A method for controlling hot-rolled scale of steel strip for bell annealing stamping and the steel strip

Abstract

The present invention provides a method for controlling hot-rolled scale of strip steel for bell-type annealing stamping, comprising the following steps: (1) heating the slab to 1190 - 1230 °C and soaking for 30 - 90 min; (2) rough rolling the soaked slab, descaling the slab, and the rough rolling starting temperature being 1175 - 1210 °C; (3) finish rolling the rough-rolled slab, the finish rolling starting temperature being 1020 - 1050 °C, the finish rolling ending temperature being 860 - 900 °C, the finish rolling starting rolling speed being 1.45 - 1.55 m / s, and the thickness reduction ratios of the last two rolling mill stands being ≤17% and ≤12% respectively; (4) cooling the finish-rolled slab in the order of first pre-cooling, first air-cooling, second pre-cooling, second air-cooling, and laminar flow cooling, and then coiling to obtain strip steel; the cooling speeds of the first pre-cooling and the second pre-cooling are 5 - 10 °C / s, and the cooling speed of the laminar flow cooling is 10 - 30 °C / s; (5) subjecting the strip steel to pickling and rolling, and the speed of the pickling process section being 170 - 190 m / min. The present invention also provides a strip steel for bell-type annealing stamping prepared by using the above method.

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 hood-recessed stamping, and also relates to a steel strip for hood-recessed stamping. Background Art

[0002] The iron oxide scale on the surface of hot-rolled steel strip has certain deformation ability and anti-corrosion performance, but its ductility and adhesion are not enough to adapt to cold forming or cold rolling with large strain (elastic deformation and plastic deformation). In order to improve the surface quality of the steel strip after cold deformation, online continuous pickling or shot blasting must be carried out. The thickness and structure of the iron oxide scale on the surface of the steel strip are related to the main process parameters such as chemical composition, rolling and cooling. The thinner the oxide layer thickness and the higher the FeO ratio, the higher the pickling efficiency.

[0003] The low speed of the pickling process, especially the pickling process, has always been the key bottleneck that limits the cold rolling capacity. The hot-rolled raw materials for annealing stamping are usually designed to be finished in the austenite zone and coiled at 550℃. The surface oxide layer structure is composed of Fe 2 O 3 , proeutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ), and a small amount of FeO, the oxide layer thickness is 12-18 μm, among which Fe 3 O 4 The ratio is ≥50%, and the eutectoid structure ratio is about 40%. 2 O 3 In the pickling process, the reaction speed with hydrochloric acid is the slowest and the most difficult to wash out. In addition, due to the Fe 3 O 4 It is relatively dense and has excellent plasticity and adhesion. The chemical reaction efficiency between the iron oxide scale and hydrochloric acid in the pickling stage is not high. 2 O 3 Therefore, in the production process, a low-speed, high-concentration, high-temperature hydrochloric acid pickling process is usually used to organize production (the pickling process speed is about 130m / min), which is not conducive to the production efficiency of the cold rolling process, and the steel strip will be partially over-pickled, reducing the yield rate of the steel strip. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a method for controlling hot-rolled oxide scale on a steel strip for hood-recessed stamping, and also provides a steel strip for hood-recessed stamping.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for controlling hot-rolled scale on a steel strip for cover annealing stamping, comprising the following steps:

[0007] (1) Heating the slab to 1190 - 1230 °C and holding for 30 - 90 min;

[0008] (2) Rough rolling the slab after soaking, and then descaling the slab. The rough rolling starting temperature is 1175 - 1210 °C;

[0009] (3) Finish rolling the slab after rough rolling. The finish rolling starting temperature is 1020 - 1050 °C, and the finish rolling ending temperature is 860 - 900 °C. Among them, the finish rolling starting rolling speed is 1.45 - 1.55 m / s, and the thickness reduction ratios of the last two rolling mill stands are ≤17% and ≤12% respectively;

[0010] (4) Cooling the slab after finish rolling in the order of first pre-cooling, first air-cooling, second pre-cooling, second air-cooling, and laminar flow cooling, and then coiling to obtain a steel strip;

[0011] Among them, the cooling rates of the first pre-cooling and the second pre-cooling are 5 - 10 °C / s, and the cooling rate of the laminar flow cooling is 10 - 30 °C / s;

[0012] (5) Subjecting the steel strip to pickling and cold rolling, and the speed of the pickling process section is 170 - 190 m / min.

