JP4025696B2 - Method of melting molten steel that can prevent nozzle clogging - Google Patents
Method of melting molten steel that can prevent nozzle clogging Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、建築構造物、橋梁、海洋構造物や造船などの分野で使用されるＲＥＭ含有鋼材の製造に際し、鋳造時におけるノズル閉塞を防止する溶鋼の溶製方法に関する。
【０００２】
【従来の技術】
結晶粒成長抑制や粒内フェライト変態の促進などに用いられる非金属介在物 （以下、介在物と記す）を生成させる手段として、鋼中にＲＥＭを添加することはよく知られている。
例えば特許文献１には、質量％で、
Ｃ：０．０６〜０．１５％、Ｓｉ：０．０１〜０．７０％、Ｍｎ：０．５０〜２．０％、Ｐ：０．０３％以下、Ｓ：０．０１５％以下、Ａｌ：０．００５〜０．０７％、Ｖ：０．０４〜０．１０％、Ｂ：０．０００５〜０．００２０％、Ｎ：０．００４０〜０．０１００％、ＲＥＭ：０．００２０〜０．０１０％、Ｏ：０．００２５〜０．００７０％を含有させた溶接構造用高張力鋼において、ＲＥＭオキシサルファイドをピン止め粒子として利用することにより、結晶粒の微細化を図っていることが開示されている。
【０００３】
また特許文献２では、質量％で、
Ｃ：０．０１〜０．１８％、Ｓｉ：０．０２〜０．６０％、Ｍｎ：０．６０〜２．００％、Ｐ：０．０３０％以下、Ｓ：０．０１５％以下、Ｔｉ：０．００５〜０．０８％、ＲＥＭ：０．００１０〜０．０２００％、Ｃａ：０．００１０〜０．０２００％、Ａｌ：（Ｔｉ％）／５を含有した鋼に対し、質量％でＴｉ酸化物：９０％以下、Ｃａ酸化物およびＲＥＭ酸化物の合計：５〜５０％、Ａｌ2 Ｏ3 ：７０％以下からなる介在物組成を有する酸化物系介在物を２００ｎｍ以上の円相当径を有するものの個数で１×１０3 個／mm2 以上１×１０5 個／mm2 未満分散させ、これをフェライト変態核として結晶粒の微細化を図っていることが開示されている。さらに、分散させた介在物が低融点に制御されていることから、ノズル閉塞の原因となる高融点酸化物の生成を防止できると記載されている。
【０００４】
【特許文献１】
特開平１０−８８２７６号公報
【特許文献２】
特開２００１−２００３３号公報
【０００５】
【発明が解決しようとする課題】
しかし、特許文献１に記載された組成に溶鋼を制御すると、ＲＥＭ硫化物が生成する場合があり、それにより、鋳造時に取鍋あるいは浸漬ノズル閉塞を引き起こし、鋳造不能になることがある。
また特許文献２に記載された方法によると、ＲＥＭ酸化物の生成を回避することはできるものの、ＲＥＭ酸化物の生成がノズル閉塞の原因ではなく、実際にはこの方法によりＲＥＭ硫化物が生成する場合があり、それにより、ノズル閉塞を回避できないことがある。
【０００６】
本発明は、ＲＥＭ添加鋼を溶製するにあたり、ＲＥＭ硫化物生成を抑制または防止し、ノズル等の閉塞を防止する方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明の要旨は以下の通りである。
【０００８】
１） 鋼の鋳造に際してＲＥＭ含有溶鋼を溶製するにあたり、ＲＥＭ添加前の溶鋼中酸素濃度及び硫黄濃度に応じて、ＲＥＭ添加後の溶鋼中ＲＥＭ濃度が、下記（１）式に示す関係を満足する様に、ＲＥＭ添加量を調整してＲＥＭ硫化物を生成させないことを特徴とするノズル閉塞防止可能な溶鋼の溶製方法。
