Method for controlling pocklike iron sheet defects on surface of hot continuous rolling low-carbon steel

Abstract

The invention relates to the technical field of hot continuous rolling low-carbon steel, in particular to a method for controlling pock-shaped iron sheet defects on the surface of the hot continuous rolling low-carbon steel. The method comprises the following steps: 1) controlling the tapping temperature of a low-carbon steel heating furnace at 1160-1200 DEG (2) according to the change of the target thickness of the product, the inlet temperature of a finishing mill is controlled, and if the target thickness is smaller than or equal to 2.2 mm, the inlet temperature of the finishing mill is controlled to be 1035-1060 DEG C; if the target thickness is larger than 2.2 mm, the inlet temperature of a finishing mill is controlled to be 1015-1040 DEG C; (3) the first rolling mill for finish rolling is F1, and the Nth rolling mill is FN in the same way, and roll gap cooling water of F1-F5 is added; (4) hot rolling oil collecting pipes and nozzles are installed at outlets of the supporting rollers F1-F5; 5) adopting a high-speed steel working roller as a rolling mill; (6) the water pressure of F1-F7 is controlled to be 0.5-1.2 MPa; (7) the target value of the finish rolling temperature is controlled to be 750-900 DEG C; (8) the period of the high-speed steel working roller is controlled within 2-6; and (9) high-speed steel working rollers in the same batch are prevented from being in the last stage. Point-shaped iron sheet defects on the surface of hot continuous rolling low-carbon steel can be effectively controlled, and then the surface quality of strip steel is improved.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled low-carbon steel, in particular to a method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel. Background Art

[0002] Low carbon steel (mild steel) is carbon steel with a carbon content of less than 0.25%. It is also called soft steel because of its low strength, low hardness and softness. It includes most ordinary carbon structural steels and some high-quality carbon structural steels. Most of them are used for engineering structural parts without heat treatment, and some are used for mechanical parts that require wear resistance after carburizing and other heat treatments.

[0003] However, in the current production process of hot-rolled low-carbon steel, pitted scale defects often appear on the strip surface, which affects the use of downstream customers. Pitted scale appears in the production of hot-rolled strip steel. This is caused by the tertiary oxides on the surface of the strip being broken and pressed into the surface of the strip before the finishing mill. The formation mechanism of pitted scale is: when the surface of the working roll is relatively smooth, no pitted scale will be produced; when the surface of the working roll is rough and the scale on the surface of the strip is relatively thick, pitted scale will appear. At this time, the broken scale is flaky and discontinuous with each other. After subsequent rolling, it will not deform with the steel matrix, forming defects. How to effectively control the pitted scale defects on the surface of hot-rolled low-carbon steel has become a technical problem to be solved in this field. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a method for controlling pitting scale defects on the surface of hot-rolled low-carbon steel, which can effectively control pitting scale defects on the surface of hot-rolled low-carbon steel and thus improve the surface quality of the strip.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel, specifically comprising the following steps:

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

[0008] 2) Control the finishing mill inlet temperature according to the change of product target thickness:

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

[0010] If the target thickness is greater than 2.2 mm, the finishing mill inlet temperature is controlled at 1015-1040°C;

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

[0012] 4) Install hot rolling oil manifold and nozzle at the outlet of the support rolls of F1-F5;

[0013] 5) The rolling mill uses high-speed steel working rolls;

[0014] 6) The water pressure of F1-F7 is controlled at 0.5~1.2MPa;

[0015] 7) The target value of final rolling temperature is controlled at 750~900℃,

[0016] 8) The cycle of high-speed steel working rolls is controlled within 2 to 6 cycles;

[0017] 9) Avoid the same batch of high-speed steel working rolls being in the final stage.

[0018] Furthermore, in step 4), the proportion of the oil-water mixture in the hot rolling oil header is controlled, and the volume percentage of the oil in the oil-water mixture is controlled within a range of 5‰ to 45‰.

