JPS60169509A - Slagless decarburization blowing method - Google Patents

Abstract

PURPOSE:To reduce spitting and dust loss in the stage of refining a molten iron subjected to preliminary refining including desiliconization, desulfurization and dephosphorization to a steel in a converter by regulating the volumetric ratio between a bottom blowing gas and top blowing oxygen according to the depression of the molten steel surface by oxygen pressure. CONSTITUTION:A molten iron from a convertr is preliminarily desiliconized, desulfurized and dephosphorized and is then subjected to slagless oxygen blowing in a top blown converter provided with bottom blowing tuyeres by which a steel is produced. The volumetric ratio between a bottom blowing gas and top blowing oxygen (bottom blowing/top blowing ratio) is regulated according to the depth of the depression formed on the surface of the molten metal by the top blowing oxygen. More specifically, the value of the above-mentioned bottom blowing/top blowing ratio is made >=4%, >=3% and >=2% when the depth L of the depression is <=90mm., 90-140mm. and >=140mm. by which the loss of the molten steel in the form of spitting or fume dust and the consequent decrease in the yield of Fe are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to hot metal after pretreatment (IIQ Si, deP, lI
This relates to the so-called slagless decarburization blowing method, which produces an extremely small amount of slag in the hot metal (after hot metal removal). As a result, the conventional converter steel manufacturing method is undergoing major changes.

In particular, as hot metal pretreatment, nI'tsi, deP,
If the de-S treatment is performed, the reaction in the steelmaking furnace is de-C.
Basically, there is no need for slag material. Regarding decarbonization in this slag-free state, there is no cover slag, so there is a lot of spinning or wheeze.
It has the disadvantage of increased iron loss, and a modification of Y< has been desired.

In line with this, for example, Japanese Patent Application No. 182538/1982, Japanese Patent Application No. 111 (54-1780j'), Japanese Unexamined Patent Publication No. 57-60
As shown in No. 004, 1. A solution has been proposed that combines the soft blowing of blowing lanos and the stirring power of bottom blowing scum.

Bottom-blown casting is more or less desirable for cost reduction, but in the past, the optimal bottom-blown gas flow for slagless decarburization and soft blowing has not been investigated.

The present inventors attempted a large-scale test of the slagless decarburization blowing method, and as a result, they were able to reduce spinting and tastolos, improve the iron yield, or actively promote the secondary combustion of GO. It has been found that, in order to cause this to occur, the required amount of bottom blowing changes as the depth L of the concavity caused by the top blowing butylene agent is further reduced. In other words, as L becomes smaller, the oxidation of iron increases, especially in the early stage of blowing.
A large amount of eO-based slag is generated. At this time, if the amount of bottom-blown slag is too small, this phenomenon will be further accelerated, and finally a sudden reaction with C in the hot metal will cause a bumping phenomenon, resulting in a large amount of spinning loss. Moreover, safe operation becomes impossible.

Therefore, in order to improve the above product defects such as iron yield in the slagless decarburization blowing method, bottom blowing/1-Europeanization should be adjusted by adjusting the depression depth L due to -1-blowing oxygen jet, l. We discovered that this is important, and after conducting various tests, we completed the present invention.

OBJECT OF THE INVENTION The present invention was made as a result of such studies, and it reduces spinning and dust loss, and improves iron retention.
The object of the present invention is to provide a decarburization blowing method that actively causes secondary combustion of CO.

Structure and operation of the invention That is, the present invention provides a method for decarburizing hot metal that has been previously subjected to de-S1, de-P, and de-S treatment. At that time, the volume ratio of bottom-blown scum to Nordic oxygen (hereinafter referred to as bottom-blown/- is referred to as blowing ratio) is set to the depth L (H) of the dent formed on the surface of the molten iron bath by l-blown oxygen. This decarburization blowing method is characterized by adjusting as follows (however, when L is 90 mm, the bottom blow/to blow ratio is set to 4% or more, and L is 90~90 mm). 14
When 0, bottom blow/'', Europeanization is 3% or more - L, L is 1
When it is 408, it is set as bottom blowing/J-blowing ratio Europeanization% or more-■-).

Hereinafter, a detailed description of the invention will be given.

The hot metal after Ill treatment (de-S1, de-P, hot metal after de-S) is basically decarbonized in a slag-free state, and +
As mentioned in iii, under normal top-blown oxygen conditions (L/LO≧0.
8 Here, at Lo: still image bath depth), spinning or dust loss increases.

In order to suppress this, a method has been proposed that uses the well-known blow blowing ζ-L/Lo≦0.2) in combination with bottom blow gas stirring. Conventionally, hard blows and soft I blows have been distinguished based on the size of L/Lo, but the inventors of the woodworks have found that it is better to use L when considering iron yield or secondary combustion.

The absolute value of L is 80° for conventional bar I/blow.
1,000mm, whereas the softbutton here
l-(7)L is so(7)I/2- ]/10(7) 8
It is about 0 to 400 mm.

Regarding bottom-blown scum, we conducted an experiment to determine the minimum amount necessary for the amount of blown oxygen scum based on inert scum (Ar scum, N, scum). It has been found that 4% or more of 1- is preferable.

In other words, it is preferable that the required bottom-blown waste amount ratio be within a range depending on the dent depth L due to the top-blown oxygen jet.

The reason for the numerical limitation will be described in detail in the examples, but this bottom blow/
-1, this is because the spitting loss becomes large and the inferiority of the molten steel decreases significantly when it is less than 1.

In particular, the required amount of bottom blowing gas is effective in the initial stage of blowing, that is, the initial 1/3 of the total blowing period of 1) 11, or the period of about 6 minutes until the melon melts, and thereafter. If the bottom blow/top blow ratio is 2%, it is 1.min.

Also, as a bottom-blowing gas, the second explanation is based on inert gas.
However, when active scum is used, the required amount of bottom-blowing gas can be determined in inverse proportion to the number of moles decomposed.

In addition, in "-", L is based on the following formula (References: [Published by Kogyo Shinbunsha, written by Kiyoshi Seyo, Une Metallurgical Reaction-1 Science, 2nd edition, p, aθ to θ7).

1, = L ・e++p (-0,78h/L 1.)
h L h= 83.0 (kFoz /nd)' (However,
h: lance height from the hot water surface, Lh: glue when h=o, Fo2/oxygen flow rate, d: nozzle diameter, n: number of nozzles, k: coefficient depending on oxygen injection angle. ) In addition, -1- In converting blown oxygen into a soft glow, it is effective to use a porous wide-angle lance that can increase the flash point area ratio, that is, the collision coverage area ratio of secondary oxygen to the surface area of the static bath. Already filed by the inventors (Patent application 1982-
58729) can be used.

Next, examples of the present invention will be described.

The steelmaking furnace in which the example tests were conducted is a normal top-bottom blowing converter (nominal 80t).
The hot metal was pre-treated using a known method.

Test conditions and results are shown in Table 1. As a comparative example, one which deviates from the bottom blowing/4-softening of the method of the present invention is shown.

The following can be seen from Table 1.

The smaller L is, the better the molten steel yield is -■-, but L≦100
In mm, the value has reached a plateau.

Moreover, as can be seen from the comparative example, the heat that deviates from the appropriate IF bottom blowing/upper Europeanization has a spitting cross, and the molten steel yield is greatly reduced. This is also due to spitting or severe lack of coolant.

Effects of the Invention] - It can be seen that according to the method of the present invention, optimum slackless decarburization can be performed and a high yield of molten steel can be ensured.

Claims (1)

[Claims] In a method for decarburizing hot metal that has been previously subjected to de-SI, de-P, and de-S treatments, top-blown oxygen is supplied and bottom-blown scum is supplied; Volume ratio of gas and top-blown oxygen (
Hereinafter, it will be referred to as Futabuki Rin. ) is adjusted as follows according to the depth L (mm) of the dent formed on the surface of the molten iron bath by the double blowing gas. However, when L is 90 Mineko, the bottom blow/J-blow ratio is 4.
% or more, and when L is 30 to 140, the bottom blow/to blow ratio is set to 3% or more and 1. When L is 140a, the bottom blow/low blow ratio is set to 2% or more to 1.