JPH0564215B2 - - Google Patents
Info
- Publication number
- JPH0564215B2 JPH0564215B2 JP60055998A JP5599885A JPH0564215B2 JP H0564215 B2 JPH0564215 B2 JP H0564215B2 JP 60055998 A JP60055998 A JP 60055998A JP 5599885 A JP5599885 A JP 5599885A JP H0564215 B2 JPH0564215 B2 JP H0564215B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- elongation
- temperature
- strength
- phase
- 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
- 229910000831 Steel Inorganic materials 0.000 claims description 24
- 239000010959 steel Substances 0.000 claims description 24
- 229910001566 austenite Inorganic materials 0.000 claims description 22
- 238000001816 cooling Methods 0.000 claims description 18
- 229910000859 α-Fe Inorganic materials 0.000 claims description 16
- 229910001563 bainite Inorganic materials 0.000 claims description 8
- 230000032683 aging Effects 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 229910000734 martensite Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 4
- 239000012535 impurity Substances 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 16
- 230000000717 retained effect Effects 0.000 description 13
- 239000000463 material Substances 0.000 description 11
- 238000000034 method Methods 0.000 description 10
- 238000000137 annealing Methods 0.000 description 9
- 230000008569 process Effects 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 230000006866 deterioration Effects 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000005096 rolling process Methods 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000005279 austempering Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 230000002301 combined effect Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
Description
（産業上の利用分野）
本発明は延性のすぐれた高強度鋼板の製造方法
に係り、とくに引張強度80Kgｆ／mm2程度以上で、
高度の延性を併せ持つ高強度鋼板の製造方法に関
するものである。
（従来技術および問題点）
近年、自動車の燃費低減のための車体軽量化の
要請に応えて種々の高強度鋼板が開発されてい
る。このような公知の鋼板については、たとえば
特公昭58−57492号公報にみられるごとく、ルー
フ、フエンダー、ドアなど外板向けとして強度：
35〜45Kgｆ／mm2、伸び40％程度の熱延鋼板が、
また特開昭58−11734号公報にみられるごとく、
ホイール、メンバー類など強度部材として強度：
50〜60Kgｆ／mm2、伸び30％程度の熱延鋼板が重
用されている。さらに強度50Kgｆ／mm2以上でとく
に伸びの良いものを要する用途には、日本特許第
1073451号等で提案されている、フエライト・マ
ルテンサイト２相鋼（Dual Phdse鋼：DP鋼）を
用いる場合もある。この鋼は一軸引張の際、強度
のわりに低い降伏点を有すること、すなわち降伏
比（YP／TS）が0.5前後かそれ以下であること、
また降伏伸びが無いことなどの特性を有し、専ら
50〜80Kgｆ／mm2程度の強度レベルで固溶強化型や
析出強化型の鋼板よりすぐれた延性を示すものと
してよく知られているが、この種の鋼とても強度
80Kgｆ／mm2ではせいぜい伸び15％止りである。
ところで、最近になつてユーザーからはドアガ
ードバー、バンパーなどで強度80Kgｆ／mm2以上、
伸び20％以上という、上述の従来鋼の感覚からす
れば、きわめて厳しい要求例も見られるようにな
り、素材メーカーとしても従来の常識から脱した
抜本的な対策を講ずる必要に迫られている。
このような高強度・高延性の得られる唯一の例
として残留オーステナイトによる変態誘起超塑性
（Transformation Induced plasticity：TRIP）
を利用した鋼を挙げることができる。これはもと
もとZackayがTrans.AsM，60（1967），252頁に
おいて提示したもので、この場合多量のNiやCr
を含有し、複雑な工程を要するため実用的とは言
い難く、単に学問上興味の対象となり得たに過ぎ
なかつた。その後特公昭58−42246号記載の方法
が提案され、これは低合金系であり工程も比較的
単純なため、実用化の範囲に近ずいたと言える
が、成品の組織が残留オーステナイト＋ベーナイ
トあるいはマルテンサイトであるためプレス成形
（一次加工）後の靱性に難点があり、したがつて
耐衝撃特性（二次加工性）を必要とするドアガイ
ドバーやバンパーなどの強度部材として、現実の
使用に耐え得るものとはならなかつた。
（問題点を解決するための手段）
上記の実情をふまえて本発明者らは種々の検討
を行なつた結果、プレス成形品の耐衝撃特性は、
成形前素材の一軸引張試験における最高荷重点以
降破断に至るまでの伸び、つまり局部伸びと密接
に関係し、局部伸びが大となれば、衝撃吸収エネ
ルギーが増し、良好な耐衝撃特性が得られること
を見出した。TRIP効果は本来均一伸び（最高荷
重点に至るまでの伸び）を向上させるが、局部伸
びには寄与しない。局部伸びを向上させるには、
延靱性に富んだ固溶Ｃの少ない清浄かつ細粒フエ
ライト相の存在を必要とする。本発明者らは
TRIP効果をもたらす残留オーステナイト相と延
靱性のすぐれたフエライト相とを共存させるため
成分的にはＣ，Si，Mnと共にAIの適正添加、工
程的には焼鈍後の冷却速度、時効保持条件、その
後の冷却速度の適正化が不可欠であることを知見
した。
即ち、本発明者らは10％以上の残留オーステナ
イト相にもとづく変態誘起塑性により均一伸び
（一軸引張における最高荷重点に達するまでの伸
び）の向上と、細粒化したフエライト相による局
部伸び増あるいは衝撃特性向上および残部ベーナ
イト相あるいはマルテンサイト相による強度確保
の複合効果を合せて利用することによつて高強
度，高延性かつ良好な二次加工性が得られること
を見出したものである。さらに、このような組織
を得るための手段としては、既存の連続焼鈍設備
もしくは熱処理設備を利用し、製造条件のみを特
定のものに設定することによつて容易に製造でき
ることも知見した。
（発明の構成・作用）
本発明は以上のような知見にもとづいてなされ
たものであつて、その要旨は重量％でＣ：0.12〜
0.70％，Si：0.4〜1.8％，Mn：0.2〜2.5％， sol.
