Magnetism and strength collaborative optimization method based on high-silicon aluminum alloying oriented silicon steel

Abstract

The invention provides a magnetism and strength collaborative optimization method based on high-silicon-aluminum alloying oriented silicon steel, which comprises vacuum refining, multi-stage rolling, gradient annealing and coating processes, and effectively solves the problems of cold rolling brittleness and contradiction between magnetic induction and mechanical strength caused by high-silicon-aluminum alloying by accurately controlling components, rolling parameters and heat treatment conditions. The method has the advantages that cold rolling brittleness and magnetic performance requirements caused by high silicon content are effectively balanced, and through collaborative optimization of multi-stage rolling and heat treatment processes, magnetic induction stability is guaranteed while strength is improved, and texture sharpness and uniformity are improved.

Description

Technical Field

[0001] The present invention relates to the field of improving the properties of grain-oriented electrical steel, and particularly to a method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented electrical steel. Background Art

[0002] High-silicon aluminum alloying is the core strategy for improving the strength of grain-oriented electrical steel. Among them, silicon improves the resistivity and reduces iron loss through solid solution strengthening, while aluminum improves magnetic properties by refining grains and regulating precipitation phases. However, high-silicon aluminum alloyed grain-oriented electrical steel faces a series of technical problems in the process of synergistically optimizing magnetic properties and strength. First, although high silicon content can improve resistivity, it also leads to cold rolling brittleness, and warm rolling or gradient rolling processes are required to balance the processing performance. Second, there is a contradiction between magnetic induction and mechanical strength. While high silicon content improves resistivity, it reduces toughness, and grain orientation control and inhibitor design are required to balance the properties. In addition, texture sharpness and uniformity are also key issues. The orientation deviation angle of the Goss texture needs to be controlled within a small range, and coarse grains will lead to an increase in magnetostriction. Finally, the contradiction between process energy consumption and performance stability also needs to be solved. Although low-temperature heating can reduce energy consumption, nitriding is required to compensate for the shortage of inhibitors. In view of the above problems, the existing technology urgently needs to be improved. Summary of the Invention

[0003] In order to solve the above technical problems, the purpose of the present application is to provide a method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented electrical steel, which can effectively balance the cold rolling brittleness brought by high silicon content and the magnetic property requirements, and through the synergistic optimization of multi-stage rolling and heat treatment processes, ensure the magnetic induction stability while improving the strength, and improve texture sharpness and uniformity.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present application provides a method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented electrical steel. The technical solution is as follows: including the following steps,

[0006] a) Smelting and casting: adopting a vacuum refining process to control the dissolved oxygen content and sulfur content in the molten steel, and casting into a steel billet;

[0007] b) Hot rolling: heating the cast billet to 1250 - 1320 °C, with soaking time ≥ 60 min, and continuously rolling using a tandem mill;

[0008] c) Normalizing treatment: adopting a two-stage normalizing treatment, first heating to 1100 - 1200 °C, cooling to 900 - 1000 °C within 50 - 200 s; then rapidly cooling in water at 10 - 100 °C;

[0009] d) Cold rolling: Conduct one-time cold rolling or two-time cold rolling with intermediate annealing. During the cold rolling process, adjust the magnitude of the friction during cold rolling, control the reduction ratio of the first cold rolling pass according to the molten steel composition and the thickness of the hot-rolled sheet, as well as the number of cold rolling aging times and the rolling speeds of different passes, and increase the Si content to 3.6% - 3.9%;

[0010] e) Decarburizing annealing: Pass a dry mixture of nitrogen and hydrogen into the front area before decarburizing annealing, pass a wet mixture of nitrogen and hydrogen into the rear area after decarburizing annealing for decarburization, and pass a wet mixture of nitrogen and hydrogen and ammonia into the nitriding area for nitriding;

[0011] f) Nitriding treatment: Conduct two-time cold rolling after decarburizing annealing, and then cold coat with magnesium oxide isolating agent;

[0012] g) Coating annealing isolating agent: Coat the isolating agent on the cold-rolled strip steel after decarburizing annealing and nitriding treatment, dry the cold-rolled strip steel coated with the isolating agent and coat with an activating agent, and then coil to obtain a steel coil;

[0013] h) High-temperature annealing: Anneal the steel coil to obtain silicon steel;

[0014] i) Hot stretching and leveling annealing: Coat an insulating layer and conduct hot stretching and leveling on the oriented silicon steel raw material after high-temperature annealing;

[0015] j) Insulating coating: On the basis of the existing insulating coating composition, sequentially add potassium dihydrogen phosphate and zirconium oxychloride to form a high-tension coating solution and coat it on the surface of the oriented silicon steel to obtain a high-tension coating.

[0016] Furthermore, the present application also proposes that in step b), the multi-stand rolling mill is set as a 7-stand rolling mill, and during the continuous rolling process of the 7-stand rolling mill, the reduction ratio of each pass decreases successively, with the initial reduction ratio being 45% and the final reduction ratio being 5%.

[0017] Furthermore, the present application also proposes that in step b), it further includes

[0018] Segmented control of hot rolling temperature gradient and rate: Raise the temperature of the head and tail of the hot-rolled strip steel by 100 - 300 °C to compensate for the heat dissipation loss caused by the difference in cold tandem rolling rate; The rolling rate in the middle of the hot-rolled strip steel is 20 - 30% higher than that of the head and tail.

