Method for reducing hot rolling pitted surface defect

Abstract

The invention discloses a method for reducing a hot rolling pitted surface defect. The method comprises the following treatment steps: investigating main factors causing a pitted surface of a plate surface; specifying a specific implementation scheme according to the main factors; scale is removed through descaling; the generation of furnace-generated oxide scales is inhibited through adjustment; the roller-generated scale is reduced; according to the method, the dephosphorization water tank is added, the pressure of the dephosphorization water tank is controlled, so that the pressure of the dephosphorization water is improved, and the height and angle of the water nozzle are adjusted and optimized, so that the side pressure capacity of the vertical roll is improved, the generation of rough rolling oxide scale is reduced, and the roller material with good hot crack resistance is adopted, so that the production cost is reduced. A reasonable grinding system is adopted, residual cracks on the surface of the roller are thoroughly removed in time, lubricating rolling is adopted, the surface quality of the roller is improved, the unit rolling force of a rack is reduced, and therefore the situation that due to the fact that the unit rolling force is too large, microcracks on the surface of the roller expand, and roller scale is generated is effectively prevented.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, in particular to a method for reducing hot-rolled pitting defects. Background Art

[0002] The hot rolled coil rolling process is: pushing steel → heating → steel tapping → descaling → side width meter → rough rolling → intermediate roller table → flying shear → finishing rolling and dephosphorization → finishing rolling → plate type meter → side width meter → laminar cooling system → coiler → finishing → collection and storage. At present, hot rolled coil rolling is fully automatic, and the surface quality of the coil is very high. It is necessary to ensure the temperature of the rolled piece and control the surface quality of the plate. When the hot rolling production line produces strip steel, the production rhythm is fast, the steel type is different, the thickness is different, and the temperature requirements are different. In particular, the higher the temperature requirements for high-strength steel and thin plates, the average heat is 1360 degrees, and the dephosphorization after the furnace is about 1140. When the specifications of the slabs in the furnace are not uniform and the furnace temperature requirements are increased, it is very easy to cause pitting;

[0003] Moreover, under the current production conditions, there is a large temperature difference between the head and tail of the steel rolled piece coming out of the heating furnace. When the head temperature is high, different lengths of pitting will occur on the head of the strip. As the temperature of the intermediate billet increases, the number of pitting also increases. From the temperature of 1050-1150℃, the number of pitting increases. Moreover, when the rolling line increases the production rhythm, dephosphorization is used for rough and fine rolling at the same time, and the dephosphorization pressure will be reduced and cannot meet the dephosphorization requirements of the plate surface. If the dephosphorization pressure is low, the primary oxide scale produced on the plate surface is not cleanly dephosphorized, and a thinner secondary oxide scale is formed during the rolling process, which will be pressed into the surface of the strip, causing the oxide scale on the plate surface to be directly pressed into the surface and produce pitting. Summary of the invention

[0004] The present invention provides a method for reducing the defects of hot-rolled rough surfaces, which can effectively solve the problems proposed in the above-mentioned background technology on the dephosphorization pressure, the roller surface of the working roller, and the higher requirements on the steel burning level of the pyrotechnics. Low dephosphorization pressure will cause incomplete dephosphorization on the surface of the slab, high roller surface temperature will not form an oxide film and severe wear will directly cause pits on the plate surface, and the large temperature difference between the head and the tail will cause the oxidation speed of the head to affect the quality of the plate surface and the product performance.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for reducing hot rolling pitting defects, which ensures the quality of the plate surface and reduces the occurrence of pitting by ensuring the dephosphorization pressure, the quality of the work roll surface and the head-to-tail temperature difference, and comprises the following processing steps:

[0006] S1. Investigate the main factors causing the roughness of the board surface;

[0007] S2. Specify specific implementation plans based on key factors;

[0008] S3, removing iron oxide scale by descaling;

[0009] S4, inhibit the generation of furnace oxide scale by regulation;

[0010] S5, reduce the roller oxide scale;

[0011] S6. Perform head and tail cooling treatment on the intermediate billet.

[0012] According to the above technical scheme, in S1, when the heating temperature is 1250°C and the finishing rolling temperature is 1010-1030°C, there is no iron oxide scale on the surface, when the finishing rolling temperature is between 1050-1080°C, the iron oxide scale is serious, and when the finishing rolling temperature is between 1030-1040°C, there is no iron oxide scale or the iron oxide scale is lighter.

