Production method of Nb-containing pickling plate with 355 MPa grade and very thin specification

Abstract

The present application relates to the technical field of steel plate production, and particularly relates to a production method of an extremely thin Nb-containing 355MPa-grade pickling plate, which comprises the following steps: 1) slab blanking: the difference between the slab width and the target width is controlled to be within 50mm, and the slab single weight is controlled according to the single steel rolling distance within 1150m; 2) heating: the air-fuel ratio of the heating furnace is set to be 1.8-2.0, the furnace atmosphere is controlled to be weak oxidizing, the furnace outlet temperature is 1220-1240 DEG C, the second heating section + soaking time is greater than or equal to 65min, the total in-furnace time is greater than or equal to 170min, and the interval between the steel tapping is greater than or equal to 160s; 3) rough rolling: the slab outlet does not use the SP width press, the rough rolling adopts two rolling mills, and each rolling mill is rolled for three passes; the descaling water is fed in each pass; 4) finish rolling: the finish rolling inlet temperature is controlled to be 1050-1080 DEG C, and the finish rolling temperature is within the range of 860-900 DEG C; 5) when the flatness defect occurs during the coiling, the cooling setting time is increased in the coiling drum. The present application guarantees the stable rolling and improves the surface quality of the steel plate.

Description

Technical Field

[0001] This invention belongs to the field of steel plate production technology, and specifically relates to a production method for ultra-thin 355MPa grade niobium-containing pickled steel plate. Background Technology

[0002] Pickled steel sheet is a crucial product of hot-rolled production lines, requiring high surface quality and free from defects such as pitting and indentation. With the expanding applications of pickled steel sheet, the demand for thin-gauge, high-strength pickled steel sheet is continuously increasing. High-strength pickled steel sheet with a yield strength of 355 MPa has emerged to meet this need. To enhance strength, this grade of steel has a high niobium alloy content. Niobium strengthens primarily through precipitation during hot rolling, improving the steel's strength and toughness. The precipitation process is affected by temperature changes, which alter the deformation resistance during rolling, making production challenging. Stable production has become a key research focus for steel mills, as achieving stable production can significantly improve product quality and efficiency, thereby enhancing corporate competitiveness.

[0003] The production of ultra-thin 355MPa grade high-strength pickled steel sheets with a thickness of less than 2.7mm is difficult and requires high process control. The following problems are prone to occur during the production control process:

[0004] 1) The strip steel is extremely thin, with a high niobium content, and undergoes a precipitation strengthening process. Its deformation resistance is greatly affected by temperature changes. During the finishing rolling process, the strip steel is prone to deviation, resulting in breakage or jamming.

[0005] 2) High surface quality requirements: excessively high temperature or peeling of oxide film on the finishing work roll surface causes pitting defects; insufficient descaling effect results in landscape-patterned iron sheet defects on the surface.

[0006] 3) The strip steel is extremely thin, and there is a risk of flattening during winding, which will affect subsequent use. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a production method for ultra-thin 355MPa grade niobium-containing pickled steel plate, which ensures rolling stability while improving the surface quality of the steel plate.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] A method for producing ultra-thin 355MPa grade niobium-containing pickled steel plate includes:

[0010] 1) Slab shape: Control the difference between the slab width and the target width to be within 50mm, and control the slab weight per slab based on the rolling mileage of a single steel piece to be within 1150m;

[0011] 2) Heating process: Set the air-fuel ratio of the heating furnace to 1.8-2.0, control the atmosphere inside the furnace to be weakly oxidizing, the tapping temperature to 1220-1240℃, the time for the second heating section plus soaking time to be ≥65min, the total time in the furnace to be ≥170min, and the tapping interval to be ≥160s.

[0012] 3) Rough rolling process: The SP fixed width press is not used for the slabs coming out of the furnace. The rough rolling is carried out by two rolling mills, with each rolling mill rolling 3 passes; descaling water is added for each rolling pass, and the descaling water pressure is guaranteed to be above 18MPa.

[0013] 4) Finishing mill process: Control the finishing mill inlet temperature to 1050-1080℃. Use the first cycle of new work rolls for work rolls F1-F7. Ensure the descaling water pressure at the finishing mill inlet is above 20MPa. Do not use interstand descaling water, back spray water, or strip cooling water. Force the use of F1-F3 roll gap water. Slowly increase the strip speed during finishing milling. Stop increasing the speed when the final rolling temperature is higher than the target value. Control the final rolling temperature within the range of 860-900℃. Based on the side bending of the roughing mill intermediate billet, pre-adjust the roll gap deviation in the finishing mill in advance. Before the roughing mill intermediate billet enters the finishing mill, adjust the roll gap deviation of finishing mill F1-F3 in advance according to the side bending direction of the intermediate billet. The adjustment range is controlled within 5-10μm. Based on the strip deviation trend in the finishing mill stands, adjust the roll gap deviation of stands F1-F7 accordingly to keep the strip straight in the stands. The single adjustment range is controlled within 5-20μm.

[0014] 5) Winding process: If a flat roll defect occurs, increase the cooling and setting time inside the roll.

[0015] The required mass fraction of the niobium-containing acid-washed plate components is as follows: C: 0.06%~0.08%, Si≤0.07%, Mn: 0.80%~0.95%, P≤0.018%, S≤0.006%, Nb: 0.022%~0.032%.

[0016] The thickness of the niobium-containing acid-washed plate is 2.05–2.70 mm.

[0017] Step 5) involves increasing the cooling and setting time inside the roll: After winding, spray cooling water onto the roll for 40-50 seconds before unwinding.

[0018] Compared with existing technologies, the beneficial effects of this invention are:

[0019] 1. Control the single weight of the slab to reduce the finishing rolling time and prevent the intermediate slab from cooling down for too long and the temperature from being uneven.

[0020] 2. SP width-fixing presses are not used for the slabs exiting the furnace to prevent the slabs from being narrowed by SP, which would affect the temperature uniformity of the slabs. Descaling water is added in each rolling pass to improve the descaling effect and enhance surface quality.

[0021] 3. The niobium precipitation strengthening in niobium-containing pickled strips occurs precisely during the finishing rolling process. The precipitation strengthening process forms precipitates that increase deformation resistance. Temperature affects the degree of precipitation strengthening, causing uneven deformation resistance. By reducing the cooling water volume and controlling the rolling speed, the final rolling temperature can be controlled to avoid uneven temperature caused by water cooling, which could affect the uneven deformation of the strip within the stand and lead to strip deviation.

[0022] 4. By increasing the cooling and setting time inside the roll, the flat roll defect can be mitigated.

[0023] This invention combines the rolling characteristics of niobium-containing pickled steel sheets. By adjusting the processes from slab design to hot rolling, it can improve the surface descaling effect, reduce the generation of pits on the strip surface, improve the surface quality of the strip, solve the problem of easy deviation during fine rolling, and achieve stable rolling of thin-gauge 355MPa grade high-strength pickled steel sheets. Detailed Implementation

[0024] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0025] A method for producing ultra-thin 355MPa grade niobium-containing pickled steel plate includes:

[0026] 1) Slab shape: Control the difference between the slab width and the target width to be within 50mm to reduce the width reduction in the roughing rolling area; control the slab weight per slab within 1150m of rolling length per slab to reduce finishing rolling time and prevent long cooling time and uneven temperature at the tail of intermediate slabs.

[0027] 2) Heating process: The air-fuel ratio of the heating furnace is set to 1.8-2.0, and the atmosphere inside the furnace is controlled to be weakly oxidizing, so that the iron oxide scale on the surface of the slab can be fully formed and more easily removed; the tapping temperature is set to 1220-1240℃, the second heating section plus the soaking time is ≥65min, and the total time in the furnace is ≥170min, so that the slab is heated evenly inside; the tapping interval is ≥160s, so as to avoid the slab waiting time on the conveyor rollers for a long time and the temperature drops.

[0028] 3) Rough rolling process: SP width-fixing press is not used for the slabs after the furnace to prevent the slab temperature uniformity from being affected by the width reduction of SP. Rough rolling is carried out by two rolling mills, with each rolling mill rolling 3 passes to improve the side bending of the intermediate slabs in rough rolling. Descaling water is added in each rolling pass, and the pressure of the descaling water is guaranteed to be above 18MPa to improve the descaling effect and improve the surface quality.

[0029] 4) Finishing Rolling Process: The inlet temperature of the finishing mill is controlled at 1050–1080℃ to provide a suitable temperature for finishing rolling and reduce deformation resistance. Work rolls F1–F7 use new work rolls from the first cycle to ensure a complete and uniform oxide film. The descaling water pressure at the finishing mill inlet is maintained above 20 MPa. Niobium precipitation strengthening in niobium-containing pickled plates occurs at 800–950℃, and the target finishing rolling temperature is 880℃. This precipitation strengthening occurs precisely during the finishing rolling process. The precipitation strengthening process forms precipitates that increase deformation resistance. Temperature affects the degree of precipitation strengthening, causing uneven deformation resistance and affecting the uneven deformation of the strip within the mill stand, leading to strip deviation. Therefore, descaling water, backspray water, and strip cooling water between stands are not used to prevent uneven water cooling from causing uneven strip temperature within the finishing mill. Forced use of F1-F3 roll gap water is used to reduce the temperature of F1-F3 strip steel in contact with the rolls, prevent oxide film from falling off and causing pitting defects, control the finishing rolling speed, and control the final rolling temperature within the range of 880±20℃.

[0030] 5) Winding process: If a flat roll defect occurs, spray cooling water on the winding roller for 40-50 seconds after winding is completed before unwinding. By increasing the cooling and setting time inside the roll, the flat roll defect can be mitigated.

[0031] The required mass fraction of the niobium-containing acid-washed plate components is as follows: C: 0.06%~0.08%, Si≤0.07%, Mn: 0.80%~0.95%, P≤0.018%, S≤0.006%, Nb: 0.022%~0.032%.

[0032] The thickness of the niobium-containing acid-washed plate is 2.05–2.70 mm.

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] Example 1:

[0035] The production method of 2.05mm thick 355MPa grade niobium-containing pickled steel plate includes:

[0036] 1. Main component content of pickled plate: C (0.066wt%), Si (0.061wt%), Mn (0.85wt%), P (0.01wt%), S (0.001wt%), Nb (0.027wt%).

[0037] 2. The target width of the slab is 834mm, and the controlled width of the slab is 875mm, with a difference of 41mm from the target width.

[0038] 3. Based on a target steel thickness of 2.05mm, a target width of 834mm, and a slab thickness of 230mm, calculate the rolling mileage, control it within 1150m, and design the slab weight to be 15t.

[0039] 4. Heating process: A weak oxidizing atmosphere is used in the furnace, and the air-fuel ratio is set to 1.8; the furnace temperature is 1238℃, the heating time of the second heating section plus the soaking time is 165min, the total furnace time is 287min, and the steel tapping interval is 160s.

[0040] 5. Rough rolling process: The width of the slab after exiting the furnace is not reduced by the SP width-fixing press. The width is controlled by the roughing vertical rolls E1 and E2. The two roughing mills R1 and R2 roll three times according to the speed and reduction rate set by the secondary model. Descaling water is added in each pass, and the descaling pressure is 20MPa.

[0041] 6. Finishing Rolling Process: The finishing mill inlet temperature was controlled at 1073℃. Work rolls F1-F7 were new rolls from the first cycle. The descaling box cooling water pressure was 21MPa. The descaling water, backspray water, and strip cooling water between stands were all shut off, and the F1-F3 roll gap water was forcibly activated. The final rolling temperature was controlled by controlling the finishing mill rolling speed, using a smaller finishing mill acceleration and slow acceleration to achieve temperature control. The final rolling temperature was 900℃. The finishing mill centerline was straight, with no deviation. The rolling process was stable, with no breakage or steel jamming issues. The actual rolling distance was 1107m. Inspection of the work roll surfaces revealed no oxide film peeling.

[0042] The descaling box cooling water pressure is 21 MPa. The descaling water, back spray water, and strip cooling water between stands are all shut off, and the F1 to F3 roll gap water is forcibly used. The final rolling temperature is controlled by controlling the finishing rolling speed. The strip threading speed is 10.13 m / s; the primary acceleration is 0.3 m / s; the secondary acceleration is 0.3 m / s, and the acceleration is slow. When the real-time final rolling temperature reaches 890℃, the acceleration is stopped to achieve the temperature control purpose. The average final rolling temperature is 885℃.

[0043] Slight drive-side misalignment was observed in rolls F5 and F6. After adjusting the roll gap deviation, the finishing mill centerline returned to straightness, with no frequent or excessive misalignment. The rolling process was stable, without any breakage or steel jamming. The actual rolling mileage was 1107m. Inspection of the work rolls revealed no signs of oxide film peeling.

[0044] 7. Winding process: After winding, the operation was carried out by spraying cooling water on the winding roller for 50 seconds before unwinding, and no flat roll defects occurred.

[0045] 8. Surface inspection: The surface is free of defects such as pitting or unevenness, as determined by surface inspection instruments and physical inspection.

[0046] Example 2:

[0047] The production method of 2.55mm thick 355MPa grade niobium-containing pickled steel plate includes:

[0048] 1. Main component content of pickled plate: C (0.066wt%), Si (0.061wt%), Mn (0.85wt%), P (0.01wt%), S (0.001wt%), Nb (0.027wt%).

[0049] 2. The target width of the slab is 958mm, and the difference between the slab width and the target width is controlled at 42mm, so the slab width is 1000mm.

[0050] 3. Based on a target steel thickness of 2.55mm, a target width of 958mm, and a slab thickness of 230mm, calculate the rolling mileage, control it within 1150m, and design the slab weight to be 18t.

[0051] 4. Heating process: A weak oxidizing atmosphere is used in the furnace, and the air-fuel ratio is set to 1.8; the furnace temperature is 1229℃, the second heating section plus the soaking time is 106min, the total furnace time is 227min, and the steel tapping interval is 160s.

[0052] 5. Rough rolling process: The width of the slab after exiting the furnace is not reduced by the SP width-fixing press. The width is controlled by the roughing vertical rolls E1 and E2. The two roughing mills R1 and R2 roll three times according to the speed and reduction rate set by the secondary model. Descaling water is added in each pass, and the descaling pressure is 20.8MPa.

[0053] 6. Finishing Rolling Process: The finishing mill inlet temperature is controlled at 1053℃. Work rolls F1 to F7 are new work rolls from the first cycle. The descaling box cooling water pressure is 20.68MPa. The descaling water, back spray water, and strip cooling water between stands are all shut off, and the F1 to F3 roll gap water is forcibly activated. The finishing mill rolling speed is controlled to control the final rolling temperature. The strip threading speed is 9.9m / s; the primary acceleration is 0.3m / s; the secondary acceleration is 0.3m / s, and the acceleration is slow. When the real-time final rolling temperature reaches 897℃, the speed increase is stopped to achieve the temperature control purpose. The average final rolling temperature is 892℃.

[0054] F6 exhibited slight drive-side misalignment. After adjusting the roll gap deviation, the finishing mill centerline returned to straightness, with no frequent or excessive misalignment. The rolling process was stable, without any breakage or steel jamming. The actual rolling mileage was 920m. Inspection of the work rolls revealed no signs of oxide film peeling.

[0055] 7. Winding process: After winding, the operation was carried out by spraying cooling water on the winding roller for 50 seconds before unwinding, and no flat roll defects occurred.

[0056] 8. Surface inspection: The surface is free of defects such as pitting and landscape painting on the iron sheet, as determined by surface inspection instrument and physical inspection.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing an Nb-containing pickling sheet of an extra thin grade 355 MPa grade, characterized by, The niobium-containing pickling plate component mass fraction requirements: C: 0.06% to 0.08%, Si≤0.07%, Mn: 0.80% to 0.95%, P≤0.018%, S≤0.006%, Nb: 0.022% to 0.032%; the production method comprises: 1) slab blank: control the difference between the slab width and the target width within 50 mm, control the slab single weight within 1150 m according to the single steel rolling kilometer; 2) heating process: set the heating furnace air-fuel ratio to 1.8 to 2.0, control the furnace atmosphere to be weakly oxidizing, the discharge temperature is 1220 to 1240℃, the second heating section + soaking time is greater than or equal to 65 min, the total in-furnace time is greater than or equal to 170 min, and the interval between tapping is greater than or equal to 160 s; 3) rough rolling process: the discharged slab does not use SP width setting press, scale removal water is injected in each pass, and the scale removal water pressure is guaranteed to be greater than 18 MPa; 4) finishing rolling process: control the finishing rolling inlet temperature to be 1050 to 1080℃, the first cycle new work roll is used for F1 to F7 work roll, the scale removal water pressure at the finishing rolling inlet is guaranteed to be greater than 20 MPa, no scale removal water, back spray water or strip cooling water is injected between racks, F1 to F3 roll gap water is forced to be injected, the strip is slowly accelerated during finishing rolling, the acceleration is stopped when the final rolling temperature is higher than the target average, and the final rolling temperature is controlled to be within the range of 860 to 900℃; The roll gap deviation of the rack is adjusted before and during finishing rolling to keep the strip straight in the rack; 5) coiling process: if flat coil defects occur, the cooling and shaping time in the winding drum is increased.

2. The method for producing an Nb-containing pickling plate of an extra-thin gauge 355 MPa grade according to claim 1, characterized by, The thickness of the niobium-containing pickling plate is 2.05 to 2.70 mm.

3. The method of producing an Nb-containing pickling plate of an extra-thin gauge 355 MPa grade according to claim 1, characterized in that, In step 3), rough rolling is carried out by two racks, and each rack is rolled for 3 passes.

4. The method of producing an Nb-containing pickling plate of an ultra-thin gauge 355 MPa grade according to claim 1, characterized by, In step 4), the specific operation of adjusting the roll gap deviation of the rack before and during finishing rolling is as follows: according to the change of the intermediate slab side bend in rough rolling, the roll gap deviation in the finishing rolling mill is pre-adjusted; before the intermediate slab in rough rolling enters the finishing rolling mill, the roll gap deviation of F1 to F3 in the finishing rolling mill is adjusted in advance according to the direction of the intermediate slab side bend, and the adjustment range is controlled within 5 to 10 μm; according to the deviation tendency of the strip in the finishing rolling mill, the roll gap deviation of F1 to F7 racks is adjusted correspondingly to keep the strip straight in the rack, and the single adjustment range is controlled within 5 to 20 μm.

5. The method of producing an Nb-containing pickling plate of an ultra-thin gauge 355 MPa grade according to claim 1, characterized by, In step 5), the method of increasing the cooling and shaping time in the winding drum is as follows: after coiling is completed, the winding roller cooling water is sprayed for 40 to 50 s before the coil is unloaded.