JP2005314760A - Refining method having high reaction efficiency - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating molten pig iron containing little Si at high efficiency and high productivity with the use of a small amount of an auxiliary material, and for solving problems that refractory wears, that refining capability is reduced, that slopping occurs and that CaO does not form adequate slag. <P>SOLUTION: The refining method having high reaction efficiency includes adding a refining agent mainly containing CaO and Fe<SB>t</SB>O and containing a compound of CaO and Fe<SB>t</SB>O at least in one part, and blowing oxygen gas, when refining molten pig iron containing 0.20 mass% or less Si in a treatment furnace, wherein the refining agent contains 5 mass% or more of a CaO-Fe<SB>2</SB>O<SB>3</SB>phase and 20 mass% or more of a CaO component at room temperature before being added to the treatment furnace. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for enabling high-efficiency and high-productivity processing in a small amount in a refining process of molten iron using a refining agent mainly composed of CaO.

  In the refining of molten iron, a refining agent containing CaO as a main component is used to stably remove impurities. In order to reduce the amount of slag generated and reduce the refining cost, it is desirable to perform the treatment efficiently with a small amount of a refining agent. However, when quick lime or limestone is directly added as a CaO component, these hatching properties are reduced. There was a problem that it was bad and the reactivity was low.

  To date, for example, Patent Document 1 discloses a method for producing a hot metal dephosphorizing agent that has improved hatchability by adding a halide or the like. While facilitating hatching, there is a problem of causing damage to the refractory in the smelting vessel.

In Patent Document 2, the forming agent (refining agent) containing CaO 60-70%, the addition of Al ₂ O ₃ 8-13% of still slag formation improved in addition to such Fe ₂ O ₃ for the purpose Has proposed. However, when Al ₂ O ₃ is added in an amount of 8% or more, there is a problem that the dephosphorization ability is lowered because the CaO concentration is relatively lowered. Further, when the Al ₂ O ₃ concentration is high, there is a problem that the slopping phenomenon in which the slag overflows from the converter is severely disturbed.

In general, dephosphorization reaction is more advantageous as the slag basicity ((CaO mass concentration) / (SiO ₂ mass concentration)) is higher. Non-Patent Document 1 discloses a method in which the hot metal with a reduced [S] may be used for dephosphorization after removing the slag generated by this desiliconization as much as possible. In this method, since there is no SiO _{2 component} effective for allowing the CaO content to hatch, not only the hatching of CaO is inhibited and dephosphorization does not proceed, but also the unreacted CaO is not contained in the slag after the treatment. Will remain and cause major problems when slag is reused.

JP-A-57-13109 JP 55-34653 A NKK Technical Report No. 178 p. 1-5

The present invention solves the problems such as refractory wear, refining ability reduction and slopping, and poor hatching of CaO content as described above. containing compound was CaO and Fe _t O, by adding a refining agent to the main component CaO and Fe _t O, and aims to provide a highly efficient and productive processing method with a small amount of auxiliary materials To do. In this specification, it shows the sum of the different iron oxide valence and Fe _t O.

The gist of the present invention is as follows.
(1) In the case where Si concentration is refined in the process furnace 0.20 mass% or less of molten iron, including the compound of CaO and Fe _t O on at least a portion, refining agent for the main component CaO and Fe _t O A refining method with high reaction efficiency, characterized by adding and blowing.
(2) The slag on the hot metal before the start of the refining process is discharged, and then the hot metal is transferred to a processing furnace in which the slag in the furnace has already been discharged, and then the refining process is performed. The refining method with high reaction efficiency as described in (1).
(3) The refining agent is characterized in that the CaO · Fe ₂ O ₃ phase is present in an amount of 5 mass% or more and the CaO component is contained in an amount of 20 mass% or more in a state at room temperature before addition to the processing furnace. The refining method having high reaction efficiency according to (1) or (2). Here, the room temperature is assumed to be in the range of, for example, -5 ° C to 30 ° C. This temperature range is defined as a standard condition, and the mineral phase in this range is defined, and the temperature before use need not be room temperature.
More than 30 mass% of the total CaO content used in (4) the refining process, the advance is characterized by adding a refining agent As the CaO was combined with Fe _t O (1) (3) The refining method with high reaction efficiency in any one of.
(5) The reaction efficiency according to any one of (1) to (4), wherein refining is performed until a predetermined P concentration in molten iron and a C concentration in molten iron are achieved in the same treatment furnace without being discharged. High refining method.

