A method for manufacturing a medium-thickness slab oriented silicon steel by hot continuous rolling

Abstract

The present application belongs to the technical field of oriented silicon steel production, and discloses a kind of medium-thickness slab oriented silicon steel hot continuous rolling production manufacturing method.The flow of the production manufacturing method includes: steelmaking→continuous casting→soaking→hot rolling→normalizing→cold rolling→annealing, wherein the soaking temperature and soaking time need to meet a specific formula, and it also relates to the control of continuous casting and hot rolling process.The present application starts from slab thickness, heating process and organization control, by adopting the hot rolling heating process suitable for slab thickness, reduces the inhibitor segregation in the hot rolling process, obtains suitable inhibitor state, effectively improves the performance of finished product, reduces the iron loss P 1.7 / 50 of oriented silicon steel finished product by about 5% compared with the thicker slab method, and the whole roll fluctuation is reduced to ±0.01 W / kg.

Description

Technical Field

[0001] This invention belongs to the field of grain-oriented silicon steel production technology, specifically relating to a hot continuous rolling production method for medium-thickness slab grain-oriented silicon steel. Background Technology

[0002] Grain-oriented silicon steel production typically employs a straight-arc continuous casting machine, producing billets with a thickness of 200–300 mm. These billets are then hot-rolled into 2.2–2.5 mm thick hot coils. During hot rolling, inhibitors undergo solution treatment and precipitation, resulting in uniform, fine, and dispersed composite precipitates, providing a foundation for controlling and improving the magnetic properties of the finished product. However, this production method suffers from drawbacks. Due to the large billet thickness, both cooling and reheating times are prolonged. The significant temperature difference between the surface and interior of the billet during heating and cooling processes makes it prone to grain boundary cracks, which can lead to subsequent cracking and negatively impact the rolling process and finished product quality. Furthermore, the relatively low surface temperature of the billet results in larger inhibitor precipitates, necessitating higher temperatures and longer heating times before hot rolling to dissolve these inhibitors.

[0003] Another method for producing grain-oriented silicon steel is the hot rolling process of thin slabs (30-100mm), also known as CSP (Coil-Slab Process). This method offers advantages such as a shorter process flow, lower billet heating temperature, higher yield, and lower energy consumption. The resulting billets have smaller and more uniform grains, with reduced microsegregation. However, CSP production lines use tunnel furnaces, which makes precise control of heating time and temperature range difficult. This results in insufficient dissolution of inhibitors, making it challenging to control the quantity and size of inhibitors. Ultimately, the performance and surface quality of the finished product still require improvement.

[0004] With the development of continuous casting production, medium-thickness slabs (100-200mm) between the aforementioned two thicknesses are attracting increasing attention due to their advantages such as high productivity, low cost, and good continuous casting effect. This process has now become an important technology and development direction in continuous casting production. However, due to the strong correlation between silicon steel performance characterization and production process, the production of grain-oriented silicon steel from medium-thickness slabs still faces challenges such as immature processes, uncontrolled inhibitor precipitation and growth, poor overall performance, and, in particular, difficulty in meeting magnetic performance standards.

[0005] Therefore, how to overcome the shortcomings of existing medium-thickness thin slab production of oriented silicon steel and ensure that the magnetic properties meet the predetermined goals is the problem that this invention needs to solve. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a hot continuous rolling production method for medium-thickness slab-oriented silicon steel, which addresses the shortcomings of the existing technology. The present invention starts with the control of slab thickness, heating process and microstructure. By adopting a heating and hot rolling process adapted to the slab thickness, the segregation of inhibitors during hot rolling is reduced, the performance of finished product is effectively improved, and the goal of stable performance and excellent plate quality is achieved.

[0007] To solve the technical problem proposed in this invention, this invention provides a hot continuous rolling production method for medium-thickness slab-oriented silicon steel, the process of which includes: steelmaking → continuous casting → homogenization → hot rolling → normalizing → cold rolling → annealing.

[0008] In the above scheme, the chemical composition of the oriented silicon steel by mass percentage is as follows: C: 0.010-0.098%, Si: 2.50-3.60%, Al: ≤0.050%, Mn: ≤0.35%, Cu: 0.01-0.55%, P: ≤0.050%, S: ≤0.0090%, N: 0.002-0.020%, with the remainder being Fe and unavoidable impurities.

[0009] In the above scheme, the continuous casting adopts a medium-thin plate continuous casting machine, and the slab thickness is 100-200mm.

[0010] In the above scheme, the slab of the continuous casting is cut and then kept warm. It is then loaded into the heating furnace within 4 hours after being cut, and the surface temperature of the slab is ≥850℃ when it enters the furnace.

[0011] In the above scheme, the heat preservation temperature T for uniform heating satisfies the following formula:

[0012]

[0013] In the formula, T is the insulation temperature, and the unit is °C;

[0014] h represents the slab thickness in mm;

[0015] wt(Mn) and wt(Cu) are the mass percentages of Mn and Cu in oriented silicon steel, respectively, in %.

[0016] In the above scheme, the heat equalization holding time t satisfies the following formula:

[0017] 75 - 0.027 × T ≤ t ≤ 60

[0018] In the formula, t is the heat preservation time in minutes; T is the heat preservation temperature in degrees Celsius.

[0019] In the above scheme, the hot rolling includes roughing and finishing rolling. After roughing, the steel strip is kept warm in a hot coil box. The temperature of the steel strip entering the finishing mill is 1200±50℃, the final rolling temperature is 950±20℃, and laminar flow cooling is used immediately after rolling, with a final cooling temperature of 600±100℃.

[0020] The technical concept of this invention is as follows:

[0021] The continuous casting process uses a continuous medium-thin plate continuous casting machine. Because the molten steel cools more slowly in the vertical section, inclusions in the steel can be fully floated to the surface, thereby improving product performance. Controlling the tundish superheat to a small degree during continuous casting, such as 5–25°C, allows the molten steel to solidify rapidly. Inhibitors in the steel exist in a solid solution state in the billet, which can reduce the subsequent hot rolling heating temperature and time, and reduce segregation.

[0022] Using 100–200 mm thick cross-section billets ensures sufficient flotation of inclusions while maintaining a high billet temperature, reducing the preheating temperature before hot rolling and balancing production efficiency. Compared to thick slabs, the grain size of the hot-rolled grain structure in oriented silicon steel produced from medium slabs is relatively large, resulting in a larger grain size or banded grain width in the normalized and primary cold-rolled structures. Due to the heritability of the microstructure, the grain size of the intermediate-annealed samples of oriented silicon steel produced from medium slabs should also be relatively large, which is beneficial for improving the magnetic properties of the finished product, especially reducing iron loss.

[0023] After cutting, the continuously cast billets are directly loaded into the heating furnace via roller conveyors equipped with heat insulation covers, with the time interval controlled to not exceed 4 hours. This avoids differences in the solid solution state and microstructure of inhibitors caused by temperature differences between the surface and the central area, which would increase iron loss in the finished product. The surface temperature of the billets entering the furnace is ≥850℃. By reducing the temperature drop during the furnace loading process, the intermediate thickness slabs have an advantage in balancing the surface and internal temperature differences, while also reducing the probability of cracking. This also helps to reduce heat loss and prevent the precipitation and growth of inhibitors.

[0024] Several problems arise from heating above 1250℃: (1) a large amount of slag is generated on the slab surface; (2) the operability of the heating furnace is impaired; (3) surface defects occur; (4) the furnace wall of the heating furnace is severely burned; (5) the yield is low; (6) the grain boundary oxidation of the slab surface, the edge cracking depth and surface decarburization increase, resulting in poor magnetic properties of the product. The adverse effects of high-temperature heating are effectively avoided by controlling the thickness of the billet, using heat insulation covers, and adjusting the production process. The heating temperature is adjusted according to the slab thickness and alloy composition, and the heating time is adjusted according to the heating temperature, which can effectively avoid the above problems. This ensures that the billet temperature is uniform, and the finished product has no crystal structure, uniform magnetic properties in the width direction, and excellent plate shape.

[0025] After rough rolling, a hot coil box is used for insulation to ensure that the overall temperature of the steel strip is uniform and above the inhibitor precipitation temperature, thus preventing inhibitor precipitation. When the head of the strip is rolled into the finishing mill, the tail of the strip remains in the hot coil box. This allows the temperature of the head and tail of the strip to become more uniform or slightly higher at the tail, enabling a large amount of inhibitor to disperse and precipitate rapidly, reducing the performance difference between the head and tail of the finished product, and thus reducing the performance fluctuation of the entire coil.

[0026] The temperature of the steel strip entering the finishing mill is 1200±50℃, and the final rolling temperature is 950±20℃. After finishing rolling, laminar flow cooling is immediately adopted, and the final cooling temperature is 600±100℃. This is beneficial to obtain fine and uniform primary grains, while preventing AlN precipitation. It also freezes the dislocations generated during hot rolling before recovery, and the carbon content is evenly distributed, resulting in uniform magnetic properties of the finished product.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention addresses the relationship between billet thickness, heating process, and microstructure control, organically linking billet thickness, key components, heating temperature, and holding time. In the production of grain-oriented silicon steel on a continuous medium-thin plate casting machine, by employing a heating and hot-rolling process adapted to the billet thickness, it reduces inhibitor segregation during hot rolling, obtains a suitable inhibitor state, effectively improves finished product performance, and achieves stable performance and excellent plate quality, thus minimizing iron loss (P). 1.7 / 50 Compared to the thicker billet method (200-300mm), the cost is reduced by about 5%, and the overall roll fluctuation is reduced to ±0.01W / kg. Detailed Implementation

[0029] To better explain the present invention, the main contents of the present invention are further illustrated below with reference to specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0030] Examples 1-6

[0031] The chemical composition and mass percentage of the oriented silicon steel in Examples 1-6 and Comparative Examples 1-3 are as follows.

[0032] Table 1 Steel Composition (Wt%)

[0033] serial number C Si Mn P S Als N Cu Example 1 0.05 3.25 0.07 0.024 0.0032 0.021 0.007 0.01 Example 2 0.06 3.20 0.08 0.028 0.0046 0.033 0.008 0.01 Example 3 0.05 3.17 0.06 0.032 0.0043 0.025 0.009 0.02 Example 4 0.07 3.01 0.08 0.027 0.0066 0.037 0.007 0.02 Example 5 0.05 2.83 0.10 0.021 0.0081 0.028 0.007 0.03 Example 6 0.08 2.72 0.12 0.026 0.0075 0.032 0.008 0.03 Comparative Example 1 0.05 3.27 0.06 0.028 0.0027 0.027 0.007 0.01 Comparative Example 2 0.07 3.11 0.08 0.035 0.0032 0.036 0.007 0.02 Comparative Example 3 0.09 2.80 0.10 0.022 0.0021 0.029 0.006 0.03

[0034] The manufacturing process of grain-oriented silicon steel in Examples 1-6 and Comparative Examples 1-3 includes: steelmaking → continuous casting into billets → homogenization → high-pressure descaling → rough rolling → finish rolling → normalizing → cooling → cold rolling to finished thickness → continuous decarburization annealing → nitrogen diffusion → coating with magnesium oxide release agent → high-temperature purification annealing → leveling and stretching → coating with insulating layer → shearing → packaging. The specific process is as follows:

[0035] After steelmaking, Examples 1-6 used a continuous casting machine for medium-thin plates, employing a superheat of 5-25°C and a casting speed of 1.5-4 m / min suitable for this thickness (100-200 mm). Comparative Examples 1-3 used a conventional thickness casting machine, employing a superheat of 15-35°C and a casting speed of 0.6-1.5 m / min suitable for conventional thicknesses (200-300 mm). In Examples 1-6, the continuously cast slabs were cut and directly loaded into the heating furnace via roller conveyors with insulation covers, with time intervals controlled to not exceed 4 hours. The slab surface temperature upon entering the furnace was ≥850°C. In Comparative Examples 1-3, no strict insulation measures were used, and the slab surface temperature had significantly decreased upon entering the furnace. Specific parameters are shown in Table 2.

[0036] After entering the heating furnace, the holding temperature T of the slab in the furnace, as described in Examples 1-6, satisfies the following formula: The holding time t satisfies the formula: 75 - 0.027 × T ≤ t ≤ 60; then, after high-pressure descaling and rough rolling, the temperature of the steel strip entering the finishing mill is 1200 ± 50℃, and the final rolling temperature is 950 ± 20℃. After finishing rolling, laminar flow cooling is immediately adopted, and the final cooling temperature is 600 ± 100℃; while in comparative examples 1 to 3, conventional homogenization and hot rolling process parameters are used. See Table 3 for details.

