Hot rolling oxide scale control method for steel belt for cover withdrawing flux-cored wire and steel belt for cover withdrawing flux-cored wire

Abstract

The invention provides a hot-rolled oxide scale control method for a steel strip for a cover withdrawing flux-cored wire and the steel strip for the cover withdrawing flux-cored wire. According to the control method, through a specific cooling mode in a hot rolling process, soaking, rough rolling, finish rolling and coiling processes are combined, the thickness of an oxidation layer of the obtained steel strip is smaller than or equal to 10 microns, the oxidation layer structure is proeutectoid Fe3O4 + eutectoid tissue (Fe + Fe3O4) + FeO, the oxidation layer does not contain Fe2O3 phase components, the proportion of proeutectoid Fe3O4 is about 20%, the proportion of eutectoid tissue is about 70%, the proportion of FeO is about 10%, and obvious precracks exist in the oxidation layer structure. In acid rolling, the acid pickling process speed can be increased to 170-190 m / min, the defects that in an original process technology, an oxide layer is not prone to being completely washed, and over-acid pickling is prone to being formed are overcome, the problem that the environment is polluted by acid pickling rime fog does not exist, and the steel belt obtained after acid pickling is excellent in surface quality and good in technical and economic index.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for controlling hot rolled iron oxide scale of a steel strip for a flux-cored welding wire and a steel strip for a flux-cored welding wire. Background Art

[0002] Flux-cored welding wire steel is usually required to have high molten steel purity, excellent drawing performance and good performance uniformity. The surface quality level of the strip directly affects the smooth production of the wire making process. After multiple drawing passes, the cross-section of the welding wire is uniform and defect-free. Therefore, in the production process of flux-cored welding wire steel, surface quality control is very important in the whole process control system, and the control of iron oxide scale in the hot rolling process is one of the keys. In order to improve the surface quality of the finished product of the subsequent hood annealing unit, the remaining iron oxide scale must be completely removed in the pickling stage, otherwise it will lead to deterioration of the surface quality of the finished product.

[0003] The hot-rolled raw material of steel for flux-cored welding wire is usually designed as micro-carbon aluminum killed steel + austenite zone final rolling + low-temperature coiling process. The surface oxide layer thickness of the conventional process is 14~20μm, and the structure is a high proportion of pro-eutectoid Fe3O4 + eutectoid structure (Fe+Fe3O4) + Fe2O3. Fe2O3 reacts with hydrochloric acid at the slowest rate in the pickling process and is the most difficult to wash out; the Fe3O4 in the oxide layer structure is relatively dense and the chemical reaction efficiency with hydrochloric acid is not high, and the Fe2O3 phase on the surface further reduces the pickling reaction efficiency. Therefore, in the actual production of flux-cored welding wire steel, only low-speed, high-concentration, high-temperature hydrochloric acid organization production (process section speed 110 m / min) can be used, which is not conducive to the production efficiency of the cold rolling process, and will also bring about pickling white mist (poor acid tank sealing, acid volatilization) environmental problems and partial over-pickling of strip steel, which reduces the yield rate of strip steel and increases the environmental protection pressure of enterprises. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for controlling hot rolled scale of a steel strip for flux-cored welding wire and a steel strip for flux-cored welding wire. The control method not only effectively improves the capacity of the pickling process, but also improves the pickling effect of the strip steel.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for controlling hot rolled scale on a steel strip for a flux-cored welding wire, comprising the following steps:

[0007] The refined molten steel is cast to obtain a slab, the slab is subjected to soaking, rough rolling and finish rolling, and after cooling, it is coiled to obtain a steel strip, which is then acid rolled;

[0008] The cooling method is three groups of concentrated header laminar flow cooling-air cooling-four groups of sparse header laminar flow cooling;

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

[0010] The water pressure of the sparse header laminar cooling is 0.5-0.65 MPa, wherein the cooling ratios of the upper header and the lower header are 35-45% and 35-45% respectively.

[0011] Preferably, the cooling length of the three groups of concentrated header laminar cooling is 12-16 m.

[0012] Preferably, the air cooling length between the three groups of concentrated header laminar cooling and the four groups of sparse header laminar cooling is 8-12 m.

[0013] Preferably, the cooling length of the four groups of sparse header laminar cooling is 16-24 m.

