JP3610885B2 - Mold powder and continuous casting method - Google Patents
Mold powder and continuous casting method Download PDFInfo
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- JP3610885B2 JP3610885B2 JP2000171155A JP2000171155A JP3610885B2 JP 3610885 B2 JP3610885 B2 JP 3610885B2 JP 2000171155 A JP2000171155 A JP 2000171155A JP 2000171155 A JP2000171155 A JP 2000171155A JP 3610885 B2 JP3610885 B2 JP 3610885B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Description
【0001】
【発明の属する技術分野】
本発明は、鋳型内の溶鋼表面に添加されるモールドパウダに関し、さらにこのモールドパウダを用いる連続鋳造方法に関する。
【0002】
【従来の技術】
鋼の連続鋳造では、鋳型内の溶鋼表面にモールドパウダを添加して鋳造する。通常、モールドパウダには、複数種類の酸化物、フッ素化合物、炭素などの粉体を混合したものが用いられる。
【0003】
鋳型内の溶鋼表面に添加されたモールドパウダでは、溶鋼からの受熱により、溶鋼表面との接触部において溶融層が形成される。この溶融層は、鋳型内壁と凝固殻との間隙に流入し、フィルムを形成する。このフィルムは、鋳型により冷却された固相部分と、液相部分との二相からなる。
【0004】
モールドパウダは、溶融層およびフィルムとなった状態において、以下に挙げる役割を担う。
▲1▼溶鋼の保温および酸化防止
▲2▼溶鋼中気泡または介在物の吸収
▲3▼鋳型内壁と凝固殻との潤滑性の確保
▲4▼凝固殻の冷却速度の調整
連続鋳造による鋳片の表面品質に及ぼすモールドパウダの影響は大きく、鋳片表面に発生するディプレッション、または縦割れに対しては、上記役割の中でも、▲4▼の凝固殻の冷却速度の調整が重要である。鋳型内の凝固殻の冷却速度を均一化することにより、凝固殻の厚さは幅方向に均一になり、凝固収縮により生じる応力が緩和され、表面に発生するディプレッションまたは縦割れの発生を抑制できる。
【0005】
モールドパウダのフィルム中に、その冷却過程で結晶が析出すると、フィルムの伝熱抵抗が大きくなることから、鋳片の凝固収縮が抑制され鋳型壁への密着性が増し、鋳型内の凝固殻の不均一冷却が防止できることから、従来より、フィルム中に結晶析出を促進する方法が提案されてきた。
【0006】
たとえば 特開平5−15955号公報には、モールドパウダ中に含有されるCaOと、CaF2 として存在すると推定されるCa分をCaOに換算したものとの和として、下記(C)式で定義されるT.CaOのSiO2 に対する質量%の比T.CaO/SiO2 を0.9〜1.3程度に大きくし、フィルム中に結晶を析出させて、鋳型内の凝固殻の冷却速度を均一にし、かつ緩冷却することが提案されている。
【0007】
しかし、単にモールドパウダの塩基度(CaO/SiO2 、またはT.CaO/SiO2 )を高めて、フィルム中に結晶を多く析出させる方法では、結晶が析出した部分のフィルムの体積が収縮し、鋳型と凝固殻との間に空隙が生じやすくなる。鋳型と凝固殻との間に空隙が生じると、伝熱抵抗が飛躍的に増大し、凝固殻に局部的な凝固遅れを生じる場合がある。凝固遅れが生じた凝固殻の部分では、縦割れなどが発生しやすい。
【0008】
そこで、特開平7−214263号公報には、モールドパウダの塩基度を0.6〜0.9とし、結晶析出の促進剤であるZrO2 、TiO2 、CeO2 の合計の含有率を1質量%以下とし、かつ凝固点を1150℃以上とすることにより、モールドパウダのフィルム中の結晶析出量が過度になることなく、適正に保つ方法が提案されている。これにより、鋳型内の凝固殻の冷却速度の均一化が促進され、表面に発生するディプレッションまたは縦割れの発生が抑制されるのが期待できる。
【0009】
しかし、この方法では、鋳型内の溶鋼中にAl2 O3 、MnO等の酸化物が増加する場合があり、これらの酸化物が鋳型内の凝固殻に捕捉され、鋳片表層部の清浄性が悪くなりやすい。これら鋳片を素材として熱間圧延する製品に表面疵などが発生しやすい。
【0010】
【発明が解決しようとする課題】
本発明は、鋳片表面のディプレッションまたは縦割れの発生を防止でき、さらに、鋳片表層部の清浄性も良好で、品質の良好な鋳片を得ることができるモールドパウダ、およびそのモールドパウダを用いる連続鋳造方法を提供することを目的とする。
【0011】
【課題を解決するための手段】
本発明の要旨は、下記(1)および(2)に示すモールドパウダ、および下記(3)に示す連続鋳造方法にある。
(1)CaO、SiO2 、Al2O3およびフッ素化合物を基本成分とするモールドパウダであって、CaOのSiO2に対する質量%の比CaO/SiO2が1.1〜1.5であり、Al2O3を5〜15質量%、アルカリ金属を酸化物換算含有率の合計で5質量%以下、ZrO2を1質量%以下、TiO2を0〜8質量%、MgOを1質量%以下およびFを4〜12質量%含有し、1300℃における粘度が2〜6poise、凝固点が1100℃以上である連続鋳造用のモールドパウダ。
