WO2024041539A1 - 一种双相钢及其制造方法 - Google Patents

一种双相钢及其制造方法 Download PDF

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Publication number
WO2024041539A1
WO2024041539A1 PCT/CN2023/114295 CN2023114295W WO2024041539A1 WO 2024041539 A1 WO2024041539 A1 WO 2024041539A1 CN 2023114295 W CN2023114295 W CN 2023114295W WO 2024041539 A1 WO2024041539 A1 WO 2024041539A1
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Prior art keywords
dual
phase steel
steel
phase
martensite
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PCT/CN2023/114295
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English (en)
French (fr)
Inventor
李伟
朱晓东
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宝山钢铁股份有限公司
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Publication of WO2024041539A1 publication Critical patent/WO2024041539A1/zh

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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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

Definitions

  • the invention relates to the field of metallurgy, and in particular to a dual-phase steel and a manufacturing method thereof.
  • High-strength dual-phase steel has good mechanical properties and usability, and is widely used in the production and manufacturing of vehicle structural parts.
  • ultra-high-strength steel With the development of ultra-high-strength steel and current market changes, ultra-high-strength steel is expected to have both low cost and high performance.
  • 780DP (duplex) steel is still the mainstream applied steel, accounting for about 60% of the total duplex steel, and is widely used in various types of structural parts and safety parts.
  • Canadian patent document CA2526488 discloses a cold-rolled steel plate whose chemical composition is: C: 0.05 ⁇ 0.09%; Si: 0.4 ⁇ 1.3%; Mn: 2.5 ⁇ 3.2%; Choose to add Mo: 0.05 ⁇ 0.5% or Ni: 0.05 ⁇ 2%; P: 0.001 ⁇ 0.05%; S ⁇ 0.08*Ti-3.43*N+0.004; N ⁇ 0.006%; Al: 0.005 ⁇ 0.10%; Ti: 0.001 ⁇ 0.045%, you can also add Nb ⁇ 0.04% or B: 0.0002 ⁇ 0.0015%, you can add Ca for treatment; the others are Fe and unavoidable impurities.
  • the bainite content in this steel plate is greater than 7%, Pcm ⁇ 0.3.
  • US patent document US20050167007 discloses a method for manufacturing high-strength steel plates. Its chemical composition is: C: 0.05 ⁇ 0.13%, Si: 0.5 ⁇ 2.5%, Mn: 0.5 ⁇ 3.5 %, Cr: 0.05 ⁇ 1%, Mo: 0.05 ⁇ 0.6%, Al ⁇ 0.1%, S ⁇ 0.005%, N ⁇ 0.01%, P ⁇ 0.03%, Ti can be optionally added: 0.005 ⁇ 0.05%, Nb: 0.005 ⁇ 0.05%, or V: at least one of 0.005 ⁇ 0.2%.
  • Cia1363099A discloses an ultra-high strength dual-phase steel, including C: 0.14 ⁇ 0.21%, Si: 0.4 ⁇ 0.9%, Mn: 1.5 ⁇ 2.1%, P ⁇ 0.02%, S ⁇ 0.01%, Nb: 0.001 ⁇ 0.05%, V: 0.001 ⁇ 0.02%, the balance is Fe and inevitable impurities.
  • High-strength dual-phase steel is obtained by maintaining heat between 760 and 820°C after hot rolling and cold rolling, at a cooling rate of 40 to 50°C/s, and after an aging time of 180 to 300 seconds at 240 to 320°C.
  • the carbon equivalent in this steel is designed to be high and does not have balanced properties.
  • the 780MPa grade cold-rolled dual-phase strip steel has high strength, good ductility, good phosphating properties, and small anisotropy of mechanical properties.
  • the alloy design in this invention contains a large amount of Cr, Mo and other alloy contents, which is not conducive to cost reduction.
  • the present invention provides a dual-phase steel through reasonable element composition design, which has both low cost and excellent mechanical properties.
  • a first aspect of the present invention provides a dual-phase steel, which in addition to containing more than 90% Fe and inevitable impurities, also contains the following components in mass percentage: C: 0.09% to 0.11%, Si: 0.1 % ⁇ 0.3%, Mn: 1.4% ⁇ 1.6%, Al: 0.01% ⁇ 0.03%, Nb: 0.01% ⁇ 0.03%, Ti: 0.01% ⁇ 0.03%, B: 0.0020% ⁇ 0.0030%.
  • a second aspect of the present invention provides a dual-phase steel, including the following components in mass percentage: C: 0.09% to 0.11%, Si: 0.1% to 0.3%, Mn: 1.4% to 1.6%, and Al: 0.01 % ⁇ 0.03%, Nb: 0.01% ⁇ 0.03%, Ti: 0.01% ⁇ 0.03%, B: 0.0020% ⁇ 0.0030%, the balance is Fe and inevitable impurities.
  • the dual-phase steel of the present invention does not contain Mo and Cr.
  • the composition design of the dual-phase steel of the present invention is mainly C-Si-Mn, and a trace amount of the high-hardenability element B is added to further reduce the Mn content.
  • the austenite grain growth can be suppressed by the trace addition of Nb and Ti. Large, effectively refine grains.
  • the present invention allows to obtain 80-kilogram-strength dual-phase steel with both low cost and excellent mechanical properties without adding precious alloy elements such as Mo and Cr.
  • C The addition of C element can improve the strength of steel and increase the hardness of martensite in steel. If the C content in the steel is less than 0.09%, the strength of the steel plate will be affected and is not conducive to the formation and stability of austenite; when the C content in the steel is higher than 0.11%, the martensite hardness will be caused If it is too high, the grain size will be coarse, which is not conducive to the forming performance of the steel plate. At the same time, the carbon equivalent is too high, which is not conducive to the welding use of the steel. Therefore, in the present invention, the C content is controlled between 0.09% and 0.11%.
  • Si Adding Si element to steel can improve the hardenability. Moreover, the solid solution of Si in the steel can affect the interaction of dislocations, thereby increasing the work hardening rate, which can appropriately increase the elongation of dual-phase steel, which is beneficial to obtaining better formability. However, it should be noted that if the Si content in the steel is too high, it will be detrimental to the control of surface quality. Therefore, in the present invention, the Si content is controlled between 0.1% and 0.3%.
  • Mn Adding Mn element is helpful to improve the hardenability of steel and can effectively improve the strength of steel plates.
  • the Mn content in the steel is less than 1.4%, the strength of the steel plate is insufficient; when the Mn content in the steel is higher than 1.6%, the strength of the steel plate is too high, which will reduce its formability. Therefore, in the present invention, the Mn content is controlled between 1.4% and 1.6%.
  • B Adding B element is helpful to improve the hardenability of steel and can effectively improve the strength of steel plates.
  • the strength of the steel plate is insufficient; when the B content in the steel is higher than 0.0030%, the strength of the steel plate is too high, which will reduce its formability. Therefore, in the present invention, the content of B is controlled between 0.0020% and 0.0030%.
  • Al Adding Al element to steel can deoxidize and refine grains. On the other hand, the lower the Al content, the more beneficial it is to the pourability of smelting. In the present invention, the Al content is controlled between 0.01% and 0.03%.
  • Nb element is a strong carbide-forming element that refines grains. After adding a small amount of Nb to microalloy steel, it can strain-induced precipitate phases through particle pinning and sub-grain boundaries during the controlled rolling process. It can significantly reduce the recrystallization temperature of deformed austenite, provide nucleation points, and have an obvious effect on refining grains; during the continuous deaustenitization process, undissolved carbon and nitride material points will pass through The particle pinning grain boundary mechanism prevents the coarsening of soaked austenite grains, thereby effectively refining the grains.
  • the Nb content cannot be too high, otherwise it will increase production costs. Therefore, in the present invention, the Nb content is controlled between 0.01% and 0.03%, preferably between 0.015% and 0.025%.
  • Ti Similar to the role of Nb, Ti, a strong carbide-forming element added to steel, also shows a strong inhibitory effect on austenite grain growth at high temperatures, helping to refine grains. At the same time, if a large amount of Ti is added, the production cost will also increase. promote. Therefore, in the present invention, the Ti content is controlled between 0.01% and 0.03%, preferably between 0.015% and 0.025%.
  • the present invention eliminates the need to add precious alloy elements such as Mo and Cr, thereby ensuring economic efficiency.
  • the dual-phase steel of the present invention needs to ensure sufficient alloy additions of C, Mn, and B to provide sufficient hardenability for the dual-phase steel and ensure the continuous annealing gas cooling rate of the dual-phase steel at 40 to 100°C/s. Obtain high strength in the 80kg class.
  • the content of C, Mn, and B alloy elements in the dual-phase steel should not be too high, otherwise it will be difficult to ensure that the final dual-phase steel has excellent welding performance and formability.
  • the Nb content is 0.015% to 0.025% and/or the Ti content is 0.015% to 0.025%.
  • the Nb and Ti contents are too small, the corresponding grain refinement effect is not significant.
  • the Nb and Ti contents are too high, the cost will increase.
  • the hardenability factor Y Q reflects the composite effect of B and Mn in steel.
  • the present invention can further reduce the Mn content by adding an appropriate amount of B, thereby conducive to cost reduction, while utilizing the comprehensive quenching of Mn and B. It further improves the mechanical properties of dual-phase steel and is also conducive to improving the processing performance of on-site production, including the rolling stability of hot rolling and cold rolling.
  • the content of impurity elements in mass percentage satisfies: P ⁇ 0.015%, S ⁇ 0.003%, N ⁇ 0.005%.
  • P, N and S are all inevitable impurity elements in steel.
  • MnS formed by S seriously affects the forming performance, and N can easily cause cracks or bubbles on the surface of the slab. Therefore, in the dual-phase steel of the present invention, P ⁇ 0.015%, S ⁇ 0.003%, and N ⁇ 0.005% are controlled.
  • the microstructure of the dual-phase steel includes martensite and ferrite.
  • the microstructure of the dual-phase steel of the present invention consists of martensite and ferrite, where the volume percentage of martensite is The content is 55% or more and 85% or less, preferably 58 to 80%.
  • the martensite content in the steel structure of the present invention is directly related to the strength of the dual-phase steel.
  • a part of ferrite needs to be present in the steel so that the soft and hard phases can coordinate and coordinate when the steel is deformed, thereby improving the overall performance of the steel.
  • the average particle size of martensite and ferrite in the dual-phase steel of the present invention is both below 5 microns. More preferably, the average particle size of martensite and ferrite in the dual-phase steel is below 5 microns. Below, this helps improve the strength and processability of steel.
  • the dual-phase steel of the present invention is an 80-kilogram grade dual-phase steel, with a yield strength ⁇ 420MPa, preferably ⁇ 430MPa, a tensile strength ⁇ 800MPa, preferably ⁇ 820MPa, and an A 50 gauge fracture elongation ⁇ 18%, preferably ⁇ 19%.
  • the dual-phase steel of the present invention has a yield strength of ⁇ 450 MPa, a tensile strength of ⁇ 820 MPa, and an A 50 gauge elongation at break of ⁇ 20%.
  • the "80 kilogram level" mentioned in the present invention means that the steel of the present invention can bear a force of more than 80 kilograms per square centimeter. In some embodiments, the steel of the present invention can withstand a force of 80 to 90 kilograms per square centimeter, preferably 83 to 90 kilograms of force.
  • Another aspect of the present invention provides a method for manufacturing the above-mentioned dual-phase steel, which includes the following steps: smelting and continuous casting of molten steel to obtain a continuous casting billet; hot rolling the continuous casting billet; cold rolling; annealing; and tempering. ;smooth.
  • the annealing soaking temperature is controlled to be 825-855°C
  • the annealing time is 40-200s
  • the rapid cooling starting temperature of 735-760°C at a rate of 3-5°C/s and then cooled to a temperature of 40°C Rapid cooling is performed at a speed of ⁇ 100°C/s (such as 40 ⁇ 80°C/s), and the end temperature of rapid cooling is 220 ⁇ 260°C.
  • the annealing soaking temperature is 830-840°C.
  • the annealing soaking temperature within the above numerical range can make the obtained dual-phase steel have finer grain size and better mechanical properties and formability.
  • the continuous casting billet is first heated to 1160-1190°C, kept at the temperature for more than 150 minutes (such as 150-210 minutes), and then hot-rolled at 850-890°C for final rolling. After rolling, it is heated to 30-80 Rapid cooling at a speed of °C/s; control the coiling temperature to 500 ⁇ 540°C, and air cooling after coiling.
  • the hot-rolled coil can meet the production requirements without slow cooling or other treatments.
  • the cold rolling reduction ratio is 50 to 70%.
  • the tempering temperature is 220-260°C, and the tempering time is 100-400 s.
  • Long tempering time is beneficial to reducing the soft and hard difference between the ferrite and martensite phases of duplex steel.
  • the tempering time cannot be too long, otherwise steel with a strength lower than 80 kg will be obtained.
  • the flattening reduction ratio is ⁇ 0.3%.
  • the present invention allows to obtain dual-phase steel with both low cost and excellent performance (especially high strength and excellent elongation) without adding Mo and Cr.
  • This dual-phase steel is an 80-kg grade dual-phase steel. Its microstructure includes martensite + ferrite, yield strength ⁇ 420MPa, tensile strength ⁇ 800MPa, and A 50 gauge fracture elongation ⁇ 18%.
  • Figure 1 is a microstructure photograph of the dual-phase steel in Example 1 of the present invention.
  • the dual-phase steels of Examples 1-5 of the present invention are prepared through the following steps:
  • the annealing soaking temperature is 825 ⁇ 855°C
  • the annealing time is 40 ⁇ 200 seconds
  • the rapid cooling starting temperature of 735 ⁇ 760°C at a speed of 3 ⁇ 5°C/s and then cooled to 40 ⁇ 100°C /s speed of rapid cooling, the end temperature of rapid cooling is 220 ⁇ 260°C;
  • tempering temperature is 220 ⁇ 260°C
  • tempering time is 100 ⁇ 400 seconds.
  • the steel of Comparative Examples 1-14 was also produced according to the formula shown in Table 1 below using basically the same method as the above-mentioned embodiment of the present invention.
  • the difference lies in the chemical element content or manufacturing process parameters of Comparative Examples 1-14. More than one does not meet the requirements of the invention.
  • the 80-kilogram grade dual-phase steel of the present invention means that the microstructure of the steel of the present invention includes two phases, and the steel of the present invention can bear a pressure of 80 kilograms per square centimeter.
  • Table 1 lists the chemical compositions of the dual-phase steels of Examples 1-5 and the steels of Comparative Examples 1-14, and the corresponding hardenability factor Y Q values.
  • Table 2-1 and Table 2-2 list the specific process parameters of the dual-phase steel of Examples 1-5 and the steel of Comparative Examples 1-14.
  • Table 3 lists the performance test results of the dual-phase steels of Examples 1-5 and the steels of Comparative Examples 1-14.
  • Kilogram force is kilogram force, which is a common unit of force.
  • the international unit of force is Newton.
  • Examples 1-5 of the present invention have excellent comprehensive properties, with yield strength ⁇ 420MPa, tensile strength ⁇ 800MPa, and A 50 gauge elongation at break ⁇ 18%.
  • the dual-phase steel in each embodiment obtains a tensile strength greater than 800 MPa without adding precious alloy elements such as Mo and Cr, and at the same time has a good elongation.
  • the comprehensive properties of the dual-phase steels of Examples 1-5 of the present invention are significantly better than those of Comparative Examples 1-14.
  • test methods for each property in Table 3 are carried out using the GB/T228-2010 room temperature tensile test method for metal materials.
  • the A50 gauge length elongation at break indicates the parallel length ⁇ width of the tensile specimen is 50mm ⁇ 25mm.
  • Example 1 Use an optical microscope to observe the microstructure of the dual-phase steels corroded by 4% (volume fraction) nitric acid alcohol in Examples 1-5 and Comparative Examples 1-14, and use image analysis software to measure the martensite and ferrite in the steel. volume fraction and size.
  • the microstructure of Example 1 is shown in Figure 1.
  • the microstructure of the dual-phase steel in Example 1 of the present invention includes martensite and ferrite.
  • the percentage of martensite in the figure is 63%.
  • the structure of the dual-phase steel of the present invention is uniform, and any of the steel
  • the percentage of martensite shown in the cross section can be regarded as the volume percentage of martensite in the steel, that is, the volume fraction of the dual-phase steel in Example 1 is 63%, and the average particle size of martensite and the The average particle size is below 5 microns.
  • Table 4 shows the microstructure of the steels of Examples 1-5 and Comparative Examples 1-14, the volume fraction of martensite in the steel, and the average particle sizes of martensite and ferrite in the steel.
  • the dual-phase steels of Examples 1-5 have martensite and ferrite structures, and the volume fraction of martensite in the steel is between 55% and 85% as defined by the present invention, and the martensite The average particle size of both body and ferrite is below 5 microns.
  • the steels of Comparative Examples 1-14 also have martensite and ferrite structures, but because their chemical composition or manufacturing process does not meet the conditions defined by the present invention, the desired microstructure of the present invention cannot be obtained.
  • the volume of martensite Scores are not within the scope of the present invention.
  • the present invention obtains dual-phase steel with both low cost and excellent performance through reasonable chemical composition design and optimization process.

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Abstract

本发明公开了一种双相钢，除了包含90％以上的Fe及不可避免的杂质外，还包含以质量百分比计的如下成分：C：0.09％～0.11％，Si：0.1％～0.3％，Mn：1.4％～1.6％，Al：0.01％～0.03％，Nb：0.01％～0.03％，Ti：0.01％～0.03％，B：0.0020％～0.0030％。本发明通过对钢的化学组分的合理控制，获得了兼具低成本和高力学性能的双相钢。本发明还公开了上述双相钢的制造方法。

Description

一种双相钢及其制造方法 技术领域
本发明涉及冶金领域，尤其涉及一种双相钢及其制造方法。
背景技术
随着全球能源危机和环境问题的加剧，节能和安全成为了汽车制造业的主要发展方向。其中，降低车重是节能和减少排放措施之一。高强度双相钢具有良好的机械性能和使用性能，在车辆结构件的生产制造中有广泛应用。
随着超高强钢的发展以及目前市场的变化，期望超高强钢能兼具低成本和高性能。目前780DP(双相)钢仍是主流应用钢，占整个双相钢总量的60％左右，广泛地应用于各种类型的结构件和安全件中。
加拿大专利文献CA2526488(公开日为2004年12月2日)公开了一种冷轧钢板，其化学成分为：C：0.05～0.09％；Si：0.4～1.3％；Mn：2.5～3.2％；可以选择添加Mo：0.05～0.5％或者Ni：0.05～2％；P：0.001～0.05％；S≤0.08*Ti-3.43*N+0.004；N≤0.006％；Al：0.005～0.10％；Ti：0.001～0.045％，还可以添加Nb≤0.04％或者B：0.0002～0.0015％，可以添加Ca进行处理；其它为Fe和不可避免杂质。该钢板中贝氏体含量大于7％，Pcm≤0.3，其通过在Ar3以上的温度下热轧，在700℃以下卷取，冷轧、700～900℃之间退火，550～700℃开始快速冷却，最终获得了强度在780MPa以上的高强度钢。该钢具有局部变形能力强，焊接区域硬度低的特点。但是，该钢在设计中采用了较高的Mn含量，会造成严重的带状组织，从而造成钢力学性能的不均匀性。另外，在加入了高Mn的情况下，又加入了比较多的Si，这不利于钢的表面质量和焊接性能。
美国专利文献US20050167007(公开日为2005年8月4日)公开了一种高强度钢板的制造方法，其化学成分为：C：0.05～0.13％，Si：0.5～2.5％，Mn：0.5～3.5％，Cr：0.05～1％，Mo：0.05～0.6％，Al≤0.1％，S≤0.005％，N≤0.01％，P≤0.03％，可以选择性地添加Ti：0.005～0.05％，Nb：0.005～0.05％，或V：0.005～0.2％中的至少一种。其通过在Ar3温度以上进行热轧，450～700℃卷取，退火后以100℃/s的冷速从700～600℃冷却淬火，然后 在180～450℃之间回火，最终得到抗拉强度780MPa的扩孔率高于50％的高强钢。该钢的主要问题是合金总量过高，Si含量高，不利于钢的焊接性和磷化性能。
中国专利文献CN101363099A(公开日为2009年2月11日)公开了一种超高强度双相钢，包括C：0.14～0.21％，Si：0.4～0.9％，Mn：1.5～2.1％，P≤0.02％，S≤0.01％，Nb：0.001～0.05％，V：0.001～0.02％，余量为Fe及不可避免杂质。其通过在热轧冷轧后，在760～820℃间保温，冷速40～50℃/s，在240～320℃下经过180～300s的时效时间，获得了高强度的双相钢。然而，该钢中的碳当量设计较高，并且不具备性能均衡的特点。
中国专利文献CN103060703A公开了一种780MPa级冷轧双相带钢，其微观组织为细小的等轴状铁素体基体以及在铁素体基体上均匀分布的马氏体岛，且其化学元素质量百分含量为：C：0.06～0.1％；Si≤0.28％；Mn：1.8～2.3％；Cr：0.1～0.4％；当Cr≥0.3％时，不添加Mo；当Cr＜0.3％时，Mo＝0.3-Cr；Al：0.015～0.05％；Nb、Ti元素中的至少一种，且Nb+Ti在0.02～0.05％范围内；余量为Fe和其他不可避免的杂质。该780MPa级冷轧双相带钢具有较高的强度，良好的延展率，较好的磷化性，力学性能各向异性较小。然而，该发明中的合金设计含有较多的Cr、Mo等合金含量，不利于降低成本。
由此可见，现有技术中，虽然有的双相钢具有较好的成型性能，但其含有高含量C或高含量Si，或者含有较多的Cr、Ni、Mo等合金含量，不利于钢的焊接性、表面质量和磷化性能，同时成本较高；而有些高Si含量的钢虽扩孔率很高且弯曲性能较好，但屈强比高，冲压性能下降。迄今为止，尚未获得兼具高力学性能和低成本的780MPa双相钢。
发明内容
为了解决上述问题，本发明通过合理的元素成分设计，提供了一种双相钢，该双相钢同时具有低成本和优异的力学性能。
本发明的第一方面，提供了一种双相钢，除了包含90％以上的Fe及不可避免的杂质外，还包含以质量百分比计的如下成分：C：0.09％～0.11％，Si：0.1％～0.3％，Mn：1.4％～1.6％，Al：0.01％～0.03％，Nb：0.01％～0.03％，Ti：0.01％～0.03％，B：0.0020％～0.0030％。
本发明的第二方面，提供了一种双相钢，包含以质量百分比计的如下成分C：0.09％～0.11％，Si：0.1％～0.3％，Mn：1.4％～1.6％，Al：0.01％～0.03％，Nb：0.01％～0.03％，Ti：0.01％～0.03％，B：0.0020％～0.0030％，余量为Fe及不可避免的杂质。
优选地，本发明的双相钢不含Mo和Cr。
本发明的双相钢的成分设计以C-Si-Mn为主，同时添加微量高淬透性元素B以进一步降低Mn含量，另外通过Nb、Ti的微量添加，能抑制奥氏体晶粒长大，有效地细化晶粒。本发明通过上述合适的成分设计允许在不添加Mo、Cr等贵重合金元素的情况下，获得兼具低成本和优异力学性能的80公斤级强度的双相钢。
本发明中，各化学元素的设计原理如下：
C：C元素的添加可以提高钢的强度，提高钢中马氏体的硬度。若钢中C的含量低于0.09％，则钢板的强度受到影响，并且不利于奥氏体的形成量和稳定性；而当钢中C的含量高于0.11％，则会造成马氏体硬度过高，晶粒尺寸粗大，不利于钢板的成型性能，同时碳当量过高，不利于钢的焊接使用。因此在本发明中C的含量被控制在0.09％～0.11％之间。
Si：钢中添加Si元素可以提高淬透性。并且钢中固溶的Si可以影响位错的交互作用，从而增加加工硬化率，可以适当提高双相钢的延伸率，有益于获得较好的成型性。但需要注意的是，若钢中Si的含量过高，则会不利于表面质量的控制。因此，在本发明中，Si的含量被控制在0.1％～0.3％之间。
Mn：添加Mn元素有利于提高钢的淬透性，可以有效提高钢板的强度。当钢中Mn的含量低于1.4％时，钢板的强度不足；当钢中Mn的含量高于1.6％时，则钢板的强度过高，会使得其成型性能下降。因此，在本发明中，Mn的含量被控制在1.4％～1.6％之间。
B：添加B元素有利于提高钢的淬透性，可以有效提高钢板的强度。当钢中B的含量低于0.0020％时，钢板的强度不足；当钢中B的含量高于0.0030％时，则钢板的强度过高，会使得其成型性能下降。因此，在本发明中，B的含量被控制在0.0020％～0.0030％之间。
Al：钢中添加Al元素可以起到脱氧作用和细化晶粒的作用。另一方面，Al的含量越低，越有利于冶炼的可浇性，在本发明中，Al的含量被控制在0.01％～0.03％之间。
Nb：Nb元素是细化晶粒的强碳化物形成元素，在微合金钢中加入少量的Nb后，在控制轧制过程中，其可以应变诱导析出相通过质点钉扎和亚晶界的作用而相当显著的降低变形奥氏体的再结晶温度，提供形核质点，对细化晶粒作用明显；在连退奥氏体化过程中，均热未溶的碳、氮化物质点将通过质点钉扎晶界机制而阻止均热奥氏体晶粒的粗化，从而有效细化晶粒。但Nb的含量不能过高，否则会增加生产成本。因此，在本发明中，Nb的含量被控制在0.01～0.03％之间，优选地，在0.015～0.025％之间。
Ti：与Nb的作用类似，在钢中添加的强碳化物形成元素Ti在高温下也显示出一种强烈的抑制奥氏体晶粒长大的效果，有助于细化晶粒。同时Ti若大量添加，也会使生产成本 提升。因此，在本发明中，Ti的含量被控制在0.01～0.03％之间，优选地，在0.015～0.025％之间。
本发明通过上述双相钢的成分设计，无需添加Mo、Cr等贵重合金元素，从而可确保经济性。本发明的双相钢中需要保证足够的C、Mn、B的合金添加量，以给双相钢提供足够的淬透性，确保双相钢在40～100℃/s的连续退火气体冷却速度下获得80公斤级的高强度。然而，该双相钢中C、Mn、B合金元素的含量不宜过高，否则难以确保最终获得的双相钢具有优良的焊接性能及成型性能。
优选地，在本发明的双相钢中，Nb的含量为0.015％～0.025％和/或Ti的含量为0.015％～0.025％。其中当Nb和Ti含量偏小时，对应的晶粒细化作用不显著，当Nb和Ti含量过高时，会使得成本上升。
优选地，本发明双相钢的淬透性因子YQ满足：1.9≤YQ≤2.1，其按下式计算：YQ＝Mn+200×B，式中的Mn和B代表相应元素质量百分含量的百分号之前的数值。淬透性因子YQ体现钢中B与Mn的复合作用，通过将淬透性因子YQ控制在上述数值范围内，可在降低成本的同时，进一步提高双相钢的力学性能，尤其是强度。若YQ值低于1.9，则获得的钢强度无法达到80公斤级；若YQ值高于2.1，则相应的钢的延伸率不能满足要求。需要注意的是，在合金设计中，Mn含量是影响整体成本的最大当量，故本发明通过添加适量B，可进一步降低Mn的含量，从而有利于减低成本，同时利用Mn和B的综合淬透性，进一步提高双相钢的力学性能，也有利于现场生产的加工性能提升，包括热轧、冷轧的轧制稳定性。
优选地，在本发明的双相钢中，杂质元素以质量百分比计的含量满足：P≤0.015％，S≤0.003％，N≤0.005％。
P、N和S均是钢中不可避免的杂质元素，在钢中P、N和S元素含量越低，钢的性能越好。具体地，S形成的MnS严重影响成形性能，N容易导致板坯表面产生裂纹或气泡。因此，在本发明所述的双相钢中，控制P≤0.015％，S≤0.003％，N≤0.005％。
在本发明中，双相钢的微观组织包括马氏体和铁素体，优选地，本发明的双相钢的微观组织由马氏体和铁素体构成，其中马氏体的体积百分含量在55％以上且在85％以下，优选为58～80％。本发明的钢组织中马氏体的含量与双相钢的强度直接相关，同时，钢中需要存在一部分铁素体，以使钢变形时软硬相能配合协调，提升钢的整体性能。
优选地，本发明的双相钢中的马氏体和铁素体的平均粒径均在5微米以下，更优选地，双相钢中马氏体和铁素体的粒径均在5微米以下，这有助于提升钢的强度和加工性能。
优选地，本发明的双相钢为80公斤级双相钢，其屈服强度≥420MPa、优选≥430MPa，抗拉强度≥800MPa、优选≥820MPa，A50标距断裂延伸率≥18％，优选≥19％。在一些实施方案中，本发明双相钢的屈服强度≥450MPa，抗拉强度≥820MPa，A50标距断裂延伸率≥20％。
本发明所述的“80公斤级”指本发明的钢每平方厘米上可以承压80公斤以上的力。在一些实施方案中，本发明钢每平方厘米上可以承压80～90公斤的力，优选可以承受83～90公斤的力。
本发明的另一方面提供了一种制造上述双相钢的方法，包括以下步骤：对钢水进行冶炼和连铸，获得连铸坯；对连铸坯进行热轧；冷轧；退火；回火；平整。
优选地，在退火步骤中，控制退火均热温度为825～855℃，退火时间为40～200s，然后以3～5℃/s的速度冷却到快冷开始温度735～760℃，再以40～100℃/s(如40～80℃/s)的速度进行快冷，快冷结束温度为220～260℃。
优选地，退火均热温度为830～840℃。退火均热温度在上述数值范围内可以使获得的双相钢的晶粒尺寸更加细小，机械性能和成型性能更优。
优选地，在热轧步骤中，将连铸坯先加热至1160～1190℃，保温150min以上(如150～210分钟)，然后在850～890℃进行热轧终轧，轧后以30～80℃/s的速度快速冷却；控制卷取温度为500～540℃，卷取后空冷。对本发明的80公斤级双相钢，无需对热轧卷进行慢冷或其他处理即可满足生产要求。
优选地，在冷轧步骤中，冷轧压下率为50～70％。
优选地，在回火步骤中，回火温度为220～260℃，回火时间为100～400s。回火时间长对双相钢的铁素体、马氏体两相之间的软硬差的消减有利。但回火时间不能过长，否则会获得强度低于80公斤级的钢。
优选地，在平整步骤中，平整压下率≤0.3％。
本发明通过采用合理的化学成分设计并配合优化制造工艺，允许在不添加Mo、Cr的前提下，能够获得兼具低成本和优异性能(特别是高强度和优异延伸率)的双相钢，该双相钢为80公斤级双相钢，其微观组织包括马氏体+铁素体，屈服强度≥420MPa，抗拉强度≥800MPa，A50标距断裂延伸率≥18％。
附图说明
图1为本发明实施例1双相钢的微观组织照片。
具体实施方式
下面将结合具体实施例来对本发明所述的双相钢及其制造方法进行进一步的解释和说明。然而，以下描述是用于解释本发明的说明性描述，而不意在将本发明的技术范围仅限于该描述范围。
实施例1-5和对比例1-14
本发明的实施例1-5的双相钢通过如下步骤制得：
(1)根据下表1所示的配方，对钢水进行冶炼和连铸，制得连铸坯；
(2)对连铸坯进行热轧，其中将连铸坯先加热至1160～1190℃，保温150分钟以上，然后采用850～890℃的温度热轧终轧，轧后以30～80℃/s的速度快速冷却，然后卷取，卷取温度为500～540℃，卷取后空冷；
(3)冷轧：冷轧压下率为50～70％；
(4)退火：退火均热温度为825～855℃，退火时间为40～200秒，然后以3～5℃/s的速度冷却到快冷开始温度735～760℃，然后以40～100℃/s的速度快冷，快冷结束温度为220～260℃；
(5)回火：回火温度为220～260℃，回火时间为100～400秒。
(6)平整：平整压下率≤0.3％。
对比例1-14的钢也按照下述表1所示的配方采用与上述本发明实施例基本相同的方法制得，不同之处在于对比例1-14的化学元素含量或制造工艺参数中的一个以上不满足本发明要求。
本发明的80公斤级双相钢是指本发明的钢的微观组织包括两个相，并且本发明的钢每平方厘米上可以承压80公斤。
表1列出了实施例1-5的双相钢和对比例1-14的钢的化学组成，及相应的淬透性因子YQ的值。
表1.(wt％，余量为Fe和除了P、S、N以外其他不可避免的杂质)

表2-1和表2-2列出了实施例1-5的双相钢和对比例1-14的钢的具体工艺参数。
表2-1
表2-2

需要说明的是，在表2-2中，各实施例和对比例的快冷结束温度与回火温度相同，这是因为，在实际工艺操作过程中，快冷操作结束后即进行回火操作。
分别对得到的实施例1-5的双相钢和对比例1-14的钢进行取样，获得相应样本。对所得钢材样板的性能进行拉伸试验和夏比冲击试验，得到实施例和比较例的钢的性能数据。各实施例和对比例的钢的试验测试结果列于表3中。
表3列出了实施例1-5的双相钢和对比例1-14的钢的性能测试结果。
表3

注：公斤力即千克力，是力的一种常用单位，力的国际单位是牛顿。1公斤力指的是1千克的物体所受的重力(即9.8N)。所以1千克力＝9.8牛顿。
由表3可知，本发明的实施例1-5的综合性能优异，其屈服强度≥420MPa，抗拉强度≥800MPa，A50标距断裂延伸率≥18％。各实施例的双相钢在未添加Mo、Cr等贵重合金元素的前提下，获得了大于800MPa的抗拉强度，同时具有较好的延伸率。本发明实施例1-5的双相钢的综合性能明显优于对比例1-14。
其中表3各性能的测试方法采用GB/T228-2010金属材料室温拉伸试验方法进行，A50标距断裂延伸率表示拉伸试样平行长度×宽度为50mm×25mm。
由表1-3可以看出，与对比例1-14的钢相比，本发明实施例1-5的钢的化学组成落入了要求保护的范围内，同时配合优化的工艺参数，由此获得了兼具低成本和高性能的双相钢。
用光学显微镜对实施例1-5和对比例1-14采用4％(体积分数)硝酸酒精腐蚀后的双相钢的微观组织进行观察，利用图像分析软件测定钢中马氏体和铁素体的体积分数和大小。实施例1的微观组织如图1所示。由图1可知，本发明实施例1的双相钢的微观组织包括马氏体和铁素体，图中马氏体的百分比为63％，本发明的双相钢组织均匀，钢的任一截面显示的马氏体百分比可视为钢中马氏体的体积百分含量，也即实施例1中双相钢的体积分数为63％，并且马氏体的平均粒径和铁素体的平均粒径均为5微米以下。
表4示出实施例1-5和对比例1-14的钢的微观组织，钢中马氏体的体积分数，以及钢中马氏体和铁素体的平均粒径。
表4.

由表4可知，实施例1-5的双相钢具有马氏体和铁素体组织，且钢中马氏体的体积分数均在本发明限定的55％～85％之间，且马氏体和铁素体的平均粒径均在5微米以下。对比例1-14的钢也具有马氏体和铁素体组织，但由于其化学成分或者制造工艺不满足本发明限定的条件，因此不能获得本发明期望的微观组织，其马氏体的体积分数不在本发明限定的范围内。
综上所述，本发明通过合理的化学成分设计并结合优化工艺，获得了兼具低成本和性能优异的双相钢。
需要说明的是，本申请中记载的所有技术特征可以以任何方式进行自由组合或结合，除非彼此之间产生矛盾。在不脱离本发明的范围的情况下可对本发明进行各种修改和变化，这对本领域技术人员而言将是显而易见的。例如，作为一个实施方式的一部分显示或描述的特征可以与另一个实施方式一起使用以产生又一个实施方式。因此，本发明旨在涵盖落入所附权利要求及其等价物范围内的这些修改和变化。

Claims (15)

  1. 一种双相钢，其特征在于，所述双相钢除了包含90％以上的Fe及不可避免的杂质外，还包含以质量百分比计的如下成分：C：0.09％～0.11％，Si：0.1％～0.3％，Mn：1.4％～1.6％，Al：0.01％～0.03％，Nb：0.01％～0.03％，Ti：0.01％～0.03％，B：0.0020％～0.0030％。
  2. 根据权利要求1所述的双相钢，其特征在于，包含以质量百分比计的如下成分：C：0.09％～0.11％，Si：0.1％～0.3％，Mn：1.4％～1.6％，Al：0.01％～0.03％，Nb：0.01％～0.03％，Ti：0.01％～0.03％，B：0.0020％～0.0030％，余量为Fe及不可避免的杂质。
  3. 根据权利要求1或2所述的双相钢，其特征在于，所述双相钢不含Mo和Cr。
  4. 根据权利要求1或2所述的双相钢，其特征在于，所述双相钢的淬透性因子YQ满足：1.9≤YQ≤2.1，其中YQ＝Mn+200×B，式中的Mn和B代表相应元素质量百分含量的百分号之前的数值。
  5. 根据权利要求1或2所述的双相钢，其特征在于，杂质元素以质量百分比计的含量满足：P≤0.015％，S≤0.003％，N≤0.005％。
  6. 根据权利要求1或2所述的双相钢，其特征在于，所述双相钢的微观组织包括马氏体和铁素体，优选由马氏体和铁素体构成，更优选所述马氏体的体积百分比含量为55％以上且为85％以下，优选为58～80％。
  7. 根据权利要求6所述的双相钢，其特征在于，所述马氏体的平均粒径和铁素体的平均粒径均为5微米以下；优选地，所述马氏体和所述铁素体的粒径均在5微米以下。
  8. 根据权利要求1或2所述的双相钢，其特征在于，所述双相钢为80公斤级双相钢，并具有如下性能：屈服强度≥420MPa；抗拉强度≥800MPa；A50标距断裂延伸率≥18％。
  9. 根据权利要求1或2所述的双相钢，其特征在于，所述双相钢的屈服强度≥450MPa，抗拉强度≥820MPa，A50标距断裂延伸率≥20％，且所述双相钢每平方厘米上能承压83～90公斤的力。
  10. 一种制造权利要求1～9中任一项所述的双相钢的方法，其特征在于，所述方法包括以下步骤：
    1)对钢水进行冶炼和连铸，制得连铸坯；
    2)对连铸坯进行热轧；
    3)冷轧；
    4)退火；
    5)回火；以及
    6)平整，获得双相钢。
  11. 根据权利要求10所述的制造方法，其特征在于，在所述退火步骤中，退火均热温度为825～855℃，退火时间为40～200s，然后以3～5℃/s的速度冷却到快冷开始温度735～760℃，再以40～100℃/s的速度进行快冷，快冷结束温度为220～260℃；优选地，所述退火均热温度为830～840℃。
  12. 根据权利要求10或11所述的制造方法，其特征在于，在所述热轧步骤中，将连铸坯先加热至1160～1190℃，保温150min以上，然后在850～890℃进行热轧终轧，轧后以30～80℃/s的速度快速冷却；接着进行卷取，卷取温度为500～540℃，卷取后空冷。
  13. 根据权利要求10或11所述的制造方法，其特征在于，在所述冷轧步骤中，冷轧压下率为50～70％。
  14. 根据权利要求10或11所述的制造方法，其特征在于，在所述回火步骤中，回火温度为220～260℃，回火时间为100～400s。
  15. 根据权利要求10或11所述的制造方法，其特征在于，在所述平整步骤中，平整压下率＜0.3％。
PCT/CN2023/114295 2022-08-23 2023-08-22 一种双相钢及其制造方法 WO2024041539A1 (zh)

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CN109371317A (zh) * 2018-09-25 2019-02-22 邯郸钢铁集团有限责任公司 一种1000MPa级超快冷冷轧双相钢板及其制备方法
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CN115181886A (zh) * 2021-04-02 2022-10-14 宝山钢铁股份有限公司 980MPa级别低碳低合金双相钢及快速热处理制造方法
US20230203611A1 (en) * 2020-05-27 2023-06-29 Baoshan Iron & Steel Co., Ltd. 780 mpa-class cold-rolled and annealed dual-phase steel and manufacturing method therefor

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* Cited by examiner, † Cited by third party
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CN105925905A (zh) * 2016-05-17 2016-09-07 武汉钢铁股份有限公司 Nb-Ti系780MPa级热轧双相钢及其生产方法
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