Method for preparing high-strength high-nitrogen stainless steel through pre-nitrogen-increasing selective laser melting

Abstract

The invention belongs to the technical field of ferrous metallurgy, and discloses a method for preparing high-strength high-nitrogen stainless steel through pre-nitrogen-increasing selective laser melting. Comprising the following steps that (1) nitrogen increasing is conducted on 1Cr18Mn12Mo3N stainless steel alloy powder in a pre-nitrogen-increasing mode, and pre-nitrogen-increasing powder is obtained; (2) the pre-increased nitrogen powder is mixed with the 1Cr18Mn12Mo3N stainless steel alloy powder, and high-nitrogen stainless steel raw material powder is obtained; and (3) the normal-pressure selective laser melting technology is adopted for printing, and the high-nitrogen stainless steel is obtained. The high-nitrogen stainless steel is prepared by adopting the pre-nitrogen-increasing selective laser melting method, so that the powder uniformity is improved, the printing element segregation is reduced, and the nitrogen content in the product is ensured. The adopted gas atomization spherical stainless steel alloy powder is easy to prepare, the pre-nitrogen-increasing method is simple and convenient, the cost for preparing the high-nitrogen steel printing powder is reduced, reaction pressure does not need to be increased in the reaction process, and safety is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and more specifically relates to a method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogenation selective laser melting. Background Art

[0002] High nitrogen stainless steel is considered to be one of the most promising new engineering materials due to its excellent corrosion resistance in a variety of corrosive media, good comprehensive mechanical properties and excellent processing performance. It has been widely used in many fields such as bioenergy industry, aerospace, petrochemical industry, marine engineering, biomedicine, etc. At present, the methods used to prepare high nitrogen steel at home and abroad include: nitrogen pressure melting method, powder metallurgy method and surface nitriding method; the product quality obtained by nitrogen pressure melting method in the preparation of high nitrogen steel is excellent, but it is limited by its high high pressure manufacturing cost and complex equipment.

[0003] Metal additive manufacturing technology is a preparation and processing technology based on digital models, which uses high-energy heat sources to process powder materials and quickly stack them layer by layer. Selective laser melting (SLM) is an important branch of metal additive manufacturing. The SLM process is a process in which high-power lasers and metal powder materials interact with each other in a high-speed melting and solidification process and selectively stack them layer by layer.

[0004] Selective laser melting is used to prepare high-nitrogen stainless steel. Due to the overflow of nitrogen during the printing process, it is impossible to directly obtain high-nitrogen stainless steel with a nitrogen content that meets the standard. Usually, pressurization is used to suppress nitrogen overflow, but conventional 3D printing equipment does not have a pressurization function. The solubility of nitrogen in liquid steel under atmospheric pressure is very low. The traditional smelting of high-nitrogen steel is not as easy as other steels. Similarly, it is difficult to directly produce high-nitrogen stainless steel using conventional nitrogen-containing metal powders under normal pressure using the SLM process.

[0005] Therefore, how to prepare high-nitrogen stainless steel using atmospheric pressure selective laser melting technology is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0006] In order to overcome the shortcomings and deficiencies in the prior art, the present invention provides a method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting based on the powder mixing process and selective laser melting technology. The method solves the problems of low nitrogen content in stainless steel printed under normal pressure and insufficient strength and plasticity after powder mixing, and has broad application prospects.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for preparing high-strength high-nitrogen stainless steel by pre-nitrogen selective laser melting, comprising the following steps:

[0009] (1) nitrogenizing 1Cr18Mn12Mo3N stainless steel alloy powder by a pre-nitrogenizing method to obtain pre-nitrogenized powder;

[0010] (2) mixing the pre-nitrogen-enriched powder with 1Cr18Mn12Mo3N stainless steel alloy powder to obtain a high-nitrogen stainless steel raw material powder;

[0011] (3) Printing is performed using atmospheric pressure selective laser melting technology to obtain high nitrogen stainless steel;

[0012] The mass ratio of the nitrogen content of the high nitrogen stainless steel raw material powder to the target nitrogen content of the high nitrogen stainless steel is 0.8-1.2:0.5-0.9.

[0013] Preferably, the specific operation of the pre-nitrogen addition is: placing the powder in a nitrogen atmosphere, keeping it at 800° C. for 4 hours and then cooling it with the furnace.

[0014] Preferably, the target chemical composition of the high nitrogen stainless steel includes, by weight percentage: C: ≤0.1%, Cr: 17-19%, N: 0.6-1.2%, Mn: 11-13%, Mo: 2-3.03%, Ni<0.01%, Si: <0.3%, P: ≤0.01%, S: <0.1%, Fe: balance.

