JP2001220643A - Medium or high carbon steel sheet excellent in local ductility - Google Patents
Medium or high carbon steel sheet excellent in local ductilityInfo
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- JP2001220643A JP2001220643A JP2000028282A JP2000028282A JP2001220643A JP 2001220643 A JP2001220643 A JP 2001220643A JP 2000028282 A JP2000028282 A JP 2000028282A JP 2000028282 A JP2000028282 A JP 2000028282A JP 2001220643 A JP2001220643 A JP 2001220643A
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- steel
- carbides
- steel sheet
- local ductility
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、炭化物の分散形態
に特徴を有する、局部延性に優れた中・高炭素鋼板に関
するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a medium and high carbon steel sheet having excellent local ductility, which is characterized by a dispersed form of carbide.
【０００２】[0002]
【従来の技術】鋼中のＣ含有量が概ね0.10〜0.80質量％
の、いわゆる中・高炭素鋼板は、焼入れ強化が可能であ
るとともに焼鈍状態ではある程度の加工性も有している
ため、自動車部品をはじめ各種機械部品や軸受け部品の
素材として広く使用されている。部品の製造にあたって
は、一般的には打抜加工や曲げ成形が施され、さらに比
較的軽度な絞り加工，伸びフランジ成形が施されること
もある。また、部品形状が複雑な場合は、二ないし三部
品を溶接して製造される場合も多い。そしてこれらの加
工部品は熱処理を経て各種用途の部品に仕上げられてい
く。2. Description of the Related Art The C content in steel is approximately 0.10 to 0.80% by mass.
The so-called medium and high carbon steel sheets can be hardened and strengthened and have a certain degree of workability in an annealed state. Therefore, they are widely used as materials for various mechanical parts including automobile parts and bearing parts. In manufacturing parts, punching and bending are generally performed, and relatively light drawing and stretch flange forming are sometimes performed. When the shape of the part is complicated, two or three parts are often manufactured by welding. These processed parts are processed into various parts through heat treatment.
【０００３】ところが近年、部品の製造コストを低減す
べく、部品の一体成形や、部品加工の工程簡略化が進め
られている。このことは素材側から見ればより加工率の
高い（＝塑性変形量の大きい）加工に耐えなくてはなら
ないことを意味する。つまり、加工技術の高度化に伴
い、素材である中・高炭素鋼板自体にもより高い加工性
が要求されるようになってきた。特に昨今では、打抜加
工や曲げ加工のみならず、高度な伸びフランジ成形加工
（例えば穴拡げ加工）にも耐え得る局部延性に優れた鋼
板素材のニーズが高まるつつある。However, in recent years, in order to reduce the manufacturing cost of parts, integrated molding of parts and simplification of the steps of processing parts have been promoted. This means that the material must endure processing with a higher processing rate (= large plastic deformation) as viewed from the material side. In other words, with the advancement of processing technology, higher workability has been required for the medium and high carbon steel sheets as raw materials. In particular, in recent years, there is an increasing need for a steel sheet material having excellent local ductility that can withstand not only punching and bending but also advanced stretch flange forming (for example, hole expanding).
【０００４】こうした中、特公昭61-15930号公報，特公
平5-70685号公報，および特開平4-333527号公報には、
加工方法あるいは熱処理方法を工夫することによって棒
鋼中の炭化物を球状化し、棒鋼線材の加工性を改善する
技術が紹介されている。しかし、これらはいずれも棒鋼
線材を対象とするものであり、素材が板材である場合に
問題となる伸びフランジ性の改善手段は明らかにされて
いない。Under these circumstances, JP-B-61-15930, JP-B-5-70685 and JP-A-4-333527 disclose:
A technique for improving the workability of a bar steel rod by introducing a spheroidized carbide in a steel bar by devising a processing method or a heat treatment method is introduced. However, all of them are intended for bar steel wire rods, and means for improving stretch flangeability, which is a problem when the raw material is a plate, has not been clarified.
【０００５】また、特開平8-3687号公報には、Ｃを0.3m
ass％以上含有し、炭化物の占める面積率が20％以下
で、粒径1.5μｍ以上の炭化物の割合が30％以上である
加工用高炭素鋼板が示されている。これは炭化物の形態
を制御して鋼板の加工性を改善したものではあるが、局
部延性に関連する伸びフランジ性といった高度な加工性
を改善するには至っていない。また、炭化物粒径を1.5
μｍ以上と粗大化させることは、高周波焼入れ等で行わ
れる短時間の加熱処理において炭化物の固溶化を不十分
にし、焼入れ不良を起こし易くする。Japanese Patent Application Laid-Open No. 8-3687 discloses that C is 0.3 m
A high carbon steel sheet for processing containing ass% or more, having an area ratio of carbide of 20% or less, and containing 30% or more of carbide having a particle size of 1.5 μm or more is shown. Although this improves the workability of a steel sheet by controlling the form of carbides, it has not yet improved advanced workability such as stretch flangeability related to local ductility. In addition, the carbide particle size is 1.5
The coarsening of not less than μm makes the solution of carbides insufficient in a short-time heat treatment performed by induction hardening or the like, and easily causes quenching failure.
【０００６】さらに特開平8-120405号公報には、Ｃ：0.
20〜0.60％の他、Ｓｉ，Ａｌ，Ｎ，Ｂ，Ｃａ等の黒鉛化
を促進する元素を含有し、Ｃ含有量の10〜50％が黒鉛化
しており、断面の鋼組織が3μｍ以上の黒鉛粒子を特定
量含んだ球状化セメンタイトの分散したフェライト相に
なっている加工性に優れた薄鋼板が示されている。この
薄鋼板は穴拡げ性と二次加工性に優れているという。し
かしその薄鋼板は含有炭素の黒鉛化を利用して加工性を
改善したものであるから、黒鉛化を促進する元素の添加
した鋼を用いる必要があり、一般的な市販の中・高炭素
鋼種に広く適用できるものではない。またこの場合も、
粗大化した黒鉛粒子を含ませることは、高周波焼入れ等
の短時間加熱による焼入れ性を阻害する要因になる。Further, Japanese Patent Application Laid-Open No. Hei 8-120405 discloses that C: 0.
