RU2790231C1 - Cu-containing non-textured electrical steel sheet and the sheet production method - Google Patents

Abstract

FIELD: metal industry.

SUBSTANCE: invention relates to metal industry, in particular to Cu-containing non-textured electrical steel sheet. The sheet is made of steel with a chemical composition including the following elements, wt%: 0<C≤0.003, Si: 0.1-2.0, Mn: 0.1-0.55, S: up to 0.004, Cu: 0.02-0.2, Al: 0.1-1.0, Fe and inevitable impurities - the rest, where P≤0.2, N≤0.003 and O≤0.003% are inevitable impurities. The steel sheet elemental content satisfies the following condition: 60≤([Mn]+[Cu]/2)/[S]≤140. The sheet purity is high and the sheet has required magnetic properties.

EFFECT: invention may be used as a material for the motors, compressors and electrical equipment iron cores manufacturing.

13 cl, 5 dwg, 2 tbl

Description

Technical field

The present invention relates to a steel sheet and a method for manufacturing the same, in particular, a non-oriented electrical steel sheet and a method for manufacturing the same.

State of the art

In recent years, when the requirements of the user market for high efficiency, energy saving and environmental protection are becoming more stringent, the non-oriented silicon steel sheet for making iron cores of motor, compressor and electrical equipment is required to have suitable electromagnetic characteristics, that is, generally low power loss. iron and high magnetic induction to meet the urgent needs of these electrical products for high efficiency, energy saving and environmental claims, while guaranteeing a cost competitive advantage.

In order to obtain suitable electromagnetic characteristics, usually the content of silicon and aluminum in steel must be greatly increased in order to effectively improve the resistivity of materials, thereby effectively reducing iron loss and improving the magnetic induction of the finished steel sheet.

For example: CN103290190A with a publication date of September 11, 2013, entitled "Non-oriented silicon steel and method for its manufacture", discloses a non-oriented silicon steel with suitable magnetic properties, in which the technical solution disclosed in the patent has a Si content of 2.5 - 4.0 % and the content of Al 0.5 - 1.5%. Thus, with an increase in the content of Si and Al, the iron loss of the materials decreases rapidly, but the magnetic induction of the materials also decreases rapidly.

Another example: CN103014503A with a publication date of April 3, 2013, entitled "Non-oriented silicon steel having high magnetic induction, low iron loss and resistance to acid corrosion without further normalization, and a method for making it" discloses a non-oriented silicon steel with high magnetic induction, low losses in iron and resistance to acid corrosion without additional normalization and a method for its manufacture. In the technical solution disclosed in the patent, 0.20 - 0.45% (Sn+Cu) is added to steel to improve the formation of the texture of materials due to segregation along grain boundaries, obtaining a suitable magnetic induction of the material. However, Sn and Cu are expensive metals, which greatly increases the cost of production, and Cu also tends to cause defects on the surface of the steel strip.

Another example: CN1888112, with a publication date of Jan. 3, 2007, titled "High-quality, non-oriented, high-induction electrical steel and method for making the same," discloses electrical steel and a method for manufacturing the same. According to the technical solution disclosed in the patent, the content of each chemical component of electrical steel is in mass percent: C≤0.0050%, N≤0.0030%, Si: 1.50 - 2.50%, Al: 0.80 - 1.30%, Mn: 0.20 - 0.50%, P≤0.030%, S≤0.005%, Sb: 0.03 - 0.10%, Sn: 0.05 - 0.12%, B: 0.0005 - 0.0040%, the rest is Fe and inevitable impurities, while Sb and Sn are added alternately. According to the technical solution, the ideal structure of hot-rolled strip steel is obtained by optimizing the reduction ratio of each pass of rough rolling under high rolling reduction, rough roll rolling and high-temperature winding, while the reduction ratio in cold rolling is increased to obtain more energy (strain energy) for growth grains during the final recrystallization annealing. Moreover, by measures such as controlling the recrystallization annealing temperature to obtain an ideal grain structure, etc., it is possible to obtain a non-oriented electrical steel with suitable surface quality, high magnetic induction and low iron loss, which is thus most suitable for for iron core high efficiency motor.

At present, normalization or intermediate annealing in bell furnace is an effective process to improve the iron loss and magnetic induction of materials, and is widely applied in the production of high efficiency and high quality non-oriented silicon steel sheet, which can effectively reduce the iron loss in materials and greatly improve the magnetic induction of materials. . However, as new production equipment is introduced, the cost of production will increase significantly, which will extend the production and delivery cycle of materials, which will pose new challenges for technical and quality management, etc.

