Fe-Mn-Al series steel with high specific yield strength and preparation method of Fe-Mn-Al series steel

Abstract

The invention relates to Fe-Mn-Al series steel with high specific yield strength and a preparation method of the Fe-Mn-Al series steel, belongs to the technical field of additive manufacturing, and solves the technical problem that high-carbon Fe-Mn-Al series steel complex structural parts with high specific yield strength cannot be prepared in the prior art. The invention relates to Fe-Mn-Al series steel with high specific yield strength, which comprises the following components in percentage by mass: 49 to 55 percent of Fe, 28 to 32 percent of Mn, 10 to 13 percent of Al, 1.3 to 1.7 percent of C and 3 to 7 percent of Cr. The high specific yield strength is 190 MPa / (g / cm < 3 >) or more. The specific yield strength of the Fe-Mn-Al series steel is 190 MPa / (g / cm < 3 >) or above, the Fe-Mn-Al series steel can replace titanium alloy, the requirement for improving the carrying capacity of a hinge connecting piece of an aircraft control surface can be met, the weight reduction requirement of a reinforcing structural component of a new energy automobile motor shell can be met, oil consumption can be further reduced, and the endurance mileage can be remarkably increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a Fe-Mn-Al steel with high specific yield strength and a preparation method thereof. Background Art

[0002] With the continuous development of society and the economy, the global industry is strategically shifting towards lightweighting, greening, and intelligent manufacturing. In the aerospace sector, especially in the field of advanced unmanned aerial vehicles (UAVs), the material's specific yield strength (yield strength / density) is a key indicator of aircraft performance. Currently, titanium alloys are the most commonly used materials. Among these, the high-specific-yield-strength, highly complex hinged connectors for aircraft control surfaces are key to improving carrying capacity, yet these components do not require high plasticity. In the field of new energy vehicles, lightweighting has become an inevitable trend. Reducing the weight of reinforced structural components in motor housings can reduce fuel consumption and significantly increase range. These structural components often require high complexity, high specific yield strength, corrosion resistance, and the ability to withstand static loads. Therefore, lightweight, high-strength steels, such as Fe-Mn-Al alloys, are expected to achieve breakthrough applications in aerospace engineering and new energy vehicles due to their high strength, low density, and reasonable corrosion resistance.

[0003] Fe-Mn-Al low-density steel is a high-specific-strength steel that relies primarily on Al, Mn, and C elements to reduce system density and improve strength through κ phase and grain refinement. Fe-Mn-Al low-density steel produced by traditional casting, forging, and rolling methods achieves grain refinement and strength improvement through grain crushing during forging and rolling. However, as the Al, Mn, and C content increases, especially when the C content is above 1.3wt.%, the difficulty of forming increases during the traditional casting, forging, and rolling process due to defects such as element segregation, inclusions, and amorphous graphite phases at grain boundaries. Furthermore, when the C content is above 1.3wt.%, the increase in the thermal expansion coefficient of the steel itself and the precipitation of amorphous graphite phases at grain boundaries seriously affect the formability and toughness of forming methods such as welding. Patent CN113278896B discloses a Fe-Mn-Al-C high-strength low-density steel and its preparation method. The steel composition is C1.0-2.0wt%, Mn25.03-40wt%, Al10.12-14wt%, 2wt%≤Ni+Cr≤15wt%, and one or more of Mo, Si, Cu, B, Nb, Ti, V, RE, and Ca in appropriate amounts, with the balance being Fe. The preparation method includes smelting, solidification casting, hot working forging / rolling, solution treatment or solution treatment and aging treatment; or injection molding process, followed by solution treatment or solution treatment and aging treatment. Although the Fe-Mn-Al-C steel prepared by this method has a specific yield strength (yield strength / density) of up to 234MPa / (g / cm 3), but the wide range of steel composition options in this method leads to unstable specific yield strength and is not suitable for the preparation of complex structural parts.

[0004] At present, the preparation of complex structural parts is more inclined to use additive manufacturing technology. In the existing technology, patents CN118478019A and CN118513567A disclose a hot isostatic pressing process and a rapid heat treatment process for additively manufactured parts of austenitic low-density steel, respectively. The steel composition is Mn25-35wt%, Al7-15wt%, C0.7-1.5wt%, Cr0-5wt%, Ni0-5wt%, O≤0.30wt%, N≤0.30wt%, S≤0.01wt%, P≤0.01wt%, and Fe balance. The preparation process steps include laser powder bed additive manufacturing (SLM), vacuum stress relief heat treatment, hot isostatic pressing, vacuum solution quenching heat treatment / vacuum solution quenching heat treatment + vacuum aging heat treatment, machining, and sandblasting to obtain the final parts. It can be seen that although these two methods can achieve the integrated forming of large-sized, complex-structured Fe-Mn-Al-C austenitic low-density steel parts, their heat treatment processes must adopt hot isostatic pressing and vacuum heat treatment processes to eliminate microcracks, improve density, achieve alloy microstructure control, and improve its comprehensive mechanical properties. Not only are the heat treatment process steps complicated, but the final specific yield strength (yield strength / density) is also lower than 190MPa / (g / cm3).

