A normalization method for improving the magnetic properties of high-grade non-oriented silicon steel

Abstract

The present invention relates to a normalization method for improving the magnetic properties of high-grade non-oriented silicon steel, and belongs to the field of normalization process of non-oriented silicon steel. The normalization method for improving the magnetic properties of high-grade non-oriented silicon steel provided by the present invention controls the normalization and cooling process of high-grade non-oriented silicon steel, especially controls the normalization temperature and cooling rate of the strip steel, so that the hot-rolled plate structure is more uniform and the number of recrystallized grains is increased. The present invention can make the hot-rolled plate structure more uniform, increase the number of recrystallized grains, and coarsen the grains and precipitates at the same time, strengthen the {100} and {110} components and weaken the {111} component, and further improve the magnetic properties of high-grade non-oriented silicon steel.

Description

Technical Field

[0001] The invention relates to a normalization method for improving the magnetic properties of high-grade non-oriented silicon steel, and belongs to the field of normalization technology of non-oriented silicon steel. Background Art

[0002] Silicon steel is an important soft magnetic material, widely used in fields such as motor and generator rotors in rotating magnetic fields. Non-oriented silicon steel is one of the commonly used core materials, which has low iron loss and high magnetic induction intensity. Therefore, improving its magnetic properties has always been a key research direction for researchers. The manufacturing process of high-grade non-oriented silicon steel includes steelmaking, hot rolling, normalizing pickling, cold rolling, annealing and coating of insulating coatings. Among them, hot-rolled plate normalizing is a commonly used process, which aims to make the hot-rolled plate structure more uniform, coarsen the grains and precipitates, strengthen the {100} and {110} components and weaken the {111} component, thereby improving its magnetic properties.

[0003] Patent CN105779731A in the prior art proposes a hot-rolled plate normalization process for improving the electromagnetic properties of low-grade non-oriented electrical steel. The normalization process control method of the non-oriented silicon steel hot-rolled plate is used to rapidly heat and slowly cool the hot-rolled plate, so that the proportion of favorable textures (100) and (110) in the steel plate is significantly increased, and the performance of the finished product is significantly improved. However, this method is for low-grade non-oriented electrical steel products, and its normalization heating temperature is set too high, which is not suitable for high-grade non-oriented electrical steel.

[0004] Patent CN 114196887 A discloses a non-oriented silicon steel for new energy drive motors and its production method. During steelmaking, no Cu, Cr, Ni, Nb, V, or Ti is added, and Si+2Al: 4.6% to 4.9%, Al / N ≥ 200 is satisfied. At the same time, the recrystallized grain size is controlled to be 50 μm to 80 μm, and the normalizing temperature is 840°C to 860°C and kept warm for 180s to 200s. While ensuring the magnetic properties, the strength is improved, which can meet the application requirements of the drive motors of new energy vehicles. However, this method mainly improves the performance of non-oriented silicon steel through component design. The normalizing temperature is too low and the recrystallized grain size is too small. Although the strength of non-oriented silicon steel is improved, it is not conducive to the improvement of the magnetic properties of high-grade non-oriented silicon steel.

[0005] Patent CN 112322972 A discloses a method for improving the comprehensive performance of high-strength non-oriented high silicon steel by normalizing treatment, which uses only silicon as a solid solution strengthening element without adding other alloying elements, and makes the hot-rolled plate microstructure entirely composed of coarse equiaxed crystals by keeping at 800-1200°C for 0.5-60min and air cooling, and the grain size of the normalized hot-rolled plate is 100-1500μm. However, this method mainly improves the strength of the material by increasing the silicon content and utilizing its solid solution strengthening ability, and the grain size of the obtained normalized hot-rolled plate is too large, which is not suitable for the high-grade non-oriented silicon steel products targeted by the present invention.

