Method for producing weather-resistant structural steel Q550NH based on ESP endless rolling production line

Abstract

The invention belongs to the technical field of steel production, and provides a method for producing weather-proof structural steel Q550NH based on an ESP endless rolling production line, which comprises the steps of smelting, continuous casting, rough rolling, finish rolling, cooling and coiling, wherein molten steel is formed in the smelting process and comprises the following components in percentage by mass: 0.025 to 0.045 percent of C, 0.10 to 0.20 percent of Si, 1.4 to 1.5 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.15 to 0.25 percent of Ni, 0.05 to 0.08 percent of Ti, 0.40 to 0.57 percent of Cr, 0.23 to 0.33 percent of Cu and the balance of iron element and inevitable impurities. By means of the method, the Q550NH weathering resistant steel which is 1.2-4.0 mm in specification, high in strength and free of cracks after passing a 180-degree bending test can be stably produced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel production and relates to a method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling production line. BACKGROUND

[0002] Q550NH belongs to high-strength weather-resistant structural steel and is widely used in railways, oceans, highway transportation and the like and is a kind of weather-resistant steel. The weather-resistant steel is a low-alloy high-strength steel formed by adding a small amount of Cu, P, Cr, Ni and the like to plain carbon steel, so that a dense and stable rust layer is formed when it is exposed to a natural atmospheric environment. The rust layer (referred to as a "protective rust layer") can effectively block oxygen and moisture from further corroding the base material, thereby significantly slowing down the corrosion speed and achieving the purpose of long-term weather resistance.

[0003] As a product with functionality, economy and a very wide application scenario, the weather-resistant steel will still develop in the direction of high strength, ultra-thin and "from hot to cold" in the future.

[0004] At present, the high-efficiency, energy-saving and green production line represented by ESP endless rolling production line is developing vigorously. The research on various process technologies and product development based on ESP production line has been a research hotspot. So far, the development and production research of weathering steel are more, but most of them are limited to traditional hot rolling and CSP production line, which has the problems of thicker product specification (2.0 mm) and higher energy consumption. However, the research on weathering steel produced by ESP production line is less. For example, the Chinese patent with publication number CN 116479309 A discloses a process for producing 400 MPa grade weathering steel based on electric furnace thin slab endless rolling. The process adopts Cu-P-Cr-Ni element design scheme, utilizes the characteristics of a certain content of Cu, Cr, Ni and other elements in the molten steel smelted by the electric furnace, can save part of the alloy addition amount, and can reduce the nitrogen content in the steel to below 0.005% through VOD vacuum degassing, so as to stably produce 400 MPa grade weathering steel with a thickness of 1.2-3.5 mm. However, the strength of the weathering steel prepared by the scheme needs to be further improved. The Chinese patent with publication number CN 106367686 A discloses a method for producing weathering steel based on ESP thin slab continuous casting and rolling process. The raw materials used in the method include, by mass percentage, 0.01-0.06% of C, 0.30-0.60% of Si, 0.30-0.60% of Mn, 0.05-0.12% of P, 0.25-0.45% of Cu, 0.30-0.80% of Cr, ≤0.30% of Ni, ≤0.01% of S, and the rest is iron element. The raw materials are sequentially subjected to converter smelting and LF furnace smelting. The molten steel formed from the LF furnace smelting is subjected to ESP production line to generate hot-rolled strip steel with different thicknesses. In the ESP production line, the molten steel formed from the LF furnace smelting is poured into a continuous casting machine at a casting speed not less than 4.5 m / min, and the temperature at the outlet of the finishing mill is not less than 820°C. The hot-rolled strip steel is subjected to laminar cooling to 500-600°C, and then is wound into a coil by a coiling machine and stored in a warehouse. The method solves the problems of thick weathering steel and high cost of weathering steel produced by traditional hot rolling and CSP represented thin slab continuous casting and rolling process. Similarly, the strength of the weathering steel prepared by the scheme needs to be further improved. The method does not optimize the plasticity and toughness of the material, that is, the 180° bending test is not performed, and it is not clear whether the steel has good formability.

[0005] In summary, although the ESP production line has unique advantages in producing ultra-thin and low-cost products, its application potential in the field of high-strength weathering structural steel (such as Q550NH) has not been fully explored. It is of great significance to obtain high-strength weathering structural steel with no cracks through 180° bending test on the basis of thinner thickness and lower cost. SUMMARY

[0006] The application provides a method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling production line.

[0007] The technical scheme of the application is implemented as follows: The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling production line comprises smelting, continuous casting, rough rolling, finish rolling, cooling and coiling. The smelting process forms molten steel, and the molten steel comprises, in percentage by mass, 0.025-0.045% of C, 0.10-0.20% of Si, 1.4-1.5% of Mn, ≤0.015% of P, ≤0.003% of S, 0.15-0.25% of Ni, 0.05-0.08% of Ti, 0.40-0.57% of Cr and 0.23-0.33% of Cu, and the rest is iron elements and inevitable impurities.

