JP2009068068A - Steelmaking method using iron-scrap as main raw material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make reduction-recovering of a part of Mn into molten steel as a product, since most parts of Mn in raw material are disposed with oxidized slag, in a steelmaking method in an electric furnace using iron scrap as the main raw material. <P>SOLUTION: The raw material is melted and successively, the usual oxidizing-refining is performed and the greater part of the oxidized slag is remained in the furnace, and when tapping off the molten steel, this slag is moved into a ladle together with the molten steel. At the same time, a reducing agent corresponding to a low-grade oxidized amount in the slag, is charged. An upper and lower airtight cover is attached on the ladle and the pressure in the ladle is reduced and a reduction-refining is performed by performing gas-bubbling to reduction-recover Mn in the slag. The greater part of dephosphorization with the oxidizing-refining is returned back as the phosphorus, and P content is increased, but a steel ingot is formed with a continuous casting method, wherein this ingot is composed of a chilled and columnar crystal in the solidified structure without generating the center segregation. In this way, action of impurity P as a toxic element, is weakened. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、屑鉄を主原料とし、電気炉又は酸素バーナーを使用する溶解炉により該原料を溶解・精錬し、次いでレードルで仕上げ精錬し、次いで連続鋳造して鋼片を製造する方法に関している。   The present invention relates to a method of manufacturing a steel slab by using scrap iron as a main raw material, melting and refining the raw material in a melting furnace using an electric furnace or an oxygen burner, then finishing and refining with a ladle, and then continuous casting.

電気炉製鋼法又は類似の製鋼法では通常屑鉄を主原料とし、アーク加熱の溶解炉、通称電炉で溶解し、電炉内で酸化して各種不純物を除去ないし調整を行い、その後脱酸脱硫等の還元・仕上げ精錬を行ってレードルに出鋼される。最近では電炉生産性向上のため還元・仕上げ精錬はレードルで処理されることが多い。所定温度、所定成分に溶製された溶鋼は連続鋳造に供給されて鋼片とされる。   In the electric furnace steelmaking method or similar steelmaking methods, scrap iron is usually used as the main raw material, melted in an arc heating melting furnace, commonly known as an electric furnace, oxidized in the electric furnace to remove or adjust various impurities, and then deoxidized and desulfurized. After reduction and finishing refining, the steel is put into a ladle. Recently, reduction and finishing smelting are often processed in a ladle to improve electric furnace productivity. Molten steel melted at a predetermined temperature and a predetermined component is supplied to continuous casting to form a steel slab.

電炉内での酸化精錬工程は１）アークを安定させ、熱効率を向上させ、且つ精錬を誘導する塩基性スラグの生成、２）酸素吹錬による溶鋼中のＰ等の不純物の酸化・除去、３）酸素吹錬による溶鋼中Ｃの燃焼とＣＯ沸騰による脱ガス、４）Ｐ等の有害不純物を含有したスラグの炉外への排出、５）昇温等からなる。
レードルにおける還元・仕上げ精錬は１）スラグを非酸化性に再生するための再造滓、２）新スラグと還元剤、脱酸剤等の添加によるＯ，Ｓ等の不純物の除去・低減、３）成分・温度の調整等の工程から成る。
酸化性スラグ、還元性スラグとも使用後は産業廃棄物として処理される。 The oxidation refining process in the electric furnace is 1) the generation of basic slag that stabilizes the arc, improves the thermal efficiency and induces refining, 2) oxidation and removal of impurities such as P in molten steel by oxygen blowing, 3 ) Combustion of C in molten steel by oxygen blowing and degassing by CO boiling 4) Discharge of slag containing harmful impurities such as P to the outside of the furnace 5) Temperature rise.
Reduction and finishing refining in the ladle is 1) Re-smelting to regenerate slag to be non-oxidizing, 2) Removal and reduction of impurities such as O and S by adding new slag, reducing agent, deoxidizing agent, etc. 3) Consists of processes such as adjustment of ingredients and temperature.
Both oxidizing and reducing slag are treated as industrial waste after use.

酸化精錬の一対象であるＰは鋼を脆化させる不純物としてその含有量は鋼種、鋼材、用途に対応して規制されている。屑鉄は元の鋼種によりＰを約０．０１〜０．０５％含有している。今日では転炉鋼の精錬水準が向上して数十年経過し、市中屑中のＰ含有量は低下傾向にある。原料中のＰ平均含有量は屑鉄種の配合に依存し約０．０２％と見なされるが、銑鉄の配合、リン酸化成表面処理鋼板や他の不純物の混入により約０．０３〜０．０５％になると推定される。従って脱リン処理は必須である。脱リンを進めるには溶鋼を酸素吹錬してＰを酸化し、生成した酸化物を塩基性スラグに吸収させる。該酸化精錬時のスラグはＰ，Ｆｅ，Ｍｎ等の低級酸化物を多量に含有する。該スラグの一部が炉内又はレードルでの還元精錬に持ち込まれると該酸化物は還元され溶鋼中に回帰する。従ってこの復リンを抑制するため予め該スラグを炉外に排出するか又はレードルに排出しない必要がある。
ここで物質量に対する％表示は質量％とし以後同様である。 P, which is an object of oxidation refining, is an impurity that causes steel to become brittle, and its content is regulated according to the steel type, steel material, and application. Scrap iron contains about 0.01 to 0.05% P depending on the original steel type. Today, several decades have passed since the refining level of converter steel has improved, and the P content in city scraps has been on the decline. The average P content in the raw material is considered to be about 0.02% depending on the type of scrap iron, but it is about 0.03 to 0.05 depending on the mix of pig iron, phosphorylated surface-treated steel sheet and other impurities. Estimated to be%. Therefore, dephosphorization is essential. In order to proceed with dephosphorization, the molten steel is blown with oxygen to oxidize P, and the generated oxide is absorbed by the basic slag. The slag at the time of oxidative refining contains a large amount of lower oxides such as P, Fe, and Mn. When a part of the slag is brought into reductive refining in the furnace or in the ladle, the oxide is reduced and returns to the molten steel. Therefore, in order to suppress this recovery phosphorus, it is necessary to discharge the slag out of the furnace in advance or not into the ladle.
Here, the percentage display with respect to the substance amount is mass%, and the same applies hereinafter.

脱リン処理は同時に脱マンガンを併発する。屑鉄はＭｎも約０．２〜２．０％含有し、同様に平均約０．５％と見なされる。酸化精錬によりＭｎは酸化され溶鋼中の含有量は０．１〜０．２％に低下する。残りは酸化物としてスラグに吸収される。Ｍｎは硫化物安定剤として又脱酸安定剤として更に合金元素として有用な精錬補助剤であるがスラグ排出に伴い原料中のＭｎの大半は廃棄され以後何の役にも立っていない。   The dephosphorization process simultaneously involves demanganese. Scrap iron also contains about 0.2-2.0% Mn, and is similarly considered to be about 0.5% on average. By oxidation refining, Mn is oxidized and the content in the molten steel is reduced to 0.1 to 0.2%. The rest is absorbed by the slag as oxide. Mn is a refining aid that is useful as a sulfide stabilizer, as a deoxidizing stabilizer, and as an alloying element, but most of the Mn in the raw material is discarded with no use after slag discharge.

脱リン処理は程度の差があれ必要とされ、それに伴うマンガンの酸化・排出は不可避として放置されてきた。Ｍｎの還元精錬自体は特に困難ではない。多少でもＭｎ回収効果のある作業方法を探すと、高炉〜転炉による製鋼において脱リン後の溶鋼に素性の知れた屑鉄を限定量だけ挿入する場合がある。この場合屑鉄中のＭｎは回収されるが屑鉄の大量再生方法として一般的ではない。   Dephosphorization is required to some extent, and the accompanying oxidation and discharge of manganese has been left as an inevitable. Reduction refining of Mn itself is not particularly difficult. When a work method having an effect of recovering Mn is found, there is a case where a limited amount of scrap iron having a known feature is inserted into molten steel after dephosphorization in steelmaking by a blast furnace to a converter. In this case, Mn in scrap iron is recovered, but it is not a general method for mass recycling of scrap iron.

鉄筋用異形棒鋼においてはＰ含有量の規格上限は０．０５％であるので復リンはある程度許容される。従って復リンを承知で酸化精錬スラグを還元すれば多少のＭｎの回収は見込めるが、還元・脱酸精錬自体も生産性優先のため簡略化され、従って還元機能も省略されていて回収されていない。以上経済的な回収法は未実用である。   In the deformed steel bar for reinforcing steel bars, the upper limit of the P content is 0.05%, so that it is acceptable to some extent. Therefore, it is possible to recover some Mn if the oxidation refining slag is reduced with the knowledge of recovery phosphorus, but reduction / deoxidation refining itself is simplified because of productivity priority, so the reduction function is omitted and not recovered. . Thus, an economical recovery method is not practical.

Ｐ含有量の規制について検討する。規格値は通常のプロセス・材料・製品を対象として設定されている。Ｐ、Ｓ等の不純物が実害を示す場合の多くはそれらの偏析に起因している。従って多少の偏析は不可避との前提で規格が決められている。   Consider the regulation of P content. Standard values are set for normal processes, materials, and products. Many cases where impurities such as P and S show actual damage are caused by segregation thereof. Therefore, the standard is determined on the assumption that some segregation is inevitable.

偏析は３形態に分類される。第１のミクロ偏析はチル晶、柱状晶、等軸晶であれ樹枝状凝固における樹枝間の濃縮であり濃縮比と分布は規則的であり且つ大部分固溶していて実害を示さない。第２はセミマクロ偏析であり低融点の炭化物、リン化物、硫化物の介在物として等軸晶間に偏在する。柱状晶間には無い。大きさは１０〜数１００μｍになる。鋼の脆化、硬化等に対して微妙に影響し有害である。第３は中心部偏析で第２形態が中心周辺で集団となっているものであり、製品鋼材の脆化だけでなく熱延工程でワレを誘発するなど明らかに有害不純物として作用する。従って第２，第３形態の偏析を解消することができれば現行の規格外成分も問題なく使用でき、場合により合金元素としての作用を発揮させることも可能になる。   Segregation is classified into three forms. The first microsegregation is concentration between dendrites in dendritic solidification, whether it is chill, columnar or equiaxed, and the concentration ratio and distribution are regular, and most of them are solid solution and show no real harm. The second is semi-macro segregation, which is unevenly distributed between equiaxed crystals as inclusions of low melting point carbides, phosphides, and sulfides. Not between columnar crystals. The size is 10 to several 100 μm. It is delicate and harmful to steel embrittlement and hardening. The third is segregation in the center, and the second form is a group around the center, and obviously acts as a harmful impurity such as not only embrittlement of the product steel but also cracking in the hot rolling process. Therefore, if the segregation of the second and third forms can be eliminated, the current non-standard component can be used without any problem, and in some cases, the function as an alloy element can be exhibited.

特許文献１には連続鋳造工程における中心偏析の発生を解消する方法が開示されている。同時に該方法において鋳込み温度制御により凝固組織を外皮のチル晶の内側全面を柱状晶とする方法が開示されている。チル晶と柱状晶に制御することにより場合により一方向凝固鋼塊やＥＳＲ鋼塊と同様の均質鋼塊の可能性が有ると示唆されている。該文献には偏析解消を通してＰ，Ｓ等の不純物を実質的に低害化ないし無害化することが示唆されているが、不純物の規格外量もしくは過剰な混入を許容し且つ合金化へ活用する思想までは開示されていない。   Patent Document 1 discloses a method for eliminating the occurrence of center segregation in a continuous casting process. At the same time, a method is disclosed in which the solidification structure is made columnar throughout the entire inner surface of the chill crystal of the outer shell by controlling the casting temperature. It has been suggested that there is a possibility of a homogeneous steel ingot similar to a unidirectionally solidified steel ingot or ESR steel ingot by controlling to a chill crystal and a columnar crystal. This document suggests that impurities such as P and S are substantially harmless or harmless by eliminating segregation, but allow for non-standard amounts of impurities or excessive contamination and use them in alloying. The idea is not disclosed.

不純物Ｐの混入を大きく許容するとしてＭｎの還元回収方法の先行例を検討する。
一般的にはＬＦ法と称して、溶解炉において酸化精錬された溶鋼のみをレードルに移すと共に該レードルに造滓材と炭材を添加しアークで再加熱しつつ還元滓を生成し脱酸・脱硫を促進させる。酸化精錬スラグの一部が持ち込まれると該スラグ中のＰ，Ｆｅ，Ｍｎは還元され溶鋼中に移行する。精錬に通常３０分以上を要し、あまり能率的ではない。 Considering a prior example of a method for reducing and recovering Mn, the contamination of impurities P is greatly allowed.
Generally referred to as the LF method, only the molten steel that has been oxidatively refined in the melting furnace is transferred to a ladle, and a fossil and carbon material are added to the ladle and reheated with an arc to produce reduced soot and Promote desulfurization. When a part of the oxidized refining slag is brought in, P, Fe and Mn in the slag are reduced and transferred into the molten steel. Refining usually takes more than 30 minutes and is not very efficient.

特許文献２、特許文献３には高速の還元、脱酸、脱硫精錬方法が開示されている。両方法は基本的に同一原理に基づく。即ち１）非酸化性スラグの誘導、２）減圧下のガスバブリングによる非酸化性雰囲気中のガス・スラグ・溶鋼間の強力な撹拌、３）還元、脱酸剤の添加、４）電磁力による撹拌強化、等により溶鋼及びスラグの還元・脱酸反応を高度・高速に誘導している。スラグ中のＭｎは容易に還元されると開示されているが、スラグ中のＰの多量の還元をも許容する思想は全く気付かれていない。   Patent Documents 2 and 3 disclose high-speed reduction, deoxidation, and desulfurization refining methods. Both methods are basically based on the same principle. That is, 1) induction of non-oxidizing slag, 2) strong stirring between gas, slag and molten steel in non-oxidizing atmosphere by gas bubbling under reduced pressure, 3) reduction, addition of deoxidizer, 4) by electromagnetic force The reduction and deoxidation reactions of molten steel and slag are induced at high speed and high speed by strengthening stirring. Although it is disclosed that Mn in the slag is easily reduced, the idea of allowing a large amount of reduction of P in the slag is not noticed at all.

