KR100834085B1 - Method for manufacturing ultra low phosphorus steel using steel making slag - Google Patents

Abstract

A method for manufacturing ultra low phosphorus steel using converter slag is provided to reduce the consumption of quicklime and produce ultra low phosphorus steel with high quality by recycling slag generated in the converter process. A method for manufacturing ultra low phosphorus steel comprising not higher than 120 ppm(parts per million) of phosphorous using converter slag comprises: a slag coating step of coating refractories of a converter with slag remained in the previous process; an iron scrap and hot metal injecting step of charging iron scrap and hot metal into the converter; a first blowing step of dephosphorizing the hot metal such that the content of phosphorous contained in the hot metal that has been charged into the converter is controlled to not higher than 500 ppm; a first slag discharging step of intermediately discharging slag comprising at least 3.5% of P2O5; a second blowing step of decarburizing the hot metal to remove carbon contained in the hot metal; a ferroalloy injecting step of discharging the molten steel that has been dephosphorized and decarburized into a ladle and injecting ferroalloy into the ladle at the same time; and a second slag discharging step of discharging molten steel from the converter and discharging slag from the converter in a state that a portion of the slag is remained in the converter.

Description

Method for manufacturing ultra low steel using converter slag {METHOD FOR MANUFACTURING ULTRA LOW PHOSPHORUS STEEL USING STEEL MAKING SLAG}

1 is a flowchart illustrating a conventional converter process.

2 is a schematic view showing the scrap metal melting and the furnace reaction during the blowing.

Figure 3 is a work sheet showing the blowing pattern and the sub-material input pattern in the conventional converter process.

4A is a schematic diagram showing a converter process according to the present invention.

4b is a flow chart illustrating a converter process in accordance with the present invention.

5 is a work sheet showing the blowing pattern and the sub-material input pattern during the converter process according to the present invention.

6 is a graph showing the behavior of phosphorus (P) component in the converter process according to the present invention.

7 is a graph showing the height and basicity of slag forming according to the present invention.

8 is a graph showing the basicity after titration according to the present invention.

9 is a graph showing the change of the phosphorus (P) component according to the molten steel temperature after the first blowing according to the present invention.

The present invention relates to a method for manufacturing ultra low lean steel using converter slag, and more particularly, to maintain a suitable amount of slag suitable for recycling in the next converter process among slag generated during the converter process to reduce the amount of quicklime and to use high quality ultra low rinse steel. It relates to a method for producing ultra low steel using converter slag that can be produced.

Generally, the steelmaking industry consists of preliminary treatment of molten iron, converter refining, secondary refining and continuous casting. The molten iron prepared by melting iron ore in the blast furnace removes sulfur (S) and phosphorus (P) from the molten iron pretreatment process. Since the molten iron has a very high carbon content, the molten iron is placed in a converter to remove carbon, and pure oxygen is blown (hereinafter referred to as "blowing") to remove carbon in the molten iron to a certain content (0.04% by weight). The molten iron with this carbon removed is called molten steel.

After the conversion process, the molten steel is transferred to RH or LADLE FURNACE, which is a secondary refining facility, in a container called ladle, to uniform molten steel and temperature, or to remain in the molten steel. After removing the gas component or raising the temperature of the molten steel, it is solidified in a continuous casting process to produce a cast product, the final product of the steelmaking step.

1 is a flowchart illustrating a conventional converter process. Referring to the drawings, the converter will race to make the molten steel blown from the converter to the ladle. At this time, the slag having a low specific gravity among the molten steel in the converter is not pulled out and remains in the converter. After the molten steel tapping is completed, a certain amount of slag is left in the converter and the slag coating agent having the composition as shown in Table 1 is added to secure the viscosity of the slag, and then slag coating is applied to the slag to the converter refractory. .

The slag coating is applied to the nitrogen spray coating in the state in which the converter is established (S10), and then finish by idling the converter in the tilted state. In other words, the dolomite, light dolomite, and summitite injected into the slag coating agent (S20) can reduce the temperature in the slag while increasing the MgO in the slag to secure an appropriate viscosity. Thus, when MgO in slag rises and a viscosity becomes high, it is easy to adhere to a furnace refractory body.

As described above, when the coating agent is injected into the converter, the supersonic nitrogen is injected from the upper part of the converter to inject slag into the duct in the converter for 2 to 3 minutes (S30). When the nitrogen spray coating is completed, the tilting coating (S40) is performed to attach the slag to the refractory of the converter while tilting the converter to the charging side and the tapping side of the converter. The slag is carried out 2-3 times as described above and the remaining slag is discharged to facilitate the operation in the converter (S50), and the amount of slag that is left after the discharge varies between workers but is approximately 15 to 25 tons.