[0037] Hot-rolled coils with a thickness of 2.0–2.5 mm after finishing are routinely treated and pickled, then cooled to a temperature ≤80℃. They are then cold-rolled to a finished thickness of 0.23–0.35 mm using a single-stand rolling mill with either one or two cold rolling processes. After cold rolling, the steel strip undergoes continuous annealing furnace decarburization annealing, nitrogen diffusion, magnesium oxide coating, high-temperature purification annealing, leveling and stretching, and insulation coating to produce the finished product.

[0038] Table 2 Continuous Casting Process Parameters

[0039] serial number Superheat of the intermediate package (°C) Pulling speed (m / min) Slab thickness (mm) Surface temperature of slab (°C) Example 1 5 2.5 135 856 Example 2 8 2.3 140 861 Example 3 12 2.8 155 868 Example 4 10 2.6 165 873 Example 5 15 2.2 145 865 Example 6 16 2.4 155 866 Comparative Example 1 26 1.0 210 742 Comparative Example 2 19 1.2 230 733 Comparative Example 3 25 1.3 230 755

[0040] Table 3 Hot rolling process parameters

[0041]

[0042] The properties of the grain-oriented silicon steels in Examples 1-6 and Comparative Examples 1-3 were tested, mainly including the iron loss P under a magnetic field of 1.7T at 50Hz alternating magnetic field. 1.7 / 50 The magnetic field strength B under an alternating magnetic field of 800 Am and 50 Hz 800 .

[0043] Table 4 Main Performance Information

[0044]

[0045]

[0046] As can be seen from Table 4, under the same finished product thickness specifications, the iron loss of the embodiment is reduced by about 5% compared with the comparative example, and the overall roll fluctuation is small, only ±0.01W / kg, while the magnetic induction is comparable to that of the comparative example. The overall magnetic performance is better and the overall roll performance is more stable.

[0047] The above embodiments are merely best examples and not intended to limit the implementation of the present invention. In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for hot continuous rolling production of medium-thickness slab-oriented silicon steel, the process comprising: Steelmaking → Continuous casting → Soaking → Hot rolling → Normalizing → Cold rolling → Annealing, characterized in that the continuous casting adopts a medium-thin plate continuous casting machine, and the slab thickness is 100~200mm; the surface temperature of the slab when entering the heating furnace is ≥850℃, and the holding temperature and holding time for soaking in the heating furnace satisfy the following formula: 75 - 0.027 × T ≤ t ≤ 60 In the formula, T is the heat preservation temperature in °C; t is the heat preservation time in min; h is the slab thickness in mm; wt(Mn) and wt(Cu) are the mass percentages of Mn and Cu in the oriented silicon steel, respectively, in %; the mass percentage of Mn in the oriented silicon steel is ≤0.35%, and the mass percentage of Cu is 0.01~0.55%. The hot rolling includes roughing and finishing. After roughing, the steel strip is kept warm in a hot coil box. The temperature of the steel strip entering the finishing mill is 1200±50℃, and the final rolling temperature is 950±20℃. Laminar flow cooling is used immediately after rolling, and the final cooling temperature is 600±100℃.

2. The method for hot continuous rolling production of medium-thickness slab-oriented silicon steel according to claim 1, characterized in that, The thickness of the slab is 135~165mm.

3. The method for hot continuous rolling production of medium-thickness slab-oriented silicon steel according to claim 1, characterized in that, The chemical composition of the oriented silicon steel, by mass percentage, is as follows: C: 0.010~0.098%, Si: 2.50~3.60%, Al: ≤0.050%, Mn: ≤0.35%, Cu: 0.01~0.55%, P: ≤0.050%, S: ≤0.0090%, N: 0.002~0.020%, with the remainder being Fe and unavoidable impurities.

4. The hot continuous rolling production method for medium-thickness slab-oriented silicon steel according to claim 1, characterized in that, The slabs from the continuous casting process are cut and then kept warm before being loaded into a heating furnace within 4 hours of being cut.

5. The method for hot continuous rolling production of medium-thickness slab-oriented silicon steel according to claim 1, characterized in that, The surface temperature of the slab when it enters the heating furnace is ≥856℃.

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