CN113025882A

CN113025882A - Hot-base galvanized ferrite bainite high-strength steel plate and preparation method thereof

Info

Publication number: CN113025882A
Application number: CN202110155662.6A
Authority: CN
Inventors: 邹英; 韩赟; 朱国森; 滕华湘; 邱木生; 阳锋; 刘华赛; 谢春乾; 姜英花; 王松涛; 李飞; 章军
Original assignee: Shougang Corp
Current assignee: Shougang Corp
Priority date: 2021-02-04
Filing date: 2021-02-04
Publication date: 2021-06-25
Anticipated expiration: 2041-02-04
Also published as: CN113025882B

Abstract

Practice of the inventionThe embodiment discloses a hot-base galvanized ferrite bainite high-strength steel plate and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by mass: c: 0.05 to 0.12 percent, Si: 0.20-0.70%, Mn: 0.7% -1.5%, Al: 0.01 to 0.50 percent, Nb: 0.02-0.06%, Cr: 0-0.03%, Cu: 0-0.01%, Ni: 0-0.01%, Ti: 0-0.006%, B: 0-0.002%, P: 0-0.01%, S: 0 to 0.003%, and the balance of Fe and inevitable impurities. The method comprises smelting, continuous casting, hot rolling, cooling, coiling, acid pickling and hot galvanizing. The steel plate has yield strength not less than 510MPa, tensile strength not less than 620MPa and elongation percentage after fracture (A)₈₀) Not less than 20 percent, and not less than 85 percent of hole expansion rate, and has the advantages of high strength, good formability and excellent corrosion resistance.

Description

Hot-base galvanized ferrite bainite high-strength steel plate and preparation method thereof

Technical Field

The embodiment of the invention relates to the technical field of steel preparation, in particular to a hot-base galvanized ferrite bainite high-strength steel plate and a preparation method thereof.

Background

In recent years, energy is increasingly tense, the environment is increasingly worsened, the automobile industry is forced to develop towards energy conservation and environmental protection, and the realization of the light weight of the automobile body is an effective way for achieving the aim. The steel is a metal material with the largest application amount on the automobile, the application proportion of the high-strength steel on the automobile is improved, and the self weight of the automobile body can be greatly reduced. The running parts such as automobile wheels, chassis and the like account for more than 25 percent of the total weight of the automobile body, and the requirements on the surface quality of the steel plate are not high, so the steel plate is usually made of hot-rolled high-strength steel. Among them, hot-rolled dual-phase steel has been widely used because of its characteristics such as high strength, good work hardening property and continuous yield. The shapes of the automobile chassis parts are complex, and the steel plates are generally required to have higher bending, flanging and hole expanding performances. The hardness difference between two phases of ferrite/martensite dual-phase steel is large, the deformation coordination capability is poor, and cracks are easy to generate at the interface of the two phases in the forming process, so that the cracking is caused. In contrast, ferrite/bainite dual-phase steel has small hardness difference between two phases and better cooperative deformability, so that the steel is more suitable for forming parts with complex shapes.

However, at present, various automobile chassis parts such as connecting rods and control arms are manufactured by hot-rolled ferrite-bainite pickled plates without coating or some cold-rolled galvanized plates. The hot-rolled pickled plate has low corrosion resistance and short life cycle, and can be used in atmospheric environment to accelerate failure, while the cold-rolled galvanized plate has complex manufacture and higher cost.

Therefore, it is an urgent need to solve the technical problem of how to develop a low-cost hot-base galvanized ferrite bainite high-strength steel with high strength, good formability and excellent corrosion resistance.

Disclosure of Invention

The embodiment of the invention aims to provide a hot-base zinc-plated ferrite bainite high-strength steel plate and a preparation method thereof, wherein the yield strength of the steel plate is more than or equal to 510MPa, the tensile strength of the steel plate is more than or equal to 620MPa, and the elongation after fracture (A) of the steel plate₈₀) The steel plate has the advantages of high strength, good formability and excellent corrosion resistance, and the hole expansion rate is more than or equal to 20 percent.

