KR20160059824A - Refinery flux and manufacturing method for steel using the same - Google Patents

Abstract

According to the present invention, a steel manufacturing method using refined slag comprises: a process of passing molten steel through refined slag to absorb at least a portion of inclusions of the molten steel in the refined slag; a process of allowing the refined slag mixed into the molten steel which has passed through the refined slag and the inclusions of the molten steel which has passed through the refined slag to react with each other to produce a reactant; a casting process of using the molten steel which has passed through the refined slag to cast a casting; and a process of performing hot-work at a temperature at which the reactant in the casting is melted. The inclusions in steel are refined to suppress or prevent a defect caused by the inclusions.

Description

TECHNICAL FIELD [0001] The present invention relates to a refining slag and a steel material manufacturing method using the refining slag,

The present invention relates to a refining slag and a method of manufacturing a steel material using the refining slag, and more particularly, to a refining slag capable of suppressing or preventing defects by refining inclusions in the steel material and a method of manufacturing a steel material using the refining slag.

In general, when nonmetallic inclusions present in molten steel can not be removed through the casting process of molten steel or the like, the nonmetallic inclusions can cause defects such as large-scale physical scabs or slivers in the final product have. Such defects may cause disconnection in the case of the wire rod, and may cause rust in the case of the steel strip even in the case of no surface defects.

In order to remove the defects described above, the molten steel is subjected to a refining process such as decarburization and deoxidation. At this time, decarburization is performed in order to control the content of carbon in the molten steel to a target concentration. The molten steel subjected to decarburization contains a high concentration of oxygen. Therefore, an alloy or a pure material containing Al, Si, Mn, Deoxidizing agent is added to perform deoxidation.

At this time, the deoxidation products of the molten steel include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), or composite oxides, and they remain in the molten steel.

In addition, molten steel is introduced simultaneously with slag in an argan oxygen decarburization (AOD) refining furnace, and introduced into molten steel containing slag inclusions. The slag inclusions can precipitate the high melting point spinel inclusions. Since the slag inclusions adversely affect the quality of the final product, it is essential to suppress the formation of inclusions in the molten steel state, to eliminate and to eliminate harmful substances, and to control it, various methods of molten steel refining have been studied .

KR 10-1356842 B KR 10-1356928 B KR 10-1356889 B

The present invention provides a refining slag capable of suppressing the occurrence of defects due to inclusions and a method of manufacturing a steel material using the same.

The present invention provides a refining slag and a method of manufacturing a steel product using the refining slag capable of suppressing or preventing the inclusions present in the steel material from becoming defects due to refinement.

The refining slag according to the present invention is characterized in that it comprises 30 to 45% by weight of CaO, 40 to 56% by weight of SiO ₂ , 3 to 15% by weight of Al ₂ O ₃ and 3 to 7% by weight of MgO as refining slag . In this case, the refining slag may have a basicity (CaO / SiO ₂ ) of 0.6 to 1, and the sum of Al ₂ O ₃ and MgO may be more than 10% by weight and less than 20% by weight.

The refining slag may form a reaction product comprising a _{CaO-SiO 2 -Al 2 O 3} -MgO.

A method for manufacturing a steel material according to the present invention comprises the steps of passing molten steel through refining slag and absorbing at least a part of inclusions of the molten steel into the refining slag; Reacting the refining slag mixed with molten steel passing through the refining slag with inclusions of molten steel passing through the refining slag to produce a reactant; A casting step of casting the casting using molten steel passing through the refining slag; And a step of hot working the mixture to a temperature at which the reactants in the casting are melted.

And a step of cold-working the hot-worked casting after the hot-working step.

In the process of passing molten steel through the refining slag and absorbing at least a part of the inclusions of the molten steel into the refining slag, the molten steel may be made into droplets to pass through the refining slag.

The molten steel may contain at least 0.2 wt% Si and at most 10 ppm Al.

