A new energy automobile motor non-oriented high-grade silicon steel special protective slag

Abstract

The present application relates to the technical field of protecting slag, in particular to a special protecting slag for non-oriented high-grade silicon steel for new energy automobile motor, which is composed of the following raw materials: acid leaching wollastonite, glass powder, lithium-loaded hydrotalcite, zirconium oxide, silicon carbide and magnesia.The present application removes calcium impurities in wollastonite through acid leaching treatment to obtain high-activity porous SiO2, so as to quickly form a homogeneous low-melting-point silicate glass phase in the molten slag, effectively avoid the generation of high-viscosity calcium aluminum yellow longite, and keep the molten slag viscosity stable; lithium ions and CO2 gas are released from lithium-loaded hydrotalcite in the decomposition process, Li + further reduces the viscosity by charge balance depolymerization of the silicon-oxygen network; in addition, the pure base of acid leaching wollastonite enhances the viscosity reduction efficiency of Li + , and improves the ability of the slag layer to resist the impact of steel flow.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of protective slag, in particular to a special protective slag for non-oriented high-grade silicon steel for new energy automobile motor. BACKGROUND

[0002] In recent years, with the increasing emphasis on environmental protection and energy efficiency worldwide, the new energy automobile industry has developed rapidly. Permanent magnet synchronous motor has become the mainstream choice in the field of new energy automobile motor due to its high efficiency, high power density and high torque density. Non-oriented high-grade silicon steel, as a key material, has a decisive influence on the efficiency of the motor. In the continuous annealing process of silicon steel, protective slag plays a crucial role, and its performance directly affects the final quality of silicon steel, such as iron loss (P1, P2 value), magnetic induction (B50, B10 value), thickness uniformity, and the stability and economy of the production process.

[0003] At present, some protective slag used for silicon steel casting will affect the viscosity stability of the molten slag due to the high viscosity of the molten steel, which will further cause the appearance of slag inclusion defects on the surface of the casting blank. In view of this, the present application provides a special protective slag for non-oriented high-grade silicon steel for new energy automobile motor. SUMMARY

[0004] The present application aims to provide a special protective slag for non-oriented high-grade silicon steel for new energy automobile motor to solve the problem of slag inclusion defects on the surface of the casting blank caused by the high viscosity of the molten steel, which will affect the viscosity stability of the molten slag.

[0005] To achieve the above-mentioned purpose, the present application provides a special protective slag for non-oriented high-grade silicon steel for new energy automobile motor, which is composed of the following raw materials: acid leaching wollastonite, glass powder, lithium-loaded hydrotalcite, zirconia, silicon carbide and magnesia.

[0006] The acid leaching wollastonite is prepared by immersing wollastonite in oxalic acid;

[0007] The lithium-loaded hydrotalcite is prepared by embedding lithium carbonate into magnesium-aluminum hydrotalcite.

[0008] As a preferred embodiment, the acid leaching wollastonite is 33-38 parts by weight, the glass powder is 25-30 parts by weight, the lithium-loaded hydrotalcite is 3-5 parts by weight, the zirconia is 1.0-1.5 parts by weight, the silicon carbide is 1.5-2.0 parts by weight, and the magnesia is 1.5-2.5 parts by weight.

[0009] As a preferred embodiment, the preparation process of the acid leaching wollastonite is as follows:

[0010] The wollastonite powder with mesh number of 80-150 is added into oxalic acid solution at mass ratio of 1:5.0-5.5, and stirred at 300-400 rpm at 55-65 ℃ for 1.5-2.5 h; after the reaction, the solid is separated by filtration, washed with deionized water at 60-70 ℃ until neutral, and dried at 100-120 ℃ for 2.0-2.5 h to obtain the acid-leached wollastonite.

[0011] The acid-leached wollastonite removes calcium impurities selectively by oxalic acid treatment, which builds a low-melting silicate network in the slag, significantly reduces the high-temperature viscosity fluctuation, and enables the protective slag to maintain uniform spreading and stable inclusion adsorption capacity in the high-viscosity molten steel environment of silicon steel, thereby inhibiting the slag inclusion defects of the cast slab.

[0012] Preferably, the mass concentration of the oxalic acid solution is 4.5-5.5%.

[0013] Preferably, the preparation process of the lithium-loaded hydrotalcite is as follows:

[0014] Under nitrogen protection, the salt solution and the alkali solution are added into the reaction kettle in parallel flow, stirred at 300-500 rpm at 62-68 ℃ for 1-1.5 h, and the pH is maintained at 9.8-10.2 to generate precipitate; the precipitate is transferred into the hydrothermal kettle, and crystallized at 98-102 ℃ for 10-12 h to obtain the hydrotalcite precursor; the hydrotalcite precursor is dispersed in a lithium carbonate solution with a mass concentration of 1.2-1.5%, and stirred at 300-500 rpm at 78-82 ℃ for 5-6 h; after the reaction, the solid is separated, washed with anhydrous ethanol for 3-4 times, and dried at 100 ℃ for 3-4 h to obtain the lithium-loaded hydrotalcite.

[0015] The lithium-loaded hydrotalcite depolymerizes the silicate melt network by releasing lithium ions, significantly reduces the high-temperature viscosity of the slag and improves its stability, and at the same time, the decomposed CO2 forms a dynamic gas protection layer; the synergistic effect of the two enables the protective slag to maintain uniform spreading and anti-disturbance capacity in the high-viscosity silicon steel molten steel, thereby inhibiting the slag inclusion defects of the cast slab from the source.

[0016] Preferably, the salt solution is prepared by dissolving magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in deionized water at a magnesium / aluminum molar ratio of 2.5:1 to obtain a salt solution with a concentration of 1.0 mol / L;

[0017] The alkali solution is prepared by mixing sodium carbonate and sodium hydroxide at a carbonate / hydroxide molar ratio of 2:1 to obtain an alkali solution with a concentration of 1.5 mol / L.

[0018] Preferably, the mass ratio of the hydrotalcite precursor to the lithium carbonate solution is 1:8-12.

[0019] Preferably, the preparation process of the special protective slag for non-oriented high-grade silicon steel for new energy automobile motors is as follows:

[0020] S1.1, respectively, take the following weight parts of raw materials: acid leaching of 33-38 parts by weight of wollastonite, glass powder 25-30 parts by weight, lithium loaded hydrotalcite 3-5 parts by weight, zirconium oxide 1.0-1.5 parts by weight, silicon carbide 1.5-2.0 parts by weight and magnesia 1.5-2.5 parts by weight;

[0021] S1.2, the acid leaching of wollastonite, glass powder and magnesia are put into a three-dimensional mixer, mixed at a speed of 25-30 rpm for 20-30 min; then add lithium loaded hydrotalcite and zirconium oxide, the speed is reduced to 15-20 rpm for 15-20 min; finally add silicon carbide, mixed at a speed of 10-15 rpm for 10-15 min, to get the mixture;

[0022] S1.3, the mixture is pressed into a 20x15mm cylindrical blank, and is sintered in a stepwise temperature rising atmosphere to obtain a sintered slag block; the sintered slag block is fluidized in a hot air at 80-90℃ to obtain a special protective slag for non-oriented high-grade silicon steel for new energy automobile motor.

[0023] As preferred, in the S1.3, the stepwise temperature rising sintering is divided into two stages: the first stage is 400-600℃ for 1h; the second stage is 900-950℃ for 4-5h.

[0024] As preferred, in the S1.3, the sintered slag block has a mesh size of 40-80 mesh.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] In the special protective slag for non-oriented high-grade silicon steel for new energy automobile motor, the calcium impurities in the wollastonite are removed by acid leaching treatment to obtain high-activity porous SiO2, so as to quickly form a homogeneous low-melting point silicate glass phase in the molten slag, effectively avoid the generation of high-viscosity calcium aluminum yellow longite, and keep the molten slag viscosity stable; lithium ions and CO2 gas are released during the decomposition of lithium loaded hydrotalcite, Li + The viscosity is further reduced by charge balance depolymerization of the silicon-oxygen network; in addition, the pure base of the acid leaching wollastonite enhances the viscosity reduction efficiency of Li + , and improves the ability of the slag layer to resist steel flow impact. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0028] The application provides a special protective slag for non-oriented high-grade silicon steel for new energy automobile motors, which is prepared from the following raw materials: acid-leached wollastonite, glass powder, lithium-loaded hydrotalcite, zirconium oxide, silicon carbide and magnesia.

