WO2012011598A1 - High-carbon hot-rolled steel sheet having excellent fine blanking properties and process for production thereof - Google Patents

High-carbon hot-rolled steel sheet having excellent fine blanking properties and process for production thereof Download PDF

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WO2012011598A1
WO2012011598A1 PCT/JP2011/066789 JP2011066789W WO2012011598A1 WO 2012011598 A1 WO2012011598 A1 WO 2012011598A1 JP 2011066789 W JP2011066789 W JP 2011066789W WO 2012011598 A1 WO2012011598 A1 WO 2012011598A1
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steel sheet
rolled steel
fine blanking
hot
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PCT/JP2011/066789
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French (fr)
Japanese (ja)
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中村 展之
崇 小林
妻鹿 哲也
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Jfeスチール株式会社
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Priority to JP2010163469A priority patent/JP5549450B2/en
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Publication of WO2012011598A1 publication Critical patent/WO2012011598A1/en

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    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D6/00Heat treatment of ferrous alloys
    • C21D6/005Heat treatment of ferrous alloys containing Mn
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/001Ferrous alloys, e.g. steel alloys containing N
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite

Abstract

Provided are a high-carbon hot-rolled steel sheet which exhibits excellent fine blanking properties until the steel sheet is wound after hot-rolling and a process for producing the high-carbon hot-rolled steel sheet. Specifically provided is a high-carbon hot-rolled steel sheet having excellent fine blanking properties, which is characterized by having a composition comprising, in mass%, 0.10-040% of C, 1.0% or less of Si, 2.0% or less of Mn, 0.03% or less of P, 0.03% or less of S, 0.01% or less of N, 0.10% or less of Al, and a remainder made up by Fe and unavoidable impurities, wherein the area ratio of a proeutectoid ferrite phase in the entire structure is 10% or less and the steel sheet has a microstructure having a carbide spheroidizing ratio of 50% or more.

Description

ファインブランキング性に優れた高炭素熱延鋼板およびその製造方法High carbon hot-rolled steel sheet excellent in fine blanking property and manufacturing method thereof
 本発明は、自動車部品などの用途に好適な高炭素熱延鋼板、特に、熱間圧延後に焼鈍を施すことなく優れたファインブランキング性(精密打抜き性)を確保した高炭素熱延鋼板およびその製造方法に関する。 The present invention relates to a high-carbon hot-rolled steel sheet suitable for applications such as automobile parts, in particular, a high-carbon hot-rolled steel sheet that secures excellent fine blanking property (precision punching property) without annealing after hot rolling and its It relates to a manufacturing method.
 ギア、ミッション、シートリクライナーなどの複雑な形状を有する自動車部品は、JIS G 4051に規定された機械構造用高炭素鋼板を切削やブランキングによって、あるいはさらに穴広げ加工などを施して、所望の形状に加工後、硬さを確保するために焼入れ焼戻し処理を施して製造されている。最近では、寸法精度の向上と製造工程の簡略化の観点から、i)ほぼ100%剪断面の平滑なブランキング端面が得られる、ii)寸法精度が高い、iii)複雑な形状を1回のブランキングで加工できるなどのメリットを有しているファインブランキングによる加工が採用されるようになっている。 Automotive parts with complex shapes such as gears, missions, and seat recliners are made into the desired shapes by cutting or blanking high-carbon steel plates for machine structures specified in JIS G 4051, or by further expanding holes. After being processed, it is manufactured by quenching and tempering in order to ensure hardness. Recently, from the viewpoint of improving dimensional accuracy and simplifying the manufacturing process, i) a smooth blanking end surface with almost 100% shear surface can be obtained, ii) high dimensional accuracy, and iii) complicated shape once Fine blanking has been adopted, which has the advantage of being able to process with blanking.
 ファインブランキングは、工具間のクリアランスを通常のブランキングにおける鋼板厚みの5~10%程度から鋼板厚みの2%以下程度にまで極めて小さく設定し、工具切刃付近の鋼板に圧縮応力を作用させてブランキングする方法である。そのため、被ブランキング材である高炭素鋼板は極めて厳しい加工を受けるので、100%剪断面の平滑なブランキング端面が得られず、ブランキング面にクラックが生じやすくなる。 In fine blanking, the clearance between tools is set extremely small from about 5 to 10% of the steel plate thickness in normal blanking to about 2% or less of the steel plate thickness, and compressive stress is applied to the steel plate near the tool cutting edge. This is a blanking method. Therefore, the high carbon steel sheet as the blanking material is subjected to extremely severe processing, so that a smooth blanking end face having a 100% shear plane cannot be obtained, and cracks are likely to occur on the blanking face.
 そこで、こうした問題の起きない、すなわちファインブランキング性に優れた高炭素鋼板が提案されている。例えば、特許文献1には、質量%で、C:0.08~0.19%、Si:0.50%以下、Mn:0.70~1.50%、Cr:0.05~0.80%、B:0.0005~0.005%およびAl:0.08%以下を含有し、残部がFeおよび不可避的不純物からなる複合成形加工性および短時間急速加熱焼入れ性にすぐれた精密打抜き用鋼板が開示されている。 Therefore, a high carbon steel sheet that does not cause such a problem, that is, excellent in fine blanking property, has been proposed. For example, in Patent Document 1, in mass%, C: 0.08 to 0.19%, Si: 0.50% or less, Mn: 0.70 to 1.50%, Cr: 0.05 to 0. 80%, B: 0.0005 to 0.005% and Al: 0.08% or less, and the balance is made of Fe and inevitable impurities. Steel sheets for use are disclosed.
