An ultra-thin non-oriented electrical steel having a thickness of 0.3 mm or less and a production method thereof

Abstract

The application discloses a kind of 0.3mm thickness below ultra-thin non-oriented electrical steel and its production method, the chemical composition of the ultra-thin non-oriented electrical steel and percentage by weight are as follows:Als 0.70~0.95%, Si=(1.4~1.6)*Als+2%, C+S+N≤0.0060%, P≤0.0040%, Sn 0.040~0.070%, Mn 0.2~0.5%, the rest is Fe and inevitable impurities;Its production method includes the following steps: continuous casting-hot rolling-normalization-primary cold rolling-intermediate annealing-secondary cold rolling-final annealing;It has low iron loss, high magnetic induction and has excellent mechanical properties, the iron loss P 1.0 / 400 of the ultra-thin non-oriented electrical steel is 10~14W / kg, the magnetic induction B 5000 of the ultra-thin non-oriented electrical steel is ≥1.69T, the yield strength R P0.2 of the ultra-thin non-oriented electrical steel is 400~480MPa, the tensile strength R m of the ultra-thin non-oriented electrical steel is 520~600MPa, and the elongation A 50 of the ultra-thin non-oriented electrical steel is 15~20%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of non-oriented electrical steel, and particularly relates to a 0.3mm-thick ultra-thin non-oriented electrical steel and a production method thereof. BACKGROUND

[0002] The non-oriented electrical steel is mainly applied to parts such as motor rotors, compressors and generators. At present, the production of the electrical steel is performed by using a process route of converter-RH-continuous casting-hot rolling-normalizing-cold rolling-annealing, but this production method is usually used for producing the non-oriented electrical steel with a general thickness (0.5mm or more). If the process route is used for producing the ultra-thin non-oriented electrical steel with a thickness of 0.3mm or less, work hardening is prone to occurring in the rolling process, which is not conducive to cold rolling. Meanwhile, the reduction of the thickness of the ultra-thin non-oriented silicon steel is too large, which exceeds the beneficial reduction range of 75-85% of the rolling process, and thus the proportion of the adverse texture (111) generated in the rolling process is increased, and the electromagnetic performance of the product is deteriorated.

[0003] The thinner the thickness of the silicon steel finished product is, the lower the core loss is. According to the calculation formula of the eddy current loss, the thickness reduction can greatly reduce the eddy current loss of the silicon steel, but at the same time, the magnetic polarization intensity is gradually reduced, which is not conducive to the improvement of the driving power of the motor. How to reduce the core loss while considering the magnetic polarization intensity and ensuring the driving power of the motor is a technical problem to be solved at present. SUMMARY

[0004] To solve the above technical problems, the present application provides a 0.3mm-thick ultra-thin non-oriented electrical steel and a production method thereof, which have low iron loss, high magnetic induction and excellent mechanical properties.

[0005] The technical scheme adopted by the present application is as follows:

[0006] The 0.3mm-thick ultra-thin non-oriented electrical steel has the following chemical components and weight percentages: Als 0.70-0.95%, Si=(1.4-1.6)*Als+2%, C+S+N≤0.0060%, P≤0.0040%, Sn 0.040-0.070%, Mn 0.2-0.5%, and the rest is Fe and inevitable impurities.

[0007] The metallographic structure of the ultra-thin non-oriented electrical steel is ferrite; the grain size is 100-150μm; and the volume percentage of the favorable texture {110} is ≥15%.

[0008] The iron loss P 1.0 / 400 of the ultra-thin non-oriented electrical steel is 10-14W / kg, the magnetic induction B 5000 is ≥1.69T, and the yield strength R P0.2400-480 MPa, tensile strength R m 520-600 MPa, elongation A 50 15-20%.

[0009] The application further provides a production method of the ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm, which comprises the following steps: continuous casting-hot rolling-normalizing-primary cold rolling-intermediate annealing-secondary cold rolling-final annealing; the reduction rates of the hot rolling, the primary cold rolling and the secondary cold rolling are 98.9-99.1%, 55.0-76.0% and 50.0-78.0%, respectively.

