JP4834149B2 - Welded structural steel excellent in high temperature strength and low temperature toughness and its manufacturing method - Google Patents

Welded structural steel excellent in high temperature strength and low temperature toughness and its manufacturing method Download PDF

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JP4834149B2
JP4834149B2 JP2009509204A JP2009509204A JP4834149B2 JP 4834149 B2 JP4834149 B2 JP 4834149B2 JP 2009509204 A JP2009509204 A JP 2009509204A JP 2009509204 A JP2009509204 A JP 2009509204A JP 4834149 B2 JP4834149 B2 JP 4834149B2
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義之 渡部
龍治 植森
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Nippon Steel Corp
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    • C—CHEMISTRY; METALLURGY
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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Abstract

By heating a steel material comprising C: 0.003 to 0.05%, Si: 0.60% or less, Mn: 0.6 to 2.0%, P: 0.020% or less, S: 0.010% or less, Cr: 0.20 to 1.5%, Nb: 0.005 to 0.05%, Al: 0.060% or less, and N: 0.001 to 0.006%, further limiting, as an impurity, Mo to 0.03% or less, having a balance of iron and unavoidable impurities, and having a weld cracking parameter P CM value defined by P CM =C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/ 15+V/10+5B of 0.22% or less, to 1000 to 1300°C in temperature, finishing the hot rolling at 800°C or more in temperature, then cooling, steel for welded structures excellent in high temperature strength and low temperature toughness can be inexpensively provided.

Description

本発明は、火災など高温時の耐力維持を目的とした建築構造用耐火鋼を主たるターゲットとするものであるが、建築用途に限らず、海洋構造物、船舶、橋梁、各種貯槽タンク用など幅広い用途の溶接構造用鋼に適用できる。なお、主に対象とする鋼板の強度レベルは、降伏強さで２３５〜４７５ＭＰａ、引張強さで４００〜６４０ＭＰａの、いわゆる一般に４０キロ、５０キロ鋼と呼ばれるクラスである。   The present invention is mainly intended for building construction refractory steel for the purpose of maintaining proof stress at high temperatures such as fires, but is not limited to architectural use, and is widely used for marine structures, ships, bridges, various storage tanks, etc. Applicable to welded structural steel. In addition, the strength level of the target steel sheet is a class generally called 40 kg or 50 kg steel having a yield strength of 235 to 475 MPa and a tensile strength of 400 to 640 MPa.

高温耐力の確保を目的とした建築用途でのいわゆる耐火鋼は、特開平２−７７５２３号公報などをはじめとして多くの技術が開示されている。しかし、そのほとんどはＭｏを含有するものである。確かに、Ｍｏは、鋼の高温耐力を確保する上で極めて有効な元素であるが、同時に高価な元素でもある。   A number of techniques have been disclosed for so-called fire-resistant steel in architectural applications aimed at securing high-temperature proof stress, including Japanese Patent Application Laid-Open No. 2-77523. However, most of them contain Mo. Certainly, Mo is an element that is extremely effective in securing the high-temperature proof stress of steel, but is also an expensive element.

ところで、日本工業規格（ＪＩＳ）等で規格化されている一般の構造用鋼は、約３５０℃から強度低下するため、その許容温度は約３５０℃となっている。すなわち、ビルや事務所、住居、立体駐車場などの建築物に前記の鋼材を用いた場合は、火災時における安全性を確保するため、十分な耐火被覆を施すことが義務付けられており、日本の建築関連諸法令では、火災時に鋼材温度が３５０℃以上にならないように規定されている。これは、前記鋼材では、３５０℃程度で耐力が常温の２／３程度になり、必要な強度を下回るためである。このため、一般鋼材を建造物に利用する場合、火災時において鋼材の温度が３５０℃に達しないように耐火被覆を施す必要がある。   By the way, since the strength of general structural steel standardized by Japanese Industrial Standards (JIS) or the like decreases from about 350 ° C., the allowable temperature is about 350 ° C. In other words, when using the steel materials described above for buildings such as buildings, offices, residences, and multistory parking lots, it is obliged to apply sufficient fireproof coating to ensure safety in the event of a fire. The various building-related laws and regulations stipulate that the temperature of steel materials should not exceed 350 ° C in the event of a fire. This is because the steel material has a yield strength of about 2/3 of room temperature at about 350 ° C., which is lower than the required strength. For this reason, when using a general steel material for a building, it is necessary to apply a fireproof coating so that the temperature of the steel material does not reach 350 ° C. during a fire.

この耐火被覆を省略または軽減するために、６００℃などでの高温引張試験時の高温耐力（以下、特に明記がない場合は、高温とは６００℃を指し、高温強度とは高温耐力を指す。）を高めた耐火鋼が、使われるようになってきている。
一般的に耐火鋼には、高温強度維持を目的としてＭｏが添加される。しかし、Ｍｏは市況変化が大きく、添加量にもよるが、耐火被覆コストに比べ高価になる場合が多い。このため、Ｍｏを添加しない安価な耐火鋼の開発・実用化が待たれていた。 In order to omit or reduce this fireproof coating, the high-temperature strength at the time of a high-temperature tensile test at 600 ° C. or the like (hereinafter, unless otherwise specified, high temperature refers to 600 ° C., and high-temperature strength refers to high-temperature strength). ) Refractory steel with increased resistance is being used.
In general, Mo is added to refractory steel for the purpose of maintaining high-temperature strength. However, Mo has a large change in market conditions, and depending on the amount added, it is often more expensive than the fireproof coating cost. For this reason, development and practical use of an inexpensive refractory steel not containing Mo have been awaited.

本発明は、高価なＭｏを添加せずに優れた高温強度とともに、鋼材の基本性能の一つである低温靭性にも優れる溶接構造用鋼を得ることを目的とする。そのため、鋼成分を特定範囲に限定し、さらに製造方法を限定することで、高温強度に優れ、溶接割れ感受性を抑えて低温靭性を確保した耐火鋼を、工業的に安定して、しかも低コストで供給可能な方法を提供するものである。   An object of this invention is to obtain the steel for welded structures which is excellent also in the low temperature toughness which is one of the basic performances of steel materials with the outstanding high temperature strength, without adding expensive Mo. Therefore, by limiting the steel components to a specific range and further limiting the production method, refractory steel that has excellent high-temperature strength, suppressed weld cracking susceptibility, and secured low-temperature toughness is industrially stable and low-cost. It provides a method that can be supplied by

本発明のポイントは、６００℃での高温強度を安定して確保するため、高価なＭｏに代わり比較的微量のＣ量とＣｒとＮｂの複合添加により、変態組織強化とＣｒやＮｂの析出物（炭窒化物）による析出強化を利用することである。   The point of the present invention is to secure a high-temperature strength at 600 ° C. In order to stably secure a high temperature strength, a relatively small amount of C instead of expensive Mo and combined addition of Cr and Nb, transformation structure strengthening and Cr and Nb precipitates It is to use precipitation strengthening by (carbonitride).

