CN118064801A

CN118064801A - A 1180MPa grade hot-dip galvanized dual-phase steel and a preparation method thereof

Info

Publication number: CN118064801A
Application number: CN202410353156.1A
Authority: CN
Inventors: 阳锋; 刘华赛; 韩赟; 朱国森; 滕华湘; 陈斌; 邱木生; 邹英; 韩龙帅; 谢春乾; 姜英花; 于冰; 潘丽梅; 白雪; 陈洪生
Original assignee: Shougang Group Co Ltd
Current assignee: Shougang Group Co Ltd
Priority date: 2024-03-26
Filing date: 2024-03-26
Publication date: 2024-05-24

Abstract

The present application relates to a 1180MPa grade hot-dip galvanized dual-phase steel and a preparation method thereof, and belongs to the technical field of automobile steel and engineering structure steel. The technical problem to be solved by the present application is that the hydrogen-induced delayed cracking ability of dual-phase steel in the prior art is low. The technical solution provided by the present application to solve the above technical problem is: the chemical composition of the dual-phase steel includes: C: 0.10 wt%-0.15 wt%, Si: 0.2 wt%-0.5 wt%, Mn: 2.0 wt%-2.5 wt%, Cr: 0.3 wt%-0.6 wt%, Al: 0.01 wt%-0.05 wt%, P≤0.02 wt%, S≤0.01 wt%, Nb: 0-0.04 wt%, Ti: 0-0.04 wt%, Fe. The annealing treatment is carried out through a hot-dip galvanizing line, the annealing temperature is between 780-820°C, the slow cooling temperature is between 680-720°C, the rapid cooling temperature is between 250-300°C, the aging temperature is between 350-400°C, the zinc pot temperature is 450-470°C, and the belt speed is between 70-20mpm to complete the preparation of high-performance steel plates. After the steel plate obtained by the method of the present application is hydrogenated in a 0.5mol/L _H2SO4 solution at a current of 0.5mA/ ^cm2 _for 3min, the hydrogen embrittlement sensitivity index is less than 30%.

Description

1180 MPa-grade hot dip galvanized dual-phase steel and preparation method thereof

Technical Field

The application relates to the technical field of steel for automobiles and steel for engineering structures, in particular to 1180 MPa-level hot dip galvanized dual-phase steel and a preparation method thereof.

Background

With the gradual increase of the requirements of the automobile industry on energy conservation and emission reduction as well as collision safety, the requirements of the automobile industry on dual-phase steel with higher strength and good forming performance are more and more urgent. At present, 1180 MPa-grade hot dip galvanized dual-phase steel has been applied to vehicle body reinforcements in batches, but because of the strong hydrogen embrittlement sensitivity, the risk of difficult prediction exists in the use process.

Disclosure of Invention

The application provides 1180 MPa-grade hot dip galvanized dual-phase steel and a preparation method thereof, and aims to solve the technical problem of low hydrogen-induced delayed cracking capability of the dual-phase steel in the prior art.

In a first aspect, the application provides 1180 MPa-grade hot dip galvanized dual phase steel, which comprises the following chemical components:

c:0.10 wt% to 0.15 wt%, si:0.2 wt% to 0.5 wt%, mn:2.0 wt% to 2.5 wt%, cr:0.3 wt% to 0.6 wt%, al:0.01 to 0.05 weight percent, P is less than or equal to 0.02 weight percent, S is less than or equal to 0.01 weight percent, nb:0-0.04 wt.%, ti:0-0.04 wt% of Fe.

Optionally, the metallographic structure of the dual-phase steel comprises at least one of the following: ferrite, tempered martensite, bainite, carbide.

Optionally, the ferrite content is 10% to 40% by volume, the sum of the tempered martensite and bainite contents is 70% to 80% by volume, and the carbide content is greater than 0.15% by volume.

In a second aspect, the present application provides a method for preparing 1180 MPa-grade hot dip galvanized dual phase steel, for preparing the dual phase steel according to any one of the first aspect, the method comprising:

Continuously casting molten steel containing the chemical components in the first aspect to obtain a casting blank;

carrying out hot rolling on a casting blank at a set casting blank heating temperature and a set hot rolling finishing temperature;

Coiling the hot rolled casting blank at a set coiling temperature;

cold rolling the coiled casting blank under the condition of setting cold rolling deformation;

And continuously annealing the cold-rolled casting blank at the set annealing soaking temperature, the set slow cooling temperature, the set quick cooling temperature, the set aging temperature and the set belt speed.

