Non-oriented silicon steel for fixed-frequency compressor motor core and preparation method thereof

Abstract

The application discloses a non-oriented silicon steel for a fixed-frequency compressor motor core and a preparation method thereof. The preparation method comprises the following steps: steelmaking, continuous casting, and the chemical composition of the continuous casting blank is as follows in terms of mass percentage: Si: 0.7%-1.0%, Al: 0.42%-0.60%, Si / Al=1.5-1.7, Mn: 0.1%-0.3%, Nb<=0.005%, V and Ti are all <=0.006%, Cr and Ni and Cu are all <=0.03%, and the rest is Fe; the continuous casting blank is heated to 1050-1100 DEG C and kept for 180+ / -30 min, rough rolling, finish rolling and coiling; the finish rolling opening rolling temperature is 880-910 DEG C, the outlet temperature is 800-820 DEG C, and the coiling temperature is 600-620 DEG C; acid continuous rolling is carried out to prepare a cold-rolled plate with a thickness of 0.500+ / -0.005 mm; and annealing is carried out at an annealing temperature of 880-920 DEG C for an annealing time of 70s+ / -10s.

Description

Technical Field

[0001] This invention belongs to the field of steel material preparation technology, and relates to a non-oriented silicon steel for the core of a fixed-frequency compressor motor and its preparation method. Background Technology

[0002] In the study of the magnetic properties of non-oriented silicon steel products, it was found that the lower the heating temperature during the hot rolling process, the better the magnetic properties of the finished product; conversely, the higher the finishing mill exit temperature, the better the magnetic properties of the finished product. However, simultaneously lowering the heating temperature and increasing the finishing mill exit temperature are contradictory, and this can also lead to instability in the hot rolling process, reduced uniformity of the hot-rolled coil temperature, and poorer plate shape, ultimately resulting in excessive fluctuations in the magnetic properties of the non-oriented silicon steel product.

[0003] Therefore, for high-grade non-oriented silicon steel, a normalizing process is added during the preparation process. Based on the normalizing process, the finishing mill exit temperature has little impact on the magnetic properties of the finished product. Thus, the preparation process of high-grade non-oriented silicon steel will combine the normalizing process with a reduction in heating temperature and finishing mill exit temperature to improve magnetic properties, rather than using a method of simultaneously reducing heating temperature and increasing finishing mill exit temperature to improve magnetic properties.

[0004] However, high-grade non-oriented silicon steel is usually used to manufacture the core of variable frequency compressor motors, rather than the core of fixed frequency compressor motors.

[0005] For the core of a fixed-frequency compressor motor, medium- and low-grade non-oriented silicon steel is commonly used. However, unlike the preparation of high-grade non-oriented silicon steel, medium- and low-grade non-oriented silicon steel generally does not undergo a normalizing process during hot rolling. Therefore, a common method to improve the magnetic properties of non-oriented silicon steel for fixed-frequency compressor motor cores, as mentioned above, is to simultaneously reduce the heating temperature and increase the finishing mill exit temperature, as well as increase the annealing temperature. However, as discussed earlier, this method is inherently contradictory, leading to instability in the hot rolling process, reduced uniformity of the hot-rolled coil temperature, and poor sheet shape, ultimately resulting in excessive fluctuations in the magnetic properties of the finished non-oriented silicon steel product. Furthermore, it results in excessively high production costs.

[0006] Considering the improvement of the magnetic properties of non-oriented silicon steel used in the core of a fixed-frequency compressor motor, the ultimate goal is to enhance the magnetic properties of the core. Therefore, the process for manufacturing the core of a fixed-frequency compressor motor using non-oriented silicon steel is roughly as follows: slitting, stamping, lamination, and secondary annealing. The secondary annealing process aims to reduce iron loss (P). 1.5 / 50 This improves the magnetic properties of the final fixed-frequency compressor motor core. However, the iron loss reduction after secondary annealing is relatively small for existing fixed-frequency compressor motor cores made of non-oriented silicon steel.

[0007] As mentioned above, the non-oriented silicon steel used in the core of a fixed-frequency compressor motor is typically referred to as white sheet before secondary annealing and as black sheet after secondary annealing. Currently, the field is generally focused on improving the magnetic properties of white sheet, and no technology has been disclosed regarding how to increase the reduction in iron loss during secondary annealing of non-oriented silicon steel for fixed-frequency compressor motor cores. Summary of the Invention

[0008] The purpose of this invention is to provide a non-oriented silicon steel for the core of a fixed-frequency compressor motor and its preparation method.