[％ＲＥＭ] ≦ −０．６１[％Ｓ]＋１．６３ [％Ｏ] ＋０．００７３・・・（１）
ここで、[％ＲＥＭ]：質量％で表したＲＥＭ添加後の溶鋼中ＲＥＭ濃度
[％Ｓ]：質量％で表したＲＥＭ添加前の溶鋼中Ｓ濃度
[％Ｏ]：質量％で表したＲＥＭ添加前の溶鋼中Ｏ濃度
【０００９】
２） 上記（１）式において、[％Ｏ] ≦０．０１０とすることを特徴とする前記１）に記載のノズル閉塞防止可能な溶鋼の溶製方法。
３） さらに上記（１）式において、右辺≦０．０２０とすることを特徴とする前記２）に記載のノズル閉塞防止可能な溶鋼の溶製方法。
４） 溶鋼中Ａｌ濃度を０．１５質量％以下に調整することを特徴とする前記１）〜３）のいずれかに記載のノズル閉塞防止可能な溶鋼の溶製方法。
【００１０】
【発明の実施の形態】
本発明者らは、溶鋼組成を広範囲に変化させた実験を行った結果として、少なくともＳを含有する溶鋼にＲＥＭを添加した場合、ＲＥＭ硫化物によってノズル閉塞が引き起こされることを明らかにした。すなわち、ＲＥＭ硫化物を生成させないことにより、ノズル閉塞を回避できることを見出した。
従って、生成する介在物をＲＥＭ硫化物ではなく、例えばＲＥＭオキシサルファイド等にすることで、ノズル閉塞を回避できることを見出した。
【００１１】
ちなみにノズル閉塞とは、取鍋ノズル、連続鋳造時の浸漬ノズル若しくは造塊工程での注入管における詰まりを意味している。
またＲＥＭとは、Ｃｅ，Ｌａ，Ｎｄなどの希土類元素のうち一種又は二種以上により構成される合金を指している。
【００１２】
以下に本発明の実施形態について詳細に説明する。
本発明者らは、ノズル閉塞の原因となるＲＥＭ硫化物を生成させないためには、所望の酸素濃度及び硫黄濃度に調整された溶鋼に対して、この酸素濃度及び硫黄濃度に応じてＲＥＭ添加量を適切に調整することにより、達成できることを見出し、本発明に至った。
【００１３】
一般的に含ＲＥＭ介在物は、溶鋼中ＲＥＭ，Ｏ，及びＳ濃度に従ってその組成が変化する。従って、溶鋼中Ｏ，Ｓ濃度に応じてＲＥＭ添加量を調整することにより、生成する介在物の組成を変化させることができる。
前記の通り、介在物の組成のうちＲＥＭ硫化物はノズル閉塞の原因となることを明らかにした。そこで、ＲＥＭ硫化物を生成させない様に、すなわちＲＥＭ硫化物以外の介在物が生成する様に、溶鋼中Ｏ，Ｓ濃度に応じてＲＥＭ添加量を調整する必要がある。
尚、ＲＥＭ硫化物以外の介在物とは、ＲＥＭオキシサルファイドやＲＥＭ酸化物等が挙げられる。
【００１４】
但し、ＲＥＭ添加量が多すぎる場合、得られる鋼の機械的な特性が損なわれるということがあるため、製造する品種に応じて、所望のＲＥＭ添加量を予め設定することが重要である。従って、所望のＲＥＭ添加量の範囲で、ＲＥＭ硫化物以外の介在物が生成する様な溶鋼中Ｏ，Ｓ濃度に予め調整しておき、その後ＲＥＭを添加すれば良い。
【００１５】
この様にすることで、ノズル閉塞の原因となるＲＥＭ硫化物は生成しないことから、ノズル閉塞防止可能な溶鋼を溶製することができる。
溶鋼中Ｏ及びＳ濃度については、適宜サンプリングを行った溶鋼を、例えば酸素センサー、スパーク発光分光分析法などを用いて分析することができる。
【００１６】
次に、生成する介在物をＲＥＭ硫化物以外の介在物に制御するための、溶鋼中酸素、硫黄濃度およびＲＥＭ添加後の溶鋼中ＲＥＭ濃度の関係は、下記（１）式を満たす範囲とすることで実施できる。
[%ＲＥＭ] ≦−０．６１[%Ｓ] ＋１．６３[%Ｏ] ＋０．００７３……（１）
【００１７】
