CN116590614A - Nb and Ti-containing ultra-high strength cold-rolled dual-phase steel and preparation method thereof - Google Patents

Nb and Ti-containing ultra-high strength cold-rolled dual-phase steel and preparation method thereof Download PDF

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CN116590614A
CN116590614A CN202310466692.8A CN202310466692A CN116590614A CN 116590614 A CN116590614 A CN 116590614A CN 202310466692 A CN202310466692 A CN 202310466692A CN 116590614 A CN116590614 A CN 116590614A
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phase steel
cold
rolled
dual
high strength
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李烈军
刘浪
陈松军
彭政务
邹志威
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South China University of Technology SCUT
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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C21D2211/005—Ferrite
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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Abstract

The invention discloses an ultra-high strength cold-rolled dual-phase steel containing Nb and Ti and a preparation method thereof. The matrix structure of the dual-phase steel is ferrite and martensite, and the dual-phase steel comprises the following components in percentage by mass: c:0.19% -0.21%, si:0.25% -0.27%, mn:3.1% -3.3%, nb:0.04% -0.05%, ti:0.02% -0.03%, mo:0.18-0.2%, al:0.05% -0.07%, and the balance of Fe and unavoidable impurities. The preparation method of the dual-phase steel comprises the following steps: component design, smelting, forging, hot rolling, pickling, cold rolling and critical zone annealing. The dual-phase steel has ultrahigh strength and good plasticity, has the tensile strength of 1219-1644MPa, the yield strength of 546-1049MPa and the elongation after fracture of 7.00-9.87 percent, and is suitable for manufacturing automobile safety structural members.

Description

Nb and Ti-containing ultra-high strength cold-rolled dual-phase steel and preparation method thereof
Technical Field
The invention relates to the technical field of ultra-high strength automobile steel plates, in particular to ultra-high strength cold-rolled dual-phase steel containing Nb and Ti and a preparation method thereof.
Background
In recent years, due to the rapid development of the automobile industry, the production and sales of automobiles in China continuously reach the first world for many years, and the production and sales of automobiles are slowed down, but the development space of the automobile industry is still reserved, especially the new energy automobiles which are greatly developed in China still grow continuously in a period of time in the future, although the production and sales of automobiles are slowed down due to the double effects of slowing down the domestic economic growth speed and transforming and upgrading. With the development of the automobile industry and the steel industry, the development requirements and standards are continuously changed, and under the strong competition with other novel materials, the advanced steel materials for automobiles are developing towards higher strength, higher plasticity, lower cost, easy processing and forming and the like.
However, with the increase of the strength of advanced high-strength steel, particularly for high-strength steel with the strength level of more than 800MPa, the phenomena of obviously reduced plastic toughness and forming performance can occur, and forming defects such as cracking, wrinkling, rebound and the like are more likely to occur in the forming process. Therefore, scientific researchers in various countries have made great technical progress in the aspects of process foundation, metallurgical technology, material technology, mechanism research, deep processing application and the like of high-performance advanced high-strength steel in recent years, and the hot spot directions of main researches are focused on the following aspects: alloy composition, microstructure, heat treatment process, coating and deep processing technology, digital analog calculation and big data analysis.
From the aspect of performance and comprehensive cost, the high-strength steel plate is a preferred material for meeting the requirements of light weight and improving the safety performance of a vehicle body within 30 to 50 years from the foreseeable future, and the future high-quality steel for the vehicle has ultrahigh strength and good plasticity.
Chinese patent CN114606449A (high strength and elongation product, low yield ratio DP980 cold-rolled dual-phase steel and production method thereof) published by 10 and 6 of 2022, wherein the steel plate comprises the following components: 0.11% -0.14%, si:0.10% -0.15%, mn:2.22 to 2.24 percent, P is less than or equal to 0.014, S is less than or equal to 0.003 percent, mo:0.13% -0.16%, cr:0.27% -0.31%, al:0.17% -0.21%, ti:0.03% -0.05%, and the balance of Fe and unavoidable impurities. The method adds various alloy elements, but has lower tensile strength grade, common plasticity and large mechanical property improvement space.
