A 400mpa grade hot-dip galvanized sheet for new energy vehicles and a production method thereof

Abstract

The application discloses a 400MPa-grade hot-dip galvanized sheet for low-cost new energy vehicles and a production method thereof. The chemical composition of the hot-dip galvanized sheet is as follows in terms of percentage by weight: C: 0.04-0.07%, Si: 0.06-0.09%, Mn: 0.24-0.36%, P: 0.009-0.03%, S: 0.008-0.013%, Als: 0.02-0.04%, B: 0.0015-0.003%, Ce: 0.008-0.015%, N: 0.005-0.015%, and the balance of Fe and inevitable impurities. The production method comprises the steps of steelmaking, hot rolling, pickling, and galvanizing. The hot-dip galvanized sheet provided by the application has high strength, the yield strength is 230-260MPa, the tensile strength is higher than 400MPa, and the hot-dip galvanized sheet has excellent formability, dent resistance and aging resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of automobile steel, and particularly relates to a 400 MPa grade hot-dip galvanized sheet for new energy vehicles and a production method thereof. BACKGROUND

[0002] With the rapid development of automobile lightweight, under the premise of excellent formability and dent resistance, good anti-aging property, high strength and high quantification have become the main direction of development of automobile panels. At present, IF steel and BH steel are mainly used in automobile outer panels. The dent resistance of IF steel is relatively low, and the aging period of BH steel is a major problem in the application process. At present, dual-phase steel outer panels have begun to be applied to automobile coverings. However, the work hardening rate of dual-phase steel is relatively high, which greatly reduces the service life of the die. The UF steel developed by Shougang is suitable for automobile outer panels, and has good formability, anti-aging property and the like, but the content of niobium titanium micro-alloy introduced by the UF steel is relatively high, the alloy cost is relatively high, and the process window control of the steelmaking process is difficult to realize. Therefore, it is necessary to develop a high-strength automobile panel with excellent formability, dent resistance and anti-natural aging property.

[0003] The patent application with the publication number CN101353755A discloses a high tensile strength substrate, a hot-dip galvanized automobile sheet and a manufacturing method thereof. The chemical composition of the steel sheet is (wt%): C: 0.01-0.08%, Si: ≤0.1%, Mn: 0.8-1.8%, Cr: ≤1.0%, Mo: ≤0.5%, Al: 0.02-0.08%, N: ≤0.006%, P+2S: ≤0.12%, 1.6%≤Mn+3Cr+2Mo≤3.8%, and Fe: the balance. The component design of the steel sheet adopts high carbon and adds Mn, Cr and Mo and other noble metal elements, which greatly increases the alloy cost. At the same time, the microstructure of the steel sheet is pearlite + ferrite original structure, the strength is relatively high, but the elongation is relatively low (32%-36%), which is not conducive to the stamping forming of the automobile panel.

[0004] The patent application with the publication number CN201510455209.1 discloses an alloyed hot-dip galvanized steel with a tensile strength of 390 MPa for automobiles and a production method thereof. The element composition of the steel sheet is (wt%): C: 0.07-0.10%, Si: ≤0.03%, Mn: 0.7-1.0%, P: 0.010-0.025%, S≤0.010%, and Als: 0.020-0.070%. The carbon content in the component design of the steel sheet is high, which easily causes excessive solid solution C in the steel sheet and affects the anti-natural aging property of the steel sheet, and the addition of a large amount of solid solution strengthening element Mn is not conducive to the improvement of the formability of the steel sheet. SUMMARY

[0005] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a low-cost, high-formability, dent-resistant and aging-resistant 400MPa grade hot-dip galvanized sheet for new energy vehicles and its production method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A low-cost 400MPa grade hot-dip galvanized sheet for new energy vehicles has the following chemical composition by weight percentage: C: 0.04-0.07%, Si: 0.06-0.09%, Mn: 0.24-0.36%, P: 0.009-0.03%, S: 0.008-0.013%, Als: 0.02-0.04%, B: 0.0015-0.003%, Ce: 0.008-0.015%, N: 0.005-0.015%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the mass fractions of N, Al, and B in the chemical composition of the low-cost new energy vehicle 400MPa grade hot-dip galvanized sheet of the present invention satisfy Formula 1: 0.011%≤9.26[B]+3.7[Al]-7.14[N]≤0.135%.

[0009] Furthermore, the mass fractions of P, Mn, and B in the chemical composition of the low-cost new energy vehicle 400MPa grade hot-dip galvanized sheet of the present invention satisfy Formula 2: 0.15% ≤ 8[B] + 0.37[Mn] + 4.4[P] ≤ 0.29%.

[0010] The hot-dip galvanized sheet of this invention has a yield strength of 230-260 MPa, a tensile strength of over 400 MPa, and an elongation after fracture (A). 50 ≥37%, plastic strain ratio r is 2.0~2.4, strain hardening index n≥0.21, bake hardening value BH2 is 35~55MPa.