[0008] The percentage by mass of carbon is 0.025-0.045%, a low-carbon and low-phosphorus route is adopted, and the welding performance of the weather-resistant structural steel is considered to be relatively high, and a relatively high carbon is not conducive to subsequent processing and welding. The material strength is mainly improved by the solid solution strengthening of Mn and the fine-grain and precipitation strengthening of Ti; the proportion of Mn in the raw material is 1.4-1.5%, the solid solution strengthening of Mn can expand the gamma zone, reduce the gamma to alpha phase change temperature, refine the grain and be beneficial to the formation of the strengthened phase; the proportion of Ti in the raw material is 0.05-0.08%, the grain refinement, phase change behavior, the combination of Ti and C and N to form fine carbonitride can also delay recrystallization and prevent ferrite grain growth, thereby having strong fine-grain strengthening effect and strong precipitation strengthening effect.

[0009] The low-P+Cu-Ni-Cr composition system can significantly improve the atmospheric corrosion resistance of the steel material while ensuring the mechanical properties, ① the key of the low-P design is to avoid cold brittleness, and although P (0.07%-0.15%) in the traditional weather-resistant steel can improve the corrosion resistance, the low-P (≤0.015%) can reduce the grain boundary segregation and ensure the safety in extreme climate or environment, ② the welding property is improved, the low-P reduces the brittleness tendency of the welding heat-affected zone and reduces the crack risk.

[0010] Preferably, the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt concave rolls with a concave degree of 0.30-0.35 mm, the upper and lower roll shapes of the third to fifth stands adopt tapered rolls with a concave degree of 0.25-0.35 mm and a taper height of 0.8-1.0 mm.

[0011] Preferably, the continuous casting process is cast into continuous casting slabs by a continuous casting machine, and the thickness of the continuous casting slabs is 95-125 mm.

[0012] Preferably, the slab temperature at the outlet of the continuous casting machine is ≥1030℃.

[0013] Preferably, the pulling speed of the continuous casting machine is not less than 4.1 m / min.

[0014] Preferably, the rough rolling process adopts a large reduction amount rolling mill to roll the continuous casting slabs into intermediate slabs, and the thickness of the intermediate slabs is 8-18 mm, then the intermediate slabs are heated by an induction heating furnace, the temperature of the induction heating furnace is 1130-1160℃, then the scale is removed to obtain the rough rolling strip.

[0015] Preferably, the scale removal process removes the scale by a pressure of 350-370 bar.

[0016] Preferably, the finish rolling process rolls the rough rolling strip into a finish rolling strip by finish rolling, and the finish rolling temperature is 810-850℃; the thickness of the finish rolling strip is 1.2-4.0 mm.

[0017] Preferably, the cooling process cools to a temperature of 640-660℃.

[0018] Preferably, the cooling process adopts a front-stage cooling mode, and the cooling speed is 25-50℃ / s.

[0019] The beneficial effects produced by the above technical scheme are as follows: 1. The method for producing weather-resistant structural steel Q550NH based on the ESP endless rolling production line provided by the application can produce 1.2-4.0 mm weather-resistant steel Q550NH through optimization of the composition of molten steel, further expands the product types of the ESP production line, solves the problems of high cost and thick specifications compared with traditional production lines, expands the product specification from 2.0 mm to 1.2 mm compared with traditional hot continuous rolling products, realizes the production of thinner specifications, and opens up the application scenarios in downstream fields; production verification shows that the ESP endless rolling technology can stably produce 550Mpa-grade weather-resistant structural steel with a yield strength of 562-613Mpa, a tensile strength of 652-707Mpa, and an elongation after fracture of 17.5-22%, and all of which pass the 180° bending test without cracks, which proves that the material has high strength and good formability, the product performance is stable, the size tolerance is small, the corrosion resistance meets the standard requirements, and further, through the synergistic optimization of the composition of molten steel, the roll shape and the reduction rate, remarkable effects are achieved in ensuring higher strength and better plate shape and size quality.

[0020] 2. In the finishing rolling process of this invention, the upper and lower work rolls of the first to second stands are concave rolls with a concavity of 0.30–0.35 mm, and the upper and lower work rolls of the third to fifth stands are tapered rolls with a concavity of 0.25–0.35 mm and a cone height of 0.8–1.0 mm. The middle part of the roll body is designed as a concave roll, and the ends are designed as tapered rolls, which effectively compensates for the thermal crown generated when the rolls are heated, improves the uniformity of roll wear, enhances the strip deviation control capability, and stably controls the strip crown. At the same time, it maintains the straightness of the strip as needed, thereby giving the finishing mill a larger range and capability for shape adjustment. This results in stable control of the strip crown C40 within 15–25 μm, and the wedge shape within ±10 μm, further reducing shape defects. The crown hit rate is increased from 92.3–93.0% to 97.6–98.5%, achieving stable rolling of thin specifications.

