High-corrosion-resistance bake hardening steel and production method thereof

Abstract

The invention discloses high-corrosion-resistance bake-hardening steel and a production method thereof. The high-corrosion-resistance bake-hardening steel comprises the following chemical components in percentage by mass: 0.0012 to 0.0030 percent of C, 0.10 to 0.30 percent of Mn, less than or equal to 0.012 percent of S, 0.015 to 0.030 percent of P, less than or equal to 0.08 percent of Si, 0.025 to 0.055 percent of Als, 0.0040 to 0.0120 percent of Nb, 0.0020 to 0.0060 percent of Ti, less than or equal to 0.0015 percent of B, less than or equal to 0.0040 percent of N and the balance of iron and inevitable impurities. The production method comprises a molten iron pretreatment procedure, a decarburization converter procedure, an RH vacuum treatment procedure, a continuous casting procedure, a hot rolling procedure, an acid continuous rolling procedure, a continuous zinc-aluminum-magnesium hot-dip plating procedure and a finishing procedure after plating. By compounding Nb and Ti, controlling the content ratio of C to Nb and optimizing process parameters, the mechanical property and corrosion resistance of a product are improved, the finally obtained steel plate tissue is ferrite with uniform distribution, the yield strength is 180-240 MPa, the tensile strength is 300-360 MPa, A80 is larger than or equal to 34%, the bake hardening value is larger than or equal to 30 MPa within 6 months, and the yield point elongation Ae value is smaller than or equal to 0.2% within 6 months.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a high corrosion resistance bake hardening steel and a production method thereof. Background Art

[0002] Coated steel sheets have corrosion resistance, paintability, decorative properties and good formability. In recent years, the use of coated steel sheets in automobiles has been on the rise and has become the main body of thin sheets for automobiles.

[0003] Galvanized steel refers to a steel plate with a layer of zinc hot-dip coated on its surface, which can enhance the stability and strength of the vehicle body structure, while achieving the purpose of corrosion protection and beautification. With the urgent requirements of energy conservation, emission reduction, and green and low-carbon development in the automotive industry, automobile OEMs are increasingly in need of highly corrosion-resistant coated steel. Galvanized steel is more prone to various defects during the galvanizing process, such as uneven zinc layer, high active steel quality, hydrogen embrittlement, etc., and the corrosion resistance, service life, and durability of galvanized steel can no longer fully meet market demand.

[0004] After nearly 20 years of research and development, zinc-aluminum-magnesium coatings have basically been able to be applied to the entire vehicle. They have better flat corrosion resistance, edge corrosion resistance, and scratch corrosion resistance, and also have considerable advantages in terms of under-film corrosion, especially in lower body parts with high corrosion resistance requirements such as fenders, lower door panels, chassis, etc., zinc-aluminum-magnesium bake-hardened steel has more obvious application advantages. The corrosion resistance of zinc-aluminum-magnesium series products is 4 to 15 times that of pure zinc coatings, so the coating thickness can be greatly reduced, opening up a new way to save zinc resources. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a high corrosion resistance bake hardening steel and a production method thereof, and the obtained strip steel product has good corrosion resistance.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a high corrosion resistance bake hardening steel, whose chemical composition and mass percentage are: C: 0.0012-0.0030%, Mn: 0.10-0.30%, S≤0.012%, P: 0.015-0.030%, Si: ≤0.08%, Als: 0.025-0.055%, Nb: 0.0040-0.0120%, Ti: 0.0020-0.0060%, B: ≤0.0015%, N: ≤0.0040%, and the rest are iron and unavoidable impurities.

[0007] The effective carbon Ceff of the present invention is matched according to the added amounts of C and Nb, and the content of Ceff is controlled to be 9ppm≤Ceff≤16ppm, wherein Ceff=C-Nb / 7.75.

