A method for controlling the iron oxide scale of hot-rolled steel strip for hot-dip galvanizing and stamping, and the steel strip

Abstract

This invention provides a method for controlling the iron oxide scale on hot-rolled steel strip for hot-dip galvanizing and stamping, comprising the following steps: (1) heating the slab to 1200-1240℃ and homogenizing it for 30-90 minutes; (2) rough rolling the homogenized slab and descaling it, with a rough rolling start temperature of 1175-1200℃; (3) finishing rolling the rough-rolled slab, with a finishing rolling start temperature of 1010-1050℃, a finishing rolling temperature of 860-900℃, and a finishing rolling start speed of 1.45-1.5. 5 m / s, the thickness reduction rates of the last two mill stands are ≤15% and ≤10% respectively; (4) the slab after finishing 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 to obtain steel strip; the cooling rate of the first pre-cooling and second pre-cooling is 5~10℃ / s, and the cooling rate of laminar flow cooling is 10~30℃ / s; (5) the steel strip is pickled, and the pickling process speed is 160~180m / min. The present invention also provides a hot-dip galvanized stamping steel strip prepared by the above method.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for controlling the iron oxide scale of hot-rolled steel strips used in hot-dip galvanizing and stamping, and also relating to a type of steel strip used in hot-dip galvanizing and stamping. Background Technology

[0002] While the iron oxide scale on the surface of hot-rolled steel strip has some deformability, it is insufficient to support the degree of deformation during cold forming or cold rolling processes with large strain. The non-uniform deformation caused by the oxide layer leads to a deterioration in surface quality. Therefore, to improve the surface quality of steel strip after cold deformation or cold rolling, online continuous pickling or shot blasting is necessary. It is generally believed that the thinner the iron oxide scale on the surface of the steel strip and the higher the FeO ratio, the higher the pickling efficiency.

[0003] The low speed of the pickling and rolling process, especially the pickling section, has always been a bottleneck for cold rolling capacity. Ordinary hot-dip galvanized stamping steel hot-rolled raw materials are typically designed with austenitic final rolling and a 700℃ high-temperature coiling process. The surface oxide layer structure consists of Fe2O3, a high proportion of proeutectoid Fe3O4, and a small amount of FeO, with an oxide layer thickness of 14–20 μm. The Fe3O4 in the oxide layer is relatively dense and possesses excellent plasticity and adhesion. During the pickling stage, the chemical reaction efficiency between the iron oxide scale and hydrochloric acid is low, and the surface Fe2O3 phase further reduces the pickling reaction efficiency. Therefore, in production, a low-speed, high-concentration, high-temperature hydrochloric acid pickling process is usually adopted (the pickling section speed is around 120 m / min). This is detrimental to the production efficiency of the cold rolling process and can also cause localized over-pickling of the steel strip, reducing the strip yield. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for controlling the hot-rolled iron oxide scale of hot-dip galvanized stamping steel strip, and also to provide a hot-dip galvanized stamping steel strip.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for controlling the hot-rolled iron oxide scale on hot-dip galvanized stamping steel strip, comprising the following steps:

[0007] (1) Heat the slab to 1200-1240℃ and the heating time is 30-90min;

[0008] (2) The slab after homogenization is rough rolled, and then the slab is descaled. The rough rolling temperature is 1175~1200℃.

[0009] (3) The slab after rough rolling is finished rolling. The starting temperature of the finishing rolling is 1010~1050℃ and the finishing rolling temperature is 860~900℃. The starting rolling speed of the finishing rolling is 1.45-1.55m / s, and the thickness reduction rate of the last two mill stands is ≤15% and ≤10%, respectively.

[0010] (4) The slab after finishing rolling is cooled in the order of first precooling, first air cooling, second precooling, second air cooling and laminar flow cooling, and then coiled to obtain steel strip;

[0011] The cooling rates of the first and second precooling are 5 to 10 °C / s, and the cooling rate of laminar flow cooling is 10 to 30 °C / s.