For example: Chinese Patent Publication No. 102453837A with a publication date of May 16, 2012, entitled "Method for manufacturing non-oriented high magnetic induction silicon steel" discloses non-oriented high magnetic induction silicon steel. The method for manufacturing non-oriented silicon steel with high magnetic induction includes the following stages: 1) melting and casting, while the content of chemical components of non-oriented silicon steel in mass percent is as follows: Si: 0.1 - 1%, Al: 0.005 - 1%, C≤ 0.004%, Mn: 0.10 - 1.50%, P≤0.2%, S≤0.005%, N≤0.002%, Nb+V+Ti≤0.006%, rest Fe; then steel smelting, secondary refining and casting into a casting billet; 2) hot rolling with a heating temperature of 1150 - 1200°C, finishing rolling temperature of 830 - 900°C and winding at a temperature of ≥570°C; 3) straightening, carrying out cold rolling with a reduction of 2 - 5%; 4) normalization at a temperature not lower than 950°C and a heat retention time of 30 - 180 s; 5) acid pickling and cold rolling, carried out by cold rolling with a total reduction after acid pickling of 70 - 80%; 6) annealing with heating rate ≥100°C/s, keeping heat at 800 - 1000°C for 5 - 60 s, then slow cooling to 600 - 750°C at 3 - 15°C/s.

Disclosure of the essence of the invention

One object of the present invention is to provide a high purity Cu-containing non-oriented electrical steel sheet and a high-purity Cu-containing non-oriented electrical steel sheet having high purity characteristics and suitable magnetic characteristics.

In order to achieve the above object, the present invention provides a Cu-containing high purity non-oriented electrical steel sheet comprising the following chemical elements in mass percent: 0<C≤0.003%; Si: 0.1 - 2.0%; Mn: 0.1 - 0.55%; C: 0 - 0.004%; Cu: 0.003 - 0.2%; Al: 0.1 - 1.0%; and the rest is Fe and inevitable impurities.

As for the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the principle of introducing each chemical element is described below:

C: In the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, C will strongly inhibit grain growth of the finished steel sheet and tend to bond with Nb, V, Ti, and the like. with the formation of small precipitates, thereby causing an increase in losses and magnetic aging. Therefore, in the technical solution according to the present invention, the mass percent C is limited to 0<C≤0.003%.

Si: In the Cu-containing high-purity non-oriented electrical steel sheet according to the present invention, Si will improve the resistivity of the materials, which can effectively reduce the iron loss of the steel. However, if the mass percentage of Si is higher than 2.0%, the magnetic induction of the steel will be greatly reduced; when the mass percentage of Si is lower than 0.1%, the iron loss reducing effect cannot be achieved. On this basis, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the mass percentage of Si is maintained at 0.1 to 2.0%.

Mn: In the Cu-containing high-purity non-oriented electrical steel sheet according to the present invention, Mn will bond with S to form MnS, thereby reducing deterioration in magnetic characteristics. When the mass percentage of Mn is lower than 0.1%, the sulfur binding effect will be insufficient. When the mass percentage of Mn exceeds 0.55% or more, the steel recrystallization effect is suppressed. Therefore, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the mass percentage of Mn is limited to 0.1 to 0.6%.

S: With regard to the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, if the mass percentage of S exceeds 0.004%, the amount of harmful inclusions such as MnS and Cu ₂ S will be much higher, disturbing the favorable texture of the steel and preventing grain growth of the finished product. Based on this, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the mass percentage of sulfur is maintained at 0 to 0.004%.

Cu: With regard to the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, copper can improve the crystal texture of the steel. Therefore, Cu with a mass percentage exceeding 0.003% or more is preferable for adding to steel. However, if more than 0.2% copper is added to the steel, abnormal grain refinement and deterioration of the iron loss of the steel may occur. Therefore, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the weight percentage of copper is maintained at 0.003 to 0.2%.

Al: In the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, when the mass percentage of aluminum is lower than 0.1%, a suitable deoxidation effect cannot be achieved. When the mass percentage exceeds 1.0%, continuous casting will be difficult, which deteriorates cold rolling workability. Therefore, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the weight percentage of aluminum is maintained at 0.1 to 1.0%.

Preferably, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the chemical elements further satisfy the mass percent expressions: 60≤([Mn]+[Cu]/2)/ [S]≤140, where [Mn ], [Cu] and [S] represent the weight percentages of the elements.

In the above solution, the content of Mn, Cu and S can preferably be adjusted according to the above content in order to ensure early precipitation of MnS inclusions in the initial stage of solidification of the molten steel. In this way, suitable conditions such as temperature and duration can be provided for sufficient growth of MnS inclusions subsequently, and MnS inclusions of 0.5 µm or more clearly have less effect on the electromagnetic characteristics of finished materials. Meanwhile, with a constant decrease in the temperature of the continuously cast billet, the added Cu can continuously serve as an S compound for the preliminary separation of Cu ₂ S inclusions, which, on the one hand, contributes to sufficient growth of inclusions, and on the other hand, it is also advantageous that its combination with MnS inclusions gives a complex bigger size. However, the amount of precipitation must be controlled because, in the case of an equivalent size, the crystallization fixation effect will increase with the increase in the amount, which is detrimental to grain size growth and reduction of iron loss.

