JPH0583607B2 - - Google Patents
Info
- Publication number
- JPH0583607B2 JPH0583607B2 JP62009100A JP910087A JPH0583607B2 JP H0583607 B2 JPH0583607 B2 JP H0583607B2 JP 62009100 A JP62009100 A JP 62009100A JP 910087 A JP910087 A JP 910087A JP H0583607 B2 JPH0583607 B2 JP H0583607B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- temperature
- toughness
- steel
- rolling
- 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.)
- Expired - Lifetime
Links
- 238000001816 cooling Methods 0.000 claims description 62
- 229910000831 Steel Inorganic materials 0.000 claims description 46
- 239000010959 steel Substances 0.000 claims description 46
- 238000005096 rolling process Methods 0.000 claims description 41
- 238000001953 recrystallisation Methods 0.000 claims description 29
- 229910001566 austenite Inorganic materials 0.000 claims description 18
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 229910052799 carbon Inorganic materials 0.000 claims description 11
- 238000000034 method Methods 0.000 claims description 11
- 238000005098 hot rolling Methods 0.000 claims description 10
- 229910052748 manganese Inorganic materials 0.000 claims description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
- 238000009749 continuous casting Methods 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- 229910052804 chromium Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- 229910052791 calcium Inorganic materials 0.000 claims 2
- 229910052715 tantalum Inorganic materials 0.000 claims 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 18
- 230000000694 effects Effects 0.000 description 8
- 229910001563 bainite Inorganic materials 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 238000007792 addition Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 4
- 239000000956 alloy Substances 0.000 description 4
- 238000005275 alloying Methods 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 229910006639 Si—Mn Inorganic materials 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 239000000470 constituent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Description
（産業上の利用分野）
本発明は、熱間圧延を比較的低温である未再結
晶域で行う、所謂制御圧延を必要とせず、所望の
強度・靱性を有し、且つ板厚方向の断面硬度差が
小さい鋼板の高能率製造法に関するものである。
（従来の技術）
従来の水冷型高張力鋼の製造方法の一つに、例
えば特開昭54−71714号公報に示された様に、鋼
を加熱後圧延し、未再結晶域で30％以上の圧延を
行つた後、Ar3以上の温度から３℃／sec以上の
冷却速度で500℃以上650℃以下の温度域まで冷却
し、優れた強度・靱性を得る方法がある。
かかる製造方法では、すぐれた靱性を得るため
に熱間圧延を比較的低温である未再結晶域でおこ
なう所謂制御圧延が必須要件となつており、鋼板
の温度が適正な800℃程度の温度範囲まで低下す
るのを待つて圧延を終了せしめるので、通常の圧
延に比べ著しく圧延能率を低下させる工業生産上
の欠点を有している。
これに対し、特開昭55−28318号公報に示され
ているように、Ｃの上限を0.09wt％とした鋼を通
常の熱間圧延後30℃／sec以上の冷却速度で、500
℃以下まで冷却する溶接性の優れた50キロ級の高
張力鋼の製造方法がある。
この方法では、圧延能率の低下は避けられるも
のの、靱性を向上させるためにＣの上限を0.09wt
％に制限している。
かかる低Ｃ成分では、強度を確保するために30
℃／sec以上の冷却速度で500℃以下まで冷却する
ことを必須要件としており、板厚方向の断面硬度
差が大きくなる欠点を有する。
また特開昭55−115922号公報に示されているよ
うに、Ｃの上限を0.09wt％とし、さらに0.50wt％
以下のCu、0.50wt％以下のNi、0.30wt％以下の
Cr、0.30wt％以下のMo、0.10wt％以下のＶ、
0.10wt％以下のTiを１種または２種以上含有す
る鋼を、通常の熱間圧延後600℃以下まで冷却す
る溶接性の優れた50Kg／mm2以上級の高張力鋼の製
造方法がある。
この方法では、圧延能率の低下は避けられるも
のの、低Ｃ成分では50Kg／mm2以上の強度を得るた
めに、コストの高い合金元素を含有することを必
須としており、合金コスト削減上の制約を有する
欠点がある。
（発明が解決しようとする問題点）
本発明は、従来の水冷型高張力鋼で合金元素の
多量添加、もしくは低温域での制御圧延を行うこ
とによつて、はじめて得られた良好な強度・靱性
及び板厚断面硬さの均一性を、合金コストの増大
や圧延能率の低下等をもたらさず、実現しようと
するものである。
すなわち、オーステナイトの再結晶温度域での
適切な圧延条件と圧延後の制御冷却の組合わせに
よつて、低温域での制御圧延を行うこと無しに、
優れた強度・靱性を有し且つ板厚方向の断面硬度
差が小さい鋼板を製造する方法を提供するもの
で、この種用途において、経済性に優れた鋼材の
提供を可能にするものである。
（問題点を解決するための手段）
本発明は、上記の問題点を解決するために、
Ｃ：0.09wt％超0.18wt％未満、Si：0.05wt％以上
0.50wt％未満、Mn：0.7wt％以上1.8wt％未満、
Al：0.005wt％以上0.01wt％未満、Ｎ：0.006wt
％未満を含有し、又はこれらの成分の外にTi，
Zr，Nb，Ｖ，Ta，Caを0.1wt％以下、Ni，Cr，
Mo，Cuを1.0wt％以下、Ｂを0.003wt％以下の範
囲で一種または二種以上加え且つ、Ｃ＋Mn／６
＋（Cr＋Mo＋Ｖ）／５＋（Ni＋Cu）／15なる炭
素当量が0.36以下で、残部Fe及び不可避的不純物
より成る鋼を、連続鋳造後1000℃以上1200℃以下
