WO2007142197A1 - High-strength composite steel sheet having excellent moldability and delayed fracture resistance - Google Patents

High-strength composite steel sheet having excellent moldability and delayed fracture resistance Download PDF

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Publication number
WO2007142197A1
WO2007142197A1 PCT/JP2007/061301 JP2007061301W WO2007142197A1 WO 2007142197 A1 WO2007142197 A1 WO 2007142197A1 JP 2007061301 W JP2007061301 W JP 2007061301W WO 2007142197 A1 WO2007142197 A1 WO 2007142197A1
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steel sheet
strength
ferrite
delayed fracture
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PCT/JP2007/061301
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French (fr)
Japanese (ja)
Inventor
Michiharu Nakaya
Yoichi Mukai
Koichi Sugimoto
Original Assignee
Kabushiki Kaisha Kobe Seiko Sho
Shinshu Tlo Co., Ltd.
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Application filed by Kabushiki Kaisha Kobe Seiko Sho, Shinshu Tlo Co., Ltd. filed Critical Kabushiki Kaisha Kobe Seiko Sho
Priority to GB0900057.1A priority Critical patent/GB2452230B/en
Priority to US12/303,566 priority patent/US20100221138A1/en
Priority to CN2007800208296A priority patent/CN101460646B/en
Publication of WO2007142197A1 publication Critical patent/WO2007142197A1/en

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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing 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
    • 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
    • C22C38/002—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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention has, for example, a tensile strength of 980 MPa or higher, excellent formability, anti-delayed fraction property, and spot weldability, and is a structural member for automobiles (pillars, members).
  • the present invention relates to a high-strength composite steel sheet useful as body frame members such as reinforcements, bumpers, door guard bars, seat parts, suspension parts, and other reinforcing members.
  • Non-Patent Document 1 high strength is ensured by using a composite structure in which the metal structure is a bainitic ferrite main body and lath-type retained austenite.
  • a steel sheet having improved hole expansibility that is, stretch flangeability
  • TS X E1 is an indicator of strength (TS) 'ductility (E1), and is 9000-10300. That's not true.
  • the maximum heating temperature in a mass production line of actual operation using a continuous annealing furnace is about 900 ° C, and the heating time is 5 minutes or less.
  • 950 After annealing at C for 1200 seconds, 350-400 in a salt bath. It is required to cool down to C and is not suitable for actual operation.
  • Patent Document 1 discloses that the matrix is composed mainly of vinylic ferrite and contains 3% or more of retained austenite, while maintaining a tensile strength of 980 MPa class or higher while maintaining elongation ( E1) is about 20%, and stretch flangeability ( ⁇ ) is 55%.
  • E1 tensile strength
  • ⁇ stretch flangeability
  • this technology requires the addition of expensive alloying elements such as Mo, Ni, and Cu, leaving room for improvement in terms of cost.
  • Patent Document 2 obtains a high level of elongation and stretch flangeability by setting the matrix structure to tempered martensite and ferrite and the retained austenite to have a space factor of 5 to 30%.
  • the microstructure before annealing is important. Therefore, is it possible to perform continuous annealing after taking in an appropriate metal structure by performing low temperature cutting in the hot rolling process? It is necessary to perform continuous annealing at least twice.
  • the structure before annealing cannot be obtained unless the cold rolling rate is kept low, and the intended metal structure cannot be obtained.
  • Significant restrictions are added.
  • continuous annealing is performed twice, although there are no restrictions such as sheet thickness, the number of processes is increased compared to the conventional method, so an increase in cost cannot be avoided.
  • Patent Document 3 discloses a steel sheet having a total phase structure and a stretch flangeability improved by making the matrix structure mainly tempered bainite. This steel grade is being studied mainly with a tensile strength of 900MPa class or less, and therefore, the delayed fracture, which is a particular problem at 980MPa class and above, is carefully considered.
  • Non-Patent Document 1 ISIJ International, Vol.40 (2000), No.9.p920-926
  • Patent Document 1 Japanese Unexamined Patent Application Publication No. 2004-332099
  • Patent Document 2 JP 2003-171735 A Patent Document 3: Japanese Patent Laid-Open No. 2002-309334
  • the present invention has been made in view of the prior art as described above.
  • the purpose of the present invention is to provide a 980 MPa class useful as a structural part for automobiles and the like without adding expensive alloy elements such as Mo, Ni and Cu.
  • the high-strength composite steel sheet of the present invention that has solved the above-mentioned problems is: C: 0.12 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.5 to 3.0%, P: 0.15 % (Less than 0%), S: not more than 0.02% (not including 0%), A1: not more than 0.4% (not including 0%), the balance being iron and inevitable impurities
  • the content of Si, Al, Mn satisfies the relationship of the following formula (I),
  • C 0.12-0.25%
  • Si l.0-3.0%
  • Mn l.5-3.0%
  • Cr l.0% or less
  • P 0.15% or less (0 %)
  • S 0.02% or less (excluding 0%)
  • A1 0.4% or less (excluding 0%)
  • the content of Si, Al, Mn, Cr satisfies the relationship of the following formula ( ⁇ ),
  • microstructure of the longitudinal section is the space factor for the entire structure
  • Average particle size of polygonal ferrite 10 zm or less
  • Residual austenite 5. /. more than
  • the composite steel sheet according to the present invention may include Ti: 0.15% or less (including 0%) and / or Nb: 0.1% or less (including 0%) in addition to the above elements as necessary. Contains Alternatively, as another element, Ca: 30 ppm or less (not including 0%) and / or REM: 30 ppm or less (not including 0%) may be included.
  • the high strength composite steel sheet of the present invention preferably has a tensile strength of 980 MPa or more in order to make effective use of its excellent strength.
  • the chemical composition of the steel material is specified as described above, and in particular, the (Si + Al) ZMn ratio or the (Si + Al) / (Mn + Cr) ratio is controlled within a specific range.
  • the metal structure a composite structure mainly composed of vinylite ferrite (BF) and containing polygonal ferrite (PF) and retained austenite (residual ⁇ ), while maintaining a tensile strength of, for example, a level of 980 MPa or more, and It is possible to provide a low-cost composite steel sheet with good formability (stretch-stretch flangeability) and excellent strength, spot weldability, and delayed fracture resistance.
  • FIG. 1 is an explanatory view showing a heat pattern of heat treatment employed in an experimental example.
  • the first is that elongation is remarkably improved when a certain amount of fine polygonal ferrite is mixed in a structure mainly composed of vinylic ferrite.
  • the ferrite to be mixed is fine, deterioration of strength and stretch flangeability can be suppressed, and the structure should exhibit excellent performance in delayed fracture resistance.
  • C is an element that is indispensable for ensuring high strength and ensuring residual ⁇ , and is important for ensuring that a sufficient amount of C is contained in the ⁇ phase and that the desired amount of ⁇ phase remains at room temperature. Element. In order to exert such an action effectively, it is necessary to contain C in an amount of 0.1% or more, preferably 0.12% or more, more preferably 0.15% or more. However, if the amount of C is too large, there will be a noticeable adverse effect on spot weldability, so the upper limit was set to 0.25% from the viewpoint of ensuring spot weldability. Preferably it is 0.23% or less, more preferably 0.20% or less.
  • Si is an essential element for suppressing the formation of carbides by decomposition of residual ⁇ , and in order to effectively exert these effects.
  • 1.0% or more should be contained, and preferably 1.2% or more should be contained.
  • these effects saturate at 3.0%, and if it exceeds this level, it causes troubles such as spot weldability deterioration and hot brittleness, so at most 3.0% or less, preferably 2.5 It is better to keep it below%.
  • ⁇ is an element that is necessary to suppress the formation of excessive polygonal ferrite and to make a microstructure mainly composed of venetic ferrite. Further, it is an important element for stabilizing ⁇ and securing the desired residual ⁇ , and it is preferable to contain at least 1.5% or more, preferably 2.0% or more. [0026] However, since excessive additive deterioration deteriorates the resistance to delayed fracture when spot weldability is reached, at most
  • A1 is a useful element to suppress the formation of carbides and secure residual ⁇ . If too much is used, polygonal ferrite tends to form easily, so at most 0.4% or less is preferable. Should be kept below 0.2%.
  • Cr has the effect of increasing the strength by suppressing the formation of polygonal ferrite, so it can be added as necessary.
  • excessive addition may adversely affect the formation of the metal structure targeted by the present invention, so it should be suppressed to 1.0% or less at most.
  • delayed fracture resistance is also improved by controlling the ratio of the above elements within an appropriate range. Although the details of this reason are unknown, the following can be considered.
  • Mn promotes delayed fracture by reducing the grain boundary strength by segregation at the grain boundary, and also promotes the formation of voids that are the starting point of delayed fracture during processing through the formation of martensite as described above. Since A1 and A1 have the effect of increasing the allowable amount of hydrogen that induces delayed fracture, the delayed fracture property is considered to change depending on the ratio of the two.
  • the ratio of (Si + Al) / Mn (or Mn + Cr) is in the range of 0 ⁇ 74 to: 1.26, and more preferably 0. It should be adjusted to 84 or more and 1.16 or less.
  • Nb 0.1% or less
  • Ti 0.15% or less
  • Vanitic ferrite not only can easily achieve high strength at a certain degree of dislocation density, but also has the effect of reducing the hardness difference from the second phase and increasing stretch flangeability. It is also a useful structure for enhancing delayed fracture resistance. This structure has very little cementite, which is the starting point of delayed fracture, and very few dislocations. This is probably because of this. In order to exert these effects effectively, it is necessary to have 50% or more of the vitality tough light. More preferably, it is 60% or more.