And after the copper coating (S40) is to put the protective lime (S42), the protective lime should be supplied to the converter during drilling to prevent damage to the converter refractory due to the fall of the scrap metal when the scrap iron and molten iron is charged into the converter. One third (about 3.3 tonnes) of the amount of lime taken (about 10 tonnes) will be pre-injected.

When the tilting coating (S40) is completed and the residual slag is discharged (S50), the scrap iron and molten iron is charged to the converter (S60), the molten iron temperature and the composition of the major five impurities in the converter are shown in Table 2. .

Passion acid is carried out by using the conditions such as the molten iron temperature and the molten iron component, the passion acid is to use the front and rear charge (Charge). In general, in order to remove phosphorus (P) in molten iron, the calculated basicity is aimed at about 4.5 to 5.5. Equation 1 below is a formula for obtaining a basicity generally used.

In general, the actual basicity is obtained by using CaO and SiO ₂ in the slag using the formula as shown in Equation 1, and in the actual operation, the quicklime input required to convert the converter is calculated by Equation 2 below.

The quick lime input amount is obtained by the above formula, and the quick lime is added to the converter (S70), and the preparation (Flux) and the like vary depending on the input amount of quick lime. In the case of the coolant, the amount of heat remaining in the passion acid is added.

Then, when charging of the scrap iron and the molten iron is completed in the converter, the blow start is started (S80). Accordingly, as shown in FIG. 2, the melting of the scrap metal and the reaction in the furnace are caused during the blowing in the converter. When scrap iron and molten iron is charged into the converter as described above, supersonic oxygen is supplied from the upper portion of the converter using a lance, and impurities in the molten iron are removed by the following Equations 3 to 8.

Impurities in the molten iron are removed by slag and gas by the above Equations 3 to 8, and as shown in FIG. 3, a subsidiary material (S90) for degassing, dephosphorization, and decarburization is introduced. In the early stage of blowing, some solvents and coolants are added, and after the middle of the converter blowing, the solvents are divided and the lance height, flow rate and low odor of the upper odor change with the progress of the filtration.

If the amount of oxygen transferred from the lance is consistent with the calculated amount of oxygen according to the amount of oxygen calculated from the passion acid before the drilling (S100), the drilling is completed (S110), and when the drilling is completed, tap the molten steel from the converter to transfer the molten steel to the ladle ( S120). In addition, during the molten steel tapping to make the quality required by the demand of the alloy steel (S130) and then tapping the molten steel. At this time, the raceway is to tap the molten steel to the ladle, the slag injured in the molten steel is tapping (S140) just before the outflow to the ladle.

In order to produce ultra-low-lining steel, which is a high-grade steel, after pretreatment of molten iron, desalination (P), desulfurization (S), and titanium (Ti) are carried out. It is common to charge the converter to minimize Boklin (P), Boksul (S), and Botan (Ti).

However, a series of processes to remove phosphorus (P) after the removal of sulfur by performing molten iron pretreatment is not carried out in one converter, but by moving the desulfurized molten iron to another converter and then delining. And charging is repeated and productivity falls.

In addition, when calculating the basicity when the converter is blown, it is calculated without considering the amount of quicklime contained in the residual slag, and the quicklime is repeatedly added, and the quicklime is excessively added to increase the production cost.

The present invention is to solve the above problems, to reduce the amount of quicklime by recycling the slag generated during the converter process, to provide a method for producing ultra-low steel using the converter slag that can produce high-quality ultra-low steel. The purpose is.

In the technical idea of the present invention for achieving the above object, the slag coating step of coating the converter refractory using the slag remaining in the converter, and the scrap iron and the molten iron is charged to the converter after the slag coating step and A slag containing a high concentration of P ₂ O ₅ after a molten iron input step, a dephosphorization to remove P contained in the molten iron charged into the converter after the scrap iron and molten iron input step, and the primary The first slag discharging step in the middle and the second slag discharging step to remove the C contained in the molten iron after the first slag discharging step; At the same time, the ferroalloy step of injecting ferroalloy into the ladle, and the secondary slag that retains and excludes an appropriate amount of slag in the converter after finishing the tapping after the ferroalloy step. It is achieved by the pole tingling steel manufacturing method using a converter slag containing material step.

