Detection Method for Austenite Grain Size of Gear Steel

Abstract

The present invention relates to the technical field of metallographic structure detection of metal materials, and particularly relates to a method for detecting the austenite grain size of gear steel. This method uses a new grain size etchant, which is a mixed solution prepared from a saturated potassium permanganate solution + a 2-4% ferric chloride solution + a 14-16% sodium dodecylbenzenesulfonate solution. The specimen is subjected to quenching heat treatment under a suitable heat treatment process, and then after processes such as grinding and sample preparation and etching, it is observed under an optical microscope, which can clearly show the austenite grain boundaries of the gear steel, and the evaluation results are more objective and true, helping to study and analyze the performance of gear steel products.

Description

Technical Field

[0001] The present invention relates to the technical field of metallographic structure detection of metal materials, and particularly relates to a method for detecting the austenite grain size of gear steel. Background Art

[0002] The characteristics of austenite grain size and the measurement of austenite grain size play an important role in materials science. The grain size not only affects the mechanical properties of materials, but also affects the processing properties and surface properties of materials. There is a close relationship between the grain size and the hot working process it has experienced and the final heat treatment properties of the material. By observing the grains, the thermal history of the steel can be reflected and the quality problems can be analyzed. Therefore, the austenite grain size is one of the important criteria for evaluating the quality of steel during heating, and it has a very important influence on the structure and properties of the cooling transformation products of steel. For example, if the austenite grains are excessively coarse, it reflects that the quenching temperature of the steel part is high and it is prone to cracking. For the analysis of quenching cracks, it can be inferred from the coarse grains that it is caused by overheating. In high-end product technologies, the grain size level is specified, and the inspection of grain size has become an important item in metallographic inspection and the main content of failure analysis.

[0003] In the processing of general gear steel, there is a process requirement of carburizing treatment. Usually, the method for inspecting the austenite grain size of gear steel is the carburizing method. However, using the carburizing method to measure the austenite grain size of gear steel requires carburizing agents and the heat treatment time of the specimen is relatively long, which greatly increases the cost.

[0004] Therefore, how to inspect and determine the austenite grain size in gear steel has become an important item in the industry's metallography. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: in order to overcome the deficiencies in the prior art, the present invention provides a method for detecting the austenite grain size of gear steel with simple and fast process operations, so as to accurately and clearly identify the austenite grain size in the steel and ensure product quality.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a method for detecting the austenite grain size of gear steel, including: sampling - heat treatment - specimen grinding - specimen etching - cleaning - metallographic inspection. The specific process flow is as follows:

[0007] (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a specimen length of 30 - 50mm using a metallographic cutting machine;

[0008] (2) Heat treatment: Perform overall quenching treatment on the selected gear steel round bar specimen: Place it in a quenching heating furnace, heat it at 830 - 860°C and hold for 1h, and finally perform water quenching treatment at room temperature to cool to room temperature to obtain a quenched specimen;

[0009] (3) Specimen grinding: Take out the heat-treated specimen, cut off about 5 mm of its cross-section, and polish the oxide scale on the specimen surface until it is clean. Then, coarsely grind the specimen with a belt grinder, and successively grind it with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpapers. Use a metallographic polishing agent with a particle size of 3.5 μm (commercially available silica polishing agent) to polish the surface to be inspected of the specimen, obtaining a bright, smooth surface like a mirror for inspection;

[0010] (4) Specimen etching: Immerse the polished specimen for grain size measurement in a metallographic etching agent, which is a mixed solution prepared by mixing saturated potassium permanganate solution + 2 - 4% ferric chloride solution + 14 - 16% sodium dodecylbenzenesulfonate solution at room temperature. During the immersion process of the specimen, continuously and slowly shake it to ensure the uniformity of etching. Conduct etching at room temperature and control the etching time to be 20 - 30 s.

[0011] (5) Specimen cleaning: First, wipe the oxide film on the surface of the etched specimen with an alcohol cotton ball, then rinse it with clean water for 8 - 10 s, and blow it dry;

[0012] (6) Metallographic inspection: Finally, observe under a metallographic microscope to determine the austenite grain size grade of the gear steel.

[0013] The beneficial effects of the present invention are as follows: The present invention sets the heat treatment process according to the manufacturing and use state of the gear steel, and then detects the austenite grain size after heat treatment; by using a suitable mixed solution of potassium permanganate solution + ferric chloride + sodium dodecylbenzenesulfonate etching agent, the austenite grain boundaries of the gear steel can be clearly shown, facilitating the grading of the grains.

[0014] The following further illustrates the present invention in conjunction with the accompanying drawings and embodiments. Description of the Drawings

[0015] Figure 1 is a photograph of the best austenite grain size morphology of the gear steel observed under a microscope in Example 1 of the present invention.

