CN113528945A

CN113528945A - High-hole-expansion-ratio alloying hot-dip galvanized high-strength steel and preparation method thereof

Info

Publication number: CN113528945A
Application number: CN202110674649.1A
Authority: CN
Inventors: 王川; 刘华赛; 刘李斌; 韩赟; 滕华湘; 邱木生; 李振; 王崇学; 黄学启; 陈瑾; 刘再旺; 尉冬; 李明远
Original assignee: Shougang Group Co Ltd
Current assignee: Shougang Group Co Ltd
Priority date: 2021-06-16
Filing date: 2021-06-16
Publication date: 2021-10-22
Anticipated expiration: 2041-06-16
Also published as: CN113528945B

Abstract

The invention provides high-hole-expansion-ratio alloying hot-dip galvanized high-strength steel, belonging to the technical field of production and manufacturing of cold-rolled ultrahigh-strength steel, and comprising the following chemical components: c: 0.07 to 0.15%, Si: 0.1-0.4%, Mn: 1.6-2.2%, P: less than or equal to 0.01 percent, S: less than or equal to 0.005 percent, Al: 0.02-0.06%, Cr: 0.4-0.8%, Mo: 0.3-0.7%; further comprising at least one of the following elements: ti: 0.01-0.04%, B: 0.002-0.008%; the balance being Fe and unavoidable impurities. The tensile strength of the high-strength steel is more than or equal to 980MPa, and the hole expansion rate can reach 45% or more, so that the high-strength steel is particularly suitable for automobile parts which have flanging hole expansion design and need certain forming capability. The invention also provides a preparation method of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel.

Description

High-hole-expansion-ratio alloying hot-dip galvanized high-strength steel and preparation method thereof

Technical Field

The invention belongs to the technical field of production and manufacturing of cold-rolled ultrahigh-strength steel, and particularly relates to high-hole-expansion-ratio alloying hot-galvanized high-strength steel and a preparation method thereof.

Background

With the development of automobiles towards the direction of energy conservation, environmental protection, safety and comfort, the trend of automobile lightweight tends to be normalized, and practices show that one of the most effective methods for realizing automobile lightweight, high reliability and high cost performance is to improve the application proportion of the advanced high-strength steel and the ultrahigh-strength steel of the automobile, and realize the lightweight of an automobile body by the methods of structural thinning, part structure optimization and the like. The automobile body is developing towards light weight, the requirements on corrosion resistance and impact resistance are higher and higher, and the competitive pressure from materials such as aluminum, magnesium, plastics and the like is added, so that the automobile steel is forced to develop towards high strength and galvanization. Compared with pure zinc plating, the alloyed galvanized layer has good corrosion resistance, heat resistance, painting property, weldability, antirust capacity after painting and good scratch resistance, and the application proportion of the alloyed galvanized sheet on the automobile body is improved year by year due to the excellent characteristics of the alloyed galvanized sheet.

The microstructure of Dual Phase Steel (DP) is composed of polygonal ferrite and martensite, the ferrite provides ductility of Steel, and the martensite provides strength and hardness, but the common high-strength Steel has poor hole-expanding capability, and is not suitable for preparing parts with the requirements of hole-expanding, bending and forming. Therefore, the development of high-strength steel with both high hole expanding performance and good forming performance is urgently needed, and the common requirements of hole expanding and drawing forming are met.

Prior art documents:

chinese patent publication CN201610438785 discloses a dual-phase steel with tensile strength of 1000MPa and a production method thereof. The dual-phase steel comprises the following components: c: 0.08 to 0.11 percent; si: 0.2 to 0.6 percent; mn: 2.0% -2.5%; p: less than or equal to 0.01 percent; s: less than or equal to 0.01 percent; AI: 0.02% -0.06%; cr: 0.4 to 0.6 percent; ti: 0.02% -0.05%; n: less than or equal to 0.003 percent, and the balance of Fe and inevitable impurities, the method solves the technical problems of reducing the alloy cost and improving the hole expansion performance and the delayed fracture resistance of the material on the basis of meeting the strength requirement, but compared with the hole expansion rate of complex phase steel, the hole expansion rate of not more than 35 percent still cannot meet the requirements of flanging and hole expanding of parts.

