KR20120057368A - Tundish flux composite and Method of manufacturing the same - Google Patents

Abstract

PURPOSE: A tundish flux composition and a manufacturing method thereof are provided to effectively control SiO2(Silicon Dioxide) and Al2O3(Alumina) inclusions produced during manufacture of tire cord steel. CONSTITUTION: A tundish flux composition comprises CaO(Calcium Oxide) of 43-47wt.%, SiO2 of 36-40wt.%, MgO(Magnesium Oxide) of 5-12wt.%, Al2O3 of 0.5-3wt.%, T.Fe(Total Iron) of 0.1-1wt.%, and MnO(Manganese Oxide) of 2-4wt.%. The weight ratio of SiO2 and CaO is 1.1-1.3:1.

Description

Tundish flux composite and method of manufacturing the same

The present invention relates to a tundish flux composition having a specific composition and a method for manufacturing the same, and also to a method for manufacturing a tire cord steel having improved cleanliness using the tundish flux composition.

Tire cord steel is a new wire that processes 5.5 mm ø diameter wire rod up to 0.175 ~ 0.15 mm ø fine wire, and should not be disconnected during processing.The factors of such disconnection include non-metallic inclusions and center segregation. As nonmetallic inclusions, Al ₂ O ₃ inclusions act as the main factor.

According to existing literature and patents, in order to control such Al ₂ O ₃ inclusions in the steelmaking and refining process, RH (Rheinstahl and Heraeus, vacuum degassing equipment) is omitted during the steelmaking process, the special ladle refractories made of zircon, alloy Al or Al ₂ O ₃ to eliminate Al mixing source, such as management of Al content and ferrous alloy injection time and improvement of performance functional refractory material The part where there is a concern about mixing evenly improves that there is almost no Al. However, this series of efforts to reduce Al ₂ O ₃ inclusions result in higher oxygen in the steel, resulting in increased SiO ₂ inclusions produced by LF->tundish-> casting temperature drop and reoxidation of molten steel. Doing. In addition, when Al in the molten steel is not controlled to the level of 5 ppm, there is a problem in that Al ₂ O ₃ inclusions are generated during the LF->tundish-> casting process.

In order for the tire cord steel to be processed into ultra-fine wires with a diameter of less than 0.10 mmø for cutting silicon for semiconductors, SiO ₂ inclusions must be removed together with Al ₂ O ₃ inclusions in the steel. In particular, since tire cord steel controls oxygen in the steel by Si, the amount of SiO ₂ inclusions tends to be largely influenced by the amount of oxygen, and the oxygen in the steel is combined with the ladle slag present in the upper part of the molten steel together with the components in the molten steel. When molten steel is injected into the tundish for performance, it depends on the composition of the tundish flux that is injected into the top of the tundish molten steel.

Secondary refining ladle slag in use is controlled to 0.9 ~ 1.1 weight ratio of CaO / SiO ₂ for low melting point control of inclusions in tire cord steel, and T.Fe of ladle slag is 1 ~ 2% by weight. I'm in control. The amount of T.Fe is an amount that can cause the oxidation reaction of Si and Al in the steel, and acts as a factor causing the generation of SiO ₂ and Al ₂ O ₃ inclusions, and the slag composition of the low melting point is used to stir the molten steel during the LF heating operation. The possibility of slag entering the molten steel by argon (Ar) gas and remaining as a large inclusion in the molten steel increases. Therefore, in order to reduce the mixing of the ladle slag during stirring with the control of T.Fe in the ladle slag, an element having excellent oxidation power to increase the CaO / SiO ₂ weight ratio of the ladle slag or to remove oxygen from the ladle slag There is a method for deoxidizing the ladle slag by inputting.

