JPH0581644B2 - - Google Patents
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- Publication number
- JPH0581644B2 JPH0581644B2 JP62312304A JP31230487A JPH0581644B2 JP H0581644 B2 JPH0581644 B2 JP H0581644B2 JP 62312304 A JP62312304 A JP 62312304A JP 31230487 A JP31230487 A JP 31230487A JP H0581644 B2 JPH0581644 B2 JP H0581644B2
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- 229910000831 Steel Inorganic materials 0.000 claims description 38
- 239000010959 steel Substances 0.000 claims description 38
- 238000001816 cooling Methods 0.000 claims description 24
- 238000005098 hot rolling Methods 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 22
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- 238000004519 manufacturing process Methods 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 17
- 238000005496 tempering Methods 0.000 claims description 13
- 238000003303 reheating Methods 0.000 claims description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 12
- 230000000694 effects Effects 0.000 claims description 9
- 230000001186 cumulative effect Effects 0.000 claims description 8
- 239000012535 impurity Substances 0.000 claims description 8
- 229910052748 manganese Inorganic materials 0.000 claims description 8
- 229910000851 Alloy steel Inorganic materials 0.000 claims description 5
- 229910001209 Low-carbon steel Inorganic materials 0.000 claims description 5
- 229910052758 niobium Inorganic materials 0.000 claims description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 4
- 229910052750 molybdenum Inorganic materials 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- 238000005096 rolling process Methods 0.000 description 19
- 229910000859 α-Fe Inorganic materials 0.000 description 16
- 238000010438 heat treatment Methods 0.000 description 13
- 230000007423 decrease Effects 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 238000005452 bending Methods 0.000 description 4
- 230000009466 transformation Effects 0.000 description 3
- 238000007670 refining Methods 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000004881 precipitation hardening Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
Description
［産業上の利用分野］
本発明は降伏比の低い鋼材の製造方法に関する
ものである。
［従来の技術］
近年造船、産業機械等の各分野にわたつて競争
力向上のため溶接施工の減少、曲げ加工性を代表
として鋼材特性の極限追求、溶接性の向上および
鋼材コストの低減など各種の要求が強まつてい
る。
このうち厚鋼板の曲げ加工性改善のためには、
低降伏比を有する厚鋼板の開発が必要である。ま
た建築、橋梁分野では構造物の安全性向上のた
め、特に耐震性向上のために降伏比の低下が望ま
れている。
従来の制御圧延−制御冷却プロセスにおいて
は、低温靭性向上のため熱間圧延で、できる限り
細粒にすると共に、オーステナイト１相域から加
速冷却することが採用されている。
しかしながらこの方法によつても、フエライト
の細粒化と硬化及び一部パーライトのベーナイト
化によつて降伏点が上昇し、降伏比の上昇となつ
て曲げ加工性が低下する問題がある。
［発明が解決しようとする問題点］
本発明者等の一部は特開昭59−211528号公報及
び特願昭62−52856号、特願昭62−55428号におい
て、低降伏比非調質鋼の製法を提案した。これは
制御圧延−制御冷却プロセスを用いて降伏点を低
下させる方法について検討した結果、細粒フエラ
イトで良好な低温靭性を得ながら、かつ低降伏点
で低降伏比を有する鋼板の製造方法を開発したこ
とによる。
しかしその後さらに低降伏比に対する要求が強
まり、先に提案した内容では、厳しい要求に対し
て不十分となつてきた。
［問題点を解決するための手段］
このため引き続き降伏比を低下させるために、
多数の実験と詳細な検討を加えた結果、降伏比を
低下させるためには、鋼のミクロ組織をフエライ
トと第２相の炭化物の２相混合組織にする。さら
に降伏比を下げるためには、降伏点を下げ、引張
り強さを高めることが重要である。
降伏点を下げるためにはフエライトの面積率を
増加させ、かつあまり細粒化しないこと、引張り
強さを高めるためには、急冷で硬くなつた第２相
の炭化物（ベーナイト又はマルテンサイト）を焼
もどしにより、必要以上に軟化させないことが重
要であることを見い出したのである。
第１図にフエライト面積率と降伏比の関係を示
すが、フエライト面積率の増加に従い、降伏比は
大幅に低下していく。
本発明はこのような知見にもとずき、低降伏比
を有する鋼板の製造を可能としたもので、その要
旨とするところは(1)重量％にて、Ｃ：0.30％以
下、Si：0.05〜0.60％、Mn：0.5〜2.5％、Al：
0.01〜0.10％を基本成分とし、残Feおよび不可避
不純物からなる低炭素鋼スラブを1050〜1250℃に
加熱し、熱間圧延後250℃以下まで急冷し、次い
でAc1＋20℃〜Ac1＋80℃に再加熱し、ひきつづ
き水冷した後200〜600℃の温度範囲で焼もどしす
ることを特徴とする。
(2) (1)において熱間圧延を1050℃以下900℃超の
温度で終了することを特徴とする。
(3) (1)において熱間圧延を900℃〜Ar3間で終了
