JP2600537B2 - Manufacturing method of hot-rolled high-strength steel sheet with good hole expansion - Google Patents
Manufacturing method of hot-rolled high-strength steel sheet with good hole expansionInfo
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- JP2600537B2 JP2600537B2 JP25554991A JP25554991A JP2600537B2 JP 2600537 B2 JP2600537 B2 JP 2600537B2 JP 25554991 A JP25554991 A JP 25554991A JP 25554991 A JP25554991 A JP 25554991A JP 2600537 B2 JP2600537 B2 JP 2600537B2
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Description
【０００１】[0001]
【産業上の利用分野】本発明は、孔拡げ性の良い熱延高
張力鋼板の製造方法、特にホィールディスクをはじめと
して、自動車足廻り部品、内板等の自動車部品に好適に
用いることができる引張り強さ80 kgf/mm2クラスの熱延
高張力鋼板の製造方法に関するものである。The present invention can be suitably applied to a method for producing a hot-rolled high-strength steel sheet having good hole-expandability, and particularly to an automobile part such as a wheel disk, an automobile suspension part, and an inner plate. method of manufacturing a hot rolled high tensile steel strength 80 kgf / mm 2 class tensile relates.
【０００２】[0002]
【従来の技術】近年に至り、地球環境問題の重要性の認
識の高まりに伴い、自動車産業においても、燃費低減、
発生CO2 量の低減のために、種々の対策が検討されてき
ている。特に車体軽量化は、効果的な対策と考えられ、
積極的に開発・研究が行われている。そして、材料面か
らは、優れた成形性をもった高強度鋼板の開発が要求さ
れる。2. Description of the Related Art In recent years, with the increasing awareness of the importance of global environmental issues, the automobile industry has been working to reduce fuel consumption,
Various measures have been studied to reduce the amount of generated CO 2 . In particular, reducing body weight is considered an effective measure,
Active development and research. From the viewpoint of materials, development of a high-strength steel sheet having excellent formability is required.
【０００３】かかる高強度鋼板として、低降伏比で、強
度−延性のバランスに優れるフェライト・マルテンサイ
ト組織からなる混合組織鋼が広く知られている。しか
し、このようなフェライト・マルテンサイト混合組織鋼
は、変形の初期割れを生じるため、孔拡げ性に劣るとい
う問題がある。[0003] As such a high-strength steel sheet, a mixed structure steel comprising a ferrite-martensite structure having a low yield ratio and an excellent balance between strength and ductility has been widely known. However, such a ferritic-martensitic mixed-structure steel has a problem in that the initial cracking of the deformation is generated, so that the hole expandability is poor.
【０００４】[0004]
【発明が解決しようとする課題】かかる問題を解決する
手段として、フェライト・ベイナイトの複合組織をもつ
高強度鋼板を使用することが考えられる。例えば、特公
昭62−4450号公報に示されるように、Ｃ−Si−Mn−Cr−
Ti鋼で靱性に優れたフェライト・ベイナイト複合組織を
もつ熱延鋼板の製造方法が示されているが、成分元素の
添加量の孔拡げ性への影響、熱間圧延条件の孔拡げ性へ
の影響は不明である。As a means for solving such a problem, it is conceivable to use a high-strength steel sheet having a composite structure of ferrite and bainite. For example, as disclosed in JP-B-62-4450, C-Si-Mn-Cr-
A method of manufacturing a hot-rolled steel sheet having a ferrite-bainite composite structure with excellent toughness in Ti steel is shown, but the effect of the addition amount of component elements on the hole expansion property and the effect of hot rolling conditions on the hole expansion property are shown. The effect is unknown.