Patent CN109097676A Chinese patent document discloses an alloyed galvanized dual-phase steel with tensile strength of 1000MPa and a production method thereof. The dual-phase steel comprises the following components: c: 0.10 to 0.15 percent; si: 0.2 to 0.5 percent; mn: 2.0% -2.4%; and (3) Alt: 0.02% -0.05%; ti: 0.015% -0.03%; cr: 0.4 to 0.6 percent; mo: 0.1 to 0.3 percent; p: less than or equal to 0.01 percent; s: less than or equal to 0.01 percent; n: less than or equal to 0.005 percent, the balance of Fe and trace elements, and no mention is made of the product hole expansion ratio, namely, the hole expansion ratio only meets the requirement of the common hole expansion ratio (20 percent to 35 percent) and is difficult to meet the requirement of flanging and hole expanding of parts.

Disclosure of Invention

In order to solve the technical problem that the hole expansion performance of the existing alloying hot-dip galvanized high-strength steel is poor, the invention provides the alloying hot-dip galvanized high-strength steel with the high hole expansion rate, the tensile strength of the high-strength steel is more than or equal to 980MPa, and the hole expansion rate can reach 45% or more, so that the alloying hot-dip galvanized high-strength steel is particularly suitable for automobile parts which need a certain forming capacity while having a flanging hole expansion design.

The invention also provides a preparation method of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel.

The invention is realized by the following technical scheme:

the application provides a high-strength alloyed hot-dip galvanized steel with high hole expansion ratio, which comprises the following chemical components in percentage by mass:

C：0.07％～0.15％，Si：0.1～0.4％，Mn：1.6～2.2％，P：≤0.01％，S：≤0.005％，Al：0.02～0.06％，Cr：0.4～0.8％，Mo：0.3～0.7％；

further comprising at least one of the following elements:

Ti：0.01～0.04％，B：0.002～0.008％；

the balance of Fe and inevitable impurities;

the metallographic structure of the high-strength steel comprises, in area fraction: 80-90% of tempered martensite structure, 5-15% of ferrite structure and 5-10% of bainite structure.

Optionally, the grain size of the tempered martensite structure is 1-4 μm, and the grain size of the ferrite structure is 1-6 μm; the grain size of the bainite structure is 1-5 μm.

Optionally, the high-strength steel comprises the following chemical components in percentage by mass:

C：0.07～0.1％，Si：0.1～0.3％，Mn：1.6～1.9％，P≤0.01％，S：≤0.005，Al：0.03～0.05％，Cr：0.5～0.7％，Mo：0.4～0.6％；

and Ti: 0.02-0.04% and/or B: 0.002-0.004%; the balance being Fe and unavoidable impurities.

Based on the same inventive concept, the application also provides a preparation method of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel, which comprises the following steps:

obtaining a casting blank of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel;

heating and hot rolling the casting blank before rolling to obtain a hot rolled plate;

pickling the hot rolled plate, and then cold rolling to obtain a cold and hard steel coil;

continuously annealing and alloying hot galvanizing the cold and hard steel coil, and then finishing to obtain a hot galvanized coil;

performing secondary isothermal heat treatment on the hot-dip galvanized coil to obtain the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel;

wherein the heating temperature of the heating before rolling is 1200-1250 ℃, and the heat is preserved for 1-2 h;

in the hot rolling, the outlet temperature of rough rolling is 1000-1100 ℃, the finishing temperature is 850-900 ℃, and the coiling temperature is 550-620 ℃.

Optionally, in the cold rolling, 5-pass rolling is adopted

And (3) making, wherein the total reduction rate is 50-60%, and the first-pass cold rolling reduction rate accounts for 20-30% of the total reduction rate.

Optionally, the continuous annealing specifically includes:

heating the cold and hard steel coil to 220 ℃ at a heating speed of 8-12 ℃/s to obtain strip steel;

heating the strip steel to 760-880 ℃ at a heating speed of 1.5-10 ℃/s, and preserving the heat for 60-100 s;

cooling the strip steel to 700-740 ℃ after heat preservation, wherein the cooling speed is 8-12 ℃/s;

and cooling the strip steel cooled to 700-740 ℃ to 450-460 ℃.

