JP2968105B2 - Steel plate having good fatigue characteristics and method for producing the same - Google Patents
Steel plate having good fatigue characteristics and method for producing the sameInfo
- Publication number
- JP2968105B2 JP2968105B2 JP31564891A JP31564891A JP2968105B2 JP 2968105 B2 JP2968105 B2 JP 2968105B2 JP 31564891 A JP31564891 A JP 31564891A JP 31564891 A JP31564891 A JP 31564891A JP 2968105 B2 JP2968105 B2 JP 2968105B2
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- Prior art keywords
- rolling
- less
- pearlite
- fatigue
- steel
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Description
【０００１】[0001]
【産業上の利用分野】本発明は、溶接構造物の疲労強度
を向上させるために疲労亀裂先端にマイクロクラックを
多数発生させる組織を有する鋼板とその製造法に関する
ものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet having a structure that generates many microcracks at the tip of a fatigue crack in order to improve the fatigue strength of a welded structure, and a method for producing the same.
【０００２】[0002]
【従来の技術】構造物の軽量化、大容量化の要求に応
え、構造用鋼板の高強度化が急速に進んでいる。しかし
ながら、繰り返し荷重を受ける構造物では、降伏強度の
みならず疲労強度を考慮しなければならず、高強度化の
ニーズに応えることができない場合があり、疲労強度の
向上が切望されている。特に、溶接構造物では溶接止端
部から疲労亀裂の発生する場合が多く、鋼材の強度を向
上させても疲労強度は殆ど向上しない。2. Description of the Related Art In response to demands for lighter structures and larger capacities of structures, the strength of structural steel sheets is rapidly increasing. However, in a structure subjected to repeated loads, not only the yield strength but also the fatigue strength must be taken into consideration, and it may not be possible to meet the need for higher strength. In particular, in a welded structure, fatigue cracks often occur from the weld toe, and even if the strength of the steel material is improved, the fatigue strength hardly improves.
【０００３】溶接構造物の疲労強度は、主として溶接部
の止端部形状によって支配されることが知られており、
溶接部の止端部処理等の疲労強度向上策が適用されるこ
とがある。しかし、止端部処理は、構造物の建造工数を
増大させるばかりでなく、溶接部位によっては止端部処
理が実施できない場合も多く、鋼材面から疲労強度向上
が切望されている。It is known that the fatigue strength of a welded structure is mainly governed by the shape of the toe of the weld.
In some cases, measures for improving fatigue strength such as treatment of a toe portion of a welded portion are applied. However, the toe treatment not only increases the number of man-hours for building the structure, but also often cannot be carried out depending on the welded portion, and there is a strong demand for improvement in fatigue strength from the steel surface.
【０００４】溶接継手部の疲労破壊は一般に応力集中の
大きな溶接止端部から発生するため、発生特性は溶接止
端部形状に大きく影響され、鋼材組成、組織には殆ど影
響しないことが知られている。そこで、鋼材組織を制御
して疲労特性を向上させるためには、止端部で発生した
疲労亀裂の伝播を遅延させることが有効である。[0004] Since fatigue fracture of a welded joint generally occurs from a weld toe where stress concentration is large, it is known that the occurrence characteristics are greatly affected by the shape of the weld toe and have little effect on the steel material composition and structure. ing. Therefore, in order to improve the fatigue properties by controlling the steel structure, it is effective to delay the propagation of the fatigue crack generated at the toe.
【０００５】疲労亀裂伝播を遅延させるためには、疲労
亀裂伝播面に垂直方向に亀裂を分岐させることが有効で
あることがＰｒｏｃｅｅｄｉｎｇｓ ｏｆ ａｎｉｎｔ
ｅｒｎａｔｉｏｎａｌ ｃｏｎｆｅｒｅｎｃｅ ｓｐｏ
ｎｓｏｒｅｄ ｂｙ Ｍｅｔａｌｓ Ｓｏｃｉｅｔｙ
（２１−２３，Ｏｃｔｏｂｅｒ，１９８１，Ｌｏｎｄｏ
ｎ）のＰ．７９〜に記載されている。また同様な方法と
して日本造船学会論文集Ｖｏｌ．１６９，ｐｐ．２５７
〜２６６では微小セパレーションによる疲労亀裂伝播速
度向上効果を示しており、セパレーション指数が大きい
程微小セパレーションも発生しやすいとの報告がなされ
ている。In order to delay the fatigue crack propagation, it is effective to branch the crack in a direction perpendicular to the fatigue crack propagation surface.
electronic conference spo
nsored by Metals Society
(21-23, October, 1981, London)
n). 79-. As a similar method, the Transactions of the Shipbuilding Society of Japan Vol. 169, pp. 257
266 show the effect of improving the fatigue crack propagation speed by micro-separation, and reports that micro-separation is more likely to occur as the separation index increases.
【０００６】しかしながら、発明者らが、通常のセパレ
ーション指数として用いられているシャルピー試験片か
ら求めたＳＩmax と疲労伝播速度の関係を調査した結
果、ＳＩmax と疲労伝播特性の間には直接関係が認めら
れないことのあることを確認した。[0006] However, the inventors of the present invention have investigated the relationship between SI max and fatigue propagation speed obtained from a Charpy test piece used as a normal separation index, and found that there is a direct relationship between SI max and fatigue propagation characteristics. It was confirmed that sometimes was not recognized.
