Steel for high-strength and high-corrosion-resistance chromium-titanium photovoltaic bracket and preparation method of steel

Abstract

The invention provides steel for a high-strength and high-corrosion-resistance chromium-titanium photovoltaic support and a preparation method of the steel, and belongs to the technical field of metal material preparation. The high-strength, high-toughness and high-corrosion-resistance steel for the chromium-titanium photovoltaic bracket is obtained through smelting, casting, forging and rolling in a vacuum induction furnace; according to the method, vacuum induction furnace two-stage titanium adding is combined with the high-purity argon stirring and composite deoxidation slagging technology, the titanium element yield and the oxygen content in steel are accurately controlled, and finally the purity of the molten steel w (T.O) is smaller than or equal to 40 ppm; through the dynamic recrystallization regulation and control technology in the multidirectional forging and temperature control rolling process, high-density uniform distribution of nanoscale (Ti, Cr) C precipitated phases larger than or equal to 3 * 10 < 15 > / m < 2 > is achieved; the yield strength of the prepared steel for the chromium-titanium photovoltaic support is larger than or equal to 650 MPa, the tensile strength is larger than or equal to 780 MPa, and the percentage elongation after fracture is larger than or equal to 18%; the salt spray corrosion rate is smaller than or equal to 0.05 mm / a, the pitting potential is larger than or equal to 0.85 V, an intergranular corrosion test has no tendency, the cost is reduced through waste steel, and the method is suitable for industrial production and has good application prospects in the field of photovoltaic support materials.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material preparation, and in particular to a high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel and a preparation method thereof. Background Art

[0002] Steel used in photovoltaic racking systems is primarily in the rack structure, which consists primarily of columns, main beams, purlins, and other components. Raw materials used include aluminum alloy, 304 stainless steel, Q235 steel plate with hot-dip galvanized steel, and galvanized steel plate, with Q235 steel plate with hot-dip galvanized steel being the predominant type. The production of photovoltaic racking components involves converting purchased steel plates through multiple processes, including cold bending, stamping, sawing, laser cutting, plasma cutting, welding, and hot-dip galvanizing. These processes place high demands on precision, efficiency, and consistent quality. Corrosion resistance is the most important material requirement for photovoltaic racking systems. The steel structure must be robust and reliable for 25 years, withstanding harsh environmental conditions, wind and snow loads, and other external effects, ensuring maximum performance with minimal installation costs. Galvanized racking systems are widely used due to their stable performance, mature manufacturing process, high load-bearing capacity, and easy installation. However, as demand for cost-effective photovoltaic projects continues to rise, the trend toward high-strength, lightweight, and environmentally friendly photovoltaic racking systems is accelerating. Therefore, developing a steel for photovoltaic brackets that has high strength, high corrosion resistance and controllable preparation process has become a technical problem that needs to be urgently solved in this field. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a technical solution: a method for preparing high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel, comprising the following steps:

[0004] (1) Vacuum induction furnace smelting: stainless steel scrap and chromium and titanium alloy raw materials are added to the vacuum induction furnace, and the vacuum degree is ≤1×10 -1 Melting under Pa conditions, controlling the molten steel temperature to 1550-1650°C; adding titanium alloy in two stages during the refining period: in the first stage, adding 65%-70% of the total titanium amount, and in the second stage, adding the remaining titanium 8-10 minutes before the end of refining; introducing high-purity argon gas for stirring throughout the process at a flow rate of 10-15 L / min, and adding silicon calcium barium and metallurgical lime for deoxidation and slagging, with a stirring time of ≥15 minutes, to obtain a molten steel with w(TO) ≤40 ppm;

[0005] (2) Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 10-25°C / s by controlling the cooling water flow rate to obtain an ingot;

[0006] (3) Forging: The ingot is heated to 1150-1220℃ and kept at this temperature for 1-3 hours, and then multi-directional forging is performed: the first fire is deformed 40%-50% along the axial direction, the second fire is deformed 30%-40% after rotating 90° radially, and the third fire is deformed 10%-20% after rotating 45° radially; the final forging temperature is ≥850℃, the cumulative deformation is 60%-80%, and the furnace is cooled to below 600℃ after forging;

[0007] (4) Rolling: Heat the forging billet to 1050-1150℃ and keep it for 1h, then perform temperature-controlled rolling in stages: Rough rolling stage: start rolling temperature 1050-1100℃, single pass deformation 15%-20%; Finish rolling stage: start rolling temperature 880-920℃, 3-5 passes cumulative deformation 50%-60%, and the deformation rate of the last three passes ≥8s -1 The final rolling temperature is 780-850℃. The rolled plate is placed in a box furnace and kept at 700-750℃ for 60-90min, then air-cooled to room temperature.

