A manufacturing method of a high-strength weather-resistant steel coil for a photovoltaic support using Ti-Nb complex precipitation regulation

Abstract

The application belongs to the technical field of steel smelting, and particularly discloses a manufacturing method of high-strength weather-resistant steel coil for photovoltaic support by using Ti-Nb compound precipitation regulation, which comprises the following steps: heating, rough rolling, rough rolling temperature waiting, dephosphorization, hot rolling, finish rolling, laminar flow cooling and coiling, and through the above steps, the continuous casting slab is rolled into a steel coil with a thickness of 1.5-3.0 mm; the heating temperature of the continuous casting slab is 1230-1270 DEG C, the rough rolling starting temperature is 1130-1170 DEG C, the total deformation of rough rolling is 82-88%, the rough rolling temperature waiting temperature is 1000-1050 DEG C, the temperature waiting time is 15-30 s, the hot rolling temperature is 1020-1070 DEG C, the finish rolling starting temperature is 960-1020 DEG C, the total deformation of finish rolling is 85-92%, the final rolling temperature is 860-890 DEG C, and the coiling temperature is 540-570 DEG C. The product manufactured by the method can meet the requirement of the photovoltaic support for serving in a harsh environment without coating, and good economic and social benefits can be obtained.

Description

Technical Field

[0001] This invention relates to the field of steel smelting technology, specifically to a method for manufacturing high-strength weather-resistant steel coils for photovoltaic brackets using Ti-Nb composite precipitation regulation. Background Technology

[0002] In recent years, with the rapid growth of the photovoltaic industry and the deepening of the "dual carbon" goal, the greening and lightweighting of photovoltaic brackets have become important development directions. High-strength weathering steel, due to its excellent atmospheric corrosion resistance and high strength, allows photovoltaic brackets to be used bare or with reduced coating in harsh environments such as deserts, Gobi, and coastal areas, significantly reducing coating and maintenance costs. Currently, the use of Ti microalloying combined with controlled rolling and cooling processes to prepare high-strength photovoltaic bracket steel coils has become the mainstream technology in the industry; however, the following key technical bottlenecks still exist in actual production.

[0003] First, the strength of Ti microalloyed steel mainly depends on the precipitation strengthening of TiC, but the TiC precipitation process is highly sensitive to temperature and time. In conventional laminar flow cooling processes, rapid cooling from the final rolling temperature (approximately 870~900℃) to the coiling temperature (approximately 550~580℃) results in insufficient time for TiC to fully precipitate, leaving a large amount of Ti in a solid solution state in the matrix, leading to low Ti element utilization. Conversely, excessively slow cooling leads to coarsening of ferrite grains, reducing the material's toughness and plasticity. Therefore, ensuring TiC precipitation while maintaining microstructure refinement is the core challenge in the production of Ti microalloyed steel.

[0004] Secondly, existing technologies mostly adopt a single Ti microalloying system or a design with a high Ti content (Ti: 0.080~0.100%). High Ti content not only increases the cost of the alloy, but also easily produces coarse TiN inclusions during continuous casting, affecting the surface quality and weldability of the steel.

[0005] Finally, when using a single cooling mode, the cooling conditions of the steel coils used in existing photovoltaic brackets differ between the head and tail of the coil, resulting in large performance fluctuations at both ends of the same coil. The yield strength can fluctuate by 80~100MPa, which seriously affects the stability of the product and the safety of the project. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for manufacturing high-strength weather-resistant steel coils for photovoltaic brackets using Ti-Nb composite precipitation regulation. The core innovation of this invention lies in: through precise alloy design (low Ti + trace Nb), utilizing the differences in the precipitation behavior of Ti and Nb at different temperatures, establishing a staged precipitation regulation mechanism of "high-temperature precipitation pinning of Nb (C, N) during rough rolling – solid solution Ti entering the matrix during finish rolling – low-temperature ordered precipitation of TiC during laminar cooling"; coupled with an innovative "three-stage" laminar flow cooling path (rapid cooling in the front stage to suppress ferrite coarsening – heat preservation in the middle stage to promote TiC precipitation – slow cooling to coiling temperature in the rear stage), ensuring that TiC fully precipitates within the optimal temperature range, significantly improving Ti element utilization and the stability of precipitation strengthening effect, while reducing performance fluctuations at the beginning and end of the coil; employing a 6-pass finish rolling process effectively improves rolling efficiency and reduces energy consumption; and by rationally controlling the coiling temperature, utilizing the residual heat after hot rolling to self-temper the steel coil effectively eliminates residual stress.