In order to achieve the above object, an embodiment of the present invention provides a hot-base galvanized ferrite bainite high-strength steel plate, which comprises the following chemical components by mass: c: 0.05 to 0.12 percent, Si: 0.20-0.70%, Mn: 0.7% -1.5%, Al: 0.01 to 0.50 percent, Nb: 0.02-0.06%, Cr: 0-0.03%, Cu: 0-0.01%, Ni: 0-0.01%, Ti: 0-0.006%, B: 0-0.002%, P: 0-0.01%, S: 0 to 0.003%, and the balance of Fe and inevitable impurities.

Further, the internal microstructure of the hot-base galvanized ferrite bainite high-strength steel plate comprises the following components in percentage by volume: 60-80% of ferrite, 20-40% of bainite and 0-5% of carbide, wherein the difference between the hardness of the ferrite and the hardness of the bainite is less than or equal to 120kgf/mm²。

Further, the thickness of the steel plate is 1.8 mm-3.0 mm.

The embodiment of the invention also provides a preparation method of the hot-base galvanized ferrite bainite high-strength steel plate, which comprises the following steps:

smelting by adopting chemical components of the heat-based zinc-plated ferrite bainite high-strength steel plate to obtain molten steel, and continuously casting the molten steel to obtain a plate blank;

heating, rough rolling and finish rolling the plate blank in sequence to obtain a finish rolled plate;

cooling the finish rolling plate after rolling to obtain a rolled cooling plate; wherein, the cooling after rolling includes front end concentrated water cooling stage and air cooling stage, the front end concentrated water cooling stage is: cooling the finish rolling plate to 550-650 ℃ at the speed of 40-80 ℃/s to obtain a first cooling plate; the air cooling stage is as follows: cooling the first cooling plate to 420-480 ℃ at the speed of 10-30 ℃/s to obtain the rolled cooling plate;

coiling, uncoiling and pickling the rolled cooling plate to obtain a galvanized substrate;

and hot galvanizing the galvanized substrate, and finishing to obtain the hot-base galvanized ferrite bainite high-strength steel plate.

Further, heating, rough rolling and finish rolling are sequentially carried out on the plate blank to obtain a finish rolled plate, and the method specifically comprises the following steps:

and heating the plate blank, discharging the plate blank out of the furnace at the temperature of 1220-1260 ℃, then carrying out rough rolling, finish rolling and coiling, and then carrying out air cooling to room temperature to obtain the hot rolled plate.

Further, the initial rolling temperature of the rough rolling is 1090-1160 ℃, and the finishing temperature of the rough rolling is 1030-1100 ℃.

Furthermore, the start rolling temperature of the finish rolling is 980-1040 ℃, and the finish rolling temperature is 840-920 ℃.

Further, the coiling temperature is 420-480 ℃.

Further, the hot galvanizing the galvanized substrate specifically comprises:

preheating the galvanized substrate to 210-230 ℃, then heating to 640-660 ℃ at the speed of 2-3 ℃/s, and preserving heat for 15-20 s to perform pre-oxidation; then continuously heating to 660-720 ℃ at the speed of 0-0.5 ℃/s, soaking for 100-140 s, then slowly cooling to 600-640 ℃ at the speed of 1-3 ℃/s, rapidly cooling to 450-470 ℃ at the speed of 10-20 ℃/s, putting into a zinc pot for galvanizing, and cooling to room temperature.

Further, in the finishing, the finishing elongation is 1.8% -2.2%.

One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

according to the hot-base galvanized ferrite bainite high-strength steel plate provided by the embodiment of the invention, each component is adjusted on the component, and the component elements are optimized, specifically, Si: 0.20-0.70%, and Si has a strong solid solution strengthening effect, can improve the hardness and strength of ferrite, reduces the hardness difference of two phases of ferrite and bainite, and is favorable for improving the hole expansion performance. Mn: 0.7 to 1.5 percent of Mn, which is also a common alloy element in steel, has a solid solution strengthening effect and is beneficial to improving the strength of a matrix structure, and can also improve the hardenability and promote the bainite phase transformation; the steel plate obtained finally has a ferrite-bainite dual-phase structure, and meanwhile, in the preparation method, a two-stage cooling mode of front-end centralized water cooling and air cooling is adopted, namely, the front end of a laminar cooling section is subjected to water cooling, and the cooling water is closed in the back half part for air cooling. Compared with the three-stage cooling of water cooling, air cooling and water cooling commonly adopted by ferrite-bainite dual-phase steel, the cooling method provided by the embodiment of the invention can reduce the non-uniformity of the cooling temperature of the hot rolled plate, is easier to control the coiling temperature and obtain good plate shape, and is more suitable for thin-specification hot basesAnd (4) production of a galvanized substrate. The steel plate has yield strength not less than 510MPa, tensile strength not less than 620MPa and elongation percentage after fracture (A)₈₀) The steel plate has the advantages of high strength, good formability and excellent corrosion resistance, and the hole expansion rate is more than or equal to 20 percent.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a microstructure diagram of a hot rolled plate coil of a hot-base galvanized ferrite bainite high-strength steel provided in example 1 of the present invention;