に加熱し、オーステナイトの再結晶域で全圧下率
を60％以上確保し、且つ再結晶温度域で圧延を終
了する熱間圧延後、鋼板の温度がAr3温度以上か
ら、15℃／sec以上の冷却速度で500℃以上650℃
以下の温度域まで冷却することを特徴とする強
度・靱性に優れ且つ、板厚方向の断面硬度差が小
さい鋼板の製造法である。
（作用）
本発明の構成要件の各限定は次の各理由に基づ
いて定めている。
即ちＣは強度を高めるのに有効な元素である
が、多すぎるとＰcm値（Ｐcm＝Ｃ＋１／30Si＋
１／20Mn＋１／20Cu＋１／60Ni＋１／20Cr＋
１／15Mo＋１／10V＋5B）を高め、溶接性を損
うので、上限を0.18wt％未満にすると共に、Ｃが
0.09wt％以下では強度が不足するので、Ｃの添加
範囲を0.09wt％超0.18wt％未満とする。
Siは脱酸及び地鉄の強化に加え、0.05wt％以上
の添加より、靱性の向上に有効であるため下限を
0.05wt％に、また多すぎると溶接性及びHAZ部
靱性に有害なので上限を0.5wt％未満とする。
Mnは強度・靱性を高めるのに必要な元素であ
るが、0.7wt％未満では強度が不十分であつたり
靱性を劣化させ、また1.8wt％以上とすると溶接
性が著しく悪くなるので、Mnの添加範囲を
0.7wt％以上1.8wt％未満とする。
Alは脱酸と細粒化に必要で、そのための充分
な量として0.005wt％以上0.1wt％未満に限定す
る。Ｎは溶接性及び継手部の靱性を良好に保つた
めに、0.006wt％未満にする。
以上の成分範囲限定に加え、Ｃ＋Mn／６＋
（Cr＋Mo＋Ｖ）／５＋（Ni＋Cu）／15なる炭素
当量が、0.36超では溶接性が劣化するので0.36以
下に限定する。
上記成分範囲の鋼を製造するにあたり、加熱前
の鋳片（以下スラブと称する）の凝固組織並びに
Alその他の従量元素の析出物の粗大化を防止し、
スラブ加熱時のオーステナイト粒を細かくするこ
とが重要で、連続鋳造工程を必須要件とする。
このようにして得たスラブの加熱温度は、オー
ステナイト粒の粗大化防止のために、低温程好ま
しいが、圧延中の温度低下を考慮して1000℃以上
1200℃以下に限定する。
次に再結晶域圧延はオーステナイト粒を、微細
な再結晶オーステナイト粒にするために重要であ
る。この際、圧下率が大きい程細粒化に有効であ
るので、再結晶域の全圧下率を60％以上に限定す
る。
再結晶域で上記限定の圧延を行わない場合は、
細粒化が十分でないので靱性が劣化し、板厚方向
の硬度差が増大する等の問題が生じる。
熱間圧延を再結晶温度域で終了するのは、再結
晶したオーステナイトのポリゴナルな粒から水冷
を行うことにより強度・靱性の優れたベイナイト
変態組織を得るためである。
再結晶温度域で圧延を終了せず、未再結晶域ま
で圧延を継続した場合は、オーステナイト粒が伸
長する。かかるオーステナイト粒から水冷を行つ
た場合は、ポリゴナルなオーステナイト粒から水
冷した場合に比較して焼入性が低下し、フエライ
ト組織が多く生成するため、優れた靱性は得られ
るものの強度が低下する。
熱間圧延後、冷却開始までの時間は可能な限り
短時間が好ましく、圧延後長時間放置すると、結
晶粒の粗大化や温度むらが生じ、更にはAr3温度
以下に下がるとフエライト変態が始まるので、最
大10分以内にAr3温度以上から冷却を開始する必
要がある。
厚板圧延のような、多パス圧延における再結晶
下限温度については、Si−Mn系での再結晶下限
温度は850℃程度、NbやMoのような再結晶抑制
効果を有する元素を含有する場合には、再結晶下
限温度は950℃程度となることが知られている
［例えば、日本鉄鋼協会主催・西山記念技術講座
（テキスト）P.146、「新制御圧延技術」（昭和57年
11月１〜２日）］。
従つて、本発明でのSi−Mn系の再結晶下限温
度は850℃程度、Nb或はＶ等の選択元素添加系で
は、再結晶下限温度は950℃程度である。本発明
では、再結晶温度域での圧延終了を要件としてお
り、圧延仕上げ温度は、上記再結晶下限温度以上
となる。
冷却時の冷却速度は鋼の強度及び靱性向上に必
要なベイナイト組織を得るため、15℃／sec以上
とした。また冷却を完了する温度、すなわち水冷
停止温度の上限を650℃としたのは、これより高
い停止温度ではベイナイト組織が得られず、強
度・靱性が劣化し、下限を500℃としたのは、こ
れより低い温度では島状マルテンサイト等の低温
変態生成物が生じ、靱性を著しく劣化させるから
である。
従来、水冷型高張力厚鋼板の強度・靱性を向上
させるためには、合金元素の多量添加、あるいは
低温域での制御圧延を行うことが必須要件とされ
ている。
本発明は、本発明者等がオーステナイトの再結
晶温度域での適切な圧延条件と圧延後の制御冷却
を組合せることによつて、圧延能率を低下させる
低温域での制御圧延を用いること無く、優れた強
度・靱性を有し、かつ板厚方向の断面硬度が小さ
い鋼板を製造出来ることを見出したことに基づい
ている。
特に、比較的細粒とした再結晶オーステナイト
粒から15℃／sec以上の冷却速度で500℃以上650
℃以下の温度域まで水冷することにより、従来、
靱性の劣化を招くとされていたベイナイト組織
で、優れた強度及び靱性が得られることを見出し
た。
以下その点を中心に述べる。
第１図〜第３図は本発明者等が上記の検討のた
めに行つた実験の結果を示す。
第１図はＣを0.13wt％、Mnを1.2wt％、Siを
0.2wt％含む鋼において、スラブを1050℃に加熱
後、再結晶域で異なるスラブ厚から30mmまで圧延
し、冷却速度15℃／secで550℃まで水冷した場合
の全圧下率（％）と靱性（vTrs）及び板厚方向
の断面硬度差（ΔHv（10Kg））の関係を示す。
ここでΔHv（10Kg）とは鋼板断面の表層部と中
心部のビツカース硬さを荷重10Kgにて測定した硬
さの差である。
第１図に明らかなように、再結晶域での全圧下
率が60％未満では、良好な靱性を得ることができ
ない上に、板厚方向の断面硬度差も増加する。上
記の結果から、良好な靱性を得且つ、断面硬度差
を小さくするために、下限の全圧下率として60％
を規定するのである。
また第２、第３図は冷却条件に関する実験結果
を示す。
第２図は第１図と同じ成分の180mm厚スラブを、
1050℃に加熱後板厚30mmまで再結晶域で圧延した
鋼板を、Ar3温度以上から24℃／ｓの冷却速度
で、種々の温度まで水冷した場合の靱性及び板厚
方向断面硬度差と水冷停止温度の関係を示す。
第２図に明らかなように、水冷停止温度の低下
により靱性は著しく劣化する。これは、500℃未
満の水冷停止温度では、靱性に有害である島状マ
ルテンサイト等の低温変態生成物が生じるためで
ある。また、650℃超の高温で水冷を停止した場
合は、靱性が劣化する。これは、組織がベイナイ
ト主体とならず、粗大なフエライト・パーライト
となつたためである。
一方、断面硬度差は水冷停止温度が500℃未満
では著しく大きくなるが、500℃以上の水冷停止
により、十分小さな値とすることができる。以上
の結果から良好な靱性を得、且つ、断面硬度差を
小さくするために、水冷停止温度を500℃以上650
℃以下に規定するのである。
第３図は第２図と同じスラブを、同様にだ圧延
後、鋼板をAr3温度以上から種々の冷却速度に
て、500℃以上650℃以下の温度まで水冷した場合
の靱性及び板厚方向断面硬度差と、冷却速度の関
係を示す。
図から明らかな様に靱性は冷却速度の増加によ
り向上する。冷却速度が15℃／sec未満では靱性
の劣化が大きい。また15℃／secの冷却速度は、
組織がフエライト・パーライトからベイナイト主
体へ変化する点に対応している。
これらから、再結晶したポリゴナルなオーステ
ナイト粒から水冷する場合、冷却速度を15℃／
sec以上に上昇させてベイナイト主体の組織とす
ると、靱性が向上する事実が見出されたのであ
る。
一方、板厚方向の断面硬度差は、冷却速度を上
昇させても水冷停止温度を、500℃以上650℃以下
とすることにより、十分小さな値にすることがで
きることを見出した。以上の結果から冷却速度の
下限を15℃／secに規定する。
本発明は上記の諸元の数値制限に加え、さらに
厚鋼板の用途に応じて、一般公知の効能元素、例
えば、靱性向上元素として、0.1％以下のTi，
Zr，Ta，Ca、強度向上元素として、0.1％以下
のNb，Ｖ、及び1.0％以下のNi，Cr，Mo，Cu、
及び0.003％以下のＢの中から、１種又は２種以
上を加えることによつて、より一層の強度、及び
又は靱性を向上させた厚鋼板を製造することが可
能である。
そこで、靱性向上元素の含有量を0.1％以下と
する理由は、周知のように0.1％超とすると鋼の
精錬過程で添加した際に、酸化生成して残つた介
在物が表層部に多く集積し欠陥部となるためであ
る。
又、強度向上元素はいずれの場合もその上記含
有量を超えると、周知のように溶接継手靱性が悪
くなるためである。
（実施例）
表１及び２は表中の各成分の各鋼を付記した熱
延条件及び冷却条件にて製造し、その機械的性質
として引張試験、衝撃試験及び板厚方向断面硬度
差（ΔHv（10Kg））を示したものである。
記号１〜５はＣ量を0.055〜0.17wt％、Mn量を
0.65〜1.71wt％に変化して添加した鋼である。
本発明例２，３及び４はいずれも強度（TS）
が50Kgｆ／mm2以上でかつvTrsも−40℃以下の良
好な値を示すのに対し、比較例１は、靱性は良好
なもののTSは50Kgｆ／mm2未満の値を示し、本発
明のＣ添加による強度上昇効果が明らかに認めら
れる。また比較例５はMnが低いため強度も靱性
も劣化する。
一方、記号６〜16はＣを0.13wt％、Siを0.23wt
％、Mnを1.2wt％含む鋼に於いて、表中に示す
製造条件を変化させた。
記号６は加熱温度が1250℃の比較例で、本発明
例の記号７の加熱温度1200℃のものと比較する
と、靱性レベルがvTrsで28℃程度劣り、これは
加熱温度が高いためオーステナイト粒が粗大にな
つたためである。また、靱性の劣化に加え、記号
６では板厚方向の断面硬度差ΔHvも本発明例７
に比し増大しており、疲労特性等の特性劣化がみ
られた。
記号８は比較例で水冷開始温度が700℃と低い
もので、本発明例の記号９の水冷開始温度が892
℃のものと比べると、強度・靱性共に劣り、本発
明の冷却開始温度の確保が、強度・靱性改善に有
効なことが明らかである。
記号10，11は冷却速度の影響を見たものであ
る。比較例の記号11は冷却速度が８℃／secと遅
い場合で、本発明例記号９及び10の冷却速度が15
℃／sec以上と比較すると強度・靱性共に劣つて
おり、本発明の冷却速度の確保が強度・靱性の向
上に有効なことが明らかである。
記号12は水冷停止温度が300℃と低い場合で、
本発明例の記号９の水冷停止温度が530℃のもの
に比較して、靱性が著しく劣化しており、本発明
の水冷停止温度の確保が強度・靱性の向上に有効
なことが明らかである。
記号13は再結晶域の全圧下率が50％と低い場合
で、本発明例記号14の全圧下率60％以上を確保し
たものに比べて、vTrsが35℃程度劣化しており、
ΔHvも増大している。本発明の再結晶域での圧
延の確保が、靱性の向上に有効なことが明らかで
ある。
記号15は仕上温度が810℃と低く、未再結晶域
まで圧延を続けた比較例である。本発明例記号16
に比較して、靱性はやや優れているが、強度が低
く50Kg／mm2を満足していない。本発明の再結晶オ
ーステナイトからの水冷が、靱性をあまり損なう
こと無く強度を高めるのに有効なことが明らかで
ある。
表２は合金添加例を示す。記号17〜21はＣ，
Si，Mn，Alに加え、表に示す合金元素を添加し
た本発明例である。表１の記号９の合金を添加し
ていない発明例に比べ、強度・靱性共に向上する
ことが明らかである。
(Industrial Application Field) The present invention does not require so-called controlled rolling, in which hot rolling is performed in a non-recrystallized region at a relatively low temperature, and has desired strength and toughness, as well as a cross section in the thickness direction. This invention relates to a highly efficient manufacturing method for steel plates with small hardness differences. (Prior art) One of the conventional manufacturing methods of water-cooled high-strength steel is to heat and then roll the steel, as shown in Japanese Patent Application Laid-Open No. 54-71714, to reduce the amount of water to 30% in the non-recrystallized region. After performing the above rolling, there is a method of obtaining excellent strength and toughness by cooling from a temperature of Ar 3 or higher to a temperature range of 500°C or higher and 650°C or lower at a cooling rate of 3°C/sec or higher. In this manufacturing method, in order to obtain excellent toughness, so-called controlled rolling, in which hot rolling is performed in a relatively low-temperature non-recrystallized region, is an essential requirement, and the temperature of the steel plate must be within the appropriate temperature range of about 800°C. Since rolling is terminated after waiting for the rolling temperature to decrease to a certain level, this has the disadvantage in industrial production that the rolling efficiency is significantly reduced compared to normal rolling. On the other hand, as shown in Japanese Patent Application Laid-Open No. 55-28318, steel with an upper limit of 0.09wt% C is rolled at a cooling rate of 30℃/sec or more after normal hot rolling.
There is a method for manufacturing 50 kg class high tensile strength steel with excellent weldability that is cooled to below ℃. Although this method avoids a decrease in rolling efficiency, the upper limit of C is set at 0.09wt to improve toughness.
It is limited to %. In such a low C component, 30
It is an essential requirement to cool down to 500°C or less at a cooling rate of °C/sec or more, which has the disadvantage of increasing the difference in cross-sectional hardness in the thickness direction. In addition, as shown in Japanese Patent Application Laid-open No. 115922/1983, the upper limit of C is set to 0.09wt%, and furthermore to 0.50wt%.
