A method for controlling surface pitting defects of hot continuous rolling low carbon steel

Abstract

The present application relates to the technical field of hot continuous rolling low carbon steel, in particular to a method for controlling the surface pitted scale defects of hot continuous rolling low carbon steel. 1) The temperature of the low carbon steel heating furnace is controlled at 1160-1200 DEG C; 2) according to the change of the target thickness of the product, the entry temperature of the finishing mill is controlled: if the target thickness is less than or equal to 2.2 mm, the entry temperature of the finishing mill is controlled at 1035-1060 DEG C; if the target thickness is greater than 2.2 mm, the entry temperature of the finishing mill is controlled at 1015-1040 DEG C; 3) the first rolling mill of the finishing mill is F1, and the Nth rolling mill is FN in turn, and the roll gap cooling water of F1-F5 is put in; 4) the hot rolling oil manifold and nozzle are installed at the outlet of the backup roll of F1-F5; 5) the high speed steel work roll is used for the rolling mill; 6) the water pressure of F1-F7 is controlled at 0.5-1.2 MPa; 7) the target value of the finish rolling temperature is controlled at 750-900 DEG C; 8) the cycle of the high speed steel work roll is controlled within 2-6 cycles; 9) the same batch of high speed steel work roll is avoided to be at the end period. The surface pitted scale defects of hot continuous rolling low carbon steel can be effectively controlled, and the surface quality of the strip steel is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot continuous rolling of low carbon steel, in particular to a method for controlling surface pitted scale defects of hot continuous rolling of low carbon steel. BACKGROUND

[0002] Mild steel is a carbon steel with carbon content less than 0.25%. It is also called soft steel due to its low strength and low hardness. It includes most ordinary carbon structural steel and part of high-quality carbon structural steel, most of which are used for engineering structural parts without heat treatment, and some of which are used for mechanical parts requiring wear resistance after carburizing and other heat treatment.

[0003] However, at present, in the production process of hot continuous rolling of low carbon steel, the surface of the strip steel often appears pitted scale defects that affect the use of downstream customers. Pitted scale appears in hot rolling strip steel production, which is caused by the crushing and pressing of the third oxide on the surface of the strip steel before the finishing mill. The formation mechanism of the pitted scale is: when the surface of the work roll is smooth, no pitted scale will be produced; when the surface of the work roll is rough and the scale on the surface of the strip steel is thick, pitted scale will appear, at this time, the broken scale is in the form of sheet and is discontinuous between each other, which will not deform with the steel matrix after subsequent rolling, forming defects. How to effectively control the pitted scale defects on the surface of hot continuous rolling of low carbon steel has become a technical problem to be solved in the field. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the present application provides a method for controlling pitted scale defects on the surface of hot continuous rolling of low carbon steel, which can effectively control the pitted scale defects on the surface of hot continuous rolling of low carbon steel, thereby improving the surface quality of the strip steel.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0006] A method for controlling pitted scale defects on the surface of hot continuous rolling of low carbon steel, specifically comprising the following steps:

[0007] 1) The discharge temperature of the low carbon steel heating furnace is controlled at 1160-1200℃;

[0008] 2) According to the change of the target thickness of the product, the inlet temperature of the finishing mill is controlled:

[0009] If the target thickness is ≤2.2mm, the inlet temperature of the finishing mill is controlled at 1035-1060℃;

[0010] If the target thickness is >2.2mm, the inlet temperature of the finishing mill is controlled at 1015-1040℃;

[0011] 3) The first finishing mill is F1, and the Nth finishing mill is FN , the roll gap cooling water of F1-F5 is put in;

[0012] 4) installing hot rolling oil manifold and nozzle at the exit of the backup roll of F1-F5;

[0013] 5) the work roll of the rolling mill is made of high speed steel;

[0014] 6) the water pressure of F1-F7 is controlled in 0.5-1.2 MPa;

[0015] 7) the target value of the finishing temperature is controlled in 750-900℃,

[0016] 8) the cycle of the high speed steel work roll is controlled in 2-6 cycles;

[0017] 9) avoiding the high speed steel work roll in the same batch being in the end period.

[0018] Further, in step 4), the proportion of the oil-water mixture in the hot rolling oil manifold is controlled, and the volume percentage of the oil in the oil-water mixture is controlled in 5‰-45‰.

[0019] Further, in step 8), the cycle of the high speed steel work roll of F1-F3 is controlled in 3-6 cycles.

[0020] Further, in step 8), the cycle of the high speed steel work roll of F4 is controlled in 2 cycles.

[0021] Further, in step 9), the high speed steel work roll adopts the collocation mode of early period+early period and early period+end period and end period+early period.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] By reasonably collocating the work roll of the finishing mill, combining with the control of the rolling line process temperature system, such as reasonably controlling the range of the heating temperature and the finishing inlet temperature, and optimizing the control of the backup roll process lubrication flow and the work roll cooling water pressure, the present application improves the control level of the surface quality of the hot continuous rolling low carbon steel, and restrains the occurrence of the surface quality defects.

