Non-oriented electrical steel with a strength of not less than 500 MPa, preparation method thereof, and motor core

Abstract

The present invention provides a non-oriented electrical steel with a magnetic field of not less than 500 MPa, a preparation method, and a motor core, and relates to the technical field of soft magnetic metal functional materials and electrical materials for motors. The non-oriented electrical steel has a thickness of 0.15-0.30 mm and a magnetic induction B 5000 Not less than 1.61T, iron loss P 1.0 / 400 Not higher than 40W / kg, and yield strength not lower than 500MPa. The preparation method includes molten steel smelting + continuous casting, homogenization heat treatment + hot rolling, normalization treatment + first cold rolling, continuous annealing treatment + second cold rolling, and recovery annealing treatment. The present invention creatively and comprehensively utilizes two strengthening methods, solid solution strengthening and dislocation strengthening, and obtains a coarse network-like high dislocation density organization by regulating the heat treatment and rolling process. While improving the strength level, it greatly reduces the degree of deterioration of magnetic properties caused by dislocation strengthening, and realizes the preparation of non-oriented electrical steel with both high strength and low iron loss.

Description

Technical Field

[0001] The invention relates to the technical field of soft magnetic metal functional materials and electrical materials for motors, and in particular to a non-oriented electrical steel with a strength of not less than 500MPa, a preparation method and a motor core. Background Art

[0002] Non-oriented electrical steel is a key soft magnetic functional material for realizing electromagnetic conversion of motors. The comprehensive performance of the core stacked by non-oriented electrical steel directly determines the performance indicators of the motor. In recent years, as the field of power electronics continues to develop towards high efficiency, the application frequency and design speed of motors continue to increase. The strength of some types of motor core materials can no longer meet the requirements. For example, under high speed conditions, the stress on the magnetic bridge of the permanent magnet synchronous motor rotor core has exceeded the yield limit of conventional electrical steel materials, and the width of the magnetic bridge must be increased. However, the increase in the width of the magnetic bridge will increase the leakage flux and reduce the efficiency of the motor.

[0003] At present, the simplest and most effective means to improve the strength of electrical steel materials is to introduce dislocation strengthening. The basic principle is to use the entanglement of high-density dislocation tissue to hinder dislocation movement and improve strength. If the dislocation density in the metal is high, the dislocations are prone to intersect with each other during movement, forming steps, causing dislocation entanglement, thus causing obstacles to dislocation movement, making it difficult to continue plastic deformation, thereby improving the strength of the metal. The existing dislocation strengthening process technology mainly adopts low-temperature annealing or introduces alloy elements to inhibit recrystallization and cooperates with annealing process to obtain a certain proportion of recrystallization and deformation structure, and uses the high-density dislocations remaining in the deformed structure to improve the strength level. However, for soft magnetic electrical steel materials, high-density dislocations will hinder the reversible movement of magnetic domain walls while improving strength, greatly deteriorating the magnetic properties. In short, the defects of electrical steel dislocation strengthening technology are high dislocation density and large magnetic deterioration caused by other alloys or second phases.

[0004] For example, Chinese patent CN114540711A discloses a high-grade non-oriented electrical steel and a preparation method thereof, in which the alloy element content is low, the composition of the elements satisfies complex conditions, and the operation is difficult; although the required electrical steel can be obtained by hot rolling + normalizing + pickling + cold rolling + annealing + coating, the heating and insulation time of the ingot is long, the normalizing time is short, the thickness of the cold-rolled plate is thick, and the annealing temperature is high. Since the yield strength ratio of electrical steel is generally between 0.60-0.75, the yield strength of the prepared electrical steel is lower than 500MPa, which cannot meet the strength requirements of certain types of motor core materials.

[0005] Chinese patent CN103060701A discloses a non-oriented high-silicon electrical steel strip and a preparation method thereof, which is prepared by adding high chromium content, high silicon content and casting rolling + hot rolling + pickling + warm rolling + annealing treatment; although the required electrical steel is obtained by casting rolling + hot rolling + pickling + warm rolling + annealing, the thickness of the strip after warm rolling is large, the annealing temperature is high, and the room temperature brittleness and low processing performance of the prepared strip seriously restrict its application in the industrial field.

[0006] Chinese patent CN111057821A discloses a non-oriented electrical steel and its preparation method and application. High-cost rare metal elements are added to the composition, and the steel is prepared by hot rolling + normalizing treatment + pickling + primary cold rolling + continuous annealing + secondary cold rolling. Obviously, the yield strength of the prepared electrical steel is lower than 500MPa, which cannot meet the strength requirements of certain types of motor core materials.

[0007] Therefore, it is urgent to develop a new technology to achieve dislocation strengthening of non-oriented electrical steel while reducing the negative impact on magnetic properties. Summary of the invention

[0008] In order to solve the problem that the non-oriented electrical steel in the prior art improves the strength by increasing the dislocation density, but also causes the magnetic properties to decrease due to the obstruction of the reversible movement of the magnetic domain wall, there are also technical problems such as improving the magnetic properties while reducing the strength by adjusting the content of alloy elements and improving the preparation method, and improving the magnetic properties and strength by adjusting the content of alloy elements and improving the preparation method, but causing the room temperature brittleness and low processing performance of the prepared material; therefore, the embodiment of the present invention provides a non-oriented electrical steel of not less than 500MPa, a preparation method, and a motor core that can synergistically improve the magnetic properties, strength and processing performance and reduce the room temperature brittleness. The technical solution is as follows:

[0009] A non-oriented electrical steel with a strength of not less than 500 MPa, wherein the thickness of the non-oriented electrical steel with a strength of not less than 500 MPa is 0.15-0.30 mm, the yield strength is not less than 500 MPa, and the chemical composition is as follows by mass percentage: C≤0.0040%, Si 1.50-4.50%, Al 0.20-1.20%, Mn 0.20-1.30%, Cr 0.1-1.5%, Sn 0.010-0.10%, S≤0.0020%, N≤0.0020%, O≤0.0050%, V≤0.0050%, Ti≤0.0050%, Nb≤0.0050%, and the balance is Fe and unavoidable impurity elements; wherein the element contents of C, S, N, O, V, Ti and Nb cannot be 0.

