Bearing steel austenite grain size sample processing display method

Abstract

The invention belongs to the technical field of bearing steel material inspection, and particularly relates to a bearing steel austenite grain size sample machining display method which comprises the following steps of standard sample machining, pretreatment, quenching treatment, grinding and polishing machining, corrosion and inspection display. According to the actual machining and using process of the bearing steel, specific pretreatment and quenching treatment are combined, the austenite grain size is visually and accurately displayed, and the accuracy of grain size evaluation is improved; the sample machining process of the method is consistent with the actual machining and using process of the bearing steel, and structural research and analysis of the bearing steel are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of bearing steel material inspection, and in particular relates to a method for processing and displaying a bearing steel austenite grain size sample. Background Art

[0002] Bearing steel contains about 1.0% carbon and 2.0% alloy, and is a high-carbon hypereutectoid steel. During the continuous casting process, carbide segregation is very likely to occur due to the uneven solidification of carbon and alloy elements. In the subsequent heating and rolling process, if the carbide segregation is not effectively eliminated, the uneven carbide will inevitably affect the detection and display of austenite grain size.

[0003] The austenite grain size and uniformity of bearing steel have an important influence on the mechanical properties, physical properties and fatigue life of bearings. According to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", the processing and display methods of austenite grain size samples of steel include oxidation method, cementite network method and direct quenching method. Among them, cementite network method and direct quenching method are more commonly used. However, in production practice, due to the unevenness of carbides and the matching of heating temperature, the detection and display of austenite grain size is incomplete.

[0004] Therefore, based on the actual processing, production and use of bearing steel, a fast, efficient, intuitive and accurate method for processing and displaying austenite grain size samples of bearing steel is proposed. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for processing and displaying austenite grain size samples of bearing steel, so as to solve the problem that the detection display of austenite grain size of bearing steel is greatly different from the actual one and the display is incomplete.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for processing and displaying austenite grain size sample of bearing steel, and the specific operation steps are as follows: Step 1: Standard sample processing: Process the bearing steel into standard samples; Step 2: Pretreatment: Pretreat the standard sample to eliminate the influence of carbide segregation; Step 3: Quenching treatment: Place the pretreated standard sample in a quenching heating furnace for heating, keep it warm for a certain period of time, and then quench it. Take it out after the sample is completely cooled; Step 4: Grinding and polishing: rough grinding, fine grinding and polishing of the quenched standard specimen; Step 5: Corrosion: Use picric acid solution to corrode the polished standard specimen; Step 6: Inspection and display: Carry out inspection and display of austenite grain size on the standard sample after corrosion.

[0007] Furthermore, the bearing steel includes the following components: C: 0.95~1.05%, Si: 0.15~0.35%, Mn: 0.25~0.45%, P≤0.020%, S≤0.015%, Cr: 1.40~1.65%, Ni: ≤0.10%, Cu: ≤0.10%, Mo: ≤0.10%, Al: ≤0.05%, Ti: ≤0.003%, and the rest are Fe and impurities Ca, As, Pb, Sn, Sb, etc.

[0008] Furthermore, in the processing of the standard sample in step 1, a sample is taken at half the radius of the bearing steel according to the bearing steel specification to make a standard test specimen.

[0009] Furthermore, the pretreatment in step 2 specifically comprises the following steps: the standard sample is first kept at 790±10°C for 2 to 2.5 hours, then slowly cooled to 720±10°C for 3.5 to 4 hours, and finally cooled with the furnace to ≤600°C and air-cooled before being taken out of the furnace.

[0010] Furthermore, in step three, the quenching treatment is performed at a heating temperature of 840±10°C, a holding time of 30-60 minutes, and a coolant of bright quenching oil.

[0011] Furthermore, in step 4, the grinding and polishing process is firstly performed by coarse grinding with sandpaper having a particle size of 100-1000 mesh, then fine grinding with sandpaper having a particle size of 1200-2000 mesh, and finally polishing with diamond paste having a particle size of 2.5 μm.

[0012] Furthermore, in step five, 5% picric acid solution is selected for corrosion.

[0013] The advantages and technical effects of the present invention are: The method for processing and displaying austenite grain size samples of bearing steel proposed by the present invention, according to the actual processing and use process of bearing steel, the sample is heated to 790°C together with the heating furnace to avoid stress cracking caused by rapid heating of the sample, which affects corrosion and inspection, and is kept warm at 790°C, which can promote the homogenization of the austenite structure, while keeping the carbide particles in an incompletely dissolved state, avoiding the growth of austenite grains, and reducing the problem of grains being difficult to fully display when the austenite structure is uneven; subsequently, the sample is kept warm at 720°C for a long time to promote the segregation of impurity elements such as S and P to the grain boundaries, thereby significantly reducing the corrosion resistance of the grain boundaries, making the grain boundaries more complete and clear, and improving the accuracy of grain size evaluation; the sample processing process of the present method is consistent with the actual processing and use process of bearing steel, which is beneficial to the organizational research and analysis of bearing steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them: Figure 1 This is the austenite grain structure diagram of the bearing steel of comparative example 1 of the present invention.

