High carbon stainless steel grain size etchant and its preparation method and grain size display method

Abstract

The present invention belongs to the technical field of metallographic detection of metal materials, and specifically relates to a high-carbon stainless steel grain size etchant, a preparation method thereof, and a method for displaying the grain size. The etchant comprises, by weight, 3-4 parts of ferric chloride, 2-4 parts of hydrochloric acid, and 70-80 parts of water. The chemical composition of the high-carbon stainless steel suitable for the etchant comprises, by weight percentage, the following: C: 1.0%-1.2%, Cr: 14%-15%, Mo: 3.6-4.3%, and V: 1.0%-1.4%. The high-carbon stainless steel grain size etchant provided by the present invention is safe and non-explosive. Using the etchant can accurately and clearly display the grain boundaries of the high-carbon stainless steel material, facilitating accurate grain size assessment.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic detection of metal materials, and particularly relates to a high-carbon stainless steel grain size etchant, a preparation method thereof, and a grain size display method. Background Art

[0002] High-carbon stainless bearing steel (Fe-1.1C-14.5Cr-4.0Mo-1.2V) is the most widely used molybdenum-containing high-carbon stainless bearing steel in the world. In addition to the characteristics of general bearings, it also has high high-temperature stability, high-temperature hardness, and high-temperature contact fatigue performance. It can be used for a long time at an operating temperature below 315°C. It is mainly used for aircraft engine bearings and other high-temperature resistant bearings.

[0003] The grain size of metal materials has a decisive influence on their mechanical properties at room temperature and high temperature, and is an important parameter of steel. Therefore, it is necessary to test the grain size of high-carbon stainless bearing steel during the production process to ensure its performance.

[0004] Currently, the primary etchant for determining grain size in high-carbon stainless bearing steel during direct quenching is a supersaturated aqueous solution of picric acid. However, picric acid is toxic and explosive, and has been placed under strict national control in recent years. Therefore, finding a safer etchant to replace picric acid solution and determine the austenite grain size of high-carbon stainless bearing steel has become a pressing technical challenge. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a high-carbon stainless steel grain size etchant, a preparation method thereof, and a grain size display method. The high-carbon stainless steel grain size etchant provided by the present invention is safe and non-explosive. The grain size etchant provided by the present invention can accurately and clearly display the grain boundaries of the high-carbon stainless steel material, thereby facilitating the accurate assessment of grain size grading.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A first aspect of the present invention provides a grain size etchant for high-carbon stainless steel. The etchant comprises, by weight, 3-4 parts of ferric chloride, 2-4 parts of hydrochloric acid, and 70-80 parts of water. The chemical composition of the high-carbon stainless steel suitable for the etchant comprises, by weight percentage, the following: C: 1.0%-1.2%, Cr: 14%-15%, Mo: 3.6-4.3%, and V: 1.0%-1.4%.

[0008] The high-carbon stainless steel grain size etchant provided by the present invention is safe and non-explosive. The grain boundaries of the high-carbon stainless steel material can be accurately and clearly displayed by using the grain size etchant provided by the present invention, which is conducive to the accurate assessment of the grain size level.

[0009] In the above-mentioned high carbon stainless steel grain size etchant, as a preferred embodiment, the hydrochloric acid is hydrochloric acid with a mass fraction of hydrogen chloride of 36%-38%, that is, commercially available concentrated hydrochloric acid.

[0010] Among the above-mentioned high carbon stainless steel grain size etchants, as a preferred embodiment, the high carbon stainless steel grain size etchant is suitable for corrosion visualization of grain size inspection of high carbon stainless steel with a chemical composition (wt %) of Fe-1.1C-14.5Cr-4.0Mo-1.2V.

[0011] The second aspect of the present invention provides a method for preparing the high carbon stainless steel grain size etchant according to the first aspect, comprising the following steps:

[0012] The etchant is obtained by mixing 3-4 parts of ferric chloride, 70-80 parts of water and 2-4 parts of hydrochloric acid in parts by weight.

[0013] The third aspect of the present invention provides a method for displaying the grain size of high carbon stainless steel, comprising the following steps: sample preparation, corrosive agent preparation, sample corrosion, sample cleaning and sample drying, wherein:

[0014] The etchant is the high-carbon stainless steel grain size etchant described in the first aspect or the etchant prepared by the preparation method of the high-carbon stainless steel grain size etchant described in the second aspect;

[0015] The sample corrosion includes placing (immersing) the prepared sample in the prepared corrosive agent, and the corrosion time is 50s-70s (for example, it can be 50s, 55s, 60s, 65s or 70s, etc.).

[0016] The present invention can achieve the best corrosion effect by limiting the corrosion time to 50s-70s. If the time is too short, the corrosion effect is relatively light and the grain boundaries cannot be clearly revealed; if the time is too long, the grain boundaries will appear at the same time as the structure, affecting the grain size rating.

[0017] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, during the sample etching step, the sample is stationary at room temperature, preferably 20°C-25°C. The sample is removed from the etchant when a light yellow layer appears on the surface of the sample. Through extensive creative work, the inventors have discovered that the best etching effect is achieved when the sample is removed when the color is light yellow. Gray or white indicates mild corrosion, while dark yellow or black indicates severe corrosion.

[0018] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, the sample preparation includes grinding, polishing and cleaning the heat-treated sample to ensure the cleanliness of the surface of the sample to be corroded.

[0019] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, the heat treatment method of the sample is: the sample is kept at 1110-1130°C for 30-60min (for example, it can be 30min, 40min, 50min or 60min, etc.) and then oil quenched. After the oil quenching, low-temperature tempering is performed, and the tempering temperature of the low-temperature tempering is 140°C-160°C. After tempering and keeping for 50min-70min (for example, it can be 50min, 60min or 70min, etc.), it is taken out of the furnace and air-cooled. In the present invention, if the oil quenching is replaced by water quenching, it will cause the sample to crack. In the present invention, the corrosion mechanism of the high-carbon stainless steel is that it needs to be heat treated first, and then the grain boundaries are revealed by the corrosive agent of the present invention. In the present invention, low-temperature tempering can improve the tissue contrast and facilitate the visualization of grain boundaries, and the oil on the surface of the sample can be dried, which is convenient for the preparation of the sample, and a tempered martensite structure can be obtained.

[0020] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, the sample cleaning includes immediately rinsing the sample with alcohol to remove stains on the sample surface after removing the sample from the corrosive agent, and then rinsing it again with water.

[0021] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, the sample drying includes pouring alcohol on the surface of the cleaned sample and then using a hair dryer to dry the sample to obtain a sample for metallographic analysis.

[0022] In the above-mentioned method for displaying the grain size of high-carbon stainless steel, as a preferred embodiment, after the sample drying step, the method for displaying the grain size of high-carbon stainless steel further comprises:

[0023] Sample observation: Observe the corrosion effect and grain size morphology of the grain size sample under a metallographic microscope and grade them according to the standards.

[0024] Compared with the prior art, the present invention has at least one of the following advantages:

[0025] (1) The grain size etchant for high-carbon stainless steel provided by the present invention is safe and non-explosive. The grain size etchant provided by the present invention can accurately and clearly display the grain boundaries of high-carbon stainless steel materials, which is conducive to the accurate assessment of grain size levels.

[0026] (2) After adopting the etchant and grain size display method provided by the present invention, the grain size of the high carbon stainless bearing steel sample can be clearly observed under a metallographic microscope and is suitable for rating by grain size software.

[0027] (3) The etchant of the present invention has the advantages of simple proportioning, non-toxicity, non-explosiveness, and environmental friendliness. The etchant can be reused, saving costs. Compared with picric acid corrosion, it does not require heating and can be corroded at room temperature. It is easy to operate and highly efficient, suitable for large-scale production, and can replace picric acid solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a grain size effect diagram of a sample obtained by etching using the grain size display method of Example 1.

[0029] Figure 2 This is a grain size effect diagram of a sample obtained by etching using the grain size display method of Example 2.

[0030] Figure 3 This is a grain size effect diagram of the sample obtained by etching using the grain size display method of Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0032] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0033] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0034] Throughout this disclosure, unless otherwise specified and / or explained, all references to component amounts are in parts by weight. Process parameters in the following examples, where specific conditions are not specified, generally follow conventional conditions. The experimental reagents used in the following examples, unless otherwise noted, are conventional biochemical reagents; and the amounts of experimental reagents used, unless otherwise noted, are those used in routine experimental procedures.

[0035] In a first aspect, an embodiment of the present invention provides a high-carbon stainless steel grain size etchant, which comprises, by weight, 3-4 parts of ferric chloride, 2-4 parts of hydrochloric acid, and 70-80 parts of water, wherein the hydrochloric acid is hydrochloric acid having a mass fraction of hydrogen chloride of 36%-38%. The high-carbon stainless steel grain size etchant is suitable for corrosion visualization of grain size inspection of high-carbon stainless steel having a chemical composition (wt%) of Fe-1.1C-14.5Cr-4.0Mo-1.2V.

[0036] The role of the ferric chloride aqueous solution is to produce a chemical reaction with the sample surface to reveal the grain size structure, and the role of adding hydrochloric acid is to accelerate the reaction rate.

[0037] In a second aspect, an embodiment of the present invention provides a method for preparing a high-carbon stainless steel grain size etchant according to the first aspect, comprising the following steps: mixing 3-4 parts of ferric chloride, 70-80 parts of water, and 2-4 parts of hydrochloric acid by weight to obtain the etchant.

[0038] In a third aspect, an embodiment of the present invention provides a method for displaying the grain size of high-carbon stainless steel, the method comprising the following steps: sample preparation, corrosive agent preparation, sample corrosion, sample cleaning, sample drying and sample observation, wherein the sample preparation comprises grinding, polishing and cleaning the heat-treated sample to ensure the cleanliness of the surface of the sample to be corroded, and the heat treatment method of the sample is as follows: the sample is kept at 1110-1130°C for 30-60 minutes and then oil quenched, and low-temperature tempering is performed after the oil quenching is completed, the tempering temperature of the low-temperature tempering is 140°C-160°C, and the sample is taken out of the furnace and air-cooled after tempering and keeping warm for 50 minutes-70 minutes; the corrosive agent is the grain size corrosive agent of the high-carbon stainless steel described in the first aspect or the preparation of the grain size corrosive agent of the high-carbon stainless steel described in the second aspect The invention discloses an etchant prepared by the method; the sample corrosion comprises placing a prepared sample into the prepared etchant for 50 seconds to 70 seconds, wherein the sample is in a stationary state and the corrosion temperature of the sample is room temperature, preferably 20°C to 25°C, and the sample is taken out from the etchant when a layer of light yellow appears on the surface of the sample; the sample cleaning comprises immediately rinsing the sample with alcohol after taking it out of the etchant to remove stains on the surface of the sample, and then rinsing it again with water; the sample drying comprises pouring alcohol on the surface of the cleaned sample and then using a hair dryer to dry the sample to obtain a sample for metallographic analysis; the sample observation comprises observing the corrosion effect and grain size morphology of the grain size sample under a metallographic microscope and performing rating according to standards.

[0039] The high carbon stainless steel grain size etchant, its preparation method and grain size display method provided by the present invention are described in detail below with reference to specific embodiments.

[0040] The samples used in the following examples and comparative examples are all Fe-1.1C-14.5Cr-4.0Mo-1.2V high carbon stainless bearing steel, and the chemical composition by mass percentage includes: C: 1.1%; Cr: 14.5%; Mo: 4.0%; V: 1.2%.

[0041] The mass percentage concentration of the hydrochloric acid used in the following examples and comparative examples is 37%, which is concentrated hydrochloric acid.

[0042] Example 1

[0043] The grain size etchant provided in this embodiment includes, by weight, 3 parts of ferric chloride, 3 parts of hydrochloric acid, and 80 parts of water.

[0044] The preparation method of the grain size etchant provided in this embodiment comprises the following steps: pouring 3 parts by weight of ferric chloride into a container, adding 80 parts of water, adding 3 parts of hydrochloric acid, and stirring the solution thoroughly with a glass rod to obtain the grain size etchant.

[0045] The grain size display method provided in this embodiment includes the following steps:

[0046] S1. Sample preparation: Grind, polish, and clean the heat-treated sample to ensure the cleanliness of the sample surface to be corroded. The heat treatment method of the sample is as follows: the sample is kept at 1120°C for 60 minutes and then oil quenched. After the oil quenching, low-temperature tempering is performed at a tempering temperature of 150°C. After tempering and holding for 60 minutes, the sample is taken out of the furnace and air-cooled.

