A method and system for controlling iron oxide scale on the surface of hot rolled strip steel

Abstract

The present invention belongs to the field of hot rolling process, and particularly relates to a control method and system for the iron scale on the surface of hot rolling strip, which is applied to the laminar cooling back-end cooling mode: before the strip enters the laminar cooling zone back-end, the corresponding strip surface iron scale control water cooling mode is selected to be turned on according to the properties of the rolled product itself; the strip is controlled to enter the air cooling section after the final rolling of the finishing mill according to the selected water cooling mode for the iron scale on the surface of the strip to control the iron scale on the surface of the strip; after the control is completed, the strip enters the laminar cooling zone back-end for laminar cooling until the strip reaches the target coiling temperature. The control method can reduce the thickness of the iron scale on the surface of the strip to less than 15μm, with a dense structure, and it is not easy to fall off in large pieces / sheets to form black ash, and at the same time, it also realizes the prefabrication of cracks in the iron scale layer on the surface of the strip to a certain extent, and improves the pickling efficiency by 15%-20%.

Description

Technical Field

[0001] The invention belongs to the field of hot rolling technology, and in particular relates to a control method and system for iron oxide scale on the surface of hot rolled strip steel. Background Art

[0002] During the rolling and cooling process of hot-rolled strip, a certain thickness of iron oxide scale will be formed on the surface. Therefore, in the subsequent deep processing process, chemical methods (pickling) or physical methods are usually used to remove it, which not only increases production costs, but also causes environmental pollution.

[0003] Studies have shown that in the production process of hot-rolled strip, in the temperature range of 800℃-1200℃, the thickness of the light oxide scale on the surface of the strip increases exponentially with the increase of temperature. The final rolling temperature of hot-rolled strip is usually in the range of 800℃-900℃, and the thickening of the oxide scale is still an important link after the finish rolling of the strip. Usually, after the final finishing rolling, the strip quickly enters the laminar cooling zone and is quickly cooled to a temperature below 700℃ or even lower, and the thickening of the iron oxide is effectively controlled. However, according to the need for controlled cooling, the laminar cooling control mode includes: front-stage cooling, rear-stage cooling and sparse cooling modes. Under the conditions of the rear-stage cooling, the strip usually runs at a high temperature of more than 800℃ for 5s-12s after the final rolling and then enters the laminar cooling area for cooling. At this stage, the oxide scale on the surface of the strip rapidly thickens to 30μm-50μm, or even thicker. The thickened iron oxide is preserved until the final state of the strip. See the cooling mode for the controlled cooling of the rear-stage cooling of the strip. Figure 1 . In the subsequent deep processing process, the pickling efficiency will be reduced, up to 20% or more, and the acid consumption will be increased. At the same time, the thickened surface oxide scale will produce a large amount of oxide scale falling off to form "black ash" during the finishing or user stamping process. With the development of the entire steel industry and the improvement of downstream processing technology, while higher requirements are placed on the performance and dimensional accuracy of hot-rolled strip steel, new requirements are also put forward for surface quality, especially for hot-rolled steel plates directly used in structural parts. For the frequent surface powdery oxide scale shedding (powdering) defects of hot-rolled strip steel, users nowadays react very strongly, because this defect not only damages the surface quality of the steel plate, but also pollutes the environment, endangers the health of workers, and even damages equipment during the finishing or user processing process. Therefore, the control of the oxide scale on the surface of the strip steel under such process control conditions has become an urgent and critical issue in the industry. However, the cooling control mode of the back-end cooling and the control of the generation of oxide scale are a pair of control contradictions.

[0004] There are other solutions for the generation of iron oxide scale in the prior art. For example, the patent with the publication number CN114054515A proposes a method for controlling the iron oxide scale of cold-rolled base material after rolling, which adopts a two-stage cooling method of sparse cooling and concentrated cooling. The sparse cooling method cools the hot-rolled strip to 780-820°C at a cooling rate of 20-30°C / s, and the laminar cooling water pressure is controlled at 4.7-5.3bar; the concentrated cooling method cools at a cooling rate of 40-50°C / s, and the laminar cooling water pressure is controlled at 6.8-7.2bar. After the hot-rolled strip is cooled to 560-600°C, it enters the coiling step. The surface of the manufactured finished strip is clean and smooth, and no iron oxide scale defects are generated. After testing, the thickness of the iron oxide scale is only 6-8μm. Following the customer's pickling, the pickling speed can be increased to 180m / min. The pickling plate surface is smooth and there is no problem of pickling incompleteness, which fully meets the user's use requirements.

[0005] Another patent with publication number CN110624960B discloses a strip cooling control method combining ultra-fast cooling and conventional laminar cooling. The entire area is divided by a control system. On the rolling line, along the rolling direction of the steel plate, there are three parts: ultra-fast cooling section, laminar cooling rough cooling section, and laminar cooling fine cooling section. The control system cools the strip in sections according to the different water spraying amounts in each cooling section. The patent also involves sparse cooling in the ultra-fast cooling section, that is, starting to open the valve intermittently to achieve slow cooling. None of the above methods involve control in the rear cooling mode. Summary of the invention

[0006] In view of the above problems, the present invention discloses a method for controlling the iron scale on the surface of hot rolled strip steel, wherein the control method is applied in a laminar cooling rear cooling mode, and comprises the following steps:

[0007] Before the strip enters the rear section of the laminar cooling zone, the corresponding strip surface oxide scale control water cooling mode is selected according to the properties of the rolled product;

[0008] According to the selected water cooling mode for controlling the iron scale on the surface of the strip, the strip is controlled to enter the air cooling section after the final rolling of the finishing mill to control the iron scale on the surface of the strip;

[0009] After the control is completed, the strip enters the laminar post-cooling zone for laminar post-cooling until the strip reaches the target coiling temperature.

[0010] Furthermore, the properties of the rolled product include target thickness, final rolling temperature, target coiling temperature and rolling speed;

[0011] The water cooling mode for controlling the iron oxide scale on the surface of the strip steel includes a water cooling mode for controlling the iron oxide scale on the surface of the strip steel for one section and a water cooling mode for controlling the iron oxide scale on the surface of the strip steel for two sections;

[0012] The water cooling mode for controlling the iron oxide scale on the surface of the first strip steel includes first-stage cooling, first-stage air cooling and laminar rear-stage cooling in sequence;

[0013] The water cooling modes for controlling the iron oxide scale on the surface of the two sections of strip steel include stage I cooling, stage I air cooling, stage II cooling, stage II air cooling and laminar rear cooling in sequence.

[0014] Furthermore, the water cooling mode of controlling the iron oxide scale on the surface of the two sections of strip steel specifically includes the following steps:

[0015] After the strip enters the air cooling section, the first group of cooling headers is immediately opened to carry out stage I cooling;

[0016] After the first stage of cooling is completed, the first stage of air cooling is carried out within the set interval time or the set length;

[0017] After the first stage of air cooling is completed, the second group of cooling headers are opened to cool the strip steel in the second stage;

[0018] After the second stage cooling is completed, the second stage air cooling is carried out within the set interval time or the set length;

[0019] After the second stage of air cooling, the strip enters the laminar cooling zone for cooling.

[0020] Furthermore, the water cooling mode of controlling the iron oxide scale on the surface of the strip steel section specifically comprises the following steps:

[0021] After the strip enters the air cooling section, the first group of cooling headers is immediately opened to carry out stage I cooling;

[0022] After the first stage of cooling is completed, the first stage of air cooling is carried out within the set interval time or the set length;

[0023] After the first stage of air cooling, the strip enters the laminar cooling zone for cooling.

[0024] Furthermore, the cooling water pressure of the stage I cooling or stage II cooling is 0.06-0.08MPa;

[0025] The setting time is 3-5s, and the setting length is 10-15m.

[0026] Furthermore, the flow rate of the cooling stage I is controlled at 100-120m 3 / h, the flow rate of stage II cooling is controlled at 80-100m 3 / h.

[0027] Furthermore, the method can also be applied to a hot rolling production line equipped with front-end ultra-fast cooling.

[0028] Furthermore, the first group of cooling headers are the first 1-3 headers of the laminar cooling zone, and the first group of cooling headers are opened symmetrically up and down.

[0029] On the other hand, the present invention also proposes a control system for iron oxide scale on the surface of hot rolled strip steel, and the control system is used to execute the control method.

[0030] Further, the control system includes a cooling temperature control model;

[0031] The cooling temperature control model is used to analyze the properties of the rolled product before entering the rear section of the laminar cooling zone, and configure the corresponding strip surface oxide scale control water cooling mode according to the analysis results to ensure stable temperature control.

[0032] Beneficial effects of the present invention:

[0033] The present invention proposes a method for controlling the surface scale of strip steel after final rolling in a controlled cooling mode of the back section of laminar cooling during hot rolling. The method is implemented to achieve hot rolling to ensure that the controlled rolling and controlled cooling process meets the conditions, and the product performance is stable, and the method focuses on solving the problem of significantly inhibiting the thickening of the surface scale of strip steel under the condition of long-term controlled cooling of the strip steel. The method has been industrially applied for one year, and nearly 1 million tons of strip steel has been produced, including hot rolling commodity materials and cold rolling raw materials. The specific varieties include carbon structural steel, vanadium microalloyed steel, atmospheric corrosion resistant steel, low-carbon aluminum killed steel and ultra-deep drawing steel, etc. The mechanical properties of the product are stable, the thickness of the surface scale of the strip steel is reduced to less than 15μm, the structure is dense, and it is not easy to fall off in large pieces / sheets to form black ash. At the same time, it also realizes the prefabrication of the surface scale cracks of the strip steel to a certain extent, and improves the pickling efficiency by 15%-20%.

[0034] The control method proposed in the present invention is suitable for hot rolling control cooling and quality control, and can realize process automation control in the industrial production process, meet the coiling temperature precision control of the rolling process, and has strong creativity and practicality; and based on the existing process equipment and control, there is no need to increase investment, the practical effect is good, and it has good promotion and application value. The process technology is mature, the implementation and application are convenient and reliable, and the reproduction and reproducibility are good.

[0035] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 The figure shows the controlled cooling mode of the hot strip after final rolling in the prior art;

[0038] Figure 2 A flow chart showing a method for controlling iron oxide scale on the surface of hot rolled strip steel in an embodiment of the present invention is shown;

[0039] Figure 3 A schematic diagram of a process for controlling iron scale on the surface of a hot-rolled strip in a laminar flow controlled cooling mode after final rolling of the hot-rolled strip in an embodiment of the present invention is shown;

[0040] Figure 4 The statistical distribution diagram of the yield strength of the strip steel produced in the embodiment of the present invention is shown;

[0041] Figure 5 The statistical distribution diagram of the tensile strength of the strip steel produced in the embodiment of the present invention is shown;

[0042] Figure 6 The result statistical distribution diagram of the elongation of the strip steel produced in the embodiment of the present invention is shown;

[0043] Figure 7 The metallographic structure diagram of the inner part of the strip steel produced in the embodiment of the present invention is shown;

[0044] Figure 8 A physical picture showing a steel strip produced in an embodiment of the present invention after deep bending at 90° is shown;

[0045] Fig. 9 A schematic diagram showing the upper surface of a steel strip produced in an embodiment of the present invention is shown;

[0046] Fig.10 A schematic diagram of the lower surface of the steel strip produced in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present invention provides a control technology for the iron oxide scale on the surface of a steel strip after final rolling in a laminar cooling rear stage controlled cooling mode during hot rolling, focusing on solving the problem of significantly suppressing the thickening of the iron oxide scale on the surface of the steel strip under the condition of long-term controlled cooling of the steel strip.

[0049] The method for controlling the iron scale on the surface of hot rolled strip steel proposed by the present invention is as follows: Figure 2 As shown, it is applied in the rear cooling mode, including the following steps:

[0050] Before the strip enters the rear section of the laminar cooling zone, the corresponding strip surface oxide scale control water cooling mode is selected according to the properties of the rolled product;

[0051] According to the selected water cooling mode for controlling the iron scale on the surface of the strip, the strip is controlled to enter the air cooling section after the final rolling of the finishing mill to control the iron scale on the surface of the strip;

[0052] After the control is completed, the strip enters the laminar post-cooling zone for laminar post-cooling until the strip reaches the target coiling temperature.

[0053] It should be noted that the properties of the rolled product include target thickness, final rolling temperature, target coiling temperature and rolling speed; the water cooling mode for controlling the oxide scale on the strip surface includes a one-stage water cooling mode for controlling the oxide scale on the strip surface and a two-stage water cooling mode for controlling the oxide scale on the strip surface; the one-stage water cooling mode for controlling the oxide scale on the strip surface includes stage I cooling, stage I air cooling and laminar rear cooling in sequence; the two-stage water cooling mode for controlling the oxide scale on the strip surface includes stage I cooling, stage I air cooling, stage II cooling, stage II air cooling and laminar rear cooling in sequence.

