A method of controlling edge cracking of high silicon electrical steel

Abstract

The present application relates to a kind of method for controlling high silicon electrical steel edge crack, belong to high silicon electrical steel technical field.The method of the present application includes the following steps: S1, slab is continuously cast;Continuous casting includes slab width control, corner grain and temperature control, and the process parameters of slab width control are as follows: the drawing speed is 0.8m / min-1m / min, the tundish superheat is 25℃-30℃, the cooling intensity is 0.8L / kg-1.5L / kg, and the width coefficient of crystallizer is 0.995-1.005;Corner grain and temperature control are realized by once cooling in crystallizer and secondary cooling in fan-shaped section;S2, the slab after continuously casting in S1 is heated;Heating is divided into three stages, and the temperature of preheating section is 1190℃-1210℃, the temperature of entering heating section is 1100℃-1150℃, and the temperature of exiting heating section is 1290-1390℃;S3, the slab after heating in S2 is roughed and finished, and high silicon electrical steel with excellent edge structure and edge quality is obtained, solve the technical problem of long-existing hot-rolled coil edge crack in the process of large-scale production of high silicon electrical steel in the industry.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-silicon electrical steel, and particularly relates to a method for controlling edge cracks of high-silicon electrical steel. BACKGROUND

[0002] Electrical steel is an important core material and 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 a low-carbon content, high-silicon (3.30%), high-manganese content, low-aluminum content, and a mass fraction of about 0.5% Cu. The Cu2S (or ε-Cu) + AlN is used as an inhibitor. The slab is heated at high temperature, hot rolled, and then subjected to secondary cold rolling. Decarburization is performed during intermediate annealing. After secondary cold rolling, MgO is coated for high-temperature annealing. The finished product has very excellent magnetic properties.

[0003] To obtain excellent magnetic properties, the slab needs to be heated at high temperature during the hot rolling production process of grain-oriented electrical steel to ensure that the inhibitor is fully dissolved. Compared with plain carbon steel, the slab discharge temperature is increased by about 100℃. The grains of the slab heated at high temperature grow abnormally large, and even grain boundary oxidation occurs. Therefore, the material is very brittle, and many factors in each link of the production process can have a significant impact on edge cracks. The industry has long regarded the elimination of edge cracks in electrical steel containing more than 3.0% silicon as a long-term and arduous task for technical research and development.

[0004] At present, major steel plants at home and abroad mainly adopt the following means to solve this problem: first, implement intermediate slab edge heating. The edge heater is used in the hot rolling production line to compensate for the temperature of the intermediate slab edge, prevent the generation of edge defects in the subsequent rolling process due to low slab temperature and poor plasticity. Second, adjust the rough rolling reduction rate. Based on the conditions of the hot rolling production line with a fixed width press and multiple stand roller units, the large side pressure process system is used after rough rolling to concentrate the side pressure load on the last two stand roller mills for continuous rolling. At this time, the thickness of the rolled piece is small, and the temperature is relatively low. The increase of the deformation resistance of both sides will promote the edge recrystallization. Third, control the slab heating conditions, reduce the heating temperature, furnace time, control the protective atmosphere, and reduce the decarburization degree.

[0005] However, the existing method still has the following shortcomings: firstly, the edge heater of the hot rolling production line has certain positive contribution to the edge quality improvement of high silicon steel, but the investment is huge. If the edge heater function is not reserved at the beginning of the design of the hot rolling production line, the later increase will be limited by the existing production line conditions, such as insufficient position, conflict with existing equipment, etc., resulting in larger investment. In addition, with the increase of the edge temperature of the strip steel, the edge drop of the strip steel increases with the use of the edge heater, the edge drop area of the hot coil increases obviously, and the convexity hit rate decreases, which seriously affects the requirement of the raw material shape for the next process production. Secondly, the large side pressing technology of the rough rolling rear stage has certain requirements for the implementation of the production line equipment. It is suitable for the production line with more control means for the slab width, such as the production line should have a sizing press, at least two edger roller units and the like, and the width of the production line is more than 1580mm. For the 1450mm production line without sizing press and only one edger roller unit, the process has no guiding effect. In addition, the side pressing capacity of the 1450mm hot rolling strip steel production line is limited, and the large side pressing technology of the rear stage must ensure that the total side pressing amount of the rough rolling unit is sufficient and stable. For example, when the total measurement amount is very small, even if the rear stage side pressing amount is 100%, it is also very small, which cannot achieve the purpose of large side pressing.

[0006] In order to improve the hot rolling edge crack, some steel plants reduce the heating temperature and the furnace time. Although this method has a great effect on improving the hot coil edge crack, it will affect the magnetic properties of the finished product. For example, the core of grain-oriented electrical steel production is to form strong Goss texture. One of the main technical means is to control the inhibitor. High temperature and long time heating in the hot rolling process ensures the sufficient solid solution of the inhibitor in the inherent composition system, so as to obtain excellent magnetic properties of the final product. Therefore, this will greatly reduce the hit rate of the finished product. SUMMARY

[0007] In order to solve the above technical problems, the present application provides a method for controlling the edge crack of high silicon electrical steel. Based on the thick slab and under the condition of no edge heater in hot rolling, high temperature copper-containing grain-oriented electrical steel and other high silicon varieties (silicon content ≥3.0%) are produced. Through the slab width control, corner grain and temperature control in the continuous casting process, the heating and rolling process are combined to eliminate the edge crack defect of the hot rolling coil.

[0008] The purpose of the present application is to provide a method for controlling the edge crack of high silicon electrical steel, which comprises the following steps:

[0009] S1, continuously casting the slab; the continuously casting comprises slab width control, corner grain and temperature control, process parameters of the slab width control are: a casting speed is 0.8 m / min-1 m / min, a tundish superheat is 25 DEG C-30 DEG C, a cooling intensity is 0.8 L / kg-1.5 L / kg, and a width coefficient of the crystallizer is 0.995-1.005; the corner grain and temperature control are realized by primary cooling in the crystallizer and secondary cooling in a fan-shaped section; a water flow speed of the primary cooling is 15 m / s-35 m / s; the secondary cooling is divided into three modules, a first module sets a cooling water flow of zones 1-2 to be 600 L / min-800 L / min, a second module sets a cooling water flow of zones 3-5 to be 30 L / min-100 L / min, and a third module cancels cooling of zones 6-9;

[0010] S2, heating the slab after continuously casting in S1; the heating is divided into three stages, a temperature of a preheating section is 1190 DEG C-1210 DEG C, a temperature of an entering heating section is 1100 DEG C-1150 DEG C, and a temperature of an exiting heating section is 1290 DEG C-1390 DEG C;

[0011] S3, rough rolling and finish rolling the slab after heating in S2.

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

[0013] In an embodiment of the present application, 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.

[0014] In an embodiment of the present application, in S1, the thickness of the slab is 203 mm-213 mm, the width is 700 mm-1320 mm, and the length is 8000 mm-12500 mm.

[0015] In an embodiment of the present application, in S1, through the corner grain and temperature control, the corner surface layer grain of the slab is controlled to be within 25 μm, and the corner temperature when exiting the fan-shaped section is 600 DEG C-800 DEG C.

[0016] In one embodiment of the present invention, in S2, the furnace loading temperature of the slab is 500℃-700℃, and the furnace loading spacing is 50mm-120mm.

[0017] In one embodiment of the invention, in S2, the heating rate and cooling rate are independently 0.5℃ / min-1.5℃ / 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 table are independently within 15°C.

[0019] In one embodiment of the present invention, during S2, the residual oxygen content in the furnace is 0.5%-3.5% and the calorific value of the gas is 7000 KJ / m³. 3 -8000KJ / m 3 The pressure before the regulating valve of the main gas pipeline is 8 kPa-15 kPa.

[0020] In one embodiment of the present invention, in S3, the roughing is performed in 5 passes, the reduction rate of the first 4 passes is 15%-38% independently, the reduction rate of the 5th pass is 25%-50%, the thickness of the intermediate billet after roughing is 32mm-48mm, the temperature of the narrow face on both sides of the intermediate billet is 1050℃-1200℃, and 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 finishing rolling is carried out in 7 passes, with the cumulative reduction rate of the last 3 passes being 35%-55% and the reduction rate of the last pass being 1%-12%.

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

[0023] The method described in this invention uses thick slabs to produce hot-rolled coils of high-silicon electrical steel. Under the condition that there is no intermediate slab edge heating device in the hot rolling production line, high-silicon electrical steel with excellent edge microstructure and edge quality is obtained by controlling the slab width, corner grains and temperature in the continuous casting process, combined with heating and rolling processes. This solves the technical problem of edge cracking of hot-rolled coils that has long existed in the mass production of high-silicon electrical steel in the industry, and provides hot-rolled coils with excellent edge quality for the next process. It also reduces the huge cost investment of intermediate slab edge heating devices to solve hot-rolling edge cracking under traditional process conditions.

[0024] The hot rolling production line of the method does not need to increase the investment of the edge heater for improving the edge crack, reduces the investment, avoids the edge drop deterioration problem caused by the investment of the edge heater for solving the edge crack of the high-silicon electrical steel, is applicable under the working condition of the ambient temperature above-35℃, has obvious edge crack improvement effect, is suitable for all regional steel plants in China, does not need to reduce the factors such as the steel heating temperature and time which play a crucial role in the magnetic properties of the final product to improve the edge crack, and therefore can guarantee the excellent magnetic properties of the grain-oriented high-silicon electrical steel final product. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to make the content of the present application more easily and clearly understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, in which:

[0026] Figure 1 It is a physical diagram of the driving side of the hot coil of the high-silicon electrical steel of the test example 1 of the present application; wherein the left drawing is example 1, and the right drawing is comparative example 1.

[0027] Figure 2 It is a metallographic structure splicing diagram of the operation side and the driving side of the high-silicon electrical steel of the test example 2 of the present application; wherein the upper drawing is example 1, and the lower drawing is comparative example 1. DETAILED DESCRIPTION

[0028] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application. Example 1

[0029] The method for controlling the edge crack of the high-silicon electrical steel of the present embodiment specifically includes the following steps:

[0030] S1, slab selection

[0031] Composition: Si 3.21%, C 0.04%, Mn 0.2%, P 0.01%, S 0.008%, N 0.01%, and the balance is other inevitable impurities and iron;

[0032] Size specification: the thickness is about 208mm, the width is about 1090mm, and the length is about 10960mm;

[0033] Slab shape: the head is about 18mm, the buckle is about 8mm, and the sickle bend is about 20mm.

[0034] S2, continuous casting process

[0035] S21: the process parameters of the slab width control are shown in Table 1:

[0036] Table 1

[0037]

[0038] S22: Corner grain and temperature control is achieved by primary cooling in the crystallizer and secondary cooling in the fan-shaped section; the corner surface layer grain of the slab is controlled to be within 25 μm, and the corner temperature when exiting the fan-shaped section is about 700°C, and the specific process is as follows:

[0039] The flow rate of the primary cooling water is 25 m / s;

[0040] In the first and second zones of the secondary cooling, high-efficiency cooling nozzles are arranged, and the cooling water flow rate is 700 L / min; the edge cooling nozzles in the third, fourth, and fifth zones are independently controlled, and the water flow rate of the edge cooling nozzles is controlled to be 80 L / min; the edge cooling of the sixth, seventh, eighth, and ninth zones is cancelled.

[0041] S3, heating process

[0042] S31, furnace charging control: a large-scale walking beam heating furnace is used for heating, and the slab charging temperature is ensured to be 559°C; the residence time on the charging roller is 2 min, and the charging interval is set to 100 mm.

[0043] S32, steel heating control:

[0044] The furnace micro-positive pressure is controlled, the residual oxygen content is 2.5%, and the coal gas heat value is 7500 KJ / m 3 The pressure before the main gas pipeline regulating valve is 10 KPa;

[0045] The total furnace time is 270 min, the preheating section temperature is 1200°C, the entry heating section temperature is 1118°C, the exit heating section temperature is 1292°C, the total time of the heating section is 126 min, and the temperature change rate is 1.38°C / min;

[0046] The head-to-tail temperature difference and the surface-to-middle temperature difference of the slab are about 10°C.

[0047] S4, rolling process

[0048] S41, rough rolling process

[0049] Machine set selection: E1 edger mill + R1 four-high reversible rough rolling mill set, without intermediate slab edge heater;

[0050] The furnace after descaling is put into use, and the rough rolling only uses one pass descaling, and the finishing rolling descaling is not used;

[0051] The side pressure amount of the edger for three passes is: E1 is 48.32 mm, E3 is 47.00 mm, and E5 is 12 mm;

[0052] The 5-pass rolling is adopted, and the reduction rates are 18.50%, 21.69%, 24.43%, 24.77% and 35.69% respectively.

[0053] The thickness of the intermediate blank after rough rolling is 40 mm, the temperature of the narrow surface of the intermediate blank is 1100℃, the temperature difference between the head and tail is about 100℃, and the actual width of the finished product is 1071 mm.

[0054] S42, finishing rolling process

[0055] Machine set selection: 7-stand four-roll irreversible full-hydraulic rolling mill is adopted.

[0056] 7-pass rolling is adopted, and the cumulative reduction rate of the last 3 passes is 40%, and the reduction rate of the last pass is 8%. Example 2

[0057] The method for controlling edge cracking of high-silicon electrical steel in this embodiment specifically comprises the following steps:

[0058] S1, slab selection

[0059] Composition: Si 3.23%, C 0.035%, Mn 0.21%, P 0.08%, S 0.009%, N 0.011%, and the balance is other unavoidable impurities and iron.

[0060] Size specification: thickness is about 208 mm, width is about 1140 mm, and length is about 11600 mm.

[0061] Slab shape: head deflection is about 18 mm, head buckling is about 8 mm, and sickle bending is about 20 mm.

[0062] S2, continuous casting process

[0063] S21: The process parameters for slab width control are shown in Table 2:

[0064] Table 2

[0065]

[0066] S22: Corner grain and temperature control is achieved by primary cooling in the mold and secondary cooling in the fan-shaped section; the corner surface layer grain of the slab is controlled to be within 25 μm, and the corner temperature when exiting the fan-shaped section is about 700℃, and the specific process is as follows:

[0067] The water flow rate of the primary cooling is 25 m / s.

[0068] The first and second zones of the secondary cooling are provided with high-efficiency cooling nozzles, and the cooling water flow is 700 L / min; the edge cooling nozzles of the third, fourth and fifth zones are independently controlled, and the water flow of the edge cooling nozzles is 80 L / min; the sixth, seventh, eighth and ninth zones cancel the slab edge cooling.

[0069] S3, heating process

[0070] S31, furnace charging control: a large-scale walking beam heating furnace is used for heating, so that the slab charging temperature is 612℃, the residence time on the charging roller is 2 min, and the charging interval is set to 100 mm.

[0071] S32, steel heating control:

[0072] The furnace is controlled at a slight positive pressure, the residual oxygen content is 2.3%, and the coal gas heat value is 7500 KJ / m 3 The pressure before the main coal gas pipeline regulating valve is 10 KPa.

[0073] The total furnace time is 330 min, the preheating section temperature is 1200℃, the entry heating section temperature is 1125℃, the exit heating section temperature is 1293℃, the total heating section time is 115 min, and the temperature change rate is 1.46℃ / min.

[0074] The head-to-middle-to-tail temperature difference and the surface-to-middle temperature difference of the slab are about 10℃.

[0075] S4, rolling process

[0076] S41, rough rolling process

[0077] Machine set selection: E1 vertical roll mill + R1 four-roll reversible rough rolling mill set, without intermediate slab edge heater;

[0078] The furnace after descaling is used, and the rough rolling only uses one pass descaling, and the finishing rolling descaling is not used;

[0079] The vertical roll three-pass side pressure amount is: E1 is 42.30 mm, E3 is 39.52 mm, and E5 is 15 mm;

[0080] Five passes are adopted, and the reduction rates are respectively: 18.44%, 20.65%, 23.57%, 27.15%, and 39.2%;

[0081] The thickness of the intermediate slab after rough rolling is 40 mm, the temperature of the two sides of the intermediate slab is 1100℃, the head-to-tail temperature difference is about 100℃, and the actual width of the finished product is 1115 mm;

[0082] S42, finishing rolling process

[0083] Machine set selection: seven-rack four-roll irreversible full-hydraulic rolling mill is adopted;

[0084] The 7-pass rolling is adopted, and the cumulative reduction rate of the last 3 passes is 40%, and the reduction rate of the last pass is 8%. Comparative Example 1

[0085] The basic process is the same as that of Example 1, except that the process parameters for slab width control are as follows: the drawing speed is 1.2 m / min, and the cooling intensity is 0.7 L / kg.

[0086] Test Example 1

[0087] The actual drive side of the high-silicon electrical steel of Example 1 (first group) and Comparative Example 1 is shown in Figure 1 As shown in the figure, the drive side of the high-silicon electrical steel of Example 1 has a small amount of small edge cracks on the inner and outer rings, and no large edge cracks are observed; the drive side of the high-silicon electrical steel of Comparative Example 1 has severe sawtooth-shaped cracks, and the edge is obviously deformed and thinned, and there are deep scratches on the surface.

[0088] Test Example 2

[0089] The high-silicon electrical steel of Example 1 (first group) and Comparative Example 1 is subjected to metallographic electron microscope detection, and a transverse cross-section sample is taken perpendicularly to the edge for metallographic electron microscope detection. The metallographic structure splicing results of the edge of the operation side and the drive side are shown in Figure 2 As shown in the figure, the fibrous unrecrystallized structure of the high-silicon electrical steel of Example 1 is present in the surface layer, and the length is only 9 mm, and the single-edge shearing amount of the pickling unit disc shear is 15 mm; the fibrous unrecrystallized structure of the high-silicon electrical steel of Comparative Example 1 is as high as 21 mm and 16.5 mm, respectively, and the fibrous unrecrystallized structure is the root cause of the edge crack, and the single-edge shearing amount of the pickling unit is ≥25 mm to completely remove the abnormal structure at the edge, so that the cold-rolled edge will not produce new edge cracks.

[0090] Obviously, the above examples are merely examples for clarity and do not limit the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method of controlling edge cracking of high silicon electrical steel characterized by, The method comprises the following steps: S1, continuously casting a slab; the continuous casting comprises slab width control, corner grain and temperature control, the process parameters of the slab width control are: a casting speed of 0.8 m / min-1 m / min, a tundish superheat of 25℃-30℃, a cooling intensity of 0.8 L / kg-1.5 L / kg, and a width coefficient of the crystallizer of 0.995-1.005; the corner grain and temperature control is realized through primary cooling in the crystallizer and secondary cooling in the fan-shaped section; the water flow rate of the primary cooling is 15 m / s-35 m / s; the secondary cooling is divided into three modules, the first module sets the cooling water flow rate of zones 1-2 to be 600 L / min-800 L / min, the second module sets the water flow rate of the edge cooling nozzle of zones 3-5 to be 30 L / min-100 L / min, and the third module cancels the slab edge cooling of zones 6-9; through the corner grain and temperature control, the corner surface layer grain of the slab is controlled to be within 25 μm, and the corner temperature when the slab exits the fan-shaped section is 600℃-800℃; S2, heating the slab continuously cast in S1; the heating is divided into three stages, the temperature of the preheating stage is 1190℃-1210℃, the temperature when entering the heating stage is 1100℃-1150℃, and the temperature when exiting the heating stage is 1290-1390℃; S3, rough rolling and finish rolling the slab heated in S2; in the rough rolling process, there is no edge heater for the intermediate slab; the rough rolling adopts 5 passes of rolling, the reduction rate of the first 4 passes is independently 15%-38%, the reduction rate of the 5th pass is 25%-50%, the thickness of the intermediate slab after rough rolling is 32 mm-48 mm, and the temperature of the two sides of the intermediate slab is 1050℃-1200℃; the temperature difference between the head and tail of the intermediate slab is within 150℃.

2. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S1, the slab has the following element composition and mass percentage: 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 of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S1, the slab has a thickness of 203 mm-213 mm, a width of 700 mm-1320 mm, and a length of 8000 mm-12500 mm.

4. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S2, the slab has a charging temperature of 500℃-700℃, and a charging interval of 50 mm-120 mm.

5. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S2, the heating rate and the cooling rate of the heating are independently 0.5℃ / min-1.5℃ / min.

6. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S2, during the heating process, the temperature difference between the head and tail of the slab and the temperature difference between the surface and the middle of the slab are independently within 15℃.

7. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S2, during the heating process, the residual oxygen content in the hearth is 0.5%-3.5%, the coal gas heat value is 7000 KJ / m 3 -8000 KJ / m 3 , and the pressure before the main coal gas pipeline regulating valve is 8 KPa-15 KPa.

8. The method of controlling edge cracking of high-silicon electrical steel of claim 1, wherein, In S3, the finish rolling adopts 7 passes of rolling, the cumulative reduction rate of the last 3 passes is 35%-55%, and the reduction rate of the last pass is 1%-12%.

Images