[0019] Furthermore, the present application also proposes that in step b), it further includes that after hot rolling, it is necessary to coil at 530 - 580 °C to make AlN precipitate dispersively along the austenite grain boundary.

[0020] Furthermore, the present application also proposes that in step a), it further includes remelting the steel billet for directional solidification to make the columnar crystals grow along the <001> direction and reduce the deviation angle of the transverse texture divergence by <5°.

[0021] Further, the present application also proposes that in step a), the dissolved oxygen content in the molten steel is controlled to be ≤20 ppm, and the sulfur content is controlled to be ≤50 ppm.

[0022] Further, the present application also proposes that in step d), it further includes

[0023] Deformation energy storage gradient design: Adopt a "high - low - high" pass reduction rate to form a layered energy storage structure during cold rolling.

[0024] Further, the present application also proposes that in step e), it further includes

[0025] Precise control of annealing atmosphere: During annealing, a gradient heating from 50 °C / h to 20 °C / h is adopted, so that the standard deviation of the secondary grain size is reduced from the conventional 35% to 18%.

[0026] Further, the present application also proposes that in step g), the components of the active agent include low - melting - point compounds, and the melting point of the low - melting - point compounds is ≤900 °C.

[0027] Further, the present application also proposes that in step i), it further includes

[0028] In a furnace filled with N2 + H2 protective gas, under the furnace condition of 700 °C, apply an appropriate tension to the steel strip for coating sintering and hot stretch leveling.

[0029] As can be seen from the above, a method for synergistically optimizing the magnetism and strength of high - silicon aluminum alloyed grain - oriented silicon steel provided by the present application includes vacuum refining, multi - stage rolling, gradient annealing, and coating processes. By precisely controlling the composition, rolling parameters, and heat treatment conditions, it effectively solves the cold - rolling brittleness and the contradiction between magnetic induction and mechanical strength brought about by high - silicon aluminum alloying, effectively balances the cold - rolling brittleness brought about by high - silicon content and the magnetic property requirements, and through the synergistic optimization of multi - stage rolling and heat treatment processes, while improving the strength, ensures the stability of magnetic induction, and improves the sharpness and uniformity of the texture. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the steps of a method for synergistically optimizing the magnetism and strength of high - silicon aluminum alloyed grain - oriented silicon steel according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0032] In the description of the present invention, it should be understood that if there are terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0033] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0034] As Figure 1 shown, in the prior art, there is a contradictory relationship between the magnetic properties and mechanical strength of grain-oriented electrical steel. In the traditional process, when increasing the silicon content to enhance the resistivity, edge cracking defects often occur in the cold rolling process due to the brittleness of the material. The coarse austenite grains formed by the conventional hot rolling process will reduce the magnetic induction index, while the low-temperature annealing can refine the grains but affect the perfection degree of secondary recrystallization. In the decarburization treatment stage, it is difficult to balance the surface decarburization and the formation of internal inhibitors with a single atmosphere control, resulting in disordered magnetic domain structures.

[0035] To solve the above problems, the R & D personnel found that element segregation in the high-silicon aluminum alloying system is the main cause of induced brittleness, and it is necessary to optimize the element distribution through the reengineering of the whole process technology. A gradient rolling strategy is proposed to compensate for the heat dissipation loss in view of the grain size difference caused by the uneven temperature field during the hot rolling process. To solve the problem of brittle cracking in cold rolling, a dynamic reduction rate adjustment mechanism is adopted to balance the deformation energy storage and stress release. Facing the timing contradiction between decarburization and nitriding, surface modification and internal precipitate phase co-control are achieved through zoned gas regulation.

[0036] Therefore, this application proposes a process system including smelting and casting, hot rolling, normalizing treatment, cold rolling, decarburizing annealing, nitriding treatment, release agent coating, high-temperature annealing, hot stretch leveling, and insulation coating. Among them, the vacuum refining process refers to a method of removing gas inclusions in molten steel using a vacuum environment, which can be specifically achieved by vacuum induction melting combined with inert gas protection to effectively reduce the hindrance of oxygen and sulfur elements to the movement of magnetic domains. The multi-stand continuous rolling refers to using rolling equipment with multiple stands arranged continuously for slab forming. For example, a seven-stand continuous rolling mill is configured to achieve uniform plastic deformation through a decreasing reduction rate for each pass. The two-stage normalizing treatment refers to a heat treatment process in which the sheet is first heated evenly at a high temperature and then rapidly cooled, which can be performed using a radiant tube heating furnace combined with a water spray cooling device to refine the original austenite grains through phase transformation control. The dynamic cold rolling control refers to a process of adjusting rolling parameters in real time according to the composition and thickness of the sheet. For example, a hydraulic AGC system is used to online adjust the reduction per pass and rolling speed to balance the deformation resistance and work hardening effect of high-silicon materials. The zoning gas-controlled decarburizing annealing refers to a method of introducing different atmospheres in different sections of the annealing furnace. For example, a dry mixed gas is used in the front section to improve the decarburization efficiency, and a wet gas is introduced in the rear section to promote the penetration of nitrogen elements to achieve a gradient distribution of surface carbon content. The layered energy storage cold rolling design refers to constructing a differential dislocation density distribution through changes in the reduction rate per pass. For example, a combination of high-low-high reduction rates is used to form a gradient deformation energy field to provide a driving force difference for subsequent recrystallization.

