A heat treatment method for improving the signal-to-noise ratio of high-carbon chromium bearing steel high-frequency flaw detection and a method for high-carbon chromium bearing steel high-frequency flaw detection

Abstract

The invention discloses a heat treatment method for improving the signal-to-noise ratio of high-frequency flaw detection of high-carbon chromium bearing steel and a method for high-frequency flaw detection of high-carbon chromium bearing steel. The heat treatment method comprises the following steps: charging a hot furnace with hot-rolled high-carbon chromium bearing steel, first heating the temperature to 680-700°C at a heating rate of 3.5-4.5°C / min and keeping the temperature for 85-95min; then heating the temperature to 780-800°C at a heating rate of 0.6-1.2°C / min and keeping the temperature for 210-230min; then cooling the temperature to 710-730°C at a cooling rate of 0.4-0.8°C / min; isothermally keeping the temperature at 710-730°C for 180-200min; then cooling the temperature to 655-640°C at a cooling rate of 0.5-0.7°C / min, and finally air cooling the temperature to room temperature. The method can improve the microstructure of the high-carbon chromium bearing steel after spheroidizing annealing, thereby improving the signal-to-noise ratio on a water immersion ultrasonic flaw detection C-scan diagram and improving the accuracy of water immersion flaw detection of the material.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and specifically relates to a heat treatment method for improving the signal-to-noise ratio of high-carbon chromium bearing steel high-frequency flaw detection and a method for high-carbon chromium bearing steel high-frequency flaw detection. Background Art

[0002] With the rapid development of modern industry, higher challenges are posed to the material performance of industrial basic parts. For bearings, the harsh service environment requires the support of raw materials with better performance to meet the requirements of high temperature resistance, wear resistance, low noise, and long life of bearing parts. Under high requirements, not only the surface quality, chemical composition, organization, and performance of raw materials are required to meet the technical requirements of GB / T18254, but also the fatigue life requirements of materials are very high. The number, size, and shape of non-metallic inclusions in steel are one of the important factors affecting the fatigue performance of materials. High-frequency flaw detection is a very effective method for detecting large-sized inclusions inside materials.

[0003] The commonly used high-frequency flaw detection method for bearing steel is water immersion ultrasonic flaw detection. This flaw detection method has extremely high requirements on the state of bearing steel sample bars. However, due to the poor matching between the spheroidizing annealing process of bearing steel materials and the produced bearing steel materials, the ultrasonic water immersion flaw detection C-scan signal diagram has a high noise ratio, a low signal-to-noise ratio, and low scanning result accuracy, which can easily misjudge the quality of bearing steel materials.

[0004] Chinese patent CN110018234A discloses a method for dual-frequency ultrasonic detection of inclusions in bearing steel, which uses a 10MHz flat probe and a 25MHz focused probe to jointly detect the sample, and analyzes the A and C scan images formed by scanning synchronously to determine the size, quantity and distribution of inclusions in medium-carbon bearing steel; this patent improves the inspection accuracy of medium-carbon bearing steel through testing means rather than improving the inspection accuracy through the material itself. Summary of the invention

[0005] The purpose of the present invention is to provide a heat treatment method for improving the signal-to-noise ratio of high-frequency flaw detection of high-carbon chromium bearing steel. The method can improve the organizational morphology of high-carbon chromium bearing steel after spheroidizing annealing, thereby improving the signal-to-noise ratio on the water immersion ultrasonic flaw detection C-scan image and reducing the misjudgment of material quality during the flaw detection process.

[0006] The purpose of the present invention is also to provide a method for high-frequency flaw detection of high-carbon chromium bearing steel. Before high-frequency flaw detection, the sample is first treated by the heat treatment method of the present invention. The high-frequency flaw detection signal-to-noise ratio of this method is between 20% and 30%, and the ultrasonic echo height is between 10% and 15%.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A heat treatment method for improving the high-frequency flaw detection signal-to-noise ratio of high-carbon chromium bearing steel, the heat treatment method comprising the following steps: charging the hot-rolled high-carbon chromium bearing steel into a hot furnace, first heating the temperature to 680-700°C at a heating rate of 3.5-4.5°C / min and keeping the temperature for 85-95min; then heating the temperature to 780-800°C at a heating rate of 0.6-1.2°C / min and keeping the temperature for 210-230min; then cooling the temperature to 710-730°C at a cooling rate of 0.4-0.8°C / min; isothermally keeping the temperature at 710-730°C for 180-200min; then cooling the temperature to 655-640°C at a cooling rate of 0.5-0.7°C / min, and finally air cooling the temperature to room temperature.

[0009] The heat treatment method comprises the following steps: firstly, heating the temperature to 690°C at a heating rate of 4.1°C / min and keeping the temperature for 90 minutes; then heating the temperature to 790°C at a heating rate of 0.9°C / min and keeping the temperature for 222 minutes; then cooling to 720°C at a cooling rate of 0.64°C / min; keeping the temperature isothermally at 720°C for 192 minutes; then cooling to 650°C at a cooling rate of 0.58°C / min, and finally air cooling to room temperature.

[0010] The metallographic structure of the hot-rolled high-carbon chromium bearing steel is pearlite+cementite.

[0011] The metallographic structure of the hot-rolled high-carbon chromium bearing steel after heat treatment is spherical pearlite+cementite, the spheroidized structure level is 3.0, and the grain size is 8.0.

[0012] The high carbon chromium bearing steel is GCr15 steel.

[0013] The high carbon chromium bearing steel includes the following chemical components in weight percentage: C: 0.94-1.04%, Si: 0.15-0.35%, Mn: 0.30-0.40%, P≤0.020%, S≤0.015%, Cr: 1.40-1.60%, Mo≤0.10%, Ni≤0.30%, Cu≤0.20%, and the rest is Fe and unavoidable impurities.

[0014] The high-frequency flaw detection signal-to-noise ratio of the hot-rolled high-carbon chromium bearing steel after heat treatment is between 20% and 30%, and the ultrasonic echo height is between 10% and 15%.

[0015] The present invention also provides a method for high-frequency flaw detection of high-carbon chromium bearing steel, comprising the following steps:

[0016] (1) Sampling hot-rolled high carbon chromium bearing steel;

[0017] (2) heat treating the sample by the heat treatment method of the present invention, and then turning and fine grinding;

[0018] (3) Test the sample using an immersion ultrasonic flaw detector.

[0019] In step (1), the sampling specification is φ50~80mm.

[0020] In step (3), before testing, the sample is installed horizontally on the immersion ultrasonic flaw detector, the sample is flipped 360° around its central axis, the instrument is started to return the system to zero, and then the 10 MHz probe is moved, the probe incident angle and probe height are adjusted respectively, and the interface wave is increased in combination with the gain, so that the probe is vertically incident, and a 10 MHz scanning test is performed to draw a DAC curve.

[0021] The final microstructure of hot-rolled high-carbon bearing steel GCr15 is pearlite + cementite, so that the full-screen noise ratio in the water immersion flaw detection C scan of the material is between 60% and 80%, and the distribution is uneven. In the heat treatment method for improving the high-frequency flaw detection signal-to-noise ratio of high-carbon chromium bearing steel provided by the present invention, a step-by-step spheroidizing annealing process is performed to make the microstructure of the spheroidized high-carbon chromium bearing steel spheroidized pearlite and cementite, and its microstructure reduces the signal interference of high-frequency flaw detection ultrasonic echoes.

[0022] The spheroidizing annealing process of the high carbon chromium bearing steel provided by the present invention is divided into six stages of heating, heat preservation, isothermal and cooling, and the heating rate, heating temperature, heat preservation temperature, heat preservation time, cooling rate and cooling temperature are clearly specified. According to the AC1 line temperature of the bearing steel GCr15, the second stage heat preservation temperature of the spheroidizing annealing is designed to be 780-800°C, and the heat preservation time is 210-230min, so that the pearlite lamellae of the hot-rolled structure of the bearing steel are dissolved, and a certain amount of carbides and undissolved carbide particles in the grain boundaries are precipitated, which provides carbide nucleation and spheroidization sites for the isothermal process. It is more conducive to the spheroidization of pearlite and cementite in the subsequent isothermal process, and then cooled to 710-730℃ at a cooling rate of 0.4-0.8℃ / min, isothermally kept at 710-730℃ for 180-200min, and then cooled to 655-640℃ at a cooling rate of 0.5-0.7℃ / min, and finally air-cooled to room temperature. These processes are mainly the processes of nucleation and growth of carbide particles. Appropriate isothermal temperature, holding time and cooling rate can obtain standardized 2-4 level spheroidized structure and ≥8.0 level refined grain size.

