JP3344305B2 - High-strength steel sheet for line pipe excellent in resistance to hydrogen-induced cracking and method for producing the same - Google Patents
High-strength steel sheet for line pipe excellent in resistance to hydrogen-induced cracking and method for producing the sameInfo
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- JP3344305B2 JP3344305B2 JP35853297A JP35853297A JP3344305B2 JP 3344305 B2 JP3344305 B2 JP 3344305B2 JP 35853297 A JP35853297 A JP 35853297A JP 35853297 A JP35853297 A JP 35853297A JP 3344305 B2 JP3344305 B2 JP 3344305B2
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Description
【０００１】[0001]
【発明の属する技術分野】この発明は、引張強度が900M
Pa以上というような高強度の鋼板であって、耐水素誘起
割れ性に優れたラインパイプ用鋼板、およびその製造方
法に関する。BACKGROUND OF THE INVENTION The present invention, argument ChoTsutomu degree of 900 M
The present invention relates to a steel sheet for a line pipe having a high strength of Pa or more and excellent in resistance to hydrogen-induced cracking, and a method for producing the same.
【０００２】[0002]
【従来の技術】近年、ラインパイプについては、高強度
であることと共に耐腐食性に優れることが要求されるこ
とが多い。これは油田等から産出される天然ガス中に硫
化水素（H2S）等の腐食性ガスを多量に含まれることが
あるため、その輸送に使用されるラインパイプにはこれ
らのガスに対する耐食性が要求されるからである。2. Description of the Related Art In recent years, line pipes are often required to have high strength and excellent corrosion resistance. This is because natural gas produced from oil fields and the like may contain a large amount of corrosive gas such as hydrogen sulfide (H 2 S), so the line pipes used for transportation must be resistant to these gases. Because it is required.
【０００３】しかしながら、一般に、鋼材を高強度化す
るために合金成分の添加量を増やすと炭素当量（Ceq.）
および溶接割れ感受性（Pcm）が上昇し、溶接熱影響部
の靭性劣化や低温割れが生じるだけでなく、腐食性ガス
中にさらされた場合には水素誘起割れ（以下「HIC」と
略記する）が発生する。このHICは、鋼材の強度が高く
なるほど発生しやすくなる。However, in general, the addition amount of increase when the carbon equivalent of the alloy components in order to increase the strength of the steel material (Ceq.)
In addition, the cracking susceptibility (Pcm) increases and not only deteriorates the toughness and low-temperature cracking of the weld heat affected zone, but also causes hydrogen induced cracking (hereinafter abbreviated as "HIC") when exposed to corrosive gas. Occurs. This HIC is more likely to occur as the strength of the steel material increases.
【０００４】また、HICは鋼材の成分偏析にも影響さ
れ、特に連続鋳造鋳片（ＣＣスラブ）から製造した鋼板
では中心偏析に起因する水素誘起割れが問題視され、そ
の防止対策が種々提案されている。しかし、引張り強度
が900MPa以上というような高強度鋼においてHICの発生
を抑制するような技術は未だ知られていない。[0004] HIC is also affected by the segregation of steel components. In particular, in steel sheets manufactured from continuous cast slabs (CC slabs), hydrogen-induced cracking due to central segregation is regarded as a problem, and various measures have been proposed to prevent such cracks. ing. However, a technique for suppressing the generation of HIC in a high-strength steel having a tensile strength of 900 MPa or more has not yet been known.
【０００５】[0005]
【発明が解決しようとする課題】本発明は、連続鋳造ス
ラブを素材としながら、900MPa以上の引張強度を有し、
しかも良好な耐食性、特に耐HIC性をも備えたラインパ
イプ用高強度鋼板、およびその製造方法を提供すること
を目的としてなされたものである。DISCLOSURE OF THE INVENTION The present invention has a tensile strength of 900 MPa or more while using a continuously cast slab as a raw material.
Moreover, it is an object of the present invention to provide a high-strength steel sheet for line pipes having good corrosion resistance, particularly HIC resistance, and a method for producing the same.
【０００６】[0006]
【課題を解決するための手段】本発明は、下記(1)の高
強度鋼板および下記(2)のその製造方法を要旨とする。SUMMARY OF THE INVENTION The gist of the present invention is a high-strength steel sheet of the following (1) and a method of manufacturing the same according to the following (2).
【０００７】(1) 重量％で、Ｃ：0.02〜0.10％、Si：
0.05〜0.50％、Mn：0.80〜1.40％、Ｐ：0.02％以下、
Ｓ：0.002％以下、Mo：0.60％を超えて1.50％まで、T
i：0.005〜0.030％、Ｂ：0.0005〜0.0020％、Ｎ：0.006
％以下、Cu：0.50％以下、Ni：1.50％以下、Cr：0.60％
以下、Nb：0.10％以下、Ｖ：0.10％以下、Al：0.10％以
下、Ca：0.0050％以下、残部Feおよび不可避的不純物
で、Ceqが0.42〜0.58％の鋼からなり、金属組織が水に
よる急冷組織で、且つ引張強度が900MPa以上である耐水
素誘起割れ性に優れたラインパイプ用高強度鋼板。(1) By weight%, C: 0.02 to 0.10%, Si:
0.05 to 0.50%, Mn: 0.80 to 1.40%, P: 0.02% or less,
S: 0.002% or less, Mo: Over 0.60% to 1.50%, T
i: 0.005 to 0.030%, B: 0.0005 to 0.0020%, N: 0.006
%, Cu: 0.50% or less, Ni: 1.50% or less, Cr: 0.60%
Below, Nb: 0.10% or less, V: 0.10% or less, Al: 0.10% or less, Ca: 0.0050% or less, balance Fe and inevitable impurities
It is made of steel with Ceq of 0.42 ~ 0.58% ,
High-strength steel sheet for line pipes with excellent quenching structure and tensile strength of 900MPa or more and excellent resistance to hydrogen-induced cracking.
