A method for reducing the amount of surface peeling of low-carbon steel ingots

Abstract

The present invention belongs to the field of iron and steel metallurgy, specifically a method for reducing the amount of surface peeling of low-carbon steel ingots. By controlling the outlet angle of the submerged nozzle during continuous casting, the impact depth of the molten steel in the crystallizer after it flows out of the submerged nozzle is increased. This method prevents large inclusions in the molten steel from floating up and being captured by the shell of the ingot, forming large inclusions near the surface. Furthermore, the wide surface of the ingot is divided into a central peeling area and an edge peeling area, with different peeling processes being used for each peeling area. This method can effectively reduce the peeling depth of the ingot while simultaneously ensuring the surface quality and yield rate of the low-carbon steel product.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, in particular to a method for reducing the amount of surface scaling of a low-carbon steel ingot. Background Art

[0002] Low-carbon production is a key area of ​​transformation and development in steel production. Low-carbon steel is often used in the production of deep-drawn cold-rolled sheet, such as automotive panels, which requires high surface quality. Continuously cast low-carbon steel ingots are a key intermediate product in this production. Due to the flow field within the mold during continuous casting, large inclusions tend to accumulate near the surface of the ingot. These large inclusions are a major cause of surface defects in low-carbon deep-drawn steel. Stripping of the ingot is often required to prevent large inclusions from forming on the cold-rolled sheet during subsequent hot and cold rolling operations, leading to surface defects. However, this process results in significant steel loss, which can increase carbon emissions from steel production. Therefore, controlling large inclusions near the surface of the ingot and performing precise stripping based on the distribution of these inclusions can improve steel production yields and reduce carbon emissions. Summary of the Invention

[0003] Aiming at the formation mechanism of surface defects of low-carbon steel cold-rolled plates and the formation and control mechanism of inclusions near the surface of continuous casting billets, the present invention proposes a method that combines the control of large-sized inclusions near the surface of the billets in the low-carbon steel continuous casting production process and the precise peeling method based on the distribution characteristics of large-sized inclusions near the surface of the continuous casting billets, which can significantly reduce the amount of peeling on the surface of low-carbon steel billets.

[0004] According to one aspect of the present invention, the present invention provides the following technical solutions:

[0005] A method for reducing the amount of surface peeling of a low-carbon steel ingot comprises the following steps:

[0006] S1. Control the outlet angle of the submerged nozzle during continuous casting (i.e., the angle at which the outlet direction is offset downward relative to the nozzle cross section) to increase the impact depth of the molten steel in the crystallizer after it flows out of the submerged nozzle outlet. This controls the floating of large-sized inclusions in the molten steel and allows them to be captured by the shell of the ingot, forming large-sized inclusions near the surface. This can also control the fluctuation of the crystallizer liquid level, suppress slag coiling near the crystallizer liquid level, and avoid the formation of large-sized slag coiling inclusions.

[0007] S2. Divide the wide surface of the ingot (i.e., the inner and outer arc surfaces of the ingot) into a central peeling area and an edge peeling area of ​​the wide surface of the ingot, and adopt differentiated peeling processes for different peeling areas.

[0008] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots according to the present invention, in step S1, the outlet angle of the submerged nozzle can be calculated, and the outlet angle θ of the submerged nozzle is:

[0009] θ=25·w α ·v β

[0010] Wherein, θ is the outlet angle of the submerged nozzle, °; w is the crystal width, m; v is the pulling speed, m / min; α and β are coefficients, with values ​​ranging from 0.5 to 1.0;

[0011] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots described in the present invention, in step S1, the large-sized inclusions are Al2O3 inclusions larger than 50 μm.

[0012] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots described in the present invention, in step S2, the total width of the peeling area in the center of the wide surface of the ingot is 1 / 2-3 / 4 of the width of the ingot, and the total width of the peeling area on both sides of the wide surface of the ingot is 1 / 4-1 / 2 of the width of the ingot.

[0013] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots described in the present invention, wherein: in the step S2, the wide surface of the ingot is peeled by a slab grinding machine; the peeling depth of the central peeling area of ​​the wide surface of the ingot is 1.5-2.5 mm, and the peeling depth of the edge peeling area of ​​the wide surface of the ingot is 2-3.5 mm; the peeling depth of the central peeling area of ​​the wide surface of the ingot is less than the peeling depth of the edge area of ​​the wide surface of the ingot, and the difference is 0.5-1.0 mm.

[0014] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots described in the present invention, in step S2, the narrow surface area of ​​the ingot is peeled by flame cleaning, and the peeling depth is 1.0-2.0 mm.

[0015] As a preferred embodiment of the method for reducing the amount of surface peeling of low-carbon steel ingots described in the present invention, in step S2, the corners of the ingots are peeled off by flame cleaning to form chamfers, the angle between the chamfered surface and the wide surface of the ingot is 110-160°, and the cleaning distance on the wide surface of the ingot is 1.5-3.0 mm.

[0016] The beneficial effects of the present invention are as follows:

[0017] This invention proposes a method for reducing the amount of surface peeling on low-carbon steel ingots. By controlling the outlet angle of the submerged nozzle during continuous casting, the impact depth of the molten steel in the mold after it flows out of the submerged nozzle is increased. This prevents large inclusions in the molten steel from floating up and being captured by the ingot shell, forming large inclusions near the surface. Furthermore, the wide surface of the ingot is divided into a central peeling area and an edge peeling area, with different peeling processes being used for each area. This method effectively reduces the peeling depth while ensuring the surface quality and yield rate of low-carbon steel products. DETAILED DESCRIPTION

[0018] The following will be a clear and complete description of the technical solutions in the embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0019] The present invention proposes a method that combines the control of large-sized inclusions near the surface of the ingot during the continuous casting production process of low-carbon steel and the precise peeling according to the distribution characteristics of large-sized inclusions near the surface of the continuous casting ingot, which can significantly reduce the amount of peeling on the surface of the low-carbon steel ingot.

