JP2012246520A - Steel material excellent in fatigue-crack propagation resistance and low-temperature toughness at weld heat-affected zone, and method for production thereof - Google Patents
Steel material excellent in fatigue-crack propagation resistance and low-temperature toughness at weld heat-affected zone, and method for production thereof Download PDFInfo
- Publication number
- JP2012246520A JP2012246520A JP2011117869A JP2011117869A JP2012246520A JP 2012246520 A JP2012246520 A JP 2012246520A JP 2011117869 A JP2011117869 A JP 2011117869A JP 2011117869 A JP2011117869 A JP 2011117869A JP 2012246520 A JP2012246520 A JP 2012246520A
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel material
- temperature toughness
- fatigue crack
- crack growth
- 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
本発明は船舶、海洋構造物その他の耐疲労亀裂進展特性および溶接熱影響部（以下、「ＨＡＺ」という。）の低温靭性が要求される溶接構造物などに用いるのに適した鋼材並びにその製造方法に関する。 The present invention relates to a steel material suitable for use in a welded structure or the like that requires low-temperature toughness of marine structures, marine structures and other fatigue crack propagation resistance and weld heat affected zone (hereinafter referred to as “HAZ”). Regarding the method.
近年、溶接構造物が大型化される傾向が顕著になっており、高強度化および軽量化が望まれている。しかし、高強度鋼を使用する際には設計応力が上昇するため、溶接部から疲労破壊が発生し易くなり、その改善が望まれている。一般に、構造部材に使用される厚鋼板では、溶接施工が施されるため、溶接部から疲労破壊が発生する可能性がある。従って、溶接部からのき裂発生を抑制し、き裂が発生した場合にも進展する疲労き裂を鋼材で停留させることができれば、構造物の疲労寿命延長に有効である。このため、耐疲労き裂進展特性を有する鋼板が種々提案されている。一方、近年では、大入熱溶接を適用され、ＨＡＺの低温靭性が要求される鋼材に対しても耐疲労き裂進展特性を有することが望まれている。 In recent years, the tendency to increase the size of welded structures has become prominent, and higher strength and lighter weight are desired. However, when using high-strength steel, the design stress rises, so that fatigue fracture is likely to occur from the welded portion, and improvement thereof is desired. In general, a thick steel plate used for a structural member is subjected to welding work, so that fatigue failure may occur from the welded portion. Therefore, it is effective in extending the fatigue life of a structure if crack generation from a welded part is suppressed and a fatigue crack that propagates even when a crack occurs can be retained by a steel material. For this reason, various steel plates having fatigue crack growth resistance have been proposed. On the other hand, in recent years, it has been desired to have fatigue crack growth resistance even for steel materials to which high heat input welding is applied and where low temperature toughness of HAZ is required.
例えば、特許文献１には、鋼材表面下の介在物を制御することで、耐疲労き裂進展特性を有する技術が提案されている。 For example, Patent Document 1 proposes a technique having fatigue crack growth resistance characteristics by controlling inclusions below the steel surface.
特許文献１で提案された技術は、耐疲労き裂進展特性の観点から組成の限定、介在物の制御がなされている。しかし、鋼材は温度の低い環境下で使用される場合もあるところ、当該技術はＨＡＺにおける低温靭性を考慮したものではない。耐疲労き裂進展特性に加えてＨＡＺの低温靭性が求められる場合もある。 In the technique proposed in Patent Document 1, the composition is limited and inclusions are controlled from the viewpoint of fatigue crack growth resistance. However, steel materials are sometimes used in a low-temperature environment, and the technology does not consider low temperature toughness in HAZ. In addition to fatigue crack growth resistance, the low temperature toughness of HAZ may be required.
本発明は、このような状況に鑑み、耐疲労き裂進展特性を有するだけでなくＨＡＺの低温靭性をも確保できる鋼材を提供することを目的とする。 In view of such circumstances, an object of the present invention is to provide a steel material that not only has fatigue crack growth resistance but also can ensure low temperature toughness of HAZ.
本発明者らは、上記の目的を達成するべく、ＨＡＺの低温靭性を確保するための組成を基本としつつ、耐疲労き裂進展特性と金属組織、機械的性質の影響を調査した。その結果、次の(a)〜(d)に示す知見が得られた。 In order to achieve the above object, the present inventors investigated the effects of fatigue crack growth resistance, metal structure, and mechanical properties, based on a composition for ensuring low temperature toughness of HAZ. As a result, the following findings (a) to (d) were obtained.
(a)耐疲労き裂進展特性の向上のためには、表層部の硬度と板厚中心部の硬度の差を限定することが有効である。この理由は、表層部と板厚中心部の硬度差を小さくすることで、疲労き裂が不均一に進展することが抑制され、構造物が外力を受けた際にも、板厚の一部分が優先的に変形することが無くなるためである。 (a) In order to improve the fatigue crack growth resistance, it is effective to limit the difference between the hardness of the surface layer portion and the hardness of the plate thickness center portion. The reason for this is that by reducing the hardness difference between the surface layer portion and the center portion of the plate thickness, fatigue cracks are prevented from growing unevenly, and even when the structure receives external force, a portion of the plate thickness is reduced. This is because there is no preferential deformation.
(b)ＨＡＺの低温靭性の改善のためには、Ｂの添加が有効である一方、Ｂが溶接時にＢＮを形成せず、固溶Ｂとして存在した場合には、靭性を劣化させる。よって、溶接時に固溶Ｂが過剰にならないように、窒化物生成元素の添加比率が重要となる。 (b) In order to improve the low temperature toughness of HAZ, addition of B is effective. On the other hand, when B does not form BN during welding and exists as solid solution B, the toughness is deteriorated. Therefore, the addition ratio of the nitride-forming element is important so that the solid solution B does not become excessive during welding.
(c)しかし、耐疲労き裂進展特性の向上のためには、寧ろ積極的に固溶Ｂを活用し、ベイナイト組織を有効に生成させることが有効となる。 (c) However, in order to improve the fatigue crack growth resistance, it is effective to actively use the solute B to effectively generate a bainite structure.
(d)そして、下記式(1)および(2)を満足するように、Ｔｉ、ＢおよびＮの含有量を適正に制御することによって、耐疲労き裂進展特性とＨＡＺの低温靭性を両立させることができることを見出した。
Ｔｉ／Ｎ≦３．４・・・・・・・・・・・(1)式
０．０００３≦Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）≦０．００３・・(2)式
ただし、式中の元素記号は、各元素の含有量（質量％）を意味する。
(d) And, by appropriately controlling the contents of Ti, B and N so as to satisfy the following formulas (1) and (2), the fatigue crack growth resistance and the low temperature toughness of HAZ are compatible. I found that I can do it.
Ti / N ≦ 3.4 (1) Formula 0.0003 ≦ B-10.8 / 14.1 × (N—Ti / 3.4) ≦ 0.003 -(2) Formula However, the element symbol in a formula means content (mass%) of each element.
本発明は、このような知見に基づいて完成したものであり、その要旨は、下記の（１）〜（４）に示す耐疲労き裂進展特性およびＨＡＺの低温靭性に優れる鋼材、ならびに、下記の（５）に示す耐疲労き裂進展特性およびＨＡＺの低温靭性に優れる鋼材の製造方法にある。 The present invention has been completed on the basis of such findings, and the gist of the present invention is a steel material excellent in fatigue crack growth resistance and low temperature toughness of HAZ shown in the following (1) to (4), and The method for producing a steel material having excellent fatigue crack growth characteristics and low temperature toughness of HAZ shown in (5).
