Preparation method of medium-high carbon steel hot-rolled coil and medium-high carbon steel

Abstract

The invention discloses a preparation method of a medium-high carbon steel hot-rolled coil and medium-high carbon steel. The preparation method of the medium-high carbon steel hot-rolled coil comprises the steps that slab continuous casting is conducted, specifically, molten medium-high carbon steel is subjected to casting and drawing to obtain a slab, the slab is subjected to pre-descaling treatment to reduce oxide on the surface of the slab, and a pretreated slab is obtained; plate blank heating, specifically, the pretreated plate blank is subjected to heating treatment, high-pressure water descaling treatment is conducted after heating treatment is finished, and a to-be-machined plate blank is obtained; and rolling is conducted, specifically, the to-be-machined plate blank is rolled, and strip steel is obtained. According to the preparation method disclosed by the embodiment of the invention, the slab subjected to slab continuous casting is subjected to pre-descaling treatment before being put into a furnace to be heated, and is subjected to high-pressure water descaling treatment before being rolled after being heated, so that the initial thicker oxide scale on the surface of the slab is removed, and the uniformity of the oxide scale formed on the surface of the slab during hot rolling is ensured to be good.

Description

Technical Field

[0001] The present application belongs to the technical field of medium-high carbon steel rolling, and in particular relates to a method for preparing a medium-high carbon steel hot-rolled coil and the medium-high carbon steel. Background Art

[0002] In the production of existing medium-high carbon steel (0.2% < C < 1.3%) hot-rolled strip, due to the high carbon content, the rolling force is much higher than that of general steel grades, which requires the slab to be heated at a higher temperature and a certain heating time. Therefore, the slab surface oxide scale is thicker, and the strip oxide scale formed after hot rolling is also thicker. If the scale is not removed cleanly, it may even cause indentation. During the rolling process of the finishing mill, a thick and difficult-to-remove oxide scale is generated on the surface of the strip. In addition, when the strip or coil is cooled, there are large differences in the cooling speed between the edge and the middle, and between the head, tail and middle, resulting in large differences in the thickness and structure of the oxide scale in the transverse and longitudinal directions of the hot-rolled strip. Summary of the invention

[0003] The embodiments of the present application provide a method for preparing a hot-rolled medium-high carbon steel coil and the medium-high carbon steel. By adjusting the heating and rolling processes of the medium-high carbon steel, the structure of the oxide scale is improved while the thickness of the oxide scale is reduced, thereby effectively reducing the oxide residue in the strip or coil.

[0004] In the first aspect, the present application provides a method for preparing medium-high carbon steel hot-rolled coils, comprising: slab continuous casting: casting and drawing medium-high carbon steel molten steel to obtain slabs, pre-descaling the slabs to reduce oxides on the surface of the slabs to obtain pre-treated slabs; slab heating: heating the pre-treated slabs, and performing high-pressure water descaling after the heating treatment to obtain slabs to be processed; rolling: rolling the slabs to be processed to obtain strip steel.

[0005] According to the present application, the slab after continuous casting in this method is pre-descaled before heating treatment, and is descaled with high-pressure water before rolling after heating treatment to remove the initial thick iron oxide scale on the surface of the slab and ensure that the iron oxide scale formed on the surface of the slab during rolling is uniform.

[0006] In some embodiments, the pre-descaling treatment is to use 5mbar to 15mbar water to clean the surface of the slab; and / or, the high-pressure water descaling treatment is performed using a descaling machine, the descaling pressure of the front header of the descaling machine is 200mbar-240mbar, and the descaling pressure of the rear header of the descaling machine is 300mbar-340mbar.

[0007] In some embodiments, in the step of continuous casting of the slab, the thickness of the slab is 60 mm-70 mm.

[0008] In some embodiments, the slab heating step is carried out in a heating furnace, the heating furnace is provided with multiple heating zones, the air-fuel ratio of each heating zone is between 3.0-3.5; and / or the furnace outlet temperature of the pretreated slab is 1150℃-1200℃; and / or the heating treatment time is 15min-40min.

