A production method for controlling the thickness of scale on steel plates based on a single-stand reversing mill

Abstract

The present invention relates to the field of metallurgical technology, and specifically discloses a production method for controlling the thickness of scale on steel plates based on a single-stand reversing mill, which includes optimizing the charging into the furnace; heating furnace control: controlling the air-fuel ratio in each heating section of the heating furnace, controlling the stopping-rolling heating time and heating temperature in each heating section of the heating furnace, and reasonably controlling the furnace pressure of the heating furnace and the opening degree of the air inlet valve of the dilution fan; coiling furnace control: controlling the temperatures of the front-of-machine coiling furnace and the behind-machine coiling furnace under different dimensions of the steel plate, and controlling the air-fuel ratio of the two coiling furnaces to be 1.05; intermediate billet: for thick-specification steel plates, an IC ultra-fast cooling device is used for cooling the intermediate billet; rolling: multiple passes are adopted for the rolling passes; the present invention reduces the problem of the thickness of scale on the steel plate, improves the appearance quality of the steel plate, reduces quality objections, the spraying on the steel plate surface is clearly visible and not easy to fall off, the appearance quality is good, and the product image is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and particularly relates to a production method for controlling the thickness of scale on steel plates based on a single-stand Steckel mill. Background Art

[0002] Scale is an iron-containing oxide generated on the surface of steel during the rolling process in a rolling mill when the rolled piece is rapidly cooled by water. It accounts for between 3% and 5% of the processed steel, and its w(Fe) is as high as 80% - 90%. During the forging and hot rolling of steel, due to the reaction of iron and steel with oxygen in the air, a large amount of scale is often formed, causing accumulation and wasting resources. If these resources are reasonably utilized, the production cost can be reduced, and at the same time, it can play a role in environmental protection and energy conservation. The main components of scale are Fe2O3, Fe3O4, and FeO. Among them, the outermost layer of scale is Fe2O3, accounting for about 10% of the scale thickness, which prevents oxidation; the middle layer is Fe3O4, accounting for about 50%, and the innermost layer in contact with iron is FeO, accounting for about 40%. Generally, the scale has three layers: the outermost layer is Fe2O3, accounting for about 10% of the entire scale thickness. Its properties are: delicate, shiny, brittle, and easy to fall off; and it has the effect of preventing further intense oxidation inside; the second layer is a mixture of Fe2O3 and FeO, usually written as Fe3O4, accounting for about 50% of the total thickness; the third layer connected to the metal body is FeO, accounting for about 40% of the scale thickness. The property of FeO is sticky and not easy to remove when sticking to the steel material.

[0003] The patent application number CN201310219854.4 discloses a method for reducing the thickness of scale on the surface of hot-rolled steel plates. During hot rolling, multi-stand continuous rolling is used, which is different from the structure of the single-stand reciprocating rolling equipment in the Steckel production line and the product types, and is not suitable for plate production. The patent application number CN201910017644.4 discloses control from the perspective of descaling for medium and heavy plate products, which is not suitable for the Steckel mill rolling production. The steel plates rolled by the Steckel mill are longer than those rolled by the medium and heavy plate mill. The length of the steel plates rolled by the Steckel mill is 60m - 450m, while the medium and heavy plate mill rolls about 50m. In view of the problems existing in the above-mentioned prior art, a method for controlling the thickness of scale on the surface of steel plates is designed, which is aimed at a heating furnace, a single-stand Steckel mill, and front and rear coiling furnaces, and controls the thickness of scale on the steel plate surface from aspects such as heating furnace temperature control, coiling furnace temperature control, furnace atmosphere adjustment, heating furnace idling heating system, charging plan, and production process. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a production method for controlling the thickness of scale on steel plates based on a single-stand Steckel mill.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a production method for controlling the scale thickness of steel plates based on a single-stand reversing mill, comprising the following steps:

[0006] 1) Furnace charging optimization: Steel plates with a thickness H≥12mm and those with a thickness H<12mm are charged separately in batches.