[0021] 3. The method for producing weathering structural steel Q550NH based on the ESP headless rolling production line provided by this invention adopts a thin slab continuous casting machine with a continuous casting outlet slab temperature ≥1030℃. It makes full use of the heat stored inside the slab and directly rolls it into intermediate plates in a large reduction roughing mill, reducing the load on the roughing mill and further saving the energy consumption of the roughing mill. It achieves the goal of energy saving and consumption reduction by "replacing cold with heat", which can solve the problems of high cost and high energy consumption of traditional hot rolling production lines, realize the substitution of similar products, and has high social and economic benefits. Attached Figure Description

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is a metallographic microstructure diagram of Example 3 of the method for producing weathering structural steel Q550NH based on the ESP headless rolling production line of the present invention.

[0024] Figure 2 This is a schematic diagram of the work roll shape of a method for producing weathering structural steel Q550NH based on an ESP headless rolling production line according to the present invention.

[0025] In the diagram, A: a schematic diagram of a conical roller; B: a schematic diagram of a concave roller. In Figure A, segment ab represents a straight segment, segment bc represents a concave segment (also called a parabolic segment), segment cd represents a conical segment, H1 represents concavity, H2 represents cone height (the horizontal height between points cd), L1 represents the length of the straight segment, L2 represents the distance between points bc in the concave segment (also called the concave segment length), and L3 represents the horizontal distance between points cd in the conical segment (also called the conical segment length). In Figure B, segment ab represents a straight segment, segment bc represents a concave segment, segment cd represents a straight segment, H1 represents concavity, L1 represents the length of the straight segment, L2 represents the distance between points bc in the concave segment (also called the concave segment length), and L3 represents the horizontal distance between points cd in the conical segment. Detailed Implementation

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0027] It should be noted that ESP (Endless Strip Production) is a kind of thin slab continuous casting and rolling production line, which can realize production of a whole strip steel in one pouring, and there is no frequent strip threading, so it is a kind of full-continuous endless strip production line.

[0028] The present application is based on a method for producing weather-resistant structural steel Q550NH on an ESP endless rolling production line, which comprises smelting, continuous casting slab, rough rolling, finish rolling, cooling and coiling. Specifically, the method comprises the following steps: A. Smelting: molten steel is formed by smelting, and the composition of the molten steel comprises, by mass percentage, 0.025-0.045% of C, 0.10-0.20% of Si, 1.4-1.5% of Mn, ≤0.015% of P, ≤0.003% of S, 0.15-0.25% of Ni, 0.05-0.08% of Ti, 0.40-0.57% of Cr, 0.23-0.33% of Cu, and the rest is iron elements and inevitable impurities; B. Continuous casting: the continuous casting slab is cast by a high-speed continuous casting machine, and the thickness of the continuous casting slab is 95-125 mm; the slab temperature at the outlet of the continuous casting machine is ≥1030℃, and the casting speed of the continuous casting machine is not less than 4.1 m / min; C. Rough rolling: then directly enter three large reduction ratio rolling mills for rough rolling, the large reduction ratio rolling mill is arranged in the rough rolling area, the cumulative reduction ratio of the three rough rolling mills is set to be 84-92%, so as to ensure that the austenite grains are elongated, crushed and rapidly nucleated, and the austenite structure is refined, the continuous casting slab is rolled into an intermediate plate in the large reduction ratio rolling mill, the thickness of the intermediate plate is 8-18 mm, a swing shear waste pushing rack is arranged after the large reduction ratio rolling mill, which is used for cutting off the intermediate plate when the intermediate plate is disconnected from the ingot rod and the subsequent equipment has a problem, then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1130-1160℃, after the surface scale is removed by high-pressure water descaling, the high-pressure water descaling is always maintained at a pressure of 350-370 bar for descaling, and the rough rolling strip steel is obtained; it should be noted that the ESP production line is rigidly connected with the continuous casting machine and the rolling mill, the production line fully utilizes the residual heat of the continuous casting slab for rough rolling, and a traditional gas heating furnace is omitted, so that the slab residual heat is fully utilized for rolling and the energy consumption of the rough rolling mill is saved; D, finish rolling: the strip steel after rough rolling is rolled by finish rolling mill to obtain finish rolling strip steel; the thickness of the finish rolling strip steel obtained by the finish rolling process is 1.2-4.0 mm, and the finish rolling temperature is 810-850 DEG C; the finish rolling process comprises a five-stand finish rolling mill unit, the upper and lower work rolls of the first and second stands adopt concave rolls with a concave degree of 0.30-0.35 mm, and the upper and lower roll shapes of the third to fifth stands adopt tapered rolls with a concave degree of 0.25-0.35 mm and a taper height of 0.8-1.0 mm; It should be noted that the middle part of the roll body is designed as a concave roll, and the end part is designed as a taper, the main advantage is to effectively compensate the thermal crown generated when the roll is heated, improve the uniformity of roll wear, improve the strip deviation control ability, and stably realize the control of the strip crown, while maintaining the flatness of the strip according to the needs, thereby giving the finish rolling mill a larger plate shape adjustment range and ability, thereby stably controlling the plate shape crown C40 to be 15-25 mu m, the wedge shape is stably controlled within ± 10 mu m, further reducing the plate shape defects, the crown hit rate is improved from 92.3-93.0% to 97.6-98.5%, and stable rolling of thin specifications is realized. It should be noted that in order to ensure the stability of the finish rolling process, reduce the vibration and steel stacking accidents caused by excessive individual reduction rate or excessive load, the maximum reduction rate of each stand is set, F1≤60%, F2≤45%, F3≤41%, F4≤35%, F5≤25%. In the present application, the composition design is the basis, and the low-carbon and low-phosphorus composition system fundamentally ensures the excellent welding performance and low-temperature toughness of the steel, reduces the risk of cracks caused by composition segregation, and lays a foundation for subsequent stable rolling and high yield. The front stand concave roll (concave degree 0.30-0.35 mm) resists the bending of the roll caused by the huge rolling force and ensures the stable shape of the strip, and the rear stand tapered roll (concave degree 0.25-0.35 mm, taper height 0.8-1.0 mm) provides dynamic plate shape control ability, combined with the decreasing reduction rate design of F1-F5 stands, to ensure the extreme stability of the rolling process. The combination of the three: this synergistic effect effectively eliminates production accidents such as steel stacking, rolling, and deviation, reduces unplanned downtime, and ensures the thickness and plate shape accuracy of the product in the full length range. The small reduction rate of the rear stand cooperates with the tapered roll (F5≤25%), avoiding the rolling vibration of the last stand and eliminating the periodic vibration marks on the surface. The excellent plate shape control ability of the tapered roll (stabilizing the plate shape crown C40 to 15-25 mu m) ensures the flatness of the strip, avoiding the secondary defects such as creases and indentations caused by undulations and warping in the cooling and coiling process. Through the synergy of composition-roll shape-reduction rate, the present application stably produces 1.2 mm ultra-thin specifications of Q550NH weathering steel with higher strength and better plate shape size quality, and the comprehensive economic benefits are significant.

