Novel process production method for DC51D + Z galvanized product

Abstract

The invention relates to the technical field of metallurgy, and particularly discloses a novel process production method for a DC51D + Z galvanized product, which comprises the following steps: adopting ESP (Electronic Spatial Product) full endless rolling, directly feeding a continuous casting billet produced by a continuous casting machine into a high-rolling-reduction rolling mill, rolling into an intermediate billet, heating by an induction heating furnace, carrying out high-pressure descaling, then feeding into a finishing mill for finish rolling, and coiling to form a rolled finished product steel coil; according to the thickness specification of a galvanized steel product, the compression ratio of a rolling mill under each thickness specification in the acid rolling process is set to be 33-55%; the galvanizing technology of the galvanized steel comprises the specific steps of uncoiling, welding, electrolytic cleaning, alkali liquor washing and strip steel surface residue cleaning. In-furnace heating adopts induction heating and heat preservation, after cooling, zinc plating is conducted in a zinc pot, and the hydrogen proportion, the oxygen content and the dew point control temperature of nitrogen and hydrogen protection gas are set for zinc plating; and finally, leveling, straightening and coiling to obtain a galvanized steel finished product. After acid pickling, rolling is conducted through a rolling mill with the low compression ratio of 33-55%, safety and environment friendliness are achieved, the heating speed is high, and the production cost is low.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a new process for producing DC51D+Z galvanized products. Background Technology

[0002] The fully automated casting and rolling line (ESP), a landmark technology of the "Third Technological Revolution" in the steel industry, achieves a high degree of integration and continuity in the production process through the rigid connection of continuous casting and rolling processes. With its advanced automated control system and optimized production line configuration, it can not only significantly reduce energy consumption and carbon emissions and improve yield, but also achieve high-precision production of thin-gauge strip steel.

[0003] Traditional galvanized steel product production processes begin with rolling raw steel coils at a compression ratio of 70-85% using a rolling mill. The resulting fibrous steel coils undergo recrystallization annealing on the galvanizing line using gas heating or radiant tube heating. After galvanizing in a zinc pot and subsequent passivation treatment in a leveling machine, the final galvanized product is produced. With fierce competition in the steel industry, reducing production costs and achieving breakthroughs in product technology are key areas of focus for major steel mills. Existing high-compression rolling methods for producing galvanized steel coils result in slow heating and high costs. Therefore, a new DC51D+Z galvanized product production process needs to be designed to address the high production costs of existing galvanized products. Summary of the Invention

[0004] To address the problems existing in the prior art, the purpose of this invention is to provide a new process for producing DC51D+Z galvanized products. The galvanized products are produced by induction heating annealing in a galvanizing furnace and are widely used in the home appliance, pipe manufacturing, and electrical industries.

[0005] The technical solution adopted by this invention to solve its technical problem is: a new process for producing DC51D+Z galvanized products, comprising the following steps:

[0006] S1. The chemical composition of galvanized steel by mass percentage is: C≤0.040%, Si: 0.038-0.055%, Mn: 0.06-0.20%, P≤0.028%, S≤0.003%, Alt: 0.020-0.050%, B: 0.0013-0.0025%, Ti≤0.0030%, with the remainder being iron and unavoidable impurities;

[0007] S2. Using ESP fully headless rolling, the continuously cast billets produced by the continuous casting machine directly enter the large reduction rolling mill, are rolled into intermediate billets, are heated by induction heating furnace under high pressure to remove scale, and then enter the finishing rolling mill for finishing rolling, and are coiled into rolled finished steel coils.

[0008] S3. Based on the thickness specifications of galvanized steel products (0.4-2.5mm), set the mill compression ratio for each thickness specification in the pickling and rolling process to 33-55%;

[0009] S4. The specific steps of the galvanizing process for galvanized steel include uncoiling, welding, electrolytic cleaning, and alkaline water washing to remove residues from the surface of the strip steel.

