A method for producing a plate product and a plate product

Abstract

The application provides a preparation method of a medium plate product and the medium plate product, and belongs to the field of medium plate production. The method comprises the following steps: sequentially performing heating, descaling by a descaling machine and rough rolling on a slab, and performing descaling in the last pass of rough rolling to obtain a first steel plate; performing pre-rolling descaling on the first steel plate by using a descaling machine of a finishing rolling mill in a way of descaling without a reduction amount to obtain a second steel plate; performing finishing rolling on the second steel plate, performing descaling in the first three passes and the last pass of the finishing rolling, and then air cooling to a set final cooling temperature to obtain a third steel plate; performing hot straightening on the third steel plate at a set straightening temperature, and then performing slow cooling to obtain the medium plate product. By adopting the process means of air-pass descaling, controlled rolling, air cooling and slow cooling, the integrity and uniformity of the whole steel plate skin are ensured, the plate shape of the thick gauge steel plate is ensured, and the surface quality is ensured to be good. Therefore, on the basis of meeting the plate shape of the medium plate, the surface quality of the medium plate product is improved.

Description

Technical Field

[0001] This application relates to the field of medium and heavy plate production technology, and in particular to a method for preparing medium and heavy plate products and medium and heavy plate products. Background Technology

[0002] With the development of medium and heavy plate products, some users have raised higher requirements for the surface quality of these products. The demand for high-surface-quality medium and heavy plate products in fields such as construction and engineering machinery is gradually increasing. In the future, there may be more and more medium and heavy plate products with higher surface quality requirements, necessitating process development to address these demands. Simultaneously, some steel plate specifications (15mm~30mm) require both high surface quality and guaranteed performance.

[0003] However, since steel plates of this specification generally require a heating period to ensure their performance meets requirements, the scale formed during this heating process undergoes repeated deformation during subsequent finishing rolling and low-temperature deformation during straightening. This poses a greater challenge to the final surface quality of the steel plate. Furthermore, due to the large thickness of the steel plate, if the post-rolling shape is poor, excessive straightening force during the straightening process can cause the scale to crack, leading to the problem of scale bursting. Therefore, improving the surface quality of medium and heavy plate products while simultaneously meeting both shape and performance requirements is a pressing technical issue that needs to be addressed. Summary of the Invention

[0004] This application provides a method for preparing medium-thick plate products and medium-thick plate products to solve the following technical problem: how to improve the surface quality of medium-thick plate products while meeting the plate shape requirements.

[0005] In a first aspect, this application provides a method for preparing a medium-thick plate product, the method comprising:

[0006] The slab is sequentially heated, descaled by a descaling machine, and rough rolled, and descaling is performed in the last pass of the rough rolling to obtain the first steel plate;

[0007] The first steel plate is descaled before finishing rolling using a descaling machine on a finishing mill with no reduction, to obtain the second steel plate.

[0008] The second steel plate is precision rolled, and descaling is performed in the first three passes and the last pass of the precision rolling. Then it is air-cooled to the set final cooling temperature to obtain the third steel plate.

[0009] The third steel plate is hot-straightened at a set straightening temperature and then slowly cooled to obtain a medium-thick plate product.

[0010] Optionally, the number of descaling passes before finishing rolling is 1 to 2, and the descaling before finishing rolling can be carried out in a single pre-mill or post-mill descaling, or simultaneously in both pre-mill and post-mill descaling.

[0011] Optionally, the starting temperature for descaling before finishing rolling is 860℃~920℃.

[0012] Optionally, the cumulative reduction rate of the finishing mill is ≤50%.

[0013] Optionally, the set final cooling temperature is 680℃~750℃.

[0014] Optionally, the thermal straightening is a single thermal straightening process, and the set straightening temperature is ≥650℃.

[0015] Optionally, the slow cooling is cooling in a slow cooling pit, wherein the temperature at which the material enters the slow cooling pit is ≥400℃ and the temperature at which it exits the slow cooling pit is ≤80℃.

[0016] Optionally, the heating temperature is 1130℃~1180℃, the heating time in the furnace is 240min~280min; and / or, the rough rolling adopts multi-pass descaling.

[0017] Secondly, this application provides a medium-thick plate product prepared by the method described in any one of the embodiments of the first aspect, wherein the thickness of the medium-thick plate product is 15mm to 30mm.

