JP4926447B2 - Manufacturing method of high strength steel with excellent weld crack resistance - Google Patents
Manufacturing method of high strength steel with excellent weld crack resistance Download PDFInfo
- Publication number
- JP4926447B2 JP4926447B2 JP2005308535A JP2005308535A JP4926447B2 JP 4926447 B2 JP4926447 B2 JP 4926447B2 JP 2005308535 A JP2005308535 A JP 2005308535A JP 2005308535 A JP2005308535 A JP 2005308535A JP 4926447 B2 JP4926447 B2 JP 4926447B2
- Authority
- JP
- Japan
- Prior art keywords
- steel
- temperature
- toughness
- strength
- cooling
- 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.)
- Active
Links
Description
本発明は、引張強さ５７０Ｎ／ｍｍ２以上の耐溶接割れ性に優れた高張力鋼の製造方法に関するものである。 The present invention relates to a method for producing high-tensile steel having a tensile strength of 570 N / mm 2 or more and excellent weld crack resistance.
近年、構造物の大型化により、５７０Ｎ／ｍｍ２以上の高張力鋼が用いられる場合が増加している。一般に高張力鋼は強度向上の目的から多くの合金元素を添加するために、耐溶接割れ性は良好であるとは言えない。そこで、溶接割れ感受性を表す指標であるＰｃｍ値を低く抑制した鋼が、例えば、特許文献１において提案されている。 In recent years, the use of high-tensile steel of 570 N / mm 2 or more is increasing due to the increase in size of structures. In general, high tensile steel is not good in weld crack resistance because many alloy elements are added for the purpose of improving strength. Therefore, for example, Patent Document 1 proposes a steel in which the Pcm value, which is an index representing the weld crack sensitivity, is suppressed to a low level.
この特許文献１記載の発明では、ＶとＮｂを複合添加することにより、高降伏点化が達成できる冷却停止温度が広がり、安定的に高降伏点鋼材が製造可能になるという知見に基づいている。特に冷却停止温度範囲（例えば３５０〜４５０℃）においては、ＮｂとＶの複合添加によるマトリクス強化が主として作用し、高降伏点化が達成され、高い冷却停止温度範囲（例えば４５０〜６５０℃）においては、ＮｂとＶの析出硬化機構により、４５０Ｍｐａ以上もの高降伏点が得られる点に着目している。また、鋼の成分を特許文献１記載の範囲に限定することにより、優れた靭性及び溶接性を併せ持たせることができるという知見にも基づいている。 In the invention described in Patent Document 1, the combined addition of V and Nb increases the cooling stop temperature at which a high yield point can be achieved, and is based on the knowledge that a high yield point steel material can be manufactured stably. . In particular, in the cooling stop temperature range (for example, 350 to 450 ° C.), the matrix strengthening by the combined addition of Nb and V mainly acts to achieve a high yield point, and in the high cooling stop temperature range (for example, 450 to 650 ° C.). Focuses on the fact that a high yield point of 450 Mpa or more can be obtained by the precipitation hardening mechanism of Nb and V. Moreover, it is also based on the knowledge that excellent toughness and weldability can be provided by limiting the components of steel to the range described in Patent Document 1.
また、５７０Ｎ／ｍｍ２以上の高張力鋼では、鋼の焼き入れ性を確保するためにＢを添加する場合が多い。Ｂは粒界偏析元素であると同時にＡｌ、Ｔｉに次ぐ強力な窒化物形成元素である。特許文献２の開示技術では、溶接熱を受けた後の冷却時において、亜粗粒域ＨＡＺでは窒化物ＢＮを形成し、粗粒域では、固溶Ｂとして存在するＢとＮとの組み合わせがあれば、全領域に亘って良好な靭性が得られる点に着目している。また、種々のＢ及びＮの鋼を作製し、組織と靭性を調査した結果、重量％で、Ｂを０．０００３〜０．００３％、Ｎを０．０００３〜０．００８％とした場合に、ＨＡＺ全域に亘って組織及び靭性が改善されることに基づいている。 Further, in a high strength steel of 570 N / mm 2 or more, B is often added in order to ensure the hardenability of the steel. B is a grain boundary segregation element and at the same time a strong nitride forming element next to Al and Ti. In the disclosed technique of Patent Document 2, during cooling after receiving welding heat, nitride BN is formed in the sub-coarse grain region HAZ, and in the coarse grain region, the combination of B and N existing as solid solution B is formed. If it exists, it is paying attention to the point from which favorable toughness is acquired over the whole area | region. Moreover, as a result of producing various B and N steels and investigating the structure and toughness, when B was 0.0003 to 0.003% and N was 0.0003 to 0.008% by weight% This is based on the fact that the structure and toughness are improved over the entire HAZ.
しかし、Ｂの添加は精錬、鋳造時の化学成分や製造条件の変動による母材特性の不安定さが問題となる場合がある。また、溶接部においては顕著な硬化が著しく耐溶接割れ性が悪化する場合がある。 However, when B is added, instability of the base material characteristics due to variations in chemical components and manufacturing conditions during refining and casting may be a problem. Moreover, remarkable hardening may be remarkable in the welded portion, and the weld crack resistance may deteriorate.
このため、上述の如きＢ添加による耐溶接割れ性の低下を改善する観点から、特許文献３に記載の発明のように単純にＢの添加を行わない鋼も提案されている。この特許文献３記載の発明は、溶接割れ感受性指数としてのＰｃｍ値を指標として定義されており、さらにその鋼の成分は、下記の知見に基づいている。（１）化学成分をＮｂ添加系とし、かつ直接焼入れ法の採用により圧延加熱時に固溶させたＮｂによる焼入れ性向上効果を活用できる点。（２）直接焼入れ後の焼戻し処理によりＮｂ炭窒化物の析出硬化を活用できる点。（３）鋼材の低温靭性の改善に有効なオーステナイト未再結晶域での圧延は、オーステナイト再結晶温度を上昇せしめるＮｂ添加により、極端に低温での圧下を実施することなく実現できる点。（４）オーステナイト未再結晶域での圧下量によって鋼材の圧延方向に平行な方向と垂直な方向との音速比（音響異方性）が増加するにつれ、シャルピー衝撃試験の破面遷移温度で表される低温靭性が極端に低温での圧下を加えることなく改善される点。 For this reason, steel which does not add B simply like the invention of patent document 3 is proposed from a viewpoint which improves the fall of the weld crack resistance by B addition as mentioned above. The invention described in Patent Document 3 is defined by using the Pcm value as a weld crack sensitivity index as an index, and the components of the steel are based on the following findings. (1) The chemical component is an Nb-added system, and the effect of improving the hardenability by Nb that is dissolved at the time of rolling and heating by adopting the direct quenching method can be utilized. (2) The point that precipitation hardening of Nb carbonitride can be utilized by tempering treatment after direct quenching. (3) The rolling in the austenite non-recrystallized region which is effective for improving the low temperature toughness of the steel material can be realized without performing reduction at an extremely low temperature by adding Nb which raises the austenite recrystallization temperature. (4) As the sound velocity ratio (acoustic anisotropy) between the direction parallel to the rolling direction of steel and the direction perpendicular to the rolling direction of steel increases with the amount of reduction in the non-recrystallized region of austenite, The low temperature toughness that can be improved without adding extremely low temperature reduction.
しかしながら、Ｂは、ベイナイト組織あるいはマルテンサイト組織の生成を促進する効果を有する。またＢは、微量の添加によって焼入れ性を向上させ、焼入れ時の焼入れ深さを高めることによりねじり強度を向上、ひいては高張力鋼の溶接部靱性を改善する効果もある。このため、かかるＢを添加しない場合には溶接部の靱性を低下させてしまうという欠点もあった。
そこで、本発明は、上述した問題点に鑑みて案出されたものであり、その目的とするところは、上述した耐溶接割れ性を改善するために、Ｐｃｍを一定値以下に制限し、製造安定性や耐溶接割れ性の観点からＢを添加しない高張力鋼において懸念される溶接部靱性を顕著に改善することを目的とする。 Therefore, the present invention has been devised in view of the above-mentioned problems, and the object is to limit Pcm to a certain value or less in order to improve the above-described weld crack resistance, and to manufacture The object is to remarkably improve the weld toughness which is a concern in high-strength steel not containing B from the viewpoint of stability and weld crack resistance.
