Hot rolling oxide scale control method for cover-withdrawing deep-drawing structural steel strip and cover-withdrawing deep-drawing structural steel strip

Abstract

The invention provides a hot rolling oxide scale control method for a cover-withdrawing deep-drawing structural steel strip and the cover-withdrawing deep-drawing structural steel strip. By controlling a cooling mode in a hot rolling process and combining rough rolling, finish rolling and coiling processes, the thickness of an oxidation layer of the obtained steel strip is smaller than or equal to 11 microns, the oxidation layer structure is a proeutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO, the oxidation layer is free of a Fe2O3 phase, the proportion of the proeutectoid Fe3O4 is 70-80%, the proportion of the eutectoid structure is 10-20%, the proportion of FeO is about 10%, and obvious precracks exist in the oxidation layer structure. On the basis, during acid rolling, the acid pickling speed can be increased to 160-180 m / min, the defects that in an original technology, an oxide layer is not prone to being completely washed, and the defects of over-acid pickling and under-acid pickling are likely to be 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 hood-annealed deep-drawn structural steel strip and a hood-annealed deep-drawn structural steel strip. Background Art

[0002] The surface oxide scale structure of pickled raw materials of hood-annealed deep-drawn structural steel is usually 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 edge is a strip-shaped Fe2O3 red rust zone. In order to improve the surface quality of the subsequent annealing unit product, the remaining oxide scale must be completely removed during the pickling stage.

[0003] The pickling process, especially the low unit rate of the pickling process section, has always been a problem faced by cold rolling manufacturers at home and abroad. The hot rolling raw material of ordinary annealing deep drawing steel is usually designed as Ti microalloyed ultra-low carbon steel, and the surface oxide layer structure is Fe2O3 + high proportion of proeutectoid Fe3O4 (volume fraction of more than 90%) + a small amount of FeO, and the oxide layer thickness is 14~20 μm. Among them, the Fe3O4 in the oxide layer structure is relatively dense, has strong adhesion to the matrix, and also has a certain ductility for small deformation. However, compared with the FeO phase, the chemical reaction rate of Fe3O4 and hydrochloric acid is low, and the Fe2O3 phase in the iron sheet structure further reduces the reaction efficiency. Therefore, in the actual production of deep-drawn structural steel, only low-speed, high-concentration, high-temperature hydrochloric acid can be used to organize production (process section speed 110 m / min), which is not conducive to the production efficiency of the cold rolling process, and will also bring about environmental problems such as pickling white mist (poor acid tank sealing, acid volatilization) and local over-pickling of the strip, which reduces the yield rate of the strip and increases the environmental protection pressure of the enterprise. 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 deep-drawn structural steel strip during annealing and a deep-drawn structural steel strip during annealing. The control method not only effectively improves the capacity of the pickling process, but also improves the pickling effect of the strip.

[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 of a deep-drawn structural steel strip, comprising the following steps:

[0007] 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.

[0008] Preferably, the cooling method is two groups of concentrated header laminar cooling-air cooling-two groups of sparse header laminar cooling.

[0009] Preferably, the water pressure of the concentrated 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] Preferably, 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 45-55% and 45-55% respectively.

[0011] Preferably, the spacing length between the cooling headers in the two groups of centralized header laminar cooling is 4.5-6 m.

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

[0013] Preferably, the spacing length between the cooling headers in the two groups of sparse header laminar cooling is 8 to 12 m.

[0014] Preferably, the cooling rate of the two groups of concentrated header laminar cooling is 25-45°C / s, the cooling rate of the air cooling is 5-10°C / s, and the cooling rate of the two groups of sparse header laminar cooling is 15-30°C / s.

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

[0016] Preferably, the chemical composition of the refined molten steel, calculated on a simple basis, 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%, and the rest is Fe.

[0017] Preferably, the soaking temperature is 1200-1240° C. and the soaking time is 0.5-1.5 h.

[0018] Preferably, a dephosphorization step is included before the rough rolling, and the water pressure of the dephosphorization is 17-19 MPa.

[0019] Preferably, the initial rolling temperature of the rough rolling is 1175-1210° C. to ensure that there is no fayalite phase on the surface which is difficult to descale.

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

[0021] Preferably, a dephosphorization step is included before the finish rolling, and the water pressure of the dephosphorization is 24-26 MPa.

