JPH1192858A - Steel excellent in ductile crack propagation resistance under repeated large deformation and its production - Google Patents

Steel excellent in ductile crack propagation resistance under repeated large deformation and its production

Info

Publication number
JPH1192858A
JPH1192858A JP9251082A JP25108297A JPH1192858A JP H1192858 A JPH1192858 A JP H1192858A JP 9251082 A JP9251082 A JP 9251082A JP 25108297 A JP25108297 A JP 25108297A JP H1192858 A JPH1192858 A JP H1192858A
Authority
JP
Japan
Prior art keywords
less
steel
ferrite
pearlite
steel material
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
Application number
JP9251082A
Other languages
Japanese (ja)
Other versions
JP3849244B2 (en
Inventor
Nobuyuki Ishikawa
信行 石川
Yasuo Kobayashi
泰男 小林
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Engineering Corp
Original Assignee
NKK Corp
Nippon Kokan Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by NKK Corp, Nippon Kokan Ltd filed Critical NKK Corp
Priority to JP25108297A priority Critical patent/JP3849244B2/en
Publication of JPH1192858A publication Critical patent/JPH1192858A/en
Application granted granted Critical
Publication of JP3849244B2 publication Critical patent/JP3849244B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Abstract

PROBLEM TO BE SOLVED: To produce a steel for structural purpose excellent in crack propagation resistance and unstable destruction resistance even in repeated large deformation caused by an earthquake by providing the steel with a specified compsn. in which the content of S is reduced and executing rolling at a low temp. and at a draft of specified value or above so as to form a ferrite + pearlite steel. SOLUTION: This steel has a compsn. contg., by weight, 0.08 to 0.2% C, 0.01 to 0.5% Si, 0.1 to 2% Mn, 0.001 to 0.1% Al, <=0.005% S, and the balance Fe and whose metallic structure is composed of a ferrite + pearlite one of >=20% area fraction. The average grain size of ferrite is regulated to <=10 μm, and, as the steel components, one or more kinds among <=0.5% Cu, <=0.5%Ni, <=1% Cr, <=0.6% Mo, <=0.06% Nb, <=0.1% V, <=0.1% Ti and <=0.005% Ca may be incorporated therein. As for the method for producing the steel, the slab having the above compsn. is heated at 1050 to 1180 deg.C, is subjected to hot rolling in such a manner that the cumulative draft at <=900 deg.C is regulated to >=50% and the rolling finishing temp. is regulated to 650 to 850 deg.C and is thereafter subjected to air cooling.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【0001】[0001]

【発明の属する技術分野】本発明は土木建築分野におけ
る各種建造物に利用される構造用鋼材に関し、特に地震
による繰返しの大変形を受けた場合に、応力集中部から
発生する延性き裂に対して高い進展抵抗が要求される建
造物への利用に適した構造用鋼材及びその製造方法に関
する。
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural steel material used for various structures in the field of civil engineering and construction, and particularly to a ductile crack generated from a stress concentrated portion when subjected to repeated large deformation due to an earthquake. TECHNICAL FIELD The present invention relates to a structural steel material suitable for use in a building that requires high and high resistance to growth and a method for producing the same.

【0002】[0002]

【従来の技術】建築分野における耐震設計法では、鋼材
の塑性変形によって地震のエネルギーを吸収することに
より、建築物の崩壊を防ごうとする設計がなされている
が、このような建築物に適用される鋼材には優れた塑性
変形能が要求されており、特開昭55−119152号
公報、特開昭63−223123号公報、特開平1−1
156422号公報、特開平3−115524号公報等
では、降伏比を低下させることにより一様延び特性を向
上させた鋼材が提案されている。またJIS・G313
6の建築構造用圧延鋼材においても降伏比を80%以下
とすることが規定されているように、耐震性向上に関す
る鋼材面からの対応としては、低降伏比による塑性変形
能の向上が中心となっている。
2. Description of the Related Art In a seismic design method in the building field, a design is made to prevent collapse of a building by absorbing seismic energy by plastic deformation of a steel material. The steel materials to be used are required to have excellent plastic deformability, and are disclosed in JP-A-55-119152, JP-A-63-223123, and JP-A-1-1-1.
JP-A-156422 and JP-A-3-115524 propose steel materials in which the yield ratio is reduced to improve the uniform elongation characteristics. JIS G313
As specified in the rolled steel for building structure No. 6, the yield ratio is set to be 80% or less, the improvement of the seismic resistance from the steel surface mainly focuses on the improvement of the plastic deformability by the low yield ratio. Has become.

【0003】[0003]

【発明が解決しようとする課題】しかし、1995年1
月の阪神淡路大地震では多くの鉄骨構造物が甚大な被害
を受けたが、鉄骨建築物の柱梁接合部や、門型橋脚の隅
角部等の破壊では、脆性的な破壊の前に延性き裂の進展
が認められた例が報告されている。これは、地震による
繰返しの変形を受けることにより、柱梁接合部や門型橋
脚の隅角部等の形状不連続部(応力集中部)で延性き裂
が発生、進展したために、不安定破壊を生じやすくなっ
たことが原因といえるが、阪神大震災が極めて大きな地
震であったことに起因する、今までには見られなかった
新しい破壊形態といえる。このことは、たとえ低降伏比
で伸び特性の高い鋼材を用いていたとしても、応力集中
部から延性亀裂が発生進展する場合は、その塑性変形能
力が十分に発揮される前に不安定破壊を生じてしまうこ
とを意味している。
However, in 1995, 1
Many steel structures were severely damaged in the Great Hanshin-Awaji Earthquake of the month.However, in the case of column-beam joints of steel structures and corners of portal piers, brittle There have been reports of ductile crack growth. This is due to the occurrence of ductile cracks at shape discontinuities (stress concentrated parts) such as column-beam joints and corners of portal piers due to repeated deformation due to earthquakes, and unstable fracture This is because the Great Hanshin Earthquake was an extremely large earthquake, which is a new type of destruction that has never been seen before. This means that even if a steel material with a low yield ratio and high elongation characteristics is used, if a ductile crack is generated and propagated from the stress concentration part, unstable fracture will occur before its plastic deformation capacity is fully exhibited. It means that it will happen.