[0054] Specifically, in the laminar cooling rear section controlled cooling mode, the strip enters the air cooling section after final rolling by the finishing mill. Before the strip enters the laminar cooling zone, the laminar cooling starts the rear section cooling mode, and the first group of cooling headers (one each for the upper and lower) are started at the same time. After an interval of 3-5s or 10-15m, it is determined whether to start another group of cooling headers according to the needs, that is, an interval cooling process is realized, which specifically includes two situations:

[0055] The first is a water cooling mode that controls the iron oxide scale on the surface of two-stage strip steel: the cooling process of stage I cooling - stage I air cooling - stage II cooling - stage II air cooling - entering the cooling area after laminar cooling is carried out in sequence, so that the strip steel is cooled to the target coiling temperature.

[0056] The second is a water cooling mode that controls the iron oxide scale on the surface of two-stage strip steel: the cooling process of stage I cooling - stage I air cooling - entering the cooling area of ​​the laminar cooling rear section is carried out in sequence, so that the strip steel is cooled to the target coiling temperature.

[0057] It should be noted that whether the second stage cooling is turned on or not is selected according to the target thickness of the rolled product, the final rolling temperature, the target coiling temperature and the rolling speed. However, the first stage cooling must be turned on to achieve the temperature of the strip to drop to or close to 700°C through the full air cooling section.

[0058] Furthermore, in the above process, the cooling flow rate of stage I is controlled at 100-120m 3 / h, the cooling flow rate of stage II is controlled at 80-100m 3 / h, achieved by opening 1-3 single headers for laminar cooling. The first 1-3 headers for laminar cooling must be opened symmetrically up and down to ensure uniform cooling of the strip;

[0059] Further, the cooling water pressure of stage I cooling or stage II cooling is 0.06-0.08MPa, and the side spray of the group to which it belongs is turned on;

[0060] In another embodiment of the present invention, when the method is applied to a hot rolling production line equipped with a front-stage ultra-fast cooling (UFC), stage I cooling is started from the first stage of ultra-fast cooling, the cooling water pressure is adjusted to 0.06-0.08 MPa, and the flow rate is controlled according to the above flow control conditions;

[0061] Furthermore, during rolling, under the condition that the control capability of the production line process equipment is met, the finishing mill is used for high-speed rolling, and the rolling speed of the last stand is ≥5.0m / s.

[0062] The control method effectively solves the problem of iron oxide scale on the surface of the strip while ensuring the required laminar cooling control process conditions of the strip.

[0063] Based on the above-mentioned control method for the iron oxide scale on the surface of hot-rolled strip, a control system for the iron oxide scale on the surface of hot-rolled strip is designed to execute the above-mentioned control method, and the water cooling mode of the iron oxide scale control on the surface of the strip is modeled: according to the process control requirements, the water cooling mode of the iron oxide scale control on the surface of the strip is written into the process control model, the iron oxide scale suppression water that is turned on participates in the laminar cooling temperature control model control, and is solidified into a special control mode to ensure stable temperature control, and the corresponding cooling temperature control model is set;

[0064] The control system includes a cooling temperature control model; it is used to analyze the properties of the rolled product before entering the rear section of the laminar cooling zone, and configure the corresponding strip surface oxide scale control water cooling mode according to the analysis results to ensure stable temperature control.

[0065] The control method is described below in conjunction with embodiments.

[0066] Example 1 (taking two-stage cooling mode as an example)

[0067] by Figure 3 Take the schematic diagram shown as an example, Figure 3 The first two-stage cooling mode is shown, that is, the cooling process of stage I cooling - stage I air cooling - stage II cooling - stage II air cooling - entering the cooling area after laminar cooling. Figure 3 The process of interval cooling is explained in detail. The first stage cooling adopts symmetrically opening one cooling header on the upper and lower sides (i.e., first stage cooling). After an interval of 10-15m (i.e., air cooling), another group of cooling headers are symmetrically opened (i.e., second stage cooling). After an interval of 10-15m (i.e., air cooling), the strip enters the cooling area after laminar cooling.

[0068] Test Example 1

[0069] According to the above control method, 80 heats of strip steel are produced, and the performance of the produced 80 heats of strip steel and the metallographic structure inside the strip steel are tested, wherein the performance of the strip steel includes the test of yield strength, tensile strength and elongation. The test results are as follows: Figure 4-Figure 7 As shown;

[0070] in, Figure 4 The statistical distribution diagram of the yield strength of the strip steel produced according to the method of the present invention is shown. It can be seen that the yield strength of the produced strip steel is above 335 MPa, and most of the yield strengths are between 356-375 MPa and between 376-395 MPa;

[0071] Figure 5 The statistical distribution diagram of the tensile strength of the steel strips produced according to the method of the present invention is shown. It can be seen that the tensile strength of the steel strips produced is above 440 MPa, most of which are concentrated between 461-480 MPa and 481-500 MPa;

[0072] Figure 6 The statistical distribution diagram of the elongation of the strip steel produced by the method of the present invention is shown. It can be seen that the elongation of the produced strip steel is above 26%, among which most of them are concentrated between 33-35% and 36-38%;

[0073] Figure 7The metallographic structure diagram of the inner part of the steel strip produced according to the method of the present invention is shown. It can be seen that the metallographic structure of the steel strip produced is good.

[0074] Test Example 2: The iron oxide scale on the surface of the manufactured steel strip was tested.

[0075] The strip steel produced by the control method of the present invention is bent deep by 90°, as shown in the figure below. Figure 8 As shown in the figure, it can be seen that the iron oxide scale on the surface of the strip does not fall off in large pieces to form "black ash". Further observation of the upper surface of the strip (such as Fig. 9 as shown) and the lower surface (as Fig.10 As shown), it can be seen that the iron oxide scale on the surface of the strip is thin and dense, and there is a certain degree of crack prefabrication, which realizes the prefabrication of cracks in the iron oxide scale layer on the surface of the strip and improves the pickling efficiency by 15%-20%.

[0076] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling iron oxide scale on the surface of hot rolled strip, characterized in that: The control method is applied in the laminar cooling rear cooling mode, and comprises the following steps: Before the strip enters the rear section of the laminar cooling zone, the corresponding strip surface scale control water cooling mode is selected to be turned on according to the properties of the rolled product itself; the strip surface scale control water cooling mode includes a one-stage strip surface scale control water cooling mode and a two-stage strip surface scale control water cooling mode; the one-stage strip surface scale control water cooling mode includes I-stage cooling, I-stage air cooling and laminar rear section cooling in sequence; the two-stage strip surface scale control water cooling mode includes I-stage cooling, I-stage air cooling, II-stage cooling, II-stage air cooling and laminar rear section cooling in sequence; the two-stage strip surface scale control water cooling mode specifically includes the following steps: immediately after the strip enters the air cooling section, the first group of cooling headers are turned on to perform I-stage cooling; I After the first stage of cooling, perform stage I air cooling within the set interval time or set length; after the first stage of air cooling, open the second group of cooling headers to perform stage II cooling on the strip; after the second stage of cooling, perform stage II air cooling within the set interval time or set length; after the second stage of air cooling, the strip enters the laminar cooling zone for cooling; the water cooling mode for controlling the iron oxide scale on the surface of the first stage of strip specifically includes the following steps: immediately open the first group of cooling headers after the strip enters the air cooling section to perform stage I cooling; after the first stage of cooling, perform stage I air cooling within the set interval time or set length; after the first stage of air cooling, the strip enters the laminar cooling zone for cooling; the first group of cooling headers are the first 1-3 headers in the laminar cooling zone, and the first group of cooling headers are opened symmetrically up and down; According to the selected water cooling mode for controlling the iron scale on the surface of the strip, the strip is controlled to enter the air cooling section after the final rolling of the finishing mill to control the iron scale on the surface of the strip; After the control is completed, the strip enters the laminar post-cooling zone for laminar post-cooling until the strip reaches the target coiling temperature.

2. The method for controlling the iron oxide scale on the surface of hot rolled strip according to claim 1, characterized in that: The inherent properties of the rolled product include target thickness, final rolling temperature, target coiling temperature and rolling speed.

3. The method for controlling the iron oxide scale on the surface of hot rolled strip according to claim 1, characterized in that: The cooling water pressure of the first stage cooling or the second stage cooling is 0.06-0.08MPa; The setting time is 3-5s, and the setting length is 10-15m.

4. The method for controlling the iron oxide scale on the surface of hot rolled strip according to claim 1, characterized in that: The flow rate of the first stage cooling is controlled at 100-120 , the flow rate of stage II cooling is controlled at 80-100 .

5. The method for controlling the iron oxide scale on the surface of hot rolled strip according to any one of claims 1 to 4, characterized in that: The method can also be applied to a hot rolling production line equipped with front-end ultra-fast cooling.

6. A control system for iron oxide scale on the surface of hot rolled strip, characterized in that: The control system is used to execute the control method described in any one of claims 1-5.

7. The control system according to claim 6, characterized in that: The control system includes a cooling temperature control model; The cooling temperature control model is used to analyze the properties of the rolled product before entering the rear section of the laminar cooling zone, and configure the corresponding strip surface oxide scale control water cooling mode according to the analysis results to ensure stable temperature control.

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