0.01-0.2% and Nb 0.01-0.10%.
[0015] Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the content of Cr+Mo+Ni ≤ 3%.
[0016] Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the content of Cr+Mo+Ni ≤ 2.5%.
[0017] In the anti-fatigue low-alloy ultra-high strength steel provided by this application, the content of Cr+Ni+Mo ≤ 3%, preferably the content of Cr+Ni+Mo ≤ 2.5%, which is lower than 3.1% of 300M steel, and has significant economy.
[0018] Optionally, for the anti-fatigue low-alloy ultra-high strength steel, the tensile strength ≥ 2200 MPa, the yield strength ≥ 1700 MPa, the elongation ≥ 8%, the reduction of area ≥ 30%, and the fracture toughness ≥ 55 MPa·m 1 / 2 。
[0019] In the second aspect, this application provides a preparation method for an anti-fatigue low-alloy ultra-high strength steel, adopting the following technical solution:
[0020] A preparation method for an anti-fatigue low-alloy ultra-high strength steel, the preparation method includes a heat treatment method, and the heat treatment method includes a quenching treatment and a tempering treatment.
[0021] Optionally, the quenching treatment includes: heating the bar to 860-960 °C, holding for 1-2 h, and oil quenching.
[0022] Optionally, the tempering treatment includes: heating the bar to 150-300 °C, holding for 1-6 h, and air cooling to room temperature.
[0023] After obtaining an ultra-high strength steel that meets the chemical composition and microstructure requirements through an appropriate melting and deformation process, the final product meets the performance requirements of this application through quenching and tempering treatments.
[0024] Further, the melting process refers to preparing an ultra-high strength steel with a chemical composition within the range required by this application using methods including but not limited to converters, electric furnaces, vacuum induction furnaces, LF furnaces, vacuum consumables, electroslag remelting, etc., or a combination of multiple methods.
[0025] Further, the deformation process refers to preparing an ultra-high strength steel with a grain size that meets the requirements of this application using methods including but not limited to rolling, forging, etc.
[0026] In a third aspect, this application provides the use of the above-mentioned anti-fatigue low-alloy ultra-high strength steel in materials for aircraft landing gears.
[0027] In summary, this application includes at least one of the following beneficial technical effects:
[0028] In view of the problem that the strength grade of the main landing gear materials in service cannot meet the development of future large passenger aircraft, this application develops a 2200MPa-grade ultra-high strength steel with anti-fatigue and low cost.
[0029] This application provides control of the contents of elements such as C, Si, Mn, Cr, Mo, Ni, etc. in the steel, and obtains a tempered martensite matrix structure and a high-density nano-scale ε precipitation phase through the process of quenching + tempering. The content of Cr + Ni + Mn ≤ 2.5%, and the material economy is remarkable.
[0030] The anti-fatigue low-alloy ultra-high strength steel provided by this application has a tensile strength of more than 2200MPa, a yield strength ≥ 1700MPa, an elongation ≥ 8%, a reduction of area ≥ 30%, and a fracture toughness ≥ 55MPa·m 1 / 2 . Detailed implementation manners
[0031] Before describing the embodiments of this application in detail, it should be understood that the terms used herein are only for the purpose of describing specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this term belongs.
[0032] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of this application, unless otherwise stated, "a plurality of" means two or more.
[0033] In the ranges disclosed in this application, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.
[0034] In this application, the term "comprising" or "including" is an open-ended expression, that is, it includes the content specified in this application, but does not exclude other aspects of the content.
[0035] This application provides an anti-fatigue low-alloy ultra-high-strength steel. The chemical composition of the anti-fatigue low-alloy ultra-high-strength steel in mass percentage includes: C 0.46 - 0.56%, Si 0.5 - 2%, Mn 0.5 - 1.8%, Cr 0.1 - 0.7%, Mo 0.5 - 2%, Ni 0.5 - 1.4%, and the balance is Fe and inevitable impurities. Optionally, V 0.01 - 0.2% and Nb 0.01 - 0.10% can be added.
[0036] The following specifically describes the functions and dosage selections of the components contained in this application:
[0037] In mass percentage, the ultra-high-strength steel of this application includes C: 0.46 - 0.56%. C is the most important strengthening element in steel and is the key to ensuring that the material strength reaches 2200 MPa level. It is necessary to control the C content to be higher than 0.46%, but the higher the C content, the worse the toughness and plasticity of the material. Therefore, the upper limit of the C content is controlled at 0.56%.
[0038] In mass percentage, the ultra-high-strength steel of this application includes Si: 0.5 - 2% and Mn: 0.5 - 1.8%. Si and Mn are key elements in low-alloy ultra-high-strength steel grades, which are beneficial to improving the tempering resistance of the material. In this application, Si can inhibit the decomposition transformation of retained austenite into Fe3C, improve the tempering resistance of martensite, and significantly increase the tempering temperature, but high Si will reduce the decarburization performance; Mn can improve the hardenability and strength of steel, but too high Mn content will sharply reduce the Ms point, resulting in too much retained austenite content. The reasonable combination of Si and Mn can enable the steel to obtain excellent strength and toughness matching at an appropriate tempering temperature. Therefore, the Si content is controlled at 0.5 - 2% and the Mn content is controlled at 0.5 - 1.8%.