[0008] Preferably, the composition of the molten steel in step (1) is as follows by mass percentage: C: 0.08% to 0.12%, Cr: 16.0% to 20.0%, Ti: 0.45% to 0.75%, Mn: 0.8% to 1.2%, Si: 0.3% to 0.8%, P≤0.015%, S≤0.008%, N≤0.010%, the remainder being Fe and impurities, and the Ti / C mass ratio is ≥4.5.

[0009] Preferably, the amount of silicon calcium barium in step (1) is 1.0-1.5 kg / ton of steel, and the amount of metallurgical lime is 3-5 kg / ton of steel.

[0010] Preferably, during the forging process of step (3), the temperature of the blank after each deformation is ≥850°C, and the deformation amount of the first pass is ≥30%.

[0011] The present invention also provides a high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel prepared by the above method, wherein the microstructure of the steel is a dual-phase of ferrite and martensite, the grain size is ≤8 μm, the width of the martensite lath is ≤0.5 μm, and the density of the nanoscale (Ti, Cr) C precipitation phase is ≥3×10 15 pcs / m 2 ; The mechanical properties of the steel are: yield strength ≥650MPa, tensile strength ≥780MPa, and elongation after fracture ≥18%; the corrosion resistance of the steel is: corrosion rate ≤0.05mm / a (1000h) in a 5wt% NaCl salt spray test, pitting potential ≥0.85V (vs.SCE), and no tendency in the intergranular corrosion test.

[0012] Preferably, a composite passivation film with Cr2O3 as the matrix and Ti2O3 dispersedly distributed is formed on the surface of the steel, the composite passivation film has a thickness of 8 to 15 nm, an inclusion level of ≤1.0, and w(TO)≤40 ppm.

[0013] The advantages of the present invention compared with the prior art are:

[0014] Chromium and titanium elements have a synergistic reinforcement effect in high-strength and high-corrosion-resistant stainless steel. In the present invention, chromium forms a continuous Cr2O3 passivation film to improve corrosion resistance. As a ferrite-forming element, chromium forms a dual-phase structure with martensite, and improves strength through phase boundary and solid solution strengthening; titanium forms a nanoscale precipitate phase with carbon, pinning dislocations and inhibiting grain growth. Because its affinity with carbon is higher than that of chromium, it avoids chromium depletion at the grain boundaries. At the same time, it forms high-melting-point inclusions with oxygen and nitrogen to improve purity. The two are coupled through a composite passivation film and a precipitate phase-dual-phase structure to achieve synergistic optimization of strength and corrosion resistance.

[0015] This invention utilizes a two-stage titanium addition process in a vacuum induction furnace, combined with high-purity argon stirring and composite deoxidation and slagging, to precisely control titanium yield and oxygen content in the steel. Dynamic recrystallization control techniques during multi-directional forging and temperature-controlled rolling achieve a high-density, uniform distribution of nanoscale precipitates. This process improves the purity and overall performance of high-strength, high-corrosion-resistant chromium-titanium steel for photovoltaic brackets. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart for preparing high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel according to the present invention.

[0017] Figure 2 This is the metallographic structure diagram of the steel prepared in Example 1 of the present invention.

[0018] Figure 3 This is the metallographic structure diagram of the steel prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0020] This embodiment discloses a method for preparing high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel, comprising the following steps:

[0021] (1) Vacuum induction furnace smelting: stainless steel scrap and chromium and titanium alloy raw materials are added to the vacuum induction furnace, and the vacuum degree is ≤1×10 -1Melting under Pa conditions, controlling the molten steel temperature to 1550-1650°C; adding titanium alloy in two stages during the refining period: in the first stage, adding 65%-70% of the total titanium amount, and in the second stage, adding the remaining titanium 8-10 minutes before the end of refining; introducing high-purity argon gas for stirring throughout the process at a flow rate of 10-15 L / min, and adding silicon calcium barium and metallurgical lime for deoxidation and slagging, with a stirring time of ≥15 minutes, to obtain a molten steel with w(TO) ≤40 ppm;

[0022] (2) Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 10-25°C / s by controlling the cooling water flow rate to obtain an ingot;

[0023] (3) Forging: The ingot is heated to 1150-1220℃ and kept at this temperature for 1-3 hours, and then multi-directional forging is performed: the first fire is deformed 40%-50% along the axial direction, the second fire is deformed 30%-40% after rotating 90° radially, and the third fire is deformed 10%-20% after rotating 45° radially; the final forging temperature is ≥850℃, the cumulative deformation is 60%-80%, and the furnace is cooled to below 600℃ after forging;

[0024] (4) Rolling: Heat the forging billet to 1050-1150℃ and keep it for 1h, then perform temperature-controlled rolling in stages: Rough rolling stage: start rolling temperature 1050-1100℃, single pass deformation 15%-20%; Finish rolling stage: start rolling temperature 880-920℃, 3-5 passes cumulative deformation 50%-60%, and the deformation rate of the last three passes ≥8s -1 The final rolling temperature is 780-850℃. The rolled plate is placed in a box furnace and kept at 700-750℃ for 60-90min, then air-cooled to room temperature.

[0025] Example 1

[0026] A method for preparing high-strength and high-corrosion-resistant chromium-titanium steel for photovoltaic supports. The molten steel comprises the following components by mass percentage: C: 0.10%, Cr: 18.0%, Ti: 0.60%, Mn: 1.0%, Si: 0.5%, P: 0.012%, S: 0.005%, N: 0.008%, the remainder being Fe and impurities, and Ti / C = 6.0.

[0027] The specific preparation method comprises the following steps:

[0028] S1: Vacuum induction furnace smelting: stainless steel scrap and chromium and titanium alloy raw materials are added to the vacuum induction furnace at a vacuum degree of 8×10 -3The steel was melted under Pa conditions, with the molten steel temperature controlled at 1600°C. The titanium alloy was added in two stages during the refining phase: 70% of the total titanium was added in the first stage, and the remaining titanium was added 9 minutes before the end of the refining phase in the second stage. High-purity argon was introduced throughout the refining process with stirring at a flow rate of 12 L / min. Silica calcium barium (1.2 kg / ton of steel) and metallurgical lime (4 kg / ton of steel) were added for deoxidation and slagging, and the stirring time was 18 minutes to obtain a molten steel with w(TO) = 38 ppm.

[0029] S2: Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 15°C / s by controlling the cooling water flow rate to obtain an ingot;

[0030] S3: Forging: The ingot is heated to 1180℃ and held for 2 hours. Multi-directional forging is performed: the first fire is 45% axial deformation, the second fire is 35% deformation after 90° radial rotation, and the third fire is 15% deformation after 45° radial rotation. The final forging temperature is 880℃, the cumulative deformation is 70%, and the ingot is cooled to 550℃ after forging.

[0031] S4: Rolling: The forging billet is heated to 1100℃ and kept at this temperature for 1h. The temperature-controlled rolling is carried out in stages: Rough rolling stage: the starting rolling temperature is 1080℃, and the deformation of a single pass is 18%; Finishing rolling stage: the starting rolling temperature is 900℃, the cumulative deformation of 4 passes is 55%, and the deformation rate of the last three passes is 9s -1 The final rolling temperature is 820℃. The rolled plate is placed in a box furnace and kept at 720℃ for 75min, and then air-cooled to room temperature.

[0032] After testing, the high-strength and high-corrosion-resistant chromium-titanium photovoltaic bracket steel prepared in this embodiment has a yield strength of 665 MPa, a tensile strength of 795 MPa, and an elongation at break of 20%; after 1000 hours of 5wt% NaCl salt spray test, the corrosion rate is 0.045 mm / a, the pitting potential is 0.86 V (vs. SCE), and there is no tendency in the intergranular corrosion test; the surface composite passivation film thickness is 10 nm, the inclusion level is 1.0, and w(TO) = 38 ppm.

[0033] Example 2

[0034] A method for preparing high-strength and high-corrosion-resistant chromium-titanium steel for photovoltaic brackets. The molten steel comprises the following components by mass percentage: C: 0.08%, Cr: 16.0%, Ti: 0.45%, Mn: 0.8%, Si: 0.3%, P: 0.015%, S: 0.008%, N: 0.010%, the remainder being Fe and impurities, and Ti / C = 5.6.

[0035] The specific preparation method comprises the following steps:

[0036] S1: Vacuum induction furnace smelting: stainless steel scrap and chromium and titanium alloy raw materials are added to the vacuum induction furnace at a vacuum degree of 7×10-3 The steel was melted under Pa conditions, with the molten steel temperature controlled at 1550°C; titanium alloy was added in two stages during the refining phase: 65% of the total titanium was added in the first stage, and the remaining titanium was added 10 minutes before the end of refining in the second stage; high-purity argon was introduced throughout the process for stirring at a flow rate of 10 L / min, and silicon calcium barium (1.0 kg / ton of steel) and metallurgical lime (3 kg / ton of steel) were added for deoxidation and slagging, with stirring for 15 minutes to obtain a molten steel with w(TO) = 40 ppm;

[0037] S2: Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 10°C / s by controlling the cooling water flow rate to obtain an ingot;

[0038] S3: Forging: The ingot is heated to 1150℃ and held for 3 hours. Multi-directional forging is performed: the first fire deforms the ingot 40% along the axial direction, the second fire deforms the ingot 30% after rotating the ingot 90° radially, and the third fire deforms the ingot 10% after rotating the ingot 45° radially. The final forging temperature is 850℃, the cumulative deformation is 60%, and the ingot is cooled to 600℃ in the furnace after forging.

[0039] S4: Rolling: The forging billet is heated to 1050℃ and kept for 1h. The temperature is controlled and rolled in stages: Rough rolling stage: the rolling temperature is 1050℃, and the deformation of a single pass is 15%; Finishing rolling stage: the rolling temperature is 880℃, the cumulative deformation of 5 passes is 50%, and the deformation rate of the last three passes is 8s -1 The final rolling temperature is 780℃. The rolled plate is placed in a box furnace and kept at 700℃ for 90 minutes, and then air-cooled to room temperature.

[0040] After testing, the prepared high-strength and high-corrosion-resistant chromium-titanium photovoltaic bracket steel has a yield strength of 650MPa, a tensile strength of 780MPa, and an elongation at break of 18%; after 1000h of 5wt% NaCl salt spray test, the corrosion rate is 0.05mm / a, the pitting potential is 0.85V (vs.SCE), and there is no tendency in the intergranular corrosion test; the surface composite passivation film thickness is 8nm, the inclusion level is 1.0, and w(TO)=40ppm.

[0041] Example 3

[0042] A method for preparing high-strength and high-corrosion-resistant chromium-titanium steel for photovoltaic supports. The molten steel comprises the following components by mass percentage: C: 0.12%, Cr: 20.0%, Ti: 0.75%, Mn: 1.2%, Si: 0.8%, P: 0.010%, S: 0.003%, N: 0.005%, the remainder being Fe and impurities, and Ti / C = 6.25.

[0043] The specific preparation method comprises the following steps:

[0044] S1: Vacuum induction furnace smelting: Stainless steel scrap and chromium and titanium alloy raw materials are added to a vacuum induction furnace and smelted under a vacuum of 9×10-3Pa. The molten steel temperature is controlled to 1650°C. The titanium alloy is added in two stages during the refining phase: 68% of the total titanium is added in the first stage, and the remaining titanium is added 8 minutes before the end of the refining phase in the second stage. High-purity argon is introduced throughout the process for stirring at a flow rate of 15L / min. Silicon calcium barium (1.5kg / ton steel) and metallurgical lime (5kg / ton steel) are added for deoxidation and slagging. The stirring time is 20 minutes to obtain a molten steel with w(TO) = 35ppm.

[0045] S2: Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 25°C / s by controlling the cooling water flow rate to obtain an ingot;

[0046] S3: Forging: The ingot is heated to 1220℃ and held for 1 hour. Multi-directional forging is performed: the first fire deforms the ingot 50% along the axial direction, the second fire deforms the ingot 40% after rotating the ingot 90° radially, and the third fire deforms the ingot 20% after rotating the ingot 45° radially. The final forging temperature is 900℃, the cumulative deformation is 80%, and the ingot is cooled to 500℃ after forging.

[0047] S4: Rolling: The forging billet is heated to 1150℃ and kept at this temperature for 1h. The temperature-controlled rolling is carried out in stages: Rough rolling stage: the starting rolling temperature is 1100℃, and the deformation of a single pass is 20%; Finishing rolling stage: the starting rolling temperature is 920℃, the cumulative deformation of 3 passes is 60%, and the deformation rate of the last three passes is 10s -1 The final rolling temperature is 850℃. The rolled plate is placed in a box furnace and kept at 750℃ for 60min, then air-cooled to room temperature.

[0048] After testing, the high-strength and high-corrosion-resistant chromium-titanium photovoltaic bracket steel prepared in this embodiment has a yield strength of 700 MPa, a tensile strength of 830 MPa, and an elongation at break of 19%; after 1000 hours of 5wt% NaCl salt spray test, the corrosion rate is 0.035 mm / a, the pitting potential is 0.89 V (vs. SCE), and there is no tendency in the intergranular corrosion test; the surface composite passivation film thickness is 12 nm, the inclusion level is 0.8, and w(TO) = 35 ppm.

[0049] This invention utilizes a two-stage titanium addition process in a vacuum induction furnace, combined with high-purity argon stirring and composite deoxidation slag-forming technology, to precisely control titanium yield and oxygen content in the steel. Dynamic recrystallization control technology during multi-directional forging and temperature-controlled rolling achieves a high-density, uniform distribution of nanoscale precipitates. This improves the purity and overall performance of high-strength, high-corrosion-resistant chromium-titanium steel for photovoltaic brackets.

[0050] The present invention and its embodiments are described above. This description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs structures and embodiments similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel, characterized in that: The following steps are involved: (1) Vacuum induction furnace smelting: stainless steel scrap and chromium and titanium alloy raw materials are added to the vacuum induction furnace, and the vacuum degree is ≤1×10 -1 Melting under Pa conditions, controlling the molten steel temperature to 1550-1650°C; adding titanium alloy in two stages during the refining period: in the first stage, adding 65%-70% of the total titanium amount, and in the second stage, adding the remaining titanium 8-10 minutes before the end of refining; introducing high-purity argon gas for stirring throughout the process at a flow rate of 10-15 L / min, and adding silicon calcium barium and metallurgical lime for deoxidation and slagging, with a stirring time of ≥15 minutes, to obtain a molten steel with w(TO) ≤40 ppm; (2) Casting: Molten steel is poured into a water-cooled copper mold, and the cooling rate is maintained at 10-25°C / s by controlling the cooling water flow rate to obtain an ingot; (3) Forging: The ingot is heated to 1150-1220℃ and kept at this temperature for 1-3 hours, and then multi-directional forging is performed: the first fire is deformed 40%-50% along the axial direction, the second fire is deformed 30%-40% after rotating 90° radially, and the third fire is deformed 10%-20% after rotating 45° radially; the final forging temperature is ≥850℃, the cumulative deformation is 60%-80%, and the furnace is cooled to below 600℃ after forging; (4) Rolling: Heat the forging billet to 1050-1150℃ and keep it for 1h, then perform temperature-controlled rolling in stages: Rough rolling stage: start rolling temperature 1050-1100℃, single pass deformation 15%-20%; Finish rolling stage: start rolling temperature 880-920℃, 3-5 passes cumulative deformation 50%-60%, and the deformation rate of the last three passes ≥8s -1 The final rolling temperature is 780-850℃. The rolled plate is placed in a box furnace and kept at 700-750℃ for 60-90min, then air-cooled to room temperature.

2. The preparation method according to claim 1, wherein: The composition of the molten steel in step (1) is as follows by mass percentage: C: 0.08% to 0.12%, Cr: 16.0% to 20.0%, Ti: 0.45% to 0.75%, Mn: 0.8% to 1.2%, Si: 0.3% to 0.8%, P≤0.015%, S≤0.008%, N≤0.010%, the remainder being Fe and impurities, and the Ti / C mass ratio is ≥4.

5.

3. The preparation method according to claim 1, wherein: The amount of silicon calcium barium in step (1) is 1.0-1.5 kg / ton of steel, and the amount of metallurgical lime is 3-5 kg / ton of steel.

4. The preparation method according to claim 1, wherein: During the forging process of step (3), the temperature of the blank after each deformation is ≥850°C, and the deformation amount of the first pass is ≥30%.

5. A high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel prepared by the method according to any one of claims 1 to 4, characterized in that: The microstructure of the steel is a dual phase of ferrite and martensite, with a grain size of ≤8 μm, a martensite lath width of ≤0.5 μm, and a nano-scale (Ti, Cr) C precipitate density of ≥3×10 15 pcs / m 2 ; The mechanical properties of the steel are: yield strength ≥650 MPa, tensile strength ≥780 MPa, and elongation after fracture ≥18%; the corrosion resistance of the steel is: corrosion rate ≤0.05 mm / a (1000 h) in a 5 wt% NaCl salt spray test, pitting potential ≥0.85 V (vs. SCE), and no tendency in an intergranular corrosion test.

6. The high-strength and high-corrosion-resistant chromium-titanium photovoltaic support steel according to claim 5 is characterized by: A composite passivation film with Cr2O3 as the matrix and Ti2O3 dispersedly distributed is formed on the surface of the steel. The composite passivation film has a thickness of 8 to 15 nm, an inclusion level of ≤1.0, and w(TO)≤40 ppm.

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