Low-cost non-oriented electrical steel sheet with extremely low aluminum content and manufacturing method thereof

Abstract

A low-cost, non-oriented electrical steel sheet with a very low aluminum content is disclosed, the sheet having the following chemical elements in weight percent: C is 0.003% or less, Si is 0.1% to 1.2%, Mn is 0.1% to 0.4%, P is 0.01% to 0.2%, S is 0.003% or less, Al is 0.001% or less, O is 0.003% to 0.01%, N is 0.003% or less, and Sn is 0.005% to 0.05%, where Si is 2 / P: 0.89 to 26.04 is satisfied. Additionally, a method for producing a non-oriented electrical steel sheet is further disclosed. The method comprises the following steps: (1) a smelting step; (2) a continuous casting step; (3) a hot rolling step, in which the hot-rolled sheet is subjected to soaking and warming using the residual heat of the hot-rolled steel coil rather than being subjected to normalizing treatment or cover furnace annealing after coiling; (4) a primary cold rolling step; and (5) a continuous annealing step. The non-oriented electrical steel sheet of the present invention uses rational chemical raw materials and process design, and is not only economical but also has the properties of high magnetic induction and low core loss.

Description

[Technical field]

[0001] The present invention relates to a steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet and a manufacturing method thereof. [Background technology]

[0002] background The grain direction inside non-oriented electrical steel sheet is not unique, and non-oriented electrical steel sheet is a functional material with excellent electromagnetic properties. For a long time, non-oriented electrical steel sheet has been developed in two directions: first, high-efficiency and high-grade steel with excellent electromagnetic properties and mechanical properties, but with high manufacturing costs and complicated production processes; and second, medium-grade and low-grade steel with low manufacturing costs, simple production processes, and excellent electromagnetic properties and mechanical properties.

[0003] According to statistics, due to different application opportunities, the number of medium and low grade non-oriented electrical steel sheets accounts for more than 70% of the total number of non-oriented electrical steel sheets. Therefore, it is of great practical significance to study how to produce medium and low grade non-oriented electrical steel sheets more economically and conveniently, and to further improve their cost performance. At the same time, considering that medium and low grade non-oriented electrical steel sheets are mostly used in small and medium motors, EI cores, small generators, etc., the user market is constantly demanding the reduction of the iron loss of steel sheets, and at the same time, it is more urgent to improve the magnetic induction of steel sheets to more effectively reduce the copper loss of the core.

[0004] Additionally, the study showed that in the electromagnetic performance indicators of non-oriented electrical steel sheets, the core loss and magnetic induction are mutually limited, and it is difficult to simultaneously achieve low core loss and high magnetic induction unless normalizing or cover furnace annealing is performed on the hot rolled steel sheets, which will greatly increase the manufacturing cost of the finished steel sheets.

[0005] In recent years, many scientists and engineers have made many useful attempts on how to effectively improve the electromagnetic properties of non-oriented electrical steel sheets while reducing their manufacturing costs without performing normalizing treatment or cover furnace annealing treatment on the hot-rolled sheets.

[0006] China Patent Publication No. 101992210, published on March 30, 2011 and entitled "Method for Producing Aluminum-Free Grades of Cold-Rolled Non-Oriented Silicon Steel", discloses a method for producing aluminum-free grades of cold-rolled non-oriented silicon steel, and includes controlling Al≦0.0010% and controlling the content of residual elements that are prone to form nitrides, and adopting low-temperature heating and temperature-controlled rolling for hot rolling, first cold rolling or second cold rolling with intermediate annealing. It is pointed out that by using the above-mentioned aluminum-free cold-rolled non-oriented silicon steel and implementing comprehensive performance control measures such as wet hydrogen decarburization, recrystallization temperature annealing, etc., mass production of aluminum-free cold-rolled non-oriented silicon steel with high efficiency can be achieved under existing equipment conditions with lower production costs, and its electromagnetic properties are better than those of the same grade of cold-rolled non-oriented silicon steel produced by the conventional process, the iron loss is reduced by about 0.4 W / kg on average, and the magnetic induction is increased by 0.2 T on average. The specific control methods are as follows: the content of residual aluminum taken in during the alloying process, including deoxidizing aluminum, materials, and heat-resistant materials, is controlled, and Al is controlled to be less than 0.0010%, and Si deoxidation is used in the refining and deoxidation process; the content of nitrogen and the content of residual elements that are easy to form nitrides during smelting are controlled, and the contents of N, Ti, Nb and V are each controlled to be less than 0.0020%; hot rolling is performed by temperature-controlled rolling (i.e., ferrite single rolling ... low temperature heating and final rolling are adopted to implement rolling in the annealing phase region, and the two-phase precipitation state is controlled; the hot rolled billet heating temperature is 1000-1150°C, the initial rolling temperature is 950°C or higher, the final rolling temperature is 840°C or higher, and the coil winding temperature is 690°C or higher; the cold rolling adopts primary cold rolling or secondary cold rolling with intermediate annealing for rolling to the finished thickness; and the annealing adopts cover furnace continuous annealing and recrystallization temperature annealing for wet hydrogen decarburization. A non-oriented electrical steel sheet and a manufacturing method thereof are provided.The non-oriented electrical steel sheet contains the following components in weight percentages: C 0.03-0.15%, Si 0.15% or less, Mn 1.0-1.8%, P 0.025% or less, S 0.015% or less, Ti 0.08-0.18%, Nb 0.02-0.07%, Al 0.02-0.10%, N 0.010% or less, and the remainder iron and residuals.

