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CN115612934A - 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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CN115612934A
CN115612934A CN202211296954.2A CN202211296954A CN115612934A CN 115612934 A CN115612934 A CN 115612934A CN 202211296954 A CN202211296954 A CN 202211296954A CN 115612934 A CN115612934 A CN 115612934A
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phase steel
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CN115612934B (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
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Abstract

The invention relates toAnd the field of automobile steel manufacturing, in particular to a 590 MPa-grade high-formability hot-dip galvanized dual-phase steel plate and a preparation method thereof. Comprises the following components: c:0.05% -0.09%, si: 0.5-0.9%, mn: 1.0-1.8%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and inevitable impurities, and the alloy satisfies the following conditions:
Figure DDA0003897096150000011
w is weight percent. Compared with the conventional DP590, the invention has the advantages that under the condition that the yield strength and the tensile strength are basically kept consistent, the elongation (A80 longitudinal direction) can be improved by more than 20 percent, and n 10‑20/Ag The value can be improved by more than 22%, the hole expanding rate can be improved by more than 28%, and the stamping ductility and the flanging formability of the material are synchronously improved. The existing conventional steel-making, hot rolling, cold rolling and hot galvanizing production lines are used for producing the products meeting the requirements of drawing, flanging and corrosion resistance of complex parts, and the products can replace the conventional DP590 and DP490, thereby widening 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 automobile steel manufacturing, in particular to 590 MPa-grade high-formability hot-dip galvanized dual-phase steel and a preparation method thereof.
Background
In recent years, with the increasing severity of energy problems and environmental problems, the global environment is protected and the CO is intensified for reducing the greenhouse effect 2 The limitation of the amount of emissions and the reduction of the weight of automobile bodies contributing to low fuel consumption have become an important research topic in the modern automobile industry.
The cold-rolled hot-galvanized dual-phase steel has the characteristics of low yield ratio, high initial work hardening rate, good strength and ductility matching, better bake-hardening performance, higher collision energy absorption capacity and the like, meets the requirements of light weight, collision safety, rust resistance and the like of an automobile body, and is widely applied.
The stamping forming of the hot galvanizing dual-phase steel plate mainly comprises drawing forming and flanging forming. From the reflection of various current automobile processing matching factories and host factories, automobile parts are gradually changed from simple forming into complex forming, and the materials are required to have higher elongation, work hardening rate n value and hole expanding rate.
However, the existing 590MPa grade hot galvanizing dual-phase steel cannot meet the stamping requirements of parts with complex drawing and flange flanging forming requirements, and the problem of stamping cracking occurs, and particularly, for some parts with larger flanging characteristics, a plurality of drawing cracking and/or flanging cracking phenomena occur, which has become a difficult problem in the industry at present.
CN 103146992B discloses a "high strength hot dip galvanized steel sheet with excellent workability", which comprises 0.05 to 0.3% of C, si:0.01 to 2.5%, mn:0.5 to 3.5%, P:0.003 to 0.1%, S:0.02 or less, al: 0.01-1.5%, the structure mainly comprises more than 20% of ferrite, less than 10% of martensite, 10% -60% of tempered martensite and 3-10% of retained austenite. On one hand, in order to improve the elongation and the hole expansibility, a quenching-partitioning Q & P process is adopted to obtain tempered martensite and refined retained austenite, namely, the tempered martensite and the refined retained austenite are cooled to a temperature range from 750 ℃ to (Ms point-100 ℃) to (Ms point-200 ℃) and then heated to 350-600 ℃. The traditional hot galvanizing production line needs to put in tens of millions of RMB reheating equipment to realize the reheating function. Otherwise, the mass production can not be realized on the traditional hot galvanizing production line. And the process needs to invest more electric energy, and the production cost is increased. On the other hand, there is no mention of how to solve the surface quality problem brought about by high Si.
CN 107099739B discloses a tensile strength 600MPa grade low-cost high-hole-expansion steel plate and a production method thereof. The main chemical components are C:0.15 to 0.2 percent of Si, less than or equal to 0.30 percent of Si, 0.8 to 1.0 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, 0.02 to 0.05 percent of Als, ti:0.01 to 0.03 percent of N and less than or equal to 0.0060 percent of N. Tensile strength: 600-650MPa, the lower yield strength is 500-550MPa, the steel-making and hot rolling process control is mainly adopted, the high-carbon design (C: 0.15-0.2%) is adopted, the high-carbon steel has high hole expansion rate, but the yield ratio is high, the material is not beneficial to stamping and forming, and the hot galvanizing process is not involved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a 590 MPa-grade high-formability hot-dip galvanized dual-phase steel plate and a preparation method thereof. The elongation and the hole expanding rate are improved, the stamping ductility and the flanging formability of the material are synchronously improved, and the requirements of the drawing, the flanging formability and the corrosion resistance of complex parts are met.