[0006] Patent CN 114606445 A discloses a production method for non-oriented silicon steel, wherein the chemical composition of the continuous casting billet includes, by mass percentage, C≤0.003%, Si: 3.5-4.5%, Al: 0.8-1.2%, Mn: 0.25-0.80%, Ni: 0.5-0.98%, P≤0.02%, S≤0.0020%, N≤0.0020%, Nb≤0.0020%, V≤0.0020%, Ti≤0.0020%, and the rest is Fe and unavoidable impurities; the addition relationship of Ni and Si / Al content is Ni=2*(Si-2.5) / 5+(Al-0.3) / 5; the normalizing annealing soaking temperature=850+120*x, and the soaking time is 120-150s; the normalizing annealing soaking temperature is in °C, x is the addition amount of Ni, in %, and the average grain size after normalization is 90±20μm. However, this method is aimed at non-oriented silicon steel products with high silicon content. By reasonably adding the micro-alloy element Ni, the toughness of the high silicon steel material is improved to obtain a non-oriented silicon steel product with high strength. However, the influence of normalizing cooling on the organizational structure is not considered, and it is not suitable for the high-grade non-oriented silicon steel products targeted by the present invention. Summary of the invention

[0007] In order to solve the problems existing in the above-mentioned prior art, the present invention provides a normalization method for improving the magnetic properties of high-grade non-oriented silicon steel. The present invention can make the hot-rolled plate structure more uniform, increase the number of recrystallized grains, coarsen the grains and precipitates, strengthen the {100} and {110} components and weaken the {111} component, and further improve the magnetic properties of high-grade non-oriented silicon steel.

[0008] To achieve the above object, the technical solution provided by the present invention is: a normalization method for improving the magnetic properties of high-grade non-oriented silicon steel, which at least includes non-oriented silicon steel, and the applicable non-oriented silicon steel components and weight percentage contents are: C≤0.003%, Si: 2.8%-3.2%, Al 0.9-1.4%, Mn 0.25-0.40%, P≤0.015%, S≤0.0020%, N≤0.0015%, Nb≤0.0020%, V≤0.0020%, Ti≤0.0020%, and the rest are Fe and unavoidable impurities, which comprises the following steps:

[0009] (1) Pre-treating the ingot: continuously casting the molten steel smelted in the converter, and heating the ingot obtained after continuous casting to 1100-1220° C.;

[0010] (2) Normalizing annealing of the ingot: After conventional hot rolling, the ingot is subjected to normalizing annealing, the ingot is heated to temperature T for a normalizing time of 150s to 220s;

[0011] The normalizing annealing soaking temperature T is determined according to the Si, Al and N contents in the steel, and the relationship is as follows:

[0012] 860+20×([Si]+2.5[Al])+8×ln[N]≤T≤900+35×([Si]+2.5[Al])+18×ln[N](1)Wherein: T is the normalizing annealing soaking temperature, unit is °C; [Si] is the amount of Si added, unit is %; [Al] is the amount of Al added, unit is %; [N] is the amount of N added, unit is %;

[0013] (3) Ingot cooling: After normalization, the ingot is first cooled by mist at a rate of 2-15°C / s to 550-620°C, and then cooled by water spray at a rate of 30-60°C / s to below 80°C.

[0014] (4) Cold-rolled strip: then cold-rolled to the finished thickness;

[0015] (5) Finished product processing: Finally, the finished product is annealed and an insulating coating is applied.

[0016] In step (2), since Si and Al are both beneficial to promoting grain growth, the normalizing annealing soaking temperature T is positively correlated with the Si and Al contents in the steel. N is an interstitial solid solution element. An increase in the N content easily leads to the precipitation of fine AlN and SiN inhibitors, which hinder grain growth and cause the magnetic properties of the steel plate to deteriorate. Therefore, the normalizing annealing soaking temperature T is negatively correlated with the N content. When the normalizing temperature of the hot-rolled plate satisfies formula (1), the grain size of the finished product after the final annealing is larger; when the normalizing temperature of the hot-rolled plate is greater than or less than formula (1), the grain size of the finished product after the final annealing will be too small.