（１）質量％で、Ｃ：０．０１〜０．１０％、Ｓｉ：０．０４〜０．６０％、Ｍｎ：０．５〜２．０％、Ｐ：０．０１５％以下、Ｓ：０．００４％以下、Ａｌ：０．００５〜０．０７％、Ｔｉ：０．００４〜０．０２５％、Ｂ：０．０００５〜０．００４０％、Ｎ：０．００４０〜０．００９０％を含有し、残部はＦｅ及び不純物からなり、金属組織が面積率で５０％以上のベイナイト組織、５％以下のパーライト組織、残部がフェライト組織であり、表層部と板厚中心部の硬度差がビッカース硬さで５０以内であり、かつ下記式(1)および(2)を満足することを特徴とする耐疲労き裂進展特性および溶接熱影響部の低温靭性に優れた鋼材。
Ｔｉ／Ｎ≦３．４・・・・・・・・・・・(1)式
０．０００３≦Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）≦０．００３・・(2)式
ただし、式中の元素記号は、各元素の含有量（質量％）を意味する。
(1) By mass%, C: 0.01 to 0.10%, Si: 0.04 to 0.60%, Mn: 0.5 to 2.0%, P: 0.015% or less, S: 0.004% or less, Al: 0.005-0.07%, Ti: 0.004-0.025%, B: 0.0005-0.0040%, N: 0.0040-0.0090% The balance is Fe and impurities, the metal structure is a bainite structure with an area ratio of 50% or more, the pearlite structure is 5% or less, the balance is a ferrite structure, and the difference in hardness between the surface layer and the center of the plate thickness is Vickers. A steel material excellent in fatigue crack growth resistance and low temperature toughness of the weld heat affected zone, characterized by being within 50 in hardness and satisfying the following formulas (1) and (2).
Ti / N ≦ 3.4 (1) Formula 0.0003 ≦ B-10.8 / 14.1 × (N—Ti / 3.4) ≦ 0.003 -(2) Formula However, the element symbol in a formula means content (mass%) of each element.
（２）さらに、質量％で、Ｃｕ：０．４０％以下、Ｃｒ：０．２０％以下、Ｍｏ：０．２０％以下およびＶ：０．１０％以下の中から選ばれる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）の耐疲労き裂進展特性および溶接熱影響部の低温靭性に優れた鋼材。 (2) Furthermore, by mass%, Cu: 0.40% or less, Cr: 0.20% or less, Mo: 0.20% or less, and V: 0.10% or less The steel material which is excellent in the fatigue crack growth characteristics of the above (1) and the low temperature toughness of the weld heat affected zone, characterized by containing the above.
（３）さらに、質量％で、Ｎｉ：０．４０％以下およびＮｂ：０．０５％以下の一方または両方を含有することを特徴とする、上記（１）または（２）の耐疲労き裂進展特性および溶接熱影響部の低温靭性に優れた鋼材。 (3) The fatigue crack resistance according to (1) or (2) above, further comprising one or both of Ni: 0.40% or less and Nb: 0.05% or less by mass%. Steel material with excellent growth characteristics and low temperature toughness of weld heat affected zone.
（４）さらに、質量％で、Ｓｎ：０．５０％以下を含有することを特徴とする、上記（１）〜（３）のいずれかの耐疲労き裂進展特性および溶接熱影響部の低温靭性に優れた鋼材。 (4) The fatigue crack growth characteristics of any of the above (1) to (3) and the low temperature of the weld heat-affected zone, characterized by further containing Sn: 0.50% or less by mass%. Steel material with excellent toughness.
（５）上記（１）〜（４）のいずれかに記載の組成を有する鋼片を、１０００〜１２００℃に加熱後、９００℃以下の累積圧下量が３０％以上となるように圧延を行い、７４０〜８５０℃で仕上げ圧延を行い、圧延後１２０秒以内、かつ仕上げ圧延からの温度低下が３０℃以内で冷却速度が５℃/sec以上となるような水冷を行い、４００℃以下で水冷を停止することを特徴とすることを特徴とする耐疲労き裂進展特性および溶接熱影響部の低温靭性に優れた鋼材の製造方法。 (5) After heating the steel slab having the composition according to any one of (1) to (4) above to 1000 to 1200 ° C, the steel slab is rolled so that the cumulative reduction amount at 900 ° C or less is 30% or more. Finishing rolling at 740-850 ° C., water cooling is performed within 120 seconds after rolling, temperature drop from finishing rolling is within 30 ° C. and cooling rate is 5 ° C./sec or more, and water cooling is performed at 400 ° C. or less. A method for producing a steel material excellent in fatigue crack growth characteristics and low temperature toughness of a weld heat affected zone, characterized in that the method is characterized in that the process is stopped.
本発明の鋼材は、耐疲労き裂進展特性およびＨＡＺの低温靭性に優れているので、船舶、海洋構造物その他の耐疲労亀裂進展特性およびＨＡＺの低温靭性が要求される溶接構造物などに用いるのに適している。 Since the steel material of the present invention is excellent in fatigue crack growth resistance and low temperature toughness of HAZ, it is used for marine and other marine structures and other welded structures that require fatigue crack growth resistance and low temperature toughness of HAZ. Suitable for
以下、本発明の各要件について詳しく説明する。 Hereinafter, each requirement of the present invention will be described in detail.
Ａ．本発明の鋼材の化学組成について
まず、本発明の鋼材の化学組成について説明する。以下の説明において、含有量についての「％」は、「質量％」を意味する。
A. About the chemical composition of the steel material of this invention First, the chemical composition of the steel material of this invention is demonstrated. In the following description, “%” for the content means “% by mass”.
Ｃ：０．０１〜０．１０％
Ｃは強度を上げるのに有効な元素である。また、耐疲労き裂進展特性を確保するためのベイナイト組織生成のためには必須となる元素である。こうした効果を得るためには、０．０１％以上の添加が必要である。一方、含有量が０．１０％以上となるとＨＡＺの低温靭性確保が困難となる。よって添加量の上限は０．１０％とした。Ｃの好ましい下限は０．０３％、好ましい上限は０．０８％である。
C: 0.01 to 0.10%
C is an element effective for increasing the strength. In addition, it is an essential element for generating a bainite structure for ensuring fatigue crack growth resistance. In order to obtain such an effect, addition of 0.01% or more is necessary. On the other hand, when the content is 0.10% or more, it becomes difficult to ensure the low temperature toughness of the HAZ. Therefore, the upper limit of the addition amount is 0.10%. The preferable lower limit of C is 0.03%, and the preferable upper limit is 0.08%.
Ｓｉ：０．０４〜０．６０％
Ｓｉは、脱酸作用を有する。しかし、その含有量が０．０４％未満ではその効果に乏しい。一方、Ｓｉの含有量が０．６０％を超えるとＨＡＺの低温靭性が低下するようになる。したがって、Ｓｉの含有量を０．０４〜０．６０％とした。Ｓｉの好ましい下限は０．１０％、好ましい上限は０．５０％である。
Si: 0.04 to 0.60%
Si has a deoxidizing action. However, if the content is less than 0.04%, the effect is poor. On the other hand, when the Si content exceeds 0.60%, the low temperature toughness of the HAZ is lowered. Therefore, the Si content is set to 0.04 to 0.60%. The preferable lower limit of Si is 0.10%, and the preferable upper limit is 0.50%.