【0004】応力集中部を有する鋼材が大変形を受けた
場合に、応力集中部から延性亀裂が発生することは、日
本建築学会構造系論文報告集、No.454、119〜
125頁(1994年発行)にも指摘されており、延性
き裂の発生特性は鋼材の一様伸び特性に依存することが
わかっている。しかし、延性き裂発生抵抗が高い鋼材で
も応力集中が厳しくなれば容易に延性き裂が発生してし
まうことから、上記したような破壊を防ぐためには、応
力集中部からの延性き裂発生後のき裂進展抵抗及びその
後の不安定破壊に対する抵抗が高い鋼材が必要となると
いえる。
When a steel material having a stress concentration portion undergoes a large deformation, a ductile crack is generated from the stress concentration portion. 454, 119-
It is pointed out on page 125 (issued in 1994) that it is known that the ductile crack initiation characteristics depend on the uniform elongation characteristics of the steel material. However, even in steel materials with high ductile crack initiation resistance, ductile cracks are easily generated if the stress concentration becomes severe. It can be said that a steel material having high crack growth resistance and high resistance to unstable fracture thereafter is required.

【0005】本発明の目的は、上記した問題点を解決す
るために、地震で生じる繰返しの大変形下においても、
き裂進展抵抗及びその耐不安定破壊特性が優れた構造用
鋼材及びその製造方法を提供することにある。
[0005] The object of the present invention is to solve the above-mentioned problems, even under repeated large deformation caused by an earthquake.
An object of the present invention is to provide a structural steel material excellent in crack growth resistance and its unstable fracture resistance and a method for producing the same.

【0006】[0006]

【課題を解決するための手段】前記課題を解決し目的を
達成するために、本発明は以下に示す手段を用いてい
る。 (1)本発明の鋼材は、重量%で、C:0.08〜0.
2%と、Si:0.01〜0.5%と、Mn:0.1〜
2%と、Al:0.001〜0.1%と、S:0.00
5%以下とを含有し、残部がFe及び不可避的不純物か
らなり、且つ金属組織は、パーライト面積分率が20%
以上のフェライト+パーライト組織であることを特徴と
する、繰返し大変形下での延性き裂進展抵抗の優れた鋼
材である。 (2)本発明の鋼材は、重量%で、C:
0.08〜0.2%と、Si:0.01〜0.5%と、
Mn:0.1〜2%と、Al:0.001〜0.1%
と、S:0.005%以下とを含有し、残部がFe及び
不可避的不純物からなり、且つ金属組織は、パーライト
面積分率が10%以上のフェライト+パーライト組織で
あり、フェライトの平均結晶粒径が10μm以下である
ことを特徴とする、繰返し大変形下での延性き裂進展抵
抗の優れた鋼材である。
In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The steel material of the present invention has a C content of 0.08 to 0.
2%, Si: 0.01 to 0.5%, Mn: 0.1 to
2%, Al: 0.001 to 0.1%, and S: 0.00
5% or less, the balance being Fe and inevitable impurities, and the metal structure has a pearlite area fraction of 20%.
A steel material excellent in ductile crack growth resistance under repeated large deformation characterized by having the above ferrite + pearlite structure. (2) The steel material of the present invention is represented by C:
0.08 to 0.2%, Si: 0.01 to 0.5%,
Mn: 0.1 to 2%, Al: 0.001 to 0.1%
And S: 0.005% or less, the balance being Fe and unavoidable impurities, and the metal structure is a ferrite + pearlite structure having a pearlite area fraction of 10% or more, and the average crystal grain size of the ferrite. A steel material excellent in ductile crack growth resistance under repeated large deformation characterized by having a diameter of 10 μm or less.

【0007】(3)本発明の鋼材は、鋼成分として、重
量%でさらに、Cu:0.5%以下、Ni:0.5%以
下、Cr:1%以下、Mo:0.6%以下、Nb:0.
06%以下、V:0.1%以下、Ti:0.1%以下、
及びCa:0.005%以下の群から選択された1種ま
たは2種以上を含有することを特徴とする、上記(1)
または(2)に記載の繰返し大変形下での延性き裂進展
抵抗の優れた鋼材である。 (4)本発明の製造方法
は、重量%で、C:0.08〜0.2%と、Si:0.
01〜0.5%と、Mn:0.1〜2%と、Al:0.
001〜0.1%と、S:0.005%以下とを含有
し、残部がFe及び不可避的不純物からなる鋼片を10
50〜1180℃の温度に加熱し、900℃以下での累
積圧下率50%以上、圧延終了温度650〜850℃で
熱間圧延を行った後、空冷することを特徴とする、繰返
し大変形下での延性き裂進展抵抗の優れた鋼材の製造方
法である。
(3) The steel material of the present invention further contains, as a steel component, by weight%, Cu: 0.5% or less, Ni: 0.5% or less, Cr: 1% or less, Mo: 0.6% or less. , Nb: 0.
06% or less, V: 0.1% or less, Ti: 0.1% or less,
And Ca: at least one selected from the group of 0.005% or less, wherein (1)
Or it is a steel excellent in ductile crack growth resistance under repeated large deformation according to (2). (4) In the production method of the present invention, C: 0.08 to 0.2% and Si: 0.
01-0.5%, Mn: 0.1-2%, Al: 0.
001-0.1% and S: 0.005% or less, the balance being 10% of a slab consisting of Fe and unavoidable impurities.
It is heated to a temperature of 50 to 1180 ° C, hot rolled at a rolling reduction temperature of 650 to 850 ° C at a cumulative reduction of 50% or more at 900 ° C or less, and then air-cooled. This is a method for producing a steel material having excellent ductile crack growth resistance.