A：0.01〜0.07％，Total Ｎ：0.02％以下を含
み残部Feおよび不可避的不純物よりなる鋼板を
昇温速度１〜100℃／秒でAc3温度以上に加熱し、
３分以下の焼鈍ののち、350〜500℃の温度域まで
冷却速度１〜200℃／秒で冷却し該温度域で30秒
〜10分時効処理し、さらに少くとも150〜250℃の
温度域までは冷却速度50℃／秒以下で冷却し、そ
の後は任意の手段により室温まで冷却することを
特徴とする、残留オーステナイト相：10％以上、
フエライト相：１％超、70％以下、残部マルテン
サイト相とベーナイト相からなる延性のすぐれた
高強度鋼板の製造方法にある。
以下本発明を詳細に説明する。
まずＣの下限を0.12％としたのは、Ｃをこれ未
満とすると残留オーステナイト相が少くなるた
め、均一伸び向上効果が小さくなるからで、一方
Ｃの上限を0.70％としたのは、これを超えると、
たとえ組織中に或程度のフエライト相を有しても
なお２次加工性の低下は救い難く、然も溶接性の
劣化も甚しく現実の使用に耐えないものとなるか
らである。なお強度80Kgｆ／mm2クラス以上で一次
加工性、二次加工性および溶接性を有効にバラン
スさせるには、Ｃ量を0.20〜0.40％とすることが
望ましい。
Siの下限を0.4％としたのもＣと同様残留オー
ステナイト量が少なくなり、均一伸び向上効果が
得難くなるからである。上限を1.8％としたのは、
これを超えて添加しても効果が飽和に近づきフエ
ライト相自体も硬質化し、二次加工における脆化
を招くだけで実質上のメリツトは得られないから
である。
Mnの下限を0.2％としたのは、熱延工程におけ
る熱間脆性防止のため最低限これだけのMnを必
要とするからである。またＣ，Si同様Mnも残留
オーステナイトを増す元素と言えるが、Ｃ，Siを
上述の範囲に限定する場合、2.5％を超えてもオ
ーステナイト安定化の効果はほとんど変らずむし
ろフエライト相の脆化を招くので上限を2.5％と
する。
sol.Alについては脱酸元素として、またAINに
よる最終的に細粒フエライト相を得るために0.01
〜0.07％の添加を必要とする。0.01％未満では細
粒化効果が無く、0.07％を超えると逆に介在物に
よる局部伸び低下を招き、したがつて靱性劣化を
生じる。
Total Ｎについては、Ms点を下げ残留オース
テナイトを増す意味もしくは上記AINによる材
質向上の意味で0.02％以下を必要とするが、0.02
％を超えても効果にとくに変りはないので0.02％
以下とする。
以上が本発明の対象とする鋼の基本成分である
が、この他Ｐ：0.1％以下，Ni：３％以下，Cu：
0.5％以下，Cr：１％以下，Ti，Nb，Ｖ，Moを
それぞれ0.5％以下Ｂ：20PPM以下添加すること
は、いずれもオーステナイトの安定化に大なり小
なり寄与し、残留オーステナイト量を増加させる
ので、材質的にはむしろ望ましいことである。
このような成分上の制約はつぎに述べる工程上
の制約と密接に関係していることは言うまでもな
い。以下に工程上の限定理由を詳述する。
本発明で用いる素材は通常の熱延工程を経て製
造された熱延鋼板である。これらは酸洗され、冷
延され、もしくはそのまま直接以下に述べる熱履
歴を経ることにより、所期の目的が達成される。
まず、鋼板は１〜100℃／秒の昇温速度でAc3
温度以上に加熱される。昇温速度が100℃／秒を
超えると、部分的に未再結晶の状態でAc3以上に
到達するため、最終的に材質のばらつきが大き
い。一方１℃／秒未満の昇温速度では時間がかか
り過ぎ、生産能率に影響する。したがつて昇温速
度は１〜100℃／秒と限定する。材質のばらつき
を避け最も効率良く昇温するには、Ac1温度に至
るまでを10℃／秒以上、Ac1温度以上を１〜30
℃／秒とすることが望ましい。
焼鈍温度をAc3以上とするのは、ひきつづく冷
却工程と併せてフエライト相の微細再析出をはか
るもので、二次加工性向上に一層有効となる。焼
