JPS5919170B2 - Molten steel refining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for refining molten steel, and its purpose is to improve the electric power consumption and production efficiency of refining using an arc furnace.

When attempting to manufacture a desired steel starting from composite material, an arc furnace requires a large amount of power consumption.

Therefore, in order to reduce power consumption, efforts have been made to supply all or part of the heat required to melt the material without relying on electric power.

For example, scrap raw materials charged into a furnace are preheated with high-temperature exhaust gas discharged from a heating furnace, or heated with an oil burner.

Attempts have also been made to cause an exothermic reaction by blowing oxygen gas onto a material that has reached a certain degree of roughness.

These efforts can reduce the power consumption to a considerable extent as far as heating the composite material until its melting is concerned, but the power consumption from melting to tapping cannot be reduced.

Therefore, reducing power consumption at this stage remained an issue.

An object of the present invention is to provide a refining method that achieves energy savings from melting to tapping.

Generally, in order to improve the electric power consumption in refining molten steel using an arc furnace, it is necessary to shorten the refining time.

Needless to say, shortening the time also results in improved efficiency, which is preferable from that point of view as well.

In order to shorten the refining time, it is most effective to shorten the heating time to the refining temperature after the material has melted.

The present inventors focused on this point and conducted repeated research.

First, we attempted to increase the heating rate by selecting and melting the material so that the C content in the molten steel would be high after the melt was blown with oxygen, but the C content after the oxygen blowing was It was found that the amount was not stable and it was inconvenient to perform the desired refining.

Therefore, on the contrary, we can control the C content and shorten the refining time by blowing oxygen to quickly raise the temperature and lowering the C content below the standard, and then blowing carbon powder into it. The intention was to do this together, and it was successful.

The invention is based on this approach.

The method for refining molten steel according to the present invention, when refining molten steel using an arc furnace, is designed to accelerate the melting of the material charged into the furnace and/or to speed up the temperature rise after the melting has finished. Oxygen blowing is performed to lower the C content in the molten steel below the standard value, and then carbon powder is blown into the melt in the furnace along with a flow of carrier gas to remove the slag on the surface of the molten steel. The slag is characterized by forming a foam layer and wrapping the arc in the foam layer of the slag to improve thermal efficiency while refining.

To explain with reference to the drawings, in the arc furnace 1 after oxygen blowing, there is a layer 6 of molten steel and a layer 5 of molten slag covering it, and the arc between the electrode 2 and the molten steel 6 is Heat is supplied by

Carbon powder is placed on a flow of carrier gas such as argon supplied from a tank (not shown) and introduced into the molten steel 6 through a lance pipe 3 whose tip is immersed in the molten steel.

The flow of the introduced carrier gas and carbon powder is dispersed and floats in the molten steel 6 and the slag 5.

During this time, the carbon powder melts into the molten steel and slag to increase its C content, and reacts with oxygen therein, particularly oxygen in iron oxide, to generate CO gas.

The generated CO gas adds to the originally blown carrier gas to increase the gas volume.

If the viscosity of the slag is appropriately high, a foam layer 5A is formed by the floating of these gas bubbles, and the slag layer 5,
In particular, its upper portion includes at least a portion of the raised arc.

Under favorable conditions, the slag envelops the arc-generating portion at the bottom of the electrode, and the entire arc becomes enveloped in slag.

While the slag foam breaks and disappears at the top, it is replenished by the gas that constantly floats up from below, so the foam layer 5A is always maintained at a certain level.

As a result of this phenomenon, the heat generated by the arc is hardly radiated to the outside, but is transferred to the molten steel through the slag.

Of course, the foamy slag itself also has a heat-insulating effect that reduces heat radiation from the surface of the molten steel.

As can be easily understood from the above, the carbon powder and carrier gas are injected directly under or near the electrode to maximize the effect of arc envelopment due to the formation of a foam layer of slag. Should.

Moreover, the depth of blowing is changed according to the C content in the molten steel.

That is, as long as the C content is low in terms of the steel specifications to be achieved by refining, it is kept in the molten steel layer, and when the C content reaches a predetermined value, it is moved to the slag layer and the injection is continued.

The carrier gas need only be substantially inert with respect to the refining operation; argon is of course preferred, but nitrogen can also be used as long as its blowing does not cause an increase in the nitrogen content in the steel bath.

Air can also be used, since oxygen in the carrier gas is acceptable provided that the mixture with the carbon powder is outside the explosive limits under blowing operating conditions.

The most important factor for forming and maintaining a suitable amount of slag foam layer is the amount of carbon powder injected.

A suitable value is 0.3 to 1.7 kg/m per ton of molten steel.
in.

is within the range of

Other conditions, ie, the particle size of the carbon powder, the pressure of the carrier gas, the amount used, etc., can be appropriately determined by those skilled in the art, if necessary, by performing a little experimentation.

Typical values for a normal size (approximately 30 tons) arc furnace, including the amount of carbon powder injected as described above, are as follows.

Blow time Particle size of carbon powder during heating up after melting down Average 1+ut Blow amount 30 kg/min Carrier gas Argon, pressure 1.2 kg/crfL, flow rate 12801! /min Lance pipe Diameter 25 mm, Caloride pipe 1 Blow angle 30, Depth 30 (1 m (in case of molten steel) Consideration should also be given to the thickness of the layer, its melt viscosity, and the distance between the electrode and the molten steel surface.

According to the present invention, the temperature rises rapidly from the time of refining of molten steel to the time of full-scale refining.

That is, the rate of increase, which was conventionally about 10° C./min, is doubled to about 20° C./min according to the present invention.

Such rapid temperature rise is achieved because the heating efficiency of electric power during the heating period, which is conventionally about 40 degrees, doubles to 80 degrees when operated as described above.

This is an improvement sufficient to reduce the tap-to-tap interval by well over 10 minutes.

[Brief explanation of the drawing]

The drawing is for explaining an embodiment of the present invention, and shows a longitudinal section of an arc furnace during refining. DESCRIPTION OF SYMBOLS 1... Arc furnace, 2... Electrode, 3... Lance pipe, 5... Molten slag, 5A... Slag foam layer, 6
...molten steel.

Claims (1)

[Claims] 1. When refining molten steel using an arc furnace, oxygen blowing is performed to quickly raise the temperature and lower the C content in the molten steel below the standard value, and then the molten steel in the furnace is A method of refining molten steel characterized by blowing carbon powder along with a carrier gas flow to form a foam layer in the slag on the surface of the molten steel, and by enveloping the arc with the foam layer of the slag, refining is carried out while increasing thermal efficiency. Refining method. 2. The refining method according to claim 1, wherein the carbon powder is injected directly under or near the electrode. 3. The refining method according to claim 1, wherein the carrier gas is argon or nitrogen. 4. The injecting of carbon powder is continued in the molten steel layer while the C content of the molten steel is lower than a predetermined value, and when the carbon content reaches the predetermined value, the carbon powder is transferred to the slab layer and continued. 1
Section refining method.