In order to achieve the purpose, the invention adopts the following technical scheme:
a590 MPa-grade high-formability hot-dip galvanized dual-phase steel comprises the following components in percentage by weight:
c:0.05% -0.09%, si: 0.5-0.9%, mn: 1.0-1.8%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and inevitable impurities.
And satisfies the following conditions:
Figure BDA0003897096130000021
w is weight percent.
A 590 MPa-grade high-forming hot-dip galvanized dual-phase steel plate, the thickness of the steel plate is 0.5-2.3 mm, the yield strength is 330-430 MPa, the tensile strength is 590-700MPa, the A80 longitudinal elongation is more than 28 percent, and the tensile strain hardening index n 10-20/Ag 0.17-0.24, and the hole expanding rate is 50-70%.
A preparation method of a 590 MPa-level high-formability hot-dip galvanized dual-phase steel plate comprises converter steelmaking, LF furnace refining, slab continuous casting, hot continuous rolling, acid pickling cold continuous rolling and continuous annealing, galvanizing and flattening on a continuous hot-dip galvanizing production line, and specifically comprises the following steps:
1) Slab continuous casting
The continuous casting machine adopts dynamic soft reduction, and the reduction is 3-6 mm.
2) Hot rolling
The hot rolling temperature is 1150-1250 ℃, the finishing temperature of a finishing mill is 850-940 ℃, and the coiling is carried out after laminar cooling, wherein the coiling temperature is 540-630 ℃;
3) Pickling-cold continuous rolling
The total cold rolling reduction rate is 54-80%;
4) Continuous annealing, galvanizing and leveling on continuous hot galvanizing production line
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 ℃, and the dew point of the heating section is as follows: the temperature of the fast cooling section is 450-490 ℃ at minus 5 ℃ to minus 25 ℃, and the temperature of the steel plate in 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 ℃ below zero and 55 ℃ below zero and controlling the humidifying quantity of nitrogen of the furnace nose to be between 0 and 3m 3 /h。
As a further improvement of the invention, the step 4) further comprises the steps 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 galvanizing coating in the step 4) is pure zinc hot galvanizing or zinc-aluminum-magnesium hot galvanizing.
Compared with the prior art, the invention 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 carbide in ferrite, purify ferrite, improve the movable dislocation density in the ferrite, form a fine dislocation cellular structure and improve the work hardening rate (n) 10-20/Ag 0.18 or more), and further the elongation (A) is improved 80 Longitudinal direction: more than 28%), and the stamping ductility is improved.
2. According to the invention, 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 is reduced; the low carbon (C: 0.05% -0.09%) design can reduce the carbon content in austenite under the condition of the same annealing temperature, thereby reducing the hardness of a martensite phase after quenching.
The reduction of the hardness difference of the two phases of martensite and ferrite is beneficial to improving the coordinated deformation capability of the two phases of the steel plate in the plastic deformation process, and finally improving the hole expansion rate of the two-phase steel.
3. The dynamic soft reduction is put into the slab in the continuous casting process, 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 the element diffusion and grain boundary migration speed are reduced, thereby inhibiting the growth of ferrite grains, refining the grains, improving the uniformity of the structure, leading austenite to be distributed in the ferrite matrix in a fine and dispersed way when annealing is carried out in a continuous hot galvanizing annealing furnace, obtaining a martensite structure distributed in the ferrite matrix in a fine and dispersed way when cooling, lightening the formation of a martensite belt, and leading the martensite structure distributed in a dispersed way to inhibit the expansion of cracks when flanging and reaming, and finally improving the reaming ratio of the dual-phase steel.