[0022] Preferably, the start rolling temperature of the finish rolling is 1010-1050° C., the final rolling temperature is 900-940° C., and the rolling speed of the finish rolling is 1.10-1.70 m / s.

[0023] Preferably, the thickness reduction ratios of the last two rolling mills of the finishing rolling are ≤15% and ≤10% respectively. In the present invention, the initial rolling is a two-stand reversible rolling mill, and the final rolling is a 7-stand continuous rolling mill.

[0024] Preferably, the number of passes of the finish rolling is 5 to 7.

[0025] Preferably, the coiling temperature is 700-740°C.

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

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

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

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

[0030] In a second aspect, the present invention provides a hood-annealed deep-drawn structural steel strip, which controls the hot-rolled iron oxide scale by the above-mentioned control method.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention provides a method for controlling hot-rolled scale of deep-drawn steel strips. By controlling the cooling method in the hot rolling process and combining the rough rolling, finishing rolling and coiling processes, the thickness of the oxide layer of the steel strip is ≤11 μm, the oxide layer structure is pre-eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4)+FeO, the oxide layer has no Fe2O3 phase, the pre-eutectoid Fe3O4 ratio is 70-80%, the eutectoid structure ratio is 10-20%, the FeO ratio is about 10%, and there are obvious prefabricated cracks in the oxide layer structure. Based on this, in the present invention, the speed of the pickling process section can be increased to 160-180 m / min during pickling, avoiding the shortcomings of the original process technology that the oxide layer is not easy to wash out, and it is easy to form over-pickling and under-pickling defects, and there is no problem of white mist pollution of the environment after pickling. The surface quality of the steel strip after pickling is excellent, and the technical and economic indicators are good.

[0033] Furthermore, compared with the steel plates produced by the conventional deep-drawing structural steel manufacturing process, the production process adopted by the present invention is simple, the efficiency of the pickling process section in the pickling rolling is improved, the comprehensive performance of the product is excellent, and the prospect of promotion and use is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is an optical microscopic image of the steel strip obtained in Example 1;

[0035] Figure 2 This is an optical microscopic image of the steel strip obtained in Example 2;

[0036] Figure 3 This is an optical microscope image of the steel strip obtained in Comparative Example 1. DETAILED DESCRIPTION

[0037] 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.

[0038] The present invention provides a method for controlling hot rolled iron oxide scale of a deep-drawn structural steel strip, comprising the following steps:

[0039] 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.

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

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

[0042] Exemplarily, the converter smelting is specifically to smelt molten steel from blast furnace molten iron and smelting charge in a converter, and then deoxidize and alloy the molten steel during the steel-making process. The blast furnace molten iron and smelting charge are conventional raw materials in the art, and are not particularly limited. In the alloying step, aluminum-iron alloy, low-carbon ferromanganese, etc. are added to the molten steel to obtain molten steel (based on the total weight of the molten steel, in terms of single substance, w%): 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 rest is Fe. The smelting time is the conventional smelting time, preferably 35~45 min.

[0043] In the present invention, after the molten steel is obtained, it is refined. In the present invention, the refining includes LF refining and RF refining in sequence.

[0044] In the present invention, the LF refining 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 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; the exit temperature is 1610-1635°C, preferably 1620-1630°C. The method adopted for LF refining is a method known to those skilled in the art.

[0045] In the present invention, the RH refining is performed with final deoxidation, molten steel temperature adjustment and alloying treatment, and metal manganese, ferrotitanium, etc. are added to the molten steel after final deoxidation in the alloying treatment. The treatment time of the RH refining is 30-40 min, preferably 32-35 min; the exit temperature is 1590-1615°C, preferably 1600-1610°C. In some embodiments of the present invention, according to the chemical composition requirements of deep drawing steel, the molten steel obtained after the RH refining (based on the total weight of the molten steel, calculated as a single substance, w%) is: 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%, and the rest is Fe. The method adopted by the RH refining is a method known to those skilled in the art.

