Method for reducing nitrogen surface modification temperature of austenitic stainless steel by adopting ultrasonic frequency ion injection and infiltration technology

Abstract

The invention relates to a method for reducing the nitrogen surface modification temperature of austenitic stainless steel, in particular to a method for reducing the nitrogen surface modification temperature of the austenitic stainless steel through an ultrasonic frequency ion injection infiltration technology. The invention aims to solve the problem that the low-temperature nitrogen surface modification treatment temperature of the existing austenitic stainless steel generally ranges from 400 DEG C to 450 DEG C and cannot be further reduced. The method comprises the following steps: 1, fixing austenitic stainless steel on a metal sample table in large-area ion implantation and deposition equipment, and then vacuumizing; 2, introducing nitrogen into the vacuum chamber, and controlling the air pressure in the vacuum chamber; and thirdly, after a pulsed bias power supply is started and nitrogen plasma is excited, the temperature of the austenitic stainless steel is increased to 200-350 DEG C through high-energy ion bombardment, and the gamma N phase modified layer on the surface of the austenitic stainless steel is prepared under the condition that the temperature is 200-350 DEG C. The method is used for reducing the nitrogen surface modification temperature of the austenitic stainless steel by adopting the ultrasonic frequency ion injection infiltration technology.

Description

Technical Field

[0001] This invention relates to a method for reducing the nitrogen surface modification temperature of austenitic stainless steel. Background Technology

[0002] Nitrogen surface modification can improve the surface hardness of austenitic stainless steel. However, high-temperature nitrogen surface modification above 450℃ usually causes Cr nitride precipitation, resulting in Cr depletion on the stainless steel workpiece surface. This leads to a significant reduction in corrosion resistance while increasing surface hardness, thus losing the inherent properties of stainless steel. Low-temperature nitrogen surface modification processes below 450℃ do not cause nitride precipitation but instead form a high-nitrogen face-centered metastable phase (γ-ray distillate) on the stainless steel surface. N (Phase I) can improve the surface hardness of stainless steel and enhance its corrosion-fatigue resistance without reducing or even improving its corrosion resistance.

[0003] However, conventional low-temperature nitrogen surface modification processes still require pre-treatment such as oxide film removal and anti-oxidation, and utilize atmospheres such as hydrogen and ammonia. This not only poses significant risks but also introduces hydrogen atoms into the matrix, creating a risk of hydrogen embrittlement. More importantly, nitrogen surface modification heavily relies on the thermal diffusion of nitrogen atoms within the matrix, thus limiting the low-temperature nitrogen surface modification treatment temperature to between 400°C and 450°C. Such temperatures result in significant thermal deformation of the workpiece, failing to meet the requirements of high-precision components. While secondary processing after surface modification can improve dimensional accuracy, uneven thermal deformation and variations in the thickness of the reinforcing layer removed at different locations create noticeable weak points on the surface, hindering a significant improvement in component lifespan. Therefore, lowering the nitrogen surface modification temperature to control thermal deformation within dimensional accuracy limits, while simultaneously achieving both long component lifespan and high precision, is a pressing challenge for the industry. Summary of the Invention

[0004] This invention aims to address the problem that the existing low-temperature nitrogen surface modification treatment temperature for austenitic stainless steel is generally between 400°C and 450°C, and cannot be further reduced. Therefore, it provides a method for reducing the nitrogen surface modification temperature of austenitic stainless steel using ultrasonic ion implantation technology.

[0005] A method for reducing the nitrogen surface modification temperature of austenitic stainless steel using ultrasonic ion implantation technology, comprising the following steps:

[0006] 1. Fix the austenitic stainless steel onto the metal sample stage in the large-area ion implantation and deposition equipment, and then evacuate the vacuum.

[0007] 2. Introduce nitrogen into the vacuum chamber and control the gas pressure inside the vacuum chamber;

[0008] 3. Connect the metal sample stage to the output of the pulsed bias power supply. Under conditions of voltage amplitude of 2kV~7kV, frequency of 20kHz~40kHz, and pulse width of 5μs~20μs, excite nitrogen plasma and use high-energy ion bombardment to raise the temperature of austenitic stainless steel to 200℃~350℃. Under the temperature condition of 200℃~350℃, achieve γ-ray diffraction on the surface of austenitic stainless steel. N Preparation of phase-modified layers.

