Niobium microalloyed nitrogen-controlled high-strength martensitic stainless steel and preparation method thereof

Abstract

The invention relates to the technical field of high-strength stainless steel, in particular to niobium microalloying nitrogen-controlled high-strength martensitic stainless steel and a preparation method thereof. The martensitic stainless steel comprises the following chemical components in percentage by mass: 0.1 to 0.16 percent of C, 10.5 to 12 percent of Cr, 1.4 to 1.8 percent of Ni, 1.5 to 2 percent of W, 0.35 to 0.5 percent of Mo, 0.18 to 0.3 percent of V and the balance of Fe and inevitable impurities. The alloy further comprises an element N and an element Nb which are non-impurity elements, the content of N is 0.02%-0.12%, and the content of Nb is 0.01%-0.15%. The high-strength martensitic stainless steel with excellent durability is developed to solve the problem that the durability of an existing turbine shaft material cannot meet the requirement of an aero-engine.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high-strength stainless steel, in particular to a niobium microalloyed controlled-nitrogen high-strength martensitic stainless steel and a preparation method thereof. BACKGROUND

[0002] The turbine shaft mainly transmits high torque in an aero-engine, and has the characteristics of large length-diameter ratio, thin wall and variable cross section. When working, the turbine shaft not only bears various loads such as torsional moment, bending moment, axial tensile force and centrifugal force, but also bears temperature load in the high-temperature working part. Therefore, the turbine shaft needs to have high tensile strength, shear strength and fatigue resistance.

[0003] The typical representative of the martensitic heat-resistant stainless steel is 1Cr11Ni2W2MoV steel, which is originally developed as an engine material and is based on 12%Cr steel, and a large amount of W, Mo and V elements are added to improve the high-temperature strength, corrosion resistance and thermal fatigue resistance of the steel, so as to obtain a new type of martensitic stainless steel. The steel has good comprehensive mechanical properties and has been widely used in the manufacture of important parts such as engine blades, discs and shafts working below 600 DEG C in the aviation industry, and is favored due to its excellent comprehensive mechanical properties, good corrosion resistance and high-temperature resistance.

[0004] With the continuous progress of smelting and forging technology of the steel industry in China, the purity and conventional performance of 1Cr11Ni2W2MoV steel are continuously improved. However, it is found that with the improvement of purity, the endurance performance is continuously decreased. In order to improve the service life and safety of the turbine shaft during service, the problem of endurance performance decrease of 1Cr11Ni2W2MoV steel caused by the improvement of purity must be solved.

[0005] Therefore, it is urgent to optimize the composition within the high-purity smelting condition and the composition standard range of 1Cr11Ni2W2MoV steel at the present stage to obtain a high-strength martensitic stainless steel with higher endurance performance. SUMMARY

[0006] The application provides a niobium microalloyed controlled-nitrogen high-strength martensitic stainless steel and a preparation method thereof.

[0007] The application develops a high-strength martensitic stainless steel with excellent endurance performance aiming at the problem that the endurance performance of the turbine shaft material in service cannot meet the development of the aero-engine.

[0008] In a first aspect, the application provides a niobium microalloyed controlled-nitrogen high-strength martensitic stainless steel, which adopts the following technical scheme: The niobium micro-alloyed nitrogen controlled high-strength martensitic stainless steel comprises, in percentage by mass, C 0.1-0.16%, Cr 10.5-12%, Ni 1.4-1.8%, W 1.5-2%, Mo 0.35-0.5%, V 0.18-0.3%, and the balance of Fe and inevitable impurities; and further comprises N element as a non-impurity element, with a content of 0.02-0.12%.

[0009] Optionally, the high-strength martensitic stainless steel further comprises Nb element as a non-impurity element, with a content of 0.01-0.15%.

[0010] The high-strength martensitic stainless steel provided by the application comprises N element and Nb element as non-impurity elements in the composition. A certain amount of N element and Nb element is added within the standard range of the steel composition, so as to ensure the conventional performance of the martensitic stainless steel while improving the high-temperature durability of the martensitic stainless steel.

[0011] In a second aspect, the application further provides a heat treatment method of the high-strength martensitic stainless steel. The heat treatment method of the high-strength martensitic stainless steel comprises the following steps: quenching and tempering the high-strength martensitic stainless steel obtained by smelting and meeting the chemical composition requirements.