[0010] S5. The furnace heating adopts induction heating and heat preservation. After cooling, it enters the zinc pot for galvanizing. The hydrogen ratio, oxygen content and dew point control temperature of the nitrogen-hydrogen protective gas are set.

[0011] S6. Finally, flatten, straighten, and coil the steel to obtain the finished galvanized steel product.

[0012] Specifically, in step S2, the thickness of the intermediate billet is 8-15mm. After being heated to 1100-1200℃ in an induction heating furnace, it is descaled under high pressure. The temperature after finishing rolling is 870±10℃, and the coiling temperature is 700±20℃. Throughout the rolling process, the strip is directly connected from the continuous casting machine to the coiler, and is slit by a high-speed flying shear in front of the coiler.

[0013] Specifically, the thickness specification design of the galvanized steel product in step S3 is as follows:

[0014] (1) The thickness of the galvanized steel product order is T, the upper limit of the thickness delivery tolerance of the finished product order is T1, the lower limit of the thickness delivery tolerance is T2, and the design target thickness of the galvanized steel product is t, t=T-(T1-T2) / 2;

[0015] (2) Galvanizing production line: finishing elongation e, tension straightening elongation f;

[0016] (3) Under the conditions of different thickness specifications, different zinc layer thicknesses, and different preset process equipment elongation values, calculate the hot-rolled zinc layer thickness T3 = [nominal zinc layer weight / 50 (g / m)] 2 )]×7.1×10 -3 (mm);

[0017] (4) Target thickness t1 at the mill exit, t1 = (t - T3) * (1 + (e + f));

[0018] (5) Acid leveling process: extensibility a of the phosphorus crusher, compression ratio b of the rolling mill;

[0019] Raw material thickness design, raw material thickness t 原料 =t1 / (1-ab).

[0020] Specifically, the uncoiling process in step S4 involves uncoiling the pickled rolled steel coil using an uncoiler.

[0021] Specifically, the welding process in step S4 uses a welding machine for lap welding; the welding thickness varies as follows: when the thickness is <0.6mm, the thickness difference between the two plates is ≤0.15mm; when the thickness is ≥0.6mm-0.8mm, the thickness difference between the two plates is ≤0.3mm; when the thickness is >0.8mm-1.0mm, the thickness difference between the two plates is ≤0.40mm; when the thickness is ≥1.0mm, the thickness difference between the two plates is ≤0.50mm, and each welding parameter is adjusted within ±10%.

[0022] Specifically, the electrolytic cleaning process in step S4 is as follows: after the strip steel is rolled by the rolling mill, there are residual rolling iron powder and rolling emulsion residues on the surface of the strip steel. The residues on the surface of the strip steel are removed by electrolytic cleaning, alkaline cleaning, and hot water rinsing to ensure the cleanliness of the strip steel surface after entering the furnace and the zinc pot.

[0023] (1) Alkali immersion cleaning: temperature 65-75℃, conductivity 50-70ms / cm, liquid level >40%;

[0024] (2) Alkali brush cleaning: temperature 65-75℃, conductivity 50-70ms / cm, alkaline brush current: 8-15A, liquid level >40%;

[0025] (3) Electrolytic cleaning: temperature 70-75℃, conductivity 60-80ms / cm, liquid level >40%;

[0026] (4) Rinsing and cleaning: Temperature 70-80℃, liquid level > 40%;

[0027] (5) Rinsing and high-pressure spray cleaning: temperature 75-80℃, conductivity <5ms / cm, liquid level >40%;

[0028] (6) Strip drying: drying temperature 80-100℃;

[0029] (7) Squeeze roller pressure: 3-6 bar.

[0030] Specifically, in step S5, the induction heating is provided in the heating section of the galvanizing furnace with three 6000kW, 50kHz inductors and one 1500kW, 150kHz inductor, and the total power of the electric radiation tube insulation section is ≥1000kW.

[0031] Specifically, in step S5, the hydrogen ratio of the nitrogen-hydrogen protective gas for galvanizing is set to 5-10%, the oxygen content to ≤200ppm, and the dew point control temperature to ≤-30℃; the zinc pot process parameters are: zinc liquid aluminum content: 0.25±0.05%, and zinc pot temperature: 460±2℃.

[0032] Specifically, the parameters for leveling and straightening in step S6 are set as follows: for thickness < 1.0 mm, finishing 0.6% and straightening 0.4%; for thickness ≥ 1.0 mm, finishing 1.0% and straightening 0.4%.

[0033] The present invention has the following beneficial effects:

[0034] The invention presents a novel process for producing DC51D+Z galvanized products. By selecting raw material coils with suitable composition, pickling, and then rolling them on a rolling mill with a low compression ratio of 33-55%, the rolled steel coils undergo recrystallization annealing in an induction heating annealing furnace. With appropriate process speed and holding time, galvanized products with a thickness of 0.4-2.5mm can be produced. Compared with open flame heating and radiant tube heating, the induction heating method requires less investment in equipment, is safe and environmentally friendly, has a fast heating speed, and low production cost. Attached Figure Description

[0035] Figure 1 This is a production flow chart for the rolling process.

[0036] Figure 2 This is a flowchart of the galvanizing process. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Example 1.

[0039] A new process for producing DC51D+Z galvanized products, wherein the thickness of the galvanized steel products is designed to be 0.4-2.5mm and the width is 900-1250mm.

[0040] 1. The chemical composition of galvanized steel by mass percentage is: C≤0.040%, Si: 0.038-0.055%, Mn: 0.06-0.20%, P≤0.028%, S≤0.003%, Alt: 0.020-0.050%, B: 0.0013-0.0025%, Ti≤0.0030%, with the remainder being iron and unavoidable impurities. The addition of element B, which has strong diffusion ability, allows it to combine with nitrogen in the steel during the high-temperature annealing process of galvanizing to form boron nitrides, reducing the solid solution nitrogen content, improving ductility, effectively reducing product performance, and slowing down the aging of the strip steel.

[0041] Strictly controlling the Ti content allows the Ti element to refine the grains and combine with C / N elements to form fine carbides, which play a precipitation strengthening role and increase the strength of the product.

[0042] 2. ESP Endless Rolling Process:

[0043] The continuously cast billets produced by the continuous casting machine go directly into the high-reduction rolling mill and are rolled into 8-15mm intermediate billets. After being heated to 1100-1200℃ in an induction heating furnace, they are descaled under high pressure and then enter the finishing mill for finishing rolling. The temperature after finishing rolling is 870±10℃, and the coiling temperature is 700±20℃. Throughout the process, the strip steel is directly connected from the continuous casting machine to the coiler and is slit by a high-speed flying shear in front of the coiler.

[0044] Considering that the subsequent processes of this invention use a low compression ratio rolling process of 33-55%, compared with the traditional product's 75-85% high reduction rolling process, the strip steel grains have less internal energy storage, which affects the product performance after subsequent galvanizing and annealing. Therefore, the hot rolling process adopts high-temperature final rolling and high-temperature coiling processes, which coarsens the strip steel grains, stores more energy, and is beneficial for subsequent galvanizing and annealing.

[0045] 3. Rolling process, such as Figure 1 As shown, the process includes raw material processing, uncoiling, welding, scale breaking, pickling, rolling, coiling, and finished product rolling.

[0046] 4. Galvanizing process, such as Figure 2 As shown, the process includes pickling raw materials, uncoiling, welding, electrolytic cleaning, alkaline water washing, furnace heating, zinc plating in a zinc pot, finishing, tension straightening, passivation, coiling, and finished zinc plating.

[0047] 5. Raw material thickness design.

[0048] (1) The thickness of the galvanized steel product order is T, the upper limit of the thickness delivery tolerance of the finished product order is T1, the lower limit of the thickness delivery tolerance is T2, and the design target thickness of the galvanized steel product is t, t=T-(T1-T2) / 2;

[0049] (2) Galvanizing production line: finishing elongation e, tension straightening elongation f;

[0050] (3) Under the conditions of different thickness specifications, different zinc layer thicknesses, and different preset process equipment elongation values, calculate the hot-rolled zinc layer thickness T3 = [nominal zinc layer weight / 50 (g / m)] 2 )]×7.1×10 -3 (mm);

[0051] (4) Target thickness t1 at the mill exit, t1 = (t - T3) * (1 + (e + f));

[0052] (5) Acid leveling process: extensibility a of the phosphorus crusher, compression ratio b of the rolling mill;

[0053] Raw material thickness design: raw material thickness t_raw material = t1 / (1-ab).

[0054] The pickling and rolling process uses a two-stand, six-high mill. The thickness T of the galvanized steel product order corresponds to the raw material thickness t. 原料 The values ​​for compression by the rolling mill are shown in Table 1.

[0055] Table 1. Comparison table of raw material thickness, finished product thickness, and mill compression ratio.

[0056]

[0057] 6. Galvanizing process.

[0058] 1) Uncoiling: Pickled steel coils are uncoiled by an uncoiler.

[0059] 2) Welding: The strip thickness is 0.4-2.5mm. Welding machines are used for lap welding to ensure continuous production on the production line.

[0060] Welding thickness variation: When the thickness is <0.6mm, the thickness difference between the two plates is ≤0.15mm; when the thickness is ≥0.6mm-0.8mm, the thickness difference is ≤0.3mm; when the thickness is >0.8mm-1.0mm, the thickness difference is ≤0.40mm; when the thickness is ≥1.0mm, the thickness difference is ≤0.50mm. Each welding parameter should be adjusted within ±10%.

[0061] 3) Electrolytic cleaning: Since the strip steel has been rolled by the rolling mill, there are residual rolling iron powder and rolling emulsion on the surface of the strip steel. Electrolytic cleaning and alkaline cleaning and hot water rinsing are used to clean the residue on the surface of the strip steel to ensure the cleanliness of the strip steel surface after entering the furnace and zinc pot.

[0062] a) Alkali immersion cleaning: temperature 65-75℃, conductivity 50-70ms / cm, liquid level >40%.

[0063] b) Alkaline brush cleaning: temperature 65-75℃, conductivity 50-70ms / cm, alkaline brush current: 8-15A, liquid level >40%.

[0064] c) Electrolytic cleaning: Temperature 70-75℃, conductivity 60-80ms / cm, liquid level >40%.

[0065] e) Rinsing and cleaning: Temperature 70-80℃, liquid level >40%.

[0066] f) Rinsing and high-pressure spray cleaning: temperature 75-80℃, conductivity <5ms / cm, liquid level >40%.

[0067] d) Strip drying: Drying temperature 80-100℃.

[0068] g) Squeeze roller pressure: 3-6 bar.

[0069] 7. Furnace heating process.

[0070] Traditional galvanized product production involves heating the strip steel in a galvanizing furnace using open flames or radiant tubes heated by coal gas. The strip steel is heated to the recrystallization annealing temperature and then held at that temperature before being rapidly cooled and then placed into a zinc pot for galvanizing.

[0071] The technical content of this invention is induction heating temperature, and the heating section is configured with three 6000kW, 50kHz inductors and one 1500kW, 150kHz inductor. The total power of the electric radiation tube insulation section is ≥1000kW.

[0072] This invention employs induction heating technology to achieve recrystallization annealing of strip steel, followed by holding at that temperature for a certain time and rapid cooling before galvanizing in a zinc pot. Compared to open flame heating and radiant tube heating, induction heating requires less investment, is safer and more environmentally friendly, and has lower production costs. Compared to traditional galvanizing annealing furnaces, the induction heating furnace in this invention provides rapid heating, reaching 700℃ for the strip steel in 4-5 seconds. Extremely thin strip steel (0.4mm and 0.5mm) is prone to edge or center waviness issues, and wrinkles can easily appear on the strip surface during rapid heating, potentially leading to strip breakage. These wrinkles after annealing are commonly referred to in the industry as "yield lines," "slip lines," or "tensile strain marks." After annealing, low-carbon steel exhibits a distinct "yield plateau" in its stress-strain curve. On this plateau, under external force, the stress does not increase or fluctuates only slightly, but the strain increases significantly. To ensure stable production of 0.4mm and 0.5mm products, a low-temperature heating process with a high homogenization temperature is adopted to complete recrystallization annealing and grain growth, ensuring uniform heating in the thickness direction of the strip and guaranteeing product performance while ensuring product quality.

[0073] Table 2 shows the temperature parameters inside the galvanizing furnace corresponding to the thickness specifications of the ordered products.

[0074] Table 2. Correspondence between the thickness specifications of the ordered products and the temperature inside the galvanizing furnace.

[0075]

[0076] 8. Nitrogen-hydrogen protective gas hydrogen ratio setting: 5-10%; oxygen content ≤200ppm, dew point control ≤-30℃.

[0077] Zinc pot process: Zinc liquid aluminum content: 0.25±0.05%; Zinc pot temperature: 460±2℃;

[0078] 9. Post-plating cooling: Top roller temperature ≤290℃, water quenching plate temperature ≤160℃, water quenching plate temperature ≤45℃.

[0079] 10. The parameters of the leveling machine and tension leveling are shown in Table 3:

[0080] Table 3. Parameters of leveling machine and tension straightening machine.

[0081] Finished product thickness (mm) Polishing (%) Pull-correction (%) Elongation (%) of coating equipment （0.4-1.0】 0.6 0.4 1.0 （1.0-2.5】 1.0 0.4 1.4

[0082] 10. Product specifications: Yield strength ≤ 280 MPa, tensile strength ≤ 390 MPa, elongation A80 ≥ 31%.

[0083] This invention utilizes a suitable ESP (Electro-Semiconductor Process) raw material composition containing B, a high final rolling temperature, and a two-stand low compression ratio (33-55%) pickling and rolling process. Induction heating technology within a galvanizing furnace is employed to complete the strip annealing and recrystallization. Compared to traditional galvanized product production, this method offers faster heating and lower costs. Product performance achieves a yield strength ≤280MPa, tensile strength ≤390MPa, and elongation (A80) ≥31%. This invention enables the production of low compression ratio galvanized products, which are widely used in the home appliance, pipe manufacturing, and electrical industries.

[0084] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0085] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A new process for producing DC51D+Z galvanized products, characterized in that, Includes the following steps: S1. The chemical composition of galvanized steel by mass percentage is: C≤0.040%, Si: 0.038-0.055%, Mn: 0.06-0.20%, P≤0.028%, S≤0.003%, Alt: 0.020-0.050%, B: 0.0013-0.0025%, Ti≤0.0030%, with the remainder being iron and unavoidable impurities; S2. Using ESP fully headless rolling, the continuously cast billets produced by the continuous casting machine directly enter the large reduction rolling mill, are rolled into intermediate billets, are heated by induction heating furnace under high pressure to remove scale, and then enter the finishing rolling mill for finishing rolling, and are coiled into rolled finished steel coils. S3. Based on the thickness specifications of galvanized steel products (0.4-2.5mm), set the mill compression ratio for each thickness specification in the pickling and rolling process to 33-55%; S4. The specific steps of the galvanizing process for galvanized steel include uncoiling, welding, electrolytic cleaning, and alkaline water washing to remove residues from the surface of the strip steel. S5. The furnace heating adopts induction heating and heat preservation. After cooling, it enters the zinc pot for galvanizing. The hydrogen ratio, oxygen content and dew point control temperature of the nitrogen-hydrogen protective gas are set. S6. Finally, flatten, straighten, and coil the steel to obtain the finished galvanized steel product.

2. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The thickness of the intermediate billet in step S2 is 8-15mm. After being heated to 1100-1200℃ in an induction heating furnace, it is descaled under high pressure. The temperature after finishing rolling is 870±10℃, and the coiling temperature is 700±20℃. During the entire rolling process, the strip is directly connected from the continuous casting machine to the coiler, and is slit by a high-speed flying shear in front of the coiler.

3. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The thickness specification design of the galvanized steel product in step S3 is as follows: (1) The thickness of the galvanized steel product order is T, the upper limit of the thickness delivery tolerance of the finished product order is T1, the lower limit of the thickness delivery tolerance is T2, and the design target thickness of the galvanized steel product is t, t=T-(T1-T2) / 2; (2) Galvanizing production line: finishing elongation e, tension straightening elongation f; (3) Under the conditions of different thickness specifications, different zinc layer thicknesses, and different preset process equipment elongation values, calculate the hot-rolled zinc layer thickness T3 = [nominal zinc layer weight / 50 (g / m)] 2 )]×7.1×10 -3 (mm); (4) Target thickness t1 at the mill exit, t1 = (t - T3) * (1 + (e + f)); (5) Acid leveling process: extensibility a of the phosphorus crusher, compression ratio b of the rolling mill; Raw material thickness design, raw material thickness t 原料 =t1 / (1-ab).

4. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The uncoiling process in step S4 involves uncoiling the pickled rolled steel coil using an uncoiler.

5. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The welding process in step S4 uses a welding machine for lap welding; the welding thickness varies as follows: when the thickness is <0.6mm, the thickness difference between the two plates is ≤0.15mm; when the thickness is ≥0.6mm-0.8mm, the thickness difference between the two plates is ≤0.3mm; when the thickness is >0.8mm-1.0mm, the thickness difference between the two plates is ≤0.40mm; when the thickness is ≥1.0mm, the thickness difference between the two plates is ≤0.50mm. Each welding parameter is adjusted within ±10%.

6. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The electrolytic cleaning process in step S4 is as follows: after the strip steel is rolled by the rolling mill, there are residual rolling iron powder and rolling emulsion on the surface of the strip steel. The residue on the surface of the strip steel is removed by electrolytic cleaning, alkaline cleaning and hot water rinsing to ensure the cleanliness of the strip steel surface after entering the furnace and zinc pot. (1) Alkali immersion cleaning: temperature 65-75℃, conductivity 50-70ms / cm, liquid level >40%; (2) Alkali brush cleaning: temperature 65-75℃, conductivity 50-70ms / cm, alkaline brush current: 8-15A, liquid level >40%; (3) Electrolytic cleaning: temperature 70-75℃, conductivity 60-80ms / cm, liquid level >40%; (4) Rinsing and cleaning: Temperature 70-80℃, liquid level > 40%; (5) Rinsing and high-pressure spray cleaning: temperature 75-80℃, conductivity <5ms / cm, liquid level >40%; (6) Strip drying: drying temperature 80-100℃; (7) Squeeze roller pressure: 3-6 bar.

7. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, In step S5, the induction heating is provided in the heating section of the galvanizing furnace with three 6000kW, 50kHz inductors and one 1500kW, 150kHz inductor, and the total power of the electric radiation tube insulation section is ≥1000kW.

8. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, In step S5, the hydrogen ratio of the nitrogen-hydrogen protective gas for zinc plating is set to 5-10%, the oxygen content to ≤200ppm, and the dew point control temperature to ≤-30℃; the zinc pot process parameters are: zinc liquid aluminum content: 0.25±0.05%, zinc pot temperature 460±2℃.

9. The new process for producing DC51D+Z galvanized products according to claim 1, characterized in that, The parameters for the leveling and straightening in step S6 are set as follows: thickness < 1.0 mm, finishing 0.6%, and straightening 0.4%. Thickness ≥ 1.0 mm, finishing 1.0%, tensioning 0.4%.

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