A manufacturing process for DC04 steel for high surface area deep drawing

Abstract

This invention discloses a production process for DC04 steel grade used in high-surface-area deep drawing. This method effectively eliminates surface defects such as adhesion marks and grayish-white oxide discoloration at the edges of steel coils, and is applicable to the production of DC04 steel grade for high-surface-area deep drawing. Using this method, DC04 steel grade has been successfully trial-produced, completely eliminating surface oxide discoloration defects at the edges and adhesion marks in the center. Its performance meets delivery requirements, and customers have expressed positive feedback. This invention is applicable to bell-type furnace production of DC04 steel grade, has a wide range of applications, and is suitable for raw material supply in the automotive deep-drawing sheet industry, possessing significant potential for widespread adoption.

Description

Technical Field

[0001] This invention relates to a production process for DC04 steel for high surface area deep drawing. Background Technology

[0002] The cold rolling area of ​​Baosteel uses an EBNER high-convection all-hydrogen protective gas single-stack bell-type furnace to directly recrystallize and brighten cold-rolled coils. No degreasing treatment is performed before annealing. After annealing, the grade of DC04 steel is downgraded by 50% due to adhesion defects during the leveling process. The grayish-white oxide color defect on the edges of annealed DC04 steel cannot be completely eliminated. The performance of DC04 steel coils is unstable at both ends; the required pressure is 130-175 MPa, but the actual pressure is 180-195 MPa. DC04 steel coils experience stamping cracking during use. Controlling the amount of surface anti-rust oil applied is one of the contributing factors. Ensuring the correct amount of oil applied for stamping while avoiding environmental contamination with anti-rust oil is a key control point in the production of this steel grade.

[0003] Literature review: The article "Analysis of Optimization and Control of Production Process of DC04 Cold-Rolled Strip Steel" by Tian Shizhang mainly analyzes the pickling, cold rolling, annealing, and leveling processes. During cold rolling, the strip reduction rate is controlled at 55%–90%. In the annealing process, the grain size of deep-drawing steel is generally controlled at level 6–8, but the annealing temperature differs from this process. The elongation rate of DC04 during leveling is controlled at (0.7±0.1)%, which is significantly different from this process. However, it does not elaborate on the key control points of the recoiling unit. The article "Trial Production of DC04 Cold-Rolled Deep-Drawing Steel" by Hu Honglin and Ma Xiaojuan discusses the hot rolling and cold rolling processes, but does not discuss the relevant rolling parameters. During production, grayish-white oxide defects appear on the edges, and after the leveling process, the grade is reduced by 50% due to adhesion defects. The performance of the steel coil head and tail is unstable, requiring 130-175 MPa, but actually reaching 180-195 MPa. The paper "Practice to Reduce Adhesion Defects in Cold-Rolled Coils" by Zhao Aiwei mainly analyzes the effects of coiling tension, surface roughness, post-rolled strip straightness, strip convexity, and post-rolling cooling on adhesion, without quantitative research. The paper "Control of Surface Oxidation Defects in Cold-Rolled Phosphorus-Containing IF High-Strength Steel Strip" by Luo Xiaoyang, Wang Jin, Zhao Xiaolong, and Zhang Liang discusses the annealing atmosphere and the need to add higher levels of Mn alloying elements to the steel, which falls under the category of routine production. Mn alloying elements are essential for steel coils, but the paper does not elaborate on key control parameters. The paper "Exploration of the Causes and Prevention Measures of Oxidation Color in Bell-Type Annealed Steel Coils" by Li Xiaoxiao analyzes the equipment and process of bell-type annealing furnaces and the incoming materials, which falls under the category of routine oxidation color control. However, the feasibility of control measures for the grayish-white oxidation color defect on the edges of deep-drawing DC04 steel is insufficient. Among the aforementioned influencing factors, the main influencing 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, but the relevant technical indicators are unclear. Summary of the Invention

[0004] To further prevent edge-colored oxide stains and center adhesion defects in steel coils, while ensuring the straightness, dimensional accuracy, and mechanical properties of the strip, this invention discloses a production process for DC04 steel for high-surface-area deep drawing.

[0005] The technical solution adopted in this invention is a production process for DC04 steel for high surface area deep drawing, which is implemented according to the following steps:

[0006] First, the steel composition is designed as follows: For steel tapping mark DP0131D1, C content ≤ 0.002%; Si content ≤ 0.035%; Mn content 0.08~0.22%; P content ≤ 0.018%; S content ≤ 0.01%; Al content 0.03-0.05%; residual elements [Cr] ≤ 0.1%, [Ni] ≤ 0.1%, [Cu] ≤ 0.15%;

[0007] II. Requirements for steelmaking raw materials:

[0008] (1) Requirements for molten iron: Depending on the conditions of the molten iron and the production needs, the molten iron can be desulfurized and pretreated. The molten iron directly fed into the furnace has a [S] ≤ 0.01%. The requirements for molten iron before desulfurization are: Si content ≤ 0.08%, P content ≤ 0.14%, S content ≤ 0.04%, and temperature ≥ 1280℃. The triggering condition for molten iron pretreatment is: when the molten iron before desulfurization has [S] > 0.01%, desulfurization pretreatment must be carried out; if the molten iron before desulfurization has [S] ≤ 0.01%, it can be directly fed into the furnace.