Ｍｎ：０．５〜２．０％
Ｍｎは、強度の確保に有効な元素である。しかし、その含有量が０．５％未満ではその効果に乏しい。一方、Ｍｎの含有量が２．０％を超えると溶接性が低下するので溶接施工が困難となり、構造用鋼材としての使用領域が著しく限定されてしまう。したがって、Ｍｎの含有量を０．５〜２．０％とした。Ｍｎの好ましい下限は０．８％、好ましい上限は１．６％である。
Ｐ：０．０１５％以下
Mn: 0.5 to 2.0%
Mn is an element effective for securing strength. However, if the content is less than 0.5%, the effect is poor. On the other hand, if the Mn content exceeds 2.0%, the weldability is deteriorated, so that welding is difficult, and the use area as a structural steel material is remarkably limited. Therefore, the Mn content is set to 0.5 to 2.0%. The preferable lower limit of Mn is 0.8%, and the preferable upper limit is 1.6%.
P: 0.015% or less
Ｐ：０．０１５％以下
Ｐは、不純物として鋼中に不可避的に存在する。その含有量が０．０１５％を超えると、粒界に偏析して靭性を低下させるのみならず、溶接時に高温割れを招く。したがって、Ｐの含有量を０．０１５％以下とする必要がある。
P: 0.015% or less P is unavoidably present in steel as an impurity. If its content exceeds 0.015%, it not only segregates at the grain boundaries and lowers toughness, but also causes hot cracking during welding. Therefore, the P content needs to be 0.015% or less.
Ｓ：０．００４％以下
Ｓは、不純物として鋼中に不可避的に存在する。Ｓ含有量が多いと中心偏析を助長したり、延伸したＭｎＳが多量に生成したりするため、母材およびＨＡＺの低温靭性が劣化する。したがって、Ｓの含有量を０．００４％以下とする必要がある。Ｓの含有量は少ないほど好ましいため下限は特に規定するものではない。
S: 0.004% or less S is unavoidably present in steel as an impurity. When the S content is large, center segregation is promoted or stretched MnS is generated in a large amount, so that the low temperature toughness of the base material and the HAZ deteriorates. Therefore, the S content needs to be 0.004% or less. The lower the content of S, the better, so the lower limit is not particularly specified.
Ａｌ：０．００５〜０．０７％
Ａｌは、脱酸作用を有する。しかし、その含有量が０．００５％未満では添加効果に乏しく、一方、０．０７％を超えると、ＨＡＺ入熱溶接熱影響部の低温靱性が低下するし、鋼の清浄性も悪くなる。したがって、Ａｌの含有量を０．００５〜０．０７％とした。
Al: 0.005 to 0.07%
Al has a deoxidizing action. However, if the content is less than 0.005%, the effect of addition is poor. On the other hand, if it exceeds 0.07%, the low temperature toughness of the HAZ heat input welding heat affected zone is lowered, and the cleanliness of the steel is also deteriorated. Therefore, the content of Al is set to 0.005 to 0.07%.
Ｔｉ：０．００４〜０．０２５％
Ｔｉは、ＴｉＮを形成しＨＡＺの結晶粒の粗大化を抑制する効果を持つ。この効果を得るためには０．００４％以上含有させる必要がある。しかし、その含有量が０．０２５％を超えると却って靭性が低下するようになる。したがって、Ｔｉの含有量を０．００４〜０．０２５％とした。Ｔｉの好ましい下限は０．００８％、好ましい上限は０．０２０％である。
Ti: 0.004 to 0.025%
Ti has the effect of suppressing the coarsening of HAZ crystal grains by forming TiN. In order to acquire this effect, it is necessary to contain 0.004% or more. However, when the content exceeds 0.025%, the toughness is lowered. Therefore, the Ti content is set to 0.004 to 0.025%. The preferable lower limit of Ti is 0.008%, and the preferable upper limit is 0.020%.
Ｂ：０．０００５〜０．００４０％
Ｂは焼入れ性を向上させて強度を高め、ベイナイト生成を促進することを通じて母材の高強度化および耐疲労き裂進展特性の改善に寄与する。この効果を得るために、Ｂの含有量を０．０００５％以上とする必要がある。一方、Ｂの含有量が０．００４０％を超えると、強度を高める効果が飽和し、さらに母材とＨＡＺの低温靱性劣化の傾向が著しくなる。したがって、Ｂの含有量を０．０００５〜０．００４０％とした。
B: 0.0005 to 0.0040%
B improves the hardenability and increases the strength and promotes the formation of bainite, thereby contributing to an increase in the strength of the base material and improvement in fatigue crack resistance. In order to obtain this effect, the B content needs to be 0.0005% or more. On the other hand, when the B content exceeds 0.0040%, the effect of increasing the strength is saturated, and the tendency of low-temperature toughness deterioration of the base material and HAZ becomes remarkable. Therefore, the content of B is set to 0.0005 to 0.0040%.
Ｎ：０．００４０〜０．００９０％
ＮはＴｉＮを形成しＨＡＺの結晶粒の粗大化を抑制する効果を持つ。この効果を得るために、Ｎの含有量を０．００４０％以上とする必要がある。一方、０．００９０％を超えると、過剰な固溶Ｎが母材とＨＡＺの低温靭性を劣化させる。したがって、Ｎの含有量を０００４０〜０．００９０％とした。
N: 0.0040 to 0.0090%
N forms TiN and has the effect of suppressing coarsening of HAZ crystal grains. In order to obtain this effect, the N content needs to be 0.0040% or more. On the other hand, if it exceeds 0.0090%, the excessive solute N deteriorates the low temperature toughness of the base material and the HAZ. Therefore, the N content is set to 0400 to 0.0090%.
Ｔｉ／Ｎ≦３．４・・・・・・・・・・・(1)式
ＴｉとＮは、ＴｉＮを形成しＨＡＺの低温靭性を改善させるが、Ｔｉ／Ｎが３．４を超えるとＴｉが過剰となり、Ｔｉ炭化物生成を通じてＨＡＺの低温靭性を劣化させる。したがって、(1)式に示すように、Ｔｉ／Ｎは３．４以下とした。
Ti / N ≦ 3.4 (1) Formula Ti and N form TiN and improve the low temperature toughness of HAZ, but when Ti / N exceeds 3.4 Ti becomes excessive and deteriorates the low temperature toughness of the HAZ through the formation of Ti carbide. Therefore, as shown in the formula (1), Ti / N is set to 3.4 or less.
０．０００３≦Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）≦０．００３・・(2)式
Ｂは鋼中にフリーなＮが存在するとＢＮを生成する。一方、Ｎは固定されＴｉＮとして固定される。よって、鋼中の固溶Ｂ量はＮとＴｉの量に依存し、Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）で表される。固溶Ｂ量が０．０００３％未満では母材のベイナイト組織生成が難しくなり、耐疲労き裂進展特性が確保できない。一方、固溶Ｂ量が０．００３％を超えると母材、ＨＡＺの低温靱性劣化の傾向が著しくなる。したがって、(2)式に示すように、Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）を０．０００３〜０．００３％とした。
0.0003 ≦ B-10.8 / 14.1 × (N—Ti / 3.4) ≦ 0.003 (2) Formula B generates BN when free N is present in the steel. On the other hand, N is fixed and fixed as TiN. Therefore, the amount of solute B in the steel depends on the amounts of N and Ti, and is represented by B-10.8 / 14.1 × (N—Ti / 3.4). If the amount of solute B is less than 0.0003%, it becomes difficult to form a bainite structure of the base material, and fatigue crack resistance cannot be ensured. On the other hand, when the amount of dissolved B exceeds 0.003%, the tendency of the base material and HAZ to deteriorate at low temperature toughness becomes remarkable. Therefore, as shown in the formula (2), B-10.8 / 14.1 × (N—Ti / 3.4) is set to 0.0003 to 0.003%.
