Manufacturing method of zinc-aluminum-magnesium high-strength steel with yield strength of 500 MPa

Abstract

The invention discloses a production method of high-strength zinc-aluminum-magnesium structural steel, a coating comprises the following components in percentage by mass: 5-9% of Al, 2-4% of Mg and the balance of Zn and inevitable impurity elements, and the high-strength zinc-aluminum-magnesium structural steel comprises the following chemical components in percentage by mass: less than or equal to 0.20% of C, less than or equal to 0.020% of P, less than or equal to 0.020% of S, less than or Less than or equal to 0.20% of Si; mn < = 1.20%; p is less than or equal to 0.035%; s is less than or equal to 0.025%; alt is greater than or equal to 0.015%; ti is greater than or equal to 0.060%, and the balance is Fe and inevitable impurities. The production method comprises the following steps: steelmaking, hot rolling, cold rolling and galvanizing. The production cost is low, and international ROSH and Reach environmental protection requirements are met. The product performance meets the requirements that the yield strength is larger than or equal to 500 MPa, the tensile strength is larger than or equal to 550 MPa, and the percentage elongation after fracture is larger than or equal to

Description

Technical Field

[0001] The invention belongs to the technical field of steel metallurgy and steelmaking technology, and in particular relates to a method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500MPa. Background Art

[0002] With the growing global demand for clean energy, the photovoltaic market has ushered in unprecedented development opportunities. As an important part of the photovoltaic system, the selection of materials for photovoltaic brackets is directly related to the stability, durability and economy of the system. Zinc-aluminum-magnesium steel plates are increasingly widely used in the field of photovoltaic brackets due to their excellent corrosion resistance, high strength and good processing performance, and the market demand continues to grow.

[0003] With the continuous improvement and innovation of photovoltaic bracket production technology, the strength and plasticity of zinc-aluminum-magnesium steel plates will be further improved. For example, by optimizing the composition design, rolling process, annealing process, hot-dip plating process parameters, and improving the uniformity of the coating, the mechanical properties and corrosion resistance of zinc-aluminum-magnesium steel plates can be further improved. This will make the application of zinc-aluminum-magnesium steel plates in the field of photovoltaic brackets more extensive and in-depth.

[0004] The existing literature and patent research are as follows:

[0005] The production method of the searched patent 1 "A method for producing high-strength zinc-aluminum-magnesium structural steel" adopts two rough rolling mills + 7-stand continuous rolling to produce raw materials, and the zinc-aluminum-magnesium products are produced by acid rolling + annealing + galvanizing. The chemical composition is calculated by mass percentage: C≤0.22%; Si≤0.60%; Mn≤1.50%; P≤0.035%; S≤0.025%; Alt≥0.015%; Ti≥0.060%, and the rest is Fe and unavoidable impurities. The yield strength of the steel strip is greater than 550MPa, and the tensile strength is greater than 560MPa.

[0006] Search patent "A hot-dip galvanized aluminum-magnesium high-strength steel, preparation method and application". Hot-dip galvanized aluminum-magnesium high-strength steel includes a substrate and a zinc-aluminum-magnesium alloy coating on the surface of the substrate. Through composition design and production process control based on composition design, a process production plan and core production technology of smelting, hot rolling, cold rolling and annealing with CSP thin slab continuous casting and rolling production line and ordinary hot-dip galvanizing production line as the core process are formed. The yield strength of hot-dip galvanized aluminum-magnesium high-strength steel is greater than 550MPa, and the elongation is greater than 17%. It is suitable for industries with high corrosion resistance requirements such as photovoltaic brackets and highway guardrails.

[0007] The search patent "A hot-dip galvanized aluminum-magnesium high-strength steel and its manufacturing method" shows that the high-strength steel includes a substrate and a coating attached to the surface of the substrate, wherein the chemical composition of the substrate in terms of mass percentage is: C0.18-0.22%, Si0.2-0.3%, Mn0.5-1.0%, Als0.02-0.05%, P≤0.02%, S≤0.008%, N≤0.008%. The substrate of the present invention does not contain micro-alloying elements such as Nb, Ti, and V, and adopts a low-alloy, low-cost design. Through a carefully designed formula combined with effective regulation of the coiling temperature, cold rolling annealing temperature, and plating solution temperature, a yield strength of more than 400MPa, a tensile strength of more than 500Mpa, and an elongation of more than 10% is obtained, and it meets the international ROSH and Reach environmental protection requirements. Summary of the invention