The refining slag contains 30 to 45 wt% of CaO, 40 to 56 wt% of SiO ₂ , 3 to 15 wt% of Al ₂ O ₃ and 3 to 7 wt% of MgO, and the basicity (CaO / SiO ₂ ) Lt; / RTI >

The refining slag reacts with the inclusion of molten steel passing through the refining slag to form a reaction product of CaO 30 wt% - SiO ₂ 55 wt% - Al ₂ O ₃ 10 wt% - MgO 5 wt%.

The hot working may be performed at a temperature of 1200 ° C or higher.

During the hot working, the reactant may be melted and changed into a liquid phase. At this time, the molten reactant may be stretched in the longitudinal direction of the casting during the hot working.

The cold working process may cause the elongated reactant to be broken after being solidified, and the coagulated reactant may be broken to a size of 10 mu m or less in the cold working process.

According to the embodiments of the present invention, inclusions present in molten steel can be lowered in melting point so that they can be melted in a processing step for producing a subsequent steel. Accordingly, when the casting is processed to produce a steel material, the inclusions can be melted and elongated along the machining direction of the steel material. In the course of processing the steel material, the elongated inclusion can be coagulated and fractured to be refined. Therefore, it is possible to suppress or prevent the inclusions from acting as defects in the steel due to their existence in the state of being refined in the steel, and it can help to reduce the wire diameter and thickness when manufacturing the wire rod or sheet have.

1 and 2 show an apparatus for refining molten steel in a method of manufacturing a steel material according to an embodiment of the present invention.
3 is a flowchart illustrating a method of manufacturing a steel material according to an embodiment of the present invention.
4 is a view schematically illustrating a state in which refining slag in a steel material is mixed in a steel material manufacturing method according to an embodiment of the present invention.
5 is a view for explaining the principle of refining the reactants contained in the steel material produced in the steel material manufacturing method according to the embodiment of the present invention.
6 is a photograph showing the reactants contained in the cast steel and the cross-sectional shape of the steel according to the experimental example of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of other various forms of implementation, and that these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know completely.

The present invention is a technique for manufacturing clean steel capable of suppressing the occurrence of defects due to inclusions in molten steel. More specifically, the present invention relates to a technology for deoxidizing molten steel and removing inclusions therefrom in order to minimize the occurrence of defects due to inclusions of Si deoxidized steel having a concentration of 10 ppm or less of high-quality wire materials (wire materials) to be. Here, the Si deoxidized steel may be a steel of molten steel which is deoxidized by using Si.

Various techniques have been known as methods for producing high-cleaned molten steel by suppressing or eliminating the formation of inclusions from the steelmaking process to the playing process before the solidification of molten steel is completed. Among them, a method for dropping molten steel and passing it through a refining slag to absorb inclusions in the molten steel by refining slag has been disclosed (Korean Patent No. 1356928). This is a method of removing inclusions in molten steel by increasing the reaction surface area between molten steel and refining slag. However, there is still a problem that the reactants generated by the reaction between inclusions in the molten steel and the refining slag are mixed and remain in the molten steel. These reactants act as a cause of disconnection when thin wires, wire cords such as tire cords, saw wires and the like, especially ultra fine wires, are drawn.

Accordingly, the present invention provides a refining slag capable of refining reactants to inhibit or prevent such reactants from acting as defects in a product, that is, defects in the production of steel products, and a method of manufacturing a steel product using the same.

First, the refining slag according to the embodiment of the present invention comprises 30 to 45 wt% of CaO, 40 to 56 wt% of SiO ₂ , 3 to 15 wt% of Al ₂ O ₃ , 3 to 7 wt% of MgO, / SiO ₂ ) of 0.6 to 1, and Al ₂ O ₃ And MgO is more than 10% by weight and less than 20% by weight. At this time, components other than CaO, SiO ₂ , Al ₂ O ₃ and MgO may inevitably be included.