【０００７】また、セパレーションによる疲労亀裂伝播
速度遅延効果はΔＫ値の低いレベルで有効なことが、前
述の日本造船学会論文集Ｖｏｌ．１６９，ｐｐ．２５７
−２６６に記載されているが、セパレーションは結晶方
位の異なる集合組織間の塑性異方性により発生するもの
であり、ΔＫ値の低い領域では塑性域が小さいためセパ
レーションの発生が困難となる。そこで、低Ｋ値レベル
でも疲労亀裂の伝播を遅延させるようなマイクロクラッ
クを発生させるのに必要な組織制御に関する技術の開発
が望まれている。Further, the effect of the separation of the fatigue crack propagation speed by the separation is effective at a low ΔK value. 169, pp. 257
As described in -266, separation occurs due to plastic anisotropy between textures having different crystal orientations. In a region having a low ΔK value, the plastic region is small, so that separation is difficult to occur. Therefore, there is a demand for the development of a technique for controlling the structure required to generate a microcrack that delays the propagation of a fatigue crack even at a low K value level.
【０００８】[0008]
【発明が解決しようとする課題】本発明は、疲労特性の
良い鋼板および疲労強度を向上させるために、疲労亀裂
先端に低ΔＫ領域でもマイクロクラックを多数発生させ
る組織制御の製造方法を提供することを課題とするもの
である。SUMMARY OF THE INVENTION It is an object of the present invention to provide a steel sheet having good fatigue properties and a method of controlling the structure in which a large number of microcracks are generated at the tip of a fatigue crack even in a low ΔK region in order to improve the fatigue strength. Is the subject.
【０００９】[0009]
【課題を解決するための手段】本発明の要旨は、厚みが
２μｍ以下で間隔が２０μｍ以下のパーライトバンドが
縞状に存在し、かつパーライトバンド相の間のマトリッ
クス組織はアスペクト比（長径／短径の比）が４以上で
短径が１０μｍ以下の集合組織コロニーからなる疲労特
性の優れた鋼板である。The gist of the present invention is that a pearlite band having a thickness of 2 μm or less and an interval of 20 μm or less exists in stripes, and a matrix structure between the pearlite band phases has an aspect ratio (long diameter / short diameter). This is a steel sheet having excellent fatigue properties consisting of textured colonies having a diameter ratio of 4 or more and a minor axis of 10 μm or less.
【００１０】更に本発明は構造用鋼である鋼片もしくは
鋼板をγ再結晶域で１℃／秒以上の冷却速度で冷却しな
がら圧下率３０％以上の圧延を行い、引き続いて３０％
以上の未再結晶域圧延を実施した後、Ａｒ3 〜Ａｒ1 温
度域での累積圧下率ｄAr3 −ｄAr1 がα分率：ａ（％）
の増加に応じて ０．６×ａ≦ｄAr3 −ｄAr1 （％）≦０．４×ａ−１０ を満足するようにα分率の増加に応じて、累積圧下率を
増加させるα−γ二相域圧延を行い、厚みが２μｍ以下
で間隔が２０μｍ以下のパーライトバンドが縞状に存在
し、かつパーライトバンド相の間のマトリックス組織は
アスペクト比（長径／短径の比）が４以上で短径が１０
μｍ以下の集合組織コロニーをうることを特徴とする疲
労特性の優れた鋼板の製造方法である。[0010] Further, the present invention provides rolling of a slab or steel plate as a structural steel at a reduction rate of 30% or more while cooling at a cooling rate of 1 ° C / sec or more in a γ recrystallization region.
After performing the above-mentioned unrecrystallization zone rolling, the cumulative rolling reduction dAr 3 −dAr 1 in the Ar 3 to Ar 1 temperature range is α fraction: a (%)
Α-γ that increases the cumulative draft as the α-fraction increases so as to satisfy 0.6 × a ≦ dAr 3 −dAr 1 (%) ≦ 0.4 × a-10 according to the increase of The two-phase zone rolling is performed, and a pearlite band having a thickness of 2 μm or less and an interval of 20 μm or less exists in stripes, and the matrix structure between the pearlite band phases has an aspect ratio (major axis / minor axis ratio) of 4 or more. Minor axis is 10
This is a method for producing a steel sheet having excellent fatigue characteristics, characterized in that a texture colony of not more than μm is obtained.
【００１１】本発明が対象とする構造用鋼は、例えば特
公昭５８−１４８４９号公報に記載され、次記するよう
に、通常の溶接構造用鋼が所要の材質を得るために、従
来から当業分野での活用で確認されている作用・効果の
関係を基に定めている添加元素の種類と量を同様に使用
して同等の作用と効果が得られる。従って、これ等を含
む鋼を本発明は対象鋼とするものである。The structural steel to which the present invention is directed is described, for example, in Japanese Patent Publication No. 58-14849, and as described below, conventional welding structural steel has been conventionally used in order to obtain the required material. Equivalent functions and effects can be obtained by using the types and amounts of the additional elements determined based on the relation between the functions and effects confirmed in the application in the industrial field. Therefore, the present invention is intended to include steels including these.
