A production process of cold-rolled thin-gauge SPCC-M steel

Abstract

The application discloses a production process of cold-rolled thin-gauge SPCC-M steel, wherein the process control design of cold-rolled pickling and rolling mill is as follows: 1) the temperature of 1-4# tank hydrochloric acid is controlled to 65-75 DEG C, and the process section running speed is controlled to 60-130 m / min; 2) the acid pickling unit is replaced with new acid 60-80 m3 in advance for 4 hours before producing special steel, so that the HCL content of the acid liquid in the 1# acid tank is ensured to be greater than or equal to 50 g / L, and the iron ion content is less than or equal to 100 g / L; 3) the water temperature at the outlet of the filter of the 1# rinsing tank is 60 DEG C-80 DEG C, the water conductivity of the 2# rinsing tank is less than or equal to 100 us / cm, and the wedge-shaped convexity of the hot-rolled coil raw material is less than or equal to 40 um; the occurrence of the steel coil surface sticking and texturing defects can be effectively prevented, and the production of the SPCC-M steel with the thickness of 0.30-0.60 mm is suitable.

Description

Technical Field

[0001] This invention relates to a production process for cold-rolled thin-gauge SPCC-M steel. Background Technology

[0002] The cold rolling area of ​​Baosteel Company uses an EBNER strong convection all-hydrogen protective gas single-stack bell furnace to directly recrystallize and brighten cold-rolled coils. There is no degreasing treatment process before the bell annealing. After annealing, the grade of SPCC-M steel with a thickness of 0.30~0.60mm is downgraded by 40% due to adhesion defects after production in the leveling process. At the same time, it seriously affects the production rhythm. When the adhesion is severe, the leveling unit can only produce 1 coil of steel in 2 hours. Moreover, there have been many accidents caused by strip breakage due to strip adhesion and tearing, which seriously affects the production rhythm and production cost.

[0003] Literature search results: "Analysis of Causes and Control Measures for Adhesion Defects in Cold-Rolled Steel Coils" by Wang Hongfeng. This literature mainly analyzes the thickness adhesion defects, which mainly occur in ordinary steel with a thickness of less than 1.2 mm. The analysis of pickling and rolling mainly focuses on the influence of incoming sheet shape, coiling tension, and roughness on adhesion. The analysis of annealing process mainly focuses on the influence of heating rate and cooling rate on adhesion.

[0004] The paper "Causes and Preventive Measures of Adhesion Defects in Cold-Rolled Steel Coils" by Deng Han mainly analyzes the shape and rolling process of hot-rolled steel coils, including surface roughness and cleanliness, coiling tension, shape control, bell-type furnace annealing process conditions and leveling process. However, it still does not conduct research-based quantitative analysis on surface roughness and cleanliness, coiling tension, shape control, bell-type furnace annealing process conditions and leveling process.

[0005] The paper "Practice to Reduce Adhesion Defects in Cold-Rolled Coils" by Zhao Aiwei mainly analyzes the influence of coiling tension, surface roughness, post-rolled strip straightness, strip convexity, and post-rolling cooling on adhesion. However, it does not conduct research-based quantitative analysis on surface roughness and cleanliness, coiling tension, strip shape control, bell-type furnace annealing process conditions, and leveling process.

[0006] The inventor of "A Cold Rolling Production Process for Steel for Door Panels (SPCC-M)" is Hu Honglin, Hu Lekang, Ma Xiaojuan, and Lu Pengcheng. Publication number: CN104372150A. The main focus is on analyzing the key process points of each step. While the process involves cooling under a heating hood for 5 hours with rapid cooling, adhesion defects were not effectively eliminated in actual production. Furthermore, the patent did not refine or optimize the raw material shape, emulsion iron powder control, hot-rolled coil wedge convexity, coil diameter during furnace loading, surface roughness, and mill coiling tension. This invention patent represents a significant advancement upon the original patent.

[0007] Among the aforementioned influencing factors, the main factors within the controllable range of cold rolling mills include: rolling process (strip surface roughness and cleanliness, coiling tension, sheet shape control, etc.), annealing process, and leveling process. These factors, when combined with other conditions, also have a significant impact on adhesion formation, and the relevant technical indicators are unclear. Summary of the Invention

[0008] To further prevent adhesion defects on steel coils while ensuring the straightness, dimensional accuracy, and mechanical properties of the strip, this invention discloses a production process for cold-rolled thin-gauge SPCC-M steel. This method effectively controls adhesion defects on the surface of the steel coil.

[0009] The technical solution adopted in this invention is a production process for cold-rolled thin-gauge SPCC-M steel.

