JPH0569903B2 - - Google Patents
Info
- Publication number
- JPH0569903B2 JPH0569903B2 JP63316167A JP31616788A JPH0569903B2 JP H0569903 B2 JPH0569903 B2 JP H0569903B2 JP 63316167 A JP63316167 A JP 63316167A JP 31616788 A JP31616788 A JP 31616788A JP H0569903 B2 JPH0569903 B2 JP H0569903B2
- Authority
- JP
- Japan
- Prior art keywords
- steel
- strength
- manganese
- carbon
- silicon
- 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 46
- 239000010959 steel Substances 0.000 claims description 46
- 229910052748 manganese Inorganic materials 0.000 claims description 21
- 239000011572 manganese Substances 0.000 claims description 21
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 19
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 18
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 11
- 229910052710 silicon Inorganic materials 0.000 claims description 11
- 239000010703 silicon Substances 0.000 claims description 11
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
- 229910001566 austenite Inorganic materials 0.000 claims description 8
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 239000011651 chromium Substances 0.000 claims description 6
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 239000011733 molybdenum Substances 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- 229910052758 niobium Inorganic materials 0.000 claims description 4
- 239000010955 niobium Substances 0.000 claims description 4
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 claims description 4
- 238000005096 rolling process Methods 0.000 claims description 4
- 229910052720 vanadium Inorganic materials 0.000 claims description 4
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 3
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 229910052715 tantalum Inorganic materials 0.000 claims description 3
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 3
- 239000010936 titanium Substances 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 239000010937 tungsten Substances 0.000 claims description 3
- 229910000617 Mangalloy Inorganic materials 0.000 claims description 2
- 238000001816 cooling Methods 0.000 description 17
- 238000000137 annealing Methods 0.000 description 11
- 229910045601 alloy Inorganic materials 0.000 description 8
- 239000000956 alloy Substances 0.000 description 8
- 238000010438 heat treatment Methods 0.000 description 8
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 7
- 238000005275 alloying Methods 0.000 description 7
- 229910000734 martensite Inorganic materials 0.000 description 7
- 238000003466 welding Methods 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 6
- 238000010791 quenching Methods 0.000 description 5
- 230000000171 quenching effect Effects 0.000 description 5
- 230000003014 reinforcing effect Effects 0.000 description 5
- 229910000851 Alloy steel Inorganic materials 0.000 description 4
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 4
- 229910000746 Structural steel Inorganic materials 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000011159 matrix material Substances 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 230000000717 retained effect Effects 0.000 description 3
