JPS609084B2 - Molten iron desulfurization method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for desulfurizing molten metal.

A method of adding magnesium metal (hereinafter referred to as Mg) to molten metal and removing sulfur contained in the molten moat is known.

However, Mg has a high vapor pressure, and at the melting temperature of the metal (molten metal), it has a vapor pressure of 15 atmospheres or more.

Therefore, when it is added to the molten metal, it not only causes a rapid reaction, which is extremely dangerous to work with, but also the desulfurization efficiency is not constant and the reaction rate of Mg is low. Methods to improve these drawbacks include, for example, a method using coke impregnated with Mg, a method using an iron turning layer compact impregnated with Mg, and a method using a Fe-Si-Mg alloy. There are methods using alloys such as Mg, but these methods may not necessarily be satisfactory, such as the quality of the metal being degraded due to accompanying impurities or the rapid reaction of Mg not being completely suppressed. This is not a method to obtain a desulfurization effect. The present inventors conducted research on the properties of Mg suitable for use as a desulfurization agent for molten metal, and found that ultrafine powder of Mg
``Moreover, the surface is magnesium oxide (Mg0)
It has been discovered that when Mg coated with Mg is added to molten metal, it reacts very efficiently and gently, and has good desulfurization efficiency.

In order to obtain such Mg used in the present invention, Mg0 is reduced at high temperature with a carbonaceous reducing agent, and the resulting product is added to the reaction system with a gas that is relatively inert and kept at a temperature lower than the reaction temperature.
For example, by contacting with a hydrocarbon gas such as helium, hydrogen, argon, nitrogen, or methane and/or a gas containing a small amount of carbon monoxide gas in these gases, the reverse reaction of the reduction product can be suppressed from the reaction temperature. Obtain by quenching to temperature.

At this time, the speed of rapid cooling is extremely fast. The reaction products obtained by rapid cooling in this manner are obtained as dust containing Mg, Mg○, carbon substances, and the like.

The Mg contained in this dust has a diameter of approximately 10 mm or less.
It is an ultrafine powder with a size of less than 100 ml (see Figure 11), and the surface of Mg is approximately coated with Mg○. (Figure 12
reference). The composition of the obtained dust can be arbitrarily changed by changing the flow rate of the cooling gas mentioned above when it is brought into contact with the reaction product or the carbon monoxide concentration contained in the cooling gas, but usually the Mg concentration 5-95% by weight as
It is.

Although this composition dust can be used as it is as a desulfurizing agent for metallization, it is preferable to use an organic polymer compound such as acrylic resin, styrene resin, polyvinyl alcohol, carboxymethylcellulose, etc. as it is or to use benzene, toluene, xylene, etc. , ethyl acetate, methyl ethyl ketone, or other general-purpose solvents, or molded bodies heated and molded in an inert atmosphere at a temperature above the melting point of Mg, preferably up to 1100 oo, for desulfurization of molten metal. It is preferable to use the organic polymer substance in terms of handling and storage.
It is preferable to use a solution having a resin concentration of 25% by weight, preferably 5 to 1% by weight, based on the dust.

The size of these molded objects is not particularly limited, but from the viewpoint of handling, spherical objects or pellet-like objects with a diameter of 0.5 to 5 mm are preferable. The method of adding the Mg-containing desulfurization agent obtained by the above method to the molten metal is not particularly limited, and conventional methods,
For example, this can be carried out by spraying the desulfurizing agent along with carrier gas, or by filling a plunger or iron pipe with the desulfurizing agent and adding it by immersing it in the molten metal. In the blowing method that uses an inert gas such as nitrogen gas as a carrier gas, the method of the present invention has good fluidity of the added desulfurizing agent, so there is no need to interrupt blowing midway through, and the desulfurizing agent can be added uniformly to the sun. can.

In addition, the method of the present invention does not cause blockage in the lance, which has been a problem in conventional injection of Mg into molten metal, due to melting of Mg or the formation of Mg nitrides such as Mg3N2. Mg is extremely natural in the form of ultrafine powder, but the present invention uses Mg0 as a diluent without artificially coating the surface of Mg.
Since Mg originally coated with Mg0 is used, it is not only extremely safe to handle, but also because the Mg used is an ultrafine powder, the reaction efficiency is high and the desulfurization efficiency is therefore high.

Next, the present invention will be explained with examples.

Example: A mixture of Mg0 and oil coke was used as a raw material.
Mg-containing dust A (Mg: 60 wt%
, Mg0: 30.5% by weight, Carbon: 9% by weight, Nitrogen: 0
．． 5% by weight) and Mg-containing dust B (Mg: 30% by weight, Mg0:5 obtained by adjusting the flow rate of cooling gas (nitrogen gas)
3.5% by weight, carbon: 16% by weight, nitrogen 0.5% by weight
), a toluene solution with an acrylic resin concentration of 5% by weight was added to the dust in an amount of 8% by weight to form a sphere with a diameter of approximately 0.7cm/skin, and the resulting molded body was dried at 80°C. It was used in the desulfurization test of ductile pig iron described below.

Pig iron (4k9, molten metal depth 10 skin) is 1400-145
000 and using a carbon lance as a carrier of nitrogen gas (8 parts), the molded bodies were added to each molten metal.
A desulfurization test was conducted by blowing for 5 minutes.

The test was conducted in the atmosphere. Also, for comparison, CaC2 powder (
(purity 80%) was blown into the molten metal under the same conditions as above.

The conditions and results are shown in the table below. * Desulfurization efficiency (%) = (
Amount of sulfur before treatment (yX-- amount of sulfur after treatment)
-X IOOx 32 However, in the case of A and B, x = 6 (amount of M), y = 24 (atomic weight of M), in the case of CaC2, x = 16, y = 64 (C
Molecular weight of aC2) The properties of Dust A used are shown in Figure 11.
The results obtained from an electron micrograph (1000M sound) and an electron diffraction image are shown in a schematic diagram in Figure 12.

The values of lattice spacing obtained from the results of electron diffraction were as shown below.

dobs 2.80 (Spot) M evening 2.43 'Debye) M evening 02-12
ku 〃 ) 〃 1.49 ( 〃 ) 〃 dobs 1.22 ( 〃 ) 〃 1.02 (Spot) 1 is Mg, 2 is Mg○, 3 is SpoL 4 is e of De show.

[Brief explanation of the drawing]

FIG. 11 is an electron micrograph of dust containing Mg used in Examples. Further, FIG. 12 is a schematic diagram of the results similarly obtained from an electron diffraction image photograph of dust. In FIG. 12, 1 indicates Mg and 2 indicates Mg0.
Figure 1I Figure 12

Claims (1)

[Scope of Claims] 1. A method for desulfurizing molten iron, which comprises adding a mixture containing ultrafine metal magnesium and magnesium oxide, or a compact thereof, when desulfurizing molten iron. 2. The method according to claim 1, which uses a mixture containing magnesium metal and magnesium oxide obtained by contacting an inert gas with a reduction product obtained by reducing magnesium oxide at high temperature and quenching it.