On the other hand, after ladle refining (secondary refining) molten steel is injected into the tundish, in which the tundish flux is injected into the upper portion of the molten steel in order to prevent re-oxidation of the molten steel. This tundish flux prevents reoxidation of molten steel and absorbs and removes inclusions in the steel. However, the molten steel temperature is lowered in the process of injecting molten steel into the tundish from the ladle, thereby reducing the solubility of Si and Al in the molten steel, thereby promoting the production of SiO ₂ and Al ₂ O ₃ . When this composition of the inclusions in the tundish can increase the SiO ₂ and Al ₂ O ₃ and finally changed to SiO _2, Al ₂ O ₃ inclusions sex. In particular, in order to improve productivity, every steel mill has been actively performing and trying to increase the number of rings, while the tundish flux, once put into the first charge of the cast, is used to prevent molten steel from being heated on top of it. It is currently difficult to reinject the tundish flux while the tanwa rice hull (SiO ₂ is composed of 45 to 60% by weight) is introduced and the performance is in progress. In addition, as the performance progresses, the inclusions in the river rise and are absorbed into the tundish flux, and the tanwa bran is also dissolved in the tundish flux, so that the composition of the tundish flux is increased in SiO ₂ , Al ₂ O ₃ , and T.Fe also increases. Will be displayed. Therefore, as the performance progresses, SiO ₂ , Al ₂ O _{3 in} the steel of the tundish flux Absorption capacity of inclusions decreases gradually, and inclusion potentials such as SiO _{2 in} steel by T.Fe gradually increase, resulting in problems affecting the cleanliness of steel. However, since there is currently no way to refresh the composition of the tundish flux during the performance, the composition of the tundish flux to be injected into the first charge of the performance is different from the existing method, and the input amount needs to be improved.

Accordingly, the present inventors have found that SiO ₂ existing in the tire cord steel in order to manufacture the tire cord steel into the ultra fine wire, and even the ultra fine wire. And Al ₂ O ₃ to minimize or prevent the generation of these materials, and after a long study, the use of tundish flux with a specific composition and composition ratio in the production of tire cord steel, increasing the SiO in the molten steel during the casting process ₂ And Al ₂ O ₃ It was found that the inclusions can be controlled, and the present invention was completed by recognizing that the tundish flux can be recycled as it is, ladle slag obtained by adding calcium to the upper ladle slag in the LF.

Accordingly, an object of the present invention is to provide a tundish flux composition having a specific composition and a method of manufacturing the same, and also to provide a method of manufacturing a tire coat steel using the tundish flux.

To achieve the above object, the present invention relates to a tundish flux, CaO 43 to 47% by weight, SiO ₂ 36 to 40% by weight, MgO 5 to 12% by weight, Al ₂ O ₃ 0.5 to 3% by weight, T 0.1 to 1% by weight of Fe, and 2 to 4% by weight of MnO.

In addition, the present invention relates to a method for manufacturing the tundish flux, and after the secondary refining of the molten steel refined converter in a ladle furnace (LF, Ladle furnace), the second refined molten steel is supplied to the tundish When manufacturing the tire cord steel by the soft casting process of casting the bloom, during the second refining process, 15 to 40 kg of calcium (Ca) per ton of ladle slag is added to the upper part of the ladle slag to provide ladle slag. It is another feature to deoxidize to produce tundish flux compositions.

In addition, the present invention relates to a method for manufacturing a tire cord steel, after the secondary refined molten steel in the ladle furnace, and then supplied the secondary refined molten steel to the tundish, and then the tundish flux composition is added to bloom Another feature is the manufacture of a tire cord steel by a cast casting process.

The tundish flux composition of the present invention can recycle the ladle slag generated in the secondary refining, and because the melting point is lower than the conventional tundish flux, SiO ₂ generated during the production of tire cord steel And Al ₂ O ₃ The bar can effectively control the inclusions, it can provide a tire cord steel with excellent mechanical properties and workability, and when the wire rod of the tire cord steel material is processed to produce ultra-fine wire, even ultra-fine wire, there is a problem that the wire is broken It is possible to provide a tire cord steel with excellent cleanliness.

Figure 1 shows the composition change of the deoxidized ladle slag and conventional ladle slag carried out in the present invention, MgO is 5% by weight state phase (CaO-SiO ₂ -Al ₂ O ₃ ).
Figure 2 shows the change in the composition of the existing tundish flux (A-type flux) being used commercially and compatible with the tundish flux composition of the present invention, A is a state phase without Ca (O-SiO ₂ -Al ₂ O ₃ ) , B is a state phase (CaO-SiO ₂ -Al ₂ O ₃ ) having MgO of 5% by weight.
3 is a graph showing the relationship between T.Fe and wire T. [O] performed in the experimental example.
4 is a graph showing the relationship between the wire T. [O] and the size of the wire inclusions carried out in the experimental example.

