JP3543200B2

JP3543200B2 - Manufacturing method of steel sheet for metal saw substrate

Info

Publication number: JP3543200B2
Application number: JP17480894A
Authority: JP
Inventors: 勝之飯原; 利郎山田; 知明諌山
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 1994-07-04
Filing date: 1994-07-04
Publication date: 2004-07-14
Anticipated expiration: 2019-07-14
Also published as: JPH0813030A

Description

【０００１】
【産業上の利用分野】
本発明は，メタルソー基板に適用される高強度・高靱性の鋼板の製造方法に関する。
【０００２】
【従来の技術】
高速度鋼の刃部を別鋼種の基板に溶接してなるメタルソー（帯鋸や丸鋸等）は高価な高速度鋼の使用量を低減できることのほか，基板での強度・靭性の付与によってブレード自体の耐用性を向上させることができるので，特にメタルバンドソー分野に多用されている。
【０００３】
かようなメタルソー基板には，十分な強度と靭性を具備することのほか，多量の合金元素を含有する高速度鋼との溶接性が良好でまた高速度鋼との熱処理性の整合性も要求されることになる。このような要求を満たすべく，従来より種々のメタルソー基板材料が提案されており，例えば特開昭４９−８８７１３号公報，特開昭５４−７６４１４号公報，特公昭５５−３２７７８号公報には，各種の合金鋼が記載されており，これらをメタルソー基板とすると，刀部高速度鋼との溶接部の特性劣化が少なく，また刀部との同一温度域での熱処理によっても十分な強度と靭性が保たれるとされている。
【０００４】
とくに特開昭４９−８８７１３号公報および特開昭５４−７６４１４号に記載の成分系の材料では，溶接時の溶融メタル中での刃材側と基板側との炭素活量の差に基づく基板側から刃材側に炭素が拡散する現象（刃材側では浸炭，基板材側では脱炭の現象）が起きにくく，また焼戻し軟化抵抗が大きいため刃部と同一の高温焼入焼戻し熱処理によっても十分な強度と靱性が保たれるので，メタルバンドソーの基板材として好適であり，実用化されているものもある。
【０００５】
【発明が解決しようとする課題】
メタルソー基板には，前記のように各種の特性が要求されるが，このような特性が要求される特殊鋼をどのようにして製造するか，前記の公報には全く示されていない。とくに最近の鉄鋼製造の趨勢である大ロットの連続鋳造−熱間圧延工程での製造方法については一切開示されていない。
【０００６】
すなわち，通常の鋼を対象とした連続鋳造工程−熱間圧延工程−連続酸洗工程−冷間圧延工程を経る鋼帯の製造ラインで，メタルソー基板のような特殊材料が製造できるか否かは全く不明であった。本発明者らの経験によると，ホットストリップミルを経たこの系統の熱延鋼帯を連続酸洗ラインに通板すると，ライン内の種々の半径のロール群で曲げ応力を受けながら案内される過程で破断する事故が発生しやすく，このような鋼帯を安定して製造することは困難である。
【０００７】
本発明の目的は，メタルソー基板に要求される諸性質を具備した高強度高靭性の鋼板を大ロットの連続鋳造−熱間圧延工程を経て安価に製造する点にある。
【０００８】
【課題を解決するための手段】
本発明によれば，重量％で，
Ｃ：０．３０〜０．６０％，
Ｓｉ：０．４０％以下（好ましくは０．１０〜０．４０％），
Ｍｎ：０．６０％以下（好ましくは０．２０〜０．６０％），
Ｃｒ：１．００〜３．００％，
Ｍｏ：０．４０〜１．００％，
Ｖ：０．２０〜０．４０％，
Ｐ：０．０１０％以下，
Ｓ：０．００６％以下，
Ａｌ：酸可溶Ａｌとして０．０１０〜０．１０％
を含有し，残部がＦｅおよび不可避的不純物からなるメタルソー基板用の鋼板を少なくとも連続鋳造工程，熱間圧延工程および連続酸洗工程を経る鋼帯製造ラインで製造する方法であって，前記の熱間圧延工程を
スラブ加熱温度：１２００℃〜１３５０℃，
仕上温度：８００℃〜９００℃，
巻取温度：４００℃〜６００℃，
粗圧延〜仕上圧延での総圧下率：９８％以上
の条件で実施してベイナイト単相組織の熱延鋼帯とすることを特徴とするメタルソー基板用鋼板の製造方法を提供する。
【０００９】
【作用】
