High-strength steel for household appliance plate with good organization and forming property and preparation method thereof

Abstract

The present application relates to the field of material and metallurgy, and particularly relates to a high-strength steel for household appliance plate with good structure and forming performance and a preparation method thereof.The steel contains the following chemical components: C, Si, Mn, P≤0.010%, S≤0.004%, Cr, Mo, Ti, N, O, B, Alt, and 1.58≤B / N≤3.30, and 2.1≤(La+Pr+Ce) / S≤4.0 is additionally added, and the balance is Fe and inevitable impurities.The present application solves the problems of the existing material, such as soft strength (generally, the yield strength is not more than 220MPa), poor surface roughness, structure uniformity and plate shape control, and produces a high-strength steel product for household appliance plate with excellent weldability, deep drawing formability, performance consistency and coating performance.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and in particular to high-strength steel for household appliance panels with good microstructure and formability, and its preparation method. Background Technology

[0002] Cold-rolled steel sheets for home appliances are among the high-end cold-rolled products, widely used in home appliances such as washing machines, televisions, refrigerators, and microwave ovens. Demand for large home appliances (such as refrigerators) is constantly increasing, and these products have high added value. With the improvement of people's living standards, more and more downstream users are demanding products with lower emissions from home appliances. At the same time, international steel companies are actively promoting low-carbon emission products. Against this backdrop, green and low-carbon technologies are being rapidly applied in the field of steel for home appliances. The steel industry is actively promoting the research and development and production of low-carbon steel technologies for home appliances.

[0003] Currently, cold-rolled appliance sheets are produced using a continuous annealing process, resulting in relatively soft material strength (generally yield strength not exceeding 220MPa). Surface roughness, microstructure uniformity, and sheet shape control have always been technical challenges for major steel mills. To further improve quality and save costs, the appliance industry is placing increasingly stringent technical requirements on steel sheets. These requirements demand that while reducing sheet thickness, the sheets must also possess excellent weldability, deep-drawing formability, performance consistency, and coating performance. Green, low-carbon, high-strength appliance sheets will be the future development trend for cold-rolled appliance sheets.

[0004] To promote the innovation and application of low-carbon emission technologies for steel used in home appliances, we should currently develop high-quality, low-cost, uniformly structured, and green low-carbon emission high-strength steel varieties for home appliances. Summary of the Invention

[0005] This invention provides a high-strength steel for appliance panels with good microstructure and formability, and a method for preparing the same. The aim is to address the problems of existing materials having relatively low strength (generally yield strength not exceeding 220 MPa), poor surface roughness, microstructure uniformity, and poor shape control; and to produce high-strength steel products for appliance panels with excellent weldability, deep-drawing formability, performance consistency, and coating properties.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This high-strength steel for appliance panels has good microstructure and formability. The chemical composition of the steel, by weight percentage, is as follows: C: 0.0062%–0.0074%, Si≤0.02%, Mn: 1.64%–1.74%, P≤0.010%, S≤0.004%, Cr: 0.61%–0.69%, Mo: 0.32%–0.38%, Ti: 0.074%–0.086%, N: 0.0014%–0.0024%, O: 0.0004%–0.0018%, B: 0.0038%–0.0046%, Alt: 0.46%–0.58%, with 1.58≤B / N≤3.30. It also contains 2.1≤(La+Pr+Ce) / S≤4.0, with the balance being Fe and unavoidable impurities.

[0007] The carbon equivalent Ceq ≤ 0.30%, and the carbon equivalent formula is as follows: Ceq = C + Si / 55 + Cr / 20 + Mn / 19 + Al / 18 + 2.2 × P + 3.24 × B + 0.133 Mn × Mo.

[0008] The rationale for the alloy design of this invention is as follows: C: Carbon is the most effective way to improve the strength of materials. The distribution and migration of carbon can effectively control the M / F ratio. When the carbon content is high, the transformation energy of austenite increases, which greatly reduces the toughness and plasticity of the material. In order to achieve a high work hardening rate and good deep drawing performance, the present invention controls the C content to 0.0062-0.0074%.

[0009] Si has the function of inhibiting the formation of cementite, delaying the decomposition of austenite and the precipitation of carbides. Si can improve the strength of ferrite through solid solution strengthening, so that the steel can obtain the required strength value. However, if the Si content is too high, it is easy to generate ferriliths during hot rolling production, which will damage the surface quality and coating performance of the strip. In this invention, the Si content is controlled to be ≤0.02%.

