A 490MPa grade duplex steel outer plate and its production method

Abstract

This invention discloses a 490MPa grade duplex steel outer plate and its production method. Its chemical composition and mass percentage are as follows: C≤0.09%, Si≤0.08%, Mn: 1.40~1.60%, P: 0.010~0.030%, Al≤0.15%, Cr: 0.20~0.40%, V: 0.13~0.17%, B: 0.002~0.005%, with the balance being Fe and unavoidable impurities. The production method includes converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing. This duplex steel replaces traditional mild steels such as IF steel and BH steel, and is used to manufacture automotive, especially passenger car, door outer panels, engine hood outer panels, and fender outer panels. It possesses excellent dent resistance, flanging properties, formability, and high surface quality meeting O5 plate requirements, exhibiting superior overall performance.

Description

Technical Field

[0001] This invention belongs to the field of steel production and manufacturing technology, specifically relating to a 490MPa grade duplex steel outer plate and its production method. Background Technology

[0002] Door panels, side panels, roof, fenders, hood panels, and trunk panels together constitute the exterior body panels of a car. Due to their large size and high weight percentage, these panels are highly effective at achieving lightweighting, and are typically manufactured in-house by individual automakers. There are two main methods for lightweighting exterior body panels: using aluminum sheets and reducing the thickness using high-strength steel. In recent years, the research and application of aluminum alloy hoods and doors have received widespread attention, but their application remains limited due to limitations in forming, joining, and cost. Exterior body panels have evolved from using DC06 grade IF steel to high-strength IF steel and bake-hardening steel as the mainstream products. These products require appropriate basic mechanical properties, high formability, dent resistance, flanging performance, and low resilience, while also ensuring good surface quality.

[0003] As a key component of the automotive supply chain's transformation, steel, through the adoption of new technologies and processes to manufacture green materials, can provide a source guarantee for low-carbon emissions and recyclability for car users. Systematic low-carbon product application solutions can provide technical and product guarantees for the green development of car users throughout their entire lifecycle. This invention proposes a method for manufacturing exterior body panels using 490MPa-grade duplex steel with higher strength. This increases strength while reducing thickness, achieving lightweighting of the car body and enhancing safety performance. It replaces existing body-in-white exterior body panel materials, employing a smelting process and raw materials of DRI sponge iron and scrap steel to achieve carbon reduction and create a novel product. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a 490MPa grade duplex steel outer panel and its production method, replacing traditional automotive outer panel steel materials, increasing strength by more than 30%, and reducing the weight of each passenger car body-in-white by more than 6KG. Based on carbon manganese steel, phase transformation strengthening is utilized, and through a unique production process design, the overall performance and surface quality meet the manufacturability requirements of outer panel components.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 490MPa grade duplex steel outer plate, wherein the chemical composition and mass percentage (wt%) of the duplex steel outer plate are: C≤0.09%, Si≤0.08%, Mn: 1.40~1.60%, P: 0.010~0.030%, Al≤0.15%, Cr: 0.20~0.40%, V: 0.13~0.17%, B: 0.002~0.005%, with the balance being Fe and unavoidable impurities.

[0006] The chemical composition of the duplex steel outer plate of the present invention also contains any one or more of the following elements: Nb≤0.05%, Ti≤0.15%, Mo≤0.20%, Cu≤0.25%, Ni≤0.30%.

[0007] The mechanical properties of the duplex steel outer plate of the present invention are as follows: yield strength 290~370MPa, tensile strength 490~570MPa, elongation ≥35%, strain hardening index ≥0.20, plastic strain ratio ≥2.30, bake hardening value ≥42MPa, and hole expansion rate ≥95%.

[0008] The comprehensive performance of the duplex steel outer plate described in this invention is as follows: zinc coating adhesion grade 0, salt spray test for 1000 hours, single-sided corrosion width ≤ 1.5 mm, surface quality grade O5, dent resistance stiffness under 100N loading deformation ≤ 4.0 mm, dent resistance under 200N loading residual deformation after unloading ≤ 0.01 mm, forming limit FLC0 ≥ 0.35, flange surface dimensional deviation ≤ ±0.4 mm, punch springback angle ≤ 11°, and die springback angle ≤ 8°.

[0009] This invention also provides a method for producing a 490MPa grade duplex steel outer plate, wherein the production method includes converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing, and the specific process control is as follows:

[0010] (1) The converter or electric furnace smelting: the raw materials are 20-25% sponge iron, ≥30% scrap steel and molten iron, which are then refined and micro-alloyed in an RH vacuum furnace and then continuously cast into billets;

[0011] (2) The billet obtained in step (1) is cold-sent or directly sent to the hot rolling heating furnace and heated to ≥1200℃, held for ≤90min, the final rolling temperature of hot continuous rolling is controlled at Ar3±20℃, the coiling temperature after cooling is controlled at 400~600℃, and the thickness of hot rolled steel coil is controlled at 2.8~3.2mm.