【００１２】これ等の各成分元素とその添加理由を以下
に示す。Ｃは、鋼の強度を向上する有効な成分とするも
のであるが、０．２０％を超える過剰な含有量では、二
相域圧延時の変形抵抗を増して圧延を困難にするばかり
か、溶接部に島状マルテンサイトを析出し、鋼の靭性を
著しく劣化させるので、０．２０％以下に規制する。The following is a description of each of these constituent elements and the reasons for their addition. C is an effective component for improving the strength of steel, but an excessive content of more than 0.20% not only increases the deformation resistance at the time of two-phase rolling, making rolling difficult, Since island martensite precipitates in the welded portion and significantly deteriorates the toughness of steel, the content is restricted to 0.20% or less.
【００１３】Ｓｉは溶鋼の脱酸元素として必要であり、
また強度増加元素として有用であるが、１．０％を超え
ると、鋼の加工性を低下させ、溶接部の靭性を劣化させ
る。また、０．０１％未満では脱酸効果が不十分なた
め、含有量を０．０１〜１．０％に規制する。Si is necessary as a deoxidizing element of molten steel,
Further, it is useful as a strength increasing element, but if it exceeds 1.0%, the workability of the steel is reduced, and the toughness of the weld is deteriorated. If the content is less than 0.01%, the deoxidizing effect is insufficient, so the content is restricted to 0.01 to 1.0%.
【００１４】Ｍｎも脱酸成分元素として必要であり、
０．３％未満では鋼の清浄度を低下し、加工性を害す
る。また鋼材の強度を向上する成分として０．３％以上
が必要である。しかし、Ｍｎは変態温度を下げるので、
過剰の含有は二相域圧延温度が下がりすぎ、変形抵抗の
上昇をきたすので、２．０％を上限とする。Mn is also required as a deoxidizing component element,
If it is less than 0.3%, the cleanliness of the steel is reduced and the workability is impaired. Further, 0.3% or more is required as a component for improving the strength of the steel material. However, since Mn lowers the transformation temperature,
An excessive content lowers the rolling temperature in the two-phase region too much and increases the deformation resistance, so the upper limit is 2.0%.
【００１５】ＡｌおよびＮは、Ａｌ窒化物による鋼の微
細化の他、圧延過程での固溶、析出により、鋼の結晶方
位の整合および再結晶に有効な働きをさせるために添加
する。しかし、添加量が少ないときにはその効果がな
く、過剰の場合には鋼の靭性を劣化させるので、Ａｌ：
０．００１〜０．２０％、Ｎ：０．０２０％以下に限定
する。Al and N are added to refine the steel by the use of Al nitrides, and also to provide a solid solution and precipitation during the rolling process to make the steel crystal crystal orientation and recrystallization effective. However, when the addition amount is small, the effect is not obtained, and when the addition amount is excessive, the toughness of the steel is deteriorated.
0.001 to 0.20%, N: 0.020% or less.
【００１６】以上が、本発明が対象とする鋼の基本成分
であるが、母材強度の上昇あるいは、継手靭性の向上の
目的のため、要求される性質に応じて、合金元素を添加
する場合は、変態温度を下げすぎると二相域での変形抵
抗が増し、圧延が困難になる。従って、合金の添加量と
しては、Ｎｉ，Ｃｒ，Ｍｏ，Ｃｕ，Ｗ，Ｐ，Ｃｏ，Ｖ，
Ｎｂ，Ｔｉ，Ｚｒ，Ｔａ，Ｈｆ，希土類元素，Ｙ，Ｃ
ａ，Ｍｇ，Ｔｅ，Ｓｅ，Ｂを１種類以上添加してよい
が、合計で４．５％以内に規制する。The above are the basic components of the steel to which the present invention is applied. For the purpose of increasing the strength of the base material or improving the toughness of the joint, the alloy element is added according to the required properties. If the transformation temperature is too low, the deformation resistance in the two-phase region increases, and the rolling becomes difficult. Therefore, the addition amounts of the alloys are Ni, Cr, Mo, Cu, W, P, Co, V,
Nb, Ti, Zr, Ta, Hf, rare earth element, Y, C
One or more of a, Mg, Te, Se, and B may be added, but the total amount is regulated within 4.5%.
【００１７】次に本発明における組織の規定理由を示
す。疲労亀裂先端でマイクロクラックを発生し易くする
ためには、フェライト・パーライト鋼では脆性第二相で
あるパーライト組織の形態制御が重要である。マイクロ
クラックを生じ易くするためには、セメンタイトが濃縮
したパーライト相を縞状に分散させることが重要であ
り、そのためパーライトバンドの厚みを３μｍ以下とし
た。また、マイクロクラックの発生頻度を大きくさせる
ためにパーライト間隔を規定したのである。Next, the reasons for defining the organization in the present invention will be described. In order to facilitate the occurrence of microcracks at the tip of a fatigue crack, it is important to control the morphology of the pearlite structure, which is the brittle second phase, in ferrite-pearlite steel. In order to facilitate the occurrence of microcracks, it is important to disperse the pearlite phase in which cementite is concentrated in a striped manner. Therefore, the thickness of the pearlite band is set to 3 μm or less. In addition, the pearlite interval was defined in order to increase the frequency of occurrence of microcracks.
【００１８】さらに該パーライトバンドからマイクロク
ラックを容易に発生させるためには集合組織の発達が有
用であるので、そのため集合組織コロニーのアスペクト
比を４以上とした。Further, since the development of texture is useful for easily generating microcracks from the pearlite band, the aspect ratio of the texture colony is set to 4 or more.
【００１９】また集合組織コロニーの短軸径を１０μｍ
以下にしたのは、繰り返し荷重下において塑性域の小さ
な低ΔＫ領域でも結晶方位の異なるコロニー間での塑性
異方性から局所変形を生じさせマイクロクラックを容易
に発生させるためである。The short axis diameter of the textured colony is 10 μm.
The reason for this is to cause local deformation due to plastic anisotropy between colonies having different crystal orientations even in a low ΔK region having a small plastic region under repeated load, thereby easily generating microcracks.
【００２０】次に製造方法に関して、再結晶圧延量を３
０％以上に規定したのは、γの再結晶によりパーライト
バンドの起源となるミクロ偏析帯間隔を小さく分断する
ためであり、再結晶域での冷却速度を１℃／秒と規定し
たのは再結晶したフェライト相の粒成長を抑制するため
である。さらに未再結晶圧延量を３０％以上としたのは
集合組織コロニーの構成単位となるフェライト粒径を小
さくするためである。Next, regarding the production method, the recrystallization rolling amount is set to 3
The reason for setting the cooling rate in the recrystallization region to 1 ° C./sec is to set the cooling rate in the recrystallization region to 1 ° C./sec. This is for suppressing the grain growth of the crystallized ferrite phase. The reason why the unrecrystallized rolling amount is set to 30% or more is to reduce the grain size of ferrite, which is a constituent unit of the texture colony.
【００２１】また、二相域圧延において１パス当りの圧
下量を規定したのは、変形抵抗がα相よりγ相の方が小
さい歪領域で圧延することにより加工フェライトの生成
を抑制しつつ、パーライトバンドの厚みを小さくするた
めに残留γを偏平化させるためである。Further, the reduction amount per pass is specified in the two-phase zone rolling because rolling is performed in a strain region in which the γ phase is smaller in deformation resistance than the α phase, thereby suppressing the formation of processed ferrite. This is to flatten the residual γ in order to reduce the thickness of the pearlite band.
【００２２】[0022]
【作用】発明者らは、ＳＩmax の異なる種々の鋼材を用
いて、ＳＩmax と疲労強度の関係を調査した。その結
果、ＳＩmax と疲労伝播特性の間には直接関係が認めら
れないことがあった。そこで疲労破面を詳細に調査した
結果、ＳＩmax の大きい鋼板ほどΔＫ値の大きい領域で
のセパレーションは顕著であったが、疲労強度を決定し
ている低ΔＫ領域でのセパレーションの出現状態はＳＩ
max には依存しないことを知見した。[Action] inventors used various steel materials of different SI max, and investigated the relationship SI max and fatigue strength. As a result, a direct relationship was sometimes not found between SI max and fatigue propagation characteristics. Therefore, as a result of investigating the fatigue fracture surface in detail, the separation in the region where the ΔK value is large was remarkable as the steel plate having a larger SI max was found, but the appearance of the separation in the low ΔK region where the fatigue strength was determined was SI.
It was found that it did not depend on max .
【００２３】そこで、特開平３−４４４４４号に記載さ
れているように、伝播中の脆性亀裂に先だってセメンタ
イト相からマイクロクラックが発生し亀裂先端の応力状
態を緩和させていることに着眼し、伝播中の疲労亀裂先
端にマイクロクラックを生じせしめる脆性第二相組織の
形態について種々検討を行った。Therefore, as described in Japanese Patent Application Laid-Open No. 3-44444, attention was paid to the fact that microcracks were generated from the cementite phase prior to the brittle crack during propagation and the stress state at the tip of the crack was relaxed. Various investigations were made on the morphology of the brittle second-phase structure that causes microcracks at the tip of the fatigue crack in the medium.
【００２４】その結果、疲労亀裂先端では、脆性亀裂先
端よりも低いＫ値でマイクロクラックを生じさせる必要
があり、且つ疲労亀裂伝播速度遅延にはマイクロクラッ
クの発生頻度も増加させる必要のあることを知見した。As a result, it is necessary to generate microcracks at a K value lower than that of a brittle crack tip at the fatigue crack tip, and it is necessary to increase the frequency of microcracks at the fatigue crack propagation speed delay. I learned.
【００２５】図１はパーライトバンド相の厚みを変化さ
せてマイクロクラックの発生の容易性を示す板厚方向の
限界破壊応力を調査した結果である。図に示すように、
集合組織を発達させた場合（集合組織コロニーの長径／
短径の比であるアスペクト比が４．１の場合）と顕著な
集合組織の存在しない場合（アスペクト比が１．２の場
合）で傾向が異なるものの、集合組織が発達している場
合でもパーライトバンド相の厚みが４μｍ以上ではセメ
ンタイトの凝集状態が十分でなくマイクロクラックは発
生しにくいと考えられるが、３μｍ以下になるとフェラ
イトとパーライトバンド相の剥離強度が低下しマイクロ
クラックが発生し易くなり、それに伴ってＴ字継手部の
疲労寿命も改善された。FIG. 1 shows the results of investigation of the critical fracture stress in the thickness direction, which indicates the easiness of microcracking, by changing the thickness of the pearlite band phase. As shown in the figure,
When texture is developed (Long diameter of texture colony /
Although the tendency is different between the case where the aspect ratio which is the ratio of the minor axis is 4.1) and the case where no remarkable texture is present (when the aspect ratio is 1.2), the pearlite is obtained even when the texture is developed. When the thickness of the band phase is 4 μm or more, it is considered that the aggregation state of the cementite is insufficient and microcracks are unlikely to occur, but when the thickness is 3 μm or less, the peel strength of the ferrite and the pearlite band phase is reduced and microcracks are easily generated, Accordingly, the fatigue life of the T-shaped joint has been improved.
