A method for controlling hot rolled mill scale of a coated deep drawing structural steel strip and a coated deep drawing structural steel strip

Abstract

This invention provides a method for controlling the oxide scale of hot-rolled steel strip with a hooded and annealed deep-drawing structure, as well as a hooded and annealed deep-drawing steel strip structure. By controlling the cooling method in the hot rolling process and combining roughing, finishing, and coiling processes, this invention achieves an oxide layer thickness ≤11μm in the steel strip. The oxide layer structure is proeutectoid Fe3O4 + eutectoid microstructure (Fe + Fe3O4) + FeO, with no Fe2O3 phase. The proportion of proeutectoid Fe3O4 is 70-80%, the proportion of eutectoid microstructure is 10-20%, and the proportion of FeO is approximately 10%. Furthermore, the oxide layer structure exhibits obvious pre-cracks. Based on this, the pickling speed in pickling rolling can be increased to 160-180 m / min, avoiding the shortcomings of the original process, such as difficulty in removing the oxide layer, over-pickling, and under-pickling defects. It also eliminates the environmental pollution problem caused by pickling white mist, resulting in excellent surface quality and good technical and economic indicators for the pickled steel strip.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for controlling the iron oxide scale of hot-rolled steel strip with a hooded and deep-drawn structure, and a hooded and deep-drawn steel strip. Background Technology

[0002] The oxide scale structure on the surface of pickled raw materials for deep-drawn structural steel typically consists of a high proportion of proeutectoid Fe3O4 + a small amount of FeO, with an oxide layer thickness of 14~20 μm. Under conventional process conditions, its edges are banded Fe2O3 red rust zones. To improve the surface quality of the finished product after subsequent annealing, the residual oxide scale must be completely removed during the pickling stage.

[0003] Low speeds in the pickling and rolling process, especially in the pickling section, have long been a problem faced by cold-rolled steel producers both domestically and internationally. The hot-rolled raw material for ordinary deep-drawing steel is typically designed as Ti microalloyed ultra-low carbon steel, with a surface oxide layer structure of Fe2O3 + a high proportion of proeutectoid Fe3O4 (volume fraction above 90%) + a small amount of FeO, and an oxide layer thickness of 14~20 μm. The Fe3O4 phase in the oxide layer is relatively dense, exhibits strong adhesion to the matrix, and also possesses a certain degree of ductility with small deformation. However, compared to the FeO phase, the chemical reaction rate of Fe3O4 with hydrochloric acid is low, and the Fe2O3 phase in the iron scale structure further reduces the reaction efficiency. Therefore, in the actual production of deep-drawn structural steel, only low-speed, high-concentration, and high-temperature hydrochloric acid can be used for production (process speed 110 m / min). This is detrimental to the production efficiency of the cold rolling process, and will also bring environmental problems such as pickling white mist (poor sealing of the acid tank and evaporation of acid) and local over-pickling of the strip steel, which reduces the yield of the strip steel and increases the environmental pressure on enterprises. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a method for controlling the iron oxide scale of hot-rolled deep-drawn steel strip with a shroud and a method for controlling the iron oxide scale of hot-rolled steel strip with a shroud and a deep-drawn steel strip with a shroud. This control method not only effectively improves the pickling process capacity, but also enhances the pickling effect of the steel strip.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for controlling the iron oxide scale of hot-rolled steel strip with a hooded deep-drawing structure, comprising the following steps:

[0007] After refining the molten steel, a slab is obtained by casting it. The slab is then subjected to homogenization, rough rolling, and finish rolling. After cooling, it is coiled to obtain a steel strip, which is then pickled.

[0008] Preferably, the cooling method is laminar flow cooling with two sets of centralized manifolds - air cooling - laminar flow cooling with two sets of sparse manifolds.

[0009] Preferably, the water pressure for the laminar flow cooling in the centralized manifold is 0.5~0.65 MPa, wherein the cooling ratios of the upper manifold and the lower manifold are 85~95% and 70~80%, respectively.

[0010] Preferably, the water pressure for laminar flow cooling in the sparse manifold is 0.5~0.65 MPa, wherein the cooling ratio of the upper manifold and the lower manifold is 45~55% and 45~55%, respectively.