 特許文献2には、質量%で、C:0.15~0.90%、Si:0.4%以下、Mn:0.3~1.0%、P:0.03%以下、全Al:0.10%以下、残部が実質的にFeの組成をもち、球状化率80%以上、平均粒径0.4~1.0μmの炭化物がフェライトマトリックスに分散した組織をもち、JIS 5号引張試験片の平行部長手方向中央部における幅方向両サイドに開き角45度、深さ2mmのVノッチを入れた試験片を用いて引張試験し、平行部長手方向中央部の標点距離10mmに対する破断後の伸び率として表わされる切欠き引張伸びが20%以上である精密打抜き性に優れた高炭素鋼板が開示されている。 In Patent Document 2, in mass%, C: 0.15 to 0.90%, Si: 0.4% or less, Mn: 0.3 to 1.0%, P: 0.03% or less, all Al : 0.10% or less, balance is substantially Fe composition, spheroidization rate is 80% or more, and has a structure in which carbide with an average particle size of 0.4 to 1.0 μm is dispersed in ferrite matrix, JIS No. 5 Tensile test was performed using a test piece having a V notch with an opening angle of 45 degrees and a depth of 2 mm on both sides in the width direction at the center in the longitudinal direction of the parallel part of the tensile test piece. There is disclosed a high carbon steel sheet excellent in precision punching property, in which a notch tensile elongation expressed as an elongation percentage after fracture with respect to is 20% or more.
 特許文献3には、質量%で、C:0.15~0.45%、Si:0.25%以下、Mn:0.3~1.2%、P:0.02%以下、S:0.02%以下、Al:0.01~0.1%、N:0.008%以下を含有し、残部が不可避的不純物とFeの組成をもち、パーライト+セメンタイトの割合が10%以下、かつフェライト粒の平均粒径が10~20μmのファインブランキング性に優れた高炭素鋼板が開示されている。 In Patent Document 3, in mass%, C: 0.15 to 0.45%, Si: 0.25% or less, Mn: 0.3 to 1.2%, P: 0.02% or less, S: 0.02% or less, Al: 0.01 to 0.1%, N: 0.008% or less, the balance has the composition of inevitable impurities and Fe, the ratio of pearlite + cementite is 10% or less, In addition, a high carbon steel sheet excellent in fine blanking property having an average grain size of ferrite grains of 10 to 20 μm is disclosed.
 特許文献4には、質量%で、C:0.1~0.5%、Si:0.5%以下、Mn:0.2~1.5%、P:0.03%以下、S:0.02%以下を含み、残部Feおよび不可避的不純物からなる組成と、フェライトおよび炭化物を主体とする組織とを有し、前記フェライトの平均粒径が1~10μm、前記炭化物の球状化率が80%以上で、かつ前記炭化物のうち、フェライトの結晶粒界に存在する炭化物の量Sgb={Son/(Son+Sin)}×100(Son:単位面積あたりに存在する炭化物のうち、フェライト粒界上に存在する炭化物の総占有面積、Sin:単位面積あたりに存在する炭化物のうち、フェライト粒内に存在する炭化物の総占有面積)が40%以上であるファインブランキング性に優れた鋼板が開示されている。 In Patent Document 4, in mass%, C: 0.1 to 0.5%, Si: 0.5% or less, Mn: 0.2 to 1.5%, P: 0.03% or less, S: 0.02% or less, having a composition composed of the balance Fe and inevitable impurities, a structure mainly composed of ferrite and carbide, the average particle diameter of the ferrite is 1 to 10 μm, and the spheroidization rate of the carbide is 80% or more and of the carbides, the amount of carbides present at the ferrite grain boundaries Sgb = {Son / (Son + Sin)} × 100 (Son: Of the carbides present per unit area, on the ferrite grain boundaries A steel sheet excellent in fine blanking property is disclosed, in which the total occupied area of carbides present in Sin: the total occupied area of carbides present in ferrite grains among carbides present per unit area is 40% or more ing.
 このうち、特許文献1に記載の鋼板は巻取りままの熱延鋼板であり、特許文献2~4の鋼板は巻取り後の熱延鋼板を焼鈍、あるいは冷間圧延後焼鈍を行って炭化物の球状化(特許文献2、4では、球状化率80%以上)が施された高炭素鋼板である。 Among these, the steel sheet described in Patent Document 1 is a hot-rolled steel sheet as wound, and the steel sheets of Patent Documents 2 to 4 are formed by annealing the hot-rolled steel sheet after winding or annealing after cold rolling. It is a high carbon steel plate that has been spheroidized (in Patent Documents 2 and 4, the spheroidization rate is 80% or more).
特開昭59−76861号公報JP 59-76861 A 特開2000−265240号公報JP 2000-265240 A 特開2001−140037号公報JP 2001-140037 A 特開2007−231416号公報JP 2007-231416 A
 しかしながら、特許文献1に記載の巻取りままの熱延鋼板では、100%剪断面の平滑なブランキング端面が得られず、ブランキング面にクラックが発生しやすくなり、ファインブランキング性に劣る。特許文献2~4の鋼板では、球状化率80%を超える炭化物の球状化が図られているため、良好なファインブランキング性が得られるが、巻取り後の熱延鋼板を焼鈍、あるいは冷間圧延後焼鈍する必要があり、コスト高である。 However, the unrolled hot-rolled steel sheet described in Patent Document 1 does not provide a smooth blanking end face with a 100% shear plane, and cracks are likely to occur on the blanking face, resulting in poor fine blanking properties. In the steel sheets of Patent Documents 2 to 4, since the spheroidization of carbide exceeding 80% is achieved, good fine blanking properties can be obtained, but the hot-rolled steel sheet after winding is annealed or cooled. It is necessary to anneal after hot rolling, which is expensive.
