JPH0140954B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for quickly and continuously analyzing hydrogen in molten steel without sampling the molten steel.

Conventionally, the method for analyzing the gas components of molten steel is to collect a portion of the molten steel, cool it and solidify it, then cut a portion of this solid sample into a small sample, which is then heated or melted to release gas. A common method is to quantify the released gas using a gas chromatograph or the like.

However, this type of analysis method has several drawbacks as described below, so it is not sufficient to meet the requirements for gas component control in the steelmaking process.

First of all, it takes a long time to collect a portion of molten steel and then go through operations such as cooling and solidification, transferring the sample, cutting, weighing, and analysis to obtain analytical values.

In order to feed back analysis values and use them to control operations, it is necessary to reduce the time required for analysis to 2 to 3 minutes, but currently it takes about 10 to 20 minutes, so it is necessary to fundamentally rethink the sampling-analysis system. We need to do it faster.

As a gas analysis method that does not require direct sample collection, it is possible to use a sensor made of solid electrolyte, but the only method that has been put into practical use is one that targets oxygen. To date, no material with heat resistance that can be used in molten steel has been developed.

Second, aside from the time required for the analysis, if we consider the analytical values themselves, especially in the case of hydrogen analysis, the hydrogen that dissipates during the rapid solidification of molten steel and the subsequent sample preparation cannot be ignored, and the hydrogen that dissipates Since the proportion of hydrogen varies greatly depending on the work operation, the current method has a very large analytical error.

This is thought to be because the solubility of hydrogen rapidly decreases during solidification of molten steel, and the diffusion constant of hydrogen in steel is extremely large.

In order to collect the hydrogen released during solidification of the sample, there is a method of sucking the molten steel into a quartz tube with a vacuum inside and cooling it in mercury, but this method is difficult to work with and is similar to pre-furnace analysis. It is not suitable when analysis results are required in a short time.

On the other hand, attempts have recently been made to analyze the gas discharged from vacuum degassing equipment such as RH and DH to track changes in the hydrogen concentration in molten steel, but no established analytical method has been developed.

Since it measures the gas concentration in the vacuum chamber, analysis is difficult due to the following reasons, in addition to the disturbances caused by the steam evaporator with a low absolute value of gas partial pressure or leaks in the vacuum chamber. considered to be a thing.

In other words, the hydrogen and nitrogen gases released into the vacuum chamber by vacuum degassing equipment such as RH and DH are sucked up into the vacuum chamber and are semi-isolated from the molten steel remaining in the ladle, etc. This is because molten steel comes into contact with vacuum or argon bubbles.

In other words, the partial pressure of gases such as hydrogen and nitrogen in the vacuum chamber corresponds to the hydrogen and nitrogen concentrations in the molten steel drawn up into the vacuum chamber, and the true hydrogen and nitrogen concentrations in the molten steel in the ladle. It is thought that it does not reflect the

Particularly regarding hydrogen, even during degassing treatment, hydrogen is constantly supplied to the molten steel through the slag layer on the molten steel in the ladle, using atmospheric moisture as a source, so hydrogen can be extracted from the hydrogen partial pressure in the vacuum chamber. It is very difficult to determine the hydrogen concentration in the molten steel in the ladle.

In view of the above circumstances, it is an object of the present invention to make real-time and accurate hydrogen analysis in molten steel, and to make it possible to monitor the progress of degassing from time to time, for example, during degassing treatment of molten steel. .

In the present invention, the procedures for sampling, quenching, and solidifying molten steel are not taken, and it is sufficient to simply determine the hydrogen partial pressure in the inert gas that has passed through the molten steel.

Therefore, the time required for analysis or the analysis delay time is determined by the time it takes for the gas to pass through the pipe and reach the analyzer, and can be kept within 1 to 2 minutes.

Also, since inert gas is continuously blown into the
Analysis can also be carried out continuously.

In the present invention, since the inert gas bubbles pass through the bulk molten steel, the gas partial pressure in the bubbles directly reflects the gas concentration in the molten steel.

The present invention will be explained in detail below with reference to FIG.

A gas collector 5 is immersed in molten steel 1 so that slag 2 does not enter therein. Next, inert gas 10
is blown into the molten steel through the nozzle 3 at a constant flow rate using the constant flow valve 6.

The blown inert gas becomes bubbles 4 and rises from the nozzle tip. Although the inert gas is blown in downward direction in FIG. 1, it may also be blown upward or sideways.

While the bubbles 4 rise in the molten steel, N in the molten steel,
Gas components such as H move into the bubbles. The inert gas containing each gas component is collected in the gas collector 5,
After passing through a pipe 7 and removing dust by a filter 8, it is introduced into an analyzer 9.

The purpose of the gas collector is to collect any rising inert gas bubbles and to prevent the collected gas from coming into contact with the slag. Care should be taken here to ensure that the molten steel in the region through which the inert gas bubbles rise and pass through the gas collector is not significantly isolated from other molten steel.

To achieve this, for example, measures such as increasing the inner diameter of the gas collector shown in Figure 1 and increasing the inert gas injection depth, that is, the nozzle immersion depth, are taken compared to the gas collector immersion depth. All you have to do is keep it.

When the molten steel in the collector is isolated, blowing inert gas into the collector means degassing the isolated molten steel. Therefore, even if the gas in the collector is analyzed, the degassing process of the molten steel in the collector will be observed, and the analytical value will not be representative of the value of the entire molten steel.

It is also not preferable to reduce the pressure inside the gas collector to 550 mmHg or less. When the pressure is reduced to below 500mmHg,
For example, in the case of molten steel, the gas bubbles are blown upwards of approximately 44 cm into the collector, and no matter how deep the nozzle is immersed in the molten steel, the gas bubbles will pass through the molten steel, which is isolated from the outside molten steel. This will give an error.

The analyzer measures the hydrogen concentration in an inert gas that passes through the molten steel and is in equilibrium with the hydrogen concentration in the molten steel. If the inert gas injection flow rate and depth, nozzle shape, and molten steel temperature are constant, the relationship between the partial pressure of each gas component in the inert gas and the gas component concentration in the molten steel will also be constant. Therefore, if this relationship is investigated in advance, the hydrogen concentration in molten steel can be determined from the gas partial pressure in the inert gas.

In the case of hydrogen in particular, the rate of extraction from molten steel is fast, so if appropriate conditions are chosen, the relationship between the hydrogen partial pressure in the bubbles and the hydrogen concentration in the molten steel will reach equilibrium while the inert gas bubbles rise to the surface of the molten steel. , Sicverts' law, [H]
= K√ _H2 , the hydrogen concentration in molten steel can be easily determined.

Next, as an example according to the present invention, analysis results of hydrogen concentration in molten steel during RH vacuum degassing will be shown.

Argon was used as the inert gas, and a mass spectrometer was used as the analyzer. The flow rate of argon blowing was 100 Nml/min. Figure 2 shows how to connect the gas collector and mass spectrometer. The inner diameter of the gas collector was 3 cm, the immersion depth of the collector was 1 cm, and the pressure inside the collector was approximately 780 mmHg.

Most of the gas transmitted from the gas collector is
It is discharged into the atmosphere via bypass 11. The remaining gas (2 ml/min) passes through capillary 12,
It is introduced into the mass spectrometer 13. Such a connection method provides an extremely fast response speed.

The pumping capacity of the oil diffusion pump 14 used as a pack-up for the mass spectrometer is 2400/min, which can maintain the inside of the analyzer at a vacuum level that allows analysis against a fixed leak of 2 ml/min.

First, in order to find the conditions under which the hydrogen concentration in molten steel and the hydrogen partial pressure in argon bubbles reach equilibrium, a gas collector was immersed in molten steel with a known concentration (10 ppm, 1 ppm), and the argon gas was blown to the depth. The hydrogen partial pressure in the argon bubbles was measured by changing the

The results are shown in Figure 3.

The vertical axis in FIG. 3 indicates the ratio of the actual hydrogen partial pressure to the hydrogen partial pressure at equilibrium, which is 1 if equilibrium has been reached.

From Figure 3, when the hydrogen concentration in molten steel is 10 ppm or less and the blowing depth is 10 cm or more, the hydrogen concentration in molten steel and the hydrogen partial pressure in argon (P _H2 ) reach equilibrium.
Directly from hydrogen partial pressure in argon [H] = K√ _H2 ,
It was found that the hydrogen concentration in molten steel could be determined.

Therefore, argon gas was blown to a depth of 10 cm, and the RH
Figure 4 was obtained as a result of tracking the temporal change in hydrogen concentration in molten steel due to vacuum degassing.

Note that the analysis delay time is based on a steel pipe with an inner diameter of 2 mm.
When piping was done at m, it took about 30 seconds.

In the examples, argon was used as the inert gas, but rare gases such as helium and neon may also be used.

Further, in the embodiment, a mass spectrometer was used as the analyzer, but a gas chromatograph, a thermal conductivity type gas analyzer, an infrared type gas analyzer, etc. can be employed depending on the blown gas and the gas to be analyzed.

As explained above, according to the present invention, hydrogen in molten steel can be analyzed accurately in real time, and the H component can be easily managed.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the analysis system of the present invention, Figure 2
The figure shows how to connect a mass spectrometer to a gas collector, Figure 3 is a graph showing the relationship between the equilibrium reaching speed of hydrogen in bubbles and the injection depth, and Figure 4 is a graph showing the relationship between the equilibrium reaching speed of hydrogen in bubbles and the injection depth. 2 is a graph showing changes over time in hydrogen concentration in molten steel during RH vacuum degassing. 1... Molten steel, 2... Slag layer, 3... Inert gas blowing nozzle, 4... Inert gas bubbles, 5... Gas collector, 6... Constant flow valve, 7... Piping, 8... Filter,
9... Gas analyzer, 10... Inert gas, 11... Bypass, 12... Capillary, 13... Mass spectrometer,
14...Oil diffusion pump.

Claims (1)

[Claims] 1 A gas in which inert gas is continuously blown into the molten steel from a depth of 10 cm or more below the surface of the molten steel, the hydrogen dissolved in the molten steel is transferred into inert gas bubbles, and the rising inert gas is maintained at a pressure of 500 mmHg or more. The hydrogen partial pressure in the inert gas is measured by collecting it in a collector and introducing it into an analyzer, and from the equilibrium relationship established between the hydrogen concentration in the molten steel and the hydrogen partial pressure in the inert gas, A method for analyzing hydrogen in molten steel, which is characterized by determining the hydrogen concentration in molten steel.