[0010] Optionally, the metallographic composition of the non-oriented electrical steel with a yield strength not less than 500 MPa is a single-phase ferrite structure.

[0011] Optionally, the average size of grains in the non-oriented electrical steel with a pressure not less than 500 MPa is 90-160 μm.

[0012] Optionally, the density of the non-oriented electrical steel not less than 500 MPa is 7.6-7.7 g / cm 3 , hardness is 210-330HV, saturation flux density is 1.71-1.85T, initial magnetic permeability is 1900-3600H / m, magnetostriction coefficient is 2.6-7.6ppm, magnetic induction B 5000 Not less than 1.61T, iron loss P 1.0 / 400 Not higher than 40W / kg, tensile strength not less than 595MPa, yield strength not less than 500MPa, yield strength ratio of 0.84-0.96, elongation at break not less than 5%, elastic modulus not less than 187GPa, dislocation density of 5×10 13 -1×10 16 pcs / m 2 ; The tensile strength at 150℃ is not less than 520MPa, the yield strength is not less than 420MPa, the yield strength ratio is 0.85-0.97, the elongation at break is not less than 3%, the elastic modulus is not less than 165GPa, and the dislocation density is 5×10 13 -1×10 16 pcs / m 2 .

[0013] A method for preparing the non-oriented electrical steel having a strength of not less than 500 MPa based on the above-mentioned method comprises the following steps:

[0014] S1. Molten steel smelting + continuous casting: using molten iron from a blast furnace or electric furnace as raw material, desulfurization, carbon removal, RH refining and continuous casting are performed to obtain electrical steel slabs with the chemical composition ratio;

[0015] S2, homogenization heat treatment + hot rolling: the S1 electrical steel slab is subjected to homogenization heat treatment to obtain a homogenized electrical steel slab; the homogenized electrical steel slab is fully heated and then taken out of the furnace for hot rolling, and after the hot rolling is completed, it is coiled to obtain an electrical steel hot-rolled coil with a set chemical composition;

[0016] S3, normalizing treatment + first cold rolling: the S2 electrical steel hot rolled coil is normalized to obtain a normalized coil with grown grains, and then the first cold rolling is performed to obtain a first chilled coil;

[0017] S4, continuous annealing treatment + second cold rolling: the S3 first chilled coil is continuously annealed to obtain an annealed coil with further grown grains; then a second cold rolling is performed to obtain a second chilled coil with residual original grain boundaries;

[0018] S5. Recovery annealing treatment: The secondary cold-hardened coil of S4 with the original grain boundary residue is subjected to recovery annealing to obtain a non-oriented electrical steel with fully recovered interior of the deformed grains and a yield strength of not less than 500 MPa.

[0019] Optionally, the temperature of the homogenization heat treatment in S2 is 1000-1150°C, and the soaking time is 20-30min; the hot rolling includes rough rolling and finish rolling, the number of rough rolling passes is 4-6 passes, the rough rolling temperature is 1000-1150°C, the total reduction rate is 80-90%, the number of finish rolling passes is 6-7, the finish rolling temperature is 880-1050°C, the final rolling temperature is not less than 830°C, the total reduction rate is 90-95%, the coiling temperature is 500-750°C, and the coil thickness of the hot rolled coil is 2.0-2.6mm.

[0020] Optionally, the temperature of the normalizing treatment in S3 is 950-1050°C, the treatment time is 2-10min, and the average size of the normalized grains after growth is 100-200μm; the first cold rolling deformation is 80-93%, and the thickness of the first cold-hardened coil is 0.15-0.43mm.

[0021] Optionally, the temperature of continuous annealing in S4 is 950-1050°C, and the processing time is 0.5-3.0min; the deformation of the second cold rolling is 5-30%, the thickness of the secondary cold-hardened coil with the original grain boundary residue is 0.15-0.30mm, and the average size of the grains after growth is 100-160μm.

[0022] Optionally, the recovery annealing temperature in S5 is 500-700° C., the processing time is 30-300 min, and the final average size of the grains is 90-160 μm.

[0023] Optionally, the raw material of the high-speed motor core includes non-oriented electrical steel with a strength of not less than 500 MPa prepared by any of the above preparation methods.

[0024] Technical principle of the present invention:

[0025] The main alloying element selection mechanism in the electrical steel of the present invention is as follows:

[0026] In electrical steel, C is the main element that produces magnetic aging. When the residual C content in the steel is high, the coercive force increases, the hysteresis loss increases, and magnetic aging also occurs. For example, the C content can be 0.004%, 0.003%, 0.002%, 0.001%, etc.

[0027] The main function of Si is to increase resistivity and reduce eddy current loss Pe. Si reduces the magnetic anisotropy constant and saturation magnetostriction constant of Fe, resulting in a reduction in hysteresis loss Ph. Therefore, adding Si can significantly reduce the core loss Pt and reduce the magnetostriction of electrical steel. When the Si content is increased to 6.5%, the magnetostriction is close to zero. However, when the Si content is increased to more than 4.5%, the plasticity of the strip is greatly reduced, and it is difficult to roll and produce. Therefore, the Si content is required to be controlled below 4.5%. For example, the Si content can be 1.50%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, etc.

