A method for grain size corrosion of high-temperature bearing alloy steel

Abstract

A method for grain size corrosion of high-temperature bearing alloy steel. The present invention relates to the technical field of physical and chemical detection of bearing materials. The present invention aims to solve the technical problems of low corrosion efficiency and unstable corrosion effect existing in the existing corrosion methods. The method includes: first, preparing a corrosion agent; second, performing etching treatment; third, cleaning and air-drying. The grain size corrosion method provided by the present invention can clearly show the grain boundaries completely and clearly compared with the ordinary corrosion method, and has the characteristics of fast speed and high efficiency, greatly improving the work efficiency. At the same time, good results have also been achieved in the display of metal flow lines. The present invention is used for grain size corrosion of high-temperature bearing alloy steel.

Description

Technical Field

[0001] The present invention relates to the technical field of physical and chemical detection of bearing materials. Background Art

[0002] The grain size in steel is an important characteristic reflecting the comprehensive properties of the material, and it significantly affects the strength, toughness, plasticity, and machinability of steel, etc. In the whole process of bearing processing, the problem of grain size display of nitrided steel has not been solved. Conventional test methods recommended at home and abroad cannot accurately display the grain size of the material, so technicians have been working hard to develop a method for displaying the grain size of this material.

[0003] For this material, the currently more commonly used method is to corrode with a 4% nitric acid and ethanol solution. Since this material has many alloying elements and strong corrosion resistance, this method has a slow corrosion rate during application. Generally, it takes about half an hour to observe very shallow grain boundaries, which brings certain troubles to metallographic personnel for tissue grading.

[0004] At the same time, the corrosion method with nitric acid and ethanol solution has many disadvantages such as high requirements for corrosion experience and unstable grain size display quality. To ensure the stable output of the grain size display quality, it is of great significance to develop a corrosion method with high corrosion efficiency and stable corrosion quality. Summary of the Invention

[0005] The present invention provides a grain size corrosion method for high-temperature bearing alloy steel in order to solve the technical problems of low corrosion efficiency and unstable corrosion effect existing in the existing corrosion methods.

[0006] A grain size corrosion method for high-temperature bearing alloy steel is specifically carried out according to the following steps:

[0007] First, concentrated nitric acid, lactic acid, ferrous chloride, calcium chloride, and potassium chloride are added to deionized water and mixed evenly to obtain a corrosion agent;

[0008] Control the amount of concentrated nitric acid to be 50 - 100 mL, the amount of lactic acid to be 50 - 100 mL, ferrous chloride to be 0.1 - 2.0 g, calcium chloride to be 0.1 - 3.0 g, potassium chloride to be 0.1 - 4.0 g, and deionized water to be 50 - 100 mL;

[0009] Second, the alloy steel to be corroded is completely immersed in the corrosion agent prepared in the first step for etching treatment,

[0010] Third, the alloy steel after the etching treatment in the second step is cleaned and then air-dried to complete the grain size corrosion.

[0011] Among them, the alloy steel grade is Cr4Mo4Ni4V.

[0012] Grain boundary corrosion is a selective electrochemical corrosion process. Due to the disordered atomic arrangement and higher free energy at the grain boundaries, the grain boundary positions are compounds of alloying elements with higher free energy. There is compositional segregation at the grain boundaries, which causes a potential difference between the grain boundaries and the grain interior, forming a corrosion microcell. The potential of the grain boundaries is relatively negative compared to the grain interior, and they dissolve as anodes, forming corrosion grooves. The grain interior, as the cathode, is a ferrite-carbon solid solution.

[0013] For the grain boundary display of steel, acidic solutions are used for etching. However, the selection and screening of etchants vary for different materials. The most crucial aspect of grain boundary corrosion is the correct selection of the etchant. If the etchant is not properly selected, it is very difficult to display the grain boundaries. Therefore, when formulating a new etchant by compounding, the mechanism and function of each component should be fully considered.

[0014] The reagent formed in the corrosion method of the present invention includes nitric acid, lactic acid, ferrous chloride, calcium chloride, and potassium chloride. When selecting these components, the alloying element components of the material were fully considered, and different reagents were used for different elements to achieve a complete display of the grain boundaries.

[0015] The mechanism of action of each reagent:

[0016] 1. Nitric acid: It is the most primitive driving reagent for initiating metal corrosion. This material belongs to a high-alloy material, and it is necessary to utilize the hydrogen ions ionized by the strong acidity of nitric acid to cause hydrogen evolution corrosion with the metal. Utilizing the strong oxidizing property of nitric acid, it easily reacts with the positions with high free energy at the grain boundaries, and strong contrast is easily produced when observed under an optical microscope.

[0017] 2. Lactic acid: The steel grade of this steel is Cr4Mo4Ni4V, and the nickel content is as high as 4%. Nickel is relatively inert and reacts slowly with conventional strong acids. However, nickel easily undergoes a complexation reaction with lactic acid. At the same time, in the entire solution system, lactic acid is a weak electrolyte that can inhibit the ionization of nitric acid, enabling nitric acid to stably release hydrogen ions, thereby achieving a uniform corrosion effect.

[0018] 3. Ferrous chloride: The addition of this reagent is mainly to increase the concentration (activity) of Fe2+ ions in the solution system. According to the Nernst equation, when the activity of iron ions increases, the electrode potential of iron increases, thereby reducing the corrosion rate of iron, and thus playing an inhibition role on the grain interior. Chloride ions have a strong complexing effect on chromium elements, which is beneficial to the corrosion process.

[0019] Calculated by the Nernst equation:

[0020] E = E0 + 0.035lgα Fe 2+

[0021] In the formula, E0 is the standard electrode potential of iron;

[0022] α Fe 2+—— Activity of ferric ion.

[0023] It can be seen from the above formula that when the concentration of ferric ion increases, the activity of ferric ion also increases, which raises the electrode potential of iron, thus reducing the corrosion rate of iron. Therefore, adding steel sheets can also play a corrosion inhibition role. Distilled water has a higher purity and fewer impurities than tap water. Preparing the solution with distilled water has a better effect than tap water.

[0024] 4. Calcium chloride: Chloride ions have a strong complexing effect on chromium elements, which is beneficial to corrosion. Calcium ions belong to cathodic inhibitors. The interior of the crystal is the cathode. Calcium ions can inhibit intracrystalline corrosion, prevent the appearance of a large amount of intracrystalline tissue, and interfere with grain boundary observation.

[0025] 5. Potassium chloride: This reagent is a strong electrolyte and can increase the activity of each ion in the solution. Lactic acid inhibits the ionization of nitric acid, and potassium chloride strengthens the role of hydrogen ions. The two cooperate to achieve an ideal corrosion effect and promote the entire corrosion process. At the same time, the chloride ions ionized by the reagent have a strong complexing effect on chromium elements, which is beneficial to corrosion.

[0026] Advantages of the present invention:

[0027] A method for grain size corrosion provided by the present invention can clearly show the grain boundaries completely and clearly compared with the ordinary corrosion method, and has the characteristics of fast speed and high efficiency, greatly improving the working efficiency. At the same time, good results have also been achieved in the display of metal flow lines.

[0028] The present invention is used for grain size corrosion of high-temperature bearing alloy steel. Description of the drawings

[0029] Figure 1 It is a partial metallographic photo of alloy steel for grain size corrosion in Example 1;

[0030] Figure 2 It is another partial metallographic photo of alloy steel for grain size corrosion in Example 1;

[0031] Figure 3 It is a metallographic photo of alloy steel for grain size corrosion in the comparative experiment. Specific implementation manners

[0032] Specific implementation manners: A method for grain size corrosion of high-temperature bearing alloy steel in this implementation manner is specifically carried out according to the following steps:

[0033] I. Add concentrated nitric acid, lactic acid, ferrous chloride, calcium chloride and potassium chloride to deionized water, and mix evenly to obtain a corrosion agent;

[0034] Control the amount of concentrated nitric acid to be 50 - 100 mL, the amount of lactic acid to be 50 - 100 mL, the amount of ferrous chloride to be 0.1 - 2.0 g, the amount of calcium chloride to be 0.1 - 3.0 g, the amount of potassium chloride to be 0.1 - 4.0 g, and the amount of deionized water to be 50 - 100 mL;

[0035] Second, completely immerse the alloy steel to be corroded in the corrosion agent prepared in the first step for etching treatment,

[0036] Third, clean the alloy steel after the etching treatment in the second step, and then air dry it to complete the grain size corrosion.

[0037] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that in the first step, control the amount of concentrated nitric acid to be 60 - 90 mL, the amount of lactic acid to be 60 - 90 mL, the amount of ferrous chloride to be 0.2 - 1.0 g, the amount of calcium chloride to be 0.2 - 2.5 g, the amount of potassium chloride to be 0.1 - 3.0 g, and the amount of deionized water to be 50 - 80 mL. Others are the same as Specific Embodiment 1.

[0038] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that in the first step, a magnetic stirrer is used for mixing and stirring. Others are the same as Specific Embodiment 1 or 2.

[0039] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the alloy steel to be corroded in the second step is a material after cutting, quenching, grinding, polishing, cleaning the surface, and drying. Others are the same as any one of Specific Embodiments 1 to 3.

[0040] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that anhydrous ethanol is used to clean the surface. Others are the same as any one of Specific Embodiments 1 to 4.

[0041] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that a hair dryer is used for drying. Others are the same as any one of Specific Embodiments 1 to 5.

[0042] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that the percentage content of each element in the alloy steel to be corroded in the second step is: C: 0.11 - 0.15%, Mn: 0.15 - 0.35%, Si: 0.10 - 0.25%, Cr: 4.00 - 4.25%, Mo: 4.00 - 4.50%, Ni: 3.2 - 3.6%, S ≤ 0.005%, V: 1.13 - 1.33% and the balance of iron. Others are the same as any one of Specific Embodiments 1 to 6.

[0043] Embodiment VIII: The difference between this embodiment and any one of Embodiments I - VII is that in Step 2, the etching temperature is controlled at 30 - 40°C and the etching time is 3 - 5 min. Others are the same as any one of Embodiments I - VII.

[0044] Embodiment IX: The difference between this embodiment and any one of Embodiments I - VIII is that in Step 3, running water rinsing is adopted first, and then anhydrous ethanol rinsing is adopted. Others are the same as any one of Embodiments I - VIII.

[0045] Embodiment X: The difference between this embodiment and any one of Embodiments I - IX is that in Step 3, a hair dryer is used for drying. Others are the same as any one of Embodiments I - IX.

[0046] The content of the present invention is not limited to the content of the above embodiments. The combination of one or several of the specific embodiments can also achieve the purpose of the invention.

[0047] Example 1:

[0048] A method for grain size corrosion of high - temperature bearing alloy steel in this example is carried out specifically according to the following steps:

[0049] I. Concentrated nitric acid, lactic acid, ferrous chloride, calcium chloride and potassium chloride are added to deionized water and mixed evenly to obtain a corrosion agent.

[0050] The amount of concentrated nitric acid is controlled at 50 mL, the amount of lactic acid is 50 mL, ferrous chloride is 1.0 g, calcium chloride is 1.0 g, potassium chloride is 3.0 g, and deionized water is 80 mL.

[0051] II. The alloy steel to be corroded is completely immersed in the corrosion agent prepared in Step I for etching treatment, and the etching temperature is controlled at 30°C and the etching time is 4 min.

[0052] III. The alloy steel after the etching treatment in Step II is cleaned and then air - dried to complete the grain size corrosion.

[0053] The alloy steel to be corroded in Step II is the material after cutting, quenching, grinding, polishing, cleaning the surface and drying.

[0054] For convenient corrosion operation, the specimen is embedded by a cold - embedding method into a round cake shape with a diameter of 30 mm - 40 mm, and only the mirror surface part of the specimen is exposed, and the rest of the specimen is seamlessly wrapped by the embedding material.

