JPH10204520A - Method for adding lead into molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the adding yield of lead, to reduce number of the lead defects and disperse the lead powder into molten steel under fine powder condition by dipping a lance pipe into the molten steel and adding the lead powder together with carrying gas into the molten steel while rotating round the axis of the lance pipe. SOLUTION: The molten steel 2 is incorporated into a vessel 7 providing a heat means, and the lance pipe 8 is dipped into the molten steel 2. At the time of rotating the lance pipe 8 in the molten steel 2, the molten steel 2 starts the rotating movement in the same direction on the rotating direction of the lance pipe 8 and starts the fluidize. A prescribed quantity of the lead powder is charged from the upper part of the molten steel 2 in this state. The lead is mixed with the fluidized molten steel 2 and the dispersion of the lead powder into the molten steel 2 is progressed. The lead powder is carried with the carrying gas from a pressurized tank 11 to the pipe 8a of a pipe 8 and injected into the molten steel 2 together with the carrying gas from a hole 8c opened at the lower end part. By this method, the lead powder is uniformly dispersed into the molten steel 2 to prevent dissipation caused by vaporization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adding lead to molten steel, and more particularly, to a method for increasing the yield of lead added to molten steel and capable of uniformly dispersing fine lead powder in molten steel, thereby improving quality. The present invention relates to a method for adding lead to molten steel, which enables the production of simple lead free-cutting steel.

[0002]

2. Description of the Related Art Lead free-cutting steel is manufactured by adding a predetermined amount of lead powder or lead oxide powder to molten steel having a predetermined composition and then casting the molten metal. Specifically, lead is added as follows. That is, as shown in FIG. 6, first, the ladle 1 is charged with molten steel 2 having a predetermined composition, and the ladle 1 is fitted with the dust collection cover 3. Then, from the bottom of the ladle 1 by injecting an inert gas 4, such as Ar or N ₂ molten steel 2
Is dropped from the hopper 5 attached to the dust collection cover 3 onto the molten steel 2 while stirring.

[0003] Here, lead hardly dissolves in molten steel.
The specific gravity is about 11.3, which is considerably larger than the specific gravity of molten steel of 7 to 8, and is a volatile element. Therefore, a part of the lead powder added to the molten steel 2 volatilizes and escapes from the exhaust port 3a of the dust collecting cover 3 to the outside of the system, and a part of the lead powder sinks in the molten steel and is deposited on the bottom of the ladle 1. It precipitates and the remainder is dispersed in the molten steel while riding on the stirred flow of the molten steel 2.

[0004]

The above-mentioned conventional lead addition method has the following problems. First, the first problem is that the amount of lead volatilization and sedimentation is relatively large, so that the amount of lead powder dispersed in the molten steel is reduced, and the following formula: 100 × the amount of lead in the molten steel / the total amount of added lead. The lead addition yield (%) shown is a low level of 50-60%. This means that the entire amount of the added lead powder is not effectively utilized, which is not industrially preferable.

[0005] A second problem is that the added lead powders tend to associate with each other into larger particles. Therefore, when the obtained ingot is sliced and its sliced surface is observed, it is often the case that lead particles having a large particle diameter segregate and appear on the sliced surface with a small number of distribution. This is usually referred to as a lead defect, and is a problem to be suppressed in view of preparing a high-quality free-cutting steel by uniformly dispersing a large number of fine lead particles.

In any case, in the conventional method of adding lead to molten steel, there have been problems that the yield of adding lead is low and the number of lead defects tends to increase. The present invention solves the above-mentioned problem, and the lead addition yield is increased,
At the same time, an object of the present invention is to provide a method for adding lead to molten steel, in which the number of lead defects is reduced, and the added lead powder can be uniformly dispersed in a fine powder state.

[0007]

In order to achieve the above object, the present invention is characterized in that a lance pipe is immersed in molten steel, and lead powder is added to the molten steel while rotating the lance pipe. A method for adding lead to molten steel is provided.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for adding lead according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an apparatus for performing the method of the present invention. In FIG. 1, a container 7 provided with a heating means (not shown) contains molten steel 2 having a predetermined composition. A lance pipe 8 is attached to the molten steel 2.
Is immersed.

As shown in FIG. 2, which is a cross-sectional view taken along the line II-II of FIG. 1, the lance pipe 2 has a pipe 8a made of, for example, heat-resistant steel and a refractory disposed so as to surround the outer periphery of the pipe 8a. 8b, a hole 8c having a predetermined diameter is formed in a side wall of a lower end portion thereof, and the whole is suspended by a joint mechanism 9 capable of rotating about a shaft. For example, a bevel gear 10a is fixed to the pipe 8a, and a bevel gear 10b of the drive motor 10 is fitted to the bevel gear 10a. When the drive motor 10 is operated, the pipe 8a, that is, the lance pipe 8 is molten steel 2a. The shaft can be rotated while being suspended inside. By controlling the rotation speed of the drive motor 10, the rotation speed of the lance pipe 8 can also be controlled.

[0010] When this apparatus is used, lead is added as follows. First, the drive motor 10 is operated to rotate the lance pipe 8 in molten steel.
The viscous drag caused by the rotation of the lance pipe 8 causes the vessel 7
The molten steel 2 starts rotating in the same direction as the rotation direction of the lance pipe 8 and starts flowing. Then, by introducing a predetermined amount of lead powder from above the molten steel 2 in this state, the lead powder is mixed with the flowing molten steel 2 and dispersion of the lead powder in the molten steel 2 proceeds.

In this case, the quality of the dispersed state of the lead powder is greatly affected by the flow state of the molten steel 2. For example, if the molten steel 2 is flowing violently, the dispersion state of the lead powder is also good, and if the molten steel 2 is not flowing, the dispersion is poor, leading to a decrease in the lead addition yield and an increase in the number of lead defects. . The flow state of the molten steel 2 is determined by the lance pipe 8
, The thickness of the lance pipe 8, the immersion depth of the lance pipe 8 in the molten steel, the charge amount of the molten steel 2, and the like.

For example, if the rotation speed of the lance pipe 8 is too low, the lead powder is in the form of fine powder in the molten steel and is not easily dispersed uniformly, and the lead addition yield is low. Therefore, the rotation speed is preferably high. However, when the rotation speed becomes too high, the viscous resistance between the lance pipe and the molten steel increases,
In particular, the refractory of the lance pipe may be damaged at the contact portion with the slag covering the upper part of the molten steel. For this reason, it is preferable that the rotation speed of the lance pipe 8 be within the range of 10 to 120 rpm.

On the other hand, if the diameter of the lance pipe 8 is too small, the effect of flowing the molten steel 2 is reduced, so that the larger the diameter, the better. However, since the thickness is regulated by the size of the container 7 containing molten steel, it may be appropriately selected in relation to the capacity of the container used. Further, if the immersion depth of the lance pipe 8 in the molten steel 2 is too shallow, even if the lance pipe is rotated axially, the molten steel flows only at the upper portion and does not flow as a whole. It is preferable to set the depth of the pipe 8 to a limit depth that does not make contact with the bottom of the container 7.

In the case of the above-described addition method, since the lead powder is directly charged into the molten steel 2, a part of the lead powder is volatilized and dissipated into the air, so that the yield of addition tends to decrease.
For such a problem, lead can be added by an apparatus as shown in FIG. The device shown in FIG.
The lead powder feeder system A is connected to the pipe 8a of the apparatus shown in FIG.

The feeder system A is provided with an inlet 11 for lead powder.
a pressurized gas pipe 12a connected to the upper part of the pressurized tank 11 and a carrier gas pipe 12b connected to the lower part of the pressurized tank 11; 12b is connected to the pipe 8a of the lance pipe 8. Lead addition using the apparatus shown in FIG. 3 is performed as follows.

First, lead powder is charged into the pressurized tank 11 from the charging port 11a. Then, the drive motor 10 is operated to rotate the lance pipe 8 to make the molten steel 2 flow properly, and the valves 13a, 13b, and 13c of the feeder system A are opened to open the pressurized gas pipe 12a from, for example, N _2. Pressurized tank 1 by introducing a pressurized gas consisting of an inert gas such as
1. Pressurize the lead powder in 1. Lead powder is the carrier gas line 12b
And transported to the pipe 8a of the lance pipe 8 by a carrier gas formed of an inert gas such as N ₂ or Ar introduced through the valve 13c.

Thereafter, the lead powder is pumped through the pipe 8a, and is ejected into the molten steel 2 together with the carrier gas from the hole 8c opened on the side wall of the lower end of the lance pipe 8. In this case, the lead powder is directly added into the flowing molten steel 2, so that not only uniform dispersion but also dissipation by evaporation is prevented. Furthermore, since the molten steel 2 is stirred by the action of the carrier gas ejected from the hole 8c, the dispersion of the lead powder into the molten steel proceeds more effectively.

[0018]

【Example】

Example 1 In the apparatus shown in FIG.
An air induction furnace having a volume of 0 mm and a depth of 400 mm was prepared, and molten steel of AISI12L14 was accommodated therein and maintained at a temperature of 1670 ° C.

On the other hand, a lance pipe 8 having an alumina-based refractory disposed outside a heat-resistant steel pipe having a diameter of 3 mm and having an overall diameter of 60 mm was prepared and immersed in the molten steel 2. The immersion depth was 200 mm. Then, while the drive motor 11 was operated to rotate the lance pipe 8, the lead powder having a particle size of about 0.5 mm was directly charged from above the molten steel 2. The charging amount was 0.5% by weight based on the molten steel 2, and the entire amount was charged over about 5 minutes. At this time, the lance pipe 8
Was changed.

The obtained molten steel was subjected to lead analysis to calculate the addition yield. The results are shown by the -O- marks in FIG. 4 as a relationship diagram with the rotation speed of the lance pipe. Further, the molten steel was made into an ingot, and the ingot was sliced, and a perspiration test (at a temperature of 600 ° C.) was performed on the sliced surface, and visually observed, and the number of lead defects of 0.1 mm or more was counted. The results are shown by the -O- marks in FIG. 5 as a relationship diagram with the rotation speed of the lance pipe.

Example 2 The apparatus shown in FIG. 3 was used, and the particle size of the lead powder was 5 μm.
The lead speed was 2.8 kg / min · t
Except for being on, lead powder was added to molten steel in the same manner as in Example 1. The addition yield of lead in the obtained molten steel, and the number of lead defects in the sweat test, respectively,
In FIG. 4 and FIG.

The following will be apparent from FIGS. 1) When lead is added while rotating the lance pipe, the lead addition yield increases and the number of lead defects decreases. In this case, the addition yield increases as the number of revolutions of the lance pipe increases, but the effect of improving the yield shows a saturation tendency from about 50 rpm.

2) When the particle size of the lead powder to be added is small, the lead addition yield becomes high (FIG. 4). The number of lead defects decreases as the rotation speed of the lance pipe increases. 3) As is clear from FIGS. 4 and 5, the addition of the lead powder into the molten steel together with the carrier gas improves the yield of addition of the lead and improves the fine powder, rather than directly charging the molten steel from above. Is advantageous in terms of uniform dispersion.

[0024]

As is apparent from the above description, according to the method of the present invention, the yield of adding lead to molten steel can be increased, and the lead powder can be finely and uniformly dispersed in molten steel. It is possible to manufacture simple lead free-cutting steel.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an apparatus used for a lead addition method of the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a schematic diagram showing another example of an apparatus used in the lead addition method of the present invention.

FIG. 4 is a graph showing a relationship between a lead addition yield and a rotation speed of a lance pipe.

FIG. 5 is a graph showing a relationship between the number of lead defects and the rotation speed of a lance pipe.

FIG. 6 is a schematic diagram showing an example of an apparatus used for a conventional lead addition method.

[Explanation of symbols]

 Reference Signs List 1 ladle 2 molten steel 3 dust collecting cover 3a gas outlet 4 inert gas 5 hopper 6 lead powder 7 container 8 lance pipe 8a pipe 8b refractory 8c hole 9 joint mechanism 10 drive motor 10a, 10b bevel gear 11 pressurized tank 11a Lead powder inlet 12a Pressurized gas line 12b Carrier gas line 13a, 13b, 13c Valve

Claims (3)

[Claims] 1. A method for adding lead to molten steel, comprising immersing a lance pipe in the molten steel, and adding lead powder to the molten steel while rotating the lance pipe axially. 2. The method for adding lead to molten steel according to claim 1, wherein the lead powder is pressed into the molten steel together with a carrier gas from a tip of the lance pipe. 3. The rotation speed of the lance pipe is 10-12.
3. The method for adding lead to molten steel according to claim 1, wherein the rotation speed is 0 rpm.