[0011] Preferably, the distance between the cooling manifolds in the two sets of centralized manifold laminar flow cooling is 4.5~6 m.

[0012] Preferably, the air cooling length between the two sets of centralized manifold laminar flow cooling and the two sets of sparse manifold laminar flow cooling is 8~12 m.

[0013] Preferably, the distance between the cooling manifolds in the two sets of sparse manifold laminar flow cooling is 8~12 m.

[0014] Preferably, the cooling rate of the two sets of centralized manifold laminar flow cooling is 25~45 ℃ / s, the cooling rate of the air cooling is 5~10 ℃ / s, and the cooling rate of the two sets of sparse manifold laminar flow cooling is 15~30 ℃ / s.

[0015] Preferably, the molten steel is obtained by smelting blast furnace iron in a converter; the refining includes LF refining and RF refining.

[0016] Preferably, the chemical composition of the refined molten steel, calculated as elements, includes: C ≤ 0.0050%, Si 0~0.10%, Mn 0.15~0.35%, P 0~0.025%, S 0~0.010%, Als 0.015~0.060%, Ti 0.045~0.075%, with the remainder being Fe.

[0017] Preferably, the temperature for heat equalization is 1200~1240℃ and the time is 0.5~1.5 h.

[0018] Preferably, the rough rolling process includes a dephosphorization step, wherein the water pressure for dephosphorization is 17-19 MPa.

[0019] Preferably, the initial rolling temperature of the rough rolling is 1175~1210℃ to ensure that there is no difficult-to-remove fritillary phase on the surface.

[0020] Preferably, the thickness of the intermediate billet obtained after rough rolling is 34~38 mm.

[0021] Preferably, the process before finishing rolling includes a descaling step, wherein the water pressure for descaling is 24-26 MPa.

[0022] Preferably, the initial rolling temperature of the finishing mill is 1010~1050℃, the final rolling temperature is 900~940℃, and the rolling speed of the finishing mill is 1.10~1.70 m / s.

[0023] Preferably, the thickness reduction rates of the last two stands in the finishing rolling mill are ≤15% and ≤10%, respectively. In this invention, the initial rolling is a two-stand reversible rolling mill, and the final rolling is a seven-stand continuous rolling mill.

[0024] Preferably, the finishing rolling passes are 5 to 7.

[0025] Preferably, the winding temperature is 700~740℃.

[0026] Preferably, the thickness of the oxide layer in the steel strip is ≤11 μm, and its structure is proeutectoid Fe3O4 + eutectoid structure + FeO, with no Fe2O3 phase in the oxide layer, and the eutectoid structure includes Fe + Fe3O4.

[0027] Preferably, the proportion of preeutectoid Fe3O4 is 70-80%, the proportion of eutectoid structure is 10-20%, and the proportion of FeO is 5-10%.

[0028] Preferably, the pickling speed in the pickling process is 160~180 m / min, and the tensile elongation is 1.00~1.50%.

[0029] Preferably, the cold rolling reduction rate in the pickling process is 60-85%.

[0030] Secondly, the present invention provides a deep-drawing steel strip with a hooded design, wherein the hot-rolled iron oxide scale is controlled by the above-mentioned control method.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention provides a method for controlling the oxide scale of hot-rolled steel strip with a hooded and deep-drawn structure. By controlling the cooling method in the hot rolling process and combining roughing, finishing, and coiling processes, the resulting steel strip oxide layer thickness is ≤11 μm. The oxide layer structure is proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, with no Fe2O3 phase. The proportion of proeutectoid Fe3O4 is 70-80%, the proportion of eutectoid structure is 10-20%, and the proportion of FeO is about 10%. Furthermore, the oxide layer structure contains obvious pre-cracks. Based on this, in pickling rolling, the pickling speed can be increased to 160-180 m / min, avoiding the shortcomings of the original process, such as difficulty in removing the oxide layer, over-pickling, and under-pickling defects. It also eliminates the environmental pollution problem caused by pickling white mist, resulting in excellent surface quality and good technical and economic indicators for the pickled steel strip.

[0033] Furthermore, compared with steel plates produced by conventional deep-drawing structural steel manufacturing processes, the production process adopted in this invention is simple, the efficiency of the pickling process section in pickling and rolling is improved, the overall performance of the product is excellent, and the prospects for promotion and application are good. Attached Figure Description

[0034] Figure 1 An optical micrograph of the steel strip obtained in Example 1;

[0035] Figure 2 The image shows an optical micrograph of the steel strip obtained in Example 2.

[0036] Figure 3 This is an optical micrograph of the steel strip obtained in Comparative Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] This invention provides a method for controlling the iron oxide scale of hot-rolled steel strip with a deep-drawing structure, comprising the following steps:

[0039] After refining the molten steel, a slab is obtained by casting it. The slab is then subjected to homogenization, rough rolling, and finish rolling. After cooling, it is coiled to obtain a steel strip, which is then pickled.

[0040] In this invention, the molten steel is obtained by smelting blast furnace iron in a converter.

[0041] The method used in the converter smelting is any method known to those skilled in the art.

[0042] For example, the converter smelting specifically involves smelting blast furnace iron and smelting furnace charge in a converter to obtain molten steel, and then deoxidizing and alloying the molten steel during the tapping process. The blast furnace iron and smelting furnace charge can be conventional raw materials in the art and are not particularly limited. In the alloying step, aluminum-iron alloys, low-carbon ferromanganese, etc., are added to the molten steel to obtain molten steel (based on the total weight of molten steel, in terms of elemental composition, w%) with the following composition: C ≤0.06, Si 0~0.10, Mn 0.15~0.35, P 0~0.025, S 0~0.010, Als 0.015~0.060, and the remainder being Fe. The smelting time is a conventional smelting time, preferably 35~45 min.

[0043] In this invention, after obtaining molten steel, it is refined. The refining process in this invention sequentially includes LF refining and RF refining.

[0044] In this invention, the LF refining process only involves temperature adjustment of the molten steel and bottom blowing of argon gas into the ladle. Argon gas at a pressure of 200-400 Pa is introduced into the bottom of the ladle for 4-6 minutes, preferably 250-350 Pa for 4.5-5 minutes. The argon gas flow rate is kept low enough to prevent excessive turbulence in the molten steel, thus avoiding secondary oxidation and rapid temperature drop. This allows inclusions in the steel to float to the surface, further improving the cleanliness of the steel. The LF refining process takes 10-25 minutes, preferably 15-20 minutes; the outlet temperature is 1610-1635℃, preferably 1620-1630℃. Any method known to those skilled in the art can be used for LF refining.

[0045] In this invention, the RH refining process includes final deoxidation, molten steel temperature adjustment, and alloying treatment. During alloying, metallic manganese, ferrotitanium, etc., are added to the molten steel after final deoxidation. The RH refining treatment time is 30-40 min, preferably 32-35 min; the outlet temperature is 1590-1615℃, preferably 1600-1610℃. In some embodiments of this invention, based on the chemical composition requirements for deep-drawing steel, the molten steel obtained after RH refining (based on the total weight of molten steel, in terms of elemental composition, w%) has the following composition: C ≤ 0.0050%, Si 0-0.10%, Mn 0.15-0.35%, P 0-0.025%, S 0-0.010%, Als 0.015-0.060%, Ti 0.045-0.075%, with the remainder being Fe. The RH refining method can be any method known to those skilled in the art.

[0046] According to this invention, after refining, the refined molten steel is cast to obtain a slab. The casting is continuous casting, which can be performed using methods known to those skilled in the art. In some embodiments of this invention, the refined molten steel is cast into a pre-heated tundish and then cast into a slab using a continuous casting machine with full process protection. After casting, it can be cooled using conventional methods, such as natural cooling at room temperature.

[0047] Then, according to the present invention, the obtained slab is hot rolled.

[0048] The hot rolling process involves heating the cast slab before rolling it. This heating is typically a homogenization process, where the homogenization temperature refers to the temperature at which the steel billet (i.e., the previously obtained slab) exits the heating furnace. Preferably, the homogenization time is 0.5–1.5 h, more preferably 0.8–1.2 h, and the homogenization temperature is 1200–1240 °C, more preferably 1210–1230 °C. At this temperature, microalloying elements can be fully dissolved, eliminating chemical element segregation caused by dendrite deviation in the cast slab. Simultaneously, the AlN particles formed in the as-cast state are dissolved back, avoiding adverse effects on the microstructure, mechanical properties, and grain orientation from subsequent rolling and annealing processes.

