KR101091932B1 - Method for Refining Molten Steel in Converter - Google Patents

Abstract

The converter refining method according to the present invention is different from the converter refining method according to the titanium content in the molten iron to prevent the occurrence of the slope caused when the titanium content in the molten iron is high, and due to equipment burnout or unstable refining reaction due to the slope. Prevents quality deterioration.

If the titanium content in the molten iron is 0.7% or more, the residual slag should be kept below 10 tons before charging, and light dolomite will be added at the start of the blow, and the blow pattern will be changed in the middle of the process. Pre-injection to prevent slope. Particularly, when the content of titanium in the molten iron is 1.5% or more, the blowing is paused at the time of 20-25% of the blowing process to remove slag and continuously blow in the same pattern as described above.

Molten iron, converter, titanium, slope, blow

Description

Method for Refining Molten Steel in Converter}

1 is a process flow diagram illustrating the operation of the present invention.

Figure 2 is a perspective view schematically showing the overall configuration of the converter and the surrounding equipment.

3 is a graph showing the effect of titanium on the converter slag melting point.

4 is a graph showing the effect of titanium on converter slag melt rate.

Figure 5 is a ternary diagram showing the viscosity of the slag according to the titanium content.

6 is the MgO saturation solubility of slag.

7 is a graph showing the relationship between MgO concentration and slag equilibrium in slag.

8 is a graph showing the change of exhaust gas according to the progress of the blow during the refining operation.

9 is a schematic diagram showing a blowing pattern of the prior art.

10 is a schematic view showing the blowing pattern of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: converter 2: lance

3: winch motor 4: basis weight hopper

10: HMI 11: PLC

20: exhaust gas detection stage 21: gas analyzer

The present invention relates to a converter refining method, and more particularly to a converter refining method according to the titanium content in the molten iron.

In general, operations in converters are as follows.

Upon completion of the last charge of the charge, a certain amount of slag in the converter is removed from the slag port. The converter is established, the coating of light dolomite or saint dolomite is added, and the inner wall of the converter is coated by spraying high pressure nitrogen gas to scatter slag. The remaining residual slag is coated by tilting the converter to the charging and tapping side where erosion occurs most rapidly. At this time, the operator performs passionate operation considering heat balance in the furnace while checking main raw materials such as molten iron and scrap metal. First, various components in the molten iron, that is, components such as silicon (Si), phosphorus (P), vanadium (V), titanium (Ti), and carbon (C) are identified, and passionate work is performed in comparison with the previous charge. After finishing the Passion, the scrap iron and molten iron are charged into the converter, and the upper part is blown to supply oxygen gas. In the process of blowing, the solvent and coolant such as quicklime, light dolomite, ore and coolant are added according to the basicity calculated by the passion acid, and the final oxygen content is measured by measuring the temperature and carbon in the molten steel at a rate rate at which the reaction of carbon is lowered. It depends on the temperature and oxygen. When the blow is completed, the temperature and oxygen of the molten steel are measured, and when the target is hit, tapping is performed.

During the blowing operation, in order to remove carbon and impurities in the molten iron, oxygen gas is injected to the molten iron surface at high speed, and the injected oxygen gas and carbon in the molten iron react to generate carbon monoxide (CO) gas as shown in the following reaction formula.

1/2 O ₂ + [C] = CO _(g)

The carbon monoxide produced by the above reaction, in particular, has a very small bubble size and fine carbon monoxide is not easily released to the outside through the slag layer, but is stagnated in the upper part of the molten iron and the slag layer, and then the upper part of the slag and the molten iron is rapidly abruptly. May cause a slag foaming. In addition, the generation of carbon monoxide gas can cause the slag and molten iron to be ejected out of the converter during the blow, which is called the "slopping". This phenomenon is affected by the amount and composition of the slag, the molten iron condition, the rate of carbon monoxide generation and the size of the generated gas. For example, when the Si component in the molten iron is 0.6% or more, a lot of heat of reaction is generated initially, thereby accelerating the quicklime melting rate. That is, a large amount of liquid slag is formed from the beginning, and as a result, a large amount of slag is ejected out of the furnace at a 30% point in which the decarburization reaction is vigorous.

