JP3188787B2 - Method for producing high-strength hot-rolled steel sheet with excellent hole expandability and ductility - Google Patents
Method for producing high-strength hot-rolled steel sheet with excellent hole expandability and ductilityInfo
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- JP3188787B2 JP3188787B2 JP08094593A JP8094593A JP3188787B2 JP 3188787 B2 JP3188787 B2 JP 3188787B2 JP 08094593 A JP08094593 A JP 08094593A JP 8094593 A JP8094593 A JP 8094593A JP 3188787 B2 JP3188787 B2 JP 3188787B2
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- steel sheet
- ductility
- strength
- hole expandability
- rolled steel
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- Heat Treatment Of Sheet Steel (AREA)
Description
【０００１】[0001]
【産業上の利用分野】本発明は主としてプレス加工され
る自動車足廻り部品等を対象とし、１．４〜６．０mm程
度の板厚で、５９０〜７８０Ｎ／mm2 の引張強度を有
し、穴拡げ性と延性に優れた熱延高強度鋼板の製造方法
に関するものである。BACKGROUND OF THE INVENTION The present invention is primarily directed to automotive underbody parts or the like which is press working a plate thickness of about 1.4～6.0Mm, has a tensile strength of 590~780N / mm 2, The present invention relates to a method for producing a hot-rolled high-strength steel sheet having excellent hole expandability and ductility.
【０００２】[0002]
【従来の技術】近年、自動車の燃費改善対策としての車
体軽量化、部品の一体成形によるコストダウンのニーズ
が強まり、プレス加工性に優れた熱延高強度鋼板の開発
が進められてきた。従来、加工用熱延鋼板としては、フ
ェライト・マルテンサイト組織からなるＤｕａｌ Ｐｈ
ａｓｅ鋼板が知られている。Ｄｕａｌ Ｐｈａｓｅ鋼板
は、軟質なフェライト相と硬質なマルテンサイト相の複
合組織で構成されており、著しく硬度の異なる両相の界
面からボイドが発生して割れを生じるため穴拡げ性に劣
る問題があり、足廻り部品等の高い穴拡げ性が要求され
る用途には、不向きであった。2. Description of the Related Art In recent years, there has been an increasing need for weight reduction of a vehicle body as a measure for improving fuel efficiency of automobiles and cost reduction by integral molding of parts, and development of a hot-rolled high-strength steel sheet excellent in press workability has been promoted. Conventionally, as a hot-rolled steel sheet for processing, Dual Ph having a ferrite-martensite structure has been used.
ase steel plates are known. Dual Phase steel sheets are composed of a composite structure of a soft ferrite phase and a hard martensite phase, and voids are generated from the interface between the two phases with remarkably different hardness, causing cracks. It is not suitable for applications requiring high hole expandability, such as underbody parts.
【０００３】このため特開平４−８８１２５号公報、特
開平３−１８０４２６号公報にベーナイトを主体とした
組織から構成される、穴拡げ性の優れた熱延鋼板の製造
方法が提案されている。しかしながら自動車のさらなる
軽量化指向、部品の複雑化等を背景に上記技術では対応
しきれない高度な加工性、さらなる高強度化が求められ
ている。For this reason, Japanese Patent Application Laid-Open Nos. 4-88125 and 3-180426 propose a method for producing a hot-rolled steel sheet having a structure mainly composed of bainite and having excellent hole expanding properties. However, due to the trend toward further weight reduction of automobiles and the complexity of parts, etc., there is a demand for advanced workability and higher strength that cannot be met by the above-mentioned technology.
