Non-oriented electromagnetic steel sheet and method for producing the same

Abstract

In the present invention, an isotropic electromagnetic steel sheet is disclosed. In addition to Fe and inevitable impurities, the electromagnetic steel sheet contains the following chemical elements in mass percentage: 0 < C ≤ 0.01%, 0 < Si ≤ 4.5%, Mn: 0.05 - 2.0%, Al: 0.1 - 2.0%, and Cr: 0.005 - 0.2%. The ratio of the mass percentage of Al to Cr satisfies 10 ≤ Al / Cr ≤ 80. Further, in the present invention, a method for manufacturing the above isotropic electromagnetic steel sheet, comprising: (1) a step of smelting and casting to obtain a continuous casting slab; (2) a step of heating and rolling to obtain a hot-rolled steel sheet, wherein when heating the continuous casting slab in a heating furnace to raise the temperature to 1020 °C or higher, controlling the heating rate to 0.8 - 2.0 °C / min and controlling the soaking time of the continuous casting slab in the heating furnace / the time the continuous casting slab is in the heating furnace to 0.10 - 0.25 hours; (3) a step of pickling the hot-rolled steel sheet; (4) a step of cold-rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet; (5) a step of continuously annealing the cold-rolled steel sheet to obtain a finished steel sheet; and (6) a step of applying a coating to the surface of the finished steel sheet is also disclosed.

Description

Technical Field

[0001] The present invention relates to a steel sheet and a method for manufacturing the same, and particularly to an isotropic electromagnetic steel sheet and a method for manufacturing the same.

Background Art

[0002] In recent years, at many steel mills, due to the requirements of the user market for excellent electromagnetic properties of steel sheets, the requirements for the purity of isotropic electromagnetic steel sheets have been increasingly high when actually producing isotropic electromagnetic steel sheets.

[0003] At the current technical level, in order to obtain a high-purity isotropic electromagnetic steel sheet, usually, the contents of nitrogen and sulfur, which are harmful elements in steel, are expected to be as low as possible, and particularly the nitrogen content is expected to be as low as possible. This is because nitrogen and sulfur elements in steel are finally converted into nitride and sulfide inclusions and remain in the steel, which ultimately inhibits the growth of crystal grain size and the development of a favorable structure in the finished steel sheet. However, it should be noted that excessive reduction of the nitrogen and sulfur contents in steel also greatly increases the difficulty of steel production.

[0004] Therefore, at present, researchers have conducted many studies and proposed various new solutions in the hope of effectively reducing nitride inclusions in steel without excessively reducing the nitrogen content.

[0005] For example, Japanese Patent Publication No. 06-128618, published on May 10, 1994, titled "Method for Producing Electromagnetic Steel Sheet with Low Inclusion Content," discloses a method for producing an electromagnetic steel sheet with low inclusion content. In this method, after converter refining is completed, FeSi is used as a preliminary deoxidizer to preliminarily deoxidize the molten steel, controlling the free oxygen content in the steel to 300 - 500 ppm, and it is necessary to control the alkalinity of the slag above the ladle to 2 - 10; then, the RH degassing device requires three-stage refining treatment, and it is necessary to control the free oxygen content in the steel to 400 ppm or less before the final deoxidation using FeSi, and more than 6 cycles are required after the final deoxidation of the molten steel. As another example, Chinese Patent Publication No. 101914730, published on December 15, 2010, titled "Vanadium-Containing Titanium-Containing Cold-Rolled Non-Oriented Electromagnetic Steel and Method for Producing the Same," discloses a vanadium-containing titanium-containing cold-rolled non-oriented electromagnetic steel and a method for producing the same, whereby the precipitation of finely dispersed vanadium-titanium carbonitrides can be effectively reduced by a reasonable design of the composition. In this technical solution, in the adopted production method, in order to further suppress the formation and influence of vanadium-titanium precipitates from the perspectives of thermodynamics and kinetics through the process design, the temperature of the heating step is controlled to 1140 - 1170 °C, the starting rolling temperature of the finish rolling is controlled to 1030 °C or higher, the final rolling temperature is controlled to 890 - 930 °C, and the temperature of the coiling step is controlled to 650 °C or higher. By suppressing the adverse effects of vanadium and titanium, this technical solution can effectively produce a vanadium-containing titanium-containing non-oriented electromagnetic steel that meets the requirements of electromagnetic performance. Therefore, it can expand the range of raw material sources for smelting non-oriented electromagnetic steel, especially the utilization of recycled steel, and effectively reduce the production cost of non-oriented electromagnetic steel.