 本発明は、巻取り後の熱延鋼板を焼鈍、あるいは冷間圧延後焼鈍することなく、すなわち低コストで、優れたファインブランキング性を有する巻取りままの高炭素熱延鋼板およびその製造方法を提供することを目的とする。 The present invention does not anneal a hot-rolled steel sheet after winding or annealing after cold rolling, that is, low-cost, high-carbon hot-rolled steel sheet as wound and having excellent fine blanking properties, and a method for producing the same The purpose is to provide.
 本発明者らは、巻取りままで優れたファインブランキング性が得られる高炭素熱延鋼板を鋭意検討した結果、以下のことを見出した。 The present inventors have intensively studied a high carbon hot-rolled steel sheet that can obtain excellent fine blanking properties as it is wound, and as a result, have found the following.
 i)成分組成を適正化した上で、組織全体に占める初析フェライト相の面積率が10%以下で、炭化物の球状化率が50%以上であるミクロ組織にすれば、巻取りままでも優れたファインブランキング性が得られる。 i) If the microstructure is such that the area ratio of the pro-eutectoid ferrite phase in the entire structure is 10% or less and the spheroidization ratio of the carbide is 50% or more after optimizing the component composition, it is excellent even when wound. Fine blanking performance can be obtained.
 ii)こうしたミクロ組織は、800~950℃の仕上温度で熱間圧延した後、650℃以上の冷却開始温度から50℃/s以上の平均冷却速度で450~600℃の冷却停止温度まで冷却し、3s以内に巻取る方法により得られる。 ii) Such a microstructure is hot-rolled at a finishing temperature of 800 to 950 ° C. and then cooled from a cooling start temperature of 650 ° C. or higher to a cooling stop temperature of 450 to 600 ° C. at an average cooling rate of 50 ° C./s or higher. It is obtained by a method of winding within 3 s.
 本発明は、このような知見に基づいてなされたものであり、質量%で、C:0.10~0.40%、Si:1.0%以下、Mn:2.0%以下、P:0.03%以下、S:0.03%以下、N:0.01%以下、Al:0.10%以下を含み、残部がFeおよび不可避的不純物からなる組成を有し、組織全体に占める初析フェライト相の面積率が10%以下で、炭化物の球状化率が50%以上であるミクロ組織を有することを特徴とするファインブランキング性に優れた高炭素熱延鋼板を提供する。 The present invention has been made on the basis of such findings. In mass%, C: 0.10 to 0.40%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.03% or less, N: 0.01% or less, Al: 0.10% or less, and the balance is composed of Fe and inevitable impurities, and occupies the entire structure Provided is a high carbon hot-rolled steel sheet excellent in fine blanking property, characterized by having a microstructure in which the area ratio of a pro-eutectoid ferrite phase is 10% or less and the spheroidization ratio of carbide is 50% or more.
 本発明の高炭素熱延鋼板では、上記の組成に加え、質量%で、B:0.0010~0.0050%を含有させ、かつ0.50≦(14[B])/(10.8[N])の関係を満足させることが好ましい。ただし、[B]、[N]はそれぞれB、Nの含有量(質量%)を表す。さらにまた、質量%で、Ti、Nb、Vのうちの少なくとも1種:合計で0.1%以下、Ni、Cr、Moのうちの少なくとも1種:合計で1.5%以下、Sb、Snのうちの少なくとも1種:合計で0.003~0.10%を、個別にあるいは同時に含有させることが好ましい。 In the high carbon hot-rolled steel sheet of the present invention, in addition to the above composition, B: 0.0010 to 0.0050% is contained in mass%, and 0.50 ≦ (14 [B]) / (10.8 [N]) is preferably satisfied. However, [B] and [N] represent the contents (mass%) of B and N, respectively. Furthermore, at least one of Ti, Nb, and V in total: 0.1% or less in total, at least one of Ni, Cr, and Mo: 1.5% or less in total, Sb, Sn It is preferable to contain at least one of them: 0.003 to 0.10% in total or individually or simultaneously.
 本発明の高炭素熱延鋼板は、上記の組成を有する鋼を、800~950℃の仕上温度で熱間圧延した後、650℃以上の冷却開始温度から50℃/s以上の平均冷却速度で450~600℃の冷却停止温度まで冷却し、3s以内に巻取る方法により製造可能である。 The high carbon hot-rolled steel sheet of the present invention is obtained by hot rolling a steel having the above composition at a finishing temperature of 800 to 950 ° C., and then at an average cooling rate of 50 ° C./s or more from a cooling start temperature of 650 ° C. or more. It can be manufactured by a method of cooling to a cooling stop temperature of 450 to 600 ° C. and winding up within 3 s.
 本発明の製造方法では、巻取り後の鋼板を、巻取られた状態で保熱装置に装入することが好ましい。 In the production method of the present invention, it is preferable that the steel plate after winding is inserted into a heat retaining device in a wound state.
