Steel plate for 700MPa tracking support and manufacturing method of steel plate

Abstract

The invention relates to the technical field of steel for photovoltaic supports, in particular to a steel plate for 700MPa tracking supports and a manufacturing method of the steel plate. The steel plate comprises the following chemical components in percentage by mass: 0.06%-0.09% of C, 0.43%-0.63% of Si, 1.33%-1.53% of Mn, less than or equal to 0.015% of S, less than or equal to 0.015% of P, less than or equal to 0.015% of Al, 0.073%-0.098% of Ti, 0.53%-0.73% of Cr, less than or equal to 0.005% of N, less than or equal to 0.005% of O, 0.0025%-0.0043% of B and the balance of Fe and other inevitable impurities. The Ti, Cr and B component design and a'water-air-oil 'cooling mode are adopted, so that the material strength is improved, and meanwhile, the corrosion resistance and wear resistance of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel for photovoltaic brackets, and in particular to a 700MPa tracking bracket steel plate and a manufacturing method thereof. Background Art

[0002] With the energy crisis facing the world, new energy plays an important role. Solar power generation has been built in large quantities. With years of reform and upgrading, photovoltaic brackets have been upgraded from ordinary fixed brackets to tracking brackets, and the power generation efficiency has increased by 21% to 43%. However, many problems have followed. The steel used for brackets is now generally coated. If the coating falls off during service, pitting will occur and continue to intensify, causing the bracket to break; at the same time, as the bracket rotates with the sunlight, it is bound to wear, resulting in steel failure, maintenance and frequent replacement, increasing its cost. Therefore, manufacturing steel suitable for tracking brackets has become a top priority.

[0003] Patent CN116200678A discloses a 700MPa grade high-strength light photovoltaic support hot-rolled coil and its manufacturing method. Its composition includes C: 0.055% ~ 0.09%, Si: 0.10% ~ 0.35%, Mn: 1.30% ~ 1.7%, S: ≤ 0.002%, P: ≤ 0.03%, Al: 0.015% ~ 0.060%, Nb: 0.020% ~ 0.050%, Ti: 0.045% ~ 0.070%, Cr: 0.2% ~ 0.5%, N ≤ 0.007%, V: ≤ 0.020%, and the rest is Fe and unavoidable impurities. However, its corrosion resistance and wear resistance are poor, which cannot meet the use of tracking brackets.

[0004] Patent CN117488208A discloses a thin-gauge 800MPa hot-rolled weathering steel plate for photovoltaic brackets and its preparation method. Its composition includes C: 0.05% to 0.10%, Si: 0.35% to 0.55%, Mn: 0.85% to 1.05%, P: 0.070% to 0.100%, S≤0.008%, Cr: 1.10% to 1.30%, Cu: 0.25% to 0.35%, Ti: 0.080% to 0.100%, Als: 0.010% to 0.040%, N≤0.0050%, and the balance is Fe and unavoidable impurities. Although the steel coil produced according to its process has a certain corrosion resistance, its cost is relatively high. At the same time, the product obtained by adopting its technical solution contains a large amount of pearlite, and the wear resistance is affected to a certain extent during use.

[0005] Patent CN116497280A discloses a 700MPa grade hot-rolled high-strength high-weathering steel and its preparation method and application. Its composition includes C: 0.043% to 0.048%, Si: 0.51% to 0.59%, Mn: 0.61% to 0.68%, P: 0.041% to 0.049%, S: 0.0031% to 0.0038%, Al: 0.071% to 0.079%, Ti: 0.092% to 0.099%, Cu: 0.251% to 0.259%, Cr: 1.81% to 1.98%, N: 0.0031% to 0.0034%, and the rest is Fe and unavoidable impurities. Increasing the Cr content to improve the hardenability of steel will increase costs on the one hand, and hinder the precipitation of effective Ti compounds on the other hand, forcing it to require a more stringent hot rolling process to ensure its strength; at the same time, if the Al content is too high, it will lead to increased precipitation of AlN, increase the crack sensitivity of the ingot, and reduce the yield rate.