[0012] (3) After the hot-rolled steel coil from step (2) is acid-rolled to 0.60±0.02mm, it is heated in the annealing section of the hot-dip galvanizing production line at a temperature of ≥800℃, slowly cooled to 600~710℃, and the final temperature of rapid cooling is controlled at 400~460℃. Then, it is heated to the outlet zinc pot plate temperature of 460~500℃, and then hot-dip galvanized in the zinc pot. The finishing elongation is controlled at 0.2~1.5%. It is cooled in the air to room temperature~130℃ and then coiled into a steel coil.

[0013] In step (3) of the present invention, the temperature of the zinc liquid is controlled at 451-455℃.

[0014] In step (3) of the present invention, the hot-dip galvanizing temperature is controlled at 800-840℃.

[0015] The beneficial effects of adopting the above technical solution are as follows: 1. Through reasonable chemical composition and process design, this invention has excellent galvanizing performance (zinc layer adhesion reaches level 0), painting performance (hardness 2H without scratches, impact resistance reaches 50kg / cm with no cracking on both sides, cupping test with no cracking or peeling of 6mm paint film), corrosion resistance (salt spray test 1000 hours, single-sided corrosion width ≤1.5mm), and high surface quality (O5 level). In particular, the unique chemical composition and process of the steel plate of this invention result in strong manufacturability of the parts, and the produced products have good dent resistance (dent resistance stiffness under 100N loading deformation ≤4.0mm, dent resistance under 200N loading with residual deformation ≤0.01mm after unloading), high formability (forming limit FLC0 ≥0.35, hole expansion rate ≥95%), and high flanging performance (flanged surface dimensional deviation ≤±0.4). 1. The material exhibits excellent properties (mm) and low resilience (punch springback angle ≤11°, die springback angle ≤8°), meeting the requirements for manufacturing exterior body panels. It is exclusively used in the manufacturing of the body-in-white of a joint venture high-end brand passenger vehicle. 2. This invention fully utilizes the comprehensive strengthening technology of various chemical elements, and has strong process window feasibility, reducing production difficulty, increasing yield and indirectly reducing production costs, resulting in strong market competitiveness. 3. This invention uses duplex steel to replace traditional mild steel such as IF steel and BH steel, and can be used to manufacture car door outer panels, body outer panels, engine hood outer panels, fender outer panels, trunk outer panels, etc., with good market application prospects. Attached Figure Description

[0016] Figure 1 Microstructure diagram of the hot-dip galvanized product in Example 1;

[0017] Figure 2 This is a microscopic morphology diagram of the transverse bending performance test in Example 1. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to specific embodiments; however, these embodiments should not be construed as limiting the present invention. Example 1

[0019] A method for producing 490MPa grade duplex steel outer plates, the method comprising converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing, with specific process control as follows:

[0020] (1) Steelmaking process: The raw materials for converter smelting are 23% sponge iron + 30% scrap steel + molten iron, which are then refined and micro-alloyed in RH vacuum furnace, and then continuously cast into billets;

[0021] (2) The billet obtained in step (1) is directly sent to the hot rolling furnace and heated to 1250°C. It is held for 60 minutes. The final rolling temperature of the hot continuous rolling is controlled at Ar3°C. After cooling, the coiling temperature is controlled at 400°C. The thickness of the hot rolled coil is controlled at 2.8 mm.

[0022] (3) After the hot-rolled steel coil from step (2) is acid-rolled to 0.60±0.01mm, it is heated in the annealing section of the hot-dip galvanizing production line at a temperature of 800℃, then slowly cooled to 600℃, and the final temperature of rapid cooling is controlled at 430℃. Then, it is heated to the outlet zinc pot plate temperature of 460℃, and then hot-dip galvanized in the zinc pot. The zinc liquid temperature is controlled at 454℃, the finishing elongation is controlled at 0.2%, and it is cooled in the air to 130℃ and then rolled into a steel coil. Example 2

[0023] A method for producing 490MPa grade duplex steel outer plates, the method comprising converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing, with specific process control as follows:

[0024] (1) Steelmaking process: The raw materials for converter smelting are 20% sponge iron + 35% scrap steel + molten iron, which are then refined and micro-alloyed in RH vacuum furnace, and then continuously cast into billets;

[0025] (2) The billet obtained in step (1) is cold-sent to a hot rolling furnace and heated to 1200℃. It is held for 90 minutes. The final rolling temperature of the hot continuous rolling is controlled at Ar3±5℃. After cooling, the coiling temperature is controlled at 500℃. The thickness of the hot rolled coil is controlled at 3.2mm.

