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JP2003193186A - High strength steel sheet and high strength electroplated steel sheet having excellent ductility, stretch-flanging property and impact absorbing property and production method therefor - Google Patents

High strength steel sheet and high strength electroplated steel sheet having excellent ductility, stretch-flanging property and impact absorbing property and production method therefor

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Publication number
JP2003193186A
JP2003193186A JP2001398712A JP2001398712A JP2003193186A JP 2003193186 A JP2003193186 A JP 2003193186A JP 2001398712 A JP2001398712 A JP 2001398712A JP 2001398712 A JP2001398712 A JP 2001398712A JP 2003193186 A JP2003193186 A JP 2003193186A
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JP
Japan
Prior art keywords
mass
steel sheet
less
strength
stretch
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP2001398712A
Other languages
Japanese (ja)
Other versions
JP3932892B2 (en
Inventor
Akio Tosaka
章男 登坂
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
JFE Steel Corp
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Filing date
Publication date
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Priority to JP2001398712A priority Critical patent/JP3932892B2/en
Publication of JP2003193186A publication Critical patent/JP2003193186A/en
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a high strength steel sheet and a high strength electroplated steel sheet which have a tensile strength of 400 to 540 MPa, excellent ductility and stretch-flanging properties, and excellent impact absorbing properties, and to provide a production method therefor. <P>SOLUTION: The steel sheets have a componential composition containing, by mass, 0.02 to 0.08% C, ≤0.50% Si, 0.5 to 1.5% Mn, ≤0.04% P, ≤0.005% S, ≤0.1% Al, and ≤0.025% N, and further containing Cr and Mo so as to satisfy Cr+1.2Mo≥0.2%, and have a structure in which the fraction of a ferritic structure as the main phase is ≥85% in an area ratio, and the ratio of a martensitic structure is 2 to 10% in an area ratio, and the total fraction of the second phase containing the above martensite is ≤15% in an area ratio. <P>COPYRIGHT: (C)2003,JPO

Description

【発明の詳細な説明】Detailed Description of the Invention

【0001】[0001]

【発明の属する技術分野】本発明は、自動車用鋼板等と
して用いられる、高い延性と伸びフランジ性と衝撃吸収
特性を有する高強度鋼板(高張力鋼板とも云う)及び高強
度電気めっき鋼板並びにそれらの製造方法に関するもの
である。
TECHNICAL FIELD The present invention relates to a high-strength steel sheet (also referred to as a high-strength steel sheet) and a high-strength electroplated steel sheet having high ductility, stretch flangeability, and shock absorption characteristics, which are used as steel sheets for automobiles and the like. The present invention relates to a manufacturing method.

【0002】[0002]

【従来の技術】自動車の車体には、各種の薄鋼板が使用
されているが、とくに成形性に優れた冷延鋼板が多く使
われている。また、最近は、自動車車体の軽量化を図る
ために高張力鋼板の使用量が増大している。しかし、強
度が比較的低い冷延鋼板に代わって、従来の高張力鋼板
を採用する場合、以下のような問題点があった。 1)延性および伸びフランジ性が劣る。 2)機械的性質の面内異方性が大きい。 3)特に、引張強度TSが400MPa〜540MPaの強度範囲の
鋼板は、材質のばらつきが大きく、安定して製造するこ
とが難しい。 4)衝撃吸収特性の向上代が少なく、高張力鋼板を使用
するメリットが少ない。
2. Description of the Related Art Various thin steel sheets are used for automobile bodies, but cold-rolled steel sheets having excellent formability are often used. Further, recently, the amount of high-tensile steel plates used has been increasing in order to reduce the weight of automobile bodies. However, when the conventional high-strength steel sheet is adopted instead of the cold-rolled steel sheet having relatively low strength, there are the following problems. 1) Ductility and stretch flangeability are poor. 2) In-plane anisotropy of mechanical properties is large. 3) In particular, a steel sheet having a tensile strength TS in the strength range of 400 MPa to 540 MPa has a large variation in material and is difficult to manufacture stably. 4) There is little margin for improving shock absorption characteristics, and there is little merit in using high-tensile steel plate.

【0003】上記した問題点を解決するために、従来、
C量の低減、S量の低減などの対策が講じられている。
しかし、これらの対策だけでは、上記のすべての問題点
を解決することはできなかった。その他の対策として
は、Nb,Ti等の元素を微量添加して、伸びフランジ性を
改善する技術が提案されているが、この技術は、これら
の元素(Nb,Ti等)が鋼の熱間変形抵抗を増加させるた
め、熱間圧延が困難となるという問題点があった。しか
も、これらの元素の添加は、析出強化作用のために、引
張り強度(TS)が540MPa以下の比較的低強度の高成形性
鋼板を製造することを困難にし、さらには、冷延後の焼
鈍において、再結晶の遅延を招いて、焼鈍条件に対する
材質変動が大きくなるという問題点があった。さらに他
の従来技術としては、母相組織の微細化、組織の単相化
(主としてベイナイト化)により伸びフランジ性を改善す
る方法も提案されている。しかし、この提案は、自動車
の足廻り部品に使用されるような比較的厚物(板厚>3mm
程度)で高強度(概ね540MPa以上)の鋼板を対象としたも
ので、延性も十分ではないという問題点があった。
In order to solve the above-mentioned problems, conventionally,
Measures such as reduction of C amount and reduction of S amount are taken.
However, these measures alone could not solve all the above problems. As another measure, a technology has been proposed to improve the stretch flangeability by adding a small amount of elements such as Nb and Ti, but this technology is because these elements (Nb, Ti, etc.) Since the deformation resistance is increased, there is a problem that hot rolling becomes difficult. Moreover, the addition of these elements makes it difficult to produce a relatively low strength and high formability steel sheet having a tensile strength (TS) of 540 MPa or less due to the precipitation strengthening action, and further, annealing after cold rolling. However, there is a problem in that the recrystallization is delayed and the material changes greatly depending on the annealing conditions. Still other conventional technologies include miniaturization of matrix structure and single phase structure.
A method for improving stretch-flangeability by (mainly bainizing) is also proposed. However, this proposal is for relatively thick materials (thickness> 3 mm) such as those used for undercarriage parts of automobiles.
It is intended for steel sheets of high strength (about 540 MPa or more) and its ductility is not sufficient.

【0004】[0004]

【発明が解決しようとする課題】ところで、自動車用部
材の中には、例えば、フロントやリアサイドメンバー、
クロスメンバー等の各種メンバー類およびこれらに接続
される各種補強部材等のように、その用途によっては、
深絞り成形はしないものの、比較的高強度でかつ高い延
性と伸びフランジ性を要求されるものがある。これらの
部材には、板厚が0.8mm以上2.3mm以下で、引張強度が40
0MPa以上540MPa以下の高強度冷延鋼板が主に用いられ
る。また、これらの部材は、従来、静的な強度のみが要
求されていたが、昨今の自動車の衝突に対する安全性確
保の要請から、優れた衝撃吸収特性が要求されるように
なった部品群でもある。しかし、上述したように、従来
の技術では、これら全ての要求特性を満足する鋼板を、
工業的に安価に、かつ安定して製造する技術はなかっ
た。
By the way, among automobile members, for example, front and rear side members,
Depending on the application, such as various members such as cross members and various reinforcing members connected to them,
Although not subjected to deep drawing, there are some which require relatively high strength and high ductility and stretch flangeability. These members have a plate thickness of 0.8 mm or more and 2.3 mm or less and a tensile strength of 40 mm.
High-strength cold-rolled steel sheets of 0 MPa or more and 540 MPa or less are mainly used. Further, conventionally, only static strength was required for these members, but even in the group of parts which have been required to have excellent shock absorption characteristics due to the recent demand for ensuring safety against automobile collisions. is there. However, as described above, in the conventional technology, a steel plate satisfying all these required characteristics is
There was no industrially inexpensive and stable manufacturing technology.

【0005】本発明の目的は、引張強度が400MPa以上54
0MPa以下の中程度の強度を有しながら、優れた延性と伸
びフランジ性を有しかつ衝撃吸収特性にも優れる高強度
鋼板ならびに該鋼板にめっき処理を施した高強度電気め
っき鋼板とそれらの製造方法を提案することにある。
The object of the present invention is to have a tensile strength of 400 MPa or more.
A high-strength steel sheet having excellent ductility and stretch-flangeability, and excellent impact absorption characteristics while having a medium strength of 0 MPa or less, a high-strength electroplated steel sheet obtained by plating the steel sheet, and their production. To propose a method.

