A heat treatment process for specimens used for water immersion ultrasonic testing of bearing steel

Abstract

The present invention relates to the field of bearing steel detection technology, and specifically to a heat treatment process for bearing steel samples for water immersion ultrasonic testing. The heat treatment process includes the following steps: (1) sampling bearing steel to detect carbide inhomogeneity; (2) heat treating the bearing steel sample according to the test results, and the heat treatment process is selected from normalizing + isothermal annealing process or reciprocating spheroidizing annealing process. After heat treatment, the carbide band of the sample is less than level 2.5 and the average metal grain size reaches level 5 or above. The heat treatment process of the present invention can effectively improve the uniformity and consistency of the internal structure of the bearing steel sample, reduce the generation of echo interference signals during water immersion ultrasonic testing, and ensure the accuracy of the test results.

Description

Technical Field

[0001] The invention relates to the technical field of bearing steel detection, and in particular to a heat treatment process for a specimen used for bearing steel water immersion ultrasonic detection. Background Art

[0002] High carbon chromium bearing steel is the most widely used steel in the bearing industry, mainly used to manufacture various types of bearings and some high-load mechanical parts. As the joints of industrial equipment, bearings need to withstand rolling contact stress and periodic alternating stress during use, requiring them to have high strength, wear resistance and fatigue life, which also puts higher requirements on processing technology and materials. In terms of bearing steel quality, high purity and good carbide distribution uniformity are mainly required. The purity of bearing steel mainly refers to the level of inclusion control in the steel. Studies have shown that the contact fatigue life of bearing steel is mainly related to the organizational structure of its surface, especially the type, size, shape, distribution and aggregation state of non-metallic inclusions on the surface, and is approximately inversely proportional to the length of non-metallic inclusions in steel. Therefore, the evaluation and control of large non-metallic inclusions in bearing steel is particularly important.

[0003] Water immersion ultrasonic testing of bearing steel can detect various defects inside and on the surface of the material non-destructively by utilizing the influence of the acoustic properties of the material itself or internal defects on the propagation of ultrasonic waves. It can objectively and comprehensively reflect the defects in the material, especially the distribution of large and medium inclusions in bearing steel. Compared with traditional inclusion detection methods such as metallographic method and non-destructive extraction, the high-frequency ultrasonic testing system can detect a larger sample volume and can more intuitively reflect the distribution, quantity, size, location and other information of large and medium inclusions in steel.

[0004] Water immersion ultrasonic testing has the characteristics of high frequency, short wavelength, and high detection accuracy. Its echo signal contains a lot of information related to the nature of the defect, but it is also very susceptible to various interferences, especially the seemingly randomly distributed echoes generated by scattering centers (such as particle boundaries and other particles) inside the material being tested. These echoes have similar frequency distribution characteristics to the defect reflection echoes, and it is difficult to separate them in the frequency domain, which brings difficulties to the detection of defects. Therefore, the sample tissue for water immersion ultrasonic testing should be completely refined and homogenized to eliminate the echo interference signal caused by the uneven tissue inside the material and ensure the accuracy of the test results.

[0005] The standards for water immersion ultrasonic testing of bearing steel are mainly ASTM E588, SEP 1927, GB / T 38683 and GB / T 4162. Most of these standards require that the sample be heat treated before processing so that its grain size reaches level 5 or finer as specified in GB / T 6394 or ASTM E112 to meet the sensitivity of the test. However, the existing standards do not have clear requirements for the heat treatment process of the sample. From the information currently available, the research results of water immersion ultrasonic testing are mostly focused on the selection, design and sensitivity analysis of detection parameters, such as "Research on Water Immersion Focused Ultrasonic Testing Technology for Metal Bars", "Plane Wave Frequency Domain Fast Imaging Algorithm for Water Immersion Ultrasonic Testing", "Effect of Water Layer Thickness on Sensitivity of Water Immersion Ultrasonic Testing of Pipeline Welds", and some scholars focus on the analysis of test results, such as "Application of Water Immersion Ultrasonic Testing in Purity Evaluation of Bearing Steel", "Research on High-Frequency Water Immersion Ultrasonic Testing and Evaluation Methods for Inclusions in Steel", etc. There is no corresponding research result on heat treatment of bearing steel ultrasonic testing samples published. Chinese invention patent application CN112760461A provides a heat treatment method for high-frequency ultrasonic testing samples of steel. It divides the heat treatment process according to the carbon content of the steel type, and does not take the original quality level of the sample into consideration. In practical applications, it cannot guarantee the quality requirements of the sample for water immersion ultrasonic testing, and is difficult to use as a guide for practical applications.