[0037] Specifically, in the smelting stage, the oxygen and sulfur contents are precisely controlled through vacuum refining to provide a pure matrix for subsequent rolling. In the hot rolling process, a gradient temperature compensation mechanism is adopted, where the temperature rise at the head offsets the heat dissipation caused by roll contact, and the speed is increased in the middle to ensure rolling stability. In the two-stage normalizing treatment, the residual stress from hot rolling is first eliminated through high-temperature soaking, and then rapid cooling is used to inhibit excessive grain growth. In the cold rolling stage, the reduction of the first pass is adjusted according to the composition of the sheet detected in real time. For example, when the silicon content reaches the upper limit, the reduction rate is appropriately reduced, and aging treatment is combined to release the processing stress. In the front zone of the decarburizing annealing, the dry atmosphere accelerates the outward diffusion of carbon elements, and in the rear zone, the wet environment promotes the penetration of nitrogen atoms into the matrix to form a composite structure with low carbon and high nitrogen on the surface. After nitriding treatment, secondary cold rolling induces the precipitation of nitrides along the grain boundaries, and the magnesium oxide release agent coating provides a uniform grain boundary migration environment for high-temperature annealing. The activator coating forms a liquid film layer at the initial stage of annealing through low-melting compounds to promote grain boundary sliding and eliminate local stress concentration. The final high-tension insulation coating matches the thermal expansion coefficient of the matrix to inhibit the interfacial peeling phenomenon caused by magnetostriction.

[0038] Compared with the existing technology, the traditional method uses a single-stage normalizing treatment, which is prone to uneven grain size distribution. This solution uses two-stage temperature control to achieve precise control of the phase change process. Conventional decarburization annealing uses a single atmosphere, which leads to competitive penetration of carbon and nitrogen elements. The partitioned gas strategy allows decarburization and nitriding to proceed in an orderly manner step by step. The existing cold rolling process uses a constant reduction rate, which is prone to stress concentration. The dynamic adjustment mechanism can adaptively match the deformation energy distribution according to the material properties. Ordinary insulating coatings only consider insulation properties. This solution achieves a coordinated match between coating tension and substrate deformation by adding specific compounds.

[0039] Through the above technical scheme, the present application achieves the synergistic improvement of the magnetic properties and mechanical strength of high-silicon aluminum alloyed oriented silicon steel. The coordinated control of the smelting and hot rolling processes effectively suppresses element segregation, and the dynamic adjustment mechanism in the cold rolling stage alleviates the brittle cracking tendency of high-silicon materials. Partitioned gas decarburization annealing reduces iron loss while ensuring uniform precipitation of inhibitors, and the gradient deformation energy design promotes the preferential growth of favorable textures during recrystallization. The interface bonding strength between the insulating coating and the substrate is improved, so that the finished silicon steel can still maintain a stable magnetic performance output when subjected to mechanical loads.

[0040] The present application further proposes configuring seven continuous rolling mills for continuous rolling in the hot rolling process, wherein the reduction rate of each pass is set according to a decreasing gradient, the initial pass reduction rate is set to 45%, and the final pass reduction rate is set to 5%.

[0041] Among them, the seven-tandem mill refers to a unit with seven groups of continuously arranged rollers, which can be realized by a tandem finishing mill, and a multi-pass continuous deformation channel is formed by a series arrangement. The reduction rate decreasing gradient refers to the gradual reduction of the reduction between adjacent passes, which can be realized by adjusting the roll gap parameters in real time through a computer automatic control system. The gradient setting can balance the deformation resistance distribution between each pass.

[0042] Specifically, a high pressure reduction rate is used in the initial stage to quickly break the cast coarse-grained structure and promote dynamic recrystallization of austenite grains. As the rolling process progresses, the deformation amount of a single pass is gradually reduced, so that the subsequent deformation process gradually turns into the grain orientation adjustment stage. The last pass micro-reduction operation not only maintains the overall dimensional accuracy of the material, but also induces the orientation rotation of the crystal through local lattice slip. Through this progressive deformation distribution mechanism, the plastic deformation energy at different stages can act on the two key links of grain refinement and orientation control respectively.

[0043] Compared with the existing technology, the traditional hot rolling process generally adopts a fixed reduction rate or a random adjustment method, which easily leads to stress concentration in local areas and disordered grain growth direction. However, this scheme achieves the directional release of deformation energy by establishing an orderly reduction gradient sequence, making the internal stress field distribution of the material more uniform, and at the same time provides a favorable orientation basis for the subsequent recrystallization process.

[0044] Through the above technical solution, the present application effectively solves the problems of uneven internal stress distribution and inaccurate grain orientation control during hot rolling. While ensuring the processing stability of the material, it creates favorable conditions for obtaining a microstructure with a regular orientation distribution.