本発明によると，メタルソー基板に要求される諸特性を具備した鋼板が，鋼の連続鋳造設備および熱間圧延設備を用いて大ロットで生産が可能となり，高品質で安価なメタルソー基板を提供することができる。特に熱間圧延によってベイナイト単相組織の熱延鋼帯とするので，これを連続酸洗工程に通板しても，破断トラブルなく良好に酸洗ができるようになり，この材料の大ロット生産が可能となった。
【００１０】
以下に本発明で規定する鋼成分とその含有量並びに製造条件の意味するところを作用と共に個別に説明する。
【００１１】
〔鋼の成分組成について〕
Ｃ：鋼の強度と靱性を決定する基本的な元素である。メタルソー基板材として必要な強度を確保するためにはＣ量は０．３０％以上が必要である。鋼の強度はＣ量が多いほど増加はするが，他方メタルソー基板材として必要な靱性はＣ量が０．６０％を超えると逆に低下してしまう。このためＣ量は０．３０〜０．６０％とした。
【００１２】
Ｓｉ：鋼の脱酸元素として必要かつ有効であり，またフェライトの固溶強化元素としても有効に作用する元素であるが，熱延や焼鈍さらには熱処理において表面直下に内部酸化を生じる原因にもなる元素である。種々の工程における内部酸化を防止するためにはＳｉ量を０．４０％以下とすることが必要であるので，その上限を０．４０％とした。好ましいＳｉ量は０．１０〜０．４０％である。なお
鋼の脱酸は他の元素例えばＭｎやＡｌで補うことができるが，この場合にはＳｉは無添加でも構わない。
【００１３】
Ｍｎ：鋼の脱酸元素として必要かつ有効であり，オーステナイトの焼入性を高める元素であるが，Ｓｉと同様に，熱延や焼鈍さらには熱処理において表面直下に内部酸化を生じる原因となる元素でもある。種々の工程において内部酸化を防止するためには，Ｍｎ量を０．６０％以下とすることが必要であるので，その上限を０．６０％とした。好ましいＭｎ量は０．２０〜０．６０％である。なお鋼の脱酸は他の元素例えばＳｉやＡｌで補うことができるが，この場合にはＭｎは無添加でも構わない。
【００１４】
Ｃｒ：鋼の焼入性，強度，靱性を向上させる元素として，またＣの拡散を抑制する元素として必須である。本発明材料と高速度鋼との溶接時に溶接部の浸炭または脱炭（刃材側の浸炭，基板材側の脱炭）を防止し，また，刃部と同一の高温焼入焼戻し熱処理によっても十分な強度と靱性を保つためには，Ｃｒ量は１．００％以上が必要である。しかしＣｒを３．００％を超えて含有させても前記の溶接部の浸炭・脱炭の防止効果や，強度と靱性を増加させるは効果はともに飽和するうえ，中間製品の製造性が著しく低下してしまうので，その上限を３．００％とした。
【００１５】
Ｍｏ：鋼の焼入性，強度，靱性を向上させる元素として，またＣの拡散を抑制する元素として，Ｃｒと同様に必須である。また高速度鋼との溶接部の浸炭または脱炭を防止し且つ刃部と同一の高温焼入焼戻し熱処理によっても十分な強度と靱性を保つためには，Ｍｏ量は０．４０％以上が必要である。しかし，Ｍｏ量が１．００％を超えると，高速度鋼との溶接部での浸炭・脱炭防止効果や，強度と靱性を増加させるは効果はともに飽和し，中間製品の製造性が著しく低下してしまうので，その上限を１．００％とした。
【００１６】
Ｖ：オーステナイト結晶粒径を微細にする作用により鋼の強度と靱性を向上させる元素として，またＣの拡散を抑制する元素として有効に作用する。高速度鋼との溶接部における浸炭・脱炭を防止し，また刃部と同一の高温焼入焼戻し熱処理によっても十分な強度と靱性を保つためには，Ｖ量は０．２０％以上が必要である。しかしＶを０．４０％を超えて含有しても，高速度鋼との溶接部の浸炭・脱炭防止効果や，強度と靱性を増加させるは効果はともに飽和し，中間製品の製造性が著しく低下してしまうので，その上限を０．４０％とした。
【００１７】
Ｐ：結晶粒界に偏析し焼入焼戻し後の靱性を低下させるので，Ｐ量は低いほど好ましい。メタルソー基板材として必要な靱性はＰ量を０．０１０％以下とすることにより達成できるので，その上限を０．０１０％とした。
【００１８】
Ｓ：主としてＭｎＳなる非金属介在物を形成し，鋼の加工性，強度，靱性に悪影響を及ぼす。とくに，圧延材においては，ＭｎＳが圧延方向に展伸するため，鋼の加工性，強度，靱性の面内異方性が大きく現れてしまう。このようなＳの悪影響を防止するためには，Ｓ量を０．００６％以下とする必要があるので，その上限を０．００６％とした。
【００１９】