In addition, china patent CN113584393A (tensile strength 780 MPa-level dual-phase steel and production method thereof) published by 11/2/2021, wherein the steel plate comprises the following components: 0.06% -0.10%, si: less than 1.0%, mn+Cr:2.0% -2.8%, nb+Ti:0.03% -0.08%, al:0.02% -0.08%, P: less than 0.03%, S: less than 0.008%, N: less than 0.006%, and the balance of Fe and unavoidable impurities. The yield ratio of the dual-phase steel prepared by the method reaches 0.65-0.80, rebound in the stamping forming process of the part can be obviously reduced, but the tensile strength is 780MPa only, and the dual-phase steel has a larger lifting space.
Disclosure of Invention
In view of the above background, the present invention aims to provide an ultra-high strength cold-rolled dual-phase steel and a preparation method thereof, which can reduce the thickness of a steel plate while meeting the strength of the steel plate for an automobile, and provide an effective measure for the weight reduction of the automobile.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the microstructure of the ultra-high strength cold-rolled dual-phase steel is fine ferrite and martensite, wherein the volume fraction of the martensite is 38-80%, the volume fraction of the ferrite is 20-62%, the grain size of the ferrite is 1.28-1.75 mu m, and the ultra-high strength cold-rolled dual-phase steel also comprises a small amount of fine dispersed nano-scale second phase particles, and the size of the second phase particles is generally smaller than 20nm.
The ultra-high strength cold-rolled dual-phase steel comprises the following chemical components in percentage by mass: c:0.19% -0.21%, si:0.25% -0.27%, mn:3.1% -3.3%, nb:0.04% -0.05%, ti:0.02% -0.03%, mo:0.18% -0.2%, al:0.05% -0.07%, and the balance of Fe and unavoidable impurities.
In the composition design of the ultra-high strength cold-rolled dual-phase steel, the functions of the elements are as follows:
c: carbon is a solid solution strengthening element, and ensures that the material has high strength. The carbon content in the dual-phase steel is generally 0.03% -0.23%. When the carbon content is too low, the austenite content is low when heating in the same critical region (ferrite and austenite), so that the volume fraction of the martensite obtained after quenching can be reduced, and the high strength is not easily obtained; however, too high a carbon content may deteriorate the weldability of the material, and thus the design of the carbon component should be as low as possible on the basis of satisfying the strength.
Si: silicon is a solid solution strengthening element, so that on one hand, the strength of the material can be improved, and on the other hand, the carbon can be accelerated to be offset into austenite, and ferrite can be purified, so that the performance of a finished product is improved.
Mn: manganese is an element that strongly enhances the hardenability of austenite, and austenite containing an appropriate amount of Mn can obtain a desired structure through different rapid cooling termination temperatures, thereby obtaining products of different properties. Meanwhile, mn can be solid-dissolved in ferrite to form solid-solution strengthening.
Nb and Ti: niobium and titanium are carbonitride precipitation elements, so that grains can be refined, carbonitride can be precipitated, the material strength is improved, fine crystals and precipitation strengthening of the two are obvious, more importantly, the low content of Nb and Ti can lead to weakening of strengthening effect, and the high content of Nb and Ti can lead to increase of the size of a precipitation phase and increase of cost, so that the content of Nb and Ti is required to be controlled to be 0.04% -0.05% and 0.02% -0.03% respectively.
Mo: molybdenum is a medium-strength carbide forming element, so that the temperature of A3 and A1 is increased, the GS line moves to the upper left, the transformation of proeutectoid ferrite is delayed, the formation of acicular ferrite and bainite is promoted, and the problem of uneven structural performance caused by uneven cooling speed and deformation in the thickness direction can be obviously solved in the production of thick-specification steel plates.
Al: the trace Al can play a role in purifying molten steel and refining grains in the smelting and forging processes.