Cu below 0.50wt%, Ni below 0.30wt%
Cr, 0.30wt% or less Mo, 0.10wt% or less V,
There is a method for manufacturing high-strength steel of 50Kg/mm2 or higher class with excellent weldability, in which steel containing one or more types of Ti at 0.10wt% or less is cooled to 600℃ or less after normal hot rolling. . Although this method avoids a decrease in rolling efficiency, it requires the inclusion of expensive alloying elements in order to obtain a strength of 50 kg/mm 2 or more for low C components, which imposes constraints on alloy cost reduction. There are some drawbacks. (Problems to be Solved by the Invention) The present invention provides good strength and strength that can be obtained for the first time by adding a large amount of alloying elements to conventional water-cooled high-strength steel or by performing controlled rolling in a low temperature range. The objective is to achieve uniformity in toughness and thickness cross-sectional hardness without increasing alloy cost or reducing rolling efficiency. In other words, by combining appropriate rolling conditions in the austenite recrystallization temperature range and controlled cooling after rolling, the rolling process can be performed without controlling rolling in the low temperature range.
The present invention provides a method for manufacturing a steel plate that has excellent strength and toughness and has a small difference in cross-sectional hardness in the thickness direction, making it possible to provide a steel material with excellent economic efficiency for this type of use. (Means for solving the problems) In order to solve the above problems, the present invention has the following features:
C: more than 0.09wt% and less than 0.18wt%, Si: 0.05wt% or more
Less than 0.50wt%, Mn: 0.7wt% or more and less than 1.8wt%,
Al: 0.005wt% or more and less than 0.01wt%, N: 0.006wt
% or in addition to these components, Ti,
Zr, Nb, V, Ta, Ca less than 0.1wt%, Ni, Cr,
Adding one or more types of Mo, Cu in a range of 1.0wt% or less and B in a range of 0.003wt% or less, and C+Mn/6
+ (Cr + Mo + V) / 5 + (Ni + Cu) / 15, a steel with a carbon equivalent of 0.36 or less, the balance consisting of Fe and unavoidable impurities, is heated to 1000°C or more and 1200°C or less after continuous casting, and all of the steel is heated in the austenite recrystallization region. After hot rolling, which ensures a reduction ratio of 60% or more and finishes rolling in the recrystallization temperature range, the temperature of the steel plate changes from Ar 3 temperature or higher to 500℃ or higher and 650℃ at a cooling rate of 15℃/sec or higher.
This is a method for producing a steel plate with excellent strength and toughness and a small difference in cross-sectional hardness in the thickness direction, which is characterized by cooling to the following temperature range. (Operation) Each limitation of the constituent elements of the present invention is determined based on the following reasons. In other words, C is an effective element for increasing strength, but if it is present too much, the Pcm value (Pcm=C+1/30Si+
1/20Mn+1/20Cu+1/60Ni+1/20Cr+
1/15Mo + 1/10V + 5B) and impairs weldability, so the upper limit should be less than 0.18wt% and C
If it is less than 0.09wt%, the strength will be insufficient, so the range of addition of C is set to be more than 0.09wt% and less than 0.18wt%. In addition to deoxidizing and strengthening the base steel, Si is effective in improving toughness when added at 0.05wt% or more, so the lower limit is set.
