CN114045437A - Enhanced plasticity dual-phase steel for 800 MPa-level hot galvanizing and preparation method thereof - Google Patents

Enhanced plasticity dual-phase steel for 800 MPa-level hot galvanizing and preparation method thereof Download PDF

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CN114045437A
CN114045437A CN202111354574.5A CN202111354574A CN114045437A CN 114045437 A CN114045437 A CN 114045437A CN 202111354574 A CN202111354574 A CN 202111354574A CN 114045437 A CN114045437 A CN 114045437A
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mpa
phase steel
hot galvanizing
steel
dual
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余灿生
郑之旺
郑昊青
王敏莉
周磊磊
黄洁
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Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
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Pangang Group Panzhihua Iron and Steel Research Institute Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/16—Control of thickness, width, diameter or other transverse dimensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/28—Control of flatness or profile during rolling of strip, sheets or plates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/46—Roll speed or drive motor control
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • 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
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • 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

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Abstract

The invention belongs to the technical field of cold-rolled strip production, and particularly relates to reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing and a preparation method thereof. The invention aims to provide reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing and a preparation method thereof. According to the invention, through reasonable design of chemical components of the dual-phase steel and adjustment of preparation process parameters, the yield strength of the obtained enhanced plasticity dual-phase steel for 800 MPa-level hot galvanizing is 455-525 MPa, the tensile strength is 810-880 MPa, and the elongation A is8023.0 to 29.0 percent; the microstructure of the steel plate is composed of 40-50% of ferrite, about 25-30% of martensite, 5-25% of bainite and 5-10% of residual austenite.

Description

Enhanced plasticity dual-phase steel for 800 MPa-level hot galvanizing and preparation method thereof
Technical Field
The invention belongs to the technical field of cold-rolled strip production, and particularly relates to reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing and a preparation method thereof.
Background
With the rapid development of science and technology, the development of automotive steel towards high strength has become an inevitable trend in order to reduce the weight of the automobile body and improve the safety performance of the automobile body. The high-strength steel plate is adopted to replace the traditional material, so that the energy absorption capacity can be obviously improved, the elastic strain area is enlarged, the deformation resistance of the component is increased, the dent resistance is improved while the high formability is maintained, and conditions are created for realizing the light weight of the automobile. The dual-phase steel is the most widely used high-strength steel, the structure of the dual-phase steel mainly comprises a softer ferrite matrix and martensite with higher strength, and the structure has the performance characteristics of lower yield ratio, higher strength and the like, and is suitable for producing stamping parts; however, with the advance of light weight of automobiles, the usage amount of the dual-phase steel is larger and larger, the high-strength grade product instead of the low-strength grade product becomes an irreversible trend, the corresponding plasticity of the low-strength product is difficult to achieve after the strength is increased, the complex (extremely complex) part is easy to crack in the stamping process, and the plasticity (required elongation A) of the current 800MPa cold-rolled dual-phase steel is high80Not less than 14 percent) can not meet the requirement of complex (extremely complex) parts, and the plasticity (elongation A) needs to be greatly improved80Not less than 20%), require tongHigh plasticity is achieved by introducing a certain amount of retained austenite to generate the TRIP effect.