[0014] Preferably, the cooling rate of the concentrated header laminar cooling is 30-50° C. / s.

[0015] Preferably, the cooling rate of the air cooling is 5-10°C / s.

[0016] Preferably, the cooling rate of the sparse header laminar cooling is 15-35°C / s.

[0017] Preferably, the soaking temperature is 1185-1225° C. and the soaking time is 0.5-1.5 h.

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

[0019] Preferably, the start rolling temperature of the finish rolling is 1000-1030°C, the start rolling speed is 1.4-1.6 m / s, and the final rolling temperature is 860-900°C.

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

[0021] Preferably, the number of passes of the finish rolling is 5 to 7.

[0022] Preferably, the coiling temperature is 530-570°C.

[0023] Preferably, after the slab is obtained, it is subjected to soaking, dephosphorization, rough rolling, dephosphorization, finish rolling, cooling, coiling and pickling in sequence.

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

[0025] Preferably, the water pressure for dephosphorization before finish rolling is 24-26 MPa.

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

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

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

[0029] Preferably, the pickling speed in the pickling rolling is 170-190 m / min, and the tensile elongation is 1.00-1.50%;

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

[0031] More preferably, the cold rolling reduction ratio in the acid rolling is 75-80%.

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

[0033] Preferably, the chemical composition of the refined molten steel, calculated on a simple basis, 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%, and the remainder is Fe.

[0034] In a second aspect, the present invention provides a steel strip for flux-cored welding wire, the surface of which is processed by the above-mentioned control method for controlling hot-rolled iron oxide scale.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a method for controlling hot-rolled iron oxide scale of a steel strip for a flux-cored welding wire. By using a specific cooling method in a hot rolling process and combining soaking, rough rolling, finish rolling and coiling processes, the oxide layer thickness of the obtained steel strip is ≤10 μm, the oxide layer structure is pro-eutectoid Fe3O4+eutectoid structure (Fe+ Fe3O4)+FeO, the oxide layer has no Fe2O3 phase component, the proportion of pro-eutectoid Fe3O4 is about 20%, the proportion of eutectoid structure is about 70%, the proportion of FeO is about 10%, and obvious prefabricated cracks exist in the oxide layer structure.

[0037] Based on this, in the present invention, the speed of the pickling process section can be increased to 170-190 m / min during pickling, thereby avoiding the shortcomings of the original process technology, such as the difficulty in washing out the oxide layer, the easy formation of over-pickling and under-pickling defects, and the problem of environmental pollution caused by pickling white mist. The surface quality of the steel strip after pickling is excellent, and the technical and economic indicators are good.

[0038] Furthermore, compared with the steel plates produced by the conventional manufacturing process of flux-cored welding wire steel, the steel strip produced by the above-mentioned control method adopted in the present invention has a simple process, improved efficiency of the pickling process section unit, excellent comprehensive product performance, and good prospects for promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a morphology diagram of prefabricated cracks in the hot-rolled oxide scale of the steel for the flux-cored welding wire in Example 1 of the present invention;

[0040] Figure 2 This is a morphology diagram of prefabricated cracks in the hot-rolled oxide scale of the steel for the flux-cored welding wire in Example 2 of the present invention;

[0041] Figure 3 This is a morphology diagram of the hot-rolled oxide scale of the steel for the flux-cored welding wire without prefabricated cracks in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0044] The refined molten steel is cast to obtain a slab, which is then subjected to soaking, rough rolling and finish rolling, and then coiled after cooling. After obtaining a steel strip, it is acid-rolled.

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

[0046] Specifically, the converter smelting is to smelt blast furnace molten iron and smelting charge in a converter to obtain molten steel, and then pre-deoxidize the molten steel during the steel-making process; the molten steel (based on the total weight of the molten steel, in terms of single substance, wt%) is: 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, and the rest is Fe. The smelting time is the conventional smelting time, preferably 35-45 min. The technology adopted in the converter smelting process is a method well known to those skilled in the art.

[0047] In the present invention, after the molten steel is obtained, it is refined, and the refining preferably includes LF refining and RH refining.

