JPS59166617A - Refining of molten steel containing chromium - Google Patents

Abstract

PURPOSE:To control the generated amount or the splash height above the surface of steel bath at a low level, by a method wherein the mixture of O2 and inert gas is blown into from the lower surface of molten bath and further O2 is blown into by controlling the height or/and the O2 amount of top-blown lance depending on the transition of C amount in molten bath. CONSTITUTION:In decarburizing the carbon in molten steel 4 containing chromium with a refining vessel 10, the mixed gas of inert gas and O2 are bottom-blown from a tuyere 11 and O2 14 is top-blown from a top-blown lance 12 together therewith. In that case, the molten steel is refined by controlling both on either of the lance height from the molten steel surface of lance 12 and the top-blown O2 amount depending upon the transition of the C amount in molten steel containing chromium, that is, the proceeding degree of decarburization reaction in molten steel containing chromium. That is, the splash generated from the surface of molten bath in refining above-mentioned, the splash due to bottom-blow is effectively controlled by adjusting the height of lance 12 or/and the top-blown amount. Thus, by raising the O2 blow amount without enlarging the vessel volume compared with the molten steel amount, the decarburization speed is accelerated and simultaneously the heat of formation in decarburizing reaction according to the blow-in of O2 can be effectively utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining chromium-containing molten steel, and more particularly, the present invention relates to a method for refining chromium-containing molten steel, and more particularly, it increases the decarburization rate by increasing the amount of oxygen blown into the furnace without increasing the capacity of the furnace relative to the amount of molten steel. The present invention relates to a method for refining chromium-containing molten steel that can effectively utilize the heat generated during decarburization reaction.

Currently, the AOD method is widely used as a decarburization process for chromium-containing molten steel such as stainless steel.

However, in order to increase the decarburization rate and improve work efficiency using the AOD method, there are equipment problems such as an increase in the furnace capacity, and it is desired to develop a refining method that does not have these problems.

That is, FIG. 1 is a sectional view of an example of a refining vessel for carrying out the AOD method, and a double tuyere 2 is provided at the bottom of this vessel 1. In the AOD method, a mixed gas 3 of inert gas and oxygen is bottom-blown into the chromium-containing solution @ 4 from the tuyere 2 to lower the P co value that regulates the carbon-chromium equilibrium condition.

As a result, decarburization is performed without preferentially oxidizing chromium (hereinafter referred to as Cr). After the completion of decarburization, further finishing refining is carried out. At this time, VC adds a reducing agent such as silicon, a bath agent such as 1 lime, and fluorite, and blows only inert gas through the 0 tuyere 2 to form molten steel. Refining is performed by stirring the slag and cooling.

this In addition, in the 7-A OD method, carbon in molten steel (hereinafter referred to as carbon) is used.

It's called C. ) in the high C region (for example, in molten steel with a Cr content of about 18%, C0.4% or more).

The decarburization rate will increase in proportion to the amount of oxygen blown.

Therefore, in order to shorten the refining time σ) and improve work efficiency, it is preferable to blow a large amount of oxygen to increase the decarburization rate σ).

However, in reality, an increase in the amount of oxygen blown from the bottom of the furnace σ) not only leads to melting of the refractory on the furnace wall surface, but also increases the amount of splash generated from the steel bath surface. becomes higher.

In order to cope with this, it is necessary to increase the capacity of the refining container σ). For this reason, the required amount of refractories σ) for furnace construction θ) increases, and in addition to this, the amount of refractory erosion increases, resulting in a significant increase in the unit power of refractories.

From this point (σ), the AOD method usually has a value of 0.7 to 1? "l+
A refining vessel h designed to have a flow rate of approximately 02/l/min is used, and it is difficult to increase the amount of blown oxygen due to equipment constraints.

With the present invention, even under the equipment constraints such as σ) above, the amount of oxygen blown can be reduced to 1, for example, 2Nn? 02/l/min, and the amount and height of splash generated from the steel bath surface can be suppressed.