[0009] To achieve the above-mentioned objective, one embodiment of the present invention provides a method for preparing non-oriented silicon steel. The preparation method includes:

[0010] Steelmaking and casting are carried out to obtain continuously cast billets, the chemical composition of which, by mass percentage, is: C≤0.004%, S≤0.003%, N≤0.003%, Si:0.7%~1.0%, Al:0.42%~0.6%, Si / Al=1.5~1.7, Mn:0.1%~0.3%, P≤0.03%, Nb≤0.005%, V≤0.006%, Ti≤0.006%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, with the remainder being Fe and unavoidable impurities;

[0011] The continuously cast billet is heated to 1050℃~1100℃ and held for 180±30min. Then, it is first rough rolled into an intermediate billet, and then made into a hot-rolled plate through 7 passes of finishing rolling and coiling. The finishing rolling is carried out entirely in the ferrite region. The starting temperature of the finishing rolling is 880℃~910℃, the exit temperature of the finishing rolling is 800℃~820℃, and the coiling temperature is 600℃~620℃.

[0012] After the hot-rolled sheet is uncoiled, it is subjected to acid continuous rolling to produce a cold-rolled sheet with a thickness of 0.500±0.005mm;

[0013] The cold-rolled sheet is annealed at a temperature of 880℃~920℃ for a time of 70s±10s.

[0014] Preferably, the microstructure of the hot-rolled plate is deformed ferrite, the crown of the hot-rolled plate is ≤30μm, and the wedge shape of the hot-rolled plate is ≤4μm.

[0015] Preferably, the rolling force for each of the 7-pass finishing rolling is as follows:

[0016] F1: 11000~12000kN; F2: 10000~11000kN; F3: 9000~10000kN; F4: 10000~11000kN; F5: 8000~9000kN; F6: 7000~8000kN; F7: 6000~7000kN.

[0017] Preferably, during the continuous acid rolling process, pickling is performed first, with a pickling speed of 160-180 m / min, an acid concentration of 110-150 g / L, and an acid temperature of 60-80°C.

[0018] Preferably, the cold-rolled sheet has a crown of ≤5μm and a wedge shape of ≤2μm.

[0019] Preferably, during the annealing process, the cold-rolled sheet is produced at a constant speed in a continuous annealing furnace in a mixed atmosphere of H2+N2, and the tension in the annealing furnace section is 6-10kN.

[0020] Preferably, the preparation method further includes: after annealing, coating a layer with a thickness of 0.8 to 1.0 μm on the surface of the steel plate, and then drying and sintering, with a drying temperature of 600 to 650°C, a sintering temperature of 530 to 580°C, and a total drying and sintering time of 20 to 25 seconds.

[0021] Preferably, the preparation method further includes: performing a second annealing, and the holding temperature during the second annealing is 800-820℃.

[0022] Preferably, the iron loss P of silicon steel after secondary annealing is lower than that before secondary annealing. 1.5 / 50 The reduction rate is over 30%, and the average grain size growth rate is over 300%.

[0023] Preferably, the heating rate during the secondary annealing is 6–8 °C / s, the holding time is 2–3 h, and the cooling rate is 3–5 °C / s.

[0024] To achieve the above-mentioned objective, one embodiment of the present invention provides a non-oriented silicon steel. The method for preparing the non-oriented silicon steel includes:

[0025] Steelmaking and casting are carried out to obtain continuously cast billets, the chemical composition of which, by mass percentage, is: C≤0.004%, S≤0.003%, N≤0.003%, Si:0.7%~1.0%, Al:0.42%~0.6%, Si / Al=1.5~1.7, Mn:0.1%~0.3%, P≤0.03%, Nb≤0.005%, V≤0.006%, Ti≤0.006%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, with the remainder being Fe and unavoidable impurities;

[0026] The continuously cast billet is heated to 1050℃~1100℃ and held for 180±30min. Then, it is first rough rolled into an intermediate billet, and then finished rolled and coiled into a hot-rolled plate. The finishing rolling is carried out entirely in the ferrite region. The starting temperature of the finishing rolling is 880℃~910℃, the exit temperature of the finishing rolling is 800℃~820℃, and the coiling temperature is 600℃~620℃.