[0028] Al plays a role in improving resistivity and strength in non-oriented electrical steel. The increase of Al content reduces the magnetic induction intensity, coarsens the size of the AlN-containing precipitated phase, and is conducive to the coarsening of grains. For example, the Al content can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, etc.

[0029] Mn has a similar effect to Si, which is to increase strength while reducing iron loss. Its main function is to increase resistivity and coarsen sulfides, but excessive addition of Mn reduces saturation magnetic induction. For example, the content of Mn can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.3%, etc.

[0030] Cr can increase the resistivity of steel and significantly reduce high-frequency iron loss. At the same time, adding Cr can also improve corrosion resistance. If the Cr addition exceeds 3.0%, the increase in Cr carbides will worsen the iron loss. For example, the Cr content can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.0%, 1.3%, 1.5%, etc.

[0031] The addition of the segregation element Sn generally plays a role in interface and surface segregation, improves the texture type during the recrystallization process, and thus improves the magnetic induction. For example, the content of Sn can be 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.1%, etc.

[0032] In non-oriented electrical steel, S is the main precipitate-forming element, mainly in the form of MnS and CuS. Such sulfides hinder grain growth and worsen iron loss. For example, the S content may be 0.002%, 0.0015%, 0.001%, etc.

[0033] Like C, N will deteriorate magnetic properties. The N element in steel is very easy to combine with Al to form fine AlN precipitates, which inhibit grain growth and magnetic domain movement in the finished product. For example, the N content can be 0.002%, 0.0015%, 0.001%, etc.

[0034] The O element easily forms oxidized inclusions such as CaO and SiO2 with elements in steel, which greatly reduces the magnetic induction of the product. For example, the content of O can be 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, etc.

[0035] V is a harmful element in the non-oriented electrical steel in the embodiment of the present application. V is a strong carbonitride forming element and is very likely to form fine precipitates to deteriorate the magnetic properties. For example, the content of Ti can be 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, etc.

[0036] Ti and Nb are both strong carbonitride-forming elements, which are very easy to form fine precipitates in non-oriented silicon steel and deteriorate magnetic properties, and have a strong deterioration effect on iron loss. Generally, Ti and Nb are harmful elements in electrical steel like V. For example, the contents of Ti and Nb can be 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, etc., respectively.

[0037] The process parameter selection mechanism of the present invention is as follows:

[0038] In some methods, obtaining a hot rolled coil having a set chemical composition comprises:

[0039] The slab with set chemical composition is heated, then rolled and coiled to obtain a hot rolled coil with set chemical composition; wherein the heating process parameters include: heating temperature 1000-1150°C, soaking time ≥20min; and / or,

[0040] The rolling includes finish rolling, the finish rolling temperature is 880-1050° C., and the final rolling temperature is ≥830° C.; and / or,

[0041] In some methods, the coiling temperature is 500-750°C.

[0042] In the present application, the heating temperature of the slab can be 1000-1150°C, and the soaking time of the slab can be ≥20min, to ensure the solid solution of MnS and AlN in the steel, to avoid subsequent excessive precipitation and deterioration of magnetic properties, because the Jared temperature setting can take into account both high process stability and no deterioration of magnetic properties. In addition, the soaking time of the slab is greater than 20min, which can ensure that the slab can transfer heat evenly and heat thoroughly. Exemplarily, the heating temperature can be 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, 1120°C, 1140°C, 1150°C, etc.; the soaking time can be 20min, 22min, 24min, 26min, 28min, etc.

[0043] Rolling includes rough rolling and finishing rolling. The finishing rolling temperature can be 880℃~1050℃. During the finishing rolling process, the steel plate material is always in the two processes of deformation hardening and dynamic recrystallization softening. A higher finishing rolling start temperature is conducive to promoting the dynamic recrystallization of the material and obtaining a larger dynamic recrystallization structure. For example, the finishing rolling temperature can be 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 950℃, 970℃, 1000℃, 1020℃, 1040℃, 1050℃, etc.

[0044] The final rolling temperature of the rolling can be ≥830°C. When the final rolling temperature is high, static recrystallization and grain growth are more likely to occur in the steel plate material from the end of the final rolling to the beginning of cooling, and a coarser grain structure is obtained. The hot rolling thickness can be 2.0-2.6mm. For example, the final rolling temperature of the rolling can be 830°C, 840°C, 850°C, 860°C, 870°C, etc.

[0045] The coiling temperature may be 500-750°C. After the steel coil is coiled, the temperature drops very slowly. The residual heat of coiling can be used to further grow the recrystallized grains. For example, the coiling temperature may be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, etc. In addition, the above-mentioned slab is obtained by smelting, RH refining, and continuous casting.

[0046] In some methods, the normalizing temperature is 950-1050°C.

[0047] In the present application, a continuous normalizing unit or a bell-type furnace is used for normalizing, and the normalizing temperature can be 950-1050°C, so that the grains of the hot-rolled coils grow fully and evenly. A higher normalizing temperature means that a larger normalized plate grain structure can be obtained, while also avoiding the normalizing temperature being higher than 1050°C, which will cause the precipitates to dissolve back and precipitate again in a fine dispersed state, deteriorating the electromagnetic properties. Exemplarily, the normalizing temperature can be 950°C, 970°C, 1000°C, 1030°C, 1050°C, etc. In addition, the holding time of the normalizing equalization section can be 2-10min. Generally speaking, in order to obtain a normalized hot-rolled coil with a good surface state, the normalized hot-rolled coil is sprayed with water for cooling, and then shot blasted and pickled to remove the iron oxide scale on the surface of the strip.