[0008] The purpose of the present invention is to provide a method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500MPa, which not only has low production cost, but also meets the international ROSH and Reach environmental protection requirements. The product performance meets the following requirements: yield strength ≥500MPa, tensile strength ≥550MPa, and elongation after fracture ≥12%.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa, comprising the following steps: steelmaking step + hot rolling step + cold rolling step + galvanizing step, specifically comprising:

[0011] The tapping temperature of the converter is ≥1620℃ to ensure that the composition and temperature are coordinated. During the tapping process, aluminum iron, manganese iron, silicon iron and other alloys are added for deoxidation and alloying. The converter supplies LF molten steel with Mn0.75-0.95%, Si≤0.06%, and Alt≥0.040%;

[0012] LF furnace slag desulfurization, and adding aluminum iron, silicon iron, manganese iron alloy to adjust the composition to the target value;

[0013] During the casting process of slab continuous casting, the superheat control range of the intermediate ladle is 15-30℃, and the production casting speed is 1.0-1.8m / min;

[0014] The thickness of the ingot is 230mm, the hot-rolled thickness is 2.1-5.0mm, and the cooling method is pre-dispersion;

[0015] The heating temperature of hot-rolled slab is 1210-1270℃, the finishing temperature is 870-920℃, and the coiling temperature is 550-630℃;

[0016] The chemical composition of the high-strength zinc-aluminum-magnesium structural steel is calculated by mass percentage as follows: C≤0.20%; Si≤0.20%; Mn≤1.20%; P≤0.035%; S≤0.025%; Alt≥0.015%; Ti≥0.060%, and the rest is Fe and inevitable impurities. The coating composition is Al 5-9%, Mg 2-4%, and the balance is Zn and inevitable impurity elements.

[0017] Furthermore, the cold-rolled thickness is 0.8-2.5 mm.

[0018] Furthermore, in the galvanizing process, the heating temperature is 710-740°C, the soaking temperature is 720-740°C, the temperature of entering the zinc pot is 430±10°C, the elongation of the leveler is 0.20-0.60%, and the running speed of the steel strip is ≥70m / min.

[0019] Furthermore, the KR desulfurization process requires that the sulfur content of the molten iron entering the converter is less than 0.010%, and the slag removal area of ​​the molten iron is greater than 90%. The surface of the molten iron is relatively clean after slag removal.

[0020] Furthermore, the nitrogen addition amount during the continuous casting process is required to be less than 10 ppm.

[0021] Furthermore, the rolling thickness is 2.1-5.0 mm.

[0022] Furthermore, the acid rolling reduction rate is designed to be 50%-71%, and the outlet thickness is 0.6-2.5 mm.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] According to the chemical composition, hot rolling process, acid rolling process and galvanizing process of the present invention, a zinc-aluminum-magnesium steel strip with a yield strength of 500MPa and mainly fine grain and precipitation strengthening can be manufactured, which has various indicators such as good corrosion resistance and meets the processing and use requirements of photovoltaic brackets. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] Figure 1 This is the metallographic structure of the zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa. DETAILED DESCRIPTION

[0027] A method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa, comprising:

[0028] Smelting process

[0029] Desulfurization process: The sulfur content of the molten iron entering the converter is required to be less than 0.010%, and the slag removal area of ​​the molten iron is greater than 90% (the surface of the molten iron is cleaner after slag removal).

[0030] Converter smelting process: steel tapping temperature ≥ 1620℃. During the converter tapping process, alloys such as ferroaluminum, ferrosilicon and ferromanganese are added for deoxidation and alloying.

[0031] LF process: LF furnace slag desulfurization, and add aluminum iron, silicon iron, manganese iron and other alloys to adjust the composition to the target value.

[0032] Continuous casting process: The casting machine adopts constant casting speed control, and the casting speed range is 1.0-1.8m / min; the nitrogen addition amount in the continuous casting process is required to be less than 10ppm.

[0033] Hot rolling process

[0034] The ingot was heated in a walking beam heating furnace (the heating process is shown in Table 1), the rough rolling adopted the 3+3 mode, the finishing rolling adopted F1-F7 continuous rolling, the cooling method was front concentrated, and the rolling thickness was 2.1-5.0 mm. The specific hot rolling process is shown in Table 2.

[0035] Table 1 Billet heating system

[0036]

[0037] Table 2 Rolling process

[0038]

[0039] Acid rolling process

[0040] The acid rolling reduction rate is designed to be 50%-71%, and the outlet thickness is 0.6-2.5mm.

[0041] Galvanizing process

[0042] The outlet temperature control conditions of each section of the galvanizing annealing furnace are shown in Table 3, and the elongation settings of the leveler and straightening machine are shown in Table 4.

[0043] Table 3 Annealing process

[0044]

[0045] Table 4 Leveling machine and tension leveling machine process

[0046]

[0047] Example Analysis

[0048] Steelmaking ingredients

[0049] According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 5.

[0050] Table 5 Chemical composition of examples wt.%

[0051]

[0052] Hot rolling process

[0053] According to the above hot rolling process requirements, the hot rolling thickness is 2.3-5.0mm, and the actual process is shown in Table 6

[0054] Table 6 Billet heating system

[0055]

[0056] Table 2 Rolling process

[0057]

[0058] Galvanizing process

[0059] According to the above galvanizing process requirements, the outlet temperature control of each section of the galvanizing annealing furnace is shown in Table 3, and the elongation settings of the leveler and straightening machine are shown in Table 8.

[0060] Table 7 Annealing process

[0061]

[0062] Table 8 Leveling machine and tension leveling machine process

[0063]

[0064] Finished product properties and microstructure

[0065] The room temperature tensile mechanical properties of the finished product are shown in Table 6. The product yield is 521-683MPa, the tensile strength is 593-763MPa, the elongation is 13.0-20.0%, and the plasticity is good, which can meet the needs of photovoltaic bracket bending and forming processing. Figure 1 , mainly composed of fine-grained ferrite + precipitates, and is evenly distributed.

[0066] Table 6 Tensile mechanical properties of finished products

[0067]

[0068] Corrosion resistance

[0069] The neutral salt spray corrosion test shows that the product has excellent corrosion resistance. Under the zinc layer thickness of 275g, the white rust corrosion area in the neutral salt spray test is ≤5% for 72 hours, and there is no red rust for more than 3000 hours.

[0070] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa, comprising the following steps: steelmaking step + hot rolling step + cold rolling step + galvanizing step, characterized in that: Specifically include: The tapping temperature of the converter is ≥1620℃ to ensure that the composition and temperature are coordinated. During the tapping process, aluminum iron, manganese iron, silicon iron and other alloys are added for deoxidation and alloying. The converter supplies LF molten steel with Mn0.75-0.95%, Si≤0.06%, and Alt≥0.040%; LF furnace slag desulfurization, and adding aluminum iron, silicon iron, manganese iron alloy to adjust the composition to the target value; During the casting process of slab continuous casting, the superheat control range of the intermediate ladle is 15-30℃, and the production casting speed is 1.0-1.8m / min; The thickness of the ingot is 230mm, the hot-rolled thickness is 2.1-5.0mm, and the cooling method is pre-dispersion; The heating temperature of hot-rolled slab is 1210-1270℃, the finishing temperature is 870-920℃, and the coiling temperature is 550-630℃; The chemical composition of the high-strength zinc-aluminum-magnesium structural steel is as follows by mass percentage: C≤0.20%; Si≤0.20%; Mn≤1.20%; P≤0.035%; S≤0.025%; Alt≥0.015%; Ti≥0.060%, and the rest is Fe and unavoidable impurities.

2. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: The cold rolled thickness is 0.8-2.5mm.

3. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: In the galvanizing process, the heating temperature is 710-740℃, the soaking temperature is 720-740℃, the temperature of entering the zinc pot is 430±10℃, the elongation of the leveling machine is 0.20-0.60%, and the running speed of the steel strip is ≥70m / min.

4. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: KR desulfurization process: The sulfur content of the molten iron entering the converter is required to be less than 0.010%, and the slag removal area of ​​the molten iron is greater than 90%. The surface of the molten iron is relatively clean after slag removal.

5. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: The nitrogen addition amount during the continuous casting process is required to be less than 10ppm.

6. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: Rolling thickness 2.1-5.0mm.

7. The method for manufacturing zinc-aluminum-magnesium high-strength steel with a yield strength of 500 MPa according to claim 1, characterized in that: Acid rolling process: The acid rolling reduction rate is designed to be 50%-71%, and the outlet thickness is 0.6-2.5mm.

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