High-strength bainite weathering steel for photovoltaic frame and preparation method of high-strength bainite weathering steel

Abstract

The invention relates to the technical field of photovoltaic module accessories, and particularly discloses high-strength bainite weathering steel for a photovoltaic frame and a preparation method of the high-strength bainite weathering steel. The alloy comprises the following alloy elements in percentage by mass: 0.08%-0.15% of C, 1.4%-2.2% of Mn, 0.2%-0.5% of Si, 0.5%-1.2% of Cr, 0.2%-0.5% of Ni, 0.2%-0.5% of Cu, 0.04%-0.08% of Nb, 0.02%-0.10% of V, 0%-0.02% of Ti and the balance of Fe. The weathering steel has excellent toughness and cold forming performance, the bearing capacity, impact resistance and good forming performance of the photovoltaic frame are guaranteed, the single-face corrosion rate in the atmospheric environment is smaller than or equal to 0.01 mm / year, treatment such as galvanization on the photovoltaic frame is not needed, the service life of the photovoltaic frame is greatly prolonged, and the production cost is saved.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic component accessories, and specifically discloses a high-strength bainite weathering steel for a photovoltaic frame and a preparation method thereof. Background Art

[0002] At present, the main material of photovoltaic frames is aluminum alloy. However, due to the low strength and insufficient pressure bearing capacity of aluminum alloy, in order to improve the bearing capacity of the module frame, the thickness of the frame is relatively thick, which makes the module bulky and difficult to install. In addition, the high cost of aluminum alloy also affects the economic efficiency of module manufacturing. Compared with aluminum alloy, steel has higher strength and elastic modulus, and has more room for lightweighting. In recent years, the development of alloy steel frames has gradually received great attention from the industry.

[0003] In order to improve the corrosion resistance of photovoltaic frames and extend their service life, alloy steel frames currently mainly include two technical routes. One is to use low-alloy steel with a coating (mainly galvanized) on the surface, and the other is to use weathering steel. The problem with using galvanized steel sheets is that the galvanized layer will crack during the forming process, which can easily cause local corrosion to intensify. In addition, the strength and plasticity of galvanized steel sheets are currently mismatched. High-strength galvanized steel sheets have low plasticity and are not conducive to forming. Weathering steel can improve its weather resistance by forming a dense rust layer on the steel surface. It does not require additional coatings, can avoid cracking during the forming process, and can further reduce costs. However, the strength level of commercial weathering steel is generally 450-550MPa, and the total amount of high-strength weathering steel alloys is high, which increases the alloy cost on the one hand and is not conducive to forming on the other.

[0004] In addition, in the existing disclosed technologies, such as a Cr, Mn alloyed TRIP steel and its preparation method (CN201910772997.5) disclosed by Shougang Group Co., Ltd., the process is complex and requires softening annealing, isothermal treatment, reverse phase transformation treatment, etc.

[0005] Therefore, it is of great significance to develop a low-cost low-alloy weathering steel. Summary of the invention

[0006] The purpose of the present invention is to develop a high-strength bainite weathering steel suitable for photovoltaic frames to solve the problems of insufficient strength, poor forming performance, insufficient corrosion resistance, etc. of existing frame materials.

[0007] On the one hand, the present invention claims protection for a high-strength bainite weathering steel for photovoltaic frames, which adopts the following technical solution:

[0008] A high-strength bainite weathering steel for photovoltaic frames, the alloy elements and mass percentages are:

[0009] C: 0.08~0.15%,

[0010] Mn: 1.4~2.2%,

[0011] Si: 0.2~0.5%,

[0012] Cr: 0.5~1.2%,

[0013] Ni: 0.2~0.5%,

[0014] Cu: 0.2~0.5%,

[0015] Nb: 0.04~0.08%,

[0016] V: 0.02~0.10%,

[0017] Ti: 0~0.02%,

[0018] The rest is Fe.

