JP2007260736A - Method of adding rare earth metal to steel ingot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of adding a rare earth metal to a steel ingot with which a high product yield can be achieved by assuring the uniformity of a distribution of the rare earth metal in a longitudinal direction in the steel ingot. <P>SOLUTION: The method of adding the rare earth metal to the steel ingot includes a process of forming an isolation pipe 7 capable of isolating a molten steel S and the rare earth metal M until after the solidification of the molten steel S within an ingot casting mold 2, and a process of arranging the isolation pipe 7 filled with the rare earth metal M by aligning the longitudinal direction of the ingot produced by the ingot casting mold 2 and the longitudinal direction of the isolation pipe 7 within the ingot casting mold 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of adding a rare earth metal to a steel ingot, and in particular, it is possible to achieve a high product yield by ensuring the uniformity of the distribution of the rare earth metal in the longitudinal direction in the steel ingot. The present invention relates to a method for adding a rare earth metal to a steel ingot.

In recent years, ingots of steel ingots using molds have been added rare earth metals to molten steel in the molds in order to improve the mechanical properties of the steel ingots to be ingoted.
As a conventional method of adding a rare earth metal to molten steel in a mold, for example, a method of adding a rare earth metal to a molten steel in a casting mold shown in FIG. 2 is known (see Patent Document 1).
In the method of adding rare earth metal to the molten steel in the lower casting mold shown in FIG. 2, a single pipe 22 made of 0.5 to 2.0 mm thick metal filled with rare earth metal 20 to 20 to 90% of the total height of the lower casting mold 21 is used. Individual or plural pieces are fixed vertically in each of the above-described molds 21, and the molten steel 23 in which the inside of the molds 21 is made an inert atmosphere and the sulfur content is adjusted to 0.010% or less in advance is injected into the submerged injection pipe 24. A configuration is adopted in which the pipe 22 is sequentially melted as the molten metal surface in the mold 21 rises.

And according to the method of adding a rare earth metal to the molten steel in the casting mold according to Patent Document 1, the pipe 22 is sequentially melted as the molten metal surface in the mold 21 rises, whereby the uniformity of the rare earth metal 20 in the molten steel. It is also possible to improve the yield.
Japanese Patent Laid-Open No. 50-16609

Here, since the specific gravity of the rare earth metal is generally higher than the specific gravity of the molten steel, when the rare earth metal is added to the molten steel, the rare earth metal sinks downward in the molten steel.
Therefore, in the method of adding a rare earth metal to the molten steel in the casting mold according to Patent Document 1, when the melting of the pipe starts due to the rise of the molten metal surface in the mold, the rare earth metal in the pipe sinks below the molten steel, There is a problem in that rare earth metals are unevenly distributed downward in the manufactured steel material, resulting in poor product yield.
The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to ensure a uniform distribution of the rare earth metal in the longitudinal direction in the steel ingot, thereby achieving a high product yield. An object of the present invention is to provide a method for adding a rare earth metal to a steel ingot capable of achieving distillation.

The method of adding a rare earth metal to a steel ingot according to claim 1 of the present invention includes a step of forming an isolation tube capable of isolating molten steel and rare earth metal in a mold until after the molten steel is solidified;
Disposing the isolation tube filled with the rare earth metal in the mold so that the longitudinal direction of the steel ingot formed by the mold coincides with the longitudinal direction of the isolation tube. To do.

  According to the method for adding a rare earth metal to a steel ingot according to claim 1 of the present application, a step of forming an isolation tube capable of isolating molten steel and rare earth metal in a mold until after the molten steel is solidified, and filling the rare earth metal The longitudinal direction in the steel ingot is configured to include the step of arranging the isolation tube in the mold such that the longitudinal direction of the steel ingot formed by the mold coincides with the longitudinal direction of the isolation tube. It is possible to ensure the uniformity of the distribution of the rare earth metal in and to achieve a high product yield.

Hereinafter, a method for adding a rare earth metal to a steel ingot according to an embodiment of the present invention will be described with reference to the drawings.
The method for adding a rare earth metal to a steel ingot according to the present invention is used in the ingot making of a steel ingot that is rolled into a billet, a wire, etc. In this embodiment, The case where the rare earth metal addition method is applied to the production of a welding wire will be described as an example.

Here, since the welding wire is melted again at the time of welding, it is sufficient that the distribution of the rare earth metal in the longitudinal direction is ensured in the welding wire, and the rare earth in the entire welding wire is not necessarily required. Since it is not necessary to ensure the uniformity of the metal distribution, it is particularly suitable for application of the method for adding a rare earth metal to a steel ingot according to the present invention.
FIG. 1 is a sectional view of a steel ingot casting apparatus for welding wire.
The welding wire steel ingot casting apparatus 1 includes an ingot casting mold 2 into which molten steel S is poured, and the ingot casting mold 2 is disposed below the die portion 3 and the die portion 3 as shown in FIG. It has a pouring passage 4 that is provided and communicates with the inside of the mold portion 3, and a pouring port 5 that is formed at the end of the pouring passage 4.

Next, the manufacturing method of the welding wire using the steel ingot casting apparatus 1 for welding wires is demonstrated.
In the production of the welding wire, first, the steel ingot for welding wire is formed using the steel ingot casting apparatus 1 for welding wire.
In ingot making of a steel ingot for welding wire using such a steel ingot casting apparatus for welding wire 1, first, an isolation tube 7 disposed inside the mold part 3 of the ingot casting mold 2 is formed.
The isolation tube 7 includes a pipe member 8 formed in a bottomed pipe shape filled with the rare earth metal M, and a lid portion 9 fixed to the upper end of the pipe member 8. The pipe member 8 and the lid 9 are not particularly limited as long as they are made of steel, but are preferably formed with a high melting point.

The isolating tube 7, in the mold part 3 is formed so as to allow separating the molten steel S and rare earth metal M until after solidification of the molten steel S, the internal diameter D _i of the isolating tube 7 is determined as follows.
First, from the area S1 of the mold bottom surface 11 and the area S2 of the molten metal surface 12 of the molten steel S, the average area S of the horizontal section of the mold part 3 is calculated by the following formula (1).
S = (S1 + S2) / 2 (1)
Here, when the rare earth metal content in the target steel ingot is the target rare earth metal content X (mass fraction), the following formula (2) is established.
X = (ρ _REM · D _i ² · π / 4) / (ρ _Fe · S) (2)
However, the density of the rare earth metal is ρ _REM (g / cm ³ ), and the density of the rare earth metal is ρ _Fe (g / cm ³ ).
The previously obtained experimentally the target rare earth metal content X, the inner diameter D _i of the isolating tube 7 is calculated by the following equation (3).

In addition, the outer diameter of the separator tube 7 is such that the separator tube 7 cannot be completely melted before the molten steel S solidifies in consideration of the solidification time of the molten steel S and the heat transfer of the molten steel S to the separator tube 7. It is set to be a thickness.
Further, the longitudinal direction (vertical direction in FIG. 1) of the isolation tube 7 is such that the upper end of the isolation tube 7 protrudes from the upper surface of the molten metal S surface 12 when the isolation tube 7 is placed in the mold part 3. Therefore, the upper end of the separator tube 7 is determined to have the same height as the molten metal surface 12, and preferably the upper end of the separator tube 7 is slightly lower than the molten metal surface 12.

  Next, with respect to the isolation tube 7 formed by the above method, the pipe member 8 is filled with the rare earth metal M, and the lid portion 9 is fixed to the upper end of the pipe member 8. Here, the lid portion 9 is fixed because the rare earth metal M is easily oxidized when exposed to a high temperature in the air, so that the air is blocked. As the rare earth metal M, a misch metal (Ce: La: Nd = 5: 3: 2 (mass ratio)) is usually used.

  Then, the isolation tube 7 filled with the rare earth metal M is disposed in the mold part 3. In this case, the isolation tube 7 is a mold in a state where the isolation tube 7 is erected so that the longitudinal direction of the steel ingot formed by the mold unit 3 and the longitudinal direction of the isolation tube 7 coincide with each other. Arranged on the bottom surface 11. Here, the arrangement of the isolation tube 7 on the mold bottom surface 11 can be arbitrarily determined. However, in order to prevent the isolation tube 7 from being dissolved, it is preferable that the isolation tube 7 be arranged close to the side wall of the mold part 3. .

Next, after placing the isolation pipe 7 in the mold part 3, the pouring of the molten steel S is started from the pouring port 5, and the molten steel S is poured into the mold part 3 through the pouring channel 4.
As the molten steel S is poured into the mold portion 3, the outer surface of the isolation tube 7 is gradually melted by the heat of the molten steel S. In this case, since the separator tube 7 is formed to a thickness that does not completely melt before the molten steel S poured into the mold part 3 is solidified, the molten steel S is solidified and the steel ingot for welding wire is formed. Even after the is formed, the isolation tube 7 remains in the steel wire ingot for welding wire as it is filled with the rare earth metal M. Thereby, the uniformity of the distribution of the rare earth metal M in the longitudinal direction in the steel ingot for welding wire can be ensured, and a high product yield can be achieved.

Further, the welding wire (not shown) is formed by rolling the welding wire ingot formed by the welding wire ingot casting apparatus 1. In this case, even in the welding wire formed by rolling the steel ingot for welding wire, since the rare earth metal M remains uniformly in the longitudinal direction, a high product yield can be achieved as a welding wire. It becomes possible.
Although the embodiments of the present invention have been described above, various modifications can be made in the embodiments of the present invention.
For example, in the embodiment of the present invention, the ingot casting mold 2 of the ingot casting apparatus 1 for welding wire is configured as a lower casting mold, but may be configured as an upper casting mold.

  Next, when a steel ingot is made by the steel wire ingot casting apparatus 1 according to the present invention and a welding wire is manufactured using the steel ingot, and before the molten steel S is solidified in the mold. A case where a steel ingot is formed by a steel ingot casting apparatus for a welding wire according to a comparative example to which a method of suspending a bag filled with a melting rare earth metal M is applied, and a welding wire is manufactured using the steel ingot. The effect will be described by comparison.

  In addition, the manufacturing process of the welding wire in a present Example makes a steel ingot 30t ingot with each steel wire ingot casting apparatus, and puts this steel ingot into a soaking furnace, and makes it a steel piece. The steel slab discharged from the soaking furnace is subjected to breakdown rolling and rolled into a 175 square billet. Further, the rolled 175 square billet was subjected to wire rolling to produce a wire rod, and a welding wire was manufactured.

Further, the welding wire in this example is set to C: 0.05 mass%, Si: 0.5 mass%, and REM (rare earth element): 0.03 ± 0.005 mass%.
As a result, when the welding wire is manufactured using the welding wire ingot casting apparatus according to the comparative example, the product yield is 70% at maximum, whereas the welding wire ingot casting apparatus 1 is used for welding. The product yield in the case of manufacturing a wire can achieve 95% or more.

  This is because when the steel ingot is cast by the steel wire ingot casting apparatus according to the comparative example, the specific gravity of the rare earth metal is heavy relative to the specific gravity of the molten steel S, so the rare earth metal M is molten before the molten steel S solidifies. It will sink below in S, and the density | concentration difference of the rare earth metal M will arise in the longitudinal direction in the ingot steel ingot. Then, when breakout rolling or wire rolling is performed on a steel ingot having a concentration difference in the longitudinal direction, cracks are generated in a portion where the concentration of rare earth metal M in the steel ingot is high, and the product yield is deteriorated. . In addition, when the concentration difference of the rare earth metal M in the longitudinal direction in the steel ingot is large, the quality of the welding wire produced by rolling the steel ingot will vary, resulting in a deterioration in product yield. It is because it will do.

It is sectional drawing of the steel ingot casting apparatus for welding wires. It is explanatory drawing of the method of adding a rare earth metal to the molten steel in a casting mold which concerns on patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel ingot casting apparatus for welding wire 2 Ingot casting mold 3 Type | mold part 4 Pouring channel 5 Pouring spout 7 Separation pipe 8 Pipe member 9 Lid S Molten steel M Rare earth metal 11 Mold bottom surface 12 Hot water surface 20 Rare earth metal 21 Bottom casting mold 22 Metal pipe 23 Molten steel 24 Injection pipe for subcontracting

Claims (1)

Forming a separating pipe capable of isolating the molten steel and the rare earth metal in the mold until the molten steel is solidified;
Disposing the isolation tube filled with the rare earth metal in the mold so that the longitudinal direction of the steel ingot formed by the mold coincides with the longitudinal direction of the isolation tube. To add rare earth metal to the steel ingot.

Images