JPH08199218A - Converter process recycling decarburized slag - Google Patents

Abstract

PURPOSE: To suppress sudden boiling of molten iron at next charge by scattering/solidifying while blowing top blowing gas to remaining slag under specific condition after the molten steel produced through dephosphorizing/decarburizing of molten iron in a converter is tapped. CONSTITUTION: A molten iron 4 is poured into a converter 1 without discharging the slag 6 produced at the preceding charge, an oxygen 7 is supplied from a top lance 2 at about 1200-1450 deg.C, and the slag produced through dephosphorization refining is discharged. Successively, after decarburizing is executed with supplying an oxygen 7 from the top blowing lance 2, a molten steel produced is tapped. Further, in such a state that a slag 6 remains in furnace, a gas 8 of one or more kinds of N, Ar, etc., is blown at a flow rate of 80-250Nm<3> /Hr.ton so that the ratio (Ls/Lso) between a dent depth (Ls) formed to the slag due to top blown gas and slag thickness (Lso) is turned to 2-15. By this method, scattering of the slag 6 to furnace wall and erosion of furnace bottom refractory is efficiently prevented in short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter steelmaking method for recycling decarburized slag.

[0002]

2. Description of the Related Art Regarding the minimization of the total cost of steelmaking and the stable melting of low-phosphorus steel, the conventional method for dephosphorizing hot metal has been
(1) A method for performing preliminary dephosphorization by injecting a flux for dephosphorization (iron oxide, quick lime, etc.) on the hot metal in the tope car, (2) Injecting a flux for dephosphorization on the hot metal in a ladle, Alternatively, a method of performing preliminary dephosphorization by spraying, or (3) a method of performing dephosphorization on one side and decarburization on the other side using two converters (for example, JP-A-63-195210) ) Is used. However, the methods (1) and (2) are (TF
Although e) is low and (CaO / SiO ₂ ) is high, there is an advantage that desulfurization reaction proceeds simultaneously with dephosphorization, but iron oxide represented by iron ore and scale powder is used as an oxidizing agent. However, there is a problem that the temperature decreases during processing, the scrap consumption in the converter, which is the next step, decreases, and the molten steel production decreases. On the other hand, in the method (3), since oxygen gas is used as the oxidant and scrap can be used for temperature control during the dephosphorization process, the scrap consumption does not decrease, but the hot metal dephosphorization process is performed. Since decarburization and decarburization are performed in separate reaction vessels, heat loss occurs due to hot metal transfer and scrap consumption is reduced.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 4-072007, charging of hot metal, dephosphorization desulfurization smelting, slag, decarburization smelting, tapping, and decarburization slag, the next charge of hot metal is called. A method for producing molten steel in which the steps are continuous is disclosed. In this method, heat loss due to hot metal transfer does not occur, but decarburization slag has a high (T · Fe), so when the next charge of hot metal is charged in the molten state, it rapidly reacts with the carbon in the hot metal. There is a problem that so-called bumping occurs, in which hot metal and slag are ejected outside the furnace. To avoid this,
A method of adding limestone or scrap as a cold material to the slag and tilting the converter several times before charging the hot metal is used, but there is a problem that productivity is significantly impaired because it takes a long time.

By the way, Japanese Patent Laid-Open No. 61-56223 discloses a method for coating a converter with slag.
A method is disclosed in which air or a slow-reactive gas is blown from a top blowing lance to the decarburizing slag remaining in the furnace to splash the slag onto the furnace wall. However, in this method, the conditions for splashing the slag onto the furnace wall in a short time and the conditions for preventing melting damage of the furnace bottom refractory, and the conditions for avoiding bumping when the next charge hot metal is received in that state are related. There is a problem that there is no description and it cannot be applied as it is.

[0005]

The present invention is disclosed in Japanese Unexamined Patent Publication No.
In the technology disclosed in Japanese Patent Publication No. 072007, there is a problem that productivity is significantly impaired because it takes a long time to avoid bumping at the time of hot metal charging, and JP-A-61-5622.
There is no description in the technology disclosed in Japanese Patent No. 3 publication regarding the conditions for splashing the slag onto the furnace wall in a short time and the conditions for avoiding bumping while preventing melting loss of the furnace bottom refractory, and is applied as it is. The purpose is to solve the problem of not being able to do so and to enable recycling of decarburizing slag with high productivity without the risk of bumping.

