Method for improving fatigue life and consistency of Cr4Mo4V series bearing steel

Abstract

The invention discloses a method for prolonging the fatigue life of Cr4Mo4V series bearing steel and improving the fatigue life consistency of the Cr4Mo4V series bearing steel. The method aims at prolonging the rolling contact fatigue life of the Cr4Mo4V series bearing steel and improving the life consistency of the Cr4Mo4V series bearing steel. The bearing steel treatment method comprises the steps that firstly, Cr4Mo4V series bearing steel workpieces are subjected to ultrasonic cleaning; 2, the cleaned bearing steel workpiece is subjected to pulsed magnetic field treatment, and the magnetic field intensity is controlled to be 2-3.5 T; thirdly, Ar ion sputtering cleaning is conducted on the workpiece treated through the pulsed magnetic field; and 4, N2 is introduced into the working chamber to excite N plasma, and then N ion implantation is carried out. According to the method, dislocation motion is promoted through magnetic field treatment, and the uniformity of residual stress on the surface of a material is improved; and then a strengthening layer is generated on the surface of the material in an N ion implantation mode, and through pulsed magnetic field and N ion implantation composite treatment, the rolling contact fatigue life and the life consistency of the Cr4Mo4V series bearing steel are synchronously and greatly improved.

Description

Technical Field

[0001] The present invention relates to a method for improving the surface residual stress uniformity and surface hardness of Cr4Mo4V series bearing steel by pulse magnetic field + N ion implantation composite treatment, thereby achieving simultaneous and substantial improvement of rolling contact fatigue life and consistency thereof. Background Art

[0002] Cr4Mo4V series steel (foreign grade M50) is a high-carbon high-alloy quenching steel, which can be divided into Cr4Mo4V steel, 8Cr4Mo4V steel, S8Cr4Mo4V steel, etc. due to different purities. After complete quenching and tempering treatment, this steel will produce a large amount of dispersed carbides, and the residual austenite content is extremely low. Therefore, it has good high-temperature mechanical properties and dimensional stability, and has been widely used in the field of aviation bearings.

[0003] With the development of aviation technology, further improving the life and reliability of bearings has always been the goal pursued by researchers. After heat treatment, Cr4Mo4V series bearing steel will produce more dislocations inside. In the subsequent cold processing, the dislocations begin to move, proliferate, and entangle with each other under the action of processing stress, resulting in stress concentration and eventually causing early failure of the material, affecting the life and reliability of the bearing.

[0004] Pulsed magnetic field treatment is a non-contact energy transfer process that changes the arrangement, matching, and migration of atoms and molecules in materials by applying a pulsed magnetic field to the material. For ferromagnetic materials, the magnetic field treatment process is accompanied by domain wall displacement and magnetic domain rotation, as well as magnetostriction, magneto-induced phase transition and other effects, and promotes dislocation movement in the material, making the residual stress uniform, thereby improving the consistency of fatigue life.

[0005] Ion implantation is a typical surface modification technology that injects the desired atoms into the surface of the material by applying high voltage, thereby significantly changing its physical and chemical properties. Current research shows that ion implantation can form a strengthening layer on the surface of the material, effectively improving the surface hardness of the material, thereby reducing the possibility of fatigue crack initiation, thereby extending the fatigue life of the material. Summary of the invention

[0006] The purpose of the present invention is to improve the rolling contact fatigue life and life consistency of Cr4Mo4V series bearing steels, and to provide a method for improving the fatigue life and consistency of Cr4Mo4V series bearing steels.

[0007] The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel of the present invention is implemented by the following steps:

[0008] 1. Ultrasonic cleaning:

[0009] Ultrasonic cleaning is performed on Cr4Mo4V series bearing steel workpieces to obtain cleaned bearing steel workpieces;

[0010] 2. Pulse magnetic field treatment:

[0011] The cleaned bearing steel workpiece is subjected to pulse magnetic field treatment, the magnetic field strength is controlled to be 2-3.5T, the pulse frequency is 0.05-1Hz, and the workpiece treated with pulse magnetic field is obtained after demagnetization;

[0012] 3. Ar ion sputtering cleaning:

[0013] The workpiece treated by the pulse magnetic field is placed in the working chamber of the ion implantation equipment, and Ar gas is introduced after vacuuming to generate Ar ions for ion sputtering cleaning, thereby obtaining the workpiece cleaned by ion sputtering;

[0014] 4. N ion implantation:

[0015] N is introduced into the working chamber 2 The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel is completed by exciting N plasma, controlling the working gas pressure to 0.1-0.5Pa, the injection voltage to 5-50kV, the pulse frequency to 100-1000Hz, and the pulse width to 5-50μs for N ion injection.