[0005] In summary, how to use a relatively simple and efficient processing technology to prepare complex structural parts of high-carbon Fe-Mn-Al steel with higher yield strength has become a technical problem that needs to be solved. Summary of the Invention

[0006] In response to the above technical problems, the present invention provides a Fe-Mn-Al steel with high specific yield strength and a preparation method thereof, so as to solve the technical problem that the existing technology cannot prepare high-carbon Fe-Mn-Al steel complex structural parts with higher specific yield strength.

[0007] The purpose of the present invention is mainly achieved through the following technical solutions:

[0008] On the one hand, the present invention provides a Fe-Mn-Al steel with high specific yield strength. The Fe-Mn-Al steel comprises, by weight percentage, Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, and Cr: 3-7%. The high specific yield strength is 190 MPa / (g / cm 3 )above.

[0009] Furthermore, the composition of the Fe-Mn-Al steel is as follows, calculated by mass percentage: Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, Cr: 4-6%.

[0010] Furthermore, the volume fraction of austenite in the matrix structure of the Fe-Mn-Al steel is above 99%.

[0011] On the other hand, the present invention also provides a method for preparing the above-mentioned Fe-Mn-Al steel, comprising the following steps:

[0012] Step 1, additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selective laser melting printer and additive printing is performed according to the set process parameters;

[0013] The printing process is as follows: the printing chamber is filled with high-purity argon gas so that the oxygen concentration in the printing chamber is less than 0.01%. The substrate is a 316L stainless steel substrate. The substrate heating temperature is 25-150°C, the spot diameter is 0.05-0.055mm, the scanning spacing is 0.05-0.055mm, the overlap rate is -10-+10%, the laser power is 40-65W, the scanning speed is 300-490mm / s, the single layer powder thickness is 0.02-0.04mm, and the energy density is 40-55J / mm 3 ,The scanning partition is strip-type, with a strip width of 6 to 9 mm and a rotation of 45° to 67° layer by layer;

[0014] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution heat treatment and aging heat treatment.

[0015] Furthermore, in step 1, the Fe-Mn-Al steel powder comprises, by weight percentage, Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, Cr: 3-7%, P ≤ 0.005%, S ≤ 0.002%, H ≤ 1 ppm, O ≤ 200 ppm, and N ≤ 300 ppm; the powder has a bulk density of 4.3-4.7 g / cm 3 , tap density 5.2~5.6g / cm 3 , fluidity 19~21s / 50g.

[0016] Furthermore, the Fe-Mn-Al steel powder comprises, in terms of mass percentage, Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, Cr: 4-6%, P≤0.005%, S≤0.002%, H≤1ppm, O≤200ppm, and N≤300ppm.

[0017] Furthermore, in step 2, the solution heat treatment process is: solution temperature 1000-1100° C., holding time 15-30 min, and water cooling to room temperature.

[0018] Furthermore, in step S2, the aging heat treatment process is: aging temperature 350-400°C, holding time 15-30 minutes, and air cooling to room temperature.

[0019] Furthermore, the Fe-Mn-Al steel obtained by the above method has a density of more than 99.7% and an actual density of 6.20-6.32 g / cm 3 between.

[0020] Furthermore, the volume fraction of austenite in the Fe-Mn-Al steel matrix structure obtained by the above method is above 99%.

[0021] Compared with the prior art, the present invention can achieve at least one of the following technical effects:

[0022] (1) The Fe-Mn-Al steel of the present invention has a specific yield strength of 190 MPa / (g / cm 3 ) and above, it can not only replace titanium alloy and meet the demand for improving the carrying capacity of the hinged connectors of the aircraft control surfaces, but also achieve the weight reduction requirements of the reinforced structural components of the motor housing of new energy vehicles, which can further reduce fuel consumption and significantly improve the cruising range.

[0023] (2) Compared with titanium alloys prepared by additive printing, the Fe-Mn-Al steel of the present invention has a higher yield strength than titanium alloys, a comparable specific yield strength, and a lower raw material cost than titanium alloys, thus having advantages in performance and cost.

[0024] (3) Due to the presence of a relatively high carbon content, the volume fraction of austenite in the matrix structure of the Fe-Mn-Al steel of the present invention is above 99%, which is almost a complete austenite single-phase structure, and the fine κ-type carbides precipitated in the austenite can play a role in grain refinement and strength improvement.

[0025] (4) The contents of Al, C, and Cr in the Fe-Mn-Al steel of the present invention have an important influence on the type, size, and formation conditions of carbides, and thus have an important influence on the performance of the steel. Therefore, the Al, C, and Cr of the present invention interact synergistically with each other, and the combination of their contents is an organic combination.

[0026] (5) The present invention combines the SLM additive printing process with the traditional, relatively simple solid solution and aging heat treatment process to prepare Fe-Mn-Al steel complex structural parts, which not only solves the technical problem that Fe-Mn-Al steel with high Al, Mn and C content, especially Fe-Mn-Al steel with a C content of more than 1.3wt.%, is difficult to form using traditional casting, forging and rolling, but also solves the technical problem that the existing additive printing parts heat treatment process steps are complicated and the yield strength is low.

[0027] (6) The formation of carbides in the Fe-Mn-Al steel of the present invention is not only related to the alloy composition, but the thermodynamic and kinetic processes of carbide precipitation are also closely related to the additive printing process and heat treatment system. Therefore, the alloy composition, additive printing process and heat treatment system of the present invention belong to an organic whole.