上記（１）式の右辺とＲＥＭ濃度の関係を図１に示す。この様に、図１に示した発明範囲内に溶鋼組成を制御することにより、ＲＥＭ硫化物の介在物が生成せず、すなわちＲＥＭ化物以外の介在物が生成するため、ノズル閉塞を回避することができる。
【００１８】
また、ＯはＲＥＭ硫化物の生成を回避するために必要な元素であるが、溶鋼中に０．０１０質量％を超えて存在していた場合、粗大な酸化物が生成し、鋼の清浄性が低下する傾向がある。従って、Ｏ濃度の上限は０．０１０質量％とするのが好ましい。なお、Ｏ濃度が０．００２５質量％未満である場合、清浄性がさらに向上するため、より好ましい。
【００１９】
また、ＲＥＭは結晶粒微細化などを目的とした介在物生成のために鋼に添加される。しかし、０．０２０質量％を超える添加により、鋼の機械的な特性が損なわれる傾向があるため、上限を０．０２０質量％とするのが好ましい。
なお、ＲＥＭはＦｅ−ＲＥＭ合金やミッシュメタルと呼ばれる複数種のＲＥＭにより構成される合金として鋼に添加されるが、いずれの形態によっても効果は同等である。
【００２０】
Ａｌは脱酸元素として溶鋼に添加するが、０．１５０質量％を超えて添加した場合には生成する介在物がＲＥＭオキシサルファイドからＡｌ2 Ｏ3 へと変化する傾向がある。また、Ａｌ濃度が高いほどＡｌ2 Ｏ3 の生成量が増加する。
介在物がＡｌ2 Ｏ3 の場合、あまり生成量が多過ぎると、凝集合体して粗大化した介在物が溶鋼に残留する場合があるため、ノズル閉塞の原因となる。従って、Ａｌ濃度の上限は０．１５０質量％とするのが好ましい。
【００２１】
さらに、ＲＥＭ硫化物以外の介在物において、少なくともＲＥＭオキシサルファイドについては、介在物が大きくなるほどノズルに付着し易くなり、ノズル閉塞の原因となることがある。従って、含有する介在物の組成がＲＥＭオキシサルファイドの場合、粗大な介在物を少なくすることで、より確実にノズルの閉塞を防止できるため、好ましい。
【００２２】
以下に、含有するＲＥＭオキシサルファイド介在物の、好ましいサイズ及びその個数密度の好ましい範囲について説明する。
具体的には、含有するＲＥＭオキシサルファイド介在物の円相当径１０μｍ以上のＲＥＭ2 Ｏ2 Ｓ個数を１０個／cm2 未満とすることで、より確実にノズルの閉塞を防止できるため、好ましい。
介在物のサイズ及びその個数密度の測定は、ＳＥＭ−ＥＤＸで行うことができる。
【００２３】
また、上記の通り、ＲＥＭオキシサルファイド介在物の円相当径１０μｍ以上のＲＥＭ2 Ｏ2 Ｓ個数を１０個／cm2 未満とするには、真空精錬装置（ＲＨ）における還流時間を長くしてＲＥＭ2 Ｏ2 を凝集合体させて浮上させるか、もしくは連続鋳造時に溶鋼の流路に堰を設けてＲＥＭ2 Ｏ2 が鋳片に混入するのを防止する等の方策により実施することができる。
【００２４】
【実施例】
転炉で脱炭吹錬を行って出鋼時に合金を添加し、さらに真空精錬装置（ＲＨ）を用いて、表１に示す成分に調整した種々の鋼を溶製した。このとき、スパーク放電発光分光分析法（JIS G1253:2002）により溶鋼中Ｓ濃度を、通常鉄鋼業で用いられるジルコニア固体電解質による酸素センサーを用いて溶鋼中Ｏ濃度を測定し、この値に従ってＲＥＭ濃度を調整した。
また、サンプリング装置により溶鋼を採取し、溶鋼中介在物種の同定と介在物のサイズおよび個数密度の定量を、ＳＥＭ−ＥＤＸにより実施した。
【００２５】
ノズルについては、鉄鋼業で一般に用いられるアルミナ・グラファイト質のものを使用して連続鋳造を行い、鋳片を製造した。
鋳造時の取鍋ノズルと浸漬ノズルのいずれか、又は両方の詰まり傾向、さらに鋳造後のノズルへの付着物を調査した。調査結果を表１に併せて示す。
