Method for characterizing micrograin size of martensitic stainless steel

Abstract

This invention discloses a method for characterizing the microcrystalline grain size of martensitic stainless steel. The specific steps of the method are as follows: Step 1: Take a martensitic stainless steel sample and quench it at 1050±10℃ for 1 hour, then cool it. Step 2: Perform chemical etching on the quenched martensitic stainless steel sample. This method for characterizing the microcrystalline grain size of martensitic stainless steel allows for evaluation to be completed in one heat treatment + one grinding, polishing, and etching process. The total evaluation time is reduced from 31 hours (multiple heat treatment and etching tests) to 6 hours (3 hours for quenching + 3 hours for preparation, etching, and observation). The grain size display effect after etching meets the conditions for comparative rating. Verification shows that the reproducibility of the grain size rating value is controlled within ±0.5 levels.

Description

Technical Field

[0001] This invention relates to a method for characterizing specific materials in the field of metallographic analysis, and in particular provides a method for characterizing the microcrystalline grain size of martensitic stainless steel. Background Technology

[0002] Based on surveys and consultations with domestic industry experts and international standards, the original method for characterizing the microcrystalline grain size of martensitic stainless steel primarily used picric acid as the main etchant. However, due to the toxicity and explosiveness of picric acid, its production and sale in China have been banned since 2018, and alternative corrosion methods are not yet mature, with no dedicated method available. Currently, the company mainly borrows corrosion methods from other materials for the corrosion of martensitic stainless steel. This approach suffers from problems such as inconsistent pre-corrosion heat treatment methods, lack of reproducibility in the corrosion process, and unclear grain size and grain boundary corrosion. Multiple tests are required to ensure testing quality, severely impacting the effectiveness and efficiency of assessing the microcrystalline grain size of martensitic stainless steel.

[0003] There is an urgent need to obtain a technically effective method for characterizing the micrograin size of martensitic stainless steel. Summary of the Invention

[0004] The purpose of this invention is to provide a characterization method for the microcrystalline grain size of martensitic stainless steel with excellent technical effects, so as to achieve clear observation and efficient evaluation of the microcrystalline grain size of martensitic stainless steel.

[0005] The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows:

[0006] Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it.

[0007] Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are as follows: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 3-4g: 80-100ml: 15-25ml: 0.5-1.5g. The etching solution is prepared on-site and used immediately. The etching method is to wipe and etch at room temperature for 180-300s.

[0008] Preferably, the cooling method in step one is oil cooling or air cooling.

[0009] The characterization process for determining the microcrystalline grain size of martensitic stainless steel is as follows:

[0010] First, heat treatment experiments were conducted to verify the impact of different heat treatment methods on corrosion resistance.

[0011] Metallographic samples were cut and quenched and quenched + tempered heat treatments were performed on three materials, 1C12Ni3Mo2VN (M152), 1Cr11Ni2W2MoV, and 0Cr17Ni4Cu4Nb, respectively, at the temperatures specified in the corresponding technical standards.

[0012] Forged material samples that have undergone quenching, quenching and tempering, and no heat treatment were subjected to chemical corrosion and electrolytic corrosion tests with the same corrosion parameters. The corrosion effects under the same corrosion method were compared to determine the optimal heat treatment preparation method for different materials before corrosion.

[0013] Secondly, we conducted tests to improve the formulation of the corrosive agent and adjust the corrosion parameters to determine the optimal corrosive agent ratio and corrosion parameters.

[0014] The main components are sulfuric acid + water and CrO3 + water. Other components are added to optimize the corrosion effect. Electrolytic corrosion tests are carried out to explore the effects of electrolysis voltage and time on grain corrosion.

[0015] By changing the ratio, five chemical etchants that can corrode martensite were selected, and the corrosion parameters were adjusted according to the effect of grain corrosion.

[0016] Finally, corrosion verification tests were conducted to solidify the corrosion methods for different martensitic materials, and operating instructions were established.

[0017] The method for characterizing the micrograin size of martensitic stainless steel, through experimentation and verification, determined the etchant formulation and optimal corrosion method for martensitic stainless steel micrograin size. Compared to the original corrosion method, the corrosion effect is significantly improved, the grain size characterization is clearer, and the accuracy and repeatability of the rating are significantly enhanced. This invention allows the evaluation work to be completed in one heat treatment + one grinding and polishing corrosion process. The total evaluation time has been reduced from 31 hours of multiple heat treatment and corrosion tests to 6 hours: 3 hours for quenching + 3 hours for preparation corrosion observation. The grain size display effect after corrosion meets the conditions for comparative rating, and the reproducibility of the grain size rating value is controlled within ±0.5 level. Attached Figure Description

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0019] Figure 1 The microstructure of 1Cr11Ni2W2MoV after quenching is shown in the diagram.

[0020] Figure 2 Microstructure of 1Cr11Ni2W2MoV after quenching and tempering;

[0021] Figure 3 The microstructure of 1Cr11Ni2W2MoV in its unheated forged state is shown in the diagram.

[0022] Figure 4 This is a microstructure diagram of 0Cr17Ni4Cu4Nb after quenching;

[0023] Figure 5 Microstructure of 0Cr17Ni4Cu4Nb after quenching and tempering;

[0024] Figure 6 The microstructure of 0Cr17Ni4Cu4Nb in its unheated forged state is shown in the diagram.

[0025] Figure 7 The microstructure of 1Cr12Ni3Mo2VN (M152) after quenching is shown in the diagram.

[0026] Figure 8 Microstructure of 1Cr12Ni3Mo2VN (M152) after quenching and tempering;

[0027] Figure 9 The microstructure of 1Cr12Ni3Mo2VN (M152) in its unheated forged state is shown.

[0028] Figure 10 Microstructure after electrolytic etching of 1C12Ni3Mo2VN (M152) with 10% oxalic acid solution;

[0029] Figure 11 Microstructure after electrolytic corrosion of 1Cr11Ni2W2MoV with 10% oxalic acid solution;

[0030] Figure 12 Microstructure after electrolytic corrosion of 1C12Ni3Mo2VN (M152) with 4% chromic acid solution;

[0031] Figure 13 Microstructure after electrolytic corrosion of 1Cr11Ni2W2MoV by 4% chromic acid solution;

[0032] Figure 14 Microstructure after electrolytic corrosion of 1Cr11Ni2W2MoV by 10% sulfuric acid solution;

[0033] Figure 15 Microstructure after electrolytic corrosion of 1C12Ni3Mo2VN (M152) with 10% sulfuric acid solution;

[0034] Figure 16 Microstructure of martensitic stainless steel after wiping with HNO3 + ethanol for 300 seconds;

[0035] Figure 17 Microstructure of martensitic stainless steel after wiping with CuCl2 + ethanol + hydrochloric acid for 60 seconds;

[0036] Figure 18Microstructure of martensitic stainless steel after wiping with CuSO4 + ethanol + hydrochloric acid for 90 seconds.

[0037] Figure 19 Microstructure of martensitic stainless steel after wiping with CuSO4 + ethanol + hydrochloric acid + ethanol for 120 seconds;

[0038] Figure 20 Microstructure of martensitic stainless steel after wiping with CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate for 240 seconds;

[0039] Figure 21 Microstructure of martensitic stainless steel after wiping with CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate + ethanol for 240 seconds;

[0040] Figure 22 Microstructure of martensitic stainless steel after heating with concentrated sulfuric acid, potassium permanganate and water for 600 seconds;

[0041] Figure 23 Microstructure of martensitic stainless steel after heating with concentrated sulfuric acid, potassium permanganate, and water for 400 seconds followed by wiping for 200 seconds. Detailed Implementation

[0042] Example 1

[0043] ① Compare the effects of heat treatment on the microstructure of martensitic stainless steel:

[0044] Three materials, 1C12Ni3Mo2VN (M152), 1Cr11Ni2W2MoV, and 0Cr17Ni4Cu4Nb, were subjected to quenching and quenching + tempering heat treatments, respectively. After heat treatment, all three materials exhibited relatively fine acicular martensite structures. In the quenched material, grain boundary outlines were still faintly visible; while the quenched + tempered material primarily showed intragranular martensite bundles, with relatively indistinct grain boundaries; the untreated forged structure was similar to the quenched + tempered structure, with even less clearly defined grain boundaries. See Appendix for details. Figure 1-9 .

[0045] After subjecting martensitic stainless steel samples to "quenching" and "quenching + tempering" heat treatments respectively, the corrosion effect, from highest to lowest compared to the original forged state, was: "quenching" > "quenching + tempering" > original forged state. Therefore, the optimal treatment method for the samples is quenching, avoiding the time required for tempering and reheat treatment.

[0046] ② Compare the corrosion effects of electrolytic corrosion and chemical corrosion on martensitic stainless steel:

[0047] The microstructure of martensitic stainless steel was not fully revealed after electrolytic corrosion, making it unsuitable for grain-level corrosion. The microstructure of 1C12Ni3Mo2VN (M152) after electrolytic corrosion using a 10% oxalic acid solution and a 10V voltage for 120 seconds is shown in the attached diagram. Figure 10 The microstructure of 1Cr11Ni2W2MoV after electrolytic corrosion using a 10% oxalic acid solution and a 10V voltage applied for 120 seconds is shown in the attached diagram. Figure 11 The microstructure of 1C12Ni3Mo2VN (M152) after electrolytic etching using a 4% chromic acid solution and a 10V voltage applied for 120 seconds is shown in the attached diagram. Figure 12 The microstructure of 1Cr11Ni2W2MoV after electrolytic corrosion using a 4% chromic acid solution and a 10V voltage applied for 120 seconds is shown in the attached diagram. Figure 13 The microstructure of 1Cr11Ni2W2MoV after electrolytic corrosion using a 10% sulfuric acid solution and a 10V voltage applied for 120 seconds is shown in the attached diagram. Figure 14 The microstructure of 1C12Ni3Mo2VN (M152) after electrolytic corrosion using a 10% sulfuric acid solution and a 10V voltage applied for 120 seconds is shown in the attached diagram. Figure 15 .

[0048] Corrosion is achieved through appropriate chemical corrosion and corrosion parameters suitable for the grain size. For martensitic stainless steel, HNO3 + ethanol is used; after wiping for 300 seconds, the microstructure is shown in the attached diagram. Figure 16 For martensitic stainless steel, a solution of CuCl2 + ethanol + hydrochloric acid was used. After wiping for 60 seconds, the microstructure is shown in the attached diagram. Figure 17 For martensitic stainless steel, a solution of CuSO4 + ethanol + hydrochloric acid was used. After wiping for 90 seconds, the microstructure is shown in the attached diagram. Figure 18 For martensitic stainless steel, a solution of CuSO4 + two parts ethanol + hydrochloric acid was used. After wiping for 120 seconds, the microstructure is shown in the attached diagram. Figure 19 For martensitic stainless steel, a solution of CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate was used. After wiping for 240 seconds, the microstructure is shown in the attached diagram. Figure 20 For martensitic stainless steel, a solution of CuSO4 + two parts ethanol + hydrochloric acid + sodium alkylbenzene sulfonate was used. After wiping for 240 seconds, the microstructure is shown in the attached diagram. Figure 21 For martensitic stainless steel, a mixture of concentrated sulfuric acid, potassium permanganate, and water was heated for 600 seconds. See the attached diagram for the microstructure. Figure 22 For martensitic stainless steel, a mixture of concentrated sulfuric acid, potassium permanganate, and water was used. The mixture was heated for 400 seconds and then wiped for 200 seconds. See the attached diagram for the microstructure. Figure 23 The optimal corrosion method is to use CuSO4 + two parts ethanol + hydrochloric acid + sodium alkylbenzene sulfonate for chemical corrosion (ratio of 4g:80ml:20ml:0.5g), and the corrosion method is to wipe at room temperature for 240 seconds.

[0049] Corrosion tests determined that the optimal corrosion method for martensitic stainless steel is chemical corrosion using "CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate". This method can achieve good microstructure and grain size in a single corrosion process, avoiding repeated embedding, grinding, corrosion and observation.

[0050] Verification tests show that grain boundaries after heat treatment and corrosion in the above manner can be effectively identified and can be rated according to the comparative method in GB / T6394 "Method for Determination of Average Grain Size of Metals". The reproducibility of the grain size rating values ​​of the same batch of samples is controlled within ±0.5 grade.

[0051] Example 2

[0052] ① Heat treatment test of martensitic stainless steel specimens

[0053] Martensitic stainless steel samples were cut and subjected to quenching, quenching + tempering, and tempering heat treatments at temperatures specified in commonly used technical standards for three materials: 1Cr11Ni2W2MoV, 0Cr17Ni4Cu4Nb, and 1Cr12Ni3Mo2VN. The selected heat treatment regimes are shown in Table 1. The quenching holding time and tempering holding time were both 1 hour.

[0054]

[0055] Table 1

[0056] After heat treatment, the samples were ground into martensitic stainless steel samples. All samples were etched with Kalling etchant, and their microstructure was observed. The etching time was 30 seconds, and the magnification was 100 times.

[0057] After heat treatment, all three materials exhibited a relatively fine acicular martensite structure. In the directly quenched microstructure, grain boundary outlines were still faintly visible; while the microstructure after quenching and tempering primarily showed intragranular martensite bundles, with grain boundaries being relatively unclear; the untreated forged microstructure was similar to the quenched and tempered microstructure, with even less clear grain boundaries. Based on observation of the martensite bundles, no significant change in grain size was found before and after heat treatment.

[0058] Heat treatment test results

[0059] First, the grain boundaries are not clearly visible, and grain size is mainly determined by martensite bundle analysis.

[0060] Second, the relative grain boundary display effect: Quenched > Quenched + Tempered > Forged

[0061] Third, the grain size did not change significantly before and after heat treatment.

[0062] Based on the results of the heat treatment test, the grain boundaries of the sample that was only quenched were clearer than those of the sample that was quenched and tempered. It is recommended that, if the standard allows, the sample be quenched before the grain size rating of the martensite to create a better basis for the grain size rating.

[0063] ② Electrolytic corrosion test of martensitic stainless steel samples

[0064] Referring to the electrolytic corrosion test protocol in Table 2, corrosion tests were conducted on the "quenched" samples of the three materials using three different corrosive agents: oxalic acid solution, chromic acid solution, and sulfuric acid solution. The electrolysis equipment used was the Electromet 4 electropolishing machine from Böhler. The electrolysis voltage was 3V-10V, and the electrolysis time was 10s-120s.

[0065]

[0066] Table 2

[0067] Electrolysis of three types of martensitic stainless steel with a 10% oxalic acid solution at 3V, 5V, and 10V was performed. No significant changes were observed on the sample surface during the electrolysis process. The typical corrosion effect under maximum voltage and time conditions did not fully reveal the microstructure, indicating that this corrosive agent is unsuitable for corroding the grain size of martensitic stainless steel.

[0068] For 4% chromic acid solution, the electrolytic corrosion effect of chromic acid solution is slightly stronger than that of oxalic acid solution, but under the maximum design parameters, the microstructure is not fully displayed, and it is also not suitable for the corrosion of martensitic stainless steel grain size.

[0069] For a 10% sulfuric acid solution, electrolytic corrosion at 3V showed no significant changes. Changes appeared on the sample surface at 5V and 10V. At 10V and 180s, the microstructure was clearly visible, but grain boundaries were only locally displayed, and the clarity was insufficient for grain size assessment. Therefore, this etchant is unsuitable for etching martensitic stainless steel grains.

[0070] ③ Chemical corrosion test of martensitic stainless steel samples

[0071] The chemical corrosion test protocol is shown in Table 3. Chemical corrosion tests were conducted on the three materials respectively. The corrosives were HNO3 + ethanol, CuCl2 + ethanol + hydrochloric acid (Kalling corrosive), CuSO4 + ethanol + hydrochloric acid, CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate, and concentrated sulfuric acid + potassium permanganate + water. These five corrosives were used for the corrosion tests. The samples were selected in the "quenched" state.

[0072]

[0073] Table 3

[0074] For HNO3 + ethanol, the corrosion time is 30s-300s. The corrosion results show that this corrosive agent has difficulty corroding the microstructure of martensitic stainless steel; with prolonged corrosion time, only a slight change in the microstructure becomes apparent.

[0075] For CuCl2 + ethanol + hydrochloric acid, the corrosion time is 20-60 seconds. The corrosion results show that this corrosive agent preferentially corrodes the martensitic structure of martensitic stainless steel. With prolonged corrosion time, grain boundaries begin to appear, but are not completely visible. Further magnification using dark-field microscopy reveals a significant height difference between the grain boundaries and the grains after prolonged corrosion, thus making the grain boundaries visible. However, the strip-shaped martensitic needles within the grains also begin to corrode, indicating over-corrosion and interfering with the identification of grain boundaries.

[0076] For CuSO4+ethanol+hydrochloric acid / CuSO4+ethanol+hydrochloric acid+alkylbenzenesulfonate sodium salt, CuSO4+ethanol+hydrochloric acid, compared to CuCl2+ethanol+hydrochloric acid, exhibits slower corrosion and more uniform corrosion. Unlike CuCl2+ethanol+hydrochloric acid, which is more corrosive to certain strengthening phases and microstructures, such as the δ phase of high-temperature alloys, CuSO4+ethanol+hydrochloric acid is more suitable for the corrosion of martensite.

[0077] Three materials were etched using CuSO4 + ethanol + hydrochloric acid, with etching times ranging from 20 to 90 seconds. The etching results showed that this etchant had a similar effect on martensitic stainless steel as CuCl2 + ethanol + hydrochloric acid, with martensite being etched preferentially followed by grain boundaries, but with a relatively higher grain size clarity.

[0078] Experimental results demonstrated that CuSO4 + ethanol + hydrochloric acid had a good corrosion effect on martensite grains, but the revealed grain boundaries were still insufficient to accurately determine grain size. Slowing down the corrosion rate of the martensite needles should facilitate the full manifestation of grain size. Based on this analysis, improvements to the formulation were made, primarily through two approaches: increasing the ethanol content to reduce the corrosive agent concentration; and adding sodium alkylbenzene sulfonate, a surfactant found in detergents, as a corrosion inhibitor.

[0079] Improved experiments show that in the CuSO4 + ethanol + hydrochloric acid etching process, the addition of both ethanol and sodium alkylbenzene sulfonate as etchants helps to slow down the corrosion of martensitic structures and reveal grain boundaries. The optimal etchant ratio is to add both simultaneously and extend the wiping corrosion time, specifically: CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate: 4g + 80ml + 20ml + 0.5g, with the corrosion method being wiping at room temperature for 180-300 seconds. Sodium alkylbenzene sulfonate can be replaced with commercially available household detergent containing approximately 12% sodium alkylbenzene sulfonate, approximately 4ml. This etching method is effective for grain corrosion of martensitic stainless steel, and grain boundaries are generally revealed, making it suitable for grain size detection.

[0080] For the concentrated sulfuric acid + potassium permanganate + water solution, the first corrosion was carried out at room temperature, with a maximum corrosion time of 300 seconds. Observation revealed that the microstructure of all samples was not fully revealed, making it impossible to assess grain size. Given the slow speed of the first corrosion, the second corrosion was conducted under heating. The samples were immersed in the etching solution and heated to boiling. After 300 seconds of corrosion, surface corrosion began. Figure 20 The martensitic structure was fully displayed, but the grain boundaries were not complete. The samples were re-immersed in the etching solution for further etching, extending the etching time to 600 seconds. During the etching process, a large amount of corrosion products were observed on the surface. One group of samples was removed after 400 seconds of etching, the corrosion layer was wiped off, and etching continued. The other group of samples was etched continuously and then ultrasonically cleaned for 30 seconds. According to the etching results, the grain size of the samples that were re-treated after 400 seconds of etching was better than that of the samples that were etched continuously for 600 seconds. This indicates that removing the corrosion layer on the sample surface during the etching process is beneficial for uniform etching and the display of grain boundaries. Therefore, when using "concentrated sulfuric acid + potassium permanganate + water" as an etchant to etch martensitic stainless steel, it should be carried out under heating and for a longer time to display grain boundaries. Removing corrosion products midway will yield better results. The optimal etching method is "concentrated sulfuric acid + potassium permanganate + water: 10ml + 2.5g + 90ml", boiling for 400 seconds, then removing the sample, wiping off the corrosion layer, and continuing etching for 600 seconds.

[0081] Through testing and verification of chemical etchants, CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate at room temperature, and concentrated sulfuric acid + potassium permanganate + water at heated state, both showed good corrosion effects on the grain boundaries of martensitic stainless steel and can be used as etchants for grain size assessment. However, considering the complexity of the testing process, the latter requires the removal of surface corrosion products before observation, making the operation complex and resulting in higher pollution. Furthermore, potassium permanganate also faces chemical control issues and is recommended as an alternative.

[0082] ④ Verification test

[0083] Based on the above experimental results, the optimal heat treatment method for martensitic stainless steel is quenching, and the optimal corrosive agent is CuSO4 + ethanol + hydrochloric acid + sodium alkylbenzene sulfonate for chemical corrosion. The corrosion method is wiping at room temperature for 240 seconds. Three samples each of three materials—1Cr11Ni2W2MoV, 0Cr17Ni4Cu4Nb, and 1C12Ni3Mo2VN—were selected and subjected to quenching heat treatment in the same manner, followed by grinding, polishing, and corrosion. The corroded samples were observed under 100x magnification and compared with the standard rating chart.

[0084] After one corrosion test, almost all the grains of the three materials were exposed. The evaluation results of each group of samples were basically consistent. The reproducibility of the grain size rating value of the same batch was 0.5. The verification test plan is shown in Table 4.

[0085]

[0086] Table 4

[0087] Example 3

[0088] The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows:

[0089] Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it.

[0090] Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are as follows: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 3-4g: 80-100ml: 15-25ml: 0.5-1.5g. The etching solution is prepared on-site and used immediately. The etching method is to wipe and etch at room temperature for 180-300s.

[0091] The cooling method in step one is oil cooling or air cooling.

[0092] Example 4

[0093] The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows:

[0094] Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it.

[0095] Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 3g: 80ml: 15ml: 0.5g. The etching solution is prepared on-site and used immediately. The etching method is to wipe and etch at room temperature for 180-300s.

[0096] The cooling method in step one is oil cooling or air cooling.

[0097] Example 5

[0098] The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows:

[0099] Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it.

[0100] Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 4g: 100ml: 25ml: 1.5g. The etching solution is prepared on-site and used immediately. The etching method is to wipe and etch at room temperature for 180-300s.

[0101] The cooling method in step one is oil cooling or air cooling.

[0102] Example 6

[0103] The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows:

[0104] Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it.

[0105] Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 3.5g: 90ml: 20ml: 1g. The etching solution is prepared on-site and used immediately. The etching method is to wipe and etch at room temperature for 180-300s.

[0106] The cooling method in step one is oil cooling or air cooling.

Claims

1. A method for characterizing the microcrystalline grain size of martensitic stainless steel, characterized in that: The specific steps of the method for characterizing the microcrystalline grain size of the martensitic stainless steel are as follows: Step 1: Take a martensitic stainless steel sample and quench it for heat treatment. The condition is to hold it at 1050±10℃ for 1 hour, and then cool it. Step 2: After metallographic preparation of the quenched martensitic stainless steel sample, chemical etching is performed. The specific composition and ratio of the etching solution are as follows: CuSO4: ethanol: hydrochloric acid: sodium alkylbenzene sulfonate = 3-4g: 80-100ml: 15-25ml: 0.5-1.5g. The etching solution is prepared on-site and used immediately. The etching method is wiping etching at room temperature for 180-300s. The cooling method in Step 1 is oil cooling or air cooling.

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