[0018] Optionally, the medium-thick plate product meets at least one of the following properties: surface sheet thickness ≥ 40 μm, surface sheet Fe3O4 mass fraction ≥ 60%, and plate shape unevenness ≤ 3 mm / m.

[0019] The technical solutions provided in this application have the following advantages compared with the prior art:

[0020] This application provides a method for preparing medium and heavy plate products, comprising: sequentially heating a slab, descaling it with a descaling machine, and rough rolling it, and descaling it in the last pass of the rough rolling to obtain a first steel plate; using a finishing mill descaling machine, descaling the first steel plate before finishing rolling using a non-reduction descaling method to obtain a second steel plate; finishing rolling the second steel plate, and descaling it in the first three passes and the last pass of the finishing rolling, and then air cooling it to a set final cooling temperature to obtain a third steel plate; hot straightening the third steel plate at a set straightening temperature, and then slow cooling to obtain a medium and heavy plate product. The key technical approach of this application combines two technical routes: First, the process emphasizes thorough descaling before finishing rolling to ensure the complete removal of scale formed during the warm-up process, preventing cracks or even severe scale bursting during deformation in the finishing rolling stage. Second, post-rolling, based on strict control of final rolling and air cooling processes, the steel plate achieves deformation within the high plasticity temperature range of the iron oxide scale through a relatively high straightening temperature. The slow cooling process ensures the formation of high-quality, relatively dense bluish-black scale on the surface of the rolled steel plate, exhibiting a higher proportion of Fe3O4 at the microscopic level for better scale density. Based on these technical routes, excellent surface quality and good plate shape are achieved simultaneously. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The plasticity of different types of iron oxides as a function of temperature is shown in the embodiments of this application.

[0024] Figure 2 A schematic flowchart illustrating a method for preparing a medium-thick plate product according to an embodiment of this application;

[0025] Figure 3 A physical image of the medium-thick plate product provided for Comparative Example 1 of this application;

[0026] Figure 4 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 1 of this application;

[0027] Figure 5 A physical image of the medium-thick plate product provided in Comparative Example 2 of this application;

[0028] Figure 6 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 2 of this application;

[0029] Figure 7 A physical image of the medium-thick plate product provided in Comparative Example 3 of this application;

[0030] Figure 8 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 3 of this application;

[0031] Figure 9 A physical image of the medium-thick plate product provided in Comparative Example 4 of this application;

[0032] Figure 10 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 4 of this application;

[0033] Figure 11 This is a physical image of the medium-thick plate product provided in Embodiment 1 of this application;

[0034] Figure 12 This is a microscopic sheet metal image of the medium-thick plate product provided in Embodiment 1 of this application;

[0035] Figure 13 This is a physical image of the medium-thick plate product provided in Embodiment 2 of this application;

[0036] Figure 14 This is a microscopic sheet metal diagram of the medium-thick plate product provided in Embodiment 2 of this application. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0039] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0041] The inventive concept of this application is as follows:

[0042] In existing technologies, methods for improving the surface quality of medium and heavy plates generally optimize the surface quality without addressing the specific surface issues at different sub-specification levels. This patented technology focuses on steel plates with a thickness of 15mm to 30mm. On one hand, steel plates in this range require a heating period before finishing rolling, and due to their thickness, this extended heating time creates conditions for the formation and thickening of iron oxide scale. Excessively thick scale increases descaling difficulty and can lead to scale indentation problems later. On the other hand, steel plates in this range require a straightening process after rolling to optimize their shape, during which significant deformation still occurs. Furthermore, the increased straightening force due to the thickness of the steel plate compared to thinner plates poses a greater challenge to the plasticity of the iron oxide scale. Figure 1 The graphs showing the plasticity of different types of iron oxides as a function of temperature, provided in the embodiments of this application, are from... Figure 1 It is known that if the straightening temperature is around 600℃, the overall plasticity of FeO is poor. Furthermore, due to the thickness of the steel plate, the straightening force increases during the straightening process, which makes the iron oxide scale on the steel plate surface more prone to breakage under high straightening force. This ultimately leads to the problem of iron oxide scale peeling on the steel plate surface, affecting the user's processing (the location of the peeling on the steel plate surface affects the processing accuracy—such as laser cutting) and long-term storage (the peeling location has more red rust and poor corrosion resistance).

