Austenitic low-density steel for aerospace applications and heat treatment process thereof

Abstract

This invention discloses an austenitic low-density steel for aerospace applications and its heat treatment process. The chemical composition, by mass percentage, is: Mn: 26.5%–30%, Al: 8.00%–11.00%, C: 1.00%–1.5%, Mo: 0.4%–0.7%, Ti: 0.1%–0.30%, Nb: 0.1%–0.3%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities. By controlling the content of alloying elements such as Mo, Ti, and Nb in the Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel and its solution-aging heat treatment process, a Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel with excellent low-temperature mechanical properties and high austenite stability at low temperatures is obtained. The density of the low-density steel of this invention can reach 6.20–6.60 g / cm³. 3 Compared with traditional alloy steel, it can achieve a weight reduction of 14.5% to 17.5%, a tensile strength of 800 to 1000 MPa, an elongation of 50% to 65%, and an impact energy of 80 to 90 J at -90℃. It possesses high strength and good low-temperature toughness, and has broad application prospects in the field of aerospace motion mechanisms.

Description

Technical Field

[0001] This invention relates to the field of low-density steel technology, and in particular to a Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel and its heat treatment process. Background Technology

[0002] Compared to traditional quenched and tempered steel, Fe-Mn-Al low-density steel exhibits superior strength and toughness along with lower density. Weight reduction of approximately 8-20% can be achieved by altering the Al content. Among Fe-Mn-Al low-density steels, Fe-Mn-Al austenitic low-density steel possesses the best mechanical properties, exhibiting both high strength and good low-temperature toughness. Currently, Fe-Mn-Al low-density steel is primarily used in the automotive industry. However, with the development of the aerospace industry, there is a need for low-temperature resistant lightweight materials to cope with even harsher low-temperature environments. Domestic and international research is gradually exploring the application of Fe-Mn-Al low-density steel in the aerospace field. Using Fe-Mn-Al low-density steel can reduce the weight of aerospace motion mechanisms, significantly reducing energy consumption.

[0003] C, Al, and Mn each play different roles in reducing the density of steel. Adding 1 wt.% Al reduces the steel density by approximately 1.3%; adding 1 wt.% C reduces the density by approximately 5.2%; and adding 1 wt.% Mn also reduces the steel density by approximately 0.1%. This invention rationally designs the main lightweight elements C, Al, and Mn, while adding microalloying elements such as Mo, Ti, and Nb to ensure both low density and high strength of the steel. Summary of the Invention

[0004] The purpose of this invention is to provide a Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel and its heat treatment process, so as to obtain a Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel with high strength and high low-temperature toughness.

[0005] To achieve the above objectives, the present invention provides the following technical solution.

[0006] This invention provides a low-density austenitic steel for low-temperature applications using a Fe-Mn-Al-Mo-Ti-Nb alloy. The chemical composition, by mass percentage, is as follows: C: 1.00%–1.5%, Mn: 26.5%–30%, Al: 8.00%–11.00%, Mo: 0.4%–0.7%, Ti: 0.1%–0.30%, Nb: 0.1%–0.3%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

[0007] The present invention also provides a method for preparing the above-mentioned Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel, comprising the following steps.

[0008] Ingredients: Pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium are used as raw materials, and the ingredients are prepared according to the requirements of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel.

[0009] Smelting: The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium are added to a vacuum induction melting furnace to complete the smelting process;

[0010] Steel tapping: Molten steel is poured into a mold and air-cooled to obtain cast steel.

[0011] Forging: The cast steel is heated and then forged. The initial forging temperature is 150-250℃, and the final forging temperature is 850-900℃.

[0012] Heat treatment: Heat treatment is carried out using a box furnace. Solution treatment at 1100-1250℃ for 1-3 hours, followed by water cooling, aging at 450-700℃ for 3-10 hours, and then air cooling to room temperature.

[0013] As a further preferred embodiment of the present invention, the carbon raiser in the ingredients is made of natural graphite or artificial graphite.

[0014] As a further preferred embodiment of the present invention, the optimal temperature during the forging process is 900°C.

[0015] As a further preferred embodiment of the present invention, the solution treatment temperature is 1200°C and the solution treatment time is 2 hours.

[0016] As a further preferred embodiment of the present invention, the aging temperature is 500°C and the aging time is 5 hours.

[0017] The Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel of this invention, after solution treatment and aging, consists of dispersed Ti, Nb carbides, κ carbides, and an austenitic matrix. Ti, Nb carbides, and κ carbides play a precipitation strengthening role. Simultaneously, Mo, Ti, and Nb elements dissolved in the austenitic matrix also contribute to solid solution strengthening.