【０００５】「孔拡げ性」とは、打抜き孔をバーリング
成形することで、材料の伸びフランジ成形性を評価する
ものであって、今日のようにハイテン材の円筒部品と構
造部材を一体成形する場合には、自動車の足回り部品、
ホィールディスクなどの用途には必要不可欠の特性であ
る。従来、かかる部品は複数部品を溶接により一体化成
形していたためであって、特に注目されることはなかっ
た。ここに、本発明の目的は、孔拡げ性の良い、引張強
さ80 kgf/mm2の熱延高張力鋼板の製造方法を提供するこ
とである。[0005] The "hole expanding property" is to evaluate the stretch flangeability of a material by burring a punched hole. As in today, a high-tensile cylindrical part and a structural member are integrally formed. In some cases, car undercarriage parts,
This is an indispensable property for applications such as wheel discs. Heretofore, such parts have not been particularly noticed because a plurality of parts have been integrally formed by welding. Here, an object of the present invention is to provide a method for producing a hot-rolled high-tensile steel sheet having good hole expandability and a tensile strength of 80 kgf / mm 2 .
【０００６】[0006]
【課題を解決するための手段】本発明者は、このような
現状を鑑み、Ｃ−Si−Mn−Cr−Ti系鋼に着目し、その鋼
の成分元素の添加量を所定の範囲内とするとともに、熱
間圧延の仕上温度、仕上圧下率、巻取温度を制御するこ
とにより、強度・延性バランスが良好で、しかも孔拡げ
性に優れた熱延鋼板を得ることができることを知り、本
発明を完成した。In view of the above situation, the present inventor has focused on C-Si-Mn-Cr-Ti-based steel and set the amount of the element added to the steel within a predetermined range. In addition to knowing that by controlling the finishing temperature, finishing reduction rate, and winding temperature of hot rolling, it is possible to obtain a hot-rolled steel sheet with a good balance between strength and ductility and excellent hole expansion properties. Completed the invention.
【０００７】よって、本発明は、孔拡げ性に良好な熱延
高張力鋼板の製造方法であって、重量％で Ｃ: 0.03〜0.10％、 Si: 1.2 〜2.0 ％、 Mn: 1.2 〜
2.0 ％、 Ｐ: 0.01以下、 Ｓ: 0.005 ％以下、 Ti: 0.04〜
0.10％、 Cr: 0.5 〜1.3 ％、 Ca: 0.01％以下、 かつ、２×Ti/48 ≧N/14となるようなＮを含み、残部Fe
および不可避的不純物より成る組成を有する鋼を、圧延
仕上温度Ar3 変態点〜940 ℃、仕上圧下率85％以上で熱
間圧延し、420 〜550 ℃にて巻取ることを特徴とする。Therefore, the present invention relates to a method for producing a hot-rolled high-tensile steel sheet having good hole expandability, wherein C: 0.03-0.10%, Si: 1.2-2.0%, Mn: 1.2-% by weight.
2.0%, P: 0.01 or less, S: 0.005% or less, Ti: 0.04 ~
0.10%, Cr: 0.5 to 1.3%, Ca: 0.01% or less, and N containing 2 × Ti / 48 ≧ N / 14, with the balance being Fe
And a steel having a composition consisting of unavoidable impurities is hot-rolled at a rolling finish temperature of the Ar 3 transformation point of 940 ° C. and a finish reduction of 85% or more, and wound at 420 to 550 ° C.
【０００８】かくして、本発明により製造される熱延高
張力鋼板は、フェライト・ベイナイトの複合組織からな
り、自動車足回り部品、ホィールディスクとして特に必
要な特性である孔拡げ性に優れている。[0008] Thus, the hot-rolled high-strength steel sheet produced by the present invention has a composite structure of ferrite and bainite, and has excellent hole expandability, which is a characteristic particularly required for undercarriage parts for automobiles and wheel disks.
【０００９】[0009]
【作用】次に、本発明において鋼組成および熱間圧延条
件を上述のように限定した理由を詳述する。まず、本発
明における冶金学的組織上の全般的特徴は次の通りであ
る。高Ｃまたは高Ｃ−高Mn系鋼では、高強度となるが、
延性が著しく劣化する。そのため、本発明にあっては、
低Ｃ化により延性向上を図り、強度低下分をSi、Mn、Cr
添加で強度補償をしている。Next, the reason why the steel composition and the hot rolling conditions in the present invention are limited as described above will be described in detail. First, the general features of the metallurgical organization in the present invention are as follows. With high C or high C-high Mn steels, the strength is high,
The ductility is significantly deteriorated. Therefore, in the present invention,
The ductility is improved by lowering C, and the strength reduction is reduced by Si, Mn, and Cr.