[0015] Preferably, the 1Cr18Mn12Mo3N stainless steel alloy powder is an atomized spherical stainless steel alloy powder with a particle size of 15 to 53 μm and a nitrogen content of 0.43%.

[0016] Preferably, the nitrogen content of the pre-nitrogenated powder is 4.3%.

[0017] Preferably, the mass ratio of the 1Cr18Mn11Mo3N stainless steel alloy powder to the pre-nitrogenated powder is 17:3.

[0018] Preferably, the process parameters of the atmospheric pressure selective laser melting technology include: laser power 180W-240W, scanning speed 700mm / s-900mm / s, scanning interval 0.10mm, powder layer thickness 0.03mm.

[0019] Preferably, the specific operation of the atmospheric pressure selective laser melting technology is: evacuating the powder supply chamber of the selective laser melting 3D printer, filling it with argon gas, and starting printing after preheating the substrate to 150°C.

[0020] The present invention also provides high nitrogen stainless steel prepared according to the method.

[0021] It can be seen from the above technical solution that, compared with the prior art, the present invention provides a method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting, which has the following beneficial effects:

[0022] The present invention adopts a pre-nitrogenation selective laser melting method to prepare high-nitrogen stainless steel, which improves the uniformity of the powder, reduces the segregation of printing elements, and ensures the nitrogen content in the product; the existing technology for preparing high-nitrogen steel powder is extremely costly and difficult to process. The gas-atomized spherical stainless steel alloy powder used in the present invention is easy to prepare, the pre-nitrogenation method is simple, the cost of preparing high-nitrogen steel printing powder is reduced, and the reaction process does not need to increase the reaction pressure, which improves safety.

[0023] The present invention improves the nitrogen content and controllability of high nitrogen steel prepared by selective laser melting by adjusting the element content of the mixed powder raw materials, effectively improves the pitting corrosion resistance and stress corrosion resistance of stainless steel materials, has higher yield and tensile strength, can prepare a variety of high nitrogen steel printing powders, and increases the feasibility of high nitrogen steel 3D printing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 The nitrogen content of high nitrogen stainless steel raw material powder with a nitrogen content of 1.01wt% after printing at different laser powers; among them, (a) scanning speed 900mm / s; (b) scanning speed 800mm / s; (c) scanning speed 700mm / s; (d) scanning speed 600mm / s.

[0026] Figure 2 This is a tensile test specimen diagram of the molded part obtained in Example 1 of the present invention.

[0027] Figure 3 This is a physical picture of the molded part obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The present invention discloses a method for preparing high-strength high-nitrogen stainless steel by pre-nitrogenation selective laser melting. The high-nitrogen stainless steel is prepared by powder mixing and selective laser melting 3D printing, which can effectively increase the nitrogen content of complex parts.

[0030] Technical principle:

[0031] The key to the pre-nitrogen-enriched selective laser melting method lies in two aspects: first, configure the appropriate amount of powder by pre-nitrogen-enriched mixed powder, accurately calculate the nitrogen overflow amount according to the nitrogen escape rate experiment, and ensure the nitrogen content after printing; second, formulate a reasonable selective laser melting solidification process to reduce nitrogen segregation.

[0032] In order to obtain accurate nitrogen content and ensure uniform distribution of nitrogen in steel, the nitrogen overflow rate during selective laser melting was calculated to obtain the over-matched powder composition. A reasonable selective laser melting process was obtained through experimental methods.

[0033] Example 1

[0034] A method for preparing high-strength high-nitrogen stainless steel by pre-nitrogen selective laser melting, comprising the following steps:

[0035] (1) The 1Cr18Mn12Mo3N stainless steel alloy powder was nitrogen-enriched by pre-nitrogenation, placed in a nitrogen atmosphere, kept at 800°C for 4 hours, and then cooled with the furnace to obtain a pre-nitrogenated powder with a nitrogen content of 4.3%, the composition of which is shown in Table 3;

[0036] 1Cr18Mn12Mo3N stainless steel alloy powder is a gas-atomized spherical stainless steel alloy powder with a particle size of 15 to 53 μm and a nitrogen content of 0.43%, and the composition is shown in Table 2;

[0037] The target chemical composition of high nitrogen stainless steel raw material powder is shown in Table 1;

[0038] Table 1 Target chemical composition of high nitrogen stainless steel raw material powder (mass %)