つまり、Ｍｏフリー下で、適正量のＣｒを添加含有させることで、鋼の焼入性が向上して変態温度が低下し、セメンタイトを含む硬質組織がベイニティックとなることを見出した。   That is, it has been found that by adding an appropriate amount of Cr under the Mo-free condition, the hardenability of the steel is improved, the transformation temperature is lowered, and the hard structure containing cementite becomes bainitic.

それにより常温および高温強度が上がるとともに、マトリックスが比較的低温で変態した微細なベイニティック組織であるがゆえに、高温時にはＣｒとＮｂの複合添加によるＣｒおよびＮｂの単独または複合した炭窒化物が、そのマトリックス中にきわめて微細に析出し、高温強度を高いレベルで確保、維持できることを見出し、本願発明に至ったものである。   As a result, the strength at room temperature and high temperature is increased, and the matrix is a fine bainitic structure transformed at a relatively low temperature. Therefore, at high temperatures, Cr and Nb combined with Cr and Nb alone or combined with carbonitride are combined. The inventors have found that it is very finely precipitated in the matrix, and that high-temperature strength can be secured and maintained at a high level, resulting in the present invention.

上記したように、Ｍｏを含有しない耐火鋼は、それ自体きわめて画期的であると同時に、焼入性の高いＭｏを含有しないことで、溶接構造用鋼としての基本性能（強度、靭性）はもちろん、溶接性やガス切断性をもかえって向上させることにもつながる。   As described above, the refractory steel not containing Mo is very innovative in itself, and at the same time, the basic performance (strength and toughness) as a welded structural steel is low by not containing Mo with high hardenability. Of course, it also leads to improved weldability and gas cutting performance.

本願発明は、Ｃｒ、Ｎｂのみならず、Ｃ、Ｓｉ、Ｍｎをはじめとする個々の元素量および溶接割れ感受性組成ＰＣＭを規定し、さらに製造条件を限定することで、高価なＭｏを使用せず優れた高温強度と低温靭性を両立させただけでなく、溶接構造用鋼としての各種使用性能を確保したものである。その要旨は、以下の通りである。
（１）成分が質量％で、
Ｃ ：０．０２〜０．０５％
Ｓｉ：０．６０％以下
Ｍｎ：０．６〜２．０％
Ｐ ：０．０２０％以下
Ｓ ：０．０１０％以下
Ｃｒ：０．５６〜１．５％
Ｎｂ：０．００５〜０．０２８％
Ａｌ：０．０６０％以下
Ｎ ：０．００１〜０．００６％であって、
さらに、不純物としてＭｏを０．０３％以下に制限し、残部が鉄および不可避的不純物からなり、
ＰCM＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｕ／２０＋Ｎｉ／６０＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／１０＋５Ｂで定義される溶接割れ感受性組成ＰCM値が０．２２％以下である鋼材を、１０００〜１３００℃の温度に加熱し、８００℃以上の温度で熱間圧延を終了し、その後７５０℃以上の温度から５５０℃以下の温度まで加速冷却し、該加速冷却が、板厚方向に表面から板厚の１／４の位置で加速冷却開始温度から５５０℃までの平均冷却速度が３℃／秒以上であることを特徴とする高温強度と低温靭性に優れる溶接構造用鋼の製造方法。
（２）さらに、質量％で、
Ｖ ：０．０１〜０．１０％
Ｔｉ：０．００５〜０．０２５％
のいずれか１種または２種を含有することを特徴とする（１）に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。
（３）さらに、質量％で
Ｎｉ：０．０５〜０．５０％
Ｃｕ：０．０５〜０．５０％
Ｂ ：０．０００２〜０．００３％
Ｍｇ：０．０００２〜０．００５％
のいずれか１種または２種以上を含有することを特徴とする（１）または（２）に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。
（４）さらに、質量％で
Ｃａ ：０．０００５〜０．００４％
ＲＥＭ：０．０００５〜０．００８％
のいずれか１種を含有することを特徴とする（１）〜（３）のいずれか1項に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。
（５）成分が質量％で、
成分が質量％で、
Ｃ ：０．０２〜０．０５％
Ｓｉ：０．６０％以下
Ｍｎ：０．６〜２．０％
Ｐ ：０．０２０％以下
Ｓ ：０．０１０％以下
Ｃｒ：０．５６〜１．５％
Ｎｂ：０．００５〜０．０２８％
Ａｌ：０．０６０％以下
Ｎ ：０．００１〜０．００６％であって、
さらに、不純物としてＭｏを０．０３％以下に制限し、残部が鉄および不可避的不純物からなり、
ＰCM＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｕ／２０＋Ｎｉ／６０＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／１０＋５Ｂで定義される溶接割れ感受性組成ＰCM値が０．２２％以下である鋼材を、１０００〜１３００℃の温度に加熱し、８００℃以上の温度で熱間圧延を終了し、その後７５０℃以上の温度から加速冷却を開始し、５５０℃以下の温度で加速冷却を停止することを特徴とする高温強度と低温靭性に優れる溶接構造用鋼。 The present invention specifies not only Cr and Nb but also individual element amounts including C, Si, and Mn and weld cracking sensitive composition PCM, and further limits the manufacturing conditions, so that expensive Mo is not used. In addition to achieving both excellent high-temperature strength and low-temperature toughness, it ensures various use performances as welded structural steel. The summary is as follows.
(1) The component is mass%,
C: 0.0 2 ~0.05%
Si: 0.60% or less Mn: 0.6-2.0%
P: 0.020% or less S: 0.010% or less Cr: 0.56-1.5%
Nb: 0.005~0.0 28%
Al: 0.060% or less N: 0.001 to 0.006%,
Furthermore, Mo is limited to 0.03% or less as an impurity, and the balance consists of iron and inevitable impurities,
The P CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + steel weld crack susceptibility composition P CM value defined by 5B is less than 0.22%, was heated to a temperature of 1000 to 1300 ° C., Hot rolling is finished at a temperature of 800 ° C. or higher, and then accelerated cooling is performed from a temperature of 750 ° C. or higher to a temperature of 550 ° C. or lower. The accelerated cooling is performed at a position 1/4 of the plate thickness from the surface in the thickness direction. method for manufacturing a welding structural steel average cooling rate from accelerated cooling starting temperature to 550 ° C. is excellent in high temperature strength and low temperature toughness characterized by der Rukoto than 3 ° C. / sec.
(2 ) Furthermore, in mass%,
V: 0.01-0.10%
Ti: 0.005-0.025%
Any one or two of these are contained, The manufacturing method of the steel for welded structures which is excellent in the high temperature strength and low temperature toughness as described in (1 ) characterized by the above-mentioned.
( 3 ) Furthermore, in mass% Ni: 0.05-0.50%
Cu: 0.05 to 0.50%
B: 0.0002 to 0.003%
Mg: 0.0002 to 0.005%
The method for producing a steel for welded structure having excellent high-temperature strength and low-temperature toughness according to (1) or (2) , characterized by containing any one or more of the above.
( 4 ) Furthermore, in mass% Ca: 0.0005 to 0.004%
REM: 0.0005 to 0.008%
Any one of these is contained, The manufacturing method of the steel for welded structures which is excellent in the high temperature strength and low temperature toughness of any one of (1)-( 3 ) characterized by the above-mentioned.
( 5 ) component is mass%,
Ingredient is% by mass
C: 0.0 2 ~0.05%
Si: 0.60% or less Mn: 0.6-2.0%
P: 0.020% or less S: 0.010% or less Cr: 0.56-1.5%
Nb: 0.005~0.0 28%
Al: 0.060% or less N: 0.001 to 0.006%,
Furthermore, Mo is limited to 0.03% or less as an impurity, and the balance consists of iron and inevitable impurities,
The P CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + steel weld crack susceptibility composition P CM value defined by 5B is less than 0.22%, was heated to a temperature of 1000 to 1300 ° C., Welding with excellent high-temperature strength and low-temperature toughness, characterized in that hot rolling is finished at a temperature of 800 ° C. or higher, accelerated cooling is started at a temperature of 750 ° C. or higher, and accelerated cooling is stopped at a temperature of 550 ° C. or lower. Structural steel.

