CN116179941A - Low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel and preparation method thereof - Google Patents

Low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel and preparation method thereof Download PDF

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CN116179941A
CN116179941A CN202211585263.4A CN202211585263A CN116179941A CN 116179941 A CN116179941 A CN 116179941A CN 202211585263 A CN202211585263 A CN 202211585263A CN 116179941 A CN116179941 A CN 116179941A
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王亮赟
余灿生
王敏莉
常智渊
苏冠侨
刘庆春
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Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
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    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
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    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Abstract

The invention provides low-cost boron-containing 780 MPa-grade hot dip galvanized dual-phase steel and a preparation method thereof. The invention comprises the following chemical components in percentage by mass: c:0.10 to 0.15 percent, si:0.10 to 0.40 percent of Mn:1.45 to 1.85 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.010 percent, als:0.010 to 0.060 percent, N is less than or equal to 0.006 percent, cr:0.20% -0.60%, nb:0.01% -0.05%, ti:0.005% -0.040%, B:0.001% -0.0045% and the rest element is Fe and unavoidable impurities. The invention adopts a Ti+Nb+B composite microalloyed C-Si-Mn route, utilizes Ti to fix N element to fully play the role of B element in obviously improving hardenability, reduces alloy addition, and obtains the low-cost boron-containing 780 MPa-grade hot dip galvanized dual-phase steel, thereby greatly reducing cost and improving market competitiveness.

Description

Low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel and preparation method thereof
Technical Field
The invention relates to the technical field of cold-rolled sheet strip production, in particular to low-cost boron-containing 780 MPa-level hot-dip galvanized dual-phase steel and a preparation method thereof.
Background
Currently, low carbon green sustainable development aimed at achieving "carbon peak", "carbon neutralization" has been raised to unprecedented heights. The automobile industry is an important industry of carbon emission, and oil consumption and emission are greatly reduced along with the weight reduction of the automobile body. Advanced high-strength steel is the most developed automobile material in recent years. The dual-phase steel has the characteristics of high strength, low yield ratio and good formability, and becomes the first advanced high-strength steel for automobiles. Along with the continuous improvement of the corrosion resistance requirement, the use amount of the hot dip galvanized dual phase steel is larger and larger. In the face of serious market challenges, the development of low-cost high-performance products is favorable for improving market competitiveness, 780 MPa-grade hot dip galvanized dual-phase steel is advanced high-strength steel with the largest use amount, and is favored by various large steel enterprises and automobile manufacturing enterprises. Through the inquiry of related patents, patents which are relatively similar to low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel are as follows:
CN 109825768A discloses 780 MPa-grade ultrathin hot dip galvanized dual phase steel and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by mass: 0.03 to 0.07 percent of C, 0.001 to 0.10 percent of Si, 1.00 to 1.80 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.006 percent of S, 0.60 to 1.20 percent of Al, 0.010 to 0.050 percent of Nb, 0.010 to 0.050 percent of Ti, 0.10 to 0.30 percent of Cr, 0.20 to 0.40 percent of Mo, less than or equal to 0.004 percent of N, less than or equal to 0.20 percent of Ni, less than or equal to 0.20 percent of Cu, and the balance of Fe and unavoidable impurities; and C-0.003 xSi+0.014xMn-0.040xP-0.222 xS+0.023 xNi+0.003 xCu-0.004 xMo is not more than 0.085; mo+Cr is more than or equal to 0.30. The final rolling temperature of the hot rolling is 820-900 ℃, and the thickness of the hot rolled plate is 0.6-1.6 mm; the average cooling rate of the strip steel is more than or equal to 20 ℃/s, and the coiling temperature is 550-650 ℃; the cold rolling reduction rate is controlled to be 30-70%, the annealing temperature is 780-850 ℃, the heat preservation time is 30-200 s, the heat preserved strip steel is cooled, the cooling speed is more than or equal to 30 ℃/s, the dew point in the annealing furnace is minus 15-minus 60 ℃, and the hydrogen content H in the furnace is higher than or equal to 30 ℃/s 2 At 1-10%, the temperature of the strip steel when entering a zinc pot is 450-500 ℃, the temperature of zinc liquid is 450-470 ℃, the aluminum content of the zinc liquid is 0.15-0.25%, and the strip steel is cooled to below 200 ℃ at a cooling speed of more than or equal to 15 ℃/s after exiting the zinc pot. The addition of Mo with higher content (0.20-0.40%) increases alloy cost, and Al with higher content (0.60-1.20%) has the problem of easy water blocking during casting, which results in increased production difficulty and adverse effect on smooth production. The cooling speed requirement of the strip steel after the strip steel is discharged from the zinc pot is higher (more than or equal to 15 ℃/s), which is not beneficial to the development of production.
