Non-oriented silicon steel sheet and method for manufacturing the same

Abstract

The present invention provides a non-oriented silicon steel sheet and a method for manufacturing the same. By precisely controlling the Si and Al contents in the non-oriented silicon steel based on the (Si / Al) / (Si+Al) value and combining it with precise control of the manufacturing process, the microstructure of the silicon steel substrate is optimized, the iron loss after secondary annealing is reduced, and the loss of electrical products is significantly reduced. Furthermore, the total amount of Si and Al added to the non-oriented silicon steel sheet is small, the alloy cost is low, and the manufacturing process is simple. Therefore, the overall cost of the non-oriented silicon steel sheet is relatively low, and the market competitiveness of the product is high.

Description

Technical Field

[0001] The present invention relates to the field of alloy technology, and particularly to non-oriented silicon steel sheets and a method for manufacturing the same.

Background Art

[0002] In the punching process of the stator and rotor of an electric motor, non-oriented silicon steel sheets are prone to internal stress and local plastic deformation, which causes lattice distortion and destruction of the magnetic domain structure, resulting in a decrease in magnetic permeability and an increase in hysteresis loss, ultimately causing an increase in the loss of the electric motor. At the same time, the mechanical and magnetic imbalance in the cutting area of the stator tooth part during the punching process also affects the frictional torque of the electric motor. In order to improve the properties of the silicon steel sheet after punching, downstream users of the silicon steel sheet, particularly compressor manufacturers, need to perform secondary annealing on the stator and rotor. This is mainly to remove the residual stress and lattice distortion after punching and restore the magnetic properties of the silicon steel sheet. However, when different silicon steel compositions and manufacturing processes are adopted, there are differences in the recovery and improvement effects after secondary annealing, and there are also silicon steel sheets whose iron loss reduction is not significant even after secondary annealing, and the loss of the electric motor core manufactured using this may still exceed the reference value in some cases.

[0003] Therefore, optimizing the composition and process of non-oriented silicon steel sheets to ultimately achieve lower losses and stable comprehensive properties has become an important issue for secondary annealing users. Currently, many solutions aim to improve magnetic properties by adding effective elements or adding manufacturing processes. For example, Chinese Patent CN103667879A discloses a non-oriented electromagnetic steel sheet with excellent magnetic and mechanical properties and its manufacturing method, which adds Sn or Sb elements. However, the alloy cost is high, and since annealing is required, the manufacturing cost is also high. Chinese Patent CN104195426B discloses a semi-processed non-oriented silicon steel sheet, which performs recrystallization annealing in a box-type furnace. However, the production efficiency is low, and skin pass tempering must be performed after box-type annealing. Since additional production equipment is required for the tempering process, the manufacturing process is complex. Since the above methods have high alloy and manufacturing costs and their manufacturing processes are also complex, it is necessary to provide a manufacturing method for non-oriented silicon steel sheets with low cost and a simple manufacturing process.

Summary of the Invention

[0004] An object of the present invention is to provide a non-oriented silicon steel sheet and a manufacturing method thereof.

[0005] The present invention provides a manufacturing method for a non-oriented silicon steel sheet. This steel sheet contains, by mass percentage, C: 0.005% or less, Si: 0.60 - 1.60%, Al: 0.40 - 0.80%, Mn: 0.20 - 0.80%, S: 0.003% or less, N: 0.003% or less, and the balance consists of Fe and inevitable impurities. The inevitable impurities include C: 0.005% or less, S: 0.003% or less, N: 0.003% or less, and the contents of Si and Al satisfy

Number

[0006] The manufacturing method is Based on the above chemical composition, a step of smelting, casting to obtain a cast slab A step of heating the cast slab and performing hot rolling treatment on the heated cast slab to obtain a hot-rolled steel sheet A step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, A step of subjecting the cold-rolled steel sheet to a recrystallization annealing treatment of holding at a temperature of 800 to 950 °C for 50 to 200 seconds to obtain a primary annealed steel sheet, and A step of subjecting the primary annealed steel sheet to a secondary annealing treatment of holding at a temperature of 750 to 850 °C for 1 to 3 hours to obtain a secondary annealed steel sheet.

