A production method for improving the rollability of hot-rolled substrate

Abstract

A production method for improving the rollability of a hot-rolled base plate includes heating, roughing, finishing, cooling, and coiling steps of the cast slab. During the finishing step, the strip threading limit speed Vt is determined by the following formula: Vt = -a-1.75*TH-0.000766*W-0.0612*RH-0.0227*FET + 0.0694*FDT. When the final stand finishing mill set speed Vs ≤ Vt, the actual final stand finishing mill strip threading speed Va = Vs; when the final stand finishing mill set speed Vs > Vt, the actual final stand finishing mill strip threading speed Va = Vt. The present invention controls the rolling and cooling of the cast slab, controlling the layer cooling rate of the strip by stabilizing the rolling speed of the finishing step, effectively resolving the problem of large temperature fluctuations at the intermediate point when using two-stage cooling.

Description

Technical Field

[0001] The present invention belongs to the field of hot-rolled strip steel, and further belongs to the field of hot-rolled base plates with a width of more than 1500 mm. Background Art

[0002] Hot-rolled strip production pursues large-scale wide strip mills, high speeds, and high coil weights. Hot-rolled tinplate substrates for steel strips with widths exceeding 1500mm are used for slitting. Flexible width slitting, minimal trimming losses, and high yields offer significant cost advantages and facilitate production organization at downstream tinplate cold-rolling mills, making them highly popular in the market. However, some wide strip production lines do not utilize hot coil boxes and employ a straight-through process between roughing and finishing mills. This results in a large temperature difference between the head and tail of the intermediate bar, and a large speed fluctuation during finishing mill ramp-up. The finishing mill threading speed differs by nearly 40% from the maximum speed. Furthermore, small crown control requirements (target crown of 1% of thickness) are required for production widths exceeding 1500mm. When hot-rolling thin-gauge, low-carbon, aluminum-killed steel tinplate substrates, large rolling speed fluctuations can lead to unstable rolling and difficult shape control. This poor shape can easily cause uneven cooling of the wide strip, resulting in large strength fluctuations and excessive cold-rolled thickness tolerances. The minimum thickness of conventional production for specifications with a width of more than 1500mm is 2.5mm. With the development of lightweight tinplate packaging, the specification of tinplate products with a single cold rolling of 0.17mm is the main specification of tinplate. It requires that the hot-rolled raw materials are rolled into finished products in one rolling process (without annealing in the middle), and the total cold rolling reduction rate is more than 93%. The hot-rolled products are required to have good rollability.

[0003] Products with good rollability require uniform microstructure and properties across the length and width of the steel strip, along with high elongation. This invention employs an algorithm that optimizes the control of inter-stand cooling water to reduce fluctuations in the steel strip rolling speed, improving rolling stability. Furthermore, a special cooling strategy is employed to achieve uniform product properties and high elongation. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to improve the rollability of a hot-rolled tin-plated substrate of low-carbon aluminum-killed steel with a width of more than 1500 mm.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a production method for improving the rollability of hot-rolled base plates, the method including the heating, rough rolling, finishing rolling, cooling and coiling processes of the ingot, in the finishing rolling process, the threading limit speed Vt is determined by the following formula 1, before the strip enters the finishing mill, the following logical judgment is performed, and the actual threading speed Va of the strip of the last stand finishing mill is determined according to the judgment result: when the setting speed Vs≤Vt of the last stand finishing mill, the actual threading speed Va=Vs of the strip of the last stand finishing mill; when the setting speed Vs>Vt of the last stand finishing mill, the actual threading speed Va=Vt of the strip of the last stand finishing mill; by dynamically limiting the threading speed of the strip, the accuracy of the final rolling temperature of the strip head and the temperature of the intermediate point of the layer cooling is improved.

[0006] Vt = -a-1.75×TH-0.000766×W-0.0612×RH-0.0227× FET+ 0.0694×FDT (1)

[0007] In formula 1, 17.7≤a≤17.9, Vt is the threading limit speed, RH is the intermediate billet thickness, FET is the head temperature at the finishing entrance, TH is the finished product thickness, W is the finished product width, FDT is the final rolling set temperature, the units of TH, W, and RH are all mm, the units of FET and FDT are all ℃, and the units of Vt, Vs, and Va are all m / .

[0008] Furthermore, in the formula 1, a=17.8.

[0009] Furthermore, during the finishing process, before the start of finishing rolling, the four inter-stand cooling water groups between the first five mills are initially enabled by default. When V7 satisfies (V7-Va) / Va>4%, the cooling water between stands F4-F5 is disabled. When (V7-Va) / Va>7%, the cooling water between stands F3-F4 and F4-F5 is disabled. When (V7-Va) / Va>10%, only the cooling water between stands F1-F2 is enabled, while the cooling water between all other stands is disabled. When (V7-Va) / Va>15%, all inter-stand cooling water is disabled. Va is the actual strip threading speed of the last finishing stand, and V7 is the instantaneous speed of the last finishing stand after threading. By dynamically adjusting the inter-stand cooling water on and off, the strip speed increase is reduced, minimizing the temperature fluctuation range at the intermediate point of layer cooling. This process is completed by automatic control. After it is put into operation, the speed increase of finishing rolling can be limited to within 20%, and the temperature of the middle point of the layer cooling can be controlled within the range of ±20℃ of the target temperature.

[0010] Furthermore, the starting cooling temperature of the strip in the cooling process is 860±20℃, and in the cooling process, only one group of low-pressure sparse cooling is put into the ultra-fast cooling section, and the other three groups are not put into use, and the seven groups of conventional layer cooling sections are not put into use, and six groups of encrypted cooling sections and two groups of fine-tuning sections are put into sparse cooling, and the final cooling temperature is 580±20℃.

[0011] Furthermore, the composition and mass percentage of the low-carbon aluminum-killed steel are: C: 0.04-0.06%, Mn: 0.15-0.26%, S: ≤0.015%, P: ≤0.022%, Si: ≤0.03%, Als: 0.02-0.06%, N≤0.006%, and the rest are Fe and unavoidable impurities.

[0012] The operating side and transmission side mentioned in the present invention are used to distinguish the positions on both sides of the hot-rolled strip, wherein the operating side refers to the side where the rolling mill operating table is located, and the transmission side refers to the side where the rolling mill transmission motor is located.

[0013] The beneficial effects of adopting the above technical solution are:

[0014] The present invention controls the rolling and cooling of the ingot, and controls the layer cooling rate of the strip by stabilizing the rolling speed of the finishing rolling process. This effectively solves the problem of large fluctuations in the temperature of the intermediate point when using two-stage cooling, improves the size and proportion of ferrite precipitation, and obtains a finished product with uniform mechanical properties. The fluctuations in the transverse tensile strength Rm and yield strength ReL of the produced product are both less than 25MPa, the elongation is increased by about 4%, and the grain size grade is reduced by one level compared to conventional production methods. The present invention mainly applies the principle of precise control of phase structure transformation in steel, has low production control difficulty, and the product is beneficial to the production and use of downstream cold rolling users, which is conducive to increasing market share and can generate great economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a typical microstructure photo of hot-rolled finished strip steel. Figure 1 From left to right, these are 200X metallographic photos of the steel belt from the operating side to the transmission side. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0017] The production process of the present invention is that the casting billet is subjected to heating, rough rolling, finish rolling, cooling and coiling steps in sequence;

[0018] The following equipment is used: regenerative heating furnace, two roughing mills, seven finishing mills, laminar cooling equipment, and downcoiler.

[0019] Ingot: Thickness 230mm, Width 1850mm. The mass percentage of each component in the ingot is: C: 0.04-0.06%, Mn: 0.15-0.26%, S: ≤0.015%; P: ≤0.022%, Si: ≤0.03%, Als: 0.02-0.06%, N ≤0.006%, and the remainder is Fe and unavoidable impurities. The process of each step is as follows:

[0020] (1) Heating process: The billet heating and steel tapping temperature is 1190-1230℃.

[0021] (2) Rough rolling process: After heating, the ingot is rolled on a two-roller reversible mill R1 for three passes to reduce the thickness to 125 mm; finally, it is rolled on a four-roller reversible mill R2 for three passes to form an intermediate billet with a thickness of 40 mm.

[0022] (3) Finishing rolling process: Finishing rolling start temperature: 1030~1060, final rolling temperature 880℃±20, after detecting the finishing rolling entrance temperature, the strip threading speed of the first finishing mill is dynamically limited before biting the steel (the threading speed is limited according to the formula 1 Vt = -a-1.75×TH-0.000766×W-0.0612×RH-0.0227×FET+ 0.0694×FDT, and the logic judgment is performed: when the set speed Vs of the last finishing mill is ≤Vt, the actual threading speed Va=Vs; when Vs>Vt, Va=Vt. The units of Vt, Vs, and Va are all m / s). After the strip is threaded through the last finishing mill, the speed increase of the strip is dynamically adjusted by switching the inter-stand cooling water. (Adjustment strategy: when the instantaneous speed V7 of the last finishing mill after threading the strip satisfies (V7-Va) / Va>4%, the cooling water between the F4-F5 stands is turned off; when (V7-Va) / Va>7%, the cooling water between the F3-F4 and F4-F5 stands is turned off; when (V7-Va) / Va>10%, only the cooling water between the F1-F2 stands is turned on, and the cooling water between the other stands is turned off; when (V7-Va) / Va>15%, all inter-stand cooling water is turned off).

[0023] (4) Cooling and coiling process: In the cooling process, only one group of low-pressure sparse cooling is put into the ultra-fast cooling section, and the other three groups are not put into use. The seven groups of conventional layer cooling section are not put into use. The six groups of dense cooling section and the two groups of fine adjustment section are put into sparse cooling. The final cooling temperature is 580±20℃, and the hot-rolled strip for tinplate is obtained by coiling.

[0024] The present invention will be further described in detail below with reference to specific embodiments.

[0025] Examples 1-7

[0026] Examples 1-7 were produced according to the above-mentioned implementation mode, Table 1 shows the process parameters of the heating and rough rolling steps, Table 2 shows the process parameters of the finishing rolling step, and Table 3 shows the performance test results of the finished hot-rolled steel strip in the width direction. The "operating side 1 / 8" is a position at a distance of 1 / 8 of the steel strip width from the edge of the operating side steel strip, the "operating side 1 / 4" is a position at a distance of 1 / 4 of the steel strip width from the edge of the operating side steel strip, the "drive side 1 / 8" is a position at a distance of 1 / 8 of the steel strip width from the edge of the drive side steel strip, the "drive side 1 / 4" is a position at a distance of 1 / 4 of the steel strip width from the edge of the drive side steel strip, and the "middle 1 / 2" is a position at a distance of 1 / 2 of the steel strip width from both the drive side and operating side steel strip edges.

[0027] Table 1

[0028]

[0029] Table 2

[0030]

[0031] Table 3

[0032]

[0033] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A production method for improving the rollability of hot-rolled substrate, comprising the steps of heating, rough rolling, finish rolling, cooling, and coiling the cast billet, characterized in that: In the finishing mill process, the strip threading limit speed Vt is determined by the following formula 1. Before the strip enters the finishing mill, the following logical judgment is performed, and the actual strip threading speed Va of the last stand finishing mill is determined according to the judgment result: when the set speed Vs of the last stand finishing mill is ≤ Vt, the actual strip threading speed Va of the last stand finishing mill is = Vs; when the set speed Vs of the last stand finishing mill is > Vt, the actual strip threading speed Va of the last stand finishing mill is = Vt; Vt = -a-1.75*TH-0.000766*W-0.0612*RH-0.0227* FET+ 0.0694*FDT (1) In formula 1, 17.7≤a≤17.9, Vt is the threading limit speed, RH is the intermediate billet thickness, FET is the head temperature at the finishing entrance, TH is the finished product thickness, W is the finished product width, FDT is the final rolling set temperature, the units of TH, W, and RH are all mm, the units of FET and FDT are all °C, and the units of Vt, Vs, and Va are all m / s.

2. A production method for improving the rollability of a hot-rolled substrate according to claim 1, characterized in that: In the above formula (1), a=17.

8.

3. The method for improving the rollability of a hot-rolled substrate according to claim 1, characterized in that: In the finishing rolling process, before the start of finishing rolling, the cooling water between the four groups of stands of the first five rolling mills is initially turned on by default. When V7 satisfies (V7-Va) / Va>4%, the cooling water between the stands F4-F5 is turned off; when (V7-Va) / Va>7%, the cooling water between the stands F3-F4 and F4-F5 is turned off; when (V7-Va) / Va>10%, only the cooling water between the stands F1-F2 is turned on, and the cooling water between the other stands is turned off; when (V7-Va) / Va>15%, all the cooling water between the stands is turned off; Va is the actual strip threading speed of the last finishing mill, and V7 is the instantaneous speed of the last finishing mill after threading.

4. The method for improving the rollability of a hot-rolled substrate according to claim 1, characterized in that: The starting cooling temperature of the strip in the cooling process is 860±20℃. In the cooling process, only one group of low-pressure sparse cooling is put into the ultra-fast cooling section, and the other three groups are not put into use. Seven groups of conventional layer cooling sections are not put into use. Six groups of dense cooling sections and two groups of fine-tuning sections are put into sparse cooling. The final cooling temperature is 580±20℃.

5. The method for improving the rollability of a hot-rolled substrate according to claim 1, characterized in that: The composition and mass percentage of the ingot are as follows: C: 0.04-0.06%, Mn: 0.15-0.26%, S: ≤0.015%, P: ≤0.022%, Si: ≤0.03%, Als: 0.02-0.06%, N ≤0.006%, and the rest are Fe and unavoidable impurities.

Images