[0016] Figure 2 is a photograph of the austenite grain size morphology of the gear steel observed under a microscope in Example 2 of the present invention.

[0017] Figure 3 is a photograph of the austenite grain size morphology of the gear steel observed under a microscope in Example 3 of the present invention.

[0018] Figure 4 is a photograph of the austenite grain size morphology of the gear steel observed under a microscope in Comparative Example 1.

[0019] Figure 5 is a photograph of the austenite grain size morphology of the gear steel observed under a microscope in Comparative Example 2.

[0020] Figure 6 It is a micrograph of the austenite grain size of the gear steel observed under a microscope in Example 5.

[0021] Figure 7 It is a micrograph of the austenite grain size of the gear steel observed under a microscope in Comparative Example 3. Detailed implementation manners

[0022] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will take 20CrMnTiH steel as an example to describe the present invention in detail.

[0023] Example 1

[0024] A method for detecting the austenite grain size of gear steel, the specific implementation steps are as follows:

[0025] (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a length of 50mm using a metallographic cutting machine;

[0026] (2) Heat treatment process: Place the selected grain size specimen in a quenching heating furnace, heat it at 830°C and hold for 1h, and finally perform water quenching at room temperature to obtain a quenched specimen.

[0027] (3) Specimen preparation: Cut about 5mm from the cross-section of the treated specimen, and polish the oxide scale on the specimen surface. First, rough grind with a sanding machine, and then grind with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpapers in sequence (note: when changing to the next sandpaper for grinding, it should be ensured that the scratches made by the previous sandpaper are removed, and finally obtain a test surface with only the scratches made by the finest sandpaper); after grinding, polish the test surface of the specimen with a 3.5μm grain size metallographic polishing agent to obtain a bright and smooth test surface like a mirror;

[0028] (4) Preparation of metallographic staining agent:

[0029] At room temperature, a mixed solution prepared by mixing 50ml of saturated potassium permanganate solution + 3ml of 2% ferric chloride aqueous solution + 2ml of 15% sodium dodecylbenzenesulfonate aqueous solution is used as the grain size etchant;

[0030] (5) Erosion treatment of the specimen inspection surface:

[0031] Immerse the specimen prepared in step (3) into the metallographic staining agent prepared in step (4), erode while shaking slowly and continuously to ensure the uniformity of erosion, erode at room temperature, and control the erosion time to 30S. After erosion is completed, first wipe the oxide film on its surface with an alcohol cotton ball, then rinse with water for 10S, and blow dry.

[0032] (6) Observation of the microstructure:

[0033] Place the grain size specimen after etching and cleaning in step (5) under a metallurgical microscope, continuously adjust the coarse / fine adjustment knob until the field of view is clear. (Note: When adjusting to a clear field of view, it is necessary to adjust to clarity at a small magnification and then switch to a high magnification), and collect pictures to obtain Figure 1 the grain size structure. Under a color electronic image, the austenite grain boundaries are black and gray, the grain boundary surface is relatively clean, and the grain boundaries are shown to be relatively complete and uniform.

[0034] Example 2

[0035] (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a length of 50mm using a metallurgical cutting machine;

[0036] (2) Heat treatment process: Place the selected grain size specimen in a quenching heating furnace for heating at 830°C and holding for 1 hour, and finally perform water quenching at room temperature to obtain a quenched specimen.

[0037] (3) Specimen preparation: After heat treatment, cut off about 5mm of the cross-section of the specimen, and polish the oxide scale on the specimen surface. First, rough grind with a sand belt machine, and then grind successively with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpaper. (Note: When changing to the next sandpaper for grinding, it should be ensured that the scratches made by the previous sandpaper are ground off, and finally obtain a test surface with only the scratches made by the finest sandpaper); After grinding, polish the test surface of the specimen with a 3.5μm grain size metallographic polishing agent to obtain a bright, smooth and mirror-like test surface;

[0038] (4) Preparation of metallographic staining agent:

[0039] At room temperature, prepare a mixed solution of 50ml saturated potassium permanganate solution + 3ml 3% ferric chloride aqueous solution + 5ml 14% sodium dodecylbenzenesulfonate aqueous solution as the grain size etching agent;

[0040] (5) Erosion treatment of the specimen inspection surface:

[0041] Immerse the specimen prepared in step (3) into the metallographic staining agent prepared in step (4), erode while shaking continuously and slowly to ensure the uniformity of erosion, erode at room temperature, and control the erosion time to 30S. After erosion, first wipe the oxide film on its surface with an alcohol cotton ball, then rinse with water for 10S, and blow dry.

[0042] (6) Observation of the microstructure:

[0043] Place the grain size specimen that has been etched and cleaned in step (5) under a metallurgical microscope, continuously adjust the coarse / fine adjustment knobs until the field of view is clear. (Note: When adjusting to a clear field of view, it is necessary to adjust to clarity at a low magnification first and then switch to a high magnification), and collect pictures to obtain Figure 2 the grain size structure.