Here, it is preferable to further include a step of excluding 15 to 20% of the slag remaining in the converter before the step of adding the scrap iron and molten iron.

In addition, in the first blowing step, it is preferable to apply a soft blowing upsetting pattern having a cavity depth / melt of 0.1 to 0.15.

In addition, the oxygen flow rate supplied to the molten iron during the first blowing is preferably 20 to 30% of the total amount of oxygen depending on the Si contained in the molten iron.

In the primary slag discharging step, it is preferable that the slag having a content of P ₂ O _{5 in} the slag is 3.5% or more in between.

In addition, in the secondary blowing step, it is preferable that the indentation pattern of 0.5 or more of the cavity depth / melt height of the converter is applied.

Hereinafter, embodiments according to the present invention will be described in more detail with reference to the accompanying drawings.

4A is a schematic diagram illustrating a converter process according to the present invention, and FIG. 4B is a flowchart illustrating the converter process according to the present invention. Referring to the drawings, the molten iron from the blast furnace is charged into the ladle, which is a container for the molten iron and then subjected to molten iron preliminary treatment to remove some sulfur (S) and phosphorus (P) contained in the molten iron. Then, the molten iron is charged into the converter and blown with pure oxygen by blowing it into the converter.

The molten steel finished in the converter is raced to step out to the ladle, wherein the slag having a low specific gravity among the molten steel in the converter is not left but remains in the converter. When the molten steel tapping is completed, the converter is established (S210) and slag coating agents such as dolomite, light dolomite, and tailing stone are added (S220) to increase the MgO in the slag, and to lower the temperature in the slag so that the proper viscosity can be maintained. do.

Then, when the slag coating agent is injected into the converter (S220), the supersonic nitrogen is injected from the upper part of the converter to spray the slag on the duct in the converter to perform the nitrogen injection coating (S230). When the nitrogen spray coating (S230) is completed as described above, while performing a tilting coating (S240) to attach the slag to the refractory of the converter while tilting the converter to the charging side, the tapping side of the converter.

When the tilt coating is completed, the protection lime is added to prevent damage of the converter refractory due to the fall of the scrap metal to be charged into the converter (S242), and the residual slag having a high viscosity in the converter is disposed about 15 to 20% (S250).

When the residual slag is discharged (S250) is charged into the converter and the molten iron (S260), and the primary blow (S270) to blow the high-purity oxygen into the converter at a supersonic speed to remove impurities contained in the molten iron is carried out, Impurity in the molten iron is removed by slag and gas by the first blow, and as shown in FIG. 5, primary secondary raw material input (S280) is performed for desulfurization and dechlorination.

Here, when the first blow (S270) is supplied to the molten steel in the converter through a lance of high pressure high purity oxygen, in this case, the uptake pattern is relatively high in the lance height and keep the oxygen flow rate, the depth of the cavity of the converter It is preferable to apply soft blowing in which the height of the melt is 0.1 to 0.15. Accordingly, it is possible to selectively induce a delineation reaction and suppress the decarburization reaction through low cavity formation between the molten steel and the slag interface.

In addition, the oxygen flow rate supplied to the molten iron during the first blowing is preferably 20 to 30% of the total amount of oxygen depending on the Si contained in the molten iron. That is, according to the concentration of Si contained in the molten iron and transmits the oxygen gas of 20 to 30% of the total oxygen amount to complete the first blow (S290). When the oxygen flow rate is controlled according to the Si contained in the molten iron as described above, the phosphorus (P) component in the molten steel that has completed the primary blowdown is controlled to 500 ppm or less.

As described above, when the primary subsidiary material is added simultaneously with the primary blow, it is delineated to remove P contained in the molten iron, and the P contained in the molten iron moves to the slag and contains a high concentration of P ₂ O ₅ . It will form a slag.

Then, when the primary blow is completed (S290), the primary slag excretion (S300) for intermediately disposing slag containing a high concentration of P ₂ O ₅ is carried out. Here, the high concentration of P ₂ O ₅ refers to a case in which the proportion of P ₂ O ₅ in the slag weight generated after the first blow is 3.5% or more, and when P ₂ O ₅ in the slag weight is 3.5% or more. Intermediate exclusion of the slag.

To this end, the primary slag discharge (S300) is continuously tilted to reach the shortest time to the molten steel non-ejection safety angle, for example, the converter tilt angle up to 85 °, and after the converter tilt angle reaches 90 °, In addition, the slag is intermittently displaced. At this time, the amount of slag excreted as the primary slag is to be excluded more than 70% of the amount of slag remaining in the entire converter.