[0043] Therefore, specific process designs are needed for medium and heavy plate products with high surface quality requirements and prone to scale breakage to meet user needs. During the rolling process, the iron oxide scale generated during oxidation must be thoroughly removed through descaling, especially avoiding the indentation of scale generated during the warming process during the finishing rolling stage. Simultaneously, considering that the rolled plate shape of 15mm–30mm steel plates still exhibits some waviness, the scale will still undergo significant deformation during straightening, resulting in a certain amount of plastic deformation of the iron oxide scale on the steel plate surface. If the straightening temperature is too low, there is a risk of cracking due to insufficient plasticity of the iron oxide scale. Furthermore, a subsequent slow cooling process further promotes the formation of Fe3O4 on the steel plate surface, resulting in a denser iron oxide scale.

[0044] Therefore, this application employs air-cooling, controlled rolling, air cooling, and slow cooling processes to ensure the integrity and uniformity of the sheet metal on the entire steel plate. This guarantees the shape of thick steel plates while ensuring good surface quality. Simultaneously, the sheet metal is dense, intact, and free of bulging, resolving the issues of red-hot sheet metal, localized bulging, and sheet metal indentation that lead to unsatisfactory surface quality. Thus, while meeting the shape requirements of medium-thick plates, the surface quality of medium-thick plate products is improved.

[0045] Figure 2This is a schematic flowchart illustrating a method for preparing a medium-thick plate product according to an embodiment of this application.

[0046] Based on the above analysis, please refer to Figure 2 This application provides a method for preparing a medium-thick plate product, the method comprising:

[0047] S1. The slab is heated, descaled by a descaling machine and rough rolled in sequence, and descaling is performed in the last pass of the rough rolling to obtain the first steel plate;

[0048] In some embodiments, the heating temperature is 1130°C to 1180°C, the heating time in the furnace is 240 min to 280 min; and / or, the rough rolling employs multi-pass descaling.

[0049] In the above embodiments, the rolling process is ensured to proceed smoothly by controlling the heating conditions. For example, the heating temperature can be 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, etc., and the furnace heating time can be 240min, 250min, 260min, 270min, 280min, etc.

[0050] S2. Using a descaling machine on a finishing mill, the first steel plate is descaled before finishing milling using a descaling method without reduction, to obtain the second steel plate.

[0051] The number of descaling passes before finishing rolling is 1 to 2. The descaling before finishing rolling can be carried out in a single pre-roll or post-roll descaling, or simultaneously in both pre-roll and post-roll descaling.

[0052] In the above embodiments, by descaling before the finishing rolling stage, the iron oxide scale generated on the surface of the steel plate during the waiting process is fully removed without deformation, thus avoiding the problem of iron scale being pressed in during rolling if the scale is not completely removed.

[0053] In some embodiments, the starting temperature for the pre-rolling descaling is 860°C to 920°C.

[0054] In the above embodiments, the descaling temperature before finishing rolling is increased by 30°C to 50°C compared to the conventional initial rolling temperature. The main purpose is to shorten the waiting time, inhibit the growth of iron oxide scale on the steel plate surface, and thus ensure better descaling results. Simultaneously, this ensures that the temperature drops after the initial descaling process to meet the initial rolling temperature required for the subsequent finishing rolling process. For example, the starting temperature for descaling before finishing rolling can be 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, etc.

[0055] S3. The second steel plate is precision rolled, and descaling is performed in the first three passes and the last pass of the precision rolling. Then it is air-cooled to the set final cooling temperature to obtain the third steel plate.

[0056] It should be noted that this finishing rolling stage is a normal rolling process. A normal rolling process requires descaling in the first three passes and the final pass. This ensures that the scale generated during the rolling process is thoroughly removed.

[0057] In some embodiments, the cumulative reduction rate of the finishing mill is ≤50%.

[0058] In the above embodiments, reducing the deformation during the finishing rolling stage ensures that the deformation of the iron oxide scale is within an acceptable range, thereby avoiding subsequent scale cracking and bursting problems. For example, the cumulative reduction rate of finishing rolling can be 30%, 32%, 35%, 40%, 45%, 50%, etc.

[0059] In some embodiments, the set final cooling temperature is 680°C to 750°C.

