JPH08188847A - Steel plate with composite structure, excellent in fatigue characteristic, and its production - Google Patents
Steel plate with composite structure, excellent in fatigue characteristic, and its productionInfo
- Publication number
- JPH08188847A JPH08188847A JP5895A JP5895A JPH08188847A JP H08188847 A JPH08188847 A JP H08188847A JP 5895 A JP5895 A JP 5895A JP 5895 A JP5895 A JP 5895A JP H08188847 A JPH08188847 A JP H08188847A
- Authority
- JP
- Japan
- Prior art keywords
- less
- phase
- bainite
- ferrite
- martensite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Landscapes
- Heat Treatment Of Steel (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、自動車、鉄道等の車両
において、プレス加工、打抜加工等によって形成され、
頻繁な繰り返し荷重の作用する構造部材に好適に用いる
ことができる疲労特性にすぐれる複合組織熱延鋼板及び
その製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is formed in a vehicle such as an automobile or a railroad by press working, punching working, etc.
The present invention relates to a composite structure hot-rolled steel sheet having excellent fatigue characteristics, which can be suitably used for a structural member subjected to frequent repeated loading, and a method for manufacturing the same.
【０００２】[0002]
【従来の技術】自動車、鉄道等の車両において、燃料費
用やエネルギー効率の向上の必要から軽量化の要求が高
く、従来の軟鋼板に代えて、高張力鋼板の使用が増加し
ている。しかも、これらの車両の寿命は、材料の疲労強
度で決まっているため、高強度であると共に、疲労特性
にすぐれる鋼板への要求が高い。2. Description of the Related Art In vehicles such as automobiles and railroads, there is a strong demand for weight reduction due to the need to improve fuel cost and energy efficiency, and the use of high-tensile steel plates instead of conventional mild steel plates is increasing. Moreover, since the life of these vehicles is determined by the fatigue strength of the material, there is a strong demand for a steel sheet having high strength and excellent fatigue characteristics.
【０００３】そこで、このような要求に応えるため、材
料の組成や微視組織を調整した種々の鋼板が開発されて
おり、代表的なものとしては、特開平４−１３６１１９
号公報等に記載されているように、フェライトを母相と
して、これに硬質の第２相を分散させることによって疲
労強度を改善したフェライト−マルテンサイト鋼、所謂
デュアル・フェイズ（Dual Phase）鋼が知られている。In order to meet such demands, various steel sheets in which the composition of materials and the microstructure have been adjusted have been developed, and a typical one is Japanese Patent Laid-Open No. 4-136119.
As described in Japanese Unexamined Patent Publication (Kokai), there is a ferrite-martensite steel, which is a so-called dual phase steel, in which ferrite is used as a matrix phase and a hard second phase is dispersed in the matrix to improve fatigue strength. Are known.
【０００４】しかし、上記用途向けの薄鋼板は、プレス
加工、打抜加工等を経て所要の部材に加工され、実用に
供されるので、加工性をにすぐれることが必要である。
上記デュアル・フェイズ鋼は、降伏比が低く、強度に比
べて伸びが大きく、成形性の面でもすぐれた特性を有し
ているが、伸びフランジ性の面で劣っており、そのため
に成形時に穴拡げ部から割れが発生する等の問題を有し
ている。However, since the thin steel sheet for the above-mentioned applications is processed into a required member through press working, punching working, etc. and is put into practical use, it is necessary to have excellent workability.
The above dual phase steel has a low yield ratio, a larger elongation than strength, and excellent properties in terms of formability, but it is inferior in terms of stretch-flangeability. There are problems such as cracking from the expanded part.
【０００５】そこで、このようなデュアル・フェイズ鋼
における問題を解決するために、特開平１−０３３５４
３号公報に記載されているように、低降伏比を有すると
共に、すぐれた強度−伸びバランスと伸びフランジ性を
有するフェライト−ベイナイト−マルテンサイトの３相
組織を持つ複合組織鋼板が提案されている。しかしなが
ら、このような３相複合組織鋼板によれば、伸びフラン
ジ性を付与した代償として、疲労強度が低いことが多
く、かくして、疲労特性が十分とはいえず、最適の微視
組織が求められている。Therefore, in order to solve the problem in such a dual phase steel, Japanese Unexamined Patent Publication No. 1-03354.
As described in Japanese Patent Publication No. 3, a composite structure steel sheet having a three-phase structure of ferrite-bainite-martensite having a low yield ratio and an excellent strength-elongation balance and stretch flangeability has been proposed. . However, with such a three-phase composite structure steel sheet, the fatigue strength is often low at the cost of imparting stretch-flangeability, and thus the fatigue properties are not sufficient and an optimum microstructure is required. ing.
【０００６】[0006]
【発明が解決しようとする課題】本発明者らは、従来の
複合組織鋼板における上述したような問題を解決して、
上記要望に応えるために、良好な伸びフランジ性を有す
るフェライト−ベイナイト−マルテンサイト複合組織鋼
板の疲労強度と微視組織の関係を明らかにすべく、鋭意
研究した結果、母相であるフェライトと、これより硬さ
の高いベイナイトとマルテンサイトの結晶粒径、硬さ及
び分散状態を制御することによって、伸びフランジ性を
損なうことなく、疲労特性にすぐれる３相複合組織鋼板
を得ることができることを見出して、本発明に至つたも
のである。DISCLOSURE OF THE INVENTION The present inventors have solved the above-mentioned problems in the conventional steel sheet having a composite structure,
In order to meet the above-mentioned demand, in order to clarify the relationship between the fatigue strength and the microstructure of a ferrite-bainite-martensite composite steel sheet having good stretch-flangeability, as a result of diligent research, a ferrite that is a matrix phase, and By controlling the crystal grain size, hardness and dispersion state of bainite and martensite having higher hardness than this, it is possible to obtain a three-phase composite structure steel sheet having excellent fatigue properties without impairing stretch flangeability. The present invention has been found by the finding.
【０００７】[0007]
【課題を解決するための手段】本発明による疲労特性に
すぐれる複合組織鋼板は、重量％で、Ｃ 0.０３〜0.
１５％、Ｓｉ 0.３〜1.５％、Ｍｎ 0.１〜2.０％、Ｐ
0.１％以下、Ａｌ 0.００５〜0.１％、Ｓ 0.０
０５％以下を含有し、残部鉄及び不可避的不純物よりな
り、フェライト相中に硬質のベイナイト相とマルテンサ
イト相を含有し、フェライトの結晶粒径が４〜１５μ
ｍ、フェライトのビッカース硬さ（Ｈｖ）が１４０〜１
８０、ベイナイトの結晶粒径が６μｍ以下、ベイナイト
のビッカース硬さ（Ｈｖ）が２５０〜４００、マルテン
サイトの結晶粒径が６μｍ以下、マルテンサイトのビッ
カース硬さ（Ｈｖ）が４００〜７００である３相複合組
織からなり、更に、硬質相全体の体積率が５〜４０％の
範囲にあり、硬質相全体の平均自由行程が２０μｍ以下
であることを特徴とする。A composite structure steel sheet having excellent fatigue properties according to the present invention has a C% of 0.03 to 0.
15%, Si 0.3-1.5%, Mn 0.1-2.0%, P
0.1% or less, Al 0.005-0.1%, S 0.0
It contains less than 05%, consists of the balance iron and unavoidable impurities, contains a hard bainite phase and a martensite phase in the ferrite phase, and has a ferrite grain size of 4 to 15 μm.
m, Vickers hardness (Hv) of ferrite is 140 to 1
80, the grain size of bainite is 6 μm or less, the Vickers hardness (Hv) of bainite is 250 to 400, the grain size of martensite is 6 μm or less, and the Vickers hardness (Hv) of martensite is 400 to 700 3. It is characterized by comprising a phase composite structure, further having a volume ratio of the entire hard phase in the range of 5 to 40% and having an average free path of 20 μm or less.
【０００８】本発明による複合組織鋼板には、上記元素
に加えて、Ｃａ 0.０１％以下を添加することができ
る。更に、本発明による複合組織鋼板には、上記Ｃａに
加えて、又は上記Ｃａとは別に、Ｃｕ 0.１〜２％、Ｎ
ｉ 0.１〜２％、Ｃｒ 0.０５〜２％、Ｍｏ 0.０５〜
１％、Ｖ 0.０１〜0.５％、Ｔｉ 0.０１〜0.３％、
Ｎｂ 0.０１〜0.２％、Ｂ 0.０００５〜0.０１％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 addition to the above elements, Ca of 0.01% or less can be added to the steel sheet having a composite structure according to the present invention. Further, in the composite structure steel sheet according to the present invention, in addition to the above Ca or separately from the above Ca, Cu 0.1 to 2%, N
i 0.1-2%, Cr 0.05-2%, Mo 0.05-
1%, V 0.01 to 0.5%, Ti 0.01 to 0.3%,
At least one element selected from the group consisting of Nb 0.01 to 0.2% and B 0.0005 to 0.01% can be added.
