JPH06322425A - Nitrogen content reduction method of arc furnace cast iron - Google Patents

Abstract

(57) [Abstract] [Purpose] Melt materials containing high nitrogen content materials such as inferior steel scraps and return scraps can be manufactured inexpensively in an arc furnace, the nitrogen content is low, and there are almost no gas defects and chilling occurs. The purpose is to produce a cupola with no tendency and cast iron similar to a low-frequency furnace. [Composition] Molten material consisting of steel scrap, return scrap, and ductile pig is put into an arc furnace and melted by energizing the arc electrode, and when the melt temperature reaches 1420 ° C, oxygen blowing is started in the melt. When the temperature of the molten metal reaches 1500 ° C. or higher, the oxygen blowing is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing the nitrogen content of cast iron melted in an arc furnace, and particularly from a molten material containing a high nitrogen content material such as bad steel scrap to a cupola furnace or a low frequency furnace. The present invention relates to a method for reducing the nitrogen content of an arc furnace cast iron for producing cast iron having a nitrogen content as low as that of conventional cast iron.

[0002]

2. Description of the Related Art Conventionally, in the production of cast iron, a melting material composed of steel scrap, return scrap, pig iron, ductile pig, etc. was charged into an Eru arc furnace, and the melting material was melted and heated to reach a specified temperature. After that, the slag was removed and the components were adjusted in the furnace before tapping. The arc furnace 10 is, as shown in FIG.
An electric arc is generated by the carbon electrode 13 by the electric current passing through the transformer 16 into the molten material charged in 1 and is heated by the heat source to form the molten metal P. When the molten metal is discharged, the furnace main body 11 is tilted and the ladle is ladle. I was bathing in 20.

[0003]

However, the molten material charged into the arc furnace contains inferior steel scrap, and the advantage of being able to melt using such inferior steel scrap is the arc. On the other hand, in the furnace operation, on the other hand, inferior steel scraps and return scraps have a higher nitrogen content than that of ductile pig iron, as shown in Table 1, for example. As a result, since the nitrogen content is high, gas defects such as pinholes and air bubbles are likely to occur in cast iron products, and there is a risk of promoting the chilling tendency. Also,
The cast iron products of the arc furnace had the same CE (carbon equivalent) and tended to have too high strength as compared with the cupola and the molten cast iron of the low frequency furnace. If the strength is too high, there is a problem that brittleness increases, and products similar to cupola and low frequency furnaces could not be obtained with conventional arc furnaces.

[0004]

[Table 1]

[0005]

In order to solve the problems described above, in the present invention, a melting material such as steel scrap, return scrap, pig iron, ductile pig, etc. is charged into an arc furnace to melt and heat it.・ In the method for producing cast iron in which the temperature is raised, the molten material is melted by energizing the arc electrode, and when the temperature of the molten metal reaches 1420 ° C, oxygen blowing is started in the molten metal, and the molten metal temperature is 1500 ° C or more. Oxygen ejaculation was stopped when the temperature reached.

[0006]

In the method of the present invention, when the temperature of the molten metal reaches 1420 ° C. during the heating and heating period of the arc furnace, oxygen is blown into the molten metal, and the molten metal is boiled and stirred by the CO gas exothermic reaction to be contained in the molten metal. Float the nitride. Melt temperature is 15
When the temperature exceeds 00 ° C, the oxygen sperm is stopped and the supply of oxygen and the energization are stopped. After that, the slag is removed and the molten metal is transferred to a simple ladle refining furnace for component adjustment and refining.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 to 4 relate to an embodiment of the present invention,
Figure 1 is a schematic vertical sectional view of an arc furnace and a simple ladle refining furnace.
2 is a manufacturing process explanatory diagram, FIG. 3 is a comparative diagram showing a correlation between nitrogen content rate of cast iron and mechanical strength, and FIG. 4 is a characteristic curve diagram showing a correlation between oxygen blowing time and nitrogen content rate of cast iron. . The arc furnace 10 shown in FIG. 1 has a capacity of 30 tons, the transformer has a transformer capacity of 15000 KVA, and the lining is basic.
Eru furnace type. The molten material charged into the arc furnace 10 is composed of, for example, 50% steel scrap, 40% return scrap, and 10% ductile pig iron. After charging the arc furnace 10, the electrode 1
Start power transmission to 3 and heat. In the manufacturing process, as shown in FIG. 2, the carbon electrode 13 alone is heated from room temperature to 1420 ° C., and when the temperature reaches 1420 ° C., the carbon gas is heated and the oxygen injection pipe 19 connected to the oxygen cylinder 19 a is discharged from the outlet 17. Insert it almost horizontally and bury the bent part of the tip in the melt. At this time, oxygen gas is blown after the tip is immersed to a depth of 500 mm so that the incident angle is about 30 ° to the liquid surface of the molten metal P. The carbon contained in the molten metal P reacts with the blown oxygen to cause an oxidative exothermic reaction, and the temperature of the molten metal rises rapidly while denitrifying during this period. When the temperature of the molten metal exceeds 1500 ° C., the oxygen blowing is stopped and the electricity to the arc electrode 13 is also stopped.
The oxygen blowing pipe 19 was taken out of the furnace, the arc furnace 10 was tilted, and floated on the surface of the molten metal from the outlet port 17 to 20 to 90.
The mm slag is removed, and the arc furnace 10 is tilted again in the opposite direction and tapped into the simple ladle refining furnace 30 that stands by near the tap hole 18. In the simple ladle refining furnace 30, the auxiliary material Q is added to the molten metal P to adjust the components so that the desired components are obtained with reference to the chemical component analysis results. The simple ladle refining furnace 30 has a structure in which a refractory material is lined in a cylindrical steel container, and a nozzle is provided on the bottom surface so that it can be discharged to the outside by raising and lowering the stopper 32. Furthermore, absorption of oxygen from the atmosphere is avoided as much as possible. An inert gas such as argon gas G is injected from the bottom at about 50 to 60 Nl / min so that the melt inside can be stirred and mixed, and the auxiliary material Q is uniformly mixed with the melt. When the correlation between the nitrogen content and the mechanical strength of the cast iron products obtained by the above furnace operation is compared, as shown in Fig. 3, when oxygen is blown in an arc furnace, oxygen is not blown. Deflection (deflection) compared to conventional methods
Although the hardness is almost the same, the hardness decreases and the tensile strength also decreases, and it is comparable to cast iron by a low-frequency furnace and cupola. Therefore, the conventional drawback of abnormally increased mechanical strength and increased brittleness is improved. As shown in FIG. 4, the relationship between the oxygen sparging time and the nitrogen content is reduced substantially with the spouting time for both free nitrogen and total nitrogen obtained by adding a nitride to the free nitrogen.

As described above, in the present invention, the nitrogen content in the arc furnace is reduced by performing the denitrification reaction on the dissolved material containing a large amount of inferior steel and return debris having a high nitrogen content by the oxygen blowing. Since it can be reduced, it is possible to manufacture cast iron of the same quality as a cupola or a low-frequency furnace at low cost.

[0009]

As described above, according to the present invention, even if a high nitrogen content material such as inferior steel scrap or return scrap is subjected to oxygen blowing in an arc furnace, the nitrogen content can be reduced. In addition to preventing gas defects and chilling tendency due to high nitrogen content, cast iron can be manufactured inexpensively from inferior molten material, and a cast iron product equivalent to a cupola or low frequency furnace can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an arc furnace and a simple ladle refining furnace according to an embodiment of the present invention.

FIG. 2 is a manufacturing process explanatory view showing an embodiment of the present invention.

FIG. 3 is a comparative diagram showing a correlation between nitrogen content and mechanical strength in the present invention and conventional cast iron.

FIG. 4 is a characteristic curve diagram showing a correlation between oxygen blowing time and nitrogen content of cast iron according to the present invention.

FIG. 5 is an overall vertical sectional view of a conventional arc furnace.

[Explanation of symbols]

 10 arc furnace 11 furnace body 12 furnace lid 13 carbon electrode 14 electrode clamp 15 furnace lid rising and turning device 16 transformer 17 outlet slag 18 outlet tap 19 oxygen blowing pipe 19a oxygen cylinder 20 ladle 30 simple ladle refining furnace 32 stopper G Argon gas P Molten metal Q Secondary material

Claims (1)

[Claims] 1. A method for producing cast iron, wherein molten materials such as steel scraps, return scraps, pig iron, and ductile pigs are charged into an arc furnace to melt, heat, and raise the temperature. When the temperature of the molten metal reaches 1420 ° C as it melts, oxygen sparging starts in the molten metal, and the temperature of the molten metal becomes 1
A method for reducing the nitrogen content of arc furnace cast iron, which stops oxygen blowing when the temperature reaches 500 ° C or higher.