  • this Vignite toughlite is clearly different from the bainitic structure in that it does not have carbides in the structure, and has a dislocation-free force or a polygome having an extremely small substructure. It is also different from the nal ferrite structure and the quasi-polygonal ferrite structure with substructures such as fine subgrains. These differences can be easily identified by TEM (transmission electron microscope) observation.
  • polygonal ferrite having an average grain size as described below is contained in a steel sheet of 980 MPa class or higher with a tensile strength of vinylic ferrite (BF) as the matrix, elongation is further improved.
  • BF vinylic ferrite
  • 5% or more of polygonal ferrite must be contained.
  • More preferable space factor of polygonal ferrite is 10% or more and 30% or less.
  • Average diameter of polygonal ferrite 10 ⁇ m or less
  • the average grain size of polygonal ferrite must be 10 ⁇ m or less. This is because by making the ferrite finer, the dispersion as the second phase is made uniform, the stretch flangeability and strength are both improved, and the delayed fracture resistance is also improved. This is thought to be because hydrogen is trapped at the ferrite grain boundaries, which increase as the polygonal ferrite is refined, and the concentration of hydrogen at the hazardous site is suppressed.
  • the average particle diameter of polygonal ferrite referred to here is the average value of the equivalent circle diameters of polygonal ferrite (the diameters of the circles having the same area). [0044] Residual ⁇ 5%
  • Residual ⁇ promotes hardening of the deformed part by transforming into martensite when the material is deformed due to strain, and has the effect of preventing strain concentration (TRIP effect).
  • TRIP effect strain concentration
  • There is no upper limit on the amount of residual flaws but a large amount of C is required to produce excessive residual ⁇ , making it difficult to achieve both spot weldability and workability, especially stretch flangeability. However, it is preferable to keep it below 30%.
  • martensite, bainite, pearlite, and the like may exist as the remaining structure other than the above, but these other structures do not adversely affect the above-described effects. It is desirable to keep it below 5%.
  • the production conditions for obtaining the above-described metal structure defined in the present invention are not particularly limited.
  • a general steel plate production procedure for example, continuous forging ⁇ hot rolling ⁇ pickling ⁇ cold rolling ⁇
  • the heating temperature, heating rate, holding temperature, cooling start temperature, cooling rate, etc. can be controlled appropriately.
  • it is only necessary to perform appropriate temperature control including the continuous hot-dip zinc plating line but the most important for obtaining the above metal structure is the heat treatment conditions in the continuous annealing line. An explanation will be given focusing on the preferred heat treatment conditions in the line.
  • Heating temperature during annealing Ac + 10 ° C or more
  • the heating temperature during annealing should be set to “Ac + 10 ° C. or higher”.
  • the heating temperature is “Ac + 30 ° C. or higher”.
  • the cooling rate after annealing is preferably faster because it suppresses the formation of polygonal ferrite, but considering the restrictions on equipment and the difficulty of temperature control, polygonal ferrite can be used depending on the individual component system. In order to keep it below a certain amount, preferably 25 ° CZsec or more, more preferably Preferably, it should be 30 ° C / sec or higher.
  • the temperature at which rapid cooling after annealing should be stopped should be below the temperature at which fine polygonal ferrite is formed, preferably below 650 ° C, more preferably below 600 ° C. If the quenching stop temperature increases, polygonal ferrite becomes coarse, and the object of the present invention cannot be achieved. However, since a sufficient amount of polygonal ferrite cannot be obtained when the temperature is too low, it should be about 360 ° C or higher, more preferably 400 ° C.
  • a preferable holding temperature for obtaining the metal structure of the present invention is in the range of 360 to 440 ° C.
  • the preferred holding time is 1 minute or longer.
  • the holding temperature needs to be lower than the rapid cooling stop temperature. As a result, after passing through a temperature range where fine ferrite is likely to be generated, it is brought to the vinegar toughness transformation temperature range.
  • the high-strength composite steel sheet according to the present invention uses a steel material having a specified chemical component as described above, and adopts appropriate heat treatment conditions including cooling conditions, holding conditions, etc. By securing the structure, it is possible to provide a low-cost composite steel sheet having high strength of 980 MPa or higher, good formability, and excellent spot weldability and delayed fracture resistance.
  • Heating temperature 1200 ° C x 60 minutes
  • Cooling Cooled to 720 ° C at 40 ° C / second, air-cooled for 10 seconds, then cooled to 500 ° C at 40 ° C / second, held at 500 ° C for 60 minutes, and then cooled in the furnace.
  • the metal structure of the obtained cold-rolled steel sheet was confirmed by the following method, and each test steel sheet was subjected to a tensile test, a hole expansion test, a spot welding test, and a delayed fracture resistance test. And obtained the result.
  • PF can be distinguished from residual ⁇ and martensite white because it corrodes gray.
  • the circumference of polygonal ferrite in the SEM photograph by the above ⁇ was traced, and the equivalent circle diameter was calculated from the trace image by image analysis.
  • the average value of the equivalent circle diameter was defined as the average particle diameter of polygonal ferrite.
  • Vinety Tough Light (BF): With a transmission electron microscope (TEM: magnification of 15000), it was confirmed that the structure was not other structures such as bainite and pseudofluorite. Martensite ( ⁇ ) and bainite ( ⁇ ) were reduced.
  • Tensile test Measured with a JIS No. 5 tensile test piece.
  • Experiments Nos. 1 to 10 and 16 are examples that satisfy all of the specified requirements of the present invention, and all have tensile strength of 98 OMPa class or higher, strength X elongation characteristics, strength X elongation flange characteristics The formability evaluated by the properties is good, and even if spot weldability is poor in delayed fracture resistance, good results can be obtained.
  • Experiment No. 11 was evaluated based on strength X elongation characteristics and strength X elongation flange characteristics because the C content of the steel material was insufficient and the amount of vanitic ferrite in the metal structure was also insufficient. The moldability is also poor.
  • the experiment No. 12 since the Si content of the steel used is out of the (Si + Al) / (Mn + Cr) ratio specified range as well as lack, there is no residual ⁇ in the metal structure, strength X Elongation characteristics and strength The formability evaluated by the X-stretch flange characteristics is inferior and delayed fracture resistance is poor.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
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Abstract

Disclosed is a high-strength composite steel sheet having a tensile strength of 980 MPa or greater and excellent in moldability, delayed fracture resistance and spot weldability. The steel sheet comprises a steel having the following chemical composition: C: 0.12-0.25%, Si: 1.0-3.0%, Mn: 1.5-3.0%, P: 0.15% or less, S: 0.02% or less, Al: 0.4% or less, and Cr: 1.0% or less, with the remainder being iron and unavoidable impurities, wherein the contents of Si, Al, Mn and Cr satisfy the relationship expressed by the following formula: (Si+Al)/Mn or (Si+Al)/(Mn+Cr)=0.74-1.26 and the steel sheet has a specified microstructure.

Description

明 細 書  Specification
成形性、耐遅れ破壊性に優れた高強度複合組織鋼板  High-strength composite steel sheet with excellent formability and delayed fracture resistance
技術分野  Technical field
[0001] 本発明は、例えば 980MPa級以上の引張強度を有すると共に、成形性と耐遅れ破 壊性（anti-delayed fraction property)、更にはスポット溶接性に優れ、 自動車用構造 部材（ピラー、メンバー、リンフォース類などのボディー骨格部材、バンパー、ドアガー ドバー、シート部品、足回り部品その他の強化部材)などとして有用な高強度の複合 組織鋼板に関するものである。  [0001] The present invention has, for example, a tensile strength of 980 MPa or higher, excellent formability, anti-delayed fraction property, and spot weldability, and is a structural member for automobiles (pillars, members). In addition, the present invention relates to a high-strength composite steel sheet useful as body frame members such as reinforcements, bumpers, door guard bars, seat parts, suspension parts, and other reinforcing members.
背景技術  Background art
[0002] 近年、 自動車などの車体重量の軽量化による燃費の軽減や、衝突時の安全性確 保などを目的として高強度鋼板の需要はますます増大している。それに伴って、鋼板 の引張強度に対する要望も、従来の 590MPa級から 980MPa級以上が求められる 様になっている。しかし、 980MPa級以上の高強度鋼板になると成形性の低下が避 けられず、複雑形状の部品には適用し難いため用途面の制約を受ける。  [0002] In recent years, the demand for high-strength steel sheets has been increasing for the purpose of reducing fuel consumption by reducing the weight of automobile bodies and the like and ensuring safety in the event of a collision. Along with this, the demand for the tensile strength of steel sheets has been demanded from the conventional 590 MPa class to 980 MPa class or higher. However, if it becomes a high-strength steel sheet of 980 MPa class or higher, it will not be possible to avoid a decrease in formability, and it will be difficult to apply it to parts with complex shapes.
[0003] また、引張強度が 980MPa級以上の高強度鋼板になると、プレス成形時に生じる 残留応力も大きくなつて遅れ破壊の危険性が高まる。即ち遅れ破壊は、特に高強度 の鋼板において、腐食環境もしくは雰囲気中の水素が鋼材組織中の転位や空孔、 粒界などに拡散'集積して材料を脆化させ、応力が付加された時に破壊を起こす現 象であり、鋼材の延性ゃ靭性に重大な影響をもたらす。  [0003] In addition, when a high-strength steel sheet having a tensile strength of 980 MPa or higher is formed, the residual stress generated during press forming increases and the risk of delayed fracture increases. In other words, delayed fracture occurs when hydrogen in a corrosive environment or atmosphere diffuses and accumulates in dislocations, vacancies, grain boundaries, etc. in the steel structure, embrittles the material and stress is applied, especially in high-strength steel sheets. It is a phenomenon that causes fracture, and the ductility of steel materials has a significant effect on toughness.
