JPH04285109A - Converter refining method - Google Patents

Abstract

PURPOSE:To improve the efficiency of converter refining by specifying the pressure at the main of upward blow oxygen, the diameter of an upward blow lance nozzle and the flow rate of oxygen. CONSTITUTION:In converter refining where decarburization, dephosphorization, elevating temp., etc., are carried out by blowing oxygen to molten iron and molten steel in a converter through an upward blow lance, the pressure P0 at the main of upward blow oxygen and the diameters D1 D2 of upward blow lance nozzles are controlled to a proper value, refining is performed so that the flow rate of oxygen may be commensurate with the rate of decarburization. Thereby the efficiency of decarburization can be improved and slag and the concentration of oxygen in steel can be decreased without causing metal to stick to the nozzles to prevent trouble in blow smelting oxygen converter steelmaking.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a converter scouring method, in particular,
The present invention relates to a converter refining method in which oxygen is blown into hot metal or molten steel in a converter through a top blowing lance to decarburize, dephosphorize, raise temperature, etc.

0002

BACKGROUND OF THE INVENTION At present, a converter is most commonly used as a refining furnace for producing steel from hot metal produced in a blast furnace. In particular, the top-blown converter smelting method is a smelting method that efficiently performs refining reactions such as decarburization and dephosphorization, as well as temperature increases, by blowing a supersonic oxygen jet onto hot metal or molten steel in the furnace through a top-blowing lance. be.

[0003] A Laval nozzle is generally used for the top blowing lance of a converter. FIG. 1 schematically shows a horizontal cross section of a Laval nozzle. This Laval nozzle 10 consists of a throat section 12 and a flared section 14, and oxygen from an external oxygen supply source (not shown) is supplied as indicated by the arrow in the figure. It is sprayed at supersonic speed through the nozzle port 16 toward the surface of the molten steel in the furnace. At this time, in order to efficiently blow oxygen into the converter, it is necessary to set the nozzle throat diameter D1, outlet diameter D2, oxygen source pressure P0, and furnace atmospheric pressure P2 to satisfy the following formula (1). It is said that (“Iron and Steel”
62 (1976) p. 1795)

0004

[Case 2]

Generally, P2 is 1 atm, so once the nozzle shape (D1, D2) is determined, the oxygen source pressure P0 is almost uniquely determined from equation (1). With a normal nozzle shape, the oxygen source pressure P0 is approximately 5 to 11 atm (5 to
11kg/cm2).

[0006] Therefore, normally, top-blown O2 is used in converters.
The variable range of flow rate is very small, ±30% of the designed oxygen flow rate.
That's about it. In particular, it has been difficult to reduce the amount of oxygen supplied by lowering P0.

On the other hand, FIG. 2 is a graph schematically showing the fluctuations in the decarburization rate during the refining period. Because of the large fluctuations, there were problems such as a decrease in oxygen efficiency and an increase in the amount of oxygen in slag and molten steel during the initial and final stages of refining.

[0008]

[Problems to be Solved by the Invention] An object of the present invention is to provide a converter refining method that solves the above-mentioned problems, reduces [O] in steel, and improves the yield of Fe and Mn. It is.

Another object of the present invention is to provide a converter refining method that can improve the oxygen efficiency particularly at the initial stage and final stage of refining by widening the variable range of the oxygen flow rate as much as possible. be.

0010

[Means for Solving the Problems] In order to achieve the above object, the present inventor has aimed to improve the oxygen efficiency, especially in the initial and final stages of refining, and to eliminate slag and molten steel by widening the variable range of the oxygen flow rate of the top blowing lance. In order to reduce the amount of oxygen inside,
As a result of various studies, we discovered the following two facts.

(i) A nozzle that satisfies the above equation (1) at a certain original oxygen pressure Po (for example, 10 kg/cm2.G) is operated at a pressure lower than Po (for example, 6 kg/cm2.G).
cm2・G), jet instability and problems with metal attachment inside the nozzle are likely to occur;
), the above-mentioned troubles are unlikely to occur.

(ii) Very low oxygen source pressure (eg 4
When top-blowing oxygen at a rate of 1 kg/cm2・G), trouble often occurs with metal adhesion inside the nozzle, even if the nozzle satisfies equation (1).

Based on these facts, the present inventor developed a high-pressure Po (13 kg/cm2.
G or higher), the inventors have discovered that if the nozzle shape is set to an appropriate value, the variable range of top-blown oxygen can be widened without any trouble, and the present invention has been completed.

[0014] Here, the present invention provides that, in converter refining in which oxygen is blown into hot metal or molten steel in a converter through a top blowing lance, the original pressure Po of oxygen blown from the top blowing lance is kept at 60% of the total refining time. 13kg/cm2・G over %
This is a converter refining method characterized by the above.

According to a preferred embodiment of the present invention, the ratio D1/D2 of the throat diameter D1 and the outlet diameter D2 of the Laval nozzle of the top blowing lance is determined so as to satisfy the following formula.

[0016]

[Chemical formula 3]

[0017]

[Operation] The structure and operation of the present invention will be explained.

In the present invention, the oxygen source pressure P0 is set to 13 kg.
/cm2・G or more is because if it is less than that, the oxygen source pressure will be low when the oxygen flow rate is reduced, causing trouble with attaching the metal to the nozzle, and as a result, the variable range of the oxygen flow rate will be narrow. This is because it will become.

In particular, although there is no upper limit to the original oxygen pressure, in general, if it exceeds 25 kg/cm 2 ·G, it will require major modification of the equipment, which is not preferable from an economic standpoint, as it will lead to higher costs.

According to a preferred embodiment of the present invention, the lower limit of the R value defined below is set to 1.1, and the R value is an index representing the stability of a supersonic jet, and its value is 1.
If it is less than 1, the jet tends to become unstable when the oxygen flow rate is lowered, and as a result, the variable range of the flow rate becomes narrower.On the other hand, the upper limit of the R value is set to 1.5 because
This is because if the value exceeds 1.5, the distance from the proper shape of the nozzle shown by equation (1) increases, resulting in a peeling phenomenon and the jet becoming unstable.

[0021]

[C4]

FIG. 3 is a diagram schematically explaining the above-mentioned peeling phenomenon, and shows the oxygen jet 18 from the nozzle tip.
This refers to a state in which the oxygen jet 18 appears to have peeled off from the nozzle inner surface 19 and is blown out in a constricted state from the middle. If such a peeled part 20 is observed, the flow of the oxygen jet 18 becomes extremely unstable.

[0023] When operating according to the above-mentioned formula (1), the R value is 1. At this time, the oxygen jet becomes most stable.

In the present invention, the oxygen source pressure P0 is set to 13 kg/
The operation at cm2·G or more is maintained for 60% or more of the total refining time, but if the refining time is shorter than that, the oxygen flow rate will decrease and the productivity of the converter will decrease.

When converter operation is divided into the initial, middle, and final stages of blowing, according to a preferred embodiment of the present invention, the above-mentioned high oxygen source pressure is When blowing is carried out, blowing with high oxygen efficiency becomes possible, and the yield of Mn and Fe is greatly improved.

[0026]

[Example] The present invention will be explained in detail with reference to Examples.

Example 1 250T of hot metal was charged into a converter, and 1 ton of Ar was applied from the bottom blowing nozzle.
While blowing at 000Nm3/hr, from the top blowing lance shown in Fig. 1, the lance shape and blowing conditions shown in Table 1 were used.
Refined for a minute.

[0028] Molten steel in the method of the present invention and Comparative Examples 1 to 3 [
%C] = 0.04%, the oxygen in the molten steel is 42
0ppm, 450ppm, 550ppm, 510ppm
The method of the present invention had the lowest result. The less oxygen there is in molten steel, the more the yield of Mn and Fe can be improved.

Further, in Comparative Example 1, metal adhesion was observed inside the nozzle of the top blowing lance.

Example 2 250T of hot metal was charged into a converter and refined under the same bottom blowing conditions as in Example 1, with the lance shape and blowing conditions shown in Table 1.

[%C]=0.
Oxygen in molten steel at 0.04% is 405 ppm and 4%, respectively.
It was 35 ppm. Furthermore, in the comparative example, since the R value was less than 1.1, metal adhesion was observed inside the nozzle of the top blowing lance.

[0032]

[Table 1]

[0033]

Effects of the Invention Since the present invention is configured as described above, the oxygen flow rate can be decarburized while controlling the original pressure Po of top-blown oxygen and the nozzle diameters D1 and D2 of the top-blowing lance to appropriate values. By setting a value commensurate with the speed, it is possible to improve decarburization oxygen efficiency and reduce the oxygen concentration in slag and steel without causing metal adhesion to the nozzle, which is extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of a Laval nozzle used in the present invention.

FIG. 2 is a graph schematically showing the change in decarburization rate over the entire period of converter refining.

FIG. 3 is a schematic illustration of a jet separation phenomenon.

[Explanation of symbols]

Claims (2)

[Claims] Claim 1: In converter refining by blowing oxygen into hot metal or molten steel in a converter through a top blowing lance, the original pressure Po of oxygen blown from the top blowing lance is set to 60% of the total refining time.
% or more and 13 kg/cm2・G or more. 2. The converter refining method according to claim 1, wherein the ratio D1/D2 of the throat diameter D1 and the outlet diameter D2 of the Laval nozzle of the top blowing lance is determined to satisfy the following formula. [Chemical formula 1]