CN113249646B - High-strength-plasticity hot-base galvanized medium manganese steel sheet and preparation method thereof - Google Patents

High-strength-plasticity hot-base galvanized medium manganese steel sheet and preparation method thereof Download PDF

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CN113249646B
CN113249646B CN202110403518.XA CN202110403518A CN113249646B CN 113249646 B CN113249646 B CN 113249646B CN 202110403518 A CN202110403518 A CN 202110403518A CN 113249646 B CN113249646 B CN 113249646B
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manganese steel
steel sheet
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medium manganese
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CN113249646A (en
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邹英
韩赟
朱国森
滕华湘
邱木生
阳锋
刘华赛
谢春乾
姜英花
李飞
章军
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Shougang Group 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
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Abstract

The invention discloses a high-strength plastic hot-base galvanized medium manganese steel sheet which comprises the following components in percentage by mass: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo0 to 0.005%, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of iron and inevitable impurities. The preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet provided by the invention has the advantages of low cost and high efficiency, and the obtained high-strength plastic hot-base galvanized medium manganese steel sheet has high strength and plasticity and no yield platform.

Description

High-strength-plasticity hot-base galvanized medium manganese steel sheet and preparation method thereof
Technical Field
The invention belongs to the technical field of high-strength steel manufacturing, and particularly relates to a high-strength plastic hot-base galvanized medium manganese steel sheet for an automobile and a preparation method thereof.
Background
With the increasingly prominent energy and environmental problems, the demand for lightweight automobile bodies has been reluctant. Automotive body materials will be dominated by steel for the present and even long term future. Therefore, increasing the application ratio of thin gauge high strength steel to vehicle bodies is an important approach for reducing the weight of automobiles.
Currently, high-strength steels applied to vehicle bodies are generally first-generation high-strength steels represented by Dual Phase (DP) steels. Second generation high strength steels represented by Twin induced plasticity (TWIP) steels have not been popularized due to their high material cost and manufacturing difficulty. High-strength steels for automobiles have been developed to the third generation nowadays, and the medium manganese steel is the representative steel grade which has received much attention and research.
However, the high-strength and high-plasticity medium manganese steel sheet is slowly developed in industrial production and application. This is because of the bottleneck problem in the production and application of medium manganese steel sheet. Firstly, the hardenability of the steel is increased by the higher Mn content (5-12%) in the medium manganese steel, so that the microstructure of the medium manganese steel hot rolled plate is a single martensite with extremely high hardness, and a cold rolling and thinning process with a large compression ratio cannot be realized; secondly, the manganese steel in cold rolling is fully recrystallized in the annealing process to form fine equiaxed ferrite and metastable austenite, and the texture structure easily causes a long yield platform on the tensile deformation curve of the steel plate, thereby seriously affecting the stamping quality of the steel plate
Chinese patent applications 201810102864.2, 201810455858.5 and 201610455155.3 disclose solutions for reducing the difficulty of cold rolling by performing a bell-type softening annealing on a hot rolled medium manganese steel sheet, however, such a treatment would undoubtedly increase the industrial production flow and the manufacturing cost.
The chinese patent application 201810968412.2 discloses a 1000MPa grade low manganese dual-partitioning cold rolled steel sheet and a method for manufacturing the same, which is obtained by performing twice critical zone annealing on cold rolled medium manganese steel to obtain strip-shaped ferrite and retained austenite structures to eliminate a yield plateau of tensile deformation. However, this solution also increases the cost and reduces the production efficiency.
Therefore, the development of a high-strength-plasticity hot-base galvanized medium manganese steel sheet and a preparation method thereof are needed, so that the medium manganese steel sheet with high strength and plasticity and without yield platform is obtained on the premise of reducing the production cost and improving the production efficiency.
Disclosure of Invention
In view of the above problems, the present invention provides a high-strength plastic hot-base galvanized medium manganese steel sheet and a method for manufacturing the same. The preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet provided by the invention has the advantages of low cost and high efficiency, and the obtained high-strength plastic hot-base galvanized medium manganese steel sheet has high strength and plasticity and no yield platform.
The technical scheme for realizing the purpose is as follows:
in one aspect of the present invention, there is provided a high-strength plastic hot-base galvanized medium manganese steel sheet, wherein the high-strength plastic hot-base galvanized medium manganese steel sheet comprises, in mass percent: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of iron and unavoidable impurities.
In some embodiments of the invention, the high strength plastic hot-based galvanized medium manganese steel sheet according to the invention comprises, in mass percent: 0.20 to 0.30% of C, 4.0 to 5.0% of Mn, 0.9 to 1.2% of Al, 0.42 to 0.6% of Si, 0.04 to 0.06% of Nb, 0.005 to 0.01% of P, 0.001 to 0.005% of S, and the balance of Fe and inevitable impurities.
In some embodiments of the invention, the high strength plastic hot-based galvanized medium manganese steel sheet according to the invention comprises, in mass percent: 0.27% of C, 4.9% of Mn, 1.1% of Al, 0.4% of Si, 0.05% of Nb, 0.008% of P, 0.003% of S, and the balance of Fe and inevitable impurities.
In some embodiments of the present invention, in the high-strength plastic hot-base galvanized medium manganese steel sheet according to the present invention, the microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet includes 60 to 75% by area of ferrite and 25 to 40% by area of retained austenite.
In some embodiments of the invention, in the microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet, the area percentage of ferrite and retained austenite in the form of an elongated strip is more than or equal to 70%.
In some embodiments of the invention, the high-strength plastic hot-base galvanized medium manganese steel sheet has the tensile strength of more than or equal to 900MPa and the elongation after fracture (A) 50 ) Not less than 30 percent, the product of strength and elongation not less than 30 GPa%, and no yield platform on the room-temperature tensile deformation curve.
In another aspect of the invention, the invention also provides a preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, which comprises the following steps:
smelting molten iron to obtain molten steel;
carrying out sheet billet continuous casting on the molten steel to obtain a casting blank;
carrying out rough rolling, finish rolling and coiling on the casting blank to obtain a hot rolled steel coil;
uncoiling and pickling the hot-rolled steel coil to obtain a hot-rolled substrate;
sequentially carrying out preheating treatment, first heating treatment, preoxidation treatment, second heating treatment, soaking treatment, slow cooling treatment, fast cooling treatment, galvanizing and finishing on the hot rolled substrate, and then cooling to the temperature of 18-31 ℃ to obtain the high-strength plastic hot-base galvanized medium manganese steel sheet;
wherein, by mass percent, the casting blank comprises: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of Fe and inevitable impurities.
In some embodiments of the invention, in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention, the cast slab comprises, in mass percent: 0.20 to 0.30% of C, 4.0 to 5.0% of Mn, 0.9 to 1.2% of Al, 0.42 to 0.6% of Si, 0.04 to 0.06% of Nb, 0.005 to 0.01% of P, 0.001 to 0.005% of S, and the balance of Fe and inevitable impurities.
In some embodiments of the invention, in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention, the cast slab comprises, in mass percent: 0.27% of C, 4.9% of Mn, 1.1% of Al, 0.4% of Si, 0.05% of Nb, 0.008% of P, 0.003% of S, and the balance of iron and inevitable impurities.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1100-1150 ℃;
the initial rolling temperature of the fine rolling is 1000-1050 ℃, and the final rolling temperature of the fine rolling is 820-920 ℃;
the coiling temperature is 450-600 ℃.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1110-1130 ℃;
the initial rolling temperature of the finish rolling is 1010-1030 ℃, and the final rolling temperature of the finish rolling is 850-890 ℃;
the coiling temperature is 460-520 ℃.
In some embodiments of the invention, in the method for preparing the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1120 ℃;
the initial rolling temperature of the finish rolling is 1010 ℃, and the final rolling temperature of the finish rolling is 860 ℃;
the coiling temperature was 480 ℃.
In some embodiments of the invention, the pre-heating treatment in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention comprises: heating the hot-rolled substrate from the temperature of 18-31 ℃ to the temperature of 210-230 ℃;
the first heat treatment includes: heating the hot-rolled substrate subjected to the preheating treatment from 210-230 ℃ to 640-660 ℃ at a heating rate of 3-4 ℃/s;
the pre-oxidation treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the first heating treatment for 10-20 s at the temperature of 640-660 ℃;
the second heating treatment includes: heating the pre-oxidized hot-rolled substrate from 640-660 ℃ to 700-750 ℃ at a heating rate of 0.2-0.5 ℃/s;
the soaking treatment comprises the following steps: and preserving the heat of the hot-rolled substrate subjected to the second heating treatment for 90-200 s at the temperature of 700-750 ℃.
In some embodiments of the invention, in the method for preparing a high-strength plastic hot-base galvanized medium manganese steel sheet, the slow cooling treatment comprises: cooling the hot rolled substrate subjected to soaking treatment from 700-750 ℃ to 680-700 ℃ at a cooling rate of 1-3 ℃/s;
the rapid cooling treatment comprises the following steps: cooling the hot-rolled substrate subjected to the slow cooling treatment from 680-700 ℃ to 450-470 ℃ at a cooling rate of 15-30 ℃/s;
the galvanization comprises the following steps: the temperature of the zinc liquid in the zinc pot is 450-470 ℃.
In some embodiments of the present invention, in the method for manufacturing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the present invention, during the pre-oxidation treatment, the atmosphere is a mixed gas including nitrogen and air;
the oxygen content in the mixed gas is 2000-10000 ppm;
in the soaking treatment process, the dew point is-40 to-60 ℃, and the percentage content of hydrogen in the soaking furnace is 5 to 10 percent.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the finishing elongation in the finishing process is 0.2-0.6%.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the thickness of the casting blank is 100-120 mm;
the thickness of the hot-rolled steel coil is 1.2-2.5 mm.
Through a great deal of research, aiming at the purpose of the invention, the invention limits the chemical components and the content of the high-strength plastic hot-base galvanized medium manganese steel sheet, and the thought is as follows:
the C element is an important alloy element in the medium manganese steel, can improve the hardness and the strength of a strip steel matrix structure, and can improve the stability of reverse transformed austenite by reversely transforming austenite to the strip steel in the annealing process. For medium manganese steel prepared by an industrial continuous annealing or continuous hot galvanizing line, the C element is an important factor for stabilizing the austenite of strip steel. This is because, in the continuous annealing or hot galvanizing process of the strip steel, the retention time of the strip steel in the soaking treatment stage is short, the Mn element with a slow diffusion rate is not completely enriched in the austenite of the strip steel, and the C element with a high diffusion rate can be rapidly diffused to the strip steel to reverse the austenite and improve the stability thereof. In order to achieve the purpose of the invention, the inventor limits C to be 0.15-0.35% through a large amount of screening. Wherein the content of C is at least 0.15%. However, when the C content exceeds 0.35%, the weldability of the medium manganese steel sheet is greatly degraded.
Mn is a strong austenite stabilizing element of the strip steel. According to the invention, through a series of processes of the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the enrichment of Mn elements into strip steel reverse transformation austenite continuously can be realized in the soaking treatment stage of continuous hot galvanizing, and further, the stability of austenite and the content of austenite at room temperature can be improved. The Mn element is a solid solution strengthening element at the same time, and can obviously improve the strength of the medium manganese steel matrix structure. In order to obtain the tensile strength of over 900MPa and the elongation after fracture of over 30 percent, the invention limits Mn to be 2.8-5.5 percent through a large number of tests. Wherein, the content of Mn element is controlled to be 2.8% or more. In addition, the casting blank is obtained by a thin slab continuous casting and rolling process, and is thinner than a conventional hot rolled sheet, and the quality problems of edge cracking and the like of a hot rolled steel coil are easily caused due to the excessively high content of the Mn element, so that the Mn content is limited to be not more than 5.5%.
Al is a ferrite-forming element which suppresses precipitation of carbides and promotes reverse austenite enrichment of C to the strip. For the manganese steel in continuous hot galvanizing, Al element is adopted to replace partial Si element, so that the surface quality of a hot rolled steel coil can be improved, and the adhesion capability of a zinc layer can be improved to a certain extent. Therefore, for the high-strength plastic hot-base galvanized medium manganese steel sheet of the present invention, the inventors finally chose to limit the lower limit of the addition of the Al element to 0.8%. However, excessive addition of Al element may decrease the strength of the medium manganese steel sheet and easily cause a sticking alarm during continuous casting of molten steel, and the inventors finally selected to limit the upper limit of the content of Al element to 1.6%.
The main functions of the Si element in the medium manganese steel are solid solution strengthening and carbide precipitation inhibition. Since the Si element deteriorates the surface quality of the hot rolled steel coil and affects the galvanizing effect to some extent, the content of the Si element is limited to 1.2% or less in the present invention.
The Nb element has the function of refining the prior austenite grains of the strip steel in the hot rolling process of the medium manganese steel, and further can improve the strength of the strip steel through the fine grain strengthening function. The inventors finally selected and limited the content of Nb element to 0.02% or more through a great deal of studies. Meanwhile, Nb is also a relatively strong carbide forming element and is easy to compete with reversed austenite for C, so that the enrichment degree of C in austenite is reduced, and the content of Nb is limited to be not more than 0.06%.
It should be noted that the elements Cu, Ni, Cr, Mo, Ti and B are relatively expensive alloying elements, and the contents of the elements Cu, Ni, Cr, Mo, Ti and B are limited in consideration of the alloy cost according to the object of the present invention. The high-strength plastic hot-base galvanized medium manganese steel sheet provided by the invention is not added with the elements intentionally, and if the elements inevitably exist in an impurity state, the content is limited to the following range: 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, and 0 to 0.0005% of B.
The P element can improve the strength of the steel strip properly, but the plasticity of the steel strip is easy to be deteriorated due to grain boundary segregation, and for the purpose of the invention, the content of the P element is limited to be not more than 0.01 percent, and the content of the P element is preferably 0.005 to 0.01 percent.
The S element is easily combined with the Mn element to form coarse MnS inclusions which deteriorate the formability of the strip steel such as punching. Therefore, the inventors finally selected to limit the upper limit of the S content to 0.005% through extensive studies.
The N element belongs to harmful impurity elements in the medium manganese steel. In order to reduce the adverse effect of the N element on the comprehensive performance of the strip steel, the content of the N element is limited to be below 0.008 percent.
One or more technical embodiments of the present invention have at least the following technical effects or advantages:
(1) according to the invention, specific chemical components and contents of the steel are limited, and the microstructure of the obtained high-strength plastic hot-base galvanized medium manganese steel sheet is elongated strip-shaped ferrite + retained austenite, which is obviously different from the fine equiaxed ferrite and retained austenite of the cold-rolled medium manganese steel in the prior art. The microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention shows continuous yield in the uniaxial tensile deformation process, and a yield platform of cold-rolled medium manganese steel in the prior art can not be generated, so that the high-strength plastic hot-base galvanized medium manganese steel sheet has good stamping performance.
(2) The high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention has the thickness of 1.2-2.5 mm, the tensile strength of more than or equal to 900MPa and the elongation percentage after fracture (A) 50 ) Not less than 30 percent and the product of strength and elongation not less than 30 GPa. The thickness specification and the mechanical property are the same as those of common cold rolling in the prior artThe manganese steel is equivalent to or even better, can realize the replacement of cold by heat, and is a medium manganese steel material with higher added value.
(3) On the basis of limiting the specific chemical components and the contents of the specific chemical components of the steel, the preparation process is extensively and deeply researched: by adopting a specific continuous casting and rolling technology of thin casting billets, the casting billets are discharged from a furnace and directly subjected to hot rolling (rough rolling and finish rolling), and the casting billet heating procedure in the conventional flow is omitted. More importantly, the thickness of the casting blank is 100-120 mm, which is one half of the thickness (230-240 mm) of the conventional casting blank in the prior art. In addition, the thin-gauge medium manganese steel plate with the thickness can be produced by hot rolling the casting blank without cold rolling, and the defect that the medium manganese steel is difficult to cold roll in the prior art is overcome.
(4) According to the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the specific process conditions are adopted, namely, the acid-washed hot-rolled substrate is subjected to preheating treatment, first heating treatment, pre-oxidation treatment, second heating treatment, soaking treatment, slow cooling treatment and fast cooling treatment, and then direct galvanizing is carried out, so that the coating adhesiveness and corrosion resistance of the high-strength plastic hot-base galvanized medium manganese steel sheet can be obviously improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 shows a microstructure of a hot-rolled steel coil according to an embodiment of the present invention.
FIG. 2 shows a microstructure of a high strength plastic hot-based galvanized manganese steel sheet according to an embodiment of the present invention.
Figure 3 shows a uniaxial tensile stress-strain plot for a high tensile plastic hot-based galvanized medium manganese steel sheet according to an embodiment of the present invention.
FIG. 4 shows a uniaxial tensile stress-strain plot in accordance with an embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw steels, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the embodiment of the invention provides the following general ideas:
in some embodiments of the present invention, there is provided a high strength plastic hot-based galvanized medium manganese steel sheet, wherein the high strength plastic hot-based galvanized medium manganese steel sheet comprises, in mass percent: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of Fe and inevitable impurities.
According to the invention, specific chemical components and contents of the steel are limited, and the microstructure of the obtained high-strength plastic hot-base galvanized medium manganese steel sheet is elongated strip-shaped ferrite + retained austenite, which is obviously different from the fine equiaxed ferrite and retained austenite of the cold-rolled medium manganese steel in the prior art. The microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention shows continuous yield in the uniaxial tensile deformation process, and a yield platform of cold-rolled medium manganese steel in the prior art can not be generated, so that the high-strength plastic hot-base galvanized medium manganese steel sheet has good stamping performance.
In some embodiments of the invention, the high strength plastic hot-based galvanized medium manganese steel sheet according to the invention comprises, in mass percent: 0.20 to 0.30% of C, 4.0 to 5.0% of Mn, 0.9 to 1.2% of Al, 0.42 to 0.6% of Si, 0.04 to 0.06% of Nb, 0.005 to 0.01% of P, 0.001 to 0.005% of S, and the balance of Fe and inevitable impurities.
The invention can obtain further better technical effect by further limiting the specific chemical component content of the manganese steel sheet in the high-strength plastic hot-base galvanizing.
In some embodiments of the present invention, the high strength plastic hot-based galvanized medium manganese steel sheet according to the present invention comprises, in mass percent: 0.27% of C, 4.9% of Mn, 1.1% of Al, 0.4% of Si, 0.05% of Nb, 0.008% of P, 0.003% of S, and the balance of iron and inevitable impurities.
According to the invention, the most suitable specific chemical component content of the steel is screened out, so that a product with further improved stamping performance can be obtained.
In some embodiments of the present invention, in the high-strength plastic hot-base galvanized medium manganese steel sheet according to the present invention, the microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet includes 60 to 75% by area of ferrite and 25 to 40% by area of retained austenite.
The inventor finds that ferrite is a matrix structure of the medium manganese steel, belongs to a softer phase, bears most of strain in the deformation process and is an important composition phase for ensuring the plasticity of the medium manganese steel. When the middle manganese steel is continuously annealed, only ferrite and reverse transformed austenite exist in the two-phase region, so that the content and stability of the reverse transformed austenite in the two-phase region can be adjusted to a certain extent by adjusting the proportion of the ferrite in the middle manganese steel. Therefore, in order to obtain the residual austenite content and the stability of the high-strength plastic hot-base galvanized medium manganese steel sheet in a proper proportion, the area percentage of ferrite in the steel needs to be controlled between 60 and 75 percent. Wherein, when the area percentage of ferrite is less than 60%, the content of reverse transformed austenite in the two-phase region is too high, and the average enrichment degree of C, Mn elements is reduced, and it is easily transformed into martensite during the subsequent cooling process. When the area percentage of ferrite exceeds 75%, the content of reverse transformed austenite is low, resulting in insufficient content of residual austenite in the final product structure, which is not favorable for improving the plasticity of the medium manganese steel.
In addition, retained austenite is an important constituent phase for ensuring good plasticity of medium manganese steel. Whether the medium manganese steel can obtain the optimal strong plasticity is critical in whether the area percentage of the retained austenite and the stability regulation are reasonable or not. If the area percentage of the retained austenite in the structure of the final product is less than 25%, the TRIP effect of the retained austenite does not occur sufficiently at the time of the tensile deformation, and the desired elongation cannot be achieved. However, when the area percentage of the retained austenite exceeds 40%, the stability thereof is significantly lowered due to the decrease in the enrichment of C, Mn element and is easily transformed into martensite at an early stage of a subsequent cooling process and tensile deformation, thereby failing to provide a sustained TRIP effect. Therefore, the present inventors limited the area percentage of retained austenite to 25 to 40%.
In some embodiments of the invention, in the high-strength plastic hot-base galvanized medium manganese steel sheet, the microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet has an area percentage of ferrite plus retained austenite of more than or equal to 70% in the form of strips.
Further, the inventors have found that the hardenability is high because C, Mn element is added to the high-strength plastic hot-base galvanized manganese steel sheet in a high content. Therefore, even if the hot rolled steel coil having a higher content of C, Mn elements is subjected to a lower cooling rate, a single lath martensite or a lath martensite-based microstructure is formed. The present inventors have conducted a large number of experiments and have adopted a specific manufacturing process, that is, a hot rolled substrate is directly galvanized without being cold-rolled after being sequentially subjected to a preheating treatment, a first heating treatment, a pre-oxidation treatment, a second heating treatment, a soaking treatment, a slow cooling treatment, and a rapid cooling treatment, and thus a two-phase region is annealed to form ferrite and retained austenite in a form of a long and thin strip based on lath martensite. This is significantly different from the prior art solution using equiaxed recrystallized ferrite and austenite formed during annealing of cold rolled medium manganese steel. The microstructure obtained by the invention is incompletely recovered, and the internal part of the microstructure is partially dislocated, so that the microstructure is easy to show continuous yield during tensile deformation. Therefore, in order to ensure that the yield platform does not appear when the medium manganese steel sheet is subjected to tensile deformation, the invention selects that the area percentage of ferrite and retained austenite in the strip shape of the slender plate is more than or equal to 70 percent in the microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet.
In some embodiments of the invention, the high-strength plastic hot-base galvanized medium manganese steel sheet has the tensile strength of more than or equal to 900MPa and the elongation after fracture (A) 50 ) More than or equal to 30 percent, the product of strength and elongation more than or equal to 30GPa per cent, and no yield platform in the room-temperature tensile deformation curve.
In another aspect of the invention, the invention also provides a preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, which comprises the following steps:
smelting molten iron to obtain molten steel;
carrying out sheet billet continuous casting on the molten steel to obtain a casting blank;
carrying out rough rolling, finish rolling and coiling on the casting blank to obtain a hot rolled steel coil;
uncoiling and pickling the hot-rolled steel coil to obtain a hot-rolled substrate;
sequentially carrying out preheating treatment, first heating treatment, preoxidation treatment, second heating treatment, soaking treatment, slow cooling treatment, fast cooling treatment, galvanizing and finishing on the hot rolled substrate, and then cooling to the temperature of 18-31 ℃ to obtain the high-strength plastic hot-base galvanized medium manganese steel sheet;
wherein, by mass percent, the casting blank comprises: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of Fe and inevitable impurities.
In some embodiments of the invention, in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention, the cast slab comprises, in mass percent: 0.20 to 0.30% of C, 4.0 to 5.0% of Mn, 0.9 to 1.2% of Al, 0.42 to 0.6% of Si, 0.04 to 0.06% of Nb, 0.005 to 0.01% of P, 0.001 to 0.005% of S, and the balance of Fe and inevitable impurities.
In some embodiments of the invention, in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention, the cast slab comprises, in mass percent: 0.27% of C, 4.9% of Mn, 1.1% of Al, 0.4% of Si, 0.05% of Nb, 0.008% of P, 0.003% of S, and the balance of iron and inevitable impurities.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1100-1150 ℃;
the initial rolling temperature of the fine rolling is 1000-1050 ℃, and the final rolling temperature of the fine rolling is 820-920 ℃;
the coiling temperature is 450-600 ℃.
In order to better achieve the aim of the invention, the finish rolling temperature of the finish rolling is limited to 820-920 ℃, so that the microstructure of the finish rolling is regulated and controlled, and the surface quality of a hot rolled steel coil is good. When the finish rolling temperature of the finish rolling is higher than 920 ℃, the structure crystal grains of the hot rolled steel coil are coarse, and the tensile strength of the finished steel plate is easy to be insufficient. In addition, the present invention limits C, Mn contained in the alloy composition to a high content, and if the finish rolling temperature of the finish rolling is lower than 820 ℃, the deformation resistance of the hot rolled steel coil is too large, thereby increasing the rolling load of the hot rolling mill and risking edge cracking of the steel sheet. In addition, controlling the coiling temperature is advantageous for obtaining a desired microstructure of the hot rolled steel coil. Among them, when the coiling temperature is higher than 600 ℃, equiaxed ferrite appears in the structure of the hot-rolled steel coil, which is not beneficial to the formation of reverse transformed austenite in the annealing and galvanizing process. When the coiling temperature is less than 450 ℃, the deformation resistance of the hot-rolled steel coil is increased, so that the load of a coiling machine is increased to influence the coiling quality.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1110-1130 ℃;
the initial rolling temperature of the finish rolling is 1010-1030 ℃, and the final rolling temperature of the finish rolling is 850-890 ℃;
the coiling temperature is 460-520 ℃.
In order to further enhance the beneficial effect of the high-strength plastic hot-base galvanized medium manganese steel sheet, the invention selects that the initial rolling temperature of rough rolling is 1110-1130 ℃, the initial rolling temperature of finish rolling is 1010-1030 ℃, the finish rolling temperature of finish rolling is 850-890 ℃, and the coiling temperature is 460-520 ℃.
In some embodiments of the invention, in the method for preparing the high-strength plastic hot-base galvanized medium manganese steel sheet, the initial rolling temperature of the rough rolling is 1120 ℃;
the initial rolling temperature of the finish rolling is 1010 ℃, and the final rolling temperature of the finish rolling is 860 ℃;
the coiling temperature was 480 ℃.
Further, the inventors finally selected the initial rolling temperature for the rough rolling to be 1120 ℃; the initial rolling temperature of the finish rolling is 1010 ℃, and the final rolling temperature of the finish rolling is 860 ℃; the coiling temperature was 480 ℃. Thereby leading the obtained high-strength plastic hot-base galvanized medium manganese steel sheet to have the best comprehensive performance.
In some embodiments of the invention, the pre-heating treatment in the method for producing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the invention comprises: heating the hot-rolled substrate from the temperature of 18-31 ℃ to the temperature of 210-230 ℃;
the first heat treatment includes: heating the hot-rolled substrate subjected to the preheating treatment from 210-230 ℃ to 640-660 ℃ at a heating rate of 3-4 ℃/s;
the pre-oxidation treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the first heating treatment for 10-20 s at the temperature of 640-660 ℃;
the second heating treatment includes: heating the pre-oxidized hot-rolled substrate from 640-660 ℃ to 700-750 ℃ at a heating rate of 0.2-0.5 ℃/s;
the soaking treatment comprises the following steps: and preserving the heat of the hot-rolled substrate subjected to the second heating treatment for 90-200 s at the temperature of 700-750 ℃.
Through a large number of screening tests, the inventor finds that according to the defined composition of alloy components in the high-strength plastic hot-base galvanized manganese steel sheet, the process parameters in the pre-oxidation treatment are defined as follows: and preserving the heat of the hot-rolled substrate subjected to the first heating treatment for 10-20 s at the temperature of 640-660 ℃, so that the thickness and the compactness of an oxide layer can be better.
In addition, the inventor has found through a large number of screening tests that if the soaking temperature is lower than 700 ℃, the area percentage of reversed austenite in the two-phase region is low according to the defined composition of the alloy components in the high-strength plastic hot-base galvanized manganese steel sheet, which leads to insufficient residual austenite content in the final product and thus leads to reduction of the high-strength plastic property of the steel sheet. If the soaking temperature is more than 750 ℃, the area percentage of reverse transformed austenite in the two-phase region is too high, resulting in a low average enrichment degree of the C, Mn elements inside, and the grain size is significantly increased, which leads to insufficient stability of the retained austenite, and phase transformation occurs during cooling or at an early stage of tensile deformation, failing to provide a positive TRIP effect. If the soaking time is less than 90s, the C, Mn element will not sufficiently diffuse from ferrite to retained austenite, resulting in insufficient austenite stability. If the soaking time exceeds 200 seconds, the grains of the reverse transformed austenite grow and coarsen, and the stability of the steel material is also lowered.
In some embodiments of the invention, in the method for preparing a high-strength plastic hot-base galvanized medium manganese steel sheet, the slow cooling treatment comprises: cooling the hot rolled substrate subjected to soaking treatment from 700-750 ℃ to 680-700 ℃ at a cooling rate of 1-3 ℃/s;
the rapid cooling treatment comprises the following steps: cooling the hot-rolled substrate subjected to the slow cooling treatment from 680-700 ℃ to 450-470 ℃ at a cooling rate of 15-30 ℃/s;
the galvanization comprises the following steps: the temperature of the zinc liquid in the zinc pot is 450-470 ℃.
In order to better achieve the aim of the invention, the slow cooling and quick cooling parameters and the temperature of a zinc pot are limited so as to better adjust the microstructure characteristics of the strip steel. Wherein, the cooling is slowly carried out at a cooling speed of 1-3 ℃/s, which is beneficial to the further distribution of C, Mn elements; rapidly cooling to the galvanizing temperature at a cooling speed of 15-30 ℃/s, so as to be beneficial to preventing the non-return transformation austenite from being decomposed due to overlong retention time in a high-temperature region; when the temperature of the zinc pot is set to 450-470 ℃, the fluidity of the zinc liquid and the bonding property with the surface of the steel plate are the best.
In some embodiments of the present invention, in the method for manufacturing a high-strength plastic hot-based galvanized medium manganese steel sheet according to the present invention, during the pre-oxidation treatment, the atmosphere is a mixed gas including nitrogen and air;
the oxygen content in the mixed gas is 2000-10000 ppm;
in the soaking treatment process, the dew point is-40 to-60 ℃, and the percentage content of hydrogen in the soaking furnace is 5 to 10 percent.
In some embodiments of the present invention, the oxygen content during the pre-oxidation treatment is controlled to obtain better oxide layer performance. Wherein, if the oxygen content is too low, a dense oxide layer cannot be formed. If the oxygen content is too high, the selective oxidation effect is poor, so that the reduction reaction in the subsequent high-temperature reduction process is incomplete, and the adhesion capability of the zinc layer is influenced. Therefore, the inventors have defined that during the pre-oxidation treatment, the atmosphere is a mixed gas including nitrogen and air; the oxygen content in the mixed gas is 2000-10000 ppm.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the finishing process has a finishing elongation of 0.2-0.6%.
The inventors of the present invention have conducted a number of experiments on a limited range of the temper rolling elongation in order to better adjust the yield characteristics of the strip and to obtain good surface roughness and sheet shape quality for better achieving the object of the invention. Wherein, if the finishing elongation is less than 0.2%, the roughness of the steel plate surface and the quality of the plate shape cannot be guaranteed. If the finished elongation is more than 0.6%, the yield strength of the steel plate exceeds the standard.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the thickness of the casting blank is 100-120 mm;
the thickness of the hot-rolled steel coil is 1.2-2.5 mm.
The alloy components of the high-strength plastic hot-base galvanized manganese steel sheet steel plate provided by the invention contain high-content C and Mn elements, which can cause the hardness of a hot-rolled steel coil to be high, so that when the thickness of the hot-rolled steel coil is less than 1.2mm, the edge crack phenomenon is easy to occur; when the thickness of the hot rolled steel coil is more than 2.5mm, it is not favorable to maintain a proper heating rate in the continuous hot galvanizing process, thereby affecting the transformation of the microstructure in the annealing process.
In some embodiments of the invention, in the preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet, the burnishing elongation in the burnishing process is 0.2-0.6%.
The high-strength plastic hot-base galvanized medium manganese steel sheet and the method for manufacturing the same according to the present application will be described in detail with reference to examples, comparative examples, and experimental data.
Examples
In the following embodiments 1 to 8, the method for preparing a high-strength plastic hot-base galvanized medium manganese steel sheet according to the present invention includes:
firstly, smelting molten iron to obtain molten steel;
secondly, carrying out continuous sheet billet casting on the molten steel to obtain a casting blank with the thickness of 100-120 mm;
wherein, by mass percent, the casting blank comprises: 0.15 to 0.35% of C, 2.8 to 5.5% of Mn, 0.8 to 1.6% of Al, 0 to 1.2% of Si, 0.02 to 0.06% of Nb, 0 to 0.01% of Cu, 0 to 0.01% of Ni, 0 to 0.005% of Cr, 0 to 0.005% of Mo, 0 to 0.002% of Ti, 0 to 0.0005% of B, 0 to 0.01% of P, 0 to 0.005% of S, 0 to 0.008% of N, and the balance of Fe and inevitable impurities, wherein the casting slab has the chemical composition shown in Table 1.
Thirdly, carrying out rough rolling, finish rolling and coiling on the casting blank to obtain a hot rolled steel coil with the thickness of 1.2-2.5 mm;
wherein the initial rolling temperature of rough rolling is 1100-1150 ℃; the initial rolling temperature of the fine rolling is 1000-1050 ℃, and the final rolling temperature of the fine rolling is 820-920 ℃; the coiling temperature is 450-600 ℃.
Fourthly, uncoiling and pickling the hot-rolled steel coil to obtain a hot-rolled substrate;
fifthly, sequentially carrying out preheating treatment, first heating treatment, preoxidation treatment, second heating treatment, soaking treatment, slow cooling treatment, fast cooling treatment, galvanizing and finishing on the hot rolled substrate, and then cooling to the temperature of 18-31 ℃ to obtain the high-strength plastic hot-base galvanized medium manganese steel sheet;
wherein the preheating treatment comprises: heating the hot-rolled substrate from the temperature of 18-31 ℃ to the temperature of 210-230 ℃;
the first heat treatment includes: heating the hot-rolled substrate subjected to the preheating treatment from 210-230 ℃ to 640-660 ℃ at a heating rate of 3-4 ℃/s;
the pre-oxidation treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the first heating treatment for 10-20 s at the temperature of 640-660 ℃;
the second heating treatment includes: heating the pre-oxidized hot-rolled substrate from 640-660 ℃ to 700-750 ℃ at a heating rate of 0.2-0.5 ℃/s;
the soaking treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the second heating treatment for 90-200 s at the temperature of 700-750 ℃;
the slow cooling treatment comprises the following steps: cooling the hot rolled substrate subjected to soaking treatment from 700-750 ℃ to 680-700 ℃ at a cooling rate of 1-3 ℃/s;
the rapid cooling treatment comprises the following steps: cooling the hot-rolled substrate subjected to the slow cooling treatment from 680-700 ℃ to 450-470 ℃ at a cooling rate of 15-30 ℃/s;
the galvanization comprises the following steps: the temperature of the zinc liquid in the zinc pot is 450-470 ℃;
in the pre-oxidation treatment process, the atmosphere is mixed gas comprising nitrogen and air;
the oxygen content in the mixed gas is 2000-10000 ppm;
in the soaking treatment process, the dew point is-40 to-60 ℃, and the percentage content of hydrogen in the soaking furnace is 5 to 10 percent;
in the polishing process, the polishing elongation is 0.2-0.6%.
The specific process parameters are shown in tables 2 and 3.
Table 1: chemical components (%) contained in the cast slab in examples 1 to 8 of the present invention
Group of C Mn Al Si Nb P S
Example 1 0.25 3.5 1.3 0.6 0.06 0.008 0.004
Example 2 0.30 4.0 1.2 0.2 0.05 0.009 0.005
Example 3 0.35 2.8 0.8 1.2 0.04 0.009 0.005
Example 4 0.20 4.5 0.9 0.4 0.03 0.008 0.005
Example 5 0.15 5.0 1.5 0.5 0.03 0.007 0.004
Example 6 0.27 4.9 1.1 0.4 0.05 0.008 0.003
Example 7 0.19 5.4 1.4 0.7 0.02 0.005 0.001
Example 8 0.31 5.5 1.6 0 0.05 0.01 0.005
Table 2: rolling process parameters of embodiments 1 to 8 of the invention
Figure BDA0003021291060000181
Table 3: annealing galvanizing process parameters of embodiments 1 to 8 of the invention
Figure BDA0003021291060000182
FIG. 1 shows a microstructure of a hot rolled steel coil according to example 4 of the present invention, showing that the hot rolled structure is a single lath martensite.
Fig. 2 shows a microstructure of a high-strength plastic hot-based galvanized medium manganese steel sheet according to example 4 of the present invention, which shows that the microstructure of the steel sheet according to the present invention is mainly composed of lath-shaped ferrite and retained austenite, and is significantly different from the equiaxed structure characteristics of the conventional cold-rolled medium manganese steel.
FIG. 3 shows the uniaxial tensile stress-strain curve of the high-strength plastic hot-base galvanized medium manganese steel sheet according to example 4 of the invention, which shows that the steel sheet of the invention has no yield plateau in the uniaxial tensile curve and good strength and plasticity.
Fig. 4 shows a uniaxial tensile stress-strain curve of comparative example 6, indicating that the stress-strain curve of the cold rolled manganese steel prepared by the prior art has a long yield plateau.
Comparative example
In the following comparative examples 1 to 6, the process parameters for preparing the medium manganese steel sheet are shown in tables 4 to 6:
table 4: chemical composition (%) contained in the steel slabs of comparative examples 1 to 6
Group of C Mn Al Si Nb P S
Comparative example 1 0.10 4.0 1.2 0.2 0.05 0.007 0.0005
Comparative example 2 0.18 2.5 0.8 0.02 0.03 0.008 0.0006
Comparative example 3 0.25 3.5 1.0 0.6 0.04 0.008 0.0005
Comparative example 4 0.20 5.0 1.5 0.02 0.03 0.007 0.0008
Comparative example 5 0.23 4.9 1.4 0.04 0.03 0.008 0.0006
Comparative example 6 0.21 5.0 1.5 0 0.04 0.009 0.0005
Table 5: rolling process parameters of comparative examples 1 to 6
Figure BDA0003021291060000191
Figure BDA0003021291060000201
Table 6: comparative examples 1-6 annealing galvanizing process parameters
Figure BDA0003021291060000202
Performance testing
The performance test is carried out on the medium manganese steel sheets obtained in comparative examples 1-8 and comparative examples 1-6 of the invention: a sample for microstructure observation was prepared, etched with a 4% by volume aqueous solution of nitric acid and alcohol, and observed and an image was obtained under a metallographic microscope. The ferrite was bright white, and the martensite and the retained austenite were gray black, and the area ratio of the ferrite was determined. And (4) performing electrolytic polishing on the tissue observation sample. The electrolyte is perchloric acid, distilled water and alcohol with the volume ratio of 1: 2: 13 in perchloric acid alcohol. The area ratio of the retained austenite is measured by Electron Back Scattering Diffraction (EBSD), and then the area ratio of ferrite and the retained austenite is subtracted from the entire 100% area to obtain the area ratio of martensite.
Performance detection items: and (3) detecting the yield strength, the tensile strength and the elongation after fracture by using a ZWICK/Roell Z100 tensile testing machine according to the GB/T228.1-2010 standard. The results obtained are shown in Table 7:
table 7: performance test results of medium manganese steel sheets obtained in comparative examples 1-8 and comparative examples 1-6 of the invention
Figure BDA0003021291060000211
As can be seen from fig. 1 to 4 and table 7, compared with the comparative example and the prior art, the present invention performs a large amount of and deep screening of the preparation process on the basis of defining the specific chemical components and contents thereof of the steel: the method adopts specific rough rolling, finish rolling and coiling processes and specific preheating treatment, first heating treatment, preoxidation treatment, second heating treatment, soaking treatment, slow cooling treatment, fast cooling treatment, galvanizing and finishing processes, so that the obtained high-strength plastic hot-base galvanized medium manganese steel sheet at least has the following technical effects:
(1) the high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention has the thickness of 1.2-2.5 mm, the tensile strength of more than or equal to 900MPa and the elongation percentage after fracture (A) 50 ) Not less than 30 percent and the product of strength and elongation not less than 30 GPa. The thickness specification and the mechanical property are equivalent to or even better than those of common cold-rolled medium manganese steel in the prior art, the hot-rolled medium manganese steel can replace cold, is a medium manganese steel material with higher added value, and can obviously improve the coating adhesiveness and the corrosion resistance of the high-strength plastic hot-base galvanized medium manganese steel sheet.
(2) The microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention is slender strip-shaped ferrite + retained austenite, which is obviously different from the fine equiaxed ferrite and the retained austenite of the cold-rolled medium manganese steel in the prior art. The microstructure of the high-strength plastic hot-base galvanized medium manganese steel sheet obtained by the invention shows continuous yield in the uniaxial tensile deformation process, and a yield platform of cold-rolled medium manganese steel in the prior art can not be generated, so that the high-strength plastic hot-base galvanized medium manganese steel sheet has good stamping performance.
(3) The thickness of the casting blank is 100-120 mm, which is half of the thickness (230-240 mm) of the conventional casting blank in the prior art. In addition, the thin medium manganese steel plate with the thickness can be produced by hot rolling the casting blank without cold rolling, and the defect that the medium manganese steel is difficult to cold roll in the prior art is overcome.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred comparative examples of the present invention have been described, additional variations and modifications in those comparative examples may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including the preferred comparative examples and all changes and modifications that fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (4)

1. The high-strength plastic hot-base galvanized medium manganese steel sheet is characterized by comprising the following components in percentage by mass: 0.15-0.35% of C, 2.8-5.5% of Mn, 0.8-1.6% of Al, 0-1.2% of Si, 0.02-0.06% of Nb, 0-0.01% of Cu, 0-0.01% of Ni, 0-0.005% of Cr, 0-0.005% of Mo, 0-0.002% of Ti, 0-0.0005% of B, 0-0.01% of P, 0-0.005% of S and 0-0.008% of N, and the balance of Fe and inevitable impurities, wherein in the microstructure of the high-strength plastic hot-base galvanized manganese steel sheet, the ferrite accounts for 60-75% by area, the residual austenite accounts for 25-40%, the thickness of the high-strength plastic high-strength hot-base galvanized manganese steel sheet is 1.2-2.5 mm, the tensile strength is not less than 900MPa, and the elongation A after fracture is 50 The preparation method of the high-strength plastic hot-base galvanized medium manganese steel sheet comprises the following steps of:
smelting molten iron to obtain molten steel;
carrying out sheet billet continuous casting on the molten steel to obtain a casting blank;
carrying out rough rolling, finish rolling and coiling on the casting blank to obtain a hot rolled steel coil;
uncoiling and pickling the hot-rolled steel coil to obtain a hot-rolled substrate;
carrying out preheating treatment, first heating treatment, preoxidation treatment, second heating treatment, soaking treatment, slow cooling treatment, fast cooling treatment, galvanizing and finishing on the hot rolled substrate, and then cooling to the temperature of 18-31 ℃ to obtain the high-strength plastic hot-base galvanized medium manganese steel sheet, wherein the thickness of the casting blank is 100-120 mm; the thickness of the hot-rolled steel coil is 1.2-2.5 mm;
the initial rolling temperature of the rough rolling is 1100-1150 ℃; the initial rolling temperature of the fine rolling is 1000-1050 ℃, and the final rolling temperature of the fine rolling is 820-920 ℃; the coiling temperature is 450-600 ℃;
the preheating treatment comprises the following steps: heating the hot-rolled substrate from the temperature of 18-31 ℃ to the temperature of 210-230 ℃;
the first heat treatment includes: heating the hot-rolled substrate subjected to the preheating treatment from 210-230 ℃ to 640-660 ℃ at a heating rate of 3-4 ℃/s;
the pre-oxidation treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the first heating treatment for 10-20 s at the temperature of 640-660 ℃;
the second heating treatment includes: heating the pre-oxidized hot-rolled substrate from 640-660 ℃ to 700-750 ℃ at a heating rate of 0.2-0.5 ℃/s;
the soaking treatment comprises the following steps: preserving the heat of the hot-rolled substrate subjected to the second heating treatment for 90-200 s at the temperature of 700-750 ℃;
the slow cooling treatment comprises the following steps: cooling the hot rolled substrate subjected to soaking treatment from 700-750 ℃ to 680-700 ℃ at a cooling rate of 1-3 ℃/s;
the rapid cooling treatment comprises the following steps: cooling the hot-rolled substrate subjected to the slow cooling treatment from 680-700 ℃ to 450-470 ℃ at a cooling rate of 15-30 ℃/s;
in the pre-oxidation treatment process, the atmosphere is mixed gas comprising nitrogen and air;
the oxygen content in the mixed gas is 2000-10000 ppm;
in the soaking treatment process, the dew point is-40 to-60 ℃, and the percentage content of hydrogen in the soaking furnace is 5 to 10 percent.
2. The high-strength plastic hot-based galvanized medium manganese steel sheet according to claim 1, characterized in that the microstructure of the high-strength plastic hot-based galvanized medium manganese steel sheet is characterized in that the area percentage of ferrite + retained austenite in the form of strips of the elongated sheet is not less than 70%.
3. The high strength plastic hot-based galvanized medium manganese steel sheet according to claim 1,
the temperature of the zinc liquid in the zinc pot in the galvanizing process is 450-470 ℃.
4. The high-strength plastic hot-base galvanized medium manganese steel sheet according to claim 1, characterized in that the burnishing elongation in the burnishing process is 0.2-0.6%.
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