[0045] The present application further proposes a method of using segmented control of temperature gradient and rate during hot rolling. Specifically, it includes raising the temperature of the head and tail parts of the hot-rolled strip by 100 - 300 °C, and controlling the rolling rate in the middle part of the hot-rolled strip to be 20 - 30% higher than that of the head and tail parts.

[0046] Among them, the increase in the temperature of the head and tail parts of the hot-rolled strip refers to compensating for the heat dissipation loss during the rolling process through local heating. Specifically, an induction heating device or a resistance heating device can be used to compensate the temperature of the head and tail areas of the strip. This measure reduces the influence of edge temperature drop on the deformation uniformity of the material by balancing the temperature field distribution.

[0047] Among them, the control of the rolling rate difference refers to adjusting the rolling speed according to the heat dissipation characteristics of different areas of the strip. Specifically, it can be achieved through the linkage of the main drive system of the rolling mill and the cooling device. Using a higher rolling rate in the middle area can improve the rolling efficiency by utilizing its stable heat dissipation characteristics, and at the same time form a gradient of deformation energy storage.

[0048] Specifically, by segmentally regulating the temperature and the rolling rate, the temperature compensation in the head and tail areas effectively suppresses the phenomenon of too rapid temperature drop caused by the difference in the cold tandem rolling rate. The establishment of the temperature gradient makes the dynamic recrystallization process tend to be uniform, avoiding excessive grain size differences. After increasing the rolling rate in the middle area, on the premise of maintaining rolling stability, an interface structure favorable for secondary recrystallization is formed by utilizing the difference in deformation energy storage. The coordinated control of the temperature field and the rate field enables the material to form a gradient tissue distribution during rolling, thereby reducing performance fluctuations.

[0049] Compared with the prior art, the traditional hot rolling process usually adopts uniform heating and a constant rolling rate, resulting in temperature fluctuations in the head and tail areas due to heat dissipation differences, and further causing uneven grain structure. This solution not only solves the contradiction between heat dissipation loss and rolling efficiency through regional temperature compensation and rate differentiation adjustment, but also optimizes the microstructure evolution path of the material through the design of the deformation energy storage gradient. This segmented control strategy breaks through the limitations of the single temperature-rate matching mode in the traditional process.

[0050] Through the above technical solution, the present application can effectively compensate for the heat dissipation loss at the head and tail of the hot-rolled strip, and suppress the abnormal grain growth caused by the temperature gradient; at the same time, it optimizes the distribution of deformation energy storage by increasing the rolling rate in the middle part, providing favorable interface conditions for the subsequent recrystallization process. The synergistic effect of the two significantly reduces the material performance fluctuations during rolling, and improves the tissue uniformity and magnetic property stability.

[0051] This application further proposes that coiling should be carried out at 530 - 580 °C after hot rolling, so that AlN precipitates dispersedly along the austenite grain boundaries.

[0052] Among them, the coiling temperature range of 530 - 580 °C refers to the temperature control range for coiling the strip into a coil after the hot rolling process, and it can be specifically achieved by using a laminar flow cooling device in combination with a temperature closed-loop control system. The selection of this temperature window is based on the critical point of AlN precipitation kinetics during the austenite-to-ferrite phase transformation. Among them, the dispersed precipitation of AlN means that aluminum nitride compounds are uniformly distributed in the austenite grain boundary region in the form of nanoscale particles, and it can be specifically achieved by controlling the cooling rate and holding time during the coiling stage. This precipitation behavior can form an effective grain boundary pinning effect and inhibit abnormal grain growth during subsequent heat treatment. Among them, the austenite grain boundary refers to the crystal interface formed by the austenite phase in steel at high temperature, and it is specifically manifested as the preferential position for element diffusion and precipitation phase nucleation during the phase transformation process.

[0053] Specifically, by coiling the hot-rolled strip in a specific temperature range, using the phase transformation process of austenite to ferrite, it promotes the selective segregation of Al and N elements in the grain boundary region. When the temperature is maintained in the range of 530 - 580 °C, the nucleation driving force of AlN reaches the critical value, and at this time, the high-energy state at the grain boundary provides a preferential nucleation site for the precipitation phase. Along with the slow cooling during the coiling process, AlN particles precipitate dispersedly and uniformly in the grain boundary region. This distribution pattern forms a steric hindrance effect during subsequent cold rolling and annealing processes, which not only restricts the excessive growth of primary recrystallized grains but also provides a uniform nucleation substrate for secondary recrystallization. The AlN precipitated at the grain boundary also plays a role in fine grain strengthening, improving the material strength by hindering dislocation movement, and realizing the coordinated regulation of magnetic domain structure and mechanical properties.

[0054] Compared with the prior art, the traditional process usually uses a coiling temperature above 600 °C or a rapid cooling method. A higher coiling temperature will cause the coarsening and aggregation of AlN precipitation phases, reducing the pinning efficiency; while rapid cooling inhibits the full nucleation of AlN. This solution overcomes the defects of uneven precipitation phase distribution and insufficient pinning effect by precisely controlling the coiling temperature and cooling rate, ensuring both the full precipitation of AlN and maintaining the nanoscale size of the precipitation phase.

[0055] Through the above technical solutions, this application effectively solves the technical problems of large grains and uneven precipitation phase distribution in high-silicon aluminum alloyed grain-oriented silicon steel after hot rolling. By regulating the precipitation morphology and distribution characteristics of AlN, it not only inhibits abnormal grain growth during subsequent processing but also improves the material strength through the fine grain strengthening mechanism, ultimately realizing the coordinated optimization of magnetic properties and mechanical properties.

[0056] The present application further proposes a technical solution in the smelting and casting steps, which remelts the steel billet and implements directional solidification, enabling the columnar crystals to grow along the <001> direction, thereby controlling the deviation angle of the transverse texture divergence to less than 5°.

[0057] Among them, remelting directional solidification means that after the solidified steel billet is remelted, crystal directional growth is achieved by controlling the temperature gradient. Specifically, it can be realized by the liquid metal cooling method. By regulating the cooling rate and the heat flow direction, the melt is solidified sequentially along the predetermined direction. This feature eliminates the randomly oriented grains in the original casting billet by reconstructing the solidification structure.

[0058] Among them, the growth of columnar crystals along the <001> direction means that by utilizing the preferential growth characteristics of cubic crystals, the main axis of the columnar crystals is aligned with the direction of the easy magnetization axis. Specifically, it can be achieved by applying an axial magnetic field with an electromagnetic stirring device, and the magnetic field intensity is controlled within the range of 0.05 - 0.5 Tesla, for example. This feature provides a favorable texture basis for subsequent rolling by the crystal orientation consistency.

[0059] Specifically, during the secondary melting of molten steel, an axial temperature gradient is established through a unidirectional heat dissipation device. When the melt temperature drops below the liquidus, crystal nuclei with <001> orientation are formed along the heat dissipation direction and compete for growth. The control of the temperature gradient enables the dominant orientation grains to continue growing, while the grains with deviated orientations are gradually eliminated. The directional advancement of the solidification front promotes the regular arrangement of columnar crystals, and the initial texture formed thereby can reduce the randomness of grain orientation during the subsequent rolling process. This directional solidification process acts synergistically with the subsequent nitriding process to further stabilize the magnetic domain structure of grain-oriented silicon steel through the fine regulation of the surface nitrogen content gradient.

[0060] Compared with the prior art, the traditional casting process adopts the free solidification method, forming a mixed structure of equiaxed crystals and columnar crystals, and the grain orientation distribution shows anisotropy. In the conventional process, the deviation angle of the transverse texture usually exceeds 10°, resulting in an increase in energy loss during the magnetic domain rotation. However, this solution reconstructs the crystal growth mode through directional solidification, significantly improving the orientation consistency of the initial texture, and providing an accurate orientation template for the secondary recrystallization in the subsequent rolling and annealing stages.

[0061] Through the above technical solution, the present application effectively solves the problem of magnetic property deterioration caused by excessive transverse texture divergence in high-silicon aluminum alloyed grain-oriented silicon steel. The regular columnar crystal structure formed by directional solidification reduces the grain orientation deviation angle to a controllable range, and the energy loss during the magnetic domain rotation is reduced. At the same time, the consistency of crystal orientation provides a stable texture development basis for the subsequent rolling process, enabling the final product to obtain better magnetic induction performance while maintaining high strength.

[0062] The present application further proposes to control the dissolved oxygen content in molten steel not exceeding 20 ppm and the sulfur content not exceeding 50 ppm during the smelting and casting stages, and add nanoparticles with a core-shell structure. The nanoparticles contain yttrium element, with an alumina coating layer on the outer layer and a yttrium-based alloy on the inner layer, and the particle size is controlled in the range of 50 - 200 nm.

[0063] Among them, the control of the dissolved oxygen content refers to reducing the concentration of free oxygen in liquid steel through a vacuum refining process. Specifically, a multi-stage vacuum degassing device can be used to gradually reduce the system pressure to below 5 Pa, combined with electromagnetic stirring to make oxide inclusions float and be removed. This measure can reduce the generation probability of Al2O3 inclusions and avoid large-sized inclusions from splitting the matrix continuity. The control of the sulfur content refers to limiting the sulfur element concentration to a lower level through hot metal pretreatment for desulfurization. For example, the KR method is used with a magnesium-based desulfurizing agent to reduce the total amount of sulfide inclusions to below the critical value, preventing the sulfur element from forming a composite precipitation phase with the aluminum element. The addition of the core-shell structure nanoparticles refers to evenly dispersing the prefabricated particles into the molten steel through the wire feeding method. Its alumina shell can delay the premature oxidation of the yttrium element, and the inner layer yttrium-based alloy preferentially reacts with residual oxygen and sulfur elements during solidification to form fine and dispersed Y2O2S inclusions.

[0064] Specifically, during the solidification process of molten steel, the nanoparticles act as heterogeneous nucleation substrates. When the supercooling degree of the molten steel reaches the critical value, the yttrium element preferentially combines with free oxygen to form a Y-O compound core, and then the sulfur element adsorbs on its surface to form a stable inclusion. These nano-scale inclusions serve as non-uniform nucleation sites to promote the formation of fine equiaxed crystals. At the same time, the residual aluminum element is retained and combines with the nitrogen element in the subsequent nitriding treatment to form uniformly distributed AlN inhibitors. In the hot rolling stage, the clean matrix environment enables AlN to precipitate directionally along the austenite grain boundaries, creating favorable conditions for the preferred growth of Goss texture during the secondary recrystallization process.

[0065] Compared with the prior art, conventional smelting processes usually control the oxygen content above 30 ppm and the sulfur content above 80 ppm, resulting in the average size of Al2O3 inclusions exceeding 5 μm, and MnS and AlN are prone to form coarse composite precipitates. This solution combines the control of two impurity elements with nanoparticle modification to reduce the average size of inclusions to below 1 μm, and the distribution density is increased to 200 - 500 per square millimeter, effectively suppressing the abnormal expansion of deformation bands during the cold rolling process.

[0066] Through the above technical solutions, the present application can significantly reduce the destructive effect of oxide and sulfide inclusions on the matrix structure, ensuring the effective release of deformation energy storage and the precise control of grain boundary migration during subsequent rolling and annealing processes. The oriented silicon steel obtained thereby can maintain high magnetic induction performance while the tensile strength can stably reach the advanced level of the industry, and the fluctuation range of hysteresis loss is reduced by about 40%.

[0067] The present application further proposes to adopt a design of strain energy storage gradient during the cold rolling process, specifically by rolling with a high-low-high reduction rate sequence to form a layered energy storage structure.

[0068] Among them, the design of strain energy storage gradient refers to adjusting the internal strain distribution of the sheet by combining the reduction rates of different passes. Specifically, it can be achieved by a combination mode of a high reduction rate in the initial pass, a low reduction rate in the middle pass, and a high reduction rate in the final pass. This design coordinates the contradiction between work hardening and energy storage distribution through the rapid accumulation of surface dislocation density and the control of the core strain gradient.

[0069] Among them, the high-low-high reduction rate sequence refers to a combination of process parameters in which the reduction rate of each pass changes non-monotonically. Specifically, it can be achieved by a reduction rate distribution mode of 45% → 30% → 40%. This sequence forms a gradient energy storage distribution from the surface to the core by rapidly introducing high strain on the surface in the first pass, relieving work hardening in the middle pass, and strengthening the core energy storage in the final pass.

[0070] Specifically, a relatively high reduction rate is adopted in the initial stage of cold rolling to rapidly accumulate dislocations on the surface and form a {110}<001> texture. The reduction rate is reduced in the middle stage to reduce the risk of crack propagation inside the sheet, and the reduction rate is increased again in the final stage to increase the core strain energy. This layered energy storage structure induces the high-energy storage region on the surface to preferentially recrystallize to form a fine grain layer during the annealing process, while the medium-energy storage region in the core provides the driving force for secondary recrystallization. Through the synergistic effect of surface fine grain strengthening and core sharp texture, the brittle risk during the cold rolling process of high-silicon steel and the requirement for uniform annealing structure are effectively balanced.

[0071] Compared with the prior art, the traditional cold rolling process usually adopts a monotonically decreasing reduction rate mode, resulting in insufficient energy storage difference between the surface and the core, and it is difficult to balance the processing performance and the control of annealing structure. This solution designs an asymmetric reduction rate sequence, which not only avoids the cracking of the sheet caused by continuous high reduction rates but also overcomes the insufficient energy storage gradient caused by a single decreasing mode, significantly improving the uniformity of the recrystallization structure.

[0072] Through the above technical solution, the present application solves the problem of non-uniform annealing structure caused by uneven strain energy storage distribution during the cold rolling process of high-silicon aluminum alloyed grain-oriented silicon steel, and realizes the synergistic effect of surface fine grain strengthening and core texture optimization, thereby improving the magnetic property stability and mechanical strength of the final product.

[0073] The present application further proposes to adopt a gradient heating strategy during the decarburization annealing process, specifically by heating at a relatively high rate in the initial stage of annealing and then gradually reducing the heating rate.

[0074] Among them, the gradient heating strategy refers to adjusting the temperature rise rate of the annealing process in stages, which can be specifically achieved by a segmented heating control system, and the power output of the resistance furnace is adjusted to match the preset heating curve. This strategy coordinates the energy supply for recrystallization nucleation and grain growth processes by dynamically controlling the driving force for grain growth.

[0075] Among them, the regulation of the annealing atmosphere includes the zonal switching of dry and wet mixed gases, which can be specifically achieved by a dual-gas supply device cooperating with a dew point detection feedback system, and the formation state of the oxide layer on the steel strip surface is adjusted by controlling the water content of the gas. This regulation mechanism establishes a uniform interface environment for subsequent preferred grain growth by optimizing the thickness and compactness of the oxide layer.

[0076] Specifically, in the initial stage when the steel strip enters the annealing furnace, a relatively high heating rate promotes partial dissolution of the inhibitor particles, releasing solute atoms that pin the interface migration. As the temperature rises to the critical point, reducing the heating rate enables the redistribution of solute atoms to form a dispersion barrier, inhibiting the overgrowth of abnormal grains. During this process, the dense oxide layer formed in the dry atmosphere acts as a diffusion barrier and synergistically interacts with the active interface generated in the wet atmosphere to establish a stable grain boundary migration resistance gradient.

[0077] Compared with the prior art, when the conventional annealing process uses a constant heating rate, the driving force for grain growth changes linearly, resulting in local overburning or growth stagnation during the secondary recrystallization process. This solution solves the problem of grain size differentiation caused by thermal inertia in the traditional process by establishing a non-linear energy input mode, enabling the grain growth front to be always in a controlled advancing state.

