CN115216688B - 800 MPa-grade hot-rolled low-alloy high-strength steel, steel matrix thereof and preparation method thereof - Google Patents

Abstract

The application particularly relates to 800 MPa-grade hot-rolled low-alloy high-strength steel, a steel matrix and a preparation method thereof, which belong to the technical field of steel preparation, wherein the steel matrix comprises the following chemical components in percentage by mass: 0.10 to 0.15 percent of C, 0.1 to 0.3 percent of Si, 1.7 to 2.3 percent of Mn, 0.03 to 0.06 percent of Al, 0.05 to 0.1 percent of Cr, 0 to 0.05 percent of Mo, 0 to 0.05 percent of V, 0.1 to 0.14 percent of Ti, 0 to 0.008 percent of P, 0 to 0.001 percent of S, 0 to 0.005 percent of N, and the balance of Fe; v, ti microalloying is adopted, the yield strength reaches 800MPa or more, the hole expansion rate is more than or equal to 70%, the minimum bent core diameter R of a 90-degree V-shaped bending test is less than or equal to 0.5T (T is the thickness of high-strength steel), the ultrahigh strength and excellent local forming performance are achieved, and the requirements of light weight and complex forming of vehicle body parts in the automobile industry are met.

Description

800 MPa-grade hot-rolled low-alloy high-strength steel, steel matrix thereof and preparation method thereof

Technical Field

The application belongs to the technical field of steel preparation, and particularly relates to 800 MPa-grade hot-rolled low-alloy high-strength steel, a steel matrix thereof and a preparation method thereof.

Background

The hot-rolled low-alloy high-strength steel has good local forming performances such as bending, reaming and the like, and is a preferable material for manufacturing automobile chassis parts such as various beams, fender supporting plates and the like.

Currently, the highest strength grade hot rolled low alloy high strength steel for commercial applications is 700MPa. With the gradual increase of the requirements of the automobile industry for light weight, energy conservation and emission reduction, the development of automobile steel with higher strength level and higher local forming capability is a necessary trend of light weight development.

In addition, the hot-rolled low-alloy high-strength steel is mainly supplied in a hot-rolled bare plate and a hot-rolled pickling plate state at present, and a layer of primer is coated on the surface of the steel plate through a pickling plate and electrophoresis process or a pickling plate and hot-dip galvanizing and electrophoresis process so as to achieve the aim of corrosion prevention. However, due to the harsh operating environment of the chassis, a thicker zinc or paint layer is often required, which presents challenges for both stamping and welding. More importantly, with the diversification of the service environment of the automobile, the electrophoretic paint film is often peeled off and scratched due to stone breakdown, so that the exposed steel plate substrate is corroded. It can be seen that the conventional hot rolled or pickled low alloy high strength steel can not meet the high corrosion resistance requirement of chassis parts. Therefore, there is a need to develop a low alloy high strength steel with higher strength level, better local formability and better corrosion resistance.

Disclosure of Invention

The application aims to provide 800 MPa-grade hot-rolled low-alloy high-strength steel, a steel matrix and a preparation method thereof, so as to solve the problem of insufficient yield strength of the existing high-strength steel.

The embodiment of the application provides a steel matrix of 800 MPa-grade hot-rolled low-alloy high-strength steel, which comprises the following chemical components in percentage by mass: c:0.10 to 0.15 percent, si:0.1 to 0.3 percent of Mn:1.7 to 2.3 percent of Al:0.03 to 0.06 percent, cr:0.05 to 0.1 percent of Mo:0 to 0.05 percent, V:0 to 0.05 percent, ti:0.1 to 0.14 percent, P:0 to 0.008 percent, S:0 to 0.001 percent, N:0 to 0.005 percent, and the balance of Fe and unavoidable impurities.

Optionally, the metallographic structure of the steel substrate comprises, in terms of area ratio: 80% -95% ferrite and 5% -20% horse/aoisland, wherein the equivalent grain diameter of ferrite is <7 μm, and the equivalent grain diameter of horse/aoisland is <3 μm.

