A pickling-easy cold-rolled substrate and its preparation method

Abstract

This invention provides an easily pickled cold-rolled substrate and its preparation method, comprising: sequentially roughing, finishing, and coiling a continuously cast billet to obtain an easily pickled cold-rolled substrate; the composition of the continuously cast billet, by mass percentage, includes: C 0.012~0.026%, Mn 0.1~0.3%, P ≤0.018%, Al 0.03~0.06%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.001%, Ni+Cr+Cu 0.001~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities; the billet exits the furnace at a temperature of 1100~1250℃, and the residence time in the furnace at a furnace gas temperature ≥1060℃ is ≤100min; the finishing rolling adopts multi-stand continuous rolling, with the rolling speed of each stand increasing sequentially. The preparation method of this invention is simple and convenient to operate.

Description

Technical Field

[0001] This invention relates to the fields of iron and steel metallurgy and rolling technology, and in particular to an easily pickled cold-rolled substrate and its preparation method. Background Technology

[0002] In the production of hot-rolled strip steel, iron oxide scale is one of the core challenges affecting product surface quality and subsequent cold rolling processes. In the heating furnace area, accumulated iron oxide scale can clog the slideways, reducing thermal efficiency and increasing cleaning and maintenance costs. In the rolling zone, iron oxide scale causes fluctuations in rolling force, affecting strip thickness and shape accuracy, while also exacerbating roll wear. In the pickling and cold rolling stages, the severity of iron oxide scale directly affects the difficulty of pickling; incomplete pickling can lead to surface defects during continuous cold rolling and subsequent galvanizing. Furthermore, during the leveling process of the steel coil, detached iron oxide scale, when rolled by straightening rolls, can form pits, severely damaging the finished product's appearance. Therefore, improving the quality of iron oxide scale defects in strip steel is of great significance for improving the overall product quality throughout the entire process.

[0003] In existing technologies, methods for improving iron oxide scale mainly focus on adjusting the coiling temperature or changing the cooling mode. For example, the thickness of iron oxide scale is adjusted by controlling the coiling temperature, but the formation of iron oxide scale in the heating furnace and rough rolling stage is not effectively controlled. Another example is the addition of silicon (Si) to steel to increase strength, but high Si content can lead to the formation of Fe2SiO4 (ferroolitic olivine) on the matrix surface, causing iron oxide scale to embed in the matrix, making it difficult to remove and worsening pickling performance. Therefore, this invention provides an easily pickled cold-rolled substrate and its preparation method to solve the problems of existing methods' difficulty in suppressing iron oxide scale formation and the difficulty of pickling. Summary of the Invention

[0004] This invention provides an easily pickled cold-rolled substrate and its preparation method, aiming to solve the technical problems of existing methods being unable to suppress the formation of iron oxide scale and the difficulty of pickling.

[0005] To achieve the above objectives, the present invention provides a method for preparing an easily pickled cold-rolled substrate, comprising: sequentially subjecting a continuously cast billet to rough rolling, finish rolling and coiling to obtain an easily pickled cold-rolled substrate.

[0006] The composition of the continuously cast billet, by mass percentage, includes: C 0.012~0.026%, Mn 0.1~0.3%, P ≤0.018%, Al 0.03~0.06%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.001%, Ni+Cr+Cu 0.001~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities.

[0007] The tapping temperature of the continuously cast billet is 1100~1250℃.

[0008] The residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is ≤100min.

[0009] The finishing mill adopts multi-stand continuous rolling, and the rolling speed of each stand increases sequentially. The rolling speed of the first stand is 1.0~1.5m / s, and the rolling speed of the last stand is 7.2~13.2m / s.

[0010] According to an embodiment of this application, the exit temperature of the roughing mill is 1020~1100℃.

[0011] According to an embodiment of this application, the inlet temperature of the finishing mill is 980~1020℃.

[0012] The exit temperature of the finishing mill is 820~880℃.

[0013] According to an embodiment of this application, the winding temperature is 600~650°C.

[0014] After finishing rolling, the temperature is cooled to the coiling temperature at a cooling rate of 10~20℃ / s.

[0015] According to the embodiments of this application, after the rough rolling and before the finish rolling, a descaling process is also included.

[0016] The phosphorus removal pressure is 20~22 MPa.

