Method for reducing depth of solidification hook of low-carbon steel continuous casting billet

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a method for reducing the depth of a solidification hook of a low-carbon steel continuous casting billet, in the continuous casting process, the content of Al, Ti, N and total oxygen of molten steel entering a crystallizer is controlled, precipitation of a high-melting-point phase in casting powder is inhibited, and development and growth of a slag ring are inhibited; crystallizer casting powder with low alkalinity, low Na2O and Al2O3, low melting point and low crystallization temperature is adopted, cooling solidification and crystal precipitation of the casting powder near a meniscus are controlled, and developed growth of a slag ring is inhibited; the solidification hook depth of the low-carbon steel continuous casting billet is reduced, the surface scalping depth of the casting billet is reduced, and the surface quality and the yield of a low-carbon steel product are improved.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a method for reducing the solidification hook depth of a low-carbon steel continuous casting billet. Background Art

[0002] The carbon content in low carbon steel is extremely low, the two-phase zone is narrow, and the solidification rate of the molten steel is relatively high under strong cooling conditions. Therefore, the molten steel at the slag-steel interface at the top of the crystallizer is very easy to solidify into a hook-shaped billet shell along the shape of the meniscus. Then, during the downward process of the billet, the molten steel overflows over the hook-shaped billet shell, covering it under the surface of the billet, and finally forming a solidification hook under the billet skin.

[0003] Due to the special shape and structure of the solidification hook, it can intercept and capture the floating inclusions, so that a large number of inclusions are enriched on the surface of the ingot. Among them, large-sized inclusions will form inclusion defects during the rolling process, seriously affecting the surface quality of the cold-rolled plate. In order to reduce or eliminate the impact of the solidification hook on the surface quality of low-carbon steel products, the low-carbon steel ingot needs to be peeled on the surface. The peeling depth is often greater than the solidification groove depth, resulting in a large loss of ingot quality, increasing the production cost and carbon emission level of low-carbon steel.

[0004] In order to control the solidification hook of low-carbon steel ingot, some metallurgical workers have conducted research and proposed some improvement measures, such as increasing the continuous casting speed, increasing the superheat of molten steel pouring, etc. However, these measures are the results obtained under specific production process equipment conditions, and often cannot solve the problem when the production conditions change. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a method for reducing the solidification hook depth of low-carbon steel continuous casting billet.

[0006] According to one aspect of the present invention, the present invention provides the following technical solution:

[0007] A method for reducing the solidification hook depth of a low-carbon steel continuous casting billet comprises controlling the Al, Ti, N and total oxygen contents of the molten steel entering a crystallizer during the continuous casting process, and using a crystallizer protective slag with low basicity, low Na2O and Al2O3, low melting point and low crystallization temperature.

[0008] As a preferred embodiment of the method for reducing the solidification hook depth of low-carbon steel continuous casting billet according to the present invention, for low-carbon steel with a Ti content of ≤0.02wt%, the Al content in the molten steel is controlled to be less than 0.04wt%, and the total oxygen content is controlled to be less than 13.0×10 -6 , N content <30.0×10 -6 For low carbon steel with Ti content > 0.02wt%, the mass ratio of Al to Ti in the molten steel should be ≥ 0.4, and the total oxygen content should be < 13.0×10 -6, N content<25.0×10 -6 .

[0009] As a preferred embodiment of the method for reducing the solidification hook depth of low carbon steel continuous casting billet described in the present invention, the mass ratio of CaO to SiO2 in the crystallizer protection slag is 0.85-1.0, the content of Na2O is ≤5.5wt%, the content of Al2O3 is ≤4.8wt%, the crystallization temperature of the crystallizer protection slag is ≤1050℃, and the melting point is ≤1180℃.

[0010] As a preferred embodiment of the method for reducing the solidification hook depth of a low-carbon steel continuous casting billet described in the present invention, in the continuous casting process, the temperature of the molten steel in the crystallizer is controlled to be at least 25° C. higher than the liquidus temperature of the molten steel.

[0011] As a preferred embodiment of the method for reducing the solidification hook depth of low-carbon steel continuous casting billet described in the present invention, in which: during the continuous casting process, medium and high steel throughput is adopted for continuous casting, and the continuous casting steel throughput Q is controlled to be:

[0012]

[0013] Among them, Q is the continuous casting steel throughput, t / min; n is the total number of castings of the continuous casting machine; S i is the cross-sectional area of ​​the crystallizer for the i-th stream in m 2 δ is the coefficient, δ≥8.0. When δ<8.0, it is low-throughput continuous casting, and when δ≥8.0, it is medium-high-throughput continuous casting.

[0014] As a preferred embodiment of the method for reducing the solidification hook depth of low-carbon steel continuous casting billet described in the present invention, in which: during the continuous casting process, high-frequency small-amplitude crystallizer vibration is adopted, specifically, the crystallizer vibration frequency is controlled to be ≥140 times / min, and the crystallizer amplitude is ≤5.0mm.

[0015] As a preferred embodiment of the method for reducing the solidification hook depth of low-carbon steel continuous casting billet described in the present invention, wherein: during the continuous casting process, the depth of the crystallizer submerged water nozzle inserted into the molten steel is controlled to be 120-220 mm, and the outlet angle of the crystallizer submerged water nozzle is controlled to be 20-45°.

[0016] As a preferred embodiment of the method for reducing the solidification hook depth of a low-carbon steel continuous casting billet described in the present invention, during the continuous casting process, the fluctuation of the liquid level in the crystallizer is controlled within ±5.0 mm.

[0017] The beneficial effects of the present invention are as follows:

[0018] The present invention provides a method for reducing the solidification hook depth of a low-carbon steel continuous casting billet. During the continuous casting process, the Al, Ti, N and total oxygen contents of the molten steel entering the crystallizer are controlled to inhibit the precipitation of high-melting-point phases in the protective slag and inhibit the growth of the slag ring. A crystallizer protective slag with low basicity, low Na2O and Al2O3, low melting point and low crystallization temperature is used to control the cooling and solidification of the protective slag near the meniscus and the precipitation of crystals to inhibit the growth of the slag ring. The present invention reduces the solidification hook depth of the low-carbon steel continuous casting billet, reduces the peeling depth of the billet surface, and improves the surface quality and yield rate of the low-carbon steel product. DETAILED DESCRIPTION

[0019] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The present invention proposes a method for reducing the solidification hook depth of a low-carbon steel continuous casting billet. Starting from controlling the slag-steel reaction in a crystallizer, during the continuous casting process, the Al, Ti, N and total oxygen contents of the molten steel entering the crystallizer are controlled to inhibit the precipitation of high-melting point phases in the protective slag and inhibit the growth of the slag ring; a crystallizer protective slag with low basicity, low Na2O and Al2O3, low melting point and low crystallization temperature is used to control the cooling and solidification of the protective slag near the meniscus and the precipitation of crystals to inhibit the growth of the slag ring; and the solidification hook depth of the low-carbon steel continuous casting billet is reduced.

[0021] At the same time, during the continuous casting process, the present invention also takes into account the influence of the continuous casting process and its parameters, and controls the temperature of the molten steel in the crystallizer to be at least 25°C higher than the liquidus temperature of the molten steel, which can increase the temperature of the protective slag layer in the crystallizer, control the condensation of the protective slag on the wall of the crystallizer, inhibit the development and growth of the slag ring, and promote the melting of the tip of the solidification hook; adopting medium and high steel throughput continuous casting can improve the flow and heat transfer of the molten steel in the meniscus area of ​​the crystallizer and inhibit the freezing of the meniscus; adopting high-frequency and small-amplitude crystallizer vibration can inhibit the length and depth of the initial solidified billet shell being pressed into the interior of the molten steel; controlling the crystallizer liquid level fluctuation can control the development of the slag ring; controlling the insertion depth of the immersion nozzle and the steel outlet angle can promote the flow and heat transfer of the molten steel near the meniscus, control the reaction of the molten steel and the protective slag, control the liquid level fluctuation in the crystallizer, control the development of the slag ring and promote the melting of the tip of the solidification hook. The present invention further controls the temperature of the molten steel, the properties of the protective slag, the flow and fluctuation of the molten steel in the crystallizer, thereby realizing comprehensive control of the development of the slag ring in the crystallizer, the deformation of the initial solidification shell, and the melting and breaking of the tip of the solidification hook, thereby better realizing the depth control of the low-carbon steel solidification hook.

[0022] According to one aspect of the present invention, the present invention provides the following technical solution:

[0023] A method for reducing the solidification hook depth of a low-carbon steel continuous casting billet comprises controlling the Al, Ti, N and total oxygen contents of the molten steel entering a crystallizer during the continuous casting process, and using a crystallizer protective slag with low basicity, low Na2O and Al2O3, low melting point and low crystallization temperature.