し、この温度範囲で仕上板厚に対し５％以上30
％未満の累積圧下率の圧下を施すことを特徴と
する。
(4) 重量％にて、Ｃ：0.30％以下、Si：0.05〜
0.60％、Mn：0.5〜2.5％、Al：0.01〜0.10％を
基本成分とし、更にCu：2.0％以下、Ni：４％
未満、Cr：5.5％以下、Mo：2.0％以下、Nb：
0.15％以下、Ｖ：0.3％以下、Ti：0.15％以下、
Ｂ：0.0003〜0.0030％の強度改善元素群の内よ
り少くとも１種を含有し、残Feおよび不可避
不純物からなる、低炭素低合金鋼スラブを1050
〜1250℃に加熱し、熱間圧延後250℃以下まで
急冷し、次いでAc1＋20℃〜Ac1＋80℃に再加
熱し、ひきつづき水冷した後200〜600℃の温度
範囲で焼もどしすることを特徴とする。
(5) (4)において熱間圧延を1050℃以下900℃超の
温度で終了することを特徴とする。
(6) (4)において熱間圧延を900℃〜Ar3間で終了
し、この温度範囲で仕上板厚に対し５％以上30
％未満の累積圧下率の圧下を施すことを特徴と
する。
(7) 重量％にて、Ｃ：0.30％以下、Si：0.05〜
0.60％、Mn：0.5〜2.5％、Al：0.01〜0.10％を
基本成分とし、更にCa：0.006％以下を含有し、
残Feおよび不可避不純物からなる低炭素鋼ス
ラブを1050〜1250℃に加熱し、熱間圧延後250
℃以下まで急冷し、次いでAc1＋20℃〜Ac1＋
80℃に再加熱し、ひきつづき水冷した後200〜
600℃の温度範囲で焼もどしすることを特徴と
する。
(8) (7)において熱間圧延を1050℃以下900℃超の
温度で終了することを特徴とする。
(9) (7)において熱間圧延を900℃〜Ar3間で終了
し、この温度範囲で仕上板厚に対し５％以上30
％未満の累積圧下率の圧下を施すことを特徴と
する。
(10) 重量％にて、Ｃ：0.30％以下、Si：0.05〜
0.60％、Mn：0.5〜2.5％、Al：0.01〜0.10％を
基本成分とし、更にCu：2.0％以下、Ni：４％
未満、Cr：5.5％以下、Mo：2.0％以下、Nb：
0.15％以下、Ｖ：0.3％以下、Ti：0.15％以下、
Ｂ：0.0003〜0.0030％の強度改善元素群のうち
少くとも１種と、介在物形態制御作用のある
Ca：0.006％以下を含有し、残Feおよび不可避
不純物からなる、低炭素低合金鋼スラブを1050
〜1250℃に加熱し、熱間圧延後250℃以下まで
急冷し、次いでAc1＋20℃〜Ac1＋80℃に再加
熱し、ひきつづき水冷した後200〜600℃の温度
範囲で焼もどしすることを特徴とする。
(11) (10)において熱間圧延を1050℃以下900℃超の
温度で終了することを特徴とする。
(12) (10)において熱間圧延を900℃〜Ar3間で終了
し、この温度範囲で仕上板厚に対し５％以上30
％未満の累積圧下率の圧下を施すことを特徴と
する。
ここに本発明で使用するAr3（℃）は、Ar3（℃）
＝868−369・Ｃ（wt％）＋24.6・Si（wt％）−68.1・
Mn（wt％）−36.1・Ni（wt％）−20.7・Cu（wt％）
−24.8・Cr（wt％）＋29.6・Mo（wt％）で求めた
ものとする。
［作用］
本発明においては、加熱温度を高めにしかつ熱
間圧延において再結晶圧延のみか、もしくは未再
結晶域圧延を行つてもその累積圧下率を低くする
ことにより、必要以上の細粒化をしないこと、そ
の後Ac1〜Ac3変態点間で、低めの方に加熱し、
そこから水冷することによりフエライト面積率を
大幅に増加させる。
さらに焼もどし温度を低くすることで、第２相
の部分を必要以上に軟化させないことの相乗的効
果により、降伏比の低い鋼材の製造を可能にした
ものである。
次に本発明の加熱・圧延・冷却条件について述
べる。
加熱温度は加熱時のオーステナイト粒を必要以
上に細粒にしないように、1050℃を下限とする。
一方、余り高くしても材質上の効果がなく、逆に
省エネ上不都合になるので1250℃を上限とする。
圧延については900℃を超える圧延と、900℃以
下での圧延に分けられるが、低降伏比鋼板が使用
される用途では、900℃を超える温度での制御圧
延による靭性向上で十分であり、900℃超での圧
延完了が望ましいので下限は950℃とする。
一方加熱温度が1050℃〜1250℃の温度範囲であ
るため、圧延中の温度降下を考えると、圧延終了
温度は1050℃以下となるので上限は1050℃とす
る。
また、900℃以下で圧延を終了する場合は、900
℃以下の制御圧延での累積圧下を30％以上にする
と、必要以上のフエライトの細粒化と、第２相の
炭化物の微細化により高降伏比となる。
そこで900℃〜Ar3間で圧延終了する場合、900
℃〜Ar3間の累積圧下率は仕上板厚に対して30％
未満とする。一方下限は圧延の効果を充分内部に
及ばせるため５％以上必要である。
次に圧延後の加速冷却の冷却停止温度を250℃
以下としたのは、250℃を超える高温域で冷却停
止し、その後焼もどし熱処理すると、強度が若干
低下すると同時に低温靭性が劣化するからであ
る。
ここに加速冷却は、鋼板が均一に冷却されるよ
う水量密度を0.3m3／m2・min以上とすることが
好ましい。
次に再加熱温度をAc1＋20℃以上Ac1＋80℃以
下にしたのは、この温度範囲に加熱することによ
りフエライト面積率が大幅に向上するためであ
る。すなわちAc1直上ではまだ充分変態が進ま
ず、第２相の炭化物の部分の硬化が不充分である
のに対し、Ac1＋20℃以上になると変態も充分進
み、第２相の部分の硬化も充分となる。
フエライト面積率はこのAc1＋20℃より加熱温
度が高くなるに従い低下していく。そしてAc1＋
80℃以下になると、本発明の目的とする低降伏比
を得るためのフエライト面積率が得られなくなる
ためこれを上限としている。
このように再加熱温度をAc1＋20℃〜Ac1＋80
℃とAc1〜Ac3の温度範囲のまん中より低温側を
中心に限定しているのは、Ac1に近い側の加熱に
より、加熱時のフエライト・オーステナイトの面
積比でフエライト部分が大きくなり、この状態を
次に規定する急冷により凍結することで、フエラ
イト面積率を大きくし低降伏比をねらつている。
Ac1＋20℃〜Ac1＋80℃再加熱後の水冷は、再
加熱時にオーステナイト化したＣが濃化した部分
を焼入れ組織にすることで充分硬化させ、引張り
強さを高め低降伏比を得るためである。水冷条件
としては急冷し焼入れ組織が容易に得られる浸漬
あるいはローラークエンチによる水冷でよい。
さらに焼もどし温度については、フエライトと
第２相の炭化物の２相混合組織について、その前
の水冷で充分硬化した第２相部分をあまり高温で
焼もどしすると軟化しすぎ、これが引張り強さの
低下ひいては降伏比を上げるため、上限を600℃
とする。しかし焼もどし温度が低くて、200℃未
満になるとほとんど焼もどしの効果がなくなり、
靭性が低下するため焼もどし温度の下限は200℃
とする。
本発明法は低炭素鋼またはこれに特殊元素を添
加した低炭素低合金鋼に適用し好結果を得ること
ができる。本発明において成分を限定する理由は
次の通りである。Ｃは強度確保のため必要な元素
であるが、多くなると鋼の靭性及び溶接性を害す
るので0.30％以下とする。Siは脱酸のため0.05％
以上は必要で添加されるが多くなると溶接性を損
なうので0.60％以下とする。Mnは安価に強度を
あげる元素として有用であり、強度確保のため
0.5％以上は必要であるが、多くなると溶接性を
損なうので2.5％以下とする。
Alは脱酸のため0.01％以上必要であるが、多く
なると鋼中介在物が多くなりすぎ、鋼の性質を悪
化させるため0.1％以下とする。
Cuは強度上昇、耐食性向上に有用で添加され
るが、2.0％を超えて添加しても強度の上昇代が
ほとんどなくなるので、含有量の上限は2.0％と
する。
Niは焼入れ性向上による強度上昇と低温靭性
改善に有用で添加されるが、高価な元素であるた