本発明の要旨とするところは、以下のとおりである。まず、（ａ）鋼の耐溶接割れ性を改善するためにＰｃｍ（＝Ｃ％＋Ｓｉ％／３０＋Ｍｎ％／２０＋Ｃｕ％／２０＋Ｎｉ％／３０＋Ｃｒ％／２０＋Ｍｏ％／１５＋Ｖ％／１０＋５Ｂ％）を一定値以下に制限する。この値は、小さければ小さいほど耐溶接割れ性は改善され、溶接を行う前に行う鋼材の予熱温度を低下させることができ、作業効率を増加させることができる。特にＰｃｍが０．２６以下となると予熱温度が室温程度となり予熱が不要となる。従って、Ｐｃｍの上限は０．２６とすることが望ましい。しかしながらＰｃｍを低下させることは、概ね焼き入れ性を低下させたり、固溶強化や析出強化を通じて強度に寄与する元素を低減することであるから鋼の強度を低下させる。そこで、このような（ｂ）鋼の強化を行うために圧延終了後にはＡｒ3点以上の温度から室温〜６５０℃の範囲に強制冷却を行い、鋼の組織をベイナイトやマルテンサイトなどにして変態組織強化を行う。但し、（ｃ）目標とする鋼の強度によって固溶元素や析出元素をＰｃｍの上限を超えない範囲で添加し、強化を増加する。このとき、Ｂ（ボロン）はＰｃｍをあまり増加させずに、鋼の焼き入れ性を増加させ強度を得やすくする元素であるが、一方で、精錬、鋳造時の化学成分のばらつきや製造条件の変動による効果や特性の不安定さがある。そこで、（ｄ）製造不安定性を回避する観点からＢを添加しない。しかし、Ｂは溶接部の金属組織の焼き入れ性を高めることによって、高張力鋼の溶接部の低温靱性を改善する効果があるので、これを添加しない場合には溶接部の靱性が低下するという欠点がある。本発明者等はこのようなＢを添加しない場合の溶接部靱性に及ぼす各元素の影響を調査した。その結果、（ｅ）Ｍｎを従来通常の使用範囲を超えて、より多く２〜５％添加することにより強度を増加させ、かつ溶接部靱性が向上した。Ｍｎ添加による溶接部靱性の向上は同程度の焼き入れ性をＮｉなどＭｎ以外の元素で補った場合より、あきらかに良好であった。Ｂを添加しない系において、Ｍｎを２％以上添加することによって焼き入れ性の向上による母材強度と溶接部の靱性という相反する特性を両立することができたのである。この改善効果の起源は明確ではないが、Ｂ添加がない場合にＭｎの変態組織を微細にする効果（ベイナイトや粒内変態の核生成を促進する一方で結晶粒の成長を抑制するような効果）が表れたものと考えられる。
The gist of the present invention is as follows. First, (a) Pcm (= C% + Si% / 30 + Mn% / 20 + Cu% / 20 + Ni% / 30 + Cr% / 20 + Mo% / 15 + V% / 10 + 5B%) is set to a certain value or less in order to improve the weld crack resistance of the steel. Restrict. As this value is smaller, the weld crack resistance is improved, the preheating temperature of the steel material to be performed before welding can be lowered, and the working efficiency can be increased. In particular, when Pcm is 0.26 or less, the preheating temperature becomes about room temperature, and preheating becomes unnecessary. Therefore, the upper limit of Pcm is desirably 0.26. However, lowering Pcm generally lowers the hardenability and reduces the elements that contribute to strength through solid solution strengthening and precipitation strengthening, and therefore lowers the strength of steel. Therefore, in order to strengthen such steel (b), after the rolling is completed, forced cooling is performed from the temperature of the Ar 3 point or higher to the range of room temperature to 650 ° C., and the steel structure is transformed into bainite or martensite. Strengthen the organization. However, (c) Solid solution elements and precipitation elements are added within a range not exceeding the upper limit of Pcm depending on the strength of the target steel, and the strengthening is increased. At this time, B (boron) is an element that increases the hardenability of the steel and makes it easy to obtain strength without increasing Pcm so much. There are effects due to fluctuations and instability of characteristics. Therefore, (d) B is not added from the viewpoint of avoiding production instability. However, since B has the effect of improving the low temperature toughness of the welded portion of high-strength steel by enhancing the hardenability of the metal structure of the welded portion, the toughness of the welded portion is reduced when this is not added. There are drawbacks. The present inventors investigated the influence of each element on the weld zone toughness when B was not added. As a result, the strength was increased by adding 2 to 5% of (e) Mn exceeding the conventional normal use range, and the weld zone toughness was improved. The improvement in weld toughness by addition of Mn was clearly better than the case where the same hardenability was supplemented with elements other than Mn such as Ni. In the system in which B is not added, by adding 2% or more of Mn, it was possible to achieve both contradictory properties of the base material strength and the toughness of the welded portion due to the improvement of the hardenability. The origin of this improvement effect is not clear, but the effect of making the transformation structure of Mn finer in the absence of B addition (the effect of suppressing the growth of crystal grains while promoting the nucleation of bainite and intragranular transformation) ) Appears.
以上、（ａ）〜（ｅ）によって、耐溶接割れ性が優れ、製造安定性と溶接部靱性を兼ね備えた高張力鋼を得るため、本発明者は、以下の高張力鋼の製造方法を発明した。 As described above, in order to obtain a high-strength steel having excellent weld cracking resistance and having both production stability and welded portion toughness according to (a) to (e), the present inventors have invented the following method for producing high-strength steel. did.
（１） 質量％で、Ｃ：０．０００２〜０．１５％、Ｓｉ：０．０１〜２％、Ｍｎ：２〜５％、Ｂ≦０．０００３％、Ａｌ：０．０００１〜０．１％、Ｎ ：０．０００１〜０．０１％、Ｎｂ：０．０００１〜０．１％を含有し、さらにＣｕ：０．００１〜３％、Ｎｉ：０．００１〜１％、Ｃｒ：０．００１〜３％、Ｍｏ：０．００１〜３％、Ｖ ：０．０００１〜０．２％、Ｔｉ：０．０００１〜０．２％、ＲＥＭ：０．０００１〜０．１％、Ｍｇ：０．０００１〜０．０２％、Ｃａ：０．０００１〜０．０２％からなる群より選ばれた１種又は２種以上の成分を含有し、かつ
Ｐｃｍ＝Ｃ％＋Ｓｉ％／３０＋Ｍｎ％／２０＋Ｃｕ％／２０＋Ｎｉ％／３０＋Ｃｒ％／２０＋Ｍｏ％／１５＋Ｖ％／１０＋５Ｂ％≦０．２５％
を満たし、残部Ｆｅおよび不可避的不純物からなる鋼を鋳造し、
室温まで冷却することなくそのまま、または一度室温まで冷却し、
９５０〜１２５０℃に再加熱し、Ａｒ3点以上の温度で圧延を終了し、かつ、Ａｒ3点以上の温度から室温〜６５０℃の温度域に強制冷却することを特徴とする、引張強さ５７０Ｎ／ｍｍ2以上の、耐溶接割れ性に優れた高張力鋼の製造方法。
(1) By mass%, C: 0.0002 to 0.15%, Si: 0.01 to 2%, Mn: 2 to 5%, B ≦ 0.0003%, Al: 0.0001 to 0.1 %, N: 0.0001 to 0.01% , Nb: 0.0001 to 0.1%, Cu: 0.001 to 3%, Ni: 0.001 to 1%, Cr: 0.00. 001 to 3%, Mo: 0.001 to 3%, V: 0.0001 to 0.2 %, Ti: 0.0001 to 0.2%, REM: 0.0001 to 0.1%, Mg: 0 Containing one or more components selected from the group consisting of 0.0001 to 0.02%, Ca: 0.0001 to 0.02%, and Pcm = C% + Si% / 30 + Mn% / 20 + Cu% /20+Ni%/30+Cr%/20+Mo%/15+V%/10+5B%≦0.25%
And casting the steel consisting of the balance Fe and inevitable impurities,
Without cooling to room temperature, or once cooled to room temperature,
Reheated to: 950 ° C., and ends the rolling at Ar 3 point or more temperature, and characterized by forced cooling from Ar 3 point or more temperature to a temperature range of room temperature to 650 ° C., the tensile strength A method for producing high-tensile steel having an excellent weld crack resistance of 570 N / mm 2 or more.
（２）さらに、質量％で、Ｚｒ：０．０００１〜０．３％、Ｔａ：０．０００１〜０．３％、Ｈｆ：０．０００１〜０．３％の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）に記載の耐溶接割れ性に優れた高張力鋼の製造方法。
(2) Further, by mass%, one or more of Zr: 0.0001 to 0.3%, Ta: 0.0001 to 0.3%, Hf: 0.0001 to 0.3% are contained. A method for producing a high-strength steel excellent in weld crack resistance according to the above (1).
（３） 前記強制冷却の後に、１００〜６２０℃の温度で熱処理を施すことを特徴とする、上記（１）または（２）に記載の耐溶接割れ性に優れた高張力鋼の製造方法。
( 3 ) The method for producing high-strength steel excellent in weld crack resistance according to (1) or ( 2), wherein heat treatment is performed at a temperature of 100 to 620 ° C. after the forced cooling.
本発明によれば、Ｐｃｍを一定値以下に制限することにより耐溶接割れ性を向上させつつ、溶接部低温靱性の良好な５７０Ｎ／ｍｍ２以上の高張力鋼を提供することが可能となる。従って、本発明によれば、橋梁、建築物等に代表される大型構造物の主要部材に対して十分な特性を有する鋼材を提供することが可能となる。 ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide 570 N / mm < 2 > or more high-tensile steel with favorable weld-part low temperature toughness, improving a weld cracking resistance by restricting Pcm to below a fixed value. Therefore, according to the present invention, it is possible to provide a steel material having sufficient characteristics with respect to main members of large structures represented by bridges, buildings and the like.
本発明の要旨とするところは以下の通りである。まず、（ａ）鋼の耐溶接割れ性を改善するために、溶接割れ感受性を示すＰｃｍ（＝Ｃ％＋Ｓｉ％／３０＋Ｍｎ％／２０＋Ｃｕ％／２０＋Ｎｉ％／３０＋Ｃｒ％／２０＋Ｍｏ％／１５＋Ｖ％／１０＋５Ｂ％）を０．２６以下に制限する。次に、Ｐｃｍを低下させたことにより想定される焼き入れ性や強度の低下に対しては、（ｂ）圧延終了後にＡｒ３点以上の温度から室温〜６５０℃の範囲に強制冷却を行い鋼の組織をベイナイトやマルテンサイトなどにして変態組織強化を行う。さらに、（ｃ）目標とする鋼の強度によって固溶元素や析出元素をＰｃｍの上限を超えない範囲で添加し、強化を増加する。このとき、Ｂは、Ｐｃｍをあまり増加させずに、鋼の焼き入れ性を増加させ強度を得やすくする元素であるが、一方で、精錬、鋳造時の化学成分のばらつきや製造条件の変動による効果や特性の不安定さがある。そこで、（ｄ）製造不安定性を回避する観点からＢを添加しない。しかし、Ｂは溶接部の金属組織の焼き入れ性を高めることによって、高張力鋼の溶接部の低温靱性を改善する効果があるので、これを添加しない場合には溶接部の靱性が低下するという欠点がある。本発明者等はこのようなＢを添加しない場合の溶接部靱性に及ぼす各元素の影響を調査した結果、（ｅ）Ｍｎを通常より多く２〜５％添加することにより強度を増加させ、かつ溶接部靱性を向上させることができることが分かった。これら（ａ）〜（ｅ）の知見によって、耐溶接割れ性が優れ、製造安定性と溶接部靱性を兼ね備えた高張力鋼を得るものである。 The gist of the present invention is as follows. First, (a) In order to improve the weld crack resistance of steel, Pcm (= C% + Si% / 30 + Mn% / 20 + Cu% / 20 + Ni% / 30 + Cr% / 20 + Mo% / 15 + V% / 10 + 5B%) indicating weld crack sensitivity ) Is limited to 0.26 or less. Next, to reduce the hardenability and strength assumed by lowering Pcm, (b) steel is subjected to forced cooling from the temperature of Ar 3 point or higher to room temperature to 650 ° C. after rolling. The transformation structure is strengthened by using bainite or martensite as the structure. Furthermore, (c) a solid solution element or a precipitation element is added within a range not exceeding the upper limit of Pcm depending on the strength of the target steel, and the strengthening is increased. At this time, B is an element that increases the hardenability of the steel and makes it easy to obtain strength without increasing Pcm so much, but on the other hand, due to variations in chemical components during refining and casting, and variations in manufacturing conditions There is instability in effect and characteristics. Therefore, (d) B is not added from the viewpoint of avoiding production instability. However, since B has the effect of improving the low temperature toughness of the welded portion of high-strength steel by enhancing the hardenability of the metal structure of the welded portion, the toughness of the welded portion is reduced when this is not added. There are drawbacks. As a result of investigating the influence of each element on the weld zone toughness when B is not added, the inventors have increased the strength by adding 2 to 5% of Mn more than usual, and It has been found that weld toughness can be improved. Based on these findings (a) to (e), high-strength steel having excellent weld crack resistance and having both production stability and welded portion toughness is obtained.
ちなみに、ここでいう高張力鋼とは、いわゆる高張力鋼板をさし、厚鋼板及び熱延鋼板等を含む概念である。 Incidentally, the high-strength steel here refers to a so-called high-strength steel plate, and is a concept including a thick steel plate and a hot-rolled steel plate.
これらの思想を実現するために必要な条件について、以下に各成分、製造方法の限定理由として説明する。以下、組成における質量％は、単に％と記載する。 The conditions necessary for realizing these ideas will be described below as reasons for limiting each component and the production method. Hereinafter, the mass% in the composition is simply described as%.
Ｃは、鋼の焼き入れ性を制御し、強度を高めたり、セメンタイトをはじめとする炭化物を生成し、強度を向上させるために添加する。しかし、このＣを過剰に含有させると、パーライトやマルテンサイトあるいはセメンタイトといった硬質の第二相組織の形成量が増加して鋼の延性や靱性の低下を招くとともに溶接性や溶接部の靱性を著しく劣化させる。
このため、鋼の高強度化を図る観点から、Ｃの下限を０．０００２％とした。これに対して、Ｃの含有量が０．１５％を越えると、加工性、溶接性、靭性が著しく劣化するため、Ｃの上限を０．１５％に設定した。
C is added to control the hardenability of the steel, increase the strength, generate carbides such as cementite, and improve the strength. However, if this C is contained excessively, the amount of hard second phase structure such as pearlite, martensite or cementite increases, resulting in a decrease in the ductility and toughness of the steel, and the weldability and the toughness of the welded portion are remarkably increased. Deteriorate.
For this reason, from the viewpoint of increasing the strength of the steel, the lower limit of C is set to 0.0002%. On the other hand, if the C content exceeds 0.15%, the workability, weldability and toughness deteriorate significantly, so the upper limit of C was set to 0.15%.
Ｓｉは、鋼材の脱酸元素であり、通常Ｍｎとともに鋼の酸素濃度を低減する目的で添加される。またこのＳｉは、固溶強化元素として、強度の上昇に寄与する。このＳｉが０．０１％未満では、上述した固溶強化を図ることができない。また、Ｓｉが２％を超えると低温靱性や鋼の表面性状を損なう。このため、Ｓｉの濃度範囲を０．０１〜２％とした。 Si is a deoxidizing element for steel and is usually added together with Mn for the purpose of reducing the oxygen concentration of the steel. Further, this Si contributes to an increase in strength as a solid solution strengthening element. If this Si is less than 0.01%, the above-mentioned solid solution strengthening cannot be achieved. On the other hand, if Si exceeds 2%, the low temperature toughness and the surface properties of the steel are impaired. Therefore, the Si concentration range is set to 0.01 to 2%.
Ｍｎは、Ｓｉとともに脱酸にも効用があるが、鋼中にあって材料の焼き入れ性を高め、強度向上に寄与する元素である。また、このＭｎは、安価であることからＣに次いで活用される元素である。これらの従来知見に加えて、Ｍｎを２％以上に亘って増量添加することにより、鋼の溶接部の低温靱性を改善する効果があることが判明した。このため、本発明では、Ｍｎの下限を２％とした。これに対して、Ｍｎの濃度が５％を越えると鋼の加工性を劣化させるため、その上限を５％とした。 Mn has an effect on deoxidation as well as Si, but is an element in steel that enhances the hardenability of the material and contributes to the improvement of strength. Further, Mn is an element that is utilized next to C because it is inexpensive. In addition to these conventional findings, it has been found that adding Mn over 2% or more has the effect of improving the low-temperature toughness of the steel weld. For this reason, in the present invention, the lower limit of Mn is set to 2%. On the other hand, if the Mn concentration exceeds 5%, the workability of the steel deteriorates, so the upper limit was made 5%.
ＢはＰｃｍをあまり増加させることなく、焼入れ性の向上を介して鋼の強度を増加させる作用を有するが、精錬、鋳造時の化学成分のばらつきや製造条件の変動による効果や特性の不安定さがある。そこで、製造不安定性を回避する観点から、本発明においては、原則としてＢを添加しない。しかしながら、Ｂを極めて微量に添加することにより、上述の如き高強度化に寄与することから、その濃度０．０００３％を上限として添加を許容することとした。特に実用鋼においては、不可避的不純物として、この程度のＢを含有している可能性があるので注意が必要である。
Ｎｂは、熱間圧延時の未再結晶温度域を広げ制御圧延を容易にし、強度及び靭性を向上させる際に有効な元素である。但し、０．０００１％未満では効果がなく、０.１％を超えると母材の靱性や延性、溶接部の靱性に悪影響を及ぼすことから、Ｎｂの濃度範囲を０．０００１〜０．１％とした。
B has the effect of increasing the strength of the steel through the improvement of hardenability without increasing Pcm so much, but the effect and instability of characteristics due to variations in chemical composition during refining and casting, and fluctuations in manufacturing conditions. There is. Therefore, from the viewpoint of avoiding production instability, B is not added in principle in the present invention. However, the addition of B in an extremely small amount contributes to the increase in strength as described above. Therefore, the addition was allowed with the concentration being 0.0003% as the upper limit. In particular, in practical steel, attention should be paid because there is a possibility that this amount of B may be contained as an inevitable impurity.
Nb is an element effective in widening the non-recrystallization temperature range during hot rolling to facilitate controlled rolling and improving strength and toughness. However, if it is less than 0.0001%, there is no effect, and if it exceeds 0.1%, the toughness and ductility of the base metal and the toughness of the welded part are adversely affected, so the Nb concentration range is 0.0001 to 0.1%. It was.
溶接割れ感受性を示すＰｃｍを上述の如く０．３％以下とした。これはＰｃｍが０．３％程度となると溶接に先立って行う鋼材の予熱温度が室温程度となり予熱作業が不要となるメリットがあるからである。但し、Ｐｃｍは鋼の強度が低いほど下げることが可能であるので、目標強度に応じて、０．１８質量％程度を下限としつつできるだけ低減することが望ましい。０．１８質量％程度を目標値とするのは、これ以上Ｐｃｍを低減しても予熱が不要であることに変わりがないからである。 Pcm which shows a weld crack sensitivity was made into 0.3% or less as mentioned above. This is because when the Pcm is about 0.3%, the preheating temperature of the steel material to be performed prior to welding becomes about room temperature, and there is an advantage that the preheating work is not required. However, since Pcm can be lowered as the strength of the steel is lower, it is desirable to reduce it as much as possible while setting the lower limit to about 0.18% by mass according to the target strength. The reason why the target value is about 0.18% by mass is that preheating is not necessary even if Pcm is further reduced.
Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏは鋼の焼き入れ性や強度を増加させる目的で選択的に添加することができる。 Cu, Ni, Cr, and Mo can be selectively added for the purpose of increasing the hardenability and strength of the steel.
Ｃｕは、焼入れ性の向上に有効であり、またフェライト中に固溶し、この固溶強化によって鋼の強度を向上させる。またＣｕは、析出硬化に有効な元素であり、金属Ｃｕの析出相を形成し、微細組織の形成の促進や延性の劣化を抑制した析出強化を実現することが可能となる。但し、０．００１％未満の濃度では析出量が不十分で、本発明での課題とする機械的特性が得られないことから、下限値を０．００１％とした。また、Ｃｕの濃度が３％を超える場合には、析出強化が著しくなり、鋳造時に粒界に析出して内部割れを引き起こし、圧延製造工程中に鋼塊や鋼板で疵を発生させやすくなり、鋼の熱間加工性や母材靱性、溶接部の靱性などを劣化させる要因ともなる。このため、Ｃｕの上限値が３％となるように設定した。 Cu is effective for improving the hardenability, and is solid-solved in ferrite, and the strength of the steel is improved by this solid solution strengthening. Cu is an element effective for precipitation hardening, and forms a precipitation phase of metallic Cu, and it is possible to realize precipitation strengthening that promotes formation of a microstructure and suppresses deterioration of ductility. However, if the concentration is less than 0.001%, the amount of precipitation is insufficient, and the mechanical properties that are the subject of the present invention cannot be obtained. Therefore, the lower limit is set to 0.001%. Moreover, when the concentration of Cu exceeds 3%, precipitation strengthening becomes significant, and precipitates at grain boundaries during casting to cause internal cracks, and it is easy to generate flaws in the steel ingot and steel plate during the rolling manufacturing process, It is also a factor that deteriorates the hot workability, base metal toughness, and weld toughness of steel. For this reason, it set so that the upper limit of Cu might be 3%.
Ｎｉは、強度を向上させる作用を有し、特に靭性を低下させることなく強度向上が図れる点で有用な元素である。このＮｉが０．００１％未満の濃度では靭性向上にはほとんど機能しないことから下限値を０．００１％とした。また、３％を超えるＮｉを含有させても、効果が飽和し、含有量に見合う効果が期待できなくなり、経済的に不利になるとともに焼き入れ強化による強度上昇が顕著となり、靱性や延性の劣化をまねく。このため、かかるＮｉの上限値が３％となるように設定した。Ｎｉの上限値は、実施例に基づいて１％とする。
Ni is an element that has the effect of improving strength and is particularly useful in that strength can be improved without reducing toughness. Since this Ni hardly functions to improve toughness at a concentration of less than 0.001%, the lower limit is set to 0.001%. Moreover, even if Ni is contained in excess of 3%, the effect is saturated, and the effect commensurate with the content cannot be expected, which is economically disadvantageous and increases in strength due to quenching strengthening, and deteriorates toughness and ductility. I will. Therefore, the upper limit value of Ni is set to 3%. The upper limit of Ni is set to 1% based on the example.
Ｃｒは、焼入れ性の向上と析出硬化により、母材の強度向上に有効な元素である。このＣｒは、０．００１％未満の添加では上述した強度上昇効果は充分に発揮されず、３％を超える濃度では靭性が低下する。したがってＣｒの濃度範囲を０．００１〜３％に限定した。 Cr is an element effective for improving the strength of the base material by improving hardenability and precipitation hardening. If this Cr is added in an amount of less than 0.001%, the above-described effect of increasing the strength is not sufficiently exerted, and if it exceeds 3%, the toughness decreases. Therefore, the Cr concentration range is limited to 0.001 to 3%.
Ｍｏは、焼入れ性の向上、析出強化に寄与して強度を向上させる。Ｍｏの濃度が０．００１％未満では析出強化に寄与する事ができず、十分な強度が確保できない。これに対して、Ｍｏの濃度が３％を超えてしまうと、強度が顕著に上昇して靭性の劣化が生じる。従って、Ｍｏの濃度範囲を０．００１〜３％に限定した。 Mo contributes to improving hardenability and strengthening precipitation, and improves strength. If the Mo concentration is less than 0.001%, it cannot contribute to precipitation strengthening, and sufficient strength cannot be secured. On the other hand, when the concentration of Mo exceeds 3%, the strength is remarkably increased and the toughness is deteriorated. Therefore, the concentration range of Mo is limited to 0.001 to 3%.
Ｖ、Ｔｉは結晶粒の微細化と析出強化の面で有効に機能するので靭性を劣化させない範囲で選択的に添加できる。
V, T i can be selectively added in a range not to deteriorate the toughness so to function effectively in terms of strengthening grain refinement and precipitation.
Ｖは、析出強化を通じて高降伏点化をもたらす働きをする元素である。このＶの濃度が０．０００１％未満では、上述した析出強化による効果を得ることができず、また０．２％を超えてしまうと、溶接性、靭性の低下を招く。このため、Ｖの濃度範囲を０．０００１〜０．２％に限定した。 V is an element that works to bring about a high yield point through precipitation strengthening. If the concentration of V is less than 0.0001%, the above-described effect of precipitation strengthening cannot be obtained, and if it exceeds 0.2%, weldability and toughness are reduced. For this reason, the concentration range of V is limited to 0.0001 to 0.2%.
また、Ｔｉの濃度範囲は、０．０００１〜０．２％とした。０.００１％以上添加することで、炭窒化物を形成し、強度上昇や金属組織の細粒化に大きく寄与し、強度上昇や母材や溶接部の靱性を向上する。しかし、０.２％を超えると析出物の粗大化などにより逆に靭性の劣化を招くため、上述の如き濃度範囲に限定した次第である。 The concentration range of Ti was set to 0.0001 to 0.2%. Addition of 0.001% or more forms carbonitrides, greatly contributes to strength increase and fine metal structure, and improves strength and toughness of the base metal and welds. However, if it exceeds 0.2%, the toughness is deteriorated due to the coarsening of the precipitates, etc., so that it is limited to the concentration range as described above.
ＲＥＭ、Ｍｇ、Ｃａは、いずれも脱酸に寄与することに加えて硫化物を形成して靭性低下の要因となるＭｎＳの生成を抑制することができ、Ｓの無害化に有効である。このため、これらＲＥＭ、Ｍｇ、Ｃａは、何れも選択的に添加できるが、過度に添加してしまうと、大型の介在物として存在することとなり靭性の低下を効果的に抑制することができなくなる。このため、ＲＥＭについては０．１０％以下とし、Ｍｇ、Ｃａについては０．０２％以下に限定している。また、それぞれの下限値を０．０００１％としたのは、これ以下では効果が得られないからである。 In addition to contributing to deoxidation, REM, Mg, and Ca can suppress the formation of MnS, which forms sulfides and causes a decrease in toughness, and is effective in detoxifying S. For this reason, all of these REM, Mg, and Ca can be selectively added. However, if they are added excessively, they will exist as large inclusions and the reduction in toughness cannot be effectively suppressed. . For this reason, REM is limited to 0.10% or less, and Mg and Ca are limited to 0.02% or less. Also, the reason why the respective lower limit values are set to 0.0001% is that an effect cannot be obtained below this value.
Ａｌは、溶鋼の脱酸などに活用される元素であるが、鋼中のＮと結合し、オーステナイト生成時に結晶粒を微細化する作用があり、靭性や延性を向上させる効果がある。本発明でのＡｌ以外の成分濃度範囲においては０．０００１％未満では、脱酸が不十分であることから下限を０．０００１％に限定した。また、０．１％を超える濃度までＡｌを添加しても、その効果が飽和することから、上限を０．１％に限定した。 Al is an element utilized for deoxidation of molten steel, etc., but has the effect of combining with N in the steel and making the crystal grains finer when austenite is produced, improving the toughness and ductility. In the concentration range of components other than Al in the present invention, if it is less than 0.0001%, deoxidation is insufficient, so the lower limit was limited to 0.0001%. Moreover, even if Al is added to a concentration exceeding 0.1%, the effect is saturated, so the upper limit was limited to 0.1%.
Ｚｒ、Ｔａ、Ｈｆは脱酸元素あるいは炭窒化物形成元素として選択的に添加できる。但し、Ｚｒ、Ｔａ、Ｈｆについては０．３％を越えると、鋼の靱性や表面性状を劣化させてしまう。またこれらの元素が０．０００１％未満では、効果が得られない。このため、Ｚｒ、Ｔａ、Ｈｆの濃度範囲を０．０００１％〜０．３％に限定した。 Zr, Ta, and Hf can be selectively added as a deoxidizing element or a carbonitride forming element. However, if Zr, Ta, and Hf exceed 0.3%, the toughness and surface properties of the steel are deteriorated. If these elements are less than 0.0001%, the effect cannot be obtained. For this reason, the concentration range of Zr, Ta, and Hf was limited to 0.0001% to 0.3%.
Ｎは、溶鋼処理中に空気中の窒素が取り込まれることから、鋼中に不可避的に混入する元素である。このＮは、ＴｉおよびＡｌ、Ｚｒ、Ｔａ、Ｈｆと窒化物を形成し、オーステナイトの細粒化およびフェライトの再結晶粒の微細化に有効に作用するため靭性を劣化させない範囲で選択的に添加できる。したがって、Ｎは低濃度であることが望ましいため、下限値を０．０００１とした。また、０．０５％を超える濃度では、オーステナイト粒の微細化を図ることができず、靭性低下が著しくなることから、０．０５％を上限値とした。 N is an element that is inevitably mixed in steel because nitrogen in the air is taken in during the treatment of molten steel. This N forms nitrides with Ti and Al, Zr, Ta, Hf, and acts effectively in the refinement of austenite and the recrystallized grains of ferrite. it can. Therefore, since it is desirable that N has a low concentration, the lower limit is set to 0.0001. On the other hand, if the concentration exceeds 0.05%, the austenite grains cannot be refined and the toughness is significantly reduced.
その他、不可避的不純物であるＰは、オーステナイトの粒界に偏析し、粒界強度を低下させることにより、ねじり延性や靱性を低下させることから、０．０２％以下とすることが望ましい。また不可避的不純物であるＳは、Ｐと同様に不純物として含有される元素であり、意図的に添加される元素ではないが、不純物として偏析し、またＭｎＳなどの硫化物系介在物を形成し、高温における加工性や靭性を低下させることから、０．０１％以下とすることが望ましい。 In addition, P, an inevitable impurity, segregates at the austenite grain boundaries and lowers the grain boundary strength, thereby reducing torsional ductility and toughness. S, which is an unavoidable impurity, is an element that is contained as an impurity in the same manner as P, and is not an element that is intentionally added, but segregates as an impurity and forms sulfide inclusions such as MnS. In order to reduce workability and toughness at high temperatures, it is desirable that the content be 0.01% or less.
次に、鋼の製造条件について説明する。鋼は所定の成分に調整された後、例えば連続鋳造やインゴット鋳造等の方法により鋳造される。かかる鋳造を終了後、室温まで冷却することなくそのままか、あるいは鋳造後に一度室温まで冷却させる。この時の冷却については特にその方法を規定しない。加熱炉内で徐々に冷却する炉冷、大気中での放冷、水冷などによる強制冷却などが可能である。但し、強度、靱性向上の目的には、水冷により強制冷却することが好ましい。その後９５０〜１２５０℃に再加熱する。次に、この再加熱された鋼に対して圧延処理を実行していくことになるが、この圧延終了時の温度は、Ａｒ３点以上であることが必須となる。圧延処理を終了させた後、Ａｒ３点以上の温度から室温〜６５０℃の範囲に鋼を強制冷却する。ちなみに、この圧延処理時における総圧下率は、理想的には７５〜９９％としてもよいが、実際には３０％以上、望ましくは５０％以上であってもよい。また、オーステナイトの未再結晶状態で圧延を行うことを目的に概ね９００℃以下の温度で圧延を行う制御圧延を実施することもできる。この場合、９００℃以下の温度での総圧下率は実際には１０％以上、望ましくは３０％以上が望ましい。また、前記圧延後の強制冷却は、例えば水冷で板厚２０ｍｍ〜７５ｍｍの鋼を冷却する場合に、その冷却速度は、４℃／ｓ〜７０℃／ｓ程度としてもよい。 Next, manufacturing conditions for steel will be described. Steel is cast by a method such as continuous casting or ingot casting after being adjusted to a predetermined component. After the completion of the casting, it is left as it is without being cooled to room temperature, or is cooled to room temperature once after casting. There is no particular method for cooling at this time. Furnace cooling that gradually cools in the heating furnace, cooling in the atmosphere, forced cooling by water cooling, and the like are possible. However, for the purpose of improving strength and toughness, it is preferable to perform forced cooling by water cooling. Then reheat to 950-1250 ° C. Next, a rolling process is performed on the reheated steel, and it is essential that the temperature at the end of the rolling is Ar 3 or higher. After finishing the rolling process, the steel is forcibly cooled to a range of room temperature to 650 ° C. from a temperature of 3 or more points of Ar. Incidentally, the total rolling reduction during the rolling process may be ideally 75 to 99%, but may actually be 30% or more, preferably 50% or more. Moreover, the controlled rolling which performs rolling at the temperature of about 900 degrees C or less for the purpose of rolling in the non-recrystallized state of austenite can also be implemented. In this case, the total rolling reduction at a temperature of 900 ° C. or lower is actually 10% or more, preferably 30% or more. Moreover, the forced cooling after the rolling may be performed at a cooling rate of about 4 ° C./s to 70 ° C./s when, for example, steel having a thickness of 20 mm to 75 mm is cooled by water cooling.
なお、上述した再加熱時の温度は、鋼の金属組織がオーステナイト単相となる必要があるので、その下限を９５０℃とした。また、再加熱温度の上限を１２５０℃としたのは、これを超える温度では、オーステナイト結晶粒の成長が速く、粗大となり、鋼の低温靱性を劣化させてしまうからである。 In addition, since the temperature of the reheating mentioned above needs to be austenite single phase, the lower limit was set to 950 degreeC. Further, the upper limit of the reheating temperature is set to 1250 ° C., if the temperature exceeds this, the growth of austenite crystal grains becomes fast and coarse, and the low temperature toughness of the steel is deteriorated.
また、圧延をＡｒ３点以上で終了するのは、Ａｒ３温度以下での圧延では金属組織中に加工されたフェライトが混在し、鋼の靱性を劣化させるからである。また、圧延後の冷却をＡｒ３点以上から行うのは、Ａｒ３点以下から冷却を行ったのでは冷却開始前に粗大なフェライトが生成し、強度を低下させるとともに靱性を劣化させるからである。また、冷却は水冷によって実施するのが望ましいが、これと同等の冷却速度が得られればどのような方法でも良い。このような強制冷却により、鋼組織を未変態オーステナイトとベイナイトの混合組織とすることができ、鋼材の強度上昇を図ることが可能となる。 The reason why rolling is finished at Ar 3 or higher is that, when rolling at Ar 3 temperature or lower, ferrite processed in the metal structure is mixed and the toughness of the steel is deteriorated. The reason why cooling after rolling is performed from Ar 3 points or more is that if cooling is performed from Ar 3 points or less, coarse ferrite is generated before the start of cooling, and the strength is lowered and the toughness is deteriorated. . The cooling is preferably performed by water cooling, but any method may be used as long as a cooling rate equivalent to this can be obtained. By such forced cooling, the steel structure can be a mixed structure of untransformed austenite and bainite, and the strength of the steel material can be increased.
また、冷却の終了温度を６５０℃以下としたのは、これを超える温度では、金属組織にフェライトが増加し、鋼の強度を高められないからである。さらに冷却の終了温度を室温以上としたのは水冷などの現在の設備能力としてこれ以下まで冷却することが困難であるからである。なお冷却停止温度については、所期の強度レベルに応じて適宜調整することができる。 Further, the reason why the cooling end temperature is set to 650 ° C. or lower is that if the temperature exceeds this, ferrite increases in the metal structure and the strength of the steel cannot be increased. Furthermore, the reason why the cooling end temperature is set to room temperature or higher is that it is difficult to cool to below this level as the current facility capacity such as water cooling. The cooling stop temperature can be appropriately adjusted according to the intended strength level.
最後に、前記の室温から６５０℃への強制冷却の後に実施する１００〜７００℃の温度での熱処理については、目標とする強制冷却の終了温度以下であれば室温を含み、そこまで放冷されている過程のどのようなタイミングで実施してもよい。但し、このような場合は、実施可能な熱処理温度の選択範囲が制限されることになるが、その効果は変わらない。また、熱処理の温度範囲を１００℃以上としたのは、１００〜３００℃の温度であれば固溶炭素原子や窒素原子による転位の固着が生じ、いわゆる時効硬化による強化が得られるからである。さらに、３００℃以上の温度では、いわゆる焼戻しの効果により、セメンタイトやその他の炭窒化物の析出による析出強化が得られるとともに、強度の調整等によって靱性の改善がもたらされる。しかし、一方で極度に高温の熱処理では、セメンタイトやその他の炭窒化物および金属結晶粒の成長、粗大化により強度の低下や靱性の劣化をもたらす。そこで、熱処理の最高温度は７００℃とした。熱処理の最高温度は、実施例に基づいて６２０℃とする。なお、熱処理時の昇温速度や保持時間、冷却方法については特に規定を設けないが、急速加熱や保持時間の短縮および熱処理後の強制冷却はいずれも鋼の強度を増加させ、靱性を改善するので、必要に応じて適宜条件を選択、調整すれば良い。
Finally, for the heat treatment at a temperature of 100 to 700 ° C., which is performed after the forced cooling from room temperature to 650 ° C., if the temperature is equal to or lower than the target forced cooling end temperature, it is allowed to cool to that temperature. It may be performed at any time during the process. However, in such a case, the selection range of the heat treatment temperature that can be performed is limited, but the effect is not changed. The reason why the temperature range of the heat treatment is set to 100 ° C. or higher is that dislocations are fixed by solid solution carbon atoms or nitrogen atoms at a temperature of 100 to 300 ° C., and strengthening by so-called age hardening is obtained. Furthermore, at a temperature of 300 ° C. or higher, the so-called tempering effect provides precipitation strengthening due to precipitation of cementite and other carbonitrides, and toughness is improved by adjusting the strength. However, extremely high temperature heat treatment, on the other hand, causes strength reduction and toughness deterioration due to growth and coarsening of cementite, other carbonitrides and metal crystal grains. Therefore, the maximum temperature for heat treatment was set to 700 ° C. The maximum temperature of the heat treatment is 620 ° C. based on the examples. In addition, there are no specific provisions regarding the heating rate, holding time, and cooling method during heat treatment, but rapid heating, shortening of holding time, and forced cooling after heat treatment all increase the strength of steel and improve toughness. Therefore, the conditions may be selected and adjusted as necessary.
以下に本発明の実施例について説明をする。表１は、上述した化学成分の範囲内にある本発明を適用した高張力鋼（以下、発明鋼という。）と、本発明から逸脱した化学成分からなる鋼（以下、比較鋼という。）の成分構成例を示している。
鋼種Ａ〜Ｓは、発明鋼に該当し、鋼種Ａ１〜Ｔ３は比較鋼に該当する。ちなみに、鋼種Ａ１並びにＩ３は、Ｍｎを上記化学成分の範囲より低く設定している。また、鋼種Ａ３は、Ｍｎを上記化学成分の範囲より高く設定している。また鋼種Ａ２は、Ｃを上記化学成分の範囲より高く設定し、鋼種Ｉ１、Ｉ２は、Ｂを上記化学成分の範囲より高く設定している。さらにＭ１、Ｍ２、Ｍ３、Ｍ４は、それぞれＭｏ、Ｃｒ、Ｃｕ、Ｎｉの化学成分を本発明において限定した化学成分から逸脱させている。またＴ１はＶについて、Ｔ２はＴｉについて、さらにＴ３はＮｂについて、上記化学成分の範囲より高く設定している。
Steel types A to S correspond to invention steels, and steel types A1 to T3 correspond to comparative steels. Incidentally, steel types A1 and I3 set Mn lower than the range of the above chemical components. Steel type A3 sets Mn higher than the range of the chemical component. Steel type A2 sets C higher than the range of the chemical component, and steel types I1 and I2 set B higher than the range of the chemical component. Further, M1, M2, M3, and M4 deviate the chemical components of Mo, Cr, Cu, and Ni from those limited in the present invention, respectively. T1 is set higher than V, T2 is set higher than Ti, and T3 is higher than Nb.
上述の如き化学成分からなる発明鋼と比較鋼について、素材厚、製品板厚、製造条件につき、互いに異ならせて機械的特性を評価した。ちなみに製造条件に関しては、上述した鋼の製造プロセスに沿って、再加熱温度、圧延終了温度、冷却開始温度、冷却終了温度、焼戻し温度、Ａｒ３温度のそれぞれについて、条件を異ならせている。 The mechanical properties of the inventive steels and the comparative steels composed of the chemical components as described above were evaluated by making them different from each other with respect to the material thickness, product plate thickness, and production conditions. By the way, regarding the production conditions, the reheating temperature, the rolling end temperature, the cooling start temperature, the cooling end temperature, the tempering temperature, and the Ar 3 temperature are varied according to the steel manufacturing process described above.
表２は、発明鋼並びに比較鋼の各種条件に対する機械的特性を示している。
機械的特性は、母材の降伏応力ＹＳ（Ｎ／ｍｍ２）、母材の引張り強度ＴＳ（Ｎ／ｍｍ２）、靱性（シャルピー試験に於ける延性-脆性破面遷移温度ｖＴｒｓ）、及び溶接部靱性（溶接入熱７ＫＪ／ｍｍ相当、シャルピー試験の−５℃における吸収エネルギー）、斜めｙ型割れ試験結果の各項目に亘っている。 Mechanical properties include base material yield stress YS (N / mm 2 ), base material tensile strength TS (N / mm 2 ), toughness (ductility-brittle fracture surface transition temperature vTrs in Charpy test), and welding. It covers each item of part toughness (equivalent to welding heat input 7 KJ / mm, absorbed energy at −5 ° C. of Charpy test), and oblique y-type crack test results.
ちなみに、母材の降伏応力ＹＳや引張り強度ＴＳを測定する上での引っ張り試験においては、ＪＩＳ４号試験片を利用し、低温靱性は、ＪＩＳ４号Ｖノッチシャルピー試験に基づいて測定した。斜めｙ型割れ試験は低水素溶材を用いて室温で行った。この斜めｙ型割れ試験結果に示される◎は割れ無し、×は割れ有りを表す。 Incidentally, in the tensile test for measuring the yield stress YS and tensile strength TS of the base material, a JIS No. 4 test piece was used, and the low temperature toughness was measured based on the JIS No. 4 V notch Charpy test. The oblique y-type crack test was performed at room temperature using a low hydrogen melt. In this oblique y-type crack test result, ◎ indicates no crack and x indicates crack.
その結果、上記比較鋼Ａ１〜Ｔ３は、全て溶接部靭性が１００Ｊ以下まで悪化し、中にはｙ型割れ試験結果において割れが発生する供試鋼もあった。 As a result, all of the comparative steels A1 to T3 deteriorated in weld joint toughness to 100 J or less, and some of the test steels had cracks in the y-type crack test results.
また、番号２の比較鋼は発明鋼Ａと、番号５、６の比較鋼は発明鋼Ｃと、また番号２７、２８の比較鋼は発明鋼Ｈと、また番号４７、４８の比較鋼は発明鋼Ｏと、また番号５６の比較鋼は発明鋼Ｓと、それぞれ同一の成分として構成されながらも、各製造条件における温度範囲を上述した本発明の温度範囲から逸脱させている。 The comparative steel number 2 is invention steel A, the comparison steel numbers 5 and 6 are invention steel C, the comparison steel numbers 27 and 28 are invention steel H, and the comparison steel numbers 47 and 48 are inventions. Although the steel O and the comparative steel number 56 are configured as the same components as the inventive steel S, the temperature ranges in the respective production conditions deviate from the above-described temperature ranges of the present invention.
番号２の比較鋼は、再加熱温度、圧延終了温度、冷却開始温度を本発明の温度範囲よりも低めに設定しているが、その結果、溶接部靭性が悪化してしまうことが示されている。番号５、４７の比較鋼は、冷却開始温度のみを、番号６、４８の比較鋼は、圧延終了温度並びに冷却開始温度を、それぞれ低めに設定しているが、その結果、溶接部靭性を悪化することに加え、さらに母材特性も劣化してしまうことが示されている。番号２７、２８、５６の比較鋼は、焼戻し温度を７００℃よりも高く設定しているが、その結果、焼戻しによる靭性向上を図ることができない旨が示されている。 In the comparative steel of No. 2, the reheating temperature, the rolling end temperature, and the cooling start temperature are set lower than the temperature range of the present invention. As a result, it is shown that the weld toughness deteriorates. Yes. The comparative steels of Nos. 5 and 47 set the cooling start temperature only, and the comparative steels of Nos. 6 and 48 set the rolling end temperature and the cooling start temperature lower, respectively. In addition to this, it is shown that the base material characteristics are further deteriorated. The comparative steels of Nos. 27, 28 and 56 have tempering temperatures set higher than 700 ° C., but as a result, it is shown that the toughness cannot be improved by tempering.
このような比較鋼の実験結果から、上述した知見を確認することができ、また上述した成分限定の根拠を裏付けることが可能となる。 From the experimental results of such comparative steel, the above-described knowledge can be confirmed, and the basis for the above-mentioned component limitation can be supported.
Claims (3)
Ｃ ：０．０００２〜０．１５％、
Ｓｉ：０．０１〜２％、
Ｍｎ：２〜５％、
Ｂ≦０．０００３％、
Ａｌ：０．０００１〜０．１％、
Ｎ ：０．０００１〜０．０１％、
Ｎｂ：０．０００１〜０．１％
を含有し、
さらにＣｕ：０．００１〜３％、
Ｎｉ：０．００１〜１％、
Ｃｒ：０．００１〜３％、
Ｍｏ：０．００１〜３％、
Ｖ ：０．０００１〜０．２％、
Ｔｉ：０．０００１〜０．２％、
ＲＥＭ：０．０００１〜０．１％、
Ｍｇ：０．０００１〜０．０２％、
Ｃａ：０．０００１〜０．０２％
からなる群より選ばれた１種又は２種以上の成分を含有し、かつ
Ｐｃｍ＝Ｃ％＋Ｓｉ％／３０＋Ｍｎ％／２０＋Ｃｕ％／２０＋Ｎｉ％／３０
＋Ｃｒ％／２０＋Ｍｏ％／１５＋Ｖ％／１０＋５Ｂ％≦０．２５％
を満たし、残部Ｆｅおよび不可避的不純物からなる鋼を鋳造し、
室温まで冷却することなくそのまま、または一度室温まで冷却し、
９５０〜１２５０℃に再加熱し、Ａｒ3点以上の温度で圧延を終了し、かつ、Ａｒ3点以上の温度から室温〜６５０℃の温度域に強制冷却することを特徴とする、引張強さ５７０Ｎ／ｍｍ2以上の、耐溶接割れ性に優れた高張力鋼の製造方法。 % By mass
C: 0.0002 to 0.15%,
Si: 0.01-2%
Mn: 2 to 5%
B ≦ 0.0003%,
Al: 0.0001 to 0.1%,
N: 0.0001~0.01%,
Nb: 0.0001 to 0.1%
Containing
Furthermore, Cu: 0.001 to 3%,
Ni: 0.001 to 1%,
Cr: 0.001 to 3%,
Mo: 0.001 to 3%,
V: 0.0001 to 0.2 %,
Ti: 0.0001 to 0.2%,
REM: 0.0001 to 0.1%,
Mg: 0.0001 to 0.02%,
Ca: 0.0001 to 0.02%
And one or more components selected from the group consisting of: Pcm = C% + Si% / 30 + Mn% / 20 + Cu% / 20 + Ni% / 30
+ Cr% / 20 + Mo% / 15 + V% / 10 + 5B% ≦ 0.25%
And casting the steel consisting of the balance Fe and inevitable impurities,
Without cooling to room temperature, or once cooled to room temperature,
Reheated to: 950 ° C., and ends the rolling at Ar 3 point or more temperature, and characterized by forced cooling from Ar 3 point or more temperature to a temperature range of room temperature to 650 ° C., the tensile strength A method for producing high-tensile steel having an excellent weld crack resistance of 570 N / mm 2 or more.
Ｚｒ：０．０００１〜０．３％、
Ｔａ：０．０００１〜０．３％、
Ｈｆ：０．０００１〜０．３％
の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に記載の耐溶接割れ性に優れた高張力鋼の製造方法。 Furthermore, in mass%,
Zr: 0.0001 to 0.3%,
Ta: 0.0001 to 0.3%,
Hf: 0.0001 to 0.3%
1 or 2 types or more of these are contained, The manufacturing method of the high tensile steel excellent in the weld crack resistance of Claim 1 characterized by the above-mentioned.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2005308535A JP4926447B2 (en) | 2005-05-13 | 2005-10-24 | Manufacturing method of high strength steel with excellent weld crack resistance |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2005140758 | 2005-05-13 | ||
| JP2005140758 | 2005-05-13 | ||
| JP2005308535A JP4926447B2 (en) | 2005-05-13 | 2005-10-24 | Manufacturing method of high strength steel with excellent weld crack resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2006342421A JP2006342421A (en) | 2006-12-21 |
| JP4926447B2 true JP4926447B2 (en) | 2012-05-09 |
Family
ID=37639594
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2005308535A Active JP4926447B2 (en) | 2005-05-13 | 2005-10-24 | Manufacturing method of high strength steel with excellent weld crack resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4926447B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101505292B1 (en) | 2013-05-31 | 2015-03-31 | 현대제철 주식회사 | High strength steel and manufacturing method of the same |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5194571B2 (en) * | 2007-06-07 | 2013-05-08 | 新日鐵住金株式会社 | Method for producing high-strength steel excellent in weld crack sensitivity with tensile strength of 570 N / mm2 or higher |
| JP4358898B1 (en) | 2008-04-01 | 2009-11-04 | 新日本製鐵株式会社 | Method for producing high-tensile thick steel plate having a tensile strength of 780 MPa or more, excellent in weldability and joint low-temperature toughness |
| BRPI0907853B1 (en) * | 2008-10-23 | 2018-02-06 | Nippon Steel & Sumitomo Metal Corporation | THICK BITOLA STEEL SHEET WITH A TRACE RESISTANCE OF 780 MPA OR MORE |
| JP5354164B2 (en) * | 2008-12-09 | 2013-11-27 | Ｊｆｅスチール株式会社 | Low yield ratio high strength thick steel plate and method for producing the same |
| JP5407987B2 (en) * | 2010-03-30 | 2014-02-05 | Ｊｆｅスチール株式会社 | Method for detecting longitudinal cracks in slabs |
| JP5874402B2 (en) * | 2012-01-10 | 2016-03-02 | Ｊｆｅスチール株式会社 | Welded steel pipe excellent in weld crack resistance and slurry corrosion wear resistance and method for producing the same |
| CN103586304B (en) * | 2013-11-11 | 2015-12-02 | 沈阳工业大学 | A kind of preparation method of magnesium aluminum composite board |
| CN110586648B (en) * | 2019-09-06 | 2021-04-02 | 鞍钢股份有限公司 | Anti-weld crack rolling method for high-carbon equivalent composite blank |
| CN113667888B (en) * | 2021-07-14 | 2023-03-28 | 武汉钢铁有限公司 | 690 MPa-grade low-silicon corrosion-resistant bridge steel and preparation method thereof |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01176030A (en) * | 1987-12-28 | 1989-07-12 | Kobe Steel Ltd | Manufacture of high-tensile steel plate with low yield ratio by accelerated cooling method |
| JP3817887B2 (en) * | 1997-02-25 | 2006-09-06 | 住友金属工業株式会社 | High toughness high strength steel and method for producing the same |
| JP2002146471A (en) * | 2000-11-07 | 2002-05-22 | Nippon Steel Corp | Ultrahigh strength steel plate and ultrahigh strength steel pipe each having excellent toughness at low temperature and toughness in heat-affected zone, and their manufacturing method |
| JP4507708B2 (en) * | 2003-06-12 | 2010-07-21 | Ｊｆｅスチール株式会社 | Low yield ratio high strength high toughness steel sheet manufacturing method |
| JP4066905B2 (en) * | 2003-07-31 | 2008-03-26 | Ｊｆｅスチール株式会社 | Manufacturing method of low yield ratio high strength high toughness steel sheet with excellent weld heat affected zone toughness |
-
2005
- 2005-10-24 JP JP2005308535A patent/JP4926447B2/en active Active
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101505292B1 (en) | 2013-05-31 | 2015-03-31 | 현대제철 주식회사 | High strength steel and manufacturing method of the same |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2006342421A (en) | 2006-12-21 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4926447B2 (en) | Manufacturing method of high strength steel with excellent weld crack resistance | |
| 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 | |
| JP5659758B2 (en) | TMCP-Temper type high-strength steel sheet with excellent drop weight characteristics after PWHT that combines excellent productivity and weldability | |
| JPWO2006009299A1 (en) | Welded structural steel excellent in low temperature toughness of heat affected zone and its manufacturing method | |
| JP5194572B2 (en) | Method for producing high-tensile steel material with excellent weld crack resistance | |
| JP2008075107A (en) | Method for manufacturing high-strength/high-toughness steel | |
| JPH10306316A (en) | Production of low yield ratio high tensile-strength steel excellent in low temperature toughness | |
| JP3864536B2 (en) | High strength steel with excellent delayed fracture resistance and method for producing the same | |
| JP4096839B2 (en) | Manufacturing method of high yield thick steel plate with low yield ratio and excellent toughness of heat affected zone | |
| JP7411072B2 (en) | High-strength, extra-thick steel material with excellent low-temperature impact toughness and method for producing the same | |
| JP5130472B2 (en) | Method for producing high-tensile steel material with excellent weld crack resistance | |
| JP4507669B2 (en) | Manufacturing method of low yield ratio steel for low temperature with excellent weld toughness | |
| JP4770415B2 (en) | High tensile steel plate excellent in weldability and method for producing the same | |
| KR20150050701A (en) | Oil tubular country goods and method of manufacturing the same | |
| JP6277679B2 (en) | High-tensile steel plate with excellent gas cut cracking resistance and high heat input weld toughness | |
| JP4133175B2 (en) | Non-water cooled thin low yield ratio high strength steel with excellent toughness and method for producing the same | |
| JP2006241510A (en) | Steel for high strength welded structure having excellent low temperature toughness in high heat input weld haz and its production method | |
| JP2002363685A (en) | Low yield ratio high strength cold rolled steel sheet | |
| JPH11131177A (en) | Steel plate for medium-or ordinary-temperature pressure vessel, capable of omitting post weld heat treatment, and its production | |
| JP4264296B2 (en) | Low yield ratio 570 MPa class high strength steel with excellent weld toughness and slitting characteristics and method for producing the same | |
| JP5194571B2 (en) | Method for producing high-strength steel excellent in weld crack sensitivity with tensile strength of 570 N / mm2 or higher | |
| JP4105990B2 (en) | High strength welded structural steel with excellent low temperature toughness of large heat input weld HAZ and method for producing the same | |
| JP4250113B2 (en) | Steel plate manufacturing method with excellent earthquake resistance and weldability | |
| JP5151510B2 (en) | Manufacturing method of high strength steel with excellent low temperature toughness and crack propagation stop properties | |
| JP4742597B2 (en) | Production method of non-tempered high strength steel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20080306 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20101110 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20101221 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20110221 |
|
| A02 | Decision of refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A02 Effective date: 20110823 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20111122 |
|
| A911 | Transfer of reconsideration by examiner before appeal (zenchi) |
Free format text: JAPANESE INTERMEDIATE CODE: A911 Effective date: 20111206 |
|
| 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: 20120131 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20120208 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150217 Year of fee payment: 3 |
|
| R151 | Written notification of patent or utility model registration |
Ref document number: 4926447 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R151 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150217 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150217 Year of fee payment: 3 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150217 Year of fee payment: 3 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| 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 |