[0009] (2) Alloy selection: low-carbon ferromanganese, metallic manganese, sintered manganese balls, ferrotitanium, ferroaluminum, ferroboron;

[0010] (3) The converter ladle and argon blowing conditions are good, and there must be no cold steel or slag on the bottom or wall of the ladle;

[0011] Converter process control:

[0012] (1) Endpoint component control: [C] ≤ 0.04%, [P] ≤ 0.012%, [S] ≤ 0.008%;

[0013] (2) Tapping requirements: Before tapping, the oxygen level in the furnace should be set. Deoxidizer should be added according to the oxygen level. The tapping port should be well maintained. The tapping time should be ≥3.5 minutes. Slag should be blocked by the sliding plate during tapping. The thickness of the slag layer in the ladle should be controlled. The phosphorus return of the converter tapping should not be greater than 0.003%.

[0014] III. Refining Requirements:

[0015] (1) Steel ladle material requirements: Carbon-free steel ladles are required;

[0016] (2) LF treatment: heating and reduction and upgrading of ladle top slag;

[0017] (3) RH: decarbonization, deoxidation, composition, and temperature adjustment;

[0018] Before DC04 steelmaking production, the vacuum level of the RH refining equipment must be confirmed. The RH vacuum level should not exceed 180Pa, and the processing time should not be less than 18 minutes. Before production, the RH tank should be washed with low-carbon aluminum killed steel. To avoid steel contamination, residual steel must not be left in the tank. The pure degassing time for this treatment should be at least 8 minutes. Aluminum ferroalloys are added during the RH furnace, while titanium ferroalloys and boron ferroalloys are added at the end of the treatment.

[0019] IV. Slab continuous casting control and inspection requirements:

[0020] 1) Continuous casting employs argon protection throughout the process, using carbon-free protective slag and carbon-free ladle covering agent; the superheat of the tundish in the first continuous casting furnace is ≤45℃, and the superheat of the tundish in the continuous casting furnace is ≤35℃. Constant casting speed protection is required, with a maximum casting speed of 1.6m / min; the dryness requirements for protective slag and covering agent are that H2O is not greater than 0.5%; the requirements for argon-sealed protection casting are: argon flow rate of 250~300L / min in the tundish, 250~300L / min in the long nozzle, 3~5L / min in the stopper rod, 3~5L / min in the tundish top nozzle, and 10~12L / min between plates;

[0021] 2) The liquidus temperature of tap mark DP0131D1 is 1535℃; the liquidus temperature of tap mark DP0531D1 is 1535℃;

[0022] 3) The slab should not be hot-sent. After chamfering, it should be cold-inspected and released. The size of the chamfered corner should be 30×50mm, or a chamfering crystallizer should be used for production.

[0023] V. Key points for conventional process control in hot rolling:

[0024] (1) Temperature regime, steel grade DC04, heating thickness layer 1.2-6mm, rough rolling thickness layer mm and corresponding rough rolling temperature °C are: 1.2-2.2, 1070±30; 2.201-2.999, 1050±30; 3-3.999, 1040±30; 4-6, 1030±30; finishing rolling thickness layer 1.2-6mm, finishing rolling temperature 920±20℃, coiling thickness layer 1.2-6mm, coiling temperature 670±20℃;

[0025] (2) Heating time: The heating time is greater than 160 minutes, the temperature difference between the head and tail of the slab is less than 20℃, and descaling is carried out at the three inlets of rough rolling 1, 3 and 5;

[0026] (3) Heating temperature control: In order to ensure the requirements of head and tail performance, microstructure and low yield strength ratio, the temperature and cooling mode are strictly controlled according to the production and sales system requirements. Hot rolling: DC04 requires a heating temperature of 1170±30℃ to the lower limit and a final rolling temperature of 920±20℃ to the upper limit.

[0027] (4) Hot rolling plan preparation: Steel coils must be prepared after 21 coils in each plan, with 6 transition coils. The transition coils shall use Q215, SPHC or steel grades with low requirements, and the temperature jump shall not exceed 20℃;

[0028] (5) Convexity requirement: wedge shape ≤ convexity ≤ 50μm;

[0029] VI. Process control design for cold rolling pickling and rolling mill:

[0030] (1) The hydrochloric acid temperature in tanks 1-4 is controlled at 65-75℃, and the running speed of the process section is controlled at 60-130m / min;

[0031] (2) Before producing special steel grades, the pickling unit should replace the acid with 60-80 ml of fresh acid 4 hours in advance. 3 Ensure that the HCl content of the acid solution in acid tank #1 is ≥50g / L and the iron ion content is ≤100g / L, and prevent the occurrence of under-acid washing.

[0032] (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, all the surface and operating condition of the squeeze rollers must be intact, and the roller surface is not allowed to have serious wear, adhesion, scratches, peeling, or heat damage defects, and there must be no blockage during operation;

[0033] (4) The reduction rate of DC04 is controlled at 78-82%;

[0034] (5) In addition to conventional parameter control, the main control of the rolling mill unit is to control the residual emulsion on the surface of the strip steel, and at the same time make full preparations for the annealing of the bell furnace unit.

[0035] The previous shift before production ensured that all parameters of the rolling mill's emulsion were met. Emulsion A system: concentration target 2%, saponification value 140-160 mg / g, impurity oil content ≤20%, iron powder content ≤200 ppm, emulsion temperature requirement: 50~60℃, pH value requirement:

[0036] 6.0~6.5, conductivity <300us / cm; Emulsion B system: emulsion concentration target 1.2%, saponification value 140~160mg(KOH) / g, impurity oil content ≤15%, iron powder content ≤120ppm;

[0037] (6) Before production, ensure that the last stand of the rolling mill is in good working order, that there is no emulsion residue on the surface of the strip, and that the rolling mill outlet purging pressure is >0.6MPA; that the nozzles are not missing or blocked, and that the condensate from the rolling mill outlet stand is not allowed to drip onto the surface of the strip.

[0038] (7) Coiling tensile stress: 26.0–29.5 MPa;

[0039] (8) The slab shape shall be controlled according to the micro-double-sided wave control, and the presence of medium waves shall be strictly prohibited. The standard control curve A2 of the slab shape instrument shall be set to +4, and the width shall be suitable for all widths from 930 to 1250 mm.

[0040] (9) Each time the support roller is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not blocked and the nozzle angle meets the process requirements.

[0041] (10) Control the deformation of No. 5 rolling mill at 13%-15%, and maintain the roughness of the new work roll at the roughness limit.

[0042] 2.88-3.12μm, while optimizing the roll changing process to ensure that the surface roughness of the strip is controlled within 0.8μm-1.9μm;

[0043] VII. Process control design of bell-type annealing furnace:

[0044] The bell-type furnace annealing process uses full hydrogen annealing, and the temperature of the steel coil exiting the furnace must not exceed 100℃;

[0045] (1) Reduce overflow edge defects of steel coils and optimize stacking methods: For steel coils with a thickness of less than 0.45 mm, overflow edge defects are not allowed when loading them into the furnace. However, if overflow edge defects occur, they should be handled according to the actual overflow edge situation of the steel coil. For defective coils with overflow edge greater than 10 mm, they should be leveled and repaired before being loaded into the furnace for annealing. For slight overflow edge defects, thin convection plates should be used for stacking to increase the contact area between the convection plate 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, the edge adhesion of slight overflow edge defects was significantly reduced. For defective coils with overflow edge exceeding 10 mm on one side, the steel coil should be placed on the top layer with the overflow edge facing upward.

[0046] (2) Before production, clean the furnace platform of accumulated ash and carbon black until there is no ash;

[0047] (3) The hydrogen blowing rate in the second and third stages is controlled at 20-25m. 3 / h, to ensure that residual emulsion is fully evaporated;

[0048] (4) Annealing is carried out using a three-platform system, with an additional 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and a 730℃ holding platform for more than 15 hours; the furnace load is 55-75 tons, the temperature is controlled at 730℃, the heating time is 19 hours, the holding time is ≥14 hours, the waiting time for the cover is 6 hours, the furnace exit temperature is 95℃, the heating stage has a 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and hydrogen is used for pressure holding at 600℃ without hydrogen purging; the furnace load is >75 tons, the temperature is controlled at 730℃, the heating time is 20 hours, the holding time is ≥15 hours, the waiting time for the cover is 7 hours, the furnace exit temperature is 100℃, the heating stage has a 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and hydrogen is used for pressure holding at 600℃ without hydrogen purging.

[0049] (5) Extend the cooling time with the heating cover to 7 hours, and reduce the temperature of the material chamber to below 600°C when the heating cover is removed;

[0050] VIII. Process Control Design of Leveling Unit:

[0051] (1) Production using rolling force mode, finished product thickness ≤ 0.85mm, finished product width ≤ 1035mm, rolling force 1000kN; if finished product width > 1035mm, then the rolling force is 1100kN; finished product thickness > 0.85mm, finished product width is all widths, rolling force is 1200-1300kN;

[0052] (2) During the production of leveling, the belt threading speed is 15m / min, and the speed is directly increased to 600-700m / min at the end. The tail speed is directly reduced from high speed to tail speed of 30m / min, and there should be no pause in the middle.

[0053] (3) The leveling unit uses rolls with a roughness of 2.5±0.1μm for rolling, and the surface roughness of the steel coil after rolling is controlled to 0.8-1.3μm;

[0054] IX. Process Control Design of Rewinding Unit:

[0055] (1) All steel coils with a thickness at the beginning and end that is 0.015 mm less than the target thickness are cut off;

[0056] (2) Before production, wipe the roller system and use ordinary SPCC steel for at least 40 tons;

[0057] (3) The amount of oil applied to the upper and lower surfaces should be controlled to 1.3-1.5 g / m². 2 .

[0058] Using the method of this invention, DC04 steel grade was successfully trial-produced, completely eliminating surface edge oxidation defects and central adhesion defects. Its performance meets delivery requirements, and customers have reported positive results. This invention is applicable to bell-type furnace production of DC04 steel grade, has a wide range of applications, and is suitable for raw material supply in the automotive deep-drawing sheet industry, possessing significant potential for widespread adoption. Detailed Implementation

[0059] A production process for DC04 steel for high surface area deep drawing is carried out according to the following steps:

[0060] First, the steel composition is designed as follows: For steel tapping mark DP0131D1, C content ≤ 0.002%; Si content ≤ 0.035%; Mn content 0.08~0.22%; P content ≤ 0.018%; S content ≤ 0.01%; Al content 0.03-0.05%; residual elements [Cr] ≤ 0.1%, [Ni] ≤ 0.1%, [Cu] ≤ 0.15%;

[0061] II. Requirements for steelmaking raw materials:

[0062] (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%. Before desulfurization, the requirements for molten iron are: Si content ≤0.08%, P content ≤0.14%, S content ≤0.04%, and temperature ≥1280℃.

[0063] (2) Alloy selection: low-carbon ferromanganese, metallic manganese, sintered manganese balls, ferrotitanium, ferroaluminum, ferroboron;

[0064] (3) The converter ladle and argon blowing conditions are good, and there must be no cold steel or slag on the bottom or wall of the ladle;

[0065] Converter process control:

[0066] (1) Endpoint component control: [C] ≤ 0.04%, [P] ≤ 0.012%, [S] ≤ 0.008%;

[0067] (2) Tapping requirements: Before tapping, the oxygen level in the furnace should be set. Deoxidizer should be added according to the oxygen level. The tapping port should be well maintained. The tapping time should be ≥3.5 minutes. Slag should be blocked by the sliding plate during tapping. The thickness of the slag layer in the ladle should be controlled. The phosphorus return of the converter tapping should not be greater than 0.003%.

[0068] III. Refining Requirements:

[0069] (1) Steel ladle material requirements: Carbon-free steel ladles are required;

[0070] (2) LF treatment: heating and reduction and upgrading of ladle top slag;

[0071] (3) RH: decarburization, deoxidation, composition and temperature adjustment; before DC04 steelmaking production, the vacuum degree of the RH refining equipment must be confirmed. The RH vacuum degree should not be greater than 180Pa and the treatment time should not be less than 18min; before production, the RH tank should be washed with low carbon aluminum killed steel. To avoid steel contamination, residual steel should not be left in the tank; the pure degassing time of this treatment should be ensured to be more than 8 minutes; aluminum ferrophosphate is added in the RH furnace, and titanium ferrophosphate and boron ferrophosphate are added at the end of the treatment.

[0072] IV. Slab continuous casting control and inspection requirements:

[0073] 1) Continuous casting employs argon protection throughout the process, using carbon-free protective slag and carbon-free ladle covering agent; the superheat of the tundish in the first continuous casting furnace is ≤45℃, and the superheat of the tundish in the continuous casting furnace is ≤35℃. Constant casting speed protection is required, with a maximum casting speed of 1.6m / min; the dryness requirements for protective slag and covering agent are that H2O is not greater than 0.5%; the requirements for argon-sealed protection casting are: argon flow rate of 250~300L / min in the tundish, 250~300L / min in the long nozzle, 3~5L / min in the stopper rod, 3~5L / min in the tundish top nozzle, and 10~12L / min between plates;

[0074] 2) The liquidus temperature of tap mark DP0131D1 is 1535℃; the liquidus temperature of tap mark DP0531D1 is 1535℃;

[0075] 3) The slab should not be hot-sent. After chamfering, it should be cold-inspected and released. The size of the chamfered corner should be 30×50mm, or a chamfering crystallizer should be used for production.

[0076] V. Key points for conventional process control in hot rolling:

[0077] (1) Temperature regime, steel grade DC04, heating thickness layer 1.2-6mm, rough rolling thickness layer mm and corresponding rough rolling temperature °C are: 1.2-2.2, 1070±30; 2.201-2.999, 1050±30; 3-3.999, 1040±30; 4-6, 1030±30; finishing rolling thickness layer 1.2-6mm, finishing rolling temperature 920±20℃, coiling thickness layer 1.2-6mm, coiling temperature 670±20℃;

[0078] (2) Heating time: The heating time is greater than 160 minutes, the temperature difference between the head and tail of the slab is less than 20℃, and descaling is carried out at the three inlets of rough rolling 1, 3 and 5;

[0079] (3) Heating temperature control: In order to ensure the requirements of head and tail performance, microstructure and low yield strength ratio, the temperature and cooling mode are strictly controlled according to the production and sales system requirements. Hot rolling: DC04 requires a heating temperature of 1170±30℃, which is slightly lower than the limit of 1140~1170℃, and a final rolling temperature of 920±20℃, which is slightly higher than the limit of 920~940℃.

[0080] (4) Hot rolling plan preparation: Steel coils must be prepared after 21 coils in each plan, with 6 transition coils. The transition coils shall use Q215, SPHC or steel grades with low requirements, and the temperature jump shall not exceed 20℃;

[0081] (5) Convexity requirement: wedge shape ≤ convexity ≤ 50μm;

[0082] VI. Process control design for cold rolling pickling and rolling mill:

[0083] (1) The hydrochloric acid temperature in tanks 1-4 is controlled at 65-75℃, and the running speed of the process section is controlled at 60-130m / min;

[0084] (2) Before producing special steel grades, the pickling unit should replace the acid with 60-80 ml of fresh acid 4 hours in advance. 3 Ensure that the HCl content of the acid solution in acid tank #1 is ≥50g / L and the iron ion content is ≤100g / L, and prevent the occurrence of under-acid washing.

[0085] (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, all the surface and operating condition of the squeeze rollers must be intact, and the roller surface is not allowed to have serious wear, adhesion, scratches, peeling, or heat damage defects, and there must be no blockage during operation;

[0086] (4) The reduction rate of DC04 is controlled at 78-82%;

[0087] (5) In addition to the conventional parameter control, the main control of the rolling mill unit is the residual emulsion on the surface of the strip steel, and at the same time, it is necessary to make full preparations for the annealing of the bell furnace unit. The various indicators of the emulsion of the rolling mill are implemented one shift before production. Emulsion A system: concentration target 2%, saponification value 140-160mg / g, impurity oil content ≤20%, iron powder content ≤200ppm, emulsion temperature requirement: 50~60℃, pH value requirement: 6.0~6.5, conductivity <300us / cm; Emulsion B system: emulsion concentration target 1.2%, saponification value 140~160mg(KOH) / g, impurity oil content ≤15%, iron powder content ≤120ppm;

[0088] (6) Before production, ensure that the last stand of the rolling mill is in good working order, that there is no emulsion residue on the surface of the strip, and that the rolling mill outlet purging pressure is >0.6MPA; that the nozzles are not missing or blocked, and that the condensate from the rolling mill outlet stand is not allowed to drip onto the surface of the strip.

[0089] (7) Coiling tensile stress: 26.0–29.5 MPa;

[0090] (8) The slab shape shall be controlled according to the micro-double-sided wave control, and the presence of medium waves shall be strictly prohibited. The standard control curve A2 of the slab shape instrument shall be set to +4, and the width shall be suitable for all widths from 930 to 1250 mm.

[0091] (9) Each time the support roller is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not blocked and the nozzle angle meets the process requirements.

[0092] (10) Control the deformation of No. 5 rolling mill at 13%-15%, and maintain the roughness of the new work roll at the roughness limit.

[0093] 2.88-3.12μm, while optimizing the roll changing process to ensure that the surface roughness of the strip is controlled within 0.8μm-1.9μm;

[0094] VII. Process control design of bell-type annealing furnace:

[0095] The bell-type furnace annealing process uses full hydrogen annealing, and the temperature of the steel coil exiting the furnace must not exceed 100℃;

[0096] (1) Reduce overflow edge defects of steel coils and optimize stacking methods: For steel coils with a thickness of less than 0.45 mm, overflow edge defects are not allowed when loading them into the furnace. However, if overflow edge defects occur, they should be handled according to the actual overflow edge situation of the steel coil. For defective coils with overflow edge greater than 10 mm, they should be leveled and repaired before being loaded into the furnace for annealing. For slight overflow edge defects, thin convection plates should be used for stacking to increase the contact area between the convection plate 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, the edge adhesion of slight overflow edge defects was significantly reduced. For defective coils with overflow edge exceeding 10 mm on one side, the steel coil should be placed on the top layer with the overflow edge facing upward.

[0097] (2) Before production, clean the furnace platform of accumulated ash and carbon black until there is no ash;

[0098] (3) The hydrogen blowing rate in the second and third stages is controlled at 20-25m. 3 / h, to ensure that residual emulsion is fully evaporated;

[0099] (4) Annealing is carried out using a three-platform system, with an additional 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and a 730℃ holding platform for more than 15 hours; the furnace load is 55-75 tons, the temperature is controlled at 730℃, the heating time is 19 hours, the holding time is ≥14 hours, the waiting time for the cover is 6 hours, the furnace exit temperature is 95℃, the heating stage has a 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and hydrogen is used for pressure holding at 600℃ without hydrogen purging; the furnace load is >75 tons, the temperature is controlled at 730℃, the heating time is 20 hours, the holding time is ≥15 hours, the waiting time for the cover is 7 hours, the furnace exit temperature is 100℃, the heating stage has a 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and hydrogen is used for pressure holding at 600℃ without hydrogen purging.

[0100] (5) Extend the cooling time with the heating cover to 7 hours, and reduce the temperature of the material chamber to below 600°C when the heating cover is removed;

[0101] VIII. Process Control Design of Leveling Unit:

[0102] (1) Production using rolling force mode, finished product thickness ≤ 0.85mm, finished product width ≤ 1035mm, rolling force 1000kN; if finished product width > 1035mm, then the rolling force is 1100kN; finished product thickness > 0.85mm, finished product width is all widths, rolling force is 1200-1300kN;

[0103] (2) During the production of leveling, the belt threading speed is 15m / min, and the speed is directly increased to 600-700m / min at the end. The tail speed is directly reduced from high speed to tail speed of 30m / min, and there should be no pause in the middle.

[0104] (3) The leveling unit uses rolls with a roughness of 2.5±0.1μm for rolling, and the surface roughness of the steel coil after rolling is controlled to 0.8-1.3μm;

[0105] IX. Process Control Design of Rewinding Unit:

[0106] (1) All steel coils with a thickness at the beginning and end that is 0.015 mm less than the target thickness are cut off;

[0107] (2) Before production, wipe the roller system and use ordinary SPCC steel for at least 40 tons;

[0108] (3) The amount of oil applied to the upper and lower surfaces should be controlled to 1.3-1.5 g / m².

[0109] Example: 1. Ensure the plate shape is straight, prevent abnormal wear of the rolls, and reduce rib defects;

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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).

[0114] 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.

[0115] 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.

[0116] 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;

[0117] 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. 3Simultaneously, 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;

[0118] 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.

[0119] 2.5 A residual iron content test must be performed daily on the steel strip surface, and the residual iron content must be <120mg / Ms.

[0120] 3. Optimize the coiling tension of the rolling mill in the 1420 pickling and rolling zone.

[0121] 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.

[0122] 4. Strictly control the surface roughness of the board.

[0123] The deformation of the No. 5 rolling mill is controlled at around 13%-15%. When the roughness of the new work roll is put into operation, the roughness is maintained at 2.88-3.12μm. At the same time, the roll changing process is optimized to ensure that the surface roughness of the strip is controlled at 0.8μm-1.9μm.

[0124] 5. The total reduction rate of DC04 is controlled at 78-82%, and the C content is ≤0.002%.

[0125] 6. Process control of bell-type furnace

[0126] 6.1 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.

[0127] 6.2 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.

[0128] 6.3 For single-sided overflow defects, the steel coil can be placed on the top layer with the overflow side facing upwards.

[0129] 6.4 Before production, clean the furnace platform of accumulated ash (carbon black) until there is no ash, and wipe all water off the furnace platform;

[0130] 6.5 The hydrogen blowing rate in stages 2 and 3 should be controlled at 20-25m³. 3 / h, to ensure that the residual emulsion is fully evaporated;

[0131] 6.6 Annealing is carried out using a three-platform system, with an additional 430℃ holding platform for 6-7 hours, a 600℃ holding platform for 2-3 hours, and a 730℃ high-temperature holding platform for more than 15 hours.

[0132] 1) Furnace loading capacity: 55-75 tons; temperature control: 730℃; heating time: 19 hours; holding time: ≥14 hours; waiting time before hood: 6 hours.

[0133] The furnace exit temperature is 95℃. During the heating stage, the furnace is held at 430℃ for 6-7 hours and at 600℃ for 2-3 hours. At 600℃, hydrogen is used for pressure maintenance, and hydrogen purging is not performed.

[0134] 2) For furnace loading > 75 tons, control temperature 730℃, heating time 20h, holding time ≥ 15h, waiting time for cover 7h, furnace exit temperature 100℃, during the heating stage, the 430℃ holding platform is held for 6-7 hours, the 600℃ holding platform is held for 2-3 hours, and hydrogen pressure is used for 600℃, without hydrogen purging.

[0135] 6.7 Extend the cooling time with the heating cover to 7 hours, and reduce the temperature of the material chamber to below 600℃ when the heating cover is removed; 1.6 Appropriately reduce the annealing cooling rate.

[0136] 7. Optimize leveling mode

[0137] 7.1 Production using rolling force mode: ;

[0138] 7.2 During the leveling process, the threading speed is 15m / min, and the speed is increased directly to 600-700m / min at the end. The tail speed is reduced directly from high speed to 30m / min at the tail end, and there should be no pause in the middle.

[0139] 7.3 The leveling unit uses rolls with a roughness of 2.5±0.1μm for rolling, and the surface roughness of the steel coil after rolling is controlled to 0.8-1.3μm.

[0140] 7.4 Steel coils must be placed stably during hoisting and placement before and after production to prevent crushing pits.

[0141] 8. Process control of the rewinding unit

[0142] 8.1 Steel coils with a thickness at the beginning and end that is 0.015 mm less than the target thickness shall be cut off.

[0143] 8.2 Before production, wipe the roller system and use ordinary SPCC steel for at least 40 tons. 8.3 Control the oil application amount on the upper and lower surfaces to 1.3-1.5 g / m². 2 .

Claims

1. A production process of DC04 steel grade for high surface deep drawing, characterized in that The following steps are implemented: I. First, the composition of steel material is designed: tapping mark DP0131D1, C content ≤0.002%; Si content ≤0.035%; Mn content 0.08-0.22%; P content ≤0.018%; S content ≤0.01%; Al content 0.03-0.05%; residual elements [Cr] ≤0.1%, [Ni] ≤0.1%, [Cu] ≤0.15%; II. Steelmaking raw material requirements: (1) Hot metal requirements: hot metal can be desulfurized pretreatment according to hot metal conditions and production needs, straight up into the furnace hot metal [S] ≤0.01%, desulfurized hot metal requirements: Si element content ≤0.08%, P element content ≤0.14%, S element content ≤0.04%, temperature ≥1280℃, hot metal pretreatment trigger condition: when desulfurized hot metal [S] >0.01%, desulfurization pretreatment must be carried out; if desulfurized hot metal [S] ≤0.01%, it can be straight up into the furnace; (2) Alloy selection: low-carbon ferromanganese, metallic manganese, sintered manganese ball, titanium iron, aluminum iron, boron iron; (3) The converter ladle, argon blowing condition is good, the ladle bottom and wall are strictly prohibited to have cold steel and slag accumulation; Converter process control: (1) End point composition control: [C] ≤0.04%, [P] ≤0.012%, [S] ≤0.008%; (2) Tapping requirements: maintain oxygen in the furnace before tapping, add deoxidizer according to the oxygen setting, maintain the tapping hole, the tapping time is ≥3.5 minutes, slide plate slag stopping tapping, the ladle slag layer thickness control, the converter tapping phosphorus increase is not more than 0.003%; III. Refining requirements: (1) Ladle material requirements: carbon-free ladle is required; (2) LF treatment: temperature raising, ladle top slag reduction and modification; (3) RH: decarburization, deoxidation, composition and temperature adjustment; Before DC04 steelmaking production, the RH refining equipment vacuum degree needs to be confirmed, the RH vacuum degree is not more than 180Pa, the treatment time is not less than 18min; before production, the RH needs to use low-carbon aluminum killed steel washing tank, to avoid steel pollution, residual steel is prohibited to remain in the tank; the pure degassing time of this treatment is ensured to be more than 8 minutes; aluminum iron is added in the RH furnace, titanium iron and boron iron are added at the end of the treatment; IV. Slab continuous casting control and inspection requirements: 1) Continuous casting adopts full-range argon protection casting, uses carbon-free protective slag and carbon-free ladle covering agent; the first ladle superheat is ≤45℃, the continuous casting ladle superheat is ≤35℃, constant speed protection casting is required, the maximum drawing speed is 1.6m / min; the protective slag and covering agent dryness requirement is that H2O is not more than 0.5%; Argon sealing protection protection casting requirements: tundish argon flow 250-300L / min, long nozzle argon flow 250-300L / min, stopper argon flow 3-5L / min, tundish upper nozzle argon flow 3-5L / min, slab argon flow 10-12L / min; 2) The liquidus temperature of tapping mark DP0131D1 is 1535℃; the liquidus temperature of tapping mark DP0531D1 is 1535℃; 3) slab can not be hot sent, chamfering after cold inspection qualified release, the size of the corner cleaning is 30 x 50 mm, or use chamfering crystallizer production; Five, the main points of conventional process control of hot rolling: (1) temperature system, steel grade DC04, heating thickness layering 1.2-6mm, roughing thickness layering mm and the corresponding roughing temperature ℃ respectively: 1.2-2.2, 1070±30; 2.201-2.999, 1050±30; 3-3.999, 1040±30; 4-6, 1030±30; finishing thickness layering 1.2-6mm, finish rolling temperature 920±20℃, coiling thickness layering 1.2-6mm, coiling temperature 670±20℃; (2) heating time: heating time is greater than 160 minutes, slab head and tail temperature difference is less than 20℃, roughing 1, 3, 5 three inlet descaling; (3) heating temperature control: to ensure the head and tail performance and organization and low yield ratio requirements, temperature and cooling mode strictly according to the requirements of the production and marketing system control, hot rolling: DC04 requires heating temperature 1170±30℃, lower limit 1140-1170℃, upper limit 920-940℃; (4) hot rolling plan preparation: steel coil must be prepared in each plan after 21 blocks, 6 blocks of transition material, transition material using Q215, SPHC or not high requirements of steel, temperature jump should not exceed 20℃; (5) crown requirements: wedge ≤ crown ≤ 50μm; Six, the process control design of cold rolling and pickling, rolling mill: (1) 1-4# tank hydrochloric acid temperature control to 65-75℃, process section running speed control to 60-130m / min; (2) The pickling unit is replaced with new acid 60-80m 3 4 hours before producing special steel, ensuring that the HCl content in the 1# acid tank is ≥50g / L, the iron ion content is ≤100g / L, and the phenomenon of insufficient pickling is eliminated. (3) 1# rinsing tank filter outlet temperature 60℃-80℃, 2# rinsing tank rinsing water conductivity test value ≤100us / cm, rinsing water make-up valve opening degree is increased by 25%-40% than ordinary steel, all the wringing rollers surface, running state must be perfect, the roller surface is not allowed to have serious wear, bonding, scratch, peeling, thermal damage defects, and should not appear the blocked phenomenon when running; (4) DC04 reduction rate control in 78-82%; (5) in addition to the conventional parameter control of rolling mill unit, the main control of the residual emulsion on the surface of strip steel, and make full preparation for the annealing of hood type furnace unit; before production, the indicators of emulsion of rolling mill are implemented, emulsion A system: concentration target 2%, saponification value 140-160mg / g, impurity oil content ≤20%, iron powder content ≤200ppm, emulsion temperature requirement: 50-60℃, pH value requirement: 6.0-6.5, conductivity <300us / cm; emulsion B system: emulsion concentration target 1.2%, saponification value 140-160mg(KOH) / g, impurity oil content ≤15%, iron powder content ≤120ppm; (6) before production, ensure that the blowing device of the last rack of rolling mill is normal, the emulsion residual on the surface of strip steel is not allowed, the blowing pressure of rolling mill outlet is >0.6MPa; the nozzle is not allowed to be missing or blocked, the condensate water of rolling mill outlet portal should not drop on the surface of strip steel; (7) Coiling tension 26.0-29.5 MPa; (8) The shape of the sheet is controlled according to the micro double edge wave, and the middle wave is strictly prohibited. The sheet shape instrument standard control curve A2 control coefficient is set to +4, and the width is 930-1250 mm, all of which are suitable; (9) Each time the support roll is replaced, the emulsion nozzle is checked and confirmed to ensure that the emulsion nozzle is not blocked and the nozzle angle meets the process requirements; (10) The deformation of the 5# rolling mill is controlled at 13%-15%, the roughness of the new work roll is kept at 2.88-3.12 μm when the roughness is online, and the roll changing process is optimized to ensure that the strip surface roughness is controlled at 0.8-1.9 μm; Seven, process control design of bell type annealing furnace: The process of bell type annealing is full hydrogen complete annealing, and the coil temperature out of the furnace shall not be higher than 100℃; (1) Reduce the steel coil overflow edge defects, optimize the stacking method: For steel coils with a thickness of less than 0.45 mm, no overflow edge defects are allowed when loading, but when overflow edge defects occur, the actual overflow edge of the steel coil is treated; The coil with overflow edge more than 10 mm is annealed after leveling repair; The slight overflow edge defect must be stacked with thin convection plates to increase the contact area between the convection plate and the strip and reduce the unit extrusion force of the steel coil; Through the test, it is found that the edge bonding of the coil with slight overflow edge defect is significantly reduced after being stacked with thin material convection plate; For the single-side overflow edge defect coil with more than 10 mm, the coil is placed on the top layer with the overflow edge facing up; (2) Clean the accumulated dust and carbon black on the furnace table before production; (3) The hydrogen blowing amount in paragraphs 2 and 3 is controlled at 20-25 m 3 / h, to ensure that the emulsion residual liquid is fully volatilized; (4) Use three platforms for annealing, add 430℃ holding platform for 6-7 hours, 600℃ holding platform for 2-3 hours, and 730℃ holding for more than 15 hours; The loading capacity is 55-75 tons, the control temperature is 730℃, the heating time is 19h, the holding time is ≥14h, the waiting cover time is 6h, the out-of-furnace temperature is 95℃, the heating stage is 430℃ holding platform for 6-7 hours, 600℃ holding platform for 2-3 hours, 600℃ using hydrogen pressure, no hydrogen blowing; The loading capacity is >75 tons, the control temperature is 730℃, the heating time is 20h, the holding time is ≥15h, the waiting cover time is 7h, the out-of-furnace temperature is 100℃, the heating stage is 430℃ holding platform for 6-7 hours, 600℃ holding platform for 2-3 hours, 600℃ using hydrogen pressure, no hydrogen blowing; (5) The heating cover cooling time is extended to 7h, and the material chamber temperature is reduced to below 600℃ when the heating cover is removed; Eight, process control design of leveling unit: (1) Use rolling force mode production, finished product thickness ≤0.85mm, finished product width ≤1035mm, rolling force 1000kN; If the finished product width >1035mm, the rolling force is 1100kN; The finished product thickness >0.85mm, the finished product width is all the width, the rolling force is 1200-1300kN; (2) During the leveling production, the strip speed is 15m / min, the end is directly raised to 600-700m / min, the tail is directly reduced to 30m / min from high speed, and the middle part must not stop; (3) The roughness of the rolling mill is 2.5±0.1μm, and the surface roughness of the steel coil after rolling is controlled to 0.8-1.3μm; Nine, the process control design of the rewinding unit: (1) The steel coil with a head and tail thickness less than the target thickness of 0.015㎜ is all cut off; (2) After wiping the roll system before production, at least over 40 tons of ordinary SPCC steel is used; (3) The oil coating amount on the upper and lower surfaces is controlled to 1.3-1.5 g / m 2 .