め、含有量は4.0％未満とする。
Crは強度上昇に有用で添加されるが、多くな
ると低温靭性、溶接性を阻害するため含有量は
5.5％を上限とする。
Moは強度上昇に有用であるが、多くなると溶
接性を阻害するため含有量は2.0％を上限とする。
NbはTiと同様オーステナイト粒の細粒化に有
用で添加されるが、多くなると溶接性を阻害する
ので含有量の上限は0.15％とする。
Ｖは析出硬化に有用であるが、多くなると溶接
性を阻害するため含有量は0.3％を上限とする。
Tiはオーステナイト粒の細粒化に有用で添加
されるが、多くなると溶接性を阻害するため含有
量は0.15％を上限とする。
Ｂは微量の添加によつて、鋼の焼入れ性を著し
く高める効果を有する。かかる効果を有効に得る
ためには、少なくとも0.0003％を添加することが
必要である。しかし過多に添加するときは、Ｂ化
合物を生成して、靭性を劣化させるので、上限は
0.0030％とする。
Caは硫化物系介在物の形態制御に有用で添加
されるが、多くなると鋼中介在物を形成し鋼の性
質を悪化させるため、含有量は0.006％を上限と
する。
［実施例］
第１表に供試材の化学成分を示し、第２表に加
熱、圧延、冷却、熱処理条件と得られた鋼板の機
械的性質を示す。
鋼Ａ，Ｇ，Ｈ，Ｉ，Ｊ，Ｋ，Ｌ，Ｍ，Ｎ，Ｏ，
Ｐは50Kg／mm2級、鋼Ｂ，Ｃ，Ｄ，Ｅ，Ｆ，Ｑ，
Ｒ，Ｓ，Ｔ，Ｕは60Kg／mm2級、Ｖは80Kg／mm2級の
強度をねらつた成分系で、第２表に示す如く鋼板
No.A1，A9，B1，C1，D1，E1，F1，G1，H1，
I1，J1，K1，L1，M1，N1，O1，P1，Q1，R1，
S1，T1，U1，V1は本発明実施例であり、それ
ぞれ50Kg／mm2，60Kg／mm2，80Kg／mm2級鋼として充
分な強度と良好な低温靭性を備え、本発明のねら
いとする低降伏比（降伏比70％以下）を達成して
いる。
これに対し鋼板No.A2は加熱温度が低すぎるた
め降伏比が高くなつている。A3は900℃〜Ar3間
累積圧下率が高すぎるため降伏比が高くなつてい
る。A4は冷却停止温度が高すぎるため低温靭性
が低下している。A5は再加熱温度が低すぎるた
め、A6は再加熱温度が高すぎるため降伏比が高
くなつている。A7は焼もどし温度が高すぎるた
め降伏比が高くなつている。A8は焼もどしを行
つていないため低温靭性が低下している。B2は
再加熱温度が高すぎるため、B3は焼もどし温度
が高すぎるため降伏比が高くなつている。
[Industrial Application Field] The present invention relates to a method for producing steel materials with a low yield ratio. [Conventional technology] In recent years, in order to improve competitiveness in various fields such as shipbuilding and industrial machinery, various efforts have been made to reduce welding work, pursue the ultimate properties of steel materials such as bending workability, improve weldability, and reduce steel material costs. The demand for Among these, in order to improve the bending workability of thick steel plates,
It is necessary to develop thick steel plates with low yield ratios. Furthermore, in the fields of architecture and bridges, it is desired to reduce the yield ratio in order to improve the safety of structures, especially in order to improve their seismic resistance. In the conventional controlled rolling-controlled cooling process, in order to improve low-temperature toughness, hot rolling is performed to make the grains as fine as possible, and accelerated cooling is performed from the austenite 1 phase region. However, even with this method, there is a problem that the yield point increases due to grain refinement and hardening of the ferrite and part of the pearlite becomes bainitic, resulting in an increase in the yield ratio and a decrease in bending workability. [Problems to be Solved by the Invention] Some of the present inventors have proposed low yield ratio non-temperature treatment in Japanese Patent Application Laid-open No. 59-211528, Japanese Patent Application No. 62-52856, and Japanese Patent Application No. 62-55428. He proposed a method for manufacturing steel. As a result of studying a method of lowering the yield point using a controlled rolling-controlled cooling process, we developed a method for manufacturing steel sheets that has good low-temperature toughness with fine-grained ferrite, as well as a low yield point and low yield ratio. Depends on what you did. However, since then the demand for a lower yield ratio has become even stronger, and the content proposed earlier is no longer sufficient to meet the strict demands. [Means to solve the problem] Therefore, in order to continue to lower the yield ratio,
