A preparation method of high magnetic induction oriented electrical steel

Abstract

The invention relates to a preparation method of high magnetic induction oriented electrical steel, which comprises steelmaking, continuous casting, heating of ingots, hot rolling, normalizing annealing, cold rolling, continuous annealing and coating of an isolation layer, high temperature annealing, and hot stretching and flattening. The continuous annealing process comprises a nitriding treatment process, and the nitriding atmosphere of the nitriding treatment process satisfies the following relationship: wherein T is the nitriding temperature, unit, ° C; is the partial pressure of H2 in the nitriding atmosphere; t is the treatment time, unit, s; is the partial pressure of NH3 in the nitriding atmosphere; N1 is the nitrogen content in the steel after nitriding; in the nitriding treatment process, the invention can efficiently and accurately control the nitriding amount by adjusting the relationship between the nitriding parameters and the nitrogen content after nitriding, thereby improving the yield rate and the nitriding efficiency in the production process of electrical steel.

Description

Technical Field

[0001] The invention relates to the technical field of electrical steel manufacturing, and in particular to a method for preparing high magnetic induction oriented electrical steel, specifically comprising a nitriding method for high magnetic induction oriented electrical steel. Background Art

[0002] Silicon steel has excellent magnetic properties such as low loss and low magnetostriction. As a magnetic material, it has important applications in the power and electronics industries. The traditional process flow of high magnetic induction oriented electrical steel is: smelting-continuous casting-normalizing pickling-cold rolling-annealing-coating. The commonly used production method is: steelmaking in a converter, refining outside the furnace, and continuous casting into slabs. Its basic chemical composition is C: 0.04-0.10%, Si: 3.0-4.0%, Mn: 0.03-0.12%, S: 0.015-0.055%, Als: 0.02-0.06%, N: 0.002-0.010%. Some component systems also contain at least one of the elements Cu, Se, B, etc., and the rest are iron and unavoidable impurities. The slab is heated to a temperature of 1360-1400℃ in a special high-temperature heating furnace and kept warm for at least 120 minutes to fully dissolve the favorable inclusions MnS and AlN, and then rolled. The final rolling temperature reaches above 950℃, and it is quickly cooled to below 600℃ by spraying water, and then coiled. In order to precipitate fine and dispersed AlN second phase particles in the silicon steel matrix, the hot-rolled plate needs to be normalized and then pickled, and then cold-rolled to the finished thickness, and finally decarburized annealed and coated with an isolation agent. During the high-temperature annealing process, the steel plate undergoes secondary recrystallization to form a Mg2SiO4 bottom layer and purify the steel. After coating with an insulating coating and stretching annealing, a high magnetic induction oriented silicon steel with low iron loss is obtained.

[0003] If a low-temperature process is used for production, nitriding treatment is usually required after decarburization annealing. Patent CN106755873A discloses a production method for high-magnetic steel oriented silicon steel, which comprehensively considers the relationship between the nitriding amount and the nitriding temperature, and proposes a relationship and control range between the two, but does not disclose the influence of the nitriding atmosphere on the nitriding during the nitriding process. In order to effectively solve the above problems, the present invention aims to provide a preparation method of low-temperature high-magnetic induction oriented electrical steel, especially a nitriding method therein, so as to efficiently and accurately control the nitriding amount and improve the yield rate. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for preparing high magnetic induction oriented electrical steel, which includes steelmaking, continuous casting, heating of ingots, hot rolling, normalizing annealing, cold rolling, continuous annealing and coating of an isolation layer, high temperature annealing, and hot stretching and flattening. The continuous annealing process includes a nitriding treatment process, wherein the nitriding atmosphere of the nitriding treatment process is The following relationship is satisfied:

[0005]

[0006] In formula (1)

[0007] T is the nitriding temperature, unit: °C;

[0008] is the partial pressure of H2 in the nitriding atmosphere;

[0009] t is the treatment time, unit: s;

[0010] is the partial pressure of NH3 in the nitriding atmosphere;

[0011] N1 is the nitrogen content in the steel after nitriding;

[0012] And, after nitriding treatment, the grain size of the steel strip satisfies the following relationship:

[0013] D1 / D2 = 0.8 - 0.9 Formula (2)

[0014] In formula (2)

[0015] D1 is the average grain diameter of the upper and lower surfaces of the steel strip after nitriding treatment;

[0016] D2 is the average grain diameter in the center plane in the thickness direction after nitriding treatment.