[0020] The technical solution of the present invention is further described below with reference to specific embodiments.

[0021] Example 1

[0022] A domestic steel mill produced a single run of ultra-low carbon steel. The mold's submerged nozzle exit angle was originally 15°. The mold was 230 mm thick and 1500 mm wide, with a casting speed of 1.0 m / min. The stripping depth of the ingot was 4 mm to meet the surface quality requirements of the cold-rolled product, and the stripping method was flame grinding.

[0023] According to the method of the present invention, taking α=0.5 and β=0.5, it is calculated that the outlet angle of the submerged nozzle should be 30°. When using this angle nozzle for production, the fluctuation of the liquid level in the crystallizer within the casting is less than or equal to ±6mm. The peeling method of the wide side of the billet is unified as peeling with a grinding machine, and the peeling depth is changed to 2.5mm for the peeling area in the center of the wide side of the billet (this area is the 3 / 4 area in the center of the wide side of the billet), and the peeling depth is changed to 3.5mm for the peeling area on the edge of the wide side of the billet (this area is the 1 / 8 area on both sides of the wide side of the billet); flame cleaning is uniformly adopted for the narrow side and corner areas of the billet, wherein the peeling depth of the narrow side of the billet is 1mm, and the corners are cleaned into chamfers, the angle between the chamfered surface and the wide side of the billet is 120°, and the cleaning distance of the chamfer in the direction of the wide side of the billet is 2mm.

[0024] The inclusion degradation rate of the cold-rolled sheet prepared by the cast billet after peeling in this embodiment is reduced by 3%.

[0025] Example 2

[0026] A domestic steel mill produces a single run of low-carbon steel. The mold's submerged nozzle exit angle was originally 20°. The mold was 230 mm thick and 1900 mm wide, with a casting speed of 1.3 m / min. The stripping depth for the ingot was 5 mm, based on the surface quality requirements for the cold-rolled product. The stripping was performed using a grinding machine.

[0027] According to the method of the present invention, taking α=0.5 and β=0.5, it is calculated that the outlet angle of the submerged nozzle should be 40°. When using this angle nozzle for production, the fluctuation of the liquid level in the crystallizer within the casting is less than or equal to ±6mm. The peeling method of the wide side of the billet is unified as peeling with a grinding machine, and the peeling depth is changed to 2mm for the peeling area in the center of the wide side of the billet (this area is the 3 / 4 area in the center of the wide side of the billet), and the peeling depth is changed to 2.7mm for the peeling area on the edge of the wide side of the billet (this area is the 1 / 8 area on both sides of the wide side of the billet); the narrow side and corner areas of the billet are uniformly flame cleaned, wherein the peeling depth of the narrow side of the billet is 1.5mm, and the corners are cleaned into chamfers, with the angle between the chamfered surface and the wide side of the billet being 120°, and the cleaning distance of the chamfer in the direction of the wide side of the billet is 2mm.

[0028] The inclusion degradation rate of the cold-rolled sheet prepared by the cast slab after peeling in this embodiment is reduced by 4%.

[0029] 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 transformations made by using the contents of the present invention specification under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for reducing the amount of surface peeling of low-carbon steel ingots, characterized in that: The steps include: S1. Control the outlet angle of the submerged nozzle during continuous casting to increase the impact depth of the molten steel in the crystallizer after it flows out of the submerged nozzle outlet, and control the large-sized inclusions in the molten steel to float up and be captured by the shell of the ingot, forming large-sized inclusions near the surface; S2. Divide the wide surface of the ingot into a central peeling area and an edge peeling area of ​​the wide surface of the ingot, and adopt different peeling processes for different peeling areas; In step S1, the outlet angle θ of the submerged nozzle is: θ=25·w α ·v β Where, θ is the outlet angle of the submerged nozzle, °; w is the width of the crystallizer, m; v is the casting speed, m / min; α and β are coefficients, with values ​​ranging from 0.5 to 1.0; In the step S1, the large-sized inclusions are Al2O3 inclusions larger than 50 μm.

2. The method for reducing the amount of surface peeling of low-carbon steel ingots according to claim 1, characterized in that: In step S2, the total width of the peeling area in the center of the wide surface of the ingot is 1 / 2-3 / 4 of the width w of the ingot, and the total width of the peeling areas on both sides of the wide surface of the ingot is 1 / 4-1 / 2 of the width w of the ingot.

3. The method for reducing the amount of surface peeling of low-carbon steel ingots according to claim 1, characterized in that: In the step S2, the wide surface of the ingot is peeled using a slab grinding machine; the peeling depth of the central peeling area of ​​the wide surface of the ingot is 1.5-2.5 mm, and the peeling depth of the edge peeling area of ​​the wide surface of the ingot is 2-3.5 mm; the peeling depth of the central peeling area of ​​the wide surface of the ingot is less than the peeling depth of the edge area of ​​the wide surface of the ingot, and the difference is 0.5-1.0 mm.

4. The method for reducing the amount of surface peeling of low-carbon steel ingots according to claim 1, characterized in that: In step S2, the narrow surface area of ​​the ingot is flame cleaned and peeled, and the peeling depth is 1.0-2.0 mm.

5. The method for reducing the amount of surface peeling of low-carbon steel ingots according to claim 1, characterized in that: In step S2, the corners of the ingot are cleaned and peeled by flame to form chamfers, the angle between the chamfered surface and the wide surface of the ingot is 110-160 degrees, and the cleaning distance on the wide surface of the ingot is 1.5-3.0 mm.