Corrosion-resistant non-oriented electrical steel as well as preparation method and application thereof

Abstract

The invention relates to corrosion-resistant non-oriented electrical steel as well as a preparation method and application thereof, and belongs to the technical field of alloys. The preparation method of the corrosion-resistant non-oriented electrical steel comprises the following steps: S1, in a three-electrode system, taking the non-oriented electrical steel as an anode, immersing the non-oriented electrical steel into a composite electrolyte, and applying a constant potential for passivating treatment; the composite electrolyte comprises phosphate, silicate, a silane coupling agent and nano boron nitride; s2, the non-oriented electrical steel subjected to passivation treatment is placed in a nano SiO2 aqueous solution for hole sealing treatment; and S3, the non-oriented electrical steel subjected to hole sealing treatment is subjected to annealing treatment in the inert gas atmosphere at 400-500 DEG C, and the corrosion-resistant non-oriented electrical steel is obtained. According to the preparation method, a uniform and compact passivation film can be formed on the surface of the non-oriented electrical steel, so that the corrosion resistance, the insulating property and the oxidation resistance of the non-oriented electrical steel are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloys, in particular to a corrosion-resistant non-oriented electrical steel and a preparation method and application thereof. BACKGROUND

[0002] The corrosion resistance of non-oriented electrical steel is one of the key factors affecting its application in electrical equipment such as motors and generators. At present, the existing technology mainly forms a protective film layer on the surface of the non-oriented electrical steel to improve its corrosion resistance. For example, a phosphating film is formed on the surface of the non-oriented electrical steel by using a treatment liquid composed of phosphoric acid, zinc salt, fluoride and surfactant to improve its corrosion resistance, or a siliconizing film is formed on the surface of the non-oriented electrical steel by using argon and silane mixed gas to improve its corrosion resistance. However, in actual application, the uniformity and stability of the phosphating film formed by traditional phosphating treatment are poor, and the wear resistance and compactness of the siliconizing film formed by traditional siliconizing treatment are poor, resulting in limited improvement in the corrosion resistance of the non-oriented electrical steel. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provide a corrosion-resistant non-oriented electrical steel and a preparation method and application thereof.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0005] In a first aspect, the present application provides a preparation method of a corrosion-resistant non-oriented electrical steel, which comprises the following steps:

[0006] S1. In a three-electrode system, taking the non-oriented electrical steel as the anode, immersing it in a composite electrolyte to apply a constant potential for passivation treatment; the composite electrolyte comprises phosphate, silicate, silane coupling agent and nano boron nitride;

[0007] S2. Placing the passivated non-oriented electrical steel in a nano-SiO2 aqueous solution for sealing treatment;

[0008] S3. Annealing the sealing-treated non-oriented electrical steel in an inert gas atmosphere at 400-500℃ (for example, any one of 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃ or a range value of any two thereof) to obtain a corrosion-resistant non-oriented electrical steel.

[0009] The application takes phosphate, silicate, silane coupling agent and nano boron nitride as the key components of the composite electrolyte, and forms a passivation film on the surface of the non-oriented electrical steel by combining with electrochemical passivation treatment. Phosphate is used to construct a dense and stable inner barrier on the surface of the non-oriented electrical steel, and silicate can be complementary with the subsequent SiO2 sol to form a multilayer gradient structure. The silane coupling agent can hydrolyze to generate -Si(OH)3 in the composite electrolyte, which can bond with the hydroxyl or oxide on the surface of the non-oriented electrical steel to form Fe-O-Si bond to improve the adhesion between the passivation film layer and the non-oriented electrical steel substrate. Meanwhile, -Si(OH)3 can also undergo polycondensation in the passivation film layer to construct Si-O-Si network to densify the phosphate / silicate skeleton to reduce the porosity of the passivation film. In addition, the high thermal conductivity and excellent oxidation resistance of nano boron nitride are used to reduce the local overheating ablation of the passivation film during the subsequent annealing process, to promote the full solidification of the Si-P-BN composite network in the passivation film during the annealing process, and to promote the heat dissipation of the core and reduce the thermal stress cracks, to avoid thermal oxidation, stress cracking and degradation of the substrate magnetic properties, thereby improving the corrosion resistance, insulation performance and oxidation resistance of the non-oriented electrical steel.