[0048] Among them, the LF refining process only carries out molten steel temperature adjustment and ladle bottom blowing argon treatment. Argon gas with a pressure of 200~400 Pa is introduced into the bottom of the molten steel tank for 4~6 minutes, preferably argon gas with a pressure of 250~350 Pa is introduced for 4.5~5 minutes. The argon gas flow rate is based on the condition that the molten steel does not overturn, which can avoid secondary oxidation of the molten steel and too fast temperature drop, so that the inclusions in the steel can fully float up, and further improve the cleanliness of the steel. The processing time of LF refining is 10~25 minutes, preferably 15~20 minutes, and the exit temperature is 1610~1625℃, preferably 1615~1620℃. The technology adopted by LF refining is a method known to those skilled in the art.

[0049] The RH refining process carries out decarburization and alloying treatment, and in the alloying step, metallic manganese is added to the molten steel after final decarburization. The exit temperature of the RH process is 1575~1590°C, preferably 1580~1585°C. After RH treatment, the molten steel obtained (based on the total weight of the molten steel, in terms of single substance, wt%) is: 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, and the rest is Fe. The technology adopted for RH refining is a method well known to those skilled in the art.

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

[0051] The continuous casting step can adopt a method known to those skilled in the art. In the method of the present invention, the refined molten steel is cast into a pre-baked tundish, and cast into a slab by a slab continuous casting machine with full process protection. After casting, cooling can be carried out according to conventional methods, such as natural cooling at room temperature.

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

[0053] In the present invention, the hot rolling step is to roll the cast slab after reheating. In the present invention, the reheating temperature of hot rolling, i.e., the soaking temperature, refers to the temperature of the steel billet out of the heating furnace. The preferred soaking temperature of the present invention is 1185~1225°C, preferably 1190~1220°C. Heating at this temperature can fully dissolve microalloying elements and eliminate the chemical element segregation caused by dendrite bias in the casting; at the same time, the AlN particles formed in the casting state are dissolved back to avoid the adverse effects of rolling and annealing processes on the organization, mechanical properties and grain orientation. The soaking time is 0.5~1.5 h, preferably 0.8~1.2 h.

[0054] In the present invention, the purpose of the rolling is to make the continuous casting slab reach the required hot rolling thickness.

[0055] In the present invention, the initial rolling temperature of the hot rolling, that is, the initial rolling temperature of the rough rolling is 1175-1200° C., preferably 1180-1190° C., to ensure that there is no hard-to-descale fayalite on the surface.

[0056] In the present invention, the hot rolling start temperature is to ensure the removal of the low-melting-point FeO / Fe2SiO4 eutectic compounds on the surface of the slab, and to prevent the formation of red rust defects that are not conducive to pickling after cooling. The final rolling temperature refers to the temperature of the steel strip leaving the finishing mill. In order to make the thickness and mechanical properties of the finished product uniform and to avoid the formation of Fe2O3 phase during the finishing rolling process, the final rolling temperature should be increased as much as possible. The present invention adopts the hot coil box process technology of the hot-rolled intermediate billet to maintain a specific final rolling temperature at the head, middle and tail of the hot-rolled intermediate billet before finishing rolling. The lower the finishing rolling start temperature, the faster the rolling speed and the thinner the oxide layer thickness. Therefore, the start rolling temperature should be reduced as much as possible and the rolling speed should be 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; the final rolling temperature is 860~900℃, preferably 870~890℃.

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

[0058] In some preferred embodiments of the present invention, dephosphorization steps are included before rough rolling and before finish rolling. The purpose of descaling is to remove the heavy iron oxide scale formed by the surface combining with O at high temperature. Generally, it is necessary to ensure the minimum descaling pressure and arrange the descaling nozzle position reasonably. 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] In order to meet the performance requirements of the finished product, the hot-rolled microstructure is F+a small amount of P+a small amount of Fe3C, and the ferrite grain size is 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 inhibit the precipitation of AlN particles, and then slowly precipitate AlN during the recrystallization annealing process to obtain a good texture orientation to improve the forming performance.