Patent CN109825768A discloses 780 MPa-grade ultrathin specification hot-dip galvanized dual-phase steel and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by weight: c: 0.03 to 0.07 percent of Si: 0.001-0.10%, Mn: 1.00-1.80%, P is less than or equal to 0.012%, S is less than or equal to 0.006%, Al: 0.60 to 1.20%, Nb: 0.010-0.050%, Ti: 0.010-0.050%, Cr: 0.10-0.30%, Mo: 0.20-0.40%, N is less than or equal to 0.004%, Ni is less than or equal to 0.20%, and Cu is less than or equal to 0.20%. The rolling process adopts the steps that the final rolling temperature is 820-900 ℃, the thickness of a hot rolled plate is 0.6-1.6 mm, the hot rolled plate is rapidly cooled after final rolling, the rapid cooling rate is more than or equal to 20 ℃/s, the coiling temperature is 550-650 ℃, and the cold rolling reduction rate is controlled to be 30-70%; the hot galvanizing comprises strip steel heating, soaking, slow cooling, fast cooling, balanced heat preservation and hot galvanizing, wherein the soaking temperature is 780-850 ℃, the soaking time is 30-200 s, the strip steel after heat preservation is cooled, the cooling speed is more than or equal to 30 ℃/s, the dew point in an annealing furnace is-15 to-60 ℃, and the hydrogen content in the furnace is H21-10%, the temperature of the strip steel when the strip steel enters a zinc pot is 450-500 ℃, the temperature of zinc liquid is 450-470 ℃, and the aluminum content of the zinc liquid is 0.15-0.25%; the strip steel is cooled to below 200 ℃ at a cooling speed of more than or equal to 15 ℃/s. The steel contains more noble metal elements such as Nb and Mo, so that the cost is increased, the thickness of a hot rolled plate is small, the natural temperature drop is large, and the process stability control difficulty is large. In addition, the product with different thickness specifications is not subjected to fine adjustment in the process, and the stability and controllability of the product performance are difficult to realize.
Meanwhile, chinese patent CN110331341A discloses a high formability and high strength hot-dip galvanized dual-phase steel and a production method thereof, which comprises the following chemical components by weight percent: c: 0.05-0.10%, Si: 0.20 to 0.50%, Mn: 1.50-2.50%, Cr: 0.40-1.00%, Mo: 0.10 to 0.50%, Al: 0.02-0.06%, Nb: 0.010-0.050%, V: 0.04-0.10 percent of Fe, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.006 percent of N, and the balance of Fe and inevitable impurities. In the hot rolling procedure, the initial rolling temperature of finish rolling is 1000-1100 ℃, the final rolling temperature is 840-920 ℃, and the coiling temperature is 580-630 ℃; the cold rolling reduction rate is 40-70%; in the hot galvanizing annealing process, heating is carried out in an oxidation furnace, then recrystallization annealing is carried out in a reduction furnace with protective atmosphere, and finally hot galvanizing is carried out in a zinc pot under the sealing condition; the heating temperature in the oxidation furnace is controlled to be 690-750 ℃, the annealing temperature in the hot galvanizing annealing process is 760-800 ℃, the zinc bath is rapidly cooled from the annealing temperature to the temperature of 440-460 ℃ of a zinc bath nose, the rapid cooling rate CR1 is 50-80 ℃/s, and the zinc bath is cooled to the room temperature at the final cooling rate CR2 of 4-10 ℃/s after being galvanized. The chemical components of the steel contain precious alloys Mo and Nb and relatively more Cr, so that the alloy cost is increased; in addition, the product with different thickness specifications is not subjected to fine adjustment in the process, and the stability and controllability of the product performance are difficult to realize.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing and a preparation method thereof.
The invention aims to solve the first technical problem of providing reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing, which comprises the following chemical components in percentage by weight: c: 0.16-0.21%, Si: 0.20 to 0.40%, Mn: 1.75-2.40%, Als: 0.50-0.80%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, N is less than or equal to 0.0060%, and the balance of Fe and inevitable impurities.
Preferably, the reinforced plastic dual-phase steel for 800 MPa-grade hot galvanizing comprises the following chemical components in percentage by weight: c: 0.165-0.205%, Si: 0.25 to 0.35%, Mn: 1.85-2.05%, Als: 0.65-0.80%, P is less than or equal to 0.010%, S is less than or equal to 0.005%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities.
The reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing has the yield strength of 455-525 MPa, the tensile strength of 810-880 MPa and the elongation A8023.0 to 29.0%.
Wherein the microstructure of the enhanced plasticity dual-phase steel for the 800 MPa-level hot galvanizing consists of 40-50% of ferrite, 25-30% of martensite, 5-25% of bainite and 5-10% of austenite.