[0007] To achieve the above objectives, the basic solution provided by this invention is as follows: a method for manufacturing high-strength weather-resistant steel coils for photovoltaic brackets using Ti-Nb composite precipitation regulation, comprising: heating, rough rolling, rough rolling preheating, descaling, hot rolling, finish rolling, laminar flow cooling, and coiling processes, wherein a continuous casting slab of a specific size with a special alloy composition is rolled into a steel coil with a thickness of 1.5~3.0mm; the heating temperature of the continuous casting slab is 1230~1270℃, the rough rolling start temperature is 1130~1170℃, the total rough rolling deformation is 82~88%, the rough rolling preheating temperature is 1000~1050℃, the preheating time is 15~30s, the hot rolling temperature is 1020~1070℃, the finish rolling start temperature is 960~1020℃, the total finish rolling deformation is 85~92%, the final rolling temperature is 860~890℃, and the coiling temperature is 540~570℃.

[0008] Preferably, the chemical element composition of the continuously cast slab is as follows (%): C: 0.04~0.06; Si: 0.35~0.50; Mn: 0.80~1.00; S: ≤0.003; Ni: ≤0.05; P: ≤0.015; Cu: 0.20~0.30; Cr: 0.90~1.30; Al: 0.020~0.045; Nb: 0.010~0.025; Ti: 0.060~0.085%; N: 50~70ppm, where N is a residue after steelmaking and does not need to be added additionally.

[0009] Specifically, the alloy design concept of this invention is as follows: Ti is the main precipitation strengthening element, which precipitates in the form of TiC during the laminar cooling stage, providing dispersion strengthening; Nb is an auxiliary microalloying element, which preferentially precipitates in the form of Nb(C,N) during the rough rolling warming stage, "pinning" the austenite grain boundaries and preventing austenite grain growth during the rough rolling warming period, thus providing a refined austenite structure for finish rolling. Compared with the existing technology where the Ti content is 0.080~0.140%, this invention reduces the Ti content to 0.060~0.085% by adding trace amounts of Nb to partially replace the grain refining function of Ti, effectively reducing alloy cost and the risk of TiN inclusion formation during continuous casting without reducing strength. The synergistic addition of Cr and Cu elements gives the material good atmospheric corrosion resistance.

[0010] Preferably, the in-furnace heating time is 180-240 minutes, and the furnace exit temperature of the continuously cast slab is 1215-1255℃. A suitable heating time ensures the slab has good plastic processing properties; its purpose is to ensure the slab's microstructure is austenitic single phase.

[0011] Preferably, the rough rolling process involves rolling a rectangular slab with a length of 8-12m, a width of 1100±10mm, and a thickness of 220±10mm into an intermediate slab with a thickness of 28-32mm in 5 passes; wherein the deformation amount in the first and second passes is 22-28%, and the deformation amount in the third to fifth passes is 30-40%.

[0012] Preferably, the finishing rolling process is completed in 6 passes, wherein the deformation amount of the first pass is 45-55%, the deformation amount of the second and third passes is 15-22%, and the deformation amount of the fourth, fifth and sixth passes is 5-12%.

[0013] Preferably, the laminar flow cooling process adopts an innovative "three-stage" cooling path, specifically: in the first stage, the thin steel plate obtained after precision rolling is rapidly cooled to 750-780°C at a cooling rate of 20-35°C / s; in the second stage, the steel plate is slowly cooled from 750-780°C to 620-660°C at a slower cooling rate of 5-10°C / s; and in the third stage, the steel plate is cooled to a coiling temperature of 540-570°C at a cooling rate of 10-15°C / s. The first stage of rapid cooling is to suppress the excessive growth of proeutectoid ferrite, refine the ferrite grains, and obtain a uniform and fine phase transformation structure. The second stage of slow cooling and holding is the core temperature range for TiC to fully precipitate. According to the formula for the solid solubility product of TiC, TiC has the greatest precipitation driving force within this temperature range. The temperature window of 15~30℃ provides sufficient time and thermodynamic conditions for the nucleation and growth of TiC, allowing the Ti elements dissolved in the matrix to precipitate in the form of a large number of fine and dispersed TiC particles, which plays a strong dispersion strengthening role. The third stage of moderately accelerating the cooling rate is to prevent the precipitated TiC particles from becoming excessively coarsened and to maintain the fine and dispersed distribution of the precipitates.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Using the above-mentioned method for manufacturing high-strength weather-resistant steel coils for photovoltaic brackets with Ti-Nb composite precipitation control, the ferrite grain size of the steel coils is 11.5~12.5 grade, with a tensile strength greater than 800MPa, a yield strength greater than 650MPa, a yield ratio greater than 0.80, and an elongation greater than 20%. The microstructure of the obtained steel coils is fine and uniform ferrite with a small amount of pearlite. The yield strength fluctuation of the same coil does not exceed 50MPa, and the performance uniformity is excellent. The atmospheric corrosion resistance index I of the material is ≥6.5, and the corrosion rate relative to Q355B is ≤38%.