Preferably, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, inevitable impurities include: P≤0.2%, N≤0.003%, O≤0.003%.

In the above solution, the unavoidable impurities should be controlled to be as small as possible while maintaining P at ≤0.2%, since the cold brittleness phenomenon tends to occur when the mass percentage of P exceeds 0.2%, thereby reducing workability. cold rolling process. Moreover, N is maintained at ≦0.003% because precipitates such as Nb, V, Ti, and Al nitrides greatly increase when the mass percentage of N exceeds 0.003%, which greatly inhibits grain growth and degrades the magnetic properties of the steel. In addition, the content of O is maintained at ≤0.003% because the amount of oxide inclusions will greatly increase when the mass percentage of O exceeds 0.003%, which worsens the correction of the favorable content for inclusions and further deteriorates the magnetic characteristics of the steel.

Preferably, the high purity Cu-containing non-oriented electrical steel sheet according to the present invention has sulfide inclusions, where the sulfide inclusions include at least one compound of a separate MnS or MnS coated Cu _x S and a separate Cu _x S. MnS coated Cu _x S is a core-shell composite inclusion formed from MnS as the core and Cu _x S as the shell. A separate MnS indicates that the inclusion is a MnS compound, and a separate Cu _x S indicates that the inclusion is a Cu _x S compound.

Preferably, in the Cu-containing high purity non-oriented electrical steel sheet of the present invention, the sulfide inclusions are in the form of a sphere or spheroid, and the proportion of sulfide inclusions having a size in the range of 0.2 to 1.0 µm is ≥75%.

Preferably, in the Cu-containing high purity non-oriented electrical steel sheet according to the present invention, the amount of individual Cu _x S ≤3.0×10 ⁷ /mm ³ .

Therefore, the Cu-containing non-oriented electrical steel sheet of the present invention has high purity by controlling sulfide inclusions.

Preferably, the Cu-containing high purity non-oriented electrical steel sheet according to the present invention has an iron loss P _15/50 ≦4.1 W/kg and a magnetic induction B ₅₀ ≧1.72 T.

Moreover, it is another object of the present invention to provide a continuous annealing process for the above Cu-containing high purity non-oriented electrical steel sheet. The production efficiency of the continuous annealing plant can be effectively improved and the energy consumption can be reduced to a large extent by the continuous annealing process. What's more, the continuous annealing process is stable in production and has high processability when switching the process.

In order to achieve the above object, the present invention provides a process for continuous annealing of Cu-containing high purity non-oriented electrical steel sheet, comprising the steps of:

heating the cold-rolled steel sheet from the rapid heating start temperature T _initial to the rapid heating end temperature T _final ; T _final =T _initial +kv ₁ where v ₁ represents the first heating rate in the range of 50 - 800°C/s; k represents the rapid heating coefficient in the range of 0.5 - 2.0/s; and heating to the holding temperature T _holding at the second heating rate v ₂ to carry out the holding and heat storage, while v ₂ ≤30°C/s.

In the continuous annealing process according to the present invention, the _final rapid heating end temperature T is dependent on the initial rapid heating _initial temperature T, the first heating rate v ₁ and the rapid heating holding coefficient k, under the same conditions, the higher the rapid heating initial temperature T _initial and first heating rate v ₁ , the higher will be, respectively, the final temperature of rapid heating T _final . However, the rapid heating end temperature T _final must be removed from the continuous annealing holding temperature within a certain range, for example, within 30 to 80°C, in order to save energy consumption to the greatest extent and complete the recrystallization effect of the steel sheet sufficiently to ensure suitable conditions for recovery. and grain growth at the holding stage.

It should be noted that in the formula, the range of k is 0.5 - 2.0/s, which mainly depends on the mass percentage of Si in the steel, and the higher the mass percentage of Si, the larger the k value will be, resulting in a higher final temperature. rapid heating T _final . The greater the first heating rate v ₁ , the greater the nucleation rate during recrystallization will be, which will also lead to more nuclei and a higher rapid heating final temperature T _final . However, the first heating rate v ₁ does not affect the value of k.

Here, it should be noted that too long an interval between the heating process at the second heating rate and the heating process at the first heating rate would lead to a high cooling rate, which would lead to the formation of stress in the inside of the steel sheet, resulting in the corresponding subsequent heating rate and temperature holding time cannot be achieved in a short time, and finally, the electromagnetic performance of the finished steel sheet is degraded. Thus, in order to guarantee the heating effect of the steel sheet and a stable process in the soaking step, the second heating rate v ₂ must be kept at ≤30°C/s so that the recrystallization structure can rapidly grow with a uniform and coarse grain size in a short and limited time. Thus, the time of the entire continuous annealing step can be advantageously shortened, and the holding temperature and the holding time can be correspondingly reduced, which effectively reduces the energy consumption of the continuous annealing step while ensuring the final electromagnetic properties.

