JPH0475767A - Detection of slag outflow used commonly for nitriding of molten steel - Google Patents

Abstract

PURPOSE:To exactly decide the outflow of slag by blowing a nitrogen-contg. gas from an aperture on the lower side of a nozzle to nitride the molten steel and supplying the inert gas sucked by the pouring flow of the molten steel from the aperture on the upper side of the nozzle, then detecting a change in the flow rate and back pressure thereof. CONSTITUTION:Suction force is generated in the gas supply hole part 2a in the nozzle 2 and the degree thereof depends largely on the kinetic energy of the pouring flow of the molten steel. The suction force in the gas supply hole 2a part is charged by the difference in the kinetic energy generated from a density difference if the pouring flow changes form the molten steel 4 to slag 5 in such a state. The presence or absence of the outflow of the slag is decided by recognizing the change in the flow rate and/or back pressure of the inert gas. Since the gas supply hole 3a for supplying gaseous nitrogen for nitriding is provided below the supply hole 2a of the inert gas, the detection of the slag outflow is not affected at all even if the flow rate of the gaseous nitrogen is increased. The molten steel is thus nitrided while the presence or absence of the flag outflow is detected.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention provides a method for injecting molten steel in a ladle into an intermediate container such as a tundish through a nozzle provided at the bottom of the ladle, injecting nitrogen-containing gas into the molten steel. This is to perform nitrification by blowing slag into the intermediate container, and to prevent the slag from flowing into the intermediate container as much as possible.

(Prior art) As for the technology related to nitriding of molten steel, for example, Japanese Patent Publication No. 62-0
As disclosed in Japanese Patent No. 0964, it is known to increase the nitrogen content in the steel by feeding a nitrogen-containing fluid into the pouring stream while the molten steel flows from the upper vessel into the lower vessel. .

Also, during the final stage of tapping when molten steel is supplied from a refining furnace such as a converter to a ladle through a tapping hole, or when pouring molten steel from the ladle through a nozzle into an intermediate container such as a tundish. At the end of pouring, slag flows out together with the molten steel, and this slag reacts with the ferroalloy added in the molten steel.
There are disadvantages such as a decrease in the yield of ferroalloy and quality deterioration due to reoxidation of molten steel, and a slag outflow detection technology disclosed in Japanese Patent Application Laid-Open No. 2-70372 is known as an attempt to avoid such disadvantages. It is being

(61 Problems to be Solved by the Invention) The technology disclosed in Japanese Unexamined Patent Publication No. 1 Hei 2-70372 supplies inert gas from a gas supply hole provided in the outlet hole of a refining furnace or the inner wall of a nozzle of a ladle. At the same time, measure the static pressure (negative pressure) inside the nozzle, and understand the change (pressure change inside the nozzle when the pouring water changes from molten steel to slag).Secondly, detect the outflow of the slab. In order to improve productivity and work efficiency in pouring work, when nitriding is performed without detecting slag outflow, such detection technology and nitriding technology should be combined. (An attempt was made to do 4.

However, in the above-mentioned combination of conventional technologies, since the detection technology detects pressure changes within the nozzle, when blowing nitrogen gas from the inner wall of the nozzle to nitridize molten steel, for example, The flow rate of nitrogen gas blown into the nozzle for nitriding is determined by the throughput of the molten steel) 6 t/
When 1 llin is set to 3ON/+in or more, the nitrogen gas is forced into the nozzle, so the pressure inside the nozzle goes from negative pressure to above atmospheric pressure, and the pressure change when slag flows out is detected. There was a disadvantage in not being able to do so (see Figure 5).

When feeding the molten steel in the ladle to an intermediate container such as a tundish, effective nitriding is performed to increase the nitrogen content in the molten steel, and the flow of slag into the intermediate container can be avoided as much as possible. It is an object of this invention to improve the method.

(Means for Solving the Problems) The present invention provides a method for pouring molten steel stored in the ladle into an intermediate container through a nozzle provided at the bottom of the ladle, in the longitudinal direction of the nozzle. At least two openings are provided along the nozzle, and a nitrogen-containing gas is blown into the pouring stream of molten steel passing through the nozzle through the opening at the bottom of the nozzle to nitrify it. It is characterized by supplying an inert gas sucked in by the pouring flow of molten steel through the hole, and determining the outflow of slag into the intermediate container by detecting changes in the flow rate and/or back pressure of the inert gas. This is a slag outflow detection method that involves nitriding of molten steel.

Now, Fig. 1 shows a schematic diagram of equipment suitable for carrying out the present invention, as an example applied to a ladle-tundish in continuous steel casting. It is a pot nozzle having a gas supply hole 2a on the wall surface,
An inert gas useful for detecting the outflow of slag is supplied from the gas supply hole 2a. 3 is a long nozzle connected at the lower part of the pan nozzle 2, and this nozzle 3 has a gas supply hole 3a on its inner wall surface for supplying nitrogen for nitriding. Further, 4 is the molten steel stored in the ladle 1, 5 is the slag on the top surface of the molten steel 4, 6 is a tundish used when pouring out the molten steel in the ladle 1, and 7 is the gas supply to the ladle nozzle 2. A gas supply pipe connected to the hole 2a, 8 a flow meter installed in the gas supply pipe 7, 9 a back pressure gauge also installed in the gas supply pipe 7, 10 measurement signals from the flow meter 8 and the back pressure gauge 9 A slag detector is input to detect the presence or absence of slag outflow, and 11 is a gas supply pipe connected to the gas supply hole 3a of the long nozzle 3. 2 and long nozzle 3 (
When injecting into the tundish 6 through the nozzle I (hereinafter simply referred to as nozzle I) (no gas blowing into the nitriding reservoir is performed),
A suction force is generated at the part of the hair gas supply hole 2a in the nozzle L, and the degree of the suction force largely depends on the kinetic energy of the molten steel pouring flow. In such a state, for example, when the pouring flow changes from molten steel 4 to slag 5, the suction force at the gas supply hole 2a changes due to the difference in kinetic energy resulting from the density difference. Slab outflow detection technology is based on this principle, and in reality, inert gas is supplied from the gas supply hole 2a, and the flow rate and/or back pressure of this inert gas sucked in by the molten steel pouring flow is controlled. By understanding the changes, it is determined whether slag is flowing out or not.

As previously mentioned, if nitrogen gas is injected in an amount exceeding the amount of inert gas sucked in by the above suction force, it will be impossible to detect slag outflow due to fluctuations in the suction force. As mentioned above, in this invention, the gas supply hole 3a for supplying nitrogen gas for nitriding is provided below the inert gas supply hole 2a, so that the flow rate of nitrogen gas is reduced. Listen to people 12. However, there is no effect on the detection of slag outflow, and therefore it is possible to carry out nitriding while detecting the presence or absence of slag outflow.

It is important that the gas supply hole 3a for supplying nitrogen gas is provided below the gas supply hole 2a for detecting fluctuations in the suction force of the inert gas as described above.
a, 3a may be installed only on the pot nozzle 2, only on the long nozzle 3, or may be installed on each of them individually), and this gas supply hole 3
A can be provided in plural numbers as long as the condition is satisfied. Further, the number of gas supply holes 2a for supplying inert gas can be increased as necessary.

The flow rate of inert gas when detecting the outflow of slag depends on the flow rate of molten steel in the nozzle, but is generally IN (2/1 inch).
A flow rate of approximately 50 NI2/gin is preferable, and the flow rate of nitrogen gas is determined by the amount of nitrogen gas required, but is generally 40 H1/sin or less. In addition, in this invention, the gas supply hole 2a
It is also possible to blow the inert gas supplied from the gas supply hole 3a with the nitrogen gas at 1. In this case, the flow rate of the nitrogen gas blown from the gas supply hole 3a is equal to the amount of nitrogen gas supplied from the gas supply hole 2a from the required amount of nitrogen gas. Let's just assume it's 7.

(Example) A ladle (capacity 230 t, size of ladle nozzle: inner diameter 80 mm) was prepared by applying the equipment configured as shown in Fig. 1 above.

The molten forging housed in the long nozzle (with an inner diameter of 115 m) was poured through the long nozzle while blowing nitrogen gas under the conditions shown in Figure 2 at 6 t/sin, 3 t/sin, and 1°2. The molten steel is then nitrided, and at the same time, a flow of 1:14? Jj! /
win, back pressure: -0.3kgf/cm! A under the conditions of
R gas was supplied and the slag outflow situation was investigated. As a result, as shown in Figures 3 and 4, even if the outflow of slag is detected during carnitrification, there is no effect from blowing in nitrogen gas, and the flow rate of G and Ar gas is low, about 4 seconds before visual judgment. An increase in back pressure was observed, and it was confirmed that the presence or absence of slag outflow could be quickly detected.

In this example, the nitrogen gas supply hole (size 5 pieces) for nitriding is replaced with the inert gas supply hole (size 3 piece) for slag outflow detection.
A long nozzle (hereinafter referred to as the 10th nozzle) provided below the 50 mm cut of tuna and a long nozzle provided below the 100 mm cut (hereinafter referred to as the 20th nozzle) were used. As shown in Fig. 5, when the throughput of molten steel is 6t/5Iin using the 10th nozzle, the gas flow rate of nitrogen gas is 100Nβ/sin, the increase in nitrogen NΔN is about 20p, and the 20th nozzle Even when using a throughput of 1-5t/sin, the gas flow is 11100N 1 /p
At ain, ΔN was approximately 20 ppm.

Further, in the case of a throughput of 3 t/min, ΔN was about 20 ppm at a gas flow rate of 11 t/14 on 127 min for both the first 20° nozzles.

(Effects of the Invention) Thus, according to the present invention, it is possible to prevent the outflow of slag, which is difficult to detect when nitriding the molten steel stored in a ladle while pouring it into an intermediate container such as a tundish. Can be accurately grasped.

[Brief explanation of drawings]

Fig. 1 is a diagram illustrating the configuration of equipment suitable for carrying out the present invention. Fig. 2 is a graph showing the relationship between the nozzle internal pressure and the gas flow rate of the blown gas. Figs. 3 and 4 are graphs showing the relationship between the Ar gas flow rate and the Ar Graphs illustrating changes in gas back pressure, respectively. FIG. 5 is a graph illustrating the relationship between nitrogen gas cooling and ΔN. 1... Ladle 2... Pot nozzle 2a...
・Gas supply hole 3... Long nozzle 3a... Gas supply hole 4... Molten steel 5... Slag
6...Kundish 7 Gas supply pipe 8...
・Flow rate needle 9...Back pressure gauge 10...Slag detector 11...Gas supply pipe Fig. 1 Fig. 3 Fig. 4 Fig. 2 Opening IN force "' Large flow rate (N!/Cooling) Figure 5

Claims (1)

[Claims] 1. When injecting the molten steel contained in the ladle into the intermediate container through a nozzle provided at the bottom of the ladle, at least two openings are provided along the longitudinal direction of the nozzle. Nitrogen-containing gas is blown into the flow of molten steel passing through the nozzle through the opening at the bottom of the nozzle to nitrate it, and the flow of molten steel is sucked in through the opening at the top of the nozzle. A slag that also serves as a nitrider of molten steel, characterized in that the outflow of slag into an intermediate container is determined by supplying an inert gas such that the inert gas flows and/or detecting changes in the flow rate and/or back pressure of the inert gas. Spill detection method.