A method for improving hydrogen embrittlement properties of 3D printed stainless steel with plasma

Abstract

The application discloses a method for improving hydrogen embrittlement performance of 3D printing stainless steel by plasma, and belongs to the field of metal 3D printing. The method comprises the following steps: (1) performing plasma discharge modification treatment on stainless steel powder; (2) performing 3D printing on the modified powder obtained in the step (1), or performing drying and screening on the modified stainless steel powder in the step (1) and then performing 3D printing, to obtain a 3D printing metal component. The 3D printing stainless steel material prepared by the method has an ultimate tensile strength of 712 MPa at room temperature, a hardness of 285 HV, an elongation after fracture of 53%, and a hydrogen embrittlement resistance of slight hydrogen embrittlement, and then in a hydrogen environment, compared with a conventional material, the 3D printing stainless steel material has less cracking, good plasticity and a longer working life.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal 3D printing, more particularly to a method for improving the hydrogen embrittlement performance of 3D printed stainless steel by using plasma. BACKGROUND

[0002] Austenitic stainless steel (ASS) is often used in sensitive hydrogen (H) storage, hydrogen infrastructure and transportation applications because they are generally less susceptible to hydrogen embrittlement (HE) compared to ferritic steels. As an emerging manufacturing technology that can replace many traditional production processes, the austenitic stainless steel manufactured by additive manufacturing (AM) has higher stability and mechanical properties. However, due to the processing characteristics of laser layer-by-layer reciprocating scanning, the temperature gradient of the molten pool is large, and the microstructure grain is small. The ordinary additive manufacturing austenitic stainless steel is prone to have large residual stress and many void defects, which leads to poor plasticity of the formed piece, and still occurs moderate hydrogen embrittlement in the hydrogen environment, and does not have significant performance improvement in hydrogen embrittlement resistance compared to traditional manufacturing austenitic stainless steel.

[0003] Currently, the method for improving the hydrogen embrittlement resistance of additive manufacturing austenitic stainless steel mainly focuses on optimizing the AM process, but this method is time-consuming and costly, and its application is limited. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a method for improving the hydrogen embrittlement performance of 3D printed stainless steel by using plasma, so as to optimize the ultimate tensile strength, elongation, Vickers hardness and hydrogen embrittlement resistance of SLM technology formed stainless steel, improve the high hydrogen sensitivity and easy hydrogen embrittlement of 3D printed stainless steel, and obtain more excellent mechanical properties and hydrogen embrittlement resistance.

[0005] The purpose of the present application is achieved by the following technical solutions.

[0006] A method for improving the hydrogen embrittlement performance of 3D printed stainless steel by using plasma, comprising the following steps:

[0007] (1) Plasma discharge modification treatment is performed on the stainless steel powder;

[0008] (2) The modified powder obtained in step (1) is subjected to 3D printing to obtain a 3D printed metal component.

[0009] Preferably, in step (1), the current required for exciting the plasma is 150 mA-500 mA, and the plasma discharge modification treatment time is 9-12 hours.

[0010] Preferably, the plasma discharge modification treatment in step (1) uses low-temperature cold field plasma; and the plasma is generated by exciting ionization of the required gas filled with 100 Pa-0.1 MPa.

[0011] Preferably, the gas for the plasma discharge modification treatment in step (1) is one or more of argon, nitrogen, and ammonia.

[0012] Preferably, in step (1), the current required for exciting the plasma is 100-500 mA, and the frequency of the pulsed high-voltage discharge is 8-15 kHz.

[0013] Preferably, in step (1), the amplitude of the vibration of the powder during the plasma discharge modification treatment is greater than 10 mm.

[0014] Preferably, in step (1), the plasma discharge modification treatment time is 9-12 hours.

[0015] Further preferably, in step (1), the plasma discharge modification treatment time is 12 hours.

[0016] Preferably, the modified stainless steel powder from step (1) is dried, sieved, and then 3D printed to obtain a 3D printed metal component.

[0017] Further preferably, the drying is vacuum drying at 80°C for 1-4 hours.

