CN115612934B - 590 MPa-level high-formability hot dip galvanized dual-phase steel plate and preparation method thereof - Google Patents

590 MPa-level high-formability hot dip galvanized dual-phase steel plate and preparation method thereof Download PDF

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CN115612934B
CN115612934B CN202211296954.2A CN202211296954A CN115612934B CN 115612934 B CN115612934 B CN 115612934B CN 202211296954 A CN202211296954 A CN 202211296954A CN 115612934 B CN115612934 B CN 115612934B
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CN115612934A (en
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郭强
郑连辉
吴庆美
缪心雷
王玉斌
佟皑男
夏晶
王少新
张保田
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Tkas Auto Steel Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/04—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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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  • Heat Treatment Of Sheet Steel (AREA)
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Abstract

The invention relates to the field of steel manufacturing for automobiles, in particular to a 590 MPa-level high-formability hot dip galvanized dual-phase steel plate and a preparation method thereof. Comprises the following components: c:0.05 to 0.09 percent, si:0.5 to 0.9 percent, mn:1.0 to 1.8 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and unavoidable impurities, and satisfies the following conditions:w is a weight percentage. Compared with the conventional DP590, the elongation (A80 longitudinal direction) can be improved by more than 20 percent under the condition that the yield strength and the tensile strength are basically consistent, and n 10‑20/Ag The value can be increased by more than 22%, the hole expansion rate can be increased by more than 28%, and the punching ductility and flanging formability of the material are synchronously improved. The conventional steel-making, hot-rolling, cold-rolling and hot-galvanizing production line is used for producing the steel which meets the requirements of drawing, flanging flanges and corrosion resistance of complex parts, can replace conventional DP590 and DP490, and widens the application range of the dual-phase steel.

Description

590 MPa-level high-formability hot dip galvanized dual-phase steel plate and preparation method thereof
Technical Field
The invention relates to the field of manufacturing of steel for automobiles, in particular to 590 MPa-level high-formability hot dip galvanized dual-phase steel and a preparation method thereof.
Background
In recent years, with the increasing severity of energy and environmental problems, the CO is enhanced to reduce the greenhouse effect, protect the earth environment 2 The limitation of the emission amount, which contributes to the weight reduction of the automobile body with low fuel consumption, is an important research topic in the modern automobile industry.
Because cold-rolled hot-dip galvanized dual-phase steel has the characteristics of low yield ratio, high initial work hardening rate, good strength and ductility matching, good bake hardening performance, high collision energy absorption capacity and the like, the requirements of light weight, collision safety, rust resistance and the like of an automobile body are met, and the cold-rolled hot-dip galvanized dual-phase steel is widely applied.
The stamping forming of the hot dip galvanized dual-phase steel plate mainly comprises drawing forming and flanging forming. From the reflection of the existing automobile processing matching factories and host factories, automobile parts are gradually changed from simple forming to complex forming, and materials are required to have higher elongation, work hardening rate n value and hole expansion rate.
However, the existing 590 MPa-level hot dip galvanized dual-phase steel cannot meet the stamping requirements of parts with complicated drawing and flange flanging forming requirements, and has the problem of stamping cracking, and particularly, for certain parts with larger flanging characteristics, a plurality of drawing cracking and/or flanging cracking phenomena appear, so that the existing industrial problems are solved.
CN 103146992B discloses a "high strength hot dip galvanized steel sheet with excellent workability", the main chemical components are C0.05-0.3%, si:0.01 to 2.5 percent, mn:0.5 to 3.5 percent, P:0.003 to 0.1 percent, S: less than 0.02, al:0.01 to 1.5 percent of structure mainly comprises more than 20 percent of ferrite, less than 10 percent of martensite, 10 to 60 percent of tempered martensite and 3 to 10 percent of residual austenite. On the other hand, in order to increase the elongation and the hole expansion ratio, it is necessary to obtain tempered martensite and refined retained austenite by a quenching-partitioning Q & P process, that is, cooling from 750 ℃ to a temperature range of (Ms point-100 ℃) to (Ms point-200 ℃) and then heating to 350 to 600 ℃. The reheating function of the reheating equipment of tens of millions of primordial notes must be put into the traditional hot galvanizing production line. Otherwise, the mass production cannot be realized in the traditional hot galvanizing production line. And the process requires larger electric energy input, and increases the production cost. On the other hand, there is no mention of how to solve the surface quality problem at high Si.
CN 107099739B discloses a "low-cost high-reaming steel plate with tensile strength of 600MPa level" and its production method. The main chemical components are C:0.15 to 0.2 percent, si is less than or equal to 0.30 percent, mn is 0.8 to 1.0 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, als is 0.02 to 0.05 percent, ti:0.01 to 0.03 percent, and N is less than or equal to 0.0060 percent. Tensile strength: 600-650MPa, the lower yield strength of 500-550MPa, mainly adopting steelmaking-hot rolling process control, adopting high-carbon design (C: 0.15-0.2%), having higher hole expansion ratio but higher yield ratio, being unfavorable for material stamping forming, and not involving hot galvanizing process.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a 590 MPa-level high-formability hot dip galvanized dual-phase steel plate and a preparation method thereof. The elongation and the hole expansion rate are improved, the stamping ductility and the flanging formability of the material are synchronously improved, and the requirements of drawing, flanging formability and corrosion resistance of complex parts are met.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
the 590 MPa-level high-formability hot dip galvanized dual phase steel comprises the following components in percentage by weight:
c:0.05 to 0.09 percent, si:0.5 to 0.9 percent, mn:1.0 to 1.8 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and unavoidable impurities.
And satisfies the following:
w is a weight percentage.
The thickness of 590 MPa-level high-formability hot-dip galvanized dual-phase steel plate is 0.5-2.3 mm, the yield strength is 330-430 MPa, the tensile strength is 590-700 MPa, the longitudinal elongation of A80 is more than 28%, and the tensile strain hardening index n is equal to or greater than 10-20/Ag 0.17 to 0.24 percent and 50 to 70 percent of hole expansion rate.
A590 MPa-level high-formability hot dip galvanized dual phase steel plate preparation method comprises converter steelmaking, LF furnace refining, slab continuous casting, hot continuous rolling, pickling cold continuous rolling and continuous hot dip galvanizing production line continuous annealing-galvanization-flattening, and specifically comprises the following steps:
1) Continuous casting of slabs
The continuous casting machine adopts dynamic light pressing, and the pressing amount is 3-6 mm.
2) Hot rolling
The hot rolling heat preservation temperature is 1150-1250 ℃, the finishing rolling temperature of the finishing mill is 850-940 ℃, the coiling is carried out after laminar cooling, and the coiling temperature is 540-630 ℃;
3) Pickling-cold tandem rolling
The total rolling reduction rate is 54-80 percent;
4) Continuous annealing-galvanizing-leveling on continuous hot galvanizing production line
In the annealing furnace of the continuous hot galvanizing production line, the temperature of a heating section is 790-830 ℃, the temperature of a heat preservation section is 790-830 ℃, and the dew point of the heating section is: the temperature of the rapid cooling section is 450-490 ℃ at minus 5 ℃ to minus 25 ℃ and the temperature of the steel plate entering the zinc pot is 450-490 ℃.
As a further improvement of the invention, the step 4) also comprises the steps of controlling the dew point temperature of the furnace nose to be between-40 ℃ and-55 ℃ and controlling the nitrogen humidification amount of the furnace nose to be between 0 and 3m 3 /h。
As a further improvement of the invention, the step 4) also comprises the step of controlling the continuous hot galvanizing production line speed to be 50-100 m/min and controlling the elongation of the finishing machine to be 0.2-0.6%.
As a further improvement of the invention, the hot dip galvanizing coating in the step 4) is pure zinc hot dip galvanizing and zinc aluminum magnesium hot dip galvanizing.
Compared with the prior art, the method has the beneficial effects that:
1. the invention adopts the design of low carbon (C: 0.05% -0.09%) and high silicon (Si: 0.5% -0.9%), the high Si can inhibit the generation of ferrite carbide, purify ferrite, improve the movable dislocation density in ferrite, form a fine dislocation cell structure and improve the work hardening rate (n) 10-20/Ag More than 0.18), thereby improving the elongation (A) 80 Longitudinal direction: 28% or more) and improves the punching ductility.
2. According to the invention, more Si (0.5% -0.9%) is added and is dissolved in ferrite, so that the ferrite matrix is further strengthened, and the hardness difference between ferrite and martensite phases is reduced; the low carbon (C: 0.05% -0.09%) design can reduce the carbon content in austenite under the same annealing temperature, and further reduce the hardness of the martensite phase after quenching.
The reduction of the hardness difference between the martensite and ferrite phases is beneficial to improving the coordinated deformation capacity of the two phases in the plastic deformation process of the steel plate, and finally improving the hole expansion rate of the dual-phase steel.
3. The dynamic soft reduction is put into the continuous casting process of the slab, so that the uniformity of the internal structure of the slab is improved, the internal banded structure is reduced, and the formability of the material is improved.
4. The invention adopts lower hot rolling coiling temperature, and reduces the element diffusion and grain boundary migration speed, thereby inhibiting the growth of ferrite grains, refining the grains, improving the uniformity of the structure, enabling austenite to be finely and dispersedly distributed in a ferrite matrix during annealing in a continuous hot galvanizing annealing furnace, obtaining a martensite structure finely and dispersedly distributed on the ferrite matrix during cooling, reducing the formation of martensite bands, inhibiting the expansion of cracks by the dispersed martensite structure during flanging and reaming, and finally improving the hole expansion rate of the dual-phase steel.
5. The invention realizes the internal oxidation of Si, mn and other elements by controlling the dew point of the heating section through the preoxidation technology in the annealing furnace, and avoids the elements from diffusing to the surface of the steel plate to form oxides; the secondary oxidation of the surface of the steel plate is controlled by controlling the furnace nose dew point control technology, so that the Fe2Al5 layer is prevented from being difficult to form due to the fact that diffusion between Fe and Al is restrained, and further the missing plating defect is generated. By the coupling control technology of the dew point of the heating section of the annealing furnace and the dew point of the furnace nose, the influence of high Si on the surface quality of the steel plate is eliminated, the technical problem that the Si content of the hot dip galvanized dual-phase steel is difficult to exceed more than 0.5% in batch industrial production is innovatively solved, and the surface corrosion resistance of the hot dip galvanized dual-phase steel is ensured.
6. Compared with the conventional DP590, the elongation (A80 longitudinal direction) can be improved by more than 20 percent under the condition that the yield strength and the tensile strength are basically consistent, and n 10-20/Ag The value can be increased by more than 22%, the hole expansion rate can be increased by more than 28%, and the punching ductility and flanging formability of the material are synchronously improved. The conventional steel-making, hot-rolling, cold-rolling and hot-galvanizing production line is used for producing the steel which meets the requirements of drawing, flanging flanges and corrosion resistance of complex parts, can replace conventional DP590 and DP490, and widens the application range of the dual-phase steel.
Drawings
FIG. 1 is a metallographic structure of example 1 of the present invention.
FIG. 2 is a scanning organization chart of embodiment 1 of the present invention.
FIG. 3 is a typical engineering stress-strain curve for example 1 of the present invention.
Detailed Description
The invention discloses a 590 MPa-level high-formability hot dip galvanized dual-phase steel plate and a preparation method thereof. Those skilled in the art can, with the benefit of this disclosure, suitably modify the process parameters to achieve this. It is expressly noted that all such similar substitutions and modifications will be apparent to those skilled in the art, and are deemed to be included in the present invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those skilled in the relevant art that variations and modifications can be made in the methods and applications described herein, and in the practice and application of the techniques of this invention, without departing from the spirit or scope of the invention.
The following detailed description of the invention is further illustrative, but is not intended to limit the scope of the invention:
the 590 MPa-level high-formability hot dip galvanized dual phase steel comprises the following components in percentage by weight:
c:0.05 to 0.09 percent, si:0.5 to 0.9 percent, mn:1.0 to 1.8 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, al:0.02% -0.05%; cr:0.2 to 0.8 percent, and the balance of Fe and unavoidable impurities.
The invention optimally designs the chemical components of the steel grade:
1) C is an austenite stabilizing element and mainly plays a role of transformation strengthening in the dual-phase steel so as to generate second phases such as martensite outside ferrite and the like and improve the tensile strength. By adopting a low-carbon design, the carbon content in austenite can be reduced under the condition of the same annealing temperature, and the hardness of a martensitic phase after quenching is further reduced. If the C content is less than 0.05%, the second phase content outside the ferrite is difficult to ensure, and the tensile strength requirement cannot be met; if the C content is higher than 0.09%, on the one hand, the weldability is deteriorated, on the other hand, the C content in the final martensite is high, the strength is increased, the toughness is lowered, and most importantly, the hardness difference between the martensite and ferrite is increased, and the hole expansion property is lowered. Therefore, the content of the C element is controlled to be 0.05 to 0.09 percent.
2) The high Si can inhibit the generation of ferrite carbide, enrich C in ferrite into austenite, has a purifying effect on ferrite, improves the dislocation density in ferrite, forms a fine dislocation cellular structure, improves the work hardening rate, further improves the elongation rate and improves the stamping extensibility. Meanwhile, more Si (0.5% -0.9%) is added and dissolved in ferrite to further strengthen the ferrite matrix, so that the hardness difference between ferrite and martensite phases is reduced, and the hole expansion rate is improved.
The Si content is too low to play a role in improving the work hardening rate, the elongation and the hole expansion rate; the Si content is too high, the surface of the steel plate is easy to oxidize during hot galvanizing annealing, the defects of zinc layer adhesion, plating omission and the like are reduced, and meanwhile, the spot welding performance of the steel plate is also deteriorated. Therefore, the content of Si element is controlled to be 0.5-0.9%.
3) Mn is an element for expanding an austenite region, and delays transformation of pearlite and bainite in a supercooled austenite cooling process, thereby improving hardenability of steel and promoting formation of martensite in a rapid cooling process after slow cooling is completed. When the manganese content is too low, hardenability is insufficient, and a desired amount of martensite cannot be obtained, and tensile strength cannot be ensured. When the manganese content is excessively high, it is oxidized or deposited on the surface of the steel sheet during annealing, deteriorating the galvanization wettability and also deteriorating the spot welding performance of the steel sheet. Therefore, the Mn element content is controlled to be 1.0% -1.8% in the invention.
4) Al is a deoxidizer in the steelmaking process in the traditional process, and meanwhile, al can be combined with N in steel to form AlN and refine grains. However, if the aluminum content is too high, alumina inclusions are increased, and the nozzle is easily blocked in the continuous casting process. Meanwhile, the Al content is too high, special and independent covering slag is needed, and the casting slag cannot be continuously cast with other products with conventional Al content, so that the casting slag is not beneficial to mass production of tissues. Therefore, the content of Al element is controlled to be in the range of 0.02-0.06%.
5) Cr element is an austenite stabilizing element in steel, enlarges an austenite phase region, improves hardenability of the steel plate, remarkably delays pearlite and bainite transformation, enables austenite to be fully transformed into a martensite structure, and increases martensite content. However, the chromium content should not be excessively high, and if the chromium content is excessively high, chromium carbide is formed, reducing ductility of the galvanized steel sheet. Therefore, the content of Cr element is controlled to be in the range of 0.3-0.9%.
6) The P element is a harmful element in steel, and the lower the content is, the better. In consideration of cost, the content of the P element is controlled to be less than or equal to 0.02 percent.
7) The S element is a harmful element in steel, and the lower the content is, the better. In view of cost, the content of S element is controlled to be less than or equal to 0.01 percent.
8) Meanwhile, as Cu, ni, mo, V, nb elements are not added in the invention, the elements are not considered in the CEN, the CEN is simplified into a formula only containing C, si, mn, cr, and the following relation is required to be satisfied:
w is a weight percentage.
The main reasons are as follows: when the CEN is lower than 0.16, the yield strength and the tensile strength of the steel plate are low; when CEN is higher than 0.24, the steel plate has higher strength due to more alloy element content, and the welding joint has higher hardness in the heat affected zone, poorer toughness and easy occurrence of defects such as welding cold cracks.
590 MPa-level high-formability hot-dip galvanized dual-phase steel plate, wherein the thickness range of the steel plate is 0.5-2.3 mm, the yield strength is 330-430 MPa, the tensile strength is 590-700 MPa, the longitudinal elongation of A80 is more than 28 percent, and the tensile strain hardening index n is equal to or greater than 10-20/Ag 0.18 to 0.24 percent and the hole expansion rate is 50 to 70 percent.
A method for preparing 590 MPa-level high-formability hot dip galvanized dual phase steel plate specifically comprises the following steps:
1) Converter smelting
Smelting by a converter to obtain molten steel which meets the following component requirements in percentage by weight: 0.05 to 0.09 percent, si:0.5 to 0.9 percent, mn:1.0 to 1.8 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and unavoidable impurities. And satisfies the following:
the temperature of the molten steel is between 1500 and 1650 ℃.
2) Dynamic soft depression
The continuous casting machine adopts dynamic light pressing, and the pressing amount is 3-6 mm. Dynamic soft reduction is adopted in the continuous casting process, so that internal banded tissues can be effectively reduced, and the cast blank has genetic action on hot galvanizing after continuous casting, hot rolling and cold rolling, so that the formation of martensite bands in the material can be effectively reduced.
3) Hot continuous rolling
The casting blank can be charged at the temperature of more than 500 ℃ to save energy, and can be charged at room temperature to facilitate arrangement production. The heating temperature is 1150-1250 ℃, the finishing temperature is 850-940 ℃, and the coiling temperature is 540-630 ℃.
The heating temperature of the slab in the hot rolling heating furnace is 1150-1250 ℃, the heating temperature of a casting blank is too high, a low-melting-point compound is easy to appear at a grain boundary in steel, the heating temperature is too low, the requirement of finish rolling start rolling temperature cannot be met, and the problems of overlarge rolling force or difficult biting and the like are caused.
The final rolling temperature is 850-940 ℃, if the final rolling temperature is too low, the deformation resistance of the hot rolled plate is too large, and the hot rolled plate is difficult to roll to the target thickness; the finishing temperature is too high, the grains are coarse, and the mechanical property of the steel plate is deteriorated.
The coiling temperature is between 540 and 630 ℃, the invention adopts lower hot rolling coiling temperature, and the element diffusion and grain boundary migration speed is reduced, thereby inhibiting the growth of ferrite grains, refining the grains, improving the uniformity of the structure, enabling austenite to be finely and dispersedly distributed in a ferrite matrix during annealing in a continuous hot galvanizing annealing furnace, obtaining a martensite structure finely and dispersedly distributed on the ferrite matrix during cooling, avoiding the formation of martensite bands, inhibiting the expansion of cracks by the dispersed martensite structure during flanging and reaming, and finally improving the hole expansion rate of the dual-phase steel. However, if the coiling temperature is too low, a bainite or martensite structure will appear in the structure, and the rolling difficulty of the subsequent cold rolling is increased.
4) Pickling cold continuous rolling
The iron scale on the surface of the steel coil is removed by acid liquor before cold rolling, and the cold rolling reduction rate is 54-80%. Too high a reduction ratio can result in too high deformation resistance, and is difficult to roll to a target thickness; the rolling reduction is too low, and the elongation of the steel plate is reduced.
5) Continuous annealing hot dip galvanizing
In an annealing furnace of a continuous hot galvanizing production line, the temperature of a heating section is 790-830 ℃, the temperature of a heat preservation section is 790-830 ℃, the heating and heat preservation temperature is too low, austenitizing is insufficient, the quantity of austenite is less, a sufficient quantity of martensite is difficult to form in the subsequent cooling process, and the tensile strength of the dual-phase steel is insufficient. The heating and heat preservation temperature is too high, the austenitization is sufficient, but the ferrite content in the steel is too low, austenite grains are coarse, the yield strength is increased, and the elongation is reduced.
The temperature of the quick cooling section is 450-490 ℃, the cooling temperature is too high, the cooling rate is too low, the strip steel easily enters into the zinc pot to produce more ferrite and upper bainite, the tensile strength is influenced, and meanwhile, the cooling temperature is too high, the temperature of the strip steel entering into the zinc pot is higher, and the surface performance of a coating is influenced. The cooling temperature is too low, the cooling rate is too low, si does not have enough time to enrich C in ferrite into austenite, the elongation and n value, the hole expansion rate and the average minimum relative bending radius are affected, meanwhile, the cooling temperature is too low, the temperature of the strip steel entering a zinc pot is too low, and the plating property of a plating layer is affected.
Through the preoxidation technology in the annealing furnace, the internal oxidation of Si, mn and other elements is realized by controlling the dew point of the heating section to be between-5 ℃ and-25 ℃, and the diffusion of the Si, mn and other elements to the surface of the steel plate is avoided to form oxides. The nitrogen humidification amount of the furnace nose is controlled to be 0-3 m 3 And/h, the dew point temperature of the furnace nose is controlled to be between minus 40 ℃ and minus 55 ℃, the secondary oxidation of the surface of the steel plate is controlled, and the defect that a Fe2Al5 layer is difficult to form due to the fact that diffusion between Fe and Al is inhibited is prevented, and then the miss-plating defect is generated. By the coupling control technology of the dew point of the heating section of the annealing furnace and the dew point of the furnace nose, the influence of high Si on the surface quality of the steel plate is eliminated, the technical problem that the Si content of the hot dip galvanized dual-phase steel cannot exceed more than 0.5% is innovatively solved, and the surface corrosion resistance of the hot dip galvanized dual-phase steel is ensured.
After the strip steel comes out of the furnace nose, the strip steel enters a zinc pot for hot galvanizing, and the temperature of the steel plate entering the zinc pot is 450-490 ℃. When the pure zinc hot dip Galvanizing (GI) coating is manufactured, the Al content of the zinc pot is 0.19-0.24%, and when the zinc aluminum magnesium hot dip galvanizing (ZM) coating is manufactured, the Al content of the zinc pot is 1-5%, and the Mg content is 1-5%.
The elongation of the finishing machine is controlled to be 0.2-0.6%, the yield stress of the strip steel is adjusted by eliminating the yield stress of the strip steel, and the specified surface roughness is obtained. The finishing elongation is too low to play a role in eliminating the yield platform and obtaining the rough and excessive surface; too high finishing elongation, increased yield strength, reduced elongation, etc.
The continuous hot galvanizing production line speed is 50-100 m/min. The speed is too low, and defects such as zinc fluctuation and the like appear on the surface of the strip steel; the speed is too high, the stay time of the strip steel in the furnace is too short, the elongation rate, n value and the hole expansion rate of the strip steel are low, and the average minimum relative bending radius value is high.
The thickness of the 590 MPa-level high-formability hot dip galvanized dual phase steel plate is 0.5-2.3 mm.
In the microstructure of the invention, according to volume fraction, 67-80% of ferrite, 13-25% of martensite and the balance of a small amount of bainite: 0-8%. The absence of the inclusion of retained austenite in the structure may improve the formability of the material, and thus, the addition of sufficient carbon to stabilize the retained austenite is not required. The low-carbon design is adopted, the carbon equivalent is low, and the welding performance of the strip steel is good.
The yield strength of the hot dip galvanized dual-phase steel plate obtained by the method is 330-430 MPa, the tensile strength is 590-700 MPa, the longitudinal elongation of A80 is more than 28%, and the tensile strain hardening index n is equal to or higher than 10-20/Ag 0.18 to 0.24 percent and the hole expansion rate is 50 to 70 percent. Meets the requirements of high strength, high elongation and high reaming and flanging performances of the automobile body structural part, and can improve the elongation by more than 20 percent and n compared with the conventional DP590 steel 10-20/Ag The value can be increased by more than 22%, the hole expansion rate can be increased by more than 28%, and the punching ductility and flanging formability of the material are synchronously improved. The conventional steel-making, hot-rolling, cold-rolling and hot-galvanizing production line is used for producing the steel which meets the requirements of drawing, flanging flange and corrosion resistance of complex parts, meets the requirement of welding performance, can replace the conventional DP590 and DP490, and widens the application range of the dual-phase steel.
[ example ]
The following description of the embodiments of the present invention and comparative examples will be given by way of example only with reference to 6 examples, the details of which are as follows:
the chemical compositions, continuous casting, hot rolling, cold rolling process parameters, annealing and hot galvanizing process parameters, mechanical properties, hole expansibility, surface quality and welding performance evaluations of the steel sheets of examples 1 to 6 are shown in tables 1 to 4, respectively.
The mechanical properties of the steel sheet were measured using a ZWICK Z100 stretcher, the samples were a80 machine direction, the yield strength, tensile strength, elongation measurements performed ISO 6892-1 standard, the strain hardening index (n value) measurements performed ISO 10275-2007, and the bake hardening value measurements performed GBT 24174-2009.
The hole expansibility was measured using an Erichsen sheet former with a template size of 100mm x 100mmD and the hole expansibility values of steel sheets of different compositions and under process were measured according to ISO 16630-2009 standard.
The surface quality of the steel sheet was measured using a Parsymec system according to the surface quality standard of "grade 7 sheet" of hot dip galvanized steel sheet.
And (3) measuring the macroscopic metallographic structure of the cross section of the spot welding joint under the maximum welding current process by using an MI5000M type microscope according to the SEP1220-2 standard, and comprehensively evaluating the nugget diameter, the penetration and the internal defect number.
TABLE 1 chemical composition wt% (of the example steel)
Table 2 continuous casting, hot rolling and cold rolling processes of the steel sheet of examples
Table 3 annealing and hot dip galvanizing process for example steel sheet
Table 4 evaluation of mechanical properties, hole expansibility, surface quality and welding properties of example steel sheets
Fig. 1 is a metallographic structure diagram of the embodiment 1 of the present invention, fig. 2 is a scanning structure diagram of the embodiment 1 of the present invention, and fig. 3 is a typical engineering stress-strain curve of the embodiment 1 of the present invention. As shown in the figure, the invention meets the requirements of high strength, high elongation and high reaming and flanging performances of the automobile body structural part and the outer covering part, and the elongation can be improved by more than 20 percent compared with the conventional DP590 steel, and n 10-20/Ag The value can be increased by more than 22%, the hole expansion rate can be increased by more than 28%, and the punching ductility and flanging formability of the material are synchronously improved. The conventional steel-making, hot-rolling, cold-rolling and hot-galvanizing production line is used for producing the steel which meets the requirements of drawing, flanging flange and corrosion resistance of complex parts, meets the requirement of welding performance, can replace the conventional DP590 and DP490, and widens the application range of the dual-phase steel.
The invention does not need to add new production equipment, has stable production process, and the final steel plate has the characteristics of high n value, high elongation and high reaming and meets the requirements of high ductility and high reaming and flanging of complex vehicle body structural members.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (3)

1. The 590 MPa-level high-formability hot dip galvanized dual phase steel plate is characterized by comprising the following components in percentage by weight:
c:0.05 to 0.09 percent, si:0.6 to 0.9 percent, mn:1.0 1 to 8 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.01 percent, and Al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and unavoidable impurities;
and satisfies the following:
；
w is a weight percentage;
67-80% of ferrite, 13-25% of martensite and 0-8% of bainite in the microstructure according to volume fraction;
the thickness range of the steel plate is 0.5-2.3 mm, the yield strength is 330-430 MPa, the tensile strength is 590-700 MPa, the longitudinal elongation of A80 is more than 28%, and the tensile strain hardening index n is equal to or greater than 10-20/Ag 0.18-0.24% and a hole expansion rate of 50-70%.
2. A method for preparing the 590 MPa-level high-formability hot-dip galvanized dual-phase steel sheet according to claim 1, which comprises converter steelmaking, LF furnace refining, slab continuous casting, hot continuous rolling, pickling cold continuous rolling and continuous hot-dip galvanizing production line, and is characterized by comprising the following steps:
1) Continuous casting of slabs
Dynamic light pressing is adopted by the continuous casting machine, and the pressing amount is 3-6 mm;
2) Hot rolling
The hot rolling heat preservation temperature is 1150-1250 ℃, the finishing rolling temperature of the finishing mill is 850-940 ℃, the coiling is carried out after laminar cooling, and the coiling temperature is 540-630 ℃;
3) Pickling-cold tandem rolling
The total rolling reduction rate is 54-80 percent;
4) Continuous annealing-galvanizing-leveling on continuous hot galvanizing production line
In the annealing furnace of the continuous hot galvanizing production line, the temperature of a heating section is 790-830 ℃, the temperature of a heat preservation section is 790-830 ℃, and the dew point of the heating section is: -5 ℃ to-25 ℃, the temperature of a rapid cooling section is 450 ℃ to 490 ℃, and the temperature of the strip steel entering a zinc pot is 450 ℃ to 490 ℃; the dew point temperature of the furnace nose is controlled between minus 40 ℃ and minus 55 ℃, and the furnace is provided with a furnace bodyThe nitrogen humidification amount of the nose is controlled to be 0-3 m 3 /h; the continuous hot galvanizing production line speed is 50-100 m/min, and the elongation of the finishing machine is controlled to be 0.2-0.6%.
3. The method for preparing 590 MPa-level high-formability hot-dip galvanized dual-phase steel sheet according to claim 2, wherein the hot-dip galvanized coating in the step 4) is pure zinc hot dip galvanization or zinc aluminum magnesium hot dip galvanization.
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