[0026] (3) After the hot-rolled steel coil from step (2) is acid-rolled to 0.60 mm, it is heated in the annealing section of the hot-dip galvanizing production line at a temperature of 820°C, then slowly cooled to 710°C, and the final temperature of rapid cooling is controlled at 400°C. Then, it is heated to the outlet zinc pot plate temperature of 500°C, and then hot-dip galvanized in the zinc pot. The zinc liquid temperature is controlled at 453°C, the finishing elongation is controlled at 1.5%, and it is cooled in the air to 80°C and then rolled into a steel coil. Example 3

[0027] A method for producing 490MPa grade duplex steel outer plates, the method comprising converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing, with specific process control as follows:

[0028] (1) Steelmaking process: The raw materials for electric furnace smelting are 25% sponge iron + 40% scrap steel + molten iron, which are then refined and micro-alloyed in RH vacuum furnace, and then continuously cast into billets.

[0029] (2) The billet obtained in step (1) is cold-sent to a hot rolling furnace and heated to 1230°C. It is held for 30 minutes. The final rolling temperature of the hot continuous rolling is controlled at Ar3±20°C. After cooling, the coiling temperature is controlled at 600°C. The thickness of the hot rolled coil is controlled at 3.2 mm.

[0030] (3) After the hot-rolled steel coil from step (2) is acid-rolled to 0.60±0.01mm, it is heated in the annealing section of the hot-dip galvanizing production line at a temperature of 840℃, slowly cooled to 600℃, and the final temperature of rapid cooling is controlled at 460℃. Then, it is heated to the outlet zinc pot plate temperature of 500℃, and then put into the zinc pot for hot-dip galvanizing treatment. The zinc liquid temperature is controlled at 455℃, the finishing elongation is controlled at 1.5%, and it is cooled in the air to 100℃ and then rolled into a steel coil.

[0031] Example 4

[0032] A method for producing 490MPa grade duplex steel outer plates, the method comprising converter or electric furnace smelting, RH refining, continuous casting into billets, heating in a heating furnace, hot rolling, coiling, pickling, and hot-dip galvanizing, with specific process control as follows:

[0033] (1) Steelmaking process: The raw materials for electric furnace smelting are 25% sponge iron + 40% scrap steel + molten iron, which are then refined and micro-alloyed in RH vacuum furnace, and then continuously cast into billets.

[0034] (2) The billet obtained in step (1) is cold-sent to a hot rolling furnace and heated to 1200℃. It is held for 45 minutes. The final rolling temperature of the hot continuous rolling is controlled at Ar3±10℃. After cooling, the coiling temperature is controlled at 400℃. The thickness of the hot rolled coil is controlled at 2.8mm.

[0035] (3) After the hot-rolled steel coil from step (2) is rolled to 0.60±0.02mm by pickling, it is heated in the annealing section of the hot-dip galvanizing production line at a temperature of 815℃, then slowly cooled to 710℃, and the final temperature of rapid cooling is controlled at 430℃. Then, it is heated to the outlet zinc pot plate temperature of 460℃, and then hot-dip galvanized in the zinc pot. The zinc liquid temperature is controlled at 451℃, the finishing elongation is controlled at 0.2%, and it is cooled to room temperature in the air and then rolled into a steel coil.

[0036] According to the above process, the specific chemical composition of each embodiment is shown in Table 1, and the performance of each embodiment is shown in Tables 2 and 3.

[0037] The 490MPa grade duplex steel outer plates obtained in Examples 1-4 of this invention exhibit excellent galvanizing performance (zinc layer adhesion reaches grade 0), painting performance (hardness 2H with no scratches, impact resistance up to 50kg / cm with no cracking on both sides, and no cracking or peeling of the 6mm paint film in the cupping test), corrosion resistance (salt spray test for 1000 hours, single-sided corrosion width ≤1.5mm), and high surface quality (grade O5). The duplex steel outer plates also possess good dent resistance (dent stiffness under 100N loading with deformation ≤4.0mm, dent resistance under 200N loading with residual deformation ≤0.01mm after unloading), high formability (forming limit FLC0 ≥0.35, hole expansion rate ≥95%), high flanging performance (flanged surface dimensional deviation ≤±0.4mm), and low resilience (punch springback angle ≤11°, die springback angle ≤8°).

