JPH0313524A - Production of thick high-toughness high tensile steel plate having excellent toughness on steel plate surface and in central part of thickness - Google Patents
Production of thick high-toughness high tensile steel plate having excellent toughness on steel plate surface and in central part of thicknessInfo
- Publication number
- JPH0313524A JPH0313524A JP14736689A JP14736689A JPH0313524A JP H0313524 A JPH0313524 A JP H0313524A JP 14736689 A JP14736689 A JP 14736689A JP 14736689 A JP14736689 A JP 14736689A JP H0313524 A JPH0313524 A JP H0313524A
- Authority
- JP
- Japan
- Prior art keywords
- steel plate
- toughness
- temperature
- rolling
- thickness
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 53
- 239000010959 steel Substances 0.000 title claims abstract description 53
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 238000005096 rolling process Methods 0.000 claims abstract description 58
- 238000001816 cooling Methods 0.000 claims abstract description 34
- 230000009467 reduction Effects 0.000 claims abstract description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 4
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 4
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 3
- 238000010438 heat treatment Methods 0.000 claims description 8
- 238000000034 method Methods 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 2
- 229910052742 iron Inorganic materials 0.000 claims description 2
- 229910052757 nitrogen Inorganic materials 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 abstract description 3
- 229910052791 calcium Inorganic materials 0.000 abstract description 2
- 229910052799 carbon Inorganic materials 0.000 abstract description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 abstract 1
- 229910001566 austenite Inorganic materials 0.000 description 9
- 230000000694 effects Effects 0.000 description 8
- 238000001953 recrystallisation Methods 0.000 description 6
- 229910000859 α-Fe Inorganic materials 0.000 description 6
- 239000010949 copper Substances 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 230000007704 transition Effects 0.000 description 5
- 239000010953 base metal Substances 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 3
- 238000003466 welding Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Abstract
Description
（産業上の利用分野）
本発明は、板厚中央部の靭性が優れ、なお且つ鋼板表面
の靭性にも優れている板厚５０ｍｍ以上の厚内高靭性高
張力鋼板の製造方法に関する。
（従来の技術及び解決しようとする＊題）氷海域海洋構
造物に用いられる鋼板には、溶接時に予熱が不要で、な
お且つ低温靭性の優れた高強度の板厚５０ＩＩＩ１１以
上の厚肉鋼板が要求されている。
このような鋼板の製造には、板厚中央部の靭性向上のた
めの低温圧延、及び炭素当量の低減が可能な加速冷却法
を適用することが有効であることは既に知られている。
すなわち、板厚中央部の靭性向上のための低温圧延に関
しては、板厚中央部においてオーステナイト未再結晶温
