JP4772454B2 - Hot metal refining method - Google Patents

Description

  The present invention relates to a method that enables highly efficient refining in hot metal dephosphorization using a converter.

In steel refining, in order to improve the de-P reaction efficiency, hot metal preliminary treatment is widely performed in which de-P / decarburization is divided and de-P treatment is performed before decarburization. Hot metal pretreatment methods are broadly divided into methods that use hot metal transport containers such as torpedo cars and hot metal ladle, and methods that use a converter. The method that uses a converter maximizes the characteristics of the converter. It was used,
1) The volume of the container is large, and there are few problems such as operational failures due to forming (= slag foaming phenomenon) and slopping (= slag and molten iron overflowing from the container).
2) Gaseous oxygen can be sent at high speed, so high-speed de-P treatment is possible.
3) De-P treatment at a low basicity is possible, and free CaO can be reduced, which is a problem in terms of reduction of smelting quicklime and effective use of slag.
4) For the above reasons, pre-silicon removal treatment before de-P treatment is unnecessary, and de-siliconization and de-P can be performed simultaneously.
5) Since the amount of solid oxygen (= iron oxide, etc.) used is small, the heat tolerance is high and the scrap ratio can be improved.
6) There are advantages such that it is easy to reuse hot decarburized slag in the converter vessel as a P-deposition material.

  Furthermore, when an idle converter or an existing converter can be used, the amount of new capital investment is small, and this method is highly advantageous in terms of resource saving and energy saving.

In the hot metal preliminary de-P treatment method using a converter, after the de-P treatment, while leaving the hot metal in the converter, the converter is tilted to remove only the de-P slag, and then in the same converter There are methods for carrying out decarburization blowing (for example, see Patent Document 1), and methods for using two or more converters as dedicated furnaces for de-P and decarburization (for example, see Patent Document 2). Compared to the latter, the former method
1) Since there is no process of picking up and recharging after de-P treatment, the cycle time of the converter is short.
2) Because there is no hot metal transfer process, there is no heat loss due to transfer.
3) It is easy to leave the decarburized slag in the furnace and use it as a P-making material.
There are advantages such as.

  On the other hand, in the former method, since the converter is tilted while leaving the hot metal in the converter and the de-P slag is discharged, it is difficult to completely discharge only the slag while suppressing the outflow of the hot metal. There is a problem that recovery P occurs from the slag remaining in the furnace during decarburization blowing. In view of this, various proposals have been made as follows for efficient exclusion methods.

  First, a method in which gas is blown from a plurality of tuyere provided on the furnace belly and the bottom of the furnace and slag is moved to the furnace port side to be exhausted (for example, refer to Patent Document 1), and slag forming is blown by oxidizing gas. However, in these methods, it is necessary to modify the converter to install tuyere in the furnace belly, refractory melting In converters where damage has progressed, the slag position changes due to changes in the internal volume, the tuyere position deviates from the optimum position, and it is necessary to constantly blow in gas to prevent tuyere clogging during blowing. There are problems such as an increase in gas cost which is essentially unnecessary.

  In addition, a method of selectively rejecting only slag using electromagnetic force (for example, see Patent Document 4) has been proposed, but it requires high capital investment costs, and is in a poor environment with high temperature and severe vibration. There are problems such as an increase in maintenance costs.

  Furthermore, a method has been proposed in which the position of the hot metal is detected by electrical continuity or an optical fiber, and the converter tilting position optimum for waste is determined and discharged (see, for example, Patent Document 5 and Patent Document 6). These methods can detect the position of the hot metal and determine the optimum converter tilting position, but are not sufficient to promote exhaustion.

  In addition, a method of scraping slag with a waste plate that is used as a method for removing a torpedo car or pan (for example, see Patent Document 7) may be applied to the converter, but considering the capacity of the converter The facilities are too big to be realistic.

  In the methods of Patent Literature 1 and Patent Literature 8, it is possible to reduce the amount of refining material added during the de-P treatment by recycling the decarburized soot to the de-P treatment. For example, in the molten steel after decarburization In the case of melting low P steel having a P concentration of 0.015% by mass or less, P contained in the recycled decarburized iron may cause variations and an obstacle to low P. .