FIG. 2 is a microstructure diagram of a final product of a hot-base galvanized ferrite bainite high-strength steel provided in example 1 of the present invention;

fig. 3 is an engineering stress-strain curve of a hot-base galvanized ferrite bainite high-strength steel provided in example 1 of the present invention.

Detailed Description

The embodiments of the present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the embodiments of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that the present embodiments and examples are illustrative of the present invention and are not to be construed as limiting the present invention.

Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the invention belong. If there is a conflict, the present specification will control.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the examples of the present invention are commercially available or can be obtained by an existing method.

The hot-base galvanized ferrite bainite high-strength steel plate provided by the embodiment of the invention has the following general idea:

according to a typical implementation manner of the embodiment of the invention, the hot-base galvanized ferrite bainite high-strength steel plate is provided, and the chemical components of the hot-base galvanized ferrite bainite high-strength steel plate are as follows: c: 0.05 to 0.12 percent, Si: 0.20-0.70%, Mn: 0.7% -1.5%, Al: 0.01 to 0.50 percent, Nb: 0.02-0.06%, Cr: 0-0.03%, Cu: 0-0.01%, Ni: 0-0.01%, Ti: 0-0.006%, B: 0-0.002%, P: 0-0.01%, S: 0 to 0.003%, and the balance of Fe and inevitable impurities.

The embodiment of the invention forms the hot-base galvanized ferrite bainite high-strength steel plate with the chemical components by optimizing the composition elements, and is based on the following principle:

the control principle in the chemical composition design of the embodiment of the invention is as follows:

c: 0.05-0.12 percent, C is the most common strengthening element in steel, can improve the hardness and the strength of a matrix structure, and can also improve the hardenability and promote the formation of hard phase structures such as bainite. In order to obtain ideal tensile strength and bake hardening performance without damaging welding and forming performance, the content of C is controlled to be 0.05-0.12 percent.

Si: 0.20-0.70%, Si is an important ferrite forming element, which can promote ferrite phase transformation and delay bead formation. Si has a strong solid solution strengthening effect, can improve the hardness and strength of ferrite, reduces the hardness difference of two phases of ferrite and bainite, and is favorable for improving the hole expansion performance. However, since the Si content is too high to deteriorate the surface quality of the hot rolled coil and to influence the galvanizing effect to some extent, the Si content is controlled to 0.20 to 0.70% in the present invention.

Mn: 0.7 to 1.5 percent of Mn, which is also a common alloy element in steel, has a solid solution strengthening effect and is beneficial to improving the strength of a matrix structure, and the Mn can also improve the hardenability and promote bainite transformation, so that the content of Mn is controlled to be 0.7 percent or more. However, when the Mn content is too high, not only martensite formation is easily promoted but also element segregation is easily caused, which are disadvantageous in steel sheet formability, so that the Mn content is set to not more than 1.5%.

Al: 0.01-0.50%, Al can inhibit carbide precipitation and promote ferrite formation. Al is adopted to replace partial Si, so that the surface quality of the hot rolled coil can be improved, and the adhesion of a zinc layer is improved. Meanwhile, in order to avoid the decrease in the strength of the steel sheet due to the excessive addition of Al, the upper limit of the Al content is set to 0.50%.

Nb: 0.02 to 0.06 percent, and Nb has the functions of inhibiting recrystallization and refining prior austenite grains, and can improve the strength and the forming performance through fine grain strengthening, so the invention adds more than 0.02 percent of Nb. Meanwhile, Nb is a relatively expensive microalloying element, and excessive addition thereof causes an increase in cost, so that the addition amount thereof is limited to not more than 0.06%.

Cr：0～0.03％，Cu：0～0.01％，Ni：0～0.01％，Ti：0～0.006％：

Cr, Cu, Ni and Ti are expensive alloying elements and must be limited from the viewpoint of controlling the alloy cost. Therefore, the present invention does not intentionally add these elements, and if they are inevitably present in an impurity state, the content thereof is limited to the above range.

B: 0-0.002%, B has the effect of obviously improving hardenability, when the components of the thick hot-rolled base plate are designed, a small amount of B can be properly added to improve the hardenability of the steel plate so as to promote the generation of a bainite structure, and the addition amount is not more than 0.002%.

P: 0 to 0.01%, P is not more than 0.01%, preferably 0.005 to 0.01%, because P can suitably improve the strength of the steel sheet, but tends to form segregation at grain boundaries to deteriorate plasticity.

S: 0-0.003%, S is easy to combine with Mn to form coarse MnS inclusions, which deteriorate the formability of the steel plate such as hole expansion and flanging, so the upper limit of the S content is set to 0.003%.

The hot-base galvanized ferrite bainite high-strength steel plate provided by the embodiment of the invention has the thickness of 1.8-3.0 mm, the yield strength of more than or equal to 510MPa, the tensile strength of more than or equal to 620MPa and the elongation after fracture (A)₈₀) Not less than 20%, and hole expansion rate not less than85 percent, has excellent strong plasticity and forming performance, and is very suitable for forming parts with complex shapes, such as various connecting rods, control arms and the like; compared with non-coating ferrite bainite dual-phase steel, the corrosion resistance is very excellent, and the service life of parts can be greatly prolonged.

In the microstructure of the hot-base galvanized ferrite bainite high-strength steel plate, the area ratio of ferrite is 60-80%, the area ratio of bainite is 20-40%, and the area ratio of carbide is 0-5%, wherein the micro Vickers hardness difference of ferrite and bainite is 120kgf/mm²Within.

The following illustrates the limitations of the microstructure:

ferrite: 60% -80%, ferrite low in strength, little in hardness, easy to deform, bear most of strain in the deformation process, and are important composition phases for ensuring the plasticity and the formability of the ferrite bainite high-strength steel plate. When the ferrite proportion is less than 60%, the strength of the steel sheet is improved, but the plasticity and formability are deteriorated; when the ferrite proportion exceeds 80%, the bainite proportion is excessively low, resulting in insufficient strength of the steel sheet.

Bainite: 20-40%, bainite is the hard phase structure which guarantees the strength in the ferrite bainite dual-phase steel. When the bainite proportion is less than 20%, the tensile strength of more than 600MPa cannot be ensured, and because the proportion is low, the bainite obtained by hot rolling is highly rich in carbon, and carbide is easily decomposed in the subsequent high-temperature annealing galvanization process, so that the hole expansion performance of the finished steel plate is reduced. When the bainite ratio is more than 40%, the steel sheet cannot obtain desired plasticity and formability.

Carbide: 0-5%, and carbides are not expected to be obtained in the microstructure of the heat-base galvanized ferrite bainite high-strength steel plate. However, the higher soaking temperature of the annealing of the invention inevitably leads to the decomposition of carbides from part of the hot-rolled bainite, which is detrimental to formability. Therefore, if carbide exists in the structure, the content is limited to 5%.

The difference of micro Vickers hardness between ferrite and bainite is 120kgf/mm²The following reasons are: the microhardness difference between ferrite and bainite is controlled at 120kgf/mm²The main purpose is to ensure good hole expansion performance. If the hardness difference between the two phases is too large, cracks are easily formed at the interface between the two phases during hole expansion, resulting in a decrease in hole expansion performance.

According to another exemplary embodiment of the embodiments of the present invention, there is provided a method of manufacturing the hot-basis galvanized ferrite bainite high strength steel sheet, the method including:

The preparation method of the hot-base galvanized ferrite bainite high-strength steel plate provided by the embodiment of the invention is based on the following principle:

in the embodiment of the invention, the front end centralized water cooling and air cooling are adopted as the cooling mode, and compared with the three-stage cooling of water cooling, air cooling and water cooling which is commonly adopted for ferrite bainite dual-phase steel, the two-stage cooling mode of the front end centralized water cooling and air cooling is adopted, so that the nonuniformity of the cooling temperature of a hot rolled plate can be reduced, the coiling temperature can be controlled more easily, and a good plate shape can be obtained, therefore, the method is more suitable for the production of a thin-specification hot-base galvanized substrate.

In this embodiment, the pre-oxidation is performed by heating to 640-660 ℃ at a rate of 2-3 ℃/s and holding for 15-20 s because: according to the characteristics of the alloy components of the steel plate, pre-oxidation is carried out at 640-660 ℃, so that the thickness and the compactness of an oxidation layer can be better; the pre-oxidation temperature is preferably 650 ℃.

In the embodiment, the continuous heating to 660-720 ℃ at the rate of 0-0.5 ℃/s and soaking for 100-140 s are selected to ensure the pre-oxidation effect and the continuity of the galvanizing process, the soaking temperature in the embodiment of the invention cannot be lower than 650 ℃, so the lower limit of the soaking temperature is set to 660 ℃. However, when the soaking temperature is higher than 720 ℃, bainite tempering is serious, more carbides are formed, even the bainite tempering enters a two-phase region to form a large amount of austenite, and undesirable structures such as epitaxial ferrite and martensite may appear in the subsequent slow cooling and quick cooling processes, so that not only is the process control difficulty increased, but also the formability of the steel plate is reduced. In addition, too high soaking temperature can also greatly increase production costs. Soaking time: 100 s-140 s is that the thickness of the steel plate is between 1.8 mm-3.0 mm, and the steel plate belongs to a thicker specification compared with a conventional cold-rolled plate, so in order to ensure the temperature uniformity in the thickness direction, the soaking time is not suitable to be less than 100 s; however, when the soaking time exceeds 140s, bainite tempering is severe, and it is easily decomposed to form carbide, which is disadvantageous in formability of the steel sheet.

In addition, the preparation method of the hot-base galvanized ferrite bainite high-strength steel plate provided by the embodiment of the invention omits the conventional cold rolling procedure, directly plates zinc on the surface of the pickled hot-rolled substrate, can obtain good zinc layer adhesion effect by a pre-oxidation technology, simplifies the process flow and greatly reduces the manufacturing cost.

As an alternative embodiment, the step of sequentially heating, rough rolling and finish rolling the slab to obtain a finish rolled plate specifically includes:

and heating the plate blank, discharging the plate blank out of the furnace at the temperature of 1220-1260 ℃, then carrying out rough rolling, finish rolling and coiling, and then carrying out air cooling to room temperature to obtain the hot rolled plate. If the tapping temperature is too high, the crystal grains are coarse, and the mechanical property of a final product is influenced; if the tapping temperature is too low, the hot rolling finish rolling stage is easy to enter a non-recrystallization area, so that a hot rolling structure has a relatively obvious deformation zone, and the hole expansion performance is further deteriorated.

As an optional implementation mode, the initial rolling temperature of the rough rolling is 1090-1160 ℃, and the finishing temperature of the rough rolling is 1030-1100 ℃. The initial rolling temperature of the finish rolling is 980-1040 ℃, and the final rolling temperature is 840-920 ℃. The finishing temperature is controlled to control the hot rolled structure and to obtain good hot rolled coil quality. When the finishing temperature is higher than 920 ℃, the hot rolling structure crystal grains are large, so that the tensile strength of the finished steel plate is easy to be insufficient; the finishing temperature is lower than 840 ℃, the deformation resistance of the hot rolled plate is increased, the rolling load of a hot rolling mill is increased, the microstructure is also in an obvious strip shape, and the forming performance of the final steel plate is influenced.

As an alternative embodiment, the coiling temperature is 420 ℃ to 480 ℃. The coiling temperature is controlled to obtain the desired microstructure and its proportional relationship. When the coiling temperature is higher than 480 ℃, the proportion of ferrite is increased, the bainite tempering is obvious, and the strength of the hot-rolled substrate is insufficient; when the coiling temperature is lower than 420 ℃, the enrichment degree of bainite carbon is high, and a martensite structure is easy to appear, so that the hardness difference between adjacent phases is increased, and the forming performance of the steel plate is influenced.

As an optional embodiment, in the finishing, the finishing elongation is 1.8% to 2.2%. The finishing elongation execution range is defined mainly for adjusting the steel sheet yield characteristics and obtaining good sheet shape quality. The annealing temperature of the heat-base galvanized ferrite bainite high-strength steel plate is 660-720 ℃, which is equivalent to high-temperature tempering, the yield strength of the steel plate before finishing is obviously reduced relative to that of a hot-rolled substrate, and a tensile curve usually has an obvious yield platform. For the reasons, the invention sets the finishing elongation between 1.8 percent and 2.2 percent, on one hand, the yield strength can be improved, and on the other hand, the yield plateau can be eliminated.

A hot-dip galvanized ferrite bainite high strength steel sheet and a method for manufacturing the same according to the present invention will be described in detail with reference to examples, comparative examples, and experimental data.

(1) Molten steels of examples 1 to 5 and comparative examples 1 to 2 were prepared and cast into slabs having chemical compositions as shown in table 1.

TABLE 1 mass percents of chemical components of examples and comparative examples

(2) And heating the plate blank, and sequentially carrying out rough rolling, finish rolling, cooling after rolling and coiling to obtain a hot-rolled plate coil with the thickness of 1.8-3.0 mm. The discharging temperature of the plate blank is 1220-1260 ℃, the initial rolling temperature of rough rolling is 1090-1160 ℃, the finishing temperature of rough rolling is 1030-1100 ℃, the initial rolling temperature of finish rolling is 980-1040 ℃, and the finishing temperature is 840-920 ℃; and the cooling after rolling adopts a two-stage cooling mode of front-end concentrated water cooling and air cooling, wherein the cooling rate of the front-end concentrated water cooling is 40-80 ℃/s, the cooling is carried out to 550-650 ℃, the cooling rate of the air cooling is 10-30 ℃/s, the cooling is carried out to 420-480 ℃, and the rolling is carried out at the temperature.

(3) Uncoiling the hot rolled plate coil, pickling and removing the iron scale to obtain a galvanized substrate with good surface quality; specific process parameters for each example and comparative example are shown in table 2.

TABLE 2 Rolling and Cooling Process parameters for the examples and comparative examples

(4) The galvanized substrate is galvanized on a continuous hot galvanizing production line, and the specific process comprises the following steps: preheating a steel plate to 210-230 ℃, heating to 650 ℃ at the speed of 2-3 ℃/s, preserving heat for 15-20 s for pre-oxidation, continuously heating to 660-720 ℃ at the speed of 0-0.5 ℃/s, soaking for 100-140 s, slowly cooling to 600-640 ℃ at the speed of 1-3 ℃/s, rapidly cooling to 450-470 ℃ at the speed of 10-20 ℃/s, putting into a zinc pot for zinc plating, cooling to room temperature, and controlling the finishing elongation to be 1.8-2.2% by a finishing machine after continuous hot galvanizing.

The continuous hot dip galvanizing process parameters of each example and comparative example are shown in table 3.

TABLE 3 continuous hot-dip galvanizing process parameters of each example and comparative example

Tissue detection: preparing a sample for observing a microstructure, corroding the sample by using a 4% nital solution by volume ratio, and observing and acquiring images under a metallographic microscope and a scanning electron microscope for counting each phase example. Meanwhile, the micro-hardness difference between the soft phase ferrite and the hard phase bainite/martensite is measured by using an FM-700 Vickers hardness tester.

And (3) performance detection: detecting yield, tensile strength and elongation after fracture by using a ZWICK/Roell Z100 tensile testing machine according to the GB/T228.1-2010 standard; the hole expansion rate was measured according to ISO 16630-2003 standard using a ZWICK BUP1000 formation tester.

The microstructure and mechanical properties of each of the examples and comparative examples are shown in Table 4.

TABLE 4 microstructure and mechanical Properties of the examples and comparative examples

From the data in table 4, it can be seen that:

in comparative example 1, the contents of Si and Mn are out of the range of the examples of the present invention, and the yield strength of the steel is only 392MPa, and the tensile strength is only 492 MPa;

in comparative example 2, the soaking temperature is 760 ℃, the slow cooling temperature is 680 ℃ which is not in the range of the embodiment of the invention, the yield strength of the prepared steel is only 425MPa, and the hole expansion rate is only 63%;

the steel sheets of examples 1 to 5 had a yield strength of not less than 510MPa, a tensile strength of not less than 620MPa, and a post-fracture elongation (A)₈₀) Not less than 20 percent and not less than 85 percent of hole expansion rate;

description of the drawings:

FIG. 1 shows that the microstructure of the hot rolled plate coil of the hot-base galvanized ferrite bainite high-strength steel plate is ferrite and bainite;

FIG. 2 shows that the finished microstructure of the hot-base galvanized ferrite bainite high-strength steel plate is ferrite, bainite and a small amount of carbide;

FIG. 3 and Table 4 show that the steel plate of the present invention has yield strength not less than 510MPa, tensile strength not less than 620MPa, and elongation after fracture (A)₈₀) The hole expansion ratio is more than or equal to 20 percent, the hole expansion ratio is more than or equal to 85 percent, the high-plasticity-ratio plastic has excellent strong plasticity and forming performance, and the high-plasticity-ratio plastic is very suitable for forming parts with complex shapes, such as various connecting rods, control arms and the like.

In conclusion, the steel plate of the present invention has very excellent corrosion resistance compared to non-plated ferrite-bainite dual phase steel, and the service life of parts can be greatly improved. The preparation method of the heat-based galvanized ferrite bainite high-strength steel plate adopts a two-stage cooling mode of front-end concentrated water cooling and air cooling, reduces the non-uniformity of the cooling temperature of a hot rolled plate, is easier to control the coiling temperature and obtains good plate shape, and is more suitable for the production of thin-specification heat-based galvanized substrates. In addition, the preparation method of the invention omits the conventional cold rolling procedure, directly plates zinc on the surface of the acid-washed hot-rolled substrate, can obtain good zinc layer adhesion effect by the pre-oxidation technology, simplifies the process flow and greatly reduces the manufacturing cost.

Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the embodiments of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims of the embodiments of the present invention and their equivalents, the embodiments of the present invention are also intended to encompass such modifications and variations.

Claims

1. The hot-base galvanized ferrite bainite high-strength steel plate is characterized by comprising the following chemical components in percentage by mass: c: 0.05 to 0.12 percent, Si: 0.20-0.70%, Mn: 0.7% -1.5%, Al: 0.01 to 0.50 percent, Nb: 0.02-0.06%, Cr: 0-0.03%, Cu: 0-0.01%, Ni: 0-0.01%, Ti: 0-0.006%, B: 0-0.002%, P: 0-0.01%, S: 0 to 0.003%, and the balance of Fe and inevitable impurities.

2. The hot-base galvanized ferrite bainite high-strength steel plate according to claim 1, wherein the internal microstructure of the hot-base galvanized ferrite bainite high-strength steel plate comprises, in volume percent: 60-80% of ferrite, 20-40% of bainite and 0-5% of carbide, wherein the difference between the hardness of the ferrite and the hardness of the bainite is less than or equal to 120kgf/mm²。

3. The hot-base galvanized ferrite bainite high-strength steel plate as claimed in claim 1, wherein the thickness of the steel plate is 1.8mm to 3.0 mm.

4. A method for manufacturing a hot-basis galvanized ferrite bainite high strength steel sheet according to any one of claims 1 to 3, characterized by comprising:

smelting by using the chemical components of the heat-based galvanized ferrite bainite high-strength steel plate as claimed in any one of claims 1 to 3 to obtain molten steel, and continuously casting the molten steel to obtain a plate blank;

5. The method for preparing the hot-base galvanized ferrite bainite high-strength steel plate according to claim 4, wherein the plate blank is sequentially subjected to heating, rough rolling and finish rolling to obtain a finish-rolled plate, and the method specifically comprises the following steps:

6. The method for preparing a hot-base galvanized ferrite bainite high-strength steel plate according to claim 4, wherein the initial rolling temperature of the rough rolling is 1090 ℃ to 1160 ℃, and the finishing temperature of the rough rolling is 1030 ℃ to 1100 ℃.

7. The method for preparing a hot-base galvanized ferrite bainite high-strength steel plate according to claim 4, wherein the start rolling temperature of the finish rolling is 980 ℃ to 1040 ℃, and the finish rolling temperature is 840 ℃ to 920 ℃.

8. The method for preparing a hot-basis galvanized ferrite bainite high strength steel plate according to claim 4, wherein the coiling temperature is 420 to 480 ℃.

9. The method for preparing a hot-dip galvanized ferritic bainite high-strength steel sheet according to claim 4, wherein the hot-dip galvanizing the galvanized substrate specifically comprises:

10. The method for preparing a hot-base galvanized ferrite bainite high-strength steel plate according to claim 4, wherein in the finishing, the finishing elongation is 1.8% to 2.2%.