【０００８】上記の成分の中で、ＰとＳおよびＮは不純
物であって、できるだけ少ない方が望ましい。また、Cu
からCaまでの成分は、必須成分ではないが、必要に応じ
てそれぞれの上限値までの範囲で含有させてもよい成分
である。なお、Ceqは、下記の式で表されるものであ
る。[0008] Among the above components, P, S and N are impurities, and it is desirable that they be as small as possible. Also, Cu
Components up pressurized et al Ca is not an essential component, a good component be contained in the range up to each upper limit if necessary. Ceq is represented by the following equation.
【０００９】 Ceq（％）＝Ｃ+(Mn/6)+｛(Cu+Ni)/15｝+｛（Cr+Mo+Ｖ)/5｝ (2) 上記(1)に記載の化学組成を持つ連続鋳造スラブを
1000〜1200℃に加熱した後、表面温度が700〜800℃の範
囲で仕上げ圧延し、圧延終了後直ちに鋼板の冷却速度が
５〜30℃／secとなるように、650℃以上の温度域から40
0℃以下まで水冷することを特徴とする金属組織が水に
よる急冷組織で、且つ引張強度が900MPa以上の耐水素誘
起割れ性に優れたラインパイプ用高強度鋼板の製造方
法。Ceq (%) = C + (Mn / 6) + {(Cu + Ni) / 15} + {(Cr + Mo + V) / 5} (2) The chemical composition described in the above (1) Have a continuous cast slab
After heating to 1000-1200 ° C, finish rolling at a surface temperature in the range of 700-800 ° C, and immediately after the end of rolling, from the temperature range of 650 ° C or higher, so that the cooling rate of the steel sheet becomes 5-30 ° C / sec. 40
Metal structure characterized by water cooling to 0 ° C or less
A method for producing a high-strength steel sheet for line pipes having a quenched structure and excellent tensile strength of 900 MPa or more and excellent resistance to hydrogen-induced cracking.
【００１０】本発明鋼板は、上記(1)に記載のとおりの
化学組成によって、素材が連続鋳造スラブであっても、
高強度でかつ優れた耐HIC性を有するラインパイプ用と
して好適な鋼板になる。そして、その鋼板は、素材（ス
ラブ）の化学組成とともに、圧延条件および加速冷却条
件を適正に選定した(2)の製造方法によって量産規模で
比較的容易に製造することができる。[0010] The steel sheet of the present invention has a chemical composition as described in (1) above, even if the material is a continuous cast slab.
It is a steel plate suitable for line pipes having high strength and excellent HIC resistance. The steel sheet can be relatively easily manufactured on a mass production scale by the manufacturing method (2) in which the rolling conditions and the accelerated cooling conditions are appropriately selected together with the chemical composition of the raw material (slab).
【００１１】[0011]
【発明の実施の形態】１．本発明鋼板（素材スラブ）の
化学組成について 本発明鋼板の化学組成を前記のように決定した理由を各
成分の作用効果と共に説明する。なお、この化学組成
は、前記の本発明の製造方法で使用する素材（連続鋳造
スラブ）の化学組成と同じであるから、ここの説明は連
続鋳造スラブの組成の限定理由にも相当する。以下、成
分含有量についての％は重量％を意味する。BEST MODE FOR CARRYING OUT THE INVENTION Regarding Chemical Composition of Steel Sheet (Material Slab) of the Present Invention The reason why the chemical composition of the steel sheet of the present invention was determined as described above will be described together with the operational effects of each component. Note that this chemical composition is the same as the chemical composition of the raw material (continuously cast slab) used in the above-described manufacturing method of the present invention, and thus the description here also corresponds to the reason for limiting the composition of the continuously cast slab. Hereinafter,% for the component content means% by weight.
【００１２】Ｃ：0.02〜0.10％ Ｃ含有量が0.02％未満では所定の強度が得難く、一方、
0.10％を超えてしまうとPcmが高くなって溶接割れ感受
性が大きくなり、かつ連続鋳造スラブの凝固過程におけ
る包晶反応の影響でスラブ割れが発生しやすくなる。さ
らにスラブの中心部にＣが過度に濃化し偏析帯を形成し
てしまうことによりHICの発生を助長する。以上の理由
でＣ含有量の適正範囲は0.02〜0.10％である。C: 0.02 to 0.10% If the C content is less than 0.02%, it is difficult to obtain a predetermined strength.
If it exceeds 0.10%, Pcm increases and the susceptibility to weld cracking increases, and slab cracking is likely to occur due to the peritectic reaction in the solidification process of the continuously cast slab. Further, C is excessively concentrated in the central portion of the slab to form a segregation zone, thereby promoting the generation of HIC. For the above reasons, the appropriate range of the C content is 0.02 to 0.10%.
【００１３】なお、上記のPcmは、下記の式で表される
ものである。The above Pcm is represented by the following equation.