The term "T. [O]" used in the present invention is an index indicating the amount of inclusions in the wire rod, and is a cost solution that exists as soluble oxygen (free oxygen) and oxide inclusions present in the tire cord steel. Refers to the amount of oxygen in which oxygen is added (insoluble oxygen), and "T.Fe" represents the total weight percentage of Fe present in the form of iron oxide contained in the tundish flux.

In addition, the term "wire" used in the present invention means a wire for tire cords.

Hereinafter, the present invention will be described in more detail.

The tundish flux is introduced into the tundish for the purpose of preventing reoxidation of the molten steel and removing the inclusions in the molten steel into the flux while the molten steel is injected into the tundish.

The present invention relates to a tundish flux composition capable of minimizing the occurrence of silicon oxide inclusions and aluminum oxide inclusions produced during the production of tire steel by adjusting the composition of the tundish flux, CaO, SiO ₂ , MgO, Al ₂ O ₃ , T.Fe, and MnO, characterized in that the tundish flux may further include other impurities unavoidable in addition to these compositions.

Specifically, the composition ratio of the tundish flux composition of the present invention, CaO 43 to 47% by weight, SiO ₂ 36 to 40% by weight, MgO 5 to 12% by weight, Al ₂ O ₃ 0.5 to 3% by weight, T. It contains 0.1 to 1% by weight of Fe, and 2 to 4% by weight of MnO, and if the components are outside the composition ratio proposed by the present invention, since the silicon oxide inclusions and aluminum oxide inclusions generated during the production of the tire steel can not be controlled, Tired steel having physical properties or properties to be produced cannot be obtained.

In addition, the present invention is preferably characterized in that the weight ratio of CaO and SiO _{2 in} the tundish flux composition is 1.1 to 1.3: 1, and comprises 0.1 to 0.5% by weight or less of the T.Fe.

In the tundish flux composition of the present invention, after refining molten steel for the second time in a molten steel heating apparatus (LF, Ladle furnace), the second refined molten steel is supplied to the tundish, followed by the casting of bloom In the process of manufacturing the tire cord steel in the reproducing process, by deoxidizing the ladle slag generated in the LF, the composition is the same as the deoxidized laid slag, through the description of the laid slag, the present invention It will help to understand the tundish flux composition of the.

The composition of the ladle slag is a very important factor in terms of the composition of silicon oxide and aluminum oxide inclusions and removing them. In manufacturing tire cord steel, the existing ladle slag composition has a basic degree of ladle slag as shown in FIG. Phosphorus CaO / SiO ₂ weight ratio was 0.9 to 1.0 level, Al ₂ O ₃ concentration in the ladle slag was controlled to within 3% by weight, MgO concentration in the ladle slag at the LF start is approximately 5 to 10% by weight, T Fe was 1-2% by weight and T.Fe + MnO was 5% by weight. However, the deoxidized ladle slag composition in the present invention has a CaO / SiO ₂ weight ratio of 1.1 to 1.3, which is related to the T.Fe content of the ladle slag. Ladle As the CaO / SiO ₂ weight ratio in the slag increases, the smaller the content of T.Fe, the T.Fe The lower the oxygen potential in the molten steel becomes lower by re-oxidation SiO ₂ The inclusions and Al ₂ O ₃ inclusions are less generated. In view of this, it is preferable to adjust the CaO / SiO ₂ weight ratio higher than the existing ladle slag composition. However, the CaO / SiO ₂ weight ratio in order to reduce the problem because the slag does not melt occurs, T.Fe content in the molten steel to a temperature of about 1550 ℃ if CaO / SiO ₂ weight ratio is increased slag melting point is increased, as shown in Figure 1 You can't increase it. Therefore, in the present invention, the ladle slag is deoxidized to 1% by weight or less, preferably 0.1 to 1% by weight, and more preferably 0.1 to 0.5% by weight, so that the CaO / SiO ₂ weight ratio and T.Fe The content was adjusted.

Since the material of the lag slag MgO is MgO component of the slag line portion of the ladle slag, the MgO should be controlled to prevent refractory loss. In addition, when the Al ₂ O ₃ in the ladle slag exceeds 3% by weight, the Al ₂ O ₃ concentration of the inclusions increases, so it is likely to be a hard inclusions, so it is 3% by weight or less, preferably 0.5 to 3% by weight. Must be controlled in%

Deoxidized ladle slag having the above composition has a low melting point of 1400 to 1480 ° C, preferably 1400 to 1450 ° C.