[0060] In addition, in order to obtain prefabricated oxide layer cracks, the cooling mode of the present invention is three groups of concentrated header laminar cooling after rolling (water pressure is 0.5~0.65 MPa, wherein the cooling ratios of the upper header and the lower header are 85~95% and 70~80%, respectively) - air cooling - four groups of sparse header laminar cooling (water pressure is 0.5~0.65 MPa, wherein the cooling ratios of the upper header and the lower header are 35~45% and 35~45%, respectively), each group of header cooling water length is about 5 m, and the air cooling interval between the concentrated header laminar cooling and the sparse header laminar cooling is about 10 m. It should be noted that the above cooling mode is specifically selected by the present invention. If the number of groups of concentrated header laminar cooling or sparse header laminar cooling is increased or decreased at will, the results will be adversely affected. At the same time, the order of concentrated cooling first, air cooling second, and sparse cooling last cannot be changed at will.

[0061] In the present invention, the water pressure of the three groups of concentrated header laminar cooling is 0.5~0.65 MPa, preferably 0.6 MPa. Among them, the cooling ratios of the upper header and the lower header are 85~95% and 70~80% respectively, wherein the cooling ratio of the upper header can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95%, and the cooling ratio of the lower header can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79% or 80%. The reason for this arrangement is that it is conducive to the formation of surface oxide scale pre-cracks without affecting the hot-rolled microstructure. In some embodiments of the present invention, the cooling ratios of the upper header and the lower header are preferably 100% and 80% respectively.

[0062] In the present invention, the water pressure of the four groups of sparse header laminar cooling is 0.5~0.65 MPa, preferably 0.6 MPa. Among them, the cooling ratios of the upper header and the lower header are 35~45% and 35~45% respectively, and the cooling ratio of the upper header (or lower header) can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%. The reason for this setting is that it is conducive to regulating the hot-rolled oxidized iron scale structure and microstructure. In some embodiments of the present invention, the cooling ratios of the upper header and the lower header are preferably 40% and 40% respectively.

[0063] In the present invention, the cooling length of the three groups of concentrated header laminar cooling is 12~16 m, preferably 13~14 m; the air cooling length between the three groups of concentrated header laminar cooling and the four groups of sparse header laminar cooling is 8~12 m, preferably 9~10 m; the cooling length of the four groups of sparse header laminar cooling is 16~24 m, preferably 18~20 m.

[0064] In the present invention, the steel strip coming out of the rolling mill is prefabricated with oxide layer cracks in a very short time and at a very high cooling rate, and is cooled to the coiling temperature for coiling. Therefore, the cooling rate of the concentrated cooling is 30-50°C / s, preferably 35-45°C / s; the cooling rate of the air cooling is 5-10°C / s, preferably 6-8°C / s; the sparse laminar cooling rate is 15-35°C / s, preferably 20-30°C / s; and then cooled to the coiling temperature of 530-570°C, preferably 540-560°C.

[0065] In the present invention, the concentrated header laminar cooling and the sparse header laminar cooling can be set according to the contents well known to those skilled in the art.

[0066] It should be noted that the present invention is conducive to regulating the iron sheet structure and prefabricating iron sheet cracks through a specific cooling method, namely, first 3 groups of concentrated cooling, then air cooling, and finally 4 groups of sparse cooling. It should be noted that if the groups of concentrated header laminar cooling and sparse header laminar cooling are increased or decreased at will, it will lead to the failure to prefabricate iron sheet cracks or cause abnormal hot rolled microstructure, thereby affecting the final microstructure and performance of the finished product.

[0067] After the coiling is completed, the thickness and structure of the oxide scale of the obtained steel strip can be tested by the metal microstructure inspection method of GB / T13298.

[0068] As a result, it is found that the oxide layer thickness of the hot-rolled oxide scale control method for steel strip for flux-cored welding wire of the present invention is ≤10 μm, and the oxide layer thickness can be measured by methods known to those skilled in the art. The test sample can be a polished or corroded metallographic sample, the sample corrosive agent is 1-2% hydrochloric acid alcohol solution, and the corrosion time is 5-8 s, such as the GB / T 6394 metallographic method.

[0069] The oxide layer structure of the hot-rolled scale control method of the steel strip for the flux-cored welding wire of the present invention is pro-eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4)+FeO, the oxide layer has no Fe2O3 phase component, the proportion of pro-eutectoid Fe3O4 is about 20%, the proportion of eutectoid structure is about 70%, the proportion of FeO is about 10%, and prefabricated cracks exist in the oxide layer structure. Preferably, the proportion of the pro-eutectoid Fe3O4 is 15-25%, the proportion of the eutectoid structure is 65-75%, and the proportion of FeO is 0-20%. More preferably, the proportion of the pro-eutectoid Fe3O4 is 15-20%, the proportion of the eutectoid structure is 70-75%, and the proportion of FeO is 5-15%.

[0070] The oxide layer structure can be measured by methods known to those skilled in the art. The test sample can be a polished or corroded metallographic sample. The sample corrosive agent is 1-2% hydrochloric acid alcohol solution, and the corrosion time is 5-8 s, such as GB / T 13298 metal microstructure inspection method.

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

[0072] In the present invention, after the coiling is completed, pickling treatment is performed.

[0073] In the present invention, the step of pickling treatment can adopt various conventional methods. Usually, the thin steel strip rolled by hot rolling is welded at the head of the pickling mill to form a continuous steel strip, and is continuously rolled after straightening, tension and phosphorus removal, pickling, alkali washing, drying, and trimming. The cold rolling mill can adopt various conventional cold rolling mills, such as 4-5 stand cold rolling mills. The thickness of the steel plate is reduced to the raw material thickness of the hood annealing unit after pickling. The cold rolling reduction rate is 70-80%, preferably 75%, and the pickling process section speed is 170-190 m / min; the pickling tension elongation is 1.00-1.50%; the surface iron oxide scale is removed and the surface quality is improved. The pickling step can adopt 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 hot-rolled scale of steel strip for flux-cored welding wire is as follows:

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

[0076] The present invention adopts the above technical scheme, and the oxide layer cracks are preformed in the oxide layer of the steel strip surface, which effectively promotes the removal of pickling scale. After production, the surface quality inspection results show that the pickling surface quality of the steel for the flux-cored welding wire produced by this method is excellent, the pickling process speed is increased to more than 170-190 m / min, and the technical and economic indicators of the finished product are good.

[0077] In summary, the steel strip used for the flux-cored welding wire in the present invention reduces the thickness of the oxide layer, introduces FeO phase into the oxide layer structure, and prefabricates the oxide layer, etc., which increases the pickling reaction efficiency of the pickling process, and the pickling quality of the product is significantly improved, which can effectively adapt to the demand for raw materials of the strip-smoothing unit. Therefore, the above-mentioned technology of the present invention is adopted, on the one hand, to effectively improve the capacity of the pickling process, and on the other hand, to improve the pickling effect of the strip, which has a significant promoting effect on reducing the surface quality defects of the strip. Under the current good external conditions of the market, the present invention can effectively improve the production capacity of Pangang's general cold products, improve the surface quality level of the products, and has a good prospect for promotion and application.

[0078] To further illustrate the present invention, the following examples are provided for detailed description. The semi-steel used in the following examples of the present invention refers to molten iron after vanadium is extracted from molten iron in a blast furnace.

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

[0080] The method for detecting the thickness, structure and microstructure of the iron oxide scale in the present invention is the metal microstructure inspection method of GB / T13298.

[0081] Example 1

[0082] a. Smelting molten steel: The smelting equipment is a top-blown converter. The semi-steel after vanadium extraction from blast furnace molten iron is used as raw material. The temperature is 1364℃. Steelmaking auxiliary materials are added to melt to 1660℃ and tapped into the molten steel tank. When 1 / 3 of the steel is tapped, 400 kg of aluminum iron is added for pre-deoxidation. The molten steel tank is bottom-blown with argon gas at a pressure of 300 Pa for 4 minutes on a small platform behind the furnace. The molten steel obtained (based on the total weight of the molten steel, calculated as a single substance) is C: 0.05, Si: 0.01, Mn: 0.10, P: 0.017, S: 0.006, Als: 0.025, and the rest is Fe;

[0083] b. LF electric heating: Argon gas with a certain pressure (350 Pa) is introduced into the bottom of the molten steel tank for 5 minutes. The argon gas flow rate is based on the condition that the molten steel does not overturn. The LF treatment outlet temperature is 1612℃;

[0084] c. RH treatment: decarburization and alloying treatment, the alloying order is aluminum iron, metal manganese. The RH process treatment time is 25 minutes, and the exit temperature is 1586℃. After RH treatment, the molten steel (based on the total weight of the molten steel, calculated as a single substance, w%) is: C: 0.020, Si: 0.01, Mn: 0.28, P: 0.017, S: 0.006, Als: 0.042, and the rest is Fe;