[0048] In some methods, the temperature of the continuous annealing is 950-1050°C.

[0049] In the present application, the temperature of continuous annealing can be 950-1050°C. A higher continuous annealing temperature is conducive to promoting grain growth, while avoiding excessively high continuous annealing temperatures, which will cause the precipitates to dissolve back and precipitate again in a fine dispersed state, thereby deteriorating the electromagnetic properties. The control of the normalizing and continuous annealing processes uses higher heat treatment temperatures and holding times to obtain larger grain structure sizes, thereby avoiding grain fragmentation during the subsequent second cold rolling process, and ultimately making it easier to obtain a coarse dislocation-like network structure by recovery annealing. Exemplarily, the temperature of continuous annealing can be 950°C, 970°C, 1000°C, 1030°C, 1050°C, etc. In addition, the soaking time of continuous annealing can be 0.5-3min.

[0050] In some methods, the deformation amount of the second cold rolling is ≤30%.

[0051] In the present application, a second cold rolling is performed again with a small deformation on a twenty-high rolling mill or a continuous rolling mill. The deformation of the second cold rolling can be ≤30%. A small deformation can play a work hardening role to obtain an annealed coil with dislocation strengthening. At the same time, the small deformation can ensure that the original coarse grain boundary structure of the annealed coil is not destroyed; however, too high a deformation, although it will make the strengthening effect of the annealed coil better, will destroy the original grain boundary structure of the annealed coil. Exemplarily, the deformation of the second cold rolling can be 30%, 28%, 26%, 24%, etc.

[0052] In some methods, the recovery annealing temperature is 500-700°C.

[0053] In the present application, in order to achieve a coarse network dislocation structure, the present application method adopts a small reduction second cold rolling to accurately control the strengthening effect, and further controls the recovery annealing process, so that the internal dislocations of the deformed crystals of the annealed coil after the second cold rolling are fully recovered and eliminated, while retaining the dislocation structure that is not easy to recover and eliminate at the grain boundary and deformation band, forming a coarse network dislocation structure organization, wherein the network dislocation can improve the yield strength, the dislocation density in the recovery area between the network dislocations is low, the magnetization performance is restored to a state close to the complete recrystallization state, and the magnetic properties are better, thereby achieving the balance of high strength and low iron loss of non-oriented electrical steel, and solving the problem that the existing dislocation strengthening technology has high strength but deteriorated magnetic properties. The temperature of recovery annealing in the bell furnace can be 500-700℃, which can ensure that the annealed coil material after the second cold rolling has a certain degree of recovery; if the temperature is too high, the recovery degree may be too large or recrystallization may occur; if the temperature is too low, the recovery degree may be low, resulting in the difficulty of eliminating the dislocation structure inside the deformed grain. For example, the temperature of the recovery annealing may be 500° C., 550° C., 600° C., 650° C., 700° C., etc. In addition, the time of the recovery annealing may be ≥30 min.

[0054] In summary, in order to improve the strength level of the final product, by reasonably adding solid solution elements such as Si, Mn, Al, Cr, etc., the solid solution strengthening of steel is achieved and the resistivity is increased to reduce the iron loss on the basis of rollability. On the basis of utilizing the production capacity of the existing production line, the normalizing and continuous annealing processes are controlled to obtain annealed coils with large grains. The annealed coils are subjected to the second minimum reduction cold rolling and low-temperature recovery annealing treatment. Under the premise of small deformation without destroying the original grain boundary structure, deformation dislocations are introduced to improve the strength. Further, through recovery annealing treatment, the dislocation density inside the grains is greatly reduced and the high dislocation density at the grain boundaries and deformation band structures is maintained, so that the dislocation density distribution inside the non-oriented electrical steel forms a network-like structure. While obtaining the dislocation strengthening effect, the magnetization performance can be improved through the intracrystalline recovery organization.

[0055] In the present application, by controlling the organizational state before the second cold rolling and the second cold rolling process, the annealed coil after the second cold rolling has a deformed organization with residual original grain boundaries, and the interior of the deformed grains of the deformed organization is fully restored by low temperature and long time annealing to form a network structure with low intracrystalline dislocation density and high grain boundary dislocation density, so as to achieve the dislocation strengthening effect while reducing the influence of dislocation on magnetic domain movement, thereby preparing a non-oriented silicon steel product with a thickness of 0.15-0.30mm and a yield strength Rp 0.2 ≥500MPa, magnetic induction B 5000 ≥1.61T, iron loss P 1.0 / 400 ≤40W / kg. Magnetic induction refers to the magnetization intensity or magnetic flux density obtained by the core material under the external magnetic field, and iron loss refers to the loss of the core material under the alternating magnetic field.

[0056] The non-oriented electrical steel of the present application is realized based on the preparation method of the non-oriented electrical steel. The specific steps of the preparation method of the non-oriented electrical steel can refer to the specific preparation method. Since the non-oriented electrical steel adopts part or all of the technical solutions of the above method, it at least has all the beneficial effects brought by the technical solutions of the above method.

[0057] The present application provides a motor core, wherein the raw material of the motor core comprises the non-oriented electrical steel prepared by any one of the above methods.

[0058] The motor core is realized based on the above non-oriented electrical steel. The specific preparation method of the non-oriented electrical steel can refer to the above method. Since the motor core adopts part or all of the technical solutions of the above method, it at least has all the beneficial effects brought by the technical solutions of the above method.

