JPS58117815A - Steel making method by converter - Google Patents

Abstract

PURPOSE:To improve a stirring effect and to operate a converter with good efficiency in a converter wherein top blowing and bottom blowing are used in combination by providing a bottom nozzle having a specific angle of upward inclination in a position deviated from the furnace center and giving turning motion to the molten metal. CONSTITUTION:Oxygen is blown through a top blowing lance 1 into the steel bath 4 in a converter, and a gas or a gas and a slag forming agent are blown through a bottom nozzle 6. The nozzle 6 is of double pipe tuyere construction consisting of an inside pipe 7 and an outside pipe 8, and has 30-70 deg. angle alpha of upwad inclination with respect to the furnace bottom. Said nozzle is installed in the position deviated from the furnace center and one or plural pieces of the nozzles are used. Thus the molten metal 4 is turned and moved in the furnace by the bottom blowing from the nozzles 6, and the time for mixing uniformly is reduced considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for refining hot metal in an oxygen top-blowing converter using a combination of oxygen top-blowing by a lance and bottom-blowing by a companion bottom nozzle installed at an angle to the bottom of the furnace. Regarding the law.

The oxygen top-blown converter method is popular, in which hot metal, scrap, auxiliary materials, etc. are charged into a furnace and refined by blowing oxygen onto the bath surface using a lance, but a major problem with this refining method is that This is a decrease in stirring of molten steel.

In other words, the stirring of the molten metal in this top-blown refining is mainly caused by carbon 9 oxide gas generated by the reaction between carbon p and oxygen in the molten steel, but in the early and middle stages of refining where there are many 9-containing ridges, this carbon 9 oxide Even if the stirring by the scum can be performed effectively, at the final stage of refining (C (1st and 2nd stage)) where the 9 content is low, the amount of -carbon oxide gas generated decreases, and the stirring becomes weaker accordingly.

When this stirring decreases, the oxygen efficiency decreases, and the decarburization rate also decreases. Also, due to this decrease in stirring power,
The molten steel becomes overoxidized near the flash point of the top-blown oxygen, and the iron oxide content in the slag increases significantly in this low carbon range.At the same time, the oxygen level in the molten steel also increases rapidly, causing problems in many buildings. For example, slag containing iron (hereinafter %T
, Fe) increases, leading to resource loss due to a decrease in the durability of large furnace wall materials and a decrease in the yield of valuable metals such as Fe and Mn. Various problems arise, such as quality deterioration due to contamination.

For this reason, other stirring means have been proposed to assist in stirring the molten metal in the oxygen top-blown converter method. For example, methods have been proposed in which an electromagnetic stirrer is installed near the bottom of the furnace, or a top blowing lance is rotated or swirled to assist in stirring the molten metal. However, the former method requires bulky equipment and VC is not very effective, so it is rarely used, and the latter method can strengthen the stirring of the slag, but it does not reach the level of strengthening the stirring of the steel bath. do not have.

On the other hand, an oxygen top-blowing refining method using both top-blowing and bottom-blowing is disclosed, for example, in JP-A No. 55-65313 and JP-A-55-1999.
This method has been proposed in Japanese Patent Application Laid-open No. 138015, Japanese Patent Application Laid-Open No. 158209-1982, and Japanese Patent Application Laid-Open No. 161014-1987. Since the methods described in these publications use bottom blowing in addition to top blowing, agitation is strengthened compared to the case of top blowing alone, and it is thought that they exhibit a certain effect.

However, in the methods and converter structures described in these publications, the use of a straight nozzle (perpendicular to the furnace bottom) is disclosed as the bottom blowing nozzle. The injected fluid rises vertically throughout the bath. Although the stirring of the hot water is strengthened to some extent by this upward flow of the blown fluid,
A large amount of blown gas is required to obtain uniform mixing, which can be said to be sufficient in model experiments (described later) by the present inventors.