Ａｌ：鋼の脱酸元素として必要かつ有効な元素であり，さらに鋼中のＮと結合してＡｌＮを形成し，熱処理におけるオーステナイト結晶粒の異常成長を抑制する元素として有効である。これらのＡｌの作用は，酸可溶Ａｌとして０．０１０％以上含有することによって発揮されるので，その下限を０．０１０％とした。これらのＡｌの作用は，酸可溶Ａｌとして０．１０％までの量で十分であり，それ以上のＡｌを添加しても，いたずらに製造コストの上昇を招くのみならずＡｌに起因する表面疵等の増加をも招き得策ではないので，その上限を０．１０％とした。
【００２０】
〔製造条件〕
以上のように成分組成を有する特殊鋼のメタルソー基板を製造するにあたり，本発明では当該鋼を，転炉あるいは電気炉にて溶製した後真空脱ガス装置を経て成分調整し，鋼の連続鋳造設備によって連鋳スラブとし，このスラブを熱間圧延工程，連続酸洗工程，冷間圧延工程（必要に応じて焼鈍を挟んで圧下を行なう）を経て，普通鋼と同様の冷延コイルに製造しようとするものであるが，かような特殊鋼であっても，熱間圧延条件を適正にしてこの鋼の組織を制御すれば酸洗ラインで破断なく製造できることがわかった。以下に本発明で採用する熱間圧延条件について説明する。
【００２１】
連続鋳造設備で製造した室温まで冷却された当該鋼のスラブまたは連続鋳造後の高温のスラブを用いて熱延を行う場合，連続鋳造ままのスラブでは偏析が著しく，当該鋼の本来の性能を発揮させるためには，熱延の段階で偏析を可能な限り軽減することが肝要となる。このためには，スラブ加熱温度は１２００℃以上とする必要がある。しかし，１３５０℃を超える温度に加熱しても偏析を軽減する効果は飽和し，かえってスケール損が大きくなり，かつ所要エネルギーがいたずらに増加するのみであるので，スラブ加熱温度の上限は１３５０℃する。
【００２２】
他方，熱間圧延工程を経てコイル状に巻き取られた熱延鋼帯は，焼鈍と冷延を繰り返す冷延工程に移る前に，連続酸洗工程にて熱延板の表面に生じた酸化スケールを除去しなければならない。この酸洗ラインでは，種々の半径のロール群で通板経路が構成されているので，ここを通過する鋼帯は，破断することなく通過できる延性と靱性を具備しなければならない。しかし，前記の成分組成をもつ当該鋼はその変態特性からフェライトおよびパーライト変態は遅いので，その熱延鋼帯は過冷変態を起こした組織となり，いきおい高強度を示す（例えば１０００Ｎ／ｍｍ^２以上）ので，酸洗ラインで破断するおそれがある。
【００２３】
本発明者らはこの問題を解決すべく試験を重ねたが，前記の温度に加熱したスラブを熱延するさいに，熱延仕上温度を８００℃〜９００℃，巻取温度を４００℃〜６００℃，そして粗圧延から仕上圧延での総圧下率を９８％以上として熱延すれば，フエライトを実質上含まない微細なベイナイト単相組織を有する熱延鋼帯となり，前記の問題が解消できることがわかった。
【００２４】
これら熱延条件の意味するところを説明すると，仕上温度を９００℃以下としかつ粗圧延〜仕上圧延における総圧下率を９８％以上にすると，仕上圧延終了直後のオーステナイトは未再結晶状態でかつ結晶粒が微細化する。このため，以後の冷却過程で微細なベイナイト組織が得られる。
【００２５】
これに対して，仕上温度を９００℃を超える高温とするか，または粗圧延〜仕上圧延における総圧下率を９８％未満にすると，仕上圧延終了段階のオーステナイト結晶粒が粗大となり，また再結晶が進行してしまい，最終的に微細なベイナイト組織が得られない。
【００２６】
他方，仕上温度を８００℃未満の低温にすると，フェライト変態が促進されてベイナイトとフェライトの混合組織が生成した熱延鋼帯となる。この場合には，酸洗ライン通板時において，軟質なフェライト組織部分に歪が集中して板破断を起こし易くなる。加えて，熱延段階でもオーステナイトの変形抵抗が増加して圧延負荷が増大し，いたずらに製造コストがかさむことにもなる。
【００２７】
巻取温度については，巻取温度を４００℃未満ではベイナイト変態が十分に進行せずにマルテンサイトが生成し，熱延鋼帯の材質が硬質化して酸洗ライン通板中に板破断が起きやすくなってしまう。また巻取温度を６００℃を超える温度とすると，フェライトとパーライトが生成してベイナイト単相組織とはならない。したがって，本発明鋼の熱延巻取温度は４００〜６００℃の範囲とする必要がある。
【００２８】
【実施例】
〔実施例１〕
表１に示した化学成分値の鋼を転炉で溶製し，厚さ２００ｍｍのスラブに連続鋳造した。このスラブを１２５０℃に加熱し，熱延仕上温度８５０℃，巻取温度５５０℃で通常のホットストリップミルで熱間圧延し，板厚２．８ｍｍの熱延鋼帯を製造した。
【００２９】