[0007] As a further improvement of the present invention, the heating of the slab specifically includes heating the slab to a temperature range of 1050 to 1200 °C, with a heating time of 150 to 200 minutes, and controlling the temperature variation within ±20 °C.

[0008] As a further improvement of the present invention, obtaining the hot-rolled steel sheet by hot-rolling the slab after the heating specifically includes controlling the starting temperature of hot rolling to 1200 °C or lower, controlling the finishing rolling temperature to 840 °C or higher, and controlling the variation of the finishing rolling temperature within ±20 °C.

[0009] As a further improvement of the present invention, obtaining the hot-rolled steel sheet by hot-rolling the slab after the heating, after the hot-rolling treatment, laminar cooling the hot-rolled steel sheet and then performing coil winding, with the winding temperature being 700 °C or lower and controlling the variation of the winding temperature within ±20 °C.

[0010] As a further improvement of the present invention, cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet specifically includes cold rolling the hot-rolled steel sheet to a thickness of 0.47 to 0.51 mm.

[0011] As a further improvement of the present invention, after manufacturing the primary annealed steel sheet by the recrystallization annealing treatment of the cold-rolled steel sheet, further includes forming an insulating film on the surface of the primary annealed steel sheet.

[0012] As a further improvement of the present invention, the cold-rolled steel sheet is subjected to the recrystallization annealing treatment in a hydrogen-nitrogen mixed atmosphere, and the primary annealed steel sheet is subjected to the secondary annealing treatment in a nitrogen gas or DX gas atmosphere.

[0013] The present invention further provides a non-oriented silicon steel sheet. This non-oriented silicon steel sheet is manufactured by the above-described method for manufacturing a non-oriented silicon steel sheet, and the iron loss reduction rate ΔP 15 / 50 / P 15 / 50 of the non-oriented silicon steel sheet is 15% or more.

[0014] The present invention further provides a non-oriented silicon steel sheet. The composition of the non-oriented silicon steel contains, in mass percent, C≦0.005%, Si: 0.60 to 1.60%, Al: 0.40 to 0.80%, Mn: 0.20 to 0.80%, S≦0.003%, N≦0.003%, with the balance being Fe and inevitable impurities, and the inevitable impurities contain C≦0.005%, S≦0.003%, N≦0.003%. Further, the contents of Si and Al satisfy

Number

[0015] As a further improvement of the present invention, the iron loss reduction rate P 15 / 50 / P 15 / 50 of the non-oriented silicon steel sheet is 15% or more.

[0016] The effects of the present invention are as follows. The present invention precisely controls the contents of Si and Al in the non-oriented silicon steel based on the value of (Si / Al) / (Si + Al), and in combination with precise control of the manufacturing process, optimizes the grain structure of the silicon steel substrate, reduces the iron loss after secondary annealing, and thereby can significantly reduce the losses of motor products. Further, since the total amount of Si and Al added to the present non-oriented silicon steel sheet is small, the alloy cost is low and the manufacturing process is simplified. Therefore, the overall cost of the non-oriented silicon steel sheet is relatively low, and the product has a high market competitiveness.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] To make the object, technical means, and effects of the present invention clearer, hereinafter, based on the embodiments of the present invention and the corresponding drawings, the technical means of the present invention will be clearly and completely described. It should be noted that the embodiments described herein are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments that can be obtained by those skilled in the art without creative labor are also included in the protection scope of the present invention.

[0019] Hereinafter, the embodiments of the present invention will be described in detail. Examples of the embodiments are shown in the drawings, and the same or similar reference numerals from the beginning to the end in the drawings indicate the same or similar elements, or elements having the same or similar functions. The embodiments described below with reference to the drawings are exemplary and are for explaining the present invention and should not be construed as limiting the present invention.

[0020] This embodiment provides a non-oriented silicon steel sheet and a manufacturing method thereof. By introducing the value of (Si / Al) / (Si + Al) (where the elemental symbol indicates the mass percentage of each element) as a control factor for the addition amounts of Si and Al and combining it with the control of the manufacturing process, the aggregation structure of the silicon steel substrate can be effectively optimized, and the iron loss after secondary annealing can be reduced. As a result, when used as an electromagnetic steel sheet for electrical machinery products, the losses of motor products can be significantly reduced.