[0010] A. First, the steel composition is designed as follows: Steel marking AP1451C1, C content 0.03-0.06%, Si content ≤0.04%, Mn content 0.15-0.22%, P content ≤0.015%, S content ≤0.012%, Al content 0.03-0.05%, residual elements [Cr] ≤0.1%, [Ni] ≤0.1%, [Cu] ≤0.15%, [N] ≤0.0060%;

[0011] B. Requirements for steelmaking raw materials: 1) Requirements for molten iron: Depending on the molten iron conditions and production needs, molten iron can be desulfurized and pretreated. The molten iron directly fed into the furnace has a [S] content of ≤0.01%. Requirements for molten iron before desulfurization: Si content ≤1.2%, P content ≤0.18%, S content ≤0.06%, and temperature ≥1250℃; 2) The converter ladle and argon blowing conditions should be good. There should be no large amount of cold steel or slag on the bottom and wall of the ladle.

[0012] C. Converter process control: 1) Endpoint composition control: [C] ≤ 0.04%, [P] ≤ 0.012%, [S] ≤ 0.012%; 2) Tapping requirements: Add deoxidizer according to carbon content, maintain the tapping spout, tapping time ≥ 3.5 minutes, slag blocking during tapping, control the thickness of the slag layer in the ladle, and require that the phosphorus return during tapping is not greater than 0.003%;

[0013] D. Refining requirements: 1) Direct process: soft blowing argon stirring to remove inclusions and fine-tune composition; 2) LF treatment: temperature increase, composition adjustment, desulfurization, degassing, and inclusion removal.

[0014] E. Slab continuous casting control and inspection requirements: 1) Continuous casting adopts argon protection throughout the process, and uses carbon-free protective slag and carbon-free ladle covering agent; baffles are installed in the tundish; the superheat of the tundish in the first continuous casting is ≤45℃, the superheat of the tundish in the next continuous casting is ≤35℃, and the maximum casting speed is ≤1.6m / min; 2) The liquidus temperature of the tap mark AP1451C1 is 1530℃; 3) Slabs that pass the hot inspection can be hot-charged and hot-delivered.

[0015] F. Key points for conventional hot rolling process control: heating time greater than 160 minutes, temperature difference between the head and tail of the slab less than 20℃, descaling at the three entry points of the roughing mill; final rolling temperature 870±20℃, rapid cooling mode in the later stage, and coiling temperature 600±20℃.

[0016] G. Process control design for cold rolling pickling and rolling mill: 1) The hydrochloric acid temperature in tanks 1-4 should be controlled at 65-75℃, and the operating speed of the process section should be controlled at 60-130m / min; 2) Before producing special steel grades, the pickling unit should replace 60-80m³ of acid with fresh acid 4 hours in advance to ensure that the HCl content of the acid solution in tank 1 is ≥50g / L and the iron ion content is ≤100g / L, and to prevent under-pickling; 3) The outlet temperature of the filter in tank 1 should be 60℃-80℃, and the conductivity of the rinsing water in tank 2 should be ≤100us / cm. The rinsing water replenishment valve should be... The opening degree is increased by 25% to 40% compared to ordinary steel grades. All squeeze roll surfaces and operating conditions must be intact. The roll surface is not allowed to have serious wear, adhesion, scratches, peeling, or heat damage defects. There must be no stalling during operation. 4) Wedge crown of hot-rolled coil raw material: wedge < crown ≤ 40μm; 5) In addition to conventional parameter control, the main control of the rolling mill unit is the residual emulsion on the strip surface, while making full preparations for the bell-type furnace unit annealing. The emulsion indicators of the rolling mill are implemented one shift before production. Emulsion A system: concentration target 1.8% to 2.2%, saponification value 140-160 mg / g, impurity oil content ≤ 20%, iron powder content ≤ 200ppm, emulsion temperature requirement: 50 to 60℃, pH value requirement: 6.0 to 6.5, conductivity < 300us / cm; Emulsion B system: emulsion concentration target 1% to 1.5%, saponification value 140 to 160 mgKOH / g, impurity oil content ≤15%, iron powder content ≤120ppm; 6) Iron powder testing method, improve the magnetic rod filter guide channel. When testing the iron powder content, the crucible containing iron powder must be placed in a muffle furnace at a temperature of 770℃ for heating for at least 1 hour to ensure accurate measurement of iron powder content; optimize the emulsion magnetic rod filter guide channel, add a screw conveyor in the guide channel to prevent iron soap from falling back into the emulsion system; perform regular bottom discharge treatment of emulsion B system according to iron powder content, the bottom discharge point is the magnetic rod filter of the clean liquid tank; open and clean the clean liquid tank and return tank of the emulsion system once a year; 7) Ensure the last stand of the rolling mill is clean before production. The purging device is functioning normally; no emulsion residue is allowed on the strip surface; the mill exit purging pressure is >0.6MPa; nozzles must not be missing or clogged; condensate from the mill exit arch must not drip onto the strip surface; 8) Coiling tension is 26.0~29.5Mpa; 9) Strip shape is controlled according to micro-double-sided wave control, and medium waves are strictly prohibited. The standard control curve A2 control coefficient of the strip shape meter is set to +4, which is suitable for widths from 930 to 1250 mm; 10) Each time the support roll is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not clogged and the nozzle angle meets the process requirements; 11) Optimize the coil diameter for widths of 927-1000 mm and thicknesses less than 0.For 45mm SPCC-M steel coils, the coil diameter should be controlled below 1750mm; 12) Strictly control the surface roughness of the strip; 13) Control the deformation of the No. 5 rolling mill to about 13%-15%, and maintain the surface roughness at 3±5%μm when the new work rolls are ready. At the same time, optimize the roll changing process to ensure that the surface roughness of the strip is controlled between 0.6μm and 1.9μm.