【００２６】
ここで、ノズル閉塞あり（×）というのは、取鍋ノズルと浸漬ノズルのいずれか一方でも閉塞により、操業が困難になった状況を意味している。
また、ノズルへの付着物が観察される（△）というのは、取鍋ノズル若しくは浸漬ノズルのいずれかに介在物の付着が観察されたものの、操業には悪影響がなかった場合を意味している。
さらに、ノズル閉塞なし（○）は、取鍋ノズル若しくは浸漬ノズルのいずれにも介在物の付着がほとんど観察されなかった場合を意味している。
【００２７】
【表１】
本発明例である No.１〜６では、全て％ＲＥＭ(calc.) に対して鋼中ＲＥＭ濃度が低くなっていて、前記（１）式を満足している場合であり、介在物としてＲＥＭ硫化物が生成していなかった。
従って、ノズルへの介在物の著しい付着、及びノズル閉塞はおこらず、介在物の組成制御によってノズル閉塞を回避することができた。
【００２９】
一方、比較例 No.７〜９では、％ＲＥＭ(calc.) に対して、鋼中ＲＥＭ濃度が高くなっていて、（１）式を満足していない場合であり、介在物としてＲＥＭ硫化物が生成していた。従って、ＲＥＭ硫化物によるノズル閉塞が起こったために、操業が困難になった。
【００３０】
【発明の効果】
本発明によれば、ＲＥＭ含有鋼の製造にあたり、鋳造ノズルの閉塞を防止し、鋼の機械的な特性を確保しながら、操業上の重大な障害を回避することができる。
【図面の簡単な説明】
【図１】ＲＥＭ硫化物を生成させないための溶鋼組成の範囲を示す図である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a molten steel melting method for preventing nozzle clogging during casting in the production of REM-containing steel materials used in the fields of building structures, bridges, offshore structures, shipbuilding, and the like.
[0002]
[Prior art]
It is well known that REM is added to steel as a means for producing non-metallic inclusions (hereinafter referred to as inclusions) used for suppressing grain growth and promoting intragranular ferrite transformation.
For example, Patent Document 1 includes mass%,
C: 0.06 to 0.15%, Si: 0.01 to 0.70%, Mn: 0.50 to 2.0%, P: 0.03% or less, S: 0.015% or less, Al : 0.005-0.07%, V: 0.04-0.10%, B: 0.0005-0.0020%, N: 0.0040-0.0100%, REM: 0.0020-0 In high-tensile steel for welded structures containing 0.010% and O: 0.0025 to 0.0070%, REM oxysulfide is used as pinning particles to refine crystal grains. It is disclosed.