[0015] Figure 2 This is the austenite grain structure diagram of the bearing steel of comparative example 2 of the present invention.

[0016] Figure 3 This is the austenite grain structure diagram of the bearing steel in Example 1 of the present invention.

[0017] Figure 4 This is the austenite grain structure diagram of the bearing steel in Example 2 of the present invention.

[0018] Figure 5 This is the austenite grain structure diagram of the bearing steel in Example 3 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to examples, but the present invention is not limited to these embodiments.

[0020] Comparative Example 1: The chemical composition and components of the bearing steel in this comparative example are C: 1.01%, Si: 0.23%, Mn: 0.27%, P: 0.013%, S: 0.001%, Cr: 1.45%, Ni: 0.02%, Cu: 0.02%, Mo: 0.006%, Al: 0.013%, Ti: 0.002%, and the rest are Fe and impurities Ca, As, Pb, Sn, Sb, etc.

[0021] Φ5.5mm bearing steel hot rolled wire rod austenite grain size sample processing display: (1) Standard sample processing: According to the sampling requirements of GB / T 6394-2017 "Method for determination of average grain size of metals", a Φ5.5 mm circular austenite grain size sample was cut.

[0022] (2) Quenching treatment: Place the sample in a muffle furnace and heat it at 860°C for 1 hour. After the heat preservation, quickly place the sample in bright quenching oil for quenching.

[0023] (3) Grinding and polishing: The quenched specimens are subjected to coarse grinding, fine grinding, polishing and cleaning in sequence.

[0024] (4) Corrosion: The polished specimens were corroded with 5% picric acid solution. After corrosion, they were first rinsed with clean water and finally rinsed with anhydrous ethanol and then blown dry.

[0025] (5) Inspection results: The corroded sample was placed under a metallographic microscope for observation. The austenite grain size picture is attached. Figure 1 , the austenite grain size rating is 7.5.

[0026] Comparative Example 2: The chemical composition and components of the bearing steel in this comparative example are C: 0.96%, Si: 0.3%, Mn: 0.32%, P: 0.013%, S: 0.001%, Cr: 1.55%, Ni: 0.02%, Cu: 0.02%, Mo: 0.006%, Al: 0.013%, Ti: 0.002%, and the rest are Fe and impurities Ca, As, Pb, Sn, Sb, etc.

[0027] Φ25mm bearing steel hot rolled wire rod austenite grain size sample processing display: (1) Standard sample processing: According to the sampling requirements of GB / T 6394-2017 "Method for determination of average grain size of metals", a 10mm*10mm square austenite grain size sample was cut.

[0028] (2) Quenching treatment: Place the sample in a muffle furnace and heat it at 860°C for 1 hour. After the heat preservation, quickly place the sample in bright quenching oil for quenching.

[0029] (3) Grinding and polishing: The quenched specimens are subjected to coarse grinding, fine grinding, polishing and cleaning in sequence.

[0030] (4) Corrosion: The polished specimens were corroded with 5% picric acid solution. After corrosion, they were first rinsed with clean water and finally rinsed with anhydrous ethanol and then blown dry.

[0031] (5) Inspection results: The corroded sample was placed under a metallographic microscope for observation. The austenite grain size picture is attached. Figure 2 , the austenite grain size rating is 7. Example 1

[0032] The chemical composition and components of the bearing steel in this embodiment are the same as those in Comparative Example 1.

[0033] Φ5.5mm bearing steel hot rolled wire rod austenite grain size sample processing display: (1) Standard sample processing: According to the sampling requirements of GB / T 6394-2017 "Method for determination of average grain size of metals", a Φ5.5 mm circular austenite grain size sample was cut.

[0034] (2) Pretreatment: Place the sample in a muffle furnace preheated to 785°C, keep it at that temperature for 2 hours, then slowly cool it to 720°C with the furnace, keep it at that temperature for 3.5 hours, and finally cool it to 550°C with the furnace, and then air cool it out of the furnace.

[0035] (3) Quenching treatment: The pretreated sample is placed in a muffle furnace and heated at 840 °C for 0.5 hours. The sample is then quickly placed in bright quenching oil for quenching.

[0036] (4) Grinding and polishing: The quenched sample was first coarsely ground with 600-grit sandpaper, then finely ground with 1000-grit sandpaper, and finally polished with 2.5 μm diamond paste, and then the sample was cleaned.

[0037] (5) Corrosion: The polished specimens were corroded with 5% picric acid solution. After corrosion, they were first rinsed with clean water and finally rinsed with anhydrous ethanol and then blown dry.

[0038] (6) Inspection results: The corroded sample was placed under a metallographic microscope for observation. The austenite grain size picture is attached. Figure 3 , the austenite grain size rating is 9. Example 2

[0039] Φ10mm bearing steel hot rolled wire rod austenite grain size sample processing display: (1) Standard sample processing: According to the sampling requirements of GB / T 6394-2017 "Method for determination of average grain size of metals", a Φ10 mm circular austenite grain size sample was cut.