Optionally, the heating temperature of the casting blank is set to 1150-1250 ℃, and the final rolling temperature of the hot rolling is set to 880-900 ℃.

Optionally, the set coiling temperature takes a value of 540-560 ℃.

Optionally, the set cold rolling deformation value is 40% -65%.

Optionally, the set annealing soaking temperature is 780-820 ℃, and the set slow cooling temperature is 680-720 ℃.

Optionally, the set rapid cooling temperature is 250-300 ℃, and the set aging temperature is 350-400 ℃.

Optionally, the set belt speed takes a value of 70mpm to 120mpm.

Compared with the prior art, the technical scheme provided by the embodiment of the application has the following advantages:

According to the method provided by the embodiment of the application, a large amount of diffusion-distributed metastable carbide is introduced into the structure of the hot dip galvanized dual-phase steel, and the metastable carbide is an effective hydrogen trap, so that the diffusion of hydrogen atoms to a stress concentration area can be effectively prevented after the metastable carbide adsorbs the hydrogen atoms, and the hydrogen induced delayed cracking capability of the material is effectively improved.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.

In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.

FIG. 1 is a typical microstructure of 1180 MPa-grade hot dip galvanized dual phase steel provided by an embodiment of the application;

FIG. 2 is a graph showing the comparison of the stress-strain curves of the slow strain rate tensile engineering before and after hydrogen flushing according to the embodiment of the present application.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

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.

Various embodiments of the application may exist in a range of forms; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the application; it is therefore to be understood that the range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that a description of a range from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, wherever applicable. In addition, whenever a numerical range is referred to herein, it is meant to include any reference number (fractional or integer) within the indicated range.

In the present application, unless otherwise specified, terms such as "upper" and "lower" are used specifically to refer to the orientation of the drawing in the figures. In addition, in the description of the present specification, the terms "include", "comprising" and the like mean "including but not limited to".

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. Herein, "and/or" describing an association relationship of an association object means that there may be three relationships, for example, a and/or B, may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. Herein, "at least one" means one or more, and "a plurality" means two or more. "at least one", "at least one" or the like refer to any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a. b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

The technical scheme provided by the embodiment of the application aims to solve the technical problems, and provides the following overall thought:

In the embodiment, the positive effect that the mass fraction of C is 0.10% -0.15% is that the strength of the strip steel is ensured to be in a reasonable range, and the strip steel is ensured to have certain hardenability; when the mass fraction is larger than the maximum value of the range or smaller than the minimum value of the range, the strength of the strip steel is higher or lower.

In the embodiment, the positive effect that the mass fraction of Si is 0.2% -0.5% is that the strength of the strip steel is ensured to be in a reasonable range and the surface quality of the strip steel; when the value of the mass fraction is larger than the maximum value of the range, the strength of the strip steel is higher and the surface quality is poor, and when the value of the mass fraction is smaller than the minimum value of the range, the strength of the strip steel is lower.

In the embodiment, the mass fraction of Mn is 2.0% -2.5%, and the positive effect is that the hardenability of the strip steel is ensured to be in a reasonable range; when the value of the mass fraction is larger than the maximum value of the end point of the range, the adverse effect is that the strength of the strip steel is higher, and when the value of the mass fraction is smaller than the minimum value of the end point of the range, the adverse effect is that the hardenability of the strip steel is insufficient and the martensite content in the tissue is insufficient.

In the embodiment, the positive effect that the mass fraction of Cr is 0.3-0.6% is that the hardenability of the strip steel is ensured to be in a reasonable range; when the value of the mass fraction is larger than the end point maximum value of the range, the adverse effect is that the alloy cost is too high, and when the value of the mass fraction is smaller than the end point minimum value of the range, the adverse effect is that the hardenability of the strip steel is insufficient.

In the embodiment, al is a deoxidizer in the smelting process, and the mass fraction is 0.01% -0.05%; when the value of the mass fraction is larger than the end point maximum value of the range, the adverse effect will be caused by excessive inclusion, and when the value of the mass fraction is smaller than the end point minimum value of the range, the adverse effect will be caused by insufficient deoxidizing effect.

In the embodiment, P is a residual element in the steelmaking process, and is generally controlled to be less than or equal to 0.02 percent; when the mass fraction is greater than the end point maximum of the range, the adverse effect is that the tissue is more brittle.

In the embodiment, S is a residual element in the steelmaking process, and is generally controlled to be less than or equal to 0.01 percent; when the mass fraction is larger than the end point maximum of the range, the adverse effect is excessive inclusion.

In the embodiment, the positive effect of 0-0.04% of Nb is grain refinement; when the mass fraction is larger than the end point maximum of the range, the adverse effect is that the alloy cost is too high.

In the embodiment, the positive effect of 0-0.04% of Ti by mass fraction is to provide precipitation strengthening; when the mass fraction is larger than the end point maximum of the range, the adverse effects are high alloy cost and large performance fluctuation.

In some embodiments, the metallographic structure of the dual phase steel comprises at least one of: ferrite, tempered martensite, bainite, carbide.

In some embodiments, the ferrite is present in an amount of 10% to 40% by volume, the sum of the tempered martensite and bainite is present in an amount of 70% to 80% by volume, and the carbide is present in an amount of greater than 0.15% by volume.

In this embodiment, the positive effect of ferrite volume fraction of 10-40% is to ensure that the strength and elongation of the strip steel are in a reasonable range, and when the volume fraction is greater or less than the end value of the range, the adverse effect is lower or higher strength. The positive effect of the tempered martensite and bainite with volume fractions of 60-90% is to ensure that the strength of the strip steel is in a reasonable range, and when the volume fraction is larger or smaller than the end value of the range, the adverse effect is that the strength is higher or lower. The positive effect of the carbide volume fraction of 0.15-1% is to ensure the delayed cracking resistance of the strip steel, when the carbide volume fraction is smaller than the end value of the range, the delayed cracking resistance is insufficient, and when the carbide volume fraction is larger than the end value of the range, the strength of the strip steel is easy to be lower.

Coiling the hot rolled casting blank at a set coiling temperature;

In some embodiments, the set slab heating temperature is from 1150 ℃ to 1250 ℃ and the set hot rolling finishing temperature is from 880 ℃ to 900 ℃.

In this embodiment, the heating temperature of the casting blank is set to 1150-1250 ℃ for tissue homogenization and solid solution of the micro-alloy elements, and excessive temperature may cause abnormal growth of crystal grains, and excessive temperature may cause uneven composition structure and insufficient solid solution of the micro-alloy elements. The setting of the hot rolling finishing temperature to 880-900 ℃ is mainly to ensure that a good hot rolling structure is obtained, grains may become coarse when the finishing temperature is too high, and mixed crystals may occur when the finishing temperature is too low.

In some embodiments, the set take-up temperature takes a value of 540 ℃ to 560 ℃.

In this example, the coiling temperature is set between 540 ℃ and 560 ℃, the influences of the load of the cold rolling mill and the surface quality of the cold rolled finished coil are comprehensively considered, cold rolling becomes difficult when the coiling temperature is too low, and the surface quality of the finished coil becomes poor when the coiling temperature is too high.

In some embodiments, the set cold rolling deformation value is 40% -65%.

In the embodiment, the cold rolling reduction is set to 40% -65% based on two aspects, if the reduction is too low, finer tissues are not beneficial to be obtained, and the yield strength of the material is low; if the rolling reduction is too high, the rolling mill load is too large, which is unfavorable for plate type control.

In some embodiments, the set annealing soak temperature is 780 ℃ to 820 ℃ and the set slow cooling temperature is 680 ℃ to 720 ℃.

In the embodiment, the annealing soaking temperature is 780-820 ℃ and is positioned in the two-phase region temperature of the metallographic structure component. The slow cooling section has almost no heating capacity and is controlled at 680-720 deg.c in order to regulate ferrite content.

In some embodiments, the set rapid cooling temperature is a value of 250 ℃ to 300 ℃ and the set aging temperature is a value of 350 ℃ to 400 ℃.

In this embodiment, the rapid cooling temperature is between 250 ℃ and 300 ℃ to promote transformation of austenite formed in the two-phase region into martensite and bainite. The aging temperature is 320-360 ℃ to separate out a large amount of diffusion-distributed metastable carbide in the martensitic matrix, thereby playing a role in fixing hydrogen element.

In some embodiments, the set belt speed takes a value of 70mpm to 120mpm.

In the embodiment, the positive effect of the belt speed between 70 and 120mpm is to ensure the mechanical property and the coating quality of the strip steel, when the belt speed is lower than the end value of the range, the defect of insufficient strength and surface slag inclusion of the strip steel is easily caused, and when the belt speed is higher than the end value of the range, the defect of higher strength and plating omission of the strip steel is easily caused.

The application will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application. The experimental procedures, which are not specified in the following examples, are generally determined according to national standards. If the corresponding national standard does not exist, the method is carried out according to the general international standard, the conventional condition or the condition recommended by the manufacturer.

Related experiment and effect data:

The preparation method of the embodiment comprises the following steps:

(1) Molten steel is smelted by a converter, and a continuous casting mode is adopted to obtain a continuous casting blank, 5 furnace steel is smelted in a total mode in the embodiment of the application, and the actual chemical composition of the continuous casting blank of the 5 furnace steel is shown in table 1.

Table 1 1-5 chemical composition of furnace steel

Furnace number	C	Si	Mn	Cr	Al	P	S	Nb	Ti
										1#	0.12	0.35	2.3	0.40	0.05	0.011	0.003	0.025	0.025
2#	0.155	0.32	2.3	0.41	0.05	0.011	0.003	0.025	0.025
										3#	0.12	0.1	2.3	0.42	0.05	0.011	0.003	0.025	0.025
4#	0.12	0.31	2.6	0.42	0.05	0.011	0.003	0.025	0.025
										5#	0.12	0.35	2.3	0.75	0.05	0.011	0.003	0.025	0.025

(2) The continuous casting billet is subjected to machine cleaning and then is hot-charged into a furnace, the heating temperature of the continuous casting billet is 1150-1250 ℃, the hot rolling finishing temperature is 890 ℃, and the coiling temperature is 550 ℃. The hot-rolled plate is further subjected to cold rolling to obtain chilled strip steel, and the cold rolling deformation is 50%.

(3) And carrying out continuous annealing treatment on the chilled strip steel to obtain a finished product, wherein the annealing process and the mechanical properties are shown in Table 2. The oven numbers of examples 1-4 were 1#, and the oven numbers of examples 5-8 were 2#, respectively, as shown in Table 2. The annealing temperature of the strip steel is 780-820 ℃, the quick cooling temperature is 250-300 ℃, the aging temperature is 320-360 ℃, and the strip speed is 70-120mpm.

To test the delayed cracking resistance of the material under different annealing processes, the tensile samples were stretched on a slow stretcher after being charged with 0.5mA/cm ² of hydrogen for 3min in 0.5mol/L H ₂SO₄ solution (0.5 g/L thiourea was added as a poisoning agent) at a strain rate of 5X 10 ^-5/s, as shown in FIG. 2. The hydrogen embrittlement sensitivity of the samples was calculated using the formula hei= (1-TE _H/TE₀) ×100%, where HEI (Hydrogen Embrittlement Index) is the hydrogen embrittlement sensitivity index, TE _H is the elongation after hydrogen charging, and TE ₀ is the elongation without hydrogen charging. The performance and hydrogen embrittlement susceptibility index of the different annealing processes are shown in the table below.

TABLE 2 indexes of mechanical properties and hydrogen embrittlement sensitivity under different annealing processes

The rapid cooling temperature of example 1 was the same as the aging temperature, resulting in no precipitation of a large amount of dispersed metastable carbides in the matrix, and the measured carbide volume fraction was less than 0.1%, resulting in an excessively high hydrogen embrittlement sensitivity index. Examples 2 and 3 were shown to have a rapid cooling temperature of 250 ℃ and an aging temperature of 320 ℃ and 360 ℃ respectively, which is advantageous for precipitation of dispersed metastable carbides in the matrix, and the measured integral numbers of metastable carbides are 0.28% and 0.33% respectively, so that the hydrogen embrittlement sensitivity index is low, and the delayed cracking resistance is excellent. The higher aging temperature of example 3 resulted in a higher fraction of carbides in the tissue and better delayed cracking resistance. The belt speed of example 4 was too fast, resulting in a lower number of metastable carbides in the matrix and a higher hydrogen embrittlement sensitivity index. The annealing process of examples 5-8 was substantially identical to that of example 3, but the C content of example 5 was significantly higher (see Table 1), resulting in significantly higher tensile strength of the strip and reduced resistance to delayed cracking. The Si content of example 6 is significantly lower, resulting in a tensile strength below the lower limit of 1180 MPa. Examples 7 and 8 have a higher Mn content and Cr content (see Table 1), which also results in a higher tensile strength and a higher hydrogen embrittlement sensitivity index. FIG. 1 shows a typical microstructure of a hot dip galvanized dual phase steel according to an embodiment of the application.

The difference of the delayed cracking resistance of the embodiment shows that the thought of the invention can obviously improve the hydrogen embrittlement resistance of 1180 MPa-grade hot dip galvanized dual-phase steel.

In the present application, unless otherwise specified, terms such as "upper" and "lower" are used specifically to refer to the orientation of the drawing in the figures. In addition, in the description of the present specification, the terms "include", "comprising" and the like mean "including but not limited to". 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. Herein, "and/or" describing an association relationship of an association object means that there may be three relationships, for example, a and/or B, may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. Herein, "at least one" means one or more, and "a plurality" means two or more. "at least one", "at least one" or the like refer to any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.

The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A 1180MPa grade hot-dip galvanized dual-phase steel, characterized in that the chemical composition of the dual-phase steel includes:

C: 0.10 wt%-0.15 wt%, Si: 0.2 wt%-0.5 wt%, Mn: 2.0 wt%-2.5 wt%, Cr: 0.3 wt%-0.6 wt%, Al: 0.01 wt%-0.05 wt%, P≤0.02 wt%, S≤0.01 wt%, Nb: 0-0.04 wt%, Ti: 0-0.04 wt%, Fe.

2 . The dual-phase steel according to claim 1 , wherein the metallographic structure of the dual-phase steel comprises at least one of the following: ferrite, tempered martensite, bainite, and carbide.

3. The dual-phase steel according to claim 2, characterized in that the content of the ferrite is 10 volume %-40 volume %, the sum of the contents of the tempered martensite and the bainite is 70 volume %-80 volume %, and the content of the carbide is greater than 0.15 volume %.

4. A method for preparing 1180MPa grade hot-dip galvanized dual-phase steel, characterized in that it is used to prepare the dual-phase steel according to any one of claims 1 to 3, and the method comprises:

Continuously casting the molten steel containing the chemical composition of claim 1 to obtain a cast ingot;

Hot rolling the cast slab at a set heating temperature for the cast slab and a set hot rolling final rolling temperature;

Coiling the hot-rolled ingot at a set coiling temperature;

cold rolling the coiled ingot under a set cold rolling deformation amount;

The cold-rolled ingot is continuously annealed under the conditions of a set annealing soaking temperature, a set slow cooling temperature, a set rapid cooling temperature, a set aging temperature and a set belt speed.

5. The method according to claim 4, characterized in that the set billet heating temperature is 1150°C-1250°C, and the set hot rolling final rolling temperature is 880°C-900°C.

6. The method according to claim 4, characterized in that the set coiling temperature is 540°C-560°C.

7. The method according to claim 4, characterized in that the set cold rolling deformation value is 40%-65%.

8. The method according to claim 4, characterized in that the set annealing soaking temperature is 780°C-820°C, and the set slow cooling temperature is 680°C-720°C.

9. The method according to claim 4, characterized in that the set rapid cooling temperature is 250°C-300°C, and the set aging temperature is 350°C-400°C.

10. The method according to claim 4, characterized in that the set belt speed is 70 mpm-120 mpm.