JP3840793B2 - Production method of steel containing B - Google Patents
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- JP3840793B2 JP3840793B2 JP08870598A JP8870598A JP3840793B2 JP 3840793 B2 JP3840793 B2 JP 3840793B2 JP 08870598 A JP08870598 A JP 08870598A JP 8870598 A JP8870598 A JP 8870598A JP 3840793 B2 JP3840793 B2 JP 3840793B2
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【０００１】
【発明の属する技術分野】
本発明は、含Ｂ鋼の製造方法に関する。
【０００２】
【従来の技術】
硼素（以下、元素記号のＢで示す）は、鋼の焼き入れ性を改善したり、中性子線吸収性能を有することから、特殊鋼およびステンレス鋼の重要な添加元素として用いられる。
【０００３】
Ｂを鋼に製鋼段階で調整するには、Ｂを含有するスクラップ原料を多配合したり、合金鉄すなわちＦｅ−Ｂを添加する方法が用いられている。
特開平６−２７９８２８号公報には、スラグからＦｅ、Ｍｎ、Ｃｒ等の有価金属をＡｌ、Ｓｉ等の還元剤を用いて脱酸工程で回収する方法が示されている。この方法は、酸化精錬工程でスラグに酸化物の形態で移行したＦｅ、Ｍｎ、Ｃｒ等の金属元素を還元するために、スラグ量を渦流センサーで、有価金属量を炭素還元により求めて、これらの結果から還元剤量を推算する方法であり、収率よく回収する方法は開示されていない。
【０００４】
また、特開平９−９５７５５号公報には、Ｂ入りオーステナイト系ステンレス鋼の製造法に関して、ステンレス鋼にＢを０．０５〜５．０重量％を添加して、造塊時の溶鋼過熱度を３０℃から１３０℃の範囲で鋳造することにより、Ｂをボライドとして鋼に分散、析出させる方法が開示されているが、Ｂ酸化物を収率よく溶鋼中に添加する方法を開示したものではない。
【０００５】
【発明が解決しようとする課題】
本発明は、Ｂを含有する一般鋼、特殊鋼およびステンレス鋼を溶製するに際し、高価な合金鉄に頼らず、安価な酸化物を原料に８５％以上の高収率で溶鋼中に添加する製造方法を提供することにある。
【０００６】
【課題を解決するための手段】
溶鋼中にはＢを合金鉄ではなく、酸化物で代替するには、以下の（１）から（３）の課題を解決する必要がある。
【０００７】
（１） 酸化物を還元する還元剤は、酸化物の添加・還元による冷却作用を熱補償できるだけの反応熱をもつものを選択する。
（２） 還元速度が十分に早く、合金鉄添加並みの処理時間で終了する。
【０００８】
（３） 高い収率で還元でき、溶鋼濃度の調整の制度も良好である。
本発明者等は、かかる目的を達成すべく種々検討を重ね、以下の（Ａ） 〜（Ｅ） の知見を得た。
【０００９】
（Ａ） 最も一般的な還元剤のひとつであるＡｌを用いれば、高い還元能力とＡｌ燃焼で生じる酸化熱による熱補償の両立を図れる。
（Ｂ） 酸化物の還元速度を適正な速度にするには、通常の溶鋼の攪拌状態であれば、溶鋼の温度管理をすることが必要である。
【００１０】
（Ｃ） 酸化物の収率の低下は、添加時の飛散、蒸発およびスラグへの移行ロスによるものであり、これらを防止する観点からも温度管理をすることが必要である。
【００１１】
（Ｄ） 温度管理の指標として、鋼種に固有な液相線温度（固相と液相の境界温度）と酸化物を添加時の温度および添加終了時における溶鋼温度との差△Ｔを基に管理すると酸化物の収率を管理できる。
【００１２】
（Ｅ） Ｂは、比較的酸素と親和力の大きい元素であるので、それ自身が脱酸反応に関与することから、その濃度制御には、溶鋼中の金属比［Ｂ］／［Ａｌ］を制御することが有効である。
【００１３】
ところで、特開平７−４１８２２号公報には、金属酸化物としてＳｉＯ２ 、ＡｌおよびＣａＯを添加し、ＳｉＯ２ をＳｉに還元することにより、粗大な凝集物（２／３ＣａＯ・Ａｌ２ Ｏ３ ）を生成し、溶鋼中の全酸素濃度を低減させる方法が開示されている。しかし、同公報の発明の要旨は、Ａｌにより前記金属酸化物のＳｉＯ２ が還元されると、粗大な凝集物（２／３ＣａＯ・Ａｌ２ Ｏ３ ）の生成を促進できるという触媒的な作用を見出したことにあり、Ｓｉを溶鋼に添加する方法を示したものではなく、金属酸化物の一例としてＶ２Ｏ５を例示しているに過ぎない。また、開示された反応メカニズムから推定すると、前記ＳｉＯ２ が還元された金属Ｓｉは、大半が凝集物に付着除去され、溶鋼中には、ほとんど止まらないと判断できる。
【００１４】
本発明は、以上の知見に基づいてなされたもので、その要旨は以下の通りである。
（1） 溶鋼の出鋼時から２次精錬を行う期間中に、ＡｌおよびＢ酸化物を溶鋼に添加して目的とする所定の溶鋼中の［Ｂ］濃度を得る含Ｂ鋼の製造方法であって、ＡｌおよびＢ酸化物を添加する際の温度条件として、添加前温度、添加後の温度、２次精錬後の各温度が前記溶鋼の液相線温度より５０℃〜３００℃高い温度であり、かつ前記溶鋼中の［Ｂ］濃度と溶鋼中の［Ａｌ］濃度の比［Ｂ］／［Ａｌ］を０．２〜２０にすることを特徴とする含Ｂ鋼の製造方法。
【００１５】
【発明の実施の形態】
本発明で使用するＢ酸化物は、Ｂ酸化物と不可避的不純物からなる天然または人工的に存在する化合物を意味し、特に限定しないが、例えば、無水硼砂等がある。好適酸化物としては、Ｂ酸化物ではＢ２ Ｏ３ （無水硼酸）あるいはＨ３ＢＯ３ （硼酸）であり、これらの酸化物はＢ純分当りで通常の合金鉄よりも１０〜３０％安価であるばかりでなく、酸素を除くＢ純分が９５％以上でＣやＳといった不純物も少なく製鋼原料として極めて適している。好適形態としては、フレーク状もしくは塊状の飛散しにくい形態がよく、ブリケット加工されたものおよび缶等に圧縮封入したものがよい。
【００１６】
酸化物を還元する還元剤としてＡｌを選択する。このＡｌの形態は、通常製鋼用に使われる金属ＡｌあるいはＡｌ−Ｆｅ合金でよく、特に限定されない。
本発明における還元剤および酸化物の添加時期は、例えば、一次精錬後の転炉、電気炉等の出鋼時または／および２次精錬後、例えば、ＶＯＤ脱炭後、または、ＲＨ真空脱ガス処理後の脱酸処理時である。２次精錬後の添加は、［Ｂ］／［Ａｌ］を制御するための微調整的なものである。
【００１７】
また、Ｂ酸化物を溶鋼に添加して目的とする所定の溶鋼中の［Ｂ］濃度を得るに際し、ＡｌおよびＢ酸化物を添加する際の温度条件として、添加前温度、添加後の温度、２次精錬後の各温度が全て前記溶鋼の液相線温度より５０〜３００℃高い温度であることが必要であるが、この理由は、可能な限り長い時間、適正な温度を確保し、有効な反応時間を長くとることにより、収率を高くすることができるからである。
【００１８】
還元剤および酸化物の添加方法は、ホッパーやクレーンからの投入等の常法でよい。
Ｂ酸化物からの溶鋼への収率η（％）は下記（１） 式で定義され、酸化物から必要元素Ｍ（以下、Ｂを示す）が還元され、溶鋼中に溶解し、溶鋼中の［Ｍ］濃度（重量％）になったものに、溶鋼量Ｗｓ （ｋｇ）を乗じて得られるＭの重量すなわち回収重量（ｋｇ）を、溶鋼中に投入した酸化物中に含まれるＭの重量すなわち原料重量（ｋｇ）で除したものである。
【００１９】
【数１】
上記収率が予想できれば、必要［Ｍ］濃度から、添加酸化物量ＷＭｘＯｙ（ｋｇ）が決定でき、下記（２） 式から、添加Ａｌ量ＷＡｌ（ｋｇ）を決定できる。
【００２１】
【数２】
以下に限定理由について述べる。
図１に、ＡｌおよびＢ酸化物を一括添加した時の添加前の温度を液相線温度からの温度差△Ｔ（℃）とし、温度差△Ｔ（℃）とＢ酸化物の収率η（％）との関係を示す。
【００２３】
図１は、以下の２水準の溶鋼中の［Ｂ］濃度、［Ｂ］／［Ａｌ］を選択して試験結果をまとめて示すグラフである。
（１） ［Ｂ］＝０．０４０〜０．０６０％、［Ｂ］／［Ａｌ］＝０．５〜１．０
（２） ［Ｂ］＝０．９０〜１．１０％、［Ｂ］／［Ａｌ］＝４〜６
図１に示すように、△Ｔが５０℃〜３００℃の温度差の範囲で、ＡｌおよびＢ酸化物を一括添加すれば、目標収率の８５％以上の値が得られている。なお、添加処理後および２次精錬後の温度差も上記範囲に入ることが必要である。
【００２４】
Ｂ酸化物の収率低下の原因は、△Ｔが５０℃未満では、還元速度が遅くなり、Ｂ酸化物では、３００℃を越えると、スラグへの分配比がそれぞれ増大し、酸化物の蒸発も生じ易くなるからである。好ましい範囲は、Ｂ酸化物では、１００℃〜２５０℃である。
【００２５】
図２に、Ｂ添加鋼における［Ｂ］／［Ａｌ］と収率との関係を示す。
なお、図２は、溶鋼中の［Ｂ］濃度を０．０１〜３．０％の範囲で求めたものである。
【００２６】
図２に示すように、収率は［Ｂ］／［Ａｌ］を２０より低くすると、約９５％が得られる。しかし、０．２未満でその効果は飽和しており、溶鋼中の［Ａｌ］濃度の過剰な添加になりコスト悪化を招くため、０．２以上でよい。一方、［Ｂ］／［Ａｌ］が２０を越えると収率は８５％未満に低下する。この収率の低下原因は、目標の溶鋼中の［Ｂ］濃度に対して、溶鋼中の［Ａｌ］濃度が小さいと還元速度が遅くなり、かつスラグへの分配比も増大してスラグへの残存量が増加するからである。
【００２７】
以上から、臨界的な［Ｂ］／［Ａｌ］比は、下記の（３）式に示す通りである。
０．２≦［Ｂ］／［Ａｌ］≦２０ （３）
好ましい範囲は、１≦［Ｂ］／［Ａｌ］≦１２である。
【００２８】
なお、転炉または電気炉等からの流出スラグは、一般にスラグ中の（ＦｅＯ＋ＭｎＯ）濃度が１０％以上の高濃度であり、添加したＡｌが消費されるおそれがあり、常法の流出スラグ抑制法あるいはスラグ還元法を適用すると、溶鋼中の［Ａｌ］濃度の制御性が良くなるので本発明を実施する上で好ましい。
【００２９】
酸化物を用いて還元利用する方法は、製鋼コストの低減にとどまらず、前述のように、これら酸化物は通常の合金鉄よりも不純物が少なく、合金鉄を使用する場合に不可避的に入る炭素Ｃを含まず、ＳやＰも低く高純度鋼の製造に適した方法である。
【００３０】
本発明の対象となる鋼種は、一般鋼、特殊鋼およびステンレス鋼のうち、ＢまたはＢおよびＶを含有する鋼で特に限定されないが、好適鋼の組成例（重量％）を以下に示す。
【００３１】
［Ｖ］：０．０１〜２．０％
［Ｂ］：０．００１〜３．０％
［Ｃ］：０．００１〜０．３％
［Ｓｉ］：０．０１〜１．０％
［Ｍｎ］：０．０５〜３．０％
［Ｃｒ］：０〜３０％
［Ｎｉ］：０〜１５％
【００３２】
【実施例】
（実施例１）
電気炉ーＶＯＤ炉プロセスを用いて、溶鋼中の［Ｂ］濃度が０．９〜１．１％、［Ｃｒ］が１９％、「Ｎｉ」が９．５％、［Ｓｉ］が０．４％、［Ｍｎ］が１％、［Ａｌ］が０．２％以下の組成を有し、Ａｌ脱酸を必要とする中性子線遮蔽材用Ｂ含有オーステナイト系ステンレス鋼４０ｔを溶製した。
【００３３】
電気炉から未脱酸で出鋼し、除滓した後ＶＯＤ炉に搬送して酸素吹精による脱炭を行った。その後、常法にしたがって生石灰、蛍石等の造滓剤を添加した。この造滓剤を添加した後のＶＯＤ脱炭後に、Ｂ２Ｏ３（無水硼酸）を添加するとともに、酸化物を還元しかつ溶鋼を脱酸するためのＡｌを添加した。
【００３４】
さらに添加精度を向上させる目的で、このＶＯＤ還元工程の真空攪拌後にＡｌを再添加し、微調整を行い、［Ｂ］／［Ａｌ］が９〜１６の適正な範囲になるように制御した。その後、常法にしたがって鋳造し、鋼塊を得た。
【００３５】
表１に、本発明例１〜５および比較例１〜３の結果を示す。
【００３６】
【表１】
本発明例１〜３では、ＶＯＤ脱炭後の添加前の溶鋼温度が１５８６℃および１６０８℃の範囲にあった。この鋼種の液相線温度が１３６１℃であるから、△Ｔは、ＶＯＤ脱炭後の添加前で２２５℃〜２４７℃の範囲に制御できた。その結果、酸化物収率は８５％以上の値を得た。
【００３８】
本発明例４〜５では、ＶＯＤ還元工程の真空攪拌後にＡｌを再添加し、添加微調整を行い、［Ｂ］／［Ａｌ］を９〜１１の範囲に制御することにより、収率は９５％以上となった。
【００３９】
比較例１および２に示したように、ＶＯＤ脱炭後の添加前の溶鋼温度が液相線温度とのが△Ｔ３００℃を超えたり、ＶＯＤ還元処理後温度と液相線温度との差が５０℃未満の場合には、いずれもＢ酸化物の収率が８５％未満と悪化した。
【００４０】
【発明の効果】
本発明により、Ｂを含有する一般鋼、特殊鋼およびステンレス鋼を溶製するに際し、高価な合金鉄に頼らず、安価な酸化物を８５％以上の高収率で使用できる。
【図面の簡単な説明】
【図１】 Ｂ添加鋼における液相線温度との溶鋼の温度差△ＴとＢ酸化物の収率との関係を示すグラフである。
【図２】Ｂ添加鋼における溶鋼中の［Ｂ］／［Ａｌ］とＢ酸化物の収率との関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing steel containing B.
[0002]
[Prior art]
Boron (hereinafter referred to as element symbol B) is used as an important additive element in special steel and stainless steel because it improves the hardenability of steel and has neutron absorption capability.
[0003]
In order to adjust B to steel in the steelmaking stage, a method of adding a large amount of scrap raw materials containing B or adding alloy iron, that is, Fe-B, is used.
Japanese Patent Application Laid-Open No. 6-279828 discloses a method for recovering valuable metals such as Fe, Mn and Cr from slag in a deoxidation step using a reducing agent such as Al and Si. In this method, in order to reduce metal elements such as Fe, Mn, Cr, etc. that have been transferred to the slag in the form of oxides in the oxidative refining process, the slag amount is obtained by an eddy current sensor and the valuable metal amount is obtained by carbon reduction. From this result, the amount of reducing agent is estimated, and a method for recovering with good yield is not disclosed.
[0004]
JP-A-9-95755 discloses a method for producing B-containing austenitic stainless steel by adding 0.05 to 5.0% by weight of B to the stainless steel, and the degree of superheat of the molten steel during ingot formation. Although a method of dispersing and precipitating B as a boride in steel by casting in the range of 30 ° C. to 130 ° C. is disclosed, it does not disclose a method of adding B oxide in molten steel in a high yield. .
[0005]
[Problems to be solved by the invention]
In the present invention, when melting general steel, special steel and stainless steel containing B, an inexpensive oxide is added to the raw steel in a high yield of 85% or more without relying on expensive alloy iron. It is to provide a manufacturing method.
[0006]
[Means for Solving the Problems]
In order to replace B in the molten steel with an oxide instead of an iron alloy, it is necessary to solve the following problems (1) to (3).
[0007]
(1) A reducing agent that reduces oxides is selected so as to have a heat of reaction sufficient to compensate for the cooling effect due to the addition and reduction of oxides.
(2) The reduction rate is sufficiently high and finishes with a processing time comparable to that of addition of iron alloy.
[0008]
(3) It can be reduced with a high yield, and the system for adjusting the molten steel concentration is also good.
The inventors of the present invention have made various studies in order to achieve this object, and have obtained the following findings (A) to (E).
[0009]
(A) If Al, which is one of the most common reducing agents, is used, it is possible to achieve both high reducing ability and heat compensation by oxidation heat generated by Al combustion.
(B) In order to set the reduction rate of the oxide to an appropriate rate, it is necessary to control the temperature of the molten steel as long as it is a normal stirring state of the molten steel.
[0010]
(C) The decrease in the yield of the oxide is due to scattering at the time of addition, evaporation and loss of transition to slag, and it is necessary to control the temperature from the viewpoint of preventing these.
[0011]
(D) As an index of temperature control, based on the difference ΔT between the liquidus temperature (boundary temperature between the solid phase and the liquid phase) inherent to the steel type and the temperature at the time of adding the oxide and the molten steel temperature at the end of the addition. If managed, the yield of oxide can be controlled.
[0012]
(E) Since B is an element having a relatively large affinity for oxygen, it itself participates in the deoxidation reaction. Therefore, the concentration ratio is controlled by controlling the metal ratio [B] / [Al] in the molten steel. It is effective to do.
[0013]
By the way, in JP-A-7-41822, SiO 2 , Al and CaO are added as metal oxides, and SiO 2 is reduced to Si, whereby coarse aggregates (2 / 3CaO · Al 2 O 3 ). And a method for reducing the total oxygen concentration in the molten steel is disclosed. However, the gist of the invention of the publication is that the catalytic action of promoting the formation of coarse aggregates (2 / 3CaO.Al 2 O 3 ) when the metal oxide SiO 2 is reduced by Al. However, it does not show a method of adding Si to molten steel, but merely illustrates V 2 O 5 as an example of a metal oxide. Further, when estimated from the disclosed reaction mechanism, it can be determined that most of the metal Si in which the SiO 2 is reduced is adhered to and removed from the aggregate and hardly stops in the molten steel.
[0014]
The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) A method for producing B-containing steel, in which Al and B oxides are added to molten steel during the period of secondary refining from the time when molten steel is produced to obtain the desired [B] concentration in the molten steel. As temperature conditions for adding Al and B oxides, the temperature before addition, the temperature after addition, and the temperature after secondary refining are temperatures higher by 50 ° C. to 300 ° C. than the liquidus temperature of the molten steel. And a ratio [B] / [Al] of the [B] concentration in the molten steel to the [Al] concentration in the molten steel is set to 0.2 to 20, wherein the method for producing B-containing steel is characterized.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The B oxide used in the present invention means a natural or artificial compound composed of B oxide and inevitable impurities, and is not particularly limited, and examples thereof include anhydrous borax. Preferred oxides are B 2 O 3 (boric anhydride) or H 3 BO 3 (boric acid) for B oxides, and these oxides are 10 to 30% less expensive than ordinary alloy iron per B pure fraction. In addition, the B pure content excluding oxygen is 95% or more, and there are few impurities such as C and S, making it extremely suitable as a steelmaking raw material. As a preferred form, a flake-like or lump-like form that is difficult to scatter is preferable, and a briquette-formed one and a one that is compressed and enclosed in a can or the like are preferred.
[0016]
Al is selected as the reducing agent for reducing the oxide. The form of Al may be metal Al or Al—Fe alloy usually used for steel making, and is not particularly limited.
The timing of addition of the reducing agent and oxide in the present invention is, for example, at the time of steelmaking in a converter, electric furnace or the like after primary refining or / and after secondary refining, for example, after VOD decarburization, or RH vacuum degassing At the time of deoxidation after the treatment. The addition after the secondary refining is a fine adjustment for controlling [B] / [Al].
[0017]
In addition, when obtaining the [B] concentration in a desired predetermined molten steel by adding B oxide to the molten steel, the temperature conditions when adding Al and B oxide are the temperature before addition, the temperature after addition, Each temperature after secondary refining is required to be 50 to 300 ° C. higher than the liquidus temperature of the molten steel. The reason for this is to ensure an appropriate temperature for as long as possible and to be effective. This is because the yield can be increased by taking a long reaction time.
[0018]
The addition method of a reducing agent and an oxide may be a conventional method such as charging from a hopper or a crane.
The yield η (%) from the B oxide to the molten steel is defined by the following formula (1). The necessary element M (hereinafter referred to as B) is reduced from the oxide and dissolved in the molten steel. The weight of M obtained by multiplying [M] concentration (% by weight) by the molten steel amount W s (kg), that is, the recovered weight (kg), is the amount of M contained in the oxide introduced into the molten steel. It is divided by weight, that is, raw material weight (kg).
[0019]
[Expression 1]
If the yield can be predicted, the added oxide amount W MxOy (kg) can be determined from the necessary [M] concentration, and the added Al amount W Al (kg) can be determined from the following equation (2).
[0021]
[Expression 2]
The reason for limitation will be described below.
In FIG. 1, the temperature before the addition of Al and B oxides at once is defined as the temperature difference ΔT (° C.) from the liquidus temperature, and the temperature difference ΔT (° C.) and the yield of B oxide η (%).
[0023]
FIG. 1 is a graph collectively showing test results by selecting [B] concentration and [B] / [Al] in the following two levels of molten steel.
(1) [B] = 0.040-0.060%, [B] / [Al] = 0.5-1.0
(2) [B] = 0.90-1.10%, [B] / [Al] = 4-6
As shown in FIG. 1, a value of 85% or more of the target yield is obtained when Al and B oxides are added together within a temperature difference of ΔT of 50 ° C. to 300 ° C. Note that the temperature difference after the addition treatment and after the secondary refining needs to be within the above range.
[0024]
The reason for the decrease in the yield of B oxide is that the reduction rate is slow when ΔT is less than 50 ° C., and the distribution ratio to slag increases when the oxide of B exceeds 300 ° C. It is because it becomes easy to produce. A preferable range is 100 ° C. to 250 ° C. for the B oxide.
[0025]
FIG. 2 shows the relationship between [B] / [Al] and yield in the B-added steel.
In addition, FIG. 2 calculates | requires [B] density | concentration in molten steel in 0.01 to 3.0% of range.
[0026]
As shown in FIG. 2, when the [B] / [Al] is lower than 20, the yield is about 95%. However, if it is less than 0.2, the effect is saturated and excessive addition of [Al] concentration in the molten steel causes cost deterioration, so 0.2 or more is sufficient. On the other hand, when [B] / [Al] exceeds 20, the yield decreases to less than 85%. The reason for the decrease in the yield is that when the [Al] concentration in the molten steel is small relative to the [B] concentration in the target molten steel, the reduction rate is slowed, and the distribution ratio to the slag is increased, leading to the slag. This is because the remaining amount increases.
[0027]
From the above, the critical [B] / [Al] ratio is as shown in the following equation (3).
0.2 ≦ [B] / [Al] ≦ 20 (3)
A preferred range is 1 ≦ [B] / [Al] ≦ 12.
[0028]
In addition, slag slag from converters or electric furnaces generally has a high concentration of (FeO + MnO) in the slag of 10% or more, and there is a possibility that the added Al may be consumed. Alternatively, it is preferable to apply the slag reduction method because the controllability of the [Al] concentration in the molten steel is improved.
[0029]
The reduction method using oxides is not limited to the reduction of steelmaking costs, and as mentioned above, these oxides have fewer impurities than ordinary alloy irons, and are unavoidable when using alloy irons. It is a method that does not contain C, is low in S and P, and is suitable for producing high-purity steel.
[0030]
The steel type that is the subject of the present invention is not particularly limited to steel containing B or B and V among general steel, special steel, and stainless steel, but a composition example (% by weight) of a suitable steel is shown below.
[0031]
[V]: 0.01 to 2.0%
[B]: 0.001 to 3.0%
[C]: 0.001 to 0.3%
[Si]: 0.01 to 1.0%
[Mn]: 0.05 to 3.0%
[Cr]: 0 to 30%
[Ni]: 0 to 15%
[0032]
【Example】
Example 1
Using the electric furnace-VOD furnace process, the [B] concentration in the molten steel is 0.9 to 1.1%, [Cr] is 19%, "Ni" is 9.5%, and [Si] is 0.4. %, [Mn] is 1%, and [Al] is 0.2% or less, and B-containing austenitic stainless steel 40t for neutron shielding material that requires Al deoxidation was melted.
[0033]
The steel was undeoxidized from the electric furnace, removed and then transferred to a VOD furnace for decarburization by oxygen blowing. Thereafter, a fossilizing agent such as quicklime and fluorite was added according to a conventional method. After VOD decarburization after the addition of this iron making agent, B 2 O 3 (boric anhydride) was added, and Al for reducing oxides and deoxidizing molten steel was added.
[0034]
In order to further improve the accuracy of addition, Al was added again after vacuum stirring in this VOD reduction step, fine adjustment was performed, and control was performed so that [B] / [Al] was in an appropriate range of 9-16. Then, it casted in accordance with the conventional method and obtained the steel ingot.
[0035]
Table 1 shows the results of Invention Examples 1 to 5 and Comparative Examples 1 to 3.
[0036]
[Table 1]
In Invention Examples 1 to 3, the molten steel temperature before addition after VOD decarburization was in the range of 1586 ° C and 1608 ° C. Since the liquidus temperature of this steel type is 1361 ° C., ΔT can be controlled in the range of 225 ° C. to 247 ° C. before addition after VOD decarburization. As a result, the oxide yield was 85% or more.
[0038]
In Invention Examples 4-5, Al was re-added after vacuum stirring in the VOD reduction step, fine adjustment was performed, and [B] / [Al] was controlled in the range of 9-11, yield was 95. It became more than%.
[0039]
As shown in Comparative Examples 1 and 2, the temperature of the molten steel before addition after VOD decarburization exceeds ΔT300 ° C, or the difference between the temperature after VOD reduction and the liquidus temperature is In all cases where the temperature was less than 50 ° C., the yield of B oxide deteriorated to less than 85%.
[0040]
【The invention's effect】
According to the present invention, when melting general steel, special steel and stainless steel containing B, inexpensive oxides can be used in a high yield of 85% or more without relying on expensive alloy iron.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the temperature difference ΔT of molten steel and the liquidus temperature of B-added steel and the yield of B oxide.
FIG. 2 is a graph showing the relationship between [B] / [Al] in molten steel and the yield of B oxide in B-added steel.
Claims (1)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP08870598A JP3840793B2 (en) | 1998-04-01 | 1998-04-01 | Production method of steel containing B |
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| JP08870598A JP3840793B2 (en) | 1998-04-01 | 1998-04-01 | Production method of steel containing B |
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| JP2006172975A Division JP4274203B2 (en) | 2006-06-22 | 2006-06-22 | Method for producing V-containing steel |
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| JP3840793B2 true JP3840793B2 (en) | 2006-11-01 |
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| CN115852233B (en) * | 2022-12-07 | 2024-04-02 | 江苏永钢集团有限公司 | Method for controlling gear steel boron element |
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