[0013] According to the above technical solution, in S1, according to the different equipment of each hot rolling mill and the steel quality produced, when the finishing rolling temperature is controlled at 1030°C to produce high-strength steel or high-carbon steel, the rolling force of the first three stands is too high, which will damage the equipment;

[0014] Depending on the material of the rolling mill rolls, the finishing rolling temperature should be controlled at 1010-1030°C, which can effectively reduce the temperature of the upstream stand rolls and reduce the occurrence of roll oxide scale.

[0015] According to the above technical solution, in S2, the scale defect of the finishing mill is the so-called roll scale, and the main factors affecting the roll scale are the roll material and the roll temperature;

[0016] When the roller surface contacts the steel plate surface, it becomes hot instantly, and the surface temperature rises sharply and expands. Generally, the instantaneous contact temperature of the hot rolling roller is 600-800℃, showing a high compressive stress. When the rolled piece leaves the roller, the roller cools down sharply due to the cooling of the cooling water. The roller temperature of the finishing mill is generally 60-90℃, and the surface turns into tensile stress. This is repeated, and fatigue cracks are prone to appear on the roller surface, causing the surface oxide film to be damaged. The damaged surface is imprinted into the steel plate surface, forming roller oxide scale defects. The generation of plate surface hemp can be reduced by ensuring the dephosphorization pressure, the quality of the working roller surface, and the temperature difference between the head and the tail.

[0017] According to the above technical scheme, in S3, during the production process of hot-rolled steel plates, the steel billet will be oxidized when heated in the heating furnace to generate primary iron oxide scale, which adheres to the surface of the steel billet. In addition, during the rolling process, the steel billet will also be secondary oxidized to form secondary iron oxide scale. The oxidation of the rolled piece not only causes the metal to be lost due to oxidation, but also, under the rolling of the rolling wheel, part of the iron oxide scale is broken into small pieces and automatically falls off, while the other part is pressed into the metal surface to form inclusions, pitting or scars, etc., causing surface quality defects of the steel plate. Therefore, removing the iron oxide scale is a very critical process link in the hot rolling production process, and this process of removing the iron oxide scale is called descaling.

[0018] According to the above technical scheme, in S3, during the specific treatment, a set of descaling water tanks is added, and the pressure is maintained at 18-21Mpa. The surface of the slab is cleanly dephosphorized, and the production rhythm is adjusted to ensure that the descaling water is not opened at the same time. By increasing the descaling water pressure, adjusting and optimizing the height and angle of the water nozzle, the side pressure capacity of the vertical roll is increased to reduce the rough rolling iron oxide scale.

[0019] According to the above technical solution, in S4, during the adjustment process, the generation of furnace-generated iron oxide scale is suppressed mainly by lowering the heating temperature, reducing the time in the furnace, and adjusting the atmosphere in the furnace to a reducing atmosphere;

[0020] Specifically, the reversing heating time of the heating furnace is adjusted from the original 90s to 70±5s. In order to further increase the equalizing effect of the equalizing section of the heating furnace, the temperature of the first and second sections is increased by 100°C, and the temperature gradient of the heating in the furnace is reduced to further enhance the temperature capacity of the equalizing slab.

[0021] According to the above technical scheme, in S5, the roller scale is reduced mainly by using a roller material with good thermal cracking resistance, adopting a reasonable grinding system, timely and thoroughly removing residual cracks on the roller surface, and at the same time using lubrication rolling to improve the roller surface quality, reduce the unit rolling force of the frame, and prevent the roller scale from being generated due to the expansion of micro cracks on the roller surface caused by excessive unit rolling force.

[0022] According to the above technical solution, in S5, the water volume at the inlet of the roller cooling water frame is made smaller than the outlet water volume, and the cooling water volume of the intermediate frame rollers is increased to ensure that the rollers are cooled quickly, the finishing rolling temperature is equal to 1030°C, and the roller temperature of the upstream frame of the finishing rolling is reduced.

[0023] According to the above technical solution, in S6, the head and tail cooling treatment of the intermediate billet is mainly carried out by designing and manufacturing a set of spray water devices for cooling the head and tail of the intermediate billet, and the spray water devices are respectively installed in the rough rolling area and the flying shear area;

[0024] The start and stop of the water spraying device adopts the existing thermal detection slab temperature numerical signal, and precise switch control is carried out by writing a PLC program. The control end is merged into the rolling control screen to facilitate manual operation, so as to ensure the reduction of secondary iron oxide generation during the rolling process.