The second technical problem to be solved by the invention is to provide a preparation method of the reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing, which comprises the following steps:
a. smelting: smelting according to the set chemical components, and casting into a plate blank;
b. a hot rolling procedure: heating, dephosphorizing, roughly rolling, finely rolling and laminar cooling the plate blank to obtain a hot-rolled coil;
c. acid rolling process: pickling the hot rolled coil, and cold rolling the hot rolled coil into thin strip steel with the thickness of 0.7-2.5 mm; the cold rolling reduction rate is 50-74%;
d. hot galvanizing procedure: and (3) carrying out hot galvanizing annealing on the thin strip steel to prepare the required hot galvanizing dual-phase steel.
Wherein in the step b, the finishing temperature is 860-930 ℃.
In the step b, the laminar cooling adopts a front-section cooling mode, and the cooling rates of the upper surface and the lower surface are 40-50% and 70-80% respectively.
In the step b, the coiling temperature of the head and the tail of the strip steel is 670-730 ℃, and the coiling temperature of the middle part of the strip steel is 630-680 ℃.
And c, gradually reducing the cold rolling reduction rate along with the increase of the cold rolling thickness of the thin strip steel. When the thickness of the thin strip steel is increased by 0.3mm, the thickness of the hot rolled plate is correspondingly adjusted, and the cold rolling reduction rate is reduced by 4%.
In the step d, the thin strip steel is heated in a segmented mode, the preheating section is heated to 290-320 ℃, and the heating speed is 15.0-20.0 ℃/s; heating the mixture to 690-720 ℃ in a first heating period at a heating speed of 4.0-10.0 ℃/s; the two heating sections and the three heating sections are heated to 765-795 ℃, and the heating speed is 0.50-3.0 ℃/s.
In the step d, the target temperature is increased by 10 ℃ when the thickness of the thin strip is increased by 0.6mm in the sectional heating process.
In the step d, after the thin strip is heated in sections, soaking and heat preservation are carried out for 25-90 s, then slow cooling is carried out to 680-740 ℃ and fast cooling is carried out to 450-470 ℃ respectively at the speed of 1-5 ℃/s and 10-25 ℃/s, then galvanizing treatment is carried out after balanced heat preservation, the time is 10-40 s, and the thin strip is cooled to the room temperature at the speed of more than or equal to 5 ℃/s after being taken out of a zinc pool.
Wherein in the step d, the speed of the unit is 70-160 m/min. The speed of the machine set is gradually reduced along with the increase of the cold-rolled thickness of the thin strip steel, and the speed of the machine set is reduced by 15m/min when the thickness specification of the cold-rolled thin strip steel is increased by 0.3 mm.
Wherein, in the step d, the flat elongation is within the range of 0.35-0.65%. The flat elongation of the material is reduced by 0.05% when the thickness of the material is increased by 0.3 mm.
Has the advantages that: the enhanced plasticity dual-phase steel for 800MPa hot galvanizing provided by the invention has the yield strength of 455-525 MPa, the tensile strength of 810-880 MPa and the elongation A8023.0 to 29.0 percent; the microstructure comprises 40 to 50% of ferrite having an average grain size of 8.5 μm, about 25 to 30% of martensite having an island-like distribution and an average grain size of 2.0 μm, 5 to 25% of bainite having an average grain size of 4.5 μm, and 5 to 10% of retained austenite.
According to the dual-phase steel disclosed by the invention, the generation of cementite is inhibited by adding Si and Al, the stability of austenite is increased, a small amount of austenite is stored to room temperature, and the residual austenite generates transformation induced plasticity (TRIP effect) in the plastic deformation process, so that the elongation of the product is greatly improved. Meanwhile, the dual-phase steel eliminates the addition of micro alloy elements such as precious alloy elements Mo, Nb, Ti and the like, reduces the alloy cost, reduces the alloy content, reduces the recrystallization temperature and the cold rolling load, thereby realizing larger cold rolling reduction and improving the deformation energy storage.
In the hot galvanizing process for preparing the dual-phase steel, the lower soaking temperature is adopted, the alloy and process cost is reduced, and good economic benefit is generated. And the fine adjustment of each process is carried out according to the thickness of the product, and the product performance is stable and controllable through flexible control.
Drawings
FIG. 1 is a metallographic photograph of a dual phase steel according to example 2 of the present invention; FIG. 2 is a scanning electron micrograph of a dual phase steel obtained in example 2 of the present invention; FIG. 3 is a graph showing the measurement of the residual austenite content of the dual phase steel obtained in example 1 of the present invention.
Detailed Description
The invention firstly provides reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing, which comprises the following chemical components in percentage by weight: c: 0.16-0.21%, Si: 0.20 to 0.40%, Mn: 1.75-2.40%, Als: 0.50-0.80%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, N is less than or equal to 0.0060%, and the balance of Fe and inevitable impurities.
Preferably, the reinforced plastic dual-phase steel for 800 MPa-grade hot galvanizing comprises the following chemical components in percentage by weight: c: 0.165-0.205%, Si: 0.25 to 0.35%, Mn: 1.85-2.05%, Als: 0.65-0.80%, P is less than or equal to 0.010%, S is less than or equal to 0.005%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities.
The following alloy elements have the functions of the reinforced plastic dual-phase steel for 800MPa hot galvanizing of the invention:
carbon: c is the most obvious element for the solid solution strengthening effect in the steel material, the solid solution C content in the steel is increased by 0.1 percent, and the strength can be improved by about 450 MPa. And directly influences the volume fractions of bainite, martensite and the like in the reinforced plastic dual-phase steel after the treatment of the critical zone, and when the content of C is too low, the stability of austenite and the hardenability of martensite are reduced, so that the strength is lower. A large amount of alloying elements such as Mn, Cr, etc. are required to be added to secure the strength, resulting in an increase in cost. Therefore, the content of C in the invention is 0.16-0.21%, preferably 0.165-0.205%.
Silicon: si can be dissolved in ferrite and austenite in a solid solution mode to improve the strength of the steel, the effect of the Si is second to C, P, and the Si is stronger than Mn, Cr, Ti, Ni and other elements; si can also inhibit carbide in ferrite from being precipitated, so that solid-solution C atoms are fully enriched in austenite, and the Si content with excessively low stability is improved, and residual austenite is difficult to obtain at room temperature. However, when the content of Si is too high, the surface iron scale formed by Si in the heating furnace is difficult to remove, so that the dephosphorization difficulty is increased; meanwhile, SiO is easily enriched and formed on the surface in the annealing process2Resulting in surface defects such as skip plating. Therefore, the Si content of the present invention is 0.20 to 0.40%, preferably 0.25 to 0.35%.
Manganese: mn is added to increase hardenability over the cooling rate capability range of a conventional continuous annealing/galvanizing line. Mn also contributes to solid solution strengthening, which increases tensile strength and strengthens the ferrite phase, thereby contributing to stabilization of the retained austenite. Mn reduces the austenite to ferrite transformation temperature range of the complex phase steel. In addition, Mn is a good deoxidizer and desulfurizer, and is also a solid solution strengthening element commonly used in steel. Mn can be combined with C to form various carbides to play a role in precipitation strengthening, and can also be dissolved in a matrix to enhance the solid solution strengthening effect. Mn is easily combined with S to form a high melting point compound MnS, thereby eliminating or weakening hot embrittlement caused by FeS and improving hot workability of the steel. Mn can improve the stability of austenite and shift the C curve to the right, thereby obviously reducing the critical cooling rate of martensite. However, when the Mn content is too high, the surface is easily enriched in the annealing process to form a large amount of manganese compounds, thereby causing the reduction of the surface galvanizing quality. Therefore, the Mn content in the present invention is 1.75 to 2.40%, preferably 1.85 to 2.05%.
Aluminum: al is a strong deoxidizing element, a certain amount of Al needs to be added in order to ensure that the oxygen content in the steel is as low as possible, meanwhile, soluble Al is often used as a micro-alloy element to combine nitrogen in the steel, and finely dispersed AlN prevents austenite grains from growing. During the gamma-alpha transformation, AlN nucleates, thereby accelerating the austenite transformation. Meanwhile, Al and Si have the same function of inhibiting cementite generation, and are beneficial to obtaining residual austenite at room temperature; however, addition of a large amount of Al tends to form alumina agglomerates. Therefore, the content of Als in the present invention is 0.50 to 0.80%, preferably 0.65 to 0.80%.
