Green low-carbon household appliance steel and preparation method thereof

Abstract

The invention discloses green low-carbon steel for household appliances, which comprises the following components in percentage by weight: 0.0008-0.10% of C; 0.0009 to 0.20% of Si (silicon); mn: 0.05 to 0.90%; p is less than 0.030%; s is less than 0.012%; the content of Als is 0.012 to 0.070 percent; 0 to 0.07 percent of Ti; 0 to 0.07 percent of Nb; 0 to 0.07 percent of V; 0.008% or less of N; the balance is Fe and inevitable impurities; the preparation method comprises the following steps: adding the recycled steel in batches in the stages of blast furnace molten iron smelting and molten iron tank transfer, wherein the addition amount is 10-18wt% of the tapping amount; converter smelting, converter steel casting to a steel ladle, LF furnace treatment or RH treatment stage, and addition of recycled steel in batches, wherein the addition amount is 10-45wt% of the tapping amount; according to the method, a large amount of recycled steel is doped, carbon dioxide emission in the ironmaking process is reduced, meanwhile, negative effects caused by doping of the recycled steel are overcome by changing the production technology, the product performance is ensured, and finally the purpose of preparing the steel for the household appliances at low cost and low carbon emission is achieved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a green and low-carbon steel for home appliances and its preparation method. Background Technology

[0002] With social progress and improved living standards, China's home appliance manufacturing industry has developed rapidly, becoming the world's largest home appliance manufacturing base. Its white goods production capacity accounts for 60-70% of global capacity, small appliance production capacity accounts for 80%, and home appliance exports account for 37% of the global export market. The home appliance manufacturing industry has become one of my country's important pillar industries. The development of the home appliance industry is mainly due to my country's accelerated urbanization process, consumption upgrading, and environmental protection policies driving the industry towards intelligent and green transformation. In particular, the implementation of these policies has further promoted the green transformation of the home appliance industry. Against this backdrop, the development and application of green and environmentally friendly steel for home appliances will experience rapid growth in the future.

[0003] The steel used in home appliances produced by existing technology involves loading coke, ore or pellets, limestone or dolomite into a blast furnace in batches according to a layered structure. The molten iron is then produced through a high-temperature reduction reaction. The molten iron is then sent to a steel plant to be smelted into steel and cast into slabs. After hot rolling, cold rolling, annealing, hot-dip galvanizing and other processes, the steel products used in home appliances are manufactured. This process emits approximately 2.89 tCO2eq / t of carbon dioxide, which cannot meet the industry's requirements for green and environmentally friendly products.

[0004] A search of existing technical literature revealed that Chinese patent CN 114635093 A discloses a method for manufacturing cold-rolled low-carbon steel for household appliances. The purpose of this invention is to develop a method for manufacturing cold-rolled low-carbon steel for household appliances, achieving low cost and good comprehensive performance of steel for household appliances through composition, hot rolling, and continuous annealing processes, meeting the needs of the household appliance and steel furniture industries while improving the profitability of steel mills.

[0005] Chinese Patent CN 114908286 B discloses an aging-resistant hot-dip aluminized zinc steel sheet for household appliances and its manufacturing method. The purpose of this invention is to solve the problems of poor aging performance and high manufacturing cost of hot-dip aluminized zinc steel sheets with a yield strength of 550MPa, and to develop a hot-dip aluminized zinc steel sheet with good aging resistance, high temperature resistance, strong corrosion resistance, and high strength, so as to meet the needs of the household appliance industry for high-strength hot-dip aluminized zinc steel sheets through roll forming and plastic processing.

[0006] As can be seen from the above, the steel used in home appliances currently produced by technology is all aimed at obtaining low cost and good overall performance, without considering the issue of reducing carbon dioxide emissions during the manufacturing process, and thus cannot meet the industry's requirements for sustainable development and environmental protection. Summary of the Invention

[0007] While existing technologies can manufacture the steel products required by the home appliance industry, they do not consider the carbon dioxide emissions during the manufacturing process, which is detrimental to the industry's sustainable development and environmental impact, failing to meet national requirements for green and environmentally friendly manufacturing. The purpose of this invention is to reduce carbon dioxide emissions during ironmaking by incorporating a large amount of recycled steel, while simultaneously overcoming the negative impacts of incorporating recycled steel through changes in the production process, ensuring product performance, and ultimately achieving low-cost, low-carbon emission production of steel for home appliances.

[0008] To achieve the above objectives, the following technical solution is adopted: A green, low-carbon steel for home appliances has the following chemical composition by weight percentage: C: 0.0008–0.10%; Si: 0.0009–0.20%; Mn: 0.05–0.90%; P: less than 0.030%; S: less than 0.012%; Als: 0.012–0.070%; Ti: 0–0.07%; Nb: 0–0.07%; V: 0–0.07%; N: less than 0.008%; balance Fe and unavoidable impurities.

[0009] The above-mentioned preparation method of green and low-carbon steel for home appliances includes blast furnace smelting, molten iron ladle transfer, molten iron pretreatment, converter smelting, converter casting to ladle, argon blowing treatment, LF furnace treatment or RH treatment, continuous casting into slabs, slab heating, rough rolling and finish rolling, cooling and coiling, pickling and cold continuous rolling, heat treatment, hot-dip galvanizing, leveling, tension leveling, coiling, and packaging. Specifically, recycled steel is added in batches during the blast furnace smelting and molten iron ladle transfer stages, with an addition amount of 10-18 wt% of the tapped iron; recycled steel is added in batches during the converter smelting, converter casting to ladle, LF furnace treatment, or RH treatment stages, with an addition amount of 10-45 wt% of the tapped steel.

[0010] According to the above plan, during the blast furnace molten iron smelting stage, the amount of recycled steel added accounts for 10-16% of the tapped iron, and the tapping temperature is controlled at ≥1500℃; during the molten iron ladle transfer stage, 0-5% of recycled steel is added, and the temperature of the molten iron ladle before being poured into the iron ladle is controlled at ≥1400℃.

[0011] According to the above scheme, the S content in the molten iron should be controlled to be ≤0.004%, Si content ≤0.6%, Cu content ≤0.12%, and P ≤0.10% during the molten iron pretreatment stage.

[0012] According to the above plan, 10-30% of recycled steel is added during the converter smelting stage to control the tapping temperature ≥1680℃; 0-15% of recycled steel is added to the ladle furnace during the converter casting to ladle stage; and 0-10% of recycled steel is added during the LF furnace treatment or RH treatment stage to control the temperature of the molten steel before casting ≥1546℃.

[0013] According to the above scheme, the furnace exit temperature during the billet heating stage is 1210~1300℃, and the heating time is controlled to be ≥130min.

[0014] According to the above scheme, the roughing and finishing rolling stages control the roughing exit temperature to 1010-1100℃ and the finishing rolling temperature to 870-950℃.

[0015] According to the above scheme, laminar flow cooling is used in the cooling and coiling stage to cool the rolled strip to a coiling temperature of 630-750℃; the strip waviness is controlled: waviness height ≤10mm, crown 20-60μm, and local high point ≤9μm.

[0016] According to the above scheme, after the steel coil is cooled to below 70°C during the pickling and cold rolling stages, the pickling temperature is controlled at 86-90°C, the total hydrochloric acid concentration is controlled at 200-210 g / L, the cold rolling reduction rate is controlled at 65-85%, and the rolling exit thickness is 0.35-2.50 mm; the strip waviness is controlled as follows: the steepness is ≤2%, and the waviness height is ≤5 mm.

[0017] According to the above scheme, the heat treatment stage includes cleaning the surface of the strip steel with a reflectivity of ≥90%, controlling the heating temperature to 730~850℃, holding time to 20~90s, rapid cooling outlet temperature to 450~550℃, and controlling the cooling rate of the rapid cooling section to 12~60℃ / s.

[0018] According to the above scheme, in the hot-dip galvanizing stage, the immersion temperature of the strip steel in the galvanizing solution is controlled at 445-520℃, the galvanizing solution temperature is controlled at 450-468℃, the air knife height is 60-450mm, the air knife distance is 6-18mm, and the air knife pressure is 50-350mbar. After exiting the air knife, the strip steel is cooled to no more than 230℃ at a cooling rate of 6-20℃ / s. The strip steel is then leveled, and the leveling elongation is controlled at 0.6-1.5%. Finally, tension straightening is performed, and the tension straightening elongation is 0-0.4%.

[0019] According to the above scheme, it also includes surface coating treatment of the strip steel after continuous hot-dip galvanizing, with the thickness of the surface coating film controlled at 500-1500 mg / m². 2 The coating is then dried and cured, with the drying temperature controlled between 280 and 350°C.

[0020] This invention not only solves the high carbon emission problem in the manufacturing process of steel for home appliances, but also, through the matching and control of composition and process, obtains green and low-carbon steel products for home appliances with good plate shape, comprehensive mechanical properties, and excellent corrosion resistance. By adding recycled steel to molten iron and precisely controlling the content of S, Si, Cu, and P in the molten iron composition, as well as by adding recycled steel during converter smelting and refining, carbon emissions in the molten iron and steel manufacturing process can be reduced.

[0021] During the billet heating stage, the homogenization of the billet structure and the full diffusion of carbides and nitrides ensure the homogenization of the billet structure and its internal structure. This ensures uniform recrystallization nucleation during the recrystallization zone rolling process at roughing exit temperature of 1010–1100℃ and final rolling temperature of 870–950℃, resulting in uniform austenite grains. In the subsequent laminar cooling process to coiling temperature of 630–750℃, uniform ferrite and pearlite structures are obtained, thus ensuring the acquisition of hot-rolled strip with good plate shape.

[0022] By controlling the pickling temperature and acid concentration, the surface iron oxide scale is removed while the steel substrate surface is flat, ensuring good surface quality for the subsequent strip. By controlling the total cold rolling reduction rate, a fibrous structure with a certain distortion energy is obtained. The magnitude of the distortion energy and the size and uniformity of the fiber structure play a decisive role in the stress distribution inside the cold-rolled strip, the temperature control in the subsequent heat treatment process, and the performance control of the final product. This ensures that the rolled strip has low steepness and waviness, as well as good mechanical properties and final microstructure.

[0023] Based on the distortion energy and fiber structure size and uniformity of the strip after rolling, through repeated experiments, and matching the appropriate control of strip surface reflectivity, heating temperature, holding time, rapid cooling exit temperature and cooling rate, it is possible to obtain a good sponge iron morphology on the strip surface, as well as a uniform ferrite structure and a small amount of cementite structure uniformly diffused on the ferrite matrix. This ensures the strip shape and excellent comprehensive mechanical properties, as well as the acquisition of a uniform inhibition layer at the interface between the steel base and the coating.

[0024] By matching and controlling the immersion temperature, plating bath temperature, and air knife parameters, a uniform and thin Fe2Al5 inhibition layer is obtained, thereby ensuring good coating adhesion and coating structure uniformity for steel products used in home appliances. Matching the surface coating treatment film thickness control and drying temperature precise control ensures that the final product steel plate surface has good corrosion resistance.

[0025] Without altering the steel manufacturing equipment, this invention achieves the production of green and low-carbon steel for home appliances through multi-process recycling of steel smelting and green electricity. This invention not only meets the various performance requirements of steel materials used in the home appliance industry, but also meets the industry's demand for green, environmentally friendly, and low-carbon emission products, thus promoting the upgrading and sustainable development of materials used in the industry. Attached Figure Description

[0026] Figure 1 Micrograph of the steel for household appliances obtained in Example 5 of this invention. Detailed Implementation

[0027] The following embodiments further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0028] The specific implementation provides a method for preparing green and low-carbon steel for home appliances: including blast furnace molten iron smelting, molten iron ladle transfer, molten iron pretreatment, converter smelting, converter steel pouring to ladle, argon blowing treatment, LF furnace treatment or RH treatment, continuous casting into slabs, slab heating, rough rolling and finish rolling, cooling and coiling, pickling and cold continuous rolling, heat treatment, hot-dip galvanizing, leveling, tension straightening, coiling, and packaging; 1) For blast furnace molten iron, recycled steel is added in a stepped manner, controlling the amount of recycled steel added to 10-16% of the tapped iron to reduce carbon dioxide emissions during ironmaking. The silicon content of the molten iron is controlled to ≤0.6%, and the tapping temperature is ≥1500℃. The molten iron is transported to the steel plant via a mixing car or ladle. Depending on the volume of the mixing car or ladle, 0-5% recycled steel can be added while ensuring the molten iron temperature. Before pouring the molten iron into the ladle, a certain proportion of recycled steel can be added to the ladle while ensuring the molten iron temperature is ≥1400℃. The manufacturing process uses green electricity, further reducing emissions by minimizing carbon dioxide emissions from coke combustion during ironmaking. During the molten iron pretreatment stage, the S content in the molten iron is controlled to ≤0.004%, Si content ≤0.6%, Cu content ≤0.12%, and P ≤0.10%.

[0029] 2) In converter smelting, 10-30% of recycled steel is added to the converter according to the converter volume and the temperature of the molten iron, and the tapping temperature is controlled to be ≥1680℃; 0-15% of recycled steel is added to the ladle furnace during the stage of converter casting to ladle; 0-10% of recycled steel is added during the LF furnace treatment or RH treatment stage, and the temperature of the molten steel before casting is controlled to be ≥1546℃. 3) The billet is heated to a furnace temperature of 1210-1300℃, and the heating time is controlled to be ≥130min. The electricity used in the process is green electricity. 4) The billet is rough rolled and finish rolled, with the rough rolling exit temperature controlled at 1010-1100℃ and the finish rolling temperature controlled at 870-950℃. The electricity used in the process is green electricity. 5) Perform laminar flow cooling to cool the rolled strip to the coiling temperature. Control the coiling temperature to 630-750℃ and control the strip waviness: waviness height ≤10mm, crown 20-60μm, local high point ≤9μm. Use green electricity for the process. 6) Pickling and cold rolling are carried out. After the hot-rolled steel coil is cooled to below 70°C, the cold rolling reduction rate is controlled at 65-85%. The thickness at the rolling exit is 0.35-2.50 mm. The strip waviness is controlled as follows: the steepness is ≤2% and the waviness is ≤5 mm. Green electricity is used in the process. 7) Heat treatment is performed. After cold rolling, the steel coils are sent to the hot-dip galvanizing production line for heat treatment and surface coating. After uncoiling, the surface of the steel coil is cleaned. After cleaning, the surface reflectivity of the strip is ≥90%. The heating temperature is controlled at 730~850℃, the holding time is 20~90s, the rapid cooling outlet temperature is 450~550℃, and the cooling rate of the rapid cooling section is controlled at -12~-60℃ / s. The electricity used in the process is green electricity. 8) Perform continuous hot-dip galvanizing, controlling the strip immersion temperature at 445–520℃, the galvanizing bath temperature at 450–468℃, the air knife height at 60–450 mm, the air knife distance at 6–18 mm, and the air knife pressure at 50–350 mbar. After exiting the air knife, cool the strip to no more than 230℃ at a cooling rate of 6–20℃ / s. Level the strip, controlling the leveling elongation at 0.6–1.5%. Perform tension straightening, with a tension straightening elongation of 0–0.4%. Use green electricity for the process. 9) Steel strips after continuous hot-dip galvanizing are used for packaging and manufacturing appliance parts for home appliance users, or for surface coating treatment of the steel strips. The surface coating film can be an environmentally friendly organic or inorganic coating, or a fingerprint-resistant coating. The film thickness can be controlled between 500 and 1500 mg / m³ depending on the service environment. 2 The coating is dried and cured, with the drying temperature controlled between 280 and 350°C. The coated steel coils are then packaged and sent to appliance users for the manufacture of appliance parts. The electricity used in the process is green electricity.

[0030] The chemical composition values ​​of the specific embodiments and comparative examples are shown in Table 1.

[0031] The main process parameters for specific embodiments and comparative examples are shown in Tables 2 and 3.

[0032] The performance data of the products obtained from specific embodiments and comparative examples are shown in Table 4.

[0033] Table 1 Chemical composition (wt.%)

[0034] Table 2

[0035] Table 3

[0036] Table 4

[0037] The microstructure of the steel used in household appliances obtained in Example 5 is shown in the attached image. Figure 1 As shown, the metallographic structure of the steel for household appliances obtained by the present invention is ferrite + a small amount of cementite, wherein the ferrite content is ≥90% and the cementite content is <10%.

[0038] In summary, this invention, through component design and a matching preparation process, as well as the addition of recycled steel and the application of green electricity, successfully achieves a steel that, while meeting the requirements for formability and corrosion resistance of home appliance parts, also exhibits excellent carbon dioxide emission reduction effects. This meets the needs of the home appliance industry for green and low-carbon products and is of great significance for promoting the green, low-carbon, and sustainable development of the home appliance industry chain. This specific embodiment is merely a best example and is not intended to limit the implementation of the technical solution of this invention.

Claims

1. A steel for green low-carbon home appliances, characterized by Chemical composition in terms of weight percentage is as follows: C: 0.0008-0.10%; Si: 0.0009-0.20%; Mn: 0.05-0.90%; P: 0.030% or less; S: 0.012% or less; Als: 0.012-0.070%; Ti: 0-0.07%; Nb: 0-0.07%; V: 0-0.07%; N: 0.008% or less; balance of Fe and inevitable impurities.

2. The method of claim 1, wherein the steel for green low-carbon home appliances is prepared by the steps of: It includes blast furnace hot metal smelting, hot metal ladle transfer, hot metal pretreatment, converter smelting, converter steel pouring to ladle, argon blowing treatment, LF furnace treatment or RH treatment, continuous casting into slab, casting slab heating, rough rolling and finish rolling, cooling coiling, pickling and cold continuous rolling, heat treatment, hot dip plating, flattening, straightening, coiling, packaging; ​ Among them, the recycled steel is added in batches in the stages of blast furnace hot metal smelting and hot metal ladle transfer, and the addition amount is 10-18wt% of the tapping amount; the recycled steel is added in batches in the stages of converter smelting, converter steel pouring to ladle, LF furnace treatment or RH treatment, and the addition amount is 10-45wt% of the tapping amount.

3. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... In the stage of blast furnace hot metal smelting, the addition amount of recycled steel accounts for 10-16% of the tapping amount, and the tapping temperature is controlled to be greater than or equal to 1500℃; 0-5% of recycled steel is added in the stage of hot metal ladle transfer, and the temperature before the hot metal ladle is poured into the iron ladle is controlled to be greater than or equal to 1400℃; the S content in the hot metal is controlled to be less than or equal to 0.004%, the Si content is controlled to be less than or equal to 0.6%, the Cu content is controlled to be less than or equal to 0.12%, and the P content is controlled to be less than or equal to 0.10% in the stage of hot metal pretreatment; 10-30% of recycled steel is added in the stage of converter smelting, and the tapping temperature is controlled to be greater than or equal to 1680℃; 0-15% of recycled steel is added in the stage of converter steel pouring to ladle; 0-10% of recycled steel is added in the stage of LF furnace treatment or RH treatment, and the temperature of molten steel before pouring is controlled to be greater than or equal to 1546℃.

4. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... The out-of-furnace temperature in the stage of casting slab heating is 1210-1300℃, and the heating time is controlled to be greater than or equal to 130min.

5. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... The rough rolling and finish rolling stage controls the rough rolling outlet temperature to be 1010-1100℃, and controls the finish rolling temperature to be 870-950℃.

6. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... In the cooling coiling stage, the rolling strip steel is cooled to the coiling temperature of 630-750℃ by using laminar flow cooling; the wave shape of the strip steel is controlled as follows: wave height ≤10mm, convexity 20-60μm, local high point ≤9μm.

7. The method of claim 2, wherein the steel is prepared by the steps of: In the pickling and cold continuous rolling stage, the steel coil is cooled to below 70℃, the pickling temperature is controlled to be 86-90℃, the total hydrochloric acid concentration is controlled to be 200-210g / l, the cold rolling reduction is controlled to be 65-85%, the rolling outlet thickness is 0.35-2.50mm; the wave shape of the strip steel is controlled as follows: steepness ≤2%, wave height ≤5mm. ​ 8. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... In the heat treatment stage, the surface reflectivity of the strip steel is controlled to be greater than or equal to 90%, the heating temperature is controlled to be 730-850℃, the holding time is 20-90s, the fast cooling outlet temperature is 450-550℃, and the cooling speed in the fast cooling section is controlled to be 12-60℃ / s.

9. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... In the hot-dip plating stage, the strip steel is immersed in the plating solution at a temperature of 445-520℃, the plating solution is controlled at a temperature of 450-468℃, the air-knife height is 60-450mm, the air-knife distance is 6-18mm, the air-knife pressure is 50-350mbar, the strip steel is cooled after the air-knife, and the strip steel is cooled to not more than 230℃ at a cooling speed of 6-20℃ / s, the strip steel is leveled, the leveling elongation is controlled at 0.6-1.5%, and the strip steel is drawn and straightened, and the drawing and straightening elongation is 0-0.4%.

10. The method for preparing green and low-carbon steel for home appliances as described in claim 2, characterized in that... Also included is a surface coating treatment of the continuously hot-dipped strip, with the surface coating film thickness controlled at 500-1500 mg / m 2 The coating is subjected to a drying and curing treatment, with the drying temperature controlled at 280-350°C.

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