度域での相当量の圧下を確保する必要があるが、圧延中
のスラブ中央部の温度が表面温度に比べて高いために、
一般にスラブ表面温度がＡｒ）よりも低い低温域での相
当量の圧下を含む制御圧延が施される。これにより、板
厚中央部において、シャルピー破面遷移温度が一６０℃
以下という靭性の非常に優れた厚肉鋼板の製造が可能と
なっている。
しかし、圧延温度がスラブ表面においてはＡｒ。
よりも低いため５表面部には圧延途中の段階において初
析フェライトが生成し、粗大化する現象がみられ、最終
的に製造された鋼板の表面近傍の靭性は、板厚中央部に
比べ劣っているという欠点を有している。
本発明は、か＼る従来技術の欠点を解消し、板厚中央部
の靭性が優れ、なお且つ鋼板表面の靭性にも優れている
板厚５０＋＋ｖ＋以上の厚肉高靭性高張力鋼板の製造方
法を提供することを目的とするものである。
（課題を解決するための手段）
本発明者らは、前記従来技術の問題点を解決すべく鋭意
研究を行った結果、表面部の靭性劣化の原因となる圧延
途中の段階における初析フェライトの生成、粗大化を極
力抑制する方法を見い出し、ここに鋼板表面及び板厚中
央部の靭性の優れた厚肉高靭性高張力鋼板を製造する方
法を開発するに至ったのである。
すなわち、本発明は、Ｃ：０．０１〜０．１０％、Ｓｉ
：０．１０〜０．５０％、Ｍｎ：０．５〜２．０％、Ｐ
：０．０１５％以下、Ｓ：Ｏ，００３％以下、ＡＱ：０
．０１０〜０．１００％、Ｔｉ：０．００５〜０．０２
０％及びＮ：２０〜７０ｐｐｍを含有し、必要に応じて
、更にＣｕ： １ 、５％以下、Ｎｉ： ３ 、０％以
下、Ｎｂ：０．０３％以下及びＣａ：Ｏ，ＯＯ５０％以
下のうちの１種又は２種以上を含有し、残部がＦｅ及び
不可避的不純物よりなる鋼をＡｃ）以上、１１５０℃以
下に加熱後、鋼板表面温度がＡｒ３以上、（Ａｒ２＋
１００℃）以下の温度範囲で１５％以上の圧下を含む粗
圧延を行い、その後、鋼板表面温度が（Ａｒ、−１０℃
）以下、（Ａｒ、−５０℃）以上の温度範囲で圧下量３
０％以上の仕上圧延を行って鋼板表面温度が（Ａｒ、−
５０℃）以上で所定の板厚に仕上げ、直ちに５５０℃以
下の温度域まで１〜ｂに際し、粗圧延終了温度から仕上
圧延ヒバ始温度までの間に１回以上の間欠的な水冷を行
い、かつ。
この間を次式（１）を満足する平均の冷却速度ＣＲ（”
Ｃ／ ５ｅｅ）で冷却することを特徴とする鋼板表面及
び板厚中央部の靭性の優れた板厚５０＋ｓ＋ｎ以上の厚
肉高靭性高張力鋼板の製造方法を要旨とするものである
。
ＣＲ＞１．５ｘ（０，１６６−６，１４Ｘ１０−’ｔ）
・・・（１）ここで、
ｔ：粗圧延完了時のスラブ厚（■■）
以下に本発明を更に詳細に説明する。
（作用）
まず、本発明における化学成分の限定理由は以下のとお
りである。
Ｃ：
Ｃは強度上昇に有効な元素であり、そのためには０．０
１％以上が必要である。しかし、靭性の確保及び耐溶接
割れ性の低下防止の観点から上限をｏ、ｉｏ％に規制す
る必要がある。したがって。
Ｃ量は０．０１〜０．１０％の範囲とする。
Ｓｉ：
Ｓｉは脱酸元素であり、０．１０％以上の添加が必要で
あるが、過度の添加は靭性を劣化させるために上限を０
．５０％とする。このため、Ｓｉ量は０．１０〜０．５
０％の範囲とする。
Ｍｎ：
Ｍｎは強度上昇に有効であり、そのためには０６５％以
上が必要であるが、２．０％を超えて添加すると靭性が
劣化する。したがって、Ｍｎ量は０．５〜２．０％の範
囲とする。
Ｐ ：
Ｐは偏析傾向の強い元素であり、母材及び溶接部の靭性
を劣化させる。このため、Ｐ量は低く抑える必要があり
、０．０１５％以下に抑制する。
Ｓ：
ＳはＡ系介在物を形成し、板厚方向の絞り特性、耐ラメ
ラ−ティア−特性、更には靭性を劣化させる。したがっ
て、Ｎ量は極力低くする必要があり、０．００３％以下
に規制する。
Ｔｉ：
Ｔｉは難溶性の炭窒化物を形成し、スラブ加熱時又は溶
接時のオーステナイト粒の成長を抑制するため、母材及
び溶接時の靭性を向上させる効果を有する元素である。
そのためには０．００５％以上が必要であるが、０．０
２０％を超えて添加すると粗大な介在物を形成し、靭性
を劣化させる。
したがって、Ｔｉ量は０．００５〜０．０２０％の範囲
とする。
ＡＱ：
ＡＱは脱酸元素であり、０．０１％以上が必要であるが
、過度の添加は介在物を形成し、靭性を劣化させるため
、上限を０．１０％とする。したがって、ＡＱ量は０．
０１〜０．１０％の範囲とする。
Ｎ：
ＮはＴｉとの間で難溶性の炭窒化物を形成し、母材及び
溶接部の靭性を向上させる効果があり、そのためには２
０ｐｐｍ以上が必要であるが、７０ＰＰＭを超える過度
の含有は、逆に母材及び溶接部の靭性を著しく劣化させ
る。したがって、Ｎ量は２０〜７０ｐｐ鳳の範囲とする
。
以上の各元素を必須成分とするが、必要ルこ応じて、以
下に示すＣｕ、Ｎｉ、Ｎｂ及びＣａのうちの１種又は２
種以上を適量で添加することができる。
Ｃｕ：
Ｃｕは固溶強化、析出強化或いは焼入性向上による変態
強化に有効な元素であるが、過度の添加は靭性を劣化さ
せるため、１．５％以下とする。
Ｎｊ：
Ｎｉは低温靭性を改善する効果があるが、高価であるの
で、経済性を考慮して３．０％以下とする。
Ｎｂ：
Ｎｂは固溶状態でオーステナイトの再結晶を抑制し、制
御圧延の効果を高め、更に圧延後の加速冷却による変態
強化を促進して強度及び靭性の向上に寄与する元素であ
るが、過度の添加は溶接部の靭性を劣化させるため、０
．０３％以下とする。
Ｃａ：
また、靭性改善の目的でＣａを添加することができるが
、過度の添加は逆に靭性を著しく損なうので、Ｃａ量は
０．００５０％以下とする。
次に１本発明における上記化学成分を有する鋼に対する
加熱、圧延、冷却条件の限定理由について説明する。
圧延に先立つ加熱は、鋳片全体を完全にオーステナイト
化する必要があり、このためにはＡｃ、以上に加熱する
必要があるが、１１５０℃よりも高い加熱温度ではオー
ステナイト粒の粗大化による靭性劣化を来たすので望ま
しくない、このため、加熱温度は、Ａｃっ以上、１１５
０℃以下と規定する。
前記温度範囲に加熱された鋳片を熱間圧延するに際して