[0008] The present invention also provides a production method of high corrosion resistance bake hardening steel, including a molten iron pretreatment process, a decarburization converter process, an RH vacuum treatment process, a continuous casting process, a hot rolling process, an acid continuous rolling process, a continuous hot-dip galvanizing aluminum-magnesium process, and a post-plating skin finishing process; The decarburization converter step is to decarburize to 0.040-0.060wt% in the decarburization converter; In the RH vacuum treatment process, the RH outgoing C content is controlled at 0.057-0.077wt%; The continuous casting process is a protective casting process, and C is controlled at 0.060-0.080wt%; In the hot rolling process, the finishing rolling temperature is 920±20°C and the coiling temperature is 700±20°C; In the acid continuous rolling process, the total reduction rate of acid rolling is 73-83%.

[0009] In the continuous hot-dip galvanizing aluminum-magnesium process, the annealing temperature is 840±10°C, the dew point of the heating section of the furnace area is required to be below -45°C; the dew points of the slow cooling section and the fast cooling section are both required to be below -15°C, and the medium in the reducing atmosphere in the annealing furnace is a mixed gas of H2 and N2.

[0010] The hot-dip galvanized aluminum-magnesium coating has the following mass percentages: Al: 1.3-2.0%, Mg: 1.2-1.8%, a total of 0.02-0.08% of La and Ce elements, and the remainder of Zn and other unavoidable impurities; the plating solution temperature and the temperature when entering the plating pot are 460±10°C; The post-plating finishing process has a finishing elongation of 1.4±0.1%.

[0011] The design ideas of the chemical composition of the present invention are as follows: C: Ultra-low carbon bake hardening steel is significantly different from other stamping steel plates in that the carbon content C cannot be greater than 0.005%. The ultra-low carbon component treatment improves the plasticity and toughness of the steel plate. At the same time, the reduction of carbon content in the steel matrix will also save the amount of alloy niobium and titanium added, saving raw materials and reducing costs. Considering the need to ensure bake hardening performance, the carbon content is best controlled between 0.0012% and 0.0030%.

[0012] Nb: Niobium is a strong carbide-forming element. Niobium interacts with carbon atoms to form carbides. The increase of niobium content in steel plates is beneficial to the deep drawing performance of automobile plates. However, excessive addition will adsorb carbon atoms in the steel plates, restrict the diffusion movement of carbon atoms, affect the bake hardening performance of the steel plates, and reduce the bake hardening value. Therefore, the niobium content is controlled at 0.0040-0.0120%.

[0013] Mn: Manganese element will play a role in solid solution strengthening to improve the strength of steel, but if too much is added, the deep drawing performance will be reduced. The manganese content should be controlled at 0.10-0.30%.

[0014] Al: It can not only deoxidize and improve the utilization rate of strong carbonitride forming elements, but also prevent nitrogen and oxygen from forming inclusions. Therefore, the aluminum content cannot be less than 0.01%, but the aluminum content should not be too high (greater than 0.20%) so as to reduce plasticity and toughness. The acid aluminum content is controlled at 0.025-0.055%.

[0015] Ti: It can combine with O, C, N, and S in steel to form oxides, carbides, nitrides, sulfides, and carbon sulfides. Since the precipitation of bake-hardened steel is more complicated and the precipitation form is greatly affected by the fluctuation of hot rolling reheating temperature, a Nb and Ti composite component system is usually used in production. The titanium content is controlled at 0.0020-0.0060%.

[0016] The beneficial effects of adopting the above technical solution are: 1. The present invention uses a Nb and Ti composite component system, within a certain component range, by controlling the C and Nb content ratio during the smelting process, to ensure that the final solid solution carbon of the finished product is within the range of 9 to 16 ppm, and adjusts the subsequent process parameters, controls the dew point of each heating section of the annealing furnace, and improves the mechanical properties and corrosion resistance of the product. The final steel plate structure is uniformly distributed ferrite, the yield strength is 180 to 240 MPa, the tensile strength is 300 to 360 MPa, and the A 80 ≥34%, bake hardening value ≥30MPa within 6 months, yield point elongation Ae value ≤0.2% within 6 months.

[0017] 2. The zinc-aluminum-magnesium coating of the present invention has the characteristics of high surface quality, low waviness and high corrosion resistance. When applied to automobile panels, it can not only improve their anti-sag ability, but also improve the surface vividness and significantly improve the corrosion resistance of the panels. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The middle is a photo of a sample of pure zinc-coated bake-hardened steel subjected to neutral salt spray corrosion test; Figure 2 This is a photograph of the sample of the high corrosion resistant bake hardening steel produced in Example 1 subjected to a neutral salt spray corrosion test. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to specific embodiments.

