Method for rolling YT2 pure iron flat steel at low temperature through blooming mill

Abstract

The invention innovatively provides a process technology for rolling the pure iron flat steel by heating and blooming at a low temperature of 1000 DEG C, solves the problem of high corner crack ratio of the pure iron flat steel (Mn / S is less than 3) rolled by a blooming mill at a high temperature, ensures that the pure iron flat steel is smoothly rolled, and meets the high-quality, efficient and stable supply requirements of the variety.

Description

Technical Field

[0001] The present invention relates to the field of metal pressure processing, and particularly to a method for cold rolling YT2 pure iron flat steel by a blooming mill. Background Art

[0002] YT2 belongs to industrial pure iron and is raw material pure iron. Its chemical composition is mainly iron, with the characteristics of having harmful elements, high steel purity, and good electromagnetic properties. It is mainly used to manufacture precision instruments, amorphous alloys, new energy batteries, cathode rods for electrolytic aluminum, etc. The raw material pure iron itself has relatively strict requirements for elements such as S, P, Mn, and Ti. At the same time, due to the characteristic of too soft steel, it has a high requirement for the Mn / S ratio during hot rolling. When the Mn / S ratio is lower than 5, there is an obvious cracking tendency during rolling, especially serious corner cracking when the temperature drops too quickly. When YT2 pure iron is used as a cathode rod for the electrolytic aluminum industry and other purposes, in order to stabilize indicators such as electrical conductivity, there are not allowed to be defects such as corner cracks and splits on the rolling surface.

[0003] At the same time, in order to improve electrical conductivity, the pure iron cathode rod for electrolytic aluminum has an upper limit requirement for the Mn content. Generally, the internal control requirement is Mn≤0.02%. The normal sulfur content of pure iron is in the range of 0.004 - 0.005%, and the Mn / S ratio is generally less than 3.5. The cracking tendency during rolling is large, and the forming difficulty is great. Especially for rolling large - sized flat steel from cut blanks, the surface cracking ratio is as high as more than 40%, which cannot meet the production needs.

[0004] Therefore, it is urgent to design the process for rolling YT2 flat steel by a blooming mill to solve the above problems. The conventional process flow of pure iron flat steel is: steelmaking continuous casting slab - cutting and dividing - heating - rolling - cutting to fixed length - inspection and warehousing.

[0005] Through research on the characteristics and production methods of YT2 pure iron, the present invention independently designs and provides a process method for rolling pure iron flat steel by a blooming mill in a specific temperature range to meet the production needs. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for cold rolling YT2 pure iron flat steel by a blooming mill in view of the above problems.

[0007] The object of the present invention is achieved as follows: A method for cold rolling YT2 pure iron flat steel on a blooming mill, comprising the following steps: Step 1: Cutting and dividing the continuous casting slab of steelmaking; Step 2: Heating: The cut billets are horizontally placed in a soaking pit in a cross shape, and 3 - 4 soaking pits are heated simultaneously. The heating rate of the soaking pit is 80 - 100 °C / h, and the temperature is raised to 1000 °C ± 10 °C for low-temperature heating. The actual steel temperature of the cut billets is 980 - 1000 °C. After holding for 1.5 - 2 hours, they are taken out of the furnace for rolling. After tapping, the temperature is restored to 950 °C - 1000 °C and held for 30 - 40 minutes for continuous circulation; Step 3: Rolling: The rolling is divided into 9 - 11 passes.

[0008] The reduction of the blooming pass during rolling is controlled within 50 - 70 mm, and the reduction of the finishing pass is controlled within ≤10 mm.

[0009] The beneficial effects of the present invention are: Through the design and development of the cold rolling process technology for HYT2 flat steel, the cold rolling process technology is innovatively adopted, solving the problems of corner cracking and surface scratches of pure iron flat steel, avoiding the generation of corner cracks and scratches, and ensuring the smooth progress of rolling. Brief Description of the Drawings

[0010] The present invention will be further described below in conjunction with the accompanying drawings.

[0011] Figure 1 is the high-temperature heating process diagram of the original process.

[0012] Figure 2 is the low-temperature heating process diagram of the present invention.

[0013] Figure 3 is the schematic diagram of the production process flow of the present invention. Detailed Embodiments

[0014] Since the Mn / S ratio of YT2 pure iron is only about 2, when horizontally placed in the soaking pit, the temperatures on the upper and lower surfaces of the slab are uneven. During rolling, the material is soft, the forces on the upper and lower surfaces are uneven, the temperature at the corners drops significantly, and due to uneven deformation, cracks appear at the corners of the flat steel.

[0015] The present invention analyzes from the characteristics of YT2 pure iron and the rolling method. Since pure iron is relatively soft, during the rolling process, due to uneven deformation, the corners are the first to cool down and are prone to tearing. Analyzing that the temperature unevenness is the key factor. Therefore, starting from optimizing the heating process to solve this problem, four key links need to be controlled: one is the horizontal loading of the soaking pit, the second is low-temperature heating to reduce the temperature difference between the upper and lower surfaces of the slab, the third is circulating tapping during rolling, and the fourth is optimizing the reduction scheme during the rolling process to control the bottleneck link of cold rolling width and prevent the generation of grooves.

[0016] By adopting the above low-temperature heating process, the problem of angle cracking of flat steel caused by the characteristics of pure iron during rolling can be solved, and the surface qualification rate and production efficiency of large-sized YT2 rolling can be improved.

[0017] The present invention adopts technologies such as soaking furnace low-temperature heating, circulating tapping, and special reduction scheme for blooming mill rolling: 1. The continuous casting slab of steelmaking is cut into blocks. The original width of the continuous casting slab of steelmaking is 1260 mm, and it is evenly cut into 3 pieces, cut into three strips with a width of 420 mm. 2. The cut billets are horizontally placed in a soaking furnace in a cross shape, and 3 - 4 soaking furnaces are heated simultaneously. 3. The heating temperature of the cut billets is low-temperature heated at 1000 ± 10 °C, and the actual steel temperature is in the range of 980 - 1000 °C. After holding for 1.5 - 2 hours, it is taken out of the furnace for rolling. 4. 3 - 4 soaking furnaces tap steel in a cycle, tap steel in layers and batches for rolling, and after tapping steel, the temperature is returned to 950 °C - 1000 °C and held for 30 minutes to continue the cycle. 5. Improve the rolling reduction scheme. A large reduction is adopted for rolling in the transition pass, the flat steel allowance in the first pass is reduced to 15 mm, and the reduction for the finished pass is rolled with the steel turned over up and down to avoid defects such as grooves caused by poor low-temperature spreading. Example 1

[0018] This method is implemented on the 1000 mm blooming mill of the section steel division of Taiyuan Iron and Steel Group. The rolled steel type is HYT2, the raw material used is 220*420 mm, the rolling specification is 160*230*2215 mm multiple-length, and the total length after rolling is about 9.5 m. The specific heating and rolling process is as Figure 2 .

[0019] The rolling reduction scheme is shown in Table 1.

[0020]

[0021] The specific implementation process steps are as follows: 1. The 220*420 mm cut billets are horizontally placed in the soaking pits in a cross shape. 4 pits are loaded simultaneously. 2. Heat up to 990 °C at a speed of 90 °C / hour and hold for 2 hours. 2. Two layers are taken out from each soaking pit, the temperature is returned to 950 °C and held for 30 minutes, and the following two layers are cycled out, and so on. 3. The billets are rolled according to the reduction scheme in Table 1. A 15 mm allowance is left for the reduction in the transition pass to prevent blooming grooves. When rolling into the finished pass, it is rolled in a single pass and turned over twice to ensure uniform iron flow on the upper and lower narrow surfaces and reduce the generation of unilateral grooves. 4. During the rolling process, the pusher clamps and moves the billets throughout the process to ensure the external dimensions of the billets. Example 2

[0022] This method is implemented on the 1000 mm blooming mill of the section steel division of Taiyuan Iron and Steel Group. The rolled steel type is HYT2, the raw material used is 220*420 mm, the rolling specification is 160*230*2215 mm multiple-length, and the total length after rolling is about 9.5 m. The specific heating and rolling process is as Figure 2 .

[0023] The rolling reduction scheme is shown in Table 1.

[0024]

[0025] The specific implementation process steps are as follows: 1. Cut the billets of 220*420mm and install them in the soaking pits in a flat crosswise manner. Install 3 pits at the same time. 2. Heat up to 1000°C at a speed of 80°C per hour and hold for 2 hours. 2. Take out two layers from each soaking pit, cool back to 970°C and hold for 30 minutes, then cycle to take out the following two layers, and so on. 3. Roll the billets according to the reduction plan in Table 1. Leave a margin of 15mm for the reduction of the transition pass to prevent the formation of blooming grooves. When rolling into the finishing pass, perform single-pass rolling and turn the billets over twice to ensure uniform iron flow on the upper and lower narrow surfaces and reduce the generation of unilateral grooves. 4. During the rolling process, the pusher clamps and moves the billets throughout the process to ensure the external dimensions of the billets.

[0026] The above are only specific embodiments of the present invention, but the structural features within the scope of protection of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for cold rolling YT2 pure iron flat steel on blooming mill, characterized in that: It includes the following steps: Step 1: Cut and divide the continuous casting slab for steelmaking into pieces; Step 2: Heating: The cut billets are placed horizontally in a checkerboard pattern in the soaking pit, and 3 - 4 soaking pits are heated simultaneously. The heating rate of the soaking pit is 80 - 100 °C / h, and it is heated to 1000 °C ± 10 °C for low-temperature heating. The actual steel temperature of the cut billets is 980 - 1000 °C. After holding for 1.5 - 2 hours, it is taken out of the furnace for rolling. After tapping, the temperature is reheated to 950 °C - 1000 °C and held for 30 - 40 minutes for continuous circulation; Step 3: Rolling: The rolling is divided into 9 - 11 passes.

2. The method for cold rolling YT2 pure iron flat steel on blooming mill according to claim 1, characterized in that: The reduction of the blooming pass for rolling is controlled at 50 - 70 mm, and the reduction of the finishing pass is controlled at ≤10 mm.

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