[0023] The present invention provides a heat treatment method for improving the signal-to-noise ratio of high-frequency flaw detection of high-carbon chromium bearing steel. The heat treatment method of the present invention is used to treat high-carbon chromium bearing steel samples with a specification of φ50 to φ80 mm, thereby improving the microstructure of the high-carbon chromium bearing steel after spheroidizing annealing, thereby improving the signal-to-noise ratio on the water immersion ultrasonic flaw detection C-scan image and improving the accuracy of water immersion flaw detection of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1This is the metallographic structure diagram of hot-rolled high carbon chromium bearing steel;

[0025] Figure 2 is the metallographic structure diagram of the high carbon chromium bearing steel sample after heat treatment in Example 1;

[0026] Figure 3 The A and C scanning images of the ultrasonic water immersion flaw detection of the high carbon chromium bearing steel sample in Example 1, wherein the left image is the A scanning image and the right image is the C scanning image;

[0027] Figure 4 is a schematic diagram of the heat treatment process in Example 1;

[0028] Figure 5 This is an A-scan image of ultrasonic water immersion flaw detection of high carbon chromium bearing steel in Comparative Example 1;

[0029] Figure 6 The spheroidized structure diagram (left) and ultrasonic water immersion flaw detection A-scan diagram of the high carbon chromium bearing steel after heat treatment in Comparative Example 2;

[0030] Figure 7 This is the spheroidized structure diagram (left) and ultrasonic water immersion flaw detection A-scan diagram of the high carbon chromium bearing steel after heat treatment in Comparative Example 3.

[0031] Figure 8 This is the spheroidized structure diagram (left) and ultrasonic water immersion flaw detection A-scan diagram of the high carbon chromium bearing steel after heat treatment in Comparative Example 4. DETAILED DESCRIPTION

[0032] The samples in each embodiment and comparative example are all taken from the same hot-rolled high carbon chromium bearing steel GCr15, and its metallographic structure is as follows: Figure 1 As shown, the structure is pearlite + cementite;

[0033] The immersion ultrasonic flaw detector uses a 10MHz flat probe and a flat-bottom hole standard sample rod to calibrate and draw the DAC curve. The sample process is as follows: before testing, the sample is installed horizontally on the immersion ultrasonic flaw detector. The sample can be flipped 360° around its central axis. The instrument is started to return the system to zero, and then the 10MHz probe is moved. The probe incident angle and probe height are adjusted respectively, and the interface wave is increased in combination with the gain, so that the probe is vertically incident, and a 10MHz scanning test is performed.

[0034] Example 1

[0035] A method for high-frequency flaw detection of high-carbon chromium bearing steel comprises the following steps:

[0036] (1) A sample bar with a size of φ60 mm × 500 mm was cut from hot-rolled high carbon chromium bearing steel;

[0037] (2) The sample was subjected to spheroidizing annealing treatment. The spheroidizing annealing process was as follows: hot furnace loading, first heating temperature 690°C, heating rate 4.1°C / min, heat preservation 90min; second heating temperature 790°C, heating rate 0.94°C / min, heat preservation 222min; third cooling temperature 720°C, cooling rate 0.64°C / min; fourth isothermal temperature 720°C, heat preservation time 192min; fifth cooling temperature 650°C, cooling rate 0.58°C / min, sixth cooling air cooling to room temperature; then the sample surface was fine turned and fine ground to a roughness of ≤0.8μm; the metallographic structure of the sample after spheroidizing annealing treatment is as follows Figure 2 The schematic diagram of the spheroidizing annealing process is shown in Figure 4 As shown, from Figure 2 It can be seen that the heat treatment method of the present invention makes the φ60mm high carbon bearing steel GCr15 ball ball structure between level 2 and 4, and the grain size ≥ level 8.0;

[0038] (3) After testing with an immersion ultrasonic flaw detector, the test results are as follows: Figure 3 As shown in the figure, the A scan is a real-time ultrasonic scanning echo map, and the C scan is the accumulation of the A real-time scanning map. It can be seen from the A scan that the average ultrasonic height of the A scan real-time scanning of water immersion flaw detection is 10% to 15%, and the signal-to-noise ratio of the C scan is between 20% and 30%, which improves the accuracy of material flaw detection.

[0039] Comparative Example 1

[0040] A method for high-frequency flaw detection of high-carbon chromium bearing steel comprises the following steps:

[0041] (1) A sample bar with a size of φ60 mm × 500 mm was cut from hot-rolled high-carbon chromium bearing steel, and the surface was fine-turned and fine-ground to a roughness of ≤0.8 μm without heat treatment;

[0042] (2) After testing with an immersion ultrasonic flaw detector, the test results are as follows: Figure 5 The A-scan is a real-time ultrasonic scanning echo map, and the average height of the entire waveform is 30% to 50%, and the highest can reach about 67%.

[0043] Comparative Example 2

[0044] A method for high-frequency flaw detection of high-carbon chromium bearing steel comprises the following steps:

[0045] (1) A sample bar with a size of φ60 mm × 500 mm was cut from hot-rolled high carbon chromium bearing steel;

[0046] (2) The sample was subjected to spheroidizing annealing treatment. The spheroidizing annealing process was as follows: hot furnace loading, first heating temperature 680°C, heating rate 4.1°C / min, holding temperature 90min; second heating temperature 810°C, heating rate 0.94°C / min, holding temperature 222min; third cooling temperature 720°C, cooling rate 0.64°C / min; fourth isothermal temperature 720°C, holding time 192min; fifth cooling temperature 650°C, cooling rate 0.58°C / min, sixth cooling air cooling to room temperature; then the sample surface was fine turned and fine ground to a roughness of ≤0.8μm; the metallographic structure of the sample after spheroidizing annealing treatment is as follows Figure 6 As shown in the left picture;

[0047] (3) After testing with an immersion ultrasonic flaw detector, the test results are shown in the attached figure. Figure 6 As shown in the right figure; the A-scan is a real-time ultrasonic scanning echo map, and the average height of the entire waveform is 30% to 40%, and the highest can reach about 48%.

[0048] Comparative Example 3

[0049] (1) A sample bar with a specification of φ60 mm × 500 mm was cut from hot-rolled high carbon chromium bearing steel;

[0050] (2) The sample was subjected to spheroidizing annealing treatment. The spheroidizing annealing process was as follows: hot furnace loading, first heating temperature 680°C, heating rate 4.1°C / min, holding time 108min; second heating temperature 790°C, heating rate 2.4°C / min, holding time 222min; third cooling temperature 720°C, cooling rate 1.2°C / min; fourth isothermal temperature 720°C, holding time 192min; fifth cooling temperature 650°C, cooling rate 0.89°C / min, sixth cooling air cooling to room temperature; then the sample surface was fine turned and fine ground to a roughness of ≤0.8μm; the metallographic structure of the sample after spheroidizing annealing treatment is as follows Figure 7 As shown on the left, the spheroidized structure is ≥ grade 4.0, which does not meet the standard requirements.

[0051] (3) After testing with an immersion ultrasonic flaw detector, the test results are shown in the attached figure. Figure 7 As shown on the right; the A-scan image is a real-time ultrasonic scanning echo image, and the average height of the entire waveform is 30% to 40%, and the highest can reach about 58%.

[0052] Comparative Example 4

[0053] (1) A sample bar with a specification of φ60 mm × 500 mm was cut from hot-rolled high carbon chromium bearing steel;

[0054] (2) The sample was subjected to spheroidizing annealing treatment. The spheroidizing annealing process was as follows: hot furnace loading, heating temperature 800°C, heating rate 3.8°C / min, holding for 120 min and then cooling to 765°C, holding for 1 h and then cooling to 745°C, holding for 1 h and then cooling to 730°C, holding for 1 h and then cooling to 720°C, holding for 2 h and then cooling to below 600°C and then taking out of the furnace. The cooling rate of the furnace cooling was 0.5°C / min. The sample surface was then fine-turned and fine-ground to a roughness of ≤0.8 μm. The metallographic structure of the sample after spheroidizing annealing treatment was as follows: Figure 8 As shown on the left;

[0055] (3) After testing with an immersion ultrasonic flaw detector, the test results are as follows: Figure 8 As shown on the right; the A-scan image is a real-time ultrasonic scanning echo image, and the average height of the entire waveform is 20% to 35%, and the highest can reach about 45%.

