JPH05295416A - Detection of slag at the time of tapping molten steel from converter - Google Patents

Abstract

PURPOSE:To provide slag detecting method which can surely detect in early time, in the slag detecting method at the time of completing molten steel tapping utilizing the magnetic permeabilities of the molten steel and the slag. CONSTITUTION:A basicity of the slag in a converter at the time of stopping the blowing is controlled in the range of 2-8 and shape of a refractory for steel tapping hole 6 at the inside of the furnace is made to be a funnel-type having >=1.0 radius of carvature (r) to the refractory thickness (t). By this method, the tapped molten steel flow is stabilized and the flow-out of the slag can precisely be detected in the early time. Further, the slag quantity in a ladle is reduced to 40-60% and the yield of ferro alloy of Al, etc., is improved and the effect which rephosphorization from the slag into the molten steel is reduced, is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting slag when tapping a converter, and more particularly to a method for detecting slag that can surely and quickly detect outflow of slag, and can be widely used in the field of steelmaking.

[0002]

2. Description of the Related Art A converter tapping steel will be described with reference to FIG. Converter 2
The trunnion ring 4 provided on the outer circumference of the furnace body is connected to the tilting device and can rotate 360 degrees.
A steel tapping hole 6 is provided in the upper side wall of the converter 2, and the molten steel 8 in the converter 2 is tapped into the ladle 10 through the tapping hole 6 when the furnace body is tilted. The molten steel 8 in the converter 2 is covered with a slag 12.

At the time of tapping after the completion of blowing, the slag 12 floats in the molten steel 8 in the converter 2, so that the slag 12 may flow out into the ladle 10 together with the molten steel 8. Slag 1
Since 2 contains a large amount of FeO and other oxides, when it flows into the ladle 10, the amount of deoxidizing agent such as aluminum must be increased and the cost of the product increases, and at the same time, these deoxidizing agents are added. However, the quality defects of the product increase as inclusions.
Therefore, it is extremely important to detect the outflow of slag at the end of tapping.

As a method of detecting the outflow of slag at the end of tapping in a converter, there has been a method of utilizing the difference in magnetic permeability between the molten steel 8 and the slag 12. That is, as shown in FIG.
The primary coil 14 and the secondary coil 16 are provided in the tapped hole 6 of
It is designed so that the molten steel 8 can pass through its center.
When an alternating current I is supplied to the primary coil 14, a magnetic field H is generated, an overcurrent is induced in the molten steel, an induced voltage V is generated in the secondary coil at this time, and the induced voltage V is measured to measure the molten steel. Measure the slag volume fraction of. That is, the induced voltage V generated on the secondary side consists of two components that are out of phase by an angle of 90 degrees, and the slag volume fraction is measured from the composite voltage. At the end of tapping, when the slag volume fraction increases and the secondary coil induced voltage V rises and reaches a certain value, it is determined that tapping has ended. FIG. 5 is an oscillograph diagram showing a typical detection signal waveform at the time of tapping by the above slag outflow detection method. The number of tapped holes is usually 50 to 80,
In this case, the induced voltage V has a constant value during tapping, but when the slag starts to flow out at the end of tapping, the induced voltage V starts to rise, and when the slag detection set voltage is reached, a slug alarm is issued.

However, in the state where the number of tapping holes is small and the vicinity of the entrance of the tapping hole 6 is not melted, the pressure loss at the entrance is large and slag and air are entrapped, and the induced voltage is generated even during tapping. V may rise, and it was difficult to distinguish it from the slag outflow due to the true end of tapping. In order to solve this problem, JP-A-3-123309 proposes a method of suspending the refractory on the molten metal surface directly above the tap hole, but it is not economical in terms of refractory cost and the tap hole Floating refractory on the surface of the molten metal directly above requires unique technology, and its effects vary widely. At present, the current slag detection method has a problem in accuracy as described above.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems of the prior art and provide a slag detecting method capable of reliably detecting slag outflow at the end of tapping regardless of the number of tapping holes. There is

[0007]

Means and Actions for Solving the Problems The gist of the present invention is as follows. That is, when tapping from the tapping hole of the converter, the slag detection method at tapping of the converter, which detects the outflow of slag by utilizing the difference in magnetic permeability between molten steel and slag, Slag basicity (Ca
O / SiO ₂ ) is controlled in the range of 2 to 8, and the shape of the refractory inside the furnace of the tapping hole is a funnel shape having a radius of curvature of 1.0 times or more the thickness of the refractory. And a method for detecting slag when tapping a converter.

In the present invention, the slag basicity (CaO / SiO ₂ ) in the converter at the time of blowing is ₂ to 8, preferably 4
By controlling the melting point of the slag and lowering the fluidity of the slag itself by controlling in the range of ˜6, slag entrainment was prevented and the cause of erroneous detection of slag outflow was eliminated. If the basicity of the slag exceeds 8, the slag slag forming property is reduced and dephosphorization becomes poor, and refining of steel is hindered. On the other hand, if the basicity of the slag is less than 2, the fluidity of the slag becomes excessive and the effect of preventing slag entrapment becomes unstable. Therefore, in the present invention, the slag basicity at the time of blowing is limited to the range of 2 to 8.

Generally, the pressure loss energy at the inlet of the pipe is expressed by the following equation. _{△ P / ρ = KV 2/} 2 (J / Kg) where △ P: Pressure loss energy [rho: molten steel Density V _2: tube section average speed (m / s) K: loss coefficient K by most tube inlet shape Since the pressure loss energy ΔP is minimized, the tapped hole 6 shown in FIG.
When the slag detection situation was investigated by changing the radius of curvature r of the refractory inside the furnace of 1.0, 1.0
Since the optimum result was obtained when the funnel shape having the above radius of curvature r was obtained, in the present invention, the refractory shape of the tapped hole 6 is set to a radius of curvature r of 1.0 or more of the refractory thickness. Limited to. In the present invention, the basicity of the slag at the time of blowing is limited to the range of 2 to 8, and the radius of curvature r of the tapped hole is limited to a funnel shape having a refractory thickness of 1.0 or more, thereby stabilizing the tapped steel flow. However, it became possible to detect slag outflow accurately and quickly.

[0010]

[Examples] In a converter having a capacity of 300 tons, slag detection during tapping was performed by the method of the present invention. That is, the thickness is 24 mm
The refractory shape inside the furnace of the tap hole is made into a funnel shape with a radius of curvature of 30 mm, and the basicity of the blow-stop slag in the converter is controlled within the range of 4 to 6. Steel tapping was performed and the induced voltage V during tapping was measured. On the other hand, using the same converter as above, as a conventional example, the shape of the refractories inside the furnace of the tapping hole is a funnel shape with a radius of curvature of 30 mm, and the basicity of the slag at the time of blowing is not controlled I tapped at.

FIG. 5 shows the above embodiment and the conventional example.
The peak value of the induced voltage during tapping shown in Fig. 2 was obtained for each tapping hole number and shown in Fig. 2. In the figure, the black circles represent the embodiments of the present invention,
White circles are conventional examples. In FIG. 2, the peak value is controlled to be 150 mV or less and stable in the embodiment of the present invention, but in the conventional example, the peak value often exceeds the slag detection setting voltage, which may cause erroneous detection. This tendency is particularly serious at the initial stage of the number of tapping holes.

[0012]

As is apparent from the above embodiment, the present invention controls the basicity of the slag at the time of blowing to be in the range of 2 to 8, and the shape of the tapped hole inside the furnace is the refractory thickness t. Against 1.
By making the funnel shape with a radius of curvature r of 0 or more, it becomes possible to stabilize the tapping flow and detect the slag outflow accurately and early, and the slag thickness of the ladle is about 40 to 60 compared with the conventional one.
%, The yield of alloy iron such as Al is improved, and the effect of reducing re-phosphorus in molten slag steel can be achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a converter tap hole for explaining the shape of the tap hole of the present invention.

FIG. 2 is a relationship diagram showing the relationship between the number of tapped holes and the peak value of induced voltage during tapping in the example of the present invention and the conventional example.

FIG. 3 is a schematic cross-sectional view showing steel output from a converter.

FIG. 4 is a schematic diagram illustrating a slag outflow detection method that uses a difference in magnetic permeability between molten steel and slag.

FIG. 5 is a diagram showing a change in induced voltage (mV) with the elapse of tapping time (minutes) in the slag outflow detection method.

[Explanation of symbols]

 2 Converter 6 Steel tapping hole 8 Molten steel 10 Ladle 12 Slag 14 Primary coil 16 Secondary coil

Claims (1)

[Claims] 1. A slag detection method at tapping of a converter, which detects outflow of slag by utilizing a difference in magnetic permeability between molten steel and slag when tapping steel from a tapping hole of a converter. The basicity (CaO / SiO ₂ ) of the slag in the converter is controlled in the range of 2 to 8, and the refractory shape inside the furnace of the tapped hole is set to have a radius of curvature of 1.0 times or more the refractory thickness. A method for detecting slag when tapping a converter, wherein the slag has a funnel shape.