[0017] According to the embodiments of this application, the exit temperature of the roughing mill is 1020~1050°C.

[0018] The inlet temperature of the finishing mill is 980~1000℃.

[0019] The exit temperature of the finishing mill is 820~850℃.

[0020] According to the embodiments of this application, the residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is ≤60min.

[0021] According to the embodiments of this application, the finishing rolling adopts a 7-stand continuous rolling mill, and the rolling speeds of the first to seventh stands are F1: 1.0~1.5m / s, F2: 2.0~2.4m / s, F3: 3.0~3.9m / s, F4: 4.0~5.6m / s, F5: 5.0~8.0m / s, F6: 6.0~10.5m / s, and F7: 7.2~13.2m / s.

[0022] This invention provides an easily acid-washable cold-rolled substrate, which is prepared using the method described above.

[0023] According to an embodiment of this application, the volume fraction of the FeO phase in the iron oxide layer on the surface of the easily pickled cold-rolled substrate is 50-70%.

[0024] Compared with the prior art, the beneficial effects of the present invention are: The aforementioned easily pickled cold-rolled substrate and its preparation method, through the synergistic optimization of continuous casting billet composition design, heating process control, and rolling process parameters, effectively control the formation and occurrence state of iron oxide scale, significantly reducing the pickling difficulty of the cold-rolled substrate. Specifically, the continuous casting billet composition adopts a Si-free design, avoiding the formation of low-melting-point Fe2SiO4 compounds on the matrix surface when the Si content is too high, which leads to iron oxide scale embedding in the matrix and difficulty in descaling. By controlling the continuous casting billet's exit temperature and limiting its residence time in the heating furnace to no more than 100 minutes, the amount of iron oxide scale generated in the heating furnace is reduced from the source. The finishing rolling adopts a multi-stand continuous rolling method with sequentially increasing rolling speeds for each stand, effectively shortening the oxidation time in the finishing rolling section and further suppressing the formation of iron oxide scale.

[0025] The preparation method of the present invention is simple and easy to operate. Through the synergistic control of composition, process steps and parameters, it not only significantly inhibits the formation of iron oxide scale, but also optimizes the phase composition and structural morphology of iron oxide scale. It fundamentally solves the technical problems of large amount of iron oxide scale formation and difficult pickling in the prior art, and obtains cold-rolled substrate with excellent surface quality and high pickling efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a SEM image of the iron oxide scale on the surface of the easily pickled cold-rolled substrate obtained in Example 1 of the present invention.

[0028] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] The technical solutions of the various embodiments of the present invention can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0031] To achieve the above objectives, the present invention provides a method for preparing an easily pickled cold-rolled substrate, comprising: sequentially subjecting a continuously cast billet to rough rolling, finish rolling and coiling to obtain an easily pickled cold-rolled substrate.

[0032] The composition of the continuously cast billet, by mass percentage, includes: C 0.012~0.026%, Mn 0.1~0.3%, P ≤0.018%, Al 0.03~0.06%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.001%, Ni+Cr+Cu 0.001~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities.

[0033] The tapping temperature of the continuously cast billet is 1100~1250℃.

[0034] The residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is ≤100min.

[0035] The finishing mill adopts multi-stand continuous rolling, and the rolling speed of each stand increases sequentially. The rolling speed of the first stand is 1.0~1.5m / s, and the rolling speed of the last stand is 7.2~13.2m / s.

[0036] In some embodiments, the composition of the continuously cast billet, by mass percentage, includes: C 0.015~0.026%, Mn 0.1~0.2%, P ≤0.015%, Al 0.03~0.05%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.001%, Ni+Cr+Cu 0.005~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities.

[0037] In some embodiments, the composition of the continuously cast billet, by mass percentage, includes: C 0.018~0.022%, Mn 0.12~0.16%, P ≤0.015%, Al 0.03~0.05%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.0008%, Ni+Cr+Cu 0.01~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities.

[0038] In some embodiments, the composition of the continuously cast billet, by mass percentage, includes: C 0.018~0.022%, Mn 0.1~0.18%, P ≤0.015%, Al 0.03~0.05%, S ≤0.015%, Ti 0.002~0.01%, B 0.0004~0.0008%, Ni+Cr+Cu 0.02~0.06%, and does not contain Si, with the balance being iron and unavoidable impurities.