は、粗圧延、仕上圧延、及び粗圧延温度から仕上圧延温
度に鋳片の温度を調整する間の鋳片の冷却速度をコント
ロールする必要がある。
まず、厚肉鋼板の板厚中央部の靭性の向上には、板厚中
央部におけるオーステナイト再結晶温度域での圧下及び
オーステナイト未再結晶温度域での圧下が不可欠である
。
この点、本発明で規定した粗圧延温度（Ａｒ、以上、（
Ａｒ、 ＋ １００℃）以下）並びに仕上圧延温度（Ａ
ｒ、 −１０℃）以下、（Ａｒ、 −５０℃）以上）は
、それぞれ板厚中央部のオーステナイト再結晶温度、並
びにオーステナイト未再結晶温度に相当している。そし
て、板厚中央部で一６０℃以下のシャルピー破面遷移温
度を確保するためには、粗圧延。
仕上圧延で各々１５％以上、３０％以上の圧下量を確保
する必要がある。
また、仕上温度は、その後の加速冷却による強度上昇効
果を確保するために（Ａｒ、−５０℃）以上とする。
次に、本発明の最も重要なポイントである鋼板表面の靭
性向上のための手段について説明する。
本発明者らは、低温圧延された鋼板の表面部の靭性劣化
の原因が、圧延途中の段階で生成した初析フェライトの
粗大化によるものであることを見い出したが、更に検討
を重ねた結果、この裏面部初析フェライトの生成、粗大
化が主に粗圧延完了から仕上圧延開始温度まで大気中で
放冷される間に起こっていることを究明した。
そこで、この間の平均冷却速度と裏面部靭性の関係を調
査した結果、第１図に示すように、粗圧延完了時のスラ
ブ厚で、１回以上の間欠的な水冷を実施し、且つ（１）
式を満足する平均の冷却速度ＣＲで冷却す、ることによ
り１表面部の靭性が著しく向上することを発見した。す
なわち１表面部の靭性を向上させるためには、粗圧延完
了から仕上圧延温度開始温度までの間に粗圧延完了時の
スラブ厚で１回以上の間欠的な水冷の実施により、次式
の大気放冷の冷却速度（実験式） ＣＲＡＣ（’Ｃ／
５ｅｅ）ＣＲＡＣ＝ ０．１６６−６．１４ Ｘ １０
−’ ｔここで、ｔ：粗圧延完了時のスラブ厚（ｍｕ）
の１．５倍以上で冷却する必要がある。この間の間欠的
な水冷の実施は、銅板の表面温度を−Ｈフエライト粒が
成長し易い温度以下に低下させることにより、鋼板表面
部に生成したフェライトの粒成長を著しく抑制するとい
う重要な役割を担っており、本発明の必須の要因である
。
なお、仕上圧延後、５５０℃以下の温度域まで１〜ｂ
強度を得るためである。冷却停止温度が５５０℃よりも
高いとこの強度上昇の効果が得られず、また冷却速度が
１℃／ｓｅｃ未満では強度上昇効果が少なく、２０℃／
ｓｅｃよりも速いと強度上昇が過大になり靭性の劣化を
きたすため、この範囲に規定する必要がある。
次に本発明の実施例を示す。
（実施例）
第１表に示す化学成分を有する鋼につき、第２表に示す
条件で加熱、圧延、冷却して、所定の板厚の鋼板を製造
した。
得られた鋼板について引張強さ、降伏強さ、及び鋼板表
面部（鋼板表面下１■の部位）と板厚中央部のシャルピ
ー破面遷移温度を調べた。その結果を第２表に併記する
。
第２表より以下のように考察される。
試験＆３〜Ｈａ ５は加熱、圧延条件が本発明範囲を外
れているため、板厚中央部のシャルピー破面遷移温度（
ｖＴｒｓ）が−６０℃以上となっており。
低温用鋼板として適当な性能を有していない。
また、試験ＮＱＩＯ，Ｍａｉｌは、鋼の化学成分が本発
明範囲外であるために、いずれも板厚中央部の靭性が劣
っている。
また、試験Ｎａ２．＆７、Ｎａ９は、板厚中央部の靭性
は低温用鋼板として十分な性能を有しているものの、粗
圧延終了から仕上圧延開始までを大気放冷したために、
鋼板表面部の靭性が板厚中央部に比べて著しく劣ってい
る。
これらの比較例に対して、本発明例の試験＆１゜＆６、
Ｎａ８はいずれも、板厚中央部で優れた低温靭性を有し
ている共に、粗圧延終了から仕上圧延開始までの間を本
発明で規定した適切な冷却速度で冷却したために、鋼板
表面部においても、板厚中央部を遥かに上回る優れた低
温靭性を有している。(Industrial Application Field) The present invention relates to a method for manufacturing a high-toughness, high-strength steel plate having a thickness of 50 mm or more, which has excellent toughness in the central part of the plate thickness and also has excellent toughness on the surface of the steel plate. (Prior art and the *problem to be solved) Steel plates used for offshore structures in ice-covered areas include high-strength steel plates with a thickness of 50III11 or more that do not require preheating during welding and have excellent low-temperature toughness. requested. It is already known that it is effective to apply low-temperature rolling to improve the toughness of the central part of the sheet thickness and accelerated cooling methods that can reduce carbon equivalent in the production of such steel sheets. In other words, regarding low-temperature rolling to improve the toughness of the central part of the slab, it is necessary to ensure a considerable reduction in the austenite non-recrystallization temperature range at the central part of the slab, but the temperature at the central part of the slab during rolling is is higher than the surface temperature,
Generally, controlled rolling including a considerable amount of reduction is performed in a low temperature range where the slab surface temperature is lower than Ar). As a result, the Charpy fracture surface transition temperature is 160°C at the center of the plate thickness.
It is now possible to manufacture thick steel plates with extremely excellent toughness as shown below. However, when the rolling temperature is Ar on the slab surface. 5, pro-eutectoid ferrite is generated in the surface area during rolling, and a phenomenon of coarsening is observed, and the toughness near the surface of the final manufactured steel plate is inferior to that at the center of the plate thickness. It has the disadvantage of being The present invention eliminates the drawbacks of the prior art and provides a method for manufacturing a thick high-toughness steel plate with a thickness of 50++v+ or more, which has excellent toughness in the central part of the plate thickness and also has excellent toughness on the surface of the steel plate. The purpose is to provide the following. (Means for Solving the Problems) As a result of intensive research to solve the problems of the prior art, the present inventors found that pro-eutectoid ferrite during rolling, which causes deterioration of surface toughness, They found a method to suppress the formation and coarsening as much as possible, and developed a method for manufacturing thick-walled, high-toughness, high-strength steel plates with excellent toughness on the steel plate surface and in the center of the plate thickness. That is, in the present invention, C: 0.01 to 0.10%, Si
:0.10~0.50%, Mn:0.5~2.0%, P
: 0.015% or less, S: O, 003% or less, AQ: 0
．． 010-0.100%, Ti: 0.005-0.02
0% and N: 20 to 70 ppm, and if necessary, further contains Cu: 1, 5% or less, Ni: 3, 0% or less, Nb: 0.03% or less, and Ca: O, OO 50% or less. After heating a steel containing one or more of these and the remainder consisting of Fe and unavoidable impurities to a temperature of Ac) or higher and 1150°C or lower, the steel plate surface temperature is Ar3 or higher, (Ar2+
Rough rolling including a reduction of 15% or more is performed in a temperature range of 100℃ or less, and then the steel plate surface temperature is (Ar, -10℃
) and below, the reduction amount is 3 in the temperature range of (Ar, -50°C) or higher.
After finish rolling of 0% or more, the steel plate surface temperature reaches (Ar, -
50 ° C.) or higher to a predetermined thickness, immediately bring the temperature to a temperature range of 550 ° C. or lower in steps 1 to b, and perform intermittent water cooling one or more times between the rough rolling end temperature and the finish rolling start temperature, and. During this period, the average cooling rate CR(”
The gist of this invention is a method for producing a thick-walled, high-toughness, high-strength steel plate having a thickness of 50+s+n or more, which is characterized by cooling at a temperature of 50+s+n or more and exhibits excellent toughness on the steel plate surface and in the center of the thickness. CR>1.5x (0,166-6,14X10-'t)
...(1) Here, t: Slab thickness at completion of rough rolling (■■) The present invention will be explained in more detail below. (Function) First, the reasons for limiting the chemical components in the present invention are as follows. C: C is an effective element for increasing strength, and for that purpose 0.0
1% or more is required. However, from the viewpoint of ensuring toughness and preventing deterioration of weld cracking resistance, it is necessary to limit the upper limit to o or io%. therefore. The amount of C is in the range of 0.01 to 0.10%. Si: Si is a deoxidizing element and needs to be added in an amount of 0.10% or more, but excessive addition will reduce the upper limit to 0.
．． It shall be 50%. Therefore, the amount of Si is 0.10 to 0.5
The range is 0%. Mn: Mn is effective in increasing strength, and for this purpose, 0.65% or more is required, but if added in excess of 2.0%, toughness deteriorates. Therefore, the amount of Mn is set in the range of 0.5 to 2.0%. P: P is an element with a strong tendency to segregate, and deteriorates the toughness of the base metal and weld zone. Therefore, the amount of P needs to be kept low, and is suppressed to 0.015% or less. S: S forms A-based inclusions and deteriorates drawing properties in the thickness direction, lamellar tear resistance, and further toughness. Therefore, the amount of N needs to be as low as possible, and is regulated to 0.003% or less. Ti: Ti is an element that forms hardly soluble carbonitrides and suppresses the growth of austenite grains during slab heating or welding, so it has the effect of improving the toughness of the base metal and during welding. For that purpose, 0.005% or more is required, but 0.0
When added in an amount exceeding 20%, coarse inclusions are formed and the toughness is deteriorated. Therefore, the amount of Ti is in the range of 0.005 to 0.020%. AQ: AQ is a deoxidizing element and requires 0.01% or more, but excessive addition forms inclusions and deteriorates toughness, so the upper limit is set to 0.10%. Therefore, the AQ amount is 0.
The range is 0.01 to 0.10%. N: N forms a hardly soluble carbonitride with Ti, which has the effect of improving the toughness of the base metal and weld zone.
Although 0 ppm or more is required, excessive content exceeding 70 ppm will conversely significantly deteriorate the toughness of the base metal and weld zone. Therefore, the amount of N is set in the range of 20 to 70 ppp. Each of the above elements is an essential component, but depending on the necessity, one or two of the following elements: Cu, Ni, Nb, and Ca.
Seeds or more can be added in appropriate amounts. Cu: Cu is an effective element for solid solution strengthening, precipitation strengthening, or transformation strengthening by improving hardenability, but excessive addition deteriorates toughness, so it is limited to 1.5% or less. Nj: Ni has the effect of improving low-temperature toughness, but is expensive, so it is set to 3.0% or less in consideration of economic efficiency. Nb: Nb is an element that suppresses recrystallization of austenite in a solid solution state, enhances the effect of controlled rolling, and promotes transformation strengthening by accelerated cooling after rolling, contributing to improvement of strength and toughness. Since the addition of 0 deteriorates the toughness of the weld,
．． 03% or less. Ca: Further, Ca can be added for the purpose of improving toughness, but excessive addition significantly impairs toughness, so the amount of Ca is set to 0.0050% or less. Next, the reasons for limiting the heating, rolling, and cooling conditions for steel having the above chemical components in the present invention will be explained. It is necessary to completely austenite the entire slab in the heating process prior to rolling, and for this purpose it is necessary to heat the slab to a temperature higher than 1150°C, but heating at a temperature higher than 1150°C will cause the austenite grains to coarsen and deteriorate the toughness. This is undesirable because it causes
Defined as 0℃ or below. When hot rolling a slab heated to the above temperature range, it is necessary to control the cooling rate of the slab during rough rolling, finishing rolling, and adjusting the temperature of the slab from the rough rolling temperature to the finishing rolling temperature. There is. First, in order to improve the toughness of the central part of a thick steel plate, reduction in the austenite recrystallization temperature range and reduction in the austenite non-recrystallization temperature range in the central part of the thickness are essential. In this respect, the rough rolling temperature (Ar, or higher, (
(Ar, +100℃) or less) and finish rolling temperature (A
r, −10° C.) or lower, and (Ar, −50° C. or higher) respectively correspond to the austenite recrystallization temperature at the center of the plate thickness and the austenite non-recrystallization temperature. In order to ensure a Charpy fracture surface transition temperature of -60°C or less at the center of the plate thickness, rough rolling is required. It is necessary to ensure a rolling reduction of 15% or more and 30% or more in finish rolling, respectively. Further, the finishing temperature is set at (Ar, -50° C.) or higher to ensure the effect of increasing strength due to subsequent accelerated cooling. Next, a description will be given of means for improving the toughness of the steel plate surface, which is the most important point of the present invention. The present inventors discovered that the cause of the deterioration of toughness on the surface of cold-rolled steel sheets was due to the coarsening of pro-eutectoid ferrite generated during rolling. It was found that the formation and coarsening of pro-eutectoid ferrite on the back surface mainly occurred during cooling in the atmosphere from the completion of rough rolling to the starting temperature of finish rolling. Therefore, as a result of investigating the relationship between the average cooling rate and back surface toughness during this period, we found that, as shown in Figure 1, intermittent water cooling was performed one or more times at the slab thickness at the completion of rough rolling, and )
It has been discovered that the toughness of one surface area can be significantly improved by cooling at an average cooling rate CR that satisfies the formula. In other words, in order to improve the toughness of one surface area, between the completion of rough rolling and the start temperature of finish rolling, intermittent water cooling is performed once or more at the slab thickness at the time of completion of rough rolling, and the atmospheric pressure is reduced by the following formula: Cooling rate of natural cooling (empirical formula) CRAC ('C/
5ee) CRAC= 0.166-6.14 X 10
-' t, where t: slab thickness at completion of rough rolling (mu)
It is necessary to cool the temperature at 1.5 times or more. Intermittent water cooling during this period plays an important role in significantly suppressing the growth of ferrite grains formed on the surface of the steel sheet by lowering the surface temperature of the copper sheet below the temperature at which -H ferrite grains are likely to grow. This is an essential factor of the present invention. This is to obtain a strength of 1 to b up to a temperature range of 550° C. or lower after finish rolling. If the cooling stop temperature is higher than 550°C, this strength-increasing effect cannot be obtained, and if the cooling rate is less than 1°C/sec, the strength-increasing effect is small;
If the speed is faster than sec, the strength will increase too much and the toughness will deteriorate, so it is necessary to set the speed within this range. Next, examples of the present invention will be shown. (Example) A steel having a chemical composition shown in Table 1 was heated, rolled, and cooled under the conditions shown in Table 2 to produce a steel plate having a predetermined thickness. The tensile strength, yield strength, and Charpy fracture surface transition temperature of the steel plate surface (1 inch below the steel plate surface) and the center of the plate thickness were investigated for the obtained steel plate. The results are also listed in Table 2. The following considerations can be made from Table 2. In Tests &3 to Ha5, the heating and rolling conditions were outside the range of the present invention, so the Charpy fracture surface transition temperature (
vTrs) is -60°C or higher. It does not have suitable performance as a steel plate for low temperature use. Further, in both tests NQIO and Mail, the toughness at the center of the plate thickness was poor because the chemical composition of the steel was outside the scope of the present invention. In addition, test Na2. &7, Na9 has sufficient toughness in the center of the plate thickness as a steel plate for low temperature use, but because it was cooled in the atmosphere from the end of rough rolling to the start of finish rolling,
The toughness of the surface of the steel sheet is significantly inferior to that of the center of the sheet thickness. Compared to these comparative examples, the tests of the present invention example &1°&6,
All Na8 has excellent low-temperature toughness at the center of the sheet thickness, and because it is cooled at the appropriate cooling rate specified in the present invention from the end of rough rolling to the start of finish rolling, it has excellent toughness at the surface of the steel sheet. It also has excellent low-temperature toughness that far exceeds that at the center of the plate thickness.
（発明の効果）
以上詳述したように、本発明によれば、化学成分を適切
に調整すると共に、適切な加熱、圧延、冷却条件、特に
粗圧延完了から仕上圧延開始までの間においてスラブを
適切な冷却速度で冷却する構成としたので、板厚中央部
及び鋼板表面部のいずれにおいても優れた低温靭性を有
する板厚５０Ｉａｍ以上の厚肉高靭性高張力鋼板の製造
が可能となる。(Effects of the Invention) As detailed above, according to the present invention, the chemical components are appropriately adjusted and the slab is processed under appropriate heating, rolling, and cooling conditions, especially between the completion of rough rolling and the start of finish rolling. Since the structure is configured to cool at an appropriate cooling rate, it is possible to produce a thick-walled, high-toughness, high-strength steel plate having a thickness of 50 Iam or more and having excellent low-temperature toughness in both the central part of the plate thickness and the surface part of the steel plate.
第１図は粗圧延完了から仕上圧延開始までのスラブの冷
却速度と鋼板表面部及び板厚中央部のシャルピー破面遷
移温度（ｖＴｒｓ）との関係を示す図である。FIG. 1 is a diagram showing the relationship between the cooling rate of a slab from the completion of rough rolling to the start of finish rolling and the Charpy fracture surface transition temperature (vTrs) of the surface portion of the steel sheet and the center portion of the sheet thickness.
Claims (2)
０％、Ｓｉ：０．１０〜０．５０％、Ｍｎ：０．５〜２
．０％、Ｐ：０．０１５％以下、Ｓ：０．００３％以下
、Ａｌ：０．０１０〜０．１００％、Ｔｉ：０．００５
〜０．０２０％及びＮ：２０〜７０ｐｐｍを含有し、残
部がＦｅ及び不可避的不純物よりなる鋼をＡｃ＿３以上
、１１５０℃以下に加熱後、鋼板表面温度がＡｒ＿３以
上、（Ａｒ＿３＋１００℃）以下の温度範囲で１５％以
上の圧下を含む粗圧延を行い、その後、鋼板表面温度が
（Ａｒ＿３−１０℃）以下、（Ａｒ＿３−５０℃）以上
の温度範囲で圧下量３０％以上の仕上圧延を行って鋼板
表面温度が（Ａｒ＿３−５０℃）以上で所定の板厚に仕
上げ、直ちに５５０℃以下の温度域まで１〜２０℃／ｓ
ｅｃの冷却速度で冷却して鋼板を製造するに際し、粗圧
延終了温度から仕上圧延開始温度までの間に１回以上の
間欠的な水冷を行い、かつ、この間を次式（１）を満足
する平均の冷却速度ＣＲ（℃／ｓｅｃ）で冷却すること
を特徴とする鋼板表面及び板厚中央部の靭性の優れた板
厚５０ｍｍ以上の厚肉高靭性高張力鋼板の製造方法。 ＣＲ＞１．５×（０．１６６−６．１４×１０＾−＾４
ｔ）・・・（１）ここで、 ｔ：粗圧延完了時のスラブ厚（ｍｍ）(1) In weight% (the same applies hereinafter), C: 0.01 to 0.1
0%, Si: 0.10-0.50%, Mn: 0.5-2
．． 0%, P: 0.015% or less, S: 0.003% or less, Al: 0.010 to 0.100%, Ti: 0.005
After heating a steel containing ~0.020% and N: 20 to 70 ppm, with the balance consisting of Fe and unavoidable impurities to a temperature of Ac_3 or higher and 1150°C or lower, the steel plate surface temperature is Ar_3 or higher and (Ar_3+100°C) or lower. Perform rough rolling with a reduction of 15% or more in the range, and then perform finish rolling with a reduction of 30% or more in a temperature range where the steel plate surface temperature is below (Ar_3-10℃) and above (Ar_3-50℃). Finish the steel plate to the specified thickness when the surface temperature is (Ar_3-50℃) or higher, and immediately heat the plate at 1 to 20℃/s to a temperature range of 550℃ or lower.
When manufacturing a steel plate by cooling at a cooling rate of EC, intermittent water cooling is performed one or more times between the rough rolling end temperature and the finish rolling start temperature, and during this period, the following formula (1) is satisfied. A method for producing a thick-walled, high-toughness, high-strength steel plate having a thickness of 50 mm or more and having excellent toughness on the steel plate surface and in the center of the plate thickness, characterized by cooling at an average cooling rate CR (° C./sec). CR＞1.5×(0.166-6.14×10^-^4
t)...(1) Here, t: Slab thickness at completion of rough rolling (mm)
０％以下、Ｎｂ：０．０３％以下及びＣａ：０．００５
０％以下のうちの１種又は２種以上を含有するものであ
る請求項１に記載の方法。(2) The steel further contains Cu: 1.5% or less, Ni: 3.
0% or less, Nb: 0.03% or less and Ca: 0.005
The method according to claim 1, wherein the method contains one or more of 0% or less.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14736689A JPH0313524A (en) | 1989-06-10 | 1989-06-10 | Production of thick high-toughness high tensile steel plate having excellent toughness on steel plate surface and in central part of thickness |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP14736689A JPH0313524A (en) | 1989-06-10 | 1989-06-10 | Production of thick high-toughness high tensile steel plate having excellent toughness on steel plate surface and in central part of thickness |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH0313524A true JPH0313524A (en) | 1991-01-22 |
Family
ID=15428593
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP14736689A Pending JPH0313524A (en) | 1989-06-10 | 1989-06-10 | Production of thick high-toughness high tensile steel plate having excellent toughness on steel plate surface and in central part of thickness |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0313524A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06240355A (en) * | 1993-02-22 | 1994-08-30 | Sumitomo Metal Ind Ltd | Production of high toughness thick tmcp steel plate |
| JPH0841536A (en) * | 1994-07-29 | 1996-02-13 | Kawasaki Steel Corp | Production of high tensile strength steel plate small in nonuniformity of hardness in plate thickness direction and excellent in dwtt property |
| WO2009072753A1 (en) * | 2007-12-04 | 2009-06-11 | Posco | High-strength steel sheet with excellent low temperature toughness and manufacturing method thereof |
| KR100951296B1 (en) * | 2007-12-04 | 2010-04-02 | 주식회사 포스코 | Steel plate for linepipe having high strength and excellent low temperature toughness and manufacturing method of the same |
| KR101018159B1 (en) * | 2008-05-15 | 2011-02-28 | 주식회사 포스코 | High-strength steel sheet with excellent low temperature toughness and manufacturing method thereof |
| JP2011214116A (en) * | 2010-04-01 | 2011-10-27 | Nippon Steel Corp | Thick high strength steel plate having excellent brittle crack propagation arresting property, and method for producing the same |
| CN107012395A (en) * | 2017-03-02 | 2017-08-04 | 唐山钢铁集团有限责任公司 | A kind of method that rough rolling step improves low-alloy special heavy plate center portion quality |
-
1989
- 1989-06-10 JP JP14736689A patent/JPH0313524A/en active Pending
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06240355A (en) * | 1993-02-22 | 1994-08-30 | Sumitomo Metal Ind Ltd | Production of high toughness thick tmcp steel plate |
| JPH0841536A (en) * | 1994-07-29 | 1996-02-13 | Kawasaki Steel Corp | Production of high tensile strength steel plate small in nonuniformity of hardness in plate thickness direction and excellent in dwtt property |
| WO2009072753A1 (en) * | 2007-12-04 | 2009-06-11 | Posco | High-strength steel sheet with excellent low temperature toughness and manufacturing method thereof |
| KR100951296B1 (en) * | 2007-12-04 | 2010-04-02 | 주식회사 포스코 | Steel plate for linepipe having high strength and excellent low temperature toughness and manufacturing method of the same |
| US8647564B2 (en) | 2007-12-04 | 2014-02-11 | Posco | High-strength steel sheet with excellent low temperature toughness and manufacturing thereof |
| KR101018159B1 (en) * | 2008-05-15 | 2011-02-28 | 주식회사 포스코 | High-strength steel sheet with excellent low temperature toughness and manufacturing method thereof |
| JP2011214116A (en) * | 2010-04-01 | 2011-10-27 | Nippon Steel Corp | Thick high strength steel plate having excellent brittle crack propagation arresting property, and method for producing the same |
| CN107012395A (en) * | 2017-03-02 | 2017-08-04 | 唐山钢铁集团有限责任公司 | A kind of method that rough rolling step improves low-alloy special heavy plate center portion quality |
| CN107012395B (en) * | 2017-03-02 | 2018-06-19 | 唐山钢铁集团有限责任公司 | A kind of method that rough rolling step improves low-alloy special heavy plate center portion quality |
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