[0013] Further, the composition of the slab in step (1) by weight percentage is: C: ≤0.08, Si: 0 - 0.10, Mn: 0.15 - 0.35, P: 0 - 0.025, S: 0 - 0.015, Als: 0.015 - 0.060, and the rest is Fe.

[0014] Further,

[0015] After step (1), it further includes a step of descaling the slab, and the descaling water pressure is 17 - 18 Mpa;

[0016] In step (2), water with a descaling water pressure of 17 - 18 Mpa is used for descaling.

[0017] Further, in step (3), the coiling temperature is 540 - 570 °C.

[0018] Further, in step (4), the water pressure during the first pre-cooling and the second pre-cooling is 3 Mpa, and the water pressure during the laminar flow cooling is 12 Mpa.

[0019] Further, in step (5), the pickling and temper rolling elongation is 1.0 - 1.50%, and after pickling, it further includes a step of cold tandem rolling the steel strip, where the cold rolling reduction ratio is 65 - 80%.

[0020] Furthermore, the thickness of the hot-rolled oxide scale on the steel strip is ≤ 12 μm, and there are prefabricated cracks in the oxide scale.

[0021] Furthermore, the structure of the hot-rolled oxide scale on the steel strip is proeutectoid Fe 3 O 4 , with a eutectoid structure containing Fe and Fe 3 O 4 , and no Fe 2 O 3 phase. Among them, the proportion of proeutectoid Fe 3 O 4 is 25 - 35%, and the proportion of the eutectoid structure is 65 - 75%.

[0022] Furthermore, before step (1), there are also steps of smelting molten steel, LF refining, and continuous casting.

[0023] The present invention also provides a cold rolled and annealed steel strip for stamping prepared by the above method.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] (1) In the production process of the method of the present invention, process measures such as controlling the chemical composition range, hot rolling heating temperature, finish rolling starting temperature, descaling pressure, finish rolling temperature, cooling system, and coiling temperature are adopted. The obtained steel strip has an oxide layer thickness of ≤ 12 μm, and the oxide layer structure is proeutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ), the oxide layer has no Fe 2 O 3 phase, the proportion of proeutectoid Fe 3 O 4 is 25 - 35%, and the proportion of the eutectoid structure is 65 - 75%. There are obvious prefabricated cracks in the oxide layer structure, effectively promoting the removal effect of pickling oxide scale.

[0026] (2) The speed of the pickling process section is increased to 170 - 190 m / min, avoiding the deficiencies of the original process technology such as the oxide layer being difficult to wash out, prone to over-pickling and under-pickling defects. After pickling, the surface quality is excellent, and the technical and economic indicators are good.

[0027] (3) Compared with the steel plates produced by the conventional manufacturing process of cold rolled and annealed steel strips for stamping, the production process adopted in the technical solution of the present invention is simple, the efficiency of the pickling process section unit is improved, the comprehensive performance of the product is excellent, and the promotion and application prospect is good. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is the morphology diagram of the prefabricated crack of the hot-rolled scale of the steel strip for cover annealing stamping in Embodiment 1 of the present invention;

[0030] Figure 2 It is the morphology diagram of the prefabricated crack of the hot-rolled scale of the steel strip for cover annealing stamping in Embodiment 2 of the present invention;

[0031] Figure 3 It is the morphology diagram of the prefabricated crack of the hot-rolled scale of the steel strip for cover annealing stamping in Embodiment 3 of the present invention;

[0032] Figure 4 It is the morphology diagram of the hot-rolled scale of the steel strip for cover annealing stamping without prefabricated crack in Comparative Example 1 of the present invention. Detailed implementation manners

[0033] To make the purpose, technical solutions and advantages of the present invention clearer and more understandable, the following will further elaborate on the embodiments of the present invention in detail in combination with specific embodiments and with reference to the drawings.

