A method for detecting grain size of P92 steel
By combining functional polishing fluid and electrochemical auxiliary methods, the problems of unclear grain boundary display and low efficiency in P92 steel grain size detection were solved, and rapid and accurate grain size assessment was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUZHOU JIKAISI TESTING SERVICE CO LTD
- Filing Date
- 2026-03-26
- Publication Date
- 2026-06-12
AI Technical Summary
Existing methods for detecting grain size in P92 steel cannot clearly display grain boundaries, have low detection efficiency, poor reagent applicability, and cannot meet the needs for rapid and accurate detection.
A functional polishing slurry combined with an electrochemical-assisted method was used to selectively erode grain boundaries and perform short-term polishing, allowing for microscopic observation of grain size.
It achieves clear display of grain boundaries at 100x magnification, improves detection efficiency by more than 50%, meets GB/T 6394 standard, and has good reproducibility.
Smart Images
Figure CN122192875A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of metal material testing technology, specifically to a method for detecting the grain size of P92 steel. Background Technology
[0002] P92 steel, a high-performance martensitic heat-resistant steel, possesses excellent high-temperature strength, oxidation resistance, and creep resistance, and is widely used in key components such as main steam pipes and headers of ultra-supercritical generator sets. Grain size, as a core indicator for evaluating the microstructure quality of P92 steel, directly affects its mechanical properties and service safety.
[0003] However, P92 steel contains various alloying elements such as Cr, Mo, W, V, and Nb, and its surface oxide film structure is dense, making it difficult for conventional corrosion reagents to effectively erode the grain boundaries. Currently used metal grain size corrosion methods, such as nitric acid-alcohol corrosion, are almost ineffective against P92 steel, only revealing the microstructure and failing to clearly show the grain boundaries. Some electrolytic corrosion methods, such as the one disclosed in patent CN110553892B, which describes an etching method suitable for T / P91 and T / P92 steels, can reveal grain boundaries to some extent, but they have the following technical drawbacks: after electrolytic corrosion, the grain boundaries are often covered with corrosion products or oxide films, resulting in blurred grain boundaries under low magnification microscopes. High magnification (above 500x) is required for observation and rating, leading to low detection efficiency.
[0004] Therefore, developing a detection method that can quickly and clearly display the grain boundaries of P92 steel and has good reproducibility is of great significance for ensuring the quality and safety of P92 steel components. Summary of the Invention
[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, the present invention aims to overcome the deficiencies of existing P92 steel grain size detection technologies, such as unclear grain boundary display, low detection efficiency, and poor reagent applicability. The invention provides a method for P92 steel grain size detection that can quickly and clearly display P92 steel grain boundaries, is applicable to P92 steel samples under different heat treatment conditions, and meets the requirements of GB / T 6394 standard for accurate grain size assessment.
[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A method for grain size detection in P92 steel includes the following steps: S1 Sample preparation: The P92 steel sample is polished until the surface is bright mirror-like and free of scratches. S2 Etching Treatment: The surface of the sample treated with S1 is etched with an etching agent to selectively erode the grain boundaries; S3 Grain Boundary Activation: The sample after S2 etching is placed in a functional polishing solution for short-term polishing treatment. The functional polishing solution contains deionized water, surfactant and complexing agent. A weak anodic current is applied during the polishing treatment to perform electrochemical assisted activation. S4 Microscopic observation and rating: The grain boundaries of the sample after S3 treatment are observed under a metallographic microscope and the grain size is rated.
[0007] Preferably, the S2 corrosion treatment is an electrolytic corrosion method or a cold immersion corrosion method.
[0008] Preferably, in the electrolytic corrosion, the corrosion reagent is an aqueous solution of an oxyacid, which is an aqueous solution of oxalic acid or sulfuric acid, with a mass-volume percentage concentration of 10%; the process parameters of the electrolytic corrosion are: voltage 12V, current 6A, and electrolysis time 30s to 60s.
[0009] Preferably, in the cold immersion corrosion, the corrosion reagent is a mixed acid aqueous solution, which is a hydrofluoric acid-nitric acid aqueous solution or a hydrochloric acid-nitric acid-ferric oxide aqueous solution.
[0010] Preferably, in the S3 grain boundary activation, the functional polishing solution contains a surfactant with a mass-volume percentage concentration of 0.5% to 2% and a complexing agent with a mass-volume percentage concentration of 0.1% to 1.0%.
[0011] Preferably, the surfactant is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or alkylphenol polyoxyethylene ether; and the complexing agent is at least one of citric acid, ethylenediaminetetraacetic acid, or tartaric acid.
[0012] Preferably, in the S3 grain boundary activation, the polishing pressure is 0.1MPa to 0.2MPa and the polishing time is 3s to 10s.
[0013] Preferably, in the S3 grain boundary activation, the voltage of the anolyte current is 0.5V to 1.0V, and the application time is 3s to 8s.
[0014] Preferably, in the S3 grain boundary activation, the functional polishing solution further includes a grain boundary sensitizer, which is sodium thiosulfate or thiourea, and its concentration in the functional polishing solution is 0.1 g / L to 0.5 g / L.
[0015] Furthermore, in the hydrofluoric acid-nitric acid aqueous solution, the volume ratio of hydrofluoric acid, nitric acid and deionized water is 4:4:96.
[0016] Furthermore, in the hydrochloric acid-nitric acid-ferric oxide aqueous solution, specifically, for every 100ml of deionized water, add 20ml of hydrochloric acid with a mass fraction of 37%, 5ml of nitric acid with a mass fraction of 65%, and 5g of ferric oxide.
[0017] (III) Beneficial Effects The purpose of this invention is to provide a method for detecting the grain size of P92 steel, which has the following beneficial effects: Firstly, the grain boundary display is highly clear: This invention, through the synergistic chemical and mechanical effects of the functional polishing fluid, not only removes surface corrosion products but also actively enhances grain boundary contrast. Experiments show that samples treated using this method can obtain clear and continuous grain boundary images at 100x magnification, with the grain boundaries appearing as deep black lines, exhibiting a significantly superior contrast compared to existing technologies.
[0018] Secondly, it can significantly improve detection efficiency: Since the rating can be directly observed at 100x magnification without switching to 500x high magnification or performing magnification conversion, the single detection time is shortened to 15-20 minutes, which is more than 50% more efficient than existing technologies, and is especially suitable for rapid detection of batch samples.
[0019] Finally, bright-field observation is sufficient: the samples treated by this invention have high grain boundary contrast and can be clearly identified under conventional bright-field illumination, without the need for dark-field illumination or special optical devices. This reduces the requirements for microscope equipment and facilitates widespread application in ordinary laboratories and on-site. Furthermore, due to the consistent and controllable chemical action of the functional polishing solution, combined with optimized process parameters, the test results obtained from different batches and by different operators show good reproducibility, meeting the standardized requirements for quality assessment. Attached Figure Description
[0020] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a metallographic photograph observed under a 100x microscope in Embodiment 1 of this application.
[0021] Figure 2 This is a metallographic photograph observed under a 100x microscope in Embodiment 2 of this application.
[0022] Figure 3 This is a metallographic photograph observed under a 100x microscope in Embodiment 3 of this application.
[0023] Figure 4 This is a metallographic photograph observed under a 100x microscope in Embodiment 4 of this application.
[0024] Figure 5 This is a metallographic photograph observed under a 100x microscope in Embodiment 5 of this application.
[0025] Figure 6 This is a metallographic photograph observed under a 100x microscope in Embodiment 6 of this application.
[0026] Figure 7 This is a metallographic photograph of Comparative Example 1 of this application, observed under a 100x microscope.
[0027] Figure 8 This is a metallographic photograph of Comparative Example 2 of this application, observed under a 100x microscope.
[0028] Figure 9 This is a metallographic photograph of Comparative Example 3 of this application, observed under a 100x microscope. Detailed Implementation
[0029] The following will refer to the appendix in the examples of this invention. Figures 1-9 The technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] Example 1: S1 Sample Preparation: Take a P92 steel sample and process it to a size of 10mm × 10mm × 5mm. Grind it sequentially with 400#, 800#, and 1200# silicon carbide sandpaper, then polish it with diamond polishing paste (1μm grit) until the surface is a bright, mirror-like finish without scratches. After polishing, rinse the sample with deionized water, dehydrate it with anhydrous ethanol, and dry it with cold air for later use.
[0031] S2 Corrosion Treatment: Weigh 10g of oxalic acid (analytical grade), add it to 90ml of deionized water, and stir until completely dissolved to obtain a 10% oxalic acid aqueous solution. Using the 10% oxalic acid aqueous solution as the electrolyte, clamp the sample onto the anode clamp of the electrolyzer, connect the graphite electrode to the cathode of the electrolyzer, and immerse it in the electrolyte. Set the electrolysis parameters: voltage 12V, current 6A. Start the electrolyzer and perform electrolytic corrosion for 45s. After electrolysis, quickly remove the sample and rinse the surface with deionized water to remove residual electrolyte.
[0032] S3 Grain boundary activation: Weigh 1g of sodium dodecylbenzenesulfonate and 0.5g of citric acid, add them to 100ml of deionized water, and stir until completely dissolved. The surfactant concentration is 1% by volume, and the complexing agent concentration is 0.5% by volume. A basic functional polishing solution is thus prepared. The sample was held in a polishing apparatus using a basic functional polishing slurry. The apparatus was connected to a weak DC power supply, with the anode connected to a graphite rod immersed in the polishing slurry. The surface of the sample to be observed was placed on a velvet polishing cloth soaked in the polishing slurry. Polishing was performed under a pressure of 0.15 MPa while simultaneously applying an anode voltage of 0.8 V for 5 seconds. The polishing cloth was kept moist during the polishing process. After polishing, the sample surface was immediately rinsed with plenty of deionized water, then dehydrated with anhydrous ethanol, and finally dried with cold air.
[0033] S4 Microscopic observation and grading: Place the dried sample under a metallographic microscope, such as... Figure 1 As shown, the grain boundary morphology was observed at 100x magnification. The results showed that the grain boundaries were clear and continuous, appearing as dark black lines, distributed in a complete network pattern, with the intragranular structure clearly discernible and extremely high contrast. The grain size was rated according to the comparative method specified in GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals". The grain size of the sample in this example was grade 6.0.
[0034] Example 2: S1 Sample preparation: Same as in Example 1.
[0035] S2 corrosion treatment: Measure 90 ml of deionized water, slowly add 10 ml of concentrated sulfuric acid (98% by mass, analytical grade) while stirring, and cool to room temperature to obtain a 10% sulfuric acid aqueous solution.
[0036] A 10% sulfuric acid aqueous solution was used as the electrolyte, the sample was the anode, and the graphite electrode was the cathode. The electrolysis parameters were set as follows: voltage 12V, current 6A, and electrolysis time 60s. After electrolysis, the sample surface was rinsed with deionized water.
[0037] S3 Grain boundary activation: Weigh 1g of sodium dodecylbenzenesulfonate and 0.5g of citric acid, add them to 100ml of deionized water, and stir until completely dissolved. The surfactant concentration is 1% by volume, and the complexing agent concentration is 0.5% by volume. A basic functional polishing solution is thus prepared. The sample was clamped onto the polishing apparatus using a basic functional polishing slurry. A weak DC power supply was connected to the anode, and a graphite rod was immersed in the polishing slurry at the cathode. Polishing was performed simultaneously at a pressure of 0.15 MPa and an anode voltage of 0.8 V for 5 seconds. After polishing, the sample was rinsed, dehydrated, and dried.
[0038] S4 Microscopic observation and rating: such as Figure 2 As shown, at 100x magnification, the grain boundaries are clear and continuous with good contrast, and the rating is 6.5.
[0039] Example 3: S1 Sample preparation: Same as in Example 1.
[0040] S2 Corrosion treatment: Same as step S2 in Example 1, electrolysis for 45 seconds.
[0041] S3 Grain Boundary Activation: A functional polishing slurry containing a sensitizer is used. Specifically, sodium thiosulfate is added to a basic functional polishing slurry to a concentration of 0.3 g / L, and the mixture is stirred and dissolved. Polishing is performed under a pressure of 0.15 MPa while applying an anodic voltage of 0.8 V for 5 seconds. After polishing, the mixture is rinsed, dehydrated, and dried.