[0007] China Patent Publication No. 101306434, published on November 19, 2008 and entitled "Preparation Method for Low Carbon Low Silicon Aluminum-Free Semi-Processed Non-oriented Electrical Steel", discloses a preparation method for producing low carbon low silicon aluminum-free semi-processed non-oriented electrical steel. The process steps are as follows: hot rolling raw material composition design requires the chemical composition of the cast slab to be as follows: C is less than 0.005%, Si is 0.1-1.0%, Mn is less than 0.35%, P is less than 0.08%, S is less than 0.01%, N is less than 0.008%, O is less than 0.015%, and the balance is Fe and unavoidable impurities; and semi-processed non-oriented electrical steel with excellent magnetic properties is obtained from the cast slab through hot charging, hot rolling, critical deformation cold rolling and user stress relief annealing. The characteristics of semi-processed non-oriented electrical steel are that the casting slab heating temperature is 900-1150℃, the final rolling temperature is required to be 10-50℃ lower than the Ar3 transformation point, and the thickness of the hot-rolled sheet is 2.0-2.5mm; intermediate annealing is carried out at 600-850℃ for 1-2 minutes under the intermediate annealing atmosphere of H2 and N2 mixed gas, the ratio of H2 is 10-40%, and humidification and decarburization are not required, and the recrystallization rate after intermediate annealing is guaranteed to be more than 40%; critical deformation cold rolling is performed to ensure that the steel strip after intermediate annealing has a critical deformation of 0.5mm with a reduction of 0.5-15%. semi-processed non-oriented electrical steels are characterized by the fact that the final product has excellent magnetic properties and P 15 / 50 = 3.35 to 5.05 W / kg, and B 5000=1.69~1.76T. The cast slab does not contain alloying elements such as Al, Sn, Sb, Cu, Cr, Ni, B, rare earths, etc., and the production cost is greatly reduced. A larger critical reduction is used, and the annealing process is optimized, so that the produced finished products have better magnetic properties. Summary of the Invention

[0008] overview One of the objectives of the present invention is to provide a low-cost non-oriented electrical steel sheet with an extremely low aluminum content. By optimizing the chemical composition of the steel, the non-oriented electrical steel sheet has the technical features of extremely low aluminum content in the steel and suitable oxidizing properties in the steel and slag, which reduces the quality of special alloys for deoxidation and alloying in RH refining, greatly reducing the steel production cost and effectively controlling the alloy cost. Compared with the conventional products of the same grade, the iron loss P of the non-oriented electrical steel sheet is 15 / 50 The magnetic induction B of the non-oriented electrical steel sheet decreased by an average of 0.2 to 0.8 W / kg. 50 In other words, compared with the existing conventional products of the same grade, the iron loss P 15 / 50 The average reduction in magnetic induction B was 0.2 to 0.8 W / kg. 50 The non-oriented electrical steel sheet is characterized by an average increase in magnetic flux density of 0.01 to 0.04 T, and is not only economical but also has the characteristics of high magnetic induction and low iron loss. The above reference values ​​of the electromagnetic properties are those of ordinary non-oriented electrical steel sheets in the existing user market. Conventional Among the electromagnetic properties of grade B50A1300, iron loss P 15 / 50 is generally 5.5 to 6.5 W / kg, and the magnetic induction B 50 is 1.74~1.76T; the iron loss P 15 / 50 is generally 5.0 to 5.5 W / kg, and the magnetic induction B 50 is 1.71 to 1.73 T; and among the electromagnetic properties of the conventional grade B50A600, the iron loss P 15 / 50is generally 3.9 to 4.5 W / kg, and the magnetic induction B 50 is 1.68~1.71T.

[0009] In order to achieve the above object, the present invention provides a low-cost non-oriented electrical steel sheet with a very low aluminum content, which comprises the following chemical elements in mass %: C is 0.003% or less, Si is 0.1% to 1.2%, Mn is 0.1% to 0.4%, P is 0.01% to 0.2%, S is 0.003% or less, Al is 0.001% or less, O is 0.003% to 0.01%, N is 0.003% or less, and Sn is 0.005% to 0.05%, and the condition Si 2 / P:0.89~26.04 is satisfied.

[0010] Furthermore, the non-oriented electrical steel sheet according to the present invention comprises the following chemical elements, in mass %: C is 0.003% or less, Si is 0.1% to 1.2%, Mn is 0.1% to 0.4%, P is 0.01% to 0.2%, S is 0.003% or less, Al is 0.001% or less, O is 0.003% to 0.01%, N is 0.003% or less, Sn is 0.005% to 0.05%, and the balance is Fe and other unavoidable impurities, and the condition Si 2 / P:0.89~26.04 is satisfied.

[0011] In the non-oriented electrical steel sheet of the present invention, the design principles of chemical elements are as follows:

[0012] C: In the non-oriented electromagnetic steel sheet according to the present invention, carbon is one of the strong aging-forming elements. When the content of the C element in the steel is more than 0.003%, the C element easily combines with Nb, V, Ti, etc. to form a large amount of fine inclusions, resulting in a significant increase in the loss of the finished steel sheet. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of C is controlled so that C ≦ 0.003%. In the non-oriented electromagnetic steel sheet of the present invention, the less the C element content is controlled, the better it is. Specifically, the mass% of C is controlled so that 0 < C ≦ 0.003%.

[0013] Si: In the non-oriented electromagnetic steel sheet according to the present invention, the Si element can significantly increase the resistivity of the material. However, if the content of the Si element in the steel is less than 0.1%, the iron loss of the finished steel sheet cannot be effectively reduced; and it should be noted that if the content of the Si element in the steel is more than 1.2%, the magnetic induction of the finished steel sheet will be significantly deteriorated. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of Si is controlled to be 0.1% - 1.2%.

[0014] Mn: In the non-oriented electromagnetic steel sheet according to the present invention, the Mn element combines with the S element to form MnS, thereby effectively improving the magnetic properties of the finished steel sheet. To ensure that the Mn element can play an effective role, it is necessary to add 0.1% or more of Mn to the steel, but it should be noted that the content of the Mn element should not be too much. If the content of the Mn element in the steel is more than 0.4%, the recrystallized structure of the finished steel sheet will be significantly damaged. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of Mn is controlled to be 0.1% - 0.4%.

[0015] P: In the non-oriented electromagnetic steel sheet according to the present invention, the P element can significantly improve the strength of the material. When the content of the P element in the steel is less than 0.01%, the strength of the finished steel sheet cannot be effectively improved. If the content of the P element in the steel is more than 0.2%, the rollability of cold rolling will be significantly reduced. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of P is controlled to be 0.01% - 0.2%.

[0016] S: In the non-oriented electromagnetic steel sheet according to the present invention, the content of S element should not be too much. When the content of S element in the steel is more than 0.003%, the number of inclusions such as MnS and Cu2S will increase significantly, which will prevent grain growth and deteriorate the magnetic properties of the finished steel sheet. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of S is controlled so that 0 < S ≤ 0.003%. In the non-oriented electromagnetic steel sheet of the present invention, the less the S element content is controlled, the better it is. Specifically, the mass% of S is controlled so that 0 < S ≤ 0.003%.

[0017] Al: In the non-oriented electromagnetic steel sheet according to the present invention, the content of Al element in the steel should not be too much. When Al in the steel is more than 0.001%, a large amount of AlN harmful inclusions will be formed, which will significantly deteriorate the magnetic properties of the finished steel sheet. Therefore, in the non-oriented electromagnetic steel sheet according to the present invention, the mass% of Al is controlled so that Al ≤ 0.001%. In the non-oriented electromagnetic steel sheet of the present invention, the less the Al element content is controlled, the better it is. Specifically, the mass% of Al is controlled so that 0 < Al ≤ 0.001%.

[0018] In some preferred embodiments, the mass% of Al can be controlled so that Al ≤ 0.0005%.

[0019] О: In the non-oriented electromagnetic steel sheet according to the present invention, when the content of О element in the steel is less than 0.003%, it does not help to control the contents of Al and Ti. And if the content of О element in the steel is more than 0.01%, a large amount of oxygen inclusions will be formed, which will deteriorate the magnetic properties of the finished steel sheet. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of О is controlled to be 0.003% - 0.01%.

[0020] In some preferred embodiments, the mass% of О 0 can be controlled to be 0.045% - 0.007%.

[0021] N: In the non-oriented electromagnetic steel sheet according to the present invention, the content of N element in the steel should not be too high. When the content of N element in the steel exceeds 0.003%, the N-containing Nb, V, Ti, and Al inclusions increase significantly, which hinders grain growth and deteriorates the magnetic properties of the finished steel sheet. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of N is controlled such that N ≦ 0.003%. In the non-oriented electromagnetic steel sheet of the present invention, the lower the N element content is controlled, the better it is. Specifically, the mass% of N is controlled such that 0 < C ≦ 0.003%.

[0022] Sn: In the non-oriented electromagnetic steel sheet according to the present invention, Sn is a grain boundary segregation element. An appropriate amount of the beneficial element Sn added to the steel can improve grain boundary segregation during hot rolling and improve the microscopic and beneficial structure. When the content of Sn element in the steel is less than 0.005%, the segregation effect cannot be effectively obtained. If the content of Sn element in the steel exceeds 0.05%, atomization will be caused and the magnetic properties of the finished steel sheet will deteriorate. Therefore, in the non-oriented electromagnetic steel sheet of the present invention, the mass% of Sn is controlled to be 0.005% - 0.05%.

[0023] In some preferred embodiments, the mass% of Sn can be controlled to be 0.005% - 0.02%.

