Method for producing a hot-rolled wide strip coil of a rupture-resistant 60si2mn spring steel and hot-rolled wide strip coil

Abstract

This application provides a method for preparing hot-rolled wide coils of 60Si2Mn spring steel with anti-strip breakage properties, and the hot-rolled wide coils thereof. The method includes: heating a 60Si2Mn spring steel slab to obtain a heated slab; hot-rolling the heated slab to obtain a hot-rolled wide strip steel with a width of 900-1500 mm; subjecting the hot-rolled wide strip steel to laminar flow cooling to obtain laminar flow cooled hot-rolled wide strip steel, wherein the laminar flow cooling consists of a pre-stage non-water cooling treatment and a post-stage rapid cooling treatment, with a target temperature of 760-800℃ for the pre-stage non-water cooling treatment and a cooling rate of 10-20℃ / s for the rapid cooling treatment; and coiling and cooling the laminar flow cooled hot-rolled wide strip steel to obtain hot-rolled wide coils of 60Si2Mn spring steel with anti-strip breakage properties. Using the embodiments of this application, hot-rolled wide coils of 60Si2Mn spring steel with anti-strip breakage properties can be produced, and they will not break during subsequent processing steps.

Description

Technical Field

[0001] This application relates to the field of steel manufacturing technology, and in particular to a method for preparing a hot-rolled wide steel coil of 60Si2Mn spring steel with anti-breakage properties and the hot-rolled wide steel coil thereof. Background Technology

[0002] 60Si2Mn is a silicon-manganese spring steel widely used in the automotive industry, railway transportation, mold and mechanical parts, aerospace, agricultural machinery and other industries. Its chemical composition contains 0.56-0.64% C, 1.50-2.00% Si and 0.60-0.90% Mn. This composition combination makes 60Si2Mn perform better than ordinary carbon steel after heat treatment, especially its high yield strength ratio and fatigue resistance.

[0003] 60Si2Mn exists in various forms, including bars, wires, flat bars, and strips. Wide strip steel, in particular, is less common in the market due to its significantly higher technical difficulty compared to narrow strip steel. Among these technical challenges, controlling strip breakage in wide strip steel is crucial. Wide strip steel is extremely prone to breakage during hot rolling, leveling, pickling, and cold rolling processes. Achieving a fine and uniform microstructure in wide strip steel is even more difficult than in narrow strip steel. Any microstructural inhomogeneity can easily create continuous weak zones in wide strip steel, becoming fracture paths. Therefore, ensuring the smooth operation and mass production of wide strip steel is currently a primary challenge for the industry. Summary of the Invention

[0004] This application provides a method for preparing hot-rolled wide steel coils of 60Si2Mn spring steel with anti-strip breakage, and the hot-rolled wide steel coils thereof, which can prevent strip breakage of 60Si2Mn spring steel hot-rolled wide steel coils during subsequent production.

[0005] In a first aspect, this application provides a method for preparing hot-rolled wide coils of 60Si2Mn spring steel with anti-breakage properties, the method comprising: Provide 60Si2Mn spring steel slabs; The 60Si2Mn spring steel slab was heat-treated to obtain the heat-treated slab. The heat treatment temperature was 1150-1200℃ and the heat treatment time was 150-220min. The slab after heat treatment is hot rolled to obtain hot-rolled wide strip steel. The final rolling temperature of the hot rolling process is 820-850℃, and the width of the hot-rolled wide strip steel is 900-1500mm.

[0006] Hot-rolled wide strip steel is subjected to laminar flow cooling treatment to obtain hot-rolled wide strip steel after laminar flow cooling. The laminar flow cooling treatment consists of a front-stage non-water cooling treatment and a rear-stage rapid cooling treatment. The cooling rate of the front-stage non-water cooling treatment is 2-8℃ / s, and the target cooling temperature is 760-800℃. The cooling rate of the rapid cooling treatment is 10-20℃ / s. Hot-rolled wide strip steel after laminar flow cooling is coiled and cooled to obtain hot-rolled wide strip steel coils of 60Si2Mn spring steel with anti-breakage strip.

[0007] Secondly, this application also provides a hot-rolled wide steel coil, which is prepared by the method for preparing a 60Si2Mn spring steel hot-rolled wide steel coil with anti-breakage properties as described in the first aspect.