[0028] (7) The fine spot diameter in the printing process of the present invention results in a refined molten pool that produces fine grains after solidification, with an average grain size in the micrometer range. The heat treatment process of the present invention can maintain fine grains to the greatest extent possible while also achieving a significant proliferation of high-angle grain boundaries, exceeding 60%, thereby achieving a microstructure with synergistically improved strength and toughness. Furthermore, the heat treatment process of the present invention promotes a tendency for ferrite to further transform into austenite.

[0029] (8) The density of Fe-Mn-Al steel prepared by SLM additive printing in the present invention is above 99.7%, and the actual density is between 6.20 and 6.32 g / cm 3 The tensile strength is above 1270MPa, the yield strength is above 1200MPa, and the specific yield strength is above 190MPa / (g / cm 3 ) and above, and the elongation is above 13%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings are only for purposes of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference numerals designate like components throughout the drawings.

[0031] Figure 1 This is a scanning electron microscope image of the Fe-Mn-Al steel powder used in Example 1;

[0032] Figure 2 The electron micrographs of Examples 1 to 4 and Comparative Examples 1 and 2 are shown;

[0033] Figure 3 The grain boundary diagrams of the Fe-Mn-Al steel in the printed and heat-treated states of Example 3;

[0034] Figure 4 The Fe-Mn-Al steel phase diagram in the printed and heat-treated states of Example 3;

[0035] Figure 5 This is the stress-strain curve of the tensile test of Example 5. DETAILED DESCRIPTION

[0036] The following is a further detailed description of a Fe-Mn-Al steel with high specific yield strength and its preparation method in conjunction with specific examples. These examples are only for comparison and explanation purposes, and the present invention is not limited to these examples.

[0037] First, the present invention proposes a Fe-Mn-Al steel with high specific yield strength, whose components include Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, and Cr: 3-7% in terms of mass percentage.

[0038] It should be noted that the specific yield strength is the ratio of the yield strength of a material to its apparent density, i.e., yield strength / density. The higher the specific yield strength, the lighter the material used to achieve the corresponding yield strength. High-quality structural materials should have a high specific strength so that they can meet the strength requirements with a smaller cross-section as much as possible and significantly reduce the weight of the structure itself. The specific yield strength of the Fe-Mn-Al steel of the present invention is 190 MPa / (g / cm 3 )above.

[0039] The basis of composition design of the present invention is as follows:

[0040] Manganese (Mn): Manganese is a major alloying element in Fe-Mn-Al steels. It is an austenite-forming element that inhibits ferrite formation. Mn can improve the strength and hardness of steel and refine grain size. However, when the Mn content exceeds 35%, it may lead to the formation of β-Mn phase, causing brittle fracture. Therefore, the present invention limits the Mn content to 28-32%, such as 28.5%, 29%, 30%, 30.5%, 31%, 31.5%, etc.

[0041] Aluminum (Al): Aluminum is the most effective element for reducing the density of Fe-Mn-Al steels and increasing the stacking fault energy. It can increase the content of kappa carbides in steel and also provides deoxidation, antioxidant and corrosion resistance, solid solution strengthening, and grain refinement. The present invention limits the Al content to 10-13%, such as 10.5%, 11%, 11.5%, and 12%.

[0042] Carbon (C): Carbon is also an austenite stabilizing element in Fe-Mn-Al steel. While stabilizing austenite, it can also improve the mechanical properties of steel. For every 0.1% increase in C content, the yield strength of the steel increases by 30-40 MPa. At the same time, for every 1% addition of C, the density of the steel decreases by 0.41 g / cm 3Carbon promotes the precipitation of nano-κ carbides within grains, further increasing the yield strength of steel. However, excessively high C content can lead to the precipitation of κ phase and amorphous graphite phase at grain boundaries, potentially causing cracks and reducing overall performance. Therefore, the present invention limits the carbon content to 1.3-1.7%, such as 1.35%, 1.40%, 1.45%, 1.50%, 1.55%, 1.60%, 1.65%, etc.

[0043] Chromium (Cr): The addition of chromium effectively inhibits the precipitation of kappa carbides in steel, improving the steel's strength, hardness, and formability. Furthermore, the addition of Cr further reduces the steel's density and improves its corrosion resistance, high-temperature oxidation resistance, and creep resistance. Therefore, the present invention adds 3-7% Cr, such as 3.5%, 4.0%, 4.5%, 4.9%, 5.0%, 5.5%, 5.8%, 6.0%, 6.5%, etc.

[0044] Furthermore, the Fe-Mn-Al steel with high specific yield strength preferably has the following composition, calculated by mass percentage: Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, Cr: 4-6%.

[0045] It should be noted that in the Fe-Mn-Al ternary system, when the Mn content is approximately 30% and the Al content is above 10%, a dual-phase structure of ferrite and austenite should form. However, due to the relatively high carbon content of the present invention, the volume fraction of austenite in the matrix structure is above 99%, with the remainder being ferrite or ferrite plus other structures, resulting in an almost completely austenitic single-phase structure. Furthermore, since the Al, C, and Cr contents in steel all significantly influence the type, size, and formation conditions of carbides, and the presence of carbides significantly influences steel properties, such as the steel's specific yield strength, the Al, C, and Cr in the present invention do not act independently but rather interact synergistically, meaning that their combined contents constitute an organic combination.