(2)Al2O3、TiO2およびFの含有率が、下記(A)式を満足する上記(1)に記載の連続鋳造用のモールドパウダ。
2≦(Al2O3)×(TiO2)≦10+15×(F)・・・(A)
ここで、(Al2O3):モールドパウダ中のAl2O3含有率(質量%)
(TiO2):モールドパウダ中のTiO2含有率(質量%)
(F):モールドパウダ中のF含有率(質量%)
(3)上記(1)または(2)に記載のモールドパウダを用いる連続鋳造方法であって、下記(B)式で定義される溶鋼の化学組成Cpとモールドパウダ中のAl2O3含有率との間の関係が、下記(C)式または(D)式を満足する条件で鋳造する連続鋳造方法。
Cp=C+0.02×Mn+0.04×Ni−0.01×Si +0.02×Cr+0.07×S・・・(B)
ここで、C、Mn、Ni、Si、CrおよびS:溶鋼中の含有率(質量%)
|Cp−0.12|≦0.05の場合;
5+2000×|Cp−0.12|2 ≦(Al2O3)≦ 10+2000×|Cp−0.12|2 ・・・(C)
|Cp−0.12|>0.05の場合;
10≦(Al2O3)≦15 ・・・(D)
ここで、|Cp−0.12|:Cpの値から0.12を引いた値の絶対値
(Al2O3):モールドパウダ中のAl2O3含有率(質量%)
本発明者らは、下記(a)の知見に基づいて、下記(b)および(c)の対策を採ることにより前述の課題を解決した。
(a)モールドパウダの塩基度が0.6〜0.9と低い場合に、鋳型内の溶鋼中にAl2 O3、MnO等の酸化物が増加するのは、溶融層中のSiO2の活量が高くなり、鋳型内の溶鋼とモールドパウダの溶融層との界面において、Al、Mn等の溶鋼中成分が酸化されやすくなるからである。
【0012】
そこで、鋳型内の凝固殻の冷却速度を均一化するには、モールドパウダの塩基度を高めることが重要である。しかし、モールドパウダの塩基度を高め、フィルム中に結晶を多く析出させる方法では、鋳型と凝固殻との間に空隙が生じ、凝固殻に局部的な凝固遅れを生じやすいという課題がある。
【0013】
本発明者らは、CaO、SiO2 およびフッ素化合物を基本成分とするモールドパウダにおいて、CaOのSiO2 に対するCaOの質量%の比CaO/SiO2 が1.1〜1.5であっても、Al2 O3 を5〜15質量%配合することにより、フィルム中の結晶の析出が過度になることなく、鋳型内の凝固殻冷却を均一な状態に維持することが可能であることを見いだした。両性酸化物であるAl2 O3 を配合すると、塩基度の高いモールドパウダの溶融層中では、Al2 O3 が酸性的な存在となり、フィルム中の結晶の析出が適度に抑制されるのである。(b)そこで、本発明のモールドパウダでは、上記(a)の知見に基づき、CaO、SiO2 、Al2 O3 およびフッ素化合物を基本成分とし、前述の(1)に示す組成を有するモールドパウダとする。
【0014】
これにより、塩基度が1.1〜1.5と高くても、フィルム中の結晶の析出を適度に抑制し、鋳型内の凝固殻冷却を均一化できる。さらに、塩基度が高いので、鋳型内の溶鋼中にAl2 O3 、MnOなどの酸化物が増加することを防止できる。
(c)本発明の方法では、前述の(B)式で定義される溶鋼の化学組成Cpとモールドパウダ中のAl2 O3 含有率との間の関係が、前述の(C)式または(D)式を満足する条件で鋳造する。
【0015】
|Cp−0.12|は、鋼の化学組成が亜包晶反応を起こしやすい組成かどうかを示す指標である。亜包晶反応を起こす鋼の鋳片表面に縦割れが発生しやすいことは、よく知られている。そこで、|Cp−0.12|≦0.05の場合、すなわち、亜包晶反応を起こしやすい鋼では、モールドパウダ中のAl2 O3 含有率を、前述の(C)式を満足するように、低い含有率とする。
【0016】
Al2 O3 含有率を低くくして、フィルム中の結晶の析出を適度に増加させ、亜包晶反応に伴う凝固殻収縮を抑制し鋳型壁への密着性を高めることにより、鋳型内の凝固殻不均一冷却を抑制し、鋳片表面の縦割れの発生を防止するのである。
【0017】
【発明の実施の形態】
本発明のモールドパウダおよびこのモールドパウダを用いた連続鋳造方法について、以下に具体的に説明する。
【0018】
本発明のパウダは、CaO、SiO2 、Al2 O3 およびフッ素化合物を基本組成としている。その含有率は、CaOが25〜50%程度、SiO2 が20〜40%程度、Al2 O3 が5〜15%、Fが4〜12%である。さらに、アルカリ金属を酸化物換算含有率の合計で5質量%以下、ZrO2 を1質量%以下含有し、また、必要に応じてTiO2 を0〜8質量%の範囲で含有することができる。
【0019】
本発明のパウダを製造する際に使用する原料は、一般的に使用されているもので構わない。CaO原料として生石灰、石灰石、セメント、SiO2 原料としては珪砂、軽藻土、Al2 O3 原料としてはアルミナ、F原料としては蛍石、アルカリ金属の酸化物として、たとえば、Na2 O原料としてはソーダ灰、炭酸ナトリウム、フッ化ナトリウム、TiO2 原料としてはルチルサンド、ZrO2 原料としてはジルコンサンドなどが挙げられる。また、原料の粒度は100μm以下の粉末が望ましい。なお、これらの原料にはFe2 O3 、Fe3 O4 等の酸化物が含有され、パウダにも不可避的に含まれるようになるが、これらの不純物が存在しても、とくに差し支えない。