The tundish flux composition of the present invention recycles such deoxidized ladle slag, and because the composition is the same as the deoxidized ladle slag, even when molten steel is injected into the tundish, low during ladle refining (secondary refining). The composition of the inclusions controlled by the melting point composition also does not change.

Existing tundish flux (type A flux) that is commercially used as shown in Figure 2 is 40 to 48% by weight of CaO, 48 to 56% by weight of SiO ₂ , Al ₂ O ₃ 2 to 4% by weight and other unavoidable components Although the melting point is 1500 to 1550 ° C., the tundish flux composition of the present invention not only melts at a higher speed than the same amount as the conventional A-type flux, but also increases the amount of flux covering the molten steel in a liquid state. It has characteristics. Furthermore, since the CaO / SiO ₂ weight ratio is higher than that of the conventional A-type flux, the amount of inclusions in the molten steel is also reduced, and the absorption capacity of the inclusions in the molten steel can be continued even if the performance is performed.

Further, the tundish flux composition of the present invention is characterized by having an average particle diameter of 10 mm or less, preferably 8 mm or less, and more preferably 1 to 5 mm. The size distribution of the tundish flux is largely related to the rate of dissolution of the particles. As the tundish flux melts at the same time as it is added, the liquid phase thickness of the flux in contact with the molten steel must be generated quickly to reduce the reoxidation of the molten steel and to perform the smooth playing operation. In view of this, the tundish flux according to the present invention has a melting point lower than that of the conventional A-type flux, but in order to obtain a more effective dissolution rate, the average particle diameter is preferably 10 mm or less.

In addition, when the tire cord steel is manufactured using the tundish flux composition of the present invention, the following Equation 1 is satisfied.

[Equation 1]

In Equation 1, T [0] refers to the total amount of oxygen combined with dissolved oxygen (Free oxygen) present in the tire cord steel and undissolved oxygen present as an oxide inclusion, and T.Fe is a tundish. It represents the total weight percentage of Fe present in the form of iron oxide contained in the flux.

In addition, the tundish flux composition of the present invention described above is carbon (C) 0.69 to 0.94% by weight, silicon (Si) 0.15 to 0.25% by weight, manganese (Mn) 0.25 to 0.55% by weight, sulfur (S) 0.007% by weight or less And when manufacturing a tire steel containing 0.013% by weight of phosphorus (P), it is preferred to use the added to the cast.

Hereinafter will be described in detail with respect to the manufacturing method of the tundish flux composition of the present invention.

According to the present invention, after refining molten steel for the second time in a molten steel heating furnace (LF, Ladle furnace), the second refined molten steel is supplied to the tundish, and then the tire cord steel is cast in a bloom casting process. In preparing the second step, 15 to 40 kg of calcium (Ca) per ton of ladle slag is added to the upper part of the ladle slag to deoxidize the ladle slag to prepare a tundish flux composition. have.

And, the ladle slag before deoxidation is CaO 35 to 45% by weight, SiO ₂ 38 to 45% by weight, Al ₂ O ₃ 3% or less, T.Fe 1 to 2% by weight, MnO 2 to 5% by weight, MgO 5 To 10 wt%.

When Ca is added, Ca has a relatively stronger binding force with oxygen than Fe, which deprives the oxygen from Fe oxide and reduces the oxygen potential, and when only Ca itself is added to the slag, Ca is added before the proper reaction with Fe oxide. Since the reaction efficiency may be reduced by evaporation of the gas, it may be added in the form of metal-calcium (Ca) alloy, and more preferably in the form of Fe-Ca alloy. However, as described above, but in the form of an alloy, the amount of Ca is added to adjust the amount of alloy so that the amount of 15 to 45 kg per slag, the Ca amount is 30% of the real rate Ca is dissolved in the slag to react with Fe oxide It is the range calculated in consideration of the amount capable of reducing all about 1% by weight of the Fe oxide present in the slag and slag, and when Ca is added to molten steel, it can react directly with oxygen in the steel to generate inclusions having high CaO. It is preferable to feed into slag, not molten steel.