Preferably, in the continuous annealing process according to the present invention, the initial rapid heating temperature T _initial is a temperature from room temperature to 550°C.

In the above solution, the rapid heating start temperature T _initial is adjusted from room temperature to 550°C, because in this way it is advantageous to select the appropriate rapid heating _initial temperature T based on the need for convenient production control, combined with the special electromagnetic performance requirements of the finished steel plate, so that save energy consumption and improve the inhibition effect of harmful texture of cold rolled steel sheet. Here, the detrimental texture is mainly wedge-shaped domains and the like, which hinders obtaining an easily magnetizable crystal structure, resulting in the finished steel sheet having a fine or uneven grain size, and finally increasing iron loss and reducing magnetic induction. finished steel sheet. The higher the initial temperature of rapid heating T _initial , the less suitable it is for inhibiting the growth of detrimental texture, and thus detrimental to the reduction of energy consumption and the controllability of the heating rate in the subsequent high-temperature stage.

Preferably, in the continuous annealing process according to the present invention, the rapid heating end temperature T _end ≤ _holding T - (30 - 80).

Preferably, in the continuous annealing process according to the present invention, the v ₁ range is 100 to 600°C/s in order to achieve high fast heating efficiency, suitable fast heating effect, smooth continuous annealing process, and stable switching process.

Preferably, in the continuous annealing process according to the present invention, the _switching interval t between the heating process at the second heating rate and the heating process at the first heating rate is 1 to 5 seconds.

In addition, another object of the present invention is to provide a method for manufacturing a Cu-containing high purity non-oriented electrical steel sheet, and a high purity electrical steel sheet with suitable magnetic characteristics can be obtained by the manufacturing method.

In order to achieve the above object, the present invention provides a method for manufacturing a Cu-containing high purity non-oriented electrical steel sheet, comprising the steps of:

melting and casting;

hot rolling;

normalization;

cold rolling;

performing the above-described continuous annealing process; And

application of an insulating coating to obtain a finished sheet of non-oriented electrical steel.

Preferably, in the manufacturing method according to the present invention, the temperature control operation is performed on the steel sheet after the casting step, so that _{the charge} surface temperature T before entering the hot rolling heating furnace is ≤600°C.

More preferably, in the manufacturing method according to the present invention, the temperature control operation is performed on the steel sheet after the casting step, so that _{the charge} surface temperature T before entering the hot rolling heating furnace is ≤300°C.

In the above solution, the surface temperature of the casting billet before entering the hot rolling heating furnace is controlled so that the low surface temperature of the casting billet before entering the hot rolling heating furnace is used to further enhance the growth of MnS during the heating of the casting billet. As the charge temperature of the cast billet rises, the magnetic induction B ₅₀ will decrease rapidly, and when the charge temperature T _{of the charge} is 600° C. or more, the magnetic induction B ₅₀ generally remains at a relatively low level. Therefore, from the point of view of practical production control, it is better to keep the surface temperature T of the casting _charge before entering the hot rolling heating furnace at 600° C. or less or lower (for example, T _charge ≦300° C.).

Compared with the prior art, the Cu-containing high-purity non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention have the following advantages and positive effects:

The Cu-containing high purity non-oriented electrical steel sheet according to the present invention has the characteristics of high purity and suitable magnetic characteristics, while iron loss and magnetic induction can reach P _15/50 ≤4.1 W/kg and B ₅₀ ≥ 1.72 T, respectively. Here, the electromagnetic characteristic measurement method is based on the Epstein frame method (GB 10129 - 1988) using Germany Brockhaus magnetic measurement equipment, where P _15/50 represents iron losses measured under conditions of 1.0 T and 50 Hz, and B ₅₀ represents magnetic induction measured at 5000 A/m.

In addition, the continuous annealing process according to the present invention can greatly improve the production efficiency of the continuous annealing plant and reduce energy consumption as much as possible. Moreover, the continuous annealing process is stable and highly adaptable to process switching.

In addition, the manufacturing method according to the present invention also has the above advantages and positive effects.

Brief description of the drawings

Fig. 1 is a schematic diagram of a curve showing various annealing processes according to the present technical solution and prior art, respectively.

Fig. 2 schematically represents the relationship between different load temperatures and magnetic induction B ₅₀ .

Fig. 3 schematically represents the relationship between the weight percent of Mn, Cu and S and the magnetic induction B ₅₀ .

Fig. 4 is a scanning electron microscope (SEM) image of a Cu-containing high purity non-oriented electrical steel sheet according to Example A13.