モールドパウダのCaO、SiO2 の含有率についてはすでに述べたが、これらの含有率は目安を示すものであり、本発明では、CaO/SiO2 の値を1.1〜1.5とする。塩基度が1.1未満では、溶鋼酸化の抑制効果は小さい。また、塩基度が1.5を超えると、フィルム中に過度に結晶が析出し、さらに、凝固点が過剰に高くなるので、鋳型内における潤滑性の悪化や凝固殻の冷却が不均一になりやすいという弊害を生じる。
【0020】
モールドパウダ中のAl2 O3 含有率は5〜15質量%とする。5質量%未満では、フィルム中に結晶が過度に析出し、鋳型内の凝固殻の冷却が不均一になりやすい。また、15質量%を超えると、モールドパウダの溶融層の粘度が過度に上昇したり、凝固点が高くなり、溶融層が鋳型と凝固殻の隙間に流れ込みにくくなる。
【0021】
モールドパウダ中のアルカリ金属の酸化物換算含有率の合計は5質量%以下とする。アルカリ金属の酸化物は、通常の原料配合によってモールドパウダ中に含有される。ただし、5質量%を超えて含有すると、鋳型内において未溶融のモールドパウダが焼結しやすく、鋳型内溶鋼保温性の悪化を来す。さらに、溶融層が鋳型と凝固殻の隙間に均一に流れ込みにくくなる。したがって、アルカリ金属の酸化物換算含有率の合計を5質量%以下とする。
【0022】
モールドパウダ中のZrO2 の含有率は1質量%以下とする。ZrO2 は、TiO2 の原料を配合する場合に、モールドパウダ中に含有される。ただし、モールドパウダ中に数%程度の少量が存在した状態でも、結晶の析出が促進され、また凝固点の上昇が著しい。したがって、ZrO2 の含有率は1質量%以下とする。
【0023】
モールドパウダ中のFの含有率は4〜12質量%とする。Fは、凝固点の調整および適度の結晶析出を目的として含有させる。4質量%未満では、その効果が小さい。12質量%を超えると、溶融層の粘度が過度に低下し、溶鋼中に巻き込まれやすいばかりか、鋳型と凝固殻との隙間に過度に流れ込み、かえって鋳片表面に縦割れが発生しやすい。
【0024】
モールドパウダ中には、必要に応じてTiO2 を添加する。その際、TiO2 の含有率は0〜8質量%とする。TiO2 は、従来、フィルム中への結晶析出の促進剤として用いられているが、本発明では、適度のTiO2 添加により、凝固点の低下に著しい効果があり、さらに、凝固点が低下しても、粘度が低下しにくいことを見出した。そこで、粘度を下げずに、凝固点を低下させる目的で、TiO2 を0〜8質量%含有させることができる。
【0025】
モールドパウダの凝固点は1100℃以上とし、1300℃における粘度は2〜6poiseとする。また、望ましい凝固点の上限は1300℃である。凝固点を上記範囲とすることにより、フィルム中の結晶析出サイトである固相部分の厚みを確保することができる。また、粘度を上記範囲とすることにより、溶融モールドパウダが鋳型内の溶鋼中に巻き込まれたりすることを防止できる。
【0026】
モールドパウダ中のAl2 O3 、TiO2 およびFの含有率は、前述の(A)式を満足する範囲とするのが望ましい。本発明者らは、TiO2 の望ましい含有率は、Al2 O3 およびFの含有率により影響を受けることを見出した。つまり、TiO2 およびAl2 O3 の含有率の積を一定範囲内とすることにより、モールドパウダの凝固点、または溶融層の粘度を適正に調整することが容易になるのである。さらに、TiO2 およびAl2 O3 の含有率の積の適正な範囲が、F含有率の影響を受けることも見出した。TiO2 およびAl2 O3 の含有率の積が2未満では、凝固点の低下量が小さく、前述の(A)式の右辺の値を超えると、凝固点が高くなりやすい。
【0027】
本発明の方法では、前述の(B)式で定義される溶鋼の化学組成Cpとモールドパウダ中のAl2 O3 含有率との間の関係が、前述の(C)式または(D)式を満足する条件で鋳造する。
|Cp−0.12|≦0.05の場合、すなわち、亜包晶反応を起こしやすい鋼では、モールドパウダ中のAl2 O3 含有率を、前述の(C)式を満足するように、低い含有率とする。Al2 O3 含有率を低くくして、フィルム中の結晶の析出を適度に増加させ、亜包晶反応に伴う凝固殻収縮を抑制し鋳型壁への密着性を高めることにより、鋳型内の凝固殻不均一冷却を抑制し、鋳片表面の縦割れの発生を防止するのである。
【0028】
|Cp−0.12|>0.05の場合には、とくに、Al2 O3 含有率を低くしなくても、鋳片表面の縦割れの発生を防止できる。むしろ、Al2 O3 含有率を10〜15質量%とやや多くすることにより、モールドパウダの溶融層の粘度を適度に高くする、とともにフィルム中の過度な結晶析出を抑制し鋳型内の凝固殻冷却を均一化するのがよい。
【0029】
【実施例】