- 238000005496 tempering Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- 229910001021 Ferroalloy Inorganic materials 0.000 description 1
- 229910000922 High-strength low-alloy steel Inorganic materials 0.000 description 1
- 229910018619 Si-Fe Inorganic materials 0.000 description 1
- 229910008289 Si—Fe Inorganic materials 0.000 description 1
- 229910001035 Soft ferrite Inorganic materials 0.000 description 1
- PANOZBQEHCCVOC-UHFFFAOYSA-N [Mn].[Si].[C].[Fe] Chemical compound [Mn].[Si].[C].[Fe] PANOZBQEHCCVOC-UHFFFAOYSA-N 0.000 description 1
- 230000003679 aging effect Effects 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000010894 electron beam technology Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- QMQXDJATSGGYDR-UHFFFAOYSA-N methylidyneiron Chemical compound [C].[Fe] QMQXDJATSGGYDR-UHFFFAOYSA-N 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Articles (AREA)
Description
〔産業上の利用分野〕
本発明は構造用鋼として機械的性質にすぐれか
つ溶接用の良好に二相組織鋼に関する。
〔従来の技術〕
船体、橋梁、圧力容器、自動車等の一般構造用
あるいは溶接構造用として用いられる圧延鋼材に
は、機械的強度にすぐれ、靱性を有すると共に、
溶接性がよく、また普通鋼材のように多量生産が
可能であるなどの経済性が必要とされる。
炭素鋼の強度を向上させるためには、炭素含有
量を増加させるのが最も簡単であるが、炭素量が
増すと、伸びや絞り等の延性が低下し、また、溶
接性が劣化する。このため、特に溶接性を考慮し
て低炭素系を基本に珪素、マンガン、ニツケル、
クローム、銅等の合金元素の１種または数種を少
量添加して、固溶体強化あるいは結晶微細化等を
利用し、強化を図つた低炭素低合金鋼が低合金高
張力鋼（HSLA鋼）として多用されるようになつ
ている。
しかし、圧延のままの非調質状態で用いる低合
金高張力鋼では、フエライトバーライト組織のま
まで珪素、マンガンその他の合金元素を添加して
強化を図つているので引張り強さは60Kgｆ／mm2ま
でが限度とされており、それ以上の強度を有する
高張力鋼においては、さらにニツケル、クローム
等の合金元素の添加量を増やし、焼入れ焼戻しを
行うことによつて、焼戻しマルテンサイト相によ
る引張り強さ100Kgｆ／mm2程度までの強化が図ら
れている。
一方、このような高張力鋼域の成分で特別な熱
処理によつてフエライトマトリツクスにマルテン
サイト相を分散させた二相組織からなる鋼が開発
され、延性を保持しつつ強度を確保し、溶接性も
良好であるということで、構造部品の軽量化用途
に注目されている。例えば、引張り強さ600MPa
で伸び20％を示す0.05％Ｃ−0.02％Si−0.32％Mn
−残Feからなる低合金高張力鋼を約790℃のフエ
ライトとオーステナイトの二相域で焼鈍してから
急冷し、オーステナイトをマルテンサイトに変え
て得られる二相鋼は、引張り強さ650MPaで伸び
30％程度になり、低炭素のため溶接性も良好であ
る。
〔発明が解決しようとする課題〕
しかしながら、前記高張力鋼等の第一の要求と
する高強度をさらに推進させようとする場合、前
記の調質高張力鋼においては、高価な合金元素の
種類及び添加量を増やす傾向にあるが、延性の犠
牲もなくその目的を達成するのは困難であり、ま
た溶接に際しては、溶接割れを発生し易い。すで
に従来の強度レベルのものにおいてさえも、溶接
熱影響の急熱急冷による硬化そして冷間割れが発
生し易く、このような溶接部の脆化防止のため、
予熱を必要とし、また入熱制限が設けられている
という問題がある。さらに、前記の低合金二相鋼
においても、炭素添加量を低い値に抑え、ニツケ
ル、クローム、バナジウム等の高価な合金元素の
種類及び添加量を増やして強度を確保するように
しているが、急冷処理を含む高価な熱処理を必要
とすることと併せて、得られる性能の割に高価な
ものになつており、例えば二相鋼の開発当初に意
図された自動車の軽量化用途即ち車体用薄板とし
ての用途には適しないなど、経済性に問題があつ
た。また、上記のような合金元素が多くなると、
溶接硬化の目安となる炭素当量が基準量の約0.4
％を超えて過大となり、溶接に際し、溶接熱影響
部が硬化して脆化することのため、実用性のある
これ以上の高強度合金鋼を得ることは難しいとい
う問題があつた。
なお、炭素素低合金高張力鋼において、溶接性
を保持しつつ、残留オーステナイトの変態誘起塑
性（TRIP）を利用して、加工時において30％以
上の伸びを得る技術も開示されて注目されている
が、組織中の残留オーステナイト量を確保するた
め、煩雑な熱処理を必要とし、経済性に問題があ
る。
従つて、本発明は高価な強化合金元素を多く添
加する必要がなく、また調質熱処理が容易で、延
性を余り損なうなくさらに高い機械的強度が得ら
れ、しかも溶接性が良好であり、従つて製造コス
トが安く、実用性の大きい構造用鋼を提供するこ
とを目的とする。
〔課題を解決するための手段〕
上記の目的を達成するため、本発明は、重量％
として、炭素0.02〜0.3％、マンガン2.8〜5.0％及
び珪素0.2〜1.5％を含み、残部が鉄及び不可避不
純物からなる鋼を、圧延後、700〜800℃のフエラ
イトオーステナイト二相域に保持して焼鈍した
後、冷却した高強度で溶接性にすぐれる構造用高
マンガン二相鋼を、また、前記鋼が重量％とし
て、炭素0.02〜0.3％、マンガン2.8〜5.0％及び珪
素0.2〜1.5％のほかに、それぞれ0.02〜0.1％のモ
リブデン、ニオブ、タンタル、タングステン、チ
タン、バナジウム及び硼素と0.02〜0.3％のクロ
ームからなる群のうちの１種または２種以上の元
素を含み、残部が鉄及び不可避不純物からなる高
強度で溶接性にすぐれる構造用高マンガン二相鋼
を提案するものである。
以下、本発明を詳細に説明する。
本発明の高マンガン二相鋼は、原料を転炉、電
気炉、高周波誘導炉等通常の製鋼炉に装入して溶