CN 109097705a discloses 800MPa grade cold-rolled hot-dip galvanized dual-phase steel and a production method thereof, wherein the cold-rolled hot-dip galvanized dual-phase steel comprises the following chemical components in percentage by mass: c:0.05-0.10%, mn:1.60-2.30%, als 0.010-1.0%, si:0.10-0.60%, nb:0.010-0.050%, cr:0.05-0.30%, mo:0.05-0.30%, P is less than or equal to 0.015%, S is less than or equal to 0.010%, N is less than or equal to 0.008%, the balance is Fe and unavoidable impurities, and noble metal elements Cr and Mo satisfy the relation: cr+Mo is more than or equal to 0.05 and less than or equal to 0.30, and C+Si/30+Mn/20 is more than or equal to 0.22. The casting superheat degree in the steelmaking process is 15-30 ℃, and the tapping temperature of the slab in the hot rolling process is 1180-1300 ℃ and heating time of 150-300 min, hot rolling finishing temperature of 850-950 ℃, average cooling rate of the strip steel is not less than 15 ℃/s when the strip steel temperature is not less than 620 ℃, coiling temperature of 500-620 ℃, cold rolling reduction rate is controlled within 40% -70%, hot galvanizing annealing temperature is 760-840 ℃, wherein the heating rate of not more than 760 ℃ is not more than 5 ℃/s, heat preservation time of 760-840 ℃ is 60-300s, cooling rate is not less than 15 ℃/s, dew point in an annealing furnace is 0-40 ℃, and H in a furnace is not less than 40 ℃ 2 The content is 1-5%, H 2 O/H 2 The temperature of the strip steel which is less than or equal to 1.0 and enters a zinc pot is 440-500 ℃, the temperature of the zinc liquid is 450-470 ℃, the aluminum content of the zinc liquid is 0.15-0.25%, and the alloy cost is increased by adding Mo (0.05-0.30%), mn (1.60% -2.30%) and Nb (0.010-0.050%) which are higher in content.
CN 109943765A discloses a 800MPa high yield ratio cold-rolled dual-phase steel and a preparation method thereof, wherein the cold-rolled dual-phase steel comprises the following chemical components in percentage by mass: c:0.08-0.10%, si:0.6-0.8%, mn:1.8-2.0%, cr:0.6-0.8%, als:0.03-0.06%, nb:0.04-0.06%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, and the balance is Fe and unavoidable impurities; heating a casting blank or an ingot to 1180-1260 ℃, rolling the casting blank or the ingot for 5-10 times by a roughing mill, wherein the thickness of the casting blank or the ingot after rough rolling is 30-50mm, rolling for 5-7 times by a hot continuous rolling unit, coiling into a steel coil within a T1 temperature range after rolling to a required thickness, and the T1 temperature range is 540-620 ℃; cold rolling reduction rate is 50-75%, cold rolled steel treated in the pickling cold rolling step is slowly heated to 170 ℃ and then quickly heated to a temperature range of T2, and heat preservation is carried out for 90-160 s; cooling to a T3 temperature range at a V1 speed, rapidly cooling to a T4 temperature range at a V2 cooling speed, performing overaging treatment for 350-700 s, and cooling to room temperature; the temperature range of T2 is 830-850 ℃, the temperature range of T3 is 640-700 ℃, and the temperature range of T4 is 300-340 ℃; the value range of V1 is 5-7deg.C/s, and the value range of V2 is 36-60deg.C/s. The high Si content is unfavorable for obtaining good surface quality, and meanwhile, the high Si content is a large difference between a cold rolling continuous annealing product and a hot galvanizing product.
Disclosure of Invention
According to the technical problems, the low-cost boron-containing 780 MPa-grade hot dip galvanized dual-phase steel and the preparation method thereof are provided. The invention adopts the following technical means:
the low-cost boron-containing 780 MPa-grade hot dip galvanized dual phase steel comprises the following chemical components in percentage by mass: c:0.10 to 0.15 percent, si:0.10 to 0.40 percent of Mn:1.45 to 1.85 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.010 percent, als:0.010 to 0.060 percent, N is less than or equal to 0.006 percent, cr:0.20% -0.60%, nb:0.01% -0.05%, ti:0.005% -0.040%, B:0.001% -0.0045% and the rest element is Fe and unavoidable impurities.
Preferably, the chemical components comprise the following components in percentage by mass: c:0.11 to 0.14 percent, si:0.20 to 0.35 percent, mn:1.50 to 1.70 percent, P is less than or equal to 0.012 percent, S is less than or equal to 0.008 percent, als:0.020 to 0.055 percent, N is less than or equal to 0.005 percent, cr:0.25% -0.45%, nb:0.015% -0.030%, ti:0.015 to 0.030 percent, B:0.002% -0.003%, and the balance of Fe and unavoidable impurities.
Further, the microstructure of the dual-phase steel is 50 to 65% of ferrite matrix (average grain size is 1.2 μm) +35 to 50% of martensite in island and block form (average grain size is 0.8 μm).
Further, the yield strength of the dual-phase steel is 436-492 MPa, the tensile strength is 785-840 MPa, and the elongation A is that 80 The value is 17.0-22.0%.
The principle and content design reasons of the chemical components of the invention are as follows:
c, one of the most important components in steel, determines the strength, plasticity and formability of the steel sheet. C is the element with the most obvious solid solution strengthening effect in the steel material, and meanwhile, the element C can obviously improve the hardenability and avoid pearlite transformation. When the content of C is too low, the stability of austenite and the hardenability of martensite in the dual-phase steel are reduced, so that the strength is lower, and the content of C in the dual-phase steel is generally not lower than 0.02%; when the C content is too high, the plasticity and weldability of the high-strength steel are lowered, and therefore, the C content of the present invention is 0.10 to 0.15%, preferably 0.11 to 0.14%.
Si plays a remarkable solid solution strengthening role in steel, effectively inhibits carbide precipitation, delays pearlite transformation and the like in the phase transformation process, but the excessively high content of Si can remarkably increase the deformation resistance during thin-gauge rolling, is unfavorable for the thin-gauge rolling, and silicon can improve the activity of carbon elements and promote the segregation of carbon in a manganese-rich region. When the two-phase region is insulated, the carbon diffusion to austenite is accelerated, the ferrite is obviously purified, the purity of the ferrite in the dual-phase steel is improved, the formation of the ferrite is promoted, the process window for forming the ferrite is enlarged, and therefore, the lower yield ratio is obtained. On the other hand, too high a silicon content increases brittleness of martensite, causes deterioration of toughness, and forms high melting point oxides on the surface of the steel sheet to affect the surface quality of the steel sheet, and it is necessary to reduce the silicon content in the steel as much as possible. Therefore, the Si content of the present invention is 0.10% to 0.40%, preferably 0.20% to 0.35%.
Mn is a good deoxidizer and desulfurizing agent, and is also a common solid solution strengthening element in steel. Mn can be combined with C to form various carbides to play a role in precipitation strengthening, and can be dissolved in a matrix to strengthen the solid solution strengthening effect. Mn is easy to combine with S to form high-melting point compound MnS, so that the hot embrittlement phenomenon caused by FeS is eliminated or weakened, and the hot workability of the steel is improved. Mn can improve austenite stability, shift the C curve to the right, and thereby significantly reduce the critical cooling rate of martensite. However, when the Mn content is too high, the Mn is easily enriched to the surface in the annealing process, and a large amount of manganese compounds are formed, so that the quality of surface galvanization is reduced. Therefore, the Mn content in the present invention is 1.45% to 1.85%, preferably 1.50% to 1.70%.
Al is a common deoxidizer in steel, and can form AlN pinning grain boundary at the same time, thereby playing a role of refining grains; in addition, al acts similarly to Si and can suppress carbide precipitation, so that austenite is sufficiently rich in carbon, but when the Al content is too high, the cost, the risk of inclusion, and the like are increased. Therefore, the Al content in the present invention is 0.010% to 0.060%, preferably 0.020% to 0.055%.