[0012] (5) The steel strip is pickled and rolled at a speed of 160-180 m / min.

[0013] Further, the composition of the slab in step (1) by weight percentage is: C: ≤0.07, Si: 0~0.10, Mn: 0.15~0.35, P: 0~0.025, S: 0~0.015, Als: 0.015~0.060, with the remainder being Fe.

[0014] Furthermore,

[0015] After step (1), the process also includes a descaling step on the slab, with a descaling water pressure of 17-18 MPa.

[0016] In step (2), descaling is performed using water with a descaling pressure of 17-18 MPa.

[0017] Furthermore, in step (3), the winding temperature is 680–740°C.

[0018] Furthermore, in step (4), the water pressure during the first and second precooling is 3 MPa, and the water pressure during laminar flow cooling is 12 MPa.

[0019] Furthermore, in step (5), the pickling and straightening elongation is 1.0 to 1.50%, and after pickling, the steel strip is further subjected to a cold rolling step, wherein the cold rolling reduction is 65-80%.

[0020] Furthermore, the thickness of the hot-rolled iron oxide scale on the steel strip is ≤12μm, and the iron oxide scale has pre-existing cracks.

[0021] Furthermore, the structure of the hot-rolled iron oxide scale of the steel strip is proeutectoid Fe3O4, a small amount of eutectoid structure with Fe and Fe3O4, and FeO, but without Fe2O3 phase. The proportion of proeutectoid Fe3O4 is 60-80%, the proportion of eutectoid structure is 5-15%, and the proportion of FeO is 15-25%.

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

[0023] The present invention also provides a hot-dip galvanized stamping steel strip prepared using the above method.

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

[0025] (1) The method of the present invention adopts process measures such as controlling the range of chemical composition, hot rolling heating temperature, finishing rolling start temperature, descaling pressure, final rolling temperature, cooling regime, and coiling temperature in the production process. The thickness of the oxide layer of the obtained steel strip is ≤12μm. The oxide layer structure is proeutectoid Fe3O4, a small amount of eutectoid structure (Fe and Fe3O4), and FeO. There is no Fe2O3 phase in the oxide layer. The proportion of proeutectoid Fe3O4 is 60-80%, the proportion of eutectoid structure is 5-15%, and the proportion of FeO is 15-25%. There are pre-cracks in the oxide layer structure, which effectively promotes the removal of iron oxide scale by pickling.

[0026] (2) The pickling process speed is increased to 160-180 m / min, which avoids the shortcomings of the original process technology, such as the oxide layer being difficult to remove, the easy formation of over-pickling and under-pickling defects. The surface quality after pickling is excellent and the technical and economic indicators are good.

[0027] (3) Compared with the steel plates produced by conventional hot-dip galvanizing and stamping steel manufacturing processes, the technical solution of the present invention adopts a simple production process, improves the efficiency of the pickling process unit, and has excellent comprehensive performance of the product, with good prospects for promotion and use. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a morphological diagram of the pre-cracks in the hot-rolled iron oxide scale of the hot-dip galvanized stamping steel strip in Embodiment 1 of the present invention.

[0030] Figure 2 This is a morphological diagram of the pre-cracks in the hot-rolled iron oxide scale of the hot-dip galvanized stamping steel strip in Embodiment 2 of the present invention.

[0031] Figure 3 This is a morphological diagram of the pre-cracks in the hot-rolled iron oxide scale of the hot-dip galvanized stamping steel strip in Embodiment 3 of the present invention.

[0032] Figure 4 This is a morphological diagram of the hot-rolled iron oxide scale of hot-dip galvanized stamping steel strip without pre-existing cracks in Comparative Example 1 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] This invention provides a method for controlling the iron oxide scale of hot-rolled steel strip for hot-dip galvanizing and stamping, which generally includes the following steps: converter smelting → LF refining → continuous casting → reheating → descaling → rough rolling → descaling → finish rolling → cooling → coiling → pickling → continuous hot-dip galvanizing → finishing → tension leveling → packaging → warehousing.