融し、成分調整を行つて鋳造し、これを熱間圧延
または冷間圧延して所定形状のものを得、さらに
これに熱処理を施すことによつて得られる。熱処
理は700〜800℃のフエライトオーステナイト二相
域に10分程度保持して焼鈍したのち、空冷、水焼
入れ、油焼入れ等徐冷または急冷することによつ
て行う。
本発明の高マンガン二相鋼の場合、高マンガン
量の含有により、変態温度A1及びA3が著しく低
下し、また等温度変態曲線が長時間側にずれるの
で、700〜800℃という比較的低い焼鈍温度域から
の水焼入れ等の急冷のみならず、空冷等の徐冷に
よつても二相鋼を得ることができる。その二相組
織は、比較的軟質なフエライトマトリツクス中に
硬いマルテンサント相が細かく針状、粒状あるい
は島状に分散した状態をなしている。本発明の高
マンガン二相鋼はその組織に基いて、高強度で延
性に富み、焼入れ状態で1000Mpa以上の引張り
強さと約20％以上の破断伸びが容易に得られ、ま
た焼戻し処理を行うことにより、引張りの強さを
700MPa程度に保持しながら40％以上の破断伸び
を持たせることができる。
本発明の高マンガン二相鋼また、典型的な二相
鋼の特徴を備えており、引張り測定で得られる応
力−歪み曲線は連続的であり、急激な降伏現象を
表わさず、引張り強さに対する降伏強さの比即ち
降伏応力比も0.4〜0.7と小さく、良好な冷間加工
性を有している。さらに、僅かな歪みを与えた
後、荷重を取り除き、比較的低温度で短時間加熱
すると降伏強さが著しく増加するという歪み時効
性または焼付け硬化性をも有する。
本発明の高マンガン二相鋼はマンガン含有量が
高いのにも拘らず、溶接性にすぐれているのが大
きい特徴であり優れた利点である。即ち従来溶接
のための鋼の炭素当量は0.4以下を必要としてい
るが、例えば、本発明の基本的な二相鋼でもある
0.1％Ｃ−３％Mn−0.5％Si−Fe合金の場合、そ
の炭素当量は0.6であるにも拘らず、溶接性は良
好である。このことはTIG溶接及び電子線溶接に
よつて確められている。何れの場合も、溶接部は
アルゴンガス若しくは真空中で放冷されるが、こ
の時に得られる溶接部の構造は常にフエライトマ
トリツクス中のマルテンサイト相が細かく分散し
た二相降特有の構造を示している。冷却速度が大
であればマルテンサイト相の量は増加するが、放
冷する場合でもその容積率は常に全体の50％以下
であり、従つて溶接部の機械的強度は高くなる
が、依然としてかなり延性を保つている。このた
め、引張り測定では、溶接作業を順調に行なわれ
た試験片の場合、溶接部外で破断し、溶接しない
試験片と略同じ引張り特性を示す。また、溶接部
をさらに700℃程度に10分間加熱する焼戻し処理
を行つて空冷すれば溶接部のマルテンサイト相の
量は減少し、試験片全体を延性に富んだ鋼とする
ことができる。
次に本発明の高マンガン二相鋼における各元素
の含有量の限定理由について説明する。
炭素は強度は向上させる有用な元素であるが、
0.3％以上では構造用材料としては機械的性質が
脆くなるので上限を0.3％とした。また、炭素に
よる強化作用が認められる0.02％を下限とした。
マンガンは、本発明においては、炭素と共に、
焼入れ性を向上させると共に得られる二相鋼を強
化する最も重要な基本成分元素であるが、多すぎ
ると残留オーステナイト相が増えて別種の鋼とな
り、本来の意味の二相鋼ではなくなるし、また脆
くなる傾向があるので、経済性をも考慮し、５％
な上限とした。また、他の添加元素による若干の
変動はあるものの、二相域からの空冷によつて本
発明の意図する二相組織が得られることと、従来
の構造用のマンガン鋼や前記低合金高張力鋼にお
ける上限値が略1.7％であること及び強度を考慮
し、特に2.8％を下限とした。
珪素は強化作用を有するが、1.5％を超えると
却つて強度が低下し、また0.2％を下廻ると顕著
な強化作用を示さないので、好適範囲として0.2
〜1.5％を採用した。
モリブデン、タンタル、ニオブ、タングステ
ン、チタン、バナジウム、硼素及びクロームは、
少量の添加で結晶粒を小さくし、マルテンサイト
相の分散を助ける有力な強化剤であるが高価な元
素であり、また多くなると延性が得られ難くなる
ので0.1、％を上限とし、クロームについてのみ
上限を0.3％とした。また、何れも、強化効果の
認められる0.02％を下限とした。
〔実施例〕
原料としてアームコ鉄、電解マンガン、４％炭
素−鉄合金及びフエロアロイを各種配合して用
い、高周波誘導炉で各種合金鋼を溶製し、アルゴ
ンガス雰囲気下で水冷鋳型に鋳造し、２Kgの鋳塊
とした。溶製した合金鋼の成分を一括して第１表
に示す。鋳塊は1100℃で20時間アルゴンガス流の
もとで均質化処理を行い、次に1100℃での熱間圧
延により20mmの厚塊を5.5mmまで圧減し、さらに
冷間圧延で５mmに圧延したのち、900℃の熱間圧
延で４mmの圧減し、これを常温まで空冷した。こ
の平板から機械切削により厚さ３mm、有効部長さ
32mm及び幅6.25mmの平板引張り試験片を多数作成
し、適宜試験に供した。
[Industrial Application Field] The present invention relates to a dual-phase structural steel that has excellent mechanical properties as a structural steel and is suitable for welding. [Prior Art] Rolled steel materials used for general structures such as ship hulls, bridges, pressure vessels, and automobiles, or for welded structures, have excellent mechanical strength and toughness.
It is required to be economical in that it has good weldability and can be mass-produced like ordinary steel. In order to improve the strength of carbon steel, it is easiest to increase the carbon content, but as the carbon content increases, ductility such as elongation and reduction of area decreases, and weldability deteriorates. For this reason, in particular considering weldability, we use low carbon based materials such as silicon, manganese, nickel, etc.