Optionally, the metallographic structure of the steel substrate further comprises, in terms of area ratio: 1.4 to 2.0 percent of carbide distributed at the ferrite matrix and the grain boundary, wherein the average equivalent diameter of the carbide is 10 to 80nm.

Based on the same inventive concept, the embodiment of the application also provides a preparation method of the 800 MPa-level hot rolled low-alloy high-strength steel matrix, which comprises the following steps:

smelting molten iron, and then carrying out continuous casting to obtain a plate blank;

and hot rolling the slab to obtain a steel matrix.

Optionally, the final rolling temperature of the hot rolling is 880-920 ℃, the cooling of the hot rolling adopts an air cooling and laminar water cooling mode, the end temperature of the air cooling is more than or equal to 800 ℃, the cooling speed of the laminar water cooling is 10-20 ℃/s, and the coiling temperature of the hot rolling is 400-500 ℃.

Based on the same inventive concept, the embodiment of the application also provides 800 MPa-grade hot rolled low-alloy high-strength steel, which comprises a steel matrix and a plating layer attached to the steel matrix, wherein the steel matrix is the steel matrix.

Optionally, the plating layer is a zinc-aluminum-magnesium alloy plating layer, the thickness of the zinc-aluminum-magnesium alloy plating layer is 8-20 μm, and the chemical components of the zinc-aluminum-magnesium alloy plating layer comprise, in mass fraction: al:5% -7%, mg:2% -4% of Zn and unavoidable impurities in balance.

Based on the same inventive concept, the embodiment of the application also provides a preparation method of the 800 MPa-level hot rolled low-alloy high-strength steel, which comprises the following steps:

flattening the steel matrix, and then carrying out acid washing to obtain an acid washing plate;

and carrying out continuous hot galvanizing on the pickling plate to obtain the high-strength steel.

Optionally, the flattening rolling force is 2000kN to 2500kN.

Optionally, carrying out continuous hot galvanizing on the pickling plate to obtain high-strength steel, which specifically comprises the following steps:

preheating the pickling plate to obtain a preheating plate;

heating the preheating plate to obtain a heating plate;

cooling the heating plate to obtain a cooling plate;

putting the cooling plate into a pot to plate zinc, aluminum and magnesium to obtain plating steel;

carrying out air knife blowing on the coated steel, and then carrying out air jet cooling to obtain high-strength steel;

wherein the heating rate of the preheating is 2 ℃/s-5 ℃/s, and the temperature of the preheating plate is 210 ℃ -230 ℃; the heating rate of the heating is 10 ℃/s-25 ℃/s, the soaking temperature of the heating is 640-720 ℃, and the soaking time of the heating is 40-180 s; the cooling speed is 5 ℃/s-20 ℃/s, and the temperature of the cooling plate is 450-470 ℃.

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

the steel matrix of the 800 MPa-grade hot rolled low-alloy high-strength steel provided by the embodiment of the application adopts V, ti microalloying, the yield strength reaches 800MPa or more, the hole expansion rate is more than or equal to 70%, the minimum bend core diameter R of a 90-degree V-shaped bending test is less than or equal to 0.5T (T is the thickness of the high-strength steel), the ultrahigh strength and excellent local forming performance are achieved, and the requirements of light weight of the automobile industry and complex forming of parts of the automobile body are met.

The foregoing description is only an overview of the present application, and is intended to be implemented in accordance with the teachings of the present application in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present application more readily apparent.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of a method provided by an embodiment of the present application;

fig. 2 is a microstructure of a high strength steel provided by an embodiment of the present application.

Detailed Description

The advantages and various effects of the present application will be more clearly apparent from the following detailed description and examples. It will be understood by those skilled in the art that these specific embodiments and examples are intended to illustrate the application, not to limit the application.

Throughout the specification, unless specifically indicated otherwise, the terms used herein should be understood as meaning as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In case of conflict, the present specification will control.

Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present application are commercially available or may be prepared by existing methods.

The technical scheme of the embodiment of the application aims to solve the technical problems, and the overall thought is as follows:

according to an exemplary embodiment of the present application, there is provided a steel substrate of 800 MPa-grade hot rolled low alloy high strength steel, the steel substrate comprising, in mass fraction: c:0.10 to 0.15 percent, si:0.1 to 0.3 percent of Mn:1.7 to 2.3 percent of Al:0.03 to 0.06 percent, cr:0.05 to 0.1 percent of Mo:0 to 0.05 percent, V:0 to 0.05 percent, ti:0.1 to 0.14 percent, P:0 to 0.008 percent, S:0 to 0.001 percent, N:0 to 0.005 percent, and the balance of Fe and unavoidable impurities.

The control principle of the chemical components of the application is as follows:

c is a main strengthening element in steel. In the low-alloy high-strength steel, C is solid-solution strengthened through gaps to improve the hardness and strength of a matrix structure, and forms carbide with micro-alloy elements such as V, ti and the like to precipitate on a ferrite matrix to play a role in precipitation strengthening. However, the C content cannot be too high, otherwise the weldability is impaired. In order to ensure the yield strength of the high-strength steel of the application above 800MPa, the C content is controlled to be 0.10-0.15%.

Si is a ferrite forming element, has a strong solid solution strengthening effect, can improve the hardness and strength of ferrite, reduces the hardness difference between ferrite and martensite/austenite islands, and is beneficial to improving the local forming performance. However, high Si content can cause scale on the surface of the hot rolled coil, and the hot rolled coil is difficult to clean in the pickling stage, and can easily cause defects of plating omission, dezincification and zinc flow marks. The application controls the content of Si to be 0.1-0.3% by comprehensively considering the effect of Si.

Mn is a solid solution strengthening element, and in order to ensure that the yield and tensile strength of the low-alloy high-strength steel are over 800MPa, the Mn content is not less than 1.7%. However, when the Mn content is too high, hardenability is improved, hard phase structures such as bainite and martensite are liable to be excessively formed, segregation is liable to be formed, and the structure is not uniform, and thus formability is impaired, so that the Mn content in the steel is set to not more than 2.3%.

In the present application, al exists mainly as a deoxidizing element, and thus the Al content is set to 0.03% to 0.06%.

Cr is an element for improving hardenability and is also a strengthening element, which is beneficial to improving the strength of the low-alloy high-strength steel. However, cr tends to undergo external oxidation on the surface of the steel sheet during the annealing galvanization, which is liable to cause surface skip plating. Therefore, the Cr content is set to 0.05% to 0.1%.

Mo is the same as Cr, belongs to the element for improving the hardenability, and is a stronger strengthening element. However, mo is an expensive alloying element, and excessive addition increases the alloy cost, so the present application sets the upper limit of Mo content to 0.05%.

V is a stronger carbonitride forming element. In the continuous hot galvanizing aluminum magnesium process of the high-strength steel, soaking annealing is carried out at 640-720 ℃ for 40-180 seconds, the temperature range is favorable for precipitation of V carbide, good precipitation strengthening effect can be obtained, and further, the yield strength and yield ratio of the low-alloy high-strength steel are improved, and the continuous hot galvanizing aluminum magnesium process is favorable for improving local forming performances such as reaming, bending and the like. In addition, unlike Nb, V does not significantly increase the recrystallization temperature, can avoid or reduce the formation of a fibrous structure along the rolling direction in the hot rolling process, and is favorable for reducing the difference of transverse and longitudinal structures and mechanical properties, thereby obtaining higher structure uniformity.