  On the other hand, in order to avoid such obstacles, without recycling the decarburized slag, while leaving the hot metal in the converter after the de-P treatment, the converter is tilted to remove only the de-P slag, Thereafter, when decarburization blowing is carried out in the same converter, there is a problem that the slag removal performance is poor due to a delay in dissolution of the refining material introduced at the time of the de-P treatment, so that it cannot be sufficiently discharged.

Japanese Patent No. 2558292 Japanese Patent No. 1761646 JP 05-279721 A JP 05-247514 A JP 05-288479 A Japanese Patent Laid-Open No. 06-235016 JP 59-13009 A Japanese Patent Laid-Open No. 04-72007

  Preliminary de-P removal of hot metal in the converter, while the hot metal remains in the converter after the de-P treatment, when the slag is discharged by tilting the converter, The object is to provide a refining method with a small amount of slag.

The gist of the present invention is as follows.
(1) Hot re-use of pre-charged decarburized iron in the converter vessel as a dephosphorization ironmaking material, hot metal dephosphorizing treatment in the converter, and after dephosphorizing treatment, the hot metal is converted into the converter In the refining method of hot metal, in which the slag is exhausted by tilting the converter while leaving it inside, followed by decarburization treatment in the same converter,
In the dephosphorization step subsequent to the dephosphorization treatment, the amount of reuse of the pre-charged decarburized iron is set to 7 kg / t-molten metal or more and 24.9 kg / t-molten metal or less, and contains 2CaO · Fe ₂ O ₃ in an amount of 30 mass% or more. The refining material is added , and the CaO substitution rate represented by the ratio obtained by dividing the amount of CaO added by the added refining material by the total amount of CaO charged into the converter by hot metal dephosphorization is 30% by mass or more. A hot metal refining method characterized in that forming is promoted by generation of CO bubbles .
(2) wherein A 2CaO · Fe ₂ O ₃ of 30 wt% or more inclusive refining material, occupy the entire at least 70 mass% in the sum of CaO and Fe ₂ O _3, balance Al, Mn, Mg, P, Si The method for refining hot metal as described in (1), wherein the refining agent comprises one or more oxides of the above.

  According to the present invention, the hot metal is preliminarily removed in the converter, and the molten iron is prevented from flowing out when the converter is tilted and the slag is discharged while the hot metal remains in the converter after the de-P treatment. However, refining with a small amount of residual slag becomes possible, and as a result, the total P amount in the furnace at the start of decarburization blowing can be stabilized at a low level. As a result, the amount of refining material such as quick lime used in the decarburization process can be reduced and the end point P concentration can be stabilized.

The present invention can be implemented in the following forms. To the hot metal charged in the converter, a refining material containing 2CaO · Fe ₂ O ₃ is added together with CaO, iron oxide, and other refining materials. Oxygen gas is blown to oxidize and remove P which is an impure component in the hot metal. After that, the converter is tilted while leaving the hot metal in the furnace to discharge the de-P slag, and then decarburization blowing is performed in the same converter.

  The effects of the present invention will be described below.

  In order to realize a high rejection rate after the P removal treatment, it is important that the P removal slag is in an appropriate forming state. Forming is a state in which a gas is suspended in a liquid slag, and is affected by the surface tension, viscosity, and density of the slag. Therefore, when undissolved solid remains, forming is suppressed, and as a result, the evacuation property is greatly deteriorated.

On the other hand, according to experiments conducted by the present inventors, a refining material containing 2CaO.Fe ₂ O ₃ (hereinafter referred to as a compound refining material) is added and blown, so that the CaO content and the iron oxide content are reduced. As compared with the case where each is added separately, dissolution of CaO is promoted, and as a result, the reached [P] concentration after de-P treatment (the mass concentration of P in the metal is indicated as [P]; the same applies hereinafter). It has been found that in addition to stabilization at a low level, the rejection rate after de-P treatment is improved.

As an example, FIG. 1 shows the relationship between the 2CaO · Fe ₂ O ₃ concentration (mass%) in the compound refining material and the rejection rate. In this example, using a 300T scale top-bottom blow converter, the total CaO unit 10-20 kg / T-molten iron, the mass ratio of CaO to the total CaO in the compound refining material (= replacement rate) is 30-80. It is the result in mass%. The rejection rate is an estimated value calculated from the mass balance of Ti that is completely oxidized and removed during de-P blowing. From this figure, it can be seen that the rejection rate is improved when the concentration of 2CaO · Fe ₂ O ₃ in the compound refining material is 30% or more.

  Up to now, there has been an example in which application of a refining material for the purpose of promoting hatching of the CaO content has been studied, but the present inventors have clarified that the rejection rate is improved for the first time. By improving the rejection rate, the amount of slag carried over to the decarburization process can be reduced, and by reducing the variation in the rejection rate, the variation in [P] concentration in the steel after decarburization can also be reduced.

Thus, in the refining method according to the first invention of the present invention, preliminary de-P treatment is performed in the converter, and the slag is discharged by tilting the converter while leaving the hot metal in the converter after the de-P treatment. In the method of dripping, a refining method is characterized in that a refining material containing 30% by mass or more, preferably 50% by mass or more of 2CaO · Fe ₂ O ₃ is added and blown.

Further, the dephosphorization rate increases monotonously with the increase in the content of 2CaO · Fe ₂ O _{3 in} the smelted material, but saturates at 60 mass% or more. However, the upper limit value is not particularly defined, and may be 100 mass%.

Furthermore, as for other components in the refining material, one or both of Al and Si, CaO.Fe ₂ O ₃ , CaO and the like can be mentioned. Further, the content is preferably in the following range from the viewpoint of improving the de-P efficiency.

Since Al and Si need only be contained, the lower limit of the content is over 0%. Moreover, although an upper limit is not specified in particular, it can be exemplified as 10% or less. The CaO · Fe ₂ O ₃ content is preferably 50 mass% or less, and the lower limit is not particularly specified, but it is recommended to be 5% or more. Furthermore, the CaO content is preferably 5 to 20 mass%. When there is a balance, usually Fe ₂ O ₃ is contained.

Furthermore, according to the experiments by the present inventors, as the CaO content used in the preliminary de-P treatment, the CaO substitution rate defined as the mass fraction occupied by the CaO in the compound refining material in the total CaO used in the treatment (λ : (%), Calculated by [Expression 1]) is 30% or more, it was found that de-P was promoted and the rejection rate was stabilized. By replacing a part of the CaO component with the compound refining material, the quick lime is rapidly dissolved. As a result, the de-P reaction proceeds, the fluidity is improved, and the rejection rate is highly stabilized.
λ = W _CaO ^Flux / W _CaO ^Total × 100 (1 set)
Here, W _CaO ^Flux is the CaO content (kg / t-molten metal) contained in the compound refining material, and W _CaO ^Total is the total CaO content (kg / t-molten metal) charged in the converter.

  Thus, the refining method according to the second invention of the present invention is a refining method characterized in that the CaO content contained in the compound refining material is 30% by mass or more of the total CaO used. Here, in the case where 30% by mass or more of the total CaO is used as a compound refining material, a melting acceleration effect is sufficiently obtained, and since the effect is increased by increasing the ratio from the mechanism, the upper limit is not particularly defined, What is necessary is just to set suitably.

  In further experiments, it was found that by adding a compound refining material, a CaO dissolution accelerating effect equal to or higher than that obtained by recycling decarburized soot was obtained.

  Conventionally, hot recycling of decarburized soot has been carried out for the purpose of ensuring the exhaustability and reducing the refining material for de-P, but because of the P component brought in from the decarburized soot, the production of low P steel is There was a drawback that it was difficult.

  By using the compound refining material of the present invention, it becomes possible to ensure the exhaustability without recycling the decarburized soot, for example, in the hot metal after decarburization that was difficult to cope with in the prior art [ P] Low P steel having a concentration of 0.015% by mass or less can be melted. In other words, by using compound refining materials, a high exhaust rate can be maintained without recycling decarburized soot, and the amount of decarburized soot brought in is reduced, so [P] is stabilized at a low level after decarburization. did.

  Therefore, in the refining method according to the third invention of the present invention, in the dephosphorization treatment of the hot metal, the decarburized iron is not recycled, so that the decarburized metal is 20 kg / t-hot metal or less. 2 It was set as the refining method as described in invention. Here, the amount of decarburized iron is 20 kg / t-molten or less from the result of maximum 20 kg / t-molten iron obtained from mass balance analysis of actual machine data as a part inevitably mixed in such as furnace wall adhesion. It was.

  Since the gas generation amount is one of the controlling factors, the formation of CO bubbles due to the decarburization reaction is effective for promoting the forming. In addition, there is a fact that the dissolution of CaO is promoted by agitation, and the agitation of the top slag in the converter largely depends on the gas at the top and bottom.

The degree of the decarburization reaction can be arranged by the desiliconized oxygen (defined by [Formula 2], unit Nm ³ / t-molten iron) excluding the oxygen consumed for the desiliconization reaction. According to the experiments by the present inventors, the removal rate was further improved when deoxygenated oxygen of 5 Nm ³ / t-molten or higher was introduced.
Q _O2 ^{ex. De-Si} = Q _O2 ^gas + Q _O2 ^sol.− Δ [Si] / 28 × 224 (2 formulas)
Here, Q _O2 ^{ex. De-Si} : oxygen outside desiliconization (Nm ³ / t-input pig iron), Q _O2 ^gas : gaseous oxygen (Nm ³ / t-input pig iron), Q _O2 ^{sol .} : Oxygen (Nm ³ / t-input pig iron) supplied as iron ore, dust or iron oxide in the refining material used in the present invention during de-P treatment, Δ [Si] : Difference in Si concentration (mass%) in steel before and after oxygen addition.

The average composition of the refining material of the present invention is preferably in the following range. The sum of CaO and Fe ₂ O ₃ occupies 70 mass% or more of the whole, and the balance is composed of one or more oxides of Al, Mn, Mg, P, and Si. The P ₂ O ₅ concentration is preferably ₂ mass% or less, more preferably 1 mass% or less. The CaO concentration is 20-70 mass%, but 30-50% CaO shows a high effect.

  Here, an example of the manufacturing method of the refining material described above is shown below.

  As a raw material, powdery limestone and powdered iron ore are used as the main raw materials, and powdered carbonaceous material used as a fuel and a blended raw material mixed with the returned ore into the raw material are sintered by a sintering machine. Based on this, the smelting material of the present invention can be produced by appropriately carrying out the following conditions 1) to 4) together. In addition, return ore here means the part less than 5 mm returned to a raw material among the refined materials of a product.

1) The particle size of either or both of limestone and iron ore should be 3 mm or less 2) The Ca / Fe ratio in the raw material should be in the range of 2.5 to 1.5 3) Returning 4) When preparing the blended raw material, limestone and iron ore are pulverized and mixed in advance with a high-speed stirring mixer, and then the charcoal is added and granulated to prepare the raw material. Be present around the particles.

  Below, using a 300 t scale upper bottom blow converter, the hot metal is dephosphorized, and after the dephosphorization process, the hot metal is left in the converter and the converter is tilted to remove slag, Then, decarburization processing was performed in the same converter. The Example and a comparative example are shown.

In both Examples and Comparative Examples, the molten iron temperature was 1300 to 1320 ° C., and the hot metal content was (the ratio of the amount of molten iron in the converter charging main raw material, the molten metal mass / (molten metal mass + scrap mass + cold iron mass) × 100. 90-92% by mass), [Si] concentration in the hot metal is 0.38-0.42% by mass, and similarly [P] concentration in the hot metal is 0.100-0.105% by mass. The rate (the amount of oxygen blown in the entire charge divided by the blowing time) is 29000-30000 Nm ³ / h, and the temperature after dephosphorization is 1350-1370 ° C.

  The decarburized soot was left in the furnace so as to be a predetermined amount, and the furnace was tilted several times to be solidified and received. As the residual amount of decarburized soot, a value estimated from the tilt angle of the furnace at the time of exhausting was used. In addition, even if the furnace is completely inverted and exhausted completely, slag adhering to the furnace wall remains unavoidably, but the amount is an average value obtained from mass balance analysis of actual data. It was set at 0 kg / t.

  The compound refining material used has the composition shown in Table 2. Table 2 also shows the average composition of the decarburized soot. Table 1 shows the amount of refining material used for de-P. These amounts are shown as mass (kg) per ton of pig iron. In addition to these refining materials, iron ore was added to control the blowing temperature.

  In addition, the refined material by this invention was manufactured by the method of sintering with the sintering machine what added the water | moisture content to the limestone adjusted to the particle size of 1-3 mm, iron ore, and coke, and granulated.

  The size of the refining material was about 5-50 mm or less, excluding the decarburized soot that was the residual slag of the precharge. The CaO content in quicklime was 95%, and the balance was volatiles such as moisture. After completion of the de-P treatment, the converter was tilted while the hot metal was left in the furnace to discharge slag, and then quick lime and iron ore were added to perform decarburization blowing. The CaO content newly added at the time of decarburization blowing was about 20 kg / t-molten iron and added with quick lime.

  [P] concentration in steel after decarburization was used as a standard for judging the blowing result. Moreover, as the controllability factor, the iron [P] after the de-P treatment and the rejection rate were investigated. As the [P] concentration in the steel after decarburization, a value obtained by analyzing the metal collected from the furnace using a sub lance after stopping the oxygen blowing during the decarburization period by the QV analysis (emission spectroscopic analysis) method was used. Similarly, for [P] after de-P, a value obtained by analyzing the metal collected from the furnace using a sub lance after stopping the oxygen blowing in the de-P phase by the QV method was used.

In addition, the discharge rate is determined by calculating the amount of slag in the furnace SV _P ^Total (kg / t – input pig iron) before discharge obtained by mass balance calculation and the amount of discharged slag SV _P ^Ex. kg / t-input pig iron) and calculated as SV _P ^Total / SV _P ^Ex × 100. If the range of operating conditions is constant within a narrow range, investigate the relationship between the above value and the tilt angle at the time of rejection, and execute it even if the rejection rate is estimated from the tilt angle based on the result. Above is no problem.

  When Example 1-9 is evaluated based on Comparative Example 1-3, the [P] concentration in the steel after the decarburization treatment is reduced, and a good treatment result is obtained. This is because the compound refining material is used, the CaO substitution rate is increased, and the amount of P in the system carried over to the decarburization treatment is improved by reducing the amount of decarburized soot. Reduced.

Relationship between concentration of 2CaO · Fe ₂ O ₃ + CaO · Fe ₂ O _{3 in} refining material and rejection rate

Claims (2)

In the converter vessel, the pre-charged decarburized iron is reused hot as a dephosphorizing material, and the hot metal is dephosphorized in the converter, and after the dephosphorizing treatment, the hot metal is left in the converter. In the hot metal refining method, the converter is tilted and the slag is exhausted and then decarburized in the same converter.
In the dephosphorization step subsequent to the dephosphorization treatment, the amount of reuse of the precharged decarburized iron is set to 7 kg / t-molten metal or more and 24.9 kg / t-molten metal or less, and contains 2CaO · Fe ₂ O ₃ in an amount of 30 mass% or more. The refining material is added , and the CaO substitution rate λ (%) expressed by the ratio obtained by dividing the amount of CaO added by the added refining material by the total amount of CaO charged into the converter by the hot metal dephosphorization treatment is A hot metal refining method characterized in that forming is promoted by generating CO bubbles at 30% or more . 2CaO · Fe ₂ O _Three Refining material containing 30 mass% or more of CaO and Fe ₂ O _Three The refining agent is composed of one or more oxides of Al, Mn, Mg, P, and Si. Refining method.

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