A production method for reducing the incidence of cracks on the edge of Q235 wide and thick slabs

Abstract

The present invention provides a production method for reducing the incidence of edge cracks of Q235 wide and thick slabs, comprising the following steps: (1) converter smelting, with an iron-steel ratio of 850 kg / t, and adding silicon-manganese alloy and ferrosilicon weak deoxidation during the steel tapping process; (2) adding fluorite, lime, calcium carbide, and Taiwan aluminum to LF for strong stirring to promote sufficient pre-melting of the slag, diffusion deoxidation, and then power supply to form white slag, with the LF outlet composition controlled as follows: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, ALs: 0.007-0.015%, S≤0.010%; (3) continuous casting process :A. The cross-section of the slab casting machine is 300mm×2200mm, and the casting speed is 0.80m / min; B. An immersion nozzle with an outlet inclination angle of 12°, an area of ​​4500 square millimeters, and an insertion depth of 110-140mm is adopted; C. Low melting point, low alkalinity, and low viscosity mold slag is used to slow down heat transfer; D. Weak cooling is adopted for secondary cooling water distribution; E. The side taper of the crystallizer is 1.2%; F. The sum of the inner and outer arcs of the wide surface taper of the crystallizer is controlled at 1.6-2.4mm, and the inner and outer arcs are both controlled at 0.8-1.2mm. The method of the present invention can reduce the incidence of subcutaneous cracks on the edge of Q235 wide and thick slabs to below 1%.

Description

Technical Field

[0001] The present invention relates to the technical field of steelmaking, in particular to a production method for reducing the incidence of cracks at deviated edges of Q235 wide and thick slabs. Background Art

[0002] Medium and heavy plate is widely used in industries such as construction, shipbuilding, naval vessels, automobiles, engineering machinery, pressure vessels, and bridges. It is a vital steel material upon which the national economy depends. Edge cracking is a major quality defect in medium and heavy plate. Plates with edge cracks are generally trimmed, and severe edge cracks may result in the plate being lost to stock. Q235 wide and heavy plate (thickness ≥ 300mm, width ≥ 2000mm) is prone to cracks that deviate from the edge (50-500mm from the edge). Cracks exceeding 1mm in depth require trimming, resulting in the plate being lost to stock, resulting in significant losses.

[0003] Many factors influence subcutaneous cracking in Q235 wide and thick slabs (thickness ≥ 300mm, width ≥ 2000mm), including steel grade composition, vibration mark depth, mold slag adaptability, molten steel nitrogen content, and equipment accuracy. The most significant factor is the difficulty centering the submerged nozzles and uniform cooling of the molten steel in the mold. This can lead to uneven shrinkage of the primary mold shell, uneven flow of mold slag into the air gap between the copper plate and the shell, and even to the absence of slag in some weak areas. In severe cases, this can cause the liquid mold slag to break. The absence of mold slag or the thinness of the slag in these areas can lead to severe uneven cooling, resulting in subcutaneous cracking in the slab. Summary of the Invention

[0004] The present invention aims to address the problem of Q235 wide and thick slabs being prone to cracks that deviate from the edges, with crack depths exceeding 1 mm. This problem requires trimming, resulting in the product becoming a ready-to-use product. The present invention provides a production method that reduces the incidence of deviating from the edges cracks in Q235 wide and thick slabs. The method can effectively address the problem of subcutaneous cracks in Q235 wide and thick slabs, reducing the incidence of subcutaneous cracks in Q235 wide and thick slabs to less than 1%.

[0005] The present invention provides a production method for reducing the incidence of deviated edge cracks of Q235 wide and thick slabs, wherein the Q235 wide and thick slabs contain the following chemical elements in percentage by mass: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, S≤0.010%, Als: 0.007-0.015%, N≤0.0045%;

[0006] The production method for reducing the incidence of cracks at the edge of Q235 wide and thick slabs comprises the following steps:

[0007] (1) Converter smelting

[0008] A 130t converter is used for smelting, with a total charge of 165-170t of molten iron and scrap steel. To ensure a good converter heat balance, the iron-to-steel ratio is 850kg / t. Argon is blown from the bottom throughout the blowing process to ensure single-tap tapping. 7.3-7.6kg / t of silicon-manganese alloy and 0.6-0.8kg / t of ferrosilicon are added during the converter tapping process for weak deoxidation. No aluminum is added during the tapping process. The converter tapping composition is controlled as follows: Mn: 0.30-0.50%, Si: 0.20-0.25%, N ≤ 0.0030%.

