Method for controlling edge cracks of high-silicon electrical steel

Abstract

The invention relates to a method for controlling edge cracks of high-silicon electrical steel, and belongs to the technical field of high-silicon electrical steel. The method comprises the following steps that S1, continuous casting is conducted on a plate blank; the continuous casting comprises slab width control and corner grain and temperature control, and the technological parameters of slab width control are as follows: the pulling speed is 0.8 m / min-1 m / min, the superheat degree of a tundish is 25-30 DEG C, the cooling strength is 0.8-1.5 L / kg, and the width coefficient of a crystallizer is 0.995-1.005; the corner grain and temperature control is realized through primary cooling in a crystallizer and secondary cooling in a fan-shaped section; s2, the slab subjected to continuous casting in the step S1 is heated; the heating is divided into three stages, the temperature of the preheating stage is 1190-1210 DEG C, the temperature of the heating stage is 1100-1150 DEG C, and the temperature of the heating stage is 1290-1390 DEG C; and S3, rough rolling and finish rolling are conducted on the plate blank heated in the S2, the high-silicon electrical steel with the excellent edge structure and edge quality is obtained, and the technical problem that in the industry, in the large-scale production process of the high-silicon electrical steel, hot-rolled coil plate edge cracks exist for a long time is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-silicon electrical steel, and in particular relates to a method for controlling edge cracks of high-silicon electrical steel. Background Art

[0002] As an important iron core material, electrical steel is widely used in the power industry. The traditional thick slab process is the main method for industrial production of grain-oriented electrical steel. According to the heating temperature, it can be divided into slab high-temperature heating and slab low-temperature heating processes. The high-temperature copper-containing grain-oriented electrical steel production process adopts low carbon content, high silicon (3.30%), high manganese content, low aluminum content and Cu with a mass fraction of about 0.5% in the composition design, with Cu2S (or ε-Cu) + AlN as an inhibitor. The slab is heated at high temperature, and then hot-rolled and cold-rolled twice. Decarburization is carried out during intermediate annealing. After the secondary cold rolling, MgO is coated for high-temperature annealing. The finished product has excellent magnetic properties.

[0003] In order to obtain excellent magnetic properties, the slabs in the hot rolling production process of grain-oriented electrical steel need to be heated at high temperature to ensure that the inhibitors are fully dissolved. Compared with ordinary carbon steel, the slab furnace temperature is increased by about 100°C. After high-temperature heating, the grains of the slabs grow abnormally coarse, and even grain boundary oxidation occurs, so the material is very brittle. Many factors in each link of the production process may have a significant impact on edge cracks. The industry has regarded the elimination of edge cracks in electrical steel with a silicon content of more than 3.0% as a long-term and arduous topic for technical research and development.

[0004] At present, the main measures taken by major steel mills at home and abroad to address this problem are as follows: First, implement edge heating of the intermediate billet. The hot rolling production line uses an edge heater to compensate for the edge temperature of the intermediate billet to prevent edge defects in the subsequent rolling process caused by low slab temperature and poor plasticity. Second, adjust the rough rolling reduction rate. Based on the hot rolling production line under the conditions of a fixed-width press and multiple vertical roller units, a large side pressure process system is adopted in the rear section of rough rolling to concentrate the side pressure load on the last two vertical roller mills for continuous rolling. At this time, the thickness of the rolled piece is small and the temperature is relatively low. The increase in deformation resistance on both sides will promote edge recrystallization. Third, control the heating conditions of the slab, reduce the heating temperature and the time in the furnace, control the protective atmosphere, and reduce the degree of decarburization.

[0005] However, the existing methods still have the following disadvantages: First, the hot rolling production line uses edge heaters, which have a certain positive contribution to improving the edge quality of high-silicon steel grades, but the investment is huge (more than 100 million yuan). If the edge heater function is not reserved at the beginning of the hot rolling production line design, the subsequent addition will be limited by the existing production line conditions, such as insufficient space, conflict with existing equipment, etc., resulting in greater investment. In addition, the use of edge heaters will increase the edge drop of the strip as the edge temperature of the strip increases, the edge drop area of ​​the hot coil will increase significantly, and the convexity hit rate will decrease, which will seriously affect the requirements of the next process for the raw material plate shape. Second, the large side pressure technology in the back stage of rough rolling has certain requirements for the implementation of the production line equipment. It is suitable for production lines that have more control means over the width of the slab, such as the production line should have a fixed-width press, at least 2 vertical roller units, etc. for production lines with a width of more than 1580mm. For the 1450mm production line without a fixed-width press and only one vertical roller unit, this process has no guiding role. Moreover, the side pressure capacity of the 1450mm wide hot-rolled strip production line is limited. The large side pressure technology in the back stage must ensure that the total side pressure of the rough rolling unit is sufficient and stable. If the total measured amount is very small, even if it is 100% allocated to the back stage, the side pressure amount is very small, and the purpose of large side pressure cannot be achieved.