The tundish flux composition will recycle deoxidized lag slag, and the tundish flux composition and the deoxidized lag slag have the same composition as described above.

In addition, the present invention relates to a method for producing a tire cord steel using the tundish flux composition, after the secondary refined molten steel in the ladle furnace, and then supply the secondary refined molten steel to the tundish, The tire cord steel may be manufactured by a soft casting process in which the tundish flux composition described above is bloom cast, and the composition of the manufactured tire cord steel is carbon (C) 0.69 to 0.94 wt% and silicon (Si) 0.15 to 0.25 Wt%, manganese (Mn) 0.25 to 0.55 wt%, sulfur (S) 0.007 wt% or less and phosphorus (P) 0.013 wt%, and may also include other indispensable ingredients.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the scope of the present invention is not limited by the following examples.

[ Example ]

Example

Tires containing 0.69 to 0.94% by weight of carbon (C), 0.15 to 0.25% by weight of silicon (Si), 0.25 to 0.55% by weight of manganese (Mn), 0.007% by weight or less of sulfur (S) and 0.013% by weight of phosphorus (P) In order to manufacture cord steel, 100 tons of molten steel manufactured from an actual converter was pulled out with CaO and CaO-SiO ₂ fluxes and FeSi and FeMn alloy irons as zircon refractory ladles, and then transferred to LF. The molten steel component was finally controlled with the molten steel temperature rising. Then, approximately 110 kg of Fe-Ca alloy was evenly added to the upper slag so that the amount of Ca per ton of ladle slag was 15 kg, thereby preparing deoxidized ladle slag having the composition of Table 1 below. However, the composition of Table 1 below excludes other indispensable compositions. In addition, the ladle slag composition of Table 1 was obtained using XRF (X-ray Fluorescence, X-ray fluorescence spectrometer) to determine the composition and composition ratio.

CaO SiO ₂ MgO Al ₂ O ₃ T.Fe MnO CaO / SiO ₂ Melting temperature 46
weight% 39
weight% 10.1
weight% 2
weight% 0.4
weight% 2.5
weight% 1.18
Weight ratio 1435 ℃

Manufacturing example

After injecting molten steel of ladle refining (secondary refining) in the LF of the above embodiment into a tundish, a bloom was prepared using a 400 mm × 500 mm bloom machine, which was then rolled into a 160 mm × 160 mm steel piece, Wire rod for 5.5 mm tire cord was manufactured through wire rod process. Then, the deoxidized ladle slag prepared in the above example was pulverized to 10 mm or less, and the recycled tundish flux was added once to the upper part of the first charge of the lead.

Experimental Example

T. [O], which is an indicator of indirectly indicating the amount of inclusions in the tire cord wire manufactured in the manufacturing example, and the tundish flux used in the manufacturing example (recycled deoxidized ladle slag prepared in the example) Data showing the relationship with T.Fe contained in) is shown in FIG. 3. Here, T. [O] was analyzed by an O ₂ / N ₂ simultaneous analyzer (LECO Co., Ltd.) capable of simultaneously analyzing oxygen and nitrogen in steel.

In addition, T. [O] in the wire rod and Max. T, the wire inclusion inclusion size, were measured, and the results are shown in FIG. 4. Here, Max.t randomly samples the tire cord wire rod and processes it with a cross section of 5.5mm × 12mm, and then uses the optical microscope to measure the thickness of the inclusion having the largest thickness among all inclusions observed within the cross-sectional area. it means. In the process of reducing the size of the steel during processing of the slabs and wire rods in the bloom, the inclusions in the steel are also subjected to the compressive forece and stretched in the longitudinal direction of the steel. The harder inclusions do not increase, the softer inclusions increase well and the thickness becomes smaller, and the thicknesses of these inclusions are measured by optical microscopy, and the thickness of the largest inclusions is selected as Max.t.

 3 and 4 show the relationship between the T. [O] of the wire of the tire cord steel manufactured using the commercially available A-type flux and the T.Fe of the A-type flux and the size of the wire inclusions.

3, when the T.Fe in the tundish plus as controlled by the present invention, such as 1% by weight or less, preferably 0.5% by weight T. [O] is stable to 10 ppm level compared to the conventional 15 ppm level You can see that it is being controlled.