[0038] Appendix Figure 1 This is a microstructure diagram of the hot-dip galvanized product from Example 1. Figure 2 The image shown is a microscopic morphology diagram of the transverse bending performance test in Example 1 (the corresponding figures for other examples are similar and therefore omitted). Through... Figure 1 It can be seen that the microstructure of the hot-dip galvanized product is carbon-rich ferrite + carbon-depleted martensite. Because the ferrite phase in the microstructure of the dual-phase steel outer plate of this invention is carbon-rich, the hardness difference between the ferrite and martensite phases is reduced, thereby improving the overall forming performance. Figure 1 The test results for the flanging performance showed that the surface was smooth, without cracks or wrinkles, and there was no localized shrinkage along the width direction of the test sample. Figure 2 .

[0039] Table 1 Chemical composition (wt%) of duplex steel outer plates in Examples 1-4

[0040]

[0041] Table 2 Mechanical properties of duplex steel outer plates in Examples 1-4

[0042]

[0043] Table 3. Comprehensive performance of duplex steel outer plates in Examples 1-4

[0044]

[0045] 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 method for producing a 490 MPa grade dual phase steel outer plate, characterized by, The chemical composition of the dual-phase steel outer plate and its mass percentage are as follows: C≤0.09%, Si≤0.08%, Mn: 1.40-1.60%, P: 0.010-0.030%, Al≤0.15%, Cr: 0.20-0.40%, V: 0.13-0.17%, B: 0.002-0.005%, and the balance being Fe and inevitable impurities; the production method comprises converter or electric furnace smelting, RH refining, continuous casting, heating furnace heating, hot rolling, coiling, pickling and hot-dip galvanizing, and the process is specifically controlled as follows: (1) the converter or electric furnace smelting: the raw materials are sponge iron 20-25%, scrap steel≥30% and molten iron, which are then refined by RH vacuum furnace and micro-alloyed, and then continuously cast into a casting blank; (2) the casting blank obtained in step (1) is cold sent or directly sent to a hot rolling heating furnace and heated to≥1200℃, the holding time is≤90 min, the final rolling temperature of the hot continuous rolling is controlled at Ar3±20℃, the coiling temperature after cooling is controlled at 400-600℃, and the thickness of the hot-rolled steel coil is controlled at 2.8-3.2 mm; (3) after the hot-rolled steel coil in step (2) is rolled to 0.60±0.02 mm by pickling, the soaking temperature in the annealing section of the hot-dip galvanizing production line is controlled at≥800℃, the slow cooling temperature is 600-710℃, the fast cooling end temperature is controlled at 400-460℃, then, the temperature of the heated steel coil entering the zinc pot is 460-500℃, after that, the hot-dip galvanizing treatment is carried out in the zinc pot, the finishing elongation is controlled at 0.2-1.5%, the steel coil is coiled after being cooled to room temperature-130℃ in the air.

2. A method of producing a 490 MPa grade dual phase steel outer plate according to claim 1, characterized in that, The zinc liquid temperature in step (3) is controlled at 451-455℃.

3. A method of producing a 490 MPa grade dual phase steel outer plate according to claim 1, characterized in that, The hot-dip galvanizing soaking temperature in step (3) is controlled at 800-840℃.

4. A method of producing a 490 MPa grade dual phase steel outer panel according to claim 1, 2 or 3, characterized in that, The dual-phase steel outer plate further contains any one or several of the following elements: Nb≤0.05%, Ti≤0.15%, Mo≤0.20%, Cu≤0.25%, and Ni≤0.30%.

5. A method of producing a 490 MPa grade dual phase steel outer panel according to claim 1, 2 or 3, characterized in that, The mechanical properties of the dual-phase steel outer plate are as follows: yield strength 290-370 MPa, tensile strength 490-570 MPa, elongation≥35%, strain hardening index≥0.20, plastic strain ratio≥2.30, baking hardening value≥42 MPa, and hole expansion ratio≥95%.

6. A method of producing a 490 MPa grade dual phase steel outer panel according to claim 1, 2 or 3, characterized in that, The comprehensive performance of the dual-phase steel outer plate is as follows: zinc layer adhesion 0 level, salt spray test 1000 hours, single-side corrosion width≤1.5 mm, surface quality O5 level, dent resistance loading 100 N deformation≤4.0 mm, dent resistance loading 200 N after unloading residual deformation≤0.01 mm, forming limit FLC0≥0.35, flanging surface size deviation≤±0.4 mm, punch springback angle≤11°, and die springback angle≤8°.

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