[0008] The present application provides a method for preparing a hot-rolled wide coil of 60Si2Mn spring steel with anti-fracture properties, and the hot-rolled wide coil thereof has the following beneficial effects: 1) When heat-treating 60Si2Mn spring steel slabs, the heat treatment temperature is set to 1150-1200℃ and the time is 150-220min to achieve medium-low temperature rapid heating of the slab. On the one hand, this can prevent severe decarburization of the slab surface and ensure the carbon content of the strip surface after hot rolling. On the other hand, it can prevent the coarsening of austenite grains in the slab, laying a good foundation for the formation of a uniform and fine microstructure in the subsequent strip.

[0009] 2) When hot rolling the heat-treated slab, setting a lower final rolling temperature of 820-850℃ helps to obtain a finer austenitic microstructure after hot rolling, while reducing the thickness of secondary iron oxide scale on the strip surface, which is beneficial for subsequent pickling.

[0010] 3) When performing laminar flow cooling on hot-rolled wide strip steel obtained after hot rolling, the initial cooling process without water is performed first, which can be regarded as air cooling. The cooling rate is relatively slow, at 2-8℃ / s, and the target cooling temperature is 760-800℃. This allows the hot-rolled wide strip steel to form a proeutectoid ferrite structure at a relatively high temperature. At this time, due to the optimization of process parameters in the aforementioned heating and hot rolling processes, the austenite grains are made smaller, which greatly increases the total grain boundary area and provides more dispersed nucleation sites. This allows ferrite nuclei to form simultaneously in more places, suppressing the ferrite grain growth rate, and ultimately obtaining fine ferrite grains.

[0011] After the initial waterless cooling treatment is completed, a high cooling rate of 10-20℃ / s is used for the subsequent rapid cooling treatment, which allows the remaining austenite to undergo a eutectoid reaction and transform into pearlite. At the same time, the fine ferrite grains generated after the initial waterless cooling treatment turn the remaining austenite into smaller sub-regions. When these sub-regions are subsequently transformed into pearlite, the size of the formed pearlite clusters also becomes very small.

[0012] 4) After laminar flow cooling treatment with no water cooling in the front section and rapid cooling in the back section, coiling and cooling treatment are carried out to obtain a fine and uniform dual-phase structure of ferrite and pearlite, in which the austenite grain size is ≥7, the ferrite content is 10-20%, and the pearlite content is 80-90%. Such a dual-phase microstructure is beneficial to reduce the strength and hardness of the strip steel and improve its plasticity and toughness. The 60Si2Mn spring steel hot-rolled wide strip produced by this method will not have strip breakage problems in the subsequent pickling, cold rolling, leveling and slitting processes. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a schematic flowchart of a method for preparing hot-rolled wide coils of 60Si2Mn spring steel with anti-breakage strip provided in one embodiment of this application; Figure 2 This is a schematic diagram of the microstructure of the hot-rolled wide coil of 60Si2Mn spring steel prepared in Example 3. Detailed Implementation

[0015] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0016] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover 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.

[0017] Currently, most 60Si2Mn strip steel is narrow strip steel. Compared with narrow strip steel, wide strip steel has higher production efficiency, lower energy consumption, higher dimensional accuracy, and better surface quality. However, wide strip steel products are rare on the market, mainly because of the high technical difficulty and production difficulty, especially the tendency to break the strip, and insufficient ability to achieve stable commercial mass production.

[0018] The reasons for strip breakage in hot-rolled wide strip steel of 60Si2Mn spring steel are as follows: First, in terms of chemical composition, 60Si2Mn spring steel has very high C and Si content, and these two elements are solid solution strengthening elements. Therefore, the high C and Si content results in high strength but low plasticity and toughness, and it is also very brittle. Furthermore, as the thickness increases, the grain size inside the hot-rolled 60Si2Mn strip also increases, leading to increased brittleness. Second, improper temperature control during hot rolling can lead to the formation of abnormal structures such as coarse pearlite and highly brittle upper bainite, both of which can cause the strip to fracture during subsequent production. Third, 60Si2Mn is extremely sensitive to surface quality during hot working. If the surface is subjected to severe compression or abrasion, stress concentration points or microcracks will form. During subsequent processing, these cracks rapidly propagate, leading to cracking or strip breakage.

[0019] To address the issue of easy breakage in hot-rolled wide strip steel of 60Si2Mn spring steel, such as... Figure 1 As shown, this application provides a method for preparing hot-rolled wide coils of 60Si2Mn spring steel with anti-breakage properties. This method may include steps S100 to S500: Step S100: Provide 60Si2Mn spring steel slab.

[0020] In 60Si2Mn, 60 indicates an average carbon content of 0.60%, which typically ranges from 0.56% to 0.64%; Si2 indicates an average silicon content of 2.00%, which typically ranges from 1.50% to 2.00%; and Mn indicates the presence of manganese, which typically ranges from 0.60% to 0.90%.