[0047] S2. Etchant preparation: Prepare the etchant for displaying the sample grain size according to the etchant formula and preparation method designed in this embodiment.

[0048] S3. Sample corrosion: prepare the sample clamp first, and use the sample clamp to soak the prepared sample in the prepared corrosive agent. There is no need to wipe or shake the sample with absorbent cotton for static corrosion. When a light yellow layer appears on the surface of the sample, take it out. The corrosion time is 68s. The corrosion conditions are: corrosion at room temperature (20℃).

[0049] S4. Sample cleaning: After the sample is taken out of the corrosive agent, immediately sprinkle it with alcohol to rinse off the stains on the sample surface (alcohol is more effective in removing stains on the sample surface after corrosion than directly using water. Compared with direct water washing, the obtained sample is more suitable for metallographic analysis), and then rinse again with natural water to rinse off the corrosive agent on the sample surface and other places.

[0050] S5. Sample drying: After cleaning, sprinkle alcohol on the surface of the sample, and then use a hair dryer to dry the sample to obtain the sample for metallographic analysis.

[0051] S6. Sample observation: Observe the corrosion effect and grain size morphology of the sample obtained by corrosion under a metallographic microscope, and rate them according to the standards.

[0052] Figure 1 The grain size effect diagram of the sample obtained by etching using the grain size display method of this embodiment is shown in FIG. Figure 1 As shown in the figure, the grain boundary of the sample is clearly displayed, and the grain size grade is 8.0, which can accurately assess the grain size grade.

[0053] Example 2

[0054] The grain size etchant provided in this embodiment includes, by weight, 4 parts of ferric chloride, 3 parts of hydrochloric acid, and 70 parts of water.

[0055] The preparation method of the grain size etchant provided in this embodiment comprises the following steps: pouring 4 parts by weight of ferric chloride into a container, adding 70 parts of water, adding 3 parts of hydrochloric acid, and stirring the solution thoroughly with a glass rod to obtain the grain size etchant.

[0056] The grain size display method provided in this embodiment includes the following steps:

[0057] S1. Sample preparation: Grind, polish, and clean the heat-treated sample to ensure the cleanliness of the sample surface to be corroded. The heat treatment method of the sample is as follows: the sample is kept at 1120°C for 60 minutes and then oil quenched. After the oil quenching, low-temperature tempering is performed at a tempering temperature of 150°C. After tempering and holding for 60 minutes, the sample is taken out of the furnace and air-cooled.

[0058] S2. Etchant preparation: Prepare the etchant for displaying the sample grain size according to the etchant formula and preparation method designed in this embodiment.

[0059] S3. Sample corrosion: prepare the sample clamp first, and use the sample clamp to soak the prepared sample in the prepared corrosive agent. Static corrosion does not require wiping with absorbent cotton or shaking the sample. When a light yellow layer appears on the surface of the sample, take it out. The corrosion time is 63s. Corrosion conditions: corrosion at room temperature (25℃).

[0060] S4. Sample cleaning: After the sample is taken out of the corrosive agent, immediately sprinkle it with alcohol to rinse off the stains on the sample surface (alcohol is more effective in removing stains on the sample surface after corrosion than directly using water. Compared with direct water washing, the obtained sample is more suitable for metallographic analysis), and then rinse again with natural water to rinse off the corrosive agent on the sample surface and other places.

[0061] S5. Sample drying: After cleaning, sprinkle alcohol on the surface of the sample, and then use a hair dryer to dry the sample to obtain the sample for metallographic analysis.

[0062] S6. Sample observation: Observe the corrosion effect and grain size morphology of the sample obtained by corrosion under a metallographic microscope, and rate them according to the standards.

[0063] Figure 2 The figure is a grain size effect diagram of the sample obtained by etching using the grain size display method of this embodiment. Figure 2 As shown in the figure, the grain boundary of the sample is clearly displayed, and the grain size grade is 7.5, which can accurately assess the grain size grade.

[0064] Comparative Example 1

[0065] The grain size etchant provided in this comparative example is substantially the same as that in Example 1, except that the weight percentage of hydrochloric acid is higher. Specifically, the etchant comprises 3 parts of ferric chloride, 10 parts of hydrochloric acid and 80 parts of water, calculated by weight.

[0066] The grain size etchant was prepared by referring to the preparation method of the grain size etchant provided in Example 1.

[0067] The rating was performed according to the grain size display method provided in Example 1.

[0068] Figure 3 The grain size effect diagram of the sample obtained by etching using the grain size display method of this comparative example is shown in FIG. Figure 3 As shown, the corrosion effect is not good, the obtained structure has the problems of blurred grain boundary outline and unclear grain morphology. The tempered martensite structure has begun to appear before the grain boundary is fully revealed, which has a certain impact on the evaluation of the grain size grade. This shows that the corrosive agent in this comparative example is not suitable for this steel grade. A good corrosive agent should fully reveal the grain boundary before the structure is revealed. The applicant speculates that the reason may be that the hydrochloric acid concentration is too high, which will make the corrosion degree difficult to control and prone to over-corrosion, which is not conducive to the rating.

[0069] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. Application of a high carbon stainless steel grain size etchant, characterized in that: The etchant comprises, by weight, 3-4 parts of ferric chloride, 2-4 parts of hydrochloric acid, and 70-80 parts of water, wherein the chemical composition of the high-carbon stainless steel suitable for the etchant comprises, by weight percentage, C: 1.0%-1.2%, Cr: 14%-15%, Mo: 3.6-4.3%, and V: 1.0%-1.4%; The high carbon stainless steel grain size etchant is used for testing the grain size of the high carbon stainless steel.

2. The use of the high carbon stainless steel grain size etchant according to claim 1, characterized in that: The hydrochloric acid is hydrochloric acid with a mass fraction of hydrogen chloride of 36%-38%.

3. The use of the high carbon stainless steel grain size etchant according to claim 1, characterized in that: The high carbon stainless steel grain size etchant is used for corrosion visualization of grain size inspection of high carbon stainless steel having a chemical composition (wt%) of Fe-1.1C-14.5Cr-4.0Mo-1.2V.

4. A method for displaying the grain size of high carbon stainless steel, characterized in that: The grain size display method comprises the following steps: sample preparation, etchant preparation, sample etching, sample cleaning and sample drying, wherein: The sample preparation includes grinding, polishing and cleaning the heat-treated sample to ensure the cleanliness of the sample surface to be corroded; the heat treatment method of the sample is as follows: the sample is kept at 1110-1130°C for 30-60 minutes and then oil-quenched, and then low-temperature tempering is performed after the oil quenching is completed. The tempering temperature of the low-temperature tempering is 140-160°C, and the tempering is kept at 50-70 minutes before being removed from the furnace and air-cooled; the sample is high-carbon stainless steel, and the chemical composition of the high-carbon stainless steel includes, by mass percentage, C: 1.0%-1.2%, Cr: 14%-15%, Mo: 3.6-4.3%, and V: 1.0%-1.4%; The etchant comprises 3-4 parts of ferric chloride, 2-4 parts of hydrochloric acid and 70-80 parts of water; The sample corrosion includes placing the prepared sample into the prepared corrosive agent, and the corrosion time is 50s-70s.

5. The method for displaying the grain size of high carbon stainless steel according to claim 4, characterized in that: In the sample corrosion step, the sample is in a static state, the corrosion temperature of the sample is room temperature, and the sample is taken out from the corrosive agent when a layer of light yellow appears on the surface of the sample.

6. The method for displaying the grain size of high carbon stainless steel according to claim 4, characterized in that: The sample cleaning includes taking the sample out of the corrosive agent, immediately rinsing it with alcohol to remove stains on the sample surface, and then rinsing it again with water; And / or, the sample drying includes pouring alcohol on the surface of the cleaned sample and then using a hair dryer to dry the sample, thereby obtaining a sample for metallographic analysis.

7. The method for displaying the grain size of high carbon stainless steel according to claim 4, characterized in that: After the sample drying step, the method for displaying the grain size of high carbon stainless steel further comprises: Sample observation: Observe the corrosion effect and grain size morphology of the grain size sample under a metallographic microscope and grade them according to the standards.

8. The method for displaying the grain size of high carbon stainless steel according to claim 4, characterized in that: The hydrochloric acid is hydrochloric acid with a mass fraction of hydrogen chloride of 36%-38%.

9. The method for displaying the grain size of high carbon stainless steel according to claim 4, characterized in that: The high carbon stainless steel is Fe-1.1C-14.5Cr-4.0Mo-1.2V.

Images