[0060] In the above embodiments, controlling the final cooling temperature of air cooling avoids the problem of cracking caused by insufficient plasticity of the poorly plastic iron oxide scale during straightening deformation at low temperatures. As the cracks in the scale gradually expand during subsequent cooling, it eventually leads to obvious peeling of the steel plate. For example, the final cooling temperature of air cooling can be 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, etc.

[0061] S4. The third steel plate is hot-straightened at a set straightening temperature and then slowly cooled to obtain a medium-thick plate product.

[0062] In some embodiments, the thermal straightening is a single thermal straightening process, and the set straightening temperature is ≥650°C.

[0063] In the above embodiments, a high straightening temperature is used to ensure a smaller deformation of the iron sheet, preventing excessive deformation from causing the iron oxide scale on the steel plate surface to break. For example, the straightening temperature can be 650℃, 670℃, 690℃, 710℃, 730℃, 750℃, etc.

[0064] In some embodiments, the slow cooling is cooling in a slow cooling pit, wherein the temperature at which the material enters the slow cooling pit is ≥400°C and the temperature at which it exits the slow cooling pit is ≤80°C.

[0065] In the above embodiments, the FeO in the iron oxide scale is ensured to react fully at a temperature around 500°C to generate more Fe3O4, thereby ensuring a dense oxide layer on the surface of the steel plate. For example, the entry temperature into the slow cooling pit can be 400°C, 410°C, 420°C, 430°C, 440°C, etc., and the exit temperature can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.

[0066] Based on a general inventive concept, this application provides a medium-thick plate product prepared by the method described in any embodiment of the first aspect, wherein the thickness of the medium-thick plate product is 15mm to 30mm.

[0067] In some embodiments, the medium-thick plate product meets at least one of the following properties: surface sheet thickness ≥ 40 μm, surface sheet Fe3O4 mass fraction ≥ 60%, and plate shape unevenness ≤ 3 mm / m.

[0068] The pressureless descaling measures implemented in the first two passes of finishing rolling in this application ensure that the scale generated during the warming process is fully removed, preventing surface problems caused by scale indentation during rolling. Simultaneously, increasing the finishing rolling start temperature by 30–50°C offsets the temperature drop caused by air descaling, and this measure also effectively shortens the warming time, reducing scale growth time. Post-rolling air cooling allows the steel plate to achieve a higher straightening temperature, ensuring that the iron oxide scale deforms under higher plasticity conditions and preventing problems such as scale bursting. Slow cooling in the pit at high temperature ensures the formation of more Fe3O4 in the steel plate, resulting in a denser, bluish-black scale on the surface, ultimately contributing to scale integrity and better surface quality.

[0069] The medium-thick plate product is realized based on the above-mentioned preparation method of medium-thick plate product. The specific steps of the preparation method of medium-thick plate product can be referred to the above embodiments. Since the medium-thick plate product adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated here.

[0070] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0071] This embodiment provides a method for preparing a medium-thick plate product, the method comprising the following steps:

[0072] S11. The 200mm slab is heated in the furnace in sequence. After exiting the furnace, the slab is descaled by the descaling machine and rough rolled. Descaling is carried out in the last pass of rough rolling to obtain the first steel plate of 60mm. The chemical composition of the slab is shown in Table 1.

[0073] S21. Using a finishing mill descaling machine, the first steel plate is descaled in two passes before finishing milling using a descaling method without reduction, to obtain the second steel plate.

[0074] S31. The second steel plate is precision rolled, and descaling is performed in the first three passes and the last pass of the precision rolling. Then it is air-cooled to the set final cooling temperature to obtain the third steel plate.

[0075] S41. The third steel plate is hot-straightened at a set straightening temperature and then slowly cooled to obtain a 25mm medium-thick plate product. The parameters of the preparation method of the medium-thick plate product are shown in Table 2.