[0036] The converter smelting process specifically involves smelting blast furnace iron and smelting furnace charge in a converter to obtain molten steel. The molten steel is then deoxidized and alloyed during the tapping process and in an LF refining furnace. In the alloying step, aluminum-iron alloys and metallic manganese are added to the deoxidized molten steel, resulting in molten steel (based on total weight, by elemental composition, w%) with the following composition: C: ≤0.07, Si: 0–0.10, Mn: 0.15–0.35, P: 0–0.025, S: 0–0.015, Als: 0.015–0.060, with the remainder being Fe. 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 involves temperature adjustment of the molten steel, fine-tuning of alloy content, and bottom blowing of argon gas into the ladle. Argon gas at a pressure of 200–400 Pa is introduced into the bottom of the ladle for 4–6 minutes, with the argon flow rate controlled to prevent excessive turbulence in the molten steel. This avoids secondary oxidation and excessively rapid temperature drop, allowing inclusions in the steel to float to the surface and further improving the cleanliness of the steel. The LF refining process takes 10–25 minutes, with an outlet temperature of 1610–1635℃. The resulting molten steel (based on total weight, in terms of elemental composition, w%) contains: C: ≤0.07, Si: 0–0.10, Mn: 0.15–0.35, P: 0–0.025, S: 0–0.015, Als: 0.015–0.060, with the remainder being Fe. It should be understood that the technical solution used 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 be performed using methods known to those skilled in the art. The method of this invention involves casting refined molten steel into a pre-baked tundish, and then casting it into a slab using a slab continuous casting machine with full process protection. After casting, it can be cooled using conventional methods, such as natural cooling at room temperature. The composition of the slab, by weight percentage, is: C: ≤0.07, Si: 0~0.10, Mn: 0.15~0.35, P: 0~0.025, S: 0~0.015, Als: 0.015~0.060, with the remainder being Fe.

[0039] The next steps for processing the slab are reheating → descaling → rough rolling → descaling → finish rolling → cooling → coiling → pickling, as follows: Figure 1 As shown, the specific steps include:

[0040] (1) Heat the slab to 1200-1240℃ for 30-90 minutes. After step (1), the slab is descaled by water pressure of 17-18 MPa.

[0041] (2) After the slab is heated, it is rough rolled and then descaled. The rough rolling temperature is 1175-1200℃, and descaling is carried out using water with a descaling pressure of 17-18Mpa.

[0042] (3) The slab after rough rolling is finished rolling. The starting temperature of the finishing rolling is 1010-1050℃ and the finishing rolling temperature is 860-900℃. The starting rolling speed of the finishing rolling is 1.45-1.55m / s, and the thickness reduction rate of the last two mill stands is ≤15% and ≤10%, respectively.

[0043] (4) The slab after finishing 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 680-740℃ to obtain steel strip.

[0044] The cooling rates for the first and second precooling processes are 5–10 °C / s, while the cooling rate for laminar flow cooling is 10–30 °C / s. The water pressure during the first and second precooling processes is 3 MPa, and the water pressure during laminar flow cooling is 12 MPa.

[0045] (5) The steel strip is pickled and rolled, wherein the pickling and straightening elongation is 1.0-1.50%, and the pickling speed is 160-180 m / min. After pickling, the steel strip is further subjected to a cold rolling step, wherein the cold rolling reduction is 65-80%.

[0046] The hot-rolled iron oxide scale prepared by the method of this invention has a thickness ≤12μm and exhibits pre-existing cracks. The structure of the hot-rolled iron oxide scale consists of proeutectoid Fe3O4, a small amount of eutectoid structure containing Fe and Fe3O4, and FeO, but without the Fe2O3 phase. Specifically, the proportion of proeutectoid Fe3O4 is 60-80%, the proportion of eutectoid structure is 5-15%, and the proportion of FeO is 15-25%.