各熱延鋼帯から供試材を切出し，酸洗後球状化焼鈍し，さらに焼入れ焼戻し処理を施した。焼入れは１２６０℃で３分間保持後７０℃の油浴中で冷却した。焼戻しは５６０℃で６０分間保持を３回繰り返した。各熱処理材の硬さと衝撃値を測定しまた表層の内部酸化の有無を調べた。その結果を表１に併記した。
【００３０】
【表１】

【００３１】
表１の結果から次のことがわかる。Ｃ含有量が本発明で規定するより低い比較鋼Ｂは焼入れ・焼戻し後の硬さが低く，メタルソー基板として要求される強度が得られないうえに，酸化物を作りやすいＭｎの含有量が高いので，表層に内部酸化も認められた。
【００３２】
本発明で規定するよりもＣ含有量が高い比較鋼Ｃは強度は充分であるものの靱性が低く，また酸化物を作りやすいＳｉの含有量が高いため内部酸化を生じている。したがってメタルソー基板としての使用に耐えない。
【００３３】
比較鋼Ｅは，Ｃｒ，Ｍｏ，Ｖなどの炭化物形成元素の含有量が少ないため，焼入れ・焼戻し後の強度が確保できない。他方，比較鋼Ｆはこれら炭化物形成元素の含有量が本発明で規定するよりも多く含有するものであるが，本発明鋼と比べて強度・靱性ともに大きな特性の向上は認められず，これらの元素を過剰に添加しても製造性を損なうばかりか経済的にも不利となることがわかる。
【００３４】
これに対して，本発明鋼Ａ，ＤおよびＧはいずれも焼入れ焼戻し後にメタルソー基板として必要な強度と靱性を同時に具備しており，また表層の内部酸化も認められない。
【００３５】
〔実施例２〕
表１のＡ鋼を転炉で溶製し，厚さ１００〜２００ｍｍのスラブ６本に連続鋳造した。これらのスラブを，表２に示すように加熱温度１２００〜１３００℃，仕上温度７７０〜９２０℃，巻取温度３８０〜６３０℃，総圧下率９６．６〜９８．５の各種条件のもとで通常のホットストリップミルで熱間圧延し，板厚３．０〜３．６ｍｍの熱延鋼帯を製造した。
【００３６】
得られた各熱延鋼帯から供試材を切出し，鋼の熱延金属組織を調べ，また各熱延材の曲げ試験を行うことによって酸洗ラインの通板性を調べた。その結果を表２に併記した。曲げ試験は半径３０ｍｍのポンチによる突曲げを２０回繰り返し行った時の破断の有無によって評価した。この試験による破断の有無は，連続酸洗工程に通板する際に必要な延性および靱性を判定する目安となり，破断しないものは十分に通板可能である。
【００３７】
【表２】

【００３８】
表２の結果から次のことがわかる。
【００３９】
比較例ｃは，厚さ２００ｍｍのスラブに連続鋳造した後，板厚３．４ｍｍまで熱延したものであるが，仕上温度が低いので熱延材の金属組織はフェライトとベイナイトの２層となり，曲げ試験では軟質なこのフェライト部に歪が集中して破断に至った。
【００４０】
比較例ｄは，厚さ１００ｍｍのスラブから板厚３．４ｍｍまで熱延したものであるが，仕上温度が高く総圧下率が低いため組織は粗大なベイナイトとなり，曲げ特性が低下している。
【００４１】
比較例ｅとｆは，それぞれ厚さ２００ｍｍのスラブから板厚３．０ｍｍと３．６ｍｍまで熱延したものであるが，比較例ｅでは巻取温度が低いのでベイナイトのほかにマルテンサイトが生じた組織となり，材料の延性が低下して曲げ試験にて破断した。また比較例ｆは巻取温度が高いのでフェライトとパーライトが生成した組織となり，曲げ試験では局部的に歪が集中して破断した。
【００４２】
これに対して，本発明例ａとｂでは，それぞれ厚さ２００ｍｍのスラブから板厚３．０ｍｍと３．６ｍｍまで熱延したものであり，本発明で規定する範囲の条
件で熱延されているので，いずれも微細なベイナイト単相組織となり，曲げ試験でも破断に至らず優れた延靱性を示している。
【００４３】
このように，本発明の方法に従う熱延鋼帯は酸洗ラインに安定して通板可能となり，大ロット生産が可能となった。なお酸洗された熱間圧延は次工程の焼鈍と冷延によって必要厚みの冷延鋼帯とされ，メタルソー基板用途に供される。
【００４４】
【発明の効果】
以上説明したように，本発明によれば，メタルソー基板に必要な特性を満足する高強度・高靭性の鋼板を通常の大ロット式鋼帯製造ラインで製造可能となり，安価で高品質のメタルソー基板用素材を提供できる。[0001]
[Industrial applications]
The present invention relates to a method for manufacturing a high-strength and high-toughness steel plate applied to a metal saw substrate.