[0029] E、When the strip steel is out of the last stand finishing mill at the required final rolling temperature, it is cooled to the coiling temperature of 640-660℃ by the laminar flow cooling front stage cooling mode, and finally coiled into a hot rolled coil by the underground coiler. It should be noted that the present application sets a lower coiling temperature of 640-660℃ and a faster cooling speed of 25-50℃ / s in combination with the low-carbon design of molten steel smelting. It should be noted that in combination with the laminar flow cooling model, a uniform and fine structure can be further obtained at a lower carbon content, thereby obtaining a strength standard that meets the national standard requirements.

[0030] Example 1 The method for producing weather-resistant structural steel Q550NH based on the ESP endless rolling production line specifically includes the following steps: A, smelting: smelting to form molten steel, the composition of the molten steel includes the elements in Table 1 below in terms of mass percentage, and the rest is iron and unavoidable impurities; B, continuous casting: cast into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 115mm; the slab temperature at the outlet of the continuous casting machine is 1040℃, and the casting speed of the continuous casting machine is 4.1m / min; C, rough rolling: then directly enter the three-stand large reduction rolling mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction rolling mill, the thickness of the intermediate plate is 12mm, a swing shear scrap pushing rack is arranged after the large reduction rolling mill, which is used for cutting off the intermediate plate for offline when the ingot rod is detached and the subsequent equipment fails, then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1150℃, and after removing the surface iron scale by high-pressure water descaling, the high-pressure water descaling is always maintained at a pressure of 350bar for descaling, to obtain a rough rolling strip steel; D, finishing rolling: the rough rolling strip steel is rolled to obtain a finishing rolling strip steel; the thickness of the finishing rolling strip steel obtained in the finishing rolling process is 2.0mm, and the final rolling temperature is 826℃; the finishing rolling process includes a five-stand finishing mill unit, the upper and lower work rolls of the first and second stands adopt a concave roll shape, the concavity is 0.30mm, the upper and lower roll shapes of the third to fifth stands adopt a conical roll shape, the concavity is 0.25mm, and the cone height is 0.8mm; the reduction rates of each stand are set as F1: 43%, F2: 33%, F3: 29%, F4: 25%, and F5: 18%; Specifically, as Figure 2 -A represents a conical roll shape schematic diagram, wherein the ab section represents a straight section, the bc section represents a concave section, also known as a parabolic section, the cd section represents a conical section, H1 represents the concavity, H2 represents the cone height, i.e. the horizontal height between the cd points, L1 represents the length of the straight section, L2 represents the distance between the concave sections bc, also known as the concave section length, and L3 represents the horizontal distance between the conical section cd points, also known as the conical section length; the straight section length L1 is 210mm, the concave section length L2 is 1330mm, and the conical section length L3 is 660mm; As Figure 2-B represents a concave roll profile schematic diagram, wherein ab section represents a flat section, bc section represents a concave section, cd section represents a flat section, H1 represents a concave degree, L1 represents a length of the flat section, L2 represents a distance between the concave sections bc, also called a concave section length, L3 represents a horizontal distance between the points of the taper section cd, the concave section length L2: 1330mm, the flat section length L1=L2=310mm; it should be noted that the diagram is a schematic diagram, and the actual size can be adjusted by a person skilled in the art according to the width of the rolling mill; preferably, the flat section length, the concave section length and the taper section length of the concave roll and the taper roll are optimized according to the size of the rack, the flat section length is 200-220mm, the concave section length is 1300-1350mm, and the taper section length is 650-670mm; E. When the strip steel reaches the last stand of the finishing mill at the required finishing temperature, it is cooled to the coiling temperature 640℃ by laminar cooling at a cooling rate of 25℃ / s, and then it is coiled into a coil by the coiling machine, and the product is stored.