[0019] The composition design of the present invention is based on the following ideas: (1) low-carbon Mn-Si-Cr is used as the main design component to promote the formation of an appropriate amount of bainite structure during the continuous cooling process, avoiding the traditional complex processes such as isothermal quenching, two-phase zone quenching, and staged controlled cooling; (2) Cr-Ni-Cu elements are used to promote the formation of dense oxides and improve the weather resistance of steel. At the same time, Mn-Si, as an easily oxidized element, forms silicon manganese oxides, regulates the composition of the oxide layer, fills the gaps in the oxide layer, and further improves the weather resistance of steel. At the same time, avoiding the addition of excessive Ni and Cu content is beneficial to reducing the alloy cost; (3) Nb-V-Ti microalloying elements are used to refine the structure and expand the non-recrystallization zone of the steel, which can simplify the hot rolling process and avoid the traditional cumbersome controlled rolling and controlled cooling process.

[0020] On the other hand, the present invention claims protection for a method for preparing high-strength bainite weathering steel for photovoltaic frames, which adopts the following technical solution:

[0021] A method for preparing high-strength bainite weathering steel for photovoltaic frames, the method comprising smelting, casting, hot rolling and cold rolling the bainite weathering steel having the corresponding alloy element components.

[0022] Preferably, the hot rolling process is: keeping the ingot at 1050-1100°C for 1-2 hours, then performing multi-stage temperature step hot rolling to hot-roll a steel plate with a thickness of 2-3 mm, then air-cooling to 550-650°C for coiling, and naturally cooling to room temperature after coiling to obtain a ferrite / bainite hot-rolled steel coil.

[0023] Preferably, the multi-stage temperature-grade hot rolling process is: rough rolling at 1000-1050°C, finish rolling at 900-950°C, and final rolling temperature of 850-900°C.

[0024] Preferably, high-pressure water dephosphorization is required before both the rough rolling and the finish rolling.

[0025] The present invention adopts a low-carbon Mn-Si-Cr composition design, which can achieve air cooling to 550-650°C for coiling after hot rolling to obtain ferrite / bainite structure, and also avoids problems such as plate shape deterioration caused by laminar cooling. At the same time, based on the heat treatment system of air cooling + coiling + natural cooling, on the one hand, it avoids complex processes such as laminar cooling and controlled cooling during hot rolling; on the other hand, a ferrite / bainite structure with excellent cold rolling performance is formed in the hot-rolled steel coil, which can avoid softening annealing in the subsequent cold rolling process, greatly simplifying the process.

[0026] Preferably, the cold rolling process is: after pickling the coiled steel plate, cold rolling it through 3 to 5 passes to a cold-rolled thin plate with a thickness of 0.9 to 1.1 mm.

[0027] The present invention avoids controlled cooling during hot rolling through reasonable component design, forms ferrite / bainite structure in the hot-rolled steel coil, has excellent cold rolling performance, reduces the number of cold rolling passes, and avoids the softening annealing process.

[0028] Preferably, the bainite cold-rolled sheet is prepared into high-strength bainite weathering steel by continuous annealing.

[0029] Preferably, the continuous annealing process is: heating the cold-rolled sheet to 820-920° C. and keeping the temperature for 2-5 minutes, and then continuously cooling the sheet to room temperature at a cooling rate of 2-10° C. / s.

[0030] The present invention adopts a low-carbon Mn-Si-Cr composition design, and can form a ferrite+bainite structure by a continuous cooling process during the continuous annealing process, thereby avoiding the need for stage-by-stage controlled cooling, isothermal quenching and other processes in the traditional process.

[0031] Preferably, the bainitic weathering steel is produced by vacuum smelting.

[0032] In a third aspect, the present invention claims protection for a photovoltaic frame, which is made of the above-mentioned high-strength bainite weathering steel material for the photovoltaic frame.

[0033] Compared with the prior art, the present invention has at least the following beneficial effects:

[0034] (1) Excellent strength and toughness matching: tensile strength ≥ 950MPa, yield strength ≥ 650MPa, A50 elongation ≥ 18%, which ensures the load-bearing capacity and impact resistance of the photovoltaic frame;

[0035] (2) Excellent cold forming performance: When the bending radius is 1 / 10 of the plate thickness, the cold bending angle is ≤30°, which ensures good forming performance of the photovoltaic frame;

[0036] (3) Excellent weather resistance: The single-sided corrosion rate in atmospheric environment is ≤0.01mm / year. This performance avoids the need for galvanizing and other treatments on the photovoltaic frame, greatly improving the service life of the photovoltaic frame and saving costs.

[0037] (4) Simple hot rolling, cold rolling and continuous annealing process: It avoids the controlled cooling and laminar cooling in the traditional hot rolling process, avoids the softening annealing in the traditional cold rolling process, reduces the number of cold rolling passes, and avoids the complex process of staged controlled cooling in the traditional continuous annealing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the microstructure diagram of Example 3;

[0039] Figure 2 This is the microstructure diagram of Comparative Example 2. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] A high-strength bainite weathering steel for photovoltaic frames and a preparation method thereof, as follows:

[0043] High-strength bainite weathering steel is smelted in vacuum, and its alloy elements and mass percentages are C: 0.08%, Mn: 2.2%, Si: 0.5%, Cr: 1.2%, Ni: 0.5%, Cu: 0.5%, Nb: 0.04%, V: 0.02%, Ti: 0, and the rest is Fe. Then, it is cast into a steel billet, and the billet is kept at 1100°C for 1 to 2 hours, and then rough rolled at 1000 to 1050°C, and finished rolled at 900 to 950°C. High-pressure water dephosphorization is performed before rough rolling and finish rolling. The final rolling temperature is 850°C, and hot rolled into a steel plate with a thickness of 3 mm, and then air-cooled to 550°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 0.9 mm cold-rolled thin plate through 5 passes. The cold-rolled thin plate was heated to 920°C and kept at this temperature for 2 minutes, and then cooled to room temperature at a cooling rate of 10°C / s to obtain bainitic weathering steel for photovoltaic frames.

[0044] The measured properties of the bainitic weathering steel for photovoltaic frames obtained in Example 1 are as follows: tensile strength: 956 MPa, yield strength: 657 MPa, A50 elongation: 21%, cold bending angle: 0°, single-sided corrosion rate in atmospheric environment: 0.008 mm / year.

[0045] Example 2

[0046] A high-strength bainite weathering steel for photovoltaic frames and a preparation method thereof, as follows:

[0047] High-strength bainite weathering steel is smelted in vacuum, and its alloy elements and mass percentages are C: 0.12%, Mn: 2.0%, Si: 0.4%, Cr: 1.0%, Ni: 0.4%, Cu: 0.3%, Nb: 0.06%, V: 0.04%, Ti: 0.01, and the rest is Fe. Then, it is cast into a steel billet, and the billet is kept at 1100°C for 1-2 hours, and then rough rolled at 1000-1050°C, and finished rolled at 900-950°C. High-pressure water dephosphorization is performed before rough rolling and finish rolling. The final rolling temperature is 870°C, and hot rolled into a steel plate with a thickness of 2.8 mm, and then air-cooled to 600°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 1.0 mm cold-rolled thin plate through 4 passes. The cold-rolled thin plate was heated to 860°C and kept at this temperature for 3 minutes, and then cooled to room temperature at a cooling rate of 8°C / s to obtain bainitic weathering steel for photovoltaic frames.

[0048] The measured properties of the bainitic weathering steel for photovoltaic frames obtained in Example 2 are as follows: tensile strength: 966 MPa, yield strength: 658 MPa, A50 elongation: 22%, cold bending angle: 0°, single-sided corrosion rate in atmospheric environment: 0.009 mm / year.