Strength is compensated by addition.
【００１０】また、Siは他の添加元素に比べ、延性低下
が少ないので、その積極的添加で優れた強度・延性バラ
ンスを得ることができる。そのため、本発明ではSi:2.0
％まで積極的添加を行っている。[0010] Since Si is less reduced in ductility than other added elements, an excellent balance between strength and ductility can be obtained by its positive addition. Therefore, in the present invention, Si: 2.0
% Is actively added.
【００１１】しかし、Ｃ、Si、Mn、Cr添加だけでは、孔
拡げ性に優れた鋼板は得られない。何故なら、孔拡げ性
はミクロ組織の影響を大きく受けるためである。孔拡げ
性を向上させるにはミクロボイド、クラックの生成、進
展を防ぐ必要がある。そのためには、ミクロ組織全体を
できるだけ均一な延性と強度をもつような組織にしなく
てはならない。このとき、強度−延性のバランスの劣化
も防ぐ必要があるので、組織的には、延性向上効果の大
きいポリゴナルフェライトと、強度確保かつフェライト
と整合性のよいベイナイトとの２相を微細に均一に分散
させたものが高強度、高成形性 (延性＋孔拡げ性)材料
となる。[0011] However, a steel sheet excellent in hole expandability cannot be obtained only by adding C, Si, Mn, and Cr. This is because the pore expandability is greatly affected by the microstructure. In order to improve the hole spreading property, it is necessary to prevent the generation and progress of microvoids and cracks. For this purpose, the entire microstructure must be made as uniform as possible in ductility and strength. At this time, it is necessary to prevent the strength-ductility balance from being deteriorated. The material dispersed in the material becomes a high-strength, high-formability (ductile + hole-expanding) material.
【００１２】そのための手法として、次のような手段を
取っている。 成分系からは、Ti添加により、熱間圧延時に、Ti系析
出物によるオーステナイト組織の均一微細化を行う必要
がある。また、同時にTi添加により孔拡げ性低下を招く
MnS を低減させる。つまり、TiS を形成させるのであ
る。As a method for this, the following means are taken. From the component system, it is necessary to uniformly refine the austenite structure by Ti-based precipitates during hot rolling by adding Ti. At the same time, the addition of Ti causes a decrease in hole expandability.
Reduce MnS. That is, TiS is formed.
【００１３】熱間圧延条件からは、オーステナイト組
織の微細化をさらに促進させるために、圧下率を大きく
する。その結果、微細なオーステナイト粒が多数存在す
る状態で圧延が完了するので、冷却の初期段階では、フ
ェライトが容易に生成し、ポリゴン化する。次いで、第
２段階として、巻取温度をベイナイトのみが容易に生成
する温度に保持することで、ポリゴナルフェライトの粒
界からのみベイナイトだけが生成することとなる。From the hot rolling conditions, the rolling reduction is increased in order to further promote the refinement of the austenite structure. As a result, the rolling is completed in a state where many fine austenite grains are present, so that ferrite is easily generated and turned into polygons in the initial stage of cooling. Next, as a second stage, by maintaining the winding temperature at a temperature at which only bainite is easily formed, only bainite is formed only from the grain boundaries of polygonal ferrite.
【００１４】以上の特定成分系、特定熱延条件を経たと
きにのみ、ポリゴナルフェライトと、ベイナイトを均一
に微細分散させることが可能となる。もし、巻取温度が
高過ぎると、TiC 析出による降伏強さ(YS)の増加を招
き、一方、低過ぎると、ベイナイト以外にマルテンサイ
トも生成し、ミクロ組織の強度が局所的に不均一となり
孔拡げ性の低下を招く。以下、これらについてさらに具
体的にその限定理由を述べる。[0014] Polygonal ferrite and bainite can be uniformly and finely dispersed only under the above-mentioned specific component system and specific hot rolling conditions. If the winding temperature is too high, the yield strength (YS) increases due to TiC precipitation, while if it is too low, martensite is formed in addition to bainite, and the microstructure strength becomes locally uneven. This leads to a decrease in hole expandability. Hereinafter, the reasons for the limitation will be described more specifically.