[0015] (2) The innovative Ti-Nb composite microalloying design reduces the Ti content to 0.060~0.085% by replacing part of the Ti with trace amounts of Nb, which effectively reduces the alloy cost and the risk of TiN inclusions in continuous casting.

[0016] (3) The innovative rough rolling waiting temperature process utilizes the residual temperature of the intermediate billet to preferentially precipitate Nb (C, N) while Ti remains in a solid solution state, thus realizing the time separation of Nb and Ti precipitation behavior without the need for additional equipment investment.

[0017] (4) The innovative "three-stage" laminar flow cooling path provides the best temperature window for TiC precipitation through slow cooling and heat preservation in the middle section, which greatly improves the utilization rate of Ti element and the precipitation enhancement effect.

[0018] (5) The yield strength fluctuation of the same roll is controlled within 50MPa, and the performance uniformity is significantly better than that of the existing technology.

[0019] (6) The adoption of a 6-pass precision rolling process improves rolling efficiency and reduces energy consumption.

[0020] (7) The product has high strength, good toughness and excellent weather resistance, which can meet the requirements of photovoltaic brackets to be used without painting in harsh environments, and achieve good economic and social benefits. Detailed Implementation

[0021] The present invention will be further described in detail below through specific embodiments: Example 1

[0022] The sample contains the following chemical elements: C: 0.055; Si: 0.42; Mn: 0.90; S: 0.002; Ni: 0.03; P: 0.012; Cu: 0.26; Cr: 1.15; Al: 0.035; Nb: 0.020; Ti: 0.080%; N: 62ppm. Steel containing Fe and impurities is heated to 1255℃, held in the furnace for 225 minutes, and exited at 1240℃. The material is then rolled through rough rolling, rough rolling warming, descaling, hot coiling, finish rolling, laminar flow cooling, and coiling processes. The rough rolling start temperature is 1160℃, and the material undergoes five passes. The deformation amounts in the first and second passes are 26% and 24%, respectively, and the deformation amounts in the third to fifth passes are 36%, 38%, and 35%, respectively, rolling a 220mm thick slab into a 30mm thick plate. The rough rolling warming temperature is 1025℃, and the warming time is 22 seconds. The slab is then hot-coiled in a hot coiling box at 1045℃. Finally, the hot-coiled slab is finished using a finish rolling mill. The slab is rolled at a finishing temperature of 1010℃, with a deformation of 50% in the first pass, 18% and 20% in the second and third passes, and 10%, 8%, and 5% in the fourth, fifth, and sixth passes, respectively. The final rolling temperature is 880℃, rolling the slab into a 2.0mm thick sheet. The finished sheet is then rapidly passed through a laminar flow cooling line, first cooled to 765℃ at a cooling rate of 28.0℃ / s, then slowly cooled to 640℃ at a cooling rate of 7.0℃ / s, and finally cooled to 555℃ at a cooling rate of 12.0℃ / s. The cooled sheet is then coiled at 550℃, bundled, and cooled to room temperature to obtain the steel coil.