In addition to 20 to 0.60%, it contains elements that promote graphitization such as Si, Al, N, B, Ca, etc., and 10 to 50% of the C content is graphitized, and the steel structure of the cross section is 3 μm or more. A thin steel sheet excellent in workability, which is a ferrite phase in which spheroidized cementite containing a specific amount of graphite particles is dispersed is shown. The steel sheet is said to be excellent in hole expandability and secondary workability. However, since the thin steel sheet has improved workability by utilizing graphitization of carbon contained, it is necessary to use steel to which elements that promote graphitization are added, and general commercial medium and high carbon steel grades are used. Is not widely applicable. Also in this case,
Inclusion of coarse graphite particles is a factor that impairs the hardenability by short-time heating such as induction hardening.
【０００７】[0007]
【発明が解決しようとする課題】以上のように、加工性
の中でも「伸びフランジ性」といった、特に局部延性を
改善した中・高炭素鋼板のニーズが高まりつつあるが、
一般的な中・高炭素の鋼種において、鋼板の局部延性を
改善する手法は確立されていない。その理由として、局
部延性を向上させ得るに足る鋼板の金属組織が未だ十分
には明らかにされていないことが挙げられる。As described above, there is a growing need for medium- and high-carbon steel sheets with improved local ductility, such as "stretch flangeability" among workability.
No method has been established for improving the local ductility of steel sheets in general medium and high carbon steel grades. The reason is that the metallographic structure of the steel sheet sufficient to improve the local ductility has not yet been sufficiently clarified.
【０００８】そこで本発明は、「伸びフランジ性」等の
局部延性を安定的に改善することができる金属組織を特
定し、特殊な元素を添加することなく一般的な中・高炭
素鋼の鋼種において局部延性に優れた鋼板を提供するこ
とを目的とする。Accordingly, the present invention specifies a metal structure capable of stably improving local ductility such as "stretch flangeability" and provides a general medium and high carbon steel grade without adding a special element. The purpose of the present invention is to provide a steel sheet having excellent local ductility.
【０００９】[0009]
【課題を解決するための手段】上記の目的は、請求項１
の発明、すなわち、Ｃ：0.10〜0.80質量％の鋼からな
り、下記(a)で定義される炭化物分散度が｛７５―４７
×(Ｃ％)(2/3)｝％以下であるように炭化物がフェライ
ト中に分散している局部延性に優れた中・高炭素鋼板に
よって達成される。 (a)炭化物分散度：鋼板断面の金属組織観察において、
観察視野を10μm×10μmのメッシュに分割して、その各
区画中に存在する炭化物数を測定し、１区画当たりの炭
化物数の標準偏差を１区画当たりの平均炭化物数で割っ
た100分率（％）をいう。The above object is achieved by the present invention.
In other words, the steel of C: 0.10 to 0.80 mass% has a carbide dispersity defined by the following (a) of {75-47}.
× (C%) (2/3) This is achieved by a medium- and high-carbon steel sheet having excellent local ductility in which carbides are dispersed in ferrite such that the content is not more than｝%. (a) Carbide dispersion degree: In observing the metallographic structure of the steel sheet cross section,
The observation field of view was divided into a mesh of 10 μm × 10 μm, the number of carbides present in each section was measured, and the standard deviation of the number of carbides per section was divided by the average number of carbides per section, which was 100 fraction ( %).
【００１０】請求項２の発明は、請求項１の発明におい
て、下記(b)で定義される平均炭化物粒径が 0.4〜1.2μ
ｍである鋼としたものである。 (b)平均炭化物粒径：鋼板断面の金属組織観察におい
て、観察視野内の個々の炭化物について測定した円相当
径を全測定炭化物について平均した値をいう。ただし、
観察視野は炭化物総数が300個以上となる領域とする。According to a second aspect of the present invention, in the first aspect, the average carbide particle size defined by the following (b) is 0.4 to 1.2 μm.
m. (b) Average carbide particle size: A value obtained by averaging the equivalent circle diameters measured for individual carbides in the observation visual field for all measured carbides in the observation of the metal structure of the cross section of the steel sheet. However,
The observation visual field is an area where the total number of carbides is 300 or more.
【００１１】請求項３の発明は、請求項１または２の発
明において、対象とする鋼を特に、質量％において、
Ｃ：0.10〜0.80％，Ｓ：0.01％以下である鋼としたもの
である。According to a third aspect of the present invention, in the first or second aspect of the invention, the target steel is particularly
C: 0.10 to 0.80%, S: 0.01% or less.
【００１２】請求項４の発明は、請求項１または２の発
明において、対象とする鋼を特に、質量％において、
Ｃ：0.10〜0.80％，Ｓｉ：0〜0.40％（無添加を含
む），Ｍｎ：0〜1.0％（無添加を含む）を含有し、Ｐ：
0.03％以下，Ｓ：0.01％以下，Ｔ.Ａｌ：0.1％以下で、
残部が鉄および不可避的不純物である鋼としたものであ
る。ここでＴ.Ａｌは、鋼中に含まれるトータルＡｌを
意味する。According to a fourth aspect of the present invention, in the first or second aspect of the invention, the target steel is particularly
C: 0.10 to 0.80%, Si: 0 to 0.40% (including no addition), Mn: 0 to 1.0% (including no addition), P:
0.03% or less, S: 0.01% or less, T.Al: 0.1% or less,
The balance is iron and steel which is an unavoidable impurity. Here, T.Al means the total Al contained in the steel.
【００１３】請求項５の発明は、請求項１または２の発
明において、対象とする鋼を特に、質量％において、
Ｃ：0.10〜0.80％，Ｓｉ：0〜0.40％（無添加を含
む），Ｍｎ：0〜1.0％（無添加を含む），Ｃｒ：0〜1.6
％（無添加を含む），Ｍｏ：0〜0.3％（無添加を含
む），Ｃｕ：0〜0.3％（無添加を含む），Ｎｉ：0〜2.0
％（無添加を含む）を含有し、Ｐ：0.03％以下，Ｓ：0.