[0004] 従って、上述した様な高強度化の要請に応えるには、強度に加えて成形性 (即ち、 伸びと伸びフランジ性（stretch flangeability) )と耐遅れ破壊性の改善が極めて重要と なる。  [0004] Therefore, in order to meet the demand for higher strength as described above, improvement in formability (ie, elongation and stretch flangeability) and delayed fracture resistance in addition to strength is extremely important. .
[0005] ところで、優れた成形性を示す高強度鋼板としては、金属組織中に残留オーステナ イトを含む種々の鋼板が実用化されてレ、る。  [0005] By the way, as high-strength steel sheets having excellent formability, various steel sheets containing residual austenite in the metal structure have been put into practical use.
[0006] 例えば、非特許文献 1には、金属組織がベィニテイツタフヱライト（bainitic ferrite)主 体でラス状 (lath-type)残留オーステナイトを有する複合組織とすることで、高強度を 確保しつつ穴拡げ性 (即ち、伸びフランジ性）を高めた鋼板が開示されている。しかし この鋼板は、引張強度 (TS)が 980MPa級以上になると、強度 (TS) '延性 (E1)の指 標となる TS X E1でせぃぜレヽ 9000〜10300を示すに止まり、満足し得るものとはい えない。 [0006] For example, in Non-Patent Document 1, high strength is ensured by using a composite structure in which the metal structure is a bainitic ferrite main body and lath-type retained austenite. However, a steel sheet having improved hole expansibility (that is, stretch flangeability) is disclosed. However When the tensile strength (TS) is 980 MPa class or higher, this steel plate can only be satisfied with TS X E1, which is an indicator of strength (TS) 'ductility (E1), and is 9000-10300. That's not true.
[0007] また、連続焼鈍炉を用いた実操業の量産ラインでの最高加熱温度は 900°C程度、 加熱時間は 5分以下とされているが、この文献に開示されている製造条件では、 950 。Cで 1200秒の焼鈍の後、ソルトバス（salt bath)で 350〜400。Cまで冷却することを 求めており、実操業にそぐわない。  [0007] In addition, the maximum heating temperature in a mass production line of actual operation using a continuous annealing furnace is about 900 ° C, and the heating time is 5 minutes or less. However, under the manufacturing conditions disclosed in this document, 950. After annealing at C for 1200 seconds, 350-400 in a salt bath. It is required to cool down to C and is not suitable for actual operation.
[0008] また特許文献 1には、母相をべィニティックフェライト主体の組織とし、 3%以上の残 留オーステナイトを含有させることで、 980MPa級以上の引張強度を確保しつつ、伸 び (E1)で 20%程度、伸びフランジ性（λ )で 55%レベルを得ている。しかしこの技術 では、高価な合金元素である Moや Ni， Cuなどの添加が不可欠であり、コスト的に改 善の余地を残している。  [0008] In addition, Patent Document 1 discloses that the matrix is composed mainly of vinylic ferrite and contains 3% or more of retained austenite, while maintaining a tensile strength of 980 MPa class or higher while maintaining elongation ( E1) is about 20%, and stretch flangeability (λ) is 55%. However, this technology requires the addition of expensive alloying elements such as Mo, Ni, and Cu, leaving room for improvement in terms of cost.
[0009] 更に特許文献 2には、母相組織を焼戻しマルテンサイトおよびフェライトとし、残留 オーステナイトを占積率で 5〜30%とすることで、高レベルの伸びと伸びフランジ性を 得ている。し力 この技術で求める金属組織を得るには、焼鈍前のミクロ組織が重要 となるため、熱延工程で低温卷取りを行うことで適正な金属組織を取込んだ後に連 続焼鈍を行うか、連続焼鈍を 2回以上行う必要がある。ところが、熱延工程で低温卷 取りを行った場合は、その後の冷間圧延率を低く抑えないと焼鈍前の組織が崩れて 意図する金属組織が得られないため、板厚や板厚公差に著しい制約が加わる。また 連続焼鈍を 2回行う場合は、板厚などの制約は受けなレ、ものの、常法に比べて工程 数が増えるためコストアップが避けられない。  [0009] Further, Patent Document 2 obtains a high level of elongation and stretch flangeability by setting the matrix structure to tempered martensite and ferrite and the retained austenite to have a space factor of 5 to 30%. In order to obtain the metal structure required by this technology, the microstructure before annealing is important. Therefore, is it possible to perform continuous annealing after taking in an appropriate metal structure by performing low temperature cutting in the hot rolling process? It is necessary to perform continuous annealing at least twice. However, when cold rolling is performed in the hot rolling process, the structure before annealing cannot be obtained unless the cold rolling rate is kept low, and the intended metal structure cannot be obtained. Significant restrictions are added. In addition, when continuous annealing is performed twice, although there are no restrictions such as sheet thickness, the number of processes is increased compared to the conventional method, so an increase in cost cannot be avoided.
[0010] 更に特許文献 3には、母相組織を焼戻しべイナイト主体とすることで全伸びと伸び フランジ性を高めた鋼板が開示されている。し力 この鋼種は、引張強度で 900MPa 級以下を中心に検討されているため、 980MPa級以上で特に問題となる遅れ破壊 につレ、ては十分考慮されてレ、なレ、。  [0010] Further, Patent Document 3 discloses a steel sheet having a total phase structure and a stretch flangeability improved by making the matrix structure mainly tempered bainite. This steel grade is being studied mainly with a tensile strength of 900MPa class or less, and therefore, the delayed fracture, which is a particular problem at 980MPa class and above, is carefully considered.
非特許文献 1 : ISIJ International,Vol.40(2000),No.9.p920-926  Non-Patent Document 1: ISIJ International, Vol.40 (2000), No.9.p920-926
特許文献 1 :特開 2004— 332099号公報  Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-332099
特許文献 2 :特開 2003— 171735号公報 特許文献 3：特開 2002— 309334号公報 Patent Document 2: JP 2003-171735 A Patent Document 3: Japanese Patent Laid-Open No. 2002-309334
発明の開示  Disclosure of the invention
発明が解決しょうとする課題  Problems to be solved by the invention
[0011] 本発明は上記の様な従来技術に鑑みてなされたものであり、その目的は、 Mo, Ni , Cuといった高価な合金元素を添加することなぐ 自動車用構造部品などとして有用 な 980MPa級の引張強度を有し、且つ優れた成形性 (伸び-伸びフランジ性）を有 する他、スポット溶接性ゃ耐遅れ破壊性にも優れた高強度鋼板を提供することにある 課題を解決するための手段 [0011] The present invention has been made in view of the prior art as described above. The purpose of the present invention is to provide a 980 MPa class useful as a structural part for automobiles and the like without adding expensive alloy elements such as Mo, Ni and Cu. To provide a high-strength steel sheet that has excellent tensile strength and excellent formability (elongation-elongation flangeability), as well as spot weldability and delayed fracture resistance. Means
[0012] 上記課題を解決することのできた本発明の高強度複合組織鋼板とは、 C:0.12〜 0.25%、Si:l.0〜3.0%、Mn:l.5〜3.0%、P:0.15%以下（0%を含まなレ、） 、 S:0.02%以下（0%を含まない）、 A1:0.4%以下（0%を含まない）、を満足し、残 部が鉄および不可避不純物よりなる鋼からなり、上記 Si, Al, Mnの含有量が下記式 (I)の関係、を満たし、 [0012] The high-strength composite steel sheet of the present invention that has solved the above-mentioned problems is: C: 0.12 to 0.25%, Si: 1.0 to 3.0%, Mn: 1.5 to 3.0%, P: 0.15 % (Less than 0%), S: not more than 0.02% (not including 0%), A1: not more than 0.4% (not including 0%), the balance being iron and inevitable impurities The content of Si, Al, Mn satisfies the relationship of the following formula (I),
(Si+Al)/Mn:0.74〜： 1.26……（I)  (Si + Al) /Mn:0.74〜: 1.26 …… (I)
或は、 C:0.12〜0.25%、 Si:l.0〜3.0%、 Mn:l.5〜3.0%、 Cr:l.0%以下 (0%を含まない）、 P:0.15%以下（0%を含まない）、 S:0.02%以下（0%を含まな レ、）、 A1:0.4%以下（0%を含まない）、を満足し、残部が鉄および不可避不純物より なる鋼からなり、上記 Si, Al, Mn, Crの含有量が下記式 (Π)の関係を満たし、  Or, C: 0.12-0.25%, Si: l.0-3.0%, Mn: l.5-3.0%, Cr: l.0% or less (excluding 0%), P: 0.15% or less (0 %), S: 0.02% or less (excluding 0%), A1: 0.4% or less (excluding 0%), and the balance is made of steel consisting of iron and inevitable impurities. The content of Si, Al, Mn, Cr satisfies the relationship of the following formula (Π),
(Si+Al)/(Mn+Cr) :0.74~1.26……（II)  (Si + Al) / (Mn + Cr): 0.74 ~ 1.26 …… (II)
なお且つ、縦断面のミクロ組織が、全組織に対する占積率で、  In addition, the microstructure of the longitudinal section is the space factor for the entire structure,
1)べィニティックフェライト： 50%以上、  1) Vinylic ferrite: 50% or more,
2)ポリゴナルフェライト：5〜35%、  2) Polygonal ferrite: 5-35%,
3)ポリゴナルフェライトの平均粒径： 10 zm以下、  3) Average particle size of polygonal ferrite: 10 zm or less,
4)残留オーステナイト： 5。/。以上  4) Residual austenite: 5. /. more than
であることを特徴とする、成形性と耐遅れ破壊性優れた高強度複合組織鋼板である。  It is a high-strength composite steel sheet excellent in formability and delayed fracture resistance.