[0009] In some embodiments, the rolling step is performed by a finishing mill, the finishing mill comprises N stands, N is an integer not less than 5; and / or the final rolling temperature (FDT) of the rolling is 820°C-920°C.

[0010] In some embodiments, the reduction rate of the first stand is greater than 45%; and / or the rolling speed of the first stand is greater than 0.6 m / s; and / or the reduction rate of the second stand is greater than 35%; and / or the cooling water between the N-3 stand and the N-2 stand is closed, the cooling water between the N-2 stand and the N-1 stand is closed, and the cooling water between the N-1 stand and the N stand is closed; and / or the side water sprays of the N-2 stand, the N-1 stand and the N stand are all closed.

[0011] According to this embodiment, the method for preparing medium-high carbon steel hot-rolled coils of the present application can effectively reduce the thickness of the oxide scale generated during the rolling process by controlling the low furnace temperature and rolling temperature, the higher rolling speed, and reducing the contact between the strip and the air.

[0012] At the same time, the cooling water flow rate on the front side of the coiling is reduced, the uniformity of the lateral temperature of the strip is improved, the consistency of the oxide scale structure is improved, and it is easier to remove it by pickling.

[0013] In some embodiments, the steel strip is subjected to laminar cooling treatment, and after the laminar cooling treatment, the steel strip is curled into a steel coil and slowly cooled; preferably, the laminar cooling treatment adopts a front-stage cooling mode, and the redundant side water spraying of the laminar cooling is turned off, while the flow rate of the cooling water of the side guide and pinch rollers is reduced by not less than 45%; and / or, the temperature of the coiled steel strip is 600°C-700°C; and / or, the slow cooling time is not less than two days.

[0014] According to this embodiment, the preparation method of medium and high carbon steel hot-rolled coils of the present application adopts a front-stage cooling mode and reduces the cooling water flow of the pinch rollers to improve the uniformity of the steel coil temperature, improve the internal and external temperature difference after coiling, improve performance stability, and at the same time improve the longitudinal uniformity of the hot-rolled iron oxide scale.

[0015] At the same time, compared with the existing process, the preparation method of the medium and high carbon steel hot-rolled coil of the present application adopts a lower coiling temperature and a faster cooling rate. On the one hand, the thickness of the iron oxide scale generated during the cooling process is reduced. On the other hand, the contact time between the surface of the strip and the air is short, and the combination of oxygen and Fe makes it easier to obtain an iron oxide scale with a ferrous oxide structure, which is looser than the structure of ferroferric oxide and is easy to pickle.

[0016] In some embodiments, the method for preparing medium-high carbon steel hot-rolled coil of the present application may further include pickling: pickling the steel strip or steel coil.

[0017] In some embodiments, the concentration of the pickling acid solution is 100 g / L-200 g / L; and / or the pickling speed is 50 mpm-150 mpm.

[0018] According to this embodiment, the method for preparing medium-high carbon steel hot-rolled coils of the present application adopts a reasonable pickling process, which can effectively reduce the residual iron oxide scale of the medium-high carbon steel pickling.

[0019] In a second aspect, the present application provides a medium-high carbon steel, which is prepared according to the method for preparing a medium-high carbon steel hot-rolled coil according to any embodiment of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 This is a photo of the surface of the steel coil after pickling of S50C in Example 1 of the present application using the method of the present application;

[0022] Figure 2 This is a sampling test diagram of the hot rolled coil of S50C in Example 1 of the present application before pickling using the method of the present application;

[0023] Figure 3 This is a photo of the surface of the 65Mn steel coil after pickling using the method of the present application in Example 2 of the present application;

[0024] Figure 4 This is a sampling test diagram of the hot rolled coil of 65Mn before pickling using the method of the present application in Example 2 of the present application;

