JP2005097694A - Method for manufacturing non-heat-treated high-strength thick steel plate superior in brittle crack arrestability - Google Patents

Method for manufacturing non-heat-treated high-strength thick steel plate superior in brittle crack arrestability Download PDF

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JP2005097694A
JP2005097694A JP2003334755A JP2003334755A JP2005097694A JP 2005097694 A JP2005097694 A JP 2005097694A JP 2003334755 A JP2003334755 A JP 2003334755A JP 2003334755 A JP2003334755 A JP 2003334755A JP 2005097694 A JP2005097694 A JP 2005097694A
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brittle crack
strength
steel plate
rolling
thick steel
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Kimihiro Nishimura
公宏 西村
Akio Omori
章夫 大森
Toshiyuki Hoshino
俊幸 星野
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JFE Steel Corp
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JFE Steel Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-heat-treated high-strength thick steel plate having a high tensile strength of 700 MPa or higher together with a superior brittle crack arrestability. <P>SOLUTION: A base steel material has a composition comprising, by mass%, 0.005-0.03% C, 0.05-0.5% Si, 1.3-3.0% Mn, 0.01-0.08% Al, 0.005-0.05% Ti, 0.005-0.060% Nb, 0.0015-0.0040% B, 0.05% or less P, and 0.0050% or less S and the balance Fe with unavoidable impurities. The method for manufacturing a thick steel plate comprises heating the base material to 1,000 to 1,300°C, then hot-rolling it in conditions of a cumulative rolling reduction in an austenitic non-recrystallizing region of 60% or higher and a rolling termination temperature of 700 to 850°C, and then cooling it to 450°C or lower at a cooling rate of 10°C/s or higher. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、特に船舶、橋梁、建築物、建築機械、産業機械、海洋構造物およびペンストック等に用いて好適な、引張強さが 700 MPa以上の高強度を有し、かつ脆性亀裂伝播停止性能に優れた非調質厚鋼板の製造方法に関するものである。   The present invention is particularly suitable for use in ships, bridges, buildings, construction machinery, industrial machinery, offshore structures, penstock, etc., and has a high tensile strength of 700 MPa or more and stops brittle crack propagation. The present invention relates to a method for producing a non-tempered thick steel plate having excellent performance.

船舶、海洋構造物、低温貯蔵タンク、ラインパイプおよび土木・建築等の分野の溶接構造物に使用される鋼材は、高い靱性を備えることが必要とされ、TMCP法(Thermo-Mechanical Control Process )に代表される技術によって優れた靱性を有する鋼材が製造されている。また、実際の構造物においては、予想しない施工上の欠陥や腐食、地震および衝突による変形などにより、脆性破壊が発生する可能性を完全に払拭することは不可能であるため、脆性破壊が発生したときに亀裂の進展を停止する能力(脆性亀裂伝播停止性能)が要求される。さらに、実際の構造物における脆性亀裂は、ある程度の塑性変形の後に発生することが想定されることから、鋼材に予歪を与えた後にも優れた脆性亀裂伝播停止性能を保持することが望まれる。   Steel materials used in ships, offshore structures, cold storage tanks, line pipes and welded structures in the fields of civil engineering and construction are required to have high toughness, and TMCP method (Thermo-Mechanical Control Process) A steel material having excellent toughness is manufactured by a representative technique. In actual structures, brittle fractures occur because it is impossible to completely eliminate the possibility of brittle fractures due to unexpected construction defects, corrosion, deformation due to earthquakes and collisions, etc. Therefore, the ability to stop the growth of cracks (brittle crack propagation stopping performance) is required. Furthermore, since brittle cracks in actual structures are assumed to occur after a certain degree of plastic deformation, it is desirable to maintain excellent brittle crack propagation stopping performance even after pre-straining the steel material. .

従来から、特に船舶、海洋構造物およびラインパイプなどの分野では、脆性亀裂伝播停止性能が重要な材料特性として注目されてきた。
例えば、特許文献1には、(α+γ)2相域圧延を行うことによって、フェライト−パーライト組織の徹底した微細化を図ると共に、加工フェライトによるセパレーションの効果によって、脆性亀裂伝播抵抗を向上させる技術が提示されている。しかしながら、2相域圧延を用いる本技術では、低温での圧延が不可欠なため、生産能率が低下したり、フェライト域での加工に起因したシャルピー吸収エネルギーの極端な低下といった問題があった。また、この技術は、フェライト−パーライトを基本組織とする技術であるため、490MPa (50 kgf/mm2)程度までの引張強度レベルの鋼材にしか適用できなかった。
Conventionally, brittle crack propagation stopping performance has attracted attention as an important material property, particularly in the fields of ships, offshore structures and line pipes.
For example, Patent Document 1 discloses a technique for thoroughly reducing the ferrite-pearlite structure by performing (α + γ) two-phase region rolling and improving brittle crack propagation resistance by the effect of separation by processed ferrite. Presented. However, in this technique using two-phase region rolling, rolling at a low temperature is indispensable, so that there is a problem that production efficiency is lowered and Charpy absorbed energy is extremely lowered due to processing in the ferrite region. Further, since this technology is a technology having ferrite-pearlite as a basic structure, it could be applied only to steel materials having a tensile strength level of up to about 490 MPa (50 kgf / mm 2 ).

また、特許文献2には、鋼板の表層部のフェライト粒径を3μm 未満にまで微細化することによって、脆性亀裂伝播停止性能を向上させる技術が示されている。この方法は、板厚方向の温度分布が冷却中に不均一になることを利用して、鋼板表層部のみを改質するものである。従って、必然的に板厚方向の材質が不均一になることに加え、鋼材間のばらつきを抑えて安定した特性を維持するには、非常に高精度の温度制御が要求されるため、大量生産に際しては様々な困難が予想される。また、鋼材の成分や圧延方法にも、様々な制約があると考えられる。
さらに、脆性亀裂伝播停止性能の向上を達成する上で、フェライト結晶粒の細粒化を利用する技術は、原理的に高強度化が困難である。つまり、高強度化のためには合金成分を添加して炭素当量を上げる必要であるが、これにより熱間圧延中にフェライトが生成し難くなるので、その細粒化を図るというプロセスに相反するのである。
Patent Document 2 discloses a technique for improving brittle crack propagation stopping performance by refining the ferrite grain size of the surface layer portion of the steel sheet to less than 3 μm. This method uses only the fact that the temperature distribution in the plate thickness direction becomes non-uniform during cooling, and modifies only the surface layer portion of the steel plate. Therefore, in addition to inevitably non-uniform material in the plate thickness direction, very high temperature control is required to maintain stable characteristics by suppressing variations between steel materials. At that time, various difficulties are expected. Moreover, it is thought that there are various restrictions also on the component of steel materials and the rolling method.
Furthermore, in order to achieve improvement in brittle crack propagation stopping performance, it is difficult in principle to increase the strength of the technology using the finer ferrite crystal grains. In other words, in order to increase the strength, it is necessary to add an alloy component to increase the carbon equivalent, but this makes it difficult for ferrite to form during hot rolling, which contradicts the process of reducing the grain size. It is.

その他、特許文献3には、圧延中の鋼材温度の極端に精密な制御を必要とせずに、鋼材表面と内部の特性差あるいは鋼材間の材質のばらつきを少なくしながら、塑性変形後の脆性亀裂伝播停止性能に優れた鋼材を製造する方法として、鋼材全体を極低炭素ベイナイト組織とし、圧延条件によってその集合組織を制御して脆性亀裂伝播停止性能の向上を図る方法が提案されている。
しかしながら、この技術では、高強度化については何ら検討がなされていない。
In addition, Patent Document 3 discloses a brittle crack after plastic deformation while reducing the difference in characteristics between the steel surface and the interior or the material variation between the steel materials without requiring extremely precise control of the steel material temperature during rolling. As a method for producing a steel material having excellent propagation stop performance, a method has been proposed in which the entire steel material has an extremely low carbon bainite structure and the texture is controlled by rolling conditions to improve brittle crack propagation stop performance.
However, this technique has not been studied at all for increasing the strength.

この点、高強度と脆性亀裂伝播停止性能を両立させた技術として、特許文献4に開示された技術がある。しかしながら、この技術では、表層のみを冷却した状態で、復熱前に10%以上の圧延を施す必要があるため、不可避的に低温での圧延が必要となり、その結果生産能率が低下するという問題がある。   In this regard, there is a technique disclosed in Patent Document 4 as a technique that achieves both high strength and brittle crack propagation stopping performance. However, with this technique, it is necessary to perform rolling of 10% or more before reheating in a state where only the surface layer is cooled, so inevitably rolling at a low temperature is required, resulting in a decrease in production efficiency. There is.

特開昭55−148746号公報JP 55-148746 特開平5−148542号公報JP-A-5-148542 特開2002−241891号公報JP 2002-241891 A 特開2000−336428号公報JP 2000-336428 A

本発明は、上記の現状に鑑み開発されたもので、生産性の低下を招いたり、製造上の制約を受けることなしに、引張強さが 700 MPa以上の高強度と、優れた脆性亀裂伝播停止性能を兼ね備える非調質高強度厚鋼板の有利な製造方法を提案することを目的とする。
本発明において、引張強さの目標値を 700 MPa以上としたのは、近年、鋼構建造物の軽量化や施工コストの低減という要望に応えるために、鋼材の高強度化が求められているからである。
The present invention has been developed in view of the above-mentioned present situation, and has high tensile strength of 700 MPa or more and excellent brittle crack propagation without causing a drop in productivity or being restricted by manufacturing. It aims at proposing the advantageous manufacturing method of the non-tempered high strength thick steel plate which has stop performance.
In the present invention, the target value of the tensile strength is set to 700 MPa or more because, in recent years, in order to meet the demand for weight reduction of steel structures and reduction of construction costs, higher strength of steel materials is required. It is.

さて、発明者らは、上記した引張強さが 700 MPa以上の高強度と優れた脆性亀裂伝播停止性能の両立という課題を達成すべく、鋼材の成分組成および製造条件とくに熱間圧延条件について詳細な検討を行った。
その結果、鋼材に含有されるC量を0.03mass%以下に制限し、かつ他の合金成分を適正化した鋼素材に、オーステナイト未再結晶域で強加工を加えた上で、加速冷却を用いて、ミクロ組成をベイナイト単相組織とすることが、極めて有効であることの新規知見を得た。
Now, in order to achieve the problem of achieving both the above-mentioned high strength of 700 MPa or more and excellent brittle crack propagation stopping performance, the inventors have detailed the composition of steel materials and production conditions, particularly hot rolling conditions. The examination was done.
As a result, the amount of C contained in the steel is limited to 0.03 mass% or less, and the steel material with other alloy components optimized is subjected to strong processing in the austenite non-recrystallized region, and then accelerated cooling is used. Thus, the present inventors have obtained new knowledge that it is extremely effective to make the microcomposition a bainite single phase structure.

すなわち、従来の技術では、胞性亀裂伝播停止性能を向上させるためにフェライト粒の細粒化を利用していたが、発明者らの研究によれば、鋼材のC量を低減し、ひずみが蓄積されたオーステナイトから変態させたベイナイト単相組織とすることにより、引張強さが700 MPa 以上の高強度と共に、優れた脆性亀裂伝播停止性能が併せて得られることが新たに究明されたのである。
本発明は、上記の知見に基づき、さらに研究を重ねた末に完成されたものである。
That is, in the prior art, the refinement of ferrite grains was used to improve the performance of stopping cystic crack propagation, but according to the study by the inventors, the amount of C in the steel material was reduced and strain was accumulated. It was newly discovered that by using a bainite single phase structure transformed from the austenite formed, a high strength of 700 MPa or more and an excellent brittle crack propagation stopping performance can be obtained together.
The present invention has been completed after further research based on the above findings.

すなわち、本発明の要旨構成は次のとおりである。
1.質量%で
C:0.005 〜0.03%、
Si:0.05〜0.5 %、
Mn:1.3 〜3.0 %、
Al:0.01〜0.08%、
Ti:0.005 〜0.05%、
Nb:0.005 〜0.060 %、
B:0.0015〜0.0040%、
P:0.05%以下および
S:0.0050%以下
を含有し、残部がFeおよび不可避的不純物の組成になる鋼素材を、1000〜1300℃に加熱後、オーステナイト未再結晶域での累積圧下率:60%以上、圧延終了温度:700 〜850 ℃の条件で熱間圧延を施し、熱間圧延終了後、冷却速度:10℃/s以上で冷却し、冷却停止温度を 450℃以下とすることを特徴とする、引張強さが 700 MPa以上の脆性亀裂伝播停止性能に優れた非調質高強度厚鋼板の製造方法。
That is, the gist configuration of the present invention is as follows.
1. In mass% C: 0.005 to 0.03%,
Si: 0.05 to 0.5%,
Mn: 1.3-3.0%,
Al: 0.01-0.08%,
Ti: 0.005 to 0.05%,
Nb: 0.005 to 0.060%,
B: 0.0015-0.0040%,
P: 0.05% or less and S: 0.0050% or less, the steel material having the balance of Fe and inevitable impurities is heated to 1000-1300 ° C, and the cumulative reduction ratio in the austenite non-recrystallized region: 60 %, At the end of rolling: 700 to 850 ℃, hot rolling is performed, and after the end of hot rolling, the cooling rate is 10 ℃ / s or more, and the cooling stop temperature is 450 ℃ or less. A method for producing a non-tempered high-strength thick steel plate with excellent tensile strength and brittle crack propagation stopping performance of 700 MPa or more.

2.上記1において、鋼素材が、質量%でさらに
Cu:0.05〜2.0 %、
Ni:0.05〜2.0 %、
Cr:0.05〜2.0 %、
Mo:0.05〜1.0 %、
V:0.003 〜0.08%、
Ca:0.0003〜0.0030%、
REM:0.0003〜0.010 %および
Mg:0.0003〜0.005 %
のうちから選んだ1種または2種以上を含有する組成になることを特徴とする、引張強さが 700 MPa以上の脆性亀裂伝播停止性能に優れた非調質高強度厚鋼板の製造方法。
2. In 1 above, the steel material is further mass%.
Cu: 0.05-2.0%,
Ni: 0.05-2.0%,
Cr: 0.05-2.0%,
Mo: 0.05-1.0%,
V: 0.003 to 0.08%,
Ca: 0.0003 to 0.0030%,
REM: 0.0003-0.010% and
Mg: 0.0003 to 0.005%
A method for producing a non-tempered high-strength thick steel plate excellent in brittle crack propagation stopping performance having a tensile strength of 700 MPa or more, characterized in that the composition contains one or more selected from among them.

本発明によれば、引張強さが 700 MPa以上の高強度と、優れた脆性亀裂伝播停止性能とを兼ね備える非調質高強度厚鋼板を、生産性の低下を招いたり、製造上の制約を受けることなしに、安定して製造することができる。   According to the present invention, a non-heat treated high-strength thick steel plate having a high strength with a tensile strength of 700 MPa or more and an excellent brittle crack propagation stopping performance can be caused by a decrease in productivity or manufacturing restrictions. It can be manufactured stably without receiving.

以下、本発明を具体的に説明する。
まず、本発明において、鋼素材の成分組成を上記の範囲に限定した理由について説明する。なお、成分に関する「%」表示は特に断らない限り質量%を意味するものとする。
C:0.005 〜0.03%
Cは、鋼の強度を増加させる有用元素であり、本発明では所定の強度を確保するために0.005 %以上の含有を必要とするが、0.03%を超えて含有させると靱性が劣化し易くなるので、Cは 0.005〜0.03%の範囲に限定した。好ましくは 0.015〜0.025 %の範囲である。
The present invention will be specifically described below.
First, the reason why the component composition of the steel material is limited to the above range in the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.005 to 0.03%
C is a useful element that increases the strength of steel. In the present invention, it is necessary to contain 0.005% or more in order to ensure a predetermined strength, but if it exceeds 0.03%, the toughness tends to deteriorate. Therefore, C is limited to the range of 0.005 to 0.03%. Preferably it is 0.015 to 0.025% of range.

Si:0.05〜0.5 %
Siは、脱酸剤として有用な元素であり、本発明では製鋼上、少なくとも0.05%のSiの含有を必要とするが、0.5 %を超えて含有させると、かえって靱性の劣化を招くため、Siは0.05〜0.5 %の範囲に限定した。好ましくは0.20〜0.35%の範囲である。
Si: 0.05-0.5%
Si is an element useful as a deoxidizer, and in the present invention, it is necessary to contain at least 0.05% of Si in steelmaking. However, if it exceeds 0.5%, the toughness is deteriorated. Was limited to the range of 0.05-0.5%. Preferably it is 0.20 to 0.35% of range.

Mn:1.3 〜3.0 %
Mnは、鋼の強度を増加させる元素であり、母材の引張強さを 700 MPa以上とするためには、少なくとも 1.3%の含有を必要とする。一方、3.0 %を超える含有は、母材の靱性を劣化させ、ひいては脆性亀裂伝播停止性能を劣化させるので、Mnは 1.3〜3.0 %の範囲に限定した。
Mn: 1.3 to 3.0%
Mn is an element that increases the strength of steel. To make the tensile strength of the base metal 700 MPa or more, it must contain at least 1.3%. On the other hand, if the content exceeds 3.0%, the toughness of the base metal is deteriorated and, consequently, the brittle crack propagation stopping performance is deteriorated, so Mn is limited to the range of 1.3 to 3.0%.

Al:0.01〜0.08%
Alは、脱酸剤として作用し、このためには少なくとも0.01%の含有を必要とするが、含有量が0.08%を超えると、母材の靱性を劣化させるだけでなく、溶接金属郡への希釈によって溶接金属部の靱性も劣化させるため、Alは0.01〜0.08%の範囲に限定した。好ましくは0.02〜0.04%の範囲である。
Al: 0.01-0.08%
Al acts as a deoxidizer and for this purpose it needs to contain at least 0.01%, but if the content exceeds 0.08%, it not only degrades the toughness of the base metal, but also contributes to the weld metal county. Since the toughness of the weld metal part is also deteriorated by dilution, Al is limited to the range of 0.01 to 0.08%. Preferably it is 0.02 to 0.04% of range.

Ti:0.005 〜0.05%
Tiは、TiNを形成して鋼中のNを固定することにより、Bの効果を有効に発揮させる有用元素である。また、スラブ加熱時や溶接熱影響部でのオーステナイト粒成長を抑制して組織を微細化する効果もある。これらの効果を十分に発揮させるためには 0.005%以上の含有を必要とするが、0.05%を超えて含有させると母材の靱性が劣化するので、Tiは 0.005〜0.05%の範囲に限定した。好ましくは 0.008〜0.02%の範囲である。
Ti: 0.005 to 0.05%
Ti is a useful element that effectively exhibits the effect of B by forming TiN and fixing N in the steel. In addition, there is also an effect of refining the structure by suppressing austenite grain growth at the time of slab heating or at the weld heat affected zone. In order to fully exhibit these effects, 0.005% or more is required, but if it exceeds 0.05%, the toughness of the base material deteriorates, so Ti was limited to the range of 0.005 to 0.05%. . Preferably it is 0.008 to 0.02% of range.

Nb:0.005 〜0.060 %
Nbは、焼入れ性を向上させて鋼の強度を高める元素であり、母材の高強度化に有効に作用する。また、オーステナイト未再結晶域を拡大させる作用を持ち、母材靱性の向上および脆性亀裂伝播停止性能の向上に有効に作用する。この効果を得るためには、0.005 %以上の含有を必要とするが、含有量が 0.060%を超えると、靱性に悪影響を与えるため、Nbは 0.005〜0.060 %の範囲に限定した。好ましくは 0.020〜0.040 %の範囲である。
Nb: 0.005 to 0.060%
Nb is an element that improves the hardenability and increases the strength of the steel, and effectively acts to increase the strength of the base material. Moreover, it has the effect | action which expands an austenite non-recrystallized area and acts effectively in the improvement of a base material toughness, and the improvement of a brittle crack propagation stop performance. In order to obtain this effect, 0.005% or more must be contained, but if the content exceeds 0.060%, the toughness is adversely affected, so Nb is limited to a range of 0.005 to 0.060%. Preferably it is 0.020 to 0.040% of range.

B:0.0015〜0.0040%
Bは、微量の添加によって旧オーステナイト粒界エネルギーを減少させ、フェライトの核生成を抑制するのに有効に寄与する。この効果を発現させるには、0.0015%以上の添加が必要であるが、0.0040%を超えると母材の靱性を劣化させるので、Bは0.0015〜0.0040%の範囲に限定した。好ましくは0.0015〜0.0025%である。
B: 0.0015-0.0040%
B contributes effectively in reducing the prior austenite grain boundary energy and suppressing the nucleation of ferrite by adding a small amount. In order to exhibit this effect, 0.0015% or more of addition is necessary, but when it exceeds 0.0040%, the toughness of the base material is deteriorated, so B is limited to a range of 0.0015 to 0.0040%. Preferably it is 0.0015 to 0.0025%.

P:0.05%以下、S:0.0050%以下
Pは、含有量が0.05%を超えると溶接部の靱性を劣化させるので、0.05%以下に抑制するものとする。
同じく、Sも、0.0050%を超えると母材および溶接部の靱性を劣化させるので、0.0050%以下に抑制するものとする。
P: 0.05% or less, S: 0.0050% or less P, if the content exceeds 0.05%, deteriorates the toughness of the welded portion, so it should be suppressed to 0.05% or less.
Similarly, if S exceeds 0.0050%, the toughness of the base metal and the welded portion is deteriorated, so that S is suppressed to 0.0050% or less.

以上、基本成分について説明したが、本発明ではその他にも、鋼の強度改善成分として、以下に述べる元素を適宜含有させることができる。
Cu:0.05〜2.0 %
Cuは、固溶強化および析出強化によって鋼の強度を上昇させる有用元素である。本発明では、含有させる場合には、0.05%以上とすることが好ましいが、2.0 %を超えて含有させると靱性の劣化を招くので、Cuは0.05〜2.0 %の範囲で含有させることが好ましい。
Although the basic components have been described above, in the present invention, the following elements can be appropriately contained as other steel strength improving components.
Cu: 0.05-2.0%
Cu is a useful element that increases the strength of steel by solid solution strengthening and precipitation strengthening. In the present invention, when it is contained, it is preferably 0.05% or more. However, if it exceeds 2.0%, toughness is deteriorated, so Cu is preferably contained in the range of 0.05 to 2.0%.

Ni:0.05〜2.0 %
Niは、母材靱性を保ちつつ強度を増加できる有用元素である。本発明では、含有させる場合には、0.05%以上とすることが好ましいが、2.0 %を超えて含有させてもその効果は飽和し、含有量に見合う効果が期待できなくなるだけでなく、コスト的にも不利となるので、Niは0.05〜2.0 %程度とするのが好ましい。
Ni: 0.05-2.0%
Ni is a useful element that can increase strength while maintaining base material toughness. In the present invention, when it is included, it is preferably 0.05% or more, but even if it exceeds 2.0%, the effect is saturated, and not only an effect commensurate with the content can not be expected, but also in terms of cost Therefore, Ni is preferably set to about 0.05 to 2.0%.

Cr:0.05〜2.0 %
Crは、鋼の強度を上昇させる有用元素である。本発明では、含有させる場合には、0.05%以上とすることが好ましいが、2.0 %を超えて含有させると靱性が劣化するので、Crは0.05〜2.0 %の範囲で含有させることが好ましい。
Cr: 0.05-2.0%
Cr is a useful element that increases the strength of steel. In the present invention, when it is contained, it is preferably 0.05% or more, but if it exceeds 2.0%, the toughness deteriorates, so Cr is preferably contained in the range of 0.05 to 2.0%.

Mo:0.05〜1.0 %
Moは、少量の添加によって鋼の強度を向上させる有用元素である。本発明では、含有させる場合には、0.05%以上とすることが好ましいが、1.0 %を超えて含有させると溶接部靱性の劣化を招くので、Moは0.05〜1.0 %の範囲で含有させることが好ましい。
Mo: 0.05-1.0%
Mo is a useful element that improves the strength of steel by adding a small amount. In the present invention, when it is included, it is preferably 0.05% or more. However, if it exceeds 1.0%, the toughness of the welded portion is deteriorated, so Mo should be included in the range of 0.05 to 1.0%. preferable.

V:0.003 〜0.08%
Vは、V(C,N) として析出し、この析出強化により強度上昇に有効に寄与する元素である。しかしながら、含有量が 0.003%に満たないとその添加効果に乏しく、一方0.08%を超えて含有されると、靱性が低下するので、Vは 0.003〜0.08%の範囲で含有させることが好ましい。
V: 0.003 to 0.08%
V is an element which precipitates as V (C, N) and contributes effectively to an increase in strength by this precipitation strengthening. However, if the content is less than 0.003%, the effect of addition is poor. On the other hand, if the content exceeds 0.08%, the toughness decreases, so V is preferably contained in the range of 0.003 to 0.08%.

Ca:0.0003〜0.0030%
Caは、介在物の形態制御により、S,Oと適正にバランスさせることによってHAZ 靱性を向上させる有用元素である。しかしながら、含有量が0.0003%に満たないとその添加効果に乏しく、一方0.0030%を超えて含有させてもその効果は飽和するので、Caは0.0003〜0.0030%の範囲で含有させることが好ましい。
Ca: 0.0003 to 0.0030%
Ca is a useful element that improves HAZ toughness by appropriately balancing S and O by controlling the form of inclusions. However, if the content is less than 0.0003%, the effect of addition is poor. On the other hand, even if the content exceeds 0.0030%, the effect is saturated, so Ca is preferably contained in the range of 0.0003 to 0.0030%.

REM : 0.0003〜0.010 %
REM は、REM(O,S)を形成して HAZ靱性を向上させる有用元素である。この効果は、含有量が0.0003%以上で認められるが、0.010 %を超えて含有させてもその効果は飽和するので、REM は0.0003〜0.010 %の範囲で含有させることが好ましい。
REM: 0.0003 to 0.010%
REM is a useful element that improves the HAZ toughness by forming REM (O, S). This effect is recognized when the content is 0.0003% or more, but even if the content exceeds 0.010%, the effect is saturated. Therefore, REM is preferably contained in the range of 0.0003 to 0.010%.

Mg:0.0003〜0.005 %
Mgは、介在物を微細分散させて HAZ靱性を向上させる有用元素である。この効果は、含有量が0.0003%以上で認められるが、0.005 %を超えて含有させてもその効果は飽和するので、Mgは0.0003〜0.005 %の範囲で含有させることが好ましい。
Mg: 0.0003 to 0.005%
Mg is a useful element that improves the HAZ toughness by finely dispersing inclusions. This effect is recognized when the content is 0.0003% or more, but even if the content exceeds 0.005%, the effect is saturated. Therefore, Mg is preferably contained in the range of 0.0003 to 0.005%.

上記した成分以外の残部は、Feおよび不可避的不純物である。不可避的不純物中、特にNは0.0080%以下で許容できる。   The balance other than the above components is Fe and inevitable impurities. Among inevitable impurities, especially N is acceptable at 0.0080% or less.

次に、本発明の製造方法を具体的に説明する。
まず、上記の好適成分組成に調整した溶鋼を、転炉等の通常公知の溶製方法で溶製し、連続鋳造等の通常公知の鋳造方法で鋼素材とする。
ついで、鋼素材を、1000〜1300℃の温度に加熱し、鋼素材を完全にオーステナイト化する。ここに、加熱温度が1000℃未満では、熱間圧延温度が低すぎて圧延能率が低下する。一方、加熱温度が1300℃を超えると、結晶粒が粗大化するだけでなく、酸化ロスが顕著となり歩留りが低下する。
Next, the production method of the present invention will be specifically described.
First, the molten steel adjusted to the above preferred component composition is melted by a generally known melting method such as a converter, and is made into a steel material by a generally known casting method such as continuous casting.
Next, the steel material is heated to a temperature of 1000 to 1300 ° C., and the steel material is completely austenitic. If the heating temperature is less than 1000 ° C., the hot rolling temperature is too low and the rolling efficiency is lowered. On the other hand, when the heating temperature exceeds 1300 ° C., not only the crystal grains become coarse, but also the oxidation loss becomes remarkable and the yield decreases.

上記の加熱後、熱間圧延を行うが、本発明では、オーステナイト未再結晶域での累積圧下率を60%以上、圧延終了温度を 700〜850 ℃とすることが肝要である。
オーステナイト未再結晶域で累積圧下率が60%以上となる熱間圧延を行うことにより、単位面積(単位体積)当たりのオーステナイト結晶粒界の量を大幅に増大させることができ、かつ圧延による歪エネルギーを蓄積させることができる。これにより、オーステナイト粒界およびオーステナイト粒内からのベイナイト変態が促進される。そして、上記したオーステナイト未再結晶域での強加工によるオーステナイト粒の微細化との相乗効果により、母材靱性は向上し、また脆性亀裂伝播停止性能も向上する。
なお、本発明におけるオーステナイト未再結晶温度域は、概ね 700〜950 ℃の範囲である。
Although hot rolling is performed after the above heating, in the present invention, it is important to set the cumulative rolling reduction in the austenite non-recrystallized region to 60% or more and the rolling end temperature to 700 to 850 ° C.
By performing hot rolling in which the cumulative reduction ratio is 60% or more in the austenite non-recrystallized region, the amount of austenite grain boundaries per unit area (unit volume) can be greatly increased, and strain due to rolling can be increased. Energy can be stored. Thereby, the bainite transformation from the austenite grain boundary and the austenite grain is promoted. And, by the synergistic effect with the above-mentioned refinement of austenite grains by strong processing in the austenite non-recrystallized region, the base material toughness is improved and the brittle crack propagation stopping performance is also improved.
The austenite non-recrystallization temperature range in the present invention is generally in the range of 700 to 950 ° C.

熱間圧延終了温度は 700〜850 ℃の範囲に制限する必要がある。というのは、圧延終了温度が 700℃を下回ると、圧延中にフェライトが生成し、高靱性は得られるものの高強度が得られなくなり、一方圧延終了温度が 850℃超では、上記した制御圧延の効果が十分には得られず、高靱性と高い脆性亀裂伝播停止性能を得ることができないからである。   The hot rolling end temperature should be limited to the range of 700-850 ° C. This is because if the rolling end temperature is lower than 700 ° C, ferrite is generated during rolling, and high strength can be obtained although high toughness is obtained. On the other hand, if the rolling end temperature exceeds 850 ° C, This is because the effect cannot be obtained sufficiently and high toughness and high brittle crack propagation stopping performance cannot be obtained.

上記の熱間圧延終了後、鋼板を冷却速度:10℃/s以上の速度で、450 ℃以下まで冷却する。
ここに、冷却速度を10℃/s以上としたのは、冷却速度が10℃/s未満では高温で変態が始まるため、ベイナイトとはいえない硬度が高くないものが生成し、またベイナイト結晶粒の粗大化を余儀なくされる結果、母材の強度不足を生じるからである。また、ベイナイト変態を良好に完了させるためには、冷却停止温度は 450℃以下とする必要がある。
After completion of the above hot rolling, the steel sheet is cooled to 450 ° C. or lower at a cooling rate of 10 ° C./s or higher.
Here, the cooling rate was set to 10 ° C./s or higher because when the cooling rate was less than 10 ° C./s, transformation started at a high temperature, so that bainite was not high in hardness, and bainite crystal grains This is because the strength of the base material is insufficient as a result of forced coarsening. In order to complete the bainite transformation satisfactorily, the cooling stop temperature needs to be 450 ° C. or lower.

上記の工程により、引張強さが 700 MPa以上で、脆性亀裂伝播停止性能に優れた非調質高強度厚鋼板を得ることができる。
なお、本発明における厚鋼板とは、板厚が6〜100 mm程度のものを意味する。
By the above process, a non-tempered high strength thick steel plate having a tensile strength of 700 MPa or more and excellent brittle crack propagation stopping performance can be obtained.
In addition, the thick steel plate in this invention means a thing with a board thickness of about 6-100 mm.

表1に示す種々の成分組成になる溶鋼を、転炉で溶製し、連続鋳造法で鋼素材(スラブ)とした。これらのスラブ(板厚:250 mm)に対し、表2に示す条件で、加熱処理、圧延処理および冷却処理を施して、板厚:25mmの厚鋼板とした。
得られた厚鋼板の引張特性、母材靱性および脆性亀裂伝播停止性能について調査した結果を表2に併記する。
Molten steel having various component compositions shown in Table 1 was melted in a converter and used as a steel material (slab) by a continuous casting method. These slabs (plate thickness: 250 mm) were subjected to heat treatment, rolling treatment and cooling treatment under the conditions shown in Table 2 to obtain a thick steel plate having a plate thickness of 25 mm.
The results of investigations on the tensile properties, base metal toughness and brittle crack propagation stopping performance of the obtained thick steel plates are also shown in Table 2.

なお、各特性は次のようにして評価した。
(1) 引張特性
各厚鋼板の板厚1/4t位置から、JIS 4 号引張試験片を採取して引張試験を実施し、降伏点(Y.P.)および引張強さ(T.S.)を測定した。
(2) 母材靱性
各厚鋼板の板厚中心部から、JIS 4 号衝撃試験片を採取し.シャルピー試験を実施して母材の脆性破面遷移温度(vTrs) を求めた。
(3) 脆性亀裂伝播停止性能
日本溶接協会の鋼種認定試験方法に規定される方法に準拠して試験を行った。すなわち、500 mm正方試験片に29mm深さのノッチを加工した試験(ESSO試験)により、脆性亀裂伝播停止性能(Kca値)が 6000 N/mm1.5 を示す温度(Tk)(℃)を求めることにより評価した。
Each characteristic was evaluated as follows.
(1) Tensile properties JIS No. 4 tensile test specimens were collected from the position of 1/4 ton thickness of each thick steel plate, the tensile test was performed, and the yield point (YP) and tensile strength (TS) were measured.
(2) Base material toughness JIS No. 4 impact test specimens were collected from the center of the thickness of each thick steel plate. A Charpy test was performed to determine the brittle fracture surface transition temperature (vTrs) of the base metal.
(3) Brittle crack propagation stop performance The test was conducted in accordance with the method specified in the steel type certification test method of the Japan Welding Association. In other words, the temperature (Tk) (° C) at which the brittle crack propagation stop performance (Kca value) is 6000 N / mm 1.5 is obtained by a test (ESSO test) in which a 29 mm deep notch is machined on a 500 mm square test piece. It was evaluated by.

表2に示したとおり、発明例はいずれも、引張強さが 700 MPa以上の高強度が得られ、また靱性も良好であった。さらに、、脆性亀裂伝播停止性能もTk <−50℃と極めて良好であった。   As shown in Table 2, in all of the inventive examples, a high strength with a tensile strength of 700 MPa or more was obtained, and the toughness was also good. Furthermore, the brittle crack propagation stopping performance was also very good at Tk <-50 ° C.

Claims (2)

質量%で
C:0.005 〜0.03%、
Si:0.05〜0.5 %、
Mn:1.3 〜3.0 %、
Al:0.01〜0.08%、
Ti:0.005 〜0.05%、
Nb:0.005 〜0.060 %、
B:0.0015〜0.0040%、
P:0.05%以下および
S:0.0050%以下
を含有し、残部がFeおよび不可避的不純物の組成になる鋼素材を、1000〜1300℃に加熱後、オーステナイト未再結晶域での累積圧下率:60%以上、圧延終了温度:700 〜850 ℃の条件で熱間圧延を施し、熱間圧延終了後、冷却速度:10℃/s以上で冷却し、冷却停止温度を 450℃以下とすることを特徴とする、引張強さが 700 MPa以上の脆性亀裂伝播停止性能に優れた非調質高強度厚鋼板の製造方法。
In mass% C: 0.005 to 0.03%,
Si: 0.05 to 0.5%,
Mn: 1.3-3.0%,
Al: 0.01-0.08%,
Ti: 0.005 to 0.05%,
Nb: 0.005 to 0.060%,
B: 0.0015-0.0040%,
P: 0.05% or less and S: 0.0050% or less, the steel material having the balance of Fe and inevitable impurities is heated to 1000-1300 ° C, and the cumulative reduction ratio in the austenite non-recrystallized region: 60 %, At the end of rolling: 700 to 850 ℃, hot rolling is performed, and after the end of hot rolling, the cooling rate is 10 ℃ / s or more, and the cooling stop temperature is 450 ℃ or less. A method for producing a non-tempered high-strength thick steel plate with excellent tensile strength and brittle crack propagation stopping performance of 700 MPa or more.
請求項1において、鋼素材が、質量%でさらに
Cu:0.05〜2.0 %、
Ni:0.05〜2.0 %、
Cr:0.05〜2.0 %、
Mo:0.05〜1.0 %、
V:0.003 〜0.08%、
Ca:0.0003〜0.0030%、
REM:0.0003〜0.010 %および
Mg:0.0003〜0.005 %
のうちから選んだ1種または2種以上を含有する組成になることを特徴とする、引張強さが 700 MPa以上の脆性亀裂伝播停止性能に優れた非調質高強度厚鋼板の製造方法。
The steel material according to claim 1, wherein the steel material is
Cu: 0.05-2.0%,
Ni: 0.05-2.0%,
Cr: 0.05-2.0%,
Mo: 0.05-1.0%,
V: 0.003 to 0.08%,
Ca: 0.0003 to 0.0030%,
REM: 0.0003-0.010% and
Mg: 0.0003 to 0.005%
A method for producing a non-tempered high-strength thick steel plate excellent in brittle crack propagation stopping performance having a tensile strength of 700 MPa or more, characterized in that the composition contains one or more selected from among them.
JP2003334755A 2003-09-26 2003-09-26 Method for manufacturing non-heat-treated high-strength thick steel plate superior in brittle crack arrestability Pending JP2005097694A (en)

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