【0008】(5)本発明の製造方法は、鋼成分とし
て、重量%でさらに、Cu:0.5%以下、Ni:0.
5%以下、Cr:1%以下、Mo:0.6%以下、N
b:0.06%以下、V:0.1%以下、Ti:0.1
%以下、及びCa:0.005%以下の群から選択され
た1種または2種以上を含有することを特徴とする、上
記(4)に記載の繰返し大変形下での延性き裂進展抵抗
の優れた鋼材の製造方法である。
(5) In the production method of the present invention, as a steel component, Cu: 0.5% or less, Ni: 0.
5% or less, Cr: 1% or less, Mo: 0.6% or less, N
b: 0.06% or less, V: 0.1% or less, Ti: 0.1
% Or less, and one or more selected from the group of Ca: 0.005% or less, characterized in that the ductile crack growth resistance under repeated large deformation according to (4) above, This is an excellent method for producing steel materials.

【0009】[0009]

【発明の実施の形態】本発明者らは、繰返しの変形を受
ける鋼材のき裂進展特性について鋭意研究を重ねた結
果、以下の知見を得るに至った。応力集中部からのき裂
発生特性は素材の一様伸びによってほぼ決まるが、フェ
ライト+パーライト鋼におけるき裂進展は、主に介在物
やフェライト+パーライト界面でのボイドの発生・連結
により起こる。このとき、ボイドの発生場所となるパー
ライトが多量にかつ微細分散していれば、き裂先端部近
傍でのボイドの生成量が増え、変形エネルギーがボイド
の発生・連結に消費されるとともに、き裂の進展経路に
多くの分岐を生じるため、き裂進展速度が低下する。
BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on the crack growth characteristics of a steel material subjected to repeated deformation, and as a result, have obtained the following knowledge. The crack initiation characteristic from the stress concentration part is almost determined by the uniform elongation of the material, but the crack propagation in ferrite + pearlite steel is mainly caused by the generation and connection of inclusions and voids at the ferrite + pearlite interface. At this time, if the pearlite, which is the place where voids are generated, is large and finely dispersed, the amount of voids generated near the crack tip will increase, and deformation energy will be consumed for the generation and connection of voids, and Since many branches occur in the crack propagation path, the crack propagation speed decreases.

【0010】また、パーライトが少ない場合でも、フェ
ライト結晶粒径が微細で、パーライト間の平均距離が短
ければ同様の効果が得られ、き裂進展速度を小さくする
ことが可能となるものである。
Further, even when the amount of pearlite is small, the same effect can be obtained if the ferrite crystal grain size is fine and the average distance between pearlite is short, and the crack growth rate can be reduced.

【0011】このような特性を有する鋼材を得るために
は、C含有量を一定値以上に高めた鋼を用いて、低温で
一定量以上の圧下率で圧延を行えばよく、パーライト面
積率が高くかつ微細分散した組織となり、き裂進展抵抗
の高い鋼材が得られるものである。
[0011] In order to obtain a steel material having such characteristics, it is only necessary to roll a steel having a C content increased to a certain value or more at a low temperature and a reduction ratio of a certain amount or more. A steel material having a high and finely dispersed structure and high crack propagation resistance can be obtained.

【0012】0.15%C−0.25%Si−1.4%
Mn−0.01%Nb鋼を用いて、図1に示した環状切
欠を有する丸棒試験片により標点間平均歪で±1%×7
回の繰返し引張圧縮変形を加えた時のき裂発生状況を図
2に示す。切欠底1から長さ約0.65mmのき裂2が
進展していることが確認できる。図3は0.15%C−
0.25%Si−1.4%Mn−0.01%Nb鋼でパ
ーライト面積分率及びフェライト結晶粒径の異なる供試
鋼についての、繰返し数と切欠底からのき裂進展量との
関係であるが、パーライト面積分率が多い場合またはフ
ェライト結晶粒径が小さい場合に同一回数でのき裂進展
量が少なくなっていることがわかる。また、硫化物系介
在物を多く含有する鋼材では、繰返しの変形を受けた場
合、き裂先端近傍以外でも硫化物系介在物を起点とした
ボイドが発生・成長するため、不安定破壊を起こしやす
いことが判明した。
0.15% C-0.25% Si-1.4%
Using Mn-0.01% Nb steel, the average strain between gauge points was ± 1% × 7 using a round bar specimen having an annular notch shown in FIG.
FIG. 2 shows the state of crack initiation when tensile and compressive deformations were applied repeatedly. It can be confirmed that a crack 2 having a length of about 0.65 mm has propagated from the notch bottom 1. FIG. 3 shows 0.15% C-
Relationship between the number of repetitions and the amount of crack propagation from the notch bottom for test steels of 0.25% Si-1.4% Mn-0.01% Nb steel with different pearlite area fractions and ferrite grain sizes However, it can be seen that when the pearlite area fraction is large or the ferrite crystal grain size is small, the amount of crack propagation at the same number of times is small. In addition, in steel materials containing a large amount of sulfide-based inclusions, when subjected to repeated deformation, voids originating from sulfide-based inclusions are generated and grown in areas other than near the crack tip, causing unstable fracture. It turned out to be easy.

【0013】図4はS量の異なる鋼材(0.15%C−
0.25%Si−1.4%Mn−0.01%Nb鋼)を
用いて、図1の環状切欠丸棒試験片により繰返し引張圧
縮試験を行った結果であり、S含有量と不安定破壊を生
ずるまでの繰返し数を示したものである。S含有量が多
い場合は少ない繰返し数で不安定破壊を生じており、き
裂進展抵抗を高めると同時に、S系介在物を低減し、不
安定破壊に対する抵抗を高めることが重要であることが
わかる。
FIG. 4 shows steel materials having different S contents (0.15% C-
FIG. 1 shows the results of repeated tensile and compression tests using the annular notched round bar test piece shown in FIG. 1 using 0.25% Si-1.4% Mn-0.01% Nb steel). It shows the number of repetitions until breakage occurs. When the S content is high, unstable fracture occurs at a small number of repetitions, and it is important to increase the crack propagation resistance, reduce S-based inclusions, and increase the resistance to unstable fracture. Recognize.

【0014】以上の知見に基づき、本発明者は、S含有
量を低減した鋼を用いて、金属組織が一定値以上のパー
ライト面積分率を有するフェライト+パーライト鋼とな
るように、低温で一定量以上の圧下率で圧延を行うよう
にして、き裂進展抵抗を高めると同時に、不安定破壊に
対する抵抗を高める繰返し大変形下での延性き裂進展抵
抗の優れた鋼材及びその製造方法を見出し、本発明を完
成させた。すなわち、本発明は、鋼組成、金属組織およ
び製造条件を特定することにより、地震で生じる繰返し
の大変形下においても、き裂進展抵抗及びその耐不安定
破壊特性が優れた構造用鋼材を提供することができる。
[0014] Based on the above findings, the present inventor has proposed that a steel having a reduced S content be used at a low temperature so that the metal structure becomes a ferrite + pearlite steel having a pearlite area fraction of a certain value or more. A steel material having excellent ductile crack growth resistance under repeated large deformation and a method for producing the same, which increase the crack growth resistance and increase the resistance to unstable fracture by rolling at a rolling reduction of not less than the amount. The present invention has been completed. That is, the present invention provides a structural steel material having excellent crack propagation resistance and its unstable fracture resistance even under repeated large deformation caused by an earthquake by specifying the steel composition, metal structure and manufacturing conditions. can do.

【0015】以下に本発明の成分添加理由、成分限定理
由、金属組織の限定理由及び製造条件の限定理由につい
て説明する。 (1)成分組成範囲 C:0.08〜0.2% Cは鋼材の強度を確保するために必要な元素であるが、
0.08%未満ではパーライト面積分率が少なくなりす
ぎるため、十分な延性き裂進展抵抗が得られない。ま
た、0.2%を越えて添加すると溶接性を損ねるので、
その含有量は0.08〜0.2%である。 Si:0.01〜0.5% Siは鋼材の強度を高めるとともに製鋼過程における脱
酸剤として必要であるが、0.01%未満ではその効果
が不十分であり、0.5%を越えて添加すると溶接部の
靭性を劣化させるので、その含有量は0.01〜0.5
%である。
The reasons for adding the components of the present invention, the reasons for limiting the components, the reasons for limiting the metallographic structure, and the reasons for limiting the manufacturing conditions will be described below. (1) Component composition range C: 0.08 to 0.2% C is an element necessary for securing the strength of the steel material.
If it is less than 0.08%, the pearlite area fraction becomes too small, so that sufficient ductile crack growth resistance cannot be obtained. Also, if added in excess of 0.2%, the weldability is impaired.
Its content is 0.08-0.2%. Si: 0.01-0.5% Si is necessary as a deoxidizing agent in the steel making process while increasing the strength of the steel material, but if it is less than 0.01%, its effect is insufficient, and it exceeds 0.5%. Addition deteriorates the toughness of the weld, the content is 0.01 to 0.5
%.

【0016】Mn:0.1〜2% Mnは鋼材の強度を高めるために添加されるが、0.1
%未満では強度が不足し、2%を越えて添加すると中心
偏析が多くなり板厚中央の靭性が劣化するため、その含
有量は0.1〜2%である。 Al:0.001〜0.1% Alは脱酸剤として必要であるが、0.001%未満で
は脱酸が不十分であり、0.1%を越えて添加されると
連鋳スラブの表面疵の原因となるため、その含有量は
0.001〜0.1%である。 S:0.005%以下 Sは硫化物系介在物を生成する元素であるが、地震によ
り繰返しの変形を受ける場合は、硫化物系介在物を核と
してボイドが発生成長するため、不安定破壊を助長す
る。不安定破壊に対する抵抗を高めるためにはS含有量
を厳しく制限する必要があるが、0.005%以下では
問題ないので、その含有量の上限は0.005%であ
る。
Mn: 0.1 to 2% Mn is added to increase the strength of the steel material.
If it is less than 2%, the strength is insufficient, and if it exceeds 2%, the center segregation increases and the toughness at the center of the sheet thickness deteriorates, so the content is 0.1 to 2%. Al: 0.001 to 0.1% Al is necessary as a deoxidizing agent, but if it is less than 0.001%, the deoxidizing is insufficient. Since it causes surface flaws, its content is 0.001 to 0.1%. S: 0.005% or less S is an element that forms sulfide-based inclusions, but when subjected to repeated deformation due to an earthquake, voids are generated with sulfide-based inclusions as nuclei, causing unstable destruction. To encourage. In order to increase the resistance to unstable fracture, it is necessary to severely limit the S content. However, since there is no problem if the S content is 0.005% or less, the upper limit of the S content is 0.005%.

【0017】本発明では上記の合金元素のほかに、鋼材
の強度・靭性を高めるためにCu、Ni、Cr、Mo、
Nb、V、Ti、Caのうちの1種または2種以上を含
有してもよいが、以下にその成分の限定理由を述べる。
In the present invention, in addition to the above alloying elements, Cu, Ni, Cr, Mo,
One or more of Nb, V, Ti, and Ca may be contained, but the reasons for limiting the components are described below.

