An etching agent for air valve tissue and its preparation method and application

Abstract

The application discloses an etchant for gas valve structure and a preparation method and application thereof, and belongs to the technical field of metallographic detection. The etchant is prepared from sulfuric acid, hydrochloric acid and water in a specific proportion. The etchant is used for etching a gas valve sample, and after being washed and dried, clear and complete austenite structure can be observed under a microscope. The etchant can effectively obtain the metallographic structure of commonly used steel of a gas valve, and improve the precision of quantitative metallographic analysis. Furthermore, the etchant is simple to prepare and easy to popularize.

Description

Technical Field

[0001] This invention belongs to the field of metallographic testing technology, specifically relating to an etchant for valve structures, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Valve is a crucial working component and vulnerable part of an engine. Its operating conditions are exceptionally harsh, requiring frequent, high-speed reciprocating motion and friction in high-temperature, high-pressure, and corrosive combustion gases, resulting in significant impact loads. Therefore, it demands high-temperature performance and corrosion resistance. Its proper functioning directly affects engine performance, making the material requirements for valve manufacturing extremely stringent. Currently, new engines widely use nickel-based alloys as valve materials due to their excellent high-temperature oxidation resistance, good plasticity and thermal conductivity, and the ability to maintain a certain strength at high temperatures.

[0004] As a high-purity nickel-based material, its microstructure is mainly a single-phase austenitic structure (face-centered cubic structure). In the annealed or rolled state, the microstructure exhibits uniform equiaxed grains with clear grain boundaries and no obvious second-phase precipitation (due to the low content of alloying elements and the fact that nickel is a single-phase solid solution). If cold working is performed, characteristics such as grain elongation and deformation bands may appear, but these can be restored to a uniform equiaxed grain structure after annealing.

[0005] The steel used for valves has an austenitic microstructure at room temperature. Traditional nitric acid alcohol solution etching cannot produce a clear and complete microstructure, or other existing etching agents have complex formulations and are not easy to operate. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an etchant for gas valve microstructure, its preparation method, and its application. An etchant and a gas valve sample are prepared. The prepared etchant is used to etch the gas valve sample. After rinsing and drying, a clear and complete austenitic microstructure of the gas valve heat-resistant steel can be observed under a microscope. Using the etchant provided by this invention, the metallographic structure of commonly used heat-resistant steel for gas valves can be effectively obtained, improving the accuracy of quantitative metallographic analysis. Furthermore, the etchant is simple to prepare and easy to promote.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides an eroding agent for a valve structure, which is prepared from sulfuric acid, hydrochloric acid and water.

[0008] In one or more embodiments, the volume ratio of sulfuric acid, hydrochloric acid, and water is (18~22):(13~16):(8~12), more preferably (19~20):(14~15):(9~10), and most preferably 20:15:10. The ratio of the three components affects the effectiveness of the etchant.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned etchant for a gas valve structure, comprising the following steps: Dissolve sulfuric acid in water, let it stand and cool, then add hydrochloric acid to obtain the product.

[0010] Thirdly, the present invention provides the application of an etchant for the above-described valve structure, or an etchant for the valve structure prepared by the above-described preparation method, in the corrosion of valves. The valve includes an engine valve. The structure is austenitic steel.

[0011] Fourthly, the present invention provides a method for using an eroding agent on a gas valve structure, comprising the following steps: The engine valve sample is pretreated by immersing it completely in an etchant and holding it at room temperature for a set time or under heating conditions for a certain time. The sample is then removed, rinsed, and dried to obtain the final product.

[0012] One or more of the above technical solutions have the following advantages or beneficial effects: (1) The present invention provides an etchant for gas valve structure prepared by sulfuric acid, hydrochloric acid and water in a specific ratio. The etchant is simple to prepare, applicable, low in cost and easy to promote and use in the laboratory.

[0013] (2) When using the etchant for engine valve structure provided by the present invention, for different valves, in order to obtain clearer grain boundaries, the etching method can be selected at room temperature or under heating. The test operability and efficiency are greatly improved, and the etching grain boundaries are clear and the etching effect is good.

[0014] (3) The etchant for engine valve structure provided by the present invention makes the grain boundaries and twin boundaries of valve steel clearer and the structure easier to identify. It can effectively obtain the metallographic structure of commonly used austenitic steel for valves, improve the accuracy of metallographic quantitative analysis; and the etchant is simple to prepare and easy to promote, improves the clarity of grain boundaries and twin boundaries, and thus improves the accuracy of calculating the average grain size level of heat-resistant steel for valves. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 The metallographic structure of gas valve 21-4N in Example 1; Figure 2 The metallographic structure of gas valve 21-4NWNb in Example 2; Figure 3 The metallographic structure of the gas valve in Example 3 is 6Cr21Mn10MoVNbN. Figure 4 The metallographic structure of the gas valve ST412 in Example 4; Figure 5 The metallographic structure of the gas valve TS913 in Example 5; Figure 6 The metallographic structure of gas valve N80A in Example 6; Figure 7 The metallographic structure of the gas valve GH152 in Example 7; Figure 8 The metallographic structure of the gas valve TS913 in Comparative Example 1; Figure 9 The metallographic structure of gas valve N80A in Comparative Example 2; Figure 10 The metallographic structure of the gas valve in Comparative Example 3 is 6Cr21Mn10MoVNbN. Figure 11 The metallographic structure of the gas valve TS913 in Comparative Example 4; Figure 12 The metallographic structure of gas valve 21-4NWNb in Comparative Example 5; Figure 13 The metallographic structure of the gas valve TS913 in Comparative Example 6; Figure 14 The metallographic structure of gas valve N80A in Comparative Example 7; Figure 15 The metallographic structure of the gas valve GH152 in Comparative Example 8; Figure 16 The metallographic structure of the gas valve TS913 in Comparative Example 9; Figure 17 The metallographic structure of the gas valve TS913 in Comparative Example 10; Figure 18 The metallographic structure of the gas valve TS913 in Comparative Example 11; Figure 19 Metallographic structure of gas valve N80A in Comparative Example 12; Figure 20 The metallographic structure of gas valve N80A in Example 8; Figure 21 The metallographic structure of the gas valve GH152 in Example 9. Detailed Implementation

[0017] Gas valves are a core component of gas engines, and their quality directly determines the engine's operational reliability, power performance, and service life. In recent years, frequent valve failures (such as blowouts, sinking, and breakage) have become a prominent issue hindering the improvement of gas engine quality, increasing production and after-sales costs and potentially posing safety hazards. To accurately pinpoint the root causes of valve failures and optimize production processes, this study investigates the influence of valve materials and metallographic structures on gas engine failures, aiming to address the bottleneck in valve quality control.

[0018] In order to provide an etchant with a simple formulation, easy and convenient use, and capable of obtaining a complete and clear metallographic structure, the present invention provides an etchant for valve structures prepared by sulfuric acid, hydrochloric acid and water. The etchant is simple to prepare, applicable, low in cost, and easy to promote and use in the laboratory.

[0019] In one typical embodiment, the present invention provides an eroding agent for a valve structure, which is prepared from sulfuric acid, hydrochloric acid and water.

[0020] In one or more embodiments, the volume ratio of sulfuric acid, hydrochloric acid, and water is (18~22):(13~16):(8~12), more preferably (19~20):(14~15):(9~10), and most preferably 20:15:10. The ratio of the three components affects the effectiveness of the etchant.

[0021] Both the sulfuric acid and hydrochloric acid were of analytical grade.

[0022] The etchant provided by this invention can be applied to the display of austenitic microstructure in valve steels with similar compositions.

[0023] In one or more embodiments, the valve structure includes one or more of the following: valve 21-4N metallographic structure, valve 21-4NWNb metallographic structure, valve 6Cr21Mn10MoVNbN metallographic structure, valve ST412 metallographic structure, valve TS913 metallographic structure, valve N80A metallographic structure, and valve GH152 metallographic structure.

[0024] In one or more embodiments, the mass fraction concentration of the sulfuric acid is 95-98%, most preferably 98%.

[0025] In one or more embodiments, the mass fraction concentration of hydrochloric acid is 35-37%, most preferably 37%.

[0026] In a typical embodiment, the present invention provides a method for preparing the above-mentioned etchant for a gas valve structure, comprising the following steps: Dissolve sulfuric acid in water, let it stand and cool, then add hydrochloric acid to obtain the product.

[0027] In one or more embodiments, the preparation method specifically includes: first, slowly adding sulfuric acid to water, stirring until uniform, allowing it to stand and cool, and then slowly adding hydrochloric acid to prepare an etchant.

[0028] In one or more embodiments, the static cooling period is 5 to 15 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, etc., preferably 8 to 12 minutes, and more preferably 10 minutes.

[0029] In a typical embodiment, the present invention provides an etchant for the above-described valve structure, or an etchant for the valve structure prepared by the above-described method, for the application of etchant in valve etching. The valve includes an engine valve. The structure is austenitic steel. The etchant can achieve a clear grain boundary structure in the engine valve.

[0030] In one typical embodiment, the present invention provides a method for using an eroding agent on a gas valve structure, comprising the following steps: The engine valve sample is pretreated by immersing it completely in an etchant and holding it at room temperature for a set time or under heating conditions for a certain time. The sample is then removed, rinsed, and dried to obtain the final product.

[0031] Different methods of application should be selected for different types of valves. Different corrosion times and temperatures will affect the grain boundary formation. For example, short corrosion times may result in unclear grain boundaries, while long corrosion times may lead to over-corrosion.

[0032] Gas valves 21-4N, 21-4NWNb, 6Cr21Mn10MoVNbN, and ST412 are not suitable for heat corrosion, as this can easily lead to over-corrosion. Therefore, they are better suited for obtaining clear and complete grain boundaries at room temperature. During the use of the etchant, the residence time should not be too long, as this can also cause over-corrosion.

[0033] In one or more embodiments, for gas valves 21-4NWNb, 6Cr21Mn10MoVNbN, and ST412, in order to obtain clearer grain boundaries, the etchant is used as follows: at room temperature, the etching agent is left for 25-40 seconds, specifically 25s, 26s, 27s, 28s, 29s, 30s, 31s, 32s, 33s, 34s, 35s, 36s, 37s, 38s, 39s, 40s, etc., preferably 30-35 seconds, and more preferably 30 seconds.

[0034] In one or more embodiments, for gas valve 21-4N, in order to obtain clearer grain boundaries, the etchant is used as follows: at room temperature, it is left for 55~65s, specifically 55s, 56s, 57s, 58s, 59s, 60s, 61s, 62s, 63s, 64s, 65s, etc., preferably 58~62s, and more preferably 60s.

[0035] Gas valves TS913, N80A, and GH152 facilitate the formation of clear and intact grain boundaries during heating. If the temperature exceeds 100℃, the etchant is prone to splashing, making operation difficult. Too low a temperature hinders corrosion and increases corrosion time, reducing efficiency. Tests at 60℃ with a constant corrosion time showed that TS913's corrosion effect was unsatisfactory. At 90-100℃, TS913 showed over-etching of grain boundaries after 60 and 90 seconds of corrosion (increasing the test temperature caused over-etching of TS913). At 90-100℃, N80A showed unclear grain boundaries after 60 seconds of corrosion; after 90 seconds, the grain boundaries were clear (increasing the test temperature had little effect on N80A). At 90-100℃, GH152 showed clear grain boundaries after 3 minutes of corrosion.

[0036] In one or more embodiments, the etchant used for the TS913 gas valve is applied as follows: the heating temperature is 70~80℃, specifically 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, etc., preferably 74~76℃; the residence time is 80~95s, specifically 80s, 81s, 82s, 83s, 84s, 85s, 86s, 87s, 88s, 89s, 90s, 91s, 92s, 93s, 94s, 95s, preferably 88~94s. Temperatures that are too low or too high, or residence times that are too long, will affect the clarity of the grain boundaries after etching.

[0037] In one or more embodiments, for the gas valve N80A, in order to obtain clearer grain boundaries, the etchant is used as follows: under heating conditions of 70~95℃ (specifically 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, etc., preferably 75~90℃) for 80~95s (specifically 80s, 82s, 85s, 88s, 90s, 91s, 92s, 93s, 94s, 95s, etc.), preferably 85~95s, and most preferably 88~94s. The temperature cannot be room temperature; it must be under heating conditions to obtain clear grain boundaries. However, the heating time cannot be too short, otherwise the grain boundaries may become unclear.

[0038] In one or more embodiments, for the gas valve GH152, to obtain clearer grain boundaries, the etchant is applied as follows: under heating conditions of 85~100℃ (specifically 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, etc., preferably 90~100℃) for 2~5 minutes (specifically 2 minutes, 2.5 minutes, 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, etc.), preferably 2~4 minutes, and most preferably 3 minutes. To obtain clear grain boundaries, etching needs to be performed under heating conditions.

[0039] In one or more embodiments, the rinsing includes rinsing sequentially with water and an alcohol solvent. The alcohol solvent includes anhydrous ethanol. The anhydrous ethanol is analytical grade. The mass fraction of the anhydrous ethanol is 95-99.9%, preferably 99.0-99.5%, and specifically 99.5%. The drying includes air drying. The specific operation of air drying is as follows: the air blower is set to the cool air setting, the airflow is horizontal to the sample surface, and the air is blown until the surface is dry and there is no anhydrous ethanol residue.

[0040] In one or more embodiments, the pretreatment includes: grinding the surface of the valve sample to be tested on sandpaper of progressively finer texture, followed by polishing until the polished surface is mirror-like and scratch-free, then rinsing and drying. Further, the rinsing includes rinsing sequentially with water and an alcohol solvent. The alcohol solvent includes anhydrous ethanol. The anhydrous ethanol is analytical grade. The mass fraction of the anhydrous ethanol is 95-99.9%, preferably 99.0-99.5%, and specifically 99.5%. The drying includes air drying. The specific air drying operation is as follows: the air blower is set to the cold air setting, the airflow is horizontal to the sample surface, and the air is blown until the surface is dry and there is no anhydrous ethanol residue.

[0041] In one or more embodiments, the dried sample was observed under a microscope to examine its metallographic structure. The sample size was such that the inspection surface area was less than 400 mm². 2 The sample height should be 15mm~20mm.

[0042] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0043] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0044] Example 1 This embodiment uses valve material 21-4N as an example to illustrate its metallographic structure, which includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing the etching agent, leave for 60 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0045] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 1 ,Depend on Figure 1 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0046] Example 2 This embodiment uses valve material 21-4NWNb as an example to illustrate its metallographic structure, which includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing the etching agent, leave for 30 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0047] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 2 ,Depend on Figure 2 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0048] Example 3 This embodiment takes the valve material 6Cr21Mn10MoVNbN as an example, and the method for showing its metallographic structure includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing the etching agent, leave for 30 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0049] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 3 ,Depend on Figure 3 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0050] Example 4 This embodiment uses ST412, a material for gas valves, as an example to illustrate its metallographic structure. The method includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing the etching agent, leave for 30 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0051] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 4 ,Depend on Figure 4 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0052] Example 5 This embodiment uses TS913 valve material as an example to illustrate its metallographic structure, which includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing an etchant, heat to 75°C, stay for 90 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0053] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 5 ,Depend on Figure 5 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0054] Example 6 This embodiment uses valve material N80A as an example to illustrate its metallographic structure, which includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing an etchant, heat to 75°C, stay for 90 seconds, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0055] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 6 ,Depend on Figure 6 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0056] Example 7 This embodiment uses GH152, a material for gas valves, as an example to illustrate its metallographic structure. The method includes the following steps: 1) Preparation of etching agent: First, slowly add 20ml of 98% sulfuric acid to 10ml of water, stir well, let it stand and cool for 10 minutes, then slowly add 15ml of 37% hydrochloric acid, stir well, and prepare the etching agent. 2) Sample preparation: Cut the gas valve sample, grind and polish the surface to be tested until it is mirror-like and free of scratches, rinse it with tap water, then rinse it with 99.5% anhydrous ethanol and blow it dry. 3) Sample etching: Immerse the observation surface of the metallographic sample prepared in step (2) completely into a petri dish containing an etchant, heat to 90°C, stay for 3 minutes, take out the sample, rinse it with tap water, rinse it with 99.5% anhydrous ethanol, and blow it dry; observe the room temperature austenitic structure under a microscope.

[0057] The metallographic structure of the heat-resistant steel used in the air valve in this embodiment is shown below. Figure 7 ,Depend on Figure 7 It is evident that the sample exhibits uniform corrosion, clear and complete grain boundaries, and distinct twin grain boundaries.

[0058] Example 8 Taking the valve material N80A as an example, unlike Example 6, N80A corrodes for 90 seconds when the heating temperature is 90°C.

[0059] like Figure 20 As shown, at a temperature of 90-100℃, N80A is etched for 90 seconds with clear grain boundaries (the effect of increasing the test temperature on N80A is not significant).

[0060] Example 9 Taking the valve material GH152 as an example, unlike Example 7, when the heating temperature is 95℃, GH152 is corroded for 3 minutes.

[0061] like Figure 21 As shown, when the temperature is 90-100℃, after 3 minutes of GH152 corrosion, the grain boundaries are clear.

[0062] Comparative Example 1 Taking the valve material TS913 as an example, the volume ratio of sulfuric acid, hydrochloric acid and water is different from that in Example 5.

[0063] The volume ratio of sulfuric acid, hydrochloric acid, and water used was 15:15:30. The resulting etchant showed the following results. Figure 8 As shown. By Figure 8 It is evident that the corrosion grain boundaries of the sample are unclear and indistinct.

[0064] Comparative Example 2 Taking the valve material N80A as an example, the volume ratio of sulfuric acid, hydrochloric acid and water is different from that in Example 6.

[0065] The volume ratio of sulfuric acid, hydrochloric acid, and water used was 15:15:20. The resulting etchant showed the following results. Figure 9 As shown. By Figure 9 It is evident that the corrosion grain boundaries of the sample are unclear and indistinct.

[0066] Comparative Example 3 Taking the valve material 6Cr21Mn10MoVNbN as an example, unlike Example 3, the prepared etchant was used for heat corrosion at 75°C for 30 seconds. The results are as follows... Figure 10 As shown. By Figure 10 It is evident that the sample is severely over-corroded, with blackened and widened grain boundaries and unclear microstructure.

[0067] Comparative Example 4 Taking the valve material TS913 as an example, unlike Example 5, the prepared etchant was used for heat corrosion at a temperature of 70-80℃ for 5 minutes. The results are as follows... Figure 11 As shown. By Figure 11 It is evident that the sample is excessively corroded, resulting in widened grain boundaries.

[0068] Comparative Example 5 Taking valve material 21-4NWNb as an example, unlike Example 2, the prepared etchant, when used, requires a residence time of 60 seconds if the residence time is extended. The results are as follows... Figure 12 As shown. By Figure 12 It is evident that the sample is slightly over-corroded, and the grain boundaries are widened.

[0069] Comparative Example 6 Taking the valve material TS913 as an example, unlike Example 5, the prepared etchant is not heated during use, and the residence time is 5 minutes. The results are as follows... Figure 13 As shown. By Figure 13 It is evident that the corrosion grain boundaries of the sample are unclear and indistinct.

[0070] Comparative Example 7 Taking valve material N80A as an example, unlike Example 6, the prepared etchant is not heated during use, and the residence time is 5 minutes. The results are as follows... Figure 14 As shown. By Figure 14 It is evident that the corrosion grain boundaries of the sample are unclear and indistinct.

[0071] Comparative Example 8 Taking the valve material GH152 as an example, unlike Example 7, the prepared etchant is not heated during use, and the residence time is 5 minutes. The results are as follows... Figure 15 As shown. By Figure 15It is evident that the corrosion grain boundaries of the sample are unclear and indistinct.

[0072] The three materials of air valve TS913, air valve N80A and air valve GH152 have poor corrosion effect when not heated. Even after a long period of corrosion, the grain boundaries are still not obvious, see comparative examples 6, 7 and 8.

[0073] Comparative Example 9 Taking the valve material TS913 as an example, the difference from Example 5 is that the heating temperature is 60°C and the residence time is 90 s.