鈍温度はAc3未満であると、フエライト相の大き
い混粒組織となり、これも材質ばらつきの原因と
なる。Ac3温度以上での焼鈍時間についてはごく
短時間で十分であり、３分を超えて保持すること
は成分均質化を招き、残留オーステナイトを得る
意味で有害となるので３分以下とする。最も望ま
しいのは、Ac3点以上で40秒以下の焼鈍にとどめ
ることである。
つぎに本発明で制約した成分の場合、Ac3温度
以上から350〜500℃の温度域まで１〜200℃／秒
の冷却速度で冷却する必要がある。これは冷却途
中で部分的にフエライト相を析出させ、かつパー
ライトの生成をできるだけ避けるためのもので、
冷却速度が200℃／秒を超えるとフエライト相は
殆んど析出せず、１℃／秒未満であると、多量の
パーライトが析出するため本発明の効果を発揮で
きない。
またAc3温度以上から600〜700℃の温度域に至
るまでを１〜30℃／秒、その温度域以下350〜500
℃の温度域に至るまでを30〜200℃／秒で冷却す
るという２段の冷却法も、オーステナイトを安定
化する点で望ましい方法である。
350〜500℃で時効処理する意味はいわゆるオー
ステンパー処理であり、この段階でベーナイト生
成と同時にＣがオーステナイトに富化し、これを
安定化させる。この効果は350℃未満の温度では、
ベーナイト変態が遅く時間がかかり過ぎ、500℃
を超す温度ではパーライトを生ずるため所期の伸
びが得られない。したがつて時効処理温度の下限
を350℃、上限を500℃とする。時効処理時間につ
いては、30秒未満ではベーナイト生成不十分でオ
ーステナイトが安定化せず、また10分を超えると
ベーナイト比率が増し、オーステナイトが減ずる
ので、30秒〜10分に限定する。材質と生産性を考
慮した最滴時間は１〜２分である。
なお、以上の説明から明らかなように350〜500
℃の温度域内で連続的に降温もしくは降温，昇温
を繰返す処理、あるいはこれらを段階的に行なう
ことは、該温度域で経る時間が30秒〜10分の範囲
内である限り、本発明の効果を増大こそすれ、何
ら損うものではない。
時効処理後は、少くとも150〜250℃の温度域ま
で50℃／秒以下の冷却速度で冷却する必要があ
る。これは、オーステナイトを更に安定化すると
同時にフエライト相の清浄化が一層進み均一伸
び、局部伸び共更に向上するからである。50℃／
秒を超える冷却では、上記の効果は得られない。
この後は室温まで冷却すればよく、その際、冷却
手段、冷却速度等については、とくに限定の必要
はない。
なお、以上の熱処理を経た鋼板に形状矯正のた
めスキンパス圧延を施す場合には、残留オーステ
ナイトの効果を保存するために、1.5％以下ので
きるだけ軽度の圧下で行なうことが望ましい。
上記のようにして得られた鋼板は、少くとも１
〜50％のフエライト相と10％以上の残留オーステ
ナイト相を含む複合組織を有するものとなる。フ
エライト相が１％以下では、局部伸びが小さく、
70％程度を超えると、残留オーステナイトおよび
ベーナイト、マルテンサイト各相のバランスがく
ずれて所期の強度や伸び、あるいは強度−延性バ
ランスが得られない。残留オーステナイト相が10
％未満であると、均一伸び、したがつて全伸びも
低下する。
以下実施例により、本発明の効果をさらに具体
的に説明する。
（実施例）
第１表に成分を示す熱延鋼板（3.2mm厚）を酸
洗、冷延し、1.4mm厚としたものを用いて、第２
表記載の条件で種々の供試材を作成した。なお、
形状矯正のため1.0％のスキンパスを施している。
これからJIS13号Ｂ引張試験片を採取し（Ｌ方向）
引張速度10mm／minで引張し、強度、全伸びおよ
び局部伸びを調べた。ここで全伸びの値はプレス
成形、曲げ成形など成形性の評価尺度として、局
部伸びの値については、これが小さいと成形後の
材料が脆くなり、衝撃特性不良となることから、
成形品の二次加工性の評価尺度としたものであ
る。
第３表に見られるように本発明例である試料No.