Ti is similar to V and is a stronger carbonitride forming element, and in the hot rolling process, the carbonitride of Ti has obvious grain refining effect, so that the strength of the low-alloy high-strength steel can be improved, and the local forming performance can be improved. In addition, in the annealing soaking process, ti carbide can be further separated out, so that the hardness and strength of ferrite tissues are improved, and the yield strength of more than 800MPa can be obtained. However, if the Ti content is too high, the precipitation effect becomes saturated and the cost increases, so that the Ti content is limited to 0.1% to 0.14% in the present application.

As interstitial solid solution atoms, P can properly improve the strength of the steel sheet, but is also liable to be biased at grain boundaries to deteriorate the plasticity and formability, so the upper line of P content is set to 0.008%.

S is easily combined with Mn to form coarse MnS inclusions, and the formability of a steel sheet such as hole expansion and flanging is deteriorated, so that the upper limit of S content is set to 0.001%.

In steel, N is an inevitable impurity element, and the binding force between N and Ti is stronger than that between C, and the high content of N consumes Ti excessively, so that the formation amount of Ti carbide is reduced, and the N content needs to be controlled to be 0.005% or less.

In some embodiments, the metallographic structure of the steel substrate comprises in area percent: 80% -95% of ferrite, 5% -20% of horse/austenite islands, 1.4% -2.0% of carbide distributed at the ferrite matrix and the grain boundary, wherein the equivalent grain diameter of the ferrite is less than 7 mu m, the equivalent grain diameter of the horse/austenite islands is less than 3 mu m, and the average equivalent grain diameter of the carbide is between 10nm and 80nm.

Ferrite is a matrix structure, has relatively low hardness and strength, is easy to deform, and is an important constituent phase for ensuring the plasticity and formability of low-alloy high-strength steel. The martensite/austenite islands are structures obtained by incomplete transformation of austenite to martensite, and have strength and hardness higher than those of ferrite and plasticity and toughness lower than those of ferrite. When the ferrite ratio is less than 80% and the ma/aoisland ratio exceeds 20%, the formability of the steel sheet is deteriorated; when the ferrite proportion exceeds 95%, it is difficult to ensure a yield strength of 800MPa and above.

Grain refinement can improve both the strength of the steel sheet and the plasticity and formability. In addition, the finer the crystal grains, the more the crystal grain boundaries, the stronger the inhibition effect on crack growth in the deformation process, and the better the local formability of the steel plate such as reaming, bending and the like, so the application limits the equivalent crystal grain diameter of ferrite to below 7 μm and the equivalent crystal grain diameter of martensite/austenite island to below 3 μm.

Carbides include both cementite and those of the micro-alloy V, ti. Cementite is formed in the annealing soaking process and is decomposed by partial martensite/austenite islands; v, ti carbide is formed during hot rolling coiling and annealing soaking. The carbide is separated out at the ferrite matrix and the grain boundary, so that the strength of ferrite is obviously improved, the hardness difference between ferrite and the martensite/austenite island is reduced, and the formation and the expansion of cracks in the deformation process are inhibited, thereby improving the reaming and bending performances. When the total amount of carbide is less than 1.4%, the strengthening effect on the yield strength is insufficient; since the precipitation amount of V, ti carbide is limited, when the total amount of carbide is more than 2.0%, it is proved that excessive decomposition of the horse/ao island occurs, which results in insufficient tensile strength. Thus, the carbide area fraction is defined to be between 1.4% and 2.0%.

Carbides increase yield strength through interactions with dislocations. At carbide equivalent diameters less than 10nm, interaction with dislocations is typically a cut-through mechanism, in which case the smaller the equivalent diameter, the worse the strengthening effect; when the equivalent diameter of carbide reaches 80nm, the action mechanism of dislocation is mostly bypass mechanism, and the larger the equivalent diameter is, the worse the strengthening effect is. Therefore, in order to obtain a good strengthening effect, it is desirable to limit the average equivalent diameter of the carbide to 10nm to 80nm.

According to another exemplary embodiment of the present application, there is provided a method for preparing a steel substrate of 800 MPa-grade hot rolled low alloy high strength steel as described above, the method comprising:

s1, smelting molten iron, and then carrying out continuous casting to obtain a plate blank;

s2, hot rolling the slab to obtain a steel matrix.

In some embodiments, the final rolling temperature of the hot rolling is 880 ℃ to 920 ℃, the cooling of the hot rolling adopts an air cooling and laminar water cooling mode, the end temperature of the air cooling is more than or equal to 800 ℃, the cooling speed of the laminar water cooling is 10 ℃/s to 20 ℃/s, and the coiling temperature of the hot rolling is 400 ℃ to 500 ℃.

In order to avoid the formation of a fibrous structure in the rolling direction due to the hot rolling into the non-recrystallized region, the formability of the low alloy high strength steel is deteriorated, and the finishing temperature must not be lower than 880 ℃; when the finishing temperature is higher than 920 ℃, austenite grains are relatively coarse, and ferrite and martensite/austenite island grains formed in the cooling and coiling processes are increased in size, which is unfavorable for the strong plasticity and hole expansion performance of the steel plate.

The air cooling speed is relatively low, and ferrite phase transformation and micro-alloy carbide precipitation are easy to occur in the air cooling process. When the air-cooling terminal temperature is lower than 800 ℃, microalloy carbide is gradually precipitated, and the carbide which is precipitated early can be coarsened greatly in the subsequent coiling and soaking annealing processes, so that the precipitation strengthening effect is weakened. Therefore, in order to retain more microalloy elements until precipitation during the annealing soaking process, precipitation during hot rolling cooling must be suppressed. For the above purpose, the present application sets the hot-rolling air cooling temperature not to be lower than 800 ℃.

The purpose of water cooling is to make the hot rolled steel plate enter the bainite transformation zone quickly and further inhibit precipitation of microalloy carbide in the cooling process. When the water cooling speed is less than 10 ℃/s, ferrite tissues are excessively generated, so that the ultimate tensile strength is insufficient; when the water cooling speed is more than 20 ℃/s, the coiling temperature is not easy to control accurately.

The coiling temperature influences the organization structure and the surface quality of the steel plate. When the coiling temperature is lower than 400 ℃, martensite enters a martensitic transformation zone, and the martensite belongs to a hard and brittle phase, so that the local forming performance of the steel plate is not good; when the coiling temperature is higher than 500 ℃, excessive V, ti carbide can be precipitated and grown up, so that the precipitation strengthening effect in the annealing soaking stage is weakened. In addition, the high coiling temperature also easily causes the surface of the hot rolled plate to generate oxide scales, which affects the surface quality of the subsequent galvanization.

According to another exemplary embodiment of the present application, there is provided 800 MPa-grade hot rolled low alloy high strength steel including a steel substrate and a plating layer attached to the steel substrate, the steel substrate being the steel substrate as described above.

In some embodiments, the coating is a zinc-aluminum-magnesium alloy coating, the thickness of the zinc-aluminum-magnesium alloy coating is 8-20 μm, and the chemical components of the zinc-aluminum-magnesium alloy coating comprise, in mass percent: al:5% -7%, mg:2% -4% of Zn and unavoidable impurities in balance.

According to another exemplary embodiment of the present application, there is provided a method for preparing 800 MPa-grade hot rolled low alloy high strength steel as described above, the method comprising:

s1, smelting molten iron, and then carrying out continuous casting to obtain a plate blank;

s2, hot rolling the slab to obtain a steel matrix;

s3, flattening the steel matrix, and then carrying out acid washing to obtain an acid washing plate;

in some embodiments, the temper rolling force is in the range of 2000kN to 2500kN.

When the flattening rolling force is lower than 2000kN, the strip steel plate shape is poor, and the strip steel is deviated in an annealing galvanization furnace due to the existence of the wave defect; when the temper rolling force is higher than 2500kN, transverse roll mark defects appear on the surface of the strip steel, and the strip steel is inherited to a galvanized finished product, so that the appearance quality of the product is poor.

S4, carrying out continuous hot galvanizing on the pickling plate to obtain high-strength steel;

in some embodiments, the continuous hot dip galvanization aluminum magnesium process is: preheating the strip steel to 210-230 ℃ at the speed of 2-5 ℃/s, heating to 640-720 ℃ at the speed of 10-25 ℃/s, soaking for 40-180 s, cooling to 450-470 ℃ at the speed of 5-20 ℃/s, zinc-aluminum-magnesium plating, cooling to 420 ℃ after the strip steel is taken out of the zinc pot, and finally cooling to room temperature by nitrogen/hydrogen mixed gas injection.

The soaking temperature is controlled to be 640-720 ℃; when the soaking temperature is lower than 640 ℃, the carbide precipitation driving force of the micro alloy V, ti is insufficient, a good precipitation strengthening effect cannot be realized, and the chemical action between the plating solution and the surface of the steel plate is weak at the soaking temperature, so that surface defects such as plating omission, zinc flow marks and the like are easy to occur. When the soaking temperature is higher than 720 ℃, carbide grows up and coarsens obviously, precipitation strengthening effect is weakened obviously, and the low alloy high strength steel cannot reach yield and tensile strength of 800MPa or above due to the recovery softening of the structure.

When the soaking time is controlled to be 40-180 s and the soaking time is less than 40s, the precipitation quantity of the micro-alloy V, ti carbide is small, the size is smaller, and the precipitation strengthening effect is limited; when the soaking time exceeds 180s, V, ti carbide grows up and coarsens, and the horse/ao island is excessively decomposed, so that the yield strength and the tensile strength are not improved.

In some embodiments, the method further comprises the step of: s5, surface finishing is carried out on the high-strength steel.

The low-alloy high-strength steel is characterized in that a yield platform is always arranged on a tensile curve, which can lead to the occurrence of a Ludbis band on the surface of a steel plate during stamping forming, and the improvement of the finishing elongation is a feasible method for eliminating the yield platform. In addition, the improvement of the finishing elongation can also improve the plating uniformity. For the steel plate of the application, the finishing elongation is lower than 0.4%, and the yield platform cannot be completely eliminated; when the finishing elongation is more than 0.8%, the steel plate can be seriously hardened, the yield strength is too high, and finishing roll marks can be formed on the surface, so that the appearance quality is affected.

The 800 MPa-grade hot rolled low alloy high strength steel, the steel matrix and the preparation method thereof according to the present application will be described in detail with reference to examples, comparative examples and experimental data.

Examples and comparative examples

(1) Molten steels of examples 1 to 8 and comparative examples 1 to 4 were prepared and cast into slabs having chemical compositions shown in Table 1.

Table 1 mass percent of chemical components of each of examples and comparative examples

(2) And carrying out hot rolling on the slab to obtain a hot rolled coil with the thickness of 2.0-4.0 mm. The final rolling temperature of the hot rolling is 880-920 ℃, the hot rolling cooling adopts an air cooling and laminar water cooling mode, the air cooling end temperature is more than or equal to 800 ℃, the laminar water cooling speed is 10-20 ℃/s, and the coiling temperature is 400-500 ℃.

(3) And uncoiling the hot rolled plate coil, leveling, pickling, and removing hot rolled iron scales to obtain a pickled plate. The flattening rolling force of the flattening process is 2000 kN-2500 kN.

The specific process parameters for each example and comparative example are shown in table 2.

Table 2 hot rolling and leveling process parameters for each of examples and comparative examples

(4) Annealing and galvanizing the pickled plate on a continuous hot galvanizing aluminum magnesium production line, wherein the specific process comprises the following steps of: preheating the strip steel to 210-230 ℃ at the speed of 2-5 ℃/s, heating to 640-720 ℃ at the speed of 10-25 ℃/s, soaking for 40-180 s, cooling to 450-470 ℃ at the speed of 5-20 ℃/s, zinc-aluminum-magnesium plating, cooling to 420 ℃ after the strip steel is taken out of the zinc pot, and finally cooling to room temperature by nitrogen/hydrogen mixed gas injection.

(5) And (3) surface finishing the galvanized aluminum magnesium steel plate, wherein the finishing elongation controlled by the finishing machine is 0.4-0.8%.

The continuous hot dip zinc aluminum magnesium and surface finishing process parameters of each example and comparative example are shown in table 3.

Table 3 continuous hot dip galvanised aluminium magnesium and surface finishing process parameters for each example and comparative example

Experimental example

The microstructure of the low-alloy high-strength steel is analyzed by using a Zeiss Ultra-55 scanning electron microscope and a transmission electron microscope, the yield strength, the tensile strength and the elongation after fracture of the low-alloy high-strength steel are detected by using a ZWICK/Roell Z100 tensile testing machine, the hole expansion rate is detected by using a ZWICK BUP1000 forming testing machine, and the minimum relative bent core diameter is measured by using a microcomputer-controlled electrohydraulic servo bending testing machine.

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

Table 4 microstructure and mechanical Properties of examples and comparative examples

From the table, the yield strength of the high-strength steel prepared by the method provided by the embodiment of the application is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa, the hole expansion rate is more than or equal to 70%, and the minimum bend core diameter R of a 90-degree V-shaped bending test is less than or equal to 0.5T (T is the thickness of the high-strength steel). In comparative example 1, the Mn content is not in the range of the embodiment of the application, the yield strength of the prepared low-alloy high-strength steel is only 744MPa, the tensile strength is only 808MPa, and the hole expansion rate is only 72%; in comparative example 2, the Ti content is not in the range of the embodiment of the application, the carbide ratio of the prepared low alloy high strength steel is only 1.2%, the yield strength is only 768MPa, and the hole expansion ratio is only 66%; in comparative example 3, the coiling temperature is not in the range of the embodiment of the application, the horse/aoisland ratio of the prepared low alloy high strength steel is lower than 5%, the equivalent diameter of carbide reaches 92nm, the yield strength is only 727MPa, and the tensile strength is only 813MPa; in comparative example 4, the soaking temperature was not within the range of the examples of the present application, the yield strength of the produced low alloy high strength steel was only 652MPa, the hole expansion ratio was only 45%, and the minimum bend core diameter R exceeded 0.5T.

Detailed description of fig. 2:

as shown in fig. 2, a microstructure of the high-strength steel according to the embodiment of the present application is shown, and the microstructure of the steel is mainly composed of ferrite, martensite/austenite islands and carbide.

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

(1) The steel matrix provided by the embodiment of the application adopts V, ti microalloying, the yield strength reaches 800MPa or more, the hole expansion rate is more than or equal to 70%, the minimum bend core diameter R of a 90-degree V-shaped bending test is less than or equal to 0.5T (T is the thickness of high-strength steel), the steel matrix has ultrahigh strength and excellent local forming performance, and the requirements of light weight and complex forming of vehicle body parts in the automobile industry are met;

(2) Compared with hot-rolled pickled low-alloy high-strength steel without a coating, the high-strength steel provided by the embodiment of the application has the advantages that the corrosion resistance of the low-alloy high-strength steel is greatly improved, and the problem that the steel for an automobile chassis is easy to rust is solved. In addition, the corrosion resistance of the zinc-aluminum-magnesium coating is more than 6 times that of a pure zinc coating, and the thickness of the electrophoretic primer can be properly reduced by applying the zinc-aluminum-magnesium coating, so that the effect of saving the cost is achieved;

(3) The preparation method of the high-strength steel provided by the embodiment of the application belongs to a hot-rolled pickled plate surface coating process, has short process flow, can realize 'replacing cold with hot', reduces energy consumption and reduces emission.

Finally, it is also 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 application 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. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the application.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (6)

1. An 800 MPa-grade hot rolled low alloy high strength steel, characterized in that the high strength steel comprises a steel substrate and a plating layer attached to the steel substrate, the steel substrate comprising, in mass fraction: c:0.10 to 0.15 percent, si:0.1 to 0.3 percent of Mn:1.7 to 2.3 percent of Al:0.03 to 0.06 percent, cr:0.05 to 0.1 percent of Mo:0 to 0.05 percent, V:0 to 0.05 percent, ti:0.1 to 0.14 percent, P:0 to 0.008 percent, S:0 to 0.001 percent, N:0 to 0.005 percent, and the balance of Fe and unavoidable impurities; the metallographic structure of the steel matrix comprises the following components in percentage by area: 80% -95% ferrite and 5% -20% martensite/austenite islands, wherein the equivalent grain diameter of ferrite is <7 μm, the equivalent grain diameter of martensite/austenite islands is <3 μm, and the metallographic structure of the steel matrix further comprises, in terms of area ratio: 1.4 to 2.0 percent of carbide distributed at the ferrite matrix and the grain boundary, wherein the average equivalent diameter of the carbide is 10 to 80nm, the yield strength of the high-strength steel is more than or equal to 800MPa, the tensile strength is more than or equal to 850MPa, the hole expansion rate is more than or equal to 70 percent, and the minimum bend core diameter R of a 90-degree V-shaped bending test is less than or equal to 0.5T, wherein T is the thickness of the high-strength steel.

2. The 800 MPa-grade hot-rolled low-alloy high-strength steel according to claim 1, wherein the coating is a zinc-aluminum-magnesium alloy coating, the thickness of the zinc-aluminum-magnesium alloy coating is 8-20 μm, and the chemical components of the zinc-aluminum-magnesium alloy coating include, in mass fraction: al:5% -7%, mg:2% -4% of Zn and unavoidable impurities in balance.

3. A method for producing 800 MPa-grade hot-rolled low-alloy high-strength steel according to any one of claims 1 to 2, characterized in that it comprises:

smelting molten iron, and then carrying out continuous casting to obtain a plate blank;

carrying out hot rolling on the slab to obtain a steel matrix;

flattening the steel matrix, and then carrying out acid washing to obtain an acid washing plate;

and carrying out continuous hot galvanizing on the pickling plate to obtain the high-strength steel.

4. The method for producing 800 MPa-grade hot-rolled low-alloy high-strength steel according to claim 3, wherein the final rolling temperature of the hot rolling is 880 ℃ to 920 ℃, the cooling of the hot rolling adopts an air cooling+laminar water cooling mode, the end temperature of the air cooling is not less than 800 ℃, the cooling rate of the laminar water cooling is 10 ℃/s to 20 ℃/s, and the coiling temperature of the hot rolling is 400 ℃ to 500 ℃.

5. A method for producing 800 MPa-grade hot-rolled low-alloy high-strength steel according to claim 3, characterized in that the temper rolling force is 2000kN to 2500kN.

6. The method for preparing 800 MPa-grade hot-rolled low-alloy high-strength steel according to claim 4, wherein the pickling plate is subjected to continuous hot-dip galvanizing of aluminum magnesium to obtain high-strength steel, and the method specifically comprises:

preheating the pickling plate to obtain a preheating plate;

heating the preheating plate to obtain a heating plate;

cooling the heating plate to obtain a cooling plate;

putting the cooling plate into a pot to plate zinc, aluminum and magnesium to obtain plating steel;

carrying out air knife blowing on the coated steel, and then carrying out air jet cooling to obtain high-strength steel;

wherein the heating rate of the preheating is 2 ℃/s-5 ℃/s, and the temperature of the preheating plate is 210 ℃ -230 ℃; the heating rate of the heating is 10 ℃/s-25 ℃/s, the soaking temperature of the heating is 640-720 ℃, and the soaking time of the heating is 40-180 s; the cooling speed is 5 ℃/s-20 ℃/s, and the temperature of the cooling plate is 450-470 ℃.