[0011] The orientation density of the texture of the hot-dip galvanized steel sheet for automobiles described in this invention satisfies S {111}<110> +S {111}<112> ≥21; the S {111}<110> With S {111}<112> For having {111} <110> With {111} <112> Density of oriented tissue.

[0012] The production method of low-cost 400MPa grade hot-dip galvanized sheet for new energy vehicles according to the present invention includes steelmaking, hot rolling, pickling and galvanizing processes.

[0013] Furthermore, in the steelmaking process of the present invention, a continuously cast slab is obtained through smelting, RH refining, and continuous casting, wherein rare earth alloys are added during the RH refining process, and the superheat of the cast steel is controlled at 15-30°C.

[0014] Further, the hot rolling process of the application, the slab is in the furnace soaking time 150~205min, the soaking temperature 1190~1220℃, through rough rolling and finish rolling target thickness, wherein the finish rolling temperature is 900~925℃;Laminar flow cooling adopts the way of front concentrated cooling, coiling temperature 660~710℃, get hot-rolled coil.

[0015] Further, the pickling process of the application, the free acid concentration of pickling process is 150~200g / L, the emulsion temperature is 55℃~60℃, the cold rolling reduction is 70~85%.

[0016] Further, the galvanizing process of the application, the soaking temperature is 830~860℃, the holding time is 70~100s, the slow cooling temperature is 640~660℃, the cooling speed is 1~5℃ / s, the fast cooling temperature is 430~470℃, the cooling speed is 10~30℃ / s, the zinc pot temperature is 456~464℃, the finishing elongation is 0.8~1.3%.

[0017] The application principle and the beneficial technical effects of the application are as follows:

[0018] The BN formed by B and N in the automobile steel plate has precipitation strengthening effect, and by controlling the mass fraction of N and Al and B in the chemical composition of the automobile steel plate to satisfy the relationship formula two: 0.011% ≤ 9.26[B] + 3.7[Al] -7.14[N]≤0.135%, it is ensured that there is enough N to react with B and Al, that is, the strength and aging resistance of the material are improved; at the same time, the mass fraction of P and Mn and B satisfies the relationship formula three: 0.15% ≤8 [B]+0.37 [Mn]+4.4[P] ≤0.29%, the mechanical properties of the galvanized plate are guaranteed, and the three synergies realize the accurate regulation and control of carbonitride, and the B element not only can inhibit the grain boundary segregation of P to reduce the secondary cold working brittleness of the material, but also can improve the solid solubility of P in ferrite to realize the effect of solid solution strengthening. However, too high B content will reduce the grain boundary energy and reduce the recrystallization nucleation rate, causing the decrease of the r value of the galvanized plate, thereby deteriorating the formability of the material. The precipitation of Mn and rare earth Ce is beneficial to the nucleation of carbonitride, and Ce not only can promote the spheroidization and dispersion distribution of MnS precipitates, but also can promote the formation of gamma texture during annealing process, improve the aging resistance and formability of the galvanized plate. The low-temperature heating + high-temperature finish rolling and coiling process of hot rolling realizes the effective regulation and control of BN precipitation, avoids the segregation and ripening caused by excessive precipitation at high temperature, and is beneficial to the formation of {111} / / ND texture. Since Mn is a weak carbide forming element, high-temperature annealing and slow cooling are adopted to promote the precipitation of manganese-containing carbide and rare earth carbonitride, thereby reducing the content of free carbonitride, and thus guaranteeing the aging resistance and anti-dent resistance of the material.

[0019] The present application provides a hot-dip galvanized sheet for automobiles, the texture of which is oriented to satisfy S {111}<110> +S {111}<112> ≥21, so that the steel sheet finally obtains a γ texture which is favorable for forming. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 ODF diagram of {111} <110> and {111} <112> texture of hot-dip galvanized sheet of Example 1. DETAILED DESCRIPTION

[0021] In order to make the personnel in the technical field better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should belong to the scope of protection of the present application.

[0022] A 400MPa-grade hot-dip galvanized sheet for low-cost new energy vehicles, the production method comprising steelmaking, hot rolling, pickling and galvanizing processes, specifically as follows:

[0023] (1) Steelmaking process: through smelting, RH refining and continuous casting, a continuous casting slab is obtained, wherein a rare earth alloy is added in the RH refining process; the composition of the cast slab and the superheat of the molten steel in the casting process of each embodiment are shown in Table 1.

[0024] Table 1 Composition of cast slab (%) and superheat of molten steel (℃) of each embodiment

[0025]

[0026] (2) Hot rolling process: the slab is heated and kept in a heating furnace, and then hot-rolled coils are obtained through rough rolling, finish rolling, layer cooling and coiling; the specific hot rolling process parameters of each embodiment are shown in Table 2.