[0021] The components of the non-oriented silicon steel provided in this embodiment, in mass percentage, include C: 0.005% or less, Si: 0.60 - 1.60%, Al: 0.40 - 0.80%, Mn: 0.20 - 0.80%, S: 0.003% or less, N: 0.003% or less, the balance being Fe and inevitable impurities, and the inevitable impurities include C: 0.005% or less, S: 0.003% or less, N: 0.003% or less.

[0022] The core idea of the design of the chemical composition of the steel sheet in the present invention is to add only a small amount of Si and Al, and control the compositional content of Si and Al based on the value of (Si / Al) / (Si + Al), so as to improve the microstructure of the steel sheet, further reduce the iron loss of the steel sheet after secondary annealing, and make the magnetic properties more stable. Compared with the non-oriented silicon steel sheet added with elements such as Sn or Sb, the steel sheet in this embodiment has a lower alloy cost, and the process of the manufacturing method used is simple, and the manufacturing difficulty and cost are low.

[0023] Specifically, the design principle of the chemical composition of the steel sheet is as follows.

[0024] Si: Si is the most important alloying element in the electrical steel sheet, which can effectively improve the electrical resistivity of the steel and reduce the eddy current loss. However, with the increase of the Si content, the magnetic flux density decreases and the magnetic flux density deteriorates. Therefore, in this embodiment, the Si content is controlled to be 0.60 - 1.60%.

[0025] Al: Al also has the same effect as Si, can improve the electrical resistivity, and reduce the eddy current loss. When the Al content is different, the size distribution of the precipitation phase AlN is different, and the inhibitory effect on grain growth is also different. When the Al content is low, the fine and dispersed AlN formed by the combination of Al and N significantly inhibits the grain growth during annealing and significantly deteriorates the magnetic properties. When the Al content is 0.005% - 0.01%, since the size of the formed AlN inclusions is less than 1 μm, it shows a significant pinning effect on magnetic domains and causes deterioration of magnetic properties. When the Al content is high, the size of the precipitation phase AlN becomes large, which is advantageous for the coarsening of grains. Therefore, increasing the Al content is very advantageous for improving magnetic properties, especially the magnetic properties of non-oriented silicon steel with extremely low iron loss.

[0026] Furthermore, Al reduces the austenite phase region, promotes grain growth and the improvement of the microstructure, and can reduce iron loss. In non-oriented silicon steel, the {100} and {110} microstructures are microstructures advantageous for magnetic properties, and the {111} and {112} microstructures are disadvantageous microstructures. The {111} microstructure, which is disadvantageous for magnetic properties, is likely to nucleate at grain boundaries and inclusions. Therefore, when the grain size is small, the number of grain boundaries increases, and the nucleation of the disadvantageous microstructure becomes easy. As a result, the strength of the disadvantageous microstructure increases and the magnetic properties deteriorate. An appropriate Al content promotes grain growth, reduces the strength of {111}, which is a component of the disadvantageous microstructure, thereby reducing iron loss.

[0027] However, while Al reduces iron loss, it also deteriorates the magnetic flux density. Therefore, in this embodiment, the Al content is controlled to be 0.40 - 0.80%.

[0028] Furthermore, the Si and Al contents satisfy the following formula.

Equation

[0029] Al has a greater reduction in iron loss than Si and a smaller deterioration in magnetic flux density than Si, and its advantageous effect becomes more prominent as the Si content increases. To reduce the magnetic properties after secondary annealing, especially the iron loss of the black plate after secondary annealing, the Si and Al contents are defined by the above formula. This ratio has a great influence on the iron loss reduction rate △P 15 / 50 / P 15 / 50 and when the value of the formula is less than 1.67, the microstructure is significantly improved, the iron loss reduction rate increases, and the effect of secondary annealing is significantly enhanced. When the ratio is less than 0.83, the fluctuation of magnetic properties is significant and the stability is weak.

[0030] Mn: Mn combines with S to form MnS, thereby preventing the formation of low-melting-point FeS along the grain boundaries and avoiding the hot brittleness phenomenon of hot-rolled steel sheets. Therefore, it is necessary to add a certain amount of Mn to the steel to improve the hot-rolling plasticity. Furthermore, Mn expands the austenite phase region, and since the solubility product of MnS in the austenite phase is lower than that in the ferrite phase, it promotes the coarsening of MnS, reduces the pinning effect on the grain boundaries, and is beneficial to grain growth and P 15 / 50 reduction of iron loss. However, on the other hand, an increase in the Mn content reduces the ferrite phase region, thereby lowering the annealing temperature and being disadvantageous to grain growth. Therefore, the Mn content is usually controlled to be 0.20 - 0.80%.

[0031] C: In non-oriented silicon steel sheets, C is a harmful element. When the C content is too high, magnetic aging is likely to occur. Also, when the C content in the product steel sheet increases, the iron loss P 15 / 50 increases. Therefore, it is necessary to control the C content at a low level. In this embodiment, the C content is controlled to be C0.005% or less.

[0032] S: S is a harmful element. When S combines with Mn to form fine MnS, it strongly inhibits the grain growth during steel sheet annealing, and at any Mn content, the iron loss P 15 / 50 increases as the S content increases. Therefore, it is necessary to control the S content to be 0.003% or less.

[0033] N: N is a harmful element, which is likely to form fine AlN particles and inhibit grain growth. When the N content exceeds 0.0025%, the iron loss P 15 / 50 is likely to increase significantly. Moreover, N is an element prone to magnetic aging, and its influence on aging is greater than that of C. Therefore, it is necessary to control the N content below 0.003%.

[0034] As shown in Figure 1, the method for manufacturing non-oriented silicon steel sheets includes the following steps. S1: According to the above chemical composition ratio, smelting and casting are carried out to obtain a cast slab. S2: The cast slab is heated, and after heating, hot rolling treatment is performed on the cast slab to obtain a hot-rolled steel sheet. S3: Cold rolling treatment is performed on the hot-rolled steel sheet to obtain a cold-rolled steel sheet. S4: Recrystallization annealing treatment is performed on the cold-rolled steel sheet to obtain a primary annealed steel sheet. The recrystallization annealing temperature is controlled at 800 - 950 °C, and the holding time is controlled at 50 - 200 seconds. Then, secondary annealing treatment is performed on the primary annealed steel sheet to obtain a secondary annealed steel sheet. The secondary annealing temperature is controlled at 750 - 850 °C, and the holding time is controlled at 1 - 3 hours.

[0035] In step S1, after obtaining molten steel by converter smelting or electric furnace smelting, the obtained molten steel can be subjected to secondary refining and continuous casting to obtain a cast slab. The methods of the smelting, refining, and continuous casting processes adopted can refer to existing general steel sheet manufacturing processes.

[0036] Specifically, step S2 includes heating the cast slab to a temperature range of 1050 - 1200 °C, controlling the heating time at 150 - 200 minutes, and controlling the temperature fluctuation within ±20 °C.

[0037] In Process S2, before rolling, the slab is heated to a uniform temperature suitable for rolling, which improves the plasticity of the steel, reduces the deformation resistance, makes the slab easier to deform, and thus allows a large reduction ratio to be used in the slab rolling process. Also, the internal structure and properties of the slab are improved by heating, and the non-uniform structure and non-metallic inclusions are homogenized by the diffusion effect due to high-temperature heating. However, an excessively long heating time reduces the magnetic properties of the steel plate, so it is necessary to control the heating time and avoid an excessively long heating time. Furthermore, at an excessively high heating temperature, the precipitates in the slab dissolve, and fine inclusions precipitate during hot rolling, suppressing the grain growth during annealing, causing an increase in iron loss and a decrease in magnetic flux density, so the heating temperature is controlled.

[0038] The heating of the slab can adopt either cold-slab heating or heating furnace heating by charging hot slabs.

[0039] Furthermore, in Process S2, the specific process of subjecting the slab to hot rolling after heating to obtain a hot-rolled steel plate includes the following.

[0040] Control the starting temperature of hot rolling to 1200°C or lower and the finishing rolling temperature to 840°C or higher. By controlling the rolling temperature, the acceleration of the recrystallization rate during hot rolling is avoided, the deterioration of the hot-rolled steel plate structure is prevented, and the increase in iron loss and the decrease in magnetic flux density of the product plate are prevented.

[0041] After obtaining the hot-rolled steel plate, laminar cooling is applied to the hot-rolled steel plate and then coiling is carried out, and the coiling temperature is controlled to 700°C or lower. This avoids the precipitation of fine and dispersed inclusions in the hot-rolled steel plate and prevents the suppression of grain growth during annealing.

[0042] Furthermore, control the fluctuations of the finishing rolling temperature and the coiling temperature within ±20°C to ensure the stability of the magnetic properties of the steel plate.

[0043] After hot rolling, the hot-rolled steel plate is further cold-rolled to form a cold-rolled steel plate with a thickness of 0.47 - 0.51 mm.

[0044] In step S4 and step S5, the cold-rolled steel sheet is subjected to recrystallization annealing under a hydrogen-nitrogen protective atmosphere, and the primary annealed steel sheet is subjected to secondary annealing under a nitrogen gas or DX gas protective atmosphere. This prevents oxidation on the surface of the cold-rolled steel sheet. Further, an insulating coating is applied to the surface of the primary annealed steel sheet to further protect the steel sheet and prevent oxidation of the steel sheet surface.

[0045] By primary annealing and secondary annealing treatments, the steel sheet is sufficiently recrystallized, the influence of shear stress is removed, and the microstructure of the steel sheet is adjusted.

[0046] Hereinafter, the specific embodiments of the present invention will be further described with reference to five examples and three comparative examples.

[0047] In Examples 1 to 5 and Comparative Examples 1 to 3, production was carried out according to the above manufacturing method. The Si and Al element contents, some process parameters, and magnetic properties of Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1. For elements other than Si and Al elements, in Examples 1 to 5 and Comparative Examples 1 to 3, addition was carried out according to the contents described above.

[0048]

Table 1

[0049] It can be seen from Table 1 that the magnetic properties of the final silicon steel sheet are closely related to the value of (Si / Al) / (Si + Al). Compared with the comparative examples, the magnetic properties after secondary annealing in the examples are more excellent. Particularly in terms of iron loss characteristics, even when the iron loss before secondary annealing is the same under the same conditions, the reduction in iron loss after secondary annealing is large, and the iron loss reduction rate is high.

[0050] The aggregate structure analysis of Example 3 and Comparative Example 1 was carried out. The total amount of Si+Al alloy in both was approximated, and the magnetic property levels were also close. The quantitative analysis of the aggregate structures of both is shown in FIGS. 2a and 2b. These are the aggregate structure distribution diagrams of Example 3 and Comparative Example 1. In Example 3, {111}<112>, which is an unfavorable aggregate structure, is weaker than that in Comparative Example 1, and {001}<110> and {001}<120>, which are more favorable aggregate structures, appear stronger. From this, it can be understood that in non-oriented silicon steel with an approximated total amount of Si+Al alloy, the aggregate structure can be optimized by adjusting the (Si / Al) / (Si+Al) ratio, and the magnetic properties of non-oriented silicon steel can be further improved.

[0051] As described above, in the present embodiment, the Si and Al contents in non-oriented silicon steel are precisely controlled based on the (Si / Al) / (Si+Al) value, and combined with precise control of the manufacturing process, the aggregate structure of the silicon steel substrate is optimized, the iron loss after secondary annealing is reduced, and the loss of electrical products can be significantly reduced. Furthermore, the total amount of Si and Al added to the non-oriented silicon steel sheet is small, the alloy cost is low, and the manufacturing process is simple. Therefore, the overall cost of the non-oriented silicon steel sheet is relatively low, and the market competitiveness of the product is high.

[0052] Although this specification is described by embodiments, it should be understood that each embodiment does not include only a single independent technical solution, and such a description method in the specification is only for clarity. Those skilled in the art can grasp the specification as a whole, and by appropriately combining the technical solutions in each embodiment, other embodiments understandable to those skilled in the art can be formed.

[0053] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and are not used to limit the protection scope of the present invention. Any equivalent embodiments or modifications that do not deviate from the technical spirit of the present invention are all included within the protection scope of the present invention.

Claims

1. A method for manufacturing a non-oriented silicon steel sheet, wherein the non-oriented silicon steel sheet contains, by mass percentage, C: 0.005% or less, Si: 0.60 to 1.60%, Al: 0.40 to 0.80%, Mn: 0.20 to 0.80%, S: 0.003% or less, N: 0.003% or less, the balance being Fe and unavoidable impurities, and the unavoidable impurities contain C: 0.005% or less, S: 0.003% or less, N: 0.003% or less, and the contents of Si and Al satisfy 【Number 1】 where the elemental symbols in the formula indicate the mass percentages of the respective elements, the manufacturing method includes a step of smelting and casting based on the above chemical composition to obtain a cast slab, a step of heating the cast slab and then subjecting the heated cast slab to hot rolling to obtain a hot-rolled steel sheet, a step of cold rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, a step of performing a recrystallization annealing treatment on the cold-rolled steel sheet by holding it at a temperature of 800 to 950 °C for 50 to 200 seconds to obtain a primary annealed steel sheet, and a step of performing a secondary annealing treatment on the primary annealed steel sheet by holding it at a temperature of 750 to 850 °C for 1 to 3 hours to obtain a secondary annealed steel sheet, the method for manufacturing a non-oriented silicon steel sheet including these steps.

2. The heating of the cast slab includes heating the cast slab to a temperature range of 1050 to 1200 °C, setting the heating time to 150 to 200 minutes, and controlling the temperature variation within ±20 °C. The method for manufacturing a non-oriented silicon steel sheet according to Claim 1 is characterized by this.

3. Obtaining the hot-rolled steel sheet by subjecting the cast slab to hot rolling after heating includes controlling the starting temperature of hot rolling to 1200 °C or less, controlling the finish rolling temperature to 840 °C or more, and controlling the variation of the finish rolling temperature within ±20 °C. The method for manufacturing a non-oriented silicon steel sheet according to Claim 2 is characterized by this.

4. Obtaining the hot-rolled steel sheet by subjecting the cast slab to hot rolling after heating includes, after the hot rolling treatment, laminar cooling the hot-rolled steel sheet and then performing coil winding, setting the winding temperature to 700 °C or less, and controlling the variation of the winding temperature within ±20 °C. The method for manufacturing a non-oriented silicon steel sheet according to Claim 3 is characterized by this.

5. Obtaining the cold-rolled steel sheet by cold rolling the hot-rolled steel sheet includes cold rolling the hot-rolled steel sheet to a thickness of 0.47 to 0.51 mm. The method for manufacturing a non-oriented silicon steel sheet according to Claim 1 is characterized by this.

6. After manufacturing the primary annealed steel sheet by the recrystallization annealing treatment of the cold-rolled steel sheet, The method for manufacturing a non-oriented silicon steel sheet according to claim 1, further comprising forming an insulating film on the surface of the primary annealed steel sheet.

7. The method for manufacturing a non-oriented silicon steel sheet according to claim 1, wherein the cold-rolled steel sheet is subjected to the recrystallization annealing treatment in a hydrogen-nitrogen mixed atmosphere, and the primary annealed steel sheet is subjected to the secondary annealing treatment in a nitrogen gas or DX gas atmosphere.

8. A non-oriented silicon steel sheet containing, by mass percentage, C: 0.005% or less, Si: 0.60 to 1.60%, Al: 0.40 to 0.80%, Mn: 0.20 to 0.80%, S: 0.003% or less, N: 0.003% or less, the balance being Fe and unavoidable impurities, the unavoidable impurities containing C: 0.005% or less, S: 0.003% or less, N: 0.003% or less, and the contents of Si and Al satisfy 【Number 2】 where the elemental symbols in the formula indicate the mass percentages of the respective elements. Iron loss reduction rate ΔP １５／５０ / P １５／５０ is 15% or more, characterized by an isotropic silicon steel sheet.

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