Preparation method of medium-thickness plate product and medium-thickness plate product

Abstract

The invention provides a preparation method of a medium-thickness plate product and the medium-thickness plate product, and belongs to the field of medium-thickness plate production. Comprising the steps that a plate blank is sequentially subjected to heating, descaling through a descaling machine and rough rolling, descaling is conducted in the last pass of rough rolling, and a first steel plate is obtained; the first steel plate is subjected to descaling before finish rolling in a non-rolling-reduction descaling mode through a finish rolling mill dephosphorization machine, and a second steel plate is obtained; the second steel plate is subjected to finish rolling, descaling is conducted in the first three passes and the last pass of finish rolling, then air cooling is conducted to the set final cooling temperature, and a third steel plate is obtained; and the third steel plate is subjected to hot straightening at the set straightening temperature, then slow cooling is conducted, and a medium-thickness plate product is obtained. By adopting the technological means of empty descaling, controlled rolling, air cooling and slow cooling, the integrity and uniformity of the whole sheet iron of the steel plate are guaranteed, the shape of the thick steel plate is guaranteed, and meanwhile good surface quality can be guaranteed. Therefore, on the basis that the plate shape of the medium-thickness plate is met, the surface quality of the medium-thickness plate product is improved.

Description

Technical Field

[0001] The present application relates to the technical field of medium and thick plate production, and in particular to a preparation method of a medium and thick plate product and a medium and thick plate product. Background Art

[0002] With the development of medium and thick plate products, some users have put forward higher requirements for the surface quality of medium and thick plate products. The demand for high surface quality medium and thick plate products in the fields of construction and engineering machinery has gradually increased. In the future, there may be more and more medium and thick plate products with higher requirements for surface quality, and process research and development is needed to meet the higher requirements for surface quality medium and thick plate products. At the same time, some specifications of steel plates (15mm~30mm) require higher surface quality while ensuring performance.

[0003] However, since this specification of steel plates generally need to be heated to ensure that the performance level of the steel plates meets the requirements, the iron scale formed during the heating process needs to undergo repeated deformation during the subsequent finishing rolling process and low-temperature deformation during the straightening process, which will bring greater challenges to the final surface quality of the steel plates. In addition, due to the large thickness of the steel plates, once the plate shape is poor after rolling, the excessive straightening force during the straightening process will cause the steel plate iron scale to crack and then cause the occurrence of the skin bursting problem. Therefore, how to improve the surface quality of medium and thick plate products while meeting the plate shape requirements and performance requirements is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a method for preparing a medium and thick plate product and a medium and thick plate product to solve the following technical problem: how to improve the surface quality of the medium and thick plate product on the basis of satisfying the plate shape of the medium and thick plate.

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

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

[0007] Descaling the first steel plate before finishing rolling by using a dephosphorization machine of a finishing mill in a descaling method without reduction, to obtain a second steel plate;

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

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

[0010] Optionally, the number of descaling passes before finishing rolling is 1 to 2 times, and the descaling before finishing rolling adopts a single descaling before the machine or after the machine, or simultaneously performs descaling before the machine and after the machine.

[0011] Optionally, the starting temperature of descaling before finish rolling is 860°C to 920°C.

[0012] Optionally, the cumulative reduction rate of the finish rolling is ≤50%.

[0013] Optionally, the final cooling temperature is set to 680°C to 750°C.

[0014] Optionally, the heat straightening is one-time heat straightening, and the set straightening temperature is ≥ 650°C.

[0015] Optionally, the slow cooling is cooling in a slow cooling pit, the entry temperature of the slow cooling pit is ≥400°C, and the exit temperature of the slow cooling pit is ≤80°C.

[0016] Optionally, 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 adopts multiple descaling passes.

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

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

[0019] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0020] The present application provides a method for preparing medium and thick 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; descaling the first steel plate before finish rolling by using a dephosphorizing machine of a finishing mill in a descaling manner without reduction to obtain a second steel plate; finish rolling the second steel plate, and descaling it in the first three passes and the last pass of the finish 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 slowly cooling it to obtain a medium and thick plate product. The key technical ideas of the technology of this application are to take into account two technical routes: First, the process technology of this application emphasizes the full removal of the iron scale formed during the warming process by strengthening the descaling before the finishing rolling, so as to prevent the formation of cracks during the deformation process of the finishing rolling stage and even the subsequent serious skin explosion problem; second, the application is based on strict final rolling and air cooling process control after rolling to ensure that the steel plate can achieve deformation within the high plasticity temperature range of the oxidized iron scale through a higher straightening temperature, and the slow cooling process ensures that high-quality and relatively dense blue-black iron scale is generated on the surface of the steel plate after rolling, and a higher proportion of Fe3O4 is reflected in the microscopic view to achieve better density of the oxidized iron scale. Based on the above technical routes, while achieving excellent surface quality, a good plate shape level can also be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0023] Figure 1 A graph showing the change in plasticity of different types of iron oxides with temperature provided in the embodiments of the present application;