 本発明により、低コストで、優れたファインブランキング性を有する巻取りままの高炭素熱延鋼板を製造できるようになった。本発明の高炭素熱延鋼板は、ギア、ミッション、シートリクライナーなどの自動車用部品に好適である。 According to the present invention, it is possible to produce an as-rolled high carbon hot rolled steel sheet having excellent fine blanking properties at low cost. The high carbon hot-rolled steel sheet of the present invention is suitable for automotive parts such as gears, missions, and seat recliners.
 以下に、本発明である高炭素熱延鋼板およびその製造方法について詳細に説明する。なお、成分の含有量の単位である「%」は特に断らない限り「質量%」を意味するものとする。 Hereinafter, the high carbon hot-rolled steel sheet and the manufacturing method thereof according to the present invention will be described in detail. Note that “%”, which is a unit of component content, means “% by mass” unless otherwise specified.
 1)組成
 C:0.10~0.40%
 C量が0.1%未満では自動車部品として要求される焼入れ後の硬さを得ることができなくなる。一方、C量が0.40%を超えると鋼板が硬質化し、ブランキング時の金型への負荷が大きくなりすぎ、ブランキング用金型寿命が工業的に十分なほどに確保できなくなる。したがって、C量は0.10~0.40%とする。
1) Composition C: 0.10 to 0.40%
If the amount of C is less than 0.1%, the hardness after quenching required for automobile parts cannot be obtained. On the other hand, if the amount of C exceeds 0.40%, the steel sheet becomes hard, the load on the die during blanking becomes too large, and the blanking die life cannot be secured to an industrially sufficient level. Therefore, the C content is 0.10 to 0.40%.
 Si:1.0%以下
 Si量が1.0%を超えるとフェライト相が硬質化し、ファインブランキング性が低下したり、赤スケールと呼ばれる表面欠陥が発生する。したがって、Si量は1.0%以下、好ましくは0.35%以下とする。
Si: 1.0% or less When the Si content exceeds 1.0%, the ferrite phase becomes hard and the fine blanking property is lowered, or a surface defect called red scale occurs. Therefore, the Si content is 1.0% or less, preferably 0.35% or less.
 Mn:2.0%以下
 Mn量が2.0%を超えるとフェライト相が硬質化し、ファインブランキング性が低下する。したがって、Mn量は2.0%以下とする。なお、焼入れ性向上のために、Mn量は0.2%以上とすることが好ましい。
Mn: 2.0% or less If the amount of Mn exceeds 2.0%, the ferrite phase becomes hard and the fine blanking property decreases. Therefore, the Mn content is 2.0% or less. In order to improve hardenability, the amount of Mn is preferably 0.2% or more.
 P:0.03%以下
 P量が0.03%を超えると粒界等に偏析し、ファインブランキング性などの加工性が低下する。したがって、P量は0.03%以下、好ましくは0.02%以下とするが、少ないほどより好ましい。
P: 0.03% or less When the amount of P exceeds 0.03%, segregation occurs at grain boundaries and the like, and workability such as fine blanking property is deteriorated. Accordingly, the P content is 0.03% or less, preferably 0.02% or less, but the smaller the amount, the more preferable.
 S:0.03%以下
 S量が0.03%を超えると硫化物を形成し、ファインブランキング性などの加工性が低下したり、焼入れ後の靱性が低下する。したがって、S量は0.03%以下、好ましくは0.02%以下とする。
S: 0.03% or less When the amount of S exceeds 0.03%, a sulfide is formed, and workability such as fine blanking property is lowered, and toughness after quenching is lowered. Therefore, the S content is 0.03% or less, preferably 0.02% or less.
 N:0.01%以下
 NはAl等と窒化物を形成し、オーステナイト粒の粗大化を防止する作用を有するが、N量が0.01%を超えて多くなりすぎると、加工性が劣化する。したがって、N量は0.01%以下、好ましくは0.005%以下とする。
N: 0.01% or less N forms a nitride with Al and the like and has the effect of preventing coarsening of austenite grains. However, if the N content exceeds 0.01%, the workability deteriorates. To do. Therefore, the N content is 0.01% or less, preferably 0.005% or less.
 Al:0.10%以下
 Al量が0.10%を超えると鋼の清浄度が低下するだけでなく、焼入れ処理の加熱時にオーステナイト粒が微細化し過ぎ、冷却時にフェライト相の生成が促進し、焼入れ後に必要な硬さが得られなくなる。したがって、Al量は0.10%以下とする。なお、Alには、Nと結合してAlNを形成し、オーステナイト粒の粗大化を防止したり、Bによる焼入れ性を効果的に発揮させる作用を有するので、Al量は0.01%以上とすることが好ましい。
Al: 0.10% or less When the Al content exceeds 0.10%, not only the cleanliness of the steel decreases, but also the austenite grains become too fine during the heating of the quenching treatment, and the formation of the ferrite phase is promoted during cooling, The required hardness cannot be obtained after quenching. Therefore, the Al content is 0.10% or less. In addition, since Al has an action of bonding with N to form AlN to prevent coarsening of austenite grains or effectively exhibit the hardenability by B, the Al amount is 0.01% or more. It is preferable to do.