[0009] The beneficial effects of this invention are:

[0010] This invention creatively proposes an ultrasonic nitrogen ion implantation method. The core of this method lies in applying a high-voltage, ultrasonic frequency (20kHz~40kHz) pulsed bias voltage to the sample. The negative bias voltage excites nitrogen discharge in the vacuum chamber and provides acceleration energy for the ionized nitrogen ions. The high-voltage pulsed bias voltage can excite a higher density nitrogen plasma at the same average power. On the one hand, it accelerates the implantation into the workpiece, forming a local high nitrogen concentration region on the workpiece surface; on the other hand, the high-density, high-energy nitrogen ions continuously bombard the workpiece surface, raising its temperature to the required process temperature of 200℃~350℃ without an external heating source. The lattice vibrations generated by ultrasonic ion implantation can create high-density vacancies and other material defects inside the workpiece, thereby significantly increasing the diffusion rate of implanted ions. The combination of these two factors ultimately results in a γ-ray diffusion effect on the workpiece surface. N The formation rate of the phase-modified layer is significantly increased, thereby reducing the processing temperature. This method can achieve the same strengthening effect as conventional low-temperature nitrogen surface modification at temperatures below 350℃, with a processing temperature reduction of approximately 100℃. This significantly reduces the thermal deformation of parts, meeting the high precision and long service life requirements of basic components such as bearings and gears. Simultaneously, the higher bias voltage causes high-energy ions to continuously bombard the substrate surface, effectively removing the oxide film from the substrate surface. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of the large-area ion implantation and deposition equipment described in step one of the present invention;

[0012] Figure 2 The glow discharge plasma and its spectrum generated during the nitriding process in step three of Example 1;

[0013] Figure 3 The images show the cross-section and surface morphology of austenitic stainless steel after nitriding treatment in Example 1. a is the cross-sectional morphology after etching with Marble reagent, and b is the surface morphology.

[0014] Figure 4 The γ-rays in the austenitic stainless steel after nitriding treatment in Examples 1 to 8 N X-ray diffraction patterns of the modified layer, a for Examples 1 to 4, b for Examples 5 to 8;

[0015] Figure 5 In Example 1, γ-rays were observed in austenitic stainless steel after nitriding treatment. N The mechanical and tribological properties of the modified layer were tested, where a represents γ. N Phase-modified layer hardness / modulus-depth curve, b represents austenitic stainless steel matrix and γ N The cross-section of the wear mark on the modified layer. Detailed Implementation

[0016] Specific implementation method one, combined with Figure 1 Detailed explanation: This embodiment describes a method for reducing the nitrogen surface modification temperature of austenitic stainless steel using ultrasonic ion implantation technology, which is carried out according to the following steps:

[0017] 1. Fix the austenitic stainless steel onto the metal sample stage in the large-area ion implantation and deposition equipment, and then evacuate the vacuum.

[0018] 2. Introduce nitrogen into the vacuum chamber and control the gas pressure inside the vacuum chamber;

[0019] 3. Connect the metal sample stage to the output of the pulsed bias power supply. Under conditions of voltage amplitude of 2kV~7kV, frequency of 20kHz~40kHz, and pulse width of 5μs~20μs, excite nitrogen plasma and use high-energy ion bombardment to raise the temperature of austenitic stainless steel to 200℃~350℃. Under the temperature condition of 200℃~350℃, achieve γ-ray diffraction on the surface of austenitic stainless steel. N Preparation of phase-modified layers.