[0013] 本発明に係る上記複合組織鋼板は、必要により上記元素以外に、 Ti:0.15%以 下（0%を含まなレ、）および/または Nb:0. 1%以下（0%を含まなレ、）が含まれてい てもよく、あるいは更に他の元素として、 Ca : 30ppm以下（0%を含まない）および/ または REM： 30ppm以下（0%を含まない）を含むものであってもよい。 [0013] The composite steel sheet according to the present invention may include Ti: 0.15% or less (including 0%) and / or Nb: 0.1% or less (including 0%) in addition to the above elements as necessary. Contains Alternatively, as another element, Ca: 30 ppm or less (not including 0%) and / or REM: 30 ppm or less (not including 0%) may be included.
[0014] 本発明の高強度複合組織鋼板は、その優れた強度をより有効に生かすため、引張 強さで 980MPa以上を有するものが特に好ましい。 [0014] The high strength composite steel sheet of the present invention preferably has a tensile strength of 980 MPa or more in order to make effective use of its excellent strength.
発明の効果  The invention's effect
[0015] 本発明によれば、上記の様に鋼材の化学成分を特定し、特に（Si+Al) ZMn比ま たは（Si+ Al) / (Mn + Cr)比を特定範囲に制御すると共に、金属組織をべィニティ ックフヱライト（BF)主体で、ポリゴナルフェライト（PF)と残留オーステナイト (残留 γ ) を含む複合組織とすることで、引張強さで例えば 980MPaレベル以上を確保しつつ 、なお且つ成形性 (伸び一伸びフランジ性）が良好で、し力もスポット溶接性ゃ耐遅 れ破壊性にも優れた複合組織鋼板を安価に提供できる。  According to the present invention, the chemical composition of the steel material is specified as described above, and in particular, the (Si + Al) ZMn ratio or the (Si + Al) / (Mn + Cr) ratio is controlled within a specific range. By making the metal structure a composite structure mainly composed of vinylite ferrite (BF) and containing polygonal ferrite (PF) and retained austenite (residual γ), while maintaining a tensile strength of, for example, a level of 980 MPa or more, and It is possible to provide a low-cost composite steel sheet with good formability (stretch-stretch flangeability) and excellent strength, spot weldability, and delayed fracture resistance.
図面の簡単な説明  Brief Description of Drawings
[0016] [図 1]実験例で採用した熱処理のヒートパターンを示す説明図である。  FIG. 1 is an explanatory view showing a heat pattern of heat treatment employed in an experimental example.
発明を実施するための最良の形態  BEST MODE FOR CARRYING OUT THE INVENTION
[0017] 本発明者らは前述した様な解決課題の下で、ベィニテイツタフヱライトを母相とする  [0017] Under the above-described problems, the present inventors use the vine tough light as the parent phase.
980MPa級以上の TRIP (TRansformation Induced Plasticity：変態誘起塑性）鋼板 に焦点を絞り、その成形性やスポット溶接性、耐遅れ破壊特性を更に改善すベぐ金 属組織中の第 2相の形態と、化学成分、特に Si, Al, Mn (あるいは更に Cr)に着目し て改質研究を重ねた結果、次の様な知見を得た。  Focusing on TRIP (TRansformation Induced Plasticity) steel sheet of 980MPa class or higher, and the second phase in the metal structure to further improve its formability, spot weldability and delayed fracture resistance, As a result of repeated modification studies focusing on chemical components, especially Si, Al, Mn (or even Cr), the following findings were obtained.
[0018] 1)その第 1は、べィニティックフェライト主体の組織に微細なポリゴナルフェライトを所 定量混入させると、伸びが著しく改善されることである。しかも、混入させるフヱライト が微細なものであれば、強度や伸びフランジ性の低下が抑えられ、なお且つ該組織 は耐遅れ破壊特性においても優れた性能を示すこと。  [0018] 1) The first is that elongation is remarkably improved when a certain amount of fine polygonal ferrite is mixed in a structure mainly composed of vinylic ferrite. In addition, if the ferrite to be mixed is fine, deterioration of strength and stretch flangeability can be suppressed, and the structure should exhibit excellent performance in delayed fracture resistance.
[0019] 2)鋼の化学成分のうち、（Si+Al)と Mnまたは（Mn + Cr)が所定比率となる様に調 整すれば、スポット溶接性の低下を抑えつつ、 980MPa級以上の強度をもった所望 の組織が得られること。  [0019] 2) Of the chemical components of the steel, adjusting (Si + Al) and Mn or (Mn + Cr) to have a predetermined ratio will suppress a decrease in spot weldability, while maintaining a 980 MPa class or higher. A desired structure with strength should be obtained.
[0020] そこでこうした知見を生かし、鋼成分中の Si, Al, Mn, Cr含量と金属組織が、当該 鋼板の強度や成形性、更にはスポット溶接性や遅れ破壊特性に及ぼす影響を主体 にして研究を重ねてきた。その結果、前述した如く特定成分組成の鋼材を使用するこ とを前提として、金属組織中に占めるべィニティックフェライトの占積率を制御すると 共に、ポリゴナルフェライトと残留 γの占積率、更にはポリゴナルフェライトの平均粒 径を特定値以下に制御してやれば、上記目的に叶う高性能の高強度複合組織鋼板 が得られることを確認し、本発明に想到した。 [0020] Therefore, by taking advantage of these findings, the effects of the Si, Al, Mn, Cr content and metal structure in the steel components on the strength and formability of the steel sheet, as well as spot weldability and delayed fracture characteristics are mainly considered. I have been doing research. As a result, on the premise that the steel material having a specific component composition is used as described above, the space factor of vinylic ferrite in the metal structure is controlled, and the space factor of polygonal ferrite and residual γ, Furthermore, it was confirmed that if the average grain size of polygonal ferrite was controlled to a specific value or less, a high-performance high-strength composite steel sheet meeting the above-mentioned purpose was obtained, and the present invention was conceived.
[0021] 以下、鋼材の化学成分および金属組織を定めた理由を追って、本発明の具体的な 構成を明らかにしていく。  [0021] Hereinafter, the specific composition of the present invention will be clarified following the reasons for determining the chemical composition and metal structure of the steel material.
[0022] まず、鋼材の化学成分を定めた理由について説明する。  [0022] First, the reason for determining the chemical composition of the steel material will be described.
[0023] C : 0. 10%以上、 0. 25%以下  [0023] C: 0.10% or more, 0.25% or less
Cは、高強度を保障すると共に残留 γを確保する上でも欠くことのできない元素で あり、 γ相中に十分な量の Cを含有せしめ、室温でも所望量の γ相を残留させるため に重要な元素である。こうした作用を有効に発揮させるには、 Cを 0. 10%以上含有 させることが必要であり、好ましくは 0. 12%以上、より好ましくは 0. 15%以上含有さ せるのがよい。但し、 C量が多過ぎるとスポット溶接性に顕著な悪影響が現れてくるの で、スポット溶接性確保の観点から上限を 0. 25%とした。好ましくは 0. 23%以下、よ り好ましくは 0. 20%以下である。  C is an element that is indispensable for ensuring high strength and ensuring residual γ, and is important for ensuring that a sufficient amount of C is contained in the γ phase and that the desired amount of γ phase remains at room temperature. Element. In order to exert such an action effectively, it is necessary to contain C in an amount of 0.1% or more, preferably 0.12% or more, more preferably 0.15% or more. However, if the amount of C is too large, there will be a noticeable adverse effect on spot weldability, so the upper limit was set to 0.25% from the viewpoint of ensuring spot weldability. Preferably it is 0.23% or less, more preferably 0.20% or less.
[0024] Si : 1. 0〜3. 0%  [0024] Si: 1. 0 to 3.0%
Siは、固溶強化（solution hardening)元素として有効に作用する他、残留 γが分解 して炭化物が生成するのを抑える上でも必須の元素であり、これらの作用を有効に発 揮させるには、 1. 0%以上含有させねばならず、好ましくは 1. 2%以上含有させるの がよい。但し、それらの効果は 3· 0%で飽和し、それ以上になると、スポット溶接性の 劣化や熱間脆性を起こすなどの障害を招くので、多くとも 3. 0%以下、望ましくは 2. 5%以下に抑えるのがよい。  In addition to effectively acting as a solution hardening element, Si is an essential element for suppressing the formation of carbides by decomposition of residual γ, and in order to effectively exert these effects. 1.0% or more should be contained, and preferably 1.2% or more should be contained. However, these effects saturate at 3.0%, and if it exceeds this level, it causes troubles such as spot weldability deterioration and hot brittleness, so at most 3.0% or less, preferably 2.5 It is better to keep it below%.
[0025] Μη: 1. 5〜3. 0%  [0025] Μη: 1.5 to 3.0%
Μηは、過度のポリゴナルフェライト（polygonal ferrite)の生成を抑えてベィニテイツ クフェライト主体の組織とするために必要な元素である。また、 γを安定化し所望の残 留 γを確保する上でも重要な元素であり、少なくとも 1. 5%以上、好ましくは 2. 0% 以上含有させるのがよい。 [0026] しかし、過度の添カ卩はスポット溶接性ゃ耐遅れ破壊特性を劣化させるので、多くともΜη is an element that is necessary to suppress the formation of excessive polygonal ferrite and to make a microstructure mainly composed of venetic ferrite. Further, it is an important element for stabilizing γ and securing the desired residual γ, and it is preferable to contain at least 1.5% or more, preferably 2.0% or more. [0026] However, since excessive additive deterioration deteriorates the resistance to delayed fracture when spot weldability is reached, at most
3. 0%以下、好ましくは 2. 5%以下に抑えるのがよい。 3. It should be suppressed to 0% or less, preferably 2.5% or less.