Low-carbon, low-alloy steel that is strengthened by adding small amounts of one or more alloying elements such as chromium and copper and utilizing solid solution strengthening or crystal refinement is known as low-alloy high-strength steel (HSLA steel). It is becoming widely used. However, low-alloy high-strength steel used in the as-rolled, unheated state retains its ferrite-barrite structure and is strengthened by adding silicon, manganese, and other alloying elements, resulting in a tensile strength of 60 Kgf/mm. 2 , and for high-strength steels with higher strength, by increasing the amount of alloying elements such as nickel and chromium, and performing quenching and tempering, the tensile strength due to the tempered martensitic phase can be improved. The strength has been strengthened to around 100Kgf/ mm2 . On the other hand, a steel with a two-phase structure in which a martensitic phase is dispersed in a ferrite matrix through special heat treatment using components in the high-strength steel range has been developed, which maintains ductility and ensures strength, making it easy to weld. Due to its good properties, it is attracting attention for its use in reducing the weight of structural parts. For example, tensile strength 600MPa
0.05%C-0.02%Si-0.32%Mn showing 20% elongation at
- Dual-phase steel obtained by annealing low-alloy high-strength steel consisting of residual Fe in a two-phase region of ferrite and austenite at approximately 790°C and then rapidly cooling it to change austenite to martensite has a tensile strength of 650 MPa and elongation.
30%, and has good weldability due to its low carbon content. [Problems to be Solved by the Invention] However, in order to further improve the high strength that is the first requirement of the above-mentioned high-strength steel, it is necessary to use expensive alloying elements in the above-mentioned annealed high-tensile strength steel. Although there is a tendency to increase the amount of Ni added, it is difficult to achieve this goal without sacrificing ductility, and weld cracking is likely to occur during welding. Even with conventional strength levels, hardening and cold cracking are likely to occur due to rapid heating and cooling due to the effects of welding heat, and in order to prevent such embrittlement of welds,
There are problems in that preheating is required and there are heat input limitations. Furthermore, even in the above-mentioned low-alloy duplex steel, the amount of carbon added is kept to a low value, and the types and amounts of expensive alloying elements such as nickel, chromium, and vanadium are increased to ensure strength. In addition to requiring expensive heat treatment including quenching treatment, the product is expensive in comparison to the performance obtained.For example, duplex steel has been used for lightening automobiles, which was originally intended when it was developed, i.e., thin sheets for car bodies. There were problems with economic efficiency, such as not being suitable for use as a. In addition, when the alloying elements mentioned above increase,
Carbon equivalent, which is a guideline for weld hardening, is about 0.4 of the standard amount.
