Method for eliminating surface plaque defects of medium-high carbon steel pickled plate

Abstract

The invention relates to a method for eliminating surface plaque defects of a medium-high carbon steel pickling plate, and belongs to the technical field of medium-high carbon steel pickling surface quality control. The method comprises the following steps: obtaining a steel billet with set chemical components, wherein the set chemical components comprise C, Si, Mn, Al, Ni, Cr, Mo and Fe; wherein in percentage by mass, the total content of Ni and Cr is 0.15%-0.5%, and the content of Mo is 0.2%-0.4%; the steel billet is heated in a furnace, and the tapping temperature of heating in the furnace is controlled; performing rough rolling on the heated steel billet to obtain an intermediate billet; carrying out first cooling on the intermediate blank; sequentially carrying out finish rolling, laminar cooling and coiling on the intermediate billet subjected to the first cooling to obtain a hot-rolled coil; pickling the hot-rolled coil to obtain a medium-high carbon steel pickled plate; wherein a washing agent for pickling comprises an inhibitor. According to the embodiment, the surface plaque defect of the medium-high carbon steel pickling plate is eliminated.

Description

Technical Field

[0001] This application relates to the technical field of surface quality control for pickling medium and high carbon steel, and particularly to a method for eliminating patchy defects on the surface of pickled medium and high carbon steel sheets. Background Art

[0002] The production process of medium and high carbon steel strip has only been developed for less than twenty years. Due to its relatively low cost and good mechanical properties after heat treatment, it is widely used in precision stamping fields such as saw blades, leaf springs, and box rulers. Compared with European and American countries, there are problems such as poor dimensional accuracy and unstable surface quality during the production of precision stamping steel. In particular, the frequent occurrence of patchy defects on the surface after pickling has a great impact on the deep processing of downstream users.

[0003] The research on pickling surface color difference defects mainly focuses on low carbon steel. Most of them focus on solving the problem from the perspective of removing scale, and do not involve the influence of element C in the composition on the formation of scale, which is not suitable for the composition system of medium and high carbon steel. Summary of the Invention

[0004] This application provides a method for eliminating patchy defects on the surface of pickled medium and high carbon steel sheets to solve the following technical problem: how to eliminate patchy defects on the surface of pickled medium and high carbon steel sheets.

[0005] In a first aspect, an embodiment of this application provides a method for eliminating patchy defects on the surface of pickled medium and high carbon steel sheets, the method comprising:

[0006] Obtaining a steel billet with a set chemical composition, the set chemical composition including C, Si, Mn, Al, Ni, Cr, Mo, and Fe; wherein, by mass fraction, the total content of Ni and Cr is 0.15% - 0.5%, and the content of Mo is 0.2% - 0.4%;

[0007] Heating the steel billet in a furnace and controlling the tapping temperature of the in-furnace heating;

[0008] Rough rolling the heated steel billet to obtain an intermediate billet;

[0009] Performing a first cooling on the intermediate billet;

[0010] Successively performing finish rolling, a second cooling, and coiling on the intermediate billet after the first cooling to obtain a hot rolled coil;

[0011] Pickling the hot rolled coil to obtain a pickled medium and high carbon steel sheet; wherein, the pickling agent includes an inhibitor.

[0012] Optionally, the tapping temperature is 1200°C - 1230°C.

[0013] Optionally, the time of heating in the furnace is 170 min to 200 min, and / or the air excess coefficient of the heating furnace for heating in the furnace is 0.85 to 1.0.

[0014] Optionally, the first cooling method is water cooling, and the pressure of the water cooling is 0.5 MPa to 0.8 MPa.

[0015] Optionally, the mass concentration of the inhibitor is 1% to 3%.

[0016] Optionally, the washing agent further includes acid solution, and the mass concentration of the acid solution is 45 g / L to 60 g / L.

[0017] Optionally, the pickling speed is 60 m / min to 80 m / min.

[0018] Optionally, the rough rolling includes R1 rolling mill and R2 rolling mill; wherein, the R1 rolling mill rolls for 1 pass, and the R2 rolling mill rolls for 5 passes.