垂直曲げ型連続鋳造機を用いて、厚さ230mm、幅1220mmの鋳片に、速度1.1m/分または1.4m/分で鋳造した。用いた鋼の化学組成を表1に示す。鋼は低炭素鋼および亜包晶系の中炭素鋼であり、表1には、本発明の方法で定義する化学組成Cpを示す。低炭素鋼のCpは0.043質量%で、中炭素鋼のCpは0.117質量%であり、それぞれ|Cp−0.12|は、低炭素鋼が0.077、中炭素鋼が0.003であり、また、中炭素鋼の|Cp−0.12|2 は、0.000009となる。したがって、低炭素鋼を鋳造する場合の望ましいモールドパウダ中のAl2 O3 含有率は、前述の(D)式より10〜15質量%、中炭素鋼を鋳造する場合の望ましいモールドパウダ中のAl2 O3 含有率は、前述の(C)式より5〜10質量%となる。
【0030】
【表1】
試験に用いたモールドパウダの組成を表2に示す。モールドパウダaは塩基度と粘度、モールドパウダbは塩基度、モールドパウダcはAl2 O3 含有率、モールドパウダdはAl2 O3 含有率と粘度、モールドパウダeはTiO2 含有率が、それぞれ発明で規定する条件を外れているモールドパウダである。試験条件および試験結果を表3に示す。
【0031】
【表2】
【表3】
表3中に示す指標の中で、「のろピン」は、鋳片表面をスカーフィングした際に認められたのろかみ疵およびピンホール疵の発生個数である。指標A:なし、指標B:1〜5個、指標C:6〜10個、指標D:11〜20個、指標E:21〜50個、指標F:51個以上を示し、指標AおよびBは、とくに問題のない発生個数である。また、「縦割れ」は、鋳造した鋳片のうち、縦割れの発生した分子の割合である。指標A:3%未満、指標B:3%以上6%未満、指標C:6%以上10%未満、指標D:10%以上であり、指標AおよびBは、とくに問題のない発生状況である。さらに「銅板温度変動」は、鋳造中における鋳型銅板に埋設した熱電対の温度変動量であり、指標小:±3℃未満、指標中:±10℃未満、指標大:±10℃以上であり、指標小および中は、とくに問題のない状況である。
【0032】
低炭素鋼を速度1.4m/分で鋳造した試験では、比較例の試験No.6と比べて、本発明例の試験No.1およびNo.3〜5では、いずれものろかみ疵およびピンホール疵が減少し、鋳片表面品質の向上していることがわかる。比較例の試験No.7およびNo.10では、凝固点がいずれも1300℃以上と高く、鋳造に使用出来なかった。比較例の試験No.8およびNo.9では、結晶析出が過多あるいは不安定であるため、鋳型銅板温度の変動が大きく、縦割れが発生するものもあった。また、凝固点または粘度が高いために潤滑性が悪く、鋳片表面には拘束痕等の不良部が多く見られた。
【0033】
中炭素鋼を速度1.1m/分で鋳造した試験では、比較例の試験No.16と比べて、本発明例の試験No.11および〜No.13〜15では、いずれものろかみ疵およびピンホール疵、縦割れ、および鋳型銅板温度の変動がいずれも減少し、鋳片表面品質の向上していることがわかる。比較例の試験No.17およびNo.20では、凝固点がいずれも1300℃以上と高く、鋳造に使用出来なかった。比較例の試験No.18およびNo.19では、結晶析出が過多あるいは不安定であるため、鋳型銅板温度の変動が大きく、No.19では縦割れも発生した。
【0034】
【発明の効果】
本発明のモールドパウダおよびそのモールドパウダを用いる本発明の連続鋳造方法の適用により、鋳片表面にディプレッションまたは縦割れの発生のない、さらに、鋳片表層部の清浄性も良好な鋳片を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mold powder added to the surface of molten steel in a mold, and further relates to a continuous casting method using the mold powder.
[0002]
[Prior art]
In continuous casting of steel, mold powder is added to the surface of the molten steel in the mold for casting. In general, a mixture of powders of a plurality of types of oxides, fluorine compounds, carbon and the like is used for the mold powder.
[0003]
In the mold powder added to the molten steel surface in the mold, a molten layer is formed at the contact portion with the molten steel surface by receiving heat from the molten steel. This molten layer flows into the gap between the mold inner wall and the solidified shell to form a film. This film consists of two phases, a solid phase portion cooled by a mold and a liquid phase portion.
[0004]
The mold powder plays the following role in the state of being a molten layer and a film.
