A method for manufacturing a medium-high carbon steel hot-rolled coil and a medium-high carbon steel

Abstract

The application discloses a preparation method of a medium-high carbon steel hot-rolled coil and the medium-high carbon steel. The preparation method of the medium-high carbon steel hot-rolled coil comprises the following steps: slab continuous casting: medium-high carbon steel liquid steel is cast and drawn to obtain a slab, and a pre-descaling treatment is performed on the slab to reduce oxides on the surface of the slab, thereby obtaining a pretreated slab; slab heating: the pretreated slab is subjected to a heating treatment, and after the heating treatment, a high-pressure water descaling treatment is performed, thereby obtaining a to-be-processed slab; rolling: the to-be-processed slab is rolled to obtain a strip steel. According to the embodiment of the application, the slab after the slab continuous casting is subjected to the pre-descaling treatment before the slab is heated in a furnace, and after the heating treatment, the high-pressure water descaling treatment is performed before rolling, thereby removing the initial thick iron oxide scale on the surface of the slab and ensuring that the uniformity of the iron oxide scale formed on the surface of the slab during hot rolling is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of medium-high carbon steel rolling, and particularly relates to a preparation method of a medium-high carbon steel hot-rolled coil and the medium-high carbon steel. BACKGROUND

[0002] In the production of existing medium-high carbon steel (0.2% < C < 1.3%), because of the high carbon content, the rolling force is much higher than that of general steel, which leads to the need to provide a higher heating temperature and a certain heating time for the slab, so that the surface scale of the slab is thicker, and the scale formed after hot rolling of the strip is also thicker. When the scale is not cleaned, even the pressing-in phenomenon occurs. During the rolling process of the finishing mill, the scale on the surface of the strip is thicker and more difficult to remove. In addition, when the strip or the steel coil is cooled, there is a large difference in the cooling speed between the edge and the middle, and between the head and tail and the middle, which leads to a large difference in the thickness and structure of the scale on the hot-rolled strip in the transverse and longitudinal directions. SUMMARY

[0003] The application provides a preparation method of a medium-high carbon steel hot-rolled coil and the medium-high carbon steel, which adjusts the heating and rolling processes of the medium-high carbon steel, improves the structure of the scale, thins the thickness of the scale, and effectively reduces the residual oxides of the strip or the steel coil.

[0004] In the first aspect, the application provides a preparation method of a medium-high carbon steel hot-rolled coil, which comprises: slab continuous casting: casting and drawing the medium-high carbon steel molten steel to obtain a slab, and performing pre-scale removal treatment on the slab to reduce the oxides on the surface of the slab, thereby obtaining a pretreated slab; slab heating: performing heating treatment on the pretreated slab, and performing high-pressure water scale removal treatment after the heating treatment is completed, thereby obtaining a to-be-processed slab; rolling: rolling the to-be-processed slab to obtain a strip.

[0005] According to the application, the slab after the slab continuous casting is subjected to the pre-scale removal treatment before the heating treatment and the high-pressure water scale removal treatment before the rolling, so that the initial thick scale on the surface of the slab is removed, and the uniformity of the scale formed on the surface of the slab during rolling is ensured.

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

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

[0008] In some embodiments, the slab heating step is performed in a heating furnace, the heating furnace is provided with a plurality of heating zones, and the air-fuel ratio of each heating zone is between 3.0-3.5; and / or, the discharge 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 rolling mill group, the finishing rolling mill group comprises N stands, N is an integer not less than 5; and / or, the final rolling temperature (FDT) of the rolling is 820℃-920℃.

[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 0.6m / s; and / or, the reduction rate of the second stand is greater than 35%; and / or, the cooling water is turned off between the N-3th stand and the N-2th stand, between the N-2th stand and the N-1th stand, and between the N-1th stand and the Nth stand; and / or, the side water spray of the N-2th stand, the N-1th stand and the Nth stand is turned off.

[0011] According to the present embodiment, the preparation method of the medium-high carbon steel hot-rolled coil can effectively reduce the thickness of the iron oxide scale generated during rolling by controlling the low discharge temperature and rolling temperature, the high rolling speed, and reducing the contact of the strip with air.