[0002]
[Prior art]
Metal saws (band saws, circular saws, etc.) made by welding the high-speed steel blade to another steel type substrate can reduce the amount of expensive high-speed steel used, and the strength and toughness of the substrate itself contributes to the blade itself. Since it can improve the durability of the metal band saw, it is widely used especially in the metal band saw field.
[0003]
Such metal saw substrates must have sufficient strength and toughness, good weldability with high-speed steel containing a large amount of alloying elements, and compatibility with heat treatment with high-speed steel. Will be done. In order to satisfy such demands, various metal saw substrate materials have been conventionally proposed. For example, JP-A-49-88713, JP-A-54-76414, and JP-B-55-32778 disclose such materials. Various alloy steels are described. If these are used as metal saw substrates, there is little deterioration in the characteristics of the welded part with the high-speed steel at the sword section, and sufficient strength and toughness can be obtained by heat treatment with the sword section at the same temperature range. Is to be kept.
[0004]
In particular, in the case of the component-based materials described in JP-A-49-88713 and JP-A-54-76414, the substrate based on the difference in the carbon activity between the blade material side and the substrate side in the molten metal during welding. The phenomenon of carbon diffusion from the side to the blade material side (carburization on the blade material side, decarburization on the substrate material side) is unlikely to occur, and since the tempering softening resistance is large, the same high-temperature quenching and tempering heat treatment as the blade part can be performed. Since sufficient strength and toughness are maintained, it is suitable as a substrate material for metal band saws, and some of them have been put to practical use.
[0005]
[Problems to be solved by the invention]
The metal saw substrate is required to have various characteristics as described above, but the above-mentioned publication does not show how to manufacture special steel requiring such characteristics. In particular, there is no disclosure of a production method in a continuous casting-hot rolling process of a large lot, which is a recent trend in steel production.
[0006]
In other words, whether or not a special material such as a metal saw substrate can be manufactured in a steel strip manufacturing line that goes through a continuous casting process, a hot rolling process, a continuous pickling process, and a cold rolling process for ordinary steel. It was completely unknown. According to the experience of the present inventors, when a hot-rolled steel strip of this system passed through a hot strip mill is passed through a continuous pickling line, it is guided by a group of rolls of various radii in the line under bending stress. It is difficult to manufacture such a steel strip stably because of the fact that it is easy for the steel strip to break.
[0007]
An object of the present invention is to manufacture a high-strength and tough steel plate having various properties required for a metal saw substrate at low cost through a continuous casting-hot rolling process of a large lot.
[0008]
[Means for Solving the Problems]
According to the invention, in weight%:
C: 0.30 to 0.60%,
Si: 0.40% or less (preferably 0.10 to 0.40%),
Mn: 0.60% or less (preferably 0.20 to 0.60%),
Cr: 1.00 to 3.00%,
Mo: 0.40-1.00%,
V: 0.20 to 0.40%,
P: 0.010% or less,
S: 0.006% or less,
Al: 0.010 to 0.10% as acid-soluble Al
The method for producing a steel sheet for a metal saw substrate comprising Fe and the balance consisting of Fe and unavoidable impurities in a steel strip production line through at least a continuous casting step, a hot rolling step and a continuous pickling step. The slab heating temperature is 1200 ° C to 1350 ° C
Finishing temperature: 800 to 900 ° C,
Winding temperature: 400 to 600 ° C,
Provided is a method for producing a steel sheet for a metal saw substrate, which is performed under conditions of a total rolling reduction in rough rolling to finish rolling: 98% or more to obtain a hot-rolled steel strip having a bainite single-phase structure.
[0009]
[Action]
Advantageous Effects of Invention According to the present invention, a steel sheet having various characteristics required for a metal saw substrate can be produced in a large lot using continuous casting equipment and hot rolling equipment for steel, and a high quality and low cost metal saw substrate is provided. be able to. In particular, since hot-rolled steel strip with a bainite single-phase structure is formed by hot rolling, it can be pickled satisfactorily without breaking even if it is passed through a continuous pickling process. Became possible.
[0010]
Hereinafter, the meanings of the steel components and the contents thereof and the production conditions specified in the present invention will be individually described together with the operation.
[0011]
[Steel composition]
C: A basic element that determines the strength and toughness of steel. In order to secure the required strength as a metal saw substrate material, the C content needs to be 0.30% or more. Although the strength of steel increases as the C content increases, the toughness required as a metal saw substrate material, on the other hand, decreases when the C content exceeds 0.60%. Therefore, the C content is set to 0.30 to 0.60%.