[0020] Embodiment 1: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0015%; Si: 0.01%; Mn: 0.25%; P: 0.018%; S: 0.007%; Als: 0.039%; Nb: 0.0045%; Ti: 0.0033%; B: 0.0007%; N: 0.0017%, and the rest are Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 9.2ppm.

[0021] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.047wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.061wt%; (3) Continuous casting process: Protective casting is performed throughout the entire continuous casting process to control C at 0.066wt%; (4) Hot rolling process: finishing rolling outlet temperature 900°C, coiling temperature 705°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 73%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace uniform temperature 846°C, bath temperature 460°C, plating pot temperature 462°C, furnace heating section dew point -48°C; slow cooling section and fast cooling section dew points -41°C and -26°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.5%, Mg: 1.6%, total amount of La and Ce elements 0.06%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.4%.

[0022] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0023] Embodiment 2: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0016%; Si: 0.01%; Mn: 0.21%; P: 0.025%; S: 0.004%; Als: 0.047%; Nb: 0.0040%; Ti: 0.0032%; B: 0.0009%; N: 0.0029%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 10.8ppm.

[0024] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.051wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.065wt%; (3) Continuous casting process: Protective casting is performed throughout the entire continuous casting process, and C is controlled at 0.070wt%; (4) Hot rolling process: finishing rolling outlet temperature 918°C, coiling temperature 704°C; (5) Acid rolling process: Acid rolling reduction rate 78%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 830°C, bath temperature 452°C, plating pot temperature 453°C, furnace heating section dew point -46°C; slow cooling section and fast cooling section dew points -43°C and -26°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.7%, Mg: 1.5%, total amount of 0.04% La and Ce elements, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.3%.

[0025] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0026] Embodiment 3: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0020%; Si: 0.01%; Mn: 0.26%; P: 0.019%; S: 0.005%; Als: 0.042%; Nb: 0.0058%; Ti: 0.0052%; B: 0.0007%; N: 0.0040%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 12.5ppm.

[0027] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.043wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.059wt%; (3) Continuous casting process: Protective casting is performed throughout the entire continuous casting process to control C at 0.062wt%; (4) Hot rolling process: finishing rolling outlet temperature 923°C, coiling temperature 714°C; (5) Pickling continuous rolling process: Pickling reduction rate 79%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 835°C, bath temperature 458°C, plating pot temperature 462°C, furnace heating section dew point -49°C; slow cooling section and fast cooling section dew points -48°C and -27°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.8%, Mg: 1.2%, total amount of La and Ce elements 0.03%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.4%.

[0028] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0029] Embodiment 4: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0017%; Si: 0.06%; Mn: 0.18%; P: 0.024%; S: 0.006%; Als: 0.055%; Nb: 0.0057%; Ti: 0.0020%; B: 0.0008%; N: 0.0015%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 9.6ppm.

[0030] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.060wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.057wt%; (3) Continuous casting process: Protective casting is performed throughout the continuous casting process, and C is controlled at 0.060wt%; (4) Hot rolling process: finishing rolling outlet temperature 925°C, coiling temperature 690°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 75%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 840℃, bath temperature 463℃, plating pot temperature 465℃, furnace heating section dew point -51℃; slow cooling section and fast cooling section dew points -40℃ and -25℃ respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 2.0%, Mg: 1.3%, total amount of 0.08% La and Ce elements, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.4%.

[0031] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0032] Embodiment 5: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0026%; Si: 0.01%; Mn: 0.30%; P: 0.030%; S: 0.004%; Als: 0.039%; Nb: 0.0079%; Ti: 0.0038%; B: 0.0010%; N: 0.0021%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 15.8ppm.

[0033] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.040wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.058wt%; (3) Continuous casting process: Protective casting is performed throughout the continuous casting process to control C at 0.063wt%; (4) Hot rolling process: finishing rolling outlet temperature 916°C, coiling temperature 713°C; (5) Acid rolling process: Acid rolling reduction rate 80%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 834°C, bath temperature 455°C, plating pot temperature 458°C, furnace heating section dew point -47°C; slow cooling section and fast cooling section dew points -45°C and -28°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.4%, Mg: 1.8%, total amount of La and Ce elements 0.07%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.5%.

[0034] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0035] Embodiment 6: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0023%; Si: 0.03%; Mn: 0.24%; P: 0.027%; S: 0.0012%; Als: 0.042%; Nb: 0.0068%; Ti: 0.0060%; B: 0.0007%; N: 0.0019%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 14.2ppm.

[0036] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.052wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.065wt%; (3) Continuous casting process: Protective casting is performed throughout the continuous casting process to control C at 0.071wt%; (4) Hot rolling process: finishing rolling outlet temperature 930°C, coiling temperature 720°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 75%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 850°C, bath temperature 463°C, plating pot temperature 465°C, furnace heating section dew point -50°C; slow cooling section and fast cooling section dew points -43°C and -28°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.5%, Mg: 1.4%, total amount of La and Ce elements 0.05%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.5%.

[0037] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0038] Embodiment 7: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0018%; Si: 0.01%; Mn: 0.10%; P: 0.023%; S: 0.003%; Als: 0.025%; Nb: 0.0053%; Ti: 0.0038%; B: 0.0015%; N: 0.0017%, and the rest are Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 11.2ppm.

[0039] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.042wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.058wt%; (3) Continuous casting process: Protective casting is performed throughout the entire continuous casting process, and C is controlled at 0.080wt%; (4) Hot rolling process: finishing rolling outlet temperature 940°C, coiling temperature 698°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 77%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 846°C, bath temperature 461°C, plating pot temperature 450°C, furnace heating section dew point -47°C; slow cooling section and fast cooling section dew points -45°C and -25°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.3%, Mg: 1.6%, total amount of La and Ce elements 0.02%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.3%.

[0040] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0041] Embodiment 8: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0020%; Si: 0.08%; Mn: 0.18%; P: 0.026%; S: 0.005%; Als: 0.046%; Nb: 0.0062%; Ti: 0.0037%; B: 0.0008%; N: 0.0016%, and the rest is Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 12ppm.

[0042] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.041wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.077wt%; (3) Continuous casting process: Protective casting is performed throughout the continuous casting process to control C at 0.063wt%; (4) Hot rolling process: finishing rolling outlet temperature 928°C, coiling temperature 680°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 83%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace uniform temperature 843°C, bath temperature 456°C, plating pot temperature 459°C, furnace heating section dew point -51°C; slow cooling section and fast cooling section dew points -41°C and -26°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.7%, Mg: 1.7%, total amount of La and Ce elements 0.05%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.4%.

[0043] The performance results of the high corrosion resistance bake hardening steel obtained after the above process are shown in Table 1.

[0044] Embodiment 9: A high corrosion resistance bake hardening steel, the chemical components and their mass percentages of the steel are: C: 0.0030%; Si: 0.05%; Mn: 0.16%; P: 0.015%; S: 0.005%; Als: 0.047%; Nb: 0.0120%; Ti: 0.0036%; B: 0.0008%; N: 0.0019%, and the rest are Fe and unavoidable impurities. The amount of Nb added and the ratio of the content of Nb to C satisfy Ceff = C-Nb / 7.75 = 14.5ppm.

[0045] The production method of the high corrosion resistance bake hardening steel in this embodiment has the following specific process steps: (1) Decarburization converter process: After pretreatment, the molten iron is decarburized to 0.046wt% in a decarburization converter; (2) RH vacuum treatment process: RH outgoing C content is controlled at 0.061wt%; (3) Continuous casting process: Protective casting is performed throughout the entire continuous casting process to control C at 0.067wt%; (4) Hot rolling process: finishing rolling outlet temperature 922°C, coiling temperature 695°C; (5) Pickling continuous rolling process: Pickling rolling reduction rate 77%; (6) Continuous hot-dip galvanizing aluminum-magnesium process: annealing furnace soaking temperature 837°C, bath temperature 463°C, plating pot temperature 470°C, furnace heating section dew point -48°C; slow cooling section and fast cooling section dew points -44°C and -25°C respectively; hot-dip galvanizing aluminum-magnesium coating composition mass percentage: Al: 1.5%, Mg: 1.5%, total amount of La and Ce elements 0.04%, balance Zn and other unavoidable impurities; (7) Post-plating finishing process: finishing elongation 1.5%.