[0059] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0060] The above scheme, the present invention proposes a non-oriented electrical steel with a strength of not less than 500MPa and a preparation method and a motor core, which can solve the technical problems in the prior art that the strength of non-oriented electrical steel is improved by increasing the dislocation density, but the magnetic properties will decrease due to the obstruction of the reversible movement of the magnetic domain wall; the magnetic properties are improved by adjusting the content of alloy elements and improving the preparation method, while the strength is reduced; and the magnetic properties and strength are improved by adjusting the content of alloy elements and improving the preparation method, but the room temperature brittleness and low processing performance of the prepared material are caused.

[0061] The present invention improves the composition system of the existing non-oriented silicon steel, adds a high content of Cr elements on the basis of the existing conventional composition, and further increases the content of alloy elements such as Al and Mn, with the purpose of fully improving the resistivity. The addition of higher Cr elements can reduce iron loss and improve processing performance. This is different from the traditional dislocation-strengthened high-strength non-oriented silicon steel, which generally uses Nb, V, and Ti additions and low-temperature annealing. The composition system does not consider the requirements of high-strength non-oriented silicon steel for optimizing magnetic properties.

[0062] The present invention is different from the existing low-temperature annealing process for dislocation strengthening. It adopts the method of small deformation rolling + recovery annealing to control dislocation density and dislocation distribution. The core of yield strength control is to set a reasonable final rolling reduction rate (0-30%), and then perform long-term recovery annealing at the recrystallization temperature of electrical steel and below, so that the dislocation density inside the grains is greatly reduced and the high dislocation density at the grain boundaries and deformation band structures is maintained, thereby achieving a balance between yield strength and soft magnetic properties of non-oriented electrical steel.

[0063] The present invention normalizes a hot-rolled coil with a set chemical composition and controls the normalization temperature, so that the grains of the hot-rolled coil can grow sufficiently and evenly; the hot-rolled coil is subjected to a first cold rolling after normalization, so that the thickness required for the subsequent second rolling can be obtained; the chilled coil is subjected to continuous annealing, and the temperature of the continuous annealing is controlled, so that the grains in the chilled coil can be promoted to grow; the coordinated control of the normalization temperature and the continuous annealing temperature can obtain a large grain structure in the steel, and avoid the deterioration of electromagnetic properties caused by the dissolution of precipitates in the steel, the precipitation in a fine dispersed state, and the grain fragmentation occurring during the cold rolling process, so that the final recovery annealing makes it easier to obtain a coarse dislocation network structure.

[0064] The present invention performs a second cold rolling on the annealed coil after continuous annealing and controls the deformation amount of the second cold rolling, thereby introducing deformation dislocations to improve strength without destroying the original grain boundary structure of the annealed coil, so that the annealed coil has a deformed structure that remains at the original grain boundary, laying a solid foundation for subsequent recovery annealing to improve magnetic properties, strength and processing performance and reduce room temperature brittleness.

[0065] The present invention performs low-temperature and long-term recovery annealing on the annealed coil after the second cold rolling, so that the deformed grains of the annealed coil after the second cold rolling can be fully recovered, the dislocation density inside the grains can be greatly reduced, and the high dislocation density at the grain boundaries and deformation band structures can be maintained, so that the dislocation density distribution forms a network-like structure, thereby obtaining the dislocation strengthening effect while reducing the influence of dislocations on the movement of magnetic domains.

[0066] In summary, compared with other traditional methods, the method of the present invention creatively and comprehensively utilizes two strengthening methods, solid solution strengthening and dislocation strengthening, and obtains a coarse network-like high dislocation density organization by regulating the heat treatment and rolling process. While improving the strength level, the degree of deterioration of magnetic properties caused by dislocation strengthening is greatly reduced, thereby realizing the preparation of non-oriented electrical steel with both high strength and low iron loss. It also has high resource utilization, low production cost, short process, easy operation, high efficiency, and is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0068] Figure 1 It is a process flow chart of a method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to the present invention;

[0069] Figure 2This is a microstructure diagram of a low-cost 600MPa grade high-strength non-oriented silicon steel according to Example 4 of the present invention. DETAILED DESCRIPTION

[0070] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0071] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0072] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0073] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0074] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0075] A non-oriented electrical steel with a strength of not less than 500 MPa, wherein the thickness of the non-oriented electrical steel with a strength of not less than 500 MPa is 0.15-0.30 mm, the yield strength is not less than 500 MPa, and the chemical composition is as follows by mass percentage: C≤0.0040%, Si 1.50-4.50%, Al 0.20-1.20%, Mn 0.20-1.30%, Cr 0.1-1.5%, Sn 0.010-0.10%, S≤0.0020%, N≤0.0020%, O≤0.0050%, V≤0.0050%, Ti≤0.0050%, Nb≤0.0050%, and the balance is Fe and unavoidable impurity elements; wherein the element contents of C, S, N, O, V, Ti and Nb cannot be 0.

[0076] Particularly, the metallographic composition of the non-oriented electrical steel with a yield strength not less than 500 MPa is a single-phase ferrite structure.

[0077] Particularly, the average size of the grains in the non-oriented electrical steel having a pressure of not less than 500 MPa is 90-160 μm.

[0078] In particular, the density of the high magnetic non-oriented electrical steel not less than 500 MPa is 7.6-7.7 g / cm 3 , hardness is 210-330HV, saturation flux density is 1.71-1.85T, initial magnetic permeability is 1900-3600H / m, magnetostriction coefficient is 2.6-7.6ppm, magnetic induction B 5000 Not less than 1.61T, iron loss P 1.0 / 400 Not higher than 40W / kg, tensile strength not less than 595MPa, yield strength not less than 500MPa, yield strength ratio of 0.84-0.96, elongation at break not less than 5%, elastic modulus not less than 187GPa, dislocation density of 5×10 13 -1×10 16 pcs / m 2 ; The tensile strength at 150℃ is not less than 520MPa, the yield strength is not less than 420MPa, the yield strength ratio is 0.85-0.97, the elongation at break is not less than 3%, the elastic modulus is not less than 165GPa, and the dislocation density is 5×10 13 -1×10 16 pcs / m 2 .

[0079] A method for preparing the non-oriented electrical steel having a strength of not less than 500 MPa based on the above-mentioned method comprises the following steps:

[0080] S1. Molten steel smelting + continuous casting: using molten iron from a blast furnace or electric furnace as raw material, desulfurization, carbon removal, RH refining and continuous casting are performed to obtain electrical steel slabs with the chemical composition ratio;

[0081] S2, homogenization heat treatment + hot rolling: the S1 electrical steel slab is subjected to homogenization heat treatment to obtain a homogenized electrical steel slab; the homogenized electrical steel slab is fully heated and then taken out of the furnace for hot rolling, and after the hot rolling is completed, it is coiled to obtain an electrical steel hot-rolled coil with a set chemical composition;

[0082] S3, normalizing treatment + first cold rolling: the S2 electrical steel hot rolled coil is normalized to obtain a normalized coil with grown grains, and then the first cold rolling is performed to obtain a first chilled coil;

[0083] S4, continuous annealing treatment + second cold rolling: the S3 first chilled coil is continuously annealed to obtain an annealed coil with further grown grains; then a second cold rolling is performed to obtain a second chilled coil with residual original grain boundaries;

[0084] S5. Recovery annealing treatment: The secondary cold-hardened coil of S4 with the original grain boundary residue is subjected to recovery annealing to obtain a non-oriented electrical steel with fully recovered interior of the deformed grains and a yield strength of not less than 500 MPa.

[0085] In particular, the temperature of the homogenization heat treatment in S2 is 1000-1150°C, and the soaking time is 20-30min; the hot rolling includes rough rolling and finish rolling, the number of rough rolling passes is 4-6 passes, the rough rolling temperature is 1000-1150°C, the total reduction rate is 80-90%, the number of finish rolling passes is 6-7, the finish rolling temperature is 880-1050°C, the final rolling temperature is not less than 830°C, the total reduction rate is 90-95%, the coiling temperature is 500-750°C, and the coil thickness of the hot rolled coil is 2.0-2.6mm.

[0086] In particular, the temperature of the normalizing treatment in S3 is 950-1050°C, the treatment time is 2-10min, and the average size of the normalized grains after growth is 100-200μm; the first cold rolling deformation is 80-93%, and the thickness of the first cold hardened coil is 0.15-0.43mm.

[0087] In particular, the temperature of continuous annealing in S4 is 950-1050℃, the processing time is 0.5-3.0min; the deformation of the second cold rolling is 5-30%, the thickness of the secondary cold hardened coil with the original grain boundary residue is 0.15-0.30mm, and the average size of the grain after growth is 100-160μm

[0088] In particular, the recovery annealing temperature in S5 is 500-700° C., the treatment time is 30-300 min, and the final average size of the grains is 90-160 μm.

[0089] In particular, the raw material of the iron core for the high-speed motor includes non-oriented electrical steel with a strength of not less than 500 MPa prepared by any of the above preparation methods.

[0090] The present embodiment provides a method for preparing a non-oriented electrical steel having a strength of not less than 500 MPa. Figure 1 Follow these steps:

[0091] S1. Molten steel smelting + continuous casting: using molten iron from a blast furnace or electric furnace as raw material, the content is precisely controlled according to the chemical composition ratio in Table 1, refined and continuously cast to obtain electrical steel slabs with the chemical composition ratio in Table 1;

[0092] S2, homogenization heat treatment + hot rolling: the S1 electrical steel slab is subjected to homogenization heat treatment to obtain a homogenized electrical steel slab; the homogenized electrical steel slab is fully heated and then taken out of the furnace for hot rolling, and after the hot rolling is completed, it is coiled to obtain an electrical steel hot-rolled coil with a set chemical composition; the process parameters of the heating and hot rolling of the cast slab of the non-oriented electrical steel in the embodiment are shown in Table 2;

[0093] S3, normalizing treatment + first cold rolling: the S2 electrical steel hot rolled coil is normalized to obtain a normalized coil with grown grains, and then the first cold rolling is performed to obtain a first chilled coil;

[0094] S4, continuous annealing treatment + second cold rolling: the S3 first chilled coil is continuously annealed to obtain an annealed coil with further grown grains; then a second cold rolling is performed to obtain a second chilled coil with residual original grain boundaries;

[0095] S5, recovery annealing treatment: The secondary cold hardened coil with the original grain boundary residue in S4 is subjected to recovery annealing to obtain a non-oriented electrical steel with fully recovered internal deformed grains and a yield strength of not less than 500MPa. The microstructure diagram of a low-cost 600MPa grade high-strength non-oriented silicon steel in Example 4 is as follows: Figure 2 shown.

[0096] The process parameters of S3-S5 are shown in Table 3.

[0097] Table 1 Chemical composition (wt%) of non-oriented electrical steel of Example, the remainder is Fe and unavoidable impurities

[0098]

[0099] Table 2 Process parameters for heating and hot rolling of non-oriented electrical steel in Example

[0100]

[0101] Table 3 Process parameters of normalizing, continuous annealing and recovery annealing of non-oriented electrical steel in Example

[0102]

[0103] The preparation method of the comparative example is the same as that of the embodiment, and the chemical composition is shown in Table 4.

[0104] Table 4 Chemical composition (wt%) of comparative non-oriented electrical steel, the remainder is Fe and unavoidable impurities

[0105]

[0106] The process parameters of the slab heating and hot rolling corresponding to the comparative example are shown in Table 5.

[0107] Table 5 Process parameters for heating and hot rolling of non-oriented electrical steel in comparative example

[0108]

[0109] The process parameters of S3-S5 corresponding to the comparative example are shown in Table 6.

[0110] Table 6 Process parameters of normalization, continuous annealing and recovery annealing of comparative non-oriented electrical steel

[0111]

[0112] The mechanical properties and magnetic properties of the non-oriented electrical steels with fully recovered internal deformed grains and a yield strength of not less than 500 MPa prepared in the embodiments and comparative examples are shown in Table 7.

[0113] Table 7 Mechanical properties and magnetic properties of non-oriented electrical steel

[0114]

[0115] As shown in Table 7, the non-oriented electrical steels of Examples 1-6 can achieve both high strength of ≥500MPa and excellent magnetic properties through the improvement of chemical composition and preparation process parameters, and their comprehensive performance is better than that of the non-oriented electrical steels of Comparative Examples 1-5. 5000 Reduce iron loss P 1.0 / 400 Increase; in Comparative Example 2, the continuous annealing temperature is low, resulting in magnetic induction B 5000 Reduce iron loss P 1.0 / 400 Increase; in Comparative Example 3, the normalizing temperature is low, and the continuous annealing temperature is low, resulting in the magnetic induction B 5000 In Comparative Example 4, the recovery annealing temperature is high. Although the non-oriented electrical steel has excellent magnetic properties, the yield strength Rp 0.2 In comparative example 5, the second cold rolling deformation is too high, resulting in the magnetic induction B 5000 Reduce iron loss P 1.0 / 400 Increase.

[0116] The above scheme, the present invention proposes a non-oriented electrical steel with a strength of not less than 500MPa and a preparation method and a motor core, which can solve the technical problems in the prior art that the strength of non-oriented electrical steel is improved by increasing the dislocation density, but the magnetic properties will decrease due to the obstruction of the reversible movement of the magnetic domain wall; the magnetic properties are improved by adjusting the content of alloy elements and improving the preparation method, while the strength is reduced; and the magnetic properties and strength are improved by adjusting the content of alloy elements and improving the preparation method, but the room temperature brittleness and low processing performance of the prepared material are caused.

[0117] The present invention improves the composition system of the existing non-oriented silicon steel, adds a high content of Cr elements on the basis of the existing conventional composition, and further increases the content of alloy elements such as Al and Mn, with the purpose of fully improving the resistivity. The addition of higher Cr elements can reduce iron loss and improve processing performance. This is different from the traditional dislocation-strengthened high-strength non-oriented silicon steel, which generally uses Nb, V, and Ti additions and low-temperature annealing. The composition system does not consider the requirements of high-strength non-oriented silicon steel for optimizing magnetic properties.

[0118] The present invention is different from the existing low-temperature annealing process for dislocation strengthening. It adopts the method of small deformation rolling + recovery annealing to control dislocation density and dislocation distribution. The core of yield strength control is to set a reasonable final rolling reduction rate (0-30%), and then perform long-term recovery annealing at the recrystallization temperature of electrical steel and below, so that the dislocation density inside the grains is greatly reduced and the high dislocation density at the grain boundaries and deformation band structures is maintained, thereby achieving a balance between yield strength and soft magnetic properties of non-oriented electrical steel.

[0119] The present invention normalizes a hot-rolled coil with a set chemical composition and controls the normalization temperature, so that the grains of the hot-rolled coil can grow sufficiently and evenly; the hot-rolled coil is subjected to a first cold rolling after normalization, so that the thickness required for the subsequent second rolling can be obtained; the chilled coil is subjected to continuous annealing, and the temperature of the continuous annealing is controlled, so that the grains in the chilled coil can be promoted to grow; the coordinated control of the normalization temperature and the continuous annealing temperature can obtain a large grain structure in the steel, and avoid the deterioration of electromagnetic properties caused by the dissolution of precipitates in the steel, the precipitation in a fine dispersed state, and the grain fragmentation occurring during the cold rolling process, so that the final recovery annealing makes it easier to obtain a coarse dislocation network structure.

[0120] The present invention performs a second cold rolling on the annealed coil after continuous annealing and controls the deformation amount of the second cold rolling, thereby introducing deformation dislocations to improve strength without destroying the original grain boundary structure of the annealed coil, so that the annealed coil has a deformed structure that remains at the original grain boundary, laying a solid foundation for subsequent recovery annealing to improve magnetic properties, strength and processing performance and reduce room temperature brittleness.

[0121] The present invention performs low-temperature and long-term recovery annealing on the annealed coil after the second cold rolling, so that the deformed grains of the annealed coil after the second cold rolling can be fully recovered, the dislocation density inside the grains can be greatly reduced, and the high dislocation density at the grain boundaries and deformation band structures can be maintained, so that the dislocation density distribution forms a network-like structure, thereby obtaining the dislocation strengthening effect while reducing the influence of dislocations on the movement of magnetic domains.

[0122] In summary, compared with other traditional methods, the method of the present invention creatively and comprehensively utilizes two strengthening methods, solid solution strengthening and dislocation strengthening, and obtains a coarse network-like high dislocation density organization by regulating the heat treatment and rolling process. While improving the strength level, the degree of deterioration of magnetic properties caused by dislocation strengthening is greatly reduced, thereby realizing the preparation of non-oriented electrical steel with both high strength and low iron loss. It also has high resource utilization, low production cost, short process, easy operation, high efficiency, and is conducive to large-scale industrial production and promotion.

[0123] It should be understood that the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship, but it may also indicate an "and / or" relationship. Please refer to the context for specific understanding.

[0124] In the present invention, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can be represented by: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0125] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0126] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A non-oriented electrical steel with a strength of not less than 500 MPa, characterized in that: The non-oriented electrical steel with a strength of not less than 500 MPa has a thickness of 0.15-0.30 mm, a yield strength of not less than 500 MPa, and chemical compositions by mass percentage: C≤0.0040%, Si 1.50-4.50%, Al 0.20-1.20%, Mn 0.20-1.30%, Cr 0.1-1.5%, Sn 0.010-0.10%, S≤0.0020%, N≤0.0020%, O≤0.0050%, V≤0.0050%, Ti≤0.0050%, Nb≤0.0050%, and the balance is Fe and unavoidable impurity elements; wherein the element contents of C, S, N, O, V, Ti and Nb are not 0; The density of the non-oriented electrical steel not less than 500 MPa is 7.6-7.7 g / cm 3 , hardness is 210-330HV, saturation flux density is 1.71-1.85T, initial magnetic permeability is 1900-3600H / m, magnetostriction coefficient is 2.6-7.6ppm, magnetic induction B 5000 Not less than 1.61T, iron loss P 1.0 / 400 Not higher than 40W / kg, tensile strength not less than 595MPa, yield strength not less than 500MPa, yield strength ratio of 0.84-0.96, elongation at break not less than 5%, elastic modulus not less than 187GPa, dislocation density of 5×10 13 -1×10 16 pcs / m 2 ; The tensile strength at 150℃ is not less than 520MPa, the yield strength is not less than 420MPa, the yield strength ratio is 0.85-0.97, the elongation at break is not less than 3%, the elastic modulus is not less than 165GPa, and the dislocation density is 5×10 13 -1×10 16 pcs / m 2 .

2. The non-oriented electrical steel with a strength of not less than 500 MPa according to claim 1, characterized in that: The metallographic structure of the non-oriented electrical steel with a yield strength not less than 500 MPa is a single-phase ferrite structure.

3. The non-oriented electrical steel with a strength of not less than 500 MPa according to claim 1, characterized in that: The average size of the grains in the non-oriented electrical steel having a pressure of not less than 500 MPa is 90-160 μm.

4. A method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to claim 1, characterized in that: The method for preparing the non-oriented electrical steel with a strength of not less than 500 MPa comprises the following steps: S1. Molten steel smelting + continuous casting: Using molten iron from a blast furnace or electric furnace as raw material, desulfurization, carbon removal, RH refining and continuous casting are carried out to obtain electrical steel slabs with chemical composition; S2, homogenization heat treatment + hot rolling: the S1 electrical steel slab is subjected to homogenization heat treatment to obtain a homogenized electrical steel slab; the homogenized electrical steel slab is fully heated and then taken out of the furnace for hot rolling, and after the hot rolling is completed, it is coiled to obtain an electrical steel hot-rolled coil with a set chemical composition; S3, normalizing treatment + first cold rolling: the S2 electrical steel hot rolled coil is normalized to obtain a normalized coil with grown grains, and then the first cold rolling is performed to obtain a first chilled coil; S4, continuous annealing treatment + second cold rolling: the S3 first chilled coil is continuously annealed to obtain an annealed coil with further grown grains; then the second cold rolling is performed to obtain a second chilled coil with residual original grain boundaries; S5. Recovery annealing treatment: The secondary cold-hardened coil of S4 with the original grain boundary residue is subjected to recovery annealing to obtain a non-oriented electrical steel with fully recovered interior of the deformed grains and a yield strength of not less than 500 MPa.

5. The method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to claim 4, characterized in that: The temperature of homogenization heat treatment in S2 is 1000-1150℃, and the soaking time is 20-30min; hot rolling includes rough rolling and finish rolling, the number of rough rolling passes is 4-6 passes, the rough rolling temperature is 1000-1150℃, the total reduction rate is 80-90%, the number of finish rolling passes is 6-7, the finish rolling temperature is 880-1050℃, the final rolling temperature is not less than 830℃, the total reduction rate is 90-95%, the coiling temperature is 500-750℃, and the coil thickness of the hot rolled coil is 2.0-2.6mm.

6. The method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to claim 4, characterized in that: The temperature of normalizing treatment in S3 is 950-1050℃, the treatment time is 2-10min, and the average size of normalized grains after growth is 100-200μm; the deformation of the first cold rolling is 80-93%, and the thickness of the first cold hardened coil is 0.15-0.43mm.

7. The method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to claim 4, characterized in that: The temperature of continuous annealing in S4 is 950-1050°C, and the processing time is 0.5-3.0min; the deformation of the second cold rolling is 5-30%, the thickness of the secondary cold-hardened coil with the original grain boundary residue is 0.15-0.30mm, and the average size of the grain after growth is 100-160μm.

8. The method for preparing non-oriented electrical steel with a strength of not less than 500 MPa according to claim 4, characterized in that: The recovery annealing temperature in S5 is 500-700°C, the processing time is 30-300 min, and the final average size of the grains is 90-160 μm.

9. A core for a high-speed motor, characterized in that: The raw material of the iron core for the high-speed motor includes non-oriented electrical steel with a strength of not less than 500 MPa prepared by the preparation method according to any one of claims 4 to 8.

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