Production method for solving surface chromatic aberration of boron-containing deep drawing IF steel

Abstract

The invention discloses a production method for solving surface chromatic aberration of boron-containing deep drawing I-F steel, which specifically solves the problem of surface chromatic aberration of the boron-containing deep drawing I-F steel caused by uneven oxide scale, emulsion residue and structural stress difference through collaborative optimization of a hot rolling, cold rolling, annealing and leveling full-flow process. Specifically, the surface color difference grade of a finished steel coil stably meets the enterprise standard requirement by accurately controlling the hot rolling finishing temperature and the coiling temperature, optimizing the cold rolling emulsion parameters and adjusting the annealing process curve and the flattening elongation, the surface roughness Ra is controlled to be 0.5-0.9 mu m, meanwhile, the deep drawing performance of the material is guaranteed (the value of n is larger than or equal to 0.22, and the value of r is larger than or equal to 1.8), and the product quality is improved. The method is suitable for the fields of automobile panels, household appliance shells and the like with strict requirements on surface quality, and has remarkable industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of steel material processing technology, and in particular relates to a production method for solving the surface color difference of boron-containing deep-drawing IF steel. Background Technology

[0002] Boron-containing deep-drawing IF (interstitial atom-free) steel significantly improves deep-drawing performance and aging stability due to the addition of boron. It also contributes to lightweighting and impact resistance in home appliances, making it widely used in high-end products with stringent surface quality and mechanical performance requirements, such as the casings of mid-to-high-end appliances. However, boron, being a highly reactive element, fundamentally alters the oxidation behavior of steel, leading to surface color differences during production. This has become a key bottleneck restricting its application expansion. These color differences manifest as streaks, spots, or regional color variations on the surface of the strip, particularly noticeable within 30-100mm of the edge in the width direction. Subsequent coating processes amplify these differences due to diffuse light reflection, severely impacting product appearance consistency and resulting in a scrap rate as high as 5-8% in high-end applications. In-depth research has revealed that the core causes of surface color difference in boron-containing deep-drawing IF steel include: firstly, under high-temperature conditions, boron easily accumulates at the interface, forming a composite oxide phase with silicon oxides, reducing the adhesion between the iron oxide scale and the substrate, and easily leading to iron oxide scale indentation or residue, resulting in hidden color differences; secondly, improper pickling parameters lead to over-pickling at the edges, or alloying elements accumulate and oxidize during the annealing stage, further exacerbating color difference defects. Therefore, in-depth research and exploration are needed to improve the surface quality of boron-containing IF steel to fundamentally solve the surface color difference problem.

[0003] The existing literature and patent research are as follows:

[0004] 1. The patent CN201910461385.4, "A Method for Reducing Color Difference Defects on the Surface of IF Steel", only introduces the concentration of cold rolling emulsion and the emulsion spray flow rate, and reduces the contact angle of rolling oil in the emulsion to improve the uniformity of oil film spreading and increase the flatness elongation of the flattening section after continuous annealing of steel strip. It does not involve the linkage optimization of hot rolling and annealing processes and cannot solve the inherent defects of iron oxide scale caused by boron.

[0005] 2. A search of patent CN201711049844.5, "A Method for Eliminating Surface Color Difference Defects in High-Strength IF Steel Containing Phosphorus," reveals that it partially eliminates surface color differences in high-strength IF steel containing phosphorus by controlling rolling temperature, coiling temperature, and reduction rate. This patent, however, studies ultra-low carbon IF steel (non-high-strength IF steel) with the addition of trace amounts of boron, and solves the problem of surface color difference defects through process control.

[0006] 3. The patent CN201911328579.3, "A Manufacturing Method for Boron-Containing Pickled Steel Strip," mainly describes how to improve the surface oxide scale structure and reduce color difference of ordinary low-carbon steel strips by controlling the final cooling temperature after hot rolling (e.g., 600-700℃), using tension leveling to break scale before pickling (elongation 0.20-0.50%), and optimizing the pickling process (acid temperature 50-80℃, concentration 5-15%). This patent does not involve the synergistic optimization of cold rolling and annealing processes, and does not specify the specific process parameters for deep-drawing IF steel. Summary of the Invention

[0007] The purpose of this invention is to provide a production method for solving the surface color difference of boron-containing deep-drawing IF steel. By precisely controlling the process parameters of the entire process, including hot rolling, cold rolling, annealing, and leveling, the method can synergistically solve the color difference problems caused by uneven iron oxide scale and emulsion residue, thereby achieving simultaneous optimization of surface quality and deep-drawing performance.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] This invention discloses a production method for solving the surface color difference of boron-containing deep-drawing IF steel, comprising:

[0010] 1) Design and principle of chemical composition based on mass percentage

[0011] Ultra-low carbon design: Carbon is the most important interstitial atom in steel. It can increase yield strength and reduce elongation through "solid solution strengthening", which will destroy the "interstitial" characteristics of IF steel. If the carbon content is too high, it will also generate too many carbides with Ti / Nb, which will further deteriorate the plasticity. Therefore, the carbon content is controlled at C≤0.0025%.