[0046] The mechanical properties of the high corrosion resistance bake hardening steel produced in Examples 1-9 were tested, and the results are shown in Table 1; Table 1 Mechanical properties of high corrosion resistance bake hardening steel

[0047] As shown in Table 1, the yield strength of the high corrosion resistance bake hardening steel produced by the present invention is 180-240 MPa, the tensile strength is 300-360 MPa, and the A 80 ≥34%, bake hardening value ≥30MPa within 6 months, yield point elongation Ae value before stamping ≤0.2%, which meets the performance requirements of bake hardening steel.

[0048] In order to objectively evaluate the corrosion resistance of different coating compositions, a neutral salt spray corrosion comparison test was conducted using the high corrosion resistance bake hardening steel of Example 1 and the pure zinc coating bake hardening steel.

[0049] The test sample was observed. After 120 hours of pure zinc coating bake hardening steel sample, red rust began to appear on the sample surface. See the sample photo. Figure 1 The high corrosion resistance bake hardening steel of Example 1 did not show red rust on the sample surface until 576h later. See the sample photo. Figure 2 From the comparative test, it can be seen that the high corrosion resistance bake hardening steel of the present invention has excellent plane corrosion resistance.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high corrosion resistance bake hardening steel, characterized in that: Its chemical composition and mass percentage are: C: 0.0012~0.0030%, Mn: 0.10~0.30%, S≤0.012%, P: 0.015-0.030%, Si: ≤0.08%, Als: 0.025~0.055%, Nb: 0.0040~0.0120%, Ti: 0.0020~0 .0060%, B: ≤0.0015%, N: ≤0.0040%, and the rest are iron and unavoidable impurities.

2. A highly corrosion resistant bake hardening steel as claimed in claim 1, characterized in that: The mass ratio of the added amount of the Nb component to the C component satisfies 9ppm≤Ceff≤16ppm, wherein Ceff=C-Nb / 7.

75.

3. The method for producing high corrosion resistant bake hardening steel according to claim 1, characterized in that: It includes molten iron pretreatment process, decarburization converter process, RH vacuum treatment process, continuous casting process, hot rolling process, acid continuous rolling process, continuous hot-dip galvanizing aluminum-magnesium process, and post-plating finishing process; The decarburization converter step is to decarburize to 0.040-0.060wt% in the decarburization converter; In the RH vacuum treatment process, the RH outgoing C content is controlled at 0.057-0.077wt%; The continuous casting process is a protective casting process, and C is controlled at 0.060-0.080wt%; In the hot rolling process, the finishing rolling temperature is 920±20°C and the coiling temperature is 700±20°C; In the acid continuous rolling process, the total reduction rate of acid rolling is 73-83%.

4. The method for producing high corrosion resistant bake hardening steel according to claim 3, characterized in that: In the continuous hot-dip galvanizing aluminum-magnesium process, the annealing temperature is 840±10°C, the dew point in the heating section of the annealing furnace is required to be below -45°C; the dew points in the slow cooling section and the fast cooling section are both required to be below -15°C.

5. The method for producing high corrosion resistant bake hardening steel according to claim 3, characterized in that: The medium in the reducing atmosphere in the annealing furnace is a mixed gas of H2 and N2.

6. The method for producing high corrosion resistant bake hardening steel according to claim 5, characterized in that: In the continuous hot-dip galvanizing aluminum-magnesium process, the mass percentage of the hot-dip galvanizing aluminum-magnesium coating composition is: Al: 1.3-2.0%, Mg: 1.2-1.8%, the total amount of La and Ce elements is 0.02-0.08%, and the balance is Zn and other inevitable impurities; the plating solution temperature and the temperature when entering the plating pot are 460±10°C.

7. The method for producing high corrosion resistant bake hardening steel according to claim 3, characterized in that: The post-plating finishing process has a finishing elongation of 1.4±0.1%.

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