【００１５】C:炭素(C) は、鋼の強度確保のため添加さ
れ、引張強さ(TS)80 kgf/mm2クラスの強度を実現するに
は少なくとも0.03％添加されるが、0.10％を超えると、
孔拡げ性の劣化をもたらすので、本発明ではC:0.03〜0.
10％に限定する。好ましくはＣ:0.10 未満とする。C: Carbon (C) is added to secure the strength of the steel, and at least 0.03% is added to achieve a tensile strength (TS) of 80 kgf / mm 2 class strength, but 0.10% is added. If exceeded,
In the present invention, C: 0.03-0.
Limited to 10%. Preferably, C is less than 0.10.
【００１６】Si:ケイ素(Si)は、鋼の強化、延性向上、
ポリゴナルフェライトの生成促進の作用を有する。1.2
％より少ないと強度確保が困難であって、ポリゴナルフ
ェライト生成の駆動力が小さいため、強度−延性バラン
ス向上の効果が十分でない。一方、2.0 ％を超えるとス
ケール性状および溶接性が劣化する。好ましくは1.2 ％
超配合する。Si: Silicon (Si) is used to strengthen steel, improve ductility,
It has the effect of promoting the production of polygonal ferrite. 1.2
%, The strength is difficult to secure, and the driving force for producing polygonal ferrite is small, so that the effect of improving the strength-ductility balance is not sufficient. On the other hand, if it exceeds 2.0%, the scale properties and weldability deteriorate. Preferably 1.2%
Super blend.
【００１７】Mn:マンガン(Mn)は、鋼の強度確保および
パーライト変態の抑制のために添加されるが、1.2 ％未
満ではそのような効果が十分でない。しかし、2.0 ％を
超えると、延性が劣化し、さらに溶接性を害し、またＡ
系介在物が生じ易くなり、孔拡げ性を低下させる。Mn: Manganese (Mn) is added to secure the strength of the steel and to suppress the pearlite transformation, but if it is less than 1.2%, such effect is not sufficient. However, if it exceeds 2.0%, the ductility is deteriorated, and the weldability is impaired.
System inclusions are likely to be generated, and the hole expandability is reduced.
【００１８】P:燐(P) の存在は、溶接性を害する。また
P 偏析部からの割れが生じ易くなるため、孔拡げ性を低
下される。本発明では0.01％以下に制限する。P: The presence of phosphorus (P) impairs weldability. Also
Since cracks from the P segregation part are likely to occur, the hole expandability is reduced. In the present invention, it is limited to 0.01% or less.
【００１９】S:硫黄(S) は、0.005 ％以下に制限する
が、それを超えるとＡ系介在物が生じ易くなり、孔拡げ
性を低下させるからである。S: Sulfur (S) is limited to 0.005% or less. If the S content is more than 0.005%, A-based inclusions are likely to be generated, and the pore expandability is reduced.
【００２０】Ti:チタン(Ti)は、結晶粒粗大化防止およ
びＡ系介在物低減を通して、孔拡げ性を改善するために
添加するが、そのような効果は、Ti:0.04 ％以上の添加
で確保される。しかし、0.10％超では微細化効果の他
に、析出強化が大きく作用し、却って高YSとなってしま
う。本発明ではTi:0.04 〜0.10％に制限する。Ti: Titanium (Ti) is added in order to improve the hole expandability through the prevention of coarsening of crystal grains and the reduction of A-based inclusions. Such an effect is obtained by adding Ti: 0.04% or more. Secured. However, if the content exceeds 0.10%, precipitation strengthening acts greatly in addition to the effect of miniaturization, resulting in high YS. In the present invention, Ti is limited to 0.04 to 0.10%.