[0010] It should be noted that the phosphate in the above-mentioned composite electrolyte includes but is not limited to sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium dihydrogen phosphate dihydrate (NaH2PO4·2H2O), etc., and is preferably NaH2PO4·2H2O; the silicate includes but is not limited to potassium silicate, sodium silicate, sodium metasilicate (Na2SiO2), etc., and is preferably Na2SiO2; the silane coupling agent includes but is not limited to 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, etc., and is preferably 3-aminopropyltriethoxysilane. The above-mentioned nano SiO2 aqueous solution refers to a colloidal solution in which nano-sized silicon dioxide particles are dispersed in water, i.e. a dispersion of water-phase silicon dioxide nanoparticles.

[0011] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel according to the application, the concentration of the phosphate in the composite electrolyte is 50-80 g / L, which can be any one of 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L or a range value of any two thereof. It is found that by adjusting the concentration of the phosphate in the composite electrolyte within the above range, not only the excessive dissolution of the anode can be inhibited, but also the rapid formation of the dense film layer on the surface of the non-oriented electrical steel can be maintained.

[0012] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the concentration of silicate in the composite electrolyte is 20-40 g / L, for example, any one of 20 g / L, 23 g / L, 25 g / L, 28 g / L, 30 g / L, 33 g / L, 35 g / L, 38 g / L, 40 g / L or a range value of any two of them.

[0013] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the pH value of the composite electrolyte is 5-6.5, for example, any one of 5, 5.3, 5.5, 5.7, 6, 6.3, 6.5 or a range value of any two of them.

[0014] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the temperature of the composite electrolyte is 25-35℃, for example, any one of 25℃, 26℃, 27℃, 28℃, 29℃, 30℃, 31℃, 32℃, 33℃, 34℃, 35℃ or a range value of any two of them.

[0015] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the annealing treatment time is 30-60 min, for example, any one of 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or a range value of any two of them.

[0016] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the mass percentage of nano-boron nitride is 3%-5% based on the total mass of the composite electrolyte, for example, any one of 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.7%, 5% or a range value of any two of them. By adjusting the mass percentage of nano-boron nitride within the above range, the nano-boron nitride can be better filled in the micropores and cracks of the passivation film, thereby significantly reducing the porosity of the passivation film layer and prolonging the diffusion path of the corrosion medium, thereby improving the corrosion resistance life of the non-oriented electrical steel.

[0017] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the composite electrolyte in step S1 further comprises cerium nitrate (Ce(NO3)3) and boric acid (H3BO3).

[0018] It is found that when the composite electrolyte contains cerium nitrate, the structure and performance of the passivation film can be better optimized, thereby enhancing the corrosion resistance and oxidation resistance of the passivation film; when the composite electrolyte contains boric acid, the boric acid can play a role in pH buffering and adjustment, thereby stabilizing the acidity and alkalinity of the system, preventing excessively strong or weak local reactions during deposition, and thereby improving the uniformity of the passivation film.

[0019] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the concentration of cerium nitrate is 5-10 g / L, for example, any one of 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L or a range value of any two of them.

[0020] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the concentration of boric acid is 5-10 g / L, for example, any one of 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 10 g / L or a range value of any two of them.

[0021] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the concentration of the nano-SiO2 aqueous solution in step S2 is 10-15 g / L, for example, any one of 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L or a range value of any two of them. Research has found that by adjusting the concentration of the nano-SiO2 aqueous solution within the above range, the SiO2 in the solution can better penetrate and fill the micropores of the passivation film, and form a dense Si-O-Si network after annealing, thereby better improving the volume resistance, dielectric strength and corrosion resistance life of the passivation film.