Optionally, the galvannealing specifically includes:

hot galvanizing the strip steel continuously annealed to 450-460 ℃, and then cooling to 420-430 ℃ to obtain a hot galvanized coil;

heating the hot-dip galvanized coil to 500-550 ℃ for alloying treatment of the coating;

and cooling the hot-dip galvanized coil subjected to coating alloying treatment to 250-300 ℃ at a cooling speed of 6-9 ℃.

Optionally, in the finishing, the finishing elongation is 0.3% to 0.6%.

Optionally, the secondary isothermal heat treatment of the hot dip galvanized coil specifically includes:

and heating the hot dip galvanized coil to 100-550 ℃, preserving heat for 4-8 hours, and then cooling to room temperature along with the furnace.

One or more technical schemes in the invention at least have the following technical effects or advantages:

1. the high-hole-expansion-ratio alloying hot-dip galvanized high-strength steel improves the chemical components of the steel, controls the microstructure, obtains the high-strength steel with the hole expansion ratio of more than or equal to 45 percent, the yield strength of 630-930 MPa, the tensile strength of 980-1150 MPa, the uniform elongation of more than or equal to 6 percent and the elongation after breakage of more than or equal to 10 percent, has good hole expansion performance and forming performance, and is particularly suitable for automobile parts with flanging hole expansion design and certain forming capability.

2. The invention relates to a preparation method of high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel, which adopts the processes of hot rolling, acid washing, cold rolling, continuous annealing, hot dipping and secondary isothermal treatment to obtain the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel, improves the chemical components and the preparation process of the high-strength steel, controls the microstructure type of the high-strength steel, and obtains the high-strength steel with the hole expansion ratio of more than or equal to 45 percent, the yield strength of 630-930 MPa, the tensile strength of 980-1150 MPa, the uniform elongation of more than or equal to 6 percent, the elongation after fracture of more than or equal to 10 percent, and simultaneously has good hole expansion performance and forming performance.

The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.

Drawings

In order to more clearly illustrate the technical solutions in the present application, the drawings needed to be used in the description of the embodiments will be 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 without creative efforts.

FIG. 1 is a flow chart of a preparation method of high hole expansion rate alloying hot galvanizing high-strength steel.

FIG. 2 is a metallographic structure diagram of a high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel manufactured in example 6 of the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the 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 this invention belongs. 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 present invention are commercially available or can be prepared by existing methods.

It should be further 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.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

In order to solve the technical problems, the general idea is as follows:

according to a typical embodiment of the invention, the high-strength alloyed hot-dip galvanized steel with high hole expansibility comprises the following chemical components in percentage by mass:

further comprising at least one of the following elements:

Ti：0.01～0.04％.B：0.002～0.008％；

the balance of Fe and inevitable impurities;

The principle of the chemical component design of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel is as follows:

c: the C element is used as an important component element of the ultrahigh-strength steel, can enable the strength level of the material to reach 1000MPa, but the excessively high C element can obviously influence the welding performance of the product,

since the element C strongly inhibits the progress of Zn-Fe alloying, the content of C is set to 0.07 to 0.15%, preferably 0.07 to 0.1% in the present invention.

Si: si is also a strengthening element, and it does not enter cementite at the time of solid solution strengthening, and precipitation of carbide can be suppressed. However, since the addition of Si has a significant influence on the surface of the steel strip and tends to cause residual scale on the surface, the Si content cannot be excessively high, and when the Si content is 0.6% or more and the Si/Mn ratio is 0.39 or more, the surface state is seriously deteriorated and a large amount of residual scale exists, so that the Si content is set to 0.1 to 0.4% in the present invention. Preferably 0.1 to 0.3%.

Mn: mn is also a solid solution strengthening element and an austenite stabilizing element, and the addition of Mn can prevent the transformation of austenite to pearlite in the cooling process and improve the hardenability of the material. When the Mn content is too low, the retained austenite stability is poor, and when the Mn content is too high, segregation of P and S elements is caused, thereby deteriorating the workability of the material, so the Mn element content is set to 1.6 to 2.2%, preferably 1.6 to 1.9%.

P and S: p and S are taken as impurity elements, wherein the P element exists in ferrite in a solid solution mode and can cause the toughness of the material to be poor, so that the lower the content of the P element is, the better the material is; the S element interacts with the Mn element to form MnS, which affects the hole-expanding performance and corrosion resistance of the material, so that the lower the content of the S element is, the better the content is, in the present invention, the upper limit of the P content is set to 0.01%, and the upper limit of the S content is set to 0.005%.

