JP2007031749A - Steel for welded structure with excellent toughness in weld heat-affected zone, and its manufacturing method - Google Patents
Steel for welded structure with excellent toughness in weld heat-affected zone, and its manufacturing method Download PDFInfo
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本発明は、船舶、海洋構造物、橋梁、建材などに使用される溶接熱影響部の靭性に優れた溶接構造用鋼材およびその製造方法に関する。特に、近年要求の高まっている、溶接熱影響部が安定した高靭性を有する鋼材に関する。 The present invention relates to a welded structural steel material excellent in toughness of a weld heat affected zone used for ships, offshore structures, bridges, building materials, and the like, and a method for producing the same. In particular, the present invention relates to a steel material having a high toughness with a stable weld heat-affected zone, which has been increasingly demanded in recent years.
近年、船舶、海洋構造物、橋梁、建築などの大型構造物に使用される溶接構造用鋼材の材質特性に対する要望は厳しさを増しており、母材の靭性と同様に溶接熱影響部の靭性への要求も厳しさを増している。例えば、タンカーが破壊すると海洋汚染を引き起こし、海洋環境に甚大な被害を及ぼす場合がある。そのような事故の防止にも溶接熱影響部の靱性に優れた鋼材が必要である。以下、溶接熱影響部をＨＡＺと略記することがある。 In recent years, the demand for material properties of welded structural steel materials used in large structures such as ships, offshore structures, bridges, and buildings has become stricter, and the toughness of the weld heat affected zone as well as the toughness of the base metal. The demand for is increasing. For example, if a tanker is destroyed, it may cause marine pollution and cause serious damage to the marine environment. In order to prevent such an accident, a steel material excellent in the toughness of the weld heat affected zone is required. Hereinafter, the weld heat affected zone may be abbreviated as HAZ.
例えば、特許文献１（特開2002-256379号公報）には、鋼材中のＣａ、Ｏ（酸素）、Ｓの含有量を調整し、大入熱溶接をした際に、溶接熱影響部を微細な組織とすることにより、優れたＨＡＺ靭性を有する大入熱溶接用鋼材に関する発明が記載されている。この特許文献１に開示される発明では、鋼板を溶製する際の凝固段階でＣａＳを晶出させ、さらに、ＣａＳの表面上にＭｎＳを析出させる。さらにＭｎＳ上には、ＴｉＮ、ＢＮ、ＡｌＮ、ＶＮ等のフェライト生成核を析出させることにより、大入熱溶接時の高温下でも溶解しないフェライト変態生成核を微細に分散させ、ＨＡＺ組織を微細なフェライト−パーライト組織として高靭性化を達成している。 For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2002-256379), when the contents of Ca, O (oxygen), and S in a steel material are adjusted and large heat input welding is performed, the heat affected zone is finely defined. An invention relating to a steel material for high heat input welding having excellent HAZ toughness by being made into a simple structure is described. In the invention disclosed in Patent Document 1, CaS is crystallized in a solidification stage when melting a steel sheet, and MnS is further precipitated on the surface of CaS. Furthermore, ferrite transformation nuclei such as TiN, BN, AlN, and VN are precipitated on MnS to finely disperse ferrite transformation nuclei that do not dissolve even at high temperatures during high heat input welding, and the HAZ structure becomes fine. High toughness is achieved as a ferrite-pearlite structure.
また、特許文献２（特開2001-288509号公報）には、製鋼における脱酸剤をＴｉ、Ａｌ、Ｃａの順に添加し、さらにＡｌを添加する鋼材の製造方法に関する発明が記載されている。その発明では、Ｃａ、ＡｌおよびＴｉのいずれか２種以上を含有する酸化物の微細分散と個数増加を図り、オーステナイト粒の細粒化や微細フェライト生成によって優れたＨＡＺ靭性を持つ鋼材が製造できるとされている。 Patent Document 2 (Japanese Patent Laid-Open No. 2001-288509) describes an invention relating to a method for producing a steel material in which a deoxidizer in steelmaking is added in the order of Ti, Al, and Ca, and Al is further added. In that invention, a steel material having excellent HAZ toughness can be manufactured by finely dispersing and increasing the number of oxides containing any two or more of Ca, Al and Ti, and by making austenite grains finer and producing fine ferrites. It is said that.
前述のとおり、近年、鋼構造物に対する安全性確保の要求はますます高まっており、従来であれば、シャルピー試験においても、靭性値の平均値で満足すれば、それでよしとする風潮があったが、最近では安定な高靭性が求められ、シャルピー試験の個々の測定値のバラツキまで問題にされるようになってきた。その背景は、次の２点である。 As mentioned above, in recent years, there has been an increasing demand for securing safety for steel structures, and in the past, if the average value of the toughness value was satisfied even in the Charpy test, there was a favorable trend. Recently, stable high toughness has been demanded, and variations in individual measurement values of the Charpy test have become a problem. The background is the following two points.
第一は、平均値が高くても、個々の測定値にバラツキがあるということは、本質的に靭性が安定しておらず、何度か試験を繰り返すと、平均値としても低値を示す確率が高いと考えられるようになってきたことである。 First, even if the average value is high, the fact that the individual measured values are uneven means that the toughness is essentially not stable, and when the test is repeated several times, the average value shows a low value. This is because the probability is high.
第二に、重要な鋼構造物に対しては、安全性確認のために、例えば溶接長１００ｍ当り１回のシャルピー試験を行い合格することを求められる場合があることである。そのような場合には、シャルピー試験の個々の測定値のレベルで安定した高靭性が得られなければ、何度も繰り返される試験にすべて合格することはおぼつかない。 Secondly, for an important steel structure, it may be required to pass a Charpy test once per 100 m of weld length, for example, for safety confirmation. In such a case, if a stable high toughness is not obtained at the individual measurement level of the Charpy test, it is difficult to pass all the tests repeated many times.
上記のようなことから、本発明は、重要構造物に用いられる鋼材であって、溶接熱影響部（ＨＡＺ）の靭性について、安定して高い値を確保できる鋼材およびその鋼材を製造する方法の提供を目的としている。 As described above, the present invention is a steel material used for an important structure, and a steel material capable of stably ensuring a high value for the toughness of the weld heat affected zone (HAZ) and a method for producing the steel material. The purpose is to provide.
本発明者は、溶接熱影響部においても安定した高靭性を得られる鋼材の開発を目的として、適正な介在物制御とシャルピー試験時の応力集中緩和効果とを組み合わせることによって得られる、新たな金属学的効果を知見して本発明に至った。本発明の要旨は、以下のとおりである。 The present inventor has developed a new metal obtained by combining proper inclusion control and stress concentration relaxation effect during Charpy test for the purpose of developing a steel material capable of obtaining stable high toughness even in the heat affected zone. The present inventors have found a scientific effect to arrive at the present invention. The gist of the present invention is as follows.
