JP2005046884A - Atmosphere melting and casting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atmosphere melting and casting apparatus with which the production of a high nitrogen steel can easily be performed at low cost. <P>SOLUTION: The atmosphere melting and casting apparatus 1 for producing high nitrogen steel by means of a reverse gravity casting process is provided with: a vessel 3 for producing casting atmosphere in which a mold 35 is encapsuled; a vessel 2 for forming melting atmosphere in which a crucible 25 is encapsuled; and a tube member 4 for molten metal passage which connects both inner space parts of the mold 35 and the crucible 25 and whose distal end 41 at the crucible 25 side is arranged so as to be insertable/extractive to/from the molten metal in the crucible 25. Further, in the apparatus, when the tube member 4 for the molten metal passage is defined as a center axis, the size of the apparatus on the cross section orthogonally crossing the center axis is smaller at a position between the vessel 3 for producing casting atmosphere and the vessel 2 for forming melting atmosphere than in the other zone. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an atmosphere melting casting apparatus.

  The high nitrogen steel is, for example, an austenitic or martensitic stainless steel that is increased in hardness and corrosion resistance by increasing the nitrogen concentration in the steel. Its applications range from air shafts, ball bearings, bearing steel, tool steel to biomaterials. In particular, biomaterials have the advantage that hardness and corrosion resistance can be maintained by including nitrogen as an element that replaces Ni, which is an element undesirable for the human body. Such high nitrogen steel dissolves nitrogen by introducing nitrogen gas into the atmosphere at the refining stage and applying a high nitrogen partial pressure to the molten metal, but it must be carried out until casting while maintaining its equilibrium state. It is difficult to manufacture (Patent Documents 1 and 2 below).

JP 2000-202611 A Japanese Patent Laid-Open No. 2000-212631 Japanese Patent Publication No. 45-19585

  Since an apparatus for producing high nitrogen steel has to perform from melting to casting while maintaining the pressure inside the apparatus, for example, Patent Document 1 has to have a large internal volume. For this reason, the amount of processing gas (mainly nitrogen gas) required and the filling time become enormous, and the production efficiency and cost are increased. Moreover, since the entire apparatus is enlarged by increasing the internal volume or applying a pressure-resistant structure, there is a problem that the apparatus cost increases.

  The subject of this invention is providing the atmosphere melt | dissolution casting apparatus which can manufacture high nitrogen steel easily and cheaply.

Means for solving the problems / effects of the invention

In order to solve the above problems, in the atmosphere melting and casting apparatus of the present invention,
An atmosphere melting casting apparatus capable of producing high nitrogen steel by a reverse gravity casting process,
The casting atmosphere forming container in which the mold is enclosed, the melting atmosphere forming container in which the crucible is enclosed, and the inner space of the mold and the crucible are connected, and the tip on the crucible side can be inserted into and removed from the molten metal in the crucible. A molten metal passage pipe member provided,
When the pipe member for the molten metal passage is used as the central axis, the size of the cross-sectional device shape orthogonal to the central axis is reduced from other regions at a position between the casting atmosphere forming container and the melting atmosphere forming container. It is characterized by.

  In the above-described atmospheric melting casting apparatus of the present invention, a reverse gravity casting process is used for producing high nitrogen steel. The inverse gravity casting process is, for example, as shown in Patent Document 3, in which a pressure difference is generated between a melting atmosphere forming container in which a crucible is sealed and a casting atmosphere forming container in which a mold is sealed. This is a technique in which a molten metal is pushed up from a crucible to a mold through a pipe member for passage.

  In such an atmosphere melting and casting apparatus, there are two containers, a casting atmosphere forming container and a melting atmosphere forming container, and the internal spaces are communicated with each other by a molten metal passage pipe member. And in this invention, the magnitude | size of the cross-sectional apparatus shape orthogonal to a center axis | shaft (pipe member for molten metal passages) in the position between these containers is reduced rather than another area | region (area | region of each container). It becomes. For example, as in Patent Document 3, in the case where most of the molten metal passage pipe member is present in one container, the container includes the surrounding area, and the internal volume becomes large. Inevitable. However, in the present invention, the shape of the apparatus having a constriction at a position between the casting atmosphere forming container and the melting atmosphere forming container (for example, in a shape along the molten metal passage pipe member), that is, a wasteful internal volume is reduced. Because of the shape, the amount of processing gas (mainly nitrogen gas) can be reduced, and the weight of the apparatus can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an atmosphere melting casting apparatus capable of producing high nitrogen steel will be described. FIG. 1 is a schematic view showing the internal structure of the atmosphere melting casting apparatus 1. The atmosphere melting casting apparatus 1 connects the casting atmosphere forming container 3 in which the mold 35 is enclosed, the melting atmosphere forming container 2 in which the crucible 25 is enclosed, and the inner spaces of the mold 35 and the crucible 25 to each other, and the crucible 25. The molten metal passage pipe member 4 is provided so that the tip 41 on the side is detachable with respect to the molten metal in the crucible 25.

  The crucible 25 in the melting atmosphere forming container 2 is for producing a molten metal by melting raw materials, and is configured as an induction melting furnace in which an induction coil 26 is formed. Further, an atmosphere forming means 5 for introducing an atmosphere gas into the container is provided on the wall portion of the melting atmosphere forming container 2. Thereby, it is possible to control the components and partial pressure of the atmosphere applied to the melting atmosphere forming container 2 (and the casting atmosphere forming container 3 communicated therewith), and eventually to the molten metal.

  The molten metal passage pipe member 4 is fixed to the casting atmosphere forming container 3 side, is inserted into the through hole 21 in the wall portion of the melting atmosphere forming container 2, and is slidable with the inner surface of the through hole 21. Thus, the relative position of the melting atmosphere forming container 2 and the casting atmosphere forming container 3 changes in the insertion direction, so that the tip 41 on the crucible 25 side can be inserted into and removed from the molten metal in the crucible 25. ing.

  Moreover, as for the pipe member 4 for molten metal passages, the surface (part which is immersed in molten metal among all the inner surfaces and outer surfaces) in contact with a molten metal is comprised with the refractory material. Even if the surface is made of a refractory material, it may melt if it is immersed in the molten metal. Therefore, during the refining of the molten metal, the tip 41 on the crucible 25 side of the molten metal pipe member 4 is 25 is in a state of being retracted from the liquid level of the molten metal in 25. In addition, when the molten metal pipe member 4 is immersed in the molten metal for casting, the molten metal pipe member 4 needs to be heated so as not to cause a significant temperature difference between the two. Since the pipe member 4 is configured to be positioned immediately above the molten metal, it is heated together with the refining of the molten metal.

  The atmosphere forming means 5 can be formed only in the melting atmosphere forming container 2. At the time of refining, the tip 41 on the crucible 25 side of the molten metal passage pipe member 4 is in a state of being retracted from the molten metal, so that the casting atmosphere forming container 3 communicated via the molten metal pipe member 4 is also melted. It can be made the same atmosphere as the inside atmosphere forming container 2. Further, at the time of casting, the tip 41 on the crucible 25 side of the molten metal passage pipe member 4 is immersed in the molten metal, and an inert gas is introduced only into the melting atmosphere forming container 2 as described later. Therefore, it is sufficient to form the atmosphere forming means 5 only in the melting atmosphere forming container 2. However, the present invention is not limited to this, and the atmosphere forming means 5 may be provided in each of the melting atmosphere forming container 2 and the casting atmosphere forming container 3.

  A casting mold 35 of the casting atmosphere forming container 3 is connected to the melting atmosphere forming container 2 through the molten metal passage tube member 4, with the tip 42 on the mold 35 side of the molten metal pipe member 4 being fixed. Moreover, the casting_mold | template 35 is divided | segmented up and down with the casting atmosphere formation container 3 after casting, for example, and can be comprised so that an ingot can be taken out.

  When the atmosphere melting casting apparatus 1 has the molten metal passage pipe member 4 as a central axis, the size of the cross-sectional apparatus shape perpendicular to the central axis is between the casting atmosphere forming container 3 and the melting atmosphere forming container 2. It is reduced in position than other areas. In other words, the shape of the apparatus is constricted at a position between the casting atmosphere forming container 3 and the melting atmosphere forming container 2 (for example, in a shape along the molten metal passage pipe member 4). This can be referred to as an hourglass shape, for example. Since the wasteful internal volume is reduced in this way, the amount of processing gas (mainly nitrogen gas) can be reduced, and the weight of the apparatus can be reduced.

  Specifically, the casting atmosphere forming container 3 and the melting atmosphere forming container 2 are located with a space therebetween, and a part of the molten metal passage pipe member 4 is exposed in the space. Thus, since both containers 2 and 3 are located across the space, the relative positions of the melting atmosphere forming container 2 and the casting atmosphere forming container 3 change in the insertion direction of the molten metal passage pipe member 4. The tip 41 on the crucible 25 side of the molten metal passage pipe member 4 can be inserted into and removed from the molten metal in the crucible 25. Further, in the space between the melting atmosphere forming container 2 and the casting atmosphere forming container 3, a part of the molten metal passage pipe member 4, for example, the melting atmosphere forming container 2 and the casting atmosphere forming container 3 are respectively provided. Parts other than the inserted part are exposed.

  As described above, by providing the melting atmosphere forming container 2 and the casting atmosphere forming container 3 separately, the containers (crucible 25 or the mold 35) in which the respective containers 2, 3 are enclosed are included. The minimum necessary shape is possible. That is, since unnecessary spaces can be suppressed in the containers 2 and 3, the amount of processing gas (mainly nitrogen gas) can be reduced, and the weight of the apparatus can be reduced.

Next, the manufacturing method of the high nitrogen steel using the above atmosphere melting casting apparatus 1 is demonstrated. FIG. 2 is a diagram showing a manufacturing process of high nitrogen steel.
First, in the state where the tip 41 on the crucible 25 side of the molten metal passage tube member 4 is retracted from the liquid level of the molten metal in the crucible 25, the molten metal is melted so that the nitrogen concentration in the molten metal becomes the target nitrogen concentration. Nitrogen gas is introduced into the atmosphere forming container 2 and a predetermined target nitrogen partial pressure is applied (step 1). At this time, since the tip 41 on the crucible 25 side of the molten metal passage tube member 4 is in a state of being retracted from the molten metal, the melting atmosphere forming vessel 3 communicated via the molten metal passage tube member 4 is also formed with a melting atmosphere. The same nitrogen partial pressure and atmospheric pressure (total pressure) as in the container 2 are used.

  Second, the tip 41 on the crucible 25 side of the molten metal passage pipe member 4 is immersed in the molten metal in the crucible 25 while maintaining the target nitrogen partial pressure (step 2). As a result, the melting atmosphere forming container 2 and the casting atmosphere forming container 3 are spatially separated. At this time, the insides of these containers 2 and 3 remain at the same nitrogen partial pressure and atmospheric pressure (total pressure), respectively.

  Thirdly, in the melting atmosphere forming container 2, while maintaining the target nitrogen partial pressure, an inert gas (for example, argon gas) for pressurization is introduced to increase the atmospheric pressure (total pressure), thereby providing a crucible. The molten metal in the molten metal 25 is cast into the mold 35 through the molten metal passage tube member 4 (step 3). Thereby, in each container 2 and 3 maintained at the same nitrogen partial pressure and atmospheric pressure (total pressure), a difference occurs in the atmospheric pressure (total pressure), and the molten metal passes through the molten metal passage pipe member 4 and the mold. It flows out into 35. Casting is performed as described above, but in the melting atmosphere forming container 2, an inert gas that does not react with the molten metal is introduced to increase only the atmospheric pressure (total pressure). The pressure does not change, and the nitrogen partial pressure in the one casting atmosphere forming container 3 is maintained at the same nitrogen partial pressure as in the melting atmosphere forming container 2 as described above. Therefore, since the nitrogen partial pressure applied to the molten metal is maintained from refining to casting, high nitrogen steel can be easily manufactured.

  Further, the addition of nitrogen to the molten metal can be performed by introducing nitrogen gas into the melting atmosphere forming container 2 and charging an alloy containing nitrogen. Thereby, in addition to the addition of nitrogen from the atmosphere to the molten metal, the nitrogen content of the molten metal can be reduced by using the addition of nitrogen by charging the alloy containing nitrogen, which has been performed in the production of conventional high nitrogen steel. The desired level can be reached quickly.

  Moreover, it is preferable to set the target nitrogen concentration of a molten metal below the nitrogen concentration which can be dissolved in the steel after solidification. Since the saturated nitrogen concentration of the steel after solidification is small compared to the saturated nitrogen concentration at the time of the molten metal, when a target nitrogen concentration exceeding that is set for the molten metal, an amount of nitrogen corresponding to the difference in the saturated nitrogen concentration is released during the solidification. This is because there is a possibility of causing blow defects in the steel.

The nitrogen concentration in the molten alloy steel, which is in equilibrium with the atmospheric nitrogen partial pressure of 1 atm, is said to correlate with the temperature of the molten steel and the chemical composition of the alloy. The Japan Society for the Promotion of Science and the 19th Committee of Steelmaking Using the recommended equilibrium value of steelmaking reaction published and edited by the author, for example, the following equation (1):
log [N] eq = −518 / T−1.063 + 0.046 [Cr] −0.00028 [Cr] 2 + 0.02 [Mn] −0.007 [Ni] −0.048 [Si] +0.12 [O] −0.13 [C] +0.011 [Mo] -0.059 [P] -0.007 [S] (1)
Here, [N] eq: equilibrium nitrogen concentration at 1 atm (wt%), []: melting concentration of each element in molten steel (wt%), T: temperature of molten steel (K)
It can be obtained by.

On the other hand, regarding the relationship between the nitrogen dissolved concentration under atmospheric pressure and the nitrogen dissolved concentration under pressure P, in accordance with the law of so-called “Sieverts' law”, the following equation (2):
[N] Patm = KP1 / 2 = [N] 1atm × P1 / 2 (2)
Here, [N] Patm: Nitrogen dissolved concentration (wt%) at atmospheric nitrogen partial pressure P atmosphere, [N] 1 atm: Nitrogen dissolved concentration (wt%) at atmospheric nitrogen partial pressure 1 atmosphere, P: Nitrogen in atmosphere It is said that it can be obtained by partial pressure (atmospheric pressure), K: coefficient.

  In consideration of the above relationship, the nitrogen partial pressure applied to the molten metal and the composition of the molten metal are determined to produce high nitrogen steel. Such high nitrogen steel can be applied to various alloy steels. Particularly effective are austenitic or martensitic stainless steel, austenitic or martensitic heat resistant steel, and tool steel (plastic molds, high speed steel, hot tool steel, cold tool steel). It is. This is because, according to the above formula (1), the equilibrium nitrogen concentration of the molten metal increases with an increase in the dissolved amount of chromium (Cr), and the effect is particularly obtained on an alloy steel having a Cr content of 3% by weight or more. Becomes prominent. As described above, a high nitrogen steel in which the nitrogen concentration in the steel is increased to improve the hardness and corrosion resistance is obtained.

Hereinafter, comparison with Patent Document 3 will be performed.
In FIG. 4 of Patent Document 3, the casting atmosphere forming container in which the mold is enclosed, the melting atmosphere forming container in which the crucible is enclosed, and the inner spaces of the mold and the crucible are connected, and the tip on the crucible side is There is disclosed an atmosphere melting and casting apparatus having a molten metal passage pipe member that can be inserted into and removed from a molten metal in a crucible. However, since it is not intended for the production of high nitrogen steel in the first place, from the state where both containers are kept at the same atmospheric pressure, it is a configuration in which the molten metal flows out into the mold by reducing the atmospheric pressure in the casting atmosphere forming container, As in the present invention, from the state where both containers are kept at the same atmospheric pressure, an inert gas partial pressure is introduced into the melting atmosphere forming container, the atmospheric pressure (total pressure) is increased, and the molten metal flows into the mold. Thus, there is no disclosure about the idea of performing from refining to casting while maintaining the nitrogen partial pressure applied to the molten metal.
Further, since most of the molten metal passage pipe member is present in the melting atmosphere forming container, the melting atmosphere forming container has a useless space on the crucible and around the molten metal pipe member. Thus, unnecessary space is not reduced by reducing the apparatus shape between the casting atmosphere forming container and the melting atmosphere forming container. Therefore, the internal volume of the container becomes large, the amount of processing gas (mainly nitrogen gas) required and the filling time become coarse, and it is presumed that there is a lot of waste in production efficiency and cost.

Schematic showing the internal structure of the atmosphere melting casting apparatus 1 Diagram showing manufacturing process of high nitrogen steel

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Atmosphere melt | dissolution casting apparatus 2 Melting atmosphere formation container 21 Pipe through-hole 25 Crucible 26 Inductive coil 3 Casting atmosphere formation container 35 Mold 4 Melt passage pipe member 5 Atmosphere formation means

Claims (4)

An atmosphere melting casting apparatus capable of producing high nitrogen steel by a reverse gravity casting process,
A casting atmosphere forming container in which a mold is sealed, a melting atmosphere forming container in which a crucible is sealed, and the inner space of the mold and the crucible are connected to each other, and a tip on the crucible side with respect to the molten metal in the crucible A pipe member for a molten metal passage provided so as to be removable.
When the pipe member for the molten metal passage is used as a central axis, the size of the cross-sectional device shape orthogonal to the central axis is larger than that in other regions at a position between the casting atmosphere forming container and the melting atmosphere forming container. An atmosphere melting casting apparatus characterized by being reduced.   2. The casting atmosphere forming container and the melting atmosphere forming container are located with a space therebetween, and a part of the molten metal passage pipe member is exposed in the space. The atmosphere melting casting apparatus as described. The molten metal passage pipe member is fixed to the casting atmosphere forming container side, is inserted into a through hole in the wall of the melting atmosphere forming container, and is configured to be slidable with the inner surface of the through hole. ,
The relative position of the melting atmosphere forming container and the casting atmosphere forming container changes in the insertion direction, so that the tip on the crucible side can be inserted into and removed from the molten metal in the crucible. The atmosphere melting casting apparatus according to claim 1 or 2. In the melting atmosphere forming container such that the nitrogen concentration in the molten metal becomes the target nitrogen concentration in a state in which the crucible side end of the molten metal passage tube member is retracted from the liquid surface of the molten metal in the crucible. Applying a predetermined target nitrogen partial pressure by introducing nitrogen gas into
A step of immersing the crucible side tip of the molten metal passage tube member in the molten metal in the crucible while maintaining the target nitrogen partial pressure;
In the melting atmosphere forming container, while maintaining the target nitrogen partial pressure, by introducing an inert gas for pressurization to increase the atmospheric pressure, the molten metal in the crucible is replaced with the molten metal passage tube member. A process of casting the molten metal by flowing into the mold through,
The atmosphere melting casting apparatus according to any one of claims 1 to 3, wherein the high nitrogen steel is manufactured by sequentially performing the steps.

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