[0007] 2) Heating furnace control: Control the air-fuel ratio in each heating section of the heating furnace, control the stop-rolling heating time and heating temperature in each heating section of the heating furnace, and reasonably control the furnace pressure of the heating furnace and the opening degree of the air inlet valve of the dilution fan.

[0008] 3) Coiling furnace control: Control the temperatures of the front coiling furnace and the rear coiling furnace in front of the mill for steel plates of different sizes and specifications, and control the air-fuel ratio of the two coiling furnaces to be 1.05.

[0009] 4) Descaling: Ensure 100% primary descaling, and high-pressure water descaling must be carried out during the second pass rolling.

[0010] 5) Intermediate billet: For thick-specification steel plates, an IC ultra-fast cooling device is used for cooling the intermediate billet. After cooling, it returns to the rolling mill for continuous rolling. Based on the principle of cooling the intermediate billet through, by means of floating and waiting for temperature control measures, the rolling start temperature in the finish rolling stage is controlled with the target that the steel plate turns red by less than 30°C after the finish rolling stage.

[0011] 6) Rolling: The rolling passes adopt multi-pass rolling, control the final rolling temperature of the steel plate at 770 - 780°C, and the surface quality of the steel plate is good, without red rust, mottling, and thick scale phenomena.

[0012] Specifically, for the steel plates in step 1), when the thickness 12mm≤H<16mm, width>2800mm, and length is less than 60000mm, they are designed according to the maximum material.

[0013] For steel plates with a thickness H<12mm and width<2800mm, they are designed according to the minimum material.

[0014] Specifically, for the heating furnace in step 2), the air-fuel ratio of the heating furnace is as follows: 1.05 in the preheating section, 1.25 in the first heating section, 1.15 in the second heating section and the soaking section. The theoretical air-fuel ratio of blast furnace gas is 0.68 - 0.73, the air excess coefficient is controlled according to 1.05, and the detected value of residual oxygen in the furnace is controlled according to <3%.

[0015] Specifically, the heating temperature of the heating furnace in step 2): the temperature of the first heating section of the heating furnace is 1060 - 1070°C, the temperature of the second heating section is 1180°C, the soaking section temperature is 1180°C, the temperature after descaling is 997 - 1005°C. For flat rolling with a thick specification > 20mm, gradually reduce the furnace temperature and the temperature after descaling from the end of thin-specification coiling rolling. The target temperature after descaling is below 1000°C. The controlled residence time of the red-hot billet in the furnace should not be too long. There must be a gap between flat-rolled billets before and after coiling rolling to ensure that the furnace temperature meets the requirements.

[0016] Specifically, reasonably control the furnace pressure of the heating furnace in step 2) to be 4 - 16 Pa, without flames or cold air suction at the furnace head and furnace tail, and the front and rear furnace doors are not opened simultaneously. Steel is not discharged during the steel charging process, and steel is not charged during the steel discharging process.

[0017] Specifically, reasonably control the opening degree of the air inlet valve of the dilution fan in step 2), and control the air preheating temperature at 450 - 500°C.

[0018] Specifically, the temperature control range of the coiler in front of the mill and the coiler behind the mill in step 3) is 830 - 990°C.

[0019] Specifically, in step 4), two high-pressure pumps are turned on for descaling, namely No. 1 and No. 2 descaling pumps, and descaling is carried out in six passes: passes 1, 2, 3, 5, 6, and 7.

[0020] The present invention has the following beneficial effects:

[0021] The production method for controlling the thickness of scale on steel plates designed by the present invention based on a single-stand furnace coil rolling mill is applicable to the surface quality control of flat-rolled steel plates with a length of 70 meters produced by a single-stand furnace coil rolling mill and the surface control of coiled rolling of steel plates with a length of 80 - 400 meters, and is applicable to the surface control of longer steel plate production;

[0022] Reduce the furnace temperature of each section of the heating furnace, reasonably control the air-fuel ratio, the furnace temperature of the heating furnace < 1150°C, and the temperature after descaling for thick-specification flat rolling ≤ 1050°C. This can not only reduce the quality problems of scale on the steel plate surface but also reduce the specific consumption of gas in the heating furnace. During long-term shutdowns, implement the heating furnace stop-rolling and temperature-holding heating system to avoid large fires in the heating furnace and high-temperature holding, and also reduce the specific consumption of gas in the heating furnace;

[0023] The single-stand furnace coil rolling mill adopts the IC cooling mode, reducing the long-term temperature-holding waiting time of the intermediate billet, improving the rolling rhythm, increasing the hourly output, and reducing various energy consumptions accordingly;

[0024] Reduce the problem of thick scale on the steel plate, improve the appearance quality of the steel plate, reduce quality objections, the spraying on the steel plate surface is clearly visible and not easy to fall off, with good appearance quality, and enhance the product image. Description of the Drawings

[0025] Figure 1 It is the process diagram of a Steckel mill.

[0026] In the figure: 1 - Single furnace reheating furnace; 2 - Coiling furnace in front of the mill; 3 - Single stand Steckel mill; 4 - Coiling furnace behind the mill; 5 - IC ultra-fast cooling equipment. Specific implementation manners

[0027] The following will further describe in detail the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] Scale can be divided into primary scale, secondary scale, tertiary scale and red scale.

[0029] 1. Primary scale

[0030] Before hot rolling, steel is often heated and held at 1100 - 1300 °C. At this temperature, the steel surface reacts with the high-temperature furnace gas to generate primary scale with a thickness of 1 - 3 mm, which is also caused by insufficient side pressing and incomplete descaling in rough rolling. This primary scale is also called primary scale. There are relatively large cavities inside the primary scale. The primary scale is a grayish-black scale layer, covering the steel plate surface in flakes. The main component of the scale layer is composed of magnetite (Fe3O4).

[0031] 2. Secondary scale

[0032] After the hot-rolled steel billet comes out of the reheating furnace and the primary scale is removed by high-pressure water, that is, the surface scale falls off, and then rough rolling is carried out. During the short rough rolling process, the steel billet surface comes into contact with water and air, and secondary scale is generated on the steel billet surface, which is also called secondary scale. The secondary scale is thinner due to the influence of horizontal rolling, and the interfacial stress between the steel billet and the scale is small, so the peelability is poor. If the high-pressure water spraying cannot completely remove the secondary scale and the scale remains on the steel plate surface during finish rolling, defects will appear on the product surface. The secondary scale is a red scale layer, showing obvious long strips and pressed-in shapes, distributed in bands along the rolling direction. The main components of the scale layer are composed of fine particles such as wüstite (FeO) and hematite (Fe2O3).

[0033] 3. Tertiary scale

[0034] During the hot rolling finish rolling process, a surface scale layer will be generated when the strip steel enters the rolling mill. The tertiary scale defects are visible to the naked eye: dark brown and small boat-shaped. They are relatively densely, finely and scattered like sand on the surface of the defective strip steel. There is a tactile feeling when touching it gently. After pickling, small pinhole-like pits with different depths are left on the surface defects of the strip steel, and they are invisible on the surface of normal hot-rolled strip steel.

[0035] 4. Red scale

[0036] Red scale only occurs on specific steel grades with high silicon content, mainly due to the strong engagement between the surface oxide and the base metal during the heating of the steel billet. It has no obvious depth and appears as irregular flakes. There are two types of red scale: one is unevenly distributed in the width direction of the plate, mainly in the middle, leaning towards the operating side, with obvious water marks at the red and blue areas, and it is also uneven in the length direction of the steel plate, being slightly lighter in some parts. This type of red scale is thicker and can break off during straightening, and can be blown off with high-pressure air. The residual red color can be easily wiped off, and this red scale is more appropriately called red rust. The other type of red scale is relatively evenly distributed along the width of the plate, generally being slightly heavier within 100 mm from the edge, and the outside of the coil is heavier than the inside. This type of red scale is thinner and the color is not easily wiped off, and the thicker the steel plate, the heavier the red color. This type of red scale also exists in some other steel grades and has a certain degree of universality.

[0037] As Figure 1 shown, the Steckel mill is a single-stand reciprocating rolling mill that rolls longitudinally to the end and cannot rotate the steel, greatly weakening the ability to damage the scale on the steel plate surface. Moreover, coiling furnaces are arranged before and after the Steckel mill (such as Figure 1 ), which can not only perform flat rolling but also coiling rolling. The coiling rolling process takes place in the coiling furnaces in front of and behind the mill for coiling and heat preservation, and finally the steel plate is rolled. The length of the coiled rolled steel plate is relatively long. Just from the perspective of rolling descaling, the problem of thick scale on the steel plate surface cannot be solved. It is only possible to control the thickness of the scale on the steel plate surface from aspects such as the charging plan, heating furnace temperature control, coiling furnace temperature control, furnace atmosphere adjustment, heating furnace idle heating system, and production process.

[0038] A production method for controlling the thickness of scale on a steel plate based on a single-stand Steckel mill includes the following steps:

[0039] 1. Optimize charging

[0040] Charge the steel plates with a thickness H≥12 mm and those with a thickness H<12 mm separately.

[0041] For 12 mm≥H<16 mm, with a length less than 60000 mm and a width>2800 mm, design according to the largest material.

[0042] For steel plates with a thickness H less than 12 mm and a width<2800 mm, design according to the smallest material.

[0043] 2. Heating furnace control

[0044] Air-fuel ratio of the heating furnace: 1.05 in the preheating section, 1.25 in the first heating section, and 1.15 in the second heating section and soaking section. The theoretical air-fuel ratio of blast furnace gas is 0.68 - 0.73. The air excess coefficient is controlled at 1.05, and the detected value of residual oxygen in the furnace is controlled at <3%.

[0045] For flat rolling of thick specifications > 20mm, the temperature in the first heating zone of the heating furnace is 1060 - 1070°C, the temperature in the second heating zone is 1180°C, the temperature in the soaking section is 1180°C, and the temperature after descaling is 997 - 1005°C. Starting from the end of thin-specification coiling, gradually reduce the furnace temperature and the temperature after descaling. The target temperature after descaling is below 1000°C. The controlled residence time of the red-hot billets in the furnace should not be too long to avoid surface mottling. Before and after coiling, the flat-rolled billets must be spaced apart to ensure that the furnace temperature reduction meets the requirements.

[0046] Reasonably control the furnace pressure (4 - 16 Pa) to ensure that there is no flame or cold air suction at the furnace head and tail, and reduce heat loss. The front and rear furnace doors should not be opened simultaneously. Steel should not be discharged during the steel charging process, and steel should not be charged during the steel discharging process.

[0047] Reasonably control the opening degree of the air inlet valve of the dilution fan to increase the preheating temperature of the air in the heating furnace, i.e., control the air preheating temperature at 450 - 500°C.

[0048] 3. Coiling furnace control

[0049] The temperature control of the coiling furnace in front of the mill and the coiling furnace behind the mill is as shown in Table 1 below, and the air-fuel ratio of the coiling furnace is 1.05.

[0050] Table 1

[0051]

[0052] 4. Descaling

[0053] Ensure 100% primary descaling. High-pressure water descaling must be carried out for the second rolling pass. Two high-pressure pumps, namely No. 1 and No. 2 descaling pumps, are used for descaling, and descaling is carried out in six passes: Passes 1, 2, 3, 5, 6, and 7.

[0054] 5. Intermediate billet

[0055] For thick specifications, IC is adopted, and the intermediate billet is cooled using an ultra-fast cooling device. After cooling, it returns to the rolling mill for continuous rolling. To prevent excessive residence time and reduce secondary scale, the principle of cooling the intermediate billet through is adopted. Through measures such as floating and waiting for temperature, control the rolling start temperature in the finishing rolling stage with the goal that the steel plate returns to a temperature less than 30°C after the finishing rolling stage.

[0056] 6. Rolling

[0057] Due to the high core temperature of thick specifications, during the rolling process, the front and rear coiling furnaces are not conducive to heat dissipation in the rolling passes. Multiple passes of rolling are advisable for the rolling passes, with 6 + 6 rolling pass control. The final rolling temperature of the steel plate is controlled below 800°C, around 770 - 780°C, where the surface quality of the steel plate is the best, without red rust, mottling, or thick scale phenomena.

[0058] 7. The heating furnace shutdown and waiting temperature heating system is as shown in Table 2

[0059] Table 2

[0060]

[0061] The present invention is not limited to the above embodiments. Any person should be aware that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, fall within the protection scope of the present invention.

[0062] The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A production method for controlling the thickness of scale on steel plates based on a single-stand reversing mill, characterized in that, It includes the following steps: 1) Optimize charging: The steel plates with a thickness H≥12mm and those with a thickness H<12mm are charged separately. For steel plates with a thickness of 12mm≤H<16mm, a width>2800mm, and a length less than 60000mm, they are designed according to the maximum material. For steel plates with a thickness H<12mm and a width<2800mm, they are designed according to the minimum material; 2) Heating furnace control: Control the air-fuel ratio in each heating section of the heating furnace. The air-fuel ratio of the heating furnace is: 1.05 in the preheating section, 1.25 in the first heating section, 1.15 in the second heating section and the soaking section. The theoretical air-fuel ratio of blast furnace gas is 0.68 - 0.73, the air excess coefficient is controlled at 1.05, and the detected value of residual oxygen in the furnace is controlled at <3%; Control the stop-rolling heating time and heating temperature in each heating section of the heating furnace. The heating temperature of the heating furnace is: the temperature in the first heating section of the heating furnace is 1060 - 1070°C, the temperature in the second heating section is 1180°C, the temperature in the soaking section is 1180°C, the temperature after descaling is 997 - 1005°C. For thick flat-rolled products with a thickness >20mm, gradually reduce the furnace temperature and the temperature after descaling from the end of thin-gauge coiling. The target temperature after descaling is below 1000°C. The control time of the red-hot billet in the furnace should not be too long. There must be a gap between the flat-rolled billets before and after coiling to make the furnace temperature meet the requirements, and reasonably control the furnace pressure of the heating furnace and the opening degree of the dilution fan inlet valve; 3) Coiling furnace control: Control the temperatures of the front-of-machine coiling furnace and the rear-of-machine coiling furnace for steel plates of different sizes. The temperature control range of the front-of-machine coiling furnace and the rear-of-machine coiling furnace is 830 - 990°C, and control the air-fuel ratio of the two coiling furnaces to be 1.05; 4) Descaling: Ensure 100% primary descaling, and high-pressure water descaling must be carried out for the second rolling start; 5) Intermediate billet: Thick-gauge steel plates are cooled by an IC ultra-fast cooling device for the intermediate billet, and after cooling, they return to the rolling mill for continuous rolling. Follow the principle of thorough cooling of the intermediate billet. Through the floating waiting temperature measure, control the rolling start temperature in the finishing stage with the target that the steel plate returns red by less than 30°C after the finishing stage; 6) Rolling: The rolling passes adopt multi-pass rolling, control the final rolling temperature of the steel plate at 770 - 780°C, and the surface quality of the steel plate is good, without red rust, mottling, and thick scale phenomena.

2. The production method for controlling the thickness of the scale on a steel plate based on a single-stand reversing mill according to claim 1, wherein, The reasonable control of the furnace pressure of the heating furnace in step 2) is 4 - 16Pa, there is no fire or cold air suction at the furnace head and furnace tail, the front and rear furnace doors are not opened simultaneously, no steel is discharged during the steel charging process, and no steel is charged during the steel discharging process.

3. The production method for controlling the thickness of the mill scale on the steel plate based on a single-stand reversing mill according to claim 1, characterized in that, The reasonable control of the opening degree of the dilution fan inlet valve in step 2), and the air preheating temperature is controlled at 450 - 500°C.

4. The production method for controlling the thickness of the mill scale on a steel plate based on a single-stand reversing mill according to claim 1, characterized in that, For the descaling in step 4), two high-pressure pumps, namely No. 1 and No. 2 descaling pumps, are started, and descaling is carried out in six passes: passes 1, 2, 3, 5, 6, and 7.

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