[0006] In order to improve the edge cracking of hot rolling, some steel mills reduce the heating temperature and furnace time. Although this practice has a great effect on improving the edge cracking of hot rolling, it also affects the magnetic properties of the finished product. For example, the core of grain-oriented electrical steel production is to eventually form a strong Gaussian texture. One of the main technical means is to control the inhibitors. The high temperature and long time heating during the hot rolling process is to ensure the full solid solution of the inhibitors under the inherent component system, so as to obtain the excellent magnetic properties of the final product. Therefore, this move will greatly reduce the hit rate of the brand number. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method for controlling edge cracks of high-silicon electrical steel, which is based on thick slabs and produces high-silicon varieties (silicon content ≥ 3.0%) such as high-temperature copper-containing grain-oriented electrical steel under the condition of hot rolling without edge heaters. The edge crack defects of hot-rolled coils are eliminated by controlling the slab width, corner grains and temperature in the continuous casting process and combining heating and rolling processes.

[0008] The object of the present invention is to provide a method for controlling edge cracks in high silicon electrical steel, comprising the following steps:

[0009] S1. Continuously casting the slab; the continuous casting includes slab width control, corner grain and temperature control, and the process parameters of the slab width control are: drawing speed is 0.8m / min-1m / min, tundish superheat is 25℃-30℃, cooling intensity is 0.8L / kg-1.5L / kg, and crystallizer width coefficient is 0.995-1.005; the corner grain and temperature control is achieved by primary cooling in the crystallizer and secondary cooling in the fan-shaped segment; the water flow rate of the primary cooling is 15m / s-35m / s; the secondary cooling is divided into three modules, the first module sets the cooling water flow rate of zone 1-2 to 600L / min-800L / min, the second module sets the cooling water flow rate of zone 3-5 to 30L / min-100L / min, and the third module cancels the cooling of zone 6-9;

[0010] S2, heating the slab after continuous casting in S1; the heating is divided into three stages, the temperature of the preheating section is 1190°C-1210°C, the temperature of the heating section is 1100°C-1150°C, and the temperature of the heating section is 1290-1390°C;

[0011] S3, performing rough rolling and finish rolling on the slab heated in S2.

[0012] In one embodiment of the present invention, in S1, the slab width is mainly affected by the superheat of the tundish, the pulling speed and the cooling intensity. The superheat of the tundish is proportional to the slab width, that is, the higher the superheat of the tundish, the wider the slab width; the pulling speed is proportional to the slab width, that is, the faster the pulling speed, the wider the slab width; the cooling intensity is inversely proportional to the slab width, that is, the greater the cooling intensity, the narrower the slab width.

[0013] In one embodiment of the present invention, in S1, the element composition of the slab and its mass percentage are: Si 3.0%-3.5%, C 0.030%-0.045%, Mn 0.18%-0.23%, P 0-0.015%, S 0.006%-0.010%, N 0.008%-0.012%, and the balance is other inevitable impurities and iron.

[0014] In one embodiment of the present invention, in S1, the slab has a thickness of 203 mm to 213 mm, a width of 700 mm to 1320 mm, and a length of 8000 mm to 12500 mm.

[0015] In one embodiment of the present invention, in S1, the surface grains at the corners of the slab are controlled to be within 25 μm by controlling the corner grains and temperature, and the corner temperature when exiting the fan-shaped segment is 600° C.-800° C.

[0016] In one embodiment of the present invention, in S2, the charging temperature of the slab is 500°C-700°C, and the charging distance is 50mm-120mm.

[0017] In one embodiment of the present invention, in S2, the heating rate of temperature increase and the cooling rate of temperature decrease are independently 0.5°C / min-1.5°C / min.

[0018] In one embodiment of the present invention, in S2, during the heating process, the temperature difference between the head, middle and tail of the slab and the temperature difference in the surface are independently within 15°C.

[0019] In one embodiment of the present invention, in S2, during the heating process, the residual oxygen content in the furnace is 0.5%-3.5%, and the calorific value of the coal gas is 7000KJ / m 3 -8000KJ / m 3 , the pressure before the main gas pipeline regulating valve is 8Kpa-15Kpa.

[0020] In one embodiment of the present invention, in S3, the rough rolling is performed in 5 passes, the reduction rates of the first 4 passes are independently 15%-38%, the reduction rate of the 5th pass is 25%-50%, the thickness of the intermediate billet after rough rolling is 32mm-48mm, the temperature of the narrow surfaces on both sides of the intermediate billet is 1050℃-1200℃; the temperature difference between the head and tail of the intermediate billet is within 150℃.

[0021] In one embodiment of the present invention, in S3, the finish rolling is performed by 7 passes, the cumulative reduction rate of the last 3 passes is 35%-55%, and the reduction rate of the last pass is 1%-12%.

[0022] The technical solution of the present invention has the following advantages over the prior art:

[0023] (1) The method described in the present invention uses thick slabs to produce high-silicon electrical steel hot-rolled coil products. Under the condition that the hot rolling production line does not have an intermediate slab edge heating device, the slab width control, corner grain and temperature control, combined with heating and rolling processes during the continuous casting process are performed to obtain high-silicon electrical steel with excellent edge structure and edge quality. The technical problem of hot-rolled coil edge cracking that has long existed in the industry during the large-scale production of high-silicon electrical steel is solved, and hot-rolled coils with excellent edge quality are provided for the next process, reducing the huge cost investment in the intermediate slab edge heating device for solving the hot rolling edge cracking under traditional process conditions.

[0024] (2) The hot rolling production line of the method described in the present invention does not need to increase the investment in edge heaters due to improving edge cracks, thereby reducing investment; it avoids the problem of edge degradation caused by investing in edge heaters to solve the edge cracking of high-silicon electrical steel; it is applicable to working conditions under ambient temperatures above -35°C, has a significant effect on improving edge cracks, and is suitable for steel mills in all regions of the country; it does not need to reduce factors such as steel burning temperature and time that play a crucial role in the magnetic properties of the final product to improve edge cracks, thereby ensuring the excellent magnetic properties of the final product of grain-oriented high-silicon electrical steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 This is a physical picture of the transmission side of the hot coil of high-silicon electrical steel in Test Example 1 of the present invention; wherein the left picture is Example 1, and the right picture is Comparative Example 1;

[0027] Figure 2 This is a splicing diagram of the metallographic structures of the operating side and the transmission side of the high-silicon electrical steel of Test Example 2 of the present invention; wherein the upper figure is Example 1, and the lower figure is Comparative Example 1. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0029] Example 1

[0030] The method for controlling edge cracking of high silicon electrical steel of the present embodiment specifically comprises the following steps:

[0031] S1. Slab selection

[0032] Composition: Si 3.21%, C 0.04%, Mn 0.2%, P 0.01%, S 0.008%, N 0.01%, the balance is other inevitable impurities and iron;

[0033] Size: thickness is about 208mm, width is about 1090mm, length is about 10960mm;

[0034] Slab shape: the warp is about 18mm, the buckle is about 8mm, and the sickle bend is about 20mm.

[0035] S2. Continuous casting process

[0036] S21: The process parameters for slab width control are shown in Table 1:

[0037] Table 1

[0038]

[0039] S22: Corner grain and temperature control is achieved through primary cooling in the crystallizer and secondary cooling in the fan-shaped segment; the surface grain of the slab corner is controlled to be within 25μm, and the corner temperature when leaving the fan-shaped segment is about 700℃. The specific process is as follows:

[0040] The water flow rate for primary cooling is 25m / s;

[0041] In the 1st and 2nd zones of secondary cooling, high-efficiency cooling nozzles are installed, and the cooling water flow rate is 700L / min; the edge cooling nozzles in the 3rd, 4th and 5th zones are individually controlled, and the water flow rate of the edge cooling nozzles is controlled to 80L / min; the edge cooling of the slab is cancelled in the 6th, 7th, 8th and 9th zones.

[0042] S3. Heating process

[0043] S31, furnace charging control: adopt large-scale walking beam heating furnace for heating, ensure that the slab charging temperature is 559℃, the residence time on the furnace roller is 2min, and the charging spacing is set to 100mm.

[0044] S32, Steel Burning Control:

[0045] The furnace is slightly positively pressure controlled, the residual oxygen content is 2.5%, and the calorific value of the gas is 7500KJ / m 3 , the pressure before the main gas pipeline regulating valve is 10Kpa;

[0046] The total time in the furnace is 270 minutes, the temperature of the preheating section is 1200°C, the temperature of the heating section is 1118°C, the temperature of the heating section is 1292°C, the total time of the heating section is 126 minutes, and the temperature change rate is 1.38°C / min;

[0047] The temperature difference between the head, middle and tail of the slab and the temperature difference in the table is about 10℃.

[0048] S4, rolling process

[0049] S41, Rough rolling process

[0050] Unit selection: E1 vertical roll mill + R1 four-roller reversible roughing mill, without intermediate billet edge heater;

[0051] Descaling is used after the furnace, only one pass of descaling is used in the rough rolling, and descaling is not used in the finishing rolling;

[0052] The side pressure of the vertical roller in three passes is: E1 is 48.32mm, E3 is 47.00mm, and E5 is 12mm;

[0053] Five rolling passes were used, with reduction ratios of 18.50%, 21.69%, 24.43%, 24.77%, and 35.69% respectively;

[0054] The thickness of the intermediate billet after rough rolling is 40mm, the temperature of the narrow surface on both sides of the intermediate billet is 1100℃, the temperature difference between the head and the tail is about 100℃, and the actual width of the finished product is 1071mm;

[0055] S42, finishing process

[0056] Unit selection: 7-stand four-roller irreversible fully hydraulic rolling mill;

[0057] Seven rolling passes are adopted, with the cumulative reduction rate of the last three passes being 40% and the reduction rate of the last pass being 8%.

[0058] Example 2

[0059] The method for controlling edge cracking of high silicon electrical steel of the present embodiment specifically comprises the following steps:

[0060] S1. Slab selection

[0061] Composition: Si 3.23%, C 0.035%, Mn 0.21%, P 0.08%, S 0.009%, N 0.011%, the balance is other inevitable impurities and iron;

[0062] Size: thickness is about 208mm, width is about 1140mm, length is about 11600mm;

[0063] Slab shape: the warp is about 18mm, the buckle is about 8mm, and the sickle bend is about 20mm.

[0064] S2. Continuous casting process

[0065] S21: The process parameters for slab width control are shown in Table 2:

[0066] Table 2

[0067]

[0068] S22: Corner grain and temperature control is achieved through primary cooling in the crystallizer and secondary cooling in the fan-shaped segment; the surface grain of the slab corner is controlled to be within 25μm, and the corner temperature when leaving the fan-shaped segment is about 700℃. The specific process is as follows:

[0069] The water flow rate for primary cooling is 25m / s;

[0070] In the 1st and 2nd zones of secondary cooling, high-efficiency cooling nozzles are installed, and the cooling water flow rate is 700L / min; the edge cooling nozzles in the 3rd, 4th and 5th zones are individually controlled, and the water flow rate of the edge cooling nozzles is controlled to 80L / min; the edge cooling of the slab is cancelled in the 6th, 7th, 8th and 9th zones.

[0071] S3. Heating process

[0072] S31, furnace charging control: adopt large-scale walking beam heating furnace for heating, ensure that the slab charging temperature is 612℃, the residence time on the furnace roller is 2min, and the charging spacing is set to 100mm.

[0073] S32, Steel Burning Control:

[0074] The furnace is slightly positively pressure controlled, the residual oxygen content is 2.3%, and the calorific value of the gas is 7500KJ / m 3 , the pressure before the main gas pipeline regulating valve is 10Kpa;

[0075] The total time in the furnace is 330 minutes, the temperature of the preheating section is 1200°C, the temperature of the heating section is 1125°C, the temperature of the heating section is 1293°C, the total time of the heating section is 115 minutes, and the temperature change rate is 1.46°C / min;

[0076] The temperature difference between the head, middle and tail of the slab and the temperature difference in the table is about 10℃.

[0077] S4, rolling process

[0078] S41, Rough rolling process

[0079] Unit selection: E1 vertical roll mill + R1 four-roller reversible roughing mill, without intermediate billet edge heater;

[0080] Descaling is used after the furnace, only one pass of descaling is used in the rough rolling, and descaling is not used in the finishing rolling;

[0081] The side pressure of the vertical roller in three passes is: E1 is 42.30mm, E3 is 39.52mm, and E5 is 15mm;

[0082] Five rolling passes were used, with reduction rates of 18.44%, 20.65%, 23.57%, 27.15%, and 39.2% respectively;

[0083] The thickness of the intermediate billet after rough rolling is 40mm, the temperature of the narrow surface on both sides of the intermediate billet is 1100℃, the temperature difference between the head and the tail is about 100℃, and the actual width of the finished product is 1115mm;

[0084] S42, finishing process

[0085] Unit selection: 7-stand four-roller irreversible fully hydraulic rolling mill;

[0086] Seven rolling passes are adopted, with the cumulative reduction rate of the last three passes being 40% and the reduction rate of the last pass being 8%.