[0006] Based on this, different from the above-mentioned existing technical solutions, the inventors of the present invention designed and expect to obtain a new non-oriented electromagnetic steel sheet with low nitride inclusion content and a method for producing the same in order to improve the purity of non-oriented silicon steel and thus meet the needs of the market and users.

Summary of the Invention

Problems to be Solved by the Invention

[0007] One object of the present invention is to provide a non-oriented electrical steel sheet with a low nitride inclusion content, aiming to improve the purity of the non-oriented electrical steel sheet and solve the problem of the inclusion control effect. This steel sheet can effectively meet the needs of the market and users, and has good prospects for popularization and application.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention provides a non-oriented electrical steel sheet. In addition to Fe and inevitable impurities, this steel sheet contains the following chemical elements in mass percentage: 0 ≦ C ≦ 0.01%, 0 < Si ≦ 4.5%, Mn: 0.05 - 2.0%, Al: 0.1 - 2.0%, Cr: 0.005 - 0.2% and the ratio of the mass percentages of Al and Cr satisfies 10 ≦ Al / Cr ≦ 80, preferably 13.9 ≦ Al / Cr ≦ 49.

[0009] Preferably, the non-oriented electrical steel sheet according to the present invention contains the following chemical elements in mass percentage: 0 ≦ C ≦ 0.01%, 0 < Si ≦ 4.5%, Mn: 0.05 - 2.0%, Al: 0.1 - 2.0%, Cr: 0.005 - 0.2%, balance: Fe and inevitable impurities and the ratio of the mass percentages of Al and Cr satisfies 10 ≦ Al / Cr ≦ 80, preferably 13.9 ≦ Al / Cr ≦ 49.

[0010] In the non-oriented electrical steel according to the present invention, the design principle of the chemical elements is as follows. C: Element C can strongly inhibit the growth of the crystal grains of the finished strip steel. Element C easily combines with Nb, V, Ti, etc. to form fine precipitates, thereby causing an increase in loss and magnetic aging. Therefore, considering the influence of C on the properties of the steel, in the non-oriented electrical steel sheet according to the present invention, the C content must be strictly controlled, and the mass percentage content of C is particularly controlled to be 0 < C ≦ 0.01%.

[0011] Si: The element Si can increase the resistivity of the material and effectively reduce the iron loss of the steel. It should be noted that the Si content in the steel should not be too high. When the Si content in the steel is higher than 4.5%, the magnetic induction of the steel will decrease significantly, causing the strip to break during cold rolling. Therefore, in the non-oriented electrical steel sheet according to the present invention, the content of Si must be strictly controlled, and the mass percentage content of Si is particularly controlled to satisfy 0 < Si ≦ 4.5%.

[0012] Mn: Mn and S can combine to form MnS, effectively reducing the damage to the magnetic properties of the steel. When the Mn content in the steel is less than 0.05%, the S-fixing effect of the Mn element is insufficient. When the Mn content in the steel is higher than 2.0%, the manufacturing cost of the steel will increase significantly. Therefore, in the non-oriented electrical steel sheet according to the present invention, the mass percentage content of Mn is controlled to be 0.05 - 2.0%.

[0013] Al: Al is an important deoxidizing element. When the Al content in the steel is less than 0.1%, a good deoxidizing effect cannot be obtained. When the Al content in the steel exceeds 2.0%, it will cause casting difficulties in continuous casting and reduce the workability of cold rolling. Based on this, in order to exert the beneficial effect of Al, in the non-oriented electrical steel sheet according to the present invention, the mass percentage content of Al is controlled to be 0.1 - 2.0%, preferably 0.47 - 2.0%.

[0014] Cr: The Cr element can effectively fix N by combining with N to generate Cr2N. When the Cr content in the steel is less than 0.005%, the N-fixing effect of Cr decreases. When the Cr content in the steel exceeds 0.2%, it will cause abnormal grain refinement. Therefore, in order to exert the beneficial effect of Cr, in the non-oriented electrical steel sheet according to the present invention, the mass percentage content of Cr in the steel must be strictly controlled, and the mass percentage content of Cr is particularly controlled to be 0.005 - 0.2%.

[0015] Certainly, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage content of Cr can be more preferably controlled to be 0.01-0.12%.

[0016] As a result, while controlling the mass percentage content of a single chemical element, the present invention further controls such that the ratio of the mass percentages of Al and Cr in the steel satisfies 10 ≤ Al / Cr ≤ 80, preferably 13.9 ≤ Al / Cr ≤ 49.

[0017] In the present invention, the ratio of the mass percentages of Al and Cr in the steel is controlled to satisfy 10 ≤ Al / Cr ≤ 80, whereby an appropriate amount and ratio of AlN and Cr2N inclusions are formed during solidification in the casting of molten steel and during hot rolling of the continuous casting slab, thereby achieving the control requirement of 0.8 ≤ [AlN] / ([AlN]+[Cr2N]) ≤ 0.99. This is because Al preferentially combines with N to form AlN inclusions during solidification in the casting of molten steel. Generally, the lower the contents of Al and N, and the lower the temperature of the molten steel, the slower the precipitation of AlN inclusions, the smaller the size of the AlN inclusions, and the greater the harm of the AlN inclusions. In this case, by adding an appropriate amount of Cr to the steel, Cr combines with N at the end of continuous casting together with Al to form a small amount of Cr2N inclusions with a coarse size in advance, thereby greatly reducing the harm of AlN precipitation in the subsequent stage. Therefore, in order to ensure the quality of the steel, it is controlled here to be 10 ≤ Al / Cr ≤ 80, preferably 13.9 ≤ Al / Cr ≤ 49.

[0018] When the Al / Cr ratio in the steel is greater than 80, it means that the content ratio of the Cr element in the steel is too low. As a result, the formation of Cr2N is significantly delayed, the size of Cr2N when precipitated becomes smaller, and the harm of Cr2N increases. When the Al / Cr ratio in the steel is less than 10, it means that the Cr content in the steel is too high. In this case, the precipitation of AlN is significantly delayed, the amount of AlN formed is small, the size is small, and the harm increases. At the same time, the formation of Cr2N is significantly accelerated, and the amount of Cr2N when precipitated increases significantly. Since the melting point of Cr2N is low, when the amount of Cr2N is large, Cr2N redissolves during the hot rolling process, and then redeposits during the finish rolling and coiling processes, resulting in a sharp decrease in size, a significant increase in amount, and an increase in harm. Therefore, [Al] / [Cr] in the steel must be strictly limited.

[0019] Preferably, in the non-oriented electrical steel sheet according to the present invention, among inevitable impurities, P≦0.2%, S≦0.005%, N≦0.005%, and O≦0.005%.

[0020] In the non-oriented electrical steel according to the present invention, the P element, S element, N element, and O element are all impurity elements in the non-oriented electrical steel sheet, and are impurity elements introduced from steel raw materials, auxiliary raw materials, or the production process. Under the conditions allowed by technical conditions, in order to obtain steel with better performance and better quality, the content of impurity elements in the steel should be reduced as much as possible.

[0021] P: When the mass percentage of P in the steel exceeds 0.2%, it is likely to cause low-temperature brittleness and the manufacturability during the cold rolling process is likely to decrease. Therefore, in the non-oriented electrical steel sheet according to the present invention, the mass percentage of P is controlled to P≦0.2%.

[0022] S: When the mass percentage of S in the steel exceeds 0.005%, the amount of harmful inclusions such as MnS and Cu2S increases significantly, deteriorating the iron loss of the steel. Therefore, in the non-oriented electrical steel sheet according to the present invention, the mass percentage of S is controlled to S≦0.005%.

[0023] N: When the mass percentage of N in the steel exceeds 0.005%, the precipitates with N such as Nb, V, Ti, and Al increase significantly, strongly inhibiting the growth of crystal grains, thereby deteriorating the magnetic properties of the steel. Therefore, in the non-oriented electrical steel sheet according to the present invention, the mass percentage of N is controlled to N≤0.005%.