[0006] Therefore, it is necessary to explore and establish a heat treatment process for bearing steel water immersion ultrasonic testing samples. Summary of the invention

[0007] In view of the technical problem that echo interference signals are caused by the uneven internal structure of the material during water immersion ultrasonic testing of bearing steel, the present invention provides a heat treatment process for bearing steel samples for water immersion ultrasonic testing, which can effectively improve the uniformity and consistency of the internal structure of the bearing steel samples, reduce the generation of echo interference signals during water immersion ultrasonic testing, and ensure the accuracy of the test results.

[0008] The technical solution of the present invention is as follows:

[0009] A heat treatment process for a bearing steel sample for water immersion ultrasonic testing comprises the following steps:

[0010] (1) Sampling of bearing steel to detect carbide inhomogeneity;

[0011] (2) According to the test results, the bearing steel sample is heat treated, and the heat treatment process is selected from the normalizing + isothermal annealing process or the reciprocating spheroidizing annealing process. The normalizing + isothermal annealing process is to first heat the sample to 900~920℃ and keep it for 40min~2h, then disperse air cooling after taking it out of the furnace, and then heat the sample to 770~790℃ and keep it for 3~5h, then cool it to 700~720℃ with the furnace at 10~30℃ / h, keep it for 4~6h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse air cooling;

[0012] The reciprocating spheroidizing annealing process is to first heat the bearing steel to 770~780℃ and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then heat it to 770~780℃ at a heating rate of 30~50℃ / h and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0013] Furthermore, the bearing steel is GCr15 bearing steel.

[0014] Furthermore, after heat treatment, the carbide banding of the sample is less than level 2.5 and the average grain size of the metal reaches more than level 5.

[0015] Furthermore, step (1) is to perform a carbide band inspection on the bearing steel after sampling.

[0016] Furthermore, for bearing steel with a diameter of ≤80 mm and carbide banding higher than grade 2.5, normalizing + isothermal annealing process is used for heat treatment;

[0017] Normalizing is to heat the sample to 900~920℃ and keep it at that temperature for 40~90min, and then disperse and air cool it after it comes out of the furnace;

[0018] Isothermal annealing is to heat the sample to 770~790℃ and keep it for 3~4h, cool it to 700~720℃ with the furnace at 10~30℃ / h, keep it for 4~5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0019] Furthermore, for bearing steel with a diameter of ≤80 mm and carbide banding not higher than grade 2.5, a reciprocating spheroidizing annealing process is used for heat treatment.

[0020] Furthermore, for bearing steel with diameter of 80 mm < diameter ≤ 150 mm and carbide banding higher than grade 3, normalizing + isothermal annealing process is used for heat treatment;

[0021] Normalizing is to heat the sample to 900~920℃ and keep it at this temperature for 90~120min, and then disperse and air cool it after it comes out of the furnace;

[0022] Isothermal annealing is as follows: the sample is heated to 770~790℃ and kept at this temperature for 4~5h, then cooled with the furnace to 700~720℃ at a rate of 10~30℃ / h, kept at this temperature for 5~6h, then cooled with the furnace to 650℃, taken out of the furnace and dispersedly air-cooled.

[0023] Furthermore, for bearing steel with diameter of 80 mm < diameter ≤ 150 mm and carbide banding not higher than grade 3, a reciprocating spheroidizing annealing process is used for heat treatment.

[0024] Furthermore, carbide inhomogeneity (carbide banding) is measured in accordance with GB / T 18254.

[0025] Furthermore, the average grain size of the metal is measured in accordance with GB / T 6394.

[0026] The beneficial effects of the present invention are:

[0027] The present invention adopts different heat treatment methods to heat treat water immersion ultrasonic testing samples for bearing steels of different quality levels, which solves the ambiguity of the heat treatment process regulations in the testing standards, and at the same time ensures the uniformity and consistency of the structure of the testing samples, avoids image signal interference during water immersion ultrasonic testing, and thus ensures the accuracy and reliability of water immersion ultrasonic testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 It is a schematic diagram of the normalizing + isothermal annealing process of a specific implementation mode of the present invention.

[0030] Figure 2 It is a schematic diagram of a reciprocating spheroidizing annealing process according to a specific embodiment of the present invention.

[0031] Figure 3 This is a first photo of the detection of band-shaped carbides in the GCr15 bearing steel bar after heat treatment in Example 1 of the present invention.

[0032] Figure 4 This is the second photo of the detection of band-shaped carbides of the GCr15 bearing steel bar after heat treatment in Example 1 of the present invention.

[0033] Figure 5 This is a photograph of the detection of band-shaped carbides at the edge of the GCr15 bearing steel bar after heat treatment in Example 2 of the present invention.

[0034] Figure 6This is a photograph of the detection of banded carbides at the radial position of the GCr15 bearing steel bar after heat treatment in Example 2 of the present invention.

[0035] Figure 7 This is a photograph of the detection of band-shaped carbides at the center of the GCr15 bearing steel bar after heat treatment in Example 2 of the present invention.

[0036] Figure 8 This is a metallographic photograph of the GCr15 bearing steel bar after heat treatment in Example 2 of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0038] Example 1

[0039] The GCr15 bearing steel bars with a diameter of 75 mm were subjected to sample heat treatment before water immersion ultrasonic testing.

[0040] (1) According to the method specified in GB / T 18254, samples of bearing steel were taken to test the carbide inhomogeneity of the bearing steel. The test result showed that the carbide banding was grade 3.

[0041] (2) The bearing steel is treated by normalizing + isothermal annealing process. The specific process is as follows:

[0042] ① Normalizing: Heat the sample to 905℃ and keep it for 90min, then disperse and air cool it after it comes out of the furnace;

[0043] ②Isothermal annealing: heat the sample to 782℃ and keep it for 4h, then cool it to 703℃ with the furnace at a rate of 10~30℃ / h, keep it for 5h and then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0044] According to the method specified in GB / T 18254, the carbide inhomogeneity test was carried out on the heat-treated sample, and the test result showed that the carbide banding was level 2.

[0045] According to the method specified in GB / T 6394, the average grain size of the metal was tested on the heat-treated sample, and the test result was level 6.

[0046] Example 2

[0047] The GCr15 bearing steel bars with a diameter of 50 mm were subjected to sample heat treatment before water immersion ultrasonic testing.

[0048] (1) According to the method specified in GB / T 18254, samples of bearing steel were taken to test the carbide inhomogeneity of the bearing steel. The test result showed that the carbide banding was grade 3.

[0049] (2) The bearing steel is treated by normalizing + isothermal annealing process. The specific process is as follows:

[0050] ① Normalizing: Heat the sample to 905℃ and keep it for 90min, then disperse and air cool it after it comes out of the furnace;

[0051] ②Isothermal annealing: heat the sample to 782℃ and keep it for 4h, then cool it to 703℃ with the furnace at a rate of 10~30℃ / h, keep it for 5h and then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0052] According to the method specified in GB / T 18254, the carbide inhomogeneity test was carried out on the heat-treated sample, and the test result showed that the carbide banding was level 2.

[0053] According to the method specified in GB / T 6394, the average grain size of the metal was tested on the heat-treated sample, and the test result was level 6.

[0054] Example 3

[0055] The GCr15 bearing steel bars with a diameter of 120 mm were subjected to sample heat treatment before water immersion ultrasonic testing.

[0056] (1) According to the method specified in GB / T 18254, samples of bearing steel were taken to test the carbide inhomogeneity of the bearing steel. The test result showed that the carbide banding was grade 3.5.

[0057] (2) The bearing steel is treated by normalizing + isothermal annealing process. The specific process is as follows:

[0058] ① Normalizing: Heat the sample to 915℃ and keep it at this temperature for 120min, then disperse and air cool it after it comes out of the furnace;

[0059] ②Isothermal annealing: Heat the sample to 772℃ and keep it for 5h, then cool it to 716℃ with the furnace at a rate of 10~30℃ / h, keep it for 6h and then cool it to 650℃ with the furnace, then take it out of the furnace and disperse it in air cooling.

[0060] According to the method specified in GB / T 18254, the carbide inhomogeneity test was carried out on the heat-treated sample, and the test result showed that the carbide banding was level 2.5.

[0061] According to the method specified in GB / T 6394, the average grain size of the metal was tested on the heat-treated sample, and the test result was level 5.

[0062] Example 4

[0063] The GCr15 bearing steel bars with a diameter of 148 mm were subjected to sample heat treatment before water immersion ultrasonic testing.

[0064] (1) According to the method specified in GB / T 18254, samples of bearing steel were taken to test the carbide inhomogeneity of the bearing steel. The test result showed that the carbide banding was grade 3.

[0065] (2) The bearing steel is treated by reciprocating spheroidizing annealing process. The specific process is as follows:

[0066] First, heat the bearing steel to 780℃ and keep it for 2.5h, then cool it to 706℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3h, then heat it to 772℃ with a heating rate of 30~50℃ / h and keep it for 3h, then cool it to 693℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0067] According to the method specified in GB / T 18254, the carbide inhomogeneity test was carried out on the heat-treated sample, and the test result showed that the carbide banding was level 2.5.

[0068] According to the method specified in GB / T 6394, the average grain size of the metal was tested on the heat-treated sample, and the test result was level 5.

[0069] Example 5

[0070] The GCr15 bearing steel bars with a diameter of 60 mm were subjected to sample heat treatment before water immersion ultrasonic testing.

[0071] (1) According to the method specified in GB / T 18254, samples of bearing steel were taken to test the carbide inhomogeneity of the bearing steel. The test result showed that the carbide banding was grade 2.

[0072] (2) The bearing steel is treated by reciprocating spheroidizing annealing process. The specific process is as follows:

[0073] First, heat the bearing steel to 770℃ and keep it for 3.5h, then cool it to 695℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 5h, then heat it to 778℃ with a heating rate of 30~50℃ / h and keep it for 2h, then cool it to 705℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

[0074] According to the method specified in GB / T 18254, the carbide inhomogeneity test was carried out on the heat-treated sample, and the test result showed that the carbide banding was level 2.

[0075] According to the method specified in GB / T 6394, the average grain size of the metal was tested on the heat-treated sample, and the test result was level 5.

[0076] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A heat treatment process for a specimen of bearing steel for water immersion ultrasonic testing, characterized in that: The steps include: (1) After sampling the bearing steel, perform carbide band inspection; (2) According to the test results, the bearing steel sample is heat treated, and the heat treatment process is selected from normalizing + isothermal annealing process or reciprocating spheroidizing annealing process. After the heat treatment, the carbide band of the sample is less than 2.5 level and the average grain size of the metal reaches 5 level or above; For bearing steel with a diameter of ≤80mm and carbide banding higher than grade 2.5, normalizing + isothermal annealing process is used for heat treatment; Normalizing is to heat the sample to 900~920℃ and keep it at that temperature for 40~90min, and then disperse and air cool it after it comes out of the furnace; Isothermal annealing is to heat the sample to 770~790℃ and keep it for 3~4h, then cool it to 700~720℃ with the furnace at 10~30℃ / h, keep it for 4~5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling; For bearing steel with a diameter of ≤80mm and carbide banding not higher than grade 2.5, the reciprocating spheroidizing annealing process is used for heat treatment; The reciprocating spheroidizing annealing process is to first heat the bearing steel to 770~780℃ and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then heat it to 770~780℃ with a heating rate of 30~50℃ / h and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling; For bearing steel with diameter of 80mm<diameter≤150mm and carbide banding higher than grade 3, normalizing + isothermal annealing process is used for heat treatment; Normalizing is to heat the sample to 900~920℃ and keep it at this temperature for 90~120min, and then disperse and air cool it after it comes out of the furnace; Isothermal annealing is to heat the sample to 770~790℃ and keep it for 4~5h, then cool it to 700~720℃ with the furnace at a rate of 10~30℃ / h, keep it for 5~6h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling; For bearing steel with diameter of 80mm<≤150mm and carbide banding not higher than grade 3, reciprocating spheroidizing annealing process is used for heat treatment; The reciprocating spheroidizing annealing process is to first heat the bearing steel to 770~780℃ and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then heat it to 770~780℃ at a heating rate of 30~50℃ / h and keep it for 2~4h, then cool it to 690~710℃ with the furnace at a cooling rate of 10~30℃ / h and keep it for 3~5h, then cool it to 650℃ with the furnace, take it out of the furnace and disperse it in air cooling.

2. The heat treatment process according to claim 1, characterized in that: The bearing steel is GCr15 bearing steel.

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