[0049] In this invention, the purpose of the rolling process is to achieve the required hot-rolled thickness for the continuously cast slab, which generally includes roughing and finishing rolling.

[0050] In this invention, the initial rolling temperature of the rough rolling is 1175~1210℃, preferably 1180~1200℃, to ensure that there is no difficult-to-remove fritillary phase on the surface.

[0051] In this invention, the thickness of the intermediate billet obtained after rough rolling is 34~38 mm, preferably 35~36 mm.

[0052] In this invention, the initial rolling temperature of the finishing mill is 1010~1050℃, preferably 1020~1040℃, to ensure the removal of low-melting-point FeO / Fe2SiO4 eutectic compounds from the slab surface and prevent the formation of red rust defects that are unfavorable for pickling after cooling. In this invention, the final rolling temperature refers to the temperature at which the steel strip exits the finishing mill. To ensure uniform thickness and mechanical properties of the finished product and to avoid the formation of Fe2O3 phase during the finishing rolling process, the final rolling temperature should be increased as much as possible. In this invention, a hot-rolled intermediate slab hot-rolling box process is used to maintain specific final rolling temperatures at the head, middle, and tail of the hot-rolled intermediate slab before finishing rolling. Therefore, in this invention, the final rolling temperature of the finishing mill is 900~940℃, preferably 910~930℃. Furthermore, the lower the initial rolling temperature of the finishing mill, the faster the rolling speed and the thinner the oxide layer thickness. Therefore, this invention aims to reduce the initial rolling temperature and increase the rolling speed as much as possible to reduce the oxide layer thickness of the finished product. In this invention, the rolling speed of the finishing mill is 1.10~1.70 m / s, preferably 1.20~1.50 m / s.

[0053] Furthermore, in order to avoid the formation of the edge Fe2O3 phase during the finishing rolling process, the rolling reduction rate of the last two stands in the rolling mill is controlled to prevent the edge FeO from transforming into the Fe2O3 phase. The thickness reduction rates of the last two stands are ≤15% and ≤10%, respectively.

[0054] In some preferred embodiments of the present invention, both the rough rolling and finish rolling processes include a descaling step. The purpose of descaling is to remove the thick iron oxide scale formed on the surface by the combination of iron oxide and oxygen at high temperatures. This technical effect requires ensuring a minimum descaling pressure and a reasonable arrangement of the descaling nozzles. Therefore, in the present invention, the descaling water pressure before rough rolling is 17-19 MPa, preferably 18 MPa; the descaling water pressure before finish rolling is 24-26 MPa, preferably 25 MPa.

[0055] In this invention, the roughing rolling can be done in one pass, while the finishing rolling can be done in multiple passes, preferably 5 to 7 passes, specifically 5, 6, or 7 passes, and more preferably 7 passes.

[0056] Typically, hot-rolled thin steel strips are cooled to adjust their internal microstructure before being coiled. To meet the performance requirements of the finished product, the hot-rolled microstructure must be 100% ferrite (F), with a ferrite grain size of 8.5~10.5. Simultaneously, to improve the stamping performance of the finished product and obtain a good texture orientation, high-temperature coiling is used in the hot rolling process to precipitate Ti(C,N) and AlN particles. This is then followed by suppression of F growth during recrystallization annealing, resulting in a good texture orientation and improved deep-drawing performance.

[0057] Based on this, the cooling method after hot rolling is laminar flow cooling of two sets of centralized manifolds - air cooling - laminar flow cooling of two sets of sparse manifolds.

[0058] In this invention, both the centralized manifold laminar flow cooling and the sparse manifold laminar flow cooling can be configured according to the content known to those skilled in the art.

[0059] This invention utilizes a combination of centralized cooling, air cooling, and finally sparse cooling to effectively control the microstructure of the sheet metal and pre-initiate sheet metal cracks. It is important to note that arbitrarily increasing or decreasing the number of centralized manifold laminar flow cooling and sparse manifold laminar flow cooling groups can prevent the pre-initiation of sheet metal cracks or cause abnormal microstructure in the hot-rolled state, thereby affecting the final microstructure and properties of the finished product.

