A method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing

Abstract

The present invention belongs to the technical field of high nitrogen steel manufacturing, and specifically discloses a method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing, comprising the following steps: (1) weighing raw materials according to the designed proportions of the components of the high nitrogen steel, and ball-milling the raw materials into high nitrogen steel powder; (2) designing the concentration of nitrogen in the high nitrogen steel, and calculating the composition of the mixed protective gas according to the formula; (3) placing the high nitrogen steel powder prepared in step (1) into a molding chamber of a selective laser melting device, introducing a mixed protective gas, and printing and preparing high nitrogen steel according to set 3D printing parameters, and evaluating the prepared high nitrogen steel by laser volume energy density. The present invention can control the nitrogen content in the prepared high nitrogen steel and improve the mechanical properties of the high nitrogen steel by using a mixed protective gas to suppress nitrogen loss and nitrogen pores during the preparation process.

Description

Technical Field

[0001] The present invention belongs to the field of high nitrogen steel manufacturing, and specifically relates to a method for preparing high nitrogen steel with controllable nitrogen content through additive manufacturing. Background Art

[0002] Increasing the nitrogen content in traditional stainless steel to make high nitrogen steel can significantly improve the corrosion resistance and mechanical properties of steel, such as creep resistance and fatigue strength. At the same time, high nitrogen steel has better biocompatibility than traditional stainless steel, and can also replace nickel-improved medical stainless steel in the medical field. Therefore, high nitrogen steel has become a hot topic of research at home and abroad.

[0003] However, due to the low solubility of nitrogen in steel at normal pressure (γ austenite phase is 2.8wt%, L liquid phase is 0.04wt%, δ ferrite phase is 0.0128wt%), it is difficult to prepare high nitrogen steel with a nitrogen content of more than 0.4wt% at normal pressure. At present, high nitrogen steel is mainly prepared by pressure melting method, but the conventional pressure melting method requires expensive special equipment, has the disadvantages of complex process, difficult to control nitrogen content, macro segregation, poor near net forming ability, and the high strength and hardness of high nitrogen steel lead to its poor cutting performance, making it difficult to process complex components by traditional methods, limiting its development and application.

[0004] At present, the existing technology, such as the Chinese patent with publication number CN115446331B, provides a method for preparing high nitrogen stainless steel by selective laser melting of pure metal overmatched powder. It adopts the method of selective laser melting of overmatched powder for preparation, and replaces nickel with manganese nitrogen, which can ensure the nitrogen content in the product, reduce the preparation cost of high nitrogen steel, and increase the feasibility of 3D printing of high nitrogen steel.

[0005] However, the above technology still has the following problems: 1. When using nitriding alloy (manganese nitrogen) to increase the nitrogen content in molten steel, excessive impurity elements such as oxygen and sulfur in the nitriding alloy will cause secondary contamination of the molten steel; 2. When using selective laser melting technology, there will be nitrogen loss and nitrogen pore defects during the printing process, which will lead to uncontrollable nitrogen content in the prepared high nitrogen steel, and then cause the mechanical properties of the prepared high nitrogen steel to decrease. Summary of the invention

[0006] In response to the technical problem mentioned in the above background technology that the nitrogen content in high nitrogen steel prepared by selective laser melting technology is uncontrollable, which leads to a decrease in the mechanical properties of the prepared high nitrogen steel, the present invention uses a mixed protective gas to suppress nitrogen loss and nitrogen pores during the preparation process, thereby controlling the nitrogen content in the prepared high nitrogen steel and improving the mechanical properties of the high nitrogen steel.

[0007] The present invention adopts the following technical solution: a method for preparing high nitrogen steel by additive manufacturing with controllable nitrogen content, comprising the following steps:

[0008] (1) weighing raw materials according to the designed proportions of each component of high nitrogen steel, and ball-milling the raw materials into high nitrogen steel powder;

[0009] (2) Design the nitrogen concentration in high nitrogen steel and calculate the mixed protective gas composition according to the formula;

[0010] (3) The high nitrogen steel powder prepared in step (1) is placed in a molding chamber of a selective laser melting device, a mixed protective gas is introduced, and the high nitrogen steel is printed according to the set 3D printing parameters, and the prepared high nitrogen steel is evaluated by the laser volume energy density.

[0011] Furthermore, in step (1), the high nitrogen steel powder comprises the following components by weight: 0.1-0.5% C, 4-15% Cr, 1-15% Mo, 1-8% V, 0.1-5% Si, 0.01-5% O, and the balance is Fe.

[0012] Furthermore, the ball milling parameters in step (1) are ball milling time of 5 to 20 hours, ball milling speed of 200 to 600 r / min, ball to material ratio of 1 / 10 to 1 / 2, and the powder particle size after ball milling is 20 to 60 μm.

[0013] Furthermore, the mixed protective gas in step (2) includes nitrogen and ammonia, and the volume ratio of ammonia in the mixed protective gas is 1 to 20%.

[0014] Further, the formula in step (2) is:

[0015] The K 1 and K 2 are the equilibrium constants of the reactions of ammonia and nitrogen, A is the effective collision factor, and f N is the activity coefficient of nitrogen in steel under solid solution nitriding conditions, X is NH 3 The volume fraction of the mixed protective gas, P is the solid solution nitriding pressure.

[0016] Furthermore, the K 1 The calculation formula is The K 2 The calculation formula is

[0017] Furthermore, the f N The calculation formula is:

[0018] Said are the interaction coefficients between the corresponding elements and the N element respectively.

[0019] Furthermore, in step (3), the volume fraction of oxygen content in the molding chamber is lower than 100 ppm.

[0020] Furthermore, in the step (3), when the high nitrogen steel is prepared by selective laser melting, the laser power P is 100-180 W, the scanning speed V is 600-1200 mm / s, the layer thickness t is 30 μm, and the spot diameter d is 100 μm, 50-100 μm.

[0021] Furthermore, the laser volume energy density evaluation formula in step (3) is E v =P / (vht), where P is the laser power, v is the laser scanning speed, h is the laser path spacing, t is the thickness of each layer of powder, and the laser volume energy density is 60-80 J / m 3 .

[0022] The beneficial effect of the present invention is that, compared with the prior art,

[0023] 1) In the present invention, a mixed gas of nitrogen and ammonia is used as a protective gas, which can improve the nitrogen potential and increase the nitriding efficiency in the process of preparing high nitrogen steel by selective laser melting. At the same time, in the selective laser melting preparation process, nitrogen and ammonia are respectively N 2 →2[N] and 2NH 3 →3H 2 +2[N] process, the two reaction processes restrict each other, and adding ammonia can make N 2 →2[N] reaction process is dominant, which is beneficial to further diffusion of nitrogen atoms and improve nitriding efficiency.

[0024] 2) The present invention provides a method for calculating the ratio of ammonia and nitrogen in the mixed protective gas according to the nitrogen concentration in the designed high nitrogen steel according to a calculation formula, so that the nitrogen content in the prepared high nitrogen steel can be controlled during the reaction. By accurately controlling the nitrogen content, the adverse effects caused by excessive nitrogen content, such as increased brittleness, decreased processing performance and poor welding performance, can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a physical picture of the high nitrogen steel prepared in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides a method for preparing high nitrogen steel by additive manufacturing with controllable nitrogen content, comprising the following steps:

[0029] (1) weighing raw materials according to the designed proportions of each component of high nitrogen steel, and ball-milling the raw materials into high nitrogen steel powder;

[0030] Specifically, the mass ratio of the high nitrogen steel powder raw material is designed to be 0.15% C, 15% Cr, 2.6% Mo, 2% V, 0.2% Si, 0.1% O, and the balance is Fe. The corresponding raw materials are weighed and put into a ball mill for uniform mixing. The ball milling parameters in the ball mill are ball milling time of 10h, ball milling speed of 400r / min, ball-to-material ratio of 1 / 5, and the powder particle size after ball milling is 38μm.

[0031] (2) Design the nitrogen concentration in high nitrogen steel and calculate the mixed protective gas composition according to the formula;

[0032] Specifically, the concentration of nitrogen in the high nitrogen steel in the designed finished product [N%] = 1.66, and the designed reaction temperature is 950°C. First, according to the formula:

[0033] Calculate f N =0.011, where are the interaction coefficients of the corresponding elements and the N element, and the values ​​are shown in Table 1 below:

[0034] Table 1: Interaction coefficients of Cr and Mn elements with N element

[0035]

[0036] According to the calculation formula:

[0037] Calculate K 1 =5766,K 2 =0.0275.

[0038] Finally, according to the formula:

[0039] It is calculated that X=0.025, that is, the volume fraction of ammonia in the mixed protective gas is 2.5%.

[0040] (3) The high nitrogen steel powder prepared in step (1) is placed in a molding chamber of a selective laser melting device, a mixed protective gas is introduced, and the high nitrogen steel is printed according to the set 3D printing parameters, and the prepared high nitrogen steel is evaluated by the laser volume energy density.

[0041] Specifically, the high nitrogen steel powder prepared in step (1) is placed in the molding chamber of the selective laser melting equipment, and the mixed protective gas prepared according to the calculation in step (2) is rushed into the molding chamber, and the oxygen content (volume fraction) continuously introduced into the chamber is less than 100ppm. According to the set three-dimensional model of the high nitrogen steel structure, the printing parameters are set to P = 140W, scanning speed V = 900mm / s, layer thickness t = 30μm, spot diameter d = 100μm, scanning spacing 80μm, and laser volume energy density 64.81J / m 3 Print out the required structural parts model.

[0042] Example 2

[0043] The difference between this embodiment and embodiment 1 is that the high nitrogen steel powder used has a different composition.

[0044] Specifically, the mass ratio of the high nitrogen steel powder raw material is designed to be 0.2% C, 15% Cr, 2.6% Mo, 3% V, 1% Si, 0.06% O, and the balance is Fe. The corresponding raw materials are weighed and put into a ball mill for uniform mixing. The ball milling parameters in the ball mill are ball milling time 8h, ball milling speed 400r / min, ball to material ratio 1 / 5, and the powder particle size after ball milling is 34μm.

[0045] The designed nitrogen concentration in high nitrogen steel in the finished product [N%] = 1.66, and the designed reaction temperature is 950℃. First, according to the formula:

[0046]

[0047] Calculate f N =0.011;

[0048] According to the calculation formula:

[0049] Calculate K 1 =5766,K 2 =0.0275.

[0050] Finally, according to the formula:

[0051] It is calculated that X=0.025, that is, the volume fraction of ammonia in the mixed protective gas is 2.5%.

[0052] The high nitrogen steel powder prepared in step (1) is placed in the molding chamber of the selective laser melting equipment, and the mixed protective gas prepared according to the calculation in step (2) is flushed into the molding chamber, and the oxygen content (volume fraction) continuously introduced into the chamber is less than 100ppm. According to the set three-dimensional model of the high nitrogen steel structure, the printing parameters are set to P = 140W, scanning speed V = 900mm / s, layer thickness t = 30μm, spot diameter d = 100μm, scanning spacing 80μm, and laser volume energy density 64.81J / m 3 Print out the required structural parts model.

[0053] Example 3

[0054] The difference between this embodiment and embodiment 1 is that the designed nitrogen content of the high nitrogen steel is different from the composition of the mixed protective gas used in step (2).

[0055] Specifically, the mass ratio of the high nitrogen steel powder raw material is designed to be 0.15% C, 15% Cr, 2.6% Mo, 2% V, 0.2% Si, 0.1% O, and the balance is Fe. The corresponding raw materials are weighed and put into a ball mill for uniform mixing. The ball milling parameters in the ball mill are ball milling time of 10h, ball milling speed of 400r / min, ball-to-material ratio of 1 / 5, and the powder particle size after ball milling is 38μm.

[0056] The designed nitrogen concentration in high nitrogen steel in the finished product [N%] = 2.15, and the designed reaction temperature is 950℃. First, according to the formula:

[0057]

[0058] Calculate f N =0.018;

[0059] According to the calculation formula:

[0060] Calculate K 1 =13289,K 2 =0.023,

[0061] Finally, according to the formula:

[0062] It is calculated that X=0.018, that is, the volume fraction of ammonia in the mixed protective gas is 1.8%.

[0063] The high nitrogen steel powder prepared in step (1) is placed in the molding chamber of the selective laser melting equipment, and the mixed protective gas prepared according to the calculation in step (2) is flushed into the molding chamber, and the oxygen content (volume fraction) continuously introduced into the chamber is less than 100ppm. According to the set three-dimensional model of the high nitrogen steel structure, the printing parameters are set to P = 140W, scanning speed V = 900mm / s, layer thickness t = 30μm, spot diameter d = 100μm, scanning spacing 80μm, and laser volume energy density 64.81J / m 3 Print out the required structural parts model.

[0064] Example 4

[0065] The difference between this embodiment and embodiment 1 is that the composition of the high nitrogen steel powder used and the composition of the mixed protective gas used are different.

[0066] Specifically, the mass ratio of the high nitrogen steel powder raw material is designed to be 0.2% C, 15% Cr, 2.6% Mo, 3% V, 1% Si, 0.06% O, and the balance is Fe. The corresponding raw materials are weighed and put into a ball mill for uniform mixing. The ball milling parameters in the ball mill are ball milling time 8h, ball milling speed 400r / r / min, ball to material ratio 1 / 5, and the powder particle size after ball milling is 34μm.

[0067] The designed nitrogen concentration in high nitrogen steel in the finished product [N%] = 2.15, and the designed reaction temperature is 950℃. First, according to the formula:

[0068]

[0069] Calculate f N =0.018;

[0070] According to the calculation formula:

[0071] Calculate K 1 =13289,K 2 =0.023,

[0072] Finally, according to the formula:

[0073] It is calculated that X=0.018, that is, the volume fraction of ammonia in the mixed protective gas is 1.8%.

[0074] The high nitrogen steel powder prepared in step (1) is placed in the molding chamber of the selective laser melting equipment, and the mixed protective gas prepared according to the calculation in step (2) is flushed into the molding chamber, and the oxygen content (volume fraction) continuously introduced into the chamber is less than 100ppm. According to the set three-dimensional model of the high nitrogen steel structure, the printing parameters are set to P = 140W, scanning speed V = 900mm / s, layer thickness t = 30μm, spot diameter d = 100μm, scanning spacing 80μm, and laser volume energy density 64.81J / m 3 Print out the required structural parts model.

[0075] The structural parts prepared in the above embodiment were tested, and the experimental data are listed in the following Table 1:

[0076] Table 1: Summary of experimental parameters of the examples

[0077]

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing, characterized in that: The following steps are involved: (1) weighing raw materials according to the designed proportions of each component of high nitrogen steel, and ball-milling the raw materials into high nitrogen steel powder; (2) Design the nitrogen concentration in high nitrogen steel and calculate the mixed protective gas composition according to the formula; (3) The high nitrogen steel powder prepared in step (1) is placed in a molding chamber of a selective laser melting device, a mixed protective gas is introduced, and the high nitrogen steel is printed according to the set 3D printing parameters, and the prepared high nitrogen steel is evaluated by the laser volume energy density.

2. The method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 1, characterized in that: The high nitrogen steel powder in step (1) comprises the following components by weight: 0.1-0.5% C, 4-15% Cr, 1-15% Mo, 1-8% V, 0.1-5% Si, 0.01-5% O, and the balance is Fe.

3. The method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 2, characterized in that: The ball milling parameters in step (1) are ball milling time of 5 to 20 hours, ball milling speed of 200 to 600 r / min, ball to material ratio of 1 / 10 to 1 / 2, and the powder particle size after ball milling is 20 to 60 μm.

4. The method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 1, characterized in that: The mixed protective gas in step (2) includes nitrogen and ammonia, and the volume ratio of ammonia in the mixed protective gas is 1-20%.

5. A method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 4, characterized in that: The formula in step (2) is: K1 and K2 are the equilibrium constants of the reaction of ammonia and nitrogen respectively, A is the effective collision factor, f N is the activity coefficient of nitrogen in steel under solid solution nitriding conditions, X is the volume fraction of NH3 in the mixed protective gas, and p is the solid solution nitriding pressure.

6. A method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 5, characterized in that: The calculation formula of K1 is: The calculation formula of K2 is:

7. A method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 6, characterized in that: The f N The calculation formula is: Said are the interaction coefficients between the corresponding elements and N elements respectively.

8. The method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 1, characterized in that: In the step (3), the volume fraction of oxygen content in the molding chamber is lower than 100 ppm.

9. The method for preparing high nitrogen steel with controllable nitrogen content by additive manufacturing according to claim 8, characterized in that: In the step (3), when the high nitrogen steel is prepared by selective laser melting, the laser power P=100-180W, the scanning speed V=600-1200mm / s, the layer thickness t=30μm, the spot diameter d=100μm, 50-100μm.

10. The method for preparing a method for additively manufacturing high nitrogen steel with controllable nitrogen content according to claim 9, characterized in that: The laser volume energy density evaluation formula in step (3) is E v =P / (vht), where P is the laser power, v is the laser scanning speed, h is the laser path spacing, t is the thickness of each layer of powder, and the laser volume energy density is 60-80 J / m 3 .

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