Method for preventing low-alloy high-strength steel strip from running off in a continuous vertical annealing furnace and application thereof

Abstract

The present application relates to the metallurgical technical field, specifically relates to a kind of method and application for preventing low alloy high-strength steel strip from running deviation in continuous vertical annealing furnace.The method includes that low alloy high-strength steel strip is annealed before first transition material is passed in, so that conveying speed and furnace temperature reach target value;The relationship between the soaking section outlet temperature of low alloy high-strength steel strip and target value is judged, and the conveying speed or furnace temperature is adjusted in steps;When abnormal speed reduction occurs, lower the furnace temperature, tension, and increase the conveying speed.The present application prevents and adjusts the running deviation of low alloy steel strip in continuous vertical annealing furnace, reduces the running deviation accident downtime rate, avoids the decline of steel quality, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method and its application for preventing low-alloy high-strength steel strips from deviating in a continuous vertical annealing furnace. Background Technology

[0002] With the rapid development of cold rolling production technology, continuous vertical annealing furnaces have gradually replaced horizontal and bell-type annealing furnaces due to their advantages such as high production efficiency, good surface quality, and uniform mechanical properties. The annealing process of a vertical continuous annealing furnace includes preheating, heating, homogenization, slow cooling, rapid cooling, and over-aging processes. It mainly performs recrystallization annealing on cold-rolled hard steel strips, enabling the steel strips to achieve grain recovery, recrystallization, and growth after continuous annealing, ultimately forming products with uniform structure and good strength and toughness, which is beneficial for subsequent deep processing.

[0003] Existing continuous vertical annealing furnaces are generally designed with a steel strip running length of around 2000 meters inside the furnace. Due to the numerous rollers and the enclosed structure of the furnace, which makes observation difficult, if a steel strip misalignment occurs and cannot be stopped in time, the steel strip will scrape against the furnace wall, causing a strip breakage and a complete shutdown. After a strip breakage in the furnace area, it is necessary to cool down before restarting the furnace to repair the breakage. After repair, the strip needs to be threaded back, the furnace closed for airtightness testing, and heating up, resulting in at least 3 days of downtime, which will seriously affect production efficiency. In addition, tens of tons of substandard steel strip will be generated during the cooling, testing, and heating processes. Especially for cold-rolled low-alloy high-strength steel, the higher the strength and the thicker the steel strip, the worse its fit with the annealing furnace rollers, and the greater the risk of misalignment. Furthermore, during the long-term operation of a continuous vertical annealing furnace, various abnormal situations and accidents may cause abnormal speed reductions in the steel belt conveyor. During these abnormal speed reductions, the steel belt stays in the annealing furnace for a longer period due to the reduced transport speed, which in turn prolongs the heating time. This can lead to the steel belt temperature exceeding the target value. If measures are not taken in time, the quality of the steel belt will deteriorate, and the incidence of steel belt misalignment and breakage accidents will be further increased.

[0004] In existing technologies, methods for handling strip misalignment and abnormal speed reduction in continuous vertical annealing furnaces mainly include adjusting the conveyor speed and furnace temperature. However, when using existing methods to address strip misalignment, excessive adjustments to the conveyor speed and furnace temperature can easily lead to poor annealing results, resulting in substandard steel strip quality during the strip misalignment treatment period, wasting resources, and affecting production efficiency.

[0005] CN111850280A discloses a method for controlling strip deviation in a continuous annealing mill. The method includes: 1) controlling the incoming strip shape; 2) controlling the crown and wedge values ​​of the hot-rolled strip; sealing and unloading or reworking coils with crown values ​​<40μm or crown values ​​>80μm and wedge values ​​>50μm; 3) cutting off severely defective sections of the strip shape at the beginning and end of the coil, and sealing coils with poor overall shape; 4) controlling strip deviation in the furnace area; when the furnace temperature drops below 700℃, controlling the strip speed at the deviation point, causing it to crawl out of the furnace at a speed of V≤30m / min, and only increasing the furnace speed after the strip deviation is ≤50mm. This invention only focuses on reducing the incidence of deviation accidents and does not consider correcting the quality of steel produced during deviation, which can easily lead to substandard steel quality. Summary of the Invention

[0006] To address the technical problem in existing technologies where excessive adjustments to conveying speed and furnace temperature can lead to poor annealing results, substandard steel strip quality, and resource waste when dealing with strip misalignment in continuous vertical annealing furnaces, this invention provides a method for preventing low-alloy high-strength steel strip misalignment in continuous vertical annealing furnaces. This method prevents and adjusts the misalignment of low-alloy steel strips in continuous vertical annealing furnaces, reducing downtime due to misalignment accidents while avoiding steel quality degradation and improving production efficiency.

[0007] In a first aspect, the present invention provides a method for preventing low-alloy high-strength steel strips from deviating within a continuous vertical annealing furnace, the measures including:

[0008] Before annealing, a transition material is first introduced into the low-alloy high-strength steel strip to ensure that the conveying speed and furnace temperature reach the target values.

[0009] Determine the relationship between the outlet temperature of the soaking section of the low-alloy high-strength steel strip and the target value, and adjust the conveying speed or furnace temperature in a stepwise manner.

[0010] When an abnormal speed reduction occurs, reduce the furnace temperature and tension, and increase the conveyor speed.

[0011] Furthermore, the quantity of transition material is 3-5 rolls, the temperature of each roll of transition material is adjusted not to exceed 15℃, and the speed of each roll of transition material is adjusted not to exceed 20m / min. Simultaneous temperature and speed adjustment during transition material introduction allows the furnace temperature and conveying speed in the continuous vertical annealing furnace to be adjusted to the target temperature and speed suitable for annealing low-alloy high-strength steel. Controlling the parameter adjustment range of each roll of transition material allows for stable regulation of the furnace temperature and conveying speed, ensuring the stability of the furnace roll profile in the vertical annealing furnace.

[0012] Furthermore, when the outlet temperature of the heat-soaking section of the low-alloy high-strength steel strip is higher than the target value, the conveying speed is increased in stages until the outlet temperature of the heat-soaking section of the low-alloy high-strength steel strip decreases to the target value, with an interval of ≥1 minute between each adjustment; for low-alloy high-strength steel strips with a thickness <1.0mm, the single increase in conveying speed is ≤20% of the target value; for steel strips with a thickness ≥1.0mm, the single increase in conveying speed is ≤10m / min.

[0013] When the outlet temperature of the soaking section of the low-alloy high-strength steel strip is lower than the target value, the furnace temperature is increased in stages until the outlet temperature of the soaking section of the low-alloy high-strength steel strip rises to the target value. The interval between each adjustment is ≥2 minutes, the single temperature increase is ≤10℃, and the total temperature increase is ≤30℃.

[0014] When the temperature is high, the conveying speed is increased in stages; when the temperature is low, the furnace temperature is increased in stages. This ensures a smooth temperature transition for the low-alloy high-strength steel strip, avoids quality problems, and reduces the risk of strip breakage or misalignment.

[0015] Furthermore, when an abnormal rate reduction occurs, the furnace temperature is lowered to ensure that the temperature change of the low-alloy high-strength steel strip during the abnormal rate reduction period does not exceed 20°C.

[0016] Furthermore, during the process of increasing the conveyor speed when an abnormal speed reduction occurs, the single speed increase should be ≤20m / min, and the interval between two adjustments should be ≥3min. Adjusting the conveyor speed or furnace temperature according to the operation of the continuous vertical annealing furnace can reduce the risk of deviation accidents caused by excessive temperature during abnormal speed reduction or excessive speed increase during speed increase of low alloy high strength steel strip.

[0017] Furthermore, during normal operation of the low-alloy high-strength steel strip, the tension should be controlled to not exceed 115% of the set value; in the event of abnormal speed reduction, the tension should be reduced by 15%-30% of the set value; after the speed recovers, the tension should be restored to the set value. Reducing the tension during abnormal speed reduction reduces the risk of belt breakage or deviation accidents caused by excessive tension during the speed reduction period.

[0018] Furthermore, the furnace rollers inside the continuous vertical annealing furnace are double-tapered rollers with a surface roughness Ra of 7-10µm. During operation, the double-tapered rollers interact with the low-alloy high-strength steel strip via a conical rolling effect. The low-alloy high-strength steel strip experiences frictional forces from its edges towards the center on both sides, achieving a certain degree of automatic correction and alignment.

[0019] Secondly, the present invention provides an application of the above-mentioned method in the production of low-alloy high-strength steel.

[0020] Furthermore, low-alloy high-strength steel refers to cold-rolled low-alloy high-strength steel with a strength of 260MPa-500MPa.

[0021] Furthermore, the chemical composition and mass percentage of low alloy high-strength steel are as follows: C: 0.07%-0.01%, Si≤0.3%, Mn: 0.65%-1.35%, P: 0.015%-0.03%, S≤0.02%, Als: 0.03%-0.06%, Nb: 0.03%-0.05%, Ti≤0.06%, N≤0.005%, with the remainder being Fe and unavoidable impurities.

[0022] The beneficial effects of this invention are as follows:

[0023] 1. This invention provides a method for preventing low-alloy high-strength steel strip from deviating in a continuous vertical annealing furnace. This method employs measures such as using transition material, adjusting the conveying speed or furnace temperature in stages based on the outlet temperature of the soaking zone, and adjusting the conveying speed, furnace temperature, and tension according to operational conditions. These measures ensure stable regulation of the conveying speed and temperature of the low-alloy high-strength steel strip within the continuous vertical annealing furnace, reducing the downtime rate due to deviating while preventing drastic temperature changes in the strip. This further balances the internal stress of the low-alloy high-strength steel strip, preventing quality problems, reducing the yield of substandard steel, minimizing material and energy waste, and improving production efficiency.

[0024] 2. This invention addresses the stable regulation of the conveying speed, furnace temperature, and tension of low-alloy high-strength steel strips within a continuous vertical annealing furnace. When abnormal speed reduction occurs, it controls the temperature and tension of the low-alloy high-strength steel strip to prevent excessive temperature or stress leading to deviation, thereby further reducing the downtime rate due to deviation accidents and the production rate of substandard steel.

[0025] 3. This invention is applicable to cold-rolled low-alloy high-strength steel strips with strengths ranging from 260MPa to 500MPa. It can be applied to continuous vertical annealing furnaces. The continuous vertical annealing furnace of this invention can achieve continuous and stable production of low-alloy high-strength steel strips, and has good promotion and application value. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0027] Example 1

[0028] A method for preventing low-alloy high-strength steel strip from deviating in a continuous vertical annealing furnace, wherein the furnace rollers inside the annealing furnace are double-tapered rollers with a surface roughness Ra=7.2-9.5µm, comprising:

[0029] Before annealing, a transition material is first introduced into the low-alloy high-strength steel strip to ensure that the conveying speed and furnace temperature reach the target values. The temperature of each roll of transition material introduced shall not exceed 15℃, and the speed of each roll of transition material introduced shall not exceed 20m / min.

[0030] To determine the relationship between the outlet temperature of the homogenization section of the low-alloy high-strength steel strip and the target value, when the outlet temperature of the homogenization section of the low-alloy high-strength steel strip is higher than the target value, the conveying speed is increased in stages until the outlet temperature of the homogenization section of the low-alloy high-strength steel strip decreases to the target value. The interval between each adjustment is ≥1 min. For low-alloy high-strength steel strips with a thickness <1.0 mm, the single increase in conveying speed is ≤20% of the target value. For steel strips with a thickness ≥1.0 mm, the single increase in conveying speed is ≤10 m / min.

[0031] When the outlet temperature of the soaking section of the low-alloy high-strength steel strip is lower than the target value, the furnace temperature is increased in stages until the outlet temperature of the soaking section of the low-alloy high-strength steel strip rises to the target value. The interval between each adjustment is ≥2 minutes, the single temperature increase is ≤10℃, and the total temperature increase is ≤30℃.

[0032] When an abnormal rate reduction occurs, the furnace temperature should be lowered to ensure that the temperature change of the low-alloy high-strength steel strip during the abnormal rate reduction period does not exceed 20°C.

[0033] When an abnormal speed reduction occurs, during the process of increasing the conveying speed, the single speed increase amount should be ≤20m / min, and the interval between two adjustments should be ≥3min;

[0034] When the low-alloy high-strength steel strip is running normally, the tension should be controlled to not exceed 115% of the set value; when an abnormal speed drop occurs, the tension should be reduced by 15%-30% of the set value; after the speed recovers, the tension should be restored to the set value.

[0035] Example 2

[0036] An application of the method of Example 1 in the production of low-alloy high-strength steel, the low-alloy high-strength steel being HC260LA steel, whose chemical composition and mass percentage content are C: 0.07%, Si: 0.05%, Mn: 0.65%, P: 0.015%, S: 0.016%, Als: 0.03%, Nb: 0.03%, N: 0.005%, with the remainder being Fe and unavoidable impurities, the finished product having a thickness of 1.0 mm and a width of 1500 mm.

[0037] The initial conveying speed of the continuous vertical annealing furnace is 260 m / min, and the initial furnace temperature is 750℃. Based on the properties of HC260LA steel strip, the target conveying speed is set to 200 m / min, and the target annealing temperature is set to 790℃. Three rolls of SPCC steel of the same specification are selected as transition material for the transition. During the process of introducing the transition material, the conveying speed and furnace temperature are adjusted to the target values. The speed adjustment range of a single roll is 20 m / min, and the temperature adjustment range of a single roll is 13.3℃.

[0038] During the operation of the steel belt, the highest outlet temperature of the soaking section was 808℃, which was higher than the target value of 790℃. The conveying speed was then increased in stages: the first increase was 5 m / min, followed by a second increase of 5 m / min after a 1-minute interval, and a third increase of 10 m / min after another 1-minute interval. After these three increases, the steel belt temperature returned to 790℃.

[0039] During the operation of the steel strip, a speed reduction occurred, which lowered the furnace temperature. The steel strip temperature rose to a maximum of 807℃, 17℃ higher than the target value. After the abnormal speed reduction, the speed was increased by 10 m / min, and after stabilizing for 3.5 minutes, it was increased again by 20 m / min. After two speed increases, both the annealing temperature and speed returned to the target set values.

[0040] The tension of the steel belt is controlled at 106% of the set value during normal operation. When an abnormal speed drop occurs, the tension value is reduced by 20%. After the speed returns to the target set value, the tension value is restored to the set value.

[0041] By controlling the production of HC260LA low-alloy high-strength steel through the above measures, no steel strip deviation accidents occurred in the continuous vertical annealing furnace.

[0042] Example 3

[0043] An application of the method of Example 1 in the production of low-alloy high-strength steel, the low-alloy high-strength steel being HC340LA steel, whose chemical composition and mass percentage content are C: 0.08%, Si: 0.04%, Mn: 0.8%, P: 0.02%, S: 0.008%, Als: 0.058%, Nb: 0.038%, N: 0.004%, with the remainder being Fe and unavoidable impurities, the finished product having a thickness of 1.5 mm and a width of 1300 mm.

[0044] The initial conveying speed of the continuous vertical annealing furnace is 260 m / min, and the initial furnace temperature is 765℃. Based on the properties of HC340LA steel strip, the target conveying speed is set to 220 m / min, and the target annealing temperature is set to 780℃. Four rolls of DC01 steel of the same specification are selected as transition material for the transition. During the process of introducing the transition material, the conveying speed and furnace temperature are adjusted to the target values. The speed adjustment range for a single roll is 10 m / min, and the temperature adjustment range for a single roll is 5℃.

[0045] During the operation of the steel belt, the highest outlet temperature of the heat-soaking section was 795℃, which was higher than the target value of 780℃. The conveying speed was increased in stages. The first increase was 10m / min, and after a 1min interval, the second increase was 15m / min. The single increase was less than 20% of the target value. After the two increases, the temperature of the steel belt dropped back to 780℃.

[0046] During the operation of the steel strip, a speed reduction occurred, which lowered the furnace temperature. The steel strip temperature rose to a maximum of 792℃, 12℃ higher than the target value. After the abnormal speed reduction, the speed was increased by 10 m / min, and after stabilizing for 3 minutes, the speed was increased again by 15 m / min. After two speed increases, both the annealing temperature and speed returned to the target set values.

[0047] The tension of the steel belt is controlled at 113% of the set value during normal operation. When an abnormal speed drop occurs, the tension value is reduced by 27%. After the speed returns to the target set value, the tension value is restored to the set value.

[0048] By controlling the production of HC340LA low-alloy high-strength steel through the above measures, no steel strip deviation accidents occurred in the continuous vertical annealing furnace.

[0049] Example 4

[0050] An application of the method in Example 1 in the production of low-alloy high-strength steel, the low-alloy high-strength steel being HC500LA steel, with the following chemical composition and mass percentage: C: 0.096%, Si: 0.28%, Mn: 1.33%, P: 0.026%, S: 0.011%, Als: 0.042%, Nb: 0.05%, Ti: 0.056%, N: 0.004%, with the remainder being Fe and unavoidable impurities. The finished product has a thickness of 1.5 mm and a width of 1300 mm.

[0051] The initial conveying speed of the continuous vertical annealing furnace is 200 m / min, and the initial furnace temperature is 780℃. Based on the properties of HC500LA steel strip, the target conveying speed is set to 150 m / min, and the target annealing temperature is set to 765℃. Three rolls of HC340LA steel and two rolls of HC420LA steel of the same specification are selected as transition materials. During the process of introducing the transition materials, the conveying speed and furnace temperature are adjusted to the target values. The speed adjustment range for a single roll is 10 m / min, and the temperature adjustment range for a single roll is 3℃.

[0052] The lowest temperature at the outlet of the soaking section during the operation of the steel strip is 750℃, which is lower than the target value of 765℃. The furnace temperature is increased in stages. The first temperature increase is 5℃, and the second temperature increase is carried out after an interval of 2 minutes. The temperature increase rate is 10m / min. After the two temperature increases, the temperature of the steel strip rises to 765℃.

[0053] No speed reduction occurred during the operation of the steel belt; the steel belt maintained normal operation, and the tension was controlled at 110% of the set value.

[0054] By controlling the production of HC500LA low-alloy high-strength steel through the above measures, no steel strip deviation accidents occurred in the continuous vertical annealing furnace.

[0055] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preventing low-alloy high-strength steel strip from deviating in a continuous vertical annealing furnace, characterized in that, include: Before annealing, a transition material is first introduced into the low-alloy high-strength steel strip to ensure that the conveying speed and furnace temperature reach the target values. The amount of transition material is 3-5 rolls. The temperature of each roll of transition material should not exceed 15℃, and the speed of each roll of transition material should not exceed 20m / min. Determine the relationship between the outlet temperature of the soaking section of the low-alloy high-strength steel strip and the target value, and adjust the conveying speed or furnace temperature in a stepwise manner. Specifically, when the outlet temperature of the heat-soaking section of the low-alloy high-strength steel strip is higher than the target value, the conveying speed is increased in stages until the outlet temperature of the heat-soaking section of the low-alloy high-strength steel strip decreases to the target value, with an interval of ≥1 minute between each adjustment; for low-alloy high-strength steel strips with a thickness <1.0mm, the single increase in conveying speed is ≤20% of the target value; for steel strips with a thickness ≥1.0mm, the single increase in conveying speed is ≤10m / min. When the outlet temperature of the soaking section of the low-alloy high-strength steel strip is lower than the target value, the furnace temperature is increased in stages until the outlet temperature of the soaking section of the low-alloy high-strength steel strip rises to the target value. The interval between each adjustment is ≥2 minutes, the single temperature increase is ≤10℃, and the total temperature increase is ≤30℃. When an abnormal speed reduction occurs, reduce the furnace temperature and tension, and increase the conveyor speed; Among them, when the low alloy high strength steel strip is running normally, the tension is controlled to not exceed 115% of the set value; when an abnormal speed drop occurs, the tension is reduced by 15%-30% of the set value; after the speed is restored, the tension is restored to the set value. The inner rollers of the continuous vertical annealing furnace are double-tapered rollers with a surface roughness Ra=7-10µm.

2. The method as described in claim 1, characterized in that, When an abnormal rate reduction occurs, the furnace temperature should be lowered to ensure that the temperature change of the low-alloy high-strength steel strip does not exceed 20°C during the abnormal rate reduction period.

3. The method as described in claim 1, characterized in that, When an abnormal speed reduction occurs, during the process of increasing the conveying speed, the single speed increase should be ≤20m / min, and the interval between two adjustments should be ≥3min.

4. The application of the method as described in claim 1 in the production of low-alloy high-strength steel.

5. The application as described in claim 4, characterized in that, Low-alloy high-strength steel is cold-rolled low-alloy high-strength steel with a strength of 260MPa-500MPa.

6. The application as described in claim 4, characterized in that, The chemical composition and mass percentage of low alloy high-strength steel are as follows: C: 0.07%-0.01%, Si≤0.3%, Mn: 0.65%-1.35%, P: 0.015%-0.03%, S≤0.02%, Als: 0.03%-0.06%, Nb: 0.03%-0.05%, Ti≤0.06%, N≤0.005%, with the remainder being Fe and unavoidable impurities.