[0018] Further preferably, the sieving is to 15-55 microns.

[0019] Preferably, in step (2), the 3D printing is performed using nitrogen to purge the printer chamber before forming, so that the oxygen content is less than 100 ppm, ensuring that the component does not oxidize during the forming process.

[0020] A 3D printed metal component obtained by the method of any one of the above for improving the hydrogen embrittlement performance of 3D printed stainless steel using plasma.

[0021] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0022] (1) The stainless steel metal component obtained by the present application has better plasticity, elongation, Vickers hardness, and hydrogen embrittlement resistance.

[0023] (2) The present application can make the 3D printed stainless steel have better balanced mechanical properties and hydrogen embrittlement resistance, which is more conducive to the application of stainless steel in a hydrogen environment. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A flowchart of the method of the present application for improving the hydrogen embrittlement performance of 3D printed stainless steel using plasma.

[0025] Figure 2The figure is a schematic diagram of the tensile strength and hydrogen embrittlement resistance of the stainless steel before and after modification. Wherein, (a) is a schematic diagram of the tensile strength before and after modification using Ar in Example 2; (b) is a schematic diagram of the tensile strength before and after modification using Ar and NH3 in Example 1 and Example 3; (c) is a schematic diagram of the hydrogen embrittlement degree before and after modification using NH3 in Example 3; (d) is a schematic diagram of the hydrogen embrittlement degree before and after modification using Ar in Example 1; (e) is a schematic diagram of the hydrogen embrittlement degree of the original sample in Example 1; (f) is a schematic diagram of the tensile strength when the modification time is 9 / 12h in Example 5 using Ar modification; (g) is a schematic diagram of the tensile strength when the current is 150mA / 500mA in Example 6 using Ar modification.

[0026] Figure 3 The figure is a comparison diagram of the micro Vickers hardness of the stainless steel before and after modification.

[0027] Figure 4 The figure is a picture of the modified stainless steel powder in Comparative Example 1. DETAILED DESCRIPTION

[0028] The present application is further described in detail by the following drawings and examples. It should be understood that the specific examples described herein are intended to explain the present application and are not intended to limit the present application.

[0029] The flow chart of the present application is shown in Figure 1 .

[0030] Example 1

[0031] Step one: Put the newly purchased commercial stainless steel powder into the plasma vibration cavity, seal and extract air.

[0032] Step two: Fill the plasma vibration cavity with 0.05MPa gas for exciting plasma, and connect the wire. The current required for exciting plasma is 150mA, and the pulse high-voltage discharge frequency is 8-15kHz; the powder vibration amplitude is greater than 10mm, and the plasma modification powder time is 12 hours.

[0033] Step three: Put the modified stainless steel powder into a vacuum drying box, extract to a vacuum state, heat to 80℃, and take out after constant temperature drying for 1-4h, and put it into a 15-55μm standard test sieve for screening treatment.

[0034] Step four: the modified stainless steel powder after drying and screening is subjected to forming treatment. Selective laser melting (SLM) 3D printing technology is selected to form the required stainless steel alloy parts. Nitrogen is used to purge the printer cabin before forming to ensure that the oxygen content is less than 110 ppm, so that the parts will not be oxidized during the forming process. Finally, the modified stainless steel 304L alloy that meets GB / T 20878-2007 mechanical properties, i.e. tensile strength greater than 520 MPa, yield strength greater than 205 MPa, and Vickers hardness greater than 200, is obtained, which is only slightly hydrogen embrittlement in a hydrogen environment.

[0035] The modification process parameters used in the application are obtained through the following steps:

[0036] S1: The 304L stainless steel alloy powder of China Airlines Mai Te is selected, and the powder is subjected to surface modification by argon plasma ion excitation. The working parameters selected during modification are current intensity 0.15 A, pulse high-voltage discharge frequency 10.9 kHz, voltage 5.9 kV, vibration table gravity acceleration 8-10 g, and amplitude peak-to-peak value 10-13 mm. After working for half an hour, stop and cool for half an hour, a total of 12 hours of work.

[0037] S2: SLM 3D printing technology is used to form stainless steel tensile test pieces and block test pieces. The forming process parameters are: powder layer thickness 15 μm, laser power 170 W, and scanning speed 1000 mm / s. The tensile test piece is 60 mm long, 2 mm thick, 10 mm wide at the clamping end, 22 mm long in the parallel section, and has a transition arc with a radius of 5 mm between the clamping end and the parallel section. The block test piece is 20x20x10mm in size. It should be noted that the test piece formed by the powder not subjected to argon plasma modification is denoted as Raw, and the test piece formed by the powder subjected to argon plasma modification is denoted as Ar-PT. The tensile test piece and the block test piece are obtained by printing, which is because their shapes are more convenient for subsequent corresponding tests.

[0038] S3: The tensile test pieces in the formed state are subjected to tensile property testing and hydrogen embrittlement testing, and the block test pieces are subjected to Vickers hardness testing. The ultimate tensile strength, yield strength, elongation, and hydrogen embrittlement resistance are obtained, and the Vickers hardness test is performed on the block test pieces to obtain the Vickers hardness.

[0039] Among them, the tensile test pieces before and after electrochemical hydrogen charging are respectively subjected to tensile test using an electronic universal testing machine, the tensile rate is 0.132 mm / min, the extensometer with a gauge length of 12.5 mm is used to measure the strain during the tensile process, each type of tensile test piece is tested 3 times, and the final result is the average value. For example Figure 2The average tensile strength of the Raw tensile specimen is 709.7 MPa, the average yield strength is 486.5 MPa, and the average elongation is 43.5%, as shown in (b) of FIG. 1. Figure 2 The Ar-PT tensile specimen is moderately hydrogen embrittled, as shown by the relative elongation (RE) before and after electrochemical hydrogen charging in (e) of FIG. 1. The average tensile strength of the Ar-PT tensile specimen is 689.9 MPa, the average yield strength is 467.7 MPa, and the average elongation is 53.1%, as shown in (e) of FIG. 1. Figure 2 The Ar-PT tensile specimen is moderately hydrogen embrittled, as shown by the relative elongation (RE) before and after electrochemical hydrogen charging in (e) of FIG. 1. The average tensile strength of the Ar-PT tensile specimen is 689.9 MPa, the average yield strength is 467.7 MPa, and the average elongation is 53.1%, as shown in (e) of FIG. 1.

[0040] The Vickers hardness test is performed by a Vickers hardness tester on the Vickers hardness HV1.0 of the block specimen. The Vickers hardness HV1.0 of the Raw block specimen and the Ar-PT block specimen is tested 10 times, and the final result is obtained by averaging. As shown in (d) of FIG. 1, the average Vickers hardness HV1.0 of the Raw block specimen is 235.30, and the average Vickers hardness HV1.0 of the Ar-PT block specimen is 244.52. Figure 3

[0041] Meanwhile, the microstructure test and observation are performed on the Raw tensile specimen and the Ar-PT tensile specimen, including tensile fracture morphology observation, XRD test, and metallographic observation. The tensile fracture morphology observation is performed on the tensile specimen, and the XRD test and the metallographic observation are performed on the block specimen.

[0042] The tensile fracture morphology characteristics of the tensile specimen are observed by a scanning electron microscope. The results show that the tensile specimen of Raw without hydrogen charging has a ductile fracture feature with dimples. The tensile specimen of Ar-PT without hydrogen charging has deep and dense dimples, which belongs to a ductile fracture. The dimples gradually deepen, indicating that the plasticity is improved.

[0043] S4: According to the results of the tensile test, the tensile fracture morphology, the Vickers hardness test, the XRD, and the metallographic observation, the argon plasma modification and reshaping make the microstructure and composition more uniform, and obtain more balanced mechanical properties, which is more conducive to the application of 3D printed stainless steel alloy in general environment or hydrogen environment.

[0044] Example 2

[0045] The steps of this example are basically the same as those of Example 1, except that the modification is not followed by screening and drying, and the tensile specimen is obtained by 3D molding.

[0046] ​The Raw sample in this embodiment is a sample manufactured for the second time using the SLM device, and thus the performance is different from that of Raw in Embodiment 1, and thus is denoted as Raw'. The Ar-PT sample is also a sample manufactured for the second time using the SLM device, and thus the performance is different from that of Ar-PT in Embodiment 1, and thus is denoted as Ar-PT'.

[0047] The tensile test pieces before and after electrochemical hydrogen charging are respectively subjected to tensile test using an electronic universal testing machine, the tensile rate is 0.132 mm / min, a tensometer with a gauge length of 12.5 mm is used to measure the strain during the tensile process, each kind of tensile test piece is tested for 3 times, and the final result is taken as an average value. As shown in (a) of Figure 2 , the average tensile strength of the Raw' tensile test piece is measured as 689.9 MPa, the average yield strength is 535.6 MPa, and the average elongation is 35.4%, which is moderate hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging; the average tensile strength of the Ar-PT' tensile test piece is 712.0 Mpa, the average yield strength is 541.5 MPa, and the average elongation is 42.1%, which is slight hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging.

[0048] The Vickers hardness test is performed by a Vickers hardness tester on the Vickers hardness HV1.0 of the block test piece, the Raw' block test piece and the Ar-PT' block test piece are each tested for 10 times, and the final result is taken as an average value. The average Vickers hardness HV1.0 of the Raw' block test piece is measured as 265.20; the average Vickers hardness HV1.0 of the Ar-PT' block test piece is 278.60.

[0049] Embodiment 3

[0050] The steps of this embodiment are basically the same as those of Embodiment 1, except that the plasma vibration cavity is filled with ammonia (NH3) to modify the stainless steel powder, and the tensile test piece is obtained by 3D molding.

[0051] The tensile test pieces before and after electrochemical hydrogen charging are respectively subjected to tensile test using an electronic universal testing machine, the tensile rate is 0.132 mm / min, a tensometer with a gauge length of 12.5 mm is used to measure the strain during the tensile process, each kind of tensile test piece is tested for 3 times, and the final result is taken as an average value. As shown in (a) of Figure 2 , the average tensile strength of the Raw tensile test piece is measured as 709.7 MPa, the average yield strength is 486.5 MPa, and the average elongation is 43.5%, which is moderate hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging; the average tensile strength of the NH3-PT tensile test piece is 665.3 Mpa, the average yield strength is 456.7 MPa, and the average elongation is 36.5%, which is moderate hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging. Figure 2 Figure 2 ​The relative elongation (RE) before and after electrochemical hydrogen charging in (c) can be known as no hydrogen embrittlement.

[0052] The Vickers hardness test is tested by a Vickers hardness tester on the Vickers hardness HV1.0 of the block sample. Each of the Raw block sample and the NH3-PT block sample is tested 10 times, and the final result is obtained by averaging. As shown in Figure 3 The average Vickers hardness HV1.0 of the Raw block sample is 235.30; and the average Vickers hardness HV1.0 of the NH3-PT block sample is 240.45

[0053] Example 4

[0054] The steps of this example are basically the same as those of Example 1, except that the stainless steel powder modified by filling ammonia (NH3) into the plasma vibration cavity is not dried and sieved, and the tensile sample is obtained by 3D molding.

[0055] The Raw sample in this example is a sample manufactured for the second time using an SLM device, so the performance is different from that of Raw in Example 1, and is denoted as Raw'. The NH3-PT sample is also a sample manufactured for the second time using an SLM device, so the performance is different from that of NH3-PT in Example 1, and is denoted as NH3-PT'.

[0056] The tensile test is performed on the tensile sample before and after electrochemical hydrogen charging using an electronic universal testing machine, and the tensile rate is 0.132 mm / min. The extensometer with a gauge length of 12.5 mm is used to measure the strain during the tensile process. Each type of tensile sample is tested 3 times, and the final result is obtained by averaging. The average tensile strength of the Raw' tensile sample is 689.9 MPa, the average yield strength is 535.6 MPa, and the average elongation is 35.41%. Compared with the relative elongation (RE) before and after electrochemical hydrogen charging, it is known as moderate hydrogen embrittlement. The average tensile strength of the NH3-PT' tensile sample is 691.6 MPa, the average yield strength is 537.5 MPa, and the average elongation is 37.5%. Compared with the relative elongation (RE) before and after electrochemical hydrogen charging, it is known as no hydrogen embrittlement.

[0057] The Vickers hardness test is tested by a Vickers hardness tester on the Vickers hardness HV1.0 of the block sample. Each of the Raw block sample and the NH3-PT block sample is tested 10 times, and the final result is obtained by averaging. As shown in

[0058] Example 5

[0059] The procedure of this example is basically the same as that of Example 2, except that the time for modification of the powder in the plasma vibration chamber is 9 h (the modification of 9 h is named as Ar-PT-9h, and the modification of 12 h in Example 2 is named as Ar-PT-12h), and then no drying and screening of the powder are performed, and the tensile test pieces are obtained by 3D molding.

[0060] The tensile test pieces before and after electrochemical hydrogen charging are respectively subjected to tensile test using an electronic universal testing machine, the tensile rate is 0.132 mm / min, the extensometer with a gauge length of 12.5 mm is used to measure the strain during the tensile process, each kind of tensile test piece is tested for 3 times, and the final result is taken as an average value. The average value of the tensile strength of the Ar-PT-12h tensile test piece is 712.0 MPa, the average value of the yield strength is 541.5 MPa, and the average value of the elongation is 42.1%, which is slightly hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging. The average value of the tensile strength of the Ar-PT-9h tensile test piece is 708.4 MPa, the average value of the yield strength is 536.7 MPa, and the average value of the elongation is 39.8%, which is slightly hydrogen embrittlement according to the relative elongation (RE) before and after electrochemical hydrogen charging.

[0061] The Vickers hardness test is performed by a Vickers hardness tester on the Vickers hardness HV1.0 of the block test piece, each of the Ar-PT-12h block test piece and the Ar-PT-9h block test piece is tested for 10 times, and the final result is taken as an average value. The average value of the Vickers hardness HV1.0 of the Ar-PT-12h block test piece is 278.60, and the average value of the Vickers hardness HV1.0 of the Ar-PT-9h block test piece is 274.23.

[0062] Example 6

[0063] The procedure of this example is basically the same as that of Example 2, except that the excitation current of the plasma in the plasma vibration chamber is 500 mA (0.50 A, the Ar-PT' with the excitation current of 0.15 A in Example 2 is named as Ar-PT-0.15A, and the one with the excitation current of 0.50 A is named as Ar-PT-0.50A), and then no drying and screening of the powder are performed, and the tensile test pieces are obtained by 3D molding.

[0064] The tensile test of the tensile test piece before and after the electrochemical hydrogen charging was carried out by using an electronic universal testing machine, the tensile rate was 0.132 mm / min, the extensometer with a gauge length of 12.5 mm was used to measure the strain during the tensile process, each kind of tensile test piece was tested for 3 times, and the average value was taken as the final result. The average tensile strength of Ar-PT-0.15A tensile test piece was 712.0 MPa, the average yield strength was 541.5 MPa, and the average elongation was 42.1%. Compared with the relative elongation (RE) before and after the electrochemical hydrogen charging, it was slightly hydrogen embrittlement; the average tensile strength of Ar-PT-0.50A tensile test piece was 699.8 MPa, the average yield strength was 502.3 MPa, and the average elongation was 41.6%. Compared with the relative elongation (RE) before and after the electrochemical hydrogen charging, it was slightly hydrogen embrittlement.

[0065] The Vickers hardness test was carried out by using a Vickers hardness tester to test the Vickers hardness HV1.0 of the block test piece. The Ar-PT-0.15A block test piece and the Ar-PT-0.50A block test piece were each tested for 10 times, and the average value was taken as the final result. The average Vickers hardness HV1.0 of the Ar-PT-0.15A block test piece was 278.60; the average Vickers hardness HV1.0 of the Ar-PT-0.50A block test piece was 275.83.

[0066] Comparative Example 1

[0067] The steps of this comparative example were basically the same as those of Example 2, except that the current used when exciting the plasma was 1000 mA and 1500 mA.

[0068] Under this parameter, the powder modification would appear burnt, and the subsequent 3D forming operation could not be carried out (see Figure 4 ).

[0069] Comparative Example 2

[0070] The steps of this comparative example were basically the same as those of Example 2, except that after the plasma modified powder was modified for 6 hours, the tensile test piece was obtained by 3D forming.

[0071] The tensile test of the tensile test piece before and after electrochemical hydrogen charging was carried out by using an electronic universal testing machine, the tensile rate was 0.132 mm / min, the extensometer with a gauge length of 12.5 mm was used to measure the strain during the tensile process, each kind of tensile test piece was tested for 3 times, and the average value was taken as the final result. The average tensile strength of the Raw tensile test piece was 689.9 MPa, the average yield strength was 535.6 MPa, and the elongation was in the range of 34.4%, and the relative elongation (RE) before and after electrochemical hydrogen charging showed that it was moderate hydrogen embrittlement; the average tensile strength of the Ar-PT tensile test piece was 699.4 MPa, the average yield strength was 534.6 MPa, and the average elongation was 34.9%, and the relative elongation (RE) before and after electrochemical hydrogen charging showed that it was moderate hydrogen embrittlement.

[0072] The Vickers hardness test was carried out by using a Vickers hardness tester to test the Vickers hardness HV1.0 of the block test piece, the Raw block test piece and the Ar-PT block test piece were each tested for 10 times, and the average value was taken as the final result. The Vickers hardness HV1.0 of the Raw block test piece was in the range of 265.20; the Vickers hardness HV1.0 of the Ar-PT block test piece was in the range of 235.30.

[0073] The performance summary results of all the above examples and comparative examples are shown in Table 1

[0074] Table 1 Performance summary

[0075]

[0076]

[0077] Those skilled in the art can understand that the above description is only preferred examples of the application and is not used to limit the application, although the application is described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma, characterized in that, Includes the following steps: (1) Plasma discharge modification treatment of stainless steel powder; (2) The modified powder obtained in step (1) is used for 3D printing to obtain 3D printed metal components; In step (1), the current required to excite the plasma is 150mA-500mA, and the plasma discharge modification treatment time is 9-12 hours. The gas used in the plasma discharge modification treatment in step (1) is one or more of argon, nitrogen, and ammonia; In step (1), the pulse high voltage discharge frequency during plasma excitation is 8-15kHz, and the powder vibration amplitude is greater than 10mm.

2. The method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma according to claim 1, characterized in that, The plasma discharge modification treatment in step (1) uses low-temperature cold field plasma; the plasma is generated by the excitation and ionization of the desired gas filled with 100Pa-0.1MPa.

3. The method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma according to claim 1, characterized in that, In step (1), the plasma discharge modification treatment time is 12 hours.

4. A method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma according to claim 1, characterized in that, The modified stainless steel powder from step (1) is dried, sieved, and then 3D printed to obtain 3D printed metal components.

5. A method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma according to claim 4, characterized in that, The drying process involves vacuum drying at 80°C for 1-4 hours; the sieving process involves sieving to a size of 15-60 micrometers.

6. A method for improving the hydrogen embrittlement resistance of 3D-printed stainless steel using plasma according to claim 1, characterized in that, In step (2), the 3D printing process involves purging the printer chamber with nitrogen gas before molding to ensure that the oxygen content is below 100 ppm, thus preventing oxidation of the parts during the molding process.

7. A 3D printed metal component prepared by a method for improving the hydrogen embrittlement resistance of 3D printed stainless steel using plasma, as described in any one of claims 1-6.

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