JPH06339749A - Method for producing high nitrogen-containing stainless steel wire and apparatus therefor - Google Patents

Abstract

PURPOSE:To provide a castable high nitrogen-containing stainless steel wire having a uniform composition by preventing the variation of nitrogen concn. in molten steel during casting for long term. CONSTITUTION:In a horizontal continuous casting method for wire rod, gaseous nitrogen is supplied from a gaseous nitrogen cylinder 20 into a tundish 10 in a producing device 1, and further, gaseous argon is supplied from a gaseous argon cylinder 30. Then the partial pressure of the gaseous nitrogen in this mixed gas atmosphere is made equal to the saturated vapor pressure of the nitrogen in the molten steel 2 which can produce the stainless steel wire 3 having the aimed composition, to cast the stainless steel wire 3 containing 0.08-0.60wt.% nitrogen. By this method, always the nitrogen concn. in the molten steel can be kept constant during casting for the long term, and the stainless steel wire having 0.08-0.60wt.% nitrogen concn. can continuously be cast in the uniform nitrogen concn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for producing a wire rod made of stainless steel, and in particular, a stainless steel wire containing 0.08 to 0.60 wt% of nitrogen element (N) is melted from a molten steel by a horizontal continuous casting machine. The present invention relates to a method and an apparatus for producing a high nitrogen content stainless steel wire obtained by direct casting.

[0002]

2. Description of the Related Art A wire rod horizontal continuous casting machine in which a mold is installed horizontally following a tundish is used to supply molten steel (molten metal) from the tundish into the mold, and a long wire rod is required for several hours. In continuous casting, the inside of the tundish is usually in an inert gas atmosphere. this is,
Prevents reoxidation of molten steel stored in the tundish,
This is done to produce a highly clean steel wire, and conventionally argon (Ar) or helium (He) was used as an inert gas.
Was used.

[0003]

However, when a stainless steel wire is cast in the tundish in an atmosphere of argon gas or helium gas as described above, it is 0.08.
When the nitrogen content was less than wt%, there was no composition change and a relatively uniform wire rod was obtained, but the nitrogen content was 0.08 wt%.
If it exceeds, the nitrogen concentration in the drawing direction of the wire may become non-uniform.

In order to investigate the cause of the unevenness,
When the inventor examined the composition change of the molten steel in the tundish, as in the conventional example shown by the plot of Δ in FIG.
It was found that the nitrogen concentration in the molten steel gradually decreased with the passage of casting time. Furthermore, when a study was conducted to investigate the cause, Fe (iron) -Cr (chromium) -Ni was found to have a long nitrogen concentration in the molten steel and a long casting time.
It has been found that nitrogen atoms in the (nickel) -based molten steel become nitrogen gas (N ₂ ) and are vaporized in large amounts in the argon gas (or helium gas) atmosphere.
This means that until the equilibrium is established between the nitrogen atoms in the molten steel and the evaporated nitrogen gas, for example, according to the above-mentioned conventional example of FIG. 2, the nitrogen concentration of the molten steel reaches about 0.08% by weight (1 It means that the reaction shown in the equation goes to the left. 1 / 2N ₂ (g) = N (in liq. Fe-Cr-Ni) (1)

The present invention has been made in view of the above circumstances, and an object thereof is to prevent the nitrogen concentration of molten steel from changing during casting for a long period of time, thereby providing a stainless steel wire having a uniform composition. It is an object of the present invention to provide a method for producing a high nitrogen content stainless steel wire that can be cast. Another object of the present invention is to provide a manufacturing apparatus used in the above manufacturing method.

[0006]

In order to achieve the above object, the present inventor mixes nitrogen gas with an inert gas atmosphere in a tundish so that the above equation (1) does not move to the left. I thought I should do it. As a result of intensive studies, an optimum amount of nitrogen gas mixed was found.

That is, for example, when the inside of the tundish is filled with only nitrogen gas (when there is too much nitrogen gas),
As in the comparative example shown by the plot of □ in FIG. 2, the nitrogen concentration of the molten steel increases with time. This is because the above equation (1) proceeds to the right. Therefore, from the beginning of casting, the atmosphere in the tundish should be adjusted to the above (1)
It has been found that it is preferable to make an equilibrium state in which the equation does not advance to the left or right. Then, for that purpose, it was found that the partial pressure of nitrogen gas in the atmosphere should be the same as the saturated vapor pressure of nitrogen in the liquid phase of the target composition (that is, molten steel).