[0024] Additionally, in the non-oriented electromagnetic steel sheet according to the present invention, while controlling the content of a single chemical element, the Si element and the P element are also subject to the condition Si 2 / P: controlled to satisfy 0.89-26.04, where both Si and P represent the numbers before the % symbol of the mass% of the corresponding element. It should be noted that the properties of Si element and P element are similar, which can significantly improve the resistance of the material and reduce the iron loss of the finished steel plate, but at the same time, it will deteriorate the magnetic induction of the finished steel plate. In terms of improving the mechanical strength of the finished steel plate, P element has a very good and significant effect, but it will deteriorate the rollability of cold rolling under the condition of high Si content. Therefore, considering the electromagnetic properties and mechanical properties of the finished steel plate, Si 2 In the non-oriented electrical steel sheet of the present invention, / P is controlled to be 0.89 to 26.04.

[0025] In some preferred embodiments, for better implementation, Si 2 / P can be controlled to be between 0.89 and 16.67.

[0026] Additionally, it should be noted that in the non-oriented electrical steel sheet according to the present invention, the inevitable impurities in the steel include Nb, V, Ti, Ca, Mg and REM, which are rare earth elements and may simply be referred to as RE.

[0027] Furthermore, the non-oriented electrical steel sheet according to the present invention contains 0.0005% or less of Al.

[0028] Furthermore, in the non-oriented electrical steel sheet according to the present invention, O is 0.0 0 Contains 45-0.007%.

[0029] Furthermore, the non-oriented electrical steel sheet according to the present invention contains 0.005 to 0.02% Sn.

[0030] Furthermore, in the non-oriented electrical steel sheet according to the present invention, Si 2 / P is 0.89 to 16.67.

[0031] Furthermore, in the non-oriented electrical steel sheet according to the present invention, the iron loss P15 / 50 The magnetic induction B of non-oriented electrical steel sheet decreased by an average of 0.2 to 0.8 W / kg. 50 increases by an average of 0.01 to 0.04 T. Furthermore, the non-oriented electrical steel sheet of the present invention has a thickness of 0.5±0.1 mm.

[0032] Therefore, another object of the present invention is to provide a method for producing a low-cost non-oriented electrical steel sheet with an extremely low aluminum content, which has a simple production process, a low production cost, and a low iron loss P compared with conventional products of the same grade. 15 / 50 The average reduction in magnetic induction B was 0.2 to 0.8 W / kg. 50 In addition, non-oriented electrical steel sheets have the characteristics of high magnetic induction and low core loss.

[0033] In order to achieve the above object, the present invention proposes a method for producing a non-oriented electrical steel sheet, comprising the following steps: (1) Smelting step; (2) Continuous casting step; (3) a hot rolling step, in which the hot rolled sheet is not subjected to normalizing or cover furnace annealing after coiling, but is subjected to soaking and warming with the residual heat of the hot rolled steel coil; (4) a primary cold rolling step; and (5) Continuous annealing step It is.

[0034] In the manufacturing method according to the present invention, the hot rolling process mainly includes slab heating, rough rolling, final rolling and coiling. Normalizing or cover furnace annealing refers to a process of performing intermediate annealing on the hot rolled coil after hot rolling and before cold rolling to improve the electromagnetic properties of the finished product. In the present invention, in step (3), the hot rolled sheet is not subjected to normalizing or cover furnace annealing after coiling, but is subjected to soaking and warming with the residual heat of the hot rolled steel coil, which can effectively promote the segregation of the trace element Sn, improve the recrystallization structure of the hot rolled steel sheet, and promote the growth of grain size, thus realizing the effect of replacing or supplementing normalizing annealing or cover furnace annealing. In addition, this operation can also effectively simplify the process, reduce the production load and manufacturing difficulty, and reduce the production cost.

[0035] Furthermore, in the manufacturing method of the present invention, in step (1), ferrophosphorus, ferrosilicon and ferromanganese are added in this order during the deoxidation and alloying of the RH refinement.

[0036] In the manufacturing method of non-oriented electrical steel sheet according to the present invention, in step (1), ferrophosphorus, ferrosilicon and ferromanganese are added in sequence during the deoxidation and alloying of RH refining. That is, at the end of RH refining, ferrophosphorus, ferrosilicon and ferromanganese are added to the molten steel to remove the free oxygen in the steel, and elemental components are added according to the requirements of the present invention. In this manner, the molten steel is in an aerobic state, and Al, Ti, Nb, V, Ca, Mg, REM, etc. in ferrophosphorus and ferrosilicon will rapidly undergo oxidation and reduction reactions, and large particles of oxides will be generated one after another and float in the top slag, so that the cleanliness of the steel will not be deteriorated. Therefore, after a large number of experimental studies, the control requirements of some harmful elements in ferrophosphorus and ferrosilicon are effectively reduced, which can greatly reduce the production cost of steelmaking. Ferrophosphorus, ferrosilicon and ferromanganese refer to alloys containing P, Si and Mn, and their composition ratios are not limited as long as the composition of the steel plate formed after addition satisfies the above content requirements.

[0037] In addition, it should be noted that the amount of ferrosilicon added should consider two aspects: on the one hand, ferrosilicon is added according to the chemical composition P, and on the other hand, Si 2ferrosilicon is added according to the chemical composition O to ensure that the O content in the steel is adjusted by Si deoxidation under the condition of very low aluminum content, preventing the O content from being too low or too high. When the amount of ferrosilicon added is too much, the deoxidation ability is strong, the O content in the steel is low, and a large amount of deoxidation product SiO2 generated will enter the slag, which will result in the reduction of Al, Ti, Nb, V, Ca, Mg, REM and other elements to enter the steel again; when the amount of ferrosilicon added is too little, the deoxidation ability is weak, the O content in the steel is too high, and during the final continuous casting, with the continuous decrease in the temperature of the molten steel, a large amount of small-sized secondary deoxidation product SiO2 will be generated again due to supersaturation, which cannot float and cannot be removed at this time, but will remain in the steel and provide nuclei for the precipitation of MnS inclusions during the subsequent hot rolling. Therefore, it is necessary to add ferrosilicon according to the chemical composition O to ensure that the O content in the steel is strictly controlled to be 0.003%-0.01%. The abbreviation of the above continuous casting is CC, and casting refers to casting molten steel into a continuous cast piece.

[0038] Furthermore, in the production method of the present invention, the ferrosilicon has Al≦0.1% and / or Ti≦0.03%.

[0039] Furthermore, in the manufacturing method according to the present invention, in step (3), the initial rolling temperature is controlled to be 1050 to 1150°C, the final rolling temperature is controlled to be 650 to 950°C, the coil winding temperature is controlled to be 650 to 850°C, the soaking and heat-holding temperature is controlled to be 650 to 850°C, and the heat-holding time is controlled to be at least 10 s.

[0040] In the above solution, in step (3), controlling the soaking and heat-holding temperature to be 650-850°C can effectively promote the segregation of trace element Sn, improve the recrystallization structure of the hot-rolled steel sheet, and promote the growth of grain size. The heat-holding time is controlled to be at least 10s, and can be appropriately extended to increase the improvement effect if the temperature conditions allow. For example, the heat-holding time may further be controlled to be 10s-60h, and still further, the heat-holding time may be controlled to be within 24h (e.g., 2h-24h).

[0041] Furthermore, in the manufacturing method according to the present invention, in step (3), the rough rolling and final rolling are completed in 2 to 8 passes. One pass means one rolling, and 2 to 8 passes means 2 to 8 rollings.

[0042] Furthermore, in the manufacturing method according to the present invention, in step (5), annealing is carried out at 650-950°C under an annealing atmosphere of a mixed gas of H2 and N2, and the volume ratio of H2 is 20-60%. Nitrogen will contain a small amount of oxygen, which will easily cause the surface of the steel sheet to be oxidized and blackened. Hydrogen is added mainly to avoid the oxidation of the surface of the strip steel. The effect of hydrogen with the above volume ratio is better, and the cost can be controlled within a reasonable range.

[0043] Compared with the prior art, the low-cost non-oriented electrical steel sheet with a very low aluminum content and the manufacturing method thereof according to the present invention have the following advantages and beneficial effects:

[0044] By optimizing the chemical composition design of steel, the low-cost non-oriented electrical steel sheet with extremely low aluminum content has the technical features of extremely low aluminum content in steel and suitable oxidizing property contained in steel and slag, which reduces the quality of special alloys for deoxidation and alloying in RH refining, greatly reducing the steel manufacturing cost and effectively controlling the alloy cost. Compared with conventional products of the same grade, the iron loss P of non-oriented electrical steel sheet is 15 / 50 The magnetic induction of non-oriented electrical steel sheet B50 The average increase is 0.01 to 0.04 T, achieving the characteristics of high magnetic induction and low iron loss while maintaining good economic efficiency.

[0045] In addition, the manufacturing method of the present invention has a simple production process and low manufacturing cost, and by controlling the process conditions (especially the hot rolling process), the hot rolled plate is not subjected to normalizing treatment or cover furnace annealing after coiling, but is subjected to soaking and heat retention by the residual heat of the hot rolled steel coil, so that the trace elements in the steel can be segregated, and the effect of improving the recrystallization structure of the hot rolled steel plate and promoting the growth of grain size can be achieved. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 shows a schematic diagram of the relationship between the oxygen content in a non-oriented electrical steel sheet according to the present invention and the core loss P15 / 50 of the finished steel sheet. [Diagram 2] FIG. 2 is a microstructure diagram of the hot-rolled steel sheet in Example 2. [Diagram 3] FIG. 3 is a microstructure diagram of the hot-rolled steel sheet in Comparative Example 2. [Figure 4] FIG. 4 is a microstructure diagram of the completed non-oriented electrical steel sheet in Example 3. [Diagram 5] FIG. 5 is a microstructure diagram of the completed steel sheet in Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Detailed Description The low-cost non-oriented electrical steel sheet with very low aluminum content and its manufacturing method according to the present invention will be further explained and described below with reference to specific examples and drawings, which, however, do not constitute undue limitations on the technical solutions of the present invention.

