A method for manufacturing a large scrap ratio galvanized home appliance steel with a content of 20% or more

Abstract

The application discloses a manufacturing method of galvanized household appliance steel with a content of scrap steel of more than or equal to 20%, and comprises the following steps: (1) molten iron pretreatment; (2) scrap steel proportioning: the total proportion of scrap steel in the total loading amount of the converter is more than or equal to 20%; wherein the proportion of post-consumer recycled material is more than or equal to 5%; (3) alloy auxiliary material; (4) tapping parameters; (5) requirements for RH molten steel; (6) requirements for continuous casting molten steel; (7) hot rolling production process; and (8) continuous annealing process. By adding more than 20% of scrap steel, the mechanical properties, corrosion resistance and other indexes of the green steel BTRC20 product developed by using the existing smelting, hot rolling, cold rolling and galvanizing process equipment all reach the delivery technical standards, and the product has the ability of stable batch production and delivery. The product meets the use requirements of high-end household appliance hot-dip galvanized fingerprint-resistant plates, and can be applied to high-end household appliance outer plates such as computers, servers, audio-visual systems and automatic office systems.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical sheet metal production technology, and in particular relates to a method for manufacturing galvanized household appliance steel with a high scrap steel content of ≥20%. Background Technology

[0002] Green steel refers to high-quality steel produced using green and environmentally friendly processes. Its production reduces the use of fossil fuels, lowers carbon dioxide emissions, and achieves clean production, exhibiting high environmental friendliness and sustainability. The home appliance industry has increasingly stringent requirements for "green steel," with major OEMs proposing carbon reduction roadmaps for steel used in home appliances. While scrap steel is not green steel, its recycling and reuse are crucial for achieving sustainable development goals. Scrap steel reuse effectively reduces the production of new steel, saves energy, and reduces CO2 emissions, contributing to environmental protection and promoting the sustainable development of the steel industry.

[0003] This invention adds more than 20% scrap steel. The requirements for scrap steel used in converter smelting are as follows: the proportion of scrap steel added to the furnace must be greater than or equal to 20% of the total charge; the scrap steel added to the furnace must be a mixture of pre-consumption and post-consumption recycled materials; and the proportion of post-consumption recycled materials added during production must be greater than or equal to 5% of the total charge. The invention also develops hot-dip galvanized green steel BTRC20 for household appliances. Through tackling key equipment, process, and quality issues in the smelting, hot rolling, and cold rolling processes, especially optimizing and improving various performance characteristics, stable mass production of the product has been ensured. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing galvanized household appliance steel with a high scrap steel content (≥20%). By adding more than 20% scrap steel and utilizing existing equipment in the smelting, hot rolling, cold rolling, and galvanizing processes, a method for developing and overcoming technical challenges in hot-dip galvanized green steel BTRC20 for household appliances is achieved. The developed green steel BTRC20 product meets delivery technical standards in terms of mechanical properties, corrosion resistance, and other indicators, and possesses stable mass production and supply capabilities. It meets the requirements for fingerprint-resistant hot-dip galvanized steel sheets for high-end household appliances and can be applied to the outer panels of high-end household appliances such as computers, servers, audio-visual equipment, and automated office systems.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for manufacturing galvanized household appliance steel with a high scrap steel content (≥20%), comprising:

[0007] (1) Hot metal pretreatment: Hot metal is desulfurized by KR, and the S content of the hot metal entering the converter is ≤0.002%. The area of ​​desulfurization slag removal is ≥95%, and there is no obvious slag residue on the surface of the hot metal.

[0008] (2) Scrap steel ratio: The total proportion of scrap steel entering the furnace is ≥20% based on the total amount of converter charge; of which the proportion of post-consumption recycled material is ≥5%. The scrap steel is composed of pre-consumption recycled material and post-consumption recycled material. The scrap steel is free from oil stains, severe rust, and foreign matter.

[0009] (3) Alloy auxiliary materials: The alloy auxiliary materials such as aluminum granules and ferromanganese are pure and meet the internal control standards of steelmaking. The top slag modifier is suitable for the oxygen content and slag discharge control requirements of converter steel.