[0085] d. Continuous casting: The molten steel tank is transported to the casting position, and the Al stopper rod is inserted into the bottom of the molten steel tank. The molten steel automatically flows into the tundish, passes through the Al stopper rod, and is drained to the crystallizer for continuous casting. The whole process uses protective slag for protective casting, and after casting, it is cooled into a hot-rolled slab with a thickness of 200 mm;

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

[0087] e. Pickling: The steel strip is rolled to a thickness of 1.0 mm by the pickling mill, with a cold rolling reduction of 75%, a straightening elongation of 1.2% by the pickling mill, and a process section speed of 190 m / min;

[0088] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The thickness of the oxide layer on the surface of the strip was 7.0μm, and the oxide layer structure was pro-eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4)+FeO, with no Fe2O3 phase component, pro-eutectoid Fe3O4 ratio of 20%, eutectoid structure ratio of 75%, FeO structure ratio of 5%, and prefabricated cracks in the oxide layer structure. The surface quality of the strip after pickling was good, with no residual pickling oxide scale defects, which met the technical requirements for pickling raw materials of steel strip for flux-cored welding wire.

[0089] Example 2

[0090] The preparation method is basically the same as that of 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 rest is Fe, (Wt, %). The hot rolled steel plate produced by the above molten steel has a soaking temperature of 1220℃, soaking time of 40 min, rough rolling start temperature of 1175℃, rough rolling descaling pressure of 17.2 MPa, finishing descaling water pressure of 26 MPa, finishing rolling start temperature of 1035℃, finishing rolling start rolling speed of 1.6 m / s, thickness reduction ratios of the last two rolling mill stands of 12% and 8% respectively, and final rolling temperature of 900℃; the cooling method adopts three groups of centralized cooling after rolling (water pressure of 0.6 MPa, upper / lower header cooling ratio of 95% / 80%) - air cooling - four groups of sparse laminar cooling (water pressure of 0.6 MPa, upper / lower header cooling ratio of 40% / 40%); coiling temperature of 550℃. The thickness after rough rolling is 34 mm, the number of finishing rolling passes is 7, and the thickness after finishing rolling is 4 mm. The steel strip is rolled to a thickness of 1.0 mm in the pickling mill, with a cold rolling reduction of 75%, a straightening elongation of 1.3% in the pickling mill, and a process section speed of 180 m / min.

[0091] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The thickness of the oxide layer on the surface of the strip is 9.0μm, and the oxide layer structure is pro-eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4)+FeO, with no Fe2O3 phase component, pro-eutectoid Fe3O4 ratio of 25%, eutectoid structure ratio of 70%, FeO structure ratio of 5%, and obvious pre-cracks in the oxide layer structure. The surface quality of the strip after pickling is good, and there is no residual pickling oxide scale defect, which meets the technical requirements of pickling raw materials for steel strips for flux-cored welding wires.

[0092] Comparative Example

[0093] The preparation method is basically the same as that of Example 1, except that the molten steel obtained by converter smelting has a composition of C: 0.020, Si: 0.01, Mn: 0.27, P: 0.019, S: 0.008, Als: 0.047, and the rest is Fe (wt%). The hot-rolled steel plate produced by the above-mentioned molten steel has a soaking temperature of 1230°C for the hot-rolled slab, a soaking time of 35min, a rough rolling temperature of 1130°C, a rough rolling descaling pressure of 17.2 MPa, a finishing descaling water pressure of 26MPa, a finishing rolling temperature of 1070°C, a finishing rolling speed of 0.85 m / s, and the thickness reduction ratios of the last two rolling mill stands are 18% and 13% respectively, and the final rolling temperature is 880°C; the cooling method adopts three groups of front-stage laminar cooling (water pressure 0.6 MPa, upper / lower header cooling ratios of 75% / 50% respectively) water cooling-air cooling, and the coiling temperature is 550°C. The thickness after rough rolling is 34 mm, the number of passes for finishing rolling is 7, and the thickness after finishing rolling is 4.0 mm. The thickness of the steel strip is rolled to 1.0 mm by the pickling mill, the cold rolling reduction is 75%, the pickling mill stretching elongation is 1.5%, and the process section speed is 110 m / min.