(1) Heat insulation and prevention of oxidation of molten steel (2) Absorption of bubbles or inclusions in molten steel (3) Ensuring lubricity between mold inner wall and solidified shell (4) Adjustment of cooling rate of solidified shell The influence of the mold powder on the surface quality is great, and the adjustment of the cooling rate of the solidified shell (4) is important for the depletion or vertical crack generated on the surface of the slab, among the above roles. By uniformizing the cooling rate of the solidified shell in the mold, the thickness of the solidified shell becomes uniform in the width direction, the stress caused by solidification shrinkage is relieved, and the occurrence of depletion or vertical cracks occurring on the surface can be suppressed. .
[0005]
If crystals precipitate in the film of the mold powder during the cooling process, the heat transfer resistance of the film increases, so the solidification shrinkage of the slab is suppressed and the adhesion to the mold wall is increased, and the solidified shell in the mold is Since non-uniform cooling can be prevented, methods for promoting crystal precipitation in a film have been proposed.
[0006]
For example, in Japanese Patent Laid-Open No. 5-15955, the sum of CaO contained in mold powder and CaO estimated to exist as CaF 2 is defined by the following formula (C). T. Ratio of mass% CaO to SiO 2 The CaO / SiO 2 is increased to about 0.9 to 1.3, to precipitate crystals in the film, a uniform cooling rate of the solidified shell in the mold, and be slow cooling has been proposed.
[0007]
However, by simply increasing the basicity of the powder (CaO / SiO 2 or T.CaO / SiO 2 ) and precipitating a large amount of crystals in the film, the volume of the film where the crystals are deposited shrinks. A gap is likely to be generated between the mold and the solidified shell. When an air gap is generated between the mold and the solidified shell, the heat transfer resistance increases dramatically, and a local solidification delay may occur in the solidified shell. Longitudinal cracks are likely to occur in the solidified shell portion where the solidification delay has occurred.
[0008]
Therefore, in JP-A-7-214263, the basicity of the mold powder is 0.6 to 0.9, and the total content of ZrO 2 , TiO 2 , and CeO 2 that is an accelerator for crystal precipitation is 1 mass. % And a freezing point of 1150 ° C. or higher has been proposed to keep the amount of crystals precipitated in the film of the mold powder appropriately without being excessive. As a result, the uniform cooling rate of the solidified shell in the mold is promoted, and it can be expected that the occurrence of depletion or vertical cracks occurring on the surface is suppressed.
[0009]
However, in this method, oxides such as Al 2 O 3 and MnO may increase in the molten steel in the mold, and these oxides are trapped by the solidified shell in the mold, and the cleanliness of the slab surface layer portion. Tends to get worse. Surface flaws are likely to occur in products that are hot-rolled using these slabs as raw materials.
[0010]
[Problems to be solved by the invention]
The present invention provides a mold powder capable of preventing the occurrence of depletion or vertical cracks on the surface of a slab, and having a good quality slab with good cleanliness of the surface part of the slab, and its mold powder. It aims at providing the continuous casting method to be used.
[0011]
[Means for Solving the Problems]
The gist of the present invention resides in the mold powder shown in the following (1) and (2) and the continuous casting method shown in the following (3).
(1) CaO, and SiO 2, Al 2 O 3 and fluorine compound a mold powder having a basic component, the ratio CaO / SiO 2 mass% with respect to SiO 2 of CaO is 1.1 to 1.5, al 2 O 3 5 to 15 wt%, 5 wt% of an alkali metal in a total of oxide conversion content below the ZrO 2 1 wt% or less, the TiO 2 0 to 8 mass%, 1 mass% of MgO And 4 to 12% by mass of F, a mold powder for continuous casting having a viscosity at 1300 ° C. of 2 to 6 poise and a freezing point of 1100 ° C. or higher.
(2) The mold powder for continuous casting according to the above (1), wherein the contents of Al 2 O 3 , TiO 2 and F satisfy the following formula (A).
2 ≦ (Al 2 O 3 ) × (TiO 2 ) ≦ 10 + 15 × (F) (A)
Here, (Al 2 O 3 ): Al 2 O 3 content (% by mass) in the mold powder
(TiO 2 ): TiO 2 content in mold powder (mass%)
(F): F content (% by mass) in the mold powder
(3) A continuous casting method using the mold powder according to (1) or (2) above, wherein the chemical composition Cp of the molten steel defined by the following formula (B) and the Al 2 O 3 content in the mold powder A continuous casting method in which casting is performed under a condition that satisfies the following formula (C) or (D).
Cp = C + 0.02 × Mn + 0.04 × Ni−0.01 × Si + 0.02 × Cr + 0.07 × S (B)
Here, C, Mn, Ni, Si, Cr and S: Content ratio (% by mass) in molten steel
When | Cp−0.12 | ≦ 0.05;
5 + 2000 × | Cp−0.12 | 2 ≦ (Al 2 O 3 ) ≦ 10 + 2000 × | Cp−0.12 | 2 (C)
When | Cp−0.12 |>0.05;
10 ≦ (Al 2 O 3 ) ≦ 15 (D)
Here, | Cp−0.12 |: absolute value obtained by subtracting 0.12 from the value of Cp (Al 2 O 3 ): Al 2 O 3 content (% by mass) in the mold powder
Based on the findings of (a) below, the present inventors have solved the above-mentioned problems by taking the measures of (b) and (c) below.
(A) When the basicity of the mold powder is as low as 0.6 to 0.9, oxides such as Al 2 O 3 and MnO increase in the molten steel in the mold because of the SiO 2 in the molten layer. This is because the activity increases and components in the molten steel such as Al and Mn are easily oxidized at the interface between the molten steel in the mold and the molten layer of the mold powder.
[0012]
Therefore, in order to make the cooling rate of the solidified shell in the mold uniform, it is important to increase the basicity of the mold powder. However, the method of increasing the basicity of the mold powder and precipitating a large amount of crystals in the film has a problem that voids are generated between the mold and the solidified shell, and local solidification delay tends to occur in the solidified shell.
[0013]
The present inventors have, CaO, SiO 2 and fluorine compound in the mold powder having a basic composition, mass% ratio CaO / SiO 2 of CaO with respect to SiO 2 of CaO even with 1.1 to 1.5, It has been found that by blending 5 to 15% by mass of Al 2 O 3 , the solidification shell cooling in the mold can be maintained in a uniform state without excessive precipitation of crystals in the film. . When Al 2 O 3 which is an amphoteric oxide is blended, Al 2 O 3 becomes acidic in the molten layer of the mold powder having a high basicity, and the precipitation of crystals in the film is moderately suppressed. . (B) Therefore, in the mold powder of the present invention, based on the knowledge of the above (a), the mold powder having CaO, SiO 2 , Al 2 O 3 and a fluorine compound as basic components and having the composition shown in (1) above. And
[0014]
Thereby, even if basicity is as high as 1.1-1.5, precipitation of the crystal | crystallization in a film can be suppressed moderately and the solidification shell cooling in a casting_mold | template can be equalize | homogenized. Furthermore, because of the high basicity, it is possible to prevent the oxide such as Al 2 O 3, MnO increases in the molten steel in the mold.
(C) In the method of the present invention, the relationship between the chemical composition Cp of the molten steel defined by the above-described formula (B) and the Al 2 O 3 content in the mold powder is expressed by the above-described formula (C) or ( D) Cast under conditions that satisfy the equation.
[0015]
| Cp−0.12 | is an index indicating whether or not the chemical composition of steel is a composition that easily causes a subperitectic reaction. It is well known that vertical cracks are likely to occur on the surface of a steel slab that undergoes a subperitectic reaction. Therefore, in the case of | Cp−0.12 | ≦ 0.05, that is, in a steel that easily undergoes a subperitectic reaction, the Al 2 O 3 content in the mold powder satisfies the above-mentioned formula (C). And a low content.
[0016]
By reducing the content of Al 2 O 3 to moderately increase the precipitation of crystals in the film, suppressing the shrinkage of the solidified shell accompanying the subperitectic reaction and increasing the adhesion to the mold wall, solidification in the mold This suppresses the uneven cooling of the shell and prevents the occurrence of vertical cracks on the slab surface.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The mold powder of this invention and the continuous casting method using this mold powder are demonstrated concretely below.
[0018]
The powder of the present invention has a basic composition of CaO, SiO 2 , Al 2 O 3 and a fluorine compound. Its content, CaO about 25 to 50%, SiO 2 of about 20~40%, Al 2 O 3 is 5 to 15%, F is 4-12%. Furthermore, the alkali metal is contained in an amount of 5% by mass or less in terms of oxide content, 1% by mass or less of ZrO 2 , and TiO 2 can be contained in the range of 0 to 8% by mass as necessary. .
[0019]
The raw materials used when producing the powder of the present invention may be those generally used. Quick lime, limestone, cement as CaO raw material, silica sand, light algae earth as SiO 2 raw material, alumina as Al 2 O 3 raw material, fluorite as F raw material, oxide of alkali metal, for example, Na 2 O raw material Includes soda ash, sodium carbonate, sodium fluoride, rutile sand as the TiO 2 raw material, and zircon sand as the ZrO 2 raw material. The raw material preferably has a particle size of 100 μm or less. These raw materials contain oxides such as Fe 2 O 3 and Fe 3 O 4 and are inevitably contained in the powder. However, these impurities may be present in particular.
The contents of CaO and SiO 2 in the mold powder have already been described, but these contents are indicative, and in the present invention, the value of CaO / SiO 2 is 1.1 to 1.5. When the basicity is less than 1.1, the effect of suppressing the oxidation of molten steel is small. On the other hand, if the basicity exceeds 1.5, crystals are excessively precipitated in the film and the freezing point becomes excessively high, so that the lubricity in the mold is deteriorated and the cooling of the solidified shell tends to be uneven. This causes the harmful effect.
[0020]
The Al 2 O 3 content in the mold powder is 5 to 15% by mass. If it is less than 5% by mass, crystals are excessively precipitated in the film, and cooling of the solidified shell in the mold tends to be uneven. On the other hand, when the content exceeds 15% by mass, the viscosity of the molten layer of the mold powder increases excessively, the freezing point increases, and the molten layer hardly flows into the gap between the mold and the solidified shell.
[0021]
The total oxide content of alkali metal in the mold powder is 5% by mass or less. Alkali metal oxides are contained in the mold powder by blending ordinary raw materials. However, if the content exceeds 5% by mass, the unmelted mold powder is easily sintered in the mold, which deteriorates the heat retaining property of the molten steel in the mold. Furthermore, it becomes difficult for the molten layer to uniformly flow into the gap between the mold and the solidified shell. Accordingly, the total oxide content of alkali metals is set to 5 mass% or less.
[0022]
The content of ZrO 2 in the mold powder is 1% by mass or less. ZrO 2 is contained in the mold powder when a raw material of TiO 2 is blended. However, even when a small amount of about several percent is present in the mold powder, crystal precipitation is promoted and the freezing point is remarkably increased. Accordingly, the content of ZrO 2 is set to 1% by mass or less.
[0023]
The content rate of F in a mold powder shall be 4-12 mass%. F is contained for the purpose of adjusting the freezing point and moderate crystal precipitation. If it is less than 4% by mass, the effect is small. When it exceeds 12% by mass, the viscosity of the molten layer is excessively lowered, and not only is it easily caught in molten steel, but also excessively flows into the gap between the mold and the solidified shell, so that vertical cracks are likely to occur on the surface of the slab.
[0024]
TiO 2 is added to the mold powder as necessary. At that time, the content of TiO 2 is 0 to 8 mass%. TiO 2 has been conventionally used as an accelerator for crystal precipitation in a film, but in the present invention, addition of an appropriate amount of TiO 2 has a significant effect on lowering the freezing point, and even if the freezing point is lowered. It was found that the viscosity is difficult to decrease. Therefore, 0 to 8% by mass of TiO 2 can be contained for the purpose of lowering the freezing point without lowering the viscosity.
[0025]
The freezing point of the mold powder is 1100 ° C. or higher, and the viscosity at 1300 ° C. is 2 to 6 poise. The upper limit of the desired freezing point is 1300 ° C. By setting the freezing point in the above range, the thickness of the solid phase portion that is a crystal precipitation site in the film can be ensured. Moreover, it can prevent a molten mold powder being caught in the molten steel in a casting_mold | template by making a viscosity into the said range.
[0026]
The content ratios of Al 2 O 3 , TiO 2 and F in the mold powder are preferably set in a range satisfying the above-described formula (A). The inventors have found that the desired content of TiO 2 is affected by the content of Al 2 O 3 and F. That is, by setting the product of the content ratios of TiO 2 and Al 2 O 3 within a certain range, it is easy to appropriately adjust the solidification point of the mold powder or the viscosity of the molten layer. Furthermore, it has also been found that an appropriate range of the product of the content ratios of TiO 2 and Al 2 O 3 is affected by the F content ratio. When the product of the content ratios of TiO 2 and Al 2 O 3 is less than 2, the amount of decrease in freezing point is small, and when the value on the right side of the above-described formula (A) is exceeded, the freezing point tends to be high.
[0027]
In the method of the present invention, the relationship between the chemical composition Cp of the molten steel defined by the above-described formula (B) and the Al 2 O 3 content in the mold powder is the above-described formula (C) or (D) Cast under conditions that satisfy.
In the case of | Cp−0.12 | ≦ 0.05, that is, in a steel that easily undergoes a subperitectic reaction, the Al 2 O 3 content in the mold powder is set so as to satisfy the above-described formula (C). Low content. By reducing the content of Al 2 O 3 to moderately increase the precipitation of crystals in the film, suppressing the shrinkage of the solidified shell accompanying the subperitectic reaction and increasing the adhesion to the mold wall, solidification in the mold This suppresses the uneven cooling of the shell and prevents the occurrence of vertical cracks on the slab surface.
[0028]
In the case of | Cp−0.12 |> 0.05, the occurrence of vertical cracks on the surface of the slab can be prevented without reducing the Al 2 O 3 content. Rather, by slightly increasing the content of Al 2 O 3 to 10 to 15% by mass, the viscosity of the molten layer of the mold powder is moderately increased, and excessive crystal precipitation in the film is suppressed, and the solidified shell in the mold It is better to make the cooling uniform.
[0029]
【Example】
Using a vertical bending type continuous casting machine, casting was performed on a slab having a thickness of 230 mm and a width of 1220 mm at a speed of 1.1 m / min or 1.4 m / min. Table 1 shows the chemical composition of the steel used. The steel is low carbon steel and hypoperitectic medium carbon steel, and Table 1 shows the chemical composition Cp defined by the method of the present invention. Cp of the low carbon steel is 0.043 mass%, Cp of the medium carbon steel is 0.117 mass%, and | Cp−0.12 | is 0.077 for the low carbon steel and 0 for the medium carbon steel, respectively. .003, and | Cp−0.12 | 2 of the medium carbon steel is 0.000009. Therefore, the desirable Al 2 O 3 content in the mold powder when casting low carbon steel is 10 to 15% by mass from the above formula (D), and the desired Al content in mold powder when casting medium carbon steel. The 2 O 3 content is 5 to 10% by mass based on the formula (C).
[0030]
[Table 1]
Table 2 shows the composition of the mold powder used in the test. Mold powder a has basicity and viscosity, mold powder b has basicity, mold powder c has Al 2 O 3 content, mold powder d has Al 2 O 3 content and viscosity, mold powder e has TiO 2 content, Each is a mold powder that does not satisfy the conditions specified in the invention. Test conditions and test results are shown in Table 3.