[0024] Preferably, for low carbon steel with Ti content ≤ 0.02wt%, the Al content in the molten steel is controlled to be less than 0.04wt% and the total oxygen content is controlled to be less than 13.0×10 -6 , N content <30.0×10 -6 For low carbon steel with Ti content > 0.02wt%, the mass ratio of Al to Ti in the molten steel should be ≥ 0.4, and the total oxygen content should be < 13.0×10 -6 , N content<25.0×10 -6 . Control the Ti in the molten steel to enter the protective slag liquid slag layer; through these measures, control the precipitation of high melting point substances in the molten steel in the protective slag;

[0025] Preferably, the mass ratio of CaO to SiO2 in the crystallizer protective slag is 0.85-1.0, the content of Na2O is ≤5.5wt%, the content of Al2O3 is ≤4.8wt%, the crystallization temperature of the crystallizer protective slag is ≤1050℃, and the melting point is ≤1180℃; at the same time, by increasing the supply of protective slag around the crystallizer, etc., the thickness of the protective slag liquid slag layer near the crystallizer wall in the crystallizer is ensured to be ≥10mm, so as to control the cooling and solidification of the protective slag near the meniscus and the precipitation of crystals, thereby inhibiting the developed growth of the slag ring.

[0026] Preferably, during the continuous casting process, the temperature of the molten steel in the crystallizer is controlled to be at least 25° C. higher than the liquidus temperature of the molten steel. The temperature of the protective slag layer is increased to control the development of the slag ring and promote the melting of the tip of the solidification hook.

[0027] Preferably, in the continuous casting process, medium and high steel throughput continuous casting is adopted, and the continuous casting steel throughput Q is controlled to be:

[0028]

[0029] Among them, Q is the continuous casting steel throughput, t / min; n is the total number of castings of the continuous casting machine; S i is the cross-sectional area of ​​the crystallizer for the i-th stream in m 2 δ is a coefficient, δ≥8.0. In the present invention, it is considered that when δ<8.0, it is low-throughput continuous casting, and when δ≥8.0, it is medium-high-throughput continuous casting.

[0030] Preferably, during the continuous casting process, high-frequency and small-amplitude crystallizer vibration is used, specifically, the crystallizer vibration frequency is controlled to be ≥140 times / min, and the crystallizer amplitude is ≤5.0 mm, so as to fully control the depth and length of the initial solidified shell in the crystallizer pressed into the molten steel.

[0031] Preferably, during the continuous casting process, the depth of the crystallizer submerged nozzle inserted into the molten steel is controlled to be 120-220 mm, and the outlet angle of the crystallizer submerged nozzle is controlled to be 20-45° to promote the flow and heat transfer on the surface of the crystallizer molten steel.

[0032] Preferably, during the continuous casting process, the fluctuation of the liquid level in the crystallizer is controlled within ±5.0 mm to suppress the development of the slag ring.

[0033] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] A domestic steel plant produces low carbon steel DC06. During continuous casting, by optimizing the refining outside the furnace and protective pouring technology, the C content of the molten steel in the crystallizer is 0.0020wt%, the Al content is 0.030wt%, the Ti content is 0.065wt%, and the N content is 18.0×10 -6 , the total oxygen content is 11.0×10 -6 The components of the mold protective slag used are: 41.14wt% SiO2, 4.45wt% Al2O3, 36.64wt% CaO, 3.99wt% Na2O, 0.156wt% TiO2, 3.01wt% MgO, and the rest are carbon, K2O, FeO, etc. The melting point of the protective slag is 1125℃, and the crystallization temperature is 960℃. When adding protective slag to the crystallizer, priority is given to ensuring the protective slag induction near the crystallizer wall around the crystallizer, where the average thickness of the liquid slag layer is 12mm; the continuous casting machine has two-stream ingots, and the cross-sectional area of ​​the two-stream crystallizer is 0.375m 2 The total steel throughput of the two streams is 6.5t / min; the continuous casting mold vibration adopts high-frequency and small-amplitude mode for continuous casting. The vibration frequency of the continuous casting machine mold is greater than 160 times / min, and the crystallizer amplitude is 5.0mm; the crystallizer immersion nozzle is inserted into the molten steel to a depth of 120-220mm, and the nozzle outlet angle is 25°; the crystallizer liquid level fluctuation is controlled within ±5mm during continuous casting production.

