Method for improving continuous pickling quality of high-silicon cold-rolled ultra-high strength steel

Abstract

The present invention discloses a method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel, belonging to the field of metallurgical technology. It includes the processes of steelmaking, hot rolling, temper rolling, and pickling. In the pickling process, the tension leveling machine adopts a bending leveling mode, the leveling tension is 250 - 400 KN, and the leveling parameters are controlled in grades according to the Si content in the ultra-high-strength steel. The pickling time is controlled within 40 - 60 s, and the pickling speed is set according to the coiling temperature. The present invention has the advantages of low process control difficulty, strong operability, simple method, and low cost. The white brightness L value of the surface color of the high-silicon cold-rolled high-strength steel produced by the present invention is ≥ 70, and the dark chroma h ≤ 13.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel. Background Art

[0002] In the cold rolling production of high-silicon cold-rolled ultra-high-strength steel, it often occurs that the surface scale is difficult to remove and the surface turns black. During the rolling process, accidents such as roll skidding and strip cracking often occur, seriously affecting the production rhythm of acid-rolled high-strength steel and reducing production efficiency. Therefore, strip cold rolling generally needs to go through tension leveling and pickling to remove the scale of hot-rolled raw materials. At present, most strip pickling processes are continuous pickling processes, that is, the tail of the previous hot-rolled strip coil and the head of the next coil are welded together and continuously passed through several pickling tanks for pickling.

[0003] As one of the main elements of ultra-high-strength steel, Si cannot form carbides at high temperatures and usually exists in the oxide layer in the form of solid solution oxides, resulting in a high viscosity of its oxide layer, a strong bonding force with the matrix, deteriorating the oxide layer stripping ability, reducing the effect of high-pressure water descaling. During the subsequent rolling process, the unpeeled oxide layer will be pressed into the strip surface, causing product downgrading.

[0004] The invention patent "A Heating Method and Device for Silicon Steel Pickling Line" with the publication number CN 101519784B and the invention patent "CGO Oriented Silicon Steel One-Stage Rolling Acid Continuous Rolling Process Method" with the publication number CN 109365526B respectively propose corresponding pickling processes for different silicon steels, and the silicon content in silicon steel is generally relatively high, with the silicon content being 3% or more. The research of the literature "Research on High-Temperature Oxidation and Oxide Layer Removal of Fe-Si Alloy Steel Plates" shows that original cracks reaching the internal oxidation zone will appear in the outer oxide layer of silicon steel after coiling and cooling. During the pickling process, the HCl solution can penetrate into the oxide layer along the original cracks, resulting in the preferential lateral dissolution of the low-valent oxides that are easily soluble in the inner layer. Therefore, silicon steel can skip the "incubation period" and directly enter the "acceleration period" at the initial stage of pickling, and ultimately, under the same cooling conditions, the pickling time of silicon steel is shorter. However, the silicon content in high-silicon cold-rolled ultra-high-strength steel is generally lower than that in silicon steel. Empirically, it is known that if the usual pickling method is used, the dissolution rate of the surface scale becomes slower.

[0005] Cold-rolled ultra-high-strength steel generally contains relatively more alloying elements, especially the addition of alloying elements such as Cr, Ni, and Nb, which further deteriorates the oxide layer stripping ability together with the Cu and As elements introduced during the steelmaking and ironmaking processes. And due to the relatively high silicon content in high-silicon cold-rolled ultra-high-strength steel, the removal of the oxide layer is more difficult. During the production process, tension leveling and pickling are generally combined to improve the pickling effect, but it is still difficult to achieve the removal effect of the oxide layer of high-silicon cold-rolled ultra-high-strength steel.

[0006] Therefore, the use of a reasonable pickling process to improve the surface quality of high-silicon cold-rolled ultra-high-strength steel strip has become a key factor in reducing the cost of pickling and improving the yield rate. Summary of the invention

[0007] The invention provides a method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel, so as to solve the technical problems of poor surface quality of high-silicon ultra-high-strength steel pickling plates and difficulty in removing iron oxide scale.

[0008] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is:

[0009] A method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel, comprising steelmaking, hot rolling, leveling, and pickling processes;

[0010] In the pickling process, the straightening machine adopts the bending straightening mode, the straightening tension is 250-400KN, and the straightening parameters are controlled in stages according to the Si content in the ultra-high strength steel, specifically:

[0011] When 0.4%≤Si content<0.8%, the tensile elongation is 1.0~2.0%, and the toothing amount is 30~35mm;

[0012] When 0.8%≤Si content<1.3%, the tensile elongation is 1.0~2.0%, and the tooth length is 36~40mm;

[0013] When the Si content is 1.3%≤≤2.5%, the tensile elongation is 1.0~2.2%, and the tooth length is 41~45mm;

[0014] The pickling time is controlled at 40 to 60 seconds. The pickling speed is set according to the coiling temperature. Specifically:

[0015] When 400℃≤coiling temperature<600℃, the maximum pickling speed is 200m / min;

[0016] When 600℃≤coiling temperature<650℃, the maximum pickling speed is 180m / min;

[0017] When 650℃≤coiling temperature≤700℃, the maximum pickling speed is 150m / min;

[0018] The minimum pickling speed for the weld area is 30m / min; except for the weld area, the minimum pickling speed for other areas is 60m / min.

[0019] In the pickling process of the present invention, anti-wrinkle rollers are used at the uncoiling position, the pressing force is controlled at 35-45 KN, the head and tail of the hot-rolled strip are laser welded, the welding speed is 0.8-1.2 m / s, the welding power is 7-10 KW, and the welding seam heating temperature before and after welding is controlled at 500°C±50°C.

[0020] For the pickling process described in the present invention, a shallow-tank turbulent pickling process is adopted. The free acid concentrations in the three pickling tanks are successively: 60 - 100 g / L, 100 - 140 g / L, and 140 - 200 g / L. The concentration of the accelerator in the three pickling tanks is 0.2 - 0.5 wt%. The iron ion concentration in the acid solution is ≤ 130 g / L. The pickling temperature is 80 - 90 °C, and the acid solution spraying pressure is 0.25 - 0.35 MPa. When the acid solution concentration in the 1# pickling tank is < 60 g / L or the iron ion concentration in the acid solution > 130 g / L, waste acid is discharged once. In other cases, waste acid is discharged once every 50 coils produced, so as to reduce the formation of complexes of excessive iron and silicon elements in the acid solution and their adhesion to the strip surface, thereby reducing the pickling effect.

[0021] For the steelmaking process described in the present invention, smelting is carried out in a converter, and after LF refining + RH vacuum treatment, it is continuously cast into slab. Among them, the requirements for the molten steel composition are: O ≤ 0.05%, S ≤ 0.05%, Ca 0.0025 - 0.0035%, and As ≤ 0.003%.

[0022] The hot rolling process described in the present invention includes the steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1200 - 1250 °C, the holding time is 180 - 240 min, and the H2S atmosphere in the heating atmosphere is ≤ 75 mg / m 3 , and the descaling water pressure for rough rolling is 19 - 30 MPa.

[0023] In the hot rolling process described in the present invention, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1150 - 1250 °C; secondary scale is removed before finish rolling of the rough rolled slab; the starting rolling temperature for finish rolling is 1000 - 1050 °C, the finishing rolling temperature is 870 - 920 °C, the cumulative reduction of finish rolling is 85 - 95%, the rolling speed of finish rolling is 5 - 10 m / s, the descaling water pressure for finish rolling is 20 - 25 MPa, and the oil film lubrication pressure is 2 - 6 Mpa; before rolling, it is ensured that the water pressure impact force of the overlapping part of the finish rolling nozzles is more than 85% of the water pressure at the nozzle position.

[0024] For the skin pass rolling process described in the present invention, the hot rolled strip is skin pass rolled on the skin pass rolling line in a 1 - 3% elongation mode.

[0025] The composition of the ultra-high strength steel described in the present invention includes the following main elements (wt%): C: 0.06 - 0.25%, Si: 0.4 - 2.5%, Mn: 1.0 - 2.8%, Cr: 0.2 - 0.65%, Nb ≤ 0.08%, Ti ≤ 0.1%; among them, Si + Cr ≥ 0.8%, and Nb + Ti ≥ 0.03%.

[0026] The yield strength of the ultra-high strength steel described in the present invention is ≥ 500 MPa, and the tensile strength is ≥ 780 MPa.

[0027] The most important indicators for evaluating the surface color of the steel plate are the white brightness L value and the dark chromaticity h. The larger the L value, the whiter and brighter the steel plate, indicating better pickling effect; conversely, the smaller the h value, the whiter and brighter the steel plate, indicating better pickling effect. The range of the L value is 0-100, and the range of the h value is 0-30. The white brightness L value of the surface color of the high-silicon cold-rolled high-strength steel produced by the method of the present invention is ≥70, and the dark chromaticity h≤13.

[0028] Compared with the prior art, the present invention has the advantages of small process control difficulty, strong operability, simple method, low cost, etc. The present invention utilizes the existing equipment and process conditions of the steel rolling mill, which neither increases equipment investment and production cost, nor can effectively remove the oxide layer of the high-silicon cold-rolled ultra-high-strength steel, and provides guarantee for the subsequent rolling stability, and provides strong technical support for the high-quality development of high-silicon cold-rolled high-strength steel and even cold-rolled high-strength steel in automobile lightweighting. Detailed implementation mode

[0029] The present invention will be further described in detail below with reference to specific embodiments. Embodiment 1

[0030] The composition of the cold-rolled ultra-high-strength steel in this embodiment includes the following main elements (wt%): C: 0.06%, Mn: 1.75%, Si: 0.5%, Cr: 0.3%, Ti: 0.09%.

[0031] The yield strength of the cold-rolled ultra-high-strength steel in this embodiment is 500-560 MPa, and the tensile strength is 780-830 MPa.

[0032] The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel in this embodiment includes steelmaking, hot rolling, tempering, and pickling processes. The specific steps are as follows:

[0033] (1) Steelmaking process: Smelted by a converter, and after LF refining + RH vacuum treatment, continuously cast into slab. Among them, the composition of the molten steel is O: 0.04 wt%, S: 0.05 wt%, Ca: 0.0035 wt%, As: 0.001%.

[0034] (2) Hot rolling process: It includes the steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1200 °C, the holding time is 180 min, and the H2S atmosphere in the heating atmosphere is 75 mg / m 3 , and the descaling water pressure for rough rolling is 19 MPa;

[0035] Hot rolling process: In R1 + R2, a 3 + 5 pass mode is adopted, and the starting rolling temperature is 1150 °C. Secondary scale is removed from the rough-rolled slab before finish rolling. The starting rolling temperature for finish rolling is 1000 °C, the final rolling temperature is 870 °C, the cumulative reduction ratio in finish rolling is 85%, the rolling speed in finish rolling is 5 m / s, the descaling water pressure in finish rolling is 24 MPa, and the oil film lubrication pressure is 3 MPa. The water pressure impact force at the overlapping part of the spray nozzles before finish rolling is 86 - 92% of the water pressure at the nozzle position.

[0036] (3)Skin pass rolling process: The hot-rolled strip is skin pass rolled on the skin pass line in a 1% elongation mode.

[0037] (4)Pickling process: Anti-wrinkle rollers are used at the uncoiling station, and the pressing force is controlled at 37 KN. The head and tail of the hot-rolled strip are laser welded, the welding speed is 0.9 m / s, the welding power is 7 KW, and the heating temperature of the weld seam before and after welding is controlled at 450 °C - 480 °C;

[0038] The tension leveling machine adopts the bending and leveling mode, the tension leveling tension is 250 - 400 KN, the tension leveling elongation is 1.0 - 2.0% according to the Si content in the ultra-high strength steel, and the bite amount is 30 - 35 mm;

[0039] A shallow-tank turbulent pickling process is adopted. The free acid concentrations in the three pickling tanks are 90 g / L, 120 g / L, and 150 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.2% of the acid solution mass, and the iron ion concentration in the acid solution is 125 g / L. The pickling temperature is 80 - 90 °C, and the acid solution spraying pressure is 0.25 MPa. Waste acid is discharged once when the acid concentration in the 1# pickling tank < 60 g / L or the iron ion concentration in the acid solution > 130 g / L, and in other cases, waste acid is discharged once every 50 coils to reduce the formation of complexes of excessive iron and silicon elements in the acid solution adhering to the strip surface and reduce the pickling effect.

[0040] According to the coiling temperature of 700 °C, the pickling speed is set at 150 m / min, and the pickling time is controlled at 60 s; the minimum pickling speed at the weld seam part is 30 m / min; except for the weld seam part, the minimum pickling speed at the other parts is 60 m / min.

[0041] The white brightness L value of the surface color of the cold-rolled ultra-high strength steel obtained in this example is 85, and the dark chromaticity h value is 5.0. Example 2

[0042] The composition of the cold-rolled ultra-high strength steel in this example includes the following main elements (wt%): C: 0.21%, Mn: 2.2%, Si: 1.2%, Cr: 0.2%, Nb: 0.02%, Ti: 0.06%.

[0043] The yield strength of the cold-rolled ultra-high strength steel in this example is 830 - 960 MPa, and the tensile strength is 1180 - 1260 MPa.

[0044] The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel in this embodiment includes steelmaking, hot rolling, temper rolling, and pickling processes. The specific steps are as follows:

[0045] (1) Steelmaking process: Smelt using a converter, and after LF refining + RH vacuum treatment, continuously cast into slabs. Among them, in the molten steel composition, O: 0.05 wt%, S: 0.05 wt%, Ca: 0.0035 wt%, As: 0.002%.

[0046] (2) Hot rolling process: It includes steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1250 °C, the holding time is 210 min, and the H2S atmosphere in the heating atmosphere is 55 mg / m 3 , and the descaling water pressure for rough rolling is 30 MPa;

[0047] In the hot rolling process, the R1+R2 adopts a 3+5 pass mode, and the starting rolling temperature is 1150 °C; secondary scale is removed before finish rolling of the rough rolled slab; the starting rolling temperature of finish rolling is 1000 °C, the finishing rolling temperature is 920 °C, the cumulative reduction of finish rolling is 95%, the rolling speed of finish rolling is 10 m / s, the descaling water pressure for finish rolling is 24 MPa, and the oil film lubrication pressure is 3 MPa. The water pressure impact force of the overlapping part of the spray nozzles before finish rolling is 87-95% of the water pressure at the nozzle position.

[0048] (3) Temper rolling process: Temper the hot rolled strip in the temper rolling line using a 3% elongation mode.

[0049] (4) Pickling process: Anti-wrinkle rollers are used at the uncoiler, and the pressing force is controlled at 35 KN. The head and tail of the hot rolled strip are laser welded, the welding speed is 0.8 m / s, the welding power is 10 KW, and the heating temperature of the weld before and after welding is controlled at 480 °C - 530 °C;

[0050] The tension leveling machine adopts a bending leveling mode, the leveling tension is 250 - 400 KN, and the leveling elongation is 1.0 - 2.0% according to the Si content in the ultra-high strength steel, and the bite amount is 36 - 40 mm;

[0051] Adopt a shallow groove turbulent flow pickling process. The free acid concentrations in the three pickling tanks are 90 g / L, 140 g / L, and 200 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.2% of the acid solution mass, and the iron ion concentration of the acid solution is 121 g / L. The pickling temperature is 90 °C, and the acid solution spraying pressure is 0.35 MPa. When the acid solution concentration in the 1# pickling tank < 60 g / L or the iron ion concentration of the acid solution > 130 g / L, waste acid is discharged once. In other cases, waste acid is discharged once every 50 coils produced to reduce the formation of complexes of excessive iron and silicon elements in the acid solution and adhere to the strip surface, reducing the pickling effect.

[0052] According to the coiling temperature of 600 °C, set the pickling speed to 180 m / min, and control the pickling time within 40 s; the minimum pickling speed at the weld part is 30 m / min; except for the weld part, the minimum pickling speed at the other parts is 60 m / min.

[0053] The white brightness L value of the surface color of the cold-rolled ultra-high strength steel obtained in this example is 85, and the dark chroma h value is 5.0. Example 3

[0054] The composition of the cold-rolled ultra-high strength steel in this example includes the following main elements (wt%): C: 0.25%, Mn: 1.85%, Si: 2.5%, Cr: 0.3%, Nb: 0.02%, Ti: 0.10%.

[0055] The yield strength of the cold-rolled ultra-high strength steel in this example is 1330 - 1408 MPa, and the tensile strength is 1510 - 1660 MPa.

[0056] The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel in this example includes steelmaking, hot rolling, tempering, and pickling processes. The specific steps are as follows:

[0057] (1) Steelmaking process: Use a converter for smelting, and after LF refining + RH vacuum treatment, continuously cast into slabs. Among them, in the molten steel composition, O: 0.03 wt%, S: 0.04 wt%, Ca: 0.0030 wt%, As: 0.0021%.

[0058] (2) Hot rolling process: It includes steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1206 °C, the holding time is 240 min, and the H2S atmosphere in the heating atmosphere is 35 mg / m 3 , and the descaling water pressure for rough rolling is 19 MPa;

[0059] In the hot rolling process, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1150 °C; remove the secondary scale from the rough rolled slab before finish rolling; the starting rolling temperature for finish rolling is 1050 °C, the final rolling temperature is 890 °C, the cumulative reduction of finish rolling is 90%, the rolling speed of finish rolling is 7 m / s, the descaling water pressure for finish rolling is 22 MPa, and the oil film lubrication pressure is 4 MPa. The water pressure impact force of the overlapping part of the spray nozzles before finish rolling is 86 - 94% of the water pressure at the nozzle position.

[0060] (3) Tempering process: Temper the hot-rolled strip in the tempering line in a 1% elongation mode.

[0061] (4) Pickling process: Use an anti-wrinkle roll at the uncoiling position, control the pressing force at 35 KN, laser weld the head and tail of the hot-rolled strip, the welding speed is 1.0 m / s, the welding power is 10 KW, and control the heating temperature of the weld before and after welding at 470 °C - 520 °C;

[0062] The tension leveling machine adopts the bending and leveling mode, with a tension leveling tension of 250 - 400 KN, a tension leveling elongation of 1.0 - 2.2% according to the Si content in the ultra-high strength steel, and a bite amount of 41 - 55 mm;

[0063] The shallow groove turbulent flow pickling process is adopted. The free acid concentrations in the three pickling tanks are 80 g / L, 130 g / L, and 180 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.2% of the acid solution mass, and the iron ion concentration of the acid solution is 121 g / L. The pickling temperature is 85 °C, and the acid solution spraying pressure is 0.25 MPa. When the acid solution concentration in the 1# pickling tank < 60 g / L or the iron ion concentration of the acid solution > 130 g / L, waste acid is discharged once. In other cases, waste acid is discharged once every 50 coils to reduce the formation of complexes of excessive iron and silicon elements in the acid solution adhering to the strip surface and reduce the pickling effect.

[0064] According to the coiling temperature of 530 °C, the pickling speed is set to 200 m / min, and the pickling time is controlled within 40 s; the minimum pickling speed at the weld part is 30 m / min; except for the weld part, the minimum pickling speed at the other parts is 60 m / min.

[0065] The white brightness L value of the surface color of the cold-rolled ultra-high strength steel obtained in this example is 70, and the dark chromaticity h value is 8.9. Example 4

[0066] The composition of the cold-rolled ultra-high strength steel in this example includes the following main elements (wt%): C: 0.10%, Mn: 2.5%, Si: 0.4%, Cr: 0.65%, Nb: 0.05%.

[0067] The yield strength of the cold-rolled ultra-high strength steel in this example is 730 - 908 MPa, and the tensile strength is 980 - 1040 MPa.

[0068] The method for improving the continuous pickling quality of the high-silicon cold-rolled ultra-high strength steel in this example includes the steelmaking, hot rolling, tempering, and pickling processes, and the specific steps are as follows:

[0069] (1) Steelmaking process: Smelting is carried out using a converter, and after LF refining + RH vacuum treatment, it is continuously cast into a slab. Among them, in the molten steel composition, O: 0.045 wt%, S: 0.04 wt%, Ca: 0.0025 wt%, As: 0.0015%.

[0070] (2) Hot rolling process: It includes the steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1205 °C, the holding time is 202 min, and the H2S atmosphere in the heating atmosphere is 66 mg / m 3 , and the descaling water pressure for rough rolling is 25 MPa;

[0071] In the hot rolling process, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1250 °C; secondary scale is removed before the rough rolled slab enters the finish rolling; the starting rolling temperature of the finish rolling is 1010 °C, the final rolling temperature is 900 °C, the cumulative reduction of the finish rolling is 87%, the rolling speed of the finish rolling is 8 m / s, the descaling water pressure of the finish rolling is 25 MPa, and the oil film lubrication pressure is 2 MPa. The water pressure impact force at the overlapping part of the spray nozzles before the finish rolling is 85 - 92% of the water pressure at the nozzle position.

[0072] (3)Skin pass rolling process: The hot rolled strip is skin pass rolled on the skin pass rolling line with a 2% elongation mode.

[0073] (4)Pickling process: Anti - wrinkling rollers are used at the uncoiling position, and the pressing force is controlled at 35 KN. The head and tail of the hot rolled strip are laser welded, the welding speed is 0.8 m / s, the welding power is 8 KW, and the heating temperature of the weld before and after welding is controlled at 460 °C - 500 °C;

[0074] The tension leveling machine adopts a bending and leveling mode, the leveling tension is 250 - 400 KN, the leveling elongation is 1.0 - 2.0% according to the Si content in the ultra - high strength steel, and the bite amount is 30 - 35 mm;

[0075] A shallow - trough turbulent - flow pickling process is adopted. The free acid concentrations in the three pickling tanks are 85 g / L, 119 g / L, and 165 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.5% of the acid solution mass, and the iron ion concentration in the acid solution is 117 g / L. The pickling temperature is 84 °C, and the acid solution spraying pressure is 0.30 MPa. When the acid concentration in the 1# pickling tank < 60 g / L or the iron ion concentration in the acid solution > 130 g / L, waste acid is discharged once. In other cases, waste acid is discharged once every 50 coils to reduce the formation of complexes of excessive iron and silicon elements in the acid solution attaching to the strip surface and reducing the pickling effect.

[0076] According to the coiling temperature of 570 °C, the maximum pickling speed is set to 200 m / min, and the pickling time is controlled at 45 s; the minimum pickling speed at the weld part is 30 m / min; except for the weld part, the minimum pickling speed at the other parts is 60 m / min.

[0077] The white brightness L value of the surface color of the cold - rolled ultra - high strength steel obtained in this example is 87, and the dark chroma h value is 10.8. Example 5

[0078] The component composition of the cold - rolled ultra - high strength steel in this example includes the following main elements (wt%): C: 0.06%, Mn: 1.0%, Si: 1.5%, Cr: 0.50%, Nb: 0.02%, Ti: 0.04%.

[0079] The yield strength of the cold - rolled ultra - high strength steel in this example is 608 - 710 Mpa, and the tensile strength is 800 - 930 MPa.

[0080] The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel in this embodiment includes steelmaking, hot rolling, tempering, and pickling processes, and the specific steps are as follows:

[0081] (1) Steelmaking process: Smelt in a converter, and after LF refining + RH vacuum treatment, continuously cast into slabs. The chemical composition of the molten steel is O: 0.03wt%, S: 0.02wt%, Ca: 0.0025wt%, and As: 0.0017%.

[0082] (2) Hot rolling process: It includes steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1220°C, the holding time is 202 min, and the H2S atmosphere in the heating atmosphere is 52 mg / m 3 , and the descaling water pressure for rough rolling is 25 MPa;

[0083] In the hot rolling process, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1230°C; secondary scale is removed before finish rolling of the rough rolled slab; the starting rolling temperature of finish rolling is 1040°C, the final rolling temperature is 900°C, the cumulative reduction of finish rolling is 88%, the rolling speed of finish rolling is 6 m / s, the descaling water pressure of finish rolling is 20 MPa, and the oil film lubrication pressure is 5 MPa. The water pressure impact force of the overlapping part of the spray nozzles before finish rolling is 86 - 95% of the water pressure at the nozzle position.

[0084] (3) Tempering process: Temper the hot rolled strip in the tempering line in a 1.5% elongation mode.

[0085] (4) Pickling process: Anti-wrinkle rollers are used at the uncoiler, and the pressing force is controlled at 43 KN. The head and tail of the hot rolled strip are laser welded, the welding speed is 1.0 m / s, the welding power is 9 KW, and the heating temperature of the weld seam before and after welding is controlled at 480 - 530°C;

[0086] The tension leveling machine adopts a bending leveling mode, the leveling tension is 250 - 400 KN, the leveling elongation is 1.0 - 2.2% according to the weight content of Si in the ultra-high-strength steel, and the bite amount is 41 - 45 mm;

[0087] Adopt a shallow tank turbulent flow pickling process. The free acid concentrations in the three pickling tanks are 90 g / L, 100 g / L, and 150 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.2% of the acid solution mass, and the iron ion concentration of the acid solution is 117 g / L. The pickling temperature is 80 - 90°C, and the acid solution spraying pressure is 0.28 MPa. When the acid solution concentration in the 1# pickling tank < 60 g / L or the iron ion concentration of the acid solution > 130 g / L, waste acid is discharged once. In other cases, waste acid is discharged once every 50 coils to reduce the formation of complexes of excessive iron and silicon elements in the acid solution and adhesion to the strip surface, thereby reducing the pickling effect.

[0088] According to the coiling temperature of 610°C, the maximum pickling speed is set to 180 m / min, and the pickling time is 50 s; the minimum pickling speed at the weld part is 30 m / min; except for the weld part, the minimum pickling speed at the remaining parts is 60 m / min.

[0089] The L value of the whiteness brightness of the surface color of the cold-rolled ultra-high-strength steel obtained in this example is 79, and the h value of the dark chromaticity is 12. Example 6

[0090] The composition of the cold-rolled ultra-high-strength steel in this example includes the following main elements (wt%): C: 0.17%, Mn: 2.8%, Si: 1.0%, Cr: 0.45%, Nb: 0.05%.

[0091] The yield strength of the cold-rolled ultra-high-strength steel in this example is 708 - 850 MPa, and the tensile strength is 990 - 1085 MPa.

[0092] The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel in this example includes steelmaking, hot rolling, tempering, and pickling processes. The specific steps are as follows:

[0093] (1) Steelmaking process: Smelt using a converter, and after LF refining + RH vacuum treatment, continuously cast into slabs. Among them, in the molten steel composition, O: 0.04 wt%, S: 0.05 wt%, Ca: 0.0029 wt%, As: 0.0011%.

[0094] (2) Hot rolling process: Includes slab heating → rough rolling → finish rolling → coiling → hot coil finished product steps. The temperature of slab heating is controlled at 1205°C, the holding time is 190 min, and the H2S atmosphere in the heating atmosphere is 40 mg / m 3 , and the descaling water pressure for rough rolling is 20 MPa;

[0095] In the hot rolling process, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1220°C; secondary scale is removed before finish rolling of the rough rolling slab; the starting rolling temperature for finish rolling is 1030°C, the final rolling temperature is 907°C, the cumulative reduction of finish rolling is 90%, the rolling speed of finish rolling is 9 m / s, the descaling water pressure for finish rolling is 23 MPa, and the oil film lubrication pressure is 6 MPa. The water pressure impact force at the overlapping part of the finish rolling nozzle spray before rolling is 88 - 96% of the water pressure at the nozzle position.

[0096] (3) Tempering process: Temper the hot-rolled strip in the tempering line using a 2.6% elongation rate mode.

[0097] (4) Pickling process: Use an anti-wrinkle roll at the uncoiler, control the pressing force at 41 KN, laser weld the head and tail of the hot-rolled strip, the welding speed is 1.2 m / s, the welding power is 8.5 KW, and the heating temperature of the weld before and after welding is controlled at 510°C - 550°C;

[0098] The tension leveling machine adopts the bending and leveling mode, with a tension leveling tension of 250 - 400 KN, a tension leveling elongation of 1.0 - 2.0% according to the Si content in the ultra-high strength steel, and a bite amount of 36 - 40 mm;

[0099] The shallow groove turbulent flow pickling process is adopted. The free acid concentrations in the three pickling tanks are 60 g / L, 110 g / L, and 140 g / L in sequence. The concentration of the accelerator in the three pickling tanks is 0.4% of the acid solution mass, and the iron ion concentration of the acid solution is 117 g / L. The pickling temperature is 80 °C, and the acid solution spraying pressure is 0.27 MPa. Waste acid is discharged once when the acid solution concentration in the 1# pickling tank < 60 g / L or the iron ion concentration of the acid solution > 130 g / L, and once every 50 coils produced in other cases, in order to reduce the formation of complexes of excessive iron and silicon elements in the acid solution and the attachment of the complexes to the strip surface, thus reducing the pickling effect.

[0100] According to the coiling temperature of 650 °C, the maximum pickling speed is set to 150 m / min, and the pickling time is 45 s; the minimum pickling speed at the weld part is 30 m / min; except for the weld part, the minimum pickling speed at other parts is 60 m / min.

[0101] The white brightness L value of the surface color of the cold-rolled ultra-high strength steel obtained in this example is 77, and the dark chromaticity h value is 11.5.

Claims

1. A method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel, characterized in that, It includes steelmaking, hot rolling, skin pass rolling, and pickling processes; In the pickling process, the tension leveling machine adopts a bending and leveling mode, the leveling tension is 250 - 400 KN, and the leveling parameters are controlled in grades according to the Si content in the ultra-high strength steel. Specifically: When 0.4% ≤ Si content < 0.8%, the leveling elongation is 1.0 - 2.0%, and the bite amount is 30 - 35 mm; When 0.8% ≤ Si content < 1.3%, the leveling elongation is 1.0 - 2.0%, and the bite amount is 36 - 40 mm; When 1.3% ≤ Si content ≤ 2.5%, the leveling elongation is 1.0 - 2.2%, and the bite amount is 41 - 45 mm; The pickling time is controlled within 40 - 60 s, and the pickling speed is set according to the coiling temperature. Specifically: When 400℃ ≤ coiling temperature < 600℃, the maximum pickling speed is 200 m / min; When 600℃ ≤ coiling temperature < 650℃, the maximum pickling speed is 180 m / min; When 650℃ ≤ coiling temperature ≤ 700℃, the maximum pickling speed is 150 m / min; The minimum pickling speed at the weld position is 30 m / min; Except for the weld position, the minimum pickling speed of the remaining parts is 60 m / min; The composition of the ultra-high strength steel includes the following elements with the main contents: C: 0.06 - 0.25 wt%, Si: 0.4 - 2.5 wt%, Mn: 1.0 - 2.8 wt%, Cr: 0.2 - 0.65 wt%, Nb ≤ 0.08 wt%, Ti ≤ 0.1 wt%; where Si + Cr ≥ 0.8 wt%, Nb + Ti ≥ 0.03 wt%.

2. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 1, wherein In the pickling process, an anti-wrinkle roll is used at the uncoiler, the pressing force is controlled at 35 - 45 KN, the head and tail of the hot-rolled strip are laser welded, the welding speed is 0.8 - 1.2 m / s, the welding power is 7 - 10 KW, and the heating temperature of the weld before and after welding is controlled at 500℃ ± 50℃.

3. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 2, characterized in that, In the pickling process, a shallow-tank turbulent pickling process is adopted. The free acid concentrations in the three pickling tanks are 60 - 100 g / L, 100 - 140 g / L, and 140 - 200 g / L in sequence. The concentrations of the accelerator in the three pickling tanks are all 0.2 - 0.5 wt%, the iron ion concentration of the acid solution is ≤ 130 g / L, the pickling temperature is 80 - 90℃, and the acid solution spraying pressure is 0.25 - 0.35 MPa.

4. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 3, characterized in that In the steelmaking process, converter smelting is adopted. After LF refining + RH vacuum treatment, it is continuously cast into slab. The requirements for the molten steel composition are O ≤ 0.05 wt%, S ≤ 0.05 wt%, Ca 0.0025 - 0.0035 wt%, and As ≤ 0.003 wt%.

5. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 4, wherein The hot rolling process includes the steps of slab heating → rough rolling → finish rolling → coiling → hot coil finished product. The temperature of slab heating is controlled at 1200 - 1250 °C, the holding time is 180 - 240 min, and the H2S atmosphere in the heating atmosphere is ≤ 75 mg / m 3 , and the descaling water pressure for rough rolling is 19 - 30 MPa.

6. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 5, characterized in that, For the hot rolling process, R1 + R2 adopts a 3 + 5 pass mode, and the starting rolling temperature is 1150 - 1250 °C; the secondary scale is removed from the rough rolled slab before finish rolling; the finish rolling starting temperature is 1000 - 1050 °C, the finishing rolling temperature is 870 - 920 °C, the cumulative reduction of finish rolling is 85 - 95%, the rolling speed of finish rolling is 5 - 10 m / s, the descaling water pressure of finish rolling is 20 - 25 MPa; the oil film lubrication pressure is 2 - 6 MPa; before rolling, it is ensured that the water pressure impact force of the overlapping part of the finish rolling nozzles is more than 85% of the water pressure at the nozzle position.

7. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high strength steel according to claim 6, characterized in that, For the temper rolling process, the hot rolled strip is temper rolled on the temper rolling line in a mode with an elongation rate of 1 - 3%.

8. The method for improving the continuous pickling quality of high-silicon cold-rolled ultra-high-strength steel according to claim 7, characterized in that, The yield strength of the ultra-high strength steel is ≥500 MPa, and the tensile strength is ≥780 MPa.