[0017] H. Process control design of bell-type annealing furnace: The bell-type furnace annealing process uses full hydrogen annealing. The temperature of the steel coil exiting the furnace must not exceed 100℃. Hydrogen has reducing properties and can reduce the oxides in the steel coil during heating. During annealing, because the temperature is still very high, hydrogen can reduce some oxidized metals. Based on this principle, a complete set of process control points for drum steel in bell-type annealing furnaces is formulated: 1) Reduce steel coil overflow defects and optimize stacking methods. For steel coils with a thickness of less than 0.45 mm, overflow defects are not allowed when loading them into the furnace. However, when overflow defects occur, they should be handled according to the actual overflow condition of the steel coil; 2) For defective coils with overflow edges greater than 10 mm, they should be leveled and repaired before being loaded into the furnace for annealing; 3) For minor overflow defects, thin convection plates should be used for stacking to increase the contact area between the convection plates and the strip steel and reduce the unit extrusion pressure of the steel coil; Through experiments, it was found that after loading the furnace with thin convection plates for minor overflow defects, the edge adhesion was significantly reduced; 4) For defective coils with overflow edges exceeding 10 mm on one side, the steel coils can be placed on the top layer with the overflow edge facing upwards. 5) Clean the furnace platform of accumulated ash and carbon black before production until there is no ash accumulation; 6) Control the hydrogen blowing rate in the second and third stages at 20-25 m³ / h to ensure that the residual emulsion is fully volatilized; 7) Use a double platform for annealing, and add a 430℃ holding platform for 2-3 hours; For thickness ≤0.6, furnace load <45 tons, control temperature 710℃, heating time 7h, holding time ≥8h, waiting time for cover 7h, furnace discharge temperature 70℃; For thickness ≤0.6, furnace load 45-55 tons, control temperature 710℃, heating time 8h... h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 80℃; thickness ≤0.6, furnace loading 55~75 tons, controlled temperature 710℃, heating time 9h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 95℃; thickness ≤0.6, furnace loading >75 tons, controlled temperature 710℃, heating time 10h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 100℃; 8) Extend the cooling time with heating cover to 7h, and reduce the material chamber temperature to below 610℃ when removing the heating cover;

[0018] I. Process control design of the leveling unit: 1) During the production of the leveling unit, add 6 thin iron sheets with a thickness of 1-2 mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively; 2) Increase the uncoiling tension by 2~5KN; 3) If a slight sticking texture defect appears, use a rolling force of 1000kN for leveling and level it again using the rolling force mode. Before leveling, add 6 thin iron sheets with a thickness of 1-2 mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively to prevent secondary scratch defects.

[0019] When produced using the method of this invention, the degradation rate of SPCC-M steel with a thickness of 0.30~0.60mm after annealing and leveling process due to adhesion defects reaches less than 1.0%. This invention is applicable to bell-type furnace production of SPCC-M steel with a thickness of 0.30~0.60mm, has a wide range of applications, is suitable for the raw material supply of high-grade door panel steel, and has great potential for widespread promotion. Implementation

[0020] A production process for cold-rolled thin-gauge SPCC-M steel grade.

[0021] A. First, the steel composition is designed as follows: Steel marking AP1451C1, C content 0.03-0.06%, Si content ≤0.04%, Mn content 0.15-0.22%, P content ≤0.015%, S content ≤0.012%, Al content 0.03-0.05%, residual elements [Cr] ≤0.1%, [Ni] ≤0.1%, [Cu] ≤0.15%, [N] ≤0.0060%;

[0022] B. Requirements for steelmaking raw materials: 1) Requirements for molten iron: Depending on the molten iron conditions and production needs, molten iron can be desulfurized and pretreated. The molten iron directly fed into the furnace has a [S] content of ≤0.01%. Requirements for molten iron before desulfurization: Si content ≤1.2%, P content ≤0.18%, S content ≤0.06%, and temperature ≥1250℃; 2) The converter ladle and argon blowing conditions should be good. There should be no large amount of cold steel or slag on the bottom and wall of the ladle.

[0023] C. Converter process control: 1) Endpoint composition control: [C] ≤ 0.04%, [P] ≤ 0.012%, [S] ≤ 0.012%; 2) Tapping requirements: Add deoxidizer according to carbon content, maintain the tapping spout, tapping time ≥ 3.5 minutes, slag blocking during tapping, control the thickness of the slag layer in the ladle, and require that the phosphorus return during tapping is not greater than 0.003%;

[0024] D. Refining requirements: 1) Direct process: soft blowing argon stirring to remove inclusions and fine-tune composition; 2) LF treatment: temperature increase, composition adjustment, desulfurization, degassing, and inclusion removal.

[0025] E. Slab continuous casting control and inspection requirements: 1) Continuous casting adopts argon protection throughout the process, and uses carbon-free protective slag and carbon-free ladle covering agent; baffles are installed in the tundish; the superheat of the tundish in the first continuous casting is ≤45℃, the superheat of the tundish in the next continuous casting is ≤35℃, and the maximum casting speed is ≤1.6m / min; 2) The liquidus temperature of the tap mark AP1451C1 is 1530℃; 3) Slabs that pass the hot inspection can be hot-charged and hot-delivered.

[0026] F. Key points for conventional hot rolling process control: heating time greater than 160 minutes, temperature difference between the head and tail of the slab less than 20℃, descaling at the three entry points of the roughing mill; final rolling temperature 870±20℃, rapid cooling mode in the later stage, and coiling temperature 600±20℃.

[0027] G. Process control design for cold rolling pickling and rolling mill: 1) The hydrochloric acid temperature in tanks 1-4 should be controlled at 65-75℃, and the operating speed of the process section should be controlled at 60-130m / min; 2) Before producing special steel grades, the pickling unit should replace 60-80m³ of acid with fresh acid 4 hours in advance to ensure that the HCl content of the acid solution in tank 1 is ≥50g / L and the iron ion content is ≤100g / L, and to prevent under-pickling; 3) The outlet temperature of the filter in tank 1 should be 60℃-80℃, and the conductivity of the rinsing water in tank 2 should be ≤100us / cm. The rinsing water replenishment valve should be... The opening degree is increased by 25% to 40% compared to ordinary steel grades. All squeeze roll surfaces and operating conditions must be intact. The roll surface is not allowed to have serious wear, adhesion, scratches, peeling, or heat damage defects. There must be no stalling during operation. 4) Wedge crown of hot-rolled coil raw material: wedge < crown ≤ 40μm; 5) In addition to conventional parameter control, the main control of the rolling mill unit is the residual emulsion on the strip surface, while making full preparations for the bell-type furnace unit annealing. The emulsion indicators of the rolling mill are implemented one shift before production. Emulsion A system: concentration target 1.8% to 2.2%, saponification value 140-160 mg / g, impurity oil content ≤ 20%, iron powder content ≤ 200ppm, emulsion temperature requirement: 50 to 60℃, pH value requirement: 6.0 to 6.5, conductivity < 300us / cm; Emulsion B system: emulsion concentration target 1% to 1.5%, saponification value 140 to 160 mgKOH / g, impurity oil content ≤15%, iron powder content ≤120ppm; 6) Iron powder testing method, improve the magnetic rod filter guide channel. When testing the iron powder content, the crucible containing iron powder must be placed in a muffle furnace at a temperature of 770℃ for heating for at least 1 hour to ensure accurate measurement of iron powder content; optimize the emulsion magnetic rod filter guide channel, add a screw conveyor in the guide channel to prevent iron soap from falling back into the emulsion system; perform regular bottom discharge treatment of emulsion B system according to iron powder content, the bottom discharge point is the magnetic rod filter of the clean liquid tank; open and clean the clean liquid tank and return tank of the emulsion system once a year; 7) Ensure the last stand of the rolling mill is clean before production. The purging device is functioning normally; no emulsion residue is allowed on the strip surface; the mill exit purging pressure is >0.6MPa; nozzles must not be missing or clogged; condensate from the mill exit arch must not drip onto the strip surface; 8) Coiling tension is 26.0~29.5Mpa; 9) Strip shape is controlled according to micro-double-sided wave control, and medium waves are strictly prohibited. The standard control curve A2 control coefficient of the strip shape meter is set to +4, which is suitable for widths from 930 to 1250 mm; 10) Each time the support roll is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not clogged and the nozzle angle meets the process requirements; 11) Optimize the coil diameter for widths of 927-1000 mm and thicknesses less than 0.For 45mm SPCC-M steel coils, the coil diameter should be controlled below 1750mm; 12) Strictly control the surface roughness of the strip; 13) Control the deformation of the No. 5 rolling mill to about 13%-15%, and maintain the surface roughness at 3±5%μm when the new work rolls are ready. At the same time, optimize the roll changing process to ensure that the surface roughness of the strip is controlled between 0.6μm and 1.9μm.

[0028] H. Process control design of bell-type annealing furnace: The bell-type furnace annealing process uses full hydrogen annealing. The temperature of the steel coil exiting the furnace must not exceed 100℃. Hydrogen has reducing properties and can reduce the oxides in the steel coil during heating. During annealing, because the temperature is still very high, hydrogen can reduce some oxidized metals. Based on this principle, a complete set of process control points for drum steel in bell-type annealing furnaces is formulated: 1) Reduce steel coil overflow defects and optimize stacking methods. For steel coils with a thickness of less than 0.45 mm, overflow defects are not allowed when loading them into the furnace. However, when overflow defects occur, they should be handled according to the actual overflow condition of the steel coil; 2) For defective coils with overflow edges greater than 10 mm, they should be leveled and repaired before being loaded into the furnace for annealing; 3) For minor overflow defects, thin convection plates should be used for stacking to increase the contact area between the convection plates and the strip steel and reduce the unit extrusion pressure of the steel coil; Through experiments, it was found that after loading the furnace with thin convection plates for minor overflow defects, the edge adhesion was significantly reduced; 4) For defective coils with overflow edges exceeding 10 mm on one side, the steel coils can be placed on the top layer with the overflow edge facing upwards. 5) Clean the furnace platform of accumulated ash and carbon black before production until there is no ash accumulation; 6) Control the hydrogen blowing rate in the second and third stages at 20-25 m³ / h to ensure that the residual emulsion is fully volatilized; 7) Use a double platform for annealing, and add a 430℃ holding platform for 2-3 hours; For thickness ≤0.6, furnace load <45 tons, control temperature 710℃, heating time 7h, holding time ≥8h, waiting time for cover 7h, furnace discharge temperature 70℃; For thickness ≤0.6, furnace load 45-55 tons, control temperature 710℃, heating time 8h... h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 80℃; thickness ≤0.6, furnace loading 55~75 tons, controlled temperature 710℃, heating time 9h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 95℃; thickness ≤0.6, furnace loading >75 tons, controlled temperature 710℃, heating time 10h, heat preservation time ≥9h, waiting time for cover 7h, furnace exit temperature 100℃; 8) Extend the cooling time with heating cover to 7h, and reduce the material chamber temperature to below 610℃ when removing the heating cover;

[0029] I. Process control design of the leveling unit: 1) During the production of the leveling unit, add 6 thin iron sheets with a thickness of 1-2 mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively; 2) Increase the uncoiling tension by 2~5KN; 3) If a slight sticking texture defect appears, use a rolling force of 1000kN for leveling and level it again using the rolling force mode. Before leveling, add 6 thin iron sheets with a thickness of 1-2 mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively to prevent secondary scratch defects. Example

[0030] 1. Ensure the plate is flat, prevent abnormal wear of the rolls, and reduce rib defects.

[0031] 1.1 Use the roll change time to check for emulsion nozzle blockage, measure and adjust the nozzle angle monthly, and ensure uniform roll cooling.

[0032] 1.2 When judging hot-rolled coils, the shape control chart must be consulted. The wedge shape < crown ≤ 40μm. If the pickling unit finds obvious rib defects with annular bulges on the steel coils when accepting raw materials, the specifications must be modified.

[0033] 1.3 If a defect of rib formation is found in the rolling mill unit, an emergency response should be taken in time, that is, the bell furnace should be notified to place the steel coil on the top layer, and the cooling time with the heating hood should be increased by 1 to 2 hours.

[0034] 1.4 The slab shape should be controlled according to the micro-double-sided wave control, and the presence of medium waves is strictly prohibited. The standard control curve A2 control coefficient of the slab shape instrument is set to +4 (suitable for widths from 930 to 1250 mm).

[0035] 2. Optimize the iron powder testing method for emulsion in the 1420 pickling and rolling mill unit and improve the guide groove of the magnetic rod filter. The iron powder content in emulsion A system is ≤200ppm and the iron powder content is ≤120ppm.

[0036] 2.1 When testing the iron powder content, the crucible containing the iron powder must be placed in a muffle furnace at a temperature of 770℃ and heated for at least 1 hour to ensure accurate measurement of the iron powder content.

[0037] 2.2 The emulsion magnetic rod filter guide channel was optimized by adding a screw conveyor to the guide channel to prevent iron soap from falling back into the emulsion system;

[0038] 2.3 When the iron powder content is close to 120 ppm, the emulsion from system B is reversed to system A, with a reversal rate of 40 m³ per shift. 3 Simultaneously, the solution is prepared again. For emulsion B system with an iron powder content >120ppm, the solution is periodically allowed to stand for 4 hours before bottom discharge treatment, with the bottom discharge location being the magnetic rod filter in the clean liquid tank;

[0039] 2.4 The clean liquid tank and return tank of the emulsion system shall be opened and cleaned twice a year to prevent the accumulation of sludge at the bottom of the tank.

[0040] 2.5 A residual iron content test must be performed daily on the steel strip surface, and the residual iron content must be <120 mg / Ms.

[0041] 3. Optimize the coiling tension of the rolling mill in the 1420 pickling and rolling zone.

[0042] A tension roller is added in front of the winding machine's guide roller, and edge tension variable tension winding is performed, that is, the winding tension decreases continuously from the core to the outer ring, and the winding tension is controlled to 26.0~29.5 MPa.

[0043] 4. Control of steel coil diameter

[0044] For SPCC-M steel coils with a width of 927-1000 mm and a thickness of less than 0.45 mm, the coil diameter should be controlled below 1750 mm to reduce the temperature difference ΔT.

[0045] 5. Strictly control the surface roughness of the board.

[0046] The deformation of the No. 5 rolling mill was controlled at around 8% to 10%, and the roll changing process was optimized to ensure that the surface roughness of the strip was controlled at 0.6 to 1.0 μm.

[0047] 6. Process control of bell-type furnace

[0048] 1.1 For steel coils with a thickness of less than 0.5 mm, overflow edge defects are not allowed when loading them into the furnace. However, if overflow edge defects occur, they shall be handled according to the actual overflow edge condition of the steel coil. In severe cases, the coil shall be flattened, re-coiled, and then loaded into the furnace for annealing.

[0049] 1.2 For minor overflow edge defects, thin convection plates should be stacked to increase the contact area between the convection plates and the strip steel and reduce the extrusion pressure on the steel coil. Through experiments, it was found that after using thin convection plates to load the furnace for minor overflow edge defects, edge adhesion was significantly reduced.

[0050] 1.2 For single-sided overflow defects, the steel coil can be placed on the top layer with the overflow side facing upwards.

[0051] 1.3 Before production, clean the furnace platform of accumulated ash (carbon black) until there is no ash left;

[0052] 1.4 The hydrogen blowing rate in the second and third stages should be controlled at 20-25 m³ / h to ensure that the residual emulsion is fully volatilized;

[0053] 1.5 Annealing is performed using a dual-platform system, with an additional 430℃ heat preservation platform for 2-3 hours.

[0054] Thickness ≤ 0.6, furnace loading < 45 tons, controlled temperature 710℃, heating time 7h, holding time ≥ 8h, waiting time for cover 7h, furnace exit temperature 70℃;

[0055] Thickness ≤ 0.6, furnace loading 45~55 tons, controlled temperature 710℃, heating time 8h, holding time ≥ 9h, waiting time for cover 7h, furnace exit temperature 80℃;

[0056] Thickness ≤ 0.6, furnace loading 55~75 tons, controlled temperature 710℃, heating time 9h, holding time ≥ 9h, waiting time for cover 7h, furnace exit temperature 95℃;

[0057] Thickness ≤ 0.6, furnace loading > 75 tons, controlled temperature 710℃, heating time 10h, holding time ≥ 9h, waiting time for cover 7h, furnace exit temperature 100℃;

[0058] 1.6 Appropriately reduce the annealing cooling rate

[0059] The cooling time with the heating cover is extended to 7 hours, and the temperature of the material chamber is reduced to below 610℃ when the heating cover is removed.

[0060] 7. Optimize leveling mode

[0061] 7.1 During the production of the leveling unit, add 6 thin iron sheets with a thickness of 1-2 mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively;

[0062] 7.2 Increase the unwinding tension by 2~5KN;

[0063] 7.3 If a slight adhesive texture defect appears, use a rolling force of 1000kN to level the coil and level it again using the rolling force mode. Before leveling, add 6 thin iron sheets with a thickness of 1~2mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively to prevent secondary scratch defects.

Claims

1. A production process for cold-rolled thin-gauge SPCC-M steel, characterized in that, The aforementioned production process is applicable to SPCC-M steel with a thickness of 0.30~0.60mm and includes the following steps: A. First, the steel composition is designed as follows: Steel marking AP1451C1, C content 0.03~0.06%, Si content ≤0.04%, Mn content 0.15~0.22%, P content ≤0.015%, S content ≤0.012%, Al content 0.03~0.05%, residual elements [Cr] ≤0.1%, [Ni] ≤0.1%, [Cu] ≤0.15%, [N] ≤0.0060%; B. Requirements for steelmaking raw materials: 1) Requirements for molten iron: Depending on the molten iron conditions and production needs, molten iron can be desulfurized and pretreated. The molten iron directly fed into the furnace has a [S] content of ≤0.01%. Requirements for molten iron before desulfurization: Si content ≤1.2%, P content ≤0.18%, S content ≤0.06%, and temperature ≥1250℃; 2) The converter ladle and argon blowing conditions should be good. There should be no large amount of cold steel or slag on the bottom and wall of the ladle. C. Converter process control: 1) Endpoint composition control: [C] ≤ 0.04%, [P] ≤ 0.012%, [S] ≤ 0.012%; 2) Tapping requirements: Add deoxidizer according to carbon content, maintain the tapping spout, tapping time ≥ 3.5 minutes, slag blocking during tapping, control the thickness of the slag layer in the ladle, and require that the phosphorus return during tapping is not greater than 0.003%; D. Refining requirements: 1) Direct process: soft blowing argon stirring to remove inclusions and fine-tune composition; 2) LF treatment: temperature increase, composition adjustment, desulfurization, degassing, and inclusion removal. E. Slab continuous casting control and inspection requirements: 1) Continuous casting adopts argon protection throughout the process, and uses carbon-free protective slag and carbon-free ladle covering agent; baffles are installed in the tundish; the superheat of the tundish in the first continuous casting is ≤45℃, the superheat of the tundish in the next continuous casting is ≤35℃, and the maximum casting speed is ≤1.6m / min; 2) The liquidus temperature of the tap mark AP1451C1 is 1530℃; 3) Slabs that pass the hot inspection can be hot-charged and hot-delivered. F. Key points for conventional hot rolling process control: heating time greater than 160 minutes, temperature difference between the head and tail of the slab less than 20℃, descaling at the three entry points of the roughing mill; final rolling temperature 870±20℃, rapid cooling mode in the later stage, coiling temperature 600±20℃; wedge shape of hot-rolled coil raw material < convexity ≤ 40μm; G. Process control design for cold rolling pickling and rolling mill: 1) The hydrochloric acid temperature in tanks 1-4 should be controlled at 65-75℃, and the operating speed of the process section should be controlled at 60-130 m / min; 2) Before producing special steel grades, the pickling unit should replace 60-80 m³ of acid with fresh acid 4 hours in advance to ensure that the HCl content of the acid solution in tank 1 is ≥50g / L and the iron ion content is ≤100g / L. g / L, to prevent under-pickled conditions; 3) The outlet temperature of the filter in the No. 1 rinsing tank is 60℃~80℃, the conductivity of the rinsing water in the No. 2 rinsing tank is ≤100us / cm, the opening of the rinsing water replenishment valve is increased by 25%~40% compared with ordinary steel grades, all extrusion rolls must be in good condition, and the roll surface must not have serious wear, adhesion, scratches, peeling, or heat damage defects, and there must be no blockage during operation; 4) In addition to the conventional parameter control, the main control of the rolling mill unit is the residual emulsion on the strip surface, and at the same time, it is necessary to make full preparations for the annealing of the bell furnace unit; the emulsion indicators of the rolling mill are implemented one shift before production, emulsion A system: concentration target 1.8%~2.2%, saponification value 140~160mgKOH / g, impurity oil content ≤20%, iron powder content ≤200 ppm; emulsion temperature requirement: 50~60℃; pH value requirement: 6.0~6.5; conductivity <300 us / cm; Emulsion B system: emulsion concentration target 1%~1.5%; saponification value 140~160mgKOH / g; impurity oil content ≤15%; iron powder content ≤120 ppm; 