[0021] Refined molten 60Si2Mn spring steel can be placed in a continuous casting machine to obtain continuously cast slabs of 60Si2Mn spring steel. Producing slabs through continuous casting is not only highly efficient but also facilitates hot charging and hot delivery of the slabs.

[0022] Step S200: Heat-treat the 60Si2Mn spring steel slab to obtain the heat-treated slab.

[0023] The heating temperature can be 1150-1200℃, and the heating time can be 150-220min.

[0024] The combination of temperature and time described above for heat treatment is used to achieve rapid heating of the slab at medium and low temperatures. On the one hand, this prevents severe decarburization of the slab surface, ensuring the carbon content of the surface layer after hot rolling. Severe decarburization of the slab surface leads to the lower carbon content surface austenite transforming into proeutectoid ferrite earlier than the internal austenite during subsequent cooling. Furthermore, the earlier-formed proeutectoid ferrite grains are coarser, resulting in an uneven microstructure. On the other hand, it avoids coarsening of the austenite grains inside the slab, laying a foundation for the subsequent formation of a uniform and fine microstructure.

[0025] The essence of decarburization is the reaction and loss of carbon atoms on the slab surface with oxygen, water vapor, etc., within the heating device, while carbon atoms inside the slab continuously diffuse to the surface to replenish them. The effect of medium-low temperature heating is to reduce the diffusion coefficient of carbon atoms inside the slab within austenite due to temperature. Even if carbon atoms on the slab surface react, carbon atoms inside the slab cannot quickly replenish the surface, thus limiting the depth of the decarburized layer. The effect of rapid firing is to shorten the total residence time of the slab in the heating device, i.e., to narrow the time window for carbon atom diffusion, thereby reducing the total amount of carbon atoms lost through diffusion from the interior to the surface. In summary, medium-low temperature rapid firing inhibits the diffusion rate of carbon atoms and shortens the diffusion time, thus avoiding severe decarburization of the slab surface, at most forming only a very shallow surface decarburized layer.

[0026] The essence of austenite grain coarsening is grain boundary migration, where smaller grains are engulfed by larger grains, reducing the total grain boundary area and energy. Medium-low temperature firing reduces the grain boundary mobility of austenite grains within the slab due to temperature variations. Rapid firing shortens the residence time of the slab in the heating device, preventing grain boundaries from migrating a long distance. In summary, medium-low temperature rapid firing limits the driving force of grain boundary migration and shortens the migration distance, thus preventing austenite grain coarsening within the slab.

[0027] Step S300: The heat-treated slab is hot-rolled to obtain hot-rolled wide strip steel.

[0028] The width of the hot-rolled wide strip steel is 900-1500 mm. This application, through research, has developed a special process route and process parameters that can stably produce wide 60Si2Mn hot-rolled strip steel.

[0029] The final rolling temperature for hot rolling can be 820-850℃. Controlling the final rolling temperature below the non-recrystallization temperature of austenite can prevent the current dynamic recrystallization of austenite from forming new, but potentially coarse, austenite grains. While ensuring fine austenite grains, the austenite grains are flattened by the hot rolling force, thus further increasing the grain surface area. This also means a further increase in grain boundary area, providing more nucleation sites for proeutectoid ferrite, which can, to some extent, prevent excessive growth of proeutectoid ferrite grains during subsequent cooling.

[0030] Step S400: Perform laminar flow cooling treatment on the hot-rolled wide strip steel to obtain hot-rolled wide strip steel after laminar flow cooling treatment.

[0031] The laminar flow cooling process consists of a front-stage non-water cooling treatment and a rear-stage rapid cooling treatment. The laminar flow cooling device is divided into two cooling sections along the running direction of the hot-rolled wide strip steel: the front section is the cooling section upstream of the finishing mill, and the rear section is the cooling section downstream of the coiling mill. Any micro-element on the hot-rolled wide strip steel undergoes both the front-stage non-water cooling treatment and the rear-stage rapid cooling treatment sequentially as it passes through the entire laminar flow cooling device.

[0032] Taking a micro-element on a hot-rolled wide strip steel as an example, this micro-element leaves the finishing mill exit at a final rolling temperature of 820-850°C and enters the front section of the laminar flow cooling device. Because the front section employs a non-water-cooling strategy, this micro-element cools slowly through radiation during its operation, with a cooling rate of approximately 2-8°C / s and a target cooling temperature of 760-800°C. This non-water-cooling process allows the hot-rolled wide strip steel to partially transform austenite into proeutectoid ferrite at a higher temperature. Proeutectoid ferrite refers to ferrite that precipitates separately from austenite before eutectoid formation. The eutectoid reaction refers to the simultaneous precipitation of ferrite and cementite from austenite, forming pearlite. Based on the cooling rate and target temperature of the non-water-cooling process, it can be deduced that the shorter cooling time in the front section prevents the proeutectoid ferrite grains from growing, resulting in finer proeutectoid ferrite grains.

