CN113025883B - 1000MPa cold-rolled dual-phase steel with excellent local forming performance and preparation method thereof - Google Patents
1000MPa cold-rolled dual-phase steel with excellent local forming performance and preparation method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
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- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Abstract
The invention discloses 1000MPa cold-rolled dual-phase steel with excellent local forming performance and a preparation method thereof, wherein the steel comprises the following chemical components in percentage by mass: c: 0.06-0.11%, Si: 0.1 to 0.3%, Mn: 1.5-2.4%, Cr: 0.2-0.6%, Mo: 0.2-0.6%, P: less than or equal to 0.010 percent, S: less than or equal to 0.006 percent, Ti: 0.01 to 0.04%, Al: 0.1-0.3%, B: 0.0001-0.005% of iron and inevitable impurities as the rest, wherein Mn + Cr + B is more than 2.1%; according to the invention, by reasonably designing chemical components, limiting the addition of the easy segregation element Mn, refining crystal grains, forming a nano precipitated phase in ferrite, strengthening a ferrite structure, obtaining balance of strength, elongation and hole expansion performance, and the product has excellent local forming performance.
Description
Technical Field
The invention relates to the technical field of steel preparation, in particular to 1000MPa cold-rolled dual-phase steel with excellent local forming performance and a preparation method thereof.
Background
With increasingly stringent requirements of the automobile industry on light weight, safety, low emission and the like, the use proportion of high-strength steel in new automobile models is continuously increased. The typical representation of the automobile body structure is that in the automobile body structure designed by the project of 'ultra-light steel automobile body-advanced automobile concept', the proportion of high-strength steel with the tensile strength of 1000MPa is the largest, and the high-strength steel accounts for about 29-30% of the weight of the automobile body.
The traditional dual-phase steel structure mainly comprises a softer ferrite matrix and martensite with higher strength, and the structure has the characteristic of lower yield ratio and excellent elongation and is suitable for producing parts formed by stamping. However, admittedly, the dual-phase steel has a high cracking rate in the part forming process required for hole expansion and flanging, while the prior art complex-phase steel shows that the improvement of the hole expansion performance plays a positive role in the improvement of the edge ductility, but the prior art generally has the surface defects of poor phosphorization and the like caused by selective oxidation in the annealing process due to the addition of alloy elements; therefore, on the basis of the traditional dual-phase steel, the local forming performance of the dual-phase steel is further optimized, and the development of the dual-phase steel with excellent hole expanding performance can further meet the use requirements of different users.
Therefore, how to prepare 1000MPa cold-rolled dual-phase steel with excellent local forming performance becomes a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide 1000MPa cold-rolled dual-phase steel with excellent local forming performance and a preparation method thereof, and the 1000MPa cold-rolled dual-phase steel is good in coating performance and local forming performance.
In order to achieve the above object, the present invention provides a 1000MPa cold-rolled dual-phase steel having excellent local formability, the steel having chemical compositions in mass fraction of: c: 0.06-0.11%, Si: 0.1 to 0.3%, Mn: 1.5-2.4%, Cr: 0.2-0.6%, Mo: 0.2-0.6%, P: less than or equal to 0.010 percent, S: less than or equal to 0.006 percent, Ti: 0.01 to 0.04%, Al: 0.1-0.3%, B: 0.0001-0.005% and the balance of iron and inevitable impurities, wherein the mass fraction of Mn, Cr and B elements satisfies: mn + Cr + B is more than 2.1 percent.
Further, the Mn: 1.5 to 1.8 percent.
Further, the internal structure of the steel is a dual-phase structure, wherein the dual-phase structure comprises 60-90% of martensite in percentage by volume, and the balance is ferrite; the martensite comprises martensite islands with the size of 2-4 mu m, and the volume of the martensite islands with the size of 2-4 mu m accounts for more than 80% of the total volume of the martensite.
The invention also provides a preparation method of the 1000MPa cold-rolled dual-phase steel with excellent local forming performance, which comprises the following steps:
smelting and forging the chemical components of the 1000MPa cold-rolled dual-phase steel with excellent local forming performance to obtain a billet;
heating, rough rolling, finish rolling and coiling the billet before rolling to obtain a hot rolled plate;
cold rolling the hot rolled plate to obtain cold-hard strip steel;
annealing the cold-hard strip steel to obtain an annealed steel plate; the annealing comprises a heating section, a soaking section,A slow cooling section and a fast cooling section, wherein the heating section is heated to 780-835 ℃ from room temperature at the rate of 0.9-21 ℃/s; the atmosphere of the soaking section adopts N2-H2Mixed gas of said H2The content is 5 to 15 percent, the soaking temperature is 780 to 835 ℃, the soaking time is 28 to 210 seconds, the dew point is minus 45 to minus 41 ℃, and the oxygen content is 2 to 5 ppm; the slow cooling section is slowly cooled to 600-700 ℃ from the soaking temperature; the fast cooling section is cooled to 250-330 ℃ from 600-700 ℃ at the speed of more than or equal to 30 ℃/s;
and carrying out flattening treatment on the annealed steel plate to obtain the 1000MPa cold-rolled dual-phase steel with excellent local forming performance.
Further, in the heating before rolling, the heating temperature before rolling is controlled to be 1150-1300 ℃, the soaking time is 130-250 min, the steel is discharged from the furnace after soaking, and the discharging temperature is controlled to be 1120-1230 ℃.
Further, the outlet temperature of the rough rolling is 910-1030 ℃, and the rough rolling passes are 6-10.
Further, the finish rolling temperature of the finish rolling is 880-940 ℃; the coiling temperature is 540-660 ℃.
Further, the cold rolling reduction is 45-60%.
Furthermore, the speed of the strip steel passing through the heating section, the soaking section, the slow cooling section and the fast cooling section in the annealing process is controlled to be 120-170 m/min.
Further, during the leveling treatment, the leveling elongation is 0.1% -0.2%.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the 1000MPa cold-rolled dual-phase steel with excellent local forming performance and the preparation method thereof provided by the invention have the advantages that the addition of the easily segregated element Mn is limited by reasonably designing chemical components, and the Mn + Cr + B is controlled to be more than 2.1%; the formation of a final product banded structure is inhibited from a steelmaking source, and a certain microalloy element Ti is added without adding expensive Nb, so that the cost is saved, the effect of further refining grains is achieved, a nanometer precipitated phase is formed in ferrite, the ferrite structure is strengthened, the balance of strength, elongation and hole expansion performance is obtained, and the special continuous annealing process is matched to temper the martensite structure, so that the purpose of reducing the hardness difference of two phases of martensite and ferrite is achieved; the final product has yield strength not less than 600MPa, tensile strength not less than 1000MPa, elongation not less than 12% and hole expansion rate not less than 60%, does not crack along the 180-degree bending radius 0.5T in the rolling direction, and shows excellent local forming performance.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a metallographic structure diagram of a 1000MPa cold-rolled dual-phase steel having excellent local formability according to example 1 of the present invention;
FIG. 2 shows the analysis results of Cr and Mn EPMA of a 1000MPa cold-rolled dual-phase steel having excellent local formability, prepared in example 1 of the present invention; wherein (A) is the EPMA analysis result of Cr; (B) EPMA analysis result for Mn
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 obtained by an existing method.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
according to a typical embodiment of the invention, the 1000MPa cold-rolled dual-phase steel with excellent local forming performance is provided, and the chemical components of the steel in mass fraction are as follows: c: 0.06-0.11%, Si: 0.1 to 0.3%, Mn: 1.5-2.4%, Cr: 0.2-0.6%, Mo: 0.2-0.6%, P: less than or equal to 0.010 percent, S: less than or equal to 0.006 percent, Ti: 0.01 to 0.04%, Al: 0.1-0.3%, B: 0.0001-0.005% and the balance of iron and inevitable impurities, wherein the mass fraction of Mn, Cr and B elements satisfies: mn + Cr + B is more than 2.1 percent.
The 1000MPa cold-rolled dual-phase steel with excellent local forming performance and the above chemical components is formed by optimizing the constituent elements and introducing the middle layer-nickel plating layer, and is based on the following principle:
c: 0.06-0.11%, wherein the C element is the most important solid solution strengthening element and austenite hardenability improving element in the cold-rolled dual-phase steel, and the C content is controlled to be 0.06-0.11% in order to obtain enough martensite in the cooling process to ensure the strength and avoid the welding performance deterioration caused by the over-high C content.
Si: 0.1-0.3%, Si is also an important solid solution strengthening element, and Si can effectively promote the enrichment of C element to austenite, improve the austenite hardenability, purify ferrite phase and improve the elongation, but the defect of Si is that the surface enrichment during the continuous annealing process can be influenced by the excessively high content (more than 0.3%), so that the Si content needs to be controlled at 0.1-0.3%.
Mn: 1.5-2.4%, and Mn is also an important element for solid solution strengthening and austenite stabilizing, and plays an important role in strengthening, but too high Mn content easily causes structure segregation, easily causes forming cracking, deteriorates the comprehensive performance of steel, and also enriches to the surface in the annealing process, so the Mn content is not too high, and needs to be controlled to be 1.5-2.4%. In order to avoid the structure segregation, the structure segregation causes stress concentration to induce the early cracking of the segregation part, and further deteriorates the hole expanding and bending performance, the preferable Mn is less than or equal to 1.8%.
P: less than or equal to 0.010 percent, and the P element can inhibit the formation of carbide, so the P element with a very small content is considered to be favorable, but the segregation at the grain boundary can cause the reduction of the grain boundary strength so as to deteriorate the mechanical property of the material, and the P element content is controlled below 0.010 percent for the invention as a significant influence element of the carbon equivalent contribution.
S: less than or equal to 0.006 percent, and S element is used as a harmful element, which mainly prevents MnS from being generated by combining with Mn so as to deteriorate the material performance, and contributes significant influence elements to carbon equivalent, and the content of the S element is controlled below 0.006 percent.
Cr: 0.2-0.6%, Cr element can improve austenite hardenability, so that enough martensite is obtained to ensure strength, and a certain content of Cr is added to obtain strength, so that the alloy manufacturing cost is low enough; but at the same time, Cr is a ferrite area expanding element, and excessive Cr can cause the two-phase area to be reduced and can also hinder bainite transformation, so that the addition of Cr is limited to ensure that a certain amount of bainite can be obtained, and the Cr content needs to be controlled to be 0.2-0.6%.
Mo: 0.2-0.6%, and the Mo element can also improve the austenite hardenability, so that a sufficient amount of martensite is obtained to ensure the strength, but too much Mo element is easy to be segregated in ferrite to deteriorate the ductility, and meanwhile, the Mo element is high in cost, so that the Mo content needs to be controlled in a proper range. Therefore, the Mo content should be controlled to 0.2-0.6%.
Ti: 0.01-0.04%, Ti as a microalloy element can be combined with C to generate a nano precipitated phase, so that the effects of grain refinement and precipitation strengthening are achieved, the effects of improving the structure form and the yield strength are obvious, the elongation is adversely affected when the content is too high, and the balance of the strength, the elongation and the hole expanding performance can be obtained by adding a certain amount of Ti. Meanwhile, the Ti microalloy is added to inhibit the formation of MnS harmful impurities and is beneficial to reducing micro-crack nucleation points during local forming, so that the content of the Ti microalloy needs to be controlled to be 0.01-0.04 percent.
B: 0.0001-0.005%, the addition of a trace amount of B can obviously improve the hardenability of the steel, the strength of the material is improved, and other properties are not obviously influenced, but the brittleness is caused by the excessively high content of B, so the content of B is required to be controlled to be 0.0001-0.0005%.
Al: 0.1-0.3%, Al is used as a main deoxidizer for steelmaking, the thermodynamic action of the Al is similar to that of Si, the formation of carbides can be inhibited, and austenite is indirectly stabilized, wherein the aluminum content of the invention needs to be controlled to be 0.1-0.3% of Al.
In order to ensure that enough martensite can be obtained after continuous annealing to ensure the tensile strength, the content of elements such as Mn, Cr, B and the like with improved hardenability needs to be further limited, and the invention provides that Mn + Cr + B is more than 2.1 percent.
As a preferred embodiment, the Mn: 1.5 to 1.8 percent. Further enough martensite is obtained to ensure the tensile strength.
In a preferred embodiment, the internal structure of the steel is a dual-phase structure, and the dual-phase structure comprises 60 to 90 volume percent of martensite and the balance of ferrite; the martensite comprises martensite islands with the size of 2-4 mu m, and the volume of the martensite islands with the size of 2-4 mu m accounts for more than 80% of the total volume of the martensite.
The nano precipitated phase formed in the ferrite can strengthen the ferrite structure, and balance of strength, elongation and hole expanding performance is obtained; simultaneously, the aging section is matched with the continuous annealing process to temper the martensite structure, so that the volume of 2-4 mu m martensite islands accounts for more than 80% of the total volume of the martensite, and the aim of reducing the hardness difference of the martensite and the ferrite is fulfilled. A nano precipitated phase is formed in the ferrite, and the volume of the nano precipitated phase accounts for less than 1% of the volume fraction of the ferrite; if the volume fraction of the 2-4 mu m martensite islands is too low, the large-size martensite induces the risk of cracking along the phase interface, and has adverse effect on the improvement of local forming performance;
according to another exemplary embodiment of the present invention, there is provided a method of manufacturing the 1000MPa cold-rolled dual-phase steel having excellent local formability, the method including:
smelting and forging the chemical components of the 1000MPa cold-rolled dual-phase steel with excellent local forming performance to obtain a billet;
heating, rough rolling, finish rolling and coiling the billet before rolling to obtain a hot rolled plate;
cold rolling the hot rolled plate to obtain cold-hard strip steel;
annealing the cold-hard strip steel to obtain an annealed steel plate; the annealing comprises a heating section, a soaking section, a slow cooling section and a fast cooling section, wherein the heating section is heated to 780-835 ℃ from room temperature at the rate of 0.9-21 ℃/s; the atmosphere of the soaking section adopts N2-H2Mixed gas of said H2The content is 5 to 15 percent, the soaking temperature is 780 to 835 ℃, the soaking time is 28 to 210 seconds, the dew point is minus 45 to minus 41 ℃, and the oxygen content is 2 to 5 ppm; the slow cooling section is slowly cooled to 600-700 ℃ from the soaking temperature; the fast cooling section is cooled to 250-330 ℃ from 600-700 ℃ at the speed of more than or equal to 30 ℃/s;
and carrying out flattening treatment on the annealed steel plate to obtain the 1000MPa cold-rolled dual-phase steel with excellent local forming performance.
The special continuous annealing process (annealing comprises a heating section, a soaking section, a slow cooling section and a quick cooling section) of the invention tempers the martensite structure, thus achieving the purpose of reducing the hardness difference between the martensite and the ferrite; the final product has yield strength not less than 600MPa, tensile strength not less than 1000MPa, elongation not less than 12% and hole expansion rate not less than 60%, does not crack along the 180-degree bending radius 0.5T in the rolling direction, and shows excellent local forming performance.
As an optional embodiment, in the pre-rolling heating, the temperature of the pre-rolling heating is controlled to be 1150-1300 ℃, the soaking time is 130-250 min, the steel is discharged after soaking, and the temperature of the discharged steel is controlled to be 1120-1230 ℃.
As an optional embodiment, the rough rolling outlet temperature is 910-1030 ℃, and the rough rolling passes are 6-10.
As an optional embodiment, the finish rolling temperature of the finish rolling is 880-940 ℃; the coiling temperature is 540-660 ℃.
As an alternative embodiment, the cold rolling reduction is 45% to 60%.
As an optional implementation mode, the speed of the strip steel passing through the heating section, the soaking section, the slow cooling section and the fast cooling section in the annealing process is controlled to be 120-170 m/min. The control within the speed is favorable for controlling the time of the strip steel in each section of the furnace area within a certain range, and has important influence on the control organization.
As an optional embodiment, during the leveling treatment, the leveling elongation is 0.1% to 0.2%. Is favorable for obtaining better surface quality and further adjusting the yield strength.
Hereinafter, a 1000MPa cold rolled dual phase steel having excellent local formability and a method for manufacturing the same according to the present application will be described in detail with reference to examples, comparative examples and experimental data.
(1) Smelting molten steel in a converter, and obtaining a continuous casting blank in a continuous casting mode; the actual chemical composition is shown in table 1.
TABLE 1-1000MPa Cold-rolled Dual-phase Steel chemical composition (wt%)
| Group of | C | Si | Mn | P | S | Cr | Alt | Ti | Mo | B |
| Example 1 | 0.07 | 0.2 | 1.7 | 0.007 | 0.003 | 0.45 | 0.15 | 0.03 | 0.2 | 0.003 |
| Example 2 | 0.10 | 0.15 | 1.7 | 0.008 | 0.004 | 0.42 | 0.11 | 0.02 | 0.22 | 0.002 |
| Example 3 | 0.08 | 0.25 | 1.65 | 0.007 | 0.003 | 0.48 | 0.12 | 0.01 | 0.24 | 0.0023 |
| Example 4 | 0.08 | 0.25 | 2.4 | 0.007 | 0.003 | 0.4 | 0.14 | 0.01 | 0.24 | 0.0023 |
| Example 5 | 0.10 | 0.15 | 1.6 | 0.007 | 0.003 | 0.4 | 0.12 | 0.01 | 0.24 | 0.0023 |
| Comparative example 1 | 0.07 | 0.2 | 1.3 | 0.007 | 0.003 | 0.45 | 0.15 | 0.03 | 0.2 | 0.003 |
| Comparative example 2 | 0.07 | 0.2 | 1.7 | 0.007 | 0.003 | 0.45 | 0.15 | 0.03 | 0.2 | 0.003 |
(2) And (2) carrying out hot rolling on the continuous casting slab to obtain a hot rolled plate, heating the continuous casting slab to 1150-1300 ℃, carrying out heat preservation, carrying out final rolling at a temperature of 880-940 ℃, carrying out coiling at a temperature of 540-660 ℃, and further carrying out cold rolling on the hot rolled plate to obtain cold-hard strip steel, wherein the cold rolling deformation is 45-60%, and is shown in Table 2.
TABLE 2-1000MPa Cold-rolled Dual-phase Steel Hot-Rolling Process and product thickness
(3) And carrying out continuous annealing process treatment on the cold-hard strip steel to obtain a finished product. The continuous annealing process is shown in table 3.
Continuous annealing process for cold-rolled dual-phase steel with surface 31000 MPa
The mechanical properties of the samples were tested and the results are shown in Table 4.
TABLE 4-1000MPa Cold-rolled Dual-phase Steel mechanical Properties
| Group of | Rm/MPa | Rp0.2/MPa | A80/％ | Hole expansion ratio/% |
| Example 1 | 1022 | 674 | 13 | 66 |
| Example 2 | 1011 | 682 | 13 | 65 |
| Example 3 | 1024 | 708 | 12 | 64 |
| Example 4 | 1043 | 742 | 12 | 44 |
| Example 5 | 972 | 666 | 13 | 62 |
| Comparative example 1 | 852 | 528 | 18 | 45 |
| Comparative example 2 | 1110 | 682 | 1- | 28 |
From the data in table 4, it can be seen that:
the hole expansion rate is used for measuring the hole flanging capability of the steel plate during stamping, and the higher the hole expansion rate is, the better the local deformation resistance of the material is;
in the comparative example 1, Mn + Cr + B is less than 2.1%, the rest steps are the same as those in the example 1, and the strength is lower;
in comparative example 2, the annealing process of the present invention was not employed, and the remaining steps were the same as in example 1, with higher strength, poorer plasticity, and lower hole expansion performance;
the final product in the examples 1-5 has yield strength of more than or equal to 600MPa, tensile strength of more than or equal to 1000MPa, elongation of more than or equal to 12 percent, hole expansion rate of more than or equal to 60 percent, and no cracking along the rolling direction with 180-degree bending radius of 0.5T;
detailed description of the drawings fig. 1:
FIG. 1 is a photograph showing a typical microstructure of a cold-rolled dual-phase steel sample of example 1. As can be seen from fig. 1, the microstructure includes ferrite in which a nano precipitated phase is formed, and martensite; the martensite comprises martensite islands with the size of 2-4 mu m, and the volume of the martensite islands with the size of 2-4 mu m accounts for more than 80% of the total volume of the martensite.
As can be seen from the attached FIG. 2, the Cr and Mn elements are distributed very uniformly, which further illustrates the uniformity of the components in the strip steel, and eliminates the band-shaped defects caused by the component segregation, thereby further improving the uniformity of the strain in each phase during the local forming.
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 (9)
1. A1000 MPa cold-rolled dual-phase steel with excellent local forming performance is characterized in that the steel comprises the following chemical components in percentage by mass: c: 0.06-0.11%, Si: 0.1 to 0.3%, Mn: 1.5-2.4%, Cr: 0.2-0.6%, Mo: 0.2-0.6%, P: less than or equal to 0.010 percent, S: less than or equal to 0.006 percent, Ti: 0.01 to 0.04%, Al: 0.1-0.3%, B: 0.0001-0.005% and the balance of iron and inevitable impurities, wherein the mass fraction of Mn, Cr and B elements satisfies: the Mn + Cr + B is more than 2.1%, the internal structure of the steel is a dual-phase structure, the dual-phase structure comprises 60-90% of martensite in percentage by volume, and the balance is ferrite; a nano precipitated phase is formed in the ferrite, and the volume of the nano precipitated phase accounts for less than 1% of the volume fraction of the ferrite; the martensite comprises 2-4 mu m martensite islands, the volume of the 2-4 mu m martensite islands accounts for more than 80% of the total volume of the martensite, the yield strength of the cold-rolled dual-phase steel is more than or equal to 600MPa, the tensile strength is more than or equal to 1000MPa, the elongation is more than or equal to 12%, the hole expansion rate is more than or equal to 60%, and the martensite is not cracked along the rolling direction by bending the martensite at 180 degrees and with the radius of 0.5T.
2. The 1000MPa cold rolled dual phase steel having excellent local formability according to claim 1, wherein the Mn: 1.5 to 1.8 percent.
3. A method for producing a 1000MPa cold rolled dual phase steel having excellent local formability according to any one of claims 1 to 2, comprising:
smelting and forging the chemical components of the 1000MPa cold-rolled dual-phase steel with excellent local forming performance according to any one of the claims 1-2 to obtain a billet;
heating, rough rolling, finish rolling and coiling the billet before rolling to obtain a hot rolled plate;
cold rolling the hot rolled plate to obtain cold-hard strip steel;
annealing the cold-hard strip steel to obtain an annealed steel plate; the annealing comprises a heating section, a soaking section, a slow cooling section and a fast cooling section, wherein the heating section is heated to 780-835 ℃ from room temperature at the rate of 0.9-21 ℃/s; the atmosphere of the soaking section adopts N2-H2Mixed gas of said H2The content is 5 to 15 percent, the soaking temperature is 780 to 835 ℃, the soaking time is 28 to 210 seconds, the dew point is minus 45 to minus 41 ℃, and the oxygen content is 2 to 5 ppm; the slow cooling sectionSlowly cooling the mixture from the soaking temperature to 600-700 ℃; the fast cooling section is cooled to 250-330 ℃ from 600-700 ℃ at the speed of more than or equal to 30 ℃/s;
and carrying out flattening treatment on the annealed steel plate to obtain the 1000MPa cold-rolled dual-phase steel with excellent local forming performance.
4. The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3, wherein in the heating before rolling, the heating temperature before rolling is controlled to be 1150-1300 ℃, the soaking time is 130-250 min, the steel is discharged after soaking, and the discharging temperature is controlled to be 1120-1230 ℃.
5. The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3, wherein the rough rolling outlet temperature is 910-1030 ℃, and the rough rolling pass is 6-10.
6. The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3, wherein the finish rolling temperature of the finish rolling is 880 ℃ to 940 ℃; the coiling temperature is 540-660 ℃.
7. The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local formability according to claim 3, wherein the cold rolling reduction is 45-60%.
8. The method for preparing 1000MPa cold-rolled dual-phase steel with excellent local forming performance according to claim 3, wherein the speed of the strip steel passing through the heating section, the soaking section, the slow cooling section and the fast cooling section in the annealing process is controlled to be 120-170 m/min.
9. The method of manufacturing 1000MPa cold-rolled dual-phase steel having excellent local formability according to claim 3, wherein the temper rolling elongation is 0.1 to 0.2%.
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| JP2014201765A (en) * | 2013-04-02 | 2014-10-27 | 新日鐵住金株式会社 | Cold rolled steel sheet and method of producing cold rolled steel sheet |
| CN106119702A (en) * | 2016-06-21 | 2016-11-16 | 宝山钢铁股份有限公司 | A kind of 980MPa level hot-rolled high-strength height reaming steel and manufacture method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2014201765A (en) * | 2013-04-02 | 2014-10-27 | 新日鐵住金株式会社 | Cold rolled steel sheet and method of producing cold rolled steel sheet |
| CN106119702A (en) * | 2016-06-21 | 2016-11-16 | 宝山钢铁股份有限公司 | A kind of 980MPa level hot-rolled high-strength height reaming steel and manufacture method thereof |
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