[0049] Example 3

[0050] A high-strength bainite weathering steel for photovoltaic frames and a preparation method thereof, as follows:

[0051] High-strength bainite weathering steel is smelted in vacuum, and its alloy elements and mass percentages are C: 0.12%, Mn: 1.8%, Si: 0.4%, Cr: 1.0%, Ni: 0.3%, Cu: 0.3%, Nb: 0.04%, V: 0.02%, Ti: 0.01%, and the rest is Fe. Then, it is cast into a steel billet, and the billet is kept at 1050°C for 1 to 2 hours, and then rough rolled at 1000 to 1050°C, and finished rolled at 900 to 950°C. High-pressure water dephosphorization is performed before rough rolling and finish rolling. The final rolling temperature is 880°C, and the steel plate with a thickness of 2.5 mm is rolled, and then air-cooled to 650°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 1.0 mm cold-rolled thin plate through 3 passes. The cold-rolled thin plate was heated to 840°C and kept at this temperature for 3 minutes, and then cooled to room temperature at a cooling rate of 5°C / s to obtain bainitic weathering steel for photovoltaic frames.

[0052] The microstructure of the bainite weathering steel for photovoltaic frame obtained in Example 3 is shown in Figure 1, a ferrite / bainite structure is formed. The measured properties of weathering steel are as follows: tensile strength: 986MPa, yield strength: 678MPa, A50 elongation: 21%, cold bending angle: 0°, single-sided corrosion rate in atmospheric environment: 0.009mm / year.

[0053] Example 4

[0054] A high-strength bainite weathering steel for photovoltaic frames and a preparation method thereof, as follows:

[0055] High-strength bainite weathering steel is smelted in vacuum, and its alloy elements and mass percentages are C: 0.14%, Mn: 1.6%, Si: 0.3%, Cr: 0.8%, Ni: 0.2%, Cu: 0.2%, Nb: 0.08%, V: 0.1%, Ti: 0.02%, and the rest is Fe, and then cast into a steel billet, and the billet is kept at 1050°C for 1-2 hours, and then rough rolled at 1000-1050°C, and finished rolled at 900-950°C, and high-pressure water is used for dephosphorization before rough rolling and finish rolling, and the final rolling temperature is 900°C, and rolled into a steel plate with a thickness of 2.0 mm, and then air-cooled to 600°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 1.1 mm cold-rolled thin plate through 4 passes. The cold-rolled thin plate was heated to 820°C and kept at this temperature for 5 minutes, and then cooled to room temperature at a cooling rate of 2°C / s to obtain bainitic weathering steel for photovoltaic frames.

[0056] The measured properties of the bainitic weathering steel for photovoltaic frames obtained in Example 4 are as follows: tensile strength: 1021 MPa, yield strength: 768 MPa, A50 elongation: 20%, cold bending angle: 30°, single-sided corrosion rate in atmospheric environment: 0.01 mm / year.

[0057] Example 5

[0058] A high-strength bainite weathering steel for photovoltaic frames and a preparation method thereof, as follows:

[0059] High-strength bainite weathering steel is smelted in vacuum, and its alloy elements and mass percentages are C: 0.15%, Mn: 1.4%, Si: 0.2%, Cr: 0.8%, Ni: 0.2%, Cu: 0.2%, Nb: 0.08%, V: 0.1%, Ti: 0.02%, and the rest is Fe. Then, it is cast into a steel billet, and the billet is kept at 1050°C for 1 to 2 hours, and then rough rolled at 1000 to 1050°C, and finished rolled at 900 to 950°C. High-pressure water dephosphorization is performed before rough rolling and finish rolling. The final rolling temperature is 900°C, and the steel plate with a thickness of 2.0 mm is rolled, and then air-cooled to 600°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 1.0 mm cold-rolled thin plate through 5 passes. The cold-rolled thin plate was heated to 830°C and kept at that temperature for 4 minutes, and then cooled to room temperature at a cooling rate of 3°C / s to obtain bainitic weathering steel for photovoltaic frames.

[0060] The measured properties of the bainitic weathering steel for photovoltaic frames obtained in Example 5 are as follows: tensile strength: 1041 MPa, yield strength: 818 MPa, A50 elongation: 18%, cold bending angle: 30°, single-sided corrosion rate in atmospheric environment: 0.01 mm / year.

[0061] Comparative Example 1

[0062] The difference from Example 1 is that the Mn content is higher than 2.2%, as follows:

[0063] Bainite weathering steel is smelted by vacuum, and its alloy elements and mass percentages are C: 0.1%, Mn: 2.5%, Si: 0.5%, Cr: 1.2%, Ni: 0.5%, Cu: 0.5%, Nb: 0.04%, V: 0.02%, Ti: 0, and the rest is Fe. Then it is cast into a steel billet, and the billet is kept at 1100°C for 1 to 2 hours, and then rough rolled at 1000 to 1050°C, and finished rolled at 900 to 950°C. High-pressure water dephosphorization is used before rough rolling and finishing rolling. The final rolling temperature is 850°C, and it is rolled into a steel plate with a thickness of 3 mm, and then air-cooled to 550°C for coiling, and naturally cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 0.9 mm cold-rolled sheet through 5 passes. The cold-rolled sheet is heated to 860°C and kept for 2 minutes, and then cooled to room temperature at a cooling rate of 10°C / s to obtain weathering steel for photovoltaic frames.

[0064] The measured properties of the bainitic weathering steel obtained in Comparative Example 1 are as follows: tensile strength: 1036 MPa, yield strength: 745 MPa, A50 elongation: 12%, cold bending angle: 60°, single-sided corrosion rate in atmospheric environment: 0.012 mm / year.

[0065] It can be seen that the Mn content in the bainitic weathering steel composition of the present invention is very critical to the performance of bainitic weathering steel. The specific amount of Mn, Si and Cr constitute the main component of Mn-Si-Cr, which can promote the formation of an appropriate amount of bainite structure during the continuous cooling process, avoiding the traditional isothermal quenching, two-phase zone quenching, staged controlled cooling and other complex processes. In addition, Mn-Si is combined as an easily oxidized element to form silicon manganese oxide, which is used to regulate the composition of the oxide layer and fill the gaps in the oxide layer, thereby further improving the weather resistance of the steel. If the Mn is too high, it will not only lead to a decrease in its weather resistance, but also cause its cold bending angle to become larger, the plastic deformation ability of the steel to decrease, and it is easy to break when bent in a cold state, which cannot be applied to the plasticity requirements of photovoltaic frame forming.

[0066] Comparative Example 2

[0067] Different from Example 2, the steel plate is hot rolled into a steel plate with a thickness of 2.8 mm, and then laminar cooled to 600°C for coiling. After coiling, it is cooled to room temperature to form a bainite / martensite structure. The microstructure is shown in FIG. Figure 2 .

[0068] The steel of Comparative Example 2 forms a bainite / martensite structure, and its preparation method requires softening annealing in the subsequent cold rolling process, and the number of cold rolling passes is 8, which greatly increases the complexity of the process and is not conducive to the control of production costs in practical applications. The weathering steel of the present invention forms a bainite / martensite structure through a specific composition design and a process of air cooling + coiling + natural cooling. Figure 1 The ferrite / bainite structure not only ensures excellent strength / weather resistance and cold forming performance, so that it can be widely used in photovoltaic frame materials, but also does not require complex processes such as softening annealing and segmented controlled cooling, significantly reducing the production cost of photovoltaic frames.

[0069] Comparative Example 3

[0070] The difference from Example 3 is that the cold-rolled sheet is heated to 950°C and kept at this temperature for 3 minutes, and then cooled to room temperature at a cooling rate of 20°C / s, as follows:

[0071] The bainite weathering steel is smelted in vacuum, and the alloy elements and mass percentages are C: 0.12%, Mn: 1.8%, Si: 0.4%, Cr: 1.0%, Ni: 0.3%, Cu: 0.3%, Nb: 0.04%, V: 0.02%, Ti: 0.01%, and the rest is Fe. Then, the steel billet is cast, and the billet is kept at 1050°C for 1 to 2 hours, and then rough rolled at 1000 to 1050°C, and finished rolled at 900 to 950°C. High-pressure water dephosphorization is performed before rough rolling and finish rolling. The final rolling temperature is 880°C, and the steel plate with a thickness of 2.5 mm is rolled, and then cooled to 650°C by 8°C / s for coiling, and then air-cooled to room temperature after coiling. After pickling, the coiled steel plate is cold-rolled to a 1.0 mm cold-rolled sheet through 3 passes. The cold-rolled thin plate was heated to 950°C and kept warm for 3 minutes, and then cooled to room temperature at a cooling rate of 20°C / s to obtain weathering steel for photovoltaic frames.

[0072] The measured properties of the weathering steel obtained in Comparative Example 3 are as follows: tensile strength: 1123MPa, yield strength: 789MPa, A50 elongation: 12%, cold bending angle: 60°, single-sided corrosion rate in atmospheric environment: 0.01mm / year. Comparative Example 3 is cooled to room temperature at a cooling rate of 20°C / s, and the structure is no longer bainite, but martensite, resulting in its performance being different from that of Example 3. The cold bending angle of the steel is greater than 30°, and the plasticity is poor, which is not suitable for photovoltaic frame forming applications.

[0073] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A high-strength bainite weathering steel for photovoltaic frames, characterized in that: Alloy elements and mass percentages are: C:0.08～0.15％， Mn: 1.4~2.2%, Si: 0.2~0.5%, Cr:0.5～1.2％， Ni: 0.2~0.5%, Cu: 0.2~0.5%, Nb: 0.04~0.08%, V:0.02～0.10％， Ti: 0~0.02%, The rest is Fe.

2. A method for preparing the high-strength bainite weathering steel for photovoltaic frames according to claim 1, characterized in that: The bainitic weathering steel with corresponding alloy element content is prepared by smelting, casting, hot rolling and cold rolling.

3. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 2, characterized in that: The hot rolling process is as follows: the ingot is kept at 1050-1100°C for 1-2 hours, then multi-stage temperature step hot rolling is performed to hot roll the ingot into a steel plate with a thickness of 2-3 mm, then air-cooled to 550-650°C for coiling, and then naturally cooled to room temperature after coiling to obtain a ferrite / bainite hot-rolled steel coil.

4. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 3, characterized in that: The multi-stage temperature-grade hot rolling process comprises: rough rolling at 1000-1050°C, finish rolling at 900-950°C, and final rolling temperature at 850-900°C.

5. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 4, characterized in that: High pressure water dephosphorization is required before both the rough rolling and the finish rolling.

6. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 2, characterized in that: The cold rolling process is as follows: after pickling the coiled steel plate, the coiled steel plate is cold rolled for 3 to 5 passes to a cold rolled thin plate with a thickness of 0.9 to 1.1 mm.

7. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 6, characterized in that: The bainite cold-rolled thin plate is prepared into high-strength bainite weathering steel through continuous annealing treatment.

8. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 7, characterized in that: The continuous annealing process is as follows: heating the cold-rolled thin plate to 820-920° C. and keeping the temperature for 2-5 minutes, and then continuously cooling the cold-rolled thin plate to room temperature at a cooling rate of 2-10° C. / s.

9. The method for preparing high-strength bainite weathering steel for photovoltaic frames according to claim 2, characterized in that: The bainite weathering steel is made by vacuum smelting.

10. A photovoltaic frame, characterized in that: The photovoltaic frame is made of the high-strength bainite weathering steel material described in claim 1.

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