[0036] The average depth of the solidification hooks of the casting blank prepared by the above method is 0.65 mm, and the maximum depth is 1.52 mm. The average depth of the solidification hooks of the casting blank without the method of the present invention is 2.1 mm, and the maximum depth is 3.5 mm.

[0037] Example 2

[0038] A domestic steel plant produces low carbon steel DC03. During continuous casting, by optimizing the refining outside the furnace and protective pouring technology, the C content of the molten steel in the crystallizer is 0.0020wt%, the Al content is 0.022wt%, the Ti content is 0.01wt%, and the N content is 24.0×10 -6 , the total oxygen content is 12.0×10 -6 The components of the mold protective slag used are: 43.25wt% SiO2, 4.8wt% Al2O3, 38.93wt% CaO, 3.65wt% Na2O, 0.23wt% TiO2, 3.01wt% MgO, and the rest are carbon, K2O, FeO, etc. The melting point of the protective slag is 1103℃, and the crystallization temperature is 982℃. When adding protective slag to the crystallizer, priority is given to ensuring the protective slag induction near the crystallizer wall around the crystallizer, where the average thickness of the liquid slag layer is 12mm; the continuous casting machine has two-stream casting billets, and the cross-sectional area of ​​the two-stream crystallizer is 0.375m 2 The total steel throughput of the two streams is 7.98t / min; the continuous casting mold vibration adopts high-frequency and small-amplitude mode for continuous casting. The vibration frequency of the continuous casting machine mold is greater than 160 times / min, and the crystallizer amplitude is 4.8mm; the crystallizer immersion nozzle is inserted into the molten steel to a depth of 150-210mm, and the nozzle outlet angle is 22°; the crystallizer liquid level fluctuation is controlled within ±5mm during continuous casting production.

[0039] The average depth of the solidification hooks of the casting blank prepared by the above method is 0.73 mm, and the maximum depth is 1.32 mm. The average depth of the solidification hooks of the casting blank without the method of the present invention is 2.0 mm, and the maximum depth is 3.2 mm.

[0040] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for reducing the solidification hook depth of a low-carbon steel continuous casting billet, characterized in that: During the continuous casting process, the Al, Ti, N and total oxygen contents of the molten steel entering the crystallizer are controlled, and a crystallizer protective slag with low basicity, low Na2O and Al2O3, low melting point and low crystallization temperature is used.

2. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: For low carbon steel with Ti content ≤ 0.02wt%, the Al content in the molten steel is controlled to be less than 0.04wt% and the total oxygen content is controlled to be less than 13.0×10 -6 , N content <30.0×10 -6 For low carbon steel with Ti content > 0.02wt%, the mass ratio of Al to Ti in the molten steel should be ≥ 0.4, and the total oxygen content should be < 13.0×10 -6 , N content<25.0×10 -6 .

3. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: The mass ratio of CaO to SiO2 in the crystallizer protection slag is 0.85-1.0, the content of Na2O is ≤5.5wt%, the content of Al2O3 is ≤4.8wt%, the crystallization temperature of the crystallizer protection slag is ≤1050℃, and the melting point is ≤1180℃.

4. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: During the continuous casting process, the temperature of the molten steel in the crystallizer is controlled to be at least 25°C higher than the liquidus temperature of the molten steel.

5. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: In the continuous casting process, medium and high steel throughput is adopted, and the continuous casting steel throughput Q is controlled as follows: Among them, Q is the continuous casting steel throughput, t / min; n is the total number of castings of the continuous casting machine; S i is the cross-sectional area of ​​the crystallizer for the i-th stream in m 2 ; δ is the coefficient, δ≥8.

0.

6. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: During the continuous casting process, high-frequency and small-amplitude crystallizer vibration is adopted to control the crystallizer vibration frequency to be ≥140 times / min and the crystallizer amplitude to be ≤5.0mm.

7. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: During the continuous casting process, the depth of the crystallizer submerged nozzle inserted into the molten steel is controlled to be 120-220 mm, and the outlet angle of the crystallizer submerged nozzle is controlled to be 20-45°.

8. The method for reducing the solidification hook depth of low carbon steel continuous casting billet according to claim 1, characterized in that: During the continuous casting process, the crystallizer liquid level fluctuation is controlled within ±5.0mm.

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