JPS5937323B2 - Molten steel refining method to adjust blow-stop manganese - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refining method in which the amount of molten steel [Mn:] is controlled more rationally and at a lower level than in conventional methods.

The molten steel referred to here refers to the oxygen steelmaking method (a method in which pure oxygen is sprayed or injected into hot metal to carry out refining reactions such as decarburization and dephosphorization, and includes top-blown and bottom-blown converter methods, etc.). Become.

) refers to steel in a molten state at the time of blow-off (at the end of decarburization before deoxidation and composition adjustment).

The current method for adjusting the amount of molten steel [Mn:] generally takes the following method.

That is, a manganese source is blended into the blast furnace charge, and the reducing atmosphere inside the blast furnace is utilized to make the hot metal contain [Mn:].

Generally, hot metal [Mn:] is around 0.5 ratio.

When the same hot metal is charged into an oxygen steelmaking furnace and oxidized with oxygen, the manganese in the hot metal is oxidized and turns into slag whose main component is lime. is determined, and at the end of the blow, [Mn,! is usually in the range of 0.1 to 0.2.

When steel is tapped from a converter, iron-manganese alloys with various carbon contents are added to achieve the desired steel composition.

This current method has the following drawbacks: i) 0.5
%[Mn,l] is as low as 0.1 to 0.2% at the time of blow-off, and a large amount of manganese is lost, even though hot metal containing Mnl is used as the raw material.

ii) Molten steel [To adjust the composition of Mnl, an expensive iron-manganese alloy must be used.

Ferro-manganese alloys are generally produced by reducing and melting ferro-manganese ore in an electric furnace, but the electricity consumption in this process is still as high as 105KWH/l/ferroalloy, and the unit price will continue to rise. Conceivable.

The present invention aims to improve the problems of this current method, and by using inexpensive ferro-manganese ore instead of ferro-manganese alloy, the amount of ferro-manganese alloy used can be greatly reduced. It is an attempt to solve a problem.

It can be said that the above-mentioned problems are caused by blowing in the coexistence of steelmaking slag mainly composed of CaO.

In other words, MnO oxidized during refining is captured in the slag and is not reduced in the bath [C] until the end of blowing, so the MnO in the molten steel [
Mn] content decreases.

Based on this reaction mechanism, refining without slag solves the problem of manganese being oxidized and turning into slag.

That is, when oxidative refining is performed without slag or with a small amount of slag, the once oxidized (Mn) reacts with the molten steel and becomes a molten steel component again.

In this way, it was discovered that in the oxygen steelmaking process without slag or with a small amount of slag, there is a unique phenomenon in which the (Mn) content in the charging material can be maintained at the end of the flow without significantly reducing it. It was done.

By utilizing this phenomenon, the following new and rational (Mn) adjustment method becomes possible.

In other words, it refers to ores or manganese-containing substances (such as slag containing manganese in the form of oxides) that directly contain manganese in hot metal in an oxygen steelmaking furnace.

In the description of this invention, the same shall apply hereinafter.

) is reduced by the hot metal [C] and dissolved in the hot metal.

Because this manganese is not oxidized due to the above-mentioned phenomenon and is retained at the end of the blowout, it is possible to set the (Mn, l) at the time of the end of the blowout to values close to the target steel type (MHD). The use of alloys can be replaced by cheaper manganese-containing materials.

However, in order to perform such refining, the charge (hot metal) to the oxygen steelmaking furnace must be sufficiently dephosphorized and desulfurized in advance, and the oxygen steelmaking furnace only performs decarburization.

There are no restrictions on the method for producing low-phosphorus, low-sulfur pig iron, which is the prerequisite for this operation, but one of the inventors of the present invention has already applied for a molten iron alloy refining method that recycles auxiliary materials. is a good idea.

In addition, although there are no regulations regarding the composition of the hot metal, it must be refined in advance in an oxygen steelmaking furnace to the extent that all auxiliary materials such as quicklime and dolomite are not used, or only a small amount of less than 10 kq/t steel is used. Refers to the composition of

This auxiliary material is not used to expect refining reactions such as dephosphorization and desulfurization during decarburization, but is instead added for the purpose of protecting the oxygen steelmaking furnace refractories from silicon contained in the pre-refined hot metal. The basic unit varies depending on the [Si] content.

It is also known that manganese ore is used in the normal steelmaking process that uses quicklime, but the purpose of this is to use it as a medium to accelerate the formation of quicklime into slag, and as in the present invention, it is It can be said that this technique is different from the present invention as it is not aimed at manganese adjustment of molten steel.

In other words, the difference is obvious just by looking at the refining in the absence of slag.

As a method for adjusting the composition of molten steel using manganese ore, a method for adding manganese in the smelting of high chromium steel described in Japanese Patent Publication No. 13492/1980 is known.

However, this method assumes that oxidation occurs by the end of decarburization, and is characterized by reduction using a reducing agent.

On the other hand, the method of the present invention is characterized by reducing the amount of slag that inhibits the reduction of manganese oxide produced by oxidation.
The technical concept is completely different from the above method.

The hot metal used in the method of the present invention is refined by dephosphorization and desulfurization in the same vessel or another reaction vessel under conditions that prevent the decarburization reaction from proceeding as much as possible before the hot metal for steelmaking is refined by the oxygen steelmaking method. Naturally, the [Si] content also decreases.

This pre-smelting is performed to reduce as much as possible the amount of slag that coexists during decarburization in the oxygen steelmaking furnace.For this purpose, the content of [P] and [S] in the hot metal after refining is determined by the [P] and [S] contents of the hot metal after refining. ], [S] content is preferably close to or lower than that.

Although the pre-refining method for this purpose is not a limitation of the present invention,
The refining method of recycling an alkali metal compound, which has already been filed by one of the inventors of the present invention, can be said to be the most ideal method in terms of refining costs and work stability.

According to this refining method, the hot metal components after pre-refining can be easily [C
] Medium 4.0%, (Si, l<0.08%, [P] 0
．． 030, [S] is 0.010%, and since decarburization is only performed in a generally known oxygen steelmaking furnace, slag for the purpose of dephosphorization and desulfurization is not required.

When this hot metal is used, it is possible to decarburize and smelt auxiliary materials such as quicklime completely (or to decarburize with a unit of quicklime or dolomite that is much smaller than normal operations whose main purpose is to protect refractories). can be done.

When using the same hot metal, the hot metal is charged into an oxygen steelmaking furnace and then pure oxygen is sprayed or injected into the hot metal in the furnace to cause a decarburization reaction.

If the temperature of the molten steel after refining is predicted to be higher than the target blow-off temperature, it is the same as normal operation to mix coolant such as scrap iron or iron oxide to control the bath temperature. be.

Manganese ore and manganese-containing slag can be used as the manganese-containing ore or manganese-containing substance to be charged as a manganese source, but it is preferable to use a manganese ore with a low content of other than manganese and iron. Ferromanganese ore used as a raw material for manganese-iron alloys and manganese ore used as a raw material for manganese-iron alloys are desirable.

The dimensions of the manganese-containing ore or manganese-containing substance are preferably 50 mm or less in diameter and 1 mm or more in order to prevent scattering due to the gas flow in the steelmaking furnace and to facilitate reaction with the bath. It can also be used as a briquette using a binder (for example, a tar-based binder).

Since the purpose is to reduce the steel in the bath [C], it is appropriate to charge the steel into the steelmaking furnace when the bath [C] is high, that is, before the middle stage of blowing.

In the case of smelting in which manganese-containing ores or manganese-containing substances are added in this manner, the relationship between blow-off [C] and the residual rate of manganese in the bath is determined as shown in FIG.

In the figure, it is assumed that the [Mn] of the charged hot metal does not change during refining, and that the increase in [seed] is entirely due to the charged manganese-containing ore or manganese-containing material.

(Actual performance of 75T top blowing converter furnace) As is clear from the same figure, it can be seen that about 70% of r remains until the blow stop [C,l = 0.1].

Blow-off (C) (At 0,050, 0,1 in the bath also becomes high, the residual rate decreases overall, and the fluctuation becomes large.

In this way, in the case of a steel type with a blow-off [C]>0.050%, it is possible to increase [Mnl] up to the target value in advance.

However, as the Mnl increases, the loss due to volatilization also increases, so it is desirable that the detailed residual rate be determined for each furnace, taking into account variables such as the furnace volume, lance type, and oxygen supply conditions.

An example in which the present invention is applied to a large furnace is shown below.

75T of low-phosphorus, low-value hot metal obtained by oxidizing and refining hot metal for steelmaking in soda ash was charged into a top-blowing converter having a capacity of 75T, and blowing was performed using a top-blowing lance.

The blowing process used only pre-refined hot metal and did not use regular steelmaking pig iron.

Table 1 shows the composition of hot metal before and after pre-smelting.

In blowing using the same hot metal, there is no need to perform dephosphorization and desulfurization as is clear from Table 1, so 3 kg/t of quicklime was charged solely for the purpose of protecting the converter refractories.

In order to clarify the features of the present invention, we will explain the blowing process in which ferromanganese ore is charged during blowing and the blowing process in which ferromanganese ore is not charged (Mn,
l was compared.

The charged ferromanganese ore was Mn/33.4%, Fe/
It has a composition of 21.8% and is sized to a diameter of 2 to 30 m.

The furnace was charged 5 minutes after the start of blowing.

Comparing [Mn, l at the end of the blowout, Table 2 shows that
In blowing A to which the present invention is applied, blowing [Mnl is 0.32%]
shows a high value.

As seen in the table, it is clear that the present invention can significantly reduce the amount of expensive iron-manganese alloy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the residual rate of manganese in the bath and the blowout [%C].

Claims (1)

[Claims] 1. Using hot metal that has been previously dephosphorized and desulfurized, the refining function in the oxygen steelmaking furnace is limited to decarburization as much as possible, and slag is not present or heat is dissipated from the surface of the hot metal. , and collects oxides in the molten iron bath generated by oxidation.
Furthermore, by performing refining in the presence of as little slag as possible to prevent melting of the refractories and adding manganese-containing ores or manganese-containing substances to the bath, A molten steel refining method for adjusting blow-stop manganese characterized by increasing the molten steel Mn content. 2. A method for refining molten steel for preparing blow-off manganese according to claim 1, which uses hot metal that has been previously dephosphorized and desulfurized using an alkali metal compound as an auxiliary material.