JP4212277B2 - In-furnace atmosphere stabilization method in a batch annealing furnace using a heat insulating material that absorbs and releases CO2 on the furnace wall - Google Patents
In-furnace atmosphere stabilization method in a batch annealing furnace using a heat insulating material that absorbs and releases CO2 on the furnace wall Download PDFInfo
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- JP4212277B2 JP4212277B2 JP2002000144A JP2002000144A JP4212277B2 JP 4212277 B2 JP4212277 B2 JP 4212277B2 JP 2002000144 A JP2002000144 A JP 2002000144A JP 2002000144 A JP2002000144 A JP 2002000144A JP 4212277 B2 JP4212277 B2 JP 4212277B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、酸化物が付着した鋼材を直接焼鈍処理する炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉における炉内雰囲気安定化処理方法に関するものである。
【０００２】
【従来の技術】
従来、酸化物が付着している鋼材（線材コイル等）の焼鈍処理方法として、炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉において、酸化物が表面に付着した鋼材を還元性雰囲気中で所定時間加熱保持し、前記酸化物を還元させたのち、焼鈍温度まで加熱する方法が知られている。
【０００３】
すなわち、まず、酸化物が付着した鋼材を炉内に装入したのち、炉内に不活性ガス（たとえば、Ｎ２ガス）を供給して炉内雰囲気をパージして炉内雰囲気中のＯ２濃度を所定値以下とし、その後、炉内に吸熱型変成ガスである還元性ガスを供給しながら、炉内温度を鋼材に酸化・脱炭が生じない温度（５５０〜６８０℃）で加熱する。
【０００４】
通常、前記還元性ガスの供給初期時には、還元性ガス中の主要成分であるＣＯやＨ２が前記酸化物と反応し多量のＣＯ２やＨ２Ｏが放出し、反応が飽和すれば、それ以後ＣＯ２やＨ２Ｏの放出は徐々に減少するが、その間、炉内雰囲気中のＣＯ２濃度が所定濃度になるまで加熱保持し、その後、焼鈍温度まで炉内雰囲気の炭素ポテンシャル値（以下、ＣＰ値という）を調整しながら加熱する（この期間を、雰囲気安定処理期間という）。
【０００５】
【発明が解決しようとする課題】
しかしながら、前記雰囲気安定処理期間の初期において発生する大量の不純ガスは炉壁を構成する、ＣＯ２を吸収、放出する断熱材中に侵入し、その後、炉内の不純ガス量の低下とともに炉内に放出されるため、炉内の不純ガスの減少速度は極めて緩やかで、雰囲気安定化処理期間が長くなる。つまり、生産性が悪いという課題を有していた。
【０００６】
そこで、本発明は前記雰囲気安定処理期間の初期において大量に発生する不純ガスをパージすることにより、雰囲気安定処理期間を短縮して生産性を向上することのできる炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉における炉内雰囲気安定化処理方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は前記目的を達成するために、酸化物が付着した鋼材を炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉で焼鈍するに際し、鋼材が装入された炉内に不活性ガスを供給して炉内雰囲気を不活性ガス雰囲気に置換したのち、吸熱型変成ガスからなる還元性ガスを供給して炉内雰囲気を還元性雰囲気に変更し、この還元性雰囲気下で、かつ、前記鋼材の酸化および浸炭が生じない温度域で鋼材を酸化物と還元性ガスとの反応によって生じる炉内ＣＯ２濃度がピーク値に達するまで加熱保持し、その後、還元性ガスの供給を停止して不活性ガスを炉内に供給し、炉内ＣＯ２濃度が１．５体積％未満になるまでパージしたのち、還元性ガスを炉内に再供給して炉内ＣＯ２濃度が１．５体積％未満で、かつ、炉内炭素ポテンシャルが所定値になったのち、炉内雰囲気の炭素ポテンシャルを管理しながら焼鈍温度まで加熱することを特徴とする炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉における炉内雰囲気安定化処理方法である。
【０００８】
【発明の実施の形態】
つぎに、本発明の実施の形態を図１にしたがって説明する。
まず、炉内を鋼材に酸化や脱炭が生じない５５０〜６８０℃に加熱保持した炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉内に、酸化物が付着した線材コイル等の鋼材を装入したのち、炉内に不活性ガスを供給して炉内雰囲気を不活性雰囲気に置換する。この場合、つぎの還元性ガスの炉内供給時に爆発が生じるのを防止するため、不活性ガスの供給は炉内雰囲気中のＯ２濃度が０．８体積％以下になるまで行なわれる。
【０００９】
ついで、炉内雰囲気のＯ２濃度が０．８体積％以下になると、不活性ガスの供給量を減少させるとともに、還元性ガスを供給する。この場合、還元性ガスの供給量は、酸化物と還元性ガスとの反応を十分に行なわせるため所定時間かけて、最低、炉内容積の３〜５倍量（温度換算値）供給するのが好ましい。
【００１０】
そして、前述のように、炉内に還元性ガスが供給されると、酸化物と還元性ガス中の主要成分であるＣＯやＨ２とが反応し、多量の不純ガス（ＣＯ２，Ｏ２，Ｈ２Ｏ）が発生して炉内ＣＯ２濃度が急激に増加する。この炉内ＣＯ２濃度がほぼピーク値に達すると、還元性ガスの炉内供給を停止する一方、不活性ガスの炉内供給量を増加して前記不純ガスを炉内からパージする。すなわち、多量の不純ガスが炉内に滞留する時間を短縮することになり、炉内壁を構成するＣＯ２を吸収、放出する断熱材中への不純ガスの侵入量は軽減する。
【００１１】
不活性ガスの炉内供給に基づく前記不純ガスのパージにより、炉内雰囲気中のＣＯ２濃度が１．５体積％未満、好ましくは１．０〜１．３体積％、さらに好ましくは０．１〜０．５体積％に達すると、不活性ガスの供給量を減少させる一方、還元性ガスを炉内に再供給するとともに、炉内雰囲気の炭素ポテンシャル値の検知を開始する。この場合、還元性ガスの再供給により、鋼材に付着した残りの酸化物は還元性ガスと反応を行なって一時的に比較的多量の不純ガスが発生するとともに、炉壁のＣＯ２を吸収、放出する断熱材からも不純ガスが放出されるが、前述のように、ＣＯ２を吸収、放出する断熱材中に侵入する不純ガス量は少ないので比較的短時間で不純ガス濃度は低下することになる。
【００１２】
そして、炉内ＣＯ２濃度が１．５体積％未満となり、かつ、炉内ＣＰ値が所定値に達すると、以後、鋼材に、浸炭現象および脱炭現象が起こらないようにＣＰ制御を行ないながら焼鈍温度への加熱を行なう。なお、炉内雰囲気中のＣＯ２濃度を１．５体積％未満とするのは、１．５体積％以上であれば、つぎの焼鈍温度への加熱時に炭素ポテンシャル制御（ＣＰ制御）を行なっても浸炭と脱炭が同時に進行して所定の品質を確保できないという経験に基づくものである。また、炉内ＣＰ値は当該温度で鋼材が脱炭や浸炭を起さない値であり、鋼種によって適宜決定されるもので、たとえば、ＳＣＲ４３０では６８０℃の加熱でＣＰ値は約１３０である。
【００１３】
なお、焼鈍時のＣＰ値は、前述と同様に、処理対象鋼材の種類によって決定されるもので、たとえば、ＳＣＲ４３０では１３０〜１４０に管理される。
【００１４】
【発明の効果】
以上の説明で明らかなように、本発明によれば、炉壁にＣＯ２を吸収、放出する断熱材を使用したバッチ式焼鈍炉で酸化物が表面に付着した鋼材を還元性雰囲気中で加熱し、その酸化物を還元する場合に発生する不純ガスを、一旦、不活性ガスにてパージするため、また、このパージにより炉内ＣＯ２を吸収、放出する断熱材が高濃度の不純ガスを含有する雰囲気に曝される時間が短く、すなわち、その後炉内に放出される不純ガス量も少なく、鋼材の炉内装入から焼鈍温度に到達するまでの期間（雰囲気安定化期間）が、従来においては１３時間１５分のところ、本発明では８時間５６分と約３３％短縮され、それだけ生産性が向上したものである。
【図面の簡単な説明】
【図１】 本発明方法における炉温、炉内ＣＯ２濃度、ＣＰ値、および還元性ガスと不活性ガスの炉内供給状態を示すグラフ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-furnace atmosphere stabilization treatment method in a batch annealing furnace using a heat insulating material that absorbs and releases CO 2 on a furnace wall that directly anneals steel material to which an oxide is attached.
[0002]
[Prior art]
Conventionally, as a method of annealing treatment of steel materials (wire coils, etc.) with oxides attached, steel materials with oxides attached to the surface in a batch-type annealing furnace using a heat insulating material that absorbs and releases CO 2 on the furnace wall Is known to be heated and held in a reducing atmosphere for a predetermined time to reduce the oxide and then heat to an annealing temperature.
[0003]
That is, first, after the steel material to which the oxide has adhered is charged into the furnace, an inert gas (for example, N 2 gas) is supplied into the furnace to purge the furnace atmosphere, and O 2 in the furnace atmosphere. The concentration is set to a predetermined value or less, and then the furnace temperature is heated to a temperature (550 to 680 ° C.) at which the steel material is not oxidized or decarburized while supplying a reducing gas that is an endothermic transformation gas into the furnace.
[0004]
Usually, at the initial stage of supply of the reducing gas, if CO or H 2 which are main components in the reducing gas react with the oxide to release a large amount of CO 2 or H 2 O and the reaction is saturated, Thereafter, the release of CO 2 and H 2 O gradually decreases. During this time, the CO 2 concentration in the furnace atmosphere is heated and held until the predetermined concentration is reached, and then the carbon potential value of the furnace atmosphere up to the annealing temperature (below) (Referred to as CP value) (this period is referred to as an atmosphere stabilization treatment period).
[0005]
[Problems to be solved by the invention]
However, a large amount of impure gas generated at the beginning of the atmosphere stabilization treatment period penetrates into the heat insulating material that constitutes the furnace wall and absorbs and releases CO 2 . Therefore, the reduction rate of the impure gas in the furnace is very gradual, and the atmosphere stabilization processing period becomes long. That is, it has a problem that productivity is poor.
[0006]
Therefore, the present invention absorbs and releases CO 2 to the furnace wall, which can shorten the atmosphere stabilization treatment period and improve productivity by purging a large amount of impure gas generated at the beginning of the atmosphere stabilization treatment period. It aims at providing the furnace atmosphere stabilization processing method in the batch type annealing furnace which uses the heat insulating material to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention achieves the above-mentioned object by annealing a steel material to which an oxide is adhered in a batch-type annealing furnace using a heat insulating material that absorbs and releases CO 2 into the furnace wall. After supplying the inert gas to the furnace and substituting the atmosphere in the furnace with an inert gas atmosphere, the reducing gas consisting of endothermic metamorphic gas is supplied to change the furnace atmosphere to a reducing atmosphere. In addition, the steel material is heated and held in a temperature range where oxidation and carburization of the steel material does not occur until the in-furnace CO 2 concentration generated by the reaction between the oxide and the reducing gas reaches a peak value, and then the reducing gas After stopping the supply and supplying an inert gas into the furnace and purging until the CO 2 concentration in the furnace becomes less than 1.5% by volume, the reducing gas is re-supplied into the furnace and the CO 2 concentration in the furnace Is less than 1.5% by volume and the carbon potential in the furnace Furnace in a batch annealing furnace using a heat insulating material that absorbs and releases CO 2 on the furnace wall, which is heated to the annealing temperature while controlling the carbon potential of the furnace atmosphere This is an inner atmosphere stabilization treatment method.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of the present invention will be described with reference to FIG.
First, a wire rod in which oxide is deposited in a batch-type annealing furnace using a heat insulating material that absorbs and releases CO 2 in a furnace wall heated and held at 550 to 680 ° C., where oxidation and decarburization do not occur in the steel material in the furnace. After charging a steel material such as a coil, an inert gas is supplied into the furnace to replace the furnace atmosphere with an inert atmosphere. In this case, in order to prevent an explosion from occurring when the next reducing gas is supplied in the furnace, the inert gas is supplied until the O 2 concentration in the furnace atmosphere becomes 0.8% by volume or less.
[0009]
Next, when the O 2 concentration in the furnace atmosphere becomes 0.8% by volume or less, the supply amount of the inert gas is reduced and the reducing gas is supplied. In this case, the supply amount of the reducing gas is at least 3 to 5 times the amount (temperature conversion value) of the furnace volume over a predetermined time in order to sufficiently react the oxide and the reducing gas. Is preferred.
[0010]
As described above, when the reducing gas is supplied into the furnace, the oxide reacts with CO and H 2 which are main components in the reducing gas, and a large amount of impure gas (CO 2 , O 2). , H 2 O) is generated and the CO 2 concentration in the furnace increases rapidly. When the in-furnace CO 2 concentration reaches a peak value, the supply of the reducing gas in the furnace is stopped, while the in-furnace supply amount of the inert gas is increased to purge the impure gas from the furnace. That is, the time during which a large amount of impure gas stays in the furnace is shortened, and the amount of impure gas entering the heat insulating material that absorbs and releases CO 2 constituting the furnace inner wall is reduced.
[0011]
By purging the impure gas based on the inert gas supply in the furnace, the CO 2 concentration in the furnace atmosphere is less than 1.5% by volume, preferably 1.0 to 1.3% by volume, more preferably 0.1%. When it reaches ˜0.5% by volume, the supply amount of the inert gas is decreased, while the reducing gas is supplied again into the furnace, and the detection of the carbon potential value in the furnace atmosphere is started. In this case, due to resupply of the reducing gas, the remaining oxide adhering to the steel material reacts with the reducing gas to temporarily generate a relatively large amount of impure gas, and absorbs CO 2 on the furnace wall. Impurity gas is also released from the heat insulating material to be released, but as described above, since the amount of impure gas entering the heat insulating material that absorbs and releases CO 2 is small, the concentration of the impurity gas decreases in a relatively short time. become.
[0012]
Then, when the in-furnace CO 2 concentration becomes less than 1.5% by volume and the in-furnace CP value reaches a predetermined value, CP control is performed so that carburization and decarburization do not occur in the steel. Heat to annealing temperature. If the CO 2 concentration in the furnace atmosphere is less than 1.5% by volume, if the volume is 1.5% by volume or more, carbon potential control (CP control) is performed during heating to the next annealing temperature. Also, it is based on the experience that carburization and decarburization proceed at the same time and a predetermined quality cannot be ensured. The in-furnace CP value is a value at which the steel material does not cause decarburization or carburization at the temperature, and is appropriately determined depending on the steel type. For example, in SCR430, the CP value is about 130 by heating at 680 ° C.
[0013]
In addition, the CP value at the time of annealing is determined by the kind of steel material to be processed, as described above, and is managed to be 130 to 140 in the SCR 430, for example.
[0014]
【The invention's effect】
As is apparent from the above description, according to the present invention, a steel material with oxide attached to the surface is heated in a reducing atmosphere in a batch annealing furnace using a heat insulating material that absorbs and releases CO 2 on the furnace wall. The impure gas generated when the oxide is reduced is once purged with an inert gas, and the heat insulating material that absorbs and discharges CO 2 in the furnace by this purge generates a high concentration of impure gas. The exposure time to the contained atmosphere is short, that is, the amount of impure gas released into the furnace after that is small, and the period from when the steel material enters the furnace to the annealing temperature (atmosphere stabilization period) Is 13 hours and 15 minutes, and in the present invention, it is shortened by about 33% to 8 hours and 56 minutes, and the productivity is improved accordingly.
[Brief description of the drawings]
FIG. 1 is a graph showing furnace temperature, furnace CO 2 concentration, CP value, and reducing gas and inert gas supply conditions in the method of the present invention.
Claims (1)
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| Application Number | Priority Date | Filing Date | Title |
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| JP2002000144A JP4212277B2 (en) | 2002-01-04 | 2002-01-04 | In-furnace atmosphere stabilization method in a batch annealing furnace using a heat insulating material that absorbs and releases CO2 on the furnace wall |
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| JP2002000144A JP4212277B2 (en) | 2002-01-04 | 2002-01-04 | In-furnace atmosphere stabilization method in a batch annealing furnace using a heat insulating material that absorbs and releases CO2 on the furnace wall |
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| JP4212277B2 true JP4212277B2 (en) | 2009-01-21 |
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