Fig. 5 is a scanning electron microscope (SEM) image of a conventional steel sheet according to Comparative Example A4.

Implementation of the invention

A Cu-containing high purity non-oriented electrical steel sheet and a manufacturing method thereof are explained and illustrated below with reference to the description drawings and specific implementations. However, the explanation and illustrations do not unduly limit the technical solution of the present invention.

Examples A6 - A17 and Comparative Examples A1 - A5

The Cu-containing high purity non-oriented electrical steel sheet according to the above examples A6 to A17 and the ordinary steel sheet according to Comparative examples A1 to A5 were produced in the following steps:

(1) Melting and casting based on the chemical components listed in Table 1, while molten iron and steel scrap are mixed in a certain ratio, then converter melting is carried out, as well as decarburization, deoxidation and circulation vacuuming to obtain a continuously cast billet with a thickness of 120 - 250mm and a width of 800 - 1400 mm.

(2) Hot rolling: The continuously cast billet is sequentially subjected to rough rolling and finishing rolling to obtain a hot-rolled steel sheet with a thickness of 1.5 to 2.8 mm.

(3) Normalizing: The hot-rolled steel sheet is subjected to a normalizing treatment. Normalizing holding temperature 800 - 1000°C, holding time 1 - 180 s.

(4) Cold rolling: cold rolling is performed on a continuous/reversing mill to obtain a cold-rolled steel sheet with a thickness of 0.50 mm.

(5) Performing a continuous annealing process including: heating the cold-rolled steel sheet from the rapid heating start temperature T _initial to the rapid heating end temperature T _final ; T _final =T _initial +kv ₁ where v ₁ represents the first heating rate in the range of 50 - 800°C/s; the k value is related to the Si content of the steel, and the higher the Si content, the larger the k value will be. The value of k is limited to 0.5 - 2.0/s; then heating the steel sheet to a holding temperature T _holding at a second heating rate v ₂ so as to hold and keep warm, v ₂ ≦30°C/s.

(6) Applying an insulating coating to a steel sheet to obtain a final non-oriented electrical steel sheet with a thickness of 0.50 mm.

It should be noted that after the casting step is completed, a temperature control operation of the continuously cast billet is performed so that _{the charge} temperature T before entering the hot rolling heating furnace is ≤600°C.

In addition, in some preferred implementations, the initial temperature of rapid heating T _initial is from room temperature to 550°C.

Alternatively, in some preferred embodiments, the rapid heating end temperature T _end ≤ _hold T - (30 - 80).

Alternatively, in some preferred embodiments, the v ₁ range is 100-600°C/s.

Alternatively, in some preferred embodiments, the interval between the heating process at the second heating rate and the heating process at the first heating rate is 1 to 5 seconds.

Table 1 shows the mass percentages of all chemical elements in the Cu-containing high purity non-oriented electrical steel sheet according to Examples A6 to A17 and in the conventional steel plate according to Comparative Examples A1 to A5.

Table 1. (% wt.), the rest is Fe and unavoidable impurities, except for P, N and O)

no. C Si Mn P S Al O N Cu ([Mn]+[Cu]/2)/[S] Note A1 0.0018 0.21 0.18 0.10 0.0035 0.37 0.0012 0.0017 / 51 Comparative Example A2 0.0011 0.45 0.37 0.05 0.0039 1.11 0.0007 0.0021 0.005 96 Comparative Example A3 0.0022 1.21 0.89 0.04 0.0041 0.85 0.0018 0.0009 0.07 226 Comparative Example A4 0.0027 1.65 0.25 0.02 0.0018 0.002 0.0029 0.0011 0.14 178 Comparative Example A5 0.0008 2.23 0.41 0.02 0.0030 0.25 0.0011 0.0021 0.002 137 Comparative Example A6 0.0014 0.18 0.25 0.20 0.0027 0.98 0.0030 0.0012 0.04 100 Example A7 0.0027 0.27 0.23 0.09 0.0038 0.74 0.0021 0.0017 0.02 63 Example A8 0.0030 0.52 0.10 0.10 0.0019 0.63 0.0016 0.0022 0.12 84 Example A9 0.0019 0.88 0.38 0.04 0.0037 0.10 0.0022 0.0010 0.009 104 Example A10 0.0021 0.98 0.55 0.02 0.0040 0.44 0.0017 0.0007 0.004 138 Example A11 0.0030 1.25 0.35 0.06 0.0026 0.27 0.0009 0.0013 0.003 135 Example A12 0.0006 1.45 0.24 0.02 0.0022 0.18 0.0023 0.0018 0.07 125 Example A13 0.0022 1.63 0.25 0.04 0.0024 0.35 0.0011 0.0022 0.011 106 Example A14 0.0013 1.68 0.18 0.03 0.0032 0.23 0.0016 0.0030 0.20 88 Example A15 0.0024 2.00 0.21 0.02 0.0022 0.54 0.0011 0.0018 0.16 132 Example A16 0.0019 0.10 0.55 0.04 0.0040 1.00 0.0017 0.0011 0.01 139 Example A17 0.0020 0.85 0.33 0.08 0.0031 0.81 0.0013 0.0023 0.16 132 Example

Table 2 lists the specific processing parameters of the Cu-containing high purity non-oriented electrical steel sheet according to Examples A6 to A17 and those of the conventional steel sheet of Comparative Examples A1 to A5.

From Tables 1 to 2, it can be seen that the Cu-containing high purity non-oriented electrical steel sheet according to Examples A6 to A17 of the present invention has an iron loss P _15/50 ≤4.1 W/kg and a magnetic induction B ₅₀ ≥1.72 Tl.

However, on the contrary, with regard to Comparative Example A1, since Cu is not added, a value of 51 for ([Mn]+[Cu]/2)/[S] is obtained and the rapid heating used to perform continuous annealing is not used, the ordinary steel sheet according to Comparative example A1 has high iron loss and low magnetic induction, which are 4.85 W/kg and 1.719 T, respectively. With regard to Comparative Example A2, since the Al content is controlled to substantially exceed the upper limit of the present invention, and the surface temperature of the continuously cast billet reaches 750°C before entering the hot rolling heating furnace, and since the value of k is 2.5, the conventional steel sheet of Comparative Example A2 has high iron loss and low magnetic flux density, which are 4.47 W/kg and 1.682 T, respectively. Meanwhile, with regard to Comparative Example A3, since the mass percentage of Mn and S exceeds the range limited by the present invention, a high value of ([Mn]+[Cu]/2)/[S] is obtained, and v ₁ reaches 1000°C/ s (exceeding the range of 50 - 800°C/s defined in the present invention), as well as T _exposure 200°C higher than T _final , and v ₂ 200°C/s (significantly exceeds the control requirement of 30°C/s ), the conventional steel sheet according to Comparative Example A3 has high iron loss and low magnetic induction. With regard to Comparative Example A4, since the mass percentage of Al does not satisfy the range limited by the present invention, and the value of ([Mn]+[Cu]/2)/[S] is high, and also T _holding up to 1000°C, but no difference in T _final and v ₂ equal to 400°C/s (significantly exceeding the control requirement of 30°C/s), the resulting finished steel sheet has high iron loss and low magnetic induction. In addition, with respect to Comparative Example A5, since the mass percentage of Cu and Si does not satisfy the range limited in the present invention, and the starting temperature of 600°C exceeds the upper limit of the control requirement of 550°C, and the interval between _holding T and T _ending equal to 300°C, v ₂ 100°C/s (exceeding the upper limit of 30°C/s) and the _switching time t 10 s, exceeding the control range of 1 to 5 s, the finished steel sheet as a result has a high iron loss and low magnetic induction.

Fig. 1 is a schematic diagram of a curve showing various annealing processes according to the present technical solution and prior art, respectively.

As shown in FIG. 1, the continuous annealing process used in the present invention is rapid heating annealing, which is different from the conventional heating annealing process. The cold-rolled steel sheet is heated from room temperature to a rapid heating target temperature T _initial by flue gas or electric heating, and then rapidly heated by electromagnetic induction heating; or cold rolled steel sheet is rapidly heated from room temperature by direct electromagnetic induction heating. Here, the rapid heating start temperature T _initial represents a temperature from room temperature to 550°C. The purpose is to appropriately select the rapid heating start temperature T _initial based on the requirements of conventional production management, combined with the specific requirements of the electromagnetic performance of the finished steel sheet, so as to save energy consumption and improve the harmful texture inhibition effect for the cold rolled steel sheet. The higher the rapid heating start temperature T _initial , the worse it is for inhibiting the growth of unfavorable texture, and thus the reduction in energy consumption and controllability of the heating rate in the subsequent high-temperature stage is worse. The first heating rate v ₁ is then adjusted to 50 - 800°C/s, because the greater the investment in equipment, the higher the energy consumption will be. Although higher energy consumption still plays a positive role in improving the electromagnetic performance of the finished steel sheet, the range of 50 to 800°C/s will result in high rapid heating efficiency, suitable rapid heating effect, smooth continuous annealing process and stable switching process. The final temperature of rapid heating T _final depends on the initial temperature of rapid heating T _initial , the first heating rate v ₁ and the holding coefficient for rapid heating k, and under the same conditions, the higher the initial temperature of rapid heating T _{the initial} and first heating rates v ₁ , correspondingly higher final temperature of rapid heating T _final . However, the rapid heating end temperature T _final must be removed from the continuous annealing holding temperature within a certain range, for example, within 30 to 80°C, in order to save energy consumption to the greatest extent and to carry out the recrystallization of the steel sheet sufficiently to provide suitable conditions for recovery and grain growth at the holding stage.

In the formula, the k range is 0.5 - 2.0/s, which mainly depends on the Si content of the steel, and the higher the Si content, the larger the k value will be, resulting in faster heating to the final temperature T _final . The larger the first heating rate v ₁ , the higher the recrystallization nucleation rate will be (resulting in more nuclei) and the rapid heating end temperature T _final . However, the first heating rate v ₁ does not affect the value of k. Here, attention must be paid to the transition between rapid heating using electromagnetic induction and conventional heating using flue gas or electric heating, and the time interval for switching is defined as _switching t, which can be limited to 1 to 5 s. If the time interval is long, the cooling rate is high, stress is easily generated inside the steel sheet, and the corresponding subsequent heating rate and holding temperature cannot be reached in a short time, which ultimately deteriorates the electromagnetic performance of the finished steel sheet. In order to guarantee the heating effect of the steel sheet and stable process in the holding stage after using the flue gas or electric heating, the second heating rate v ₂ should be controlled at ≤ 30℃/s so that the recrystallization structure can quickly produce a uniform and coarse grain size within a short limited time. Thus, the time of the entire continuous annealing step can be advantageously shortened, and the holding temperature and the holding time can be correspondingly reduced, which effectively reduces the power consumption of the continuous annealing step while maintaining the final characteristics of the electromagnetic properties.

Fig. 2 schematically shows the relationship between different load temperatures and magnetic induction B ₅₀ .

As shown in FIG. 2, the continuous annealing process applied in the present solution is rapid heating annealing in which the temperature control operation of the steel sheet is performed after the casting step, so that the surface temperature of the steel sheet before entering the hot rolling heating furnace (namely, the charge temperature of the continuously cast workpiece, represented on the x-axis in Fig. 2) is maintained at ≤600°C, preferably ≤300°C. This is because: The low surface temperature of the continuously cast billet before entering the hot rolling heating furnace is used to further enhance the growth of MnS during the heating of the casting billet. From FIG. 2 it can be seen that with an increase in the loading temperature of the casting billet, the magnetic induction B ₅₀ quickly decreases, and at a loading temperature T _{loading of} 600°C or more, the magnetic induction B ₅₀ generally remains at a relatively low level.

Fig. 3 schematically shows the relationship between the mass fraction of Mn, Cu and S and the magnetic induction B ₅₀ .

As shown in FIG. 3, an appropriate amount of Cu is added to the steel during the smelting process to produce large sulfide composite inclusions together with Mn and S, thereby reducing the harm of S. Meanwhile, Cu, acting as a grain boundary segregation element, can increase grain boundary segregation in continuous annealing process and effectively avoid the undesirable phenomena such as oxidation and yellowing of the surface of the steel sheet during the continuous annealing process. In addition, as shown in FIG. 3, as ([Mn]+[Cu]/2)/[S] increases, the magnetic induction B ₅₀ first increases and then rapidly decreases, while the magnetic induction B ₅₀ has optimal performance when ([Mn]+[Cu] /2)/[S] is in the range 60 - 140.

In addition, the Mn, Cu and S components in the steel must be in an appropriate ratio to ensure early precipitation of MnS inclusions at the initial stage of solidification of the molten steel. Thus, suitable conditions such as temperature and duration can be provided for sufficient growth of MnS inclusions afterwards, and MnS inclusions of 0.5 µm or more clearly reduce the effect on the electromagnetic characteristics of finished materials. Meanwhile, with a constant decrease in the temperature of the continuously cast billet, the added Cu can continuously serve as an S compound for early precipitation of Cu ₂ S inclusions, which, on the one hand, contributes to sufficient growth of inclusions, and on the other hand, their combination with MnS inclusions to form a complex is also beneficial. bigger size. However, the amount of precipitation must be strictly controlled, because in the case of an equivalent size, the crystallization fixing effect will increase with the increase in the amount, which is detrimental to grain size growth and reduction of iron loss.

Based on this, the content of chemical elements can additionally satisfy the conditions: 60≤([Mn]+[Cu]/2)/[S]≤140.

Fig. 4 is a scanning electron microscope (SEM) image of a Cu-containing high purity non-oriented electrical steel sheet according to Examples A13. Fig. 5 is a scanning electron microscope (SEM) image of an ordinary steel sheet according to Comparative Example A4.