[0010] Mn can refine grains and strengthen through solid solution, delay the transformation of austenite, and improve the hardenability of strip steel. However, if the Mn content is too low, the undercooled austenite is not stable enough, which reduces the processing properties of strip steel such as plasticity and toughness. If the Mn content is too high, banded structures are easily formed. At the same time, MnS is prone to becoming hydrogen accumulation sites, which deteriorates the strip steel's resistance to delayed cracking and its weldability, and increases the cost of steel strip alloy. Therefore, in this invention, the Mn content is controlled at 1.64-1.74%.

[0011] P is a ferrite strengthening element, but P is very prone to aggregate at grain boundaries, causing central segregation of the steel strip, which seriously reduces the plasticity and toughness of the steel. The lower its content, the better. In this invention, the P content is controlled to ≤0.010%.

[0012] S combines with Mn to form MnS non-metallic inclusions, which reduce the formability and ductility of steel and reduce its low-temperature impact toughness. In this invention, the S content is controlled to be ≤0.004%.

[0013] Alt (Al): Delays austenite decomposition and carbide precipitation, playing a role in deoxidation and grain refinement in steel, strengthening ferrite. Aluminum also inhibits carbide precipitation within bainite, improving the ductility of the steel plate. However, excessive aluminum content reduces the fluidity of molten steel, leading to nozzle nodule formation. Therefore, in this invention, the Al content is controlled at Alt: 0.46–0.58%.

[0014] Cr: Promotes the diffusion of C into austenite, improves austenite stability, ensures the strength of the strip by increasing the hardenability of the steel, further refines the grains, and increases the strength-ductility product of the strip. In this invention, the Cr content is controlled at 0.61-0.69%.

[0015] Mo (Mo) is beneficial for stabilizing austenite and promoting martensite transformation. It is a strengthening element in steel and has a significant effect on improving the hardenability of steel. Mo causes the CCT curve to shift to the right, shrinking the austenite phase region, but it is also relatively expensive. In this invention, the Mo content is controlled at 0.32–0.38%.

[0016] Ti is a strong carbide- and nitride-forming and deoxidizing element. During heating, it first forms TiN, effectively inhibiting the growth of austenite grains and refining the grains. Further precipitation of TiC and Ti(C, N) enhances the strength and toughness of the steel strip through grain refinement and precipitation strengthening. In this invention, the Ti content is selected to be 0.074–0.086%.

[0017] Nitrogen (N): In low-carbon steel, it is an impurity element that easily causes failure hardening, severely deteriorates the plasticity of the steel, and increases the risk of fracture. This invention selects N at a concentration of 0.0014–0.0024%.

[0018] O: Oxides form inclusions in steel, reducing the material's toughness and low-temperature impact toughness. Generally, deoxidation treatment is required at the end of smelting to reduce oxide inclusions and bubbles, improving the internal quality of the strip steel and simultaneously enhancing material properties and low-temperature impact toughness. This invention selects O: 0.0004–0.0018%.

[0019] B combines with N to form BN particles. BN exhibits good stability, is not easily dissolved at high temperatures, and can reduce grain boundary brittleness. Furthermore, B segregates at austenite grain boundaries to suppress proeutectoid ferrite precipitation, allowing carbides to disperse and precipitate in the low-temperature region. In this invention, B is selected at 0.0038–0.0046%, while controlling the ratio to be 1.58 ≤ B / N ≤ 3.30.

[0020] La, Pr, and Ce react with S and O in steel to form inclusions with higher melting points. They can also transform MnS and Al2O3 inclusions into smaller, uniformly distributed spherical inclusions, avoiding the cracking defects caused by elongated MnS and blocky Al2O3 inclusions during forming. This improves the strength and plasticity of the strip while further reducing its anisotropy. In this invention, 2.1 ≤ (La + Pr + Ce) / S ≤ 4.0 is selected.

[0021] The size of inclusions in the steel of this invention is ≤10µm, and the thickness of the steel plate is 0.5~2.2mm.