[0018] Compared with traditional alloy structural steel, the present invention has the following advantages:

[0019] 1) This invention achieves a significant lightweight effect through a high-Al alloy design, reducing the density by approximately 14.5–17.5% compared to traditional structural steel. Simultaneously, the Al element also improves its low-temperature toughness.

[0020] 2) This invention improves the austenite stability of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel through high-Mn alloy design. Simultaneously, the high Mn content increases the stacking fault energy of the steel, transforming the deformation mode from transformation-induced plasticity to twin-induced plasticity.

[0021] 3) This invention utilizes Mo to improve corrosion resistance and the solubility of microalloying elements in steel.

[0022] 4) This invention utilizes the solid solution strengthening of Ti and Nb to improve strength and toughness. At the same time, Ti and Nb will form stable MC-type carbides with C elements, which together with the κ carbides formed in the matrix pin grain boundaries and dislocations.

[0023] 5) The preparation process of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel of the present invention is simple. Only a simple solution aging heat treatment process is required to obtain Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel with high strength and high and low temperature toughness. Attached Figure Description

[0024] Figure 1 This is a high-magnification SEM micrograph of the tissue from Example 1.

[0025] Figure 2 This is a high-magnification SEM micrograph of the tissue from Example 2.

[0026] Figure 3 This is a high-magnification SEM micrograph of the tissue from Example 3.

[0027] Figure 4 This is a high-magnification SEM micrograph of the tissue from Example 4.

[0028] Figure 5 This is a high-magnification SEM micrograph of the tissue from Example 5. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, which will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary. The terms "comprising," "including," "having," "containing," etc., as used herein are open-ended, meaning they include but are not limited to.

[0033] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0034] Example 1

[0035] The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium were added to a vacuum induction melting furnace for smelting and then cast into ingots. The chemical composition was C: 1.20%, Mn: 28.89%, Al: 9.03%, Mo: 0.48%, Ti: 0.19%, Nb: 0.15%, with the remainder being Fe and unavoidable impurities. The ingots were heated to 1150℃ and held for 3 hours before forging. The final forging temperature was 950℃, resulting in round bars with a diameter of approximately 100 mm. The forged round bars were then solution-treated at 1200℃ for 2 hours, water-cooled, and aged at 600℃ for 5 hours.

[0036] Microstructure and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel after solution treatment and aging were observed. The mechanical properties are shown in Table 1.

[0037] Table 1. Density and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel in Example 1

[0038]

[0039] Example 2

[0040] The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium were added to a vacuum induction melting furnace for smelting and then cast into ingots. The chemical composition was C: 1.19%, Mn: 29.13%, Al: 9.12%, Mo: 0.51%, Ti: 0.19%, Nb: 0.16%, with the remainder being Fe and unavoidable impurities. The ingots were heated to 1150℃ and held for 3 hours before forging. The final forging temperature was 950℃, resulting in round bars with a diameter of approximately 100 mm. The forged round bars were then solution-treated at 1200℃ for 2 hours, water-cooled, and aged at 500℃ for 5 hours.

[0041] Microstructure and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel after solution treatment and aging were observed. The mechanical properties are shown in Table 2.

[0042] Table 2. Density and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel in Example 2

[0043]

[0044] Example 3

[0045] The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium were added to a vacuum induction melting furnace for smelting and then cast into ingots. The chemical composition was C: 1.17%, Mn: 28.75%, Al: 10.79%, Mo: 0.48%, Ti: 0.18%, Nb: 0.14%, with the remainder being Fe and unavoidable impurities. The ingots were heated to 1150℃ and held for 3 hours before forging. The final forging temperature was 950℃, resulting in round bars with a diameter of approximately 100 mm. The forged round bars were then solution-treated at 1200℃ for 2 hours, water-cooled, and aged at 500℃ for 5 hours.

[0046] Microstructure and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel after solution treatment and aging were observed. The mechanical properties are shown in Table 3.

[0047] Table 3. Density and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel in Example 3

[0048]

[0049] Example 4

[0050] The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium were added to a vacuum induction melting furnace for smelting and then cast into ingots. The chemical composition was C: 1.42%, Mn: 28.89%, Al: 10.92%, Mo: 0.48%, Ti: 0.29%, Nb: 0.27%, with the remainder being Fe and unavoidable impurities. The ingots were heated to 1150℃ and held for 3 hours before forging. The final forging temperature was 950℃, resulting in round bars with a diameter of approximately 100 mm. The forged round bars were then solution-treated at 1200℃ for 2 hours, water-cooled, and aged at 600℃ for 5 hours.

[0051] Microstructure and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel after solution treatment and aging were observed. The mechanical properties are shown in Table 4.

[0052] Table 4. Density and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel in Example 4

[0053]

[0054] The Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel of this invention achieves lightweighting through a high-Al alloy design. Al is a ferrite-forming element, and to ensure its microstructure is pure austenite, a high-Mn, high-C alloy design is used to stabilize the austenite phase. Furthermore, high strength and toughness are achieved through solid solution strengthening with Ti and Nb elements, and precipitation strengthening through κ carbides and TiC, NbC, and other precipitates formed by Ti and Nb elements.

[0055] Example 5

[0056] The prepared pure iron, electrolytic manganese flakes, pure aluminum blocks, carbon raiser, ferromolybdenum, sponge titanium, and ferroniobium were added to a vacuum induction melting furnace for smelting and then cast into ingots. The chemical composition was C: 1.05%, Mn: 28.89%, Al: 10.92%, Mo: 0.42%, Ti: 0.13%, Nb: 0.19%, with the remainder being Fe and unavoidable impurities. The ingots were heated to 1150℃ and held for 3 hours before forging. The final forging temperature was 950℃, resulting in round bars with a diameter of approximately 100 mm. The forged round bars were then solution-treated at 1200℃ for 2 hours, water-cooled, and aged at 600℃ for 5 hours.

[0057] Microstructure and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel after solution treatment and aging were observed. The mechanical properties are shown in Table 1.

[0058] Table 5. Density and mechanical properties of Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel in Example 5

[0059]

[0060] The Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel of this invention achieves lightweighting through a high-Al alloy design. Al is a ferrite-forming element, and to ensure its microstructure is pure austenitic, a high-Mn, high-C alloy design is used to stabilize the austenitic phase. Furthermore, high strength and toughness are achieved through solid solution strengthening with Ti and Nb elements, and precipitation strengthening through κ carbides and TiC and NbC precipitates formed by Ti and Nb elements. Its tensile strength can reach 800–1000 MPa, elongation can reach 50–65%, and impact energy at -90℃ can reach 80–100 J.

Claims

1. An aerospace-grade austenitic low-density steel, specifically an Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel, characterized in that... The chemical composition, by mass percentage, is as follows: C: 1.00%~1.5%, Mn: 26.5%~30%, Al: 8.00%~11.00%, Mo: 0.4%~0.7%, Ti: 0.1%~0.30%, Nb: 0.1%~0.3%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities. The materials are fed according to the designed chemical composition, smelted, and cast into steel ingots. These ingots are then heated and forged to obtain… The forging material is then subjected to solution treatment and aging treatment to obtain Fe-Mn-Al-Mo-Ti-Nb austenitic low-density steel. The heating temperature is 1100~1200℃ for 3 hours; the final forging temperature is 850~900℃; the solution treatment temperature is 1100~1250℃ for 1~3 hours; the aging temperature is 450~700℃ for 3~10 hours; after solution treatment, the material is oil-cooled to room temperature and then aging treatment is performed, followed by air cooling to room temperature.

2. The austenitic low-density steel for aerospace applications according to claim 1, characterized in that, The chemical composition of this aerospace-grade austenitic low-density steel, by mass percentage, is as follows: C: 1.20%, Mn: 28.89%, Al: 9.03%, Mo: 0.48%, Ti: 0.19%, Nb: 0.15%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

3. The austenitic low-density steel for aerospace applications according to claim 1, characterized in that, The chemical composition of this aerospace-grade austenitic low-density steel, by mass percentage, is as follows: C: 1.19%, Mn: 29.13%, Al: 9.12%, Mo: 0.51%, Ti: 0.19%, Nb: 0.16%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

4. The austenitic low-density steel for aerospace applications according to claim 1, characterized in that, The chemical composition of this aerospace-grade austenitic low-density steel, by mass percentage, is as follows: C: 1.17%, Mn: 28.75%, Al: 10.79%, Mo: 0.48%, Ti: 0.18%, Nb: 0.14%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

5. The austenitic low-density steel for aerospace applications according to claim 1, characterized in that, The chemical composition of this aerospace-grade austenitic low-density steel, by mass percentage, is as follows: C: 1.42%, Mn: 28.89%, Al: 10.92%, Mo: 0.48%, Ti: 0.29%, Nb: 0.27%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

6. The austenitic low-density steel for aerospace applications according to claim 1, characterized in that, The chemical composition of this aerospace-grade austenitic low-density steel, by mass percentage, is as follows: C: 1.05%, Mn: 28.89%, Al: 10.92%, Mo: 0.42%, Ti: 0.13%, Nb: 0.19%, P≤0.005%, S≤0.003%, N≤0.002%, with the remainder being Fe and unavoidable impurities.

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