[0078] Through the above technical solutions, this application realizes the uniform control of the secondary grain size distribution during annealing, enables the grain growth kinetics and the dissolution behavior of the inhibitor to form a spatio-temporal match, effectively inhibits the attenuation of texture sharpness caused by local overheating, and ensures the batch stability of magnetic properties.

[0079] This application further proposes that the composition of the active agent includes a low-melting-point compound, and the melting point of the low-melting-point compound does not exceed 900 °C.

[0080] Among them, the low-melting-point compound refers to a compound that can melt under high-temperature annealing conditions, which can be specifically realized by sodium borate or potassium silicate, and its melting point range is controlled at 700 - 890 °C. Such substances can form a liquid phase in the initial stage of annealing, promoting the interfacial bonding between the isolating agent and the matrix.

[0081] Among them, the limitation that the melting point does not exceed 900 °C is to ensure that the compound is melted in the initial stage of the high-temperature annealing process, which can be specifically achieved by adjusting the ratio of metal elements to non-metal elements in the compound. For example, increasing the potassium element content to 15-25% can lower the melting point of the silicate. This temperature range can not only meet the requirement of sufficient liquid-phase spreading but also avoid premature volatilization or decomposition due to too low a melting point.

[0082] Specifically, during the high-temperature annealing process, the low-melting-point compound is melted into a liquid state and fills the microscopic gaps between the separator coating and the surface of the steel strip through capillary action. The liquid substance covers the grain boundary region, inhibits the local stress concentration caused by grain boundary migration, and thus reduces the formation of coating cracks. At the same time, the molten compound reduces the interfacial tension, promotes the uniform adhesion of the separator to the surface of the steel strip, and avoids abnormal distribution of magnetic domains caused by local absence of the coating.

[0083] In some specific embodiments, the low-melting-point compound can be a mixture of sodium borate and lead oxide, such as the Na2B4O7-PbO system mixed in a mass ratio of 3:1, whose melting point is 820 °C. This mixture is completely melted when the annealing temperature rises to 850 °C and then forms a continuous covering layer on the surface of the steel strip.

[0084] Compared with the prior art, high-melting-point separator active ingredients (such as magnesium oxide with a melting point of 2852 °C) are usually used in the prior art, and solid-state diffusion is required to achieve interfacial bonding, which is likely to cause coating peeling due to poor microscopic contact. However, in this solution, by introducing a low-melting-point compound and utilizing the liquid-phase flow characteristics to eliminate interfacial voids, the coating continuity is significantly improved.

[0085] Through the above technical solution, this application solves the problem of magnetic domain pinning caused by uneven coating of the separator during the high-temperature annealing of high-silicon aluminum-alloyed grain-oriented silicon steel, effectively reduces the incidence of surface defects, and at the same time ensures the inhibitory effect of the coating on grain boundary migration, improving the magnetic induction uniformity of the final product.

[0086] This application further proposes that under the condition that the furnace temperature is controlled at 700 °C in a furnace filled with a nitrogen-hydrogen mixed protective gas, a tension is applied to the steel strip for coating sintering and hot stretch leveling.

[0087] Among them, the nitrogen-hydrogen mixed protective gas refers to a non-oxidizing atmosphere with nitrogen as the main body and hydrogen mixed in. Specifically, a mixed gas with a volume ratio of nitrogen to hydrogen of 4:1 to 9:1 can be used to achieve this. By means of the reducing gas, the formation of oxides on the surface of the steel strip is inhibited, and at the same time, the chemical reaction of the coating components is promoted. The furnace temperature of 700°C means that the temperature inside the furnace is precisely controlled within the range of 700 ± 10°C. Specifically, a segmented temperature-controlled resistance heating system can be used to achieve this. This temperature range not only meets the melting conditions required for the sintering of the insulating coating but also avoids the decline in magnetic properties caused by excessive grain coarsening. Applying an appropriate tension means applying a linear tension according to the thickness and material of the steel strip. Specifically, a tension roller system with closed-loop feedback can be used to dynamically adjust the tension value. Through plastic deformation, the internal residual stress is eliminated and the magnetic domain structure is regulated, so as to balance the flatness of the material and the stability of the magnetic properties.

[0088] Specifically, in the nitrogen-hydrogen mixed protective atmosphere, the oxidation reaction on the surface of the steel strip is effectively inhibited, and the bonding strength between the coating components and the substrate is improved. When the furnace temperature is stabilized at 700°C, the magnesium oxide isolating agent is fully melted to form a dense insulating layer. At the same time, the grain growth rate is limited within a reasonable range, avoiding the deterioration of the sharpness of the Gaussian texture due to grain coarsening. During the process of applying tension, the internal residual stress of the steel strip is released through plastic deformation, and the magnetic domain structure is rearranged under the action of tension, resulting in a reduction in the resistance of the magnetic domain wall movement and an improvement in the iron loss performance.