本発明に係る鋼材は、上記の化学組成を有し、残部がＦｅおよび不純物からなる。ここで、不純物とは、鋼材を工業的に製造する際に鉱石やスクラップ等のような原料をはじめとして製造工程の種々の要因によって混入する成分であって、本発明に悪影響を与えない範囲で許容されるものを意味する。 The steel material according to the present invention has the above-described chemical composition, with the balance being Fe and impurities. Here, the impurities are components that are mixed due to various factors of the manufacturing process including raw materials such as ore and scrap when industrially manufacturing steel materials, and in a range that does not adversely affect the present invention. It means what is allowed.
本発明の鋼材には、必要に応じて、次の第１群から第３群までの少なくとも１群から選んだ成分の１種以上を含有させることができる。以下、これらの群に属する成分について述べる。 The steel material of the present invention may contain one or more components selected from at least one group from the following first group to third group, if necessary. Hereinafter, components belonging to these groups will be described.
第１群の成分：Ｃｕ、Ｃｒ、Ｍｏ、Ｖ
Ｃｕ：０．４０％以下
Ｃｕは、必要に応じて含有させることができる。Ｃｕを含有させると、大きな靭性劣化を伴わずに強度を向上させることができる。しかしながら、その含有量が０．４０％を超えると、熱間での加工の際、表面に微小な割れを発生させるので、その含有量の上限は０．４０％とする。なお、Ｃｕによる強度向上効果を安定的に発現させるためには、Ｃｕを０．１０％以上含有させることが好ましい。
First group of components: Cu, Cr, Mo, V
Cu: 0.40% or less Cu can be contained as necessary. When Cu is contained, the strength can be improved without significant deterioration in toughness. However, if the content exceeds 0.40%, minute cracks are generated on the surface during hot processing, so the upper limit of the content is 0.40%. In order to stably develop the strength improvement effect by Cu, it is preferable to contain Cu by 0.10% or more.
Ｃｒ：０．２０％以下
Ｃｒは、必要に応じて含有させることができる。Ｃｒを含有させると、強度を上昇させることができる。しかしながら、その含有量が０．２０％を超えると、靭性の劣化をきたし、更に、ＨＡＺに硬化した組織を形成し低温靭性を劣化させるので、その含有量の上限は０．２０％とする。なお、Ｃｒによる強度向上効果を安定的に発現させるためには、Ｃｒを０．０５％以上含有させることが好ましい。
Cr: 0.20% or less Cr can be contained as necessary. When Cr is contained, the strength can be increased. However, if the content exceeds 0.20%, the toughness is deteriorated, and further, a hardened structure is formed in the HAZ and the low-temperature toughness is deteriorated. Therefore, the upper limit of the content is 0.20%. In order to stably develop the strength improvement effect by Cr, it is preferable to contain 0.05% or more of Cr.
Ｍｏ：０．２０％以下
Ｍｏは、必要に応じて含有させることができる。Ｍｏを含有させると、焼入性を高め、強度を向上させることができる。しかしながら、Ｍｏの含有はコストアップ要因となり、また、その含有量が０．２０％を超えると、却ってＨＡＺの低温靭性を劣化させるので、その含有量の上限は０．２０％とする。なお、Ｍｏによる焼入性と強度の向上効果を安定的に発現させるためには、Ｍｏを０．０５％以上含有させることが好ましい。
Ｖ：０．１０％以下
Ｖは、必要に応じて含有させることができる。Ｖを含有させると焼入性の向上および析出硬化による強度の向上に有効となる。しかしながら、Ｖの含有量が０．１０％を超えると、靱性の著しい劣化をもたらすので、含有させる場合のＶの含有量は０．１０％以下とする。含有させる場合のＶ含有量の好ましい上限は０．０６％である。なお、Ｖによる焼入性と強度の向上効果を安定的に発現させるためには、Ｖを０．００３％以上含有させることが好ましい。
Mo: 0.20% or less Mo can be contained as necessary. When Mo is contained, the hardenability can be improved and the strength can be improved. However, the content of Mo becomes a cost increase factor, and if the content exceeds 0.20%, the low temperature toughness of the HAZ is deteriorated, so the upper limit of the content is 0.20%. In order to stably exhibit the effect of improving the hardenability and strength by Mo, it is preferable to contain 0.05% or more of Mo.
V: 0.10% or less V can be contained as necessary. Inclusion of V is effective for improving hardenability and improving strength by precipitation hardening. However, if the content of V exceeds 0.10%, the toughness is significantly deteriorated. Therefore, when V is contained, the content of V is set to 0.10% or less. The upper limit with preferable V content in the case of making it contain is 0.06%. In order to stably develop the hardenability and strength improvement effect by V, it is preferable to contain V by 0.003% or more.
第２群：Ｎｉ、Ｎｂ
Ｎｉ：０．４０％以下
Ｎｉは、必要に応じて含有させることができる。Ｎｉを含有させると、鋼板の靭性を向上させることができる。しかしながら、Ｎｉの含有はコストアップ要因となるため、その含有量を０．４０％以下とする。なお、Ｎｉによる靭性向上効果を安定的に発現させるためには、Ｎｉを０．１０％以上含有させることが好ましい。
Second group: Ni, Nb
Ni: 0.40% or less Ni can be contained as necessary. When Ni is contained, the toughness of the steel sheet can be improved. However, since the Ni content causes an increase in cost, the content is made 0.40% or less. In order to stably develop the toughness improving effect by Ni, it is preferable to contain Ni by 0.10% or more.
Ｎｂ：０．０５％以下
Ｎｂは、必要に応じて含有させることができる。Ｎｂを含有させると、組織の微細化、靱性の向上、焼入性の向上および析出硬化による強度上昇に有効である。しかしながら、Ｎｂの含有量が０．０５％を超えると、析出物の増加により却って靱性の劣化をもたらす。したがって、Ｎｂの含有量を０．０５％以下とする。なお、Ｎｂの効果を安定的に発現させるためには、Ｎｂを０．００５％以上含有させることが好ましい。
Nb: 0.05% or less Nb can be contained as necessary. When Nb is contained, it is effective for refining the structure, improving toughness, improving hardenability, and increasing strength by precipitation hardening. However, when the Nb content exceeds 0.05%, the increase in precipitates causes toughness deterioration. Therefore, the Nb content is 0.05% or less. In order to stably express the effect of Nb, it is preferable to contain 0.005% or more of Nb.
