A rolling method for solving uneven galvanizing of longitudinal rough strip

Abstract

This invention provides a rolling method to solve the problem of uneven galvanizing in longitudinally cut strip steel. Using a cast billet longitudinally flame-cut with a vertical side as the raw material, the method includes four steps: heating, rough rolling, finish rolling, and coiling. The rough rolling step employs a 2+N pass set of vertical rolling rollers for reciprocating rolling. First, two passes of adjusting vertical rollers are used to adjust the edge shape of the cast billet, appropriately lowering the edge line on the original open surface. Then, N passes of single-stand flat rollers are used for normal rolling. The opening of the adjusting vertical rollers is consistent with the width of the cast billet, and the reduction rate of the adjusting vertical rollers is zero. This invention controls the downward movement of the upper edge of the flame-cut surface of the cast billet, preventing the cut surface from being flipped onto the surface of the cast billet during subsequent rough rolling. Furthermore, combined with the finished product specifications, the total reduction from vertical to flat rolling is controlled, ensuring that when edge flipping occurs during the vertical rolling process, the flame-cut side remains at the edge of the rolled piece and does not flip upwards to affect the strip surface, thus eliminating the problem of uneven galvanizing at the edges of the longitudinally cut strip steel.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and in particular to a rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel. Background Technology

[0002] With economic development and continuous improvement in smelting technology, steel companies are increasingly producing wider continuously cast billets to improve production efficiency. They are also employing longitudinal cutting methods to divide the wider billets into two sections to meet the requirements of narrower billet widths. Currently, longitudinal cutting of billets typically uses flame cutting. However, the center of the continuously cast billet is a region where various elements tend to segregate. During flame cutting, this is equivalent to secondary melting, which leads to secondary segregation during cooling. This increases the concentration of elements such as C, Si, Mn, and Al, affecting the composition of the steel matrix and reducing the adhesion of subsequent localized galvanizing. Furthermore, during the widening process in hot rolling roughing, the cut surface flips onto the strip surface during vertical-horizontal rolling, causing zinc detachment at the edges of the strip surface during subsequent galvanizing, resulting in severe uneven galvanizing on the flame-cut side. Therefore, solving the problem of uneven galvanizing of longitudinally cut strips has become an urgent issue. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a rolling method for solving the problem of uneven galvanizing of longitudinally rolled strip steel, avoiding the strip from tipping over to the edge of the steel surface during flame-cutting rolling, thereby improving the downstream galvanizing quality.

[0004] The technical solution adopted by this invention to solve its technical problem is:

[0005] A rolling method for solving the problem of uneven galvanization in longitudinally cut steel strips uses a cast billet that has been longitudinally flame-cut with a vertical side as raw material. The method includes four steps: heating, rough rolling, finish rolling, and coiling. The rough rolling step uses a 2+N pass set of rough rolling vertical rolls for reciprocating rolling. First, two passes of adjusting vertical rolls are used to adjust the edge shape of the cast billet, so that the edge line on the original open billet surface is appropriately lowered. Then, N passes of single-stand flat rolls are used for normal rolling. The opening of the adjusting vertical rolls is consistent with the width of the cast billet, and the reduction rate of the adjusting vertical rolls is zero.

[0006] A further improvement of the present invention is that: the roller structure of the adjusting vertical roller includes an inverted conical portion at the top and a cylindrical portion at the bottom, the included angle α between the outer wall of the inverted conical portion and the vertical direction ranges from 10° to 30°, and the height L of the cylindrical portion... x =H-50~H-10, where H is the height of the billet.

[0007] A further improvement of the present invention is that the total reduction rate of roughing is controlled at 75% to 85%, and the total reduction ΔH of roughing satisfies the formula ΔH ≥ 0.234 (HL). x)-0.38α+68.86-2.86W+2.86W1,

[0008] H—Slab height, in mm;

[0009] L x — Height of the cylindrical section, in mm;

[0010] α—The angle between the outer wall of the inverted cone and the vertical direction, in degrees;

[0011] W—Total width of the cast billet, in mm;

[0012] W1—Width of intermediate billet after rolling, in mm.

[0013] A further improvement of the present invention is that the width W1 of the intermediate billet after rough rolling satisfies: W1≤HW / [H-(HL)] x )*sin 2 α].

[0014] A rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel specifically includes the following steps:

[0015] S1, Heating

[0016] After the billet is opened, the continuous casting billet is transported to the heating furnace for heating at a temperature of 1240℃~1260℃ for 90min~120min.

[0017] S2, rough rolling

[0018] The rolling process is carried out by a 2+N pass roughing roll group, with an initial rolling temperature of 1150℃.

[0019] S3, precision rolling

[0020] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 820℃~900℃, and each stand uses flat roll rolling.

[0021] S4, winding

[0022] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃~620℃.

[0023] The beneficial effects of this invention are:

[0024] This invention discloses a rolling method to solve the problem of uneven galvanization in longitudinally rolled strip. Before the roughing process, a special type of adjusting vertical roll is used to adjust the shape of the cast billet, controlling the downward movement of the upper edge of the flame-cut surface of the cast billet to prevent the cut surface from being flipped onto the surface of the cast billet during subsequent roughing. At the same time, combined with the specifications of the rolled product, the total reduction of the vertical-horizontal rolling in roughing is controlled so that when the edge flips during the vertical roll rolling process, the flame-cut side is always located at the edge of the rolled piece and will not flip up and affect the surface of the strip. In the subsequent finishing rolling step, it is always kept at the edge of the strip, thus achieving uniform control of the surface composition of the strip and eliminating the problem of uneven galvanization at the edge of the longitudinally rolled strip. Attached Figure Description

[0025] Figure 1 This is a diagram of the roll profile of the roughing mill adjusting vertical roll of the present invention;

[0026] Figure 2 This is the cross-sectional morphology of the billet after two roughing passes according to the present invention;

[0027] Figure 3 The shape of the head and tail of the billet after two passes of rough rolling;

[0028] Figure 4 This refers to the head and tail shapes of the intermediate billet after rough rolling;

[0029] Figure 5 This is a diagram showing the relationship between the length of the strip fishtail and the dimensions of the vertical roll;

[0030] Figure 6 This is a schematic diagram showing the changes in width and height during the rough rolling deformation process.

[0031] Figure 7 This is a photograph of the surface of the galvanized steel strip obtained in Example 1;

[0032] Figure 8 The image shown is an electron microscope (EM) image of the cross-section of the galvanized steel strip obtained in Example 1.

[0033] Figure 9 This is a photograph of the surface of the galvanized steel strip obtained in Example 2;

[0034] Figure 10 The image shown is an electron microscope image of the cross-section of the galvanized steel strip obtained in Example 2.

[0035] Figure 11 This is a photograph of the surface of the galvanized steel strip obtained in Example 3;

[0036] Figure 12 The image shown is an electron microscope image of the cross-section of the galvanized steel strip obtained in Example 3.

[0037] Figure 13 This is a photograph of the surface of the galvanized steel strip obtained in Comparative Example 1.

[0038] Figure 14 This is an electron microscope image of the cross-section of the galvanized steel strip obtained in Comparative Example 1. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] A rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel uses a flame-cut billet as raw material, with one longitudinal side of the billet being the flame-cut surface. Through five steps—heating, rough rolling, finish rolling, cooling, and coiling—uniformly galvanized longitudinally rolled strip steel is prepared.

[0041] Specifically, the rolling method includes the following steps:

[0042] S1, Heating

[0043] After the billet is opened, the continuous casting billet is transported to the heating furnace for heating at a temperature of 1240℃~1260℃ for 90min~120min.

[0044] S2, rough rolling

[0045] The roughing mill uses a 2+N pass set of vertical rolls for reciprocating rolling. Here, 2 is the rolling pass of the adjusting vertical rolls at the front of the roughing mill with zero reduction rate. The opening of the vertical rolls is consistent with the width of the billet. N is the rolling pass of the normal single-stand flat rolls. First, the adjusting vertical rolls at the front of the roughing mill are used to adjust the edge shape of the billet, so that the edge line on the original billet surface is appropriately lowered. Then, the normal rolling is carried out using the single-stand flat rolls.

[0046] The roller profile structure of the adjusting vertical roller is as follows: Figure 1 As shown, it includes an inverted conical portion at the top and a cylindrical portion at the bottom. The angle between the outer wall of the inverted conical portion and the vertical direction is α, and the value of α ranges from 10° to 30°. The height L of the cylindrical portion is... x =H-50~H-10, where H is the total height of the billet, in mm.

[0047] The initial rolling temperature of the roughing mill is 1150℃; the total reduction rate of the roughing mill is 75% to 85%, and the total reduction ΔH of the roughing mill satisfies the following formula:

[0048] △H≥0.234(HL x )-0.38α+68.86-2.86W+2.86W1

[0049] In the formula,

[0050] H—Slab height, in mm;

[0051] L x —Adjust the height of the cylindrical part of the vertical roller, in mm;

[0052] α — The angle between the outer wall of the inverted cone and the vertical direction, in degrees;

[0053] W—Total width of the cast billet, in mm;

[0054] W1—Width of intermediate billet after rolling, in mm;

[0055] The width W1 of the intermediate billet after rolling should also satisfy: W1≤HW / [H-(HL)] x )*sin 2 α].

[0056] During the calculation, the range of the total reduction amount △H is calculated in two ways, and the integer within the overlapping range is taken as the total reduction amount △H; then the reduction rate of the N passes of the flat roller is allocated based on the total reduction amount value.

[0057] S3, precision rolling

[0058] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 820℃~900℃, and each stand uses flat roll rolling.

[0059] S4, winding

[0060] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃~620℃.

[0061] In the roughing step of this invention, two sets of adjusting vertical rolls are installed before a conventional flat-roll roughing mill. These two sets of adjusting vertical rolls lower the upper edge of the flame-cut surface of the billet, as shown below. Figure 2 As shown, by combining the specifications of the rolled product and controlling the total reduction of the roughing vertical-horizontal rolling, the flame-cut side is always located at the edge of the rolled piece when the edge flips during the vertical roll rolling process, and will not flip to the surface of the strip steel, thereby eliminating the problem of uneven galvanizing at the edge of the longitudinally opened strip steel.

[0062] Regarding the roughing mill vertical roll profile: When using a flat-vertical roll configuration, during roughing, the vertical roll's side pressure creates dog-bone-like protrusions, which widen to varying degrees during the flat roll's pressing action. Meanwhile, the metal at the corners of the rolled piece slightly moves towards the top surface, resulting in side flattening. To prevent this flattening of the original billet's side surface, a perforated vertical roll is used to press the corners of the billet, reducing the height of the original side surface in the vertical plane. The vertical roll profile uses an upper inverted cone and a lower cylinder design, where the upper inverted cone has a cone angle of α and the cylinder height is L. x When a 2+N pass rolling process is adopted, the cross-sectional shape of the billet after the first two passes is as follows: Figure 2 As shown, the apex angle on the cut surface of the original billet decreases to the middle of the inclined surface under the rolling pressure of the inverted cone of the adjusting vertical roll. On the vertical surface, the height by which the boundary of the original side surface decreases is h. x =(H-Lx)*sin 2α. However, during the first two rolling passes, due to the small deformation of the corners of the workpiece by the vertical rolls, the deformation process only occurs at the corners of the workpiece, and under the action of the vertical rolls, longitudinal surface extension is generated along the direction of the workpiece, forming bulges on both sides of the upper surface, see... Figure 3 As shown, it extends during subsequent rolling, causing irregular head and tail shapes in the intermediate billet, resulting in a fishtail shape. Figure 4 As shown; and with the increase in the height L of the lower cylindrical roller x As the angle α decreases and the inclination angle increases, the length of the uneven deformation region at the head and tail of the rolled piece increases, ultimately increasing the amount of material removed from the head and tail. Based on continuous experimental statistics, the length of the fishtail at the head and tail is related to L. x The relationship between α and α is as follows: Figure 7 As shown, to keep the amount of head and tail resection within 250mm, L is taken. x H-50~H-10mm, α is 10°~30°.

[0063] Regarding the vertical-horizontal roughing rolling process: During the vertical-horizontal roughing rolling process, the deformation of the rolled piece can be decomposed into width expansion deformation and longitudinal elongation deformation. During the width expansion process, because the reduction in the side surface area of ​​the rolled piece is greater than the increase in the contact area between the roll and the rolled piece, a phenomenon of side-to-surface flattening occurs. For example... Figure 6 As shown, during the deformation process, the height at which the side flattens out is Δh, which can be decomposed into the width of the rolled piece as W. x The side height is H-Δh, and the length, width, and thickness of the longitudinally extended intermediate billet are L1, W1, and H1, respectively. Since the width remains constant during longitudinal extension deformation, according to the principle of constant volume, the decomposed width W... x The area of ​​the cross-section on the vertical plane remains unchanged. Therefore, according to the principle of constant volume, we know...

[0064] L*W*H=L1*W1*H1;

[0065] According to the width W x Since the area of ​​the cross section on the vertical plane remains unchanged, we can obtain (H-△h)*L=L1*H1;

[0066] △h=(L*H-L1*H1) / L=HW*H / W1.

[0067] To ensure that the original cast billet side surface does not flatten, Δh ≤ hx; that is, HW*H / W1 ≤ (HL) x )*sin 2 α, after conversion, the width W1 of the intermediate billet should satisfy the following formula:

[0068] W1≤HW / [H-(HL x )*sin 2 α];

[0069] In vertical roll rolling with an upper conical and lower cylindrical section, after the first two passes, chamfers appear on both sides of the upper surface of the workpiece. During subsequent rolling processes, the width expansion changes due to the chamfers on both sides. The width of the rolled workpiece is affected by the chamfers, decreasing compared to when there are no chamfers. Furthermore, the free width after rolling increases with the reduction in that pass and is affected by the chamfer length (HL). x The free width extension Δw after rolling decreases with the increase of the chamfer angle α and decreases with the decrease of the chamfer angle α. Linear regression analysis shows that the free width extension Δw after rolling is related to the cone angle α of the upper chamfer and the cylinder height L. x The relationship between the compression amount ΔH and the compression amount is as follows:

[0070] △w=0.35△H-0.082(HL x )+0.133α-24.1.

[0071] Then, after rolling, W1 ≤ Δw + W = 0.35ΔH - 0.082(HL) x )+0.133α-24.1+W, which is the total reduction in rough rolling.

[0072] △H≥0.234(HL x )-0.38α+68.86-2.86W+2.86W1, where L x H-50~H-10mm, α is 10°~30°.

[0073] The present invention will be further explained and illustrated below using examples and comparative examples.

[0074] Example 1

[0075] The dimensions of the continuously cast billet after roughing are 7.0m*500mm*200mm (length*width*height), and the design specifications for the rolled strip are 3.5mm*530mm.

[0076] The roughing mill adjusting vertical roll profile consists of an upper inverted cone section and a lower cylindrical section, with the cylindrical section having a height L. x =150mm, the angle α between the outer wall of the inverted cone and the vertical is 30°. Substitute these values ​​into the calculation to obtain the rolling width W1 of the intermediate billet after adjustment of the vertical rolls.

[0077] W1≤H*W / [H-(H-Lx)*sin 2 α]=200*500 / [200-(200-150)*sin 2 π / 6] = 533.3 mm, that is

[0078] W1≤533.3mm, the design specifications of the rolled strip are 3.5mm*530mm, and the roll type of the adjusting vertical roll meets the rolling requirements.

[0079] A rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel includes the following steps:

[0080] S1, Heating

[0081] The continuously cast billet after roughing is transported to a heating furnace for heating at a temperature of 1260℃ for 100 minutes.

[0082] S2, rough rolling

[0083] The roughing mill uses a 2+5 pass vertical roll group for reciprocating rolling. Pass 2 is the rolling pass of the adjusting vertical rolls at the front of the roughing mill with zero reduction. The opening of the vertical rolls is consistent with the width of the billet. Pass 5 is the rolling pass of the normal single-stand flat rolls. The adjusting vertical rolls at the front of the roughing mill are used first to adjust the edge shape of the billet, so that the edge line of the original billet surface is moved down. Then, the normal rolling is carried out using the single-stand flat rolls. The roughing mill opening temperature is 1150℃.

[0084] The total reduction ΔH in roughing rolling must meet two conditions simultaneously. The specific calculation process is as follows:

[0085] (1) Condition 1: △H≥[0.234(HL) x )-0.38α+68.86-2.86W+2.86*W1]

[0086] Substituting the values, △H≥[0.234(HL)] x )-0.38α+68.86-2.86W+2.86*W1]=

[0087] {0.234*(200-150)-0.38*30+68.86-2.86*500+2.86*530}=154.8mm;

[0088] That is, △H ≥ 154.8 mm;

[0089] (2) Condition 2: Total reduction rate is 75%–85%.

[0090] Substituting the values, the total reduction ΔH range at a total reduction rate of 75% to 85% is: 0.75*200mm~0.85*200mm=150mm~170mm, that is, ΔH=155mm~170mm;

[0091] Combining the two conditions △H≥154.8mm and △H=155mm~170mm, the integer within their overlapping range is taken, and the total reduction △H is set to 160mm. This is used to adjust the opening of the vertical rolls (the opening of the cylindrical part of the vertical rolls) in the two roughing passes and the roll gap value of the five flat rolls. The specific settings are as follows:

[0092] 1 500 200 2 500 200 3 500 150 4 550 110 5 530 80 6 550 55 7 530 40

[0093] S3, precision rolling

[0094] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 850℃. Each stand uses flat rolls to roll into a strip steel of 3.5mm*530mm.

[0095] S4, winding

[0096] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃.

[0097] Take a strip steel coil and measure its actual width; the fluctuation range is 530mm to 533mm, which is basically consistent with the expected width. After trimming the edges, pickling, and galvanizing, the surface of the galvanized steel strip appears as follows: Figure 7 As shown, the steel strip surface coating is smooth, and the quality of the flame-cut side is normal; its cross-sectional electron microscope image is as follows. Figure 8 As shown, the steel substrate surface is smooth and the coating thickness is uniform, all around 28μm.

[0098] Example 2

[0099] The dimensions of the continuous casting billet after roughing are 7.0m*500mm*200mm (length*width*height), and the design specifications for the rolled strip are 3.5mm*490mm.

[0100] The roughing mill adjusting vertical roll profile consists of an upper inverted cone section and a lower cylindrical section, with the cylindrical section having a height L. x =190mm, the angle α between the outer wall of the inverted cone and the vertical is 10°. Substitute these values ​​into the calculation to obtain the rolling width W1 of the intermediate billet after adjustment of the vertical rolls.

[0101] W1≤HW / [H-(HL x )*sin 2 α]=200*500 / [200-(200-190)*sin 2 π / 18] = 500.8 mm, that is

[0102] W1≤500.8mm; the design specifications for the rolled strip are 3.5mm*490mm, and the roll type of the adjusting vertical roll meets the rolling requirements.

[0103] A rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel comprises the following steps:

[0104] S1, Heating

[0105] The continuously cast billet after roughing is transported to a heating furnace for heating at 1260℃ for 100 minutes.

[0106] S2, rough rolling

[0107] A 2+5 pass roughing mill vertical roll group is used for reciprocating rolling. Pass 2 is the rolling pass with zero reduction rate for adjusting the vertical rolls before the roughing mill, with the roll opening consistent with the width of the cast billet. Pass 5 is the normal single-stand flat roll rolling pass. First, the adjusting vertical rolls before the roughing mill are used to adjust the edge shape of the cast billet, causing the edge line of the original billet surface to shift downwards. Then, normal rolling is performed using the single-stand flat rolls. The initial roughing temperature is 1150℃.

[0108] The total reduction ΔH in roughing rolling must meet two conditions simultaneously. The specific calculation process is as follows:

[0109] (1) Condition 1: △H≥[0.234(HL) x )-0.38α+68.86-2.86W+2.86*W1]

[0110] Substituting the values, △H≥[0.234(HL)] x )-0.38α+68.86-2.86W+2.86*W1]

[0111] =[0.234*(200-190)-0.38*10+68.86-2.86*500+2.86*490]=38.8mm;

[0112] That is, △H ≥ 38.8 mm;

[0113] (2) Condition 2: Total reduction rate is 75%–85%.

[0114] Substituting the values, the range of total reduction ΔH at a total reduction rate of 75%–85% is:

[0115] 0.75*200mm~0.85*200mm=150mm~170mm, that is, △H=155mm~170mm;

[0116] Combining the conditions △H≥38.8mm and △H=155mm~170mm, the integer within their overlapping range is taken, and the total reduction △H is set to 160mm. This is used to adjust the opening of the vertical rolls (the opening of the cylindrical part of the vertical rolls) in the two roughing passes and the roll gap value of the five flat rolls. The specific settings are as follows:

[0117] 1 500 200 2 500 200 3 500 150 4 530 110 5 490 80 6 530 55 7 490 40

[0118] S3, precision rolling

[0119] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 850℃. Each stand uses flat rolls to roll into a strip steel of 3.5mm*490mm.

[0120] S4, winding

[0121] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃.

[0122] The actual width of the strip measured after rolling fluctuated between 490mm and 492mm, which is basically consistent with the expected width. After edge trimming, pickling, and galvanizing, the surface of the galvanized strip is as follows: Figure 9 As shown, the coating on the surface and edges of the steel strip is smooth, and the quality of the flame-cut side is normal; its cross-sectional electron microscope image is shown below. Figure 10 As shown, the steel substrate surface is relatively smooth and the coating thickness is uniform.

[0123] Example 3

[0124] The dimensions of the continuous casting billet after roughing are 7.0m*450mm*180mm (length*width*height), and the design specifications for the rolled strip are 3.5mm*475mm.

[0125] The roughing mill adjusting vertical roll profile consists of an upper inverted cone section and a lower cylindrical section, with the cylindrical section having a height L. x =130mm, the angle α between the outer wall of the inverted cone and the vertical is 30°. Substitute these values ​​into the calculation to obtain the rolling width W1 of the intermediate billet after adjustment of the vertical rolls.

[0126] W1≤H*W / [H-(HL x )*sin 2 α]=180*450 / [180-(180-130)*sin 2 π / 6] = 483.6 mm, that is

[0127] W1≤483.6mm; the design specifications for the rolled strip are 3.5mm*475mm, and the roll type of the adjusting vertical roll meets the rolling requirements.

[0128] A rolling method for solving the problem of uneven galvanization in longitudinally rolled strip steel includes the following steps:

[0129] S1, Heating

[0130] The continuously cast billet after roughing is transported to a heating furnace for heating at 1260℃ for 100 minutes.

[0131] S2, rough rolling

[0132] The roughing mill uses a 2+5 pass vertical roll group for reciprocating rolling. Pass 2 is the rolling pass of the adjusting vertical rolls at the front of the roughing mill with zero reduction. The opening of the vertical rolls is consistent with the width of the billet. Pass 5 is the rolling pass of the normal single-stand flat rolls. The adjusting vertical rolls at the front of the roughing mill are used first to adjust the edge shape of the billet, so that the edge line of the original billet surface is moved down. Then, the normal rolling is carried out using the single-stand flat rolls. The roughing mill opening temperature is 1150℃.

[0133] The total reduction ΔH in roughing rolling must meet two conditions simultaneously. The specific calculation process is as follows:

[0134] (1) Condition 1: △H≥[0.234(HL) x )-0.38α+68.86-2.86W+2.86*W1]

[0135] Substituting the values, △H≥[0.234(HL)] x )-0.38α+68.86-2.86W+2.86*W1]

[0136] =[0.234*(180-130)-0.38*30+68.86-2.86*450+2.86*475]=140.7mm;

[0137] That is, △H ≥ 140.7 mm;

[0138] (2) Condition 2: Total reduction rate is 75%–85%.

[0139] Substituting the values, the range of total reduction ΔH at a total reduction rate of 75%–85% is:

[0140] 0.75*180mm~0.85*180mm=135mm~153mm, that is, △H=141mm~153mm;

[0141] Combining the two conditions △H≥140.7mm and △H=141mm~153mm, the integer within their overlapping range is taken, and the total reduction △H is set to 150mm. This is used to adjust the opening of the vertical rolls (the opening of the cylindrical part of the vertical rolls) in the two roughing passes and the roll gap value of the five flat rolls. The specific settings are as follows:

[0142] 1 450 180 2 450 180 3 450 140 4 500 100 5 475 70 6 500 50 7 475 30

[0143] S3, precision rolling

[0144] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 850℃. Each stand uses flat rolls to roll into a strip steel of 3.5mm*475mm.

[0145] S4, winding

[0146] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃.

[0147] The actual width of the strip measured after rolling fluctuated between 475-477 mm, which is basically consistent with the expected width. The strip was trimmed at the edges, pickled, and then galvanized. The surface of the galvanized strip was as follows: Figure 11 As shown, the coating on the surface and edges of the steel strip is smooth, and the quality of the flame-cut side is normal; its cross-sectional electron microscope image is shown below. Figure 12As shown, the steel substrate surface is smooth and the coating thickness is uniform.

[0148] Comparative Example 1

[0149] This comparative example is a comparative example of Example 1. The only difference between this comparative example and Example 1 is that the width of the intermediate billet is different. The width of the intermediate billet in this comparative example exceeds the calculation range.

[0150] The continuous casting billet and roughing mill adjusting vertical roll profile used in Example 1 and Comparative Example 1 are the same, that is, the dimensions of the continuous casting billet after billet preparation are 7.0m*500mm*200mm (length*width*height), and the roughing mill adjusting vertical roll profile adopts an upper inverted cone section + a lower cylindrical section, with the cylindrical section having a height L. x =150mm, the angle α between the outer wall of the inverted cone and the vertical direction is 30°.

[0151] Substitute into the calculation of the intermediate billet rolling width W1, W1≤H*W / [H-(HL)] x )*sin 2 α]

[0152] =200*500 / [200-(200-150)*sin 2 π / 6] = 533.3mm, that is, W1 ≤ 533.3mm.

[0153] The comparative example uses rolled strip steel with a specification of 3.5mm*535mm, which exceeds the requirement of W1≤533.3mm.

[0154] The rolling process includes the following steps:

[0155] S1, Heating

[0156] The continuously cast billet after roughing is transported to a heating furnace for heating at 1260℃ for 100 minutes.

[0157] S2, rough rolling

[0158] The roughing mill uses a 2+5 pass vertical roll group for reciprocating rolling. Pass 2 is the rolling pass of the adjusting vertical rolls at the front of the roughing mill with zero reduction. The opening of the vertical rolls is consistent with the width of the billet. Pass 5 is the rolling pass of the normal single-stand flat rolls. The adjusting vertical rolls at the front of the roughing mill are used first to adjust the edge shape of the billet, so that the edge line of the original billet surface is moved down. Then, the normal rolling is carried out using the single-stand flat rolls. The roughing mill opening temperature is 1150℃.

[0159] Based on the maximum width expansion Δw = 0.35ΔH - 0.082(HL) xTo ensure the intermediate billet width reaches 535mm, Δw ≥ 35mm is required, i.e., ΔH ≥ [35 + 24.1 - 0.133 * 30 + 0.082 * (200 - 150)] / 0.35 = 169.3mm, i.e., ΔH ≥ 169.3mm. At the same time, the total reduction ΔH range is calculated to be 0.75 * 200mm ~ 0.85 * 200mm = 150mm ~ 170mm under a total reduction rate of 75% to 85%. Combining the two ranges of ΔH ≥ 169.3mm and ΔH = 169.3mm ~ 170mm, the integer value of the overlapping range is taken, i.e., the total reduction ΔH is taken as 170mm.

[0160] The first two passes are rolled with a 0 reduction rate. The vertical roll opening (cylindrical vertical roll opening) and the flat roll gap are set as follows for each pass.

[0161] 1 500 200 2 500 200 3 500 150 4 550 110 5 535 80 6 550 50 7 535 30

[0162] S3, precision rolling

[0163] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 850℃. Each stand uses flat rolls to roll into a strip steel of 3.5mm*535mm.

[0164] S4, winding

[0165] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃.

[0166] The strip steel coil was taken, and the actual width of the rolled strip ranged from 535mm to 538mm, which is basically consistent with the expected width. After pickling and galvanizing the edges of the strip steel, obvious uneven galvanizing strip defects were found within a 10mm range on the flame-cut side edge. See [link to relevant documentation]. Figure 8 As shown.

[0167] The strip steel was trimmed, pickled, and then galvanized. The surface of the galvanized steel strip was as follows: Figure 12 As shown, there are obvious uneven galvanizing strip-like defects within a 10mm range on the side of the flame-cut section; its cross-sectional electron microscope image is shown below. Figure 13 As shown, the coating thickness is obviously uneven, with the thickest part reaching 52μm and the thinnest part only 6.7μm, showing a significant difference.

[0168] This comparative example shows that when the rolling width of the intermediate billet exceeds the limit, during the deformation process under the pressure of the vertical roll and the flat roll, with a fixed total reduction, as the pressure of the vertical roll decreases, the drum-shaped width of the dog bone decreases, and the flattening width increases. This causes more of the side of the rolled piece to flip to the surface. That is, the position of the top corner of the original billet's cut surface, which is lowered under the rolling pressure of the inverted cone of the vertical roll, will still be transferred to the middle of the intermediate billet during the subsequent rolling process. As a result, a part of the original cut surface will still be located on the edge of the strip surface after rolling, affecting the subsequent galvanizing.

[0169] Comparative Example 2

[0170] This comparative example is a comparative example of Example 1. The only difference between this comparative example and Example 1 is that the total reduction ΔH in rough rolling is different. The total reduction ΔH in this comparative example is beyond the calculation range.

[0171] The dimensions of the continuously cast billet after roughing are 7.0m*500mm*200mm (length*width*height). The roughing mill adjusting vertical roll profile adopts an upper inverted cone section + a lower cylindrical section, with the cylindrical section having a height of L. x =150mm, the angle α between the outer wall of the inverted cone and the vertical is 30°. The intermediate billet rolling width W1 ≤ H*W / [H-(HL)] x )*sin 2 α]=200*500 / [200-(200-150)*sin 2 π / 6]=533.3mm, that is, W1≤533.3mm; the rolled strip specification is taken as 3.5mm*530mm, which meets the rolling requirements.

[0172] S1, Heating

[0173] The continuously cast billet after roughing is transported to a heating furnace for heating at 1260℃ for 100 minutes.

[0174] S2, rough rolling

[0175] The roughing mill uses a 2+5 pass vertical roll group for reciprocating rolling. Pass 2 is the rolling pass of the adjusting vertical rolls at the front of the roughing mill with zero reduction. The opening of the vertical rolls is consistent with the width of the billet. Pass 5 is the rolling pass of the normal single-stand flat rolls. The adjusting vertical rolls at the front of the roughing mill are used first to adjust the edge shape of the billet, so that the edge line of the original billet surface is moved down. Then, the normal rolling is carried out using the single-stand flat rolls. The roughing mill opening temperature is 1150℃.

[0176] Total reduction during rough rolling ΔH ≥ [0.234(HL)] x )-0.38α+68.86-2.86W+2.86*W1]

[0177] =[0.234*(200-150)-0.38*30+68.86-2.86*500+2.86*530]=154.8mm;

[0178] In addition, the total reduction range corresponding to a total reduction rate of 75% to 85% is 0.75*200mm.

[0179] 0.85 * 200 mm = 150 mm ~ 170 mm, that is, △H = 155 mm ~ 170 mm.

[0180] In this comparative example, the nearest integer outside the two ranges of ΔH ≥ 154.8 mm and ΔH = 155 mm to 170 mm is taken, so the total reduction ΔH is taken as 150 mm.

[0181] The first two passes are rolled with a 0 reduction rate. The vertical roll opening (cylindrical vertical roll opening) and the flat roll gap are set as follows for each pass.

[0182] 1 500 200 2 500 200 3 500 160 4 550 130 5 530 100 6 550 70 7 530 50

[0183] S3, precision rolling

[0184] The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 850℃. Each stand uses flat rolls to roll into a strip steel of 3.5mm*530mm.

[0185] S4, winding

[0186] After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃.

[0187] The actual width of the strip measured after rolling fluctuated between 523mm and 527mm, which was lower than the expected width. The strip dimensions were unqualified and could not meet the requirements of the strip products.

[0188] This comparative example shows that when the total reduction in roughing is insufficient, the driving force for the workpiece to flow in the width direction is low during the deformation process under the flat roll, and the width expansion is reduced, resulting in the width of the strip after rolling being lower than the specification requirements.

[0189] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A rolling method for solving unevenness of galvanizing of longitudinal slit cast strip, characterized by: Using a cast billet longitudinally cut by flame with a vertical side as raw material, the process includes four steps: heating, rough rolling, finish rolling, and coiling. The rough rolling step uses a 2+N pass rough rolling vertical roll group for reciprocating rolling. First, two passes of adjusting vertical rolls are used to adjust the edge shape of the cast billet, so that the edge line on the original billet surface is appropriately lowered. Then, N passes of single-stand flat rolls are used for normal rolling. The opening of the adjusting vertical rolls is consistent with the width of the cast billet, and the reduction rate of the adjusting vertical rolls is zero. The roller structure of the adjusting vertical roller includes an inverted conical portion at the top and a cylindrical portion at the bottom. The angle α between the outer wall of the inverted conical portion and the vertical direction ranges from 10° to 30°, and the height L of the cylindrical portion is... x =H-50~H-10, where H is the height of the billet; The total reduction rate of roughing is controlled between 75% and 85%, and the total reduction ΔH of roughing satisfies the formula ΔH ≥ 0.234(HL). x )-0.38α+68.86-2.86W+2.86W1, H—Slab height, in mm; L x —cylindrical part height, in mm; α—The angle between the outer wall of the inverted cone and the vertical direction, in degrees; W—Total width of the cast billet, in mm; W1—Width of intermediate billet after rolling, in mm; The intermediate blank width W1 after rough rolling satisfies: W1≤HW / [H-(H-L x )×sin 2 α] The rolling method specifically includes the following steps: S1, Heating After the billet is opened, the continuous casting billet is transported to the heating furnace for heating at a temperature of 1240℃~1260℃ for 90min~120min. S2, rough rolling The rolling process is carried out by a 2+N pass roughing roll group, with an initial rolling temperature of 1150℃. S3, precision rolling The intermediate billet after rough rolling is sent to the finishing mill for rolling. The final rolling temperature is 820℃~900℃, and each stand uses flat roll rolling. S4, winding After finishing, the strip steel is cooled by laminar flow and then coiled and packaged at a coiling temperature of 580℃~620℃.

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