[0003]
Moreover, in patent document 2, it is the mass%,
C: 0.01 to 0.18%, Si: 0.02 to 0.60%, Mn: 0.60 to 2.00%, P: 0.030% or less, S: 0.015% or less, Ti : 0.005 to 0.08%, REM: 0.0010 to 0.0200%, Ca: 0.0010 to 0.0200%, Al: (Ti%) / 5% by mass relative to the steel containing Ti oxide: 90% or less, total of Ca oxide and REM oxide: 5 to 50%, Al 2 O 3 : 70% or less of oxide inclusions having an inclusion composition of 200 nm or more It is disclosed that 1 × 10 3 pieces / mm 2 or more and less than 1 × 10 5 pieces / mm 2 are dispersed in the number of those having the above, and this is used as a ferrite transformation nucleus to refine crystal grains. Further, it is described that since the dispersed inclusions are controlled to have a low melting point, generation of a high melting point oxide that causes nozzle clogging can be prevented.
[0004]
[Patent Document 1]
JP-A-10-88276 [Patent Document 2]
Japanese Patent Laid-Open No. 2001-20033
[Problems to be solved by the invention]
However, when the molten steel is controlled to have the composition described in Patent Document 1, REM sulfide may be generated, which may cause clogging of a ladle or a dipping nozzle during casting, which may make casting impossible.
Further, according to the method described in Patent Document 2, although the generation of REM oxide can be avoided, the generation of REM oxide is not the cause of nozzle clogging, and REM sulfide is actually generated by this method. In some cases, nozzle blockage may not be avoided.
[0006]
An object of the present invention is to provide a method for suppressing or preventing REM sulfide formation and preventing clogging of nozzles and the like when melting REM-added steel.
[0007]
[Means for Solving the Problems]
The gist of the present invention is as follows .
[0008]
1 ) When melting molten steel containing REM during casting of steel, the REM concentration in molten steel after REM addition satisfies the relationship shown in the following formula (1) according to the oxygen concentration and sulfur concentration in molten steel before REM addition. as to the method of melting of the nozzle clogging preventable molten steel, characterized in that by adjusting the REM addition amount does not produce a REM sulfides.
[% REM] ≦ −0.61 [% S] +1.63 [% O] +0.0073 (1)
Here, [% REM]: REM concentration in molten steel after REM addition expressed in mass%
[% S]: S concentration in molten steel before REM addition expressed in mass%
[% O]: O concentration in molten steel before REM addition expressed in mass%
2 ) In the above formula (1), [% O] ≦ 0.010, wherein the molten steel can be prevented from being clogged, according to 1 ).
3 ) Further, in the formula (1), the right side ≦ 0.020, wherein the molten steel can be prevented from being clogged, according to 2 ).
4 ) The method for melting molten steel capable of preventing nozzle clogging according to any one of 1) to 3 ) above, wherein the Al concentration in the molten steel is adjusted to 0.15% by mass or less.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As a result of conducting experiments in which the molten steel composition was changed over a wide range, the present inventors have clarified that when REM is added to molten steel containing at least S, nozzle clogging is caused by REM sulfide. That is, it was found that nozzle clogging can be avoided by not generating REM sulfide.
Therefore, it has been found that nozzle clogging can be avoided by using, for example, REM oxysulfide instead of REM sulfide as the inclusions to be generated.
[0011]
Incidentally, the nozzle clogging means clogging in the ladle nozzle, the immersion nozzle at the time of continuous casting, or the injection pipe in the ingot forming process.
REM refers to an alloy composed of one or more of rare earth elements such as Ce, La, and Nd.
[0012]
Hereinafter, embodiments of the present invention will be described in detail.
In order to prevent the generation of REM sulfide that causes nozzle clogging, the present inventors have added REM to the molten steel adjusted to a desired oxygen concentration and sulfur concentration in accordance with the oxygen concentration and sulfur concentration. The present inventors have found that it can be achieved by appropriately adjusting the above, and have reached the present invention.