[0056] The above-mentioned reference embodiments provide a detailed description of a heat treatment method for improving the signal-to-noise ratio of high-carbon chromium bearing steel high-frequency flaw detection and a method for high-carbon chromium bearing steel high-frequency flaw detection. This is illustrative rather than restrictive, and several embodiments may be listed within the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the signal-to-noise ratio of high-frequency flaw detection of high-carbon chromium bearing steel, characterized in that: The heat treatment method comprises the following steps: charging a hot-rolled high-carbon chromium bearing steel into a hot furnace, first heating the steel to 680-700°C at a heating rate of 3.5-4.5°C / min and keeping the temperature for 85-95min; then heating the steel to 780-800°C at a heating rate of 0.6-1.2°C / min and keeping the temperature for 210-230min; then cooling the steel to 710-730°C at a cooling rate of 0.4-0.8°C / min; keeping the temperature isothermally at 710-730°C for 180-200min; then cooling the steel to 655-640°C at a cooling rate of 0.5-0.7°C / min, and finally air cooling the steel to room temperature; The ultrasonic echo height of the high-frequency flaw detection method of the hot-rolled high-carbon chromium bearing steel after heat treatment is between 10% and 15%.

2. The heat treatment method according to claim 1, characterized in that The heat treatment method comprises the following steps: firstly, heating the temperature to 690°C at a heating rate of 4.1°C / min and keeping the temperature for 90 minutes; then heating the temperature to 790°C at a heating rate of 0.9°C / min and keeping the temperature for 222 minutes; then cooling to 720°C at a cooling rate of 0.64°C / min; keeping the temperature isothermally at 720°C for 192 minutes; then cooling to 650°C at a cooling rate of 0.58°C / min, and finally air cooling to room temperature.

3. The heat treatment method according to claim 1, characterized in that: The metallographic structure of the hot-rolled high-carbon chromium bearing steel is pearlite+cementite.

4. The heat treatment method according to claim 1, characterized in that: The metallographic structure of the hot-rolled high-carbon chromium bearing steel after heat treatment is spherical pearlite+cementite, and the grain size is 8.

0.

5. The heat treatment method according to claim 1, characterized in that: The high carbon chromium bearing steel is GCr15 steel.

6. The heat treatment method according to claim 1, characterized in that: The high carbon chromium bearing steel includes the following chemical components in weight percentage: C: 0.94-1.04%, Si: 0.15-0.35%, Mn: 0.30-0.40%, P≤0.020%, S≤0.015%, Cr: 1.40-1.60%, Mo≤0.10%, Ni≤0.30%, Cu≤0.20%, and the rest is Fe and unavoidable impurities.

7. A method for high-frequency flaw detection of high-carbon chromium bearing steel, characterized in that: The following steps are involved: (1) Sampling hot-rolled high carbon chromium bearing steel; (2) heat treating the sample by the heat treatment method according to any one of claims 1 to 6, and then turning and fine grinding; (3) Test the sample using an immersion ultrasonic flaw detector.

8. The method for high-frequency flaw detection of high-carbon chromium bearing steel according to claim 7, characterized in that: In step (1), the sampling specification is φ50~80mm.

9. The high-frequency flaw detection method for high-carbon chromium bearing steel according to claim 7, characterized in that: In step (3), before testing, the sample is installed horizontally on the immersion ultrasonic flaw detector, the sample is flipped 360° around its central axis, the instrument is started to return the system to zero, and then the 10 MHz probe is moved, the probe incident angle and probe height are adjusted respectively, and the interface wave is increased in combination with the gain, so that the probe is vertically incident, and a 10 MHz scanning test is performed to draw a DAC curve.

Images