第３群：Ｓｎ
Ｓｎ：０．５０％以下
Ｓｎは、Ｓｎ２＋となって溶解し、酸性塩化物溶液中でのインヒビター作用により腐食を抑制する作用を有する。また、Ｆｅ３＋を速やかに還元させ、酸化剤としてのＦｅ３＋濃度を低減する作用を有することにより、Ｆｅ３＋の腐食促進作用を抑制するので、高飛来塩分環境における耐候性を向上させる。また、Ｓｎには鋼のアノード溶解反応を抑制し耐食性を向上させる作用がある。これらの作用は、Ｓｎの含有量が０.５０％を超えると飽和する。したがって、Ｓｎの含有量を０．５０％以下とする。なお、Ｓｎの効果を安定的に発現させるためには、Ｓｎを０．０３％以上含有させることが好ましい。
Third group: Sn
Sn: 0.50% or less Sn dissolves as Sn 2+ and has an action of inhibiting corrosion by an inhibitor action in an acidic chloride solution. Further, rapidly to reduce the Fe 3+, by having an effect of reducing Fe 3+ concentration as oxidizing agent, since inhibit corrosion promoting effect of Fe 3+, thereby improving the weather resistance in high airborne salt environments. Moreover, Sn has the effect | action which suppresses the anodic dissolution reaction of steel and improves corrosion resistance. These effects are saturated when the Sn content exceeds 0.50%. Therefore, the Sn content is 0.50% or less. In order to stably exhibit the effect of Sn, 0.03% or more of Sn is preferably contained.
Ｂ．本発明の鋼材の金属組織について
本発明の鋼材の金属組織は、面積率で５０％以上のベイナイト組織、５％以下のパーライト組織、残部がフェライト組織からなる。
B. About the metal structure of the steel material of the present invention The metal structure of the steel material of the present invention is composed of a bainite structure of 50% or more by area ratio, a pearlite structure of 5% or less, and the balance being a ferrite structure.
ベイナイト組織は繰り返し荷重を受けた際に軟化する特性を有しており、これによってき裂先端の応力集中を緩和することができるため、優れた耐疲労き裂進展特性を有している。耐疲労き裂進展特性は、母材組織を主としてベイナイト組織とすること、すなわち面積率で５０％以上のベイナイト組織を生成させること、で向上させることができる。 The bainite structure has a characteristic of softening when subjected to repeated loads, which can relieve stress concentration at the crack tip, and thus has excellent fatigue crack propagation characteristics. The fatigue crack growth resistance can be improved by making the base material structure mainly a bainite structure, that is, by generating a bainite structure having an area ratio of 50% or more.
ベイナイト単相組織でも耐疲労き裂進展特性を期待できるが、母材を硬相であるベイナイト組織、軟相であるフェライト組織の２相組織とすれば、疲労き裂の進展に際して、き裂の分岐、屈曲が起こることを通じてき裂進展速度が低下しさらに耐疲労き裂進展特性が向上する。このため、基本的にベイナイト組織以外の組織がフェライト組織であるとよい。フェライト組織は面積率で１０％以上存在することが好ましく、２０％以上存在することがより好ましい。 Fatigue crack growth resistance can be expected even in a bainite single-phase structure, but if the base material is a two-phase structure of a bainite structure that is a hard phase and a ferrite structure that is a soft phase, Through the occurrence of branching and bending, the crack growth rate is lowered and the fatigue crack growth resistance is further improved. For this reason, the structure other than the bainite structure is basically preferably a ferrite structure. The ferrite structure is preferably present in an area ratio of 10% or more, and more preferably 20% or more.
ただし、耐疲労き裂進展特性を改善させないパーライト組織の存在は好ましくなく、面積率で５％以下とする必要がある。パーライト組織は少ないほど好ましい。 However, the presence of a pearlite structure that does not improve fatigue crack growth resistance is not preferable, and the area ratio needs to be 5% or less. The smaller the pearlite structure, the better.
Ｃ．本発明の鋼材の硬度について
本発明の鋼材の硬度は、表層部と板厚中心部の硬度差がビッカース硬さで５０以内である。
C. About the hardness of the steel material of this invention As for the hardness of the steel material of this invention, the hardness difference of a surface layer part and plate | board thickness center part is less than 50 in Vickers hardness.
鋼材が荷重を受けた際、不均一に変形を受ける場合がある。このような不均一な変形は鋼材が場所により硬度が異なることに起因し、この変形を受けた箇所に応力集中が起きると、耐疲労き裂進展特性が劣化する。
表層部と板厚中心部の硬度差が大きい場合、板厚の一部分が優先変形し、さらに疲労き裂が不均一に進展しやすくなる。このことから、表層部と板厚中心部の硬度差がビッカース硬さで５０以下とした。
When a steel material receives a load, it may be deformed unevenly. Such non-uniform deformation is caused by the fact that the hardness of the steel material varies depending on the location, and if stress concentration occurs at the location where this deformation has occurred, the fatigue crack growth resistance characteristics deteriorate.
When the difference in hardness between the surface layer portion and the center portion of the plate thickness is large, a part of the plate thickness is preferentially deformed, and further, fatigue cracks are likely to develop unevenly. From this, the hardness difference between the surface layer portion and the plate thickness center portion was set to 50 or less in terms of Vickers hardness.
Ｄ．本発明の鋼材の製造方法について
本発明に係る鋼材は、前述の化学組成を有するスラブに対し、例えば、以下(i)〜(iii)の工程で順次処理することにより製造することができる。
D. About the manufacturing method of the steel materials of this invention The steel materials which concern on this invention can be manufactured by processing sequentially in the process of the following (i)-(iii) with respect to the slab which has the above-mentioned chemical composition.
(i)加熱工程
この工程では、圧延素材としてのスラブを１０００〜１２００℃の温度に加熱する。加熱温度が高い場合、オーステナイト粒の粗大化により母材の低温靭性が劣化する。このため、加熱温度の上限は１２００℃とした。加熱温度の好ましい上限は１１５０℃である。加熱温度が下がるほど、低温靭性は改善するが、１０００℃以下の温度ではスラブの変形抵抗が大きく、後工程である圧延工程での生産性を阻害する。このため、加熱温度の下限は１０００℃とした。加熱温度の好ましい下限は１０５０℃である。
(i) Heating step In this step, the slab as a rolling material is heated to a temperature of 1000 to 1200 ° C. When the heating temperature is high, the low temperature toughness of the base material deteriorates due to coarsening of austenite grains. For this reason, the upper limit of heating temperature was 1200 degreeC. The upper limit with preferable heating temperature is 1150 degreeC. As the heating temperature is lowered, the low temperature toughness is improved, but at a temperature of 1000 ° C. or lower, the deformation resistance of the slab is large, and the productivity in the subsequent rolling process is hindered. For this reason, the minimum of heating temperature was 1000 degreeC. A preferred lower limit of the heating temperature is 1050 ° C.
(ii)圧延工程
この工程では、所望の仕上げ板厚を得るため、９００℃以下の累積圧下量が３０％以上となるように圧延を行い、７４０℃〜８５０℃で仕上げ圧延を行う。こうした圧延を行うのは、先ず９００℃の温度域で累積圧下量３０％以上の圧延を行うことによって、オーステナイト粒の再結晶を促進させ、結晶粒の微細化を行うためである。更に、圧延仕上げ温度は７４０℃〜８５０℃とする。仕上げ温度が高くなると、未再結晶域の圧下が不十分となり、後工程での水冷後の結晶粒が十分に細粒化されない。一方、仕上げ温度が過度に低い場合には、変形抵抗が大きくなることを通じて生産能率が低下する他、後工程である水冷の開始温度も低下することになり、所望の組織を得ることができない。よって圧延仕上げ温度は７４０℃〜８５０℃とする。
(ii) Rolling step In this step, in order to obtain a desired finished sheet thickness, rolling is performed so that the cumulative reduction amount of 900 ° C. or less is 30% or more, and finish rolling is performed at 740 ° C. to 850 ° C. The reason why such rolling is performed is to first promote recrystallization of austenite grains and refine crystal grains by performing rolling with a cumulative reduction of 30% or more in a temperature range of 900 ° C. Furthermore, the rolling finishing temperature is set to 740 ° C to 850 ° C. When the finishing temperature is high, the reduction in the non-recrystallized region becomes insufficient, and the crystal grains after water cooling in the subsequent process are not sufficiently refined. On the other hand, when the finishing temperature is excessively low, the production efficiency is lowered through an increase in deformation resistance, and the starting temperature of water cooling, which is a subsequent process, is also lowered, so that a desired structure cannot be obtained. Therefore, the rolling finishing temperature is set to 740 ° C to 850 ° C.
(iii)水冷工程
所望の組織を得るために圧延後１２０秒以内、かつ仕上げ圧延からの温度低下が３０℃以内で冷却速度が５℃/sec以上となるような水冷を行い、４００℃以下で水冷を停止する。水冷開始を圧延後１２０秒以内とするのは、圧延から水冷開始までの経過時間が長い場合、圧延によって導入された歪が解放され、低温靭性が低下するからである。この圧延後水冷開始までの時間は短いほどよい。また、仕上げ圧延からの温度低下を３０℃以内とするのは、水冷を開始する温度が仕上げ温度から大きく低下した場合、耐疲労き裂進展特性を得るため重要なベイナイト組織が効率よく得られないからである。好ましくは仕上げ圧延からの温度低下を２０℃以内とする。また、良好な耐疲労き裂進展特性を得るためには、ベイナイト中の転位組織を大きくする必要がある。この観点から、冷却速度は５℃/sec以上、水冷を停止する温度は４００℃以下とする。
(iii) Water cooling step To obtain a desired structure, water cooling is performed within 120 seconds after rolling, the temperature drop from finish rolling is within 30 ° C., and the cooling rate is 5 ° C./sec or more. Stop water cooling. The reason for starting the water cooling within 120 seconds after rolling is that when the elapsed time from the rolling to the start of water cooling is long, the strain introduced by the rolling is released and the low temperature toughness is lowered. The shorter the time until the start of water cooling after rolling, the better. Moreover, the temperature drop from finish rolling is set to within 30 ° C. When the temperature at which water cooling is started is greatly reduced from the finish temperature, an important bainite structure cannot be obtained efficiently in order to obtain fatigue crack growth resistance. Because. Preferably, the temperature drop from finish rolling is within 20 ° C. In order to obtain good fatigue crack growth characteristics, it is necessary to enlarge the dislocation structure in bainite. From this viewpoint, the cooling rate is 5 ° C./sec or more, and the temperature at which water cooling is stopped is 400 ° C. or less.
以下、実施例によって本発明をより具体的に説明するが、本発明はこれらの実施例に限定されるものではない。 EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to these Examples.
表１に示す化学組成を有する鋼を実験室の真空溶解炉にて溶製し、得られた１８０ｋｇのスラブを小型圧延機にて圧延し、板厚６０ｍｍの鋼材とした。表２に製造条件を示す。各製造条件の中で加熱温度、圧延仕上げ温度、仕上げから水冷開始までの温度低下代、水冷停止温度は、鋼板の表面温度を測定した値、またその表面温度からの計算した値である。冷却速度は水冷開始から水冷停止までの平均冷却速度を示している。 Steel having the chemical composition shown in Table 1 was melted in a laboratory vacuum melting furnace, and the obtained 180 kg slab was rolled by a small rolling mill to obtain a steel material having a thickness of 60 mm. Table 2 shows the manufacturing conditions. Among the production conditions, the heating temperature, the rolling finishing temperature, the temperature reduction allowance from the finishing to the start of water cooling, and the water cooling stop temperature are values obtained by measuring the surface temperature of the steel sheet, and values calculated from the surface temperature. The cooling rate indicates the average cooling rate from the start of water cooling to the stop of water cooling.
表３には鋼板の機械的特性、ミクロ組織観察結果を示した。鋼材のＹＰ（Yield point：降伏点）、ＴＳ(Tensile strength：引張強度)は、JIS Z 2241に基づいた引張試験により測定した。試験片はJIS4号試験片とし、板厚(t)のt/4位置において圧延方向と垂直に試験片を採取した。 Table 3 shows the mechanical properties and microstructure observation results of the steel sheet. YP (Yield point: yield point) and TS (Tensile strength: tensile strength) of the steel were measured by a tensile test based on JIS Z 2241. The test piece was a JIS No. 4 test piece, and the test piece was taken perpendicular to the rolling direction at the position t / 4 of the plate thickness (t).
母材のvTrsはJIS Z 2242に基づいたシャルピー試験によって測定した。試験片はJIS4号試験片とし、板厚(t)のt/4位置で圧延方向と平行に試験片を採取した。本発明では、ＨＡＺ部の低温靭性改善を目的の一つとしてなされたものであるが、ＨＡＺ部の低温靭性が要求される場合には、当然母材の低温靭性も同時に要求される。そこで、母材のvTrsが−６０℃以下の場合に十分な低温靭性を有していると判定した。 The vTrs of the base material was measured by a Charpy test based on JIS Z 2242. The test piece was a JIS No. 4 test piece, and the test piece was taken in parallel with the rolling direction at a position t / 4 of the plate thickness (t). In the present invention, one of the purposes is to improve the low temperature toughness of the HAZ part, but when the low temperature toughness of the HAZ part is required, naturally the low temperature toughness of the base material is also required. Therefore, it was determined that the base material has sufficient low-temperature toughness when vTrs of the base material is −60 ° C. or lower.
また、ＨＡＺ部の低温靭性については、得られた鋼板を入熱３６ＫＪ／ｃｍのＥＧＷ溶接を行って評価した。開先はＶ型とし、鋼板表面下２ｍｍの位置からJIS4号シャルピー試験片を採取し、そのノッチ位置はF.L．(Fusion Line：溶融線)とした。ここで、−４０℃で６０Ｊ以上のエネルギー値を示すものが、十分な低温靭性を有していると判定した。 Moreover, about the low temperature toughness of a HAZ part, the obtained steel plate was evaluated by performing EGW welding of heat input 36KJ / cm. The groove was V-shaped, and a JIS4 Charpy specimen was collected from a position 2 mm below the surface of the steel plate. The notch position was F.L. (Fusion Line). Here, what showed the energy value of 60 J or more at -40 degreeC was determined to have sufficient low-temperature toughness.
耐疲労き裂進展特性の評価については、ASTM E647に基づいて測定し、ΔK=25MPa√mのとき、疲労き裂進展速度(da/dN)が7.9×10-5mm/cycle以下の場合に十分な耐疲労き裂進展特性を有していると判定した。 Evaluation of fatigue crack growth resistance is based on ASTM E647, and when ΔK = 25 MPa√m, the fatigue crack growth rate (da / dN) is 7.9 × 10 -5 mm / cycle or less. It was determined that it had sufficient fatigue crack growth characteristics.
金属組織は鋼材を切り出し鏡面研磨後、ナイタールでエッチングすることで観察した。観察面は圧延方向と平行とし、組織分率については、５視野観察し、それぞれの組織の面積率の平均値で求めた。 The metal structure was observed by cutting out a steel material and polishing it with nital after mirror polishing. The observation surface was parallel to the rolling direction, and the structure fraction was observed with 5 visual fields, and the average value of the area ratio of each structure was obtained.
