JPH07258713A - Method for pre-treating molten iron - Google Patents

Abstract

PURPOSE:To efficiently produce a low in Mn steel and a high Mn steel by adding molten iron subjected to desilicon and dephosphorus treatments and carbon into slag after demanganese treatment and stirring. CONSTITUTION:After executing the demanganese treatment by supplying iron oxide, etc., into the molten iron tapped from a blast furnace, this molten iron is discharged while leaving the slag after the demanganese treatment in a vessel and supplied into a converter process, and blow-refining in the converter is executed to produce the demanganesed steel. The low silicon and low phosphorus molten iron subjected desilicon and dephosphorus treatments is received into the vessel remaining the demanganese slag. After receiving the molten iron, the carbon source is supplied to execute the manganese reducing treatment and Mn concn. is increased. At the time of adding the carbon source, the stirring is performed. By this method, the molten iron pretreating method can be obtained corresponding to the Mn concn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a high M due to hot metal pretreatment.
It is a method for efficiently refining n steel and low Mn steel.

[0002]

2. Description of the Related Art In recent years, in the production of ultra-low sulfur steel and ultra-low phosphorus steel, control of chemical components in steel has become more and more strict. Removing impurities only by blowing in the converter is a heavy burden, so iron oxide is added to the hot metal to desiliconize it, and the slag produced is separated and removed, and then dephosphorization flux is added to remove it. A method of performing phosphorus treatment and blowing the obtained treated hot metal in a converter is known (Patent publication: Showa 60-5996).
2). With this treatment method, phosphorus and sulfur are efficiently removed. The hot metal pretreatment slag is basic, and, since the phosphorus concentration is lowered in the converter blowing of the hot metal after hot metal pretreatment, the amount of slag can be reduced, and the blow-off Mn can be easily increased. Especially for thick plates, steel pipes, steel bars,
For example, it is effective in reducing the ferroalloy of high Mn steel with a Mn concentration exceeding 1%.

Further, as known from Japanese Patent Publication No. 3-77245, in the hot metal stage, the Mn concentration is positively increased, the blown Mn of the converter is increased, and the amount of Mn alloy iron used is further reduced. It is possible.

However, a thin plate material which is required to have workability is required to have a low Mn concentration from the viewpoint of material quality, and for example, a steel material having a Mn concentration of 0.10% or less is required. In this case, it is difficult to reduce Mn in the conventional hot metal pretreatment, and the amount of slag is increased in the converter to reduce Mn. This method is not economically disadvantageous because the effect of reducing the amount of slag in the converter, which is the effect of hot metal pretreatment, cannot be obtained.

In addition, due to the restrictions on the production form of steel mills, high Mn steels for thick plates and steel pipes and low Mn steels for thin plates are often manufactured continuously in one steelmaking process, and the Mn concentration Control has become an important issue.

[0006]

The object of the present invention is to provide Mn.
The hot metal pretreatment method according to the concentration is presented.

[0007]

The present invention advantageously solves the above-mentioned problems, and its gist is as follows.

[0008] The hot metal is demanganized, then only the hot metal is discharged out of the container, and the hot metal that has been desiliconized and dephosphorized and carbon are added to the container in which the slag after the demanganization process remains. A hot metal pretreatment method characterized by stirring and stirring.

The hot metal pretreatment method for controlling the Mn concentration of the present invention will be described in detail below. A flow sheet for carrying out the present invention is shown in FIG. The present invention aims to efficiently produce low-Mn steel and high-Mn steel.
The route indicates a melting route for low Mn steel, and the route indicates a melting route for high Mn steel.

First, the route for low Mn steel will be described.

Iron oxide and / or gaseous oxygen is supplied to the hot metal tapped from the blast furnace to carry out a demanganization treatment to reduce the Mn concentration in the hot metal. After the de-Mn treatment, the molten iron is discharged and supplied to the converter process while the slag after the de-manganese treatment is left in the container (for example, a torpedo car and a hot metal ladle) is blown to the converter to perform de-Mn steel removal. To manufacture.

Next, the melting route of the high Mn steel will be described.

MnO is added to the slag after the demanganization treatment of
Due to its high content, the manganese in this slag is
Hot metal for collecting and manufacturing molten steel with high manganese concentration
Perform reduction processing. That is, demanganesed slag remains
The silicon-filled container was desiliconized and dephosphorized to remove low silicon and
It receives the hot metal and supplies the carbon source simultaneously with or after the hot metal.
To reduce the manganese concentration and increase the Mn concentration.
It Here, low silicon and low phosphorus hot metal means Si<
0.03%, P<Point to 0.03% level of hot metal
At these levels, slag with Si or P
The reduction of manganese in it cannot be expected. Also, the return of manganese
This process uses a carbon source as a base agent, but
This is because couscous and coal are economical. In addition, raise the temperature
If it is necessary to raise the temperature, use gaseous oxygen together, and
Lime may be used in combination to control the composition of gluten. This melt
Refining with the main purpose of decarbonization in a converter using pig iron. Melting
Since phosphorus dephosphorization is carried out, dephosphorization treatment is practical in the converter.
Qualitatively unnecessary, the amount of slag can be reduced and Mn residue in the converter
The retention rate increases. Therefore, add Mn ore into the converter.
Then, the Mn concentration at the time of blowing is increased to manufacture high Mn steel.
It

As described above, in order to efficiently produce a low Mn steel, hot metal de-Mn treatment is performed, and the slag once produced for producing a low Mn steel is used to melt the high Mn hot metal for a high Mn steel. The steel is manufactured and the high Mn steel is melted economically.

[0015]

EXAMPLE Next, an example will be described.

[0016] The hot metal received from the blast furnace with a torpedo car is demanganesed with iron oxide and gaseous oxygen.
The manganese concentration in the hot metal was reduced from 0.43% to 0.09%. The MnO concentration of the slag after the demanganization treatment is 13
%Met. While leaving the slag inside the torpedo car,
This hot metal was discharged, supplied to a converter process, and subjected to converter blowing to produce a 0.05% low Mn steel. On the other hand, the torpedo car in which the manganese-depleted slag having a MnO concentration of 13% remained was subjected to desiliconization and dephosphorization. Si concentration is 0.
12% of hot metal and coke with a P concentration of 0.009%
kg / (ton hot metal) was added, N ₂ gas was blown in, and the mixture was stirred, and the Mn concentration of the hot metal rose from 0.34% to 0.62%. This hot metal was supplied to the converter process and refined mainly for decarbonization. Since the P concentration of the hot metal is low, dephosphorization treatment is substantially unnecessary in the converter, the amount of slag can be reduced, and the Mn residual rate in the converter increases. 1 Mn ore in converter
By adding 8 kg / (ton molten steel), the Mn concentration at the time of blowing can be increased to 1.02%, and a high Mn steel could be economically manufactured.

[0017]

As described above, according to the present invention, low M
n steel and high Mn steel can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a refining process of a low Mn steel and a high Mn steel according to the present invention.

Claims (1)

[Claims] 1. A hot-dipped pig iron that has been desiliconized and dephosphorized in a container in which the hot metal is demanganized, then only the hot metal is discharged to the outside of the container, and the slag after demanganization is left in the container. A hot metal pretreatment method comprising adding and stirring.