[0013]
Generally, the composition of the REM-containing inclusions changes according to the REM, O, and S concentrations in the molten steel. Therefore, the composition of the inclusions to be generated can be changed by adjusting the amount of REM added according to the O and S concentrations in the molten steel.
As described above, it was clarified that REM sulfide in the composition of inclusions causes nozzle clogging. Therefore, it is necessary to adjust the amount of REM added according to the O and S concentrations in the molten steel so that REM sulfide is not generated, that is, inclusions other than REM sulfide are generated.
Examples of inclusions other than REM sulfide include REM oxysulfide and REM oxide.
[0014]
However, if the amount of REM added is too large, the mechanical properties of the resulting steel may be impaired. Therefore, it is important to set a desired amount of REM added in advance according to the type to be manufactured. Therefore, it is sufficient to adjust the O and S concentrations in the molten steel so that inclusions other than REM sulfide are generated within a desired REM addition amount, and then add REM.
[0015]
By doing in this way, since REM sulfide which causes nozzle blockage is not generated, molten steel capable of preventing nozzle blockage can be produced.
About the O and S concentration in molten steel, the molten steel which sampled suitably can be analyzed using an oxygen sensor, a spark emission spectrometry, etc., for example.
[0016]
Next, in order to control the inclusions to be generated to inclusions other than REM sulfide, the relationship among oxygen, sulfur concentration in molten steel and REM concentration in molten steel after addition of REM is within a range satisfying the following formula (1). Can be implemented.
[% REM] ≦ −0.61 [% S] +1.63 [% O] +0.0073 (1)
[0017]
The relationship between the right side of the above equation (1) and the REM concentration is shown in FIG. In this way, by controlling the molten steel composition within the scope of the invention shown in FIG. 1, REM sulfide inclusions are not generated, that is, inclusions other than REM products are generated, so nozzle blockage is avoided. Can do.
[0018]
In addition, O is an element necessary for avoiding the formation of REM sulfide, but if it is present in the molten steel in an amount exceeding 0.010% by mass, a coarse oxide is generated, and the cleanliness of the steel. Tends to decrease. Therefore, the upper limit of the O concentration is preferably 0.010% by mass. In addition, since O cleanliness improves further when O concentration is less than 0.0025 mass%, it is more preferable.
[0019]
Further, REM is added to steel for inclusion generation for the purpose of grain refinement. However, since the addition of more than 0.020% by mass tends to impair the mechanical properties of the steel, the upper limit is preferably 0.020% by mass.
In addition, although REM is added to steel as an alloy comprised by multiple types of REM called an Fe-REM alloy or Misch metal, an effect is equivalent by any form.
[0020]
Al is added to molten steel as a deoxidizing element, but when it is added in an amount exceeding 0.150% by mass, the generated inclusions tend to change from REM oxysulfide to Al 2 O 3 . Further, the higher the Al concentration, the more Al 2 O 3 is generated.
When the inclusions are Al 2 O 3 , if the amount of production is too large, the inclusions that are agglomerated and coarsened may remain in the molten steel, causing nozzle clogging. Therefore, the upper limit of the Al concentration is preferably 0.150% by mass.
[0021]
Furthermore, in inclusions other than REM sulfide, at least REM oxysulfide is likely to adhere to the nozzle as the inclusion increases, which may cause nozzle blockage. Therefore, when the composition of the inclusions contained is REM oxysulfide, it is preferable to reduce the coarse inclusions to prevent the clogging of the nozzles more reliably.
[0022]
Below, the preferable range of the preferable size and the number density of the REM oxysulfide inclusion to contain is demonstrated.
Specifically, it is preferable that the number of REM 2 O 2 S having an equivalent circle diameter of 10 μm or more of the REM oxysulfide inclusions to be contained is less than 10 / cm 2 because the nozzle can be more reliably prevented from clogging.
The size of inclusions and the number density thereof can be measured by SEM-EDX.