１〜10のものは、いずれも80Kgｆ／mm2クラス以上
の強度を有し、全伸び30％以上、局部伸び５％以
上と極めて満足すべきものとなつていることが明
らかである。これに対し、比較例の試料No.11〜26
は強度或は全伸びもしくは局部伸びのいずれかが
不十分であるため本発明の目的を達成することが
できない。
（発明の効果）
以上の実施例からも明らかなごとき本発明によ
れば、80Kgｆ／mm2クラス以上の引張強度を有する
上に高度の延性，２次加工性も併せ持つ鋼板の提
供が可能となり、産業上の効果は極めて顕著であ
る。
(Industrial Application Field) The present invention relates to a method for manufacturing high-strength steel sheets with excellent ductility, particularly those having a tensile strength of about 80 Kgf/mm 2 or more,
This invention relates to a method for manufacturing high-strength steel sheets that also have a high degree of ductility. (Prior Art and Problems) In recent years, various high-strength steel plates have been developed in response to demands for lighter vehicle bodies to reduce fuel consumption. Regarding such known steel plates, for example, as seen in Japanese Patent Publication No. 58-57492, strength is determined for external panels such as roofs, fenders, doors, etc.
A hot-rolled steel plate with 35 to 45Kgf/mm 2 and an elongation of about 40% is
Also, as seen in Japanese Patent Application Laid-Open No. 58-11734,
Strength as strength components such as wheels and members:
Hot-rolled steel sheets with a strength of 50 to 60 Kgf/mm 2 and an elongation of about 30% are frequently used. Furthermore, for applications that require a strength of 50 kgf/mm 2 or more and particularly good elongation, Japanese Patent No.
In some cases, ferrite-martensitic dual phase steel (Dual Phdse steel: DP steel), which is proposed in No. 1073451, etc., is used. In uniaxial tension, this steel has a low yield point relative to its strength, that is, the yield ratio (YP/TS) is around 0.5 or less.
It also has characteristics such as no yield elongation, and is used exclusively for
It is well known that it exhibits superior ductility than solid solution strengthened or precipitation strengthened steel sheets at a strength level of about 50 to 80 kgf/ mm2 , but this type of steel has very high strength.
At 80Kgf/ mm2 , the elongation is only 15% at most. By the way, recently, users have requested that door guard bars, bumpers, etc. have a strength of 80 kgf/mm 2 or more.
Compared to the above-mentioned conventional steel, which has an elongation of 20% or more, we are now seeing extremely strict requirements, and material manufacturers are under pressure to take drastic measures that go beyond conventional wisdom. Transformation induced plasticity (TRIP) by retained austenite is the only example that can achieve such high strength and high ductility.
One example is steel that utilizes This was originally proposed by Zackay in Trans.AsM, 60 (1967), p. 252, and in this case large amounts of Ni and Cr
It was difficult to say that it was practical because it contained a complex process and could only be a subject of academic interest. Later, the method described in Japanese Patent Publication No. 58-42246 was proposed, and since it uses a low alloy system and the process is relatively simple, it can be said that it was close to the range of practical application. Since it is martensite, its toughness after press forming (primary processing) is difficult, so it is not suitable for actual use as strength members such as door guide bars and bumpers that require impact resistance (secondary processing). It wasn't something I could bear. (Means for Solving the Problems) Based on the above-mentioned circumstances, the present inventors conducted various studies and found that the impact resistance properties of press-formed products are as follows:
It is closely related to the elongation from the highest load point to breakage in the uniaxial tensile test of the pre-molded material, that is, the local elongation, and the larger the local elongation, the more impact absorption energy will be obtained, and good impact resistance properties will be obtained. I discovered that. The TRIP effect originally improves uniform elongation (elongation up to the maximum load point), but does not contribute to local elongation. To improve local elongation,
It requires the presence of a clean, fine-grained ferrite phase with high ductility and low solid solution C. The inventors
In order to coexist the retained austenite phase, which brings about the TRIP effect, and the ferrite phase, which has excellent elongation toughness, the components include C, Si, and Mn, as well as the appropriate addition of AI.In terms of process, the cooling rate after annealing, the aging holding conditions, and the subsequent We found that it is essential to optimize the cooling rate. In other words, the present inventors achieved improvement in uniform elongation (elongation until reaching the maximum load point in uniaxial tension) through transformation-induced plasticity based on retained austenite phase of 10% or more, and localized elongation increase due to the fine-grained ferrite phase. It has been discovered that high strength, high ductility, and good secondary workability can be obtained by combining the combined effect of improving impact properties and securing strength through the residual bainite phase or martensite phase. Furthermore, it has been found that such a structure can be easily manufactured by using existing continuous annealing equipment or heat treatment equipment and setting only specific manufacturing conditions. (Structure and operation of the invention) The present invention has been made based on the above knowledge, and the gist thereof is that C: 0.12 to 0.12 by weight%.
0.70%, Si: 0.4-1.8%, Mn: 0.2-2.5%, sol.
A: 0.01 to 0.07%, Total N: 0.02% or less, the balance Fe and unavoidable impurities A steel plate is heated to Ac 3 temperature or higher at a heating rate of 1 to 100°C/sec,
After annealing for 3 minutes or less, it is cooled to a temperature range of 350 to 500 °C at a cooling rate of 1 to 200 °C/sec, aged in this temperature range for 30 seconds to 10 minutes, and further heated to a temperature range of at least 150 to 250 °C. Retained austenite phase: 10% or more;
Ferrite phase: more than 1%, less than 70%, and the remainder consists of a martensite phase and a bainite phase, which is a method for producing a high-strength steel sheet with excellent ductility. The present invention will be explained in detail below. First, the lower limit of C was set at 0.12% because if the C content is less than this, the retained austenite phase decreases and the effect of improving uniform elongation becomes smaller.On the other hand, the upper limit of C was set at 0.70% because this If you exceed
This is because even if the structure has a certain amount of ferrite phase, the deterioration in secondary workability cannot be cured, and the deterioration in weldability is also so severe that it cannot withstand actual use. In addition, in order to effectively balance primary workability, secondary workability, and weldability with a strength of 80 Kgf/mm 2 class or higher, it is desirable that the C content be 0.20 to 0.40%. The reason for setting the lower limit of Si to 0.4% is that, like C, the amount of retained austenite decreases, making it difficult to obtain the effect of improving uniform elongation. The upper limit was set at 1.8% because
This is because, if added in excess of this amount, the effect approaches saturation, and the ferrite phase itself becomes hard, leading to embrittlement in secondary processing without any substantial benefit. The lower limit of Mn is set at 0.2% because this amount of Mn is required at least to prevent hot brittleness in the hot rolling process. Also, like C and Si, Mn can be said to be an element that increases retained austenite, but when C and Si are limited to the above range, the effect of stabilizing austenite will hardly change even if it exceeds 2.5%, but rather it will cause embrittlement of the ferrite phase. The upper limit is set at 2.5%. 0.01 for sol.Al as a deoxidizing element and to finally obtain a fine-grained ferrite phase by AIN.
~0.07% addition required. If it is less than 0.01%, there will be no grain refining effect, and if it exceeds 0.07%, it will conversely cause a decrease in local elongation due to inclusions, resulting in deterioration of toughness. Regarding Total N, it is required to be 0.02% or less in order to lower the Ms point and increase residual austenite, or to improve the material quality by the above AIN, but 0.02% or less is required.
There is no particular difference in the effect even if it exceeds 0.02%.
The following shall apply. The above are the basic components of the steel targeted by the present invention, but in addition, P: 0.1% or less, Ni: 3% or less, Cu:
Adding 0.5% or less, Cr: 1% or less, Ti, Nb, V, and Mo each at 0.5% or less B: 20PPM or less all contribute to the stabilization of austenite to a greater or lesser degree and increase the amount of retained austenite. This is rather desirable from a material standpoint. It goes without saying that such restrictions on the components are closely related to the restrictions on the process described below. The reasons for the limitations in the process will be explained in detail below. The material used in the present invention is a hot-rolled steel sheet manufactured through a normal hot-rolling process. The intended purpose is achieved by pickling, cold rolling, or directly passing through the thermal history described below. First, the steel plate is heated to Ac 3 at a heating rate of 1 to 100℃/sec.
heated above the temperature. When the heating rate exceeds 100°C/sec, Ac 3 or higher is reached in a partially unrecrystallized state, resulting in large variations in the final material quality. On the other hand, a temperature increase rate of less than 1° C./second takes too much time and affects production efficiency. Therefore, the temperature increase rate is limited to 1 to 100°C/sec. In order to avoid variations in material and increase the temperature most efficiently, increase the temperature at least 10℃/sec until reaching Ac 1 temperature, and 1 to 30℃ above Ac 1 temperature.
It is desirable to set it to °C/second. Setting the annealing temperature to Ac 3 or higher aims at fine redecipitation of the ferrite phase in conjunction with the subsequent cooling process, which is more effective in improving secondary workability. If the annealing temperature is less than Ac 3 , a mixed grain structure with a large ferrite phase will result, which will also cause variations in material quality. Regarding the annealing time at a temperature of Ac 3 or higher, a very short time is sufficient; holding the annealing for more than 3 minutes leads to homogenization of the components, which is harmful in terms of obtaining retained austenite, so the annealing time is set to 3 minutes or less. The most desirable thing is to limit the annealing time to 40 seconds or less at Ac 3 or higher. Next, in the case of the components restricted by the present invention, it is necessary to cool them from the Ac 3 temperature or higher to a temperature range of 350 to 500°C at a cooling rate of 1 to 200°C/sec. This is to partially precipitate the ferrite phase during cooling and to avoid pearlite formation as much as possible.
When the cooling rate exceeds 200° C./sec, hardly any ferrite phase is precipitated, and when the cooling rate is less than 1° C./sec, a large amount of pearlite precipitates, making it impossible to exhibit the effects of the present invention. Also, from Ac 3 temperature or higher to the temperature range of 600 to 700 °C, the speed is 1 to 30 °C/sec, and below that temperature range is 350 to 500 °C.