[0024] Figure 2 A schematic diagram of a process for preparing a medium and thick plate product provided in an embodiment of the present application;

[0025] Figure 3 A physical picture of the medium and thick plate product provided for comparative example 1 of this application;

[0026] Figure 4 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 1 of the present application;

[0027] Figure 5 A physical picture of the medium and thick plate product provided for Comparative Example 2 of this application;

[0028] Figure 6 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 2 of the present application;

[0029] Figure 7 A physical picture of the medium and thick plate product provided for Comparative Example 3 of this application;

[0030] Figure 8 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 3 of the present application;

[0031] Fig. 9 A physical picture of the medium and thick plate product provided for Comparative Example 4 of this application;

[0032] Fig.10 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 4 of the present application;

[0033] Fig.11 A physical picture of the medium and thick plate product provided in Example 1 of the present application;

[0034] Fig.12 A microscopic iron sheet image of a medium and thick plate product provided in Example 1 of the present application;

[0035] Fig.13 A physical picture of the medium and thick plate product provided in Example 2 of the present application;

[0036] Fig.14 This is a microscopic iron sheet image of the medium and thick plate product provided in Example 2 of the present application. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0038] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have 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., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0039] In addition, in the description of the specification of the present application, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second", etc. are only used 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 article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" means one or more, and "plurality" means two or more. "At least one", "the following at least one item (items)" or similar expressions refer to any combination of these items, including any combination of single items (items) or plural items (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, c can be single or plural, respectively.

[0040] Unless otherwise specified, various 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:

[0042] In the prior art, the methods for improving the surface quality of medium and thick plate products generally optimize the surface quality of medium and thick plate products, without paying attention to the special surface problems under different subdivided specifications. This patented technology focuses on steel plates with specifications of 15mm to 30mm. On the one hand, the steel plates in this specification range need to be kept warm for a period of time before finish rolling. At the same time, since the steel plates are thicker, they need to be kept warm for a longer time, which creates conditions for the formation and thickening of iron oxide scale. Too thick iron scale can easily increase the difficulty of descaling and cause subsequent iron scale pressing problems. On the other hand, the steel plates in this specification range need to undergo a straightening process after rolling to optimize the plate shape. During the straightening process, the steel plates will still undergo relatively large deformations. At the same time, due to the thick thickness of the steel plate, the straightening force is significantly increased relative to thin specifications, which poses a greater challenge to the plasticity of the iron scale. Figure 1 The plasticity of different types of iron oxides provided in the embodiments of the present application varies with temperature. Figure 1 It can be seen that if the straightening temperature is around 600°C, the overall plasticity of FeO is poor, and the straightening force increases during the straightening process due to the thicker steel plate specifications, which will cause the iron oxide scale on the steel plate surface to be more easily broken under high straightening force, and eventually cause the iron oxide scale on the steel plate surface to crack, affecting the user's processing (the cracking position on the steel plate surface affects the processing accuracy - such as laser cutting, etc.) and long-term storage (the cracking position has more red rust and poor corrosion resistance).

[0043] Therefore, it is necessary to carry out corresponding process design for medium and thick plate products with high surface quality requirements that are prone to scale cracking in order to meet user requirements. The scale produced by the oxidation process during the rolling process must be fully removed by descaling, especially to avoid the scale produced during the waiting process from being pressed into the scale during the finishing rolling stage. At the same time, considering that there are still certain wave-shaped problems in the rolled plate shape of 15mm to 30mm steel plates, the scale will still deform to a large extent during the straightening process, so the scale on the surface of the steel plate will still undergo a certain amount of plastic deformation during the straightening process. If the temperature of the straightening process is low, there is a risk of cracking of the scale due to insufficient plasticity. In addition, the formation of Fe3O4 on the surface of the steel plate is further promoted through the subsequent slow cooling process, thereby obtaining a denser scale.

[0044] Therefore, the present application adopts the process means of air descaling, controlled rolling, air cooling and slow cooling to ensure the integrity and uniformity of the iron scale of the whole steel plate to ensure the shape of the thick steel plate while ensuring good surface quality. At the same time, the iron scale is dense and complete without bulging, solving the problem that the surface quality caused by the redness of the iron scale, local bulging and the pressing of the iron scale is difficult to meet the user's requirements. Thus, on the basis of meeting the shape of the medium and thick plate, the surface quality of the medium and thick plate products is improved.