[0023] Example 2

[0024] The sample contains the following chemical elements: C: 0.050; Si: 0.38; Mn: 0.85; S: 0.001; Ni: 0.02; P: 0.010; Cu: 0.23; Cr: 0.95; Al: 0.028; Nb: 0.015; Ti: 0.070%; N: 55ppm. Steel containing Fe and impurities is heated to 1240℃, held in the furnace for 210 minutes, and exited at 1225℃. The material is then rolled through rough rolling, rough rolling warming, descaling, hot coiling, finish rolling, laminar flow cooling, and coiling processes. The rough rolling start temperature is 1140℃, and it undergoes five passes. The deformation amounts in the first and second passes are 24% and 22%, respectively, and the deformation amounts in the third to fifth passes are 34%, 36%, and 33%, respectively, rolling a 225mm thick slab into a 32mm thick plate. The rough rolling warming temperature is 1010℃, and the warming time is 18 seconds. The slab is then hot-coiled in a hot coiling box at 1035℃. Finally, the hot-coiled slab is finished using a finish rolling mill. The slab is rolled at a starting temperature of 975℃, with a deformation of 48% in the first pass, 16% and 18% in the second and third passes, and 10%, 8%, and 5% in the fourth, fifth, and sixth passes, respectively. The final rolling temperature is 870℃, rolling the slab into a 2.2mm thick sheet. The thin steel sheet obtained after finishing rolling is then rapidly passed through a laminar flow cooling line, first cooled to 755℃ at a cooling rate of 25.0℃ / s, then slowly cooled to 630℃ at a cooling rate of 6.0℃ / s, and finally cooled to 548℃ at a cooling rate of 11.0℃ / s. Finally, the cooled sheet is coiled at 545℃, bundled, and cooled to room temperature to obtain the steel coil.

[0025] Example 3

[0026] A steel containing chemical elements C: 0.045; Si: 0.36; Mn: 0.82; S: 0.002; Ni: 0.01; P: 0.008; Cu: 0.21; Cr: 0.92; Al: 0.022; Nb: 0.012; Ti: 0.065%; N: 52 ppm, with the balance being Fe and impurities, is heated to 1235°C, held in the furnace for 195 min, and discharged from the furnace at 1220°C; the material is rolled through the processes of rough rolling, rough rolling temperature waiting, descaling, hot coiling, finish rolling, laminar cooling and coiling. The rough rolling start temperature is 1135°C, rolling is performed through 5 passes, the deformation amounts of the first pass and the second pass are 22% and 20% respectively, and the deformation amounts of the third to fifth passes are 30%, 34% and 32% respectively, so that the slab with a thickness of 215 mm is rolled into a thin plate with a thickness of 30 mm; the rough rolling temperature waiting temperature is 1005°C, and the temperature waiting time is 15 s; then the hot coiling process is carried out by a hot coiling box, and the hot coiling temperature is 1025°C; the slab after hot coiling is finish rolled by a finishing mill, the finish rolling start temperature is 965°C, the deformation amount of the first pass is 46%, the deformation amounts of the second and third passes are 15% and 18% respectively, the deformation amounts of the fourth, fifth and sixth passes are 10%, 8% and 5% respectively, the finish rolling temperature is 865°C, and the slab is rolled into a thin plate with a thickness of 2.5 mm; then the thin steel plate obtained after finish rolling is rapidly passed through the laminar cooling line, the steel plate is first cooled to 750°C at a cooling rate of 22.0°C / S, then slowly cooled to 625°C at a cooling rate of 5.5°C / S, and finally cooled to 542°C at a cooling rate of 10.0°C / S; finally, the cooled thin plate is coiled at a coiling temperature of 540°C, bundled and then cooled to room temperature to obtain the steel coil.

[0027] Example 4

[0028] The sample contains the following chemical elements: C: 0.058; Si: 0.48; Mn: 0.98; S: 0.001; Ni: 0.04; P: 0.014; Cu: 0.28; Cr: 1.28; Al: 0.042; Nb: 0.023; Ti: 0.083%; N: 68ppm. Steel containing Fe and impurities is heated to 1265℃, held in the furnace for 235 minutes, and exited at 1250℃. The material is then rolled through rough rolling, rough rolling warming, descaling, hot coiling, finish rolling, laminar flow cooling, and coiling processes. The rough rolling start temperature is 1165℃, and it undergoes five passes. The deformation amounts in the first and second passes are 28% and 25%, respectively, and the deformation amounts in the third to fifth passes are 38%, 40%, and 37%, respectively, rolling a 222mm thick slab into a 29mm thick plate. The rough rolling warming temperature is 1045℃, and the warming time is 28 seconds. The slab is then hot-coiled in a hot coiling box at 1065℃. Finally, the hot-coiled slab is finish-rolled using a finish rolling mill. The finishing rolling process begins at 1018℃, with a deformation rate of 53% in the first pass, 20% and 22% in the second and third passes, and 12%, 10%, and 7% in the fourth, fifth, and sixth passes, respectively. The final rolling temperature is 888℃, rolling the slab into a 1.6mm thick sheet. The finished steel sheet is then rapidly passed through a laminar flow cooling line, first cooled to 775℃ at a cooling rate of 33.0℃ / s, then slowly cooled to 655℃ at a cooling rate of 9.0℃ / s, and finally cooled to 565℃ at a cooling rate of 14.0℃ / s. Finally, the cooled sheet is coiled at 560℃, bundled, and cooled to room temperature to obtain the steel coil.