[0023]
Further, as described above, in order to reduce the number of REM 2 O 2 S having an equivalent circle diameter of 10 μm or more of the REM oxysulfide inclusions to less than 10 / cm 2 , the reflux time in the vacuum refining apparatus (RH) is increased and the REM is increased. It can be carried out by measures such as agglomerating and coalescing 2 O 2 or by providing a weir in the flow path of molten steel during continuous casting to prevent REM 2 O 2 from being mixed into the slab.
[0024]
【Example】
Decarburization blowing was performed in a converter, an alloy was added at the time of steel production, and various steels adjusted to the components shown in Table 1 were melted using a vacuum refining apparatus (RH). At this time, the S concentration in molten steel was measured by spark discharge optical emission spectrometry (JIS G1253: 2002), and the O concentration in molten steel was measured using an oxygen sensor with a zirconia solid electrolyte usually used in the steel industry, and the REM concentration was determined according to this value. Adjusted.
Moreover, molten steel was extract | collected with the sampling apparatus, and the identification of the inclusion kind in molten steel, and the fixed_quantity | quantitative_quantity of the size and number density of inclusion were implemented by SEM-EDX.
[0025]
As for the nozzle, continuous casting was performed using an alumina / graphite material generally used in the steel industry to produce a slab.
The clogging tendency of either or both of the ladle nozzle and the immersion nozzle during casting, and the deposits on the nozzle after casting were investigated. The survey results are also shown in Table 1.
[0026]
Here, nozzle clogging (x) means a situation in which operation becomes difficult due to clogging of either the ladle nozzle or the immersion nozzle.
In addition, the fact that the deposit on the nozzle is observed (△) means that the inclusion was observed on either the ladle nozzle or the immersion nozzle, but the operation was not adversely affected. Yes.
Furthermore, no nozzle clogging (O) means that almost no inclusions were observed on either the ladle nozzle or the immersion nozzle.
[0027]
[Table 1]
In Nos. 1 to 6 which are examples of the present invention, the REM concentration in the steel is low with respect to% REM (calc.) And satisfies the above formula (1). Sulfide was not generated.
Therefore, the remarkable inclusion of the inclusion to the nozzle and the nozzle clogging did not occur, and the nozzle clogging could be avoided by controlling the composition of the inclusion.
[0029]
On the other hand, Comparative Examples No. 7 to 9 are cases where the REM concentration in the steel is higher than% REM (calc.) And does not satisfy the formula (1). Was generated. Therefore, nozzle clogging due to REM sulfide has occurred, making operation difficult.
[0030]
【The invention's effect】
According to the present invention, in the production of REM-containing steel, it is possible to prevent a clogging of a casting nozzle and avoid a serious operational obstacle while ensuring mechanical properties of the steel.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a range of a molten steel composition not to generate REM sulfide.
Claims (4)
[％ＲＥＭ] ≦ −０．６１[％Ｓ]＋１．６３ [％Ｏ] ＋０．００７３・・・（１）
ここで、[％ＲＥＭ]：質量％で表したＲＥＭ添加後の溶鋼中ＲＥＭ濃度
[％Ｓ]：質量％で表したＲＥＭ添加前の溶鋼中Ｓ濃度
[％Ｏ]：質量％で表したＲＥＭ添加前の溶鋼中Ｏ濃度 Upon for melting the REM-containing molten steel during casting of steel, depending on the oxygen concentration and sulfur concentration in the molten steel before the REM addition, the molten steel during REM concentration after REM addition, as to satisfy the relationship shown in equation (1) below the method melting of nozzle clogging preventable molten steel, characterized in that by adjusting the REM addition amount does not produce a REM sulfides.
[% REM] ≦ −0.61 [% S] +1.63 [% O] +0.0073 (1)
Here, [% REM]: REM concentration in molten steel after REM addition expressed in mass%
[% S]: S concentration in molten steel before REM addition expressed in mass%
[% O]: O concentration in molten steel before REM addition expressed in mass%
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