As a result of numerous experiments and detailed studies, we found that in order to lower the yield ratio, the microstructure of the steel should be a two-phase mixed structure of ferrite and second phase carbide. In order to further lower the yield ratio, it is important to lower the yield point and increase the tensile strength. In order to lower the yield point, the area ratio of ferrite should be increased and the grains should not be made too fine. In order to increase the tensile strength, the second phase carbide (bainite or martensite), which has become hard due to rapid cooling, should be sintered. They discovered that it is important not to soften the material more than necessary during restoring. FIG. 1 shows the relationship between the ferrite area ratio and the yield ratio, and as the ferrite area ratio increases, the yield ratio decreases significantly. Based on this knowledge, the present invention has made it possible to manufacture a steel plate with a low yield ratio.The main points of the present invention are (1) In terms of weight percent, C: 0.30% or less, Si: 0.05~0.60%, Mn: 0.5~2.5%, Al:
A low carbon steel slab consisting of 0.01~0.10% as a basic component, residual Fe and unavoidable impurities is heated to 1050~1250℃, then rapidly cooled to below 250℃ after hot rolling, and then heated to Ac 1 +20℃~Ac 1 +80℃ It is characterized by being reheated to , followed by water cooling, and then tempered at a temperature range of 200 to 600 degrees Celsius. (2) In (1), the hot rolling is completed at a temperature of 1050°C or lower and over 900°C. (3) In (1), hot rolling is completed between 900℃ and Ar 3 , and within this temperature range 5% or more of the finished plate thickness.
%. (4) In weight%, C: 0.30% or less, Si: 0.05~
0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10% as basic components, further Cu: 2.0% or less, Ni: 4%
Less than, Cr: 5.5% or less, Mo: 2.0% or less, Nb:
0.15% or less, V: 0.3% or less, Ti: 0.15% or less,
B: 1050 low carbon low alloy steel slab containing at least one type from the strength improving element group of 0.0003 to 0.0030% and consisting of residual Fe and unavoidable impurities.
The material is heated to ~1250°C, hot-rolled, rapidly cooled to below 250°C, then reheated to Ac 1 +20°C ~ Ac 1 +80°C, successively water-cooled, and then tempered at a temperature range of 200-600°C. Features. (5) In (4), the hot rolling is completed at a temperature of 1050°C or lower and over 900°C. (6) In (4), hot rolling is completed between 900℃ and Ar 3 , and within this temperature range 5% or more of the finished plate thickness.
%. (7) In weight%, C: 0.30% or less, Si: 0.05~
The basic components are 0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10%, and further contains Ca: 0.006% or less,
A low carbon steel slab consisting of residual Fe and unavoidable impurities is heated to 1050~1250℃, and after hot rolling it is heated to 250℃.
℃ or below, then Ac 1 +20℃ ~ Ac 1 +
After reheating to 80℃ and subsequent water cooling, 200~
It is characterized by tempering in a temperature range of 600℃. (8) In (7), the hot rolling is completed at a temperature of 1050°C or lower and over 900°C. (9) In (7), hot rolling is completed between 900℃ and Ar 3 , and within this temperature range 5% or more of the finished plate thickness.
%. (10) In weight%, C: 0.30% or less, Si: 0.05~
0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10% as basic components, further Cu: 2.0% or less, Ni: 4%
Less than, Cr: 5.5% or less, Mo: 2.0% or less, Nb:
0.15% or less, V: 0.3% or less, Ti: 0.15% or less,
B: 0.0003 to 0.0030% of at least one type of strength-improving element group and an inclusion form control effect.
1050 low carbon low alloy steel slab containing Ca: 0.006% or less, residual Fe and unavoidable impurities
The material is heated to ~1250°C, hot-rolled, rapidly cooled to below 250°C, then reheated to Ac 1 +20°C ~ Ac 1 +80°C, successively water-cooled, and then tempered at a temperature range of 200-600°C. Features. (11) In (10), the hot rolling is completed at a temperature of 1050°C or lower and higher than 900°C. (12) In (10), hot rolling is completed between 900℃ and Ar 3 , and within this temperature range 5% or more of the finished plate thickness.
%. Ar 3 (℃) used in the present invention is Ar 3 (℃)
=868−369・C(wt%)+24.6・Si(wt%)−68.1・
Mn (wt%) −36.1・Ni (wt%) −20.7・Cu (wt%)
-24.8・Cr (wt%) + 29.6・Mo (wt%). [Function] In the present invention, by increasing the heating temperature and performing only recrystallization rolling during hot rolling, or by lowering the cumulative reduction rate even if rolling in a non-recrystallized region is performed, unnecessarily fine graining is achieved. Then heat to a lower temperature between Ac 1 and Ac 3 transformation point,
From there, water cooling significantly increases the ferrite area ratio. Furthermore, by lowering the tempering temperature, the second phase portion is not softened more than necessary, which has a synergistic effect, making it possible to manufacture steel materials with a low yield ratio. Next, the heating, rolling and cooling conditions of the present invention will be described. The lower limit of the heating temperature is 1050°C so as not to make the austenite grains finer than necessary during heating.
On the other hand, if the temperature is set too high, there will be no effect on the quality of the material, and on the contrary, it will be disadvantageous in terms of energy conservation, so the upper limit is set at 1250°C. Rolling can be divided into rolling at temperatures above 900℃ and rolling at temperatures below 900℃, but in applications where low yield ratio steel plates are used, improved toughness through controlled rolling at temperatures above 900℃ is sufficient; Since it is desirable to complete rolling at a temperature exceeding ℃, the lower limit is set at 950℃. On the other hand, since the heating temperature is in the temperature range of 1050°C to 1250°C, considering the temperature drop during rolling, the rolling end temperature will be 1050°C or less, so the upper limit is set to 1050°C. In addition, when finishing rolling at 900℃ or less, 900℃
When the cumulative reduction in controlled rolling at temperatures below 30°C is set to 30% or more, a high yield ratio is obtained due to the finer grains of ferrite and the finer grains of the second phase carbide. Therefore, when finishing rolling between 900℃ and Ar 3 , 900℃
The cumulative rolling reduction rate between ℃ and Ar 3 is 30% of the finished plate thickness.
less than On the other hand, the lower limit is required to be 5% or more in order to sufficiently extend the effect of rolling to the inside. Next, set the cooling stop temperature for accelerated cooling after rolling to 250℃.
The reason for the following is that if cooling is stopped in a high temperature range exceeding 250°C and then tempering heat treatment is performed, the strength will decrease slightly and the low-temperature toughness will deteriorate at the same time. In accelerated cooling, the water density is preferably 0.3 m 3 /m 2 ·min or more so that the steel plate is uniformly cooled. Next, the reason why the reheating temperature was set to Ac 1 +20°C or more and Ac 1 +80°C or less is that heating to this temperature range significantly improves the ferrite area ratio. In other words, directly above Ac 1 , the transformation has not yet progressed sufficiently and the hardening of the second phase carbide portion is insufficient, whereas at Ac 1 +20°C or higher, the transformation has progressed sufficiently and the hardening of the second phase portion is also insufficient. It will be enough. The ferrite area ratio decreases as the heating temperature becomes higher than Ac 1 +20°C. And Ac 1 +
If the temperature falls below 80°C, the area ratio of ferrite to obtain the low yield ratio targeted by the present invention cannot be obtained, so this is set as the upper limit. In this way, change the reheating temperature from Ac 1 +20℃ to Ac 1 +80
The reason why it is mainly limited to the lower temperature side than the middle of the temperature range of ℃ and Ac 1 to Ac 3 is that due to heating on the side closer to Ac 1 , the ferrite part becomes larger in terms of the area ratio of ferrite to austenite during heating. By freezing this state by rapid cooling as specified below, we aim to increase the ferrite area ratio and achieve a low yield ratio. Ac 1 ＋20℃〜Ac 1 ＋80℃ After reheating, water cooling is performed to sufficiently harden the part where C, which has become austenitized during reheating, becomes a quenched structure to increase tensile strength and obtain a low yield ratio. It is. The water cooling conditions may be water cooling by immersion or roller quenching, which makes it easy to obtain a rapidly quenched and quenched structure. Furthermore, regarding the tempering temperature, for the two-phase mixed structure of ferrite and second phase carbide, if the second phase part, which has been sufficiently hardened by previous water cooling, is tempered at too high a temperature, it will become too soft, resulting in a decrease in tensile strength. In order to increase the yield ratio, the upper limit was set at 600℃.
shall be. However, if the tempering temperature is low, below 200℃, the tempering effect will be almost gone.