[0047] Hot rolling involves heating and rolling the cast slab. The purpose of rolling is to achieve the required hot-rolled thickness for the continuously cast slab. The reheating and homogenization temperature for hot rolling refers to the temperature at which the billet exits the heating furnace. Heating at this temperature allows for the full dissolution of microalloying elements, eliminating chemical element segregation caused by dendrite slabs in the cast slab; simultaneously, it allows the AlN particles formed in the as-cast state to dissolve back, avoiding the adverse effects of rolling and annealing processes on the microstructure, mechanical properties, and grain orientation. The roughing temperature for hot rolling is to ensure the removal of low-melting-point FeO / Fe2SiO4 eutectic compounds from the slab surface, preventing the formation of red rust defects after cooling that are unfavorable for pickling. The descaling process for the steel strip aims to remove the thick iron oxide scale formed by the combination of O2 with the surface at high temperatures. This requires ensuring minimum descaling pressure and a reasonable arrangement of descaling nozzles. The final rolling temperature refers to the temperature at which the steel strip exits the finishing mill. To ensure uniform thickness and mechanical properties of the finished product and to avoid the formation of Fe2O3 phase during the finishing rolling process, the final rolling temperature should be increased as much as possible. The hot-rolled intermediate billet hot-rolling box process technology is adopted to maintain specific final rolling temperatures at the head, middle, and tail sections of the hot-rolled intermediate billet before finishing rolling. The higher the starting rolling temperature of finishing rolling, the slower the rolling speed and the thicker the oxide layer. Lowering the starting rolling temperature and increasing the rolling speed as much as possible helps to reduce the thickness of the oxide layer in the finished product. In the finishing rolling process, in order to avoid the formation of the edge Fe2O3 phase, the rolling reduction rate of the last two stands is controlled to prevent the transformation of edge FeO to Fe2O3 phase.

[0048] The cooling process after rolling consists of two pre-cooling steps (3 MPa water pressure) followed by laminar flow cooling (12 MPa water pressure). The first and second pre-cooling devices are spaced 15 m apart, as are the second pre-cooling device and the laminar flow cooling device. Various conventional methods can be used. Typically, hot-rolled thin steel strips undergo a cooling phase transformation to adjust the internal microstructure before being coiled. To meet the performance requirements of the finished product, the hot-rolled microstructure consists of ferrite (F) and a small amount of phosphorus (P), with a ferrite grain size of 9.5–10.5 mm. Simultaneously, to improve the mechanical properties of the finished product, high-temperature coiling is used during hot rolling to promote AlN particle precipitation. The recrystallization annealing process in the hot-dip galvanizing process utilizes AlN particles to inhibit ferrite grain growth, thereby improving the steel strength through fine-grain strengthening and second-phase strengthening mechanisms. In addition, in order to obtain pre-oxidized layer cracks, the cooling mode of the present invention is pre-cooling after rolling (1 set of cooling nozzles, 3MPa) - air cooling - pre-cooling (1 set of cooling nozzles, 3MPa) - air cooling - laminar flow cooling (3-7 sets of cooling nozzles, 12MPa). The steel strip coming out of the rolling mill must pre-oxidize the oxide layer cracks and cool to the coiling temperature in a very short time and at a very high cooling rate before coiling.

[0049] Pickling and rolling can comprise two consecutive steps: pickling and cold rolling, and can employ various conventional methods. Typically, hot-rolled thin steel strips are welded together at the head of the pickling mill to form a continuous strip. After straightening, tension straightening to remove scale, pickling, alkali washing, drying, and edge trimming, it undergoes continuous rolling. Various conventional cold rolling mills can be used, such as 4-5 stand cold rolling mills. After pickling and rolling, the thickness of the steel sheet is reduced to the thickness of the raw material in the continuous hot-dip galvanizing mill. The cold rolling reduction rate is 65-80%, which is the total reduction rate of the cold rolling process. The finished product thickness is set according to the thickness of the pickled raw material. The pickling process speed is 160-180 m / min, removing surface oxide scale and improving surface quality. Some processes in the pickling and rolling steps can employ methods and techniques known to those skilled in the art.

