JPS63195206A - Melting reduction method for chromium oxide - Google Patents

Abstract

PURPOSE:To execute decarbonization of molten iron and reduction of Cr2O3 in molten slag at the same time and at quick reaction velocity, by supplying lump coke having the specific size to molten slag surface except firing point by top blowing oxygen at the specific velocity at the time of adding Cr by Cr ore into the molten iron in the top and bottom blowing converter. CONSTITUTION:At the time of producing a stainless steel in the top and bottom blowing converter, the Cr ore is added in the molten slag on the molten iron surface in the converter, to contain Cr2O3 in the molten slag. Under this condition, the oxygen gas from a top blowing lance is blown at low pressure, the lump coke having 5-50mm size is charged at the position except the firing point by oxygen jet at 0.1-0.5F(kg/ton.hr) velocity to the oxygen supplying velocity F(Nm<3>/ton-hr), while bringing the oxygen into no contact with the molten iron surface. By reduction reaction of the lump coke with the Cr2O3 in the molten slag, Cr is contained in the molten slag and also by injecting the oxygen from the bottom blowing tuyere, the oxidized decarbonizing reaction of the molten iron is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to the melting and reduction of chromium ore in a top-bottom blowing converter.

(Prior art) A smelting reduction method of chromium ore using a top-bottom blowing converter type refining vessel is described, for example, in Tetsu to Hagane, 70 (1984), 511.
As shown in Figure 6, this is a technology that is already widely used.

In order to carry out this method efficiently, it is necessary to maintain a temperature of 1550° C. or higher and to satisfy the following four points at the same time.

1. Mix carbonaceous material into a large amount of slag to promote reduction of chromium oxide at the slag-carbonaceous interface.

2. The oxidizing gas supplied from the top blowing lance does not collide directly with the steel bath, but is soft blown to burn the carbonaceous material in the slag.

3. N20° and Mg contained in the chromium ore input
Flux is added and diluted so that the total amount of O in the slag is about 40% or less.

4. Stir the steel bath and slag with bottom-blown gas.

Of these, the oxidation reaction of C, which supplies heat due to factor 2, is performed above the slag phase, and by separating the location from the reduction reaction of chromium oxide that occurs inside the slag phase, the oxidation reaction in the same container can be carried out in the same container. This makes it possible for the reduction reaction to proceed simultaneously. However, since the oxidizing gas and the steel bath do not react directly, decarburization of the steel bath cannot be expected, and since carbonaceous material must always be present in the slag, the C in the steel bath always remains at a saturated concentration. It will remain at . Therefore, for example, when manufacturing stainless steel, it is necessary to remove the slag after melting and reduction, and then perform decarburization equivalent to normal converter blowing, which takes a long time and hinders conversion to CC. This may cause problems such as To overcome this, for example, iron and steel, 7
Smelting reduction using C-unsaturated hot metal has been attempted as shown in N1985), 5142, but according to experimental results, the reduction rate with unsaturated C hot metal is lower than that with saturated C hot metal or carbonaceous material. Much slower, especially C in hot metal
It has been revealed that this difference becomes extremely large when the r concentration is 5% or more. Therefore, when decarburizing hot metal, C becomes unsaturated and the carbonaceous material in the slag also disappears, so the reduction rate of Cr decreases.On the other hand, in order to increase the reduction rate, carbonaceous material is required in the slag, so the hot metal A contradictory problem arises in that C becomes saturated and decarburization cannot be carried out at the same time.

(Problems to be Solved by the Invention) The present invention enables decarburization of a steel bath and reductive dissolution of Cr oxides to be performed simultaneously and at a high speed, and continuous decarburization and refining by suppressing the saturation of C in the bath. The purpose of the present invention is to provide a dissolution reduction method that can shorten the process and increase the yield.

(Means for solving the problem) The present invention has a lance that supplies oxidizing gas upward,
When chromium ore is melted and reduced in a refining device that has tuyeres that supply stirring gas to the bottom of the furnace, lump carbonaceous material with a diameter of 5 to 50 m is heated at an oxygen supply rate F (N cd
/ (ton-Hr) ) 0.1F to 0.5
This is a method for dissolving and reducing chromium oxide, which is characterized in that an oxygen jet is supplied falling at a rate of F (ktz/(ton - Hr)) to a location other than the hot spot where it collides with the steel bath surface.

As a result of numerous experiments conducted by the present inventors, this method has shown that even if C in the hot metal is unsaturated, as long as carbonaceous material is present in the slag, the reduction rate of Cr is high. This is based on the discovery that the reduction reaction can proceed sufficiently even during the time it takes to dissolve in a steel bath.

In order to put this principle into practice, it is essential to suspend the charged carbon material in the slag without burning it due to the oxidizing gas from the top blowing and the slag, and to do this, the size of the carbon material must be 5fi. In addition to making the diameter above, it is necessary to add the oxygen to a place other than the surface where the oxygen jet collides with the steel bath surface, that is, the so-called ignition point. However, increasing the size of the carbon material causes a reduction reaction to occur at the slag-carbon material interface, resulting in a reduction in the reaction rate.

Therefore, as a result of considering a method to maintain a high reduction reaction rate, it was found that when the diameter of the carbon material is in the form of a lump, the diameter is 50 or less.
It turned out to be necessary. In addition, as a practical requirement, in order to increase the reduction rate, it is necessary to keep the temperature high because the activation energy is as large as approximately 50 car / 1 aol, but at temperatures above 1600 °C, the refractory will melt. is remarkable, and the reduction rate itself is low below 1450°C, so a range of 1450 to 1600°C is required.

On the other hand, in order to increase the reduction rate, it is necessary to dilute the concentration of Al2O3 and MgO contained in the chromium ore in the slag to quickly dissolve the chromium oxide spinel in the slag.

However, in the case of stainless steel, the melting point is lower than that of ferrochrome, so the reduction temperature can be lowered, but in the above temperature range, if the total of M2O and MgO in the slag exceeds 55%, the dissolution rate of spinel is very slow. If it is less than 30%, the amount of slag increases, resulting in a decrease in yield and destabilization of operation, so a range of 30 to 55% is required. Cab is an inexpensive flux used for this purpose.
5iO1 is considered, but CaO/SiO
It is necessary to set 2 to 0.5 to 1.5.

In addition, regarding the supply rate of carbonaceous material, in order to keep the steel bath saturated with C in conventional smelting reduction of chromium oxide, the total oxygen supply rate from above and below is set to F(Nn(/(ton-Hr)).
), considering the reaction of 2C+0z=2CO, 1
．． 07 F (kg/ (ton-Hr)) or more, or 0.54 F ( considering the reaction of C+0t=COt)
It was necessary to supply carbonaceous material of k+r/(ton-fir) or more according to the secondary combustion rate.

However, if the charging speed of this lumpy carbonaceous material is high, the amount suspended in the slag increases and the reduction reaction rate increases, but not all of the carbonaceous material is consumed in the reduction reaction, so other carbonaceous materials will eventually dissolve in the steel bath, so if the feeding rate of carbonaceous material is increased too much, the decarburization time itself will become longer.

As a condition that satisfies these two factors, the total oxygen supply rate (F, NrI?/(ton-Hr)) is set as the carbonaceous material supply rate.
) to 0.1 F to 0.5 F (kg/ (t
On-Hr)) is required, and as a result, the decarburization time remains at most 10 minutes longer than in the case where no carbon material is added, and a predetermined Cr reduction rate can be obtained.

The charging speed of this lump carbonaceous material is 0.1 F (kg/ (t)
On・Hr)) If the temperature is lower than 0.5F, the reduction of chromium will decrease rapidly, while if the temperature is higher than 0.5F, even if chromium reduction can be achieved, the C content in the bath will rise sharply, which will interfere with the decarburization refining process in the next step. Become.

The chromium ore used in the present invention includes not only general chromium ore with a Cr content of 10 to 50%, but also chromium ores enriched with prize ores, or reduced chromium ores such as pellets. This applies to products containing chromium oxide. Further, as the lump carbon material, simple lump coal or coke, or briquette formed by forming these or the like is used.

In addition, if the top blowing lance nozzle is a straight nozzle, except for the fire point of the oxygen jet that adds these, ±
Assuming that 0□ gas spreads at an angle of 12°, assume that the area other than the part calculated from the lance gap is assumed to be lower than the area calculated from the lance gap, and in the case of a Laval nozzle, the actual lance gap is lowered by the core length (Hc) calculated using the following formula. , ± from that position
0 at 12°! The area was defined as a region other than the area where gas is calculated to spread.

Hc = (3,52Poe 1.26) XdHere, POG is Fax = 0.456 (nd”)
Obtained from O,96X Poe.

Fo, ; Top blowing acid rate (Nrd/Hr) d; Throat system (Tsuru) n; Number of nozzles [Example] First, an example in which a small melting furnace is used will be shown. Figure 1 shows about 60kg of hot metal held at about 1550℃.
By adding kg of chromium ore, M, 03 and Mg in the slag
The sum of O concentrations is 35%, and CaO/5iOz is 1.
This is an investigation of the change in Cr concentration in the slag over time when CaO and Sing were mixed so that the concentration of Cr was 0.

Curve A is for the case where C in the hot metal is unsaturated;
It can be seen that the rate of decrease in Cr is significantly lower than curve B when C is saturated and curve C when C in the hot metal is saturated and about 400 g of coke with a diameter of 5 to 10 days is added to the slag. However, even if C is unsaturated, as shown in the curve, when a small amount of coke of about 50 g is added at a certain time, the CrflJ degree in the slag instantly decreases.

This is different from the conventional idea that carbonaceous material added to slag is immediately dissolved in a C-unsaturated steel bath and does not contribute to reduction. This shows that if the composition and temperature are maintained to keep the Cr oxide sufficiently molten, the reduction of the Cr oxide proceeds faster than the dissolution of the carbonaceous material into the steel bath.

In response to this, a test was conducted using a 100 ton scale top-bottom blowing converter. The slag and temperature conditions were the same as in the small-scale test. Cr ore has [%C] of 2 along with coke.
%, continuous upward addition was made. In the case of an actual furnace, oxygen is supplied from the top blowing lance for decarburization and heat supply, so when carbon material is supplied to the fire point, it immediately burns and produces Cr.
As shown in curve 1 of FIG. 2, the CrtJI degree in the steel did not increase. However, as shown in curve 2, when the carbonaceous material was added at a location other than the fire point using a special addition method, [%Cr] increased significantly, confirming that this method is effective.

Based on these results, 100 t under the operating conditions shown in Table 1.
7.5% Cr stainless steel was melted using hot metal of 1000 mL and compared with conventional operation. Here, the total oxygen delivery rate is 20
00ON rd/Hr, total Cr ore input amount is 25t
It's on.

As is clear from Table 1, the method of the present invention requires a total refining time of C
It can be seen that this method is clearly superior to the comparative example in that it can shorten the cycle time (approximately 40 minutes) for continuous casting of C and achieve a high chromium yield.

(Effects of the Invention) As described above, by using the method for dissolving and reducing chromium ore according to the present invention, chromium can be effectively reduced even with the minimum necessary carbon material, and (C) in the bath can be effectively reduced.
It is an extremely excellent dissolution reduction method because it suppresses the amount of carbon to an unsaturated region, thereby shortening the continuous de(C) refining, improving the yield, and reducing costs.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the results of a melt reduction test using a small melting furnace, and Fig. 2 is a diagram showing the experimental results using a 100 ton scale top-bottom blowing converter. In the explanatory diagram of the symbols, A is an example where the hot metal C is unsaturated. B is an example when hot metal C is saturated. C is an example when the hot metal C is saturated and carbonaceous material is always added. D is an example in which hot metal C is unsaturated, but carbonaceous material is added at 14 minutes. Curve 1 is an example when carbon material is supplied to the hot spot. Curve 2 is an example where charcoal material is supplied to a location other than the fire point. Figure 1 701! 1 Rin j addition 徨 α facing M (to) Figure 2 0 10 2θ Jθ Hosin Tokitomo (to) Procedural amendment (voluntary) 1988 May 8th, Commissioner of the Japan Patent Office, Kuro 1) Mr. Akihiro 1, Indication of the case, Patent Application No. 29362 of 1988, 2, Name of the invention, Method for dissolving and reducing chromium oxide 3, Person making the amendment, Relationship with the case, Patent application Person: 2-6-3 Otemachi, Chiyoda-ku, Tokyo (665) Representative Takeshi, Nippon Steel Corporation 1) Amount: 4, Agent: 2-4-1 Marunouchi, Chiyoda-ku, Tokyo, 100 (no changes to the content) )

Claims (1)

[Claims] In top-bottom blown converter refining, chromium ore and carbonaceous materials are added to molten iron and melted and reduced by blowing oxidizing gas from above and supplying oxygen or inert gas through the bottom tuyere.
A lumpy carbonaceous material having a diameter of ~50 mm is added to a location other than the fire point of the top-blown oxygen jet, and the lumpy carbonaceous material is added to the total oxygen supply rate F (Nm^3/(ton Hr)). A method for dissolving and reducing chromium oxide, the method comprising adding at a rate of 0.1F to 0.5F (kg/(ton·Hr)).