AI: AI is a deoxidizing element in steel making, and when the content is less than 0.02%, the deoxidizing ability is insufficient, and when it is too high, Al may be generated in molten steel₂O₃The Al content is not too high because non-metallic inclusions are formed and the viscosity of molten steel is high during casting to block a nozzle, and the Al content is set to 0.02 to 0.06%, preferably 0.03 to 0.05%.

Cr: the main function of the Cr element is to delay transformation of bainite, so that a bainitic ferrite structure can be obtained in a final finished product, the bainitic ferrite structure can ensure that the material obtains higher hole expansion performance, but the excessive Cr can seriously reduce the uniform deformation capacity of the material, and therefore, the content of the Cr element is preferably 0.4-0.8%, and preferably 0.5-0.7%.

Ti: the Ti element can form TiC and TiN precipitation with C, N element, can obviously improve the yield strength of the material, can prevent ferrite grains from growing so as to refine the grains and improve the strength, but the excessive precipitation of the TiC and TiN can reduce the forming performance, so the content of the Ti element is set to be 0.01-0.04%.

Mo: mo element increases hardenability of steel, but too much Mo decreases ductility of the material, so that the content of Mo element is set to 0.3 to 0.7%.

B: the B element can improve the hardenability of steel, the solid solution of B also promotes the formation of fine bainite structures after controlled rolling and controlled cooling, but the material brittleness is caused by high B content, and therefore, the content of the B element is set to be 0.002-0.008%.

According to the invention, the chemical components of the steel are improved, the microstructure is controlled, the hole expansion rate of the obtained high-strength steel is more than or equal to 45%, the yield strength is 630-930 MPa, the tensile strength is 980-1150 MPa, the uniform elongation is more than or equal to 6%, the elongation after fracture is more than or equal to 10%, and the high-strength steel has good hole expansion performance and forming performance, and is particularly suitable for automobile parts which need a certain forming capability while having a flanging hole expansion design.

In an alternative embodiment, the grain size of the tempered martensite structure is 1 to 4 μm, and the grain size of the ferrite structure is 1 to 6 μm; the grain size of the bainite structure is 1-5 μm.

In the application, the metallographic structure of the high-strength steel comprises 80-90% of tempered martensite structure, 5-15% of ferrite structure and 5-10% of bainite structure, and the three microstructures have the grain sizes, the metallographic structure type brings the advantages of low ferrite content, high total content of tempered martensite and bainite and can enable the material to obtain high hole expansion rate, the adverse effect brought by too low area fractions of the three microstructures is that the tempered martensite and bainite content is low and the ferrite content is high, so that the phase-to-phase strength difference is obvious, the hole expansion rate is not high, the adverse effect brought by too high ferrite content reduces the material strength, the total content of tempered martensite and bainite leads to reduction of hole expansion rate, the adverse effect brought by too large grain size leads to remarkable strength difference between ferrite and martensite because of too large grain size, resulting in a low rate of hole expansion.

As a preferred embodiment, the high-strength steel has the following chemical composition in mass fraction:

In the present application, the chemical composition of the high-strength steel adopts the above preferred composition, which brings about the advantages of achieving relatively better performance and reducing performance fluctuation.

According to another exemplary embodiment of the present invention, there is provided a method for preparing a high-strength galvannealed steel with high hole expansibility, as shown in fig. 1, the method including:

s1, obtaining a casting blank of the high-hole-expansion-ratio alloying hot-dip galvanizing high-strength steel;

s2, heating and hot rolling the casting blank before rolling to obtain a hot rolled plate;

s3, carrying out acid pickling on the hot rolled plate, and then carrying out cold rolling to obtain a cold and hard steel coil;

s4, continuously annealing and alloying hot galvanizing the cold and hard steel coil, and then finishing to obtain a hot galvanized coil;

s5, carrying out secondary isothermal heat treatment on the hot-dip galvanized coil to obtain the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel;

According to the invention, hot rolling, pickling, cold rolling, continuous annealing, hot galvanizing and secondary isothermal treatment processes are adopted to obtain the high-hole-expansion-rate alloying hot galvanizing high-strength steel, the chemical components and the preparation process of the high-strength steel are improved, the microstructure type of the high-strength steel is controlled, the hole expansion rate of the obtained high-strength steel is more than or equal to 45%, the yield strength is 630-930 MPa, the tensile strength is 980-1150 MPa, the uniform elongation is more than or equal to 6%, and the elongation after fracture is more than or equal to 10%, and meanwhile, the high-hole-expansion-rate alloying hot galvanizing high-strength steel has good hole expansion performance and forming performance.