[0019] Furthermore, in step 8), the cycle of the high-speed steel working rolls of F1-F3 is controlled within 3 to 6 cycles.

[0020] Furthermore, in step 8), the cycle of the high-speed steel working roll of F4 is controlled within 2 cycles.

[0021] Furthermore, in step 9), the high-speed steel working rolls are matched in the early stage + early stage, early stage + late stage, and late stage + early stage.

[0022] Compared with the existing method, the beneficial effects of the present invention are:

[0023] The present invention improves the control level of the surface quality of hot-rolled low-carbon steel and curbs the occurrence of surface quality defects by reasonably matching the working rolls of the finishing mill and controlling the process temperature system of the rolling line, such as reasonably controlling the range of the heating temperature and the finishing inlet temperature, and optimizing the control of the process lubrication flow of the support rolls and the cooling water pressure of the working rolls.

[0024] By adopting the method of the present invention, the density of pits on the surface of low carbon steel can be controlled to 30 / m 2 The surface quality defect rate of the strip steel dropped from 12.32% to below 1%. DETAILED DESCRIPTION

[0025] The present invention discloses a method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0026] A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel, specifically comprising the following steps:

[0027] 1. The temperature out of the low carbon steel heating furnace is controlled at 1160~1200℃.

[0028] 2. According to the change of product target thickness, control the inlet temperature of the finishing mill. Target thickness ≤2.2mm, FT0 (finishing mill inlet temperature): 1035-1060℃; >2.2mm, FT0 (finishing mill inlet temperature): 1015-1040℃.

[0029] 3. According to the different target thickness of the product, set different amounts of roll gap cooling water to ensure the stability of strip cooling control during the rolling process, and give priority to the roll gap cooling water of F1-F5.

[0030] 4. Use support roller lubrication technology to optimize the hot rolling oil ratio. The outlets of the support rollers of F1-F5 are equipped with hot rolling oil headers and nozzles to control the ratio of the oil-water mixture in the hot rolling oil header. The volume percentage of oil in the oil-water mixture is controlled at 5‰ to 45‰.

[0031] 5. The rolling mill uses high-speed steel working rolls, which have little wear on the roll surface and good strip surface quality.

[0032] 6. Reasonable roller cooling water pressure control, the water pressure control range of F1-F7 is 0.5-1.2MPa.

[0033] 7. In terms of final rolling temperature control, the lower and middle limits of the target value are mainly used.

[0034] 8. The cycle of high-speed steel working roll is controlled within 2-6 cycles, the front frame is long and the middle frame is short.

[0035] 9. Reasonable high-speed steel working roll matching scheme, avoid the same batch being in the final stage, and adopt the matching method of early stage + early stage, early stage + final stage, and final stage + early stage.

[0036] Embodiment 1:

[0037] A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel, specifically comprising the following steps:

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

[0039] 2. Taking 2.65mm thick low carbon steel SPHC as an example, FT0: 020±10℃;

[0040] 3. Add cooling water to the roll gap of F1-F5 to ensure the stability of strip cooling control during the rolling process;

[0041] 4. The volume percentage of oil in the oil-water mixture of the support rollers of F1-F5 is controlled at: 15‰, 35‰, 30‰, 25‰, 15‰;

[0042] 5. F1-F4 adopts high-speed steel working rolls, which reduces the wear of the roll surface and improves the surface quality of the strip;

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

[0044] 7. Regarding the final rolling temperature control, the target value (885°C) is controlled at -15 to +5°C;

[0045] 8. The maximum service life of F1-F4 high speed steel working rolls is 6, 6, 3, 2;

[0046] 9. F1 and F2 both use the 6th cycle working rolls, and F3F4 both use the 1st cycle working rolls.

[0047] The pit density on the surface of the low carbon steel in this embodiment is ≤25 / m 2 , the color is white. The pit 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.

[0048] Embodiment 2: A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel, comprising the following steps:

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

[0050] 2. Taking 3.0mm thick low carbon steel SPHC as an example, FT0: 1010±10℃;

[0051] 3. Add cooling water to the roll gap of F1-F5 to ensure the stability of strip cooling control during the rolling process;

[0052] 4. The volume percentage of oil in the oil-water mixture of the support rollers of F1-F5 is controlled at: 15‰, 30‰, 30‰, 25‰, 15‰;

[0053] 5. F1-F4 adopts high-speed steel working rolls, which reduces the wear of the roll surface and improves the surface quality of the strip;

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

[0055] 7. Regarding the final rolling temperature control, it is controlled at -15 to +5°C according to the target value (900°C);

[0056] 8. The maximum service life of F1-F4 high speed steel working rolls is 6, 6, 3, 2;

[0057] 9. F1 and F2 both use the first cycle working rolls, and F3 and F4 use the third and first cycle working rolls respectively.

[0058] The pit density on the surface of the low carbon steel in this embodiment is ≤10 / m 2 , the color is white. The pit 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 pitting iron scale defects on the surface of hot-rolled low-carbon steel, comprising the following steps:

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

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

[0062] 3. Add cooling water to the roll gap of F1-F4 to ensure the stability of strip cooling control during the rolling process;

[0063] 4. The volume percentage of oil in the oil-water mixture of the support rollers of F1-F5 is controlled at: 15‰, 35‰, 30‰, 25‰, 20‰;

[0064] 5. F1-F4 adopts high-speed steel working rolls, which reduces the wear of the roll surface and improves the surface quality of the strip;

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

[0066] 7. Regarding the final rolling temperature control, it is controlled at -15 to +5°C according to the target value (900°C);

[0067] 8. The maximum service life of F1-F4 high speed steel working rolls is 6, 6, 3, 2;

[0068] 9. F1 and F2 both use the 3rd cycle working rolls, and F3F4 use the 2nd and 1st cycle working rolls respectively.

[0069] The pit density on the surface of the low carbon steel in this embodiment is ≤15 / m 2 , the color is white. The pit 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.

[0070] The present invention can effectively control pitting iron scale defects on the surface of hot-rolled low-carbon steel, thereby improving the surface quality of the strip steel.

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel, characterized in that: The specific steps include: 1) The temperature out of the low carbon steel heating furnace is controlled at 1160~1200℃; 2) Control the inlet temperature of the finishing mill according to the change of product target thickness: If the target thickness is ≤2.2mm, the finishing mill inlet temperature is controlled at 1035-1060℃; If the target thickness is greater than 2.2 mm, the finishing mill inlet temperature is controlled at 1015-1040°C; 3) The first rolling mill for finishing is F1, and the Nth rolling mill is F N , add cooling water to the roll gap of F1-F5; 4) Install hot rolling oil manifold and nozzle at the outlet of the support rolls of F1-F5; 5) The rolling mill uses high-speed steel working rolls; 6) The water pressure of F1-F7 is controlled at 0.5~1.2MPa; 7) The target value of the final rolling temperature is controlled at 750-900°C; 8) The cycle of high-speed steel working rolls is controlled within 2 to 6 cycles; 9) Avoid the same batch of high-speed steel working rolls being in the final stage.

2. A method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel according to claim 1, characterized in that: In step 4), the proportion of the oil-water mixture in the hot rolling oil header is controlled, and the volume percentage of the oil in the oil-water mixture is controlled to be 5‰ to 45‰.

3. The method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel according to claim 1, characterized in that: In step 8), the cycle of the high-speed steel working rolls of F1-F3 is controlled within 3 to 6 cycles.

4. The method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel according to claim 1, characterized in that: In step 8), the cycle of the high-speed steel working roll of F4 is controlled within 2 cycles.

5. The method for controlling pitting iron scale defects on the surface of hot-rolled low-carbon steel according to claim 1, characterized in that: In step 9), the high-speed steel working rolls are matched in the early stage + early stage, early stage + final stage, and final stage + early stage.