[0006] Considering that tracking brackets are larger in size, bear higher loads and are more susceptible to wear than fixed brackets, the required steel grade needs to have higher strength, stronger corrosion resistance and better wear resistance. Summary of the invention

[0007] The purpose of the present invention is to provide a 700MPa tracking bracket steel plate and a manufacturing method thereof, which adopts Ti, Cr, B component design and a unique "water-air-oil" cooling mode to increase the corrosion resistance and wear resistance of the material while improving the material strength. The tracking bracket steel plate manufactured by the present invention can serve in various environments, and the bracket service life meets the standard requirement of 25 years, and is suitable for tracking photovoltaic bracket steel used in deserts or vast lands.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] In one aspect, the present invention provides a 700MPa steel plate for a tracking bracket, wherein the chemical composition of the steel plate is as follows by mass percentage:

[0010] C: 0.06%~0.09%, Si: 0.43%~0.63%, Mn: 1.33%~1.53%, S: ≤0.015%, P: ≤0.015%, Al: ≤0.015%, Ti: 0.073%~0.098%, Cr: 0.53%~0.73%, N: ≤0.005%, O: ≤0.005%, B: 0.0025%~0.0043%, and the rest are Fe and other unavoidable impurities.

[0011] In the above technical solution, further, the yield strength of the steel plate is ≥700MPa, the tensile strength is ≥800MPa, the elongation is ≥15%, the hardness is ≥300HV, and the corrosion rate relative to Q355B is ≤45%.

[0012] In the above technical solution, further, the steel plate has a thickness of 2.0 to 5.0 mm and a width of 1450 to 2150 mm.

[0013] The functions of the main elements in the 700MPa tracking bracket steel plate of the present invention are described in detail below:

[0014] C: The C element can significantly improve strength and hardness, but since the present invention is used for tracking brackets, a certain toughness is required. The present invention adopts a low C content design, abandons the simplest and most direct way to improve the wear resistance of the material, and improves the material hardness by regulating the organizational morphology through a rolling process.

[0015] Si: Si element can deoxidize, reduce the Al content in the composition design, reduce the precipitation of AlN, improve the quality of the ingot, and increase the yield rate. At the same time, it can form a Si-rich layer, which can improve the corrosion resistance on the one hand and reduce the cracks caused by Cu embrittlement on the other.

[0016] Mn: Mn is a commonly used element for solid solution strengthening and improving material strength. It can also expand the austenite phase region, reduce the martensite transformation temperature, increase the amount of retained austenite, and thus increase the bainite content.

[0017] Ti: Ti is one of the most commonly used elements for improving strength through microalloying. Fine grain strengthening can significantly improve the strength and toughness of materials.

[0018] Cr: Cr element can improve the material's hardenability, strength, hardness, wear resistance, corrosion resistance and oxidation resistance.

[0019] B: The B element can improve the hardenability and carburizing properties of the material, and improve the strength and fatigue performance of the material.

[0020] Another aspect of the present invention provides a method for manufacturing the above-mentioned 700MPa tracking bracket steel plate, the method comprising the following steps:

[0021] (1) The continuous casting billet is loaded into a heating furnace and heated in stages. The first stage is heated to 450°C ± 5°C and kept warm for 8 to 12 minutes. The second stage is heated to 900°C ± 5°C and kept warm for 5 to 8 minutes. The third stage is heated to 1160°C ± 5°C and kept warm for 70 to 90 minutes. The fourth stage is heated to 1240 to 1250°C and kept warm for ≤ 35 minutes.

[0022] (2) Rough rolling and finishing rolling are then carried out. The finishing rolling temperature is 870-890°C. The cooling section is divided into three stages. In the first stage, water spray cooling is carried out after the final rolling, and the temperature is reduced to 630-670°C for 3-5s. In the second stage, water spraying is stopped and air cooling is carried out for 5-7s. In the third stage, oil spray cooling is carried out to 360-450°C. The steel is then coiled and sent to a heat preservation pit for storage, and then hoisted out and air cooled to room temperature.

[0023] In the above technical solution, further, in step (1), the thickness of the continuous casting billet is ≤200 mm and the length is ≤10 m.