As described above, the secondary blowing material (S310) for decarburization is proceeded to the molten iron after excluding the slag containing the high concentration of P ₂ O ₅ , and at the same time, the secondary secondary raw material is added to the decarburization (S320).

Here, in the initial stage of the secondary blow (S310), a secondary raw material (sintered light, etc.) containing ladle slag and iron oxide for promoting quicklime ash and reforming (modifying) slag is introduced. At this time, the basicity is applied to the 3.8 ~ 4.3 during the second blow and by re-forming the slag, P ₂ O ₅ in the slag after the converter blow The concentration can be controlled to 2.0% or less. That is, by applying the basicity of 3.8 ~ 4.3 in the second blow (S310) to induce the actual basicity of the end point slag to 3.5 or more P ₂ O ₅ of the slag The concentration can be controlled to 2.0% or less.

At this time, the quicklime input for controlling the basicity of the secondary secondary raw materials for decarburization can be calculated by Equation 2, the calculated quicklime input is 40% at the beginning of the second drilling and the second drilling 40 From the progress of%, up to 80%, the remaining amount of quicklime input (60%) will be divided.

In addition, when the secondary blow (S310) is supplied to the molten steel in the converter through a lance, high-pressure high-purity oxygen, in this case, the uptake pattern relatively lower the lance height and maintains the oxygen flow rate, the depth of the cavity of the converter It is preferable to apply so that the height of a molten metal may be 0.5 or more.

In addition, in the initial stage of the secondary drilling for decarburization, as shown in FIG. 5, the slag volume is secured by securing the slag volume through the lance height upward and the upward flow rate, and the secondary lance height downward and the peak flow rate are increased. Induce rapid rapid decarburization reaction to shorten the blowing time, and at the end of the second blowing can promote the quicklime ash through the lance height up and down the flow rate to maximize the control of the end point (P) component.

Then, according to the amount of oxygen transferred from the lance in accordance with the amount of oxygen calculated from the passion acid before the injecting after the secondary sub-material is fed (S330), the blowing is completed (S340).

When the drilling is completed, the molten steel is pulled out from the converter to transfer the molten steel to the ladle (S350). In addition, during the molten steel tapping, in order to make the quality required by the demand, alloy steel is added to the ladle together with the tapping (S360). At this time, the raceway is to tap the molten steel to the ladle, the slag injured in the molten steel is tapping until just before the outflow to the ladle (S370).

As described above, an appropriate amount of slag to be used for the next charge is left in the converter completed with tapping with the ferroalloy (S380), and the second slag discharge (S380) for discharging the other slag is performed. And after the secondary slag is excavated (S210) and the slag coating agent, such as dolomite, light dolomite, and summit stone is added to the remaining slag (S220) to repeat the series of converter processes as described above.

According to the method of manufacturing ultra low lean steel using the converter slag of the present invention as described above, it is possible to control the components of phosphorus (P) by using a low base degree and residual slag during the first drilling, the molten steel at the time when the second drilling is completed The component of phosphorus (P) contained in it can be controlled to 120 ppm or less as shown in FIG.

In other words, 80% to 85% of the total amount of slag remaining in the converter in the remaining slag discharge (S250), which is a step before charging the scrap iron and molten iron in the converter (S260), and proceeds with the primary drilling. That is, conventionally, the basicity in slag at the time of completion of converter blow is about 4.0 ~ 4.5% level as can be seen in the composition of slag after the conventional converter tapping in Table 3, where P ₂ O ₅ is approximately 2.5% level. to be.

If the amount of residual slag is 25 tons, the amount of quicklime contained in the double is calculated to be approximately 8750-12500 kg. And, the slag forming for the primary slag excretion (S300) carried out after the first blow (S290) to remove the P contained in the molten iron in the converter is about 4 ~ 5m as shown in FIG. In order to optimize, the basicity target should be 1.0 to 1.5. However, in order to maintain about 500 ppm of phosphorus (P) in the converter after the first blow (S290), the required basicity is appropriate 2.0 to 2.5 (see Fig. 8).

Therefore, the amount of molten iron charged into the converter is 300 tons, the Si content in the molten iron is 0.4%, and when the required amount of quicklime satisfying the required basicity 2.0 is calculated using Equation 2, it is 5,136 kg. In addition, SiO2 is 2,500 kg when the end point slag is 10%, and when the quicklime is 40%, the amount of quicklime is 10,000 kg, and the basicity is 4.0.