[0020] The beneficial effects of this embodiment are:

[0021] This embodiment creatively proposes an ultrasonic nitrogen ion implantation method. The core of this method lies in applying a high-voltage, ultrasonic frequency (20kHz~40kHz) pulsed bias voltage to the sample. The negative bias voltage excites nitrogen discharge in the vacuum chamber and provides acceleration energy for the ionized nitrogen ions. The high-voltage pulsed bias voltage can excite a higher density nitrogen plasma at the same average power. On the one hand, it accelerates the implantation into the workpiece, forming a local high nitrogen concentration region on the workpiece surface; on the other hand, the high-density, high-energy nitrogen ions continuously bombard the workpiece surface, raising its temperature to the required process temperature of 200℃~350℃ without an external heating source. The lattice vibrations generated by ultrasonic ion implantation can create high-density vacancies and other material defects inside the workpiece, thereby significantly increasing the diffusion rate of implanted ions. The combination of these two factors ultimately results in a γ-ray diffusion effect on the workpiece surface. NThe formation rate of the phase-modified layer is significantly increased, thereby reducing the processing temperature. This method can achieve the same strengthening effect as conventional low-temperature nitrogen surface modification at temperatures below 350℃, with a processing temperature reduction of approximately 100℃. This significantly reduces the thermal deformation of parts, meeting the high precision and long service life requirements of basic components such as bearings and gears. Simultaneously, the higher bias voltage causes high-energy ions to continuously bombard the substrate surface, effectively removing the oxide film from the substrate surface.

[0022] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the sample stage described in step one is insulated from the vacuum chamber wall. Everything else is the same as in Specific Implementation Method One.

[0023] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, the vacuum is evacuated to a background vacuum of less than 1×10⁻⁶. -2 Pa. The rest is the same as in specific implementation method one or two.

[0024] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that nitrogen gas at a flow rate of 50 sccm to 200 sccm is introduced into the vacuum chamber in step two. Everything else is the same as in Specific Implementation Methods One to Three.

[0025] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the air pressure in the vacuum chamber is controlled to be 2 Pa to 50 Pa in step two. Everything else is the same as in Specific Implementation Methods One to Four.

[0026] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step three, the austenitic stainless steel surface γ is prepared under a temperature of 200℃~350℃. N The phase modification layer is applied for 2 to 5.5 hours. Other procedures are the same as in embodiments one through five.

[0027] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: the γ prepared in step three... N The thickness of the phase-modified layer is 0.7 μm to 9 μm. Other aspects are the same as in embodiments one through six.

[0028] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One through Seven in that: in step three, γ... N The formation rate of the phase-modified layer is 0.13 μm / h to 1.64 μm / h. Other aspects are the same as in embodiments one through seven.

[0029] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that, in step three, under the conditions of a voltage amplitude of 6.4kV, a frequency of 20kHz~40kHz, and a pulse width of 5μs, the temperature of austenitic stainless steel is raised to 320℃ using high-energy ion bombardment. Everything else is the same as in Specific Implementation Methods One to Eight.

[0030] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that: in step three, the austenitic stainless steel surface γ is prepared at a temperature of 320℃. N The phase modification layer lasts for 5.5 hours. Everything else is the same as in embodiments one through nine.

[0031] The beneficial effects of the present invention are verified using the following embodiments:

[0032] Example 1:

[0033] A method for reducing the nitrogen surface modification temperature of austenitic stainless steel using ultrasonic ion implantation technology, comprising the following steps:

[0034] 1. Fix the austenitic stainless steel onto the metal sample stage in the large-area ion implantation and deposition equipment, and then evacuate to a background vacuum of less than 1×10⁻⁶. -2 Pa;

[0035] The austenitic stainless steel is AISI 316L stainless steel; the sample stage is insulated from the vacuum chamber wall;

[0036] 2. Introduce 100 sccm of nitrogen into the vacuum chamber and control the pressure inside the vacuum chamber to 8 Pa;

[0037] 3. Connect the metal sample stage to the output of the pulsed bias power supply. Under the conditions of a voltage amplitude of 6.4 kV, a frequency of 20 kHz, and a pulse width of 5 μs, excite nitrogen plasma and use high-energy ion bombardment to raise the temperature of austenitic stainless steel to 320 °C. At the temperature of 320 °C, prepare γ-rays on the surface of austenitic stainless steel. N After 5.5 hours of phase modification layering, austenitic stainless steel with nitriding treatment is obtained.

[0038] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 9 μm, and the generation rate is 1.64 μm / h.

[0039] Example 2: This example differs from Example 1 in that the voltage amplitude in step 3 is 4kV and the temperature is 230℃. Everything else is the same as in Example 1.

[0040] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 0.8 μm, and the generation rate is 0.15 μm / h.

[0041] Example 3: This example differs from Example 1 in that the voltage amplitude in step 3 is 4.8kV and the temperature is 260℃. Everything else is the same as in Example 1.

[0042] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 1.7 μm, and the generation rate is 0.31 μm / h.

[0043] Example 4: This example differs from Example 1 in that the voltage amplitude in step 3 is 5.5kV and the temperature is 280℃. Everything else is the same as in Example 1.

[0044] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 3.3 μm, and the generation rate is 0.6 μm / h.

[0045] Example 5: This example differs from Example 1 in that: in step 2, the air pressure inside the vacuum chamber is controlled at 14 Pa; in step 3, the voltage amplitude is 5.5 kV and the temperature is 310 °C. Everything else is the same as in Example 1.

[0046] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 6.5 μm, and the generation rate is 1.18 μm / h.

[0047] Example 6: This example differs from Example 5 in that the voltage amplitude in step 3 is 3.2kV ​​and the temperature is 220℃. Everything else is the same as in Example 5.

[0048] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 0.7 μm, and the generation rate is 0.13 μm / h.

[0049] Example 7: This example differs from Example 5 in that the voltage amplitude in step 3 is 4kV and the temperature is 260℃. Everything else is the same as in Example 5.

[0050] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 1.2 μm, and the generation rate is 0.22 μm / h.

[0051] Example 8: This example differs from Example 5 in that the voltage amplitude in step 3 is 4.8kV, and the temperature is 290℃. Everything else is the same as in Example 5.

[0052] The γ prepared in step three of this embodiment N The thickness of the phase-modified layer is 2.2 μm, and the generation rate is 0.40 μm / h.

[0053] Figure 2The figure shows the glow discharge plasma and its spectrum generated during the nitriding process in step three of Example 1. As can be seen from the figure, only one peak, N II, exists in the spectrum, indicating that nitrogen gas is excited into N2 with a positive charge. + ion.

[0054] Figure 3 Figure 1 shows the cross-sectional and surface morphology of austenitic stainless steel after nitriding treatment in Example 1. Figure a shows the cross-sectional morphology after Marble reagent etching, and figure b shows the surface morphology. In Figure a, the red curve represents the nitrogen distribution curve of the cross-section. After Marble reagent etching, the grain boundaries of the stainless steel matrix are revealed, while γ N The nitrided layer showed no obvious characteristics, demonstrating its good corrosion resistance. Measurements and calculations showed that under these experimental conditions, the sample temperature was only 320℃, while the γ-ray... N The phase formation rate is as high as 1.64 μm / h, and the thickness is 9 μm. Figure b shows the surface morphology of the austenitic stainless steel after nitriding treatment. Plasma preferential sputtering etching traces along the grain boundaries caused by high-energy nitrogen ion bombardment are visible on the sample surface.

[0055] Figure 4 The γ-rays in the austenitic stainless steel after nitriding treatment in Examples 1 to 8 N X-ray diffraction patterns of the modified layers, a for Examples 1 to 4, b for Examples 5 to 8; the figures show the γ-ray diffraction patterns prepared under working pressures of 8 Pa and 14 Pa. N X-ray diffraction pattern of the modified layer. As can be seen from the figure, this process can obtain single, precipitated γ-rays within a wide process window. N The nitrided layer exhibits typical face-centered cubic structure characteristics. Apart from this, no nitrides such as CrN, γ'-Me4N, or ε-Me are present. 2-3 N exists in the nitrided layer. As the applied bias voltage amplitude gradually increases, γ N The peak intensity of the phase gradually increases.

[0056] Figure 5 In Example 1, γ-rays were observed in austenitic stainless steel after nitriding treatment. N The mechanical and tribological properties of the modified layer were tested, where a represents γ. N Phase-modified layer hardness / modulus-depth curve, b represents austenitic stainless steel matrix and γ N The cross-section of the wear scar in the modified layer. Figure a shows the preparation of γ-rays by ultrasonic nitrogen ion implantation. NThe hardness / modulus-depth curves of the phase-modified layer show that the maximum hardness of the modified layer reaches 13.2 GPa, a significant improvement compared to approximately 3 GPa of the stainless steel substrate. The elastic modulus also increases from approximately 180 GPa of the substrate to 250 GPa. Figure b shows the cross-sectional morphology of the wear tracks after friction tests on the modified layer and the stainless steel substrate. Compared to the stainless steel substrate, the wear track width of the modified layer decreases from approximately 750 μm to 184 μm, and the wear track depth decreases from approximately 11 μm to 1 μm. Calculations show that the wear rate of the modified layer is as low as 1.04 × 10⁻⁶. -5 mm 3 ·N -1 ·m -1 The wear rate was only 1 / 40th of that of the substrate. The test results demonstrate that the γ-ray alumina prepared by ultrasonic frequency nitrogen ion implantation... N The phase-modified layer performs as well as conventional nitrogen surface modification processes, exhibiting excellent hardness and wear resistance.

[0057] Table 1. γ-rays in austenitic stainless steel after nitriding treatment in Examples 1-8 N Comparison Table of Mechanical and Tribological Properties Test Data of Modified Layer

[0058] Example Hardness (GPa) Elastic modulus (GPa) Wear mark width (μm) Wear track depth (μm) <![CDATA[Wear rate (mm 3 ·N -1 ·m -1 )]]> one 13.2 250 184 1.0 <![CDATA[1.04×10 -5 ]]> three 12.2 224 400 5.3 <![CDATA[7.71×10 -5 ]]> Four 13.1 231 196 1.4 <![CDATA[1.32×10 -5 ]]> five 12.2 241 185 1.5 <![CDATA[1.54×10 -5 ]]> seven 10.6 206 469 5.2 <![CDATA[8.26×10 -5 ]]> eight 12.0 233 247 1.7 <![CDATA[2.22×10 -5 ]]>

Claims

1. A method for reducing the temperature of surface modification of austenitic stainless steel by nitrogen using ultrasonic ion implantation technology, characterized by It is carried out according to the following steps: I. Fixing the austenitic stainless steel on a metal sample table of a large-area ion implantation and deposition equipment, and then vacuumizing; II. Introducing nitrogen into the vacuum chamber and controlling the air pressure in the vacuum chamber; III. The metal sample table is connected to the output end of the pulse bias power supply. Under the conditions of a voltage amplitude of 2-7 kV, a frequency of 20-40 kHz, and a pulse width of 5-20 μs, nitrogen plasma is excited, and the temperature of the austenitic stainless steel is raised to 200-350°C by high-energy ion bombardment. Under the condition of a temperature of 200-350°C, the surface γ N Preparation of the phase-modified layer.

2. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that The sample table in step I is insulated from the wall of the vacuum chamber.

3. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that Step one vacuum to a base vacuum of less than 1 x 10 -2 Pa.

4. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that In step II, 50sccm-200sccm of nitrogen is introduced into the vacuum chamber.

5. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that In step II, the air pressure in the vacuum chamber is controlled to be 2Pa-50Pa.

6. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that The austenitic stainless steel surface γ N The phase modification layer 2h~5.5h.

7. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that The γ prepared in Step three N The thickness of the phase modification layer is 0.7 μm to 9 μm.

8. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that Gamma in step three N The phase modification layer has a formation rate of 0.13 μm / h to 1.64 μm / h.

9. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, characterized in that In step III, the temperature of the austenitic stainless steel is increased to 320℃ by high-energy ion bombardment under the conditions of a voltage amplitude of 6.4kV, a frequency of 20kHz-40kHz, and a pulse width of 5μs.

10. The method of lowering the temperature of surface modification of austenitic stainless steel by nitrogen according to claim 1, wherein In step three, the surface of the austenitic stainless steel was prepared for the gamma N Phase modification layer 5.5h.

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