The refining slag reacts with molten steel containing not less than 0.2% by weight of Si and not more than 10 ppm of Al to form a reaction product of 30% by weight of CaO - 55% by weight of SiO ₂ - 10% by weight of Al ₂ O ₃ - 5% by weight of MgO . Such reactants are low-melting point reactants and may be present in a liquid state at a temperature of 1200 ° C or higher.

The refining slag having such a composition reacts with the inclusions in the molten steel to form a low melting point reactant, which is absorbed in the steel material and then melted and drawn in the course of processing the steel material, cooled down, and then refined to a size of 10 탆 or less to be harmless .

1 and 2 are views showing an apparatus for refining molten steel in a steel material manufacturing method according to an embodiment of the present invention. FIG. 3 is a flowchart for explaining a steel material manufacturing method according to an embodiment of the present invention. FIG. 5 is a graph showing a state in which a reaction product contained in a steel material produced in the method of manufacturing a steel material according to an embodiment of the present invention is refined FIG. 6 is a photograph showing a cross-sectional shape of a steel material and a reactant contained in a steel material cast according to an experimental example of the present invention. FIG.

The refining apparatus applied to the method for manufacturing a steel material according to an embodiment of the present invention may be a refining apparatus for removing inclusions contained in molten steel until the molten steel is solidified and casted into a steel material, for example, a cast steel. This can be formed so that the molten steel can be passed through the refining slag by dripping the molten steel as in the apparatus disclosed in Korean Patent No. 1356928 mentioned above.

The refining apparatus applicable to the present invention can be configured as follows.

1 is a schematic cross-sectional view showing the structure of a ladle and a tundish for droplet formation of the present invention. The tundish can be made of a tundish body and a tundish cover, and the tundish body mentioned below can be understood as a tundish.

As shown in FIG. 1, in the refining process through the dropletization of molten steel, the molten steel 6 is first supplied from the ladle 5 to the tundish body 14. At this time, the molten steel 6 stored in the ladle 5 is connected to the opening / closing part 7 (or collector nozzle) at the lower part of the ladle 5 so that the molten steel is formed in the tundish body 14, (Not shown). When the molten steel 6 is injected from the ladle 5 through the long nozzle 9 as described above, dropping impact is reduced when the molten steel 6 is injected into the droplet forming portion 12 to prevent scattering of molten steel . The molten steel 6 injected into the droplet forming portion 12 passes through the droplet forming hole 25 of the droplet forming portion 12 and becomes dropletized. The molten molten steel falls and passes through the refining slag 15 Refined. The reference numeral 1 indicates that the dropletized molten steel falls. The molten steel passing through the refining slag 15 and having the inclusions removed therefrom can then flow down to the bottom of the weir 16 and be stored in the tundish body 14. The refining slag 15 located at the bottom of the droplet forming portion 12 is distinguished from the flux indicated by the reference numeral 17 as molten slag for refining molten steel to refine it. And the weir 16 can open a part of the lower portion to flow the refined molten steel 6.

In addition, the tundish does not have a separate molten steel receiving portion in which the molten steel to be injected from the molten steel storing portion such as a ladle is temporarily stored but passes through the droplet forming hole 25 of the molten steel forming portion 12 directly to perform the refining process can do. The droplet forming apparatus may be configured only by the droplet forming portion without having a separate molten steel receiving portion.

Fig. 2 shows a process of refining molten steel components and deoxidized molten steel in a steelmaking process by supplying molten steel from a ladle to a ladle to perform droplet refining.

There is shown a supply ladle for supplying molten steel in a molten steel supply device and a ladle for receiving molten steel as a receiving portion. At this time, in order to offset the amount of the molten steel 6 injected through the nozzle 29 in the upper side ladle 5 supplying the molten steel 6, the lower ladle 20 is provided with a separate The molten steel receiving portion 23 is formed. The upper side ladle 5 supplies molten steel to the molten steel receiving portion 23 by using the ladle opening / closing part or the long nozzle 29 or the like. The molten steel 6 stored in the molten steel receiving portion 23 flows into the droplet forming portion 22 beyond the side wall of the lower ladle 20. The molten steel 6 introduced from the droplet forming unit 22 performs a dropletization process through a plurality of droplet holes 25 '. Then, the molten steel which has been reduced in droplets passes through the slag 24 of a predetermined thickness mounted inside the lower ladle 20. The droplet forming portion 22 may be mounted on the inner surface of the lower ladle 20 or mounted on the side wall. The molten steel that has been dropletized through the plurality of droplet holes 25 'passes through the lower slag 24 while dropping, thereby performing droplet refining. At this time, the lower ladle 20 is filled with an inert gas such as argon gas to prevent the molten steel from being reoxidized. An inert gas such as argon gas can be supplied through the upper cover 27 or through the lower deodorization plug. And the lower ladle 20 may be covered by a ladle cover 27. [

It is needless to say that the refining apparatus for molten steel may be formed in various shapes that can make molten steel droplet in addition to the above structure.

Hereinafter, the principle of making the reactants contained in the steel material harmless in the process of manufacturing the steel material and the process of manufacturing the steel material will be described.

Referring to FIG. 3, a method of manufacturing a steel material according to an embodiment of the present invention includes a step S100 of preparing molten steel, a step S110 of refining and refining the molten steel, a step S120 of casting the steel, , A hot working step (S130), and a cold working step (S140). At this time, the cast steel may be formed into a thin plate shape by hot working and cold working, or may be formed into a wire shape. Hereinafter, an example in which a steel material is formed into a wire shape will be described.

The molten steel prepared in the process of preparing molten steel may have an Si content of 0.2 wt% or more and an Al content of 10 ppm or less. The molten steel may be molten steel having undergone one or more refining processes such as desulfurization, talline, decarburization and deoxidation.

The molten steel is accommodated in the ladle and can be transported to the refining apparatus for refining.

The refining process can be performed using the refining apparatus shown in FIG. 1 or FIG. 2 described above. Hereinafter, a refining method of the molten steel using the refining apparatus shown in FIG. 1 will be described.

Tundish body 14 prior to the refining of molten steel has a refining slag (15) may be provided, refining slag 15 CaO 30 to 45 wt%, SiO ₂ 40 to 56% by weight, Al ₂ O _{3 3} to (CaO / SiO ₂ ) of 0.6 to 1, and Al ₂ O ₃ And MgO in an amount of more than 10% by weight to less than 20% by weight, and components other than CaO, SiO ₂ , Al ₂ O ₃ and MgO may inevitably be included.

The molten steel (6) contained in the ladle (5) is supplied to the tundish body (14). At this time, the molten steel 6 contained in the ladle 5 is injected into the tundish body 14 through the long nozzle 9 connected to the opening / closing part 7 under the ladle 5. The molten steel 6 is injected into the droplet forming portion 12 in the tundish body 14 in the form of a stream 11 in the long nozzle 9 and the droplet forming hole 25 formed in the droplet forming portion 12 And is formed into a droplet. The molten steel droplet thus formed passes through the refining slag 15 provided in the lower part and falls in the refining slag 15 in the course of passing through the refining slag 15.

The inclusions contained in the molten steel droplets are absorbed into the refining slag 15 in the course of passing through the refining slag 15 as shown in Fig. Then, the molten steel liquid passes through the refining slag (15) and is added to the molten steel existing under the refining slag (15). However, a part of the refining slag 15 may be mixed with molten steel under the refining slag 15 to react with molten steel to form a reactant. The reaction product formed by the reaction between the refining slag 15 and inclusions in the molten steel may have a composition of 30 wt% CaO - 55 wt% SiO ₂ - 10 wt% Al ₂ O ₃ - 5 wt% MgO. Such reactants are low-melting point reactants and may be present in a liquid state at a temperature of 1200 ° C or higher.

Thereafter, refractory molten steel is used to cast castings such as casts, blocs, billets, and the like. The cast product may contain reactants generated by reaction between the refining slag 15 and inclusions in the molten steel.

Then, the casting is processed to produce a steel material.

The casting can be processed by sequentially performing hot working and cold working. The hot working and the cold working may be a rolling process for producing a thin plate or a drawing process for producing a wire rod. Here, a process for machining a wire rod of 100 탆 or less will be described.

The hot working is to heat the casting to 1200 ℃ or more to make the wire firstly to make the wire. At this time, the reaction product contained in the casting is melted and changed into a liquid phase in the process of heating the casting to 1200 ° C or higher. In the process of drawing the casting, the liquid reactant is elongated and elongated in the drawing direction of the casting, that is, in the longitudinal direction as shown in FIG.

Thereafter, the wire material produced by firstly drawing the casting material is cold-worked, that is, secondarily drawn, to produce the desired wire-shaped wire material. At this time, the cold working may be performed at a temperature of room temperature or higher, and preferably, the temperature may be lower than the temperature at which the reactants which are present in the molten state in the casting are solidified.

When the freshly drawn wire rod is secondarily drawn in a cold state, the solidified reactant solidified as shown in FIG. 5 is broken into a plurality of pieces in the process of drawing the wire rod. The reacted material in the solid phase is broken down to about 10 mu m in size and is present in the wire rod. Accordingly, even if the wire diameter of the wire rod is finely formed to about 100 탆, the size of the reactant present in the wire rod is as small as about 10 탆, so that the reactant in the wire rod can be prevented from acting as a cause of disconnection of the wire rod at the time of drawing.

Hereinafter, an experimental example for evaluating the quality of the steel material produced by the steel material manufacturing method according to the embodiment of the present invention will be described.

Experimental Example 1)

Firstly, refined molten steel was deoxidized and desulfurized to refine the components of the molten steel (LF, Ladle Furnace).

Thereafter, the casting was cast using the molten steel, the casting was heated to 1200 ° C, hot rolled, and then cold rolled to produce a steel.

Experimental Example 2)

Molten steel was subjected to liquid refining by using a tire cord steel (Al: 0.0001% to 0.001%, C: 0.75%, Si: 0.3%, Mn: 0.4%) having an Al content of 10 ppm or less. The refining slag contains 13.6 to 48.3% of CaO, 41.5 to 54.7% of SiO ₂ , and 10 to 29% of MgO, and the contents of CaO, SiO ₂ and MgO satisfy the following formula 1 .

(MgO)? -23.6 (CaO / SiO2) + 38.3

Thereafter, the casting was cast, the casting was heated to 1200 DEG C, hot rolled, and then cold rolled to produce a steel.

Experimental Example 3)

Molten steel having an Si content of 0.2 wt% or more and an Al content of 10 ppm or less was subjected to droplet refining. At this time, the refining slag CaO 30 to 45% by weight, SiO ₂ 40 to 56% by weight, Al ₂ O ₃ 3 to 15% by weight, and include MgO 3 to 7% by weight, and the basicity (CaO / SiO ₂₎ 0.6 to 1, and the sum of Al ₂ O ₃ and MgO is more than 10% by weight and less than 20% by weight, and components other than CaO, SiO ₂ , Al ₂ O ₃ and MgO may inevitably be included.

Thereafter, the casting was cast, the casting was heated to 1200 DEG C, hot rolled, and then cold rolled to produce a steel.

The specimens were taken from the steels prepared in Experimental Examples 1 to 3, and the number of inclusions (reactants) of 10 탆 or less per 1 g of specimen was measured and described in Table 1 below.

Number of inclusions (reactants) larger than 10 μm per 1 g of specimen Experimental Example 1 11-25 Experimental Example 2 16-26 Experimental Example 3 0

Referring to Table 1, in the case of Experimental Example 1, inclusion in the molten steel was not removed properly because the molten steel was refined by the general LF method.

In the case of Experimental Example 2, the refining slag was mixed with the molten steel in the process of refining the molten steel, and a large amount of the reactant formed by reacting with the inclusions in the molten steel was present in the steel. The reactants contained in the steel material produced in Experimental Example 2 had a high melting point and formed solid solid inclusions (CaMgSi ₂ O ₆ ) due to the high MgO content, and maintained a solid phase without being deformed into a liquid phase during hot rolling, As shown in FIG. Further, as shown in Fig. 6, they existed in the steel material with a size of 10 mu m or more, and they acted as a cause of disconnection in the steel material processing.

In the case of Experimental Example 3, a steel material was manufactured using refining slag according to an embodiment of the present invention. In the specimen collected from the steel material produced in Experimental Example 3, inclusions having a diameter of 10 탆 or more, i.e., a reactant, were not measured. This is because when the refining slag incorporated into the molten steel is refined by refining the molten steel, the reactant generated by the reaction with the inclusions in the molten steel is lowered in melting point, the reactant is changed into the liquid phase during the processing of the steel material and the elongated slag is solidified and fractured And it is understood that it is refined to 10 μm or less.

Although the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. Therefore, the scope of the present invention should not be limited by the described embodiments, but should be defined by the appended claims and equivalents thereof.

5: Ladle 6: Molten steel
7: opening / closing part 9: long nozzle
12: droplet forming unit 14: tundish body
15: refining slag 16: weir
17: flux 25: droplet forming hole
27: Ladle cover

Claims (14)

As refining slag,
30 to 45 wt% of CaO, 40 to 56 wt% of SiO ₂ , 3 to 15 wt% of Al ₂ O ₃ , and 3 to 7 wt% of MgO. The method according to claim 1,
The refining slag has a basicity (CaO / SiO ₂ ) of 0.6 to 1, and Al ₂ O ₃ And MgO is greater than 10 wt% to less than 20 wt%. The method of claim 2,
The refining slag refining slag to form a reaction product comprising a _{CaO-SiO 2 -Al 2 O 3} -MgO. Passing molten steel through the refining slag and absorbing at least a part of the inclusions of the molten steel into the refining slag;
Reacting the refining slag mixed with molten steel passing through the refining slag with inclusions of molten steel passing through the refining slag to produce a reactant;
A casting step of casting the casting using molten steel passing through the refining slag;
A step of subjecting the reactant in the casting to a hot melting process;
≪ / RTI > The method of claim 4,
And performing cold working of the hot-worked casting after the hot working. The method of claim 5,
Wherein the process of passing molten steel through the refining slag and absorbing at least a part of the inclusions of the molten steel into the refining slag comprises making the molten steel into droplets and passing the refining slag. The method of claim 6,
Wherein the molten steel contains at least 0.2 wt% Si and at most 10 ppm Al. The method of claim 7,
The refining slag comprises 30 to 45 wt% of CaO, 40 to 56 wt% of SiO ₂ , 3 to 15 wt% of Al ₂ O ₃ and 3 to 7 wt% of MgO,
Basicity (CaO / SiO ₂₎ is 0.6 to 1 in the steel material production method. The method of claim 8,
Wherein the refining slag reacts with inclusions of molten steel passing through the refining slag to form a reactant of CaO 30 wt% - SiO ₂ 55 wt% - Al ₂ O ₃ 10 wt% - MgO 5 wt%. The method of claim 9,
Wherein the hot working is performed at a temperature of 1200 ° C or higher. The method of claim 10,
Wherein the reactant is melted and changed into a liquid phase during the hot working. The method of claim 11,
Wherein the molten reactant is stretched in the longitudinal direction of the casting during the hot working. The method of claim 12,
Wherein the cold working step is a step of coagulating and breaking the elongated reactant. 14. The method of claim 13,
Wherein the coagulated reactant is fractured to a size of 10 mu m or less in the cold working process.

Images