Cr can replace Mn, so that the strength of the steel is improved, and the segregation is reduced. Pearlite transformation can also be suppressed. In addition, the addition of a certain amount of Cr in the present invention can also improve the surface quality. After Cr is added, cr can react with oxygen and aggregate at the junction of the iron scale and the iron matrix to generate compact rich (Fe, cr) 2 O 3 Or (Fe, cr) 3 O 4 The presence of the spinel film prevents oxygen diffusion and reduces the generation of iron scales, so that the addition of Cr can effectively reduce the thickness of the iron scales and the formation of AlN and improve the adhesion performance of the iron scales, thereby effectively reducing pit and pit defects caused by the pressing of the iron scales, but when the Cr content is too high, the cost is increased and the strength, the elongation and the like are reduced. Therefore, the Cr content in the present invention is 0.20% to 0.60%, preferably 0.25% to 0.45%.
Nb exists mainly in a form of NbC in the dual-phase steel, and has remarkable functions of grain refinement and dispersion precipitation strengthening. In the hot galvanizing annealing heating process, undissolved NbC particles can pin ferrite grain boundaries, so that the effect of refining grains is achieved; the annealing temperature is increased to a two-phase region, so that the NbC is sufficiently dissolved in the matrix, and solid solution C atoms are enriched in austenite to improve the stability of the austenite; during cooling, nbC in the ferrite will re-precipitate, producing a significant precipitation strengthening. Accordingly, the Nb content is 0.01% to 0.05%, preferably 0.015% to 0.030%.
Ti is extremely easy to combine with N element to form TiN, so that N element is fixed, and meanwhile, the TiN is pinned with grain boundaries to inhibit austenite coarsening in the hot rolling heating process, so that the Ti has good grain refinement effect and can reduce timeliness and cold brittleness; in addition, ti and C have remarkable precipitation strengthening effect. The N element cannot be completely fixed due to the too low Ti content, so that the B element is influenced to play a role in obviously improving the hardenability; ti content is too high, so that liquid-out TiN is easy to generate, the plasticity of the material is deteriorated, and the stamped part is severely cracked. Therefore, the Ti content is selected to be 0.005% to 0.040%, preferably 0.015% to 0.030%.
B has the effect of obviously improving the hardenability of austenite, and effectively promotes the formation of martensite in the dual-phase steel; meanwhile, the B content is very easy to combine with N in steel to form BN, thereby playing a role of precipitation strengthening, but the B content is too high, so that the toughness of the steel is deteriorated, and the manufacturing cost of the steel is increased, therefore, the B content is selected to be 0.001-0.0045%, and preferably 0.002-0.003%.
In order to achieve the aim of the invention, the invention also discloses a technical scheme, namely a low-cost boron-containing 780 MPa-grade hot dip galvanized dual-phase steel and a preparation method thereof, wherein the method comprises the following main specific process steps of smelting, hot rolling, acid rolling and hot dip galvanizing:
(a) Smelting: smelting according to chemical components of low-cost 780 MPa-level boron-containing hot dip galvanized dual-phase steel, and casting into a slab;
(b) Hot rolling: heating, descaling, rough rolling, finish rolling and laminar cooling the slab to obtain a hot rolled coil; the heating temperature is 1200-1250 ℃, the finish rolling start temperature is 1000-1080 ℃, the finish rolling temperature is 850-900 ℃, the coiling temperature is 580-630 ℃, U-shaped coiling (the coiling temperature of 80m before the strip head is 610-660 ℃ and the coiling temperature of 100m after the strip tail is 620-670 ℃) is adopted, the laminar cooling adopts a sparse cooling mode, and the thickness of the hot rolled coil is 2.0-6.0 mm.
(c) Acid rolling procedure: the hot rolled coil is subjected to pickling and then cold-rolled into cold-rolled thin strip steel, the thickness of a finished product is 0.6-2.5 mm, and the total rolling reduction rate of the cold rolling is 45-68%.
(d) Hot galvanizing process: the cold rolled thin strip steel is firstly heated to 300 ℃, 700 ℃ and 780-820 ℃ in sections at heating rates of 15-20 ℃/s, 4-10 ℃/s and 0.5-3 ℃/s respectively; soaking and preserving heat for 25-90 s, then slowly cooling to 700-760 ℃ at the speed of 1-5 ℃/s, then rapidly cooling to 60-120 ℃ at the speed of 20-45 ℃/s, preserving heat for 15-40 s, rapidly heating the strip steel to 450-470 ℃ by using an inductor for balanced galvanization, wherein the time is 10-40 s, and cooling to room temperature at the speed of more than or equal to 5 ℃/s after leaving a zinc pool. The unit speed is 70-160m/min, the unit speed gradually decreases along with the increase of the cold rolling thickness of the material, and the unit speed is reduced by 15m/min when the thickness specification of the cold rolling thin strip steel is increased by 0.3 mm. The flattening elongation is in the range of 0.30-0.65%, and the flattening elongation is reduced by 0.05% when the thickness of the material is increased by 0.3 mm.
The invention adopts a Ti+Nb+B composite microalloyed C-Si-Mn route, utilizes Ti to fix N element to fully play the role of obviously improving hardenability of B element, and reduces the alloy addition; meanwhile, the formed TiN inhibits austenite coarsening in the hot rolling heating process, and Nb element is added to pin grain boundary refined grains in the hot rolling finish rolling process. Meanwhile, the advantages of the production line are fully exerted, the strip steel is heated to a two-phase region (ferrite and austenite) for heat preservation for a period of time, and then the strip steel is rapidly cooled to a temperature below the Ms point to form martensite (reduce the addition amount of alloy); and the reheating function is utilized to rapidly raise the temperature of the strip steel to 460 ℃ for hot galvanizing (improve the corrosion resistance of the strip steel), and the tempering of martensite reduces the supersaturation degree, reduces the hardness difference between ferrite and martensite, improves the reaming performance, and obtains the low-cost boron-containing 780 MPa-grade hot galvanized dual-phase steel. Greatly reduces the cost, improves the market competitiveness, generates remarkable economic benefit and optimizes the product structure.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to the drawings without inventive effort to a person skilled in the art.
FIG. 1 is a scanning electron microscope image of the low-cost 780 MPa-grade boron-containing hot dip galvanized dual phase steel.
FIG. 2 is a schematic diagram of temperature control during the production process of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The embodiment provides two groups of low-cost boron-containing 780 MPa-level hot dip galvanized dual phase steel, and the chemical composition of the dual phase steel is shown in a table 1;
table 1 in the examples cold rolled duplex steel composition (wt.%)
Numbering device C Si Mn Cr Nb Ti B P S Als
1 0.13 0.25 1.65 0.28 0.020 0.022 0.0025 0.010 0.003 0.050
2 0.12 0.32 1.60 0.32 0.023 0.031 0.0028 0.008 0.002 0.037
The preparation method of the low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel comprises the following specific processes:
A. smelting: preparing a hot dip galvanized dual phase steel slab with chemical compositions shown in table 1 through a smelting process;
B. hot rolling: as shown in fig. 2, the slab is heated, descaled, hot rolled and cooled in a laminar flow to obtain a hot rolled coil, and specific hot rolling process parameters are shown in table 2;
table 2 main process parameters of hot-dip galvanized dual-phase steel with low cost and 780MPa grade boron content in examples
Figure BDA0003991956720000071
C. Acid rolling procedure: pickling the hot rolled coil, and cold-rolling the hot rolled coil into thin strip steel, wherein the thicknesses of strip steel No. 1 and strip steel No. 2 are respectively 1.2mm and 1.0mm, and the cold rolling reduction rates are respectively 60.0% and 64.3%;
D. hot galvanizing annealing process: the cold-rolled thin strip steel is manufactured into a required product after hot galvanizing annealing treatment, firstly, the strip steel is slowly heated to a soaking temperature for a period of time to form a certain amount of ferrite and austenite proportion, then the strip steel is sequentially subjected to slow cooling (a small amount of oriented auxiliary pig iron body is formed, the stability of the residual austenite is enhanced), fast cooling (cooling to below an Ms point to enable supercooled austenite to be converted into martensite), then the strip steel is heated to the hot galvanizing temperature (450-470 ℃) by utilizing an inductor to carry out balanced galvanizing (the supersaturation degree of martensite is reduced, the hardness difference between ferrite and martensite is reduced, the reaming performance is improved), finally, the strip steel is cooled to room temperature, the strip steel shape is regulated by a finishing machine, and the yield strength is increased; the specific hot dip galvanizing annealing process parameters are shown in table 3:
table 3 main process parameters of hot dip galvanizing annealing process of low cost boron 780MPa grade hot dip galvanized dual phase steel in examples
Figure BDA0003991956720000072
The microstructure of the high-strength steel with different types prepared by the process is shown in figure 1, and the low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel is tested according to GB/T228-2010 Metal Material room temperature tensile test method, and the mechanical properties are shown in the following table 4: as can be found by comparing the application with the prior art, the invention reduces the addition of other alloys, reduces the cost and can meet the requirement
Table 4 example-mechanical properties of low cost boron-containing 780MPa grade hot dip galvanized dual phase steel compared to prior art
Figure BDA0003991956720000073
Figure BDA0003991956720000081
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (6)

1. The low-cost boron-containing 780 MPa-grade hot dip galvanized dual phase steel is characterized by comprising the following chemical components in percentage by mass: c:0.10 to 0.15 percent, si:0.10 to 0.40 percent of Mn:1.45 to 1.85 percent, P is less than or equal to 0.015 percent, S is less than or equal to 0.010 percent, als:0.010 to 0.060 percent, N is less than or equal to 0.006 percent, cr:0.20% -0.60%, nb:0.01% -0.05%, ti:0.005% -0.040%, B:0.001% -0.0045% and the rest element is Fe and unavoidable impurities.