From a comparison of Fig. 4 and 5, it can be seen that the appearance and size distribution of harmful inclusions in the Cu-containing high purity non-oriented electrical steel sheet according to Example A13 is completely different from those in the ordinary steel sheet of Comparative Example A4. In the Cu-containing high purity non-oriented electrical steel sheet according to Example A13, as shown in FIG. 4, the sulfide inclusions are mainly individual MnS inclusions and/or composite MnS inclusions coated with Cu _x S, and additionally individual Cu _x S inclusions. .0 μm ≥75%, the amount of individual Cu _x S ≤3.0×10 ⁷ /mm ³ . Here, the method for analyzing and testing inclusions includes conducting electrolytic separation in a non-aqueous solution and observing with scanning electron microscopy for statistics. The amount of electrolyte for each sample is 0.1 g, the pore size of the filtering membrane is 20 nm, the area of the field of view is not less than 0.40 mm ² .

The Cu-containing high-purity non-oriented electrical steel sheet according to the present invention has the characteristics of high purity and suitable magnetic characteristics, and its iron loss and magnetic induction can reach P _15/50 ≤4.1 W/kg and B ₅₀ ≥1 .72 T, respectively.

In addition, the continuous annealing process according to the present invention can significantly improve the efficiency of the continuous annealing plant and reduce energy consumption as much as possible. Moreover, the continuous annealing process is stable in application and has high adaptability when switching the process.

In addition, the manufacturing method according to the present invention also has the above advantages and positive effects.

It should be noted that some of the objects of the prior art in the scope of the claims of the present invention is not limited to the examples given in the description. All prior art that does not conflict with the solutions of the present invention, including, but not limited to, prior patent documents, known publications, known applications, etc., may be included within the scope of the present invention.

In addition, the combination of technical features in the present specification is not limited to the combination described in the claims or the combination described in specific examples. All technical features described here can be freely combined in any way, as long as they do not contradict each other.

It should also be noted that the examples listed above are only specific examples of the present invention. Obviously, the present invention should not be unduly limited to such specific examples. It is intended that changes or modifications that can be directly or easily obtained from the present disclosure by those skilled in the art are within the scope of the present invention.

Claims (22)

1. Cu-containing non-oriented electrical steel sheet, including the following chemical elements in mass percent: 0<C≤0.003%; Si: 0.1-2.0%; Mn: 0.1-0.55%; S: up to 0.004%; Cu: 0.02-0.2%; Al: 0.1-1.0%; the rest is Fe and inevitable impurities, while the inevitable impurities include in mass percent: P≤0.2%, N≤0.003%, O≤0.003%, while the content of chemical elements in mass percent additionally satisfies the condition: 60≤([Mn]+[Cu]/2)/[S]≤140. 2. A steel sheet according to claim 1, characterized in that it has sulfide inclusions containing at least one compound from a separate MnS or MnS coated Cu _x S and a separate Cu _x S. 3. The steel sheet according to claim. 2, characterized in that the sulfide inclusions have the shape of a sphere or spheroid, and the proportion of sulfide inclusions with a size of 0.2-1.0 μm is ≥75%. 4. Steel sheet according to claim 2, characterized in that the amount of individual Cu _x S≤3.0×10 ⁷ /mm ³ . 5. Steel sheet according to any one of paragraphs. 1, 3 and 4, characterized in that it has iron losses P _15/50 ≤4.1 W/kg and magnetic induction B ₅₀ ≥1.72 T. 6. The method of continuous annealing cold-rolled steel sheet in the manufacture of Cu-containing non-oriented electrical steel sheet according to any one of paragraphs. 1-5, characterized in that it includes the following stages: heating the cold-rolled steel sheet from the rapid heating start temperature T _initial to the rapid heating end temperature T _final ; T _final =T _initial +kv ₁ where v ₁ represents the first heating rate in the range of 50-800°C/s; k represents the fast heating holding coefficient in the range of 0.5-2.0 s; And heating to the holding temperature T _holding at the second heating rate v ₂ to carry out holding and heat retention, while v ₂ ≤30°C/s. 7. The method according to claim 6, characterized in that the initial rapid heating temperature T _initial represents a temperature from room temperature to 550°C. 8. The method according to p. 6, characterized in that the final temperature of rapid heating T _final ≤T _exposure - (30-80). 9. The method according to p. 6, characterized in that the range of the first heating rate v ₁ is 100-600°C/s. 10. The method according to claim 6, characterized in that _{the switching} interval t between the heating process at the second heating rate v ₂ and the heating process at the first heating rate v ₁ is 1-5 s. 11. A method for manufacturing a Cu-containing non-oriented electrical steel sheet, characterized in that it includes the following steps: melting and casting; hot rolling; normalization; cold rolling; performing the continuous annealing method according to any one of paragraphs. 6-10; And application of an insulating coating to obtain a finished sheet of non-oriented electrical steel. 12. The method according to claim 11, characterized in that the temperature control operation is performed on the steel sheet after the casting step, so that _{the charge} surface temperature T before entering the hot rolling heating furnace is ≤600°C. 13. The method according to claim 12, characterized in that the temperature control operation is performed on the steel sheet after the casting step, so that _{the charge} surface temperature T before entering the hot rolling heating furnace is ≤300°C.

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