（１）質量％で、Ｃ：０．０１〜０．２％、Ｓｉ：０．０３〜０．５％、Ｍｎ：０．５〜２．０％、Ｐ：０．０２％以下、Ｓ：０．０１％以下、Ａｌ：０．００５％を超えて０．０８％まで、Ｔｉ：０．０００５〜０．０２％、Ｃａ：０．０００３〜０．０２％、Ｎ：０．００１〜０．００９％およびＯ（酸素）：０．００２５％以下を含有し、残部はＦｅ及び不純物からなり、下記の(1)式を満足するとともに、粒径０．５〜５μｍのＣａＯ・Ａｌ2Ｏ3系介在物が分散していることを特徴とする溶接熱影響部の靭性に優れた溶接構造用鋼材。 (1) By mass%, C: 0.01 to 0.2%, Si: 0.03 to 0.5%, Mn: 0.5 to 2.0%, P: 0.02% or less, S: 0.01% or less, Al: more than 0.005% to 0.08%, Ti: 0.0005-0.02%, Ca: 0.0003-0.02%, N: 0.001-0 0.009% and O (oxygen): 0.0025% or less, with the balance being Fe and impurities, satisfying the following formula (1), and having a particle size of 0.5 to 5 μm CaO.Al 2 O A welded structural steel material with excellent toughness in the heat affected zone, characterized by the inclusion of 3 inclusions.
０．５０≦Ｃａ／Ｏ≦１．３０ ・・・・・(1)
ただし、(1)式の元素記号はその元素の含有量（質量％）を示す。
0.50 ≦ Ca / O ≦ 1.30 (1)
However, the element symbol of the formula (1) indicates the content (% by mass) of the element.
上記の粒径０．５〜５μｍのＣａＯ・Ａｌ2Ｏ3系介在物のアスペクト比は、１〜１．９であることが望ましい。なお、アスペクト比とは、鋼材の圧延方向に平行な断面で観察される介在物の長径を短径で除した値である。 The aspect ratio of the CaO · Al 2 O 3 inclusions having a particle size of 0.5 to 5 μm is preferably 1 to 1.9. In addition, an aspect ratio is the value which remove | divided the major axis of the inclusion observed by the cross section parallel to the rolling direction of steel materials by the minor axis.
また、粒径が０．５μｍを超え、かつアスペクト比が５を超えるＡｌ2Ｏ3およびＣａＯは、それぞれ５×１０個／ｍｍ2以下であることが望ましい。 Further, it is desirable that Al 2 O 3 and CaO having a particle diameter of more than 0.5 μm and an aspect ratio of more than 5 are each 5 × 10 pieces / mm 2 or less.
上記の溶接構造用鋼材は、Ｆｅの一部に代えて、質量％で、Ｂ：０．００２％以下、Ｎｂ：０．０５％以下、Ｖ：０．１％以下、Ｃｕ：１．５％以下、Ｎｉ：６％以下、Ｃｒ：１％以下およびＭｏ：０．８％以下のなかから選んだ１種以上を含有することができる。 In the above steel for welded structure, instead of a part of Fe, in mass%, B: 0.002% or less, Nb: 0.05% or less, V: 0.1% or less, Cu: 1.5% Hereinafter, one or more selected from Ni: 6% or less, Cr: 1% or less, and Mo: 0.8% or less can be contained.
（２）溶鋼中のＡｌが０．００５％を超えて０．０８％までの範囲となるようにＡｌを添加して脱酸した後、Ｔｉを添加し、さらに脱ガス装置で１５分以上処理した後、溶鋼温度を１６００±７０℃に保った状態でＣａを添加し、鋳造し、圧延することを特徴とする上記の溶接熱影響部靭性に優れた溶接構造用鋼材の製造方法。 (2) After deoxidizing by adding Al so that Al in the molten steel exceeds 0.005% to 0.08%, Ti is added, and further treated with a degassing apparatus for 15 minutes or more. After that, the method for producing a steel material for welded structure having excellent weld heat affected zone toughness is characterized in that Ca is added, cast, and rolled while maintaining the molten steel temperature at 1600 ± 70 ° C.
まず、本発明者が知見した新たな金属学的効果について説明する。 First, the new metallurgical effect discovered by the present inventor will be described.
一般に、溶接熱影響部に高靭性が要求される重要構造物には、Ａｌにより鋼中の酸素を除去したＡｌキルド鋼が用いられる。本発明も、このような重要構造物に用いられるＡｌキルド鋼に関するものであるが、Ａｌキルド鋼の問題点は、溶接熱影響部においては、シャルピー試験などの個々の測定値のバラツキが大きいことである。 In general, Al killed steel obtained by removing oxygen in steel with Al is used for an important structure in which high toughness is required in the weld heat affected zone. The present invention also relates to Al killed steel used for such an important structure, but the problem with Al killed steel is that there are large variations in individual measured values such as the Charpy test in the weld heat affected zone. It is.
近年、破壊安全性に対する要求は更に高まり、安全確保のために溶接熱影響部においても靱性が安定していることが求められている。 In recent years, the demand for fracture safety has further increased, and it is required that the toughness be stable in the weld heat affected zone in order to ensure safety.
本発明者らは、シャルピー試験の吸収エネルギーの個々の値のバラツキについて鋭意研究した結果、その原因が鋼中の粗大介在物または圧延で点列状につらなった介在物の集合体にあることが判明した。これらの介在物が、溶接熱影響部のシャルピー試験時にき裂の発生と伝播を助長し、吸収エネルギーのバラツキの原因になるのである。従って、ＨＡＺ組織の微細化だけでは上記のバラツキは抑えられないことが明らかになった。 As a result of diligent research on variations in individual values of absorbed energy in the Charpy test, the present inventors found that the cause is coarse aggregates in steel or aggregates of inclusions formed in a sequence of lines by rolling. There was found. These inclusions promote the generation and propagation of cracks during the Charpy test of the weld heat-affected zone, and cause variations in absorbed energy. Therefore, it has been clarified that the above-mentioned variation cannot be suppressed only by reducing the HAZ structure.
鋼中の粗大介在物は、例えば、圧延で伸延された硫化物系の介在物、またはＡｌ2Ｏ3系の介在物が圧延で砕かれて点列状につらなった介在物である。これらの圧延で伸延された硫化物系の介在物やＡｌ2Ｏ3系の介在物が圧延で砕かれて点列状につらなって生じる介在物群の生成を防止することが、シャルピー試験における吸収エネルギーの個々の測定値のバラツキを防止する上で非常に重要である。 Coarse inclusions in the steel are, for example, sulfide inclusions elongated by rolling, or inclusions formed by smashing Al 2 O 3 inclusions into a series of lines by rolling. In the Charpy test, the sulfide inclusions and Al 2 O 3 inclusions that have been elongated by rolling are crushed by rolling to prevent formation of inclusions that are formed in a dotted line. This is very important in preventing variation in individual measured values of absorbed energy.
このような粗大介在物群が、シャルピー試験片のノッチ近傍に存在すれば、そこから発生する亀裂の伝播によって劈開破壊が容易となり、シャルピー試験の吸収エネルギーは著しく低下する。したがって、鋼材中の介在物形態を制御すれば、これらを防止することができる。本発明では、製鋼段階における脱酸材の添加を制御して、酸化物を制御することにより、これらを防止する。以下、本発明で定める鋼材の化学組成、介在物の分布形態および製造方法について順次説明する。なお、成分含有量についての「％」は「質量％」を意味する。
（１）化学組成
Ｃ：０．０１〜０．２％
Ｃは、母材および溶接部の強度と靭性を確保するため０．０１％以上含有させる。しかし、Ｃが多すぎると母材およびＨＡＺの靭性を低下させるとともに溶接性を劣化させるため、その上限を０．２％とする。
If such a coarse inclusion group is present in the vicinity of the notch of the Charpy test piece, the cracks generated from the cracks are easily broken and the absorbed energy of the Charpy test is significantly reduced. Therefore, these can be prevented by controlling the form of inclusions in the steel material. In the present invention, these are prevented by controlling the oxide by controlling the addition of the deoxidizer in the steelmaking stage. Hereinafter, the chemical composition of the steel material defined in the present invention, the distribution form of inclusions, and the production method will be sequentially described. In addition, “%” regarding the component content means “mass%”.
(1) Chemical composition C: 0.01 to 0.2%
C is contained in an amount of 0.01% or more in order to ensure the strength and toughness of the base material and the weld. However, too much C lowers the toughness of the base metal and the HAZ and degrades the weldability, so the upper limit is made 0.2%.
Ｓｉ：０．０３〜０．５％
Ｓｉは、予備脱酸のために鋼に添加され、また母材の強度確保に有効である。これらの効果を得るために、その含有量を０．０３％以上とする。しかし、Ｓｉが多すぎると溶接性およびＨＡＺ靭性が劣化するため、上限を０．５％とする。より良好なＨＡＺ靭性を得るためにはＳｉを０．３％以下にするのが一層望ましい。
Si: 0.03-0.5%
Si is added to the steel for preliminary deoxidation and is effective in securing the strength of the base material. In order to obtain these effects, the content is set to 0.03% or more. However, if there is too much Si, weldability and HAZ toughness deteriorate, so the upper limit is made 0.5%. In order to obtain better HAZ toughness, it is more desirable to make Si 0.3% or less.
Ｍｎ：０．５〜２．０％
Ｍｎは、母材およびＨＡＺ部の強度と靭性の確保に不可欠であり、その含有量の下限を０．５％とする。しかし、Ｍｎが多すぎるとＨＡＺ靭性の劣化や、スラブの中心偏析助長による溶接性劣化などが起こるため、上限を２．０％とする。
Mn: 0.5 to 2.0%
Mn is indispensable for ensuring the strength and toughness of the base material and the HAZ part, and the lower limit of its content is 0.5%. However, if the amount of Mn is too large, the HAZ toughness deteriorates and the weldability deteriorates due to the promotion of center segregation of the slab. Therefore, the upper limit is made 2.0%.
Ｐ：０．０２％以下
Ｐは、本発明の鋼材においては不純物であり、０．０２％以下とする。Ｐの低減は、スラブ中心偏析の軽減を通じて母材およびＨＡＺの靱性等の機械的性質を改善し、さらにはＨＡＺの粒界破壊を抑制する。
P: 0.02% or less P is an impurity in the steel material of the present invention, and is 0.02% or less. The reduction of P improves mechanical properties such as toughness of the base material and HAZ through reduction of slab center segregation, and further suppresses HAZ grain boundary fracture.
Ｓ：０．０１％以下
Ｓは、鋼中に不純物として存在し、多すぎる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の靭性等の機械的性質が劣化する。また、後述するＣａとの親和力が大きく、ＣａＳを生成するため、適正な複合酸化物の生成を阻害する。従って、Ｓは０．０１％以下とする。より好ましいのは０．００１％未満、最も好ましいのは０．０００４％未満である。
S: 0.01% or less S is present as an impurity in the steel. If it is too much, center segregation is promoted or a large amount of stretched MnS is formed. Therefore, mechanical properties such as the toughness of the base material and HAZ, etc. Properties deteriorate. Moreover, since affinity with Ca which will be described later is large and CaS is generated, generation of an appropriate composite oxide is inhibited. Therefore, S is set to 0.01% or less. More preferred is less than 0.001%, and most preferred is less than 0.0004%.
Ａｌ：０．００５％を超えて０．０８％まで
Ａｌは、本発明鋼材において脱酸剤として重要な元素の一つである。この作用を確保するために、Ａｌは０．００５％を超える量で含有させる。Ａｌを溶鋼に添加した場合、脱酸材として作用しＡｌ2Ｏ3を生成する。Ａｌ2Ｏ3は溶鋼中にてクラスターを形成し、圧延を施した場合にはこれらのクラスターが分離し、点列状につらなって鋼材中に存在することとなる。この場合、点状につらなったＡｌはシャルピー試験時の亀裂の発生起点となり、母材の靭性を劣化させる。また、Ａｌ2Ｏ3は安定な酸化物であるため溶接によっても変化せず、最終的にＨＡＺに残留するため、ＨＡＺ靭性をも劣化させる。
Al: more than 0.005% to 0.08% Al is one of the important elements as a deoxidizer in the steel of the present invention. In order to ensure this effect, Al is contained in an amount exceeding 0.005%. When Al is added to molten steel, it acts as a deoxidizer and produces Al 2 O 3 . Al 2 O 3 forms clusters in the molten steel, and when rolling is performed, these clusters are separated, and are present in the steel material in the form of dotted lines. In this case, Al formed in a dot shape becomes a starting point of crack generation during the Charpy test, and deteriorates the toughness of the base material. In addition, Al 2 O 3 is a stable oxide, so it does not change by welding and finally remains in the HAZ, so that the HAZ toughness is also deteriorated.
しかし、本発明ではＡｌとともにＣａを添加することにより、鋼中にＣａＯ・Ａｌ2Ｏ3系介在物を生成せしめる。したがって、Ａｌを０．００５％を超えて含有させることができる。より好ましいのは０．０４％を超える含有量である。一方、Ａｌ含有量が過多になると、鋼中に固溶するＡｌが増加し、溶接後の冷却過程において残留オーステナイトのセメンタイトへの分解反応を抑制して、島状マルテンサイトを増加させ、溶接部の靭性を低下させる。したがって、Ａｌ含有量の上限は０．０８％とする。 However, in the present invention, Ca and Al 2 O 3 inclusions are produced in the steel by adding Ca together with Al. Therefore, Al can be contained exceeding 0.005%. More preferred is a content exceeding 0.04%. On the other hand, if the Al content is excessive, the amount of Al dissolved in the steel increases, suppressing the decomposition reaction of residual austenite to cementite in the cooling process after welding, increasing island martensite, Reduce toughness. Therefore, the upper limit of the Al content is 0.08%.
Ｔｉ：０．０００５〜０．０２％
Ｔｉは、鋼中でＴｉＮとして析出し、ＨＡＺ部でのオーステナイトの粗大化を抑制し、かつフェライト変態の核となって靭性を向上させる。この効果を得るには、０．０００５％以上含有させる必要がある。一方、含有量が過多になると、固溶Ｔｉが増加し、ＨＡＺ靭性が低下する。そのため、０．０２％以下とする。
Ti: 0.0005 to 0.02%
Ti precipitates as TiN in the steel, suppresses the coarsening of austenite in the HAZ part, and serves as a nucleus of ferrite transformation to improve toughness. In order to acquire this effect, it is necessary to make it contain 0.0005% or more. On the other hand, when the content is excessive, the solid solution Ti increases and the HAZ toughness decreases. Therefore, it is made 0.02% or less.
Ｃａ：０．０００３〜０．０２％
Ｃａは、本発明鋼材において最も重要な元素であり、介在物の球状化を達成するためにはＡｌおよびＯ（酸素）とともに厳密に制御する必要がある。Ｃａは、脱酸剤として作用するとともに、鋼中にＣａＯ・Ａｌ2Ｏ3系介在物を形成するためにも必要な元素である。したがって、０．０００３％以上含有させる。しかし、Ｃａを大量に添加すると鋼の清浄性を低下させ、母材およびＨＡＺの靭性を劣化させる。このため、その含有量は０．０２％以下とする。
Ca: 0.0003 to 0.02%
Ca is the most important element in the steel material of the present invention, and must be strictly controlled together with Al and O (oxygen) in order to achieve inclusion spheroidization. Ca acts as a deoxidizer and is an element necessary for forming CaO.Al 2 O 3 inclusions in the steel. Therefore, 0.0003% or more is contained. However, when Ca is added in a large amount, the cleanliness of the steel is lowered and the toughness of the base material and the HAZ is deteriorated. For this reason, the content is made 0.02% or less.
Ｎ：０．００１〜０．００９％
Ｎは、ＴｉＮの析出に極めて重要な元素であり、０．００１％未満ではＴｉＮの析出量が不足し、溶接後の冷却時に有害なＴｉ炭化物が生成するため、０．００１％を下限とした。より好ましいのは０．００４％を超える含有量、最も好ましいのは０．００６％を超える含有量である。一方、固溶Ｎの増大はＨＡＺ靭性の劣化を招くので、０．００９％を上限とした。
N: 0.001 to 0.009%
N is an extremely important element for the precipitation of TiN. If it is less than 0.001%, the amount of TiN deposited is insufficient, and harmful Ti carbides are produced during cooling after welding, so 0.001% was made the lower limit. . More preferred is a content exceeding 0.004%, and most preferred is a content exceeding 0.006%. On the other hand, an increase in the solid solution N causes a deterioration of the HAZ toughness, so 0.009% was made the upper limit.
Ｏ（酸素）：０．００２５％以下
Ｏは、Ｃａとならんで本発明鋼材において最も重要な元素であり、介在物の球状化のみならず、分散個数や介在物粒径とも直接的に関わるため、その含有量は厳密に制御されなければならない。本発明の鋼材においては、０．００２５％を超える過剰なＯは、粗大な酸化物を形成するとともに、介在物個数を必要以上に増加させ、母材の清浄性を劣化させるため靭性に悪影響を及ぼす。よって、Ｏの許容上限を０．００２５％とした。一方、本発明の鋼材においては、Ｏは少ないほど好ましいので、下限値を設ける必要はないが、Ｏの低減には工業的に限界があり、通常は少なくとも０．００１０％は含まれる。
O (oxygen): 0.0025% or less O is the most important element in the steel of the present invention along with Ca, and is directly related not only to the spheroidization of inclusions but also to the number of dispersed particles and the particle size of inclusions. The content must be strictly controlled. In the steel material of the present invention, excess O exceeding 0.0025% forms a coarse oxide, unnecessarily increases the number of inclusions, and deteriorates the cleanliness of the base material, thus adversely affecting toughness. Effect. Therefore, the allowable upper limit of O is set to 0.0025%. On the other hand, in the steel material of the present invention, since it is preferable that the amount of O is as small as possible, it is not necessary to provide a lower limit value.
Ｃａ／Ｏ：０．５０〜１．３０
溶鋼中で生成されるＣａＯ・Ａｌ2Ｏ3系介在物において、ＣａＯとＡｌ2Ｏ3がほぼ１：１で共存した場合、ＣａＯ・Ａｌ2Ｏ3系介在物の融点は溶鋼温度以下に低下し液化する。この時、ＣａＯ・Ａｌ2Ｏ3系介在物には表面張力が作用し球状となる。この作用を利用してＣａＯ・Ａｌ2Ｏ3系介在物を球状化させるには、Ｃａ／Ｏを０．５０〜１.３０とする必要がある。
Ca / O: 0.50 to 1.30
In CaO · Al 2 O 3 inclusions produced in molten steel, when CaO and Al 2 O 3 coexist at a ratio of 1: 1, the melting point of CaO · Al 2 O 3 inclusions drops below the molten steel temperature. Liquefied. At this time, the surface tension acts on the CaO.Al 2 O 3 inclusions to form a spherical shape. In order to spheroidize CaO · Al 2 O 3 inclusions using this action, Ca / O needs to be 0.50 to 1.30.
Ｃａ／Ｏが１．３０を超えると、ＣａＯがＡｌ2Ｏ3よりも多くなり、また、Ｃａ／Ｏが０．５０未満であると、Ａｌ2Ｏ3がＣａＯよりも多くなり、いずれの場合も、ＣａＯ・Ａｌ2Ｏ3系介在物の融点が溶鋼温度を超えることとなり、ＣａＯ・Ａｌ2Ｏ3系介在物の球状化は困難となる。球状化をより一層促進するためにはＣａ／Ｏを０．６３〜１．１３とすることが望ましい。 When Ca / O exceeds 1.30, CaO is more than Al 2 O 3 , and when Ca / O is less than 0.50, Al 2 O 3 is more than CaO. However, the melting point of the CaO · Al 2 O 3 inclusions exceeds the molten steel temperature, making it difficult to spheroidize the CaO · Al 2 O 3 inclusions. In order to further promote spheroidization, it is desirable to set Ca / O to 0.63 to 1.13.
本発明鋼材の一つは、上記の成分のほか、残部がＦｅおよび不純物からなるものである。本発明鋼材の他の一つは、さらにＢ、Ｎｂ、Ｖ、Ｃｕ、Ｎｉ、ＣｒおよびＭｏの中から選んだ１種または２種以上を含有する鋼材である。これらの元素は、いずれも母材およびＨＡＺの強度、靱性等の機械的性質の改善に役立つ。 One of the steels of the present invention is composed of Fe and impurities in the balance in addition to the above components. Another one of the steel materials of the present invention is a steel material further containing one or more selected from B, Nb, V, Cu, Ni, Cr and Mo. All of these elements are useful for improving mechanical properties such as strength and toughness of the base material and HAZ.
Ｂ：０．００２％以下
Ｂは、焼入性を高めて母材やＨＡＺの機械的性質を向上させる。この効果を得るには、０．０００３％以上含有することが好ましい。しかし、Ｂの含有量が０．００２％を超えるとＨＡＺ靭性や溶接性が劣化する。よって上限を０．００２％とする。
B: 0.002% or less B increases the hardenability and improves the mechanical properties of the base material and HAZ. In order to acquire this effect, it is preferable to contain 0.0003% or more. However, if the B content exceeds 0.002%, the HAZ toughness and weldability deteriorate. Therefore, the upper limit is made 0.002%.
Ｎｂ：０．０５％以下
Ｎｂは、母材組織の微細化に有効な元素であり、母材の機械的性質を向上させる。この効果を得るには、０．００４０％以上含有することが好ましい。しかし、０．０５％を超えると母材およびＨＡＺの靭性が劣化する。よって上限を０．０５％とする。
Nb: 0.05% or less Nb is an element effective for refining the base material structure, and improves the mechanical properties of the base material. In order to acquire this effect, it is preferable to contain 0.0040% or more. However, if it exceeds 0.05%, the toughness of the base material and HAZ deteriorates. Therefore, the upper limit is made 0.05%.
Ｖ：０．１％以下
Ｖは、主に焼戻し時の炭窒化物析出により母材の強度を向上させる。その含有量が０．００５％未満では上記の効果が得られない。一方、０．１％を超えると母材の性能向上効果が飽和し、靱性劣化を招く。
V: 0.1% or less V improves the strength of the base material mainly by carbonitride precipitation during tempering. If the content is less than 0.005%, the above effect cannot be obtained. On the other hand, if it exceeds 0.1%, the performance improvement effect of the base material is saturated, leading to toughness deterioration.
Ｃｕ：１．５％以下
Ｃｕを含有させると、母材およびＨＡＺの靭性を劣化させずに強度を上昇させることができる。これらの効果を確実に得るには、Ｃｕは０．１％以上の含有量とすることが好ましい。しかし１．５％を超えると、鋼の焼入性を過度に高め、ＨＡＺ靱性を損なう傾向が強くなる。したがって、１．５％を超えて含有させるべきではない。
Cu: 1.5% or less When Cu is contained, the strength can be increased without deteriorating the toughness of the base material and the HAZ. In order to reliably obtain these effects, the Cu content is preferably 0.1% or more. However, if it exceeds 1.5%, the hardenability of the steel is excessively increased and the tendency to deteriorate the HAZ toughness becomes strong. Therefore, it should not be contained in excess of 1.5%.
Ｎｉ：６％以下
Ｎｉは、適正量を添加することによって、溶接性およびＨＡＺ靱性に悪影響を及ぼすこともなく、母材の強度および靱性を向上させる。含有量を０．１％以上とすると焼入性向上効果も得られるので、０．１％以上とすることが望ましい。特に、Ｃｕを添加する場合は圧延時のひび割れ（Ｃｕチェッキング）を防止するために、０．１％以上のＮｉを含有させる必要がある。Ｎｉ含有量が６％を超えると構造用鋼材として極めて高価になって経済性を失うので、添加する場合、Ｎｉ含有量は６％以下に限定する。
Ni: 6% or less By adding an appropriate amount, Ni improves the strength and toughness of the base material without adversely affecting the weldability and the HAZ toughness. If the content is 0.1% or more, the effect of improving hardenability is also obtained, so it is desirable to make it 0.1% or more. In particular, when Cu is added, it is necessary to contain 0.1% or more of Ni in order to prevent cracking (Cu checking) during rolling. If the Ni content exceeds 6%, it becomes extremely expensive as a structural steel material and loses economic efficiency. Therefore, when Ni is added, the Ni content is limited to 6% or less.
Ｃｒ：１％以下
Ｃｒは、適正量を添加することによって、焼入性を高めるのに有用である。Ｃｒのこのような効果を積極的に利用しようとする場合、０．０５％以上の含有量とするのがよい。一方、１％を超えて含有させると、他の成分の含有量の条件を満足させても、ＨＡＺ靭性が劣化する。
Cr: 1% or less Cr is useful for enhancing hardenability by adding an appropriate amount. When such an effect of Cr is to be actively used, the content is preferably 0.05% or more. On the other hand, if the content exceeds 1%, the HAZ toughness deteriorates even if the content conditions of other components are satisfied.
Ｍｏ：０．８％以下
Ｍｏは、母材の強度と靱性を向上させる効果がある。しかし、含有量が０．０５％未満ではこの効果が小さいので、０．０５％以上含有させるのが望ましい。一方、０．８％を超えると、特にＨＡＺの硬度が高まり靱性が損なわれる。
（２）介在物の分布形態
(2)−１．ＣａＯ・Ａｌ2Ｏ3系介在物
本発明に係る溶接熱影響部の靭性に優れた溶接構造用鋼材では、その組織に粒径が０．５〜５μｍのＣａＯ・Ａｌ2Ｏ3系介在物が分散していることが必要である。なお、介在物が非円形であるときは、その長径を介在物の粒径とする。
Mo: 0.8% or less Mo has an effect of improving the strength and toughness of the base material. However, if the content is less than 0.05%, this effect is small, so it is desirable to contain 0.05% or more. On the other hand, if it exceeds 0.8%, the hardness of HAZ is particularly increased and the toughness is impaired.
(2) Distribution pattern of inclusions
(2) -1. The CaO · Al 2 O 3 inclusions toughness excellent welding structural steel of the weld heat affected zone according to the present invention, the particle size to that tissue is CaO · Al 2 O 3 inclusions of 0.5~5μm It must be distributed. When the inclusion is non-circular, the major axis is the particle diameter of the inclusion.
前述のようにＣａ／Ｏをコントロールすることにより、ＣａＯ・Ａｌ2Ｏ3系介在物は球状のものとなる。ここで、介在物の粒径を０．５μｍ以上としたのは、これより小さい介在物は、破壊起点として影響する確率が低く、ＨＡＺ靭性に大きな影響を与えないためである。よって本発明では粒径が０．５μｍよりも小さい介在物に関しては、その個数および形状について問題としない。 By controlling Ca / O as described above, CaO · Al 2 O 3 inclusions become spherical. Here, the reason why the particle size of the inclusions is 0.5 μm or more is that inclusions smaller than this have a low probability of affecting the fracture starting point and do not significantly affect the HAZ toughness. Therefore, in the present invention, there is no problem with respect to the number and shape of inclusions having a particle size smaller than 0.5 μm.
また、介在物の粒径を５μｍ以下としたのは、粒径が５μｍを超えるＣａＯ・Ａｌ2Ｏ3系介在物が多数分散している場合は、たとえその球状化が達成されていたとしても、シャルピー試験時の破壊起点として作用し、特に溶接熱影響部における靭性のバラツキが大きくなるからである。 In addition, the particle size of the inclusions is set to 5 μm or less, even when a large number of CaO · Al 2 O 3 inclusions having a particle size exceeding 5 μm are dispersed, even if the spheroidization has been achieved. This is because it acts as a fracture starting point during the Charpy test, and in particular, the variation in toughness at the weld heat affected zone becomes large.
なお、本発明では、粒径が５μｍを超えるＣａＯ・Ａｌ2Ｏ3系介在物が鋼材中に存在することを否定するものではない。すなわち、粒径が５μｍを超えるＣａＯ・Ａｌ2Ｏ3系介在物であっても、その粒径が１０μｍ以下であり、その個数が１×１０個／ｍｍ2未満であれば鋼の靭性のバラツキに影響はない。即ち、粒径が５μｍを超えるＣａＯ・Ａｌ2Ｏ3系介在物は、１×１０個／ｍｍ2未満であれば許容できる。 In the present invention, it is not denied that CaO.Al 2 O 3 inclusions having a particle size exceeding 5 μm are present in the steel material. That is, even if the CaO · Al 2 O 3 inclusions having a particle size of more than 5 μm have a particle size of 10 μm or less and the number is less than 1 × 10 / mm 2 , the toughness of the steel varies. There is no effect. In other words, CaO · Al 2 O 3 inclusions having a particle size of more than 5 μm are acceptable if they are less than 1 × 10 / mm 2 .
前記のとおり、本発明鋼材には粒径が０．５〜５μｍのＣａＯ・Ａｌ2Ｏ3系介在物が分散する。ただし、ＣａＯ・Ａｌ2Ｏ3系介在物が多量に存在すると、鋼材の清浄性が劣化し、靭性に悪影響を与える。一方、ＣａＯ・Ａｌ2Ｏ3系介在物が少ないと、鋼中に存在する酸素がＣａＯ・Ａｌ2Ｏ3以外に、ＳｉやＴｉと酸化物を形成し、介在物形状のコントロールが困難となる。前記のように、工業的には鋼中のＯを完全に取り除くことは困難であり、Ｏは少なくとも０．００１０％程度は含まれているので、ＣａＯ・Ａｌ2Ｏ3系介在物を生成させ、ＳｉやＴｉの酸化物は生成させないことが肝要である。したがって、ＣａＯ・Ａｌ2Ｏ3系介在物は適度に存在していることが好ましく、具体的には、１×１０〜１×１０4個／ｍｍ2分散していることが好ましい。 As described above, CaO · Al 2 O 3 inclusions having a particle size of 0.5 to 5 μm are dispersed in the steel of the present invention. However, if a large amount of CaO · Al 2 O 3 inclusions are present, the cleanliness of the steel material is deteriorated and the toughness is adversely affected. On the other hand, if there are few CaO · Al 2 O 3 inclusions, oxygen existing in the steel forms oxides with Si and Ti other than CaO · Al 2 O 3 , making it difficult to control the inclusion shape. . As described above, industrially, it is difficult to completely remove O in steel, and since O is contained at least about 0.0010%, CaO · Al 2 O 3 inclusions are generated. It is important not to produce oxides of Si and Ti. Therefore, CaO · Al 2 O 3 inclusions are preferably present in an appropriate amount, and specifically, 1 × 10 to 1 × 10 4 particles / mm 2 are preferably dispersed.
ＣａＯ・Ａｌ2Ｏ3系介在物の分散状態は、以下のような方法で定量的に測定することができる。すなわち、鋼材の圧延方向に対し平行な断面から、好ましくはその断面の中心部から観察用試料を作製し、これを走査型電子顕微鏡（ＳＥＭ）を用いて８００〜２０００倍の倍率で少なくとも１０ｍｍ2以上の面積を観察し、ＣａＯ・Ａｌ2Ｏ3系介在物の数を測定し、単位面積当たりの個数に換算すればよい。 The dispersion state of the CaO · Al 2 O 3 inclusion can be quantitatively measured by the following method. That is, an observation sample is prepared from a cross section parallel to the rolling direction of the steel material, preferably from the center of the cross section, and this is at least 10 mm 2 at a magnification of 800 to 2000 times using a scanning electron microscope (SEM). What is necessary is just to observe the above area, measure the number of CaO.Al 2 O 3 inclusions, and convert it to the number per unit area.
ＣａＯ・Ａｌ2Ｏ3系介在物のアスペクト比は、１〜１．９であることが望ましい。介在物が球状化し、アスペクト比（長径／短径）が１に近くなった場合、シャルピー試験時の介在物およびその周辺組織への応力集中が緩和されるため、靭性が向上、安定化する。一方で、アスペクト比が、１．９を超えるＣａＯ・Ａｌ2Ｏ3系介在物がシャルピー試験片のノッチ近傍に存在する場合、応力集中源となり、そこから発生する亀裂の伝播によって靭性が著しく低下し、シャルピー衝撃試験の測定値のバラツキが大きくなる。 The aspect ratio of the CaO · Al 2 O 3 inclusion is preferably 1 to 1.9. When the inclusions are spheroidized and the aspect ratio (major axis / minor axis) is close to 1, stress concentration on the inclusions and surrounding structures during the Charpy test is alleviated, so that toughness is improved and stabilized. On the other hand, when CaO · Al 2 O 3 inclusions with an aspect ratio exceeding 1.9 are present in the vicinity of the notch of the Charpy specimen, it becomes a stress concentration source, and the toughness is significantly reduced by the propagation of cracks generated therefrom. However, the variation in the measured value of the Charpy impact test increases.
ＣａＯ・Ａｌ2Ｏ3系介在物は、Ｃａ／Ｏが０．５０〜１．３０の範囲であれば、溶鋼中で球状化し、またこの組成の介在物は圧延によって破砕や延伸されることがないため、そのアスペクト比は１に近い値となる。しかし、Ｃａ／Ｏバランスが０．５０未満の場合、または１．３０を超える場合、ＣａＯ・Ａｌ2Ｏ3系介在物は溶鋼中で完全に球状化せず、一部が圧延中に破砕され点列状につらなった形状となり、シャルピー試験における応力集中源となるため、靱性に悪影響を及ぼす。なお、点列状につらなった介在物は、一つの延伸した介在物と見なしてそのアスペクト比を測定する。 CaO · Al 2 O 3 inclusions are spheroidized in molten steel if Ca / O is in the range of 0.50 to 1.30, and inclusions of this composition may be crushed or stretched by rolling. Therefore, the aspect ratio is close to 1. However, when the Ca / O balance is less than 0.50 or exceeds 1.30, CaO · Al 2 O 3 inclusions do not completely spheroidize in the molten steel, and some of them are crushed during rolling. It becomes a shape that is connected in the form of a point sequence, and it becomes a stress concentration source in the Charpy test, which adversely affects toughness. Note that the inclusions arranged in a dot array are regarded as one extended inclusion, and the aspect ratio is measured.
(2)−２．ＣａＯおよびＡｌ2Ｏ3
粒径０．５μｍ以上でアスペクト比が５以上のＡｌ2Ｏ3またはＣａＯは、５×１０個／ｍｍ2以下であることが望ましい。
(2) -2. CaO and Al 2 O 3
The Al 2 O 3 or CaO having a particle size of 0.5 μm or more and an aspect ratio of 5 or more is desirably 5 × 10 pieces / mm 2 or less.
粒径０．５μｍ以上のＡｌ2Ｏ3やＣａＯは、圧延により延伸した粗大な介在物や点列状につらなった介在物群を形成し、シャルピー試験における応力集中源となり、ＨＡＺ靭性の安定性を著しく低下させる。特に、アスペクト比が５以上の場合、他の介在物よりも有効な応力集中源として作用する。したがって、このような延伸した粗大なＡｌ2Ｏ3またはＣａＯは５×１０個／ｍｍ2以下に抑えるのが望ましいのである。 Al 2 O 3 and CaO with a particle size of 0.5 μm or more form coarse inclusions stretched by rolling or inclusion groups connected in the form of a dotted line, which becomes a stress concentration source in the Charpy test and stabilizes HAZ toughness. Remarkably decreases the performance. In particular, when the aspect ratio is 5 or more, it acts as a more effective stress concentration source than other inclusions. Therefore, it is desirable to keep the stretched coarse Al 2 O 3 or CaO to 5 × 10 pieces / mm 2 or less.
なお、ＣａＯ・Ａｌ2Ｏ3系介在物と同様に、点列状に並んだＣａＯおよびＡｌ2Ｏ3の介在物も、一つの延伸した介在物と見なしてそのアスペクト比を測定する。 As in the CaO · Al 2 O 3 inclusions, inclusions of lined CaO and Al 2 O 3 to the point rows also to measure the aspect ratio is regarded as inclusions single stretch.
本発明のＣａＯ・Ａｌ2Ｏ3系介在物、ＣａＯおよびＡｌ2Ｏ3のアスペクト比は、鋼材の圧延方向に対し平行な断面から、好ましくは断面中心部から観察用試料を作製し、走査型電子顕微鏡（ＳＥＭ）を用いて３０００〜１００００倍の倍率で、少なくとも１００個以上の介在物を観察し、その長径を短径で除した値の平均値を算出すればよい。 The aspect ratio of the CaO · Al 2 O 3 inclusions, CaO and Al 2 O 3 of the present invention is such that a specimen for observation is prepared from a cross section parallel to the rolling direction of the steel material, preferably from the center of the cross section. What is necessary is just to calculate the average value of the value which observed at least 100 or more inclusions with the magnification of 3000-10000 times using an electron microscope (SEM), and remove | divided the major axis by the minor axis.
（３）製造方法
本発明の製造方法は、その製鋼段階に特徴を有する。すなわち、溶鋼中のＡｌが０．００５％を超えて０．０８％となるようにＡｌを添加して脱酸した後、Ｔｉを添加し、さらに脱ガス装置、例えばＲＨ装置で１５分以上処理した後、溶鋼温度を１６００±７０℃に保った状態でＣａを添加する。この溶鋼温度は、１６００℃±５０℃であるのがより望ましく、１６００±２０℃であることがさらに望ましい。なお、このＣａ添加の前にあらかじめ溶鋼の成分調整を行っておくのが望ましい。
(3) Manufacturing method The manufacturing method of this invention has the characteristics in the steelmaking stage. That is, after adding Al to deoxidize so that Al in the molten steel exceeds 0.005% to 0.08%, Ti is added, and further treated with a degassing apparatus such as an RH apparatus for 15 minutes or more. Then, Ca is added with the molten steel temperature kept at 1600 ± 70 ° C. The molten steel temperature is more preferably 1600 ° C. ± 50 ° C., and further preferably 1600 ± 20 ° C. In addition, it is desirable to adjust the components of the molten steel in advance before the Ca addition.
最初に添加するＡｌは、脱酸力が強いため、溶鋼中の固溶酸素と結合し、Ａｌ2Ｏ3を生成する。次にＡｌより脱酸力の低いＴｉを添加することにより、Ｔｉは酸化物を生成せず、ＴｉＮを生成し、ＨＡＺ靭性の改善に寄与することになる。 Since Al added first has a strong deoxidizing power, it combines with solid solution oxygen in molten steel to produce Al 2 O 3 . Next, by adding Ti having a lower deoxidizing power than Al, Ti does not produce an oxide, but produces TiN, which contributes to the improvement of HAZ toughness.
この時、Ａｌは、前記のように溶鋼中のＡｌが０．００５％を超えて０．０８％までの範囲となるように添加する。溶鋼中のＡｌが０．００５％以下の場合には、Ａｌによる脱酸が不十分となり、Ｔｉの酸化物が鋼中に生成してしまい、鋼中にＴｉＮを十分に形成させることができない。一方、溶鋼中のＡｌが０．０８％を超えると、余分なＡｌが鋼中に固溶Ａｌとして残留し、母材およびＨＡＺの靭性が劣化する。 At this time, Al is added so that Al in the molten steel exceeds 0.005% and reaches 0.08% as described above. When Al in molten steel is 0.005% or less, deoxidation by Al becomes insufficient, Ti oxides are generated in the steel, and TiN cannot be sufficiently formed in the steel. On the other hand, when Al in molten steel exceeds 0.08%, excess Al remains as solid solution Al in the steel, and the toughness of the base material and HAZ deteriorates.
さらにＲＨ法等によって１５分以上の脱ガス処理することにより、粗大なＡｌ2Ｏ3を浮上分離させた後、溶鋼中にＣａを添加する。このＣａ添加により、Ａｌ2Ｏ3介在物が一部還元され、ＣａＯ・Ａｌ2Ｏ3系介在物が形成される。このとき、溶鋼の温度を１６００±７０℃に制御することによりＣａＯ・Ａｌ2Ｏ3系介在物は液化が促進され、表面張力が作用するために、同介在物は球状化する。なお、球状化には、Ｃａ、ＡｌおよびＯの含有量を前述の含有量となるように制御することが必要である。 Furthermore, after carrying out degassing treatment for 15 minutes or more by the RH method or the like, coarse Al 2 O 3 is floated and separated, and then Ca is added to the molten steel. The addition of Ca, Al 2 O 3 inclusions are partially reduced, CaO · Al 2 O 3 inclusions is formed. At this time, by controlling the temperature of the molten steel to 1600 ± 70 ° C., liquefaction of the CaO · Al 2 O 3 inclusions is promoted and surface tension acts, so that the inclusions are spheroidized. For spheroidization, it is necessary to control the contents of Ca, Al, and O to the above-mentioned contents.
本発明の製造方法において、「Ａｌを添加した後」とは、投入したＡｌが溶鋼中に均一に混合した後のことを意味する。また、Ｔｉ添加およびＣａ添加についても同様である。 In the production method of the present invention, “after adding Al” means after the charged Al is uniformly mixed in the molten steel. The same applies to addition of Ti and addition of Ca.
上記のように溶製した鋼を鋳造し、圧延することにより溶接熱影響部の靭性に優れた溶接構造用鋼材を製造する。本発明の製造方法においては、製鋼段階後の鋳造および圧延は、通常の方法により行うことができる。圧延以後のプロセスとして、通常圧延まま、制御圧延、さらにこれと制御冷却と焼戻しの組合せ、および焼入れと焼戻しの組合せなどを行っても、ＣａＯ・Ａｌ2Ｏ3系介在物の分散状態には影響はなく、介在物が及ぼす靭性への影響にはなんら変化はない。 By casting and rolling the steel melted as described above, a welded structural steel material having excellent weld heat affected zone toughness is produced. In the production method of the present invention, casting and rolling after the steel making stage can be performed by ordinary methods. Even if the process after rolling is performed as usual, controlled rolling, and a combination of this with controlled cooling and tempering, and a combination of quenching and tempering, the dispersion state of CaO · Al 2 O 3 inclusions is affected. There is no change in the effect of inclusions on toughness.
表１に示した化学組成を有する鋼を溶製し、加熱、圧延を経て板厚１９〜２５ｍｍの鋼板を製造した。得られた鋼板を入熱１００〜５００ｋＪ／ｃｍで溶接し、−６０℃でシャルピー試験を行い、ＨＡＺ靭性を評価した。試験番号の１〜２４が本発明例、ａ〜ｋが比較例である。母材の製造条件は下記のとおりである。 Steel having the chemical composition shown in Table 1 was melted, and a steel plate having a thickness of 19 to 25 mm was produced through heating and rolling. The obtained steel plate was welded at a heat input of 100 to 500 kJ / cm, a Charpy test was performed at −60 ° C., and HAZ toughness was evaluated. Test numbers 1 to 24 are examples of the present invention, and a to k are comparative examples. The manufacturing conditions of the base material are as follows.
表２に母材の製造方法、母材特性およびＨＡＺの靭性を示す。ＨＡＺ靭性評価のためのシャルピー試験は、フュージョンラインから採取した３本の試験片で行った。表２にその３本の試験片による測定値を示す。なお、表２の各例において、アスペクト比が５を超えるＣａＯ介在物およびＡｌ2Ｏ3介在物は、ほとんど観察されなかった。そのため、同表では観察されたＣａＯ介在物およびＡｌ2Ｏ3介在物の平均粒径と個数を参考までに示した。 Table 2 shows the base material manufacturing method, base material characteristics, and HAZ toughness. The Charpy test for HAZ toughness evaluation was performed on three test pieces taken from the fusion line. Table 2 shows the measured values of the three test pieces. In each example of Table 2, almost no CaO inclusions and Al 2 O 3 inclusions having an aspect ratio exceeding 5 were observed. Therefore, in the same table, the observed average particle diameter and number of CaO inclusions and Al 2 O 3 inclusions are shown for reference.
表２から明らかなように、No.１〜２４の本発明鋼材は、比較例の鋼材と比べて、優れたＨＡＺ靭性を有し、−６０℃でのＨＡＺ靭性がいずれも７０Ｊ以上と極めて優れている。 As is apparent from Table 2, the present steel materials of Nos. 1 to 24 have excellent HAZ toughness as compared with the steel materials of the comparative examples, and the HAZ toughness at −60 ° C. is extremely excellent at 70 J or more. ing.
一方、比較例のａ〜ｋの鋼材は、いずれも−６０℃でのシャルピー試験でバラツキが大きく、３本中の少なくとも１本は７０J未満の値を示した。これらのａ〜ｋは、基本成分が本発明の要件を満たさない例である。また、ｉは、ＣａＯ・Ａｌ2Ｏ3系介在物の粒径およびアスペクト比が本発明の所定の値を超えた例、ｊおよびｋは、ともにＣａ添加温度が本発明で定める温度範囲内ではないためＨＡＺ靭性が劣化した例である。 On the other hand, all of the steel materials a to k of the comparative examples showed large variations in the Charpy test at −60 ° C., and at least one of the three steels showed a value of less than 70 J. These a to k are examples in which the basic components do not satisfy the requirements of the present invention. Further, i is an example in which the particle size and aspect ratio of CaO.Al 2 O 3 inclusions exceed the predetermined values of the present invention, and j and k are both within the temperature range in which the Ca addition temperature is defined by the present invention. This is an example in which the HAZ toughness has deteriorated because of no.
本発明の鋼材は、溶接熱影響部が安定して高靭性となる鋼材である。この鋼材は、船舶、海洋構造物などの海上構造物に用いる溶接鋼板等に好適である。本発明は、このような鋼材の製造方法をも提供するものであり、溶接構造物の安全性を高めることにおいても寄与するところが大きい。
The steel material of the present invention is a steel material in which the weld heat-affected zone is stable and has high toughness. This steel material is suitable for welded steel sheets used for marine structures such as ships and marine structures. The present invention also provides a method for producing such a steel material, and greatly contributes to enhancing the safety of the welded structure.
Claims (6)
０．５０≦Ｃａ／Ｏ≦１．３０ ・・・・・(1)
ただし、(1)式の元素記号はその元素の含有量（質量％）を示す。 In mass%, C: 0.01 to 0.2%, Si: 0.03 to 0.5%, Mn: 0.5 to 2.0%, P: 0.02% or less, S: 0.01 %: Al: over 0.005% to 0.08%, Ti: 0.0005-0.02%, Ca: 0.0003-0.02%, N: 0.001-0.009% And O (oxygen): 0.0025% or less, with the balance being Fe and impurities, satisfying the following formula (1), and having a CaO.Al 2 O 3 system particle size of 0.5 to 5 μm A welded structural steel material with excellent toughness in the heat affected zone of welds, characterized in that the material is dispersed.
0.50 ≦ Ca / O ≦ 1.30 (1)
However, the element symbol of the formula (1) indicates the content (% by mass) of the element.
After adding Al and deoxidizing so that Al in the molten steel exceeds 0.005% and reaching 0.08%, Ti is added, and after further treatment with a degassing apparatus for 15 minutes or more, The welded heat-affected zone excellent in toughness of welded heat affected zone according to any one of claims 1 to 5, wherein Ca is added, cast and rolled while the molten steel temperature is maintained at 1600 ± 70 ° C. Steel manufacturing method.
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