The lower limit of tempering temperature is 200℃ as toughness decreases.
shall be. The method of the present invention can be applied to low carbon steel or low carbon low alloy steel to which special elements are added, and good results can be obtained. The reasons for limiting the components in the present invention are as follows. C is a necessary element to ensure strength, but if too much it impairs the toughness and weldability of the steel, it should be kept at 0.30% or less. Si is 0.05% for deoxidation
The above content is necessary and is added, but if too much it impairs weldability, it should be kept at 0.60% or less. Mn is useful as an element that increases strength at low cost, and is used to ensure strength.
It is necessary to have a content of 0.5% or more, but if it increases, weldability will be impaired, so the content should be 2.5% or less. Al is required to be 0.01% or more for deoxidation, but if it is too large, inclusions in the steel will increase too much and the properties of the steel will deteriorate, so the content should be 0.1% or less. Cu is added because it is useful for increasing strength and improving corrosion resistance, but even if it is added in excess of 2.0%, there is almost no increase in strength, so the upper limit of the content is set to 2.0%. Ni is added because it is useful for increasing strength by improving hardenability and improving low-temperature toughness, but since it is an expensive element, the content should be less than 4.0%. Cr is added because it is useful for increasing strength, but as too much Cr inhibits low-temperature toughness and weldability, the content is limited.
The upper limit is 5.5%. Mo is useful for increasing strength, but since too much Mo impairs weldability, the content is limited to 2.0%. Like Ti, Nb is added because it is useful for refining austenite grains, but if too much it impedes weldability, so the upper limit of its content is set at 0.15%. V is useful for precipitation hardening, but too much V impedes weldability, so the upper limit of the content is 0.3%. Ti is added because it is useful for refining austenite grains, but if it increases, it impairs weldability, so the upper limit of the content is 0.15%. When added in a small amount, B has the effect of significantly increasing the hardenability of steel. In order to effectively obtain such an effect, it is necessary to add at least 0.0003%. However, when adding too much, B compounds are generated and the toughness deteriorates, so the upper limit is
It shall be 0.0030%. Ca is added because it is useful for controlling the morphology of sulfide-based inclusions, but if too much Ca forms inclusions in the steel and deteriorates the properties of the steel, the upper limit of the content is 0.006%. [Example] Table 1 shows the chemical composition of the test materials, and Table 2 shows the heating, rolling, cooling, and heat treatment conditions and the mechanical properties of the obtained steel sheets. Steel A, G, H, I, J, K, L, M, N, O,
P is 50Kg/mm 2nd grade, steel B, C, D, E, F, Q,
R, S, T, U are 60Kg/mm 2nd grade, V is 80Kg/mm 2nd grade strength, and the steel plate is as shown in Table 2.
No.A1, A9, B1, C1, D1, E1, F1, G1, H1,
I1, J1, K1, L1, M1, N1, O1, P1, Q1, R1,
S1, T1, U1, and V1 are examples of the present invention, and have sufficient strength and good low-temperature toughness as 50Kg/mm 2 , 60Kg/mm 2 , and 80Kg/mm class 2 steel, respectively, which is the aim of the present invention. Achieved a low yield ratio (yield ratio of 70% or less). On the other hand, steel plate No. A2 has a high yield ratio because the heating temperature is too low. A3 has a high yield ratio because the cumulative reduction rate between 900°C and Ar3 is too high. A4 has low temperature toughness because the cooling stop temperature is too high. A5's reheating temperature is too low, and A6's reheating temperature is too high, resulting in a high yield ratio. A7 has a high yield ratio because the tempering temperature is too high. Since A8 is not tempered, its low-temperature toughness is reduced. B2 has a high reheating temperature, and B3 has a high yield ratio because the tempering temperature is too high.
【表】【table】
【表】【table】
【表】
［発明の効果］
以上詳細に説明した通り、本発明は特別に高価
な合金元素を使用することなく、50Kg／mm2以上の
高強度を有し、曲げ加工性の良い低降伏比厚鋼板
を安価に製造可能としたもので、産業上その効果
は大である。[Table] [Effects of the Invention] As explained in detail above, the present invention has high strength of 50 kg/mm 2 or more without using special expensive alloying elements, and has a low yield ratio with good bending workability. This makes it possible to manufacture thick steel plates at low cost, and has great industrial effects.
第１図はフエライト面積率とY.R（降伏比％）
の関係を示すグラフである。
Figure 1 shows ferrite area ratio and YR (yield ratio %)
It is a graph showing the relationship between.
Claims (1)
なる低炭素鋼スラブを1050〜1250℃に加熱し、熱
間圧延後250℃以下まで急冷し、次いでAc1＋20
℃〜Ac1＋80℃に再加熱し、ひきつづき水冷した
後200〜600℃の温度範囲で焼もどしすることを特
徴とする降伏比の低い鋼材の製造方法。 ２ 熱間圧延を1050℃以下900℃超の温度で終了
することを特徴とする特許請求の範囲第１項記載
の降伏比の低い鋼材の製造方法。 ３ 熱間圧延を900℃〜Ar3間で終了し、この温
度範囲で仕上板厚に対し５％以上30％未満の累積
圧下率の圧下を施すことを特徴とする特許請求の
範囲第１項記載の降伏比の低い鋼材の製造方法。 ４ 重量％にて、 Ｃ：0.30％以下、Si：0.05〜0.60％、 Mn：0.5〜2.5％、Al：0.01〜0.10％ を基本成分とし、更に Cu：2.0％以下、Ni：４％未満、 Cr：5.5％以下、Mo：2.0％以下、 Nb：0.15％以下、Ｖ：0.3％以下、 Ti：0.15％以下、Ｂ：0.0003〜0.0030％ の強度改善元素群の内より少くとも１種を含有
し、残Feおよび不可避不純物からなる低炭素低
合金鋼スラブを1050〜1250℃に加熱し、熱間圧延
後250℃以下まで急冷し、次いでAc1＋20℃〜Ac1
＋80℃に再加熱し、ひきつづき水冷した後200〜
600℃の温度範囲で焼もどしすることを特徴とす
る降伏比の低い鋼材の製造方法。 ５ 熱間圧延を1050℃以下900℃超の温度で終了
することを特徴とする特許請求の範囲第４項記載
の降伏比の低い鋼材の製造方法。 ６ 熱間圧延を900℃〜Ar3間で終了し、この温
度範囲で仕上板厚に対し５％以上30％未満の累積
圧下率の圧下を施すことを特徴とする特許請求の
範囲第４項記載の降伏比の低い鋼材の製造方法。 ７ 重量％にて、 Ｃ：0.30％以下、Si：0.05〜0.60％、 Mn：0.5〜2.5％、Al：0.01〜0.10％ を基本成分とし、更に Ca：0.006％以下を含有し、 残Feおよび不可避不純物からなる低炭素鋼ス
ラブを1050〜1250℃に加熱し、熱間圧延後250℃
以下まで急冷し、次いでAc1＋20℃〜Ac1＋80℃
に再加熱し、ひきつづき水冷した後200〜600℃の
温度鋼板で焼もどしすることを特徴とする降伏比
の低い鋼材の製造方法。 ８ 熱間圧延を1050℃以下900℃超の温度で終了
することを特徴とする特許請求の範囲第７項記載
の降伏比の低い鋼材の製造方法。 ９ 熱間圧延を900℃〜Ar3間で終了し、この温
度範囲で仕上板厚に対し５％以上30％未満の累積
圧下率の圧下を施すことを特徴とする特許請求の
範囲第７項記載の降伏比の低い鋼材の製造方法。 １０ 重量％にて、 Ｃ：0.30％以下、Si：0.05〜0.60％、 Mn：0.5〜2.5％、Al：0.01〜0.10％ を基本成分とし、更に Cu：2.0％以下、Ni：４％未満、 Cr：5.5％以下、Mo：2.0％以下、 Nb：0.15％以下、Ｖ：0.3％以下、 Ti：0.15％以下、Ｂ：0.0003〜0.0030％ の強度改善元素群の内より少くとも１種と、介在
物形態制御作用のあるCa：0.006％以下を含有し、 残Feおよび不可避不純物からなる、低炭素低
合金鋼スラブを1050〜1250℃に加熱し、熱間圧延
後250℃以下まで急冷し、次いでAc1＋20℃〜Ac1
＋80℃に再加熱し、ひきつづき水冷した後200〜
600℃の温度範囲で焼もどしすることを特徴とす
る降伏比の低い鋼材の製造方法。 １１ 熱間圧延を1050℃以下900℃超の温度で終
了することを特徴とする特許請求の範囲第１０項
記載の降伏比の低い鋼材の製造方法。 １２ 熱間圧延を900℃〜Ar3間で終了し、この
温度範囲で仕上板厚に対し５％以上30％未満の累
積圧下率の圧下を施すことを特徴とする特許請求
の範囲第１０項記載の降伏比の低い鋼材の製造方
法。[Claims] 1% by weight, the basic components are C: 0.30% or less, Si: 0.05-0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10%, and the remainder consists of Fe and inevitable impurities. A low carbon steel slab is heated to 1050~1250℃, then rapidly cooled to below 250℃ after hot rolling, and then Ac 1 + 20
1. A method for producing a steel material with a low yield ratio, which comprises reheating to Ac 1 +80°C, followed by water cooling, and then tempering in a temperature range of 200 to 600°C. 2. The method for manufacturing a steel material with a low yield ratio according to claim 1, characterized in that the hot rolling is completed at a temperature of 1050°C or lower and higher than 900°C. 3. Hot rolling is completed at a temperature between 900°C and Ar 3 , and reduction is applied to the finished plate thickness at a cumulative reduction rate of 5% or more and less than 30% within this temperature range. A method for manufacturing the steel material with a low yield ratio. 4 In terms of weight%, the basic components are C: 0.30% or less, Si: 0.05 to 0.60%, Mn: 0.5 to 2.5%, Al: 0.01 to 0.10%, further Cu: 2.0% or less, Ni: less than 4%, Contains at least one element from the strength improving element group: Cr: 5.5% or less, Mo: 2.0% or less, Nb: 0.15% or less, V: 0.3% or less, Ti: 0.15% or less, B: 0.0003 to 0.0030%. Then, a low carbon low alloy steel slab consisting of residual Fe and unavoidable impurities is heated to 1050 to 1250°C, then rapidly cooled to 250°C or less after hot rolling, and then heated to Ac 1 +20°C to Ac 1
After reheating to +80℃ and subsequent water cooling, 200~
A method for manufacturing steel materials with a low yield ratio, characterized by tempering at a temperature range of 600℃. 5. The method for manufacturing a steel material with a low yield ratio according to claim 4, characterized in that the hot rolling is completed at a temperature of 1050°C or lower and higher than 900°C. 6. Claim 4, characterized in that the hot rolling is completed at a temperature between 900°C and Ar 3 , and the finished plate thickness is rolled at a cumulative reduction rate of 5% or more and less than 30% within this temperature range. A method for manufacturing the steel material with a low yield ratio. 7% by weight, the basic components are C: 0.30% or less, Si: 0.05-0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10%, and further contains Ca: 0.006% or less, remaining Fe and A low carbon steel slab consisting of unavoidable impurities is heated to 1050-1250℃ and then heated to 250℃ after hot rolling.