01％以下，Ｔ.Ａｌ：0.1％以下で、残部が鉄および不可
避的不純物である鋼としたものである。ここで、Ｓｉ，
Ｃｒ，Ｍｏ，Ｃｕ，Ｎｉの下限の0％はその元素が無添
加であることを意味する。例えば請求項５で対象とする
鋼の一例としては、これらの元素のうちＳｉとＣｒとＭ
ｏだけを規定範囲内で添加し他のＣｕ，Ｎｉは添加しな
い鋼などが挙げられる。According to a fifth aspect of the present invention, in the first or second aspect of the invention, the target steel is particularly
C: 0.10 to 0.80%, Si: 0 to 0.40% (including no addition), Mn: 0 to 1.0% (including no addition), Cr: 0 to 1.6
% (Including no addition), Mo: 0 to 0.3% (including no addition), Cu: 0 to 0.3% (including no addition), Ni: 0 to 2.0
% (Including no additives), P: 0.03% or less, S: 0.
01% or less, T.Al: 0.1% or less, the balance being iron and steel which is an unavoidable impurity. Where Si,
The lower limit of 0% for Cr, Mo, Cu, and Ni means that the element is not added. For example, as an example of steel targeted in claim 5, Si, Cr and M
Examples of the steel include steel in which only o is added within a specified range and other Cu and Ni are not added.
【００１４】[0014]
【発明の実施の形態】本発明者らは、一般的な中・高炭
素鋼種における鋼板の加工性を改善する手段について詳
細に検討してきた。その結果、一般的な打抜加工性や
曲げ加工性が向上する場合でも、伸びフランジ性等の局
部延性が改善されるとは限らないこと、炭化物を単に
球状化させるだけでは局部延性の安定した改善を図るこ
とはできないこと、そして、伸びフランジ性等の局部
延性は、鋼板中における炭化物の分散形態に大きく依存
し、具体的には炭化物のより一層の均一分散と、平均炭
化物粒径を大きくすることによって改善し得ることを知
見した。BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied in detail means for improving the workability of a steel sheet in a general medium / high carbon steel type. As a result, even when general punching workability or bending workability is improved, local ductility such as stretch flangeability is not always improved, and local ductility is stabilized only by simply spheroidizing carbide. The improvement cannot be achieved, and the local ductility such as stretch flangeability greatly depends on the dispersion form of carbides in the steel sheet.Specifically, the more uniform dispersion of carbides and the average carbide grain size are increased. It was found that it could be improved by doing.
【００１５】伸びフランジ成形加工によって生じる割れ
や亀裂は、加工変形中に生じる非常に局所的な欠陥によ
って敏感に引き起こされるものと考えられる。中・高炭
素鋼板においては、そのような欠陥の生成原因として、
炭化物（セメンタイト）を起点として生じたミクロボイ
ドの成長（連結）が挙げられる。このため、中・高炭素
鋼板の伸びフランジ性を改善するうえで、加工変形時に
おいて上記ミクロボイドの生成・成長をできるだけ抑制
できるような金属組織に調整することが重要であると考
えられる。伸びフランジ性が他の一般的な加工性の改善
に伴って必ずしも同様に改善されないのは、他の加工性
に及ぼす影響の小さいミクロ的な欠陥が、伸びフランジ
性に対しては敏感に影響するためであると推察される。
以下、本発明を特定するための事項について説明する。It is considered that cracks and cracks caused by the stretch flange forming process are sensitively caused by very local defects generated during the working deformation. In medium and high carbon steel sheets, the cause of such defects is as follows.
The growth (connection) of microvoids generated from carbide (cementite) as a starting point can be mentioned. For this reason, in order to improve the stretch flangeability of the middle- and high-carbon steel sheets, it is considered important to adjust the metal structure so that the generation and growth of the microvoids can be suppressed as much as possible during work deformation. The reason that stretch flangeability is not always improved with other general workability improvements is that micro defects having a small effect on other workability are sensitive to stretch flangeability. It is presumed that it is.
Hereinafter, matters for specifying the present invention will be described.
【００１６】本発明では、Ｃ：0.10〜0.80質量％を含有
する中・高炭素鋼を対象とする。Ｃは炭素鋼においては
最も基本となる合金元素であり、その含有量によって焼
入れ硬さおよび炭化物量が大きく変動する。Ｃ含有量が
0.10質量％以下の鋼では、各種機械構造用部品に適用す
るうえで十分な焼入れ硬さが得られない。一方、Ｃ含有
量が0.80質量％を超えると、熱間圧延後の靱性が低下し
て鋼帯の製造性・取扱い性が悪くなるとともに、焼鈍後
においても十分な延性が得られないため、加工度の高い
部品への適用が困難になる。したがって、本発明では適
度な焼入れ硬さと加工性を兼ね備えた素材鋼板を提供す
る観点から、Ｃ含有量が0.10〜0.80質量％の範囲の鋼を
対象とする。なお、Ｃ含有量が低くなるほど局部延性は
一層改善される。このため、伸びフランジ性を特に重視
する用途ではＣ含有量が0.1〜0.5質量％の鋼を使用する
ことが望ましい。The present invention is directed to a medium / high carbon steel containing 0.10 to 0.80% by mass of C. C is the most basic alloying element in carbon steel, and the quenching hardness and the amount of carbide greatly vary depending on its content. C content
If the steel is 0.10% by mass or less, sufficient quench hardness cannot be obtained for application to various machine structural parts. On the other hand, if the C content exceeds 0.80% by mass, the toughness after hot rolling is reduced and the productivity and handleability of the steel strip deteriorates, and sufficient ductility cannot be obtained even after annealing. It becomes difficult to apply to parts with high degree. Therefore, in the present invention, from the viewpoint of providing a material steel sheet having both appropriate quenching hardness and workability, steel having a C content in the range of 0.10 to 0.80 mass% is targeted. Note that the lower the C content is, the more the local ductility is improved. For this reason, it is desirable to use steel having a C content of 0.1 to 0.5% by mass in applications in which the stretch flangeability is particularly important.
【００１７】Ｓは、ＭｎＳ系介在物を形成する元素であ
る。この介在物の量が多くなると局部延性が劣化するの
で、鋼中のＳ含有量はできるだけ低減することが望まし
い。本発明で規定する炭化物分散形態を実現させれば、
Ｓ含有量を特別に低減していない一般的な市販鋼に対し
ても伸びフランジ性の向上効果は得られる。しかし、C
含有量が0.80質量％近くまで高くなった場合でも、高い
局部延性を安定して確保するためには、Ｓ含有量を0.01
質量％以下に低減した鋼を用いるのが望ましい。本願発
明ではそのような観点からＳ含有量を0.01質量％以下に
規定した。S is an element forming MnS-based inclusions. If the amount of the inclusions increases, the local ductility deteriorates. Therefore, it is desirable to reduce the S content in steel as much as possible. By realizing the carbide dispersion form defined in the present invention,
The effect of improving stretch flangeability can be obtained even for general commercial steel in which the S content is not particularly reduced. But C
Even when the content increases to nearly 0.80 mass%, in order to stably secure high local ductility, the S content must be 0.01%.
It is desirable to use steel reduced to less than mass%. In the present invention, the S content is set to 0.01% by mass or less from such a viewpoint.
【００１８】Ｐは、延性や靱性を劣化させるので、0.03
質量％以下の含有量とすることが望ましい。Ａｌは溶鋼
の脱酸剤として添加されるが、鋼中のＴ.Ａｌ量が0.1質
量％を超えると鋼の清浄度が損なわれて鋼板に表面疵が
発生しやすくなるので、Ｔ.Ａｌ含有量は0.1質量％以下
とすることが望ましい。P deteriorates ductility and toughness.
The content is desirably not more than mass%. Al is added as a deoxidizing agent for molten steel. However, if the amount of T.Al in the steel exceeds 0.1% by mass, the cleanliness of the steel is impaired and surface defects are likely to occur on the steel sheet. The amount is desirably 0.1% by mass or less.
【００１９】Ｓｉは、局部延性に対して影響の大きい元
素の１つである。Ｓｉを過剰に添加すると固溶強化作用
によりフェライトが硬化し、成形加工時に割れ発生の原
因となる。またＳｉ含有量が増加すると製造過程で鋼板
表面にスケール疵が発生する傾向を示し、表面品質の低
下を招く。そこでＳｉを添加するに際しては0.40質量％
以下の含有量となるようにする。加工性を特に重視する
用途ではＳｉ含有量は0.1質量％以下とすることが望ま
しい。Ｍｎは、鋼板の焼入性を高め、強靭化にも有効な
添加元素であるので、焼入性向上のためには添加するこ
とが望ましいが、1.0質量％を超えて多量に含有させる
とフェライトが硬化し、加工性の劣化を招く。そこで、
Ｍｎは1.0質量％以下の範囲で含有させることが望まし
い。Si is one of the elements having a large effect on local ductility. If Si is added excessively, the ferrite hardens due to the solid solution strengthening action, which causes cracking during molding. Further, when the Si content increases, a scale flaw tends to occur on the surface of the steel sheet during the manufacturing process, which causes a decrease in surface quality. Therefore, when adding Si, 0.40 mass%
The content should be as follows. In applications where workability is particularly important, the Si content is desirably 0.1% by mass or less. Mn is an additional element that enhances the hardenability of the steel sheet and is also effective for toughening. Therefore, it is desirable to add Mn to improve the hardenability. Hardens and causes deterioration in workability. Therefore,
Mn is desirably contained in a range of 1.0% by mass or less.
【００２０】また本発明では必要に応じてＣｒ，Ｍｏ，
Ｃｕ，Ｎｉ等の元素を添加して各特性の改善を図った鋼
を使用できる。Ｃｒは、焼入れ性を改善するとともに焼
戻し軟化抵抗を大きくする元素である。しかし、1.6質
量％を超える多量のＣｒが含まれるとＡ1点以下での長
時間焼鈍やＡ1点以上の加熱を利用した焼鈍を施しても
軟質化しにくく焼入れ前のプレス成形性や加工性が劣化
するようになる。したがってＣｒを添加する場合は1.6
質量％以下の範囲とする。Ｍｏは、少量の添加でＣｒと
同様に焼入れ性・焼戻し軟化抵抗の改善に寄与する。し
かし、0.3質量％を超える多量のＭｏが含まれるとＡ1点
以下での長時間焼鈍やＡ1点以上の加熱を利用した焼鈍
を施しても軟質化しにくく焼入れ前のプレス成形性や加
工性が劣化するようになる。したがってＭｏを添加する
場合は0.3質量％以下の範囲とする。Ｃｕは、熱延中に
生成する酸化スケールの剥離性を向上させるので、鋼板
の表面性状の改善に有効である。しかし、0.3質量％以
上含有させると溶融金属脆化により鋼板表面に微細なク
ラックが生じやすくなるので、Ｃｕは0.3質量％以下の
範囲で添加できる。Ｃｕ含有量の好ましい範囲は0.10〜
0.15質量％である。Ｎｉは、焼入れ性を改善するととも
に低温脆性を防止する合金成分である。またＮｉは、Ｃ
ｕ添加によって問題となる溶融金属脆化の悪影響を打ち
消す作用を示すので、特にＣｕを約0.2％以上添加する
場合にはＣｕ添加量と同程度のＮｉを添加することが極
めて効果的である。しかし、2.0質量％を超える多量の
Ｎｉが含まれるとＡ1点以下での長時間焼鈍やＡ1点以上
の加熱を利用した焼鈍を施しても軟質化しにくく焼入れ
前のプレス成形性や加工性が劣化するようになる。した
がってＮｉを添加する場合は2.0質量％以下の範囲とす
る。In the present invention, Cr, Mo,
Steel in which various properties are improved by adding elements such as Cu and Ni can be used. Cr is an element that improves hardenability and increases temper softening resistance. However, long-time annealing and press formability before softening hardly hardened even annealed using heated above A 1 point and workability below the A 1 point contains a large amount of Cr exceeding 1.6 wt% Deteriorates. Therefore, when Cr is added, 1.6
Mass% or less. Mo contributes to improvement of hardenability and tempering softening resistance similarly to Cr when added in a small amount. However, a large amount of long annealing and press formability before quenching hardly softened even annealed using heated above A 1 point and workability at Mo below The inclusion of A 1 point in excess of 0.3 mass% Deteriorates. Therefore, when Mo is added, the content is set to a range of 0.3% by mass or less. Cu improves the releasability of the oxide scale generated during hot rolling, and is therefore effective in improving the surface properties of the steel sheet. However, when the content is 0.3% by mass or more, fine cracks are easily generated on the steel sheet surface due to the embrittlement of molten metal. Therefore, Cu can be added in a range of 0.3% by mass or less. The preferred range of the Cu content is 0.10 to