【００１４】 Pcm(％)＝Ｃ+(Si/30）+｛（Mn+Cu+Cr)/20｝＋(Ni/60）+(Mo/15)+(Ｖ/10)+5Mo Si：0.05〜0.50％ Siは鋼の脱酸剤として働き、また鋼を強化する作用を持
つ。その含有量が0.05％未満では脱酸が不十分となり、
一方、0.50％を超えると溶接熱影響部（HAZ）に島状マ
ルテンサイトが多く生成して、HAZの靭性を極度に劣化
させる。従って、Si含有量の適正範囲は0.05〜0.50％で
ある。Pcm (%) = C + (Si / 30) + {(Mn + Cu + Cr) / 20} + (Ni / 60) + (Mo / 15) + (V / 10) + 5MoSi: 0.05 ~ 0.50% Si acts as a steel deoxidizer and has the effect of strengthening steel. If the content is less than 0.05%, deoxidation becomes insufficient,
On the other hand, if it exceeds 0.50%, a large amount of island martensite is generated in the heat affected zone (HAZ), and the toughness of HAZ is extremely deteriorated. Therefore, the appropriate range of the Si content is 0.05 to 0.50%.
【００１５】Mn：0.80〜1.40％ Mnは鋼を強化しかつ強靭化する元素である。しかし、0.
80％未満では本発明が目的とする高強度鋼としての必要
な強度が得られない。一方、Mnの含有量が1.40％を超え
るような過剰になると、連続鋳造スラブの中心偏析が増
大して水素誘起割れが発生し易くなる。従って、Mn含有
量は0.80〜1.40％とした。Mn: 0.80-1.40% Mn is an element that strengthens and toughens steel. But 0.
If it is less than 80%, the strength required as the high-strength steel intended by the present invention cannot be obtained. On the other hand, when the content of Mn is excessive such that it exceeds 1.40%, the segregation of the center of the continuously cast slab increases, and hydrogen-induced cracking easily occurs. Therefore, the Mn content was set to 0.80 to 1.40%.
【００１６】Ｐ：0.020％以下、Ｓ：0.002％以下 これらは、鋼の不可避的不純物であって、できる限り少
ない方が望ましい元素である。Ｐの含有量が0.020％を
超えるとスラブ中の中心偏析度が高まり、局部的な硬度
の上昇が生じる。また、Ｓが0.002％を超えると、鋼に
対して有害な介在物（MnS）が多く生成する。従ってＰ
の含有量を0.020％以下、Ｓの含有量を0.002％以下に制
限する。P: 0.020% or less, S: 0.002% or less These are inevitable impurities of steel, and it is an element that it is desirable to reduce as much as possible. When the P content exceeds 0.020%, the degree of center segregation in the slab increases, and a local increase in hardness occurs. When S exceeds 0.002%, a large amount of inclusions (MnS) harmful to steel is generated. Therefore P
Is limited to 0.020% or less, and the S content is limited to 0.002% or less.
【００１７】Mo：0.60％を超えて1.50％まで Moはスラブの凝固過程において中心偏析部に濃化し難い
元素である。また鋼板の水冷時において焼き入れ性を向
上させて鋼板の強度を上昇させる。従って、優れた耐HI
C性と高強度を両立させるのに非常に有効な成分であ
る。0.60％以下では本発明が目的とする高強度鋼に必要
な強度が得られない。しかしながら1.50％を超えると、
溶接割れが発生しやすくなり溶接時の作業性を極度に低
下させると共にコストが高くなる。従って、Moの含有量
は0.60％を超えて1.50％までが適正範囲である。Mo: more than 0.60 % to 1.50% Mo is an element that is hardly concentrated in the central segregation part in the solidification process of the slab. Further, when the steel sheet is water-cooled, the hardenability is improved to increase the strength of the steel sheet. Therefore, excellent HI resistance
It is a very effective component for achieving both C properties and high strength. If it is less than 0.60%, the strength required for the high-strength steel intended by the present invention cannot be obtained. However, if it exceeds 1.50%,
Welding cracks are likely to occur, extremely reducing workability during welding and increasing costs. Therefore, the Mo content is more than 0.60% and up to 1.50% is an appropriate range.
【００１８】Ti：0.005〜0.030％ Tiは鋼の強度を向上させ、スラブの品質も安定させる元
素であるが、0.005％未満ではその効果が十分でない。
一方、Tiを過度に添加すると、溶接熱影響部（HAZ）の
靭性を劣化させるため、Ti含有量の適正範囲は0.005〜
0.030％である。Ti: 0.005 to 0.030% Ti is an element that improves the strength of steel and stabilizes the quality of the slab, but if it is less than 0.005%, its effect is not sufficient.
On the other hand, if Ti is added excessively, the toughness of the heat affected zone (HAZ) is deteriorated.
0.030%.
【００１９】Ｂ：0.0005〜0.0020％ Ｂは鋼の焼き入れ性を高める元素であり、本発明が対象
とする高強度鋼においては、母材強度確保のため0.0005
％（５ppm）以上の含有が必要である。しかしながら、
過度の添加は母材靭性およびHAZ靭性を劣化させるた
め、含有量の上限は0.0020％(20ppm）に制限した。B: 0.0005% to 0.0020% B is an element that enhances the hardenability of steel. In the high-strength steel to which the present invention is applied, 0.0005% is used to secure base metal strength.
% (5 ppm) or more is required. However,
Excessive addition degrades base metal toughness and HAZ toughness, so the upper limit of the content was limited to 0.0020% (20 ppm).
【００２０】Ｎ：0.0060％以下 Ｎは鋼中に必然的に含有される元素であるが、できるだ
け少ない方がよい。Ｎの含有量が0.0060％を超えると、
AlＮの生成によるスラブ品質の悪化を招くため上限を0.
0060％に制限した。また、Ｎを低く抑えることによって
溶接熱影響部（HAZ）の靭性が向上する。従って、例え
ば、−40℃でのシャルピー吸収エネルギーが200Ｊ以上
と言うような、良好なHAZ靭性が要求される場合には、
Ｎの含有量を0.0010％以下に抑えるのが望ましい。N: 0.0060% or less N is an element that is inevitably contained in steel, but it is preferable that N is as small as possible. When the N content exceeds 0.0060%,
The upper limit is set to 0.
0060%. Also, by keeping N low, the toughness of the heat affected zone (HAZ) is improved. Therefore, for example, when good HAZ toughness is required, such as Charpy absorbed energy at −40 ° C. of 200 J or more,
It is desirable to keep the N content to 0.0010% or less.
【００２１】本発明の鋼板またはその素材となるスラブ
の一つは、上記の成分の外、残部が実質的にFeからなる
ものである。ただし、その炭素当量(Ceq）は、下記の範
囲になければならない。The steel sheet of the present invention or one of the slabs to be used as a material for the steel sheet has the above components and the balance substantially composed of Fe. However, the carbon equivalent (Ceq) must be in the following ranges.
【００２２】Ceq：0.42〜0.58％ 本発明が目標とする性能を備えたラインパイプ用の高強
度鋼を得るには、前記の各元素を上述した範囲内に制限
するだけでは不十分である。そこで、母材強度確保のた
め前記の式で表されるCeq.が0.42％以上となるように前
記に元素の含有量を調節することとした。他方、合金元
素の過度の添加によって、Ceqが大きくなりすぎると母
材靭性およびHAZ靭性を劣化させるため、Ceq.は0.58％
までに止めることとした。Ceq: 0.42 to 0.58% In order to obtain a high-strength steel for line pipes having the target performance of the present invention, it is not sufficient to limit the above elements to the above-mentioned ranges. Therefore, in order to secure the strength of the base material, the content of the elements is adjusted so that Ceq. Represented by the above equation is 0.42% or more. On the other hand, if the Ceq becomes too large due to excessive addition of alloying elements, the base material toughness and the HAZ toughness will be deteriorated.
I decided to stop by.
【００２３】本発明の鋼板またはその素材となるスラブ
の他の一つは、前記の成分に加えてさらに以下に述べる
Cu、Ni、Cr、Nb、Ｖ、AlおよびCaの中の１種以上を含有
するものである。それぞれの成分の作用効果と含有量の
限定理由は次のとおりである。[0023] The steel sheet of the present invention or another one of the slabs used as the material thereof is described below in addition to the above components.
It contains one or more of Cu, Ni, Cr, Nb, V, Al and Ca. The effects of each component and the reasons for limiting the contents are as follows.
【００２４】なお、これらの成分を含有する場合にもCe
qは0.42〜0.58％の範囲になければならない。It should be noted that even when these components are contained, Ce
q must be in the range of 0.42 to 0.58%.
【００２５】Cu：0.50％以下 Cuは鋼を強化する元素であるから必要に応じて添加する
が、過度の添加はCuチェッキングをひきおこすので、添
加する場合でもその含有量は0.50％までとする。なお、
Cuを添加する場合にはCuチェッキングを防止するために
NiをCuの約１／２以上の割合で添加するのが望ましい。Cu: 0.50% or less Cu is an element that strengthens steel and is added as necessary. However, excessive addition causes Cu checking, so even when added, the content is limited to 0.50%. . In addition,
When adding Cu to prevent Cu checking
It is desirable to add Ni at a ratio of about 1/2 or more of Cu.
【００２６】Ni：1.50％以下 Niは、鋼板の靭性を高めるので、必要に応じて添加して
もよい。但し、過度の添加はコスト高になるので含有量
は1.50％までに制限した。なお、Niは単独で添加しても
よく、前記のCuと複合添加して、Cuチェッキングの防止
を兼ねさせてもよい。Ni: 1.50% or less Ni may increase the toughness of the steel sheet, and may be added as necessary. However, the content was limited to 1.50% because excessive addition would increase the cost. Note that Ni may be added alone, or may be added in combination with the above-mentioned Cu to also prevent Cu checking.
【００２７】Cr：0.60％以下 Crは鋼を強化する元素であるから必要に応じて添加でき
るが、過度に添加するとコスト高になるだけでなくHAZ
靭性も劣化する。従って、添加する場合でもその含有量
は0.60％までとする。Cr: 0.60% or less Since Cr is an element that strengthens steel, it can be added as needed. However, excessive addition not only increases the cost but also increases the HAZ.
The toughness also deteriorates. Therefore, even if it is added, its content is limited to 0.60%.
【００２８】Nb：0.10％以下 Nbは鋼の強度および靭性を向上させる元素である。特
に、オーステナイト未再結晶領域で仕上げ圧延を行い、
オーステナイト粒を細粒化した後、Ar3変態点以上から
急冷するという本発明方法によって鋼板を製造した場
合、Nbは、細粒でかつ均一な組織の強靱な鋼板を得るの
に極めて有効である。従って、要求される鋼板の強度・
靭性バランスに応じて添加するのが望ましい。しかしな
がら、Nbを過度に添加すると、スラブ加熱時に固溶が不
完全になると共に、コスト高になるので、添加する場合
でもその含有量は0.10％までに抑える必要がある。Nb: 0.10% or less Nb is an element that improves the strength and toughness of steel. In particular, finish rolling in the austenite unrecrystallized region,
When a steel sheet is manufactured by the method of the present invention in which the austenite grains are refined and then quenched from the Ar3 transformation point or higher, Nb is extremely effective in obtaining a tough steel sheet having a fine grain and a uniform structure. Therefore, the required steel sheet strength
It is desirable to add according to the toughness balance. However, if Nb is added excessively, solid solution will be incomplete during slab heating and the cost will increase. Therefore, even when Nb is added, its content must be suppressed to 0.10%.
【００２９】Ｖ：0.10％以下 Ｖは、一般にはスラブ加熱時に固溶して鋼を固溶強化す
る作用と、圧延時に低温仕上げを行えば析出効果によっ
て鋼を強化する作用を持つ。しかしながら、過度の添加
はHAZ靱性を低下させるので、Ｖの含有量は固溶強化に
十分な範囲として、0.10％までに制限した。このＶも必
須ではなく、必要に応じて添加することができる成分で
ある。V: 0.10% or less V generally has the effect of forming a solid solution during slab heating and solid solution strengthening, and the effect of strengthening the steel by the precipitation effect if a low-temperature finish is performed during rolling. However, excessive addition reduces the HAZ toughness, so the V content was limited to 0.10%, a range sufficient for solid solution strengthening. This V is not essential, and is a component that can be added as needed.
【００３０】Al：0.10％以下 Alは、脱酸剤として鋼の溶製段階で用いられるが、その
含有量が多すぎると、鋼板中の介在物量が増加し耐HIC
性を低下させる。従って、Al含有量は0.10％以下に制限
する必要がある。脱酸剤として必要最小限度の添加を行
って、残存するAlをできるだけ少なくするのが望まし
く、含有量は不可避不純物の範囲あるいは実質的に０で
あってもよい。Al: 0.10% or less Al is used as a deoxidizing agent in the smelting stage of steel, but if its content is too large, the amount of inclusions in the steel sheet increases and the HIC resistance increases.
Reduce the nature. Therefore, it is necessary to limit the Al content to 0.10% or less. It is desirable to add the necessary minimum amount as a deoxidizing agent to reduce the remaining Al as much as possible, and the content may be in the range of unavoidable impurities or substantially zero.
【００３１】Ca：0.0050％以下 Caは、耐HIC鋼においては非常に有害な介在物を形態制
御し、かつ低減させるのに有効な元素である。また、Ca
を添加することによって伸長性のMnSを低減し、鋼自体
の靭性を向上させる効果もある。従って、必要に応じて
添加すればよいが、過剰に添加するとCa系の介在物が増
加すると共にコスト高になる。従って、Caを添加すると
きにもその含有量は0.0050％までとする。Ca: 0.0050% or less Ca is an element effective in controlling the form and reducing very harmful inclusions in HIC-resistant steel. Also, Ca
The effect of reducing the extensible MnS and improving the toughness of the steel itself is also obtained by the addition of. Therefore, it may be added as needed, but if it is added excessively, Ca-based inclusions increase and the cost increases. Therefore, when Ca is added, its content is limited to 0.0050%.
【００３２】（２）製造条件について 連続鋳造スラブの加熱：連続鋳造スラブの加熱温度は10
00〜1200℃とする。鋼板の靭性向上のためには加熱温度
は低い方が好ましいが、1000℃未満では所定の強度を得
ることができない場合がある。一方、加熱温度が1200℃
を超えるとオーステナイト粒が粗大化し鋼板の靭性を劣
化させるおそれがある。(2) Manufacturing Conditions Heating of continuous casting slab: The heating temperature of the continuous casting slab is 10
00-1200 ° C. To improve the toughness of the steel sheet, the lower the heating temperature, the better. However, if it is less than 1000 ° C., the desired strength may not be obtained. On the other hand, the heating temperature is 1200 ° C
If it exceeds 300, austenite grains may become coarse and the toughness of the steel sheet may be degraded.
【００３３】仕上げ圧延：本発明方法の特徴の一つは、
オーステナイト未再結晶領域で仕上げ圧延を完了し、鋼
板をAr3変態点以上から急冷することにより、細粒組織
の強靱な鋼板を得ることにある。従って、鋼板の水冷開
始温度をAr3変態点以上にする必要があるので、仕上げ
圧延の終了温度を鋼板の表面温度で800〜700℃の範囲に
制限する。表面温度が800℃を超えるようだと製品鋼板
の靭性が低下する。一方、表面温度が700℃よりも低く
なるような圧延では、圧延中にフェライト変態が起きて
均一な組織が得られず耐HIC性が低下してしまう。Finish rolling: One of the features of the method of the present invention is that
It is to obtain a tough steel sheet having a fine-grained structure by completing finish rolling in an austenite unrecrystallized region and rapidly cooling the steel sheet from the Ar3 transformation point or higher. Accordingly, since the water cooling start temperature of the steel sheet needs to be equal to or higher than the Ar3 transformation point, the finish rolling end temperature is limited to a range of 800 to 700 ° C. in terms of the surface temperature of the steel sheet. If the surface temperature seems to exceed 800 ° C., the toughness of the product steel sheet decreases. On the other hand, in rolling in which the surface temperature is lower than 700 ° C., ferrite transformation occurs during rolling, so that a uniform structure cannot be obtained and HIC resistance decreases.
【００３４】仕上げ圧延後の水冷：上記仕上げ圧延終了
後、直ちに、即ち、表面温度が650℃以上である鋼板を4
00℃以下の温度域まで冷却速度が５〜30℃/secとなるよ
うに水冷する。水冷停止温度が400℃よりも高温の場
合、細粒組織が得られず所定の強度および靭性が得られ
ない。また、水冷時の鋼板の冷却速度が30℃/secを超え
ると、過度の急冷のために鋼板中の残留応力が増大し、
鋼板の平坦度不良の発生頻度が高くなる。一方、５℃/s
ec未満では冷却速度が低くすぎて鋼板の焼き入れが不十
分となり強度および靭性が悪化する。さらに板厚中心部
の組織制御が不十分で拡散性元素が濃化し易くなり、鋼
板中の硬度分布が不均一になると共に耐HIC性が劣化す
る。なお、冷却速度は、５〜30℃/secの範囲内で鋼板の
化学組成および板厚に応じて決定する必要がある。Water cooling after finish rolling: Immediately after finishing the above-mentioned finish rolling, a steel sheet having a surface temperature of 650 ° C. or more
Water cooling is performed so that the cooling rate is 5 to 30 ° C / sec to a temperature range of 00 ° C or lower. When the water cooling stop temperature is higher than 400 ° C., a fine grain structure cannot be obtained, and a predetermined strength and toughness cannot be obtained. Also, if the cooling rate of the steel sheet during water cooling exceeds 30 ° C / sec, the residual stress in the steel sheet increases due to excessive rapid cooling,
The frequency of occurrence of poor flatness of the steel sheet increases. On the other hand, 5 ° C / s
If it is less than ec, the cooling rate is too low, and the quenching of the steel sheet becomes insufficient, and the strength and toughness deteriorate. Further, the structure control of the central part of the sheet thickness is insufficient, so that the diffusible element is easily concentrated, the hardness distribution in the steel sheet becomes uneven, and the HIC resistance is deteriorated. The cooling rate needs to be determined in the range of 5 to 30 ° C./sec according to the chemical composition and thickness of the steel sheet.
【００３５】上記のように400℃以下の温度域まで水冷
した後の冷却方法は任意である。例えば空冷に切り替え
て差し支えない。The cooling method after water cooling to a temperature range of 400 ° C. or lower as described above is optional. For example, it may be switched to air cooling.
【００３６】[0036]
【実施例】以下、実施例によって本発明の効果を具体的
に詳細する。この実施例では表１に示す組成の連続鋳造
スラブを使用して、表２に示す圧延および冷却の条件で
20mm厚×2000mm幅×20m長さの鋼板を製造した。得られ
た鋼板の性能を表３に示す。なお、母材靱性は−40℃で
のシャルピー衝撃試験での吸収エネルギー、HAZ靱性
は、溶接した継手からノッチが溶融線の部分になるよう
に採取した試験片による−20℃でのシャルピー衝撃試験
の吸収エネルギーである。溶接は、溶接金属の強度が約
1000MPaになる溶接材料を使用し、表裏面に70度の開先
を切って突き合わせた板を３電極および４電極のSAWで
表裏両面側から行った。入力は表面側で3.9KJ/mm、裏面
側で3.2KJ/mmとした。耐HIC性は、NACE液に96時間浸漬
した後の割れ発生の有無によって評価した。表３中の×
が割れの発生、○が割れの発生なし、を意味する。EXAMPLES The effects of the present invention will be specifically described below with reference to examples. In this example, a continuous cast slab having the composition shown in Table 1 was used, and the rolling and cooling conditions shown in Table 2 were used.
A 20 mm thick x 2000 mm wide x 20 m long steel plate was manufactured. Table 3 shows the performance of the obtained steel sheet. The base metal toughness is the absorbed energy in the Charpy impact test at -40 ° C, and the HAZ toughness is the Charpy impact test at -20 ° C using a specimen taken from the welded joint so that the notch is in the melting line. Is the energy absorbed. In welding, the strength of the weld metal is about
Using a welding material having a pressure of 1000 MPa , a plate whose front and back surfaces were cut with a 70-degree groove and butted was formed from both front and back surfaces with SAW of three electrodes and four electrodes. The input was 3.9 KJ / mm on the front side and 3.2 KJ / mm on the back side. The HIC resistance was evaluated by the presence or absence of cracking after being immersed in a NACE solution for 96 hours. × in Table 3
Indicates that a crack occurred, and ○ indicates that no crack occurred.
【００３７】[0037]
【表１】 [Table 1]
【００３８】[0038]
【表２】 [Table 2]
【００３９】[0039]
【表３】 [Table 3]
【００４０】表３の試験No.１〜11は、鋼の組成および
製造条件ともに本発明範囲内のものである。ここでは、
鋼板の目標性能として、降伏強度（YP）800MPa以上、引
張強度(TS）900MPa以上、母材靱性200J以上、継手靱性1
00J以上を目標とした。No.１〜11の鋼板はいずれも高い
強度と共に良好な耐HIC性および継手靭性を有している
ことがわかる。Test Nos. 1 to 11 in Table 3 are within the scope of the present invention in both the steel composition and the production conditions. here,
The target performance of steel sheet is yield strength (YP) 800MPa or more, tensile strength (TS) 900MPa or more, base material toughness 200J or more, joint toughness 1
We aimed at 00J or more. It can be seen that all of the steel sheets Nos. 1 to 11 have high strength and good HIC resistance and joint toughness.
【００４１】試験No.12〜25は鋼板の化学組成が、試験N
o.26〜31は製造条件が、それぞれ本発明で定める範囲を
はずれる比較例である。試験No.12、13、15および16の
ように、鋼板の合金成分のいずれかが本発明で定める範
囲の上限を超える場合には、中心偏析度の悪化と共に耐
HIC性が低下するとともに、母材靭性およびHAZ靭性が劣
化している。逆に、試験No.14、17、24のように合金元
素のいずれかが本発明で定める範囲の下限を下回る場合
や、試験No.17、19、21、23、25のようにCeq.が下限を
下回る場合には、母材強度が目標値に達していない。In Test Nos. 12 to 25, the chemical composition of the steel sheet was
o.26 to 31 are comparative examples in which the production conditions are out of the range defined by the present invention. When any of the alloy components of the steel sheet exceeds the upper limit of the range specified in the present invention as in Test Nos. 12, 13, 15, and 16, the center segregation degree deteriorates and the resistance increases.
As the HIC property decreases, the base material toughness and the HAZ toughness deteriorate. Conversely, when any of the alloy elements is below the lower limit of the range defined in the present invention as in Test Nos. 14, 17, 24, or when Ceq. Is as in Test Nos. 17, 19, 21, 23, 25. If the value is below the lower limit, the base metal strength has not reached the target value.
【００４２】試験No.13はSiが上限を外れているためHAZ
靭性が目標未達となっている。さらに、No.22、23はC
a、Alが上限を外れている場合である。これらの元素は
鋼中の介在物形態に影響を及ぼす元素であり、過度の添
加により介在物が増加し耐HIC性が低下していることが
分かる。In test No. 13, HAZ was found because Si exceeded the upper limit.
The toughness has not reached the target. Nos. 22 and 23 are C
a, where Al is outside the upper limit. These elements are elements that affect the form of inclusions in the steel, and it can be seen that the inclusions increase due to excessive addition and the HIC resistance decreases.
【００４３】次に圧延条件の影響であるが、No.26に見
られるようにスラブの加熱温度が高すぎる場合には母材
靭性が低下するとともに、冷却速度の低下により中心偏
析度が大きくなり、耐HIC性も低下している。Next, as shown in No. 26, when the heating temperature of the slab is too high, the base metal toughness decreases and the degree of center segregation increases due to a decrease in the cooling rate. , HIC resistance is also reduced.
【００４４】No.27は、逆に加熱温度が低くすぎる例で
あり、強度が目標値に達していない。No.28は、圧延の
仕上げ温度が高すぎるために母材靭性が目標未達であ
る。逆に、No.29のように仕上げ温度が低くすぎる場合
や、No.30のように水冷開始温度が低くすぎると、母材
強度および中心偏析度が劣化し耐HIC性が悪化する。ま
た、No.31のように水冷停止温度が400℃よりも高い場合
には、十分な焼入れ効果が確保できないため、母材強度
および靭性ともに目標値に達していない。No. 27 is an example in which the heating temperature is too low, and the strength has not reached the target value. In No. 28, the base material toughness did not reach the target because the finishing temperature of rolling was too high. Conversely, if the finishing temperature is too low, as in No. 29, or if the water cooling start temperature is too low, as in No. 30, the base metal strength and the degree of center segregation will deteriorate, and the HIC resistance will deteriorate. Further, when the water cooling stop temperature is higher than 400 ° C. as in No. 31, the sufficient quenching effect cannot be secured, so that both the base metal strength and the toughness have not reached the target values.
【００４５】なお、表１の鋼ＵはTiの含有量が低すぎる
もの、鋼ａはＮの含有量が多すぎるものである。いずれ
もAlNの生成に起因してスラブに割れが発生したため、
圧延を中止したので、試験結果は得られていない。ま
た、試験No.25（表２の条件ト）、は、圧延後の冷却速
度が大きすぎて鋼板に平坦度不良が発生した。即ち、こ
の条件は実用的ではない。The steel U in Table 1 has a too low Ti content, and the steel a has a too high N content. In both cases, cracks occurred in the slab due to the generation of AlN ,
Since the rolling was stopped, no test results were obtained. In Test No. 25 (conditions in Table 2), the cooling rate after rolling was too high, and flatness defects occurred in the steel sheet. That is, this condition is not practical.
【００４６】[0046]
【発明の効果】実施例に示したように、本発明の鋼板は
高い強度および溶接熱影響部の靱性とともに優れた耐HI
C性を有するもので、H ２ S等の腐食性ガスを含む原油や
天然ガスの輸送用ラインパイプの材料として極めて好適
なものである。この鋼板は、素材の連続鋳造スラブの化
学組成、圧延条件および圧延終了後の冷却条件を前述の
ように定めた本発明方法によって量産規模で製造するこ
とができる。As shown in the examples, the steel sheet of the present invention has high strength and toughness of the heat affected zone and excellent HI resistance.
Those having a C resistance, is extremely suitable as a material of the transport line pipe for crude oil and natural gas containing corrosive gases such as H 2 S. This steel sheet can be manufactured on a mass production scale by the method of the present invention in which the chemical composition of the continuous cast slab of the material, the rolling conditions and the cooling conditions after the completion of the rolling are determined as described above.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 濱田 昌彦 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (72)発明者 藤原 知哉 大阪府大阪市中央区北浜４丁目５番33号 住友金属工業株式会社内 (56)参考文献 特開 平６−220577（ＪＰ，Ａ) 特開 平８−225883（ＪＰ，Ａ) 特開 平９−316534（ＪＰ，Ａ) 特開 平９−111338（ＪＰ，Ａ) 特開 平７−150290（ＪＰ，Ａ) 特開 平11−172365（ＪＰ，Ａ) 特開 平11−61328（ＪＰ，Ａ) 特開 平11−36042（ＪＰ，Ａ) 特開 平10−324950（ＪＰ，Ａ) 特開 平10−298707（ＪＰ，Ａ) 特開 平10−273751（ＪＰ，Ａ) 特開 平10−244349（ＪＰ，Ａ) 特開 平10−237583（ＪＰ，Ａ) (58)調査した分野(Int.Cl.7，ＤＢ名) C22C 38/00 - 38/60 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiko Hamada 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Inside Sumitomo Metal Industries, Ltd. (72) Tomoya Fujiwara 4-chome, Kitahama, Chuo-ku, Osaka City, Osaka Prefecture No. 33 Sumitomo Metal Industries, Ltd. (56) References JP-A-6-220577 (JP, A) JP-A 8-225883 (JP, A) JP-A 9-316534 (JP, A) 9-111338 (JP, A) JP-A-7-150290 (JP, A) JP-A-11-172365 (JP, A) JP-A-11-61328 (JP, A) JP-A-11-36042 (JP, A) A) JP-A-10-324950 (JP, A) JP-A-10-298707 (JP, A) JP-A-10-273751 (JP, A) JP-A-10-244349 (JP, A) −237583 (JP, A) (58) Field surveyed (Int. Cl. 7 , DB name) C22C 38/00-38 / 60
Claims (2)
0.50％、Mn：0.80〜1.40％、Ｐ：0.02％以下、Ｓ：0.00
2％以下、Mo：0.60％を超えて1.50％まで、Ti：0.005〜
0.030％、Ｂ：0.0005〜0.0020％、Ｎ：0.006％以下、C
u：0.50％以下、Ni：1.50％以下、Cr：0.60％以下、N
b：0.10％以下、Ｖ：0.10％以下、Al：0.10％以下、C
a：0.0050％以下、残部Feおよび不可避的不純物で、Ceq
が0.42〜0.58％の鋼からなり、金属組織が水による急冷
組織で、且つ引張強度が900MPa以上である耐水素誘起割
れ性に優れたラインパイプ用高強度鋼板。(1) C: 0.02-0.10%, Si: 0.05-% by weight
0.50%, Mn: 0.80 to 1.40%, P: 0.02% or less, S: 0.00
2% or less, Mo: more than 0.60% to 1.50%, Ti: 0.005 ~
0.030%, B: 0.0005-0.0020%, N: 0.006% or less, C
u: 0.50% or less, Ni: 1.50% or less, Cr: 0.60% or less, N
b: 0.10% or less, V: 0.10% or less, Al: 0.10% or less, C
a: 0.0050% or less, with the balance Fe and unavoidable impurities, Ceq
Is made of 0.42-0.58% steel, and the metal structure is quenched by water
A high-strength steel sheet for line pipes that has a structure and a tensile strength of 900 MPa or more and is excellent in resistance to hydrogen-induced cracking.
スラブを1000〜1200℃に加熱した後、表面温度が700〜8
00℃の範囲で仕上げ圧延し、圧延終了後直ちに鋼板の冷
却速度が５〜30℃／secとなるように、650℃以上の温度
域から400℃以下まで水冷することを特徴とする金属組
織が水による急冷組織で、且つ引張強度が900MPa以上の
耐水素誘起割れ性に優れたラインパイプ用高強度鋼板の
製造方法。2. A continuous cast slab having the chemical composition according to claim 1 having a surface temperature of 700 to 8
00 finish rolling at a range of ° C., so that the cooling rate immediately steel sheet after rolling completion is 5 to 30 ° C. / sec, a metal assembly, characterized by water cooling from a temperature range of not lower than 650 ° C. to 400 ° C. or less
A method for producing a high-strength steel sheet for line pipes having a quenched structure of water and a tensile strength of 900 MPa or more and excellent in resistance to hydrogen-induced cracking.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP35853297A JP3344305B2 (en) | 1997-12-25 | 1997-12-25 | High-strength steel sheet for line pipe excellent in resistance to hydrogen-induced cracking and method for producing the same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP35853297A JP3344305B2 (en) | 1997-12-25 | 1997-12-25 | High-strength steel sheet for line pipe excellent in resistance to hydrogen-induced cracking and method for producing the same |
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| Publication Number | Publication Date |
|---|---|
| JPH11189840A JPH11189840A (en) | 1999-07-13 |
| JP3344305B2 true JP3344305B2 (en) | 2002-11-11 |
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|---|---|---|---|
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|---|---|---|---|---|
| KR100518323B1 (en) * | 2001-12-24 | 2005-10-04 | 주식회사 포스코 | High Strength Linepipe Steel and Method for Manufacturing the Steel |
| JP4341396B2 (en) * | 2003-03-27 | 2009-10-07 | Ｊｆｅスチール株式会社 | High strength hot rolled steel strip for ERW pipes with excellent low temperature toughness and weldability |
| KR101105052B1 (en) | 2004-10-15 | 2012-01-16 | 주식회사 포스코 | Method for manufacturing high strength hot rolled steel sheet having excellent uniformity in coil |
| BRPI0615215B1 (en) * | 2005-08-22 | 2014-10-07 | Nippon Steel & Sumitomo Metal Corp | SEWLESS STEEL PIPE FOR LINE PIPE AND PROCESS FOR YOUR PRODUCTION |
| KR100723166B1 (en) | 2005-12-24 | 2007-05-30 | 주식회사 포스코 | High strength linepipe steel with high toughness and high hic resistance at the h2 s containing environment, and manufacturing method therefor |
| KR100833035B1 (en) | 2006-12-20 | 2008-05-27 | 주식회사 포스코 | High-strength and high-toughness steel plate for linepipe excellent in deformability and method for manufacturing the same |
| KR101867701B1 (en) | 2016-11-11 | 2018-06-15 | 주식회사 포스코 | Pressure vessel steel plate with excellent hydrogen induced cracking resistance and manufacturing method thereof |
-
1997
- 1997-12-25 JP JP35853297A patent/JP3344305B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH11189840A (en) | 1999-07-13 |
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