In the invention, the heating temperature before rolling, the outlet temperature of rough rolling and the finishing rolling are all in a full austenite region, the coiling temperature is in a bainite transformation region, the obtained hot rolled structure is a ferrite structure and a bainite structure, a more uniform structure can be obtained during subsequent annealing, the alloy distribution in the structure is more uniform, and the over-high or over-low coiling temperature directly influences the structure composition of the annealed material, especially the proportion of martensite, which directly influences the hole expansion rate of the material.

In an optional embodiment, in the cold rolling, 5-pass rolling is adopted, the total reduction rate is 50% -60%, wherein the first-pass cold rolling reduction rate accounts for 20% -30% of the total reduction rate.

In the application, the cold rolling total reduction rate is 50% -60%, wherein the first-pass cold rolling reduction rate accounts for 20-30% of the total reduction rate, the load of a continuous rolling mill is reduced, so that a finished product has a good plate shape, the ratio of the first-pass cold rolling reduction rate is lower than or higher than the range, the length of head and tail waste materials is increased, and the final plate shape is influenced.

As an optional implementation manner, the continuous annealing specifically includes:

in the application, the preheating temperature and the heating speed are the same as the above range values, so that the strip steel is preheated, the strip shape is ensured, and the strip steel has good tissue uniformity.

the values of the heating temperature, the speed and the heat preservation time of the strip steel are within the range, so that the strip steel can be fully recovered and recrystallized.

the use of the above-mentioned values for the strip cooling temperature and the heating rate has the advantage that a certain amount of pro-eutectoid ferrite is obtained.

And cooling the strip steel cooled to 700-740 ℃ to 450-460 ℃.

The final cooling of the strip steel to 450-460 ℃ is to be equivalent to the temperature of the zinc liquid, and has the advantages of improving the wettability of the zinc liquid and reducing the energy consumption.

As an alternative embodiment, the galvannealing specifically comprises:

In the application, the alloying hot galvanizing process can obtain a normal alloying coating, and the Fe content of the coating is kept within the range of 8-13%.

As an optional embodiment, in the finishing, the finishing elongation is 0.3% to 0.6%.

In the present application, since the surface finish is a means for obtaining a suitable roughness on the surface of the strip steel, if the flat elongation is too small or too large, the surface roughness is too small or too large, and therefore the flat elongation is set to 0.2 to 0.6%, preferably 0.3 to 0.4%.

As an optional embodiment, the performing a secondary isothermal heat treatment on the hot-dip galvanized coil specifically includes:

In this application, the heating temperature and the heat preservation time of secondary isothermal heat treatment adopt the benefit that above-mentioned scope brought to improve material reaming performance, and the temperature is crossed lowly and then can not play the effect that improves the reaming rate, and too high then probably influences cladding material quality or reduces material strength.

The high hole expansibility galvannealed high strength steel and the preparation method thereof according to the present invention will be described in detail below with reference to examples, comparative examples and experimental data.

Examples

A high-hole-expansion-ratio alloying hot-dip galvanized high-strength steel is prepared by the following method:

(1) obtaining a casting blank, wherein the casting blank comprises the following chemical components in percentage by mass:

c: 0.07 to 0.15%, Si: 0.1-0.4%, Mn: 1.6-2.2%, P: less than or equal to 0.01 percent, S: less than or equal to 0.005 percent, Al: 0.02-0.06%, Cr: 0.4-0.8%, Mo: 0.3-0.7%; further comprising at least one of the following elements: ti: 0.01-0.04%, B: 0.002-0.008%; the balance being Fe and unavoidable impurities.

(2) And heating the casting blank to 1200-1250 ℃, preserving heat for 1-2 h, and then carrying out hot rolling to obtain a hot rolled plate. In the hot rolling process: the rough rolling outlet temperature is 1000-1100 ℃, the final rolling temperature is 850-900 ℃, preferably 860-890 ℃, the coiling temperature is 550-620 ℃, preferably 560-590 ℃, and the thickness of the hot rolled plate is controlled at 3.0 mm.