A two-stage cooling method in which cooling is performed at a rate of 30 to 200° C./sec until the temperature reaches the temperature range of 10° C. is also a desirable method in terms of stabilizing austenite. The meaning of aging treatment at 350 to 500° C. is so-called austempering treatment, and at this stage, C is enriched in austenite at the same time as bainite is formed, and this is stabilized. This effect occurs at temperatures below 350℃.
Bainite transformation is slow and takes too long at 500℃
If the temperature exceeds 100%, pearlite is formed and the desired elongation cannot be obtained. Therefore, the lower limit of the aging treatment temperature is set at 350°C and the upper limit is set at 500°C. The aging treatment time is limited to 30 seconds to 10 minutes because if it is less than 30 seconds, bainite formation is insufficient and austenite is not stabilized, and if it exceeds 10 minutes, the bainite ratio increases and austenite decreases. The maximum droplet time in consideration of material and productivity is 1 to 2 minutes. Furthermore, as is clear from the above explanation, 350 to 500
Continuously lowering the temperature or repeating lowering and increasing the temperature within the temperature range of °C, or performing these steps in stages, is within the scope of the present invention, as long as the time spent in the temperature range is within the range of 30 seconds to 10 minutes. It only increases the effect and does not harm it in any way. After aging treatment, it is necessary to cool at least to a temperature range of 150 to 250°C at a cooling rate of 50°C/second or less. This is because, at the same time, the austenite is further stabilized, the ferrite phase is further purified, and uniform elongation and local elongation are further improved. 50℃/
Cooling for more than seconds does not provide the above effect.
Thereafter, it may be cooled to room temperature, and in this case, there is no need to particularly limit the cooling means, cooling rate, etc. In addition, when skin pass rolling is applied to the steel sheet that has undergone the above heat treatment to correct its shape, it is desirable to perform the rolling with the slightest possible reduction of 1.5% or less in order to preserve the effect of retained austenite. The steel plate obtained as described above has at least 1
It has a composite structure containing ~50% ferrite phase and 10% or more retained austenite phase. When the ferrite phase is less than 1%, local elongation is small;
If it exceeds about 70%, the balance of retained austenite, bainite, and martensite phases will be lost, making it impossible to obtain the desired strength, elongation, or strength-ductility balance. Retained austenite phase is 10
If it is less than %, the uniform elongation and therefore the total elongation will decrease. Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples. (Example) A hot-rolled steel plate (3.2 mm thick) whose components are shown in Table 1 was pickled and cold-rolled to a thickness of 1.4 mm.
Various test materials were prepared under the conditions listed in the table. In addition,
A 1.0% skin pass is applied to correct the shape.
From this, take a JIS No. 13 B tensile test piece (L direction)
It was stretched at a tensile speed of 10 mm/min, and its strength, total elongation, and local elongation were examined. Here, the value of total elongation is used as an evaluation measure of formability such as press forming and bending, and the value of local elongation is because if it is small, the material after forming becomes brittle and the impact properties are poor.
This is an evaluation scale for the secondary processability of molded products. As shown in Table 3, sample No. 1 is an example of the present invention.
It is clear that samples Nos. 1 to 10 all have a strength of 80 Kgf/mm 2 class or higher, a total elongation of 30% or more, and a local elongation of 5% or more, which are extremely satisfactory. On the other hand, samples No. 11 to 26 of the comparative example
The object of the present invention cannot be achieved because either the strength or the total elongation or local elongation is insufficient. (Effects of the Invention) According to the present invention, as is clear from the above examples, it is possible to provide a steel plate having a tensile strength of 80 Kgf/mm 2 class or higher, as well as high ductility and secondary workability. The industrial effects are quite significant.
【表】【table】
【表】【table】
【表】【table】
Claims (1)
板を昇温速度１〜100℃／秒でAc3温度以上に加
熱し、３分以下の焼鈍ののち、350〜500℃の温度
域まで冷却速度１〜200℃／秒で冷却し、該温度
域で30秒〜10分時効処理し、さらに少なくとも
150〜250℃の温度域までは冷却速度50℃／秒以下
で冷却し、その後は任意の手段により室温まで冷
却することを特徴とする、残留オーステナイト
相：10％以上、フエライト相：１％超、70％以
下、残部マルテンサイト相とベーナイト相からな
る延性のすぐれた高強度鋼板の製造方法。[Claims] 1% by weight: C: 0.12 to 0.70% Si: 0.4 to 1.8% Mn: 0.2 to 2.5% Sol.A: 0.01 to 0.07% Total N: Contains 0.02% or less with the balance Fe and unavoidable impurities A steel plate consisting of is heated to Ac 3 temperature or higher at a heating rate of 1 to 100°C/sec, annealed for 3 minutes or less, and then cooled to a temperature range of 350 to 500°C at a cooling rate of 1 to 200°C/sec, Aging treatment is performed in the above temperature range for 30 seconds to 10 minutes, and then at least
It is characterized by cooling at a cooling rate of 50°C/sec or less up to a temperature range of 150 to 250°C, and then cooling to room temperature by any means, residual austenite phase: 10% or more, ferrite phase: more than 1% , a method for producing a high-strength steel plate with excellent ductility, consisting of 70% or less, the balance being a martensite phase and a bainite phase.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5599885A JPS61217529A (en) | 1985-03-22 | 1985-03-22 | Manufacture of high strength steel sheet superior in ductility |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5599885A JPS61217529A (en) | 1985-03-22 | 1985-03-22 | Manufacture of high strength steel sheet superior in ductility |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS61217529A JPS61217529A (en) | 1986-09-27 |
| JPH0564215B2 true JPH0564215B2 (en) | 1993-09-14 |
Family
ID=13014747
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5599885A Granted JPS61217529A (en) | 1985-03-22 | 1985-03-22 | Manufacture of high strength steel sheet superior in ductility |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS61217529A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6210496B1 (en) | 1997-06-16 | 2001-04-03 | Kawasaki Steel Corporation | High-strength high-workability cold rolled steel sheet having excellent impact resistance |
Families Citing this family (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6217134A (en) * | 1985-07-15 | 1987-01-26 | Nippon Kokan Kk <Nkk> | Manufacture of patented steel strip |
| JPH01230715A (en) * | 1987-06-26 | 1989-09-14 | Nippon Steel Corp | Manufacture of high strength cold rolled steel sheet having superior press formability |
| JP3448777B2 (en) | 1993-01-14 | 2003-09-22 | Ｊｆｅスチール株式会社 | Ultra-high strength cold rolled steel sheet excellent in delayed fracture resistance and method of manufacturing the same |
| US5634988A (en) * | 1993-03-25 | 1997-06-03 | Nippon Steel Corporation | High tensile steel having excellent fatigue strength at its weld and weldability and process for producing the same |
| JP3764411B2 (en) † | 2002-08-20 | 2006-04-05 | 株式会社神戸製鋼所 | Composite steel sheet with excellent bake hardenability |
| DE102004038159B3 (en) * | 2004-08-06 | 2006-05-18 | Ab Skf | Process for the heat treatment of workpieces made of steel or cast iron |
| JP2010065272A (en) * | 2008-09-10 | 2010-03-25 | Jfe Steel Corp | High-strength steel sheet and method for manufacturing the same |
| KR101091294B1 (en) * | 2008-12-24 | 2011-12-07 | 주식회사 포스코 | Steel Sheet With High Strength And Elongation And Method For Manufacturing Hot-Rolled Steel Sheet, Cold-Rolled Steel Sheet, Galvanized Steel Sheet And Galvannealed Steel Sheet With High Strength And Elongation |
| CA2787575C (en) | 2010-01-26 | 2015-03-31 | Kohichi Sano | High-strength cold-rolled steel sheet and method of manufacturing thereof |
| US9273370B2 (en) | 2010-07-28 | 2016-03-01 | Nippon Steel & Sumitomo Metal Corporation | Hot-rolled steel sheet, cold-rolled steel sheet, galvanized steel sheet, and methods of manufacturing the same |
| EP2692895B1 (en) | 2011-03-28 | 2018-02-28 | Nippon Steel & Sumitomo Metal Corporation | Cold-rolled steel sheet and production method thereof |
| EP2695961B1 (en) * | 2011-03-31 | 2019-06-19 | Kabushiki Kaisha Kobe Seiko Sho | High-strength steel sheet excellent in workability and manufacturing method thereof |
| EP2716783B1 (en) | 2011-05-25 | 2018-08-15 | Nippon Steel & Sumitomo Metal Corporation | Hot-rolled steel sheet and process for producing same |
| EP2762592B1 (en) | 2011-09-30 | 2018-04-25 | Nippon Steel & Sumitomo Metal Corporation | High-strength hot-dipped galvanized steel sheet and high-strength alloyed hot-dipped galvanized steel sheet, each having tensile strength of 980 mpa or more, excellent plating adhesion, excellent formability and excellent bore expanding properties, and method for producing same |
| JP6189819B2 (en) * | 2014-11-21 | 2017-08-30 | 株式会社神戸製鋼所 | High strength high ductility steel sheet |
| WO2016132549A1 (en) | 2015-02-20 | 2016-08-25 | 新日鐵住金株式会社 | Hot-rolled steel sheet |
| MX2017008622A (en) | 2015-02-20 | 2017-11-15 | Nippon Steel & Sumitomo Metal Corp | Hot-rolled steel sheet. |
| WO2016135898A1 (en) | 2015-02-25 | 2016-09-01 | 新日鐵住金株式会社 | Hot-rolled steel sheet or plate |