According to the present invention, problems in operation and refining ability such as failure of hatching of CaO, occurrence of slopping accompanying improvement of hatching, remarkable hatching failure occurring at low SiO ₂ concentration and residual unreacted CaO While avoiding the above, it is possible to reduce the amount of raw materials used and the amount of slag, and to produce slag that can be easily reused, and to perform refining stably and efficiently.

In the case where the Si concentration in the hot metal is low, that is, the case where the amount of slag is small or the basicity (the mass concentration ratio of CaO and SiO ₂ component (% CaO) / (% SiO ₂ )) is high, containing compounds of CaO and Fe _t O on at least a portion, by using a refining agent to the main component CaO and Fe _t O, stably possible efficient refining slag of CaO content is promoted I found out.

Here, CaO and Fe _t O the compound of a solid solution of _{Fe CaO, 2CaO · Fe 2 O} 3, CaO · Fe 2 O 3, etc. CaO · 2Fe ₂ O ₃ of CaO-Fe ₂ O ₃ system In addition to compounds, those in which Al, Mn, Mg, P, and Si are dissolved, and composite oxides of CaO—Fe ₂ O ₃ compounds and oxides of Al, Mn, Mg, P, and Si including. In addition, the stoichiometric composition is not necessarily required, and the oxidation number of Fe or the like is not particularly affected.

The following two cases can be considered for refining when the Si concentration in the hot metal is low. First, when the basicity is constant regardless of the Si content in the hot metal, the lower the Si content in the hot metal, the smaller the required CaO content. In this case, the lower the Si concentration in the hot metal, the smaller the amount of slag. However, in the case of a small amount of slag, the reduction rate of slag by the hot metal is relatively high, ensuring the Fe _t O concentration that contributes to the hatching of CaO. This makes hatching a problem. However, when a refining agent containing a compound of CaO and Fe _t O, rather than being dissolved by Fe _t O produced in refining reactions, for the refining agent melts themselves, slag formation Progresses without being inhibited.

In addition, when the amount of CaO charged is constant regardless of the Si content in the hot metal, the basicity increases as the Si concentration in the hot metal decreases. In general, the higher the basicity, the more advantageous for dephosphorization, but the higher the basicity, the more the CaO hatching is inhibited, and even when the Si concentration in the hot metal is low, the liquid phase slag reacts mainly with the metal. It is difficult to increase the basicity. However, when a refining agent containing a compound of CaO and Fe _t O, without waiting for lysis by Si content even when a low Si concentration in the molten iron, for the refining agent is melted itself, The basicity in the liquid phase can be increased without inhibiting the hatching of CaO.

Furthermore, in order to reduce the SiO ₂ content in the slag as much as possible, even if the amount of slag present on the metal is removed before the refining agent is added, the refining agent melts itself without relying on melting by the slag. By doing so, hatching failure can be avoided. Here, the liquid phase slag refers to a portion other than the undissolved auxiliary material in the slag. The mode of this dephosphorization reaction will be described below.

  In this specification, refining means removing C, Si, P, etc. from molten iron. Moreover, molten iron is a general term for molten iron and molten steel, and molten iron is defined as that before decarburization, and molten steel is defined as that after decarburization.

In particular, the present invention is intended for dephosphorization containing CaO as a main component (30 mass% or more in terms of CaO in the final slag). Quick lime, which is a typical CaO source, has a melting point of 2500 ° C. or more alone, and limestone and dolomite added as a CaO source contribute to the reaction after being decomposed into quick lime, and thus have the same melting point. For this reason, CaO charged in the converter cannot melt by itself and reacts with the surrounding slag to proceed with melting. At that time, SiO ₂ derived from the desiliconization reaction or derived from the carryover slag. 2CaO · SiO ₂ shells are formed around CaO. Here, the carry-over slag is the slag generated in the pretreatment of the hot metal and mixed with the hot metal and the slag remaining in the furnace for performing the treatment before the hot metal is charged. . Since this shell is almost in equilibrium with the surrounding liquid phase, unreacted CaO present inside remains as it is until the end of the reaction. As a result of investigations by the present inventors, it has been clarified that when the Fe _t O concentration of the liquid phase slag is high, the shell of 2CaO · SiO ₂ is thin and the dissolution of the internal CaO is fast, but the Si in the molten iron When the concentration is low, reduction of the Fe _t O content in the slag is likely to proceed due to the C concentration in the hot metal (hereinafter sometimes referred to as [C]), and therefore, there is a problem that the initial dissolution of CaO is hindered. is there.

On the other hand, a higher CaO concentration in the slag is advantageous for dephosphorization. In order to achieve a high CaO concentration with a small amount of CaO raw material, it is effective to reduce the SiO ₂ source that enters the slag, and the [Si] concentration is lowered by desiliconization in advance with low [Si] concentration. There is a method of dephosphorization after removing hot slag containing SiO ₂ as much as possible, but in this case, dissolution of CaO becomes a bottleneck as mentioned above, and it mainly reacts directly with metal Not only does the dephosphorization proceed without the CaO concentration of the liquid phase slag being increased, but unreacted CaO remains in the slag after treatment, thereby inhibiting the reuse of the slag.

In order to solve this problem, the present inventors have conducted detailed experiments. When only quick lime, limestone or dolomite is used, the dissolution inhibition phenomenon of CaO is [Si] ≦ 0.20 mass% and the slag basicity is 1. occurs conspicuously when exceeding .2, but under these conditions, when a refining agent containing a compound of CaO and Fe _t O was confirmed that the dissolution inhibition phenomenon CaO is suppressed. This is a compound of CaO and Fe _t O, since the low-melting phase, such as mono-calcium ferrite and dicalcium ferrite as a starting point of melting, refining agent even when relatively low FeO concentration in the liquid phase slag As a result, the CaO concentration of the liquid phase slag becomes high.

  Moreover, when the hot metal having a Si concentration of 0.20 mass% or less is refined, the amount of slag to be generated can be reduced as compared with the case where the Si concentration is higher than 0.20 mass%. Therefore, in the present invention, hot metal having a Si concentration of 0.20 mass% or less is targeted.

Furthermore, refining agents used in the present invention is at least partly those containing a compound of CaO and Fe _t O, in which the main component CaO and Fe _t O. Here, as a percentage of the total CaO and Fe _t O for refining agent total amount mainly, but as a guide to be about 70 mass% or more, more preferably at least 90 mass%. Conventionally, it has been thought that a refining agent not containing a halide such as fluorite or calcium chloride does not dissolve rapidly, but by dispersing monocalcium ferrite in the refining agent, hatching is promoted.

  Therefore, in the present invention, even when a halide is not used, hatching failure can be avoided, and further, refractory melting can be suppressed, and the cost of the refining agent can be reduced.

  Here, the halide represents a compound of F, Cl, Br, typically calcium fluoride and calcium chloride.

  The refining agent is made by using limestone and iron ore as main raw materials, preferably by heating to 1000 ° C. or higher. As an alternative to limestone, CaO-containing slag can be used in addition to quicklime and dolomite. Moreover, iron ore is added as an iron oxide component, and iron ore, sintered ore, in-house generated dust, sludge, and the like can be used.

  Further, it is not necessary to supply the entire amount of CaO as a refining agent, and there is no problem even when recycling such as decarburized soot. However, from the viewpoint of metal component fluctuation and dephosphorization ability, it is desirable that the sulfur and phosphorus concentrations in the refining agent are S <0.1 mass% and P <1 mass%.

In addition to the above [Si] concentration, the slag on the hot metal before the start of the refining process is discharged, and then the hot metal is transferred to the processing furnace where the slag in the furnace has already been discharged, and then the refining process to the case of performing, for the amount of slag in the processing furnace is low, especially conspicuous faint inhibition of CaO, by using a refining agent containing a compound of CaO and Fe _t O in this case, slag Inhibition of oxidization can be suppressed.

  Specifically, it is desirable that the carry-over slag amount calculated by the material balance is 10 kg / t-metal or less. Here, 10 kg / t-metal means that the amount of slag per 1 t of molten iron is 10 kg, and this molten iron refers to the molten iron transferred to the processing furnace. In addition, after the start of refining, not only hot metal but also molten steel may be targeted, but in that case, molten iron refers to molten steel.

As a method of obtaining the carryover slag amount by the material balance, for example, there are the following methods. Immediately before the treatment starts, components of the carry-over slag are analyzed from a sample collected from the slag on the hot metal charged in the furnace. CaO concentration carryover slag, the SiO ₂ concentration of each c1, s1 (mass%), CaO amount and SiO ₂ amount of newly added in the process, further the amount of SiO ₂ produced by the reaction, respectively C2, S2 , S3 (kg / t). If the CaO concentration and SiO ₂ concentration in the slag after treatment are c4 and s4,
(C1 · X / 100 + C2) / c4 = (s1 · X / 100 + S2 + S3) / s4
Thus, the carryover slag amount can be obtained by solving for the carryover slag amount X (kg / t). In this calculation, it is assumed that the amount of CaO added is added to the slag, but it is necessary to consider the yield of lime in accordance with the actual phenomenon.

  Since the carry-over slag component is assumed to be unknown before the start of the process, the calculation of the carry-over slag amount using the above method is performed for multiple examples of processes that have been completed in the past, and then the evacuation time, tilt angle, etc. It is desirable to secure it as a method that can be statistically estimated from the operating conditions.

In refining agent comprising a compound of CaO and Fe _t O is, CaO · Fe ₂ O ₃ phase (monocalcium ferrite phase) is present more than 5 mass% in the previous room temperature condition added, and, CaO concentration 20 mass% or more In some cases, the dissolution promoting effect is further exhibited and dephosphorization proceeds.

  These are based on the result of investigating the amount of monocalcium ferrite which is the starting point of melting of the refining agent. In this investigation, melting proceeds rapidly when monocalcium ferrite is 5 mass% or more. Further, as described above, it is better that the CaO concentration in the slag is high from the viewpoint of dephosphorization ability. If the CaO concentration in the refining agent is 20 mass% or more, a slag having a high CaO concentration can be obtained with a small amount of the refining agent. Further, when the CaO concentration is 20 mass% or more, the CaO concentration in the liquid phase directly generated by melting the refining agent is high, which is advantageous for dephosphorization. For more efficient dephosphorization, a CaO concentration of 40 mass% or more is desirable.

However, in equilibrium, monocalcium ferrite and CaO do not coexist in the majority of the region where the CaO concentration is 40 mass% or more. Accordingly, the present inventors have found that a refining agent can be produced by a process equivalent to the production of sintered ore. . In the case of melting with a sintering machine, the temperature reaches about 1400 ° C. in a short time of about 5 minutes and then cooled. For this reason, even in a composition region where the CaO concentration exceeds 40 mass%, monocalcium ferrite (CaO.Fe ₂ O ₃ ), which is essentially a non-equilibrium phase, is generated. Monocalcium ferrite has a melting point of about 1200 ° C., which is advantageous for hatching of a refining agent. Furthermore, by using a sintering machine, it is possible to use coke that is cheaper than petroleum. It is also possible to use a powder such as 3mm below as CaO content and Fe _t O content of the raw material.

Moreover, for a good dephosphorization reaction, it is desirable that the slag is CaO saturated. In order to realize highly efficient and stable dephosphorization while reducing unreacted CaO to the minimum, it is desirable that a CaO phase and a dicalcium ferrite (2CaO · Fe ₂ O ₃ ) phase exist.

The compounds of the results of actual scale experiments conducted by the present inventors, as shown in FIG. 1, more than 30 mass% of the total CaO content present in the furnace in the blowing, the CaO and Fe _t O When the CaO content of the refining agent mainly containing CaO and Fe _t O is added, the dephosphorization efficiency is further improved and stabilization can be achieved. The horizontal axis of FIG. 1 shows the proportion of CaO supplied by CaO in the refining agent among all the input CaO (refining agent replacement rate). When this proportion is 30% or more, good dephosphorization is obtained. I understand that. When it is difficult to grasp the total amount of CaO present in the furnace, the input CaO amount may be simply used as the amount of CaO present in the furnace as it is. Moreover, you may obtain | require the amount of residual slag before throwing in a CaO part by mass balance calculation etc. from the performance of the appropriate number of refining performed before the said refining.

The above is mainly intended for hot metal preliminary dephosphorization treatment, but when refining is performed in the same treatment furnace to a predetermined P concentration in molten iron and C concentration in molten iron without waste, CaO and Fe _t By using a refining agent containing a compound with O, highly efficient and stable dephosphorization becomes possible. Here, the predetermined P concentration in the molten iron and C concentration in the molten iron are concentrations that meet the management standards of the product to be manufactured, but if a separate refining process is possible in the subsequent process furnace, Concentration taking into account the component fluctuation range in processing. For example, the concentration of C in molten iron is about 0.03 to 1% by mass, and the concentration of P in molten iron is 0.002 to 0.040% by mass, but some products may have values exceeding this range. Even in such a case, the present invention has an effect.

  First, when dephosphorization is performed as a preliminary treatment and subsequently decarburization is performed, slag removal or metal transfer is required in the conventional technology. However, according to the present invention, since the decarburization process can be continuously performed in the same processing furnace without removing the slag, compared to the case of removing the slag, the time and heat associated with the transfer and slag discharge are reduced. Loss can be eliminated, which is effective in terms of productivity and cost.

Since the amount of Si in the hot metal is low and the amount of Si in the furnace is small, the CaO concentration can be increased with a small amount of CaO. Further by using a refining agent containing a compound of CaO and Fe _t O, because of the high CaO concentration in the liquid phase slag to react directly with the metal, even if the refining process with the same slag to decarburization endpoint Good dephosphorization is obtained.

Further, conventionally, the dissolution of CaO and increased Fe _t O concentration was not de Rinmo proceeds to decarburization end which proceeds by using a refining agent containing a compound of CaO and Fe _t O, refining It is possible to increase the CaO concentration of the liquid phase slag from the beginning, and therefore dephosphorization proceeds from the beginning of refining. For this reason, dephosphorization can be highly efficient and stabilized without dephosphorization as a pretreatment and without removing slag or changing metal.

  In addition, when steel materials requiring high carbon concentration and low phosphorus concentration are melted, they are blown off at an early stage compared to low carbon steel, but even in this case, dephosphorization proceeds from the beginning. Therefore, more stable dephosphorization is possible than using quick lime, limestone, dolomite and the like.

  In Examples 1 to 4 and Comparative Examples 1 and 2, hot metal preliminary dephosphorization was performed using a 300 t scale top-bottom blowing converter. In Example 5 and Comparative Example 3, blowing was continued to a low coal concentration. In either case, the hot metal discharged from the blast furnace was desiliconized to reduce the Si concentration to 0.2 mass% or less. After that, as a rule, the waste was discharged by a dragger and charged into the converter where the slag in the furnace was discharged. However, in Example 1 and Comparative Example 1, the removal time was short and the slag in the converter was removed, but the slag on the hot metal was not sufficiently removed.

In these examples, the oxygen from the top lance, 1.0~2.0 Nm ³ / min / ton- supplied with hot metal rate of bottom blowing is 2000Nm with nitrogen for general processing from the small diameter collecting pipe tuyere ³ / H was supplied.

  The initial temperature of hot metal of about 250 tons is 1330 to 1350 ° C., and this hot metal is combined with scraps of 30 to 40 tons and charged into the converter. In the examples, quick lime, iron ore and the refining agent of the present invention are added to remove the hot metal. Phosphorus refining was performed for 8-9 minutes.

Moreover, in Example 5 and Comparative Example 3, dephosphorization decarburization refining was performed. From the beginning to the end of blowing, oxygen is supplied from the top blowing lance at a rate of 1.0 to 2.5 Nm ³ / min / ton-molten iron, and the bottom blowing is CO ₂ from the small diameter collecting pipe tuyere throughout the treatment. It was supplied at a speed of 2000 Nm ³ / h. The blowing time was 15 to 16 minutes.

  Here, although the starting point of the refining process indicates the start point of the blowing process strictly, the components of the sample obtained from the pan before charging into the processing furnace are used and are shown in the table as the pre-processing molten iron components.

  In addition, the end point of the refining process strictly refers to the end point of blowing, but in Examples 1 to 4 and Comparative Examples 1 to 2, the components of the sample collected from the processing furnace with a sub lance after the end of blowing, In Example 5 and Comparative Example 3, the components of the sample obtained from the pan after the steel was removed from the processing furnace were used and indicated as the molten iron component after the treatment.

  Table 1 shows the conditions of each example, and Table 2 shows the results. The refining agent replacement rate in Table 1 indicates the ratio of CaO input as CaO in the refining agent of the present invention with respect to all input CaO.

  In all the examples, the P concentration in molten iron at the end point was 0.02 mass% or less, and the f-CaO of the slag collected at the post-treatment waste disposal site was 0.5 mass% or less, and good dephosphorization was achieved.

  In particular, in Example 4, since the refining agent substitution rate was as large as 67 mass%, dephosphorization treatment with a better P concentration in molten iron at the end point could be performed.

Relation between refining agent replacement rate of CaO and P concentration in molten iron at the end of refining

Claims (5)

When the Si concentration is refined in the process furnace 0.20 mass% or less of molten iron, least partially containing a compound of CaO and Fe _t O, adding a refining agent to the main component CaO and Fe _t O Refining method with high reaction efficiency characterized by blowing and blowing.   The slag on the hot metal before the start of the refining process is discharged, and then the hot metal is transferred to a processing furnace in which the slag in the furnace has already been discharged, and then the refining process is performed. The refining method with high reaction efficiency described in 1. The refining agent is characterized in that the CaO · Fe ₂ O ₃ phase is present in an amount of 5 mass% or more and a CaO component is contained in an amount of 20 mass% or more in a state at room temperature before addition to the processing furnace. Item 3. A refining method having high reaction efficiency according to Item 1 or 2. Described above 30 mass% of the total CaO content used in the refining process above, either in advance from claim 1, characterized in that the addition of Fe _t O the compound was refining agent As the CaO 3 of Refining method with high reaction efficiency.   The refining method with high reaction efficiency according to any one of claims 1 to 4, wherein refining is performed in a single treatment furnace until a predetermined P concentration in molten iron and C concentration in molten iron are obtained without waste.

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