[0012] At the same time, reducing the flow of the side guide cooling water before coiling improves the uniformity of the transverse temperature of the strip and improves the consistency of the structure of the iron oxide scale, facilitating clean pickling removal.

[0013] In some embodiments, the strip is subjected to laminar cooling treatment, and the strip is coiled into a steel coil after the laminar cooling treatment; preferably, the laminar cooling treatment adopts a front section cooling mode, the excess side water spray of the laminar cooling is turned off, and the flow of the side guide and pinch roll cooling water is reduced by not less than 45%; and / or, the coiling temperature of the strip is 600℃-700℃; and / or, the slow cooling time is not less than two days.

[0014] According to the present embodiment, the preparation method of the medium-high carbon steel hot-rolled coil adopts a front section cooling mode and reduces the flow of the pinch roll cooling water, improves the uniformity of the steel coil temperature, improves the internal and external temperature difference after coiling, improves the performance stability, and improves 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-high carbon steel hot-rolled coil of the present application adopts a lower coiling temperature and a faster cooling speed, which on the one hand reduces the thickness of the iron oxide scale generated during the cooling process, and on the other hand, the contact time of the strip surface with air is short, and the combination of oxygen and Fe is more likely to obtain an iron oxide scale with a ferrous oxide structure, which is relatively loose compared with a ferriferous oxide structure, and is easy to be pickled.

[0016] In some embodiments, the method for preparing the medium-high carbon steel hot-rolled coil according to the present application can further comprise pickling: pickling the strip steel or the steel coil.

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

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

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

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

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

[0022] Figure 2 is a hot-rolled coil sampling detection photo of S50C before pickling by the method of the present application in Example 1 of the present application;

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

[0024] Figure 4 is a hot-rolled coil sampling detection photo of 65Mn before pickling by the method of the present application in Example 2 of the present application;

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

[0026] Figure 6 is a hot-rolled coil sampling detection photo of S50C before pickling by the existing process in Comparative Example 1 of the present application;

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

[0028] Figure 8is the detection figure of the hot-rolled coiling sample before pickling of 65Mn in the present application comparative example 2. DETAILED DESCRIPTION

[0029] The features and exemplary embodiments of the various aspects of the present application will be described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are intended to explain the principles of the present application and are not intended to limit the present application. The present application can be implemented without some of the specific details, which are well known to those skilled in the art. The following description of the embodiments is merely provided to give a better understanding of the present application by showing examples of the present application.

[0030] For simplicity, only some numerical ranges are explicitly disclosed in the present application. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, as can any upper limit with any other upper limit to form a range not explicitly recited. Moreover, although not explicitly recited, every point or individual number within a range is included in that range. Thus, every midpoint or individual number can be combined as its own lower limit or upper limit with any other point or individual number or with other lower or upper limits to form a range not explicitly recited.

[0031] The above summary of the application is not intended to describe each disclosed embodiment or every implementation of the present application. The description that follows more particularly exemplifies illustrative embodiments. In the description of the application through the use of the following examples, guidance is provided for employing the disclosed application in a variety of combinations. In each instance, representative values are cited, but the scope of the application includes other values not explicitly listed. Additionally, the term "first", "second", etc., are used herein only to describe one example as compared to another, but do not otherwise connote relative importance or a number of indicated technical features. Thus, a feature described as "first", "second", etc., can implicitly or explicitly include at least one of the feature. In the description of the application, the meaning of "a", "an", and "the" include "at least one" and "one or more" unless otherwise indicated.

[0032] The oxide scale is a corrosion product formed by the oxidation of steel at high temperature, and its structure is sequentially from inside to outside: ferrous oxide, triiron tetroxide, and diiron trioxide. Among them, the ferrous oxide structure is loose and unstable, and its protective effect is weak, and it is easy to remove, while the triiron tetroxide and diiron trioxide structure is dense, and has good protective property, and is difficult to remove. The formation mechanism of the oxide scale is related to the temperature and time of iron and oxygen combination. When the iron at high temperature contacts with the air for a short time and the oxygen is insufficient, the structure of ferrous oxide will be generated preferentially, and when the contact time with the air is long, the ferrous oxide will be oxidized into the stable structure of triiron tetroxide and diiron trioxide.

