JPH08246097A - High strength hot rolled steel sheet excellent in stretch-flanging workability and its production - Google Patents
High strength hot rolled steel sheet excellent in stretch-flanging workability and its productionInfo
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- JPH08246097A JPH08246097A JP4850095A JP4850095A JPH08246097A JP H08246097 A JPH08246097 A JP H08246097A JP 4850095 A JP4850095 A JP 4850095A JP 4850095 A JP4850095 A JP 4850095A JP H08246097 A JPH08246097 A JP H08246097A
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Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は、強度750N/mm2 以
上の伸びフランジ加工性にすぐれる高強度熱延鋼板及び
その製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength hot-rolled steel sheet having a strength of 750 N / mm 2 or more and having excellent stretch-flange formability, and a method for producing the same.
【0002】[0002]
【従来の技術】従来、高強度熱延鋼板は、種々の用途に
広く用いられているが、特に、自動車のバンパーを含む
種々の部材に用いる場合、そのプレス成形において、伸
びフランジ加工性が強く要求される。この伸びフランジ
性を向上させる方法としては、例えば、特開昭58−4
2726号公報に記載されているように、鋼板の組織を
フェライト・ベイナイト組織とする方法、特開昭57−
70257号公報に記載されているように、フェライト
・ベイナイト・マルテンサイト組織とする方法等が知ら
れている。2. Description of the Related Art Conventionally, high-strength hot-rolled steel sheets have been widely used for various purposes. In particular, when they are used for various members including automobile bumpers, they have strong stretch-flange formability in press forming. Required. As a method for improving the stretch flangeability, for example, JP-A-58-4
As disclosed in Japanese Patent No. 2726, a method of changing the structure of a steel sheet to a ferrite bainite structure, JP-A-57-57
As described in Japanese Patent No. 70257, a method of forming a ferrite-bainite-martensite structure is known.
【0003】更に、これら以外にも、特開昭57−23
025号公報に記載されているように、フェライトに微
細パーライトを分散させる方法、特開平4−88125
号公報に記載されているように、微細セメンタイトを生
成させる方法、特開昭54−88827号公報に記載さ
れているように、微細セメンタイトを生成させる方法、
特開昭56−55525号公報に記載されているよう
に、ベイナイトラスを制御する方法等が知られている。
また、C量を低減する方法も知られている。Further, in addition to these, JP-A-57-23
Japanese Patent Laid-Open No. 4-88125, a method of dispersing fine pearlite in ferrite as described in JP-A-4-88125.
As described in JP-A No. 54-88827, a method for producing fine cementite, and a method for producing fine cementite, as described in JP-A-54-88827.
As described in JP-A-56-55525, a method for controlling bainite lath is known.
Further, a method of reducing the amount of C is also known.
【0004】しかし、従来より知られているこれらの方
法による熱延鋼板では、伸びフランジ加工性に限界があ
り、しかも、これら熱延鋼板によりも一層高強度の75
0N/mm2 以上の熱延鋼板では、伸びフランジ性が極端
に劣化する。かくして、従来の高強度熱延鋼板では、自
動車のメンバー類の製造に必要な加工成形性の要求を満
たすことができず、薄肉化による自動車重量の低減や、
燃費の改善が実現されないでいる。However, the conventionally known hot-rolled steel sheets produced by these methods have limitations in stretch-flange formability, and moreover, these hot-rolled steel sheets have a higher strength of 75.
The stretch-flange formability of the hot-rolled steel sheet of 0 N / mm 2 or more is extremely deteriorated. Thus, the conventional high-strength hot-rolled steel sheet cannot satisfy the requirement of workability required for manufacturing members of automobiles, and the reduction of automobile weight due to thinning,
Fuel economy has not been improved.
【0005】[0005]
【発明が解決しようとする課題】本発明は、従来の高強
度熱延鋼板の製造における上述したような問題を解決す
るためになされたものであって、750N/mm2 以上の
高強度化に伴う伸びフランジ加工性の劣化を防ぎ、高強
度であっても、十分な伸びフランジ加工性、通常、打抜
き穴の限界穴拡げ率90%以上を有する高強度熱延鋼板
と、そのような熱延鋼板の製造方法を提供することを目
的とする。The present invention has been made to solve the above-mentioned problems in the production of conventional high-strength hot-rolled steel sheets, and it is intended to increase the strength to 750 N / mm 2 or more. A high-strength hot-rolled steel sheet which prevents deterioration of stretch-flange formability associated therewith and has sufficient stretch-flange formability even with high strength, usually 90% or more of the limit hole expansion rate of punched holes, and such hot-rolling. An object is to provide a method for manufacturing a steel sheet.