[0031]
[Table 2]
[Table 3]
Among the indices shown in Table 3, “spin pins” are the number of occurrences of sludge creases and pinhole creases observed when the surface of the slab is scarfed. Indicator A: None, Indicator B: 1 to 5, Indicator C: 6 to 10, Indicator D: 11 to 20, Indicator E: 21 to 50, Indicator F: 51 or more, Indicator A and B Is the number of occurrences with no particular problems. The “longitudinal crack” is a ratio of molecules in which the vertical crack is generated in the cast slab. Indicator A: Less than 3%, Indicator B: 3% or more and less than 6%, Indicator C: 6% or more and less than 10%, Indicator D: 10% or more, and Indicators A and B are occurrences with no particular problems. . Furthermore, “copper plate temperature fluctuation” is the temperature fluctuation amount of the thermocouple embedded in the mold copper plate during casting, small index: less than ± 3 ° C., middle index: less than ± 10 ° C., large index: ± 10 ° C. or more. The indicators small and medium are not particularly problematic.
[0032]
In the test in which the low carbon steel was cast at a speed of 1.4 m / min, the test No. of the comparative example. Compared to test No. 6, test No. 1 and no. In 3-5, it can be seen that all the glazes and pinholes are reduced, and the surface quality of the slab is improved. Test No. of the comparative example. 7 and no. No. 10, the freezing point was as high as 1300 ° C. or higher, and could not be used for casting. Test No. of the comparative example. 8 and no. In No. 9, since the crystal precipitation was excessive or unstable, there were some fluctuations in the temperature of the mold copper plate and vertical cracks. Moreover, since the freezing point or viscosity was high, the lubricity was poor, and many defective parts such as restraint marks were observed on the surface of the slab.
[0033]
In the test in which a medium carbon steel was cast at a speed of 1.1 m / min, the test No. of the comparative example. Compared to 16, test No. 11 and ~ No. It can be seen that in Nos. 13 to 15, all the glazes and pinholes, vertical cracks, and fluctuations in the mold copper plate temperature are all reduced, and the slab surface quality is improved. Test No. of the comparative example. 17 and no. In No. 20, the freezing point was as high as 1300 ° C. or higher, and could not be used for casting. Test No. of the comparative example. 18 and no. In No. 19, since the crystal precipitation is excessive or unstable, the temperature of the mold copper plate varies greatly. No. 19 also caused vertical cracks.
[0034]
【The invention's effect】
By applying the mold powder of the present invention and the continuous casting method of the present invention using the mold powder, a slab having no depletion or vertical cracks on the slab surface and excellent cleanliness of the slab surface layer is obtained. be able to.
Claims (3)
2≦(Al2 O3 )×(TiO2)≦10+15×(F)・・・(A)
ここで、(Al2 O3 ):モールドパウダ中のAl2 O3 含有率(質量%)
(TiO2):モールドパウダ中のTiO2 含有率(質量%)
(F):モールドパウダ中のF含有率(質量%)The mold powder for continuous casting according to claim 1, wherein the content ratios of Al 2 O 3 , TiO 2 and F satisfy the following formula (A).
2 ≦ (Al 2 O 3 ) × (TiO 2 ) ≦ 10 + 15 × (F) (A)
Here, (Al 2 O 3 ): Al 2 O 3 content (% by mass) in the mold powder
(TiO 2 ): TiO 2 content in mold powder (mass%)
(F): F content (% by mass) in the mold powder
ここで、C、Mn、Ni、Si、CrおよびS:溶鋼中の含有率(質量%)
|Cp−0.12|≦0.05の場合;
|Cp−0.12|>0.05の場合;
10≦(Al2 O3 )≦15 ・・・(D)
ここで、|Cp−0.12|:Cpの値から0.12を引いた値の絶対値
(Al2 O3 ):モールドパウダ中のAl2 O3 含有率(質量%)A continuous casting method using the mold powder according to claim 1 or claim 2, between the following (B) Al 2 O 3 content of the chemical composition Cp and in mold powder of the molten steel as defined in formula A continuous casting method characterized by casting under a condition that satisfies the following formula (C) or (D):
Here, C, Mn, Ni, Si, Cr and S: Content ratio (% by mass) in molten steel
When | Cp−0.12 | ≦ 0.05;
When | Cp−0.12 |>0.05;
10 ≦ (Al 2 O 3 ) ≦ 15 (D)
Here, | Cp−0.12 |: absolute value obtained by subtracting 0.12 from the value of Cp (Al 2 O 3 ): Al 2 O 3 content (% by mass) in the mold powder
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KR100623908B1 (en) * | 2004-06-23 | 2006-09-19 | 스톨베르그 앤드 삼일 주식회사 | Fluorine-free mold flux for the continuous casting of steel and method for producing the same |
JP4508086B2 (en) * | 2005-11-14 | 2010-07-21 | 住友金属工業株式会社 | Mold powder for continuous casting of steel and continuous casting method |
EP2407563A1 (en) * | 2010-07-13 | 2012-01-18 | Denain Anzin Métallurgie D.A.MET | Covering powder for liquid steel and method for manufacturing same |
CN112756570B (en) * | 2019-11-05 | 2022-07-15 | 上海梅山钢铁股份有限公司 | Continuous casting start-up slag for casting peritectic steel |
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