[0074] Depend on Figure 16 As shown, low temperatures hinder corrosion and increase corrosion time, thus reducing work efficiency. An experiment was conducted at 60℃ with a constant corrosion time, but the corrosion effect on TS913 was unsatisfactory.

[0075] Comparative Example 10 Taking the valve material TS913 as an example, unlike Example 5, when the heating temperature is 90°C, TS913 corrodes for 60 seconds.

[0076] Comparative Example 11 Taking the valve material TS913 as an example, unlike Example 5, when the heating temperature is 90°C, TS913 corrodes for 90 seconds.

[0077] like Figure 17 and Figure 18 As shown, when the heating temperature is 90-100℃, the grain boundaries of TS913 are over-corroded after 60 s and 90 s of corrosion (increasing the test temperature will cause over-corrosion of TS913, so it is recommended to retain Example 5).

[0078] Comparative Example 12 Taking the valve material N80A as an example, unlike Example 6, N80A corrodes for 60 seconds when the heating temperature is 90°C.

[0079] like Figure 19 As shown, at temperatures of 90-100℃, N80A corrosion for 60 seconds results in unclear grain boundaries.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An eroding agent for a gas valve structure, characterized in that, Composed of sulfuric acid, hydrochloric acid and water; The volume ratio of sulfuric acid, hydrochloric acid, and water is (18~22):(13~16):(8~12); The sulfuric acid has a mass fraction concentration of 95-98%; The mass fraction concentration of hydrochloric acid is 35-37%.

2. The eroding agent for the valve structure according to claim 1, characterized in that, The volume ratio of sulfuric acid, hydrochloric acid, and water is (19~20):(14~15):(9~10); The sulfuric acid has a mass fraction concentration of 98%. The mass fraction concentration of hydrochloric acid is 37%.

3. The eroding agent for the valve structure according to claim 2, characterized in that, The volume ratio of sulfuric acid, hydrochloric acid, and water is 20:15:

10.

4. A method for preparing an etchant for the valve structure according to any one of claims 1 to 3, characterized in that, Includes the following steps: Dissolve sulfuric acid in water, let it stand and cool, then add hydrochloric acid to obtain the product.

5. The preparation method according to claim 4, characterized in that, The preparation method specifically includes: first, slowly adding sulfuric acid to water, stirring evenly, letting it stand and cool, and then slowly adding hydrochloric acid to prepare an etchant; Let it cool for 5-15 minutes.

6. The application of an etchant for the valve structure according to any one of claims 1 to 3, or an etchant for the valve structure prepared by the preparation method according to claim 4 or 5, in the erosion of valves.

7. The application according to claim 6, characterized in that, The valve includes an engine valve; the engine valve includes one or more of the following: valve 21-4N, valve 21-4NWNb, valve 6Cr21Mn10MoVNbN, valve ST412, valve TS913, valve N80A, and valve GH152.

8. A method for using an eroding agent for a gas valve structure, characterized in that, The process involves using the etchant for the valve structure according to any one of claims 1 to 3, or the etchant for the valve structure prepared by the preparation method according to claim 4 or 5, and includes the following steps: Pre-treat the valve sample by immersing it completely in the etchant and holding it at room temperature for a set time or under heating conditions for a set time. Then, remove the sample, rinse and dry it to obtain the final product.

9. The method of use according to claim 8, characterized in that, The pretreatment includes grinding, polishing, rinsing, and drying the surface of the valve sample to be inspected. Leave at room temperature for 25-90 seconds; The heating conditions are: heating temperature of 70~100℃, and holding time of 80s~5min.

10. The method of use according to claim 9, characterized in that, For gas valves 21-4NWNb, 6Cr21Mn10MoVNbN, and ST412, the method of using the etchant is as follows: at room temperature, leave for 25~40 seconds. Alternatively, for valve 21-4N, the method of using the etchant is: leave it at room temperature for 55~65 seconds; Alternatively, for the TS913 air valve, the method of using the etchant is: hold at 70~80℃ for 80~95 seconds; Alternatively, for valve N80A, the method of using the etchant is: hold at 70~95℃ for 80~95 seconds; Alternatively, for the GH152 air valve, the method of using the etchant is: heat at 85~100℃ and leave for 2~5 minutes.

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