WO2019001424A1 - 一种冷轧退火双相钢、钢板及其制造方法 - Google Patents

一种冷轧退火双相钢、钢板及其制造方法 Download PDF

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Publication number
WO2019001424A1
WO2019001424A1 PCT/CN2018/092879 CN2018092879W WO2019001424A1 WO 2019001424 A1 WO2019001424 A1 WO 2019001424A1 CN 2018092879 W CN2018092879 W CN 2018092879W WO 2019001424 A1 WO2019001424 A1 WO 2019001424A1
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cold
rolled annealed
duplex steel
annealed duplex
steel
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PCT/CN2018/092879
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English (en)
French (fr)
Inventor
李伟
朱晓东
薛鹏
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宝山钢铁股份有限公司
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Priority to EP18824845.4A priority Critical patent/EP3647455B1/en
Priority to US16/621,495 priority patent/US20230098505A1/en
Priority to KR1020197038710A priority patent/KR20200013246A/ko
Priority to ES18824845T priority patent/ES2926943T3/es
Publication of WO2019001424A1 publication Critical patent/WO2019001424A1/zh

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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
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips 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
    • 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
    • C21D8/0226—Hot rolling
    • 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
    • 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
    • C21D8/0236—Cold rolling
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • 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

Definitions

  • the present invention relates to a steel and a method of manufacturing the same, and more particularly to a duplex steel and a method of manufacturing the same.
  • the thickness specifications of ultra-high strength grade cold-rolled annealed duplex steels are mostly between 1.0 and 2.3 mm.
  • One of the objects of the present invention is to provide a cold-rolled annealed duplex steel having a tensile strength of 1000 MPa or more and an elongation at break of 12% or more and excellent bending properties.
  • the present invention proposes a cold-rolled annealed duplex steel whose microstructure is ferrite + martensite, and the chemical element mass percentage thereof is:
  • the inventor of the present invention designs various chemical elements of the cold-rolled annealed duplex steel according to the present invention, and the design principle is as follows:
  • carbon is a solid solution strengthening element, which is a guarantee for high strength of the material, and the carbon mass percentage is too high or too low to be detrimental to the performance of the steel. Therefore, the mass percentage of carbon selected is between 0.08 and 0.1%. If it is lower than 0.08%, the austenite content is low and the strength is insufficient when the same critical region (ferrite and austenite) is heated; if the quality of carbon A percentage higher than 0.1% causes an increase in carbon equivalent and is detrimental to weldability.
  • Mn Manganese is an element that strongly enhances the austenite hardenability and can effectively increase the strength of steel, but it is not good for welding. Therefore, the mass percentage of Mn is 1.95 to 2.2%, and when the mass percentage of Mn is less than 1.95%, the strength of steel Not enough; if the Mn mass percentage is higher than 2.2%, the strength is too high and the carbon equivalent is too high.
  • Si Silicon is a solid solution strengthening element. On the one hand, it can improve the strength of the material. On the other hand, it can accelerate the segregation of carbon to austenite and purify the ferrite, thereby improving the performance of the finished product.
  • silicon dissolved in the ferrite phase promotes work hardening to increase elongation and improve local stress and strain, thereby contributing to the improvement of bending.
  • excessive silicon addition tends to be concentrated on the surface to form an oxide film which is difficult to remove. Therefore, in the technical solution described in the present invention, the mass percentage of the controlled Si is 0.1 to 0.6%.
  • Nb niobium is a carbonitride precipitation element, which can refine grains and precipitate carbonitrides and increase material strength. Therefore, the cold rolled annealed duplex steel according to the present invention controls the mass percentage of Nb to be 0.020 to 0.050%.
  • Titanium is a carbonitride precipitation element for fixing nitrogen elements and refining crystal grains. Therefore, the cold-rolled annealed duplex steel according to the present invention controls the mass percentage of Ti by 0.020 to 0.050%.
  • Als acts as a deoxidizing effect and refines grains in the steel, and thus, the mass percentage of controlling Al is 0.015 to 0.045%.
  • Cr:Cr can improve the hardenability of the steel, thereby facilitating the martensite structure, and thus controlling the mass percentage of Cr in the range of 0.40 to 0.60%.
  • Mo can improve the hardenability of steel, effectively improve the strength of steel, and improve the distribution of carbides, which is beneficial to improve the overall performance of steel.
  • the technical solution according to the present invention adds Mo in a mass percentage of 0.2 to 0.4%. When the mass percentage of Mo is less than 0.2%, the effect is not obvious, and the carbide cannot be dispersed, and when the mass percentage of Mo is higher than 0.4%, the strength is too high.
  • Ca precipitates S in the form of CaS, suppresses the generation of cracks, and is advantageous for improving the bending property.
  • the mass percentage of Ca is controlled to be 0.001% or more, and if the mass percentage of Ca exceeds 0.005%, the effect is saturated. Therefore, in the cold-rolled annealed duplex steel according to the present invention, the mass percentage of Ca is controlled to be 0.001 to 0.005%.
  • N is an impurity element in steel. If it is too high, it will easily cause surface crack of the slab. Therefore, the lower the mass percentage of N, the better, considering the production cost and process conditions, and controlling N ⁇ 0.005%.
  • P:P is an impurity element in steel. The lower the mass percentage of P, the better. Considering the production cost and process conditions, P ⁇ 0.015%
  • S is an impurity element in steel. The lower the mass percentage of S, the better. Considering the production cost and process conditions, S ⁇ 0.005%.
  • the ratio of martensite is 50% or more, and the ratio of the ratio of martensite to ferrite is more than 1 and less than 4.
  • the microstructure of the cold-rolled annealed duplex steel needs a soft ferrite phase, and at the same time, a hard martensite phase is required, in order to achieve ultra-thin
  • the specification is high in strength and, therefore, requires a martensite ratio of more than 50% in the tissue.
  • the ratio of the ratio of martensite to ferrite is controlled to be greater than 1 and less than 4 because if the ratio of the ratio of martensite to ferrite is greater than 1, the local deformation ability of the material is improved.
  • the bending performance is improved, but when the ratio of the ratio of martensite to ferrite is more than 4, the corresponding ferrite content is greatly reduced, and the elongation is greatly reduced. Therefore, the ratio of the ratio of the martensite to the ferrite is controlled to be greater than 1 and less than 4.
  • the martensite average grain size is 3 to 6 ⁇ m.
  • the martensite average grain size of martensite is controlled to be 3 to 6 ⁇ m.
  • the tensile strength is ⁇ 1000 MPa or more, and the elongation after fracture is ⁇ 12%.
  • another object of the present invention is to provide a cold-rolled annealed duplex steel sheet obtained by the above-described cold-rolled annealed duplex steel.
  • the thickness thereof is 0.5 to 0.7 mm.
  • Another object of the present invention is to provide a method for producing the above-described cold-rolled annealed duplex steel sheet.
  • the steel sheet obtained by the production method of the present invention has the advantages of high strength and ultra-thin size, and is suitable for use in automobiles, especially For the preparation of the seat frame and the backboard.
  • the present invention provides a method for manufacturing the above-described cold-rolled annealed duplex steel sheet, comprising the steps of:
  • the heating temperature is preferably 1200 ° C or higher, and at the same time, in order to prevent an increase in oxidation burn-in, the heating temperature is preferred.
  • the upper limit is 1260 ° C, therefore, the final control of the slab is soaked at a temperature of 1200 to 1260 ° C; then rolling; in addition, taking into account the formability after annealing and the unevenness of the structure caused by coarse grains, the control of the final rolling
  • the temperature is 840 to 930 ° C, and after cooling, it is cooled at a rate of 20 to 70 ° C / s. Then, the coiling is carried out. From the viewpoint of control of the hot coil shape and the surface scale, the coiling temperature is preferably 500 to 620 ° C.
  • the cold rolling reduction ratio is controlled so that the polygonal ferrite is formed in a large amount of the structure. 65 to 78%.
  • the annealing soaking temperature and time determine the degree of austenitization, and finally determine the martensite and ferrite structure in the tissue.
  • the annealing soaking temperature is too high, resulting in too much martensite ratio, and the final obtained steel sheet has a high strength
  • the annealing soaking temperature is too low, the martensite ratio is too small, and the finally obtained steel sheet is obtained.
  • the strength is low; in addition, the annealing soaking time is too short, resulting in insufficient austenitization, and the annealing soaking time is too long, which makes the austenite grains coarse.
  • the controlled annealing soaking temperature is 780 to 820 ° C
  • the annealing time is 40 to 200 s
  • the rapid cooling start temperature is 650.
  • the aging temperature is 200 ⁇ 260 ° C
  • the overaging time is 100 ⁇ 400s.
  • the flattening reduction ratio is controlled to be ⁇ 0.3%.
  • the cold-rolled annealed duplex steel has a tensile strength of 1000 MPa or more and an elongation after fracture of 12% or more, and has excellent bending properties. Therefore, the steel sheets produced therefrom are suitable for use in the automotive industry, and are particularly suitable for preparing seat frames and back sheets.
  • the manufacturing method of the present invention also has the above advantages.
  • Table 1 lists the mass percentages of the respective chemical elements in the cold-rolled annealed duplex steels of Examples 1 to 6 and the conventional steels of Comparative Examples 1-9.
  • the cold-rolled annealed duplex steels of Examples 1 to 6 and the conventional steels of Comparative Examples 1 to 9 were made into steel sheets, and the method for producing the steel sheets includes the steps:
  • Hot rolling controlling the slab to be soaked at a temperature of 1200 to 1260 ° C; then rolling, controlling the finishing temperature to be 840 to 930 ° C, and cooling at a rate of 20 to 70 ° C / s after rolling; and then coiling, Control the coiling temperature to be 500-620 ° C;
  • Annealing soaking temperature is 780-820 ° C
  • annealing time is 40-200 s
  • rapid cooling at 45-100 ° C / s
  • rapid cooling start temperature is 650 ⁇ 730 ° C
  • aging temperature is 200 ⁇ 260 ° C
  • the overaging time is 100 ⁇ 400s;
  • Table 2 lists specific process parameters in the cold rolled annealed duplex steel sheets of Examples 1-6 and the conventional steel sheets of Comparative Examples 1-4.
  • Table 3 lists the typical microstructure, mechanical properties, and bending properties of the cold-rolled annealed duplex steels of Examples 1-6 and the conventional steel-made steel sheets of Comparative Examples 1-9.
  • the cold-rolled annealed duplex steel of each embodiment of the present invention has a tensile strength of ⁇ 1000 MPa or more, an elongation after fracture of ⁇ 12%, and a microstructure of ferrite + martensite, wherein Markov The ratio of the body is 50% or more, and the ratio of the ratio of martensite to ferrite is more than 1 and less than 4, and the average grain size of martensite is 3 to 6 ⁇ m.
  • the thickness of the steel sheet in each of the examples of the present invention is 0.5 to 0.7 mm. It can be seen that the steel sheets made of the cold-rolled annealed duplex steel of the embodiments of the present invention have the advantages of high strength, thin thickness and good bending performance.

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  • Engineering & Computer Science (AREA)
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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

一种冷轧退火双相钢，其微观组织为铁素体+马氏体，其化学元素质量百分比为：C：0.08～0.1％，Mn：1.95～2.2％，Si：0.1～0.6％，Nb：0.020～0.050％，Ti：0.020～0.050％，Als：0.015～0.045％，Cr：0.40～0.60％，Mo：0.2～0.4％，Ca：0.001～0.005％，余量为Fe和其他不可避免的杂质。其冷轧退火双相钢板的制造方法，包括步骤：(1)冶炼和铸造；(2)热轧；(3)冷轧；(4)退火；(5)平整。

Description

一种冷轧退火双相钢、钢板及其制造方法 技术领域
本发明涉及一种钢及其制造方法，尤其涉及一种双相钢及其制造方法。
背景技术
汽车工业出于减重的需要，要求使用更高强度的钢板。其中，抗拉强度在980Mpa及其以上的超高强度双相钢越来越成为汽车制造业的首选，因为这种强度级别的钢能有效减轻汽车车身重量，提高安全性。为了满足降低汽车车身自重达到降低能源消耗的目的，同时保证车身的安全性能不会降低，在汽车车身设计中，越来越多地采用高强度钢，尤其是先进高强钢，其中双相钢由于具有低屈服强度、高抗拉强度以及高的初始加工硬化速率等优良的性能在汽车零部件生产中广泛使用，但是随着减薄要求的程度越来越高，尤其是在汽车座椅的使用上，用户甚至提出了0.5～0.7mm厚度的需求。
然而，目前，超高强度级别冷轧退火双相钢的厚度规格大多都在1.0～2.3mm之间。
基于此，期望获得一种超薄规格1000MPa级双相钢，以满足工业上的要求。
发明内容
本发明的目的之一在于提供一种冷轧退火双相钢，该冷轧退火双相钢的抗拉强度在1000MPa以上，断后伸长率在12％以上，具有优异的弯曲性能。
为了实现上述目的，本发明提出了一种冷轧退火双相钢，其微观组织为铁素体+马氏体，其化学元素质量百分比为：
C：0.08～0.1％，Mn：1.95～2.2％，Si：0.1～0.6％，Nb：0.020～0.050％，Ti：0.020～0.050％，Als：0.015～0.045％，Cr：0.40～0.60％，Mo：0.2～0.4％，Ca：0.001～0.005％，余量为Fe和其他不可避免的杂质。
本案发明人对本发明所述的冷轧退火双相钢的各化学元素进行设计，设计 原理如下所述：
C：在本发明所述的冷轧退火双相钢中，碳是固溶强化元素，是材料获得高强度的保证，碳的质量百分比太高或太低时均对钢的性能不利。因此，选择碳的质量百分比在0.08～0.1％之间，如果低于0.08％，在相同的临界区(铁素体和奥氏体)加热时奥氏体含量低，强度不足；如果碳的质量百分比高于0.1％，造成碳当量上升，同时对焊接性不利。
Mn：锰是强烈提高奥氏体淬透性的元素，可以有效提高钢的强度，但对焊接不利，因此Mn的质量百分比为1.95～2.2％，当Mn质量百分比低于1.95％，钢的强度不够；Mn质量百分比高于2.2％，则强度过高，同时碳当量也过高。
Si：硅是固溶强化元素，一方面可以提高材料强度，另一方面，可以加速碳向奥氏体偏聚，净化铁素体，从而改善成品的性能。此外，在铁素体相中固溶的硅可以促进加工硬化提高延伸率，改善局部应力应变，从而有助于弯曲的提高。但过多的硅添加容易在表面富集形成难以去除的氧化膜，因此，在本发明所述的技术方案中，控制Si的质量百分比在0.1～0.6％。
Nb：铌是碳氮化物析出元素，可以细化晶粒和析出碳氮化物，提高材料强度，因此，本发明所述的冷轧退火双相钢控制Nb的质量百分比在0.020～0.050％。
Ti：钛是碳氮化物析出元素，用于固定氮元素和细化晶粒，因此，本发明所述的冷轧退火双相钢控制Ti的质量百分比0.020～0.050％，
Als：Al在钢中起到了脱氧作用和细化晶粒的作用，因而，控制Al的质量百分比在0.015～0.045％。
Cr：Cr可提高钢的淬透性，从而有利于获得马氏体组织，因此控制Cr的质量百分比在0.40～0.60％。
Mo：Mo可提高钢的淬透性，有效提高钢的强度；同时改善碳化物的分布，对提高钢的综合性能有好处。在不加B的情况下，本发明所述的技术方案添加质量百分比在0.2～0.4％的Mo。当Mo的质量百分比低于0.2％，作用不明显，碳化物不能弥散析出，当Mo的质量百分比高于0.4％，则强度过高。
Ca：Ca使S以CaS的形式析出，抑制裂纹产生，有利于提高弯曲性能。为达到以上效果，需要Ca的质量百分比控制在0.001％以上，而如果Ca的质 量百分比超过0.005％，效果饱和。因此，在本发明所述的冷轧退火双相钢中，控制Ca的质量百分比为0.001～0.005％。
N：N在钢中为杂质元素，过高容易导致板坯表面裂纹，因而，N的质量百分比越低越好，综合考虑生产成本和工艺条件，控制N≤0.005％。
P：P在钢中为杂质元素，P的质量百分比越低越好，综合考虑生产成本和工艺条件要求，P≤0.015％
S：S在钢中为杂质元素，S的质量百分比越低越好，综合考虑生产成本和工艺条件要求，S≤0.005％。
进一步地，在本发明所述的冷轧退火双相钢中，马氏体的相比例为50％以上，且马氏体与铁素体的相比例之比大于1且小于4。
上述方案中，从强韧性综合的角度进行考虑，所述的冷轧退火双相钢的微观组织中需要有软的铁素体相，同时以配合较硬的马氏体相，为了实现超薄规格高强度，因而，需要马氏体相比例在组织中达到50％以上。而将马氏体与铁素体的相比例之比控制在大于1且小于4是因为：如果马氏体与铁素体的相比例之比大于1，则材料的局部变形能力提高，此时弯曲性能提升，但当马氏体与铁素体的相比例之比大于4，则对应铁素体含量大大减小，延伸率大幅度降低。因而，将马氏体与铁素体的相比例之比控制在大于1且小于4。
进一步地，在本发明所述的冷轧退火双相钢中，马氏体平均晶粒尺寸为3～6μm。
上述方案中，当马氏体平均的晶粒尺寸过小，容易成为局部裂纹的起源点，局部变形能力下降，最终弯曲能力下降。然而，马氏体平均晶粒尺寸过大，则对应奥氏体化程度过高，对应材料强度偏高，延伸率偏低。因此，控制马氏体平均晶粒尺寸在3～6μm。
进一步地，在本发明所述的冷轧退火双相钢中，其抗拉强度≥1000MPa以上，断后伸长率≥12％。
相应地，本发明的另一目的在于提供一种冷轧退火双相钢板，其由上述的冷轧退火双相钢制得。
进一步地，在本发明所述的冷轧退火双相钢板中，其厚度为0.5-0.7mm。
本发明的另一目的在于提供一种上述的冷轧退火双相钢板的制造方法，采用本发明所述的制造方法所获得的钢板具有高强度超薄尺寸的优点，适用于汽 车，尤其是适用于制备座椅骨架及背板。
为了达到上述目的，本发明提出了一种上述的冷轧退火双相钢板的制造方法，包括步骤：
(1)冶炼和铸造；
(2)热轧；
(3)冷轧；
(4)退火；
(5)平整。
进一步地，在本发明所述的制造方法中，在所述步骤(2)中，为保证轧制负荷的稳定，优选加热温度1200℃以上，同时为防止氧化烧损的增大，优选加热温度的上限为1260℃，因此，最终控制铸坯以1200～1260℃的温度均热；然后轧制；此外考虑到退火后的成型性以及晶粒粗大导致的组织不均两方面因素，控制终轧温度为840～930℃，轧后以20～70℃/s的速度冷却；然后进行卷取，从热卷板形、表面氧化铁皮的控制角度考虑，优选卷取温度为500～620℃。
进一步地，在本发明所述的制造方法中，在所述步骤(3)中，通过酸洗除去表面氧化铁皮后，为使得组织较多的生成多边形铁素体，控制冷轧压下率为65～78％。
进一步地，在本发明所述的制造方法中，在所述步骤(4)中，退火均热温度和时间决定了奥氏体化的程度，最终决定了组织中马氏体和铁素体组织的相比例，退火均热温度过高导致马氏体相比例过多，最终所获得的钢板强度偏高，而当退火均热温度过低导致马氏体相比例过少，最终所获得的钢板强度偏低；此外，退火均热时间过短，导致奥氏体化程度不足，而退火均热时间过长会使得奥氏体晶粒粗大。因此，在本发明所述的制造方法中，控制退火均热温度为780～820℃，退火时间为40～200s，然后以45～100℃/s的速度快速冷却，快速冷却的开始温度为650～730℃，时效温度为200～260℃，过时效时间为100～400s。
进一步地，在本发明所述的制造方法中，在所述步骤(5)中，为保证钢板的平整度，需要进行一定的平整量，同时过大的平整量会使得屈服强度上升较多，因此，在本发明所述的制造方法中，控制平整压下率≤0.3％。
本发明所述的冷轧退火双相钢，该冷轧退火双相钢的抗拉强度在1000MPa以上，断后伸长率在12％以上，具有优异的弯曲性能。因而，其制成的钢板适用于汽车行业，尤其是适用于制备座椅骨架及背板。
本发明所述的制造方法也具有上述优点。
具体实施方式
下面将结合具体的实施例对本发明所述的冷轧退火双相钢及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-6及对比例1-9
表1列出了实施例1-6的冷轧退火双相钢以及对比例1-9的常规钢中的各化学元素的质量百分比。
表1.(wt％，余量为Fe和除了P、S、N以外的其他不可避免的杂质元素)
Figure PCTCN2018092879-appb-000001
Figure PCTCN2018092879-appb-000002
实施例1-6的冷轧退火双相钢以及对比例1-9的常规钢制成钢板，钢板的制造方法包括步骤：
(1)冶炼和铸造：按照表1所示的化学组分进行冶炼；
(2)热轧：控制铸坯以1200～1260℃的温度均热；然后轧制，控制终轧温度为840～930℃，轧后以20～70℃/s的速度冷却；然后卷取，控制卷取温度为500～620℃；
(3)冷轧：控制冷轧压下率为65～78％；
(4)退火：退火均热温度为780～820℃，退火时间为40～200s，然后以45～100℃/s的速度快速冷却，快速冷却的开始温度为650～730℃，时效温度为200～260℃，过时效时间为100～400s；
(5)平整：平整压下率≤0.3％。
表2列出了实施例1-6的冷轧退火双相钢板以及对比例1-4的常规钢板的制造方法中的具体工艺参数。
表2.
Figure PCTCN2018092879-appb-000003
Figure PCTCN2018092879-appb-000004
表3列出了实施例1-6的冷轧退火双相钢以及对比例1-9的常规钢制成钢板的典型显微组织、力学性能以及弯曲特性。
表3.
Figure PCTCN2018092879-appb-000005
Figure PCTCN2018092879-appb-000006
由表3可以看出，本案各实施例的冷轧退火双相钢的抗拉强度≥1000MPa以上，断后伸长率≥12％，且微观组织均为铁素体+马氏体，其中马氏体的相比例为50％以上，且马氏体与铁素体的相比例之比大于1且小于4，马氏体平均晶粒尺寸为3～6μm。本案各实施例的钢板厚度在0.5～0.7mm。由此可以看出，本案各实施例的冷轧退火双相钢制成的钢板具有强度高，厚度薄，弯曲性能佳的优点。
需要注意的是，以上列举的仅为本发明的具体实施例，显然本发明不限于以上实施例，随之有着许多的类似变化。本领域的技术人员如果从本发明公开的内容直接导出或联想到的所有变形，均应属于本发明的保护范围。

Claims (11)

  1. 一种冷轧退火双相钢，其微观组织为铁素体+马氏体，其特征在于，其化学元素质量百分比为：
    C：0.08～0.1％，Mn：1.95～2.2％，Si：0.1～0.6％，Nb：0.020～0.050％，Ti：0.020～0.050％，Als：0.015～0.045％，Cr：0.40～0.60％，Mo：0.2～0.4％，Ca：0.001～0.005％，余量为Fe和其他不可避免的杂质。
  2. 如权利要求1所述的冷轧退火双相钢，其特征在于，马氏体的相比例为50％以上，且马氏体与铁素体的相比例之比大于1且小于4。
  3. 如权利要求1所述的冷轧退火双相钢，其特征在于，马氏体平均晶粒尺寸为3～6μm。
  4. 如权利要求1所述的冷轧退火双相钢，其特征在于，其抗拉强度≥1000MPa以上，断后伸长率≥12％。
  5. 一种冷轧退火双相钢板，其由权利要求1-4中任意一项所述的冷轧退火双相钢制得。
  6. 如权利要求5所述的冷轧退火双相钢板，其特征在于，其厚度为0.5-0.7mm。
  7. 如权利要求5或6所述的冷轧退火双相钢板的制造方法，其特征在于，包括步骤：
    (1)冶炼和铸造；
    (2)热轧；
    (3)冷轧；
    (4)退火；
    (5)平整。
  8. 如权利要求7所述的制造方法，其特征在于，在所述步骤(2)中，控制铸坯以1200～1260℃的温度均热；然后轧制，控制终轧温度为840～930℃，轧后以20～70℃/s的速度冷却；然后卷取，控制卷取温度为500～620℃。
  9. 如权利要求7所述的制造方法，其特征在于，在所述步骤(3)中，控制冷轧压下率为65～78％。
  10. 如权利要求7所述的制造方法，其特征在于，在所述步骤(4)中，退火均热温度为780～820℃，退火时间为40～200s，然后以45～100℃/s的速度快速冷却，快速冷却的开始温度为650～730℃，时效温度为200～260℃，过时效时间为100～400s。
  11. 如权利要求7所述的制造方法，其特征在于，在所述步骤(5)中，平整压下率≤0.3％。
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