[0025] Figure 5 This is a photo of the surface of the steel coil after pickling using the existing process for S50C in Comparative Example 1 of the present application;

[0026] Figure 6 This is a sampling test diagram of the hot rolled coil of S50C before pickling using the existing process in Comparative Example 1 of the present application;

[0027] Figure 7 This is a photo of the surface of the 65Mn steel coil after pickling using the existing process in Comparative Example 2 of the present application;

[0028] Figure 8This is a sampling and testing diagram of the hot-rolled coil of 65Mn before pickling using the existing process in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0029] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0030] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unclearly recorded range; and any lower limit can be combined with other lower limits to form an unclearly recorded range, and any upper limit can be combined with any other upper limit to form an unclearly recorded range. In addition, although not clearly recorded, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unclearly recorded range.

[0031] The above-mentioned inventive content of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates an exemplary embodiment. In many places throughout the application, guidance is provided by a series of embodiments, which can be used in various combinations. In each example, the enumeration is only a representative group and should not be interpreted as exhaustive. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0032] Iron oxide scale is a corrosion product formed by oxidation of steel at high temperature. Its structure from inside to outside is: ferrous oxide, ferroferric oxide, and ferric oxide. Among them, ferrous oxide has a loose and unstable structure, weak protective effect, and is easy to remove, while ferric oxide and ferric oxide have a dense structure, good protective properties, and are difficult to remove. The formation mechanism of iron oxide scale is related to the temperature and duration of the combination of iron and oxygen. When the high-temperature iron is in contact with air for a short time and there is insufficient oxygen, the structure of ferrous oxide will be generated first. When it is in contact with air for a long time, ferrous oxide will be oxidized to a stable structure of ferric oxide and ferric oxide.

[0033] In the production of existing medium-high carbon steel (0.2% < C < 1.3%) hot-rolled strip, due to the high carbon content, the rolling force is much higher than that of general steel grades, which requires the slab to be heated at a higher temperature and a certain heating time. Therefore, the slab surface oxide scale is thicker, and the strip oxide scale formed after hot rolling is also thicker. If the scale is not removed cleanly, it may even cause indentation. During the rolling process of the finishing mill, the high temperature and slow rolling speed will cause thick and difficult-to-remove oxide scale on the surface of the strip. In addition, when the strip or coil is cooled, there are large differences in the cooling speed between the edge and the middle, and between the head, tail and middle, resulting in large differences in the thickness and structure of the oxide scale in the transverse and longitudinal directions of the hot-rolled strip. Therefore, after pickling, the hot-rolled coil of medium-high carbon steel often has the phenomenon of oxide scale indentation or residue on the surface. It is difficult to effectively improve it by optimizing the pickling process alone, which brings great losses to the production plant.

[0034] In view of the above-mentioned technical problems, an embodiment of the present application provides a method for preparing medium-high carbon steel hot-rolled coils. In this method, the slab after continuous casting is pre-descaled before heating treatment, and then high-pressure water descaling is performed before rolling after heating treatment to remove the initial thick iron oxide scale on the surface of the slab and ensure that the iron oxide scale formed on the surface of the slab during rolling is uniform.

[0035] The following first introduces the method for preparing the medium-high carbon steel hot-rolled coil provided in the embodiments of the present application.

[0036] According to the present application, the preparation method includes: slab continuous casting: casting and drawing medium-high carbon steel liquid to obtain slabs, pre-descaling the slabs to reduce oxides on the surface of the slabs to obtain pre-treated slabs; slab heating: heating the pre-treated slabs, and performing high-pressure water descaling after the heating treatment to obtain slabs to be processed; rolling: rolling the slabs to be processed to obtain strip steel.

[0037] The inventors found that after continuous casting, the slab is pre-descaled before entering the furnace for heating, and after the heating treatment, it is descaled with high-pressure water before rolling to remove the initial thick iron oxide scale on the surface of the slab and ensure that the iron oxide scale formed on the surface of the slab during hot rolling is uniform.

[0038] It should be noted that the descaling process in the existing process is only performed after the slab is heated and before rolling.

[0039] In some embodiments, the pre-descaling treatment is to use 5mbar to 15mbar water to clean the surface of the slab to remove part of the iron oxide and foreign matter on the surface of the slab, for example, it can be 5mbar, 8mbar, 9mbar, 10mbar, 12mbar, 15mbar, or any combination range of the above values; and / or, the high-pressure water descaling treatment uses a descaling machine for descaling, the descaling pressure of the front manifold of the descaling machine is 200mbar-240mbar, for example, it can be 200mbar, 210mbar, 220mbar, 230mbar, 240mbar, or any combination range of the above values, and the descaling pressure of the rear manifold of the descaling machine is 300mbar-340mbar, for example, it can be 300mbar, 310mbar, 320mbar, 330mbar, 340mbar, or any combination range of the above values.

[0040] In some embodiments, in the step of continuous casting of the slab, the thickness of the slab is 60 mm-70 mm, for example, it can be 60 mm, 61 mm, 62 mm, 64 mm, 66 mm, 68 mm, 70 mm, or any combination range of the above values.

[0041] In some embodiments, the slab heating step is carried out in a heating furnace, and the heating furnace is provided with a plurality of heating zones, and the plurality is an integer not less than 2, for example, the number of heating zones can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., and the air-fuel ratio of each heating zone is between 3.0 and 3.5, for example, it can be 3.0, 3.05, 3.1, 3.2, 3.3, 3.4, 3.5, or any combination range of the above numerical values; and / or, the furnace discharge temperature of the pretreated slab is 1150°C-1200°C, for example, it can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, or any combination range of the above numerical values; and / or, the heating treatment time is 15min-40min, for example, it can be 15min, 20min, 25min, 30min, 35min, 40min, or any combination range of the above numerical values.

[0042] In some embodiments, the rolling step is performed by a finishing mill, which includes N stands, N is an integer not less than 5, for example, N can be 5, 6, 7, 8, 9, 10, etc.; and / or the final rolling temperature (FDT) of the rolling is 820°C-920°C, for example, it can be 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, or any combination range of the above numerical values.

[0043] In some embodiments, the reduction rate of the first stand is greater than 45%, for example, it can be 45.1%, 45.5%, 46%, 48%, 50%, 52%, 55%, 60%, 65%, 70%, or any combination of the above values; and / or, the rolling speed of the first stand is greater than 0.6 m / s, for example, it can be 0.61 m / s, 0.63 m / s, 0.65 m / s, 0.67 m / s, 0.7 m / s, 0.75 m / s, 0.8 m / s, or any combination of the above values. range; and / or, the reduction rate of the second rack is greater than 35%, for example, it can be 35.1%, 35.5%, 36%, 38%, 40%, 45%, 50%, 55%, 60%, or any combination range of the above values; and / or, the cooling water between the N-3 rack and the N-2 rack is closed, the cooling water between the N-2 rack and the N-1 rack is closed, and the cooling water between the N-1 rack and the N rack is closed; and / or, the side water sprays of the N-2 rack, the N-1 rack and the N rack are all closed.

[0044] For example, taking N=7 as an example, the finishing mill group includes 7 rolling steel frames, namely F1-F7, the reduction ratios of F1 and F2 frames are greater than 45% and 35% respectively, and the rolling speed of F1 frame is greater than 0.6m / s. The inter-frame cooling water between F4-F5, F5-F6, and F6-F7 frames is turned off, and the cooling water between the first few groups of frames is turned on normally; the side spray water of F5-F7 frames is turned off.

[0045] In some of the above embodiments, the method of the present application can effectively reduce the thickness of the oxide scale generated during the rolling process by controlling the low furnace temperature of 1150℃-1200℃ and the rolling temperature of 820℃-920℃ and the rolling speed greater than 0.6m / s to reduce the contact between the strip and the air.

[0046] In some embodiments, the steel strip is subjected to laminar cooling treatment, and after the laminar cooling treatment, the steel strip is curled into a steel coil and slowly cooled; preferably, the laminar cooling treatment adopts a front-stage cooling mode, and the excess side water spraying of the laminar cooling is turned off, and the flow rate of the side guide and pinch roller cooling water is reduced by not less than 45%, for example, it can be 45%, 47%, 50%, 52%, 55%, 60%, 65%, 70%, or any combination range of the above values; the side water spraying of the finishing mill and the excess side water spraying of the laminar cooling are turned off, and the flow rate of the side guide cooling water before coiling is reduced to improve the uniformity of the transverse temperature of the steel strip, improve the consistency of the iron oxide scale structure, and facilitate pickling and removal. And / or, the temperature of the steel strip curling is 600℃-700℃, for example, it can be 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, or any combination range of the above values;

[0047] The slow cooling time is not less than two days, for example, it can be two days, three days, four days, five days, six days, etc.

[0048] In some of the above embodiments, the method of the present application adopts a front-stage cooling mode and reduces the cooling water flow of the pinch rollers to improve the uniformity of the steel coil temperature, improve the internal and external temperature difference after coiling, improve performance stability, and at the same time improve the longitudinal uniformity of the hot-rolled iron oxide scale.

[0049] At the same time, compared with the existing process, the preparation method of medium-high carbon steel hot-rolled coil of the present application adopts a coiling temperature of 600℃-700℃ and a faster cooling rate. On the one hand, the thickness of the iron oxide scale generated during the cooling process is reduced. On the other hand, the contact time between the surface of the strip and the air is short, and the combination of oxygen and Fe makes it easier to obtain an iron oxide scale with a ferrous oxide structure, which is looser than the structure of ferroferric oxide and is easy to pickle.

[0050] In some embodiments, the method for preparing medium-high carbon steel hot-rolled coil of the present application may further include pickling: pickling the steel strip or steel coil.

[0051] In some embodiments, the acid concentration of the pickling is 100 g / L-200 g / L, for example, it can be 100 g / L, 120 g / L, 140 g / L, 160 g / L, 180 g / L, 200 g / L, or any combination range of the above values; and / or, the pickling speed is 50 mpm-150 mpm, for example, it can be 50 mpm, 60 mpm, 70 mpm, 80 mpm, 90 mpm, 100 mpm, 110 mpm, 120 mpm, 130 mpm, 140 mpm, 150 mpm, or any combination range of the above values.

[0052] In some of the above embodiments, the method of the present application adopts a pickling acid concentration of 100g / L-200g / L and a pickling speed of 50mpm-150mpm, which effectively reduces the residual iron oxide scale of medium and high carbon steel pickling.

[0053] In a second aspect, the present application provides a medium-high carbon steel, which is prepared according to the method for preparing a medium-high carbon steel hot-rolled coil according to any embodiment of the first aspect.

[0054] The medium and high carbon steel produced by the method has an oxide scale structure mainly composed of ferrous oxide after hot rolling, and the oxide scale thickness is only 5-10 μm. There is no obvious oxide scale residue after pickling. Compared with the original process, the pickling surface quality is significantly improved.

[0055] According to the present application, since the medium-high carbon steel is prepared according to the method of any embodiment of the first aspect, it has the beneficial effects of any embodiment of the first aspect.

[0056] The following examples describe the present disclosure in more detail, and these examples are intended for illustrative purposes only.

[0057] Because various modifications and variations are obvious to those skilled in the art within the scope of the present disclosure. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all raw materials used in the examples are commercially available or prepared according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0058] Example 1

[0059] In this embodiment, S50C is used as a specific example. S50C is a carbon structural steel with a carbon content of about 0.5%. It is widely used in hardware, tools, automobile parts and other fields. The chemical composition is C: 0.52%, Si: 0.20%, Mn: 0.72%, P: 0.011%, S: 0.003%, Cr: 0.17%, and the rest is Fe and unavoidable impurities.

[0060] A method for reducing oxide residue in S50C hot rolled coil, comprising:

[0061] Slab continuous casting: The qualified S50C molten steel is cast and drawn in the thin slab continuous casting and rolling unit continuous casting machine, with a thickness of 65mm. The slab is pre-descaled and then enters the heating furnace to reduce the iron oxide scale on the slab surface to obtain the pre-treated slab;

[0062] Slab heating: In this embodiment, the heating furnace has a total of 7 heating zones. The pretreated slab passes through 7 heating zones after entering the furnace. The air-fuel ratio of each heating zone is set to 3.2. The furnace outlet temperature of the pretreated slab is 1184°C. The heating time of the pretreated slab in the furnace is 22 minutes. After the heating treatment, high-pressure water descaling treatment is performed to obtain the slab to be processed.

[0063] Specifically, the pre-scaling treatment in this embodiment is to use water at a pressure of about 10 mbar to clean the surface of the slab to remove part of the iron oxide scale and foreign matter on the surface of the slab.

[0064] High-pressure water descaling treatment uses a descaling machine for descaling. The descaling pressure of the front header of the descaling machine is set to 200mbar, and the descaling pressure of the rear header is set to 320mbar.

[0065] Rolling: The slab to be processed is rolled into strip steel using a finishing mill. In this embodiment, a 7-stand finishing mill is used, including seven stands F1-F7. The reduction ratios of the F1 stand and the F2 stand are 51% and 42% respectively, and the rolling speed of the F1 stand is 0.78 m / s. The inter-stand cooling water between F4-F5, F5-F6, and F6-F7 is turned off, and the first few stands are turned on normally; the side spray water of the F5-F7 stands is turned off; and the final rolling temperature (FDT) is set to 860°C.

[0066] The strip is subjected to laminar cooling treatment, and the front-stage cooling mode is adopted for the laminar cooling treatment. The redundant side water spraying of the laminar cooling is closed, and the flow rate of the cooling water of the side guide and pinch rollers is reduced by about 50%. The strip coiling temperature is controlled at 660°C. After coiling, the steel coil is concentrated for slow cooling, avoiding being placed at the tuyere, and the slow cooling is carried out for more than 2 days.

[0067] Pickling: The steel coil after slow cooling is pickled, the acid concentration is 158g / L, and the pickling speed is 80mpm.

[0068] like Figure 1 As shown in the figure, there is no obvious iron oxide scale left on the surface of the steel coil after pickling. Figure 2 As shown, the hot-rolled coil was sampled and tested before pickling. The thickness of the oxide scale in the middle and edge of the hot-rolled strip was only 4-9μm. XRD detection showed that the structure of the oxide scale was mainly ferrous oxide which was easy to pickle.

[0069] Example 2

[0070] In this embodiment, 65Mn is used as a specific example. 65Mn is a spring steel with a carbon content of about 0.65%. It is widely used in hardware, tools, automobile parts and other fields. The chemical composition is C: 0.66%, Si: 0.21%, Mn: 0.98%, P: 0.014%, S: 0.002%, Cr: 0.13%, and the rest is Fe and unavoidable impurities.

[0071] A method for reducing residual oxides in a 65Mn hot rolled coil, comprising:

[0072] Slab continuous casting: The qualified 65Mn molten steel is cast and drawn in the thin slab continuous casting and rolling unit continuous casting machine, with a thickness of 65mm. The slab is pre-descaled and then enters the heating furnace to reduce the iron oxide scale on the surface of the slab to obtain the pre-treated slab;

[0073] Slab heating: In this embodiment, the heating furnace has a total of 7 heating zones. The pretreated slab passes through 7 heating zones after entering the furnace. The air-fuel ratio of each heating zone is set to 3.12. The furnace outlet temperature of the pretreated slab is 1189°C. The heating time of the pretreated slab in the furnace is 28 minutes. After the heating treatment, high-pressure water descaling treatment is performed to obtain the slab to be processed.

[0074] Specifically, the pre-scaling treatment in this embodiment is to use water at a pressure of about 10 mbar to clean the surface of the slab to remove part of the iron oxide scale and foreign matter on the surface of the slab.

[0075] High-pressure water descaling treatment uses a descaling machine for descaling. The descaling pressure of the front header of the descaling machine is set at 200mbar, and the descaling pressure of the rear header is set at 320mbar;

[0076] Rolling: The slab to be processed is rolled into strip steel using a finishing mill. In this embodiment, a 7-stand finishing mill is used, including seven stands F1-F7. The reduction ratios of the F1 and F2 stands are 53% and 41% respectively, and the rolling speed of the F1 stand is 0.72 m / s. The inter-stand cooling water between F4-F5, F5-F6, and F6-F7 is turned off, and the first few stands are turned on normally; the side spray water of the F5-F7 stands is turned off; and the final rolling temperature (FDT) is set to 870°C.

[0077] The strip is cooled by laminar flow, and the front cooling mode is adopted for laminar flow cooling. The redundant side spray water of laminar flow cooling is closed, and the flow of cooling water of side guide and pinch roller is reduced by about 50%. The coiling temperature of the strip is controlled at 670℃. After coiling, the steel coil is concentrated and slowly cooled, avoiding being placed at the tuyere, and the slow cooling is carried out for more than 2 days.

[0078] Pickling: The steel coil after slow cooling is pickled, the acid concentration is 173g / L, and the pickling speed is 80mpm.

[0079] like Figure 3 As shown in the figure, there is no obvious iron oxide scale left on the surface after pickling. Figure 4 As shown, the hot-rolled coil was sampled and tested before pickling. The thickness of the oxide scale in the middle and edge of the hot-rolled strip was only 5-10μm. XRD detection showed that the structure of the oxide scale was mainly ferrous oxide which was easy to pickle.

[0080] Comparative Example 1

[0081] like Figure 5 As shown, the existing process is adopted: no pre-descaling treatment is carried out before the continuous casting billet enters the furnace. After entering the heating furnace, the air-fuel ratio of each zone is above 4.0, the heating and furnace discharge temperatures are as high as 1210°C, the heating time is 28min, and the F1-F7 rolling pressure is set to the second level automatically. The rolling speed of F1 is lower than 6.0m / s, and all the water between the stands are turned on normally. The final rolling temperature is 920°C, and the layer cooling adopts the rear-stage centralized cooling mode, and the layer cooling side spray water, side guide cooling water, and pinch roller cooling water are all turned on normally. The coiling temperature is 710°C, and the concentrated slow cooling is carried out after coiling. The pickling speed is 120mpm. The produced S50C has a lot of residual iron oxide scale after pickling. The hot-rolled coils before pickling are sampled and tested, such as Figure 6As shown, the thickness of the iron oxide scale in the middle and edge of the hot-rolled strip is about 8-15 μm. XRD detection shows that the structure of the iron oxide scale is mainly ferroferric oxide, which is not easy to be pickled.

[0082] Comparative Example 2

[0083] like Figure 7 As shown, the existing process is adopted: no pre-descaling treatment is carried out before the continuous casting billet enters the furnace. After entering the heating furnace, the air-fuel ratio of each zone is above 4.0, the heating and furnace discharge temperatures are as high as 1230°C, the heating time is 25min, and the F1-F7 rolling pressure is set to the second level automatically. The rolling speed of F1 is lower than 6.0m / s, and all the water between the stands are turned on normally. The final rolling temperature is 920°C, and the layer cooling adopts the rear-stage centralized cooling mode, and the layer cooling side spray water, side guide cooling water, and pinch roller cooling water are all turned on normally. The coiling temperature is 720°C, and the concentrated slow cooling is performed after coiling. The pickling speed is 120mpm. The 65Mn produced has a lot of residual pickled oxide scale. The hot-rolled coils before pickling are sampled and tested, such as Figure 8 As shown, the thickness of the iron oxide scale in the middle and edge of the hot-rolled strip is about 8-12 μm. XRD detection shows that the structure of the iron oxide scale is mainly ferroferric oxide, which is not easy to be pickled.

[0084] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing a medium-high carbon steel hot-rolled coil, characterized in that: include: Slab continuous casting: medium-high carbon steel molten steel is cast and drawn to obtain slabs, and the slabs are pre-descaled to reduce oxides on the surface of the slabs to obtain pre-treated slabs; Slab heating: heating the pretreated slab, and performing high-pressure water descaling after the heating to obtain the slab to be processed; Rolling: The slab to be processed is rolled to obtain a steel strip.

2. The method for preparing medium-high carbon steel hot-rolled coil according to claim 1, characterized in that: The pre-scaling treatment is to use 5mbar to 15mbar water to clean the surface of the slab; And or, the high-pressure water descaling treatment adopts a descaling machine for descaling, the descaling pressure of the front header of the descaling machine is 200mbar-240mbar, and the descaling pressure of the rear header of the descaling machine is 300mbar-340mbar.

3. The method for preparing medium-high carbon steel hot-rolled coil according to claim 1, characterized in that: In the step of continuous casting of the slab, the thickness of the slab is 60 mm-70 mm.

4. The method for preparing medium-high carbon steel hot-rolled coil according to claim 1, characterized in that: The slab heating step is carried out in a heating furnace, wherein the heating furnace is provided with a plurality of heating zones, and the air-fuel ratio of each heating zone is between 3.0 and 3.5; And / or, the furnace temperature of the pretreated slab is 1150° C.-1200° C.; And / or, the heating treatment time is 15min-40min.

5. The method for preparing medium-high carbon steel hot-rolled coil according to claim 1, characterized in that: The rolling step is performed by a finishing mill group, wherein the finishing mill group includes N stands, where N is an integer not less than 5; And / or, the final rolling temperature of the rolling is 820°C-920°C.

6. The method for preparing medium-high carbon steel hot-rolled coil according to claim 5, characterized in that: The first stand has a reduction ratio greater than 45%; and / or, the rolling speed of the first stand is greater than 0.6 m / s; and / or, the reduction rate of the second stand is greater than 35%; and / or, the cooling water between the N-3 rack and the N-2 rack is shut down, the cooling water between the N-2 rack and the N-1 rack is shut down, and the cooling water between the N-1 rack and the N rack is shut down; And / or, the side water sprays of the N-2 rack, the N-1 rack, and the N rack are all closed.

7. The method for preparing medium-high carbon steel hot-rolled coil according to claim 1, characterized in that: The rolling step also includes laminar cooling treatment of the steel strip, after which the steel strip is curled into a steel coil and slowly cooled; Preferably, the laminar cooling treatment adopts the front cooling mode, shuts down the redundant side water spraying of the laminar cooling, and reduces the flow rate of the cooling water of the side guide and pinch roller by not less than 45%; And / or, the temperature of the strip coiling is 600°C-700°C; And / or, the slow cooling time is not less than two days.

8. The method for preparing a medium-high carbon steel hot rolled coil according to any one of claims 1 to 7, characterized in that: It also includes pickling: pickling the strip or coil.

9. The method for preparing medium-high carbon steel hot-rolled coil according to claim 8, characterized in that: The acid concentration of the pickling is 100g / L-200g / L; And / or, the pickling speed is 50mpm-150mpm.

10. A medium-high carbon steel, characterized in that: The hot-rolled coil is prepared by the method for preparing a medium-high carbon steel hot-rolled coil according to any one of claims 1 to 9.

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