[0046] Secondly, the present invention proposes a method for preparing Fe-Mn-Al steel with high specific yield strength, comprising the following steps:

[0047] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0048] The printing process is as follows: the printing chamber is filled with high-purity argon gas so that the oxygen concentration in the printing chamber is less than 0.01%. The substrate is a 316L stainless steel substrate. The substrate heating temperature is 25-150°C, the spot diameter is 0.05-0.055mm, the scanning spacing is 0.05-0.055mm, the overlap rate is -10-+10%, the laser power is 40-65W, the scanning speed is 300-490mm / s, the single layer powder thickness is 0.02-0.04mm, and the energy density is 40-55J / mm 3 The scanning partition is strip-type, with a strip width of 6 to 9 mm and a rotation of 45° to 67° layer by layer.

[0049] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution heat treatment and aging heat treatment.

[0050] The heat treatment process is: solution temperature 1000-1100°C, holding time 15-30 minutes, water cooling to room temperature; aging temperature 350-400°C, holding time 15-30 minutes, air cooling to room temperature.

[0051] Specifically, in step 1, the composition of the Fe-Mn-Al steel powder, calculated by mass percentage, includes Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, Cr: 3-7%, P ≤ 0.005%, S ≤ 0.002%, H ≤ 1 ppm, O ≤ 200 ppm, and N ≤ 300 ppm. The powder has a bulk density of 4.3-4.7 g / cm 3 , tap density 5.2~5.6g / cm 3 , fluidity 19-21s / 50g, powder sphericity is good.

[0052] More preferably, the composition of the Fe-Mn-Al steel powder, calculated by mass percentage, includes Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, Cr: 4-6%, P ≤ 0.005%, S ≤ 0.002%, H ≤ 1ppm, O ≤ 200ppm, and N ≤ 300ppm. The powder has a bulk density of 4.3-4.7g / cm 3 , tap density 5.2~5.6g / cm 3 , fluidity 19-21s / 50g, powder sphericity is good.

[0053] Specifically, in step 1, the printing process parameters are based on the following:

[0054] Print chamber oxygen concentration: The oxygen content determines the oxygen brittleness of the formed part and the volume density of inclusions. To ensure excellent mechanical properties of the material, the oxygen concentration of the print chamber of the present invention is controlled to be less than 0.01%.

[0055] Substrate heating temperature: The heating temperature of the substrate determines the temperature gradient between the molten state and the solid state, which in turn determines the thermal stress during the cooling process, and also determines the diffusion of elements during the solidification process. Therefore, in order to maintain a high degree of element uniformity and low thermal stress, the substrate heating temperature of the present invention is controlled at 25-150°C, further such as 50-100°C.

[0056] Spot diameter: The larger the spot diameter, the more powder the laser melts per unit time and the more energy the powder absorbs. A larger spot diameter can lead to excessive surface roughness in the finished part. Furthermore, a larger spot diameter can lead to a deeper and wider remelting zone, a slower cooling rate, and increased in-situ thermal effects, leading to the precipitation of κ phase and amorphous graphite phase at grain boundaries, which in turn can cause cracks and reduce overall performance. A smaller spot diameter can result in lower efficiency in the finished part. After comprehensive consideration, the spot diameter of the present invention is controlled between 0.05 and 0.055 mm.

[0057] Scanning Spacing and Overlap: The distance between laser scanning paths affects the amount of energy absorbed by the powder layer, which in turn affects the quality of the formed part. Excessive scanning spacing can result in large gaps in the molten pool, leading to cracks in the substrate. Too small a scanning spacing can lead to low forming efficiency and excessive overlap. After comprehensive consideration, the scanning spacing in this invention is controlled between 0.05 and 0.055 mm, and the overlap ratio is controlled between -10 and +10%.

[0058] Laser power: In this application, the laser is used to transfer heat and melt the powder. Laser power significantly impacts the quality of SLM-printed parts. Excessive laser power can cause pores or even cracks in the finished part, while insufficient power can make it difficult for the powder to fuse into the matrix. After comprehensive consideration, the laser power in this application is controlled between 40 and 65W.

[0059] Scanning speed: The speed at which the laser spot moves across the powder layer, melting the powder. The laser's speed determines the amount of energy absorbed per unit area per unit time. Excessive scanning speeds result in insufficient energy being absorbed by the powder in the finished part, making it difficult to fuse into the matrix. Excessive scanning speeds result in excessive energy being absorbed by the powder in the finished part, causing balling and even cracking in the finished part. After comprehensive consideration, the scanning speed of this invention is controlled between 300 and 490 mm / s.

[0060] Scanning layer thickness: The thickness of a single powder layer reduces the amount of energy absorbed per unit volume. Excessive scanning layer thickness results in excessive surface roughness in the finished part, while too small a thickness results in low efficiency. After comprehensive consideration, the scanning layer thickness of the present invention is controlled between 0.02 and 0.04 mm, e.g., 0.03 mm.