In addition, even when the titanium (Ti) content in the molten iron may cause a large slope. 3 is a graph showing the relationship between the content of titanium and the melting point of the slag, the higher the slag melting point as the titanium content in the molten iron increases. 4 is a graph showing the relationship between the titanium content and the slag melting rate, the slag melting rate is significantly increased as the titanium content in the molten iron increases. In addition, Figure 5 shows the change in the slag viscosity with increasing titanium content. As described above, the slag material proceeds slowly due to the formation of a solid compound having a high melting point and an increase in the melting point, and the slag viscosity is high, but the temperature of molten steel increases after the middle of the blowing, and the slag viscosity is significantly reduced. Therefore, when the content of molten iron in the molten iron is large, the slag fluidity increases rapidly after the middle of the blow, which causes a large slope.In addition, the slaughter generated during the converter blow not only results in the loss of iron, which is a valuable metal, but is also very dangerous for operation safety. May cause serious air pollution.

When the slope occurs, the hot slag is blown out of the furnace, the surrounding equipment is burned out by the heat of the slag, and the equipment management becomes difficult. In addition, since the slitting occurs after the middle of the blowing, quicklime is additionally added, which causes quality deterioration due to unstable refining reaction in the furnace caused by the poor ash of the quicklime. As such, the addition of quicklime after the middle of the blowing lowers the temperature of the molten steel to inject additional oxygen gas, increases the converter refining time, causes a decrease in productivity, and increases the manufacturing cost of the molten steel. In addition, there is a problem that the coating effect in the furnace is reduced by increasing the re-use of the slag attached to the furnace wall by the nitrogen spray coating and the residual slag.

The present invention is to solve the above problems, to prevent the occurrence of large explosive slope occurs when the titanium (Ti) content in the molten iron to prevent the deterioration of quality due to equipment damage or unstable refining reaction due to the slope It is an object of the present invention to provide a converter refining method that prevents the productivity from being lowered due to the increase in manufacturing cost due to the addition of quicklime to prevent the quality deterioration and the decrease of the molten steel temperature during the input.

In order to achieve the above object, the present invention, in the converter refining method, the step of confirming the content of the Ti component of the molten iron, the step of remaining a predetermined amount of slag according to the content of the identified Ti component, charging the scrap iron and molten iron According to the step and the content of the Ti component comprises the step of performing the blowing operation, the step of performing the blowing operation is characterized in that when the content of the Ti component in the molten iron is more than 0.7%, the small dolomite is added with the start of the blow.

In addition, the step of performing the blowing operation, if the content of the Ti component in the molten iron is more than 0.7%, the lance height is changed to 0.43 to 0.45 compared to the bath surface at 50 to 60% of the drilling progress, the oxygen flow rate is changed to 550 to 600Nm ³ Characterized in that it is maintained up to 75 to 85% time point, in particular, when the content of Ti component in the molten iron is 1.5% or more, the slag is excluded from the slag pot by removing the slag at the time of 20-25% of the drilling progression, and after the completion of exclusion, the blowdown is continuously performed. It is characterized by proceeding.

In addition, the behavior of the carbon monoxide and carbon dioxide generated during the progress of the drilling is characterized in that the sedative is added if reduced simultaneously.

Hereinafter, the converter refining method according to the present invention with reference to the accompanying drawings will be described in detail.

The converter refining operation is carried out in the order of charging operation, blowing operation, tapping operation and exclusion operation, Figure 1 shows the process progress of the converter refining method according to the present invention.

After the last tapping work is completed, nitrogen spray coating is applied to remove the residual amount of slag, and the fermentation work is performed to consider the thermal balance in the furnace while checking the main raw materials such as molten iron or scrap metal. At this time, check the content of the titanium (Ti) component of the molten iron and proceeds the process according to the titanium content as follows.

First, when the titanium content in the molten iron is less than 0.7%, the slope is hardly generated, so the general converter operation is followed. Residual slag is secondarily removed and maintained at 20 to 30 tons, and scrap metal and molten iron are charged to start the blowing operation.