0.15% by mass. Ni is an alloy component that improves hardenability and prevents low-temperature brittleness. Ni is C
Since the effect of counteracting the adverse effect of molten metal embrittlement, which is a problem due to the addition of u, is exhibited, it is extremely effective to add approximately the same amount of Cu as Cu, especially when adding about 0.2% or more of Cu. However, 2.0 wt% more than a large amount of long annealing and softening be annealed using heated above A 1 point and hardly before quenching press formability and workability in Ni below The inclusion of A 1 point Deteriorates. Therefore, when adding Ni, the content is set to 2.0% by mass or less.
【００２１】次に、本発明鋼板の金属組織を特定するた
めの事項について説明する。Next, items for specifying the metal structure of the steel sheet of the present invention will be described.
【００２２】〔炭化物分散度〕炭化物分散度は先に定義
したとおりであり、フェライト中に存在している炭化物
の分散の状態を評価する指標となるものである。この炭
化物分散度の値が小さいほど各区画の炭化物数のばらつ
きが小さく、炭化物の分散が均一であることを意味す
る。なお、数値の信頼性を高めるために、350区画分の
炭化物数を測定した。[Carbide Dispersion] The carbide dispersion is as defined above and serves as an index for evaluating the state of dispersion of carbides present in ferrite. The smaller the value of the degree of carbide dispersion, the smaller the variation in the number of carbides in each section, which means that the dispersion of carbides is uniform. Note that the number of carbides in 350 sections was measured in order to increase the reliability of the numerical values.
【００２３】炭化物の分散状態を立体的に正確に捉えて
規定することは難しく、また製品鋼板の適否を判定する
うえでも煩雑である。これに対し、鋼板断面の平面的な
金属組織を観察することは容易である。本発明者らは、
鋼板断面の金属組織の中で観察される炭化物について、
上記のように分散度を捉えたとき、鋼板の局部延性に対
する炭化物分散度の影響を適切に評価できることを確認
した。そして、炭化物分散度が｛７５―４７×(Ｃ％)
(2/3)｝％以下では、その鋼板は高い局部延性を示すこ
とを見出した。It is difficult to determine the dispersion state of carbides three-dimensionally and accurately, and it is also troublesome to judge the suitability of the product steel sheet. On the other hand, it is easy to observe the planar metal structure of the steel plate cross section. We have:
Regarding carbide observed in the metal structure of the steel sheet cross section,
When the degree of dispersion was grasped as described above, it was confirmed that the influence of the degree of carbide dispersion on the local ductility of the steel sheet could be appropriately evaluated. And the degree of dispersion of carbide is $ 75-47 x (C%)
Below (2/3) ｝%, the steel sheet was found to exhibit high local ductility.
【００２４】炭化物分散度が大きい(分散が不均一)場合
には、炭化物が密に存在する部分において、変形に伴う
炭化物を起点としたミクロボイドの生成・連結が助長さ
れ、これが割れの原因となるのに対して、炭化物分散度
が小さい(分散が均一)場合には炭化物を起点としたミク
ロボイドの生成・連結が抑制されて局部延性が向上する
と考えられる。When the degree of dispersion of the carbide is large (dispersion is nonuniform), the generation and connection of microvoids starting from the carbide accompanying the deformation are promoted in the portion where the carbide is densely present, which causes cracking. On the other hand, when the degree of dispersion of the carbide is small (the dispersion is uniform), it is considered that the generation and connection of microvoids originating from the carbide are suppressed and the local ductility is improved.
【００２５】〔平均炭化物粒径〕炭化物の平均粒径を大
きくすることによっても局部延性は顕著に改善されるこ
とが確認された。鋼中の炭素量は一定であるから、平均
炭化物粒径の増大は炭化物総数の減少を意味する。炭化
物総数が減少すれば、個々の炭化物を起点として生成し
たミクロボイドの連結が抑制され、これが局部延性の顕
著な向上に寄与するものと考えられる。[Average Carbide Particle Size] It was confirmed that the local ductility was significantly improved by increasing the average particle size of the carbide. Since the amount of carbon in the steel is constant, an increase in the average carbide particle size means a decrease in the total number of carbides. If the total number of carbides is reduced, it is considered that the connection of microvoids generated from individual carbides is suppressed, and this contributes to remarkable improvement in local ductility.
【００２６】平均炭化物粒径は、鋼板断面の金属組織観
察において、観察視野内の個々の炭化物について測定し
た円相当径を全測定炭化物について平均した値をいう。
具体的には個々の炭化物について面積を測定し、その面
積から円相当径を算出する。面積の測定は画像処理装置
を用いて行うことができる。そして測定した全ての炭化
物の円相当径の総和を求め、その総和を測定炭化物の総
数で除した値を平均炭化物粒径とする。数値の信頼性を
高めるために、観察視野は測定炭化物総数が300個以上
となる領域とする。The average carbide particle diameter means a value obtained by averaging the equivalent circle diameters measured for individual carbides in the observation field of view for all the measured carbides in the observation of the metal structure of the cross section of the steel sheet.
Specifically, the area of each carbide is measured, and the equivalent circle diameter is calculated from the area. The measurement of the area can be performed using an image processing device. Then, the sum of the circle equivalent diameters of all the measured carbides is determined, and the value obtained by dividing the sum by the total number of the measured carbides is defined as the average carbide particle diameter. In order to increase the reliability of numerical values, the observation visual field is set to an area where the total number of measured carbides is 300 or more.
【００２７】本発明者は詳細な伸びフランジ成形実験の
結果、局部延性の観点からは、先に定義した炭化物分散
度を｛７５―４７×(Ｃ％)(2/3)｝％以下とし、更に平
均炭化物粒径を0.4μｍ以上とした場合に、局部延性が
さらに向上することを見出した。しかし、平均炭化物粒
径を1.2μｍ以上に粗大化させても局部延性向上の効果
は小さくなるうえ、平均炭化物粒径を1.2μｍ以上に粗
大化させるには長時間の焼鈍を施す必要があり、経済的
なデメリットを生ずる。したがって、本発明では鋼板中
の平均炭化物粒径を0.4〜1.2μｍの範囲に規定した。As a result of a detailed stretch flange forming experiment, the present inventor found that from the viewpoint of local ductility, the carbide dispersity defined above was set to {75-47 × (C%) (2/3) }% or less, Further, it has been found that when the average carbide particle size is 0.4 μm or more, the local ductility is further improved. However, even if the average carbide particle size is coarsened to 1.2 μm or more, the effect of improving local ductility is reduced, and it is necessary to perform long-time annealing to coarsen the average carbide particle size to 1.2 μm or more. This has economic disadvantages. Therefore, in the present invention, the average carbide particle size in the steel sheet is specified in the range of 0.4 to 1.2 μm.
【００２８】[0028]
【実施例】表１に示す化学成分の鋼を溶製した。表中の
焼入れ硬さは、供試材をそのまま900℃で5分間保持した
後水焼入れした場合の硬さを示した。この焼入れ硬さは
一般的な焼入れ処理によって得られる鋼材本来の硬度を
比較したものであり、本発明にかかる鋼板の焼入れ性を
示すものではない。EXAMPLES Steel having the chemical components shown in Table 1 was melted. The quenching hardness in the table indicates the hardness when the test material was kept at 900 ° C. for 5 minutes and then water-quenched. This quenching hardness is a comparison of the original hardness of a steel material obtained by a general quenching treatment, and does not indicate the quenchability of the steel sheet according to the present invention.
【００２９】[0029]
【表１】 [Table 1]
【００３０】表１のうちＡ鋼は、Ｃ量が0.07質量％と低
いので、焼入れ後の硬さが低く、機械部品として必要な
硬度が得られないものであった。Ａ鋼を除く鋼板につい
て、熱延コイル巻取温度を種々変化させた熱間圧延を行
い熱延組織を変化させた。得られた熱延板は、酸洗後、
種々の条件で冷延や焼鈍を施し、鋼板の炭化物分散度、
平均炭化物粒径を変化させた。その後、引張試験，切欠
引張試験，穴拡げ試験に供した。In Table 1, Steel A had a low C content of 0.07% by mass, so that the hardness after quenching was low, and the required hardness as a mechanical part could not be obtained. With respect to the steel sheets except steel A, hot rolling was performed by changing the coiling temperature of the hot-rolled coil variously to change the hot-rolled structure. The obtained hot rolled sheet is pickled,
Cold rolling and annealing under various conditions, the degree of carbide dispersion of the steel sheet,
The average carbide particle size was varied. Then, it was subjected to a tensile test, a notch tensile test, and a hole expansion test.
【００３１】炭化物分散度は、走査電子顕微鏡により鋼
板断面の一定領域内を観察し、画像処理装置（ニレコ社
製、ＬＵＺＥＸ IIIＵ）を利用して、観察視野を10μm
×10μmのメッシュに分割して、その各区画中に存在す
る炭化物数を350区画分測定し、１区画当たりの炭化物
数の標準偏差を１区画当たりの平均炭化物数で割った10
0分率を炭化物分散度として算出した。The degree of dispersion of the carbide is determined by observing a predetermined area of the cross section of the steel sheet with a scanning electron microscope and using an image processing apparatus (Luzex IIIU, manufactured by Nireco Co., Ltd.) to obtain an observation field of 10 μm.
The mesh was divided into a mesh of × 10 μm, the number of carbides present in each section was measured for 350 sections, and the standard deviation of the number of carbides per section was divided by the average number of carbides per section.
The 0 fraction was calculated as the degree of carbide dispersion.
【００３２】平均炭化物粒径は、走査電子顕微鏡により
鋼板断面の一定領域内を観察し、画像処理装置（ニレコ
社製、ＬＵＺＥＸ IIIＵ）を利用して、個々の炭化物の
円相当径を算出し、それを全測定炭化物について平均し
て求めた。その際、測定炭化物総数は300〜1000個の範
囲であった。The average carbide particle diameter is obtained by observing a predetermined area of the steel plate cross section with a scanning electron microscope and calculating the circle equivalent diameter of each carbide using an image processing device (LUZEX IIIU, manufactured by Nireco Co.) It was averaged for all measured carbides. At that time, the total number of measured carbides was in the range of 300 to 1,000.
【００３３】引張試験は、JIS 5号引張試験片を用い、
平行部の標点間距離を50ｍｍとして行った。切欠引張試
験は、JIS 5号引張試験片の平行部長手方向中央位置に
おける幅方向両サイドに開き角45°，深さ2ｍｍのＶノ
ッチを形成した試験片を用いて引張試験を行う方法で行
った。Ｖノッチを含む標点間距離5ｍｍに対する伸び率
を破断後に求め、その伸び率を切欠引張伸びＥｌvとし
た。In the tensile test, a JIS No. 5 tensile test piece was used.
The measurement was performed with the distance between the reference points of the parallel portion being 50 mm. The notch tensile test is performed by a method in which a tensile test is performed using a V-notch with an opening angle of 45 ° and a depth of 2 mm on both sides in the width direction at the center of the parallel part longitudinal direction of the JIS No. 5 tensile test piece. Was. The elongation percentage with respect to the gauge length of 5 mm including the V notch was determined after breaking, and the elongation percentage was defined as the notch tensile elongation Elv.
【００３４】穴拡げ試験は、150ｍｍ角の鋼板の中央部
にクリアランス20％にて10ｍｍ(ｄ0)の穴を打抜いた
後、その穴部について、50ｍｍφ球頭ポンチにて押し上
げる方法で行い、穴周囲に亀裂が発生した時点での穴径
ｄを測定して、次式で定義される穴拡げ率λ(％)を求め
た。 λ＝(ｄ−ｄ0)／ｄ0×100 これらＥｌv値およびλ値は局部延性を表す指標であ
り、伸びフランジ性を定量的に評価し得るものである。
これらの試験結果を金属組織と併せて表２に示す。The hole expansion test is performed by punching a 10 mm (d0) hole with a clearance of 20% in the center of a 150 mm square steel plate, and pushing up the hole with a 50 mmφ ball-head punch. The hole diameter d at the time of occurrence of a crack in the periphery was measured, and the hole expansion ratio λ (%) defined by the following equation was obtained. λ = (d−d0) / d0 × 100 These Elv value and λ value are indexes indicating local ductility, and can quantitatively evaluate stretch flangeability.
Table 2 shows the results of these tests together with the metal structure.
【００３５】[0035]
【表２】 [Table 2]
【００３６】表２において、比較例(No.2,4,7,11,18)の
鋼は、分散度がＤ値よりも大きいため、Ｅｌv値，λ値
とも他のものより低い。炭化物分散度が本発明で規定す
るＤ値以下である本発明例１（No.1,3,8,12,17）は、比
較例と比べていずれもＥｌv値およびλ値が向上してお
り優れた局部延性を示した。さらに炭化物分散度がＤ値
以下であり、かつ平均炭化物粒径が0.4〜1.2μｍの範囲
にある本発明例２(No.5,6,9,10,13,14,15,16,19)では、
Ｅｌv値，λ値とも、同程度のＣ量のNo.1と比べてより
高い値を示した。また、同程度のＣ量であるＥ鋼とＦ鋼
を比較すると、Ｓ量が少ないＦ鋼の方がＥｌv値，λ値
ともに高い値を示した。In Table 2, the steels of Comparative Examples (Nos. 2, 4, 7, 11, and 18) have a higher degree of dispersion than the D value, so that both the Elv value and the λ value are lower than those of the other steels. Inventive Example 1 (Nos. 1, 3, 8, 12, and 17) in which the degree of dispersion of carbides is equal to or less than the D value specified in the present invention, the Elv value and the λ value are all higher than those of Comparative Examples. It showed excellent local ductility. In addition, the present invention example 2 (No. 5, 6, 9, 10, 13, 14, 15, 16, 19) in which the degree of carbide dispersion is not more than the D value and the average carbide particle size is in the range of 0.4 to 1.2 μm. Then
Both the Elv value and the λ value showed higher values than No. 1 having the same C content. Further, when comparing the steel E and the steel F having the same C content, the steel F having a small S content showed higher values for both the Elv value and the λ value.
【００３７】図１は、表２の結果について、Ｃ含有量と
λ値の関係をプロットしたものである。Ｃ含有量が同じ
レベルであっても、本発明で規定した範囲に金属組織が
厳密にコントロールされたものは、λ値（局部延性）が
著しく向上していることがわかる。中でも、炭化物分散
度がＤ値以下であることに加えて、平均炭化物粒径が0.
4〜1.2μｍの範囲にある本発明例２はさらにλ値が向上
している。FIG. 1 plots the relationship between the C content and the λ value for the results in Table 2. It can be seen that, even when the C content is at the same level, those having a metal structure strictly controlled within the range specified in the present invention have significantly improved λ value (local ductility). Among them, in addition to the carbide dispersity being equal to or less than the D value, the average carbide particle size is 0.1%.
Inventive Example 2 in the range of 4 to 1.2 μm has further improved λ value.
【００３８】[0038]
【発明の効果】以上のように、本発明では、「炭化物分
散度」を適正な範囲に特定し、優れた局部延性を有する
中・高炭素鋼板を実現した。したがって、本発明に係る
鋼板は、従来の中・高炭素鋼板より局部変形能が著しく
向上したことにより部品形状が複雑な各種機械部品の素
材として好適に用いられ、特に伸びフランジ成形加工用
鋼板として非常に適している。また同時に、軟質化によ
りプレス金型寿命の向上にも貢献できる。As described above, according to the present invention, the "carbide dispersity" is specified within an appropriate range, and a medium / high carbon steel sheet having excellent local ductility is realized. Accordingly, the steel sheet according to the present invention is suitably used as a material for various mechanical parts having complicated component shapes due to significantly improved local deformability compared to conventional medium- and high-carbon steel sheets, particularly as a steel sheet for stretch flange forming. Very suitable. At the same time, the softening can contribute to the improvement of the life of the press die.
【図１】本発明例と比較例の鋼板におけるＣ含有量とλ
値の関係を表すグラフ。FIG. 1 shows C content and λ in steel sheets of the present invention and comparative examples.
A graph showing the relationship between values.
Claims (5)
記(a)で定義される炭化物分散度が｛７５―４７×(Ｃ
％)(2/3)｝％以下であるように炭化物がフェライト中に
分散している局部延性に優れた中・高炭素鋼板。 (a)炭化物分散度：鋼板断面の金属組織観察において、
観察視野を10μm×10μmのメッシュに分割して、その各
区画中に存在する炭化物数を測定し、１区画当たりの炭
化物数の標準偏差を１区画当たりの平均炭化物数で割っ
た100分率（％）をいう。C: 0.10 to 0.80 mass% of steel having a carbide dispersity defined by the following (a) of {75-47 × (C
( %) (2/3) Medium- and high-carbon steel sheets with excellent local ductility in which carbides are dispersed in ferrite so as to be 以下% or less. (a) Carbide dispersion degree: In observing the metallographic structure of the steel sheet cross section,
The observation field of view was divided into a mesh of 10 μm × 10 μm, the number of carbides present in each section was measured, and the standard deviation of the number of carbides per section was divided by the average number of carbides per section, which was 100 fraction ( %).
0.4〜1.2μｍである請求項１に記載の局部延性に優れた
中・高炭素鋼板。 (b)平均炭化物粒径：鋼板断面の金属組織観察におい
て、観察視野内の個々の炭化物について測定した円相当
径を全測定炭化物について平均した値をいう。ただし、
観察視野は炭化物総数が300個以上となる領域とする。2. An average carbide particle size defined by the following (b):
The medium / high carbon steel sheet having excellent local ductility according to claim 1, which has a thickness of 0.4 to 1.2 µm. (b) Average carbide particle size: A value obtained by averaging the equivalent circle diameters measured for individual carbides in the observation visual field for all measured carbides in the observation of the metal structure of the cross section of the steel sheet. However,
The observation visual field is an area where the total number of carbides is 300 or more.
10〜0.80質量％，S:0.01％以下である局部延性に優れた
中・高炭素鋼板。3. The steel according to claim 1, wherein the steel is C: 0.
Medium to high carbon steel sheet with excellent local ductility of 10 to 0.80 mass% and S: 0.01% or less.
10〜0.80質量％，Ｓｉ：0〜0.40％（無添加を含む），
Ｍｎ：0〜1.0％（無添加を含む）を含有し、Ｐ：0.03％
以下，Ｓ：0.01％以下，Ｔ.Ａｌ：0.1％以下で、残部が
鉄および不可避的不純物である局部延性に優れた中・高
炭素鋼板。4. The steel according to claim 1, wherein the steel has a carbon content of C: 0.
10 to 0.80% by mass, Si: 0 to 0.40% (including no addition),
Mn: 0 to 1.0% (including no addition), P: 0.03%
A medium / high carbon steel sheet having excellent local ductility, with S: 0.01% or less and T.Al: 0.1% or less, with the balance being iron and inevitable impurities.
10〜0.80質量％，Ｓｉ：0〜0.40％（無添加を含む），
Ｍｎ：0〜1.0％（無添加を含む），Ｃｒ：0〜1.6％（無
添加を含む），Ｍｏ：0〜0.3％（無添加を含む），Ｃ
ｕ：0〜0.3％（無添加を含む），Ｎｉ：0〜2.0％（無添
加を含む）を含有し、Ｐ：0.03％以下，Ｓ：0.01％以
下，Ｔ.Ａｌ：0.1％以下で、残部が鉄および不可避的不
純物である局部延性に優れた中・高炭素鋼板。5. The steel according to claim 1, wherein the steel is C: 0.
10 to 0.80% by mass, Si: 0 to 0.40% (including no addition),
Mn: 0 to 1.0% (including no addition), Cr: 0 to 1.6% (including no addition), Mo: 0 to 0.3% (including no addition), C
u: 0 to 0.3% (including no addition), Ni: 0 to 2.0% (including no addition), P: 0.03% or less, S: 0.01% or less, T. Al: 0.1% or less, Medium and high carbon steel sheets with excellent local ductility, with the balance being iron and inevitable impurities.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000028282A JP2001220643A (en) | 2000-02-04 | 2000-02-04 | Medium or high carbon steel sheet excellent in local ductility |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000028282A JP2001220643A (en) | 2000-02-04 | 2000-02-04 | Medium or high carbon steel sheet excellent in local ductility |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2001220643A true JP2001220643A (en) | 2001-08-14 |
Family
ID=18553713
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2000028282A Withdrawn JP2001220643A (en) | 2000-02-04 | 2000-02-04 | Medium or high carbon steel sheet excellent in local ductility |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2001220643A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012147863A1 (en) * | 2011-04-27 | 2012-11-01 | 新日本製鐵株式会社 | Steel sheet for hot stamping members and method for producing same |
| JP2013057114A (en) * | 2011-09-09 | 2013-03-28 | Nippon Steel & Sumitomo Metal Corp | Medium carbon steel plate having excellent workability and hardenability and method for producing the same |
| US11624403B2 (en) * | 2016-11-09 | 2023-04-11 | Schaeffler Technologies AG & Co. KG | Method for producing a rolling bearing ring having an improved robustness against the formation of white etching cracks (WEC) |
-
2000
- 2000-02-04 JP JP2000028282A patent/JP2001220643A/en not_active Withdrawn
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012147863A1 (en) * | 2011-04-27 | 2012-11-01 | 新日本製鐵株式会社 | Steel sheet for hot stamping members and method for producing same |
| JP5472531B2 (en) * | 2011-04-27 | 2014-04-16 | 新日鐵住金株式会社 | Steel sheet for hot stamp member and manufacturing method thereof |
| US9617624B2 (en) | 2011-04-27 | 2017-04-11 | Nippon Steel Sumitomo Metal Corporation | Steel sheet for hot stamping member and method of producing same |
| JP2013057114A (en) * | 2011-09-09 | 2013-03-28 | Nippon Steel & Sumitomo Metal Corp | Medium carbon steel plate having excellent workability and hardenability and method for producing the same |
| US11624403B2 (en) * | 2016-11-09 | 2023-04-11 | Schaeffler Technologies AG & Co. KG | Method for producing a rolling bearing ring having an improved robustness against the formation of white etching cracks (WEC) |
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