 残部はFeおよび不可避的不純物とするが、以下の理由で、B:0.0010~0.0050%、Ti、Nb、Vのうちの少なくとも1種:合計で0.1%以下、Ni、Cr、Moのうちの少なくとも1種:合計で1.5%以下、Sb、Snのうちの少なくとも1種:合計で0.003~0.10%を、個別にあるいは同時に含有させることが好ましい。 The balance is Fe and inevitable impurities, but for the following reasons, B: 0.0010 to 0.0050%, at least one of Ti, Nb, and V: 0.1% or less in total, Ni, Cr And at least one of Mo: 1.5% or less in total, and at least one of Sb and Sn: 0.003 to 0.10% in total are preferably contained individually or simultaneously.
 B:0.0010~0.0050%
 Bは、焼入れ性を高めるとともに、焼入れ処理の加熱時にBNを形成してオーステナイト粒の粗大化を抑制し、焼入れ後の靱性を向上させる元素である。こうした効果を得るには、B量は0.0010%以上にする必要がある。一方、B量が0.0050%を超えると熱間圧延の負荷が高くなり操業性が低下するととともに、ファインブランキング性などの加工性の低下も招く。したがって、B量は0.0010~0.0050%とすることが好ましく、0.0010~0.0030%とすることがより好ましい。また、Bにより焼入れ性を高めるには、焼入れ処理の加熱時に固溶Bが存在していることが必要である。しかし、BはNとの親和力が大きく、熱間圧延やその後の巻取り時あるいは焼入れ処理の加熱時にBNを形成しやすいので、Bを含有させる場合は、Nに対して0.50≦(14[B])/(10.8[N])の関係を満足するようにして固溶Bを確保する必要がある。なお、ここで[B]、[N]はそれぞれB、Nの含有量(質量%)を表す。
B: 0.0010 to 0.0050%
B is an element that enhances the toughness after quenching by improving the hardenability and suppressing the coarsening of the austenite grains by forming BN during heating in the quenching treatment. In order to obtain such an effect, the B amount needs to be 0.0010% or more. On the other hand, if the amount of B exceeds 0.0050%, the hot rolling load becomes high and the operability is lowered, and the workability such as fine blanking is also lowered. Accordingly, the B content is preferably 0.0010 to 0.0050%, and more preferably 0.0010 to 0.0030%. Moreover, in order to improve hardenability by B, it is necessary for the solid solution B to exist at the time of the heating of a hardening process. However, since B has a large affinity with N and is likely to form BN at the time of hot rolling, subsequent winding or heating during quenching, when B is contained, 0.50 ≦ (14 It is necessary to ensure the solid solution B so as to satisfy the relationship [B]) / (10.8 [N]). Here, [B] and [N] represent the contents (mass%) of B and N, respectively.
 Ti、Nb、Vのうちの少なくとも1種:合計で0.1%以下
 Ti、Nb、Vのうちの少なくとも1種の含有量が合計で0.1%を超えるとTiCなどの析出によりフェライト相が硬質化し、ブランキング用金型寿命の低下を招く。したがって、Ti、Nb、Vのうちの少なくとも1種の含有量は合計で0.1%以下とすることが好ましい。なお、Ti、Nb、Vは、Nと結合し窒化物を形成しやすく、焼入れ時のオーステナイト粒の粗大化を防止するとともに、Bにより焼入れ性の向上を図る場合は、BNの形成を防止して必要なBの添加量を少なくすることができるという効果も有するので、これらの元素のうち少なくとも1種の含有量は合計で0.01%以上とすることがより好ましい。
At least one of Ti, Nb, and V: 0.1% or less in total If the content of at least one of Ti, Nb, and V exceeds 0.1% in total, precipitation of TiC or the like causes a ferrite phase Becomes hard and causes a reduction in the life of the blanking die. Therefore, the content of at least one of Ti, Nb, and V is preferably 0.1% or less in total. Ti, Nb, and V are easy to combine with N to form nitrides, prevent austenite grains from coarsening during quenching, and prevent formation of BN when improving hardenability with B. Therefore, it is more preferable that the content of at least one of these elements is 0.01% or more in total.
 Ni、Cr、Moのうちの少なくとも1種:合計で1.5%以下
 Ni、Cr、Moのうちの少なくとも1種の含有量が合計で1.5%を超えるとフェライト相が硬質化し、ファインブランキング性が低下する。したがって、Ni、Cr、Moのうちの少なくとも1種の含有量は合計で1.5%以下とすることが好ましい。なお、Ni、Cr、Moは焼入れ性の向上に有効に作用するので、Ni、Cr、Moのうちの少なくとも1種の含有量は合計で0.1%以上とすることがより好ましい。
At least one of Ni, Cr, and Mo: 1.5% or less in total If the content of at least one of Ni, Cr, and Mo exceeds 1.5% in total, the ferrite phase becomes hard and fine Blanking performance decreases. Therefore, the content of at least one of Ni, Cr, and Mo is preferably 1.5% or less in total. In addition, since Ni, Cr, and Mo effectively act to improve hardenability, the content of at least one of Ni, Cr, and Mo is more preferably 0.1% or more in total.