[0012]
Si: An element that is necessary and effective as a deoxidizing element for steel, and also functions effectively as a solid solution strengthening element for ferrite, but also causes internal oxidation immediately below the surface in hot rolling, annealing, and heat treatment. Element. In order to prevent internal oxidation in various processes, the amount of Si needs to be 0.40% or less, so the upper limit was set to 0.40%. The preferred amount of Si is 0.10 to 0.40%. The deoxidation of the steel can be supplemented with another element, for example, Mn or Al. In this case, Si may be added without addition.
[0013]
Mn: An element that is necessary and effective as a deoxidizing element for steel and enhances the hardenability of austenite, but, like Si, an element that causes internal oxidation just below the surface during hot rolling, annealing, and heat treatment. But also. In order to prevent internal oxidation in various steps, the Mn content needs to be 0.60% or less, so the upper limit was set to 0.60%. The preferred amount of Mn is 0.20 to 0.60%. Note that deoxidation of steel can be supplemented by another element, for example, Si or Al. In this case, Mn may not be added.
[0014]
Cr: Indispensable as an element for improving the hardenability, strength and toughness of steel and as an element for suppressing the diffusion of C. Prevents carburizing or decarburization of the welded part (carburizing on the blade side, decarburizing on the substrate side) during welding of the material of the present invention and high-speed steel, and also by the same high-temperature quenching and tempering heat treatment as the blade part In order to maintain sufficient strength and toughness, the Cr content needs to be 1.00% or more. However, even if Cr is contained in an amount exceeding 3.00%, the effect of preventing carburization and decarburization of the above-mentioned welds and the effect of increasing strength and toughness are both saturated, and the productivity of intermediate products is significantly reduced. Therefore, the upper limit was set to 3.00%.
[0015]
Mo: As an element for improving the hardenability, strength and toughness of steel, and as an element for suppressing the diffusion of C, it is indispensable like Cr. Mo content must be 0.40% or more to prevent carburization or decarburization of the weld with high-speed steel and maintain sufficient strength and toughness even with the same high-temperature quenching and tempering heat treatment as the blade. It is. However, when the Mo content exceeds 1.00%, both the effects of preventing carburization and decarburization at the weld with high-speed steel and the effects of increasing strength and toughness are saturated, and the productivity of intermediate products is markedly reduced. Therefore, the upper limit was set to 1.00%.
[0016]
V: Effectively acts as an element for improving the strength and toughness of steel by the action of reducing the austenite crystal grain size, and as an element for suppressing the diffusion of C. In order to prevent carburization and decarburization in the weld with high-speed steel, and to maintain sufficient strength and toughness even with the same high-temperature quenching and tempering heat treatment as the blade, the V content must be 0.20% or more. It is. However, even if V is contained in excess of 0.40%, the effect of preventing carburization and decarburization of the weld with high-speed steel and the effect of increasing strength and toughness are both saturated, and the productivity of intermediate products is reduced. Since it is significantly reduced, the upper limit is set to 0.40%.
[0017]
P: The P content is preferably as low as possible because it segregates at the crystal grain boundaries and decreases the toughness after quenching and tempering. Since the toughness required as a metal saw substrate material can be achieved by setting the P content to 0.010% or less, the upper limit is set to 0.010%.
[0018]
S: Nonmetallic inclusions mainly composed of MnS are formed, which adversely affect the workability, strength and toughness of steel. In particular, in a rolled material, MnS expands in the rolling direction, so that in-plane anisotropy of workability, strength, and toughness of the steel appears significantly. In order to prevent such an adverse effect of S, the amount of S must be made 0.006% or less, so the upper limit is made 0.006%.
[0019]
Al: A necessary and effective element as a deoxidizing element of steel, it is also effective as an element that combines with N in steel to form AlN and suppresses abnormal growth of austenite crystal grains during heat treatment. Since the effect of these Al is exhibited by containing 0.010% or more as acid-soluble Al, the lower limit is set to 0.010%. The action of these Al is sufficient in the amount up to 0.10% as the acid-soluble Al. Even if more Al is added, not only the production cost is increased unnecessarily but also the surface caused by Al is increased. Since the increase of flaws and the like is not a good measure, the upper limit is set to 0.10%.
[0020]
(Manufacturing conditions)
In the production of a special steel metal saw substrate having a composition as described above, the present invention melts the steel in a converter or an electric furnace, adjusts the composition through a vacuum degasser, and continuously casts the steel. Continuously cast slab is produced by the equipment, and this slab is manufactured into a cold rolled coil similar to ordinary steel through a hot rolling process, a continuous pickling process, and a cold rolling process (depressing with annealing, if necessary). However, it has been found that even such a special steel can be manufactured in an acid pickling line without breakage by controlling the structure of the steel under appropriate hot rolling conditions. Hereinafter, the hot rolling conditions employed in the present invention will be described.