Furthermore, we propose a method for refining Cr-containing molten steel that can effectively utilize the heat generated during the decarburization reaction.

That is, one method of the present invention is to blow a mixed gas of oxygen and inert gas or oxygen and inert gas from the bottom of the steel bath, and to blow oxygen from the top blowing lance at the top of the furnace to refine chromium-containing molten steel.

This top-blowing lance is configured to be able to move up and down, and is characterized in that one or both of the height of the top-blowing lance and the amount of top-blowing oxygen are controlled in accordance with changes in the amount of carbon in the steel bath for refining.

Below, one method of the present invention will be explained in detail.

First, FIG. 2 is a sectional view of an example of a refining vessel in which the method of the present invention is carried out. A tuyere 11 is provided at the bottom of the refining vessel 10 in the same manner as shown in FIG. 1, but a top blowing lance 12 is provided at the top of the furnace.
When decarburizing C in the Cr-containing molten steel 4 in this refining vessel 101C, which can be raised and lowered by
A mixed gas 3 of inert gas and oxygen is blown from the bottom from the bottom, and at the same time, oxygen 14 is blown from the top from the top blowing lance 12. In this case, the height of the top blowing lance 12 from the molten steel surface is referred to as the lance height. ) and the amount of top-blown oxygen, or both or one of them, are controlled in accordance with the change in the amount of C in the Cr-containing molten steel, that is, the degree of progress of the decarburization reaction in the Cr-containing molten steel.

That is, splash is generated from the steel bath surface by the inertial energy of the bottom blowing gas 3 from the tuyere 11. However, since this σ) splash is suppressed by the downward energy of the oxygen jet from the top blowing lance 12,
With this oxygen jet, the height of the splash can be controlled, and the amount of oxygen can be increased even under equipment-limited conditions. In other words, by controlling the lance height and/or the amount of top-blown oxygen of the top-blowing lance 12, the oxygen momentum due to top-blowing can be controlled.1 For example, by increasing the top-blowing oxygen amount,
Alternatively, by lowering the lance height, the momentum of the top-blown oxygen can be increased, and the splash caused by the bottom-blown oxygen can be effectively controlled.

In addition, from the perspective of the refining reaction, the greater the momentum of the oxygen jet from the top blowing lance, the more conditions are met for so-called hard plow, and the efficiency of the decarburization reaction improves. On the other hand, if the momentum of the oxygen jet is low, this is a so-called soft pull condition.

Although the proportion of the top-blown oxygen reaching the steel bath surface is reduced, the CO gas produced and released by the decarburization reaction is effectively re-burned by this top-blown oxygen.

This re-combustion generates reaction heat according to the formula CO++0*→CO2, and the reaction heat is effectively transferred to the steel bath surface, raising the steel bath temperature and improving the decarburization reaction.

Furthermore, when controlling the lance height of the top blowing lance and the amount of top blowing oxygen according to changes in the amount of C in molten steel as described above, it is best to continuously change the conditions from so-called hard plow conditions to soft plow conditions. preferable.

Generally, the decarburization oxygen efficiency of Cr-containing molten steel depends on the amount of C in the molten steel. For example, the case where molten steel containing 18% Cr is decarburized by bottom blowing is shown in FIG. 3. As is clear from Figure 3, the decarburization oxygen efficiency decreases as the amount of σ)C in molten steel decreases, but the rate of decrease is relatively gradual in the high carbon region of CI 0% or more. When reaching the low carbon region of , C1.0% or less, the rate of decrease becomes remarkable, and in particular, the decarburization oxygen efficiency further decreases at C0640% or less.

In other words, in the case of bottom blowing treatment such as the AOD method, chromium oxide is generated near the siding during gas injection, and this chromium oxide reacts with carbon at the interface of rising gas bubbles in molten steel, resulting in progress of decarburization. do.

The decarburization oxygen efficiency at this time is determined by the balance between the amount of C transferred to the gas bubble interface and the amount of decarburization reaction on the gas bubble interface. Therefore, as the decarburization reaction progresses.