2. The low-cost boron-containing 780 MPa-grade hot-dip galvanized dual phase steel according to claim 1, wherein the chemical components comprise in mass percent: c:0.11 to 0.14 percent, si:0.20 to 0.35 percent, mn:1.50 to 1.70 percent, P is less than or equal to 0.012 percent, S is less than or equal to 0.008 percent, als:0.020 to 0.055 percent, N is less than or equal to 0.005 percent, cr:0.25% -0.45%, nb:0.015% -0.030%, ti:0.015 to 0.030 percent, B:0.002% -0.003%, and the balance of Fe and unavoidable impurities.
3. The low cost 780MPa class hot dip galvanized dual phase steel containing boron according to claim 1, wherein the dual phase steel microstructure is 50-65% ferrite matrix + 35-50% island and block martensite.
4. The low cost 780MPa grade boron-containing hot dip galvanized dual phase steel according to claim 1, characterized in that the dual phase steel has a yield strength of 436-492 MPa, a tensile strength of 785-840 MPa, an elongation a 80 The value is 17.0-22.0%.
5. The method for producing low-cost 780 MPa-grade hot-dip galvanized dual phase steel containing boron according to any one of claims 1 to 4, comprising the following steps:
(a) Smelting: smelting according to chemical components of low-cost 780 MPa-level boron-containing hot dip galvanized dual-phase steel, and casting into a slab;
(b) Hot rolling: heating, descaling, rough rolling, finish rolling and laminar cooling the slab to obtain a hot rolled coil; the heating temperature is 1200-1250 ℃, the finish rolling start temperature is 1000-1080 ℃, the finish rolling temperature is 850-900 ℃, the coiling temperature is 580-630 ℃, U-shaped coiling is adopted, the laminar cooling adopts a sparse cooling mode, and the thickness of the hot rolled coil is 2.0-6.0 mm;
(c) Acid rolling procedure: pickling the hot rolled coil, and cold-rolling the hot rolled coil into cold-rolled thin strip steel, wherein the thickness of a finished product is 0.6-2.5 mm, and the total rolling reduction rate of the cold rolling is 45-68%;
(d) Hot galvanizing process: the cold rolled thin strip steel is firstly heated to 300 ℃, 700 ℃ and 780-820 ℃ in sections at heating rates of 15-20 ℃/s, 4-10 ℃/s and 0.5-3 ℃/s respectively; soaking, keeping the temperature for 25-90 s, slowly cooling to 700-760 ℃ at a speed of 1-5 ℃/s, then rapidly cooling to 60-120 ℃ at a speed of 20-45 ℃/s, keeping the temperature for 15-40 s, rapidly heating the strip steel to 450-470 ℃ by using an inductor for balanced galvanization, wherein the time is 10-40 s, cooling to room temperature at a speed of more than or equal to 5 ℃/s after discharging a zinc pool, the unit speed is 70-160m/min, the unit speed is gradually reduced along with the increase of the cold rolling thickness of the material, the unit speed is reduced by 15m/min each time when the thickness of the cold rolling thin strip steel is increased, the range of the flat elongation is 0.30-0.65%, and the flat elongation is reduced by 0.05% each time when the thickness of the material is increased by 0.3 mm.
6. The method according to claim 5, wherein during the U-shaped curling, the coiling temperature of 80m before the head is 610-660 ℃ and the coiling temperature of 100m after the tail is 620-670 ℃.
CN202211585263.4A 2022-12-09 2022-12-09 Low-cost boron-containing 780 MPa-level hot dip galvanized dual-phase steel and preparation method thereof Pending CN116179941A (en)

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