[0016] The present invention adopts Cr4Mo4V series bearing steel as test material, and adopts a pulse magnetic field + N ion implantation composite treatment method. On the one hand, the pulse magnetic field treatment is used to promote the movement of dislocations in the Cr4Mo4V steel, improve the uniformity of dislocation distribution, alleviate lattice distortion, and further improve the uniformity of residual stress, while providing a uniform diffusion channel and solid solution environment for the implantation of N ions; on the other hand, a strengthening layer is formed on the surface of the steel through the N ion implantation, so that the surface hardness is significantly improved, and the residual compressive stress is further increased, thereby achieving a simultaneous and substantial improvement in the rolling contact fatigue life and life consistency of the Cr4Mo4V series bearing steel.

[0017] Compared with the traditional single technology, the present invention uses pulsed magnetic field treatment and N ion implantation technology in combination. On the one hand, the magnetic field treatment improves the uniformity of internal dislocation distribution and residual stress of Cr4Mo4V steel, and provides a uniform diffusion channel and solid solution environment for the subsequent N ion implantation; on the other hand, the N ion implantation further improves its surface hardness and residual compressive stress. The improvement of surface hardness and residual compressive stress has a positive effect on hindering the initiation and expansion of fatigue cracks, so it can effectively extend the rolling contact fatigue life of Cr4Mo4V steel, and the homogenization of residual stress has an important contribution to improving the consistency of fatigue life. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The surface hardness curve of 8Cr4Mo4V steel before and after the pulse magnetic field + N ion implantation composite treatment in the embodiment;

[0019] Figure 2 It is a Weibull distribution curve diagram of the rolling contact fatigue life of 8Cr4Mo4V steel before and after the pulse magnetic field + N ion implantation composite treatment in the embodiment. DETAILED DESCRIPTION

[0020] Specific implementation method 1: The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel in this implementation method is implemented according to the following steps:

[0021] 1. Ultrasonic cleaning:

[0022] Ultrasonic cleaning is performed on Cr4Mo4V series bearing steel workpieces to obtain cleaned bearing steel workpieces;

[0023] 2. Pulse magnetic field treatment:

[0024] The cleaned bearing steel workpiece is subjected to pulse magnetic field treatment, the magnetic field strength is controlled to be 2-3.5T, the pulse frequency is 0.05-1Hz, and the workpiece treated with pulse magnetic field is obtained after demagnetization;

[0025] 3. Ar ion sputtering cleaning:

[0026] The workpiece treated by the pulse magnetic field is placed in the working chamber of the ion implantation equipment, and Ar gas is introduced after vacuuming to generate Ar ions for ion sputtering cleaning, thereby obtaining the workpiece cleaned by ion sputtering;

[0027] 4. N ion implantation:

[0028] N is introduced into the working chamber 2 The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel is completed by exciting N plasma, controlling the working gas pressure to 0.1-0.5Pa, the injection voltage to 5-50kV, the pulse frequency to 100-1000Hz, and the pulse width to 5-50μs for N ion injection.

[0029] In the method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel in this embodiment, the homogenized stress of pulsed magnetic field treatment is used to improve the fatigue life consistency, while ion implantation can improve the surface hardness and fatigue life.

[0030] The effect of the pulsed magnetic field treatment in this embodiment is different from the pulsed magnetic field treatment on aluminum alloy or magnesium alloy, because aluminum alloy or magnesium alloy itself is not a magnetic material, will not produce magnetostriction and magneto-induced phase transition effect, and there are few dislocations inside it. Therefore, the action principle of the pulsed magnetic field treatment on aluminum alloy and magnesium alloy is different from that of ferromagnetic materials, and the effect on improving the dislocation and residual stress distribution in aluminum alloy and magnesium alloy is also small.

[0031] This embodiment improves the uniformity of residual stress on the surface of Cr4Mo4V steel by pulsed magnetic field treatment, and then increases the surface hardness and residual compressive stress by N ion implantation. The combined treatment of pulsed magnetic field + N ion implantation can significantly improve the rolling contact fatigue life and life consistency of Cr4Mo4V steel, and the improvement effect is much higher than the improvement of a single performance by a single treatment.

[0032] Specific implementation method 2: The difference between this implementation method and specific implementation method 1 is that in step 1, ethanol and acetone are used to perform ultrasonic cleaning on the Cr4Mo4V series bearing steel workpiece alternately.

[0033] Specific implementation method three: This implementation method is different from specific implementation method two in that ethanol and acetone are used and each ultrasonic cleaning time is 10 minutes to 20 minutes.

[0034] Specific implementation method 4: The difference between this implementation method and any one of specific implementation methods 1 to 3 is that the time for pulse magnetic field treatment of the cleaned bearing steel workpiece in step 2 is 100-2000s.

[0035] Specific implementation method five: This implementation method is different from specific implementation methods one to four in that in step two, the cleaned bearing steel workpiece is subjected to pulse magnetic field treatment for 400-800s, the magnetic field intensity is controlled to be 3T, and the pulse frequency is 0.1-0.5Hz.

[0036] Specific implementation method six: The difference between this implementation method and any one of specific implementation methods one to five is that in the ion sputtering cleaning process in step three, the working gas pressure is controlled to be 1-5 Pa, the working voltage is 0.1-1 kV, the pulse frequency is 1000-10000 Hz, and the pulse width is 5-50 μs.

[0037] Specific implementation method seven: The difference between this implementation method and specific implementation method six is ​​that in the ion sputtering cleaning process in step three, the working gas pressure is controlled to be 1-2Pa, the working voltage is 0.3-0.5kV, the pulse frequency is 4000-6000Hz, and the pulse width is 20-30μs.

[0038] Specific implementation eight: This implementation differs from specific implementation seven in that the ion sputtering cleaning time in step three is controlled to be 0.5-5 hours.

[0039] Specific implementation method 9: This implementation method is different from any one of specific implementation methods 1 to 8 in that in step 4, the working gas pressure is controlled to be 0.1-0.5 Pa, the injection voltage is 20-40 kV, the pulse frequency is 200-300 Hz, and the pulse width is 20-40 μs for N ion implantation.

[0040] Specific implementation method ten: This implementation method is different from specific implementation method nine in that the N ion implantation time in step four is controlled to be 20-50 hours.

[0041] Embodiment: The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel in this embodiment is implemented according to the following steps:

[0042] 1. Ultrasonic cleaning:

[0043] The 8Cr4Mo4V bearing steel workpiece was ultrasonically cleaned alternately with ethanol and acetone to remove impurities and oil stains on the surface of the sample, thereby obtaining a cleaned bearing steel workpiece;

[0044] 2. Pulse magnetic field treatment:

[0045] The cleaned bearing steel workpiece is subjected to pulse magnetic field treatment for 500s, with the magnetic field direction from top to bottom, the magnetic field intensity is controlled to be 3T, and the pulse frequency is 0.2Hz. After demagnetization, the workpiece treated with pulse magnetic field is obtained;

[0046] 3. Ar ion sputtering cleaning:

[0047] The workpiece treated by the pulse magnetic field is placed in the working chamber of the ion implantation equipment, and the back vacuum is pumped to 1×10 -4 Pa, introduce Ar gas to generate Ar ions for ion sputtering cleaning. During cleaning, the working gas pressure is 2Pa, the working voltage is 0.5kV, the pulse frequency is 5000Hz, the pulse width is 25μs, and the cleaning time is 1h to obtain the workpiece after ion sputtering cleaning;

[0048] 4. N ion implantation:

[0049] N is introduced into the working chamber 2 N plasma is excited, the working gas pressure is controlled to be 0.2 Pa, the injection voltage is 30 kV, the pulse frequency is 250 Hz, and the pulse width is 25 μs for N ion implantation for 40 hours, thereby completing the method of improving the fatigue life and consistency of Cr4Mo4V series bearing steel.

[0050] The performance test was performed on the 8Cr4Mo4V bearing steel workpiece after the pulse magnetic field + N ion implantation composite treatment in this embodiment.

[0051] The residual stress test was conducted using an X STRESS 3000 stress tester, with a Cr target as the target material. During the test, the X-ray tube voltage was 30 kV, the current was 6.7 mA, and the test inclination was -45° to 45°. The residual stress on the sample surface at different treatment stages was tested, and the mean value and standard error of the residual stress were calculated.

[0052] The surface hardness test was conducted using an Agilent Nano Indenter G200 nanoindenter, with a Berkovich triangular pyramid diamond indenter. The test was conducted using the continuous stiffness mode (CSM), testing the hardness at nine locations from the surface to 1000 nm, and then calculating the average value as the final hardness.

[0053] The fatigue test adopts ball-rod rolling contact fatigue test equipment. The rolling element is 8Cr4Mo4V steel ball, which is in three-point contact with the sample under test. The contact stress of the sample is 4.8GPa. During the test, the electric spindle drives the sample to rotate, so that it is subjected to the cyclic contact stress of the rolling element, and the speed is 10000r / min. The test process is carried out at room temperature, and 4050 aviation lubricant is used for lubrication, and the oil feed rate is 2mL / min. The stress cycle number of fatigue failure of 8Cr4Mo4V steel sample is determined, and the Weibull distribution curve is drawn.

[0054] Table 1 shows the residual stress of 8Cr4Mo4V steel samples under different treatment methods. It can be seen from the table that the average value of the surface residual compressive stress of the untreated sample is 967.9MPa, and the standard error is 36.2MPa. After the sample was treated with a single pulse magnetic field, the average value of the surface residual compressive stress was reduced to 954.3MPa, while the standard error was significantly reduced to only 4.7MPa, indicating that the magnetic field treatment significantly improved the uniformity of the residual stress. After the sample was treated with a single N ion implantation, although the surface residual compressive stress increased to 1026.4MPa, the standard error also increased to 54.3MPa, indicating that the injection of N reduced the uniformity of the residual stress to a certain extent.

[0055] After the pulsed magnetic field + N ion implantation composite treatment, the uniformity of dislocation distribution is improved after magnetic field treatment, and the local severe lattice distortion is alleviated, providing a good diffusion channel and solid solution environment for the subsequent N ion implantation. The solid solution of N atoms will further introduce residual compressive stress. Therefore, the residual compressive stress on the surface of the composite treated sample is slightly reduced to 1017.8MPa compared with the single implantation, but the standard error is also reduced to 10.8MPa.

[0056] Compared with the untreated state, the residual compressive stress on the surface of 8Cr4Mo4V steel after the pulsed magnetic field + N ion implantation composite treatment increases and the uniformity is also improved, which plays a very important role in improving its fatigue life and consistency.

[0057] Table 1 Residual stress on the surface of 8Cr4Mo4V steel during pulsed magnetic field + N ion implantation composite treatment

[0058]

[0059] Figure 1 This is the surface hardness curve of 8Cr4Mo4V steel after pulsed magnetic field + N ion implantation. As can be seen from the figure, the peak surface hardness of the untreated 8Cr4Mo4V steel is about 10.5GPa, while it reaches 14.9GPa after the composite treatment, an increase of about 42%. This increase in surface hardness comes from the solid solution strengthening after the entry of N atoms and the formation of nitride hard phases by combining with carbides, and from defect strengthening and fine grain strengthening caused by dislocation movement and proliferation.

[0060] Figure 2 The Weibull distribution curve of rolling contact fatigue life of 8Cr4Mo4V steel before and after pulse magnetic field + N ion implantation composite treatment, contact stress 4.8GPa. The fatigue life of untreated, magnetic field and N implantation single treatment, and composite treatment samples were tested by rolling contact fatigue test, that is, the number of stress cycles when fatigue spalling occurs under a set load, and then plotted as shown in the figure. Figure 2 Weibull distribution curve.

[0061] Aviation bearing parts are often based on the Weibull distribution curve under low failure probability (i.e. high reliability) cycle number L 10 And the slope β and are used as the evaluation criteria for fatigue life and life consistency. Figure 2 It can be seen that the L of the untreated sample 10 About 1.37×10 6 The slope β value of its Weibull curve is about 0.9. After the single treatment of N ion implantation, the curve shifts to the right as a whole, indicating an improvement in fatigue life; and after the single treatment of pulsed magnetic field, the β value of the curve increases significantly, indicating an improvement in life consistency.

[0062] The pulse magnetic field treatment and N ion implantation treatment are effectively combined. The fatigue life and consistency of the 8Cr4Mo4V steel after treatment are significantly improved. The β value of its Weibull distribution curve increases to 2.3, and the life L under high reliability is 10 It reached 6.43×10 7 , about 47 times that before treatment.

[0063] In summary, the present invention proposes a method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel. Through pulsed magnetic field + N ion implantation composite treatment, the fatigue life and consistency of Cr4Mo4V steel are greatly improved simultaneously.

Claims

1. A method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel, characterized in that The method to improve the fatigue life and consistency of Cr4Mo4V series bearing steel is achieved by following the steps below:

1. Ultrasonic cleaning: Ultrasonic cleaning is performed on Cr4Mo4V series bearing steel workpieces to obtain cleaned bearing steel workpieces; 2. Pulse magnetic field treatment: The cleaned bearing steel workpiece is subjected to pulse magnetic field treatment, the magnetic field strength is controlled to be 2-3.5T, the pulse frequency is 0.05-1Hz, and the workpiece treated with pulse magnetic field is obtained after demagnetization; 3. Ar ion sputtering cleaning: The workpiece treated by the pulse magnetic field is placed in the working chamber of the ion implantation equipment, and Ar gas is introduced after vacuuming to generate Ar ions for ion sputtering cleaning, thereby obtaining the workpiece cleaned by ion sputtering; 4. N ion implantation: N2 is introduced into the working chamber to excite N plasma, the working gas pressure is controlled to be 0.1-0.5Pa, the injection voltage is 5-50kV, the pulse frequency is 100-1000Hz, and the pulse width is 5-50μs for N ion injection, thereby completing the method of improving the fatigue life and consistency of Cr4Mo4V series bearing steel.

2. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 1, characterized in that In step 1, ethanol and acetone are used to perform ultrasonic cleaning on the Cr4Mo4V series bearing steel workpiece alternately.

3. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 2, characterized in that The ultrasonic cleaning time for each use of ethanol and acetone is 10 min to 20 min.

4. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 1, characterized in that In step 2, the pulse magnetic field treatment time for the cleaned bearing steel workpiece is 100-2000s.

5. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 1, characterized in that In step 2, the cleaned bearing steel workpiece is subjected to pulse magnetic field treatment for 400-800 seconds, with the magnetic field intensity controlled to be 3T and the pulse frequency to be 0.1-0.5Hz.

6. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 1, characterized in that During the ion sputtering cleaning process in step 3, the working gas pressure is controlled to be 1-5 Pa, the working voltage is 0.1-1 kV, the pulse frequency is 1000-10000 Hz, and the pulse width is 5-50 μs.

7. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 6, characterized in that During the ion sputtering cleaning process in step 3, the working gas pressure is controlled to be 1-2 Pa, the working voltage is 0.3-0.5 kV, the pulse frequency is 4000-6000 Hz, and the pulse width is 20-30 μs.

8. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 7, characterized in that In step 3, the ion sputtering cleaning time is controlled to be 0.5-5h.

9. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 1, characterized in that In step 4, the working gas pressure is controlled to be 0.1-0.5 Pa, the injection voltage is controlled to be 20-40 kV, the pulse frequency is controlled to be 200-300 Hz, and the pulse width is controlled to be 20-40 μs for N ion injection.

10. The method for improving the fatigue life and consistency of Cr4Mo4V series bearing steel according to claim 9, characterized in that In step 4, the N ion implantation time is controlled to be 20-50h.

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