[0045] Figure 2A schematic flow chart of a method for preparing a medium and thick plate product provided in an embodiment of the present application.

[0046] Based on the above analysis, see Figure 2 The present application provides a method for preparing a medium and thick plate product, the method comprising:

[0047] S1, sequentially heating, descaling by a descaling machine and rough rolling the slab, and descaling in the last pass of the rough rolling to obtain a 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 uses multiple descaling passes.

[0049] In the above embodiment, the heating conditions are controlled to ensure the smooth progress of the rolling process. For example, the heating temperature may be 1130°C, 1140°C, 1150°C, 1160°C, 1170°C, 1180°C, etc., and the heating time in the furnace may be 240min, 250min, 260min, 270min, 280min, etc.

[0050] S2, using a dephosphorization machine of a finishing mill to descale the first steel plate before finishing rolling by using a descaling method without reduction, to obtain a second steel plate;

[0051] The number of descaling passes before finishing rolling is 1 to 2 times, and the descaling before finishing rolling adopts a single descaling before the machine or after the machine, or simultaneously descaling before the machine and after the machine.

[0052] In the above embodiment, 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, thereby avoiding the problem of iron oxide being pressed in during rolling without completely removing the iron oxide scale.

[0053] In some embodiments, the starting temperature of descaling before finish rolling is 860°C to 920°C.

[0054] In the above embodiment, the descaling temperature before finishing rolling is increased by 30°C to 50°C compared with the conventional rolling temperature. The main purpose is to shorten the waiting time and inhibit the growth of iron oxide scale on the surface of the steel plate, thereby ensuring a better subsequent descaling effect. At the same time, in order to ensure that the temperature drops after the air descaling to meet the subsequent actual rolling temperature of the finishing process. Exemplarily, the starting temperature of descaling before finishing rolling can be 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, etc.

[0055] S3, finishing rolling the second steel plate, descaling the steel plate in the first three passes and the last pass of the finishing rolling, and then air cooling the steel plate to a set final cooling temperature to obtain a third steel plate;

[0056] It should be noted that the finishing rolling stage is a normal rolling process, and the normal rolling process must ensure descaling in the first three passes and the last pass, so as to ensure that the iron scale generated during the rolling process is fully removed.

[0057] In some embodiments, the cumulative reduction ratio of the finish rolling is ≤50%.

[0058] In the above embodiment, the deformation amount in the finishing rolling stage is reduced to ensure that the deformation amount of the oxidized iron scale is within an acceptable range, thereby avoiding the subsequent cracking and bursting of the iron scale. For example, the cumulative reduction rate of finishing rolling can be 30%, 32%, 35%, 40%, 45%, 50%, etc.

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

[0060] In the above embodiment, the final cooling temperature of air cooling is controlled to avoid the problem that 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 iron scale gradually expand during the subsequent cooling process, the steel plate eventually suffers from obvious cracking. Exemplarily, the final cooling temperature of air cooling can be 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, etc.

[0061] S4, performing hot straightening on the third steel plate at a set straightening temperature, and then slowly cooling the third steel plate to obtain a medium and thick plate product.

[0062] In some embodiments, the heat straightening is one-time heat straightening, and the set straightening temperature is ≥ 650°C.

[0063] In the above embodiment, a high straightening temperature is used to ensure a smaller deformation of the iron sheet to prevent the iron oxide sheet on the surface of the steel plate from breaking due to excessive deformation. For example, the straightening temperature may be 650°C, 670°C, 690°C, 710°C, 730°C, 750°C, etc.

[0064] In some embodiments, the slow cooling is cooling in a slow cooling pit, the entry temperature of the slow cooling pit is ≥400°C, and the exit temperature of the slow cooling pit is ≤80°C.

[0065] In the above embodiment, it is ensured that FeO in the iron oxide scale fully reacts at a temperature near 500°C to generate more Fe3O4 to ensure a dense oxide layer on the surface of the steel plate. Exemplarily, 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 of the slow cooling pit can be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.

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

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

[0068] In this application, the non-pressurized descaling measures in the first two passes of finishing rolling will ensure that the iron scale produced during the waiting process can be fully removed, and prevent surface problems caused by the pressing of the iron scale during the rolling process. At the same time, the temperature drop caused by the air descaling is offset by increasing the starting temperature of finishing rolling by 30 to 50°C. At the same time, this measure can also effectively compress the waiting time and reduce the growth time of the iron scale. Through air cooling after rolling, the steel plate can obtain a higher straightening temperature, thereby ensuring that the oxidized iron scale is deformed under higher plastic conditions and preventing the iron scale from cracking and other problems. Slow cooling in the pit at high temperature can ensure that the steel plate forms more Fe3O4, and then ensure that a denser blue-black iron scale is formed on the surface, which is ultimately beneficial to the integrity of the iron scale and better surface quality.

[0069] The medium and thick plate product is realized based on the preparation method of the medium and thick plate product mentioned above. The specific steps of the preparation method of the medium and thick plate product can refer to the above embodiment. Since the medium and thick plate product adopts part or all of the technical solutions of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment, which will not be described one by one here.

[0070] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to industry standards. If there is no corresponding industry standard, then the conditions recommended by the manufacturer are followed.

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

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

[0073] S21, using a dephosphorization machine of a finishing mill, descaling the first steel plate before finishing rolling for two passes by using a descaling method without reduction, to obtain a second steel plate;

[0074] S31, finishing rolling the second steel plate, descaling the steel plate in the first three passes and the last pass of finishing rolling, and then air cooling the steel plate to a set final cooling temperature to obtain a third steel plate;

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

[0076] Table 1 Chemical composition of slab (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 of medium and thick plate products

[0079]

[0080]

[0081] It should be noted that the descaling times of rough rolling + finishing rolling do not include empty descaling. Table 3 lists the iron oxide scale and plate shape properties obtained after different process treatments in this case, and compares the effects of different parameters on the final results. In this application, 2 groups of embodiments and 4 groups of comparative examples were tested for performance. According to the ordinary Q355B mechanical property requirements, their tensile strength, yield strength, elongation and impact energy were all qualified. Since the mechanical properties are not the focus of the present invention, the mechanical property results are not listed one by one in the present invention.

[0082] Table 3 Surface and shape of medium and thick plate products

[0083] Group Iron sheet thickness, μm <![CDATA[Mass fraction of Fe3O4 in iron sheet, %]]> Whether it rises suddenly Plate roughness, mm / m Example 1 45 66.8 no 2 Example 2 49 73.2 no 3 Comparative Example 1 37 43.7 Big face burst 7 Comparative Example 2 42 51.5 Big face burst 8 Comparative Example 3 45 58.1 Microburst 3 Comparative Example 4 43 61.3 no 2

[0084] Figure 3 A physical picture of the medium and thick plate product provided for comparative example 1 of this application; Figure 4 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 1 of the present application; Figure 5 A physical picture of the medium and thick plate product provided for Comparative Example 2 of this application; Figure 6 This is a microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 2 of the present application.

[0085] The present invention focuses on the 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 poor compared with the embodiment. Figures 3 to 6 It can be seen that there is an obvious peeling problem on the surface of the steel plates in Comparative Examples 1 and 2. The fundamental reason is that the final cooling temperature and the straightening temperature are low, and then the oxidized iron scale with poor plasticity at low temperature cracks due to insufficient plasticity during the straightening deformation process. As the cracks in the iron scale gradually expand during the subsequent cooling process, it eventually leads to obvious macroscopic peeling of the steel plate.

[0086] Figure 7 A physical picture of the medium and thick plate product provided for Comparative Example 3 of this application; Figure 8 The microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 3 of the present application; Fig. 9 A physical picture of the medium and thick plate product provided for Comparative Example 4 of this application; Fig.10 This is a microscopic iron sheet image of the medium and thick plate product provided in Comparative Example 4 of the present application.

[0087] Combination Figures 7-10 It can be seen that the overall local area of ​​comparative example 3 has slight peeling characteristics and the whole plate surface is reddish, while the surface iron scale of the steel plate in comparative example 4 has no peeling but the overall surface is slightly reddish. In comparative example 3, due to the slightly less number of descaling times and without slow cooling, the surface of the overall steel plate is slightly reddish and there are slight peeling in parts. In comparison 2, the descaling is further strengthened, and the red plate surface situation has improved, but there is still obvious redness at the edge due to the lack of slow cooling. From the results of SEM, the integrity of the iron scales in comparative examples 3 and 4 is significantly improved compared with comparative examples 1 and 2. However, the iron scales in comparative examples 3 and 4 are thinner than those in the embodiment, and the overall integrity is slightly worse, mainly because the air descaling and slow cooling are not adopted, resulting in a low proportion of Fe3O4 in the iron scale. In the finishing rolling stage, due to incomplete descaling, part of the iron scale in the finishing rolling stage has microcracks during the rolling process, resulting in the redness of the plate surface. At the same time, the density of the iron scale is low, which is finally reflected in the macroscopic morphology and shows a redder surface feature.

[0088] Fig.11 A physical picture of the medium and thick plate product provided in Example 1 of the present application; Fig.12 A microscopic iron sheet image of a medium and thick plate product provided in Example 1 of the present application; Fig.13 A physical picture of the medium and thick plate product provided in Example 2 of the present application; Fig.14 This is a microscopic iron sheet image of the medium and thick plate product provided in Example 2 of the present application.

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

[0090] It can be seen that the method used in the embodiment of the present application mainly considers the main challenges faced by the surface quality of the steel plate of this specification, that is, the difficulty in removing the scale of iron oxide and the damage and subsequent explosion of the scale of iron oxide caused by the straightening process, and optimizes the entire process flow in combination with process optimization and plate shape requirements. On the one hand, the steel plates in this specification range need to be kept at temperature for a period of time before finish rolling. At the same time, since the steel plates are thicker, the time required to keep at temperature is longer, which creates conditions for the formation and thickening of scale of iron oxide. Excessively thick scale of iron oxide can easily increase the difficulty of descaling and lead to the occurrence of subsequent scale pressing problems. On the other hand, the steel plates in this specification range are still prone to certain plate shape problems after rolling, and the steel plates will still undergo relatively large deformations during the straightening process. At the same time, due to the thick thickness of the steel plates, the straightening force is significantly increased relative to thin specifications, which poses a greater challenge to the plasticity of the scale of iron oxide. And combined with Figure 1 It can be seen that if the straightening temperature is below 650°C, the overall plasticity of FeO is poor, and the increase in straightening force due to the plate thickness will make the steel plate more likely to break under high straightening force.

[0091] To solve the above problems, the non-pressurized descaling measures in the first two passes of finishing rolling in this application will ensure that the iron scale produced during the waiting process can be fully removed, and prevent surface problems caused by the pressing of the iron scale during the rolling process. At the same time, the temperature drop caused by the air descaling is offset by increasing the starting temperature of finishing rolling by 30 to 50°C. At the same time, this measure can also effectively compress the waiting time and reduce the growth time of the iron scale. Through air cooling after rolling, the steel plate can obtain a higher straightening temperature, thereby ensuring that the oxidized iron scale is deformed under higher plastic conditions and preventing the iron scale from bursting and other problems. Slow cooling in the pit at high temperature can ensure that the steel plate forms more Fe3O4, and then ensure that a denser blue-black iron scale is formed on the surface, which is ultimately beneficial to the integrity of the iron scale and better surface quality.

[0092] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing a medium and thick plate product, characterized in that: The method comprises: The slab is sequentially heated, descaled by a descaling machine, and rough rolled, and descaled in the last pass of the rough rolling to obtain a first steel plate; Descaling the first steel plate before finishing rolling by using a dephosphorization machine of a finishing mill in a descaling method without reduction, to obtain a second steel plate; The second steel plate is finish rolled, and descaling is performed in the first three passes and the last pass of the finish rolling, and then air-cooled to a set final cooling temperature to obtain a third steel plate; The third steel plate is subjected to hot straightening at a set straightening temperature and then slowly cooled to obtain a medium and thick plate product.

2. The method according to claim 1, characterized in that The number of descaling passes before finishing rolling is 1 to 2 times, and the descaling before finishing rolling adopts a single descaling before the machine or after the machine, or simultaneously descaling before the machine and after the machine.

3. The method according to claim 2, characterized in that The starting temperature of descaling before finishing rolling is 860°C to 920°C.

4. The method according to claim 1, characterized in that: The cumulative reduction rate of the finish rolling is ≤50%.

5. The method according to claim 1, characterized in that The final cooling temperature is set to be 680°C to 750°C.

6. The method according to claim 1, characterized in that The heat straightening is one-time heat straightening, and the set straightening temperature is ≥650°C.

7. The method according to claim 1, characterized in that The slow cooling is cooling in a slow cooling pit, the entry temperature of the slow cooling pit is ≥400°C, and the exit temperature of the slow cooling pit is ≤80°C.

8. The method according to claim 1, characterized in that 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 adopts multiple descaling passes.

9. A medium and thick plate product prepared by the method according to any one of claims 1 to 8, characterized in that: The thickness of the medium and thick plate product is 15 mm to 30 mm.

10. The medium and thick plate product according to claim 9, characterized in that: The medium and thick plate product meets at least one of the following properties: surface iron sheet thickness ≥40 μm, surface iron sheet Fe3O4 mass fraction ≥60%, plate shape unevenness ≤3 mm / m.

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