[0033] The aforementioned micro-element proceeds from the front section to the rear section. The rear section manifold is opened, and cooling water is sprayed, causing boiling heat transfer within the micro-element. The cooling rate is relatively high, at 10-20°C / s, allowing the micro-element to decrease from a high temperature to the laminar cooling target temperature in a short time. Under rapid cooling conditions, the remaining austenite transforms into pearlite. At this point, the fine proeutectoid ferrite grains divide the remaining austenite into several smaller regions, which also facilitates the formation of fine pearlite. However, to avoid excessively rapid cooling leading to the formation of bainite or martensite, this embodiment sets the rear section rapid cooling rate to 10-20°C / s.

[0034] Step S500 involves coiling and cooling the hot-rolled wide strip steel after laminar flow cooling to obtain a hot-rolled wide strip steel coil of 60Si2Mn spring steel with anti-breakage strip.

[0035] This application embodiment achieves not only a fine and uniform dual-phase microstructure of ferrite and pearlite by synergistically controlling the heating treatment time and target temperature, the hot rolling final rolling temperature, and the cooling rate and target temperature of the two-stage laminar cooling treatment, but also by controlling the content ratio of ferrite and pearlite. This ensures that a hot-rolled wide coil of 60Si2Mn spring steel with suitable strength and hardness, as well as good plasticity and toughness, can be obtained.

[0036] In one embodiment, the step of heat-treating the slab includes: The slab is placed in a heating furnace for heating treatment, wherein the initial temperature of the slab is 200-600℃, preferably 300-600℃.

[0037] By controlling the furnace entry temperature of the slab, it is possible to reduce the residence time of the slab in the heating furnace, thereby facilitating the realization of the above-mentioned medium-low temperature rapid firing process. In addition, it can also save energy.

[0038] Generally, a hot charging and hot delivery process is used to send the continuously cast slab to a heating furnace for heating treatment.

[0039] In one embodiment, the step of hot-rolling a heat-treated slab to obtain hot-rolled wide strip steel includes: The heat-treated slab is subjected to rough rolling to obtain a rough-rolled intermediate slab. The rough-rolled intermediate slab is then subjected to finish rolling to obtain hot-rolled wide strip steel.

[0040] Optionally, the roughing process may be performed in 5-7 passes.

[0041] Optionally, the thickness of the intermediate slab after rough rolling is 30-40 mm. Minimizing the thickness of the intermediate slab helps alleviate the problem of excessive finishing load caused by the decrease in the temperature of the intermediate slab.

[0042] Optionally, the finishing rolling process may be performed in 5-7 passes.

[0043] Optionally, the thickness of the hot-rolled wide strip steel is 1.8-8.0 mm. For wide strip steel with a thickness of 6.0 mm or more, breakage at both ends is particularly likely during leveling and sizing, leading not only to equipment damage but also to scratches and dents on the strip. This application solves the strip breakage problem for wide strip steel with a thickness of up to 8.0 mm by employing heat treatment, hot rolling, laminar flow cooling (without hot water at the beginning + rapid cooling at the end), and cooling treatment of the hot-rolled wide strip steel coil. This significantly increases the freedom in selecting the thickness specification.

[0044] In one embodiment, in the step of laminar flow cooling of hot-rolled wide strip steel, the target cooling temperature of the subsequent rapid cooling treatment is 540-600°C.

[0045] The target cooling temperature for the rapid cooling process in the later stage is generally close to the winding temperature of the subsequent winding process.

[0046] In one embodiment, the steps of coiling and cooling the hot-rolled wide strip steel after laminar flow cooling may include: Hot-rolled wide strip steel after laminar flow cooling is coiled to obtain hot-rolled wide steel coils.

[0047] Hot-rolled wide steel coils are subjected to slow cooling treatment to obtain slow-cooled hot-rolled wide steel coils. Optionally, the slow cooling treatment includes slow cooling in a slow cooling pit preheated to 200-300℃. Optionally, the slow cooling treatment time is 3-6 hours. The hot-rolled wide steel coils, after slow cooling treatment, are subjected to natural cooling treatment to obtain hot-rolled wide steel coils. Optionally, the natural cooling treatment involves naturally cooling to ambient temperature in a slow cooling pit where heat preservation has been stopped.