The preparation method of the ultra-high strength cold-rolled dual-phase steel containing Nb and Ti comprises the following specific preparation steps:
(1) Casting: according to the chemical composition ratio of the dual-phase steel, placing iron ore, quicklime, ferromolybdenum, ferrotitanium, ferroniobium, aluminum oxide, ferrosilicon alloy and ferromanganese alloy into an oxidizing atmosphere furnace to smelt casting blanks;
(2) Forging: heating the casting blank to 1220-1280 ℃ and preserving heat for 2-3h to enable C, si, mn, nb, ti, mo, al elements to be fully dissolved, immediately starting forging, wherein the forging temperature is 1150-1200 ℃ to obtain a forging blank;
(3) And (3) hot rolling: heating the forging stock to 1210-1270 ℃ and preserving heat for 2-3h, wherein the initial rolling temperature is 1100-1200 ℃, the final rolling temperature is 850-950 ℃, taking out a steel plate after rolling, and cooling the steel plate to room temperature to obtain a hot rolled plate with the thickness of 3.7-4 mm;
(4) Acid pickling cold rolling: pickling and cold rolling the hot-rolled plate, polishing the oxide skin subjected to hot rolling and pickling, wherein the cold rolling reduction is 40% -60%, the cold rolling passes are 5-8 times, and the thickness of the cold-rolled plate subjected to cold rolling is 1.8-1.9mm;
(5) And (3) critical zone annealing: and (3) carrying out critical area annealing treatment on the cold-rolled sheet, wherein the transformation point Ac1 = 705 ℃, ac3 = 838 ℃ of the component steel sheet is measured by a Gleeble3800 thermal simulator, the critical area annealing temperature is 735-775 ℃, and the annealing time is 8-12min. The heating process is carried out in a tube furnace, the furnace temperature is raised to 735-775 ℃, then the cold-rolled sheet is put in, the heating speed is 5-20 ℃/s, and the dual-phase steel is obtained after oil quenching after heat preservation for 8-12min.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) The ultra-high strength cold-rolled dual-phase steel adopts reasonable component design. Controlling the appropriate carbon content (0.19% -0.21% wt) ensures both sufficient strength and good plasticity and weldability; the control of the content of suitable Si (0.25-0.27%wt) and Mn (3.1-3.3%wt) ensures the formation of a two-phase structure and the formation of good hardenability, and simultaneously plays a role in solid solution strengthening; adding a small amount of micro-alloying elements Nb (0.04-0.05%wt), ti (0.02-0.03%wt), mo (0.18-0.2%wt) and Al (0.05-0.07%wt), and on the basis of the original C-Si-Mn dual-phase steel, refining grains and precipitation strengthening can be simultaneously achieved by adding a small amount of micro-alloying elements.
(2) In the preparation process of the invention, proper cold rolling reduction (50%), critical zone annealing temperature (735-775 ℃) and annealing time are matched for 8-12min. The purpose of cold rolling at 40% -60% reduction is to refine original bainite grains to the greatest extent, and the annealing time of about 10 minutes is to obtain a dual-phase structure and avoid coarsening of the grains. The dual-phase steel prepared by the method not only ensures enough fine grains, but also ensures that the dual-phase structure maintains higher martensite volume fraction (38% -80%), and can furthest improve the mechanical properties of the cold-rolled dual-phase steel.
(3) The ultra-high strength cold-rolled dual-phase steel obtained by the invention has the tensile strength of 1219-1644MPa, the yield strength of 546-1049MPa and the elongation after break of 7.00-9.87%.
(4) According to the invention, mo, nb, ti, al elements are added on the basis of the conventional C-Si-Mn dual-phase steel, so that grains can be effectively refined; and controlling the appropriate critical zone annealing temperature and annealing time during the preparation process can ensure a sufficiently high martensite volume fraction to provide sufficiently high strength while maintaining good plasticity so that the final product serves as a suitable automotive steel member.
Drawings
Fig. 1: engineering stress-strain curve graphs of the ultra-high strength cold-rolled dual-phase steel prepared in the embodiments 1-3 of the invention;
fig. 2: thermal expansion curve graphs of the ultra-high strength cold-rolled dual-phase steel prepared in the embodiments 1-3 of the invention;
fig. 3: scanning Electron Microscope (SEM) pictures of the ultra-high strength cold-rolled dual-phase steel prepared in example 1 of the present invention;
fig. 4: scanning Electron Microscope (SEM) pictures of the ultra-high strength cold-rolled dual-phase steel prepared in example 2 of the present invention;
fig. 5: scanning Electron Microscope (SEM) pictures of the ultra-high strength cold rolled dual phase steel prepared in example 3 of the present invention.
Detailed Description
In order to facilitate understanding of the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by persons skilled in the art without making creative efforts based on the embodiments in the present invention are within the scope of protection of the present invention.