| CN107406929B (en) | 2015-02-25 | 2019-01-04 | 新日铁住金株式会社 | Hot rolled steel plate |
| WO2018026014A1 (en) | 2016-08-05 | 2018-02-08 | 新日鐵住金株式会社 | Steel sheet and plated steel sheet |
| MX2019000051A (en) | 2016-08-05 | 2019-04-01 | Nippon Steel & Sumitomo Metal Corp | Steel sheet and plated steel sheet. |
| EP3517643A4 (en) | 2016-09-21 | 2020-03-04 | Nippon Steel Corporation | Steel plate |
| EP3530768B1 (en) | 2016-10-19 | 2021-08-04 | Nippon Steel Corporation | Metal coated steel sheet, manufacturing method of hot-dip galvanized steel sheet, and manufacturing method of galvannealed steel sheet |
| BR112019010681A2 (en) | 2016-12-05 | 2019-09-17 | Nippon Steel Corp | high strength steel sheet |
| WO2019187124A1 (en) | 2018-03-30 | 2019-10-03 | 日本製鉄株式会社 | Hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5611741A (en) * | 1979-05-02 | 1981-02-05 | Deer Park Baking Co | Method and apparatus for making cookie |
| JPS5842246A (en) * | 1981-09-07 | 1983-03-11 | Toshiba Corp | Semiconductor device |
| JPS605820A (en) * | 1983-06-23 | 1985-01-12 | Nisshin Steel Co Ltd | Production of steel having high strength and high ductility |
-
1985
- 1985-03-22 JP JP5599885A patent/JPS61217529A/en active Granted
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5611741A (en) * | 1979-05-02 | 1981-02-05 | Deer Park Baking Co | Method and apparatus for making cookie |
| JPS5842246A (en) * | 1981-09-07 | 1983-03-11 | Toshiba Corp | Semiconductor device |
| JPS605820A (en) * | 1983-06-23 | 1985-01-12 | Nisshin Steel Co Ltd | Production of steel having high strength and high ductility |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6210496B1 (en) | 1997-06-16 | 2001-04-03 | Kawasaki Steel Corporation | High-strength high-workability cold rolled steel sheet having excellent impact resistance |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS61217529A (en) | 1986-09-27 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JPH0564215B2 (en) | ||
| KR101027250B1 (en) | High strength steel sheet and hot dip galvanized steel sheet having high ductility and excellent delayed fracture resistance and method for manufacturing the same | |
| JPS61157625A (en) | Manufacture of high-strength steel sheet | |
| JP3424619B2 (en) | High tensile cold rolled steel sheet and method for producing the same | |
| JP4530606B2 (en) | Manufacturing method of ultra-high strength cold-rolled steel sheet with excellent spot weldability | |
| WO2003106723A1 (en) | High strength cold rolled steel plate and method for production thereof | |
| US4436561A (en) | Press-formable high strength dual phase structure cold rolled steel sheet and process for producing the same | |
| JPH04289120A (en) | Production of ultrahigh strength cold rolled steel sheet excellent in formability and strip shape | |
| EP3450586A1 (en) | Ultrahigh-strength and high-ductility steel sheet having excellent yield ratio and manufacturing method therefor | |
| JP4457681B2 (en) | High workability ultra-high strength cold-rolled steel sheet and manufacturing method thereof | |
| KR101917452B1 (en) | Cold rolled steel sheet with excellent bendability and hole expansion property, and method for manufacturing the same | |
| JP4358418B2 (en) | Low yield ratio high strength cold-rolled steel sheet and plated steel sheet excellent in hole expansibility and method for producing the same | |
| JP4265153B2 (en) | High-tensile cold-rolled steel sheet with excellent elongation and stretch flangeability and method for producing the same | |
| JP4265152B2 (en) | High-tensile cold-rolled steel sheet with excellent elongation and stretch flangeability and method for producing the same | |
| JP2022535254A (en) | Cold-rolled and coated steel sheet and method for producing same | |
| JP4492105B2 (en) | Manufacturing method of high-strength cold-rolled steel sheet with excellent stretch flangeability | |
| JP3918589B2 (en) | Steel plate for heat treatment and manufacturing method thereof | |
| JPH0499227A (en) | Production of ultrahigh-strength cold rolled steel sheet excellent in workability | |
| JP2800541B2 (en) | Manufacturing method of high strength hot-dip galvanized steel sheet for deep drawing | |
| CN112226674B (en) | Aging-resistant cold-rolled hot-galvanized steel plate for household appliances and production method thereof | |
| KR100782760B1 (en) | Method for manufacturing cold-rolled steel sheet and galvanized steel sheet having yield ratio and high strength | |
| JPH0790488A (en) | Ultrahigh strength cold rolled steel sheet excellent in hydrogen brittlement resistance and its production | |
| KR100782759B1 (en) | Method for manufacturing cold-rolled steel sheet and galvanized steel sheet having yield ratio and high strength | |
| CN111465710B (en) | High yield ratio type high strength steel sheet and method for manufacturing same | |
| JPS61272321A (en) | Manufacture of ultra high-strength cold rolled steel sheet |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EXPY | Cancellation because of completion of term |