[0039] In terms of mass percentage, the ultra-high strength steel of the present application includes Cr: 0.1-0.7%, Mo: 0.5-2.0%. In the present application, Cr can improve the strength of the steel through solid solution strengthening and precipitation strengthening, while improving the hardenability and tempering resistance of the steel. However, too high a Cr content will significantly reduce the Ms of the steel, resulting in too much retained austenite. At the same time, there are easily Cr carbides with too high precipitation temperature before solution treatment, thus increasing the solution temperature and resulting in coarse grains and microstructure; Mo can improve the strength of the steel, improve the hardenability and tempering resistance, and inhibit the effect of temper brittleness. However, too high a Mo content will increase the quenching temperature. Therefore, the Cr content is controlled at 0.1-0.7%, and the Mo content is controlled at 0.3-1.5%.
[0040] In terms of mass percentage, the ultra-high strength steel of the present application includes Ni: 0.5-1.4%. In the present application, Ni can significantly improve the cleavage fracture resistance of the martensite matrix. However, too high a Ni content will form too much retained austenite, damaging the toughness of the steel and significantly reducing the yield strength of the material. Therefore, the Ni content is controlled at 0.5-1.4%.
[0041] In terms of mass percentage, the ultra-high strength steel of the present application optionally includes one or more of fine grain elements such as V and Nb. The V content is 0.01-0.2%, and the Nb content is 0.01-0.1%. Carbides and nitrides formed by these elements can effectively inhibit grain growth during quenching and heat preservation.
[0042] To ensure the economy of the material, the ultra-high strength steel of the present application does not contain the precious alloy element Co, and the content of Cr+Mo+Ni ≤ 3%. Preferably, the content of Cr+Mo+Ni can be controlled to ≤ 2.5%.
[0043] The ultra-high strength steel of the present application also includes inevitable impurity elements, mainly including S, P, O, N, Al, Ti, etc. S ≤ 0.0015%, P ≤ 0.004%, O ≤ 0.0015%, N ≤ 0.002%, Al ≤ 0.05%, Ti ≤ 0.01%. Effective control of the above impurity elements can improve the toughness and fatigue life of the material.
[0044] The present application also provides a heat treatment method for the above ultra-high strength steel, including: quenching treatment, tempering treatment.
[0045] The above quenching treatment includes heating the bar to 860-960 °C, holding for 1-2 h, and oil cooling;
[0046] The above tempering treatment includes heating the bar to 150-300 °C, holding for 1-6 h, and air cooling to room temperature.
[0047] The purpose of the above quenching treatment is to completely dissolve the main alloying elements in the steel into the matrix and obtain martensite structure through oil quenching. The purpose of the tempering treatment is to promote the precipitation of nano ε-carbides and soften the matrix, so as to obtain excellent strength and toughness matching.
[0048] To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present application. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application.
[0049] For those not specified in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications are followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.
[0050] The present application will be further described in detail below in conjunction with the embodiments and test results.
[0051] Example 1
[0052] This example provides a fatigue-resistant low-alloy ultra-high-strength steel. The chemical composition and heat treatment process parameters are shown in Table 1 and Table 2 specifically.
[0053] Specifically, it includes the following steps:
[0054] (1) Process of preparing the bar
[0055] The experimental steel is smelted using a 25 kg vacuum induction furnace, poured into a shell ingot after smelting, and then forged into shape through free forging.
[0056] The high-temperature homogenization holding temperature is 1200 - 1220 °C, and the holding time is 6 - 8 h; the blooming forging temperature is ≥1150 °C, the last heating temperature of the last heat is 1080 °C, and the forging ratio is ≥4. Air cooling is carried out after forging.
[0057] (2) Heat treatment
[0058] Quenching treatment: Heat the bar to 910 °C, hold for 1 h, and cool in oil;
[0059] Tempering treatment: Heat the bar to 220 °C, hold for 2 h, and air cool to room temperature.
[0060] Table 1 Chemical composition of the fatigue-resistant low-alloy ultra-high-strength steel
[0061]
[0062] Table 2 Heat treatment process parameters of the fatigue-resistant low-alloy ultra-high-strength steel
[0063] Composition Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Quenching treatment 910℃×1h 910℃×1h 910℃×1h 910℃×1h 940℃×1h 880℃×1h Tempering treatment 220℃×2h 220℃×2h 220℃×2h 220℃×2h 220℃×2h 300℃×3h
[0064] Example 2-3
[0065] Example 2-3 respectively provides a kind of anti-fatigue low-alloy ultra-high strength steel. The differences between the above examples and Example 1 lie in the chemical compositions, as shown in Table 1 specifically, and the remaining steps are the same as those in Example 1.