[0033] In the production of existing medium-high carbon steel (0.2% < C < 1.3%), the rolling force is much higher than that of general steel due to the high carbon content, which leads to the need to provide a higher heating temperature and a certain heating time for the slab, so the surface scale of the slab is thicker, and the scale formed after hot rolling is also thicker. When the scale is not cleaned, even the pressing phenomenon occurs. During the rolling process of the finishing mill set, the high rolling temperature and slow speed can cause the formation of thick and difficult-to-remove scale on the surface of the strip. In addition, during the cooling of the strip or the steel coil, there is a large difference in the cooling speed between the edge and the middle, and between the head and tail and the middle, which leads to a large difference in the thickness and structure of the scale on the hot-rolled strip in the transverse and longitudinal directions. Therefore, after the hot-rolled coil of medium-high carbon steel is pickled, the surface often has the phenomenon of scale pressing or residual, which is difficult to improve by relying on the optimization of the pickling process, causing great loss to the production plant.

[0034] In view of the above technical problems, the embodiments of the present application provide a preparation method of a medium-high carbon steel hot-rolled coil. In the method, the slab after continuous casting is subjected to pre-scale removal treatment before heating treatment, and high-pressure water scale removal treatment before rolling after heating treatment, so as to remove the initial thick scale on the surface of the slab and ensure good uniformity of the scale formed on the surface of the slab during rolling.

[0035] First, the preparation method of the medium-high carbon steel hot-rolled coil provided by the embodiments of the present application will be introduced.

[0036] According to the preparation method, the method comprises: slab continuous casting: casting and drawing the molten medium-high carbon steel to obtain a slab, and pre-scale removal treatment is performed on the slab to reduce the oxides on the surface of the slab to obtain a pretreated slab; slab heating: heating treatment is performed on the pretreated slab, and high-pressure water scale removal treatment is performed after the heating treatment is completed to obtain a to-be-processed slab; rolling: rolling the to-be-processed slab to obtain a strip.

[0037] The inventors found that the slab after continuous casting is subjected to pre-scale removal treatment before the slab is heated in the furnace, and high-pressure water scale removal treatment is performed before rolling after heating treatment, so as to remove the initial thick scale on the surface of the slab and ensure good uniformity of the scale formed on the surface of the slab during hot rolling.

[0038] It should be noted that the scale removal treatment of the existing process is only performed after the slab is heated and before rolling.

[0039] In some embodiments, the pre-descaling treatment is a water cleaning treatment with a pressure of 5 mbar to 15 mbar, for example, 5 mbar, 8 mbar, 9 mbar, 10 mbar, 12 mbar, 15 mbar, or any combination thereof; and / or the high-pressure water descaling treatment is a descaling treatment with a descaling machine, the front header descaling pressure of the descaling machine is 200 mbar to 240 mbar, for example, 200 mbar, 210 mbar, 220 mbar, 230 mbar, 240 mbar, or any combination thereof, and the rear header descaling pressure of the descaling machine is 300 mbar to 340 mbar, for example, 300 mbar, 310 mbar, 320 mbar, 330 mbar, 340 mbar, or any combination thereof.

[0040] In some embodiments, the slab casting is performed at a thickness of 60 mm to 70 mm, for example, 60 mm, 61 mm, 62 mm, 64 mm, 66 mm, 68 mm, 70 mm, or any combination thereof.

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

[0042] In some embodiments, the rolling is performed by a finishing rolling mill group, the finishing rolling mill group 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) is 820°C to 920°C, for example, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, or any combination thereof.

[0043] In some embodiments, the first stand has a reduction rate greater than 45%, for example, it can be 45.1%, 45.5%, 46%, 48%, 50%, 52%, 55%, 60%, 65%, 70%, or any combination range 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 range of the above values; and / or, the second stand has a reduction rate 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 stand and the N-2 stand is turned off, the cooling water between the N-2 stand and the N-1 stand is turned off, and the cooling water between the N-1 stand and the N stand is turned off; and / or, the side water spray of the N-2 stand, the N-1 stand, and the N stand is turned off.

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

[0045] In some of the above embodiments, the method of the present application can effectively reduce the thickness of the iron oxide scale generated during rolling by controlling the low discharge temperature of 1150-1200°C and the rolling temperature of 820-920°C, the rolling speed greater than 0.6 m / s, and reducing the contact of the strip with air.

