CN116288027A

CN116288027A - Low-density maraging steel manufactured by laser additive and preparation method thereof

Info

Publication number: CN116288027A
Application number: CN202211506358.2A
Authority: CN
Inventors: 陈浩; 汪小培; 张弛; 杨志刚; 李威挺; 王金华
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2022-11-29
Filing date: 2022-11-29
Publication date: 2023-06-23
Anticipated expiration: 2042-11-29
Also published as: CN116288027B

Abstract

The present application relates to a laser additive manufactured low density maraging steel and a method of manufacturing the same, the maraging steel comprising: 0.08 mass% or less of C or less of 0.15 mass%, 6.5 mass% or less of Cr or less of 10 mass%, 10 mass% or less of Ni or less of 12 mass%, 3 mass% or less of Al or less of 3.5 mass%, 1 mass% or less of Ti or less of 1.5 mass%, 6 mass% or less of Co or less of 7 mass%, 0.5 mass% or less of Mo or less of 0.7 mass%, and the balance of Fe and unavoidable impurities. The novel maraging steel suitable for laser additive manufacturing is developed, and the density of the steel is reduced through the addition of Ti and Al, and the matrix can be effectively reinforced. The advantages of in-situ metallurgy and near-net forming are utilized to overcome the difficulty of processing and manufacturing the high-Al low-density steel. The application provides a novel light high-strength structural material and a manufacturing technology for the aerospace field.

Description

Low-density maraging steel manufactured by laser additive and preparation method thereof

Technical Field

The invention belongs to the field of new materials and advanced manufacturing, and particularly relates to low-density maraging steel manufactured by laser additive and a preparation method thereof.

Background

The only purpose of the launch vehicle is to carry the payload, which can be increased by reducing the structural mass of the rocket. The high-strength steel is a main structural material of the carrier rocket, and the structural quality of the rocket can be effectively reduced by reducing the density of the high-strength steel.

Maraging steel has a very high strength, and has been used as a structural material for spacecraft and aircraft (e.g. engine shafts), as a structural material for automobiles, as a material for high-pressure vessels, as a material for tools, etc. However, the traditional maraging steel has high strength but high density, and cannot meet the requirement of light weight of carrier rocket structural materials.

Aluminum is a main alloying element for reducing the density of steel, and the density can be reduced by 1.3% by adding 1% by mass of aluminum to the steel. The traditional low-density steel is a Fe-Mn-Al-C system low-density steel reinforced by a B2 phase of Fe-Al and kappa carbide, is not corrosion-resistant and high-temperature oxidation-resistant, and is difficult to meet the service requirements of a carrier rocket. In addition, high Al low density steel is difficult to smelt and cast, has poor formability, has severe welding cracking tendency, and is difficult to adapt to the traditional processing and manufacturing modes.

The laser additive manufacturing technology is a reform technology facing aerospace manufacturing, provides a new way for preparing high-performance difficult-to-process metal components by virtue of in-situ metallurgy and near-net forming, and can overcome the problem of processing and manufacturing high-Al low-density steel. At present, the research on the aspect of high-strength low-density steel additive manufacturing applicable to carrier rockets in China is almost blank, and one key reason is the lack of a corresponding component system.

The Al element is a strong delta ferrite forming element, and when the content is high, a coarse columnar delta ferrite structure is formed in the molten pool during the laser additive manufacturing process. At this time, when coarse delta ferrite is dissolved in a solid and has a high Al content, it becomes very brittle, and in addition, intermetallic compounds precipitate in grain boundaries or cell walls, and the bulk material is liable to crack under the action of thermal stress and strain fields during printing. The Ni element is an element that enlarges the austenite phase region, and can not only suppress the formation of coarse δ ferrite, but also increase the toughness of the matrix. The addition of the element C can also suppress the formation of delta ferrite and can also provide a good solid solution strengthening effect. Ti is also a light-weight alloy element, and the addition of Ti can not only further reduce the density of the material but also enhance the precipitation strengthening effect of the intermetallic compound. However, when higher amounts of C and Ti are present at the same time, coarse TiC precipitates are easily formed during the smelting process, resulting in uneven distribution of C and Ti elements in the different powder particles, which can be avoided by means of powder mixing.