(3) And (3) pickling the hot rolled plate, and then cold-rolling to 1.2mm to obtain a cold-hard steel coil. In cold rolling, 5 times of rolling is adopted, the total reduction rate is 55%, wherein the first time of cold rolling reduction rate accounts for 25% of the total reduction rate.

(4) Continuous annealing and hot galvanizing:

and cooling the strip steel cooled to 700-740 ℃ to 450-460 ℃ by blowing.

Hot galvanizing the strip steel continuously annealed to 450-460 ℃, and then cooling to 420-430 ℃ by air knife blowing to obtain a hot galvanized coil;

and (3) performing front-end air cooling matching between the hot-dip galvanized coil subjected to the coating alloying treatment and the top roller, and performing rear-end air cooling to 250-300 ℃ at a cooling speed of 6-9 ℃.

(5) Finishing: the finishing elongation is 0.3-0.6%.

(6) Secondary isothermal heat treatment: and heating the hot dip galvanized coil to 100-550 ℃, preserving heat for 4-8 hours, and then cooling to room temperature along with the furnace.

Based on the above preparation method, the present invention provides 25 typical examples, and provides 4 comparative examples. In 25 examples, the high hole expansibility galvannealed high strength steel has 7 different chemical compositions in total, which are named as compositions 1-7, and the chemical compositions of the compositions 1-7 and the comparative examples are shown in table 1.

Chemical compositions (wt%) of Components 1 to 7 and comparative examples 1 to 4 in Table 1

	C	Si	Mn	P	S	Al	Cr	Mo	Ti	B
											Component 1	0.07	0.39	2.06	0.005	0.003	0.05	0.78	0.65	0.038	0.008
Component 2	0.09	0.33	1.91	0.007	0.003	0.06	0.70	0.58	0.036	0.004
											Component 3	0.09	0.30	2.17	0.007	0.002	0.05	0.69	0.51	0.032	0.002
Component 4	0.08	0.25	1.89	0.006	0.003	0.03	0.66	0.46	0.035	0.003
											Component 5	0.10	0.22	1.80	0.005	0.002	0.04	0.60	0.40	0.032	0.003
Component 6	0.13	0.23	1.87	0.005	0.002	0.05	0.42	0.38	0.013	0.004
											Component 7	0.15	0.11	1.66	0.009	0.004	0.02	0.50	0.33	0.031	0.003
Comparative example 1	0.08	0.39	2.15	0.012	0.002	0.018	0.84	0.28	0.034	0.004
											Comparative example 2	0.07	0.59	2.15	0.005	0.003	0.004	0.90	0.80	0.05	-
Comparative example 3	0.065	0.35	2.20	0.01	0.005	-	0.60	0.63	0.019	-
											Comparative example 4	0.061	0.37	2.17	0.013	0.006	-	0.37	-	0.018	-

The hot rolling and annealing, galvanizing, secondary isothermal heat treatment process parameters of examples 1 to 25 and comparative examples 1 to 4 are shown in table 2.

TABLE 2 Process parameters for examples 1-25 and comparative examples 1-4

TABLE 2 Process parameters for examples 1-25 and comparative examples 1-4

In Table 2, "composition 1, example 1" represents example 1, and the chemical composition of molten steel is composition 1, and so on, in the other examples, the rapid cooling rate represents the cooling rate of cooling the strip steel of 700 ℃ to 740 ℃ to 450 ℃ to 460 ℃.

The mechanical properties of the product obtained by the above process are shown in table 3. Wherein, the conventional mechanical properties of the obtained product are determined by adopting a tensile testing machine according to part 1 of a GBT 228.1-2010 metal material tensile test: the test is carried out by a room temperature test method, and the size of the test sample is the P6 test sample in appendix B; the hole expansion rate was measured according to GBT 15825.4-2008 sheet metal formability and test method.

TABLE 3 mechanical Properties of the finished products obtained in examples 1-25 and comparative examples 1-4

As can be seen from tables 1-3, the material of the invention combines the improvement of the process by special component design, fully excavates the potential of the existing production line, avoids the modification of the production line or the new production line, relatively reduces the cost, can reduce the alloy cost, and obtains 1000MPa alloyed hot-dip galvanized high-strength steel with the hole expansion rate of not less than 45%, the yield strength of 750MPa-910MPa, the tensile strength of 980MPa-1150MPa, the uniform elongation of at least 7% and the elongation after fracture of at least 10%. The traditional high-strength steel can only meet the requirement of forming of a reaming flange, the uniform deformation capacity is poor, and a large amount of stamping cracks can occur in cold stamping.

In contrast, the steel sheets prepared in comparative examples 1 to 4 could not satisfy the target requirements for both formability and hole expansibility.

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

(1) the high-hole-expansion-rate alloying hot-dip galvanizing high-strength steel improves the chemical components of the steel, controls the microstructure, obtains the high-strength steel with the hole expansion rate of more than or equal to 45 percent, the yield strength of 630-930 MPa, the tensile strength of 980-1150 MPa, the uniform elongation of more than or equal to 6 percent, the elongation after fracture of more than or equal to 10 percent, has good hole expansion performance and forming performance, and is particularly suitable for automobile parts which need a certain forming capacity while having a flanging hole expansion design.

(2) The preparation method of the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel adopts the processes of hot rolling, acid washing, cold rolling, continuous annealing, hot dipping and secondary isothermal treatment to obtain the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel, improves the chemical components and the preparation process of the high-strength steel, controls the microstructure type of the high-strength steel, and obtains the high-strength steel with the hole expansion ratio of more than or equal to 45 percent, the yield strength of 630-930 MPa, the tensile strength of 980-1150 MPa, the uniform elongation of more than or equal to 6 percent, the elongation after fracture of more than or equal to 10 percent, and simultaneously has good hole expansion performance and forming performance.

(3) According to the preparation method of the high-hole-expansion-ratio alloying hot-dip galvanized high-strength steel, the heating temperature before rolling, the rough rolling outlet temperature and the final rolling temperature are all in a full austenite region, the coiling temperature is in a bainite transformation region, the obtained hot rolled tissue is an iron cable body and a bainite tissue, a more uniform tissue can be obtained during subsequent annealing, the alloy distribution in the tissue is more uniform, and the too high or too low coiling temperature directly influences the tissue composition of the annealed material, especially the proportion of martensite, which directly influences the hole expansion ratio of the material.

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 invention.

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

Claims

1. The high-strength alloyed hot-dip galvanized steel with the high hole expansion ratio is characterized by comprising the following chemical components in percentage by mass:

further comprising at least one of the following elements:

Ti：0.01～0.04％，B：0.002～0.008％；

the balance of Fe and inevitable impurities;

2. The high-hole-expansion-ratio galvannealed high-strength steel according to claim 1, wherein the grain size of the tempered martensite structure is 1 to 4 μm, and the grain size of the ferrite structure is 1 to 6 μm; the grain size of the bainite structure is 1-5 μm.

3. The high-hole-expansion-ratio galvannealed high-strength steel according to claim 1, wherein the chemical composition of the high-strength steel is as follows by mass fraction:

4. A method for preparing high hole expansibility galvannealed high strength steel according to any of claims 1-3, wherein the method comprises:

5. The preparation method of the high hole expansion rate alloying hot galvanizing high-strength steel as claimed in claim 4, wherein 5 passes of rolling are adopted in the cold rolling, the total rolling reduction rate is 50% -60%, and the first pass of cold rolling reduction rate accounts for 20% -30% of the total rolling reduction rate.

6. The method for preparing the high hole expansibility alloying hot dip galvanizing high strength steel according to claim 4, wherein the continuous annealing specifically comprises:

and cooling the strip steel cooled to 700-740 ℃ to 450-460 ℃.

7. The method for preparing the high hole expansibility alloyed hot dip galvanized high strength steel according to claim 6, wherein the alloyed hot dip galvanized steel specifically comprises:

8. The method for preparing the alloyed hot-dip galvanized high-strength steel with the high hole expansibility according to claim 4, wherein the finishing elongation is 0.3-0.6%.

9. The method for preparing the high-hole-expansion-ratio alloyed hot-dip galvanized high-strength steel according to claim 4, wherein the step of performing secondary isothermal heat treatment on the hot-dip galvanized coil specifically comprises the following steps: