Production method for improving longitudinal magnetic property uniformity of low-temperature high-magnetic-induction oriented silicon steel coil

Abstract

The application discloses a production method for improving the longitudinal magnetic property uniformity of low-temperature high-magnetic-induction oriented silicon steel coils, and the method comprises the following steps: after converter smelting, the molten steel is treated by RH refining and then is poured into a slab by protective casting; the slab is heated and then is hot-rolled; the heating temperature is 1120-1250 DEG C, the temperature after finish rolling is greater than or equal to 920 DEG C, and the hot-rolled plate is rapidly water-cooled to below 600 DEG C after finish rolling; after the hot-rolled plate is normally normalized by a conventional two-stage normalizing method, the hot-rolled plate is once cold-rolled to a target thickness, then is subjected to decarburization annealing and nitriding treatment; after nitriding, the steel coil is coated with magnesium oxide release agent and is subjected to high-temperature annealing in an annular furnace; after high-temperature annealing, the steel coil is subjected to hot stretching and flattening and is coated with an insulating coating, and the iron loss of the steel coil is detected on line at the outlet side; the steel coil is subjected to laser marking or is directly sent to a product cutting and packaging device; and the longitudinal magnetic property uniformity of the steel coil is significantly improved by strictly controlling the temperature after the finish rolling machine, the heating speed during the decarburization annealing process and the total amount of nitriding, and simultaneously matching a suitable high-temperature annealing atmosphere protection system, and the longitudinal magnetic property difference is controlled to be within 3%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a production method of low-temperature high-magnetic-susceptibility oriented silicon steel. BACKGROUND

[0002] The oriented silicon steel is an important soft magnetic alloy indispensable in the electric power, electronic and military industries, and is also an important metal functional material for energy saving, and is mainly used for manufacturing various electric power transformers, distribution transformers and large-scale generator stators, and has the characteristics of high magnetic susceptibility and low iron loss. The production and manufacturing technology of the oriented silicon steel is relatively mature, and can be generally divided into a general oriented silicon steel manufacturing method, a high-temperature heating oriented silicon steel manufacturing method and a low-temperature heating oriented silicon steel manufacturing method. At present, the low-temperature heating oriented silicon steel has obtained high attention in the world due to low production cost and excellent product performance, and many domestic and foreign manufacturers have already possessed or are developing the manufacturing technology of the low-temperature heating high-magnetic-susceptibility oriented silicon steel. The low-temperature heating high-magnetic-susceptibility oriented silicon steel does not use AlN precipitated before decarburization annealing as an inhibitor, that is, does not use "inherent inhibitor", but carries out nitriding treatment after decarburization annealing, so that N and the inhibitor formed by Al in the steel, that is, the inhibitor obtained in the later process, are relied on. This technology can reduce the heating temperature of the cast blank to 1150-1200 DEG C, and a large amount of work was carried out according to this technology in 1987, and the high-temperature heating production process was completely abandoned in 1996.

[0003] The production process of the low-temperature heating high-magnetic-susceptibility oriented silicon steel has been matured through development for more than 20 years, and at present, the production process of the low-temperature heating high-magnetic-susceptibility oriented silicon steel is as follows: converter smelting, RH vacuum refining, continuous casting, low-temperature heating hot rolling, normalizing and pickling, cold rolling, decarburization annealing and nitriding, coating of isolation agent, high-temperature annealing, hot stretching and smoothing and coating of insulation coating, laser marking, finished product shearing and packaging.

[0004] In the low-temperature heating hot rolling process, when heated to the process set temperature, AlN is uniformly dissolved (AlN starts to dissolve at 1000°C), and part of the AlN is precipitated in the finishing rolling stage. Due to the temperature difference in the length direction of the slab or hot rolled coil, especially the head and tail, during hot rolling heating and finishing rolling, the AlN precipitation is uneven, and the final product magnetic properties are also uneven to varying degrees. Rapid heating during decarburization annealing can increase the energy storage required for recrystallization, making the primary grains uniform and increasing the number of secondary grain nuclei on the surface and preventing the growth of other direction grains. At the same time, match the appropriate nitriding amount, and the secondary grain growth is sufficient during high-temperature annealing, and the magnetic properties are uniform. If the primary grain size is not uniform after decarburization annealing and the nitriding amount is too high or too low, it is easy to cause the secondary recrystallization starting temperature of the middle and head and tail of the coil to be inconsistent, and the longitudinal magnetic properties of the coil are greatly different. During high-temperature annealing, especially during the heating stage, due to the large volume of the coil, the use of magnesium oxide isolation agent causes long heat transfer time, and there is a temperature difference between different parts of the coil. The inner and outer circles of the coil are less affected by heat transfer and heat up quickly, while the middle of the coil heats up slowly. The heating system at different positions of the coil is different, and the atmosphere is also significantly different. These differences will lead to the evolution of the inhibitor and the difference in strength in the steel strip, resulting in differences in the secondary recrystallization starting temperature and grain growth state, and finally causing differences in the magnetic properties of the inner and outer circles of the coil. Specifically, after high-temperature annealing, the on-line iron loss detection value of the coil during hot leveling and stretching production has a significant difference in the longitudinal direction of the coil. Generally, the on-line iron loss detection value of the head and tail of the coil is higher, and the on-line iron loss detection value of the middle part of the coil is lower, which is commonly referred to as iron loss head and tail tilt. There are also coils with low on-line iron loss detection values at the head and tail, and high on-line iron loss detection values in the middle part, which are commonly referred to as iron loss bulging.

[0005] Through literature retrieval on the uniformity of coil magnetic properties, the following contents are mainly included:

[0006] CN108004376A discloses a production method of low-temperature high-magnetic-sensing oriented silicon steel with longitudinal magnetic property uniformity. The method mainly controls the concentration of acid-soluble aluminum [Als] in the cast slab to be 250-320ppm, and the concentration of residual aluminum [Alr] to be 100-160ppm. During the decarburization annealing process, process adjustment is made to each coil from the middle of the coil at a distance L from the tail of the coil to the end of the coil production. The adjustment content mainly includes one of the decarburization temperature or the heating temperature or the reduction section temperature or the extension of the annealing time. The invention can reduce the difference in magnetic properties of the head and tail and improve the magnetic property level of the head and tail of the coil, and the difference can be reduced to within 5%.

[0007] CN113106224A discloses a method for improving the uniformity of iron loss of non-oriented silicon steel, which adopts mutually matched coiling temperature, annealing temperature and holding time, so that the uneven grain problem of hot-rolled plate caused by the low head and tail of the strip steel under high coiling temperature is eliminated in the annealing process, and the grains at the head and tail of the strip steel are fully grown under the specific annealing temperature and annealing holding time, so that the grain size tends to be consistent with that of the middle part of the strip steel, so that the strip steel has uniform magnetic properties in the longitudinal direction. After the implementation of the patent, the on-line P 1.0 / 50 The difference is 0.062-0.188W / kg, and the iron loss of non-oriented silicon steel is more uniform.

[0008] Japanese Laid-Open Patent Publication (Hei 8-311560 (1996)) discloses a production method for improving the length direction magnetic property difference of finished steel coil, which considers that the magnetic property difference of finished steel coil in the length direction is mainly caused by the temperature difference when the steel coil is heated. The normal high temperature annealing process has a highest point of 17℃ / h and a lowest point of 2.5℃ / h in the temperature rising speed between 1000-1100℃, and the finished product △P 17 =0.06W / kg. The invention patent heats at 10℃ / h to 1100℃ after holding for about 17h at about 1000℃, at which time the highest point of the temperature rising speed is 11℃ / h and the lowest point is 10℃ / h, and the finished product △P 17 =0.02W / kg, and the magnetic property of the steel coil in the length direction is obviously improved.

[0009] The uneven distribution of the longitudinal magnetic property of the steel coil is a common phenomenon, which is mainly caused by the existing production process of oriented silicon steel, such as the influence of the head and tail temperature difference on the uniformity of AlN precipitation during hot rolling, the difference in the temperature rising speed and atmosphere between the inside and outside of the steel coil during high temperature annealing, etc. Under the premise of not changing the existing low temperature oriented silicon steel production process, only by improving the process control level can the longitudinal magnetic property uniformity be reduced. The head and tail cutting waste, repeated sampling detection, poor performance stability of the transformer core made by the user caused by the uneven longitudinal magnetic property of the steel coil, especially the head and tail magnetic property difference, become problems to be solved. SUMMARY

[0010] The present application aims to provide a production method for improving the longitudinal magnetic property uniformity of low temperature high magnetic induction oriented silicon steel coil, which strictly controls the temperature after the finishing mill, the temperature rising speed during the decarburization annealing process and the total amount of nitriding, and simultaneously matches the appropriate high temperature annealing atmosphere protection system, so as to significantly improve the longitudinal magnetic property uniformity of the steel coil, and control the longitudinal magnetic property difference within 3%.

[0011] In order to achieve the above-mentioned purpose, the technical scheme is as follows:

[0012] The production method for improving the longitudinal magnetic property uniformity of low temperature high magnetic induction oriented silicon steel coil comprises the following steps:

[0013] 1) Converter smelting after RH refining treatment, continuous casting protection pouring into slab;

[0014] 2) slab after heating hot rolling; wherein the heating temperature is 1120-1250 °C, the temperature after finish rolling is ≥920 °C, and the fast water cooling after finish rolling is below 600 °C;

[0015] 3) hot rolled plate after conventional two-stage normalizing, once cold rolling to target thickness, then decarburization annealing and nitriding treatment;

[0016] 4) after nitriding, the steel coil is coated with magnesium oxide separator to high temperature annealing in a ring furnace;

[0017] 5) after high temperature annealing, hot stretch leveling and insulating coating are carried out, and iron loss on-line detection is carried out on the outlet side;

[0018] 6) the steel coil is laser marked or directly sent to product cutting and packaging.

[0019] According to the above scheme, in step 2, the heating temperature is 1120-1180 °C, the temperature after finish rolling is ≥935 °C, and the fast water cooling after finish rolling is 530-580 °C.

[0020] According to the above scheme, in step 3, the temperature rising speed above 500 °C in the decarburization annealing temperature rising stage reaches 13 °C / s or more.

[0021] According to the above scheme, in step 3, the total amount of nitrogen content in the steel strip after nitriding is controlled in the range of ([Alr]+[N0])±10ppm, wherein [Alr]=[Als]-27 / 14×[N0], and [N0] is the nitrogen content before nitriding of the steel strip.

[0022] According to the above scheme, in step 4, N2 ratio greater than 50% protective atmosphere is used before high temperature annealing is raised to 930 °C, and conventional AX protective atmosphere is used after 930 °C.

[0023] The reason why the hot rolling heating temperature is 1120-1250℃ and the temperature after finish rolling is ≥920℃ is to avoid uneven precipitation of AlN in the length direction of the hot rolling plate. When the low-temperature oriented silicon steel cast blank is heated at 1120-1250℃, AlN is not completely solid-solved, and is still in a two-phase region, and the distribution of AlN is also uneven. Because the solid solubility of AlN in the γ phase is higher than that in the α phase, the AlN precipitated in the α phase is more coarsened. Therefore, the heating temperature is as high as possible to make the proportion of the γ phase highest. The rough rolling process also breaks the coarse grains in the continuous casting blank to make the structure more uniform, and a small amount of sulfides such as MnS is precipitated along the dislocations in the finish rolling process, and a small amount of AlN is also precipitated with MnS as the particle. The temperature after finish rolling is greater than 920℃, which can reduce the precipitation of AlN and make the size of the precipitated AlN appropriate. When the temperature after finish rolling is less than 920℃, the size of the precipitated AlN will increase, and it is difficult to high-temperature solid-solution during subsequent normalizing, which causes the number of inhibition to decrease. Rapid water cooling to below 600℃ after finish rolling is also to prevent the precipitation of AlN.

[0024] The present application requires that the temperature rising speed of the decarburization annealing rising stage is greater than or equal to 13℃ / s and the total nitrogen content of the steel strip after nitriding is controlled in the range of ([Alr]+[N0])±10ppm, in order to ensure that the grains are more uniform after decarburization annealing, and to inhibit the number and size of the grains and match the subsequent high-temperature secondary recrystallization process. The rapid temperature rising in the decarburization annealing stage can improve the energy storage required for recrystallization, make the primary grains uniform, increase the number of secondary crystal nuclei in the surface layer, and prevent the growth of grains in other directions, reduce the size of secondary grains, and reduce P17. Low-temperature high-magnetic-induction oriented silicon steel cold-rolled plates generally occur at a temperature above 500℃. In the recovery grain growth stage, rapid temperature rising can make the grains grow rapidly and uniformly, avoid some grains being too large, and rapid temperature rising can also prevent the growth of grains in other directions. When the temperature rising speed is less than 13℃ / s at a temperature above 500℃ in the decarburization annealing stage, the uniformity of the primary grain size is poor, the temperature rising speed of the steel coil head and tail is fast in the subsequent high-temperature annealing stage, and the secondary recrystallization starts early, and the secondary grain orientation is poor, resulting in poor magnetic properties. Controlling the total nitrogen content of the steel strip after nitriding in the range of ([Alr]+[N0])±10ppm is to match the inhibition force and the secondary recrystallization starting temperature in the high-temperature annealing stage to ensure complete secondary recrystallization. After nitriding in the decarburization annealing stage, most of the nitrogen exists in the form of unstable nitrides such as Si3N4 and (Si,Mn)N in the surface layer of the steel strip, and in the high-temperature annealing stage, Si3N4 and (Si,Mn)N decompose and diffuse, (Al,Si)N is precipitated in the thickness direction of the steel strip, and AlN is precipitated at 900-1000℃. Research shows that as the total nitrogen content increases, the inhibition force increases, the secondary recrystallization starting temperature increases, and the finished product B800 increases. Because AlN inhibitors are finally formed after nitriding, the total nitrogen content should match the Alr in the steel strip to form appropriate AlN inhibitors. If the total nitrogen content is too high, the inhibitors will be too strong or the inhibitors will be coarsened, and the secondary recrystallization starting temperature in the middle of the steel coil will be too high during high-temperature annealing, causing incomplete secondary recrystallization and poor magnetic properties in the middle. If the nitrogen content is too low, the inhibition force is weak, and the secondary recrystallization starts early in the head and tail of the steel coil during high-temperature annealing, resulting in poor magnetic properties in the head and tail due to poor secondary grain orientation.

[0025] The reason why the N2 proportion in the protective atmosphere is greater than 50% before the high-temperature annealing temperature reaches 930 DEG C in the application is to reduce the inhibitor reduction caused by the atmosphere oxidation at the head and tail of the steel coil. The atmosphere during the high-temperature annealing process has a great influence on the secondary recrystallization and magnetism of the low-temperature high-magnetic-induction oriented silicon steel. If the nitrogen content in the protective atmosphere is too low, the free nitrogen in the steel strip will run away and cannot form fine AlN, so that the inhibition is weakened. If the nitrogen content in the protective atmosphere is appropriate, N2 and H2 are first adsorbed on the surface of the steel strip, rely on iron as a catalyst, form NH3 through the reaction of 3H2+N2→2NH3, and then decompose the NH3 to make the steel strip nitrided, so that a batch of new fine AlN is formed in the steel to strengthen the inhibition. During the high-temperature annealing stage, the NH3 decomposition and nitriding efficiency is high when the temperature is below 930 DEG C, and the NH3 decomposition and nitriding efficiency is low and can be ignored when the temperature is above 930 DEG C. During the high-temperature annealing stage, the head and tail of the steel coil are in full contact with the protective atmosphere. If the N2 proportion in the protective atmosphere is less than 50% before 930 DEG C, the inhibitor at the head and tail of the steel coil will be reduced due to oxidation, which causes the inhibition at the head and tail of the steel strip to be weak and the secondary recrystallization to occur in advance, and the secondary recrystallization orientation is poor and the magnetic performance is poor. If the N2 proportion in the protective atmosphere is greater than 50% before 930 DEG C, partial nitriding reaction can occur, which can make up for the loss of the inhibitor at the head and tail of the steel coil due to oxidation, the inhibitor strength is consistent in the length direction of the steel coil, and the uniformity of the final product magnetic performance is significantly improved.

[0026] Compared with the prior art, the application has the following beneficial effects:

[0027] The application significantly improves the longitudinal magnetic performance uniformity of the steel coil and controls the longitudinal magnetic performance difference within 3% by strictly controlling the temperature after the finishing mill, the temperature rising speed during the decarburization annealing process and the total amount of nitriding, and matching the appropriate high-temperature annealing atmosphere protection system.

[0028] After the application is implemented, the head and tail cutting waste or small coil caused by the non-uniform magnetic performance can be reduced, the on-site yield and production efficiency are improved, unnecessary repeated sampling and detection are reduced, and the longitudinal magnetic performance uniform steel coil also provides a guarantee for the stable performance of the downstream transformer core. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 : Example 4 and Comparative Example 4 online iron loss detection value comparison. DETAILED DESCRIPTION

[0030] The following examples further illustrate the technical solutions of the application, but do not limit the protection scope of the application.

[0031] The specific embodiment provides a production method for improving the longitudinal magnetic performance uniformity of a low-temperature high-magnetic-induction oriented silicon steel coil, and the main steps are as follows:

[0032] 1) After the converter smelting, the RH refining treatment is performed, and the slab is cast by protective casting;

[0033] 2) The slab is heated to a temperature of 1120-1250°C and hot-rolled, and the temperature after finish rolling is ≥920°C;

[0034] 3) The hot-rolled plate is once cold-rolled to the target thickness after conventional two-stage normalizing, and then decarburization annealing and nitriding treatment are performed, and the heating rate during the decarburization annealing stage must reach ≥13°C / s above 500°C; after decarburization, nitriding treatment is performed, and the total amount of nitrogen content in the steel strip after nitriding is controlled in the range of ([Alr]+[N0])±10ppm, wherein [Alr]=[Als]-27 / 14×[N0], and [N0] is the nitrogen content before nitriding of the steel strip;

[0035] 4) After nitriding, the steel coil is coated with magnesium oxide separator and annealed in a high-temperature furnace, and the protective atmosphere before heating to 930°C uses N2 with a proportion of more than 50%, and the conventional AX protective atmosphere is used after 930°C;

[0036] 5) After high-temperature annealing, hot-stretch leveling and insulating coating are performed, and iron loss on-line detection is performed on the outlet side;

[0037] 6) The steel coil is laser marked or directly sent to perform finished product cutting and packaging.

[0038] Example 1

[0039] A low-temperature high-magnetic-induction oriented silicon steel is smelted by using a conventional smelting process, and 10 slabs are cast by continuous casting. The acid-soluble aluminum [Als] in the smelted steel composition is 268ppm, and the residual aluminum [Alr]=[Als]-27 / 14×[N]=129ppm. The 10 slabs are heated to 1120-1250°C and held for a certain period of time, and then rolled into hot-rolled coils. Then, the key processes are shown in Table 1, such as pickling normalizing, once cold rolling, decarburization annealing and nitriding, high-temperature ring furnace annealing, hot-stretch leveling, laser marking and cutting and packaging.

[0040] Table 1 Key process parameters of examples and comparative examples

[0041]

[0042]

[0043] In the online iron loss curve evaluation, the iron loss value of the head and tail of the steel coil is more than 5% higher than the middle iron loss value, which is called head and tail tilt. Under the condition of the same steel composition of the same furnace, the temperature after finish rolling is controlled to be higher than 920℃ to avoid the difference in the amount of AlN precipitated at the head and tail of the hot-rolled coil. At the same time, the temperature rising speed at the decarburization annealing stage is controlled to be greater than 13℃ / s at a temperature higher than 500℃, the total amount of nitrogen permeation is 201±10ppm ([Alr]+[N0]=201ppm), the N2 proportion in the protective atmosphere is greater than 50% at the high temperature annealing in the ring furnace at a temperature lower than 930℃, the longitudinal magnetic properties of the final steel coil are uniform, the deviation between the head and tail iron loss value and the middle iron loss value is within 5% in the online iron loss detection, and the online iron loss detection curve is flat.

[0044] Example 2

[0045] After the conventional smelting of low-temperature high-magnetic-induction oriented silicon steel, the slab is cast into a plate, the plate is rolled into a hot-rolled coil after being kept at a temperature of 1120-1250℃ for a certain time, and the temperature after finish rolling is controlled to be higher than 920℃. Then the coil is subjected to the processes of pickling normalizing, primary cold rolling, decarburization annealing and nitrogen permeation, high-temperature ring furnace annealing, hot tensile leveling, laser marking and shearing packaging, etc. The magnetic properties of the coil are detected by taking samples from the head, middle and tail of the coil in the length direction at the shearing process.

[0046] Table 2 Key process and magnetic property detection results of examples and comparative examples

[0047]

[0048] In Example 2, the total nitrogen content range of the steel strip after nitrogen permeation is determined according to the steelmaking composition ([Alr]+[N0]), the temperature rising speed at the decarburization annealing stage is controlled to be higher than 13℃ / s at a temperature higher than 500℃, the N2 proportion in the protective atmosphere is greater than 50% at the high temperature annealing in the ring furnace at a temperature lower than 930℃, and the magnetic properties of the coil are detected by taking samples from the head, middle and tail of the coil in the length direction at the shearing process. The longitudinal magnetic property difference ΔP 17 / 50 can be controlled to be within 3%. Figure 1 For the comparison of the online iron loss detection values of Example 4 and Comparative Example 4, the online iron loss detection value of the steel coil in the length direction of 2000-7000 meters of Comparative Example 4 is 0.86W / kg, while the online iron loss detection value at the head and tail is more than 1.00W / kg, and the longitudinal magnetic property difference is more than 10.0%; the online iron loss detection value of the middle part of the steel coil of Example 4 is 0.838W / kg, the maximum online iron loss detection value at the head and tail is 0.855W / kg, and the longitudinal magnetic property difference is about 2.0%. The longitudinal magnetic property difference of the steel coils of Example 4 and Comparative Example 4 after shearing is shown in Table 2, which is basically consistent with the online iron loss detection value.

[0049] The above examples are only the best examples, and are not limited to the embodiments of the present application.

Claims

1. A production method for improving the longitudinal magnetic property uniformity of a low temperature high magnetic induction oriented silicon steel coil, characterized by The method comprises the following steps: 1) After converter smelting, RH refining treatment and continuous casting protection pouring into slab; 2) Hot rolling after heating, wherein the heating temperature is 1120-1250℃, the temperature after finishing rolling is ≥920℃, and the temperature after rapid water cooling is below 600℃; 3) After the hot-rolled plate is conventionally normalized in two stages, it is once cold-rolled to the target thickness, then decarburization annealing and nitriding treatment are carried out; the heating speed of the decarburization annealing is above 13℃ / s at 500℃; the total amount of nitrogen content of the steel strip after nitriding is controlled in the range of ([Alr]+[N0])±10ppm, wherein [Alr]=[Als]-27 / 14×[N0], and [N0] is the nitrogen content before nitriding of the steel strip; 4) After nitriding, the steel coil is coated with magnesium oxide release agent to high-temperature annealing in a ring furnace; Before high-temperature annealing is heated to 930℃, a protective atmosphere with N2 ratio greater than 50% is used, and after 930℃, a conventional AX protective atmosphere is used; 5) After high-temperature annealing, hot stretching and flattening and insulating coating are carried out, and iron loss on-line detection is carried out on the outlet side; 6) The steel coil is laser marked or directly sent to perform finished product cutting and packaging.

2. The production method of improving the longitudinal magnetic property uniformity of a low temperature high magnetic induction oriented silicon steel coil according to claim 1, characterized by In step 2, the heating temperature is 1120-1180℃, the temperature after finishing rolling is ≥935℃, and the temperature after rapid water cooling is 530-580℃.

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