[0022] The microstructure of the high-strength steel consists of ferrite (F), martensite (M), Mao island (MA), and bainite (B), with ferrite (F) accounting for 50%–58% of the area, martensite (M) accounting for 37%–42% of the area, Mao island (MA) accounting for 1%–5% of the area, and bainite (B) accounting for 1%–3% of the area.

[0023] The yield strength R of the high-strength steel p0.2 The tensile strength is 560–615 MPa, the tensile strength Rm is 885–925 MPa, and the elongation after fracture A is 560–615 MPa. 80 The yield strength ratio is 30%–35%. p0.2 / Rm is 0.60~0.70, the 180° cold bending test d=1.0a is intact, the work hardening index n: 0.19~0.24, the hole expansion rate λ: 92%~98%, and it satisfies the following formula: V=(n×UE×λ×Rm)≥7.8, where UE is the uniform elongation.

[0024] The preparation method of high-strength steel for appliance panels with good microstructure and formability includes steelmaking, hot rolling, cold rolling, pickling, and galvanizing, specifically including the following steps: S1. Eco-friendly electric arc furnace smelting + converter smelting: In the eco-friendly electric arc furnace smelting process, scrap steel accounts for 100%. Deoxidation and alloying are carried out during the tapping process. The final composition of the molten steel in the electric arc furnace is controlled at C 0.06-0.08%, P ≤ 0.015%, and S ≤ 0.035%; the molten iron is then poured into a torpedo ladle. The use of eco-friendly electric arc furnace + converter smelting reduces unit CO2 emissions, achieving green and low-carbon emissions.

[0025] Hot metal pretreatment: Semi-steel is produced by mixing 40wt%–60wt% electric furnace molten steel and 60wt%–40wt% blast furnace molten iron, and then smelting in a converter. The ladle folding cycle is controlled to ≤8min. After folding, carbonized rice husks are added to the torpedo ladle for covering, and the temperature of the semi-steel after mixing is 1372–1386℃. A mixed powder of lime and magnesium powder is added for desulfurization, with magnesium powder at 0.25–0.28 kg / t steel and lime at 1.1–1.2 kg / t steel; the slag removal amount is 9.8–10.8 kg / t steel; the treatment cycle is 32–38min, and the pretreatment blowing time is 9.2–11.2min. After pretreatment, S≤0.005%.

[0026] Converter smelting: Top and bottom blowing converter smelting is adopted, with bottom blowing of argon gas throughout the process. The converter smelting cycle is 31-36 minutes, the oxygen blowing time is 11-14 minutes, the final carbon is 0.03-0.045%, the final oxygen is 520-560 ppm, and the final temperature is 1660-1675℃. Sliding plate slag blocking is adopted to strictly control the amount of slag fed into the converter.

[0027] LF ladle furnace refining: When the molten steel reaches the LF refining treatment position, it is stirred by bottom blowing argon gas, and submerged arc slag, refining slag and lime are added. After the three electrodes are energized and heated for 13 minutes, alloying elements are added for adjustment. According to the slag condition, aluminum granules and calcium carbide are added to make white slag. The energizing time is greater than 16 minutes, and the alloy composition is adjusted. Temperature is measured and samples are taken. After the composition and temperature meet the target requirements, soft blowing argon treatment is carried out to ensure that the soft blowing + calming time reaches 14 to 16 minutes, so that the inclusions can be fully floated and removed.

[0028] RH vacuum refining: RH circulation treatment is carried out under vacuum, with a vacuum degree ≤40Pa, to remove C and H from the steel. After refining, Ar is blown softly for ≥12min, alloy fine-tuning is performed, and La, Pr, and Ce alloys are added to make the chemical composition of the molten steel meet the composition requirements of the high-strength steel for home appliance panels mentioned above.

[0029] Continuous casting: A wide slab continuous casting machine is used for continuous casting, with the casting speed controlled at 1.25 to 1.35 m / min and the superheat controlled at 21 to 25℃.

[0030] S2: Hot continuous rolling: Heating: Hot charging process is adopted, with a furnace charging temperature of 650-670℃. To ensure full solid solution of alloying elements, the slab exit temperature is controlled at 1242-1262℃, and the heating time is 126-136 minutes. The furnace atmosphere is controlled to be a weakly oxidizing atmosphere to reduce the formation of iron oxide scale.

[0031] Rough rolling: The "3+3" mode is adopted, with the initial rolling temperature of 1141~1151℃, the reduction rate of the last pass of rough rolling of 16%~20%, the total reduction rate of the rough rolling stage passes of 80%~84%, and the thickness of the intermediate billet of 26~46mm.

[0032] Finishing rolling: The 7-stand hot continuous rolling mill is used for rolling. The coil is fed into the heat preservation cover between the roughing and finishing rolling. The target temperature for the start of finishing rolling is 954-974℃, and the final rolling temperature is 896-916℃.

[0033] Laminar flow cooling and coiling: The process adopts edge shielding + rear cooling + U-shaped coiling. Laminar cooling adopts a rear sparse cooling mode. The coiling temperature of the first 40 meters of the coil is 60℃, and the coiling temperature of the last 40 meters of the coil is 60℃. The straightness of the hot-rolled strip within 5m of the head and tail is ≤35I-unit, and the straightness of the middle section is ≤15I-unit. The coiling is carried out at a temperature of 512~532℃ and then air-cooled to below 30℃. After coiling, the coil is kept horizontally in the coiler for 42~46s.

[0034] Hot-rolled raw material steel plate: After rolling, the strip has a thickness of 1.8 to 4.0 mm, a width of 1850 to 2000 mm, a crown C40 of 30 to 45 μm, a crown C80 of 20 to 32 μm, a wedge shape W40 ≤ 26 μm and C40 > W40, and a local high point ≤ 8 μm.

[0035] S3, Cold Rolled: Pickling and rolling involves transferring hot-rolled raw steel plates to a pickling and rolling mill for tension leveling, descaling, pickling, and rolling to obtain cold-hardened coils. The Mibach laser welding machine employs a low-speed, high-power welding process, with laser output power ranging from 9.5 to 11.5 kW, welding speed from 0.4 to 0.5 m / s, and heating power before and after the welding machine ranging from 4.5 to 6.5 kW. The tension leveling elongation ranges from 0.85% to 1.0%. The total reduction rate of pickling and rolling is 81.5% to 85.0%, with a reduction rate of 5% to 8% on the last stand. The edge waviness of the cold-hardened coil after rolling is ≤7.5 I-unit, and the medium waviness is ≤3.5 I-unit.

[0036] The steel plate is heated to 852–865°C at a heating rate of 3.5–4.5°C / s, with a soaking time of 155–175s. It is then slowly cooled to 705–725°C at a cooling rate of 2.0–2.8°C / s, followed by rapid cooling to 446–466°C at a cooling rate of 42–48°C / s. The temperature is then controlled at 446–462°C when it enters the zinc pot.

[0037] Hot-dip galvanizing: The zinc layer thickness of the outer panel of the appliance is controlled to be 4-7 μm along the width direction; Finishing: Finishing elongation 1.12%~1.22%, manually adjust bending rollers and tilt to make steel plate waviness ≤4I-unit; Finished steel plate: The edges are precision cut, and the shape, surface quality and performance of the steel plate are checked and confirmed. After being rolled up, the finished steel plate is obtained.

[0038] The rationale for the design of the production process in this invention is as follows: Material microstructure has heritability, and hot rolling process parameters directly affect cold rolling grain size, microstructure morphology, and surface quality of strips and sheets.

[0039] By controlling the final hot rolling temperature of the strip at 896–916℃, the steel is ensured to be rolled in the austenitic region. The coiling temperature is controlled at 512–532℃ to achieve the composite strengthening effect of microalloying elements and suppress the formation of carbides, thereby achieving effective control of carbon content in the subsequent finished product. The U-shaped coiling process eliminates the problem of uneven microstructure and excessive performance deviation caused by excessively rapid temperature drop at the beginning and end.

[0040] Annealing process parameters directly determine the microstructure and properties of the material, especially the relative content of soft ferrite and hard martensite, as well as the size and morphology of the Mao islands. This invention controls the soaking temperature at 852℃~865℃ and the soaking time at 155~175s. The microstructure is located in the α+γ two-phase region, consisting of ferrite, martensite, Mao islands, and bainite. Some carbides are not completely decomposed, and their carbon content decreases significantly with increasing austenite content during the soaking process, thus reducing austenite stability. The austenite and ferrite formed during the soaking treatment are retained after slow cooling, achieving a good microstructure match. A high rapid cooling rate is conducive to the formation of martensite and austenite islands. Setting the rapid cooling temperature to 446-466℃ can enrich the carbon in the martensite into the adjacent austenite, and at the same time, it can further strengthen the matrix with the precipitation of dispersed strengthening phases, while improving the plasticity of martensite and realizing the improvement of the material's strength and plasticity. The zinc pot temperature of 446-462℃ can effectively ensure the zinc plating thickness and surface quality.

[0041] Research has shown that adding La, Pr, and Ce to steel, while requiring 2.1 ≤ (La + Pr + Ce) / S ≤ 4.0, allows La, Pr, and Ce to combine with alloying elements in the steel to form Mn-Ti-La-B-Pr-Ce composite compounds, improving the performance of appliance panels. The remaining La, Pr, and Ce react with O and S in the steel, significantly reducing the amount of Al2O3 and MnS inclusions. Furthermore, it transforms Al2O3 and MnS inclusions into smaller elliptical and dot-like inclusions, such as (La, Pr, Ce) and (O, S), with inclusion sizes ≤ 10 μm. These inclusions are dispersed throughout the steel, acting as oxide metallurgy. Elliptical and dot-like inclusions are more stable than irregular inclusions. Simultaneously, these small inclusions also pin austenite grain boundaries and stabilize austenite, thus ensuring the strength, toughness, cold bending formability, and high elongation of the high-strength steel used in appliance panels.

[0042] It should be noted that obtaining the aforementioned high-strength steel for home appliance panels is not only related to composition design but also to the production process. Only through reasonable composition design combined with optimized production processes can the expected microstructure be obtained, thereby effectively improving the deep-drawing performance, weldability, and coating performance of the steel for home appliances.

[0043] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention provides the yield strength R of high-strength steel for home appliance panels. p0.2 The tensile strength is 560–615 MPa, and the tensile strength R is... m The strength is 885–925 MPa, and the elongation after fracture is A. 80 The yield strength ratio is 30-35%, and the yield strength ratio R is 30-35%. p0.2 / R m With a strength of 0.60 to 0.70, a 180° cold bending test result of d=1.0a, and a work hardening index of n: 0.19 to 0.24, and a hole expansion rate of λ: 92 to 98%, it can be used for appliance panels with high strength, high elongation, and high deep drawing performance requirements, meeting the lightweight development needs of the appliance industry.

[0044] 2) The appliance board provided by this invention has a low carbon equivalent (Ceq≤0.30%), excellent bending performance (180° cold bending test d=1.0a), and high elongation after fracture (A). 80 With a low C content (30-35%), combined with the composite strengthening effect of alloying elements such as Mo, Ti, B and Cr, it possesses excellent deep-drawing and welding properties.

[0045] 3) This invention controls continuous annealing at 852℃~865℃. During heating in the α+γ two-phase region, some carbides do not completely decompose. During the holding process, the carbon content decreases significantly with the increase of austenite, thus reducing the stability of austenite. The austenite and ferrite formed by the homogenization treatment can be retained after slow cooling, achieving a good microstructure match. A high rapid cooling rate is beneficial for the formation of martensite and martensite islands. Setting the rapid cooling temperature to 446~466℃ allows C in the martensite to accumulate in adjacent austenite, while simultaneously strengthening the matrix through the precipitation of dispersed strengthening phases, thereby improving the plasticity of the martensite and enhancing the material's strength and plasticity. Attached Figure Description

[0046] Figure 1 This is a flowchart of the preparation method of the present invention.

[0047] Figure 2 This is a typical metallographic structure prepared in Example 1 of the present invention. Detailed Implementation

[0048] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0049] The present invention will be further described below through specific embodiments 1 to 5.

[0050] This invention relates to a high-strength steel for home appliance panels with good microstructure and formability, and its preparation method. The preparation process is as follows: Figure 1 As shown, it includes processes such as eco-friendly electric furnace + converter smelting, continuous casting, hot continuous rolling, pickling rolling, and continuous annealing. S1. Smelting: including ecological electric furnace + converter smelting, LF refining, RH vacuum treatment, and continuous casting, producing continuously cast billets; the composition of the billets is shown in Table 1.

[0051] S2. Hot Continuous Rolling: Utilizing a hot charging and delivery process, the furnace charging temperature is required to be 650–670℃, the slab exit temperature controlled at 1242–1262℃, and the heating time 126–136 min. Roughing adopts a "3+3" pattern, with an initial roughing temperature of 1141–1151℃, a target temperature of 952–962℃ for the final roughing pass, a reduction rate of 16–20% for the final pass, and a total reduction rate of 80–84% across all roughing passes. The intermediate slab thickness is 2 mm. 6~46mm; Finishing rolling: Target temperature for the initial finishing rolling is 954~974℃, and the target temperature for the final finishing rolling is 896~916℃; Laminar flow cooling and coiling: Laminar cooling adopts a sparse cooling mode in the later stage. The coiling temperature of the first 40 meters of the coil is 60℃, and the coiling temperature of the last 40 meters of the coil is 60℃. The coiling is carried out at a temperature of 512~532℃ and then air-cooled to below 30℃. After coiling, the coil is kept horizontally in the coiler for 42~46s; The hot continuous rolling process parameters are shown in Table 2.

[0052] S3, the total reduction rate of pickling and rolling is 81.5% to 85.0%, and the reduction rate of the last stand is 5% to 8%; continuous annealing, the steel plate is heated to 852 to 865°C at a heating rate of 3.5 to 4.5°C / s, the soaking time is 155 to 175s, then slowly cooled to 705 to 725°C at a cooling rate of 2.0 to 2.8°C / s, and then rapidly cooled to 446 to 466°C at a cooling rate of 42 to 48°C / s, and the temperature of entering the zinc pot is controlled at 446 to 462°C; hot-dip galvanizing: the zinc layer thickness of the appliance outer panel is controlled to be 4 to 7μm along the width direction; finishing: the finishing elongation is 1.12% to 1.22%, and the bending rolls and tilt are manually adjusted to make the steel plate waviness ≤4I-unit.

[0053] The chemical composition of Examples 1-5 of this invention is shown in Table 1. The hot rolling process parameters of Examples 1-5 are shown in Table 2. The pickling, annealing, and galvanizing process parameters of Examples 1-5 are shown in Table 3. The performance of the products of Examples 1-5 is shown in Table 4. The metallographic structure of the products of Examples 1-5 is shown in Table 5. The crown, wedge shape, and local high point control of the hot-rolled products of Examples 1-5 are shown in Table 6.

[0054] Table 1 Chemical composition of Examples 1-5:

[0055] Table 2. Hot rolling process parameters for Examples 1-5:

[0056] Table 3. Process parameters for pickling, annealing, and galvanizing in Examples 1-5:

[0057] Table 4 Performance of Products from Examples 1-5:

[0058] Table 5. Metallographic structure of products from Examples 1-5:

[0059] Table 6 shows the control of crown, wedge shape, and local high points of the hot-rolled products in Examples 1-5:

[0060] As can be seen from Tables 1 to 4, the high-strength steel for appliance panels provided in this application, with its excellent microstructure and formability, exhibits superior mechanical properties, particularly its yield strength R. p0.2 The tensile strength is 560–615 MPa, the tensile strength Rm is 885–925 MPa, and the elongation after fracture A is 560–615 MPa. 80 The yield strength ratio is 30-35%, and the yield strength ratio R is 30-35%. p0.2 With a strength of 0.60 to 0.70, a 180° cold bending test result of d=1.0a, a V value of ≥7.8, and a carbon equivalent Ceq of ≤0.30%, it can be used for appliance panels with high strength, high elongation, and high deep drawing performance requirements, meeting the lightweight development needs of the appliance industry.

[0061] The metallographic structure of the appliance board prepared in Example 1 is as follows: Figure 2 As shown, the microstructure consists of ferrite (F), martensite (M), austenite islands (MA), and bainite (B). Ferrite, as the matrix microstructure, can coordinate the deformation of the surrounding hard phases (M+M-A+B) through its own plasticity during deformation, removing stress concentration and ensuring that the material possesses high strength while improving the toughness of the steel plate. Martensite (M), austenite islands (MA), and bainite, as hard phase microstructures, contribute significantly to improving strength during plastic deformation. During the transformation of austenite into martensite, they can effectively suppress necking of the material while simultaneously increasing its strength-ductility product.