[0019] Optionally, in the set chemical composition, by mass fraction, the content of C is 0.60% to 0.80%, the content of Si is 0.10% to 0.30%, the content of Mn is 0.3% to 0.6%, and the content of Al is 0.02% to 0.05%.

[0020] Optionally, the thickness of the steel billet is 230 mm to 240 mm; the thickness of the intermediate billet is 30 mm to 40 mm; the thickness of the hot rolled coil is 2 mm to 4 mm.

[0021] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0022] The method for eliminating patchy defects on the surface of medium and high carbon steel pickled plates provided by the embodiments of the present application includes: obtaining a steel billet with a set chemical composition, where the set chemical composition includes C, Si, Mn, Al, Ni, Cr, Mo, and Fe; among them, in terms of mass fraction, the total content of Ni and Cr is 0.15% - 0.5%, and the content of Mo is 0.2% - 0.4%; heating the steel billet in a furnace and controlling the tapping temperature of the in-furnace heating; rough rolling the heated steel billet to obtain an intermediate billet; performing a first cooling on the intermediate billet; sequentially performing finish rolling, a second cooling, and coiling on the intermediate billet after the first cooling to obtain a hot rolled coil; pickling the hot rolled coil to obtain a medium and high carbon steel pickled plate; where the pickling agent includes an inhibitor. Regarding the influence of C, Si, Mn, Al, Ni, Cr, and Mo on the hardenability, surface hardness, and surface quality of the steel, controlling the total content of Ni and Cr to be 0.15% - 0.5% can reduce the grain boundary oxidation of the steel; the content of Mo being 0.2% - 0.4% can control the uneven oxidation enrichment on the surface of other alloying elements in the steel; subsequently, by cooperating with controlling the tapping temperature of the in-furnace heating, rough rolling, and the first cooling, the decarburization and grain boundary oxidation on the steel surface can be reduced; after finish rolling, the second cooling, and coiling, the hot rolled coil, under the action of the pickling agent containing an inhibitor, can further eliminate the patchy color difference defects on the surface of the pickled plate, thereby obtaining a medium and high carbon steel pickled plate with a bright surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings here are incorporated into the description and form a part of this description, showing embodiments consistent with the present application, and are used together with the description to explain the principles of the present application.

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a schematic flow chart of a method for eliminating patchy defects on the surface of medium and high carbon steel pickled plates provided by the embodiments of the present application;

[0026] Figure 2 It is the morphology of patchy color difference defects generated on the surface of a medium and high carbon steel pickled plate provided by the embodiments of the present application;

[0027] Figure 3 It is a morphology diagram of a medium and high carbon steel pickled plate provided by Embodiment 1 of the present application;

[0028] Figure 4 It is a morphology diagram of a medium and high carbon steel pickled plate provided by Comparative Example 1 of the present application;

[0029] Figure 5 It is the morphology diagram of a medium and high carbon steel pickled plate provided for Comparative Example 2 of this application;

[0030] Figure 6 It is the morphology diagram of a medium and high carbon steel pickled plate provided for Comparative Example 3 of this application. Specific Embodiments

[0031] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0032] The 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 only for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single 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 that range, such as 1, 2, 3, 4, 5, and 6, regardless of what the range is. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0033] In this application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing direction in the accompanying drawings. Additionally, in the description of the specification of this application, the terms "including" and "comprising" etc. mean "including but not limited to". In this text, relational terms such as "first" and "second" 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 text, "and / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural.

[0034] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchase or can be prepared by existing methods.

[0035] In a first aspect, an embodiment of the present application provides a method for eliminating patchy defects on the surface of medium and high carbon steel pickling plates. Figure 1 It is a schematic flow chart of a method for eliminating patchy defects on the surface of medium and high carbon steel pickling plates provided by an embodiment of the present application; please refer to Figure 1 The method includes:

[0036] S1. Obtain a steel billet with a set chemical composition, where the set chemical composition includes C, Si, Mn, Al, Ni, Cr, Mo, and Fe; among them, in terms of mass fraction, the total content of Ni and Cr is 0.15% - 0.5%, and the content of Mo is 0.2% - 0.4%.