[0031] The product performance is shown in Table 3.

[0032] Example 2 The method for producing weather-resistant structural steel Q550NH based on the ESP endless rolling production line specifically comprises the following steps: A. Smelting: forming molten steel, the composition of the molten steel includes the elements in Table 1 below, and the rest is iron and unavoidable impurities; B. Continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 95mm; the slab temperature at the outlet of the continuous casting machine is 1045℃, and the casting speed of the continuous casting machine is 4.1m / min; C. Rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the thickness of the intermediate plate is 10mm, and a shearing and scrap pushing rack is arranged after the large reduction mill, which is used for removing the stub bar and cutting off the intermediate plate when the subsequent equipment fails, then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1130℃, and the surface iron scale is removed by high-pressure water descaling, the pressure of the high-pressure water descaling is always kept at 350bar for descaling, and a rough rolling strip steel is obtained; D. finish rolling: the rough rolled strip steel is rolled by a finish rolling mill to obtain a finish rolled strip steel; the thickness of the finish rolled strip steel obtained by the finish rolling process is 1.5 mm, and the finish rolling temperature is 820℃; the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt a concave roll with a concave degree of 0.30 mm, the upper and lower roll shapes of the third to fifth stands adopt a tapered roll with a concave degree of 0.25 mm and a taper height of 0.9 mm; specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 45%, F2: 37%, F3: 28%, F4: 26%, and F5: 19%; E. when the strip steel exits the last stand of the finish rolling mill at the required finish rolling temperature, the strip steel is cooled by laminar flow cooling to a coiling temperature of 650℃ at a cooling speed of 30℃ / s, and then the product is coiled by a coiling machine, and then the product is stored. The product performance is shown in Table 3.

[0033] Example 3 The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling line specifically comprises the following steps: A. smelting: smelting to form molten steel, the composition of the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B. continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 115 mm; the slab temperature at the outlet of the continuous casting machine is 1050℃, and the casting speed of the continuous casting machine is 4.2 m / min; C. rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the thickness of the intermediate plate is 8 mm, a shearing and scrap pushing rack is arranged after the large reduction mill for removing the stub bar and cutting off the intermediate plate when the subsequent equipment fails, and then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1150℃, and the high-pressure water descaling is performed to remove the surface iron oxide scale, the pressure of the high-pressure water descaling is always maintained at 360 bar to remove the scale, and a rough rolled strip steel is obtained; D, finishing: the rough rolled strip steel is rolled by a finishing mill to obtain a finishing strip steel; the finishing strip steel obtained in the finishing process has a thickness of 1.2 mm and a finishing temperature of 830℃; the finishing process comprises a five-stand finishing mill unit, the upper and lower work rolls of the first and second stands are concave rolls with a concave degree of 0.30 mm, the upper and lower work rolls of the third to fifth stands are tapered rolls with a concave degree of 0.30 mm and a taper height of 0.8 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 46%, F2: 37%, F3: 29%, F4: 24%, and F5: 18%; E, when the strip steel exits the last stand of the finishing mill at the required finishing temperature, the strip steel is cooled by laminar flow cooling to a coiling temperature of 640℃ at a cooling speed of 50℃ / s, and then the product is coiled by a coiling machine, and then the product is stored. The product performance is shown in Table 3. The product metallographic structure is shown in Figure 1 .

[0034] Example 4 The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling production line specifically comprises the following steps: A, smelting: smelting to form molten steel, the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B, continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the continuous casting slab has a thickness of 115 mm; the slab temperature at the outlet of the continuous casting machine is 1030℃, and the casting speed of the continuous casting machine is 4.2 m / min; C, rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the intermediate plate has a thickness of 8 mm, a shearing and scrap pushing rack is arranged after the large reduction mill, which is used for removing the stub bar and cutting off the intermediate plate when the subsequent equipment fails, then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1150℃, and the surface iron scale is removed by high-pressure water descaling, the high-pressure water descaling is always maintained at a pressure of 360 bar to remove the scale, and a rough rolled strip steel is obtained; D. finish rolling: the rough rolled strip steel is rolled by a finish rolling mill to obtain a finish rolled strip steel; the thickness of the finish rolled strip steel obtained by the finish rolling process is 1.2 mm, and the finish rolling temperature is 820℃; the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt a concave roll with a concave degree of 0.35 mm, the upper and lower roll shapes of the third to fifth stands adopt a tapered roll with a concave degree of 0.35 mm and a taper height of 1.0 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 47%, F2: 36%, F3: 28%, F4: 26%, and F5: 17%; E. when the strip steel exits the last stand of the finish rolling mill at the required finish rolling temperature, the strip steel is cooled by laminar flow cooling to a coiling temperature of 640℃ at a cooling speed of 50℃ / s, and then the product is coiled by a coiling machine, and then the product is stored. The product performance is shown in Table 3.

[0035] Example 5 The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling line specifically comprises the following steps: A. smelting: smelting to form molten steel, the composition of the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B. continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 105 mm; the slab temperature at the outlet of the continuous casting machine is 1040℃, and the casting speed of the continuous casting machine is 4.2 m / min; C. rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the thickness of the intermediate plate is 13 mm, a shearing and scrap pushing rack is arranged after the large reduction mill for removing the stub bar and cutting off the intermediate plate when the subsequent equipment fails, and then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1160℃, and the high-pressure water descaling is performed to remove the surface iron oxide scale, the pressure of the high-pressure water descaling is always maintained at 350 bar to remove the scale, and a rough rolled strip steel is obtained; D, finishing rolling: the rough rolled strip steel is rolled by a finishing rolling mill to obtain a finishing rolled strip steel; the finishing rolled strip steel obtained in the finishing rolling process has a thickness of 2.1 mm and a finishing temperature of 825℃; the finishing rolling process comprises a five-stand finishing rolling mill set, the upper and lower work rolls of the first and second stands are concave rolls with a concave degree of 0.30 mm, the upper and lower work rolls of the third to fifth stands are tapered rolls with a concave degree of 0.25 mm and a taper height of 0.9 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 43%, F2: 37%, F3: 29%, F4: 25%, and F5: 15.5%; E, when the strip steel exits the last stand of the finishing rolling mill at the required finishing temperature, the strip steel is cooled by laminar flow cooling to a coiling temperature of 650℃ at a cooling rate of 25℃ / s, and then the product is coiled and stored in a warehouse. The product performance is shown in Table 3.

[0036] Example 6 The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling line specifically comprises the following steps: A, smelting: smelting to form molten steel, the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B, continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the continuous casting slab has a thickness of 115 mm; the slab temperature at the outlet of the continuous casting machine is 1040℃, and the casting speed of the continuous casting machine is 4.2 m / min; C, rough rolling: then directly entering a three-stand large reduction rolling mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction rolling mill, the intermediate plate has a thickness of 18 mm, a shearing and pushing waste rack is arranged after the large reduction rolling mill for removing the stub bar and cutting off the intermediate plate for offline use when a subsequent device fails, then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1160℃, and the surface iron oxide scale is removed by high-pressure water descaling, the high-pressure water descaling is always maintained at a pressure of 370 bar for descaling to obtain a rough rolled strip steel; D. finish rolling: the rough rolled strip steel is rolled by a finish rolling mill to obtain a finish rolled strip steel; the thickness of the finish rolled strip steel obtained by the finish rolling process is 3.0 mm, and the finish rolling temperature is 810℃; the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt a concave roll with a concave degree of 0.35 mm, the upper and lower roll shapes of the third to fifth stands adopt a tapered roll with a concave degree of 0.35 mm and a taper height of 0.8 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 42%, F2: 35%, F3: 28%, F4: 25%, and F5: 18%; E. when the strip steel exits the last stand of the finish rolling mill at the required finish rolling temperature, the strip steel is cooled by laminar flow cooling, and the strip steel is cooled to a coiling temperature of 660℃ at a cooling speed of 26℃ / s, and then the strip steel is coiled into a coil by a coiling machine, and the product is stored in a warehouse. The product performance is shown in Table 3.

