A method for increasing the performance stability of a continuous casting and rolling production line during the transition phase

Abstract

This invention discloses a method for increasing performance stability during the transition phase of a continuous casting and rolling line. This method, pertaining to the field of steel production, comprises continuous casting, roughing rolling, induction heating, finishing rolling, and cooling and coiling. The method includes controlling the outlet temperature of the induction heating furnace and the amount of overlap between finishing and roughing rolling. Compared to existing technologies, this method can reduce the adverse effects on performance stability caused by sudden drops or increases in speed during transitions between finished product specifications and the finishing rolling mill stands during the intermediate billet phase, thereby improving the final rolling temperature hit rate.

Description

Technical Field

[0001] The present invention relates to a steel production control method, in particular to a control method and device suitable for improving product performance stability during the transition stage of finished product specifications and intermediate billets in a continuous casting and rolling production line. Background Art

[0002] In the real-world production of continuous casting and rolling lines, transition coils appear when two thickness specifications change, indicating a transition between the finished product thickness and the intermediate billet thickness. During this transition, the intermediate billet transition method in the continuous casting and rolling line is a wedge-shaped transition, with the wedge transition length accounting for 70% of the total coil length. After the automatic thickness control is activated, the finishing mill exit speed decreases or increases during this wedge transition, which in turn causes a sudden drop or increase in the speed of each finishing mill stand. This decrease or increase in the F5 exit speed directly affects the finishing temperature, resulting in a 10-20°C variation and a mismatch in the finishing temperature. This mismatch directly impacts product quality, especially for steel grades that undergo full austenitic rolling. Temperature fluctuations can cause rolling to enter the two-phase region, significantly impacting performance.

[0003] There are basically three methods for improving the hot rolling temperature hit rate in the existing technology: (1) by adding cooling hardware: such as "A cooling manifold between racks that is not easy to clog the nozzle" (CN201420107300.5); (2) by reducing the number of dephosphorization passes, such as "A hot rolling production method for improving the hot rolling temperature hit rate of silicon steel" (CN201911046980.8); (3) by adjusting the speed of each section of the production line: such as "A rolling control method for specific heating temperature of hot-rolled slabs" (CN202210245714.3). By setting a relatively high strip threading speed, while ensuring that the final rolling temperature of the first half of the strip is hit, the decrease in the heating temperature of the slab in the subsequent length direction of this type of heating curve can be effectively compensated; relatively low acceleration and throwing speed can avoid the high final rolling temperature caused by the increase in the heating temperature of the second half of the slab. However, in continuous casting and rolling lines, molten steel pouring and billet rolling proceed continuously, maintaining a constant flow rate. Continuous casting, influenced by industrial control, requires a stable casting speed. This means that line speed cannot be adjusted simply by adjusting the casting speed. Adjusting line speed in stages requires complex modeling, making implementation difficult.

[0004] Therefore, this type of transition coil now has unstable performance due to changes in the final rolling temperature. There is currently no practical control method. The current single-schedule final rolling temperature hit rate is only 85.7% to 91.5%, resulting in performance mismatch and affecting economic benefits. Summary of the Invention

[0005] The technical task of the present invention is to address the deficiencies of the above-mentioned existing technologies and provide a method for increasing the performance stability of the transition stage of the continuous casting and rolling production line, so as to reduce the adverse effects on performance stability caused by the sudden drop or increase in the speed of each frame of the finishing rolling during the transition of finished product specifications and the intermediate billet stage, improve the final rolling temperature hit rate, and make the final rolling temperature meet the requirements of the steel grade.

[0006] The technical solution of the present invention to solve its technical problem is: a method for increasing the performance stability of a continuous casting and rolling production line in the transition stage, including continuous casting → rough rolling → induction heating → finishing rolling → cooling and coiling, characterized in that: the induction heating furnace outlet temperature control and the looping amount control between finishing rolling and rough rolling are performed: the induction heating furnace outlet temperature control includes pre-adjusting the induction heating furnace outlet temperature, and compensating the production line temperature and finishing rolling outlet speed in advance; the looping amount control between finishing rolling and rough rolling is to modify the looping amount between finishing rolling and rough rolling in advance, so that the looping amount returns to the normal range during the specification transition period.

[0007] Furthermore, the above-mentioned induction heating furnace outlet temperature control is specifically as follows: 2-3 coils before the coil transfer, the induction heating furnace outlet temperature is changed, and the adjustment range is 5-20°C.

[0008] Among them, during the thinning process, the change is to increase the outlet temperature of the induction heating furnace.

[0009] Specifically, the adjustment strategy is carried out according to the thickness specifications and the P and Si contents in the composition.

[0010] Furthermore, the above adjustment strategy is specifically as follows: when P>0.02% and Si≤0.03%, the outlet temperature is adjusted by 5-10°C each time; when P>0.02% and Si>0.03%, the outlet temperature is adjusted by 10-15°C each time; when P≤0.02% and Si≤0.03%, the outlet temperature is adjusted by 10-15°C each time; when P≤0.02% and Si>0.03%, the outlet temperature is adjusted by 15-20°C each time.

[0011] Furthermore, the above-mentioned induction heating furnace outlet temperature control includes over-control, that is, the temperature increase target value is higher than the set upper limit of the induction heating furnace outlet temperature in the non-transition stage.

[0012] Furthermore, the above-mentioned excess range is 5-10°C.

[0013] Furthermore, the advance modification of the looping quantity in the above-mentioned looping quantity control between finishing rolling and roughing rolling is specifically: starting from 2-3 coils before the transfer roll.

[0014] Specifically, the change in the looper amount ΔL is determined according to the change in the intermediate billet transition amount.

[0015] Furthermore, the above-mentioned sleeve amount change ΔL is determined according to the intermediate billet thickness transition ratio p:

[0016]

[0017] Among them, h0 is the original thickness of the intermediate billet, h1 is the thickness of the intermediate billet after transition, and p is the transition ratio of the intermediate billet thickness.

[0018] Compared with the prior art, the present invention has the following outstanding beneficial effects:

[0019] 1. Aiming at the problems in transitional finished product specifications and intermediate billet stages, a hierarchical control scheme is set up to improve the overall hit rate of the final rolling temperature;

[0020] 2. Improve the uniformity of product performance along the length direction by compensating for the unstable final rolling temperature at the finishing rolling exit caused by transition;

[0021] 3. Strong operability and significant economic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the device structure of the present invention.

[0023] Figure 2 It is a schematic diagram of the calculation of the looper amount adjustment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] For purposes of the following detailed description, it should be understood that the present invention may assume various alternative variations and step sequences, unless expressly indicated to the contrary. Furthermore, except in any operating examples or where otherwise indicated, all numbers expressing, for example, the amounts of ingredients used in the specification and claims should be understood as being modified by the term "about" in all cases. At the very least, and without attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0026] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0027] It should also be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0028] In the present invention, unless otherwise specifically stated, the use of the singular includes the plural and the plural encompasses the singular. In addition, in the present invention, unless otherwise specifically stated, the use of "or" means "and / or", even if "and / or" can be explicitly used in certain circumstances. Further, in the present invention, unless otherwise specifically stated, the use of "a" or "an" means "at least one". For example, "a" first material, "a" coating composition, etc., refers to one or more of any of these items.

[0029] The present invention provides a method for increasing the performance stability of a continuous casting and rolling production line during a transition phase.

[0030] The production process of the continuous casting and rolling production line includes: continuous casting → rough rolling → induction heating → finishing rolling → cooling and coiling.

[0031] The present invention addresses the deficiencies in the prior art. The finished product and / or intermediate billet transition stage refers to the transition of the finished product thickness and / or intermediate billet thickness toward thick or thin. For ease of description, it is referred to as "transition roll." During the thickness transition process, after the automatic thickness control adjustment intervenes, the production line speed increases or decreases. While the casting speed remains constant, the production line speed increases from the rough rolling to the finishing rolling section for thin transition, and decreases from the rough rolling to the finishing rolling section for thick transition. This sudden drop or rise in speed will result in improper control of the final rolling temperature, affecting product quality. Therefore, there is an urgent need for a method to maintain the stability of the finished product specifications of the continuous casting and rolling production line and the final rolling temperature of the intermediate billet transition stage.

[0032] Specifically, the method of the present invention is to perform the following control during the transition between the intermediate billet and the finished product specifications. For better explanation, the following description takes the transition to thinness as an example, and the reverse setting of the transition to thickness can be used.

[0033] 1. Induction heating furnace outlet temperature control

[0034] Pre-adjust and control the outlet temperature of the induction heating furnace to compensate the production line temperature and finishing rolling outlet speed in advance.

[0035] Specifically: Start to gradually increase the outlet temperature of the induction heating furnace 2-3 coils before coil transfer, and the adjustment range is 5-20℃.