[0027] After the hot-rolled sheet is uncoiled, it is subjected to acid continuous rolling to produce a cold-rolled sheet with a thickness of 0.500±0.005mm;

[0028] The cold-rolled sheet is annealed at a temperature of 880℃~920℃ for a time of 70s±10s.

[0029] The iron loss P of the non-oriented silicon steel 1.5 / 50 4.5~5.5W / kg, magnetic induction intensity B 5000 ≥1.73T.

[0030] Furthermore, the non-oriented silicon steel has a yield strength of 250–270 MPa, a tensile strength of 380–400 MPa, and an elongation of 25–35%.

[0031] The microstructure of the non-oriented silicon steel is equiaxed ferrite with a grain size deviation of ≤40μm and an average grain size of 30-60μm.

[0032] The iron loss fluctuation of the non-oriented silicon steel during winding is ±0.2W / kg.

[0033] To achieve the above-mentioned objective, one embodiment of the present invention provides a non-oriented silicon steel. The method for preparing the non-oriented silicon steel includes:

[0034] Steelmaking and casting are carried out to obtain continuously cast billets, the chemical composition of which, by mass percentage, is: C≤0.004%, S≤0.003%, N≤0.003%, Si:0.7%~1.0%, Al:0.42%~0.6%, Si / Al=1.5~1.7, Mn:0.1%~0.3%, P≤0.03%, Nb≤0.005%, V≤0.006%, Ti≤0.006%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, with the remainder being Fe and unavoidable impurities;

[0035] The continuously cast billet is heated to 1050℃~1100℃ and held for 180±30min. Then, it is first rough rolled into an intermediate billet, and then finished rolled and coiled into a hot-rolled plate. The finishing rolling is carried out entirely in the ferrite region. The starting temperature of the finishing rolling is 880℃~910℃, the exit temperature of the finishing rolling is 800℃~820℃, and the coiling temperature is 600℃~620℃.

[0036] After the hot-rolled sheet is uncoiled, it is subjected to acid continuous rolling to produce a cold-rolled sheet with a thickness of 0.500±0.005mm;

[0037] The cold-rolled sheet is annealed at a temperature of 880℃~920℃ for a time of 70s±10s.

[0038] A second annealing process is performed, and the holding temperature during the second annealing is 800–820℃.

[0039] The iron loss P of the non-oriented silicon steel 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.72T.

[0040] Furthermore, the non-oriented silicon steel has a yield strength of 220–240 MPa, a tensile strength of 360–380 MPa, and an elongation of 25–35%.

[0041] The average grain size in the microstructure of the non-oriented silicon steel is 130–160 μm.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows: Based on the chemical composition, by adjusting the heating temperature, rolling temperature, and coiling temperature, the finishing rolling is completely in the ferrite region, and the resulting hot-rolled plate has a deformed ferrite structure. Compared with conventional technology (the conventional technology's hot rolling finishing entry is in the austenite phase region, the finishing exit is in the ferrite phase region, the finishing rolling process is rolled in the two-phase region, and the hot rolling stability is relatively poor), on the one hand, the hot rolling stability will be significantly improved. Specifically, (1) the rolling force of each of the 7-pass finishing rolling in hot rolling will be reduced, (2) the crown and wedge shape of the produced hot-rolled plate will be better. Since the plate crown and wedge shape are hereditary, the final cold-rolled plate's crown and wedge shape will also be better accordingly. On the other hand, the non-oriented silicon steel (i.e., white sheet) before secondary annealing has excellent mechanical properties, thus further improving the mechanical properties of the steel after stamping and stacking - secondary annealing. During the annealing process to produce the core of a fixed-frequency compressor motor, the excellent punching properties of the white sheet are ensured. Furthermore, the potential for reducing iron loss in the non-oriented silicon steel before secondary annealing is increased, improving the iron loss reduction rate after secondary annealing. Moreover, based on the above reasons, this invention allows for the relaxation of control requirements for magnetically harmful elements such as Nb, V, Ti, Cr, Ni, and Cu (i.e., a higher upper limit on their content) while ensuring the reduction potential for iron loss in the non-oriented silicon steel before secondary annealing, as well as other properties of the non-oriented silicon steel (such as mechanical properties). It also improves the uniformity of the microstructure, the uniformity and stability of the coiling performance, and ensures the sheet shape. Furthermore, this invention has low material costs, low production costs, and low production difficulty (including low steelmaking costs and difficulty, and low hot rolling costs and difficulty), thus improving production efficiency. Attached Figure Description

[0043] Figure 1 This is a metallographic photograph of the hot-rolled plate of Embodiment 4 of the present invention;

[0044] Figure 2 This is a metallographic photograph of the non-oriented silicon steel of Embodiment 4 of the present invention before secondary annealing (i.e., blank sheet);

[0045] Figure 3 This is a metallographic photograph of the non-oriented silicon steel of Embodiment 4 of the present invention after secondary annealing (i.e., black sheet).