5) Iron powder testing method, improve the magnetic rod filter guide channel. When testing iron powder content, the crucible containing iron powder must be placed in a muffle furnace at 770℃ for heating for at least 1 hour to ensure accurate iron powder content measurement; optimize the emulsion magnetic rod filter guide channel by adding a screw conveyor to the guide channel to prevent iron soap from falling back into the emulsion system; perform regular bottom discharge treatment of emulsion B system according to iron powder content, with the bottom discharge point being the magnetic rod filter of the clean liquid tank; open and clean the clean liquid tank and return tank of the emulsion system once a year; 6) Ensure the last stand mill blowing device is normal before production, with Emulsion residue is not allowed on the steel surface; the mill exit purging pressure is >0.6MPa; nozzles must not be missing or clogged; condensate from the mill exit stand must not drip onto the strip surface; 7) Coiling tensile stress is 26.0~29.5MPa; 8) Strip shape is controlled according to micro-double-sided wave control, and medium waves are strictly prohibited. The standard control curve A2 control coefficient of the strip shape meter is set to +4, which is suitable for widths from 930 to 1250mm; 9) Each time the support roll is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not clogged and the nozzle angle meets the process requirements; 10) Optimize the coil diameter for widths of 927~1000 mm and thicknesses less than 0.For 45 mm SPCC-M steel coils, the coil diameter should be controlled below 1750 mm; 11) Strictly control the surface roughness of the strip, keeping the deformation of the No. 5 rolling mill within 13%~15%, and maintaining the roughness at 3±5% μm when the new work rolls are ready. At the same time, optimize the roll changing process to ensure that the surface roughness of the strip is controlled within 0.6 μm~1.9 μm. H. Process control design of bell-type annealing furnace: The bell-type furnace annealing process uses full hydrogen annealing. The temperature of the steel coil exiting the furnace must not exceed 100℃. The following key points should be controlled: 1) Reduce steel coil overflow defects and optimize stacking methods. For steel coils with a thickness of less than 0.45mm, overflow defects are not allowed when loading the furnace. However, if overflow defects occur, they should be handled according to the actual overflow condition of the steel coil; 2) For coils with overflow defects greater than 10mm, they should be leveled and repaired before being loaded into the furnace for annealing; 3) For minor overflow defects, thin convection plates should be used for stacking to increase the contact area between the convection plates and the strip steel and reduce the unit extrusion pressure of the steel coil. Through experiments, it was found that after using thin convection plates to load minor overflow defects, edge adhesion was significantly reduced; 4) For single-sided overflow defects exceeding 10mm... For defective coils of mm, the steel coil can be placed on the top layer with the overflow edge facing upwards; 5) Clean the furnace platform of accumulated ash and carbon black until there is no ash accumulation before production; 6) Control the hydrogen blowing rate of the second and third stages at 20~25m³ / h to ensure that the residual emulsion is fully volatilized; 7) Use a double platform for annealing, and add a 430℃ holding platform for 2~3 hours; Thickness ≤0.6 mm, furnace load <45 tons, control temperature 710℃, heating time 7h, holding time ≥8h, waiting time for cover 7h, furnace exit temperature 70℃; Thickness ≤0.6 mm, furnace load 45~55 tons, control temperature 710℃, heating time 8h, holding time ≥9h, waiting time for cover 7h, furnace exit temperature 80℃; Thickness ≤0.6 mm, furnace load 55~75 tons, control temperature 710℃, heating time 9h, holding time ≥9h, waiting time for cover 7h, furnace exit temperature 95℃; Thickness ≤0.6 mm, furnace loading > 75 tons, controlled temperature 710℃, heating time 10h, holding time ≥ 9h, waiting time for cover 7h, furnace exit temperature 100℃; 8) Extend the cooling time with heating cover to 7h, and reduce the material chamber temperature to below 610℃ when removing heating cover. I. Process control design of the leveling unit: 1) During the production of the leveling unit, add 6 thin iron sheets with a thickness of 1~2mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively; 2) Increase the uncoiling tension by 2~5 kN; 3) If a slight sticking texture defect appears, use a rolling force of 1000 kN for leveling and level it again using the rolling force mode. Before leveling, add 6 thin iron sheets with a thickness of 1~2mm to the core of the steel coil, 3 on the operating side and 3 on the transmission side, and place them at 0°, 120° and 240° respectively to prevent secondary scratch defects.