【0006】[0006]
【課題を解決するための手段】本発明によれば、重量%
でC 0.02〜0.10%、Si 0.2%以下、Mn
3.0%以下、P 0.1%以下、S 0.01%以下、
及びCr 0.1〜1.0%を含み、残部鉄及び不可避的不
純物よりなり、ラス状構造を有し、セメンタイト及びパ
ーライト組織をもたず、フェライト組織を80%以上有
する伸びフランジ加工性にすぐれる強度750N/mm2
以上の高強度熱延鋼板が提供される。According to the present invention, the weight percent is
C 0.02 to 0.10%, Si 0.2% or less, Mn
3.0% or less, P 0.1% or less, S 0.01% or less,
And Cr 0.1-1.0%, balance iron and unavoidable impurities, has lath-like structure, has no cementite and pearlite structure, and has 80% or more ferrite structure for stretch flangeability. Excellent strength 750 N / mm 2
The above high strength hot rolled steel sheet is provided.
【0007】本発明による熱延鋼板は、更に、Ni 1.
0%以下、及びCu 1.0%以下よりなる群から選ばれ
る少なくとも1種の元素を含んでいてもよい。The hot rolled steel sheet according to the present invention further comprises Ni 1.
It may contain at least one element selected from the group consisting of 0% or less and Cu 1.0% or less.
【0008】本発明によれば、更に、重量%でC 0.
02〜0.10%、Si 0.2%以下、Mn 3.0%以
下、P 0.1%以下、S 0.01%以下、及びCr
0.1〜1.0%を含み、残部鉄及び不可避的不純物より
なる鋼をスラブとし、それを1100℃以上の温度に加
熱した後、(Ar3−50)℃以上、950℃以下の範囲
の温度にて熱間圧延を終了し、30℃/秒以上の冷却速
度にて、500〜200℃の範囲の温度まで冷却し、そ
の温度にて巻取ることによって、強度750N/mm2 以
上で、ラス状構造を有し、セメンタイト及びパーライト
組織をもたず、フェライト組織を80%以上有する伸び
フランジ加工性にすぐれる熱延鋼板の製造方法が提供さ
れる。According to the invention, further C 0.
02-0.10%, Si 0.2% or less, Mn 3.0% or less, P 0.1% or less, S 0.01% or less, and Cr.
A steel containing 0.1 to 1.0% and a balance of iron and unavoidable impurities is used as a slab, and the slab is heated to a temperature of 1100 ° C or higher, and then in a range of (Ar 3 -50) ° C or higher and 950 ° C or lower. With the strength of 750 N / mm 2 or more, the hot rolling is completed at the temperature of, the temperature is cooled to a temperature in the range of 500 to 200 ° C. at a cooling rate of 30 ° C./sec or more, and the coil is wound at that temperature. A method for producing a hot-rolled steel sheet having a lath-like structure, having no cementite and pearlite structure, and having a ferrite structure of 80% or more and having excellent stretch flange formability is provided.
【0009】先ず、本発明において、鋼の化学成分の限
定理由について説明する。Cは、鋼板の強度を確保する
ために必要な元素であるが、過多に添加するときは、ベ
イナイトやパーライト等の炭化物を有する組織が本発明
にて規定する範囲を越えて生成するので、目的とする伸
びフランジ加工性にすぐれる高強度熱延鋼板を得ること
ができない。しかし、添加量が不足するときは、熱間圧
延終了後の冷却中に、ラス構造を有するフェライト組織
を得ることができず、同様に、目的とする伸びフランジ
加工性にすぐれる高強度熱延鋼板を得ることができな
い。そこで、本発明によれば、炭化物を生成することな
く、ラス構造を有するフェライト組織を得るために、C
の添加量を0.02〜0.10%の範囲とする。First, the reason for limiting the chemical composition of steel in the present invention will be explained. C is an element necessary to secure the strength of the steel sheet, but when added in an excessive amount, a structure having carbides such as bainite and pearlite is formed beyond the range specified in the present invention. It is impossible to obtain a high-strength hot-rolled steel sheet having excellent stretch flangeability. However, when the addition amount is insufficient, it is not possible to obtain a ferrite structure having a lath structure during cooling after completion of hot rolling, and similarly, high strength hot rolling excellent in desired stretch flange workability is also obtained. I can't get a steel plate. Therefore, according to the present invention, in order to obtain a ferrite structure having a lath structure without forming carbides, C
Is added in the range of 0.02 to 0.10%.