【0018】Cu:0.5%以下 Cuは強度・靭性の向上に有効な元素であるが、0.5
%を越えて添加すると熱間加工性が低下するので、その
含有量は0.5%以下である。 Ni:0.5%以下 Niは靭性の向上に極めて有効な元素であるが、また非
常に高価な元素であることから0.5%を越えて添加す
るとコスト的に不利になるため、その含有量は0.5%
以下である。 Cr:1%以下 Crは強度向上に有効な元素であるが、1%を越えて添
加すると溶接性が低下するので、その含有量は1%以下
である。 Mo:0.6%以下 MoもCrと同様に強度向上に有効な元素であるが、
0.6%を越えて添加すると溶接性が低下するだけでな
く、コスト的にも不利になるため、その含有量は0.6
%以下である。 Nb:0.06%以下 NbはNb(C,N)として微細析出し強度上昇に寄与
する元素であるが、0.06%を越えて添加されると溶
接部の靭性が低下するため、その含有量は0.06%以
下である。 V:0.1%以下 VはVCとして析出し強度向上に寄与するが、0.1%
を越えて添加してもその効果が飽和するので、その含有
量は0.1%以下である。
Cu: 0.5% or less Cu is an element effective for improving strength and toughness.
%, The hot workability deteriorates, so the content is 0.5% or less. Ni: 0.5% or less Ni is an extremely effective element for improving the toughness. However, since it is a very expensive element, if it exceeds 0.5%, it is disadvantageous in terms of cost, so Ni is contained. 0.5%
It is as follows. Cr: 1% or less Cr is an element effective for improving the strength, but if added in excess of 1%, the weldability is reduced, so the content is 1% or less. Mo: 0.6% or less Mo is an element effective for improving the strength similarly to Cr,
If added in excess of 0.6%, not only will the weldability be reduced, but it will also be disadvantageous in terms of cost.
% Or less. Nb: 0.06% or less Nb is an element that precipitates finely as Nb (C, N) and contributes to an increase in strength. However, if added in excess of 0.06%, the toughness of the welded portion is reduced. The content is 0.06% or less. V: 0.1% or less V precipitates as VC and contributes to the improvement of the strength.
The effect is saturated even if added in excess of 0.1%, so the content is 0.1% or less.

【0019】Ti:0.1%以下 TiはTiNを形成し、溶接部の組織粗大化を抑制しH
AZ靭性の向上に寄与する元素であり微量の添加で大き
な効果が得られるが、0.1%を越えて添加されると逆
に溶接性が低下するため、その含有量は0.1%以下で
ある。
Ti: 0.1% or less Ti forms TiN and suppresses the formation of a coarse structure in the welded portion.
It is an element that contributes to the improvement of AZ toughness, and a large effect can be obtained with a small amount of addition. However, if added in excess of 0.1%, the weldability is reduced, so the content is 0.1% or less. It is.

【0020】Ca:0.005%以下 Caは硫化物系介在物の形状を制御することにより、靭
性を向上する元素であるが、0.005%を越えて添加
すると鋼の材質に悪影響を及ぼすため、その添加量は
0.005%以下である。 (2)金属組織 (2−1)態様1の金属組織 本発明の鋼材の金属組織は、パーライト面積分率が20
%以上のフェライト+パーライト組織である。
Ca: 0.005% or less Ca is an element that improves the toughness by controlling the shape of the sulfide-based inclusions, but if added in excess of 0.005%, adversely affects the steel material. Therefore, the amount of addition is 0.005% or less. (2) Metal Structure (2-1) Metal Structure of Aspect 1 The metal structure of the steel material of the present invention has a pearlite area fraction of 20.
% Or more of ferrite + pearlite structure.

【0021】フェライト+パーライト鋼においては、パ
ーライトは繰返し大変形を受ける場合のボイドの発生起
点となり、パーライト面積分率が大きいほどき裂先端近
傍でのボイドの発生量が多くなるため、変形エネルギー
がボイドの発生・連結に消費されるとともに、き裂の進
展経路に多くの分岐を生じ、き裂進展速度が低下する。
しかし、パーライト面積率が20%未満ではき裂が分岐
されず直線的に進展し、き裂進展速度が速くなるため、
パーライト面積分率を20%以上に規定した。
In ferrite + pearlite steel, pearlite is a starting point of void generation when repeatedly subjected to large deformation, and the larger the pearlite area fraction, the larger the amount of voids generated near the crack tip, so that the deformation energy is reduced. While being consumed for the generation and connection of voids, many branches occur in the crack propagation path, and the crack propagation speed decreases.
However, if the pearlite area ratio is less than 20%, the crack propagates linearly without branching, and the crack growth rate increases,
The pearlite area fraction was specified to be 20% or more.

【0022】(2−2)態様2の金属組織 本発明の鋼材の金属組織は、パーライト面積分率が10
%以上のフェライト+パーライト組織であり、フェライ
トの平均結晶粒径が10μm以下である。
(2-2) Metal Structure of Aspect 2 The metal structure of the steel material of the present invention has a pearlite area fraction of 10
% Ferrite + pearlite structure, and the average crystal grain size of ferrite is 10 μm or less.

【0023】フェライト結晶粒径が微細で、パーライト
間の平均距離が短くなれば、き裂進展経路の分岐がより
頻繁に起こり、き裂進展速度を小さくすることが可能で
ある。しかし、フェライト平均結晶粒径が10μmを超
えるとその効果は得られない。また、フェライト平均結
晶粒径が10μm以下の場合はパーライト面積分率が1
0%以上であれば、十分なき裂進展抵抗が得られる。
If the ferrite crystal grain size is fine and the average distance between pearlite is short, the crack propagation path branches more frequently, and the crack propagation speed can be reduced. However, if the average ferrite crystal grain size exceeds 10 μm, the effect cannot be obtained. When the average ferrite crystal grain size is 10 μm or less, the pearlite area fraction is 1
If it is 0% or more, sufficient crack growth resistance can be obtained.

【0024】上記の成分組成範囲及び金属組織に調整す
ることにより、地震で生じる繰返しの大変形下において
も、き裂進展抵抗及びその耐不安定破壊特性が優れた構
造用鋼材を得ることが可能になる。
By adjusting the composition range and the metal structure as described above, it is possible to obtain a structural steel having excellent crack propagation resistance and unstable fracture resistance even under repeated large deformation caused by an earthquake. become.

【0025】このような特性の鋼材は、以下の製造方法
により製造することができる。 (3)鋼材製造工程 (製造方法)上記した成分組成を有する鋼片(スラブ)
を1050〜1180℃の温度に加熱し、900℃以下
での累積圧下率50%以上、圧延終了温度650〜85
0℃で熱間圧延を行った後、空冷する。
The steel material having such characteristics can be manufactured by the following manufacturing method. (3) Steel material manufacturing process (Manufacturing method) Steel slab (slab) having the above component composition
Is heated to a temperature of 1050 to 1180 ° C., a rolling reduction of 50% or more at 900 ° C. or less, and a rolling end temperature of 650 to 85 ° C.
After hot rolling at 0 ° C., air cooling is performed.

【0026】a.鋼片加熱温度:1050〜1180℃ 加熱温度が1050℃未満であると、Al,Nb等の炭
窒化物形成元素の固溶量が少ないため、圧延中に析出す
る炭窒化物量が少なくなり十分な強度が得られないだけ
でなく、再結晶温度が上昇するために圧延による組織の
微細化が不十分となる。また、加熱温度が1180℃よ
り高いと、組織が粗大化するだけでなく靭性が劣化する
ため、加熱温度は1050〜1180℃である。
A. Slab heating temperature: 1050 to 1180 ° C When the heating temperature is lower than 1050 ° C, the amount of carbonitride forming elements such as Al and Nb is small, so that the amount of carbonitride precipitated during rolling is small and sufficient. Not only strength is not obtained, but also the recrystallization temperature rises, so that the micronization of the structure by rolling becomes insufficient. On the other hand, if the heating temperature is higher than 1180 ° C., not only the structure becomes coarse but also the toughness is deteriorated, so that the heating temperature is 1050 to 1180 ° C.

【0027】b.900℃以下での累積圧下率:50%
以上,圧延終了温度:650〜850℃ 900℃を超える温度では、再結晶を生じやすく組織が
粗大化し、900℃以下でも、累積圧下率が50%未満
となる場合は、組織が十分に微細化せず、高いき裂進展
抵抗が得られない。また、圧延終了温度が850℃を超
えると、冷却過程で組織が粗大化してしまい、高いき裂
進展抵抗が得られず、650℃未満になると加工歪によ
り靭性が劣化する。よって、900℃以下の累積圧下率
は50%以上,圧延終了温度は650〜850℃であ
る。
B. Cumulative reduction at 900 ° C or less: 50%
As described above, the rolling end temperature: 650 to 850 ° C. At a temperature exceeding 900 ° C., recrystallization is likely to occur, and the structure becomes coarse. At 900 ° C. or less, if the cumulative rolling reduction becomes less than 50%, the structure becomes sufficiently fine. No high crack growth resistance can be obtained. On the other hand, if the rolling end temperature exceeds 850 ° C., the structure becomes coarse in the cooling process, and high crack growth resistance cannot be obtained. If the rolling end temperature is lower than 650 ° C., the toughness is deteriorated due to processing strain. Therefore, the cumulative draft at 900 ° C or less is 50% or more, and the rolling end temperature is 650 to 850 ° C.

【0028】c.圧延後の空冷 圧延後空冷を行う理由は、圧延後の組織をフェライト−
パーライト組織とするためである。ただし、冷却過程で
の粒成長を抑制する目的で、ベイナイト変態を生じない
範囲で、空冷以上の冷却速度で冷却を行うことも可能で
ある。以下に本発明の実施例を挙げ、本発明の効果を立
証する。
C. Air cooling after rolling The reason for performing air cooling after rolling is that the structure after rolling is ferrite-based.
This is because of the pearlite structure. However, for the purpose of suppressing grain growth in the cooling process, it is also possible to perform cooling at a cooling rate higher than air cooling as long as bainite transformation does not occur. Hereinafter, examples of the present invention will be described to demonstrate the effects of the present invention.

【0029】[0029]

【実施例】【Example】

(実施例1)表1に示した成分の鋼(本発明鋼:No.
1〜13、比較鋼:No.14〜19)を溶製し、熱間
圧延により板厚25mmの板にした。そして、これらの
鋼板の板厚1/4付近のミクロ観察を行い、200倍で
10視野の写真を撮影し、画像解析によってパーライト
面積分率及びフェライト平均結晶粒径を測定した。次に
これらの素材の板厚1/4位置より、図1に示したよう
な応力集中係数3.8の切欠を有する試験片を採取し
た。そして、疲労試験機を用いて、標点間の平均歪で±
1%×10回(引張側で終了)の繰返し引張圧縮変形を
加えた。なお、試験温度は全て室温で行った。その後、
試験片を液体窒素で冷却し脆性的に破断させ、断面のS
EM写真からき裂進展量を求めた。
(Example 1) Steel having the components shown in Table 1 (Steel of the present invention: No. 1)
No. 1 to 13, comparative steel: No. 14 to 19) were melted and hot-rolled into a plate having a thickness of 25 mm. Micro-observation of these steel plates in the vicinity of 1/4 thickness was carried out, 10 photographs were taken at a magnification of 200 times, and the pearlite area fraction and the average ferrite crystal grain size were measured by image analysis. Next, a test piece having a notch having a stress concentration coefficient of 3.8 as shown in FIG. Then, using a fatigue tester, the average strain between the gauge points ±
Tensile compressive deformation of 1% × 10 times (finished on the tensile side) was applied. In addition, all the test temperatures were performed at room temperature. afterwards,
The test piece was cooled with liquid nitrogen and brittlely fractured.
The amount of crack propagation was determined from the EM photograph.