[0061] Energy Density: Because laser power, scanning speed, scanning layer thickness, and scanning spacing all influence printing results, and energy density is closely related to these process parameters, this paper uses laser energy density as a comprehensive and balanced process parameter. Laser energy density generally controls the effective residence time of the laser on the powder and directly affects the melt pool temperature, cooling rate, and final microstructure. Specifically, this paper sets the laser energy density to 40-55 J / mm³, and further, 45-50 J / mm³.

[0062] Scanning rotation angle: The scanning rotation angle is the angle between the scanning directions of the upper and lower powder layers. If the rotation angle is too small, the lower layer will not dissipate heat in time, resulting in a small temperature gradient in the upper melt pool, which will cause the material to have a strong preferred orientation. If the rotation angle is too large, the thermal history difference between the upper and lower powder layer melt pools will be large, and the temperature gradient in the upper melt pool will be large, which will easily lead to high thermal stress. To achieve low thermal stress and strong isotropy, the scanning rotation angle of the present invention is controlled to 45° to 67°.

[0063] Scanning partition mode: The scanning partition mode determines the forming rate and the forming texture. In order to obtain a higher forming rate and a weaker forming texture, the present invention limits the scanning partition mode to a strip type with a width of 6 to 9 mm.

[0064] Specifically, in step 2, the basis of the heat treatment process parameters is as follows:

[0065] Solution treatment: the temperature at which the material recrystallizes and the elements are homogenized at high temperature. If the temperature is too low and the elements diffuse unevenly in a short time, and the recrystallization rate is low, while if the temperature is too high or the time is too long, the grains are easily coarsened, thereby reducing the strength and toughness of the material. Taking into account the comprehensive consideration, the solution temperature of the present invention is controlled at 1000-1100°C, such as 1010°C, 1050°C, 1070°C, and 1090°C, and the holding time is controlled at 15-30min, such as 16min, 18min, 20min, 22min, 24min, 26min, and 28min.

[0066] Aging treatment: Aging treatment that causes the precipitation of strengthening phases within the material microstructure. When the temperature is too high or the time is too long, the strengthening phases tend to coarsen, thereby reducing the toughness. However, when the temperature is too low or the time is too short, the strengthening phases cannot precipitate, thereby reducing the strength of the material. Taking all factors into consideration, the aging temperature of the present invention is controlled at 350-400°C, such as 370°C and 390°C, and the holding time is controlled at 15-30 minutes, such as 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, and 28 minutes.

[0067] The volume fraction of austenite in the matrix structure of the Fe-Mn-Al steel prepared by the method of the present invention is above 99%, with the remainder being ferrite or ferrite plus other structures. Density and tensile properties of the parts were tested, and the density was above 99.7%, close to 100%, and the actual density was between 6.20 and 6.32 g / cm 3 The tensile mechanical properties are excellent, the yield strength is above 1200MPa, and the specific yield strength is above 190MPa / (g / cm 3 ) and above, and the elongation is above 13%. Compared with similar materials manufactured by additive manufacturing, the heat treatment process of the present invention is simple and the specific yield strength is higher. The titanium alloy used in the aerospace field has a yield strength of 860 to 1000 MPa and a specific yield strength of 185 to 220 MPa / (g / cm 3 ), currently costing approximately ¥100,000 per ton. However, the yield strength of the present invention is higher than that of titanium alloys, and its specific yield strength is comparable to that of titanium alloys, yet the current raw material cost is approximately ¥70,000 per ton, which is lower than that of titanium alloys. This demonstrates that the present invention offers both performance and cost advantages over titanium alloys produced using additive printing.

[0068] It should be noted that in addition to the alloy composition, the thermodynamic and kinetic processes of carbide precipitation in steel are also closely related to the additive printing process and heat treatment system. Therefore, it is necessary to comprehensively consider the influence of factors such as alloy composition, additive printing process, and heat treatment system on the carbide formation conditions. That is, the alloy composition, additive printing process, and heat treatment system of the present invention belong to an organic whole.

[0069] Example 1

[0070] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel was as follows: Mn: 30.0%, Al: 11.6%, C: 1.6%, Cr: 5.0%, and the rest was Fe.

[0071] The printing process is as follows: the oxygen concentration in the printing chamber is 0.008%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 25°C, the spot diameter is 0.055mm, the scanning spacing is 0.055mm, the overlap rate is 0%, the laser power is 44W, the scanning speed is 490mm / s, the single layer powder thickness is 0.03mm, and the energy density is 54J / mm 3 ,The scanning partition is strip type, the strip width is 9 mm, and it rotates 67° layer by layer.

[0072] The composition of the Fe-Mn-Al steel powder, calculated by mass percentage, is: Mn: 30.0%, Al: 11.6%, C: 1.6%, Cr: 5.0%, P: 0.005%, S: 0.002%, H: 1ppm, O: 200ppm, N: 300ppm, and the remainder is Fe. The powder has a bulk density of 4.5g / cm 3 , tap density 5.4g / cm 3 , fluidity 20s / 50g, powder sphericity is good. Figure 1 The scanning electron microscope image of the Fe-Mn-Al steel powder used in Example 1 is shown in FIG. Figure 1 It can be seen that the powder has good sphericity, with occasional satellite powder.

[0073] The printing process is as follows: the oxygen concentration in the printing chamber is 0.008%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 25°C, the spot diameter is 0.055mm, the scanning spacing is 0.055mm, the overlap rate is 0%, the laser power is 44W, the scanning speed is 490mm / s, the single layer powder thickness is 0.03mm, and the energy density is 54J / mm 3 ,The scanning partition is strip type, the strip width is 9 mm, and it rotates 67° layer by layer.

[0074] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. The micromorphology of the printed sample after polishing is as follows Figure 2 shown.

[0075] Example 2

[0076] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel was as follows: Mn: 28.1%, Al: 13%, C: 1.35%, Cr: 3.0%, and the rest was Fe, calculated by mass percentage.

[0077] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0078] The composition of the Fe-Mn-Al steel powder, calculated by mass percentage, is: Mn: 28.1%, Al: 13%, C: 1.35%, Cr: 3.0%, P: 0.004%, S: 0.001%, H: 0.5pm, O: 150ppm, N: 280ppm, and the remainder is Fe. The powder has a bulk density of 4.3g / cm 3 , tap density 5.2g / cm 3, fluidity 19s / 50g, powder sphericity is good.

[0079] The printing process is as follows: the oxygen concentration in the printing chamber is 0.008%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 150°C, the spot diameter is 0.05mm, the scanning spacing is 0.055mm, the overlap rate is -10%, the laser power is 40W, the scanning speed is 450mm / s, the single layer powder thickness is 0.04mm, and the energy density is 40J / mm 3 ,The scanning partition is strip type, the strip width is 6 mm, and the layer-by-layer rotation is 67°.

[0080] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution and aging heat treatment.

[0081] The heat treatment process is as follows: solution temperature 1080℃, holding time 29min, water cooling to room temperature; aging temperature 350℃, holding time 17min, air cooling to room temperature;

[0082] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. The printed sample was polished and then observed under an electron microscope. The micromorphology is as follows Figure 2 shown.

[0083] Example 3

[0084] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel was as follows: Mn: 29.8%, Al: 11.6%, C: 1.48%, Cr: 4.9%, and the rest was Fe.

[0085] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0086] The composition of the Fe-Mn-Al steel powder, calculated by mass percentage, is: Mn: 29.8%, Al: 11.6%, C: 1.48%, Cr: 4.9%, P: 0.004%, S: 0.002%, H: 1pm, O: 180ppm, N: 250ppm, and the remainder is Fe. The powder has a bulk density of 4.7g / cm 3 , tap density 5.6g / cm 3 , fluidity 21s / 50g, powder sphericity is good.

[0087] The printing process is as follows: the oxygen concentration in the printing chamber is 0.009%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 100°C, the spot diameter is 0.055mm, the scanning pitch is 0.053mm, the overlap rate is 3.64%, the laser power is 46W, the scanning speed is 480mm / s, the single layer powder thickness is 0.035mm, and the energy density is 52J / mm 3 ,The scanning partition is strip type, the strip width is 8mm, and it rotates 45° layer by layer.

[0088] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution and aging heat treatment.

[0089] The heat treatment process is as follows: solution temperature 1048℃, holding time 21min, water cooling to room temperature; aging temperature 373℃, holding time 23min, air cooling to room temperature;

[0090] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. The printed sample was polished and then observed under an electron microscope. The micromorphology is as follows Figure 2 shown.

[0091] Figure 3 The printed and heat-treated Fe-Mn-Al steel grain boundaries of Example 3 are shown in FIG. Figure 3 It can be seen that the grain size of the printed Fe-Mn-Al steel is relatively fine, with an average grain size of 10μm, but the proportion of large-angle grain boundaries is small, only 56%. However, the proportion of large-angle grain boundaries in the Fe-Mn-Al steel after heat treatment is as high as 92%, and the grain size is 12μm. This shows that the refined molten pool obtained by the small spot diameter during the printing process can obtain a fine grain size after solidification, and can retain fine grains to the greatest extent under the heat treatment process of the present invention. At the same time, a large-angle grain boundary proliferation can be obtained, which is about 60% or more, thereby obtaining a microstructure with synergistic improvement in strength and toughness.

[0092] Figure 4 The printed and heat-treated Fe-Mn-Al steel phase diagrams of Example 3 are shown in FIG. Figure 4 In the figure, the red part on the bottom is austenite, and the sporadic black part on it is ferrite; the volume fraction of austenite in the printed state is 99.24%, and the balance is ferrite; the volume fraction of austenite in the heat-treated state is 99.49%, and the balance is ferrite. This shows that the volume fraction of austenite structure of the Fe-Mn-Al steel of the present invention is above 99%, which is almost a complete austenite single-phase structure, and the heat treatment makes the ferrite tend to further transform into austenite.

[0093] Example 4

[0094] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel was as follows: Mn: 30.4%, Al: 12.3%, C: 1.53%, Cr: 5.2%, and the rest was Fe.

[0095] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0096] The composition of the Fe-Mn-Al steel powder, calculated by mass percentage, is: Mn: 30.4%, Al: 12.3%, C: 1.53%, Cr: 5.2%, P: 0.004%, S: 0.002%, H: 1pm, O: 180ppm, N: 250ppm, and the remainder is Fe. The powder has a bulk density of 4.4g / cm 3 , tap density 5.5g / cm 3 , fluidity 21s / 50g, powder sphericity is good.

