Control method for eliminating 300 series stainless steel roll mark defects

Abstract

The application discloses a control method for eliminating 300 series stainless steel roll mark defects, which is used in a 1549mm hot continuous rolling production line, and comprises the following steps: when a heating furnace is used to heat a strip steel, the soaking section furnace temperature of the heating furnace is controlled to be 10-20℃ lower than the second heating section furnace temperature; when a finishing mill is used to roll the strip steel, a dynamic reduction rate distribution mode is used to determine the reduction rate of each rack of the finishing mill, and the reduction rates of the F0 rack, the F1 rack and the F2 rack are controlled to be not more than the corresponding preset upper limit values of the reduction rates; when a laminar cooling device is used to cool the strip steel, a preset cooling strategy is used to strongly cool the strip steel to a coiling target temperature, and the coiling target temperature is less than the corresponding oxidation temperature of the strip steel. The control method for eliminating 300 series stainless steel roll mark defects can significantly reduce the proportion of roll mark defects of the 300 series stainless steel in the hot rolling process, thereby reducing the cost of the cold rolling process and improving the cold rolling yield.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, and in particular to a control method for eliminating roll trace defects in 300 series stainless steel. Background Technology

[0002] refer to Figure 1 The existing 1549mm hot continuous rolling production line includes a furnace area, a roughing mill area, a finishing mill area, a laminar flow cooling area, and a coiling area arranged in sequence. The furnace area includes four heating furnaces arranged in sequence. The roughing mill area includes a high-pressure water descaling box, a roughing vertical roll mill (VE0), a roughing horizontal roll mill (R0), and a heat insulation cover arranged in sequence. The finishing mill area includes a rotary drum-type flying shear, a 7-stand finishing mill, a crown gauge and a straightness gauge, as well as a width gauge and a thickness gauge arranged in sequence. The laminar flow cooling area is equipped with laminar flow cooling equipment. The coiling area has two coilers (C1, C2). The main production process of the 1549mm hot continuous rolling production line is as follows: The slab is first heated in a heating furnace at the temperature specified by the process. After being heated to the target temperature, it enters the roughing mill for rolling. The vertical rolls of the roughing mill control the width, and the horizontal rolls control the thickness. Reversible rolling is carried out in the roughing mill, generally in 5 to 7 passes. After the rolling of the roughing mill, the strip steel reaches the preset target thickness, width and temperature. Then it enters the finishing mill for seven-stand horizontal roll continuous rolling, so that the strip steel reaches the preset target thickness and temperature. After that, the strip steel is cooled by laminar flow control to reach the target coiling temperature. Finally, the strip steel is formed into a steel coil by the coiler.

[0003] 300 series stainless steel is an austenitic stainless steel. Due to its excellent acid resistance and oxidation resistance, as well as good high and low temperature mechanical properties and biocompatibility, it is widely used in industrial fields and is widely used in household products, medical devices, food industry, chemical industry, coal industry, petroleum industry and other fields.

[0004] Surface quality is the most important quality indicator for stainless steel, directly affecting its usability. Surface defects in stainless steel are the most significant factor influencing product quality. (Reference) Figure 3Roll mark defects are a common surface quality issue in the production of 300 series stainless steel on 1549mm hot continuous rolling lines. The industry's analysis of the mechanism behind these defects is as follows: During hot rolling, the strip easily adheres to the rolls, damaging the oxide film on the roll surface and creating linear defects along the rolling direction. These defects, initially generated during hot rolling, are difficult to detect due to the surface oxide film and only become apparent during subsequent annealing and pickling processes. In severe cases, they can spread across the entire surface. These defects cannot be eliminated by subsequent cold rolling processes, ultimately forming continuous linear pits on the surface of the cold-rolled product, severely affecting its appearance. Because roll mark defects cannot be eliminated by cold rolling, in actual production, the steel strip must be cut off or ground before cold rolling when they occur, which significantly impacts the production cost and yield of the cold rolling process.

[0005] Regarding the problem of roll trace defects in stainless steel, based on the above mechanism analysis, current research proposes control methods such as using high-temperature rolling in the hot rolling process, using high-speed steel rolls in the roughing and finishing rolling zones, and using balanced reduction rates to eliminate roll trace defects. However, in actual production, these control methods still cannot solve the roll trace defect problem in the production of 300 series stainless steel on a 1549mm hot continuous rolling line. Summary of the Invention

[0006] To address some or all of the technical problems existing in the prior art, the present invention provides a control method for eliminating roller trace defects in 300 series stainless steel.

[0007] The technical solution of the present invention is as follows:

[0008] A control method for eliminating roll trace defects in 300 series stainless steel is provided, the method being used in a 1549mm hot continuous rolling production line, comprising:

[0009] When heating strip steel in a heating furnace, the temperature of the soaking zone of the heating furnace should be controlled to be 10℃~20℃ lower than that of the second heating zone.

[0010] When rolling strip steel using a finishing mill, a dynamic reduction rate distribution method is adopted to determine the reduction rate of each stand of the finishing mill, and the reduction rates of the F0 stand, F1 stand and F2 stand are controlled not to exceed their corresponding preset reduction rate upper limit values.

[0011] When using laminar flow cooling equipment to cool strip steel, a preset cooling strategy is adopted to force-cool the strip steel to the target coiling temperature, which is lower than the corresponding oxidation temperature of the strip steel.

[0012] In some possible implementations, the furnace temperatures of the secondary heating section and soaking section of the heating furnace are as follows, depending on the different grades of 300 series stainless steel:

[0013] steel grades Target furnace temperature for the second heating section / °C Target furnace temperature in the soaking section / ℃ Furnace temperature difference / ℃ 301 series stainless steel 1255 1245 -10 304 series stainless steel 1257 1243 -16 316 series stainless steel 1260 1240 -20

[0014] To take control.

[0015] In some possible implementations, a dynamic reduction rate allocation method is used to determine the reduction rate of each stand in the finishing mill, and the reduction rates of stands F0, F1, and F2 are controlled to not exceed their corresponding preset reduction rate upper limits, including:

[0016] The initial reduction rate of each rack is calculated using the following formula. If the reduction rate of racks F0, F1, and F2 exceeds their corresponding preset reduction rate upper limit, the initial reduction rate of racks F0, F1, and F2 is taken as their corresponding preset reduction rate upper limit.

[0017] eps(i)=RF(i)*GBZWK / MH(i) / nnfkorr(i)

[0018] Calculate the exit thickness of each rack based on the currently determined rack reduction ratio;

[0019] Compare the difference between the final stand exit thickness and the target finishing thickness. If the ratio of the difference to the target finishing thickness is within the range of -1% to 1%, the current stand reduction rate is taken as the final stand reduction rate. If the ratio of the difference to the target finishing thickness is greater than 1%, the reduction rate of each stand is increased by 0.5%, and the comparison thickness and difference are recalculated. If the ratio of the difference to the target finishing thickness is less than -1%, the reduction rate of each stand is decreased by 0.05%, and the comparison thickness and difference are recalculated. If the reduction rate of the F0 stand, F1 stand, and F2 stand after the addition exceeds their corresponding preset reduction rate upper limit, the reduction rate of the F0 stand, F1 stand, and F2 stand is taken as their corresponding preset reduction rate upper limit.

[0020] Where i represents the finishing mill stand number, i = 0, 1, 2, 3, 4, 5, 6, i = 0 to 6, representing stands F0 to F6 respectively, eps(i) represents the initial reduction rate of the i-th stand, RF(i) represents the given reduction rate of the i-th stand, GBZWK represents the maximum rolling pressure of each stand of the finishing mill, MH(i) represents the hardness value of the steel in the i-th stand, and nnfkorr(i) represents the calculated pressure correction coefficient of the i-th stand.

[0021] In some possible implementations, the upper limit of the reduction rate for F0, F1, and F2 stands, for different grades of 300 series stainless steel, is calculated and determined according to the following table:

[0022]

[0023] When the target thickness of the finished rolling of 301 / 304 series stainless steel is between 3.0mm and 4.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit of the reduction rate corresponding to 3.0mm and 4.0mm; when the target thickness of the finished rolling of 301 / 304 series stainless steel is between 4.0mm and 5.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit of the reduction rate corresponding to 4.0mm and 5.0mm; when the target thickness of the finished rolling of 316 series stainless steel is between 4.0mm and 5.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit of the reduction rate corresponding to 4.0mm and 5.0mm.

[0024] Wherein, Lim_F0_h, Lim_F1_h, and Lim_F2_h represent the upper limit values ​​of the F0 rack reduction rate, the F1 rack reduction rate, and the F2 rack reduction rate, respectively.

[0025] In some possible implementations, the following is set: when the target thickness of stainless steel finishing rolling is 3.0mm, 4.0mm, and 5.0mm, the thickness is represented by h(j), the upper limit of the reduction rate is represented by Lim_Fi_h(j), i represents the finishing mill stand number, j represents the thickness category, and j = 0, 1, and 2 represent the upper limit of the reduction rate when the thickness is 3.0mm, 4.0mm, and 5.0mm, respectively.

[0026] When the target thickness h of stainless steel finishing rolling is between h(j) and h(j+1), the upper limit value of the reduction rate of the i-th stand corresponding to thickness h is calculated and determined using the following formula:

[0027] Lim_Fi_h=[Lim_Fi_h(j+1)-Lim_Fi_h(j)] / [h(j+1)-h(j)]*[hh(j)]+Lim_Fi_h(j).

[0028] In some possible implementations, the laminar flow cooling equipment is equipped with an upper valve, a lower valve, and a side-blowing valve, with the upper and lower valves comprising 48 sets of valves;

[0029] Laminar flow cooling equipment includes a strong cooling zone, a coarse adjustment zone, and a fine adjustment zone;

[0030] The forced cooling zone includes valves 1 through 24. The maximum flow rate of both the upper and lower valves of valves 1 through 24 is 150 m³ / s. 3 / h, both the upper and lower valves are regulating valves, and the water spray volume during rolling can be adjusted arbitrarily within the maximum water volume;

[0031] The coarse adjustment zone includes valves #25 to #40. The maximum flow rate of both the upper and lower valves of valves #25 to #40 is 66.6 m³. 3 / h, both the upper and lower valves are on / off valves, the water spray is at the maximum water volume and cannot be adjusted;

[0032] The fine-tuning zone includes valves 41 to 48. The maximum water flow rate of both the upper and lower valves of valves 41 to 48 is 33.3 m³. 3 / h, both the upper and lower valves are on / off valves, the water spray is at the maximum water volume and cannot be adjusted;

[0033] The maximum water flow of the side-blowing valve is 5m³. 3 / h is the on / off valve, and the water spray is at the maximum water volume, which cannot be adjusted;

[0034] Preset cooling strategies include:

[0035] Both the upper and lower valves are selected with valve #3 as the starting valve;

[0036] Both the upper and lower valves are opened sequentially from front to back to spray water, with the lower valve opened first and the upper valve opened last.

[0037] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0038] All side-blowing valves are open and water is being sprayed.

[0039] In some possible implementations, the target coiling temperature for different grades of 300 series stainless steel is as follows:

[0040] steel grades Target winding temperature (°C) 301 series stainless steel 670 304 series stainless steel 690 316 series stainless steel 730

[0041] To take control.

[0042] The main advantages of the technical solution of this invention are as follows:

[0043] The control method for eliminating roll trace defects in 300 series stainless steel of the present invention reduces the proportion of roll trace defects in 300 series stainless steel in the hot rolling process by adjusting the temperature difference between the heating furnace soaking section and the second heating section, limiting the reduction rate of the stand before finishing rolling, and reducing the coiling temperature by laminar flow cooling. This reduces the cost of the cold rolling process and increases the yield of cold rolled products. Attached Figure Description

[0044] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0045] Figure 1 This is a schematic diagram of the equipment layout for an existing 1549mm hot strip rolling production line.

[0046] Figure 2 for Figure 1 Schematic diagram of the layout of the mid-laminar flow cooling equipment;

[0047] Figure 3 This invention provides a diagram of roller mark defects on the surface of 300 series stainless steel.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1-Finishing rolling temperature measurement point, 2-Upper valve, 3-Lower valve, 4-Side blowing valve, 5-Laminar flow cooling target temperature measurement point. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0051] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0052] To address the roll mark defects encountered when producing 300 series stainless steel using a 1549mm hot continuous rolling line, research revealed that these defects are not caused by roll adhesion, and the roll surface remains intact after rolling. A strong correlation exists between roll mark defects and whether the steelmaking process (the step before hot rolling) involves grinding. Grinded billets account for over 40% of roll mark defects in the hot rolling process, while un-grinded billets account for approximately 10%. Furthermore, a strong correlation exists between roll mark defects and coiling temperature; lower coiling temperatures result in a lower proportion of roll mark defects.

[0053] Grinding is a process in steelmaking where a high-speed rotating grinding wheel grinds the surface of a slab to remove surface defects and oxide layers, a crucial method for improving product quality. While grinding aims to remove defects generated during steelmaking, it can easily lead to roll marks during hot rolling. Based on this, analysis suggests that roll marks in 300 series stainless steel are caused by tiny uneven areas on the slab surface during hot rolling, while those found in cold rolling are due to oxidation of these tiny defects on the strip surface during air cooling.

[0054] Since grinding is essential for eliminating defects in steelmaking, roll mark defects must be eliminated by improving the hot rolling process.

[0055] Therefore, for the production of 300 series stainless steel using a 1549mm hot continuous rolling production line, one embodiment of the present invention provides a control method for eliminating roll mark defects in 300 series stainless steel, the method comprising:

[0056] When heating strip steel in a heating furnace, the temperature of the soaking zone of the heating furnace should be controlled to be 10℃~20℃ lower than that of the second heating zone.

[0057] When rolling strip steel using a finishing mill, a dynamic reduction rate distribution method is adopted to determine the reduction rate of each stand of the finishing mill, and the reduction rates of the F0 stand, F1 stand and F2 stand are controlled not to exceed their corresponding preset reduction rate upper limit values.

[0058] When using laminar flow cooling equipment to cool strip steel, a preset cooling strategy is adopted to force-cool the strip steel to the target coiling temperature, which is lower than the corresponding oxidation temperature of the strip steel.

[0059] In a 1549mm hot strip rolling production line, each heating furnace is divided into four heating sections: a preheating section, a first heating section, a second heating section, and a soaking section, arranged sequentially. In the existing 1549mm hot strip rolling production line, when producing 300 series stainless steel, the heating furnaces employ a high-temperature heating method for temperature control. The furnace temperature of the first heating section is 1200℃, and the target furnace temperature for the second heating section is the same as that of the soaking section, both being 1250℃.

[0060] In one embodiment of the present invention, when heating strip steel in a heating furnace, by controlling the temperature of the heating furnace in the soaking section to be 10°C to 20°C lower than that in the second heating section, the uniformity of the strip steel heating in the heating furnace can be improved and the generation of roll defects can be reduced.

[0061] Specifically, after the strip steel is heated in the first heating section and the second heating section, the use of a lower temperature in the homogenization section can make the surface temperature and the center temperature of the strip steel uniform. The uniform temperature of the strip steel can make the strip steel be subjected to uniform stress during the rolling process, thereby reducing the occurrence of roll defects.

[0062] Furthermore, in one embodiment of the present invention, for different grades of 300 series stainless steel, the furnace temperatures of the second heating section and the soaking section of the heating furnace are controlled according to the following table:

[0063] Table 1. Furnace Temperature Control Table for Various Grades of 300 Series Stainless Steel

[0064] steel grades Target furnace temperature for the second heating section / °C Target furnace temperature in the soaking section / ℃ Furnace temperature difference / ℃ 301 series stainless steel 1255 1245 -10 304 series stainless steel 1257 1243 -16 316 series stainless steel 1260 1240 -20

[0065] In one embodiment of the present invention, by controlling the furnace temperature of the second heating section and the soaking section of the heating furnace according to the furnace temperature parameters specifically set above, the proportion of roll marks generated in 300 series stainless steel during hot rolling can be significantly reduced.

[0066] Since 300 series stainless steel is among the steel grades with higher rolling pressure in the 1549mm hot strip mill production line, in order to ensure the load balance of each stand and prevent malfunctions such as overcurrent and pressure exceeding limits, the existing 1549mm hot strip mill production line uses the "RF" load distribution method, i.e., dynamic reduction rate distribution method, to control and determine the reduction rate of the finishing mill stands when producing 300 series stainless steel.

[0067] The dynamic reduction rate allocation method specifically includes the following:

[0068] The initial reduction ratio of each rack is calculated using the following formula;

[0069] eps(i)=RF(i)*GBZWK / MH(i) / nnfkorr(i)

[0070] Calculate the exit thickness of each rack based on the currently determined rack reduction ratio;

[0071] Compare the difference between the final stand exit thickness and the target finishing thickness. If the ratio of the difference to the target finishing thickness is within the range of -1% to 1%, then the current stand reduction rate is taken as the final stand reduction rate. If the ratio of the difference to the target finishing thickness is greater than 1%, then the reduction rate of each stand is increased by 0.5%, and the comparison thickness and difference are recalculated. If the ratio of the difference to the target finishing thickness is less than -1%, then the reduction rate of each stand is decreased by 0.05%, and the comparison thickness and difference are recalculated.

[0072] Where i represents the finishing mill stand number, i = 0, 1, 2, 3, 4, 5, 6, i = 0 to 6, representing stands F0 to F6 respectively; eps(i) represents the initial reduction rate of the i-th stand; RF(i) represents the given reduction rate of the i-th stand, i.e., the planned reduction distribution of the stand load; GBZWK represents the maximum rolling pressure of each stand of the finishing mill, specifically 40000KN; MH(i) represents the hardness value of the steel in the i-th stand; and nnfkorr(i) represents the calculated pressure correction coefficient for the i-th stand, specifically 0.3 to 1.5.

[0073] For details on the dynamic reduction rate allocation method, please refer to the Chinese patent document with publication number CN106825064A and invention title "Method for Adjusting Reduction Rate of Thin Steel Plate Finishing Rolling on 1549mm Rolling Mill".

[0074] Under the above-mentioned reduction rate control method, the finishing mill load distribution is balanced (rolling pressure distribution is balanced) and the rolling is stable. However, there are frequent fluctuations in the reduction rate during the rolling process, especially significant fluctuations in the reduction rate of the front stand.

[0075] Research has revealed that roll mark defects in 300 series stainless steel primarily occur in stands F0 to F2, and the proportion of roll mark defects increases when the reduction rate is too high. Therefore, in one embodiment of this invention, when rolling strip steel using a finishing mill, a dynamic reduction rate allocation method is employed to determine the reduction rate of each stand in the finishing mill, and the reduction rates of stands F0, F1, and F2 are controlled to not exceed their corresponding preset upper limit values.

[0076] Specifically, a dynamic reduction rate allocation method is adopted to determine the reduction rate of each stand of the finishing mill, and the reduction rates of stands F0, F1, and F2 are controlled to not exceed their corresponding preset upper limit values, including the following:

[0077] The initial reduction rate of each rack is calculated using the following formula. If the reduction rate of racks F0, F1, and F2 exceeds their corresponding preset reduction rate upper limit, the initial reduction rate of racks F0, F1, and F2 is taken as their corresponding preset reduction rate upper limit.

[0078] eps(i)=RF(i)*GBZWK / MH(i) / nnfkorr(i)

[0079] Calculate the exit thickness of each rack based on the currently determined rack reduction ratio;

[0080] Compare the difference between the final stand exit thickness and the target finishing thickness. If the ratio of the difference to the target finishing thickness is within the range of -1% to 1%, the current stand reduction rate is taken as the final stand reduction rate. If the ratio of the difference to the target finishing thickness is greater than 1%, the reduction rate of each stand is increased by 0.5%, and the comparison thickness and difference are recalculated. If the ratio of the difference to the target finishing thickness is less than -1%, the reduction rate of each stand is decreased by 0.05%, and the comparison thickness and difference are recalculated. If the reduction rate of the F0, F1, and F2 stands after the addition exceeds their corresponding preset reduction rate upper limit, the reduction rate of the F0, F1, and F2 stands is taken as their corresponding preset reduction rate upper limit.

[0081] In one embodiment of the present invention, when rolling strip steel using a finishing mill, a dynamic reduction rate distribution method is adopted to determine the reduction rate of each stand of the finishing mill, and the reduction rates of the F0 stand, F1 stand and F2 stand are controlled not to exceed their corresponding preset reduction rate upper limit values. This can not only ensure a balanced distribution of rolling pressure and stable rolling, but also reduce the probability of stainless steel roll trace defects, reduce the cost of cold rolling process, and improve the yield of stainless steel.

[0082] Furthermore, in one embodiment of the present invention, for different grades of 300 series stainless steel, the upper limit values ​​of the reduction rate corresponding to the F0 stand, F1 stand, and F2 stand are calculated and determined according to the following table:

[0083] Table 2 Upper Limits of Frame Reduction Rate for Various Grades of 300 Series Stainless Steel (F0-F2)

[0084]

[0085] Specifically, when the target thickness of the finished rolling of 301 / 304 series stainless steel is between 3.0mm and 4.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit values ​​of the reduction rate corresponding to 3.0mm and 4.0mm given in the table above; when the target thickness of the finished rolling of 301 / 304 series stainless steel is between 4.0mm and 5.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit values ​​of the reduction rate corresponding to 4.0mm and 5.0mm given in the table above; and when the target thickness of the finished rolling of 316 series stainless steel is between 4.0mm and 5.0mm, the upper limit of the reduction rate is calculated using interpolation based on the upper limit values ​​of the reduction rate corresponding to 4.0mm and 5.0mm given in the table above.

[0086] Wherein, Lim_F0_h, Lim_F1_h, and Lim_F2_h represent the upper limit values ​​of the F0 rack reduction rate, the F1 rack reduction rate, and the F2 rack reduction rate, respectively.

[0087] Specifically, the following explains how to use interpolation to calculate the upper limit of the reduction rate:

[0088] Setting: When the target thickness of stainless steel finishing rolling is 3.0mm, 4.0mm, and 5.0mm, the thickness is represented by h(j), and the upper limit of the reduction rate is represented by Lim_Fi_h(j). i represents the finishing mill stand number, j represents the thickness category, and j = 0, 1, and 2 represent the upper limit of the reduction rate when the thickness is 3.0mm, 4.0mm, and 5.0mm, respectively.

[0089] Based on the above settings, the upper limit values ​​of the reduction rate of the F0 stand when the target thickness of the finishing mill is 3.0mm, 4.0mm, and 5.0mm are represented as Lim_F0_h(0), Lim_F0_h(1), and Lim_F0_h(2), respectively; the upper limit values ​​of the reduction rate of the F1 stand when the target thickness of the finishing mill is 3.0mm, 4.0mm, and 5.0mm are represented as Lim_F1_h(0), Lim_F1_h(1), and Lim_F1_h(2), respectively; and the upper limit values ​​of the reduction rate of the F2 stand when the target thickness of the finishing mill is 3.0mm, 4.0mm, and 5.0mm are represented as Lim_F2_h(0), Lim_F2_h(1), and Lim_F2_h(2).

[0090] Based on the above settings, when calculating the upper limit value of reduction rate using the interpolation method, when the target thickness h of the stainless steel finish rolling is between h(j) and h(j + 1), the upper limit value Lim_Fi_h of the reduction rate of the i-th stand corresponding to the thickness h satisfies the following formula:

[0091] [Lim_Fi_h - Lim_Fi_h(j)] / [h - h(j)] = [Lim_Fi_h(j + 1) - Lim_Fi_h(j)] / [h(j + 1) - h(j)]

[0092] According to the above formula, the upper limit value Lim_Fi_h of the reduction rate can be specifically calculated and determined using the following formula:

[0093] Lim_Fi_h = [Lim_Fi_h(j + 1) - Lim_Fi_h(j)] / [h(j + 1) - h(j)] * [h - h(j)] + Lim_Fi_h(j)

[0094] Based on the above settings, when calculating the reduction rates of stands F0 to F2 corresponding to stainless steel with a finish rolling target thickness of h, if the calculated reduction rate of the stand eps(i) < Lim_Fi_h, then the final reduction rate epse(i) = eps(i); if the calculated reduction rate of the stand eps(i) ≥ Lim_Fi_h, then the final reduction rate epse(i) = Lim_Fi_h.

[0095] In an embodiment of the present invention, by determining the reduction rates of each stand of the finishing mill using a dynamic reduction rate distribution method based on the upper limit values of the reduction rates of the stands specifically set above, the proportion of roll mark defects generated in 300-series stainless steel during hot rolling can be significantly reduced.

[0096] In a 1549 mm hot strip mill production line, the target coiling temperature is mainly controlled by laminar cooling. In an embodiment of the present invention, when cooling the strip using the laminar cooling equipment, the strip is strongly cooled to the coiling target temperature using a preset cooling strategy, and the coiling target temperature is controlled to be less than the oxidation temperature corresponding to the strip.

[0097] By quickly cooling the strip below the oxidation temperature when the strip exits the finishing area and enters the laminar cooling area, it is possible to avoid oxidation of the minor defects on the strip surface and cause roll mark defects, and significantly reduce the proportion of roll mark defects generated in 300-series stainless steel during hot rolling.

[0098] Refer to Figure 2 ,append Figure 2In the diagram, 1 represents the finishing rolling temperature measurement point, 2 represents the upper valve, 3 represents the lower valve, 4 represents the side-blowing valve, and 5 represents the laminar flow cooling target temperature measurement point. In one embodiment of the present invention, the laminar flow cooling equipment is equipped with an upper valve, a lower valve, and a side-blowing valve. The upper valve is located at the top, the lower valve is located directly below the upper valve, and the side-blowing valve is located to the left of the upper valve. There are a total of 48 sets of valves, namely valves 01 to 48#. Each set of valves is divided into an upper valve and a lower valve. There are a total of 25 side-blowing valves.

[0099] The laminar flow cooling equipment is divided into three zones: a strong cooling zone, a coarse adjustment zone, and a fine adjustment zone.

[0100] The forced cooling zone includes valves 1 through 24. The maximum flow rate of both the upper and lower valves of valves 1 through 24 is 150 m³ / s. 3 / h, both the upper and lower valves are regulating valves, and the water spray volume during rolling can be adjusted arbitrarily within the maximum water volume;

[0101] The coarse adjustment zone includes valves #25 to #40. The maximum flow rate of both the upper and lower valves of valves #25 to #40 is 66.6 m³. 3 / h, both the upper and lower valves are on / off valves, the water spray is at the maximum water volume and cannot be adjusted;

[0102] The fine-tuning zone includes valves 41 to 48. The maximum water flow rate of both the upper and lower valves of valves 41 to 48 is 33.3 m³. 3 / h, both the upper and lower valves are on / off valves, the water spray is at the maximum water volume and cannot be adjusted;

[0103] The maximum water flow of the side-blowing valve is 5m³. 3 / h is the on / off valve, which sprays water at the maximum flow rate and cannot be adjusted.

[0104] Furthermore, in one embodiment of the present invention, based on the above-mentioned laminar flow cooling equipment, the following cooling strategy is adopted to forcefully cool the strip steel to the target coiling temperature:

[0105] Both the upper and lower valves are selected with valve #3 as the starting valve;

[0106] Both the upper and lower valves are opened sequentially from front to back to spray water, with the lower valve opened first and the upper valve opened last; for example, the opening sequence of the upper and lower valves is: 3#, 4#, 5#, 6#, ...;

[0107] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0108] All side-blowing valves are open and water is being sprayed.

[0109] The number of valves to be opened for the upper and lower valves is determined based on the finishing rolling temperature of the strip and the target coiling temperature.

[0110] In one embodiment of the present invention, by employing the above-mentioned cooling strategy to forcefully cool the strip steel to the target coiling temperature, the strip steel can be quickly cooled to below the oxidation temperature, avoiding the oxidation of minor defects on the surface of the strip steel and causing roll defects, and significantly reducing the proportion of roll defects generated in 300 series stainless steel during hot rolling.

[0111] In one embodiment of the present invention, all side-blowing valves are opened to spray water, mainly to ensure that there is no residual water on the surface of the strip steel, so as to facilitate subsequent processes and ensure the surface quality of the finished strip steel.

[0112] Furthermore, in one embodiment of the present invention, the target coiling temperature is controlled according to the following table for different grades of 300 series stainless steel:

[0113] Table 3. Target Coiling Temperatures for Various Grades of 300 Series Stainless Steel

[0114] steel grades Target winding temperature (°C) 301 series stainless steel 670 304 series stainless steel 690 316 series stainless steel 730

[0115] In one embodiment of the present invention, by controlling the temperature of the strip steel according to the coiling target temperature specifically set above, it is possible to avoid the oxidation of minor defects on the surface of the strip steel during the cooling process, which would cause roll defects.

[0116] To make the above technical solutions of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0117] Example 1

[0118] This embodiment rolls 301 series stainless steel, coil number: 932804001, steel grade: SUS631; billet thickness 200mm, billet width 1237mm; finished strip target thickness 2.97mm, target width 1240mm.

[0119] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0120] 1. Furnace temperature control

[0121] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1255℃, and the target furnace temperature for the soaking section is 1245℃.

[0122] 2. Finishing rolling reduction rate control

[0123] According to Table 2, the thickness of this steel block is h = 2.97mm < 3.0mm. The upper limit values ​​of the reduction rate of the F0 to F2 frames are Lim_F0_h = 40, Lim_F1_h = 40, and Lim_F2_h = 38, respectively.

[0124] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 42.3, 40.7, 38.8, 25.3, 21.7, 18.6, and 15.4.

[0125] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 40.0, 40.0, 38.0, 26.9, 22.8, 19.9, 16.1.

[0126] The relevant rolling data for this steel block are as follows:

[0127]

[0128] 3. Winding temperature control

[0129] According to Table 3, the target winding temperature is 670℃.

[0130] Laminar flow cooling employs the following cooling strategies:

[0131] Both the upper and lower valves are selected with the starting valve set to #3.

[0132] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0133] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0134] All side-blowing valves are open and water is being sprayed.

[0135] During the cooling process, the maximum number of valves opened is 3 to 10 for the upper valve and 3 to 11 for the lower valve.

[0136] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0137] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0138] Example 2

[0139] This embodiment rolls 301 series stainless steel, coil number: 932804201, steel grade: SUS631; billet thickness 200mm, billet width 1237mm; finished strip steel target thickness 3.2mm, target width 1240mm.

[0140] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0141] 1. Furnace temperature control

[0142] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1255℃, and the target furnace temperature for the soaking section is 1245℃.

[0143] 2. Finishing rolling reduction rate control

[0144] According to Table 2, the thickness of this steel block is h = 3.2 mm, which is between 3.0 and 4.0 mm.

[0145] h(0)=3.0mm, h(1)=4.0mm;

[0146] Lim_F0_h(0)=40, Lim_F0_h(1)=36.5;

[0147] Lim_F1_h(0)=40, Lim_F1_h(1)=35;

[0148] Lim_F2_h(0)=38, Lim_F2_h(1)=33;

[0149] Calculate the upper limit of the reduction rate using the following formula:

[0150] Lim_F0_h=[Lim_F0_h(1)-Lim_F0_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F0_h(0)

[0151] = (36.5-40) / (4.0-3.0)*(3.2-3.0)+40

[0152] =39.3

[0153] Lim_F1_h=[Lim_F1_h(1)-Lim_F1_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F1_h(0)

[0154] = (35-40) / (4.0-3.0)*(3.2-3.0)+40

[0155] =39.0

[0156] Lim_F2_h=[Lim_F2_h(1)-Lim_F2_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F2_h(0)

[0157] = (33-38) / (4.0-3.0)*(3.2-3.0)+38

[0158] =37.0

[0159] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 40.0, 37.9, 36.2, 26.5, 23.2, 20.0, and 15.1.

[0160] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 39.3, 37.8, 36.3, 26.5, 23.3, 20.2, 15.6.

[0161] The relevant rolling data for this steel block are as follows:

[0162]

[0163]

[0164] 3. Winding temperature control

[0165] According to Table 3, the target winding temperature is 670℃.

[0166] Laminar flow cooling employs the following cooling strategies:

[0167] Both the upper and lower valves are selected with the starting valve set to #3.

[0168] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0169] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0170] All side-blowing valves are open and water is being sprayed.

[0171] During the cooling process, the maximum number of valves opened is valves 3 to 9 on the upper valve and valves 3 to 11 on the lower valve.

[0172] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0173] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0174] Example 3

[0175] This embodiment involves rolling 301 series stainless steel, coil number: 931654201, steel grade: SUS301L; billet thickness: 200mm, billet width: 1245mm; finished strip thickness: 4.5mm, target width: 1260mm.

[0176] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0177] 1. Furnace temperature control

[0178] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1255℃, and the target furnace temperature for the soaking section is 1245℃.

[0179] 2. Finishing rolling reduction rate control

[0180] According to Table 2, the thickness of this steel block is h = 4.5 mm, which is between 4.0 and 5.0 mm.

[0181] h(1)=4.0mm, h(2)=5.0mm;

[0182] Lim_F0_h(1)=36.5, Lim_F0_h(2)=33.5;

[0183] Lim_F1_h(1)=35, Lim_F1_h(2)=32;

[0184] Lim_F2_h(1)=33, Lim_F2_h(2)=30;

[0185] Calculate the upper limit of the reduction rate using the following formula:

[0186] Lim_F0_h=[Lim_F0_h(2)-Lim_F0_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F0_h(1)

[0187] = (33.5-36.5) / (5.0-4.0)*(4.5-4.0)+36.5

[0188] =35.0

[0189] Lim_F1_h=[Lim_F1_h(2)-Lim_F1_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F1_h(1)

[0190] = (32-35) / (5.0-4.0)*(4.5-4.0)+35

[0191] =33.5

[0192] Lim_F2_h=[Lim_F2_h(2)-Lim_F2_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F2_h(1)

[0193] = (30-33) / (5.0-4.0)*(4.5-4.0)+33

[0194] =31.5

[0195] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 31.2, 35.7, 28.8, 25.9, 22.2, 19., 12.8.

[0196] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 31.5, 33.5, 29.6, 26.2, 22.5, 19.9, 13.2.

[0197] The relevant rolling data for this steel block are as follows:

[0198]

[0199] 3. Winding temperature control

[0200] According to Table 3, the target winding temperature is 670℃.

[0201] Laminar flow cooling employs the following cooling strategies:

[0202] Both the upper and lower valves are selected with the starting valve set to #3.

[0203] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0204] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0205] All side-blowing valves are open and water is being sprayed.

[0206] During the cooling process, the maximum number of valves opened is: upper valves 3 to 12# and lower valves 3 to 13#.

[0207] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0208] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0209] Example 4

[0210] This embodiment rolls 301 series stainless steel, with coil number 931654301 and steel grade SUS301L; billet thickness 200mm and billet width 1240mm; the target thickness of the finished strip is 5.0mm and the target width is 1260mm.

[0211] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0212] 1. Furnace temperature control

[0213] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1255℃, and the target furnace temperature for the soaking section is 1245℃.

[0214] 2. Finishing rolling reduction rate control

[0215] According to Table 2, the thickness of this steel block is h = 5.0 mm, then...

[0216] Lim_F0_h = 33.5;

[0217] Lim_F1_h = 32;

[0218] Lim_F2_h = 30;

[0219] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 30.2, 30.9, 31.4, 24.4, 20.8, 16.7, and 13.7.

[0220] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 30.8, 31.2, 30.0, 24.6, 21.0, 16.9, 13.9.

[0221] The relevant rolling data for this steel block are as follows:

[0222]

[0223] 3. Winding temperature control

[0224] According to Table 3, the target winding temperature is 670℃.

[0225] Laminar flow cooling employs the following cooling strategies:

[0226] Both the upper and lower valves are selected with the starting valve set to #3.

[0227] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0228] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0229] All side-blowing valves are open and water is being sprayed.

[0230] During the cooling process, the maximum number of valves opened is 3 to 13 for the upper valve and 3 to 15 for the lower valve.

[0231] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0232] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0233] Example 5

[0234] This embodiment rolls 304 series stainless steel, coil number: 932E10901, steel grade: SUS304; billet thickness 200mm, billet width 1020mm; finished strip target thickness 2.85mm, target width 1035mm.

[0235] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0236] 1. Furnace temperature control

[0237] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1257℃, and the target furnace temperature for the soaking section is 1243℃.

[0238] 2. Finishing rolling reduction rate control

[0239] According to Table 2, the thickness of this steel block is h = 2.85 mm, then...

[0240] Lim_F0_h = 40;

[0241] Lim_F1_h = 40;

[0242] Lim_F2_h = 38;

[0243] The initial reduction rates (%) for each stand of this steel block are calculated as follows: 37.9, 41.1, 40.9, 27.0, 24.6, 20.7, and 13.9.

[0244] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 39.0, 40.0, 38.0, 28.2, 25.5, 21.7, 14.3.

[0245] The relevant rolling data for this steel block are as follows:

[0246]

[0247] 3. Winding temperature control

[0248] According to Table 3, the target winding temperature is 690℃.

[0249] Laminar flow cooling employs the following cooling strategies:

[0250] Both the upper and lower valves are selected with the starting valve set to #3.

[0251] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0252] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0253] All side-blowing valves are open and water is being sprayed.

[0254] During the cooling process, the maximum number of valves opened is valves 3 to 9 on the upper valve and valves 3 to 10 on the lower valve.

[0255] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0256] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0257] Example 6

[0258] This embodiment rolls 304 series stainless steel, with coil number 932E10301 and steel grade SUS304; billet thickness 200mm and billet width 1027mm; the target thickness of the finished strip is 3.8mm and the target width is 1035mm.

[0259] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0260] 1. Furnace temperature control

[0261] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1257℃, and the target furnace temperature for the soaking section is 1243℃.

[0262] 2. Finishing rolling reduction rate control

[0263] According to Table 2, the thickness of this steel block is h = 3.8 mm, which is between 3.0 and 4.0 mm.

[0264] h(0)=3.0mm, h(1)=4.0mm;

[0265] Lim_F0_h(0)=40, Lim_F0_h(1)=36.5;

[0266] Lim_F1_h(0)=40, Lim_F1_h(1)=35;

[0267] Lim_F2_h(0)=38, Lim_F2_h(1)=33;

[0268] Calculate the upper limit of the reduction rate using the following formula:

[0269] Lim_F0_h=[Lim_F0_h(1)-Lim_F0_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F0_h(0)

[0270] = (36.5-40) / (4.0-3.0)*(3.8-3.0)+40

[0271] =37.2

[0272] Lim_F1_h=[Lim_F1_h(1)-Lim_F1_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F1_h(0)

[0273] = (35-40) / (4.0-3.0)*(3.8-3.0)+40

[0274] =36.0

[0275] Lim_F2_h=[Lim_F2_h(1)-Lim_F2_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F2_h(0)

[0276] = (33-38) / (4.0-3.0)*(3.8-3.0)+38

[0277] =34.0

[0278] The initial reduction rates (%) for each stand of this steel block are calculated as follows: 33.8, 34.7, 33.6, 27.7, 23.6, 21.7, and 13.0.

[0279] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 33.8, 34.7, 33.6, 27.7, 23.6, 21.7, 13.0.

[0280] The relevant rolling data for this steel block are as follows:

[0281]

[0282] 3. Winding temperature control

[0283] According to Table 3, the target winding temperature is 690℃.

[0284] Laminar flow cooling employs the following cooling strategies:

[0285] Both the upper and lower valves are selected with the starting valve set to #3.

[0286] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0287] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0288] All side-blowing valves are open and water is being sprayed.

[0289] During the cooling process, the maximum number of valves opened is 3 to 10 for the upper valve and 3 to 11 for the lower valve.

[0290] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0291] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0292] Example 7

[0293] This embodiment rolls 304 series stainless steel, coil number: 932743401, steel grade: 06CR19NI10; billet thickness 200mm, billet width 1285mm; finished strip target thickness 4.3mm, target width 1294mm.

[0294] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0295] 1. Furnace temperature control

[0296] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1257℃, and the target furnace temperature for the soaking section is 1243℃.

[0297] 2. Finishing rolling reduction rate control

[0298] According to Table 2, the thickness of this steel block is h = 4.3 mm, which is between 4.0 and 5.0 mm.

[0299] h(1)=4.0mm, h(2)=5.0mm;

[0300] Lim_F0_h(1)=36.5, Lim_F0_h(2)=33.5;

[0301] Lim_F1_h(1)=35, Lim_F1_h(2)=32;

[0302] Lim_F2_h(1)=33, Lim_F2_h(2)=30;

[0303] Calculate the upper limit of the reduction rate using the following formula:

[0304] Lim_F0_h=[Lim_F0_h(2)-Lim_F0_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F0_h(1)

[0305] = (33.5-36.5) / (5.0-4.0)*(4.3-4.0)+36.5

[0306] =35.6

[0307] Lim_F1_h=[Lim_F1_h(2)-Lim_F1_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F1_h(1)

[0308] = (32-35) / (5.0-4.0)*(4.3-4.0)+35

[0309] =34.1

[0310] Lim_F2_h=[Lim_F2_h(2)-Lim_F2_h(1)] / [h(2)-h(1)]*[hh(1)]+Lim_F2_h(1)

[0311] = (30-33) / (5.0-4.0)*(4.3-4.0)+33

[0312] =32.1

[0313] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 31.8, 35.3, 29.7, 28.3, 22.3, 19.4, and 11.9.

[0314] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 32.1, 34.1, 30.1, 28.6, 22.5, 19.5, 12.0.

[0315] The relevant rolling data for this steel block are as follows:

[0316]

[0317]

[0318] 3. Winding temperature control

[0319] According to Table 3, the target winding temperature is 690℃.

[0320] Laminar flow cooling employs the following cooling strategies:

[0321] Both the upper and lower valves are selected with the starting valve set to #3.

[0322] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0323] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0324] All side-blowing valves are open and water is being sprayed.

[0325] During the cooling process, the maximum number of valves opened is: upper valves 3 to 11# and lower valves 3 to 12#.

[0326] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0327] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0328] Example 8

[0329] This embodiment rolls 304 series stainless steel, with coil number 932740901 and steel grade 304L; billet thickness 200mm and billet width 1235mm; the target thickness of the finished strip is 5.8mm and the target width is 1254mm.

[0330] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0331] 1. Furnace temperature control

[0332] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1257℃, and the target furnace temperature for the soaking section is 1243℃.

[0333] 2. Finishing rolling reduction rate control

[0334] According to Table 2, the thickness of this steel block is h = 5.8 mm, then...

[0335] Lim_F0_h = 33.5

[0336] Lim_F1_h=32

[0337] Lim_F2_h=30

[0338] The initial reduction rates (%) for each stand of this steel block are calculated as follows: 27.6, 28.7, 27.3, 26.3, 19.6, 15.4, and 12.1.

[0339] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 27.6, 28.7, 27.3, 26.3, 19.6, 15.4, 12.1.

[0340] The relevant rolling data for this steel block are as follows:

[0341]

[0342] 3. Winding temperature control

[0343] According to Table 3, the target winding temperature is 690℃.

[0344] Laminar flow cooling employs the following cooling strategies:

[0345] Both the upper and lower valves are selected with the starting valve set to #3.

[0346] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0347] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0348] All side-blowing valves are open and water is being sprayed.

[0349] During the cooling process, the maximum number of valves opened is 3 to 12 for the upper valve and 3 to 14 for the lower valve.

[0350] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0351] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0352] Example 9

[0353] This embodiment rolls 316 series stainless steel, coil number: 933772601, steel grade: 1.4404; billet thickness 200mm, billet width 1035mm; finished strip steel target thickness 4.0mm, target width 1045mm.

[0354] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0355] 1. Furnace temperature control

[0356] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1260℃, and the target furnace temperature for the soaking section is 1240℃.

[0357] 2. Finishing rolling reduction rate control

[0358] According to Table 2, the thickness of this steel block is h = 4.0 mm, then...

[0359] Lim_F0_h = 35.5

[0360] Lim_F1_h=34

[0361] Lim_F2_h=33

[0362] The initial reduction rates (%) for each stand of this steel block are calculated as follows: 30.9, 36.8, 32.9, 25.7, 23.4, 22.0, and 12.2.

[0363] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 31.7, 34.0, 33.0, 26.5, 23.9, 22.9, 12.5.

[0364] The relevant rolling data for this steel block are as follows:

[0365]

[0366] 3. Winding temperature control

[0367] According to Table 3, the target winding temperature is 730℃.

[0368] Laminar flow cooling employs the following cooling strategies:

[0369] Both the upper and lower valves are selected with the starting valve set to #3.

[0370] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0371] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0372] All side-blowing valves are open and water is being sprayed.

[0373] During the cooling process, the maximum number of valves opened is valves 3 to 7 on the upper valve and valves 3 to 9 on the lower valve.

[0374] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0375] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0376] Example 10

[0377] This embodiment is for rolling 316 series stainless steel, with coil number 933751301 and steel grade 316L; billet thickness 200mm and billet width 1033mm; and finished strip steel with a target thickness of 4.5mm and a target width of 1045mm.

[0378] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0379] 1. Furnace temperature control

[0380] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1260℃, and the target furnace temperature for the soaking section is 1240℃.

[0381] 2. Finishing rolling reduction rate control

[0382] According to Table 2, the thickness of this steel block is h = 4.5 mm, which is between 4.0 and 5.0 mm.

[0383] h(0)=4.0mm, h(1)=5.0mm;

[0384] Lim_F0_h(0)=35.5, Lim_F0_h(1)=33;

[0385] Lim_F1_h(0)=34, Lim_F1_h(1)=32;

[0386] Lim_F2_h(0)=33, Lim_F2_h(1)=30;

[0387] Calculate the upper limit of the reduction rate using the following formula:

[0388] Lim_F0_h=[Lim_F0_h(1)-Lim_F0_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F0_h(0)

[0389] = (33-35.5) / (5.0-4.0)*(4.5-4.0)+35.5

[0390] =34.25

[0391] Lim_F1_h=[Lim_F1_h(1)-Lim_F1_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F1_h(0)

[0392] = (32-34) / (5.0-4.0)*(4.5-4.0)+34

[0393] =33

[0394] Lim_F2_h=[Lim_F2_h(1)-Lim_F2_h(0)] / [h(1)-h(0)]*[hh(0)]+Lim_F2_h(0)

[0395] = (30-33) / (5.0-4.0)*(4.5-4.0)+33

[0396] =31.5

[0397] The initial reduction rates (%) for each stand of this steel block are calculated as follows: 28.0, 33.9, 31.1, 25.1, 23.3, 22.0, and 12.6.

[0398] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 28.2, 33.0, 31.3, 25.2, 23.4, 22.3, 12.8.

[0399] The relevant rolling data for this steel block are as follows:

[0400]

[0401] 3. Winding temperature control

[0402] According to Table 3, the target winding temperature is 730℃.

[0403] Laminar flow cooling employs the following cooling strategies:

[0404] Both the upper and lower valves are selected with the starting valve set to #3.

[0405] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0406] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0407] All side-blowing valves are open and water is being sprayed.

[0408] During the cooling process, the maximum number of valves opened is valves 3 to 8 on the upper valve and valves 3 to 9 on the lower valve.

[0409] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0410] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0411] Example 11

[0412] This embodiment involves rolling 316 series stainless steel, coil number: 933772401, steel grade: 316L; billet thickness: 200mm, billet width: 1033mm; finished strip thickness: 5.0mm, target width: 1045mm.

[0413] Based on the above stainless steel types and parameters, the hot rolling process and parameters are determined as follows:

[0414] 1. Furnace temperature control

[0415] According to Table 1, the target furnace temperature for the second heating section of this steel block is 1260℃, and the target furnace temperature for the soaking section is 1240℃.

[0416] 2. Finishing rolling reduction rate control

[0417] According to Table 2, the thickness of this steel block is h = 5.0 mm, then...

[0418] Lim_F0_h=33

[0419] Lim_F1_h=32

[0420] Lim_F2_h=30

[0421] The initial reduction rates (%) for each frame of this steel block are calculated as follows: 29.9, 35.5, 30.4, 23.8, 21.0, 15.8, and 10.6.

[0422] Based on the rules for determining the upper limit of the reduction rate of the F0 to F2 frames and the rules for judging the final reduction rate, the final reduction rate (%) of this steel block is obtained after recalculation as follows: 31.2, 32.0, 30.0, 25.1, 21.7, 16.6, 11.0.

[0423] The relevant rolling data for this steel block are as follows:

[0424]

[0425]

[0426] 3. Winding temperature control

[0427] According to Table 3, the target winding temperature is 730℃.

[0428] Laminar flow cooling employs the following cooling strategies:

[0429] Both the upper and lower valves are selected with the starting valve set to #3.

[0430] Both the upper and lower valves are opened sequentially from front to back, with the lower valve opened first and the upper valve opened later.

[0431] In the strong cooling zone, the water flow rate of the upper valve is 65% of the maximum water flow rate, and the water flow rate of the lower valve is 85% of the maximum water flow rate.

[0432] All side-blowing valves are open and water is being sprayed.

[0433] During the cooling process, the maximum number of valves opened is valves 3 to 9 on the upper valve and valves 3 to 10 on the lower valve.

[0434] In addition to the control methods and parameters given above, other control methods and parameters adopt the conventional hot rolling process control methods and parameters of the 1549mm hot continuous rolling production line.

[0435] When hot rolling of strip steel is carried out according to the above control method and parameters, the resulting strip steel is free of roll trace defects in the cold rolling process.

[0436] As can be seen, the control method for eliminating roll defects in 300 series stainless steel provided in one embodiment of the present invention can significantly reduce the proportion of roll defects in 300 series stainless steel in the hot rolling process by adjusting the temperature difference between the heating furnace soaking section and the second heating section, limiting the reduction rate of the stand before finishing rolling, and reducing the coiling temperature through laminar flow cooling. This can reduce the cost of the cold rolling process and improve the cold rolling yield.

[0437] Based on the results of multiple actual tests, the control method for eliminating roller trace defects in 300 series stainless steel provided in one embodiment of the present invention can reduce the proportion of roller trace defects in 300 series stainless steel from the existing 30% or more to less than 3%.

[0438] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0439] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for eliminating 300 series stainless steel roll mark defects, characterized by, The method is used for a 1549mm hot continuous rolling production line, and comprises the following steps: When the strip steel is heated by using the heating furnace, the soaking section furnace temperature of the heating furnace is controlled to be 10℃-20℃ lower than the second heating section furnace temperature; When the strip steel is rolled by using the finishing mill, the dynamic reduction rate distribution method is used to determine the reduction rate of each rack of the finishing mill, and the reduction rates of the F0 rack, the F1 rack and the F2 rack are controlled to be not more than the corresponding preset upper limit values of the reduction rates; When the strip steel is cooled by using the laminar cooling equipment, the strip steel is rapidly cooled to the coiling target temperature by using the preset cooling strategy, and the coiling target temperature is less than the corresponding oxidation temperature of the strip steel; For different steel grades of the 300 series stainless steel, the upper limit values of the reduction rates corresponding to the F0 rack, the F1 rack and the F2 rack are determined according to the following table: ； When the finishing target thickness of the 301\304 series stainless steel is between 3.0mm and 4.0mm, the upper limit value of the reduction rate is calculated by using the interpolation method based on the upper limit value of the reduction rate corresponding to 3.0mm and the upper limit value of the reduction rate corresponding to 4.0mm; when the finishing target thickness of the 301\304 series stainless steel is between 4.0mm and 5.0mm, the upper limit value of the reduction rate is calculated by using the interpolation method based on the upper limit value of the reduction rate corresponding to 4.0mm and the upper limit value of the reduction rate corresponding to 5.0mm; when the finishing target thickness of the 316 series stainless steel is between 4.0mm and 5.0mm, the upper limit value of the reduction rate is calculated by using the interpolation method based on the upper limit value of the reduction rate corresponding to 4.0mm and the upper limit value of the reduction rate corresponding to 5.0mm; Wherein, Lim_F0_h, Lim_F1_h, Lim_F2_h respectively represent the upper limit value of the reduction rate of the F0 rack, the upper limit value of the reduction rate of the F1 rack, and the upper limit value of the reduction rate of the F2 rack.

2. The control method for eliminating 300 series stainless steel roll mark defects according to claim 1, characterized by, For different steel grades of the 300 series stainless steel, the furnace temperatures of the second heating section and the soaking section of the heating furnace are as follows: ； Control is performed.

3. The control method for eliminating 300 series stainless steel roll mark defects according to claim 1, characterized by, The dynamic reduction rate distribution method is used to determine the reduction rate of each rack of the finishing mill, and the reduction rates of the F0 rack, the F1 rack and the F2 rack are controlled to be not more than the corresponding preset upper limit values of the reduction rates, which comprises the following steps: The initial reduction rate of each rack is calculated by using the following formula, and if the reduction rates of the F0 rack, the F1 rack and the F2 rack exceed the corresponding preset upper limit values of the reduction rates, the initial reduction rates of the F0 rack, the F1 rack and the F2 rack are taken as the corresponding preset upper limit values of the reduction rates; eps(i) = RF(i) GBZWK / MH(i) / nnfkorr(i) According to the currently determined rack reduction rate, the outlet thickness of each rack is calculated; If the difference between the exit thickness of the last stand and the target thickness of the finishing rolling is within the range of -1% to 1%, the current stand reduction rate is taken as the final stand reduction rate; if the ratio of the difference to the target thickness of the finishing rolling is greater than 1%, the reduction rate of each stand is increased by 0.5%, and the thickness and the difference are recalculated; if the ratio of the difference to the target thickness of the finishing rolling is less than -1%, the reduction rate of each stand is reduced by 0.05%, and the thickness and the difference are recalculated, wherein if the reduction rate of the F0 stand, the F1 stand, and the F2 stand after the increase exceeds the corresponding preset upper limit of the reduction rate, the reduction rate of the F0 stand, the F1 stand, and the F2 stand is taken as the corresponding preset upper limit of the reduction rate; Wherein, i represents the stand number of the finishing mill, i=0, 1, 2, 3, 4, 5, 6, i is 0-6, which respectively represents F0-F6 stands, eps(i) represents the initial reduction rate of the i-th stand, RF(i) represents the given reduction rate of the i-th stand, GBZWK represents the maximum rolling pressure of each stand of the finishing mill, MH(i) represents the hardness value of the steel of the i-th stand, and nnfkorr(i) represents the calculation pressure correction coefficient of the i-th stand.

4. The control method for eliminating 300 series stainless steel roll mark defects according to claim 3, characterized by, It is set that when the target thickness of the stainless steel finishing rolling is 3.0 mm, 4.0 mm, and 5.0 mm, the thickness is represented by h(j), the upper limit of the reduction rate is represented by Lim_Fi_h(j), i represents the stand number of the finishing mill, and j represents the thickness classification, j=0, 1, 2, which respectively represent the upper limit of the reduction rate when the thickness is 3.0 mm, 4.0 mm, and 5.0 mm; When the target thickness h of the stainless steel finishing rolling is between h(j) and h(j+1), the upper limit of the reduction rate Lim_Fi_h of the i-th stand corresponding to the thickness h is calculated and determined by the following formula: Lim_Fi_h = [Lim_Fi_h(j+1)-Lim_Fi_h(j)] / [h(j+1)-h(j)] [h-h(j)]+Lim_Fi_h(j).

5. The control method for eliminating 300 series stainless steel roll mark defects according to claim 1, characterized by, The laminar cooling equipment is provided with upper valves, lower valves and side blowing valves, and the upper valves and the lower valves include 48 groups of valves; The laminar cooling equipment includes a strong cooling zone, a coarse adjustment zone and a fine adjustment zone; The strong cooling zone includes 1~24# valves, and the maximum flow of the upper valve and the lower valve of 1~24# valves is 150m 3 / h, and the upper valve and the lower valve are regulating valves, and the water spraying amount in rolling is adjusted within the maximum water amount. The coarse adjustment area includes 25-40# valves, the maximum water flow of the upper valve and the lower valve of the 25-40# valve is 66.6m 3 / h, the upper valve and the lower valve are on-off valves, the water spray is the maximum water flow and cannot be adjusted; The fine adjustment area includes 41-48# valves, and the maximum water flow of the upper valve and the lower valve of the 41-48# valves is 33.3m 3 / h, the upper valve and the lower valve are on-off valves, the water spraying is the maximum water flow, and cannot be adjusted; Max water quantity of side blow valve 5m 3 / h, on-off valve, water spray is max water quantity, no adjustment The preset cooling strategy includes: The starting valve of the upper valve and the lower valve is 3# valve; The upper valve and the lower valve adopt the valve opening mode from front to back, and the lower valve is opened first, and then the upper valve is opened; The water quantity of the upper valve of the strong cooling zone is 65% of the maximum water quantity, and the water quantity of the lower valve is 85% of the maximum water quantity; All the side blowing valves are opened to spray water.

6. The control method for eliminating 300 series stainless steel roll mark defects according to claim 5, characterized by, For different steel grades of 300 series stainless steel, the coiling target temperature is as follows: ； Control is performed.

Images