A hot-rolled substrate for galvanizing and a method for manufacturing the same

Abstract

The application discloses a hot-rolled substrate for galvanization, and the chemical composition and mass percentage of the hot-rolled substrate are as follows: C 0.03%-0.055%, Si≤0.04%, Mn 0.1%-0.3%, P≤0.018%, S≤0.004%, Al 0.01%-0.04%, and the balance of Fe and inevitable impurities. The application controls the chemical composition of the hot-rolled substrate and key process points in the manufacturing process, so that the hot-rolled substrate has good surface quality, the problem of furnace bottom roll bite can be solved, there is no wire-shaped defect after galvanization, and the manufacturing method is efficient and stable.

Description

Technical Field

[0001] This invention relates to the field of steel product manufacturing, and more specifically to a hot-rolled substrate for galvanizing and its manufacturing method. Background Technology

[0002] Thin slab continuous casting and rolling is one of the most important technological advancements in the steel production industry in recent years, becoming a hot investment area in the steel industry in the 1990s. However, in recent years, it has become clear that the original thin slab continuous casting and rolling technology still has many shortcomings. For example, due to the influence of the funnel-shaped crystallizer in thin slabs, the steel is subject to the combined effects of mechanical and thermal stresses during casting, resulting in a higher sensitivity to cracking compared to traditional hot rolling. This makes the slab prone to defects such as longitudinal cracks, seriously affecting slab quality and finished product delivery. Simultaneously, due to the high casting speed of thin slabs, inclusions during casting are difficult to float sufficiently, thus requiring higher purity of molten steel to obtain slabs with good surface quality. The hot-rolled raw materials for galvanizing / color coating produced by the Wuhan Iron and Steel (WISCO) hot rolling mill using thin slab continuous casting and rolling exhibit discontinuous linear defects on their surface after galvanizing. The defect lengths vary, ranging from tens of millimeters to one meter, and sometimes the defects are not obvious, only faintly visible under side lighting. Meanwhile, the traditional hot-rolled base materials produced simultaneously do not exhibit these corresponding defects. Sampling and analysis of linear defects in hot-rolled raw materials after galvanizing revealed diagonally extending cracks into the steel substrate at the defect locations. The crack ends were relatively smooth, with a depth ≤10μm from the steel plate surface. Particulate matter containing slag-like components such as F and Ca was present at the corresponding defects. Multiple rounds of monitoring indicated that this defect was caused by fine microcracks on the slab surface, and the formation of these microcracks is closely related to the thin slab continuous casting process and equipment. Furthermore, the heating and rolling processes in thin slab furnaces differ from conventional hot rolling lines, and the descaling equipment is less capable. Controlling furnace bottom roll wear and iron oxide scale defects has consistently been a weak point in the process.

[0003] Therefore, it is of great significance to develop a manufacturing method for hot-rolled substrates with good surface quality, which can solve the problem of furnace bottom roll scratches and have no geometric defects after galvanizing. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hot-rolled substrate for galvanizing and a method for manufacturing the same, which addresses the shortcomings of the prior art. The manufacturing method is efficient and stable, can solve the problem of furnace bottom roll scratches, and produces a hot-rolled substrate with good surface quality and no geometric defects after galvanizing.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0006] A hot-rolled substrate for galvanizing, wherein the chemical composition of the hot-rolled substrate and its mass percentage are as follows: C 0.03% to 0.055%, Si ≤ 0.04%, Mn 0.1% to 0.3%, P ≤ 0.018%, S ≤ 0.004%, Als 0.01% to 0.04%, with the balance being Fe and unavoidable impurities.

[0007] This invention also claims protection for the above-mentioned method for manufacturing a hot-rolled substrate for galvanizing, comprising the following steps: converter smelting, LF furnace refining, slab casting, homogenization in a soaking furnace, descaling, finish rolling, laminar flow cooling, and coiling, wherein the key points for controlling the process parameters in the slab casting step are:

[0008] (1) Crystallizer water flow setting: The cooling water inlet temperature of the crystallizer is 33-35℃, the water flow rate on the wide side of the crystallizer is 5600-6700L / min, and the water flow rate on the narrow side is 200-250L / min, ensuring that the heat flux on the wide side is 2.54-2.7MW / m 3 The narrow-side heat flux is 2.0–2.2 MW / m. 3 ;

[0009] (2) The protective slag is controlled by using ultra-low carbon protective slag: basicity is 1.0±0.05R, melting point is 1030±30℃, and viscosity is 0.1±0.05Pa.s / 1300℃;

[0010] (3) The secondary cooling water adopts a weak cooling control mode, the secondary cooling water temperature is >28℃, the water flow rate of the 1.0 zone of the sector is 350~400L / min, and the cooling water flow rate of the 4.2~7.2 zones is ≤120L / min.

[0011] In the above scheme, during the converter smelting process, the sulfur content in the molten steel at the end point is controlled to be ≤0.025%, the tapping temperature is ≥1630℃, and a double-barrier slag-blocking method is used during tapping to ensure that the phosphorus content meets the requirements.

[0012] In the above scheme, the processing time in the LF furnace refining step is 50-80 minutes, and the off-site ALS is controlled at a target of 0.035%.

[0013] In the above scheme, the slab casting step further includes the control of the following process parameters:

[0014] (4) The thickness of the billet is 70-80mm, and the thickness of the copper plate of the crystallizer is ≥18mm;

[0015] (5) The casting process is protected by a tundish throughout the casting process, with a tundish tonnage of >35 tons and a continuous casting tonnage of >30 tons;

[0016] (6) The pulling speed is 4.6 to 5.0 m / min.

[0017] In the above scheme, the key process control points in the homogenization step of the homogenizing furnace are:

[0018] (1) Reserve a slab from the previous casting in the soaking furnace for cleaning the furnace rollers. After the furnace rollers are cleaned, the slab enters the soaking furnace for soaking. Control the slab exit temperature to 1170-1190℃ and the time in the furnace to not exceed 35 minutes.

[0019] (2) The running speed of the slab inside the furnace is 0.6 to 0.8 m / s.

[0020] In the above scheme, during the descaling step, the inlet pressure of the descaling water is controlled to be no less than 200 bar and the outlet pressure is no less than 300 bar to ensure that the iron oxide scale is completely removed before rolling.

[0021] In the above scheme, the finishing rolling step is carried out using a seven-stand mill, with a final rolling temperature of 880-920℃, and the cooling water of the side guide plates is turned off.

[0022] In the above scheme, in the laminar flow cooling step, a front-end interval cooling method is used to reduce the cooling intensity, and the water volume ratio of the upper pipe to the lower pipe of the laminar flow cooling manifold is 4:5 to ensure the uniformity of cooling of the upper and lower surfaces.

[0023] In the above scheme, during the winding step, the side guide plate is controlled by micro-spark, and the clamping pressure of the winding side guide plate is 2-4KN.

[0024] The design concept of this invention regarding the chemical composition of the hot-rolled substrate and the key process points in the manufacturing process is as follows:

[0025] C element: In this invention, the C content is controlled between 0.03% and 0.055%. C is the second most important element in steel after iron, directly affecting the strength, plasticity, toughness, and weldability of steel. To improve the processing and forming performance of subsequent cold-rolled galvanized materials, traditional hot rolling controls the corresponding C content between 0.03% and 0.07%. However, considering the characteristics of the CSP production line process (the strength of hot-rolled base material is slightly greater than that of traditional hot rolling, and peritectic steel cannot be cast), the C content in this invention is controlled between 0.03% and 0.055%, ensuring both strength and CSP production stability.

[0026] P and S elements: P and S are harmful elements in steel, reducing its ductility and toughness. P increases grain boundary brittleness, enhancing the steel's crack susceptibility and significantly increasing the risk of leaks and cracks during casting. S causes hot brittleness, reducing various mechanical properties. Simultaneously, SO2 is generated during heating and welding, leading to porosity in the weld. Furthermore, a decrease in sulfides increases the brittle phases in steel, reducing ductility and toughness, and also decreasing stamping performance. Therefore, this invention controls the P content to ≤0.018% and the S content to ≤0.004%.

[0027] Mn element: Lowering the Mn content helps reduce the strength of hot-rolled coils and the rolling load in cold rolling; however, increasing the Mn / S ratio in steel promotes the granular distribution of MnS at grain boundaries and in the matrix, thereby improving the high-temperature performance of the steel and reducing the influence of S on hot brittleness. Considering both performance and Mn / S ratio requirements, this invention controls the Mn content at 0.1% to 0.3%.

[0028] Converter smelting: High-temperature tapping in the converter and double-barrier slag blocking on the slide plate prevent slag from falling in and ensure that P control meets requirements. At the same time, high-temperature tapping in the converter reduces the heating time of the LF electrode, ensures nitrogen control, and reduces inclusions.

[0029] LF furnace refining: processing time is 50-80 minutes, ensuring desulfurization control.

[0030] Slightly weaker cooling in the crystallizer: Uneven heat flow in the meniscus region of the crystallizer can easily lead to uneven billet shell thickness growth, and uneven temperature gradients can cause cracks. Weak cooling in the crystallizer allows for uniform billet shell growth, thus preventing cracks; however, insufficient cooling results in a billet shell that is too thin to support the hydrostatic pressure of the molten steel, leading to longitudinal cracks within the crystallizer. Therefore, after multiple rounds of practical testing, it is concluded that slightly weaker cooling in the crystallizer is beneficial in preventing longitudinal cracks in the slab.

[0031] Secondary cooling: If the secondary cooling intensity is inadequate, the surface temperature of the billet will enter the brittle temperature range of the steel grade, making it prone to various cracks during straightening. Excessive reheating of the billet surface will also promote the precipitation of AlN and other substances, which will promote the formation of cracks at grain boundaries, increasing the brittleness of the steel. Furthermore, excessive reheating will generate excessive thermal stress within the billet, which will also increase the tendency to crack. If a weak secondary cooling water is used, the billet shell thickness will be too thin to support the static pressure of the molten steel, posing a risk of bulging and leakage. Therefore, in the secondary cooling zone, the cooling water volume should be adjusted to ensure that there is no leakage of steel from the crystallizer, but not too strong, so as not to cause crack propagation.

[0032] Homogenization in the soaking furnace: A slab is reserved for cleaning the furnace rollers during the previous casting stage to remove any adhering iron oxide scale and other deposits from the bottom rollers. Simultaneously, the slab's running speed is controlled to be low to prevent any remaining adhering iron oxide scale from damaging the lower surface of the slab.

[0033] Finishing rolling: The finishing rolling temperature is 880-900℃, and the cooling water of the side guide plate is turned off. This is to increase the edge temperature and avoid the temperature difference between the edge and the middle. Rolling the two-phase zone at the edge will cause the microstructure to be different from that in the middle, affecting the uniformity of the microstructure. This will also prevent cold rolling edge brittleness caused by the brittleness of the edge microstructure during subsequent cold rolling.

[0034] Laminar flow cooling: A front-stage intermittent cooling method (alternating switching of adjacent cooling manifolds) is employed. This serves two purposes: firstly, to suppress the increase in scale thickness on the laminar flow cooling rollers; and secondly, to avoid uneven thermal stress caused by continuous strong cooling, thus improving plate shape. The difference in water flow between the upper and lower main pipes also fully considers the issue of uniform cooling and reduces stress unevenness. During the rear-stage cooling, a larger and thicker tertiary oxide scale forms at the high temperature in the front stage of laminar flow cooling, while the front-stage cooling helps to reduce the thickness of the oxide scale.

[0035] Coiling: The coiling side guide plate of this invention adopts a lower clamping force to avoid excessive clamping force damaging the edge of the strip and affecting the stability of subsequent cold rolling quality.

[0036] Compared with existing technologies, the beneficial effects of this invention are:

[0037] (1) The present invention provides a hot-rolled substrate for galvanizing, which has good surface quality and no deformed defects after galvanizing.

[0038] (2) The present invention provides a method for manufacturing hot-rolled substrate for galvanizing. This method solves the problem of long linear defects on the surface of hot-rolled substrate after galvanizing by adopting smelting composition control and continuous casting process matching; solves the problem of furnace bottom roller damage by furnace roller cleaning and low-speed operation; and solves the problem of steel coil edge wire and edge brittleness by high-temperature precision rolling, closing the cooling water of the side guide plate and controlling the small clamping force of the coiling side guide plate.

[0039] (3) The present invention provides a method for manufacturing a hot-rolled substrate for galvanizing, which has the advantages of high overall yield and high production efficiency. Attached Figure Description

[0040] Figure 1 This is an outline drawing of the steel coil produced from the hot-rolled substrate prepared in Example 1.

[0041] Figure 2 This is a surface view of the finished product after galvanizing the hot-rolled substrate prepared in Example 1.

[0042] Figure 3 This is a diagram of the elongated linear defects on the hot-rolled substrate prepared in Comparative Example 1 after galvanization.

[0043] Figure 4 This is a diagram showing the external shape of the steel coil produced from the hot-rolled substrate prepared in Comparative Example 2. Detailed Implementation

[0044] The technical solution of the present invention will be described in full and clearly below with reference to the embodiments and accompanying drawings. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0045] A hot-rolled substrate for galvanizing, wherein the chemical composition of the hot-rolled substrate and its mass percentage are as follows: C 0.03%~0.055%, Si≤0.04%, Mn 0.1%~0.3%, P≤0.018%, S≤0.004%, Als 0.01%~0.04%, with the balance being Fe and unavoidable impurities.

[0046] The above-mentioned method for manufacturing a hot-rolled substrate for galvanizing includes the following steps: converter smelting, LF furnace refining, slab casting, homogenization in a soaking furnace, descaling, precision rolling, laminar flow cooling, and coiling.

[0047] Example

[0048] A hot-rolled substrate for galvanizing, wherein the chemical composition of the hot-rolled substrate and its mass percentage are as follows: C 0.03%~0.055%, Si≤0.04%, Mn 0.1%~0.3%, P≤0.018%, S≤0.004%, Als 0.01%~0.04%, with the balance being Fe and unavoidable impurities.

[0049] The specific production steps of the above-mentioned method for manufacturing a hot-rolled substrate for galvanizing are as follows:

[0050] 1. In converter smelting, the sulfur content in the molten steel at the final stage should be ≤0.025%, the tapping temperature should be ≥1630℃, and a double-barrier slag-blocking method should be used for tapping to ensure that the phosphorus content meets the requirements.

[0051] 2. LF furnace refining: processing time is 50-80 minutes, and the off-site ALS is controlled at a target of 0.035%;

[0052] 3. Slab casting: The key points for controlling the casting process are as follows:

[0053] 1) The thickness of the billet is 70-80mm, and the thickness of the copper plate in the crystallizer is ≥18mm;

[0054] 2) The entire casting process is protected by a tundish, with a tundish tonnage of >35 tons and a continuous casting tonnage of >30 tons;

[0055] 3) Pulling speed control: The pulling speed is kept constant at 4.6 to 5.0 m / min.

[0056] 4) The cooling water inlet temperature of the crystallizer is 33–35℃, the water flow rate on the wide side of the crystallizer is 5600–6700 L / min, and the water flow rate on the narrow side is 200–250 L / min, ensuring a heat flux of 2.54–2.7 MW / m² on the wide side. 3 The narrow-side heat flux is 2.0–2.2 MW / m. 3 ;

[0057] 5) The protective slag is controlled by using ultra-low carbon protective slag: basicity is 1.0±0.05R, melting point is 1030±30℃, and viscosity is 0.1±0.05Pa.s / 1300℃;

[0058] 6) The secondary cooling water adopts a weak cooling control mode, with the secondary cooling water temperature >28℃, the water flow rate of zone 1.0 of sector 1 is 350~400L / min, and the cooling water flow rate of zones 4.2~7.2 is ≤120L / min.

[0059] 4. Homogenization in the soaking furnace: A slab from the previous casting is reserved in the soaking furnace for cleaning of the furnace rollers. After the furnace rollers are cleaned, the slab enters the soaking furnace for homogenization. The temperature of the slab exiting the furnace is controlled at 1170-1190℃, and the time in the furnace does not exceed 35 minutes. The slab running speed is 0.6-0.8m / s.

[0060] 5. Descaling: High-pressure water is used to descale the billet, and the inlet pressure of the descaling water is controlled to be no less than 200 bar and the outlet pressure is no less than 300 bar to ensure that the iron oxide scale is completely removed before rolling.

[0061] 6. Finishing rolling: A seven-stand mill is used for finishing rolling, and the final rolling temperature is controlled at 880-920℃, while the cooling water of the side guide plates is turned off.

[0062] 7. Laminar flow cooling: The cooling is slowed down by using a front-end intermittent cooling method. The water volume ratio of the upper pipe to the lower pipe of the laminar flow cooling manifold is 4:5.

[0063] 8. Coiling: The side guide plate is controlled by micro-spark. The holding pressure of the side guide plate during coiling is 2-4KN to ensure the shape of the plate without damaging the edge of the steel coil, thus obtaining a hot-rolled substrate for galvanizing.

[0064] A batch of hot-rolled substrates were prepared according to the above-mentioned composition design and production process parameters. The specific chemical composition of the hot-rolled substrates is shown in Table 1.

[0065] Table 1 Chemical composition (wt%) of various embodiments of the present invention

[0066] Example C Si Mn P S Als 1 0.031 0.040 0.12 0.016 0.0034 0.0189 2 0.040 0.025 0.13 0.015 0.00222 0.0256 3 0.039 0.031 0.14 0.014 0.00163 0.0198 4 0.055 0.040 0.19 0.016 0.00181 0.0186 5 0.033 0.038 0.28 0.014 0.00148 0.0356 6 0.044 0.034 0.22 0.009 0.00137 0.0246 7 0.049 0.039 0.30 0.018 0.0016 0.0291

[0067] The hot-rolled substrate prepared in the example was hot-dip galvanized: the medium was zinc liquid with a Zn content of 99.5% or higher, the liquid temperature was 460-490°C, the temperature of the hot-rolled substrate when entering the zinc pot was 430-460°C, and the cooling method after galvanizing was air cooling and blow-drying with a fan, with a cooling rate of 60-100°C / s.

[0068] Figure 1 This is an external view of the steel coil produced from the hot-rolled substrate prepared in Example 1; Figure 2 This is a surface view of the finished hot-rolled substrate prepared in Example 1 after galvanizing. Figure 1It can be seen that the steel coils produced from the hot-rolled substrate prepared by this invention do not have problems with edge fraying and brittleness, and there is no problem with furnace bottom roll damage; Figure 2 It can be seen that the hot-rolled substrate prepared by the present invention has good surface quality after galvanizing and no geometric defects.

[0069] Comparative Example 1

[0070] A hot-rolled substrate for galvanizing, the chemical composition of the hot-rolled substrate and its mass percentage are as follows: C: 0.04%, Si: 0.03%, Mn: 0.25%, P: 0.019%, S: 0.003%, Als: 0.035%, with the remainder being Fe and unavoidable impurities.

[0071] The specific production steps of the above-mentioned method for manufacturing a hot-rolled substrate for galvanizing are as follows:

[0072] 1. Converter smelting, tapping temperature 1650℃, normal slag blocking during tapping.

[0073] 2. Refining is carried out in the LF furnace for 60 minutes, and the off-site Als is controlled at a target of 0.035%.

[0074] 3. Slab casting: The key points for controlling the casting process are as follows:

[0075] 1) The billet thickness is 80mm, and the copper plate thickness of the crystallizer is 17mm;

[0076] 2) The entire casting process is protected by a tundish, with a tundish capacity of 25 tons and a continuous casting capacity of 20 tons;

[0077] 3) Crystallizer water flow settings: The cooling water inlet temperature of the crystallizer is 32℃, the water flow rate on the wide side of the crystallizer is 7200L / min, the water flow rate on the narrow side is 260L / min, and the heat flux on the wide side is 2.82MW / m². 3 The narrow-side heat flux is 2.35 MW / m. 3 .

[0078] 4) Pulling speed control: The pulling speed is kept constant at 5.2m / min.

[0079] 5) Control of protective slag: Ultra-low carbon protective slag is used, with an alkalinity of 0.92R, a melting point of 990℃, and a viscosity of 0.17Pa.s / 1300℃.

[0080] 6) The secondary cooling water adopts a weak cooling control mode, with the secondary cooling water temperature controlled at 27℃. The water flow rate in zone 1.0 of sector 1 is 410L / min, and the cooling water flow rate in zones 4.2 to 7.2 is 130L / min.

[0081] 4. Homogenization in the soaking furnace: The billet exit temperature is controlled at 1170℃, and the time in the furnace is 28 minutes. The billet running speed is 0.9 m / s.

[0082] 5. Descaling: High-pressure water is used to descale the billet, and the inlet pressure of the descaling water is controlled at 240 bar and the outlet pressure is 320 bar to ensure that the iron oxide scale is completely removed before rolling.

[0083] 6. Finishing Rolling: A seven-stand mill is used for finishing rolling, with the final rolling temperature controlled at 900℃. The cooling water for the finishing rolling side guide plates is turned off.

[0084] 7. Laminar flow cooling: The front-end intermittent cooling method is adopted, and the water volume ratio of the upper pipe to the lower pipe of the laminar flow cooling manifold is 4:5.

[0085] 8. Coiling: The side guide plate is controlled by micro-spark, and the holding pressure of the side guide plate is 2-4KN to obtain the hot-rolled substrate for galvanizing.

[0086] The hot-rolled substrate prepared in Comparative Example 1 was galvanized. The medium used was zinc bath with a Zn content of 99.5% or higher. The bath temperature was 460-490℃. The temperature of the hot-rolled substrate when it entered the zinc pot was 430-460℃. The cooling method after galvanizing was air cooling, and the cooling rate was 60-100℃ / s.

[0087] Figure 3 This is a diagram showing the elongated linear defects on the hot-rolled substrate prepared in Comparative Example 1 after galvanizing. Figure 3 It can be seen that the surface of the finished product after galvanizing the hot-rolled substrate prepared in Comparative Example 1 has long linear defects.

[0088] Comparative Example 2

[0089] A hot-rolled substrate for galvanizing, wherein the chemical composition of the hot-rolled substrate and its mass percentage are as follows: C: 0.042%, Si: 0.029%, Mn: 0.17%, P: 0.018%, S: 0.003%, Als: 0.030%, with the remainder being Fe and unavoidable impurities.

[0090] The specific production steps of the above-mentioned method for manufacturing a hot-rolled substrate for galvanizing are as follows:

[0091] 1. Converter smelting, tapping temperature 1670℃, normal slag blocking during tapping.

[0092] 2. Refining is carried out in the LF furnace for 60 minutes, and the off-site Als is controlled at a target of 0.035%.

[0093] 3. Slab casting: The key points for controlling the casting process are as follows:

[0094] 1) The billet thickness is 70mm, and the copper plate thickness of the crystallizer is 21mm;

[0095] 2) The entire casting process is protected by a tundish, with a tundish capacity of 30 tons and a continuous casting capacity of 25 tons;

[0096] 3) Crystallizer water flow settings: The cooling water inlet temperature of the crystallizer is 33℃, the water flow rate on the wide side of the crystallizer is 6700L / min, the water flow rate on the narrow side is 240L / min, and the heat flux on the wide side is 2.67MW / m². 3 The narrow-side heat flux is 2.2 MW / m. 3 .

[0097] 4) Pulling speed control: The pulling speed is kept constant at 4.8m / min.

[0098] 5) Control of protective slag: Ultra-low carbon protective slag is used, with an alkalinity of 0.92R, a melting point of 990℃, and a viscosity of 0.17Pa.s / 1300℃.

[0099] 6) The secondary cooling water adopts a weak cooling control mode, with the secondary cooling water temperature controlled at 27℃. The water flow rate in zone 1.0 of sector 1 is 380L / min, and the cooling water flow rate in zones 4.2 to 7.2 is 110L / min.

[0100] 4. Homogenization in the soaking furnace: The billet exit temperature is controlled at 1170℃, and the time in the furnace is 28 minutes. The billet running speed is 0.6 m / s.

[0101] 5. Descaling: High-pressure water is used to descale the billet, and the inlet pressure of the descaling water is controlled at 240 bar and the outlet pressure is 320 bar to ensure that the iron oxide scale is completely removed before rolling.

[0102] 6. Finishing rolling: A seven-stand mill is used for finishing rolling, and the final rolling temperature is controlled at 860℃.

[0103] 7. Laminar flow cooling: The front-end cooling method is adopted, and the water volume ratio of the upper and lower pipes of the laminar flow cooling manifold is 4:5.

[0104] 8. Coiling: The side guide plate is controlled by micro-spark, and the holding pressure of the side guide plate is 4-6KN to obtain the hot-rolled substrate for galvanizing.

[0105] The hot-rolled substrate prepared in Comparative Example 2 was galvanized: the medium was zinc bath with a Zn content of 99.5% or higher, the bath temperature was 460-490℃, the temperature of the hot-rolled substrate when entering the zinc pot was 430-460℃, the cooling method after galvanizing was air cooling and blow-drying with a fan, and the cooling rate was 60-100℃ / s.

[0106] Figure 4 This is an outline drawing of the steel coil produced from the hot-rolled substrate prepared in Comparative Example 2. Figure 4 It can be seen that the steel coils produced from the hot-rolled substrate prepared in Comparative Example 2 have problems with edge brittleness and edge breakage.

[0107] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A hot-rolled substrate for galvanizing, characterized in that, The chemical composition of the hot-rolled substrate and its mass percentage are as follows: C 0.03%~0.044%, Si≤0.04%, Mn 0.1%~0.22%, P≤0.018%, S≤0.004%, Als 0.01%~0.0256%, with the balance being Fe and unavoidable impurities; The method for manufacturing the hot-rolled substrate includes the following steps: converter smelting, LF furnace refining, slab casting, homogenization in a soaking furnace, descaling, finish rolling, laminar flow cooling, and coiling. The process parameters are controlled as follows during the slab casting process: (1) Crystallizer water flow settings: The cooling water inlet temperature of the crystallizer is 33-35℃, the water flow rate on the wide side of the crystallizer is 5600-6700 L / min, the water flow rate on the narrow side is 200-250 L / min, and the heat flux on the wide side is 2.54-2.7 MW / m 3 The narrow-side heat flux is 2.0–2.2 MW / m. 3 ; (2) The protective slag is controlled by ultra-low carbon protective slag: basicity is 1.0±0.05R, melting point is 1030±30℃, and viscosity is 0.1±0.05Pa.s / 1300℃; (3) The secondary cooling water adopts a weak cooling control mode, the secondary cooling water temperature is >28℃, the water flow rate of the 1.0 zone of the sector is 350~400 L / min, and the cooling water flow rate of the 4.2~7.2 zones is ≤120 L / min; In the step of homogenizing heat in the homogenizing furnace: (1) Reserve a slab from the previous casting in the soaking furnace for cleaning the furnace rollers. After the furnace rollers are cleaned, the slab enters the soaking furnace for soaking. Control the slab exit temperature to 1170-1190℃ and the time in the furnace to not exceed 35 minutes. (2) The running speed of the slab is 0.6 to 0.8 m / s; In the descaling step, the inlet pressure of the descaling water is controlled to be no less than 200 bar and the outlet pressure is no less than 300 bar. In the finishing rolling step, a seven-stand mill is used for finishing rolling, the final rolling temperature is 880-920℃, and the cooling water of the side guide plate is turned off. In the laminar flow cooling step, a front-end interval cooling method is adopted, and the water volume ratio of the upper pipe to the lower pipe of the laminar flow cooling manifold is 4:5; in the winding step, the side guide plate is controlled by micro-spark, and the clamping pressure of the winding side guide plate is 2-4KN.

2. The hot-rolled substrate for galvanizing according to claim 1, characterized in that, In the converter smelting process, the sulfur content in the molten steel is controlled to be ≤0.025% at the end point, the tapping temperature is ≥1630℃, and a double-barrier slag-blocking method is used for tapping.

3. The hot-rolled substrate for galvanizing according to claim 1, characterized in that, In the refining step of the LF furnace, the processing time is 50 to 80 minutes, and the off-site ALS is controlled at a target of 0.035%.

4. The hot-rolled substrate for galvanizing according to claim 1, characterized in that, The slab casting process also includes the control of the following process parameters: (4) The thickness of the billet is 70-80 mm, and the thickness of the copper plate of the crystallizer is ≥18 mm; (5) The casting process is protected by a tundish throughout, with a tundish tonnage of >35 tons and a continuous casting tonnage of >30 tons; (6) The pulling speed is 4.6 to 5.0 m / min.

5. A method for manufacturing a hot-rolled substrate for galvanizing according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Converter smelting steps: control the sulfur content in the molten steel to ≤0.025% at the end point, the tapping temperature to ≥1630℃, and adopt double-barrier slag blocking at tapping; 2) LF furnace refining step: processing time is 50-80 minutes, and the off-site ALS is controlled at a target of 0.035%; 3) Slab casting steps, process parameters are controlled as follows: (1) Crystallizer water flow settings: The cooling water inlet temperature of the crystallizer is 33-35℃, the water flow rate on the wide side of the crystallizer is 5600-6700 L / min, the water flow rate on the narrow side is 200-250 L / min, and the heat flux on the wide side is 2.54-2.7 MW / m 3 The narrow-side heat flux is 2.0–2.2 MW / m. 3 ; (2) The protective slag is controlled by ultra-low carbon protective slag: basicity is 1.0±0.05R, melting point is 1030±30℃, and viscosity is 0.1±0.05Pa.s / 1300℃; (3) The secondary cooling water adopts a weak cooling control mode, the secondary cooling water temperature is >28℃, the water flow rate of section 1.0 of the sector is 350~400 L / min, and the cooling water flow rate of zone 4.2~7.2 is ≤120 L / min; (4) The thickness of the billet is 70-80 mm, and the thickness of the copper plate of the crystallizer is ≥18 mm; (5) The casting process is protected by a tundish throughout, with a tundish tonnage of >35 tons and a continuous casting tonnage of >30 tons; (6) The pulling speed is 4.6 to 5.0 m / min; 4) The homogenization process in the homogenizing furnace is controlled by the following process parameters: (1) Reserve a slab from the previous casting in the soaking furnace for cleaning the furnace rollers. After the furnace rollers are cleaned, the slab enters the soaking furnace for soaking. Control the slab exit temperature to 1170-1190℃ and the time in the furnace to not exceed 35 minutes. (2) The running speed of the slab is 0.6 to 0.8 m / s; 5) Descaling procedure: Control the inlet pressure of the descaling water to be no less than 200 bar and the outlet pressure to be no less than 300 bar; 6) Finishing rolling step: The finishing rolling is carried out using a seven-stand mill, with a final rolling temperature of 880-920℃, and the cooling water of the side guide plates is turned off; 7) Laminar flow cooling step: The front-end interval cooling method is adopted, and the water volume ratio of the upper pipe to the lower pipe of the laminar flow cooling manifold is 4:5; 8) Coiling step: The side guide plate is controlled by micro-spark, and the clamping pressure of the side guide plate is 2-4KN to obtain the hot-rolled substrate for galvanizing.

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