[0048] Examples 1 to 6 and Comparative Examples 1 to 6 Table 1 lists the mass% of chemical elements in the non-oriented electrical steel sheets in Examples 1 to 6. It should be noted that the inevitable impurities in the steel grade mainly include Nb, V, Ti, Ca, Mg and REM.

[0049] [Table 1]

[0050] All of the non-oriented electrical steel sheets in Examples 1 to 6 according to the present invention are manufactured by the following steps: (1) Smelting: Molten iron from the blast furnace and a suitable amount of scrap steel are smelted in a converter furnace, and decarburization, deoxidization and alloying are completed in sequence during RH refining, and then suitable slabs are cast. Ferrophosphorus, ferrosilicon and ferromanganese are added in sequence during deoxidation and alloying of RH refining, and Al≦0.1% and / or Ti≦0.03% in ferrosilicon. (2) Continuous casting; (3) Hot rolling: the initial rolling temperature is controlled to be 1050-1150°C, the final rolling temperature is controlled to be 650-950°C, the coil winding temperature is controlled to be 650-850°C, the soaking and heat-keeping temperature is controlled to be 650-850°C, and the heat-keeping time is controlled to be at least 10s, the rough rolling and final rolling are completed in 2-8 passes, and the target thickness of hot rolling is 1.2-2.8mm; the hot-rolled sheet is not subjected to normalizing treatment or cover furnace annealing after coil winding, but is subjected to soaking and heat-keeping by the residual heat of the hot-rolled steel coil; and after the completion of hot rolling, the hot-rolled steel coil is pickled; (4) Primary cold rolling: rolling to the target thickness in one go; and (5) Continuous annealing: annealing is carried out at 650-950°C for less than 180s under an annealing atmosphere of a mixture of H2 and N2, and the volume ratio of H2 is 20%-60%.

[0051] Tables 2-1 and 2-2 list specific process parameters for the manufacturing methods of non-oriented electrical steel sheets in Examples 1 to 6. Rough rolling and final rolling passes in Table 2-2 represent the rolling times of rough rolling and final rolling, respectively, for example, in Example 1, 4+7 means that rough rolling is completed in 4 passes and final rolling is completed in 7 passes.

[0052] [Table 2-1]

[0053] [Table 2-2]

[0054] Table 3 lists the mass percentages of the chemical elements in the non-oriented electrical steel sheets in Comparative Examples 1-6.

[0055] [Table 3]

[0056] Table 4 lists specific process parameters for the manufacturing methods of the non-oriented electrical steel sheets in Comparative Examples 1-6.

[0057] [Table 4]

[0058] It should be noted that the steel sheets in Comparative Examples 1-6 were manufactured by using only conventional process conditions, not the manufacturing process according to the present invention, and the steel sheets in Comparative Examples 1-6 correspond to those in Examples 1-6, respectively. The non-oriented electrical steel sheet in Example 1 corresponds to the domestic grade B50A1300 steel in Comparative Example 1, the non-oriented electrical steel sheet in Example 2 corresponds to the domestic grade B50A800 steel in Comparative Example 2, the non-oriented electrical steel sheet in Example 3 corresponds to the domestic grade B50A470 steel in Comparative Example 3, the non-oriented electrical steel sheet in Example 4 corresponds to the domestic grade B50A1300 steel in Comparative Example 4, the non-oriented electrical steel sheet in Example 5 corresponds to the domestic grade B50A800 steel in Comparative Example 5, and the non-oriented electrical steel sheet in Example 6 corresponds to the domestic grade B50A470 steel in Comparative Example 6.

[0059] The non-oriented electrical steel sheets having a final target thickness of 0.5±0.1 mm obtained by cold rolling in Examples 1 to 6 and the steel sheets in Comparative Examples 1 to 6 were subjected to various performance tests, and the obtained test results are listed in Table 5.

[0060] Table 5 lists the performance test results of the non-oriented electrical steel sheets in Examples 1-6 and the steel sheets in Comparative Examples 1-6.

[0061] Iron loss performance test: The iron loss performance test is carried out by using Epstein square based on the national standard GB / T 3655-2008 at a constant temperature of 20°C, the sample size is 30mm×300mm, the target mass is 0.5kg, and the test parameters are P 15 / 50 It is.

[0062] Magnetic induction performance test: The magnetic induction performance test is carried out by using Epstein square based on the national standard GB / T 3655-2008 at a constant temperature of 20°C, the sample size is 30mm×300mm, the target mass is 0.5kg, and the test parameters are B 50 It is.