[0046] According to the present invention, after refining, the refined molten steel is cast to obtain a slab. The casting is continuous casting, and the continuous casting can be performed by a method known to those skilled in the art. In some embodiments of the present invention, the refined molten steel is cast into a pre-baked tundish, and the slab is cast into a slab by a slab continuous casting machine with full process protection. After casting, cooling can be performed according to 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 is to heat the cast slab and then roll it. The heating is generally uniform heating, and the uniform heating temperature refers to the temperature of the steel billet (i.e., the slab obtained above) out of the heating furnace. The preferred uniform heating time of the present invention is 0.5~1.5 h, preferably 0.8~1.2 h, and the uniform heating temperature is 1200~1240℃, preferably 1210~1230℃. At this temperature, the micro-alloying elements can be fully dissolved, and the chemical element segregation caused by the dendrite bias of the slab after casting can be eliminated. At the same time, the AlN particles formed in the cast state can be dissolved back, avoiding the adverse effects of the subsequent rolling and annealing process on the organization, mechanical properties and grain orientation.

[0049] In the present invention, the purpose of the rolling is to make the continuous casting slab reach the required hot rolling thickness, which generally includes rough rolling and finish rolling.

[0050] In the present invention, the initial rolling temperature of the rough rolling is 1175-1210° C., preferably 1180-1200° C., to ensure that there is no fayalite phase on the surface which is difficult to descale.

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

[0052] In the present invention, the start rolling temperature of the finishing rolling is 1010~1050℃, preferably 1020~1040℃, to ensure the removal of the FeO / Fe2SiO4 eutectic compound with a low melting point on the surface of the slab, and to prevent the formation of red rust defects that are not conducive to pickling after cooling. In the present invention, the final rolling temperature of the finishing rolling refers to the temperature of the steel strip out of the finishing rolling unit. In order to make the thickness and mechanical properties of the finished product uniform and avoid the formation of Fe2O3 phase during the finishing rolling process, the final rolling temperature should be increased as much as possible. In the present invention, the hot rolling intermediate billet hot coil box process technology is adopted to keep a specific final rolling temperature at the head, middle and tail of the hot rolling intermediate billet before finishing rolling. Therefore, in the present invention, the final rolling temperature of the finishing rolling is 900~940℃, preferably 910~930℃. In addition, the lower the start rolling temperature of the finishing rolling, the faster the rolling speed, and the thinner the oxide layer thickness. Therefore, the present invention reduces the start rolling temperature as much as possible and increases the rolling speed to reduce the oxide layer thickness of the finished product. In the present invention, the rolling speed of the finish rolling is 1.10-1.70 m / s, preferably 1.20-1.50 m / s.

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

[0054] In some preferred embodiments of the present invention, a dephosphorization step is included before both rough rolling and finish rolling. The purpose of dephosphorization is to remove the heavy iron oxide scale formed by the surface combining with O at high temperature. This technical effect requires ensuring the minimum dephosphorization pressure and reasonably arranging the position of the dephosphorization nozzle. Based on this, in the present invention, the dephosphorization water pressure before rough rolling is 17~19MPa, preferably 18MPa; the dephosphorization water pressure before finish rolling is 24~26MPa, preferably 25MPa.

[0055] In the present invention, the rough rolling process may be performed in one pass, and the finishing rolling process may be performed in multiple passes, preferably 5 to 7 passes, specifically 5 passes, 6 passes, or 7 passes, and more preferably 7 passes.

[0056] Usually, the hot rolled thin steel strip is cooled to adjust the internal structure of the steel, and then coiled into a coil. In order to meet the performance requirements of the finished product, the hot rolled structure is 100% ferrite (abbreviated as: F), and the ferrite grain size is 8.5~10.5. 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 high temperature coiling precipitation rolling in hot rolling to precipitate Ti (C, N) and AlN particles, and then inhibit F growth during the recrystallization annealing process, and obtain a good texture orientation to improve deep drawing performance.

[0057] Based on this, the cooling method after hot rolling is two groups of concentrated header laminar cooling-air cooling-two groups of sparse header laminar cooling.

[0058] 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.

[0059] The present invention is advantageous for regulating the iron sheet structure and prefabricating iron sheet cracks by first centralized cooling, then air cooling, and finally sparse cooling. It should be noted that if the groups of centralized manifold laminar cooling and sparse manifold laminar cooling are arbitrarily increased or decreased, it will result in failure to prefabricate iron sheet cracks or cause abnormal hot-rolled microstructure, thereby affecting the final microstructure and performance of the finished product.

[0060] In the present invention, the water pressure of the 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 iron sheet 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 90% and 75% respectively.

[0061] The water pressure of the 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 45~55% and 45~55% respectively, and the cooling ratio of the upper header (or lower header) can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54% or 55%. The reason for this setting is that it is conducive to regulating the structure and microstructure of the hot-rolled iron sheet. In some embodiments of the present invention, the cooling ratios of the upper header and the lower header are preferably 50% and 50% respectively.

[0062] In some embodiments of the present invention, the spacing length between the cooling manifolds in the two groups of concentrated manifold laminar cooling is about 5 m, specifically 4.5 m, 5 m, 5.5 m, 6 m, preferably 5 m. The air cooling length between the two groups of concentrated manifold laminar cooling and the two groups of sparse manifold laminar cooling is about 10 m, specifically 8 m, 9 m, 10 m, 11 m, 12 m, preferably 10 m. In addition, the spacing length between the cooling manifolds in the two groups of sparse manifold laminar cooling is about 10 m, specifically 8 m, 9 m, 10 m, 11 m, 12 m, preferably 10 m. In the present invention, the steel strip brought out of the rolling mill is generally 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. Based on this, the cooling rate of the two groups of concentrated header laminar 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 groups of sparse header laminar cooling is 15~30℃ / s, preferably 18~25℃ / s; and then cooled to the coiling temperature of 700~740℃, preferably 710~730℃.

[0063] 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.

[0064] The results show that the thickness of the oxide layer in the steel strip is ≤11 μm. The thickness of the oxide layer 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.

[0065] In the present invention, the oxide layer structure is pre-eutectoid Fe3O4+eutectoid structure (Fe+Fe3O4)+FeO, and the oxide layer has no Fe2O3 phase component. Among them, the proportion of the pre-eutectoid Fe3O4 is 70-80%, the proportion of the eutectoid structure is 10-20%, the proportion of FeO is 5-10%, and there are obvious pre-cracks in the oxide layer structure, which can effectively promote the removal effect of pickling oxide scale. The oxide layer structure can be measured by methods known to those skilled in the art, and 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 6394 metallographic method.

[0066] The hot-rolled iron oxide scale control method of the deep-drawn structural steel strip provided by the present invention can obtain a steel plate whose oxide layer thickness and oxide layer structure fully meet the requirements of technical indicators.

[0067] In the present invention, after the coiling is completed, pickling treatment is performed.

[0068] 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 in the continuous rolling can adopt various conventional cold rolling mills, such as 4-5 frame 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 about 70%, which can be 60-85%, preferably 65-75%, and more preferably 70%. The pickling process section speed is 160-180 m / min, and 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.

[0069] In summary, due to the thinning oxide layer thickness of the deep-drawn structural steel strip involved in the present invention, the presence of FeO phase in the oxide layer structure that is easily reactive with hydrochloric acid, and the introduction of prefabricated cracks in the oxide layer, the pickling reaction efficiency of the pickling process is increased, and the production efficiency of the unit is significantly improved. The finished product after production has good technical and economic indicators and excellent surface quality, and can effectively meet the demand for raw materials of the annealing-leveling unit. The production technology of the present invention is adopted, on the one hand, to effectively improve the production 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, this technology can effectively improve the production capacity of Panzhihua Iron and Steel's general cold products, improve the surface quality level of the products, and has a good prospect for promotion and application.

[0070] To further illustrate the present invention, the following examples are provided for detailed description. The semi-iron molten iron used in the following examples of the present invention refers to the molten iron after vanadium is extracted from blast furnace molten iron.

[0071] The chemical composition detection method is: spark source atomic emission spectrometry analysis method for carbon steel and medium and low alloy steel, 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), the national standard is GB / T 20126.

[0072] 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.

[0073] Example 1

[0074] a. Smelting molten steel: The smelting equipment is a top-blown converter. The semi-iron molten steel after vanadium extraction from blast furnace molten iron is used as raw material. The temperature is 1374℃. Steelmaking auxiliary materials are added to melt to 1676℃ 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, followed by 450 kg of low-carbon manganese iron alloying. The molten steel tank is bottom-blown with argon gas on the small platform behind the furnace. The argon gas pressure is 350 Pa and the time is 4 minutes. The molten steel (based on the total weight of the molten steel, calculated as a single substance) is C: 0.045, Si: 0.01, Mn: 0.32, P: 0.016, S: 0.008, Als: 0.035, and the rest is Fe;

[0075] b. LF electric heating: Argon gas with a certain pressure (400 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 1622℃;

[0076] c. RH treatment: final deoxidation, molten steel temperature adjustment and alloying treatment are carried out, and the alloying order is aluminum iron, metal manganese, and titanium iron. The RH process treatment time is 35 minutes, and the exit temperature is 1597℃. After RH treatment, the molten steel obtained (based on the total weight of the molten steel, calculated as a single substance, w%) is: C: 0.0025, Si: 0.01, Mn: 0.31, P: 0.016, S: 0.008, Als: 0.034, Ti: 0.062, and the rest is Fe;

[0077] 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;

[0078] d. Hot rolling: The hot rolling slab has a soaking temperature of 1235°C, a soaking time of 40 min, a rough rolling start temperature of 1180°C, a rough rolling dephosphorization pressure of 17 MPa, a finishing rolling dephosphorization pressure of 26 MPa, a finishing rolling start temperature of 1028°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 925°C; the cooling method adopts two groups of centralized cooling (water pressure 0.6 MPa, upper / lower header cooling ratio of 90% / 75%) - air cooling - two groups of sparse laminar cooling (water pressure 0.6 MPa, upper / lower header cooling ratio of 50% / 50%), and a coiling temperature of 710°C. The thickness after rough rolling is 34 mm, the finishing rolling passes are 7, and the thickness after finishing rolling is 3.0 mm;

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

[0080] The oxide layer structure and thickness of the prepared hot-rolled steel strip were tested. The thickness of the oxide layer on the surface of the steel strip was 7.5 μm, and the oxide layer structure was pro-eutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO. There was no Fe2O3 phase in the oxide layer. The proportion of pro-eutectoid Fe3O4 was 80%, the proportion of eutectoid structure was 15%, and the proportion of FeO structure was 5%. There were obvious prefabricated cracks in the oxide layer structure, see the attached Figure 1 The surface quality of the strip after pickling is good, with no residual pickling scale defects, which meets the technical requirements for pickling raw materials of annealed deep-drawn structural steel strips.

[0081] Example 2

[0082] The preparation method is basically the same as that 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, and the rest is Fe, (Wt, %). The hot rolled steel plate produced by the above molten steel has a soaking temperature of 1228℃, soaking time of 32 min, rough rolling start temperature of 1175℃, rough rolling dephosphorization pressure of 19 MPa, finishing dephosphorization pressure of 24 MPa, finishing start temperature of 1040℃, finishing start rolling speed of 1.35m / s, thickness reduction ratios of the last two rolling mill stands of 12% and 8% respectively, and final rolling temperature of 915℃; the cooling method adopts two groups of centralized cooling (water pressure 0.6 MPa, upper / lower header cooling ratio of 90% / 75%) - air cooling - two groups of sparse laminar cooling (water pressure 0.6 MPa, upper / lower header cooling ratio of 50% / 50%), and coiling temperature of 720℃. The thickness after rough rolling is 35 mm, the number of finishing rolling passes is 7, and the thickness after finishing rolling is 4.1 mm. The thickness of the steel strip rolled by the pickling mill is 1.2 mm, the cold rolling reduction rate is 70.7%, the pickling mill stretching elongation is 1.5%, and the process section speed is 165 m / min.

[0083] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The thickness of the oxide layer on the strip surface was 8.5 μm, and the oxide layer structure was pro-eutectoid Fe3O4 + eutectoid structure (Fe + Fe3O4) + FeO. There was no Fe2O3 phase in the oxide layer. The proportion of pro-eutectoid Fe3O4 was 80%, the proportion of eutectoid structure was 10%, and the proportion of FeO structure was 10%. There were obvious prefabricated cracks in the oxide layer structure, as shown in Figure 1. Figure 2 The surface quality of the strip after pickling is good, with no residual pickling scale defects, which meets the technical requirements for pickling raw materials of annealed deep-drawn structural steel strips.

[0084] Comparative Example

[0085] The preparation method is basically the same as that of Example 1, except that the composition of the molten steel obtained after RH treatment is C: 0.0027, Si: 0.01, Mn: 0.30, P: 0.015, S: 0.004, Als: 0.042, Ti: 0.063, and the rest is Fe, (Wt, %). The hot-rolled steel plate produced by the above-mentioned molten steel has a rough rolling start temperature of 1145°C, a finishing rolling start temperature of 1080°C, a finishing rolling start rolling speed of 0.90m / s, and the thickness reduction rates of the last two rolling mill stands are 18% and 13% respectively; the cooling method adopts two groups of front-stage laminar cooling (water pressure 0.6MPa, upper / lower header cooling ratio 75% / 50%) water cooling-air cooling. The number of finishing rolling passes is 7, and the thickness after finishing rolling is 4.1 mm. The thickness of the steel strip rolled by the pickling mill is 1.2 mm, the elongation of the pickling mill is 1.5%, and the speed of the process section is 110 m / min.

[0086] The oxide layer structure and thickness of the prepared hot-rolled strip were tested. The oxide layer thickness of the strip surface was 15 μm, and the oxide layer structure was Fe2O3+pro-eutectoid Fe3O4+FeO, with the pro-eutectoid Fe3O4 ratio of 90% and the FeO ratio of about 10%. There were no prefabricated cracks in the oxide layer structure. Figure 3 The surface quality of the strip after pickling is poor, with many pickling oxide scale defects remaining, which does not meet the technical requirements for pickling raw materials for annealing deep-drawing structural steel strip.

[0087] 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 of deep drawn structural steel strip, 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 two groups of concentrated header laminar cooling-air cooling-two groups of sparse header laminar 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 45-55% and 45-55% respectively.

2. The hot rolling scale control method according to claim 1, characterized in that: The spacing length between the cooling headers in the two groups of centralized header laminar cooling is 4.5-6 m; The air cooling length between the two groups of concentrated header laminar cooling and the two groups of sparse header laminar cooling is 8 to 12 m; The spacing length between the cooling headers in the two groups of sparse header laminar cooling is 8 to 12 m.

3. The hot rolling scale control method according to claim 1 or 2, characterized in that: The cooling rate of the two groups of concentrated header laminar cooling is 25-45°C / s, the cooling rate of the air cooling is 5-10°C / s, and the cooling rate of the two groups of sparse header laminar cooling is 15-30°C / s.

4. The hot rolling scale control method according to any one of claims 1 to 3, 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≤0.0050%, Si 0-0.10%, Mn0.15-0.35%, P 0-0.025%, S 0-0.010%, Als 0.015-0.060%, Ti 0.045-0.075%, and the rest is Fe.

5. The hot rolling scale control method according to any one of claims 1 to 4, characterized in that: The soaking temperature is 1200-1240° C. and the soaking time is 0.5-1.5 h.

6. The hot rolling scale control method according to any one of claims 1 to 5, characterized in that: The step of dephosphorization is included before the rough rolling, and the water pressure of the dephosphorization is 17-19 MPa; The initial rolling temperature of the rough rolling is 1175~1210℃; The thickness of the intermediate billet obtained after the rough rolling is 34-38 mm.

7. The hot rolling scale control method according to any one of claims 1 to 6, characterized in that: The dephosphorization step is included before the finish rolling, and the water pressure of the dephosphorization is 24-26 MPa; The start rolling temperature of the finishing rolling is 1010-1050°C, the final rolling temperature is 900-940°C, and the rolling speed of the finishing rolling is 1.10-1.70 m / s; 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 finish rolling is 5 to 7.

8. The hot rolling scale control method according to any one of claims 1 to 7, characterized in that: The coiling temperature is 700-740°C; The thickness of the oxide layer in the steel strip is ≤11 μm, and its structure is pro-eutectoid Fe3O4+eutectoid structure+FeO, the oxide layer has no Fe2O3 phase, and the eutectoid structure includes Fe+Fe3O4; The proportion of the pro-eutectoid Fe3O4 is 70-80%, the proportion of the eutectoid structure is 10-20%, and the proportion of FeO is 5-10%.

9. The hot rolling scale control method according to any one of claims 1 to 8, wherein the pickling speed in the pickling rolling is 160 to 180 m / min, and the tensile elongation is 1.00 to 1.50%; The cold rolling reduction rate in the acid rolling is 60-85%.

10. A deep-drawn structural steel strip, characterized in that: The hot rolled scale of the deep drawn structural steel strip is controlled by the control method described in any one of claims 1 to 9.

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