In addition, when the content of titanium in the molten iron is 0.7% or more, the residual slag should be maintained at less than 10 tons less than that of the prior art during the second exclusion of the residual slag before charging. When the titanium content in the molten iron is 0.7% or more, the slinging occurs after the middle of the drilling.In particular, when the titanium content is 1.5% or more, the sloughing of the slag in the furnace is exploded due to the sudden increase in fluidity. You must stop to calm down the slopes. Therefore, when the content of titanium in the molten iron is high, a larger amount of residual slag is excluded, and scraping work is started by charging scrap iron and molten iron.

As shown in FIG. 7, MgO has a high phosphorus reaction equilibrium when the saturation in the slag is high, so the MgO saturation concentration in the furnace slag should be maintained at 6 to 8%. The concentration of MgO in converter refractories is about 5% .When the concentration of MgO in refractories decreases during converter refining, the amount of MgO crystallized from the refractory to slag layer increases and the erosion rate increases rapidly. As shown in Fig. 7, phosphorus reaction balance is lowered, which causes quality deterioration. Therefore, it is desirable to maintain the MgO concentration at 6 to 8% during the blowing operation.

6 is the MgO concentration over the course of blowing and initially starts at 5%. In the general converter operation, MgO is not initially added to promote the initial slag goods, but the present invention saturates MgO in the initial slag by adding light dolomite at the beginning of the blow, that is, the start of the blow, when the titanium content in the molten iron is 0.7% or more. Raise the concentration. In the general case, light dolomite is added to the slag coating. If the titanium content is 0.7% or more, as described above, only a small amount of residual slag remains below 10 tons, so the concentration of MgO in the initial slag is lowered and MgO This is because precipitation occurs and a lifespan decreases. Therefore, in order to maintain the saturation concentration of MgO in the initial slag to 6 to 8% in order to compensate for the insufficient amount of MgO by adding light dolomite at the beginning of the blow. In addition, MgO increases the slag viscosity as the saturation concentration in the slag increases, by using this property to offset the phenomenon that the slag viscosity is lowered when the titanium in the molten iron is high. Therefore, with the start of blowing, small dolomite is added to increase the saturation concentration of MgO in the initial slag and increase the surface tension in the slag to keep the slag viscosity constant.

As such, in the present invention, in order to increase the MgO saturation concentration, the light dolomite is added, and the input amount is calculated by the following equation using the following table.

Y = amount of light dolomite in Table 1-(0.5 × A)-B-(-1.8 × C)

Y = amount of light dolomite to be injected

A = amount of fresh dolomite for coating

B = amount of light dolomite for coating

C = amount of MgO pellets for coating

The amount of light dolomite injected is calculated by the above formula, and charged at the initial stage of blowing to increase the MgO saturation concentration in the slag and keep the slag viscosity constant.

In addition, when the titanium content in the molten iron is 0.7% or more, the probability of the occurrence of the slope after the middle of the blowing is high so that the blowing pattern at the middle of the blowing period is changed.

The present invention adjusts the lance height from 0.43 to 0.45 compared to the bath surface at 50 to 60% of the time of blowing, and changes the oxygen flow rate to 550 to 600 Nm ³ per minute, so that the decarburization reaction is at a rate of 75 to 85% of the time of blowing. To the point where it enters. Here, the value of the water level is the lance height / water level, and the water level is the height from the inner lower portion of the converter bar to the surface of the molten steel or the molten iron. If the lance height is less than 0.43 compared to the water surface, oxygen gas breaks the slag layer quickly and is easy to discharge carbon monoxide, but because the lance height is too low, the amount of oxygen directly reacting to the molten steel increases, which contributes only to the decarburization reaction, which causes deterioration of slag production. Become the quality. On the other hand, when the lance height is more than 0.45 compared to the bath surface, the lance height is so high that the slag reaction causes the carbon monoxide generated by the decarburization reaction to be prevented from slipping out so that the lance height is preferably maintained at 0.43 to 0.45 compared to the bath surface. In addition, the oxygen flow rate is adjusted to 550 to 600 Nm ³ per minute, which reduces the oxygen flow rate because the amount of carbon monoxide generated by the active converter refining reaction increases, the rate of exiting the flue gas through the slag is slow, and the slope is generated. . When the oxygen flow rate is 550 Nm ³ or less per minute, the converter retardation reaction is slow because the speed is too slow. On the other hand, when the oxygen flow rate is 600 Nm ³ or more per minute, the oxygen flow rate is 550 to 600 Nm ³ per minute because of the high frequency of slope occurrence. It is preferable.