[0029] In summary, the steel coils obtained in Examples 1-4 all exhibit a microstructure of fine, uniform ferrite with a small amount of pearlite. The ferrite grain size is 11.5-12.5, with a tensile strength greater than 800 MPa, a yield strength greater than 650 MPa, a yield ratio greater than 0.80, and an elongation greater than 20%. The yield strength fluctuation within the same coil does not exceed 20 MPa, demonstrating good microstructure uniformity and high mechanical properties. The material has an atmospheric corrosion resistance index I ≥ 6.5, a relative corrosion rate of ≤ 38% compared to Q355B, and can be used bare in C1-C3 corrosion environments.

[0030] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for manufacturing high-strength weather-resistant steel coils for photovoltaic brackets using Ti-Nb composite precipitation regulation, characterized in that, include: The process involves heating, rough rolling, rough rolling preheating, descaling, hot rolling, finish rolling, laminar flow cooling, and coiling, rolling a specific-sized continuous casting slab with a special alloy composition into a steel coil with a thickness of 1.5~3.0mm. The heating temperature of the continuous casting slab is 1230~1270℃, the rough rolling start temperature is 1130~1170℃, the total rough rolling deformation is 82~88%, the rough rolling preheating temperature is 1000~1050℃, the preheating time is 15~30s, the hot rolling temperature is 1020~1070℃, the finish rolling start temperature is 960~1020℃, the total finish rolling deformation is 85~92%, the final rolling temperature is 860~890℃, and the coiling temperature is 540~570℃.

2. The method for manufacturing a high-strength weather-resistant steel coil for photovoltaic brackets using Ti-Nb composite precipitation regulation as described in claim 1, characterized in that... The chemical element composition of the continuously cast slab is as follows (%): C: 0.04~0.06; Si: 0.35~0.50; Mn: 0.80~1.00; S: ≤0.003; Ni: ≤0.05; P: ≤0.015; Cu: 0.20~0.30; Cr: 0.90~1.30; Al: 0.020~0.045; Nb: 0.010~0.025; Ti: 0.060~0.085%; N: 50~70ppm. The N element is a residue after steelmaking and does not need to be added.

3. The method for manufacturing a high-strength weather-resistant steel coil for photovoltaic brackets using Ti-Nb composite precipitation regulation as described in claim 1, characterized in that, The in-furnace heating time is 180~240 min, and the furnace exit temperature of the continuously cast slab is 1215~1255℃.

4. The method for manufacturing a high-strength weather-resistant steel coil for photovoltaic brackets using Ti-Nb composite precipitation control as described in claim 1, characterized in that, The rough rolling process involves rolling a rectangular slab with a length of 8-12m, a width of 1100±10mm, and a thickness of 220±10mm into an intermediate slab with a thickness of 28-32mm in 5 passes; wherein the deformation amount in the first and second passes is 22-28%, and the deformation amount in the third to fifth passes is 30-40%.

5. The method for manufacturing a high-strength weather-resistant steel coil for photovoltaic brackets using Ti-Nb composite precipitation regulation according to claim 1, characterized in that... The finishing rolling process is completed in 6 passes, with the deformation amount of the first pass being 45-55%, the deformation amount of the second and third passes being 15-22%, and the deformation amount of the fourth, fifth, and sixth passes being 5-12%.

6. The method for manufacturing a high-strength weather-resistant steel coil for photovoltaic brackets using Ti-Nb composite precipitation regulation according to claim 1, characterized in that, The laminar flow cooling process adopts an innovative "three-stage" cooling path, specifically: in the first stage, the thin steel plate obtained after precision rolling is rapidly cooled to 750-780℃ at a cooling rate of 20-35℃ / s; in the second stage, the steel plate is slowly cooled from 750-780℃ to 620-660℃ at a slower cooling rate of 5-10℃ / s; in the third stage, the steel plate is cooled to a coiling temperature of 540-570℃ at a cooling rate of 10-15℃ / s.