%, the weld heat-affected zone hardens and becomes brittle during welding, making it difficult to obtain a practical high-strength alloy steel. In addition, a technology has been disclosed that uses transformation-induced plasticity (TRIP) of retained austenite to obtain elongation of 30% or more during processing while maintaining weldability in carbon-based low-alloy high-strength steel. However, in order to ensure the amount of retained austenite in the structure, complicated heat treatment is required, which poses an economical problem. Therefore, the present invention does not require the addition of large amounts of expensive reinforcing alloying elements, is easy to temper heat treatment, provides higher mechanical strength without significantly impairing ductility, has good weldability, The purpose of the present invention is to provide structural steel that is low in production cost and highly practical. [Means for Solving the Problems] In order to achieve the above object, the present invention provides
As such, steel containing 0.02-0.3% carbon, 2.8-5.0% manganese, and 0.2-1.5% silicon, with the balance consisting of iron and unavoidable impurities, is maintained in the ferrite-austenite two-phase region at 700-800℃ after rolling. After annealing, a structural high-manganese duplex steel with high strength and excellent weldability is cooled, and the steel contains 0.02 to 0.3% carbon, 2.8 to 5.0% manganese, and 0.2 to 1.5% silicon, as weight percent. In addition, it contains one or more elements from the group consisting of molybdenum, niobium, tantalum, tungsten, titanium, vanadium, and boron in an amount of 0.02 to 0.1%, and chromium in an amount of 0.02 to 0.3%, with the balance being iron and This paper proposes a high manganese duplex steel for structural use, which is composed of unavoidable impurities and has high strength and excellent weldability. The present invention will be explained in detail below. The high manganese duplex steel of the present invention is produced by charging the raw material into a normal steelmaking furnace such as a converter, electric furnace, or high-frequency induction furnace, melting it, adjusting the composition, casting, and hot-rolling or cold-rolling. It is obtained by rolling it into a predetermined shape and then subjecting it to heat treatment. The heat treatment is carried out by annealing by holding in a ferrite-austenite two-phase region at 700 to 800°C for about 10 minutes, followed by slow or rapid cooling such as air cooling, water quenching, oil quenching, etc. In the case of the high manganese duplex steel of the present invention, the transformation temperatures A1 and A3 are significantly lowered due to the high manganese content, and the isothermal transformation curve is shifted to the long time side, so Duplex steel can be obtained not only by rapid cooling such as water quenching from a low annealing temperature range but also by slow cooling such as air cooling. The two-phase structure has a hard martensanth phase dispersed in a relatively soft ferrite matrix in the form of fine needles, particles, or islands. The high manganese duplex steel of the present invention has high strength and high ductility based on its structure, and can easily obtain a tensile strength of 1000 MPa or more and a breaking elongation of about 20% or more in the quenched state, and can be tempered. The tensile strength is increased by
It is possible to have an elongation at break of 40% or more while maintaining the pressure at about 700 MPa. The high manganese duplex steel of the present invention also has the characteristics of a typical duplex steel, in that the stress-strain curve obtained by tensile measurement is continuous and does not exhibit a sudden yield phenomenon, and the tensile strength The yield strength ratio, that is, the yield stress ratio, is small at 0.4 to 0.7, and it has good cold workability. Furthermore, after applying a slight strain, the load is removed and the yield strength increases significantly when heated for a short time at a relatively low temperature. Although the high manganese duplex steel of the present invention has a high manganese content, it has excellent weldability, which is a major feature and an excellent advantage. That is, conventionally the carbon equivalent of steel for welding is required to be 0.4 or less, but for example, it is also the basic duplex steel of the present invention.
