Corrosive agent and method for detecting original austenite grain size after quenching of GCr15 steel

Abstract

The invention discloses a corrosive agent and a method for detecting the original austenite grain size of quenched GCr15 steel, the raw materials of the corrosive agent comprise common potassium permanganate, phosphoric acid and citric acid, the corrosive agent is easy to obtain, simple in preparation process and non-explosive, the detection safety risk is reduced to a great extent, the corrosive agent is used as a substitute of picric acid, and the corrosive agent can be used for detecting the original austenite grain size of the quenched GCr15 steel. The method effectively solves the problem that the original austenite grain size of the quenched GCr15 steel needs to be detected by using picric acid, and the picric acid belongs to an explosive and is not easy to obtain, so that the difficulty in detecting the original austenite grain size of the quenched GCr15 steel is increased, and a new technical means is provided for detecting the original austenite grain size of the quenched GCr15 steel.

Description

Technical Field

[0001] The invention relates to the field of steel material detection, and in particular to a corrosive agent for detecting austenite grain boundary display after quenching of GCr15 steel and a method for detecting the original austenite grain size. Background Art

[0002] GCr15 steel is a widely used bearing steel. In applications, it is often necessary to heat treat the material. Quenching is a commonly used heat treatment process. After quenching, the material obtains a martensitic structure, which gives the material sufficient strength. In the quenching process, the sample needs to be heated to above the complete austenitization temperature, and then quickly cooled after a certain period of heat preservation, and the structure is transformed into martensite. The performance of its martensite is closely related to the size of the original austenite grains. On the one hand, the grain size distribution directly reflects the degree of grain growth during the material heating process and the influence of the heating process system on the organization. On the other hand, the grain size also has a great influence on the mechanical properties of the material. Therefore, the detection of the original austenite grain size after quenching is of great significance for process reference and performance research.

[0003] To complete the measurement of the original austenite grain size of GCr15 steel after quenching, the austenite grain boundary must be displayed. Usually, the original austenite grain boundary display method is to corrode the sample in a heated supersaturated picric acid aqueous solution + Seagull shampoo. However, picric acid is an explosive material and a raw material for explosives. It is not only dangerous during use, but also subject to control in use, making it inconvenient to purchase; in the absence of picric acid, it becomes difficult to detect the original austenite grain size of GCr15 steel after quenching. If the carburizing method is used, the sample needs to be heated. Under the heating process, the original austenite grain size changes. The displayed grain size only reflects the grain size of the product under the carburizing process, but cannot reflect the original austenite grain size in the original state before carburizing. Summary of the invention

[0004] In view of this, the present disclosure provides a corrosive agent and grain size detection method for detecting austenite grain boundaries of GCr15 steel after quenching, so as to solve the problem that it is very difficult to detect the original austenite grain size of GCr15 steel after quenching in the absence of picric acid.

[0005] To achieve the above-mentioned object of the invention, in a first aspect, the corrosive agent for detecting the original austenite grain size of GCr15 steel after quenching comprises:

[0006] Potassium permanganate, phosphoric acid, citric acid and water;

[0007] Based on 100 ml of the water, the potassium permanganate is 2-5 g, the phosphoric acid with a mass concentration of 85% is 10-15 ml, and the citric acid is 5-10 g.

[0008] In a second aspect, a method for preparing the etchant according to the first aspect comprises:

[0009] According to the content of each component in the corrosive agent, potassium permanganate is dissolved in water, phosphoric acid is added and dissolved, and finally citric acid is added and dissolved to obtain the corrosive agent, and the water is distilled water.

[0010] In a third aspect, the method for detecting the original austenite grain size of GCr15 steel after quenching comprises:

[0011] Sample preparation, sample corrosion and grain size measurement;

[0012] The sample corrosion is performed by using the corrosive agent described in the first aspect.

[0013] In the present disclosure and possible embodiments, the sample corrosion time is 5 to 10 minutes.

[0014] In the present disclosure and possible embodiments, the sample corrosion method includes:

[0015] The detection surface of the sample is immersed in the corrosive agent, and the color of the corrosive agent slowly changes from purple-red to colorless. The sample is taken out, and the detection surface changes from mirror surface to light gray. The sample is rinsed under running water, and the surface corrosion products are removed with absorbent cotton.