【0010】Siは、ラス状構造をもつフェライト組織
の生成を阻害し、本発明において有害な元素であるの
で、鋼における含有量を極力少なくすることが好まし
い。特に、Si量が0.2%を越えるときは、通常の製造
設備における冷却条件によっては、ラス構造をもつフェ
ライト組織を得ることができない。更に、冷却速度によ
っては、双相マルテンサイト組織を生じて、伸びフラン
ジ性を極端に劣化させる。本発明に従って、ラス状構造
を有するフェライト組織を比較的安定して得るために
は、Si量は0.1%以下とするのがよい。Since Si inhibits the formation of a ferrite structure having a lath-like structure and is a harmful element in the present invention, it is preferable to minimize the content in steel. In particular, when the Si content exceeds 0.2%, it is not possible to obtain a ferrite structure having a lath structure depending on the cooling conditions in ordinary manufacturing equipment. Furthermore, depending on the cooling rate, a dual-phase martensite structure is generated, and the stretch flange formability is extremely deteriorated. In order to obtain a ferrite structure having a lath-like structure in a relatively stable manner according to the present invention, the Si content is preferably 0.1% or less.
【0011】Mnは、本発明が目的とする組織の生成に
寄与する元素の一つである。しかし、過多に添加したと
きは、ベイナイト組織等の低温変態生成物を多く生成し
て、鋼板の伸びフランジ性を低下させるので、添加量を
3.0%以下とする。Pは、本発明において、固溶強化の
ための元素として重要である。しかし、過多に添加する
ときは、点溶接性等、伸びフランジ性以外の望ましい性
質を劣化させるので、添加量の上限を0.1%とする。Mn is one of the elements that contributes to the formation of the structure aimed at by the present invention. However, if too much is added, a large amount of low-temperature transformation products such as bainite structure are generated, and the stretch-flange formability of the steel sheet is reduced.
It is 3.0% or less. In the present invention, P is important as an element for solid solution strengthening. However, if excessively added, desirable properties other than stretch flangeability such as spot weldability are deteriorated, so the upper limit of the addition amount is made 0.1%.
【0012】Sは、伸びフランジ加工性を劣化させる硫
化物を生成するので、可能な限りに低減することが必要
であり、本発明においては、0.005%以下とする。後
述するように、Caを添加することによって、Sを更に
低減して、得られる熱延鋼板の伸びフランジ性を一層高
めることができる。Since S forms a sulfide that deteriorates stretch-flange formability, it is necessary to reduce S as much as possible. In the present invention, S is 0.005% or less. As described later, by adding Ca, S can be further reduced and the stretch-flangeability of the obtained hot-rolled steel sheet can be further enhanced.
【0013】Crは、ベイナイト変態やパーライト変態
を抑え、伸びフランジ性を阻害する炭化物の生成を制御
する効果があり、また、200〜500℃の巻取中に微
細なCr化合物が生成し、これによって強度向上に寄与
させることができるので、本発明において、重要な元素
である。従来、TiやNbを添加すれば、熱延終了後の
巻取り中に炭化物が析出し、これが鋼板の強度向上に有
効な析出物を生成することが知られているが、しかし、
それには比較的高い巻取温度が必要とされ、本発明の方
法における巻取温度では、析出物は生成しない。[0013] Cr has the effect of suppressing bainite transformation and pearlite transformation and controlling the formation of carbides that hinder stretch-flange formability. Also, fine Cr compounds are produced during winding at 200 to 500 ° C, Since it can contribute to the improvement of strength, it is an important element in the present invention. Conventionally, it is known that if Ti or Nb is added, carbide precipitates during winding after hot rolling, and this forms a precipitate effective for improving the strength of the steel sheet.
It requires a relatively high winding temperature and no precipitate is formed at the winding temperature in the process of the invention.
【0014】本発明によれば、上記Crの効果は、その
添加量が0.1%から有効であるが、しかし、過多に添加
しても、効果が飽和する。そこで、製造プロセスの経済
性を考慮して、添加量の上限を1.0%とする。特に、本
発明によれば、Cr添加量が0.3〜0.7%の範囲で最も
高い効果を得ることができる。According to the present invention, the effect of Cr is effective from the addition amount of 0.1%, but the effect is saturated even if it is added in excess. Therefore, considering the economical efficiency of the manufacturing process, the upper limit of the amount added is set to 1.0%. Particularly, according to the present invention, the highest effect can be obtained when the Cr addition amount is in the range of 0.3 to 0.7%.
【0015】本発明においては、上記元素に加えて、鋼
に更に、Ni 1.0%以下、及びCu 1.0%以下より
なる群から選ばれる少なくとも1種の元素を添加するこ
とができる。In the present invention, in addition to the above-mentioned elements, at least one element selected from the group consisting of Ni 1.0% or less and Cu 1.0% or less can be added to steel.
【0016】Cuは、鋼板において耐食性を得るために
有効な元素であるが、過多に添加するときは、鋼の熱間
脆性を引き起こすおそれがあるので、添加量は1.0%以
下とする。しかし、Cuの添加は、鋼板の伸びフランジ
加工性を低減するものではない。[0016] Cu is an element effective for obtaining corrosion resistance in the steel sheet, but if it is added excessively, it may cause hot embrittlement of the steel, so the addition amount is made 1.0% or less. However, the addition of Cu does not reduce the stretch flange formability of the steel sheet.
【0017】Niは、上述したように、Cuの添加によ
って、熱間圧延中に起こる粒界割れやへげ疵を防ぐため
に、通常、Cuとほぼ同量添加される。しかし、Niの
添加も、伸びフランジ性を低減させることはなく、ま
た、NiとCuの複合添加によっても、伸びフランジ性
を低減させない。As described above, Ni is usually added in an amount almost equal to that of Cu in order to prevent intergranular cracking and dent defects during hot rolling by adding Cu. However, the addition of Ni does not reduce the stretch flangeability, and the combined addition of Ni and Cu does not reduce the stretch flangeability.
【0018】本発明によれば、更に、鋼にCaを添加す
ることができる。Caは、伸びフランジ加工性を劣化さ
せる硫化物を低減する効果を有する。そこで、本発明に
よれば、必要に応じて、鋼にCaを20ppm以下の範
囲で添加して、SをCaSとして除去することができ
る。このようにして、Ca処理を施しても、得られる熱
延鋼板の伸びフランジ加工性は劣化しない。According to the present invention, it is possible to add Ca to steel. Ca has the effect of reducing sulfides that deteriorate stretch flange formability. Therefore, according to the present invention, if necessary, Ca can be added to the steel in the range of 20 ppm or less to remove S as CaS. In this way, the stretch-flange formability of the obtained hot-rolled steel sheet does not deteriorate even if Ca treatment is performed.
【0019】次に、本発明による熱延鋼板の有する組織
について説明する。本発明による熱延鋼板が750N/
mm2 以上の高強度を有すると共に、すぐれた伸びフラン
ジ性を有するためには、ラス状構造を有するフェライト
組織、即ち、ベイニティック・フェライト組織を有する
ことが必要である。ここに、ラス状構造とは、高倍率の
透過型電子顕微鏡等で観察した場合にみられる組織であ
って、通常、マルテンサイト等の下部組織のなかで、双
晶やレンズ状とは異なった針状の組織をいい、ラス状マ
ルテンサイトとも呼ばれている。上記ベイニティック・
フェライト組織は、光学顕微鏡や走査型電子顕微鏡等に
よる比較的低倍率(約100〜5000倍)の観察で
は、ベイナイト組織と酷似している。しかし、透過型電
子顕微鏡等による高倍率(約1000〜5000倍)の
観察によれば、ベイナイト組織が内部構造に炭化物(セ
メンタイト等)を含む組織であるのに対して、ベイニテ
ィック・フェライト組織は、セメンタイト等の炭化物を
含まず、ベイナイト組織とは異なる組織である。また、
ベイニティック・フェライト組織は、ラス状構造におい
て、ポリゴナル・フェライト組織とも異なり、かくし
て、ポリゴナル・フェライト組織とも異なる組織であ
る。Next, the structure of the hot rolled steel sheet according to the present invention will be described. The hot rolled steel sheet according to the present invention is 750 N /
In order to have high strength of mm 2 or more and excellent stretch flangeability, it is necessary to have a ferrite structure having a lath-like structure, that is, a bainitic ferrite structure. Here, the lath-like structure is a structure observed when observed with a high-magnification transmission electron microscope or the like, and is usually different from a twin crystal or a lens-like structure in a substructure such as martensite. It refers to a needle-shaped structure and is also called lath martensite. Above bainitic
The ferrite structure is very similar to the bainite structure when observed at a relatively low magnification (about 100 to 5000 times) with an optical microscope or a scanning electron microscope. However, according to observation at a high magnification (about 1000 to 5000 times) with a transmission electron microscope or the like, the bainite structure is a structure containing carbides (such as cementite) in its internal structure, whereas the bainitic ferrite structure is Is a structure that does not include carbide such as cementite and is different from the bainite structure. Also,
The bainitic ferrite structure is different from the polygonal ferrite structure in the lath-like structure, and thus is also a structure different from the polygonal ferrite structure.
【0020】本発明による高強度熱延鋼板は、このよう
なベイニティック・フェライト組織を80%以上含むこ
とが必要である。しかし、残りの20%以下の組織は、
ベイナイト組織やポリゴナル・フェライト組織は勿論の
こと、炭化物やその他低温変態物、第2相等を含む組織
のいずれでもよい。The high-strength hot-rolled steel sheet according to the present invention needs to contain 80% or more of such bainitic ferrite structure. However, the remaining 20% or less of the organization
Not only the bainite structure and polygonal ferrite structure, but also any structure including carbides, other low temperature transformation products, second phase and the like may be used.
【0021】このような高強度熱延鋼板は、本発明に従
って、上述したような化学成分を有する鋼をスラブと
し、それを1100℃以上の温度に加熱した後、(Ar3
−50)℃以上の温度にて熱間圧延を終了し、30℃/
秒以上の冷却速度にて、500〜200℃の範囲の温度
まで冷却し、その温度にて巻取ることをによって得るこ
とができる。According to the present invention, such a high-strength hot-rolled steel sheet is made of a steel having the above-mentioned chemical composition as a slab, which is heated to a temperature of 1100 ° C. or higher and then (Ar 3
Hot rolling is completed at a temperature of −50) ° C. or higher, and 30 ° C. /
It can be obtained by cooling to a temperature in the range of 500 to 200 ° C. at a cooling rate of at least 2 seconds and winding at that temperature.
【0022】本発明の方法において、スラブの加熱温度
は鋼の溶体化温度である1100℃以上であることが必
要であり、好ましくは、溶体化を十分に行なって、γ域
加熱を確保するために、加熱温度は、1200℃以上で
ある。しかし、過度に高くしても、製造コストを高める
のみであるので、通常、加熱温度は、1350℃以下の
範囲である。In the method of the present invention, it is necessary that the heating temperature of the slab is not less than 1100 ° C., which is the solution temperature of steel, and preferably the solution is sufficiently solutionized to ensure heating in the γ region. In addition, the heating temperature is 1200 ° C. or higher. However, the heating temperature is usually in the range of 1350 ° C. or lower because the manufacturing cost is increased even if the temperature is excessively increased.
【0023】熱延においては、仕上熱延をAr3直上の温
度で終了することが望ましい。Ar3直上の温度では、組
織が均一で細粒のγ粒となっており、熱延後も均一組織
を有するフェライト粒を得ることができるからである。
Ar3点以下のα+γ域で圧延を行なうときは、α粒中に
歪みが加わり、不均一な加工α粒が残存しやすい。しか
し、圧延温度がAr3点以下であっても、(Ar3−50)
℃までであれば、α相の体積率も少なく、また、加工度
合いも低いため、伸びフランジ性やその他の性質を劣化
させることはない。従って、本発明においては、熱延仕
上温度を(Ar3−50)℃以上の温度とする。このよう
に、本発明によれば、仕上熱延をAr3直上の温度で終了
することが望ましいが、950℃以下であれば、特に、
支障はない。In hot rolling, it is desirable to finish hot rolling at a temperature just above Ar 3 . This is because at a temperature just above Ar 3 , the structure is uniform and becomes fine γ particles, and ferrite particles having a uniform structure can be obtained even after hot rolling.
When rolling is performed in the α + γ region of Ar 3 points or less, strain is applied to the α grains, and uneven processed α grains are likely to remain. However, even if the rolling temperature is below the Ar 3 point, (Ar 3 −50)
Up to ° C, the volume fraction of the α phase is small and the degree of processing is low, so that stretch flangeability and other properties are not deteriorated. Therefore, in the present invention, the hot rolling finishing temperature is set to a temperature of (Ar 3 -50) ° C or higher. Thus, according to the present invention, it is desirable to finish the hot rolling at a temperature just above Ar 3 , but if it is 950 ° C. or lower,
There is no hindrance.
【0024】熱延終了後の冷却速度は、ラス状構造を有
するフェライト組織を得るために、少なくとも30℃/
秒以上が必要である。この冷却速度の上限は、特に、限
定されるものではないが、実際の工場設備能力等を考慮
して、通常、100℃/秒である。The cooling rate after the hot rolling is at least 30 ° C./in order to obtain a ferrite structure having a lath-like structure.
More than a second is needed. The upper limit of the cooling rate is not particularly limited, but is usually 100 ° C./second in consideration of actual factory facility capacity and the like.
【0025】本発明において、巻取温度は、ベイナイト
やパーライトの生成を避けるため、200〜500℃の
低温とすることが必要であり、特に、Cr化合物の生成
温度等から、250〜350℃の範囲であることが好ま
しい。In the present invention, the coiling temperature is required to be a low temperature of 200 to 500 ° C. in order to avoid the formation of bainite and pearlite. It is preferably in the range.
【0026】[0026]
【実施例】以下に実施例を挙げて本発明を説明するが、
本発明はこれら実施例により何ら限定されるものではな
い。表1に示す化学成分を有する鋼を真空溶解にて溶製
した。表1において、鋼番号1〜4はC量の影響、3、
5及び6はSi量の影響、3及び7はMn量の影響、3
及び8はP量の影響をそれぞれ示す。鋼番号9はCr無
添加の場合を示し、10〜12はNi及びCuの添加の
影響、13はCaを添加した場合の影響を示す。The present invention will be described below with reference to examples.
The present invention is not limited to these examples. Steel having the chemical composition shown in Table 1 was melted by vacuum melting. In Table 1, steel numbers 1 to 4 are the effects of the amount of C, 3,
5 and 6 are effects of Si amount, 3 and 7 are effects of Mn amount, 3
And 8 show the influence of the amount of P, respectively. Steel No. 9 shows the case where Cr is not added, 10 to 12 show the effect of adding Ni and Cu, and 13 shows the effect of adding Ca.
【0027】表1に示す化学成分を有するそれぞれのス
ラブを1250℃の温度にて30分間保持した後、熱延
終了温度を約950〜750℃の範囲として、板厚30
mmから板厚2.5mmまで圧延した。これを更に空冷、ミス
ト冷却(40〜80℃/秒程度)及び水冷にて、550
〜150℃の範囲の温度の巻取処理相当の温度まで冷却
し、その温度で1時間保持し、この後、炉冷にて常温ま
で冷却して、熱延鋼板を得た。After holding each slab having the chemical composition shown in Table 1 at a temperature of 1250 ° C. for 30 minutes, the hot rolling end temperature was set in the range of about 950 to 750 ° C. and the plate thickness was 30.
mm to a plate thickness of 2.5 mm. This is further cooled by air, mist (about 40 to 80 ° C./sec) and water to 550.
Cooled to a temperature equivalent to the coiling treatment in the temperature range of up to 150 ° C., held at that temperature for 1 hour, and then cooled to normal temperature by furnace cooling to obtain a hot rolled steel sheet.
【0028】このようにして得た熱延鋼板から縦横70
mmの正方形の試験片を調製し、その中央に直径10mmの
穴をあけ、先端角60°の円錐ポンチでこの穴を広げ
て、穴の縁にクラックが発生する限界の穴径から打抜き
穴の限界穴広げ率(λ値)を計算にて求めた。結果を表
2及び表3に示す。From the hot-rolled steel sheet thus obtained, 70
A square mm test piece was prepared, a hole with a diameter of 10 mm was made in the center, and this hole was expanded with a conical punch with a tip angle of 60 °. The limit hole expansion ratio (λ value) was calculated. The results are shown in Tables 2 and 3.
【0029】また、表2及び表3において、組織の種類
は、透過型電子顕微鏡(15000倍)により同定し、
その分率は、光学顕微鏡組織(400倍)及び走査型電
子顕微鏡(2000倍)にて観察した結果から求めた。Further, in Tables 2 and 3, the type of tissue was identified by a transmission electron microscope (15,000 times),
The fraction was determined from the results of observation with an optical microscope structure (400 times) and a scanning electron microscope (2000 times).
【0030】表2及び表3において、実験番号1〜13
は、成分による影響を示し、14〜27は、巻取温度に
よる影響を示す。併せて、図1に、表1における鋼番号
3(発明鋼)と鋼番号6(比較鋼)の引張強さに及ぼす
巻取温度の影響を示し、図2に、表1における鋼番号3
(発明鋼)と鋼番号6(比較鋼)のλ値に及ぼす巻取温
度の影響を示す。また、実験番号28〜36は、熱延仕
上温度の影響を示す。併せて、図3に、表1における鋼
番号3(発明鋼)と鋼番号6(比較鋼)の引張強さに及
ぼす熱延仕上温度の影響を示し、図4に、表1における
鋼番号3(発明鋼)と鋼番号6(比較鋼)の伸びフラン
ジ性(λ値)に及ぼす熱延仕上温度の影響を示す。実験
番号37〜39は、冷却速度による影響を示す。In Tables 2 and 3, Experiment Nos. 1 to 13
Indicates the influence of the components, and 14 to 27 indicate the influence of the winding temperature. In addition, FIG. 1 shows the effect of the winding temperature on the tensile strength of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1, and FIG. 2 shows steel No. 3 in Table 1.
The influence of the winding temperature on the λ value of (invention steel) and steel No. 6 (comparative steel) is shown. Experiment numbers 28 to 36 show the influence of the hot rolling finish temperature. In addition, FIG. 3 shows the effect of the hot rolling finish temperature on the tensile strength of Steel No. 3 (inventive steel) and Steel No. 6 (comparative steel) in Table 1, and FIG. 4 shows steel No. 3 in Table 1. The influence of hot rolling finishing temperature on the stretch flangeability (λ value) of (inventive steel) and steel No. 6 (comparative steel) is shown. Experiment numbers 37-39 show the influence by the cooling rate.
【0031】図5は、表1における鋼番号3(発明鋼)
と鋼番号6(比較鋼)の引張強さ−伸びフランジ性(λ
値)に及ぼす巻取温度の影響を示すグラフである。ここ
に、引張強さ−伸びフランジ性バランスは、引張強さ×
伸びフランジ性(λ値)の積にて定義され、値の大きい
ほど、上記バランスがよい。FIG. 5 shows steel number 3 (inventive steel) in Table 1.
And tensile strength of steel No. 6 (comparative steel) -stretch flangeability (λ
It is a graph which shows the influence of the winding temperature which exerts on (value). Here, tensile strength-stretch flangeability balance, tensile strength ×
It is defined by the product of stretch flangeability (λ value), and the larger the value, the better the balance.
【0032】[0032]
【表1】 [Table 1]
【0033】[0033]
【表2】 [Table 2]
【0034】[0034]
【表3】 [Table 3]
【0035】[0035]
【発明の効果】以上のように、本発明によれば、強度7
50N/mm2 以上で、ラス状構造を有し、セメンタイト
及びパーライト組織をもたず、フェライト組織を80%
以上有し、限界穴拡げ率90%以上の伸びフランジ加工
性にすぐれる熱延鋼板を得ることができる。As described above, according to the present invention, the strength is 7
At 50 N / mm 2 or more, it has a lath-like structure, has no cementite or pearlite structure, and has 80% ferrite structure.
It is possible to obtain a hot-rolled steel sheet having the above properties and excellent stretch flange formability with a marginal hole expansion ratio of 90% or more.
【図1】は、表1における鋼番号3(発明鋼)と鋼番号
6(比較鋼)の引張強さに及ぼす巻取温度の影響を示す
グラフである。FIG. 1 is a graph showing the effect of winding temperature on the tensile strength of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1.
【図2】は、表1における鋼番号3(発明鋼)と鋼番号
6(比較鋼)のλ値に及ぼす巻取温度の影響を示すグラ
フである。FIG. 2 is a graph showing the influence of the winding temperature on the λ values of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1.
【図3】は、表1における鋼番号3(発明鋼)と鋼番号
6(比較鋼)の引張強さに及ぼす熱延仕上温度の影響を
示すグラフである。FIG. 3 is a graph showing the effect of hot rolling finishing temperature on the tensile strength of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1.
【図4】は、表1における鋼番号3(発明鋼)と鋼番号
6(比較鋼)の伸びフランジ性(λ値)に及ぼす熱延仕
上温度の影響を示すグラフである。FIG. 4 is a graph showing the effect of hot rolling finish temperature on the stretch flangeability (λ value) of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1.
【図5】は、表1における鋼番号3(発明鋼)と鋼番号
6(比較鋼)の引張強さ−伸びフランジ性(λ値)に及
ぼす巻取温度の影響を示すグラフである。FIG. 5 is a graph showing the effect of winding temperature on the tensile strength-stretch flangeability (λ value) of steel No. 3 (inventive steel) and steel No. 6 (comparative steel) in Table 1.
Claims (6)
よりなり、ラス状構造を有し、セメンタイト及びパーラ
イト組織をもたず、フェライト組織を80%以上有する
伸びフランジ加工性にすぐれる強度750N/mm2 以上
の高強度熱延鋼板。1. In weight%, C 0.02 to 0.10%, Si 0.2% or less, Mn 3.0% or less, P 0.1% or less, S 0.01% or less, and Cr 0. 1 to 1.0%, balance iron and unavoidable impurities, has lath-like structure, has no cementite and pearlite structure, has 80% or more ferrite structure and has excellent stretch flange formability 750N High-strength hot-rolled steel sheet of / mm 2 or more.
種の元素を含み、残部鉄及び不可避的不純物よりなり、
ラス状構造を有し、セメンタイト及びパーライト組織を
もたず、フェライト組織を80%以上有する伸びフラン
ジ加工性にすぐれる強度750N/mm2 以上の高強度熱
延鋼板。2. A weight percentage of (a) C 0.02 to 0.10%, Si 0.2% or less, Mn 3.0% or less, P 0.1% or less, S 0.01% or less, and Cr 0.1-1.0%, and (b) at least 1 selected from the group consisting of Ni 1.0% or less and Cu 1.0% or less.
Including the elements of the species, the balance iron and inevitable impurities,
A high-strength hot-rolled steel sheet having a lath-like structure, having no cementite or pearlite structure, and having a ferrite structure of 80% or more and having an excellent stretch flange formability of 750 N / mm 2 or more.
てなる請求項1又は2記載の高強度熱延鋼板。3. The high-strength hot-rolled steel sheet according to claim 1 or 2, further containing Ca in a range of 20 ppm or less.
よりなる鋼をスラブとし、それを1100℃以上の温度
に加熱した後、(Ar3−50)℃以上、950℃以下の
範囲の温度にて熱間圧延を終了し、30℃/秒以上の冷
却速度にて、500〜200℃の範囲の温度まで冷却
し、その温度にて巻取ることを特徴とする強度750N
/mm2 以上で、ラス状構造を有し、セメンタイト及びパ
ーライト組織をもたず、フェライト組織を80%以上有
する伸びフランジ加工性にすぐれる熱延鋼板の製造方
法。4. In weight%, C 0.02 to 0.10%, Si 0.2% or less, Mn 3.0% or less, P 0.1% or less, S 0.01% or less, and Cr 0. A steel containing 1 to 1.0% and a balance of iron and unavoidable impurities is used as a slab, and the slab is heated to a temperature of 1100 ° C. or higher, and then a temperature in the range of (Ar 3 −50) ° C. or higher and 950 ° C. or lower. The hot rolling is terminated at, the temperature is cooled to a temperature in the range of 500 to 200 ° C. at a cooling rate of 30 ° C./second or more, and the coil is wound at that temperature.
/ Mm 2 or more, having a lath-like structure, having no cementite or pearlite structure, and having a ferrite structure of 80% or more, a method for producing a hot-rolled steel sheet having excellent stretch flange formability.
種の元素を含み、残部鉄及び不可避的不純物よりなる鋼
をスラブとし、それを1100℃以上の温度に加熱した
後、(Ar3−50)℃以上、950℃以下の範囲の温度
にて熱間圧延を終了し、30℃/秒以上の冷却速度に
て、500〜200℃の範囲の温度まで冷却し、その温
度にて巻取ることを特徴とする強度750N/mm2 以上
で、ラス状構造を有し、セメンタイト及びパーライト組
織をもたず、フェライト組織を80%以上有する伸びフ
ランジ加工性にすぐれる熱延鋼板の製造方法。5. In weight%, (a) C 0.02 to 0.10%, Si 0.2% or less, Mn 3.0% or less, P 0.1% or less, S 0.01% or less, and Cr 0.1-1.0%, and (b) at least 1 selected from the group consisting of Ni 1.0% or less and Cu 1.0% or less.
A slab made of steel containing the same kind of elements and the balance of iron and inevitable impurities is heated to a temperature of 1100 ° C or higher, and then heated at a temperature in the range of (Ar 3 -50) ° C to 950 ° C. Finishing the hot rolling, cooling to a temperature in the range of 500 to 200 ° C. at a cooling rate of 30 ° C./sec or more, and winding at that temperature, strength of 750 N / mm 2 or more, lath shape A method for producing a hot-rolled steel sheet having a structure, having no cementite or pearlite structure, and having a ferrite structure of 80% or more and having excellent stretch flange formability.
加する請求項4又は5記載の熱延鋼板の製造方法。6. The method for producing a hot-rolled steel sheet according to claim 4, wherein Ca is further added to the steel in a range of 20 ppm or less.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP4850095A JPH08246097A (en) | 1995-03-08 | 1995-03-08 | High strength hot rolled steel sheet excellent in stretch-flanging workability and its production |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP4850095A JPH08246097A (en) | 1995-03-08 | 1995-03-08 | High strength hot rolled steel sheet excellent in stretch-flanging workability and its production |
Publications (1)
Publication Number | Publication Date |
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JPH08246097A true JPH08246097A (en) | 1996-09-24 |
Family
ID=12805113
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP4850095A Pending JPH08246097A (en) | 1995-03-08 | 1995-03-08 | High strength hot rolled steel sheet excellent in stretch-flanging workability and its production |
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US7879160B2 (en) | 2004-11-24 | 2011-02-01 | Nucor Corporation | Cold rolled dual-phase steel sheet |
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1995
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US7879160B2 (en) | 2004-11-24 | 2011-02-01 | Nucor Corporation | Cold rolled dual-phase steel sheet |
US7959747B2 (en) | 2004-11-24 | 2011-06-14 | Nucor Corporation | Method of making cold rolled dual phase steel sheet |
US8337643B2 (en) | 2004-11-24 | 2012-12-25 | Nucor Corporation | Hot rolled dual phase steel sheet |
US8366844B2 (en) | 2004-11-24 | 2013-02-05 | Nucor Corporation | Method of making hot rolled dual phase steel sheet |
US11155902B2 (en) | 2006-09-27 | 2021-10-26 | Nucor Corporation | High strength, hot dip coated, dual phase, steel sheet and method of manufacturing same |
US8435363B2 (en) | 2007-10-10 | 2013-05-07 | Nucor Corporation | Complex metallographic structured high strength steel and manufacturing same |
US9157138B2 (en) | 2007-10-10 | 2015-10-13 | Nucor Corporation | Complex metallographic structured high strength steel and method of manufacturing |
WO2010011791A3 (en) * | 2008-07-22 | 2010-04-29 | Nucor Corporation | Hot rolled dual phase steel sheet, and method of making the same |
KR101412277B1 (en) * | 2012-05-30 | 2014-06-25 | 현대제철 주식회사 | Steel and method of manufacturing the steel sheet |
WO2020121034A1 (en) * | 2018-12-13 | 2020-06-18 | Arcelormittal | Steels for laser cutting |
WO2020121088A1 (en) * | 2018-12-13 | 2020-06-18 | Arcelormittal | Method of laser cutting a steel |
RU2793356C2 (en) * | 2018-12-13 | 2023-03-31 | Арселормиттал | Method of steel laser cutting |
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