In the case of the 0.1%C-3%Mn-0.5%Si-Fe alloy, the weldability is good despite its carbon equivalent being 0.6. This has been confirmed by TIG welding and electron beam welding. In either case, the welded part is left to cool in argon gas or vacuum, but the structure of the welded part obtained at this time always exhibits a two-phase precipitation structure in which the martensite phase in the ferrite matrix is finely dispersed. ing. If the cooling rate is high, the amount of martensitic phase increases, but even when cooling is allowed, its volume fraction is always less than 50% of the total, and therefore, although the mechanical strength of the weld is high, it is still quite large. Maintains ductility. For this reason, in tensile measurements, a test piece that has been successfully welded will break outside the weld and exhibit approximately the same tensile properties as a non-welded test piece. In addition, if the weld is further tempered by heating it to about 700°C for 10 minutes and then air-cooled, the amount of martensitic phase in the weld will be reduced, making the entire test piece a highly ductile steel. Next, the reason for limiting the content of each element in the high manganese duplex steel of the present invention will be explained. Carbon is a useful element that improves strength, but
If it exceeds 0.3%, the mechanical properties of the structural material become weak, so the upper limit was set at 0.3%. In addition, the lower limit was set at 0.02%, where the reinforcing effect of carbon is recognized. In the present invention, manganese is used together with carbon,
It is the most important basic component element that improves the hardenability and strengthens the resulting duplex steel, but if it is present in too much, the retained austenite phase will increase and the steel will become a different type of steel, and it will no longer be a duplex steel in its original meaning. Since it tends to become brittle, considering economic efficiency, 5%
The upper limit was set as follows. In addition, although there are slight variations due to other additive elements, the two-phase structure intended by the present invention can be obtained by air cooling from the two-phase region, and the conventional structural manganese steel and the low alloy high tensile strength Considering the fact that the upper limit for steel is approximately 1.7% and strength, the lower limit was set at 2.8%. Silicon has a reinforcing effect, but if it exceeds 1.5%, the strength decreases, and if it falls below 0.2%, it does not show any significant reinforcing effect, so the preferred range is 0.2%.
~1.5% was adopted. Molybdenum, tantalum, niobium, tungsten, titanium, vanadium, boron and chromium are
It is a powerful reinforcing agent that reduces crystal grain size and helps dispersion of martensitic phase when added in small amounts, but it is an expensive element and it becomes difficult to obtain ductility when added in large quantities. The upper limit was set at 0.3%. In both cases, the lower limit was set at 0.02%, at which the reinforcing effect was recognized. [Example] Using various combinations of Armco iron, electrolytic manganese, 4% carbon-iron alloy, and ferroalloy as raw materials, various alloy steels were melted in a high-frequency induction furnace, and cast in a water-cooled mold under an argon gas atmosphere. It was made into an ingot weighing 2 kg. The components of the melted alloy steel are shown in Table 1. The ingot was homogenized at 1100℃ for 20 hours under an argon gas stream, then hot rolled at 1100℃ to reduce the 20mm thick ingot to 5.5mm, and then cold rolled to 5mm. After rolling, it was hot rolled at 900°C to reduce the thickness by 4 mm, and then air cooled to room temperature. By machine cutting from this flat plate, the thickness is 3 mm, and the effective length is
A large number of flat plate tensile test pieces with a width of 32 mm and a width of 6.25 mm were prepared and subjected to appropriate tests.
以上の説明から明らかなように、本発明によれ
ば、次ような効果が得られる。
比較的低い700〜800℃焼鈍温度からの冷却で従
来の低炭素低合金鋼以上の高強度で延性に富む、
実用上有利な二相鋼が得られる。
前記二相鋼を得るための焼鈍温度からの冷却は
急冷に限らず空冷であつてもよく、冷却速度を変
えることによつて得られる、二相鋼の性質を大き
く変えることができ、また、簡単な焼戻しで大き
い延性を得ることができる。
高いマンガン含有量に拘らす溶接性が良好で、
しかも溶接部の機械的性質は非溶接部のそれと略
同等のものが得られる。
炭素−マンガン−珪素−鉄を基本とした簡単な
組成で延性を損うことなく機械的強度を増加で
き、さらにモリブデン、ニオブ、等高融点金属の
少量添加でさらに機械的強度の向上が図れる。
基本的添加成分の炭素及びマンガン、さらに珪
素は安価な元素であり、高価なモリブデン等高融
点金属の添加は少量で済み、また調質が容易なの
で製造コストが安い。
特に、原料が安く、焼鈍温度からの空冷処理に
よつて高い強度と延性をもち、かつ溶接性にすぐ
れた二相鋼が得られることにより、多量生産が可
能な、自動車車体用途をも含む広範囲の用途に適
した、経済性にすぐれた高強度鋼が得られる。
二相鋼として特徴的に降伏応力比が小さく、加
工に有利である。
降伏強さは、二相鋼としての歪み時効性を利用
し増大を図ることができる。
As is clear from the above description, according to the present invention, the following effects can be obtained. By cooling from a relatively low annealing temperature of 700 to 800℃, it has higher strength and ductility than conventional low carbon low alloy steel.