【０００９】このような複合組織鋼板は、本発明に従っ
て、上記化学成分を有する鋼を熱間圧延する際に、９５
０〜８００℃の範囲の温度で仕上圧延し、次いで、圧延
の後、５秒以内に冷却速度１５℃／秒以上で冷却を開始
し、冷却する１次冷却を行ない、続いて、７５０〜６０
０℃の温度域において冷却速度１５℃／秒未満にて３〜
１５秒間徐冷する２次冷却を行ない、続いて、冷却速度
１５℃／秒以上にて冷却する３次冷却を行なった後、５
００℃以下の温度で巻取ることによって得ることができ
る。According to the present invention, such a steel sheet having a composite structure has a temperature of 95% when the steel having the above chemical composition is hot-rolled.
Finish rolling is performed at a temperature in the range of 0 to 800 ° C., then, after rolling, cooling is started at a cooling rate of 15 ° C./second or more within 5 seconds, and primary cooling is performed, and then 750 to 60
3 ~ at a cooling rate of less than 15 ° C / sec in the temperature range of 0 ° C
Secondary cooling is performed by slow cooling for 15 seconds, and then tertiary cooling is performed at a cooling rate of 15 ° C./second or more, and then 5
It can be obtained by winding at a temperature of 00 ° C. or lower.
【００１０】このように、本発明によれば、硬質のベイ
ナイトとマルテンサイトを含むフェライト組織を有し、
それぞれの結晶粒径と硬さを限定し、更に、疲労亀裂の
伝播を阻止するうえで重要な硬質相の平均自由行程を規
定することによって、加工性を阻害することなく、疲労
特性を向上させてなる複合組織鋼板とその製造方法が提
供される。As described above, according to the present invention, it has a ferrite structure containing hard bainite and martensite,
By limiting the grain size and hardness of each, and further defining the mean free path of the hard phase, which is important in preventing the propagation of fatigue cracks, the fatigue properties are improved without impairing workability. A composite microstructure steel sheet and a method for manufacturing the same are provided.
【００１１】本発明による複合組織鋼板の微視組織につ
いて説明する。先ず、フェライトの結晶粒径とビッカー
ス硬さの限定理由について述べる。フェライト結晶粒径
が粗大になればなるほど、引張強度、疲労強度共に低下
するので、十分な強度を得るために、本発明において
は、フェライトの結晶粒径の上限を１５μｍとする。一
方、結晶粒の微細化によって、高サイクル疲労強度は上
昇するが、しかし、過度の微細化は、低サイクル側での
寿命低下や疲労亀裂伝播の下限界値の低下を招く。本発
明においては、この低下を抑えるために下限を４μｍと
する。The microstructure of the composite structure steel sheet according to the present invention will be described. First, the reasons for limiting the crystal grain size of ferrite and the Vickers hardness will be described. As the ferrite crystal grain size becomes coarser, both tensile strength and fatigue strength decrease, so in order to obtain sufficient strength, the upper limit of the ferrite crystal grain size is set to 15 μm in the present invention. On the other hand, although the high cycle fatigue strength increases due to the refinement of crystal grains, excessive refinement causes a decrease in the life on the low cycle side and a decrease in the lower limit value of fatigue crack propagation. In the present invention, the lower limit is 4 μm in order to suppress this decrease.
【００１２】フェライトのビッカース硬さ（Ｈｖ）は、
フェライト中の疲労滑り帯や微視的な亀裂の発生に対す
る抵抗を高めるので、硬さが高いほど、疲労強度も向上
する。しかし、前述したように、必要特性の一つである
プレス成形性、伸びフランジ性、打抜加工等の成形性や
加工性は、硬さの増加により低下する。そこで、本発明
においては、成形性や加工性を阻害することなく、十分
な疲労強度を確保するために、フェライトのビッカース
硬さ（Ｈｖ）硬さの範囲を１４０〜１８０とする。The Vickers hardness (Hv) of ferrite is
The higher the hardness, the higher the fatigue strength, because it increases the resistance to the occurrence of fatigue slip bands and microscopic cracks in ferrite. However, as described above, the press formability, stretch flangeability, formability such as punching and workability, which are one of the necessary properties, are reduced due to the increase in hardness. Therefore, in the present invention, the range of the Vickers hardness (Hv) hardness of ferrite is set to 140 to 180 in order to secure sufficient fatigue strength without impairing formability and workability.
【００１３】次に、本発明による複合組織鋼板におい
て、最も重要である硬質相の条件について述べる。硬質
の第２相をフェライト中に分散させる主たる目的は、フ
ェライト中に発生した疲労滑り帯や亀裂の伝播を硬質相
の粒界で阻止し、停留させることによって、疲労強度を
向上させることである。疲労滑り帯や亀裂の伝播を阻止
するためには、これらが十分に伝播する前に硬質相に遭
遇する必要があるが、この遭遇確率は、硬質相の粒径と
分散状態に左右される。例えば、ベイナイト量を一定と
したままで、ベイナイト粒径を変化させると、図１に示
すように、ベイナイト粒径が６μｍ以上では、疲労強度
の向上には寄与しない。マルテンサイトについても同様
である。従って、本発明においては、ベイナイト及びマ
ルテンサイトの結晶粒径をそれぞれ６μｍ以下とする。Next, the conditions of the hard phase, which is the most important in the composite structure steel sheet according to the present invention, will be described. The main purpose of dispersing the hard second phase in ferrite is to improve fatigue strength by preventing propagation of fatigue slip bands and cracks that occur in ferrite at grain boundaries of the hard phase, and by retaining them. . In order to prevent the propagation of fatigue slip bands and cracks, they have to encounter the hard phase before they have propagated sufficiently, but the probability of encounter depends on the grain size and dispersion of the hard phase. For example, when the bainite grain size is changed while the bainite amount is kept constant, as shown in FIG. 1, when the bainite grain size is 6 μm or more, the fatigue strength is not improved. The same applies to martensite. Therefore, in the present invention, the crystal grain sizes of bainite and martensite are each set to 6 μm or less.
【００１４】本発明によれば、後述するように、これら
第２相量を必要以上に増加させないので、成形性や加工
性を阻害することなく、疲労強度を高めることができ
る。According to the present invention, as will be described later, since the amount of these second phases is not increased more than necessary, the fatigue strength can be increased without impairing the formability and workability.
【００１５】更に、ベイナイトがより硬質であるとき、
疲労滑り帯や亀裂の阻止に一層有効である。図２に示す
ように、疲労滑り帯や亀裂の阻止に十分な効果を得るこ
とができるように、本発明によれば、ベイナイトのビッ
カース硬さ（Ｈｖ）の下限を２５０とする。しかし、ベ
イナイトの硬質化によるこのような疲労強度の向上の効
果は、ベイナイトのビッカース硬さ（Ｈｖ）が４００を
越えても飽和するので、その上限を４００とする。Further, when bainite is harder,
It is even more effective in preventing fatigue slip bands and cracks. As shown in FIG. 2, according to the present invention, the lower limit of the Vickers hardness (Hv) of bainite is set to 250 so that a sufficient effect can be obtained in preventing fatigue slip bands and cracks. However, the effect of improving the fatigue strength by hardening the bainite is saturated even when the Vickers hardness (Hv) of the bainite exceeds 400, so the upper limit is set to 400.
【００１６】また、マルテンサイト硬さの向上も、疲労
強度の向上に寄与する。マルテンサイトの少量の生成に
よって、上記効果を十分に得ることができるように、マ
ルテンサイトのビッカース硬さ（Ｈｖ）の下限を４００
とする。しかし、硬質化しすぎても、必要以上に引張強
度を高め、その結果、成形性や加工性に悪影響を与える
ので、その上限を７００とする。Further, the improvement of martensite hardness also contributes to the improvement of fatigue strength. The lower limit of the Vickers hardness (Hv) of martensite is set to 400 so that the above effect can be sufficiently obtained by producing a small amount of martensite.
And However, even if it is hardened too much, the tensile strength is increased more than necessary, and as a result, the formability and workability are adversely affected. Therefore, the upper limit is set to 700.
【００１７】尚、本発明において、ビッカース硬さ（Ｈ
ｖ）が２５０〜７００の場合、残留オーステナイトも疲
労強度の向上に寄与するので、硬質相には、このような
残留オーステナイトをも含むものとする。In the present invention, the Vickers hardness (H
When v) is 250 to 700, retained austenite also contributes to the improvement of fatigue strength, so the hard phase also contains such retained austenite.
【００１８】次に、硬質相の平均自由行程の限定理由に
ついて述べる。前述したように、疲労滑り帯や亀裂が第
２相に遭遇する確率を決定する要因の一つに硬質相の分
散状態がある。この確率を決定する微視組織因子として
は、硬質相の面積率よりも、硬質相間の距離、即ち、硬
質相の平均自由行程が重要である。硬質相の平均自由行
程が大きければ、疲労滑り帯や亀裂が硬質相に遭遇する
前に十分な長さに成長するので、それらを硬質相で阻止
停留させることができない。即ち、図３に示すように、
平均自由行程が大きいときは、硬質相を含有させても、
疲労強度は殆ど向上しない。そこで、本発明によれば、
硬質相の平均自由行程を２０μｍ以下とする。Next, the reasons for limiting the mean free path of the hard phase will be described. As described above, the dispersed state of the hard phase is one of the factors that determine the probability that the fatigue slip band or crack will encounter the second phase. As a microstructural factor that determines this probability, the distance between the hard phases, that is, the mean free path of the hard phases is more important than the area ratio of the hard phases. If the hard phase has a large mean free path, it cannot be arrested in the hard phase as fatigue slip bands and cracks grow to a sufficient length before encountering the hard phase. That is, as shown in FIG.
When the mean free path is large, even if a hard phase is included,
Fatigue strength hardly improves. Therefore, according to the present invention,
The mean free path of the hard phase is 20 μm or less.
【００１９】最後に硬質相の体積率の限定理由を述べ
る。前述したように、プレス加工、打抜加工等によって
形成され、頻繁な繰り返し荷重の作用する構造部材に用
いられる鋼板に必要な特性は、良好な疲労特性と加工性
である。本発明では、加工性の一つの指標として、伸び
フランジ性を考慮したが、疲労特性の向上によって、伸
びフランジ性を劣化させないように、本発明において
は、硬質相全体の体積率を５〜４０％の範囲に限定す
る。Finally, the reasons for limiting the volume ratio of the hard phase will be described. As described above, the properties required for a steel sheet formed by press working, punching, etc. and used for structural members subject to frequent repeated loading are good fatigue properties and workability. In the present invention, the stretch-flangeability is taken into consideration as one index of the workability. However, in order to prevent the stretch-flangeability from being deteriorated by the improvement of the fatigue characteristics, in the present invention, the volume ratio of the entire hard phase is 5 to 40. Limit to the range of%.
【００２０】本発明による複合組織鋼板によれば、以上
のように、フェライト、ベイナイト及びマルテンサイト
のそれぞれの結晶粒径とビッカース硬さ（Ｈｖ）が規定
されるうえに、硬質相全体の面積率と硬質相の平均自由
行程が規定される。As described above, according to the composite structure steel sheet of the present invention, the crystal grain size and Vickers hardness (Hv) of ferrite, bainite, and martensite are specified, and the area ratio of the entire hard phase is determined. And the mean free path of the hard phase is defined.
【００２１】本発明によるこのような複合組織を有する
鋼板を実現するための鋼の化学成分について説明する。The chemical composition of the steel for realizing the steel sheet having such a composite structure according to the present invention will be described.
【００２２】Ｃは、適切な硬さの第２相を得るために必
要な元素であり、そのためには0.０３％以上の添加が必
要である。しかし、0.１５％を越えて添加するときは、
加工性及び溶接性の劣化が大きい。従って、本発明にお
いては、Ｃの添加量は0.０３〜0.１５％の範囲とする。
Ｓｉは、固溶強化元素であり、フェライトの硬さを高く
するために必要である。その効果を有効に発揮させるた
めには、0.３％以上の添加が必要である。しかし、1.５
％を越えて添加すると、フェライトの硬さが過度に上昇
して、成形性や加工性を低下させると共に、鋼板の表面
性状を劣化させる。従って、Ｓｉ量は0.０３〜1.５％の
範囲とする。C is an element necessary for obtaining the second phase having an appropriate hardness, and for this purpose, addition of 0.03% or more is necessary. However, when adding over 0.15%,
Significant deterioration in workability and weldability. Therefore, in the present invention, the amount of C added is in the range of 0.03 to 0.15%.
Si is a solid solution strengthening element and is necessary for increasing the hardness of ferrite. In order to exert the effect effectively, it is necessary to add 0.3% or more. But 1.5
If added in excess of%, the hardness of ferrite excessively increases, which deteriorates formability and workability and deteriorates the surface properties of the steel sheet. Therefore, the amount of Si is set in the range of 0.03 to 1.5%.
【００２３】Ｍｎは、熱間脆性を防止するために、0.１
％以上添加する必要があるが、2.０％を越えて添加する
と溶接性を損なう。従って、Ｍｎ添加量は0.１〜2.０の
範囲とする。Ｐは、置換型固溶強化元素として有効な元
素であり、高延性を与える効果がある。しかし、過多に
添加するときは、粒界に偏析し、脆化を招くので、その
上限を0.１％とする。Mn is 0.1 in order to prevent hot brittleness.
%, It is necessary to add more than 2.0%, but if added over 2.0%, the weldability is impaired. Therefore, the amount of Mn added is in the range of 0.1 to 2.0. P is an element effective as a substitutional solid solution strengthening element and has an effect of imparting high ductility. However, if too much is added, it segregates at the grain boundaries and causes embrittlement, so the upper limit is made 0.1%.
【００２４】Ａｌは、脱酸剤として、0.００５％以上の
添加が必要であるが、過多に添加しても、その効果が飽
和するだけでなく、製造費用を徒に高くするのみである
ので、その上限を0.１％とする。Ｓは、通常、鋼に0.０
０８％程度含まれているが、すぐれた成形性、特に、伸
びフランジ性を確保するために、本発明においては、0.
００５％以下とする。Al needs to be added in an amount of 0.005% or more as a deoxidizing agent. However, even if added in an excessive amount, not only the effect will be saturated, but also the production cost will be excessively increased. Therefore, the upper limit is set to 0.1%. S is usually 0.0 in steel
Although it is contained in an amount of about 08%, in the present invention, in order to secure excellent formability, particularly stretch flangeability,
005% or less.
【００２５】本発明においては、上記元素に加えて、Ｃ
ａを鋼に添加することができる。このＣａは、硫化物の
形態制御を通じて、延性、特に、伸びフランジ性を改善
する効果がある。しかし、過多に添加しても、その効果
が飽和するのみならず、鋼の清浄度を低下させるので、
その上限を0.０１％とする。In the present invention, in addition to the above elements, C
a can be added to the steel. This Ca has an effect of improving ductility, particularly stretch flangeability, through morphology control of sulfide. However, adding too much not only saturates the effect but also reduces the cleanliness of the steel.
The upper limit is set to 0.01%.
【００２６】本発明においては、上記元素に加えて、又
は上記元素とは別に、更に、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、
Ｖ、Ｔｉ、Ｎｂ及びＢよりなる群から選ばれる少なくと
も１種の元素を鋼に添加することができる。In the present invention, in addition to the above elements or separately from the above elements, Cu, Ni, Cr, Mo,
At least one element selected from the group consisting of V, Ti, Nb and B can be added to the steel.
【００２７】Ｃｕは、固溶強化及び析出強化に有効な元
素であり、フェライトの硬さを向上させ、また、伸びフ
ランジ性を損なうことなく、鋼板を強化する働きがあ
る。また、疲労特性を向上させる効果もある。これらの
効果を発揮するためには、少なくとも0.１％を添加する
必要がある。しかし、過多に添加するととは、製造費用
を高くするので、2.０％を添加量の上限とする。Cu is an element effective for solid solution strengthening and precipitation strengthening, and has the functions of improving the hardness of ferrite and strengthening the steel sheet without impairing the stretch flangeability. It also has the effect of improving fatigue characteristics. In order to exert these effects, it is necessary to add at least 0.1%. However, adding too much increases the manufacturing cost, so 2.0% is made the upper limit of the addition amount.
【００２８】Ｎｉは、溶接性を阻害することなく、焼入
れ性及び靱性を向上させる効果があり、この効果を発揮
するには、少なくとも0.１％を添加する必要がある。し
かし、過多に添加するときは、製造費用を高くするの
で、2.０％を添加量の上限とする。Ｃｒは、焼入れ性を
向上させ、所定の組織を有利に与える元素である。この
効果を発揮するためには、0.０５％以上添加する必要が
あるが、2.０％を越えて添加してもその効果は飽和し、
また、製造費用を高くする。従って、Ｃｒ添加量は0.０
５〜2.０％の範囲とする。[0028] Ni has the effect of improving hardenability and toughness without impairing weldability, and at least 0.1% must be added to exert this effect. However, if excessively added, the manufacturing cost becomes high, so 2.0% is made the upper limit of the added amount. Cr is an element that improves the hardenability and advantageously gives a predetermined structure. In order to exert this effect, it is necessary to add more than 0.05%, but even if added over 2.0%, the effect is saturated,
Also, the manufacturing cost is increased. Therefore, the Cr addition amount is 0.0
The range is 5 to 2.0%.
【００２９】Ｍｏも、焼入れ性を向上させ、所定の組織
を有利に与える元素である。この効果を有効に得るため
には、0.０５％以上添加する必要があるが、しかし、1.
０％を越えて添加しても、その効果は飽和し、また、製
造費用を高くする。従って、Ｍｏ添加量は0.０５〜1.０
％の範囲とする。Ｖ、Ｔｉ及びＮｂは、析出強化元素で
あり、フェライト硬さを向上させる効果があるが、しか
し、過度に添加するときは、その効果が飽和し、製造費
用の点からも不利である。そこで、本発明においては、
これら元素の添加量は、Ｖ0.０１〜0.５％、Ｔｉ0.０１
〜0.３０％、Ｎｂ0.０１〜0.２％の範囲とする。Mo is also an element which improves the hardenability and advantageously gives a predetermined structure. In order to obtain this effect effectively, it is necessary to add more than 0.05%, but 1.
Even if added over 0%, the effect is saturated and the manufacturing cost is increased. Therefore, the amount of Mo added is 0.05 to 1.0
The range is%. V, Ti, and Nb are precipitation strengthening elements and have the effect of improving the hardness of ferrite, but when added excessively, the effect saturates, which is also disadvantageous in terms of manufacturing cost. Therefore, in the present invention,
The addition amount of these elements is V0.01-0.5%, Ti0.01
Up to 0.30% and Nb 0.01 to 0.2%.
【００３０】Ｂは、焼入れ性を向上させるのに有効な元
素である。この効果を有効に得るためには、少なくとも
0.０００５％を添加する必要がある。しかし、過多に添
加するときは、その効果が飽和するだけでなく、延性を
低下させるので、その上限を0.０１％とする。B is an element effective for improving hardenability. To obtain this effect effectively, at least
It is necessary to add 0.0005%. However, if added excessively, not only the effect is saturated but also the ductility is lowered, so the upper limit is made 0.01%.
【００３１】次に、本発明による複合組織鋼板の製造方
法について述べる。熱間圧延における仕上温度は、得ら
れる熱延鋼板の全伸び、伸びフランジ性及び疲労特性に
重要な影響を与える。そこで、本発明によれば、先ず、
上述した化学成分を有する鋼を熱間圧延する際に、９５
０〜８００℃の範囲の温度で仕上圧延する。仕上温度を
このように規定するのは、Ａr3変態点におけるフェライ
トの生成核を増大させるためであり、延性に必要なフェ
ライトを短時間に微細に生成させ、また、硬質相を微細
に分散させるためである。Next, a method for manufacturing a composite structure steel sheet according to the present invention will be described. The finishing temperature in hot rolling has an important influence on the total elongation, stretch flangeability and fatigue properties of the hot rolled steel sheet obtained. Therefore, according to the present invention, first,
When hot rolling the steel having the above chemical composition,
Finish rolling is performed at a temperature in the range of 0 to 800 ° C. The reason for defining the finishing temperature in this way is to increase the nuclei of ferrite formation at the Ar 3 transformation point, to form the ferrite necessary for ductility minutely in a short time, and to disperse the hard phase minutely. This is because.
【００３２】仕上温度が９５０℃を越えるときは、仕上
圧延後の冷却過程において、十分な体積率にてフェライ
トを生成させると共に、フェライトと硬質相とを本発明
において規定する範囲の微細な粒径にするのが困難であ
る。仕上温度が８００℃よりも低いときは、仕上圧延時
にフェライトに歪が多量に入って、面内方向性及び延性
を阻害し、加工性が劣化する。以上から、本発明におい
ては、仕上温度を８００〜９５０℃の範囲の温度とす
る。When the finishing temperature exceeds 950 ° C., ferrite is generated in a sufficient volume ratio in the cooling process after finishing rolling, and the ferrite and the hard phase have a fine grain size within the range specified in the present invention. Difficult to do. When the finishing temperature is lower than 800 ° C., a large amount of strain is introduced into the ferrite during finishing rolling, which impairs the in-plane directivity and ductility and deteriorates the workability. From the above, in the present invention, the finishing temperature is set in the range of 800 to 950 ° C.
【００３３】更に、本発明においては、上記仕上圧延後
の冷却過程も重要であり、圧延の後の冷却を１次、２次
及び３次の３段にて行なう。即ち、本発明によれば、１
次冷却は、圧延の後、５秒以内に２次冷却まで、冷却速
度１５℃／秒以上にて急冷するものである。圧延後、１
次冷却までの時間が５秒を越えるときは、仕上圧延によ
って鋼に付与された歪が回復及び再結晶によって開放さ
れ、組織の細粒化が困難となる。通常、圧延の後、１〜
３秒程度で２次冷却が開始される。また、１次冷却の速
度が１５℃／秒未満の場合も、フェライトが高温で生成
し、成長することによって、組織の微細化が困難とな
り、本発明の組織を得るのが困難となる。１次冷却の速
度は、温度制御の点から、通常、１００℃／秒以下であ
る。Further, in the present invention, the cooling process after the finish rolling is also important, and the cooling after rolling is performed in three stages of primary, secondary and tertiary. That is, according to the present invention, 1
The secondary cooling is to perform rapid cooling at a cooling rate of 15 ° C./second or more until secondary cooling within 5 seconds after rolling. After rolling, 1
When the time until the next cooling exceeds 5 seconds, the strain imparted to the steel by the finish rolling is recovered and released by recrystallization, and it becomes difficult to make the structure fine. Usually, after rolling,
Secondary cooling starts in about 3 seconds. Further, even when the primary cooling rate is less than 15 ° C./sec, ferrite is generated and grows at a high temperature, which makes it difficult to refine the structure and makes it difficult to obtain the structure of the present invention. The rate of primary cooling is usually 100 ° C./second or less from the viewpoint of temperature control.
【００３４】２次冷却は、６００〜７５０℃の範囲の温
度域にて、１５℃／秒未満の冷却速度で３〜１５秒の範
囲の時間にわたって徐冷するものである。この２次冷却
によって、本発明にて規定する範囲の粒径のフェライト
を適量生成させると共に、硬質相の粒径と分散状態を制
御する。冷却時間が３秒未満のときは、十分なフェライ
ト量を得ることが困難であり、他方、１５秒を越えると
きは、パーライトが生成して、本発明で規定する組織を
得ることが困難である。２次冷却の速度は、通常、５℃
／秒以上である。これよりも遅いときは、保温のために
特殊な設備が必要となるので好ましくない。The secondary cooling is to gradually cool in a temperature range of 600 to 750 ° C. at a cooling rate of less than 15 ° C./sec for a time of 3 to 15 sec. By this secondary cooling, an appropriate amount of ferrite having a grain size within the range specified in the present invention is generated, and the grain size and dispersed state of the hard phase are controlled. When the cooling time is less than 3 seconds, it is difficult to obtain a sufficient amount of ferrite, while when it exceeds 15 seconds, pearlite is generated and it is difficult to obtain the structure defined by the present invention. . Secondary cooling rate is usually 5 ° C
/ Sec or more. If it is slower than this, special equipment is required for heat retention, which is not preferable.
【００３５】また、２次冷却の温度域が７５０℃よりも
高いときは、フェライト粒径が粗大となり、目的とする
フェライトを得ることが困難である。他方、２次冷却の
温度域が６００℃よりも低いときは、パーライトが生成
し、本発明で規定する組織を得ることが困難である。When the temperature range of the secondary cooling is higher than 750 ° C., the ferrite grain size becomes coarse and it is difficult to obtain the desired ferrite. On the other hand, when the temperature range of the secondary cooling is lower than 600 ° C., pearlite is generated and it is difficult to obtain the structure defined by the present invention.
【００３６】次に、３次冷却は、冷却速度１５℃／秒以
上にて５００℃以下の巻取温度まで冷却するものであ
る。この３次冷却は、巻取温度までの冷却過程におい
て、パーライトを生成させないためである。３次冷却の
速度は、温度制御の点から、通常、１００℃／秒以下で
ある。Next, in the third cooling, cooling is performed at a cooling rate of 15 ° C./sec or more to a coiling temperature of 500 ° C. or less. This tertiary cooling does not generate pearlite in the cooling process up to the winding temperature. The rate of tertiary cooling is usually 100 ° C./sec or less from the viewpoint of temperature control.
【００３７】巻取温度は、５００℃以下の温度である。
巻取温度が５００℃を越えるときは、パーライト若しく
は粗大なベイナイトが生成し、本発明で規定する組織を
得ることが困難である。The coiling temperature is 500 ° C. or lower.
When the coiling temperature exceeds 500 ° C., pearlite or coarse bainite is formed, and it is difficult to obtain the structure defined by the present invention.
【００３８】以上のように本発明によれば、化学成分を
規定した鋼を所定の条件下に熱間圧延すると共に、その
後の冷却を３段にて行なって、組織をフェライト・ベイ
ナイト・マルテンサイトの複合組織とすると共に、それ
ら組織の粒径、硬さ、体積率及び平均自由行程を制御す
ることによって、目的とする疲労特性にすぐれる複合組
織鋼板を得ることができる。As described above, according to the present invention, the steel having the defined chemical composition is hot-rolled under the predetermined conditions, and the subsequent cooling is performed in three stages to obtain the structure of ferrite bainite martensite. By controlling the grain size, hardness, volume ratio, and mean free path of these composites, it is possible to obtain a composite microstructured steel plate having excellent fatigue characteristics as a target.
【００３９】[0039]
【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。The present invention will be described below with reference to examples.
The present invention is not limited to these examples.
【００４０】実施例１ 表１に示す化学成分を有する鋼を真空溶製し、これを圧
延し、３段にて冷却し、巻き取った。製造条件を種々制
御することによって、実施例２に示すように、種々の複
合組織を有する鋼板を得ることができる。製造方法の一
例として、例えば、仕上圧延の後、７２０℃まで冷却速
度４０℃／秒にて１次冷却し、次いで、冷却速度６℃／
秒にて１０秒間、２次冷却し、その後、冷却速度４０℃
／秒にて巻取温度まで３次冷却し、４５０℃で巻き取る
方法を挙げることができる。Example 1 Steels having the chemical components shown in Table 1 were vacuum-melted, rolled, cooled in 3 stages and wound up. By controlling the manufacturing conditions variously, as shown in Example 2, steel sheets having various composite structures can be obtained. As an example of the manufacturing method, for example, after finish rolling, primary cooling is performed at a cooling rate of 40 ° C./second to 720 ° C., and then a cooling rate of 6 ° C. /
Second cooling for 10 seconds, then cooling rate 40 ℃
A method of thirdly cooling to a coiling temperature at 1 / second and coiling at 450 ° C. can be mentioned.
【００４１】このようにして得られた供試材の機械的性
質、硬さ及び顕微鏡組織観察結果を表２に示す。引張特
性は、ＪＩＳ５号引張試験片で試験し、伸びフランジ性
は、鋼板にポンチ打抜きで直径１０mmの穴を開け、先端
角６０°の円錐ポンチで試験した穴拡げ率（λ）で評価
した。疲労強度は、両振り平面曲げ疲労試験で１０7 サ
イクル以上で破断が認められなかった応力とした。Table 2 shows the mechanical properties, hardness, and microscopic observation results of the test material thus obtained. Tensile properties were tested with JIS No. 5 tensile test pieces, and stretch flangeability was evaluated by the hole expansion ratio (λ) tested by punching a steel plate to punch a hole having a diameter of 10 mm and using a conical punch having a tip angle of 60 °. Fatigue strength was defined as the stress at which fracture was not observed in 10 7 cycles or more in the double swing plane bending fatigue test.
【００４２】鋼１〜１２は本発明鋼であり、鋼１３〜１
７は比較鋼である。これらのうち、鋼１１及び１２は冷
延鋼板であり、その他は熱延鋼板である。本発明による
鋼板は、従来の鋼板と比較して、同じ引張強さで同等の
伸びフランジ性を有すると共に、引張強さの半分以上の
疲労特性を有する。化学成分が本発明て規定する範囲に
あっても、微視組織が本発明で規定する組織でないもの
は十分な疲労強度をもたない。また、微視組織が本発明
て規定するものであっても、化学成分、特に、Ｓ量が本
発明で規制する条件を満たさないものは、疲労強度にす
ぐれていても、伸びフランジ性に劣る。Steels 1 to 12 are steels of the present invention, and steels 13 to 1
7 is a comparative steel. Of these, the steels 11 and 12 are cold rolled steel sheets, and the others are hot rolled steel sheets. The steel sheet according to the present invention has the same tensile strength and the same stretch-flangeability as the conventional steel sheet, and has the fatigue property of half or more of the tensile strength. Even if the chemical composition is within the range specified by the present invention, a microstructure that does not have the structure defined by the present invention does not have sufficient fatigue strength. Further, even if the microstructure is defined by the present invention, a chemical component, particularly one whose S content does not satisfy the conditions regulated by the present invention, is excellent in stretch flangeability even if it has excellent fatigue strength. .
【００４３】[0043]
【表１】 [Table 1]
【００４４】[0044]
【表２】 [Table 2]
【００４５】実施例２ 表３に示す化学成分を有する鋼を真空溶製し、表４に示
す条件にて粗圧延して、厚さ３０mmのスラブとし、これ
を４パスにて厚さ3.５mmの熱延板とした。仕上圧延の
後、いずれも５秒以内に、通常、１〜３秒程度にて、表
４に示す冷却速度にて１次冷却を行ない、続いて、表４
に示す開始温度から、表４に示す時間にわたって、徐冷
して、２次冷却を行ない、続いて、表４に示す冷却速度
にて３次冷却を行なった後、表４に示す温度で巻き取っ
た。Example 2 A steel having the chemical composition shown in Table 3 was vacuum-melted and roughly rolled under the conditions shown in Table 4 to form a slab having a thickness of 30 mm. It was a 5 mm hot rolled sheet. After finish rolling, primary cooling was performed at a cooling rate shown in Table 4 within 5 seconds, usually about 1 to 3 seconds, and then Table 4
After gradually cooling from the start temperature shown in Table 4 to the time shown in Table 4, secondary cooling was performed, and then the tertiary cooling was carried out at the cooling rate shown in Table 4, followed by winding at the temperature shown in Table 4. I took it.
【００４６】このようにして得られた供試材の機械的性
質、硬さ及び顕微鏡組織観察結果を表５に示す。引張特
性は、ＪＩＳ５号引張試験片で試験し、伸びフランジ性
は、鋼板にポンチ打抜きで直径１０mmの穴を開け、先端
角６０°の円錐ポンチで試験した穴拡げ率（λ）で評価
した。疲労強度は、両振り平面曲げ疲労試験で１０7 サ
イクル以上で破断が認められなかった応力とした。Table 5 shows the mechanical properties, hardness, and microstructure observation results of the test material thus obtained. Tensile properties were tested with JIS No. 5 tensile test pieces, and stretch flangeability was evaluated by the hole expansion ratio (λ) tested by punching a steel plate to punch a hole having a diameter of 10 mm and using a conical punch having a tip angle of 60 °. Fatigue strength was defined as the stress at which fracture was not observed in 10 7 cycles or more in the double swing plane bending fatigue test.
【００４７】[0047]
【表３】 [Table 3]
【００４８】[0048]
【表４】 [Table 4]
【００４９】[0049]
【表５】 [Table 5]
【００５０】[0050]
【発明の効果】以上のように、本発明による複合組織鋼
板は、従来の３相複合組織鋼板と同等の加工性、特に、
伸びフランジ性を有しながら、すぐれた疲労特性を有し
ており、自動車、鉄道等の構造部材、特に、強加工の必
要な部材の製造に好適に用いることができる。As described above, the composite structure steel sheet according to the present invention has the same workability as that of the conventional three-phase composite structure steel sheet, particularly,
Since it has stretch-flangeability and excellent fatigue properties, it can be suitably used for manufacturing structural members such as automobiles and railroads, particularly members that require strong working.
【図面の簡単な説明】[Brief description of drawings]
【図１】は、得られる鋼板におけるベイナイト粒径と疲
労強度との関係を示すグラフである。FIG. 1 is a graph showing the relationship between bainite grain size and fatigue strength in the obtained steel sheet.
【図２】は、得られる鋼板におけるベイナイトのビッカ
ース硬さ（Ｈｖ）と疲労強度との関係を示すグラフであ
る。FIG. 2 is a graph showing the relationship between the Vickers hardness (Hv) of bainite and the fatigue strength of the obtained steel sheet.
【図３】は、得られる鋼板における硬質相の平均自由工
程と疲労強度との関係を示すグラフである。FIG. 3 is a graph showing the relationship between the mean free path of the hard phase and the fatigue strength in the obtained steel sheet.
フロントページの続き (72)発明者 横幕 俊典 兵庫県神戸市西区高塚台１丁目５番５号 株式会社神戸製鋼所神戸総合技術研究所内Front page continued (72) Inventor Toshinori Yokomaku 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel Works, Ltd. Kobe Research Institute
Claims (8)
イト相中に硬質のベイナイト相とマルテンサイト相を含
有し、フェライトの結晶粒径が４〜１５μｍ、フェライ
トのビッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナ
イトの結晶粒径が６μｍ以下、ベイナイトのビッカース
硬さ（Ｈｖ）が２５０〜４００、マルテンサイトの結晶
粒径が６μｍ以下、マルテンサイトのビッカース硬さ
（Ｈｖ）が４００〜７００である３相複合組織からな
り、更に、硬質相全体の体積率が５〜４０％であり、硬
質相全体の平均自由行程が２０μｍ以下である疲労特性
にすぐれる複合組織鋼板。1. By weight%, C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 ~ 0.1%, S 0.005% or less, the balance is iron and inevitable impurities, the ferrite phase contains a hard bainite phase and a martensite phase, and the ferrite grain size is 4 to 15 µm. , Ferrite Vickers hardness (Hv) is 140 to 180, bainite crystal grain size is 6 μm or less, bainite Vickers hardness (Hv) is 250 to 400, martensite crystal grain size is 6 μm or less, martensite Vickers Composed of a three-phase composite structure having a hardness (Hv) of 400 to 700, a volume ratio of the entire hard phase of 5 to 40%, and an average free path of the entire hard phase of 20 μm or less. Composite structure steel sheet.
イト相中に硬質のベイナイト相とマルテンサイト相を含
有し、フェライトの結晶粒径が４〜１５μｍ、フェライ
トのビッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナ
イトの結晶粒径が６μｍ以下、ベイナイトのビッカース
硬さ（Ｈｖ）が２５０〜４００、マルテンサイトの結晶
粒径が６μｍ以下、マルテンサイトのビッカース硬さ
（Ｈｖ）が４００〜７００である３相複合組織からな
り、更に、硬質相全体の体積率が５〜４０％であり、硬
質相全体の平均自由行程が２０μｍ以下である疲労特性
にすぐれる複合組織鋼板。2. In% by weight, C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 Content of 0.1%, S 0.005% or less, Ca 0.01% or less, balance iron and unavoidable impurities, and a ferrite phase containing a hard bainite phase and a martensite phase. The crystal grain size is 4 to 15 μm, the Vickers hardness (Hv) of ferrite is 140 to 180, the crystal grain size of bainite is 6 μm or less, the Vickers hardness (Hv) of bainite is 250 to 400, and the crystal grain size of martensite is It is composed of a three-phase composite structure having a martensite Vickers hardness (Hv) of 400 to 700, a volume ratio of the entire hard phase of 5 to 40%, and an average free path of the entire hard phase of 20 μm. Steel sheet with a composite structure that has the following fatigue properties
し、残部鉄及び不可避的不純物よりなり、フェライト相
中に硬質のベイナイト相とマルテンサイト相を含有し、
フェライトの結晶粒径が４〜１５μｍ、フェライトのビ
ッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナイトの
結晶粒径が６μｍ以下、ベイナイトのビッカース硬さ
（Ｈｖ）が２５０〜４００、マルテンサイトの結晶粒径
が６μｍ以下、マルテンサイトのビッカース硬さ（Ｈ
ｖ）が４００〜７００である３相複合組織からなり、更
に、硬質相全体の体積率が５〜４０％であり、硬質相全
体の平均自由行程が２０μｍ以下である疲労特性にすぐ
れる複合組織鋼板。3. By weight%, (a) C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 to 0.1%, S 0.005% or less, and (b) Cu 0.1 to 2%, Ni 0.1 to 2%, Cr 0.05 to 2%, Mo 0. 0.05 to 1%, V 0.01 to 0.5%, Ti 0.01 to 0.3%, Nb 0.01 to 0.2%, and B 0.0005 to 0.01%. Containing at least one element that is composed of the balance iron and unavoidable impurities, and contains a hard bainite phase and a martensite phase in the ferrite phase,
Ferrite has a crystal grain size of 4 to 15 μm, ferrite has a Vickers hardness (Hv) of 140 to 180, bainite has a grain size of 6 μm or less, bainite has a Vickers hardness (Hv) of 250 to 400, and martensite crystal grains. Vickers hardness of martensite (diameter 6 μm or less, H
v) is a three-phase composite structure of 400 to 700, further, the volume ratio of the entire hard phase is 5 to 40%, and the average free path of the entire hard phase is 20 μm or less. steel sheet.
し、残部鉄及び不可避的不純物よりなり、フェライト相
中に硬質のベイナイト相とマルテンサイト相を含有し、
フェライトの結晶粒径が４〜１５μｍ、フェライトのビ
ッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナイトの
結晶粒径が６μｍ以下、ベイナイトのビッカース硬さ
（Ｈｖ）が２５０〜４００、マルテンサイトの結晶粒径
が６μｍ以下、マルテンサイトのビッカース硬さ（Ｈ
ｖ）が４００〜７００である３相複合組織からなり、更
に、硬質相全体の体積率が５〜４０％であり、硬質相全
体の平均自由行程が２０μｍ以下である疲労特性にすぐ
れる複合組織鋼板。4. In weight%, (a) C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 to 0.1%, S 0.005% or less, Ca 0.01% or less, and (b) Cu 0.1 to 2%, Ni 0.1 to 2%, Cr 0.1. 05-2%, Mo 0.05-1%, V 0.01-0.5%, Ti 0.01-0.3%, Nb 0.01-0.2%, B 0.0005-0. Containing at least one element selected from the group consisting of 01%, the balance consisting of iron and unavoidable impurities, containing a hard bainite phase and martensite phase in the ferrite phase,
Ferrite has a crystal grain size of 4 to 15 μm, ferrite has a Vickers hardness (Hv) of 140 to 180, bainite has a grain size of 6 μm or less, bainite has a Vickers hardness (Hv) of 250 to 400, and martensite crystal grains. Vickers hardness of martensite (diameter 6 μm or less, H
v) is a three-phase composite structure of 400 to 700, further, the volume ratio of the entire hard phase is 5 to 40%, and the average free path of the entire hard phase is 20 μm or less. steel sheet.
圧延する際に、９５０〜８００℃の範囲の温度で仕上圧
延し、次いで、圧延の後、５秒以内に冷却速度１５℃／
秒以上で冷却を開始し、冷却する１次冷却を行ない、続
いて、７５０〜６００℃の温度域において冷却速度１５
℃／秒未満にて３〜１５秒間徐冷する２次冷却を行な
い、続いて、冷却速度１５℃／秒以上にて冷却する３次
冷却を行なった後、５００℃以下の温度で巻取って、フ
ェライト相中に硬質のベイナイト相とマルテンサイト相
を含有し、フェライトの結晶粒径が４〜１５μｍ、フェ
ライトのビッカース硬さ（Ｈｖ）が１４０〜１８０、ベ
イナイトの結晶粒径が６μｍ以下、ベイナイトのビッカ
ース硬さ（Ｈｖ）が２５０〜４００、マルテンサイトの
結晶粒径が６μｍ以下、マルテンサイトのビッカース硬
さ（Ｈｖ）が４００〜７００である３相複合組織からな
り、更に、硬質相全体の体積率が５〜４０％であり、硬
質相全体の平均自由行程が２０μｍ以下である疲労特性
にすぐれる複合組織鋼板の製造方法。5. By weight%, C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 ~ 0.1%, S 0.005% or less, when hot rolling steel consisting of balance iron and unavoidable impurities, finish rolling at a temperature in the range of 950 to 800 ° C, and then rolling Within 5 seconds, cool down at 15 ℃ /
The cooling is started for more than 2 seconds, the primary cooling is performed, and then the cooling rate is 15 in the temperature range of 750 to 600 ° C.
Secondary cooling is performed by gradually cooling for 3 to 15 seconds at a temperature of less than C / sec, followed by tertiary cooling at a cooling rate of 15 ° C / sec or more, and then winding at a temperature of 500 ° C or less. , Containing a hard bainite phase and a martensite phase in the ferrite phase, the ferrite grain size is 4 to 15 μm, the ferrite Vickers hardness (Hv) is 140 to 180, the bainite grain size is 6 μm or less, bainite Has a Vickers hardness (Hv) of 250 to 400, a grain size of martensite of 6 μm or less, and a Vickers hardness (Hv) of martensite of 400 to 700. A method for producing a steel sheet having a composite structure having a volume ratio of 5 to 40% and an average free path of the entire hard phase of 20 μm or less and having excellent fatigue properties.
圧延する際に、９５０〜８００℃の範囲の温度で仕上圧
延し、次いで、圧延の後、５秒以内に冷却速度１５℃／
秒以上で冷却を開始し、冷却する１次冷却を行ない、続
いて、７５０〜６００℃の温度域において冷却速度１５
℃／秒未満にて３〜１５秒間徐冷する２次冷却を行な
い、続いて、冷却速度１５℃／秒以上にて冷却する３次
冷却を行なった後、５００℃以下の温度で巻取って、フ
ェライト相中に硬質のベイナイト相とマルテンサイト相
を含有し、フェライトの結晶粒径が４〜１５μｍ、フェ
ライトのビッカース硬さ（Ｈｖ）が１４０〜１８０、ベ
イナイトの結晶粒径が６μｍ以下、ベイナイトのビッカ
ース硬さ（Ｈｖ）が２５０〜４００、マルテンサイトの
結晶粒径が６μｍ以下、マルテンサイトのビッカース硬
さ（Ｈｖ）が４００〜７００である３相複合組織からな
り、更に、硬質相全体の体積率が５〜４０％であり、硬
質相全体の平均自由行程が２０μｍ以下である疲労特性
にすぐれる複合組織鋼板の製造方法。6. In% by weight, C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 ~ 0.1%, S 0.005% or less, Ca 0.01% or less, and finish at a temperature in the range of 950 to 800 ° C during hot rolling of steel consisting of balance iron and unavoidable impurities Rolling, then cooling rate 15 ° C / within 5 seconds after rolling
The cooling is started for more than 2 seconds, the primary cooling is performed, and then the cooling rate is 15 in the temperature range of 750 to 600 ° C.
Secondary cooling is performed by gradually cooling at less than C / sec for 3 to 15 seconds, followed by tertiary cooling at a cooling rate of 15 ° C / sec or more, and then winding at a temperature of 500 ° C or less. , Containing a hard bainite phase and a martensite phase in the ferrite phase, the ferrite grain size is 4 to 15 μm, the ferrite Vickers hardness (Hv) is 140 to 180, the bainite grain size is 6 μm or less, bainite Has a Vickers hardness (Hv) of 250 to 400, a crystal grain size of martensite of 6 μm or less, and a Vickers hardness (Hv) of martensite of 400 to 700. A method for producing a steel sheet having a composite structure having a volume ratio of 5 to 40% and an average free path of the entire hard phase of 20 μm or less and having excellent fatigue properties.
し、残部鉄及び不可避的不純物よりなる鋼を熱間圧延す
る際に、９５０〜８００℃の範囲の温度で仕上圧延し、
次いで、圧延の後、５秒以内に冷却速度１５℃／秒以上
で冷却を開始し、冷却する１次冷却を行ない、続いて、
７５０〜６００℃の温度域において冷却速度１５℃／秒
未満にて３〜１５秒間徐冷する２次冷却を行ない、続い
て、冷却速度１５℃／秒以上にて冷却する３次冷却を行
なった後、５００℃以下の温度で巻取って、フェライト
相中に硬質のベイナイト相とマルテンサイト相を含有
し、フェライトの結晶粒径が４〜１５μｍ、フェライト
のビッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナイ
トの結晶粒径が６μｍ以下、ベイナイトのビッカース硬
さ（Ｈｖ）が２５０〜４００、マルテンサイトの結晶粒
径が６μｍ以下、マルテンサイトのビッカース硬さ（Ｈ
ｖ）が４００〜７００である３相複合組織からなり、更
に、硬質相全体の体積率が５〜４０％であり、硬質相全
体の平均自由行程が２０μｍ以下である疲労特性にすぐ
れる複合組織鋼板の製造方法。7. By weight%, (a) C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 to 0.1%, S 0.005% or less, and (b) Cu 0.1 to 2%, Ni 0.1 to 2%, Cr 0.05 to 2%, Mo 0. 0.05 to 1%, V 0.01 to 0.5%, Ti 0.01 to 0.3%, Nb 0.01 to 0.2%, and B 0.0005 to 0.01%. In the hot rolling of steel containing at least one kind of element, which is composed of balance iron and unavoidable impurities, finish rolling is performed at a temperature in the range of 950 to 800 ° C.,
Then, after rolling, cooling is started at a cooling rate of 15 ° C./second or more within 5 seconds, primary cooling is performed, and subsequently,
In the temperature range of 750 to 600 ° C., secondary cooling was performed by gradually cooling at a cooling rate of less than 15 ° C./sec for 3 to 15 seconds, and subsequently, tertiary cooling was performed at a cooling rate of 15 ° C./sec or more. After that, it is wound at a temperature of 500 ° C. or lower, contains a hard bainite phase and a martensite phase in the ferrite phase, has a ferrite grain size of 4 to 15 μm, and has a Vickers hardness (Hv) of 140 to 180. , Bainite has a grain size of 6 μm or less, bainite has a Vickers hardness (Hv) of 250 to 400, martensite has a grain size of 6 μm or less, and martensite has a Vickers hardness (Hv).
v) is composed of a three-phase composite structure of 400 to 700, the volume ratio of the entire hard phase is 5 to 40%, and the average free path of the entire hard phase is 20 μm or less. Steel plate manufacturing method.
し、残部鉄及び不可避的不純物よりなる鋼を熱間圧延す
る際に、９５０〜８００℃の範囲の温度で仕上圧延し、
次いで、圧延の後、５秒以内に冷却速度１５℃／秒以上
で冷却を開始し、冷却する１次冷却を行ない、続いて、
７５０〜６００℃の温度域において冷却速度１５℃／秒
未満にて３〜１５秒間徐冷する２次冷却を行ない、続い
て、冷却速度１５℃／秒以上にて冷却する３次冷却を行
なった後、５００℃以下の温度で巻取って、フェライト
相中に硬質のベイナイト相とマルテンサイト相を含有
し、フェライトの結晶粒径が４〜１５μｍ、フェライト
のビッカース硬さ（Ｈｖ）が１４０〜１８０、ベイナイ
トの結晶粒径が６μｍ以下、ベイナイトのビッカース硬
さ（Ｈｖ）が２５０〜４００、マルテンサイトの結晶粒
径が６μｍ以下、マルテンサイトのビッカース硬さ（Ｈ
ｖ）が４００〜７００である３相複合組織からなり、更
に、硬質相全体の体積率が５〜４０％であり、硬質相全
体の平均自由行程が２０μｍ以下である疲労特性にすぐ
れる複合組織鋼板の製造方法。8. In weight%, (a) C 0.03 to 0.15%, Si 0.3 to 1.5%, Mn 0.1 to 2.0%, P 0.1% or less, Al 0.005 to 0.1%, S 0.005% or less, Ca 0.01% or less, and (b) Cu 0.1 to 2%, Ni 0.1 to 2%, Cr 0.1. 05-2%, Mo 0.05-1%, V 0.01-0.5%, Ti 0.01-0.3%, Nb 0.01-0.2%, B 0.0005-0. When hot-rolling steel containing at least one element selected from the group consisting of 01% and the balance iron and unavoidable impurities, finish rolling at a temperature in the range of 950 to 800 ° C.,
Then, after rolling, cooling is started at a cooling rate of 15 ° C./second or more within 5 seconds, primary cooling is performed, and subsequently,
In the temperature range of 750 to 600 ° C., secondary cooling was performed by gradually cooling at a cooling rate of less than 15 ° C./second for 3 to 15 seconds, and subsequently, third cooling was performed at a cooling rate of 15 ° C./second or more. Thereafter, the ferrite phase contains a hard bainite phase and a martensite phase at a temperature of 500 ° C. or lower, the ferrite has a crystal grain size of 4 to 15 μm, and the ferrite has a Vickers hardness (Hv) of 140 to 180. , The grain size of bainite is 6 μm or less, the Vickers hardness (Hv) of bainite is 250 to 400, the grain size of martensite is 6 μm or less, the Vickers hardness of martensite (Hv).
v) is a three-phase composite structure of 400 to 700, further, the volume ratio of the entire hard phase is 5 to 40%, and the average free path of the entire hard phase is 20 μm or less. Steel plate manufacturing method.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00005895A JP3231204B2 (en) | 1995-01-04 | 1995-01-04 | Composite structure steel sheet excellent in fatigue characteristics and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP00005895A JP3231204B2 (en) | 1995-01-04 | 1995-01-04 | Composite structure steel sheet excellent in fatigue characteristics and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08188847A true JPH08188847A (en) | 1996-07-23 |
| JP3231204B2 JP3231204B2 (en) | 2001-11-19 |
Family
ID=11463619
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP00005895A Expired - Fee Related JP3231204B2 (en) | 1995-01-04 | 1995-01-04 | Composite structure steel sheet excellent in fatigue characteristics and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3231204B2 (en) |
Cited By (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0997548A4 (en) * | 1998-03-12 | 2001-06-13 | Kobe Steel Ltd | High strength hot rolled steel sheet excellent in formability |
| JP2003293083A (en) * | 2002-04-01 | 2003-10-15 | Sumitomo Metal Ind Ltd | Hot rolled steel sheet and method of producing hot rolled steel sheet and cold rolled steel sheet |
| WO2005031021A1 (en) * | 2003-09-29 | 2005-04-07 | Jfe Steel Corporation | Steel parts for machine structure, material therefor, and method for manufacture thereof |
| JP2007314819A (en) * | 2006-05-23 | 2007-12-06 | Kobe Steel Ltd | Steel sheet having excellent fatigue crack propagation resistance |
| JP2008088485A (en) * | 2006-09-29 | 2008-04-17 | Kobe Steel Ltd | Steel material excellent in toughness and fatigue crack progress resistance of welding heat-affected zone, and producing method therefor |
| CN103184386A (en) * | 2013-04-12 | 2013-07-03 | 莱芜钢铁集团有限公司 | Method for improving mechanical property of low-carbon silicomanganese series cold rolling dual-phase steel |
| JP2013136829A (en) * | 2011-11-30 | 2013-07-11 | Jfe Steel Corp | Steel material with excellent crashworthiness and manufacturing process therefor |
| US9149868B2 (en) | 2005-10-20 | 2015-10-06 | Nucor Corporation | Thin cast strip product with microalloy additions, and method for making the same |
| US9999918B2 (en) | 2005-10-20 | 2018-06-19 | Nucor Corporation | Thin cast strip product with microalloy additions, and method for making the same |
| US10071416B2 (en) | 2005-10-20 | 2018-09-11 | Nucor Corporation | High strength thin cast strip product and method for making the same |
| WO2019124746A1 (en) * | 2017-12-21 | 2019-06-27 | 주식회사 포스코 | Hot-rolled steel sheet having excellent expandability and method for manufacturing same |
| US11193188B2 (en) | 2009-02-20 | 2021-12-07 | Nucor Corporation | Nitriding of niobium steel and product made thereby |
| US11332803B2 (en) * | 2017-04-21 | 2022-05-17 | Nippon Steel Corporation | High strength hot-dip galvanized steel sheet and production method therefor |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5365217B2 (en) | 2008-01-31 | 2013-12-11 | Ｊｆｅスチール株式会社 | High strength steel plate and manufacturing method thereof |
| JP5703608B2 (en) | 2009-07-30 | 2015-04-22 | Ｊｆｅスチール株式会社 | High strength steel plate and manufacturing method thereof |
| WO2016021197A1 (en) | 2014-08-07 | 2016-02-11 | Ｊｆｅスチール株式会社 | High-strength steel sheet and production method for same, and production method for high-strength galvanized steel sheet |
| CN106574342B (en) | 2014-08-07 | 2018-10-12 | 杰富意钢铁株式会社 | The manufacturing method of high-strength steel sheet and its manufacturing method and high strength galvanized steel plate |
| EP3178956A4 (en) | 2014-08-07 | 2017-06-28 | JFE Steel Corporation | High-strength steel sheet and production method for same, and production method for high-strength galvanized steel sheet |
-
1995
- 1995-01-04 JP JP00005895A patent/JP3231204B2/en not_active Expired - Fee Related
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0997548A4 (en) * | 1998-03-12 | 2001-06-13 | Kobe Steel Ltd | High strength hot rolled steel sheet excellent in formability |
| JP2003293083A (en) * | 2002-04-01 | 2003-10-15 | Sumitomo Metal Ind Ltd | Hot rolled steel sheet and method of producing hot rolled steel sheet and cold rolled steel sheet |
| WO2005031021A1 (en) * | 2003-09-29 | 2005-04-07 | Jfe Steel Corporation | Steel parts for machine structure, material therefor, and method for manufacture thereof |
| US9149868B2 (en) | 2005-10-20 | 2015-10-06 | Nucor Corporation | Thin cast strip product with microalloy additions, and method for making the same |
| US10071416B2 (en) | 2005-10-20 | 2018-09-11 | Nucor Corporation | High strength thin cast strip product and method for making the same |
| US9999918B2 (en) | 2005-10-20 | 2018-06-19 | Nucor Corporation | Thin cast strip product with microalloy additions, and method for making the same |
| JP2007314819A (en) * | 2006-05-23 | 2007-12-06 | Kobe Steel Ltd | Steel sheet having excellent fatigue crack propagation resistance |
| JP2008088485A (en) * | 2006-09-29 | 2008-04-17 | Kobe Steel Ltd | Steel material excellent in toughness and fatigue crack progress resistance of welding heat-affected zone, and producing method therefor |
| US11193188B2 (en) | 2009-02-20 | 2021-12-07 | Nucor Corporation | Nitriding of niobium steel and product made thereby |
| JP2013136829A (en) * | 2011-11-30 | 2013-07-11 | Jfe Steel Corp | Steel material with excellent crashworthiness and manufacturing process therefor |
| CN103184386A (en) * | 2013-04-12 | 2013-07-03 | 莱芜钢铁集团有限公司 | Method for improving mechanical property of low-carbon silicomanganese series cold rolling dual-phase steel |
| US11332803B2 (en) * | 2017-04-21 | 2022-05-17 | Nippon Steel Corporation | High strength hot-dip galvanized steel sheet and production method therefor |
| WO2019124746A1 (en) * | 2017-12-21 | 2019-06-27 | 주식회사 포스코 | Hot-rolled steel sheet having excellent expandability and method for manufacturing same |
| CN111511949A (en) * | 2017-12-21 | 2020-08-07 | Posco公司 | Hot-rolled steel sheet having excellent expansibility and method for producing same |
| US11560607B2 (en) | 2017-12-21 | 2023-01-24 | Posco Co., Ltd | Hot-rolled steel sheet having excellent expandability and method for manufacturing same |
| US11851727B2 (en) | 2017-12-21 | 2023-12-26 | Posco Co., Ltd. | Hot-rolled steel sheet having excellent expandability and method for manufacturing same |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3231204B2 (en) | 2001-11-19 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR100799421B1 (en) | Cold-formed steel pipe and tube having excellent in weldability with 490MPa-class of low yield ratio, and manufacturing process thereof | |
| JP5146051B2 (en) | Plate thickness excellent in toughness and deformability: Steel material for high-strength steel pipes of 25 mm or more and method for producing the same | |
| JP4161935B2 (en) | Hot-rolled steel sheet and manufacturing method thereof | |
| JP5798740B2 (en) | High-strength cold-rolled steel sheet with excellent formability and manufacturing method | |
| KR20010020169A (en) | Hot Rolled High Strength Steel Sheet with Excellent Formability | |
| JP3231204B2 (en) | Composite structure steel sheet excellent in fatigue characteristics and method for producing the same | |
| JPH05179396A (en) | Low yield ratio high strength hot rolled steel sheet and manufacture thereof | |
| JPH06200351A (en) | High strength hot rolled steel plate excellent in stretch-flange formability | |
| JP2000239791A (en) | Superfine-grained hot rolled steel plate excellent in impact resistance | |
| KR102098482B1 (en) | High-strength steel sheet having excellent impact resistant property and method for manufacturing thereof | |
| JP2001220647A (en) | High strength cold rolled steel plate excellent in workability and producing method therefor | |
| JP2011080106A (en) | High strength cold-rolled steel sheet excellent in balance of extension and formability for extending flange | |
| JP2001226741A (en) | High strength cold rolled steel sheet excellent in stretch flanging workability and producing method therefor | |
| JPH10195591A (en) | High strength hot rolled steel sheet for thermal hardening excellent in stretch-flanging property and its production | |
| JP2003321727A (en) | Low yield ratio high-tensile steel plate of excellent bendability and method for manufacturing the same | |
| CN113692456B (en) | Ultrahigh-strength steel sheet having excellent shear workability and method for producing same | |
| JP4911122B2 (en) | Cold rolled steel sheet with ultrafine grain structure | |
| JP4400079B2 (en) | Method for producing cold-rolled steel sheet having ultrafine grain structure | |
| JP2008266792A (en) | Hot-rolled steel sheet | |
| JPH0987798A (en) | High tensile strength hot rolled steel plate, having superfine grain and excellent in ductility, toughness, fatigue characteristic, and strength-ductility balance, and its production | |
| JP7070814B1 (en) | Thick steel plate and its manufacturing method | |
| JP2011038121A (en) | High tensile cold-rolled steel sheet and method of producing the same | |
| JP2002363685A (en) | Low yield ratio high strength cold rolled steel sheet | |
| JP3371744B2 (en) | Low yield ratio steel material and method of manufacturing the same | |
| JP3296591B2 (en) | Low yield ratio high strength hot rolled steel sheet and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20070914 Year of fee payment: 6 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20080914 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Year of fee payment: 7 Free format text: PAYMENT UNTIL: 20080914 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090914 Year of fee payment: 8 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090914 Year of fee payment: 8 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Year of fee payment: 9 Free format text: PAYMENT UNTIL: 20100914 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Year of fee payment: 9 Free format text: PAYMENT UNTIL: 20100914 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Year of fee payment: 10 Free format text: PAYMENT UNTIL: 20110914 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110914 Year of fee payment: 10 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120914 Year of fee payment: 11 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Year of fee payment: 11 Free format text: PAYMENT UNTIL: 20120914 |
|
| FPAY | Renewal fee payment (prs date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130914 Year of fee payment: 12 |
|
| LAPS | Cancellation because of no payment of annual fees |