【0006】[0006]

【課題を解決するための手段】さて、発明者は、上記目
的を実現するため、種々の成分組成の鋼板を製造し、材
質評価実験を行った。その結果、高い延性を有し、優れ
た伸びフランジ性と衝撃吸収特性とを有する鋼板を得る
ためには、成分組成を適正範囲に制御することはもちろ
ん、とくに鋼板の微細組織の制御が有効であることを知
見した。すなわち、上述した要求特性を満足させるため
には、鋼板組織の主相を軟質なフェライト相とし、残余
の組織を、マルテンサイト相を2%以上10%以下かつ前
記マルテンサイト相を含む第2相を15%以下とすること
が必要であることを知見した。
In order to achieve the above object, the inventor manufactured steel sheets having various component compositions and conducted a material evaluation experiment. As a result, in order to obtain a steel sheet having high ductility and excellent stretch-flangeability and impact absorption characteristics, it is particularly effective to control the composition of components within an appropriate range, and particularly to control the microstructure of the steel sheet. I found that there is. That is, in order to satisfy the above-mentioned required characteristics, the main phase of the steel sheet structure is a soft ferrite phase, and the remaining structure is a second phase containing a martensite phase of 2% or more and 10% or less and the martensite phase. It was found that it is necessary to reduce the value to 15% or less.

【0007】本発明は、上記知見に基づき開発されたも
のであって、C:0.02〜0.08mass%、Si:0.50mass%以
下、Mn:0.5〜1.5mass%、P:0.04mass%以下、S:0.
005mass%以下、Al:0.1mass%以下、N:0.025mass%
以下を含有し、さらに、Cr,Mo:単独または複合添加
で、下記式、 Cr+1.2Mo≧0.2mass% を満足するよう含有し、残部がFeおよび不可避的不純物
からなり、かつ、主相であるフェライト組織の分率が面
積率で85%以上であり、面積率で2%以上10%以下のマ
ルテンサイト組織を含有し、前記マルテンサイトを含む
第2相の分率の合計が面積率で15%以下である、延性、
伸びフランジ性および衝撃吸収特性に優れた高強度鋼板
である。
The present invention has been developed on the basis of the above findings, wherein C: 0.02 to 0.08 mass%, Si: 0.50 mass% or less, Mn: 0.5 to 1.5 mass%, P: 0.04 mass% or less, S: : 0.
005mass% or less, Al: 0.1mass% or less, N: 0.025mass%
Contains the following, and further contains Cr and Mo: singly or in combination so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2 mass%, and the balance is Fe and inevitable impurities, and is the main phase The area ratio of the ferrite structure is 85% or more, the area ratio is 2% or more and 10% or less, and the total ratio of the second phase containing the martensite is 15% or less. %, Ductility,
It is a high-strength steel sheet with excellent stretch flangeability and impact absorption characteristics.

【0008】なお、本発明においては、機械的性質を向
上させるために、上記成分のほかに、B:0.0005〜0.00
40mass%、Ca:0.0010〜0.01mass%、REM:0.0010〜
0.01mass%、Ti:0.005〜0.10mass%、Nb:0.002〜0.10
mass%、V:0.005〜0.10mass%、Cu:0.01〜1.0mass
%、Ni:0.01〜1.0mass%のうちのいずれか1種または
2種以上を含有することが好ましい。
In the present invention, in order to improve the mechanical properties, in addition to the above components, B: 0.0005 to 0.00
40mass%, Ca: 0.0010-0.01mass%, REM: 0.0010-
0.01mass%, Ti: 0.005-0.10mass%, Nb: 0.002-0.10
mass%, V: 0.005-0.10mass%, Cu: 0.01-1.0mass
%, Ni: 0.01 to 1.0 mass%, and preferably one or more of them.

【0009】本発明はまた、上記鋼板の表面に、電気め
っき皮膜を被成してなる高強度電気めっき鋼板を提案す
る。
The present invention also proposes a high strength electroplated steel sheet obtained by forming an electroplated film on the surface of the above steel sheet.

【0010】本発明はまた、C:0.02〜0.08mass%、S
i:0.50mass%以下、Mn:0.5〜1.5mass%、P:0.04mas
s%以下、S:0.005mass%以下、Al:0.1mass%以下、
N:0.025mass%以下を含有し、さらに、Cr,Mo:単独
または複合添加で、下記式、 Cr+1.2Mo≧0.2mass% を満足するよう含有し、あるいはさらに、B:0.0005〜
0.0040mass%、Ca:0.0010〜0.01mass%、REM:0.00
10〜0.01mass%、Ti:0.005〜0.10mass%、Nb:0.002〜
0.10mass%、V:0.005〜0.10mass%、Cu:0.01〜1.0mas
s%、Ni:0.01〜1.0mass%のうちのいずれか1種または
2種以上を含有し、残部がFeおよび不可避的不純物から
なる鋼スラブを、熱間圧延し、その後、酸洗と冷間圧延
を行い、次いで750℃以上900℃以下に加熱後、20℃/s
以上の速度で冷却する連続焼鈍することを特徴とする、
延性、伸びフランジ性および衝撃吸収特性に優れた高強
度鋼板の製造方法を提案する。
The present invention also provides C: 0.02 to 0.08 mass%, S
i: 0.50mass% or less, Mn: 0.5 to 1.5mass%, P: 0.04mass
s% or less, S: 0.005 mass% or less, Al: 0.1 mass% or less,
N: 0.025 mass% or less, and Cr, Mo: added alone or in combination so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2 mass%, or further, B: 0.0005 to
0.0040 mass%, Ca: 0.0010 to 0.01 mass%, REM: 0.00
10-0.01mass%, Ti: 0.005-0.10mass%, Nb: 0.002-
0.10mass%, V: 0.005-0.10mass%, Cu: 0.01-1.0mass
s%, Ni: 0.01 to 1.0 mass% of any one type or two or more types of steel slabs, the balance of which is Fe and unavoidable impurities, is hot-rolled, then pickled and cold-rolled. Rolled, then heated above 750 ℃ to below 900 ℃, 20 ℃ / s
Characterized by continuous annealing with cooling at the above rate,
We propose a method for manufacturing high-strength steel sheets with excellent ductility, stretch-flangeability and impact absorption characteristics.

【0011】さらに、本発明は、C:0.02〜0.08mass
%、Si:0.50mass%以下、Mn:0.5〜1.5mass%、P:0.
04mass%以下、S:0.005mass%以下、Al:0.1mass%以
下、N:0.025mass%以下を含有し、さらに、Cr,Mo:
単独または複合添加で、下記式、 Cr+1.2Mo≧0.2mass% を満足するよう含有し、あるいはさらに、B:0.0005〜
0.0040mass%、Ca:0.0010〜0.01mass%、REM:0.00
10〜0.01mass%、Ti:0.005〜0.10mass%、Nb:0.002〜
0.10mass%、V:0.005〜0.10mass%、Cu:0.01〜1.0mas
s%、Ni:0.01〜1.0mass%のうちのいずれか1種または
2種以上を含有し、残部がFeおよび不可避的不純物から
なる鋼スラブを、熱間圧延し、その後、酸洗と冷間圧延
を行い、次いで750℃以上900℃以下に加熱後、20℃/s
以上の速度で冷却する連続焼鈍を施し、その後、電気め
っき処理を施すことを特徴とする、延性、伸びフランジ
性および衝撃吸収特性に優れた高強度電気めっき鋼板の
製造方法を提案する。
Further, according to the present invention, C: 0.02 to 0.08 mass
%, Si: 0.50 mass% or less, Mn: 0.5 to 1.5 mass%, P: 0.
It contains 04 mass% or less, S: 0.005 mass% or less, Al: 0.1 mass% or less, N: 0.025 mass% or less, and further contains Cr, Mo:
Single or in combination, so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2mass%, or further, B: 0.0005 to
0.0040 mass%, Ca: 0.0010 to 0.01 mass%, REM: 0.00
10-0.01mass%, Ti: 0.005-0.10mass%, Nb: 0.002-
0.10mass%, V: 0.005-0.10mass%, Cu: 0.01-1.0mass
s%, Ni: 0.01 to 1.0 mass% of any one type or two or more types of steel slabs, the balance of which is Fe and unavoidable impurities, is hot-rolled, then pickled and cold-rolled. Rolled, then heated above 750 ℃ to below 900 ℃, 20 ℃ / s
We propose a method for producing a high-strength electroplated steel sheet having excellent ductility, stretch flangeability, and shock absorption characteristics, which is characterized by performing continuous annealing that cools at the above rate and then performing electroplating.

【0012】[0012]

【発明の実施の形態】以下、本発明における成分組成を
限定した理由について説明する。 C:0.02〜0.08mass% Cは、強度を確保するために重要な元素である。しか
し、C量が0.08mass%を超えると、鋼中の炭化物の分率
が増加することに起因して、鋼板の伸びフランジ性が顕
著に悪化する。さらに重要な問題として、C量が、0.08
mass%を超えると、スポット溶接性、アーク溶接性など
が顕著に低下する。従って、成形性、溶接性の観点か
ら、C量は0.08mass%以下とする。成形性の向上のため
には、0.06mass%以下、より好ましくは0.05mass%以下
とする。一方、C量が0.02mass%未満となると、微細組
織が顕著に粗大化し、伸びフランジ性が低下する。さら
に、本発明の重要な要件の一つであるマルテンサイト相
を安定して得ることが困難になるため、下限値を0.02ma
ss%とする。好ましくは、0.03〜0.05mass%がよい。
BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the component composition in the present invention will be described below. C: 0.02 to 0.08 mass% C is an important element for ensuring strength. However, when the amount of C exceeds 0.08 mass%, the stretch-flange formability of the steel sheet is significantly deteriorated due to an increase in the fraction of carbides in the steel. More importantly, the amount of C is 0.08
If it exceeds mass%, the spot weldability, arc weldability, etc. are significantly reduced. Therefore, from the viewpoint of formability and weldability, the C content is 0.08 mass% or less. In order to improve the moldability, it is 0.06 mass% or less, more preferably 0.05 mass% or less. On the other hand, when the C content is less than 0.02 mass%, the fine structure is remarkably coarsened and the stretch flangeability is deteriorated. Furthermore, it becomes difficult to stably obtain the martensite phase, which is one of the important requirements of the present invention.
ss% Preferably, 0.03 to 0.05 mass% is good.

【0013】Si:0.50mass%以下 Siは、鋼板を固溶強化しつつ、伸びフランジ性を改善す
るという望ましい効果があるため、必要に応じて適宜添
加する。しかし、多量の添加は、表面性状の低下を生ず
る危険性がある。このため、このような問題のない、0.
50mass%以下に制限する。好ましくは、0.05〜0.30mass
%がよい。
Si: 0.50 mass% or less Si has the desirable effect of improving stretch flangeability while solid-solution strengthening the steel sheet, so it is appropriately added if necessary. However, addition of a large amount has a risk of deteriorating the surface properties. Therefore, without such problems, 0.
Limit to 50 mass% or less. Preferably 0.05 to 0.30 mass
% Is good.

【0014】Mn:0.5〜1.5mass% Mnは、Sによる熱間脆性を防止するのに有効な元素であ
り、含有するS量に応じて添加する必要がある。またMn
は、本発明においては、安定してマルテンサイト相を得
るために必須の添加元素である。この効果は、0.5mass
%の添加により顕著となる。また、Mnの添加量を高める
ことで、機械的性質の熱延条件感受性が顕著に改善され
るという利点がある。しかし、Mnを過度に添加すると、
延性が低下傾向となることと、マルテンサイト分率の焼
鈍温度依存性が顕著となり、製造条件による材質変動が
大きくなり、加えて伸びフランジ性も悪化する傾向にあ
る。このため、その上限を1.5mass%とする。好ましく
は0.7〜1.4mass%である。
Mn: 0.5 to 1.5 mass% Mn is an element effective in preventing hot embrittlement due to S, and it is necessary to add Mn according to the amount of S contained. Also Mn
In the present invention, is an essential additional element for stably obtaining the martensite phase. This effect is 0.5mass
% Becomes remarkable. Further, by increasing the amount of Mn added, there is an advantage that the sensitivity of mechanical properties to hot rolling conditions is significantly improved. However, if Mn is added excessively,
The ductility tends to decrease, the annealing temperature dependency of the martensite fraction becomes remarkable, the material variation due to the manufacturing conditions increases, and the stretch flangeability tends to deteriorate. Therefore, the upper limit is set to 1.5 mass%. It is preferably 0.7 to 1.4 mass%.

【0015】P:0.04mass%以下 Pは、鋼の固溶強化元素として有効であり、要求される
強度に応じて適宜添加できる。しかし、過度に添加する
と、鋼を脆化させ、溶接部の脆化をもたらす。さらに、
Pは偏析しやすい元素であり、鋼板の伸びフランジ性を
低下させる。以上のことから、その上限を0.04mass%と
した。これらの特性低下が特に重要視される場合には、
0.02mass%以下とすることが好ましい。
P: 0.04 mass% or less P is effective as a solid solution strengthening element for steel, and can be appropriately added depending on the required strength. However, if added excessively, the steel is embrittled and the welded portion is embrittled. further,
P is an element that easily segregates and reduces the stretch flangeability of the steel sheet. From the above, the upper limit was set to 0.04 mass%. When these deteriorations in characteristics are particularly important,
It is preferably 0.02 mass% or less.

【0016】S:0.005mass%以下 Sは、介在物として鋼中に存在し、鋼板の延性と伸びフ
ランジ性を低下させ、さらに耐食性の劣化をもたらす。
本発明のような、マルテンサイトを含む微細組織鋼にお
いては、とくにその傾向が顕著であることから、Sは極
力低減させることが好ましい。これらの理由から、その
上限を0.005mass%とした。特に良好な伸びフランジ性
が要求される用途においては、0.003mass%以下とする
ことが望ましい。
S: 0.005 mass% or less S is present in the steel as inclusions, reduces ductility and stretch flangeability of the steel sheet, and further deteriorates corrosion resistance.
In a microstructured steel containing martensite as in the present invention, this tendency is particularly remarkable, so it is preferable to reduce S as much as possible. For these reasons, the upper limit is set to 0.005 mass%. In applications where particularly good stretch flangeability is required, 0.003 mass% or less is desirable.

【0017】Al:0.1mass%以下 Alは、脱酸元素として添加され、鋼の清浄度を向上させ
るのに有効であり、鋼の組織微細化のためにも添加が望
ましい元素である。しかし、0.1mass%を超えて多量に
添加しても、組織の微細化効果は飽和してしまい、添加
する合金の分だけコストの増加となるので、上限は0.1m
ass%とした。材質の安定性という観点では、0.02〜0.0
6mass%がより望ましい。また、Al添加量の過度の低減
は、結晶粒の粗大化につながる懸念があるが、本発明で
は、Mn等他の合金元素を、適正範囲とし、熱延条件を最
適な範囲に制限することで防止することができる。
Al: 0.1 mass% or less Al is added as a deoxidizing element, is effective for improving the cleanliness of steel, and is also an element which is desirable for refining the structure of steel. However, even if added in excess of 0.1 mass%, the refinement effect of the structure will be saturated and the cost will increase by the amount of alloy added, so the upper limit is 0.1 m.
Ass%. From the viewpoint of material stability, 0.02 to 0.0
6 mass% is more desirable. Further, excessive reduction of Al addition amount may lead to coarsening of crystal grains, but in the present invention, other alloying elements such as Mn are set to appropriate ranges, and hot rolling conditions are limited to optimum ranges. Can be prevented.

【0018】N:0.025mass%以下 Nは、適量の添加により、フェライトを主体とした組織
を均一かつ微細化する効果を有し、これにより適正な強
度と優れた伸びフランジ性を得ることができる。また、
Nは、鋼の変態点を降下させる効果もあり、薄物で変態
点を大きく割り込んだ圧延を回避したい場合、Nの添加
は有効である。これらの効果を得るためには0.0015mass
%以上とすることが好ましく、より好ましくは0.0020ma
ss%以上とする。しかし、0.025mass%を超えて添加し
た場合には、鋼板の内部欠陥の発生率が高くなるととも
に、連続鋳造時のスラブ割れなどの原因となるため、そ
の上限を0.025mass%とした。なお、Nを添加しても、
本発明の範囲であれば溶接性等に悪影響はない。より好
ましくは、0.003〜0.015mass%とするのがよい。
N: 0.025 mass% or less N has the effect of making the structure mainly composed of ferrite uniform and fine by adding an appropriate amount thereof, whereby proper strength and excellent stretch flangeability can be obtained. . Also,
N also has the effect of lowering the transformation point of steel, and addition of N is effective when it is desired to avoid rolling with the transformation point greatly interrupted with a thin product. 0.0015mass to get these effects
% Or more, more preferably 0.0020 ma
ss% or more. However, if added in excess of 0.025 mass%, the occurrence rate of internal defects in the steel sheet increases and causes slab cracking during continuous casting, so the upper limit was made 0.025 mass%. Even if N is added,
Within the range of the present invention, weldability and the like are not adversely affected. More preferably, it is 0.003 to 0.015 mass%.

【0019】Cr,Mo:単独、または複合添加で、Cr+1.
2Mo≧0.2mass% Cr,Moは、本発明における重要な添加元素の一つであ
り、適正な量のマルテンサイトが焼鈍後に残留する焼鈍
条件を拡大するという望ましい作用がある。すなわち、
Cr,Moの添加により、より広範囲の条件で安定した機械
的性質の確保が可能となり、機械的特性のばらつきも小
さくできる。これらの元素を単独または(Cr+1.2Mo)
で、0.20mass%以上添加することで、上記のような望ま
しい効果が得られる。上限は強度の上限から決定される
が、概ね(Cr+1.2Mo)で、1mass%以下であればよい。好
ましくは、0.25〜0.8mass%がよい。
Cr, Mo: Cr + 1 when added alone or in combination.
2Mo ≧ 0.2 mass% Cr, Mo is one of the important additional elements in the present invention, and has a desirable effect of expanding an annealing condition in which an appropriate amount of martensite remains after annealing. That is,
Addition of Cr and Mo makes it possible to secure stable mechanical properties over a wider range of conditions and reduce variations in mechanical properties. These elements alone or (Cr + 1.2Mo)
Then, by adding 0.20 mass% or more, the above desired effects can be obtained. The upper limit is determined from the upper limit of strength, but it is generally (Cr + 1.2Mo) and may be 1 mass% or less. Preferably, it is 0.25 to 0.8 mass%.

【0020】本発明においては、必須とする上記元素の
ほか、各種の機械的特性を向上させるために、下記の成
分を選択的に添加することができる。 B:0.0005〜0.0040mass% Bは、マルテンサイトの生成を安定化する効果があり、
この効果は、0.0005mass%以上の添加で発揮される。一
方、0.0040mass%を超えて添加した場合には、その効果
が飽和することに加えて、スラブの表面割れ等の発生を
招き、望ましくない。
In the present invention, in addition to the above-mentioned essential elements, the following components can be selectively added in order to improve various mechanical properties. B: 0.0005 to 0.0040 mass% B has the effect of stabilizing the production of martensite,
This effect is exhibited by adding 0.0005 mass% or more. On the other hand, when it is added in an amount of more than 0.0040 mass%, the effect is saturated and in addition, surface cracking of the slab is caused, which is not desirable.

【0021】Ca:0.0010〜0.01mass% Caは、Sを固定し、伸びフランジ性を改善するのに有効
な添加元素である。また、Caを添加することにより、冷
延鋼板におけるマルテンサイト等の第2相の分布がより
等方的になるという効果も確認された。この望ましい効
果は、0.0010mass%以上の添加で発揮されるが、0.01ma
ss%を超えて添加しても、その効果が飽和することに加
え、耐食性の低下などの問題を生ずる。
Ca: 0.0010 to 0.01 mass% Ca is an additional element effective for fixing S and improving stretch flangeability. It was also confirmed that the addition of Ca has an effect that the distribution of the second phase such as martensite in the cold rolled steel sheet becomes more isotropic. This desirable effect is exhibited by adding 0.0010 mass% or more, but 0.01 ma
Even if it is added in excess of ss%, the effect is saturated, and problems such as deterioration of corrosion resistance occur.

【0022】REM:0.0010〜0.01mass% REMも、Caと同様にSを安定して固定し、機械的特性
を改善する効果がある。同様に0.0010から0.01mass%が
最適な添加量の範囲である。この効果を得るためには、
0.0010mass%以上の含有が好ましいが、0.01mass%を超
えて添加しても、その効果が飽和し、製造コストの増加
につながるため、REMは、0.0010〜0.01mass%の含有
量とすることが好ましい。
REM: 0.0010 to 0.01 mass% REM, like Ca, has the effect of stably fixing S and improving mechanical properties. Similarly, 0.0010 to 0.01 mass% is the optimum addition amount range. To get this effect,
The content is preferably 0.0010 mass% or more, but even if added in excess of 0.01 mass%, the effect is saturated and leads to an increase in manufacturing cost. Therefore, the REM content should be 0.0010 to 0.01 mass%. preferable.

【0023】Ti:0.005〜0.10mass% Tiは、組織の均一化、微細化効果により、延性、伸びフ
ランジ性の改善に寄与する。また、Tiにも、Sを安定し
て固定する望ましい効果がある。これらの効果を得るた
めには、0.005mass%以上含有することが好ましいが、
0.10mass%を超えて添加しても、その効果が飽和し、製
造コストの増加につながるため、Tiは、0.005〜0.10mas
s%の含有量とすることが好ましい。
Ti: 0.005 to 0.10 mass% Ti contributes to the improvement of ductility and stretch flangeability by the effect of making the structure uniform and fine. Ti also has a desirable effect of stably fixing S. To obtain these effects, it is preferable to contain 0.005 mass% or more,
Even if added in excess of 0.10mass%, its effect saturates, leading to an increase in manufacturing costs, so Ti is 0.005 to 0.10mass.
The content is preferably s%.

【0024】Nb:0.002〜0.10mass% Nbは、マルテンサイトの分布を、特に微細かつ均一にす
る効果があり、溶接性を損なうことなく鋼板を高強度化
するのに有効である。これらの効果を得るためには、0.
002mass%以上含有することが好ましいが、0.10mass%
を超えて添加しても、その効果が飽和し、製造コストの
増加につながるため、Nbは0.002〜0.10mass%の含有量
とすることが好ましい。
Nb: 0.002 to 0.10 mass% Nb has the effect of making the distribution of martensite particularly fine and uniform, and is effective in increasing the strength of the steel sheet without impairing the weldability. To get these effects, 0.
It is preferable to contain 002mass% or more, but 0.10mass%
If added in excess, the effect will saturate, leading to an increase in manufacturing cost. Therefore, the Nb content is preferably 0.002 to 0.10 mass%.

【0025】V:0.005〜0.10mass% Vは、Cr,Moの効果を補う望ましい効果がある。Vを添加
することで、適正量のマルテンサイトを安定して確保す
ることができるため、最終的に得られる機械的特性も優
れて安定したものとなる。これらの効果を得るため、0.
005mass%以上の含有することが好ましいが、0.10mass
%を超えて添加しても、その効果が飽和し、製造コスト
の増加につながるため、Vは0.005〜0.10mass%の含有量
とすることが好ましい。
V: 0.005 to 0.10 mass% V has a desirable effect of compensating for the effects of Cr and Mo. By adding V, an appropriate amount of martensite can be stably ensured, and thus the mechanical properties finally obtained will be excellent and stable. To get these effects, 0.
It is preferable to contain 005 mass% or more, but 0.10 mass
Even if added in excess of%, the effect is saturated, leading to an increase in manufacturing cost. Therefore, it is preferable that the content of V be 0.005 to 0.10 mass%.

【0026】Cu:0.01〜1.0mass% Cuは、鋼板の強度を増加させるために添加することがで
きる。また、大きな強度増加が得られる割に、延性、伸
びフランジ性の低下が小さいというメリットがある。こ
のような望ましい効果は、0.01mass%以上の添加で達成
されるが、1.0mass%を超えて添加しても、その効果が
飽和する傾向があるため、その含有量を0.01〜1.0mass
%とした。
Cu: 0.01 to 1.0 mass% Cu can be added to increase the strength of the steel sheet. In addition, there is a merit that ductility and stretch flangeability are less deteriorated while a large increase in strength is obtained. Such a desired effect is achieved by adding 0.01 mass% or more, but even if added over 1.0 mass%, the effect tends to saturate, so the content is 0.01 to 1.0 mass%.
%.

【0027】Ni:0.01〜1.0mass% Niは、本発明では重要なマルテンサイト分率を、製造条
件に大きく依存せず安定して制御可能とする効果があ
る。このような望ましい効果は、0.01mass%以上の添加
で達成されるが、1.0mass%を超えて添加してもその効
果が飽和する傾向があるため、その含有量を0.01〜1.0m
ass%とすることが好ましい。なお、上記したこれらの
選択的添加元素は、複合して添加しても、これらの望ま
しい効果は相殺されることはない。
Ni: 0.01 to 1.0 mass% Ni has the effect of enabling the martensite fraction, which is important in the present invention, to be controlled stably without largely depending on the manufacturing conditions. Such a desired effect is achieved by adding 0.01 mass% or more, but even if added over 1.0 mass%, the effect tends to be saturated, so the content is 0.01 to 1.0 m
It is preferably as%. In addition, even if these selective addition elements described above are added in a complex manner, their desired effects are not offset.

【0028】次いで、本発明に係る鋼板の組織を限定し
た理由について述べる。 フェライト相の面積率:85%以上 本発明は、高い伸びフランジ性が要求される自動車用鋼
板を対象としている。この用途に必要な伸びフランジ性
を確保するためには、フェライトを主相とし、フェライ
ト面積率を組織全体に対する面積率で85%以上とする必
要がある。さらにより高い伸びフランジ性が要求される
場合には、95%以上のフェライト分率が望ましい。ここ
で云うフェライトとは、加工による歪を含まないいわゆ
るポリゴナルフェライト組織をさす。さらに、炭化物の
析出を含まないベイニテイックフェライト、アシキュラ
ーフェライトも、適度な強度の増加をもたらし、伸びフ
ランジ性の低下もなく、望ましい組織であるため本願で
いうフェライトの範疇に含むものとする。なお、組織の
分率の測定は、光学顕微鏡により鋼板の断面組織を観察
することで面積率として評価することができる。
Next, the reasons for limiting the structure of the steel sheet according to the present invention will be described. Area ratio of ferrite phase: 85% or more The present invention is intended for a steel sheet for automobiles which is required to have high stretch flangeability. In order to secure the stretch-flangeability required for this application, ferrite must be the main phase and the ferrite area ratio must be 85% or more in terms of the area ratio to the entire structure. When higher stretch flangeability is required, a ferrite fraction of 95% or more is desirable. The ferrite referred to here means a so-called polygonal ferrite structure that does not include strain due to processing. Further, bainitic ferrite and acicular ferrite which do not include precipitation of carbide also bring about an appropriate increase in strength, have no deterioration in stretch-flange formability, and have a desirable structure, so they are included in the category of ferrite in the present application. The measurement of the fraction of the structure can be evaluated as the area ratio by observing the cross-sectional structure of the steel sheet with an optical microscope.

【0029】マルテンサイト分率:2%以上10%以下 マルテンサイトは、本発明が目標とする、強度と延性お
よび伸びフランジ性の優れたバランスを得るのに極めて
重要な組織である。また、マルテンサイトの分率が、組
織全体に対する面積率で2%未満では、十分な延性改善
効果が得られず、引張強度も低い。しかし、分率が面積
率で10%を上回ると、強度が大きく増加するものの、伸
びフランジ性が顕著に低下し望ましくない。また詳細な
機構は不明であるが、本発明のような強度レベルでも、
優れた耐衝撃吸収特性を付与するためには、マルテンサ
イト分率を、2〜10%の範囲に制御することが必須であ
る。
Martensite Fraction: 2% or more and 10% or less Martensite is an extremely important structure for achieving the excellent balance between strength, ductility and stretch flangeability, which is the goal of the present invention. Further, when the area ratio of martensite is less than 2% in terms of the area ratio with respect to the entire structure, a sufficient ductility improving effect cannot be obtained, and the tensile strength is also low. However, if the fraction exceeds 10% in terms of area ratio, the strength is greatly increased, but the stretch flangeability is significantly reduced, which is not desirable. Although the detailed mechanism is unknown, even at the strength level as in the present invention,
In order to give excellent impact absorption resistance, it is essential to control the martensite fraction within the range of 2 to 10%.

【0030】第2相の合計分率:15%以下 前記マルテンサイトを含む第2相分率が15%を超える
(残部はフェライト組織)と延性が低下することに加
え、伸びフランジ性が低下する傾向にある。これは第2
相分率が増加すると、各々の相が互いに連結し、バンド
状に存在するようになるためである。また、第2相分率
が15%を超えると、耐衝撃特性の異方性がおおきくな
り、衝撃吸収部品に適用した場合には、安定した衝撃吸
収特性が得られなくなる。なお、第2相に含む組織とし
ては、前記マルテンサイトの外に、パーライト、ベイナ
イト、残留オーステナイト、セメンタイトなどがあり、
目標とする強度、伸び等のレベルにより異なる組織を選
択し得る。
Total fraction of the second phase: 15% or less If the second phase fraction containing the above-mentioned martensite exceeds 15% (the balance is the ferrite structure), ductility is lowered and stretch flangeability is lowered. There is a tendency. This is the second
This is because when the phase fraction increases, the phases are connected to each other and exist in a band shape. When the second phase fraction exceeds 15%, the impact resistance anisotropy becomes large, and when applied to a shock absorbing component, stable shock absorbing characteristics cannot be obtained. The structure contained in the second phase includes pearlite, bainite, retained austenite, cementite, etc. in addition to the martensite.
Different tissues can be selected depending on the target level of strength, elongation and the like.

【0031】次いで、本発明に係る鋼板の機械的特性に
ついて述べる。 引張強度TS:400〜540MPa 本発明の鋼板は、引張強度TSが400〜540MPaの冷延鋼
板に対して適用した場合に、その優れた効果が顕著に発
揮される。この理由は、540MPa以上の高強度鋼板では、
組織の微細化が得られ易く、穴拡げ性を改善することは
比較的容易であるが、延性の低下に加え、形状凍結性が
顕著に低下し、本発明が対象とする、優れた形状凍結性
が要求される用途には適さないからである。また、TS
が400MPa以下では、従来から広く行われている固溶強化
のみの手法で、優れた機械的特性を有する鋼板を容易に
製造できるからである。
Next, the mechanical properties of the steel sheet according to the present invention will be described. Tensile Strength TS: 400 to 540 MPa When the steel sheet of the present invention is applied to a cold rolled steel sheet having a tensile strength TS of 400 to 540 MPa, its excellent effect is remarkably exhibited. The reason for this is that for high strength steel plates of 540 MPa or more,
It is easy to obtain a finer structure, and it is relatively easy to improve the hole expandability, but in addition to the decrease in ductility, the shape fixability is significantly reduced, which is the object of the present invention. This is because it is not suitable for applications that require high performance. Also, TS
Is less than 400 MPa, it is possible to easily manufacture a steel sheet having excellent mechanical properties by a method which has been widely used only for solid solution strengthening.

【0032】穴拡げ率:80%以上 伸びフランジ性は、実部品で発生するフランジ割れによ
く対応する穴拡げ性で代表される。穴拡げ性の試験は、
鉄鋼連盟規格(JFST1001)に準じた方法で行い、初期の穴
径を10mmとし、割れが板厚を貫通する時の穴径D(mm)を
測定し、下記式 ((D−10)/10)×100(%) で穴拡げ率を算出する。本発明の鋼板は、穴拡げ率が80
%以上のものである。この値が80%以上であれば、本発
明が対象とする部品においては、フランジ割れを発生す
ることなくプレス成形が可能である。穴拡げ率が100%
以上であればより好ましい。なお、本発明の鋼板は、打
ち抜き加工時のクリアランスが変化しても、安定した穴
拡げ加工性(伸びフランジ性)が得られることも特徴の1
つである。
Hole expandability: 80% or more Stretch-flangeability is represented by the hole expandability that corresponds well to flange cracks that occur in actual parts. The hole expandability test is
The method according to the Iron and Steel Federation Standard (JFST1001) was performed, the initial hole diameter was set to 10 mm, and the hole diameter D (mm) when the crack penetrates the plate thickness was measured, and the following formula ((D-10) / 10 ) × 100 (%) to calculate the hole expansion rate. The steel sheet of the present invention has a hole expansion ratio of 80.
% Or more. If this value is 80% or more, press molding can be performed on the part targeted by the present invention without causing flange cracks. 100% hole expansion rate
The above is more preferable. The steel sheet of the present invention is also characterized in that stable hole expanding workability (stretch flangeability) can be obtained even if the clearance during punching changes.
Is one.

【0033】衝撃吸収特性 本発明の鋼板においては、衝撃吸収特性も重要である。
この衝撃吸収特性は、高速引張特性、すなわち、動的強
度(引張歪速度500/sでのTS)と静的強度(通常の引張
歪速度10-3/sでのTS)との比で評価することができ
る。この比が、1.2以上であれば、衝撃吸収特性が優れ
ると判断することができる。
Impact absorption characteristics In the steel sheet of the present invention, the impact absorption characteristics are also important.
This impact absorption property is evaluated by high-speed tensile property, that is, the ratio of dynamic strength (TS at tensile strain rate of 500 / s) and static strength (TS at normal tensile strain rate of 10 -3 / s). can do. If this ratio is 1.2 or more, it can be judged that the impact absorption characteristics are excellent.

【0034】なお、本発明の効果は、上記の特性が要求
される用途から、板厚が0.8mm〜2.3mmの冷延鋼板に対し
て適用した場合に、顕著に現れる。しかし、上記以外の
板厚に対し、本発明を適用しても、その効果が損なわれ
るものではない。
The effect of the present invention is remarkable when it is applied to a cold-rolled steel sheet having a plate thickness of 0.8 mm to 2.3 mm because of the use requiring the above characteristics. However, even if the present invention is applied to plate thicknesses other than the above, the effect is not impaired.

【0035】次に、本発明に係る製造方法において、そ
の特徴的な構成について説明する。 熱間圧延 熱間圧延は、常法に従って行えばよく、特に限定されな
い。以下に、好ましい条件について説明する。 (1)スラブ加熱 上記の成分組成を有する鋼スラブは、一般に、成分の偏
析を軽減するため、連続鋳造法で製造することが望まし
いが、造塊法、薄スラブ鋳造法で製造してもよい。熱延
する前のスラブの加熱は、スラブを製造後、室温まで冷
却し、その後再加熱する従来法に加え、冷却せずに温片
のままで加熱炉に装入するあるいはわずかの保熱をおこ
なった後、直ちに圧延する直送圧延・直接圧延などの省
エネルギープロセスも問題なく適用できる。スラブの加
熱温度は、熱間圧延前の初期状態として、固溶状態のN
を確保し、前述したNの効果を得やすいという観点か
ら、1000℃以上にすることが好ましい。また、酸化重量
の増加にともなうロスを防止するためには、1280℃以下
とすることが望ましい。なお、固溶状態のNを有効に確
保するには、直送圧延は有用な技術の一つである。
Next, the characteristic structure of the manufacturing method according to the present invention will be described. Hot rolling Hot rolling may be performed according to a conventional method and is not particularly limited. The preferable conditions will be described below. (1) Slab heating Steel slabs having the above component composition are generally preferably manufactured by a continuous casting method in order to reduce segregation of the components, but may be manufactured by a slab casting method or a thin slab casting method. . For heating the slab before hot rolling, in addition to the conventional method in which the slab is cooled to room temperature after it is manufactured and then reheated, it is charged into the heating furnace as it is without cooling or with a slight heat retention. Energy-saving processes such as direct rolling and direct rolling in which rolling is performed immediately after the rolling can be applied without any problems. As for the heating temperature of the slab, the initial state before hot rolling is N of solid solution state.
From the viewpoint that the above-mentioned effect is secured and the effect of N described above is easily obtained, it is preferably 1000 ° C. or higher. Further, in order to prevent loss due to increase in oxidized weight, it is desirable to set the temperature to 1280 ° C or lower. In order to effectively secure N in a solid solution state, direct-feed rolling is one of the useful techniques.

【0036】(2)熱延仕上温度(FT) 仕上圧延温度は800℃以上とすることが好ましい。この
ような仕上温度で熱間圧延を行うと、本発明の重要な要
件である適正な範囲のマルテンサイトを含む冷延鋼板を
得るのに適した熱延母板を製造することができる。この
熱延仕上温度が800℃を下回ると、最終的な冷延・焼鈍
後の組織に異方性が生じ、伸びフランジ性が低下する場
合があるので、熱延仕上温度は800℃以上とすることが
好ましい。一方、950℃を上回ると、表面スケールに起
因する欠陥が発生する危険性が増大するため、上限は95
0℃程度が好ましい。
(2) Hot rolling finish temperature (FT) The finish rolling temperature is preferably 800 ° C. or higher. When hot rolling is performed at such a finishing temperature, it is possible to manufacture a hot-rolled base plate suitable for obtaining a cold-rolled steel sheet containing martensite in an appropriate range, which is an important requirement of the present invention. If the hot rolling finishing temperature is lower than 800 ° C, the anisotropy may occur in the final microstructure after cold rolling / annealing and the stretch flangeability may be deteriorated. Therefore, the hot rolling finishing temperature should be 800 ° C or higher. It is preferable. On the other hand, if the temperature exceeds 950 ° C, the risk of defects due to surface scale increases, so the upper limit is 95%.
About 0 ° C is preferable.

【0037】(3)熱延後の冷却 熱延後の冷却も、特に限定の必要はなく、常法で行われ
る範囲でよいが、平均冷却速度40℃/s以上として組織
を微細化し、第2相の粒径が小さくなるようにすること
が、均一性を確保する上で好ましい。また、冷却速度の
上限も特に規定はしないが、300℃/sを上回ると、却
って材質の均一性と形状の均一性の確保が難しくなる場
合があるため、上限は300℃/s程度とすることが好ま
しい。
(3) Cooling after hot rolling The cooling after hot rolling is not particularly limited and may be within the range which is carried out by an ordinary method, but the average cooling rate is 40 ° C./s or more to refine the structure, It is preferable to make the particle diameters of the two phases small in order to ensure uniformity. The upper limit of the cooling rate is also not specified, but if it exceeds 300 ° C / s, it may be difficult to secure the uniformity of the material and the uniformity of the shape. Therefore, the upper limit is set to about 300 ° C / s. It is preferable.

【0038】(4)巻取温度 熱延後の巻取温度は500℃以上とすることが好ましい。
この温度が500℃を下回ると、鋼板の形状が乱れ、冷間
圧延の際、圧延トラブルの原因となることがある。ま
た、延性の低下が起こることがあるため、500℃以上の
巻取温度とすることが好ましい。上限は特に規制されな
いが、750℃を上回ると、コイルの長手方向の材質差が
大きくなりやすい。また、脱スケール性などが問題とな
る場合は、700℃以下とすることが好ましい。
(4) Winding temperature The winding temperature after hot rolling is preferably 500 ° C. or higher.
If this temperature is lower than 500 ° C., the shape of the steel sheet may be disturbed, which may cause rolling trouble during cold rolling. Further, since the ductility may be lowered, it is preferable to set the coiling temperature to 500 ° C. or higher. The upper limit is not particularly limited, but if it exceeds 750 ° C, the difference in material in the longitudinal direction of the coil tends to increase. If descaling is a problem, the temperature is preferably 700 ° C or lower.

【0039】冷間圧延〜めっき工程 (1)冷間圧延 上記熱間圧延後、常法に従い、酸洗、冷間圧延を行う。
冷間圧延の圧下率は、特に限定されないが、伸びフラン
ジ性改善のため、30〜90%程度とすることが好ましい。
Cold Rolling to Plating Step (1) Cold Rolling After the above hot rolling, pickling and cold rolling are performed according to a conventional method.
The reduction ratio of cold rolling is not particularly limited, but is preferably about 30 to 90% in order to improve stretch flangeability.

【0040】(2)焼鈍工程 焼鈍は、冷間圧延後、750〜900℃の温度に加熱し、20℃
/s以上の速度で冷却する条件で連続焼鈍を行う。本発
明において、連続焼鈍条件は、極めて重要である。少な
くとも、750℃以上に加熱しないと十分な量のマルテン
サイトを得ることができない。しかし、加熱温度が900
℃を超えると、第2相が粗大となり、伸びフランジ性が
低下するとともに降伏応力が増加し、加工性が低下す
る。なお、上記の冷却速度は、十分な量のマルテンサイ
トを得るために、少なくとも400℃までの平均冷却速度
を20℃/s以上で急冷することが重要である。上限につ
いては特に規制しないが、通常のガスジェット冷却の設
備で達成できる100℃/s程度までは問題なく適用可能で
あり、さらに、高速の水冷(〜1000℃/s)を行っても、
同等レベルの製品は製造可能である。連続焼鈍後の鋼板
は、必要に応じて、スキンパス圧延あるいはレベラー加
工して、製品とすることができる。
(2) Annealing process Annealing is performed by heating to a temperature of 750 to 900 ° C. after cold rolling at 20 ° C.
Continuous annealing is performed under the condition of cooling at a rate of / s or more. In the present invention, continuous annealing conditions are extremely important. At least a sufficient amount of martensite cannot be obtained unless it is heated to 750 ° C or higher. However, the heating temperature is 900
If the temperature exceeds ° C, the second phase becomes coarse, the stretch-flangeability deteriorates, the yield stress increases, and the workability deteriorates. In addition, as for the above cooling rate, in order to obtain a sufficient amount of martensite, it is important that the average cooling rate up to at least 400 ° C. is rapidly cooled at 20 ° C./s or more. The upper limit is not particularly limited, but it can be applied without problems up to about 100 ° C / s that can be achieved with normal gas jet cooling equipment, and even if high-speed water cooling (~ 1000 ° C / s) is performed,
Equivalent levels of product can be manufactured. The steel sheet after the continuous annealing can be subjected to skin pass rolling or leveler processing as required to obtain a product.

【0041】(3)めっき工程 連続焼鈍後の鋼板は、さらにその後、鋼板表面に電気め
っきを行い、電気めっき鋼板としてもよい。本発明の鋼
板の特性に対するめっきの影響は小さく、冷延鋼板と同
等の強度レベルで良好な特性を確保できる。電気めっき
の種類としては、自動車用鋼板に用いられるZnめっき、
Zn−Niめっきなどが亜鉛系のめっきが好ましく、めっき
方法は常法に従えばよい。なお、スキンパス圧延あるい
はレベラー加工は、連続焼鈍直後に行ってもよいし、め
っき後行ってもよい。
(3) Plating Step The steel sheet after continuous annealing may be further electroplated on the surface of the steel sheet to obtain an electroplated steel sheet. The effect of plating on the characteristics of the steel sheet of the present invention is small, and good characteristics can be secured at a strength level equivalent to that of a cold rolled steel sheet. The types of electroplating include Zn plating used for automobile steel sheets,
Zinc-based plating such as Zn-Ni plating is preferable, and the plating method may be a conventional method. The skin pass rolling or leveling process may be performed immediately after continuous annealing or after plating.

【0042】次いで、採用することが好ましいその他の
製造条件について述べる。本発明は、自動車車体用の冷
延薄鋼板あるいは電気めっき鋼板であり、当然のことな
がら、上記の特性のほか、鋼板の形状・寸法精度の向上
および鋼板の長手方向および幅方向の材質均一化が望ま
れている。この目的達成のため、母板を製造する熱間圧
延工程において、現在、一部で実用化されている連続圧
延技術を適用することが有効である。また、同時に、材
質均一化のために、圧延温度をコイルの長手方向、幅方
向に均一化するシートバーエッジヒーター、あるいはシ
ートバーヒーターを併せて用いることも有効である。さ
らに、圧延後の冷却において、エッジ部の過冷却を防止
するために、幅方向に冷却水のマスキングを行なう技術
も材質均一化の観点では重要な技術の一つである。ま
た、熱間加工時に、荷重低減のため潤滑圧延を行なうこ
とは、形状の均一化、材質の均一化の観点からも有効で
あり、特に、潤滑圧延を、前述の連続圧延プロセスに適
用することは、熱間圧延の操業安定性の観点からも望ま
しい。
Next, other manufacturing conditions that are preferably adopted will be described. INDUSTRIAL APPLICABILITY The present invention is a cold-rolled thin steel plate or an electroplated steel plate for an automobile body. Naturally, in addition to the above characteristics, the shape and dimensional accuracy of the steel plate are improved, and the material is made uniform in the longitudinal and width directions of the steel plate. Is desired. In order to achieve this purpose, it is effective to apply a continuous rolling technique, which is currently partially put into practical use, in a hot rolling process for producing a mother plate. At the same time, in order to make the material uniform, it is also effective to use a sheet bar edge heater or a sheet bar heater which makes the rolling temperature uniform in the longitudinal direction and width direction of the coil. Further, in cooling after rolling, a technique of masking the cooling water in the width direction in order to prevent overcooling of the edge portion is also an important technique from the viewpoint of material uniformity. In addition, performing lubrication rolling to reduce the load during hot working is effective from the viewpoint of homogenizing the shape and homogenizing the material. In particular, applying lubrication rolling to the continuous rolling process described above. Is also desirable from the viewpoint of operation stability of hot rolling.

【0043】[0043]

【実施例】次に、本発明の実施例について説明する。 (実施例1)表1に示す成分組成を含み、残部が実質的
にFeからなる鋼を転炉で溶製し、この鋼スラブを、表2
に示す条件で熱間圧延し、酸洗し、板厚0.8〜1.6mmに冷
間圧延した後、連続焼鈍して冷延鋼板あるいはそれに電
気めっきした鋼板を製造した。なお、表2の電気亜鉛め
っきは、片面当たりの付着量を60g/m2として両面めっ
きしたものである。また、電気Zn−Ni合金めっきは、Ni
含有率が12mass%のZn−Ni合金めっきを、片面当たりの
付着量を20g/m2として両面めっきしたものである。こ
れらの鋼板について、組織調査、引張試験、穴拡げ試験
および高速引張特性の調査を以下の要領で行い、結果を
表3に示した。 ・組織調査:光学顕微鏡により、鋼板の断面組織を観察
し、フェライト面積率、マルテンサイト分率および第2
相分率(マルテンサイト含む)を測定した。 ・引張試験:JIS 5号試験片を使用した。 ・穴拡げ試験:前述のように、鉄鋼連盟規格に準拠して
実施した。 ・高速引張特性:引張歪速度500/sでのTSと、通常の
引張歪速度10-3/sでのTSとの比を求め、1.2以上を
優、1.2未満を劣とした。
EXAMPLES Next, examples of the present invention will be described. (Example 1) A steel containing the composition shown in Table 1 and the balance being substantially Fe was melted in a converter, and the steel slab was prepared as shown in Table 2.
After hot-rolling under the conditions shown in (1), pickling, cold-rolling to a sheet thickness of 0.8 to 1.6 mm, continuous annealing was performed to produce a cold-rolled steel sheet or a steel sheet electroplated therewith. In addition, the electrogalvanization in Table 2 is a double-sided plating with an adhesion amount per one surface of 60 g / m 2 . In addition, electric Zn-Ni alloy plating is
Zn-Ni alloy plating with a content of 12 mass% was plated on both sides with an adhesion amount per one side of 20 g / m 2 . With respect to these steel sheets, a structure investigation, a tensile test, a hole expansion test and an investigation of high-speed tensile properties were conducted in the following manner, and the results are shown in Table 3. -Structural investigation: The cross-sectional structure of the steel sheet is observed by an optical microscope, and the ferrite area ratio, martensite fraction and second
The phase fraction (including martensite) was measured. -Tensile test: JIS No. 5 test piece was used. -Hole expansion test: As described above, the test was performed in accordance with the standards of the Iron and Steel Federation. High-speed tensile property: The ratio of the TS at a tensile strain rate of 500 / s and the TS at a normal tensile strain rate of 10 −3 / s was determined, and 1.2 or more was excellent and less than 1.2 was inferior.

【0044】[0044]

【表1】 [Table 1]

【0045】[0045]

【表2】 [Table 2]

【0046】[0046]

【表3】 [Table 3]

【0047】(実施例2)C:0.055mass%、Si:0.005
mass%、Mn:1.2mass%、P:0.009mass%、S:0.001m
ass%、Al:0.055mass%、N:0.0025mass%、Cr:0.05
mass%、Mo:0.15mass%(Cr+1.2Mo:0.23mass%)の鋼
スラブを素材とし、表4に示すように、製造条件を幅広
く変化させて、冷延鋼板あるいはそれに電気めっきした
鋼板を製造し、実施例1と同様に機械的性質を調査し
た。結果を表5に示す。なお、表4の電気Zn−Niめっき
は、Ni含有率が12mass%のZn−Ni合金めっきを、片面当
たりの付着量を20g/m2として両面めっきしたものであ
る。
(Example 2) C: 0.055 mass%, Si: 0.005
mass%, Mn: 1.2mass%, P: 0.009mass%, S: 0.001m
ass%, Al: 0.055 mass%, N: 0.0025 mass%, Cr: 0.05
Mass%, Mo: 0.15 mass% (Cr + 1.2 Mo: 0.23 mass%) steel slab is used as a raw material, and as shown in Table 4, cold-rolled steel plate or electroplated steel plate is manufactured by widely changing the manufacturing conditions. Then, the mechanical properties were investigated in the same manner as in Example 1. The results are shown in Table 5. The electric Zn-Ni plating in Table 4 is a Zn-Ni alloy plating having a Ni content of 12 mass% and double-sided plating with an adhesion amount of 20 g / m 2 per surface.

【0048】[0048]

【表4】 [Table 4]

【0049】[0049]

【表5】 [Table 5]

【0050】[0050]

【発明の効果】以上説明したように、本発明によれば、
引張強度が400MPa以上540MPa以下の強度を有するととも
に、優れた延性と伸びフランジ性を有しかつ衝撃吸収特
性にも優れる高強度鋼板を安定して製造することが可能
となる。また、本発明によれば、該鋼板表面にめっき処
理を施すことにより高強度電気めっき鋼板の製造も可能
になる。本発明の鋼板は、サイドメンバーなどの耐衝突
部品に用いて好適であり、自動車車体の軽量化に寄与す
る。また、本発明の鋼板は、溶融亜鉛めっきラインで処
理することで、冷延鋼板とほぼ同等の(合金化)溶融亜鉛
めっき鋼板を製造することもできる。
As described above, according to the present invention,
It becomes possible to stably manufacture a high-strength steel sheet having a tensile strength of 400 MPa or more and 540 MPa or less, excellent ductility and stretch flangeability, and excellent impact absorption characteristics. Further, according to the present invention, it is possible to manufacture a high-strength electroplated steel sheet by subjecting the steel sheet surface to a plating treatment. INDUSTRIAL APPLICABILITY The steel sheet of the present invention is suitable for use in collision-resistant parts such as side members and contributes to weight reduction of automobile bodies. Further, the steel sheet of the present invention can be processed in a hot dip galvanizing line to produce a (galvanized) hot dip galvanized steel sheet that is almost the same as the cold rolled steel sheet.

───────────────────────────────────────────────────── フロントページの続き Fターム(参考) 4K037 EA01 EA02 EA05 EA09 EA11 EA13 EA15 EA17 EA18 EA19 EA20 EA23 EA25 EA27 EA31 EA32 EA36 EB05 EB07 EB08 EB11 FB00 FG00 FH01 FJ05 FJ06 FK03 GA05    ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4K037 EA01 EA02 EA05 EA09 EA11                       EA13 EA15 EA17 EA18 EA19                       EA20 EA23 EA25 EA27 EA31                       EA32 EA36 EB05 EB07 EB08                       EB11 FB00 FG00 FH01 FJ05                       FJ06 FK03 GA05

Claims (5)

【特許請求の範囲】[Claims] 【請求項1】C:0.02〜0.08mass%、Si:0.50mass%以
下、Mn:0.5〜1.5mass%、P:0.04mass%以下、S:0.
005mass%以下、Al:0.1mass%以下、N:0.025mass%
以下を含有し、さらに、Cr,Mo:単独または複合添加
で、下記式、 Cr+1.2Mo≧0.2mass% を満足するよう含有し、残部がFeおよび不可避的不純物
からなり、かつ、主相であるフェライト組織の分率が面
積率で85%以上であり、面積率で2%以上10%以下のマ
ルテンサイト組織を含有し、前記マルテンサイトを含む
第2相の分率の合計が面積率で15%以下である、延性、
伸びフランジ性および衝撃吸収特性に優れた高強度鋼
板。
1. C: 0.02 to 0.08 mass%, Si: 0.50 mass% or less, Mn: 0.5 to 1.5 mass%, P: 0.04 mass% or less, S: 0.
005mass% or less, Al: 0.1mass% or less, N: 0.025mass%
Contains the following, and further contains Cr and Mo: singly or in combination so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2 mass%, and the balance is Fe and inevitable impurities, and is the main phase The area ratio of the ferrite structure is 85% or more, the area ratio is 2% or more and 10% or less, and the total ratio of the second phase containing the martensite is 15% or less. %, Ductility,
High strength steel sheet with excellent stretch flangeability and shock absorption characteristics.
【請求項2】上記成分のほかに、B:0.0005〜0.0040ma
ss%、Ca:0.0010〜0.01mass%、REM:0.0010〜0.01
mass%、Ti:0.005〜0.10mass%、Nb:0.002〜0.10mass
%、V:0.005〜0.10mass%、Cu:0.01〜1.0mass%、N
i:0.01〜1.0mass%のうちのいずれか1種または2種以
上を含有することを特徴とする請求項1に記載の高強度
鋼板。
2. In addition to the above components, B: 0.0005 to 0.0040 ma
ss%, Ca: 0.0010 to 0.01 mass%, REM: 0.0010 to 0.01
mass%, Ti: 0.005-0.10mass%, Nb: 0.002-0.10mass
%, V: 0.005 to 0.10 mass%, Cu: 0.01 to 1.0 mass%, N
i: The high-strength steel sheet according to claim 1, containing one or more of 0.01 to 1.0 mass%.
【請求項3】請求項1または2のいずれか1項に記載の
鋼板表面に、電気めっき皮膜を有する高強度電気めっき
鋼板。
3. A high-strength electroplated steel sheet having an electroplated film on the surface of the steel sheet according to claim 1 or 2.
【請求項4】C:0.02〜0.08mass%、Si:0.50mass%以
下、Mn:0.5〜1.5mass%、P:0.04mass%以下、S:0.
005mass%以下、Al:0.1mass%以下、N:0.025mass%
以下を含有し、さらに、Cr,Mo:単独または複合添加
で、下記式、Cr+1.2Mo≧0.2mass%を満足するよう含有
し、あるいはさらに、B:0.0005〜0.0040mass%、Ca:
0.0010〜0.01mass%、REM:0.0010〜0.01mass%、T
i:0.005〜0.10mass%、Nb:0.002〜0.10mass%、V:0.
005〜0.10mass%、Cu:0.01〜1.0mass%、Ni:0.01〜1.
0mass%のうちのいずれか1種または2種以上を含有
し、残部がFeおよび不可避的不純物からなる鋼スラブ
を、熱間圧延し、その後、酸洗と冷間圧延を行い、次い
で750℃以上900℃以下に加熱後、20℃/s以上の速度で
冷却する連続焼鈍することを特徴とする、延性、伸びフ
ランジ性および衝撃吸収特性に優れた高強度鋼板の製造
方法。
4. C: 0.02 to 0.08 mass%, Si: 0.50 mass% or less, Mn: 0.5 to 1.5 mass%, P: 0.04 mass% or less, S: 0.
005mass% or less, Al: 0.1mass% or less, N: 0.025mass%
Contains the following, and further contains Cr, Mo: alone or in combination so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2 mass%, or further contains B: 0.0005 to 0.0040 mass%, Ca:
0.0010-0.01mass%, REM: 0.0010-0.01mass%, T
i: 0.005 to 0.10 mass%, Nb: 0.002 to 0.10 mass%, V: 0.
005 to 0.10mass%, Cu: 0.01 to 1.0mass%, Ni: 0.01 to 1.
A steel slab containing one or more of 0 mass% and the balance consisting of Fe and unavoidable impurities is hot-rolled, then pickled and cold-rolled, and then 750 ° C or higher. A method for producing a high-strength steel sheet excellent in ductility, stretch-flangeability and impact absorption characteristics, characterized by comprising continuous annealing after heating to 900 ° C or lower and cooling at a rate of 20 ° C / s or higher.
【請求項5】C:0.02〜0.08mass%、Si:0.50mass%以
下、Mn:0.5〜1.5mass%、P:0.04mass%以下、S:0.
005mass%以下、Al:0.1mass%以下、N:0.025mass%
以下を含有し、さらに、Cr,Mo:単独または複合添加
で、下記式、 Cr+1.2Mo≧0.2mass% を満足するよう含有し、あるいはさらに、B:0.0005〜
0.0040mass%、Ca:0.0010〜0.01mass%、REM:0.00
10〜0.01mass%、Ti:0.005〜0.10mass%、Nb:0.002〜
0.10mass%、V:0.005〜0.10mass%Cu:0.01〜1.0mass
%、Ni:0.01〜1.0mass%のうちのいずれか1種または
2種以上を含有し、残部がFeおよび不可避的不純物から
なる鋼スラブを、熱間圧延し、その後、酸洗と冷間圧延
を行い、次いで750℃以上900℃以下に加熱後、20℃/s
以上の速度で冷却する連続焼鈍を施し、その後、電気め
っき処理を施すことを特徴とする、延性、伸びフランジ
性および衝撃吸収特性に優れた高強度電気めっき鋼板の
製造方法。
5. C: 0.02 to 0.08 mass%, Si: 0.50 mass% or less, Mn: 0.5 to 1.5 mass%, P: 0.04 mass% or less, S: 0.
005mass% or less, Al: 0.1mass% or less, N: 0.025mass%
Contains the following, and further contains Cr and Mo: alone or in combination so as to satisfy the following formula, Cr + 1.2Mo ≧ 0.2 mass%, or further, B: 0.0005 to
0.0040 mass%, Ca: 0.0010 to 0.01 mass%, REM: 0.00
10-0.01mass%, Ti: 0.005-0.10mass%, Nb: 0.002-
0.10mass%, V: 0.005-0.10mass% Cu: 0.01-1.0mass
%, Ni: 0.01 to 1.0 mass% of any one or more of the steel slabs, the balance of which is Fe and unavoidable impurities, is hot-rolled, and then pickled and cold-rolled. Then, after heating at 750 ℃ to 900 ℃, 20 ℃ / s
A method for producing a high-strength electroplated steel sheet excellent in ductility, stretch-flange formability, and shock absorption characteristics, characterized by performing continuous annealing that cools at the above rate and then performing electroplating treatment.
JP2001398712A 2001-12-28 2001-12-28 High-strength steel plate and high-strength electroplated steel plate excellent in ductility, stretch flangeability and shock absorption characteristics and methods for producing them Expired - Fee Related JP3932892B2 (en)

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WO2006109522A1 (en) * 2005-03-31 2006-10-19 Kabushiki Kaisha Kobe Seiko Sho Hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet
JP2007262550A (en) * 2006-03-30 2007-10-11 Jfe Steel Kk Steel sheet for carburizing and quenching and its production method
US7682467B2 (en) 2004-01-21 2010-03-23 Kobe Steel, Ltd. High strength hot rolled steel sheet superior in workability, fatigue property, and surface quality
JP2011111672A (en) * 2009-11-30 2011-06-09 Nippon Steel Corp HIGH STRENGTH COLD ROLLED STEEL SHEET HAVING MAXIMUM TENSILE STRENGTH OF >=900 MPa AND HAVING EXCELLENT IMPACT ABSORBED ENERGY, METHOD FOR PRODUCING THE SAME, HIGH STRENGTH GALVANIZED STEEL SHEET, AND METHOD FOR PRODUCING THE SAME
JP2011252232A (en) * 2011-07-15 2011-12-15 Jfe Steel Corp Hot-rolled steel sheet for carburizing and quenching
CN115181916A (en) * 2021-04-02 2022-10-14 宝山钢铁股份有限公司 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7682467B2 (en) 2004-01-21 2010-03-23 Kobe Steel, Ltd. High strength hot rolled steel sheet superior in workability, fatigue property, and surface quality
WO2006109522A1 (en) * 2005-03-31 2006-10-19 Kabushiki Kaisha Kobe Seiko Sho Hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet
JP2007262550A (en) * 2006-03-30 2007-10-11 Jfe Steel Kk Steel sheet for carburizing and quenching and its production method
JP2011111672A (en) * 2009-11-30 2011-06-09 Nippon Steel Corp HIGH STRENGTH COLD ROLLED STEEL SHEET HAVING MAXIMUM TENSILE STRENGTH OF >=900 MPa AND HAVING EXCELLENT IMPACT ABSORBED ENERGY, METHOD FOR PRODUCING THE SAME, HIGH STRENGTH GALVANIZED STEEL SHEET, AND METHOD FOR PRODUCING THE SAME
JP2011252232A (en) * 2011-07-15 2011-12-15 Jfe Steel Corp Hot-rolled steel sheet for carburizing and quenching
CN115181916A (en) * 2021-04-02 2022-10-14 宝山钢铁股份有限公司 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method
CN115181916B (en) * 2021-04-02 2023-09-12 宝山钢铁股份有限公司 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot dip galvanized dual-phase steel and rapid heat treatment hot dip galvanizing manufacturing method

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