[0034] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0035] The present invention provides a control method for the hot-rolled scale of the steel strip for cover annealing stamping, which generally includes the following steps: converter smelting → LF refining → continuous casting → reheating → descaling → rough rolling → descaling → finish rolling → cooling → coiling → pickling and rolling → bell annealing → skin pass rolling → finishing → packaging → warehousing.

[0036] Converter smelting specifically involves smelting hot metal from a blast furnace and smelting furnace charge in a converter to obtain molten steel, and then deoxidizing and alloying the molten steel during the tapping process and in an LF refining furnace; during the alloying step, ferroaluminum alloy, metallic manganese, etc. are added to the deoxidized molten steel to obtain molten steel (based on the total weight of the molten steel, in elemental form, w%): C: ≤0.08, Si: 0 - 0.10, Mn: 0.15 - 0.35, P: 0 - 0.025, S: 0 - 0.015, Als: 0.015 - 0.060, and the rest is Fe. To make the content of S in the furnace charge less than or equal to 0.015% of the total weight of the hot metal charged, low-sulfur hot metal or semi-steel smelting can be used. The smelting time is the conventional smelting time, preferably 35 - 45 minutes. It should be understood that the technical solution adopted in the converter smelting process is a method well-known to those skilled in the art.

[0037] The LF refining process only performs temperature adjustment of the molten steel, fine adjustment of alloy content, and argon bottom blowing treatment of the ladle. Argon with a pressure of 200 - 400 Pa is introduced into the bottom of the molten steel ladle for 4 - 6 minutes. The argon flow rate is conditioned such that the molten steel does not overflow violently, which can avoid secondary oxidation of the molten steel and too rapid temperature drop, enabling inclusions in the steel to float up sufficiently and further improving the cleanliness of the steel. The treatment time of the LF refining process is 10 - 25 minutes, and the tapping temperature is 1610 - 1635 °C. The obtained molten steel (based on the total weight of the molten steel, in elemental form, w%) is: C: ≤0.08, Si: 0 - 0.10, Mn: 0.15 - 0.35, P: 0 - 0.025, S: 0 - 0.015, Als: 0.015 - 0.060, and the rest is Fe. It should be understood that the technical solution adopted in the LF refining process is a method well-known to those skilled in the art.

[0038] It should be understood that the continuous casting step can adopt a method well-known to those skilled in the art. The method of the present invention casts the refined molten steel into a pre-baked tundish and then into a slab through a slab continuous caster with full-process protection. After casting, cooling can be carried out according to the conventional method, such as natural cooling at room temperature. The composition of the slab by weight percentage is: C: ≤0.08, Si: 0 - 0.10, Mn: 0.15 - 0.35, P: 0 - 0.025, S: 0 - 0.015, Als: 0.015 - 0.060, and the rest is Fe.

[0039] Next, the slab will be subjected to the steps of reheating → descaling → rough rolling → descaling → finish rolling → cooling → coiling → pickling and rolling, as Figure 1 shown, specifically including the following steps:

[0040] (1) Heat the slab to 1190 - 1230 °C, and the soaking time is 30 - 90 min. After step (1), there is also a step of descaling the slab, and the descaling water pressure is 17 - 18 Mpa.

[0041] (2) The slab after soaking is rough rolled, and then descaled. The rough rolling starting temperature is 1175 - 1210 °C, and descaling is carried out with water having a descaling water pressure of 17 - 18 Mpa.

[0042] (3) The slab after rough rolling is finish rolled. The finish rolling starting temperature is 1020 - 1050 °C, and the finish rolling ending temperature is 860 - 900 °C. Among them, the finish rolling starting rolling speed is 1.45 - 1.55 m / s, and the thickness reduction ratios of the last two rolling mill stands are ≤17% and ≤12% respectively.

[0043] (4) The slab after finish rolling is cooled in the order of first pre - cooling, first air - cooling, second pre - cooling, second air - cooling, and laminar flow cooling, and then coiled at 540 - 570 °C to obtain a steel strip.

[0044] Among them, the cooling rates of the first pre - cooling and the second pre - cooling are 5 - 10 °C / s, and the cooling rate of the laminar flow cooling is 10 - 30 °C / s. The water pressure during the first pre - cooling and the second pre - cooling is 3 Mpa, and the water pressure during the laminar flow cooling is 12 Mpa.