断面硬度は、JIS Z 2244に示されるビッカース硬さ試験方法により測定した。試験力は９８Ｎとし、圧延方向に平行な面を板厚方向に１ｍｍピッチで全厚測定した。断面硬度差は、この時の最小の硬度と最大の硬度の差異とした。 The cross-sectional hardness was measured by the Vickers hardness test method shown in JIS Z 2244. The test force was 98 N, and the thickness parallel to the rolling direction was measured at a pitch of 1 mm in the plate thickness direction. The cross-sectional hardness difference was defined as the difference between the minimum hardness and the maximum hardness at this time.
試験番号１〜１４は本発明例であり、本発明の規定する範囲内にある。母材靭性、ＨＡＺ靭性、耐疲労き裂進展特性とも良好な特性を示している。 Test numbers 1 to 14 are examples of the present invention and are within the range defined by the present invention. The base metal toughness, the HAZ toughness, and the fatigue crack growth characteristics are also good.
試験番号１５〜２１は、比較例であって、それらの化学組成が本発明の規定する範囲を外れる。そのため、次のとおり、耐疲労き裂進展特性とＨＡＺ靭性の一方又は両方が劣っている。 Test numbers 15 to 21 are comparative examples, and their chemical compositions are outside the range defined by the present invention. Therefore, as described below, one or both of fatigue crack growth resistance and HAZ toughness are inferior.
試験番号１５は、Ｃ量が高いためＨＡＺ靭性が低く、また断面硬度差が大きいため耐疲労き裂進展特性も劣っている。試験番号１６は、Ｓｉ量が高いためＨＡＺ靭性が劣っていた。試験番号１７は、Ｍｎ量が高く母材靭性、ＨＡＺ靭性が低い他、断面硬度差が大きく耐疲労き裂進展特性も劣っていた。試験番号１８は、Ｔｉ量が高く、固溶Ｂ量およびＴｉ/Ｎの値も高かったため、ＨＡＺ靭性が低かった。試験番号１９は、Ｂ量および固溶Ｂ量も高かったため、ＨＡＺ靭性が低かった。試験番号２０は、Ａｌ量が高いためＨＡＺ靭性に劣る他、圧延仕上げ温度が過度に低くベイナイト面積率が低いため耐疲労き裂進展特性も劣っていた。試験番号２１は、Ｎが過度に高く固溶Ｎの影響でＨＡＺ靭性に劣っていた他、固溶Ｂ量が確保できていないためベイナイト面積率が低く、耐疲労き裂進展特性も劣っていた。 Test No. 15 has low HAZ toughness due to high C content, and also has poor fatigue crack growth characteristics due to large cross-sectional hardness difference. Test No. 16 was inferior in HAZ toughness due to the high Si content. Test No. 17 had a high Mn content and low base metal toughness and HAZ toughness, as well as a large cross-sectional hardness difference and inferior fatigue crack growth characteristics. In Test No. 18, the amount of Ti was high, and the amount of solute B and Ti / N were also high, so the HAZ toughness was low. Test No. 19 had low HAZ toughness because the B content and the solute B content were also high. Test No. 20 was inferior in HAZ toughness due to the high Al content, and also inferior in fatigue crack propagation characteristics because the rolling finish temperature was excessively low and the bainite area ratio was low. In Test No. 21, N was excessively high and inferior in HAZ toughness due to the effect of solute N, and because the amount of solute B could not be secured, the bainite area ratio was low and the fatigue crack growth resistance was also inferior. .
試験番号２２〜２６は、比較例である。それらの化学組成は本発明の規定する範囲内にあるが、金属組織または表層部と板厚中心部の硬度差が本発明で規定する範囲外にある。そのため、次のとおり、耐疲労き裂進展特性とＨＡＺ靭性の一方又は両方が劣っている。 Test numbers 22 to 26 are comparative examples. Their chemical composition is within the range defined by the present invention, but the difference in hardness between the metal structure or the surface layer portion and the center of the plate thickness is outside the range defined by the present invention. Therefore, as described below, one or both of fatigue crack growth resistance and HAZ toughness are inferior.
試験番号２２では、加熱温度が高いことを通じて母材靭性が劣化し、断面硬度差が大きいため耐疲労き裂進展特性も低下した。試験番号２３では、９００℃以下の圧下率が低く、低温で十分な圧下量が得られなかったため、母材靭性、耐疲労き裂進展特性が低下した。試験番号２４は、仕上げ〜水冷開始までの時間が過度に長く、水冷開始までの温度低下が大きかったため、パーライト面積率が大きく、断面硬度差も大きかったことから、耐疲労き裂進展特性が低下した。試験番号２５は、水冷停止温度が高くベイナイト面積率は十分でも、そのベイナイト中の転位の回復が大きく、耐疲労き裂進展特性が低下した。試験番号２６は、冷却速度が低くベイナイト中の転位密度が低くなることを通じて耐疲労き裂進展特性が低下した。 In Test No. 22, the base metal toughness deteriorated through the high heating temperature, and the fatigue crack growth resistance also deteriorated due to the large difference in cross-sectional hardness. In Test No. 23, the rolling reduction at 900 ° C. or lower was low, and a sufficient rolling amount was not obtained at a low temperature, so that the base metal toughness and fatigue crack resistance characteristics were lowered. In Test No. 24, the time from finishing to the start of water cooling was excessively long, and the temperature decrease until the start of water cooling was large, so the pearlite area ratio was large and the cross-sectional hardness difference was also large, so the fatigue crack growth resistance was reduced. did. In Test No. 25, even when the water-cooling stop temperature was high and the bainite area ratio was sufficient, the recovery of dislocations in the bainite was large, and the fatigue crack growth resistance was deteriorated. In Test No. 26, the fatigue crack growth resistance was lowered through a low cooling rate and a low dislocation density in bainite.
本発明の鋼材は、耐疲労き裂進展特性およびＨＡＺの低温靭性に優れているので、船舶、海洋構造物その他の耐疲労亀裂進展特性およびＨＡＺの低温靭性が要求される溶接構造物などに用いるのに適している。 Since the steel material of the present invention is excellent in fatigue crack growth resistance and low temperature toughness of HAZ, it is used for marine and other marine structures and other welded structures that require fatigue crack growth resistance and low temperature toughness of HAZ. Suitable for
Claims (5)
Ｔｉ／Ｎ≦３．４・・・・・・・・・・・(1)式
０．０００３≦Ｂ−１０．８／１４．１×（Ｎ−Ｔｉ／３．４）≦０．００３・・(2)式
ただし、式中の元素記号は、各元素の含有量（質量％）を意味する。 In mass%, C: 0.01 to 0.10%, Si: 0.04 to 0.60%, Mn: 0.5 to 2.0%, P: 0.015% or less, S: 0.004 %: Al: 0.005-0.07%, Ti: 0.004-0.025%, B: 0.0005-0.0040%, N: 0.0040-0.0090%, The balance consists of Fe and impurities, the metal structure is a bainite structure with an area ratio of 50% or more, a pearlite structure with 5% or less, the balance is a ferrite structure, and the hardness difference between the surface layer portion and the center of the plate thickness is Vickers hardness. A steel material excellent in fatigue crack growth resistance and low temperature toughness of the weld heat affected zone, characterized by being within 50 and satisfying the following formulas (1) and (2).