[0027] P : 0. 15%以下、 S : 0. 02%以下 [0027] P: 0.15% or less, S: 0.02% or less
これらの元素は、鋼内に不可避的に混入してくる元素であるが、含有量が多くなる と加工性やスポット溶接性を劣化させるので、それぞれ上限値以下に抑えねばなら ない。  These elements are inevitably mixed into the steel, but if the content increases, the workability and spot weldability deteriorate, so each must be kept below the upper limit.
[0028] A1 : 0. 4%以下  [0028] A1: 0.4% or less
A1は、 Siと同様に炭化物の生成を抑えて残留 γを確保するうえで有用な元素であ る力 多過ぎるとポリゴナルフェライトが生成し易くなるので、多くとも 0. 4%以下、好 ましくは 0. 2%以下に抑えるべきである。  As with Si, A1 is a useful element to suppress the formation of carbides and secure residual γ. If too much is used, polygonal ferrite tends to form easily, so at most 0.4% or less is preferable. Should be kept below 0.2%.
[0029] Cr : 1. 0%以下 [0029] Cr: 1. 0% or less
Crは、ポリゴナルフェライトの生成を抑えて強度を高める作用を有しているので、必 要に応じて添加することができる。しかし、過度に添加すると、本発明で狙いとする金 属組織の生成に悪影響を及ぼす恐れがあるので、多くとも 1. 0%以下に抑えるべき である。  Cr has the effect of increasing the strength by suppressing the formation of polygonal ferrite, so it can be added as necessary. However, excessive addition may adversely affect the formation of the metal structure targeted by the present invention, so it should be suppressed to 1.0% or less at most.
[0030] (Si+Al) /Mn (または Mn + Cr) : 0· 74〜： 1. 26 (質量比）  [0030] (Si + Al) / Mn (or Mn + Cr): 0 · 74〜: 1.26 (mass ratio)
本発明で意図する金属組織を得るには、過度のポリゴナルフェライト（PF)の生成を 抑えてベィニテイツタフヱライト（BF)変態を促進させる必要がある。しかも、べィニティ ックフェライトから排出される C (炭素）はラス状の残留 γ中に濃縮されるため、べィニ ティックフェライト変態の促進はラス状残留 γを得る上でも重要となる。  In order to obtain the metal structure intended in the present invention, it is necessary to suppress the formation of excessive polygonal ferrite (PF) and promote the vine toughite (BF) transformation. Moreover, since C (carbon) discharged from the vane ferrite is concentrated in the lath-like residual γ, the promotion of the vane ferrite transformation is important in obtaining the lath-like residual γ.
[0031] また本発明では、金属組織中に微細なフェライトを適量分散させることが必要であ る力 そのためには、フェライト生成促進元素である Siや A1と、フヱライト抑制元素で ある Mnほたは Mn + Cr)の含有比率が一定の関係を満たす様に制御することが極 めて有効であることが分かった。しかも、これらのフェライト生成促進元素 Z抑制元素 の含有比率を制御することは、耐遅れ破壊特性を高める上でも有効であることが確 認された。 [0031] In the present invention, it is necessary to disperse an appropriate amount of fine ferrite in the metal structure. For that purpose, Si and A1 which are ferrite formation promoting elements and Mn which is a ferrite suppressing element are used. It was found that it is extremely effective to control the content ratio of (Mn + Cr) to satisfy a certain relationship. Moreover, it has been confirmed that controlling the content ratio of these ferrite formation promoting elements Z-inhibiting elements is also effective in enhancing delayed fracture resistance.
[0032] ちなみに、 （Si+Al) ZMn (または Mn + Cr)比が 0. 74未満では、適度のポリゴナ ルフェライトの確保が困難になるば力、りでなぐべィニティックフェライトすらも十分に 確保できなくなる。しかも、残留 γ中に Cを十分濃縮できず、残留 γの安定性が低下 して伸びが劣化し、更には、マルテンサイト量が増大して伸びフランジ性も悪化する。 [0032] By the way, if the (Si + Al) ZMn (or Mn + Cr) ratio is less than 0.74, even if it is difficult to secure an adequate polygonal ferrite, even the vignetting ferrite is sufficient. In Cannot be secured. In addition, C cannot be sufficiently concentrated in the residual γ, the stability of the residual γ is lowered and the elongation is deteriorated, and further, the amount of martensite is increased and the stretch flangeability is also deteriorated.
[0033] 更に加えて、上記元素の比率を適正範囲にコントロールすることで耐遅れ破壊性も 改善される。この理由の詳細は不明であるが、次の様なことが考えられる。即ち Mnは 、粒界偏析により粒界強度を低下させることで遅れ破壊を助長する他、上述した様に マルテンサイトの生成を通じて加工時に遅れ破壊の起点となるボイド生成を促進する のに対し、 Siと A1は、遅れ破壊を誘発する水素の許容量を増加させる効果があるた め、両者の比により遅れ破壊性が変化するものと考えられる。  [0033] Further, delayed fracture resistance is also improved by controlling the ratio of the above elements within an appropriate range. Although the details of this reason are unknown, the following can be considered. In other words, Mn promotes delayed fracture by reducing the grain boundary strength by segregation at the grain boundary, and also promotes the formation of voids that are the starting point of delayed fracture during processing through the formation of martensite as described above. Since A1 and A1 have the effect of increasing the allowable amount of hydrogen that induces delayed fracture, the delayed fracture property is considered to change depending on the ratio of the two.
[0034] 一方、上記（Si+Al) /Mn (または Mn + Cr)比が 1. 26を超えると、ポリゴナルフエ ライトの生成が過度に促進されてその占積率が過大となる上に、フェライトの粒径も 1 O z mを超え易くなり、強度、伸びフランジ性が共に低下してくる。また、フェライト粒 径が粗大化するとフェライト粒界が減少するため、耐遅れ破壊性も低下する。  [0034] On the other hand, if the above (Si + Al) / Mn (or Mn + Cr) ratio exceeds 1.26, the formation of polygonal ferrite is excessively promoted and the space factor becomes excessive, and ferrite The particle size of the steel tends to exceed 1 O zm, and the strength and stretch flangeability both decrease. In addition, when the ferrite grain size is increased, the ferrite grain boundary is reduced, so that the delayed fracture resistance is also lowered.
[0035] よって本発明では、 （Si+Al) /Mn (または Mn+ Cr)比が 0· 74〜： 1. 26の範囲と なる様に成分調整することが重要であり、より好ましくは 0. 84以上、 1. 16以下に調 整するのがよい。  Therefore, in the present invention, it is important to adjust the components so that the ratio of (Si + Al) / Mn (or Mn + Cr) is in the range of 0 · 74 to: 1.26, and more preferably 0. It should be adjusted to 84 or more and 1.16 or less.
[0036] Nb : 0. 1 %以下、 Ti: 0. 15%以下  [0036] Nb: 0.1% or less, Ti: 0.15% or less
これらの元素は、いずれも金属組織を微細化して靭性を高める作用があるため、必 要に応じて少量添加することができる。しかし、上限値を超えて添加してもそれ以上 の効果は得られず、コストアップを招くだけであるので無駄である。  All of these elements have the effect of increasing the toughness by refining the metal structure, and can be added in small amounts as necessary. However, adding more than the upper limit is useless because no further effect is obtained and only the cost is increased.
[0037] Ca : 0. 01 %以下、 REM : 0. 01 %以下  [0037] Ca: 0.01% or less, REM: 0.01% or less
Caと REMは、少量の添加で何れも伸びフランジ性を高める作用を有しているため 、必要によっては少量添カ卩してもょレ、が、その効果は各々 0. 01%程度で飽和するの で、それ以上の添カ卩は全く無駄である。  Ca and REM both have the effect of increasing stretch flangeability when added in small amounts, so if necessary, you can add a small amount, but the effect is saturated at about 0.01% each. As a result, any additional support is useless.
[0038] Mo, Cu， Ni :各々 0. 1%程度以下  [0038] Mo, Cu, Ni: about 0.1% or less each
これらの元素は、従来技術でも記載した様に強度ゃ耐遅れ破壊性の向上に有効で あるが、本発明では、これらの元素を添加せずとも十分に優れた性能を確保すること ができ、またこれらの元素は高価でコストアップを招くので、あえて添加する必要はな レ、。しかし、不純物レベルでの混入まで規制する理由はなぐそれぞれ 0. 1%程度ま での添加は許容範囲である。 These elements are effective in improving delayed fracture resistance as described in the prior art, but in the present invention, sufficiently excellent performance can be ensured without adding these elements. In addition, these elements are expensive and incur costs, so it is not necessary to add them. However, there is no reason to limit the contamination to the impurity level, but each is about 0.1%. The addition at is acceptable.
[0039] 次に金属組織の限定理由について説明する。  [0039] Next, the reason for limiting the metal structure will be described.