[0009] (2) LF refining

[0010] After the LF furnace enters the station, first add fluorite flux (1.625-1.7kg / t) to form the bottom, then add lime (6.5-6.8kg / t). After adding fluorite and lime, add calcium carbide (1.2-1.5kg / t) and Taiwan aluminum (0.8-1.0kg / t). Strong stirring is used to promote full pre-melting of the slag and completely cover the molten steel surface for diffusion deoxidation. Then, power is supplied and the slag is refined for 6-8 minutes. The refined sample is taken for composition testing and the alloy is adjusted according to the finished product composition. White slag is produced and the white slag holding time is ≥12 minutes. The composition of the LF furnace outgoing station is controlled as follows: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, S≤0.010%, ALs: 0.010-0.020%, N≤0.0038%.

[0011] (3) Continuous casting process

[0012] A. Slab casting machine section 300mm×2200mm, casting speed 0.80m / min;

[0013] B. Use an immersion nozzle with an outlet angle of 12°, an outlet area of ​​4500 square millimeters, and an insertion depth of 110-140 mm;

[0014] C. Use mold slag with low melting point, low alkalinity and low viscosity to slow down heat transfer and improve uniformity;

[0015] D. The secondary cooling water distribution adopts weak cooling, the water volume is controlled at 0.36-0.40L / kg, and the straightening temperature is 960℃;

[0016] E. The side taper of the crystallizer is controlled at 1.2%;

[0017] F. The sum of the inner and outer arcs of the wide taper of the crystallizer is controlled within 1.6-2.4mm, and the inner and outer arcs are both controlled within 0.8-1.2mm.

[0018] The scrap steel includes steel bars and heavy scrap steel, and the scrap steel must not contain oily sludge or nitrogen-containing slag.

[0019] The silicon-manganese alloy contains the following elements in percentage by mass: Mn: 62-68%, Si: 15-18%, and the rest are Fe and unavoidable impurity elements; the ferrosilicon contains the following elements in percentage by mass: Si≥72%, and the rest are Fe and unavoidable impurity elements.

[0020] The main component of the fluorite is CaF2, the CaF2 content is ≥90%, and the rest are impurity elements.

[0021] The main component of the Taiwan aluminum is Al, the Al content is ≥99%, and the rest are impurity elements.

[0022] The protective slag with low melting point, low basicity and low viscosity used in the continuous casting process has a specific melting point of 1110-1120°C, a basicity of 1.15-1.25, a viscosity of 0.13-0.15 Pa.S1300°C, and main components: SiO2: 25.5-26.5%, Al2O3: 4.5-5.5%, CaO: 33.0-34.5%, C: 4.5-5.5%, R2O: 6.3-7.2%; wherein R is Li, Na and K among the alkali metal elements.

[0023] Compared with the prior art, the present invention has the following major improvements:

[0024] (1) Converter smelting: the iron-steel ratio is increased from 800kg / t to 850kg / t. The improved heat balance is more reasonable, avoiding the increase of nitrogen in the molten steel caused by insufficient temperature after carbon oxidation. At the same time, nitrogen-containing substances are removed from scrap steel to further reduce the nitrogen content of the steel.

[0025] (2) Argon is blown from the bottom of the converter throughout the entire blowing process, ensuring that the steel is tapped in one go, thus reducing the need for supplementary blowing and nitrogen addition;

[0026] (3) The converter steel is deoxidized by adding silicon-manganese alloy and ferrosilicon alloy instead of strong deoxidation by adding aluminum to reduce nitrogen addition in molten steel. After adopting the above method, the converter steel has N: 0.0020-0.0030%, Mn: 0.30-0.50%, and Si: 0.20-0.25%. The low N content can effectively reduce the crack incidence of the slab.