Therefore, when Si in the molten iron reacts with oxygen to become SiO 2, it becomes 1,473 kg. The calculated basicity at this time is 2.51 as in Equation (9).

In general, the residual slag is regarded as a by-product generated in the converter, and in the past, the residual slag was disposed of in the converter for disposal. However, as described above, by using an effective component of the residual slag, the amount of quicklime input to the basicity can be reduced.

On the other hand, in the case of the first blow (S270), the residual slag generated in the previous charge (Rege) is recycled, but in some cases, a small amount of quicklime (1 ~ ~) by correcting the basicity of Si in the molten iron of the charge (Charge) 2 tons) and a source of iron oxide (FeO) and raw materials containing iron oxide for cooling (sintered ore, protective lime, etc.) may be added. In addition, the sintered ore may be additionally added according to the target temperature and carbon concentration after the first blowing.

9 is a graph showing the change of the phosphorus (P) component according to the molten steel temperature after the first blowing according to the present invention. Referring to the drawings, it can be seen that as the temperature of the molten steel increases, the phosphorus (P) component after dephosphorization increases. In addition, when the temperature of molten steel is low, it can be seen that the phosphorus (P) component is kept low. Accordingly, in consideration of the target temperature after Tallinn as the tapping temperature during the first blowing for Tallinn, it is preferable to passionate at 1350 ~ 1400 ° C. When the temperature is above the above temperature, a raw material containing iron oxide may be further added.

According to the method for manufacturing ultra low lean steel using the converter slag of the present invention, the slag generated during the converter process is left in the converter, charging the scrap iron and molten iron and performing the primary blow (S270) to control the composition of phosphorus (P). By dephosphorization, and by performing the second blow for decarburization, it is possible to reduce the input amount of quicklime during the first blow, at this time can control the components of phosphorus (P) contained in the molten steel to less than 500ppm, the second When the blow is completed (S340) it is possible to control the component of the phosphorus (P) contained in the molten steel to 120ppm has the effect of producing a high-quality ultra-low steel.

On the other hand, the present invention is not limited only to the embodiments described above, but can be modified and modified within the scope not departing from the gist of the present invention, it should be seen that such modifications and variations are included in the technical idea of the present invention. do.

The method for producing ultra low lean steel using converter slag according to the present invention can reduce the amount of quicklime injected into molten iron and control the component of phosphorus (P) contained in the molten steel to 120 ppm or less, thereby providing high quality poles. Has the effect of producing low-lining steel.

Claims (6)

Slag coating step of coating the converter refractory using the slag remaining in the previous process; Scrap metal and molten iron input step of charging the scrap iron and molten iron in the converter after the slag coating step; A first blowing step of dephosphorizing so as to control P contained in the molten iron charged into the converter after the scrap iron and molten iron input step to 500 ppm or less; A first slag discharging step of intermediately disposing slag having a content of P ₂ O ₅ of 3.5% or more after the first blowing step; A second blowing step of decarburizing to remove C contained in the molten iron after the first slag excretion step; After the second blowing step, the deferring and decarburized molten steel is pulled out to the ladle and the ferroalloy is added to the ladle at the same time; And Ultra-low-lining steel production method of less than 120 ppm of phosphorus component using a converter slag including a secondary slag discharging step of remaining and excluding some slag in the converter after finishing the tapping step after the ferroalloy. The method according to claim 1, The method for producing ultra-low steel using a converter slag further comprising the step of excluding 15 ~ 20% of the slag remaining in the converter before the scrap iron and molten iron input step. The method according to claim 1, The first blowing step, ultra-low strength steel manufacturing method using a converter slag characterized in that the cavity depth of the converter / the height of the molten metal is 0.1 ~ 0.15 soft blowing uptake pattern is applied. The method according to claim 1, Oxygen flow rate supplied to the molten iron during the first blow, is a method for producing ultra-low steel using a converter slag, characterized in that 20 to 30% of the total amount of oxygen, depending on the Si contained in the molten iron. The method according to claim 1, The first slag excretion step, the ultra-low-lining steel production method using a converter slag characterized in that the intermediate slag slag content of more than 3.5% of P ₂ O _{5 in} the slag. The method according to claim 1, The second blowing step, ultra-low steel manufacturing method using a converter slag, characterized in that the cavity depth / molten metal of the converter is applied to the indentation pattern of 0.5 or more.

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