[0097] The printing process is as follows: the oxygen concentration in the printing chamber is 0.005%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 80°C, the spot diameter is 0.055mm, the scanning spacing is 0.050mm, the overlap rate is 9%, the laser power is 43W, the scanning speed is 420mm / s, the single layer powder thickness is 0.04mm, and the energy density is 51J / mm 3 ,The scanning partition is strip type, the strip width is 7 mm, and it rotates 67° layer by layer.

[0098] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution and aging heat treatment.

[0099] The heat treatment process is as follows: solution temperature 1030℃, holding time 27min, water cooling to room temperature; aging temperature 380℃, holding time 25min, air cooling to room temperature;

[0100] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. The printed sample was polished and then observed under an electron microscope. The micromorphology is as follows Figure 2 shown.

[0101] Example 5

[0102] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel was as follows: Mn: 32%, Al: 10.2%, C: 1.7%, Cr: 7.0%, and the rest was Fe, calculated by mass percentage.

[0103] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0104] The composition of the Fe-Mn-Al steel powder, calculated by mass percentage, is: Mn: 32%, Al: 10.2%, C: 1.7%, Cr: 7.0%, P: 0.002%, S: 0.001%, H: 1pm, O: 190ppm, N: 290ppm, and the remainder is Fe. The powder has a bulk density of 4.4g / cm 3 , tap density 5.5g / cm 3 , fluidity 21s / 50g, powder sphericity is good.

[0105] The printing process is as follows: the oxygen concentration in the printing chamber is 0.005%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 50°C, the spot diameter is 0.053mm, the scanning spacing is 0.05mm, the overlap rate is 6%, the laser power is 40W, the scanning speed is 485mm / s, the single layer powder thickness is 0.03mm, the energy density is 55J / mm3, the scanning partition is strip type, the strip width is 7mm, and the layer-by-layer rotation is 67°.

[0106] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution and aging heat treatment.

[0107] The heat treatment process is as follows: solution temperature 1040℃, holding time 20min, water cooling to room temperature; aging temperature 385℃, holding time 19min, air cooling to room temperature;

[0108] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tensile tests on metallic materials - Part 1: Room temperature test methods". The test results are shown in Table 1. Figure 5 This is the stress-strain curve of the tensile test of Example 5.

[0109] Comparative Example 1

[0110] The Fe-Mn-Al steel was prepared by conventional smelting and casting, forging and rolling. The chemical composition of the steel was exactly the same as that of Example 1.

[0111] Step 1: Vacuum smelting: prepare the ingredients, then smelt and cast the billet in a vacuum induction melting furnace;

[0112] Step 2, hot working: the ingot obtained from the smelting is heated and kept warm at 1250°C for 0.5h, hot forged with a forging ratio of 1.5, and then hot rolled to the target shape with a total hot rolling reduction ratio of 50% and a final hot deformation temperature of 900°C, and then water cooled to room temperature.

[0113] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. After polishing, the sample was observed under an electron microscope. The micromorphology is as follows Figure 2 shown.

[0114] Comparative Example 2

[0115] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing, and the chemical composition of the steel was exactly the same as that in Example 1.

[0116] Step 1: Additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selected laser melting (SLM) printer and additive printing is performed according to the set process parameters;

[0117] The composition and physical properties of the Fe-Mn-Al steel powder are exactly the same as those in Example 1;

[0118] The printing process is as follows: the oxygen concentration in the printing chamber is 0.008%, the substrate is a 316L stainless steel substrate, the substrate heating temperature is 25°C, the spot diameter is 0.10mm, the scanning pitch is 0.095mm, the overlap rate is 15%, the laser power is 120W, the scanning speed is 700mm / s, the single layer powder thickness is 0.03mm, and the energy density is 60J / mm 3 ,The scanning partition is strip type, the strip width is 10 mm, and it rotates 67° layer by layer.

[0119] Step 2: Heat treatment: The molded parts after additive printing are subjected to solution and aging heat treatment.

[0120] The heat treatment process is as follows: solution temperature 1200℃, holding time 35min, water cooling to room temperature; aging temperature 600℃, holding time 45min, air cooling to room temperature;

[0121] Prepare the sample, use the Archimedes drainage method to test the density, and test the tensile properties according to GB / T 228.1-2021 "Tension test of metallic materials Part 1: Room temperature test method". The test results are shown in Table 1. The printed sample was polished and then observed under an electron microscope. The micromorphology is as follows Figure 2 shown.

[0122] Comparative Example 3

[0123] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel and the powder used for additive printing were exactly the same as those in Example 1. The additive printing process parameters were exactly the same as those in Comparative Example 2. The heat treatment process parameters were exactly the same as those in Example 1.

[0124] The specimens were prepared and the density was tested using the Archimedes drainage method. The tensile properties were tested in accordance with GB / T 228.1-2021 “Tensile tests on metallic materials - Part 1: Room temperature test methods”. The inspection and test results are shown in Table 1.

[0125] Comparative Example 4

[0126] Fe-Mn-Al steel was prepared by selective laser melting (SLM) printing. The chemical composition of the steel, the powder used for additive printing, and the additive printing process parameters were exactly the same as those in Example 1, and the heat treatment process parameters were exactly the same as those in Comparative Example 2.

[0127] The specimens were prepared and the density was tested using the Archimedes drainage method. The tensile properties were tested in accordance with GB / T 228.1-2021 “Tensile tests on metallic materials - Part 1: Room temperature test methods”. The inspection and test results are shown in Table 1.

[0128] Table 1 Detection and test results of comparative examples and embodiments

[0129]

[0130] As can be seen from Table 1, the print densities of Examples 1 to 5 of the present invention are all above 99.7%, the tensile strength and yield strength are all above 1220 MPa, and the specific yield strength is all above 190 MPa / (g / cm 3 ) and above, and the elongation is above 13%. Comparative Example 1 adopts the traditional smelting, casting, forging and rolling forming methods; Comparative Example 2 adopts the powder of the present invention for SLM printing, but the printing process parameters and heat treatment parameters are different from those of the present invention; Comparative Example 3 adopts the powder of the present invention for SLM printing, and the printing process parameters are different from those of the present invention, and are exactly the same as those of Comparative Example 2, but the heat treatment process parameters are exactly the same as those of Example 1; Comparative Example 4 adopts the powder of the present invention for SLM printing, and the heat treatment process parameters are different from those of the present invention, and are exactly the same as those of Comparative Example 2, but the printing process parameters are exactly the same as those of Example 1; the various mechanical performance indicators of the above comparative examples 1 to 4 are all lower than those of the examples, indicating that the Fe-Mn-Al steel powder of the present invention must be combined with the printing process and heat treatment process of the present invention to obtain the desired technical effects.

[0131] from Figure 2It can be seen from the electron microscopic morphology images of Examples 1 to 4 and Comparative Examples 1 and 2 that Comparative Example 1, which adopts traditional smelting and casting, forging and rolling forming methods, and Comparative Example 2, which has some higher printing process parameters than the present invention, have obvious cracks and holes in their organizational morphology, and the crack width is even as high as 23μm, while Examples 1 to 4 of the present invention have no cracks and low porosity, which is also consistent with the fact that the density of Examples 1 to 4 is significantly higher than that of Comparative Examples 1 and 2 as shown in Table 1.

[0132] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A Fe-Mn-Al steel with high specific yield strength, characterized in that: The composition of the Fe-Mn-Al steel is Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, Cr: 3-7% in terms of mass percentage; the high specific yield strength is 190 MPa / (g / cm 3 )above.

2. The Fe-Mn-Al steel according to claim 1, characterized in that: Calculated by mass percentage, the Fe-Mn-Al steel comprises the following components: Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, and Cr: 4-6%.

3. The Fe-Mn-Al steel according to claim 1, characterized in that: The volume fraction of austenite in the matrix structure of the Fe-Mn-Al steel is above 99%.

4. A method for preparing the Fe-Mn-Al steel according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1, additive printing: Fe-Mn-Al steel powder with a particle size range of 15 to 53 μm is placed in a selective laser melting printer and additive printing is performed according to the set process parameters; The printing process is as follows: the printing chamber is filled with high-purity argon gas so that the oxygen concentration in the printing chamber is less than 0.01%. The substrate is a 316L stainless steel substrate. The substrate heating temperature is 25-150°C, the spot diameter is 0.05-0.055mm, the scanning spacing is 0.05-0.055mm, the overlap rate is -10-+10%, the laser power is 40-65W, the scanning speed is 300-490mm / s, the single layer powder thickness is 0.02-0.04mm, and the energy density is 40-55J / mm 3 ,The scanning partition is strip-type, with a strip width of 6 to 9 mm and a rotation of 45° to 67° layer by layer; Step 2: Heat treatment: The molded parts after additive printing are subjected to solution heat treatment and aging heat treatment.

5. The method according to claim 4, characterized in that: In step 1, the Fe-Mn-Al steel powder comprises, by weight percentage, Fe: 49-55%, Mn: 28-32%, Al: 10-13%, C: 1.3-1.7%, Cr: 3-7%, P ≤ 0.005%, S ≤ 0.002%, H ≤ 1ppm, O ≤ 200ppm, and N ≤ 300ppm; the powder has a bulk density of 4.3-4.7g / cm 3 , tap density 5.2~5.6g / cm 3 , fluidity 19~21s / 50g.

6. The method according to claim 5, characterized in that The Fe-Mn-Al steel powder comprises, in terms of mass percentage, Fe: 50-53%, Mn: 29-31%, Al: 11-12%, C: 1.4-1.6%, Cr: 4-6%, P≤0.005%, S≤0.002%, H≤1ppm, O≤200ppm, and N≤300ppm.

7. The method according to claim 4, characterized in that: In step 2, the solution heat treatment process is as follows: solution temperature 1000-1100° C., holding time 15-30 min, and water cooling to room temperature.

8. The method according to claim 4, characterized in that: In step S2, the aging heat treatment process is as follows: aging temperature 350-400° C., holding time 15-30 min, and air cooling to room temperature.

9. The method according to any one of claims 4 to 8, characterized in that: The Fe-Mn-Al steel obtained by the method has a density of more than 99.7% and an actual density of 6.20-6.32 g / cm 3 between.

10. The method according to claim 9, characterized in that: The volume fraction of austenite in the Fe-Mn-Al steel matrix structure obtained by the method is above 99%.

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