【０００４】また自動車の足廻り部品では絶えず繰り返
し疲労を受けているため、鋼板の疲労特性の劣化が大き
な問題となっている。従来の穴拡げ性に優れた鋼板はベ
ーナイト組織が主体であるため疲労特性に劣っており、
穴拡げ性と疲労特性の両立に着目した鋼板は見当らな
い。[0004] Further, since the underbody parts of automobiles are constantly subjected to repeated fatigue, deterioration of the fatigue properties of the steel sheet has become a serious problem. Conventional steel sheets with excellent hole expandability are inferior in fatigue properties because of the main bainite structure,
There is no steel sheet that focuses on both hole expandability and fatigue characteristics.
【０００５】[0005]
【発明が解決しようとする課題】本発明は強度５９０〜
７８０Ｎ／mm2 クラスで、穴拡げ比が５９０Ｎ／mm2 ク
ラスで２．１以上、７８０Ｎ／mm2 クラスで１．８以
上、伸びが５９０Ｎ／mm2クラスでＥｌ≧２６％、７８
０Ｎ／mm2 クラスでＥｌ≧２０％の鋼板を経済的に製造
する方法を提供するものである。The present invention has a strength of 590 to 590.
In 780N / mm 2 class, the hole expansion ratio is 590N / mm 2 class 2.1, 780N / mm 2 class 1.8 or more, El ≧ 26% elongation at 590N / mm 2 class, 78
An object of the present invention is to provide a method for economically producing a steel sheet of 0N / mm 2 class and El ≧ 20%.
【０００６】[0006]
【課題を解決するための手段】本発明の要旨は次の通り
である。 （１）重量％でＣ＝０．０１〜０．０８％、Ｓｉ＝０．
３０〜１．５０％、Ｍｎ＝０．５０〜２．５０％、Ｐ≦
０．０３％、Ｓ≦０．００５％を含み、残部Ｆｅおよび
不可避的成分からなる鋼を、圧延終了温度をＡｒ3 変態
点以上とする熱間圧延をし、引き続き２０℃/sec以上の
冷却速度で６５０〜７００℃まで冷却し、該温度で２〜
１５秒間空冷したのち、再度水冷して３５０〜６００℃
で巻取り、鋼組織をフェライトが９０％以上、残ベーナ
イトとすることを特徴とする穴拡げ性と延性に優れた高
強度熱延鋼板の製造方法。The gist of the present invention is as follows. (1) C = 0.01 to 0.08% by weight, Si = 0.
30-1.50%, Mn = 0.50-2.50%, P ≦
A steel containing 0.03%, S ≦ 0.005%, the balance being Fe and unavoidable components is hot-rolled so that the rolling end temperature is equal to or higher than the Ar 3 transformation point, and subsequently cooled at 20 ° C./sec or more. Cool at a speed of 650-700 ° C.
After air cooling for 15 seconds, water cooling again and 350-600 ° C
A method for producing a high-strength hot-rolled steel sheet having excellent hole expandability and ductility, characterized in that the steel structure is made of 90% or more of ferrite and residual bainite.
【０００７】（２）Ｎｂ：０．０１０〜０．０４０％、
Ｔｉ：０．０１０〜０．１５０％からなる強度改善元素
のうち何れか１種または２種を含有する（１）記載の製
造方法。 （３）Ｃａ：０．０００５〜０．０１００％を含有する
（１）記載の製造方法。 （４）Ｎｂ：０．０１０〜０．０４０％、Ｔｉ：０．０
１０〜０．１５０％からなる強度改善元素のうち何れか
１種または２種とＣａ：０．０００５〜０．０１００％
を含有する（１）記載の製造方法。(2) Nb: 0.010-0.040%,
(1) The production method according to (1), wherein one or two of the strength improving elements consisting of 0.010 to 0.150% are contained. (3) The production method according to (1), containing Ca: 0.0005 to 0.0100%. (4) Nb: 0.010-0.040%, Ti: 0.0
Any one or two of the strength improving elements consisting of 10 to 0.150% and Ca: 0.0005 to 0.0100%
(1).
【０００８】[0008]
【作用】以下に本発明の各構成要件の限定理由について
説明する。Ｃは強度確保のため少くとも０．０１％は必
要である。しかし０．０８％を超えると穴拡げ性に有害
な炭化物（セメンタイトまたはパーライト）生成するの
で好ましくない。このため０．０１〜０．０８％とし
た。The reasons for limiting the constituent elements of the present invention will be described below. C is required to be at least 0.01% in order to secure strength. However, if it exceeds 0.08%, carbides (cementite or pearlite) harmful to the hole-expanding property are generated, which is not preferable. Therefore, the content is set to 0.01 to 0.08%.
【０００９】Ｓｉは穴拡げに有害な炭化物の生成を抑え
ポリゴナルフェライトの生成を促し、フェライト主体＋
ベーナイトの複合組織を得るために重要な元素である。
またＳｉは強度と延性を両立させる作用もある。このよ
うな組織を得ること、強度、延性を高めるために０．３
０％以上の添加が必要である。一方、上限は点溶接性、
経済性から１．５％とした。Si suppresses the formation of carbides harmful to hole expansion and promotes the formation of polygonal ferrite.
It is an important element for obtaining the composite structure of bainite.
Si also has the effect of balancing strength and ductility. In order to obtain such a structure, to increase the strength and ductility, 0.3
Addition of 0% or more is required. On the other hand, the upper limit is spot weldability,
It was set to 1.5% in terms of economy.
【００１０】Ｍｎは強度を確保するのに必要な元素であ
り、最低０．５０％の含有が必要である。また焼入れ性
を高め、ベーナイト組織を得るためにも０．５０％以上
の含有が必要である。しかし多量に添加すると帯状の組
織が生成しやすくなるため加工性が劣化する。また経済
性、点溶接性を考慮し、上限は２．５０％とした。Ｐは
溶接性、加工性、２次加工性、靭性の劣化防止のため
０．０３％以下とした。Mn is an element necessary for securing the strength, and must be contained at least 0.50%. Further, in order to enhance the hardenability and obtain a bainite structure, the content must be 0.50% or more. However, when a large amount is added, a band-like structure is easily generated, so that workability is deteriorated. The upper limit is set to 2.50% in consideration of economy and spot weldability. P is set to 0.03% or less to prevent deterioration of weldability, workability, secondary workability, and toughness.
【００１１】ＳはＭｎＳ等の非金属介在物を生成し、穴
拡げ性を劣化させるので含有量は少い程好ましく、０．
００５％以下とした。Ｎｂ，Ｔｉは炭窒化物形成元素で
あり、析出硬化により引張強度の増加に有効である。効
果を有効に発揮させるためには、Ｎｂ，Ｔｉともに少く
とも０．０１％の添加が必要である。しかしこれらの元
素を過多に添加すると、析出強化が過度となり延性が劣
化し、あるいは上記効果が飽和して経済的にも不利であ
るので、添加の上限をＮｂは０．０４０％、Ｔｉは０．
１５０％とする。これらの元素は単独で添加しても効果
があり、また複合添加しても相乗的な効果を得ることが
できるので高強度を得るのに有効である。Since S forms nonmetallic inclusions such as MnS and deteriorates the hole expanding property, the content is preferably as small as possible.
005% or less. Nb and Ti are carbonitride forming elements and are effective in increasing tensile strength by precipitation hardening. In order to effectively exert the effect, it is necessary to add at least 0.01% of both Nb and Ti. However, if these elements are added excessively, precipitation strengthening becomes excessive and ductility is deteriorated, or the above effect is saturated, which is economically disadvantageous. Therefore, the upper limit of addition is 0.040% for Nb and 0% for Ti. .
It shall be 150%. These elements have an effect even if they are added alone, and a synergistic effect can be obtained even if they are added in combination, so that they are effective for obtaining high strength.
【００１２】Ｃａは硫化物系介在物を形態制御し、穴拡
げ性向上に有用で少くとも０．０００５％の添加が必要
である。一方、多量の添加は逆に鋼の清浄度を悪化させ
て穴拡げ性を損うので、上限を０．０１００％とする。[0012] Ca controls the form of sulfide inclusions and is useful for improving hole expandability, and it is necessary to add at least 0.0005%. On the other hand, if a large amount is added, on the contrary, the cleanliness of the steel is deteriorated and the hole expandability is impaired, so the upper limit is made 0.0100%.
【００１３】仕上圧延終了温度はフェライトの生成を防
ぎ穴拡げ性を良好にするためＡｒ3変態点以上とする必
要がある。しかし余り高温になると組織の粗大化による
延性の低下を生じるため９５０℃以下とすることが好ま
しい。冷却速度は穴拡げに有害な炭化物形成を抑制し、
高い穴拡げ比を得るため２０℃/sec以上が必要である。
一方、上限は高い程好ましいが現状の圧延設備の場合、
可能な上限は１５０℃/sec程度である。The finish rolling end temperature must be equal to or higher than the Ar 3 transformation point in order to prevent ferrite formation and improve hole expandability. However, if the temperature is too high, the ductility is reduced due to the coarsening of the structure. Cooling rate suppresses carbide formation harmful to hole expansion,
In order to obtain a high hole expansion ratio, 20 ° C./sec or more is required.
On the other hand, the upper limit is preferably as high as possible, but in the case of the current rolling equipment,
A possible upper limit is about 150 ° C./sec.
【００１４】連続冷却の途中６５０〜７００℃で２〜１
５秒間の空冷は本発明において特に重要な点であり、こ
れによって本発明の特徴であるフェライト主体の組織と
することができる。本発明者等が実験により知見したと
ころでは、穴拡げ性と延性の向上にはフェライト９０％
以上の占積率とすることが必要であり、そのためには上
記温度で２〜１５秒の空冷が必要となる。即ち２秒未満
ではフェライトが充分に生成できず、また１５秒超にな
ると穴拡げに有害なパーライトとセメンタイトが生成す
る。In the course of continuous cooling, 2-1 to 650 to 700 ° C.
Air cooling for 5 seconds is a particularly important point in the present invention, whereby a structure mainly composed of ferrite, which is a feature of the present invention, can be obtained. The present inventors have found from experiments that ferrite 90% is required to improve hole expandability and ductility.
It is necessary to set the above space factor, and for that purpose, air cooling at the above temperature for 2 to 15 seconds is required. That is, ferrite cannot be sufficiently formed if the time is less than 2 seconds, and pearlite and cementite which are harmful to hole expansion will be generated if the time exceeds 15 seconds.
【００１５】巻取温度が３５０℃未満だと穴拡げ性に有
害な硬質のマルテンサイトが発生するため３５０℃以上
とする。一方、上限は６００℃超になると穴拡げ性に有
害なパーライト、セメンタイトが生成するため６００℃
以下とする。このように３５０〜６００℃で巻取ると穴
拡げに有害な組織の発生がなく、前述の６５０〜７００
℃での空冷によって得たフェライト９０％以上の組織の
まま残りの１０％以下を穴拡げ性に害をなさないベーナ
イト組織とすることができ、これにより強度向上に寄与
できる。If the winding temperature is lower than 350 ° C., hard martensite harmful to hole expandability is generated. On the other hand, if the upper limit exceeds 600 ° C., pearlite and cementite, which are harmful to the hole expandability, are formed, so that the upper limit is 600 ° C.
The following is assumed. In this manner, when the film is wound at 350 to 600 ° C., no harmful tissue is generated in the hole expansion, and the above-described 650 to 700 ° C.
The remaining 10% or less of the ferrite structure obtained by air cooling at a temperature of 90 ° C. or more can be a bainite structure that does not impair the hole expandability, thereby contributing to an improvement in strength.
【００１６】以上のような成分と熱延条件の組み合わせ
により、フェライト占積率９０％以上、ベーナイト占積
率１０％以下の混合組織とし、穴拡げ性および延性に優
れた熱延鋼板を得ることができる。By the combination of the above components and hot rolling conditions, a hot-rolled steel sheet having a mixed structure having a ferrite space factor of 90% or more and a bainite space factor of 10% or less and having excellent hole expandability and ductility is obtained. Can be.
【００１７】[0017]
【実施例】表１に示す化学成分組成を有する鋼を転炉溶
製して、連続鋳造にてスラブとし、表２に示す熱延条件
で圧延・冷却し、板厚２．６〜３．２mmの熱延鋼板を得
た。EXAMPLE A steel having the chemical composition shown in Table 1 was melted in a converter and converted into a slab by continuous casting. The slab was rolled and cooled under the hot rolling conditions shown in Table 2 to obtain a sheet thickness of 2.6 to 3. A 2 mm hot-rolled steel sheet was obtained.
【００１８】[0018]
【表１】 [Table 1]
【００１９】[0019]
【表２】 [Table 2]
【００２０】このようにして得られた熱延鋼板につい
て、ＪＩＳ５号片による引張試験、穴拡げ試験、組織観
察を行った。尚、穴拡げ試験は径１２mmの打抜き穴を６
０°円錐ポンチにて押し拡げ、クラックが板厚を貫通し
た時点での穴径（ｄ）と初期穴径（ｄ0 ：１２mm）との
比（ｄ／ｄ0 ）を併せて表２に示した。尚、鋼Ａ〜Ｇは
引張強度５９０Ｎ／mm2 クラス、鋼Ｈ〜Ｊは引張強度７
８０Ｎ／mm2 クラスのものである。The hot-rolled steel sheet thus obtained was subjected to a tensile test using a JIS No. 5 piece, a hole expansion test, and a structure observation. In addition, in the hole expansion test, 6 punched holes with a diameter of 12 mm
Table 2 also shows the ratio (d / d 0 ) between the hole diameter (d) at the time when the crack penetrated the plate thickness and the initial hole diameter (d 0 : 12 mm) by pushing and spreading with a 0 ° conical punch. Was. Steels A to G have a tensile strength of 590 N / mm 2 class, and steels H to J have a tensile strength of 7
It is those of 80N / mm 2 class.
【００２１】しかして表２に示すようにNo．１，２，
３，４，７，８，９は引張強度５９０Ｎ／mm2 クラスの
本発明例であり、穴拡げ比２．２０〜２．４０、伸び２
８〜３２％を示し、またNo．１３，１５は引張強度７８
０Ｎ／mm2 クラスの本発明例であり穴拡げ比１．８０〜
１．８５、伸び２２〜２３％を示し、何れも良好な材質
となっている。一方、本発明の条件を外れた比較例では
伸び、穴拡げ値が不十分なレベルである。However, as shown in Table 2, 1,2,
3, 4, 7, 8, and 9 are examples of the present invention having a tensile strength of 590 N / mm 2 class, and have a hole expansion ratio of 2.20 to 2.40 and an elongation of 2.
No. 8 to 32%. 13 and 15 have a tensile strength of 78
An invention example of 0N / mm 2 class hole expansion ratio 1.80～
1.85, elongation 22 to 23%, all of which are good materials. On the other hand, in the comparative examples out of the conditions of the present invention, the elongation and hole expansion values are at an insufficient level.
【００２２】[0022]
【発明の効果】本発明によれば強度５９０Ｎ／mm2 クラ
スで伸び≧２６％、ｄ／ｄ0 ≧２．１０、強度７８０Ｎ
／mm2 クラスで伸び≧２０、ｄ／ｄ0 ≧１．８という従
来にない優れた強度−穴拡げバランスを有し、かつ、延
性に優れた熱延高強度鋼板を経済的に供給できるように
なったもので、産業上極めて有用なものである。According to the present invention, elongation ≧ 26%, d / d 0 ≧ 2.10 and strength 780 N in a class of strength 590 N / mm 2.
It is possible to economically supply a hot-rolled high-strength steel sheet that has an unprecedented strength-hole expansion balance of elongation ≧ 20 and d / d 0 ≧ 1.8 in the / mm 2 class and has excellent ductility. It is very useful industrially.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 山崎 一正 東海市東海町５−３ 新日本製鐵株式会 社 名古屋製鐵所内 (56)参考文献 特開 平５−80945（ＪＰ，Ａ) 特開 平４−88125（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C21D 9/46,8/02 C22C 38/00 - 38/60 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Kazumasa Yamazaki 5-3 Tokai-cho, Tokai-shi, Nippon Steel Corporation Nagoya Works (56) References JP-A-5-80945 (JP, A) Kaihei 4-88125 (JP, A) (58) Fields investigated (Int. Cl. 7 , DB name) C21D 9 / 46,8 / 02 C22C 38/00-38/60
Claims (4)
度をＡｒ3 変態点以上とする熱間圧延をし、引き続き２
０℃/sec以上の冷却速度で６５０〜７００℃まで冷却
し、該温度で２〜１５秒間空冷したのち、再度水冷して
３５０〜６００℃で巻取り、鋼組織をフェライトが９０
％以上、残ベーナイトとすることを特徴とする穴拡げ性
と延性に優れた高強度熱延鋼板の製造方法。1. C = 0.01 to 0.08% by weight% Si = 0.30 to 1.50% Mn = 0.50 to 2.50% P ≦ 0.03% S ≦ 0.005% The steel comprising the balance of Fe and unavoidable components was hot-rolled so that the rolling end temperature was equal to or higher than the Ar 3 transformation point.
After cooling to 650 to 700 ° C. at a cooling rate of 0 ° C./sec or more, air cooling at that temperature for 2 to 15 seconds, water cooling again and winding at 350 to 600 ° C.
% Or more, and a method for producing a high-strength hot-rolled steel sheet having excellent hole expandability and ductility, characterized by remaining bainite.
有する請求項１記載の製造方法。2. The method according to claim 1, further comprising one or two of the strength improving elements consisting of Nb: 0.010 to 0.040% and Ti: 0.010 to 0.150%.
含有する請求項１記載の製造方法。3. The method according to claim 1, wherein the content of Ca is 0.0005 to 0.0100%.
ａ：０．０００５〜０．０１００％を含有する請求項１
記載の製造方法。4. One or two of the strength improving elements consisting of Nb: 0.010 to 0.040% Ti: 0.010 to 0.150%, C
a: 0.0005 to 0.0100%.
The manufacturing method as described.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08094593A JP3188787B2 (en) | 1993-04-07 | 1993-04-07 | Method for producing high-strength hot-rolled steel sheet with excellent hole expandability and ductility |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08094593A JP3188787B2 (en) | 1993-04-07 | 1993-04-07 | Method for producing high-strength hot-rolled steel sheet with excellent hole expandability and ductility |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH06293910A JPH06293910A (en) | 1994-10-21 |
| JP3188787B2 true JP3188787B2 (en) | 2001-07-16 |
Family
ID=13732637
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP08094593A Expired - Lifetime JP3188787B2 (en) | 1993-04-07 | 1993-04-07 | Method for producing high-strength hot-rolled steel sheet with excellent hole expandability and ductility |
Country Status (1)
| Country | Link |
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| JP (1) | JP3188787B2 (en) |
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| DE60044180D1 (en) * | 1999-09-16 | 2010-05-27 | Jfe Steel Corp | METHOD FOR PRODUCING A THIN STAINLESS STEEL PLATE WITH HIGH STRENGTH |
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-
1993
- 1993-04-07 JP JP08094593A patent/JP3188787B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH06293910A (en) | 1994-10-21 |
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