 Sb、Snのうちの少なくとも1種:合計で0.003~0.10%
 焼入れ処理の加熱を空気を混合してカーボンポテンシャルを制御した雰囲気中で900℃前後で1時間程度の条件で行うと吸窒現象が起こり、鋼の表層部でAlNやBNが形成され、オーステナイト粒が微細化し過ぎたり、固溶B量が著しく減少して焼入れ性が低下する場合がある。そこで、本発明者らが、鋼の吸窒を抑制可能な元素として知られているSbやSnを添加し、焼入れ性について検討を行ったところ、Sb、Snのうち少なくとも1種の量を合計で0.003%以上にすれば、吸窒を抑制でき、表層部の焼入れ性を改善できることを見出した。しかし、Sb、Snのうち少なくとも1種の量を合計で0.10%を超えて添加すると焼入れ焼戻し時にオーステナイト粒界に偏析し靱性を著しく低下させる。さらに、これらの元素は、焼入れ処理前の素材の加工性にも影響を及ぼし、その量が合計で0.10%を超えると粒界に偏析し、ファインブランキング性などの加工性の低下も招く。したがって、Sb、Snのうち少なくとも1種の含有量は合計で0.003~0.10%とすることが好ましい。
At least one of Sb and Sn: 0.003 to 0.10% in total
When the heating of the quenching process is performed in an atmosphere in which air is mixed and the carbon potential is controlled at about 900 ° C. for about 1 hour, nitrogen absorption occurs, and AlN and BN are formed in the surface layer of the steel, and austenite grains May be excessively refined, or the amount of dissolved B may be remarkably reduced, resulting in a decrease in hardenability. Therefore, the present inventors added Sb and Sn, which are known as elements capable of suppressing steel nitrogen absorption, and studied hardenability. As a result, the total amount of at least one of Sb and Sn was added. It was found that if the content is 0.003% or more, nitrogen absorption can be suppressed and the hardenability of the surface layer portion can be improved. However, if the total amount of at least one of Sb and Sn exceeds 0.10%, segregation occurs at the austenite grain boundaries during quenching and tempering, and the toughness is significantly reduced. Furthermore, these elements also affect the workability of the raw material before quenching, and when the total amount exceeds 0.10%, segregation occurs at the grain boundaries, and the workability such as fine blanking is reduced. Invite. Accordingly, the content of at least one of Sb and Sn is preferably 0.003 to 0.10% in total.
 2)ミクロ組織
 本発明者らが、ファインブランキング端面性状に及ぼすミクロ組織の影響を調査したところ、100%剪断面の平滑な端面が得られなかったり、ブランキング端面にクラックが発生するのは、初析フェライト相とパーライトとの界面やパーライト中の破壊したセメンタイトに起因していることが明らかになった。したがって、優れたファインブランキング性を得るには、初析フェライト相やパーライトの生成を極力抑制することが効果的であるが、巻取りままの熱延鋼板に対しては、組織全体に占める初析フェライト相の面積率が10%以下で、炭化物の球状化率が50%以上であるミクロ組織にすれば、100%剪断面の平滑な端面が得られ、また端面にクラックが発生することのない優れたファインブランキング性が得られる。なお、上記初析フェライト相以外の組織はパーライトおよび/またはベイナイトである。不可避的にマルテンサイトなどその他の組織が生成する場合があるが、面積率で5%以下であれば本発明の鋼板特性に影響するものではなく、許容される。
2) Microstructure When the present inventors investigated the influence of the microstructure on the fine blanking end face properties, a smooth end face with a 100% shear plane could not be obtained, or cracks occurred on the blanking end face. It was revealed that this was caused by the interface between the pro-eutectoid ferrite phase and pearlite and the broken cementite in the pearlite. Therefore, in order to obtain excellent fine blanking properties, it is effective to suppress the formation of proeutectoid ferrite phase and pearlite as much as possible. If the microstructure is such that the area ratio of the deposited ferrite phase is 10% or less and the spheroidization rate of the carbide is 50% or more, a smooth end face with a 100% shear plane can be obtained, and cracks can occur on the end face. Excellent fine blanking performance can be obtained. The structure other than the pro-eutectoid ferrite phase is pearlite and / or bainite. Inevitably, other structures such as martensite may be generated, but if the area ratio is 5% or less, the steel sheet characteristics of the present invention are not affected and are allowed.
 ここで、各組織の面積率は、走査電子顕微鏡で撮影した組織写真を画像解析ソフトを用いて解析して求めた。 Here, the area ratio of each tissue was obtained by analyzing a tissue photograph taken with a scanning electron microscope using image analysis software.
 また、炭化物の球状化率は、各炭化物の最大径aと最小径bの比a/bを計算し、a/bが3以下の炭化物の数の全炭化物数に対する割合(%)として求めた。 Further, the spheroidization rate of the carbide was obtained by calculating the ratio a / b of the maximum diameter a and the minimum diameter b of each carbide and calculating the ratio (%) of the number of carbides having a / b of 3 or less to the total number of carbides. .
 3)製造条件
 熱間圧延時の仕上温度:800~950℃
 仕上温度が800℃未満ではその後の冷却時に初析フェライト相が生成しやすくなり、初析フェライト相の面積率が10%を超える。一方、仕上温度が950℃を超えるとスケール厚が増大し、スケール剥離や酸洗後のスケール残りが生じて鋼板表面性状が劣化する。したがって、熱間圧延時の仕上温度は800~950℃とする。
3) Manufacturing conditions Finishing temperature during hot rolling: 800-950 ° C
If the finishing temperature is less than 800 ° C., the pro-eutectoid ferrite phase is likely to be formed during the subsequent cooling, and the area ratio of the pro-eutectoid ferrite phase exceeds 10%. On the other hand, when the finishing temperature exceeds 950 ° C., the scale thickness increases, and scale residue after scale peeling or pickling occurs, resulting in deterioration of the steel sheet surface properties. Accordingly, the finishing temperature during hot rolling is set to 800 to 950 ° C.