[0046] In some embodiments, the strip is subjected to laminar cooling treatment, and after the laminar cooling treatment, the strip is coiled into a steel coil for slow cooling; preferably, the laminar cooling treatment adopts a front section cooling mode, the excess side water spray of the laminar cooling is turned off, and the flow of the cooling water of the side guide and the pinch roll 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 spray of the finishing rolling mill group and the excess side water spray of the laminar cooling are turned off, and the flow of the side guide cooling water before coiling is reduced to improve the uniformity of the transverse temperature of the strip and improve the consistency of the structure of the iron oxide scale, which facilitates the cleaning of the pickling. And / or, the coiling temperature of the strip is 600-700°C, for example, it can be 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, or any combination range of the above values.

[0047] The slow cooling time is not less than two days, for example, 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 the front-stage cooling mode and reduces the flow of the pinch roll cooling water, improves the uniformity of the steel coil temperature, improves the internal and external temperature difference after coiling, improves the performance stability, and improves the longitudinal uniformity of the hot-rolled iron oxide scale.

[0049] Meanwhile, compared with the existing process, the preparation method of the medium-high carbon steel hot-rolled coil of the present application adopts a coiling temperature of 600-700 DEG C and a faster cooling speed, which on the one hand reduces the thickness of the generated iron oxide scale in the cooling process, and on the other hand, the contact time of the strip surface with air is short, and the combination of oxygen and Fe is more likely to obtain the iron oxide scale of the ferrous oxide structure, which is relatively loose compared with the magnetite structure, and is easy to be pickled.

[0050] In some embodiments, the preparation method of the medium-high carbon steel hot-rolled coil of the present application can further include pickling: pickling treatment is performed on the strip or the steel coil.

[0051] In some embodiments, the acid concentration of pickling is 100-200 g / L, for example, 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 speed of pickling is 50-150 mpm, for example, 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 an acid concentration of 100-200 g / L for pickling and a speed of 50-150 mpm for pickling, which effectively reduces the residual of the pickling iron oxide scale of the medium-high carbon steel.

[0053] In a second aspect, the present application provides a medium-high carbon steel prepared by the preparation method of the medium-high carbon steel hot-rolled coil according to any one of the embodiments of the first aspect.

[0054] The medium-high carbon steel produced by using the method has an iron oxide scale structure mainly of ferrous oxide after hot rolling, and the thickness of the iron oxide scale is only 5-10 μm, and there is no obvious residual of the iron oxide scale after pickling, and the surface quality of pickling is obviously improved compared with the original process.

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

[0056] The present disclosure is described in more detail by the following examples, which are only illustrative.

[0057] As various modifications and changes can be made to the present disclosure within the scope of the application, it is intended that the application not be limited to the particular examples described. Unless otherwise stated, all percentages and proportions herein are based upon the total weight of the compositions, and all measurements made are at 25°C, and all ingredients are on a weight basis, and all tests are conducted under ambient conditions, unless otherwise indicated. All documents, including patents, are incorporated by reference.

[0058] Example 1

[0059] In this embodiment, S50C is taken as a specific example. S50C is a carbon structural steel with a carbon content of about 0.5%, which is widely used in the fields of hardware, tools, automobile parts, etc. The chemical composition of S50C 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 inevitable impurities.

[0060] A method for reducing residual oxides in a hot-rolled S50C coil, comprising:

[0061] Slab casting: the S50C molten steel that meets the smelting standards is cast and drawn on a thin slab continuous casting and rolling unit caster, and the drawing thickness is 65 mm. The slab is pre-scaled after pre-scaling treatment and enters the heating furnace to reduce the scale on the surface of the slab, thereby obtaining a pretreated slab.

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

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

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

[0065] Rolling: the slab to be processed is rolled into a strip using a finishing rolling mill set, and in this embodiment, the finishing rolling mill set adopts a 7-stand finishing rolling mill set, which includes F1-F7 seven stands, the reduction rates of F1 stand and F2 stand are 51% and 42% respectively, and the rolling speed of F1 stand is 0.78 m / s. The inter-stand cooling water between F4-F5, F5-F6 and F6-F7 is closed, and the previous groups of stands are normally opened; the side water spray of F5-F7 stands is closed; the finish rolling temperature (FDT) is set to 860℃.

[0066] The strip is subjected to laminar cooling treatment, the laminar cooling treatment adopts a front section cooling mode, the excess side water spray of the laminar cooling is closed, and the flow of the side guide and pinch roll cooling water is reduced by about 50%, and the coiling temperature of the strip is controlled at 660℃, and after coiling, the steel coil is concentrated for slow cooling, and is avoided to be placed at the tuyere, and is slowly cooled for more than 2 days.

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

[0068] As shown in Figure 1 , there is no obvious residual iron oxide scale on the surface of the steel coil after pickling. As shown in Figure 2 , the hot-rolled coiling sample before pickling is detected, and the thickness of the iron oxide scale at the middle and edge of the hot-rolled strip is only 4-9 μm, and the XRD detection of the iron oxide scale structure is mainly easy-to-pickling ferrous oxide.

[0069] Example 2

[0070] In this embodiment, 65Mn is taken as a specific example, 65Mn is a spring steel with a carbon content of about 0.65%, which is widely used in hardware, tools, automobile parts and other fields, and 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 the residual oxide in the hot-rolled coil of 65Mn, comprising:

[0072] Slab continuous casting: the qualified 65Mn molten steel is cast and drawn on a thin slab continuous casting and rolling mill set, and the drawing thickness is 65 mm, and after the slab is subjected to pre-scaling removal treatment, it enters the heating furnace to reduce the iron oxide scale on the surface of the slab, and the pre-treated slab is obtained;

[0073] Slab heating: in this embodiment, the heating furnace has 7 heating zones, and after the pre-treated slab enters the furnace, it passes through 7 heating zones, and the air-fuel ratio of each heating zone is set to 3.12, the pre-treated slab is discharged at a temperature of 1189℃, and the pre-treated slab is heated for 28 min, and after the heating treatment is completed, high-pressure water scaling removal treatment is performed, and the slab to be processed is obtained.

[0074] Specifically, in this embodiment, the pre-descaling treatment involves washing the slab surface with approximately 10 mbar of water to remove some of the iron oxide scale and foreign matter from the slab surface.

[0075] High-pressure water descaling is performed using a descaling machine. The descaling pressure in the front manifold of the descaling machine is set to 200 mbar, and the descaling pressure in the rear manifold is set to 320 mbar.

[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, consisting of seven stands, F1-F7. The reduction rates of stands F1 and F2 are 53% and 41%, respectively, and the rolling speed of stand F1 is 0.72 m / s. The interstand cooling water between stands F4-F5, F5-F6, and F6-F7 is turned off, while the first few stands are operated normally. The side spray water of stands F5-F7 is turned off. The final rolling temperature (FDT) is set to 870℃.

[0077] The strip steel undergoes laminar flow cooling, employing a front-end cooling mode. Excess side spray water is shut off during laminar flow cooling, and the flow rate of cooling water for the side guides and pinch rolls is reduced by approximately 50%. The strip steel coiling temperature is controlled at 670℃. After coiling, the coils are cooled slowly and centrally, avoiding placement near vents, for at least two days.

[0078] Pickling: The steel coils after slow cooling are pickled with an acid concentration of 173 g / L and a pickling speed of 80 mpm.

[0079] like Figure 3 As shown, no obvious iron oxide scale residue remained on the surface after pickling. Figure 4 As shown, sampling and testing of hot-rolled coils before pickling revealed that the iron oxide scale thickness in the middle and edges of the hot-rolled strip was only 5-10 μm. XRD analysis showed that the iron oxide scale structure was mainly composed of easily pickled ferrous oxide.

[0080] Comparative Example 1

[0081] like Figure 5 As shown, the existing process was used: no pre-descaling treatment was performed on the continuously cast billets before they entered the furnace; the air-fuel ratio in each zone of the heating furnace was above 4.0; the heating and exit temperatures reached 1210℃; the heating time was 28 minutes; the rolling reduction of F1-F7 was set according to the two-stage automatic setting; the rolling speed of F1 was less than 6.0 m / s; all inter-stand water was turned on normally; the final rolling temperature was 920℃; the layer cooling adopted a rear-stage centralized cooling mode; and the layer cooling side spray, side guide cooling water, and pinch roll cooling water were all turned on normally. The coiling temperature was 710℃, and centralized slow cooling was performed after coiling; the pickling speed was 120 mpm. The produced S50C had a lot of residual iron oxide scale after pickling. Samples of the hot-rolled coils before pickling were 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 analysis shows that the iron oxide scale structure is mainly composed of iron oxide, which is not easy to pickle.

[0082] Comparative Example 2

[0083] like Figure 7 As shown, the existing process was used: no pre-descaling treatment was performed on the continuously cast billets before they entered the furnace; the air-fuel ratio in each zone of the furnace was above 4.0; the heating and exit temperatures reached 1230℃; the heating time was 25 minutes; the rolling reduction of F1-F7 was set according to the two-stage automatic setting; the rolling speed of F1 was less than 6.0 m / s; all inter-stand water was turned on normally; the final rolling temperature was 920℃; the layer cooling adopted a rear-stage centralized cooling mode; and the layer cooling side spray, side guide cooling water, and pinch roll cooling water were all turned on normally. The coiling temperature was 720℃, and centralized slow cooling was performed after coiling; the pickling speed was 120 mpm. The produced 65Mn had a lot of residual iron oxide scale after pickling. Samples of the hot-rolled coils before pickling were 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 analysis shows that the iron oxide scale structure is mainly composed of iron(III) oxide, which is not easily pickled.

[0084] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing hot-rolled coils of medium and high carbon steel, characterized in that, include: Slab continuous casting: Medium and high carbon steel molten steel is cast and pulled to obtain slabs. The slabs are then pre-descaled to reduce oxides on the slab surface, resulting in pre-treated slabs. Slab heating: The pretreated slab is heated, and after the heating is completed, it is descaled by high pressure water to obtain the slab to be processed; Rolling: The slab to be processed is rolled to obtain strip steel; Pickling: Pickling is a process of pickling strips or coils. The rolling process also includes laminar flow cooling of the strip. After laminar flow cooling, the strip is rolled into a coil and cooled slowly. The laminar flow cooling process adopts a front-end cooling mode, turns off the excess side spray water of the laminar flow cooling, and reduces the flow rate of the cooling water of the side guide and pinch roll by no less than 45%. The acid concentration in the pickling step is 100g / L-200g / L, and the pickling speed is 50mpm-150mpm.

2. The method for preparing medium-high carbon steel hot-rolled coils according to claim 1, characterized in that, The pre-descaling treatment involves cleaning the surface of the slab with water at 5 mbar to 15 mbar. Alternatively, the high-pressure water descaling treatment is performed using a descaling machine, wherein the descaling pressure in the front manifold of the descaling machine is 200 mbar-240 mbar, and the descaling pressure in the rear manifold of the descaling machine is 300 mbar-340 mbar.

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

4. The method for preparing medium-high carbon steel hot-rolled coils according to claim 1, characterized in that, The slab heating step is carried out in a heating furnace, which is provided with multiple heating zones, and the air-fuel ratio of each heating zone is between 3.0 and 3.

5. And / or, the furnace exit temperature of the pretreated slab is 1150℃-1200℃; And / or, the heat treatment time is 15 min to 40 min.

5. The method for preparing medium-high carbon steel hot-rolled coils according to claim 1, characterized in that, The rolling process is carried out through a finishing mill, which includes N stands, where N is an integer not less than 5. And / or, the final rolling temperature is 820℃-920℃.

6. The method for preparing medium-high carbon steel hot-rolled coils according to claim 5, characterized in that, The reduction ratio of the first rack is greater than 45%; And / or, the rolling speed of the first stand is greater than 0.6 m / s; And / or, the reduction ratio of the second rack is greater than 35%; And / or, the cooling water between the N-3 rack and the N-2 rack is shut off, the cooling water between the N-2 rack and the N-1 rack is shut off, and the cooling water between the N-1 rack and the N rack is shut off; And / or, the side sprayers of the N-2, N-1 and Nth racks are all turned off; The temperature at which the strip is coiled is 600℃-700℃; And / or, the slow cooling time is not less than two days.

7. A medium-high carbon steel, characterized in that, It is prepared by the method for preparing medium and high carbon steel hot-rolled coils according to any one of claims 1 to 6.

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