[0006]

The inventors of the present invention selected a proper condition in a method of blowing gas from an upper blowing lance to a decarburizing slag remaining in a furnace to splash a slag onto a furnace wall. , It was clarified that the conditions for splashing slag efficiently on the furnace wall in a short time and the conditions for preventing melting damage of the furnace bottom refractory are compatible. The present invention is based on this finding.

The main points are: (1) Discharge of slag generated by pre-charging using an upper-bottom blowing converter type refining device that supplies oxygen from an upper-blowing lance and stirs a steel bath with gas. Without hot metal (step 1), a hot metal dephosphorization refining step (step 2) in which oxygen is supplied from an upper blowing lance at a temperature of 1200 to 1450 ° C., and the furnace is tilted in step 2 The step of discharging the generated slag (step 3), the step of standing the furnace upright to supply oxygen from the upper blowing lance to decarburize (step 4), and the step of tapping the generated molten steel (step 5) are successively performed. In the converter steelmaking method to be carried out, after the step 5, the furnace is erected with the slag remaining in the furnace, and the same as in the step 4 or nitrogen, Ar, CO, CO ₂ from another upper blowing lance Mix one or two or more A meta-gas 80~250Nm ³ /
Spraying at a flow rate of Hr · ton so that the ratio (L _S / L _SO ) between the calculated dent depth (L _S ) and the slag thickness (L _SO ) formed in the slag by the top-blown gas is 2 to 15. After
It is a converter steelmaking method in which decarburizing slag is recycled, characterized in that step 1 is carried out.

(2) In the converter steel making method described in (1) above, when the molten steel is tapped in step 5, the ratio of the bath depth (L _MO ) of the molten steel and the slag thickness (L _SO ) (L It is a converter steelmaking method for recycling decarburizing slag, characterized in that molten steel is left in the furnace in the range of _MO / L _SO ) of 1 to 5.

(3) In the converter steel making method described in (3) above, after step 5, the furnace is erected with the slag and the molten steel left in the furnace, and then the carbonaceous material is added. Is a converter steelmaking method that recycles decarburizing slag.

Here, the cavity depth L _s (m) due to the top-blown gas is calculated by the following formula, where the nozzle diameter d (mm), the distance between the lance and the slag surface h (mm), and the number of nozzles n. . L _s = (7/2) × {L _h × exp (−0.78 × h /
L _h )} / 100 L _h = 63 × (F × W × 60 / (n × d)) ^{2/3 Further} , the bath depth L _MO (m) of molten steel and the slag thickness L _SO (m) are calculated as follows. Molten steel density 7 (g / cm ³ ), slag density 2 (g
/ Cm ³ ) can be calculated from the geometrical shape of the converter.

[0011]

FIG. 1 schematically shows an embodiment of the present invention. The step of receiving the hot metal 4 without discharging the slag 6 generated in the pre-charge (step 1), the temperature is 120
Oxygen 7 from top blowing lance 2 under the condition of 0 to 1450 ° C.
Dephosphorization refining process of molten pig iron for refining (step 2), tilting the furnace to discharge the slag 5 generated in step 2 (step 3), standing the furnace upright and supplying oxygen 7 from the upper blowing lance 2. And decarburization process (process 4), generated molten steel 4
In the step of tapping steel (step 5), the furnace is erected in a state where the slag 6 is left in the furnace, and the same as in step 4, or from another upper blowing lance 2 of nitrogen, Ar, CO, CO ₂ seed,
Alternatively, it includes a step (step 6) of spraying the gas 8 in which two or more kinds are mixed. Here, in order to further improve the efficiency, it is desirable that the molten steel 4 is not completely discharged in step 5 but a part of the molten steel 4 is left behind, and further the gas is sprayed after adding the carbonaceous material.

First, the proper conditions for step 6 will be described below. In the present invention, it is important that the remaining slag 6 is efficiently scattered and solidified in a short time. This makes it possible to suppress bumping due to a rapid reaction between the hot metal and the slag when the next-charge hot metal 4 is charged. In the present technology, the purpose of the scattering by the top-blown gas is to separate the slag into fine particles and scatter in the space to promote heat removal and solidify during the scattering. This is a fundamental difference from the fact that when slag coating is intended, the slag particles need to be solidified after reaching the furnace wall rather than solidifying during splattering.

Therefore, as the top blowing gas, one or two or more of nitrogen, Ar, CO, and CO ₂ , which react with the granular iron remaining in the slag and do not generate heat, are mixed. Limited to gas. 80 to 25 as flow rate
If the range of 0 Nm ³ / Hr · ton is appropriate, and if it is less than this, the cooling capacity of the gas is small, and the slag particles cannot be solidified during scattering. If it is too large, it depends on the gas from the converter furnace body. Since the heat removal becomes large, the temperature of the refractory material of the converter greatly decreases and the life of the furnace deteriorates.

On the other hand, the optimum range of the gas flow velocity is that the ratio (L _S / L _SO ) between the calculated dent depth (L _S ) and the slag thickness (L _SO ) formed in the slag as shown in FIG. 2 to
The range is 15. If it is smaller than this, since the kinetic energy of the gas is small, sufficient amount of slag particles cannot be scattered and unsolidified slag remains at the bottom of the furnace, causing bumping at the time of charging the hot metal for the next charge. The top-blown gas violently attacks the bottom of the furnace and adversely affects the refractory life.

Here, in order to carry out more effectively,
As shown in FIG. 3, the molten steel during step 5, the ratio of the bath depth of the molten steel (L _MO) and slag thickness _{(L SO) (L MO /} L SO) is 1
It is preferable to leave it within the range of 5 in the furnace. This is because when the liquid is torn into small particles by the energy of the top-blown gas, it is easier to coexist with molten steel with lower viscosity than with only highly viscous slag, and molten steel with high density is present. As a result, the ratio of the energy of the top-blown gas that acts on the furnace bottom refractory is greatly reduced, wear of the furnace bottom refractory is reduced, and blockage due to insertion of slag into the bottom-blown nozzle is also avoided. If it is less than 1, the effect of leaving the molten steel is too small because the amount of molten steel is too small, and if it is more than 5, the yield rate is deteriorated and the residual molten steel acts as a cold material in the next charge. Therefore, the heat loss becomes large.

Further, when the molten steel is left, the molten steel particles having a high oxygen concentration are scattered and solidified together with the slag, so that when the hot metal of the next charge is received after the short-time blowing of 2 minutes or less. In the case of avoiding bumping completely, it is better to add carbonaceous material and remove oxygen as CO gas.

When the temperature is lower than 1200 ° C. in the step 2, the temperature does not rise sufficiently to the temperature required for stopping the blowing in the step 4, and when it is higher than 1450 ° C., the dephosphorization equilibrium is obtained. Moreover, the dephosphorization reaction is unlikely to occur and a large amount of quick lime is required, which is not efficient.

[0018]

EXAMPLES The examples shown in Table 1 were carried out in the process shown in FIG. 1 using a 175 ton top-bottom blowing converter. Nitrogen gas or oxygen gas and tuyere cooling gas was used as the bottom blowing gas, and oxygen gas was blown from the top blowing lance. In step 2, lumpy quicklime is added together with fluorspar from above, and (CaO)
/ Was controlled (SiO ₂₎ to 1.6 to 3.1. The temperature during processing is 1200 to 1 by adding scrap or iron ore
It was set to 450 ° C. In step 4, lump-shaped quick lime is added from above, (CaO) / (SiO ₂ ) is controlled to 3.1 to 4.8, and the carbon concentration of the blow stopper is 0.25 to 0.02%,
The temperature was 1580 to 1680 ° C.

In step 6, gas was supplied from the same lance as in steps 2 and 4. The top-blowing lance was changed in hole diameter and the number of holes, and the distance from the tip of the lance to the slag surface was changed to adjust L _S. The residual slag amount was about 50 kg / t and the thickness (L _SO ) was about 30 cm. Test Nos. 1 to 12 in Table 1 are examples of the present invention, and the hot metal of the next charge could be received without bumping, and the refractory was not worn. Test numbers 13 and 14 are when L _S / L _SO is too small, and test number 15 is when L _S / L _SO is proper but the gas flow rate is too small. In both cases, bumping occurs when the hot metal is charged for the next charge. It has occurred. Test number 16, 1
In No. 7, when the gas flow rate was too large and when L _S / L _SO was too large, the wear of the refractory was severe in both cases.

Here, in any of the above tests, the step 2
The dephosphorization rate was as high as 70 to 90%, and there was no problem in obtaining the predetermined blowing stop temperature in step 4. still,
As test number 18, step 6 is the same as test number 2 and the dephosphorization rate is 67% when the temperature in step 2 is 1490 ° C.
On the contrary, when the temperature was set to 1125 ° C. (Test No. 19), the calorific value in Step 4 was insufficient and it was necessary to use expensive anthracite.

As test number 20 and thereafter, step 6 and step 2
Was the same as Test No. 2 and the lance was a four-hole nozzle with a diameter of 35 mm, and nitrogen gas was blown from 2.5 m above the slag surface, and the molten steel was left in the furnace during step 5. The results are shown in Table 2. When the molten steel bath depth (L _MO ) and the slag thickness (L _SO ) ratio (L _MO / L _SO ) is left within the range of 1 to 5 as in Test Nos. 20 to 22, The yield was good, and there was no refractory wear or blockage of the bottom blowing nozzle, and short-time processing was possible. As test number 25, under the same conditions as test number 20, after step 5, the furnace was erected while leaving the slag and molten steel in the furnace, and then carbon material was added in an amount of about 10 weight percent of the slag amount. As a result, it became possible to reduce the gas spraying time to 2.5 minutes or less. Here, the carbonaceous material addition amount is 5 to 3 of the slag amount.
5 weight percent was suitable.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

EFFECTS OF THE INVENTION By using the present invention, it is possible to safely recycle decarburizing slag without causing bumping at the time of charging hot metal, and a converter steelmaking method with a small amount of quick lime basic unit and high productivity. Became possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram when the present invention is implemented.

FIG. 2 is an experimental result showing the relationship between L _S / L _SO and the occurrence state of bumping at the time of hot metal charging of the next charge.

FIG. 3 is an experimental result showing the relationship between L _MO / L _SO and the state of blockage of a bottom blowing nozzle.

[Explanation of symbols] 1 converter 2 top blowing lance 3 bottom blowing tuyere 4 hot metal or molten steel 5 dephosphorization slag 6 decarburization slag a oxygen gas b nitrogen, Ar, CO, CO ₂ 1 type, or 2 or more types Mixed gas

Claims (3)

[Claims] 1. Supplying oxygen from a top blowing lance, and
A step (step 1) of receiving hot metal without discharging the slag generated by the precharge using a top-bottom blow converter-type refining device that stirs the steel bath with gas, and the temperature is 1200 to 145.
Dephosphorization refining process of hot metal that supplies oxygen from the top blowing lance under the condition of 0 ° C (step 2), step of tilting the furnace to discharge the slag generated in step 2 (step 3), upright blowing of the furnace In the converter steel making method in which the step of supplying oxygen from the lance to decarburize (step 4) and the step of tapping the produced molten steel (step 5) are continuously performed, slag is introduced into the furnace after step 5. The furnace is erected in the state of being left, and the same as step 4,
Or nitrogen, Ar, CO, C from other top blowing lances
One O _2, or of two or more was allowed to mixed gas at a flow rate of 80~250Nm ³ / Hr · ton, dent depths of computational to form slag by the top-blown gas (L _S) slag thickness after (L _sO) ratio (L _S / L _sO) is blown such that 2-15, converter steelmaking method for recycling decarburization slag which comprises carrying out the step 1. 2. When tapping the molten steel in step 5, the ratio of the bath depth (L _MO ) of the molten steel to the slag thickness (L _SO ) (L _MO /
_LSO ) makes a molten steel remain in a furnace in the range of 1-5, The converter steelmaking method which recycles the decarburizing slag of Claim 1 characterized by the above-mentioned. 3. The decarburizing slag according to claim 2, wherein after step 5, the furnace is erected in a state where the slag and the molten steel are left in the furnace and then the carbonaceous material is added. Converter steelmaking.