 熱間圧延後の冷却条件:650℃以上の冷却開始温度から50℃/s以上の平均冷却速度で450~600℃の冷却停止温度まで冷却し、3s以内に巻取る。上記のような優れたファインブランキング性が得られるミクロ組織にするには、熱間圧延後できる限りオーステナイト単相状態を維持し、巻取り後に変態させて初析フェライト相の生成を抑制するとともに、変態熱を利用して炭化物の球状化を促進すれば可能である。そのためには、オーステナイト単相状態である650℃以上の冷却開始温度から50℃/s以上の平均冷却速度で連続変態曲線のノーズに相当する温度域450~600℃の冷却停止温度まで冷却し、3s以内に巻取る必要がある。 Cooling condition after hot rolling: Cool from a cooling start temperature of 650 ° C. or higher to a cooling stop temperature of 450 to 600 ° C. at an average cooling rate of 50 ° C./s or more, and take up within 3 s. In order to obtain a microstructure with excellent fine blanking properties as described above, maintain the austenite single phase state as much as possible after hot rolling, and transform after winding to suppress the formation of proeutectoid ferrite phase. It is possible by using transformation heat to promote the spheroidization of the carbide. For this purpose, cooling is performed from a cooling start temperature of 650 ° C. or higher in an austenite single phase state to a cooling stop temperature of 450 to 600 ° C. corresponding to the nose of the continuous transformation curve at an average cooling rate of 50 ° C./s or more, It is necessary to wind up within 3 seconds.
 なお、巻取り後の鋼板を巻取られた状態で保熱装置に装入すると、鋼板は巻取り時の温度からより徐冷されるので、炭化物の球状化が促進され、より優れたファインブランキング性が得られる。 In addition, if the steel plate after winding is inserted into the heat retaining device in a wound state, the steel plate is further gradually cooled from the temperature at the time of winding, so that the spheroidization of the carbide is promoted and the finer finer. Ranking is obtained.
 また、熱間圧延後、該650℃以上の冷却開始温度までの冷却については、特に限定する必要はなく、製造ラインに合わせて適宜調整すればよい。異方性を小さくするためオーステナイト相の再結晶を充分に図る上では、空冷とすることが好ましく、また、安定して450~600℃で冷却を停止させるためには、過冷オーステナイト単相域の下限に近い温度である650℃まで冷却することが好ましい。 Further, the cooling to the cooling start temperature of 650 ° C. or higher after hot rolling is not particularly limited, and may be appropriately adjusted according to the production line. In order to sufficiently recrystallize the austenite phase in order to reduce anisotropy, it is preferable to use air cooling, and in order to stably stop cooling at 450 to 600 ° C., a supercooled austenite single phase region It is preferable to cool to 650 ° C., which is a temperature close to the lower limit.
 本発明の高炭素鋼を溶製するには、転炉、電気炉どちらも使用可能である。また、こうして溶製された高炭素鋼は、造塊−分塊圧延または連続鋳造によりスラブとされる。スラブは、通常、加熱された後、熱間圧延される。なお、連続鋳造で製造されたスラブの場合は、そのままあるいは温度低下を抑制する目的で保熱して、圧延する直送圧延を適用してもよい。また、スラブを加熱して熱間圧延する場合は、スケールによる表面状態の劣化を避けるためにスラブ加熱温度を1280℃以下とすることが好ましい。熱間圧延では、仕上温度を確保するため、熱間圧延中にシートバーヒータ等の加熱手段により被圧延材の加熱を行ってもよい。 Both converters and electric furnaces can be used to melt the high carbon steel of the present invention. Moreover, the high carbon steel melted in this way is made into a slab by ingot-bundling rolling or continuous casting. The slab is usually heated and then hot rolled. In addition, in the case of the slab manufactured by continuous casting, you may apply the direct feed rolling which heats as it is or keeps heat in order to suppress a temperature fall. Moreover, when heating and rolling a slab, it is preferable to make slab heating temperature 1280 degrees C or less in order to avoid the deterioration of the surface state by a scale. In hot rolling, in order to ensure the finishing temperature, the material to be rolled may be heated by a heating means such as a sheet bar heater during hot rolling.
 表1に示す鋼番A~Kの組成を有する鋼を溶製し、次いで表2に示す熱延条件に従って板厚5.0mmの熱延鋼板No.1~17を作製した。 A steel having a composition of steel numbers A to K shown in Table 1 was melted, and then a hot-rolled steel plate No. 5 having a thickness of 5.0 mm according to the hot rolling conditions shown in Table 2. 1 to 17 were produced.
 このようにして作製した熱延鋼板について、上記の方法により初析フェライト相の面積率と炭化物の球状化率を求め、さらに上記した方法により初析フェライト相以外の組織も観察した。 For the hot-rolled steel sheet thus prepared, the area ratio of the pro-eutectoid ferrite phase and the spheroidization ratio of the carbide were determined by the above method, and the structure other than the pro-eutectoid ferrite phase was also observed by the above-described method.
 また、ファインブランキング性については、得られた鋼板から80mm×80mmの試験片を採取し、110ton油圧プレス機を用いて60mm×40mmの鋼片を、工具間クリアランス:0.050mm(板厚の1%)、加工力:8.5ton、潤滑:有りの条件によってブランキングし、ブランキング端面が100%剪断面であり、かつ端面にクラックが無い場合を○、それ以外を×で評価した。 In addition, for fine blanking property, a test piece of 80 mm × 80 mm was taken from the obtained steel plate, and a steel piece of 60 mm × 40 mm was removed using a 110 ton hydraulic press machine, and the clearance between tools: 0.050 mm (plate thickness 1%), processing force: 8.5 ton, lubrication: blanking was performed, and the blanking end face was 100% shear face and the end face was not cracked.