[0016] In the present disclosure and possible embodiments, the method for measuring the grain size is to place the inspection surface of the corrosion sample under a microscope, observe and capture the image of the original austenite grain morphology of the sample after quenching at a magnification of 500X, and complete the grain size measurement.

[0017] In the present disclosure and possible embodiments, the sample preparation method includes:

[0018] The quenched specimen is cut into samples, and the detection surface of the sample is inlaid, ground and polished until the detection surface reaches a mirror surface state.

[0019] In the present disclosure and possible embodiments, the method of grinding and polishing the detection surface of the sample includes:

[0020] After grinding the mounted samples with sandpaper in the order from coarse to fine, the samples are polished with diamond polishing liquid in the order from large to small particle sizes until the sample surface reaches a mirror effect.

[0021] The present invention has the following beneficial effects:

[0022] The corrosive agent for detecting the original austenite grain size of GCr15 steel after quenching of the present invention comprises commonly used potassium permanganate, phosphoric acid and citric acid as raw materials, which are not only easy to obtain and have a simple preparation process, but are also non-explosive, thus greatly reducing the safety risk of detection. The corrosive agent can replace picric acid as a corrosive solution for detecting the original austenite grain size of GCr15 steel after quenching, thus effectively solving the problem that the original austenite grain size of GCr15 steel after quenching needs to be detected using picric acid, while picric acid is an explosive product and is not easy to obtain, thus increasing the difficulty in detecting the original austenite grain size of GCr15 steel after quenching. The corrosive agent can be used to detect the original austenite grain size of GCr15 steel after quenching, thereby providing a new technical means for detecting the original austenite grain size of GCr15 steel after quenching. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The microstructure of GCr15 steel after being corroded by 4% nitric acid alcohol solution;

[0024] Figure 2 This is the original austenite grain boundary morphology of GCr15 steel after being corroded by the corrosive agent prepared in Example 1. DETAILED DESCRIPTION

[0025] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure. At the same time, unless the context clearly requires, the words "including", "comprising" and the like in the entire specification and claims should be interpreted as including rather than exclusive or exhaustive meanings; that is, the meaning of "including but not limited to".

[0026] The method for detecting the original austenite grain size of GCr1 steel after quenching in the embodiment of the present disclosure comprises the following steps:

[0027] 1. Preparation of corrosive agent:

[0028] The raw materials constituting the corrosive agent include 2-5g potassium permanganate, 10-15ml phosphoric acid with a mass concentration of 85% and 5-10g citric acid based on 100ml of distilled water.

[0029] The specific preparation process is: take 100 ml of distilled water and add it into a beaker, then add potassium permanganate and stir until it is completely dissolved, continue to add phosphoric acid and stir until it is completely dissolved, and finally add citric acid, stir evenly to obtain the corrosive agent. This corrosive agent cannot be reused.

[0030] 2. Sample preparation:

[0031] The quenched samples were prepared according to the metallographic microstructure inspection method of GB / T13298. The sample surface was prepared according to the specific process flow. After inlaying, grinding and polishing, the inspection surface of the sample reached a mirror state.

[0032] In a specific embodiment, the mounted sample is ground with sandpaper, and the grinding is performed in sequence from coarse to fine using 320#, 600#, and 800# sandpaper; after the grinding is completed, the sample is polished in sequence using diamond polishing liquid with a particle size of 3μm, 1μm, and 0.05μm until the sample surface reaches a mirror effect.

[0033] 3. Sample corrosion:

[0034] Immerse the test surface of the sample in the above-prepared corrosive agent for about 5 to 10 minutes. As the corrosion time increases, the color of the corrosive agent slowly changes from purple-red to colorless. Take out the sample, and the test surface changes from a mirror surface to light gray. Rinse the sample under running water, remove the surface corrosion products with absorbent cotton, and then observe it under a microscope.

[0035] 4. Sample testing:

[0036] The test surface after corrosion treatment was observed under a microscope at a magnification of 500X. Although the influence of martensite lath bundles and diffusely distributed carbides cannot be completely ruled out in terms of microstructural morphology, a clearer morphology of the original austenite grain boundaries can be observed under the microscope and in the collected images.

[0037] 5. Grain size measurement:

[0038] After the image is collected, the grain size of the sample is measured according to the displayed grain morphology according to the GB6394 standard method.

[0039] Example 1

[0040] Taking the GCr15 low temperature tempered sample as an example, the original austenite grain size after quenching is detected according to the method of the present invention, and the steps are as follows:

[0041] 1. Sample preparation:

[0042] (1) Cut the quenched and low-temperature tempered specimens to obtain samples, and then mount the samples.

[0043] (2) Sample grinding:

[0044] The heat-treated samples were first ground with sandpaper, and then ground with 320#, 600#, and 800# sandpaper in order from coarse to fine. After grinding, diamond polishing liquid with particle sizes of 3μm, 1μm, and 0.05μm was used to polish the samples in turn until the sample surface reached a mirror effect.

[0045] 2. Corrosion samples:

[0046] The corrosive agent used is prepared according to the ratio of 2g potassium permanganate, 10ml phosphoric acid with a mass concentration of 85%, 5g citric acid monohydrate, and 100ml distilled water.

[0047] Preparation method: Take 100 ml of distilled water and add it into a beaker, then add 2 g of potassium permanganate into the beaker, stir until completely dissolved, continue to add phosphoric acid and stir until completely dissolved, finally add monohydrate citric acid ice and stir evenly to obtain the corrosive agent.

[0048] In addition, 4% nitric acid alcohol solution was selected as the etching agent for comparison with the etching agent in Example 1.

[0049] Take out 20 ml of the corrosive agent and put it into a culture dish. Gently place the sample into the culture dish and shake it until the corrosive agent becomes colorless. The corrosion time is 5 minutes.

[0050] 3. Grain size measurement:

[0051] After the sample was corroded by 4% nitric acid alcohol solution, it was observed under a microscope at 500X magnification. Figure 1 As shown, the original austenite grain boundaries cannot be displayed.

[0052] After the sample was etched by the etchant prepared in Example 1, it was observed under a microscope at a magnification of 500X. Figure 2 As shown, the grain boundaries can be clearly shown. There are slight martensite laths and dispersed granular carbides in the grains, but they have little effect on the observation and detection of grain boundaries. Using the grain boundary morphology, the grain size of the sample is measured according to the GB6394 standard method.

[0053] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A corrosive agent for detecting the original austenite grain size of GCr15 steel after quenching, characterized in that: include: Potassium permanganate, phosphoric acid, citric acid and water; Based on 100 ml of the water, the potassium permanganate is 2-5 g, the phosphoric acid with a mass concentration of 85% is 10-15 ml, and the citric acid is 5-10 g.

2. A method for preparing the etchant according to claim 1, characterized in that: include: According to the content of each component in the corrosive agent, potassium permanganate is dissolved in water, phosphoric acid is added and dissolved, and finally citric acid is added and dissolved to obtain the corrosive agent, and the water is distilled water.

3. A method for detecting the original austenite grain size of GCr15 steel after quenching, characterized in that: include: Sample preparation, sample corrosion and grain size measurement; The sample corrosion is performed using the corrosive agent according to claim 1.

4. The method for detecting the original austenite grain size of GCr15 steel after quenching according to claim 3, characterized in that: The sample corrosion time is 5 to 10 minutes.

5. The method for detecting the original austenite grain size of GCr15 steel after quenching according to claim 4, characterized in that: The method of sample corrosion comprises: The detection surface of the sample is immersed in the corrosive agent, and the color of the corrosive agent slowly changes from purple-red to colorless. The sample is taken out, and the detection surface changes from mirror surface to light gray. The sample is rinsed under running water, and the surface corrosion products are removed with absorbent cotton.

6. The method for detecting the original austenite grain size of GCr15 steel after quenching according to claim 5, characterized in that: The method for measuring the grain size is to place the detection surface of the corrosion sample under a microscope, observe and capture the image of the original austenite grain morphology of the sample after quenching at a magnification of 500X, and complete the grain size measurement.

7. The method for detecting the original austenite grain size of GCr15 steel after quenching according to claim 5, characterized in that: The sample preparation method comprises: The quenched specimen is cut into samples, and the detection surface of the sample is inlaid, ground and polished until the detection surface reaches a mirror surface state.

8. The method for detecting the original austenite grain size of GCr15 steel after quenching according to claim 7, characterized in that: The method for grinding and polishing the detection surface of the sample comprises: After grinding the mounted samples with sandpaper in the order from coarse to fine, the samples are polished with diamond polishing liquid in the order from large to small particle sizes until the sample surface reaches a mirror effect.

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