Example 1
A preparation method of ultra-high strength cold-rolled dual-phase steel containing Nb and Ti comprises the following steps:
(1) According to the chemical composition ratio of the dual-phase steel in the following table 1, placing iron ore, quicklime, ferromolybdenum, ferrotitanium, ferroniobium, aluminum oxide, ferrosilicon alloy and ferromanganese alloy into an oxidizing atmosphere furnace to smelt casting blanks;
(2) Heating the casting blank to 1220-1280 ℃ and preserving heat for 2-3h to enable C, si, mn, nb, ti, mo, al elements to be fully dissolved, immediately starting forging, wherein the forging temperature is 1150-1200 ℃ to obtain a forging blank;
(3) Heating the forging stock to 1210-1270 ℃ and preserving heat for 2-3h, wherein the initial rolling temperature is 1100-1200 ℃, the final rolling temperature is 850-950 ℃, taking out a steel plate after rolling, and cooling the steel plate to room temperature to obtain a hot rolled plate with the thickness of 3.7-4 mm;
(4) Pickling and cold rolling the hot-rolled plate, polishing the oxide skin subjected to hot rolling and pickling, wherein the cold rolling reduction rate is 40%, the cold rolling passes are 5-8 times, and the thickness of the cold-rolled plate subjected to cold rolling is 1.8-1.9mm;
(5) And (3) carrying out critical zone annealing on the cold-rolled sheet, carrying out a heating process in a tube furnace, and putting the cold-rolled sheet into the tube furnace after the furnace temperature is raised to 775 ℃, wherein the heating speed is 5-20 ℃/s, and carrying out oil quenching after heat preservation for 8min to obtain the dual-phase steel.
Example 2
A preparation method of ultra-high strength cold-rolled dual-phase steel containing Nb and Ti comprises the following steps:
(1) According to the chemical composition ratio of the dual-phase steel in the following table 1, placing iron ore, quicklime, ferromolybdenum, ferrotitanium, ferroniobium, aluminum oxide, ferrosilicon alloy and ferromanganese alloy into an oxidizing atmosphere furnace to smelt casting blanks;
(2) Heating the casting blank to 1220-1280 ℃ and preserving heat for 2-3h to enable C, si, mn, nb, ti, mo, al elements to be fully dissolved, immediately starting forging, wherein the forging temperature is 1150-1200 ℃ to obtain a forging blank;
(3) Heating the forging stock to 1210-1270 ℃ and preserving heat for 2-3h, wherein the initial rolling temperature is 1100-1200 ℃, the final rolling temperature is 850-950 ℃, taking out a steel plate after rolling, and cooling the steel plate to room temperature to obtain a hot rolled plate with the thickness of 3.7-4 mm;
(4) Pickling and cold rolling the hot-rolled plate, polishing the oxide skin subjected to hot rolling and pickling, wherein the cold rolling reduction rate is 50%, the cold rolling passes are 5-8 times, and the thickness of the cold-rolled plate subjected to cold rolling is 1.8-1.9mm;
(5) And (3) carrying out critical zone annealing on the cold-rolled sheet, carrying out a heating process in a tube furnace, heating the tube furnace to 755 ℃, then placing the tube furnace into the cold-rolled sheet, keeping the temperature for 10min at a heating speed of 5-20 ℃/s, and carrying out oil quenching to obtain the dual-phase steel.
Example 3
A preparation method of ultra-high strength cold-rolled dual-phase steel containing Nb and Ti comprises the following steps:
(1) According to the chemical composition ratio of the dual-phase steel in the following table 1, placing iron ore, quicklime, ferromolybdenum, ferrotitanium, ferroniobium, aluminum oxide, ferrosilicon alloy and ferromanganese alloy into an oxidizing atmosphere furnace to smelt casting blanks;
(2) Heating the casting blank to 1220-1280 ℃ and preserving heat for 2-3h to enable C, si, mn, nb, ti, mo, al elements to be fully dissolved, immediately starting forging, wherein the forging temperature is 1150-1200 ℃ to obtain a forging blank;
(3) Heating the forging stock to 1210-1270 ℃ and preserving heat for 2-3h, wherein the initial rolling temperature is 1100-1200 ℃, the final rolling temperature is 850-950 ℃, taking out a steel plate after rolling, and cooling the steel plate to room temperature to obtain a hot rolled plate with the thickness of 3.7-4 mm;
(4) Pickling and cold rolling the hot-rolled plate, polishing the oxide skin subjected to hot rolling and pickling, wherein the cold rolling reduction is 60%, the cold rolling passes are 5-8 times, and the thickness of the cold-rolled plate subjected to cold rolling is 1.8-1.9mm;
(5) And (3) carrying out critical zone annealing on the cold-rolled sheet, carrying out a heating process in a tube furnace, heating the furnace to 735 ℃, then placing the cold-rolled sheet into the furnace, keeping the temperature for 12min at a heating speed of 5-20 ℃/s, and carrying out oil quenching to obtain the dual-phase steel.