【0030】これらの結果を表1にまとめて示した。た
だし、繰返し数10回以前に不安定破壊を生じたものに
ついては破断までの回数を示した。本発明鋼であるN
o.1〜13はいずれも不安定破壊を生じておらず、ま
た、繰返し数10回でのき裂進展量が0.6mm以下で
あることから、き裂進展抵抗と不安定破壊に対する抵抗
がともに高いことがわかる。一方、比較鋼であるNo.
14〜17はいずれもパーライトの面積分率またはフェ
ライト平均結晶粒径が本発明範囲から外れており、繰返
し数10回でのき裂進展量が大幅に上昇している。ま
た、比較鋼No.18,19はS含有量が本発明範囲を
越えているため、繰返し数10回以前に不安定破壊を生
じている。
The results are summarized in Table 1. However, the number of times before breakage was shown for those which had unstable fracture before the repetition of 10 times. N, the steel of the present invention
o. Nos. 1 to 13 did not cause unstable fracture, and the amount of crack growth after 10 repetitions was 0.6 mm or less, so that both crack growth resistance and resistance to unstable fracture were high. You can see that. On the other hand, the comparative steel No.
In all of Nos. 14 to 17, the area fraction of pearlite or the average crystal grain size of ferrite was out of the range of the present invention, and the amount of crack growth after 10 repetitions was significantly increased. In addition, the comparative steel No. In Nos. 18 and 19, since the S content exceeded the range of the present invention, unstable fracture occurred before the repetition of 10 times.

【0031】[0031]

【表1】 [Table 1]

【0032】(実施例2)表2に示した成分の鋼(本発
明鋼:A〜L、比較鋼:M〜O)を溶製し、表3に示し
た種々の方法で圧延し、鋼板とした(本発明例:A1,
B1,B2,C1,C2,D1,E1〜H1,H2,I
1,J1,K1,L1、比較例:D2〜D4,J2〜J
5,M1〜O1)。そして、これらの鋼板の板厚1/4
付近のミクロ観察を行い、200倍で10視野の写真を
撮影し、画像解析によってパーライト面積分率及びフェ
ライト平均結晶粒径を測定した。次にこれらの素材の板
厚1/4位置より、図1に示したような応力集中係数
3.8の切欠を有する試験片を採取した。そして、疲労
試験機を用いて、標点間の平均歪で±1%×10回(引
張側で終了)の繰返し引張圧縮変形を加えた。なお、試
験温度は全て室温で行った。その後、試験片を液体窒素
で冷却し脆性的に破断させ、断面のSEM写真からき裂
進展量を求めた。
(Example 2) Steels having the components shown in Table 2 (invention steels: A to L, comparative steels: M to O) were melted and rolled by various methods shown in Table 3, (Example of the present invention: A1,
B1, B2, C1, C2, D1, E1 to H1, H2, I
1, J1, K1, L1, Comparative Example: D2 to D4, J2 to J
5, M1 to O1). And the thickness of these steel plates is 1/4
Micro observation of the vicinity was carried out, photographs of 10 visual fields were taken at 200 times magnification, and the pearlite area fraction and the average ferrite crystal grain size were measured by image analysis. Next, a test piece having a notch having a stress concentration coefficient of 3.8 as shown in FIG. Then, using a fatigue tester, repeated tensile and compressive deformation of ± 1% × 10 times (finished on the tensile side) with an average strain between gauge points was applied. In addition, all the test temperatures were performed at room temperature. Thereafter, the test piece was cooled with liquid nitrogen to break brittlely, and the amount of crack propagation was determined from the SEM photograph of the cross section.

【0033】これらの結果を表3にまとめて示した。た
だし、繰返し数10回以前に不安定破壊を生じたものに
ついては破断までの回数を示した。本発明例(A1,B
1,B2,C1,C2,D1,E1〜H1,H2,I
1,J1,K1,L1)はいずれも不安定破壊を生じて
おらず、また、繰返し数10回でのき裂進展量が0.3
5mm以下であることから、き裂進展抵抗と不安定破壊
に対する抵抗がともに高いことがわかる。
The results are summarized in Table 3. However, the number of times before breakage was shown for those which had unstable fracture before the repetition of 10 times. Example of the present invention (A1, B
1, B2, C1, C2, D1, E1-H1, H2, I
1, J1, K1, L1) did not cause unstable fracture, and had a crack growth amount of 0.3 after 10 repetitions.
Since it is 5 mm or less, it is understood that both the crack propagation resistance and the resistance to unstable fracture are high.

【0034】一方、比較例D2〜D4,J2〜J5,M
1は成分または圧延条件が本発明範囲から外れているた
め、パーライト面積分率が低いかまたはフェライト結晶
粒径が大きくなるため、繰返し数10回でのき裂進展量
が大幅に上昇している。また、比較例N1,O1はS含
有量が本発明範囲を越えているため、繰返し数10回以
前に不安定破壊を生じている。
On the other hand, Comparative Examples D2 to D4, J2 to J5, M
In No. 1, since the component or the rolling conditions are out of the range of the present invention, the pearlite area fraction is low or the ferrite crystal grain size is large, so that the crack growth amount after 10 repetitions is significantly increased. . In Comparative Examples N1 and O1, since the S content exceeded the range of the present invention, unstable fracture occurred before the repetition of 10 times.

【0035】[0035]

【表2】 [Table 2]

【0036】[0036]

【表3】 [Table 3]

【0037】[0037]

【発明の効果】以上に示したように、本発明によれば鋼
組成、金属組織及び製造条件を特定することにより、繰
返し大変形下において応力集中部からき裂が発生進展す
る場合の、き裂進展抵抗及び不安定破壊に対する抵抗が
高い鋼材を提供することが可能であり、高い耐震性能を
要求される建造物の利用に適している。
As described above, according to the present invention, by specifying the steel composition, the metal structure, and the manufacturing conditions, the crack is generated and propagated from the stress concentrated portion under repeated large deformation. It is possible to provide a steel material having high resistance to development and unstable fracture, and is suitable for use in a building requiring high seismic performance.

【図面の簡単な説明】[Brief description of the drawings]

【図1】本発明の実施例に係る切欠丸棒試験片の形状を
示す図。
FIG. 1 is a view showing a shape of a notched round bar test piece according to an embodiment of the present invention.