In the aspect of chemical composition design, Si and Al are added to inhibit cementite generation, so that the stability of austenite is improved, a small amount of austenite (about 5%) is stored to room temperature, and transformation induced plasticity (TRIP effect) is generated in the residual austenite in the plastic deformation process, so that the elongation of the product is greatly improved. Meanwhile, the dual-phase steel eliminates the addition of micro alloy elements such as precious alloy elements Mo, Nb, Ti and the like, reduces the alloy cost, reduces the alloy content, reduces the recrystallization temperature and the cold rolling load, thereby realizing larger cold rolling reduction and improving the deformation energy storage.
The invention also provides a preparation method of the reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing, which comprises the following steps:
a. smelting: smelting according to the set chemical components, and casting into a plate blank;
b. a hot rolling procedure: heating, dephosphorizing, roughly rolling, finely rolling and laminar cooling the plate blank in the step a to obtain a hot rolled coil; the finishing temperature is 860-930 ℃; the laminar cooling adopts a front-section cooling mode, and the cooling rates of the upper surface and the lower surface are 40-50% and 70-80% respectively; the coiling temperature of 100m of the head and the tail of the U-shaped coiled steel coil is 670-730 ℃, the coiling temperature of the middle part of the strip steel is 630-680 ℃, and the coiling temperature is different from the coiling temperature of the middle part due to large temperature drop of the head and the tail of the strip steel.
c. Acid rolling process: c, pickling the hot rolled coil in the step b, and cold rolling the hot rolled coil into thin strip steel with the thickness of 0.7-2.5 mm; the cold rolling reduction rate is 50-74%, the cold rolling reduction rate is gradually reduced along with the increase of the cold rolling thickness of the thin strip steel, the thickness of the hot rolling plate is correspondingly adjusted every time the thickness of the thin strip steel is increased by 0.3mm, and the cold rolling reduction rate is reduced by 4%.
The load is larger when the product is cold-rolled thicker, so the cold rolling reduction influenced by the hot rolling raw material is lower as the thickness of the hot rolling raw material is increased, therefore, the cold rolling reduction is gradually reduced as the cold rolling thickness of the cold-rolled thin strip steel is increased, the thickness of the hot-rolled thin strip steel is correspondingly adjusted every time the thickness of the cold-rolled thin strip steel is increased by 0.3mm, and the cold rolling reduction is reduced by 4%.
d. Hot galvanizing procedure: c, heating the thin strip steel in the step c in a sectional manner, wherein the preheating section is heated to 290-320 ℃, and the heating speed is 15.0-20.0 ℃/s; heating the mixture to 690-720 ℃ in a first heating period at a heating speed of 4.0-10.0 ℃/s; heating the second section and the third section to 765-795 ℃, wherein the heating speed is 0.50-3.0 ℃/s, and the target temperature is increased by 10 ℃ when the thickness of the thin strip steel is increased by 0.6 mm; and then, after soaking and heat preservation for 25-90 s, slowly cooling to 680-740 ℃ and rapidly cooling to 450-470 ℃ respectively at the speed of 1-5 ℃/s and 10-25 ℃/s, after balanced heat preservation for a period of time, entering a zinc pool for galvanizing treatment, wherein the time is 10-40 s, and after being discharged from the zinc pool, cooling to room temperature at the speed of more than or equal to 5 ℃/s.
Wherein the speed of the hot galvanizing unit is 70-160 m/min. The speed of the machine set is gradually reduced along with the increase of the cold-rolled thickness of the thin strip steel, and the speed of the machine set is reduced by 15m/min when the thickness specification of the cold-rolled thin strip steel is increased by 0.3 mm. The flat elongation is in the range of 0.35-0.65%. The flat elongation of the material is reduced by 0.05% when the thickness of the material is increased by 0.3 mm.
The essence of the flexible control lies in that the stable control of the performance is realized by adjusting the cold rolling reduction (the cold rolling reduction is reduced by 4 percent when the thickness of the strip steel is increased by 0.3 mm), the first heating section, the second heating section, the soaking temperature (the target temperature is increased by 10 ℃ when the thickness is increased by 0.6 mm), the unit speed (the unit speed is reduced by 15m/min when the thickness is increased by 0.3 mm), the leveling elongation (the leveling elongation is reduced by 0.05 percent when the thickness is increased by 0.3 mm) and other means according to the thickness of the finished product, namely the flexible control, the control difficulty lies in that the whole process is adjusted according to the difference of raw materials, and the stable and controllable mechanical performance can be obtained only by fine regulation.
The soaking temperature, namely the 765-795 ℃ heat preservation process after the two-stage heating, influences the ratio of ferrite to austenite in the two-phase zone, and has great influence on the final structure and performance.
The invention controls slow cooling parameters to ensure the amount of the super-cooled austenite decomposed at high temperature to form the oriented periphytic ferrite and the stability of the residual austenite so as to retain residual austenite in the cooling process.
The rapid cooling end point and the balanced galvanizing function of the invention are that on one hand, the coating layer attached to the surface of the strip steel plays a role of corrosion prevention, and in addition, a small amount of bainite is formed at the stage, so that the secondary carbon enrichment and the stability enhancement of the residual austenite are realized.
The invention is further illustrated and described by the following examples.
Examples
The invention provides two groups of reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing, and the chemical components of the reinforced plastic dual-phase steel are shown in a table 1;
TABLE 1800 MPa-grade chemical composition (wt.%) of reinforced plastic dual-phase steel for hot galvanizing
Examples C si Mn P S N Als
1 0.180 0.25 1.90 0.010 0.003 0.0024 0.70
2 0.200 0.30 2.00 0.006 0.002 0.0032 0.75
The preparation method of the reinforced plastic dual-phase steel for 800 MPa-level hot galvanizing comprises the following specific processes:
A. smelting: preparing a dual-phase steel plate blank with chemical components shown in the table 1 through a smelting process;
B. a hot rolling procedure: heating, dephosphorizing, hot rolling and laminar cooling the plate blank to obtain a hot rolled coil, wherein the specific hot rolling process parameters are shown in table 2;
table 2800 MPa hot-rolling main technological parameters of reinforced plastic dual-phase steel for hot galvanizing
Examples The initial rolling temperature/. degree.C Final Rolling temperature/. degree.C Coiling temperature/. degree.C
1 1078 883 647
2 1063 917 635
C. Acid rolling process: after being acid washed, the hot rolled coil is cold rolled into thin strip steel, wherein the thickness of the thin strip steel in the embodiment 1 is 1.0mm, and the cold rolling reduction rate is 70.0 percent; the thickness of the thin strip steel of the embodiment 2 is 1.9mm, and the cold rolling reduction rate is 58.0 percent;
D. hot galvanizing procedure: the strip steel temperature at the outlet of the preheating section of the cold-rolled thin strip steel is 300 ℃, and the specific hot galvanizing processes of the two embodiments are shown in tables 3 and 4:
TABLE 3 parameter control requirements for hot dip galvanizing process
Figure BDA0003356866650000071
TABLE 4 temperature requirement for Hot galvanizing procedure
Examples Galvanizing annealing temperature/. degree.C Slow cooling end point temperature/. degree.C Fast cold end point temperature/. degree.C temperature/DEG C of zinc bath
1 772 690 465 458
2 785 720 463 455
The microstructure of the 800 MPa-grade reinforced plastic dual-phase steel for hot galvanizing prepared by the process is shown in fig. 1 and 2, the residual austenite content is shown in fig. 3, the performance of the cold-rolled 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 5:
mechanical properties of reinforced plastic dual-phase steel for hot galvanizing of surface 5800 MPa level
Examples Yield strength/MPa Tensile strength/MPa Elongation A80％
1 468 851 24.0
2 460 837 25.5

Claims (10)

1.800 MPa-level reinforced plastic dual-phase steel for hot galvanizing, which is characterized in that: the chemical components of the dual-phase steel in percentage by weight comprise: c: 0.16-0.21%, Si: 0.20 to 0.40%, Mn: 1.75-2.40%, Als: 0.50-0.80%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, N is less than or equal to 0.0060%, and the balance of Fe and inevitable impurities.
2. The reinforced plastic dual-phase steel for 800MPa grade hot galvanizing according to claim 1, characterized in that: the chemical components of the dual-phase steel in percentage by weight comprise: c: 0.165-0.205%, Si: 0.25 to 0.35%, Mn: 1.85-2.05%, Als: 0.65-0.80%, P is less than or equal to 0.010%, S is less than or equal to 0.005%, N is less than or equal to 0.003%, and the balance is Fe and unavoidable impurities.
The preparation method of the reinforced plastic dual-phase steel for 3.800 MPa-level hot galvanizing is characterized by comprising the following steps of: the method comprises the following steps:
a. smelting: smelting according to the set chemical components, and casting into a plate blank;
b. a hot rolling procedure: heating, dephosphorizing, roughly rolling, finely rolling and laminar cooling the plate blank to obtain a hot-rolled coil;
c. acid rolling process: pickling the hot rolled coil, and cold rolling the hot rolled coil into thin strip steel with the thickness of 0.7-2.5 mm; the cold rolling reduction rate is 50-74%;
d. hot galvanizing procedure: and (3) carrying out hot galvanizing annealing on the thin strip steel to prepare the required hot galvanizing dual-phase steel.
4. The preparation method of the reinforced plastic dual-phase steel for 800 MPa-grade hot galvanizing according to claim 3, characterized by comprising the following steps: in the step b, at least one of the following is satisfied:
the finishing temperature is 860-930 ℃;
the laminar cooling adopts a front-section cooling mode, and the cooling rates of the upper surface and the lower surface are 40-50% and 70-80% respectively;
the coiling temperature of the head and the tail of the strip steel is 670-730 ℃, and the coiling temperature of the middle part of the strip steel is 630-680 ℃.
5. The method for preparing the reinforced plastic dual-phase steel for 800 MPa-grade hot galvanizing according to the claim 3 or 4, characterized in that: in the step c, the cold rolling reduction is reduced by 4% when the thickness of the thin strip steel is increased by 0.3 mm.
6. The method for preparing the reinforced plastic dual-phase steel for the 800 MPa-grade hot galvanizing according to any one of claims 3 to 5, wherein the method comprises the following steps: in the step d, the thin strip steel is heated in a segmented mode: the preheating section is heated to 290-320 ℃, and the heating speed is 15.0-20.0 ℃/s; heating the mixture to 690-720 ℃ in a first heating period at a heating speed of 4.0-10.0 ℃/s; the two heating sections and the three heating sections are heated to 765-795 ℃, and the heating speed is 0.50-3.0 ℃/s.
7. The method for preparing the reinforced plastic dual-phase steel for the 800 MPa-grade hot galvanizing according to any one of claims 3 to 6, wherein the method comprises the following steps: in the step d, in the segmented heating process, the target temperature is increased by 10 ℃ when the thickness of the thin strip is increased by 0.6 mm.
8. The preparation method of the reinforced plastic dual-phase steel for 800 MPa-grade hot galvanizing according to any one of claims 3 to 7, characterized by comprising the following steps: in the step d, after the thin strip is heated in sections, soaking and heat preservation are carried out for 25-90 s, then slow cooling is carried out to 680-740 ℃ and fast cooling is carried out to 450-470 ℃ respectively at the speed of 1-5 ℃/s and 10-25 ℃/s, then galvanizing treatment is carried out after balanced heat preservation, the time is 10-40 s, and the thin strip is cooled to the room temperature at the speed of more than or equal to 5 ℃/s after being taken out of a zinc pool.
9. The method for preparing the reinforced plastic dual-phase steel for the 800 MPa-grade hot galvanizing according to any one of claims 3 to 8, wherein the method comprises the following steps: in the step d, the speed of the machine set is 70-160 m/min, and the speed of the machine set is reduced by 15m/min when the thickness specification of the cold-rolled thin strip steel is increased by 0.3 mm.
10. The method for preparing the reinforced plastic dual-phase steel for the 800 MPa-grade hot galvanizing according to any one of claims 3 to 9, wherein the method comprises the following steps: in the step d, the flat elongation is 0.35-0.65%, and the flat elongation is reduced by 0.05% when the thickness of the material is increased by 0.3 mm.
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