[0062] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-strength steel for household appliance panels with good microstructure and formability, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.0062%~0.0074%, Si≤0.02%, Mn: 1.64%~1.74%, P≤0.010%, S≤0.004%, Cr: 0.61%~0.69%, Mo: 0.32%~0.38%, Ti: 0.074%~0.086%, N: 0.0014%~0.0024%, O: 0.0004%~0.0018%, B: 0.0038%~0.0046%, Alt: 0.46%~0.58%, and 1.58≤B / N≤3.30, with 2.1≤(La+Pr+Ce) / S≤4.0 added, and the balance being Fe and unavoidable impurities.

2. The high-strength steel for appliance panels with good microstructure and formability according to claim 1, characterized in that, The carbon equivalent Ceq ≤ 0.30%, and the carbon equivalent formula is as follows: Ceq = C + Si / 55 + Cr / 20 + Mn / 19 + Al / 18 + 2.2 × P + 3.24 × B + 0.133 Mn × Mo.

3. The high-strength steel for appliance panels with good microstructure and formability according to claim 1, characterized in that, The size of inclusions in the steel is ≤10µm, and the thickness of the steel plate is 0.5~2.2mm.

4. The high-strength steel for appliance panels with good microstructure and formability according to claim 1, characterized in that, The microstructure of the high-strength steel consists of ferrite (F), martensite (M), Mao island (MA), and bainite (B), with ferrite (F) accounting for 50%–58% of the area, martensite (M) accounting for 37%–42% of the area, Mao island (MA) accounting for 1%–5% of the area, and bainite (B) accounting for 1%–3% of the area.

5. The high-strength steel for appliance panels with good microstructure and formability according to claim 1, characterized in that, The yield strength R of the high-strength steel p0.2 The tensile strength is 560–615 MPa, the tensile strength Rm is 885–925 MPa, and the elongation after fracture A is 560–615 MPa. 80 The yield strength ratio is 30%–35%. p0.2 Rm is 0.60~0.70, the 180° cold bending test d=1.0a is intact, the work hardening index n: 0.19~0.24, the hole expansion rate λ: 92%~98%, and it satisfies the following formula: (n×UE×λ×Rm)≥ 7.8, where UE is the uniform elongation.

6. A method for preparing high-strength steel for appliance panels with good microstructure and formability as described in any one of claims 1-5, comprising steelmaking, hot continuous rolling, pickling, rolling, annealing, and galvanizing, characterized in that, The hot continuous rolling process includes: a final rolling temperature of 896–916°C; and coiling at a temperature of 512–532°C. The pickling and rolling continuous annealing galvanizing process includes: a continuous annealing temperature of 852-865℃, a heating time of 155-175s, a slow cooling outlet temperature of 705-725℃, a rapid cooling outlet temperature of 446-466℃, and a zinc pot temperature controlled at 446-462℃.

7. The method for preparing high-strength steel for household appliance panels with good microstructure and formability according to claim 6, characterized in that, The hot continuous rolling also includes: Heating: Hot delivery and hot charging, charging temperature 650~670℃, slab exit temperature controlled at 1242~1262℃; Roughing: The initial rolling temperature of roughing is 1141-1151℃, and the total reduction rate of each pass in the roughing stage is 80%-84%; Finishing rolling: The coil is fed into the heat insulation cover between roughing and finishing rolling, and the starting temperature of finishing rolling is 954-974℃; Laminar flow cooling and winding: Laminar cooling adopts a sparse cooling mode in the later stage; after winding, the coil is kept horizontally in the winding machine for 42-46 seconds and then sent to the winding warehouse for air cooling to below 30°C.

8. The method for preparing high-strength steel for household appliance panels with good microstructure and formability according to claim 7, characterized in that, Hot rolling produces hot-rolled raw steel plates with a strip thickness of 1.8–4.0 mm, a crown C40 of 30–45 μm, a crown C80 of 20–32 μm, a wedge shape W40 ≤ 26 μm and C40 > W40, and local high points ≤ 8 μm.

9. The method for preparing high-strength steel for appliance panels with good microstructure and formability according to claim 6, characterized in that, The pickling and rolling continuous annealing zinc plating also includes: The total reduction rate of pickling and rolling is 81.5%–85.0%, and the reduction rate of the last stand is 5%–8%. Hot-dip galvanizing: The zinc layer thickness is controlled at 4–7 μm; Finishing: Finishing elongation 1.12%~1.22%, manually adjust bending rollers and tilt amount to make steel plate waviness ≤4I-unit.

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