[0050] The hot-dip galvanized stamping steel strip of this invention uses low-carbon aluminum-killed steel with a specific chemical composition. The hot rolling process employs a low-temperature initial rolling and high-speed final rolling technique, achieving a thinner oxide layer on the pickled raw material. For typical varieties of pickled raw material with a test roll thickness <3.5mm, the sheet thickness is ≤10μm; for typical varieties with a thickness >3.5mm, the sheet thickness is ≤12μm. The surface oxide layer structure consists of proeutectoid Fe3O4, a small amount of eutectoid structure (Fe and Fe3O4), and FeO. The oxide layer contains no Fe2O3 phase component. The proportion of proeutectoid Fe3O4 is 60-80%, the proportion of eutectoid structure is 5-15%, and the proportion of FeO is 15-25%. The laminar cooling process after finishing rolling employs a two-stage pre-cooling (3MPa water pressure) - laminar flow cooling (12MPa water pressure) scheme, pre-inducing oxide layer cracks on the steel strip surface oxide layer, effectively promoting the removal of pickled iron oxide scale. After production, the surface quality inspection results showed that the hot-dip galvanized stamping steel strip produced by this method had excellent pickling surface quality, the pickling process speed was increased to over 160m / min, and the finished product had good technical and economic indicators.

[0051] The oxide layer thickness of the hot-rolled iron oxide scale control method for hot-dip galvanized stamping steel strip of the present invention is ≤12μm. The oxide layer thickness can be measured using methods known to those skilled in the art. The test sample can be a polished or corroded metallographic sample. The sample etchant is a 1-2% hydrochloric acid-alcohol solution, and the corrosion time is 5-8s, for example, according to GB / T 6394 metallographic method. The oxide layer thickness and structure of the steel plate provided by the hot-rolled iron oxide scale control method for hot-dip galvanized stamping steel strip of the present invention fully meet the technical specifications. The chemical composition detection methods in the present invention are spark source atomic emission spectrometry analysis method for carbon steel and medium-low alloy steel, national standard GB / T4336; and determination of low carbon content in non-alloy steel, Part 2: Infrared absorption method after combustion in an induction furnace (preheated), national standard GB / T 20126-2006. The iron oxide scale thickness, structure, and microstructure detection methods in the present invention are GB / T13298 Metal Microstructure Inspection Method.

[0052] Because the oxide layer thickness of the hot-dip galvanized stamping steel strip involved in this invention is reduced, an FeO phase that readily reacts with hydrochloric acid is introduced into the original oxide layer structure. Simultaneously, pre-formed iron scale cracks are introduced into the oxide layer on the steel strip surface, further increasing the pickling reaction efficiency and significantly improving the unit's production efficiency. The finished product exhibits good technical and economic indicators and excellent surface quality, effectively meeting the raw material requirements of the galvanizing unit. The technical solution of this invention effectively increases the pickling process capacity and improves the pickling effect of the steel strip, significantly promoting the reduction of surface quality defects. Under current favorable market conditions, the technical solution of this invention effectively promotes the improvement of Panzhihua Iron and Steel Group's cold-rolled product production capacity and enhances the surface quality level of the production line, demonstrating promising prospects for widespread application.

[0053] In addition, the present invention also provides a hot-dip galvanized stamping steel strip prepared using the above method.

[0054] The present invention will be further described below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the 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 the blast furnace is used as raw material. The temperature is 1357℃. Steelmaking auxiliary materials are added and the steel is smelted to 1675℃ before being tapped into the steel ladle. When 1 / 3 of the steel is tapped, 420Kg of aluminum-iron pre-deoxidation is added, followed by 480Kg of low-carbon manganese-iron alloying. The steel ladle is then treated with bottom-blown argon gas at a pressure of 350Pa for 4 minutes on a small platform behind the furnace.

[0057] b. LF Electric Heating: Argon gas at a certain pressure (200-400 Pa) is introduced into the bottom of the molten steel ladle for 5 minutes. The argon gas flow rate is kept low to prevent the molten steel from overturning. The LF treatment is terminated at 1620℃. The LF process involves fine-tuning the alloy composition to obtain molten steel (based on the total weight of the molten steel, calculated by elemental composition) with the following composition: C: 0.04, Si: 0.01, Mn: 0.32, P: 0.017, S: 0.008, Als: 0.041, and the remainder being Fe.

[0058] c. Continuous casting: The molten steel ladle is transported to the casting position. A sliding Al-based stopper rod at the bottom of the ladle allows the molten steel to automatically flow into the tundish. From there, it is guided through the Al-based stopper rod to the crystallizer for continuous casting. The entire process uses protective slag for casting protection. After casting, the steel is cooled to a 200mm thick hot-rolled slab.

[0059] d. Hot rolling: The hot-rolled slab is homogenized at 1200℃ for 90 minutes. The roughing rolling temperature is 1175℃, the descaling pressure is 17MPa, the finishing rolling temperature is 1050℃, the finishing rolling speed is 1.45m / s, and the thickness reduction rates of the last two mill stands are 12% and 8% respectively. The final rolling temperature is 875℃. The finished slab is cooled in the following sequence: first pre-cooling (water pressure 3MPa), first air cooling, second pre-cooling (water pressure 3MPa), second air cooling, and laminar flow cooling (water pressure 12MPa). Then, it is coiled at 700℃. The cooling rate of the first and second pre-cooling is 5℃ / s, and the pre-cooling time is 0.13s. The cooling rate of laminar flow cooling is 10℃ / s, and the laminar flow cooling time is 3.75s. Afterward, it is air-cooled to the coiler for coiling. The thickness after rough rolling is 34mm, and the thickness after finishing rolling is 3.0mm after 6 rolling passes.

[0060] e. Pickling and rolling: The steel strip is rolled to a thickness of 0.8 mm by the pickling and rolling mill, with a cold rolling reduction rate of 73.3%, a tension leveling elongation rate of 1.4% by the pickling mill, and a pickling process speed of 180 m / min.

[0061] The oxide layer structure and thickness of the prepared hot-rolled steel strip were tested. The oxide layer thickness on the steel strip surface was 8.5 μm. The oxide layer structure consisted of proeutectoid Fe3O4, a small amount of eutectoid structure (Fe and Fe3O4), and FeO. No Fe2O3 phase was present in the oxide layer. The proportion of proeutectoid Fe3O4 was 80%, the proportion of eutectoid structure was 5%, and the proportion of FeO was 15%. Figure 1 As shown, pre-existing cracks exist in the oxide layer structure. The surface quality of the steel strip after pickling is good, with no residual pickling oxide scale defects, meeting the technical requirements for pickling raw materials of steel strip for hot-dip galvanizing and stamping.

[0062] Example 2

[0063] The preparation method and steel composition are basically the same as in Example 1. The hot-rolled slab is homogenized at 1240℃ for 30 min, roughing rolling temperature is 1200℃, descaling pressure is 18.0 MPa, finishing rolling temperature is 1010℃, finishing rolling speed is 1.55 m / s, and the thickness reduction rates of the last two mill stands are 13% and 8%, respectively, with a final rolling temperature of 885℃. The finished slab is cooled in the following order: first pre-cooling (water pressure 3 MPa), first air cooling, second pre-cooling (water pressure 3 MPa), second air cooling, and laminar flow cooling (water pressure 12 MPa), and then coiled at 710℃. The cooling rate of the first and second pre-cooling is 10℃ / s, and the pre-cooling time is 0.11 s. The cooling rate of the laminar flow cooling is 30℃ / s, and the laminar flow cooling time is 3.3 s. Subsequently, it is air-cooled to the coiler for coiling. The thickness after rough rolling is 35mm, and the thickness after finishing rolling is 4.1mm after 6 rolling passes. The steel strip is rolled to a thickness of 1.2mm by the pickling and rolling mill, with a cold rolling reduction rate of 70.7%, a tensile elongation rate of 1.4% by the pickling and straightening mill, and a pickling process speed of 170m / min.

[0064] The oxide layer structure and thickness of the prepared hot-rolled steel strip were tested. The oxide layer thickness on the steel strip surface was 8.0 μm. The oxide layer structure consisted of proeutectoid Fe3O4, a small amount of eutectoid structure (Fe and Fe3O4), and FeO. No Fe2O3 phase was present in the oxide layer. The proportion of proeutectoid Fe3O4 was 60%, the proportion of eutectoid structure was 15%, and the proportion of FeO was 25%. Figure 2 As shown, pre-existing cracks exist in the oxide layer structure. The surface quality of the steel strip after pickling is good, with no residual pickling oxide scale defects, meeting the technical requirements for pickling raw materials of steel strip for hot-dip galvanizing and stamping.

[0065] Example 3

[0066] The preparation method is basically the same as in Example 1, except that the steel obtained by converter smelting has the following composition: C: 0.03, Si: 0.01, Mn: 0.25, P: 0.020, S: 0.012, Als: 0.037, with the remainder being Fe (Wt, %). Hot-rolled steel plates were produced using the aforementioned steel. The hot-rolled slab was heated at 1226℃ for 42 minutes, with a roughing rolling temperature of 1182℃, a descaling pressure of 17.5 MPa, a finishing rolling temperature of 1030℃, a finishing rolling speed of 1.50 m / s, and thickness reduction rates of 13% and 8% for the last two mill stands, respectively. The final rolling temperature was 885℃. The finished slab was cooled in the following sequence: first pre-cooling (water pressure 3 MPa), first air cooling, second pre-cooling (water pressure 3 MPa), second air cooling, and laminar flow cooling (water pressure 12 MPa), and then coiled at 710℃. The first and second precooling processes have a cooling rate of 8℃ / s and a precooling time of 0.12s. The laminar flow cooling process has a cooling rate of 20℃ / s and a laminar flow cooling time of 3.53s, followed by air cooling before coiling. The thickness after rough rolling is 35mm, and the finishing rolling process has 6 passes, resulting in a thickness of 4.1mm. The steel strip is rolled to a thickness of 1.2mm using the pickling and rolling mill, with a cold rolling reduction rate of 70.7%. The stretching elongation rate of the pickling and leveling unit is 1.4%, and the pickling process speed is 160m / min.

[0067] The oxide layer structure and thickness of the prepared hot-rolled steel strip were tested. The oxide layer thickness on the steel strip surface was 9 μm. The oxide layer structure consisted of proeutectoid Fe3O4, a small amount of eutectoid structure (Fe and Fe3O4), and FeO. No Fe2O3 phase was present in the oxide layer. The proportion of proeutectoid Fe3O4 was 70%, the proportion of eutectoid structure was 10%, and the proportion of FeO was 20%. Figure 3 As shown, pre-existing cracks exist in the oxide layer structure. The surface quality of the steel strip after pickling is good, with no residual pickling oxide scale defects, meeting the technical requirements for pickling raw materials of steel strip for hot-dip galvanizing and stamping.