[0029] The acid-leached wollastonite is prepared by immersing wollastonite in oxalic acid.

[0030] The lithium-loaded hydrotalcite is prepared by embedding lithium carbonate into magnesium-aluminum hydrotalcite.

[0031] The salt solution is prepared by dissolving magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in deionized water at a magnesium / aluminum molar ratio of 2.5:1 to obtain a salt solution with a concentration of 1.0 mol / L; and the alkali solution is prepared by mixing sodium carbonate and sodium hydroxide at a carbonate / hydroxide molar ratio of 2:1 to obtain an alkali solution with a concentration of 1.5 mol / L.

[0032] Embodiment 1: A preparation process of a special protective slag for non-oriented high-grade silicon steel for new energy automobile motors, comprising the following steps:

[0033] S1.1, the following weight parts of raw materials are respectively taken: acid-leached wollastonite 33 parts by weight, glass powder 25 parts by weight, lithium-loaded hydrotalcite 3 parts by weight, zirconium oxide 1.0 parts by weight, silicon carbide 1.5 parts by weight and magnesia 1.5 parts by weight;

[0034] S1.2, the acid-leached wollastonite, glass powder and magnesia are put into a three-dimensional mixer and mixed at a speed of 30 rpm for 20 min; then the lithium-loaded hydrotalcite and zirconium oxide are added and mixed at a speed of 20 rpm for 15 min; finally, the silicon carbide is added and mixed at a speed of 10 rpm for 10 min to obtain a mixture;

[0035] S1.3, the mixture is pressed into a cylindrical blank with a size of 20*15 mm, and is subjected to stepwise sintering under an argon atmosphere (the first stage is 500 DEG C for 1 h; the second stage is 950 DEG C for 5 h) to obtain a sintered slag block; the sintered slag block with a mesh size of 60 is fluidized in a hot air at 85 DEG C to obtain a special protective slag for non-oriented high-grade silicon steel for new energy automobile motors.

[0036] Further, the preparation process of the acid-leached wollastonite is as follows:

[0037] The wollastonite powder with a mesh size of 100 is added into an oxalic acid solution with a mass concentration of 5.0% at a mass ratio of 1:5.0, and is stirred at a speed of 400 rpm at 60 DEG C for 2 h; after the reaction, the solid is separated by filtration, washed with deionized water at 60 DEG C until neutral, and dried at 110 DEG C for 2.5 h to obtain the acid-leached wollastonite.

[0038] The preparation process of the lithium-loaded hydrotalcite is as follows:

[0039] The salt solution and the lye solution are added into a reaction kettle under nitrogen protection, and stirred at 65 DEG C and 400 rpm for 1 h, while maintaining pH at 10, to generate precipitate; the precipitate is transferred into a hydrothermal kettle, and crystallized at 100 DEG C for 10 h to obtain a hydrotalcite precursor; the hydrotalcite precursor is dispersed in a lithium carbonate solution with a mass concentration of 1.5% (mass ratio 1:8), and stirred at 80 DEG C and 300 rpm for 6 h; after the reaction is completed, the solid is separated, washed with anhydrous ethanol 4 times, and dried at 100 DEG C for 4 h to obtain lithium-loaded hydrotalcite.

[0040] Example 2: A preparation process of a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors, comprising the following steps:

[0041] S1.1, respectively, the following weight parts of raw materials: acid leaching of wollastonite 38 parts by weight, glass powder 30 parts by weight, lithium-loaded hydrotalcite 5 parts by weight, zirconia 1.5 parts by weight, silicon carbide 2.0 parts by weight and magnesia 2.5 parts by weight;

[0042] S1.2, the acid leaching of wollastonite, glass powder and magnesia are put into a three-dimensional mixer, mixed at a speed of 30 rpm for 20 min; then the lithium-loaded hydrotalcite and zirconia are added, and the speed is reduced to 20 rpm for mixing for 15 min; finally, the silicon carbide is added, and the speed is 10 rpm for mixing for 10 min to obtain a mixture;

[0043] S1.3, the mixture is pressed into a 20x15mm cylindrical blank, and is subjected to stepwise sintering under argon atmosphere (the first stage is 500 DEG C for 1 h; the second stage is 950 DEG C for 5 h) to obtain a sintered slag block; the sintered slag block with a mesh size of 60 is fluidized in a hot air at 85 DEG C to obtain a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors.