[0044] Example 3

[0045] (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a specimen length of 50mm using a metallurgical cutting machine;

[0046] (2) Heat treatment process: Place the selected grain size specimen in a quenching heating furnace for heating at 830°C and holding for (1h), and finally perform water quenching treatment at room temperature to obtain a quenched specimen.

[0047] (3) Specimen preparation: After heat treatment, cut off about 5mm from the cross-section of the specimen, and polish the oxide scale on the specimen surface. First, rough grind with a belt grinder, and then grind successively with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpapers. (Note: When changing to the next sandpaper for grinding, it should be ensured that the scratches made by the previous sandpaper are ground off, and finally obtain a test surface with only the scratches made by the finest sandpaper); After grinding, polish the test surface of the specimen with a 3.5μm grain size metallographic polishing agent to obtain a bright and smooth test surface like a mirror;

[0048] (4) Preparation of metallographic staining agent:

[0049] At room temperature, prepare a mixed solution composed of 50ml of saturated potassium permanganate solution + 3ml of 4% ferric chloride aqueous solution + 5ml of 16% sodium dodecylbenzenesulfonate aqueous solution as the grain size etchant;

[0050] (5) Erosion treatment of the specimen inspection surface:

[0051] Immerse the specimen prepared in step (3) into the metallographic staining agent prepared in step (4), erode while shaking continuously and slowly to ensure the uniformity of erosion, erode at room temperature, and control the erosion time to 30S. After erosion, first wipe the oxide film on its surface with an alcohol cotton ball, then rinse with water for 10S, and blow dry.

[0052] (6) Observation of the microstructure:

[0053] Place the grain size specimen that has been etched and cleaned in step (5) under a metallurgical microscope, continuously adjust the coarse / fine adjustment knobs until the field of view is clear. (Note: When adjusting to a clear field of view, it is necessary to adjust to clarity at a low magnification first and then switch to a high magnification), and collect pictures to obtain Figure 3 the grain size structure.

[0054] Example 4

[0055] (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a sample length of 50mm using a metallographic cutting machine;

[0056] (2) Heat treatment process: Place the selected grain size sample in a quenching heating furnace, heat it to 830°C and hold for 1 hour, and finally perform water quenching at room temperature to obtain a quenched sample.

[0057] (3) Specimen preparation: After heat treatment, cut about 5mm from the cross-section of the sample, and polish the oxide scale on the sample surface. First, rough grind with a sanding machine, and then grind sequentially with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpaper. (Note: When changing to the next sandpaper for grinding, it should be ensured that the scratches made by the previous sandpaper are removed, and finally obtain a surface to be inspected with only the scratches made by the finest sandpaper); After grinding, polish the surface to be inspected of the sample with a 3.5μm grain size metallographic polishing agent to obtain a bright, smooth and mirror-like surface to be inspected;

[0058] (4) Preparation of metallographic staining agent:

[0059] At room temperature, a mixed solution prepared by mixing 50ml of saturated potassium permanganate solution + 2ml of 2% ferric chloride aqueous solution + 2ml of 14% sodium dodecylbenzenesulfonate aqueous solution is used as the grain size etchant;

[0060] (5) Etching treatment on the inspection surface of the sample:

[0061] Immerse the sample prepared in step (3) into the metallographic staining agent prepared in step (4), shake it continuously and slowly to ensure the uniformity of etching. Etch at room temperature and control the etching time to 30S. After etching, wipe the oxide film on its surface with an alcohol cotton first, then rinse with water for 10S, and blow dry.

[0062] (6) Observation of microstructure:

[0063] Place the grain size sample that has been corroded and cleaned in step (5) under a metallographic microscope, continuously adjust the coarse / fine adjustment knobs until the field of view is clear. (Note: When adjusting to a clear field of view, it is necessary to adjust to clear at a small magnification and then switch to a high magnification) and collect pictures.

[0064] Example 5

[0065] During heat treatment, control the quenching temperature at 860°C, and the others are the same as in Example 1. Under a color electronic image, the morphology photos of the austenite grain size obtained are as Figure 6 shown.

[0066] Comparative Example 1

[0067] The sample was corroded with 50 ml of saturated picric acid + 2 ml of 15% aqueous sodium dodecylbenzenesulfonate solution + 5 ml of 36% concentrated hydrochloric acid solution. Other conditions were the same as in Example 1. Under a color electronic image, the morphology photo of the obtained austenite grain size is as Figure 4 shown.