[0027] (3) Pickling and cold rolling process: the coil is pickled and cold-rolled to obtain a cold hard strip; the specific pickling and cold rolling process parameters of each embodiment are shown in Table 2.

[0028] Table 2 Hot rolling and pickling process parameters of each embodiment

[0029]

[0030] (4) Galvanizing process: the strip is heated, slowly cooled, rapidly cooled, galvanized and finished to obtain a galvanized strip; the specific galvanizing process parameters of each embodiment are shown in Table 3.

[0031] Table 3 Galvanizing process parameters of each embodiment

[0032]

[0033] The properties of the galvanized sheet strips of each example are shown in Table 4.

[0034] Table 4 Properties of the galvanized sheet of each example

[0035]

[0036] The ODF diagrams of the {111} <110> and {111} <112> textures of the hot-dip galvanized sheet of Example 1 are shown in Figure 1 It can be found from Figure 1 that the strength of the {111} <110> and {111} <112> textures are both obvious.

Claims

1. A 400 MPa grade hot-dip galvanized sheet for low-cost new energy vehicles, characterized by, The chemical composition of the hot-dip galvanized sheet is as follows in terms of percentage by weight: C: 0.04-0.07%, Si: 0.06-0.09%, Mn: 0.24-0.36%, P: 0.009-0.03%, S: 0.008-0.013%, Als: 0.02-0.04%, B: 0.0015-0.003%, Ce: 0.008-0.015%, N: 0.005-0.015%, the balance being Fe and inevitable impurities; the hot-dip galvanized sheet has a yield strength of 230-260 MPa, a tensile strength of 400 MPa or more, and an elongation A 50 ≥ 37%, a plastic strain ratio r of 2.0-2.4, a strain hardening index n ≥ 0.21, and a baking hardening value BH2 of 35-55 MPa.

2. The 400MPa-grade hot-dip galvanized sheet for low-cost new energy vehicles according to claim 1, characterized in that, The mass fraction of N and Al, B in the chemical composition of the hot galvanized plate satisfies formula one: 0.011% ≤ 9.26[B] + 3.7[Al] - 7.14[N] ≤ 0.135%.

3. The 400 MPa grade hot-dip galvanized sheet for low-cost new energy vehicles according to claim 1, characterized in that, The mass fraction of P and Mn, B in the chemical composition of the hot galvanized plate satisfies formula two: 0.15% ≤ 8[B] + 0.37[Mn] + 4.4[P] ≤ 0.29%.

4. The low-cost 400 MPa grade hot-dip galvanized sheet for new energy vehicles according to claim 1, characterized in that, The orientation density of the texture of the hot-dip galvanized sheet for automobiles satisfies S {111}<110> + S {111}<112> ≥ 21; the S {111}<110> and S {111}<112> is the density of the {111} <110> and {111} <112> orientation organizations.

5. The production method of the 400 MPa grade hot-dip galvanized sheet for low-cost new energy vehicles according to any one of claims 1-4, characterized in that, The process comprises steelmaking, hot rolling, pickling, and galvanizing.

6. The production method of a 400 MPa grade hot dip galvanized steel sheet for low cost new energy vehicles according to claim 5, characterized in that, The steelmaking process obtains a continuous casting slab through smelting, RH refining, and continuous casting, wherein a rare earth alloy is added in the RH refining process, and the overheat degree of the cast molten steel is controlled to be 15-30 DEG C.

7. The production method of a 400 MPa grade hot dip galvanized steel sheet for low cost new energy vehicles according to claim 5 or 6, characterized in that, The hot rolling process is performed on the slab at a furnace soaking holding time of 150-205 min, a soaking section temperature of 1190-1220 DEG C, a target thickness of the rough rolling and finish rolling, wherein the finish rolling temperature is 900-925 DEG C; the laminar cooling is performed in a front concentrated cooling mode, and the coiling temperature is 660-710 DEG C, thereby obtaining a hot rolled coil.

8. The production method of a 400 MPa grade hot dip galvanized steel sheet for low cost new energy vehicles according to claim 7, characterized in that, The pickling process is performed at a free acid concentration of 150-200 g / L, an emulsion temperature of 55-60 DEG C, and a cold rolling reduction of 70-85%.

9. The production method of a 400 MPa grade hot dip galvanized steel sheet for low cost new energy vehicles according to claim 8, characterized in that, The galvanizing process is performed at a soaking temperature of 830-860 DEG C, a holding time of 70-100 s, a slow cooling temperature of 640-660 DEG C, a slow cooling speed of 1-5 DEG C / s, a fast cooling temperature of 430-470 DEG C, a fast cooling speed of 10-30 DEG C / s, a zinc pot temperature of 456-464 DEG C, and a skin pass elongation of 0.8-1.3%.

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