[0055] The alloy steel to be etched described in Step 2 is Cr4Mo4Ni4V, and the percentage content of each element is as follows: C: 0.11 - 0.15%, Mn: 0.15 - 0.35%, Si: 0.10 - 0.25%, Cr: 4.00 - 4.25%, Mo: 4.00 - 4.50%, Ni: 3.2 - 3.6%, S ≤ 0.005%, V: 1.13 - 1.33%, and the balance is iron.

[0056] In Step 3, it is rinsed with running water and then rinsed with absolute ethanol.

[0057] Comparative experiment:

[0058] The difference between this comparative experiment and Example 1 is that an ethanol solution with a nitric acid volume content of 4% is used as the etchant to etch the alloy steel.

[0059] The alloy steel after grain size etching is tested.

[0060] Figure 1 It is a partial metallographic photo of the alloy steel with grain size etched in Example 1;

[0061] Figure 2 It is another partial metallographic photo of the alloy steel with grain size etched in Example 1;

[0062] Figure 3 It is the metallographic photo of the alloy steel with grain size etched in the comparative experiment.

[0063] It can be seen from the comparison of the metallographic photos that compared with the ordinary etching method (comparative experiment) of the present invention, in the comparative experiment, the grain boundaries are prominent and lath martensite appears in the grains, while the etching method of the present invention can inhibit the appearance of other tissues in the grains, can clearly show the grain boundaries completely, and has the characteristics of fast speed and high efficiency, greatly improving the work efficiency. At the same time, good results are also obtained in the display of metal flow lines.

Claims

1. A method for grain size corrosion of high-temperature bearing alloy steel, characterized in that The method is specifically carried out according to the following steps: I. Add concentrated nitric acid, lactic acid, ferrous chloride, calcium chloride and potassium chloride into deionized water, and mix evenly to obtain the etchant; Control the dosage of concentrated nitric acid to be 50 - 100 mL, the dosage of lactic acid to be 50 - 100 mL, ferrous chloride to be 0.1 - 2.0 g, calcium chloride to be 0.1 - 3.0 g, potassium chloride to be 0.1 - 4.0 g, and deionized water to be 50 - 100 mL; II. Immerse the alloy steel to be etched completely in the etchant prepared in step I for etching treatment; III. Clean the alloy steel after the etching treatment in step II, and then air-dry it to complete the grain size etching; The percentage content of each element in the alloy steel to be etched described in step II is: C: 0.11 - 0.15%, Mn: 0.15 - 0.35%, Si: 0.10 - 0.25%, Cr: 4.00 - 4.25%, Mo: 4.00 - 4.50%, Ni: 3.2 - 3.6%, S ≤ 0.005%, V: 1.13 - 1.33%, and the balance is iron; Control the etching temperature in step II to be 30 - 40 °C and the etching time to be 3 - 5 min.

2. A method for grain size corrosion of high-temperature bearing alloy steel according to claim 1, characterized in that Control the dosage of concentrated nitric acid in step I to be 60 - 90 mL, the dosage of lactic acid to be 60 - 90 mL, ferrous chloride to be 0.2 - 1.0 g, calcium chloride to be 0.2 - 2.5 g, potassium chloride to be 0.1 - 3.0 g, and deionized water to be 50 - 80 mL.

3. A method for etching the grain size of a high-temperature bearing alloy steel according to claim 1, characterized in that Use a magnetic stirrer for mixing and stirring in step I.

4. A method for grain size corrosion of high-temperature bearing alloy steel according to claim 1, characterized in that The alloy steel to be etched described in step II is a material after cutting, quenching, grinding, polishing, cleaning the surface and drying.

5. A method for grain size corrosion of high-temperature bearing alloy steel according to claim 4, characterized in that Clean the surface with anhydrous ethanol.

6. A method for etching the grain size of high-temperature bearing alloy steel according to claim 4, characterized in that Dry it with a hair dryer.

7. A method for grain size corrosion of high-temperature bearing alloy steel according to claim 1, characterized in that In step III, rinse with running water and then rinse with anhydrous ethanol.

8. A method for grain size corrosion of high-temperature bearing alloy steel according to claim 1, characterized in that Dry it with a hair dryer in step III.

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