[0076] Table 1 Chemical composition of slabs (wt, %)

[0077] Group C，％ Si,% Mn, % P，％ S，％ Als, % Example 1 0.16 0.27 1.6 0.004 0.002 0.032 Example 2 0.15 0.23 1.6 0.005 0.001 0.034 Comparative Example 1 0.16 0.26 1.6 0.004 0.001 0.031 Comparative Example 2 0.15 0.34 1.6 0.003 0.003 0.032 Comparative Example 3 0.16 0.32 1.6 0.002 0.001 0.035 Comparative Example 4 0.15 0.29 1.6 0.003 0.002 0.031

[0078] Table 2 Parameters of the preparation method for medium and thick plate products

[0079]

[0080]

[0081] It should be noted that the number of descaling cycles in rough rolling + finish rolling does not include descaling during empty passes. Table 3 lists the iron oxide scale and plate properties obtained after different process treatments in this case, and compares the influence of different parameters on the final results. Performance tests were conducted on the two sets of examples and four sets of comparative examples in this application. Based on the general mechanical property requirements of Q355B, their tensile strength, yield strength, elongation, and impact energy all met the requirements. Since mechanical properties are not the focus of this invention, the mechanical property results are not listed individually in this invention.

[0082] Table 3. Surface and shape characteristics of medium and heavy plate products

[0083] Group Sheet thickness, μm <![CDATA[Mass fraction of iron sheet Fe3O4, %]]> Will it erupt? Plate unevenness, mm / m Example 1 45 66.8 no 2 Example 2 49 73.2 no 3 Comparative Example 1 37 43.7 Large-scale outbreak 7 Comparative Example 2 42 51.5 Large-scale outbreak 8 Comparative Example 3 45 58.1 micro-storm 3 Comparative Example 4 43 61.3 no 2

[0084] Figure 3 A physical image of the medium-thick plate product provided for Comparative Example 1 of this application; Figure 4 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 1 of this application; Figure 5 A physical image of the medium-thick plate product provided in Comparative Example 2 of this application; Figure 6 Microscopic sheet metal diagram of the medium-thick plate product provided in Comparative Example 2 of this application.

[0085] This invention focuses on surface quality and plate shape. Table 3 shows that the surface quality of the steel plates in the two comparative examples is poor, and the plate shape is also relatively worse compared to the examples. Combined with... Figures 3-6 It can be seen that the steel plates in Comparative Examples 1 and 2 have obvious peeling problems. The root cause is that the final cooling temperature and straightening temperature are low. As a result, the iron oxide scale with poor plasticity at low temperature cracks due to insufficient plasticity during the straightening deformation process. As the cracks in the scale gradually expand during the subsequent cooling process, the steel plate eventually shows obvious macroscopic peeling.

[0086] Figure 7 A physical image of the medium-thick plate product provided in Comparative Example 3 of this application; Figure 8 Microscopic sheet metal image of the medium-thick plate product provided in Comparative Example 3 of this application; Figure 9 A physical image of the medium-thick plate product provided in Comparative Example 4 of this application; Figure 10 Microscopic sheet metal diagram of the medium-thick plate product provided in Comparative Example 4 of this application.

[0087] Combination Figures 7-10 It can be seen that Comparative Example 3 exhibits minor localized peeling and a reddish tinge across the entire plate surface. In Comparative Example 4, the steel plate surface shows no peeling, but the overall surface is slightly reddish. In Comparative Example 3, due to slightly fewer descaling cycles and the absence of slow cooling, the overall steel plate surface is slightly reddish with minor localized peeling. In Comparative Example 2, further enhanced descaling improved the reddish surface condition, but due to the lack of slow cooling, the edges still show significant reddish tinge. SEM results show that the integrity of the sheet metal in Comparative Examples 3 and 4 is significantly improved compared to Comparative Examples 1 and 2. However, the sheet metal in Comparative Examples 3 and 4 is thinner than in the examples, and the overall integrity is slightly worse. This is mainly because the absence of dry descaling and slow cooling resulted in a lower Fe3O4 content in the sheet metal. Incomplete descaling during the finishing rolling stage led to microcracks forming in some of the sheet metal during rolling, causing the surface to reddish. Simultaneously, the sheet metal density is lower, ultimately resulting in a redder surface characteristic in the macroscopic morphology.

[0088] Figure 11 This is a physical image of the medium-thick plate product provided in Embodiment 1 of this application; Figure 12 This is a microscopic sheet metal image of the medium-thick plate product provided in Embodiment 1 of this application; Figure 13 This is a physical image of the medium-thick plate product provided in Embodiment 2 of this application; Figure 14 This is a microscopic sheet metal diagram of the medium-thick plate product provided in Embodiment 2 of this application.

[0089] Combination Figures 11-14As can be seen, the embodiment, after undergoing air descaling + controlled rolling + air cooling + slow cooling, exhibits better integrity of the surface iron oxide scale and a more uniform iron oxide scale thickness compared to the comparative example. Through the key process control of this patent, the integrity of the surface iron scale in the embodiment has been significantly improved. This patented technology has good application and promotion potential, effectively solving the problem of iron oxide scale peeling on the surface of steel plates.

[0090] Therefore, the method adopted in this application mainly considers the main challenges of removing iron oxide scale from the surface of steel plates of this specification and the damage and bulging of the scale caused by the straightening process. The entire process is optimized in conjunction with process optimization and plate shape requirements. On the one hand, steel plates of this specification require a period of warming before finishing rolling. Furthermore, due to the thickness of the steel plate, the warming time is longer, which creates conditions for the formation and thickening of iron oxide scale. Excessively thick scale easily increases the difficulty of descaling and leads to subsequent scale indentation problems. On the other hand, steel plates of this specification are still prone to certain plate shape problems after rolling. During the straightening process, the steel plate will still undergo significant deformation. Simultaneously, due to the thickness of the steel plate, the straightening force is significantly increased compared to thinner specifications, which poses a greater challenge to the plasticity of the scale. And in conjunction with... Figure 1 It can be seen that if the straightening temperature is below 650℃, the overall plasticity of FeO is poor, and the increased straightening force due to the thickness of the plate will make the steel plate more prone to breakage under high straightening force.

[0091] To address the aforementioned issues, the descaling measures implemented in the first two passes of finishing rolling in this application ensure that the scale generated during the warming process is fully removed, preventing surface problems caused by scale indentation during rolling. Simultaneously, increasing the initial finishing rolling temperature by 30–50°C offsets the temperature drop from the air-cooled descaling process. This measure also effectively shortens the warming time, reducing scale growth time. Post-rolling air cooling allows the steel plate to achieve a higher straightening temperature, ensuring that the iron oxide scale deforms under higher plasticity conditions and preventing issues such as scale bursting. Slow cooling in the pit at high temperature ensures the formation of more Fe3O4 in the steel plate, resulting in a denser, bluish-black scale on the surface, ultimately contributing to scale integrity and better surface quality.

[0092] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a medium-thick plate product, characterized in that, The method includes: The slab is sequentially heated, descaled by a descaling machine, and rough rolled, and descaling is performed in the last pass of the rough rolling to obtain the first steel plate; The first steel plate is descaled before finishing rolling using a descaling machine on a finishing mill with no reduction, to obtain the second steel plate. The second steel plate is precision rolled, and descaling is performed in the first three passes and the last pass of the precision rolling. Then it is air-cooled to the set final cooling temperature to obtain the third steel plate. The third steel plate is hot-straightened at a set straightening temperature and then slowly cooled to obtain a medium-thick plate product. The starting temperature for descaling before finishing rolling is 860℃~920℃; The set final cooling temperature is 680℃~750℃; The thermal straightening is a single thermal straightening process, and the set straightening temperature is ≥650℃; The slow cooling refers to cooling in a slow cooling pit, with an entry temperature of 400°C and an exit temperature of ≤80°C.

2. The method according to claim 1, characterized in that, The number of descaling passes before finishing rolling is 1 to 2. The descaling before finishing rolling can be carried out in a single pre-mill or post-mill descaling, or simultaneously in both pre-mill and post-mill descaling.

3. The method according to claim 1, characterized in that, The cumulative reduction rate of the finishing mill is ≤50%.

4. The method according to claim 1, characterized in that, The heating temperature is 1130℃~1180℃, and the heating time in the furnace is 240min~280min; and / or, the rough rolling adopts multi-pass descaling.

5. A medium-thick plate product prepared by the method according to any one of claims 1 to 4, characterized in that, The thickness of the medium-thick plate product is 15mm~30mm.

6. The medium-thick plate product according to claim 5, characterized in that, The medium-thick plate product meets at least one of the following properties: surface iron sheet thickness ≥ 40 μm, surface iron sheet Fe3O4 mass fraction ≥ 60%, and plate shape unevenness ≤ 3 mm / m.

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