[0039] In some embodiments, the tapping temperature of the continuously cast billet is 1100~1200℃.

[0040] In some embodiments, the residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is 30~80min.

[0041] In some embodiments, the residence time of the continuously cast billet in the furnace gas temperature ≥1060°C is 30~60 minutes.

[0042] In some embodiments, the residence time of the continuously cast billet in the furnace gas temperature ≥1060°C is 30~40 minutes.

[0043] In some embodiments, the present invention, by strictly controlling the chemical composition of the continuously cast billet, adopts an ultra-low carbon design (C 0.012~0.026%) and limits the Mn content to 0.1~0.3%, while explicitly eliminating the presence of Si, effectively reducing the tendency and density of iron oxide scale formation. The absence of Si avoids the formation of low-melting-point, highly adhesive silicate oxides during oxidation, thereby significantly reducing the bonding strength between the iron oxide scale and the matrix, which is beneficial for the rapid dissolution and peeling of the iron oxide scale during subsequent pickling.

[0044] In some embodiments, the present invention, by adding trace amounts of Ti and B elements, not only refines the grains and improves the uniformity of the substrate structure, but also positively affects the microstructure of the iron oxide scale, further enhancing pickling efficiency. Strict control of the total amounts of Ni, Cr, and Cu elements can prevent the formation of insoluble composite oxides during high-temperature oxidation, ensuring the chemical homogeneity and pickling responsiveness of the iron oxide scale layer.

[0045] In some embodiments, the furnace exit temperature of the continuously cast billet is controlled at 1100~1250℃, and its residence time in an environment with a furnace gas temperature ≥1060℃ is controlled at ≤100min, which effectively suppresses excessive oxidation caused by high-temperature long-term heating.

[0046] In some embodiments, by shortening the residence time of the continuously cast billet in the high-temperature zone, the total amount of iron oxide scale generated can be reduced, while avoiding the coarsening and densification of iron oxide scale grains caused by prolonged high-temperature exposure. This allows the generated iron oxide scale layer to maintain a loose and porous structure, providing favorable conditions for subsequent pickling.

[0047] In some embodiments, the present invention employs a multi-stand continuous rolling process, in which the rolling speed of each stand increases sequentially, achieving a dynamic balance between deformation heat and rolling temperature drop during the finishing rolling process. Specifically, the defined roughing mill exit temperature, finishing mill inlet temperature, and finishing mill exit temperature ensure that the metal is within a suitable deformation temperature range during the finishing rolling process. This guarantees the stability of the rolling process and suppresses excessive growth of secondary iron oxide scale during the finishing rolling stage through rapid deformation and temperature drop.

[0048] In some embodiments, the rolling speed of each stand increases sequentially, allowing the continuously cast billet to pass through at a higher speed in the final section of the finishing roll, shortening the high-temperature exposure time and further controlling the amount of iron oxide scale generated.

[0049] In some embodiments, the present invention, through the coordinated control of parameters such as chemical composition, heating temperature, rolling speed, and cooling rate, prepares an iron oxide scale layer on the surface of an easily pickled cold-rolled substrate with high FeO phase content and loose structure. During the subsequent pickling process before cold rolling, the iron oxide scale can be quickly and uniformly dissolved and peeled off by the acid, significantly reducing the difficulty and cost of pickling, and improving the operating efficiency and product quality stability of the cold rolling production line.

[0050] The aforementioned method for preparing easily pickled cold-rolled substrates effectively controls the formation and presence of iron oxide scale by synergistically optimizing the composition design of continuously cast billets, heating process control, and rolling process parameters, significantly reducing the pickling difficulty of cold-rolled substrates. Specifically, the continuously cast billet uses a Si-free steel design, avoiding the formation of low-melting-point Fe2SiO4 compounds on the matrix surface when Si content is too high, which leads to iron oxide scale embedding in the matrix and difficulty in descaling. By controlling the exit temperature of the continuously cast billet and limiting its residence time in the heating furnace to no more than 100 minutes, the amount of iron oxide scale generated in the heating furnace is reduced at the source. The finishing rolling process employs multi-stand continuous rolling with progressively increasing rolling speeds for each stand, effectively shortening the oxidation time in the finishing rolling section and further suppressing iron oxide scale formation.

[0051] In some embodiments, the exit temperature of the roughing mill is 1020~1100℃.

[0052] In some embodiments, the exit temperature of the roughing mill is 1020~1080°C.

[0053] In some embodiments, the inlet temperature of the finishing mill is 980~1020°C.

[0054] The exit temperature of the finishing mill is 820~880℃.

[0055] In some embodiments, the inlet temperature of the finishing mill is 980~1000℃.

[0056] In some embodiments, the exit temperature of the finishing mill is 820~860°C.

[0057] In some embodiments, the winding temperature is 600~650°C.

[0058] After finishing rolling, the temperature is cooled to the coiling temperature at a cooling rate of 10~20℃ / s.

[0059] In some embodiments, the winding temperature is 620~650°C.

[0060] In some embodiments, the finishing rolling is followed by cooling to the winding temperature at a cooling rate of 13~20℃ / s.

[0061] In some embodiments, the finishing rolling is followed by cooling to the winding temperature at a cooling rate of 15~20℃ / s.

[0062] In some embodiments, the iron oxide scale is rapidly cooled to a winding temperature of 600-650°C at a cooling rate of 10-20°C / s, and the phase composition of the iron oxide scale is precisely controlled by adjusting the cooling rate. The faster cooling rate promotes the retention and enrichment of the FeO phase in the iron oxide scale layer, resulting in a final FeO phase volume fraction of 50-70% in the iron oxide scale layer on the substrate surface. Compared to Fe3O4 and Fe2O3, the FeO phase has higher chemical activity and acid pickling dissolution rate; therefore, the iron oxide scale layer with high FeO phase content exhibits excellent acid pickling responsiveness, significantly shortening the pickling time and reducing acid consumption.

[0063] In some embodiments, after the rough rolling and before the finish rolling, a descaling process is further included.

[0064] The phosphorus removal pressure is 20~22 MPa.

[0065] In some embodiments, controlling the dephosphorization pressure can effectively remove the primary iron oxide scale generated during the rough rolling stage, preventing it from being pressed into the substrate surface or participating in subsequent fine rolling deformation, thereby reducing the total thickness and density of the final iron oxide scale layer and laying the foundation for obtaining the surface quality of the cold-rolled substrate that is easy to pickle.

[0066] In some embodiments, the exit temperature of the roughing mill is 1020~1050°C.

[0067] The inlet temperature of the finishing mill is 980~1000℃.

[0068] The exit temperature of the finishing mill is 820~830℃.

[0069] In some embodiments, the exit temperature of the roughing mill is 1020~1050°C.

[0070] In some embodiments, the inlet temperature of the finishing mill is 980~990°C.

[0071] In some embodiments, the exit temperature of the finishing mill is 820~830°C.

[0072] In some embodiments, the residence time of the continuously cast billet in the furnace gas temperature ≥1060°C is ≤60 min.

[0073] In some embodiments, the finishing rolling is carried out using a 7-stand continuous rolling mill, and the rolling speeds of the first to seventh stands are respectively F1: 1.0~1.5m / s, F2: 2.0~2.4m / s, F3: 3.0~3.9m / s, F4: 4.0~5.6m / s, F5: 5.0~8.0m / s, F6: 6.0~10.5m / s, and F7: 7.2~13.2m / s.

[0074] In some embodiments, the finishing rolling is carried out using a 7-stand continuous rolling mill, and the rolling speeds of the first to seventh stands are respectively F1: 1.0~1.3m / s, F2: 2.0~2.4m / s, F3: 3.0~3.9m / s, F4: 4.0~5.6m / s, F5: 5.0~8.0m / s, F6: 6.0~10.5m / s, and F7: 7.9~12.5m / s.

[0075] In some embodiments, the finishing rolling is carried out using a 7-stand continuous rolling mill, and the rolling speeds of the first to seventh stands are respectively F1: 1.1~1.3m / s, F2: 2.0~2.2m / s, F3: 3.0~3.7m / s, F4: 4.2~5.5m / s, F5: 5.8~7.7m / s, F6: 6.4~10.0m / s, and F7: 7.9~12.5m / s.

[0076] The preparation method of the present invention is simple and easy to operate. Through the synergistic control of composition, process steps and parameters, it not only significantly inhibits the formation of iron oxide scale, but also optimizes the phase composition and structural morphology of iron oxide scale. It fundamentally solves the technical problems of large amount of iron oxide scale formation and difficult pickling in the prior art, and obtains cold-rolled substrate with excellent surface quality and high pickling efficiency.

