Method for detecting austenite grain size of high-carbon steel wire rod

Abstract

The invention belongs to the technical field of metallurgical detection, and relates to a method for detecting the austenite grain size of a high-carbon steel wire rod. Comprising the following steps: (1) sampling; (2) carrying out heat treatment on the obtained sample; (3) transversely cutting off the heat-treated wire rod at the middle position, processing a sample with the length of 12mm from the middle part, and grinding one transverse end; (4) embedding, pre-grinding, coarse grinding, fine grinding and accurate grinding are carried out on the transverse sample with one ground end, and finally the transverse sample is polished to a mirror surface; and (5) the polished metallographic sample is placed in a corrosive agent to be corroded, then observation is conducted under an optical microscope, and the grade of the austenite grain size of the high-carbon steel wire rod is determined. According to the technical scheme, after the high-carbon steel wire rod is rapidly cooled, an appropriate etching agent is prepared for etching, the grain boundary morphology of martensite is obtained through observation under an optical microscope, the grain size is obtained through a comparison method or a cross point method, and then the austenite grain size of the high-carbon steel wire rod can be determined.

Description

Technical Field

[0001] This invention relates to the field of metallurgical testing technology, and more specifically to a method for detecting the austenite grain size of high-carbon steel wire rod. Background Technology

[0002] Austenite grain size is one of the important indicators for evaluating the quality of steel heating. Its grain size has a crucial impact on the microstructure and properties of the cooling and transformation products of steel, as well as subsequent processing and heat treatment processes. Therefore, accurately evaluating the austenite grain size in steel is of great significance. Generally, three methods are used to evaluate the austenite grain size of steel: the comparison method, the intercept method, and the area method. However, the key is how to clearly display the austenite grain boundaries. For high-carbon steel, the commonly used methods include displaying grains using network cementite, grain boundary oxidation, the EBSD method, and martensite grain display.

[0003] High-carbon steel, due to its slightly higher carbon content than eutectoid steel, cannot form a distinct network of cementite after controlled rolling and cooling. Because of its low grain boundary recognition rate, the austenite grains cannot be visualized. The oxidation method utilizes a thin oxide layer formed on the surface for observation, but sample preparation is relatively difficult, and it is affected by decarburization, sometimes mistaking ferrite networks for austenite grains, resulting in significant errors. The EBSD method can accurately measure grain size, but it is generally unsuitable for production testing due to equipment limitations, high sample requirements, and complex statistical methods. Martensite grain visualization involves rapidly cooling the steel to preserve the austenite grain morphology at high temperatures, followed by low-temperature tempering to improve contrast, and preparing a suitable etching agent to obtain the martensite grain boundary morphology. Grain size is then determined using comparative or intercept methods; therefore, the key to martensite grain visualization is the preparation of a suitable etching agent.

[0004] Currently, oxidation methods are used to detect the austenite grain size of spring steel, but there are no reports on the detection of austenite grain size in 87B high-carbon steel. Therefore, providing a method for detecting the austenite grain size of high-carbon steel wire rod is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] To achieve the above objectives, this invention provides a method for detecting the austenite grain size of high-carbon steel wire rod. By performing a heat treatment process of quenching and low-temperature tempering on the high-carbon steel wire rod and preparing a suitable etching agent, the austenite grain size of the high-carbon steel wire rod is displayed based on the characteristics of martensite grains, thus solving the problems existing in the prior art.

[0006] The technical solution adopted in this invention is a method for detecting the austenite grain size of high-carbon steel wire rod, comprising the following steps:

[0007] (1) Take a high-carbon steel wire rod sample with a diameter of 14 mm and a length of 160 mm;

[0008] (2) Place the sample in a heat treatment furnace and heat it to 850-870°C for 20 minutes. Then cool it rapidly in a water bath. After cooling, place it in a heat treatment furnace at 220-240°C for 20 minutes for low-temperature tempering. Then air cool it to room temperature.

[0009] (3) Cut the heat-treated wire rod transversely at the middle position to eliminate the effect of decarburization during the heat treatment process; process a sample with a length of 12mm from the middle part and grind the transverse end.

[0010] (4) The transverse sample at one end of the grinding process is inlaid → pre-grinding → rough grinding → fine grinding → precision grinding, and finally polished to a mirror finish.

[0011] (5) The polished metallographic sample was placed in an etchant for etching, and then observed under an optical microscope to determine the austenite grain size level of the high carbon steel wire rod.

[0012] The corrosive agent, by mass, comprises the following components and proportions: 2-3 grams of picric acid, 1-1.5 grams of ferric chloride, 1-2 ml of detergent, and 50 ml of ethanol.

[0013] Furthermore, the preparation of the corrosive agent and the corrosion process are as follows:

[0014] Preparation of the corrosive agent: Prepare the corrosive solution in a beaker. The corrosive solution is a solution containing picric acid (a detergent), ferric chloride, and ethanol. Place the beaker on a heating mantle and heat it to 70-80°C to obtain the corrosive agent.

[0015] Etching process: Hold the polished metallographic sample with tweezers and place it into the above etchant with the polished surface facing up. Stir the etchant with a glass rod for 1-2 minutes. Use degreased cotton to repeatedly wipe the surface of the sample under tap water to rinse off any residual liquid on the sample surface and then quickly blow it dry to complete the etching process.

[0016] Furthermore, the high-carbon steel wire rod comprises the following mass percentages: C: 0.89%, Si: 0.25%, Mn: 0.70%, Cr: 0.30%, V: 0.09%, S: 0.012%, P: 0.013%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the embedding in step (4) specifically involves placing the steel sample treated in step (3) and the phenolic resin powder together into an embedding machine, heating and pressurizing for 8 to 10 minutes to embed the sample into the phenolic resin powder.

[0018] Furthermore, in step (4), the sandpaper is used for pre-grinding with 180# and 360# wet sandpaper, W48 and W28 sandpaper for coarse grinding, W14 and W7 sandpaper for fine grinding and finishing, and polishing with an abrasive with a particle size of 3.5μm.

[0019] Furthermore, the observation under an optical microscope in step (5) specifically involves: magnifying the image at 500X under an optical microscope to observe the austenite grain distribution of the entire transverse sample, taking a photograph of a representative field of view, and determining the austenite grain size level of the high-carbon steel wire rod by using a comparison method or a cut-off point method.

[0020] The beneficial effects of this invention are as follows: After rapid cooling of high-carbon steel wire rod using the technical solution of this invention, the austenite grain size can be maintained at a high temperature. With a suitable etching agent, the martensite grain boundary morphology can be observed under an optical microscope after etching. The austenite grain size of the high-carbon steel wire rod can be determined by using the comparison method or the intercept method to obtain the grain size. Importantly, the raw materials used in this invention are readily available, and no expensive equipment is required. The equipment operation and process are simple and easy to master, and can be carried out anytime and anywhere. This invention has a wide range of applications and is also suitable for the detection of austenite grain size in high-carbon low-alloy steel, bearing steel, and other steel types. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a result diagram showing the austenitic grain size of the high-carbon steel wire rod in Example 1;

[0023] Figure 2 The result diagram shows the austenitic grain size of the high-carbon steel wire rod in Comparative Example 1. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for detecting the austenite grain size of high-carbon steel wire rod, comprising the following steps:

[0026] (1) Take a high-carbon steel wire rod sample with a diameter of 14 mm and a length of 160 mm;

[0027] (2) Place the sample in a heat treatment furnace and heat it to 850-870°C for 20 minutes. Then cool it rapidly in a water bath. After cooling, place it in a heat treatment furnace at 220-240°C for 20 minutes for low-temperature tempering. Then air cool it to room temperature.

[0028] (3) Cut the heat-treated wire rod transversely at the middle position to eliminate the effect of decarburization during the heat treatment process; process a sample with a length of 12mm from the middle part and grind the transverse end.

[0029] (4) The transverse sample at one end of the grinding process is inlaid → pre-grinding → rough grinding → fine grinding → precision grinding, and finally polished to a mirror finish.

[0030] It should be noted that the inlay process is as follows: the steel sample after step (3) is placed together with the phenolic resin powder into the inlay machine, and heated and pressurized for 8 to 10 minutes to embed the sample into the phenolic resin powder.

[0031] Pre-grinding uses 180# and 360# wet sandpaper, coarse grinding uses W48 and W28 sandpaper, fine grinding and finishing grinding use W14 and W7 sandpaper, and polishing uses an abrasive with a grit size of 3.5μm.

[0032] (5) The polished metallographic sample was placed in an etchant for etching, and then observed under an optical microscope to determine the austenite grain size level of the high carbon steel wire rod.

[0033] It should be noted that the specific components and proportions of the corrosive agent, by mass, are: 2-3 grams of picric acid, 1-1.5 grams of ferric chloride, 1-2 ml of detergent, and 50 ml of ethanol.

[0034] Prepare a etching solution in a beaker. The etching solution consists of picric acid (containing detergent), ferric chloride, and ethanol. Place the beaker on a heating mantle and heat it to 70-80°C to obtain the etching agent.

[0035] Hold the polished metallographic sample with tweezers and place it in the above-mentioned etchant, with the polished surface facing upwards. Stir the etchant with a glass rod for 1-2 minutes. Wipe the surface of the sample repeatedly with degreased cotton under tap water to rinse away any residual liquid and blow dry quickly. Then, under an optical microscope at 500X magnification, observe the austenite grain distribution of the entire transverse sample. Select a representative field of view and take photographs. The austenite grain size level of the high-carbon steel wire rod can be determined by using the comparison method or the intercept method.

[0036] In the following experimental examples, the high-carbon steel wire rod was produced by steelmaking, continuous casting, heating and rolling. Its composition by mass percentage is as follows: C: 0.89%, Si: 0.25%, Mn: 0.70%, Cr: 0.30%, V: 0.09%, S: 0.012%, P: 0.013%, with the balance being Fe and unavoidable impurities.

[0037] Example 1:

[0038] A method for detecting the austenite grain size of high-carbon steel wire rod includes the following steps:

[0039] (1) Take a high-carbon steel wire rod sample with a diameter of Φ14mm and a length of 160mm;

[0040] (2) The sample was placed in a heat treatment furnace and heated to 870°C and held for 20 minutes. Then it was rapidly cooled in a water bath. After cooling, it was placed in a heat treatment furnace at 240°C and held for 20 minutes for low-temperature tempering. Then it was air-cooled to room temperature.

[0041] (3) Cut the heat-treated wire rod transversely at the middle position to eliminate the effect of decarburization during the heat treatment process; process a sample with a length of 12mm from the middle part and grind the transverse end.

[0042] (4) Place the sample treated in step (3) together with the phenolic resin powder into the embedding machine, heat and pressurize for 10 minutes, so that the sample is embedded in the phenolic resin powder. Then, pre-grind on 180# and 360# wet sandpaper, coarsely grind on W48 and W28 sandpaper, finely grind on W14 and W7 sandpaper, and finally finely grind. Next, polish the sample on a polishing machine with an abrasive with a particle size of 3.5μm, and the polished surface should reach the mirror finish.

[0043] (5) Prepare the etching solution in a beaker. The etching solution consists of 2.5 g picric acid, 1 g ferric chloride, 1 ml detergent, and 50 ml ethanol. Place the beaker on a heating mantle and heat it to 80°C. Use tweezers to hold the polished metallographic sample and place it into the beaker containing the etching solution, with the polished surface facing upwards. Stir the etching solution with a glass rod for 2 minutes. Then, use tweezers to remove the sample and repeatedly wipe the surface of the sample under running tap water with degreased cotton to remove any residual liquid. Quickly dry the sample. Then, observe the austenite grain distribution of the entire transverse sample under an optical microscope. The metallographic image of the austenite grain size of the high-carbon steel wire rod is shown below. Figure 1 The austenite grain size level of the high-carbon steel wire rod was determined to be 8.5 using the comparison method or the intercept method.

[0044] Example 2:

[0045] A method for detecting the austenite grain size of high-carbon steel wire rod includes the following steps:

[0046] (1) Take a high-carbon steel wire rod sample with a diameter of Φ14mm and a length of 160mm;

[0047] (2) The sample was placed in a heat treatment furnace and heated to 850°C and held for 20 minutes. Then it was rapidly cooled in a water bath. After cooling, it was placed in a heat treatment furnace at 220°C and held for 20 minutes for low-temperature tempering. Then it was air-cooled to room temperature.

[0048] (3) Cut the heat-treated wire rod transversely at the middle position to eliminate the effect of decarburization during the heat treatment process; process a sample with a length of 12mm from the middle part and grind the transverse end.

[0049] (4) Place the sample treated in step (3) together with the phenolic resin powder into the embedding machine, heat and pressurize for 8 minutes to embed the sample into the phenolic resin powder, and then pre-grind on 180# and 360# wet sandpaper, coarsely grind on W48 and W28 sandpaper, finely grind on W14 and W7 sandpaper, and finally finely grind. Next, use an abrasive with a particle size of 3.5μm to polish the sample on a polishing machine, requiring the polished surface to reach the mirror finish.

[0050] (5) Prepare the etching solution in a beaker. The etching solution consists of 3 g of picric acid, 1.5 g of ferric chloride, 2 ml of detergent, and 50 ml of ethanol. Then place the beaker on a heating mantle and heat it to 70°C. Use tweezers to hold the polished metallographic sample and place it into the beaker containing the etching solution, with the polished surface facing upwards. Stir the etching solution with a glass rod for 1 minute. Then remove the sample with tweezers and repeatedly wipe the surface of the sample under running tap water with degreased cotton to rinse away any residual liquid. Quickly dry the sample. Then observe the austenite grain distribution of the entire transverse sample under an optical microscope. Use the comparison method or the intercept method to determine that the austenite grain size level of the high-carbon steel wire rod is grade 8.

[0051] Comparative Example 1:

[0052] A method for detecting the austenite grain size of high-carbon steel wire rod includes the following steps:

[0053] (1) Take a high-carbon steel wire rod sample with a diameter of Φ14mm and a length of 160mm;

[0054] (2) The sample was placed in a heat treatment furnace and heated to 870°C and held for 20 minutes. Then it was rapidly cooled in a water bath. After cooling, it was placed in a heat treatment furnace at 240°C and held for 20 minutes for low-temperature tempering. Then it was air-cooled to room temperature.

[0055] (3) Cut the heat-treated wire rod transversely at the middle position to eliminate the effect of decarburization during the heat treatment process; process a sample with a length of 12mm from the middle part and grind the transverse end.

[0056] (4) Place the sample treated in step (3) together with the phenolic resin powder into the embedding machine, heat and pressurize for several minutes to embed the sample into the phenolic resin powder, and then pre-grind on 180# and 360# wet sandpaper, coarsely grind on W48 and W28 sandpaper, finely grind on W14 and W7 sandpaper, and finally finely grind. Next, use an abrasive with a particle size of 3.5μm to polish the sample on a polishing machine, requiring the polished surface to reach the mirror finish.

[0057] (5) Prepare the etching solution in a beaker. The etching solution consists of 10 g of picric acid, 2 ml of detergent, and 50 ml of water. Place the beaker on a heating mantle and heat it to 70°C. Use tweezers to hold the polished metallographic sample and place it into the beaker containing the etching solution, with the polished surface facing upwards. Stir the etching solution with a glass rod for 1 minute. Then, use tweezers to remove the sample and repeatedly wipe the surface of the sample under running tap water with degreased cotton to rinse away any residual liquid. Quickly blow dry the sample. Then, observe the austenite grain distribution of the entire transverse sample under an optical microscope. The metallographic image of the austenite grain size of the high-carbon steel wire rod is shown below. Figure 2 The austenite grain boundaries are not clearly visible, making it impossible to rate the austenite grain size of high-carbon steel wire rod.

[0058] In summary, by using the technical solution of this invention, the austenite grain size of high-carbon steel wire rod can be maintained at a high temperature after rapid cooling. After etching with a suitable etching agent, the grain boundary morphology of martensite can be observed under an optical microscope. The austenite grain size of high-carbon steel wire rod can be determined by using the comparison method or the intercept method to obtain the grain size.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for detecting the austenite grain size of high-carbon steel wire rod, characterized in that, The method includes the following steps: (1) Take a high-carbon steel wire rod sample with a diameter of 14 mm and a length of 160 mm; (2) Place the sample in a heat treatment furnace and heat it to 850-870°C for 20 minutes. Then cool it rapidly in a water bath. After cooling, place it in a heat treatment furnace at 220-240°C for 20 minutes for low-temperature tempering. Then air cool it to room temperature. (3) Cut the heat-treated wire rod transversely at the middle position, process a sample with a length of 12mm from the middle part, and grind one transverse end. (4) The transverse sample at one end of the grinding process is inlaid → pre-grinding → rough grinding → fine grinding → precision grinding, and finally polished to a mirror finish. (5) The polished metallographic sample was placed in an etchant for etching, and then observed under an optical microscope to determine the austenite grain size level of the high carbon steel wire rod. The corrosive agent, by mass, comprises the following components and proportions: 2-3 grams of picric acid, 1-1.5 grams of ferric chloride, 1-2 ml of detergent, and 50 ml of ethanol.

2. The method for detecting austenite grain size in high-carbon steel wire rod as described in claim 1, characterized in that, The preparation of the corrosive agent and the corrosion process are as follows: Preparation of the corrosive agent: Prepare the corrosive solution in a beaker. The corrosive solution is a solution containing picric acid (a detergent), ferric chloride, and ethanol. Place the beaker on a heating mantle and heat it to 70-80°C to obtain the corrosive agent. Etching process: Hold the polished metallographic sample with tweezers and place it into the above etchant with the polished surface facing up. Stir the etchant with a glass rod for 1-2 minutes. Use degreased cotton to repeatedly wipe the surface of the sample under tap water to rinse off any residual liquid on the sample surface and then quickly blow it dry to complete the etching process.

3. The method for detecting austenite grain size in high-carbon steel wire rod as described in claim 2, characterized in that, The high-carbon steel wire rod comprises the following mass percentages: C: 0.89%, Si: 0.25%, Mn: 0.70%, Cr: 0.30%, V: 0.09%, S: 0.012%, P: 0.013%, with the balance being Fe and unavoidable impurities.

4. The method for detecting austenite grain size in high-carbon steel wire rod as described in claim 3, characterized in that, The embedding process in step (4) specifically involves placing the steel sample treated in step (3) and the phenolic resin powder together into an embedding machine, heating and pressurizing for 8 to 10 minutes to embed the sample into the phenolic resin powder.

5. The method for detecting austenite grain size in high-carbon steel wire rod as described in claim 4, characterized in that, In step (4), the sandpaper is used for pre-grinding with 180# and 360# wet sandpaper, W48 and W28 sandpaper for coarse grinding, W14 and W7 sandpaper for fine grinding and finishing, and polishing with an abrasive with a particle size of 3.5μm.

6. The method for detecting austenite grain size in high-carbon steel wire rod as described in claim 5, characterized in that, The observation under an optical microscope in step (5) specifically involves: magnifying the image at 500X under an optical microscope to observe the austenite grain distribution of the entire transverse sample, taking a photograph of a representative field of view, and determining the austenite grain size level of the high-carbon steel wire rod by using the comparison method or the intercept method.

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