JP6731763B2 - Method for producing molten iron containing chromium - Google Patents

Description

The present invention relates to a method for producing molten chromium-containing iron, which comprises melting molten chromium-containing raw material in an electric furnace to produce molten chromium-containing iron.

With the JIS standardization of slag recycling, the concentration of fluorine contained in slag is regulated. In response to this, for example, as shown in Patent Document 1 below, desulfurization of molten chromium-containing iron is performed in a KR desulfurization facility without using fluorite (CaF ₂ ). The KR desulfurization equipment outputs molten iron containing chromium from an electric furnace to a ladle, and after introducing a flux composed of a desulfurizing agent (such as CaO) and a deoxidizing agent (such as Al ash) into the ladle. The equipment that accelerates the desulfurization reaction by mechanically stirring the molten iron in the ladle with an impeller.

JP, 2014-91836, A

As described above, when fluorite is not used, the basicity (CaO/SiO ₂ ) of the slag in the electric furnace is lowered to ensure the liquid phase ratio of the slag. Therefore, when fluorite is not used, the silicon concentration in molten chromium-containing iron discharged from the electric furnace may be higher than when fluorite is used. When the silicon concentration is high, the lower step may be adversely affected, for example, the amount of lime used in the converter is increased or the life of the converter is shortened.

Moreover, when fluorite is not used, the melting point of the slag in the electric furnace becomes high. That is, when fluorite is not used, the fluidity of the slag in the electric furnace decreases. For this reason, the reaction between the molten iron and the slag (metal-slag reaction) in the electric furnace is hindered, and chromium that has been oxidized during melting is tapped in the unreduced state. The chromium concentration in the slag when steel is increased. This means that chromium-containing molten iron cannot be efficiently contained in chromium, which is a factor of increasing the manufacturing cost of the chromium-containing molten iron.

The present invention has been made in order to solve the above problems, and an object thereof is to reduce the concentration of silicon in molten chromium-containing iron and the concentration of chromium in slag during tapping. It is to provide a method for producing molten iron.

The method for producing molten chromium-containing iron according to the present invention is a method for producing molten chromium-containing iron by dissolving the chromium-containing raw material in an electric furnace without using fluorite , and melting the chromium-containing raw material. by after slag containing chromium oxide is formed in an electric furnace, viewed including the placing the de珪剤consisting mainly of iron oxide in an electric furnace, when tapping the chromium-containing molten iron from the electric furnace In order to avoid the occurrence of slag foaming, the desiliconizing agent is charged into the electric furnace at a timing when the unreacted iron oxide remaining in the slag when the molten chromium-containing iron is tapped is less than a predetermined amount .

According to the method for producing molten chromium-containing iron of the present invention, after the slag containing chromium oxide is formed in the electric furnace by melting the chromium-containing raw material, the desiliconizing agent containing iron oxide as a main component is charged into the electric furnace. Therefore, the silicon concentration in the molten iron containing chromium can be reduced and the chromium concentration in the slag at the time of tapping can be reduced.

4 is a flowchart showing a manufacturing process of stainless steel according to the embodiment of the present invention. It is explanatory drawing which shows the electric furnace used in the manufacturing process of the chromium-containing molten iron of FIG. It is a binary system phase diagram of FeO _n -Cr ₂ O ₃ .

Hereinafter, modes for carrying out the present invention will be described with reference to the drawings.
Embodiment.
FIG. 1 is a flowchart showing a manufacturing process of stainless steel according to an embodiment of the present invention. Chromium-containing steel is manufactured through a manufacturing process of molten chromium-containing iron (step S1), a primary refining process (step S2), a secondary refining process (step S3), and a casting process (step S4).

The process for producing molten chromium-containing iron (step S1) is a process for producing molten chromium-containing iron by melting the chromium-containing raw material in an electric furnace.
The primary refining step (step S2) is a step of performing rough decarburization, heating, and coarse component adjustment of molten chromium-containing iron in a primary refining furnace such as a converter. The secondary refining step (step S3) is a step of performing final decarburization of molten iron and final component adjustment in a secondary refining furnace such as a vacuum degassing facility. Through these refining processes, molten chromium-containing iron is made into molten stainless steel.
The casting step (step S4) is a step of casting a slab by injecting molten stainless steel into a mold using, for example, a continuous casting facility. The slab is a thick plate of stainless steel.

Next, FIG. 2 is an explanatory diagram showing the electric furnace 1 used in the manufacturing process (step S1) of the molten chromium-containing iron of FIG. As shown in FIG. 2, the electric furnace 1 is provided with a furnace body 10, a furnace lid 11, and a plurality of electrodes 12.

The furnace body 10 is a container having an opening at the top. The furnace lid 11 is a lid for covering the upper opening of the furnace body 10. The electrode 12 is a rod-shaped body inserted into the furnace body 10 through an opening provided in the furnace lid 11. After the chromium-containing raw material is charged into the furnace body 10, the furnace lid 11 is closed. After that, by supplying electric power to the electrode 12, the chromium-containing raw material is melted and the chromium-containing molten iron 2 and the slag 3 are generated.

The manufacturing process of molten chromium-containing iron 2 in an electric furnace proceeds according to a furnace period classified into an ignition period, a boring period, a puddle formation period, a main melting period, a final melting period, and a heating period.
The ignition period is a furnace period in which the arc from the electrode 12 is stabilized between the electrode 12 and the chromium-containing raw material.
The boring period is a furnace period in which the electrode 12 is dipped in the chromium-containing raw material while melting the chromium-containing raw material located immediately below the electrode 12.
The pool formation period is a furnace period in which molten metal for protecting the hearth of the furnace body 10 is formed in the lower part of the furnace.
The main melting period is a furnace period in which maximum power is applied to the electrode 12 to rapidly dissolve the chromium-containing raw material. The main melting period can be divided into two reactor phases, a main melting early period and a main melting late period, according to the melting situation. The voltage may be lowered in the latter stage of the main melting when the bulk of the raw material in the furnace is lowered.
The final stage of melting is a furnace period in which the unmelted residue in the furnace is melted while lowering the voltage. At the end of the final stage of melting, all the chromium-containing raw materials in the furnace body 10 melt down. Chromium-containing molten iron 2 is formed from the boring period to the end of melting, and the slag 3 is formed from the main melting period to the end of melting (melting down of the chromium-containing raw material).
The heating period is a furnace period in which the molten chromium-containing metal is heated to a predetermined temperature. In the heat-raising period, oxygen may be sprayed onto the molten chromium-containing iron 2.

An auxiliary material charging device 4 is connected to the electric furnace 1. The auxiliary raw material charging device 4 is a device for charging the auxiliary raw material 4 a into the furnace body 10 through an opening provided in the furnace lid 11. The auxiliary raw material 4a is used for component adjustment, and a ferrochrome alloy, coke, etc. correspond to component adjustment.

Here, the chromium-containing molten iron 2 contains silicon (Si), and the slag 3 contains chromium oxide (Cr ₂ O ₃ ). If the silicon concentration in the molten chromium-containing iron 2 tapped from the electric furnace 1 is high, it may adversely affect the lower process, and the chromium concentration in the slag 3 when the molten chromium-containing iron 2 is tapped from the electric furnace 1. If it is high, it becomes a factor of increasing the manufacturing cost of the molten chromium-containing iron 2.

The method for manufacturing molten chromium-containing iron 2 carried out in the electric furnace 1 of the present embodiment is such that after the slag 3 containing chromium oxide is formed in the electric furnace 1 by melting the chromium-containing raw material, iron oxide is the main component. Introducing a desiliconizing agent into the electric furnace 1. The desiliconizing agent can be charged into the electric furnace 1 as the auxiliary material 4a. Having iron oxide as the main component means that the mass ratio of iron oxide to the unit mass of the silicon removal agent is the largest.

Iron oxide has a higher free energy of formation than silicon oxide. Therefore, by introducing a desiliconizing agent containing iron oxide as a main component into the electric furnace 1, the molten chromium-containing iron 2 is desiliconized, for example, as shown in the following formula 1. That is, the silicon concentration in the molten chromium-containing iron 2 is reduced by introducing the desiliconizing agent containing iron oxide as the main component into the electric furnace 1. A substance such as (Fe ₂ O ₃ ) shown in parentheses means a substance in slag, and a substance shown in [] like [Si] means a substance in molten iron.
2(Fe ₂ O ₃ )+3[Si]→4[Fe]+3(SiO ₂ )...Equation 1

Further, the iron oxide and the chromium oxide in the slag 3 generate the secondary oxide represented by the following formula 2.
(Cr ₂ O ₃ )+(FeO)=(FeCr ₂ O ₄ ).
ΔG _o =−61.9+0.017T (kJ/mol)...Equation 2
This secondary oxide also contributes to desiliconization as in the following formula 3. That is, by introducing a desiliconizing agent containing iron oxide as a main component into the electric furnace 1, the silicon concentration in the molten chromium-containing iron 2 is reduced through the secondary oxide.
(FeCr ₂ O ₄ )+2[Si]=[Fe]+2[Cr]+2(SiO ₂ ).
ΔG _o =−130.1−0.0022T (kJ/mol)...Equation 3

Furthermore, Formulas 2 and 3 mean that the chromium oxide contained in the slag 3 is reduced and migrates to the molten chromium-containing iron 2 as chromium. That is, by introducing a desiliconizing agent containing iron oxide as a main component into the electric furnace 1, the chromium concentration in the slag 3 is reduced. The reduction reaction of the chromium oxide in the slag 3 also occurs with the silicon in the chromium-containing molten iron 2.

Next, FIG. 3 is a binary system phase diagram of FeO _n —Cr ₂ O ₃ .
The vertical axis of FIG. 3 represents the melting point [° C.] of the metal body made of at least one of iron oxide (FeO _n ) and chromium oxide (Cr ₂ O ₃ ).
The lower horizontal axis of FIG. 3 represents the mass ratio [%] of iron oxide contained in the metal body. That is, the left end of the lower horizontal axis means that the metal body is composed only of chromium oxide, which means that the mass ratio of iron oxide contained in the metal body increases from the left end to the right end of the lower horizontal axis. doing.

As shown in the binary phase diagram shown in FIG. 3, the melting point of the metal body composed of at least one of iron oxide and chromium oxide tends to be lowered as the mass ratio of iron oxide increases. That is, the melting point of the slag 3 can be lowered by introducing a desiliconizing agent containing iron oxide as a main component into the electric furnace 1 to improve the fluidity of the slag 3 in the electric furnace 1. Thereby, the reaction between the chromium-containing molten iron 2 and the slag 3 (metal-slag reaction) can be promoted, and the desiliconization reaction and the chromium reduction reaction can be promoted. The reaction promoted in this way includes not only the reactions of the above formulas 1 to 3 but also the reaction between the chromium oxide of the slag 3 and the silicon of the chromium-containing molten iron 2.

If the desiliconizing agent contains chromium oxide, the melting point lowering action of the slag 3 due to iron oxide is inhibited. Therefore, it is preferable that the mass ratio of chromium oxide in the desiliconizing agent is low, and it is further preferable that the desiliconizing agent contains no or substantially no chromium oxide.

As the desiliconizing agent, one consisting only of iron oxide and unavoidable impurities may be used, but it is preferable to use a sintered ore obtained by baking powdery or granular iron ore together with limestone and coal. Iron oxide tends to be powdery and difficult to handle, but sinter ore is granular and easy to handle. Sintered ore also has the advantage that the content of water, which causes steam explosion, is extremely low. As shown in the component examples in Table 1 below, about 80 mass% of iron oxide (FeO and Fe ₂ O ₃ ) is contained in the sintered ore obtained by baking and hardening powdery or granular iron ore.

As the desiliconizing agent, a sinter having a small particle diameter of 1 mm or more and 7 mm or less can be used. Sintered ore having a diameter of 7 mm or less is one that is not suitable for charging into a blast furnace and is sieved off, and can be easily obtained. That is, the desiliconizing agent can be a by-product when selecting a sinter for blast furnace charging with a sieve. On the other hand, a sinter having a diameter of less than 1 mm is difficult to handle, like powdered iron oxide. The particle size of the sinter ore corresponds to the size of the openings of the sieve for sieving the sinter.

Here, the desiliconizing agent may be charged into the electric furnace 1 when the undissolved chromium-containing raw material remains in the electric furnace 1, but the desiliconizing agent may be added after all the chromium-containing raw materials have melted down. It is preferable to charge the electric furnace 1. This is because the slag 3 is surely formed in the electric furnace 1 after all the chromium-containing raw materials have melted down, and the desiliconizing agent can efficiently react with the slag 3.

The iron oxide contained in the desiliconizing agent charged into the electric furnace 1 is gradually consumed by the reactions shown in Formulas 1 to 3. If the period from the time of introducing the desiliconizing agent to the tapping is short, the amount of unreacted iron oxide remaining in the slag 3 during tapping increases. When a large amount of unreacted iron oxide remains in the slag 3, oxygen in the iron oxide rapidly reacts with carbon during tapping, and a phenomenon called slag foaming occurs in the slag 3. The slag forming causes an abnormal operation in which the slag 3 overflows to the outside. Therefore, in order to avoid slag foaming when tapping molten chromium-containing iron 2 from the electric furnace 1, a predetermined amount of unreacted iron oxide remains in the slag 3 during tapping of the chromium-containing molten iron 2. It is preferable to add the desiliconizing agent to the electric furnace 1 at a timing when the amount becomes smaller than that. For example, it is preferable to introduce the desiliconizing agent into the electric furnace 1 not at the latter half of the heating period but at the beginning of the heating period. This timing can be determined according to, for example, the amount of desiliconizing agent (iron oxide) added to the electric furnace 1 required for desiliconizing.

Next, examples will be given. The present inventor carried out the above-described method for producing molten chromium-containing iron 2 in producing 16Cr-Fe stainless steel. The desiliconizing agent used was a sinter containing 80.4% by weight of iron oxide as shown in Table 1 above. The particle size of the sinter was 1 mm or more and 7 mm or less, and the amount of the sinter added was 6.3 kg per 1 Ton of the chromium-containing molten iron. Then, (1) the relationship between the time when the sinter was charged and the occurrence of operational abnormality, (2) the silicon concentration of molten iron containing chromium after tapping, and (3) the chromium concentration in the slag at tapping were investigated. .. Further, as a comparative example, the silicon concentration of molten iron containing chromium after (2)' tapping and the chromium concentration in slag at tapping (3)' when no desiliconizing agent was added were also investigated.

表２に示すように、昇熱期の中期（全電力の８０％を超える電力を電気炉１に投入した時期）において焼結鉱を投入した場合にはスラグフォーミングが発生したが、電気炉１内のすべての含クロム原料が溶け落ちた後であって昇熱期を開始しようとする時期を含む昇熱期の初期（全電力の７０％以上かつ８０％未満の電力を電気炉１に投入した時期）において焼結鉱を投入した場合にはスラグフォーミングの発生を回避することができた。 Table 2 below shows the relationship between the timing of adding the sintered ore and the occurrence of operational anomalies.

As shown in Table 2, slag foaming occurred when sinter was added in the middle of the heat-up period (when more than 80% of the total electric power was supplied to the electric furnace 1). Of all the chromium-containing raw materials in the above, including the time to start the heat-up period, including the time to start the heat-up period (electric power of 1% or more and less than 80% of the total power is input to the electric furnace 1 It was possible to avoid the occurrence of slag foaming when sinter was added at the same time).

表３に含まれる「Ｓｉ投入量」は含クロム溶鉄１Ｔｏｎあたりに投入した珪素量であり、「処理後％Ｓｉ」は、出鋼後の含クロム溶鉄の珪素濃度を示している。表３に示すように、焼結鉱（酸化鉄を主成分とする脱珪剤）を電気炉に投入することで、Ｓｉ投入量を増やしても同程度の珪素濃度を得ることができた。すなわち、焼結鉱の投入により、含クロム溶鉄中の珪素濃度を低減できた。 Table 3 below is a table showing the difference in the silicon concentration of the molten iron containing chromium after tapping, depending on whether or not sinter was added.

The “Si input amount” included in Table 3 is the amount of silicon added per 1 Ton of the chromium-containing molten iron, and the “%Si after treatment” represents the silicon concentration of the chromium-containing molten iron after tapping. As shown in Table 3, by introducing sinter (desiliconizing agent containing iron oxide as a main component) into the electric furnace, it was possible to obtain the same silicon concentration even if the amount of Si added was increased. That is, the concentration of silicon in the molten chromium-containing iron could be reduced by adding the sinter.

表４に示すように、焼結鉱（酸化鉄を主成分とする脱珪剤）を電気炉に投入することで、出鋼時のスラグ中のクロム濃度を低減できることも確認された。 Table 4 below is a table showing the difference in the chromium concentration in the slag at the time of tapping, depending on whether or not the sinter is added.

As shown in Table 4, it was also confirmed that the concentration of chromium in the slag at the time of tapping can be reduced by introducing the sinter (desiliconizing agent containing iron oxide as a main component) into the electric furnace.

In such a method for producing molten iron containing chromium, after the slag 3 containing chromium oxide is formed in the electric furnace 1 by melting the raw material containing chromium, a desiliconizing agent containing iron oxide as a main component is added to the electric furnace 1. Since it is added, the silicon concentration in the molten chromium-containing iron can be reduced, and the chromium concentration in the slag at the time of tapping can be reduced.

Moreover, since the desiliconizing agent is a sintered ore obtained by baking and hardening iron ore, it can be handled more easily than when handling powdered iron oxide.

Furthermore, since the diameter of the sinter is 1 mm or more and 7 mm or less, it can be easily obtained while ensuring ease of handling.

Furthermore, in order to avoid slag foaming when tapping molten chromium-containing iron 2 from electric furnace 1, a predetermined amount of unreacted iron oxide remains in slag 3 when tapping molten chromium-containing iron 2. Since the desiliconizing agent is charged into the electric furnace 1 at a timing smaller than that, it is possible to avoid the operation stop due to the operation abnormality.

1 Electric furnace 2 Molten iron containing chromium 3 Slag

Claims (3)

A method for producing molten chromium-containing iron, which comprises melting the chromium-containing raw material in an electric furnace without using fluorite to produce molten chromium-containing iron,
After slag containing chromium oxide by dissolution of the chromium-containing raw material is formed in the electric furnace, it viewed including the placing the de珪剤consisting mainly of iron oxide into the electric furnace,
In order to avoid slag foaming when tapping the molten chromium-containing iron from the electric furnace, unreacted iron oxide remaining in the slag during tapping of the molten chromium-containing iron is less than a predetermined amount. A method for producing molten chromium-containing iron , comprising charging the desiliconizing agent into the electric furnace at a certain timing . The method for producing molten chromium-containing iron according to claim 1, wherein the desiliconizing agent is a sintered ore obtained by baking and hardening iron ore. The method for producing molten chromium-containing iron according to claim 2, wherein the diameter of the sinter is 1 mm or more and 7 mm or less.

Images