[0012] Optionally, the smelting refers to any one method or a combination of multiple methods selected from a converter, an electric furnace, a vacuum induction furnace, an LF furnace, vacuum consumable, and electric slag remelting, so as to prepare the high-strength martensitic stainless steel with a chemical composition range meeting the requirements.

[0013] Optionally, the quenching treatment comprises heating the bar to 1000-1020 DEG C, holding for 1-3 h, and oil cooling.

[0014] Optionally, the tempering treatment comprises heating the bar to 540-580 DEG C, holding for 1-4 h, and air cooling to room temperature.

[0015] In summary, the application has at least one of the following beneficial technical effects: 1. The high-strength martensitic stainless steel provided by the application can effectively improve the durability of the high-strength martensitic stainless steel by adding appropriate amounts of N and Nb elements and combining the quenching + tempering process to obtain a tempered martensitic matrix structure and fine grains.

[0016] 2. The high-strength martensitic stainless steel provided by the application has a tensile strength of ≥1220 MPa, a yield strength of ≥1020 MPa, an elongation of ≥16%, a reduction of area of ≥65%, and an impact toughness of ≥100 J / cm 2High temperature and high stress sustained fracture time ≥100h. Detailed Implementation

[0017] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0018] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0019] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0021] This application provides a niobium microalloyed nitrogen-controlled high-strength martensitic stainless steel. The chemical composition of this high-strength martensitic stainless steel, by mass percentage, includes: C 0.1-0.16%, Cr 10.5-12%, Ni 1.4-1.8%, W 1.5-2%, Mo 0.35-0.5%, V 0.18-0.3%, with the balance being Fe and unavoidable impurities; it also includes nitrogen (N) as a non-impurity element, with an N content of 0.02-0.12%.

[0022] Furthermore, the aforementioned high-strength martensitic stainless steel also includes Nb as a non-impurity element, with an Nb content of 0.01-0.15%.

[0023] The following details the function and dosage selection of the components contained in this application: The high-strength martensitic stainless steel of this application comprises C: 0.1-0.16% by mass percentage.

[0024] Carbon (C) is a major strengthening element in steel, promoting the precipitation of second-phase carbides and enhancing the mechanical properties of the material. However, carbide precipitation reduces the chromium content of the steel, and near the carbides, localized electrochemical imbalances and micro-corrosion can lead to intergranular corrosion, pitting corrosion, or stress corrosion cracking, thus exacerbating the corrosion susceptibility of stainless steel. Therefore, the upper limit of C content is controlled at 0.16%.

[0025] The high-strength martensitic stainless steel of this application comprises Cr: 10.5-12% by mass percentage.

[0026] Cr has a decisive influence on the corrosion resistance of steel. Cr reacts with oxygen to form a dense oxide film (Cr₂O₃), which is key to the corrosion resistance of stainless steel. Cr can also significantly improve the resistance of stainless steel to intergranular corrosion and enhance its hardenability, increasing its quench hardening ability and enabling it to achieve higher hardness after quenching. However, excessively high Cr content reduces the plasticity and toughness of the steel; therefore, the upper limit for Cr content is controlled at 12%.

[0027] The high-strength martensitic stainless steel of this application comprises Ni: 1.4-1.8% by mass.

[0028] Ni is a strong austenite-forming element, which can expand the austenite phase region, helping to increase the austenite content of steel and improve the toughness of the material. Secondly, Ni can improve the thermodynamic stability of stainless steel and increase its corrosion resistance. The presence of Ni can improve the hardenability of martensitic stainless steel, promoting the transformation of martensite, thereby giving the material better hardness and strength. Appropriate Ni addition can promote the deformation, ductility, and toughness of the material. However, excessive Ni content will form too much retained austenite, impairing the toughness of the steel and significantly reducing the yield strength; therefore, the upper limit of Ni content is controlled at 1.8%.

[0029] The high-strength martensitic stainless steel of this application comprises W: 1.5-2% by mass percentage.

[0030] By forming strengthening phases with other elements, wrought iron (W) can effectively enhance the wear resistance of martensitic stainless steel, enabling it to perform excellently under high load and high friction conditions. Furthermore, the presence of W helps improve the alloy's high-temperature resistance and maintain the stability of martensite, allowing it to retain excellent mechanical properties in high-temperature environments. However, excessive W will significantly increase the steel's melting temperature and reduce forging performance; too high a W content will increase the quenching temperature. Therefore, the upper limit for W content is controlled at 2%.

[0031] The high-strength martensitic stainless steel of this application comprises Mo: 0.35-0.5% by mass percentage.

[0032] Mo can significantly improve the corrosion resistance of martensitic stainless steel, effectively reducing the alloy's susceptibility to intergranular corrosion and making it more corrosion-resistant. Mo can also improve the high-temperature resistance of martensitic stainless steel, enabling it to maintain stable mechanical properties at high temperatures. However, excessive Mo can significantly increase the steel's melting temperature and reduce its forging properties; therefore, the upper limit of Mo content is controlled at 0.5%.

[0033] The high-strength martensitic stainless steel of this application, by mass percentage, includes nitrogen (N) or a combination of N and Nb, with an N content of 0.02-0.12% and an Nb content of 0.01-0.15%. These elements are not considered impurities in this application. Appropriate amounts of N and Nb do not form hard nitrides; instead, they refine the grains, thus ensuring that the performance at room temperature does not deteriorate. Under high-temperature creep rupture testing conditions, nitrides form at grain boundaries, pinning them. Because nitrides have higher thermal stability than carbides, they are less prone to coarsening under sustained high-temperature conditions, thereby significantly improving creep rupture performance.

[0034] The high-strength martensitic stainless steel of this application also includes unavoidable impurity elements, mainly including S, P, O, Al, etc., with Mn≤0.4%, S≤0.03%, Si≤0.04%, P≤0.005%, O≤0.01%, and Al≤0.04%. Effective control of the above impurity elements can improve the toughness and high-temperature creep performance of the material.

[0035] This application also provides heat treatment methods for the above-mentioned high-strength martensitic stainless steel, including: quenching treatment and tempering treatment.

[0036] The quenching process includes heating the bar to 1000-1020℃, holding it at that temperature for 1-3 hours, and then oil cooling.

[0037] The tempering process includes heating the bar to 540-580℃, holding it at that temperature for 1-4 hours, and then air-cooling it to room temperature.

[0038] The purpose of the above quenching treatment is to completely dissolve the main alloying elements in the steel into the matrix and obtain a martensitic structure through oil quenching. The purpose of tempering treatment is to promote the precipitation of nano-carbide, soften the matrix, and thus obtain an excellent combination of strength and toughness.

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0040] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0041] The present application will be further described in detail below with reference to the embodiments and test results. Example

[0042] This embodiment provides a niobium microalloyed nitrogen-controlled high-strength martensitic stainless steel.

[0043] The chemical composition of this high-strength martensitic stainless steel, by mass percentage, is shown in Table 1.

[0044] The preparation method of this high-strength martensitic stainless steel is as follows: (1) Smelting: High-strength martensitic stainless steel that meets the chemical composition requirements is obtained through smelting.

[0045] (2) Heat treatment method: Quenching treatment: Heat the bar to 1010℃, hold for 1 hour, and then oil cool; Tempering treatment: Heat the bar to 560℃, hold for 2 hours, and air cool to room temperature.

[0046] The residual austenite phase content of high-strength martensitic stainless steel was determined by XRD, and the results are shown in Table 1.

[0047] Examples 2-5 Examples 2-5 each provide a niobium microalloyed nitrogen-controlled high-strength martensitic stainless steel. The difference between these and Example 1 lies in the chemical composition of the high-strength martensitic stainless steel, as shown in Table 1. All other operating steps remain the same as in Example 1.

[0048] In the schemes of Examples 1-2, the amount of N element added meets the required range and is regarded as a non-impurity element; while the amount of Nb element added does not meet the required range and is regarded as an impurity element.

[0049] In the schemes of Examples 3-5, the amount of N element added meets the required range and is used as a non-impurity element; the amount of Nb element added also meets the required range and is used as a non-impurity element.

[0050] Apart from the elements mentioned above, the content of other elements in Examples 1-5 remained basically the same.

[0051] Table 1. Amounts of each element added in the examples and comparative examples

[0052] Comparative Examples 1-4 Comparative Examples 1-4 each provide a niobium microalloyed nitrogen-controlled high-strength martensitic stainless steel. The difference between these and Example 1 lies in the chemical composition of the high-strength martensitic stainless steel, as shown in Table 1. All other operating procedures remain consistent with Example 1.

[0053] In Comparative Example 1, the amounts of both N and Nb added did not meet the required range and were therefore considered impurity elements.

[0054] In Comparative Examples 2-3, the amount of N added does not meet the required range and is considered an impurity element or exceeds the maximum value of the required range; while the amount of Nb added does not meet the required range and is considered an impurity element.

[0055] In Comparative Example 4, the amount of N added did not meet the required range and was therefore considered an impurity element; while the amount of Nb added met the required range and was therefore considered a non-impurity element.

[0056] Apart from the elements mentioned above, the content of other elements in Comparative Examples 1-4 is basically the same, and is also basically the same as the content of other elements in Examples 1-5.

[0057] Performance testing The mechanical properties (tensile properties, including tensile strength) of the high-strength martensitic stainless steels prepared in the above embodiments and comparative examples were tested respectively. R m ), yield strength ( R p0.2 ), elongation after fracture ( A ) and reduction of area ( Z Impact toughness, including the total impact energy absorbed by the U-notch specimen. KU 2 / J), impact absorption energy per unit U-shaped notch area ( aKU / J / cm 2 And persistent performance.

[0058] The testing methods for tensile strength, yield strength, elongation, and reduction of area are in accordance with GB / T228.1-2010; the testing method for impact toughness is in accordance with GB / T 229-2020; and the testing method for high-temperature creep performance is in accordance with GB / T 2039-2012.

[0059] The test results for mechanical properties are shown in Table 2. The test results for durability properties are shown in Table 3.

[0060] Table 2 Test results of mechanical properties

[0061] Table 3. Test results of durability performance

[0062] As shown in Tables 2 and 3, comparing the results of Examples 1-5 with those of Comparative Examples 1-4, the high-strength martensitic stainless steel provided in this application has a tensile strength ≥1220MPa, a yield strength ≥1020MPa, an elongation ≥16%, a reduction of area ≥65%, and an impact toughness ≥100J / cm². 2 High temperature and high stress sustained fracture time ≥100h.

[0063] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0064] 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 skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions 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 niobium microalloyed controlled nitrogen high strength martensitic stainless steel, characterized in that, The high-strength martensitic stainless steel comprises, in mass percentage, C 0.1-0.16%, Cr 10.5-12%, Ni 1.4-1.8%, W 1.5-2%, Mo 0.35-0.5%, V 0.18-0.3%, and the balance of Fe and inevitable impurities. The high-strength martensitic stainless steel further comprises N as a non-impurity element, and the content of N is 0.02-0.12%.

2. The high-strength martensitic stainless steel according to claim 1, characterized by The high-strength martensitic stainless steel further comprises Nb as a non-impurity element, and the content of Nb is 0.01-0.15%.

3. The high strength martensitic stainless steel according to claim 1, characterized in that, The high-temperature high-stress rupture time of the high-strength martensitic stainless steel is greater than or equal to 100 hours.

4. The high strength martensitic stainless steel of claim 1, wherein, The high-strength martensitic stainless steel has a tensile strength of ≥1220 MPa, a yield strength of ≥1020 MPa, an elongation of ≥16%, a reduction of area of ≥65%, and an impact toughness of ≥100 J / cm 2 .

5. A method of heat treatment of the high-strength martensitic stainless steel according to any one of claims 1 to 4, characterized in that, The heat treatment method comprises the following steps: quenching and tempering the high-strength martensitic stainless steel obtained by smelting and satisfying the chemical composition requirements.

6. The heat treatment method according to claim 5, characterized by, The quenching comprises heating the bar to 1000-1020 DEG C, holding for 1-3 hours, and oil cooling.

7. The heat treatment method according to claim 5, wherein The tempering comprises heating the bar to 540-580 DEG C, holding for 1-4 hours, and air cooling to room temperature.

8. The heat treatment method according to claim 5, wherein The smelting refers to any one method or a combination of multiple methods selected from a converter, an electric furnace, a vacuum induction furnace, an LF furnace, vacuum consumable, and electric slag remelting, so as to prepare the high-strength martensitic stainless steel with the chemical composition in the required range.

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