Table 1 is a list of chemical composition of the above-described embodiments of the present invention;
table 2 shows the cold rolling and critical zone annealing process parameters according to the above embodiments of the present invention;
table 3 shows the structure and mechanical properties of the dual phase steel prepared in the above examples.
TABLE 1 chemical composition of examples 1-3
TABLE 2 Cold Rolling and critical zone annealing Process parameters for examples 1-3
The two-phase steels prepared in examples 1 to 3 were subjected to mechanical property tests, respectively, and the test results are shown in Table 3.
TABLE 3 Dual phase Steel Structure and mechanical Property results obtained by examples 1-3
As can be seen from tables 1-3, the cold-rolled dual-phase steel plate prepared by adopting the component design, cold rolling and heat treatment process has good mechanical properties, the tensile strength can reach 1644MPa, the yield strength can reach 1049MPa, the yield ratio is 44.8-63.8%, the elongation after breaking is 7.00-9.87%, and the product of strength and elongation is 10.7-12.1 GPa; meanwhile, the dual phase steels prepared in examples 1 to 3 have suitable microstructures in that the volume fraction of martensite is 38% -80% and the ferrite grain size is 1.30-1.75 μm. The ultra-high strength cold-rolled dual-phase steel prepared by the embodiment has excellent performance, can be suitable for manufacturing automobile safety structural parts, and has good popularization and application values and prospects.
FIG. 1 is a graph showing the engineering stress-strain curve of the ultra-high strength cold-rolled dual-phase steel prepared in examples 1-3 according to the present invention, wherein as the volume fraction of martensite increases, the yield strength of the examples increases continuously, the tensile strength increases continuously, the yield ratio increases continuously, the elongation after break decreases first and then increases, and the strength-plastic product decreases first and then increases. When the martensite volume fraction is 80%, the yield strength of example 1 reaches a maximum of 1049MPa and the tensile strength reaches a maximum of 1644MPa.
Fig. 2 is a graph showing the thermal expansion curves of the ultra-high strength cold-rolled dual-phase steels prepared in examples 1 to 3 according to the present invention, and it can be seen that transformation points Ac1 = 705 ℃, ac3 = 838 ℃, ms = 372 ℃ of the three examples of the alloy composition. The dual-phase steel can generate austenite phase transformation when heated to more than 705 ℃, the austenite phase transformation is finished at 838 ℃, the dual-phase steel is converted into a full-austenite structure, and the dual-phase steel starts to generate martensite phase transformation after being rapidly cooled to 372 ℃.
Fig. 3 is an SEM image of the ultra-high strength cold-rolled dual-phase steel prepared in example 1 of the present invention, and it can be seen that the average grain size of ferrite is 1.30 μm at a volume fraction of martensite of 80%. The matrix structure of the dual phase steel is continuous martensite.
Fig. 4 is an SEM image of the ultra-high strength cold-rolled dual-phase steel prepared in example 2 of the present invention, and it can be seen that the average grain size of ferrite is 1.28 μm at a volume fraction of martensite of 66%. The matrix structure of the dual phase steel is still continuous martensitic.
Fig. 5 is an SEM image of the ultra-high strength cold-rolled dual-phase steel prepared in example 3 of the present invention, and it can be seen that the average grain size of ferrite is 1.75 μm at a volume fraction of martensite of 38%. The matrix structure of the dual phase steel is now continuous ferrite, while many nano-scale (less than 20 nm) second phase particles are visible on the ferrite matrix.
The above-listed embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments, and similar changes or modifications will be apparent to those skilled in the art from the present disclosure, and it is intended to be within the scope of the present invention. In addition, the combination of the features described in the present application is not limited to the combination described in the claims or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradiction occurs between them.

Claims (10)

1. The ultra-high strength cold-rolled dual-phase steel containing Nb and Ti is characterized in that the formula comprises: C. si, mn, nb, ti, mo, al and Fe, wherein the mass percentages of the components are as follows: c:0.19% -0.21%, si:0.25% -0.27%, mn:3.1% -3.3%, nb:0.04% -0.05%, ti:0.02% -0.03%, mo:0.18% -0.2%, al:0.05% -0.07%, and the balance of Fe and unavoidable impurities.
2. The ultra-high strength cold rolled dual phase steel containing Nb, ti according to claim 1 wherein the formulation comprises: C. si, mn, nb, ti, mo, al and Fe, wherein the mass percentages of the components are as follows: c:0.198%, si:0.268%, mn:3.259%, nb:0.045%, ti:0.027%, mo:0.193%, al:0.06%, the balance being Fe and unavoidable impurities.
3. The preparation method of the ultra-high strength cold-rolled dual-phase steel containing Nb and Ti as claimed in claim 1, which is characterized by comprising the following steps:
(1) Casting: smelting a casting blank according to the mass percentage of the chemical components of claim 1;
(2) Forging: heating the casting blank to enable C, si, mn, nb, ti, mo, al elements to be fully solid-dissolved, and immediately starting forging to obtain a forging stock;
(3) And (3) hot rolling: rolling the forging stock in a heating state, taking out a steel plate after rolling, and air-cooling to room temperature to obtain a hot-rolled plate;
(4) Acid pickling cold rolling: pickling and cold rolling the hot-rolled sheet, and polishing oxide skin on the surface of the hot-rolled and pickled material to obtain a cold-rolled sheet;
(5) And (3) critical zone annealing: and (3) carrying out critical zone annealing treatment on the cold-rolled sheet, carrying out a heating process in a tubular furnace, heating the furnace to the set critical zone annealing temperature, then putting the cold-rolled sheet into the annealing treatment, preserving heat, and carrying out oil quenching to obtain the dual-phase steel.
4. The method for preparing the ultra-high strength cold-rolled dual-phase steel containing Nb and Ti according to claim 3, wherein the casting blank in the step (2) is heated at 1220-1280 ℃ and is kept for 2-3h; and (3) forging the casting blank in the step (2) at 1150-1200 ℃.
5. The method for preparing ultra-high strength cold rolled dual phase steel containing Nb and Ti according to claim 3 wherein the forging stock in step (3) is rolled in a heated state, specifically: heating the forging stock to 1210-1270deg.C, maintaining for 2-3h, rolling at 1100-1200deg.C, and rolling at 850-950 deg.C.
6. The method for preparing the ultra-high strength cold-rolled dual-phase steel containing Nb and Ti according to claim 3, wherein the cold rolling reduction in the step (4) is 40% -60%, the cold rolling passes are 5-8 times, and the thickness of the cold-rolled sheet after cold rolling is 1.8-1.9mm.
7. The method for preparing ultra-high strength cold-rolled dual-phase steel containing Nb and Ti as claimed in claim 3, wherein the critical zone annealing temperature is 735-775 ℃ and the annealing time is 8-12min in the step (5).
8. The method for producing ultra-high strength cold rolled dual phase steel containing Nb and Ti as claimed in claim 3, wherein the heating rate of the tube furnace in the step (5) is 5-20 ℃/s.
9. The method for preparing ultra-high strength cold-rolled dual phase steel containing Nb and Ti according to claim 3, wherein the microstructure of the finally obtained dual phase steel is fine ferrite and martensite, the volume fraction of martensite is 38% -80%, the volume fraction of ferrite is 20% -62%, the grain size of ferrite is 1.28-1.75 μm, and the ultra-high strength cold-rolled dual phase steel also contains nano-scale second phase particles which are distributed in a fine dispersion way, and the size of the second phase particles is less than 20nm.
10. The method for preparing ultra-high strength cold-rolled dual phase steel containing Nb and Ti according to claim 3, wherein the finally obtained dual phase steel has tensile strength of 1219-1644MPa, yield strength of 546-1049MPa and elongation after break of 7.00% -9.87%.
CN202310466692.8A 2023-04-26 2023-04-26 Nb and Ti-containing ultra-high strength cold-rolled dual-phase steel and preparation method thereof Pending CN116590614A (en)

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