[0037] Example 7 The method for producing the weather-resistant structural steel Q550NH based on the ESP endless rolling production line specifically comprises the following steps: A. smelting: smelting to form molten steel, the composition of the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B. continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 115 mm; the slab temperature at the outlet of the continuous casting machine is 1050℃, and the casting speed of the continuous casting machine is 4.2 m / min; C. rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the thickness of the intermediate plate is 14 mm, a shearing and scrap pushing rack is arranged after the large reduction mill, which is used for cutting off the intermediate plate for off-line when the intermediate plate is disconnected from the ingot rod and the subsequent equipment fails, and then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1160℃, and after removing the surface iron oxide scale by high-pressure water descaling, the high-pressure water descaling is always maintained at a pressure of 360 bar for descaling to obtain a rough rolled strip steel; D. finish rolling: the rough rolled strip steel is rolled by a finish rolling mill to obtain a finish rolled strip steel; the thickness of the finish rolled strip steel obtained by the finish rolling process is 2.3 mm, and the finish rolling temperature is 850℃; the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt a concave roll with a concave degree of 0.30 mm, the upper and lower work rolls of the third to fifth stands adopt a tapered roll with a concave degree of 0.30 mm and a taper height of 0.9 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the length L1 of the flat section is L2=310 mm; the reduction rates of the stands are set as F1: 42%, F2: 35%, F3: 30%, F4: 26%, and F5: 16%; E. when the strip steel exits the last stand of the finish rolling mill at the required finish rolling temperature, the strip steel is cooled by laminar flow cooling to a coiling temperature of 640℃ at a cooling speed of 27℃ / s, and then the product is coiled by a coiling machine, and then the product is stored. The product performance is shown in Table 3.

[0038] Example 8 The method for producing weather-resistant structural steel Q550NH based on an ESP endless rolling line specifically comprises the following steps: A. smelting: smelting to form molten steel, the composition of the molten steel comprises the elements in Table 1 below in terms of mass percentage, and the rest is iron elements and unavoidable impurities; B. continuous casting: casting into a continuous casting slab by a high-speed continuous casting machine, the thickness of the continuous casting slab is 115 mm; the slab temperature at the outlet of the continuous casting machine is 1050℃, and the casting speed of the continuous casting machine is 4.2 m / min; C. rough rolling: then directly entering a three-stand large reduction mill for rough rolling, the continuous casting slab is rolled into an intermediate plate in the large reduction mill, the thickness of the intermediate plate is 15 mm, a shearing and scrap pushing rack is arranged after the large reduction mill for removing the stub bar and cutting off the intermediate plate when the subsequent equipment fails, and then the intermediate plate is heated by an induction heating furnace, the temperature of the induction heating furnace is 1160℃, and the high-pressure water descaling is performed to remove the surface iron oxide scale, the pressure of the high-pressure water descaling is always maintained at 360 bar to remove the scale, and a rough rolled strip steel is obtained; D, finish rolling: the rough rolled strip steel is rolled by a finish rolling mill to obtain a finish rolled strip steel; the thickness of the finish rolled strip steel obtained by the finish rolling process is 2.5 mm, and the finish rolling temperature is 816℃; the finish rolling process comprises a five-stand finish rolling mill set, the upper and lower work rolls of the first and second stands adopt concave rolls with a concave degree of 0.30 mm, the upper and lower roll shapes of the third to fifth stands adopt tapered rolls with a concave degree of 0.30 mm and a taper height of 1.0 mm, specifically, the length L1 of the flat section of the tapered roll is 210 mm, the length L2 of the concave section is 1330 mm, and the length L3 of the tapered section is 660 mm; the length L2 of the concave section of the concave roll is 1330 mm, and the lengths L1 and L2 of the flat section are both 310 mm; the reduction rates of the stands are set as F1: 44%, F2: 36%, F3: 28%, F4: 22%, and F5: 17%. E, when the strip steel exits the last stand of the finish rolling mill at the required finish rolling temperature, the strip steel is cooled by laminar flow cooling, and is cooled to a coiling temperature of 650℃ at a cooling speed of 40℃ / s, and then is coiled by a coiling machine, and the product is stored in a warehouse. The product performance is shown in Table 3.

[0039] Table 1 Comparative Example 1 Compared with Example 3, the only difference is that the composition of the molten steel is different, which comprises the elements in Table 2 below by mass percent, and the rest is iron and inevitable impurities.

[0040] Comparative Example 2 Compared with Example 3, the only difference is that the composition of the molten steel is different, which comprises the elements in Table 2 below by mass percent, and the rest is iron and inevitable impurities.

[0041] Comparative Example 3 Compared with Example 3, the only difference is that the composition of the molten steel is different, which comprises the elements in Table 2 below by mass percent, and the rest is iron and inevitable impurities.

[0042] Comparative Example 4 Compared with Example 3, the only difference is that the composition of the molten steel is different, which comprises the elements in Table 2 below by mass percent, and the rest is iron and inevitable impurities.