As the amount of C decreases, the balance is disrupted and the 61-minute oxidation reaction becomes predominant, and as a result, as the low C region approaches, the decarburization oxygen efficiency decreases as shown in FIG. When processing Cr-containing molten steel, it is preferable to set the lance height of the top blowing lance and the top blowing oxygen amount to an optimal range according to the amount of C in the molten steel.
, in the high carbon range of 0% or more, the lance conditions are so-called hard blow conditions, the lance height is lowered, and the amount of oxygen blown is increased to directly oxidize the C in the molten steel and to
Reburning of O is also carried out.

On the other hand, in the low carbon region of C1.0% or less.

Rather, it is preferable to carry out refining under conditions that mainly re-combust CO without causing direct oxidation of C in molten steel, that is, so-called soft blow conditions, by controlling the height of the top blowing lance and the amount of oxygen blown. Therefore, ideally, it is preferable to continuously change the conditions of the top blowing lance from hard blowing to soft blowing according to the amount of C in the steel bath.

Next, examples will be described.

First, 5us containing 18% Cr, 8% Ni, 2.5% C
-3Q4 55 tons of molten steel was decarburized by the method of the present invention, and for comparison, decarburized by bottom blowing σ) by the conventional method. Any of these σ) methods.

Table 1 shows the decarburization rate and Si consumption for reduction of metal oxides upon completion of refining for each method after decarburization to 40% CO.

In this case, both methods use a mixed gas of alkon and oxygen (0□/
At-=4/1) is bottom-blown and top-blown according to the method of the present invention, a straight lance with a diameter of 1 inch is used as the top-blowing lance and is configured to be movable up and down. In particular, the lance height is as follows: The starting point was 2000, and it was changed continuously so that it became 35001 Ml at the end point of C0.4%,
Furthermore, the amount of top-blown oxygen was varied as shown in Table 1 depending on the amount of C in the molten steel.

Table 1 shows that when decarburizing is carried out by continuously changing the conditions of the top blowing lance from nod blow to soft plow as the decarburization operation progresses, oxygen efficiency, decarburization speed, operation The time (decarburization time from 5% to 0.4% C) and Si basic unit are greatly improved, and the refining process can be stabilized.

As explained in detail above, the method of the present invention is a method in which oxygen is top-blown at the same time as bottom-blowing, and the conditions of this top-blowing are adjusted in accordance with the progress of decarburization refining of molten steel. Therefore, it is possible to increase the amount of oxygen supplied under equipment constraints, and the decarburization rate can be improved by this t'L. Furthermore, the CO gas generated can be completely re-combusted, and thermal efficiency can also be improved.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a refining vessel used in the conventional AOD method, Fig. 2 is a cross-sectional view of an example of a refining vessel in which the method of the present invention is carried out, and Fig. 3 is a cross-sectional view of a refining vessel used in the conventional AOD method. It is a graph showing the relationship between the amount of C in molten steel and decarburization oxygen efficiency. Code 1: Refining vessel 2: Double tuyere 3: Mixed gas 4: Cr-containing molten steel 10: Refining vessel 11...Tuyere 12...Top blow lance 13...Lance lifting device 14...Oxygen patent applicant Nippon Yakin Kogyo Co., Ltd. Representative patent attorney Matsushita Lawyer Yoshikatsu Fumio Soejima Figure 7 Ditch? Figure 2 Lead Figure 3 Each Ginchu 9C end

Claims (1)

[Claims] In an out-of-furnace refining method for chromium-containing molten steel, a mixed gas of oxygen and inert gas or oxygen and inert gas is blown from the bottom of the steel bath, and oxygen is blown into the furnace from the top blowing lance at the top of the furnace to refine chromium-containing molten steel. When refining steel, the top-blowing lance is configured to be able to move up and down, and one or both of the height of the top-blowing lance above the molten copper surface and the amount of top-blowing oxygen can be adjusted according to changes in the amount of carbon in the steel bath. A method for refining chromium-containing molten steel characterized by controlled refining.