[0010] (4) Tapping parameters: Tapping temperature ≥1660℃, using a turnover ladle for tapping, and tapping temperature drop <70℃ to avoid excessive temperature drop of molten steel affecting subsequent refining;

[0011] (5) Requirements for RH steel supply: The composition of RH steel supplied by the converter must meet the following requirements: C≤0.045%, Si≤0.010%, Mn≤0.25%, P≤0.018%, S≤0.010%, O≤0.06%, so as to lay the foundation for RH refining, decarburization and alloying.

[0012] (6) Requirements for molten steel supplied for continuous casting: The molten steel supplied for continuous casting after RH refining shall comply with the internal control standards, namely C 0.025~0.045%, Si≤0.010%, Mn 0.20~0.30%, P 0.008~0.018%, S≤0.010%, Alt 0.020~0.045%, N≤0.0045%, O≤0.0030%, with the remainder being Fe and impurities;

[0013] (7) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet exit temperature is 1190~1220℃, rough rolling is carried out by a 2-stand rolling mill, and finish rolling is carried out by a 7-stand continuous variable crown rolling mill; finish rolling temperature is 850~920℃, hot rolled steel strip thickness is 5mm; cooling is carried out by laminar flow cooling equipment, front-dispersed cooling mode, and the coiling temperature is 600~750℃;

[0014] (8) Continuous annealing process: Unwind the cold-hardened steel strip, the heating and homogenization temperature of the annealing process is 700~770℃, the slow cooling temperature is 600~700℃, and the flattening elongation rate is set to 0.5~1.2%.

[0015] Furthermore, in manufacturing 0.8mm thick galvanized computer back panels, 22% of the steel is scrap steel fed into the furnace, of which 6% is post-consumer recycled material.

[0016] Furthermore, the molten iron is desulfurized by KR to S: 0.0018%, and the desulfurization slag is removed from 96% of the surface area. It is then mixed with scrap steel and fed into the converter, with the total proportion of scrap steel being 22%. The steel tapping temperature in the converter is 1670℃, and the temperature drop at the tapping temperature of the turnover ladle is 65℃.

[0017] Furthermore, after RH refining and decarburization, aluminum particles are added for deoxidation, followed by 4 minutes of circulation, then manganese and ferric oxide are added to adjust the composition, and vacuum circulation continues for 7 minutes.

[0018] Furthermore, the hot rolling process uses 3.80mm raw material, with a heating temperature of 1190℃, a soaking temperature of 1200℃, a finishing rolling temperature of 895℃, a coiling temperature of 655℃, and subsequent dispersion cooling.

[0019] Furthermore, the continuous hot-dip galvanizing furnace speed is 100m / min, the annealing heating homogenization zone temperature is 750℃, the zinc pot temperature is 460℃, the zinc liquid temperature is 460℃, the elongation of the finishing machine is 1.25±0.05%, the elongation of the straightening machine is 0.20±0.05%, the zinc coating is Z100, the average value of three points on both sides is 110g / m², the lowest value of single point on both sides is 86g / m², and the single side is 41g / m²; the unevenness of the steel strip after finishing is 3mm / 2000mm, and the camber is 1.5mm / 2000mm.

[0020] Furthermore, the chemical composition of the galvanized appliance steel by weight percentage is as follows: C: 0.035%, Si: 0.005%, Mn: 0.25%, P: 0.013%, S: 0.005%, Alt: 0.035%, N: 0.0030%, O: 0.0020%, with the remainder being Fe and impurities.

[0021] Furthermore, the galvanized appliance steel exhibited a 3% white rust area and a surface resistance of 0.8 mΩ after 72 hours of salt spray testing, with no obvious defects on the surface.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] (1) The present invention increases the proportion of scrap steel in the converter to ≥20% and introduces ≥5% of recycled materials after consumption, which greatly improves the utilization rate of scrap steel resources, reduces the production cost of raw materials, and conforms to the development concept of green metallurgy. At the same time, through KR desulfurization, RH refining and other processes, the composition and purity of molten steel are precisely controlled to avoid the performance decline caused by the increase of scrap steel proportion.

[0024] (2) The process parameters of each process are precisely matched. The segmented heating, rolling, annealing and finishing parameters are adopted for steel strips of different thicknesses to ensure the mechanical properties of the finished steel strips. The yield strength is 210~310MPa and the elongation is ≥30.5%. It has excellent stamping formability and is fully compatible with the complex stamping requirements of computer backplates.

[0025] (3) The zinc coating adopts an equal thickness and the zinc layer weight is ≤180g / m². The coating has excellent adhesion, no cracks or peeling when bent at 180°, and the fingerprint-resistant coating meets the requirement of ≤5% salt spray white rust area and ≤1mΩ surface resistance. It takes into account both corrosion resistance and antistatic properties, and is suitable for the use environment of computer back panel. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] Figure 1 This is a metallographic image of the present invention;

[0028] Figure 2 This is a photograph of the molded part of the present invention. Detailed Implementation

[0029] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best mode of implementation and do not limit the scope of the invention in any way.

[0030] Example 1

[0031] Manufacturing 0.8mm thick galvanized computer back panels, with 22% scrap steel in the furnace, including 6% post-consumer recycled material. Specific steps: Molten iron is desulfurized by KR to S: 0.0018%, and 96% of the desulfurization slag is removed. It is then mixed with scrap steel and fed into the converter, with a total scrap steel proportion of 22%. The converter smelting tapping temperature is 1670℃, and the temperature drop at the ladle tapping temperature is 65℃. The tapping steel composition is: C: 0.042%, Si: 0.008%, Mn: 0.23%, P: 0.016%, S: 0.009%, O: 0.055%. After RH refining and decarburization, aluminum granules are added for deoxidation. After 4 minutes of circulation, ferromanganese is added to adjust the composition, followed by 7 minutes of vacuum circulation. The refined steel composition is: C: 0.035%, Si: 0.005%, Mn: 0.25%, P: 0.013%, S: 0.005%, Alt: 0.035%, N: 0.0030%, O: 0.0020%; Hot rolling uses 3.80mm raw material, heating temperature 1190℃, soaking temperature 1200℃, finishing rolling temperature 895℃, coiling temperature 655℃, followed by dispersed cooling; continuous hot-dip galvanizing furnace speed 100m / min, annealing heating soaking section 750℃, zinc pot temperature 460℃, zinc liquid temperature 460℃, bright finish machine elongation 1.25±0.05%, tension leveler elongation 0.20±0.05%, zinc coating selected Z100, double-sided three-point average 110g / m², single-point double-sided minimum value 86g / m², single-sided 41g / m²; after finishing, the steel strip unevenness is 3mm / 2000mm, camber is 1.5mm / 2000mm, salt spray test 72h white rust area is 3%, surface resistance is 0.8mΩ, and the surface has no obvious defects.

[0032] Example 2

[0033] A 1.5mm thick galvanized computer back panel is manufactured with 25% scrap steel in the furnace, of which 7% is post-consumer recycled material. Z180 galvanizing is selected, and other process parameters are controlled according to the method of this invention. The final product has a yield strength of 250MPa, an elongation of 32%, and a white rust area of ​​4% after 72 hours of salt spray testing. After stamping, there is no deformation or coating peeling, which meets the requirements for computer back panels.

[0034] Example 3

[0035] A 1.2mm thick galvanized computer back panel was manufactured with 28% scrap steel in the furnace, of which 8% was post-consumer recycled material. Z120 galvanizing was selected, and other process parameters were controlled according to the method of this invention. The final product had a yield strength of 239MPa, an elongation of 33%, a white rust area of ​​3% after 72 hours of salt spray testing, and a surface resistivity of 0.8mΩ. After stamping, there was no deformation or coating peeling, which met the requirements for computer back panels.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20%, characterized in that: include: (1) Hot metal pretreatment: Hot metal is desulfurized by KR, and the S content of the hot metal entering the converter is ≤0.002%. The area of ​​desulfurization slag removal is ≥95%, and there is no obvious slag residue on the surface of the hot metal. (2) Scrap steel ratio: The total proportion of scrap steel entering the furnace is ≥20% based on the total amount of converter charge; of which the proportion of post-consumption recycled material is ≥5%. The scrap steel is composed of pre-consumption recycled material and post-consumption recycled material. The scrap steel is free from oil stains, severe rust, and foreign matter. (3) Alloy additives: The aluminum granules and ferromanganese alloy additives are pure and meet the internal control standards for steelmaking. The top slag modifier is suitable for the control requirements of oxygen content and slag amount in converter steel. (4) Tapping parameters: Tapping temperature ≥1660℃, using a turnover ladle for tapping, and tapping temperature drop <70℃ to avoid excessive temperature drop of molten steel affecting subsequent refining; (5) Requirements for RH steel supply: The composition of RH steel supplied by the converter must meet the following requirements: C≤0.045%, Si≤0.010%, Mn≤0.25%, P≤0.018%, S≤0.010%, O≤0.06%, so as to lay the foundation for RH refining, decarburization and alloying. (6) Requirements for molten steel supplied for continuous casting: The molten steel supplied for continuous casting after RH refining shall comply with the internal control standards, namely C 0.025~0.045%, Si≤0.010%, Mn 0.20~0.30%, P 0.008~0.018%, S≤0.010%, Alt 0.020~0.045%, N≤0.0045%, O≤0.0030%, with the remainder being Fe and impurities; (7) Hot rolling production process: billet heating—rough rolling—finish rolling—coiling; billet exit temperature is 1190~1220℃, rough rolling is carried out by a 2-stand rolling mill, and finish rolling is carried out by a 7-stand continuous variable crown rolling mill; finish rolling temperature is 850~920℃, hot rolled steel strip thickness is 5mm; cooling is carried out by laminar flow cooling equipment, front-dispersed cooling mode, and the coiling temperature is 600~750℃; (8) Continuous annealing process: Unwind the cold-hardened steel strip, the heating and homogenization temperature of the annealing process is 700~770℃, the slow cooling temperature is 600~700℃, and the flattening elongation rate is set to 0.5~1.2%.

2. The method for manufacturing galvanized appliance steel with a high scrap steel content ≥20% according to claim 1, characterized in that: The production of 0.8mm thick galvanized computer back panels involves 22% scrap steel in the furnace, of which 6% is post-consumer recycled material.

3. The method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20% according to claim 2, characterized in that: The molten iron is desulfurized by KR to S: 0.0018%, and the desulfurization slag is removed from 96% of the surface area. It is then mixed with scrap steel and fed into the converter, with the total proportion of scrap steel being 22%. The steel tapping temperature in the converter is 1670℃, and the temperature drop at the tapping temperature of the turnover ladle is 65℃.

4. The method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20% according to claim 3, characterized in that: After RH refining and decarburization, aluminum particles are added for deoxidation. After 4 minutes of circulation, manganese and iron are added to adjust the composition, and vacuum circulation is continued for 7 minutes.

5. The method for manufacturing galvanized appliance steel with a high scrap steel content ≥20% according to claim 4, characterized in that: Hot rolling uses 3.80mm raw material, heating temperature 1190℃, soaking temperature 1200℃, finishing rolling temperature 895℃, coiling temperature 655℃, and then dispersed cooling.

6. The method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20% according to claim 5, characterized in that: The continuous hot-dip galvanizing furnace speed is 100m / min, the annealing heating soaking zone temperature is 750℃, the zinc pot temperature is 460℃, the zinc liquid temperature is 460℃, the elongation of the finished product is 1.25±0.05%, the elongation of the straightening machine is 0.20±0.05%, the zinc coating is Z100, the average value of three points on both sides is 110g / m², the lowest value of a single point on both sides is 86g / m², and the single-sided minimum value is 41g / m²; the unevenness of the finished steel strip is 3mm / 2000mm, and the camber is 1.5mm / 2000mm.

7. The method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20% according to claim 6, characterized in that: The chemical composition of the galvanized household appliance steel by weight percentage is as follows: C: 0.035%, Si: 0.005%, Mn: 0.25%, P: 0.013%, S: 0.005%, Alt: 0.035%, N: 0.0030%, O: 0.0020%, with the remainder being Fe and impurities.

8. The method for manufacturing galvanized household appliance steel with a high scrap steel content ≥20% according to claim 7, characterized in that: The galvanized household appliance steel tested for 72 hours showed a white rust area of ​​3%, a surface resistance of 0.8 mΩ, and no obvious defects on the surface.

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