4, it can be seen that in the case of the present invention, T. [O] is controlled at the level of 10 ppm, and the average Max.t at this time is approximately less than 1 μm, which is much smaller than the inclusion size found in existing wire rods. Can be.

Through the above experimental example, when the tire is manufactured using the tundish flux composition of the present invention, since the T.Fe content is small in the tundish flux composition, the T [O] value is low, and thus, inclusions in the wire rod. It can be seen that the size of. That is, when the tire is manufactured through a soft casting process using the tundish flux composition of the present invention, SiO ₂ And Al ₂ O ₃ Since the inclusions can be effectively controlled, it can be confirmed that not only the mechanical properties and the workability but also the tire steel having excellent cleanability can be produced.

By using the tire steel of the present invention, it is expected that an ultrafine wire or an ultrafine wire excellent in physical properties and workability can be efficiently produced.

Claims (14)

43 to 47 weight percent CaO, 36 to 40 weight percent SiO ₂ , 5 to 12 weight percent MgO, 0.5 to 3 weight percent Al ₂ O ₃ , 0.1 to 1 weight percent T.Fe, and 2 to 4 weight percent MnO Tundish flux composition.
The tundish flux composition of claim 1, wherein the weight ratio of CaO to SiO ₂ is 1.1 to 1.3: 1.
The tundish flux composition for manufacturing a tire cord steel according to claim 1, wherein the T.Fe is present in an amount of 0.1 to 0.5 wt%.
The tundish flux composition according to claim 1, having a melting point of 1,400 ° C to 1,480 ° C.
The method of claim 1, further comprising: a tundish flux composition satisfying Equation 1 below;
[Equation 1]

In Equation 1, T [0] represents the total amount of oxygen combined with dissolved oxygen (Free oxygen) present in the tire cord steel and undissolved oxygen present as an oxide inclusion, and T.Fe is a tundish flux. It represents the total weight percentage of Fe present in the form of iron oxide contained in.
The method according to any one of claims 1 to 5,
A tundish flux composition having an average particle diameter of 10 mm or less.
The method according to claim 6,
Tires containing 0.69 to 0.94% by weight of carbon (C), 0.15 to 0.25% by weight of silicon (Si), 0.25 to 0.55% by weight of manganese (Mn), 0.007% by weight or less of sulfur (S) and 0.013% by weight of phosphorus (P) A tundish flux composition, characterized in that it is used for the production of cord steel.
After refining molten steel in secondary converter in LF (Ladle furnace), supply secondary refined molten steel to tundish, and then produce tire cord steel by soft casting process. In
When the secondary refining, 15 to 40 kg of calcium (Ca) per ton ladle slag (ton) ladle slag is added to the upper ladle slag to deoxidize the ladle slag to prepare a tundish flux composition.
The method of claim 8,
The calcium is a method for producing a tundish flux composition, characterized in that the input in the form of Fe-Ca alloy.
The method of claim 8,
And said tundish flux recycles said deoxidized ladle slag.
The method of claim 8,
The ladle slag before deoxidation may be 35 to 45% by weight of CaO, 38 to 45% by weight of SiO ₂ , 3% or less of Al ₂ O ₃ , 1 to 2% by weight of T.Fe, 2 to 5% by weight of MnO, and 5 to 10% of MgO. A method of making a tundish flux composition comprising weight percent.
The method of claim 9,
Was the deoxidizing the ladle slag and the tundish flux has the same composition, the tundish flux CaO 43 to 47 wt%, SiO ₂ 36 to 40 wt.%, MgO 5 to 12% by weight, Al ₂ O ₃ 0.5 to 3 A method of making a tundish flux composition comprising: by weight, 0.1 to 1 weight percent T.Fe, and 2 to 4 weight percent MnO.
After refining the molten steel for the second time in the ladle furnace, and supplying the secondary refined molten steel to the tundish, the tire cord steel is manufactured by the casting process of bloom casting by injecting the tundish flux composition of claim 6 How to.
The method of claim 13,
The tire cord steel is carbon (C) 0.69 to 0.94% by weight, silicon (Si) 0.15 to 0.25% by weight, manganese (Mn) 0.25 to 0.55% by weight, sulfur (S) 0.007% by weight or less (P) 0.013 weight Method for producing a tire cord steel, characterized in that it comprises a%.

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