[0010] In the continuous casting step, 2-3 pairs of electromagnetic stirring rollers are turned on, the current of the electromagnetic stirring rollers is controlled to be 350-500 A, the frequency is controlled to be 3.0-4.5 Hz, and the volume percentage of the equiaxed crystal of the casting blank is controlled to be more than 45%. By controlling the stirring amount, the current and the frequency of the electromagnetic stirring and other parameters, the proportion of the equiaxed crystal is controlled to be more than 45%, so that the proportion of the columnar crystal is prevented from being too high to cause the corrugated defect of the steel coil product; and the subsequent hot rolling with a large reduction rate is matched, so that the proportion of the beneficial texture {110} is increased to be more than 10% after the hot rolling is completed, and the electromagnetic performance is improved.

[0011] Further, in the continuous casting step, the thickness of the casting blank is 230 mm.

[0012] In the hot rolling step, the heating temperature is controlled to be 1100-1200 ℃, the heating time is controlled to be 150-220 min, the time in the soaking section is controlled to be 30-60 min, and the casting blank discharge temperature is controlled to be 1050-1150 ℃.

[0013] In the hot rolling step, the temperature after the rough rolling is completed is 920-1000 ℃, the temperature after the finish rolling is completed is 800-880 ℃, and the water cooling is performed to 550-630 ℃ for coiling.

[0014] Further, in the hot rolling step, the finish rolling is performed to a thickness of 2.0-2.5 mm. The rough rolling is performed by R1 and R2 groups; and the finish rolling is performed by 7 rolling groups.

[0015] In the normalizing step, the normalizing treatment is performed under the conditions of heating at 860-900 ℃ for 30-50 s, and the grain size of the hot coiled product after the normalizing is controlled to be 90-120 μm.

[0016] Further, after the normalizing, the steps of shot blasting and pickling are further included. The oxide layer on the surface of the steel coil is deepened after the steel coil passes through the normalizing furnace, the oxide layer on the surface of the steel coil is broken by spraying fine steel shots on the surface of the steel coil by the shot blasting machine, and thus the oxide scale on the surface of the steel coil can be removed after the steel coil enters the pickling tank for pickling.

[0017] In the first cold rolling step, the concentration of the emulsion is controlled at 4.0-5.5%, the saponification value is above 100, and the residual oil and iron on the surface of the strip after rolling are controlled within 250 mg / m².

[0018] The concentration of the emulsion refers to the concentration of the emulsion in the demineralized water after it is mixed with the directly purchased emulsion.

[0019] Furthermore, in a single cold rolling step, a 20-roll mill with a roll diameter of 60-80mm is used for rolling; the thickness is rolled to 0.6-0.9mm.

[0020] In the intermediate annealing step, the steel coil is annealed in a bell-type annealing furnace. The furnace is protected with a reducing atmosphere. The annealing temperature is controlled at 780-850℃, the holding time is controlled at 15-24h, and the coil is cooled by slow cooling inside the bell. After cooling to 80℃, the steel coil is air-cooled.

[0021] The term "in-enclosure slow cooling" refers to air cooling directly inside the enclosure without providing any heat or cold source.

[0022] Furthermore, the reducing atmosphere is hydrogen.

[0023] In the secondary cold rolling step, the product is rolled to a thickness of 0.2-0.3 mm.

[0024] Furthermore, in the secondary cold rolling step, a 20-roll mill with a roll diameter of 60-80mm is used for rolling.

[0025] In the final annealing step, a nitrogen-hydrogen mixture is used for protection, and the dew point temperature is controlled below -30℃; the heating temperature of the RTF section is controlled at 900~1000℃, and the heating time is controlled at 50~100s; the temperature of the soaking section is controlled at 950~1050℃, and the holding time is controlled at 30~50s.

[0026] Furthermore, in the final annealing step, the volume percentage of hydrogen in the nitrogen-hydrogen mixture is 5-20%.

[0027] Furthermore, the final annealing step is preceded by alkaline washing, brushing, and water washing steps.

[0028] The ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm provided by this invention controls the content of Si and Al in its composition mainly to improve the resistivity of silicon steel products, effectively reduce iron loss, and ensure the mechanical properties of the material. The residual element C+S+N is controlled to be ≤0.0060%. The lower the residual element content, the better to prevent the precipitation of the second phase and promote grain growth. The addition of Sn can promote grain boundary segregation, grain coarsening, hinder the formation of {111} texture, promote the generation of {110} texture, and at the same time cause grain boundary strengthening and solid solution strength, so as to improve the mechanical properties of non-oriented electrical steel.

[0029] The composition of the ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm provided by this invention determines the Si content based on the Al content. A high Al content can reduce the ductility of silicon steel, while a properly matched Si content facilitates rolling, reducing cracks and breakage during rolling. Furthermore, Al and Si can increase resistivity, playing a crucial role in reducing iron loss. Simultaneously, Si also improves the mechanical properties of the product. Mn increases resistivity, but its effect is relatively weaker than Si, and it also improves the mechanical properties of the steel. By controlling the Si, Mn, and Sn content in the steel, the yield strength RP0.2 of the non-oriented electrical steel is controlled at 400–480 MPa, Rm at 520–600 MPa, and elongation A50 at 15–20%. These mechanical properties ensure that the finished non-oriented electrical steel is not easily deformed during use.

[0030] In the production method of ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm provided by the present invention, the proportion of columnar crystals and equiaxed crystals is increased by controlling the electromagnetic stirring parameters of continuous casting and the large reduction rate of hot rolling. Furthermore, the proportion of the favorable texture {110} is retained or even increased by more than 10% through the rolling with a large reduction rate of hot rolling, thereby improving the electromagnetic properties.

[0031] During the cold rolling stage, work hardening caused by high reduction rate rolling is avoided by first cold rolling after normalization with reduction rates of 55.0–76.0% and 50.0–78.0% respectively, and second rolling after intermediate annealing. At the same time, by reasonably controlling the reduction rate of the two cold rolling processes and the annealing process, a suitable grain size can be obtained to increase the proportion of the favorable texture {110} to more than 15%, thereby improving the electromagnetic properties.

[0032] To ensure good surface quality of the strip steel, this invention uses a bell-type annealing furnace for annealing. By controlling the concentration of the emulsion, the saponification value, and the amount of residual oil and iron on the surface of the strip steel after rolling in a 20-roll mill, the protective atmosphere inside the bell-type furnace is coordinated to achieve the effect of cleaning the surface of the strip steel, ensuring the cleanliness of the strip steel plate surface after bell-type annealing, which is more cost-effective than conventional production.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This invention provides an ultrathin non-oriented electrical steel with a thickness of less than 0.3 mm. Its ultrathin thickness reduces iron loss, and through process control, ensures a finished grain size of 100-150 μm, with a favorable {110} texture proportion exceeding 15%, thus guaranteeing the magnetic induction B of the ultrathin non-oriented electrical steel. 5000 It has a strength of ≥1.69T and also possesses excellent mechanical properties. Attached Figure Description

[0035] Figure 1 This is a grain size diagram of the finished non-oriented electrical steel in Example 1;

[0036] Figure 2 The equiaxed crystal ratio of the billet in Example 1;

[0037] Figure 3 This is a texture diagram of the finished non-oriented electrical steel in Example 1. Detailed Implementation

[0038] This invention provides an ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm. The chemical composition and weight percentage of the ultra-thin non-oriented electrical steel are as follows: Als 0.70~0.95%, Si=(1.4~1.6)*Als+2%, C+S+N≤0.0060%, P≤0.0040%, Sn 0.040~0.070%, Mn 0.2~0.5%, with the remainder being Fe and unavoidable impurities.

[0039] The production method of the ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm includes the following steps: continuous casting—hot rolling—normalizing—first cold rolling—intermediate annealing—second cold rolling—final annealing; the reduction rates of the hot rolling, first cold rolling, and second cold rolling are 98.9-99.1%, 55.0-76.0%, and 50.0-78.0%, respectively.

[0040] In the continuous casting step, by turning on 2 to 3 pairs of electromagnetic stirring rollers and simultaneously controlling the current of the electromagnetic stirring rollers to be 350-500A and the frequency to be 3.0-4.5Hz, the volume percentage of equiaxed crystals in the billet is controlled to be above 45%.

[0041] Furthermore, in the continuous casting step, the thickness of the billet is 230 mm.

[0042] In the hot rolling step, the heating temperature is controlled at 1100-1200℃, the heating time is controlled at 150-220min, the soaking time is controlled at 30-60min, and the billet exit temperature is controlled at 1050-1150℃.

[0043] In the hot rolling step, the temperature after rough rolling is 920-1000℃, and the temperature after finish rolling is 800-880℃; the coil is then water-cooled to 550-630℃.

[0044] Furthermore, in the hot rolling step, the finish rolling is performed to a thickness of 2.0-2.5 mm. The rough rolling is carried out using R1 and R2 mills; the finish rolling is performed using a 7-stand mill.

[0045] In the normalization step, the normalization conditions are: heating and holding at 860-900℃ for 30-50s, and the grain size of the hot-rolled coil is controlled at 90-120μm after normalization.

[0046] Furthermore, after normalization, the process also includes shot blasting and pickling steps.

[0047] In the first cold rolling step, a 20-roll mill with a roll diameter of 60-80mm is used for rolling; the strip is rolled to a thickness of 0.6-0.9mm; the concentration of the emulsion is controlled at 4.0-5.5%, the saponification value is above 100, and the residual oil and iron on the surface of the strip after rolling are controlled to be within 250mg / ㎡.

[0048] In the intermediate annealing step, the steel coil is annealed in a bell-type annealing furnace. The furnace is protected with a reducing atmosphere. The annealing temperature is controlled at 780-850℃, the holding time is controlled at 15-24h, and the coil is cooled by slow cooling inside the bell. After cooling to 80℃, the steel coil is air-cooled.

[0049] Furthermore, the reducing atmosphere is hydrogen.

[0050] In the secondary cold rolling step, the product is rolled to a thickness of 0.2-0.3 mm.

[0051] Furthermore, in the secondary cold rolling step, a 20-roll mill with a roll diameter of 60-80mm is used for rolling.

[0052] In the final annealing step, a nitrogen-hydrogen mixture is used for protection, and the dew point temperature is controlled below -30℃; the heating temperature of the RTF section is controlled at 900~1000℃, and the heating time is controlled at 50~100s; the temperature of the soaking section is controlled at 950~1050℃, and the holding time is controlled at 30~50s.

[0053] Furthermore, in the final annealing step, the volume percentage of hydrogen in the nitrogen-hydrogen mixture is 5-20%.

[0054] Furthermore, the final annealing step is preceded by alkaline washing, brushing, and water washing steps.

[0055] The present invention will now be described in detail with reference to the embodiments.

[0056] The composition and weight percentage of the non-oriented electrical steel in each embodiment and comparative example are shown in Table 1.

[0057] Table 1

[0058] C Si Mn Als Sn S N P Example 1 0.0015 3.18 0.34 0.75 0.056 0.0018 0.0018 0.0025 Example 2 0.0021 3.28 0.42 0.82 0.062 0.0021 0.0017 0.0022 Example 3 0.0018 3.32 0.39 0.86 0.058 0.0019 0.0021 0.0018 Comparative Example 1 0.0022 2.85 0.36 0.65 0.035 0.0022 0.0016 0.0024 Comparative Example 2 0.0017 3.26 0.40 0.81 0.055 0.0025 0.0018 0.0031 Comparative Example 3 0.0019 3.29 0.34 0.89 0.052 0.0020 0.0019 0.0019 Comparative Example 4 0.0026 3.34 0.38 0.88 0.062 0.0015 0.0019 0.0021

[0059] The non-oriented electrical steel in each embodiment and Comparative Examples 1-3 was produced through the following process steps: continuous casting into a 230mm thick billet, hot rolling to a thickness of 2.0-2.5mm, normalizing, cold rolling once to a thickness of 0.6-0.9mm, intermediate annealing, cold rolling twice to a thickness of 0.2-0.3mm, and final annealing.

[0060] The non-oriented electrical steel in Comparative Example 4 was produced through the following process steps: continuous casting into a 230mm thick billet, hot rolling to a thickness of 2.0-2.5mm, normalizing and pickling, cold rolling into a finished product with a thickness of 0.2-0.3mm, and final annealing.

[0061] The production process parameters of the non-oriented electrical steel in each embodiment and comparative example are shown in Table 2.

[0062] Table 2

[0063]

[0064] The properties of the non-oriented electrical steel produced in each embodiment and comparative example are shown in Table 3.

[0065] Table 3

[0066]

[0067] In Comparative Example 1, the low Al content and Si content outside the range of (1.4-1.6)Als+2% resulted in low resistivity. The electromagnetic properties of the finished product, P1.0 / 400, were higher than the target range. However, the low alloy content also led to lower yield and tensile strength, which was detrimental to subsequent customer use. In Comparative Example 2, the equiaxed crystal ratio of the billet was below the range of 40-60, resulting in low {110} texture in the finished product, which affected its electromagnetic properties. Due to the high columnar crystal ratio, corrugated defects appeared on the surface. In Comparative Example 3, the improper control of the emulsion concentration in the 20-roll mill resulted in high residual oil and iron on the rolled surface. These residues could not be reduced by H2 in the bell-type annealing furnace, leading to a dirty surface on the rolled product and affecting its use. In Comparative Example 4, the product was rolled directly in one cold rolling process without two cold rolling processes, resulting in low and uneven grain size and low magnetic induction intensity B5000, which affected the driving force of the motor.

[0068] The above detailed description of an ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm and its production method, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. An ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm, characterized in that, The chemical composition and weight percentage of the ultra-thin non-oriented electrical steel are as follows: Als 0.70~0.95%, Si=(1.4~1.6)*Als+2%, C+S+N≤0.0060%, P≤0.0040%, Sn 0.040~0.070%, Mn 0.2~0.5%, with the remainder being Fe and unavoidable impurities; The microstructure of the ultrathin non-oriented electrical steel is ferrite with a grain size of 100-150 μm, and the volume percentage of the favorable texture {110} is above 15%. The iron loss P of the ultra-thin non-oriented electrical steel 1.0 / 400 10~14W / kg, magnetic induction B 5000 ≥1.69T, yield strength R P0.2 The tensile strength is 400~480MPa, and the tensile strength R is... m The strength is 520~600MPa, and the elongation is A. 50 It is 15-20%; The production method of ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm includes the following steps: continuous casting—hot rolling—normalizing—first cold rolling—intermediate annealing—second cold rolling—final annealing; the reduction rates of hot rolling, first cold rolling, and second cold rolling are 98.9~99.1%, 55.0~76.0%, and 50.0~78.0%, respectively.

2. The method for producing ultra-thin non-oriented electrical steel with a thickness of less than 0.3 mm as described in claim 1, characterized in that, The production method includes the following steps: continuous casting—hot rolling—normalizing—first cold rolling—intermediate annealing—second cold rolling—final annealing.

3. The production method according to claim 2, characterized in that, In the continuous casting step, the volume percentage of equiaxed crystals in the billet is 45% or more.

4. The production method according to claim 2, characterized in that, In the hot rolling step, the heating temperature is controlled at 1100~1200℃, the heating time is controlled at 150min~220min, the soaking time is controlled at 30~60min, and the billet exit temperature is controlled at 1050~1150℃.

5. The production method according to claim 2, characterized in that, In the hot rolling step, the roughing temperature is 920~1000℃, the finishing temperature is 800~880℃, and the coiling is carried out after water cooling to 550~630℃.

6. The production method according to claim 2, characterized in that, In the normalization step, the normalization conditions are: heating and holding at 860~900℃ for 30~50s.

7. The production method according to claim 2, characterized in that, In the first cold rolling step, the concentration of the emulsion is controlled at 4.0~5.5%, the saponification value is above 100, and the residual oil and iron on the surface of the strip after rolling are controlled within 250mg / ㎡.

8. The production method according to claim 2, characterized in that, In the intermediate annealing step, a reducing atmosphere is used for protection, the annealing temperature is controlled at 780~850℃, the holding time is controlled at 15~24h, and then the cooling is carried out by slow cooling inside the enclosure.

9. The production method according to claim 2, characterized in that, In the secondary cold rolling step, the product is rolled to a thickness of 0.2~0.3mm.

10. The production method according to claim 2, characterized in that, In the final annealing step, a nitrogen-hydrogen mixture is used for protection, and the dew point temperature is controlled below -30℃; the heating temperature of the RTF section is controlled at 900~1000℃, and the heating time is controlled at 50~100s; the temperature of the soaking section is controlled at 950~1050℃, and the holding time is controlled at 30~50s.

Images