[0060] In this invention, the water pressure for laminar flow cooling in the centralized manifold is 0.5~0.65 MPa, preferably 0.6 MPa. The cooling ratios of the upper and lower manifolds are 85~95% and 70~80%, respectively. Specifically, the cooling ratio of the upper manifold can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%, and the cooling ratio of the lower manifold can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%. This arrangement is advantageous for forming pre-cracked surface scale while not affecting the microstructure of the hot-rolled state. In some embodiments of this invention, the cooling ratios of the upper and lower manifolds are preferably 90% and 75%, respectively.

[0061] The water pressure for laminar flow cooling in the sparse manifold is 0.5~0.65 MPa, preferably 0.6 MPa. The cooling ratios of the upper and lower manifolds are 45~55% and 45~55%, respectively. The cooling ratio of the upper (or lower) manifold can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or 55%, which is advantageous for controlling the structure and microstructure of the hot-rolled sheet metal. In some embodiments of the invention, the cooling ratios of the upper and lower manifolds are preferably 50% and 50%, respectively.

[0062] In some embodiments of the present invention, the spacing between the cooling manifolds in the two sets of centralized manifold laminar flow cooling is approximately 5 m, specifically 4.5 m, 5 m, 5.5 m, or 6 m, preferably 5 m. The air cooling length between the two sets of centralized manifold laminar flow cooling and the two sets of sparse manifold laminar flow cooling is approximately 10 m, specifically 8 m, 9 m, 10 m, 11 m, or 12 m, preferably 10 m. Furthermore, the spacing between the cooling manifolds in the two sets of sparse manifold laminar flow cooling is approximately 10 m, specifically 8 m, 9 m, 10 m, 11 m, or 12 m, preferably 10 m. In the present invention, the steel strip carried out by the rolling mill generally undergoes pre-oxidation layer cracking under very short time and high cooling rate, and is cooled to the coiling temperature before coiling. Based on this, the cooling rate of the two sets of centralized manifold laminar flow cooling is 25~45 ℃ / s, preferably 30~40 ℃ / s; the cooling rate of the air cooling is 5~10 ℃ / s, preferably 6~8 ℃ / s; the cooling rate of the two sets of sparse manifold laminar flow cooling is 15~30 ℃ / s, preferably 18~25 ℃ / s; and then cooled to a winding temperature of 700~740 ℃, preferably 710~730 ℃.

[0063] After winding, the present invention can test the thickness and structure of the iron oxide scale of the obtained steel strip using GB / T13298 Metal Microstructure Inspection Method.

[0064] The results showed that the oxide layer thickness in the steel strip was ≤11 μm. The oxide layer thickness could be measured using methods known to those skilled in the art. The test sample could be a polished or etched metallographic sample. The etchant for the sample was a 1-2% hydrochloric acid-alcohol solution, and the etching time was 5-8 s, for example, the metallographic method in GB / T 6394.

[0065] In this invention, the oxide layer structure is proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, with no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 is 70-80%, the proportion of eutectoid structure is 10-20%, and the proportion of FeO is 5-10%. The oxide layer structure contains obvious pre-cracks, which effectively promotes the removal of iron oxide scale from pickling. The oxide layer structure can be measured using methods known to those skilled in the art. The test sample can be a polished or etched metallographic sample. The etchant is a 1-2% hydrochloric acid-alcohol solution, and the etching time is 5-8 seconds, for example, according to GB / T 6394 metallographic method.

[0066] The hot-rolled iron oxide scale control method for deep-drawn steel strip provided by this invention ensures that the oxide layer thickness and structure of the steel plate fully meet the technical requirements.

[0067] In this invention, after winding is completed, acid rolling is performed.

[0068] In this invention, the pickling and rolling process can employ various conventional methods. Typically, hot-rolled thin steel strips are welded together at the head of a pickling and rolling mill to form a continuous strip. After straightening, tension straightening to remove phosphorus, pickling, alkali washing, drying, and edge trimming, the strip is continuously rolled. The cold rolling mill used in this continuous rolling process can be any conventional cold rolling mill, such as a 4-5 stand cold rolling mill. After pickling and rolling, the thickness of the steel plate is reduced to the thickness of the raw material in the bell-type annealing mill. The cold rolling reduction rate is approximately 70%, but can be 60-85%, preferably 65-75%, and more preferably 70%. The pickling process speed is 160-180 m / min, and the tension straightening elongation rate is 1.00-1.50%. Surface iron oxide scale is removed, and surface quality is improved. The pickling and rolling process can employ methods and techniques known to those skilled in the art.

[0069] In summary, the thinning of the oxide layer in the deep-drawing steel strip of this invention, the presence of an FeO phase in the oxide layer structure that readily reacts with hydrochloric acid, and the introduction of pre-cracks in the oxide layer all increase the pickling reaction efficiency, significantly improving the unit's production efficiency. The finished product exhibits excellent technical and economic indicators and superior surface quality, effectively meeting the raw material requirements of the deep-drawing and leveling unit. The production technology of this invention effectively increases the pickling capacity and improves the pickling effect of the strip steel, significantly reducing surface quality defects. Under current favorable market conditions, this technology can effectively enhance the production capacity of Panzhihua Iron and Steel Group's cold-drawn products and improve their surface quality, demonstrating promising prospects for widespread application.

[0070] To further illustrate the present invention, the following embodiments provide a detailed description. In the following embodiments of the present invention, "semi-molten iron" refers to molten iron after vanadium extraction from blast furnace iron.

[0071] The methods for detecting the chemical composition are as follows: Spark source atomic emission spectrometry analysis method for carbon steel and medium and low alloy steel, national standard GB / T4336; Determination of low carbon content of non-alloy steel - Part 2 - Infrared absorption method after combustion in an induction furnace (preheated), national standard GB / T 20126.

[0072] The method for detecting the thickness, structure, and microstructure of iron oxide scale in this invention is GB / T13298, "Metallic Microstructure Inspection Method".

[0073] Example 1

[0074] a. Steelmaking: The smelting equipment is a top-blown converter. Semi-steel from vanadium extraction in blast furnace molten iron is used as raw material. At a temperature of 1374℃, steelmaking auxiliary materials are added, and the mixture is smelted to 1676℃ before being tapped into a ladle. When 1 / 3 of the steel has been tapped, 400 kg of ferroaluminum is added for pre-deoxidation, followed by 450 kg of low-carbon ferromanganese for alloying. The ladle is then subjected to bottom-blowing argon gas treatment at a pressure of 350 Pa for 4 minutes on a small platform behind the furnace. The resulting molten steel (based on total weight, in elemental composition) has the following composition: C: 0.045, Si: 0.01, Mn: 0.32, P: 0.016, S: 0.008, Als: 0.035, with the remainder being Fe.

[0075] b. LF electric heating: Argon gas at a certain pressure (400 Pa) is introduced into the bottom of the molten steel ladle for 5 minutes. The flow rate of argon gas is such that the molten steel does not overflow. The LF treatment outlet temperature is 1622℃.

[0076] c. RH Treatment: Final deoxidation, steel temperature conditioning, and alloying are performed. The alloying sequence is ferroaluminum, metallic manganese, and ferrotitanium. The RH treatment time is 35 minutes, and the outlet temperature is 1597℃. The molten steel obtained after RH treatment (based on the total weight of molten steel, in terms of elemental composition, w%) is: C: 0.0025, Si: 0.01, Mn: 0.31, P: 0.016, S: 0.008, Als: 0.034, Ti: 0.062, with the remainder being Fe;

[0077] d. Continuous casting: The molten steel ladle is transported to the casting position. A sliding Al-based stopper rod at the bottom of the ladle allows the molten steel to automatically flow into the tundish. From there, it is guided through the Al-based stopper rod to the crystallizer for continuous casting. The entire process uses protective slag for casting protection. After casting, the steel is cooled to a 200 mm thick hot-rolled slab.

[0078] d. Hot rolling: The hot-rolled slab was heated to 1235℃ for 40 min. The roughing mill opening temperature was 1180℃, the roughing mill descaling pressure was 17 MPa, the finishing mill descaling pressure was 26 MPa, the finishing mill opening temperature was 1028℃, the finishing mill opening rolling speed was 1.4 m / s, the thickness reduction rates of the last two mill stands were 13% and 8% respectively, and the final rolling temperature was 925℃. The cooling method consisted of two sets of centralized cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 90% / 75% respectively) - air cooling - two sets of sparse laminar flow cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 50% / 50% respectively), and the coiling temperature was 710℃. The thickness after roughing was 34 mm, and the finishing mill had 7 passes, resulting in a thickness of 3.0 mm.

[0079] e. Pickling and rolling: The steel strip is rolled to a thickness of 1.0 mm by the pickling and rolling unit, with a cold rolling reduction rate of 67.7%, a tension leveling elongation rate of 1.3% by the pickling unit, and a process speed of 180 m / min.

[0080] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The oxide layer thickness on the strip surface was 7.5 μm. The oxide layer structure consisted of proeutectoid Fe3O4 + eutectoid (Fe + Fe3O4) + FeO. No Fe2O3 phase was present in the oxide layer. The proportion of proeutectoid Fe3O4 was 80%, the proportion of eutectoid tissue was 15%, and the proportion of FeO tissue was 5%. Obvious pre-cracks were observed in the oxide layer structure (see attached figure). Figure 1 The surface quality of the steel strip after pickling is good, with no residual iron oxide scale defects, which meets the technical requirements for pickling raw materials of deep-drawn steel strip.

[0081] Example 2

[0082] The preparation method is basically the same as in Example 1, except that the composition of the molten steel obtained after RH treatment is C: 0.0030, Si: 0.01, Mn: 0.28, P: 0.019, S: 0.006, Als: 0.045, Ti: 0.058, with the remainder being Fe (Wt, %). The hot-rolled steel plates produced using the aforementioned molten steel had a homogenization temperature of 1228℃ and a homogenization time of 32 min. The roughing rolling start temperature was 1175℃, the roughing descaling pressure was 19 MPa, the finishing rolling descaling pressure was 24 MPa, the finishing rolling start temperature was 1040℃, the finishing rolling start speed was 1.35 m / s, the thickness reduction rates of the last two mill stands were 12% and 8%, respectively, and the final rolling temperature was 915℃. The cooling method consisted of two sets of centralized cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 90% / 75%) - air cooling - two sets of sparse laminar flow cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 50% / 50%), and the coiling temperature was 720℃. The thickness after roughing was 35 mm, and the finishing rolling had 7 passes, resulting in a thickness of 4.1 mm. The steel strip is rolled to a thickness of 1.2 mm by the pickling and rolling mill, with a cold rolling reduction rate of 70.7%, a tension leveling elongation rate of 1.5% by the pickling mill, and a process speed of 165 m / min.

[0083] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The oxide layer thickness on the strip surface was 8.5 μm. The oxide layer structure was proeutectoid Fe3O4 + eutectoid (Fe + Fe3O4) + FeO. No Fe2O3 phase was present in the oxide layer. The proportion of proeutectoid Fe3O4 was 80%, the proportion of eutectoid structure was 10%, and the proportion of FeO structure was 10%. Obvious pre-cracks were present in the oxide layer structure. Figure 2 The surface quality of the steel strip after pickling is good, with no residual iron oxide scale defects, which meets the technical requirements for pickling raw materials of deep-drawn steel strip.

[0084] Comparative Example

[0085] The preparation method is basically the same as in Example 1, except that the steel obtained after RH treatment has the following composition: C: 0.0027, Si: 0.01, Mn: 0.30, P: 0.015, S: 0.004, Als: 0.042, Ti: 0.063, with the remainder being Fe (Wt, %). Hot-rolled steel plates produced from this steel were manufactured with a roughing rolling temperature of 1145℃, a finishing rolling temperature of 1080℃, and a finishing rolling speed of 0.90 m / s. The thickness reduction rates of the last two mill stands were 18% and 13%, respectively. The cooling method employed two sets of front-end laminar flow cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratio 75% / 50%) water-cooling-air cooling. The finishing rolling had 7 passes, and the finished thickness was 4.1 mm. The steel strip is rolled to a thickness of 1.2 mm by the pickling and rolling mill, and the elongation of the pickling and straightening unit is 1.5%, with a process speed of 110 m / min.