[0094] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The thickness of the oxide layer on the surface of the strip was 16 μm, and the oxide layer structure was Fe2O3+proeutectoid Fe3O4+eutectoid structure (Fe+Fe3O4), the proportion of proeutectoid Fe3O4 was 60%, the proportion of FeO was 35%, and there were no prefabricated cracks in the oxide layer structure. The surface quality of the strip after pickling was poor, and there were many pickling oxide scale defects remaining, which did not meet the technical requirements for pickling raw materials for steel strips for flux-cored welding wires.

[0095] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling hot rolled scale on a steel strip for flux-cored welding wire, characterized in that: The following steps are involved: The refined molten steel is cast to obtain a slab, the slab is subjected to soaking, rough rolling and finish rolling, and after cooling, it is coiled to obtain a steel strip, which is then acid rolled; The cooling method is three groups of concentrated header laminar flow cooling-air cooling-four groups of sparse header laminar flow cooling; The water pressure of the centralized header laminar cooling is 0.5~0.65 MPa, wherein the cooling ratios of the upper header and the lower header are 85~95% and 70~80% respectively; The water pressure of the sparse header laminar cooling is 0.5-0.65 MPa, wherein the cooling ratios of the upper header and the lower header are 35-45% and 35-45% respectively.

2. The hot rolling scale control method according to claim 1, characterized in that: The cooling length of the three groups of centralized header laminar cooling is 12-16 m; The air cooling length between the three groups of concentrated header laminar cooling and the four groups of sparse header laminar cooling is 8 to 12 m; The cooling length of the four groups of sparse header laminar cooling is 16-24 m.

3. The hot rolling scale control method according to claim 1 or 2, characterized in that: The cooling rate of the centralized header laminar cooling is 30-50 °C / s; The cooling rate of the air cooling is 5-10 °C / s; The cooling rate of the sparse header laminar cooling is 15-35°C / s.

4. The hot rolling scale control method according to any one of claims 1 to 3, characterized in that: The soaking temperature is 1185-1225°C and the time is 0.5-1.5 h; The initial rolling temperature of the rough rolling is 1175~1200℃; The start rolling temperature of the finishing rolling is 1000-1030°C, the start rolling speed is 1.4-1.6 m / s, and the final rolling temperature is 860-900°C; The thickness reduction rates of the last two rolling mills of the finishing rolling are ≤15% and ≤10% respectively; The number of passes of the finishing rolling is 5 to 7; The coiling temperature is 530-570°C.

5. The hot rolling scale control method according to any one of claims 1 to 4, characterized in that: After the slab is obtained, it is subjected to soaking, dephosphorization, rough rolling, dephosphorization, finish rolling, cooling, coiling and pickling in sequence.

6. The hot rolling scale control method according to claim 5, characterized in that: The water pressure for dephosphorization before rough rolling is 17-19 MPa; The water pressure for dephosphorization before finishing rolling is 24-26 MPa.

7. The hot rolling scale control method according to any one of claims 1 to 6, characterized in that: The thickness of the oxide layer in the steel strip is ≤10 μm, the structure of the oxide layer is pro-eutectoid Fe3O4+eutectoid structure+FeO, and the oxide layer has no Fe2O3 phase component; the eutectoid structure includes Fe+Fe3O4; The proportion of the pro-eutectoid Fe3O4 is 15-25%, the proportion of the eutectoid structure is 65-75%, and the proportion of FeO is 0-20%.

8. The hot rolling scale control method according to any one of claims 1 to 7, characterized in that: The pickling speed in the pickling rolling is 170-190 m / min, and the tensile elongation is 1.00-1.50%; The cold rolling reduction rate in the acid rolling is 70-80%.

9. The hot rolling scale control method according to any one of claims 1 to 7, characterized in that: The molten steel is obtained by smelting molten iron from a blast furnace in a converter; The refining includes LF refining and RF refining; The chemical composition of the refined molten steel, calculated on a simple basis, 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%, and the remainder is Fe.

10. A steel strip for flux-cored welding wire, characterized in that: The hot rolled scale of the steel strip for the flux-cored welding wire is processed by the control method described in any one of claims 1 to 9.

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