A method of hot rolled mill scale control for a sheathed flux cored wire steel strip and a sheathed flux cored wire steel strip

Abstract

This invention provides a method for controlling the iron oxide scale on hot-rolled steel strips used for coated flux-cored welding wire, and a type of coated flux-cored welding wire steel strip. This control method, through a specific cooling method in the hot rolling process, combined with homogenization, rough rolling, finish rolling, and coiling processes, achieves an oxide layer thickness ≤10μm in the steel strip. The oxide layer structure is proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, with no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 is approximately 20%, the proportion of eutectoid structure is approximately 70%, and the proportion of FeO is approximately 10%. Furthermore, the oxide layer structure exhibits obvious pre-cracks. In pickling, this invention allows for a pickling process speed of 170~190 m / min, avoiding the shortcomings of the original process, such as difficulty in removing the oxide layer and the tendency for over-pickling. 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 strips used for coated and decoyed flux-cored welding wire, and a type of steel strip used for coated and decoyed flux-cored welding wire. Background Technology

[0002] The steel used for flux-cored welding wire typically requires high purity, excellent drawability, and good performance uniformity. The surface quality of the strip directly affects the smooth operation of the wire-making process. After multiple drawing passes, the welding wire should have a uniform cross-section and be free of defects. Therefore, surface quality control is crucial in the entire process control system for flux-cored welding wire steel production, and controlling iron oxide scale in the hot rolling process is one of the key aspects. To improve the surface quality of the finished product assembled in the subsequent bell-type annealing process, residual iron oxide scale must be completely removed during the pickling stage; otherwise, the surface quality of the finished product will deteriorate.

[0003] Hot-rolled raw materials for coated and stripped cored welding wire are typically designed as micro-carbon aluminum-killed steel + austenitic zone final rolling + low-temperature coiling process. The conventional process results in a surface oxide layer thickness of 14-20 μm, with a structure consisting of a high proportion of proeutectoid Fe3O4 + eutectoid (Fe + Fe3O4) + Fe2O3. Fe2O3 reacts most slowly with hydrochloric acid during the pickling process and is the most difficult to remove. The Fe3O4 in the oxide layer is relatively dense and has low chemical reaction efficiency with hydrochloric acid; the surface Fe2O3 phase further reduces the pickling reaction efficiency. Therefore, in actual production of coated and stripped cored welding wire, only low-speed, high-concentration, high-temperature hydrochloric acid production (process speed 110 m / min) can be used. This is detrimental to the production efficiency of the cold rolling process and also leads to environmental problems such as pickling white mist (poor sealing of the acid bath and acid evaporation) and localized over-pickling of the strip, reducing the strip yield and increasing the environmental burden 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 on hot-rolled steel strip for coated flux-cored welding wire, and a type of steel strip for coated flux-cored welding wire. This control method not only effectively improves the production capacity of the pickling process, but also enhances the pickling effect of the strip steel.

[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 hot-rolled iron oxide scale of steel strip used for coated flux-cored welding wire, 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] The cooling method is three sets of centralized manifold laminar flow cooling - air cooling - four sets of sparse manifold laminar flow cooling;

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

[0010] 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 35~45% and 35~45%, respectively.

[0011] Preferably, the cooling length of the three sets of centralized manifold laminar flow cooling is 12~16 m.

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

[0013] Preferably, the cooling length of the four sets of sparse manifold laminar flow cooling is 16~24 m.

[0014] Preferably, the cooling rate of the centralized manifold laminar flow cooling is 30~50 ℃ / s.

[0015] Preferably, the air cooling rate is 5~10℃ / s.

[0016] Preferably, the cooling rate of the sparse manifold laminar flow cooling is 15~35 ℃ / s.

[0017] Preferably, the temperature for heat equalization is 1185~1225℃ and the time is 0.5~1.5 h.

[0018] Preferably, the initial rolling temperature of the rough rolling is 1175~1200℃.

[0019] Preferably, the initial rolling temperature of the finishing mill is 1000~1030℃, the initial rolling speed is 1.4~1.6 m / s, and the final rolling temperature is 860~900℃.

[0020] Preferably, the thickness reduction rates of the last two mill stands in the finishing mill are ≤15% and ≤10%, respectively.

[0021] Preferably, the finishing rolling process involves 5 to 7 passes.

[0022] Preferably, the winding temperature is 530~570℃.