[0066] Comparative example
[0067] Comparative examples 1-3
[0068] Comparative examples 1-3 respectively provide a kind of ultra-high strength steel. The differences between the above comparative examples and Example 1 lie in the differences in chemical compositions and / or heat treatment processes, as shown in Table 1 and Table 2 specifically, and the remaining steps are the same as those in Example 1.
[0069] Performance test results
[0070] The anti-fatigue low-alloy ultra-high strength steel provided by the above examples and the ultra-high strength steel provided by the comparative examples are respectively subjected to the following tests.
[0071] Among them, the test methods for tensile strength, yield strength, elongation, and reduction of area refer to "GB / T 228.1-2010", the test method for fracture toughness refers to "GB / T 4161-2007", and the test method for fatigue performance refers to "GB / T3075-2021".
[0072] The test results are shown in Table 3 and Table 4.
[0073] Test results of various performances in Table 3
[0074] Number Rm / MPa Rp0.2 / MPa A / ％ Z / ％ KIC / MPa·m1 / 2 Cr + Mo + Ni content / wt% Example 1 2215 1718 10.0 33 59.0 2.49 Example 2 2203 1710 9.5 32 61.3 2.28 Example 3 2212 1725 10.0 35 58.5 2.46 Comparative Example 1 2146 1717 10.0 38 41 1.39 Comparative Example 2 2239 1833 8.5 25 41.8 5.02 Comparative Example 3 1978 1498 11.0 36.0 73.1 3.1
[0075] Test results of fatigue performance in Table 4
[0076] Number Fatigue life Nf under the conditions of Kt = 1, R = 0.06, and σmax = 1350 MPa Example 1 ≥ 3 million times Example 2 ≥ 3 million times Example 3 ≥ 3 million times
[0077] It can be seen from Table 3 and Table 4 that this application provides a method to control the contents of elements such as C, Si, Mn, Cr, Mo, and Ni in steel, and combines the process of quenching + tempering to obtain a tempered martensite matrix structure and a high-density nano-scale ε precipitation phase, with the content of Cr+Ni+Mn ≤ 2.5%, and the material economy is remarkable.
[0078] The tensile strength of the anti-fatigue low-alloy ultra-high strength steel provided by this application can reach more than 2200 MPa, the yield strength ≥ 1700 MPa, the elongation ≥ 8%, the reduction of area ≥ 30%, and the fracture toughness ≥ 55 MPa·m 1 / 2 .
[0079] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.
[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit them; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.
Claims
1. A kind of anti-fatigue low-alloy ultra-high strength steel, characterized in that, The chemical composition of the anti-fatigue low-alloy ultra-high strength steel, by mass percentage, includes: C 0.46 - 0.56%, Si 0.5 - 2%, Mn 0.5 - 1.8%, Cr 0.1 - 0.7%, Mo 0.5 - 2%, Ni 0.5 - 1.4%, and the balance is Fe and inevitable impurities.
2. The anti-fatigue low-alloy ultra-high strength steel according to claim 1, wherein The grain size of the anti-fatigue low-alloy ultra-high strength steel is ≥6 grades.
3. The anti-fatigue low-alloy ultra-high strength steel according to claim 1, wherein The anti-fatigue low-alloy ultra-high strength steel further includes grain-refining elements; Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the grain-refining elements include, but are not limited to, any one or more of V and Nb; Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the content of V is 0.01 - 0.2%; Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the content of Nb is 0.01 - 0.10%.
4. The anti-fatigue low-alloy ultra-high strength steel according to claim 1, characterized in that, In the anti-fatigue low-alloy ultra-high strength steel, the content of Cr + Mo + Ni ≤ 3%; Optionally, in the anti-fatigue low-alloy ultra-high strength steel, the content of Cr + Mo + Ni ≤ 2.5%.
5. The anti-fatigue low-alloy ultra-high strength steel according to claim 1, characterized in that, The tensile strength of the anti-fatigue low-alloy ultra-high strength steel is ≥2200 MPa, the yield strength is ≥1700 MPa, the elongation is ≥8%, the reduction of area is ≥30%, and the fracture toughness is ≥55 MPa·m 1 / 2 .
6. A method for preparing the anti-fatigue low-alloy ultra-high strength steel according to any one of claims 1-5, characterized in that, The preparation method includes a heat treatment method, and the heat treatment method includes quenching treatment and tempering treatment.
7. The preparation method according to claim 6, characterized in that, The quenching treatment includes: heating the bar to 860 - 960 °C, holding for 1 - 2 h, and cooling in oil.
8. The preparation method according to claim 6, characterized in that, The tempering treatment includes: heating the bar to 150 - 300 °C, holding for 1 - 6 h, and air-cooling to room temperature.
9. Application of the anti-fatigue low-alloy ultra-high strength steel according to any one of claims 1 - 5 in the material for aircraft landing gears.