[0046] Figure 4 The iron loss P of the non-oriented silicon steel in Embodiment 4 of this invention before secondary annealing (i.e., white sheet) during winding. 1.5 / 50 Fluctuation curve. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0048] One embodiment of the present invention provides a method for preparing non-oriented silicon steel, and a non-oriented silicon steel prepared by the method.

[0049] The chemical composition of the non-oriented silicon steel, by mass percentage, is as follows: C≤0.004%, S≤0.003%, N≤0.003%, Si:0.7%~1.0%, Al:0.42%~0.6%, Si / Al=1.5~1.7, Mn:0.1%~0.3%, P≤0.03%, Nb≤0.005%, V≤0.006%, Ti≤0.006%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, with the remainder being Fe and unavoidable impurities.

[0050] The method for preparing the non-oriented silicon steel includes:

[0051] Steelmaking and casting are carried out according to the chemical composition of the non-oriented silicon steel described above to obtain a continuous casting billet; wherein, in the steelmaking process, no other alloying elements are added except for Si, Al and Mn; furthermore, it can be understood that the chemical composition of the continuous casting billet is the same as that of the non-oriented silicon steel described above.

[0052] The continuously cast billet is heated to 1050℃~1100℃ and held for 180±30min. Then, it is first rough rolled into an intermediate billet, and then made into a hot-rolled plate through 7 passes of finishing rolling and coiling. The finishing rolling is carried out entirely in the ferrite region. The starting temperature of the finishing rolling is 880℃~910℃, the exit temperature of the finishing rolling is 800℃~820℃, and the coiling temperature is 600℃~620℃.

[0053] After the hot-rolled sheet is uncoiled, it is subjected to acid continuous rolling to produce a cold-rolled sheet with a thickness of 0.500±0.005mm;

[0054] The cold-rolled sheet is annealed at a temperature of 880℃~920℃ for a time of 70s±10s.

[0055] Thus, in one embodiment of the present invention, based on the chemical composition, the finishing rolling is carried out entirely in the ferrite region by adjusting the heating temperature, rolling temperature, and coiling temperature. Compared with conventional technology (the entry point of hot rolling finishing is in the austenite phase region, the exit point is in the ferrite phase region, the finishing rolling process is rolled in the two-phase region, and the hot rolling stability is relatively poor), on the one hand, the hot rolling stability is significantly improved. Specifically, (1) the rolling force of each of the 7-pass hot rolling finishing is reduced, (2) the crown and wedge shape of the produced hot-rolled plate are improved. Since the crown and wedge shape are hereditary, the crown and wedge shape of the final cold-rolled plate will also be improved accordingly. On the other hand, the non-oriented silicon steel (i.e., white sheet) before secondary annealing has excellent mechanical properties, and can be further processed into a fixed-frequency compressor by stamping and stacking and secondary annealing. In the process of making the motor core, the excellent stamping properties of the white sheet are ensured. Furthermore, the potential for reducing iron loss in the non-oriented silicon steel before secondary annealing is increased, improving the iron loss reduction rate after secondary annealing. Moreover, based on the above reasons, this invention can also ensure the potential for reducing iron loss in the non-oriented silicon steel before secondary annealing, and guarantee other properties of the non-oriented silicon steel (such as mechanical properties), while relaxing the control requirements for magnetically harmful elements such as Nb, V, Ti, Cr, Ni, and Cu (i.e., allowing for higher content limits), even with relaxed control requirements. It can also improve the uniformity of the microstructure, the uniformity and stability of the coiling performance, and ensure the sheet shape. Furthermore, this invention has low material costs, low production costs, and low difficulty (including low steelmaking costs and difficulty, and low hot rolling costs and difficulty), thus improving production efficiency.

[0056] Preferably, the thickness of the continuously cast billet is 200-240 mm, the thickness of the intermediate billet is 36-40 mm, and the thickness of the hot-rolled plate is 2.50-3.00 mm.