【００２６】さらに厚みが３μｍ以下のパーライトバン
ドの間隔を変化させて、疲労試験を実施した結果、図２
に示すように、破面上で板厚方向に平行に割れたマイク
ロクラックの平均間隔とパーライトバンド相の間隔とに
関係が認められ、疲労強度を大幅に向上させるために
は、パーライトバンド間隔を２０μｍ以下とする必要の
あることを知見した。Further, a fatigue test was carried out by changing the distance between pearlite bands having a thickness of 3 μm or less.
As shown in the figure, the relationship between the average spacing of microcracks cracked parallel to the sheet thickness direction on the fracture surface and the spacing of the pearlite band phase was recognized.To greatly improve fatigue strength, the pearlite band spacing was required. It has been found that the thickness needs to be 20 μm or less.
【００２７】図３（ａ），（ｂ），（ｃ）には、テンパ
ーカラー法により現出させた集合組織コロニーのアスペ
クト比と疲労試験においてマイクロクラック発生限界Ｋ
値および板厚方向限界破壊応力の関係を示す。アスペク
ト比が４以上では板厚方向限界破壊応力が低下しマイク
ロクラックの生成が容易となり、塑性域寸法の小さな低
ΔＫ領域でもマイクロクラックが生成することがわか
る。FIGS. 3 (a), 3 (b) and 3 (c) show the aspect ratio of the textured colonies revealed by the temper color method and the microcrack occurrence limit K in the fatigue test.
The relationship between the value and the critical fracture stress in the thickness direction is shown. It can be seen that when the aspect ratio is 4 or more, the critical fracture stress in the thickness direction decreases, and microcracks are easily generated, and microcracks are generated even in a low ΔK region having a small plastic region size.
【００２８】次に図４には、集合組織コロニーのアスペ
クト比が４以上の組織で、集合組織コロニーの短軸径と
マイクロクラック発生限界Ｋ値の関係を示す。セパレー
ションによる疲労強度の向上は、ΔＫが８０kg／mm1.5
以下であることが日本造船学会論文集Ｖｏｌ．１６９，
ｐｐ．２５７〜２６６に記載されており、マイクロクラ
ックでこの疲労強度向上効果を期待するためには、集合
組織コロニーサイズが１０μｍ以下である必要性を知見
した。Next, FIG. 4 shows the relationship between the minor axis diameter of the textured colony and the microcrack occurrence limit K value in the textured tissue colony having an aspect ratio of 4 or more. The improvement of fatigue strength by separation is as follows: ΔK is 80 kg / mm 1.5
The followings are the Transactions of the Shipbuilding Society of Japan Vol. 169,
pp. 257-266, and found that the texture colony size must be 10 μm or less in order to expect the effect of improving the fatigue strength by microcracking.
【００２９】したがって、パーライトバンド相からのマ
イクロクラックを利用して疲労強度を向上させるために
は、相の厚みが３μｍ以下のパーライトバンドを２０μ
ｍ以下の間隔で存在させ、かつ長径／短径の比が４以上
で短径が１０μｍ以下の集合組織コロニーを有する組織
が必要であることを知見した。Therefore, in order to improve the fatigue strength by utilizing microcracks from the pearlite band phase, a pearlite band having a phase thickness of 3 μm or less must be reduced to 20 μm.
It was found that a tissue having a textured colony having a major axis / minor axis ratio of 4 or more and a minor axis of 10 μm or less was required to be present at intervals of not more than m.
【００３０】次に、この組織を実現するために圧延条件
の検討を実施した。パーライトバンド間隔を小さくする
ためにはγ粒径を細粒化する必要がある。しかしなが
ら、γ再結晶域は高温であるため一般にγが再結晶した
後容易に粒成長が生じ微細なγ粒を得ることは容易では
ない。そこで、γ再結晶域にて再結晶後の粒成長を抑制
するため、当該温度域にて圧延中に冷却を行い、その冷
却速度とγ粒径の関係を求め、図５に示した。Next, the rolling conditions were examined in order to realize this structure. In order to reduce the pearlite band interval, it is necessary to reduce the γ particle size. However, since the γ recrystallization region is at a high temperature, grain growth generally occurs easily after γ is recrystallized, and it is not easy to obtain fine γ grains. Therefore, in order to suppress grain growth after recrystallization in the γ recrystallization region, cooling was performed during rolling in the temperature range, and the relationship between the cooling rate and the γ grain size was obtained.
【００３１】この結果より冷却速度が１℃／sec 以上で
あれば当該領域での３０％圧下率の圧延により生じた再
結晶後の粒成長が抑制されγ粒径が細粒化され、その結
果としてパーライトバンド相の間隔が１０μｍ以下とな
ることを知見した。From these results, if the cooling rate is 1 ° C./sec or more, grain growth after recrystallization caused by rolling at a rolling reduction of 30% in the region is suppressed, and the γ grain size is reduced, and as a result, It was found that the interval between the pearlite band phases was 10 μm or less.
【００３２】さらにパーライトバンド相からのマイクロ
クラックの発生を容易にするために、α／γ二相域温度
域にて圧延を行い集合組織を発達させることが必要であ
る。その結果、図６（ａ），（ｂ）に示すスケジュール
Ｂのようにα分率の低いＡｒ3 近傍の二相域状態で圧下
量が大きくなると、圧延により与えられた歪によりフェ
ライトの粒成長が生じてしまい、１０μｍ以下の集合組
織コロニーは得られず、スケジュールＣのようにα分率
の高いＡｒ1 近傍の温度で大きな圧下を行うと加工フェ
ライトが生成し、母材靭性が確保できないことが明らか
となった。Further, in order to facilitate the generation of microcracks from the pearlite band phase, it is necessary to carry out rolling in an α / γ dual phase temperature range to develop a texture. As a result, when the rolling reduction becomes large in the two-phase region near Ar 3 where the α fraction is low as in schedule B shown in FIGS. 6 (a) and 6 (b), the grain growth of ferrite is caused by the strain given by rolling. And a textured colony of 10 μm or less cannot be obtained, and when a large reduction is performed at a temperature near Ar 1 where the α fraction is high as in schedule C, processed ferrite is generated and the base material toughness cannot be secured. Became clear.
【００３３】そこで、種々検討を行い、スケジュールＡ
のように二相域温度域においてα相より残留γの変形抵
抗が小さい低加工歪領域で低圧下量多パス圧延を行え
ば、フェライト粒の異常粒成長が生じることなく、Ｃ量
の濃化した残留γ相のみを選択的に偏平化させていき、
所定の集合組織コロニー寸法を満足し、かつ厚みの薄い
パーライトバンドが生成し、その間隔を小さくできるこ
とを知見した。Therefore, various investigations were performed and schedule A
When low-pass multi-pass rolling is performed in a low strain area where the deformation resistance of residual γ is smaller than that of α phase in the two-phase temperature range, the ferrite grains do not grow abnormally and the C content is increased. Selectively flattening only the residual γ phase,
It has been found that a pearlite band which satisfies a predetermined texture colony size and has a small thickness is generated, and that the interval can be reduced.
【００３４】[0034]
【実施例】実施例の供試鋼の成分を表１に、製造条件お
よび得られた材質を表２に比較例と共に示す。EXAMPLES The components of the test steels of the examples are shown in Table 1, and the production conditions and the obtained materials are shown in Table 2 together with comparative examples.
【００３５】[0035]
【表１】 [Table 1]
【表２】 [Table 2]
【表３】 [Table 3]
【表４】 [Table 4]
【表５】 再結晶域圧延中の冷却は、本発明例の試験番号（以下鋼
番と称する）１〜１２と比較例の１７，１９，２１〜２
４にて実施しているが、試験番号１５，１９，２１は所
要の冷却速度を満足できなかった。そのため、試験番号
１５，１９，２１のパーライト間隔は本発明例と比較し
て大きくなっている。[Table 5] The cooling during the recrystallization zone rolling was performed according to the test numbers 1 to 12 of the present invention examples (hereinafter referred to as steel numbers) and 17, 19, 21 and 2 of the comparative examples.
4, the test numbers 15, 19 and 21 could not satisfy the required cooling rate. Therefore, the pearlite intervals of Test Nos. 15, 19, and 21 are larger than those of the present invention.
【００３６】また、比較例である試験番号１５，１７，
２１は二相域圧延を実施していないため集合組織の発達
がなく、集合組織コロニーのアスペクト比が４以下であ
り、マイクロクラックが疲労破面上で観察されなかっ
た。In addition, Test Nos. 15, 17, and Comparative Examples
Sample No. 21 did not undergo rolling in the two-phase zone, so there was no texture development, the aspect ratio of the texture colonies was 4 or less, and no microcracks were observed on the fatigue fracture surface.
【００３７】比較例である試験番号１８，２０は再結晶
域圧延が十分でないのでパーライトバンド間隔が大きく
なっており、試験番号２３は、未再結晶域圧延が実施さ
れておらず、集合組織コロニーの短径が大きくなってい
る。In Test Nos. 18 and 20, which are comparative examples, the pearlite band interval was large because the recrystallization zone rolling was not sufficient, and in Test No. 23, the texture colony was not subjected to the non-recrystallization zone rolling. The minor axis is larger.
【００３８】試験番号１３，１４，１６，１７，２２，
２４は、再結晶域圧延、未再結晶域圧延共所要の条件を
満足している。しかしながら、試験番号１３，１６，２
２は、二相域圧延においてα分率が小さいＡｒ3 点直下
領域で圧延したため、フェライトの異常成長を起こし、
フェライト粒径が粗大化し、集合組織コロニーの短径も
１０μｍ以上となっていた。一方、試験番号１４，１
８，２４には二相域圧延においてα分率の大きくなった
Ａｒ1 点近傍で圧延を実施したため加工フェライトの生
成が著しく、パーライトバンド相の厚みも大きくなって
おり、母材靭性も良好でない。Test numbers 13, 14, 16, 17, 22,
No. 24 satisfies the required conditions for both the recrystallization zone rolling and the non-recrystallization zone rolling. However, test numbers 13, 16, 2
No. 2 caused abnormal growth of ferrite due to rolling in the region immediately below the Ar 3 point where the α fraction was small in the two-phase region rolling.
The ferrite grain size was coarse, and the short diameter of the textured colonies was also 10 μm or more. On the other hand, test numbers 14,1
In Nos. 8 and 24, in the two-phase zone rolling, rolling was performed near the Ar 1 point where the α fraction was increased, so that the formation of processed ferrite was remarkable, the thickness of the pearlite band phase was large, and the base material toughness was not good. .
