JP2007063643A - Method for producing high-nitrogen steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method which uses the method for producing a high-nitrogen steel by melting a steel under the pressure of atmospheric gas containing nitrogen gas and inert gas at the atmospheric pressure or more, and by adding nitrogen into the steel; wherein the concentration of the added nitrogen can accurately be controlled and the high-nitrogen steel having needed nitrogen content can be produced. <P>SOLUTION: When the high-nitrogen steel is produced, where the steel is melted and cast by arranging a melting device 12 and a casting device 14 in the inner part of a closable pressure vessel 10 under atmospheric gas pressure at the atmospheric pressure or more by introducing the nitrogen gas and the inert gas in the inner part of the pressure vessel 10; a blower 34 is arranged in the inner part of the pressure vessel 10, and the nitrogen gas and the inert gas are fully mixed with a stirring action of the blower 34, and the melting and the casting are performed under mixed gas atmosphere. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing high nitrogen steel, and more particularly to a method for producing high nitrogen steel by melting and casting steel under an atmosphere gas containing nitrogen gas and inert gas.

Conventionally, nitrogen has been actively added to steel mainly for the purpose of increasing the hardness and corrosion resistance of the steel.
As a method of adding nitrogen into the steel at that time, nitrogen gas and inert gas such as argon gas are introduced into the sealable pressure vessel, and the steel is melted under atmospheric gas pressure above atmospheric pressure. Methods for dissolving nitrogen in steel are known.
For example, the following Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 disclose a method for producing this type of high nitrogen steel.

In this case, basically, the amount of nitrogen added to the steel is controlled by the partial pressure of the nitrogen gas in the atmospheric gas.
However, in actuality, even when the nitrogen gas and the inert gas are introduced so that the partial pressure of the nitrogen gas is set inside the pressure vessel, the steel is melted and cast inside the pressure vessel. There has been a problem that the nitrogen concentration of the steel, that is, the nitrogen content is not always stable, and a solution has been desired.

Special table 2003-527482 gazette Japanese Patent Laid-Open No. 3-240935 Japanese Patent Laid-Open No. 5-98393 Japanese Patent Laid-Open No. 5-98394 JP-A-6-322487

  The present invention is based on such a situation, and in a method for producing high nitrogen steel by melting steel under an atmospheric gas pressure including atmospheric pressure equal to or higher than atmospheric pressure containing nitrogen gas and inert gas, and adding nitrogen to the steel. The purpose of the present invention is to provide a production method capable of accurately controlling the concentration of nitrogen added to molten steel and producing high-nitrogen steel having a desired nitrogen content.

  Thus, according to the first aspect of the present invention, a melting device and a casting device are provided inside a pressure vessel that can be sealed, and nitrogen gas and inert gas are introduced into the pressure vessel so that the atmospheric gas pressure exceeds atmospheric pressure. When producing high nitrogen steel by melting and casting the steel under, a stirring means is provided inside the pressure vessel, and the nitrogen gas and the inert gas are forcibly mixed by the stirring action of the stirring means, and a mixed gas The melting and casting are performed under an atmosphere.

  According to a second aspect of the present invention, in the first aspect, the stirring means includes a blower.

  According to a third aspect of the present invention, in the second aspect, the stirring unit includes the blower and a pipe that distributes the gas from the blower and discharges the gas into the pressure vessel at a location different from the blower. It is characterized by.

Effects and effects of the invention

As described above, the manufacturing method according to claim 1 is provided with a stirring means provided in the pressure vessel when nitrogen gas and inert gas are introduced into the pressure vessel to melt and cast the steel to produce high nitrogen steel. The nitrogen gas and the inert gas are forcibly mixed by the stirring action, and are melted and cast in a mixed gas atmosphere.
Usually, it is usually considered that if an inert gas such as nitrogen gas and argon gas is introduced into the pressure vessel, they naturally mix with each other inside the pressure vessel.
Further, if the steel is melted by the melting device inside the pressure vessel, it is considered that the gas from the melting device or the molten metal also causes convection of the gas inside the pressure vessel and the mixing of the two kinds of gases.

  However, the present inventors have found that the concentration of nitrogen dissolved in molten steel is stable even if nitrogen gas and inert gas are accurately introduced into the pressure vessel so that the nitrogen gas partial pressure inside the pressure vessel becomes the set partial pressure. In researching and considering the reasons for not, nitrogen gas and inert gas such as argon gas are not sufficiently mixed inside the pressure vessel, and each is unevenly distributed. This is the concentration of nitrogen in the molten steel. It is thought that this may be a cause of dispersion and instability, and a stirring means is provided inside the pressure vessel, and nitrogen gas and inert gas are forcibly mixed by the stirring means to dissolve and cast the steel. As a result, the nitrogen content of the steel was found to be stable and the desired content.

In other words, it was an error to think that nitrogen gas and inert gas were naturally mixed inside the pressure vessel. Actually, nitrogen gas and inert gas were mutually mixed inside the pressure vessel. The knowledge that it is unevenly distributed was obtained.
The present invention has been made on the basis of such findings, and according to the present invention, it becomes possible to stably produce high nitrogen steel having a set nitrogen content.

In this case, the stirring means can be configured to include a blower (claim 2).
For example, it is conceivable to provide a stirring blade that performs stirring by rotating blades as a stirring means. In this case, gas mixing is partially performed only in the vicinity where the blades are rotating, or a melting device in a pressure vessel. When the convection of the gas is obstructed by such a structure, the gas mixing does not reach the entire inside of the pressure vessel, or it may take a very long time to complete the gas mixing.
However, if the stirring means is configured including the blower, the gas is mixed more efficiently inside the pressure vessel based on the gas suction and discharge pressure of the blower.

According to the third aspect of the present invention, the pipe is extended from the blower, the gas from the blower is circulated in the pipe, and the gas inside the pressure vessel is mixed by being discharged at a place different from the blower. In such a case, the gas can be mixed more efficiently.
In this case, the blower can be arranged at the lower part of the pressure vessel, and the gas from the blower can be led to the upper part of the pressure vessel by piping and discharged from the upper part.

Next, embodiments of the present invention will be described below.
In FIG. 1, 10 is a pressure vessel which can be sealed, and a melting device 12 and a casting device 14 are provided therein.
In the melting apparatus 12, 16 represents a refractory, 18 represents an induction coil, and 20 represents molten steel.
In the casting apparatus 14, reference numeral 22 denotes a mold.

The pressure vessel 10 is provided with a gas introduction port 24 for introducing gas therein.
Reference numeral 28 denotes an additional / temperature measuring device, 30 is a sampling device, and 32 is an internal monitoring window.

A blower 34 is provided in the vicinity of the bottom inside the pressure vessel 10.
The blower 34 sucks the gas inside the pressure vessel 10 from the suction port 38 and discharges it into the pipe 36.
The pipe 36 rises upward from the bottom toward the top, and the gas from the blower 34 flows through the pipe 36 and is discharged from the discharge port 40 at the upper end to the upper part inside the pressure vessel 10.
In the present embodiment, the blower 34 and the pipe 36 constitute a stirring means.

In the present embodiment, nitrogen gas and argon gas are introduced into the pressure vessel 10 and the pressure vessel 10 is filled with these gases.
And after filling, while collecting the gas inside the pressure vessel 10 at the upper gas collection point A and the lower gas collection point B inside the pressure vessel 10 of FIG. Melting and casting were performed using the melting device 12 and the casting device 14.
In the melting operation, after the charged material was completely melted, a sample for analysis was taken from the molten steel 20, and the nitrogen concentration was analyzed.
The results are also shown in Table 1.

  In Table 1, No. 1 to No. 6 represent cases where stirring by the blower 34 was not performed as comparative examples.

No. 7 to No. 12 use a blower 34, and the blower 34 discharges the gas inside the pressure vessel 10 with a discharge amount of 1.2 Nm ³ / H, and the embodiment in which gas stirring is performed. Represents.

  In Table 1, v is the gas discharge amount of the blower 34, [N] O is the target nitrogen concentration in steel, PN is the nitrogen gas partial pressure in the pressure vessel 10, and PT is the total pressure in the pressure vessel 10. VNO is the nitrogen gas concentration (calculated value) in the filling gas when the filling gas is completely mixed, VNA is the nitrogen gas concentration in the filling gas at the gas sampling point A, and VNB is at the gas sampling point B. The nitrogen gas concentration in the filling gas and [N] represent the actual nitrogen concentration of the molten steel.

As shown in Table 1, in Comparative Examples 1 to 6 where forced gas mixing was not performed, the gas sampled at the gas sampling point A and the gas sampled at the gas sampling point B were in the gas. The nitrogen gas concentrations in the are very different.
Specifically, the nitrogen concentration is high in the upper part inside the pressure vessel 10, and the nitrogen concentration is relatively low in the lower part inside the pressure vessel 10.
That is, when nitrogen gas and argon gas are simply introduced into the pressure vessel 10, the lighter specific gravity of nitrogen gas is biased toward the upper portion of the pressure vessel 10, and the higher specific gravity of argon gas is present in the pressure vessel 10. Two types of gases are separated from each other inside the pressure vessel 10 due to the bias toward the bottom.

  On the other hand, in Examples 7 to 12, the measured nitrogen gas concentration at the gas sampling point A and the measured nitrogen gas concentration at the gas sampling point B are substantially equal, and the nitrogen gas and the argon gas are inside the pressure vessel 10. And are well mixed and dispersed.

As a result, in Comparative Examples 1 to 6, the actual nitrogen concentration [N] of the molten steel is higher than the target nitrogen gas concentration [N] O in the steel. However, in Examples 7 to 12, the target nitrogen concentration [N] O of the molten steel and the actual nitrogen concentration [N] of the molten steel are in good agreement.
That is, according to this embodiment, it can be understood that the nitrogen concentration in the molten steel can be stably controlled with high accuracy to the target nitrogen concentration.

  In the manufacturing method according to the present embodiment, the pipe 36 is extended from the blower 34 disposed at the bottom of the pressure vessel 10, the gas near the bottom is sucked, and the gas is discharged at the top inside the pressure vessel 10. Mixing can be performed efficiently. As a result, nitrogen can be added to the steel in a desired and stable amount in a stable and stable manner.

It is the figure which showed the manufacturing apparatus of the high nitrogen steel used in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Pressure vessel 12 Melting apparatus 14 Casting apparatus 24 Gas inlet 34 Blower (stirring means)
36 Piping (stirring means)

Claims (3)

A melting device and a casting device are provided inside the sealable pressure vessel, and nitrogen gas and inert gas are introduced into the pressure vessel to melt and cast steel under an atmospheric gas pressure of atmospheric pressure or higher. In producing nitrogen steel,
High nitrogen characterized by providing stirring means inside the pressure vessel, forcibly mixing the nitrogen gas and inert gas by the stirring action of the stirring means, and performing the melting and casting in a mixed gas atmosphere Steel manufacturing method.   2. The method for producing high nitrogen steel according to claim 1, wherein the stirring means includes a blower.   3. The high nitrogen steel according to claim 2, wherein the agitation unit includes the blower and a pipe that distributes gas from the blower and discharges the gas into the pressure vessel at a location different from the blower. Manufacturing method.

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