[0063] [Table 5]

[0064] As can be seen from Table 5, there is a significant difference in iron loss P between the steel sheets manufactured by using the conventional process conditions in Comparative Examples 1 to 6 and the non-oriented electrical steel sheets in Examples 1 to 6. 15 / 50 and magnetic induction B 50 There is a clear difference in the electromagnetic performance test density of 7.85g / cm 3 When the iron loss P 15 / 50 is reduced by 0.4 W / kg, and the magnetic induction B in Example 1 is 50 increased by 0.04T, the main reason being that in Comparative Example 1, the Al content is about 0.01% higher (which exceeds the upper limit of 0.001% in the claimed range of the present invention), and the hot-rolled steel coil is subjected to soaking and warming at only 547°C (which does not meet the control range of 650-850°C); the electromagnetic performance test density was 7.80g / cm 3 When the iron loss P 15 / 50 is reduced by 0.6 W / kg, and the magnetic induction B in Example 2 is 50 increased by 0.02T, the main reason being that the design of the Si and P contents in Comparative Example 2 was not harmonious, and the Si 2 This is because the .DELTA. / .P is as high as 45.56 (which exceeds the upper limit of 26.04), and the hot-rolled steel coil is subjected to soaking and warming at a temperature as high as 872°C (which does not meet the control range of 650-850°C); the electromagnetic performance test density is 7.70 g / cm 3 When the iron loss P 15 / 50 is reduced by 0.8 W / kg, and the magnetic induction B in Example 3 is 50 increased by 0.01 T, which is mainly because the Si content in Comparative Example 3 was too low, and therefore the Si 2 / P is only 0.05 (which does not meet the control lower limit of 0.89), and the hot-rolled steel coil is subjected to soaking and warming at only 349°C (which does not meet the control range of 650-850°C); the electromagnetic performance test density is 7.85g / cm 3 When the iron loss P 15 / 50 is reduced by 0.8 W / kg, and the magnetic induction B in Example 4 is 50 increases by 0.04T, the main reason is that in Comparative Example 4, the composition design of Al-containing steel is used, and about 0.4% more Al is added to the steel, resulting in the O content being less than the control lower limit of 0.003% in the present invention and only 0.0022%, and at the same time, the hot-rolled steel coil is subjected to soaking and warming at 583°C (which does not meet the control range of 650-850°C), and the soaking and warming time is 0 (less than the design requirement of 10s in the present invention); the electromagnetic performance test density is 7.80g / cm 3 When the iron loss P in Example 5 is compared with that in Comparative Example 5, 15 / 50 is reduced by 0.7 W / kg, and the magnetic induction B in Example 5 is 50 increased by 0.03 T, which is mainly because the Al content in Comparative Example 5 is 0.0022% (which exceeds the control upper limit of 0.001% in the present invention) and the O content is as high as 0.0125% (which exceeds the design upper limit of 0.001% in the present invention); and the electromagnetic performance test density is 7.70 g / cm 3 When the iron loss P 15 / 50 was reduced by 0.8 W / kg, and the magnetic induction B in Example 6 50 increases by 0.04T, which is mainly because in Comparative Example 6, the O content is only 0.0019% (which is less than the lower limit of 0.003% in the design of the present invention), and when the hot rolled steel coil is subjected to soaking and warming, the soaking and warming is performed at a temperature as high as 900°C, but the soaking and warming time is 0 (which is less than the lower limit of 10s in the design of the present invention).

[0065] Therefore, it can be seen that the non-oriented electrical steel sheet according to the embodiment of the present invention has excellent properties through rational chemical composition design and process design. Compared with the conventional products of the same grade, the core loss P of the non-oriented electrical steel sheet is 15 / 50 The magnetic induction B of non-oriented electrical steel sheet decreased by an average of 0.2 to 0.8 W / kg. 50 The average increase is 0.01 to 0.04 T, achieving the characteristics of high magnetic induction and low iron loss while maintaining good economic efficiency.

[0066] FIG. 1 shows the relationship between the oxygen content in the non-oriented electrical steel sheet according to the present invention and the iron loss P 15 / 50 1 shows a schematic diagram of the relationship between

[0067] As shown in Figure 1, the relationship between oxygen content and iron loss P of the finished steel plate. 15 / 50 The steel plate shown in FIG. 1 is manufactured with the steel grade of national standard grade B50A1300 as standard, and all other raw materials of the steel plate in FIG. 1 are within the defined range of raw materials of the present invention, and its manufacturing method is also within the scope of the present invention. That is, the steel plate in FIG. 1 contains the following chemical elements, with the weight percentages of the chemical elements being: C is less than 0.003%, Si is 0.1%-1.2%, Mn is 0.1%-0.4%, P is 0.01%-0.2%, S is less than 0.003%, Al is less than 0.001%, N is less than 0.003%, Sn is 0.005%-0.05%, and the balance is Fe and other unavoidable impurities, and the condition Si 2 / P: 0.89 to 26.04 is satisfied. The method for producing the steel sheet includes the following steps: (1) a smelting step; (2) a continuous casting step; (3) a hot rolling step, in which the hot rolled sheet is not subjected to normalizing treatment or cover furnace annealing after coiling, but is subjected to soaking and warming with the residual heat of the hot rolled steel coil; (4) a primary cold rolling step; and (5) a continuous annealing step.

[0068] As can be seen from Fig. 1, the iron loss of the finished steel sheet is closely related to the oxygen content in the steel. When the oxygen content is less than 30ppm, the iron loss of the steel sheet will be more than 6.0W / kg, and the lower the oxygen content, the higher the iron loss of the steel sheet; and when the oxygen content is 30-100ppm, the iron loss of the steel sheet is generally lower, and the control effect can be stabilized at 5.5W / kg or less; after the oxygen content exceeds 100ppm, as the oxygen content increases continuously, the iron loss of the steel sheet increases monotonically and rapidly, and when the oxygen content reaches 130ppm, the iron loss of the steel sheet can even reach 8.5W / kg, which is significantly higher than the iron loss of the steel sheet corresponding to the lower oxygen content.

[0069] FIG. 2 is a microstructure diagram of the hot-rolled steel sheet in Example 2.

[0070] FIG. 3 is a microstructure diagram of the hot-rolled steel sheet in Comparative Example 2.

[0071] As shown in Figures 2 and 3, the hot-rolled steel plate corresponding to Example 2 can achieve complete recrystallization, the grains are uniform in size and coarse, and the average grain size can reach 80 μm, while the hot-rolled steel plate corresponding to Comparative Example 2 does not achieve complete recrystallization, and recrystallization is only achieved at the position close to about 5% of the upper and lower surfaces of the hot-rolled steel plate, and the center of the steel plate has a fibrous incompletely recrystallized structure. The size of the grains that can be recrystallized is relatively small, less than 50 μm on average.

[0072] FIG. 4 is a microstructure diagram of the completed non-oriented electrical steel sheet in Example 3.

[0073] FIG. 5 is a microstructure diagram of the completed steel sheet in Comparative Example 3.

[0074] 4 and 5, it can be seen that for Example 3, the microstructure of the finished strip steel is dominated by coarse equiaxed grains, the major and minor axes between the grains are close in size, the shape is regular, and the average recrystallization size is 75 μm. For Comparative Example 3 of the same grade, there exists the phenomenon that the grains cannot grow effectively, the fine grains show local clusters and segregation, and the rest of the equiaxed grains that can complete the recrystallization usually show the phenomenon of small grain size and non-uniform distribution.

[0075] It should be noted that the above examples are merely specific examples of the present invention. Naturally, the present invention is not limited to the above examples, and similar variations and modifications thereto may be directly derived or easily conceived by those skilled in the art from the contents disclosed in the present invention, all of which belong to the protection scope of the present invention.

[0076] In addition, the combinations of technical features in the present invention are not limited to the combinations described in the claims of the present invention or the combinations described in the specific examples, and all technical features described in the present invention may be freely combined or combined in any manner unless they are mutually inconsistent.

[0077] It should also be noted that the above examples are only specific examples of the present invention. Naturally, the present invention is not limited to the above examples, and similar variations and modifications thereto may be directly derived or easily conceived by those skilled in the art from the contents disclosed in the present invention, and all belong to the protection scope of the present invention.

Claims

1. 1. A method for producing a low-cost non-oriented electrical steel sheet with a very low aluminum content, the non-oriented electrical steel sheet having the following chemical elements in mass %: C is 0.003% or less, Si is 0.1% to 1.2%, Mn is 0.1% to 0.4%, P is 0.01% to 0.2%, S is 0.003% or less, Al is 0.001% or less, O is 0.003% to 0.01%, N is 0.003% or less, Sn is 0.005% to 0.05%, and the balance is Fe and other unavoidable impurities, and the condition Si ２ / P: 0.89 to 26.04 is satisfied, The method is characterized by having the following steps: (1) Smelting step; (2) a continuous casting step; (3) a hot rolling step, in which the hot rolled sheet is not subjected to normalizing treatment or cover furnace annealing after coiling, but is subjected to soaking and warming with the residual heat of the hot rolled steel coil; (4) a first cold rolling step; and (5) a continuous annealing step; In step (1), ferrophosphorus, ferrosilicon and ferromanganese are added in sequence during the deoxidation and alloying of RH refining, and in the ferrosilicon, Al≦0.1% and / or Ti≦0.03%; The manufacturing method.

2. 2. The method of claim 1, wherein in step (3), the initial rolling temperature is controlled to be 1050-1150°C, the final rolling temperature is controlled to be 650-950°C, the coil winding temperature is controlled to be 650-850°C, the soaking and heat-holding temperature is controlled to be 650-850°C, and the heat-holding time is controlled to be at least 10s.

3. The method according to claim 1 or 2, wherein in step (3), the rough rolling and final rolling are completed in 2 to 8 passes.

4. In step (5), the annealing is performed by H ２ and N ２ The annealing is carried out at 650 to 950° C. under an annealing atmosphere of a mixed gas of H ２ The method according to any one of claims 1 to 3, characterized in that the volume ratio of

5. The method according to any one of claims 1 to 4, characterized in that the non-oriented electrical steel sheet has an Al content of 0.0005% or less.

6. The method according to any one of claims 1 to 5, wherein the non-oriented electrical steel sheet is characterized by having an O content of 0.0045 to 0.007%.

7. The method according to any one of claims 1 to 6, characterized in that the non-oriented electrical steel sheet has an Sn content of 0.005 to 0.02%.

8. S ２ The method according to any one of claims 1 to 7, characterized in that / P is 0.89 to 16.67.

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