The upper limit is set to 0.05wt%, and since too much content is harmful to weldability and HAZ toughness, the upper limit is set to less than 0.5wt%. Mn is an element necessary to increase strength and toughness, but if it is less than 0.7wt%, the strength will be insufficient or the toughness will deteriorate, and if it is more than 1.8wt%, weldability will be significantly worse. addition range
0.7wt% or more and less than 1.8wt%. Al is necessary for deoxidation and grain refinement, and is limited to a sufficient amount of 0.005 wt% or more and less than 0.1 wt%. N should be less than 0.006wt% in order to maintain good weldability and joint toughness. In addition to the above component range limitations, C+Mn/6+
If the carbon equivalent (Cr+Mo+V)/5+(Ni+Cu)/15 exceeds 0.36, weldability deteriorates, so it is limited to 0.36 or less. In manufacturing steel with the above composition range, the solidification structure of the slab (hereinafter referred to as slab) before heating and
Prevents coarsening of precipitates of Al and other subordinate elements,
It is important to make the austenite grains fine when heating the slab, and a continuous casting process is essential. The heating temperature of the slab obtained in this way is preferably lower to prevent coarsening of the austenite grains, but it is preferably 1000℃ or higher to take into account the temperature drop during rolling.
Limited to 1200℃ or below. Next, recrystallization zone rolling is important for turning austenite grains into fine recrystallized austenite grains. At this time, since the larger the rolling reduction ratio is, the more effective it is for grain refinement, the total rolling reduction ratio in the recrystallization zone is limited to 60% or more. If the above-mentioned rolling is not carried out in the recrystallization area,
Since grain refinement is not sufficient, problems arise such as deterioration of toughness and increase in hardness difference in the thickness direction. The reason why hot rolling is finished in the recrystallization temperature range is to obtain a bainitic transformed structure with excellent strength and toughness by water cooling the polygonal grains of recrystallized austenite. If rolling is not ended in the recrystallization temperature range and rolling is continued until the non-recrystallization temperature range, the austenite grains will elongate. When water cooling is performed from such austenite grains, hardenability is lower than when water cooling is performed from polygonal austenite grains, and more ferrite structures are generated, so although excellent toughness is obtained, strength is reduced. It is preferable that the time from hot rolling to the start of cooling be as short as possible; if left for a long time after rolling, crystal grains will become coarse and temperature unevenness will occur, and furthermore, if the temperature drops below Ar 3 , ferrite transformation will begin. Therefore, it is necessary to start cooling from the Ar 3 temperature or higher within a maximum of 10 minutes. Regarding the minimum recrystallization temperature in multi-pass rolling such as thick plate rolling, the minimum recrystallization temperature for Si-Mn systems is approximately 850℃, and when containing elements such as Nb and Mo that have a recrystallization suppressing effect. It is known that the minimum recrystallization temperature is about 950℃ [For example, Nishiyama Memorial Technology Lecture (Text) sponsored by the Japan Iron and Steel Institute, p. 146, "New Controlled Rolling Technology" (1988)
November 1-2)]. Therefore, in the present invention, the minimum recrystallization temperature of the Si-Mn system is about 850°C, and the minimum recrystallization temperature of the system added with selective elements such as Nb or V is about 950°C. The present invention requires completion of rolling in the recrystallization temperature range, and the finishing rolling temperature is equal to or higher than the above recrystallization lower limit temperature. The cooling rate during cooling was set at 15°C/sec or higher in order to obtain the bainite structure necessary for improving the strength and toughness of the steel. The reason why we set the upper limit of the temperature at which cooling is completed, that is, the water cooling stop temperature, to 650℃ is because a bainite structure cannot be obtained at a higher stopping temperature, and the strength and toughness deteriorates, so we set the lower limit to 500℃. This is because at a temperature lower than this, low-temperature transformation products such as island-like martensite are generated, which significantly deteriorates toughness. Conventionally, in order to improve the strength and toughness of water-cooled high-tensile steel plates, it has been essential to add a large amount of alloying elements or to perform controlled rolling in a low temperature range. The present invention has been achieved by the present inventors by combining appropriate rolling conditions in the austenite recrystallization temperature range and controlled cooling after rolling, thereby eliminating the need for controlled rolling in a low temperature range that reduces rolling efficiency. This is based on the discovery that it is possible to produce a steel plate that has excellent strength and toughness and has a small cross-sectional hardness in the thickness direction. In particular, from relatively fine recrystallized austenite grains to temperatures of 500℃ and 650℃ at a cooling rate of 15℃/sec or more.
Conventionally, by water cooling to a temperature range below ℃,
It has been discovered that excellent strength and toughness can be obtained with a bainite structure, which was thought to cause deterioration of toughness. This point will be mainly discussed below. 1 to 3 show the results of experiments conducted by the present inventors for the above study. Figure 1 shows 0.13wt% C, 1.2wt% Mn, and 1.2wt% Si.
Total reduction ratio (%) and toughness of steel containing 0.2wt% when the slab is heated to 1050℃, rolled to 30mm from different slab thicknesses in the recrystallization zone, and water-cooled to 550℃ at a cooling rate of 15℃/sec. The relationship between (vTrs) and cross-sectional hardness difference in the plate thickness direction (ΔHv (10Kg)) is shown. Here, ΔHv (10Kg) is the difference in the Vickers hardness of the surface layer and center of a cross section of a steel plate measured under a load of 10Kg. As is clear from FIG. 1, if the total reduction in the recrystallization zone is less than 60%, good toughness cannot be obtained, and the difference in cross-sectional hardness in the thickness direction increases. From the above results, in order to obtain good toughness and reduce the difference in cross-sectional hardness, the lower limit of the total reduction ratio is 60%.
It stipulates. Further, FIGS. 2 and 3 show experimental results regarding cooling conditions. Figure 2 shows a 180mm thick slab with the same composition as Figure 1.
Toughness, cross-sectional hardness difference in the thickness direction, and water cooling when a steel plate heated to 1050℃ and then rolled in the recrystallization zone to a thickness of 30mm is water-cooled from Ar 3 temperature or higher to various temperatures at a cooling rate of 24℃/s. The relationship between the stop temperature is shown. As is clear from FIG. 2, the toughness significantly deteriorates as the water cooling stop temperature decreases. This is because at a water-cooling stop temperature of less than 500°C, low-temperature transformation products such as island martensite, which are detrimental to toughness, are generated. Additionally, if water cooling is stopped at a high temperature of over 650°C, toughness will deteriorate. This is because the structure is no longer mainly bainite, but instead consists of coarse ferrite and pearlite. On the other hand, the cross-sectional hardness difference becomes significantly large when the water-cooling stop temperature is less than 500°C, but it can be made to a sufficiently small value by water-cooling stopping at a temperature of 500°C or higher. From the above results, in order to obtain good toughness and reduce the difference in cross-sectional hardness, the water cooling stop temperature should be set to 500℃ or higher and 650℃ or higher.