[0077] This invention provides an easily acid-washable cold-rolled substrate, which is prepared using the method described above.

[0078] In some embodiments, the volume fraction of the FeO phase in the iron oxide layer on the surface of the easily pickled cold-rolled substrate is 50-70%.

[0079] In some embodiments, the average thickness of the iron oxide scale on the surface of the easily pickled cold-rolled substrate is ≤6.0 μm.

[0080] In some embodiments, the average thickness of the iron oxide scale on the upper surface of the easily pickled cold-rolled substrate is ≤5.8μm.

[0081] In some embodiments, the average thickness of the iron oxide scale on the upper surface of the easily pickled cold-rolled substrate is 3.51~5.65μm.

[0082] In some embodiments, the average thickness of the iron oxide scale on the lower surface of the easily pickled cold-rolled substrate is ≤5.0 μm.

[0083] In some embodiments, the average thickness of the iron oxide scale on the lower surface of the easily pickled cold-rolled substrate is 4.14~4.75μm.

[0084] To further illustrate the present invention, the following examples are provided: Example 1 A method for preparing an easily pickled cold-rolled substrate includes: sequentially roughing, finishing, and coiling a continuously cast billet to obtain an easily pickled cold-rolled substrate; the composition of the continuously cast billet, by mass percentage, is: C 0.02%, Mn 0.14%, P 0.01%, Al 0.04%, S 0.012%, Ti 0.008%, B 0.0005%, Ni+Cr+Cu 0.04%, and it does not contain Si, with the balance being iron and unavoidable impurities.

[0085] The continuous casting billet exit temperature is 1100℃; the residence time of the continuous casting billet in the heating furnace at a furnace gas temperature ≥1060℃ is 30 minutes; the exit temperature of the roughing mill is 1020℃; the inlet temperature of the finishing mill is 980℃, and the exit temperature of the finishing mill is 820℃; after roughing and before finishing, descaling is performed at a pressure of 22MPa. The finishing mill adopts a 7-stand continuous rolling mill, with the rolling speed of each stand increasing sequentially. The rolling speeds of the first to seventh stands are F1: 1.1m / s, F2: 2.2m / s, F3: 3.7m / s, F4: 5.5m / s, F5: 7.7m / s, F6: 10m / s, and F7: 12.5m / s, respectively. After finishing, the billet is cooled at a cooling rate of 20℃ / s to a coiling temperature of 650℃ to obtain an easily pickled cold-rolled substrate.

[0086] Testing showed that the average thickness of the iron oxide scale on the working surface (upper surface) of the easily pickled cold-rolled substrate prepared in Example 1 was 3.51 μm, and the average thickness on the lower surface was 4.4 μm. The volume fraction of the FeO phase in the iron oxide scale layer on the surface of the easily pickled cold-rolled substrate was 70%, and the pickling time was shorter than that of conventional products, indicating that this preparation method has good iron oxide scale control. See also Figure 1 As can be seen, the iron oxide scale on the surface of the easily pickled cold-rolled substrate prepared in Example 1 of the present invention has a uniform thickness and loose structure. The bonding force between the iron oxide scale and the substrate is weak, and there is no dense and thick oxide layer accumulation. This allows the pickling medium to quickly penetrate and wet the iron oxide scale layer, and can efficiently peel off the iron oxide scale on the substrate surface without residual oxide impurities. This proves that the easily pickled cold-rolled substrate prepared by the present invention has excellent easy pickling characteristics and effectively solves the technical problems of dense iron oxide scale, difficult pickling, and low pickling efficiency of traditional cold-rolled substrates.

[0087] Example 2 A method for preparing an easily pickled cold-rolled substrate includes: sequentially roughing, finishing, and coiling a continuously cast billet to obtain an easily pickled cold-rolled substrate; the composition of the continuously cast billet, by mass percentage, is: C 0.02%, Mn 0.14%, P 0.01%, Al 0.04%, S 0.012%, Ti 0.008%, B 0.0005%, Ni+Cr+Cu 0.04%, and it does not contain Si, with the balance being iron and unavoidable impurities.

[0088] The continuous casting billet exits the furnace at a temperature of 1250℃, and remains in the furnace at a gas temperature ≥1060℃ for 40 minutes. The roughing mill exit temperature is 1100℃; the finishing mill inlet temperature is 1020℃, and the finishing mill exit temperature is 880℃. Descaling is performed after roughing and before finishing, with a pressure of 20MPa. Finishing is done using a 7-stand continuous rolling mill, with the rolling speed increasing sequentially from the first to the seventh stand: F1: 1.3m / s, F2: 2.1m / s, F3: 3.0m / s, F4: 4.1m / s, F5: 5.5m / s, F6: 7.0m / s, and F7: 8.4m / s. After finishing, the billet is cooled at a rate of 13℃ / s to a coiling temperature of 600℃, yielding an easily pickled cold-rolled substrate.

[0089] Testing revealed that the average thickness of the iron oxide scale on the working surface (upper surface) of the cold-rolled substrate prepared in Example 2 was 5.65 μm, and the average thickness on the lower surface was 4.75 μm. The volume fraction of the FeO phase in the iron oxide scale layer on the surface of the easily pickled cold-rolled substrate was 50%, and the pickling time was shorter than that of conventional products, indicating that this preparation method has good iron oxide scale control.

[0090] Example 3 A method for preparing an easily pickled cold-rolled substrate includes: sequentially roughing, finishing, and coiling a continuously cast billet to obtain an easily pickled cold-rolled substrate; the composition of the continuously cast billet, by mass percentage, is: C 0.02%, Mn 0.14%, P 0.01%, Al 0.04%, S 0.012%, Ti 0.008%, B 0.0005%, Ni+Cr+Cu 0.04%, and it does not contain Si, with the balance being iron and unavoidable impurities.

[0091] The continuous casting billet exit temperature is 1150℃, and the residence time of the continuous casting billet in the furnace gas temperature ≥1060℃ is 35 minutes; the roughing mill exit temperature is 1050℃; the finishing mill inlet temperature is 1000℃, and the finishing mill exit temperature is 840℃; after roughing milling and before finishing milling, descaling is performed at a pressure of 22MPa. The finishing mill adopts a 7-stand continuous rolling mill, with the rolling speed of each stand increasing sequentially. The rolling speeds of the first to seventh stands are F1: 1.2m / s, F2: 2.0m / s, F3: 3.0m / s, F4: 4.3m / s, F5: 5.9m / s, F6: 7.7m / s, and F7: 9.3m / s, respectively. After finishing milling, the billet is cooled at a cooling rate of 14℃ / s to a coiling temperature of 620℃ to obtain an easily pickled cold-rolled substrate.

[0092] Testing revealed that the average thickness of the iron oxide scale on the working surface (upper surface) of the cold-rolled substrate prepared in Example 3 was 4.15 μm, and the average thickness on the lower surface was 4.14 μm. The volume fraction of the FeO phase in the iron oxide scale layer on the surface of the easily pickled cold-rolled substrate was 60%, and the pickling time was shorter than that of conventional products, indicating that this preparation method has a good effect on controlling the iron oxide scale.

[0093] Example 4 A method for preparing an easily pickled cold-rolled substrate includes: sequentially roughing, finishing, and coiling a continuously cast billet to obtain an easily pickled cold-rolled substrate; the composition of the continuously cast billet, by mass percentage, is: C 0.02%, Mn 0.14%, P 0.01%, Al 0.04%, S 0.012%, Ti 0.008%, B 0.0005%, Ni+Cr+Cu 0.04%, and it does not contain Si, with the balance being iron and unavoidable impurities.

[0094] The continuous casting billet exit temperature is 1200℃; the residence time of the continuous casting billet in the furnace gas temperature ≥1060℃ is 35min; the roughing mill exit temperature is 1080℃; the finishing mill inlet temperature is 1000℃; and the finishing mill exit temperature is 860℃. After roughing and before finishing, descaling is performed at a pressure of 22MPa. Finishing is performed using a 7-stand continuous rolling mill, with the rolling speed increasing sequentially from the first to the seventh stand: F1: 1.2m / s, F2: 2.0m / s, F3: 3.0m / s, F4: 4.2m / s, F5: 5.8m / s, F6: 7.6m / s, F7: 9.4m / s. After finishing, the billet is cooled at a rate of 15℃ / s to a coiling temperature of 620℃ to obtain an easily pickled cold-rolled substrate.

[0095] Testing revealed that the average thickness of the iron oxide scale on the working surface (upper surface) of the cold-rolled substrate prepared in Example 4 was 4.4 μm, and the average thickness on the lower surface was 4.37 μm. The volume fraction of the FeO phase in the iron oxide scale layer on the surface of the easily pickled cold-rolled substrate was 60%, and the pickling time was shorter than that of conventional products, indicating that this preparation method has a good effect on controlling the iron oxide scale.

[0096] The aforementioned easily pickled cold-rolled substrate and its preparation method, through the synergistic optimization of continuous casting billet composition design, heating process control, and rolling process parameters, effectively control the formation and occurrence state of iron oxide scale, significantly reducing the pickling difficulty of the cold-rolled substrate. Specifically, the continuous casting billet uses a Si-free steel design, avoiding the formation of low-melting-point Fe2SiO4 compounds on the matrix surface when the Si content is too high, which leads to iron oxide scale embedding in the matrix and difficulty in descaling. By controlling the continuous casting billet's exit temperature and limiting its residence time in the heating furnace to no more than 100 minutes, the amount of iron oxide scale generated in the heating furnace is reduced at the source. The finishing rolling process employs multi-stand continuous rolling with progressively increasing rolling speeds for each stand, effectively shortening the oxidation time in the finishing rolling section and further suppressing iron oxide scale formation.

[0097] The preparation method of the present invention is simple and easy to operate. Through the synergistic control of composition, process steps and parameters, it not only significantly inhibits the formation of iron oxide scale, but also optimizes the phase composition and structural morphology of iron oxide scale. It fundamentally solves the technical problems of large amount of iron oxide scale formation and difficult pickling in the prior art, and obtains cold-rolled substrate with excellent surface quality and high pickling efficiency.

[0098] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing an easily pickled cold-rolled substrate, characterized in that, include: The continuously cast billet is subjected to rough rolling, finish rolling and coiling in sequence to obtain a cold-rolled substrate that is easy to pickle; The composition of the continuously cast billet, by mass percentage, includes: C 0.012~0.026%, Mn 0.1~0.3%, P ≤0.018%, Al 0.03~0.06%, S ≤0.015%, Ti 0.002~0.01%, B 0.0001~0.001%, Ni+Cr+Cu 0.001~0.08%, and does not contain Si, with the balance being iron and unavoidable impurities; The tapping temperature of the continuously cast billet is 1100~1250℃; The residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is ≤100min; The finishing mill adopts multi-stand continuous rolling, and the rolling speed of each stand increases sequentially. The rolling speed of the first stand is 1.0~1.5m / s, and the rolling speed of the last stand is 7.2~13.2m / s.

2. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The exit temperature of the roughing mill is 1020~1100℃.

3. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The inlet temperature of the finishing mill is 980~1020℃; The exit temperature of the finishing mill is 820~880℃.

4. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The winding temperature is 600~650℃; After finishing rolling, the temperature is cooled to the coiling temperature at a cooling rate of 10~20℃ / s.

5. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The process after rough rolling and before finish rolling also includes a descaling process; The phosphorus removal pressure is 20~22 MPa.

6. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The exit temperature of the roughing mill is 1020~1050℃; The inlet temperature of the finishing mill is 980~1000℃; The exit temperature of the finishing mill is 820~850℃.

7. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The residence time of the continuously cast billet in the furnace gas temperature ≥1060℃ is ≤60min.

8. The method for preparing an easily pickled cold-rolled substrate according to claim 1, characterized in that, The finishing mill adopts a 7-stand continuous rolling mill, and the rolling speeds of the first to seventh stands are F1: 1.0~1.5m / s, F2: 2.0~2.4m / s, F3: 3.0~3.9m / s, F4: 4.0~5.6m / s, F5: 5.0~8.0m / s, F6: 6.0~10.5m / s, and F7: 7.2~13.2m / s.

9. A cold-rolled substrate that is easy to pickle, characterized in that, It is prepared by the method described in any one of claims 1 to 8.

10. The easily pickled cold-rolled substrate according to claim 9, characterized in that, The volume fraction of FeO phase in the iron oxide layer on the surface of the easily pickled cold-rolled substrate is 50-70%.

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