特許第２９８９７３７Patent No. 2998737 特許第１５７５３１６Patent No. 1575316 特許第３６５４２４８Patent No. 3654248

以上述べたように従来の屑鉄を主原料とする製鋼方法では不純物のＰを除去するため溶鋼を酸化精錬してＰを酸化物として塩基性スラグに吸収させ、該スラグを炉外に排出して残存スラグからの復リンを防止している。その際、本来有用成分である屑鉄中のＭｎも全く同様の挙動により大半が排出スラグに持ち出され回収されていない。
本発明は屑鉄中に含まれるＭｎを溶鋼に回収して精錬補助剤であるＭｎ合金の使用量を節減することを第１の目的とする。第２の目的は再造滓量を少なくしていずれ産業廃棄物となるスラグの量を削減することである。 As described above, in the conventional steelmaking method using scrap iron as a main raw material, the molten steel is oxidized and refined to remove P as an impurity, and P is absorbed as an oxide into basic slag, and the slag is discharged out of the furnace. Prevents recovery from residual slag. At that time, most of the Mn in the scrap iron, which is originally a useful component, is taken out to the discharged slag by the same behavior and is not recovered.
The first object of the present invention is to reduce the amount of Mn alloy used as a refining aid by recovering Mn contained in scrap iron in molten steel. The second purpose is to reduce the amount of slag that will eventually become industrial waste by reducing the amount of re-fabrication.

上記問題を解決するため以下の要素手段により発明を構成した。
１） 酸化精錬スラグを溶鋼と共にレードルに移行させスラグ中のＭｎを還元回収する。２） Ｍｎ回収に伴い必然的に増加する溶鋼中のＰ含有量を許容する。
３） 連続鋳造において中心偏析解消の手段を講じＰの有害作用を抑制する。 In order to solve the above problems, the invention is constituted by the following element means.
1) The oxidized refining slag is transferred to the ladle along with the molten steel, and Mn in the slag is reduced and recovered. 2) Allow the P content in the molten steel, which inevitably increases with Mn recovery.
3) Take measures to eliminate center segregation in continuous casting and suppress the harmful effects of P.

第１の発明は、屑鉄を主原料とし溶解炉において該原料を熔解し、精錬し、レードルにおいて仕上げ精錬し、次いで連続鋳造する製鋼方法において、１）溶解中及び溶落後に生成し溶鋼上に浮遊しているスラグの過半を炉内に残留させたまま酸化精錬し、２）該精錬後溶鋼と該スラグを共にレードルに出鋼し、３）該レードルにおいて還元精錬して該スラグ中のＭｎ酸化物をＭｎとして溶鋼中に０．１質量％Ｍｎ以上を回収するとともに、４）Ｐ含有量の増加を許容し、次いで５）該溶鋼から下記の連続鋳造方法によって凝固組織がチル晶と柱状晶から成る鋼片を鋳造することを特徴とする製鋼方法である。
記： 溶鋼を下方開放の湾曲鋳型に垂直に鋳込んで鋳片の外皮を形成し、該鋳片を該鋳型下方から連続的に引抜き、該鋳片の中心部が凝固するまでに円弧状に且つ半円を越えさらに鋳込面から大気圧相当静鉄圧高さを越えて上方に引き抜くことによって中空鋳片を形成し、次に該鋳片をロールによって圧下して中空内面を互いに圧接して中実鋳片とする連続鋳造方法であって、該方法において鋳込温度を過熱度で２０〜５０℃と設定することを特徴とする連続鋳造方法。 The first invention is a steelmaking method in which scrap iron is used as a main raw material, and the raw material is melted and refined in a melting furnace, finished and refined in a ladle, and then continuously cast. 1) Generated on the molten steel during and after melting. Oxidative refining with the majority of the floating slag remaining in the furnace, 2) After the refining, the molten steel and the slag are put together into a ladle, and 3) Reductive refining is performed in the ladle to reduce the Mn in the slag. In addition to recovering 0.1% by mass or more Mn in the molten steel with Mn oxide as the oxide, 4) allow the P content to increase, and then 5) solidify the chill crystals and columnar structures from the molten steel by the following continuous casting method. A steelmaking method characterized by casting a steel piece made of crystal.
Note: Molten steel is vertically cast into a downwardly open curved mold to form a slab skin, and the slab is continuously drawn from the bottom of the mold until it is solidified at the center of the slab. A hollow slab is formed by pulling upward beyond the semi-circle and further exceeding the atmospheric pressure equivalent static iron pressure height from the casting surface, and then pressing the slab with a roll to press the hollow inner surfaces together. A continuous casting method for producing a solid slab, wherein the casting temperature is set to 20 to 50 ° C. in terms of superheat.

第２の発明は、還元精錬の方法が、出鋼時に還元剤としてＳｉ含有材、Ａｌ含有材及び炭材の１種以上をレードルに投入し、該還元剤の投入量をスラグ中のＦｅＯ、ＭｎＯ、Ｐ₂Ｏ₅の化学当量の和の０．８〜１．６倍とし、その後、該スラグで覆われた溶鋼中に該レードル底面より精錬用ガスを５〜２０Ｎリットル／分／溶鋼トンの割合で吹き込んでガスバブリングしつつ溶鋼上方の雰囲気圧を６〜４０ｋＰａに減圧・維持することを特徴とする第１発明に記載の製鋼方法である。 According to a second aspect of the present invention, the refining method is such that at least one of a Si-containing material, an Al-containing material, and a carbonaceous material is introduced into the ladle as a reducing agent at the time of steel output, and the amount of the reducing agent is changed to FeO in the slag, 0.8 to 1.6 times the sum of the chemical equivalents of MnO and P ₂ O ₅ , and then refining gas from the bottom of the ladle into the molten steel covered with the slag from 5 to 20 N liters / minute / ton of molten steel The steelmaking method according to the first aspect of the invention is characterized in that the atmospheric pressure above the molten steel is reduced and maintained at 6 to 40 kPa while gas bubbling is performed at a rate of 5%.

第３の発明は、還元精錬の方法が、出鋼時に還元剤としてＳｉ含有材、Ａｌ含有材及び炭材の１種以上をレードルに投入し、該還元剤の投入量をスラグ中のＦｅＯ、ＭｎＯ、Ｐ₂Ｏ₅の化学当量の和の０．８〜１．２倍とし、その後、アーク加熱用電極を保持したカバーにより該レードルの上方を覆い、該スラグで覆われた溶鋼中に該レードル底面より精錬用ガスを吹き込んで撹拌し、溶鋼上方より炭材投入とアーク加熱によりカーバイド・スラグを生成しつつ還元することを特徴とする第１発明に記載の製鋼方法である。 According to a third aspect of the present invention, a reduction refining method is performed by introducing at least one of a Si-containing material, an Al-containing material, and a carbonaceous material into a ladle as a reducing agent at the time of steel output, and the amount of the reducing agent added is FeO in the slag, 0.8 to 1.2 times the sum of the chemical equivalents of MnO and P ₂ O ₅ , and then the upper part of the ladle is covered with a cover holding an electrode for arc heating, and the molten steel covered with the slag A refining gas is blown from the bottom surface of the ladle and stirred, and reduced while producing carbide slag by charging carbon material and arc heating from above the molten steel.

本発明による第１の効果は、原料の屑鉄中のＭｎの多くが一度は酸化されてスラグに吸収されるがレードルにおける還元処理により溶鋼に回収され、合金鉄の使用量が節減される。しかも特別のコストを要しない。   The first effect of the present invention is that much of Mn in the scrap iron as a raw material is once oxidized and absorbed by the slag, but is recovered in the molten steel by the reduction treatment in the ladle, thereby reducing the amount of alloyed iron used. Moreover, no special cost is required.

第２の効果は酸化スラグの多くが還元・仕上げ精錬スラグに持ち込まれて造滓材の使用量が大幅削減され、産業廃棄物物量が削減される。第３にスラグ量の減少に伴い消費される電力エネルギーも節減される。第４に不純物Ｐが増加するが偏析が生じない方法で連続鋳造されるので有害性が解消ないし軽減され、Ｐの合金作用（硬化、切削性、耐摩性、耐蝕性）が附加され品質改良ないし特徴有る新鋼種が容易に製造される。   The second effect is that most of the oxidized slag is brought into the reduced / finished refining slag, so that the amount of slagging material used is greatly reduced and the amount of industrial waste is reduced. Thirdly, power energy consumed as the amount of slag decreases is also saved. Fourth, impurities are increased, but since the continuous casting is performed in a manner that does not cause segregation, the harmfulness is eliminated or reduced, and the alloying action of P (hardening, machinability, abrasion resistance, corrosion resistance) is added to improve quality. A characteristic new steel grade is easily produced.

以下実施の形態について図面を参照しつつ説明する。
図１は本発明を実施する設備群の前半の例の説明図である。
主原料である屑鉄２が溶解炉１に装入され、アーク３の加熱により溶解される。溶落前より酸素ランス４により酸素吹錬して脱炭処理と共に溶鋼中の不純物Ｍｎ，Ｓｉ，Ｐ，Ｓ，Ｚｎ，Ｐｂ等の全部又は一部を酸化除去する。造滓剤として石灰を適量投入し、酸化能を持つ塩基性スラグ５を形成する。Ｍｎ，Ｓｉ，Ｐは酸化物として該スラグ５中に吸収されるがＳの一部，Ｚｎ，Ｐｂ等は気相中に移行し粉塵となり集塵処理される。 Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 is an explanatory diagram of an example of the first half of a facility group for carrying out the present invention.
Scrap iron 2 as the main raw material is charged into the melting furnace 1 and melted by heating the arc 3. Oxygen squeezing is performed by an oxygen lance 4 before smelting, and all or a part of impurities Mn, Si, P, S, Zn, Pb and the like in the molten steel are oxidized and removed together with decarburization treatment. An appropriate amount of lime is added as a koji making agent to form a basic slag 5 having oxidation ability. Mn, Si, and P are absorbed as oxides in the slag 5, but a part of S, Zn, Pb, and the like move into the gas phase and become dust and are collected.

該スラグは通常出鋼までに炉外に排出処理されるが本発明では過半を炉内に残留させ、酸化精錬終了後溶鋼６と共にレードル７へ排出する。該スラグ５はＰ₂Ｏ₅，ＭｎＯ，ＦｅＯ等の低級酸化物を約２０〜３０％含有する。出鋼時には規格Ｓｉ値に対応するフェロシリコンの他に、還元剤としてフェロシリコン、シリコマンガン及び炭材等を該レードル投入する。アルミドロス等も補助的に使用することができる。適量として該低級酸化物量の化学当量の０．８〜１．６倍が望ましい。又スラグ成分調整用として石灰等をレードルに適量投入する。該適量値の把握は当業者には困難ではない。出鋼撹拌のみでスラグ中の上記低級酸化物の一部はＣ及びＳｉ、Ａｌにより還元され溶鋼中に回帰する。分析用サンプルを取り最終成分調整の準備を行う。 The slag is normally discharged out of the furnace before the steel is discharged, but in the present invention, the majority is left in the furnace and discharged to the ladle 7 together with the molten steel 6 after completion of the oxidation refining. The slag 5 contains about 20-30% of a lower oxide such as P ₂ O ₅ , MnO, FeO. At the time of steel production, in addition to ferrosilicon corresponding to the standard Si value, the ladle is charged with ferrosilicon, silicomanganese, carbonaceous material, etc. as a reducing agent. Almidros or the like can also be used as an auxiliary. An appropriate amount is preferably 0.8 to 1.6 times the chemical equivalent of the amount of the lower oxide. An appropriate amount of lime or the like is added to the ladle for adjusting the slag component. It is not difficult for those skilled in the art to grasp the appropriate amount value. A part of the lower oxide in the slag is reduced by C, Si, and Al only by stirring the steel, and returns to the molten steel. Take a sample for analysis and prepare for final component adjustment.

受鋼したレードル７を移送して下部気密カバー８上に静置する。次ぎに合金添加用ホッパー９と排気装置１０を連接している上部気密カバー１１を該レードル７の上側に装着する。該レードル７は気密側壁を持つので、上下の気密カバーと一体化して気密構造になる。次ぎにレードル底部に付設された通気性耐火物のプラグ１２よりＡｒガス等の非酸化性のガスを吹込み、且つレードル上方空間を排気装置１０により減圧し、減圧下のガスバブリングをガス流量５〜２０Ｎリットル／分／溶鋼トンの割合で作用させる。他方溶鋼上方の雰囲気圧を６〜４０ｋＰａに減圧・維持する。   The received steel ladle 7 is transferred and left on the lower hermetic cover 8. Next, an upper hermetic cover 11 connecting the alloy addition hopper 9 and the exhaust device 10 is mounted on the upper side of the ladle 7. Since the ladle 7 has an airtight side wall, it is integrated with the upper and lower airtight covers to form an airtight structure. Next, a non-oxidizing gas such as Ar gas is blown from a plug 12 of a breathable refractory attached to the bottom of the ladle, and the space above the ladle is depressurized by the exhaust device 10, and the gas bubbling under the depressurization is performed at a gas flow rate of 5. It is made to act at a rate of ˜20 N liter / min / ton of molten steel. On the other hand, the atmospheric pressure above the molten steel is reduced and maintained at 6 to 40 kPa.

吹き込まれたガスは気泡となって上昇し溶鋼を撹拌する。気泡は溶鋼上層部に達すると急速に外圧が低下して急膨張する。その結果溶鋼とガスとスラグの３相が激しく混合し、沸騰状ではなく発泡状となり３相間の反応が強力に刺激され平衡へ移行しようとする。減圧初期には炭材と溶鋼中のＣが上記低級酸化物と反応し、ＣＯガスを発生させつつ還元が進む。その後溶鋼中のＳｉが反応主体となって還元が進み、３〜６分後にはスラグ中の上記酸化物の濃度は容易に２％以下に低下し、スラグは白色になる。スラグ中のＭｎ、Ｆｅ、Ｐはほとんど溶鋼中に回収される。従って回収量は初期スラグの残留量に依存する。Ｐ含有量の増加を無視するなら０．３〜０．４％Ｍｎの回収が期待される。
還元に併行して脱酸、脱硫、脱非金属介在物が進行する。 The injected gas rises as bubbles and stirs the molten steel. When the bubbles reach the upper layer of the molten steel, the external pressure rapidly decreases and expands rapidly. As a result, the three phases of molten steel, gas, and slag are vigorously mixed and become a foam rather than a boiling state, and the reaction between the three phases is strongly stimulated and attempts to shift to equilibrium. At the beginning of the pressure reduction, carbon in the carbon material and molten steel reacts with the lower oxide, and reduction proceeds while generating CO gas. Thereafter, Si in the molten steel is mainly reacted, and the reduction proceeds. After 3 to 6 minutes, the concentration of the oxide in the slag is easily reduced to 2% or less, and the slag becomes white. Most of Mn, Fe, and P in the slag are recovered in the molten steel. Therefore, the recovery amount depends on the residual amount of the initial slag. If the increase in the P content is ignored, recovery of 0.3 to 0.4% Mn is expected.
Along with the reduction, deoxidation, desulfurization, and non-metallic inclusions proceed.

Ｃ，Ｓｉ，Ｍｎその他合金の成分を最終調整して精錬を終了する。精錬終了後、レードルを連続鋳造機に移送し、溶鋼を連続的に鋳込んで鋼片とする。本発明による溶鋼は有害不純物Ｐを従来よりも多く含み、場合により０．０５％を越える。鋼種に対応して許容値を設定する。Ｐの増加は偏析が生ずると明らかに有害となる。従って特別の連続鋳造方法が不可欠である。   Final adjustment of the components of C, Si, Mn and other alloys is completed. After the refining is completed, the ladle is transferred to a continuous casting machine, and molten steel is continuously cast into steel pieces. The molten steel according to the present invention contains more harmful impurities P than before, sometimes exceeding 0.05%. The allowable value is set according to the steel type. The increase in P is clearly detrimental when segregation occurs. A special continuous casting method is therefore essential.

図２は本発明で使用される設備群の後半をなす連続鋳造装置の説明図であり、図に沿って本発明の鋳造方法を説明する。
精錬の終わった溶鋼をレードル（図示せず）から中間容器であるタンディシュ２２に注入し、該溶鋼２１を該タンディシュ２２から下方が開放した鋳型２３に上方より鋳込み、外皮を形成して鋳片２４とし、該鋳片２４を下方へ円弧に沿って連続的に引抜き、スプレイ冷却装置２５により冷却を進め、該鋳片２４の中心部が凝固するまでに半円を越え、さらに鋳込面から大気圧相当静鉄圧高さ（約１．４ｍ）Ｐ点を越えて上方に引き抜いて中空鋳片２６を形成し、該鋳片２６を伸直ロール２７により伸直し、圧接圧延機２８によって圧下し、内面を互いに圧接して中実鋳片２９とする。凝固終点が存在しないので中心偏析が原理的に解消される。
該連続鋳造方法の詳細については既述特許文献１に開示されているので省略する。 FIG. 2 is an explanatory view of a continuous casting apparatus constituting the latter half of the equipment group used in the present invention, and the casting method of the present invention will be described with reference to the drawing.
The refined molten steel is poured from a ladle (not shown) into a tundish 22 as an intermediate container, and the molten steel 21 is cast from above into a mold 23 whose bottom is opened from the tundish 22 to form a shell and form a slab 24 The slab 24 is continuously drawn downward along an arc, cooled by a spray cooling device 25, exceeds a semicircle until the center of the slab 24 solidifies, and further from the casting surface. Atmospheric pressure equivalent (approx. 1.4 m) The P-point is pulled upward beyond the point P to form a hollow cast slab 26, the cast slab 26 is stretched by a straightening roll 27, and is pressed by a pressure rolling mill 28. The inner surfaces are pressed against each other to form a solid cast slab 29. Since there is no solidification end point, central segregation is eliminated in principle.
Since the details of the continuous casting method are disclosed in the above-mentioned Patent Document 1, they are omitted here.

上記連続鋳造方法において鋳込温度を過熱度（＝溶鋼温度−当該成分の液相温度）で２０〜５０℃と設定すると、凝固組織は外皮がチル晶から成り、内部は柱状晶から成る。等軸晶を実質的に含まない。当該条件と結果については特許文献１に詳細に説明されている。
柱状晶自体は本来均質であるが凝固終点まで柱状晶で固めると中心偏析が発生する。従って一般には等軸晶化により中心偏析の分散が図られる。この場合中心周辺の等軸晶はセミマクロ偏析を随伴する。上記条件では等軸晶が存在しないのでセミマクロ偏析をも避けることができる。有害な偏析構造を持たないのでＰ含有量が従来規格の外でも通常の不都合は生じず、実用に供することができる。 In the above continuous casting method, when the casting temperature is set to 20 to 50 ° C. in terms of superheat (= molten steel temperature−liquid phase temperature of the component), the solidified structure is composed of chill crystals in the outer shell and columnar crystals in the interior. It is substantially free of equiaxed crystals. The conditions and results are described in detail in Patent Document 1.
The columnar crystals themselves are essentially homogeneous, but central segregation occurs when they are solidified to the end of solidification. Therefore, generally, center segregation is dispersed by equiaxed crystallization. In this case, equiaxed crystals around the center are accompanied by semi-macro segregation. Since no equiaxed crystal exists under the above conditions, semi-macro segregation can also be avoided. Since it does not have a harmful segregation structure, normal inconvenience does not occur even if the P content is outside the conventional standard, and it can be put to practical use.

以下当該プロセスの要点を補足する。
酸化精錬スラグの過半を炉内に残留させると限定した理由は、残留量が多いほどＭｎの回収量の増加が見込めるが、Ｐの増加も問題となる。炉内沸騰処理の過程でスラグの発泡により炉外に流出するスラグもある。最適量は原料以下の多くの作業条件に依存するので単純には決まらない。効果があり且つ無難な作業条件として上記の量とした。 The main points of the process are supplemented below.
The reason for limiting the majority of the smelting slag to remain in the furnace is that an increase in the recovered amount of Mn can be expected as the residual amount increases, but an increase in P also becomes a problem. Some slag flows out of the furnace due to foaming of the slag in the process of boiling in the furnace. The optimum amount depends on many working conditions below the raw material and is not simply determined. The above amount was taken as an effective and safe working condition.

不純物Ｐの規格と許容値に関して、鋼種によりＰの規格値は異なる。ＪＩＳピアノ線では０．０２５％以下、硬鋼線材では０．０３０％以下、鉄筋用異形棒鋼では０．０５％以下、その他協定値、内規では０．０１５％，０．０１％以下等がある。一般には規格値よりも低い値に管理基準が設定されている。以上からＰの妥当な許容値は鋼種や製品、需要家等により異なるから単純に設定すると無理が生ずる。
本発明では一応規格内で従来の管理基準を緩和する。場合により個別に規格外を許容する。当然規制上限が大きいほどＭｎ回収に有利となる。他方小さいと一見回収効果が無いように思えるがそうではない。上限が厳しいほど高度で高コストの不純物管理を適用しているので、Ｍｎ回収の効果の低下は脱リンコストの低減により補われる。
一般的にＰ上限値として０．０２５％以上を許容すると製鋼作業は相当楽になる。 Regarding the standard and allowable value of the impurity P, the standard value of P varies depending on the steel type. For JIS piano wire, 0.025% or less, for hard steel wire material, 0.030% or less, for deformed steel bars for reinforcing bars, 0.05% or less, other agreed values, 0.015%, 0.01% or less, etc. . In general, the management standard is set to a value lower than the standard value. From the above, the reasonable permissible value of P varies depending on the steel type, product, customer, etc., so it is impossible to set it simply.
In the present invention, the conventional management standard is relaxed within the standard. In some cases, nonstandard specifications are allowed. Of course, the larger the upper limit of regulation, the more advantageous for Mn recovery. On the other hand, it seems that there is no recovery effect at first glance, but it is not so. As the upper limit is stricter, more sophisticated and high-cost impurity management is applied, so the reduction in the effect of Mn recovery is compensated by the reduction in dephosphorization cost.
In general, if the P upper limit is allowed to be 0.025% or more, the steelmaking work becomes considerably easier.

第２発明のレードルにおける還元精錬において還元剤の量を低級酸化物量の化学当量の０．８〜１．６倍とした根拠は以下である。本発明の還元方法では還元性が大きいので本来約１．０で必要充分である。しかし１）出鋼時のＣの燃焼損、２）スラグの排出量のバラツキ、３）スラグ成分不均一性、４）分析値が即時に得られないことから統計的に処理しなければならず、経験的にある幅を設けた。０．８以下では製品成分用のＳｉの一部が還元に消費されて不都合、１．６以上では逆に製品Ｓｉ％，Ｃ％が増加傾向になって不都合になる。
同発明において、減圧下におけるガスバブリングの作業条件の根拠は特許文献２及び３に説明されており特に変わらないので省略する。 The reason why the amount of the reducing agent is 0.8 to 1.6 times the chemical equivalent of the amount of the lower oxide in the reduction refining in the ladle of the second invention is as follows. In the reduction method of the present invention, the reducibility is large, so about 1.0 is originally necessary and sufficient. However, 1) Combustion loss of C during steel output, 2) Dispersion of slag discharge, 3) Non-uniformity of slag components, 4) Analytical values cannot be obtained immediately and must be treated statistically. A certain range was empirically established. If it is 0.8 or less, a part of Si for the product component is consumed for reduction, and if it is 1.6 or more, the product Si% and C% tend to increase and become inconvenient.
In the same invention, the grounds for working conditions of gas bubbling under reduced pressure are described in Patent Documents 2 and 3, and are omitted because they are not particularly changed.

第３発明の還元精錬方法は周知事項であるから詳細は省略するが、還元剤の量の下限値は第２発明と同様の理由で同じ値とした。上限値はアーク加熱時の新たな炭材投入によるカーバイド滓の生成の効果により１．２以上では製品Ｓｉ％，Ｃ％が増加傾向になって不都合になるからである。   Although the details of the reduction and refining method of the third invention are omitted since they are well-known matters, the lower limit value of the amount of the reducing agent is set to the same value for the same reason as in the second invention. This is because the upper limit is inconvenient because the Si% and C% of the product tends to increase at 1.2 or more due to the effect of generation of carbide soot by introducing a new carbon material during arc heating.

凝固組織と偏析について補足する。
凝固の進行に伴い前面にはＣ，Ｍｎ，Ｐ，Ｓ等の溶質元素の濃縮液層が形成される。該層は柱状晶で進行する場合は樹枝状凝固の樹枝間に取り込まれ上記元素は樹枝内とある比率で分配される。即ちミクロ偏析を形成する。柱状晶はセミマクロ的には均質であり、不純物元素は多くの場合合金元素と同様に固溶している。析出相ではないので該ミクロ偏析は有害にはならない。柱状晶から等軸晶に移行すると、以後では液相中で等軸晶核が個別に成長し、中心周辺領域では多孔質の形成と併行して等軸晶を取り囲む濃縮層の集積と流動と行き詰まりが絡み、セミマクロ偏析を形成する。 It supplements about a solidification structure and segregation.
As the solidification progresses, a concentrated liquid layer of solute elements such as C, Mn, P, and S is formed on the front surface. When the layer proceeds in the form of columnar crystals, it is taken in between the dendritic solidification branches and the elements are distributed in a certain proportion with respect to the dendrites. That is, microsegregation is formed. The columnar crystals are semi-macro-homogeneous, and the impurity elements are often dissolved in the same manner as the alloy elements. Since it is not a precipitated phase, the microsegregation is not harmful. After the transition from columnar crystals to equiaxed crystals, the equiaxed nuclei grow separately in the liquid phase, and in the region around the center, the accumulation and flow of concentrated layers surrounding the equiaxed crystals occur in parallel with the formation of the porous structure. Deadlocks get involved and form semi-macro segregation.

図３は高炭素鋼ビレットの凝固組織を示す。左図に示すように柱状晶粒界には非金属相の析出が無く、フェライトの析出がある。他方右図に示す中心周辺に位置する等軸晶の粒界にはリン化物、硫化物、炭化物あるいはそれらの固溶体の非金属相が析出する。該相の偏析率と寸法はミクロ偏析を圧倒するものである。該相自体がある種の機械的性質に有害になることもあれば該相の集団が中心偏析として有害な作用を及ぼす。   FIG. 3 shows the solidification structure of the high carbon steel billet. As shown in the left figure, there is no precipitation of non-metallic phase at the columnar grain boundaries, and there is precipitation of ferrite. On the other hand, a nonmetallic phase of phosphide, sulfide, carbide or a solid solution thereof is precipitated at the equiaxed grain boundary located around the center shown in the right figure. The segregation rate and size of the phase overwhelm microsegregation. The phase itself can be detrimental to certain mechanical properties or the phase population can be detrimental as central segregation.

本発明では、Ｐは非金属の析出相として現れずに固溶しており、且つ通常より含有量が多いので合金元素としての作用を発現する。含Ｐ鋼のように鋼を硬化、脆化、切削性向上、耐蝕性向上、耐摩性向上、焼戻し脆化等の傾向が強められる。   In the present invention, P does not appear as a non-metallic precipitation phase but is dissolved, and has a higher content than usual, so that it acts as an alloy element. Like P-containing steel, the tendency of hardening, embrittlement, machinability improvement, corrosion resistance improvement, wear resistance improvement, temper embrittlement, etc. is strengthened.

Ｍｎの還元回収の経済性について検討する。
還元剤としてＳｉ、Ａｌと炭材が使用される。Ｍｎの還元過程で酸化鉄、酸化リンも還元され還元剤が消費される。低級酸化物の濃度は約２０〜３０％と既述したが、該酸化物中のＭｎＯは３０〜４０％と見なされる。概算としてＭｎ１当量に対し３当量の還元剤が必要になる。
（１）式に示すように本来Ｍｎ１ｋｇの還元にＳｉは２８／１１０×１＝０．２５ｋｇでよい。即ち質量比で１／４でよい。Ｓｉの合金鉄価格はＭｎのそれより安い。従って操業上３当量を消費してもなお充分引き合う。因みに下記反応は発熱反応であるから電力消費に問題は生じない。
２ＭｎＯ＋Ｓｉ＝２Ｍｎ＋ＳｉＯ₂ −−−（１）
原子量 ２８ １１０
低級酸化物濃度について補足すると、原料及び吹錬に起因するＦｅＯの発生量は相当多いが、吹錬時の熱効率向上のためスラグを発泡させるよう炭材も吹き込まれる。これが意外にもＦｅＯを還元しており、上記濃度範囲で安定操業になっている。 Consider the economics of Mn reduction recovery.
Si, Al and carbon materials are used as the reducing agent. During the reduction of Mn, iron oxide and phosphorus oxide are also reduced and the reducing agent is consumed. Although the concentration of the lower oxide has already been described as about 20 to 30%, MnO in the oxide is considered to be 30 to 40%. As a rough estimate, 3 equivalents of reducing agent are required for 1 equivalent of Mn.
As shown in the formula (1), Si may be 28/110 × 1 = 0.25 kg for the reduction of 1 kg of Mn. That is, the mass ratio may be 1/4. The price of Si alloy iron is cheaper than that of Mn. Therefore, even if 3 equivalents are consumed in operation, they are still attracted sufficiently. Incidentally, since the following reaction is an exothermic reaction, there is no problem in power consumption.
2MnO + Si = 2Mn + SiO _2- (1)
Atomic weight 28 110
Complementing the lower oxide concentration, the amount of FeO generated due to the raw materials and blowing is considerably large, but a carbonaceous material is also blown to foam slag in order to improve the thermal efficiency during blowing. This unexpectedly reduces FeO, and is stable in the above concentration range.

還元剤としてコスト有利な炭材の反応分を増加させると（２）、（３）式に示されるようにＳｉの消費は削減される。低価格アルミドロスの併用も有利になる。
ＭｎＯ＋Ｃ＝Ｍｎ＋ＣＯ −−−（２）
ＭｎＯ＋ＣＯ＝Ｍｎ＋ＣＯ₂ −−−（３）
低級酸化物を多量に含有するスラグに炭材を添加して減圧バブリングするとＣＯ発泡反応が促進され該酸化物の還元に作用する。
又伝統的方法であるアーク加熱により還元能を持つ塩基性スラグと炭材を反応させてカーバイド含有スラグに誘導する方法も有効である。第３発明における還元精錬は本方法を踏襲している。本方法は通称ＬＦ法と称され、レードル上方をカバーしてアーク加熱しつつ塩基性スラグに炭材を添加して還元精錬する。当該方法においてもＭｎの大部分は容易に還元回収でき、しかも炭材分の反応分が増加して好ましいが、反応速度が遅いと言う難点がある。 When the reaction amount of the carbonaceous material that is cost-effective as a reducing agent is increased, the consumption of Si is reduced as shown in equations (2) and (3). Combined use of low-cost aluminum dross is also advantageous.
MnO + C = Mn + CO --- (2)
MnO + CO = Mn + CO _2- (3)
When a carbon material is added to a slag containing a large amount of a lower oxide and bubbling under reduced pressure, the CO foaming reaction is promoted and acts to reduce the oxide.
Another effective method is to react a basic slag having a reducing ability with a carbonaceous material by arc heating to induce a carbide-containing slag. Reduction refining in the third invention follows this method. This method is commonly referred to as the LF method, in which the upper part of the ladle is covered and arc-heated, and a carbonaceous material is added to the basic slag for reduction refining. Even in this method, most of Mn can be reduced and recovered easily, and the reaction amount of the carbonaceous material is preferably increased, but there is a problem that the reaction rate is slow.

例１： 第２発明の実証試験を行った。３０トン電気炉を使用し、原料として全量屑鉄を溶解し、０．８％Ｃの高炭素鋼の溶製を行った。酸化精錬後炉内スラグの大半を排出、一部を残存させた。残存量を２水準とし、一方は従来作業条件、他方は目分量で従来に２倍とした。次いで両者ともアーク加熱しつつ新たに石灰を約３００ｋｇ投入してスラグを増量し、還元用炭材を投入したのちレードルに出鋼した。後者に対して出鋼時にはフェロシリコンを５〜１０ｋｇ通常より増加させてレードルに投入した。出鋼直後のスラグ組成は従来の通常操業では低級酸化物濃度は平均３％、試験では７〜１１％の範囲になった。次ぎに該レードルに上下の気密カバーを取付け、水封ポンプにより約０．１気圧に減圧・維持し、流量１６０Ｎリッター／分のＡｒガスを約６分吹き込んでガスバブリングし、還元・脱酸・脱硫・脱非金属介在物処理を進めた。精錬終了後のスラグ組成は、１０チャージのテストで低級酸化物濃度はすべて１．０％以下に還元されていた。当該レードル精錬方法が低級酸化物の還元に極めて有効であることが解る。
還元によりＰ濃度は通常の０．０１０から０．０１３％へ増加するのに対して０．０１０から０．０１７％になった。溶鋼中のＭｎ濃度は０．０４％の増加した。 Example 1: The verification test of the second invention was conducted. Using a 30-ton electric furnace, all scrap iron was melted as a raw material, and 0.8% C high carbon steel was melted. After oxidative refining, most of the slag in the furnace was discharged and part of it remained. The remaining amount was set at 2 levels, one was the conventional working condition, and the other was doubled in the conventional amount. Next, in both cases, about 300 kg of lime was newly added while arc heating, and the amount of slag was increased. In contrast to the latter, the ferrosilicon was increased from 5 to 10 kg from the usual level and put into the ladle at the time of steel production. The slag composition immediately after the steel was found to have an average lower oxide concentration of 3% in the conventional normal operation and 7 to 11% in the test. Next, the upper and lower airtight covers are attached to the ladle, the pressure is reduced and maintained at about 0.1 atm by a water ring pump, Ar gas is blown in for about 6 minutes at a flow rate of 160 N liters / minute, gas reduction is performed, and reduction, deoxidation, We proceeded with desulfurization and non-metal inclusion treatment. In the slag composition after refining, the lower oxide concentration was all reduced to 1.0% or less in the 10 charge test. It can be seen that the ladle refining method is extremely effective in reducing lower oxides.
The P concentration was increased from 0.010 to 0.013% by reduction to 0.010 to 0.017%. The Mn concentration in the molten steel increased by 0.04%.

例２： ばね用Ｓｉ−Ｃｒ鋼を対象に同様にＣｒ酸化物の還元試験を行った。Ｃｒの酸素との結合力はＭｎのそれに近い。従来同様の作業において出鋼前に炉内に紛状のＣｒ鉱石（Ｃｒ分３３％）を０．５％Ｃｒ鋼に相当する量４５０ｋｇだけ炉内に装入（推定低級酸化物濃度は約５０％）し、出鋼時には中和用の石灰と、該鉱石中のＣｒとＦｅの化学当量分のＳｉをフェロシリコンの形でレードルに投入した。減圧ガスバブリングによる還元精錬終了後、スラグ中の低級酸化物濃度（ＦｅＯ＋ＭｎＯ＋Ｃｒ₂Ｏ₃）濃度は１．５％に還元されていた。当該レードル精錬方法は低級酸化物の初期濃度が大きくても充分還元されることが解った。 Example 2: The reduction test of Cr oxide was similarly conducted for Si-Cr steel for springs. The binding force of Cr with oxygen is close to that of Mn. In the same operation as before, a powdery Cr ore (33% Cr content) was charged into the furnace in an amount of 450 kg corresponding to 0.5% Cr steel before the steel was released (the estimated lower oxide concentration was about 50). At the time of steel production, lime for neutralization and chemical equivalents of Cr and Fe in the ore were charged into the ladle in the form of ferrosilicon. After the reduction refining by the reduced pressure gas bubbling, the lower oxide concentration (FeO + MnO + Cr ₂ O ₃ ) concentration in the slag was reduced to 1.5%. The ladle refining method was found to be sufficiently reduced even when the initial concentration of the lower oxide was large.

例３： 例１の実験と同様に、酸化精錬後のスラグを目分量で約半分を炉外へ排出、半分を残留させ石灰を約３００ｋｇ投入して低級酸化物を希釈し、還元用炭材を投入したのちレードルに出鋼した。レードルにおいて同様の還元、脱酸、脱硫処理を行った。還元前Ｐは０．０１０％、還元後は０．０２５％を越える場合があり、ＪＩＳ硬鋼線材の規格に問題が生じた。Ｍｎの回収は０．１〜０．２％の効果が得られた。復リンを無視するなら０．２〜０．３％Ｍｎの回収は可能との見通しを得た。 Example 3: Similar to the experiment of Example 1, about half of the slag after oxidative refining is discharged outside the furnace, half is left and about 300 kg of lime is added to dilute the lower oxide, reducing carbon material Was put on the ladle. The same reduction, deoxidation, and desulfurization treatment was performed in the ladle. In some cases, P before reduction exceeds 0.010% and after reduction may exceed 0.025%, which causes a problem in the standard of JIS hard steel wires. The recovery of Mn has an effect of 0.1 to 0.2%. It was expected that recovery of 0.2-0.3% Mn would be possible if rebound was ignored.

本発明によると、屑鉄が含有していたＭｎの一部は溶鋼中に回収され、合金鉄使用量が節減される。他方で不純物Ｐも還元回帰し通常の規制値を越える場合も生ずる。
以上は現行のプロセス・設備・作業を部分修正して容易に実施することができる。Ｐの増加した溶鋼に対して、中心偏析が発生せず、且つ等軸晶間のセミマクロ偏析も発生させない連続鋳造方法（中空鋳片の圧接による中実化）を採用して鋼片を製造することによりＰの有害性を解消ないし抑制する。その結果、１）Ｍｎ合金鉄の使用量が削減され、２）スラグ量が消費及び廃棄の両面で削減され、３）スラグ量減少による省エネルギーが得られ、４）且つＰの合金化作用を誘導・活用することが可能になる。
本発明は文献１の上記連続鋳造方法の効用を新規に拡張する。 According to the present invention, a part of Mn contained in scrap iron is recovered in the molten steel, and the amount of alloy iron used is reduced. On the other hand, the impurity P may also be reduced and returned to exceed the normal regulation value.
The above can be easily implemented by partially modifying the current processes, equipment, and operations. A steel slab is manufactured by adopting a continuous casting method (solidification by pressure welding of a hollow cast slab) that does not generate center segregation and does not generate semi-macro segregation between equiaxed crystals for molten steel with increased P. This eliminates or suppresses the harmful effects of P. As a result, 1) the amount of Mn alloy iron used is reduced, 2) the amount of slag is reduced in terms of both consumption and disposal, 3) energy is saved by reducing the amount of slag, and 4) the alloying action of P is induced.・ It can be used.
The present invention newly extends the utility of the continuous casting method of Document 1.

本発明を実施する設備群の前半の例の説明図である。It is explanatory drawing of the example of the first half of the installation group which implements this invention. 本発明を実施する設備群の後半の例の説明図である。It is explanatory drawing of the example of the second half of the installation group which implements this invention. 凝固組織と不純物析出相を示す組織写真である。It is a structure | tissue photograph which shows a solidification structure | tissue and an impurity precipitation phase.

符号の説明Explanation of symbols

１：屑鉄 ２：溶解炉 ３：アーク ４：酸素ランス ５：スラグ ６：溶鋼 ７：レードル ８：下部気密カバー ９：ホッパー １０：排気装置 １１：上部気密カバー １２：プラグ ２１：溶鋼 ２２：タンディシュ ２３：鋳型 ２４：鋳片 ２５：スプレイ冷却装置 ２６：中空鋳片 ２７：伸直ロール ２８：圧接圧延機 ２９：中実鋳片 1: scrap iron 2: melting furnace 3: arc 4: oxygen lance 5: slag 6: molten steel 7: ladle 8: lower hermetic cover 9: hopper 10: exhaust device 11: upper hermetic cover 12: plug 21: molten steel 22: tundish 23 : Mold 24: Cast slab 25: Spray cooling device 26: Hollow cast slab 27: Straight roll 28: Pressure welding mill 29: Solid slab

Claims (3)

屑鉄を主原料とし溶解炉において該原料を熔解し、精錬し、レードルにおいて仕上げ精錬し、次いで連続鋳造する製鋼方法において、１）溶解中及び溶落後に生成し溶鋼上に浮遊しているスラグの過半を炉内に残留させたまま酸化精錬し、２）該精錬後溶鋼と該スラグを共にレードルに出鋼し、３）該レードルにおいて還元精錬して該スラグ中のＭｎ酸化物をＭｎとして溶鋼中に０．１質量％Ｍｎ以上を回収するとともに、４）Ｐ含有量の増加を許容し、次いで５）該溶鋼から下記の連続鋳造方法によって凝固組織がチル晶と柱状晶から成る鋼片を鋳造することを特徴とする製鋼方法。
記： 溶鋼を下方開放の湾曲鋳型に垂直に鋳込んで鋳片の外皮を形成し、該鋳片を該鋳型下方から連続的に引抜き、該鋳片の中心部が凝固するまでに円弧状に且つ半円を越えさらに鋳込面から大気圧相当静鉄圧高さを越えて上方に引き抜くことによって中空鋳片を形成し、次に該鋳片をロールによって圧下して中空内面を互いに圧接して中実鋳片とする連続鋳造方法であって、該方法において鋳込温度を過熱度で２０〜５０℃と設定することを特徴とする連続鋳造方法。 In a steelmaking method in which scrap iron is used as a main raw material, and the raw material is melted and refined in a melting furnace, finished and refined in a ladle, and then continuously cast, 1) of slag that is generated during and after melting and floats on the molten steel 2) Oxygen refining with the majority remaining in the furnace, 2) Both the molten steel and the slag after refining are put into a ladle, and 3) Reductive refining in the ladle and the Mn oxide in the slag as Mn. In addition to recovering 0.1% by mass or more of Mn therein, 4) allowing an increase in the P content, and then 5) from the molten steel a steel slab whose solidified structure is composed of chill crystals and columnar crystals by the following continuous casting method A steel making method characterized by casting.
Note: Molten steel is vertically cast into a downwardly open curved mold to form a slab skin, and the slab is continuously drawn from the bottom of the mold until it is solidified at the center of the slab. A hollow slab is formed by pulling upward beyond the semi-circle and further exceeding the atmospheric pressure equivalent static iron pressure height from the casting surface, and then pressing the slab with a roll to press the hollow inner surfaces together. A continuous casting method for producing a solid slab, wherein the casting temperature is set to 20 to 50 ° C. in terms of superheat. 還元精錬の方法が、出鋼時に還元剤としてＳｉ含有材、Ａｌ含有材及び炭材の１種以上をレードルに投入し、該還元剤の投入量をスラグ中のＦｅＯ、ＭｎＯ、Ｐ₂Ｏ₅の化学当量の和の０．８〜１．６倍とし、その後、該スラグで覆われた溶鋼中に該レードル底面より精錬用ガスを５〜２０Ｎリットル／分／溶鋼トンの割合で吹き込んでガスバブリングしつつ溶鋼上方の雰囲気圧を６〜４０ｋＰａに減圧・維持することを特徴とする請求項１に記載の製鋼方法。 In the refining method, at least one of a Si-containing material, an Al-containing material, and a carbonaceous material is added to the ladle as a reducing agent at the time of steel output, and the amount of the reducing agent is changed to FeO, MnO, P ₂ O _{5 in the} slag. The refining gas was blown into the molten steel covered with the slag at a rate of 5 to 20 N liters / minute / ton of molten steel into the molten steel covered with the slag. The steelmaking method according to claim 1, wherein the atmospheric pressure above the molten steel is reduced and maintained at 6 to 40 kPa while bubbling. 還元精錬の方法が、出鋼時に還元剤としてＳｉ含有材、Ａｌ含有材及び炭材の１種以上をレードルに投入し、該還元剤の投入量をスラグ中のＦｅＯ、ＭｎＯ、Ｐ₂Ｏ₅の化学当量の和の０．８〜１．２倍とし、その後、アーク加熱用電極を保持したカバーにより該レードルの上方を覆い、該スラグで覆われた溶鋼中に該レードル底面より精錬用ガスを吹き込んで撹拌し、溶鋼上方より炭材投入とアーク加熱によりカーバイド・スラグを生成しつつ還元することを特徴とする請求項１に記載の製鋼方法。 In the refining method, at least one of a Si-containing material, an Al-containing material, and a carbonaceous material is added to the ladle as a reducing agent at the time of steel output, and the amount of the reducing agent is changed to FeO, MnO, P ₂ O _{5 in the} slag. 0.8 to 1.2 times the sum of the chemical equivalents, and then the upper part of the ladle is covered with a cover holding an electrode for arc heating, and the gas for refining from the bottom of the ladle into the molten steel covered with the slag The steelmaking method according to claim 1, wherein the steelmaking method is reduced by generating carbide and slag from above the molten steel by adding carbonaceous material and heating by arc heating.