[0012] Nitrogen: Similar to carbon, nitrogen is a key interstitial atom that leads to age hardening of steel (increased strength and decreased plasticity). It also readily combines with boron to form the BN embrittlement phase (if B is consumed by N first, it loses its regulatory effect). Therefore, N ≤ 0.0040%.

[0013] Boron: On the one hand, it inhibits grain boundary embrittlement. Boron will rapidly segregate at the grain boundaries, hindering the enrichment of phosphorus (P) at the grain boundaries and avoiding "weakened grain boundary bonding", thus solving the problem of secondary stamping cracking in ordinary IF steel. On the other hand, it improves small-angle grain boundaries, avoids the propagation of cracks during stamping, and improves tensile strength. Generally, it is controlled at 0.0002 to 0.0010%.

[0014] Titanium: ① Fixes residual carbon / nitrogen. Ti is a strong carbide / nitride forming element, preferentially reacting with residual C and N in steel to form TiC and TiN, further eliminating interstitial atoms and supplementing the fixation effect of boron on N; ② Protects boron activity: Ti combines with N first, preventing boron from being consumed by N to form ineffective BN, ensuring that boron can preferentially act on grain boundaries (suppressing P segregation); ③ Controls the upper limit of dosage: Excessive Ti (>0.08%) will generate coarse TiC / TiN particles, leading to a decrease in elongation and stress concentration cracking during stamping. Therefore, the titanium content is controlled at 0.055~0.075%;

[0015] Silicon: It is a "solid solution strengthening element" that increases yield strength and reduces elongation, and it is also harmful in excess.

[0016] Manganese: Similar to silicon, manganese can be strengthened by solid solution, but this will sacrifice plasticity. The upper limit must be strictly controlled to ensure deep drawing performance. Therefore, the manganese content is controlled at 0.08-0.018%.

[0017] Phosphorus: Phosphorus significantly reduces the toughness and ductility of steel, and is prone to segregation at grain boundaries, leading to "secondary processing brittleness"; the phosphorus content must be controlled in the design, so the phosphorus content should be controlled to be less than 0.012%.

[0018] Sulfur: Sulfur reacts with manganese to form long MnS inclusions, which crack along the deformation direction during stamping, destroying plasticity; it needs to be strictly controlled through refining (such as KR desulfurization) to reduce the number of inclusions, so the sulfur content should be controlled ≤0.010%;

[0019] Aluminum: Deoxidizing effect. Al is a highly efficient deoxidizer, reducing oxide inclusions (such as Al2O3) in steel and improving the purity of steel. The upper limit of its usage should be controlled. Excessive Al will generate coarse Al N, which increases strength and reduces plasticity. The aluminum content should be controlled at 0.25-0.55%.

[0020] The remainder consists of Fe and impurities;

[0021] 2) Steelmaking process: KR desulfurization → converter → LF refining → RH refining → slab continuous casting;

[0022] 2.1) KR desulfurization process

[0023] The sulfur content of the molten iron entering the converter must be less than 0.002%, and the area of ​​molten iron slag removal must be greater than 95%.

[0024] 2.2) Converter smelting process

[0025] Converter tapping must use a normal turnover ladle, and the tapping temperature drop must be less than 70℃; top slag modifiers should be added according to the oxygen content of the molten steel and the amount of slag added; the composition conditions of molten steel supplied from the converter to the LF furnace are shown in the table below:

[0026] Composition of LF-supplied steel in converter (unit: %)

[0027] element C Si Mn P S O Target% ≤0.04 ≤0.01 ≤0.13 ≤0.008 ≤0.007 0.04～0.07

[0028] 2.3) LF refining process

[0029] The LF furnace is heated and raised according to the in-situ temperature, and lime and modifiers are added to modify the top slag.

[0030] 2.4) RH refining process

[0031] The RH furnace vacuum treatment process involves deep decarburization. After decarburization, deoxidizing agents and aluminum particles are added according to the oxygen content. After 4 minutes of circulation, ferromanganese, ferrotitanium, and ferroboron alloys are added to adjust the composition. Ferromanganese alloy is added and circulated for 3 minutes before ferroboron alloy is added. After adjusting the composition, vacuum circulation is ensured to be ≥6 minutes.

[0032] 2.5) Continuous casting process

[0033] The main process parameters for continuous casting are shown in Table 3 below:

[0034] Continuous casting process parameters

[0035]

[0036] The casting machine adopts constant casting speed control, with a casting speed control range of 1.0~1.8m / min;

[0037] 3) Hot rolling process optimization

[0038] ① Strictly control the time the slab spends in the furnace.

[0039] Before optimization, the slab time in the furnace was ≥180 min, and after optimization, the slab time in the furnace was controlled between 180 and 220 min; before optimization, the slab temperature at the furnace exit was 1200±20℃, and after optimization, the slab temperature at the furnace exit was controlled between 1190±10℃.

[0040] ② Strictly control the hot rolling process, with specific measures as follows:

[0041] Before rolling, change and inspect the rolls to ensure that the water nozzles are not clogged;

[0042] Descaling pressure ≥190MPa, descaling in each pass of the roughing mill, while limiting the speed of the primary descaling mill rollers to ≤1m / s;

[0043] Finishing rolling oil flow rate ≥100ml / min;

[0044] The cooling between stands F1, F2, F3, and F5 of the finishing mill is activated, with a cooling water flow rate of ≥25%.

[0045] Finishing mill inlet temperature ≤1010℃;

[0046] Control the winding tension to 18-22kN to prevent differences in oxidation rate between the edge and center areas of the strip and reduce edge color difference;

[0047] After the product comes off the production line, an insulation cover is attached to slow down cooling.

[0048] To avoid uneven initial microstructure, the final rolling temperature is controlled at 900-920℃ to ensure uniform austenite grain refinement and reduce subsequent microstructure differences; the coiling temperature is 680-720℃.

[0049] 4) Improvement of cold rolling process

[0050] Optimize pickling parameters: concentration 180-220g / L, temperature 75-85℃, time 80-100s, to ensure thorough removal of iron oxide scale, while avoiding surface roughness and unevenness caused by over-pickling;

[0051] Precise control of emulsion parameters: emulsion concentration of 3.5-4.5% and temperature of 45-50℃ for the fifth stand; rolling oil contact angle of 35-45° to ensure uniform oil film coverage and reduce friction color difference;

[0052] Reasonably allocate the reduction rate of each stand, with a total reduction rate of ≥70%, to avoid stress concentration caused by excessive local deformation and lay a uniform microstructure foundation for subsequent annealing processes;

[0053] 5) Annealing process optimization

[0054] The process employs a multi-stage curve: preheating, heating, homogenization, slow cooling, rapid cooling, over-aging, equalization section, zinc pot insertion, and thick coating cooling. The heating temperature is 790-820℃, and the furnace speed is 90-120m / min to ensure sufficient recrystallization of the microstructure and reduce residual stress.

[0055] The protective atmosphere inside the furnace has a volume fraction of H2 of 5-7% and a dew point of -40 to -35°C, which effectively prevents oxidation and decarburization on the surface of the strip and avoids color differences caused by oxidation.

[0056] 6) Leveling process coordination

[0057] Control the flattening elongation rate to 0.8-1.2%, and combine it with a rolling force of 800-1000kN to eliminate residual stress inside the strip and improve the uniformity of surface gloss; chrome-plated work rolls ensure uniform stress on the strip surface during rolling and avoid color differences caused by embossing.

[0058] Furthermore, its chemical composition by mass percentage is as follows: C: 0.021%, Si: 0.008%, Mn: 0.15%, P: 0.010%, S: 0.008%, Al: 0.035%, B: 0.0005%, N: 0.0020%, Ti: 0.065%, with the remainder being Fe and other impurities.

[0059] Furthermore, specifically:

[0060] Hot rolling process:

[0061] Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 218 minutes, held for 25 minutes, and then tapped out at 1190℃.

[0062] Finishing mill final rolling: temperature 910℃, F7 exit speed 10.5m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 198MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.8m / s; finishing mill rolling oil flow rate 200ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 35%; finishing mill inlet strip temperature 998℃.

[0063] Winding: Temperature 690℃, tension 20kN; after the product comes off the production line, cover it with an insulation cover for slow cooling;

[0064] Cold rolling process:

[0065] Pickling: Hydrochloric acid concentration 200g / L, temperature 80℃, time 90s;

[0066] Emulsion: 4.0% concentration on the fifth stand, 2000 L / min injection flow rate, 48℃ temperature, and 40° contact angle of rolling oil;

[0067] Pickling mill: total reduction rate 78%, reduction rates of each stand 30%, 23%, 19%, 13%, and 9%, speed 900m / min;

[0068] Annealing process:

[0069] Continuous annealing profile: Preheating to 420℃ → Heating to 810℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 670℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 95m / min;

[0070] Protective atmosphere: 6% H2 volume fraction, dew point -38℃;

[0071] Leveling process:

[0072] Elongation 0.9%, rolling force 900kN, work roll roughness Ra=2.5μm, speed 100m / min;

[0073] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0074] Further, the finished product inspection results are as follows: the surface color difference level meets the enterprise standard FB requirements, the surface roughness Ra = 0.85μm, the deep drawing performance yield strength = 158MPa, the tensile strength = 302MPa, the elongation = 45%, n = 0.23, r = 2.7, and there are no color difference defects.

[0075] Furthermore, its chemical composition by mass percentage is as follows: C: 0.0013%, Si: 0.007%, Mn: 0.13%, P: 0.0090%, S: 0.007%, Al: 0.032%, B: 0.0004%, N: 0.0019%, Ti: 0.067%, with the remainder being Fe and other impurities.

[0076] Furthermore, specifically:

[0077] Hot rolling process:

[0078] Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 225 minutes, held for 25 minutes, and then tapped out at 1195℃.

[0079] Finishing mill final rolling: temperature 915℃, F7 exit speed 10.8m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 195MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.7m / s; finishing mill rolling oil flow rate 220ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 32%; finishing mill inlet strip temperature 995℃.

[0080] Winding: Temperature 695℃, tension 21kN; after the product comes off the production line, a heat insulation cover is attached for slow cooling;

[0081] Cold rolling process:

[0082] Pickling: Hydrochloric acid concentration 210g / L, temperature 82℃, time 85s;

[0083] Emulsion: 4.2% concentration on the fifth stand, 2100 L / min injection flow rate, 49℃ temperature, and 42° contact angle of rolling oil;

[0084] Pickling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min;

[0085] Annealing process:

[0086] Continuous annealing profile: Preheating to 420℃ → Heating to 815℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 675℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min;

[0087] Protective atmosphere: 5% H2 volume fraction, dew point -39℃;

[0088] Leveling process:

[0089] Elongation 0.8%, rolling force 890kN, work roll roughness Ra=2.5μm, speed 105m / min;

[0090] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0091] Furthermore, according to the production method for solving the surface color difference of boron-containing deep-drawing IF steel as described in claim 1, the finished product inspection results are as follows: the surface color difference level meets the enterprise standard FB requirements, the surface roughness Ra = 0.83 μm, the deep-drawing performance yield strength = 155 MPa, the tensile strength = 301 MPa, the elongation = 44%, n = 0.23, r = 2.6, and there are no color difference defects.

[0092] Furthermore, its chemical composition by mass percentage is as follows: C: 0.0010%, Si: 0.007%, Mn: 0.12%, P: 0.0080%, S: 0.009%, Al: 0.031%, B: 0.0006%, N: 0.0018%, Ti: 0.069%, with the remainder being Fe and other impurities.

[0093] Furthermore, specifically:

[0094] Hot rolling process:

[0095] Heating of continuously cast billets: The billet is heated to 1196℃ in the furnace for 226 minutes, held for 23 minutes, and then tapped out at 1192℃.

[0096] Finishing mill final rolling: temperature 912℃, F7 exit speed 10.7m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 196MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.9m / s; finishing mill rolling oil flow rate 230ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 30%; finishing mill inlet strip temperature 996℃.

[0097] Winding: Temperature 697℃, tension 22kN; after the product comes off the production line, a heat insulation cover is attached for slow cooling;

[0098] Cold rolling process:

[0099] Pickling: hydrochloric acid concentration 213 g / L, temperature 83℃, time 86 s;

[0100] Emulsion: 4.3% concentration on the fifth stand, 2150 L / min injection flow rate, 50℃ temperature, and 43° contact angle of rolling oil;

[0101] Pickling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min;

[0102] Annealing process:

[0103] Continuous annealing profile: Preheating to 420℃ → Heating to 818℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 677℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min;

[0104] Protective atmosphere: 7% H2 volume fraction, dew point -40℃;

[0105] Leveling process:

[0106] Elongation 0.8%, rolling force 895kN, work roll roughness Ra=2.5μm, speed 109m / min;

[0107] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0108] Furthermore, the finished product inspection results are as follows: the surface color difference level meets the enterprise standard FB requirements (no color difference is allowed), the surface roughness Ra = 0.88μm, the deep drawing performance yield strength = 150MPa, the tensile strength = 298MPa, the elongation = 46%, n = 0.23, r = 2.9, and there are no color difference defects.

[0109] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0110] Significantly improved surface quality: Through collaborative optimization of the entire process, the surface color difference grade of the finished steel coils consistently meets the requirements of the enterprise standard FB, completely eliminating strip defects, and the surface roughness Ra is controlled at 0.5-0.9μm, meeting the needs of high-end coating.

[0111] Stable deep-drawing performance: While improving surface quality, the deep-drawing performance of the material (n value ≥ 0.22, r value ≥ 1.8) is ensured, and the mechanical properties do not decrease due to process adjustments;

[0112] High production efficiency: Process parameters are easy to control, no additional equipment investment is required, it can be implemented on the basis of existing production lines, the production cycle is comparable to traditional methods, the scrap rate is reduced from 5-8% to less than 1%, and the product yield is improved.

[0113] Wide applicability: It is suitable for the production of boron-containing deep-drawing IF steel of different thicknesses, and can meet the stringent requirements of the automotive, home appliance and other industries for surface quality and forming performance, and has broad industrial application prospects. Attached Figure Description

[0114] The present invention will be further described below with reference to the accompanying drawings.

[0115] Figure 1 To optimize the surface of the front strip (where there is a color difference);

[0116] Figure 2 To ensure that the surface of the strip steel is free of color difference after optimization.

[0117] Figure 3 For stamped parts; Detailed Implementation

[0118] Example 1

[0119] This embodiment focuses on the production of 0.7mm thick boron-containing deep-drawing IF steel (wt% chemical composition: C=0.021%, Si=0.008%, Mn=0.15%, P=0.010%, S=0.008%, Al=0.035%, B=0.0005%, N=0.0020%, Ti=0.065%) using the method of this invention.

[0120] Hot rolling process:

[0121] Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 218 minutes, held for 25 minutes, and then tapped out at 1190℃.

[0122] Finishing mill final rolling: temperature 910℃, F7 exit speed 10.5m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 198MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.8m / s; finishing mill rolling oil flow rate 200ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 35%; finishing mill inlet strip temperature 998℃.

[0123] Winding: Temperature 690℃, tension 20kN; after the product comes off the production line, attach an insulation cover for slow cooling.

[0124] Cold rolling process:

[0125] Pickling: Hydrochloric acid concentration 200g / L, temperature 80℃, time 90s;

[0126] Emulsion: 4.0% concentration on the fifth stand, 2000 L / min injection flow rate, 48℃ temperature, and 40° contact angle of rolling oil;

[0127] Pickling mill: total reduction rate 78%, reduction rates of each stand 30%, 23%, 19%, 13%, and 9%, speed 900m / min;

[0128] Annealing process:

[0129] Continuous annealing profile: Preheating to 420℃ → Heating to 810℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 670℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 95m / min;

[0130] Protective atmosphere: 6% H2 volume fraction, dew point -38℃;

[0131] Leveling process:

[0132] Elongation 0.9%, rolling force 900kN, work roll roughness Ra=2.5μm, speed 100m / min;

[0133] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0134] Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements (no color difference is allowed), surface roughness Ra=0.85μm, deep drawing performance yield strength=158MPa, tensile strength=302MPa, elongation=45%, n=0.23, r=2.7, and there are no color difference defects.

[0135] Example 2

[0136] This embodiment focuses on the production of 0.6mm thick boron-containing deep-drawing IF steel (wt% chemical composition: C=0.0013%, Si=0.007%, Mn=0.13%, P=0.0090%, S=0.007%, Al=0.032%, B=0.0004%, N=0.0019%, Ti=0.067%) using the method of this invention.

[0137] Hot rolling process:

[0138] Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 225 minutes, held for 25 minutes, and then tapped out at 1195℃.

[0139] Finishing mill final rolling: temperature 915℃, F7 exit speed 10.8m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 195MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.7m / s; finishing mill rolling oil flow rate 220ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 32%; finishing mill inlet strip temperature 995℃.

[0140] Winding: Temperature 695℃, tension 21kN; after the product comes off the production line, attach an insulation cover for slow cooling.

[0141] Cold rolling process:

[0142] Pickling: Hydrochloric acid concentration 210g / L, temperature 82℃, time 85s;

[0143] Emulsion: 4.2% concentration on the fifth stand, 2100 L / min injection flow rate, 49℃ temperature, and 42° contact angle of rolling oil;

[0144] Pickling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min;

[0145] Annealing process:

[0146] Continuous annealing profile: Preheating to 420℃ → Heating to 815℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 675℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min;

[0147] Protective atmosphere: 5% H2 volume fraction, dew point -39℃;

[0148] Leveling process:

[0149] Elongation 0.8%, rolling force 890kN, work roll roughness Ra=2.5μm, speed 105m / min;

[0150] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0151] Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements (no color difference is allowed), surface roughness Ra=0.83μm, deep drawing performance yield strength=155MPa, tensile strength=301MPa, elongation=44%, n=0.23, r=2.6, and there are no color difference defects.

[0152] Example 3

[0153] This embodiment focuses on the production of 0.6mm thick boron-containing deep-drawing IF steel (wt% chemical composition: C=0.0010%, Si=0.007%, Mn=0.12%, P=0.0080%, S=0.009%, Al=0.031%, B=0.0006%, N=0.0018%, Ti=0.069%) using the method of this invention.

[0154] Hot rolling process:

[0155] Heating of continuously cast billets: The billet is heated to 1196℃ in the furnace for 226 minutes, held for 23 minutes, and then tapped out at 1192℃.

[0156] Finishing mill final rolling: temperature 912℃, F7 exit speed 10.7m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 196MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.9m / s; finishing mill rolling oil flow rate 230ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 30%; finishing mill inlet strip temperature 996℃.

[0157] Winding: Temperature 697℃, tension 22kN; after the product comes off the production line, attach an insulation cover for slow cooling.

[0158] Cold rolling process:

[0159] Pickling: hydrochloric acid concentration 213 g / L, temperature 83℃, time 86 s;

[0160] Emulsion: 4.3% concentration on the fifth stand, 2150 L / min injection flow rate, 50℃ temperature, and 43° contact angle of rolling oil;

[0161] Pickling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min;

[0162] Annealing process:

[0163] Continuous annealing profile: Preheating to 420℃ → Heating to 818℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 677℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min;

[0164] Protective atmosphere: 7% H2 volume fraction, dew point -40℃;

[0165] Leveling process:

[0166] Elongation 0.8%, rolling force 895kN, work roll roughness Ra=2.5μm, speed 109m / min;

[0167] Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

[0168] Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements (no color difference is allowed), surface roughness Ra=0.88μm, deep drawing performance yield strength=150MPa, tensile strength=298MPa, elongation=46%, n=0.23, r=2.9, and there are no color difference defects.

[0169] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A production method for solving the color difference on the surface of boron-containing deep-drawing IF steel, characterized in that: include: 1) Design of chemical composition by mass percentage C≤0.0025％； N≤0.0040％； B：0.0002～0.0010％； Ti: 0.055~0.075%; Mn: 0.08~0.018%; P<0.012%; S≤0.010%; Al: 0.25–0.55%; the remainder is Fe and impurities; 2) Steelmaking process: KR desulfurization → converter → LF refining → RH refining → slab continuous casting; 2.1) KR desulfurization process The sulfur content of the molten iron entering the converter must be less than 0.002%, and the area of ​​molten iron slag removal must be greater than 95%. 2.2) Converter smelting process Converter tapping must use a normal turnover ladle, and the tapping temperature drop must be less than 70℃; top slag modifiers should be added according to the oxygen content of the molten steel and the amount of slag added; the composition conditions of molten steel supplied from the converter to the LF furnace are shown in the table below: Composition of LF-supplied steel in converter (unit: %) 2.3) LF refining process The LF furnace is heated and raised according to the in-situ temperature, and lime and modifiers are added to modify the top slag. 2.4) RH refining process The RH furnace vacuum treatment process involves deep decarburization. After decarburization, deoxidizing agents and aluminum particles are added according to the oxygen content. After 4 minutes of circulation, ferromanganese, ferrotitanium, and ferroboron alloys are added to adjust the composition. Ferromanganese alloy is added and circulated for 3 minutes before ferroboron alloy is added. After adjusting the composition, vacuum circulation is ensured to be ≥6 minutes. 2.5) Continuous casting process The main process parameters for continuous casting are shown in Table 3 below: Continuous casting process parameters The casting machine adopts constant casting speed control, with a casting speed control range of 1.0~1.8m / min; 3) Hot rolling process optimization ① Strictly control the time the slab spends in the furnace. Before optimization, the slab time in the furnace was ≥180 min, and after optimization, the slab time in the furnace was controlled between 180 and 220 min; before optimization, the slab temperature at the furnace exit was 1200±20℃, and after optimization, the slab temperature at the furnace exit was controlled between 1190±10℃. ② Strictly control the hot rolling process, with specific measures as follows: Before rolling, change and inspect the rolls to ensure that the water nozzles are not clogged; Descaling pressure ≥190MPa, descaling in each pass of the roughing mill, while limiting the speed of the primary descaling mill rollers to ≤1m / s; The flow rate of the finishing mill rolling oil is ≥100ml / min; The cooling between stands F1, F2, F3, and F5 of the finishing mill is activated, with a cooling water flow rate of ≥25%. Finishing mill inlet temperature ≤1010℃; Control the winding tension to 18-22kN to prevent differences in oxidation rate between the edge and center areas of the strip and reduce edge color difference; After the product comes off the production line, an insulation cover is attached to slow down cooling. To avoid uneven initial microstructure, the final rolling temperature is controlled at 900-920℃ to ensure uniform austenite grain refinement and reduce subsequent microstructure differences; the coiling temperature is 680-720℃. 4) Improvement of cold rolling process Optimize pickling parameters: concentration 180-220g / L, temperature 75-85℃, time 80-100s, to ensure thorough removal of iron oxide scale, while avoiding surface roughness and unevenness caused by over-pickling; Precise control of emulsion parameters: emulsion concentration of 3.5-4.5% and temperature of 45-50℃ for the fifth stand; rolling oil contact angle of 35-45° to ensure uniform oil film coverage and reduce friction color difference; Reasonably allocate the reduction rate of each stand, with a total reduction rate of ≥70%, to avoid stress concentration caused by excessive local deformation and lay a uniform microstructure foundation for subsequent annealing processes; 5) Annealing process optimization The process employs a multi-stage curve consisting of "preheating-heating-uniform heating-slow cooling-rapid cooling-over-aging-equilibrium section-into-zinc pot-thickness cooling," with a heating temperature of 790-820℃ and a furnace speed of 90-120m / min to ensure sufficient recrystallization of the microstructure and reduce residual stress. The protective atmosphere inside the furnace has a volume fraction of H2 of 5-7% and a dew point of -40 to -35°C, which effectively prevents oxidation and decarburization on the surface of the strip and avoids color difference due to oxidation. 6) Leveling process coordination Control the flattening elongation rate to 0.8-1.2%, and combine it with a rolling force of 800-1000kN to eliminate residual stress inside the strip and improve the uniformity of surface gloss; chrome-plated work rolls ensure uniform stress on the strip surface during rolling and avoid color differences caused by embossing.

2. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: C: 0.021%, Si: 0.008%, Mn: 0.15%, P: 0.010%, S: 0.008%, Al: 0.035%, B: 0.0005%, N: 0.0020%, Ti: 0.065%, with the remainder being Fe and other impurities.

3. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 2, characterized in that: Specifically: Hot rolling process: Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 218 minutes, held for 25 minutes, and then tapped out at 1190℃. Finishing mill final rolling: temperature 910℃, F7 exit speed 10.5m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 198MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.8m / s; finishing mill rolling oil flow rate 200ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 35%; finishing mill inlet strip temperature 998℃. Winding: Temperature 690℃, tension 20kN; after the product comes off the production line, cover it with an insulation cover for slow cooling; Cold rolling process: Pickling: Hydrochloric acid concentration 200g / L, temperature 80℃, time 90s; Emulsion: 4.0% concentration on the fifth stand, 2000 L / min injection flow rate, 48℃ temperature, and 40° contact angle of rolling oil; Pickling mill: total reduction rate 78%, reduction rates of each stand 30%, 23%, 19%, 13%, and 9%, speed 900m / min; Annealing process: Continuous annealing profile: Preheating to 420℃ → Heating to 810℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 670℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 95m / min; Protective atmosphere: 6% H2 volume fraction, dew point -38℃; Leveling process: Elongation 0.9%, rolling force 900kN, work roll roughness Ra=2.5μm, speed 100m / min; Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

4. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 3, characterized in that: Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements, the surface roughness Ra=0.85μm, the deep drawing performance yield strength=158MPa, the tensile strength=302MPa, the elongation=45%, n=0.23, r=2.7, and there are no color difference defects.

5. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: C: 0.0013%, Si: 0.007%, Mn: 0.13%, P: 0.0090%, S: 0.007%, Al: 0.032%, B: 0.0004%, N: 0.0019%, Ti: 0.067%, with the remainder being Fe and other impurities.

6. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 5, characterized in that: Specifically: Hot rolling process: Heating of continuously cast billets: The billet is heated to 1200℃ in the furnace for 225 minutes, held for 25 minutes, and then tapped out at 1195℃. Finishing mill final rolling: temperature 915℃, F7 exit speed 10.8m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 195MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.7m / s; finishing mill rolling oil flow rate 220ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 32%; finishing mill inlet strip temperature 995℃. Winding: Temperature 695℃, tension 21kN; after the product comes off the production line, a heat insulation cover is attached for slow cooling; Cold rolling process: Pickling: Hydrochloric acid concentration 210g / L, temperature 82℃, time 85s; Emulsion: 4.2% concentration on the fifth stand, 2100 L / min injection flow rate, 49℃ temperature, and 42° contact angle of rolling oil; Pickling and rolling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min; Annealing process: Continuous annealing profile: Preheating to 420℃ → Heating to 815℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 675℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min; Protective atmosphere: 5% H2 volume fraction, dew point -39℃; Leveling process: Elongation 0.8%, rolling force 890kN, work roll roughness Ra=2.5μm, speed 105m / min; Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

7. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 1, characterized in that: Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements, the surface roughness Ra = 0.83μm, the deep drawing performance yield strength = 155MPa, the tensile strength = 301MPa, the elongation = 44%, n = 0.23, r = 2.6, and there are no color difference defects.

8. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 1, characterized in that: Its chemical composition by mass percentage is as follows: C: 0.0010%, Si: 0.007%, Mn: 0.12%, P: 0.0080%, S: 0.009%, Al: 0.031%, B: 0.0006%, N: 0.0018%, Ti: 0.069%, with the remainder being Fe and other impurities.

9. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 8, characterized in that: Specifically: Hot rolling process: Heating of continuously cast billets: The billet is heated to 1196℃ in the furnace for 226 minutes, held for 23 minutes, and then tapped out at 1192℃. Finishing mill final rolling: temperature 912℃, F7 exit speed 10.7m / s; pre-roll change and maintenance, roll cooling water nozzles unblocked; scale pressure 196MPa, descaling water valves open for each pass of the roughing mill, primary descaling mill roll speed 0.9m / s; finishing mill rolling oil flow rate 230ml / min; finishing mill interstand cooling activated at F1, F2, F3, and F5, cooling water flow rate 30%; finishing mill inlet strip temperature 996℃. Winding: Temperature 697℃, tension 22kN; after the product comes off the production line, a heat insulation cover is attached for slow cooling; Cold rolling process: Pickling: hydrochloric acid concentration 213 g / L, temperature 83℃, time 86 s; Emulsion: 4.3% concentration on the fifth stand, 2150 L / min injection flow rate, 50℃ temperature, and 43° contact angle of rolling oil; Pickling and rolling mill: Rolling: Total reduction rate 79%, reduction rates of each stand 31%, 24%, 18%, 14%, and 8%, speed 950 m / min; Annealing process: Continuous annealing profile: Preheating to 420℃ → Heating to 818℃ (rate 18℃ / min) → Soaking for 70s → Slow cooling to 677℃ (rate 9℃ / min) → Rapid cooling to 465℃ (rate 35℃ / min) → Over-aging at 460℃ (2s) → Equalization at 460℃ → Entering the zinc pot; Furnace speed 97m / min; Protective atmosphere: 7% H2 volume fraction, dew point -40℃; Leveling process: Elongation 0.8%, rolling force 895kN, work roll roughness Ra=2.5μm, speed 109m / min; Post-finishing treatment: Electrostatic oiling, oil application rate 700mg / m² 2 Each side.

10. The production method for solving the surface color difference of boron-containing deep-drawing IF steel according to claim 9, characterized in that: Finished product inspection results: The surface color difference level meets the enterprise standard FB requirements (no color difference is allowed), surface roughness Ra=0.88μm, deep drawing performance yield strength=150MPa, tensile strength=298MPa, elongation=46%, n=0.23, r=2.9, and there are no color difference defects.

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