Rapid cooling to below, then Ac 1 +20℃~ Ac 1 +80℃
A method for producing a steel material with a low yield ratio, which comprises reheating the material to a temperature of 200 to 600°C, followed by water cooling, and then tempering with a steel plate at a temperature of 200 to 600°C. 8. The method for manufacturing a steel material with a low yield ratio according to claim 7, characterized in that hot rolling is completed at a temperature of 1050°C or lower and higher than 900°C. 9. Claim 7, characterized in that the hot rolling is completed at a temperature between 900°C and Ar 3 , and the finished sheet thickness is rolled at a cumulative reduction rate of 5% or more and less than 30% within this temperature range. A method for manufacturing the steel material with a low yield ratio. At 10% by weight, the basic components are C: 0.30% or less, Si: 0.05-0.60%, Mn: 0.5-2.5%, Al: 0.01-0.10%, further Cu: 2.0% or less, Ni: less than 4%, At least one kind from the strength improving element group of Cr: 5.5% or less, Mo: 2.0% or less, Nb: 0.15% or less, V: 0.3% or less, Ti: 0.15% or less, B: 0.0003 to 0.0030%, A low-carbon, low-alloy steel slab containing 0.006% or less of Ca, which has the effect of controlling inclusion morphology, and consisting of residual Fe and unavoidable impurities, is heated to 1050-1250℃, then hot-rolled and then rapidly cooled to 250℃ or less. Then Ac 1 +20℃~ Ac 1
After reheating to +80℃ and subsequent water cooling, 200~
A method for manufacturing steel materials with a low yield ratio, characterized by tempering at a temperature range of 600℃. 11. The method for manufacturing a steel material with a low yield ratio according to claim 10, characterized in that the hot rolling is completed at a temperature of 1050°C or lower and higher than 900°C. 12. Claim 10, characterized in that the hot rolling is completed at a temperature between 900°C and Ar 3 , and the finished sheet thickness is rolled at a cumulative reduction rate of 5% or more and less than 30% within this temperature range. A method for manufacturing the steel material with a low yield ratio.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31230487A JPH01156421A (en) | 1987-12-11 | 1987-12-11 | Manufacture of steel material having low yield ratio |
| DE8888120633T DE3874100T2 (en) | 1987-12-11 | 1988-12-09 | METHOD FOR PRODUCING STEEL WITH A LOW RATIO OF THE ELASTICITY LIMIT TO RESISTANCE TO BREAKING. |
| EP88120633A EP0320003B1 (en) | 1987-12-11 | 1988-12-09 | Method of producing steel having a low yield ratio |
| US07/282,043 US4938266A (en) | 1987-12-11 | 1988-12-09 | Method of producing steel having a low yield ratio |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31230487A JPH01156421A (en) | 1987-12-11 | 1987-12-11 | Manufacture of steel material having low yield ratio |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH01156421A JPH01156421A (en) | 1989-06-20 |
| JPH0581644B2 true JPH0581644B2 (en) | 1993-11-15 |
Family
ID=18027639
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP31230487A Granted JPH01156421A (en) | 1987-12-11 | 1987-12-11 | Manufacture of steel material having low yield ratio |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH01156421A (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5550090A (en) * | 1978-10-07 | 1980-04-11 | Kloeckner Humboldt Deutz Ag | Apparatus for vaporizing carbon by molten metal bath |
| JPS5597425A (en) * | 1979-01-19 | 1980-07-24 | Nippon Kokan Kk <Nkk> | Preparation of high-tensile steel with low yield ratio, low carbon and low alloy |
| JPS55115921A (en) * | 1979-02-28 | 1980-09-06 | Nippon Steel Corp | Production of high tensile steel plate of low yield ratio |
| JPS59211528A (en) * | 1983-05-17 | 1984-11-30 | Nippon Steel Corp | Production of non-tempered steel having low yield ratio |
| JPS62214124A (en) * | 1986-03-14 | 1987-09-19 | Kawasaki Steel Corp | Manufacture of low yield ratio high tensile steel superior in weldability |
-
1987
- 1987-12-11 JP JP31230487A patent/JPH01156421A/en active Granted
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5550090A (en) * | 1978-10-07 | 1980-04-11 | Kloeckner Humboldt Deutz Ag | Apparatus for vaporizing carbon by molten metal bath |
| JPS5597425A (en) * | 1979-01-19 | 1980-07-24 | Nippon Kokan Kk <Nkk> | Preparation of high-tensile steel with low yield ratio, low carbon and low alloy |
| JPS55115921A (en) * | 1979-02-28 | 1980-09-06 | Nippon Steel Corp | Production of high tensile steel plate of low yield ratio |
| JPS59211528A (en) * | 1983-05-17 | 1984-11-30 | Nippon Steel Corp | Production of non-tempered steel having low yield ratio |
| JPS62214124A (en) * | 1986-03-14 | 1987-09-19 | Kawasaki Steel Corp | Manufacture of low yield ratio high tensile steel superior in weldability |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH01156421A (en) | 1989-06-20 |
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