[0024] O: When the mass percentage of O in the steel exceeds 0.005%, the amount of oxide inclusions increases significantly, does not contribute to the adjustment of the proportion of favorable inclusions, and deteriorates the magnetic properties of the steel. Therefore, in the non-oriented electrical steel sheet according to the present invention, the mass percentage of O is controlled to O≤0.005%.

[0025] Preferably, in the non-oriented electrical steel sheet according to the present invention, the Cr content is 0.01 - 0.12%.

[0026] Preferably, in the non-oriented electrical steel sheet according to the present invention, the nitride inclusions in the steel are mainly single Cr₂N and / or AlN composite inclusions encapsulated by Cr₂N.

[0027] Preferably, in the non-oriented electrical steel sheet according to the present invention, the volume ratio of the nitride inclusions AlN and Cr₂N satisfies 0.80≤[AlN] / ([AlN]+[Cr₂N])≤0.99.

[0028] Preferably, in the non-oriented electrical steel sheet according to the present invention, the amount of nitride inclusions is 2.5×10 7 / mm 3 or less.

[0029] Preferably, in the non-oriented electrical steel sheet according to the present invention, the nitride inclusions with a size of 0.2 - 1.0 μm account for 50% or more of all nitride inclusions by volume percentage.

[0030] As a result, another object of the present invention is to provide a method for manufacturing the above-mentioned non-oriented electrical steel sheet, which method is simple and feasible, and thereby a high-purity non-oriented electrical steel sheet can be obtained.

[0031] In order to achieve the above object of the present invention, the present invention provides a method for manufacturing a non-oriented electromagnetic steel sheet, comprising: (1) a step of smelting and casting to obtain a continuous casting slab; (2) a step of heating and rolling to obtain a hot-rolled steel sheet, wherein when heating the continuous casting slab in a heating furnace to raise the temperature to 1020 °C or higher, the heating rate is controlled to be 0.8 to 2.0 °C / min, and the soaking time of the continuous casting slab in the heating furnace, i.e., the time the continuous casting slab is in the heating furnace, is controlled to be 0.10 to 0.25 hours; (3) a step of pickling the hot-rolled steel sheet; (4) a step of cold-rolling the hot-rolled steel sheet; (5) a step of continuously annealing to obtain a finished steel sheet; (6) a step of coating the surface of the finished steel sheet and providing a method including the above steps.

[0032] In the present invention, the inventors optimize the design of the chemical composition of the steel and define a reasonable manufacturing process. After obtaining a continuous casting slab by smelting and casting, the heating and temperature-rising process during hot rolling of the continuous casting slab is optimized and combined with subsequent pickling, cold rolling, continuous annealing and coating processes, so as to effectively produce a high-purity non-oriented electromagnetic steel sheet with a low content and large size of nitride inclusions. This high-purity non-oriented electromagnetic steel sheet has characteristics such as simplicity, easy controllability, good stability, low cost and wide application range.

[0033] In the above heating and rolling in step (2) according to the present invention, when heating a continuous casting slab in a heating furnace to raise the temperature to 1020 °C or higher, the heating rate needs to be limited to 0.8 - 2.0 °C / min. Here, mainly to be considered is that if the heating rate is lower than 0.8 °C / min, the solid solution amounts of AlN inclusions and Cr2N inclusions will increase significantly. Therefore, during the subsequent finishing rolling and coiling processes, as the temperature of the steel plate decreases, AlN and Cr2N inclusions will precipitate again. In this case, the size of the precipitated inclusions is small, and the number of precipitated inclusions increases significantly, so the purity of the steel decreases significantly. Correspondingly, when the temperature rises to 1020 °C or higher, if the heating rate is controlled to be greater than 2.0 °C / min, the solid solution amounts of AlN inclusions and Cr2N inclusions will decrease significantly. In this case, the fine AlN inclusions, especially Cr2N inclusions, precipitated at the end of solidification in the casting of molten steel cannot be fully dissolved, and exist in a single form with a small size, which is harmful to the recrystallization of the hot-rolled microstructure and the formation of a favorable microstructure. Therefore, in order to promote its effective growth and avoid harm as much as possible, it is necessary to limit the soaking time of the continuous casting slab during the hot-rolling process / the time when the continuous casting slab is in the furnace to 0.10 - 0.25 hours.

[0034] Within the limited range, it is advantageous for AlN and Cr2N inclusions to grow and coarsen under long-term high-temperature conditions. Since some nitride inclusions are mainly single Cr2N and / or AlN composite inclusions encapsulated by Cr2N, the amounts of AlN and Cr2N inclusions are greatly reduced. As a result, nitride inclusions with a size of 0.2 - 1.0 μm can account for more than 50% by volume of all nitride inclusions, and the amount of nitride inclusions in the final steel plate can be 7 / mm 3 made to be as follows.

[0035] It should be noted that if the soaking time of the continuous casting slab / the time the continuous casting slab is in the furnace is less than 0.1 hour, the AlN and Cr2N inclusions in the steel cannot effectively grow and coarsen. If this time is longer than 0.25 hour, the solid solution amount of AlN and Cr2N inclusions significantly increases, and the precipitation of AlN inclusions in the steel during the subsequent finishing rolling and coiling processes significantly increases. Nitride inclusions with a size of 0.2 - 1.0 μm cannot reach more than 50% by volume of all nitride inclusions, and the amount of nitride inclusions in the steel plate greatly exceeds 2.5×10 7 / mm 3 .

[0036] Compared with the prior art, the non-oriented electromagnetic steel sheet and its manufacturing method according to the present invention have the following advantages and beneficial effects. In the non-oriented electromagnetic steel sheet according to the present invention, the inventors optimize the chemical element composition ratio and related manufacturing processes. After obtaining a continuous casting slab by smelting and casting, the parameters of the heating and temperature rising processes of the continuous casting slab during hot rolling are optimized, and combined with the subsequent pickling, cold rolling, continuous annealing and coating processes, a high-purity non-oriented electromagnetic steel sheet with a low content and large size of nitride inclusions can be effectively produced, thereby obtaining the electromagnetic properties required by the design of the present invention.

[0037] The design concept of the chemical elements of the present invention is completely different from that of the prior art. It has characteristics such as simplicity, easy control, good stability, low cost and wide application range, and can effectively control the inclusions in the steel. The produced non-oriented electromagnetic steel sheet has high purity and good popularization prospects and application values.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0039] Hereinafter, with reference to the drawings and specific examples of this specification, the non-oriented electromagnetic steel sheet according to the present invention and its manufacturing method will be further explained and illustrated. However, the explanations and illustrations do not constitute an excessive limitation on the technical solution of the present invention.

Examples

[0040] Examples 1 to 7 and Comparative Examples 1 to 3 Table 1 shows the mass percentages of chemical elements in the non-oriented electromagnetic steel sheets of Examples 1 to 7 and in the comparative steel sheets of Comparative Examples 1 to 3.

[0041]

Table 1

[0042] The non-oriented electromagnetic steel sheets of Examples 1 to 7 and the comparative steel sheets of Comparative Examples 1 to 3 are produced by the following steps. (1) Smelting and casting at the chemical composition ratios shown in Table 1: During the smelting process, the design of the chemical composition of the steel is adjusted according to the design requirements of the present invention to ensure a specific relationship between Al and Cr, thereby obtaining molten steel that meets the design requirements of the chemical composition. Then, the molten steel is cast and solidified into a continuous casting slab of a specified size. (2) Heating and rolling: The obtained continuous casting slab is placed in a heating furnace for heating and temperature increase. During this period, the heating rate of the continuous casting slab is adjusted step by step according to the design requirements. When the temperature rises above 1020°C, the heating rate is controlled at 0.8 to 2.0°C / min. The soaking time of the continuous casting slab in the heating furnace / the time the continuous casting slab is in the furnace is controlled at 0.10 to 0.25 hours. (3) Pickling: HCl turbulent flow pickling is used to remove iron oxide scale from the surface of the hot-rolled steel sheet. (4) Cold rolling: Roll the steel plate to the target thickness at one time using a continuous rolling mill or a reciprocating rolling mill. (5) Continuous annealing: Control the annealing temperature at 650 - 1050 °C, the annealing time within 180 seconds, and the annealing atmosphere to a mixture of H2 and N2. Here, the volume ratio of H2 is 20% - 60%. (6) Coating: Apply a semi - organic insulating coating to the surface of the finished steel plate.

[0043] It should be noted that in the present invention, the chemical compositions and related process parameters of Examples 1 - 7 all meet the control requirements of the design specifications of the present invention. The comparative steels of Comparative Examples 1 - 3 are also produced by the above - mentioned process steps, but there are parameters in their chemical element compositions and / or related process parameters that do not meet the design requirements of the present invention.

[0044] Table 2 shows the specific process parameters of the non - oriented electrical steel sheets of Examples 1 - 7 and the comparative steel sheets of Comparative Examples 1 - 3 in the above - mentioned manufacturing process flow.

[0045]

Table 2

[0046] Finally, samples of the non - oriented electrical steel sheets of Examples 1 - 7 and the comparative steel sheets of Comparative Examples 1 - 3 of the finally obtained finished products are taken, and the steel samples of Examples 1 - 7 and Comparative Examples 1 - 3 are observed and analyzed. It can be seen that the steels of each example and comparative example contain various inclusion components, and the main inclusions are nitrogen - containing inclusions.

[0047] Through further analysis and tests, the amount of nitride inclusions, as well as the composition and proportion of each nitride inclusion, of the steel plate samples of Examples 1 - 7 and Comparative Examples 1 - 3 can be obtained respectively. The related results of the observation and analysis are shown in Table 3 below.

[0048] Table 3 shows the detection results of inclusions of the non - oriented electrical steel sheets of Examples 1 - 7 and the comparative steel sheets of Comparative Examples 1 - 3.

[0049]

Table 3

[0050] When the researchers observed the inclusions in the steel plates of various examples and comparative examples, it was found that in the non-oriented electromagnetic steel plates of Examples 1 to 7 produced by the present invention, the nitride inclusions in the steel were mainly single Cr2N and / or AlN composite inclusions encapsulated by Cr2N.

[0051] Thereafter, the inclusions in the steel plate samples were detected and analyzed, the amount and particle size of each nitride inclusion were counted, and the volume percentage of nitride inclusions with a particle size of 0.2 to 1.0 μm was calculated as follows.

[0052] Statistics were carried out using non-aqueous solution electrolytic extraction and scanning electron microscope observation. For each sample, the electrolysis amount was 0.1 g, the pore diameter of the filter membrane was 20 nm, and the observed field of view was 0.40 mm 2 The above is the case.

[0053] After detecting the inclusions in the steel plate samples of each example and comparative example, in the non-oriented electromagnetic steel plates of Examples 1 to 7, the amount of AlN inclusions was 0.52 to 2.41×10 7 / mm 3 and the amount of Cr2N inclusions was 0.02 to 0.31×10 7 / mm 3 and 0.82≦[AlN] / ([AlN]+[Cr2N])≦0.99, and the ratio of nitride inclusions with a size of 0.2 to 1.0 μm to all nitride inclusions was 54 to 91% by volume, and the amount of nitride inclusions was 0.58 to 2.48×10 7 / mm 3 It was found that this was the case.

[0054] However, in Comparative Example 1, the Al element and the Cr element were not added in accordance with the requirements of the present invention, the Al / Cr ratio was 6.5, which was smaller than the lower limit of 10 of the design requirements of the present invention. In addition, the heating rate of Comparative Example 1 was only 0.2 °C / min at 1020 °C or higher, which was smaller than the lower limit of 0.8 °C / min of the design requirements of the present invention. Therefore, the nitride inclusions of 0.2 to 1.0 μm in the comparative steel plate of Comparative Example 1 finally produced only accounted for 42% by volume of all the nitride inclusions, the amount of small-sized AlN and Cr2N inclusions in the steel was large, and finally the total amount of nitride inclusions in the steel was 3.0×10 7 / mm 3 and became large, and the effect of the design of the present invention could not be obtained.

[0055] In Comparative Example 2, the Al element and the Cr element were not added in accordance with the requirements of the present invention, the Al / Cr ratio was as large as 166, which was larger than the upper limit of 80 of the design requirements of the present invention. In addition, the soaking time of the continuous casting slab in the heating furnace of Comparative Example 2 / the time the continuous casting slab was in the furnace was 0.35, and as a result, the ratio of [AlN] / ([AlN]+[Cr2N]) was only 0.65, which did not meet the lower limit of 0.80 required by the design of the present invention. Due to the large amount of fine Cr2N inclusions in the corresponding steel being 1.71×10 7 / mm 3 as a result, the total amount of nitride inclusions in the steel was 4.95×10 7 / mm 3 and became large, and the effect of the design of the present invention could not be obtained.

[0056] In Comparative Example 3, when the continuous casting slab of Comparative Example 3 was in the heating furnace, the heating rate was as large as 2.2 °C / min at 1020 °C or higher, which was larger than the upper limit of 2.0 °C / min required by the design of the present invention. As a result, the small-sized AlN and Cr2N generated during solidification in the casting of the molten steel could not grow effectively or precipitate early after solid solution during the heating process of hot rolling due to the high temperature and short time. Therefore, the nitride inclusions of 0.2 to 1.0 μm in the comparative steel plate of Comparative Example 3 only accounted for 23% by volume of all the nitride inclusions, and the amount of small-sized AlN inclusions was 3.83×107 / mm 3 is large. Finally, the total amount of nitride inclusions in the steel is 4.12×10 7 / mm 3 is large, and the effect of the design of the present invention cannot be obtained.

[0057] In summary, the design concepts of the chemical elements of Examples 1 to 7 designed according to the present invention are completely different from those of the prior art, and have characteristics such as simplicity, ease of control, good stability, low cost, and wide application range, and it can be seen that the inclusions in the steel can be effectively controlled. The produced non-oriented electrical steel sheet has very high purity, and has good popularization prospects and application values.

[0058] FIG. 1 schematically shows the relationship between Al / Cr and nitride inclusions in the non-oriented electrical steel sheet according to the present invention.

[0059] As shown in FIG. 1, in the steel of the present invention, as Al / Cr increases, AlN / (AlN+Cr2N) first increases rapidly. When Al / Cr reaches 10%, AlN / (AlN+Cr2N) reaches 0.80. Then, as Al / Cr continues to increase, AlN / (AlN+Cr2N) slowly increases to the maximum value, and then gradually begins to decrease rapidly. After Al / Cr reaches 80%, AlN / (AlN+Cr2N) reaches below 0.80 again, and the design requirements according to the present invention cannot be satisfied.

[0060] FIG. 2 schematically shows the relationship between the soaking time / furnace time and the control effect of inclusions in the non-oriented electrical steel sheet of the present invention.

[0061] As shown in FIG. 2, in the specific hot rolling process of the present invention, when the continuous casting slab is heated in the heating furnace, the soaking time / furnace time must be controlled within an appropriate range, that is, 0.10 to 0.25 hours. When the soaking time / furnace time is less than 0.1 hour, the ratio of nitride inclusions of 0.2 to 1.0 μm to all nitride inclusions is less than 50% by volume, and the amount of nitride inclusions in the final steel sheet is 2.5×10 7 / mm3 It becomes larger. The ratio of inclusions with a size of 0.1 - 1.0 μm and the amount of nitride inclusions for all nitride inclusions show an increasing or decreasing trend respectively with the increase of soaking time / furnace time. When the soaking time / furnace time is longer than 0.25 hours, the amount of nitride inclusions in the final steel plate gradually increases again, reaching 2.5×10 7 / mm 3 exceeding the design requirement, and at the same time, the amount of nitride inclusions with a size of 0.2 - 1.0 μm decreases, and the ratio of nitride inclusions with a size of 0.2 - 1.0 μm to all nitride inclusions drops below 50% by volume.

[0062] Figure 3 is a photograph of the microstructure of the non - oriented electrical steel sheet of Example 6.

[0063] As shown in Figure 3, in the photograph of the typical microstructure of the non - oriented electrical steel sheet of Example 6, the amount of inclusions mainly composed of AlN is very small, and the average size of the two types of inclusions is relatively large. The statistical results show that in Example 6, the ratio of nitride inclusions in the range of 0.2 - 1.0 μm accounts for 63% by volume of all nitride inclusions, and the amount of nitride inclusions in the final steel plate is 0.93×10 7 / mm 3 indicating more.

[0064] Figure 4 is a photograph of the microstructure of the comparative steel of Comparative Example 2.

[0065] As shown in Figure 4, in the photograph of the typical microstructure of the comparative steel of Comparative Example 2, inclusions mainly composed of AlN are present in large quantities, and the average size of the two types of inclusions is very small. The statistical results show that in Comparative Example 2, the ratio of nitride inclusions in the range of 0.2 - 1.0 μm accounts for 82% by volume of all nitride inclusions, but the amount of nitride inclusions in the final steel plate is 4.95×10 7 / mm 3 indicating more.

[0066] It should be noted that the prior art part within the protection scope of the present invention is not limited to the embodiments provided in this application. Without limitation, all prior art that does not conflict with the solution of the present invention, including but not limited to prior patent documents, prior published publications, prior public use, etc., may be included within the protection scope of the present invention.

[0067] In addition, the combination ways of the technical features in the present invention are not limited to the combination ways described in the claims of the present invention or the combination ways described in the specific embodiments. All the technical features described in the present invention can be freely combined or incorporated in any way as long as they do not conflict with each other.

[0068] Furthermore, it should be noted that the above - shown embodiments are only specific examples of the present invention. Obviously, the present invention is not limited to the above - mentioned embodiments, and similar changes or modifications made thereto are obvious to those skilled in the art or can be directly obtained by those skilled in the art from the disclosure of the present invention, and all of them are included within the protection scope of the present invention.

Claims

1. An isotropic electromagnetic steel sheet, comprising, in addition to Fe and inevitable impurities, the following chemical elements in mass percentages: 0 < C ≤ 0.01%, 0 < Si ≤ 4.5%, Mn: 0.05 - 2.0%, Al: 0.1 - 2.0%, Cr: 0.005 - 0.2% wherein the ratio of the mass percentages of Al and Cr satisfies 10 ≤ Al / Cr ≤ 80, preferably 13.9 ≤ Al / Cr ≤ 49; an isotropic electromagnetic steel sheet.

2. The isotropic electromagnetic steel sheet according to claim 1, comprising, in mass percentages, the following chemical elements: 0 < C ≤ 0.01%, 0 < Si ≤ 4.5%, Mn: 0.05 - 2.0%, Al: 0.1 - 2.0%, Cr: 0.005 - 0.2%, balance: Fe and inevitable impurities wherein the ratio of the mass percentages of Al and Cr satisfies 10 ≤ Al / Cr ≤ 80, preferably 13.9 ≤ Al / Cr ≤ 49. The isotropic electromagnetic steel sheet according to claim 1.

3. The isotropic electromagnetic steel sheet according to claim 1 or 2, wherein, among the inevitable impurities, P ≤ 0.2%, S ≤ 0.005%, N ≤ 0.005%, and O ≤ 0.005%.

4. The isotropic electromagnetic steel sheet according to claim 1 or 2, wherein the content of the Cr element is 0.01 - 0.12%.

5. The nitride inclusions in the above steel are single Cr ２ N, and / or Cr ２ The non-oriented electrical steel sheet according to claim 1 or 2, comprising AlN composite inclusions encapsulated with N

6. The above nitride inclusions AlN and Cr ２ The volume ratio of N satisfies 0.80 ≦ [AlN] / ([AlN] + [Cr ２ N]) ≦ 0.99, and the non-oriented electromagnetic steel sheet according to claim 5.

7. The amount of the nitride inclusion is 2.5×10 ７ / mm ３ or less. The non-oriented electromagnetic steel sheet according to claim 5.

8. The isotropic electromagnetic steel sheet according to claim 5, wherein nitride inclusions having a size of 0.2 - 1.0 μm occupy 50% or more of all nitride inclusions by volume percentage.

9. A method for manufacturing the isotropic electromagnetic steel sheet according to any one of claims 1 - 8, comprising: (1) a step of smelting and casting to obtain a continuous casting slab; (2) a step of heating and rolling to obtain a hot-rolled steel sheet, wherein when heating the continuous casting slab in a heating furnace to raise the temperature to 1020°C or higher, controlling the heating rate to 0.8 - 2.0°C / min, and controlling the soaking time of the continuous casting slab in the heating furnace / the time the continuous casting slab is in the heating furnace to 0.10 - 0.25 hours; (3) a step of pickling the hot-rolled steel sheet; (4) a step of cold-rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet; (5) a step of continuously annealing the cold-rolled steel sheet to obtain a finished steel sheet; (6) a step of coating the surface of the finished steel sheet and including these steps.

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