[0045] (5) The steel strip is pickled and cold rolled. Among them, the pickling and temper rolling elongation is 1.0 - 1.50%, and the speed of the pickling process section is 170 - 190 m / min. After pickling, it also includes the step of cold tandem rolling the steel strip, where the cold rolling reduction ratio is 65 - 80%.

[0046] The thickness of the hot - rolled scale of the steel strip prepared by the method of the present invention is ≤12 μm, and there are pre - formed cracks in the scale. The structure of the hot - rolled scale of the steel strip is pro - eutectoid Fe 3 O 4 , has a eutectoid structure of Fe and Fe 3 O 4 , and there is no Fe 2 O 3 phase. Among them, the proportion of pro - eutectoid Fe 3 O 4 is 25 - 35%, and the proportion of the eutectoid structure is 65 - 75%.

[0047] The hot - rolling step is to roll the cast slab after heating. The purpose of rolling is to make the continuous casting slab reach the required hot - rolled thickness. The reheating and soaking temperature in hot - rolling refers to the temperature of the billet when it exits the heating furnace. Heating at this temperature can fully dissolve micro - alloying elements, eliminate chemical element segregation caused by dendritic segregation in the casting blank; at the same time, make the A1N particles formed in the as - cast state redissolve, avoiding adverse effects on the structure, mechanical properties and grain orientation during rolling and annealing. The rough rolling starting temperature in hot - rolling is to ensure the removal of low - melting - point FeO / Fe 2 SiO 4Eutectic compounds prevent the formation of red rust defects that are unfavorable for pickling after cooling. The purpose of the descaling process of the steel strip is to remove the thick scale formed by the combination of the surface and O at high temperature, and it is necessary to ensure the minimum descaling pressure and the reasonable arrangement of descaling nozzles. The finishing rolling temperature refers to the temperature of the steel strip when it exits the finishing mill. In order to make the thickness and mechanical properties of the finished product uniform and avoid the formation of Fe 2 phase during the finishing rolling process, the finishing rolling temperature should be increased as much as possible. The hot rolling intermediate billet hot coil box process technology is adopted to keep the head, middle and tail of the hot rolling intermediate billet before finishing rolling at a specific finishing rolling temperature. The higher the finishing rolling starting temperature, the slower the rolling speed, and the thicker the oxide layer. Reducing the starting temperature and increasing the rolling speed as much as possible is beneficial to reducing the thickness of the oxide layer of the finished product; in the finishing rolling process, in order to avoid the formation of Fe 2 O 3 phase at the edge, control the rolling reduction rate of the last two stands to avoid the phase transformation of FeO at the edge to Fe 2 O 3 phase. 2 O 3 phase transformation.

[0048] The post-rolling cooling step is secondary precooling (water pressure 3 MPa) - laminar flow cooling (water pressure 12 MPa). The interval between the first precooling equipment and the second precooling equipment is 15 m, and the interval between the second precooling equipment and the laminar flow cooling equipment is 15 m. Various conventional methods can be used. Usually, the thin steel strip rolled by hot rolling adjusts the internal tissue state of the steel after cooling phase transformation, and then is coiled into a coil. In order to meet the performance requirements of the finished product, the hot-rolled structure is F, a small amount of P and Fe 3 C, and the ferrite grain size is 10 - 11.0 grades; 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 adopt low-temperature rolling in hot rolling to avoid the premature precipitation of A1N particles. In addition, in order to obtain prefabricated oxide layer cracks, the cooling mode of the present invention is post-rolling precooling (1 group of cooling nozzles, 3 MPa) - air cooling - precooling (1 group of cooling nozzles, 3 MPa) - air cooling - laminar flow cooling (3 - 7 groups of cooling nozzles, 12 MPa). The steel strip coming out of the rolling mill must prefabricate oxide layer cracks and be cooled to the coiling temperature for coiling within a very short time at a very high cooling rate.