[0023] Preferably, after obtaining the slab, the slab is subjected to homogenization, descaling, rough rolling, descaling, finish rolling, cooling, coiling and pickling in sequence.

[0024] Preferably, the dephosphorization water pressure before rough rolling is 17~19 MPa.

[0025] Preferably, the dephosphorization water pressure before finishing rolling is 24~26 MPa.

[0026] Preferably, the oxide layer thickness in the steel strip is ≤10μm, and the structure of the oxide layer is proeutectoid Fe3O4 + eutectoid structure + FeO, with no Fe2O3 phase component in the oxide layer; the eutectoid structure includes Fe + Fe3O4;

[0027] The proportion of proeutectoid Fe3O4 is 15-25%, the proportion of eutectoid structure is 65-75%, and the proportion of FeO is 0-20%.

[0028] More preferably, the proportion of preeutectoid Fe3O4 is 15-20%, the proportion of eutectoid structure is 70-75%, and the proportion of FeO is 5-15%.

[0029] Preferably, the pickling speed in the pickling process is 170~190 m / min, and the tensile straightening elongation is 1.00~1.50%.

[0030] Preferably, the cold rolling reduction rate in the pickling process is 70-80%.

[0031] More preferably, the cold rolling reduction rate in the pickling process is 75-80%.

[0032] Preferably, the molten steel is obtained by converter smelting of blast furnace iron; the refining includes LF refining and RF refining;

[0033] Preferably, the chemical composition of the refined molten steel, calculated as elements, includes: C ≤ 0.025%, Si 0~0.03%, Mn 0.15~0.25%, P 0~0.015%, S 0~0.010%, Als 0.015~0.050%, with the remainder being Fe.

[0034] Secondly, the present invention provides a steel strip for coated and decoy wire, wherein the hot-rolled iron oxide scale on its surface is controlled by the above-mentioned control method.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] This invention provides a method for controlling the iron oxide scale of hot-rolled steel strips used for coated flux-cored welding wire. By using a specific cooling method in the hot rolling process, combined with homogenization, rough rolling, finish rolling, and coiling processes, the resulting steel strip has an oxide layer thickness of ≤10 μm. The oxide layer structure is proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO. The oxide layer has no Fe2O3 phase component, with approximately 20% proeutectoid Fe3O4, approximately 70% eutectoid structure, and approximately 10% FeO. Furthermore, there are obvious pre-cracks in the oxide layer structure.

[0037] Based on this, the speed of the pickling process section in the pickling rolling process of this invention can be increased to 170~190 m / min, avoiding the shortcomings of the original process technology such as the oxide layer being difficult to remove, the easy formation of over-pickling and under-pickling defects, and there is no problem of environmental pollution from pickling white fog. The surface quality of the steel strip after pickling is excellent, and the technical and economic indicators are good.

[0038] Furthermore, compared with steel plates produced by conventional steel manufacturing processes for coated flux-cored welding wire, the steel strip produced by the above-mentioned control method adopted in this invention has a simpler process, improved efficiency of the pickling process unit, excellent overall product performance, and good prospects for promotion and use. Attached Figure Description

[0039] Figure 1 This is a morphological diagram of the pre-cracks in the hot-rolled iron oxide scale of the steel used for the coated flux-cored welding wire in Embodiment 1 of the present invention.

[0040] Figure 2 This is a morphological diagram of the pre-cracks in the hot-rolled iron oxide scale of the steel used for the coated flux-cored welding wire in Embodiment 2 of the present invention.

[0041] Figure 3 This is a morphological image of the hot-rolled iron oxide scale of the coated wire used in Comparative Example 1 of the present invention, without pre-existing cracks. Detailed Implementation

[0042] 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.

[0043] This invention provides a method for controlling the iron oxide scale of hot-rolled steel strip used in flux-cored welding wire, comprising the following steps:

[0044] After refining the molten steel, a slab is cast. 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.

[0045] In this invention, the molten steel is obtained by smelting blast furnace iron in a converter.

[0046] Specifically, the converter smelting involves smelting blast furnace iron and smelting charge in a converter to obtain molten steel, followed by pre-deoxidation of the molten steel during tapping. The resulting molten steel (based on total weight, in elements, wt%) has the following composition: C: 0.03~0.06, Si: 0~0.03, Mn: 0~0.15, P: 0~0.015, S: 0~0.010, Als: 0.015~0.050, with the remainder being Fe. The smelting time is the conventional smelting time, preferably 35~45 minutes. The converter smelting process employs techniques well-known to those skilled in the art.

[0047] In this invention, after obtaining molten steel, it is refined. The refining preferably includes LF refining and RH refining.

[0048] 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 at a pressure of 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, and the outlet temperature is 1610-1625℃, preferably 1615-1620℃. The LF refining technique used is known to those skilled in the art.

[0049] The RH refining process involves decarburization and alloying. In the alloying step, metallic manganese is added to the molten steel after final decarburization. The RH process outlet temperature is 1575~1590℃, preferably 1580~1585℃. The molten steel obtained after RH treatment (based on total weight of molten steel, in wt% of elemental components) has the following composition: C: ≤0.025, Si: 0~0.03, Mn: 0.15~0.25, P: 0~0.015, S: 0~0.010, Als: 0.015~0.050, with the remainder being Fe. The RH refining technique used is known to those skilled in the art.

[0050] According to this invention, after refining, the refined molten steel is cast to obtain a slab. The casting is continuous casting (abbreviated as: continuous casting).

[0051] The continuous casting process can employ methods known to those skilled in the art. In this invention, refined molten steel is poured into a pre-heated tundish and then cast into slabs using a slab continuous casting machine with full process protection. After casting, it can be cooled using conventional methods, such as natural cooling at room temperature.

[0052] Then, according to the present invention, the obtained slab is hot-rolled.

[0053] In this invention, the hot rolling step involves reheating the cast slab before rolling. In this invention, the reheating temperature, i.e., the homogenization temperature, refers to the temperature at which the billet exits the heating furnace. Preferably, the homogenization temperature is 1185~1225℃, more preferably 1190~1220℃. Heating at this temperature allows for sufficient solid solution of microalloying elements, eliminating chemical element segregation caused by dendrite slabs in the cast slab; simultaneously, it allows the AlN particles formed in the as-cast state to dissolve back, avoiding the adverse effects of rolling and annealing processes on the microstructure, mechanical properties, and grain orientation. The homogenization time is 0.5~1.5 h, preferably 0.8~1.2 h.

[0054] In this invention, the purpose of the rolling process is to achieve the required hot-rolled thickness for the continuously cast slab.

[0055] In this invention, the initial rolling temperature of the hot rolling, i.e. the initial rolling temperature of the rough rolling, is 1175~1200℃, preferably 1180~1190℃, to ensure that there is no difficult-to-remove iron olivine on the surface.

[0056] In this invention, the initial rolling temperature of hot-rolled finishing mill is to ensure the removal of low-melting-point FeO / Fe2SiO4 eutectic compounds from the slab surface, preventing the formation of red rust defects that are unfavorable for pickling after cooling. 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 the Fe2O3 phase during finishing milling, the final rolling temperature should be increased as much as possible. This invention employs a hot-rolled intermediate slab hot-rolling box process technology to maintain specific final rolling temperatures at the head, middle, and tail sections of the hot-rolled intermediate slab before finishing milling. The lower the initial rolling temperature, the faster the rolling speed, and the thinner the oxide layer. Therefore, the initial rolling temperature should be reduced as much as possible, and the rolling speed increased to reduce the oxide layer thickness of the finished product. In summary, in some embodiments of the present invention, the finishing rolling start temperature is 1000~1030℃, preferably 1005~1025℃; the finishing rolling start speed is 1.4~1.6 m / s, preferably 1.5 m / s; and the finishing rolling temperature is 860~900℃, preferably 870~890℃.

[0057] In order to avoid the formation of the edge Fe2O3 phase in the finishing rolling process, the rolling reduction rate of the last two stands is controlled to prevent the edge FeO from transforming into the Fe2O3 phase. Therefore, the thickness reduction rates of the last two stands in the finishing rolling process are ≤15% and ≤10%, respectively, preferably ≤13% and ≤8%.

[0058] In some preferred embodiments of the present invention, descaling steps are included before rough rolling and before finish rolling. The purpose of descaling is to remove the thick iron oxide scale formed on the surface by bonding with oxygen at high temperatures. Generally, it is necessary to ensure a minimum descaling pressure and a reasonable arrangement of the descaling nozzle positions. Therefore, the descaling water pressure before rough rolling is 17~19 MPa, preferably 17.5~18.5 MPa; the descaling water pressure before finish rolling is 24~26 MPa, preferably 24.5~25 MPa.

[0059] To meet the performance requirements of the finished product, the hot-rolled microstructure should be F + a small amount of P + a small amount of Fe3C, with a ferrite grain size of 10.0~11.5. At the same time, in order to improve the stamping performance of the finished product and obtain a good texture orientation, it is necessary to use low-temperature coiling in hot rolling to suppress the precipitation of AlN particles, and then slowly precipitate AlN during the recrystallization annealing process to obtain a good texture orientation and improve the forming performance.

[0060] Furthermore, to obtain pre-formed oxide layer cracks, the cooling mode of this invention is as follows: after rolling, three sets of centralized manifold laminar flow cooling (water pressure 0.5~0.65 MPa, where the cooling ratio of the upper and lower manifolds is 85~95% and 70~80%, respectively) - air cooling - four sets of sparse manifold laminar flow cooling (water pressure 0.5~0.65 MPa, where the cooling ratio of the upper and lower manifolds is 35~45% and 35~45%, respectively). The cooling water length of each manifold is about 5 m, and the air cooling interval between the centralized manifold laminar flow cooling and the sparse manifold laminar flow cooling is about 10 m. It should be noted that the above cooling mode is specifically selected for this invention. Arbitrarily increasing or decreasing the number of centralized manifold laminar flow cooling or sparse manifold laminar flow cooling sets will adversely affect the results. At the same time, the order of centralized cooling, air cooling, and sparse cooling cannot be arbitrarily changed.

[0061] In this invention, the water pressure for laminar flow cooling in the three sets of centralized manifolds 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 beneficial for the formation of pre-cracked surface oxide 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 100% and 80%, respectively.

[0062] In this invention, the water pressure for laminar flow cooling in the four sets of sparse manifolds is 0.5~0.65 MPa, preferably 0.6 MPa. The cooling ratios of the upper and lower manifolds are 35~45% and 35~45%, respectively. The cooling ratio of the upper (or lower) manifold can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%, which is advantageous for controlling the structure and microstructure of the hot-rolled iron oxide scale. In some embodiments of this invention, the cooling ratios of the upper and lower manifolds are preferably 40% and 40%, respectively.

[0063] In this invention, the cooling length of the three sets of centralized manifold laminar flow cooling is 12-16 m, preferably 13-14 m; the air cooling length between the three sets of centralized manifold laminar flow cooling and the four sets of sparse manifold laminar flow cooling is 8-12 m, preferably 9-10 m; and the cooling length of the four sets of sparse manifold laminar flow cooling is 16-24 m, preferably 18-20 m.

[0064] In this invention, the steel strip exiting the rolling mill undergoes pre-oxidation layer cracking at a very short time and a very high cooling rate before being cooled to the coiling temperature for coiling. Therefore, the centralized cooling rate is 30~50℃ / s, preferably 35~45℃ / s; the air cooling rate is 5~10℃ / s, preferably 6~8℃ / s; the sparse laminar flow cooling rate is 15~35℃ / s, preferably 20~30℃ / s; and then cooled to the coiling temperature of 530~570℃, preferably 540~560℃.

[0065] 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.

[0066] It should be noted that this invention utilizes a specific cooling method—first three groups of centralized cooling, then air cooling, and finally four groups of sparse cooling—which is beneficial for controlling the microstructure of the sheet metal and pre-inducing sheet metal cracks. It is important to note that arbitrarily increasing or decreasing the number of groups of centralized manifold laminar flow cooling and sparse manifold laminar flow cooling can lead to the inability to pre-induce sheet metal cracks or cause abnormal microstructure in the hot-rolled state, thereby affecting the final microstructure and properties of the finished product.

[0067] 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.

[0068] The results showed that the oxide layer thickness of the hot-rolled iron oxide scale of the steel strip used for the coated flux-cored welding wire of the present invention is ≤10 μm. The oxide layer thickness can be measured by methods known to those skilled in the art. The test sample can be a polished or etched metallographic sample. The sample etchant is a 1~2% hydrochloric acid alcohol solution, and the etching time is 5~8 s, for example, GB / T 6394 metallographic method.

[0069] The method for controlling the oxide scale of hot-rolled steel strip for coated flux-cored welding wire of the present invention comprises a proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO oxide layer with no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 is approximately 20%, the proportion of eutectoid structure is approximately 70%, and the proportion of FeO is approximately 10%. Pre-existing cracks are present in the oxide layer structure. Preferably, the proportion of proeutectoid Fe3O4 is 15-25%, the proportion of eutectoid structure is 65-75%, and the proportion of FeO is 0-20%. More preferably, the proportion of proeutectoid Fe3O4 is 15-20%, the proportion of eutectoid structure is 70-75%, and the proportion of FeO is 5-15%.

[0070] 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 for the sample is a 1-2% hydrochloric acid-alcohol solution, and the etching time is 5-8 s, for example, GB / T 13298 Method for the Examination of Metal Microstructure.

[0071] The oxide layer thickness and structure of the steel plate provided by the method for controlling the iron oxide scale of hot-rolled steel strip for coated flux-cored welding wire fully meet the technical requirements.

[0072] In this invention, after winding is completed, acid rolling is performed.

[0073] 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 the 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. Various conventional cold rolling mills can be used, such as 4-5 stand cold rolling mills. 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 70-80%, preferably 75%. The pickling process speed is 170-190 m / min. The tension straightening elongation rate during pickling 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.

[0074] In summary, in some complete embodiments of the present invention, the process flow of the method for controlling the iron oxide scale of hot-rolled steel strip for flux-cored welding wire is as follows:

[0075] Converter smelting → LF refining → RH refining → continuous casting → reheating → descaling → rough rolling → descaling → finish rolling → cooling → coiling → pickling.

[0076] This invention employs the above-mentioned technical solution, which pre-forms oxide layer cracks on the surface of the steel strip, effectively promoting the removal of iron oxide scale during pickling. After production, surface quality inspection results show that the steel used for coated and stripped flux-cored welding wire produced by this method exhibits excellent pickling surface quality, with the pickling process speed increased to over 170-190 m / min, resulting in good technical and economic indicators for the finished product.

[0077] In summary, the thinning of the oxide layer in the steel strip used for the stripped flux-cored welding wire, the introduction of the FeO phase into the oxide layer structure, and the pre-initiated cracks in the oxide layer, all in this invention, increase the pickling reaction efficiency of the pickling process and significantly improve the pickling quality of the product. This effectively meets the raw material requirements of the stripping-leveling unit. Therefore, by adopting the above-mentioned technologies of this invention, on the one hand, the pickling capacity of the pickling process is effectively improved, and on the other hand, the pickling effect of the strip steel is enhanced, significantly promoting the reduction of surface quality defects in the strip steel. Under the current favorable market conditions, this invention can effectively improve the production capacity of Panzhihua Iron and Steel Group's cold-rolled products and improve the surface quality level of the products, showing good prospects for widespread application.

[0078] To further illustrate the present invention, the following embodiments provide a detailed description. In the following embodiments of the present invention, "semi-steel" refers to molten iron after vanadium extraction from blast furnace iron.

[0079] The chemical composition detection methods in this invention are spark source atomic emission spectrometry analysis method for carbon steel and medium and low alloy steel, with national standard GB / T4336; and determination of low carbon content of non-alloy steel, part 2: infrared absorption method after combustion in an induction furnace (preheated), with national standard GB / T 20126-2006.

[0080] The method for detecting the thickness, structure, and microstructure of iron oxide scale in this invention is GB / T13298, "Metallic Microstructure Inspection Method".

[0081] Example 1

[0082] a. Steelmaking: The smelting equipment is a top-blown converter. Semi-steel from vanadium extraction in blast furnace hot metal is used as raw material. The temperature is 1364℃, and steelmaking auxiliary materials are added. The mixture is smelted to 1660℃ and tapped into a ladle. When 1 / 3 of the steel has been tapped, 400 kg of aluminum-iron pre-deoxidizer is added. The ladle is then subjected to bottom-blowing argon gas treatment at a pressure of 300 Pa for 4 minutes on a small platform behind the furnace. The resulting molten steel (based on total weight, in elemental form) contains: C: 0.05, Si: 0.01, Mn: 0.10, P: 0.017, S: 0.006, Als: 0.025, with the remainder being Fe.

[0083] b. LF electric heating: Argon gas at a certain pressure (350 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 1612℃.

[0084] c. RH Treatment: Decarburization and alloying are performed, with the alloying sequence being aluminum-iron and metallic manganese. The RH treatment time is 25 minutes, and the outlet temperature is 1586℃. The molten steel obtained after RH treatment (based on the total weight of molten steel, in terms of elemental composition, w%) is: C: 0.020, Si: 0.01, Mn: 0.28, P: 0.017, S: 0.006, Als: 0.042, with the remainder being Fe;

[0085] 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.

[0086] d. Hot rolling: The hot-rolled slab homogenization temperature is 1215℃, the homogenization time is 30 min, the roughing rolling start temperature is 1185℃, the roughing rolling descaling pressure is 17.1 MPa, the finishing rolling descaling water pressure is 24 MPa, the finishing rolling start temperature is 1030℃, the finishing rolling start speed is 1.4 m / s, the thickness reduction rates of the last two mill stands are 13% and 8% respectively, and the final rolling temperature is 885℃; the cooling method adopts three sets of centralized cooling after rolling (water pressure 0.6 MPa, upper / lower manifold cooling ratio is 90% / 80% respectively) - air cooling - four sets of sparse laminar flow cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratio is 40% / 40% respectively); the coiling temperature is 555℃. The thickness after roughing rolling is 34 mm, the finishing rolling has 7 rolling passes, and the thickness after finishing rolling is 4.0 mm;

[0087] 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 75%, a straightening elongation rate of 1.2% by the pickling unit, and a process speed of 190 m / min.

[0088] The prepared hot-rolled strip steel underwent oxide layer structure and thickness testing. The oxide layer thickness on the strip steel surface was 7.0 μm, and the oxide layer structure consisted of proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, with no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 was 20%, the proportion of eutectoid structure was 75%, and the proportion of FeO structure was 5%. Pre-existing cracks were present in the oxide layer structure. The surface quality of the strip steel after pickling was good, with no residual pickling iron oxide scale defects, meeting the technical requirements for pickling raw materials of steel strip for coated flux-cored welding wire.

[0089] Example 2

[0090] The preparation method is basically the same as in Example 1, except that the composition of the molten steel obtained by converter smelting is C: 0.025, Si: 0.01, Mn: 0.25, P: 0.016, S: 0.004, Als: 0.037, and the remainder is Fe, (Wt,%). The hot-rolled steel plates produced using the aforementioned molten steel had the following characteristics: a hot-rolled slab homogenization temperature of 1220℃ and a homogenization time of 40 min; a roughing mill start temperature of 1175℃; a roughing mill descaling pressure of 17.2 MPa; a finishing mill descaling water pressure of 26 MPa; a finishing mill start temperature of 1035℃; a finishing mill start rolling speed of 1.6 m / s; thickness reduction rates of 12% and 8% for the last two mill stands, respectively; and a final rolling temperature of 900℃. The cooling method consisted of three sets of centralized post-rolling cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 95% / 80%), air cooling, and four sets of sparse laminar flow cooling (water pressure 0.6 MPa, upper / lower manifold cooling ratios of 40% / 40%). The coiling temperature was 550℃. The thickness after roughing was 34 mm, and the finishing mill had 7 rolling passes, resulting in a thickness of 4 mm. The steel strip is rolled to a thickness of 1.0 mm by the pickling and rolling mill, with a cold rolling reduction rate of 75%, and a straightening elongation rate of 1.3% by the pickling and leveling mill. The process speed is 180 m / min.

[0091] The prepared hot-rolled strip steel underwent oxide layer structure and thickness testing. The oxide layer thickness on the strip steel surface was 9.0 μm, and the oxide layer structure consisted of proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, with no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 was 25%, the proportion of eutectoid structure was 70%, and the proportion of FeO structure was 5%. Obvious pre-cracks were present in the oxide layer structure. The surface quality of the strip steel after pickling was good, with no residual pickling iron oxide scale defects, meeting the technical requirements for pickling raw materials of steel strip for coated flux-cored welding wire.

[0092] Comparative Example

[0093] The preparation method is basically the same as in Example 1, except that the steel obtained by converter smelting has the following composition: C: 0.020, Si: 0.01, Mn: 0.27, P: 0.019, S: 0.008, Als: 0.047, with the remainder being Fe (wt%). Hot-rolled steel plates produced using the aforementioned steel were manufactured with the following conditions: hot-rolled slab homogenization temperature of 1230℃, homogenization time of 35 min, roughing rolling start temperature of 1130℃, roughing descaling pressure of 17.2 MPa, finishing rolling descaling water pressure of 26 MPa, finishing rolling start temperature of 1070℃, finishing rolling start speed of 0.85 m / s, thickness reduction rates of the last two mill stands of 18% and 13% respectively, and final rolling temperature of 880℃. The cooling method employed a three-stage front-end laminar flow cooling system (water pressure 0.6 MPa, upper / lower manifold cooling ratio of 75% / 50%), water cooling-air cooling, and a coiling temperature of 550℃. The thickness after rough rolling is 34 mm, and the thickness after finishing rolling is 4.0 mm after 7 rolling passes. The steel strip is rolled to a thickness of 1.0 mm by the pickling and rolling mill, with a cold rolling reduction rate of 75%, a tensile elongation rate of 1.5% by the pickling and straightening mill, and a process speed of 110 m / min.

[0094] The prepared hot-rolled strip steel underwent oxide layer structure and thickness testing. The oxide layer thickness on the strip steel surface was 16 μm, and the oxide layer structure was Fe2O3 + proeutectoid Fe3O4 + eutectoid (Fe + Fe3O4), with a proeutectoid Fe3O4 proportion of 60% and an FeO proportion of 35%. No pre-existing cracks were found in the oxide layer structure. The surface quality of the strip steel after pickling was poor, with a large number of pickling iron oxide scale defects remaining, which did not meet the technical requirements for pickling raw materials of steel strip for coated flux-cored welding wire.

[0095] 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 on hot-rolled steel strip used for coated flux-cored welding wire, 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 three sets of centralized manifold laminar flow cooling - air cooling - four sets of sparse manifold laminar flow cooling; The cooling length of the three sets of centralized manifold laminar flow cooling is 12~16 m, and the cooling rate is 30~50 ℃ / s; the water pressure of 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 air cooling length between the three sets of centralized manifold laminar flow cooling and the four sets of sparse manifold laminar flow cooling is 8-12 m, and the cooling rate of the air cooling is 5-10 ℃ / s; the water pressure of 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 35-45% and 35-45%, respectively; The cooling length of the four sets of sparse manifold laminar flow cooling is 16~24 m, and the cooling rate of the sparse manifold laminar flow cooling is 15~35 ℃ / s.

2. The hot rolling mill scale control method according to claim 1, characterized by, The temperature for heat homogenization is 1185~1225℃, and the time is 0.5~1.5 h; The initial rolling temperature of the roughing mill is 1175~1200℃; The initial rolling temperature of the finishing mill is 1000~1030℃, the initial rolling speed is 1.4~1.6 m / s, and the final rolling temperature is 860~900℃. 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; The winding temperature is 530~570℃.

3. The hot rolling mill scale control method according to claim 1 or 2, characterized in that, After obtaining the slab, the slab is subjected to homogenization, descaling, rough rolling, descaling, finish rolling, cooling, coiling and pickling in sequence.

4. The hot rolling mill scale control method according to claim 3, characterized by, The dephosphorization water pressure before rough rolling is 17~19 MPa; The dephosphorization water pressure before finishing rolling is 24~26 MPa.

5. The hot rolling mill scale control method according to claim 1, characterized by, The oxide layer thickness in the steel strip is ≤10 μm, and the structure of the oxide layer is proeutectoid Fe3O4 + eutectoid structure + FeO, with no Fe2O3 phase component in the oxide layer; the eutectoid structure includes Fe + Fe3O4. The proportion of proeutectoid Fe3O4 is 15-25%, the proportion of eutectoid structure is 65-75%, and the proportion of FeO is 0-20%.

6. The hot rolling mill scale control method according to claim 1, characterized by, The pickling speed during pickling is 170~190 m / min, and the tensile elongation is 1.00~1.50%. The cold rolling reduction rate in the pickling process is 70-80%.

7. The hot rolling mill scale control method according to claim 1, characterized by, The molten steel is obtained by smelting blast furnace iron in a converter; the refining includes LF refining and RF refining. The chemical composition of the refined molten steel, in terms of elements, includes: C≤0.025%, Si 0~0.03%, Mn 0.15~0.25%, P 0~0.015%, S 0~0.010%, Als 0.015~0.050%, with the remainder being Fe.

8. A steel strip for removing flux-cored welding wire, characterized in that, The hot-rolled iron oxide scale of the steel strip used for the coated flux-cored welding wire is treated using the control method described in any one of claims 1 to 7.

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