5. According to the invention, the internal oxidation of elements such as Si, mn and the like is realized by controlling the heating section dew point through a pre-oxidation technology in the annealing furnace, and the elements are prevented 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 phenomenon that the diffusion between Fe and Al is inhibited, the Fe2Al5 layer is difficult to form and the plating leakage defect is generated is prevented. The influence of high Si on the surface quality of the steel plate is eliminated by the coupling control technology of the heating section dew point and the furnace nose dew point of the annealing furnace, the technical problem of batch industrial production that the Si content of the hot-dip galvanized dual-phase steel is difficult to exceed more than 0.5 percent 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 invention has the advantages that under the condition that the yield strength and the tensile strength are basically kept consistent, the elongation (A80 longitudinal direction) can be improved by more than 20 percent, and n 10-20/Ag The value can be improved by more than 22%, the hole expanding rate can be improved by more than 28%, and the stamping ductility and the flanging formability of the material are synchronously improved. The existing conventional steel-making, hot rolling, cold rolling and hot galvanizing production line is used for producing the product which meets the requirements of complex parts on drawing, flanging and corrosion resistance, can replace the conventional DP590 and DP490, and widens the application range of the dual-phase steel。
Drawings
FIG. 1 is a metallographic structure drawing in example 1 of the present invention.
FIG. 2 is a scanned tissue map according to example 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 modify the process parameters appropriately to achieve the desired results with reference to the disclosure herein. It is expressly intended that all such similar substitutes and modifications which would be obvious to one skilled in the art are deemed to be included in the invention. While the methods and applications of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations and modifications, or appropriate variations and combinations of the methods and applications described herein may be made to implement and use the techniques of this invention without departing from the spirit and scope of the invention.
The following specific embodiments of the present invention are further described, but are not intended to limit the scope of the invention:
a590 MPa-grade high-formability hot-dip galvanized dual-phase steel comprises the following components in percentage by weight:
c: 0.05-0.09%, si: 0.5-0.9%, mn: 1.0-1.8%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, al:0.02 to 0.05 percent; cr:0.2 to 0.8 percent, and the balance of Fe and inevitable impurities.
The invention carries out optimization design on the chemical components of the steel grade:
1) C is an austenite stabilizing element and mainly plays a role in phase transformation strengthening in the dual-phase steel so as to generate a second phase such as martensite outside the ferrite and improve the tensile strength. By adopting a low-carbon design, the content of carbon in austenite can be reduced under the condition of the same annealing temperature, and the hardness of a martensite phase after quenching is further reduced. If the content of C is lower than 0.05%, the content of a second phase outside the ferrite body is difficult to ensure, and the requirement on tensile strength cannot be met; if the C content is more than 0.09%, on one hand, the weldability is deteriorated, and on the other hand, the C content in the final martensite is high, the strength is increased, the toughness is reduced, and most importantly, the hardness difference between the martensite and the ferrite is increased, so that the hole expansion performance is reduced. Therefore, the content of the C element is controlled to be 0.05-0.09%.
2) The high Si can inhibit the generation of carbide in ferrite, so that C in the ferrite is enriched to austenite, the ferrite is purified, the dislocation density in the ferrite is improved, a fine dislocation cellular structure is formed, the work hardening rate is improved, the elongation is further improved, and the stamping ductility is improved. Meanwhile, more Si (0.5-0.9%) is added and dissolved in the ferrite to further strengthen the ferrite matrix, reduce the hardness difference between the ferrite and the martensite, and improve the hole expansion rate.
The Si content is too low, so that the effects of improving the work hardening rate, the elongation and the hole expanding rate cannot be achieved; the Si content is too high, the steel plate is easy to oxidize on the surface during hot galvanizing annealing, the adhesion force of a zinc layer is reduced, the defects of plating leakage and the like are caused, and the spot welding performance of the steel plate is also deteriorated at the same time, and the upper limit of the Si content is controlled by a hot galvanizing process to be not more than 0.9 percent. Therefore, the content of the Si element is controlled to be 0.5-0.9 percent in the invention.
3) Mn is an element that expands the austenite region, and delays the transformation of pearlite and bainite during the super-cooled austenite cooling process, thereby improving the hardenability of the steel and promoting the formation of martensite during the rapid cooling process after the slow cooling is completed. When the manganese content is too low, hardenability is insufficient, a desired amount of martensite cannot be obtained, and tensile strength cannot be ensured. When the manganese content is excessively high, oxidation or deposition occurs on the surface of the steel sheet during annealing, deteriorating the wettability of the zinc plating and, at the same time, deteriorating the spot weldability of the steel sheet. Therefore, the content of the Mn element is controlled to be 1.0-1.8 percent in the invention.
4) Al is a deoxidizer in the steel-making process in the traditional process, and meanwhile, al can be combined with N in steel to form AlN and refine grains. However, the content of aluminum cannot be too high, and if the content of aluminum is too high, alumina inclusions are increased, and a nozzle is easily blocked in the continuous casting process. Meanwhile, the Al content is too high, special and independent covering slag is needed to be used, and the aluminum alloy can not be continuously cast and produced with other conventional products with Al content, so that the aluminum alloy is not beneficial to tissue mass production. Therefore, the content range of the Al element is controlled to be 0.02-0.06%.
5) The Cr element is an austenite stabilizing element in steel, expands an austenite phase region, improves the hardenability of a steel plate, remarkably delays the transformation of pearlite and bainite, fully transforms austenite into a martensite structure, and increases the martensite content. However, the chromium content cannot be too high, and if the chromium content is too high, chromium carbides are formed to reduce the ductility of the galvanized steel sheet. Therefore, the content of Cr element is controlled within the range of 0.3 to 0.9 percent in the invention.
6) The P element is a harmful element in steel, and the lower the content, the better. In the invention, the content of the P element is controlled to be less than or equal to 0.02 percent in consideration of cost.
7) The S element is a harmful element in steel, and the lower the content, the better. In the invention, the content of the S element is controlled to be less than or equal to 0.01 percent in consideration of the cost.
8) Meanwhile, cu, ni, mo, V and Nb elements are not added in the CEN, so that the elements are not considered in the CEN, the CEN is simplified into a formula only containing C, si, mn and Cr, and the following relational expression is required to be satisfied:
Figure BDA0003897096130000061
w is weight percent.
The main reasons are: when the CEN is less than 0.16, the steel plate has low yield strength and tensile strength; when CEN is higher than 0.24, the steel plate has higher strength due to more addition of alloy elements, and the heat affected zone of the welding joint has higher hardness and poorer toughness, so that the defects of welding cold cracks and the like are easy to occur.
A 590 MPa-level high-formability hot-dip galvanized dual-phase steel plate, the thickness range of the steel plate is 0.5 to 2.3mm, the yield strength is 330 to 430MPa, the tensile strength is 590 to 700MPa, the A80 longitudinal elongation is more than 28 percent, and the tensile strain hardening index n 10-20/Ag 0.18-0.24, and the hole expanding rate is 50-70%.
A preparation method of a 590 MPa-grade high-formability hot-dip galvanized dual-phase steel plate specifically comprises the following steps:
1) Smelting in a converter
Smelting by a converter to obtain molten steel which meets the following component requirements in percentage by weight, C: 0.05-0.09%, si: 0.5-0.9%, mn: 1.0-1.8%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and inevitable impurities. And satisfies the following conditions:
Figure BDA0003897096130000062
the temperature of the molten steel is between 1500 and 1650 ℃.
2) Dynamic soft reduction
The continuous casting machine adopts dynamic soft reduction, and the reduction is 3-6 mm. The dynamic soft reduction is adopted in the continuous casting process, so that the internal banded structure can be effectively reduced, and the casting 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 charging temperature of the casting blank can be above 500 ℃ to save energy, and the charging temperature can be room temperature to facilitate production arrangement. The heating temperature is 1150-1250 ℃, the finishing temperature is 850-940 ℃, and the coiling temperature is 540-630 ℃.
The heating temperature of a plate blank in a hot rolling heating furnace is 1150-1250 ℃, the heating temperature of the casting blank is too high, a low-melting-point compound is easy to appear at a crystal boundary position in steel, the requirement of the finish rolling initial rolling temperature cannot be met due to too low heating temperature, and the problems of too large rolling force or difficult biting and the like are caused.
The finishing temperature is 850-940 ℃, if the finishing temperature is too low, the deformation resistance of the hot rolled plate is too high, and the hot rolled plate is difficult to roll to the target thickness; the final rolling temperature is too high, the crystal grains are coarse, and the mechanical property of the steel plate is deteriorated.
The coiling temperature is 540-630 ℃, the invention adopts lower hot rolling coiling temperature, the element diffusion and the grain boundary migration speed are reduced, thereby inhibiting the growth of ferrite grains, refining the grains, improving the structure uniformity, leading austenite to be distributed in the ferrite matrix in a fine and dispersed way when annealing in a continuous hot galvanizing annealing furnace, obtaining a martensite structure distributed in the ferrite matrix in a fine and dispersed way when cooling, avoiding the formation of a martensite belt, and the dispersed martensite structure can inhibit the expansion of cracks when flanging and reaming, and finally improving the reaming ratio of the dual-phase steel. However, if the coiling temperature is too low, bainite or martensite structures appear in the structures, and the rolling difficulty of subsequent cold rolling is increased.
4) Acid 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%. The rolling reduction is too high, so that the deformation resistance is too high, and the rolling is difficult to reach the target thickness; the reduction ratio is too low, and the elongation of the steel sheet is reduced.
5) Continuous annealing hot 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 temperatures are too low, the austenitization is insufficient, the austenite quantity is less, a sufficient amount 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, the austenite grains are coarse, the yield strength is increased, and the elongation is reduced.
The temperature of the rapid cooling section is 450-490 ℃, the cooling temperature is too high, the cooling rate is too low, the strip steel is easy to enter more ferrite and upper bainite produced, the tensile strength is influenced, and meanwhile, the cooling temperature is too high, the temperature of the strip steel entering a 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 to austenite, the elongation and the n value, the hole expansion rate and the average minimum relative bending radius are influenced, and meanwhile, the cooling temperature is too low, the temperature of the strip steel entering a zinc pot is too low, and the coating property of a coating is influenced.
By means of pre-oxidation technology in the annealing furnace, si and M are realized by controlling the dew point of the heating section to be between-5 ℃ and-25 DEG CAnd n and the like are internally oxidized, so that the elements are prevented from diffusing to the surface of the steel plate to form oxides. The amount of the nitrogen gas humidification is controlled to be 0 to 3m by controlling the furnace nose 3 And/h, keeping the dew point temperature of the furnace nose at-40 to-55 ℃, controlling the secondary oxidation of the surface of the steel plate, and preventing the diffusion between Fe and Al to prevent the Fe2Al5 layer from being formed difficultly and further generating the plating leakage defect. The influence of high Si on the surface quality of the steel plate is eliminated by the coupling control technology of the heating section dew point and the furnace nose dew point of the annealing furnace, the technical problem that the Si content of the hot-galvanized dual-phase steel cannot exceed more than 0.5 percent is innovatively solved, and the surface corrosion resistance of the hot-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 Galvanizing (GI) coating is manufactured, the Al content of a zinc pot is 0.19-0.24%, when the zinc aluminum magnesium hot 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 platform of the strip steel is eliminated, the yield strength of the strip steel is adjusted, and the specified surface roughness is obtained. The finishing elongation is too low to play a role in eliminating a yield platform and obtaining surface roughness; too high finishing elongation, increased yield strength, reduced elongation and the like.
The linear speed of the continuous hot galvanizing production line is 50-100 m/min. The speed is too low, and the defects of zinc fluctuation and the like appear on the surface of the strip steel; the speed is too high, the residence time of the strip steel in the furnace is too short, the values of the elongation, the n value and the hole expansion ratio of the strip steel are low, and the average minimum relative bending radius value is high.
The thickness of the 590MPa grade 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, ferrite 67-80%, martensite 13-25%, and a small amount of bainite: 0 to 8 percent. The absence of retained austenite in the structure improves material formability, and therefore 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, tensile strength of 590-700MPa, A80 longitudinal elongation of more than 28 percent, and tensile strain hardening index n 10-20/Ag 0.18-0.24, and 50% -70% of hole expansion rate. The requirements of high strength, high elongation and high reaming and flanging performance of the automobile body structural member are met, the elongation can be improved by more than 20% compared with the conventional DP590 steel, and n 10-20/Ag The value can be improved by more than 22%, the hole expanding rate can be improved by more than 28%, and the stamping ductility and the flanging formability of the material are synchronously improved. The existing conventional steel-making, hot rolling, cold rolling and hot galvanizing production lines are used for producing the dual-phase steel which meets the requirements of drawing, flanging 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.
[ examples ] A
The following 6 examples are given to illustrate specific embodiments of the present invention and comparative examples, and the specific contents are as follows:
the chemical compositions of the steel sheets, the continuous casting, hot rolling and cold rolling process parameters, the annealing and hot galvanizing process parameters, and the mechanical properties, the hole expansibility, the surface quality and the welding property evaluations of the steel sheets of examples 1 to 6 are respectively listed in tables 1 to 4.
The mechanical properties of the steel plate are measured by using a ZWICK Z100 drawing machine, the test sample is A80 longitudinal direction, the yield strength, the tensile strength and the elongation percentage are measured by performing ISO 6892-1 standard, the strain hardening index (n value) is measured by performing ISO 10275-2007, and the baking hardening value is measured by performing GBT 24174-2009.
And (3) measuring the hole expansion rate by using an Erichsen plate forming machine, wherein the size of a sample plate is 100mm multiplied by 100mmD, and measuring the hole expansion rate values of steel plates with different components and under different processes according to ISO 16630-2009 standard.
The surface quality of the steel plate is detected by using a Parsytec system according to the surface quality standard of a hot-dip galvanized steel plate 'grade 7 plate'.
And measuring the macroscopic metallographic structure of the cross section of the spot welding head under the maximum welding current process by using an MI5000M 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 (%)
Figure BDA0003897096130000091
TABLE 2 continuous casting, hot rolling and cold rolling process of steel sheets of examples
Figure BDA0003897096130000101
TABLE 3 annealing and hot-dip galvanizing process of steel plates of examples
Figure BDA0003897096130000102
TABLE 4 evaluation of mechanical properties, hole expansibility, surface quality and weldability of the steel sheets of the examples
Figure BDA0003897096130000103
Figure BDA0003897096130000111
FIG. 1 is a metallographic structure diagram of example 1 of the present invention, FIG. 2 is a scanning structure diagram of example 1 of the present invention, and FIG. 3 is a typical engineering stress-strain curve of example 1 of the present invention. As shown in the figure, the invention meets the requirements of high strength, high elongation and high hole expansion flanging performance of the automobile body structural part and the outer covering part, 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 improved by more than 22%, the hole expanding rate can be improved by more than 28%, and the stamping ductility and the flanging formability of the material are synchronously improved. The existing conventional steel-making, hot rolling, cold rolling and hot galvanizing production lines are used for producing the dual-phase steel which meets the requirements of drawing, flanging 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 method 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 hole expansion, and meets the requirements of high ductility and high hole expansion flanging of complex vehicle body structural parts.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (6)

1. 590MPa grade high-formability hot-dip galvanized dual-phase steel, which is characterized by comprising the following components in percentage by weight:
c:0.05% -0.09%, si: 0.5-0.9%, mn: 1.0-1.8%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, al:0.02% -0.06%; cr:0.3 to 0.9 percent, and the balance of Fe and inevitable impurities;
and satisfies the following conditions:
Figure FDA0003897096120000011
w is weight percent.
2. A steel sheet made of 590MPa grade high formability hot dip galvanized dual phase steel according to claim 1, wherein the steel sheet has a thickness in the range of 0.5 to 2.3mm, a yield strength of 330 to 430MPa, a tensile strength of 590 to 700MPa, an A80 longitudinal elongation of 28% or more, and a tensile strain hardening index n 10-20/Ag 0.18-0.24, and 50% -70% of hole expansion rate.
3. The preparation method of the 590 MPa-grade high-formability hot-dip galvanized dual-phase steel plate comprises converter steelmaking, LF furnace refining, slab continuous casting, hot continuous rolling, acid pickling cold continuous rolling and continuous annealing, galvanizing and flattening on a continuous hot-dip galvanizing production line, and is characterized by specifically comprising the following steps of:
1) Slab continuous casting
The continuous casting machine adopts dynamic soft reduction, and the reduction amount is 3-6 mm;
2) Hot rolling
The hot rolling temperature is 1150-1250 ℃, the finishing temperature of a finishing mill is 850-940 ℃, and the coiling is carried out after laminar cooling, wherein the coiling temperature is 540-630 ℃;
3) Pickling-cold continuous rolling
The total cold rolling reduction rate is 54-80%;
4) Continuous annealing, galvanizing and leveling on continuous hot galvanizing production line
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 ℃, and the dew point of the heating section is as follows: the temperature of the fast cooling section is 450-490 ℃ at minus 5 ℃ to minus 25 ℃, and the temperature of the strip steel in the zinc pot is 450-490 ℃.
4. The method for preparing a 590MPa grade high-formability galvanized dual-phase steel plate according to claim 3, wherein the step 4) further comprises controlling the furnace nose dew point temperature to be-40 ℃ to-55 ℃, and controlling the furnace nose nitrogen humidification amount to be 0-3 m 3 /h。
5. The method for preparing a 590MPa grade high-formability galvanized dual-phase steel plate according to claim 3, wherein the step 4) further comprises the steps of controlling the continuous hot galvanizing production line speed to be 50-100 m/min and controlling the elongation of a finishing machine to be 0.2-0.6%.
6. The method for preparing 590MPa grade high-formability hot-dip galvanized dual-phase steel sheet according to claim 3, wherein the hot-dip galvanized coating in the step 4) is pure zinc hot-dip galvanizing or zinc-aluminum-magnesium hot-dip galvanizing.
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