[0042] S4 Microscopic observation and rating: such as Figure 3 As shown, at 100x magnification, the grain boundaries are clear and continuous with good contrast. The rating is 6.0.
[0043] Example 4: S1 Sample preparation: Same as in Example 1.
[0044] S2 Corrosion Treatment: Measure 96 ml of deionized water into a polytetrafluoroethylene beaker, add 4 ml of nitric acid (65% by mass, analytical grade) and 4 ml of hydrofluoric acid (40% by mass, analytical grade) in sequence, and mix them to obtain a hydrofluoric acid-nitric acid aqueous solution; Pour the prepared hydrofluoric acid-nitric acid aqueous solution into the polytetrafluoroethylene etching tank. Completely immerse the prepared sample in the etching solution and allow it to stand at room temperature for 75 seconds. After etching, remove the sample with plastic tweezers and immediately rinse the surface with plenty of deionized water.
[0045] S3 Grain Boundary Activation: Using the basic functional polishing slurry as described in Example 2, the sample was clamped on the polishing apparatus, connected to a weak DC power supply, with the anode connected to a graphite rod immersed in the polishing slurry. Polishing was performed at 0.15 MPa pressure while simultaneously applying an anode voltage of 0.8 V for 5 seconds. After polishing, the sample was immediately rinsed, dehydrated, and dried.
[0046] S4 Microscopic observation and rating: such as Figure 4 As shown, at 100x magnification, the grain boundaries are clear and continuous with good contrast, and the rating is 6.0.
[0047] Example 5: S1 Sample preparation: Same as in Example 1.
[0048] S2 Etching Treatment: Pour the prepared hydrochloric acid-nitric acid-ferric oxide aqueous solution into the glass etching tank. Completely immerse the prepared sample in the etching solution and allow it to stand at room temperature for 45 seconds. After etching, remove the sample and rinse the surface with plenty of deionized water.
[0049] S3 Grain Boundary Activation: Using a basic functional polishing slurry, polishing is performed under a pressure of 0.15 MPa while simultaneously applying an anodic voltage of 0.8 V for 5 seconds. After polishing, the grains are rinsed, dehydrated, and dried.
[0050] S4 Microscopic observation and rating: such as Figure 5 As shown, at 100x magnification, the grain boundaries are clear, and the rating is 6.0.
[0051] Example 6: S1 Sample preparation: Same as in Example 1.
[0052] S2 Corrosion treatment: Same as step S2 in Example 4, immersion for 75 seconds.
[0053] S3 Grain boundary activation: A functional polishing slurry containing a sensitizer is used. Polishing is performed at a pressure of 0.15 MPa while an anodic voltage of 0.8 V is applied for 5 seconds.
[0054] S4 Microscopic observation and rating: such as Figure 6 As shown, at 100x magnification, the grain boundaries are clear, the contrast is good, and the rating is 6.0.
[0055] Comparative Example 1: S1 Sample preparation: Same as in Example 1.
[0056] S2 corrosion treatment: Same as in Example 1 (10% oxalic acid, electrolysis for 45s).
[0057] S3 Polishing treatment: Deionized water is used instead of functional polishing liquid. Polishing is performed under a pressure of 0.15MPa while applying an anodic voltage of 0.8V for 5 seconds.
[0058] S4 Microscopic observation and rating: such as Figure 7 As shown, at 100x magnification, the grain boundaries are blurred, indicating that electrochemical assistance alone cannot effectively remove corrosion products, resulting in poor grain boundary visualization. A 500x magnification observation is required for recalculation and rating.
[0059] Comparative Example 2 S1 Sample preparation: Same as in Example 1.
[0060] S2 corrosion treatment: Same as in Example 1 (10% oxalic acid, electrolysis for 45s).
[0061] S3 Polishing treatment: Polishing with deionized water, 0.15MPa for 6s, without electrochemical assistance.
[0062] S4 Microscopic observation and rating: such as Figure 8 As shown, the grain boundaries are blurred when viewed at 100x magnification; a 500x magnification is required for recalculation and rating.
[0063] Comparative Example 3: Conventional Nitric Acid-Alcohol Etching Method S1 Sample preparation: Same as in Example 1.
[0064] S2 corrosion treatment: Prepare a 4% nitric acid alcohol solution (4 ml nitric acid + 96 ml anhydrous ethanol), immerse the sample in the solution, and etch for 20 seconds at room temperature.
[0065] S3 Microscopic observation: such as Figure 9 As shown, when observed at 100x and 500x magnification, the grain boundaries are completely indistinguishable, making it impossible to perform grain size rating.
[0066] As can be seen from the above, Examples 1-6, which adopt the complete technical solution of the present invention, all obtained clear grain boundaries at 100x magnification, which can be directly rated and have high detection efficiency; Comparative Example 1 lacks functional components, and although there is electrochemical assistance, the grain boundaries are still blurry; Comparative Example 2 lacks electrochemical assistance, and the clarity of the grain boundaries is reduced, indicating that electrochemical assistance has a significant enhancing effect on grain boundary activation; Comparative Example 3 cannot display grain boundaries at all by conventional methods.
[0067] The above comparison results fully demonstrate that the synergistic effect of the functional polishing liquid and electrochemical assistance of the present invention is the key to achieving clear display of grain boundaries in P92 steel. The two complement each other and are indispensable, and the overall effect far exceeds the simple addition of each feature.
[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for detecting grain size in P92 steel, characterized in that, Includes the following steps: S1 Sample Preparation: The P92 steel sample was polished until the surface was bright and free of scratches. S2 corrosion treatment: The surface of the sample after S1 treatment is corroded with a corrosion reagent to selectively erode the grain boundaries; S3 grain boundary activation: The sample after S2 etching is placed in a functional polishing solution for short-term polishing treatment. The functional polishing solution contains deionized water, surfactant and complexing agent. A weak anodic current is applied during the polishing treatment to perform electrochemical assisted activation. S4 Microscopic observation and rating: The grain boundaries of the sample after S3 treatment are observed under a metallographic microscope and the grain size is rated.
2. The method according to claim 1, characterized in that, The S2 corrosion treatment is either electrolytic corrosion or cold immersion corrosion.
3. The method for grain size detection of P92 steel according to claim 2, characterized in that, In the electrolytic corrosion, the corrosion reagent is an aqueous solution of an oxalic acid, which is an aqueous solution of oxalic acid or sulfuric acid, with a mass-volume percentage concentration of 10%. The process parameters for the electrolytic corrosion are: voltage 12V, current 6A, and electrolysis time 30s to 60s.
4. The method for grain size detection of P92 steel according to claim 2, characterized in that, In the cold immersion corrosion, the corrosion reagent is a mixed acid aqueous solution, which is either a hydrofluoric acid-nitric acid aqueous solution or a hydrochloric acid-nitric acid-ferric oxide aqueous solution.
5. The method for grain size detection of P92 steel according to claim 1, characterized in that, In the S3 grain boundary activation, the functional polishing slurry contains a surfactant with a mass-volume percentage concentration of 0.5% to 2% and a complexing agent with a mass-volume percentage concentration of 0.1% to 1.0%.
6. The method for grain size detection of P92 steel according to claim 5, characterized in that, The surfactant is at least one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, or alkylphenol polyoxyethylene ether; the complexing agent is at least one of citric acid, ethylenediaminetetraacetic acid, or tartaric acid.
7. The method for detecting grain size in P92 steel according to claim 1, characterized in that, In the S3 grain boundary activation process, the polishing pressure is 0.1 MPa to 0.2 MPa, and the polishing time is 3 s to 10 s.
8. The method for grain size detection of P92 steel according to claim 1, characterized in that, In the S3 grain boundary activation, the voltage of the anodic current is 0.5V to 1.0V, and the application time is 3s to 8s.
9. The method for detecting grain size in P92 steel according to claim 1, characterized in that, In the S3 grain boundary activation process, the functional polishing solution also contains a grain boundary sensitizer, which is sodium thiosulfate or thiourea, and its concentration in the functional polishing solution is 0.1 g / L to 0.5 g / L.