[0022] The nano-SiO2 aqueous solution can self-assemble to form a dense inorganic SiO2 network structure on the surface and pores of the passivation film layer through a sol-gel process, to achieve the purpose of uniformly filling the micropores and defects of the passivation film layer; moreover, after drying and annealing treatment, the SiO2 particles can be further solidified and enhanced, making the SiO2 inorganic layer more firmly combined with the passivation film, and more effectively improving the corrosion resistance and insulation performance of the non-oriented electrical steel.

[0023] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the potential parameter of the anode in step S1 is 0.8-1.5 V (for example, any one of 0.8 V, 0.9 V, 1.0 V, 1.1 V, 1.2 V, 1.3 V, 1.4 V, 1.5 V or a range value of any two of them), and the current density is 10-20 mA / cm 2 (for example, any one of 10 mA / cm 2 , 12 mA / cm 2 , 14 mA / cm 2 , 16 mA / cm 2 , 18 mA / cm 2 , 20 mA / cm 210-20min (e.g. can be any one or a range value of the two of 10min, 12min, 14min, 16min, 18min, 20min).

[0024] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the Si content of the non-oriented electrical steel in step S1 is 3wt%-4.5wt%.

[0025] As a preferred embodiment of the preparation method of the corrosion-resistant non-oriented electrical steel, the non-oriented electrical steel in step S1 is pretreated, and the pretreatment comprises the following steps: first polishing the non-oriented electrical steel to a surface roughness Ra≤0.8μm, then degreasing treatment in an alkaline solution, then acid pickling treatment in an H2SO4 solution, and then HF solution activation treatment.

[0026] In a second aspect, the present application provides a corrosion-resistant non-oriented electrical steel prepared by the above preparation method.

[0027] In a third aspect, the present application provides an application of the above corrosion-resistant non-oriented electrical steel in preparing an automobile drive motor.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] Compared with the traditional phosphating or silicating process, the preparation method of the present application can form a uniform and dense passivation film on the surface of the non-oriented electrical steel, thereby significantly improving the corrosion resistance, insulation performance and oxidation resistance of the non-oriented electrical steel. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A flowchart of the preparation method of the corrosion-resistant non-oriented electrical steel in Example 1. DETAILED DESCRIPTION

[0031] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples.

[0032] Other materials, reagents, etc. used in the examples can be obtained from commercial channels unless otherwise specified.

[0033] Example 1

[0034] A preparation method of a corrosion-resistant non-oriented electrical steel, comprising the following steps (as shown in Figure 1

[0035] ​S1, pretreatment: select a 100mm*100mm*0.5mm size non-oriented electrical steel plate (Fe-3.5%Si), polish it to a surface roughness Ra≤0.8μm with sandpaper; then place it in an alkaline solution (40g / L NaOH + 15g / L Na3PO4), soak in an alkaline degreasing solution at 70℃ for 8min; then place it in a 13% H2SO4 solution, soak in an acid solution at room temperature for 45s; finally, place it in a 2% HF solution, soak in an activation solution at room temperature for 30s;

[0036] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), the pretreated non-oriented electrical steel is used as anode (i.e. working electrode, anode potential parameter is 1.2V, current density is 15mA / cm 2 ), immerse it in a composite electrolyte (pH 6, temperature 30℃) to apply constant potential for passivation treatment for 15min, to form a uniform passivation film on the surface of the non-oriented electrical steel; the composite electrolyte is composed of 65g / L sodium dihydrogen phosphate, 30g / L sodium silicate, 10g / L 3-aminopropyl triethoxysilane, nanometer boron nitride, 7.5g / L cerous nitrate, 7.5g / L boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 3%;

[0037] S3, sealing treatment: after passivation treatment, the non-oriented electrical steel is placed in deionized water for ultrasonic cleaning, then immersed in a 30g / L nanometer SiO2 aqueous solution for 2min, and then dried at 150℃ for 1h;

[0038] S4, annealing treatment: the non-oriented electrical steel after sealing treatment is annealed at 400℃ in Ar2 atmosphere for 45min, and naturally cooled to room temperature to obtain a corrosion-resistant non-oriented electrical steel.

[0039] Example 2

[0040] A method for preparing a corrosion-resistant non-oriented electrical steel, which is different from example 1 only in that the annealing temperature in step S3 is 450℃.

[0041] Specifically includes the following steps:

[0042] S1, pretreatment: select a 100mm*100mm*0.5mm size non-oriented electrical steel plate (Fe-3.5%Si), polish it to a surface roughness Ra≤0.8μm with sandpaper; then place it in an alkaline solution (40g / L of NaOH+15g / L of Na3PO4), soak in 70℃ for 8min for alkaline degreasing; then place it in a 13% H2SO4 solution, soak in room temperature for 45s for pickling; finally, place it in a 2% HF solution, soak in room temperature for 30s for activation treatment;

[0043] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), the pretreated non-oriented electrical steel is used as anode (i.e. working electrode, anode potential parameter is 1.2V, current density is 15mA / cm 2 ), immerse it in a composite electrolyte (pH is 6, temperature is 30℃) to apply constant potential for passivation treatment for 15min to form a uniform passivation film on the surface of the non-oriented electrical steel; the composite electrolyte is composed of 65g / L of sodium dihydrogen phosphate, 30g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, nanometer boron nitride, 7.5g / L of cerium nitrate, 7.5g / L of boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 3%;

[0044] S3, pore sealing treatment: the passivated non-oriented electrical steel is ultrasonically cleaned in deionized water, then immersed in a 30g / L nanometer SiO2 aqueous solution for 2min, and then dried at 150℃ for 1h;

[0045] S4, annealing treatment: the pore-sealed non-oriented electrical steel is annealed in Ar2 atmosphere at 450℃ for 45min, and naturally cooled to room temperature to obtain the corrosion-resistant non-oriented electrical steel.

[0046] Example 3

[0047] A method for preparing a corrosion-resistant non-oriented electrical steel, which is different from example 1 only in that the composite electrolyte in step S2 is composed of 50g / L of sodium dihydrogen phosphate, 40g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, nanometer boron nitride, 10g / L of cerium nitrate, 10g / L of boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 3%.

[0048] Specifically includes the following steps:

[0049] S1, pretreatment: select 100mm*100mm*0.5mm size of non-oriented electrical steel plate (Fe-3.5%Si), polish it to surface roughness Ra≤0.8μm by sandpaper; then place it in an alkaline solution (40g / L of NaOH+15g / L of Na3PO4), soak in 70℃ for 8min for alkaline degreasing; then place it in a 13% H2SO4 solution, soak in room temperature for 45s for pickling; finally, place it in a 2% HF solution, soak in room temperature for 30s for activation treatment;

[0050] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), the pretreated non-oriented electrical steel is used as anode (i.e. working electrode, anode potential parameter is 1.2V, current density is 15mA / cm 2 ), immerse it in a composite electrolyte (pH is 6, temperature is 30℃) to apply constant potential for passivation treatment for 15min, to form uniform passivation film on the surface of non-oriented electrical steel; the composite electrolyte is composed of 50g / L of sodium dihydrogen phosphate, 40g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, nanometer boron nitride, 10g / L of cerous nitrate, 10g / L of boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 3%;

[0051] S3, sealing treatment: the passivated non-oriented electrical steel is ultrasonically cleaned in deionized water, then immersed in a 30g / L nanometer SiO2 aqueous solution for 2min, and then dried at 150℃ for 1h;

[0052] S4, annealing treatment: the sealing treated non-oriented electrical steel is annealed in Ar2 atmosphere at 400℃ for 45min, and naturally cooled to room temperature to obtain the corrosion-resistant non-oriented electrical steel.

[0053] Example 4

[0054] A method for preparing a corrosion-resistant non-oriented electrical steel, which is only different from example 1 in that the composite electrolyte in step S2 is composed of 80g / L of sodium dihydrogen phosphate, 20g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, nanometer boron nitride, 5g / L of cerous nitrate, 5g / L of boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 5%.

[0055] Specifically includes the following steps:

[0056] S1, pretreatment: select 100mm*100mm*0.5mm size of non-oriented electrical steel (Fe-3.5%Si), polish it to surface roughness Ra≤0.8μm by using sandpaper; then place it in an alkaline solution (40g / L of NaOH+15g / L of Na3PO4), soak in 70℃ for 8min for alkaline degreasing; then place it in a 13% mass concentration H2SO4 solution, soak in room temperature for 45s for pickling; finally, place it in a 2% mass concentration HF solution, soak in room temperature for 30s for activation treatment;

[0057] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as the counter electrode, saturated calomel electrode as the reference electrode), the pretreated non-oriented electrical steel is used as the anode (i.e. the working electrode, the anode potential parameter is 1.2V, the current density is 15mA / cm 2 ), and it is immersed in a composite electrolyte (pH 6, temperature 30℃) to apply constant potential for passivation treatment for 15min to form a uniform passivation film on the surface of the non-oriented electrical steel; the composite electrolyte is composed of 80g / L of sodium dihydrogen phosphate, 20g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, nanometer boron nitride, 5g / L of cerous nitrate, 5g / L of boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 5%;

[0058] S3, sealing treatment: the passivated non-oriented electrical steel is ultrasonically cleaned in deionized water, and then immersed in a 30g / L nanometer SiO2 aqueous solution for 2min, and then dried at 150℃ for 1h;

[0059] S4, annealing treatment: the sealing treated non-oriented electrical steel is annealed in Ar2 atmosphere at 400℃ for 45min, and naturally cooled to room temperature to obtain the corrosion-resistant non-oriented electrical steel.

[0060] Comparative Example 1

[0061] A method for preparing a corrosion-resistant non-oriented electrical steel, which is only different from Example 1 in that the composite electrolyte in step S2 does not contain nanometer boron nitride.

[0062] Specifically includes the following steps:

[0063] S1, pretreatment: select 100mm*100mm*0.5mm size of non-oriented electrical steel (Fe-3.5%Si), adopt sandpaper to polish it to surface roughness Ra≤0.8μm; then place it in alkali solution (concentration of 40g / L of NaOH+concentration of 15g / L of Na3PO4), soak in 70℃ for 8min for alkaline degreasing; then place it in 13% mass concentration of H2SO4 solution, soak in room temperature for 45s for pickling; finally, place it in 2% mass concentration of HF solution, soak in room temperature for 30s for activation treatment;

[0064] S2, electrochemical passivation treatment: in three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), take pretreated non-oriented electrical steel as anode (i.e. working electrode, anode potential parameter is 1.2V, current density is 15mA / cm 2 ), immerse it in composite electrolyte (pH is 6, temperature is 30℃) to apply constant potential for passivation treatment for 15min, to form uniform passivation film on the surface of non-oriented electrical steel; the composite electrolyte is composed of 65g / L of sodium dihydrogen phosphate, 30g / L of sodium silicate, 10g / L of 3-aminopropyl triethoxysilane, 7.5g / L of cerous nitrate, 7.5g / L of boric acid and water;

[0065] S3, pore sealing treatment: immerse the passivated non-oriented electrical steel in deionized water for ultrasonic cleaning, then immerse it in 30g / L of nano-SiO2 aqueous solution for 2min, and then dry it at 150℃ for 1h;

[0066] S4, annealing treatment: anneal the pore-sealed non-oriented electrical steel in Ar2 atmosphere at 400℃ for 45min, and naturally cool it to room temperature to obtain corrosion-resistant non-oriented electrical steel.

[0067] Comparative example 2

[0068] A method for preparing a corrosion-resistant non-oriented electrical steel, which is different from example 1 only in that the temperature of the annealing treatment in step S3 is 300℃.

[0069] Specifically includes the following steps:

[0070] S1, pretreatment: select a 100mm*100mm*0.5mm size non-oriented electrical steel plate (Fe-3.5%Si), polish it to a surface roughness Ra≤0.8μm with sandpaper; then place it in an alkaline solution (40g / L NaOH + 15g / L Na3PO4), soak in an alkaline degreasing solution at 70℃ for 8min; then place it in a 13% H2SO4 solution, soak in an acid solution at room temperature for 45s; finally, place it in a 2% HF solution, soak in an activation solution at room temperature for 30s;

[0071] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), the pretreated non-oriented electrical steel is used as anode (i.e. working electrode, anode potential parameter is 1.2V, current density is 15mA / cm 2 ), immerse it in a composite electrolyte (pH 6, temperature 30℃) to apply constant potential for passivation treatment for 15min, to form a uniform passivation film on the surface of the non-oriented electrical steel; the composite electrolyte is composed of 65g / L sodium dihydrogen phosphate, 30g / L sodium silicate, 10g / L 3-aminopropyl triethoxysilane, nanometer boron nitride, 7.5g / L cerous nitrate, 7.5g / L boric acid and water; the mass percentage of nanometer boron nitride in the total mass of the composite electrolyte is 3%;

[0072] S3, pore sealing treatment: the passivated non-oriented electrical steel is ultrasonically cleaned in deionized water, then immersed in a 30g / L nanometer SiO2 aqueous solution for 2min, and then dried at 150℃ for 1h;

[0073] S4, annealing treatment: the pore-sealed non-oriented electrical steel is annealed at 300℃ in Ar2 atmosphere for 45min, and naturally cooled to room temperature to obtain the corrosion-resistant non-oriented electrical steel.

[0074] Comparative Example 3

[0075] A method for preparing a corrosion-resistant non-oriented electrical steel, which is different from Example 1 only in that the annealing temperature in step S3 is 600℃.

[0076] Specifically includes the following steps:

[0077] S1, pretreatment: select 100 mm * 100 mm * 0.5 mm size non-oriented electrical steel plate (Fe-3.5%Si), polish it to surface roughness Ra≤0.8 μm by sandpaper; then place it in an alkaline solution (40 g / L of NaOH + 15 g / L of Na3PO4), soak in 70°C for 8 min for alkaline degreasing; then place it in a 13% H2SO4 solution, soak in room temperature for 45 s for pickling; finally, place it in a 2% HF solution, soak in room temperature for 30 s for activation treatment;

[0078] S2, electrochemical passivation treatment: in a three-electrode system (platinum electrode as counter electrode, saturated calomel electrode as reference electrode), the pretreated non-oriented electrical steel is used as anode (i.e. working electrode, anode potential parameter is 1.2 V, current density is 15 mA / cm 2 ), immerse it in a composite electrolyte (pH is 6, temperature is 30°C) to apply constant potential for passivation treatment for 15 min, to form a uniform passivation film on the surface of the non-oriented electrical steel; the composite electrolyte is composed of 65 g / L of sodium dihydrogen phosphate, 30 g / L of sodium silicate, 10 g / L of 3-aminopropyl triethoxysilane, nano boron nitride, 7.5 g / L of cerium nitrate, 7.5 g / L of boric acid and water; the mass percentage of nano boron nitride in the total mass of the composite electrolyte is 3%;

[0079] S3, sealing treatment: the passivated non-oriented electrical steel is ultrasonically cleaned in deionized water, then immersed in a 30 g / L nano SiO2 aqueous solution for 2 min, and then dried at 150°C for 1 h;

[0080] S4, annealing treatment: the sealing treated non-oriented electrical steel is annealed in Ar2 atmosphere at 600°C for 45 min, and naturally cooled to room temperature to obtain the corrosion-resistant non-oriented electrical steel.

[0081] Comparative Example 4

[0082] A method for preparing a corrosion-resistant non-oriented electrical steel, which is only different from Example 1 in that the 30 g / L nano SiO2 aqueous solution in step S3 is replaced by a dodecamethylcyclohexasiloxane sealing solution for comparative study.

[0083] The dodecamethylcyclohexasiloxane sealing solution is prepared by the following method: 3 g of dodecamethylcyclohexasiloxane is added to an ethanol aqueous solution (composed of ethanol and deionized water in a volume ratio of 4:1), a little oxalic acid aqueous solution is added dropwise to control the pH value of the solution to 4, and a dodecamethylcyclohexasiloxane sealing solution is prepared.

[0084] Performance test

[0085] 1) corrosion resistance test: neutral salt spray test (NSS), the sample is placed in a 5wt% NaCl solution to test, pH is 6.5-7.2, the atomization temperature is 35±1℃, the sedimentation rate is 1.0-2.0mL·80cm 2 -1, the test time is 240h, every 24h is taken out to take a photo, and the corrosion (red rust or white rust) area percentage is calculated by using image analysis software, and the corrosion resistance rate (%) =1-corrosion area percentage.

[0086] 2) insulation test: concentric circle electrode method is used for testing, by adjusting the outer diameter of the upper electrode to 10mm, the inner diameter to 5mm; the lower electrode is a whole steel plate. 500V / 60s is applied, and the leakage current is recorded; the volume resistivity is determined as ρ≥5.0Ω·cm is excellent; 4.0-5.0Ω·cm is qualified; and <4.0Ω·cm is unqualified.

[0087] 3) oxidation resistance test: the surface treated non-oriented electrical steel sample is degreased, dried and accurately weighed (m0), placed in an air atmosphere box furnace at 800℃ for continuous heat preservation for 100h, cooled to room temperature, and then re-weighed after light brushing of floating dust (m1), and the oxidation weight gain rate is calculated according to Δm=(m1-m0) / m0×100%.

[0088] Table 1

[0089]

[0090]

[0091] According to the data in table 1, the corrosion resistance of the non-oriented electrical steel in examples 1-4 is ≥99.62%, the volume resistivity is ≥5.5Ω·cm, and the oxidation weight gain rate is ≤0.35%, which indicates that the preparation method of the application can form a uniform and dense passivation film on the surface of the non-oriented electrical steel, thereby significantly improving the corrosion resistance, insulation performance and oxidation resistance of the non-oriented electrical steel.

[0092] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application and not to limit the protection scope of the application. Although the application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the application.

Claims

1. A method for preparing corrosion-resistant non-oriented electrical steel, characterized in that, Includes the following steps: S1. In a three-electrode system, non-oriented electrical steel is used as the anode and is immersed in a composite electrolyte to passivate it under a constant potential; the composite electrolyte includes phosphate, silicate, silane coupling agent and nano boron nitride. S2. The passivated non-oriented electrical steel is placed in a nano-SiO2 aqueous solution for pore sealing. S3. The non-oriented electrical steel after sealing is annealed in an inert gas atmosphere at 400-500℃ to obtain corrosion-resistant non-oriented electrical steel.

2. The preparation method according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The concentration of phosphate in the composite electrolyte is 50-80 g / L; (2) The concentration of silicate in the composite electrolyte is 20-40 g / L; (3) The pH value of the composite electrolyte is 5 to 6.5 and the temperature is 25 to 35°C; (4) The annealing time is 30 to 60 minutes.

3. The preparation method according to claim 1, characterized in that, Based on the total mass of the composite electrolyte, the mass percentage of the nano-boron nitride is 3% to 5%.

4. The preparation method according to claim 1, characterized in that, The composite electrolyte in step S1 also includes cerium nitrate and boric acid.

5. The preparation method according to claim 1, characterized in that, The concentration of the nano-SiO2 aqueous solution in step S2 is 10-15 g / L.

6. The preparation method according to claim 1, characterized in that, In step S1, the potential parameters of the anode are 0.8–1.5V and the current density is 10–20 mA / cm². 2 ; and / or the passivation treatment time is 10 to 20 minutes.

7. The preparation method according to claim 1, characterized in that, The Si content in the non-oriented electrical steel described in step S1 is 3wt% to 4.5wt%.

8. The preparation method according to claim 1, characterized in that, The non-oriented electrical steel described in step S1 undergoes pretreatment, which includes the following steps: first, polishing the non-oriented electrical steel until its surface roughness Ra ≤ 0.8 μm, then degreasing it in an alkaline solution, then acid washing it in an H2SO4 solution, and finally activation treatment with an HF solution.

9. The corrosion-resistant non-oriented electrical steel prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the corrosion-resistant non-oriented electrical steel according to claim 9 in the manufacture of automotive drive motors.

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