[0037] After steel smelting and through the continuous casting process, a steel billet with a set chemical composition can be obtained. Regarding the influence of C, Si, Mn, Al, Ni, Cr, and Mo on the hardenability, surface hardness, and surface quality of the steel, controlling the total content of Ni and Cr to be 0.15% - 0.5% can reduce the grain boundary oxidation of the steel. The reason is that Ni and Cr can improve the hardness and wear resistance of carbon steel without making the steel brittle. However, adding Cr causes the steel to be prone to grain boundary oxidation, and the addition of Ni makes the thickness of the oxide scale on the surface of the steel matrix uneven. The combined addition of Ni and Cr exacerbates the grain boundary oxidation on the surface of the steel matrix, and local over-erosion of the steel matrix is likely to occur during strip pickling, resulting in patchy color difference defects. Figure 2 It is a morphology of patchy color difference defects generated on the surface of a pickling plate provided by an embodiment of the present application; please refer to Figure 2 It can be seen that there are many patchy color difference defects on the surface of this pickling plate. Therefore, the total content of Ni and Cr cannot exceed 0.5%; the content of Mo can be 0.2% - 0.4%, which can make full use of the characteristic of uniform enrichment of Mo element on the surface of the steel matrix to inhibit the grain boundary oxidation of the steel and control the uneven oxidation and enrichment of other alloy elements on the surface of the steel matrix. Exemplarily, the total content of Ni and Cr can be 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.; the content of Mo can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0038] In some embodiments, in the set chemical composition, in terms of mass fraction, the content of C is 0.60% - 0.80%, the content of Si is 0.10% - 0.30%, the content of Mn is 0.3% - 0.6%, and the content of Al is 0.02% - 0.05%.

[0039] Element C can ensure good hardenability and hardness and is the core element of medium and high carbon fine blanking steel. However, element C diffuses rapidly at high temperatures and the steel matrix is prone to decarburization. If the content of element C is less than 0.60%, it is difficult to ensure the surface hardness of the steel after decarburization; if the content is higher than 0.80%, it may lead to poor toughness of the steel. Therefore, the content of C can be 0.60% - 0.80%; there is a certain amount of Si and Mn elements in the steel billet, mainly for solid solution strengthening to ensure the strength of the steel. The strength should not be too high. The content of Si can be 0.10%

[0040] ~0.30%. If the content of Si element is higher than 0.30%, surface red rust defects are likely to occur; the content of Mn can be 0.3% - 0.6%. If the content of Mn is higher than 0.6%, it is easy to cause segregation bands in the steel structure. The banded structure makes the transverse mechanical properties of the steel worse. However, if the content of Mn is less than 0.10%, the Mn content is insufficient, which may lead to difficulty in forming enough MnS, and then increase the FeS in the steel, which has an adverse effect on the plasticity of the steel. The content of Al can be 0.02% - 0.05%, mainly playing a role in deoxidation. Exemplarily, the content of C can be 0.60%, 0.62%, 0.64%, 0.66%, 0.68%, 0.7%, 0.72%, 0.74%, 0.76%, 0.78%, 0.8%, etc.; the content of Si can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc.; the content of Mn can be 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, etc.; the content of Al can be 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc.

[0041] S2. Heat the steel billet in the furnace and control the tapping temperature of the in-furnace heating;

[0042] Heating the steel billet in the furnace can enable the atoms inside the steel billet to obtain sufficient energy for diffusion, thereby reducing or eliminating composition segregation and making the structure more uniform. Heating can reduce the hardness of the steel billet and improve its plasticity, facilitating subsequent processing and deformation. Controlling the tapping temperature of the in-furnace heating can reduce the decarburization phenomenon on the steel surface.

[0043] In some embodiments, the tapping temperature is 1200°C - 1230°C.

[0044] In some embodiments, the time of the in-furnace heating is 170 min - 200 min, and / or the air excess coefficient of the heating furnace for the in-furnace heating is 0.85 - 0.1.