[0087] Comparative Example 1

[0088] Basically the same as Example 1, except that the process parameters for controlling the slab width are: the pulling speed is 1.2 m / min, and the cooling intensity is 0.7 L / kg;

[0089] Test Example 1

[0090] The transmission side of the high silicon electrical steel of Example 1 (first group) and Comparative Example 1 is as follows: Figure 1 As shown, except for a small number of small edge cracks on the inner and outer rings of the transmission side of the high-silicon electrical steel of Example 1, no large edge cracks were observed on the rest; severe serrated cracks were observed on the transmission side of the high-silicon electrical steel of Comparative Example 1, and the edges were obviously deformed and thinned, with deep scratches on the surface.

[0091] Test Example 2

[0092] The high silicon electrical steel of Example 1 (first group) and Comparative Example 1 was subjected to metallographic electron microscopy. The transverse cross-section samples of the vertical edges were taken for metallographic electron microscopy. From the edge of the strip to the middle, the metallographic structure was spliced ​​every 1.5 mm. The metallographic structure splicing results of the operating side and the transmission side edge are shown in the figure. Figure 2 As shown, the fibrous unrecrystallized structure of the high-silicon electrical steel in Example 1 appears on the surface, with a length of only 9 mm, and the single-sided shearing amount of the disc shear of the pickling unit is only 15 mm; the lengths of the fibrous unrecrystallized structure of the high-silicon electrical steel in Comparative Example 1 are as high as 21 mm and 16.5 mm, respectively. The fibrous unrecrystallized structure is the root cause of edge cracks. The single-sided shearing amount of the pickling unit must be ≥25 mm to completely remove the abnormal structure at the edge, and new edge cracks will not occur at the cold-rolled edge.

[0093] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for controlling edge cracking of high silicon electrical steel, characterized in that: The following steps are involved: S1. Continuously casting the slab; the continuous casting includes slab width control, corner grain and temperature control, and the process parameters of the slab width control are: drawing speed is 0.8m / min-1m / min, tundish superheat is 25℃-30℃, cooling intensity is 0.8L / kg-1.5L / kg, and crystallizer width coefficient is 0.995-1.005; the corner grain and temperature control is achieved by primary cooling in the crystallizer and secondary cooling in the fan-shaped segment; the water flow rate of the primary cooling is 15m / s-35m / s; the secondary cooling is divided into three modules, the first module sets the cooling water flow rate of zone 1-2 to 600L / min-800L / min, the second module sets the cooling water flow rate of zone 3-5 to 30L / min-100L / min, and the third module cancels the cooling of zone 6-9; S2, heating the slab after continuous casting in S1; the heating is divided into three stages, the temperature of the preheating section is 1190°C-1210°C, the temperature of the heating section is 1100°C-1150°C, and the temperature of the heating section is 1290-1390°C; S3, performing rough rolling and finish rolling on the slab heated in S2.

2. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S1, the element composition and mass percentage of the slab are: Si 3.0%-3.5%, C 0.030%-0.045%, Mn 0.18%-0.23%, P 0-0.015%, S 0.006%-0.010%, N 0.008%-0.012%, and the balance is other inevitable impurities and iron.

3. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S1, the slab has a thickness of 203 mm to 213 mm, a width of 700 mm to 1320 mm, and a length of 8000 mm to 12500 mm.

4. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S1, the surface grains at the corners of the slab are controlled to be within 25 μm by controlling the corner grains and temperature, and the corner temperature when leaving the fan-shaped segment is 600°C-800°C.

5. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S2, the charging temperature of the slab is 500°C-700°C, and the charging distance is 50mm-120mm.

6. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S2, the heating temperature increase rate and the cooling rate are independently 0.5°C / min-1.5°C / min.

7. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S2, during the heating process, the temperature difference between the head, middle and tail of the slab and the temperature difference in the surface are independently within 15°C.

8. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S2, during the heating process, the residual oxygen content in the furnace is 0.5%-3.5%, and the calorific value of the gas is 7000KJ / m 3 -8000KJ / m 3 , the pressure before the main gas pipeline regulating valve is 8Kpa-15Kpa.

9. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S3, the rough rolling is performed in 5 passes, the reduction rates of the first 4 passes are independently 15%-38%, the reduction rate of the 5th pass is 25%-50%, the thickness of the intermediate billet after rough rolling is 32mm-48mm, the temperature of the narrow surfaces on both sides of the intermediate billet is 1050℃-1200℃; the temperature difference between the head and tail of the intermediate billet is within 150℃.

10. The method for controlling edge cracks of high silicon electrical steel according to claim 1, characterized in that: In S3, the finish rolling is performed by 7 passes, the cumulative reduction rate of the last 3 passes is 35%-55%, and the reduction rate of the last pass is 1%-12%.

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