[0057] Preferably, the rolling forces for each of the 7 finishing rolling passes are as follows: F1: 11000~12000kN; F2: 10000~11000kN; F3: 9000~10000kN; F4: 10000~11000kN; F5: 8000~9000kN; F6: 7000~8000kN; F7: 6000~7000kN.

[0058] Preferably, the hot-rolled plate has a crown of ≤30μm and a wedge shape of ≤4μm.

[0059] Preferably, during the continuous acid rolling process, pickling is performed first, with a pickling speed of 160-180 m / min, an acid concentration of 110-150 g / L, and an acid temperature of 60-80°C.

[0060] Preferably, the cold-rolled sheet has a crown of ≤5μm and a wedge shape of ≤2μm.

[0061] Preferably, during the annealing process, the cold-rolled sheet is produced at a constant speed in a continuous annealing furnace in a mixed atmosphere of H2+N2, and the tension in the annealing furnace section is 6-10kN.

[0062] In addition, the preparation method further includes: after annealing, coating a layer with a thickness of 0.8 to 1.0 μm is applied to the surface of the steel plate, followed by drying and sintering at a drying temperature of 600 to 650°C and a sintering temperature of 530 to 580°C, for a total drying and sintering time of 20 to 25 seconds.

[0063] In one embodiment of the present invention, the obtained non-oriented silicon steel product is a product that has not undergone secondary annealing, and it can be referred to as non-oriented silicon steel white sheet.

[0064] Regarding the magnetic properties of the non-oriented silicon steel sheet: iron loss P 1.5 / 50 4.5~5.5W / kg, magnetic induction intensity B 5000 ≥1.73T; In terms of mechanical properties: yield strength is 250~270MPa, tensile strength is 380~400MPa, elongation is 25~35%; In terms of microstructure: its microstructure is a uniform equiaxed ferrite microstructure, grain size deviation is ≤40μm, and average grain size is 30~60μm.

[0065] In addition, the through-winding iron loss P of the non-oriented silicon steel 1.5 / 50 The fluctuation is ±0.2 W / kg.

[0066] Of course, further, the preparation method may also include: performing a secondary annealing, and the holding temperature during the secondary annealing is 800-820℃. Of course, the secondary annealing is performed after the "annealing" mentioned above, specifically after sintering (for example, obtaining non-oriented silicon steel white sheets by sequentially annealing, coating, drying, and sintering, and then performing secondary annealing to obtain the finished non-oriented silicon steel).

[0067] More preferably, the heating rate during the secondary annealing is 6–8 °C / s, the holding time is 2–3 h, and the cooling rate is 3–5 °C / s.

[0068] In one embodiment of the present invention, in contrast to secondary annealing, the resulting non-oriented silicon steel product is a product that has undergone secondary annealing, and it can be referred to as non-oriented silicon steel black sheet.

[0069] Regarding the magnetic properties of the non-oriented silicon steel black sheet: iron loss P 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.72T; In terms of mechanical properties: yield strength is 220~240MPa, tensile strength is 360~380MPa, elongation is 25~35%; In terms of microstructure: the average grain size is 130~160μm.

[0070] Furthermore, the iron loss P of the non-oriented silicon steel black sheet after secondary annealing is significantly lower than that before secondary annealing. 1.5 / 50 The reduction rate is over 30%, and the average grain size growth rate is over 300%.

[0071] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0072] The following four embodiments illustrate specific implementations of the present invention. Of course, these four embodiments are only a part of the numerous variations contained in the present invention, and not all of them. The specific implementation process of these embodiments is as follows:

[0073] (1) First, steelmaking is carried out. During the steelmaking process, no other alloying elements are added except for Si, Al and Mn. Then, the molten steel is cast to obtain a continuous casting billet. The chemical composition of the continuous casting billet is shown in Table 1.

[0074] [Table 1]

[0075]

[0076] (2) The continuously cast billet is heated to the heating temperature and held for 180±30 min. Then, it is first rough rolled into an intermediate billet, and then finished rolled and coiled in 7 passes to form a hot-rolled plate. The thickness of the continuously cast billet, heating temperature, intermediate billet thickness, finishing rolling start temperature, finishing rolling exit temperature, coiling temperature and hot-rolled plate thickness are shown in Table 2. The rolling force of each finishing rolling pass is shown in Table 3. [Table 2]

[0077]

[0078] [Table 3]

[0079]

[0080] Furthermore, metallographic analysis revealed that the microstructure of the hot-rolled plates obtained in all embodiments was deformed ferrite. The metallographic photograph of the hot-rolled plate in Example 4 is shown below. Figure 1 ;

[0081] (3) After the hot-rolled plate is uncoiled, it is subjected to continuous pickling. First, it is pickled at a speed of 160-180 m / min, an acid concentration of 110-150 g / L, and an acid temperature of 60-80℃. Then it is cold-rolled to produce a cold-rolled plate with a thickness of 0.500±0.005 mm. The crown and wedge shape of the hot-rolled plate and the crown and wedge shape of the cold-rolled plate are shown in Table 4.