A practically advantageous duplex steel is obtained. Cooling from the annealing temperature to obtain the duplex steel is not limited to rapid cooling, but may be air cooling, and by changing the cooling rate, the properties of the duplex steel obtained can be greatly changed, and, High ductility can be obtained by simple tempering. Good weldability despite high manganese content,
Moreover, the mechanical properties of the welded part are approximately equivalent to those of the non-welded part. A simple composition based on carbon-manganese-silicon-iron can increase mechanical strength without impairing ductility, and addition of small amounts of high melting point metals such as molybdenum, niobium, etc. can further improve mechanical strength. The basic additive components carbon and manganese, as well as silicon, are inexpensive elements, and only a small amount of expensive high-melting point metals such as molybdenum can be added, and since refining is easy, manufacturing costs are low. In particular, since the raw materials are cheap and duplex steel with high strength and ductility and excellent weldability can be obtained by air cooling from annealing temperature, mass production is possible for a wide range of applications including automobile bodies. This produces high-strength steel that is highly economical and suitable for applications. As a duplex steel, it has a characteristically low yield stress ratio, making it advantageous for processing. The yield strength can be increased by utilizing the strain aging properties of the dual-phase steel.
第１図は本発明の高マンガン二相鋼における焼
鈍温度と引張り特性との関係を示す図、第２図
ａ，ｂ，ｃは焼鈍温度別に示した本発明の高マン
ガン二相鋼における炭素含有量と引張り特性との
関係を示す図、第３図ａ，ｂ，ｃは焼鈍温度別に
示した本発明の高マンガン二相鋼における珪素含
有量と引張り特性の関係を示す図、第４図ａ，
ｂ，ｃ，ｄ，ｅ，ｆ，ｇは本発明の高マンガン二
相鋼における焼鈍温度と引張り特性との関係を示
す図、そして第５図は本発明の高マンガン二相鋼
における焼戻し時間と引張り特性との関係を示す
図であつて、各図共通に、実線は空冷の場合を、
点線は水冷の場合を示し、δRは引張り強さ、δEは
0.2％永久伸び降伏強さ、ARは破断伸び、そして
AUは均一伸びを示す線である。
Fig. 1 is a diagram showing the relationship between annealing temperature and tensile properties in the high manganese duplex steel of the present invention, and Fig. 2 a, b, and c are graphs showing the carbon content in the high manganese duplex steel of the present invention, shown by annealing temperature. Figures 3a, b, and c are diagrams showing the relationship between silicon content and tensile properties in the high manganese duplex steel of the present invention shown at different annealing temperatures. Figure 4a is a diagram showing the relationship between silicon content and tensile properties. ，
b, c, d, e, f, g are diagrams showing the relationship between annealing temperature and tensile properties in the high manganese dual phase steel of the present invention, and Figure 5 shows the relationship between the tempering time and the tensile properties in the high manganese dual phase steel of the present invention. This is a diagram showing the relationship with tensile properties, and the solid line in each diagram indicates the case of air cooling.
The dotted line indicates the case of water cooling, δ R is the tensile strength, and δ E is the
0.2% permanent elongation yield strength, A R is elongation at break, and
A U is a line showing uniform elongation.