[0040] (2) Pretreatment: Place the sample in a muffle furnace preheated to 790°C, keep it at that temperature for 2 hours, then slowly cool it to 720°C with the furnace, keep it at that temperature for 3.5 hours, and finally cool it to 560°C with the furnace, and then air cool it out of the furnace.

[0041] (3) Quenching treatment: The pretreated sample is placed in a muffle furnace and heated at 840°C for 0.75 hours. The sample is then quickly placed in bright quenching oil for quenching.

[0042] (4) Grinding and polishing: The quenched sample was first coarsely ground with 600-grit sandpaper, then finely ground with 1000-grit sandpaper, and finally polished with 2.5 μm diamond paste, and then the sample was cleaned.

[0043] (5) Corrosion: The polished specimens were corroded with 5% picric acid solution. After corrosion, they were first rinsed with clean water and finally rinsed with anhydrous ethanol and then blown dry.

[0044] (6) Inspection results: The corroded sample was placed under a metallographic microscope for observation. The austenite grain size picture is attached. Figure 4 , the austenite grain size rating is 9. Example 3

[0045] Φ25mm bearing steel hot rolled wire rod austenite grain size sample processing display: (1) Standard sample processing: According to the sampling requirements of GB / T 6394-2017 "Method for determination of average grain size of metals", a 10mm*10mm square austenite grain size sample was cut.

[0046] (2) Pretreatment: Place the sample in a muffle furnace preheated to 795°C, keep it warm for 2.5 hours, then slowly cool it to 720°C, keep it warm for 3.75 hours, and finally cool it to 580°C and air cool it out of the furnace.

[0047] (3) Quenching treatment: The pretreated sample is placed in a muffle furnace and heated at 840 °C for 1 hour. The sample is then quickly placed in bright quenching oil for quenching.

[0048] (4) Grinding and polishing: The quenched sample was first coarsely ground with 600-grit sandpaper, then finely ground with 1000-grit sandpaper, and finally polished with 2.5 μm diamond paste, and then the sample was cleaned.

[0049] (5) Corrosion: The polished specimens were corroded with 5% picric acid solution. After corrosion, they were first rinsed with clean water and finally rinsed with anhydrous ethanol and then blown dry.

[0050] (6) Inspection results: The corroded sample was placed under a metallographic microscope for observation. The austenite grain size picture is attached. Figure 5 , the austenite grain size rating is 8.5.

[0051] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; therefore, although the present invention has been described in detail in this specification with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may still be modified or replaced by equivalents; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for processing and displaying austenite grain size samples of bearing steel, characterized in that: The following steps are included: Step 1: Standard sample processing: Process the bearing steel into standard samples; Step 2: Pretreatment: pretreat the standard sample to eliminate the influence of carbide segregation; Step 3: Quenching treatment: Place the pretreated standard sample in a quenching heating furnace for heating, keep it warm for a certain period of time, and then quench it. Take it out after the sample is completely cooled; Step 4: Grinding and polishing: rough grinding, fine grinding and polishing of the quenched standard specimen; Step 5: Corrosion: Use picric acid solution to corrode the polished standard specimen; Step 6: Inspection and display: inspect and display the austenite grain size of the corroded standard sample; The pretreatment in step 2 specifically comprises the following steps: the standard sample is first kept at 790±10°C for 2-2.5 hours, then slowly cooled to 720±10°C for 3.5-4 hours, and finally cooled to ≤600°C with the furnace and air-cooled.

2. The method for processing and displaying austenite grain size samples of bearing steel according to claim 1, characterized in that: The bearing steel includes the following components: C: 0.95~1.05%, Si: 0.15~0.35%, Mn: 0.25~0.45%, P≤0.020%, S≤0.015%, Cr: 1.40~1.65%, Ni: ≤0.10%, Cu: ≤0.10%, Mo: ≤0.10%, Al: ≤0.05%, Ti: ≤0.003%, and the rest are Fe and impurities Ca, As, Pb, Sn, Sb, etc.

3. The method for processing and displaying austenite grain size samples of bearing steel according to claim 1, characterized in that: In step 1, the standard sample processing is carried out by sampling at half the radius of the bearing steel according to the bearing steel specifications to make a standard test specimen.

4. The method for processing and displaying austenite grain size samples of bearing steel according to claim 1, characterized in that: In step 3, the quenching treatment is carried out at a heating temperature of 840±10°C, a holding time of 30 to 60 minutes, and a coolant of bright quenching oil.

5. The method for processing and displaying austenite grain size samples of bearing steel according to claim 1, characterized in that: In step 4, the surface is ground and polished by using sandpaper with a grit of 100-1000 mesh, then finely grinding with sandpaper with a grit of 1200-2000 mesh, and finally polishing with diamond paste with a grit of 2.5 μm.

6. The method for processing and displaying austenite grain size samples of bearing steel according to claim 1, characterized in that: In step 5, 5% picric acid solution is used for corrosion.

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