[0017] Furthermore, in the nitriding treatment process, the nitriding atmosphere is N2 + H2 + NH3, the partial pressure of N2 is 10 - 80%, the partial pressure of H2 is 5 - 60%, the partial pressure of NH3 is 0.5 - 15%, and after nitriding is completed, an isolation layer is coated.

[0018] Furthermore, the isolation layer is MgO.

[0019] Furthermore, in the steelmaking process, the mass percentages of the chemical components of the molten steel are: C: 0.001 - 0.075%, Si: 3.0 - 3.4%, Mn: 0.05 - 0.8%, Als: 0.002 - 0.060%, P: 0.007 - 0.080%, S: 0.001 - 0.020%, N: 0.003 - 0.020%, Sn: 0.05 - 0.28%, B: 0.0005 - 0.0050%, Sb: 0.005 - 0.015%, Mo: 0.0006 - 0.002%.

[0020] C, as an important element in the manufacture of grain-oriented silicon steel, is an element that expands the austenite phase. For high magnetic induction grain-oriented electrical steel, C can promote the hot-rolled strip deformation structure and refine the structure after hot rolling; C can increase the proportion of the austenite region during normalizing annealing. Since the solubility of N in austenite is much higher than that in ferrite, the solid solution amount of N can be increased, promoting the precipitation of AlN particles during subsequent rapid cooling; C also enables the acquisition of fine and uniform primary grains during annealing after cold rolling, promoting the development of secondary recrystallization. If C < 0.001%, the improvement effect is not obvious; however, if C > 0.075%, it will cause too long decarburization time and difficult decarburization, affecting production efficiency. Therefore, preferably, C needs to be controlled within 0.001 - 0.075%.

[0021] Si can increase the resistivity of the material and is the most effective element for reducing iron loss. When the Si content exceeds 3.4%, the steel material will be too brittle, causing difficulties in cold rolling and poor welding performance; if the Si content is lower than 3.0%, the iron loss of the finished material is too high; therefore, preferably, the Si content needs to be controlled within the range of 3.0 - 3.4%.

[0022] Mn, like Si, can increase the material resistivity to reduce iron loss, and through nitriding treatment, react with Si and N to form precipitates of (Al, Si, Mn)N, inhibiting the growth of primary recrystallization grains and promoting the formation of secondary recrystallization. If Mn > 0.8%, a large amount of (Fe, Mn) oxides and Mn oxides will easily form on the steel plate surface, which will hinder the formation of the bottom layer during high-temperature annealing; and it is easy to combine with S to form large MnS precipitates, reducing the magnetism. When Mn < 0.05%, hot brittleness is likely to occur. Therefore, preferably, the Mn content should be controlled within 0.05 - 0.8%.

[0023] P can promote the growth of primary grains, avoid non-uniform grains after nitriding treatment, and increase the starting temperature of secondary recrystallization, increasing the proportion of Goss grains in the finished product; at the same time, P is a grain boundary segregation element, which can improve the inhibition ability, increase the component of {110} in the primary recrystallization texture, and the secondary grains are small. And P segregates around MnS and AlN, which can prevent the coarsening of precipitated particles and promote the more uniform distribution of precipitated particles, so the electromagnetic properties of the material can be improved. However, if the content is too high, the brittleness of the material becomes large, resulting in difficult rolling. Therefore, preferably, the P content needs to be controlled within 0.007 - 0.080%.

[0024] S is an element with a high solid solution temperature and severe segregation during hot rolling. When > 0.020%, hot brittleness is easily caused; when < 0.001%, the number of MnS after hot rolling is too small, reducing the initial inhibition ability. Therefore, preferably, the S content needs to be controlled within 0.001 - 0.020%.

[0025] N combines with Al to form a grain growth inhibition phase. If N > 0.0020%, the primary grain size will be too small, and there will be easy swelling during casting, and defects such as peeling and blistering will occur on the product; if N < 0.003%, it will cause smelting difficulties, increase the time of subsequent nitriding treatment, and reduce production efficiency. Therefore, preferably, N needs to be controlled within 0.003 - 0.020%.

[0026] After Al combines with N, it precipitates in the form of AlN. During nitriding treatment, nitrides such as (Al, Si, Mn)N and AlN will precipitate dispersively, which can effectively inhibit grain growth. When Als < 0.008, the quantity and volume fraction of the precipitates formed are both relatively low, and the grain growth cannot be fully inhibited; when Als > 0.060%, the size of the precipitates is too large, reducing the inhibitory effect on grain growth. Therefore, preferably, Als needs to be controlled within 0.002 - 0.060%.

[0027] Sn is a grain boundary segregation element and has the effect of hindering grain boundary movement. Therefore, it can be used as an inhibitor of grain growth. Moreover, it can increase the proportion of Goss-oriented grains in the primary recrystallized structure, increase the nuclei of Goss orientation in the secondary recrystallized structure, reduce the size of the secondary recrystallized grains, and reduce the iron loss of the finished product. In addition, Sn can also prevent the growth of (Al, Si, Mn)N and AlN particles during high-temperature annealing, thereby reducing the inhibitory effect on grain growth. If Sn < 0.05%, the effect is not obvious; if Sn > 0.28%, the inhibitory force of grain growth is too strong. Therefore, the temperature of decarburizing annealing needs to be reduced to reduce the size of the primary recrystallized grains and increase the driving force of grain growth, resulting in an inappropriate thickness of the oxide layer during primary annealing, so that a good bottom layer cannot be formed during high-temperature annealing. Therefore, preferably, the Sn content is controlled within 0.005 - 0.28%.

[0028] The chemical affinity of B with N is stronger than that of Al, and the diffusion rate is also faster. BN precipitates preferentially during hot rolling and can be used as an inhibitor of grain growth. When B < 0.0005%, the effect is not obvious, but if B > 0.0050%, due to BN, it is easy to cause instability of secondary recrystallization, resulting in poor electromagnetic properties. Therefore, preferably, the B content is controlled within 0.0005 - 0.0050%.

[0029] Sb increases the proportion of Goss-oriented grains and improves the battery performance, but Sb hinders decarburization. Therefore, preferably, the Sb content is controlled within 0.005 - 0.015%.

[0030] Mo enriches on the surface, which can prevent grain boundary oxidation at high temperatures and can also reduce surface oxidation and improve the quality of the bottom layer. When Mo is too high, the surface oxidation is too little and the quality of the bottom layer changes; when it is too low, the effect is not obvious. Therefore, preferably, the Mo content is controlled within 0.0006 - 0.002%.

[0031] Furthermore, after the nitriding process, the nitrogen content N1 in the steel satisfies the following relationship:

[0032] 190+21Als+1450B-1030N <N1<205+23Als+1480B-1020N 式(3)

[0033] In formula (3)

[0034] Als is the content of Als in the chemical composition of molten steel;

[0035] B is the content of B in the chemical composition of molten steel;

[0036] N is the N content in the chemical composition of molten steel.

[0037] Furthermore, the continuous annealing process also includes a decarburization process, the decarburization atmosphere is N2+H2+H2O, the H2 content is 0-50%, and the partial pressure of H2O and H2 is reasonably controlled so that the partial pressure P H2O / P H2 Between 0.30 and 0.80, the annealing temperature is 850 to 950°C, and the holding time is 100 to 300s.

[0038] The principle of nitriding high magnetic induction oriented electrical steel in the present application is to adjust the nitriding time. Parameters can be used to efficiently and accurately control the nitriding amount and improve the yield rate.

[0039] 1) Increase the partial pressure of NH3 in the atmosphere The amount of nitrogen atoms in the nitriding atmosphere can be increased, so that more active nitrogen atoms can penetrate into the strip at the same time, and the nitrogen content in the strip will also increase;

[0040] 2) As the temperature increases, according to Fick's first law, the diffusion rate of active nitrogen atoms is proportional to the diffusion coefficient, and the diffusion coefficient is exponentially related to temperature, that is, the diffusion rate will increase sharply with the increase of temperature, which means that more active nitrogen atoms will penetrate into the strip at the same time, and the nitrogen content in the strip will also increase;

[0041] 3) Prolonging the nitriding time will increase the nitrogen content concentration on the strip surface and the nitrogen concentration gradient between the strip and the interior of the strip, thereby increasing the driving force for the nitrogen atoms to diffuse inward. More nitrogen atoms will enter the strip and the nitrogen content will increase accordingly. At the same time, as the nitriding time increases, the nitrogen content in the strip may approach saturation, thereby slowing down the nitriding growth rate.

[0042] Due to the adoption of the above technical solution, the present invention has the following beneficial effects compared with the prior art: the nitriding process in the preparation of high magnetic induction oriented electrical steel of the present invention can adjust the nitriding parameters The relationship between nitrogen content after nitriding can effectively and accurately control the nitriding amount, improve the yield rate, and improve the nitriding efficiency in the production process of electrical steel. DETAILED DESCRIPTION

[0043] The present invention provides a method for preparing high magnetic induction oriented electrical steel. In this embodiment, the chemical composition mass percentage of molten steel for preparing high magnetic induction oriented electrical steel is: C: 0.001-0.075%, Si: 3.0-3.4%, Mn: 0.05-0.8%, Als: 0.002-0.060%, P: 0.007-0.080%, S: 0.001-0.020%, N: 0.003-0.020%, Sn: 0.05-0.28%, B: 0.0005-0.0050%, Sb: 0.005-0.015%, Mo: 0.0006-0.002%, and meets: -0.1111+0.0385Si+0.0058Als-2.816B <N<-0.1100+0.039Si+0.0059Als-2.815B,式中Si、Als、B、N分别为相对应成分的含量,其余为Fe和不可避免的杂质,电工钢制备过程包括如下步骤:

[0044] 1) Steelmaking;

[0045] 2) Thin strip continuous casting and hot rolling, the molten steel in S1 is introduced into a crystallization roller to prepare a cast strip, the crystallization roller is preferably a double-roller crystallization roller, of course, other structures of the crystallization roller can also be used, the casting temperature is 1500-1600°C, the crystallization roller speed is 20-100m / min, and a cast strip with a thickness and width of 0.8-4.0mm×500-1500mm is obtained. The temperature of the cast strip coming out of the crystallization roller is relatively high. It is cooled at a cooling rate of 15-25°C / s in a protective atmosphere such as Ar and / or N2, and the temperature of the cast strip is controlled at 900-1150°C, and then 1-3 stands of hot rolling are carried out, the final rolling temperature of the hot rolling is 800-950°C, the total reduction is 10-50%, and after hot rolling, it is cooled to 500-700°C at a cooling rate of 15-35°C / s, and can be cooled by water spraying, and then coiled at 500-700°C to obtain a hot-rolled strip with a thickness of 0.5-3.5mm;

[0046] 3) Normalizing annealing: The hot-rolled strip obtained in S2 is subjected to normalizing pickling treatment on a normalizing pickling unit. The atmosphere for normalizing treatment is Ar, N2 or other inert gases, preferably N2 atmosphere, the temperature is 1120 °C, and the holding time is 30 - 220 s, or it is first heated to 950 - 1250 °C, where the time above 1020 - 1250 °C is 30 - 60 s. The cooling process is as follows: first, it is cooled at a cooling rate of 5 - 10 °C / s to 800 - 1000 °C, held for 60 - 90 s, then cooled at a cooling rate of 10 - 15 °C / s to 500 - 600 °C, and finally cooled to below 80 °C at a cooling rate greater than the previous two times. The last cooling is carried out as fast as possible. Then shot blasting is carried out to remove phosphorus until the surface cleanliness is above Sa 2.0, and pickling is carried out with 5 - 15% HCl for 60 - 150 s. Of course, the pickling solution can also use acidic solutions such as H2SO4. After pickling, a normalized pickled strip is obtained;

[0047] 4) Cold rolling: The normalized pickled strip is cold-rolled on 4 - 7 stands. A 6-high continuous rolling mill or a 6-high or 18-high or 20-high single stand can be used. The total cold rolling reduction rate is 40 - 90%, and a cold-rolled sheet with a thickness of 0.15 - 0.50 mm is obtained;

[0048] 5) Continuous annealing and decarburization nitriding: The cold-rolled sheet in S4 is subjected to annealing treatment for decarburization nitriding in a controlled atmosphere. The decarburization atmosphere is N2 + H2 + H2O, and the H2 content is 0 - 50%. The partial pressures of H2O and H2 are reasonably controlled so that the partial pressure P H2O / P H2 is between 0.30 and 0.80. The annealing temperature is 800 - 950 °C, and the holding time is 100 - 300 s; then nitriding treatment is carried out in an atmosphere of N2 + H2 + NH3, where the N2 partial pressure is 10 - 85%, the H2 partial pressure is 5 - 60%, and the NH3 partial pressure is 0.5 - 15%. The nitriding temperature is 650 - 950 °C, and the nitriding time is 15 - 60 s; after annealing, a MgO isolation layer is coated on the surface;

[0049] 6) High-temperature annealing: Annealing treatment is carried out at a temperature of 1150 - 1250 °C;

[0050] 7) Hot stretching: An insulating coating is applied on the hot stretching unit, and then the high magnetic induction oriented electrical steel in the present application can be obtained. The hot stretching annealing temperature is 550 - 950 °C.

[0051] Optimized implementation method: In the nitriding treatment process of the continuous annealing, the nitriding atmosphere satisfies the following relational expression:

[0052]

[0053] In formula (1)

[0054] T is the nitriding temperature, unit, °C;

[0055] is the partial pressure of H2 in the nitriding atmosphere;

[0056] t is the processing time, unit, s;

[0057] is the partial pressure of NH3 in the nitriding atmosphere;

[0058] N1 is the nitrogen content in the steel after nitriding.

[0059] The nitrogen content in the steel after nitriding can be determined by the following relationship, which satisfies 190+21Als+1450B-1030N <N1<205+23Als+1480B-1020N,式中Als、B、N为钢水中相对应成分的含量;

[0060] Moreover, the grain size of the steel strip after nitriding treatment satisfies the following relationship:

[0061] D1 / D2=0.8~0.9 Formula (2)

[0062] In formula (2), D1 is the average grain diameter on the upper and lower surfaces of the steel strip after nitriding treatment;

[0063] D2 is the average diameter of the grains in the center plane of the thickness after nitriding treatment.

[0064] In the above process, the overall preparation process of high magnetic induction oriented electrical steel is shortened compared with the traditional process, which is a short process manufacturing with low energy consumption; and in the nitriding process, by adjusting the nitriding parameters The relationship between nitrogen content after nitriding can effectively and accurately control the nitriding amount, improve the yield rate, and improve the nitriding efficiency in the production process of electrical steel.

[0065] Three embodiments are described below:

[0066]

[0067]

[0068]

[0069] Through the above three embodiments, the iron loss P of electrical steel 17 / 50 ≤0.875kW / kg, magnetic induction intensity B 800 ≥1.910T, among which the electrical steel prepared in Example 3 has the best performance, and is much higher than the performance of the product produced by the conventional production method (P 17 / 50 =0.850W / kg, B 800= 1.913 T), further indicating that the manufacturing method of the high magnetic induction oriented electrical steel provided by the present invention can manufacture electrical steel with excellent properties.

[0070] Those skilled in the art of this technology should understand that the present invention can be implemented in many other specific forms without departing from the spirit and scope of the present invention. Although embodiments of the present invention have been described, it should be understood that the present invention should not be limited to these embodiments, and those skilled in the art of this technology can make changes and modifications within the spirit and scope of the present invention defined by the appended claims.

Claims

1. A method for preparing high magnetic induction oriented electrical steel, which includes steelmaking, continuous casting, heating of the cast slab, hot rolling, normalizing annealing, cold rolling, continuous annealing and coating an isolation layer, high temperature annealing, and hot stretch leveling, characterized in that, The continuous annealing process includes a nitriding treatment process, wherein, in the nitriding atmosphere of the nitriding treatment process satisfies the following relational expression: In formula (1) T is the nitriding temperature, unit: °C; is the partial pressure of H2 in the nitriding atmosphere; t is the treatment time, unit: s; is the partial pressure of NH3 in the nitriding atmosphere; N1 is the nitrogen content in the steel after nitriding, unit: ppm; Moreover, after the nitriding treatment, the grain size of the steel strip satisfies the following relationship: D1 / D2 = 0.8 - 0.9 Formula (2) In formula (2) D1 is the average grain diameter of the upper and lower surfaces of the steel strip after nitriding treatment; D2 is the average grain diameter in the center plane in the thickness direction after nitriding treatment.

2. The preparation method of the high magnetic induction oriented electrical steel according to claim 1, wherein, In the nitriding treatment process, the nitriding atmosphere is N2 + H2 + NH3, the partial pressure of N2 is 10 - 80%, the partial pressure of H2 is 5 - 60%, the partial pressure of NH3 is 0.5 - 15%. After nitriding, an isolation layer is coated.

3. The preparation method of the high magnetic induction oriented electrical steel according to claim 2, wherein, The isolation layer is MgO.

4. The preparation method of the high magnetic induction oriented electrical steel according to claim 1, characterized in that During the steelmaking process, the mass percentages of the chemical components of the molten steel are: C: 0.001 - 0.075%, Si: 3.0 - 3.4%, Mn: 0.05 - 0.8%, Als: 0.002 - 0.060%, P: 0.007 - 0.080%, S: 0.001 - 0.020%, N: 0.003 - 0.020%, Sn: 0.05 - 0.28%, B: 0.0005 - 0.0050%, Sb: 0.005 - 0.015%, Mo: 0.0006 - 0.002%.

5. The preparation method of the high magnetic induction oriented electrical steel according to claim 4, wherein After the nitriding treatment process, the nitrogen content N1 in the steel satisfies the following relationship: 190 + 21Als + 1450B - 1030N < N1 < 205 + 23Als + 1480B - 1020N Formula (3) In formula (3) Als is the content of Als in the chemical components of the molten steel; B is the content of B in the chemical components of the molten steel; N is the content of N in the chemical components of the molten steel.

6. The preparation method of the high magnetic induction oriented electrical steel according to claim 1, characterized in that, The continuous annealing process further includes a decarburization treatment process. The decarburization atmosphere is N2 + H2 + H2O, and the H2 content is 0 to 50%. The partial pressures of H2O and H2 are reasonably controlled so that the partial pressure P H2O / P H2 is between 0.30 and 0.80, the annealing temperature is 850 to 950 °C, and the holding time is 100 to 300 s.

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