[0017] In step (3), after entering the cooling section, mist cooling is first adopted, which is beneficial to reduce the cooling rate of the steel plate and increase the residence time in the slow cooling section, which is beneficial to allow the second phase particles that have been precipitated, such as carbides and nitrides, to fully aggregate and grow, so as to achieve harmless treatment of the precipitates and avoid the second phase particles from inhibiting the normal growth of grains during the recrystallization annealing process after cold rolling.

[0018] According to the above technical scheme, the normalization method for improving the magnetic properties of high-grade non-oriented silicon steel provided by the present invention controls the normalization and cooling process of high-grade non-oriented silicon steel, especially controls the normalization temperature and cooling rate of the strip steel, so that the hot-rolled plate structure is more uniform and the recrystallized grains are increased. Compared with the prior art, the present invention has the following advantages:

[0019] Because the technical solution adopted by the present invention determines the normalizing annealing soaking temperature T according to the Si, Al and N contents in the steel, and increases the proportion of recrystallized grains through normalizing and cooling processes, the present invention can be beneficial for obtaining the optimal finished grain size, thereby improving the magnetic properties of the finished steel plate. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0021] A normalization method for improving the magnetic properties of high-grade non-oriented silicon steel in the technical solution provided by the present invention comprises at least non-oriented silicon steel, and the applicable non-oriented silicon steel components and weight percentage contents are: C≤0.003%, Si: 2.8%-3.2%, Al 0.9-1.4%, Mn 0.25-0.40%, P≤0.015%, S≤0.0020%, N≤0.0015%, Nb≤0.0020%, V≤0.0020%, Ti≤0.0020%, wherein:

[0022] C≤0.003%: Low carbon is conducive to reducing the solid solubility of AlN. Coarse AlN in steel is not easy to dissolve, which can prevent the precipitation of fine AlN. It can also increase the final annealing temperature to promote grain growth and improve magnetic properties. The upper limit of the C content in the present invention is set to 0.003%.

[0023] Si: 2.8%-3.2%, silicon can effectively increase the resistivity of steel sheets and reduce the iron loss of finished products. However, as the silicon content increases, the cold rolling performance decreases, making it difficult to produce in batches stably.

[0024] Al: 0.9-1.4%: The effect of aluminum on magnetic properties is similar to that of silicon, increasing the resistivity of the steel plate, causing grain growth, and reducing the iron loss of the finished product. Aluminum increases the size of inclusions and precipitates, reducing the resistance to grain growth. However, when the aluminum content increases, the viscosity of the molten steel increases during casting. The upper limit of the Al content in the present invention is set at 1.4%.

[0025] N≤0.0015%: N is easy to form TiN and AlN precipitates with alloy elements such as Al and Ti in steel, which hinders the growth of grains during cold rolling and annealing, deteriorates the magnetic properties of the finished product, and increases the steel loss of silicon steel. Therefore, the upper limit of the N content in the present invention is set to 0.0015%.

[0026] P≤0.02%: As the Si+Al content increases, the grains become larger after normalization. The P element will segregate along the grain boundary, resulting in increased brittleness of silicon steel, and the P content should be reduced. The upper limit of the P content in the present invention is set at 0.02%.

[0027] S≤0.0020%: The lower the S content, the lower the steel loss of silicon steel. Therefore, the upper limit of the S content in the present invention is set to 0.0020%.

[0028] Mn: 0.25-0.40%: Manganese and sulfur in steel form fine MnS precipitates. Mn can coarsen MnS, which is beneficial to grain growth. As the S content in steel decreases, the Mn content should also decrease. The upper limit of the Mn content in the present invention is set to 0.40%.

[0029] Nb / V / Ti≤0.0020%: Nb / V / Ti will form fine precipitates with C / N atoms in steel, which strongly hinder the growth of grains during annealing. However, the addition of such carbon and nitrogen compound forming elements can reduce iron loss and non-magnetic aging. Therefore, the upper limit of the content of Nb / V / Ti microalloying elements in the present invention is set to 0.0020%.

[0030] The normalization method includes the following steps:

[0031] (1) Pre-treating the ingot: continuously casting the molten steel smelted in the converter, and heating the ingot obtained after continuous casting to 1100-1220° C.;

[0032] (2) Normalizing annealing of the ingot: After conventional hot rolling, the ingot is subjected to normalizing annealing, the ingot is heated to temperature T for a normalizing time of 150s to 220s;

[0033] The normalizing annealing soaking temperature T is determined according to the Si, Al and N contents in the steel, and the relationship is as follows:

[0034] 860+20×([Si]+2.5[Al])+8×ln[N]≤T≤900+35×([Si]+2.5[Al])+18×ln[N](1)

[0035] Wherein: T is the normalizing annealing soaking temperature, unit is °C; [Si] is the amount of Si added, unit is %; [Al] is the amount of Al added, unit is %; [N] is the amount of N added, unit is %;

[0036] Normalizing temperature is the key to normalizing treatment. If the normalizing temperature is too low, fibrous structure will remain. It cannot coarsen the grains and precipitates of hot-rolled plates, and cannot play the role of normalization. If the temperature is too high, it is easy to cause the precipitates to solid-dissolve and the grains of hot-rolled plates to be too coarse. Normalizing annealing soaking temperature T is positively correlated with the Si and Al contents in steel, because Si and Al are both conducive to promoting grain growth, and negatively correlated with N content, because nitrogen is an interstitial solid solution element. The increase in N content is easy to cause the precipitation of fine AlN and SiN inhibitors, which hinders grain growth and causes the magnetic properties of steel plates to deteriorate.

[0037] When the normalizing temperature of the hot-rolled plate satisfies formula (1), the grain size of the finished product after the final annealing is larger; when the normalizing temperature of the hot-rolled plate is greater than or less than the above formula, the grain size of the finished product after the final annealing will be too small.

[0038] (3) Ingot cooling: After normalization, the ingot is first cooled by mist at a rate of 2-15°C / s to 550-620°C, and then cooled by water spray at a rate of 30-60°C / s to below 80°C.

[0039] (4) Cold-rolled strip: then cold-rolled to the finished thickness;

[0040] (5) Finished product processing: Finally, the finished product is annealed and an insulating coating is applied.

[0041] If the normalizing time is too long, the AlN, an innate effective inhibitor in the hot-rolled plate, will be dissolved in the steel plate, and then fine and dispersed AlN inhibitors will precipitate, hindering the growth of grains. If the normalizing time is too short, it will lead to uneven grain growth and a low proportion of recrystallized grains.

[0042] Since the inhibitor AlN is easy to precipitate in the normalizing cooling stage, controlling the cooling rate of the steel plate is conducive to promoting the aggregation and growth of the precipitated inhibitor AlN, which cannot play the role of the inhibitor. Therefore, after entering the cooling section, the mist cooling method is first used to reduce the cooling rate of the steel plate and increase the residence time in the slow cooling section, which is conducive to the aggregation and growth of the precipitated second phase particles (carbides and nitrides, etc.), so as to achieve the harmless treatment of the precipitates and avoid the inhibition of the normal growth of the grains by the second phase particles during the recrystallization annealing after cold rolling.

[0043] In this embodiment 1, the composition content is as follows: the components and weight percentage content of the applicable steel are: C≤0.003%, Si: 2.8%, Al: 0.9%, Mn 0.25-0.40%, P≤0.015%, S≤0.0020%, N: 0.0015%, Nb≤0.0020%, V≤0.0020%, Ti≤0.0020%, and the rest is Fe and unavoidable impurities. Prepare according to the following steps:

[0044] 1) The molten steel is smelted in a converter and continuously cast, and the ingot is heated to 1100-1250°C and conventionally hot rolled;

[0045] 2) Perform normalizing annealing according to the process in Table 1, the normalizing soaking temperature is 950° C., satisfying the formula (1) proposed by the present invention, and keep warm for 150 seconds.

[0046] The normalized average temperature satisfies the empirical formula:

[0047] 860+20×([Si]+2.5[Al])+8×ln[N]≤T≤900+35×([Si]+2.5[Al])+18×ln[N]

[0048] 3) Cooling is performed according to the process in Table 1, and then entering the aerosol cooling section, cooling to 550-620°C at a rate of 10°C / s; then the second water spray rapid cooling method is performed, cooling to below 80°C at a rate of 50°C / s;

[0049] 4) then cold rolled to the finished thickness;

[0050] 5) Annealing the finished product;

[0051] 6) Finally, apply the insulating coating.

[0052] The magnetic properties of the finished steel plate were measured, and the results are shown in Table 2. It can be seen from Table 2 that when the normalizing annealing and cooling process meet the scope of the technical solution of the present invention, a high-grade non-oriented silicon steel product with excellent magnetic properties can be obtained. 5000 1.701T, P 1.5 / 50 It is 3.711w / kg.

[0053] Table 1 Main process parameters of various embodiments of the present invention and comparative examples

[0054]

[0055] Table 2 Magnetic properties

[0056]

[0057] It can be seen from the experimental results of the comparative examples and embodiments that:

[0058] In Comparative Example 1, the normalization and soaking temperature is too low, 905°C, which does not satisfy the formula (1) proposed by the present invention. The magnetic properties of the steel plate are poor, and B 5000 1.581T, P 1.5 / 50 It is 3.931w / kg.

[0059] In Comparative Example 2, the cooling rate in the first stage of normalization was too fast, and the magnetic properties of the steel plate were poor. 5000 1.575T, P 1.5 / 50 It is 3.945w / kg.

[0060] In Comparative Example 3, the normalization and soaking time is too short, 140s, which does not meet the normalization time required by the present invention, and the magnetic properties of the steel plate are poor. 5000 1.577T, P 1.5 / 50 It is 3.938w / kg.

Claims

1. A normalization method for improving the magnetic properties of high-grade non-oriented silicon steel, comprising at least non-oriented silicon steel, characterized in that: The applicable non-oriented silicon steel components and their weight percentage contents are: C≤0.003%, Si: 2.8%-3.2%, Al 0.9-1.4%, Mn 0.25-0.40%, P≤0.015%, S≤0.0020%, N≤0.0015%, Nb≤0.0020%, V≤0.0020%, Ti≤0.0020%, and the rest are Fe and unavoidable impurities, which comprises the following steps: (1) Pre-treating the ingot: continuously casting the molten steel smelted in the converter, and heating the ingot obtained after continuous casting to 1100-1220° C.; (2) Normalizing annealing of the ingot: After conventional hot rolling, the ingot is subjected to normalizing annealing, the ingot is heated to temperature T for a normalizing time of 150s to 220s; The normalizing annealing soaking temperature T is determined according to the Si, Al and N contents in the steel, and the relationship is as follows: 860+20×([Si]+2.5[Al])+8×ln[N] ≤ T ≤ 900+35×([Si]+2.5[Al])+18×ln[N](1) Wherein: T is the normalizing annealing soaking temperature, unit is °C; [Si] is the amount of Si added, unit is %; [Al] is the amount of Al added, unit is %; [N] is the amount of N added, unit is %; (3) Ingot cooling: After normalization, the ingot is first cooled by mist at a rate of 2-15°C / s to 550-620°C, and then cooled by water spray at a rate of 30-60°C / s to below 80°C. (4) Cold-rolled strip: then cold-rolled to the finished thickness; (5) Finished product processing: Finally, the finished product is annealed and an insulating coating is applied.

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