[0044] Further, the preparation process of the acid leaching of wollastonite is as follows:

[0045] The wollastonite powder with a mesh size of 100 is added into an oxalic acid solution with a mass concentration of 5.0% at a mass ratio of 1:5.5, and stirred at 60 DEG C and 400 rpm for 2 h; after the reaction is completed, the solid is separated by filtration, washed with 60 DEG C deionized water until neutral, and dried at 110 DEG C for 2.5 h to obtain the acid leaching of wollastonite.

[0046] The preparation process of the lithium-loaded hydrotalcite is as follows:

[0047] The salt solution and the lye solution are added into a reaction kettle under nitrogen protection, and stirred at 65 DEG C and 400 rpm for 1 h, while maintaining pH at 10, to generate precipitate; the precipitate is transferred into a hydrothermal kettle, and crystallized at 100 DEG C for 10 h to obtain a hydrotalcite precursor; the hydrotalcite precursor is dispersed in a lithium carbonate solution with a mass concentration of 1.5% (mass ratio 1:12), and stirred at 80 DEG C and 300 rpm for 6 h; after the reaction is completed, the solid is separated, washed with anhydrous ethanol 4 times, and dried at 100 DEG C for 4 h to obtain lithium-loaded hydrotalcite.

[0048] Example 3: A preparation process of a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors, comprising the following steps:

[0049] S1.1, respectively, the following weight parts of raw materials: acid leaching of wollastonite 35 parts by weight, glass powder 27 parts by weight, lithium-loaded hydrotalcite 4 parts by weight, zirconia 1.2 parts by weight, silicon carbide 1.7 parts by weight and magnesia 2.0 parts by weight;

[0050] S1.2, the acid leaching of wollastonite, glass powder and magnesia are put into a three-dimensional mixer, mixed at a speed of 30 rpm for 20 min; then the lithium-loaded hydrotalcite and zirconia are added, and the speed is reduced to 20 rpm for mixing for 15 min; finally, the silicon carbide is added, and the speed is 10 rpm for mixing for 10 min to obtain a mixture;

[0051] S1.3, the mixture is pressed into a 20x15mm cylindrical blank, and is subjected to stepwise sintering under argon atmosphere (the first stage is 500 DEG C for 1 h; the second stage is 950 DEG C for 5 h) to obtain a sintered slag block; the sintered slag block with a mesh size of 60 is fluidized in hot air at 85 DEG C to obtain a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors.

[0052] Further, the preparation process of the acid leaching of wollastonite is as follows:

[0053] The wollastonite powder with a mesh size of 100 is added into an oxalic acid solution with a mass concentration of 5.0% at a mass ratio of 1:5.2, and stirred at 60 DEG C and 400 rpm for 2 h; after the reaction is completed, the solid is separated by filtration, washed with 60 DEG C deionized water until neutral, and dried at 110 DEG C for 2.5 h to obtain the acid leaching of wollastonite.

[0054] The preparation process of the lithium-loaded hydrotalcite is as follows:

[0055] The salt solution and the lye solution are added into a reaction kettle under nitrogen protection, and stirred at 65 DEG C and 400 rpm for 1 h, while maintaining pH at 10, to generate precipitate; the precipitate is transferred into a hydrothermal kettle, and crystallized at 100 DEG C for 10 h to obtain a hydrotalcite precursor; the hydrotalcite precursor is dispersed in a lithium carbonate solution with a mass concentration of 1.5% (mass ratio 1:10), and stirred at 80 DEG C and 300 rpm for 6 h; after the reaction is completed, the solid is separated, washed with anhydrous ethanol 4 times, and dried at 100 DEG C for 4 h to obtain lithium-loaded hydrotalcite.

[0056] Example 4: A preparation process of a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors, comprising the following steps:

[0057] S1.1, respectively, the following weight parts of raw materials: acid leaching of wollastonite 40 parts by weight, glass powder 27 parts by weight, lithium-loaded hydrotalcite 4 parts by weight, zirconia 1.2 parts by weight, silicon carbide 1.7 parts by weight and magnesia 2.0 parts by weight;

[0058] S1.2, the acid leaching of wollastonite, glass powder and magnesia are put into a three-dimensional mixer, mixed at a speed of 30 rpm for 20 min; then lithium-loaded hydrotalcite and zirconia are added, the speed is reduced to 20 rpm for mixing for 15 min; finally, silicon carbide is added, mixed at a speed of 10 rpm for 10 min to obtain a mixture;

[0059] S1.3, the mixture is pressed into a 20x15mm cylindrical blank, and is subjected to stepwise sintering under argon atmosphere (the first stage is 500 DEG C for 1 h; the second stage is 950 DEG C for 5 h) to obtain a sintered slag block; the sintered slag block with a mesh size of 60 is fluidized in hot air at 85 DEG C to obtain a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors.

[0060] Further, the preparation process of the acid leaching of wollastonite is as follows:

[0061] The wollastonite powder with a mesh size of 100 is added into an oxalic acid solution with a mass concentration of 5.0% at a mass ratio of 1:5.2, and stirred at 60 DEG C and 400 rpm for 2 h; after the reaction is completed, the solid is separated by filtration, washed with 60 DEG C deionized water until neutral, and dried at 110 DEG C for 2.5 h to obtain the acid leaching of wollastonite.

[0062] The preparation process of the lithium-loaded hydrotalcite is as follows:

[0063] The salt solution and the lye solution were added into the reaction kettle under nitrogen protection, and stirred at 65 DEG C and 400 rpm for 1 h, the pH was maintained at 10, and the precipitate was generated; the precipitate was transferred into the hydrothermal kettle, and crystallized at 100 DEG C for 10 h to obtain the hydrotalcite precursor; the hydrotalcite precursor was dispersed in the lithium carbonate solution with a mass concentration of 1.5% (mass ratio 1:10), and stirred at 80 DEG C and 300 rpm for 6 h; after the reaction was completed, the solid was separated, washed with anhydrous ethanol 4 times, and dried at 100 DEG C for 4 h to obtain the lithium-loaded hydrotalcite.

[0064] Example 5: A preparation process of a special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors, comprising the following steps:

[0065] S1.1, respectively, the following weight parts of raw materials: acid leaching of wollastonite 35 parts by weight, glass powder 27 parts by weight, lithium-loaded hydrotalcite 6 parts by weight, zirconia 1.2 parts by weight, silicon carbide 1.7 parts by weight and magnesia 2.0 parts by weight;

[0066] S1.2, the acid leaching of wollastonite, glass powder and magnesia were put into a three-dimensional mixer, mixed at a speed of 30 rpm for 20 min; then the lithium-loaded hydrotalcite and zirconia were added, and the speed was reduced to 20 rpm for mixing for 15 min; finally, the silicon carbide was added, and the speed was 10 rpm for mixing for 10 min, to obtain the mixed material;

[0067] S1.3, the mixed material was pressed into a 20x15mm cylindrical blank, and was subjected to step sintering under argon atmosphere (the first stage was 500 DEG C for 1 h; the second stage was 950 DEG C for 5 h), to obtain the sintered slag block; the sintered slag block with a mesh size of 60 was fluidized in hot air at 85 DEG C, to obtain the special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors.

[0068] Further, the preparation process of the acid leaching of wollastonite is as follows:

[0069] The wollastonite powder with a mesh size of 100 was added into the oxalic acid solution with a mass concentration of 5.0% at a mass ratio of 1:5.2, and stirred at 60 DEG C and 400 rpm for 2 h; after the reaction was completed, the solid was separated by filtration, washed with 60 DEG C deionized water until neutral, and dried at 110 DEG C for 2.5 h to obtain the acid leaching of wollastonite.

[0070] The preparation process of the lithium-loaded hydrotalcite is as follows:

[0071] The salt solution and the lye solution are added into a reaction kettle under nitrogen protection, and the stirring speed is 400 rpm at 65 DEG C for 1 h, the pH is maintained at 10, and a precipitate is generated; the precipitate is transferred into a hydrothermal kettle, and crystallization is carried out at 100 DEG C for 10 h to obtain a hydrotalcite precursor; the hydrotalcite precursor is dispersed in a lithium carbonate solution with a mass concentration of 1.5% (mass ratio 1:10), and stirring is carried out at 80 DEG C and a speed of 300 rpm for 6 h; after the reaction is completed, the solid is separated, washed with anhydrous ethanol 4 times, and dried at 100 DEG C for 4 h to obtain lithium-loaded hydrotalcite.

[0072] Comparative Example 1: The method of Example 3 is used, and in the preparation process of the special protective slag for non-oriented high-grade silicon steel for new energy automobile motors, no acid leaching of wollastonite is used, and the wollastonite is directly used.

[0073] Comparative Example 2: The method of Example 3 is used, and in the preparation process of the special protective slag for non-oriented high-grade silicon steel for new energy automobile motors, no lithium-loaded hydrotalcite is used.

[0074] In the preparation process of the non-oriented high-grade silicon steel, the special protective slag for non-oriented high-grade silicon steel prepared by acid leaching of wollastonite and lithium-loaded hydrotalcite is added, and the performance index test items and test standards of the non-oriented high-grade silicon steel prepared by the special protective slag for non-oriented high-grade silicon steel are as follows:

[0075] A plate-shaped sample is cut from the non-oriented high-grade silicon steel (thickness 0.30-0.35 mm), the gauge length is 12.5 mm, the parallel section length is greater than 50 mm, the sample is cut along the rolling direction and the edge burrs are avoided, and the gauge length L0 is marked as 50 mm; the thickness (accuracy ±0.01 mm) and width of the sample are measured by a micrometer, and the cross-sectional area S0 is calculated; the load of a universal material testing machine is cleared, the clamping distance is adjusted to be greater than 75 mm, a strain rate of 1-5 mm / min is selected, the sample is clamped and preloaded at 10 MPa to eliminate the gap, and continuous loading is carried out to fracture, and the maximum force F is recorded. m ; the tensile strength is calculated according to the formula R m =F m / S0.

[0076] A high-frequency eddy current flaw detector (frequency 100-200 kHz) is used, the probe is calibrated with a test block (containing an artificial notch: depth 0.1 mm x length 3 mm), and the probe is kept 1.0±0.2 mm away from the surface, the surface of the silicon steel casting blank is scanned at a speed of less than 1 m / s, and suspected areas are marked; a 100x100 mm sample is cut from the eddy current alarm area, a fluorescent penetrant is sprayed, and the sample is left to stand for 10-15 minutes to allow the penetrant to penetrate into the cracks; then, the excess penetrant is removed, white developer is sprayed, and the crack morphology is observed under an ultraviolet lamp, the number of cracks is recorded, and the surface crack rate is calculated.

[0077] The non-oriented high-grade silicon steel prepared by the special protective slag for non-oriented high-grade silicon steel of the above-mentioned Examples 1-5 and Comparative Examples 1-2 was tested by the above-mentioned standard, and the data obtained are shown in Table 1:

[0078] Table 1 Performance data of non-oriented high-grade silicon steel of Examples 1-5 and Comparative Examples 1-2

[0079]

[0080] As can be seen from Examples 1-3 and 4, when the weight parts of the acid-leached wollastonite are continuously increased while other components of the special protective slag for non-oriented high-grade silicon steel remain unchanged, the tensile strength of the non-oriented high-grade silicon steel first increases and then decreases, and the surface crack rate first decreases and then increases; the increase of the proportion of acid-leached wollastonite helps to improve the cleanliness of the molten steel, reduce alumina inclusions, and enhance the continuity of the matrix, thereby improving the tensile strength; the increase of CaO content promotes the formation of low-melting-point inclusions, and is more inclined to plastic deformation rather than brittle cracking during rolling; in addition, the increase of CaO helps to stabilize the viscosity of the molten slag, reduce the thickness of the liquid slag layer and the depth of the oscillation marks of the casting blank; low-iron wollastonite can reduce the floating resistance of Al2O3 inclusions and reduce the surface inclusion area; however, high CaO content can also increase the amount of melilite precipitated in the slag film, resulting in increased brittleness of the slag film, increased friction between the casting blank and the crystallizer, and increased surface micro-crack density.

[0081] Further, as can be seen from the comparison of Examples 1-3 and 5, when the weight parts of lithium-loaded hydrotalcite are continuously increased while other components of the special protective slag for non-oriented high-grade silicon steel remain unchanged, the tensile strength of the non-oriented high-grade silicon steel first increases and then decreases, and the surface crack rate first decreases and then increases; lithium ions released by lithium significantly reduce the viscosity of the protective slag, improve its fluidity, promote the thickening of the liquid slag layer, and reduce surface stress concentration, thereby improving the tensile strength; lithium also promotes the transformation of inclusions in the steel into low-melting-point lithium aluminate, causing plastic deformation rather than matrix cracking during rolling; however, excessive Li + penetrates into the austenite grain boundaries to form Li-Fe brittle phases, resulting in decreased grain boundary bonding strength, and lithium reduces the solubility of sulfur in the steel, causing sulfides to accumulate at the grain boundaries, thereby reducing the tensile strength; in addition, lithium optimizes the glassification tendency of the molten slag, making the heat transfer uniform in the slag film, reducing the surface temperature fluctuations of the casting blank, and reducing thermal stress cracks; however, high lithium content can make the slag film completely amorphous, resulting in rapid heat transfer and cracks in the surface layer of the casting blank.

[0082] According to the above test experiments, Example 3 is taken as the optimal example;

[0083] As can be seen from the comparison of Example 3 and Comparative Example 1, when acid-leached wollastonite is not used and ordinary wollastonite is directly used, the surface crack rate of the non-oriented high-grade silicon steel is significantly increased; ordinary wollastonite has a high Fe2O3 content, and Fe2O3 can form low-melting-point inclusions at high temperatures, which are more inclined to plastic deformation rather than brittle cracking during rolling; in addition, the increase of CaO content helps to stabilize the viscosity of the molten slag, reduce the thickness of the liquid slag layer and the depth of the oscillation marks of the casting blank;3+ The Al in the molten steel is reduced to form inclusions, the inclusions float to the slag-steel interface to form a rigid particle layer, which hinders the uniform spreading of the liquid slag; the inclusions not only reduce the basicity of the protective slag, but also promote the increase of the amount of armalcolite precipitated in the slag film, leading to the brittleness and cracking of the slag film; in addition, the friction coefficient between the crystallized slag film and the copper plate of the crystallizer increases, the surface tensile stress of the cast slab is concentrated, and the longitudinal crack depth increases; the cleanliness of the molten steel decreases, the total amount of oxide inclusions increases, and the inclusions precipitate along the grain boundaries as sulfide nucleation points, further weakening the grain boundary bonding force.

[0084] It can be seen from the comparison of Example 3 and Comparative Example 2 that: when lithium-loaded hydrotalcite is not used, the tensile strength of the non-oriented high-grade silicon steel is significantly reduced and the surface crack rate is significantly increased; ordinary lithium carbonate is easily hygroscopic and deliquescent in a humid environment, causing the protective slag to locally enrich Li2O, thereby causing the viscosity of the molten slag to fluctuate sharply; uneven distribution of lithium ions increases the proportion of glass phase in the slag film, causing the surface layer of the cast slab to crack due to rapid cooling; in addition, the lack of slow-release effect of Li + decreases the solubility of sulfur in the molten steel, and sulfides precipitate along the austenite grain boundaries; at the same time, due to insufficient lubrication of the slag film, slag entrapment easily occurs, leading to an increase in large inclusions in the steel, damage to the continuity of the matrix, and finally a decrease in tensile strength.