[0024] In the above technical solution, further, in step (1), the first stage of heating is from room temperature to 450°C±5°C over 30 to 40 minutes, and the second stage of heating is from 450°C±5°C to 900°C±5°C over 10 to 15 minutes.

[0025] In the above technical solution, further, in step (2), the storage time in the insulation pit is 60 to 90 minutes.

[0026] The beneficial effects of the present invention are:

[0027] (1) In the composition design of the steel plate of the present invention, Ti and Mn are used as the main strengthening elements, Cr and Si increase its corrosion resistance, and Cr and B increase its hardenability, which makes it easy to control the material structure morphology.

[0028] (2) The heating system of the present invention can not only ensure that the grain boundaries and grains inside the steel are regularized and refined, but also the uneven structure and non-metallic inclusions are homogenized through the diffusion effect of high-temperature heating, while improving the problem of difficult removal of iron scale caused by Si, O, and Fe ternary compounds.

[0029] (3) The present invention adopts water-air-oil alternating cooling, firstly adopts water cooling + air cooling to generate ferrite, and the elements such as B and Cr added by the present invention regulate the microstructure, and obtain ferrite microstructure by water cooling + air cooling; then oil cooling is adopted to cool down more evenly and quickly, thereby obtaining a fine and dispersed martensitic microstructure, reducing the problems of excessive material stress and plate warping caused by the uneven traditional water cooling, and at the same time, the oil layer adhering to the surface of the material can isolate the air and reduce the oxidation of the material.

[0030] (4) After the coiling, the present invention is put into the insulation pit, which can be self-tempered to reduce internal stress and brittleness, improve plasticity and wear resistance, and weaken some residual stress. It can also make the surface oxide scale of the material gradually uniform and dense with the change of O potential and more closely bonded with the matrix, thereby further improving corrosion resistance. DETAILED DESCRIPTION

[0031] Example 1

[0032] This embodiment uses the tracking bracket steel with a product specification of 3.0mm*1550mm produced by our company as an example to further illustrate the present invention.

[0033] The steel for the tracking bracket of this embodiment is smelted according to the alloy element ratio in Table 1 (the balance is Fe and unavoidable impurities); after the continuous casting billet (thickness 180mm, length 9m, width 1575mm) is loaded into the heating furnace, the distance between the billets is controlled to be ≥100mm to prevent the influence of heat flow. The billets loaded into the furnace are transported from the furnace entry end to the furnace exit end by the movement of the walking beam. The walking beam stops in the middle position or steps to avoid deformation and bending of the billet and aggravation of black marks. The segmented heating is adopted. In the first stage, the room temperature is heated to 452℃ in 38min and kept for 1 0min, the second stage is heated from 452℃ to 903℃ after 13min, and kept warm for 5min, the third stage is 1160℃ and kept warm for 81min, and the fourth stage is heated to 1250℃ and kept warm for 15min; then it is coiled after rough rolling and finish rolling; the final rolling temperature is controlled at 873℃, and the cooling section is divided into three sections. Among them, after the first section, water spray cooling is carried out after 4s to cool to 650℃, the second section stops water spraying and air cooling for 6s, and the third section is cooled by oil spray to 380℃, then it is coiled and sent to the insulation pit for storage for 70min, and then it is hoisted out and air-cooled to room temperature.

[0034] The mechanical properties of the steel plate manufactured according to the method of this embodiment are shown in Table 2, the corrosion properties are shown in Table 3, and the metallographic structure is martensite+ferrite.

[0035] Comparative Example 1

[0036] Comparative Example 1 adopts Ti-Nb composite microalloying design. This comparative example 1 is smelted according to the alloy element ratio in Table 1 (the balance is Fe and unavoidable impurities); after the continuous casting billet is loaded into the heating furnace, it is slowly heated to 1271°C and then kept warm for 45 minutes, with a total furnace time of 167 minutes; then it is coiled after rough rolling and finish rolling, the finishing rolling temperature is controlled at 869°C, and the cooling section is intermittently water-cooled to 622°C, and then coiled and air-cooled.

[0037] The mechanical properties of the steel plate manufactured according to the method of Comparative Example 1 are shown in Table 2, the corrosion properties are shown in Table 3, and the metallographic structure is ferrite+pearlite.