The present invention was made with the aim of further improving this, and compared to the case of using the above-mentioned known straight bottom blowing nozzle, the uniform mixing time can be greatly shortened even with the same gas flow rate, and the stirring effect is large. We have devised an oxygen top-blown converter steel manufacturing method that allows extremely efficient converter operation. That is, the present invention is a converter steel manufacturing method that uses a combination of top blowing of oxygen using a lance and bottom blowing of gas or gas and slag forming agent from a bottom nozzle to the molten metal in the furnace, and the bottom blowing is carried out. As a nozzle for this purpose, it is installed at the bottom of the furnace at an angle of upward inclination of 30 to 70 degrees with respect to the bottom surface of the furnace, and is located eccentrically from the core, and the direction of inclination is directed in the direction that imparts rotational motion to the molten metal. One or more furnace bottom nozzles are used, and the molten metal is rotated (
It is characterized by rotational) movement. During refining, the fluid injected from the furnace bottom nozzle is oxygen alone, oxygen and slag-forming material, oxygen and slag-forming material, and hydrocarbons or inert gas as cooling gas, or oxygen and hydrocarbons. Alternatively, an inert gas is used, and air and an inert gas are used during hot metal charging or tapping.

The method of the present invention will be specifically explained below with reference to the drawings.

Figure 1 shows an example of a converter for carrying out the method of the present invention, in which 1 is a top blowing lance, 2 is a furnace wall, 3 is a furnace bottom, 4 is a steel bath, and 5 is a slag furnace. It shows.

A furnace bottom nozzle 6 that penetrates the furnace bottom 3 at the furnace bottom 3vc
is provided. In the illustrated case, the hearth bottom nozzle 6 has a double control structure and consists of an inner tube 7 and an outer tube 8. However, it may also be of single tube construction. In the illustrated example, the hearth nozzle 6 is provided in the hearth with an upward inclination angle of approximately 45° relative to the hearth bottom surface, and the position of the injection port (located on the hearth bottom surface) of the hearth bottom nozzle 6 is is eccentric to the reactor core. The inclination direction of this furnace bottom nozzle 6 is directed in such a direction that the molten steel 4 is rotated by the jet of fluid from this nozzle 6.

Inner tube 7 and outer tube 8 are each connected to a source of blowing material via a flow meter (not shown).

FIG. 2 shows four furnace bottom nozzles 6 according to the invention at a furnace bottom 4V.
The bottom nozzles 6 are arranged at equal intervals (1/2r) about half the distance (r) from the core C to the outer periphery RIC of the bottom 4. The inclination angles α shown in Fig. 1 each have approximately 45 degrees. , its inclination direction is uniformly directed toward other adjacent furnace bottom nozzles. Therefore, the fluid (including powder flow) blown into the molten steel from each furnace bottom nozzle 6 is as shown in FIG. It is ejected obliquely upward in the direction indicated by the arrow, imparting a swirling (rotation) motion to the molten steel around the core C. Figure 3 shows
This diagram schematically shows the swirling motion of molten steel. This method of imparting swirling (rotational) motion to molten steel and refining with top blowing by top blowing lance IVc is thought to be unprecedented, but imparting swirling motion to molten steel in this way improves stirring efficiency. When the slag 4 becomes extremely good and the lance 1 is located at the center of rotation, the slag 4 easily moves from the fire point to the furnace wall 2 side, and good contact between the molten steel 4 and the top-blown oxygen flow is achieved. The decarburization reaction is promoted under favorable conditions.

Figure 4 shows the model experiment results;
Regarding the case where four hearth bottom nozzles are arranged in the position shown in Figure 3 (A in Figure 4) and the case where the four hearth bottom nozzles are arranged in the positional relationship as shown in Figure 4 B. , the upward inclination angle (α in Figure 1) of each is varied, and the uniform mixing time (τ
This study investigated the effects of VC. The time (τ) until uniform mixing is obtained when the fluid flow rate is kept constant is shown as a ratio compared to the case of only top blowing. It is shown that when the angle is tilted at 60 to 70 degrees, the uniform mixing time is halved compared to the conventional case where the angle is vertical (90 degrees).

Actual operation i/CU, this uniform mixing time (τ) d60~4
It was found that 0 seconds can be shortened even with the same bottom blowing flow rate compared to the conventional vertical furnace bottom nozzle (90°) VC. Further, even if the bottom blowing gas flow rate is reduced, the uniform mixing time can be shortened. For example, if the bottom blowing gas flow rate is [1.1 to 0.
It has become clear that even with a low amount such as 2 (NTVmin-Ton), the uniform mixing time can still be shortened.

However, even if an angle of inclination is provided in the arrangement as shown in FIG. 4B, the effect will not be reduced because the inclination is not in a direction that would give a turning motion.

The method of the present invention will be explained below using Example VC.

Example 1 Nozzle arrangement according to the invention shown in FIG. 2 (4-nozzle symmetrical type,
The following main raw materials and auxiliary raw materials were charged into a furnace with a nozzle angle of 45°, and 250 N7I? /min oxygen top blow and 1
Oxygen bottom blowing is performed at ON1f/min, and the end point is 0.0.
Refining steel up to 2-0.15%.

Main raw material Hot metal 85 tons Scrap 15 tons Auxiliary raw materials Quicklime 5 tons Fluorite 1 ton Sintered ore 0.9 Door pellets 0.2 tons Comparative example 1 Same nozzle arrangement as shown in Figure 2 with nozzle angle of 90° (straight). Using a furnace with
And the raw material formulation was refined under the same conditions as in Example 1.

Comparative Example 2 Top blowing alone under the same conditions as Example 1 (oxygen flow rate 250 N)
@/min) Refine your friends. □The blowing results in these Examples and Comparative Examples 1.2 are shown in Figures 5 to 8.
Shown in the figure. That is, Fig. 5 shows (%T, Fθ) in the slag at the end of the blowout, and vc in Fig. 6 shows the value at the time of the end of the blowout (7).
(%T, Fe) (%P), Fig. 7 shows 1Jc) and [%Mn] when the blow is stopped, and Fig. 8 shows [1] when the blow is stopped.
and Free O, respectively.

From Figure 5, the blowing results are shown in the case of oxygen top blowing alone (Comparative Example 2), the case of bottom blowing combined with 90° nozzle angle (Comparative Example 1), and the case of bottom blowing with a nozzle angle of 45°. It can be seen that (%T, Fe) after blowing decreases in the order of combined use (in the present invention).

In the case of the present invention, after blow-stopping [%C) = 0.06 (
%T, Fel is around 10cm, 15% of Comparative Example 2~
25%, compared to 10% to 17% in Comparative Example 1 (%T, Fe
), which shows that the blowing method according to the present invention is an excellent method. The bottom blowing gas flow rate is according to the present invention,
Although the comparative example is the same as 10 Nm/min, (%T, Fθ) is 7% lower in the present invention, and the effect of the nozzle angle is remarkable.

FIG. 6 shows the relationship between (%P) and (%T, Fe) at the time of blow-off. In the present invention, although (%T, Fe) is reduced, the value of blowstop (%P) is within a range that fully satisfies the component specification values. Further, as shown in FIG. 7, the value of blow stop [%Mn] is the highest in the case of the present invention, and a significant improvement in the Mn yield has been achieved.

As shown in Figure 8, the level of Free O in the steel bath has also decreased, resulting in benefits such as improved alloy yield.

As is clear from the above examples, the blowing method according to the present invention prevents overoxidation of the slag and steel bath, and provides good metallurgical processing characteristics, compared to the conventional oxygen top-blown converter method mentioned at the beginning. It is clear that the various shortcomings can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing an example of a converter for carrying out the method of the present invention, FIG. 2 is a plan view showing the bottom nozzle arrangement according to the present invention, and FIG. A conceptual diagram showing the rotational behavior of molten metal by the furnace bottom nozzle, Figure 4 is a relationship diagram between the inclination angle (B) of the furnace bottom nozzle and the uniform mixing time (τ), Figures 5 to 8
The figure shows the results of the example, and Figure 5 shows [C] and (
Figure 6 shows the relationship between (%T, Fe) and [
%P], FIG. 7 is a diagram showing the relationship between [%C] and [%Mn 1, and FIG. 8 is a diagram showing the relationship between C%C'] and F, ree O. 1... Lance 3... Hearth bottom 6... Hearth bottom nozzle α... Inclination angle Applicant Nissin Steel Co., Ltd. Agent Kazu 1) Ken Yarn ball: 1 1, -1 □+---- Nozzle inclination angle (α) Nozzle inclination angle (α) Fig. 5 [%C) Ept Fig. 6 [T, Fθ] F, pt

Claims (1)

[Claims] In the converter steel manufacturing method, which uses a combination of top blowing of oxygen using a lance to the molten metal in the furnace and bottom blowing of gas or gas and slag forming agent from a bottom nozzle, the furnace is used as a nozzle for carrying out the bottom blowing. One or more units installed at the bottom of the furnace at an eccentric position relative to the core with an upward inclination angle of 30 to 70° with respect to the bottom surface, and whose inclination direction is oriented in a direction that imparts rotational motion to the molten metal. A converter steel manufacturing method characterized by using a furnace bottom nozzle and rotating the molten metal in the furnace by this bottom blowing.