【００３９】これらの比較例の試験番号１３〜２４の材
質は、表２に示す通り、Ｔ字継手のＳＮ線図において繰
り返し公称応力範囲が１２kg／mm2 の時３×１０6 以下
であり、疲労強度の向上は認められなかった。As shown in Table 2, the materials of Test Nos. 13 to 24 of these comparative examples are 3 × 10 6 or less when the nominal stress range is 12 kg / mm 2 in the SN diagram of the T-joint. No improvement in fatigue strength was observed.
【００４０】これに対し、本発明例の試験番号１〜１２
の材質は、表２に示す通り、所要の製造条件を満足し、
目標の強度・靭性を満足すると共に、本発明の狙いであ
るＴ字継手の疲労特性が、繰り返し公称応力範囲が１２
kg／mm2 の時３×１０6 以上を示し、２×１０6 回の疲
労強度は１４kg／mm2 以上となり、従来鋼材に比較し、
大幅に疲労特性が向上した。On the other hand, Test Nos. 1 to 12
The material of satisfies the required manufacturing conditions as shown in Table 2,
In addition to satisfying the target strength and toughness, the fatigue characteristic of the T-joint, which is the object of the present invention, shows that the repeated nominal stress range is 12
kg / mm 2 shows 3 × 10 6 or more, and the fatigue strength after 2 × 10 6 times becomes 14 kg / mm 2 or more.
Significantly improved fatigue properties.
【００４１】[0041]
【発明の効果】本発明は上記した手段を用いて上記した
作用を利用したので、再結晶温度域で冷却しながら圧延
を実施し、未再結晶域圧延を実施した後、所定の条件で
二相域圧延を実施すれば、疲労亀裂進展中の破面にマイ
クロクラックが生じ、その結果、Ｔ字継手のように鋼板
表面から疲労亀裂が発生し、板厚方向に伝播する形態の
疲労損傷の軽減、防止を可能とするもので、当業分野は
もちろん、関連分野にもたらす効果が大きい。According to the present invention, the above-mentioned action is utilized by using the above-mentioned means, so that the rolling is carried out while cooling in the recrystallization temperature range, the rolling in the non-recrystallization region is carried out, and then the rolling is performed under a predetermined condition. If phase rolling is performed, microcracks occur on the fracture surface during fatigue crack propagation, and as a result, fatigue cracks are generated from the steel sheet surface as in a T-shaped joint, and the fatigue damage propagates in the thickness direction. It is possible to reduce and prevent it, and it has a great effect on related fields as well as this field.
【図１】パーライトバンド相の厚みと、板厚方向の限界
破壊応力の関係、およびパーライトバンド相の厚みとＴ
字継手における繰り返し公称応力範囲が１２kg／mm2 で
の疲労寿命との関係を示す図表である。FIG. 1 shows the relationship between the thickness of the pearlite band phase and the critical fracture stress in the thickness direction, and the thickness and T of the pearlite band phase.
5 is a table showing the relationship between the fatigue life when the repeated nominal stress range of the U-shaped joint is 12 kg / mm 2 .
【図２】パーライトバンド相の間隔と疲労破面で観察さ
れるマイクロクラックの間隔との関係、およびパーライ
トバンド相の間隔とＴ字継手における繰り返し公称応力
範囲が１２kg／mm2 での疲労寿命との関係を示す図表で
ある。FIG. 2 shows the relationship between the spacing of the pearlite band phase and the spacing of the microcracks observed on the fatigue fracture surface, and the relationship between the spacing of the pearlite band phase and the fatigue life when the cyclic nominal stress range in the T-joint is 12 kg / mm 2. 6 is a table showing the relationship of FIG.
【図３】（ａ）はテンパーカラー法により求めた集合組
織のコロニーのアスペクト比（長径／短径）と板厚方向
の限界破壊応力の関係、およびマイクロクラックを発生
させるのに必要な限界ΔＫ値との関係を示す図表であ
る。（ｂ）はアスペクト比の模式図である。（ｃ）はパ
ーライトバンドの模式図である。FIG. 3 (a) shows the relationship between the aspect ratio (major axis / minor axis) of the colony of the texture obtained by the temper color method and the critical fracture stress in the plate thickness direction, and the critical ΔK required to generate microcracks. 6 is a chart showing a relationship with a value. (B) is a schematic diagram of an aspect ratio. (C) is a schematic diagram of a pearlite band.
【図４】集合組織コロニーのアスペクト比が４程度およ
び１０程度の場合の短径とマイクロクラックを発生させ
るのに必要な限界ΔＫ値との関係を示す図表である。FIG. 4 is a chart showing a relationship between a minor axis and a limit ΔK value required for generating microcracks when the aspect ratio of a textured colony is about 4 and about 10.
【図５】再結晶温度域である１０００℃〜８５０℃の冷
却速度と８５０℃でのγ粒径およびパーライトバンド間
隔の関係を示す図表である。FIG. 5 is a table showing a relationship between a cooling rate in a recrystallization temperature range of 1000 ° C. to 850 ° C., a γ particle size at 850 ° C., and a pearlite band interval.
【図６】（ａ）は二相域圧延のパススケジュールと、そ
れらの圧延で得られた集合組織コロニーの短径およびパ
ーライトバンド相の厚みの関係を示す図表である。
（ｂ）は圧下率とα変態率の図表である。FIG. 6 (a) is a table showing the relationship between the pass schedule of the two-phase zone rolling, the minor axis of the textured colony obtained by the rolling, and the thickness of the pearlite band phase.
