A continuous casting process for improving the hot charging and hot delivery temperature of slabs

Abstract

This invention discloses a continuous casting process for improving the hot charging and hot delivery temperature of slabs, comprising the following steps: (1) controlling the total amount of secondary cooling water in the continuous casting process to be 1500-2000 L / min, the amount of secondary cooling water in the foot rollers and fan-shaped 0 section of the continuous casting machine to account for 75% or more of the total amount of secondary cooling water, the amount of secondary cooling water in the bending section and straightening section to be reduced to 25% or less of the total amount of secondary cooling water, and the amount of secondary cooling water in the horizontal section to be 0; (2) using electromagnetic stirring and dynamic light pressing, the pressing range of dynamic light pressing is 0.20-0.98, and the pressing amount is 2-4%; (3) adding heat insulation covers to all conveying rollers after the slab cutting position, and the surface temperature of the slab before entering the rolling mill heating furnace is 800-1000℃. This method optimizes the distribution of secondary cooling water: increasing the cooling water volume of the foot rollers and the zero section, and reducing the cooling water volume of the subsequent bending, straightening, and horizontal sections. While reducing the total water volume and the heat loss of the billet itself, the surface and center quality of the billet are ensured by using electromagnetic stirring and dynamic light pressure.

Description

Technical Field

[0001] This invention relates to continuous casting processes in the metallurgical industry, and in particular to a continuous casting process for improving the hot charging and hot delivery temperature of slabs. Background Technology

[0002] Continuous casting is a process in which the heat of molten steel is carried away by forced cooling, solidifying it into a continuous casting billet. During the solidification process, approximately 50% of the heat is released after the molten steel passes through the crystallizer, secondary cooling zone, and air cooling zone before complete solidification. The rate at which this heat is released determines the casting machine's productivity and the quality of the billet. After the billet is cut to length, approximately 50% residual heat remains. Hot charging and hot delivery technology is a new process designed to fully utilize this residual heat. This technology effectively connects the steelmaking and rolling processes, significantly reducing energy consumption, increasing metal yield, shortening product production cycles, reducing factory floor space, and saving investment. The application of hot charging and hot delivery technology for continuous casting billets in my country began in the 1980s at Wuhan Iron and Steel Company. By the 1990s, Baosteel, Shaoguan Iron and Steel, Anshan Iron and Steel, Sanming Steel Plant, and Laiwu Steel Plant had also adopted this technology to varying degrees. The main limiting factor for hot charging and hot delivery is the quality of the billet, especially surface cracks. When the surface temperature of the billet drops to the two-phase region during hot conveyor roller transport, the precipitation of microalloying elements such as Nb, Ti, and Al can cause surface cracking due to stress during subsequent heating or rolling. With the popularization and development of continuous casting technology and energy conservation becoming the main theme of development, how to improve the hot charging rate, ensure the hot charging temperature, and avoid the two-phase region where cracks are easily generated has become a key issue of concern in the industry.

[0003] Patent application CN102059331 A discloses a hot-charging and hot-delivery process for continuously cast billets to avoid surface cracks in steel plates. This method involves rapidly cooling the billet with water spray on the conveyor rollers, quickly lowering the surface temperature to below 600°C while the internal temperature remains above 800°C. This avoids the two-phase region prone to cracking and also increases the hot-charging temperature. This method is suitable for hot-charging processes over long distances of more than 1 km on the conveyor rollers. However, for processes with conveyor rollers of several hundred meters, rapid surface cooling leads to significant heat loss from the billet itself, which is detrimental to improving the efficiency of hot-charging and hot-delivery.

[0004] Patent application CN 113649537 A discloses a method for hot charging and hot delivery of thick slabs. This method involves surface quality and flaw detection of cut sample batches, followed by centralized stacking of the cast slabs in a slow cooling zone lined with refractory bricks within three hours of inspection. The hot delivery decision is based on the sample batch inspection results. This method adds an inspection step after continuous casting, reducing defects in subsequent finished products caused by surface cracks in the cast slabs and minimizing batch quality accidents. However, this method has drawbacks: the added inspection step cannot identify cracks caused by stress cracking during heating and rolling, and it also increases inspection costs, loses heat from the cast slabs, and is not conducive to improving production efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a continuous casting process that improves the hot charging and hot delivery temperature of slabs, so as to avoid surface crack defects after rolling while improving the hot charging and hot delivery rate.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention includes the following steps:

[0007] (1) Control the total amount of secondary cooling water in the continuous casting process to be 1500-2000 L / min. The amount of secondary cooling water in the foot roll and fan-shaped 0 section of the continuous casting machine accounts for 75% or more of the total amount of secondary cooling water. The amount of secondary cooling water in the bending section and straightening section accounts for 25% or less of the total amount of secondary cooling water. The amount of secondary cooling water in the horizontal section is 0.