[0068] Comparative Example 2

[0069] The sample was corroded with 50 ml of saturated potassium permanganate + 2 ml of 15% aqueous sodium dodecylbenzenesulfonate solution + 3 ml of 36% copper chloride solution (the same as in Example 1). Other conditions were the same as in Example 1. Under a color electronic image, the morphology photo of the obtained austenite grain size is as Figure 5 shown.

[0070] Comparative Example 3

[0071] The sample was corroded with 50 ml of saturated potassium perchlorate + 3 ml of 2% aqueous ferric chloride solution + 2 ml of 15% sodium dodecylbenzenesulfonate solution. Other conditions were the same as in Example 1. Under a color electronic image, the morphology of the obtained austenite grain size does not show as Figure 7 shown.

[0072] For the above Example 1, Example 2, Example 3, Example 4, Example 5 and Comparative Example 1, Comparative Example 2, Comparative Example 3, 30 groups of gear steel samples were each detected, and the comparison of the effects is shown in Table 1 below.

[0073] Table 1 Detection results of austenite grain size after corrosion with different corrosives

[0074]

[0075]

[0076] From the above comparison results, it can be seen that the detection method of the present invention can very conveniently and clearly judge and grade the austenite grain size. In addition, this detection method does not cause obvious mixed grain phenomenon, and the grain difference of the same sample is within the range of 0.5 grade. Moreover, the mixed solution of potassium permanganate + ferric chloride + sodium dodecylbenzenesulfonate prepared in the present invention can not only corrode the grain size of gear steel, but also be applicable to the grain size of other spring steels and bearing steels. The operation is simple, convenient and fast, with high repeatability, clear contrast, relatively clean surface and all the reagents used are conventional reagents, so it can be widely promoted and used.

[0077] Based on the above enlightenment of the ideal embodiment of the present invention, through the above description, relevant staff can completely make various changes and modifications within the scope not deviating from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for detecting the austenite grain size of gear steel, comprising: Sampling - Heat treatment - Specimen grinding - Specimen etching - Cleaning - Metallographic inspection, characterized in that the steps of the inspection method are as follows: (1) Sampling: Cut a φ14mm hot-rolled gear steel round bar with a specimen length of 30 - 50mm using a metallographic cutting machine; The gear steel is composed of the following components by mass percentage: C: 0.17% - 0.23%, Si: 0.17% - 0.37%, Cr: 1.00% - 1.30%, Ti: 0.04% - 0.10%, and the balance is Fe and inevitable impurities; (2) Heat treatment: Perform overall quenching treatment on the selected gear steel round bar specimen: Place it in a quenching heating furnace for heating and holding, and finally perform water quenching treatment to obtain a quenched specimen; (3) Specimen grinding: Take out the specimen after heat treatment, cut off 5mm of its cross-section, polish the scale on the specimen surface, then rough grind it with a belt grinder, then grind it with metallographic sandpaper, and polish the surface to be inspected of the specimen with a 3.5μm grain size metallographic polishing agent to obtain a bright and smooth surface to be inspected like a mirror; (4) Specimen etching: Immerse the polished specimen in a metallographic etching agent composed of potassium permanganate, ferric chloride, and sodium dodecylbenzenesulfonate. During the immersion process of the specimen, continuously and slowly shake it to ensure the uniformity of etching; The composition of the metallographic etching agent is: 50ml saturated potassium permanganate solution + 3ml 2% ferric chloride aqueous solution + 2ml 15% sodium dodecylbenzenesulfonate aqueous solution; or 50ml saturated potassium permanganate solution + 3ml 3% ferric chloride aqueous solution + 5ml 14% sodium dodecylbenzenesulfonate aqueous solution; (5) Specimen cleaning: Wipe the surface oxide film of the inspected surface of the etched specimen with an alcohol cotton first, then rinse it with clean water, and blow it dry; (6) Metallographic inspection: Observe under a metallographic microscope to determine the austenite grain size grade of the gear steel.

2. The method for detecting the austenite grain size of the gear steel according to claim 1, characterized in that: In step (2), perform heat preservation treatment at 830 - 860°C for 1h in a quenching heating furnace, and water quench and cool to room temperature to obtain a quenched specimen.

3. The method for detecting the austenite grain size of the gear steel according to claim 1, wherein: In step (3), grind with 180-mesh, 600-mesh, and 1000-mesh metallographic sandpaper in sequence.

4. The method for detecting the austenite grain size of the gear steel according to claim 1, characterized in that: In step (3), the metallographic polishing agent is a commercially available silica polishing agent.

5. The method for detecting the austenite grain size of the gear steel according to claim 1, wherein: In step (4), the etching time is 20 - 30S.

6. The method for detecting the austenite grain size of the gear steel according to claim 1, wherein: In step (5), wipe the surface oxide film of the etched specimen with an alcohol cotton first, then rinse it with clean water for 8 - 10S, and blow it dry.

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