[0045] The tapping temperature can be 1200°C to 1230°C, which can ensure sufficient solid solution of Ni and Mo while reducing decarburization on the steel surface and ensuring the surface hardness of the steel. The in-furnace heating time can be 170 min to 200 min, which has a synergistic effect with the tapping temperature. The air excess coefficient of the heating furnace during in-furnace heating can be 0.85 to 1.0, which can avoid intense oxidation in the heating furnace while reducing decarburization on the steel surface and improving the surface quality of the steel. Exemplarily, the tapping temperature can be 1200°C, 1210°C, 1220°C, 1230°C, etc.; the in-furnace heating time can be 170 min, 180 min, 190 min, 200 min, etc.; the air excess coefficient of the heating furnace during in-furnace heating can be 0.85, 0.87, 0.89, 0.91, 0.93, 0.95, 0.97, 0.99, 1.0, etc.

[0046] S3. Rough-roll the heated steel billet to obtain an intermediate billet.

[0047] In some embodiments, the rough rolling includes an R1 rolling mill and an R2 rolling mill; wherein, the R1 rolling mill performs 1 pass of rolling, and the R2 rolling mill performs 5 passes of rolling.

[0048] Adopting 1+5 rolling for rough rolling of R1 and R2 is beneficial to controlling the temperature drop during rough rolling and ensuring descaling in at least three passes.

[0049] S4. Perform the first cooling on the intermediate billet.

[0050] In some embodiments, the first cooling method is water cooling, and the pressure of the water cooling is 0.5 MPa to 0.8 MPa.

[0051] In order to control surface decarburization after rough rolling, an intermediate billet cooling device is used to cool the surface. When the water pressure of the intermediate billet cooling water is greater than 0.5 MPa, the control effect of surface decarburization is significant. At the same time, the grains on the surface layer of the steel are refined, the strength of the grain boundaries increases, and the phenomenon of grain boundary oxidation of the steel matrix is inhibited to a certain extent. However, the water pressure of the intermediate billet cooling water cannot be higher than 0.8 MPa, as it is likely to cause too low temperature at the strip edge resulting in edge cracking, and it is also not conducive to controlling the outlet temperature of subsequent finish rolling. Exemplarily, the pressure of the water cooling is 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, etc.

[0052] S5. Sequentially perform finish rolling, the second cooling, and coiling on the intermediate billet after the first cooling to obtain a hot-rolled coil.

[0053] In some embodiments, the thickness of the steel billet is 230 mm to 240 mm; the thickness of the intermediate billet is 30 mm to 40 mm; the thickness of the hot-rolled coil is 2 mm to 4 mm.

[0054] Exemplarily, the thickness of the above billet can be 230 mm, 235 mm, 240 mm, etc.; the thickness of the intermediate billet can be 30 mm, 32 mm, 34 mm, 36 mm, 38 mm, 40 mm, etc.; the thickness of the hot-rolled coil can be 2 mm, 3 mm, 4 mm, etc.

[0055] S6. Pickle the hot-rolled coil to obtain a medium-high carbon steel pickled sheet; wherein, the pickling agent for pickling includes an inhibitor.

[0056] In some embodiments, the mass concentration of the inhibitor is 1% - 3%.

[0057] Due to the addition of alloying elements such as Si, Ni, and Cr, the interface flatness of the steel (steel matrix) is poor, and the local over-pickled areas at the grain boundary oxidation positions are prone to blackening, and the patchy defects are more obvious. Therefore, an appropriate amount of inhibitor is added to avoid excessive corrosion of the steel. However, if the mass concentration of the inhibitor is higher than 3%, the pickling time is too long, and the time for removing the scale is prolonged; if the mass concentration of the inhibitor is lower than 1%, it is difficult to effectively remove the grain boundary oxide layer. Therefore, the mass concentration of the inhibitor can be 1% - 3% to effectively remove the grain boundary oxide layer of the steel and prepare a bright medium-high carbon steel pickled sheet. Exemplarily, the mass concentration of this inhibitor can be 1%, 1.5%, 2%, 2.5%, 3%, etc. This inhibitor can be hexamethylenetetramine, benzotriazole, etc.

[0058] In some embodiments, the pickling agent further includes an acid solution, and the mass concentration of the acid solution is 45 g / L - 60 g / L.

[0059] The pickling agent further includes an acid solution, and the mass concentration of the acid solution can be 45 g / L - 60 g / L. A sufficient acid solution concentration can make the pickling process sufficient. Exemplarily, the mass concentration of this acid solution can be 45 g / L, 47 g / L, 49 g / L, 51 g / L, 53 g / L, 55 g / L, 57 g / L, 59 g / L, 60 g / L, etc. The component of this acid solution is hydrochloric acid (HCl).

[0060] In some embodiments, the pickling speed is 60 m / min - 80 m / min.

[0061] The pickling speed can be 60 m / min - 80 m / min. A sufficient pickling speed can make the pickling process sufficient. Exemplarily, the pickling speed can be 60 m / min, 62 m / min, 64 m / min, 66 m / min, 68 m / min, 70 m / min, 72 m / min, 74 m / min, 76 m / min, 78 m / min, 80 m / min, etc.

[0062] The embodiment of the present application provides a method for eliminating the patchy defects on the surface of medium and high carbon steel pickling plates, which has the following advantages:

[0063] 1. The total content of Ni and Cr is 0.15% - 0.5%. These two elements can form a dense oxide film on the surface of the steel, effectively blocking the diffusion of oxygen atoms into the interior of the steel, and thus significantly reducing the phenomenon of grain boundary oxidation; the content of Mo is 0.2% - 0.4%, which regulates the oxidation behavior of other alloy elements on the surface of the steel and prevents their uneven oxidation and enrichment. During the heating and processing process, the uneven distribution of alloy elements will cause differences in surface composition and properties, resulting in patchy defects. The reasonable addition of Mo helps to avoid such problems and makes the oxidation on the steel surface more uniform;

[0064] 2. Precisely controlling the tapping temperature of the in-furnace heating, in combination with rough rolling and the first cooling link, can reduce the reaction time and degree between the steel surface and oxygen while ensuring good processing performance of the steel billet. An appropriate tapping temperature can avoid excessive oxidation of the steel at high temperatures, and the first cooling link can quickly reduce the temperature of the steel, further inhibiting the occurrence of oxidation and decarburization phenomena and improving the surface quality of the steel;

[0065] 3. Using a lotion containing inhibitors during pickling can remove the scale on the surface of the hot-rolled coil while slowing down the corrosion rate of the acid on the steel substrate and inhibiting the generation of hydrogen embrittlement. The inhibitor can also improve the pickling effect, further eliminating the patchy color difference defects on the surface of the pickling plate, making the surface of the pickling plate more bright and flat, and improving the appearance quality of the product.

[0066] The following further elaborates the present application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are usually determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0067] Example 1

[0068] A method for eliminating the patchy defects on the surface of medium and high carbon steel pickling plates includes:

[0069] Obtaining a steel billet with a set chemical composition, which includes C, Si, Mn, Al, Ni, Cr, Mo, as well as Fe and inevitable impurities; among them, in terms of mass fraction, the content of C is 0.72%, the content of Mn is 0.45%, the content of Si is 0.11%, the content of Al is 0.028%, the total content of Ni and Cr is 0.35%, and the content of Mo is 0.38%;

[0070] The steel billet is heated in the furnace, and the tapping temperature during the in-furnace heating is controlled; among them, the tapping temperature is 1210 °C, the heating time is 180 min, and the air excess coefficient of the heating furnace is 0.9;

[0071] The heated steel billet is rough rolled to obtain an intermediate billet; the rough rolling of R1 and R2 adopts 1+5 rolling;

[0072] The intermediate billet is subjected to the first cooling; the first cooling is water cooling, and the pressure of the water cooling is 0.7 MPa;

[0073] The intermediate billet after the first cooling is successively subjected to finish rolling, laminar cooling, and coiling to obtain a hot rolled coil;

[0074] The hot rolled coil is pickled to obtain a pickled sheet; among them, the pickling agent for the pickling includes an inhibitor, the pickling speed is 65 m / min, the mass concentration of the acid solution is 50 g / L, and the mass concentration of the inhibitor is 2%. The acid solution is hydrochloric acid; the inhibitor is hexamethylenetetramine.

[0075] Example 2

[0076] A method for eliminating the surface patchy defects of medium and high carbon steel pickled sheets, including:

[0077] A steel billet with a set chemical composition is obtained. The set chemical composition includes C, Si, Mn, Al, Ni, Cr, Mo, as well as Fe and inevitable impurities; among them, in terms of mass fraction, the content of C is 0.60%, the content of Mn is 0.3%, the content of Si is 0.2%, the content of Al is 0.02%, the total content of Ni and Cr is 0.15%, and the content of Mo is 0.2%;

[0078] The steel billet is heated in the furnace, and the tapping temperature during the in-furnace heating is controlled; among them, the tapping temperature is 1200 °C, the heating time is 200 min, and the air excess coefficient of the heating furnace is 0.85;

[0079] The heated steel billet is rough rolled to obtain an intermediate billet; the rough rolling of R1 and R2 adopts 1+5 rolling;

[0080] The intermediate billet is subjected to the first cooling; the first cooling is water cooling, and the pressure of the water cooling is 0.5 MPa;

[0081] The intermediate billet after the first cooling is successively subjected to finish rolling, laminar cooling, and coiling to obtain a hot rolled coil;

[0082] The hot rolled coil is pickled to obtain a pickled sheet; among them, the pickling agent for the pickling includes an inhibitor, the pickling speed is 60 m / min, the mass concentration of the acid solution is 45 g / L, and the mass concentration of the inhibitor is 1%. The acid solution is hydrochloric acid; the inhibitor is hexamethylenetetramine.

[0083] Example 3

[0084] A method for eliminating patchy defects on the surface of medium and high carbon steel pickling sheets, comprising:

[0085] Obtaining a steel billet with a set chemical composition, which includes C, Si, Mn, Al, Ni, Cr, Mo, as well as Fe and inevitable impurities; wherein, by mass fraction, the content of C is 0.80%, the content of Mn is 0.6%, the content of Si is 0.30%, the content of Al is 0.05%, the total content of Ni and Cr is 0.5%, and the content of Mo is 0.31%;

[0086] Heating the steel billet in the furnace and controlling the tapping temperature of the in-furnace heating; wherein, the tapping temperature is 1230 °C, the heating time is 190 min, and the air excess coefficient of the heating furnace is 0.9;

[0087] Rough rolling the heated steel billet to obtain an intermediate billet; The rough rolling R1 and R2 adopt 1+5 rolling;

[0088] Performing the first cooling on the intermediate billet; The first cooling is water cooling, and the pressure of the water cooling is 0.8 MPa;

[0089] Successively performing finish rolling, laminar cooling and coiling on the intermediate billet after the first cooling to obtain a hot rolled coil;

[0090] Pickling the hot rolled coil to obtain a pickling sheet; wherein, the pickling agent for the pickling includes an inhibitor, the pickling speed is 80 m / min, the mass concentration of the acid solution is 60 g / L, and the mass concentration of the inhibitor is 3%. The acid solution is hydrochloric acid; the inhibitor is hexamethylenetetramine.

[0091] Comparative Example 1

[0092] A method for eliminating patchy defects on the surface of medium and high carbon steel pickling sheets, comprising:

[0093] Obtaining a steel billet with a set chemical composition, which includes C, Si, Mn, Al, Ni, Cr, Mo, as well as Fe and inevitable impurities; wherein, by mass fraction, the content of C is 0.72%, the content of Mn is 0.5%, the content of Si is 0.21%, the content of Al is 0.030%, and the total content of Ni and Cr is 0.7%;

[0094] Heating the steel billet in the furnace and controlling the tapping temperature of the in-furnace heating; wherein, the tapping temperature is 1220 °C, the heating time is 180 min, and the air excess coefficient of the heating furnace is 1.0;

[0095] Rough rolling the heated steel billet to obtain an intermediate billet; The rough rolling R1 and R2 adopt 1+5 rolling;

[0096] Cool the intermediate billet for the first time; the first cooling is water cooling, and the pressure of the water cooling is 0.2 MPa;

[0097] Perform finish rolling, laminar cooling and coiling on the intermediate billet after the first cooling in sequence to obtain a hot-rolled coil;

[0098] Pickle the hot-rolled coil to obtain a pickled sheet; wherein, the pickling speed is 80 m / min, and the mass concentration of the acid solution is 60 g / L.

[0099] The acid solution is hydrochloric acid;

[0100] Comparative Example 2

[0101] A method for eliminating surface patchy defects of medium and high carbon steel pickled sheets, comprising:

[0102] Obtain a steel billet with a set chemical composition, and the set chemical composition includes C, Si, Mn, Al, Ni, Cr, Mo, Fe and inevitable impurities; wherein, by mass fraction, the content of C is 0.78%, the content of Mn is 0.3%, the content of Si is 0.26%, the content of Al is 0.025%, the total content of Ni and Cr is 0.45%, and the content of Mo is 0.27%;

[0103] Heat the steel billet in the furnace and control the tapping temperature of the in-furnace heating; wherein, the tapping temperature is 1260 °C, the heating time is 220 min, and the air excess coefficient of the heating furnace is 1.0;

[0104] Rough roll the heated steel billet to obtain an intermediate billet; the rough rolling of R1 and R2 adopts 1+5 rolling;

[0105] Cool the intermediate billet for the first time; the first cooling is water cooling, and the pressure of the water cooling is 0.5 MPa;

[0106] Perform finish rolling, laminar cooling and coiling on the intermediate billet after the first cooling in sequence to obtain a hot-rolled coil;

[0107] Pickle the hot-rolled coil to obtain a pickled sheet; wherein, the pickling lotion includes an inhibitor, the pickling speed is 80 m / min, the mass concentration of the acid solution is 45 g / L, and the mass concentration of the inhibitor is 0.5%. The acid solution is hydrochloric acid; the inhibitor is hexamethylenetetramine.

[0108] Comparative Example 3

[0109] A method for eliminating surface patchy defects of medium and high carbon steel pickled sheets, comprising:

[0110] A steel billet with a set chemical composition is obtained. The set chemical composition includes C, Si, Mn, Al, Ni, Cr, Mo, as well as Fe and inevitable impurities. Among them, by mass fraction, the content of C is 0.65%, the content of Mn is 0.6%, the content of Si is 0.12%, the content of Al is 0.044%, the total content of Ni and Cr is 0.35%, and the content of Mo is 0.3%.

[0111] The steel billet is heated in the furnace and the tapping temperature during the in-furnace heating is controlled. Among them, the tapping temperature is 1190 °C, the heating time is 180 min, and the air excess coefficient of the heating furnace is 0.85.

[0112] The heated steel billet is rough-rolled to obtain an intermediate billet. For rough rolling R1 and R2, 1+5 rolling is adopted.

[0113] The intermediate billet is finish-rolled, cooled, and coiled to obtain a hot-rolled coil.

[0114] The hot-rolled coil is pickled to obtain a pickled sheet. Among them, the pickling agent for pickling includes an inhibitor, the pickling speed is 70 m / min, the mass concentration of the acid solution is 55 g / L, and the mass concentration of the inhibitor is 1.5%. The acid solution is hydrochloric acid; the inhibitor is hexamethylenetetramine.

[0115] For the medium and high carbon pickled sheets prepared in Examples 1-3 and Comparative Examples 1-3, surface mottled defect tests are carried out, and the area fractions can be seen in Table 1.

[0116] Table 1 Area fraction % of surface mottled defects of medium and high carbon steel pickled sheets

[0117] Serial number Area fraction % of patchy defects on the surface of medium and high carbon steel pickled sheet Example 1 0 Example 2 7 Example 3 9 Comparative example 1 60 Comparative example 2 50 Comparative example 3 30

[0118] From Examples 1-3, Comparative Examples 1-3, and Table 1, it can be seen that the area fractions of surface mottled defects of the medium and high carbon steel pickled sheets prepared in Examples 1-3 are all below 10%, and the surface quality of the medium and high carbon steel pickled sheets prepared in Comparative Examples 1-3 is poor, all above 30%.

[0119] Figure 3 This is a morphology diagram of a medium and high carbon steel pickled sheet provided in Example 1 of this application; please refer to Figure 3 , indicating that the medium and high carbon steel pickled sheet prepared in Example 1 has no mottled color difference defects. Figure 4 This is a morphology diagram of a medium and high carbon steel pickled sheet provided in Comparative Example 1 of this application; Figure 5 This is a morphology diagram of a medium and high carbon steel pickled sheet provided in Comparative Example 2 of this application; Figure 6 This is a morphology diagram of a medium and high carbon steel pickled sheet provided in Comparative Example 3 of this application; please refer to Figures 4 - 6, indicating that the surface quality of the medium and high carbon steel pickled sheets prepared in Comparative Examples 1 to 3 is poor. In Comparative Example 1, the contents of Ni and Cr are on the high side, and Mo is not added; the water cooling pressure of the intermediate billet is insufficient, and inhibitors are not added either, resulting in the worst surface quality; in Comparative Example 2, the process parameters of in-furnace heating are not within the scope of the embodiments of the present application, and the mass concentration of the inhibitor is insufficient, so the surface quality of the medium and high carbon steel pickled sheet is also poor; in Comparative Example 3, the furnace outlet temperature is low, and the intermediate billet is not cooled, and there are also some patchy color difference defects on the surface of the medium and high carbon steel pickled sheet.

[0120] One or more technical solutions in the embodiments of the present application at least further have the following technical effects or advantages:

[0121] (1) Considering the influence of alloying elements in medium and high carbon steel on the hardenability, surface hardness and surface quality of steel, the content of Ni and Cr is controlled to reduce grain boundary oxidation, and the addition of an appropriate amount of Mo is used in the composition design to control the uneven oxidation enrichment of other alloying elements on the surface of the steel matrix. At the same time, through the reasonable application of the heating system, rough rolling passes and cooling water for the intermediate billet, surface decarburization and grain boundary oxidation are reduced. Finally, combined with the coupling control of pickling concentration, speed and the use of corrosion inhibitors, etc., the patchy color difference defects on the surface of the pickled sheet are finally reduced, and a pickled sheet with a bright surface is prepared;

[0122] (2) Solve the problem of patchy defects on the surface of medium and high carbon steel after pickling. The method is simple, economical and efficient. Using the method provided by the embodiments of the present application, it is easier to improve the surface quality of medium and high carbon steel pickling without affecting the production rhythm and mechanical properties.

[0123] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. 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 these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for eliminating patchy defects on the surface of medium and high carbon steel pickling sheets, the method comprising: Obtaining a steel billet with a set chemical composition, the set chemical composition including C, Si, Mn, Al, Ni, Cr, Mo, and Fe; wherein, by mass fraction, the total content of Ni and Cr is 0.15% - 0.5%, and the content of Mo is 0.2% - 0.4%; Heating the steel billet in a furnace and controlling the tapping temperature of the in-furnace heating; Rough rolling the heated steel billet to obtain an intermediate billet; Performing a first cooling on the intermediate billet; Successively performing finish rolling, a second cooling, and coiling on the intermediate billet after the first cooling to obtain a hot rolled coil; Pickling the hot rolled coil to obtain a medium and high carbon steel pickling sheet; wherein, the pickling agent includes an inhibitor.

2. The method according to claim 1, wherein The tapping temperature is 1200°C - 1230°C.

3. The method according to claim 1 or 2, wherein The time of the in-furnace heating is 170 min - 200 min, and / or the air excess coefficient of the heating furnace for the in-furnace heating is 0.85 - 1.

0.

4. The method according to claim 1, characterized in that The mode of the first cooling is water cooling, and the pressure of the water cooling is 0.5 MPa - 0.8 MPa.

5. The method according to claim 1, wherein The mass concentration of the inhibitor is 1% - 3%.

6. The method according to claim 1 or 5, characterized in that The pickling agent further includes an acid solution, and the mass concentration of the acid solution is 45 g / L - 60 g / L.

7. The method according to claim 1, wherein The pickling speed is 60 m / min - 80 m / min.

8. The method according to claim 1, characterized in that, The rough rolling includes an R1 rolling mill and an R2 rolling mill; wherein, the R1 rolling mill rolls 1 pass, and the R2 rolling mill rolls 5 passes.

9. The method according to claim 1, characterized in that In the set chemical composition, by mass fraction, the content of C is 0.60% - 0.80%, the content of Si is 0.10% - 0.30%, the content of Mn is 0.3% - 0.6%, and the content of Al is 0.02% - 0.05%.

10. The method according to claim 1, wherein The thickness of the steel billet is 230 mm - 240 mm; the thickness of the intermediate billet is 30 mm - 40 mm; the thickness of the hot rolled coil is 2 mm - 4 mm.

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