The present invention was made on the basis of the above-mentioned findings, and the molten steel was supplied into the mold from the tundish to reach 0.0
When casting a wire rod made of stainless steel containing 8 to 0.60% by weight of nitrogen element, the inside of the tundish was made into a mixed gas atmosphere containing nitrogen gas and an inert gas other than nitrogen gas, and the nitrogen in the mixed gas atmosphere was used. It is proposed that the partial pressure of the gas be the same as the saturated vapor pressure of nitrogen in the molten steel that can produce a stainless steel wire of the target composition. At this time, the pressure of the mixed gas in the tundish may be normal pressure. Further, the nitrogen gas and the inert gas other than the nitrogen gas may be alternately supplied into the tundish.

Here, when the nitrogen concentration in the stainless steel wire is less than the lower limit value (0.08% by weight) described above, even if casting is performed in an atmosphere consisting of argon gas containing no nitrogen gas, Nitrogen concentration does not change. The upper limit value (0.60% by weight) described above is 1500 ° C.
Since the nitrogen concentration in the molten steel is in equilibrium with nitrogen gas at 1 atm, the nitrogen concentration in the stainless steel wire does not exceed the above-mentioned upper limit value (0.60% by weight).

Further, the present invention is an apparatus used in the above manufacturing method, wherein a nitrogen gas supply source capable of supplying nitrogen gas into the tundish and an inert gas other than nitrogen gas can be supplied into the tundish. Inert gas supply source, respectively, nitrogen gas that is connected to the tundish, and between the tundish and the nitrogen gas supply source, the partial pressure of the nitrogen gas in the atmosphere in the tundish can be adjusted The present invention proposes a manufacturing apparatus provided with pressure adjusting means.

The saturated vapor pressure of nitrogen in the liquid phase having a target composition can be obtained from the equilibrium condition of the dissolution reaction of nitrogen in iron shown in the equation (2). That is, the equilibrium constant K of the reaction in the equation (2) is represented by the equation (3), and the relationship of the equation (4) is established between the equilibrium constant K and the molten steel temperature T. Therefore, the saturated vapor pressure, that is, the partial pressure of the nitrogen gas in the manufacturing method according to the present invention is determined by determining the molten steel composition and the molten steel temperature. In the equation (3), a _N is the activity of nitrogen atoms in the molten steel and is a value determined by the composition of the molten steel and the molten steel temperature T. P _N2 is the partial pressure of nitrogen gas in the atmosphere. 1 / 2N ₂ (g) = N (in liq.Fe) (2) K = a _N / √P _N2 (3) log K = -518 / T-1.063 (4)

[0012]

According to the above means, the partial pressure of nitrogen gas in the atmosphere in the tundish becomes equal to the saturated vapor pressure of nitrogen in the liquid phase, that is, in the molten steel, which can produce the solid phase of the target composition, so that the casting start From the end to the end, it is possible to prevent both the evaporation of nitrogen gas from the molten steel and the dissolution of nitrogen gas into the molten steel, and to keep the nitrogen concentration of the molten steel constant at a concentration that can produce the solid phase of the target composition. Can be kept.

[0013]

First, an example of a manufacturing apparatus according to the present invention will be described. FIG. 1 shows the outline of the manufacturing apparatus. As shown in the figure, this manufacturing apparatus 1 is similar to a conventional horizontal continuous casting machine for wire rods, including a tundish 10, a tapping nozzle 11, a break ring 12, and a mold (mold) 1.
3, a casting machine having a pinch roll 14. The tundish 10 is connected to a high-pressure nitrogen gas cylinder 20 that is a nitrogen gas supply source and a high-pressure inert gas cylinder 30 that is an inert gas supply source. Here, the inert gas cylinder 30 is filled with an inert gas other than nitrogen gas such as argon gas.

From nitrogen gas cylinder 20 to tundish 1
The gas flow path 21 reaching 0 is provided with a pressure reducing valve 22, a flow rate adjusting device 23, and a pressure adjusting device (nitrogen gas pressure adjusting means) 24. Similarly, in the gas flow path 31 from the inert gas cylinder 30 to the tundish 10, the pressure reducing valve 32,
A flow rate adjusting device 33 and a pressure adjusting device 34 are provided. The flow rate adjusting devices 23 and 33 are mass flow controllers, for example, and adjust the flow rates of the gases supplied into the tundish 10, respectively. Pressure regulator 24, 34
Adjusts the partial pressure of each gas supplied into the tundish 10. Each of the adjusting devices 23, 24, 33, 3
All 4 can be controlled by a control device (not shown) such as a computer.

Further, for example, the gas flow paths 21 and 31 are joined together and are connected to the gas introduction port 15 of the tundish 10 so as to communicate therewith. A pressure adjusting device 40 for adjusting the total gas pressure (the sum of the partial pressures of the nitrogen gas and the inert gas) in the space 10A in the tundish 10 is provided in front of the gas inlet 15. ing. This adjusting device 40
Can also be controlled by a computer or the like.

In FIG. 1, the reference numeral 2 indicates molten steel, and the reference numeral 3 indicates cast stainless steel wire. Further, in FIG. 1, in the tundish 10, an exhaust port for exhausting the space 10A, a molten steel introducing port from a ladle, and the like are not shown.

Next, the manufacturing apparatus 1 configured as described above.
The characteristics of the present invention will be clarified by giving the following examples, conventional examples, and comparative examples. In the following examples, three steel types A, which have different compositions,
A stainless steel wire made of B and C and having a diameter of 10 mm was manufactured. Table 1 shows the composition of each steel type. In addition, in Examples 2 to 4, the conventional example, and the comparative example, the conditions not specified were the same as those in Example 1.

[Table 1]

(Example 1) Table 2 shows the casting conditions. In this embodiment, steel type A is selected and the partial pressure of nitrogen gas is set to 0.
The atmospheric pressure was 6 atm, the partial pressure of argon gas was 0.4 atm, and the total gas pressure in the space 10A of the tundish 10 (the content is about 1 m ³ ) was atmospheric pressure, that is, 1 atm. Here, the partial pressure value of nitrogen gas (0.6 atm) is a value calculated based on the above equations (2) to (4). Fig. 2 shows the results of measuring the nitrogen concentration of molten steel 2 with the passage of casting time.
Is shown by the plot of ○. From the figure, it can be seen that the nitrogen concentration of the molten steel 2 is stable at 0.20 wt% which is the nitrogen concentration in the steel type A and does not change during the casting time of 5 hours.

[Table 2]

(Conventional Example and Comparative Example) Table 2 shows the casting conditions. In the conventional example, the partial pressure of nitrogen gas was 0 atm, that is, nitrogen gas was not supplied into the tundish 10 and only argon gas was supplied at 1 atm. In the comparative example, the argon gas was not supplied into the tundish 10, but only the nitrogen gas was supplied so as to have a pressure of 1 atmosphere. Steel type A was selected in each example. The result of having measured the nitrogen concentration of the molten steel 2 is shown in FIG. A plot of Δ is a conventional example, and a plot of □ is a comparative example. From the figure, the nitrogen concentration of the molten steel 2 gradually decreased in the conventional example and gradually increased in the comparative example with the elapse of the casting time.

From the above-mentioned Example 1, the conventional example and the comparative example, the nitrogen of the molten steel 2 was set for a long time by setting the partial pressure of nitrogen gas to the value calculated based on the above equations (2) to (4). It was found that the concentration can be kept stable and constant.

(Examples 2 and 3) Table 2 shows the casting conditions.
Shown in. In Example 2, steel type B was selected and the partial pressure of nitrogen gas was 0.15 atm and the partial pressure of argon gas was 0.85 atm. In Example 3, steel type C was selected, the partial pressure of nitrogen gas was 0.4 atm, and the partial pressure of argon gas was 0.6.
Atmospheric pressure was used. Here, the partial pressure values of the nitrogen gas in Examples 2 and 3 (0.15 atm and 0.4 atm)
Is a value calculated based on the above equations (2) to (4). The results of measuring the nitrogen concentration of the molten steel 2 with the elapse of casting time are shown in FIG. 3 for Example 2 and Example 3
Each is shown in FIG. From these figures, even for steel types B and C, during the casting time of 5 hours, molten steel 2
It can be seen that the nitrogen concentration is stable at the same value as the nitrogen concentration in each steel type (0.23 wt% for steel type B, 0.18 wt% for steel type C) and does not change.

From Examples 1 to 3 described above, even if the steel type is changed, that is, even for stainless steels having different nitrogen concentrations,
It has been found that setting the partial pressure of the nitrogen gas to a value calculated based on the equations (2) to (4) is effective for keeping the nitrogen concentration of the molten steel 2 constant.

(Example 4) Under the casting conditions shown in Table 3, nitrogen gas and argon gas were alternately supplied into the tundish 10. Steel type A was selected and the partial pressure of each gas was adjusted to be the same as in Example 1 above, that is, the partial pressure of nitrogen gas was 0.6 atm and the partial pressure of argon gas was 0.4 atm. . The results of measuring the nitrogen concentration of the molten steel 2 with the elapse of casting time are shown in FIG. From the figure, it can be seen that the nitrogen concentration of the molten steel 2 is stable at 0.20 wt% which is the nitrogen concentration in the steel type A and does not change during the casting time of 5 hours. That is, it was found that even if the gases were alternately supplied in this way, the same effect as in the case of simultaneously supplying the gases as in Example 1 was obtained.

[Table 3]

In the above examples, the steel grades A, B and C having nitrogen concentrations of 0.20% by weight, 0.23% by weight and 0.18% by weight were taken as examples and the effectiveness thereof was confirmed. However, it is needless to say that the same effect can be obtained by applying the manufacturing method according to the present invention even when the nitrogen concentration range is 0.08 to 0.60% by weight. Needless to say, the same effect can be obtained even when the nitrogen concentration range is less than 0.08% by weight. Furthermore, the manufacturing apparatus 1 can be modified in various ways as long as nitrogen gas and an inert gas other than nitrogen gas can be supplied into the tundish 10 while controlling the partial pressure of the nitrogen gas. Of course.

Furthermore, the present invention is applicable not only to stabilizing the concentration of components other than nitrogen in stainless steel, but also to stabilizing the concentration of components in alloys other than stainless steel. is there. In the case of a component other than nitrogen, a gas composed of a simple substance of the component or a compound containing the element may be supplied into the tundish 10 at an optimum partial pressure calculated.

[0026]

According to the method for producing a high nitrogen content stainless steel wire according to the present invention, since the partial pressure of nitrogen gas in the tundish is made to be the same as the saturated vapor pressure of nitrogen in the molten steel, it can be cast for a long time. It is possible to keep the nitrogen concentration of molten steel constant at all times during and inside. Therefore, 0.08-0.6
A stainless steel wire having a nitrogen concentration of 0 wt% can be continuously cast with a uniform nitrogen concentration. Further, according to the manufacturing apparatus of the present invention, since the nitrogen gas supply source is connected to the tundish via the pressure adjusting means, the nitrogen gas can be supplied into the tundish and the tundish can be supplied. The partial pressure of nitrogen gas in the atmosphere can be adjusted arbitrarily.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a manufacturing apparatus used for carrying out a manufacturing method according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the nitrogen concentration of molten steel and casting time in Example 1.

FIG. 3 is a characteristic diagram showing a relationship between nitrogen concentration of molten steel and casting time in Example 2.

FIG. 4 is a characteristic diagram showing a relationship between nitrogen concentration of molten steel and casting time in Example 3.

FIG. 5 is a characteristic diagram showing the relationship between the nitrogen concentration of molten steel and the casting time in Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Molten steel 3 Stainless steel wire (wire material) 10 Tundish 13 Mold 20 )

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroki Takahashi, No. 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Metallurgical Industry Co., Ltd. Kawasaki Plant (72) Hideo Yoshida 1-5, Kyobashi, Chuo-ku, Tokyo No. 8 in Nippon Yakin Kogyo Co., Ltd.

Claims (4)

[Claims] 1. When a molten steel is supplied from a tundish into a mold to cast a wire made of stainless steel containing 0.08 to 0.60% by weight of nitrogen element, the inside of the tundish contains nitrogen gas and other than nitrogen gas. A mixed gas atmosphere consisting of an inert gas, wherein the partial pressure of the nitrogen gas in the mixed gas atmosphere is the same as the saturated vapor pressure of nitrogen in molten steel capable of producing a stainless steel wire having a target composition. A method for producing a high nitrogen content stainless steel wire. 2. The method for producing a high nitrogen content stainless steel wire according to claim 1, wherein the pressure of the mixed gas in the tundish is maintained at normal pressure. 3. The method for producing a high nitrogen content stainless steel wire according to claim 1, wherein the nitrogen gas and the inert gas other than the nitrogen gas are alternately supplied into the tundish. 4. A manufacturing apparatus used in the above manufacturing method, wherein a nitrogen gas supply source capable of supplying nitrogen gas into the tundish and an inert gas capable of supplying an inert gas other than nitrogen gas into the tundish. A gas supply source is connected to the tundish, and a nitrogen gas pressure adjusting means capable of adjusting the partial pressure of the nitrogen gas in the atmosphere in the tundish between the tundish and the nitrogen gas supply source. An apparatus for producing a high nitrogen content stainless steel wire, which is characterized in that: