JPS6159367B2 - - Google Patents
Info
- Publication number
- JPS6159367B2 JPS6159367B2 JP12145280A JP12145280A JPS6159367B2 JP S6159367 B2 JPS6159367 B2 JP S6159367B2 JP 12145280 A JP12145280 A JP 12145280A JP 12145280 A JP12145280 A JP 12145280A JP S6159367 B2 JPS6159367 B2 JP S6159367B2
- Authority
- JP
- Japan
- Prior art keywords
- oxygen
- carbon concentration
- steel
- molten steel
- denitrification
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229910052799 carbon Inorganic materials 0.000 claims description 65
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 63
- 229910000831 Steel Inorganic materials 0.000 claims description 48
- 239000010959 steel Substances 0.000 claims description 48
- 238000007670 refining Methods 0.000 claims description 37
- 239000007789 gas Substances 0.000 claims description 31
- 238000000034 method Methods 0.000 claims description 31
- 238000006243 chemical reaction Methods 0.000 claims description 27
- 238000005261 decarburization Methods 0.000 claims description 23
- 238000009489 vacuum treatment Methods 0.000 claims description 19
- 230000001590 oxidative effect Effects 0.000 claims description 15
- 229910001220 stainless steel Inorganic materials 0.000 claims description 15
- 239000007800 oxidant agent Substances 0.000 claims description 14
- 239000011651 chromium Substances 0.000 claims description 12
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 7
- 239000003795 chemical substances by application Substances 0.000 claims description 7
- 229910001882 dioxygen Inorganic materials 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 229910000967 As alloy Inorganic materials 0.000 claims description 4
- 229910000963 austenitic stainless steel Inorganic materials 0.000 claims description 3
- 230000001737 promoting effect Effects 0.000 claims 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 56
- 229910052760 oxygen Inorganic materials 0.000 description 53
- 239000001301 oxygen Substances 0.000 description 53
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 51
- 229910052757 nitrogen Inorganic materials 0.000 description 28
- 238000007664 blowing Methods 0.000 description 16
- 239000000203 mixture Substances 0.000 description 11
- 230000007423 decrease Effects 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 238000003723 Smelting Methods 0.000 description 5
- 229910052742 iron Inorganic materials 0.000 description 4
- 238000007796 conventional method Methods 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 230000008018 melting Effects 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000002436 steel type Substances 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 150000002926 oxygen Chemical class 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Description
この発明は、真空精錬炉により高クロム鋼を溶
製する際、酸素吹精脱炭中に高真空処理を施して
窒素含有量の低減をはかる高クロム鋼の脱窒精錬
法に関する。
Cr：５〜35％を含有する合金鋼、フエライト
系あるいはオーステナイト系ステンレス鋼等の高
クロム鋼は、窒素溶解度が高いため低窒素化には
不利な鋼であるにも拘らず、鋼質特性上極低窒素
化が要求される。真空精錬炉による溶製法は前記
の要求に応える精錬法の一つとして開発されたも
ので、その代表的な溶製法としては、（）目的
窒素値に応じ精錬初期炭素値を決める方法、
（）真空精錬炉に炉底からArガスを導入する方
法、（）酸素の供給速度を制御する方法をあげ
ることができる。
前記（）の方法は減圧下、酸素吹精中に脱炭
反応と同時に起こる脱窒反応を期待したもので、
〓〓〓〓
初期炭素値を高くすると脱炭中の脱窒量が増大す
るというもので、脱炭反応は反応界面での酸素濃
度を低下させるだけでなく発生する大量のCOガ
スは窒素分圧（ＰN2）を低下させ、さらに反応比
界面積（Ａ／Ｖ）を増大させるため脱窒効果が得
られ、低窒素化には有効な方法とされている。ま
た、（）の方法はArガスを溶鋼中に吹込むこと
により窒素分圧（ＰN2）を低下させるとともに、
反応比界面積（Ａ／Ｖ）を増大させて脱窒を図る
方法であり、（）の方法は高炭素領域で通常約
0.4Nm3／min／tonで酸素を溶鋼中に供給し、臨
界炭素濃度以下の低炭素領域ではO2等の酸化性
ガスに不活性ガスを混入して過酸化を防止し、ク
ロム酸化を抑制しながら脱窒を図る方法である。
しかるに、前記（），（），（）の方法はい
ずれも脱窒反応には有効であるが、次のごとき欠
点を有する。
すなわち、酸素吹精中はガス発生速度が高く、
溶鋼の流動およびスプラツシユ飛散等の点から高
真空を維持できないこと、またそのために酸素吹
精による脱炭中は溶鋼中酸素濃度が高くなるた
め、脱窒反応速度は低下する。また、減圧中に底
吹Arガス量を増大することは、炉体耐火物の維
持に問題があるのみならず大量のArガスを溶鋼
中に導入すると、溶鋼温度降下をもたらし熱補償
の点でも不利である。さらにArガス導入中でも
酸素吹精期には前記のごとく操業面で高真空を維
持できない。
このように、真空精錬炉で低窒素鋼を溶製する
場合、酸素吹精初期の炭素濃度を高くしたり、高
真空にすることは窒素含有の低減に効果はあつて
も、酸素吹精中に高真空にすることは前記のごと
く操業上困難である。
この発明は、Cr：５〜35％を含有する合金
鋼、フエライト系あるいはオーステナイト系ステ
ンレス鋼等の高クロム鋼を真空精錬炉で溶製する
際、酸素ガス等の酸化性ガス、酸化剤等を用いて
脱炭処理する過程において、溶鋼中炭素濃度が臨
界炭素濃度以上の領域で前記酸素ガス等の酸化性
ガス、および／または酸化剤等の供給を一時中断
し高真空処理を施すこと、更に必要に応じて高真
空処理を施す前にAl，Ti，Zr等の脱酸剤を添加
して脱酸することにより、脱窒素反応を促進させ
ることを特徴とするものである。
真空精錬炉で、供給する酸化性ガスおよび／ま
たは酸化剤の供給速度が一定である場合、鋼の脱
炭速度はある炭素濃度以上の領域では一定で、鋼
の炭素濃度は時間に対し直線的に減少するが、一
方その炭素濃度以下で脱炭速度は急激に低下す
る。この脱炭速度が一定値から急激に低下し始め
る時点の炭素濃度を臨界炭素濃度と定義する。
一般に、臨界炭素濃度以上の領域では、第１
図、第２図および第４図に示すごとく、脱炭速
度は一定（−ｄ〔Ｃ〕／dt＝ｋ、又は〔Ｃ〕∝−
ｋ・ｔ）、〔Cr〕の酸化は余り見られない。ま
た、臨界炭素濃度以下の領域では、第１図、第２
図、第３図および第４図に示すごとく、脱炭速
度は炭素濃度に比例（−ｄ〔Ｃ〕／dt＝ｋ
〔Ｃ〕、又はlog〔Ｃ〕∝ｋ・ｔ）、〔Cr〕の酸
化は顕著になる。なお、第１図〜第４図は、溶鋼
温度1600℃、真空度20torr、送酸速度0.45Nm3／
min／tonの場合である。
この発明は、高クロム鋼を真空精錬炉で溶製す
る際、溶鋼中炭素濃度が上記臨界炭素濃度以上の
領域で酸素ガス等の酸化性ガス、および／または
酸化剤等の供給を一時中断し高真空処理を施し、
さらに脱酸剤を添加して脱窒素反応を促進させる
ことを特徴とするものである。
すなわち、この発明は真空精錬炉で極低窒素鋼
を溶製する際、脱炭過程で酸素等の酸化性ガス、
および／または酸化剤等の供給を一時中断して高
真空度を確保する方法である。ここで、高真空度
とは臨界炭素濃度以上の炭素濃度領域で10torr以
下をいう。この高真空度を得るため、脱炭過程で
酸素等の酸化性ガスまたは酸化剤等の供給を一時
停止すると、溶鋼の脱窒反応速度をあらわす下記
(1)式中、窒素溶解度が低下し、（〔Ｎ〕２−〔Ｎ〕
２ ｅ）が増大するとともに、反応界面での酸素濃度
が低下し見かけの反応速度係数k2′が増大するた
め、脱窒速度は大きくなる。
〔脱窒反応速度〕
−ｄ〔Ｎ〕／dt＝（Ａ／Ｖ）k′2（〔Ｎ〕２
−〔Ｎ〕２ ｅ） (1)式
但し、k′2＝ａ・２ Ｎ／｛１＋Ko〔Ｏ〕
＋Ks〔Ｓ〕｝２
Ａ：反応界面積
Ｖ：溶鋼体積
ａ，Ko，Ks：定数
〓〓〓〓
k′2：見かけの反応速度係数
N：窒素の活量係数
〔Ｎ〕：窒素濃度（％）
〔Ｎ〕ｅ：ガス相と平衡する窒素濃度（％）
〔Ｏ〕：酸素濃度（％）
〔Ｓ〕：硫黄濃度（％）
また同時に、酸素の平衡反応をあらわす(2)式に
より脱炭反応の進行と共に平衡酸素濃度が低下
し、見かけの反応速度係数k2′が増大する。
〔酸素の平衡反応〕
CO(g)＝Ｃ＋Ｏ (2)式
logK（＝ｃ・ｏ〔Ｃ〕・〔Ｏ〕／Pco）
＝−1160／Ｔ−2.003−0.54〔Ｏ〕
＋log〔Ｏ〕
＝（−1160／Ｔ−2.003）＋0.065〔Cr〕
＋0.25〔Ｃ〕
−log〔Ｃ〕＋logPco
〔Ｃ〕：炭素濃度
〔Ｏ〕：酸素濃度
〔Cr〕：Cr濃度
Pco：Coガス分圧
Ｔ：絶対温度
このように高真空度を得ることにより平衡窒素
溶解度低下および平衡酸素濃度を低下させること
ができる。この高真空度を得る場合、この発明で
は酸素等の酸化性ガス等、または酸化剤等の供給
を一時中断する時期を限定する。すなわち臨界炭
素濃度以上の領域で10torr以下の高真空を維持で
きる時期で、この時期には溶鋼中酸素濃度は
200ppm以下にすることができる時期でもある。
臨界炭素濃度は装置設備及び操業圧力により若
干異なるが〔Ｃ〕＝0.1〜0.3％程度であり、これ
を知る方法としては、例えば下記４項目がある。
炉から排出される排ガスを、排ガス流量計で
排ガス量Ｖ（ｌ／min）、排ガス分析機でCO，
CO2濃度（％）を測定するとともに、排ガス温
度（ｔ℃）、排ガス圧力（Ptorr）を測定し、下
記式より脱炭する炭素量Ａ（gr／min）を算出
する。
Ａ＝（％ＣＯ）＋（％ＣＯ２）／１００×１２／２
２．４
×２７３．１５／２７３．１５＋ｔ×Ｐ・Ｖ／７６
０
上記により算出した炭素量(A)と、初期溶銑重
量Wo（ton）、酸素流量Ｑ（Ｎm3／min）の値
より、時々刻々の脱炭速度dc／do2（％／Ｎ
m3）を算出し、この値の減少時期を臨界炭素濃
度領域とする。
dc／do2＝Ａ／Ｗｏ×Ｑ
過去の精錬チヤージ（溶鉄成分、溶鉄温度、
炉内圧力、酸素流量等）を鋼種や精錬条件別に
多数分類し、この個々の分類より前述の
dc／do2（％／Ｎm3）及び臨界炭素濃度領域の
関係から臨界炭素濃度領域に達するまでに必要
とする酸素量を予め定め、この酸素量（QoN
m3）と現に精錬中の酸素流量（QNm3／min）
から臨界炭素濃度領域に至る時間を求めて臨界
炭素濃度領域とする。
ｔ（時間）＝Qo（Ｎm3）／Ｑ（Ｎm3／min）
精錬中に多数回溶鋼を採取し、カントバツク
分析、又は化学分析等により、前記採取した溶
鋼の成分を求めるとともに、各採取間で脱炭速
度（dc／dt）を算出し、その減少時期を臨界炭
素濃度領域とする。
dc／dt＝（％Ｃ(i)）−（％Ｃ（ｉ＋１））／ｔ（ｉ
＋１）−ｔ(i)
過去の精錬チヤージ（溶鉄成分、溶鉄温度、
炉内圧力、酸素流量等）を鋼種や精錬条件別に
多数分類し、この分類内容と、臨界炭素濃度領
域に到る時間とを予め定めて、精錬経過時間よ
り臨界炭素濃度領域を知る。
よつて、この発明では酸素吹精脱炭過程におい
て、鋼中炭素濃度が臨界炭素濃度以上のときに酸
素等の酸化性ガスまたは酸化剤の供給を一時中断
して高真空度を得るのである。酸素等の酸化性ガ
スまたは酸化剤の供給を停止して高真空状態を保
持する時間は溶鋼温度降下との関係および設備、
装置等の条件を考慮して決定される。また高炭素
領域で高真空条件に設定する回数は１精錬過程で
１回以上必要である。
更に、一層の脱窒素を促進させるために、高真
空処理を施す前に、Al，Ti，Zr等の脱酸剤を添
加するとよい。前記脱酸剤の添加によつて、脱窒
反応界面での酸素濃度が低下し、前述の(1)式によ
り見かけの反応速度k2′が増加し、脱窒速度も大
きくなつて、一層脱窒素を促進する。なお、脱酸
剤の添加回数は１回に限らず、数回にわたり添加
〓〓〓〓
してもよく、添加量は、脱酸剤の脱酸力（反応
性）により決定すればよい。
この方法によれば、酸素吹精脱炭過程で臨界炭
素濃度以上の領域（溶鋼中酸素濃度が200ppm以
下になり得る炭素濃度の領域）で酸素等の酸化性
ガスまたは酸化剤等の供給を一時中断することに
より高真空状態を保持することができるので、脱
窒反応速度を上昇させることができ、効率よく脱
窒素が可能となる。
次に、比較のための参考例とこの発明の実施例
について説明する。
〔参考例〕
2.5トン真空精錬炉で、第１表に示す組成を有
する粗溶鋼（１―Ａ）、及び（２―Ａ）を送酸速
度0.45Nm3／min／tonで酸素上吹き吹精を実施し
た。
その際、酸素ガスによる脱炭精錬中の真空度を
20torr、温度を1600〜1620℃にそれぞれ制御し
た。そのときの溶鋼中の窒素と酸素の挙動と炭素
の変化をそれぞれ第５図Ａ，Ｂに示す。なお、第
５図Ａ，ＢのNo.１は第１表のヒートNo.（１―
Ａ）、（１―Ｂ）を、No.２はヒートNo.（２―Ａ）、
（２―Ｂ）を示し、（１―Ｂ）、（２―Ｂ）はそれぞ
れの精錬後の組成を示す。また、この時の臨界炭
素濃度は、No.１、No.２は2.5トンの真空精錬実験
であり、〔Ｃ）≒0.1％であることが判つている。
第５図の結果より、溶鋼中の酸素濃度が約
200ppm以下では脱窒素反応は進行するが、約
200ppm以上になると脱窒素反応はほぼ停止する
ことがわかる。この酸素濃度200ppmは精錬中の
臨界炭素濃度に相当する。
即ち、臨界炭素濃度以上で脱窒精錬を行なうこ
とが窒素低減のために肝用である。
The present invention relates to a denitrification refining method for high chromium steel in which high vacuum treatment is performed during oxygen-blown decarburization to reduce nitrogen content when high chromium steel is melted in a vacuum refining furnace. High chromium steels such as alloy steels containing 5 to 35% Cr, ferritic stainless steels, and austenitic stainless steels have high nitrogen solubility, making them disadvantageous for low nitrogen production. Extremely low nitrogen is required. The smelting method using a vacuum smelting furnace was developed as one of the smelting methods to meet the above requirements, and the typical smelting methods include () a method of determining the initial carbon value for refining according to the target nitrogen value;
() A method of introducing Ar gas from the bottom of the vacuum refining furnace, and () A method of controlling the oxygen supply rate. The above method () is based on the expectation that the denitrification reaction will occur simultaneously with the decarburization reaction during oxygen blowing under reduced pressure.
〓〓〓〓
Increasing the initial carbon value increases the amount of denitrification during decarburization, and the decarburization reaction not only reduces the oxygen concentration at the reaction interface, but also increases the amount of CO gas generated by increasing the nitrogen partial pressure (P N2 ). It is said to be an effective method for reducing nitrogen because it lowers the denitrification effect and increases the reaction specific interfacial area (A/V). In addition, method () lowers the nitrogen partial pressure (P N2 ) by injecting Ar gas into molten steel, and
This method aims at denitrification by increasing the reaction specific interfacial area (A/V).
Oxygen is supplied to molten steel at a rate of 0.4Nm 3 /min/ton, and in the low carbon region below the critical carbon concentration, inert gas is mixed with oxidizing gas such as O 2 to prevent overoxidation and suppress chromium oxidation. This method aims at denitrification while However, although the methods (), (), and () above are all effective for denitrification reactions, they have the following drawbacks. In other words, during oxygen blowing, the gas generation rate is high,
A high vacuum cannot be maintained due to the flow of molten steel and splashing, and as a result, the oxygen concentration in molten steel increases during decarburization by oxygen blowing, resulting in a decrease in the denitrification reaction rate. In addition, increasing the amount of bottom-blown Ar gas during depressurization not only poses a problem in maintaining the furnace refractories, but also introduces a large amount of Ar gas into the molten steel, which causes the temperature of the molten steel to drop, which is also a problem in terms of thermal compensation. It is disadvantageous. Furthermore, even when Ar gas is introduced, high vacuum cannot be maintained during the oxygen blowing period due to operational reasons. In this way, when melting low nitrogen steel in a vacuum refining furnace, increasing the carbon concentration at the initial stage of oxygen blowing or using high vacuum may be effective in reducing nitrogen content, but As mentioned above, it is operationally difficult to create a high vacuum. This invention uses oxidizing gas such as oxygen gas, oxidizing agent, etc. when melting high chromium steel such as alloy steel containing 5 to 35% Cr, ferritic stainless steel, or austenitic stainless steel in a vacuum refining furnace. In the process of decarburizing treatment using the molten steel, the supply of oxidizing gas such as oxygen gas and/or oxidizing agent is temporarily interrupted in a region where the carbon concentration in the molten steel is equal to or higher than the critical carbon concentration, and high vacuum treatment is performed. It is characterized in that the denitrification reaction is promoted by adding a deoxidizing agent such as Al, Ti, Zr, etc. to perform deoxidation before performing high vacuum treatment if necessary. In a vacuum smelting furnace, when the supply rate of oxidizing gas and/or oxidizing agent is constant, the decarburization rate of steel is constant in the region above a certain carbon concentration, and the carbon concentration of steel is linear with respect to time. However, below that carbon concentration, the decarburization rate decreases rapidly. The carbon concentration at which the decarburization rate begins to rapidly decrease from a constant value is defined as the critical carbon concentration. Generally, in the region above the critical carbon concentration, the first
As shown in Figures 2 and 4, the decarburization rate is constant (-d[C]/dt=k, or [C]∝-
k・t), oxidation of [Cr] is not seen much. In addition, in the region below the critical carbon concentration, Figures 1 and 2
As shown in Figures 3 and 4, the decarburization rate is proportional to the carbon concentration (-d[C]/dt=k
Oxidation of [C], or log [C]∝k·t), [Cr] becomes significant. In addition, Figures 1 to 4 are for molten steel temperature 1600℃, vacuum degree 20torr, and oxygen feeding rate 0.45Nm 3 /
This is the case of min/ton. This invention temporarily suspends the supply of oxidizing gas such as oxygen gas and/or oxidizing agent in a region where the carbon concentration in the molten steel exceeds the above-mentioned critical carbon concentration when high chromium steel is melted in a vacuum refining furnace. After high vacuum treatment,
Furthermore, a deoxidizing agent is added to promote the denitrification reaction. That is, this invention uses oxidizing gases such as oxygen during the decarburization process when melting ultra-low nitrogen steel in a vacuum refining furnace.
and/or a method of temporarily interrupting the supply of an oxidizing agent, etc. to ensure a high degree of vacuum. Here, the high degree of vacuum refers to a carbon concentration region of 10 torr or less in a carbon concentration region that is higher than the critical carbon concentration. In order to obtain this high degree of vacuum, when the supply of oxidizing gas such as oxygen or oxidizing agent is temporarily stopped during the decarburization process, the denitrification reaction rate of molten steel is shown below.
(1) In the formula, nitrogen solubility decreases, ([N] 2 - [N]
2 e ) increases, the oxygen concentration at the reaction interface decreases and the apparent reaction rate coefficient k 2 ' increases, so the denitrification rate increases. [Denitrification reaction rate] -d[N]/dt=(A/V) k'2 ([N] 2- [ N ] 2e ) (1) Formula However, k'2 =a・2N /{ 1+Ko[O] +Ks[S]} 2 A: Reaction interfacial area V: Molten steel volume a, Ko, Ks: Constant〓〓〓〓
k' 2 : Apparent reaction rate coefficient N : Nitrogen activity coefficient [N]: Nitrogen concentration (%) [N]e: Nitrogen concentration in equilibrium with the gas phase (%) [O]: Oxygen concentration (%) [ S]: Sulfur concentration (%) At the same time, according to equation (2) expressing the equilibrium reaction of oxygen, the equilibrium oxygen concentration decreases as the decarburization reaction progresses, and the apparent reaction rate coefficient k 2 ' increases. [Equilibrium reaction of oxygen] CO(g)= C + O (2) Formula logK (=c・o[C]・[O]/Pco) =−1160/T−2.003−0.54[O] +log[O] = (-1160/T-2.003) +0.065 [Cr] +0.25 [C] -log [C] + logPco [C]: Carbon concentration [O]: Oxygen concentration [Cr]: Cr concentration Pco: Co gas content Pressure T: Absolute temperature By obtaining a high degree of vacuum in this way, it is possible to reduce the equilibrium nitrogen solubility and the equilibrium oxygen concentration. In order to obtain this high degree of vacuum, the present invention limits the timing at which the supply of an oxidizing gas such as oxygen or an oxidizing agent is temporarily interrupted. In other words, this is the period when a high vacuum of less than 10 torr can be maintained in the region above the critical carbon concentration, and during this period the oxygen concentration in molten steel is
This is also the time when it can be reduced to 200ppm or less. The critical carbon concentration varies slightly depending on the equipment and operating pressure, but it is approximately [C] = 0.1 to 0.3%, and the following four methods can be used to determine this, for example. The exhaust gas discharged from the furnace is measured by an exhaust gas flow meter to measure the exhaust gas amount V (l/min), and by an exhaust gas analyzer to measure the exhaust gas amount V (l/min), CO,
In addition to measuring the CO 2 concentration (%), the exhaust gas temperature (t° C.) and exhaust gas pressure (Ptorr) are also measured, and the amount of carbon to be decarburized A (gr/min) is calculated from the following formula. A=(%CO)+(% CO2 )/100×12/2
2.4 ×273.15/273.15+t×P・V/76
0 From the carbon content (A) calculated above, the initial hot metal weight Wo (ton), and the oxygen flow rate Q (Nm 3 /min), the momentary decarburization rate dc / do 2 (% / N
m 3 ), and the time when this value decreases is defined as the critical carbon concentration region. dc/do 2 = A/Wo x Q Past refining charge (molten iron composition, molten iron temperature,
Furnace pressure, oxygen flow rate, etc.) are classified according to steel type and refining conditions, and from these individual classifications, the above-mentioned
The amount of oxygen required to reach the critical carbon concentration region is determined in advance from the relationship between dc/do 2 (%/Nm 3 ) and the critical carbon concentration region, and this oxygen amount (QoN
m 3 ) and the oxygen flow rate during refining (QNm 3 /min)
The time required to reach the critical carbon concentration region is determined as the critical carbon concentration region. t (time) = Qo (Nm 3 )/Q (Nm 3 /min) Molten steel is sampled many times during refining, and the components of the sampled molten steel are determined by cantback analysis or chemical analysis, and the Calculate the decarburization rate (dc/dt) and define the period of decrease as the critical carbon concentration region. dc/dt=(%C(i))-(%C(i+1))/t(i
+1)-t(i) Past refining charge (molten iron composition, molten iron temperature,
Furnace pressure, oxygen flow rate, etc.) are classified according to steel type and refining conditions, and the classification contents and the time to reach the critical carbon concentration region are determined in advance, and the critical carbon concentration region is determined from the elapsed refining time. Therefore, in the present invention, in the oxygen-blown decarburization process, when the carbon concentration in the steel exceeds the critical carbon concentration, the supply of an oxidizing gas such as oxygen or an oxidizing agent is temporarily interrupted to obtain a high degree of vacuum. The time to stop the supply of oxidizing gas such as oxygen or the oxidizing agent and maintain a high vacuum state depends on the relationship with the temperature drop of the molten steel, equipment,
It is determined by considering the conditions of the equipment, etc. Further, in the high carbon region, high vacuum conditions are required to be set at least once in one refining process. Furthermore, in order to further promote denitrification, it is preferable to add a deoxidizing agent such as Al, Ti, or Zr before performing the high vacuum treatment. By adding the deoxidizing agent, the oxygen concentration at the denitrification reaction interface decreases, and the apparent reaction rate k 2 ' increases according to equation (1) above, and the denitrification rate increases, resulting in further denitrification. Promotes nitrogen. Note that the number of times the deoxidizing agent is added is not limited to once, but can be added several times.
The amount added may be determined depending on the deoxidizing power (reactivity) of the deoxidizing agent. According to this method, an oxidizing gas such as oxygen or an oxidizing agent, etc. is temporarily supplied in an area where the carbon concentration is above the critical carbon concentration (an area where the oxygen concentration in molten steel can be reduced to 200 ppm or less) during the oxygen-blown decarburization process. By interrupting the process, a high vacuum state can be maintained, so the denitrification reaction rate can be increased, and denitrification can be carried out efficiently. Next, reference examples for comparison and examples of the present invention will be described. [Reference example] In a 2.5-ton vacuum refining furnace, crude molten steel (1-A) and (2-A) having the compositions shown in Table 1 were top-blown with oxygen at an oxygen feeding rate of 0.45 Nm 3 /min/ton. was carried out. At that time, the degree of vacuum during decarburization refining using oxygen gas is
The temperature was controlled at 20 torr and 1600-1620°C, respectively. The behavior of nitrogen and oxygen and the change in carbon in the molten steel at that time are shown in Figures 5A and B, respectively. Note that No. 1 in Figure 5 A and B is the heat No. (1-
A), (1-B), No. 2 is heat No. (2-A),
(2-B) is shown, and (1-B) and (2-B) show the respective compositions after refining. Further, the critical carbon concentration at this time was determined to be [C)≈0.1% in No. 1 and No. 2 in a 2.5 ton vacuum refining experiment. From the results shown in Figure 5, the oxygen concentration in molten steel is approximately
Denitrification reaction proceeds below 200 ppm, but about
It can be seen that the denitrification reaction almost stops when the concentration exceeds 200 ppm. This oxygen concentration of 200 ppm corresponds to the critical carbon concentration during refining. That is, it is important to perform denitrification refining at a carbon concentration higher than the critical carbon concentration in order to reduce nitrogen.
2.5トン真空精錬炉で、第２表に示す組成を有
する粗溶鋼（３―Ａ）を、送酸速度0.45Nm3／
min／tonで酸素上吹き吹精を50分間行い、その
脱炭過程で溶鋼中炭素濃度が0.3％のときに送酸
を一時停止し40分間の高真空処理を実施した。そ
の際、酸素ガス吹精をしない脱炭精錬中の真空度
は1torr、温度を1600〜1620℃にそれぞれ制御し
た。そのときの溶鋼中の窒素と酸素の挙動と炭素
の変化をそれぞれ第６図Ａ，Ｂ―１，Ｂ―２に示
す。第６図Ａ，Ｂ―１，Ｂ―２において、No.３は
従来通り高真空処理を施さなかつたもので、No.４
はこの発明の高真空処理を施したものを示し、ま
た第２表中の（３―Ｂ）に精錬後の組成を示す。
なお、この時のNo.３，No.４も参考例と同じく2.5
トンの真空精錬実験であり、〔Ｃ〕≒0.1％である
ことが判つている。
第６図の結果より明らかなごとく、酸素ガス吹
精完了時における溶鋼中の窒素濃度は本発明法採
用により従来法よりも約20ppmも低い値を得る
ことができた。
Crude molten steel (3-A) having the composition shown in Table 2 was heated in a 2.5-ton vacuum refining furnace at an oxygen flow rate of 0.45Nm 3 /
Oxygen top-blowing was performed for 50 minutes at min/ton, and during the decarburization process, when the carbon concentration in the molten steel reached 0.3%, the oxygen supply was temporarily stopped and high vacuum treatment was performed for 40 minutes. At that time, the degree of vacuum during decarburization refining without oxygen gas blowing was controlled to 1 torr, and the temperature was controlled to 1600 to 1620°C. The behavior of nitrogen and oxygen and the changes in carbon in the molten steel at that time are shown in Figures 6A, B-1, and B-2, respectively. In Figure 6 A, B-1, and B-2, No. 3 was not subjected to conventional high vacuum treatment, and No. 4
shows the material subjected to the high vacuum treatment of the present invention, and (3-B) in Table 2 shows the composition after refining.
In addition, No. 3 and No. 4 at this time are also 2.5 as in the reference example.
It is a vacuum refining experiment of 1,000 yen, and it is found that [C] is approximately 0.1%. As is clear from the results shown in FIG. 6, the nitrogen concentration in the molten steel upon completion of oxygen gas blowing was approximately 20 ppm lower by employing the method of the present invention than by the conventional method.
50トンVOD精錬炉で、第３表に示す組成を有
する粗溶鋼（４―Ａ）を、送酸速度0.45Nm3／
min／tonで酸素上吹き吹精を15分間行い、その
脱炭過程で溶鋼中の炭素濃度が0.6％のときに酸
素吹精を一時中断し、10分間の高真空処理（到達
真空度2torr）を行なつた後、再び酸素吹精をお
こない、更に炭素濃度が0.4％のときに酸素吹精
を一始中断し５分間の２度目の高真空処理を行な
つた後、酸素吹精を再開した。その結果、第３表
の（４―Ｂ）に示す組成を得た。そのときの溶鋼
中の窒素と酸素の挙動と炭素の変化を第７図Ａ，
ＢNo.５に示す。また、脱炭精錬途中で高真空処理
を施さなかつた従来法の参考例をNo.６に比較して
示す。なお、No.６の粗溶鋼の組成を第３表（５―
Ａ）に、精錬後の組成を（５―Ｂ）に示す。ま
た、この時の臨界炭素濃度は、No.５，No.６は50ト
ンVODでの結果であり、この場合〔Ｃ〕≒0.1〜
0.2％であることが判つているので、本発明は
〔Ｃ〕≧0.3％の領域で実施した。
〓〓〓〓
In a 50-ton VOD refining furnace, crude molten steel (4-A) having the composition shown in Table 3 was heated at an oxygen flow rate of 0.45Nm 3 /
Oxygen top blowing is performed for 15 minutes at min/ton, and during the decarburization process, when the carbon concentration in the molten steel reaches 0.6%, oxygen blowing is temporarily interrupted and high vacuum treatment is performed for 10 minutes (achieved vacuum level 2 torr). After that, oxygen blowing was performed again, and when the carbon concentration was 0.4%, oxygen blowing was stopped from beginning to end, and after a second high vacuum treatment for 5 minutes, oxygen blowing was resumed. did. As a result, the composition shown in (4-B) in Table 3 was obtained. Figure 7A shows the behavior of nitrogen and oxygen and changes in carbon in the molten steel at that time.
Shown in B No.5. In addition, a reference example of the conventional method in which high vacuum treatment was not performed during decarburization refining is shown in comparison with No. 6. The composition of No. 6 crude molten steel is shown in Table 3 (5-
In A), the composition after refining is shown in (5-B). In addition, the critical carbon concentration at this time is the result for No. 5 and No. 6 at 50 tons of VOD, and in this case [C] ≒ 0.1 ~
Since it is known that C is 0.2%, the present invention was carried out in the range of [C]≧0.3%. 〓〓〓〓
実施例１と同一精錬炉で、第４表（６―Ａ）に
示す粗溶鋼に0.45Nm3／min／tonの割合で酸素上
吹き吹精を行ない、臨界炭素濃度以上の領域にお
いて、高真空処理を行なうにあたり、事前にAl
を0.2Kg／ton溶鋼中に投入して強制脱酸を施しな
がら高真空処理を行なつた。第８図はこの結果を
示すもので、図中ａは、高真空処理を施さない従
来法であり、ｂは、溶鋼中炭素濃度が0.75％のと
き、及び0.60％のときに酸素吹精を一時中断し40
分間の高真空処理を実施した例を示す。またｃ
は、前記したように高真空処理を行なうにあた
り、事前にAlを溶鋼中に投入した例であり、溶
鋼中炭素濃度が0.75％のとき、及び0.60％のとき
に0.2Kg／tonのAlを溶鋼中に投入した後に酸素吹
精を一時中断し、40分間高真空処理を施した例を
示すものである。この実施例より、炭素濃度が
0.02％の時点で従来例よりも30ppm、高真空処理
のみの場合よりも10ppmも低い窒素濃度を得る
ことができた。なお、第６表（６―Ｂ）は、精錬
後の組成を示すものである。
In the same refining furnace as in Example 1, the crude molten steel shown in Table 4 (6-A) was subjected to oxygen top-blowing at a rate of 0.45 Nm 3 /min/ton, and in the region above the critical carbon concentration, high vacuum was applied. Before processing, Al
was poured into 0.2 kg/ton of molten steel and subjected to high vacuum treatment while being forcedly deoxidized. Figure 8 shows the results. In the figure, a shows the conventional method without high vacuum treatment, and b shows oxygen blowing when the carbon concentration in the molten steel is 0.75% and 0.60%. temporarily suspended 40
An example of high vacuum treatment for 1 minute is shown. Also c
This is an example in which Al was added to the molten steel in advance when performing the high vacuum treatment as described above. This shows an example in which the oxygen blowing process was temporarily interrupted and high vacuum treatment was performed for 40 minutes after the sample was placed inside. From this example, the carbon concentration is
At 0.02%, we were able to obtain a nitrogen concentration that was 30 ppm lower than in the conventional example and 10 ppm lower than in the case of only high vacuum treatment. Note that Table 6 (6-B) shows the composition after refining.
【表】
この発明は上記のごとく、高クロム鋼精錬時に
おける溶鋼中の窒素濃度を効率よく低下させるこ
とができるので、加工性、溶接性および耐食性の
すぐれたフエライト系ステンレス鋼を真空精錬炉
で製造することができ、新鋼種開発に大きく寄与
し得る。[Table] As described above, this invention can efficiently reduce the nitrogen concentration in molten steel during high chromium steel refining, so ferritic stainless steel with excellent workability, weldability, and corrosion resistance can be produced in a vacuum refining furnace. It can be manufactured and can greatly contribute to the development of new steel types.
第１図〜第４図はこの発明者らの行なつた実験
データを示すもので、第１図は溶鋼中の〔Ｃ〕の
推移を示す図表、第２図および第３図は第１図鎖
線部の拡大図表、第４図はCrと〔Ｃ〕の関係を
示す図表、第５図Ａ，Ｂはそれぞれ参考例におけ
る溶鋼中の窒素と酸素の挙動と、炭素の変化を示
す図表、第６図Ａ，Ｂ―１，Ｂ―２はそれぞれこ
の発明の実施例１における溶鋼中の窒素と酸素の
挙動と、炭素の変化を示す図表、第７図Ａ，Ｂは
それぞれ同上実施例２における炭素と窒素の挙動
と、炭素の変化を示す図表、第８図は同上実施例
３における溶鋼中の窒素と炭素の挙動を示す図表
である。
〓〓〓〓
Figures 1 to 4 show experimental data conducted by the inventors, with Figure 1 being a chart showing the transition of [C] in molten steel, Figures 2 and 3 being Figure 1. Figure 4 is a diagram showing the relationship between Cr and [C], and Figure 5 A and B are diagrams showing the behavior of nitrogen and oxygen in molten steel and changes in carbon in the reference example, respectively. Figures 6A, B-1, and B-2 are graphs showing the behavior of nitrogen and oxygen in molten steel and changes in carbon in Example 1 of the present invention, respectively, and Figures 7A and B are graphs showing the changes in carbon in Example 2 of the same, respectively. A chart showing the behavior of carbon and nitrogen and changes in carbon. FIG. 8 is a chart showing the behavior of nitrogen and carbon in molten steel in Example 3. 〓〓〓〓
Claims (1)
あるいはオーステナイト系ステンレス鋼等の高ク
ロム鋼を真空精錬炉で溶製する際、酸化性ガス、
および／または酸化剤を用いて脱炭処理する過程
において、溶鋼中炭素濃度が臨界炭素濃度以上の
領域で前記酸化性ガス、および／または酸化剤の
供給を一時中断し高真空処理を施すことにより、
脱窒素反応を促進させることを特徴とする高クロ
ム鋼の脱窒精錬法。 ２ Cr5〜35％を含有する合金鋼、フエライト系
あるいはオーステナイト系ステンレス鋼等の高ク
ロム鋼を真空精錬炉で溶製する際、酸素ガス等の
酸化性ガス、および／または酸化剤を用いて脱炭
処理する過程において、臨界炭素濃度以上の高炭
素濃度領域で前記酸化性ガス、および／または酸
化剤の供給を一時中断し、脱酸剤を添加して脱酸
処理した後に、高真空処理を施すことにより、脱
窒素反応を促進させることを特徴とする高クロム
鋼の脱窒精錬法。[Claims] 1. When high chromium steel such as alloy steel containing 5 to 35% Cr, ferritic or austenitic stainless steel is melted in a vacuum refining furnace, oxidizing gas,
and/or in the process of decarburization treatment using an oxidizing agent, the supply of the oxidizing gas and/or oxidizing agent is temporarily interrupted in a region where the carbon concentration in the molten steel is equal to or higher than the critical carbon concentration, and high vacuum treatment is performed. ,
A denitrification refining method for high chromium steel characterized by promoting denitrification reactions. 2 When high chromium steel such as alloy steel containing 5 to 35% Cr, ferritic or austenitic stainless steel is melted in a vacuum refining furnace, it is decomposed using an oxidizing gas such as oxygen gas and/or an oxidizing agent. In the process of carbon treatment, the supply of the oxidizing gas and/or oxidizing agent is temporarily interrupted in a high carbon concentration region equal to or higher than the critical carbon concentration, and after deoxidizing treatment is performed by adding a deoxidizing agent, high vacuum treatment is performed. A denitrification refining method for high chromium steel that is characterized by promoting the denitrification reaction.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12145280A JPS5763620A (en) | 1980-09-01 | 1980-09-01 | Denitriding and refining method for high chromium steel |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12145280A JPS5763620A (en) | 1980-09-01 | 1980-09-01 | Denitriding and refining method for high chromium steel |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5763620A JPS5763620A (en) | 1982-04-17 |
| JPS6159367B2 true JPS6159367B2 (en) | 1986-12-16 |
Family
ID=14811477
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12145280A Granted JPS5763620A (en) | 1980-09-01 | 1980-09-01 | Denitriding and refining method for high chromium steel |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5763620A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5356456A (en) * | 1992-10-07 | 1994-10-18 | Kawasaki Steel Corporation | Method of degassing and decarburizing stainless molten steel |
| CN102329920B (en) * | 2011-10-25 | 2013-04-24 | 宝山钢铁股份有限公司 | Method for smelting high-aluminum low-silicon ultra pure ferritic stainless steel |
-
1980
- 1980-09-01 JP JP12145280A patent/JPS5763620A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5763620A (en) | 1982-04-17 |
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