[0038] Comparative Example 2

[0039] Comparative Example 2 was smelted according to the alloy element ratio in Table 1 (the balance was Fe and unavoidable impurities); after the continuous casting billet was loaded into the heating furnace, it was slowly heated to 1269°C and then kept warm for 53 minutes, with a total furnace time of 171 minutes, and then it was coiled after rough rolling and finishing rolling. The finishing rolling temperature was controlled at 862°C, and the cooling section was intermittently water-cooled to 603°C, and then coiled and air-cooled.

[0040] The mechanical properties of the steel plate manufactured by the method of Comparative Example 2 are shown in Table 2, the corrosion properties are shown in Table 3, and the metallographic structure is uniform polygonal ferrite + a small amount of pearlite.

[0041] Table 1 Composition of steel plates of Example 1 and Comparative Examples 1-2 (%)

[0042] Serial number C Si Mn P S Ti Al Cr N B O Example 1 0.08 0.55 1.42 0.010 0.008 0.085 0.011 0.64 0.0018 0.003 0.003 Comparative Example 1 0.07 0.32 1.60 0.009 0.006 0.054 0.045(Nb) 0.35 0.0020 -- -- Comparative Example 2 0.07 0.45 0.91 0.012 0.010 0.081 -- 1.12 0.026(Cu) -- --

[0043] Table 2 Mechanical properties of the steel plates of Example 1 and Comparative Examples 1-2

[0044]

[0045]

[0046] Table 3 Corrosion performance of the steel plates of Example 1 and Comparative Examples 1-2

[0047]

[0048] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A 700MPa tracking bracket steel plate, characterized in that: The chemical composition of the steel plate is calculated by mass percentage: C: 0.06%~0.09%, Si: 0.43%~0.63%, Mn: 1.33%~1.53%, S: ≤0.015%, P: ≤0.015%, Al: ≤0.015%, Ti: 0.073%~0.098%, Cr: 0.53%~0.73%, N: ≤0.005%, O: ≤0.005%, B: 0.0025%~0.0043%, and the rest are Fe and other unavoidable impurities.

2. The 700MPa tracking bracket steel plate according to claim 1, characterized in that: The yield strength of the steel plate is ≥700MPa, the tensile strength is ≥800MPa, the elongation is ≥15%, the hardness is ≥300HV, and the relative corrosion rate of Q355B is ≤45%.

3. The 700MPa tracking bracket steel plate according to claim 1, characterized in that: The steel plate has a thickness of 2.0 to 5.0 mm and a width of 1450 to 2150 mm.

4. A method for manufacturing a 700MPa tracking bracket steel plate according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: (1) The continuous casting billet is loaded into a heating furnace and heated in stages. The first stage is heated to 450°C ± 5°C and kept warm for 8 to 12 minutes. The second stage is heated to 900°C ± 5°C and kept warm for 5 to 8 minutes. The third stage is heated to 1160°C ± 5°C and kept warm for 70 to 90 minutes. The fourth stage is heated to 1240 to 1250°C and kept warm for ≤ 35 minutes. (2) The finishing rolling temperature is 870-890°C, and the cooling section is divided into three sections. In the first section, water spray cooling is carried out after the finishing rolling, and the temperature is reduced to 630-670°C after 3-5s. In the second section, water spraying is stopped and air cooling is carried out for 5-7s. In the third section, oil spray cooling is carried out to 360-450°C, and then the steel is coiled, sent to the insulation pit for storage, and then hoisted out and air cooled to room temperature.

5. The manufacturing method according to claim 4, characterized in that: In step (1), the thickness of the continuous casting billet is ≤200 mm and the length is ≤10 m.

6. The manufacturing method according to claim 4, characterized in that: In step (1), the first stage of heating is from room temperature to 450°C±5°C over 30 to 40 minutes, and the second stage of heating is from 450°C±5°C to 900°C±5°C over 10 to 15 minutes.

7. The manufacturing method according to claim 4, characterized in that: In step (2), the storage time in the insulation pit is 60 to 90 minutes.

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