[0043] Comparative Example 5 Compared with Example 3, the only difference is that the concave degree and the taper height of the tapered roll are different, the concave degree is 0.15 mm, and the taper height is 0.7 mm.

[0044] Comparative Example 6 Compared with Example 3, the only difference is that the concave degree and the taper height of the tapered roll are different, the concave degree is 0.45 mm, and the taper height is 0.6 mm.

[0045] Table 2 Table 3 From the above examples and comparative examples, it can be seen that the mechanical properties meet the requirements of GB / T 4171-2008 "Weather Resistant Structural Steel" standard when the components and parameters are implemented according to the present application. It has been verified that the yield strength of the weather resistant steel produced by the present application is 562-613Mpa, the tensile strength is 652-707Mpa, the elongation is 17.5-22%, the bending test and the plate shape convexity can all meet the requirements, while the comparative examples cannot meet the product requirements due to the different components and roll shape parameters, resulting in the phenomenon of strength, elongation, and convexity. At the same time, after testing, the corrosion resistance of the weather resistant steel produced by the present application examples 1-8 meets the requirements of GB / T 4171-2008 "Weather Resistant Structural Steel" standard.

[0046] It should be noted that the yield strength, tensile strength, and elongation (elongation after fracture) in the present application are tested in accordance with GB / T 228.1-2021 "Metallic Materials Tensile Test Part 1: Room Temperature Test Method", and the 180° bending test is tested in accordance with GB / T 232-2010 "Metallic Materials Bending Test Method".

[0047] The convexity hit rate in the present application refers to the percentage of the number of points whose C40 value falls within the target tolerance range in the length direction of the strip steel among all convexity sampling points in the statistical period, and the calculation formula is: convexity hit rate = (number of hit points of full-length strip detection / number of points of full-length strip detection) x 100%, C40 represents the difference between the thickness at the middle of the strip width direction and the thickness at a distance of 40mm from the edge, for example, the convexity hit rate of example 1 is 98.4%, which means that in the entire rolling length of a roll of strip steel, 98.4% of the detected points have a plate shape convexity C40 value within the range of 15-25μm. Specifically, the sampling frequency is: longitudinally, sample once every 10m. Single point C40 calculation: for each group of cross-sectional data, C40 = h center −h 40 , where h center is the average thickness within the range of ±8mm from the center; h 40 is the average thickness at a distance of 40mm from the two edges.

[0048] The above is only a preferred embodiment of the present application and does not limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing weather-resistant structural steel Q550NH based on an ESP roll-bond production line, characterized in that, The process comprises smelting, continuous casting, rough rolling, finishing rolling, cooling and coiling. The smelting process forms molten steel, and the molten steel comprises, by mass percent, 0.025-0.045% C, 0.10-0.20% Si, 1.4-1.5% Mn, ≤0.015% P, ≤0.003% S, 0.15-0.25% Ni, 0.05-0.08% Ti, 0.40-0.57% Cr, 0.23-0.33% Cu, and the balance of iron and inevitable impurities.

2. The method for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line according to claim 1, characterized in that, The finishing rolling process comprises a five-stand finishing rolling mill set, the upper and lower work rolls of the first and second stands are concave rolls with a concave degree of 0.30-0.35 mm, and the upper and lower work rolls of the third to fifth stands are tapered rolls with a concave degree of 0.25-0.35 mm and a taper height of 0.8-1.0 mm.

3. The method for producing weather-resistant structural steel Q550NH based on ESP unhead rolling production line according to claim 1, characterized in that, The continuous casting process forms a continuous casting slab by a continuous casting machine, and the continuous casting slab has a thickness of 95-125 mm.

4. The method according to claim 3 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The slab temperature at the outlet of the continuous casting machine is ≥1030℃.

5. The method according to claim 3 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The pulling speed of the continuous casting machine is not less than 4.1 m / min.

6. The method according to claim 1 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The rough rolling process adopts a large reduction rolling mill, the continuous casting slab is rolled into an intermediate slab with a thickness of 8-18 mm in the large reduction rolling mill, the intermediate slab is heated in an induction heating furnace with a temperature of 1130-1160℃, then is descaled to obtain a rough rolling strip.

7. The method according to claim 6 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The descaling process is performed at a pressure of 350-370 bar.

8. The method according to claim 1 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The finishing rolling process rolls the rough rolling strip to obtain a finishing rolling strip, and the final rolling temperature is 810-850℃; the finishing rolling strip has a thickness of 1.2-4.0 mm.

9. The method according to claim 1 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The cooling process cools to a temperature of 640-660℃.

10. The method according to claim 1 for producing weather-resistant structural steel Q550NH based on ESP roll-bond production line, characterized in that, The cooling process is performed by a front-stage cooling mode, and the cooling speed is 25-50℃ / s.

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