[0086] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The oxide layer thickness on the strip surface was 15 μm, and the oxide layer structure was Fe2O3 + proeutectoid Fe3O4 + FeO, with the proportion of proeutectoid Fe3O4 being 90% and the proportion of FeO being approximately 10%. No pre-existing cracks were found in the oxide layer structure. Figure 3 The surface quality of the steel strip after pickling is poor, with a large amount of pickling iron oxide scale defects remaining, which does not meet the technical requirements for pickling raw materials of deep-drawn steel strip.

[0087] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling the iron oxide scale of hot-rolled steel strip with a deep-drawing structure, characterized in that, Includes the following steps: After refining the molten steel, a slab is obtained by casting it. The slab is then subjected to homogenization, rough rolling, and finish rolling. After cooling, it is coiled to obtain a steel strip, which is then pickled. The cooling method is two sets of centralized manifold laminar flow cooling - air cooling - two sets of sparse manifold laminar flow cooling; The water pressure for the centralized manifold laminar flow cooling is 0.5~0.65 MPa, wherein the cooling ratio of the upper manifold and the lower manifold is 85~95% and 70~80%, respectively; the cooling rate of the two sets of centralized manifold laminar flow cooling is 25~45 ℃ / s; and the distance between the cooling manifolds in the two sets of centralized manifold laminar flow cooling is 4.5~6 m. The air cooling length between the two sets of centralized manifold laminar flow cooling and the two sets of sparse manifold laminar flow cooling is 8~12 m; the air cooling rate is 5~10 ℃ / s; The water pressure for the sparse manifold laminar flow cooling is 0.5~0.65 MPa, wherein the cooling ratio of the upper manifold and the lower manifold is 45~55% and 45~55%, respectively; the distance between the cooling manifolds in the two sets of sparse manifold laminar flow cooling is 8~12m; and the cooling rate of the two sets of sparse manifold laminar flow cooling is 15~30 ℃ / s.

2. The method for controlling hot-rolled iron oxide scale according to claim 1, characterized in that, The molten steel is obtained by smelting blast furnace iron in a converter. The refining process includes LF refining and RF refining; The chemical composition of the refined molten steel, in terms of elements, includes: C ≤ 0.0050%, Si 0~0.10%, Mn 0.15~0.35%, P 0~0.025%, S 0~0.010%, Als 0.015~0.060%, Ti 0.045~0.075%, with the remainder being Fe.

3. The method for controlling hot-rolled iron oxide scale according to claim 1 or 2, characterized in that, The temperature for heat equalization is 1200~1240℃, and the time is 0.5~1.5 h.

4. The method for controlling hot-rolled iron oxide scale according to claim 1, characterized in that, The rough rolling process includes a descaling step, wherein the water pressure for descaling is 17-19 MPa. The initial rolling temperature of the roughing mill is 1175~1210℃; The thickness of the intermediate billet obtained after rough rolling is 34~38 mm.

5. The method for controlling hot-rolled iron oxide scale according to claim 1, characterized in that, The process before finishing rolling includes a descaling step, wherein the water pressure for descaling is 24~26 MPa. The initial rolling temperature of the finishing mill is 1010~1050℃, the final rolling temperature is 900~940℃, and the rolling speed of the finishing mill is 1.10~1.70 m / s. The thickness reduction rates of the last two stands in the finishing mill are ≤15% and ≤10%, respectively. The finishing rolling process consists of 5 to 7 passes.

6. The method for controlling hot-rolled iron oxide scale according to claim 1, characterized in that, The winding temperature is 700~740℃; The thickness of the oxide layer in the steel strip is ≤11 μm, and its structure is proeutectoid Fe3O4 + eutectoid structure + FeO. The oxide layer has no Fe2O3 phase, and the eutectoid structure includes Fe + Fe3O4. The proportion of proeutectoid Fe3O4 is 70-80%, the proportion of eutectoid structure is 10-20%, and the proportion of FeO is 5-10%.

7. The method for controlling iron oxide scale in hot rolling according to claim 1, wherein the pickling speed in the pickling rolling is 160~180 m / min, and the tensile leveling elongation is 1.00~1.50%; The cold rolling reduction rate in the pickling process is 60-85%.

8. A deep-drawing steel strip with a hooded design, characterized in that, The hot-rolled iron oxide scale of the deep-drawn steel strip is controlled by the control method described in any one of claims 1 to 7.

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