A steel for scaffolding and a method for producing the same

Abstract

The application discloses a preparation method of steel for scaffolds, and main chemical components and mass percentage contents are as follows: carbon 0.10-0.25%, silicon 0.1-0.3%, manganese 1.0-1.5%, sulfur ≤0.01%, phosphorus ≤0.03%, titanium 0.02-0.05%, chromium 0.10-0.25%, aluminum 0.02-0.06%, nitrogen ≤0.009%, boron 0.0025-0.005%, and the rest is Fe and residual impurity elements in the smelting process. The production process flow is as follows: hot metal pretreatment, desulfurization, converter smelting, LF refining, continuous casting, slab slow cooling, slab heating, hot continuous rolling, coil slow cooling and (pickling). The steel plate produced by the method has a thickness of 1.2-5 mm, and the tensile strength after hot forming is greater than 1350 MPa.

Description

Technical Field

[0001] This invention relates to the field of scaffolding steel processing technology, specifically to a type of scaffolding steel and its preparation method. Background Technology

[0002] Steel pipe scaffolding began to be widely used in my country in the 1960s, generally employing 235 and 355 grade low-alloy steel materials. The production standards for disc-lock scaffolding clearly stipulate that hot-dip galvanizing must be used to extend its service life. With the increasing demand for lightweight and long-life steel in the construction industry, developing a scaffolding steel that possesses both high strength and good formability, while also being adaptable to hot-dip galvanizing, has become a trend in the industry. Existing scaffolding steel technologies still have room for improvement in terms of strength, lightweight potential, and corrosion resistance. Summary of the Invention

[0003] (a) Technical problems to be solved The technical problem to be solved by the present invention is to provide a steel for scaffolding and a method for preparing the same, so that the steel can obtain a tensile strength of more than 1350MPa after hot forming and quenching, thereby realizing the lightweighting of scaffolding.

[0004] (II) Technical Solution To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: a steel for scaffolding, wherein the chemical composition of the steel for scaffolding, by mass percentage, is: carbon (C): 0.10%-0.25%, silicon (Si): 0.1%-0.3%, manganese (Mn): 1.0%-1.5%, sulfur (S): ≤0.01%, phosphorus (P): ≤0.03%, titanium (Ti): 0.02%-0.05%, chromium (Cr): 0.10%-0.25%, aluminum (Al): 0.02%-0.06%, nitrogen (N): ≤0.009%, boron (B): 0.0025%-0.005%; the remainder is Fe and impurity elements remaining during the smelting process.

[0005] As an improvement, the microstructure of the steel is ferrite + pearlite, and after hot forming and quenching, its microstructure is ferrite + martensite.

[0006] As an improvement, the thickness of the steel is 1.2-5 mm, and the tensile strength after hot forming and quenching is ≥1350 MPa.

[0007] The preparation method of scaffolding steel includes the following steps performed in sequence: hot metal pretreatment, converter smelting, LF refining, continuous casting, slab slow cooling, slab heating, hot continuous rolling, controlled cooling and coiling.

[0008] As an improvement, the molten iron pretreatment includes a KR desulfurization step to reduce the sulfur content in the molten iron to ≤0.01%.

[0009] As an improvement, in the LF refining step, the LF outlet temperature is controlled at 1540-1570℃, and the refining time is ≥35 minutes.

[0010] As an improvement, in the slab heating step, the slab heating temperature is 1200-1260℃, the heating time is ≥130min, and the solution treatment time is 20-30min.

[0011] As an improvement, hot continuous rolling adopts a thermomechanical controlled rolling and controlled cooling process, specifically including: Roughing process: The initial roughing temperature is 1160-1190℃, and the final roughing temperature is 1060-1140℃; Finishing rolling process: The initial finishing rolling temperature is 980-1060℃, and the final finishing rolling temperature is 850-900℃.

[0012] As an improvement, in the controlled cooling and coiling steps, laminar flow cooling is used to cool the hot-rolled steel strip to 560-610°C before coiling.

[0013] As an improvement, in the continuous casting step, the casting speed is controlled at 0.8-1.8 m / min, and the billet adopts a light reduction mode.

[0014] The design principles of each chemical component in this invention are as follows: Carbon (C): Carbon is the most effective and economical element for increasing the strength of steel. This invention controls the C content between 0.10% and 0.25%. When the C content is higher than 0.12%, it helps to form lath martensite in subsequent heat treatment, ensuring strength properties. Excessive C content will reduce low-temperature toughness and deteriorate weldability and corrosion resistance.

[0015] Silicon (Si): Si reduces the solubility of carbon (C) in austenite, decreases the stability of supercooled austenite, and accelerates the phase transformation process. Si inhibits carbide precipitation, increases ferrite content, and plays a role in solid solution strengthening. It also improves the elongation of steel plates, balancing strength and plasticity. Its content is controlled between 0.1% and 0.3%.

[0016] Manganese (Mn): Mn can improve hardenability and strength. However, Mn is a positive segregation element in crystallization, and excessive content can easily produce banded structures, so it should not be too high. This invention achieves the strengthening target by adding microalloying elements such as Ti, while controlling the Mn content at 1.0%–1.5%.

[0017] Sulfur (S): S is a harmful element in high-strength steel, easily causing MnS segregation and sulfide inclusions, and must be strictly controlled. S should be ≤0.01% to reduce the number and size of inclusions and improve steel plate performance.

[0018] Phosphorus (P): P is also a harmful element. While it dissolves in ferrite, increasing strength, it significantly reduces plasticity and toughness, increases the risk of temper brittleness and cold working brittleness, and also negatively affects weldability. P should be ≤0.03%.

[0019] Titanium (Ti): During continuous casting solidification, Ti combines with N to form TiN. On the one hand, this reduces the fixation effect of free nitrogen on boron, protecting the hardenability of boron; on the other hand, TiN can inhibit grain coarsening in the weld heat-affected zone. Its content is controlled at 0.02%–0.05%.

[0020] Chromium (Cr): Cr can significantly improve the strength, hardness, and wear resistance of steel, while also improving its oxidation resistance and corrosion resistance, which helps extend the service life of scaffolding. Its content is controlled between 0.10% and 0.25%.

[0021] Boron (B): The main function of boron is to significantly improve the hardenability of steel, making it easier to harden through heat treatment, thereby reducing dependence on expensive alloying elements such as nickel and chromium. Its content is controlled between 0.0025% and 0.005%.

[0022] Aluminum (Al): Al, along with a small amount of boron, promotes the formation of acicular ferrite and refines the microstructure. However, excessive Al content can impair the toughness of steel, so its content is controlled at 0.02%–0.06%.

[0023] Nitrogen (N): N can form stable nitrides with elements such as Al and Ti, achieving precipitation strengthening. However, excessive N content will reduce the toughness of steel and increase brittleness and notch sensitivity. Therefore, it needs to be strictly controlled, requiring N ≤ 0.009%.

[0024] The beneficial effects of this invention are as follows: Through precise chemical composition design and combined with thermomechanical controlled rolling and cooling (TMCP) technology, a high-strength steel suitable for scaffolding has been prepared. This steel exhibits excellent formability and no springback, making it particularly suitable for hot forming. Scaffolding manufactured using this invention's steel can achieve a 25%-35% weight reduction while ensuring safety, thereby reducing the labor intensity of workers and showing promising prospects for widespread application in the construction industry. After hot forming and quenching, the tensile strength of this invention's steel can reach over 1350 MPa, fully meeting the performance requirements of high-strength scaffolding. Attached Figure Description

[0025] Figure 1 Microstructure images of the surface layer, 1 / 4 thickness, and center of the steel plate in this embodiment of the invention.

[0026] Figure 2 The production process flow diagram of the steel used for scaffolding in this invention. Detailed Implementation

[0027] The invention will now be described in further detail with reference to specific embodiments, but this should not be construed as limiting the scope of the subject matter of the invention to the following embodiments.

[0028] The following three examples illustrate the implementation process of the present invention in detail: Molten iron is desulfurized using KR and then smelted in a 210-ton converter. It is then refined in an LF furnace by argon blowing through a ladle and continuously cast into 230mm slabs. The slabs are cooled in a stack, reheated, and rough-rolled in 5-7 passes. Finally, they undergo thermomechanical controlled rolling and controlled cooling on a 7-stand 2250mm continuous rolling mill. The hot-rolled coil thicknesses are 1.8mm, 3mm, and 3.5mm. The composition of this invention is shown in Table 1, the controlled rolling and controlled cooling process parameters are shown in Table 2, and the mechanical properties are shown in Table 3.

[0029] The chemical composition of the steel used in the scaffolding example is shown in the table below.

[0030] Table 1Chemical composition book Example C Si Mn P S Ti N Al Control range 0.10-0.25 0.1-0.3 1.0-1.5 ≤0.03 ≤0.01 0.02-0.05 ≤0.009 0.02-0.06 Example 0.223 0.36 1.19 0.01 0.008 0.035 0.0062 0.029 element B Cr Control range 0.0025-0.005 0.1-0.25 Example 0.0029 0.015

[0031] The specific heating process used in the example is 1200-1260℃, with a heating time of 130-300 min in the furnace. The first stage is rough rolling, with an initial rolling temperature of 1160-1190℃; the second stage is finish rolling, with an initial rolling temperature of 980-1060℃. After rolling, the steel strip is cooled using ACC-controlled cooling, and the coiling temperature is 560-610℃.

[0032] The specific rolling process parameters for the embodiments and comparative examples are shown in Table 2 below. Table 2 Rolling process parameters serial number Thickness (mm) Furnace temperature (°C) Roughing and finishing rolling temperatures (°C) Finishing rolling start temperature (°C) Finishing rolling temperature (°C) Winding temperature (°C) 1 1.8 1256 1103 1065 893 591 2 3 1232 1081 1049 875 583 3 3.5 1230 1078 1040 868 576 The specific mechanical properties of the embodiments and comparative examples are shown in Table 3 below. Table 3 Mechanical Properties serial number Thickness (mm) <![CDATA[R el (MPa)]]> <![CDATA[R m (MPa)]]> A（%） <![CDATA[R el (MPa) (after quenching) <![CDATA[R m (MPa) (after quenching) A (%) (after quenching) Example 1 1.8 524 623 25.5 1186 1584 7 Example 2 3 508 611 26.5 1168 1601 7.5 Example 3 3.5 499 603 27 1134 1580 8

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention. The scope of the invention is defined by the appended claims and their equivalents. In short, if those skilled in the art are inspired by this invention and design similar structural methods and embodiments without departing from the inventive spirit of the invention, they should all fall within the protection scope of the invention.

Claims

1. A type of steel for scaffolding, characterized in that, The chemical composition of the steel used for scaffolding, by mass percentage, is as follows: carbon (C): 0.10%–0.25%, silicon (Si): 0.1%–0.3%, manganese (Mn): 1.0%–1.5%, sulfur (S): ≤0.01%, phosphorus (P): ≤0.03%, titanium (Ti): 0.02%–0.05%, chromium (Cr): 0.10%–0.25%, aluminum (Al): 0.02%–0.06%, nitrogen (N): ≤0.009%, boron (B): 0.0025%–0.005%; the remainder is Fe and impurities remaining from the smelting process.

2. The scaffolding steel according to claim 1, characterized in that, The steel has a ferrite + pearlite microstructure, and after hot forming and quenching, its microstructure becomes ferrite + martensite.

3. The steel for scaffolding according to claim 1, characterized in that, The steel has a thickness of 1.2-5 mm and a tensile strength ≥1350 MPa after hot forming and quenching.

4. A method for preparing scaffolding steel as described in any one of claims 1-3, characterized in that, The process includes the following steps performed in sequence: hot metal pretreatment, converter smelting, LF refining, continuous casting, slab slow cooling, slab heating, hot continuous rolling, controlled cooling, and coiling.

5. The method for preparing scaffolding steel according to claim 4, characterized in that, The molten iron pretreatment includes a KR desulfurization step, which reduces the sulfur content in the molten iron to ≤0.01%.

6. The method for preparing scaffolding steel according to claim 4, characterized in that, In the LF refining step, the LF outlet temperature is controlled at 1540-1570℃, and the refining time is ≥35 minutes.

7. The method for preparing scaffolding steel according to claim 4, characterized in that, In the slab heating step, the slab heating temperature is 1200-1260℃, the heating time is ≥130min, and the solution treatment time is 20-30min.

8. The method for preparing scaffolding steel according to claim 4, characterized in that, The hot continuous rolling process employs thermomechanical controlled rolling and controlled cooling technology, specifically including: Roughing process: The initial roughing temperature is 1160-1190℃, and the final roughing temperature is 1060-1140℃; Finishing rolling process: The initial finishing rolling temperature is 980-1060℃, and the final finishing rolling temperature is 850-900℃.

9. The method for preparing scaffolding steel according to claim 4, characterized in that, In the controlled cooling and coiling steps, laminar flow cooling is used to cool the hot-rolled steel strip to 560-610℃ before coiling.

10. The method for preparing scaffolding steel according to claim 4, characterized in that, In the continuous casting step, the casting speed is controlled at 0.8-1.8 m / min, and the billet is cast using a light reduction mode.

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