[0089] Compared with the prior art, the traditional process often uses a single nitrogen or air atmosphere for coating sintering, resulting in an increase in the thickness of the oxide layer on the surface of the steel strip and a decrease in the coating adhesion; the temperature of hot stretch leveling is usually higher than 750°C, which is likely to cause abnormal grain growth and result in magnetic induction fluctuations. This solution optimizes the protective gas composition and temperature parameters, combined with dynamic tension control, to maintain the stability of the magnetic properties while achieving a highly dense coating.

[0090] Through the above technical solution, this application solves the problems of steel strip oxidation and grain coarsening during the coating sintering process, significantly improving the density and adhesion of the insulating coating; through the coordinated control of tension and temperature, the adverse effects of steel strip deformation on the magnetic domain structure are effectively eliminated, ensuring that the magnetic induction performance and mechanical dimension accuracy meet the standards simultaneously.

[0091] It should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for synergistically optimizing the magnetic properties and strength of grain-oriented silicon steel based on high-silicon aluminum alloying, characterized in that, It includes the following steps: a) Smelting and casting: Adopt the vacuum refining process to control the dissolved oxygen content and sulfur content in the molten steel, and cast it into steel billets; b) Hot rolling: Heat the cast billets to 1250 - 1320 °C, with soaking time ≥ 60 min, and continuously roll them using a multi-stand rolling mill; c) Normalizing treatment: Adopt two-stage normalizing treatment, first heat to 1100 - 1200 °C, and cool down to 900 - 1000 °C within 50 - 200 s; then rapidly cool in water at 10 - 100 °C; d) Cold rolling: Conduct single cold rolling or double cold rolling with intermediate annealing. During the cold rolling process, adjust the magnitude of the friction during cold rolling, control the reduction ratio of the first cold rolling pass according to the molten steel composition and the thickness of the hot-rolled sheet, as well as the number of cold rolling aging times and the rolling speeds of different passes, and increase the Si content to 3.6% - 3.9%; e) Decarburizing annealing: Pass a dry mixture of nitrogen and hydrogen into the front zone of decarburizing annealing, and pass a wet mixture of nitrogen and hydrogen into the rear zone of decarburizing annealing for decarburization, and pass a wet mixture of nitrogen and hydrogen and ammonia into the nitriding zone for nitriding; f) Nitriding treatment: Conduct double cold rolling after decarburizing annealing, and then cold coat with magnesium oxide isolating agent; g) Coating annealing isolating agent: Coat the isolating agent on the cold-rolled strip steel after decarburizing annealing and nitriding treatment, dry the cold-rolled strip steel coated with the isolating agent and coat it with an activating agent, and then coil it to obtain a steel coil; h) High-temperature annealing: Anneal the steel coil to obtain silicon steel; i) Hot stretch leveling annealing: Coat an insulating layer and conduct hot stretch leveling on the oriented silicon steel raw material after high-temperature annealing; j) Insulating coating: Based on the composition of the existing insulating coating, sequentially add potassium dihydrogen phosphate and zirconium oxychloride to form a high-tension coating solution and coat it on the surface of the oriented silicon steel to obtain a high-tension coating.

2. The method for synergistically optimizing the magnetism and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, wherein In step b), the multi-stand rolling mill is set as a 7-stand rolling mill. During continuous rolling using the 7-stand rolling mill, the reduction ratio of each pass decreases successively, with the initial reduction ratio being 45% and the final reduction ratio being 5%.

3. The method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, wherein In step b), it also includes Segmented control of hot rolling temperature gradient and rate: Raise the temperatures of the head and tail of the hot-rolled strip by 100 - 300 °C to compensate for the heat dissipation loss caused by the rate difference of cold tandem rolling; use a rolling rate 20 - 30% higher than that of the head and tail in the middle of the hot-rolled strip.

4. The method for synergistically optimizing the magnetism and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 3, wherein In step b), it also includes that after hot rolling, it is necessary to coil at 530 - 580 °C to make AlN precipitate dispersedly along the austenite grain boundaries.

5. The method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 4, characterized in that In step a), it also includes remelting the steel billet for directional solidification to make the columnar crystals grow along the <001> direction and reduce the deviation angle of the transverse texture divergence <5°.

6. The method for synergistically optimizing the magnetism and strength of grain-oriented silicon steel based on high-silicon aluminum alloying according to claim 1, characterized in that In step a), control the dissolved oxygen content in the molten steel to ≤ 20 ppm and the sulfur content to ≤ 50 ppm.

7. The method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, wherein In step d), it also includes Design of deformation energy storage gradient: Adopt a "high - low - high" reduction ratio for passes to form a layered energy storage structure during cold rolling.

8. The method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, wherein In step e), it also includes Precise regulation of annealing atmosphere: Adopt a gradient heating of 50 °C / h → 20 °C / h during annealing to reduce the standard deviation of the secondary grain size from the conventional 35% to 18%.

9. The method for synergistically optimizing the magnetism and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, characterized in that In the step g), the component of the active agent includes a low melting point compound, and the melting point of the low melting point compound is ≤ 900 °C.

10. The method for synergistically optimizing the magnetic properties and strength of high-silicon aluminum alloyed grain-oriented silicon steel according to claim 1, characterized in that, In the step i), it further includes In a furnace filled with a protective gas of N2 + H2, under the furnace condition of 700 °C, apply an appropriate tension to the steel strip for coating sintering and hot stretch leveling.

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