The present invention prevents slope by introducing a sedative in the upper portion according to the behavior of carbon monoxide (CO) and carbon dioxide (CO ₂ ) generated during the converter refining operation. FIG. 2 illustrates the front of the converter. After detecting the gas discharged when the refining operation is performed in the converter 1, the exhaust gas detection stage 20 detects a sign of a dropping occurrence, the HMI 10 recognizes and detects the PLC. In (11), the hopper is installed on the roadbed. Thus, the sedative is introduced into the converter 1 in the basis weight hopper 4 for weighing the sedative and breaks the slag equilibrium so that carbon monoxide or carbon dioxide is discharged out of the slag to prevent the slope.

8 is a graph showing the change of the flue gas detected with the progress of the blowing, carbon monoxide and carbon dioxide discharged during the refining operation tends to increase or decrease constantly. However, if carbon monoxide and carbon dioxide are simultaneously reduced, it means that the gas is stagnant and not able to penetrate the slag layer. The sedative agent instantaneously bursts the carbon monoxide bubbles in the slag during the blowing operation and releases the gas easily out of the furnace.It releases hot heat at the moment of injecting the carbon monoxide bubbles and the slag interface in the slag, and the volume expands and releases gas components. Artificially generated. The chemical composition of such sedatives is as follows.

The sedatives having the chemical components as shown in Table 2 should have the appropriate specific gravity and particle size and strength as shown below to maintain the persistence after the addition.                     

If the content of the molten iron in the molten iron is more than 1.5%, it is empirically impossible to control the slope during the blow-up stage due to the explosive slope due to the sudden increase in fluidity of the furnace slag. Therefore, when the content of titanium in the molten iron is 1.5% or more, the first blow ends at 20-25% of the blow process and the slag in the converter is excluded. The reaction proceeds without removing silicon (Si) and titanium (Ti) from the molten iron before 20% of the drilling process, and since the decarburization reaction occurs after 25% of the drilling process, the primary drilling is performed at 20 to 25%. It is advisable to exclude the slag after finishing the work. In addition, during the first blowing operation, the basicity is calculated to keep 1 to 1.5 when the quicklime is added. The primary scavenging operation is the pre-reaction of the converter smelting operation and to accelerate the composition of the slag. When the basicity is 1 or less, it is difficult to collect impurities in the slag generated during the primary scavenging operation. It is preferable that the basicity is 1 to 1.5 because the slag is difficult to rework during operation.

As such, after the completion of the first drilling operation until 20-25% of the drilling progress, impurities generated during the first drilling operation are aimed at titanium and silicon, and titanium is excluded from slag because it causes explosion in the middle of the drilling. . After the slag is excluded, the blowing operation is continuously performed, and the blowing pattern is the same as described above. That is, the lance height is adjusted to 0.43 to 0.45 compared to the bath surface at 50 to 60% of the time of blowing progress, the oxygen flow rate is changed to 550 to 600 Nm ³ per minute, and maintained until 75 to 85% of the time of the blowing progress.

9 shows a conventional blowing pattern, and FIG. 10 shows a blowing pattern according to the present invention. When the titanium content in the molten iron is 0.7% or more, as shown in FIG. 10, the oxygen flow rate and the lance height are changed to prevent the occurrence of the slope.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[Example]

Comparative Examples 1 to 20 carried out a general converter operation without division according to the titanium content in the molten iron, and proceeded to the conventional blowing pattern as shown in FIG.

In addition, Examples 1 to 10 carried out the converter operation according to the present invention according to the titanium content in the molten iron, proceeded to the blowing pattern of the present invention as shown in FIG.                     

In Comparative Examples 1 to 10, the titanium content of the molten iron is 0.7 to 1.5%, and according to the conventional refining method, it can be seen that slope occurs during the blowing operation. In Comparative Examples 1 to 2, the lance height was lower than 0.43 compared to the water surface and the oxygen flow rate was lowered to 550 Nm ³ or less per minute, and the slitting degree was relatively low. However, the oxygen flow rate was low and the lance height was too low. The manufacturing resulted in abnormal quality. In Comparative Examples 3 to 5, the lance height was lower than 0.43 compared to the water surface, the oxygen flow rate was 600 Nm ³ or more per minute, the slope occurred relatively moderate, and the amount of sedative and quicklime correction was also relatively higher than that of Comparative Examples 1 to 2. Increased. In addition, in Comparative Examples 5 to 10, since the lance height is too high, more than 0.45 compared to the water surface, the slag reaction causes the carbon monoxide generated by the decarburization reaction not to escape so that the slope is relatively large. The amount of sedative is more than 4000kg, the amount of quicklime correction is also about 1500kg, and extra personality has occurred.

In Comparative Examples 11 to 20, when the titanium content in the molten iron was 1.5% or more, the slope was exploded, and thus the slope was calmed after stopping the blow emergency. The amount of sedative was more than 5000kg and the amount of calcareous correction was more than 2000kg.

In Examples 1 to 5, when the titanium content in the molten iron is 0.7 to 1.5%, the residual slag before charging is kept at 10 tons or less than before, and the lance height is 0.43 to 0.45 compared to the bath surface in the middle of blowing and 550 to minute per minute. The work was carried out at an oxygen flow rate of 600 Nm ³ , and sedatives were prevented from dropping in advance according to the amount of carbon monoxide and carbon dioxide discharged during the blowing operation.

In Examples 6 to 10, when the titanium content in the molten iron is 1.5% or more, the primary drilling is completed at the time of 20-25% of the drilling, and the slag is removed and continuously blown in the same pattern as above to generate the slope. It disappeared.

In addition, the embodiment has a very small amount of sedatives compared to the comparative example, and prevents the addition of quicklime due to the slope to reduce the manufacturing cost, and due to the deterioration of quality and refining time due to the bad goods caused during the addition of quicklime Problems such as a decrease in productivity are prevented.

The converter refining method according to the present invention is different from the converter refining method according to the titanium (Ti) content in the molten iron to prevent the occurrence of the slope caused when the titanium content in the molten iron is high, and equipment damage or unstable refining reaction due to the slope. Prevents deterioration of quality.

In addition, by eliminating the additional input of quicklime, which is added to prevent quality deterioration, it reduces the manufacturing cost and prevents the problem of increasing the refining time by lowering the molten steel temperature during the input, thereby improving productivity.

Claims (5)

In the converter refining method, Checking the content of the Ti component of the molten iron; Leaving a predetermined amount of slag according to the content of the identified Ti component; Charging scrap metal and molten iron; And According to the content of the Ti component comprising the step of performing the blowing operation, In the step of performing the scouring operation, the converter refining method characterized in that when the content of the Ti component in the molten iron is 0.7% or more light dollomite is added with the start of the smelting. The method of claim 1, Remaining the predetermined amount of slag, A slab of 20 to 30 tons of slag when the content of Ti in the molten iron is 0.7% or less, and 10 tons or less of slag when the content of Ti in the molten iron is 0.7% or more. The method according to claim 1 or 2, The step of performing the blowing operation, If the content of Ti in the molten iron is 0.7% or more, the lance height is changed to 0.43 to 0.45 compared to the bath surface and the oxygen flow rate is changed to 550 to 600 Nm ³ at 50 to 60% at the time of the drilling to maintain the 75 to 85% of the progress of the drilling. A converter refining method characterized by the above. The method according to claim 1 or 2, The step of performing the blowing operation, When the content of the Ti component in the molten iron is more than 1.5%, the slag is excluded from the slag pot by stopping at 20-25% of the time of the drilling progress, and after the completion of the exclusion, the converter refining method characterized in that the proceeding of the smelting. The method according to claim 1 or 2, The step of performing the blowing operation, A method of refining a converter characterized in that the sedatives are added when the behavior of carbon monoxide and carbon dioxide is reduced at the same time.

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