[0039]

[0040] Table 21Chemical composition of Cr18Mn12Mo3N stainless steel alloy powder (mass %)

[0041]

[0042] Table 3 Chemical composition of pre-nitrogenated powder (mass %)

[0043]

[0044] (2) 1Cr18Mn12Mo3N stainless steel alloy powder and pre-nitrogenated powder were mixed in a mass ratio of 17:3 to obtain high nitrogen stainless steel raw material powder, the composition of which is shown in Table 4;

[0045] Table 4 Chemical composition of high nitrogen stainless steel raw material powder (mass %)

[0046]

[0047] (3) The high nitrogen stainless steel raw material powder was printed by atmospheric pressure selective laser melting technology. The powder supply chamber of the selective laser melting 3D printer was evacuated and filled with argon gas. The substrate was preheated to 150°C before printing. The process parameters are shown in Table 5. Five molded parts of high nitrogen stainless steel were obtained. The block forming size is 5×5×5mm, and the tensile specimen size is Figure 2 As shown, the actual molded parts are as follows Figure 3 The nitrogen content is shown in Table 6, and the mechanical properties are shown in Table 7.

[0048] The high nitrogen stainless steel raw material powder prepared in Example 1 was used to detect the nitrogen content after printing at different laser powers. The results are as follows: Figure 1 As shown, (a) scanning speed is 900 mm / s; (b) scanning speed is 800 mm / s; (c) scanning speed is 700 mm / s; (d) scanning speed is 600 mm / s.

[0049] Table 5 Selected laser melting block forming parameters

[0050]

[0051] Table 6 Nitrogen content of molded parts (the content of other components in the molded parts is the same as Table 2)

[0052]

[0053] Table 7 Molding properties

[0054]

[0055] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high-strength high-nitrogen stainless steel by pre-nitrogen selective laser melting, characterized in that: The following steps are involved: (1) nitrogenizing 1Cr18Mn12Mo3N stainless steel alloy powder by a pre-nitrogenizing method to obtain pre-nitrogenized powder; (2) mixing the pre-nitrogen-enriched powder with 1Cr18Mn12Mo3N stainless steel alloy powder to obtain a high-nitrogen stainless steel raw material powder; (3) Printing high nitrogen stainless steel raw material powder by atmospheric pressure selective laser melting technology to obtain high nitrogen stainless steel; The mass ratio of the nitrogen content of the high nitrogen stainless steel raw material powder to the target nitrogen content of the high nitrogen stainless steel is 0.8-1.2:0.5-0.

9.

2. The method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting according to claim 1, characterized in that: The specific operation of the pre-nitrogen addition is: placing the powder in a nitrogen atmosphere, keeping it at 800° C. for 4 hours, and then cooling it with the furnace.

3. The method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting according to claim 1, characterized in that: The target chemical composition of the high nitrogen stainless steel includes, by weight percentage: C: ≤0.1%, Cr: 17-19%, N: 0.6-1.2%, Mn: 11-13%, Mo: 2-3.03%, Ni<0.01%, Si: <0.3%, P: ≤0.01%, S: <0.1%, Fe: balance.

4. The method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting according to claim 1, characterized in that: The 1Cr18Mn12Mo3N stainless steel alloy powder is a gas-atomized spherical stainless steel alloy powder with a particle size of 15 to 53 μm and a nitrogen content of 0.43%.

5. The method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting according to claim 1, characterized in that: The nitrogen content of the pre-nitrogen-enhanced powder is 4.3%.

6. The method for preparing high-strength and high-nitrogen stainless steel by pre-nitrogen selective laser melting according to claim 1, characterized in that: The mass ratio of the 1Cr18Mn11Mo3N stainless steel alloy powder to the pre-nitrogenated powder is 17:

3.

7. The method for preparing high nitrogen stainless steel by selective laser melting of alloy overmatched powder according to claim 1, characterized in that: The process parameters of the atmospheric pressure selective laser melting technology include: laser power 180W-240W, scanning speed 700mm / s-900mm / s, scanning interval 0.1mm, and powder layer thickness 0.03mm.

8. The method for preparing high nitrogen stainless steel by selective laser melting of alloy overmatched powder according to claim 7, characterized in that: The specific operation of the atmospheric pressure selective laser melting technology is: evacuating the powder supply chamber of the selective laser melting 3D printer, filling it with argon gas, and starting printing after preheating the substrate to 150°C.

9. High nitrogen stainless steel prepared according to the method according to any one of claims 1 to 8.

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