[0021]
When hot rolling is performed using a slab of the steel cooled to room temperature or a high-temperature slab after the continuous casting manufactured by the continuous casting facility, segregation is remarkable in the slab as it is continuously cast, and the original performance of the steel is exhibited. In order to achieve this, it is important to reduce segregation as much as possible at the stage of hot rolling. For this purpose, the slab heating temperature must be 1200 ° C. or higher. However, even when heating to a temperature exceeding 1350 ° C, the effect of reducing segregation saturates, and instead the scale loss increases and the required energy only increases unnecessarily, so the upper limit of the slab heating temperature is 1350 ° C. .
[0022]
On the other hand, the hot-rolled steel strip wound into a coil through the hot-rolling process is oxidized on the surface of the hot-rolled sheet in the continuous pickling process before moving to the cold-rolling process where annealing and cold rolling are repeated. The scale must be removed. In this pickling line, since a threading path is constituted by rolls of various radii, a steel strip passing therethrough must have ductility and toughness that can pass without breaking. However, since the steel having the above-mentioned composition has a slow transformation of ferrite and pearlite due to its transformation characteristics, the hot-rolled steel strip has a supercooled transformation structure and exhibits a very high strength (for example, 1000 N / mm ² or more). ), It may be broken in the pickling line.
[0023]
The present inventors have repeated tests to solve this problem, but when hot-rolling the slab heated to the above-mentioned temperature, the hot-rolling finishing temperature was set to 800 ° C to 900 ° C and the winding temperature was set to 400 ° C to 600 ° C. If hot rolling is carried out at a temperature of ℃ and a total draft of 98% or more from rough rolling to finish rolling, it becomes a hot-rolled steel strip having a fine bainite single phase structure substantially containing no ferrite, and the above-mentioned problems can be solved. all right.
[0024]
Explaining the meaning of these hot rolling conditions, when the finishing temperature is set to 900 ° C. or less and the total rolling reduction in the rough rolling to the finish rolling is set to 98% or more, the austenite immediately after the finish rolling is in an unrecrystallized state and crystallized. The grains become finer. Therefore, a fine bainite structure is obtained in the subsequent cooling process.
[0025]
On the other hand, when the finishing temperature is set to a high temperature exceeding 900 ° C., or when the total reduction in the rough rolling to the finish rolling is set to less than 98%, the austenite crystal grains at the stage of finishing the finishing rolling become coarse and recrystallization occurs. It proceeds and a fine bainite structure cannot be finally obtained.
[0026]
On the other hand, when the finishing temperature is set to a low temperature of less than 800 ° C., the ferrite transformation is promoted, and a hot-rolled steel strip in which a mixed structure of bainite and ferrite is formed is obtained. In this case, when passing through the pickling line, the strain is concentrated on the soft ferrite structure, and the sheet is easily broken. In addition, the deformation resistance of austenite also increases in the hot rolling stage, and the rolling load increases, which unnecessarily increases the production cost.
[0027]
With regard to the winding temperature, when the winding temperature is lower than 400 ° C, bainite transformation does not proceed sufficiently, martensite is formed, the material of the hot-rolled steel strip becomes hard, and a sheet break occurs during the passing of the pickling line. It will be easier. If the winding temperature is higher than 600 ° C., ferrite and pearlite are formed, and a bainite single phase structure is not formed. Therefore, the hot-rolling winding temperature of the steel of the present invention needs to be in the range of 400 to 600 ° C.
[0028]
【Example】
[Example 1]
Steel having the chemical composition values shown in Table 1 was melted in a converter and continuously cast into a 200 mm thick slab. This slab was heated to 1250 ° C., and hot-rolled at a hot-rolling finish temperature of 850 ° C. and a winding temperature of 550 ° C. using a normal hot strip mill to produce a hot-rolled steel strip having a sheet thickness of 2.8 mm.
[0029]
A test material was cut out from each hot-rolled steel strip, pickled, spheroidized, and further quenched and tempered. The quenching was performed by holding at 1260 ° C. for 3 minutes and then cooling in an oil bath at 70 ° C. Tempering was repeated three times at 560 ° C. for 60 minutes. The hardness and impact value of each heat-treated material were measured, and the presence or absence of internal oxidation of the surface layer was examined. The results are shown in Table 1.
[0030]
[Table 1]

[0031]
The following can be seen from the results in Table 1. Comparative steel B having a lower C content than specified in the present invention has a low hardness after quenching and tempering, does not provide the strength required for a metal saw substrate, and has a high Mn content that easily forms oxides. Therefore, internal oxidation was also observed on the surface layer.
[0032]
Comparative steel C, which has a higher C content than specified in the present invention, has sufficient strength but low toughness, and has an internal oxidation due to a high Si content that easily forms an oxide. Therefore, it cannot be used as a metal saw substrate.
[0033]
Since the comparative steel E has a low content of carbide forming elements such as Cr, Mo, and V, the strength after quenching and tempering cannot be secured. On the other hand, Comparative Steel F contains more of these carbide-forming elements than specified in the present invention, but does not show significant improvement in properties in both strength and toughness as compared with the steel of the present invention. It can be seen that excessive addition of elements not only impairs productivity but also is economically disadvantageous.
[0034]
On the other hand, all of the steels A, D and G of the present invention have the necessary strength and toughness as a metal saw substrate after quenching and tempering, and no internal oxidation of the surface layer is observed.
[0035]
[Example 2]
Steel A in Table 1 was melted in a converter and continuously cast into six slabs having a thickness of 100 to 200 mm. As shown in Table 2, these slabs were heated at 1200 to 1300 ° C., finished at 770 to 920 ° C., wound at 380 to 630 ° C., and reduced at a total reduction of 96.6 to 98.5. Hot rolling was performed by a normal hot strip mill to produce a hot-rolled steel strip having a thickness of 3.0 to 3.6 mm.
[0036]
Specimens were cut out from each of the obtained hot-rolled steel strips, and the hot-rolled metallographic structure of the steel was examined. The results are shown in Table 2. The bending test was evaluated based on the presence or absence of breakage when projecting and bending with a punch having a radius of 30 mm was repeated 20 times. The presence or absence of breakage in this test is a measure of the ductility and toughness required for passing through a continuous pickling process, and those that do not break can be passed sufficiently.
[0037]
[Table 2]

[0038]
The following can be seen from the results in Table 2.
[0039]
In Comparative Example c, continuous casting was performed on a slab having a thickness of 200 mm, and then hot-rolled to a thickness of 3.4 mm. However, since the finishing temperature was low, the metal structure of the hot-rolled material was two layers of ferrite and bainite. In the bending test, the strain was concentrated on the soft ferrite portion, which led to fracture.
[0040]
In Comparative Example d, hot rolling was performed from a slab having a thickness of 100 mm to a plate thickness of 3.4 mm. However, since the finishing temperature was high and the total rolling reduction was low, the structure was coarse bainite, and the bending characteristics were reduced.
[0041]
Comparative Examples e and f were hot rolled from a 200 mm thick slab to a sheet thickness of 3.0 mm and 3.6 mm, respectively. In Comparative Example e, since the winding temperature was low, martensite was formed in addition to bainite. The structure became fractured, and the ductility of the material decreased, and it broke in the bending test. In Comparative Example f, since the winding temperature was high, the structure was such that ferrite and pearlite were formed.
[0042]
On the other hand, in Examples a and b of the present invention, the slab having a thickness of 200 mm was hot-rolled to a thickness of 3.0 mm and 3.6 mm, respectively, and was hot-rolled under the conditions specified in the present invention. Therefore, each of them has a fine bainite single-phase structure and shows excellent ductility without breaking even in a bending test.
[0043]
Thus, the hot-rolled steel strip according to the method of the present invention can be stably passed through the pickling line, and large-lot production has become possible. The pickled hot-rolled steel sheet is formed into a cold-rolled steel strip having a required thickness by annealing and cold rolling in the next step, and is used for a metal saw substrate.
[0044]
【The invention's effect】
As described above, according to the present invention, a high-strength and high-toughness steel plate satisfying the characteristics required for a metal saw substrate can be manufactured on a normal large-lot-type steel strip manufacturing line, and a low-cost, high-quality metal saw substrate can be manufactured. Material can be provided.

Claims

In weight percent,
C: 0.30 to 0.60%,
Si: 0.40% or less,
Mn: 0.60% or less,
Cr: 1.00 to 3.00%,
Mo: 0.40-1.00%,
V: 0.20 to 0.40%,
P: 0.010% or less,
S: 0.006% or less,
Al: 0.010 to 0.10% as acid-soluble Al
The method for producing a steel sheet for a metal saw substrate comprising Fe and the balance consisting of Fe and unavoidable impurities in a steel strip production line through at least a continuous casting step, a hot rolling step and a continuous pickling step. The slab heating temperature is 1200 ° C to 1350 ° C
Finishing temperature: 800 to 900 ° C,
Winding temperature: 400 to 600 ° C,
A method for producing a steel sheet for a metal saw substrate, which is performed under the condition of a total rolling reduction in rough rolling to finish rolling: 98% or more to obtain a hot-rolled steel strip having a bainite single-phase structure.

The method for producing a steel sheet for a metal saw substrate according to claim 1, wherein Si: 0.10 to 0.40%.

The method for producing a steel sheet for a metal saw substrate according to claim 1 or 2, wherein Mn is 0.20 to 0.60%.