[0025] Compared with the prior art, the present invention has the following beneficial effects: the present invention has a scientific and reasonable structure and is safe and convenient to use:

[0026] 1. By adding a dephosphorization water tank and controlling its pressure, the pressure of the descaling water is increased, and the height and angle of the water nozzle are adjusted and optimized to improve the side pressure capacity of the vertical roll and reduce the generation of rough rolling scale. At the same time, by reducing the heating temperature, reducing the furnace time, and adjusting the furnace atmosphere to a reducing atmosphere, the generation of furnace-generated scale can be effectively inhibited. In addition, the roll material with good thermal crack resistance and a reasonable grinding system are used to timely and thoroughly remove the residual cracks on the roll surface. Lubrication rolling is used to improve the roll surface quality and reduce the unit rolling force of the stand, so as to effectively prevent the generation of roll scale caused by the expansion of micro cracks on the roll surface due to excessive unit rolling force;

[0027] In addition, by installing water spray devices in the rough rolling area and the flying shear area respectively, the generation of secondary iron oxides during the rolling process can be effectively reduced. By ensuring the dephosphorization pressure, the quality of the working roll surface and the head-to-tail temperature difference, the quality of the plate surface can be effectively guaranteed, the generation of rough surfaces can be reduced, and the quality of plate surface pressing can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0029] In the attached picture:

[0030] Figure 1 is a flow chart of the steps of the processing method of the present invention;

[0031] Figure 2 It is the arrangement diagram of the dephosphorization nozzle of the present invention. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0033] Example: Figure 1 As shown, the present invention provides a technical solution, a method for reducing hot rolling pitting defects, which ensures the quality of the plate surface and reduces the generation of pitting by ensuring the dephosphorization pressure, the surface quality of the working roll and the head-to-tail temperature difference, and includes the following processing steps:

[0034] S1. Investigate the main factors causing the roughness of the board surface;

[0035] S2. Specify specific implementation plans based on key factors;

[0036] S3, removing iron oxide scale by descaling;

[0037] S4, inhibit the generation of furnace oxide scale by regulation;

[0038] S5, reduce the roller oxide scale;

[0039] S6. Perform head and tail cooling treatment on the intermediate billet.

[0040] Based on the above technical solution, in S1, when the heating temperature is 1250°C and the finishing rolling temperature is 1020°C, there is no iron oxide scale on the surface, when the finishing rolling temperature is 1065°C, the iron oxide scale is serious, and when the finishing rolling temperature is 1035°C, there is no iron oxide scale or the iron oxide scale is lighter.

[0041] Based on the above technical solution, in S1, according to the different equipment of each hot rolling mill and the steel quality produced, when the finishing rolling temperature is controlled at 1030°C to produce high-strength steel, the rolling force of the first three stands is too high, which will damage the equipment;

[0042] Depending on the material of the rolls, the finishing rolling temperature should be controlled at 1020°C, which can effectively reduce the temperature of the upstream stand rolls and reduce the occurrence of roll oxide scale.

[0043] Based on the above technical solution, in S2, the scale defect of the finishing mill is the so-called roll scale, and the main factors affecting the roll scale are the roll material and the roll temperature;

[0044] When the roller surface contacts the steel plate surface, it becomes hot instantly, and the surface temperature rises sharply and expands. Generally, the instantaneous contact temperature of the hot rolling roller is 700℃, showing a high compressive stress. When the rolled piece leaves the roller, the roller cools down sharply due to the cooling of the cooling water. The roller temperature of the finishing mill is generally 75℃, and the surface turns into tensile stress. This process is repeated, and fatigue cracks are prone to appear on the roller surface, causing the surface oxide film to be damaged. The damaged surface is imprinted into the steel plate surface, forming roller oxide scale defects. The generation of plate surface hemp can be reduced by ensuring the dephosphorization pressure, the quality of the working roller surface, and the temperature difference between the head and the tail.

[0045] Based on the above technical solution, in S3, during the production process of hot-rolled steel plates, the steel billet will be oxidized when heated in the heating furnace to generate primary iron oxide scale, which adheres to the surface of the steel billet. In addition, the steel billet will also be secondary oxidized during the rolling process to form secondary iron oxide scale. The oxidation of the rolled piece not only causes the metal to be lost due to oxidation, but also, under the rolling of the rolling wheel, part of the iron oxide scale is broken into small pieces and falls off automatically, while the other part is pressed into the metal surface, forming inclusions, pitting, and scars, causing surface quality defects of the steel plate. Therefore, removing the iron oxide scale is a very critical process in the hot rolling production process, and this process of removing the iron oxide scale is called descaling.

