Production method of low-cost galvanized structural steel for export

Abstract

The invention discloses a production method of low-cost galvanized structural steel for export. The production method comprises the following steps: smelting; a hot rolling process; acid rolling process; annealing process; the high-strength and high-toughness steel plate comprises the following chemical components in percentage by mass: 0.06%-0.08% of C, 0.01%-0.04% of Si, 0.31%-0.39% of Mn, 0.008%-0.013% of P, 0.002%-0.003% of S, 0.033%-0.038% of Alt, 0.0008%-0.015% of Ca, 0.0032%-0.0045% of N and the balance of iron and impurities. By adding C, Mn and microalloy elements, the mechanical property of the product is guaranteed; and meanwhile, products which are qualified in performance and meet the use requirements of customers can be produced in batches on the basis of ensuring the optimal configuration of the product cost through the adjusted process system measures.

Description

Technical Field

[0001] This invention relates to the field of steel product research and development technology, and in particular to a method for producing low-cost galvanized structural steel for export. Background Technology

[0002] In China, galvanized structural steel is primarily used in civilian applications, covering a wide range of sectors and demanding a broad range of specifications. Galvanized structural steel products rely on a complete production process (steelmaking, hot rolling, pickling, and galvanizing). Based on the specific requirements of downstream users and considering the unique characteristics of its own processes, and after fully identifying the technological features of other products on the production line, the company has developed its own production process regulations and principles for transitioning between these products and other products. This allows for the mass production of qualified products that meet customer requirements.

[0003] The existing patent research is as follows:

[0004] The patent "A 250MPa grade hot-dip galvanized high-strength structural steel for container containers and its production method" is for 250MPa grade hot-dip galvanized structural steel for container containers. The product strength level is different, and there are obvious differences in chemical composition design, hot rolling, pickling rolling and galvanizing process.

[0005] The patent, "A Method for Galvanizing Low-Alloy High-Strength Structural Steel," prepares the steel surface for galvanizing by treating it, preventing incomplete reaction between the steel and the galvanizing agent during the subsequent process. This invention can improve the appearance quality of the coating. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost production method for galvanized structural steel for export. By fully identifying customer requirements, service environment, and inspection criteria, and by adding C, Mn, and microalloying elements, the mechanical properties of the product are guaranteed. Simultaneously, by adjusting the hot rolling temperature regime, pickling reduction rate, and galvanizing furnace process temperature regime, the method achieves optimal cost control while enabling mass production of qualified products that meet customer requirements.

[0007] The chemical composition range of galvanized structural steel by weight percentage is: C≤0.21%; Si≤0.08%; Mn0.30~0.40%; P≤0.015%; S≤0.008%; N≤50ppm. The main process flow includes:

[0008] Steelmaking process: KR desulfurization → converter smelting → LF refining → slab continuous casting;

[0009] Hot rolling process: slab heating → high-pressure water descaling → fixed width press → E1 R1 roughing mill rolling → E2R2 roughing mill rolling → (insulation cover) → flying shear head and tail → high-pressure water descaling → F1-F7 finishing mill rolling → dense laminar flow cooling → coiling → pallet transport system → weighing → warehousing;

[0010] Pickling and rolling process: Pickling and uncoiling → Welding → Tension leveling → Pickling → Rinsing → Drying → Edge trimming → Rolling → Coiling → Weighing → Marking → Bundling → Warehousing

[0011] Galvanizing process: hot-dip galvanizing uncoiling → welding → entrance looper → cleaning → annealing furnace → zinc pot → post-galvanizing cooling → water quenching → intermediate looper → finishing machine → stretching and straightening machine → roller coating machine → dryer → air cooling device → exit looper → edge trimming → surface inspection → oiling → sampling and inspection → coiling → bundling and weighing → packaging → warehousing.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] This invention discloses a method for producing low-cost galvanized structural steel for export, comprising:

[0014] 1) Smelting process

[0015] 1.1) Converter smelting: Molten iron is pretreated and desulfurized before being smelted in a converter. Oxygen blowing is used to decarburize and raise the temperature. Ferrosilicon and ferromanganese are added in the later stage of smelting for deoxidation and alloying. The P and S content is controlled to prevent the molten steel from over-oxidizing. The tapping temperature is ≥1620℃ to ensure that the composition and temperature are coordinated when tapping. If it is a new tapping outlet or an abnormal turnover ladle, the tapping temperature is increased by 10-15℃ on the basis of the upper limit. The [P] of the converter tapping steel is ≤0.010% and [S] is ≤0.008%.

[0016] 1.2) Refining: The LF full-process argon blowing process is adopted. The refining process maintains a good reducing atmosphere. Al wire is used for deoxidation. In the later stage of LF, manganese iron and titanium iron are added for alloying. After LF, calcium treatment is carried out.

[0017] 1.3) Continuous casting: The temperature of molten steel entering the tundish is controlled at 1555-1570℃, the superheat is 25-40℃, and the casting speed is controlled at 1.00-1.50m / min;

[0018] 2) Hot rolling process

[0019] The billet is heated by a walking beam furnace. The roughing rolling adopts a double-stand R1 and R2 reciprocating rolling process with a 3+3 or 1+5 roughing mode. The finishing rolling adopts a continuous rolling process of F1-F7.

[0020] Billet heating system:

[0021]

[0022] Rolling process:

[0023] Thickness (mm) Finishing rolling temperature (°C) Winding temperature (°C) Cooling mode / code 2.2-5.0 910±15 590±15 Pre-dispersion / 11

[0024] 3) Pickling and rolling process

[0025] Pickling and rolling adopts the F1-F5 stand continuous rolling process;

[0026] Pickling and rolling specifications:

[0027]

[0028]

[0029] 4) Annealing process

[0030] Annealing was performed using a vertical continuous annealing furnace, with cooling conducted under a reducing atmosphere and a nitrogen-hydrogen mixed protective atmosphere. Annealing process:

[0031]

[0032] Leveling machine process:

[0033]

[0034]

[0035] The galvanized structural steel has the following chemical composition range by mass percentage: C 0.06-0.08%, Si 0.01-0.04%, Mn 0.31-0.39%, P 0.008-0.013%, S 0.002-0.003%, Alt 0.033-0.038%, Ca 0.0008-0.015%, N 0.0032-0.0045%, with the remainder being Fe and unavoidable impurities.

[0036] Furthermore, the chemical composition of LF refined molten steel supplied for continuous casting by mass percentage includes: C 0.06-0.08%, Si≤0.04%, Mn 0.30-0.40%, P≤0.020%, S≤0.010%, Alt 0.015-0.045%, Ca0.0008-0.0020%, N≤0.0055%, with the remainder being Fe and unavoidable impurities.

[0037] Furthermore, the microstructure of the low-cost galvanized structural steel is equiaxed ferrite with a small amount of pearlite, and the grain size is grade 9-10.

[0038] Furthermore, the grain size is grade 9-10.

[0039] Furthermore, the finished product thickness is 0.8-2.5mm.

[0040] Furthermore, the finished product's mechanical properties must meet the following requirements: yield strength ≥ 250 MPa, tensile strength ≥ 380 MPa.

[0041] Furthermore, the finished product's mechanical properties must meet the following requirement: elongation ≥ 30.5%.

[0042] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0043] The advantage of this invention lies in introducing a process method for the large-scale and stable production of galvanized structural steel with a thickness of 0.5-2.5mm that meets export product standards. Depending on the later use, it effectively matches upstream and downstream processes to produce compliant and usable galvanized structural steel products at the optimal manufacturing cost, and has good promotional value. Attached Figure Description

[0044] The present invention will be further described below with reference to the accompanying drawings.

[0045] Figure 1 The microstructure of the low-cost galvanized structural steel of this invention for export is shown.

[0046] Figure 2 This is a photograph of the finished product of the low-cost galvanized structural steel of this invention for export. Detailed Implementation

[0047] The present invention will be further described below with reference to the embodiments.

[0048] A method for producing galvanized structural steel with an export strength grade of 250 MPa includes:

[0049] 1. Steelmaking composition

[0050] Based on the above steelmaking process requirements, the actual chemical composition (mass percentage) of the slab is shown in Table 1 below.

[0051] Table 1. Chemical composition (wt%) of the example

[0052] Chemical elements C Si Mn P S Actual range 0.06-0.08 0.01-0.04 0.31-0.39 0.008-0.013 0.002-0.003 Chemical elements Alt Ca N Actual range 0.033-0.038 0.008-0.015 0.0032-0.0045

[0053] 2. Finished Product Performance

[0054] Based on the hot-rolled mechanical properties, the product was manufactured according to the acid rolling and annealing processes designed in this invention. The room temperature tensile mechanical properties of the finished product are shown in Table 2. The microstructure consists of equiaxed ferrite with a small amount of pearlite, with a grain size of 9-10. The microstructure morphology is shown in Table 2. Figure 1 .

[0055] Table 2 Mechanical Properties of Finished Products

[0056]

[0057]

[0058] 3 Product Application Areas

[0059] Our galvanized structural steel products are primarily exported to Europe, Japan, South Korea, Southeast Asia, and other regions, and are mainly used in the construction, electronics, light industry, and agriculture sectors. The products are widely used to manufacture square tubes, round tubes, structural panels, cable trays, scaffolding, and protective pipes.

[0060] In summary, this product has passed performance testing and user evaluation, meeting current market demands, and has been widely used in various civilian structural components and reinforcing plates. The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing low-cost galvanized structural steel for export, characterized in that: include: 1) Smelting process 1.1) Converter smelting: Molten iron is pretreated and desulfurized before being smelted in a converter. Oxygen blowing is used to decarburize and raise the temperature. Ferrosilicon and ferromanganese are added in the later stage of smelting for deoxidation and alloying. The P and S content is controlled to prevent the molten steel from over-oxidizing. The tapping temperature is ≥1620℃ to ensure that the composition and temperature are coordinated when tapping. If it is a new tapping outlet or an abnormal turnover ladle, the tapping temperature is increased by 10-15℃ on the basis of the upper limit. The [P] of the converter tapping steel is ≤0.010% and [S] is ≤0.008%. 1.2) Refining: The LF full-process argon blowing process is adopted. The refining process maintains a good reducing atmosphere. Al wire is used for deoxidation. In the later stage of LF, manganese iron and titanium iron are added for alloying. After the LF is completed, calcium treatment is carried out. 1.3) Continuous casting: The temperature of molten steel entering the tundish is controlled at 1555-1570℃, the superheat is 25-40℃, and the casting speed is controlled at 1.00-1.50m / min; 2) Hot rolling process The billet is heated by a walking beam furnace. The roughing rolling adopts a double-stand R1 and R2 reciprocating rolling process with a 3+3 or 1+5 roughing mode. The finishing rolling adopts a continuous rolling process of F1-F7. Billet heating system: Rolling process: 3) Pickling and rolling process Pickling and rolling adopts the F1-F5 stand continuous rolling process; Pickling and rolling specifications: 4) Annealing process Annealing was performed using a vertical continuous annealing furnace, with cooling conducted under a reducing atmosphere and a nitrogen-hydrogen mixed protective atmosphere. Annealing process: Leveling machine process: The chemical composition range of the galvanized structural steel by mass percentage is as follows: C 0.06-0.08%, Si 0.01-0.04%, Mn 0.31-0.39%, P 0.008-0.013%, S 0.002-0.003%, Alt 0.033-0.038%, Ca 0.0008-0.015%, N 0.0032-0.0045%, with the remainder being Fe and unavoidable impurities.

2. The method for producing low-cost galvanized structural steel for export according to claim 1, characterized in that: The chemical composition of LF refined steel supplied for continuous casting, by mass percentage, includes: C 0.06-0.08%, Si≤0.04%, Mn 0.30-0.40%, P≤0.020%, S≤0.010%, Alt 0.015-0.045%, Ca 0.0008-0.0020%, N≤0.0055%, the remainder is Fe and unavoidable impurities.

3. The method for producing low-cost galvanized structural steel for export according to claim 1, characterized in that: The microstructure of the low-cost galvanized structural steel is equiaxed ferrite with a small amount of pearlite, and the grain size is 9-10.

4. The method for producing low-cost galvanized structural steel for export according to claim 3, characterized in that: Grain size grade 9-10.

5. The method for producing low-cost galvanized structural steel for export according to claim 1, characterized in that: The finished product thickness is 0.8-2.5mm.

6. The method for producing low-cost galvanized structural steel for export according to claim 1, characterized in that: The finished product's mechanical properties must meet the following requirements: yield strength ≥ 250 MPa, tensile strength ≥ 380 MPa.

7. The method for producing low-cost galvanized structural steel for export according to claim 1, characterized in that: The finished product's mechanical properties must meet the following requirement: elongation ≥ 30.5%.

Images