[0024] By using the method of the present application, the pitting density of the low carbon steel surface can be controlled in 30 / m 2 The surface quality defect rate of the strip steel is reduced from 12.32% to below 1%. DETAILED DESCRIPTION

[0025] The application discloses a method for controlling surface pitted iron sheet defects of hot continuous rolling low-carbon steel. Those skilled in the art can improve the process parameters according to the content of the present application. It is particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously make changes or appropriate changes and combinations to the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0026] A method for controlling surface pitted iron sheet defects of hot continuous rolling low-carbon steel, specifically comprising the following steps:

[0027] 1. The discharge temperature of the low-carbon steel heating furnace is controlled to be 1160-1200℃.

[0028] 2. The entry temperature of the finishing mill is controlled according to the change of the target thickness of the product. When the target thickness is less than or equal to 2.2mm, FT0 (the entry temperature of the finishing mill) is 1035-1060℃; and when the target thickness is greater than 2.2mm, FT0 (the entry temperature of the finishing mill) is 1015-1040℃.

[0029] 3. Different amounts of roll gap cooling water are set according to different target thicknesses of the product, so as to ensure the stability of the cooling control of the steel strip in the rolling process, and the roll gap cooling water of F1-F5 is preferentially put into.

[0030] 4. The proportion of hot rolling oil is optimized by using the supporting roller lubrication technology. The outlet of the supporting roller of F1-F5 is provided with a hot rolling oil manifold and a nozzle, the proportion of the oil-water mixture in the hot rolling oil manifold is controlled, and the volume percentage of the oil in the oil-water mixture is controlled to be 5‰-45‰.

[0031] 5. The rolling mill adopts high-speed steel work rolls, the roll surface wear is small, and the surface quality of the steel strip is good.

[0032] 6. The roll cooling water pressure is reasonably controlled, and the water pressure control range of F1-F7 is 0.5-1.2MPa.

[0033] 7. The lower limit of the target value is mainly used in the control of the finishing temperature.

[0034] 8. The high-speed steel work roll cycle is controlled to be within 2-6 cycles, the front stand is long, and the middle stand is short.

[0035] 9. A reasonable high-speed steel work roll matching scheme is adopted to avoid the same batch being in the end period, and the matching modes of early stage+early stage, early stage+end stage and end stage+early stage are adopted.

[0036] Example 1:

[0037] A method for controlling surface pitted iron sheet defects of hot continuous rolling low-carbon steel, specifically comprising the following steps:

[0038] 1. The low carbon steel heating furnace discharge temperature control range is 1180±20℃;

[0039] 2. Taking the low carbon steel SPHC with a thickness of 2.65mm as an example, FT0:020±10℃;

[0040] 3. The roll gap cooling water of F1-F5 is put in to ensure the stability of the strip steel cooling control in the rolling process;

[0041] 4. The oil volume percentage in the oil-water mixture of the backup rolls of F1-F5 is controlled to be 15‰, 35‰, 30‰, 25‰, 15‰;

[0042] 5. High speed steel work rolls are used in F1-F4 to facilitate small roll surface wear and improve the strip surface quality;

[0043] 6. The water pressures of F1-F7 are respectively set to be 0.85MPa, 0.85MPa, 0.80MPa, 0.72MPa, 0.65MPa, 0.58MPa, 0.80MPa;

[0044] 7. In the final rolling temperature control aspect, the target value (885℃) is controlled within -15~+5℃;

[0045] 8. The maximum use period of high speed steel work rolls of F1-F4 is 6, 6, 3, 2;

[0046] 9. The work rolls of F1 and F2 are used in the 6th period, and the work rolls of F3 and F4 are used in the 1st period.

[0047] In the embodiment, the low carbon steel surface has a pimple density <=25 / m 2 , and the color is white. The pimple density refers to the number of pimples per unit area, which is evaluated by visual method, and the color refers to the surface color after sample treatment, which is evaluated by visual method.

[0048] Embodiment 2: A method for controlling the pimple-shaped iron sheet defect of hot continuous rolling low carbon steel, specifically comprising the following steps:

[0049] 1. The low carbon steel heating furnace discharge temperature control range is 1180±20℃;

[0050] 2. Taking the low carbon steel SPHC with a thickness of 3.0mm as an example, FT0:1010±10℃;

[0051] 3. The roll gap cooling water of F1-F5 is put in to ensure the stability of the strip steel cooling control in the rolling process;

[0052] 4. The oil volume percentage in the oil-water mixture of the backup rolls of F1-F5 is controlled to be 15‰, 30‰, 30‰, 25‰, 15‰;

[0053] 5. F1-F4 use high-speed steel work rolls, which facilitate small roll surface wear and improve the surface quality of the strip steel;

[0054] 6. The water pressures of F1-F7 are respectively set to 0.9 MPa, 0.9 MPa, 0.80 MPa, 0.72 MPa, 0.65 MPa, 0.65 MPa and 0.60 MPa;

[0055] 7. In the control of the finishing temperature, the target value (900℃) is controlled within the range of -15~+5℃;

[0056] 8. The maximum use periods of the high-speed steel work rolls of F1-F4 are 6, 6, 3 and 2 respectively;

[0057] 9. F1 and F2 use the first period work rolls, and F3 and F4 use the third and first period work rolls respectively.

[0058] In the embodiment, the pitting density of the surface of the low-carbon steel is <=10 / m 2 , and the color is white. The pitting density refers to the number of pits per unit area, which is evaluated by visual method, and the color refers to the surface color of the sample after treatment, which is evaluated by visual method.

[0059] Embodiment 3: A method for controlling the pitting-like scale defects on the surface of hot continuous rolling low-carbon steel, which specifically comprises the following steps:

[0060] 1. The control range of the furnace outlet temperature of the low-carbon steel heating furnace is 1180±20℃;

[0061] 2. Taking 2.1mm-thickness low-carbon steel SPHC as an example, FT0: 1045±10℃;

[0062] 3. The roll gap cooling water of F1-F4 is used to ensure the stability of the cooling control of the strip steel during rolling;

[0063] 4. The volume percentage of oil in the oil-water mixture of the backup rolls of F1-F5 is controlled to be 15‰, 35‰, 30‰, 25‰ and 20‰ respectively;

[0064] 5. F1-F4 use high-speed steel work rolls, which facilitate small roll surface wear and improve the surface quality of the strip steel;

[0065] 6. The water pressures of F1-F7 are respectively set to 1.0 MPa, 1.0 MPa, 0.90 MPa, 0.8 MPa, 0.75 MPa, 0.70 MPa and 0.70 MPa;

[0066] 7. In the control of the finishing temperature, the target value (900℃) is controlled within the range of -15~+5℃;

[0067] 8. The maximum usable period of F1-F4 high speed steel work roll is 6, 6, 3, 2;

[0068] 9. F1 and F2 use the third period work roll, and F3 and F4 use the second and first period work roll respectively.

[0069] The pitting density of the low carbon steel surface in the embodiment is <= 15 / m 2 , and the color is white. The pitting density refers to the number of pits per unit area, which is evaluated by visual method, and the color refers to the surface color after sample treatment, which is evaluated by visual method.

[0070] The present application can effectively control the pitting-like iron sheet defects on the surface of hot continuous rolling low carbon steel, and further improve the surface quality of the strip steel.

[0071] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art, according to the technical solution and the inventive concept of the present application, can make equivalent replacement or change within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method of controlling the surface scab defect of hot continuous rolling low carbon steel, characterized in that, Specifically comprising the following steps: 1) the low carbon steel heating furnace discharge temperature is controlled at 1160-1200℃; 2) according to the change of the target thickness of the product, the entry temperature of the finishing mill is controlled: If the target thickness is ≤2.2mm, the entry temperature of the finishing mill is controlled at 1035-1060℃; If the target thickness is >2.2mm, the entry temperature of the finishing mill is controlled at 1015-1040℃; 3) the first finishing stand is F1, and the Nth finishing stand is F N , the roll gap cooling water of F1-F5 is input; 4) a hot rolling oil manifold and nozzle are installed at the exit of the F1-F5 backup roll; 5) the rolling mill adopts high speed steel work roll; 6) the water pressure of F1-F7 is controlled at 0.5-1.2MPa; 7) the target value of the finishing temperature is controlled at 750-900℃; 8) the cycle of the high speed steel work roll is controlled within 2-6 cycles; 9) the high speed steel work roll adopts the collocation mode of early stage+early stage and early stage+final stage and final stage+early stage, to avoid the same batch of high speed steel work roll being in the final stage.

2. The method according to claim 1, characterized in that, in step 4), the proportion of the oil-water mixture in the hot rolling oil manifold is controlled, and the volume percentage of the oil in the oil-water mixture is controlled at 5‰-45‰.

3. The method according to claim 1, characterized in that, in step 8), the cycle of the high speed steel work roll of F1-F3 is controlled within 3-6 cycles.

4. The method according to claim 1, characterized in that, in step 8), the cycle of the high speed steel work roll of F4 is controlled within 2 cycles.

5. The method according to claim 1, characterized in that, in step 9), the high speed steel work roll adopts the collocation mode of early stage+early stage and early stage+final stage and final stage+early stage, to avoid the same batch of high speed steel work roll being in the final stage. ​ ​