[0046] like Figure 2As shown, based on the above technical solution, in S3, during the specific treatment, a set of descaling water tanks is added, the pressure is maintained at 19Mpa, the surface of the slab is dephosphorized cleanly, the production rhythm is adjusted, and the descaling water is ensured not to be opened at the same time. By increasing the descaling water pressure, adjusting and optimizing the nozzle height and angle, the side pressure capacity of the vertical roll is increased, thereby reducing the rough rolling oxide scale;

[0047] According to the investigation of the operation after the replacement of the dephosphorization water tank, the water pressure exceeded the standard as shown in Table 1:

[0048] Table 1

[0049]

[0050]

[0051] It can be seen from Table 1 that the dephosphorization pressure is guaranteed, the head and tail temperatures tend to be balanced, and the dephosphorization effect on the primary iron oxide scale is in line with expectations:

[0052] Based on the above technical solution, in S4, during the adjustment process, the generation of furnace-generated iron oxide scale is suppressed mainly by lowering the heating temperature, reducing the time in the furnace, and adjusting the atmosphere in the furnace to a reducing atmosphere;

[0053] Specifically, the reversing heating time of the heating furnace was adjusted from the original 90s to 70s. In order to further increase the equalizing effect of the equalizing section of the heating furnace, the temperature of the first and second sections was increased by 100°C, and the temperature gradient of the heating in the furnace was reduced to further enhance the temperature capacity of the equalizing slab.

[0054] The situation after adjusting the reversing heating time and reducing the temperature gradient in the furnace was investigated. The temperature of the steel slab is shown in Table 2:

[0055] Table 2

[0056]

[0057] It can be seen from Table 2 that the temperature difference between the head and tail of the slab out of the furnace is greatly reduced, and the result is in line with the expected effect of the implementation of the countermeasures;

[0058] Based on the above technical solution, in S5, the main method for reducing the roll scale is to use a roll material with good resistance to thermal cracking, adopt a reasonable grinding system, promptly and thoroughly remove residual cracks on the roll surface, and use lubrication rolling to improve the roll surface quality, reduce the unit rolling force of the frame, and prevent the expansion of micro cracks on the roll surface due to excessive unit rolling force, thereby preventing the generation of roll scale.

[0059] Based on the above technical solution, in S5, the water volume at the inlet of the roller cooling water frame is made smaller than the outlet water volume, and the cooling water volume of the intermediate frame rollers is increased to ensure that the rollers are cooled quickly, the finishing rolling temperature is equal to 1030°C, and the roller temperature of the upstream frame of the finishing rolling is reduced.

[0060] Based on the above technical solution, in S6, the head and tail cooling treatment of the intermediate billet is mainly carried out by designing and manufacturing a set of spray water devices for cooling the head and tail of the intermediate billet, and the spray water devices are respectively installed in the rough rolling area and the flying shear area;

[0061] The start and stop of the water spraying device adopts the existing thermal detection slab temperature numerical signal, and precise switch control is carried out by writing a PLC program. The control end is merged into the rolling control screen to facilitate manual operation, so as to ensure the reduction of secondary iron oxide generation during the rolling process.

[0062] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for reducing hot-rolled surface defects, characterized in that: The board surface quality is ensured and the occurrence of roughness is reduced by ensuring the dephosphorization pressure, the work roll surface quality and the head-to-tail temperature difference, including the following processing steps: S1. Investigate the main factors causing the roughness of the board surface; S2. Specify specific implementation plans based on key factors; S3, removing iron oxide scale by descaling; S4, inhibit the generation of furnace oxide scale by regulation; S5, reduce the roller oxide scale; S6. Perform head and tail cooling treatment on the intermediate billet.

2. The method for reducing hot-rolled surface defects according to claim 1, characterized in that: In S1, when the heating temperature is 1250°C and the finishing rolling temperature is 1010-1030°C, there is no iron oxide scale on the surface, when the finishing rolling temperature is between 1050-1080°C, the iron oxide scale is serious, and when the finishing rolling temperature is between 1030-1040°C, there is no iron oxide scale or the iron oxide scale is lighter.

3. A method for reducing hot-rolled surface defects according to claim 2, characterized in that: In S1, according to the different equipment and steel quality of each hot rolling mill, when the finishing rolling temperature is controlled at 1030℃ to produce high-strength steel or high-carbon steel, the rolling force of the first three stands is too high, which will damage the equipment; Depending on the material of the rolling mill rolls, the finishing rolling temperature should be controlled at 1010-1030°C, which can effectively reduce the temperature of the upstream stand rolls and reduce the occurrence of roll oxide scale.

4. The method for reducing hot-rolled surface defects according to claim 1, characterized in that: In S2, the scale defect of the finishing mill is the so-called roll scale, and the main factors affecting the roll scale are the roll material and the roll temperature; When the roller surface contacts the steel plate surface, it becomes hot instantly, and the surface temperature rises sharply and expands. Generally, the instantaneous contact temperature of the hot rolling roller is 600-800℃, showing a high compressive stress. When the rolled piece leaves the roller, the roller cools down sharply due to the cooling of the cooling water. The roller temperature of the finishing mill is generally 60-90℃, and the surface turns into tensile stress. This is repeated, and fatigue cracks are prone to appear on the roller surface, causing the surface oxide film to be damaged. The damaged surface is imprinted into the steel plate surface, forming roller oxide scale defects. The generation of plate surface hemp can be reduced by ensuring the dephosphorization pressure, the quality of the working roller surface, and the temperature difference between the head and the tail.

5. The method for reducing hot-rolled surface defects according to claim 1, characterized in that: In the S3, during the production process of hot-rolled steel plates, the steel billet will be oxidized when heated in the heating furnace to generate primary iron oxide scale, which adheres to the surface of the steel billet. In addition, during the rolling process, the steel billet will also be secondary oxidized to form secondary iron oxide scale. The oxidation of the rolled piece not only causes the metal to be lost due to oxidation, but also under the rolling of the rolling wheel, part of the iron oxide scale is broken into small pieces and automatically falls off, while the other part is pressed into the metal surface, forming inclusions, pitting or scars, etc., causing surface quality defects of the steel plate. Therefore, removing the iron oxide scale is a very critical process link in the hot rolling production process, and this process of removing the iron oxide scale is called descaling.

6. A method for reducing hot-rolled surface defects according to claim 5, characterized in that: In S3, during the specific treatment, a set of descaling water tanks is added, and the pressure is maintained at 18-21Mpa. The surface of the slab is dephosphorized and cleaned. The production rhythm is adjusted to ensure that the descaling water is not opened at the same time. By increasing the descaling water pressure, adjusting and optimizing the height and angle of the water nozzle, the side pressure capacity of the vertical roll is increased to reduce the rough rolling oxide scale.

7. The method for reducing hot-rolled surface defects according to claim 1, characterized in that: In the step S4, during the adjustment process, the generation of furnace-generated iron oxide scale is suppressed mainly by lowering the heating temperature, reducing the time in the furnace, and adjusting the atmosphere in the furnace to a reducing atmosphere; Specifically, the reversing heating time of the heating furnace is adjusted from the original 90s to 70±5s. In order to further increase the equalizing effect of the equalizing section of the heating furnace, the temperature of the first and second sections is increased by 100°C, and the temperature gradient of the heating in the furnace is reduced to further enhance the temperature capacity of the equalizing slab.

8. The method for reducing hot rolling pitting defects according to claim 1, characterized in that: In the above S5, the roller scale is reduced mainly by using a roller material with good thermal cracking resistance, adopting a reasonable grinding system, timely and thoroughly removing residual cracks on the roller surface, and adopting lubrication rolling to improve the roller surface quality, reduce the unit rolling force of the frame, and prevent the roller scale from being generated due to the expansion of micro cracks on the roller surface caused by excessive unit rolling force.

9. A method for reducing hot-rolled surface defects according to claim 8, characterized in that: In S5, the water volume at the inlet of the roller cooling water frame is made smaller than the water volume at the outlet, and the cooling water volume of the intermediate frame rollers is increased to ensure that the rollers are cooled quickly, the finishing rolling temperature is equal to 1030°C, and the roller temperature of the upstream frame of the finishing rolling is reduced.

10. The method for reducing hot-rolled surface defects according to claim 1, characterized in that: In S6, the head and tail cooling treatment of the intermediate billet is mainly carried out by designing and manufacturing a set of spray water devices for cooling the head and tail of the intermediate billet, and the spray water devices are respectively installed in the rough rolling area and the flying shear area; The start and stop of the water spraying device adopts the existing thermal detection slab temperature numerical signal, and precise switch control is carried out by writing a PLC program. The control end is merged into the rolling control screen to facilitate manual operation, so as to ensure the reduction of secondary iron oxide generation during the rolling process.

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