(B) is a chart of a reduction ratio and an α transformation ratio.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 吉川 宏 大分県大分市大字西ノ洲１番地 新日本 製鐵株式会社 大分製鐵所内 (72)発明者 川島 善樹果 大分県大分市大字西ノ洲１番地 新日本 製鐵株式会社 大分製鐵所内 (56)参考文献 特開 平５−148542（ＪＰ，Ａ) 特開 平５−148541（ＪＰ，Ａ) 特開 平３−64418（ＪＰ，Ａ) 特開 昭51−134306（ＪＰ，Ａ) (58)調査した分野(Int.Cl.6，ＤＢ名) C21D 8/02 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroshi Yoshikawa, Oita, Oita, Oita, 1st section of Nishinosu Nippon Steel Corporation Inside of Oita Works (72) Inventor, Yoshiki Kawashima 1st section of Oaza, Oita, Oita, Oita (56) References JP-A-5-148542 (JP, A) JP-A-5-148541 (JP, A) JP-A-3-64418 (JP, A) JP-A Sho 51 -134306 (JP, A) (58) Field surveyed (Int. Cl. 6 , DB name) C21D 8/02
Claims (2)
のパーライトバンドが縞状に存在し、かつパーライトバ
ンド相の間のマトリックス組織はアスペクト比（長径／
短径の比）が４以上で短径が１０μｍ以下の集合組織コ
ロニーからなることを特徴とする疲労特性の良い鋼板。1. A pearlite band having a thickness of 2 μm or less and an interval of 20 μm or less is present in a stripe pattern, and a matrix structure between pearlite band phases has an aspect ratio (major axis / major axis / length).
A steel sheet having good fatigue characteristics, comprising a textured colony having a ratio of minor axis of 4 or more and a minor axis of 10 μm or less.
結晶域で１℃／秒以上の冷却速度で冷却しながら圧下率
３０％以上の圧延を行い、引き続いて３０％以上の未再
結晶圧延を実施した後Ａｒ3 〜Ａｒ1 温度域での累積圧
下率ｄAr3 −ｄAr1 がα分率：ａ（％）の増加に応じて ０．６×ａ≦ｄAr3 −ｄAr1 （％）≦０．４×ａ−１０ を満足するようにα分率の増加に応じて、累積圧下率を
増加させるα−γ二相域圧延を行い、厚みが２μｍ以下
で間隔が２０μｍ以下のパーライトバンドが縞状に存在
し、かつパーライトバンド相の間のマトリックス組織は
アスペクト比（長径／短径の比）が４以上で短径が１０
μｍ以下の集合組織コロニーをうることを特徴とする疲
労特性の優れた鋼板の製造方法。2. A slab or steel plate as a structural steel is rolled at a reduction rate of 30% or more while cooling at a cooling rate of 1 ° C./sec or more in a γ recrystallization region, and subsequently, a non-recycle of 30% or more is performed. cumulative rolling reduction dAr 3 -dAr 1 is α fraction in Ar 3 to Ar 1 temperature range after performing the crystal rolling: a (%) in accordance with an increase of 0.6 × a ≦ dAr 3 -dAr 1 (% ) The pearlite having a thickness of 2 μm or less and an interval of 20 μm or less is subjected to α-γ two-phase region rolling in which the cumulative reduction is increased in accordance with the increase of the α fraction so as to satisfy ≦ 0.4 × a-10. The band is present in stripes, and the matrix structure between the pearlite band phases has an aspect ratio (ratio of major axis / minor axis) of 4 or more and a minor axis of 10 or more.
A method for producing a steel sheet having excellent fatigue characteristics, wherein a texture colony of not more than μm is obtained.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31564891A JP2968105B2 (en) | 1991-11-29 | 1991-11-29 | Steel plate having good fatigue characteristics and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31564891A JP2968105B2 (en) | 1991-11-29 | 1991-11-29 | Steel plate having good fatigue characteristics and method for producing the same |
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| Publication Number | Publication Date |
|---|---|
| JPH05148540A JPH05148540A (en) | 1993-06-15 |
| JP2968105B2 true JP2968105B2 (en) | 1999-10-25 |
Family
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP31564891A Expired - Fee Related JP2968105B2 (en) | 1991-11-29 | 1991-11-29 | Steel plate having good fatigue characteristics and method for producing the same |
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| Country | Link |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4875566A (en) * | 1986-12-16 | 1989-10-24 | Toyota Jidosha Kabushiki Kaisha | Gear synchronizer mechanism |
| JPS63158329A (en) * | 1986-12-18 | 1988-07-01 | Toyota Motor Corp | Synchronous meshing device |
| JP2600674B2 (en) * | 1987-05-09 | 1997-04-16 | トヨタ自動車株式会社 | Synchronizer |
| JPH0619190B2 (en) * | 1987-05-20 | 1994-03-16 | トヨタ自動車株式会社 | Synchronizer |
| CN112359191B (en) * | 2020-11-10 | 2022-04-19 | 江苏省沙钢钢铁研究院有限公司 | TMCP type bridge steel plate with small same-plate strength difference and production method thereof |
-
1991
- 1991-11-29 JP JP31564891A patent/JP2968105B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH05148540A (en) | 1993-06-15 |
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