【図2】本発明の実施の形態に係る切欠丸棒試験片の切
欠底からの亀裂発生状況を示す図。
FIG. 2 is a view showing a state of occurrence of a crack from a notch bottom of a notched round bar test piece according to an embodiment of the present invention.

【図3】本発明の実施の形態に係る切欠丸棒試験片(パ
ーライト面積分率及びフェライト結晶粒径を変えた場
合)の繰返し引張圧縮回数とき裂進展量との関係を示す
図。
FIG. 3 is a diagram showing the relationship between the number of times of repeated tensile compression and the amount of crack propagation of a notched round bar test piece (when the pearlite area fraction and ferrite crystal grain size are changed) according to the embodiment of the present invention.

【図4】本発明の実施の形態に係る切欠丸棒試験片のS
含有量と不安定破壊を生ずるまでの繰返し引張圧縮回数
との関係を示す図。
FIG. 4 shows the S of the notched round bar specimen according to the embodiment of the present invention.
The figure which shows the relationship between content and the number of times of repeated tension compression until unstable fracture arises.

【符号の説明】[Explanation of symbols]

1…切欠底 2…き裂 1 ... notch bottom 2 ... crack

Claims (5)

【特許請求の範囲】[Claims] 【請求項1】 重量%で、C:0.08〜0.2%と、
Si:0.01〜0.5%と、Mn:0.1〜2%と、
Al:0.001〜0.1%と、S:0.005%以下
とを含有し、残部がFe及び不可避的不純物からなり、
且つ金属組織は、パーライト面積分率が20%以上のフ
ェライト+パーライト組織であることを特徴とする、繰
返し大変形下での延性き裂進展抵抗の優れた鋼材。
(1) C: 0.08 to 0.2% by weight
Si: 0.01 to 0.5%, Mn: 0.1 to 2%,
Al: 0.001 to 0.1% and S: 0.005% or less, the balance being Fe and unavoidable impurities,
Further, the metal material is a ferrite having a pearlite area fraction of 20% or more and a pearlite structure, characterized by having excellent ductile crack growth resistance under repeated large deformation.
【請求項2】 重量%で、C:0.08〜0.2%と、
Si:0.01〜0.5%と、Mn:0.1〜2%と、
Al:0.001〜0.1%と、S:0.005%以下
とを含有し、残部がFe及び不可避的不純物からなり、
且つ金属組織は、パーライト面積分率が10%以上のフ
ェライト+パーライト組織であり、フェライトの平均結
晶粒径が10μm以下であることを特徴とする、繰返し
大変形下での延性き裂進展抵抗の優れた鋼材。
2. C: 0.08 to 0.2% by weight.
Si: 0.01 to 0.5%, Mn: 0.1 to 2%,
Al: 0.001 to 0.1% and S: 0.005% or less, the balance being Fe and unavoidable impurities,
The metal structure is a ferrite having a pearlite area fraction of 10% or more and a pearlite structure, and the average crystal grain size of the ferrite is 10 μm or less. Excellent steel material.
【請求項3】 鋼成分として、重量%でさらに、Cu:
0.5%以下、Ni:0.5%以下、Cr:1%以下、
Mo:0.6%以下、Nb:0.06%以下、V:0.
1%以下、Ti:0.1%以下、及びCa:0.005
%以下の群から選択された1種または2種以上を含有す
ることを特徴とする、請求項1または2に記載の繰返し
大変形下での延性き裂進展抵抗の優れた鋼材。
3. The steel component further comprises, by weight%, Cu:
0.5% or less, Ni: 0.5% or less, Cr: 1% or less,
Mo: 0.6% or less, Nb: 0.06% or less, V: 0.
1% or less, Ti: 0.1% or less, and Ca: 0.005
% Or less, selected from the group of not more than 1%, wherein the steel material excellent in ductile crack growth resistance under repeated large deformation according to claim 1 or 2.
【請求項4】 重量%で、C:0.08〜0.2%と、
Si:0.01〜0.5%と、Mn:0.1〜2%と、
Al:0.001〜0.1%と、S:0.005%以下
とを含有し、残部がFe及び不可避的不純物からなる鋼
片を1050〜1180℃の温度に加熱し、900℃以
下での累積圧下率50%以上、圧延終了温度650〜8
50℃で熱間圧延を行った後、空冷することを特徴とす
る、繰返し大変形下での延性き裂進展抵抗の優れた鋼材
の製造方法。
4. C: 0.08 to 0.2% by weight,
Si: 0.01 to 0.5%, Mn: 0.1 to 2%,
A steel slab containing Al: 0.001 to 0.1% and S: 0.005% or less, with the balance being Fe and unavoidable impurities, is heated to a temperature of 1050 to 1180 ° C. Rolling reduction temperature of 650 to 8
A method for producing a steel material having excellent ductile crack growth resistance under repeated large deformation, wherein the steel material is hot-rolled at 50 ° C. and then air-cooled.
【請求項5】 鋼成分として、重量%でさらに、Cu:
0.5%以下、Ni:0.5%以下、Cr:1%以下、
Mo:0.6%以下、Nb:0.06%以下、V:0.
1%以下、Ti:0.1%以下、及びCa:0.005
%以下の群から選択された1種または2種以上を含有す
ることを特徴とする、請求項4に記載の繰返し大変形下
での延性き裂進展抵抗の優れた鋼材の製造方法。
5. The steel component further comprises, in weight%, Cu:
0.5% or less, Ni: 0.5% or less, Cr: 1% or less,
Mo: 0.6% or less, Nb: 0.06% or less, V: 0.
1% or less, Ti: 0.1% or less, and Ca: 0.005
The method for producing a steel material having excellent ductile crack propagation resistance under repeated large deformation according to claim 4, characterized in that the steel material contains one or more selected from the group of not more than%.
JP25108297A 1997-09-16 1997-09-16 Steel material excellent in ductile crack growth resistance under repeated large deformation and its manufacturing method Expired - Fee Related JP3849244B2 (en)

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