本発明によれば、火災時など高温にさらされる環境でも十分な耐力を有する溶接構造用鋼が大量かつ安価に供給できるため、種々の用途の広範な溶接鋼構造物の安全性向上に資することが可能となる。   According to the present invention, a large amount of welded structural steel having sufficient proof strength can be supplied even in an environment exposed to a high temperature such as a fire, and this contributes to improving the safety of a wide range of welded steel structures for various applications. Is possible.

本発明で規定した各合金元素の添加範囲について説明する。
Ｃ ：０．００３〜０．０５％
Ｃは、高張力鋼としてはきわめて低いレベルに限定している。これは、他の成分とともに製造方法と密接に関係している。鋼成分の中でもＣは鋼材の特性に最も大きな影響を及ぼすものである。下限０．００３％は強度確保や溶接などの熱影響部が必要以上に軟化することのないようにするための最小値である。
Ｃ量が多すぎると焼入性が必要以上に上がり、鋼材の強度と靱性のバランス、溶接性などに悪影響を及ぼす。また、後述するように、目的とする板厚や強度によっては加速冷却を比較的低温で停止するケースがあり、その際に鋼材表裏面近傍の極端な硬化や板厚方向の材質変動を抑えるため、上限を０．０５％とした。
操業変動や他成分とのバランスから強度低下を避けるため下限は０．００５％にするのが好まく、さらに０．０１％とすることがより好ましい。また、過度な焼入れ硬化や材質変動を避けるため、上限は０．０４％が好ましく、さらに０．０３％とすることがなお好ましい。 The range of addition of each alloy element defined in the present invention will be described.
C: 0.003-0.05%
C is limited to a very low level as a high strength steel. This is closely related to the production method along with other components. Among steel components, C has the greatest influence on the properties of steel materials. The lower limit of 0.003% is a minimum value for preventing the heat-affected zone such as securing strength and welding from being softened more than necessary.
If the amount of C is too large, the hardenability is increased more than necessary, which adversely affects the balance between strength and toughness of the steel material and weldability. In addition, as will be described later, depending on the target plate thickness and strength, there are cases where accelerated cooling is stopped at a relatively low temperature, in order to suppress extreme hardening near the front and back surfaces of the steel material and material variation in the plate thickness direction. The upper limit was made 0.05%.
The lower limit is preferably 0.005%, more preferably 0.01%, in order to avoid strength reduction from the balance with operational fluctuations and other components. In order to avoid excessive quench hardening and material fluctuation, the upper limit is preferably 0.04%, and more preferably 0.03%.

Ｓｉ：０．６０％以下
Ｓｉは、脱酸のため鋼に含まれる元素であるが、多く添加すると溶接性、ＨＡＺ靭性が劣化するため、上限を０．６０％とした。鋼の脱酸はＴｉ、Ａｌでも可能であるので、それら元素とのバランスにて含有量を決定すればよい。しかし、ＨＡＺ靱性、焼入性などの観点から低いほど好ましく、無添加でもよい。このため、上限を０．４０％、０．２０％、０．１０％に制限しても差し支えない。なお、製鋼工場で鋼を製造する場合、Ｓｉ無添加でＴｉ、Ａｌにより脱酸された場合でも、０．０１％以上のＳｉが含まれることが一般的である。 Si: 0.60% or less Si is an element contained in steel for deoxidation, but if added in large amounts, weldability and HAZ toughness deteriorate, so the upper limit was made 0.60%. Since deoxidation of steel is possible with Ti and Al, the content may be determined by balance with these elements. However, it is preferably as low as possible from the viewpoints of HAZ toughness, hardenability, etc., and may be free of additives. For this reason, the upper limit may be limited to 0.40%, 0.20%, and 0.10%. In addition, when manufacturing steel in a steelmaking factory, it is common that 0.01% or more of Si is contained even when it is deoxidized by Ti and Al without adding Si.

Ｍｎ：０．６〜２．０％
Ｍｎは、常温の強度、靭性を確保する上で不可欠な元素であり、その下限は０．６％である。好ましくは０．８％以上または１．０％以上である。しかし、Ｍｎ量が多すぎると焼入性が上昇して溶接性、ＨＡＺ靭性を劣化させるだけでなく、連続鋳造スラブの中心偏析を助長するので上限を２．０％とした。好ましくは１．８％以下、より好ましくは１．６％以下または１．４％以下である。 Mn: 0.6 to 2.0%
Mn is an indispensable element for securing the strength and toughness at room temperature, and its lower limit is 0.6%. Preferably it is 0.8% or more or 1.0% or more. However, if the amount of Mn is too large, not only the hardenability is increased and the weldability and HAZ toughness are deteriorated, but also the center segregation of the continuously cast slab is promoted, so the upper limit was made 2.0%. Preferably it is 1.8% or less, More preferably, it is 1.6% or less or 1.4% or less.

Ｐ ：０．０２０％以下
Ｐは、その量が少ないとＨＡＺにおける粒界破壊を減少させる傾向があるため、少ないほど好ましい。含有量が多いと母材、溶接部の低温靭性を劣化させるため上限を０．０２０％とする。０．０１５％以下、０．０１０％以下または０．００８％以下とする方がより好ましい。もちろん無添加でもよい。 P: 0.020% or less Since the amount of P tends to decrease the grain boundary fracture in HAZ when the amount is small, the smaller the amount, the better. If the content is large, the low temperature toughness of the base metal and the weld zone is deteriorated, so the upper limit is made 0.020%. More preferably, the content is 0.015% or less, 0.010% or less, or 0.008% or less. Of course, no additives may be added.

Ｓ ：０．０１０％以下
Ｓは、母材の低温靭性の観点からは少ないほど好ましい。含有量が多いと母材、溶接部の低温靭性を劣化させるため上限を０．０１０％とする。０．００８％以下、０．００６％、０．００４％とする方がより好ましい。もちろん無添加でもよい。 S: 0.010% or less S is more preferable from the viewpoint of low temperature toughness of the base material. If the content is large, the low temperature toughness of the base metal and the welded portion is deteriorated, so the upper limit is made 0.010%. 0.008% or less, 0.006%, and 0.004% are more preferable. Of course, no additives may be added.

Ｃｒ：０．２０〜１．５％
Ｃｒは、本願発明における最も重要な元素の一つである。高温強度確保のためＮｂとともにＣｒ添加が必須である。これは、Ｃｒの焼入性向上効果により変態温度が低下し、セメンタイトを含む硬質組織がベイニティックとなるため、常温および高温時の強度を上げ、さらに高温時にはＣｒの析出物（炭窒化物）による析出強化を利用するためである。
これらの効果を享受するため、Ｃｒの含有量は、最低０．２０％が必要である。好ましくは０．３５％以上であり、は０．５０％以上、０．８％または１．０％以上とすることがより好ましい。しかし、添加量が多過ぎると、母材、溶接部の靭性および溶接性の劣化を招き、経済性も失するため上限を１．５％とした。好ましくは１．３％以下であるとよい。 Cr: 0.20 to 1.5%
Cr is one of the most important elements in the present invention. It is essential to add Cr together with Nb to ensure high temperature strength. This is because the transformation temperature is lowered due to the effect of improving the hardenability of Cr, and the hard structure containing cementite becomes bainitic, so the strength at room temperature and high temperature is increased, and further, Cr precipitates (carbonitrides at high temperatures). This is because the precipitation strengthening due to the above is utilized.
In order to enjoy these effects, the Cr content should be at least 0.20%. Preferably it is 0.35% or more, more preferably 0.50% or more, 0.8% or 1.0% or more. However, if the addition amount is too large, the base material, the toughness of the welded portion and the weldability are deteriorated and the economical efficiency is also lost, so the upper limit was made 1.5%. Preferably it is 1.3% or less.

Ｎｂ：０．００５〜０．０５％
Ｎｂは、Ｃｒとともに本願発明における最も重要な元素である。Ｃｒと同様に、高温強度確保のためＮｂの析出物（炭窒化物）による析出強化を利用しているからである。
このため、少なくとも０．００５％以上は必要である。好ましくは０．０１０％以上であるとよい。しかし、添加量が多過ぎると、溶接部の靭性劣化を招くため、上限を０．０５％とした。好ましくは０．０４５％以下、さらには０．０３０％以下であるとよい。なお、Ｎｂ添加は、オーステナイトの未再結晶温度を上昇させ、熱間圧延時の制御圧延の効果を最大限に発揮することにも寄与する。
上記のＣｒとＮｂの複合添加により、Ｍｏフリーでも高温強度を確保できるものである。従って、本願発明では、Ｍｏの意図的添加を行わない。また、不純物としてＭｏが意図せず混入した場合でもの０．０３％以下に制限する。 Nb: 0.005 to 0.05%
Nb is the most important element in the present invention together with Cr. This is because, like Cr, precipitation strengthening by Nb precipitates (carbonitrides) is used to ensure high temperature strength.
For this reason, at least 0.005% or more is necessary. Preferably it is 0.010% or more. However, if the addition amount is too large, the toughness of the weld zone is deteriorated, so the upper limit was made 0.05%. Preferably it is 0.045% or less, Furthermore, it is good in it being 0.030% or less. In addition, Nb addition raises the non-recrystallization temperature of austenite and contributes also to exhibiting the effect of the controlled rolling at the time of hot rolling to the maximum.
By the combined addition of Cr and Nb described above, high temperature strength can be secured even without Mo. Therefore, intentional addition of Mo is not performed in the present invention. Moreover, even if Mo is not intentionally mixed as an impurity, it is limited to 0.03% or less.

Ａｌ：０．０６０％以下
Ａｌは、一般に脱酸のために鋼に含まれる元素である。脱酸はＳｉまたはＴｉでもなされるため、それら元素とのバランスにて量を決めればよい。しかし、Ａｌ量が多くなると鋼の清浄度が悪くなるだけでなく、溶接金属の靭性が劣化するので上限を０．０６０％とする。好ましくは０．０４０％以下であるとよい。その量は少ないほどよく、無添加でもよい。なお、製鋼工場で鋼を製造する場合、Ａｌによる脱酸を行なわなかった場合でも、０．００１％以上のＡｌが含まれることが一般的である。 Al: 0.060% or less Al is an element generally contained in steel for deoxidation. Since deoxidation is also performed with Si or Ti, the amount may be determined in balance with these elements. However, when the amount of Al increases, not only the cleanliness of steel deteriorates but also the toughness of the weld metal deteriorates, so the upper limit is made 0.060%. Preferably it is 0.040% or less. The smaller the amount, the better. In addition, when manufacturing steel in a steelmaking factory, even when it does not deoxidize by Al, it is common that 0.001% or more of Al is contained.

Ｎ ：０．００１〜０．００６％
Ｎは、不可避的不純物として鋼中に含まれるものであるが、Ｎｂと結合して炭窒化物を形成して強度を増加させ、また、ＴｉＮを形成して前述のように鋼の性質を高める。このため、Ｎ量として最低０．００１％必要である。好ましくは０．００１５％以上であるとよい。しかしながら、Ｎ量の増加は溶接熱影響部靭性、溶接性に有害であり、本発明鋼においてはその上限は０．００６％である。より好ましくは０．００４５％以下であるとよい。
次に必要に応じて含有することができるＶ、Ｔｉの添加理由について説明する。 N: 0.001 to 0.006%
N is contained in the steel as an unavoidable impurity, but combines with Nb to form carbonitride to increase the strength, and TiN to increase the properties of the steel as described above. . For this reason, the N amount is required to be at least 0.001%. Preferably it is 0.0015% or more. However, an increase in the amount of N is detrimental to the weld heat affected zone toughness and weldability, and the upper limit of the steel of the present invention is 0.006%. More preferably, it is 0.0045% or less.
Next, the reason for the addition of V and Ti that can be contained as required will be described.

Ｖ ：０．０１〜０．１０％
Ｖは、Ｎｂとほぼ同様の効果を有し、本願発明におけるＶの役割は、Ｎｂを補完するものである。ただし、Ｖは、Ｎｂに比べて効果は小さく、焼入れ性にも影響を及ぼすため、上下限を限定した。下限はＶ添加の効果を確実に享受できる最少量として０．０１％とした。好ましくは、０．０２５％以上であるとよい。上限は後述する溶接割れ感受性組成ＰＣＭへの影響も勘案し０．１０％とした。好ましくは、０．０８％以下、さらには０．０５％以下であるとよい。 V: 0.01-0.10%
V has substantially the same effect as Nb, and the role of V in the present invention complements Nb. However, since V is less effective than Nb and affects hardenability, the upper and lower limits are limited. The lower limit was set to 0.01% as the minimum amount that can surely enjoy the effect of V addition. Preferably, it is 0.025% or more. The upper limit was set to 0.10% in consideration of the effect on the weld crack sensitive composition PCM described later. Preferably, it is 0.08% or less, further 0.05% or less.

Ｔｉ：０．００５〜０．０２５％
Ｔｉは母材および溶接熱影響部靭性向上のために添加することが望ましい。なぜならばＴｉは、Ａｌ量が少ないとき（例えば０．００３％以下）、Ｏと結合してＴｉ２Ｏ３を主成分とする析出物を形成し、粒内変態フェライト生成の核となり溶接熱影響部靭性を向上させる。
また、ＴｉはＮと結合してＴｉＮとして鋼材中に微細析出し、加熱時のγ粒の粗大化を抑え圧延組織の細粒化に有効である。さらに鋼材中に存在する微細ＴｉＮは、溶接時に溶接熱影響部組織を細粒化し、靭性を向上させる。これらの効果を得るためには、Ｔｉは最低０．００５％必要である。しかし多過ぎるとＴｉＣを形成し、低温靭性や溶接性を劣化させるので、その上限は０．０２５％とした。好ましくは、０．０２０％以下である。 Ti: 0.005-0.025%
Ti is preferably added to improve the toughness of the base material and the weld heat affected zone. This is because when Ti has a small amount of Al (for example, 0.003% or less), it combines with O to form precipitates mainly composed of Ti2O3, which becomes the nucleus of intragranular transformation ferrite formation and has a weld heat affected zone toughness. Improve.
Further, Ti is combined with N and finely precipitated in the steel as TiN, which suppresses the coarsening of γ grains during heating and is effective for making the rolled structure finer. Further, the fine TiN present in the steel material refines the weld heat affected zone structure during welding and improves toughness. In order to obtain these effects, Ti needs to be at least 0.005%. However, if it is too much, TiC is formed and low temperature toughness and weldability are deteriorated, so the upper limit was made 0.025%. Preferably, it is 0.020% or less.

次に、Ｎｉ、Ｃｕ、Ｂ、Ｍｇの添加理由について説明する。
基本となる成分に、さらにこれらの元素を添加する主たる目的は、本発明鋼の優れた特徴を損なうことなく、強度、靭性などの特性を向上させるためである。したがってその添加量は自ずと制限されるべき性質のものである。 Next, the reason for adding Ni, Cu, B, and Mg will be described.
The main purpose of adding these elements to the basic components is to improve properties such as strength and toughness without impairing the excellent characteristics of the steel of the present invention. Therefore, the amount added is of a nature that should naturally be limited.

Ｎｉ：０．０５〜０．５０％
Ｎｉは、過剰に添加しなければ、溶接性、溶接熱影響部靭性に悪影響を及ぼすことなく母材の強度、靭性を向上させる。これら効果を発揮させるためには、少なくとも０．０５％以上の添加が必須である。
一方、過剰な添加は高価なだけでなく、溶接性に好ましくない。また、Ｎｉを多く添加すると液体アンモニア中で応力腐食割れ（ＳＣＣ）を誘起する可能性が指摘されている。発明者らの実験によれば、１．０％までの添加は溶接性や液体アンモニア中でのＳＣＣを大きく劣化させず、強度、靭性向上効果の方が大きいが、経済性を優先し、上限を０．５０％とした。更に経済性を優先する場合、０．３５％に制限してもよい。 Ni: 0.05 to 0.50%
If Ni is not added excessively, it improves the strength and toughness of the base material without adversely affecting the weldability and weld heat affected zone toughness. In order to exert these effects, addition of at least 0.05% is essential.
On the other hand, excessive addition is not only expensive, but is not preferable for weldability. Further, it has been pointed out that the addition of a large amount of Ni may induce stress corrosion cracking (SCC) in liquid ammonia. According to the experiments by the inventors, addition up to 1.0% does not significantly deteriorate the weldability and SCC in liquid ammonia, and the effect of improving strength and toughness is greater. Was 0.50%. Furthermore, when priority is given to economy, it may be limited to 0.35%.

Ｃｕ：０．０５〜０．５０％
Ｃｕは、Ｎｉとほぼ同様の効果、現象を示し、上限の０．５０％は溶接性劣化に加え、過剰な添加は熱間圧延時にＣｕ−クラックが発生し製造困難となるため規制される。下限は実質的な効果が得られるための最小量とすべきで０．０５％である。経済性を優先する場合、上限を０．３０％に制限してもよい。 Cu: 0.05 to 0.50%
Cu exhibits substantially the same effects and phenomena as Ni, with the upper limit of 0.50% being restricted in terms of weldability deterioration and excessive addition because Cu-cracks are generated during hot rolling, making it difficult to manufacture. The lower limit should be the minimum amount for obtaining a substantial effect, and is 0.05%. When giving priority to economy, the upper limit may be limited to 0.30%.

Ｂ ：０．０００２〜０．００３％
Ｂは、オーステナイト粒界に偏析し、フェライトの生成を抑制することを介して、焼入性を向上させ、強度向上に寄与する。この効果を享受するため、最低０．０００２％以上必要である。
しかし、多すぎる添加は焼入性向上効果が飽和するだけでなく、靭性上有害となるＢ析出物を形成する可能性もあるため、上限を０．００３％とする。好ましくは０．００２％以下であるとよい。なお、タンク用鋼などとして、応力腐食割れが懸念されるケースでは、母材および溶接熱影響部の硬さの低減がポイントとなることが多く（例えば、硫化物応力腐食割れ（ＳＣＣ）防止のためにはロックウェル硬さでＨＲＣ≦２２（ＨＶ≦２４８）が必須とされる）、そのようなケースでは焼入性を増大させるＢ添加は好ましくない。なお、Ｂには上記のような強度向上効果があるが、Ｂ添加による熱影響部靭性等の材質劣化の問題があるため、これらの問題を回避するためには、Ｂを０．０００３％以下に制限または無添加とすることがより望ましい。 B: 0.0002 to 0.003%
B segregates at austenite grain boundaries and suppresses the formation of ferrite, thereby improving hardenability and contributing to strength improvement. In order to enjoy this effect, at least 0.0002% is necessary.
However, too much addition not only saturates the effect of improving hardenability but also may form B precipitates that are harmful to toughness, so the upper limit is made 0.003%. Preferably it is 0.002% or less. In cases where stress corrosion cracking is a concern, such as for tank steel, reduction of the hardness of the base metal and the weld heat affected zone is often the point (for example, prevention of sulfide stress corrosion cracking (SCC)). Therefore, HRC ≦ 22 (HV ≦ 248) is essential in Rockwell hardness). In such a case, addition of B which increases hardenability is not preferable. In addition, although B has the above-mentioned strength improvement effect, since there is a problem of material deterioration such as heat-affected zone toughness due to addition of B, in order to avoid these problems, B is 0.0003% or less. It is more desirable to limit or not add.

Ｍｇ：０．０００２〜０．００５％
Ｍｇは、溶接熱影響部においてオーステナイト粒の成長を抑制し、細粒化する作用があり、溶接部の強靭化が図れる。このような効果を享受するためには、Ｍｇは０．０００２％以上必要である。一方、添加量が増えると添加量に対する効果代が小さくなるため、コスト上得策ではないので上限は０．００５％とした。好ましくは０．００３５％以下であるとよい。 Mg: 0.0002 to 0.005%
Mg suppresses the growth of austenite grains in the weld heat-affected zone and has the effect of making the grains finer, so that the weld zone can be strengthened. In order to enjoy such an effect, Mg needs to be 0.0002% or more. On the other hand, since the effect cost for the added amount decreases as the added amount increases, the upper limit is set to 0.005% because this is not a cost effective measure. Preferably it is 0.0035% or less.

次に、ＣａまたはＲＥＭの添加理由について説明する。
Ｃａ ：０．０００５〜０．００４％
ＲＥＭ：０．０００５〜０．００８％
ＣａおよびＲＥＭは、ＭｎＳの形態を制御し、母材の低温靭性を向上させるほか、湿潤硫化水素環境下での水素誘起割れ（ＨＩＣ、ＳＳＣ、ＳＯＨＩＣ）感受性を低減させる。これらの効果を発揮するためには、最低０．０００５％必要である。
しかし、多すぎる添加は、鋼の清浄度を逆に悪化させ、母材靭性や湿潤硫化水素環境下での水素誘起割れ（ＨＩＣ、ＳＳＣ、ＳＯＨＩＣ）感受性を高めるため、添加量の上限はＣａ、ＲＥＭそれぞれ０．００４％、０．００８％に限定した。好ましくは、それぞれ０．００３％、０．００６％以下であるとよい。なお、ＣａとＲＥＭは、ほぼ同等の効果を有するため、いずれか１種を上記範囲で添加すればよく、両者を添加してもよい。 Next, the reason for adding Ca or REM will be described.
Ca: 0.0005 to 0.004%
REM: 0.0005 to 0.008%
Ca and REM control the morphology of MnS, improve the low temperature toughness of the base material, and reduce the susceptibility to hydrogen induced cracking (HIC, SSC, SOHIC) in a wet hydrogen sulfide environment. In order to exert these effects, 0.0005% is necessary at least.
However, too much addition adversely deteriorates the cleanliness of the steel, and increases the base metal toughness and susceptibility to hydrogen-induced cracking (HIC, SSC, SOHIC) in a wet hydrogen sulfide environment. REM was limited to 0.004% and 0.008%, respectively. Preferably, they are 0.003% and 0.006% or less, respectively. In addition, since Ca and REM have a substantially equivalent effect, any one should just be added in the said range, and you may add both.

鋼の個々の成分を限定しても、成分系全体が適切でないと優れた特性は得られない。本願発明では、各元素の含有量（質量％）から、以下の式で定義される溶接割れ感受性組成ＰＣＭの値を０．２２％以下に限定する。   Even if the individual components of the steel are limited, excellent properties cannot be obtained unless the entire component system is appropriate. In the present invention, the value of the weld cracking sensitive composition PCM defined by the following formula is limited to 0.22% or less from the content (mass%) of each element.

ＰＣＭ＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｕ／２０＋Ｎｉ／６０
＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／１０＋５Ｂ PCM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60
+ Cr / 20 + Mo / 15 + V / 10 + 5B

ＰＣＭは溶接性を表す指標で、低いほど溶接性は良好である。ＪＩＳ Ｇ ３１０６「溶接構造用圧延鋼材」では、強度レベルや板厚によっても異なるが、最も厳しいもので０．２４％以下に規定している。   PCM is an index representing weldability. The lower the PCM, the better the weldability. In JIS G 3106 “Rolled steel for welded structure”, it varies depending on the strength level and thickness, but the most severe one is specified to be 0.24% or less.

本発明者らの幅広い鋼種での各種の溶接割れ試験によれば、より厳しい拘束条件、環境条件でも確実に溶接冷間割れを防止できる条件としてＰＣＭを０．２２％以下に限定したものである。なお、下限は特に限定しないが、各成分の限定範囲から自ずと制約されるものである。   According to various weld cracking tests by the present inventors on a wide range of steel types, PCM is limited to 0.22% or less as a condition that can reliably prevent weld cold cracking even under more severe restraint conditions and environmental conditions. . Although the lower limit is not particularly limited, the lower limit is naturally limited by the limited range of each component.

続いて、製造条件について説明する。
熱間圧延に先立つ加熱温度を１０００〜１３００℃に限定した理由は、加熱時のオーステナイト粒を小さく保ち、圧延組織の微細化を図るためである。１３００℃は加熱時のオーステナイトが極端に粗大化しない上限温度であり、加熱温度がこれを超えるとオーステナイト粒が粗大混粒化し、変態後の組織も粗大化するため鋼の靭性が著しく劣化する。 Subsequently, manufacturing conditions will be described.
The reason for limiting the heating temperature prior to hot rolling to 1000 to 1300 ° C. is to keep the austenite grains during heating small and to refine the rolled structure. 1300 ° C. is an upper limit temperature at which the austenite during heating is not extremely coarsened. When the heating temperature is exceeded, the austenite grains are coarsely mixed and the structure after transformation is also coarsened, so that the toughness of the steel is remarkably deteriorated.

一方、加熱温度が低すぎると、板厚によっては後述する圧延終了温度の確保が困難となるばかりでなく、オーステナイトの未再結晶温度を上昇させ、析出強化を発現させるためのＮｂの溶体化の観点から下限を１０００℃とした。最も好ましい加熱温度範囲は、１０５０〜１２５０℃である。   On the other hand, if the heating temperature is too low, depending on the plate thickness, it is difficult not only to secure the rolling end temperature, which will be described later, but also to increase the non-recrystallization temperature of austenite and to cause the solution of Nb to develop precipitation strengthening From the viewpoint, the lower limit was set to 1000 ° C. The most preferable heating temperature range is 1050 to 1250 ° C.

上述のような条件で加熱した鋼材を、８００℃以上で熱間圧延を終了した後冷却する。冷却手段は特に問わない。大気中に放置して冷却してもよいが、７５０℃以上の温度から５５０℃以下の温度まで加速冷却をすることにより、より鋼材の特性を高めることができる。   The steel material heated on the above conditions is cooled after 800 degreeC or more complete | finishes hot rolling. The cooling means is not particularly limited. Although it may be cooled by leaving it in the atmosphere, the properties of the steel material can be further improved by performing accelerated cooling from a temperature of 750 ° C. or higher to a temperature of 550 ° C. or lower.

圧延終了温度が８００℃を下回ると、Ｃ量が比較的少ない本願発明鋼においては、フェライトが変態析出し、フェライトを加工（圧延）する恐れがあり、低温靭性確保の点で好ましくない。このため、圧延終了温度は、８００℃以上に限定する。好ましくは８２０℃以上であるとよい。
８００℃以上で熱間圧延を終了した後、比較的強度の低い、いわゆる４０キロ級鋼（例えばＪＩＳ規格のＳＭ４００、ＳＮ４００鋼）は、大気中に放置して冷却しても所定の強度を満足できる。 When the rolling end temperature is lower than 800 ° C., in the steel of the present invention having a relatively small amount of C, ferrite is likely to undergo transformation transformation and the ferrite may be processed (rolled), which is not preferable in terms of ensuring low temperature toughness. For this reason, the rolling end temperature is limited to 800 ° C. or higher. Preferably it is 820 degreeC or more.
After hot rolling at 800 ° C. or higher, so-called 40 kg class steel (for example, JIS standard SM400, SN400 steel) with relatively low strength satisfies the specified strength even if it is left to cool in the atmosphere. it can.

しかし、５０キロ級鋼（例えばＪＩＳ規格のＳＭ４９０、ＳＮ４９０鋼）や４０キロ鋼でも板厚が厚くなると大気中に放置しての冷却ままでは強度の安定確保が困難となるため、８００℃以上で熱間圧延を終了した後、７５０℃以上の温度から加速冷却することが望ましい。圧延後の加速冷却は、鋼材の特性をより高めるためであって、本願発明の優れた特徴を損なうものではない。   However, even with 50kg steel (for example, JIS standard SM490, SN490 steel) and 40kg steel, if the plate thickness is too thick, it will be difficult to ensure stable strength when left in the atmosphere. After the hot rolling is finished, it is desirable to accelerate cooling from a temperature of 750 ° C. or higher. The accelerated cooling after rolling is intended to enhance the properties of the steel material, and does not impair the excellent features of the present invention.

加速冷却は、そもそも変態域の冷速を早めることで組織を微細化し、強度と靭性を同時に向上させるためのものである。したがって、変態開始前あるいは少なくとも変態終了前に開始しなければ実質的に意味を持たない。このため、加速冷却開始温度は７５０℃以上に限定したものである。この加速冷却は、その効果を享受する上で５５０℃以下の温度まで冷却する必要がある。５５０℃を超える温度では、加速冷却時の変態が十分に進行せず、組織の微細化が不十分となるためである。好ましい加速冷却の開始温度は７６０℃以上であり、好ましい加速冷却の停止温度の範囲は、５２０以下３００℃以上である。   In the first place, accelerated cooling is intended to refine the structure by increasing the cooling speed in the transformation region and simultaneously improve strength and toughness. Therefore, it does not have any meaning unless it starts before the transformation starts or at least before the transformation ends. For this reason, the accelerated cooling start temperature is limited to 750 ° C. or higher. This accelerated cooling requires cooling to a temperature of 550 ° C. or lower in order to enjoy the effect. This is because when the temperature exceeds 550 ° C., the transformation during accelerated cooling does not proceed sufficiently, and the structure is not sufficiently refined. The preferred accelerated cooling start temperature is 760 ° C. or higher, and the preferred accelerated cooling stop temperature range is 520 or lower and 300 ° C. or higher.

なお、加速冷却時の冷却速度は、鋼成分や意図する強度や低温靭性レベルにもよるが、板厚方向に表面から板厚の１／４の位置で、加速冷却開始温度から５５０℃までの平均冷却速度が３℃／秒以上とすることが望ましい。   The cooling rate during accelerated cooling depends on the steel composition, the intended strength, and the low temperature toughness level, but from the accelerated cooling start temperature to 550 ° C. at a position 1/4 of the plate thickness from the surface in the plate thickness direction. The average cooling rate is desirably 3 ° C./second or more.

また、冷却後の圧延材に対し、Ａｃ１温度以下の焼き戻し処理を付加しても本願発明の優れた特徴を損ねることはない。冷却の不均一性をキャンセルし、材質の板内均一性を高めるためにはむしろ好ましい。   Moreover, even if the tempering process below Ac1 temperature is added with respect to the rolled material after cooling, the outstanding characteristic of this invention is not impaired. It is rather preferable in order to cancel the non-uniformity of cooling and increase the in-plate uniformity of the material.

転炉−連続鋳造−厚板工程で種々の鋼成分の鋼板（厚さ１９〜１００ｍｍ）を製造し、その材質を調査した。
表１に比較鋼とともに本願発明鋼の鋼成分を、表２に鋼板の製造条件と諸特性を示す。
本願発明にしたがって製造した鋼板（本発明鋼）は、すべて良好な特性を有する。これに対し、本願発明によらずに製造した鋼板（比較鋼）は、いずれかの特性が劣ることが分かる。 Steel sheets of various steel components (thickness 19 to 100 mm) were manufactured in the converter-continuous casting-thick plate process, and the materials were investigated.
Table 1 shows the steel components of the present invention steel together with the comparative steel, and Table 2 shows the production conditions and various properties of the steel sheet.
All the steel plates manufactured according to the present invention (present invention steel) have good characteristics. On the other hand, it can be seen that a steel sheet (comparative steel) manufactured without using the present invention is inferior in any of the characteristics.

比較鋼１１はＣ量が高いため、本願発明鋼に比較し母材、再現ＨＡＺとも低温靭性に劣る。
比較鋼１２はＮｂが添加されておらず、また、比較鋼１３はＣｒ量が低いため、いずれも高温強度が低い。
比較鋼１４は、Ｃ量が低いために高温強度が低い。
比較鋼１５はＣｒ量が高いため、母材、再現ＨＡＺとも靭性に劣る。
比較鋼１６はＮｂが高いため、ＨＡＺ靭性に劣る。
比較鋼１７−１〜３の成分は本願発明鋼５と同一である。しかし、比較鋼１７−１は圧延終了温度が低く、結果として加速冷却開始温度が確保できずに低くなってしまったため、常温、高温強度ともに低い。比較鋼１７−２は加速冷却開始温度が低いため、常温、高温強度ともに低い。比較鋼１７−３は、加速冷却停止温度が高いため、常温、高温強度ともに低い。
比較鋼１８は、個々の元素や製造方法は本願発明範囲内であり、常温、高温強度や靭性などは490MPa級としての所要特性を満足しているものの、ＰＣＭが高いため、溶接性（斜めｙ形溶接割れ試験）において割れが発生した。 Since the comparative steel 11 has a high C content, both the base material and the reproduced HAZ are inferior in low-temperature toughness compared to the steel of the present invention.
Since the comparative steel 12 is not added with Nb, and the comparative steel 13 has a low Cr content, the high temperature strength is low.
Since the comparative steel 14 has a low C content, the high temperature strength is low.
Since the comparative steel 15 has a high Cr content, both the base material and the reproduced HAZ are inferior in toughness.
Since comparative steel 16 has high Nb, it is inferior in HAZ toughness.
The components of the comparative steels 17-1 to 17-3 are the same as those of the present invention steel 5. However, the comparative steel 17-1 has a low rolling end temperature, and as a result, the accelerated cooling start temperature cannot be ensured and has become low, so both the room temperature and the high temperature strength are low. Since the comparative cooling steel 17-2 has a low accelerated cooling start temperature, both the room temperature and the high temperature strength are low. Since comparative steel 17-3 has a high accelerated cooling stop temperature, both normal temperature and high temperature strength are low.
The comparative steel 18 has individual elements and manufacturing methods within the scope of the present invention, and the room temperature, high temperature strength, toughness and the like satisfy the required characteristics as a 490 MPa class, but because of high PCM, weldability (diagonal y Cracks occurred in the shape weld cracking test.

Figure 0004834149
Figure 0004834149

Figure 0004834149
Figure 0004834149

本発明により、高温強度と低温靭性に優れた溶接構造用鋼が大量かつ安価に提供できるようになった。その結果、建築構造用として、耐火被覆の軽減または省略が可能となった。また、建築以外の用途においても、強度、靭性などの基本性能を具備した上で、さらに高温強度をも具備したため、高温に晒される可能性のある溶接構造物用鋼として、構造物の安全性を一段と高めることができるようになった。   According to the present invention, a steel for welded structure excellent in high temperature strength and low temperature toughness can be provided in a large amount and at low cost. As a result, it has become possible to reduce or omit the fireproof coating for building structures. In addition to the basic properties such as strength and toughness in applications other than construction, it also has high-temperature strength, so it can be used as a steel for welded structures that may be exposed to high temperatures. Can be further improved.

Claims (5)

成分が質量％で、
Ｃ ：０．０２〜０．０５％
Ｓｉ：０．６０％以下
Ｍｎ：０．６〜２．０％
Ｐ ：０．０２０％以下
Ｓ ：０．０１０％以下
Ｃｒ：０．５６〜１．５％
Ｎｂ：０．００５〜０．０２８％
Ａｌ：０．０６０％以下
Ｎ ：０．００１〜０．００６％であって、
さらに、不純物としてＭｏを０．０３％以下に制限し、残部が鉄および不可避的不純物からなり、
ＰCM＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｕ／２０＋Ｎｉ／６０＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／１０＋５Ｂで定義される溶接割れ感受性組成ＰCM値が０．２２％以下である鋼材を、１０００〜１３００℃の温度に加熱し、８００℃以上の温度で熱間圧延を終了し、その後７５０℃以上の温度から５５０℃以下の温度まで加速冷却し、該加速冷却が、板厚方向に表面から板厚の１／４の位置で加速冷却開始温度から５５０℃までの平均冷却速度が３℃／秒以上であることを特徴とする高温強度と低温靭性に優れる溶接構造用鋼の製造方法。Ingredient is% by mass
C: 0.0 2 ~0.05%
Si: 0.60% or less Mn: 0.6-2.0%
P: 0.020% or less S: 0.010% or less Cr: 0.56-1.5%
Nb: 0.005~0.0 28%
Al: 0.060% or less N: 0.001 to 0.006%,
Furthermore, Mo is limited to 0.03% or less as an impurity, and the balance consists of iron and inevitable impurities,
The P CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + steel weld crack susceptibility composition P CM value defined by 5B is less than 0.22%, was heated to a temperature of 1000 to 1300 ° C., Hot rolling is finished at a temperature of 800 ° C. or higher, and then accelerated cooling is performed from a temperature of 750 ° C. or higher to a temperature of 550 ° C. or lower. The accelerated cooling is performed at a position 1/4 of the plate thickness from the surface in the thickness direction. method for manufacturing a welding structural steel average cooling rate from accelerated cooling starting temperature to 550 ° C. is excellent in high temperature strength and low temperature toughness characterized by der Rukoto than 3 ° C. / sec. さらに、質量％で、
Ｖ ：０．０１〜０．１０％
Ｔｉ：０．００５〜０．０２５％
のいずれか１種または２種を含有することを特徴とする請求の範囲１に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。Furthermore, in mass%,
V: 0.01-0.10%
Ti: 0.005-0.025%
Any one or two of these are contained, The manufacturing method of the steel for welded structures excellent in the high temperature strength and low temperature toughness of Claim 1 characterized by the above-mentioned. さらに、質量％で
Ｎｉ：０．０５〜０．５０％
Ｃｕ：０．０５〜０．５０％
Ｂ ：０．０００２〜０．００３％
Ｍｇ：０．０００２〜０．００５％
のいずれか１種または２種以上を含有することを特徴とする請求の範囲１または２に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。Furthermore, in mass% Ni: 0.05 to 0.50%
Cu: 0.05 to 0.50%
B: 0.0002 to 0.003%
Mg: 0.0002 to 0.005%
Any 1 type or 2 types or more of these are contained, The manufacturing method of the steel for welded structures excellent in the high temperature strength and low temperature toughness of Claim 1 or 2 characterized by the above-mentioned. さらに、質量％で
Ｃａ ：０．０００５〜０．００４％
ＲＥＭ：０．０００５〜０．００８％
のいずれか１種を含有することを特徴とする請求の範囲１〜３のいずれか1項に記載の高温強度と低温靭性に優れる溶接構造用鋼の製造方法。Furthermore, in mass% Ca: 0.0005 to 0.004%
REM: 0.0005 to 0.008%
Any one of these is contained, The manufacturing method of the steel for welded structures which is excellent in the high temperature strength and low temperature toughness of any one of Claims 1-3 characterized by the above-mentioned. 成分が質量％で、
Ｃ ：０．０２〜０．０５％
Ｓｉ：０．６０％以下
Ｍｎ：０．６〜２．０％
Ｐ ：０．０２０％以下
Ｓ ：０．０１０％以下
Ｃｒ：０．５６〜１．５％
Ｎｂ：０．００５〜０．０２８％
Ａｌ：０．０６０％以下
Ｎ ：０．００１〜０．００６％であって、
さらに、不純物としてＭｏを０．０３％以下に制限し、残部が鉄および不可避的不純物からなり、
ＰCM＝Ｃ＋Ｓｉ／３０＋Ｍｎ／２０＋Ｃｕ／２０＋Ｎｉ／６０＋Ｃｒ／２０＋Ｍｏ／１５＋Ｖ／１０＋５Ｂで定義される溶接割れ感受性組成ＰCM値が０．２２％以下である鋼材を、１０００〜１３００℃の温度に加熱し、８００℃以上の温度で熱間圧延を終了し、その後７５０℃以上の温度から加速冷却を開始し、５５０℃以下の温度で加速冷却を停止して得られることを特徴とする高温強度と低温靭性に優れる溶接構造用鋼。Ingredient is% by mass
C: 0.0 2 ~0.05%
Si: 0.60% or less Mn: 0.6-2.0%
P: 0.020% or less S: 0.010% or less Cr: 0.56-1.5%
Nb: 0.005~0.0 28%
Al: 0.060% or less N: 0.001 to 0.006%,
Furthermore, Mo is limited to 0.03% or less as an impurity, and the balance consists of iron and inevitable impurities,
The P CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + steel weld crack susceptibility composition P CM value defined by 5B is less than 0.22%, was heated to a temperature of 1000 to 1300 ° C., High temperature strength and low temperature toughness characterized by being obtained by finishing hot rolling at a temperature of 800 ° C. or higher, then starting accelerated cooling from a temperature of 750 ° C. or higher and stopping accelerated cooling at a temperature of 550 ° C. or lower. Excellent welded structural steel.
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