[0027] (4) The LF refining process uses calcium carbide slag and Taiwan aluminum deoxidation. The refined product composition is controlled as follows: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, S≤0.010%, Als: 0.010-0.020%, N≤0.0038%. This can effectively control the air gap between the shell and the copper plate of the crystallizer, improve the shell plasticity, and reduce the shell bulging degree. After the composition adjustment, the shell bulging degree was reduced by 0.3% compared with the pre-optimization level.

[0028] (5) During the continuous casting process, the original outlet angle was 15° and the outlet area was 5400 square millimeters. This was improved to an outlet angle of 12° and an outlet area of ​​4500 square millimeters. Through this improvement, the optimized nozzle side hole size and angle better matched the molten steel pouring volume. The temperature in the wide direction during the pouring process was more uniform, which could ensure that the liquid level was moderately active and the mold slag removal effect was better.

[0029] (6) Changing the mold protection slag to a low melting point, low alkalinity, and low viscosity one can promote the mold protection slag to flow evenly into the gap between the shell and the crystallizer copper plate, improve the heat transfer effect of the crystallizer, promote the uniform growth of the shell, and reduce the probability of subcutaneous cracks.

[0030] (7) The secondary cooling water distribution was improved from a water volume of 0.6 l / kg and a straightening temperature of 935 ° C to a water volume of 0.4 l / kg and a straightening temperature of 960 ° C. This improvement is because weak cooling can avoid the brittle straightening zone and reduce the probability of bending and straightening transverse cracks.

[0031] (8) The side taper of the crystallizer was improved from 1.05% to 1.2%. This improvement was because a low back taper would cause bulging of the side and uneven cooling. After the improvement, this situation was significantly improved;

[0032] (9) The taper of the wide surface of the crystallizer is improved from 2.8mm to the sum of the inner and outer arcs of the wide surface of the crystallizer is controlled at 1.6-2.4mm, and the inner arc and outer arc are both controlled at 0.8-1.2mm. This improvement is because if the taper of the wide surface of the crystallizer is too large, the gap between the crystallizer shell and the copper plate will be too small, making it difficult for the crystallizer protective slag to flow into the mold, resulting in unevenness, and in severe cases, causing the liquid slag to break.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) By optimizing the production process of Q235 slabs through the whole process, the occurrence rate of cracks deviating from the edge can be greatly reduced to less than 1%;

[0035] (2) The present invention is simple to operate, highly operable, easy to control, and suitable for popularization and application. DETAILED DESCRIPTION

[0036] To better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any form. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the scope of protection of the present invention.

[0037] Example 1

[0038] A production method for reducing the incidence of deviated edge cracks in Q235 wide and thick slabs, comprising the following steps:

[0039] (1) Converter smelting

[0040] A 130t converter is used for smelting, with a total charge of 168t of molten iron and scrap steel. To ensure a good converter heat balance, the iron-to-steel ratio is 850kg / t. Argon is blown from the bottom throughout the blowing process, ensuring single-shot tapping. 7.4kg / t of silicon-manganese alloy and 0.7kg / t of ferrosilicon are added during the converter tapping process for weak deoxidation. No aluminum is added during the tapping process. The converter tapping composition is controlled as follows: Mn: 0.38%, Si: 0.22%, N: 0.0027%. The scrap steel includes rebar and heavy scrap steel, and must not contain oil sludge or nitrogen-containing slag.

[0041] (2) LF refining

[0042] After the LF furnace enters the station, 1.65kg / t of fluorite flux is first added to form the bottom, followed by 6.6kg / t of lime. After the addition of fluorite and lime, 1.4kg / t of calcium carbide and 0.9kg / t of Taiwan Aluminum are added. Strong stirring is carried out to promote the full pre-melting of the slag and completely cover the molten steel surface for diffusion deoxidation. Then, power is supplied and refined for 7 minutes. The refined sample is taken for composition testing and the alloy is adjusted according to the finished product composition. White slag is produced and held for 14 minutes. The composition of the LF furnace outgoing station is controlled as follows: C: 0.17%, Si: 0.22%, Mn: 0.59%, P: 0.027%, S: 0.008%, ALs: 0.010%, N: 0.0035%.

[0043] (3) Continuous casting process

[0044] A. Slab casting machine section 300mm×2200mm, casting speed 0.80m / min;

[0045] B. Use an immersion nozzle with an outlet angle of 12°, an outlet area of ​​4500 square millimeters, and an insertion depth of 110-130 mm;

[0046] C. Use mold flux with low melting point, low basicity, and low viscosity to slow down heat transfer and improve uniformity. The specific melting point, basicity, and viscosity of the mold flux used are 1115°C, 1.2 basicity, and 0.14 Pa.S1300°C. The specific composition is: SiO2: 26.09%, Al2O3: 5.05%, CaO: 33.76%, C: 4.98%, and R2O: 6.81%. R represents Li, Na, and K among the alkali metal elements.

[0047] D. The secondary cooling water distribution adopts weak cooling, the water volume is controlled at 0.38L / kg, and the straightening temperature is 960℃;

[0048] E. The side taper of the crystallizer is controlled at 1.2%;

[0049] F. The sum of the inner and outer arcs of the wide taper of the crystallizer is controlled at 2.1mm, the inner arc is controlled at 1.1mm, and the outer arc is controlled at 1.0mm.

[0050] The silicon-manganese alloy contains the following elements in percentage by mass: Mn: 62-68%, Si: 15-18%, and the rest are Fe and unavoidable impurity elements; the ferrosilicon contains the following elements in percentage by mass: Si ≥ 72%, and the rest are Fe and unavoidable impurity elements; the same below;

[0051] The main component of the fluorite is CaF2, the CaF2 content is ≥90%, and the rest are impurity elements; the same below;

[0052] The main component of the Taiwan aluminum is Al, the Al content is ≥99%, and the rest are impurity elements; the same below.

[0053] After testing, the Q235 wide and thick plates produced in this embodiment had an incidence rate of edge cracks of 0.48%.

[0054] Example 2

[0055] A production method for reducing the incidence of deviated edge cracks in Q235 wide and thick slabs, comprising the following steps:

[0056] (1) Converter smelting

[0057] A 130t converter is used for smelting, with a total charge of 165t of molten iron and scrap steel. To ensure a good converter heat balance, the iron-steel ratio is 850kg / t. Argon is blown from the bottom throughout the blowing process, ensuring single-shot tapping. 7.3kg / t of silicon-manganese alloy and 0.8kg / t of ferrosilicon are added during the converter tapping process for weak deoxidation. No aluminum is added during the tapping process. The converter tapping composition is controlled as follows: Mn: 0.30%, Si: 0.20%, N: 0.0028%. The scrap steel includes rebar and heavy scrap steel, and must not contain oil sludge or nitrogen-containing slag.

[0058] (2) LF refining

[0059] After the LF furnace enters the station, 1.625kg / t of fluorite flux is first added to form the bottom, followed by 6.5kg / t of lime. After the addition of fluorite and lime, 1.2kg / t of calcium carbide and 0.8kg / t of Taiwan Aluminum are added. Strong stirring is carried out to promote the full pre-melting of the slag and completely cover the molten steel surface for diffusion deoxidation. Then, power is supplied and refined for 7 minutes. The refined sample is taken for composition testing and the alloy is adjusted according to the finished product composition. White slag is produced and held for 15 minutes. The composition of the LF furnace outgoing station is controlled as follows: C: 0.18%, Si: 0.20%, Mn: 0.55%, P: 0.025%, S: 0.009%, ALs: 0.012%, N: 0.0034%.

[0060] (3) Continuous casting process

[0061] A. Slab casting machine section 300mm×2200mm, casting speed 0.80m / min;

[0062] B. Use an immersion nozzle with an outlet angle of 12°, an outlet area of ​​4500 square millimeters, and an insertion depth of 120-140 mm;

[0063] C. Use mold flux with low melting point, low basicity, and low viscosity to slow down heat transfer and improve uniformity. The specific melting point, basicity, and viscosity of the mold flux used are 1110°C, 1.15 basicity, and 0.13 Pa.S1300°C. The specific composition is: SiO2: 25.5%, Al2O3: 4.5%, CaO: 33%, C: 5.5%, and R2O: 6.3%. R represents Li, Na, and K among the alkali metal elements.

[0064] D. The secondary cooling water distribution adopts weak cooling, the water volume is controlled at 0.38L / kg, and the straightening temperature is 960℃;

[0065] E. The side taper of the crystallizer is controlled at 1.2%;

[0066] F. The sum of the inner and outer arcs of the wide taper of the crystallizer is controlled at 1.6mm, the inner arc is controlled at 0.8mm, and the outer arc is controlled at 0.8mm.

[0067] After testing, the incidence rate of edge cracks of the Q235 wide and thick plates produced in this embodiment was 0.52%.

[0068] Example 3

[0069] A production method for reducing the incidence of deviated edge cracks in Q235 wide and thick slabs, comprising the following steps:

[0070] (1) Converter smelting

[0071] A 130t converter is used for smelting, with a total charge of 170t of molten iron and scrap steel. To ensure a good converter heat balance, the iron-steel ratio is 850kg / t. Argon is blown from the bottom throughout the blowing process, ensuring single-shot tapping. 7.6kg / t of silicon-manganese alloy and 0.8kg / t of ferrosilicon are added during the converter tapping process for weak deoxidation. No aluminum is added during the tapping process. The converter tapping composition is controlled as follows: Mn: 0.50%, Si: 0.25%, N: 0.0025%. The scrap steel includes rebar and heavy scrap steel, and must not contain oil sludge or nitrogen-containing slag.

[0072] (2) LF refining

[0073] After the LF furnace enters the station, 1.7 kg / t of fluorite flux is first added to form the bottom, followed by 6.8 kg / t of lime. After the addition of fluorite and lime, 1.5 kg / t of calcium carbide and 1.0 kg / t of Taiwan Aluminum are added. Strong stirring is carried out to promote the full pre-melting of the slag and completely cover the molten steel surface for diffusion deoxidation. Then, power is supplied and refined for 7 minutes. The refined sample is taken for composition testing and the alloy is adjusted according to the finished product composition. White slag is produced and held for 15 minutes. The composition of the LF furnace outgoing station is controlled as follows: C: 0.15%, Si: 0.25%, Mn: 0.65%, P: 0.024%, S: 0.007%, ALs: 0.020%, N: 0.0033%;

[0074] (3) Continuous casting process

[0075] A. Slab casting machine section 300mm×2200mm, casting speed 0.80m / min;

[0076] B. Use an immersion nozzle with an outlet angle of 12°, an outlet area of ​​4500 square millimeters, and an insertion depth of 110-140 mm;

[0077] C. Use protective slag with low melting point, low basicity and low viscosity to slow down heat transfer and improve uniformity. The specific melting point of the protective slag with low melting point, low basicity and low viscosity is 1120℃, the basicity is 1.25, the viscosity is 0.15Pa.S1300℃, and the specific composition is: SiO2: 26.5%, Al2O3: 5.5%, CaO: 34.5%, C: 5.5%, R2O: 7.2%; R is Li, Na and K among the alkali metal elements.

[0078] D. The secondary cooling water distribution adopts weak cooling, the water volume is controlled at 0.40L / kg, and the straightening temperature is 960℃;

[0079] E. The side taper of the crystallizer is controlled at 1.2%;

[0080] F. The sum of the inner and outer arcs of the wide taper of the crystallizer is controlled at 2.4mm, the inner arc is controlled at 1.2mm, and the outer arc is controlled at 1.2mm.

[0081] After testing, the incidence rate of edge cracks of the Q235 wide and thick plates produced in this embodiment was 0.46%.

[0082] The production method of the embodiment of the present invention and the conventional production method were used to produce Q235 wide and thick plates. The incidence of edge cracks of the produced Q235 wide and thick plates is shown in Table 1 below:

[0083] Table 1 Incidence rate of edge cracks of Q235 thick and wide plates produced by the method of the embodiment of the present invention and the conventional production method

[0084]

[0085] As can be seen from Table 1 above, the method of the present invention standardizes and simplifies the operation, effectively controlling the incidence of off-edge cracks in Q235 steel. The off-edge crack incidence rates of the wide and thick plates produced in the three embodiments were all below 1%. In contrast, the off-edge crack incidence rate of Q235 steel produced under the conventional mode is as high as 15%, significantly impacting contract delivery rates. Furthermore, due to the loss of spot goods caused by steel trimming, economic benefits are lost. This indicates that the method of the present invention can effectively control the off-edge crack incidence rate of Q235 wide and thick plates, bringing higher economic benefits to enterprises.

Claims

1. A production method for reducing the incidence of off-edge cracks in Q235 wide and thick slabs, wherein the Q235 wide and thick slabs contain the following chemical elements by weight: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, S≤0.010%, Als: 0.007-0.015%, N≤0.0045%; The production method for reducing the incidence of cracks on the edge of Q235 wide and thick slabs is characterized by The steps include: (1) Converter smelting A 130t converter is used for smelting, with a total charge of 165-170t of molten iron and scrap steel. To ensure a good converter heat balance, the iron-to-steel ratio is 850kg / t. Argon is blown from the bottom throughout the blowing process to ensure single-tap tapping. 7.3-7.6kg / t of silicon-manganese alloy and 0.6-0.8kg / t of ferrosilicon are added during the converter tapping process for weak deoxidation. No aluminum is added during the tapping process. The converter tapping composition is controlled as follows: Mn: 0.30-0.50%, Si: 0.20-0.25%, N ≤ 0.0030%. (2) LF refining After the LF furnace enters the station, first add fluorite flux (1.625-1.7kg / t) to form the bottom, then add lime (6.5-6.8kg / t). After adding fluorite and lime, add calcium carbide (1.2-1.5kg / t) and Taiwan aluminum (0.8-1.0kg / t). Strong stirring is used to promote full pre-melting of the slag and completely cover the molten steel surface for diffusion deoxidation. Then, power is supplied and the slag is refined for 6-8 minutes. The refined sample is taken for composition testing and the alloy is adjusted according to the finished product composition. White slag is produced and the white slag holding time is ≥12 minutes. The composition of the LF furnace outgoing station is controlled as follows: C: 0.15-0.18%, Si: 0.15-0.30%, Mn: 0.55-0.65%, P≤0.035%, S≤0.010%, Als: 0.010-0.020%, N≤0.0038%. (3) Continuous casting process A. Slab casting machine section 300mm×2200mm, casting speed 0.80m / min; B. Use an immersion nozzle with an outlet angle of 12°, an outlet area of ​​4500 square millimeters, and an insertion depth of 110-140 mm; C. Use a mold flux with a low melting point, low basicity, and low viscosity to slow down heat transfer and improve uniformity. The mold flux has a melting point of 1110-1120°C, a basicity of 1.15-1.25, and a viscosity of 0.13-0.15 Pa·S at 1300°C. Its composition includes: SiO2: 25.5-26.5%, Al2O3: 4.5-5.5%, CaO: 33.0-34.5%, C: 4.5-5.5%, and R2O: 6.3-7.2%. R represents Li, Na, or K among the alkali metal elements. D. The secondary cooling water distribution adopts weak cooling, the water volume is controlled at 0.36-0.40L / kg, and the straightening temperature is 960℃; E. The side taper of the crystallizer is controlled at 1.2%; F. The sum of the inner and outer arcs of the wide taper of the crystallizer is controlled within 1.6-2.4mm, and the inner and outer arcs are both controlled within 0.8-1.2mm.

2. A production method for reducing the incidence of off-edge cracks in Q235 wide and thick slabs according to claim 1, characterized in that: The scrap steel includes steel bars and heavy scrap steel, and the scrap steel must not contain oily sludge or nitrogen-containing slag.

3. The method for reducing the incidence of off-edge cracks in Q235 wide and thick slabs according to claim 1, characterized in that: The silicon-manganese alloy contains the following elements in percentage by mass: Mn: 62-68%, Si: 15-18%, and the rest are Fe and unavoidable impurity elements; the ferrosilicon contains the following elements in percentage by mass: Si≥72%, and the rest are Fe and unavoidable impurity elements.

4. The method for reducing the incidence of off-edge cracks in Q235 wide and thick slabs according to claim 1, characterized in that: The main component of the fluorite is CaF2, the CaF2 content is ≥90%, and the rest are impurity elements.

5. The method for reducing the incidence of off-edge cracks in Q235 wide and thick slabs according to claim 1, characterized in that: The main component of the Taiwan aluminum is Al, the Al content is ≥99%, and the rest are impurity elements.

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