Electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel and application thereof

Abstract

The application discloses an electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel and application thereof, and belongs to the technical field of electrochemical machining and composite grinding machining. The electrolyte is composed of sodium nitrate, sodium gluconate and deionized water; the mass percentage content of sodium nitrate is 18.0%-22.0% based on the total mass of the electrolyte, the mass percentage content of sodium gluconate is 0.25%-1.00%, and the balance is deionized water. In the electrolyte, sodium nitrate serves as a main conductive salt, and sodium gluconate serves as a complexing and regulating additive for regulating the hydrolysis, deposition and suspension behavior of Fe, Cr and Mo metal ions in the anodic dissolution process of high-nitrogen martensitic stainless steel. The composite electrolyte is suitable for electrochemical grinding of Cronidur-30, 1.4108 or X30CrMoN15-1 high-nitrogen martensitic stainless steel, can reduce the hydrolysis and deposition of Fe, Cr, Mo and other anodic dissolution metal ions, reduce the turbidity of the electrolyte and the thickness of a porous surface layer, improve the stability of a machining current, and reduce the surface roughness after electrochemical grinding.

Description

Technical Field

[0001] This invention relates to an electrolyte and its application, particularly an electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel and its application, belonging to the field of electrochemical processing and composite grinding technology of metal materials. Background Technology

[0002] Cronidur-30 high-nitrogen martensitic stainless steel, also known as CRONIDUR® 30, typically corresponds to material number 1.4108 and steel grade X30CrMoN15-1. This type of high-nitrogen martensitic stainless steel exhibits high hardness, wear resistance, corrosion resistance, and dimensional stability, making it suitable for high-precision bearings, rolling elements, transmission components, and precision rotating parts. Due to its high content of Cr, Mo, and N elements, the material surface readily forms oxide films, hydroxide films, or chromium-containing passivation films in neutral nitrate electrolytes, exhibiting strong passivation and film-forming characteristics.

[0003] For complex curved surface parts such as bearing raceways of Cronidus-30 or similar high-nitrogen martensitic stainless steel, traditional grinding wheel grinding, while achieving material removal and surface shaping, is prone to problems such as rapid wheel wear, concentrated grinding heat, surface burns, microcracks, and low processing efficiency, making it difficult to consistently balance processing efficiency and surface integrity. Electrochemical grinding combines electrochemical anodic dissolution with mechanical grinding, reducing mechanical grinding load and improving the processing efficiency and surface quality of difficult-to-machine materials.

[0004] Electrolyte is a key factor affecting the stability and surface quality of electrochemical grinding. Sodium nitrate electrolyte is neutral, safe, and has good conductivity, making it commonly used in the electrochemical grinding of steel materials. However, when sodium nitrate electrolyte alone is used for the electrochemical grinding of Cronidus-30 or X30CrMoN15-1 high-nitrogen martensitic stainless steel, the Fe, Cr, and Mo metal ions generated by anolysine dissolution easily undergo hydrolysis reactions with OH⁻ generated in the machining gap, forming oxides, hydroxides, or flocculent precipitates. This leads to electrolyte turbidity, difficulty in removing machining products, reduced machining gap renewal capacity, thickening of the porous surface layer, and fluctuations in machining current. These phenomena affect the periodic removal effect of conductive abrasive grains on the surface layer and may lead to increased surface roughness after electrochemical grinding.

[0005] Therefore, for electrochemical grinding of Cronidus-30 or similar high-nitrogen martensitic stainless steel, it is necessary to provide a neutral composite electrolyte that can regulate the hydrolysis, deposition and suspension behavior of Fe, Cr and Mo metal ions while maintaining the conductivity and process safety of sodium nitrate, reduce the formation of flocculent precipitates and insoluble products, reduce the thickness of porous surface layers, improve the stability of processing current, and improve the surface quality after electrochemical grinding. Summary of the Invention

[0006] The purpose of this invention is to provide an electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel and its application. This addresses the problems encountered when using a single sodium nitrate electrolyte in the electrochemical grinding of Cronidus-30 or X30CrMoN15-1 high-nitrogen martensitic stainless steel, such as excessive metal ion hydrolysis precipitation, thick porous surface layer buildup, insufficient processing current stability, and high surface roughness after processing.

[0007] The technical solution of the present invention is an electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, wherein the electrolyte is composed of sodium nitrate, sodium gluconate and deionized water; based on the total mass of the electrolyte, the mass percentage content of sodium nitrate is 18.0% to 22.0%, the mass percentage content of sodium gluconate is 0.25% to 1.00%, and the balance is deionized water.

[0008] In the aforementioned electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, the electrolyte contains 20.0% sodium nitrate, 0.5% sodium gluconate, and 79.5% deionized water by mass.

[0009] The application of an electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, wherein sodium nitrate is used as the main conductive salt and sodium gluconate is used as a complexing and regulating additive to regulate the hydrolysis, deposition and suspension behavior of Fe, Cr and Mo metal ions during the anodic dissolution of high-nitrogen martensitic stainless steel.

[0010] In the aforementioned application of electrolytes for electrochemical grinding of high-nitrogen martensitic stainless steel, the high-nitrogen martensitic stainless steel includes Cronidur-30 high-nitrogen martensitic stainless steel, CRONIDUR® 30 high-nitrogen martensitic stainless steel, material number 1.4108 high-nitrogen martensitic stainless steel, or steel number X30CrMoN15-1 high-nitrogen martensitic stainless steel; the application objects include bearing raceways, bearing raceways, rolling elements, transmission parts, or precision rotating parts.

[0011] In the aforementioned application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, the grinding process specifically includes the following steps:

[0012] (1) Connect the high-nitrogen martensitic stainless steel workpiece to the positive terminal of the DC power supply so that it serves as the anode;

[0013] (2) Connect the conductive grinding wheel or conductive grinding tool to the negative terminal of the DC power supply so that it acts as the cathode;

[0014] (3) Continuously supply electrolyte to the machining gap between the workpiece and the conductive grinding wheel or conductive grinding tool;

[0015] (4) Under the action of an applied voltage, the surface of the workpiece undergoes anodic dissolution and forms oxides, hydroxides or porous surface layers;

[0016] (5) The oxides, hydroxides or porous surface layers are removed by the abrasive grains of conductive grinding wheels or conductive grinding tools, so that the fresh metal surface can continue to participate in anodic dissolution, thereby realizing the electrochemical grinding process of high nitrogen martensitic stainless steel.

[0017] In the aforementioned application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, the applied voltage is 5–30 V; the machining gap is 0.10–0.50 mm; the electrolyte temperature is 25–35 °C; and the conductive grinding wheel is a metal-bonded diamond grinding wheel, a metal-based conductive grinding wheel, or a grinding tool with a conductive substrate.

[0018] In the aforementioned application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, the applied voltage is 10–20 V.

[0019] The beneficial effects of this invention are as follows: Compared with a single sodium nitrate electrolyte, this invention has the following beneficial effects:

[0020] (1) The present invention uses sodium nitrate as the main conductive salt and the electrolyte is a neutral nitrate system, which avoids strong acid, strong alkali or chloride electrolyte from causing strong corrosion to machine tools, fixtures, pipelines and conductive grinding wheels, and has good process safety and equipment adaptability.

[0021] (2) In this invention, 0.25 wt.% to 1.00 wt.% sodium gluconate is added to the sodium nitrate electrolyte, which can regulate the hydrolysis, deposition and suspension behavior of metal ions such as Fe, Cr and Mo dissolved from the anode, reduce flocculent precipitates and insoluble products in the electrolyte after processing, and reduce the turbidity of the electrolyte.

[0022] (3) The present invention can regulate the formation of oxides, hydroxides or porous surface layers on the surface of high-nitrogen martensitic stainless steel, reduce the thickness of porous surface layers, make the surface layers thinner and more uniform, which is beneficial to the periodic removal of the surface layer by conductive grinding wheel abrasive grains.

[0023] (4) The present invention can improve the electrolyte renewal state in the processing gap, reduce the current attenuation or fluctuation caused by precipitate accumulation, excessive film thickness and local conductivity changes, and improve the stability of the processing process.

[0024] (5) The present invention can reduce the surface roughness of high nitrogen martensitic stainless steel Cronidur-30 or X30CrMoN15-1 after electrochemical grinding, and improve the processing quality of bearing grooves, bearing raceways and precision rotating surfaces. Attached Figure Description

[0025] Figure 1 Open circuit potential curves of Cronidur-30 high-nitrogen martensitic stainless steel in different electrolytes;

[0026] Figure 2 The anodic polarization curves of Cronidur-30 high-nitrogen martensitic stainless steel in different electrolytes;

[0027] Figure 3 Electrochemical impedance spectroscopy of Cronidur-30 high-nitrogen martensitic stainless steel in different electrolytes;

[0028] Figure 4 Comparison of porous surface layer thickness and surface roughness of Cronidur-30 in different electrolytes under processing voltages of 5 V, 10 V and 20 V (a1) NaGlu 0.5 Electrolyte 5V, (a2) NaGlu 0.5 Electrolyte 10 V and (a3)NaGlu 0.5 (b1) NaNO3 electrolyte 20 V; (b2) NaNO3 electrolyte 5 V; (b3) NaNO3 electrolyte 10 V; and (b4) NaNO3 electrolyte 20 V.

[0029] Figure 5 Comparison of electrolyte precipitate states after processing with different electrolytes (a) NaGlu 0.5 Electrolyte, (b) NaNO3 electrolyte);

[0030] Figure 6 Comparison of ICP-OES of electrolytes after processing with different electrolytes;

[0031] Figure 7 The current-time curves of Cronidur-30 electrochemical grinding process in different electrolytes at 20V are shown.

[0032] Figure 8 NaGlu 0.5 Comparison of surface morphology and surface roughness after electrochemical grinding with Cronidur-30 in electrolyte at 20V;

[0033] Figure 9 Comparison of surface morphology and surface roughness after electrochemical grinding with Cronidur-30 in NaNO3 electrolyte at 20V. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0035] Example 1 of the present invention: Taking the preparation of 1000 g of composite electrolyte as an example, 200.0 g of sodium nitrate, 5.0 g of sodium gluconate and 795.0 g of deionized water were weighed. During preparation, sodium nitrate was first added to part of the deionized water and stirred until completely dissolved, then sodium gluconate was added and stirred until completely dissolved, and finally deionized water was added to bring the total mass to 1000 g, resulting in a 20.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate composite electrolyte.

[0036] Example 2 of the present invention: Taking the preparation of 1000 g of composite electrolyte as an example, 180.0 g of sodium nitrate, 10.0 g of sodium gluconate and 810.0 g of deionized water were weighed. During preparation, sodium nitrate was first added to part of the deionized water and stirred until completely dissolved, then sodium gluconate was added and stirred until completely dissolved, and finally deionized water was added to bring the total mass to 1000 g, resulting in a 18.0 wt.% sodium nitrate + 1.00 wt.% sodium gluconate composite electrolyte.

[0037] Example 3 of the present invention: Taking the preparation of 1000 g of composite electrolyte as an example, 220.0 g of sodium nitrate, 2.5 g of sodium gluconate and 777.5 g of deionized water were weighed. During preparation, sodium nitrate was first added to part of the deionized water and stirred until completely dissolved, then sodium gluconate was added and stirred until completely dissolved, and finally deionized water was added to bring the total mass to 1000 g, resulting in a 22.0 wt.% sodium nitrate + 0.25 wt.% sodium gluconate composite electrolyte.

[0038] Example 4 of the present invention: Taking the preparation of 1000 g of composite electrolyte as an example, 190.0 g of sodium nitrate, 5.0 g of sodium gluconate and 805.0 g of deionized water were weighed. During preparation, sodium nitrate was first added to part of the deionized water and stirred until completely dissolved, then sodium gluconate was added and stirred until completely dissolved, and finally deionized water was added to bring the total mass to 1000 g, resulting in a 19.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate composite electrolyte.

[0039] Example 5 of the present invention: Taking the preparation of 1000 g of composite electrolyte as an example, 210.0 g of sodium nitrate, 7.5 g of sodium gluconate and 782.5 g of deionized water were weighed. During preparation, sodium nitrate was first added to part of the deionized water and stirred until completely dissolved, then sodium gluconate was added and stirred until completely dissolved, and finally deionized water was added to bring the total mass to 1000 g, resulting in a 21.0 wt.% sodium nitrate + 0.75 wt.% sodium gluconate composite electrolyte.

[0040] Example 6 of the present invention: The present invention also claims protection for the application of the electrolyte prepared in the above examples in the electrochemical grinding process of high-nitrogen martensitic stainless steel. During the grinding process, sodium nitrate in the electrolyte serves as the main conductive salt, providing a neutral nitrate conductive environment; sodium gluconate serves as a complexing and regulating additive, used to regulate the hydrolysis, deposition, and suspension behavior of metal ions such as Fe, Cr, and Mo during the anodic dissolution of high-nitrogen martensitic stainless steel, reducing the formation of insoluble hydrolysis products and flocculent precipitates, and regulating the formation state of oxides, hydroxides, or porous surface layers. The electrolytes of the present invention do not contain strong acids, strong bases, or chloride conductive salts.

[0041] The high-nitrogen martensitic stainless steel includes Cronidur-30 high-nitrogen martensitic stainless steel, CRONIDUR® 30 high-nitrogen martensitic stainless steel, material number 1.4108 high-nitrogen martensitic stainless steel, or steel number X30CrMoN15-1 high-nitrogen martensitic stainless steel; the applications include bearing raceways, bearing raceways, rolling elements, transmission parts, or precision rotating parts.

[0042] The electrochemical grinding process for high-nitrogen martensitic stainless steel includes the following steps:

[0043] (1) Connect the high-nitrogen martensitic stainless steel workpiece to the positive terminal of the DC power supply so that it serves as the anode;

[0044] (2) Connect the conductive grinding wheel or conductive grinding tool to the negative terminal of the DC power supply so that it acts as the cathode;

[0045] (3) Continuously supply electrolyte at 25-35 °C to the machining gap (0.10-0.50 mm) between the workpiece and the conductive grinding wheel or conductive grinding tool;

[0046] (4) Under the action of an applied voltage (the applied voltage is 5 to 30 V, preferably 10 to 20 V), the surface of the workpiece undergoes anodic dissolution and forms oxides, hydroxides or porous surface layers;

[0047] (5) The oxides, hydroxides or porous surface layers are removed by the abrasive grains of conductive grinding wheels or conductive grinding tools, so that the fresh metal surface can continue to participate in anodic dissolution, thereby realizing the electrochemical grinding process of high nitrogen martensitic stainless steel.

[0048] The conductive grinding wheel is a metal-bonded diamond grinding wheel, a metal-based conductive grinding wheel, or a grinding tool with a conductive substrate.

[0049] The electrolyte of this invention is mainly used to reduce flocculent precipitates and insoluble products in the electrolyte after processing, and to reduce the thickness of oxides, hydroxides or porous surface layers formed during processing; it is also used to improve the stability of processing current and to reduce the surface roughness after electrochemical grinding.

[0050] To verify the performance of the method and electrolyte of the present invention, the following experiments were conducted.

[0051] Experiment 1: Preparation of Composite Electrolyte and Evaluation of Interfacial Electrochemical Response

[0052] Taking the preparation of 1000 g of composite electrolyte as an example, weigh 200.0 g of sodium nitrate, 5.0 g of sodium gluconate, and 795.0 g of deionized water. During preparation, first add sodium nitrate to a portion of the deionized water and stir until completely dissolved. Then add sodium gluconate and continue stirring until completely dissolved. Finally, add deionized water to bring the total mass to 1000 g, resulting in a 20.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate composite electrolyte.

[0053] To evaluate the effect of sodium gluconate content on the interfacial electrochemical response of Cronidur-30, the following four electrolytes were used:

[0054] Comparative Example 1: 20.0 wt.% sodium nitrate aqueous solution, with the balance being deionized water;

[0055] Experimental Example 1-1: 20.0 wt.% sodium nitrate + 0.25 wt.% sodium gluconate aqueous solution, with the remainder being deionized water;

[0056] Experimental Example 1-2: 20.0 wt.% sodium nitrate + 0.50 wt.% sodium gluconate aqueous solution, with the remainder being deionized water;

[0057] Experimental Examples 1-3: 20.0 wt.% sodium nitrate + 1.00 wt.% sodium gluconate aqueous solution, with the remainder being deionized water.

[0058] For ease of description, the four electrolytes mentioned above will be referred to as NaNO3, NaGlu, etc. 0.25 NaGlu 0.5 And NaGlu1.

[0059] The interfacial electrochemical response of Cronidur-30 high-nitrogen martensitic stainless steel in different electrolytes was evaluated using a three-electrode electrochemical testing system. During testing, the Cronidur-30 sample was used as the working electrode, a platinum sheet as the auxiliary electrode, and an Ag / AgCl electrode as the reference electrode. The electrolyte temperature was controlled at 30 ± 1 °C. The electrolytes used were NaNO3 and NaGlu. 0.25 NaGlu 0.5 And NaGlu1.

[0060] First, an open-circuit potential test was performed for 3 hours. The results showed that Cronidur-30 reacted with NaNO3 and NaGlu. 0.25NaGlu 0.5 The stable open-circuit potentials in NaGlu1 electrolyte were approximately -142 mV, -116 mV, -95 mV, and -85 mV, respectively. Compared to sodium nitrate electrolyte alone, the addition of sodium gluconate resulted in a positive shift in the open-circuit potential of Cronidar-30, indicating that sodium gluconate can alter the interfacial stability of Cronidar-30 in the nitrate system. Figure 1 As shown.

[0061] Subsequently, anodic polarization tests were performed, with a scan potential range of -1.0 V to 3.0 V and a scan rate of 10 mV / min. The results showed that Cronidur-30 reacted with NaNO3 and NaGlu... 0.25 NaGlu 0.5 The corrosion potentials in NaGlu1 electrolyte were approximately -0.519 V, -0.487 V, -0.472 V, and -0.429 V, respectively. After the addition of sodium gluconate, the corrosion potential shifted positively, and the passivation-overpassivation response and anodic dissolution behavior changed, indicating that sodium gluconate can regulate the anodic electrochemical behavior of Cronidur-30 in the nitrate system. Figure 2 As shown.

[0062] Further electrochemical impedance spectroscopy was performed. Pre-polarization was applied at 0.5 V and 3.0 V (vs. Ag / AgCl) before testing. The test frequency range was 100 kHz to 10 mHz, and the perturbation voltage was 5 mV. The results showed that the addition of sodium gluconate altered the interfacial film response and charge transfer process of Cronidar-30 in the nitrate system, indicating that sodium gluconate can influence the formation and evolution of surface oxides, hydroxides, or passivation films. Figure 3 As shown.

[0063] Based on the combined results of open circuit potential, anodic polarization, electrochemical impedance spectroscopy, and comparisons of subsequent processing deposits, porous surface layer thickness, processing current stability, and post-processing surface roughness, a composite electrolyte of 20.0 wt.% sodium nitrate + 0.50 wt.% sodium gluconate is preferred for electrochemical grinding of Cronidur-30 high-nitrogen martensitic stainless steel.

[0064] Experiment 2: Comparison of porous surface layer thickness and surface roughness under different processing voltages

[0065] Electrochemical processing of Cronidus-30 high-nitrogen martensitic stainless steel was compared using a 20.0 wt.% sodium nitrate aqueous solution and a composite electrolyte of 20.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate.

[0066] During processing, the Cronidus-30 sample was used as the anode, and the metal tool electrode as the cathode. Electrolyte was continuously supplied to the processing gap. The processing voltages were 5 V, 10 V, and 20 V, the processing time was 60 s, the processing gap was 0.5 mm, the electrolyte temperature was 30 ± 1 ℃, and the electrolyte flow rate was 6 L / min. The 5 V, 10 V, and 20 V values ​​are the two-electrode electrochemical processing voltages used to evaluate the effect of the composite electrolyte on the formation of the porous surface layer and the regulation of surface roughness under electrochemical processing conditions. After processing, the thickness of the porous surface layer and the surface roughness Ra were measured. Detailed data are shown in Table 1, and the corresponding morphologies are as follows: Figure 4 As shown.

[0067] Table 1 Comparison of Cronidur-30 porous surface layer thickness and surface roughness

[0068] Processing voltage / V NaNO3 porous surface layer thickness / μm NaGlu 0.5 Porous surface layer thickness / μm Thickness reduction rate / % NaNO3 surface roughness Ra / μm NaGlu 0.5 Surface roughness Ra / μm Ra decrease by % 5 52.48 42.96 18.1 1.273 1.182 7.1 10 106.1 92.67 12.7 1.596 1.467 8.1 20 151.6 134.1 11.5 1.846 1.665 9.8

[0069] The results above show that, under processing voltages of 5 V, 10 V, and 20 V, compared with a single sodium nitrate electrolyte, the thickness of the porous surface layer formed by the sodium nitrate-sodium gluconate composite electrolyte was reduced, and the surface roughness Ra was also reduced. This indicates that sodium gluconate can regulate the formation of oxides, hydroxides, or porous surface layers on the surface of Cronidus-30 high-nitrogen martensitic stainless steel, reducing excessive surface layer accumulation and surface roughening, resulting in a thinner surface layer, which is beneficial for subsequent abrasive removal by conductive grinding wheels.

[0070] Experiment 3: Comparison of electrolyte precipitates, turbidity, and metal element states after processing

[0071] Electrochemical processing was performed using a 20.0 wt.% sodium nitrate aqueous solution and a composite electrolyte of 20.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate at processing voltages of 5 V, 10 V, and 20 V for comparison. The processing time was 60 s, the processing gap was 0.5 mm, and the electrolyte temperature was 30 ± 1 ℃. The state of the electrolyte precipitate was observed after processing, and the turbidity and metal element content of the supernatant were determined for the combined electrolyte samples processed at 5 V, 10 V, and 20 V.

[0072] After processing with a single sodium nitrate electrolyte, the electrolyte became noticeably turbid and a brown precipitate appeared. This indicates that the Fe, Cr, Mo, and other metal ions produced by the dissolution of the Cronidus-30 anode undergo hydrolysis with OH⁻, forming insoluble oxides, hydroxides, or flocculent products. Figure 5 As shown.

[0073] After processing with a sodium nitrate-sodium gluconate composite electrolyte, the amount of flocculent precipitate and insoluble products in the electrolyte was significantly reduced, and the turbidity of the electrolyte was decreased. Sodium gluconate can play a complexation and regulation role in the hydrolysis, deposition, and suspension behavior of metal ions such as Fe, Cr, and Mo, thereby reducing the formation of precipitates and the accumulation of suspended products in the electrolyte after processing.

[0074] In one specific embodiment, the turbidity of the sodium nitrate electrolyte after processing was approximately 178.6 mg / L, while the turbidity of the sodium nitrate-sodium gluconate composite electrolyte after processing was approximately 46.2 mg / L, representing a turbidity reduction of approximately 74.1%. This result indicates that the addition of sodium gluconate can significantly reduce the turbidity of the processed electrolyte, thereby reducing hydrolysis precipitates and suspended products.

[0075] Further, ICP-OES was used to detect the metal elements in the supernatant of the processed electrolyte. In one specific embodiment, the concentrations of Fe, Cr, and Mo in the supernatant after processing with a single sodium nitrate electrolyte were approximately 241.65 mg / L, 22.33 mg / L, and 1.51 mg / L, respectively; while the concentrations of Fe, Cr, and Mo in the supernatant after processing with a sodium nitrate-sodium gluconate composite electrolyte were approximately 84.62 mg / L, 19.49 mg / L, and 1.42 mg / L, respectively. These results indicate that sodium gluconate can alter the hydrolysis, deposition, or suspension state of metal elements such as Fe, Cr, and Mo in the processed electrolyte, thereby reducing insoluble products and flocculent precipitates in the processed electrolyte. Figure 6 As shown.

[0076] Experiment 4: Comparison of machining current stability and surface roughness after electrochemical grinding

[0077] The current stability of Cronidur-30 high-nitrogen martensitic stainless steel during electrochemical grinding was compared using a 20.0 wt.% sodium nitrate aqueous solution and a 20.0 wt.% sodium nitrate + 0.5 wt.% sodium gluconate composite electrolyte under a processing voltage of 20 V and a processing time of 30 s. The current-time curves during the processing were recorded.

[0078] The results showed that, under the same processing conditions, the processing current decreased more rapidly in the sodium nitrate-only electrolyte, while the current decrease in the sodium nitrate-sodium gluconate composite electrolyte was more gradual. This phenomenon indicates that the accumulation of hydrolyzed precipitates, thickening of the porous surface layer, and changes in the conductivity state of the processing gap are more pronounced in the sodium nitrate-only system, which easily leads to the decay of the processing current. The addition of sodium gluconate, however, can reduce precipitate formation and regulate the surface layer structure, making the electrolyte renewal and interfacial reaction state within the processing gap more stable, thereby improving the stability of the processing current.

[0079] In one specific embodiment, under conditions of 20 V and 30 s, the current in the single sodium nitrate electrolyte decreased from approximately 40.7 A to approximately 35.3 A, a decrease of approximately 5.4 A; the current in the sodium nitrate-sodium gluconate composite electrolyte decreased from approximately 40.2 A to approximately 36.5 A, a decrease of approximately 3.7 A. Compared to the single sodium nitrate electrolyte, the reduced current decay in the composite electrolyte indicates its ability to improve processing stability. Figure 7 As shown.

[0080] Further comparisons were made using the two electrolytes mentioned above to electrochemically grind the raceways of Cronidur-30 high-nitrogen martensitic stainless steel bearings. During machining, the Cronidur-30 bearing workpiece served as the anode, and the conductive grinding wheel served as the cathode. The electrolyte was continuously supplied to the machining gap between the workpiece and the conductive grinding wheel. The applied voltage was 20 V, the machining time was 30 s, and the electrolyte temperature was 25–35 °C.

[0081] The surface roughness of the bearing raceway oxide layer was measured after machining, and the final surface roughness after grinding to remove the surface layer was also tested. The results showed that when using a single sodium nitrate electrolyte, the surface roughness Ra of the Cronidar-30 bearing raceway oxide layer was approximately 1.412 μm, and the Ra after grinding to remove the surface layer was approximately 0.329 μm. When using a sodium nitrate-sodium gluconate composite electrolyte, the surface roughness Ra of the Cronidar-30 bearing raceway oxide layer was approximately 1.122 μm, and the Ra after grinding to remove the surface layer was approximately 0.297 μm. Figure 8 and 9 As shown.

[0082] The above results indicate that the sodium nitrate-sodium gluconate composite electrolyte not only improves the surface condition during the electrochemical film formation stage but also reduces the final surface roughness after grinding to remove the surface layer. This demonstrates that sodium gluconate improves the surface quality of Cronidar-30 high-nitrogen martensitic stainless steel after electrochemical grinding by reducing Fe, Cr, and Mo hydrolysis precipitation, decreasing the thickness of the porous surface layer, improving the stability of the processing current, and enhancing the abrasive film removal state.

[0083] Industrial applicability

[0084] The sodium nitrate-sodium gluconate composite electrolyte of this invention uses readily available raw materials, is simple to prepare, and has a mild system. It is free of strong acids, strong alkalis, and chloride conductive salts, making it suitable for cyclic supply in electrochemical grinding equipment. This composite electrolyte can reduce Fe, Cr, and Mo hydrolysis precipitates during the electrochemical grinding of Cronidus-30 or X30CrMoN15-1 high-nitrogen martensitic stainless steel, decrease the thickness of the porous surface layer, stabilize the processing current, and reduce the surface roughness after electrochemical grinding. It is suitable for the electrochemical grinding of high-performance bearing raceways, bearing raceways, rolling elements, transmission parts, and precision rotating parts, and has good prospects for industrial application.

Claims

1. An electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel, characterized in that: The electrolyte is composed of sodium nitrate, sodium gluconate and deionized water; based on the total mass of the electrolyte, the mass percentage content of sodium nitrate is 18.0% to 22.0%, the mass percentage content of sodium gluconate is 0.25% to 1.00%, and the balance is deionized water.

2. The electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel according to claim 1, characterized in that: The electrolyte contains 20.0% sodium nitrate, 0.5% sodium gluconate, and 79.5% deionized water by mass.

3. The application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel as described in any one of claims 1-2, characterized in that: In the electrolyte, sodium nitrate serves as the main conductive salt, and sodium gluconate serves as a complexing and regulating additive, used to regulate the hydrolysis, deposition, and suspension behavior of Fe, Cr, and Mo metal ions during the dissolution of high-nitrogen martensitic stainless steel anodes.

4. The application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel according to claim 3, characterized in that: The high-nitrogen martensitic stainless steel includes Cronidur-30 high-nitrogen martensitic stainless steel, CRONIDUR® 30 high-nitrogen martensitic stainless steel, material number 1.4108 high-nitrogen martensitic stainless steel, or steel number X30CrMoN15-1 high-nitrogen martensitic stainless steel; the applications include bearing raceways, bearing raceways, rolling elements, transmission parts, or precision rotating parts.

5. The application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel according to claim 3, characterized in that: The grinding process specifically includes the following steps: (1) Connect the high-nitrogen martensitic stainless steel workpiece to the positive terminal of the DC power supply so that it serves as the anode; (2) Connect the conductive grinding wheel or conductive grinding tool to the negative terminal of the DC power supply so that it acts as the cathode; (3) Continuously supply electrolyte to the machining gap between the workpiece and the conductive grinding wheel or conductive grinding tool; (4) Under the action of an applied voltage, the surface of the workpiece undergoes anodic dissolution and forms oxides, hydroxides or porous surface layers; (5) The oxides, hydroxides or porous surface layers are removed by the abrasive grains of conductive grinding wheels or conductive grinding tools, so that the fresh metal surface can continue to participate in anodic dissolution, thereby realizing the electrochemical grinding process of high nitrogen martensitic stainless steel.

6. The application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel according to claim 5, characterized in that: The applied voltage is 5–30 V; the machining gap is 0.10–0.50 mm; the electrolyte temperature is 25–35 °C; and the conductive grinding wheel is a metal-bonded diamond grinding wheel, a metal-based conductive grinding wheel, or a grinding tool with a conductive substrate.

7. The application of the electrolyte for electrochemical grinding of high-nitrogen martensitic stainless steel according to claim 6, characterized in that: The applied voltage is 10–20 V.

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