[0068] Comparative Example 1

[0069] The preparation method is basically the same as in Example 1, except that the steel obtained from converter smelting has the following composition: C: 0.035%, Si: 0.01%, Mn: 0.30%, P: 0.016%, S: 0.013%, Als: 0.028%, with the remainder being Fe (wt%). Hot-rolled steel plates produced using this steel were manufactured with the following conditions: hot-rolled slab homogenization temperature of 1218℃, homogenization time of 50 min, roughing rolling temperature of 1130℃, descaling pressure of 17.3 MPa, finishing rolling temperature of 1075℃, finishing rolling speed of 0.9 m / s, thickness reduction rates of 18% and 12% for the last two mill stands, and a final rolling temperature of 875℃. Cooling was achieved using front-end laminar flow cooling (water pressure 12 MPa) and a coiling temperature of 700℃. The thickness after roughing was 35 mm, and the finishing rolling consisted of 6 passes, resulting in a thickness of 4.1 mm. The steel strip is rolled to a thickness of 1.2 mm by the pickling and rolling mill, with a cold rolling reduction rate of 70.7%, a tension leveling elongation rate of 1.4% by the pickling mill, and a pickling process speed of 120 m / min.

[0070] The oxide layer structure and thickness of the prepared hot-rolled steel strip were tested. The oxide layer thickness on the steel strip surface was 16 μm, and the oxide layer structure consisted of Fe2O3, eutectoid Fe3O4, and eutectoid structure (Fe and Fe3O4). The proportion of proeutectoid Fe3O4 was 90%, and the proportion of eutectoid structure was 10%. Figure 4 As shown, there are no pre-fabricated cracks in the oxide layer structure. The surface quality of the steel strip after pickling is poor, with a large number of pickling iron oxide scale defects remaining, which does not meet the technical requirements for pickling raw materials of steel strip for hot-dip galvanizing stamping.

[0071] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0072] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for controlling the hot-rolled iron oxide scale on hot-dip galvanized stamping steel strip, characterized in that, Includes the following steps: (1) Heat the slab to 1200-1240℃ for 30-90 min. After step (1), the slab is descaled. The descaling water pressure is 17-18 MPa. (2) The slab after homogenization is rough rolled, and then the slab is descaled. The rough rolling temperature is 1175-1200℃, and descaling is carried out using water with a descaling water pressure of 17-18 MPa. (3) The slab after rough rolling is finished rolling. The starting temperature of the finishing rolling is 1010-1050℃ and the finishing rolling temperature is 860-900℃. The starting rolling speed of the finishing rolling is 1.45-1.55m / s. The thickness reduction rate of the last two mill stands is ≤15% and ≤10%, respectively, to obtain an oxide layer without Fe2O3 phase. (4) The slab after finishing rolling is cooled in the order of first precooling, first air cooling, second precooling, second air cooling and laminar flow cooling, and then coiled to obtain steel strip. The water pressure during the first precooling and second precooling is 3 MPa, and the water pressure during laminar flow cooling is 12 MPa. The cooling rates of the first and second precooling are 5 to 10°C / s, and the cooling rate of laminar flow cooling is 10 to 30°C / s, thereby creating pre-oxidation layer cracks on the oxide layer of the steel strip surface. (5) The steel strip is pickled and rolled. The pickling process speed is 160-180 m / min, and the pickling stretching elongation is 1.0-1.50%. After pickling, the steel strip is further subjected to a cold rolling step, in which the cold rolling reduction rate is 65-80%. The structure of the hot-rolled iron oxide scale of the steel strip is proeutectoid Fe3O4, a small amount of eutectoid structure with Fe and Fe3O4, and FeO, but no Fe2O3 phase. The proportion of proeutectoid Fe3O4 is 60-80%, the proportion of eutectoid structure is 5-15%, and the proportion of FeO is 15-25%.

2. The method of claim 1, wherein, The composition of the slab in step (1) by weight percentage is: C: ≤0.07, Si: 0~0.10, Mn: 0.15~0.35, P: 0~0.025, S: 0~0.015, Als: 0.015~0.060, with the remainder being Fe.

3. The method of claim 1, wherein, In step (4), the winding temperature is 680-740℃.

4. The method of claim 1, wherein, The thickness of the hot-rolled iron oxide scale on the steel strip is ≤12μm.

5. The method of claim 1, wherein, The process includes smelting molten steel, LF refining, and continuous casting before step (1).

6. A hot-dip galvanized stamping steel strip prepared using the method described in any one of claims 1-5.

Images