It is specified to be below ℃. Figure 3 shows the toughness and thickness direction of the same slab as in Figure 2, which was similarly rolled and then water-cooled from Ar 3 temperature or higher to a temperature of 500°C or higher and 650°C or lower at various cooling rates. The relationship between cross-sectional hardness difference and cooling rate is shown. As is clear from the figure, toughness is improved by increasing the cooling rate. If the cooling rate is less than 15°C/sec, the toughness will deteriorate significantly. In addition, the cooling rate of 15℃/sec is
This corresponds to the point where the structure changes from ferrite/pearlite to mainly bainite. From these, when water cooling recrystallized polygonal austenite grains, the cooling rate is 15℃/
It was discovered that toughness improves when the steel is raised above sec to create a structure consisting mainly of bainite. On the other hand, it has been found that the cross-sectional hardness difference in the plate thickness direction can be made sufficiently small even if the cooling rate is increased by setting the water cooling stop temperature to 500°C or more and 650°C or less. Based on the above results, the lower limit of the cooling rate is set at 15°C/sec. In addition to the numerical limitations of the above-mentioned specifications, the present invention further includes a generally known effective element, for example, 0.1% or less of Ti, as a toughness improving element, depending on the use of the thick steel plate.
Zr, Ta, Ca, 0.1% or less Nb, V as strength-improving elements, and 1.0% or less Ni, Cr, Mo, Cu,
By adding one or more types of B and 0.003% or less, it is possible to manufacture a thick steel plate with further improved strength and/or toughness. Therefore, the reason why the content of toughness-improving elements is set to 0.1% or less is that, as is well known, if the content exceeds 0.1%, when added during the refining process of steel, many inclusions left by oxidation will accumulate in the surface layer. This is because it becomes a defective part. Furthermore, in any case, if the content of the strength-improving element exceeds the above-mentioned content, the toughness of the welded joint deteriorates, as is well known. (Example) Tables 1 and 2 show that each steel with each component in the table was manufactured under the hot rolling conditions and cooling conditions specified, and its mechanical properties were determined by tensile test, impact test, and cross-sectional hardness difference in the thickness direction (ΔHv (10Kg)). Symbols 1 to 5 indicate the amount of C and 0.055 to 0.17wt%, and the amount of Mn, respectively.
It is a steel with added content varying from 0.65 to 1.71wt%. Invention examples 2, 3, and 4 all have strength (TS)
is 50 Kgf/mm 2 or more and vTrs is -40°C or less, whereas Comparative Example 1 has good toughness but TS of less than 50 Kgf/mm 2 , and C of the present invention. The strength-increasing effect of the addition is clearly recognized. Furthermore, in Comparative Example 5, the strength and toughness deteriorate due to the low Mn content. On the other hand, symbols 6 to 16 contain 0.13wt% C and 0.23wt% Si.
%, the manufacturing conditions shown in the table were changed for steel containing 1.2 wt% Mn. Symbol 6 is a comparative example in which the heating temperature is 1250°C, and when compared to the inventive example with heating temperature 1200°C in symbol 7, the toughness level is about 28°C lower in vTrs, and this is because the heating temperature is high, so the austenite grains This is because it has become coarse. In addition to the deterioration of toughness, in code 6, the cross-sectional hardness difference ΔHv in the plate thickness direction also decreased with respect to the present invention example 7.
, and deterioration of properties such as fatigue properties was observed. Symbol 8 is a comparative example with a water cooling start temperature as low as 700°C, and symbol 9, an inventive example, has a water cooling start temperature of 892°C.
Compared with those at 0.degree. C., both strength and toughness are inferior, and it is clear that ensuring the cooling start temperature of the present invention is effective in improving strength and toughness. Symbols 10 and 11 show the effect of cooling rate. Comparative example code 11 indicates a case where the cooling rate is as slow as 8°C/sec, and inventive examples code 9 and 10 have a cooling rate of 15
Both the strength and toughness are inferior when compared with ℃/sec or more, and it is clear that securing the cooling rate of the present invention is effective in improving the strength and toughness. Symbol 12 is when the water cooling stop temperature is as low as 300℃.
The toughness is significantly deteriorated compared to the invention example code 9 whose water-cooling stop temperature is 530°C, and it is clear that securing the water-cooling stop temperature of the present invention is effective in improving strength and toughness. . Symbol 13 is a case where the total reduction ratio in the recrystallization area is as low as 50%, and compared to the invention example symbol 14 which secured a total reduction ratio of 60% or more, vTrs has deteriorated by about 35°C.
ΔHv is also increasing. It is clear that ensuring rolling in the recrystallization zone of the present invention is effective in improving toughness. Symbol 15 is a comparative example in which the finishing temperature was as low as 810°C and rolling was continued until the non-recrystallized region. Invention example symbol 16
The toughness is slightly better than that, but the strength is low and does not satisfy 50Kg/mm 2 . It is clear that water cooling from the recrystallized austenite of the present invention is effective in increasing strength without significantly compromising toughness. Table 2 shows examples of alloy additions. Symbols 17-21 are C,
This is an example of the present invention in which the alloying elements shown in the table are added in addition to Si, Mn, and Al. It is clear that both strength and toughness are improved compared to the invention example in which alloy 9 in Table 1 is not added.
【表】【table】
【表】【table】
【表】【table】
【表】
（発明の効果）
以上説明したように、本発明は成分を限定した
溶鋼を連続鋳造し、特定した熱延条件と冷却条件
を組合せて製造するので、Ceqを0.36以下としな
がらTS50Kgｆ／mm2以上でvTrs−35〜−68℃の高
強度・高靱性でかつ板厚方向の断面硬度差が小さ
い溶接性に優れた鋼材を、生産性が低下する低温
域での制御圧延を用いることなく、製造可能とし
たものである。
これによりこの種用途分野に、品質の優れた安
価な鋼材の供給が可能となり、工業上にもたらす
効果は大きい。[Table] (Effects of the invention) As explained above, the present invention continuously casts molten steel with limited composition and manufactures it by combining specified hot rolling conditions and cooling conditions, so TS50Kgf/ mm 2 or more and vTrs -35 to -68°C, high strength and toughness steel with excellent weldability and small difference in cross-sectional hardness in the plate thickness direction, using controlled rolling in the low temperature range where productivity decreases. This made it possible to manufacture the product. This makes it possible to supply high-quality and inexpensive steel materials to this type of application field, which has a great industrial effect.
第１図は靱性及び板厚方向の断面硬度差に及ぼ
す全圧下率の影響を示すグラフ、第２図は靱性及
び板厚方向の断面硬度差に及ぼす水冷停止温度の
影響を示すグラフ、第３図は靱性及び板厚方向の
断面硬度差に及ぼす冷却速度の影響を示すグラフ
である。
Figure 1 is a graph showing the effect of total reduction on toughness and difference in cross-sectional hardness in the thickness direction, Figure 2 is a graph showing the effect of water cooling stop temperature on toughness and difference in cross-sectional hardness in the thickness direction, and Figure 3 is a graph showing the effect of water cooling stop temperature on toughness and difference in cross-sectional hardness in the thickness direction. The figure is a graph showing the influence of cooling rate on toughness and cross-sectional hardness difference in the plate thickness direction.
Claims (1)
Cu）／15なる炭素等量が0.36以下で、残部Fe及
び不可避的不純物よりなる鋼を、連続鋳造後1000
℃以上1200℃以下に加熱し、オーステナイトの再
結晶域で全圧下率60％以上を確保し、且つ再結晶
温度域で圧延を終了する熱間圧延後、鋼板の温度
がAr3温度以上から、15℃／sec以上の冷却速度
で500℃以上650℃以下の温度域まで冷却すること
を特徴とする強度・靱性に優れ板厚方向の断面硬
度の差が小さい鋼板の製造法。 ２ Ｃ：0.09％超0.18％未満 Si：0.05％以上0.50％未満 Mn：0.7％以上1.8％未満 Al：0.005％以上0.1％未満 Ｎ：0.006％未満 を含有し、更に0.1％以下のTi，Zr，Ta，Caの
中から選ばれた１種又は２種以上を加え、且つ、
Ｃ＋Mn／６＋（Cr＋Mo＋Ｖ）／５＋（Ni＋
Cu）／15なる炭素等量が0.36以下で、残部Fe及
び不可避的不純物より成る鋼を、連続鋳造後1000
℃以上1200℃以下に加熱し、オーステナイトの再
結晶域で全圧下率60％以上を確保し、且つ再結晶
温度域で圧延を終了する熱間圧延後、鋼板の温度
がAr3温度以上から、15℃／sec以上の冷却速度
で500℃以上650℃以下の温度域まで冷却すること
を特徴とする強度・靱性に優れ板厚方向の断面硬
度の差が小さい鋼板の製造法。 ３ Ｃ：0.09％超0.18％未満 Si：0.05％以上0.50％未満 Mn：0.7％以上1.8％未満 Al：0.005％以上0.1％未満 Ｎ：0.006％未満 を含有し、更に0.1％以下のNb，Ｖ、1.0％以下の
Ni，Cr，Mo，Cu及び0.003％以下のＢの中から
選ばれた１種又は２種以上を加え、且つ、Ｃ＋
Mn／６＋（Cr＋Mo＋Ｖ）／５＋（Ni＋Cu）／15
なる炭素等量が0.36以下で、残部Fe及び不可避的
不純物よりなる鋼を、連続鋳造後1000℃以上1200
℃以下に加熱し、オーステナイトの再結晶域で全
圧下率を60％以上確保し、且つ再結晶温度域で圧
延を終了する熱間圧延後、鋼板の温度がAr3温度
以上から、15℃／sec以上の冷却速度で500℃以上
650℃以下の温度域まで冷却することを特徴とす
る強度・靱性に優れ板厚方向の断面硬度の差が小
さい鋼板の製造法。 ４ Ｃ：0.09％超0.18％未満 Si：0.05％以上0.50％未満 Mn：0.7％以上1.8％未満 Al：0.005％以上0.1％未満 Ｎ：0.006％未満 を含有し、 更に0.1％以下のTi，Zr，Ta，Caの中から選
ばれた１種又は２種以上と、0.1％以下のNb，
Ｖ、1.0％以下のNi，Cr，Mo，Cu及び0.003％以
下のＢの中から選ばれた１種又は２種以上を加
え、 且つ、Ｃ＋Mn／６＋（Cr＋Mo＋Ｖ）／５＋
（Ni＋Cu）／15なる炭素等量が0.36以下で、残部
Fe及び不可避的不純物よりなる鋼を、連続鋳造
後1000℃以上1200℃以下に加熱し、オーステナイ
トの再結晶域で全圧下率60％以上を確保し、且つ
再結晶温度域で圧延を終了する熱間圧延後、鋼板
の温度がAr3温度以上から、15℃／sec以上の冷
却速度で500℃以上650℃以下の温度域まで冷却す
ることを特徴とする強度・靱性に優れ板厚方向の
断面硬度の差が小さい鋼板の製造法。[Claims] 1 Contains C: more than 0.09% and less than 0.18% Si: 0.05% and less than 0.50% Mn: 0.7% and less than 1.8% Al: 0.005% and less than 0.1% N: less than 0.006%, C + Mn/ 6+(Cr+Mo+V)/5+(Ni+
After continuous casting, steel with a carbon equivalent of 0.36 or less (Cu)/15 and the balance Fe and unavoidable impurities is
℃ to 1200℃ or less, ensure a total reduction of 60% or more in the austenite recrystallization region, and finish rolling in the recrystallization temperature region.After the temperature of the steel plate is Ar3 temperature or higher, A method for manufacturing a steel plate with excellent strength and toughness and small difference in cross-sectional hardness in the thickness direction, characterized by cooling to a temperature range of 500°C to 650°C at a cooling rate of 15°C/sec or more. 2 C: More than 0.09% and less than 0.18% Si: 0.05% and less than 0.50% Mn: 0.7% and less than 1.8% Al: 0.005% and less than 0.1% N: Contains less than 0.006%, and further contains Ti, Zr of 0.1% or less , Ta, and Ca, and
C+Mn/6+(Cr+Mo+V)/5+(Ni+
After continuous casting, steel with a carbon equivalent of 0.36 or less (Cu)/15 and the balance Fe and unavoidable impurities is
℃ to 1200℃ or less, ensure a total reduction of 60% or more in the austenite recrystallization region, and finish rolling in the recrystallization temperature region.After the temperature of the steel plate is Ar3 temperature or higher, A method for manufacturing a steel plate with excellent strength and toughness and small difference in cross-sectional hardness in the thickness direction, characterized by cooling to a temperature range of 500°C to 650°C at a cooling rate of 15°C/sec or more. 3 Contains C: more than 0.09% and less than 0.18% Si: 0.05% and less than 0.50% Mn: 0.7% and less than 1.8% Al: 0.005% and less than 0.1% N: Contains less than 0.006%, and further contains 0.1% or less Nb, V , 1.0% or less
Adding one or more selected from Ni, Cr, Mo, Cu and 0.003% or less of B, and C+
Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15
After continuous casting, steel with a carbon equivalent of 0.36 or less and the balance consisting of Fe and unavoidable impurities is heated at 1000°C or higher at 1200°C.
After hot rolling, the temperature of the steel plate changes from Ar 3 temperature or higher to 15℃/ 500℃ or more with a cooling rate of sec or more
A method for manufacturing steel plates with excellent strength and toughness and small differences in cross-sectional hardness in the thickness direction, characterized by cooling to a temperature range of 650℃ or less. 4 C: More than 0.09% but less than 0.18% Si: 0.05% or more and less than 0.50% Mn: 0.7% or more and less than 1.8% Al: 0.005% or more and less than 0.1% N: Contains less than 0.006%, and 0.1% or less of Ti, Zr , Ta, and Ca, and 0.1% or less of Nb,
Adding one or more types selected from V, 1.0% or less of Ni, Cr, Mo, Cu, and 0.003% or less of B, and C+Mn/6+(Cr+Mo+V)/5+
The carbon equivalent (Ni+Cu)/15 is 0.36 or less, and the remainder
After continuous casting, steel consisting of Fe and unavoidable impurities is heated to a temperature of 1000°C to 1200°C, ensuring a total reduction of 60% or more in the austenite recrystallization range, and finishing rolling in the recrystallization temperature range. After rolling, the steel plate temperature is cooled from Ar 3 temperature or higher to a temperature range of 500°C or higher and 650°C or lower at a cooling rate of 15°C/sec or higher.A cross section in the thickness direction with excellent strength and toughness. A method of manufacturing steel plates with small differences in hardness.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP910087A JPS63179020A (en) | 1987-01-20 | 1987-01-20 | Production of steel sheet having excellent strength and toughness and small difference in sectional hardness in thickness direction of sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP910087A JPS63179020A (en) | 1987-01-20 | 1987-01-20 | Production of steel sheet having excellent strength and toughness and small difference in sectional hardness in thickness direction of sheet |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS63179020A JPS63179020A (en) | 1988-07-23 |
| JPH0583607B2 true JPH0583607B2 (en) | 1993-11-26 |
Family
ID=11711203
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP910087A Granted JPS63179020A (en) | 1987-01-20 | 1987-01-20 | Production of steel sheet having excellent strength and toughness and small difference in sectional hardness in thickness direction of sheet |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS63179020A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH07116504B2 (en) * | 1990-12-25 | 1995-12-13 | 株式会社神戸製鋼所 | Manufacturing method of 50 kg class low yield ratio thick high-strength steel plate having a plate thickness of 50 mm or more with a small hardness difference in the plate thickness direction |
| JP4110652B2 (en) * | 1999-01-05 | 2008-07-02 | Ｊｆｅスチール株式会社 | Manufacturing method of steel material with less material variation and excellent welded portion low temperature toughness |
| JP5029748B2 (en) * | 2010-09-17 | 2012-09-19 | Ｊｆｅスチール株式会社 | High strength hot rolled steel sheet with excellent toughness and method for producing the same |
| JP5640614B2 (en) * | 2010-09-30 | 2014-12-17 | Ｊｆｅスチール株式会社 | High-strength steel pipe for line pipe, its manufacturing method, and high-strength steel pipe using high-strength steel sheet for line pipe |
| JP5605136B2 (en) * | 2010-09-30 | 2014-10-15 | Ｊｆｅスチール株式会社 | High strength steel plate with excellent material uniformity in steel plate and method for producing the same |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57143430A (en) * | 1981-02-27 | 1982-09-04 | Nippon Kokan Kk <Nkk> | Manufacture of high tensile steel with weldability and >=50kg/mm2 strength |
| JPS60204826A (en) * | 1984-03-29 | 1985-10-16 | Sumitomo Metal Ind Ltd | Production of ti high tensile steel having excellent low- temperature toughness |
-
1987
- 1987-01-20 JP JP910087A patent/JPS63179020A/en active Granted
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57143430A (en) * | 1981-02-27 | 1982-09-04 | Nippon Kokan Kk <Nkk> | Manufacture of high tensile steel with weldability and >=50kg/mm2 strength |
| JPS60204826A (en) * | 1984-03-29 | 1985-10-16 | Sumitomo Metal Ind Ltd | Production of ti high tensile steel having excellent low- temperature toughness |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS63179020A (en) | 1988-07-23 |
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