[0082] [Table 4]

[0083]

[0084] (4) The cold-rolled sheet is annealed at a constant rate in a continuous annealing furnace in a mixed atmosphere of H2+N2. The annealing temperature is 880℃~920℃, the annealing time is 70s±10s, and the tension in the annealing furnace section is 6~10kN.

[0085] (5) After annealing, a coating with a thickness of 0.8 to 1.0 μm is applied to the surface of the steel plate, and then it is dried and sintered. The drying temperature is 600 to 650℃, the sintering temperature is 530 to 580℃, and the total drying and sintering time is 20 to 25 seconds.

[0086] (6) Perform secondary annealing, and the holding temperature during secondary annealing is 800~820℃, the heating rate is 6~8℃ / s, the holding time is 2~3h, and the cooling rate is 3~5℃ / s;

[0087] The microstructure and properties of the non-oriented silicon steel before secondary annealing were tested, and the results are shown in Table 5; the microstructure and properties of the non-oriented silicon steel after secondary annealing were tested, and the results are shown in Table 6.

[0088] [Table 5]

[0089]

[0090] [Table 6]

[0091]

[0092]

[0093] In addition, the metallographic images of the white and black slides in Example 4 are respectively referred to Figure 2 , Figure 3 Parameters of the iron loss fluctuation curve Figure 4 ;

[0094] As can be seen from the above embodiments, the non-oriented silicon steel white sheet (i.e., the non-oriented silicon steel in Table 3) has excellent sheet shape, uniformity of winding, and stability. The iron loss P of the non-oriented silicon steel black sheet after secondary annealing is significantly higher than that before secondary annealing. 1.5 / 50 The reduction rate is over 30%, and the average grain size growth rate is over 300%.

[0095] In summary, the beneficial effects of this invention are as follows: Based on the chemical composition, by adjusting the heating temperature, rolling temperature, and coiling temperature, the finishing rolling is completely in the ferrite region, and the resulting hot-rolled plate has a deformed ferrite structure. Compared with conventional technology (the conventional technology's hot rolling finishing entry is in the austenite phase region, the finishing exit is in the ferrite phase region, the finishing rolling process is rolled in the two-phase region, and the hot rolling stability is relatively poor), on the one hand, the hot rolling stability will be significantly improved. Specifically, (1) the rolling force of each of the 7-pass finishing rolling will be reduced, (2) the crown and wedge shape of the produced hot-rolled plate will be improved. Since the plate crown and wedge shape are hereditary, the final cold-rolled plate's crown and wedge shape will also be improved accordingly. On the other hand, the non-oriented silicon steel (i.e., white sheet) before secondary annealing has excellent mechanical properties, thus further improving the mechanical properties of the steel through stamping and stacking-secondary annealing. In the process of processing into the iron core of a fixed-frequency compressor motor, the excellent punching properties of the white sheet are ensured. Furthermore, the potential for reducing iron loss in the non-oriented silicon steel before secondary annealing is increased, improving the iron loss reduction rate after secondary annealing. Moreover, based on the above reasons, this invention can also ensure the potential for reducing iron loss in the non-oriented silicon steel before secondary annealing, and guarantee other properties of the non-oriented silicon steel (such as mechanical properties), while relaxing the control requirements for magnetically harmful elements such as Nb, V, Ti, Cr, Ni, and Cu (i.e., allowing for higher content limits), even with relaxed control requirements. It can also improve the uniformity of the microstructure, the uniformity and stability of the coiling performance, and ensure the sheet shape. Furthermore, this invention has low material costs, low production costs, and low difficulty (including low steelmaking costs and difficulty, and low hot rolling costs and difficulty), thus improving production efficiency.

Claims

1. A method for preparing non-oriented silicon steel, characterized in that, The preparation method includes: Steelmaking and casting are carried out to obtain continuously cast billets, the chemical composition of which, by mass percentage, is: C≤0.004%, S≤0.003%, N≤0.003%, Si:0.7%~1.0%, Al:0.42%~0.6%, Si / Al=1.5~1.7, Mn:0.1%~0.3%, P≤0.03%, Nb≤0.005%, V≤0.006%, Ti≤0.006%, Cr≤0.03%, Ni≤0.03%, Cu≤0.03%, with the remainder being Fe and unavoidable impurities; The continuously cast billet is heated to 1050℃~1100℃ and held for 180±30min. Then, it is first rough rolled into an intermediate billet, and then made into a hot-rolled plate through 7 passes of finishing rolling and coiling. The finishing rolling is carried out entirely in the ferrite region. The starting temperature of the finishing rolling is 880℃~910℃, the exit temperature of the finishing rolling is 800℃~820℃, and the coiling temperature is 600℃~620℃. After the hot-rolled sheet is uncoiled, it is subjected to acid continuous rolling to produce a cold-rolled sheet with a thickness of 0.500±0.005mm; The cold-rolled sheet is annealed at a temperature of 880℃~920℃ for a time of 70s±10s.

2. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, The microstructure of the hot-rolled plate is deformed ferrite, with a crown of ≤30μm and a wedge shape of ≤4μm.

3. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, The rolling forces for each pass of the 7-pass finishing mill are as follows: F1: 11000~12000kN; F2: 10000~11000kN; F3: 9000~10000kN; F4: 10000~11000kN; F5: 8000~9000kN; F6: 7000~8000kN; F7: 6000~7000kN.

4. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, During the continuous acid rolling process, pickling is performed first. The pickling speed is 160-180 m / min, the acid concentration is 110-150 g / L, and the acid temperature is 60-80℃.

5. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, The crown of cold-rolled sheet is ≤5μm, and the wedge shape of cold-rolled sheet is ≤2μm.

6. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, During the annealing process, the cold-rolled sheet is produced at a constant speed in a continuous annealing furnace in a mixed atmosphere of H2+N2, with a tension of 6-10kN in the annealing furnace section.

7. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, The preparation method further includes: after annealing, coating a layer with a thickness of 0.8 to 1.0 μm is applied to the surface of the steel plate, followed by drying and sintering at a drying temperature of 600 to 650°C and a sintering temperature of 530 to 580°C, with a total drying and sintering time of 20 to 25 seconds.

8. The method for preparing non-oriented silicon steel according to claim 1, characterized in that, The preparation method further includes: performing a second annealing, wherein the holding temperature during the second annealing is 800-820℃.

9. The method for preparing non-oriented silicon steel according to claim 8, characterized in that, The iron loss P of silicon steel after secondary annealing compared to before secondary annealing 1.5 / 50 The reduction rate is over 30%, and the average grain size growth rate is over 300%.

10. The method for preparing non-oriented silicon steel according to claim 8, characterized in that, The heating rate during secondary annealing is 6–8 °C / s, the holding time is 2–3 h, and the cooling rate is 3–5 °C / s.

11. A non-oriented silicon steel, characterized in that, The non-oriented silicon steel is prepared by the preparation method according to any one of claims 1 to 7; The iron loss P of the non-oriented silicon steel 1.5 / 50 4.5~5.5W / kg, magnetic induction intensity B 5000 ≥1.73T.

12. The non-oriented silicon steel according to claim 11, characterized in that, The non-oriented silicon steel has a yield strength of 250-270 MPa, a tensile strength of 380-400 MPa, and an elongation of 25-35%. The microstructure of the non-oriented silicon steel is equiaxed ferrite with a grain size deviation of ≤40μm and an average grain size of 30-60μm. The iron loss P during the winding of the non-oriented silicon steel 1.5 / 50 The fluctuation is ±0.2 W / kg.

13. A non-oriented silicon steel, characterized in that, The non-oriented silicon steel is prepared by the preparation method according to any one of claims 8 to 10; The iron loss P of the non-oriented silicon steel 1.5 / 50 ≤3.8W / kg, magnetic induction intensity B 5000 ≥1.72T.

14. The non-oriented silicon steel according to claim 13, characterized in that, The non-oriented silicon steel has a yield strength of 220-240 MPa, a tensile strength of 360-380 MPa, and an elongation of 25-35%. The average grain size in the microstructure of the non-oriented silicon steel is 130–160 μm.

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