[0048] By allowing sufficient and slow cooling in the slow cooling pit for a certain period of time, the internal stress and hardness of the hot-rolled wide strip steel coil are significantly reduced, giving it high plasticity and toughness. This effectively prevents the hot-rolled wide strip steel coil from breaking during subsequent processes such as leveling, sizing, and pickling.

[0049] In one embodiment, in the step of sequentially coiling the wide strip steel after laminar flow cooling, the coiling temperature is 560-620°C.

[0050] Setting a lower winding temperature helps maintain a fine and uniform microstructure. During the process from leaving the laminar flow cooling device to entering the winding device, the core temperature of the laminar flow cooled steel is higher than the surface temperature, resulting in a certain degree of self-warming. Therefore, the actual winding temperature may be slightly higher than the target cooling temperature of the rapid cooling process.

[0051] This application also proposes a hot-rolled wide steel coil, produced by the preparation method of any of the above embodiments. The microstructure of this hot-rolled wide steel coil is ferrite and pearlite, wherein the austenite grain size is ≥7. It is worth noting that the austenite grain size here reflects the grain size of the microstructure in the hot-rolled wide steel coil. Specifically, a sample is cut from the finished hot-rolled wide steel coil, then heated to austenitize it, and then the size of the austenite grains in the austenitized sample is measured.

[0052] In one embodiment, the ferrite content in the hot-rolled wide steel coil is 10-20%, and the pearlite content is 80-90%.

[0053] Ferrite refers to proeutectoid ferrite, but does not include the ferrite that constitutes pearlite.

[0054] Pearlite has higher strength and hardness than pure ferrite, but lower plasticity and toughness. To ultimately obtain suitable strength, hardness, plasticity, and toughness, the content of ferrite and pearlite in the dual-phase microstructure of the 60Si2Mn spring steel hot-rolled wide coils with fracture-resistant strips produced by the preparation method in any of the above embodiments was also optimized.

[0055] In one embodiment, the thickness of the hot-rolled wide steel coil is 1.8-8.0 mm and the width is 900-1500 mm.

[0056] In summary, the hot-rolled wide steel coils prepared by the preparation method of any of the above embodiments can have a thickness of up to 8.0 mm. These hot-rolled wide steel coils have very fine and uniform grains, and the microstructure is a two-phase structure of proeutectoid ferrite + pearlite. This solves the problem that hot-rolled wide steel coils produced under general processes are prone to breakage during leveling, smoothing, and pickling.

[0057] Example 1 Example 1 provides a method for preparing a hot-rolled wide coil of 60Si2Mn spring steel with anti-breakage properties, comprising the following steps: 1) Provide 60Si2Mn spring steel continuous casting slabs with the following chemical composition and corresponding mass percentages: C: 0.61%, Si: 1.88%, Mn: 0.76%, Cr: 0.12%, P: 0.010%, S: 0.003%; the remainder is Fe and unavoidable impurities, with a thickness of 230mm and a width of 1270mm.

[0058] 2) The 60Si2Mn spring steel continuous casting slab was placed in a heating furnace for heat treatment, and the initial temperature of the continuous casting slab was controlled at 500℃ to obtain the heat-treated continuous casting slab. The heat treatment temperature was 1160℃ and the heat treatment time was 160min.

[0059] 3) The heat-treated continuous casting slab is subjected to 7 passes of rough rolling to obtain an intermediate slab with a thickness of 40 mm after rough rolling.

[0060] 4) The intermediate slab after rough rolling is subjected to 7 passes of finish rolling, and the final rolling temperature is controlled at 820℃ to obtain hot-rolled wide strip steel with a thickness of 8.0mm and a width of 1250mm.

[0061] 5) Place the hot-rolled wide steel plate in a laminar flow cooling device. Do not turn on the water in the front manifold, but turn on the water in the rear manifold. Let the hot-rolled wide steel plate cool for 11 seconds to 797°C, and then cool it to 560°C at a cooling rate of 20°C / s to obtain the hot-rolled wide steel plate after laminar flow cooling treatment.

[0062] 6) The hot-rolled wide strip steel after laminar flow cooling treatment is coiled at a temperature of 590℃ to obtain 60Si2Mn spring steel hot-rolled wide strip steel coil.

[0063] 7) After coiling, the 60Si2Mn spring steel hot-rolled wide steel coils are quickly removed from the production line and placed in a slow cooling pit preheated to 280℃ for 5 hours to cool slowly. Then, the heat preservation is stopped and the coils are allowed to cool naturally to the ambient temperature.

[0064] The 60Si2Mn spring steel hot-rolled wide coil prepared in Example 1 has a thickness of 8.0 mm, a width of 1250 mm, a microstructure of 18% ferrite and 82% pearlite, an austenite grain size of grade 7.0, a yield strength of 647 MPa, a tensile strength of 924 MPa, and an elongation of 6.5%. No strip breakage occurred during the leveling process of this 60Si2Mn spring steel hot-rolled wide coil into cross-cut steel plates.

[0065] Example 2 Example 2 provides a method for preparing a hot-rolled wide coil of 60Si2Mn spring steel with anti-breakage properties, comprising the following steps: 1) Provide 60Si2Mn spring steel continuous casting slabs with the following chemical composition and corresponding mass percentages: C: 0.58%, Si: 1.85%, Mn: 0.75%, Cr: 0.12%, P: 0.013%, S: 0.001%; ​​the remainder is Fe and unavoidable impurities, with a thickness of 230mm and a width of 1270mm.

[0066] 2) The 60Si2Mn spring steel continuous casting slab was placed in a heating furnace for heat treatment, and the initial temperature of the continuous casting slab was controlled at 320℃ to obtain the heat-treated continuous casting slab. The heat treatment temperature was 1180℃ and the heat treatment time was 220min.

[0067] 3) The heat-treated continuous casting slab is subjected to 7 passes of rough rolling to obtain an intermediate slab with a thickness of 38 mm after rough rolling.

[0068] 4) The intermediate slab after rough rolling is subjected to 7 passes of finish rolling, and the final rolling temperature is controlled at 840℃ to obtain hot-rolled wide strip steel with a thickness of 5.0mm and a width of 1250mm.

[0069] 5) Place the hot-rolled wide strip steel in a laminar flow cooling device. Do not turn on the water in the front manifold, but turn on the water in the rear manifold. Let the hot-rolled wide strip steel cool for 10 seconds to 783°C, and then cool it to 580°C at a cooling rate of 15°C / s to obtain the hot-rolled wide strip steel after laminar flow cooling treatment.

[0070] 6) The hot-rolled wide strip steel after laminar flow cooling treatment is coiled at a temperature of 600℃ to obtain 60Si2Mn spring steel hot-rolled wide strip steel coil.

[0071] 7) After coiling, the 60Si2Mn spring steel hot-rolled wide steel coil is quickly removed from the production line. The 60Si2Mn spring steel hot-rolled wide steel coil is placed in a slow cooling pit preheated to 270℃ and slowly cooled for 5 hours. Then the heat preservation is stopped and it is allowed to cool naturally to the ambient temperature.

[0072] The 60Si2Mn spring steel hot-rolled wide coil prepared in Example 2 has a thickness of 5.0 mm, a width of 1250 mm, a microstructure of 15% ferrite and 85% pearlite, an austenite grain size of grade 7.5, a yield strength of 658 MPa, a tensile strength of 937 MPa, and an elongation of 6.5%. This 60Si2Mn spring steel hot-rolled wide coil did not experience any strip breakage during the pickling process after leveling on the leveling line.

[0073] Example 3 Example 3 provides a method for preparing a hot-rolled wide coil of 60Si2Mn spring steel with anti-breakage properties, comprising the following steps: 1) Provide 60Si2Mn spring steel continuous casting slabs with the following chemical composition and corresponding mass percentages: C: 0.59%, Si: 1.84%, Mn: 0.78%, Cr: 0.15%, P: 0.008%, S: 0.002%; the remainder is Fe and unavoidable impurities, with a thickness of 230mm and a width of 1270mm.

[0074] 2) The 60Si2Mn spring steel continuous casting slab is placed in a heating furnace for heat treatment, and the initial temperature of the continuous casting slab is controlled at 600℃ to obtain the heat-treated continuous casting slab. The heat treatment temperature is 1200℃ and the heat treatment time is 180min.

[0075] 3) The heat-treated continuous casting slab is subjected to 7 passes of rough rolling to obtain an intermediate slab with a thickness of 30 mm after rough rolling.

[0076] 4) The intermediate slab after rough rolling is subjected to 7 passes of finish rolling, and the final rolling temperature is controlled at 850℃ to obtain hot-rolled wide strip steel with a thickness of 2.0mm and a width of 1250mm.

[0077] 5) Place the hot-rolled wide strip steel in a laminar flow cooling device. Do not turn on the water in the front manifold, but turn on the water in the rear manifold. Let the hot-rolled wide strip steel cool for 10 seconds to 775°C, and then cool it to 600°C at a cooling rate of 12°C / s to obtain the hot-rolled wide strip steel after laminar flow cooling treatment.

[0078] 6) The hot-rolled wide strip steel after laminar flow cooling treatment is coiled at a temperature of 620℃ to obtain 60Si2Mn spring steel hot-rolled wide strip steel coil.

[0079] 7) After coiling, the 60Si2Mn spring steel hot-rolled wide steel coils are quickly removed from the production line and placed in a slow cooling pit preheated to 280℃ for 5 hours to cool slowly. Then, the heat preservation is stopped and the coils are allowed to cool naturally to the ambient temperature.

[0080] Example 3 prepared a hot-rolled wide coil of 60Si2Mn spring steel with a thickness of 2.0 mm and a width of 1250 mm. Figure 2 The diagram shows a schematic microstructure of the prepared 60Si2Mn spring steel hot-rolled wide coil, with a scale of 20 pixels. The microstructure of Example 3 consists of 12% ferrite and 88% pearlite, with an austenite grain size of 8.5. The yield strength is 652 MPa, the tensile strength is 956 MPa, and the elongation is 8.0%. No strip breakage occurred during the pickling process after leveling on the leveling line with this 60Si2Mn spring steel hot-rolled wide coil.

[0081] As shown in Table 1, process parameters for the preparation methods of hot-rolled wide coils of 60Si2Mn spring steel with anti-breakage strips in Examples 1-3 are provided.

[0082] Table 1 Process parameters for Examples 1-3

[0083] Table 2 provides the specifications, microstructure, and macroscopic properties of the 60Si2Mn spring steel hot-rolled wide coils with fracture-resistant strips from Examples 1-3.

[0084] Table 2. Specifications, microstructure, and macroscopic properties of hot-rolled wide coils of 60Si2Mn spring steel with fracture resistance in Examples 1-3.

[0085] Comparative Example 1 Comparative Example 1 provides a method for preparing a hot-rolled wide strip of 60Si2Mn spring steel with anti-breakage properties. The difference between this method and Example 1 is that, in step 5), the hot-rolled wide strip steel is placed in a laminar flow cooling device, with water turned on in the front manifold and partially turned on in the rear manifold, allowing the hot-rolled wide strip steel to be cooled to 600°C, thus obtaining hot-rolled wide strip steel after laminar flow cooling treatment.

[0086] The 60Si2Mn spring steel hot-rolled wide coil produced in Comparative Example 2 has a microstructure of 100% troostite, a yield strength of 694 MPa, a tensile strength of 1003 MPa, and an elongation of 6.2%. This 60Si2Mn spring steel hot-rolled wide coil experienced strip breakage during the pickling process after leveling on the leveling line.

[0087] It can be seen that if the cooling process of front-end non-water cooling treatment + rear-end rapid cooling treatment is not adopted, it will lead to the formation of troostite. Although the strength is increased, the plasticity and toughness are reduced and the brittleness is increased, which will cause the 60Si2Mn spring steel hot-rolled wide steel coil to break in the subsequent processing.

[0088] Comparative Example 2 Comparative Example 2 provides a method for preparing hot-rolled wide strip steel coils of 60Si2Mn spring steel with anti-breakage properties. The difference between this method and Example 1 is that in step 5), the hot-rolled wide strip steel is placed in a laminar flow cooling device. The front manifold is not turned on, while the rear manifold is turned on. The hot-rolled wide strip steel is cooled for 6 seconds to 824°C, and then cooled to 640°C at a cooling rate of 8°C / s to obtain the hot-rolled wide strip steel after laminar flow cooling treatment.

[0089] The 60Si2Mn spring steel hot-rolled wide coils produced in Comparative Example 2 exhibited larger ferrite grain sizes in their microstructure. During the pickling process following leveling on the leveling line, these 60Si2Mn spring steel hot-rolled wide coils experienced strip breakage.

[0090] It can be seen that if the cooling time of the initial non-water cooling treatment is too short, the actual temperature after the initial non-water cooling treatment will be higher than the 760-800℃ specified in this application, and the cooling rate of the subsequent rapid cooling treatment will be too low, which will lead to the ferrite grain size becoming larger, that is, the formation of coarse ferrite. Coarse ferrite is one of the pathways for brittle fracture, which will cause the 60Si2Mn spring steel hot-rolled wide steel coil to break in the subsequent processing.

[0091] Comparative Example 3 Comparative Example 3 provides a method for preparing a hot-rolled wide strip of 60Si2Mn spring steel with anti-breakage properties. The difference between this method and Example 1 is that, in step 5), the hot-rolled wide strip steel is placed in a laminar flow cooling device without any water, and the hot-rolled wide strip steel is cooled to 680°C to obtain hot-rolled wide strip steel after laminar flow cooling treatment.

[0092] The 60Si2Mn spring steel hot-rolled wide coils produced in Comparative Example 2 exhibited coarse pearlite microstructure. During the pickling process following leveling on the leveling line, the 60Si2Mn spring steel hot-rolled wide coils experienced strip breakage.

[0093] It can be seen that if the cooling rate of the subsequent rapid cooling process is too low, the pearlite cluster size will increase, and the abnormally large pearlite structure will cause the hot-rolled wide coil of 60Si2Mn spring steel to break in the subsequent processing.

[0094] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing a hot-rolled wide coil of 60Si2Mn spring steel with anti-breakage properties, characterized in that, The method includes: Provide 60Si2Mn spring steel slabs; The 60Si2Mn spring steel slab is subjected to heat treatment to obtain a heat-treated slab. The heat treatment temperature is 1150-1200℃ and the heat treatment time is 150-220min. The heat-treated slab is hot-rolled to obtain hot-rolled wide strip steel. The final rolling temperature of the hot rolling process is 820-850℃, and the width of the hot-rolled wide strip steel is 900-1500mm. The hot-rolled wide strip steel is subjected to laminar flow cooling treatment to obtain hot-rolled wide strip steel after laminar flow cooling. The laminar flow cooling treatment consists of a front-stage non-water cooling treatment and a rear-stage rapid cooling treatment. The cooling rate of the front-stage non-water cooling treatment is 2-8℃ / s, and the target cooling temperature is 760-800℃. The cooling rate of the rapid cooling treatment is 10-20℃ / s. The hot-rolled wide strip steel after laminar flow cooling is subjected to coiling and cooling treatment to obtain hot-rolled wide strip steel coils of 60Si2Mn spring steel with anti-breakage strip.

2. The preparation method according to claim 1, characterized in that, The steps of coiling and cooling the hot-rolled wide strip steel after laminar flow cooling include: The hot-rolled wide strip steel after laminar flow cooling is coiled to obtain hot-rolled wide steel coils; The hot-rolled wide steel coil is subjected to slow cooling treatment to obtain a slow-cooled hot-rolled wide steel coil. Optionally, the slow cooling treatment includes slow cooling in a slow cooling pit preheated to 200-300°C. Optionally, the slow cooling treatment time is 3-6 hours. The hot-rolled wide steel coil after the slow cooling treatment is subjected to natural cooling treatment to obtain a 60Si2Mn spring steel hot-rolled wide steel coil with anti-breakage strip. Optionally, the natural cooling treatment is to naturally cool to the ambient temperature in a slow cooling pit where heat preservation has been stopped.

3. The preparation method according to claim 1, characterized in that, In the step of laminar flow cooling treatment of the hot-rolled wide strip steel, the target cooling temperature of the subsequent rapid cooling treatment is 540-600℃.

4. The preparation method according to claim 1, characterized in that, In the step of coiling the hot-rolled wide strip steel after laminar flow cooling, the coiling temperature is 560-620℃.

5. The preparation method according to claim 1, characterized in that, The step of heat-treating the 60Si2Mn spring steel slab includes: The 60Si2Mn spring steel slab is placed in a heating furnace for heating treatment, and the initial temperature of the slab is 200-600℃.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The step of hot rolling the heat-treated slab to obtain hot-rolled wide strip steel includes: The heat-treated slab is subjected to rough rolling to obtain an intermediate slab after rough rolling; optionally, the rough rolling process is performed in 5-7 passes. The intermediate slab after rough rolling is subjected to finish rolling to obtain hot-rolled wide strip steel; optionally, the finish rolling process is performed in 5-7 passes.

7. The preparation method according to claim 6, characterized in that, The thickness of the intermediate slab after rough rolling is 30-40 mm; Optionally, the thickness of the hot-rolled wide strip steel is 1.8-8.0 mm.

8. A wide steel coil, characterized in that, It is prepared by the preparation method according to any one of claims 1-7; The microstructure of the hot-rolled wide steel coil consists of ferrite and pearlite, with austenite grain size ≥ 7.

9. The hot-rolled wide steel coil according to claim 8, characterized in that, The ferrite content is 10-20%; the pearlite content is 80-90%.

10. The hot-rolled wide steel coil according to any one of claims 8 to 9, characterized in that, The hot-rolled wide steel coil has a thickness of 1.8-8.0 mm and a width of 900-1500 mm.

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