[0040] べィニティックフェライト≥ 50%  [0040] Vinylic ferrite ≥ 50%
べィニティックフェライトは、転位密度がある程度高ぐ高強度を容易に達成できる ばかりか、第 2相との硬度差を低減して伸びフランジ性を高める作用を発揮する。ま た、耐遅れ破壊性を高める上でも有用な組織であり、これは、遅れ破壊の亀裂起点と なるセメンタイトがなレ、か極めて少なく、また転位が多レ、ため水素吸蔵効果も高レ、た めと考えられる。これらの効果を有効に発揮させるには、ベィニテイツタフヱライトを 50 %以上存在させる必要がある。より好ましくは 60%以上である。  Vanitic ferrite not only can easily achieve high strength at a certain degree of dislocation density, but also has the effect of reducing the hardness difference from the second phase and increasing stretch flangeability. It is also a useful structure for enhancing delayed fracture resistance. This structure has very little cementite, which is the starting point of delayed fracture, and very few dislocations. This is probably because of this. In order to exert these effects effectively, it is necessary to have 50% or more of the vitality tough light. More preferably, it is 60% or more.
[0041] なお、このべィニテイツタフヱライトは、組織内に炭化物を有していない点で、ベイナ イト組織とは明らかに異なり、また、転位がない力、あるいは極めて少ない下部組織を 有するポリゴナルフェライト組織や、細かいサブグレイン等の下部組織を持った準ポリ ゴナルフェライト組織とも異なっており、これらの違いは TEM (透過型電子顕微鏡)観 察などによって容易に識別できる。  [0041] It should be noted that this Vignite toughlite is clearly different from the bainitic structure in that it does not have carbides in the structure, and has a dislocation-free force or a polygome having an extremely small substructure. It is also different from the nal ferrite structure and the quasi-polygonal ferrite structure with substructures such as fine subgrains. These differences can be easily identified by TEM (transmission electron microscope) observation.
[0042] ポリゴナルフェライト（PF)： 5〜35%  [0042] Polygonal ferrite (PF): 5 to 35%
べィニティックフェライト（BF)を母相とする引張強度 980MPa級以上の鋼板に、後 述する様な平均粒径のポリゴナルフェライトを所定量含有させると、伸びが更に向上 する。こうした効果を有効に発揮させるには、ポリゴナルフェライトを 5%以上含有させ ねばならない。但し、ポリゴナルフェライトが多過ぎると、引張強度や伸びフランジ性 の確保が困難となるので、多くとも 35%以下に抑えるべきである。ポリゴナルフェライ トのより好ましい占積率は 10%以上、 30%以下である。  When a predetermined amount of polygonal ferrite having an average grain size as described below is contained in a steel sheet of 980 MPa class or higher with a tensile strength of vinylic ferrite (BF) as the matrix, elongation is further improved. In order to exert such an effect effectively, 5% or more of polygonal ferrite must be contained. However, if there is too much polygonal ferrite, it will be difficult to ensure tensile strength and stretch flangeability, so it should be kept to 35% or less at most. More preferable space factor of polygonal ferrite is 10% or more and 30% or less.
[0043] ポリゴナルフェライトの平均粒径： 10 μ m以下  [0043] Average diameter of polygonal ferrite: 10 μm or less
ポリゴナルフェライトの平均粒径は 10 μ m以下にしなければならなレ、。フェライトを 微細化することで第 2相としての分散を均一にし、伸びフランジ性、強度を共に高め ると共に、耐遅れ破壊性をも向上させるためである。これは、ポリゴナルフェライトを微 細化することで増加するフェライト粒界に水素がトラップされ、危険部位への水素の 集中が抑制されるためと考えられる。なお、ここで言うポリゴナルフヱライトの平均粒径 とは、ポリゴナルフェライトの円相当径（面積が同じ円の直径）の平均値である。 [0044] 残留 γ≥5% The average grain size of polygonal ferrite must be 10 μm or less. This is because by making the ferrite finer, the dispersion as the second phase is made uniform, the stretch flangeability and strength are both improved, and the delayed fracture resistance is also improved. This is thought to be because hydrogen is trapped at the ferrite grain boundaries, which increase as the polygonal ferrite is refined, and the concentration of hydrogen at the hazardous site is suppressed. The average particle diameter of polygonal ferrite referred to here is the average value of the equivalent circle diameters of polygonal ferrite (the diameters of the circles having the same area). [0044] Residual γ≥5%
残留 γは、材料が歪を受けて変形する際にマルテンサイトに変態することで変形部 の硬化を促し、歪の集中を防ぐ効果がある (TRIP効果)。こうした効果を有効に発揮 させるには、残留 Ίを 5%以上含有させる必要がある。残留 Ί量に上限は存在しな レ、が、過度の残留 γを生成させるには多量の Cが必要になるため、スポット溶接性と の両立が困難になり、また加工性、特に伸びフランジ性が低下傾向となるので、好ま しくは 30%程度以下に抑えるのがよい。 Residual γ promotes hardening of the deformed part by transforming into martensite when the material is deformed due to strain, and has the effect of preventing strain concentration (TRIP effect). In order to exert these effects effectively, it is necessary to contain 5% or more of residual soot . There is no upper limit on the amount of residual flaws , but a large amount of C is required to produce excessive residual γ, making it difficult to achieve both spot weldability and workability, especially stretch flangeability. However, it is preferable to keep it below 30%.
[0045] 本発明の複合組織鋼板では、上記以外の残部組織としてマルテンサイト、べィナイ ト、パーライトなどが存在し得るが、これら他の組織は、上述した作用効果に悪影響を 及ぼさなレ、様、 5%以下に抑えることが望ましレ、。  [0045] In the composite structure steel sheet of the present invention, martensite, bainite, pearlite, and the like may exist as the remaining structure other than the above, but these other structures do not adversely affect the above-described effects. It is desirable to keep it below 5%.
[0046] 次に、本発明で定める上記の金属組織を得るための製造条件に格別の制限はなく 、一般的な鋼板の製造手順、例えば、連続铸造→熱間圧延→酸洗→冷間圧延→連 続焼鈍の中で、加熱温度や昇温速度、保持温度、冷却開始温度や冷却速度などを 適正に制御すればよぐまた溶融亜鉛めつき鋼板や合金化溶融亜鉛めつき鋼板の場 合は、連続溶融亜鉛めつきラインを含めて適正な温度制御を行なえばよいが、上記 金属組織を得る上で最も重要となるのは、連続焼鈍ラインにおける熱処理条件であ るので、以下、連続焼鈍ラインにおける好ましい熱処理条件を主体にして説明を加え る。  [0046] Next, the production conditions for obtaining the above-described metal structure defined in the present invention are not particularly limited. For example, a general steel plate production procedure, for example, continuous forging → hot rolling → pickling → cold rolling → In continuous annealing, the heating temperature, heating rate, holding temperature, cooling start temperature, cooling rate, etc. can be controlled appropriately. However, it is only necessary to perform appropriate temperature control including the continuous hot-dip zinc plating line, but the most important for obtaining the above metal structure is the heat treatment conditions in the continuous annealing line. An explanation will be given focusing on the preferred heat treatment conditions in the line.
[0047] 焼鈍時の加熱温度： Ac + 10°C以上  [0047] Heating temperature during annealing: Ac + 10 ° C or more
3  Three
ベィニテイツタフヱライトリッチの金属組織を得るため、ポリゴナルフェライトの生成を 抑えるには、焼鈍時の加熱温度を「Ac + 10°C以上」とするのがよい。ちなみに、 Ac  To suppress the formation of polygonal ferrite in order to obtain a vine tough, light-rich metal structure, the heating temperature during annealing should be set to “Ac + 10 ° C. or higher”. By the way, Ac
3 3 点以下で連続焼鈍を行うと、その後の冷却過程で、残存するフェライトを核にしてポリ ゴナルフェライトが生成し易くなり、本発明で意図する金属組織が得られ難くなる。よ り好ましレ、加熱温度は「Ac + 30°C以上」である。  When continuous annealing is performed at 3 points or less, polygonal ferrite is likely to be generated with the remaining ferrite as a nucleus in the subsequent cooling process, and the metal structure intended in the present invention is difficult to obtain. More preferably, the heating temperature is “Ac + 30 ° C. or higher”.
3  Three
[0048] 焼鈍後の冷却速度：  [0048] Cooling rate after annealing:
焼鈍後の冷却速度は、ポリゴナルフェライトの生成を抑制するため速い方が好まし レ、が、設備的な制約や温度コントロールの困難性を考えると、個別の成分系に応じて ポリゴナルフェライトを一定量以下に抑え得る様、好ましくは 25°CZsec以上、より好 ましくは 30°C/sec以上とするのがよい。 The cooling rate after annealing is preferably faster because it suppresses the formation of polygonal ferrite, but considering the restrictions on equipment and the difficulty of temperature control, polygonal ferrite can be used depending on the individual component system. In order to keep it below a certain amount, preferably 25 ° CZsec or more, more preferably Preferably, it should be 30 ° C / sec or higher.
[0049] 焼鈍後の急冷停止温度：  [0049] Rapid cooling stop temperature after annealing:
焼鈍後の急冷を停止する温度は、微細ポリゴナルフェライトが生成する温度以下に すべきであり、好ましくは 650°C以下、より好ましくは 600°C以下にするのがよレ、。急 冷停止温度が高くなるとポリゴナルフェライトが粗大となり、本発明の目的が果たせな くなる。但し、あまりに低温になると十分な量のポリゴナルフェライトが得られなくなるの で、 360°C程度以上、より好ましくは 400°Cまでにすべきである。  The temperature at which rapid cooling after annealing should be stopped should be below the temperature at which fine polygonal ferrite is formed, preferably below 650 ° C, more preferably below 600 ° C. If the quenching stop temperature increases, polygonal ferrite becomes coarse, and the object of the present invention cannot be achieved. However, since a sufficient amount of polygonal ferrite cannot be obtained when the temperature is too low, it should be about 360 ° C or higher, more preferably 400 ° C.
