60si2mn spring steel hot-rolled wide coil and method for manufacturing the same

Abstract

This application discloses a hot-rolled wide coil of 60Si2Mn spring steel and its preparation method. The preparation method includes: heating the continuously cast slab; the furnace inlet temperature is greater than 500℃; the atmosphere in the furnace is a weakly reducing atmosphere; the heating time is 120-150 min; the heating temperature is 800-1200℃; the heated slab is subjected to rough descaling; the rough descaling pressure is greater than 200 MPa; the rough descaling rate is 1-3 m / min; the rough descaled slab is subjected to rough rolling; 5 passes are used; the thickness of the rough rolled slab is 30-40 mm; the rough rolled slab is subjected to finish rolling; 7 passes are used; the finishing rolling temperature is 800-860℃; the thickness of the finished strip is 1.8-6.0 mm; the finished strip is subjected to laminar flow cooling using a rapid front-end cooling mode; the laminar flow cooled strip is coiled; the coiling temperature is 580-650℃; the coiling tension is 50-60 MPa. The preparation method can produce hot-rolled wide coils of 60Si2Mn spring steel with excellent microstructure and properties.

Description

Technical Field

[0001] This application relates to the field of steel rolling technology, specifically to a hot-rolled wide coil of 60Si2Mn spring steel and its preparation method. Background Technology

[0002] 60Si2Mn is a widely used silicon-manganese spring steel, characterized by its relatively high Si and C content. Currently, 60Si2Mn spring steel is mainly produced in the form of bars, wires, flat bars, and strips. With the development of steel industry technology, increasing demands for product quality, and steel companies' need to control manufacturing costs, there is a need for steel companies to develop wide-width coils of 60Si2Mn spring steel to replace traditional narrow strips. However, the production of hot-rolled wide-width coils of 60Si2Mn spring steel presents many technical challenges compared to bars, wires, and strips. Therefore, how to prepare hot-rolled wide-width coils of 60Si2Mn spring steel with excellent microstructure and properties has become an urgent technical problem to be solved. Summary of the Invention

[0003] This application provides a hot-rolled wide coil of 60Si2Mn spring steel and its preparation method, which can produce hot-rolled wide coil of 60Si2Mn spring steel with excellent microstructure and properties.

[0004] On one hand, this application proposes a method for preparing hot-rolled wide coils of 60Si2Mn spring steel. The method includes: heating a continuously cast slab to obtain a heated slab; the slab's furnace entry temperature is greater than 500℃; the atmosphere in the heating furnace is a weakly reducing atmosphere; the heating time is 120-150 min; and the heating temperature is 800-1200℃; the heated slab is subjected to rough descaling to obtain a rough descaled slab; the pressure of the rough descaling is greater than 200 MPa; and the rate of the rough descaling is 1-3 m / min; the rough descaled slab is then subjected to rough rolling to obtain... The rough-rolled slab is processed in 5 passes, resulting in a slab thickness of 30-40 mm. The rough-rolled slab is then finished, resulting in a finished slab. The finish rolling process involves 7 passes at a final rolling temperature of 800-860℃, resulting in a strip thickness of 1.8-6.0 mm. The finished strip undergoes laminar flow cooling, resulting in a laminar flow cooled strip. The laminar flow cooling process employs a rapid front-end cooling mode. The laminar flow cooled strip is then coiled, resulting in a steel coil. The coiling temperature is 580-650℃, and the coiling tension is 50-60 MPa.

[0005] According to one aspect of the embodiments of this application, the furnace temperature of the slab is 500-700°C.

[0006] According to one aspect of the embodiments of this application, the heating treatment includes a preheating section, a first heating section, a second heating section, and a soaking section; optionally, the temperature of the preheating section is 800-1000℃, the temperature of the first heating section is 950-1100℃, the temperature of the second heating section is 1050-1200℃, the temperature of the soaking section is 1130-1200℃, and the furnace exit temperature of the slab is 1150-1180℃.

[0007] According to one aspect of the embodiments of this application, the pressure of the rough descaling process is 200-250 MPa.

[0008] According to one aspect of the embodiments of this application, the cooling rate of the laminar flow cooling process is 30-50°C / s.

[0009] According to one aspect of the embodiments of this application, the preparation method further includes slowly cooling the steel coil to -20°C to 60°C.

[0010] On the other hand, this application provides a hot-rolled wide coil of 60Si2Mn spring steel, which is prepared by the preparation method of the first aspect of this application.

[0011] According to another aspect of the embodiments of this application, based on the total mass of 60Si2Mn spring steel hot-rolled wide coils as 100%, the chemical composition of the 60Si2Mn spring steel hot-rolled wide coils includes: C: 0.56%-0.64%, Si: 1.50%-2.00%, Mn: 0.70%-1.00%, Cr≤0.35%, Ni≤0.35%, Cu≤0.25%, P≤0.025%, S≤0.020%; the remainder is Fe and unavoidable impurities.

[0012] According to another aspect of the embodiments of this application, the thickness of the hot-rolled wide coil of 60Si2Mn spring steel is 1.8-6.0mm, and the width of the hot-rolled wide coil of 60Si2Mn spring steel is 900-1500mm.

[0013] According to another aspect of the embodiments of this application, the single-sided surface decarburization layer depth of 60Si2Mn spring steel hot-rolled wide coil is less than or equal to 1.0% of the nominal thickness, the flatness of the plate is ≤8mm / m, the microstructure is pearlite, and the grain size grade of the pearlite is ≥7.

[0014] In this embodiment, by adjusting the furnace inlet temperature of the heat treatment to be greater than 500℃, the atmosphere to a weakly reducing atmosphere, the heat treatment time to 120-150 min, the heat treatment temperature to 800-1200℃, the pressure of the rough descaling treatment to be greater than 200 MPa, the rough descaling rate to 1-3 m / min, using 5 passes of rough rolling, adjusting the thickness of the slab after rough rolling to 30-40 mm, and the final rolling temperature of the finish rolling treatment to 800-860℃, the relationship between strip decarburization and rolling load is balanced. The laminar flow cooling treatment uses a rapid cooling mode at the front end, and the tension of the coiling treatment is adjusted within the range of 50-60 MPa to control the shape of the steel coil. By adjusting the temperature of the finish rolling treatment to the range of 800-860℃, performing laminar flow cooling treatment on the strip after finish rolling, and adjusting the temperature of the coiling treatment to the range of 580-650℃, the microstructure of the coil can be controlled, resulting in a single, uniform, and fine full pearlite structure. This solves the problems of high rolling load, surface decarburization, and poor plate shape and surface quality in the finishing process of wide coils, improves the production efficiency of hot-rolled wide coils of 60Si2Mn spring steel, and produces hot-rolled wide coils of 60Si2Mn spring steel with excellent microstructure and properties. Attached Figure Description

[0015] The features, advantages, and technical effects of exemplary embodiments of this application will now be described with reference to the accompanying drawings.

[0016] Figure 1 This is a schematic flowchart illustrating the preparation method of hot-rolled wide coils of 60Si2Mn spring steel according to an embodiment of this application.

[0017] Figure 2 Microstructure of the hot-rolled wide coil of 60Si2Mn spring steel prepared in Example 1 of this application. Detailed Implementation

[0018] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0019] It should be noted that in this application, the terms "first," "second," etc., are used to distinguish similar objects and not to describe a specific order or sequence. Furthermore, the term "comprising," or any other variation thereof, is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C.

[0020] Thermo-Mechanical Control Process (TMCP) is a general term for technologies that, in addition to controlling the heating temperature, rolling temperature, and reduction amount during hot rolling, further implement air cooling, controlled cooling, and accelerated cooling.

[0021] TMCP technology can effectively regulate the microstructure and properties of 60Si2Mn spring steel and control surface decarburization, thereby producing high-quality 60Si2Mn spring steel products with higher quality and more competitive production costs, better meeting the quality requirements of downstream users such as wave springs, spring washers, and disc springs.

[0022] Hot-rolled wide coils of 60Si2Mn spring steel represent a new type of product due to their very high width-to-thickness ratio, presenting different technical challenges compared to traditional profiles and strips. Furthermore, the production of 60Si2Mn hot-rolled wide coils has a higher technical threshold than that of bars, wire rods, and strips. For example, the rolling load of wide strips is significantly higher than that of narrow strips, creating a significant contradiction between increasing slab temperature, reducing rolling load, and controlling surface decarburization. Additionally, while TMCP technology can effectively control microstructure and properties, it can also increase the reduction rate in certain passes or the post-rolling cooling rate, making shape control difficult and potentially leading to poor shape in hot-rolled wide coils.

[0023] Figure 1 This is a schematic flowchart illustrating the preparation method of hot-rolled wide coils of 60Si2Mn spring steel according to an embodiment of this application. Figure 1 As shown in the figure. This application provides a method for preparing hot-rolled wide coils of 60Si2Mn spring steel, the method comprising the following steps:

[0024] S10: The slab after continuous casting is heated to obtain a heated slab; the slab's furnace temperature is greater than 500℃; the atmosphere in the heating furnace for heating is a weakly reducing atmosphere; the heating time is 120-150 min; and the heating temperature is 800-1200℃.

[0025] S20: Perform rough descaling on the heat-treated slab to obtain a rough descaled slab; the pressure of the rough descaling is greater than 200MPa, and the rate of the rough descaling is 1-3m / min.

[0026] S30: The slab after rough descaling is subjected to rough rolling to obtain a rough rolled slab; the rough rolling process is carried out in 5 passes, and the thickness of the rough rolled slab is 30-40mm.

[0027] S40: The slab after rough rolling is finished to obtain a finished slab; the finishing rolling process adopts 7 passes, the final rolling temperature of the finishing rolling process is 800-860℃, and the thickness of the finished strip is 1.8-6.0mm.

[0028] S50: Laminar flow cooling is performed on the finished strip to obtain laminar flow cooled strip; the laminar flow cooling process adopts a front-end rapid cooling mode.

[0029] S60: The strip steel after laminar flow cooling is coiled to obtain a steel coil; the coiling temperature is 580-650℃ and the coiling tension is 50-60MPa.

[0030] 60Si2Mn spring steel has high elasticity and high rolling load, especially for wide, thin-gauge 60Si2Mn spring steel coils. This is the first problem encountered in the production of wide-gauge 60Si2Mn spring steel coils, and only by solving this problem can stable and smooth production be guaranteed. The most effective way to solve the rolling load problem is to increase the temperature of the workpiece during the rolling process, such as increasing the heating temperature of the slab and extending the heating time, using rapid rough descaling to reduce the temperature drop, and setting higher temperatures for the final rolling and coiling processes. However, due to the high Si content in 60Si2Mn spring steel, it is very easy to cause quality problems such as decarburization and the indentation of iron oxide scale. Therefore, how to adjust the manufacturing process to balance the rolling load, coil decarburization, and excessive surface oxides is one of the core issues of this application.

[0031] The following describes the control principles of each parameter in the heat treatment, rough descaling treatment, rough rolling treatment, finish rolling treatment, laminar flow cooling treatment, and coiling treatment in the embodiments of this application.

[0032] Heat treatment: By setting the furnace temperature for heat treatment to be greater than 500℃, the time it takes for the slab to cool from 500℃ to -20℃ to 60℃ and then heat from -20℃ to 60℃ back to 500℃ can be reduced. This reduces decarburization and surface oxidation of the slab during the cooling process, lowers the decarburized layer depth, and improves surface quality.

[0033] By controlling the atmosphere in the heating furnace to a weakly reducing atmosphere, setting the slab heating treatment temperature within the range of 800-1200℃, and setting the heating treatment time within the range of 120-150min, the temperature of the slab in the subsequent rolling process can be increased, and the degree of decarburization of the slab can be reduced. At the same time, the rolling load can be taken into account, reducing the possibility of excessive rolling load in the subsequent process.

[0034] The excess air coefficient in the heating furnace can be 2-3, for example, 2.5.

[0035] Rough descaling: By setting the pressure of rough descaling to greater than 200 MPa and the descaling rate to the range of 1-3 m / min, the descaling rate can be increased, the temperature drop of the slab can be reduced, and the temperature of the slab during rolling can be increased. At the same time, high-pressure rapid rough descaling can also remove thicker iron oxide scale from the surface of the slab.

[0036] Rough rolling: Rough rolling uses 5 passes, which can further reduce the temperature drop of the slab and reduce the rolling load of the subsequent finish rolling. The temperature of rough rolling is relatively high and the rolling is relatively easy. Therefore, the thickness of the slab after rough rolling is controlled within the range of 30-40mm. That is, the thickness of the slab after rough rolling is reduced as much as possible, thereby reducing the difficulty of the subsequent finish rolling.

[0037] Finishing rolling: By setting the final rolling temperature in the range of 800-860℃, the microstructure can be refined, the interlayer spacing between pearlite lamellae can be reduced, the microstructure of the strip can be controlled, and decarburization of the strip can be reduced.

[0038] Laminar flow cooling: Laminar flow cooling employs a rapid cooling mode in the front section, which can suppress the formation of proeutectoid ferrite, resulting in a single, uniform, and fine pearlite microstructure, thereby improving the uniformity of the microstructure. In addition, it allows for the release of internal stress by air cooling in the rear section, maintaining a better plate shape.

[0039] It should be noted that the rapid cooling mode in the front section of this application refers to directly and rapidly cooling the strip steel to near the temperature of the coiling process.

[0040] Winding process: Setting the tension of the winding process in the range of 50-60MPa can keep the tension within a wide range, thereby ensuring that the coil has a high degree of flatness.

[0041] In this embodiment, by adjusting the furnace inlet temperature of the heat treatment to be greater than 500℃, the atmosphere to a weakly reducing atmosphere, the heat treatment time to 120-150 min, the heat treatment temperature to 800-1200℃, the pressure of the rough descaling treatment to be greater than 200 MPa, the rough descaling rate to 1-3 m / min, using 5 passes of rough rolling, adjusting the thickness of the slab after rough rolling to 30-40 mm, and the final rolling temperature of the finish rolling treatment to 800-860℃, the relationship between strip decarburization and rolling load is balanced. The laminar flow cooling treatment uses a rapid cooling mode at the front end, and the tension of the coiling treatment is adjusted within the range of 50-60 MPa to control the shape of the steel coil. By adjusting the temperature of the finish rolling treatment to the range of 800-860℃, performing laminar flow cooling treatment on the strip after finish rolling, and adjusting the temperature of the coiling treatment to the range of 580-650℃, the microstructure of the coil can be controlled, resulting in a single, uniform, and fine full pearlite structure. This solves the problems of high rolling load, surface decarburization, and poor plate shape and surface quality in the hot rolling process of wide coils, improves the production efficiency of hot-rolled wide coils of 60Si2Mn spring steel, and produces hot-rolled wide coils of 60Si2Mn spring steel with excellent microstructure and properties.

[0042] In some embodiments, the furnace temperature of the slab can be 500-700°C.

[0043] In this embodiment, the furnace temperature of the slab is set within the above-mentioned range, which can shorten the furnace charging time and reduce surface oxidation and decarburization of the slab.

[0044] In some embodiments, the heating process may include a preheating section, a first heating section, a second heating section, and a soaking section.

[0045] In some embodiments, the temperature of the preheating section can be 800-1000℃, the temperature of the first heating section can be 950-1100℃, the temperature of the second heating section can be 1050-1200℃, the temperature of the soaking section can be 1130-1200℃, and the furnace exit temperature of the slab can be 1150-1180℃.

[0046] Typically, the rolling load of hot-rolled wide coils of 60Si2Mn spring steel is relatively high. Although increasing the heating temperature of the slab can reduce the rolling load, it also leads to more significant decarburization. In this embodiment, by setting the temperatures of the preheating section, the first heating section, the second heating section, and the soaking section, as well as the slab's exit temperature, within the aforementioned ranges, the temperature of the slab during subsequent rolling processes can be increased, further reducing the degree of decarburization and minimizing the possibility of excessively high subsequent rolling loads.

[0047] The upper limit of pressure for coarse descaling is determined based on the coarse descaling capacity.

[0048] In some embodiments, the pressure for the coarse descaling process can be 200-250 MPa, for example, 200 MPa, 210 MPa, 220 MPa, 230 MPa, 240 MPa, or 250 MPa.

[0049] This embodiment of the application sets the pressure of the coarse descaling process within the above-mentioned range, which can quickly remove coarse descaling and also remove the thick iron oxide scale on the surface of the slab, while reducing the load of the coarse descaling process.

[0050] In some embodiments, the cooling rate of the laminar flow cooling process can be 30-50℃ / s, for example, 30℃ / s, 35℃ / s, 40℃ / s, 45℃ / s, or 50℃ / s.

[0051] The specific operation of laminar flow cooling includes two sets of side sprays: one at the start position of water cooling and the other at the end position of water cooling.

[0052] By adjusting the cooling rate of the laminar flow cooling process within the above range, the formation of proeutectoid ferrite can be further suppressed, resulting in a single, uniform, and fine pearlite microstructure. Furthermore, the air cooling in the later stage can release internal stress and maintain a better plate shape.

[0053] In some embodiments, the preparation method further includes slowly cooling the steel coil to -20°C to 60°C, for example, -20°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or 60°C.

[0054] In this embodiment, no requirement is placed on the cooling rate of slow cooling; it is sufficient to allow the steel coil to enter the slow cooling pit. The slow cooling pit is a conventional facility in the steel coil cooling process.

[0055] In this embodiment, the steel coil is rolled out quickly and then enters a slow cooling pit to release stress slowly, which is beneficial for the subsequent processing and use of the coil.

[0056] In the embodiments of this application, the preparation process of 60Si2Mn spring steel hot-rolled wide coils uses a wide coil mill. The equipment precision of the wide coil mill is generally higher than that of the profile and narrow strip steel mills, thereby obtaining 60Si2Mn spring steel hot-rolled wide coils with higher dimensional accuracy.

[0057] This application provides an embodiment of a 60Si2Mn spring steel hot-rolled wide coil, which is prepared by the method described in this application.

[0058] In some embodiments, the chemical composition of 60Si2Mn hot-rolled wide coils of spring steel, based on 100% of the total mass, may include: C: 0.56%-0.64%, Si: 1.50%-2.00%, Mn: 0.70%-1.00%, Cr≤0.35%, Ni≤0.35%, Cu≤0.25%, P≤0.025%, S≤0.020%; the remainder being Fe and unavoidable impurities.

[0059] In the embodiments of this application, the 60Si2Mn spring steel hot-rolled wide coil has a large width-to-thickness ratio.

[0060] In some embodiments, the thickness of the hot-rolled wide coil of 60Si2Mn spring steel can be 1.8-6.0 mm, and the width of the hot-rolled wide coil of 60Si2Mn spring steel can be 900-1500 mm.

[0061] In some embodiments, the single-sided surface decarburization layer depth of 60Si2Mn spring steel hot-rolled wide coil is less than or equal to 1.0% of the nominal thickness, the flatness of the plate is ≤8mm / m, the microstructure is pearlite, and the grain size grade of the pearlite is ≥7.

[0062] Example

[0063] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0064] Example 1

[0065] The continuously cast slabs are produced using a hot-charging and hot-delivery process. The slab's initial temperature upon entering the furnace is 512-546℃, and the furnace atmosphere is weakly reducing. The preheating temperature is 850-980℃, the first heating temperature is 980-1100℃, the second heating temperature is 1100-1190℃, the soaking temperature is 1150-1180℃, the exit temperature is 1178℃, and the furnace time is 146 minutes. The pressure for rough descaling is set at 220MPa, and the descaling rate is set at 2m / min. Five passes of rough rolling are used, resulting in an intermediate slab thickness of 32mm. Seven passes of finish rolling are used, with a final rolling temperature of 860℃, producing 1.8mm thick steel coils. Laminar flow cooling is a rapid front-end cooling mode, with two sets of side water sprays activated at the start and end points of water cooling. The coiling temperature is 640℃, and the coiling tension is 52MPa. The steel coil is removed from the production line 46 minutes after rolling and placed in a slow cooling pit to be slowly cooled to ambient temperature.

[0066] The 60Si2Mn spring steel hot-rolled wide coil produced using the above method has a maximum finishing rolling force of 38000KN and exhibits stable production. The single-sided surface decarburization layer depth is 11μm, the plate straightness is 7mm / m, and there are no broken edges or waviness. The microstructure is a uniform and fine pearlite structure with a pearlite grain size grade of 8. The thickness tolerance is controlled within ±0.05mm, and the surface quality is good.

[0067] The microstructure of the hot-rolled wide coil of 60Si2Mn spring steel prepared in Example 1 is shown in the figure below. Figure 2 As shown.

[0068] Example 2

[0069] The continuously cast slabs are produced using a hot-charging and hot-delivery process. The slab's initial temperature upon entering the furnace is 524-557℃, and the furnace atmosphere is weakly reducing. The preheating temperature is 880-990℃, the first heating temperature is 990-1080℃, the second heating temperature is 1080-1180℃, the soaking temperature is 1150-1180℃, and the exit temperature is 1172℃. The furnace time is 138 minutes. The roughing descaling pressure is set to 220MPa, and the roughing descaling rate is set to 2m / min. Five passes of roughing rolling are used, resulting in an intermediate slab thickness of 36mm. Seven passes of finishing rolling are used, with a final rolling temperature of 840℃, producing a 4.0mm thick steel coil. Laminar flow cooling is a rapid front-end cooling mode, with two sets of side water sprays activated at the start and end points of water cooling. The coiling temperature was set at 620℃, and the coiling tension was 60MPa. The steel coil was removed from the production line 52 minutes after rolling and placed in a slow cooling pit to be slowly cooled to ambient temperature.

[0070] The 60Si2Mn spring steel hot-rolled wide coil produced using the above method has a maximum finishing rolling force of 37100KN and exhibits stable production. The single-sided surface decarburization layer depth is 24μm, the plate straightness is 5mm / m, and there are no broken edges or waviness. The microstructure is a uniform and fine pearlite structure with a pearlite grain size grade of 7. The thickness tolerance is controlled within ±0.07mm, and the surface quality is good.

[0071] Example 3

[0072] The continuously cast slabs are produced using a hot-charging and hot-delivery process. The slab's initial temperature upon entering the furnace is 508-541℃, and the furnace atmosphere is weakly reducing. The preheating zone temperature is 860-990℃, the first heating zone temperature is 990-1100℃, the second heating zone temperature is 1100-1170℃, the soaking zone temperature is 1140-1160℃, and the exit temperature is 1155℃. The furnace time is 130 minutes. The roughing descaling pressure is set to 220MPa, and the roughing descaling rate is set to 2m / min. Five passes of roughing rolling are used, resulting in an intermediate slab thickness of 40mm. Seven passes of finishing rolling are used, with a final rolling temperature of 820℃, producing a 6.0mm thick steel coil. Laminar flow cooling is a rapid front-end cooling mode, with two sets of side water sprays activated at the start and end points of water cooling. The coiling temperature was set at 580℃, and the coiling tension was 60MPa. The steel coil was removed from the production line 48 minutes after rolling and placed in a slow cooling pit to be slowly cooled to ambient temperature.

[0073] The 60Si2Mn spring steel hot-rolled wide coil produced using the above method has a maximum finishing rolling force of 36500KN and exhibits stable production. The single-sided surface decarburization layer depth is 26μm, the plate straightness is 5mm / m, and there are no broken edges or waviness. The microstructure is a uniform and fine pearlite structure with a pearlite grain size grade of 7. The thickness tolerance is controlled within ±0.08mm, and the surface quality is good.

[0074] Comparative Example 1

[0075] The continuously cast slabs are produced using a hot-charging and hot-delivery process. The slab's initial temperature upon entering the furnace is 512-546℃, and the furnace atmosphere is weakly reducing. The preheating temperature is 850-1020℃, the first heating temperature is 1020-1150℃, the second heating temperature is 1150-1250℃, the soaking temperature is 1200-1230℃, the exit temperature is 1220℃, and the furnace time is 146 minutes. The pressure for rough descaling is set at 220MPa, and the descaling rate is set at 2m / min. Five passes of rough rolling are used, resulting in an intermediate slab thickness of 32mm. Seven passes of finish rolling are used, with a final rolling temperature of 860℃, producing 1.8mm thick steel coils. Laminar flow cooling is a rapid front-end cooling mode, with two sets of side water sprays activated at the start and end points of water cooling. The coiling temperature is 700℃, and the coiling tension is 52MPa. The steel coil is removed from the production line 46 minutes after rolling and placed in a slow cooling pit to be slowly cooled to ambient temperature.

[0076] The 60Si2Mn spring steel hot-rolled wide coil produced using the above method has a maximum finishing rolling force of 35800KN and stable production. The decarburized layer depth on one side of the surface is significantly increased to 85μm, the flatness of the plate is 5mm / m, and there are no broken edges or waviness. The microstructure consists of a small amount of ferrite and coarsened pearlite, with a pearlite grain size grade of 5. The thickness tolerance is within ±0.05mm, and the surface quality is normal, but the surface roughness is increased, and dust accumulation is present.

[0077] Comparative Example 2

[0078] The continuously cast slabs are produced using a hot-charging and hot-delivery process. The slab's initial temperature upon entering the furnace is 512-546℃, and the furnace atmosphere is weakly reducing. The preheating zone temperature is 850-980℃, the first heating zone temperature is 980-1100℃, the second heating zone temperature is 1100-1190℃, the soaking zone temperature is 1150-1180℃, the exit temperature is 1178℃, and the furnace time is 146 minutes. The rough descaling pressure is set at 220MPa, and the descaling rate is set at 2m / min. Seven passes of rough rolling are used, resulting in an intermediate slab thickness of 32mm. Seven passes of finish rolling are used, with a final rolling temperature of 820℃, producing 1.8mm thick steel coils. Laminar flow cooling is a rapid front-end cooling mode, with two sets of side water sprays activated at the start and end points of water cooling. The coiling temperature is 570℃, and the coiling tension is 52MPa. The steel coil is removed from the production line 46 minutes after rolling and placed in a slow cooling pit to be slowly cooled to ambient temperature.

[0079] The 60Si2Mn spring steel hot-rolled wide coil produced using the above method has a maximum finishing rolling force of 45000KN, resulting in unstable production and rolling tailing. The single-sided surface decarburization layer depth is 28μm, the plate straightness is 30mm / m, and there are obvious "ruffled edges" and other broken edge waviness. The microstructure is a uniform and fine pearlite structure with a pearlite grain size grade of 8. The thickness tolerance is within ±0.10mm, and surface defects such as roll marks are present.

[0080] The maximum finishing rolling force, or rolling load, is a specific descriptive parameter that reflects the difficulty of hot rolling.

[0081] The test method for flatness of the plate shall refer to GB / T 709-2019 "Dimensions, shape, weight and permissible deviations of hot-rolled steel plates and strips".

[0082] As can be seen from Examples 1-3 and Comparative Examples 1-2 of this application, the preparation method of this application can prepare hot-rolled wide coils of 60Si2Mn spring steel with excellent microstructure and properties.

[0083] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing hot-rolled wide coils of 60Si2Mn spring steel, characterized in that, The preparation method includes: The slab after continuous casting is heated to obtain a heated slab; the furnace temperature of the slab is greater than 500℃; the atmosphere in the heating furnace for the heating treatment is a weakly reducing atmosphere; the heating treatment time is 120-150 min; and the heating treatment temperature is 800-1200℃. The heat-treated slab is subjected to coarse descaling to obtain a coarsely descaled slab; the pressure of the coarse descaling is greater than 200 MPa, and the rate of the coarse descaling is 1-3 m / min. The slab after rough descaling is subjected to rough rolling to obtain a rough rolled slab; the rough rolling process is carried out in 5 passes, and the thickness of the rough rolled slab is 30-40 mm. The rough-rolled slab is then subjected to finish rolling to obtain a finish-rolled slab. The finish rolling process consists of 7 passes, the final rolling temperature is 800-860℃, and the thickness of the finish-rolled strip is 1.8-6.0mm. The strip steel after finishing rolling is subjected to laminar flow cooling treatment to obtain laminar flow cooled strip steel; the laminar flow cooling treatment adopts a front-stage rapid cooling mode. The strip steel after laminar flow cooling is coiled to obtain a steel coil; the coiling temperature is 580-650℃ and the coiling tension is 50-60MPa. The heating process includes a preheating section, a first heating section, a second heating section, and a homogenization section; The temperature of the preheating section is 800-1000℃, the temperature of the first heating section is 950-1100℃, the temperature of the second heating section is 1050-1200℃, the temperature of the soaking section is 1130-1200℃, and the furnace exit temperature of the slab is 1150-1180℃. The cooling rate of the laminar flow cooling process is 30-50℃ / s; The 60Si2Mn spring steel hot-rolled wide coil has a single-sided surface decarburization layer depth of less than or equal to 1.0% of the nominal thickness, a plate straightness of ≤8mm / m, and a microstructure of pearlite with a grain size grade of ≥7.

2. The preparation method according to claim 1, characterized in that, The furnace temperature of the slab is 500-700℃.

3. The preparation method according to claim 1, characterized in that, The pressure for the coarse descaling process is 200-250 MPa.

4. The preparation method according to claim 1, characterized in that, The preparation method further includes slowly cooling the steel coil to -20°C to 60°C.

5. A hot-rolled wide coil of 60Si2Mn spring steel, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. The 60Si2Mn spring steel hot-rolled wide coil according to claim 5, characterized in that, Based on the total mass of the hot-rolled wide coil of 60Si2Mn spring steel as 100%, the chemical composition of the hot-rolled wide coil of 60Si2Mn spring steel includes: C: 0.56%-0.64%, Si: 1.50%-2.00%, Mn: 0.70%-1.00%, Cr≤0.35%, Ni≤0.35%, Cu≤0.25%, P≤0.025%, S≤0.020%; the remainder is Fe and unavoidable impurities.

7. The 60Si2Mn spring steel hot-rolled wide coil according to claim 5, characterized in that, The thickness of the hot-rolled wide coil of 60Si2Mn spring steel is 1.8-6.0mm, and the width of the hot-rolled wide coil of 60Si2Mn spring steel is 900-1500mm.

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