[0085] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors, characterized in that, It is composed of the following raw materials: acid-leached wollastonite, glass powder, lithium-loaded hydrotalcite, zirconium oxide, silicon carbide and magnesia; Acid-impregnated wollastonite is prepared by impregnating wollastonite in oxalic acid; Lithium-loaded hydrotalcite is prepared by embedding lithium carbonate into magnesium aluminum hydrotalcite; The preparation process of lithium-loaded hydrotalcite is as follows: Under nitrogen protection, salt solution and alkali solution are added to the reactor in parallel stream and stirred at 300-500 rpm for 1-1.5 h at 62-68℃, maintaining pH at 9.8-10.2 to form a precipitate. The precipitate is transferred to a hydrothermal reactor and crystallized at 98-102℃ for 10-12 h to obtain a hydrotalcite precursor. The hydrotalcite precursor is dispersed in a 1.2-1.5% (w / w) lithium carbonate solution and stirred at 300-500 rpm for 5-6 h at 78-82℃. After the reaction is complete, the solid is separated, washed 3-4 times with anhydrous ethanol, and dried at 100℃ for 3-4 h to obtain lithium-loaded hydrotalcite. The salt solution is prepared by dissolving magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in deionized water at a magnesium / aluminum molar ratio of 2.5:1 to obtain a salt solution with a concentration of 1.0 mol / L. The alkaline solution is prepared by mixing sodium carbonate and sodium hydroxide at a carbonate / hydroxide molar ratio of 2:1 to obtain an alkaline solution with a concentration of 1.5 mol / L.

2. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 1, characterized in that, The composition includes 33-38 parts by weight of acid-etched wollastonite, 25-30 parts by weight of glass powder, 3-5 parts by weight of lithium-loaded hydrotalcite, 1.0-1.5 parts by weight of zirconium oxide, 1.5-2.0 parts by weight of silicon carbide, and 1.5-2.5 parts by weight of magnesia.

3. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 2, characterized in that, The preparation process of the acid-leached wollastonite is as follows: Add 80-150 mesh wollastonite powder to oxalic acid solution at a mass ratio of 1:5.0-5.5, and stir at 300-400 rpm for 1.5-2.5 h at 55-65℃. After the reaction is complete, filter to separate the solid, wash the solid with deionized water at 60-70℃ until neutral, and dry at 100-120℃ for 2.0-2.5 h to obtain acid-impregnated wollastonite.

4. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 3, characterized in that, The oxalic acid solution has a mass concentration of 4.5-5.5%.

5. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 1, characterized in that, The mass ratio of the hydrotalcite precursor to the lithium carbonate solution is 1:8-12.

6. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 1, characterized in that, The preparation process of the special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors is as follows: S1.1 Weigh the following raw materials in parts by weight: 33-38 parts by weight of acid-etched wollastonite, 25-30 parts by weight of glass powder, 3-5 parts by weight of lithium-loaded hydrotalcite, 1.0-1.5 parts by weight of zirconium oxide, 1.5-2.0 parts by weight of silicon carbide, and 1.5-2.5 parts by weight of magnesia. S1.

2. Add acid-etched wollastonite, glass powder, and magnesia into a three-dimensional mixer and mix at 25-30 rpm for 20-30 min. Then add lithium-loaded hydrotalcite and zirconium oxide, and mix at 15-20 rpm for 15-20 min. Finally, add silicon carbide and mix at 10-15 rpm for 10-15 min to obtain the mixture. S1.

3. The mixture is pressed into a cylindrical blank of 20×15mm and sintered in a stepped heating atmosphere to obtain sintered slag blocks; the sintered slag blocks are fluidized in hot air at 80-90℃ to obtain special protective slag for non-oriented high-grade silicon steel for new energy vehicle motors.

7. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 6, characterized in that, In S1.3, the stepped heating sintering is divided into two stages: the first stage is to hold at 400-600℃ for 1 hour; the second stage is to hold at 900-950℃ for 4-5 hours.

8. The special protective slag for non-oriented high-grade silicon steel used in new energy vehicle motors according to claim 6, characterized in that, In S1.3, the sintered slag block has a mesh size of 40-80 mesh.

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