[0050] 冷却後の保持温度：  [0050] Holding temperature after cooling:
上記冷却後には、一定温度に保持することでベィニテイツタフヱライト変態が進行し 、また、オーステナイトへの Cの濃縮が進んで残留 γとなるので、冷却後の保持温度 を適正にコントロールすることも重要である。本発明の金属組織を得る上で好ましい 保持温度は 360〜440°Cの範囲である。好ましい保持時間は 1分以上である。ここで 、急冷停止温度よりも保持温度の方が低温となるようにする必要がある。これにより、 微細なフェライトが生成しやすい温度域を通過させてから、ベィニテイツタフヱライト変 態温度域に持っていくことになる。  After the above cooling, holding at a constant temperature proceeds the transformation of the vanity toughite, and the concentration of C to austenite proceeds to become residual γ, so the holding temperature after cooling is controlled appropriately. It is also important. A preferable holding temperature for obtaining the metal structure of the present invention is in the range of 360 to 440 ° C. The preferred holding time is 1 minute or longer. Here, the holding temperature needs to be lower than the rapid cooling stop temperature. As a result, after passing through a temperature range where fine ferrite is likely to be generated, it is brought to the vinegar toughness transformation temperature range.
[0051] 本発明の高強度複合組織鋼板は、上記の様に化学成分の特定された鋼材を使用 し、且つ冷却条件や保持条件などを含めて適正な熱処理条件を採用することで所定 の金属組織を確保することにより、 980MPa級以上の高強度を有すると共に、成形 性が良好でスポット溶接性ゃ耐遅れ破壊特性にも優れた複合組織鋼板を安価に提 供できる。  [0051] The high-strength composite steel sheet according to the present invention uses a steel material having a specified chemical component as described above, and adopts appropriate heat treatment conditions including cooling conditions, holding conditions, etc. By securing the structure, it is possible to provide a low-cost composite steel sheet having high strength of 980 MPa or higher, good formability, and excellent spot weldability and delayed fracture resistance.
実施例  Example
[0052] 以下、実験例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実 験例によつて制限を受けるものではなぐ前 ·後記の趣旨に適合し得る範囲で適当に 変更を加えて実施することも可能であり、それらは何れも本発明の技術的範囲に含ま れる。  [0052] Hereinafter, the present invention will be described in more detail with reference to experimental examples. However, the present invention is not limited by the following experimental examples and is suitable within a range that can meet the purpose described above and below. It is also possible to carry out with modifications, and they are all included in the technical scope of the present invention.
[0053] 実験例  [0053] Experimental example
表 1に示す成分組成の鋼材を溶製し、連続铸造の後、下記の条件で熱間圧延、酸 洗、冷間圧延を行い、次いで、表 2 (図 1も参照）に示す条件で熱処理 (焼鈍）すること により冷延鋼板を得た。 Steel materials with the composition shown in Table 1 are melted, and after continuous forging, hot rolling, pickling and cold rolling are performed under the following conditions, followed by heat treatment under the conditions shown in Table 2 (see also Fig. 1). (Annealing) Thus, a cold-rolled steel sheet was obtained.
[0054] ほ 間圧延]  [0054] Hot rolling
加熱温度： 1200°C X 60分  Heating temperature: 1200 ° C x 60 minutes
仕上温度： 880°C  Finishing temperature: 880 ° C
冷却： 40°C/秒で 720°Cまで冷却し、 10秒間空冷した後 40°C/秒で 500°Cまで 冷却し、その後 500°Cで 60分間保持してから炉冷した。  Cooling: Cooled to 720 ° C at 40 ° C / second, air-cooled for 10 seconds, then cooled to 500 ° C at 40 ° C / second, held at 500 ° C for 60 minutes, and then cooled in the furnace.
仕上げ板厚： 3. 2mm。  Finished plate thickness: 3.2 mm.
[0055] [酸洗、冷間圧延] [0055] [Pickling, cold rolling]
酸洗後、板厚 1. 2mmまで冷間圧延した。  After pickling, it was cold-rolled to a sheet thickness of 1.2 mm.
[0056] [熱処理 (焼鈍）] [0056] [Heat treatment (annealing)]
表 2に示す如ぐ所定の焼鈍温度に加熱して 180秒間保持した後、所定の速度で 所定の冷却停止温度まで冷却し、所定温度で 6分間保持してから炉冷した。  After heating to a predetermined annealing temperature as shown in Table 2 and holding for 180 seconds, it was cooled to a predetermined cooling stop temperature at a predetermined speed, held at the predetermined temperature for 6 minutes, and then cooled in the furnace.
[0057] 得られた冷延鋼板の金属組織を下記の方法で確認すると共に、各供試鋼板につ いて引張試験、穴拡げ試験、スポット溶接試験、耐遅れ破壊試験を行い、表 3に一括 して示す結果を得た。 [0057] The metal structure of the obtained cold-rolled steel sheet was confirmed by the following method, and each test steel sheet was subjected to a tensile test, a hole expansion test, a spot welding test, and a delayed fracture resistance test. And obtained the result.
[0058] [金属組織] [0058] [Metal structure]
組織同定方法：  Tissue identification method:
A: レぺラー腐食による光学顕微鏡観察 (1000倍)、 1視野。  A: Observation with optical microscope (1000x) due to peller corrosion, 1 field of view.
B： SEM観察（4000倍）、 4視野。  B: SEM observation (4000x), 4 fields of view.
[0059] ポリゴナルフェライト（PF)： [0059] Polygonal ferrite (PF):
上記 Aにより撮影した写真から識別する。残留 γとマルテンサイトの白に対し、 PF はグレーに腐食されるため識別できる。そして、上記 Βによる SEM写真中のポリゴナル フェライトの周囲をトレースし、そのトレース像より画像解析で円相当径を算出した。こ の円相当径の平均値をポリゴナルフェライトの平均粒径とした。  Distinguish from photos taken by A above. PF can be distinguished from residual γ and martensite white because it corrodes gray. Then, the circumference of polygonal ferrite in the SEM photograph by the above Β was traced, and the equivalent circle diameter was calculated from the trace image by image analysis. The average value of the equivalent circle diameter was defined as the average particle diameter of polygonal ferrite.
[0060] 残留 γ、マルテンサイト（Μ)、ベイナイト（Β)： [0060] Residual γ, martensite (Μ), bainite (Β):
透過型電子顕微鏡 (ΤΕΜ :倍率 15000)によって残留 γ、 Μ、 Βであることを確認し た上で、占積率は、上記 Βにより撮影した写真から算出した。  After confirming residual γ, Μ, and Β with a transmission electron microscope (ΤΕΜ: magnification 15000), the space factor was calculated from the photograph taken with 上 記.
[0061] ベィニテイツタフヱライト（BF)： 透過型電子顕微鏡 (TEM :倍率 15000)により、ベイナイトや擬フヱライトの如き他 の組織でないことを確認した上で、占積率は、 100%からポリゴナルフェライト量と上 記残留 γ量および残部のマルテンサイト（Μ)とべイナイト（Β)を減じた値とした。 [0061] Vinety Tough Light (BF): With a transmission electron microscope (TEM: magnification of 15000), it was confirmed that the structure was not other structures such as bainite and pseudofluorite. Martensite (Μ) and bainite (Β) were reduced.
[0062] [性能評価試験] [0062] [Performance evaluation test]
引張試験: JIS 5号引張試験片によって測定した。  Tensile test: Measured with a JIS No. 5 tensile test piece.
穴広げ試験：鉄鋼連盟規格 JFST 1001に準じて実施した。  Hole expansion test: The test was conducted in accordance with JFST 1001.
スポット溶接性：  Spot weldability:
下記の条件でスポット溶接を行レ、、ナゲット径 5 tの時の延性比が 0. 25以上あれ ば、スポット溶接性が良好（〇）とした。  Spot welding was performed under the following conditions, and if the ductility ratio at a nugget diameter of 5 t was 0.25 or more, the spot weldability was good (O).
[0063] ぐ溶接条件 > [0063] Gu welding conditions>
供試材厚さ： 1. 2mm、  Sample thickness: 1.2mm,
電極：ドームラジアス型 (先端直径 6mm)、  Electrode: Dome radius type (tip diameter 6mm),
加圧力： 375kg、  Applied pressure: 375kg,
アップスロープ； 1サイクル、通電時間； 12サイクル、ホールド； 1サイクル (60Hz)、 ナゲット径の調整:溶接電流により調整、  Upslope; 1 cycle, energizing time; 12 cycles, hold; 1 cycle (60 Hz), nugget diameter adjustment: adjusted by welding current,
延性比：十字引張強度（cross tensile strength) /せん断弓 |張強度。  Ductility ratio: cross tensile strength / shear bow |
[0064] [耐遅れ破壊性] [0064] [Delayed Fracture Resistance]
R= 3mmの 60° Vブロックを用いて V字曲げを施した後、曲げ部に 1500MPaの 応力を負荷して 5%塩酸水溶液中に浸漬し、割れ発生までの時間を測定した。 48時 間で割れなかったものを耐遅れ破壊良好（〇）とした。  After applying a V-shape bend using a 60 ° V block with R = 3 mm, a stress of 1500 MPa was applied to the bend and immersed in a 5% aqueous hydrochloric acid solution, and the time until cracking was measured. Those that did not crack in 48 hours were regarded as good delayed fracture resistance (◯).
[0065] [表 1] [0065] [Table 1]
/ I0n90/.00732i1d ε! Ϊ OAV· / I0n90 / .00732i1d ε! Ϊ OAV
Figure imgf000015_0001
Figure imgf000015_0001
Figure imgf000016_0001
Figure imgf000016_0001
Figure imgf000016_0002
Figure imgf000016_0002
Figure imgf000017_0001
Figure imgf000017_0001
注： PF：ホ 'リコ'ナルフェラ仆、 BF；へ' ティックフェラ仆 残部（M:マルテンサイト、 B:へ'イナイト） Note: PF: Ho 'Rico' Narufera 仆, BF; To 'Tick Blow 仆 The rest (M: Martensite, B: To' Innight)
[0068] 表 1〜3より、次の様に考えることができる。 [0068] From Tables 1 to 3, it can be considered as follows.
[0069] 実験 No. 1〜： 10, 16は、本発明の規定要件を全て満たす実施例であり、何れも 98 OMPa級以上の引張強度を有すると共に、強度 X伸び特性、強度 X伸びフランジ特 性によって評価される成形性が良好であり、更にスポット溶接性ゃ耐遅れ破壊性に ぉレ、ても良好な結果が得られてレ、る。  [0069] Experiments Nos. 1 to 10 and 16 are examples that satisfy all of the specified requirements of the present invention, and all have tensile strength of 98 OMPa class or higher, strength X elongation characteristics, strength X elongation flange characteristics The formability evaluated by the properties is good, and even if spot weldability is poor in delayed fracture resistance, good results can be obtained.
[0070] これらに対し実験 No. 11は、鋼材の C含量が不足し、金属組織中のべィニティック フェライト量も不足するため、強度不足で、強度 X伸び特性、強度 X伸びフランジ特 性によって評価される成形性も悪い。また実験 No. 12は、用いた鋼材の Si含量が不 足すると共に（Si+Al) / (Mn+ Cr)比が規定範囲を外れるため、金属組織中に残 留 Ίが存在せず、強度 X伸び特性、強度 X伸びフランジ特性によって評価される成 形性が劣悪で耐遅れ破壊性も悪レ、。 [0070] On the other hand, Experiment No. 11 was evaluated based on strength X elongation characteristics and strength X elongation flange characteristics because the C content of the steel material was insufficient and the amount of vanitic ferrite in the metal structure was also insufficient. The moldability is also poor. The experiment No. 12, since the Si content of the steel used is out of the (Si + Al) / (Mn + Cr) ratio specified range as well as lack, there is no residual Ί in the metal structure, strength X Elongation characteristics and strength The formability evaluated by the X-stretch flange characteristics is inferior and delayed fracture resistance is poor.
[0071] 実験 No. 13は、 Mn量が規定範囲を外れると共に（Si+Al) ZMn比が規定範囲を 超えているため、ポリゴナルフェライトが増え過ぎてべィニティックフェライト量が大幅 に少なくなつており、強度不足で加工性も劣悪である。実験 No. 14は、個々の含有 元素量は規定要件を満たしている力 （Si+Al) /Mn比が規定範囲を超えており、 ポリゴナルフェライトが粗大で平均粒径が規定値を超えているため、強度不足で加工 性も悪ぐ且つスポット溶接性もよくない。  [0071] In Experiment No. 13, the amount of Mn was out of the specified range and the (Si + Al) ZMn ratio was out of the specified range, so the amount of polygonal ferrite increased and the amount of vinylic ferrite was greatly reduced. The strength is insufficient and the processability is poor. Experiment No. 14 shows that the amount of each contained element satisfies the specified requirements (Si + Al) / Mn ratio exceeds the specified range, the polygonal ferrite is coarse, and the average grain size exceeds the specified value. Therefore, the strength is insufficient, workability is poor, and spot weldability is not good.
[0072] 実験 No. 15は、鋼成分は規定要件を満たしているが、熱処理条件が不適切である ため組織中のポリゴナルフェライト量が過多となってべィニティックフェライト量が不足 し、強度 X伸び特性、強度 X伸びフランジ特性によって評価される成形性が劣悪で 、耐遅れ破壊性も悪い。 [0072] In Experiment No. 15, the steel components met the specified requirements, but the heat treatment conditions were inappropriate, so the amount of polygonal ferrite in the structure was excessive, and the amount of vinylic ferrite was insufficient. The formability evaluated by strength X elongation characteristics and strength X elongation flange characteristics is poor, and delayed fracture resistance is also poor.

Claims

請求の範囲 The scope of the claims
C:0. 10〜0.25% (化学成分の場合は質量％を表す、以下同じ)、  C: 0. 10 ~ 0.25%
Si:l.0〜3.0%、  Si: l.0 ~ 3.0%,
Mn:l.5〜3.0%、  Mn: l. 5-3.0%,
P:0. 15%以下、  P: 0.15% or less,
S:0.02%以下、  S: 0.02% or less,
A1:0.4%以下、  A1: 0.4% or less,
を満足し、残部が鉄および不可避不純物よりなる鋼からなり、上記 Si, Al, Mnの含 有量が下記式 (I)の関係を満たし、 And the balance is made of steel consisting of iron and inevitable impurities, and the contents of Si, Al, and Mn satisfy the relationship of the following formula (I):
(Si+Al)/Mn:0.74〜： 1.26……（I)  (Si + Al) /Mn:0.74〜: 1.26 …… (I)
且つ、縦断面のミクロ組織が、全組織に対する占積率で、 And the microstructure of the longitudinal section is the space factor for the whole structure,
1)べィニティックフェライト： 50%以上、  1) Vinylic ferrite: 50% or more,
2)ポリゴナルフェライト：5〜35%、  2) Polygonal ferrite: 5-35%,
3)ポリゴナルフェライトの平均粒径： 10 μ m以下、  3) Average particle diameter of polygonal ferrite: 10 μm or less,
4)残留オーステナイト： 5%以上  4) Residual austenite: 5% or more
であることを特徴とする、成形性、耐遅れ破壊性に優れた高強度複合組織鋼板。 A high-strength steel sheet with excellent formability and delayed fracture resistance.
C:0. 12〜0.25%、  C: 0. 12 ~ 0.25%,
Si:l.0〜3.0%、  Si: l.0 ~ 3.0%,
Mn:l.5〜3.0%、  Mn: l. 5-3.0%,
Cr:l.0%以下、  Cr: l.0% or less,
P:0. 15%以下、  P: 0.15% or less,
S:0.02%以下、  S: 0.02% or less,
A1:0.4%以下、  A1: 0.4% or less,
を満足し、残部が鉄および不可避不純物よりなる鋼からなり、上記 Si, Al, Mn, の 含有量が下記式 (II)の関係を満たし、 And the balance is made of steel consisting of iron and inevitable impurities, and the content of Si, Al, Mn, satisfies the relationship of the following formula (II),
(Si+Al)/(Mn+Cr) :0.74~1.26……（II)  (Si + Al) / (Mn + Cr): 0.74 ~ 1.26 …… (II)
且つ、縦断面のミクロ組織が、全組織に対する占積率で、 And the microstructure of the longitudinal section is the space factor for the whole structure,
1)べィニティックフェライト： 50%以上、 2)ポリゴナルフェライト：5〜35%、 1) Vinylic ferrite: 50% or more, 2) Polygonal ferrite: 5-35%,
3)ポリゴナルフェライトの平均粒径： 10 μ m以下、  3) Average particle diameter of polygonal ferrite: 10 μm or less,
4)残留オーステナイト： 5%以上  4) Residual austenite: 5% or more
であることを特徴とする、成形性、耐遅れ破壊性優れた高強度複合組織鋼板。  A high-strength steel sheet with excellent formability and delayed fracture resistance.
[3] 鋼が、他の元素として、 [3] Steel is another element,
Ti:0.15%以下および/または Nb:0.1%以下を含有するものである請求項 1ま たは 2に記載の高強度複合組織鋼板。  The high-strength composite steel sheet according to claim 1 or 2, which contains Ti: 0.15% or less and / or Nb: 0.1% or less.
[4] 鋼が、更に他の元素として、 [4] Steel is still another element,
Ca:30ppm以下および/または REM:30ppm以下を含むものである請求項 1また は 2に記載の高強度複合組織鋼板。  3. The high-strength composite steel sheet according to claim 1 or 2, which contains Ca: 30 ppm or less and / or REM: 30 ppm or less.
[5] 引張強さが 980MPa以上である請求項 1または 2に記載の高強度複合組織鋼板。 [5] The high-strength composite steel sheet according to claim 1 or 2, wherein the tensile strength is 980 MPa or more.
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WO2014092025A1 (en) * 2012-12-12 2014-06-19 株式会社神戸製鋼所 High-strength steel plate and manufacturing method thereof
RU2680042C2 (en) * 2014-07-03 2019-02-14 Арселормиттал Method of manufacturing high-strength steel sheet with improved strength, plasticity and formability
WO2017109540A1 (en) * 2015-12-21 2017-06-29 Arcelormittal Method for producing a high strength steel sheet having improved ductility and formability, and obtained steel sheet
WO2017108866A1 (en) * 2015-12-21 2017-06-29 Arcelormittal Method for producing a high strength steel sheet having improved ductility and formability, and obtained steel sheet
EP3656880A1 (en) * 2015-12-21 2020-05-27 ArcelorMittal Method for producing a high strength steel sheet having improved ductility and formability, and obtained steel sheet
EP3910084A1 (en) * 2015-12-21 2021-11-17 ArcelorMittal Method for producing a high strength steel sheet having improved ductility and formability, and obtained steel sheet

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CN101460646A (en) 2009-06-17
JP4974341B2 (en) 2012-07-11
GB2452230B (en) 2012-02-22
KR20090016500A (en) 2009-02-13
US20100221138A1 (en) 2010-09-02
GB0900057D0 (en) 2009-02-11
JP2007321237A (en) 2007-12-13

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