[0049] The acid rolling process can include two consecutive steps of pickling and cold tandem rolling and can adopt various conventional methods. Usually, the hot-rolled thin strip steel is welded at the head of the acid rolling mill to form a continuous strip, and after straightening, skin pass breaking scale, pickling, alkali washing, drying, and trimming, continuous rolling is carried out. The cold rolling mill can adopt various conventional cold tandem rolling mills, such as a 4-5 stand cold tandem rolling mill. After acid rolling, the thickness of the steel plate is reduced to the thickness of the raw material for the bell annealing furnace. The cold rolling reduction rate is 65-80%, and the cold rolling reduction rate is the total reduction rate of cold tandem rolling. The finished product thickness is set according to the thickness of different pickling raw materials. The speed of the pickling process section is 170-190 m / min, the surface scale is removed, and the surface quality is improved. Some processes of the acid rolling step can adopt methods and technologies well-known to those skilled in the art.

[0050] The steel strip for bell annealing stamping of the present invention adopts the chemical composition of low-carbon aluminum killed steel, and the hot rolling process adopts the technical scheme of low-temperature starting rolling and high-speed finishing rolling in finish rolling, realizing the thinning of the oxide layer of the pickling raw material. For typical varieties with the thickness of the pickling raw material test coil < 3.5 mm, the scale thickness is ≤ 10 μm, and for typical varieties with the thickness > 3.5 mm, the scale thickness is ≤ 12 μm. The surface oxide layer structure is composed of proeutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ), and there is no Fe 2 O 3 phase component in the oxide layer. The proportion of proeutectoid Fe 3 O 4 is 25-35%, and the proportion of eutectoid structure is 65-75%. After finish rolling, the laminar cooling process in the laminar cooling stage adopts the scheme of secondary pre-cooling (water pressure 3 MPa) - laminar flow cooling (water pressure 12 MPa), prefabricating oxide layer cracks on the surface oxide layer of the steel strip, effectively promoting the removal effect of pickling scale. After production, the surface quality inspection results show that the pickling surface quality of the steel strip for bell annealing stamping produced by this method is excellent, the speed of the pickling process section is increased to more than 170 m / min, and the technical and economic indicators of the finished product are good.

[0051] The thickness of the oxide layer in the control method of hot-rolled scale for cold rolling and stamping steel strip of the present invention is ≤12 μm. The thickness of the oxide layer can be measured by methods well-known to those skilled in the art. The test specimen can be a polished or etched metallographic sample. The specimen etchant is 1-2% hydrochloric acid alcohol solution, and the etching time is 5-8 s, such as the metallographic method of GB / T 6394. The thickness and structure of the oxide layer of the steel plate in the control method of hot-rolled scale for cold rolling and stamping steel strip provided by the present invention fully meet the requirements of the technical indicators. In the present invention, the detection methods for chemical components are the spark source atomic emission spectrometry analysis method for carbon steel and medium and low alloy steel, and the national standard is GB / T 4336; the 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. The detection methods for the scale thickness, structure and microstructure in the present invention are the metal microstructure inspection method of GB / T 13298.

[0052] Since the control of the oxide layer structure of the cold rolling and stamping steel strip involved in the present invention is good, the oxide layer thickness is thinner, and there are obvious prefabricated cracks in the oxide layer on the surface of the steel strip, which increases the pickling reaction rate, and the production efficiency of the unit is significantly improved. The technical and economic indicators of the finished product after production are good, and the surface quality is excellent, which can effectively meet the requirements of downstream processes for raw materials. Adopting the technical solution of the present invention, on the one hand, the pickling process capacity is effectively improved, and on the other hand, the pickling effect of the steel strip is improved, which has an obvious promoting effect on reducing the surface quality defects of the steel strip. Under the current good external conditions of the market, the technical solution of the present invention expands the production capacity of Panzhihua Iron and Steel's cold-rolled products, improves the surface quality level of the production line, and has good prospects for popularization and application.

[0053] In addition, the present invention also provides a cold rolling and stamping steel strip prepared by the above method.

[0054] The following further elaborates the present invention in conjunction with specific embodiments. The embodiments are only used to illustrate the present invention and are not intended to limit the present invention in any way.

[0055] Example 1

[0056] a. Smelting molten steel: The smelting equipment is a top-blown converter. The semi-steel after vanadium extraction from blast furnace hot metal is used as the raw material, with a temperature of 1366 °C. It is melted with steelmaking auxiliary materials to 1670 °C and tapped into a ladle. When 1 / 3 of the steel is tapped, 400 Kg of ferrosilicon aluminum is added for pre-deoxidation, and then 500 Kg of low-carbon ferromanganese is added for alloying. The ladle is treated with bottom blowing argon on the small platform behind the furnace, with an argon pressure of 200-400 Pa and a time of 4 minutes.

[0057] b. LF Electric Heating: Argon gas at a certain pressure (200 - 400 Pa) is introduced into the bottom of the ladle for 5 minutes. The argon gas flow rate is conditioned such that the molten steel does not overflow significantly. The termination temperature of the LF treatment is 1625°C. During the LF process, the alloy composition is slightly adjusted to obtain molten steel (based on the total weight of the molten steel, in elemental form) with C: 0.03, Si: 0.01, Mn: 0.30, P: 0.018, S: 0.010, Als: 0.035, and the rest is Fe.

[0058] c. Continuous Casting: The ladle is transported to the casting position. The sliding gate A1 stopper rod at the bottom of the ladle allows the molten steel to flow automatically into the tundish, and then through the A1 stopper rod, it is drained into the mold for continuous casting. The entire process uses protective slag for protected casting, and after casting, it is cooled into a hot-rolled slab with a thickness of 200 mm.

[0059] d. Hot Rolling: The soaking temperature of the hot-rolled slab is 1230°C, and the soaking time is 30 min. The rough rolling starting temperature is 1210°C, the descaling pressure is 17 MPa, the finishing rolling starting temperature is 1020°C, the finishing rolling starting rolling speed is 1.45 m / s. The thickness reduction ratios of the last two rolling mill stands are 14% and 8% respectively, and the finishing rolling temperature is 900°C. The slab after finishing rolling is cooled in the order of the first pre-cooling (water pressure 3 MPa), the first air cooling, the second pre-cooling (water pressure 3 MPa), the second air cooling, and the front laminar cooling (water pressure 12 MPa), and then coiled at 570°C. The cooling rates of the first pre-cooling and the second pre-cooling are 5°C / s, the pre-cooling time is 0.13 s, the cooling rate of the laminar cooling is 10°C / s, and the laminar cooling time is 3.75 s. Subsequently, it is air-cooled until it is coiled by the coiler. The thickness after rough rolling is 34 mm, the number of rolling passes in finishing rolling is 6, and the thickness after finishing rolling is 3.0 mm.

[0060] e. Acid Pickling and Cold Rolling: The steel strip is rolled to a thickness of 0.8 mm by the acid pickling and cold rolling mill. The cold rolling reduction ratio is 73.3%, the elongation rate of the tension leveling in the pickling line is 1.5%, and the speed of the pickling process section is 170 m / min.

[0061] The prepared hot-rolled steel strip is tested for the structure and thickness of the oxide layer. The thickness of the oxide layer on the surface of the steel strip is 8 μm, and the oxide layer structure is proeutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ). There is no Fe 2 O 3 phase in the oxide layer. The proportion of proeutectoid Fe 3 O 4 is 35%, and the proportion of the eutectoid structure is 65%. As Figure 1 shown, there are obvious prefabricated cracks in the oxide layer structure. After pickling, the surface quality of the steel strip is good, without residual pickling oxide scale defects, meeting the technical requirements of the pickling raw material for the cold rolling and annealing for stamping steel strip.

[0062] Example 2

[0063] The preparation method is basically the same as that of Example 1, except that the chemical composition of the molten steel obtained by converter smelting is C: 0.03, Si: 0.02, Mn: 0.28, P: 0.017, S: 0.008, Als: 0.032, and the rest is Fe, (Wt%). The hot-rolled steel plate produced with the above molten steel has a soaking temperature of 1210°C for the hot-rolled slab, a soaking time of 60 min, a rough rolling starting temperature of 1175°C, a descaling pressure of 17.4 MPa, a finishing rolling starting temperature of 1050°C, a finishing rolling starting rolling speed of 1.5 m / s, and the thickness reduction ratios of the last two rolling mill stands are 13% and 7% respectively, and the final rolling temperature is 880°C; the slab after finishing rolling is cooled in the order of the first pre-cooling (water pressure 3 MPa), the first air cooling, the second pre-cooling (water pressure 3 MPa), the second air cooling, and the front laminar cooling (water pressure 12 MPa), and then coiled at 555°C. The cooling rates of the first pre-cooling and the second pre-cooling are 8°C / s, the pre-cooling time is 0.12 s, the cooling rate of the laminar cooling is 20°C / s, the laminar cooling time is 3.53 s, and then air-cooled to the coiler for coiling. The thickness after rough rolling is 35 mm, the number of finishing rolling passes is 6, and the thickness after finishing rolling is 4.1 mm. The steel strip is rolled to a thickness of 1.2 mm by an acid rolling mill, the cold rolling reduction ratio is 70.7%, the tension leveling elongation rate of the pickling line is 1.3%, and the speed of the pickling process section is 180 m / min.

[0064] 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 is 8.5 μm, and the oxide layer structure is proeutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ), there is no Fe 2 O 3 phase in the oxide layer, the proportion of proeutectoid Fe 3 O 4 is 30%, and the proportion of eutectoid structure is 70%. As Figure 2 shown, there are obvious prefabricated cracks in the oxide layer structure. The surface quality of the steel strip after pickling is good, without residual pickling scale defects, meeting the technical requirements of the pickling raw material for the cold rolling and stamping steel strip.

[0065] Example 3

[0066] The preparation method and chemical composition of the molten steel are basically the same as those in Example 2. The soaking temperature of the hot-rolled slab is 1190 °C, the soaking time is 90 min, the rough rolling starting temperature is 1190 °C, the descaling pressure is 18 MPa, the finishing rolling starting temperature is 1035 °C, the finishing rolling starting rolling speed is 1.55 m / s, the thickness reduction ratios of the last two rolling mill stands are 13% and 7% respectively, and the finishing rolling temperature is 860 °C; the slab after finishing rolling is cooled in the order of the first pre-cooling (water pressure 3 MPa), the first air cooling, the second pre-cooling (water pressure 3 MPa), the second air cooling, and the front laminar cooling (water pressure 12 MPa), and then coiled at 540 °C. The cooling rates of the first pre-cooling and the second pre-cooling are 10 °C / s, the pre-cooling time is 0.11 s, the cooling rate of the laminar cooling is 30 °C / s, the laminar cooling time is 3.3 s, and then it is air-cooled to be coiled by the coiler. The thickness after rough rolling is 35 mm, the number of rolling passes in finishing rolling is 6, and the thickness after finishing rolling is 4.1 mm. The steel strip is rolled to a thickness of 1.2 mm by the acid rolling mill, the cold rolling reduction ratio is 70.7%, the elongation rate of the tension leveling in the pickling line is 1.3%, and the speed of the pickling process section is 190 m / min.

[0067] 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 is 8.5 μm, and the oxide layer structure is proeutectoid Fe 3 O 4 + eutectoid structure (Fe + Fe 3 O 4 ), there is no Fe 2 O 3 phase in the oxide layer, the proportion of proeutectoid Fe 3 O 4 is 25%, and the proportion of the eutectoid structure is 75%. As Figure 3 shown, there are obvious prefabricated cracks in the oxide layer structure. After pickling, the surface quality of the steel strip is good, and there is no residual pickling scale defect, which meets the technical requirements of the pickling raw material for the cold rolling and annealing stamping steel strip.

[0068] Comparative Example 1

[0069] 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: 0.028%, Si: 0.01%, Mn: 0.25, P: 0.018, S: 0.012, Als: 0.038, and the rest is Fe (wt%). The hot rolled steel plate produced by the above molten steel has a soaking temperature of 1226°C, a soaking time of 40min, a rough rolling temperature of 1140°C, a descaling pressure of 17.0MPa, a finishing rolling temperature of 1065°C, a finishing rolling speed of 1.0m / s, and the thickness reduction rates of the last two rolling mill stands are 18% and 13% respectively, and the final rolling temperature is 865°C; the cooling method adopts front-stage laminar cooling (water pressure 12MPa) water cooling, and the coiling temperature is 550°C. The thickness after rough rolling is 35mm, the number of finishing rolling passes is 6, and the thickness after finishing rolling is 4.1mm. 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 pickling process section speed is 130 m / min.

[0070] 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 13 μm, and the oxide layer structure was Fe 2 O 3 , eutectoid Fe 3 O 4 , eutectoid structure (Fe and Fe 3 O 4 ), first eutectoid Fe 3 O 4 The ratio is 60%, and the ratio of eutectoid structure is 40%. Figure 4 As shown, there are no prefabricated cracks in the oxide layer structure. The surface quality of the steel strip after pickling is poor, and there are many pickling oxide scale defects remaining, which does not meet the technical requirements for pickling raw materials for steel strip for hood stamping.

[0071] It should be particularly pointed out that the various components or steps in the above-mentioned embodiments can be cross-linked, replaced, added, or deleted with each other. Therefore, the combinations formed by these reasonable arrangements and combinations should also fall within the scope of protection of the present invention, and the scope of protection of the present invention should not be limited to the embodiments.

[0072] Those of ordinary skill in the art should understand that: The discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention (including the claims) is limited to these examples; Under the concept of the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other variations in different aspects of the embodiments of the present invention as described above, and they are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the embodiments of the present invention shall be included within the protection scope of the embodiments of the present invention.

Claims

1. A method for controlling hot-rolled scale on steel strip for skin pass stamping, characterized in that, it includes the following steps: (1) Heating the slab to 1190 - 1230 °C, with soaking time of 30 - 90 min; (2) Rough rolling the soaked slab, and then descaling the slab. The rough rolling starting temperature is 1175 - 1210 °C; (3) Finish rolling the rough-rolled slab. The finish rolling starting temperature is 1020 - 1050 °C, and the finish rolling ending temperature is 860 - 900 °C. Among them, the finish rolling starting rolling speed is 1.45 - 1.55 m / s, and the thickness reduction ratios of the last two rolling mill stands are ≤17% and ≤12% respectively; (4) Cooling the finish-rolled slab in the order of first pre-cooling, first air-cooling, second pre-cooling, second air-cooling, and laminar flow cooling, and then coiling to obtain the steel strip; wherein, the cooling speed of the first pre-cooling and the second pre-cooling is 5 - 10 °C / s, and the cooling speed of the laminar flow cooling is 10 - 30 °C / s; (5) Subjecting the steel strip to pickling and cold rolling, and the speed of the pickling process section is 170 - 190 m / min.

2. The method according to claim 1, characterized in that, in step (1), the composition of the slab by weight percentage is: C: ≤0.08, Si: 0 - 0.10, Mn: 0.15 - 0.35, P: 0 - 0.025, S: 0 - 0.015, Als: 0.015 - 0.060, and the rest is Fe.

3. The method according to claim 1, characterized in that, after step (1), it further includes a step of descaling the slab, and the descaling water pressure is 17 - 18 Mpa; in step (2), water with a descaling water pressure of 17 - 18 Mpa is used for descaling.

4. The method according to claim 1, characterized in that, in step (4), the coiling temperature is 540 - 570 °C.

5. The method according to claim 1, characterized in that, in step (4), the water pressure during the first pre-cooling and the second pre-cooling is 3 Mpa, and the water pressure during the laminar flow cooling is 12 Mpa.

6. The method according to claim 1, characterized in that, in step (5), the pickling and temper rolling elongation is 1.0 - 1.50%, and after pickling, it further includes a step of cold tandem rolling the steel strip, wherein the cold rolling reduction ratio is 65 - 80%.

7. The method according to claim 1, characterized in that, the thickness of the hot-rolled scale on the steel strip is ≤12 μm, and there are prefabricated cracks in the scale.

8. The method according to claim 1, characterized in that, The structure of the scale on hot-rolled steel strip is proeutectoid Fe 3 O 4 , with a eutectoid structure containing Fe and Fe 3 O 4 , and without the Fe 2 O 3 phase. Among them, the proportion of proeutectoid Fe 3 O 4 is 25 - 35%, and the proportion of the eutectoid structure is 65 - 75%.

9. The method according to claim 1, characterized in that, before step (1), it further includes steps of smelting molten steel, LF refining, and continuous casting.

10. A skin pass stamping steel strip prepared by using the method according to any one of claims 1 - 9 above.

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