Claims (1)
2.8〜5.0％及び珪素0.2〜1.5％を含み、 残部が鉄及び不可避不純物からなる鋼を、圧延
後700〜800℃のフエライトオーステナイト二相域
に保持して焼鈍した後、冷却したことを特徴とす
る高強度で溶接性にすぐれる構造用高マンガン二
相鋼。 ２ 前記鋼が、重量％として、炭素0.02〜0.3％、
マンガン2.8〜5.0％及び珪素0.2〜1.5％のほかに、
それぞれ0.02〜0.1％のモリブデン、ニオブ、タ
ンタル、タングステン、チタン、バナジウム及び
硼素と0.02〜0.3％のクロームからなる群のうち
の１種または２種以上の元素を含み、残部が鉄及
び不可避不純物からなることを特徴とする請求項
１記載の高強度で溶接性にすぐれる構造用高マン
ガン二相鋼。[Claims] 1% by weight: carbon 0.02-0.3%, manganese
Steel containing 2.8 to 5.0% silicon and 0.2 to 1.5% silicon, with the balance consisting of iron and unavoidable impurities, is annealed at 700 to 800°C in the ferrite-austenite two-phase region after rolling, and then cooled. Structural high manganese duplex steel with high strength and excellent weldability. 2 The steel contains 0.02 to 0.3% carbon by weight%,
Besides manganese 2.8-5.0% and silicon 0.2-1.5%,
Contains one or more elements from the group consisting of 0.02 to 0.1% molybdenum, niobium, tantalum, tungsten, titanium, vanadium, and boron, and 0.02 to 0.3% chromium, with the remainder being iron and unavoidable impurities. The structural high manganese duplex steel having high strength and excellent weldability according to claim 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31616788A JPH02163343A (en) | 1988-12-16 | 1988-12-16 | High-manganese dual-phase steel for structural use |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31616788A JPH02163343A (en) | 1988-12-16 | 1988-12-16 | High-manganese dual-phase steel for structural use |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH02163343A JPH02163343A (en) | 1990-06-22 |
| JPH0569903B2 true JPH0569903B2 (en) | 1993-10-04 |
Family
ID=18074033
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP31616788A Granted JPH02163343A (en) | 1988-12-16 | 1988-12-16 | High-manganese dual-phase steel for structural use |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH02163343A (en) |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54150318A (en) * | 1978-05-18 | 1979-11-26 | Sumitomo Metal Ind Ltd | Manufacture of non-refined hot rolled high tensile steel strip |
| JPS57116767A (en) * | 1981-01-13 | 1982-07-20 | Nisshin Steel Co Ltd | High tensile zinc plated steel plate of good workability and its production |
| JPS6043425A (en) * | 1983-08-15 | 1985-03-08 | Nippon Kokan Kk <Nkk> | Production of hot rolled composite structure steel sheet having high strength and high workability |
| JPS6043430A (en) * | 1983-08-15 | 1985-03-08 | Nippon Kokan Kk <Nkk> | Production of composite structure steel sheet having high strength and high workability |
| JPS60152654A (en) * | 1984-01-20 | 1985-08-10 | Kobe Steel Ltd | Steel material having superior resistance to hydrogen induced cracking, high strength, ductility and toughness and its manufacture |
| JPS62182224A (en) * | 1986-02-05 | 1987-08-10 | Nippon Steel Corp | Production of high-strength steel sheet having excellent ductility |
| JPS62188729A (en) * | 1986-02-13 | 1987-08-18 | Nippon Steel Corp | Manufacture of high strength steel superior in workability |
-
1988
- 1988-12-16 JP JP31616788A patent/JPH02163343A/en active Granted
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54150318A (en) * | 1978-05-18 | 1979-11-26 | Sumitomo Metal Ind Ltd | Manufacture of non-refined hot rolled high tensile steel strip |
| JPS57116767A (en) * | 1981-01-13 | 1982-07-20 | Nisshin Steel Co Ltd | High tensile zinc plated steel plate of good workability and its production |
| JPS6043425A (en) * | 1983-08-15 | 1985-03-08 | Nippon Kokan Kk <Nkk> | Production of hot rolled composite structure steel sheet having high strength and high workability |
| JPS6043430A (en) * | 1983-08-15 | 1985-03-08 | Nippon Kokan Kk <Nkk> | Production of composite structure steel sheet having high strength and high workability |
| JPS60152654A (en) * | 1984-01-20 | 1985-08-10 | Kobe Steel Ltd | Steel material having superior resistance to hydrogen induced cracking, high strength, ductility and toughness and its manufacture |
| JPS62182224A (en) * | 1986-02-05 | 1987-08-10 | Nippon Steel Corp | Production of high-strength steel sheet having excellent ductility |
| JPS62188729A (en) * | 1986-02-13 | 1987-08-18 | Nippon Steel Corp | Manufacture of high strength steel superior in workability |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH02163343A (en) | 1990-06-22 |
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