Based on the method, the invention provides the high-strength low-density maraging steel based on the Fe-Ni-Al-Ti-C system manufactured by laser additive and the preparation method thereof by means of component design and powder mixing, and the bottleneck problem can be effectively solved. The invention provides a novel light high-strength structural material and a manufacturing technology for the carrier rocket, and is also beneficial to solving the application requirements of the aerospace field in China on the light high-strength material.

Disclosure of Invention

Based on the above, it is necessary to provide a corrosion-resistant high-temperature oxidation-resistant high-strength low-density maraging steel and a preparation method thereof, so as to meet the application requirements of light-weight high-strength carrier rocket structural materials.

In one aspect of the present application, a maraging steel is provided, consisting of the following components:

c is more than or equal to 0.08 mass percent and less than or equal to 0.15 mass percent,

cr is more than or equal to 6.5 percent and less than or equal to 10 percent,

ni is more than or equal to 10 mass percent and less than or equal to 12 mass percent,

al is more than or equal to 3% and less than or equal to 3.5% by mass

Ti is more than or equal to 1 percent and less than or equal to 1.5 percent,

co is more than or equal to 6% and less than or equal to 7% by mass

Mo is more than or equal to 0.5 mass percent and less than or equal to 0.7 mass percent,

the balance of Fe and unavoidable impurities;

the maraging steel is obtained by laser additive manufacturing.

In some of these embodiments, the maraging steel is aged with martensite and ferrite as an initial structure, the volume fraction of ferrite in the initial structure being at most 20%.

In some of these embodiments, intermetallic precipitation phases are distributed in the maraging steel structure, the intermetallic precipitation phases including a B2 phase and an L2 phase of Ni-Al-Ti ₁ And (3) phase (C).

In some of these embodiments, the maraging steel has a yield strength of at least 1100MPa at 23 ℃.

In some of these embodiments, the maraging steel has a tensile strength of at least 1400MPa at 23 ℃.

In some of these embodiments, the maraging steel has an elongation at 23 ℃ of at least 9%.

In some of these embodiments, the maraging steel has a density of not more than 7.56g/cm ³ 。

In yet another aspect of the present application, a method of producing maraging steel is provided, using a laser additive manufacturing method, comprising the steps of:

determining the raw material proportion according to the proportion of each component, and providing alloy powder conforming to the raw material proportion;

designing a three-dimensional model, and assigning values to the three-dimensional model according to entity parameters in the laser additive manufacturing process;

filling the alloy powder into a 3D printer, and carrying out laser additive manufacturing according to assigned parameters to obtain a solid material;

and aging the solid material.

In some of these embodiments, the alloy powder includes fecrniaalti alloy powder and a100 steel powder.

In some of these embodiments, the mass ratio of FeCrNiAlTi alloy powder to A100 steel powder is 0.9:1 to 1.3:1.

In some of these embodiments, the physical parameters include laser scan speed, laser power, and scan line spacing, the laser scan speed being 1000mm/s to 1200mm/s, the laser power being 120W to 160W, the scan line spacing being 70 μm to 90 μm.

In some of these embodiments, the physical parameters further comprise a layer thickness of 15 μm to 25 μm.

In some embodiments, the temperature of the aging treatment is 400-450 ℃, and the time of the aging treatment is 5-60 min.

In yet another aspect of the present application there is further provided the use of said maraging steel as a carrier rocket structure material.

Compared with the prior art, the application at least comprises the following beneficial effects:

the traditional Fe-Mn-Al-C series low density steel is difficult to smelt and cast, has poor formability and serious welding cracking tendency, and is difficult to adapt to the traditional processing and manufacturing modes. The novel maraging steel suitable for laser additive manufacturing is developed, and the advantages of in-situ metallurgy and near-net forming of laser additive manufacturing are utilized through reasonable process design, so that the difficulty in processing and manufacturing of high-Al low-density steel is overcome. According to the maraging steel, the mass fraction of the Al element is 3% -3.5%, the Ti element is further added, the density of the steel is greatly reduced, the Ni element is used for replacing Mn to form Fe-Ni-Al-Ti-C system steel, the formation of delta ferrite is restrained by controlling the content of the C element and the Ni element, the strength of the steel is enhanced, meanwhile, the Cr element is added to enhance the corrosion resistance and the high-temperature oxidation resistance of the material, and therefore the steel material with high mechanical strength and low density characteristics and corrosion resistance and high-temperature oxidation resistance is obtained.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a photograph showing the structure of the electron back-scattered diffraction image quality (EBSD image quality) of the obtained low-density maraging steel material in the printing direction;

fig. 2 shows a Transmission Electron Micrograph (TEM) of the low density maraging steel obtained.

Detailed Description

In order to facilitate an understanding of the present application, a more complete description of the present application will now be provided with reference to the relevant figures. Preferred embodiments of the present application are shown in the accompanying drawings. This application may, however, be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

In this context, the technical features described in open form include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

In this context, reference to a numerical interval is to be construed as continuous and includes the minimum and maximum values of the range, and each value between such minimum and maximum values, unless otherwise specified. Further, when a range refers to an integer, each integer between the minimum and maximum values of the range is included. Further, when multiple range description features or characteristics are provided, the ranges may be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to include any and all subranges subsumed therein.

In this context, referring to units of data range, if a unit is only carried after the right endpoint, the units representing the left and right endpoints are identical. For example, 0.3 to 0.5m/s means that the units of the left end point "0.3" and the right end point "0.5" are m/s (meters/second).

Only a few numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form a range not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself be combined as a lower limit or upper limit with any other point or individual value or with other lower limit or upper limit to form a range not explicitly recited.

In the description herein, it is to be noted that unless otherwise indicated, "not exceeding" and "at least" are inclusive of the present number.

All steps of the present application may be performed sequentially or randomly, unless otherwise specified. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

As used herein, "mechanical strength" includes yield strength and tensile strength.

Embodiments of the present application will be described in detail below.

1. Low density maraging steel

1.1 constituent elements

In each maraging steel according to the embodiment of the present application, the actions and contents of each element are as follows:

carbon: c has the effects of inhibiting delta ferrite and promoting martensite formation, and can increase the solid solution strengthening effect of a martensitic matrix. In addition, C can reduce matrix density. Too high a C content can cause the material to be brittle, thereby increasing the propensity for print cracking during laser 3D printing. Suitable C content may be at least 0.08 mass%, but not more than 0.15 mass%.

Chromium: cr has the effect of improving the corrosion resistance and high-temperature oxidation resistance of the matrix. Suitable Cr content may be at least 6.5 mass%, but not more than 10 mass%.

Nickel: ni has the effects of suppressing delta ferrite and improving toughness of the matrix. Ni can also form B2 and L2 ₁ A type intermetallic compound for strengthening the matrix. Suitable Ni content may be at least 10 mass%, but not more than 12 mass%.

Aluminum: al has the effect of significantly reducing the matrix density. Al may also form B2 and L2 ₁ A mold intermetallic compound for strengthening the matrix; al is also a strong delta ferrite forming element and other elements are required to act synergistically to suppress delta ferrite formation. When the Al content is too high, a large number of coarse columnar δ ferrite structures appear in the matrix, resulting in an increase in brittleness of the material and an increase in the tendency of print cracking during laser 3D printing. Suitable Al content may be at least 3 mass%, but not more than 3.5 mass%.

Titanium: as in the case of Al, ti also has a significant reduction in matrix density, and the effect of Ti in the present application is mainly to make up for the deficiency that Al cannot be added in excess; in addition, ti can also form L2 with Ni and Al ₁ And the precipitated phase is compositely precipitated with the B2 phase, so that the precipitation strengthening effect is improved. Suitable Ti content may be at least 1 mass%, but not more than 1.5 mass%.

Cobalt: co can increase matrix strength through solid solution strengthening and inhibit reversion of dislocation substructure in martensite, thereby providing more nucleation sites for aging precipitated phasesThe mechanical strength of the material can be further improved by adding Co. Suitable C ₀ The content may be at least 6 mass%, but not more than 7 mass%.

Molybdenum: mo can increase the martensitic matrix strength by solid solution strengthening and can increase the secondary hardening effect after aging treatment. Suitable M _O The content may be at least 0.5 mass%, but not more than 0.7 mass%.

1.2 tissue Structure

Such maraging steel can be obtained by optimizing the constituent elements and the laser additive manufacturing process. The initial structure of the maraging steel is mainly a martensitic matrix structure, i.e. a supersaturated solid solution of carbon in alpha-Fe. It is also unavoidable to include a small amount of delta ferrite, which, as a result of the increased brittleness of the maraging steel, preferably, the delta ferrite content in the original structure of the maraging steel is at most 20%. In an embodiment, the maraging steel is obtained by aging the initial structure, and the structure of the maraging steel further includes an intermetallic compound precipitated phase. The intermetallic compound precipitated phase includes B2 phase and L2 phase ₁ And a phase, wherein the phase B2 is the main phase. The intermetallic precipitate phases were all of nanoscale dimensions.

1.3 Properties

Such maraging steel can be obtained by optimizing the constituent elements, the laser additive manufacturing process and the aging heat treatment conditions. The maraging steels have a yield strength of at least 1100MPa, a tensile strength of at least 1400MPa, an elongation of at least 9% and a density of not more than 7.56g/cm at room temperature (23 ℃) ³ 。

1.4 use

Maraging steel according to the present application may be used in various applications. For example, maraging steel according to the present application is particularly suitable as carrier rocket structure material.

2. Preparation method of low-density maraging steel

Because of the difficulty in smelting and casting high Al content steels, poor formability and severe weld cracking tendency, maraging steels according to the present application avoid the use of conventional machining and manufacturing methods, optionally using laser additive manufacturing techniques.

The method for producing maraging steel according to the present application comprises the steps of:

(a) Determining the element proportion according to the specified content of each component, and providing alloy powder conforming to the element proportion;

(b) Designing a three-dimensional model, setting entity parameters in the laser additive manufacturing process, and assigning values to the three-dimensional model according to the entity parameters;

(c) And loading the alloy powder into a 3D printer and carrying out laser additive manufacturing according to the assigned parameters to obtain the solid material.

2.1 step (a)

The alloy powder may be one powder prepared by mixing all the constituent elements within the predetermined content range, or two powders prepared by mixing part of the constituent elements within the predetermined content range, as long as the ratio of the elements is satisfied. The background of the raw materials used for preparing the alloy powder and is not particularly limited, and may be selected from those most suitable for the intended purpose.

Because the maraging steel in the application has higher C content and higher Ti content, and when the higher C content and the higher Ti content exist simultaneously, coarse TiC precipitation is easy to form during smelting and pulverizing, and the C element and the Ti element are unevenly distributed in different powder particles. To avoid this, in some preferred embodiments, the alloy powder is both a fecrniaalti alloy powder and an a100 steel powder. The FeCrNiAlTi alloy powder and the A100 steel powder are mixed according to a certain proportion, and the alloy powder with expected components can be obtained after uniform stirring. The FeCrNiAlTi alloy powders may be prepared by any of the conventional methods known to those skilled in the art. The content of each constituent element in the FeCrNiAlTi alloy powder can be adjusted according to the element proportion. In some embodiments, the FeCrNiAlTi alloy powders have the following elemental contents: 10% by mass of Cr, 10% by mass of Ni, 6% by mass of Al, 2% by mass of Ti and the balance of Fe.

The alloy powder is spherical or nearly spherical, obvious agglomeration phenomenon is avoided, the powder performance meets printing conditions, and oxidation inclusion cannot be formed in the powder printing process to influence the performance of the formed part. The powder properties include powder particle size, oxygen content, bulk density, tap density, angle of repose, angle of collapse, plate angle, etc.

2.2 step (b)

The three-dimensional model can be built by modeling software according to the size of the formed part.

The physical parameters may include laser scan speed, laser power, scan line spacing, layer thickness, scan pattern, rotation increment, etc.

In some embodiments, the laser scanning speed may be anywhere between 1000mm/s and 1200mm/s.

In some embodiments, the laser power may be anywhere between 120W and 160W.

In some embodiments, the scan line spacing may be anywhere between 70 μm and 90 μm.

In some embodiments, the layer is anywhere between 15 μm and 25 μm thick.

In some embodiments, the scan pattern is a stripe pattern, the stripe size being 10mm.

In some embodiments, the rotation increment is 67 °.

2.3 step (c)

In some embodiments, the method further comprises the step of vacuum drying the alloy powder prior to initiating printing.

In some embodiments, the method further comprises the step of performing a powder flow test on the alloy powder prior to initiating printing.

In some embodiments, the method further comprises the step of preheating the substrate prior to initiating printing. Preferably, the substrate preheating temperature is about 200 ℃.

2.4 step (d)

Further, the preparation method of the maraging steel further comprises the step of aging the solid material obtained in the step (c).

Aging is a step of heating steel that has been transformed into a martensite phase at a specific temperature. The purpose of this treatment is to precipitate an intermetallic compound precipitate phase. In some preferred embodiments, the temperature of the aging treatment is 400-450 ℃ and the time of the aging treatment is 5-60 min. It is understood that the temperature of the aging treatment may be 400 ℃, 410 ℃, 420 ℃, 430 ℃, 440 ℃, 450 ℃. Understandably, the time of the aging treatment may be 5min, 10min, 20min, 30min, 40min, 50min, 60min. The cooling method may optionally be conventional methods, such as water quenching or air cooling.

The following are specific examples. Further details of the present application are intended to assist those skilled in the art and researchers in further understanding the present application, and the technical terms and the like are not intended to be limiting in any way. Any modification made within the scope of the claims of the present application is within the scope of the claims of the present application.

Unless otherwise indicated, the starting materials and reagents used in the following examples were either commercially available or may be prepared by known methods. The apparatus is a routine choice in the art. The experimental methods without specific conditions noted in the examples were carried out according to conventional conditions, such as those described in the literature, books, or recommended by the manufacturer.

The FeCrNiAlTi alloy powders and A100 steel powders used in the examples and comparative examples are as follows:

FeCrNiAlTi alloy powder composition: 10.2 mass percent of Cr, 10.12 mass percent of Ni, 6.2 mass percent of Al, 2.1 mass percent of Ti and the balance of Fe. The grain size of FeCrNiAlTi alloy powder is 15-53 μm.

A100 steel powder composition: 0.22 mass% of C, 3.21 mass% of Cr, 11.37 mass% of Ni, 0.05 mass% of Al, 0.04 mass% of Ti, 13.73 mass% of Co, 1.24 mass% of Mo and the balance of Fe. The grain size of the A100 steel powder is 15-53 mu m.

Example 1

(1) Alloy powders were provided in the elemental proportions shown in Table 1

Mixing FeCrNiAlTi alloy powder and A100 steel powder according to the mass ratio of 1:1, and stirring for 1-2 h by a powder mixer.

(2) And (3) establishing a three-dimensional model according to the size of the formed part by using modeling software, slicing and layering the three-dimensional model, wherein the thickness of each layer is 20 mu m. The scanning of the strip pattern is set, the strip size is 10mm, the rotation increment is 67 degrees, the scanning interval is 80 mu m, the laser power is 150W, and the scanning speed is 1200mm/s.

(3) And (3) filling the uniformly mixed powder in the step (1) into a laser powder bed for melting (L-PBF) to prepare printing. Before printing, argon with the purity more than or equal to 99.99% is used for washing, so that the oxygen content in a printing cabin is reduced to be below 260 ppm. The substrate was then preheated to a temperature of 200 ℃. And (3) performing laser additive manufacturing by using the three-dimensional model and parameters established in the step (2).

(4) And (3) aging the printing material manufactured by the laser additive in the step (3) at the aging temperature of 450 ℃ for 10min, and cooling the printing material to room temperature through water quenching after aging.

Example 2

The preparation method of example 2 is substantially the same as that of example 1, except that: step of aging the printing material obtained by the laser additive manufacturing in step (3) in example 1:

the aging temperature is 400 ℃, the aging time is 30min, and after the aging is finished, the printing material is cooled to room temperature through water quenching.

Example 3

(1) Mixing FeCrNiAlTi alloy powder and A100 steel powder according to the mass ratio of 1.2:1, and stirring for 1-2 h by a powder mixer.

(2) And (3) establishing a three-dimensional model according to the size of the formed part by using modeling software, slicing and layering the three-dimensional model, wherein the thickness of each layer is 20 mu m. The scanning of the strip pattern is set, the strip size is 10mm, the rotation increment is 67 degrees, the scanning interval is 80 mu m, the laser power is 140W, and the scanning speed is 1200mm/s.

(4) And (3) aging the printing material manufactured by the laser additive in the step (3) at the aging temperature of 450 ℃ for 5min, and cooling the printing material to room temperature through water quenching after the aging is finished.

The elemental ratios and time-efficient treatment process parameters for examples 1-3 are listed in table 1 below:

TABLE 1

The steel materials prepared in examples 1 to 3 were subjected to the tests of morphology, density, tensile properties and the like, and the test results are shown in table 2 below.

Wherein, the test conditions of each performance test item are:

1. morphology of

And researching the morphology of the material by adopting an electron back scattering diffraction technology and a transmission electron microscope. The type of the field emission scanning electron microscope with EBSD used is JEOL-JSM-6301F. The transmission electron microscope model used was FEI Talos F200X.

2. Density of

Density measurements were made according to the Archimedes drainage method using a Mettler Toledo ML T/02 electronic balance. The density test results are shown in table 2.

3. Tensile test

Mechanical property measurement is carried out by using an AG-IC20KN electronic universal tester, the sample gauge length is 10mm, and the stretching rate is 0.15mm/min. The test temperature used here was room temperature (23 ℃). The mechanical properties are shown in Table 2.

TABLE 2

	Density of	Yield strength of	Tensile strength of	Elongation percentage
					Example 1	7.539	1324	1636	9.1％
Example 2	7.539	1210	1576	11.8％
					Example 3	7.498	1110	1482	11.0％

Fig. 1 shows an electron back-scattering diffraction image quality (EBSD image quality) photograph of the low-density maraging steel material obtained in example 1 in the printing direction. As shown by the arrows, the columnar crystal structure with bright white color is delta ferrite, and the lath-like structure with black color is martensite. Wherein the delta ferrite content is about 16%. The steel materials obtained in examples 2 and 3 also had a mainly martensitic structure in texture and a delta ferrite content of not more than 20%.

Fig. 2 shows a Transmission Electron Micrograph (TEM) of the low density maraging steel obtained in example 1. After aging, a large amount of intermetallic compounds of Ni-Al-Ti are precipitated in the matrix, and the strength of the material is obviously improved through precipitation strengthening. The steel material matrices obtained in example 2 and example 3 also contained a large amount of ni—al—ti intermetallic compounds.

The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.

The above examples merely represent a few embodiments of the present application, which facilitate a specific and detailed understanding of the technical solutions of the present application, but are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. It should be understood that those skilled in the art, based on the technical solutions provided in the present application, can obtain technical solutions through logical analysis, reasoning or limited experiments, all fall within the protection scope of the claims attached in the present application. The scope of the patent application is therefore intended to be limited by the content of the appended claims, the description and drawings being presented to the extent that the claims are defined.

Claims

1. A laser additive manufactured low density maraging steel, characterized by the following composition:

cr is more than or equal to 6.5 percent and less than or equal to 10 percent,

al is more than or equal to 3% and less than or equal to 3.5% by mass

Ti is more than or equal to 1 percent and less than or equal to 1.5 percent,

co is more than or equal to 6% and less than or equal to 7% by mass

the balance being Fe and unavoidable impurities.

2. Maraging steel according to claim 1, characterized in that it is obtained by ageing with martensite and ferrite as initial structure, the volume fraction of ferrite in the initial structure being at most 20%.

3. Maraging steel according to claim 2, characterized in that the maraging steel structure has intermetallic precipitation phases distributed therein, the intermetallic precipitation phases comprising the B2 phase of Ni-Al-Ti and L2 ₁ And (3) phase (C).

4. Maraging steel according to claim 1, characterized in that the yield strength at 23 ℃ is at least 1100MPa.

5. Maraging steel according to claim 1, characterized in that the tensile strength at 23 ℃ is at least 1400MPa.

6. Maraging steel according to claim 1, characterized in that the elongation at 23 ℃ is at least 9%.

7. Maraging steel according to claim 1, characterized in that the density does not exceed 7.56g/cm ³ 。

8. A method of producing maraging steel as claimed in any one of claims 1 to 7, characterized in that a laser additive manufacturing method is used, comprising the steps of:

determining the element proportion according to the specified content of each component, and providing alloy powder conforming to the element proportion;

designing a three-dimensional model, setting entity parameters in the laser additive manufacturing process, and assigning values to the three-dimensional model according to the entity parameters;

and aging the solid material.

9. The method of producing maraging steel as recited in claim 8, wherein the alloy powder comprises fecrniaalti alloy powder and a100 steel powder.

10. The method of producing maraging steel as defined in claim 9, wherein the mass ratio of the fecrniaalti alloy powder to the a100 steel powder is (0.9-1.3): 1.

11. The method for producing maraging steel as claimed in claim 8, wherein the physical parameters include a laser scanning speed, a laser power and a scanning line pitch, the laser scanning speed being 1000-1200 mm/s, the laser power being 120-160W, the scanning line pitch being 70-90 μm.

12. The method of producing maraging steel as recited in claim 11, wherein the physical parameters further comprise a layer thickness of 15-25 μm.

13. The method for producing maraging steel as recited in claim 8, wherein the aging treatment is performed at a temperature of 400 to 450 ℃, and the aging treatment is performed for a time of 5 to 60 minutes.