[0008] (2) Electromagnetic stirring and dynamic light pressing are adopted, with the pressing range of 0.20 to 0.98 and the pressing amount of 2 to 4% under dynamic light pressing;

[0009] (3) All conveyor rollers after the billet cutting position are covered with heat insulation covers, and the surface temperature of the billet before entering the steel rolling heating furnace is 800-1000℃.

[0010] Furthermore, in step (3), the billet is loaded into the heating furnace within 15 minutes after cutting.

[0011] Furthermore, in step (3), no more than 5 billets should be kept waiting to be put into the steel rolling furnace.

[0012] The beneficial effects of adopting the above technical solution are as follows: This invention optimizes the distribution of secondary cooling water by increasing the cooling water volume of the foot rollers and the zero section, while reducing the cooling water volume of the subsequent bending, straightening, and horizontal sections. This reduces the total water volume and the heat loss of the billet itself, while simultaneously ensuring the surface and center quality of the billet through electromagnetic stirring and dynamic light pressure. This invention effectively avoids post-rolling surface cracks while ensuring that the surface temperature of the billet is 800–1000°C and the internal temperature is above 1000°C when it enters the heating furnace. It also improves the hot delivery and charging rate, reduces the billet heating time, and saves energy consumption.

[0013] This invention is applicable to short-process hot charging and hot conveying where the distance from continuous casting to the heating furnace is within 500m. Currently, conventional hot conveying roller conveyors in China are quite long, generally over 1km. Considering the cost of heat preservation and the long billet transportation time, most methods adopt surface rapid cooling technology and ground-level heat preservation technology, without taking measures from the perspective of continuous casting water distribution. However, this application, by controlling the secondary cooling water control process of short-process hot charging and hot conveying, effectively improves the hot charging and hot conveying rate while avoiding surface crack defects after rolling. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to specific embodiments.

[0015] This continuous casting process for increasing the hot charging and hot delivery temperature of slabs includes the following steps:

[0016] (1) A short-process hot charging and hot delivery method with a distance of less than 500m from the continuous casting to the heating furnace is adopted. The total amount of secondary cooling water in the continuous casting process is controlled to be 1500-2000L / min. The amount of secondary cooling water in the foot roll and fan-shaped 0 section of the continuous casting machine accounts for 75% or more of the total amount of secondary cooling water. The amount of secondary cooling water in the bending section and straightening section accounts for 25% or less of the total amount of secondary cooling water. The amount of secondary cooling water in the horizontal section is 0.

[0017] Compared to conventional weak cooling processes, this process reduces the total secondary cooling water volume by 200–700 L / min. The water distribution data designed for this process is used to calculate the target control temperature for each zone using an offline water distribution model of the field equipment, thereby achieving dynamic water distribution for production.

[0018] (2) Electromagnetic stirring, dynamic light pressure, and dynamic water distribution are used to ensure the center and surface quality of the billet during the solidification process; among them, electromagnetic stirring uses two pairs of electromagnetic rollers with currents of 210-250A and 330-380A respectively; the pressure range of dynamic light pressure is 0.20-0.96 and the pressure amount is 2-4%.

[0019] (3) All conveyor rollers after the billet cutting position shall be covered with heat insulation covers. The billet shall be loaded into the steel rolling heating furnace within 15 minutes after cutting. The surface temperature of the billet before entering the steel rolling heating furnace shall be 800-1000℃. Steelmaking production and steel rolling production shall be matched with each other and kept in sync in terms of production and maintenance rhythm. After cutting, the billet shall be transported to the front of the heating furnace at the maximum roller speed. No more than 5 billets shall be waiting to be put into the steel rolling heating furnace.

[0020] (4) This method is applicable to the continuous casting process of slabs. It is mainly applicable to the hot charging and hot delivery of carbon steel, low alloy steel and container steel in short process. It can achieve a hot charging rate of 95% or more and control the surface crack defects after rolling to 0.1% or less.

[0021] Example 1: The continuous casting process for improving the hot charging and hot delivery temperature of slabs is described in detail below.

[0022] A steel plant produces 260mm × 1700mm Q235B carbon steel continuous casting billets. The secondary cooling water flow rate in the foot rolls and the 0th segment of the fan-shaped section was increased to 80% of the total secondary cooling water, while the water flow rate in the bending and straightening sections was reduced to 20% of the total secondary cooling water. The water flow rate in the horizontal section was reduced to 0, resulting in a total secondary cooling water flow rate of 1500 L / min. Compared to the original process, the total secondary cooling water flow rate was reduced by 25%. Dynamic water distribution model calculations showed that the surface temperature of the fan-shaped section increased by 70℃. Dynamic light reduction was applied to the 11th and 12th fan-shaped sections, resulting in a reduction of 3.5mm, with a reduction range of 0.3–0.96mm. Electromagnetic rollers were installed at the inlet and outlet of the two fan-shaped sections, with a current of 250A at the inlet and 380A at the outlet. The billet was rated C1.0 after sulfur stamping and center segregation. The billet is sent directly to the heating furnace 3 to 10 minutes after cutting. When it enters the furnace, the surface temperature of the billet is 830 to 1000℃, the hot charging rate reaches 97%, and the heating furnace saves 15% of fuel. The surface of the rolled steel plate is free of cracks and defects.

[0023] Example 2: The continuous casting process for improving the hot charging and hot delivery temperature of slabs is described in detail below.

[0024] A steel plant produces 230mm × 1550mm low-alloy steel Q355B continuous casting billets. The secondary cooling water flow rate in the foot rolls and the 0th segment of the fan-shaped section was increased to 75% of the total secondary cooling water flow, while the flow rate in the bending and straightening sections was reduced to 25%. The flow rate in the horizontal section was reduced to zero, resulting in a total secondary cooling water flow rate of 1800 L / min. Compared to the original process, the total secondary cooling water flow rate was reduced by 22%. A dynamic water distribution model calculated that the surface temperature of the fan-shaped section increased by 55℃. Dynamic light reduction was applied to the 11th and 12th fan-shaped sections, resulting in a reduction of 6mm, with a reduction range of 0.25–0.96mm. Electromagnetic rollers were installed at the inlet and outlet of the 2nd segment of the fan-shaped section, with a current of 220A at the inlet and 350A at the outlet. The billet was rated C1.0 after sulfur stamping and center segregation. The billet is sent directly to the heating furnace 3 to 10 minutes after cutting. When it enters the furnace, the surface temperature of the billet is 840 to 1000℃, the hot charging rate reaches 96%, and the heating furnace saves 13% of fuel. The surface of the rolled steel plate is free of cracks and defects.

[0025] Example 3: The continuous casting process for improving the hot charging and hot delivery temperature of slabs is described in detail below.

[0026] A steel plant produces 260mm × 1900mm Q345R container steel continuous casting billets. The secondary cooling water flow rate in the foot rolls and the 0th segment of the fan-shaped section was increased to 78% of the total secondary cooling water, while the water flow rate in the bending and straightening sections was reduced to 22% of the total secondary cooling water. The water flow rate in the horizontal section was reduced to 0, resulting in a total secondary cooling water flow rate of 2000 L / min, a reduction of 18% compared to the original process. Dynamic water distribution model calculations showed that the surface temperature of the fan-shaped section increased by 40℃, and dynamic light pressure was applied to the 11th and 12th fan-shaped sections, resulting in a total reduction of 7mm, with a reduction range of 0.20–0.96mm. Electromagnetic rollers were installed at the inlet and outlet of the 2nd segment of the fan-shaped section, with a current of 200A at the inlet and 330A at the outlet. The billet was rated C1.0 after sulfur stamp center segregation. The billet is sent directly to the heating furnace 7 to 15 minutes after cutting. The surface temperature of the billet is 800 to 970°C when it enters the furnace, and the hot charging rate reaches 95%, saving 10% of fuel in the heating furnace. The surface crack rate of the rolled steel plate is about 0.06%.

Claims

1. A continuous casting process for improving the hot charging and hot delivery temperature of slabs, characterized in that, Includes the following steps: (1) Control the total amount of secondary cooling water in the continuous casting process to be 1500-2000 L / min. The amount of secondary cooling water in the foot roll and fan-shaped 0 section of the continuous casting machine accounts for 75% or more of the total amount of secondary cooling water. The amount of secondary cooling water in the bending section and straightening section accounts for 25% or less of the total amount of secondary cooling water. The amount of secondary cooling water in the horizontal section is 0. (2) Electromagnetic stirring, dynamic light pressing, and dynamic water distribution are used to ensure the center and surface quality of the billet during the solidification process; the electromagnetic stirring uses two pairs of electromagnetic rollers with currents of 210-250A and 330-380A respectively; the pressing range of dynamic light pressing is 0.20-0.96, and the pressing amount is 2-4%; (3) All conveyor rollers after the billet cutting position shall be covered with heat insulation covers. The billet shall be loaded into the steel rolling heating furnace within 15 minutes after cutting. The surface temperature of the billet before entering the steel rolling heating furnace shall be 800-1000℃. Steelmaking production and steel rolling production shall be matched with each other and kept in sync in terms of production and maintenance rhythm. After cutting, the billet shall be transported to the front of the heating furnace at the maximum roller speed. No more than 5 billets shall be waiting to be put into the steel rolling heating furnace.