JPH10298645A - Manufacture of hot rolled high tensile strength steel plate - Google Patents
Manufacture of hot rolled high tensile strength steel plateInfo
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- JPH10298645A JPH10298645A JP12174497A JP12174497A JPH10298645A JP H10298645 A JPH10298645 A JP H10298645A JP 12174497 A JP12174497 A JP 12174497A JP 12174497 A JP12174497 A JP 12174497A JP H10298645 A JPH10298645 A JP H10298645A
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】この発明は、電縫鋼管やスパイラ
ル鋼管あるいはＵＯ鋼管等の素材として最適な“耐水素
誘起割れ性と靱性に優れた熱延高張力鋼板”の製造方法
に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hot-rolled high-strength steel sheet having excellent resistance to hydrogen-induced cracking and toughness, which is most suitable as a material for an electric resistance welded steel pipe, a spiral steel pipe or a UO steel pipe. .
【０００２】[0002]
【従来技術とその課題】近年、原油や天然ガスの輸送に
は“熱延鋼板を成形・溶接して製造した鋼管”で構築さ
れたパイプラインが重要な役割を担うようになったが、
最近では原油，天然ガス資源の安定供給を求めて条件の
厳しい地域にまで採掘の手が延びるようになり、その結
果パイプラインも厳しい環境下に敷設されることが多く
なって、寒冷地での使用や硫化水素を含むサワ−オイ
ル，サワ−ガスを輸送することが珍しくない状況となっ
ている。また、厳しい環境下で大規模なパイプライン建
設が強いられるようになったことから、軽量化による作
業性向上の観点より、ラインパイプ用鋼板に対する高張
力化の要望も強くなってきている。従って、ラインパイ
プの素材である熱延鋼板は、造管のために成形性の良い
ことは勿論、高強度，優れた低温靱性，優れた耐サワ−
性（つまり優れた耐水素誘起割れ性）を兼ね備えること
が必要となってきた。2. Description of the Related Art In recent years, pipelines constructed of "steel pipes formed by forming and welding hot-rolled steel sheets" have come to play an important role in transporting crude oil and natural gas.
Recently, mining has been extended to areas with severe conditions in search of a stable supply of crude oil and natural gas resources. As a result, pipelines are often laid in harsh environments, and in cold regions. It is not uncommon to use and transport sour oil and sour gas containing hydrogen sulfide. In addition, since the construction of large-scale pipelines has been forced under severe environments, there has been a strong demand for higher tensile strength for line pipe steel sheets from the viewpoint of improving workability by reducing the weight. Therefore, the hot rolled steel sheet, which is the material of the line pipe, has good formability for pipe making, as well as high strength, excellent low temperature toughness, and excellent sour resistance.
It has become necessary to combine the properties (that is, excellent resistance to hydrogen-induced cracking).
【０００３】なお、ラインパイプ用熱延鋼板の靱性向上
策に関しては、例えば特開昭６３−２２７７１５号公報
に「熱間圧延を終了した鋼板の巻取温度を５００℃を下
回る低い温度域にまで下げる方法」が開示されている。
しかし、低温で巻き取るこの方法は、鋼板が硬くなるた
め巻取り装置の能力の面から製造可能範囲が限定される
ばかりか、温度ムラが発生して平坦さが崩れやすく、そ
のため巻取った際の形状（姿）が不良となってその後の
作業に支障を来たす懸念が拭えないものであった。Japanese Patent Laid-Open Publication No. 63-227715 discloses a method for improving the toughness of a hot-rolled steel sheet for a line pipe, for example, “The hot-rolled steel sheet is wound up to a low temperature range below 500 ° C. "How to lower" is disclosed.
However, this method of winding at a low temperature not only limits the manufacturable range in terms of the capacity of the winding device because the steel sheet becomes hard, but also causes unevenness in temperature due to the occurrence of unevenness, and therefore, when winding, The concern that the shape (shape) of the device became defective and hindered the subsequent work could not be wiped out.
【０００４】一方、耐水素誘起割れ性の改善については
介在物の減少に加えて偏析の抑制が重要であることが知
られており、例えば特開平６−８１０３４号公報には、
ラインパイプ用熱延鋼板の耐水素誘起割れ性改善策とし
て「連続鋳造鋳片を熱延用加熱炉にダイレクトチャ−ジ
すると共にここで１２５０℃以上の高温域に１０時間以
上加熱して偏析を拡散させる方法」が開示されている。
しかし、鋳片の高温長時間加熱を行うこの方法では、加
熱によってオ−ステナイト粒が通常方法での圧延では十
分に細粒化できないほどに大きくなり、そのため得られ
る熱延鋼板の靱性が低下するという問題があった。On the other hand, it is known that suppression of segregation is important in addition to reduction of inclusions for improvement of resistance to hydrogen-induced cracking. For example, JP-A-6-81034 discloses that
As a measure to improve the hydrogen-induced cracking resistance of hot-rolled steel sheets for line pipes, "Separate cast slabs are directly charged to a heating furnace for hot rolling and are heated to a high temperature region of 1250 ° C or more for 10 hours or more to segregate. A method of spreading "is disclosed.
However, in this method in which the slab is heated at a high temperature for a long time, the austenite grains are so large that they cannot be sufficiently refined by the conventional rolling method, so that the toughness of the obtained hot-rolled steel sheet decreases. There was a problem.
【０００５】このようなことから、本発明が目的とした
のは、前述したような従来技術の問題点を解決し、ライ
ンパイプ用として必要な高強度と優れた低温靱性，耐水
素誘起割れ性を備えると共に、良好な成形性をも有した
熱延高張力鋼板の製造方法を提供することである。In view of the above, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide high strength, excellent low-temperature toughness, and resistance to hydrogen-induced cracking required for line pipes. And a method for producing a hot-rolled high-tensile steel sheet having good formability.
【０００６】[0006]
【課題を解決するための手段】そこで、本発明者等は上
記目的を達成すべく鋭意研究を行った結果、次に示すよ
うな知見を得ることができた。即ち、熱延鋼板の素材鋼
として強度，靱性，成形性，耐水素誘起割れ性に留意し
て特定化学組成に成分調整したNb添加鋼を用いると共
に、その熱間圧延においては、粗圧延の工程で十分な圧
下率を加えた後に一旦再結晶促進のための“待機時間”
を確保し、続いて再度粗圧延を１パスだけ施して再結晶
粒の完全細粒化とフェライト粒微細化の下地を強化した
後、熱間仕上圧延を開始するまでの間で更に“待機時
間”を確保して未再結晶粒を十分に微細再結晶粒化さ
せ、熱間仕上圧延，加速冷却，適量のフェライト生成の
ための加速冷却途中の空冷，再度の加速冷却を施してか
ら巻取りを行うと、スラブの高温加熱による靱性劣化を
懸念することなく、また巻取温度を過度に低下させて靱
性改善を図る必要もなく、ラインパイプ用として必要な
高強度，優れた低温靱性，優れた耐水素誘起割れ性，良
好な成形性を兼備した熱延高張力鋼板の安定製造が可能
になることを見出したのである。The present inventors have conducted intensive studies to achieve the above object, and as a result, have obtained the following findings. That is, Nb-added steel whose composition has been adjusted to a specific chemical composition in consideration of strength, toughness, formability, and resistance to hydrogen-induced cracking is used as the material steel for the hot-rolled steel sheet. "Waiting time" to promote recrystallization once after applying sufficient rolling reduction
After that, rough rolling is again performed only one pass to strengthen the base for complete grain refinement of recrystallized grains and grain refinement of ferrite grains. To ensure that the unrecrystallized grains are sufficiently finely recrystallized and then subjected to hot finish rolling, accelerated cooling, air cooling during accelerated cooling to produce an appropriate amount of ferrite, accelerated cooling again, and then wound. By doing so, there is no need to worry about deterioration of toughness due to high temperature heating of the slab, and it is not necessary to reduce the winding temperature excessively to improve toughness. It has been found that stable production of hot-rolled high-strength steel sheets having both hydrogen-induced cracking resistance and good formability is possible.
【０００７】本発明は、上記知見事項等を基にして完成
されたものであって、 「 Ｃ：0.04〜0.12％（以降、 成分割合を表す％は重量％とする), Si： 0.5％以下， Mn： 1.0〜 1.8％， Ｐ：0.03％以下， Ｓ： 0.005％以下， Al： 0.005〜0.08％， Ｎ：0.0080％以下， Nb：0.02〜0.06％， Ti：0.04％以下 を含むか、 あるいは更に Cu： 0.5％以下， Ni： 0.5％以下， Cr： 0.5％以下， Mo： 0.5％以下， Ｖ：0.10％以下， Ca：0.01％以下 のうちの１種又は２種以上をも含むと共に残部がFe及び
不可避不純物から成る鋼片を、 １１５０〜１２５０℃に
加熱し、 まず圧下率の累計が４０％以上となる粗圧延を
行った後、 一旦３０〜１８０秒間保持し、 引き続いて９
５０〜１０５０℃の温度域で圧下率１５％以上の粗圧延
を更に１パス行って熱間粗圧延を終了し、次いで、 この
粗圧延終了の５〜１２０秒後から熱間仕上圧延を開始し
て７５０〜８５０℃で該仕上圧延を終えた後、 ３〜５０
℃/sの冷却速度で５５０〜７００℃まで冷却し、 ここで
２〜１０秒間の空冷を行ってから、 再度５００〜６２０
℃の温度域まで３〜８０℃/sの冷却速度で冷却して巻取
ることによって、 強度，低温靱性，耐水素誘起割れ性，
成形性に優れた熱延高張力鋼板を安定製造できるように
した点」を特徴とするものである。The present invention has been completed on the basis of the above findings and the like, and includes the following: "C: 0.04 to 0.12% (hereinafter,% representing the component ratio is referred to as% by weight), Si: 0.5% or less , Mn: 1.0 to 1.8%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.08%, N: 0.0080% or less, Nb: 0.02 to 0.06%, Ti: 0.04% or less, or Further, one or more of Cu: 0.5% or less, Ni: 0.5% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.10% or less, and Ca: 0.01% or less are included and the balance is included. Is heated to 1150-1250 ° C., first subjected to rough rolling so that the cumulative reduction becomes 40% or more, and then temporarily held for 30-180 seconds.
In a temperature range of 50 to 1050 ° C., rough rolling with a rolling reduction of 15% or more is further performed by one pass to complete hot rough rolling, and then hot finish rolling is started 5 to 120 seconds after the completion of the rough rolling. After finishing the finish rolling at 750-850 ° C., 3-50
Cooling to 550-700 ° C at a cooling rate of ° C / s, air cooling for 2-10 seconds here, and then 500-620 again
Cooling at a cooling rate of 3 to 80 ° C / s to the temperature range of 3 ° C and winding, the strength, low-temperature toughness, resistance to hydrogen-induced cracking,
A point that a hot-rolled high-tensile steel sheet having excellent formability can be stably manufactured. "
【０００８】上述のように、本発明は、熱延高張力鋼板
の製造に際し、１１５０〜１２５０℃の高熱延加熱温度
や５００〜６２０℃での高温巻取りを採用しても寒冷地
で使用するラインパイプ用等として十分に満足できる靱
性が確保されるように、「粗圧延での再結晶促進のため
の“待機工程”」を取り入れたことを１つの大きな特徴
点としているが、以下、本発明において素材たる鋼片の
化学組成並びに鋼片の処理条件を前記の如くに限定した
理由をその作用と共に詳述する。As described above, the present invention can be used in a cold region even when a hot-rolling heating temperature of 1150 to 1250 ° C. or a high-temperature winding at 500 to 620 ° C. is adopted in the production of a hot-rolled high-tensile steel sheet. One of the major features is that it incorporates a "standby process for promoting recrystallization in rough rolling" to ensure sufficient toughness for line pipes. The reason why the chemical composition of the steel slab and the processing conditions of the steel slab as the raw material in the present invention are limited as described above will be described in detail together with the operation.
【０００９】(A) 鋼片の化学組成 a) Ｃ Ｃは熱延鋼板に所望の高張力を確保するための重要な成
分であるが、その含有量が0.04％未満では必要な強度を
確保することができず、一方、0.12％を超えてＣを含有
させると靱性低下を招く。このため、Ｃ含有量は0.04〜
0.12％と定めたが、好ましくは0.05〜0.09％に調整する
のが良い。(A) Chemical composition of billet a) C C is an important component for ensuring a desired high tensile strength in a hot-rolled steel sheet. If its content is less than 0.04%, the required strength is secured. On the other hand, if the content of C exceeds 0.12%, the toughness is reduced. Therefore, the C content is 0.04 to
Although it is set to 0.12%, it is preferable to adjust it to 0.05 to 0.09%.
【００１０】b) Si Siは鋼の脱酸に有効な元素であるが、過剰に含有させる
と熱延鋼板の靱性を低下させることから、その含有量は
0.5％以下と定めた。B) Si Si is an element effective for deoxidizing steel. However, when contained excessively, the toughness of a hot-rolled steel sheet is reduced.
It was determined to be 0.5% or less.
【００１１】c) Mn Mnも熱延鋼板に所望の高張力を確保するための重要な成
分であるが、その含有量が 1.0％未満では必要な強度を
確保することができず、一方、 1.8％を超えてMnを含有
させると偏析が強くなって耐水素誘起割れ性が低下す
る。従って、Mn含有量は 1.0〜 1.8％と定めた。C) Mn Mn is also an important component for ensuring a desired high tensile strength in a hot-rolled steel sheet, but if its content is less than 1.0%, the required strength cannot be secured. %, The segregation becomes strong and the hydrogen-induced cracking resistance decreases. Therefore, the Mn content is determined to be 1.0 to 1.8%.
【００１２】d) Ｐ Ｐは熱延鋼板の靱性，耐水素誘起割れ性の両方に悪影響
を及ぼす好ましくない不純物元素であり、本発明では所
望の靱性及び耐水素誘起割れ性を確保するためにＰ含有
量を0.03％以下と定めた。D) PP is an undesired impurity element that adversely affects both the toughness and the resistance to hydrogen-induced cracking of a hot-rolled steel sheet. In the present invention, P is used to ensure desired toughness and resistance to hydrogen-induced cracking. The content was determined to be 0.03% or less.
【００１３】e) Ｓ Ｓは、鋼中でMnＳを形成し水素集積部となって耐水素誘
起割れ性を劣化させる好ましくない不純物元素であるた
め、本発明では所望の耐水素誘起割れ性を確保すべくＳ
含有量を 0.005％以下と定めた。ただ、好ましくはＳ含
有量を0.0015％以下にまで低減するのが良い。E) SS is an undesired impurity element that forms MnS in steel and becomes a hydrogen accumulation part to deteriorate the resistance to hydrogen-induced cracking. Therefore, the present invention ensures the desired resistance to hydrogen-induced cracking in the present invention. S to do
The content was determined to be 0.005% or less. However, it is preferable to reduce the S content to 0.0015% or less.
【００１４】f) Al Alは鋼の脱酸のために添加される元素であるが、Al含有
量が 0.005％未満では脱酸効果が十分でなく、一方、0.
08％を超えて含有させても脱酸効果は飽和してしまうの
で経済的に不利となる。従って、Al含有量は 0.005〜0.
08％と定めた。F) Al Al is an element added for deoxidizing steel. When the Al content is less than 0.005%, the deoxidizing effect is not sufficient.
If the content exceeds 08%, the deoxidizing effect is saturated, so that it is economically disadvantageous. Therefore, the Al content is 0.005 to 0.
08%.
【００１５】g) Ti Tiは鋼片（スラブ）のひび割れ防止のために添加される
成分であるが、0.04％を超えて添加してもその効果が飽
和することから、Ti含有量の上限を0.04％と定めた。G) Ti Ti is a component added to prevent cracking of a steel slab (slab). However, even if added over 0.04%, its effect is saturated, so the upper limit of the Ti content is limited. 0.04%.
【００１６】h) Ｎ Ｎは、鋼片（スラブ）の鋳造過程で窒化物として析出し
鋼片（スラブ）のひび割れの原因となる好ましくない不
純物元素であるため、その弊害を除くべくＮ含有量は0.
0080％以下と定めた。H) NN N is an undesired impurity element which precipitates as a nitride during the casting process of the slab (slab) and causes cracking of the slab (slab). is 0.
0080% or less.
【００１７】i) Nb Nbは本発明において重要な成分であり、鋼板の強度確保
に寄与すると共に、細粒化作用によって鋼板の靱性を改
善する効果を発揮する。しかし、これらの効果はNb含有
量が0.02％未満では十分に現れず、一方、0.06％を超え
て含有させても効果が飽和して経済的に不利となる。従
って、Nb含有量については0.02〜0.06％と定めた。I) Nb Nb is an important component in the present invention, and contributes to securing the strength of the steel sheet and has an effect of improving the toughness of the steel sheet by the action of grain refinement. However, these effects do not appear sufficiently when the Nb content is less than 0.02%, while the effect is saturated and causes an economic disadvantage if the Nb content exceeds 0.06%. Therefore, the Nb content was determined to be 0.02 to 0.06%.
【００１８】j) Cu，Ni，Cr，Mo，Ｖ及びCa 更に、本発明では、以下に示す理由によって鋼中にCu:
0.5％以下，Ni:0.5％以下，Cr:0.5％以下，Mo:0.5％以
下，Ｖ：0.10％以下あるいはCa：0.01％以下を単独又は
複合で含有させても良い。Cu，Ni又はCrは、何れも熱延
鋼板の強化に有効であるだけでなく、水素吸収量の低減
にも効果を発揮する成分である。ただ、何れの成分も
0.5％を超えて含有させても前記効果が飽和して経済的
でないので、それらの含有量は 0.5％以下と定めた。ま
た、Moは変態強化を通じて熱延鋼板の強化に有効である
ばかりか、降伏比を下げて成形性を改善する効果を発揮
する成分でもある。しかし、 0.5％を超えて含有させる
とその効果は飽和してしまい、更にＨＡＺ部の靱性が劣
化するようにもなる。従って、Mo含有量は 0.5％以下と
定めた。更に、Ｖは析出強化によって熱延鋼板を強化す
る作用を有しているが、0.10％を超えて含有させても効
果が飽和してしまい経済的に不利となる。従って、Ｖ含
有量は0.10％以下と定めた。そして、Caは鋼中の介在物
を制御して水素割れの原因となるMnＳの量を減少するの
に効果を発揮する成分であるが、0.01％を超えて含有さ
せてもその効果が飽和し経済的でないので、Ca含有量は
0.01％以下と定めた。J) Cu, Ni, Cr, Mo, V and Ca Further, in the present invention, Cu:
0.5% or less, Ni: 0.5% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.10% or less, or Ca: 0.01% or less may be contained alone or in combination. Cu, Ni or Cr is a component that is effective not only for strengthening a hot-rolled steel sheet but also for reducing hydrogen absorption. However, any component
If the content exceeds 0.5%, the effect is saturated and it is not economical. Therefore, their contents are set to 0.5% or less. Mo is not only effective for strengthening the hot-rolled steel sheet through transformation strengthening, but also is a component that exerts an effect of lowering the yield ratio and improving the formability. However, if the content exceeds 0.5%, the effect is saturated, and the toughness of the HAZ portion is further deteriorated. Therefore, the Mo content was determined to be 0.5% or less. Further, V has an effect of strengthening the hot-rolled steel sheet by precipitation strengthening. However, even if V is contained in an amount exceeding 0.10%, the effect is saturated, and it is economically disadvantageous. Therefore, the V content was determined to be 0.10% or less. Ca is a component that exerts an effect in controlling the inclusions in the steel to reduce the amount of MnS that causes hydrogen cracking, but its effect is saturated even if it exceeds 0.01%. Because it is not economical, the Ca content is
It was determined to be 0.01% or less.
【００１９】なお、上記以外の成分はFe及び不可避不純
物であるが、これら組成の鋼は例えば転炉，電気炉ある
いは平炉等によって溶製すれば良く、リムド鋼，キャッ
プド鋼，セミキルド鋼又はキルド鋼の何れの鋼種であっ
ても良い。また、鋼片の製造も“連続鋳造法”あるいは
“造塊−分塊圧延法”等の何れの手段によっても良い。Components other than the above are Fe and inevitable impurities. Steels having these compositions may be melted by, for example, a converter, an electric furnace, or an open hearth, and may be rimmed steel, capped steel, semi-killed steel or killed steel. Any steel type of steel may be used. Also, the production of the billet may be performed by any means such as "continuous casting method" or "ingot-bulking rolling method".
【００２０】(B) 鋼片の処理条件（熱延鋼板の製造条
件） 本発明では、熱間圧延に供する鋼片は１１５０〜１２５
０℃に加熱保持してから粗圧延を開始する。なぜなら、
加熱温度が１１５０℃未満であると強度向上に有効でな
い未固溶のNbＣが多くなって目標とする強度の確保が困
難であり、一方、１２５０℃を超える温度域に加熱する
とオ−ステナイト粒が大きくなりすぎ、その後の圧延条
件を調整しても細粒化が十分に達成されずに靱性が低下
するためである。なお、好ましい加熱温度の範囲は１１
５０〜１１９０℃である。ところで、加熱炉に挿入する
鋼片は、鋳造後の“高温のままのスラブ”でも、室温で
放置されたスラブでも構わない。(B) Slab Processing Conditions (Hot Rolled Steel Sheet Manufacturing Conditions) In the present invention, the slabs to be subjected to hot rolling are 1150 to 125
After maintaining the temperature at 0 ° C., rough rolling is started. Because
If the heating temperature is lower than 1150 ° C., it is difficult to secure the target strength due to an increase in undissolved NbC which is not effective in improving the strength. This is because, even if the subsequent rolling conditions are adjusted, grain refinement is not sufficiently achieved, and the toughness is reduced. The preferred heating temperature range is 11
50-1190 ° C. Incidentally, the steel slab to be inserted into the heating furnace may be a “slab kept at high temperature” after casting or a slab left at room temperature.
【００２１】さて、本発明では、熱間圧延での粗圧延の
条件が重要である。粗圧延では、まず累積圧下率４０％
以上まで圧延されるが、これは再結晶を利用して十分に
細粒化を図るために必要な条件である。そして、再結晶
を十分に行わせるためには、次の圧延まで３０〜１８０
秒間の待機時間を確保する必要がある。この場合、待機
時間が３０秒未満では再結晶が不十分となり、また１８
０秒を超えるとその効果が飽和すると共に生産能率が低
下する。なお、この待機時間は６０〜１２０秒とするの
が好ましい。In the present invention, the conditions for rough rolling in hot rolling are important. In rough rolling, first, the cumulative rolling reduction is 40%
Rolling is performed up to the above, which is a necessary condition for sufficiently refining by utilizing recrystallization. Then, in order to sufficiently perform recrystallization, 30 to 180 until the next rolling.
It is necessary to secure a waiting time of seconds. In this case, if the waiting time is less than 30 seconds, recrystallization becomes insufficient, and
If the time exceeds 0 seconds, the effect is saturated and the production efficiency is reduced. The waiting time is preferably set to 60 to 120 seconds.
【００２２】待機に引続く粗圧延の最終パスでは、９５
０〜１０５０℃で圧下率１５％以上の圧延を１パス行
う。この圧延では、前の粗圧延で粗大に残った未再結晶
粒を再結晶により細粒化させる効果が発揮され、また十
分に細かくなっていた再結晶粒はこの圧延では再結晶せ
ずにフェライト生成核となる変形帯等を蓄積することと
なる。上記粗圧延の最終パスでは、圧延温度が１０５０
℃を超えていると粒成長による粗大化が生じ、一方、圧
延温度が９５０℃未満であると再結晶促進作用が小さす
ぎるので、９５０〜１０５０℃で圧延すると定めたが、
好ましい範囲は９５０〜１０００℃である。In the final pass of the rough rolling following the standby, 95
One pass of rolling at a rolling reduction of 15% or more at 0 to 1050 ° C. In this rolling, the effect of recrystallizing the unrecrystallized grains remaining coarsely in the previous rough rolling is exhibited, and the recrystallized grains that have become sufficiently fine are not recrystallized in this rolling without ferrite. Deformation zones and the like serving as production nuclei are accumulated. In the final pass of the rough rolling, the rolling temperature is 1050
If the temperature exceeds ℃, coarsening occurs due to grain growth, while if the rolling temperature is less than 950 ° C, the recrystallization accelerating action is too small.
The preferred range is 950-1000 ° C.
【００２３】粗圧延後に仕上圧延（通常は連続仕上圧
延）を実施するが、粗圧延から仕上圧延までの間には５
〜１２０秒の待機時間を設ける必要がある。なぜなら、
この待機時間が５秒未満では前述の粗圧延前段までの未
再結晶粒の再結晶が不十分であり、１２０秒を超えても
効果が飽和するからである。ただ、より好ましい待機時
間は５〜３０秒である。After the rough rolling, finish rolling (usually continuous finish rolling) is performed.
It is necessary to provide a waiting time of up to 120 seconds. Because
If the waiting time is less than 5 seconds, the recrystallization of the unrecrystallized grains up to the preceding stage of the rough rolling is insufficient, and the effect is saturated even if it exceeds 120 seconds. However, a more preferable waiting time is 5 to 30 seconds.
【００２４】仕上圧延では、再結晶は起こらず、オ−ス
テナイトが加工硬化し、その後のフェライト変態で変形
帯等から微細なフェライトが生成する。仕上圧延の仕上
温度は７５０〜８５０℃とする。これは、仕上温度が８
５０℃を超えると回復によりオ−ステナイトの加工硬化
が不十分となり、一方、７５０℃未満では変態したフェ
ライトに歪が加わって延性や靱性が劣化する原因となる
からである。仕上圧延のより好ましい仕上温度は７５０
〜８００℃である。In finish rolling, recrystallization does not occur, austenite is work-hardened, and fine ferrite is formed from deformation bands and the like in the subsequent ferrite transformation. The finishing temperature of the finish rolling is 750 to 850 ° C. This is because the finishing temperature is 8
If the temperature exceeds 50 ° C., the work hardening of austenite becomes insufficient due to recovery, while if the temperature is lower than 750 ° C., strain is applied to the transformed ferrite, which causes deterioration in ductility and toughness. A more preferred finishing temperature for finish rolling is 750.
８００800 ° C.
【００２５】熱間圧延（仕上圧延）を終えた鋼板は、ま
ず冷却速度３〜５０℃/sで加速冷却する。これは、この
段階での冷却速度が３℃/s未満であるとバンド状パ−ラ
イトが生成して耐水素誘起割れ性が低下し、一方、５０
℃/sを超える冷却速度ではベイナイト量が多くなって延
性が低下するからである。The steel sheet after hot rolling (finish rolling) is first subjected to accelerated cooling at a cooling rate of 3 to 50 ° C./s. This is because if the cooling rate at this stage is less than 3 ° C./s, band-like pearlite is formed and the hydrogen-induced cracking resistance is reduced.
If the cooling rate exceeds ° C / s, the amount of bainite increases and the ductility decreases.
【００２６】そして、冷却途中の５５０〜７００℃（好
ましくは５５０〜６５０℃）から２〜１０秒間の空冷を
実施する。この空冷によって適量のフェライトが生成す
るので、降伏比を下げると共に延性を向上させることが
可能となる。この場合、空冷時間が２秒未満ではフェラ
イトの生成量が不足するため降伏比低下，延性向上の効
果が十分でなく、一方、空冷時間が１０秒を超えると材
質劣化を招くようになる。Then, air cooling is performed for 2 to 10 seconds from 550 to 700 ° C. (preferably 550 to 650 ° C.) during the cooling. Since an appropriate amount of ferrite is generated by this air cooling, the yield ratio can be reduced and the ductility can be improved. In this case, if the air cooling time is less than 2 seconds, the amount of ferrite generated is insufficient, so that the effects of lowering the yield ratio and improving the ductility are not sufficient. On the other hand, if the air cooling time exceeds 10 seconds, material deterioration is caused.
【００２７】途中空冷の後は、再度、冷却速度３〜８０
℃/sで加速冷却が行われる。この第２段目の加速冷却で
の冷却速度が３℃/s未満であるとフェライト粒界に過度
にセメンタイトが析出して靱性が劣化し、一方、８０℃
/sを超える冷却速度で冷却してもその効果は飽和する。After the air cooling on the way, the cooling rate is again 3 to 80.
Accelerated cooling is performed at ° C / s. If the cooling rate in the second stage of accelerated cooling is less than 3 ° C./s, cementite will excessively precipitate at the ferrite grain boundaries and the toughness will deteriorate.
Even if the cooling rate is more than / s, the effect is saturated.
【００２８】加速冷却は５００〜６２０℃に至るまで実
施し、加速冷却後は巻取りを行う。この場合、５００℃
を下回る温度まで加速冷却を行うと、鋼板が硬くなって
巻取りが困難になるため製造範囲が狭くなると共に、平
坦さが崩れて巻取った際の形状（姿）が不良となる。一
方、加速冷却を６２０℃よりも高い温度域で終了する
と、粒界へのセメンタイトの析出量が多くなったり、パ
−ライトバンドが生成したりして、靱性や耐水素割れ性
が低下する。なお、加速冷却終了の好ましい温度範囲
（好ましい巻取温度範囲）は５００〜５９０℃である。The accelerated cooling is performed up to 500 to 620 ° C., and after the accelerated cooling, winding is performed. In this case, 500 ° C
When accelerated cooling is performed to a temperature lower than the above, the steel sheet becomes hard and winding becomes difficult, so that the manufacturing range is narrowed, and the flatness is lost and the shape (shape) when wound is poor. On the other hand, when the accelerated cooling is completed in a temperature range higher than 620 ° C., the amount of cementite precipitated at the grain boundaries increases, or a pearlite band is formed, and the toughness and the resistance to hydrogen cracking decrease. The preferred temperature range at the end of accelerated cooling (preferable winding temperature range) is 500 to 590 ° C.
【００２９】以下、本発明を実施例によって説明する。Hereinafter, the present invention will be described with reference to examples.
【実施例】まず、表１に示す化学組成の鋼を転炉にて溶
製した後、連続鋳造によりスラブとした。EXAMPLE First, steel having the chemical composition shown in Table 1 was melted in a converter, and then slab was formed by continuous casting.
【００３０】[0030]
【表１】 [Table 1]
【００３１】次に、これら各スラブを加熱炉で再加熱
し、表２及び表３に示す条件で処理して10.2mm厚の熱延
鋼板を製造した。Next, each of these slabs was reheated in a heating furnace and treated under the conditions shown in Tables 2 and 3 to produce a hot-rolled steel sheet having a thickness of 10.2 mm.
【００３２】[0032]
【表２】 [Table 2]
【００３３】[0033]
【表３】 [Table 3]
【００３４】このようにして得られた各熱延鋼板からそ
れぞれ板幅方向に“ＡＰＩ規格引張試験片”と“２mmＶ
ノッチシャルピ−試験片”とを採取し、その機械的性質
を調べた。更に、前記各熱延鋼板からそれぞれ「５mm厚
×２０mm幅×１００mm長さ」の試験片を採取し、ＮＡＣ
Ｅ条件｛ｐＨ:3.0で液温が25℃のH2Ｓ飽和溶液(3000pm)
を使用｝で９６時間浸漬した後、超音波探傷法により割
れを測定し、水素誘起割れ性を評価した。これらの試験
による“機械的特性”と“水素誘起割れ性”の調査結果
を、表４及び表５にまとめて示した。From each of the hot-rolled steel sheets thus obtained, an “API standard tensile test piece” and a “2 mmV
Notch Charpy test specimens "were taken and their mechanical properties were examined. Further, test specimens of" 5 mm thick x 20 mm width x 100 mm length "were taken from each of the hot-rolled steel sheets, and NAC
E condition ｛Saturated H 2 S solution with pH: 3.0 and liquid temperature 25 ℃ (3000pm)
Was immersed for 96 hours in｝, and cracks were measured by ultrasonic flaw detection to evaluate hydrogen-induced cracking. Investigation results of "mechanical properties" and "hydrogen-induced cracking" by these tests are summarized in Tables 4 and 5.
【００３５】[0035]
【表４】 [Table 4]
【００３６】[0036]
【表５】 [Table 5]
【００３７】表４及び表５に示される結果からは、次の
事項を確認することができる。本発明法に従った試験番
号１〜10及び試験番号26〜35からは、得られた熱延鋼板
は何れもパイプライン用として満足できる強度，伸び及
び降伏比を有すると共に、シャルピ−衝撃試験での遷移
温度が−５０℃以下の優れた靱性を示し、超音波探傷法
での割れ率（Ｃスキャン割れ率）も１％以下であって良
好な耐水素割れ性を有していることが分かる。From the results shown in Tables 4 and 5, the following items can be confirmed. From Test Nos. 1 to 10 and Test Nos. 26 to 35 in accordance with the method of the present invention, all of the obtained hot-rolled steel sheets have satisfactory strength, elongation, and yield ratio for use in pipelines, and have a Charpy impact test. Shows an excellent toughness with a transition temperature of −50 ° C. or less, and has a crack rate (C scan crack rate) of 1% or less by an ultrasonic flaw detection method, indicating that it has good hydrogen cracking resistance. .
【００３８】これに対して、熱延加熱温度の高い試験番
号11，粗ロ−ル最終パス前の待ち時間の少ない試験番号
12，粗ロ−ル最終パス圧下率の低い試験番号13，粗ロ−
ル最終パスの温度が高い試験番号14，粗ロ−ル最終パス
の温度が低い試験番号15，粗ロ−ル最終パスから連続仕
上圧延までの待ち時間の長い試験番号16，連続仕上圧延
の仕上温度の高い試験番号17では、得られた熱延鋼板は
何れも靱性が劣っている。また、連続仕上圧延での仕上
温度の低い試験番号18では、得られた熱延鋼板は伸びが
低いと共に靱性も劣った結果となっている。On the other hand, a test number 11 with a high hot rolling heating temperature and a test number with a short waiting time before the final pass of the coarse roll
12, coarse roll final pass reduction rate test number 13, low coarse roll
Test No. 14 where the temperature of the final pass of the roll is high, Test No. 15 where the temperature of the final pass of the coarse roll is low, Test No. 16 with a long waiting time from the final pass of the coarse roll to the continuous finish rolling, Finishing of the continuous finish rolling In Test No. 17 where the temperature was high, the obtained hot rolled steel sheets were all inferior in toughness. In test number 18, which has a low finishing temperature in continuous finish rolling, the resulting hot-rolled steel sheet has low elongation and poor toughness.
【００３９】そして、第１段冷却速度の遅い試験番号1
9，巻取温度の高い試験番号24では、得られた熱延鋼板
は水素誘起割れ性に劣る結果となっている。一方、第１
段冷却速度の速い試験番号20では、得られた熱延鋼板は
伸びが低い結果となっている。更に、空冷開始温度の高
い試験番号21，空冷開始温度の低い試験番号22，空冷時
間を設けなかった試験番号23では、得られた熱延鋼板は
何れも伸びが低く、降伏比が高い結果となっている。Then, the test number 1 for which the first stage cooling rate is slow
9. In Test No. 24 with a high winding temperature, the obtained hot-rolled steel sheet was inferior in hydrogen-induced cracking. Meanwhile, the first
In test number 20, which has a high step cooling rate, the obtained hot-rolled steel sheet has a low elongation. Furthermore, in Test No. 21 with a high air-cooling start temperature, Test No. 22 with a low air-cooling start temperature, and Test No. 23 without air-cooling time, the obtained hot-rolled steel sheets have low elongation and high yield ratio. Has become.
【００４０】また、巻取り温度の低い試験番号25では、
得られた熱延鋼板の特性は良好であったものの、“平坦
さの不良”と“巻き姿不良”が生じた。そして、Nb添加
を行わなかった試験番号36及び37では、得られた熱延鋼
板は細粒化が不十分で靱性が劣る結果となっている。In test number 25 having a low winding temperature,
Although the properties of the obtained hot-rolled steel sheet were good, "poor flatness" and "poor winding" occurred. And, in Test Nos. 36 and 37 in which Nb was not added, the obtained hot rolled steel sheet had insufficient grain size and poor toughness.
【００４１】[0041]
【効果の総括】以上に説明したように、この発明によれ
ば、強度，低温靱性，耐水素誘起割れ性，成形性（延
性，低降伏比）に優れた熱延高張力鋼板を作業性良く安
定製造することが可能となり、ラインパイプ等の母材性
能の性能向上に大きく寄与することができるなど、産業
上有用な効果がもたらされる。[Summary of Effects] As described above, according to the present invention, a hot-rolled high-tensile steel sheet excellent in strength, low-temperature toughness, resistance to hydrogen-induced cracking, and formability (ductility, low yield ratio) can be obtained with good workability. Industrially useful effects such as stable production and significant contribution to improvement of the performance of base materials such as line pipes can be obtained.
Claims (2)
を、１１５０〜１２５０℃に加熱し、まず圧下率の累計
が４０％以上となる粗圧延を行った後、一旦３０〜１８
０秒間保持し、引き続いて９５０〜１０５０℃の温度域
で圧下率１５％以上の粗圧延を更に１パス行って熱間粗
圧延を終了し、次いで、この粗圧延終了の５〜１２０秒
後から熱間仕上圧延を開始して７５０〜８５０℃で該仕
上圧延を終えた後、３〜５０℃/sの冷却速度で５５０〜
７００℃まで冷却し、ここで２〜１０秒間の空冷を行っ
てから、再度５００〜６２０℃の温度域まで３〜８０℃
/sの冷却速度で冷却して巻取ることを特徴とする、耐水
素誘起割れ性と靱性に優れた熱延高張力鋼板の製造方
法。C. 0.04 to 0.12%, Si: 0.5% or less, Mn: 1.0 to 1.8%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.08%, N: A steel slab containing 0.0080% or less, Nb: 0.02 to 0.06%, Ti: 0.04% or less and the balance being Fe and unavoidable impurities is heated to 1150 to 1250 ° C, and the cumulative reduction becomes 40% or more. After rough rolling, once 30-18
Hold for 0 second, and subsequently perform one more pass of rough rolling at a reduction rate of 15% or more in a temperature range of 950 to 1050 ° C. to complete the hot rough rolling, and then 5 to 120 seconds after the completion of the rough rolling. After starting hot finish rolling and finishing the finish rolling at 750 to 850 ° C., the cooling rate is 3 to 50 ° C./s, and 550 to 550 ° C./s.
After cooling to 700 ° C, air cooling is performed for 2 to 10 seconds, and then 3 to 80 ° C to a temperature range of 500 to 620 ° C again.
A method for producing a hot-rolled high-strength steel sheet having excellent hydrogen-induced cracking resistance and toughness, characterized by cooling at a cooling rate of / s and winding.
不可避不純物から成る鋼片を、１１５０〜１２５０℃に
加熱し、まず圧下率の累計が４０％以上となる粗圧延を
行った後、一旦３０〜１８０秒間保持し、引き続いて９
５０〜１０５０℃の温度域で圧下率１５％以上の粗圧延
を更に１パス行って熱間粗圧延を終了し、次いで、この
粗圧延終了の５〜１２０秒後から熱間仕上圧延を開始し
て７５０〜８５０℃で該仕上圧延を終えた後、３〜５０
℃/sの冷却速度で５５０〜７００℃まで冷却し、ここで
２〜１０秒間の空冷を行ってから、再度５００〜６２０
℃の温度域まで３〜８０℃/sの冷却速度で冷却して巻取
ることを特徴とする、耐水素誘起割れ性と靱性に優れた
熱延高張力鋼板の製造方法。2. In a weight ratio, C: 0.04 to 0.12%, Si: 0.5% or less, Mn: 1.0 to 1.8%, P: 0.03% or less, S: 0.005% or less, Al: 0.005 to 0.08%, N: 0.0080% or less, Nb: 0.02 to 0.06%, Ti: 0.04% or less, Cu: 0.5% or less, Ni: 0.5% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.10% or less, A steel slab containing one or more of Ca: 0.01% or less and the balance consisting of Fe and unavoidable impurities is heated to 1150 to 1250 ° C. After rolling, it is held once for 30 to 180 seconds, then 9
In a temperature range of 50 to 1050 ° C., rough rolling with a rolling reduction of 15% or more is further performed by one pass to complete hot rough rolling, and then hot finish rolling is started 5 to 120 seconds after the completion of the rough rolling. After the finish rolling at 750 to 850 ° C., 3 to 50
It cools to 550-700 ° C at a cooling rate of ° C / s, performs air cooling for 2-10 seconds here, and then 500-620 again.
A method for producing a hot-rolled high-strength steel sheet having excellent resistance to hydrogen-induced cracking and toughness, characterized by cooling and winding at a cooling rate of 3 to 80 ° C / s to a temperature range of 0 ° C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12174497A JP3301348B2 (en) | 1997-04-24 | 1997-04-24 | Manufacturing method of hot-rolled high-tensile steel sheet |
Applications Claiming Priority (1)
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| JP12174497A JP3301348B2 (en) | 1997-04-24 | 1997-04-24 | Manufacturing method of hot-rolled high-tensile steel sheet |
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| Publication Number | Publication Date |
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| JPH10298645A true JPH10298645A (en) | 1998-11-10 |
| JP3301348B2 JP3301348B2 (en) | 2002-07-15 |
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| JP12174497A Expired - Fee Related JP3301348B2 (en) | 1997-04-24 | 1997-04-24 | Manufacturing method of hot-rolled high-tensile steel sheet |
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| KR100415672B1 (en) * | 1999-12-27 | 2004-01-31 | 주식회사 포스코 | A TENSILE STRENGTH OF 780MPa GRADE HOT ROLLED STEEL SHEET FOR STRUCTURAL USE AND A METHOD FOR MANUFACTURING IT |
| KR100568365B1 (en) * | 2001-12-27 | 2006-04-05 | 주식회사 포스코 | Method for manufacturing heavy gauge high strength linepipe steel with superior low temperature toughness |
| KR100584762B1 (en) * | 2001-12-26 | 2006-05-30 | 주식회사 포스코 | The method of manufacturing hot rolled steels with less anisotropic properties for linepipes |
| KR100711464B1 (en) | 2005-12-15 | 2007-04-24 | 주식회사 포스코 | A method for manufacturing hot rolled steel sheet for linepipe having low yield ratio and excellent yield strength anisotropic properties |
| KR101091282B1 (en) | 2004-09-30 | 2011-12-07 | 주식회사 포스코 | Method for manufacturing 780MPa grade hot rolled steel sheet having excellent weldability |
| KR101185359B1 (en) | 2010-10-27 | 2012-09-21 | 현대제철 주식회사 | High strength api hot-rolled steel sheet with low yield ratio and method for manufacturing the api hot-rolled steel sheet |
| JP2012229470A (en) * | 2011-04-26 | 2012-11-22 | Kobe Steel Ltd | Steel sheet having excellent low temperature toughness and fracture toughness of welded joint and method for producing the same |
| WO2013022043A1 (en) | 2011-08-09 | 2013-02-14 | 新日鐵住金株式会社 | Hot-rolled steel sheet having high yield ratio and excellent low-temperature impact energy absorption and haz softening resistance and method for producing same |
| KR101400516B1 (en) * | 2012-08-30 | 2014-05-28 | 현대제철 주식회사 | Steel sheet for line pipe and method of manufacturing the same |
| JP2015081367A (en) * | 2013-10-22 | 2015-04-27 | 株式会社神戸製鋼所 | Hot rolled steel sheet excellent in drawability and surface hardness after carburization heat treatment |
| EP1726675A3 (en) * | 2005-05-25 | 2016-09-21 | The Japan Steel Works, Ltd. | Base material for a clad steel and method for the production of clad steel from same |
| JPWO2016047023A1 (en) * | 2014-09-25 | 2017-04-27 | Ｊｆｅスチール株式会社 | Steel strip for electric resistance welded steel pipe, electric resistance welded steel pipe, and method for producing steel strip for electric resistance welded steel pipe |
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| WO2020085888A1 (en) * | 2018-10-26 | 2020-04-30 | 주식회사 포스코 | High-strength steel having excellent resistance to sulfide stress cracking, and method for manufacturing same |
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1997
- 1997-04-24 JP JP12174497A patent/JP3301348B2/en not_active Expired - Fee Related
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100415672B1 (en) * | 1999-12-27 | 2004-01-31 | 주식회사 포스코 | A TENSILE STRENGTH OF 780MPa GRADE HOT ROLLED STEEL SHEET FOR STRUCTURAL USE AND A METHOD FOR MANUFACTURING IT |
| KR100584762B1 (en) * | 2001-12-26 | 2006-05-30 | 주식회사 포스코 | The method of manufacturing hot rolled steels with less anisotropic properties for linepipes |
| KR100568365B1 (en) * | 2001-12-27 | 2006-04-05 | 주식회사 포스코 | Method for manufacturing heavy gauge high strength linepipe steel with superior low temperature toughness |
| KR101091282B1 (en) | 2004-09-30 | 2011-12-07 | 주식회사 포스코 | Method for manufacturing 780MPa grade hot rolled steel sheet having excellent weldability |
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| JP2012229470A (en) * | 2011-04-26 | 2012-11-22 | Kobe Steel Ltd | Steel sheet having excellent low temperature toughness and fracture toughness of welded joint and method for producing the same |
| WO2013022043A1 (en) | 2011-08-09 | 2013-02-14 | 新日鐵住金株式会社 | Hot-rolled steel sheet having high yield ratio and excellent low-temperature impact energy absorption and haz softening resistance and method for producing same |
| CN105648311B (en) * | 2011-08-09 | 2018-03-30 | 新日铁住金株式会社 | The excellent high yield of impact energy absorption characteristic and the softening properties of resistance to HAZ at low temperature compares hot rolled steel plate |
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| CN105658830A (en) * | 2013-10-22 | 2016-06-08 | 株式会社神户制钢所 | Hot-rolled steel sheet having excellent surface hardness after carburizing heat treatment and excellent drawability |
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| WO2021125734A1 (en) * | 2019-12-16 | 2021-06-24 | 주식회사 포스코 | Steel material having excellent resistance to sulfide stress cracking and method for manufacturing same |
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| CN114761599A (en) * | 2019-12-16 | 2022-07-15 | 株式会社Posco | Steel material having excellent sulfide stress corrosion cracking resistance and method for producing same |
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| CN114761599B (en) * | 2019-12-16 | 2023-10-31 | 株式会社Posco | Steel material excellent in sulfide stress corrosion cracking resistance and method for producing same |
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