 結果を表2に示す。 The results are shown in Table 2.
 本発明例の熱延鋼板No.1~4、11、12では、いずれもファインブランキング性は○で、優れていることがわかる。なお、本発明例の鋼組織は、表2の初析フェライト相以外はパーライトおよび/またはベイナイトであった。 Hot rolled steel sheet No. It can be seen that the fine blanking properties are all excellent in 1 to 4, 11, and 12. In addition, the steel structures of the examples of the present invention were pearlite and / or bainite except for the pro-eutectoid ferrite phase shown in Table 2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002

Claims (7)

  1.  質量%で、C:0.10~0.40%、Si:1.0%以下、Mn:2.0%以下、P:0.03%以下、S:0.03%以下、N:0.01%以下、Al:0.10%以下を含み、残部がFeおよび不可避的不純物からなる組成を有し、組織全体に占める初析フェライト相の面積率が10%以下で、炭化物の球状化率が50%以上であるミクロ組織を有することを特徴とするファインブランキング性に優れた高炭素熱延鋼板。 C: 0.10 to 0.40%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.03% or less, N: 0% by mass .01% or less, Al: 0.10% or less, with the balance being composed of Fe and inevitable impurities, the area ratio of pro-eutectoid ferrite phase in the entire structure is 10% or less, and carbide spheroidization A high carbon hot-rolled steel sheet excellent in fine blanking property, characterized by having a microstructure with a rate of 50% or more.
  2.  さらに、質量%で、B:0.0010~0.0050%を含有し、かつ0.50≦(14[B])/(10.8[N])の関係を満足することを特徴とする請求項1に記載のファインブランキング性に優れた高炭素熱延鋼板;ただし、[B]、[N]はそれぞれB、Nの含有量(質量%)を表す。 Further, it is characterized by containing B: 0.0010 to 0.0050% by mass% and satisfying the relationship of 0.50 ≦ (14 [B]) / (10.8 [N]). The high carbon hot rolled steel sheet excellent in fine blanking property according to claim 1; provided that [B] and [N] represent the contents (% by mass) of B and N, respectively.
  3.  さらに、質量%で、Ti、Nb、Vのうちの少なくとも1種:合計で0.1%以下を含有することを特徴とする請求項1または2に記載のファインブランキング性に優れた高炭素熱延鋼板。 The high carbon excellent in fine blanking property according to claim 1 or 2, further comprising at least one of Ti, Nb, and V: 0.1% or less in total by mass%. Hot rolled steel sheet.
  4.  さらに、質量%で、Ni、Cr、Moのうちの少なくとも1種:合計で1.5%以下を含有することを特徴とする請求項1から3のいずれかに記載のファインブランキング性に優れた高炭素熱延鋼板。 Furthermore, it is excellent in the fine blanking property in any one of Claim 1 to 3 which contains at least 1 sort (s) of Ni, Cr, and Mo: 1.5% or less in total by mass% High carbon hot rolled steel sheet.
  5.  さらに、質量%で、Sb、Snのうちの少なくとも1種:合計で0.003~0.10%を含有することを特徴とする請求項1から4のいずれかに記載のファインブランキング性に優れた高炭素熱延鋼板。 The fine blanking property according to any one of claims 1 to 4, further comprising, in mass%, at least one of Sb and Sn: 0.003 to 0.10% in total. Excellent high carbon hot rolled steel sheet.
  6.  請求項1から5のいずれかに記載の組成を有する鋼を、800~950℃の仕上温度で熱間圧延した後、650℃以上の冷却開始温度から50℃/s以上の平均冷却速度で450~600℃の冷却停止温度まで冷却し、3s以内に巻取ることを特徴とするファインブランキング性に優れた高炭素熱延鋼板の製造方法。 The steel having the composition according to any one of claims 1 to 5 is hot-rolled at a finishing temperature of 800 to 950 ° C, and then 450 ° C at an average cooling rate of 50 ° C / s or more from a cooling start temperature of 650 ° C or more. A method for producing a high carbon hot-rolled steel sheet having excellent fine blanking characteristics, wherein the steel sheet is cooled to a cooling stop temperature of ~ 600 ° C and wound up within 3 s.
  7.  巻取り後の鋼板を、巻取られた状態で保熱装置に装入することを特徴とする請求項6に記載のファインブランキング性に優れた高炭素熱延鋼板の製造方法。 The method for producing a high carbon hot-rolled steel sheet having excellent fine blanking properties according to claim 6, wherein the steel sheet after winding is inserted into a heat retaining device in a wound state.
PCT/JP2011/066789 2010-07-21 2011-07-19 High-carbon hot-rolled steel sheet having excellent fine blanking properties and process for production thereof WO2012011598A1 (en)

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JP2005290547A (en) * 2004-03-10 2005-10-20 Jfe Steel Kk High carbon hot-rolled steel sheet having excellent ductility and stretch-flange formability, and production method therefor
JP2006097109A (en) * 2004-09-30 2006-04-13 Jfe Steel Kk High-carbon hot-rolled steel sheet and manufacturing method therefor
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