[0036] In the optimization plan, the upward adjustment strategy is carried out according to the thickness specifications and the P and Si content in the composition:

[0037] For example: when P>0.02% and Si≤0.03%, increase the outlet temperature by 5-10℃ each time;

[0038] When P>0.02% and Si>0.03%, increase the outlet temperature by 10-15℃ each time;

[0039] When P≤0.02% and Si≤0.03%, increase the outlet temperature by 10-15℃ each time;

[0040] When P≤0.02% and Si>0.03%, increase the outlet temperature by 15-20℃ each time;

[0041] The reason for variable control is that temperature control causes a contradiction between the single rising speed of the induction heating furnace module and the occurrence of iron oxide scale on the production line. Through layered control, both temperature and surface are taken into account to avoid concentrated outbreaks of iron oxide scale.

[0042] The optimized solution includes overshoot control during the transition phase, meaning the target temperature increase exceeds the upper limit of the induction furnace outlet temperature during the non-transition phase. The overshoot range is 5-10°C. During operation, after the transition is complete and the finishing mill exit speed stabilizes, the induction furnace outlet temperature is adjusted based on the final rolling temperature.

[0043] The above description takes the transition to thinness as an example, and the reverse setting can be used for the transition to thickness.

[0044] 2. Control of the amount of rolling between finishing and roughing

[0045] The method of the present invention relies on a continuous casting and rolling production line, such as Figure 1-2 As shown, it includes a continuous casting machine 2, a roughing mill group 3, a swing shear 4, a looper device 5, a heating device 6, a finishing mill group 7, a cooling unit 8, a flying shear 9 and a coiler 10.

[0046] A crystallizer 1 is provided between the continuous casting machine 2 and the tundish. The roughing mill 3 is a three-stand roughing mill. The heating device 6 is an induction heating furnace. The flying shear 9 is used to cut the strip steel and coil it by weight; the coiler 10 coils the strip steel 11.

[0047] The finishing mill group 7 is a five-stand finishing mill group. In the optimized solution, inter-stand loopers are provided between the stands of the finishing mill group 7.

[0048] The method of the present invention adds a looper quantity control link between finishing rolling and roughing rolling. The looper device is specifically arranged between the swing shear and the heating device, that is, by modifying the looper quantity between finishing rolling and roughing rolling in advance, the advance modification of the looper quantity in the looper quantity control between finishing rolling and roughing rolling is specifically: starting from 2-3 coils before the coil transfer, the looper quantity returns to the normal range during the specification transition period, and the speed change is compensated by the looper quantity change, so as to keep the speed of each finishing rolling frame stable, and thus keep the final rolling temperature stable.

[0049] The change in sleeve volume ΔL is determined based on the change in the intermediate billet transition volume. The specific control amount is determined based on the intermediate billet thickness transition ratio p:

[0050]

[0051] Among them, h0 is the original thickness of the intermediate billet,

[0052] h1 is the thickness of the intermediate billet after transition,

[0053] p is the transition ratio of the intermediate billet thickness.

[0054] For example, if p < 5%, ΔL is 0;

[0055] For example, if 5%≤p<6%, then ΔL is 0.2m;

[0056] For example, if 6%≤p<7%, then ΔL is 0.5m;

[0057] For example, if 7%≤p<8%, then ΔL is 0.8m;

[0058] If the thickness is transitioning from thick to thin, adjust the sleeve amount downward; if the thickness is transitioning from thin to thick, adjust the sleeve amount upward. After obtaining ΔL, the loop height h is obtained by the following formula:

[0059]

[0060] Where: ΔL is the change in the set amount;

[0061] A is the horizontal distance between the fulcrum of the looper swing arm and the looper support roller;

[0062] B is the horizontal distance between the fulcrum of the looper swing arm and the looper support roller on the other side;

[0063] R is the radius of the looper swing arm;

[0064] r is the radius of the looper roller;

[0065] α is the angle between the looper arm and the horizontal line;

[0066] h is the height of the loop.

[0067] 3. Other control methods

[0068] (1) Reduce the amount of intermediate billet transition:

[0069] The optimized transition amount of the intermediate billet in a single roll is 0.2-0.5mm.

[0070] (2) Increase the pulling speed during the transition period

[0071] The pulling speed target is controlled according to specifications: the target pulling speed below 1.0mm is increased by 0.1-0.2m / min, and the target pulling speed above 1.0mm is increased by 0.1-0.3m / min.

[0072] (3) Ingredient control

[0073] The optimization plan also includes composition control: P ≤ 0.028%, Si ≥ 0.040%. This composition control reduces the occurrence of Class A scale, which can lead to unstable final rolling temperatures. To achieve fully austenitic rolling in the finishing section, higher production line temperatures are required. High-temperature production is highly susceptible to the formation of spot-like scale on the strip surface (the combined segregation of Si and P elements causes the surface scale to blister and rupture, forming spot-like scale). To ensure surface control, maximum and minimum values ​​for P and Si are set for each steel grade.

[0074] In order to better compare the technology of the present invention with the prior art, a comparative test was carried out.

[0075] The steel used is for stamping applications, with a P content of ≤ 0.028% and a Si content of ≥ 0.040%. Product performance requirements include yield strength ≤ 280 MPa, tensile strength ≤ 380 MPa, and elongation ≥ 36%. The continuous casting and rolling line requires full austenitic rolling. The final rolling temperature is between 830°C and 950°C.

[0076] Parameter settings for each embodiment group: Embodiments 1-4 are for controlling the outlet temperature of the induction heating furnace and the looping amount between finishing rolling and roughing rolling; Embodiments 5-8 are for changing only the looping height between finishing rolling and roughing rolling.

[0077] Control groups 1-4 are the existing technology, in which the temperature change control of the induction heating furnace is not performed, and there is no looper control between the finishing rolling and the roughing rolling.

[0078] The results show that the finishing temperature hit rate and performance mismatch re-judgment rate of the transition rolls in the embodiment group and the control group are as follows:

[0079]

[0080]

[0081] As shown in the table above, the control group achieved only 85.7-91.5% of the final rolling temperature hit rate for the first single run, resulting in a 10.5-13.6% reclassification rate for non-compliant performance, severely impacting economic efficiency. The present process, however, achieves a higher final rolling temperature pass rate by increasing the induction furnace outlet temperature and adding loopers between the roughing and finishing mill stands to compensate for speed variations caused by intermediate billets. This significantly reduces scrap caused by non-compliant final rolling temperatures and increases profitability.

[0082] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes to it without departing from the spirit and scope of the present invention are within the scope of protection of the present invention.

Claims

1. A method for increasing the performance stability of a continuous casting and rolling production line during the transition phase, comprising continuous casting → rough rolling → induction heating → finishing rolling → cooling and coiling, characterized in that: The method includes controlling the outlet temperature of the induction heating furnace and controlling the amount of rolling between finishing rolling and rough rolling: The induction heating furnace outlet temperature control includes pre-adjusting the induction heating furnace outlet temperature to compensate for the production line temperature and finishing rolling outlet speed in advance. The induction heating furnace outlet temperature control specifically includes: starting to change the induction heating furnace outlet temperature 2-3 coils before coil transfer, with an adjustment range of 5-20°C; adjusting the strategy based on the thickness specification and the P and Si content in the composition; the specific adjustment strategy is: when P>0.02% and Si≤0.03%, the outlet temperature is adjusted by 5-10°C each time; when P>0.02% and Si>0.03%, the outlet temperature is adjusted by 10-15°C each time; When P≤0.02% and Si≤0.03%, adjust the outlet temperature by 10-15℃ each time; When P≤0.02% and Si>0.03%, adjust the outlet temperature by 15-20℃ each time; The control of the amount of looping between finishing rolling and roughing rolling is achieved by modifying the amount of looping between finishing rolling and roughing rolling in advance, so that the amount of looping returns to the normal range during the specification transition period; the advance modification of the amount of looping in the control of the amount of looping between finishing rolling and roughing rolling is specifically: starting from 2-3 coils before the transfer coil; determining the change in the amount of looping ΔL according to the change in the transition amount of the intermediate billet.

2. The method for increasing the performance stability of a continuous casting and rolling production line during the transition phase according to claim 1, characterized in that: In the transition to thinning, the change is to increase the outlet temperature of the induction heating furnace.

3. The method for increasing the performance stability of a continuous casting and rolling production line during the transition phase according to claim 1, characterized in that: The induction heating furnace outlet temperature control includes over-control, that is, the temperature increase target value is higher than the set upper limit of the induction heating furnace outlet temperature in the non-transition stage.

4. The method for increasing the performance stability of a continuous casting and rolling production line during the transition phase according to claim 3, characterized in that: The excess range is 5-10°C.

5. The method for increasing the performance stability of a continuous casting and rolling production line during the transition phase according to claim 1, characterized in that: The sleeve change ΔL is determined according to the intermediate billet thickness transition ratio p: ， Among them, h0 is the original thickness of the intermediate billet, h1 is the thickness of the intermediate billet after transition, and p is the transition ratio of the intermediate billet thickness.

Images