Ti / N ≦ 3.4 (1) Formula 0.0003 ≦ B-10.8 / 14.1 × (N—Ti / 3.4) ≦ 0.003 -(2) Formula However, the element symbol in a formula means content (mass%) of each element.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2011117869A JP5605304B2 (en) | 2011-05-26 | 2011-05-26 | Steel materials excellent in fatigue crack growth resistance and low temperature toughness of weld heat affected zone, and manufacturing method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2011117869A JP5605304B2 (en) | 2011-05-26 | 2011-05-26 | Steel materials excellent in fatigue crack growth resistance and low temperature toughness of weld heat affected zone, and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2012246520A true JP2012246520A (en) | 2012-12-13 |
| JP5605304B2 JP5605304B2 (en) | 2014-10-15 |
Family
ID=47467254
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2011117869A Active JP5605304B2 (en) | 2011-05-26 | 2011-05-26 | Steel materials excellent in fatigue crack growth resistance and low temperature toughness of weld heat affected zone, and manufacturing method thereof |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP5605304B2 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2015206112A (en) * | 2014-04-09 | 2015-11-19 | Ｊｆｅスチール株式会社 | High strength steel material excellent in fatigue crack propagation property and manufacturing method therefor |
| JP2016074943A (en) * | 2014-10-06 | 2016-05-12 | 新日鐵住金株式会社 | Thick steel plate |
| JP2016172892A (en) * | 2015-03-17 | 2016-09-29 | Ｊｆｅスチール株式会社 | Low yield ratio high strength thick steel plate for building structure excellent in toughness in ultrahigh heat input weld zone |
| JP2016199780A (en) * | 2015-04-08 | 2016-12-01 | 新日鐵住金株式会社 | Thick steel plate excellent in fatigue characteristic and toughness of haz |
| JP6418361B1 (en) * | 2018-03-16 | 2018-11-07 | 新日鐵住金株式会社 | Steel plate for holding coal and ore carrier |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008169468A (en) * | 2006-12-14 | 2008-07-24 | Nippon Steel Corp | High-strength thick steel plate having excellent brittle crack propagation-stopping performance |
| JP2008255458A (en) * | 2007-04-09 | 2008-10-23 | Kobe Steel Ltd | Thick steel plate having haz toughness and base metal toughness |
| JP2011094214A (en) * | 2009-10-30 | 2011-05-12 | Kobe Steel Ltd | Cold-formed square steel tube having excellent earthquake resistance |
-
2011
- 2011-05-26 JP JP2011117869A patent/JP5605304B2/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008169468A (en) * | 2006-12-14 | 2008-07-24 | Nippon Steel Corp | High-strength thick steel plate having excellent brittle crack propagation-stopping performance |
| JP2008255458A (en) * | 2007-04-09 | 2008-10-23 | Kobe Steel Ltd | Thick steel plate having haz toughness and base metal toughness |
| JP2011094214A (en) * | 2009-10-30 | 2011-05-12 | Kobe Steel Ltd | Cold-formed square steel tube having excellent earthquake resistance |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2015206112A (en) * | 2014-04-09 | 2015-11-19 | Ｊｆｅスチール株式会社 | High strength steel material excellent in fatigue crack propagation property and manufacturing method therefor |
| JP2016074943A (en) * | 2014-10-06 | 2016-05-12 | 新日鐵住金株式会社 | Thick steel plate |
| JP2016172892A (en) * | 2015-03-17 | 2016-09-29 | Ｊｆｅスチール株式会社 | Low yield ratio high strength thick steel plate for building structure excellent in toughness in ultrahigh heat input weld zone |
| JP2016199780A (en) * | 2015-04-08 | 2016-12-01 | 新日鐵住金株式会社 | Thick steel plate excellent in fatigue characteristic and toughness of haz |
| JP6418361B1 (en) * | 2018-03-16 | 2018-11-07 | 新日鐵住金株式会社 | Steel plate for holding coal and ore carrier |
| WO2019176112A1 (en) * | 2018-03-16 | 2019-09-19 | 日本製鉄株式会社 | Steel sheet for coal/ore carrier hold |
Also Published As
| Publication number | Publication date |
|---|---|
| JP5605304B2 (en) | 2014-10-15 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4410836B2 (en) | Method for producing 780 MPa class high strength steel sheet having excellent low temperature toughness | |
| JP5509923B2 (en) | Method for producing high-tensile steel sheet having a tensile strength of 1100 MPa or more for laser welding or laser-arc hybrid welding | |
| JP5439973B2 (en) | High-strength thick steel plate having excellent productivity and weldability and excellent drop weight characteristics after PWHT, and method for producing the same | |
| JP4718866B2 (en) | High-strength refractory steel excellent in weldability and gas-cutting property and method for producing the same | |
| JP4848966B2 (en) | Thick-wall high-tensile steel plate and manufacturing method thereof | |
| JP5659758B2 (en) | TMCP-Temper type high-strength steel sheet with excellent drop weight characteristics after PWHT that combines excellent productivity and weldability | |
| JP4696570B2 (en) | Manufacturing method of high-tensile steel material with excellent hydrogen embrittlement resistance | |
| JP5447698B2 (en) | High-strength steel for steam piping and method for manufacturing the same | |
| JP5605304B2 (en) | Steel materials excellent in fatigue crack growth resistance and low temperature toughness of weld heat affected zone, and manufacturing method thereof | |
| JP2010222680A (en) | Method for manufacturing high strength high toughness steel excellent in workability | |
| JP2010229453A (en) | High strength thick steel plate having excellent toughness to one layer large heat input welding affected zone and method of manufacturing the same | |
| JP5477089B2 (en) | Manufacturing method of high strength and high toughness steel | |
| JP2007039795A (en) | Method for producing high strength steel having excellent fatigue crack propagation resistance and toughness | |
| JP5287553B2 (en) | Non-tempered high-tensile steel plate with yield strength of 885 MPa or more and method for producing the same | |
| JP6079611B2 (en) | Ni alloy clad steel plate excellent in low temperature toughness and HAZ toughness of base metal and corrosion resistance of laminated material, and method for producing the same | |
| JP7022822B2 (en) | Thick steel sheet with excellent low-temperature deformation aging impact characteristics and its manufacturing method | |
| JP6394378B2 (en) | Abrasion resistant steel plate and method for producing the same | |
| JPWO2010038470A1 (en) | Steel plate with excellent low temperature toughness and low strength anisotropy of base metal and weld heat affected zone, and method for producing the same | |
| JP2014177687A (en) | High tensile steel plate excellent in drop-weight characteristic and its manufacturing method | |
| JP4770415B2 (en) | High tensile steel plate excellent in weldability and method for producing the same | |
| JP2013129885A (en) | Method of producing high-strength thick steel plate excellent in brittle crack propagation arrest property | |
| JP6750572B2 (en) | Clad steel plate having high strength and excellent low temperature toughness as base material and method for producing the same | |
| JP4469353B2 (en) | Method for producing high strength steel material having tensile strength of 570 MPa class excellent in toughness of weld heat affected zone | |
| JP2008261012A (en) | Method for producing high strength steel having 500 mpa or more yield stress and 570 mpa or more tensile strength and excellent in toughness of welding heat-affected part | |
| JP4645462B2 (en) | A high-strength steel material excellent in fatigue crack propagation characteristics with low strength dependence and a method for producing the same. |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20121011 |
|
| A711 | Notification of change in applicant |
Free format text: JAPANESE INTERMEDIATE CODE: A712 Effective date: 20121011 |
|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20130812 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20140722 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20140729 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20140811 |
|
| R151 | Written notification of patent or utility model registration |
Ref document number: 5605304 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R151 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |