JPS59159921A - Adding method of ca alloy into molten steel - Google Patents

Abstract

PURPOSE:To add a molten Ca alloy into molten steel at a high yield by feeding under pressure the molten Ca alloy contained in a hermetic vessel into the molten steel without contact with air and slag. CONSTITUTION:A molten Ca alloy is contained in a hermetic vessel 1 and the vessel is sealed hermetically. The target value of the molten Ca alloy to be added to molten steel 5 and the speed of addition are set in a control device 9. A pressurized gas is fed through a feed pipe 7 into the vessel 1 and the device 9 is operated. A shutter 3a is opened by a driving device 10 to feed and add the molten Ca alloy via a feed pipe 6 into the molten steel 5. The amt. of the molten Ca alloy to be added is detected at all times by a detector 8 during this time and is outputted to the device 9. The opening degree of a shutter 3a is adjusted by a driving device 10 according to the output signal from the device 9 so that the speed of addition is maintained at a prescribed speed. When the amt. of addition attains the target value, the shutter 3a is closed and pressurized gas is fed through a feed pipe 11 into the pipe 6 so that the entire volume of the molten Ca alloy in the pipe 6 is fed into the steel 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adding Ca alloy to molten steel.

The sulfur content in the molten steel tapped from the converter deteriorates the hot strength of the steel, and also combines with Fe and ljn in the molten steel to produce Fe.
, Mn sulfide or sulfide-based inclusions with high extensibility are formed. Therefore, when steel having such inclusions is subjected to rolling, the inclusions are also elongated in the rolling direction, and the strength in the thickness direction of the plate material after rolling is significantly deteriorated. Therefore, in order to eliminate such negative effects caused by inclusions such as sulfides, Ca alloys have traditionally been added to molten steel, thereby removing as much sulfur as possible during the refining stage of the steel, and reducing the amount of sulfur formed by the remaining sulfur. Efforts are being made to control inclusions in steel so that they are difficult to elongate.

When adding Ca alloy to molten steel, it is necessary to avoid contact with slag or air as Ca alloy is active and easily oxidizes when it comes into contact with slag or air at high temperatures. To this end, techniques such as the C(1 alloy powder injection method, wire addition method, and 08 bullet projection method) have been developed and put into practical use.

However, each of these conventional methods has the following drawbacks.

First, in the Ca alloy powder injection method, Ca alloy powder is added to molten steel by injecting the Ca alloy powder together with a carrier gas into the molten steel through a lance immersed in the molten steel.
The added Ca in the alloy is gasified in a large scale in the molten steel and then dissolved in the molten steel. However, the solubility of Ca gas in molten steel changes based on the partial pressure of Ca gas, and in this Ca alloy powder injection method, the solubility of Ca gas in molten steel changes due to the presence of the carrier gas.
Since the partial pressure of a dregs becomes smaller and the solubility of Ca dregs in molten steel decreases, the yield of 08 min in the Ca alloy injected into molten steel into FIJtA becomes low, and 7~
It becomes about 10%. In addition, this method has the disadvantage that the molten steel swells due to the carrier gas injected into the molten steel together with the Ca alloy powder, and the swollen portion directly contacts the air and radiates heat, resulting in a significant drop in the temperature of the molten steel. .

In addition, the wire addition method is a method in which a wire formed by coating Ca alloy with e-tape is fed into molten steel at high speed, and the 08 bullet projection method is a method in which a capsule containing Ca alloy is fed into molten steel at high speed. In these methods, both the wire fed into the molten steel and the capsules inserted into the molten steel are partially trapped in the slag layer, resulting in a decrease in Ca yield to about 10 to 15%. Furthermore, in these methods, Ca alloy is
There is a problem in that complicated pre-processing such as covering with tape or encapsulating in a capsule is required, which increases the cost.

This invention was made in view of the above-mentioned problems of the prior art, and aims to provide a method for adding Ca alloy to molten steel, which is low cost, has a high yield, and does not cause disadvantages such as temperature drop in molten steel. do.

That is, in this invention, a molten Ca alloy is stored in a closed container, and one end is immersed in the molten Ca alloy in the closed container, and the other end is opened into the molten steel through an injection pipe. This is a method of adding Ca alloy to molten steel, which is characterized by injecting Ca alloy into molten steel under pressure.

The method of adding Ca alloy according to the present invention will be explained in more detail below.

FIG. 1 shows a Ca alloy addition device used to carry out the present invention. This Ca alloy addition device includes a closed container 1, a switch device 3 attached to the bottom opening 2 of the closed container 1, an upper end connected to the switch device 3, and a lower end connected to the molten steel 5 in a ladle 4. It has an injection pipe 6 which is opened and communicates the inside of the closed container 1 with the molten copper 5 via the opening/closing device 3. A pressurized gas supply pipe 7 is attached to the sealed container 1,
Further, this closed container 1 is provided with an addition detection device @8 such as a load cell, and an output signal from this addition amount detection device 8 is inputted to a control @8. The first enclosure 3 has a shutter 33, and a drive device 10 for this shutter 3a.
is controlled and driven by the control device 9. In addition, from the lower part of the shutter 38 to this opening/closing device @3, there is an injector 6.
A pressurized gas supply pipe 11 for supplying pressurized gas is connected therein, and a valve 12 provided on this pressurized gas supply pipe 11 is controlled to be opened and closed by the control device 9 together with the drive device 10. Ru.

In this invention, Ca alloy is added in the following manner using the Ca alloy addition process described above.

First, a molten Ca alloy is placed in a sealed container 1 and sealed.

Further, the target value and addition rate of molten Ca alloy to the molten steel 5 are set in the control device 9. Then, pressurized gas is supplied into the closed container 1 from the pressurized gas supply pipe 7, and
When the inside is pressurized and the control device @9 is activated, the shutter 38 is opened by the drive device 10, and molten Ca alloy is injected into the molten steel 5 from the closed container 1 through the injection pipe 6.

Based on the output signal, a calculation circuit provided in the control device 9 calculates the addition rate of molten Ca alloy from the closed container 1 to the molten steel 5, and based on the result, the control device 9
The opening degree of the shutter 3a is adjusted by the drive device □10 in response to an output signal from the control device 10, and the addition speed of the molten Ca alloy is maintained at the speed set in the control device 9 in advance. When the addition amount from the closed container 1 reaches the preset addition target value, the shutter 3a is closed by the drive device 10 in response to an output signal from the control device 9, and at the same time, the pressurized gas feed pipe 11 Pressurized gas is supplied into the injection pipe 6, the entire amount of molten Ca alloy in the injection pipe 6 is injected into the molten steel 5, and the addition of the molten Ca alloy into the molten a45 is completed.

Next, an example will be described in which Ca alloy was added to molten steel by the method described above using the Cδ alloy addition apparatus.

In this example, 200 jan of molten steel has a Ca purity of 3.
casi (97kg) and CaAΩ (1
Table 1 shows the temperature and composition of the molten steel before addition of the ca alloy.

The temperatures are shown in Table 2.

Then, the addition rate of the molten Ca alloy from the closed container to the molten steel is 0.1 kQ/Sec to 1.4 J based on Ca pure content.
l/5f3C, and melting C for each case.
The Ca yield in the molten steel after addition of the a-alloy and the temperature drop rate of the molten steel during the addition of the molten Ca alloy were investigated. The results are shown in FIGS. 2 and 3.

In addition, FIGS. 2 and 3 show the results when ca si and ca A (!) were added to molten steel using the conventional Ca alloy powder injection method under the same conditions as the embodiment of the present invention. The Ca yield level in molten steel and the level of temperature drop rate of molten steel are shown as a comparative example.In particular, Figure 3 shows the temperature drop rate when molten steel is left standing without adding Ca alloy etc. showed that.

As is clear from Fig. 2, according to the Ca alloy addition method of the present invention, when the pure Ca addition rate exceeds 1.0 kQ/secC, the Ca yield decreases to the same level as the conventional method; In the following cases, the Ca yield is higher than that of the conventional method. In particular, when the pure Ca addition rate is 0.3 kQ/sec or less, the Ca yield is almost 100%, and even when the addition rate is 0-4 kQ/3eC, the Ca yield is low. It is about 90%. Therefore, when implementing the Ca alloy addition method of the present invention, the Ca pure addition rate to molten steel is set at 1.0 kQ/
It is effective to keep the C sec or less, especially if the C
It is desirable to add at a rate of 0.4 ka/sea or less to achieve a yield of .

As described above, the reason why the Ca yield decreases when the Ca pure content addition rate is increased in the method of this invention is that when the addition rate of molten Ca alloy is increased, the bubble diameter of Ca vapor generated at the tip of the injection tube increases accordingly. As a result, the specific surface area at the interface between Ca vapor and molten steel decreases, and therefore,
It is inferred that the cause is that Ca vapor bubbles float in the molten steel and reach the surface of the molten steel while the Ca vapor is not fully dissolved in the molten steel.

Furthermore, as is clear from FIG. 3, according to the Ca alloy addition method of the present invention, the Ca pure addition rate is 1.0 kQ/s.
If it exceeds ec, the temperature drop rate of molten steel due to Ca alloy addition will be at the same level as the conventional method, but if it is less than that, the temperature drop rate will be slower than that of the conventional method, and in particular,
When the addition rate of caIili is 0.4 kQ/sec or less, and the above temperature drop rate is when the molten steel is left standing, it is effective to set the Call 1 minute addition rate to the molten steel to be 1.0 kQ/sec or less, Preferably 0.4kQ/sec
It turns out that it is better to do the following.

As described above, according to the present invention, by adding molten Ca alloy to molten steel, the Ca alloy is not trapped in the slag layer during the addition process, and the Ca alloy is not trapped in the slag layer. Since a carrier gas is not used during addition, unlike when a carrier gas is used, the partial pressure of Ca gas generated in the molten steel decreases due to the presence of the carrier gas, and the solubility of Ca gas in the molten steel decreases. Therefore, high yields can be achieved. In addition, even if molten Ca alloy is added, extreme turbulence such as molten steel breaking through the slag layer and rising will not occur in molten steel, and furthermore, the molten Ca alloy itself Since Ca has a large sensible heat, the method of the present invention can prevent the temperature of molten steel to which Ca alloy is added from dropping significantly. In addition, according to the method of the present invention, since a molten Ca alloy is added, complicated pretreatments such as coating the Ca alloy with e or the like to form a wire or encapsulating the Ca alloy in capsules are required. (Well, it's not necessary and costs can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a Ca alloy addition device used to implement this invention, Fig. 2 is a diagram showing the relationship between pure Ca addition rate and Ca yield when this invention is implemented, and Fig. 3 is a diagram showing the relationship between Ca pure content addition rate and Ca yield when this invention is implemented. It is a figure which shows the relationship between Ca pure content addition rate and molten steel temperature fall rate in the case of implementation. DESCRIPTION OF SYMBOLS 1... Airtight container, 3... Switching device, 4... Ladle, 6... Injection pipe, 7... Pressurized gas supply pipe, 8
... Added mother detection device, 9... Control device, 11.
...Pressurized gas supply pipe. Applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Takehisa Toyota (and one other person) Figure 1 Figure 2
Amendment writing method) June 30, 1980 Kazuo Wakasugi, Commissioner of the Japan Patent Office1, Indication of the case, Patent Application No. 33409 of 1982, Title of the invention, Method of adding Ca alloy during melting, 3, amended. Relationship with the patent case Patent applicant address 1-1-28 Kitahonmachi-dori, Chuo-ku, Kobe, Hyogo Prefecture
Title: <125') Kawasaki Steel Corporation 4, Agent address: 3-4-18@5, Mita, Minato-ku, Tokyo Date of amendment order: May 31, 1980 (shipment date) 6. Details subject to amendment Column for detailed explanation of the invention in the document and document certifying authority of representation At best;=≧S7
, Contents of the amendment (1) "2. Scope of claims" on page 1, line 14 of the specification is corrected to "3. Detailed description of the invention." (2) Submit a power of attorney as shown in the attached document. do.

Claims (2)

[Claims] (1) The molten Ca alloy is stored in a closed container, and the molten Ca in the open-mouth container is poured into A method for adding Ca alloy to molten steel, which comprises injecting the alloy into molten steel under pressure. (2) A patented method for adding Ca alloy to molten steel, characterized in that molten Ca alloy is injected into molten steel at a rate of addition of pure Ca at a rate of 1.0 kg/sec or less.