【００２１】Cr:クロム（Cr) は鋼の強化、パーライト
変態の抑制、そしてベイナイト生成の促進のために添加
するが、0.5 ％未満では、パーライト抑制効果が少な
い。一方、1.3 ％を超えた過度の添加はベイナイト生成
を促進しすぎるために、フェライト量が低減し、孔拡げ
性が低下してしまう。Cr: Chromium (Cr) is added to strengthen the steel, suppress the pearlite transformation, and promote the formation of bainite. If less than 0.5%, the effect of suppressing pearlite is small. On the other hand, excessive addition exceeding 1.3% excessively promotes the formation of bainite, so that the amount of ferrite decreases and the hole expandability decreases.
【００２２】Ｎ：窒素（Ｎ）を添加すると、TiN が多数
析出し、微細化の効果が低下するため、２×Ti/48 ≧N/
14で規定される量以下とする。TiN の析出を可及的少と
するためである。N: When nitrogen (N) is added, a large amount of TiN precipitates and the effect of miniaturization is reduced, so that 2 × Ti / 48 ≧ N /
It shall be less than the amount specified in 14. This is for minimizing the precipitation of TiN.
【００２３】Ca:カルシウム(Ca)は、Ｂ系介在物と結合
してＣ系介在物となるが、Ca添加量が0.01％超となる
と、介在物が多くなり、今度は加工性が低下する。本発
明ではCaは0.01％以下に制限する。上述のような鋼組成
を有する鋼は、熱間圧延を行うが、そのときの加工条件
は次の通りである。Ca: Calcium (Ca) binds to B-based inclusions to form C-based inclusions, but if the Ca content exceeds 0.01%, the inclusions increase and the processability decreases. . In the present invention, Ca is limited to 0.01% or less. The steel having the above-described steel composition is subjected to hot rolling, and the processing conditions at that time are as follows.
【００２４】仕上げ温度:微細粒オーステナイト域で圧
延を完了し、フェライトの生成を容易にするために、Ar
3 変態点から940 ℃の温度域で圧延を完了する。Ar3 変
態点未満では集合組織が発達し、異方性が著しくなる。
一方、940 ℃より高い温度で圧延を完了すると、十分微
細なオーステナイト粒が得られない。Finishing temperature: In order to complete rolling in the fine-grain austenite region and facilitate ferrite formation, Ar
3 Complete rolling at a temperature range of 940 ° C from the transformation point. Below the Ar 3 transformation point, a texture develops and the anisotropy becomes significant.
On the other hand, if the rolling is completed at a temperature higher than 940 ° C., sufficiently fine austenite grains cannot be obtained.
【００２５】仕上げ圧下率:本発明にあっては、仕上げ
圧下率は85％以上とするが、これはフェライト、ベイナ
イトの生成サイトを均一にかつ多数分散させるためであ
って、85％未満であると、歪みが十分に導入されず、フ
ェライトおよびベイナイトの生成サイトの数が低下する
ためである。Finish reduction: In the present invention, the finish reduction is set to 85% or more. This is for dispersing uniformly and a large number of ferrite and bainite formation sites, and is less than 85%. This is because strain is not sufficiently introduced and the number of ferrite and bainite formation sites decreases.
【００２６】巻取温度:巻取温度の規定は、できるだけ
ベイナイトのみを生成させるためである。巻取温度が42
0 ℃未満であると、フェライト量が低下し、延性が低下
する。一方、550 ℃超となると、TiC の析出が多くな
り、析出強化となって、高YSとなる。Winding temperature: The winding temperature is specified so that only bainite is produced as much as possible. Winding temperature is 42
If the temperature is lower than 0 ° C., the amount of ferrite decreases and ductility decreases. On the other hand, when the temperature exceeds 550 ° C., the precipitation of TiC increases, strengthening the precipitation and increasing the YS.
【００２７】[0027]
【実施例】表１に鋼組成を有する供試材を同じく表１に
示す熱間圧延条件で熱間圧延を行った。本発明例No.1〜
10は所定の成分を有するスラブを、本発明の熱間圧延条
件に沿って熱間圧延したものである。表１には本発明例
および比較例によって製造された各鋼板の機械的特性を
も合わせて示す。これらからも分かるように、本発明に
よれば、降伏点60〜70kgf/mm2 、引張強さ75〜85 kgf/m
m2、伸び15％以上、そして孔拡げ率80％以上という特性
を有する熱延高張力鋼板が得られる。EXAMPLES A test material having the steel composition shown in Table 1 was subjected to hot rolling under the hot rolling conditions shown in Table 1. Invention Examples No. 1 to
Reference numeral 10 denotes a slab having a predetermined component that has been hot-rolled in accordance with the hot-rolling conditions of the present invention. Table 1 also shows the mechanical properties of the steel sheets manufactured according to the examples of the present invention and the comparative examples. As can be seen from these, according to the present invention, the yield point 60~70kgf / mm 2, a tensile strength of 75-85 kgf / m
A hot-rolled high-strength steel sheet having characteristics of m 2 , elongation of 15% or more, and hole expansion rate of 80% or more is obtained.
【００２８】[0028]
【表１】 [Table 1]
【００２９】[0029]
【発明の効果】以上のように、本発明によれば、安価な
手段で成形性、特に孔拡げ性に優れた高張力鋼板が製造
される。特に、バーリング加工のように優れた孔拡げ性
が求められる自動車用材料を提供することで軽量化を実
現する本発明の今日的意義は大きい。As described above, according to the present invention, a high-strength steel sheet having excellent formability, particularly excellent hole-expandability, can be manufactured by inexpensive means. In particular, the present invention, which realizes weight reduction by providing a material for automobiles requiring excellent hole expandability such as burring, is of great significance today.
Claims (1)
2.0 ％、 Ｐ: 0.01以下、 Ｓ: 0.005 ％以下、 Ti: 0.04〜
0.10％、 Cr: 0.5 〜1.3 ％、 Ca: 0.01％以下、 かつ、２×Ti/48 ≧N/14となるようなＮを含み、 残部Feおよび不可避的不純物より成る組成を有する鋼
を、圧延仕上温度Ar3 変態点〜940 ℃、仕上圧下率85％
以上で熱間圧延し、420 〜550 ℃にて巻取ることを特徴
とする孔拡げ性の良い熱延高張力鋼板の製造方法。C. 0.03 to 0.10%, Si: 1.2 to 2.0%, Mn: 1.2 to 100% by weight.
2.0%, P: 0.01 or less, S: 0.005% or less, Ti: 0.04 ~
Rolled steel containing 0.10%, Cr: 0.5-1.3%, Ca: 0.01% or less, N containing 2 × Ti / 48 ≧ N / 14, and having the balance of Fe and unavoidable impurities Finishing temperature Ar 3 transformation point ~ 940 ° C, Finishing reduction 85%
A method for producing a hot-rolled high-strength steel sheet having good hole-expandability, wherein hot rolling is performed as described above and winding is performed at 420 to 550 ° C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25554991A JP2600537B2 (en) | 1991-10-02 | 1991-10-02 | Manufacturing method of hot-rolled high-strength steel sheet with good hole expansion |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP25554991A JP2600537B2 (en) | 1991-10-02 | 1991-10-02 | Manufacturing method of hot-rolled high-strength steel sheet with good hole expansion |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0598353A JPH0598353A (en) | 1993-04-20 |
| JP2600537B2 true JP2600537B2 (en) | 1997-04-16 |
Family
ID=17280269
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP25554991A Expired - Lifetime JP2600537B2 (en) | 1991-10-02 | 1991-10-02 | Manufacturing method of hot-rolled high-strength steel sheet with good hole expansion |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2600537B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4646871B2 (en) * | 2006-08-12 | 2011-03-09 | 株式会社神戸製鋼所 | Hot-rolled steel sheet with excellent stretch flangeability |
-
1991
- 1991-10-02 JP JP25554991A patent/JP2600537B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0598353A (en) | 1993-04-20 |
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