KR101175631B1

KR101175631B1 - System for refining continuous casting materials and method thereof

Info

Publication number: KR101175631B1
Application number: KR1020100040512A
Authority: KR
Inventors: 유석현; 도영주; 서해영
Original assignee: 현대제철 주식회사
Priority date: 2010-04-30
Filing date: 2010-04-30
Publication date: 2012-08-21
Also published as: KR20110121080A

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting material refining system and a method for producing high quality steel by increasing the solubility limit of lead (Pb) steel. A refining furnace for raising the temperature and adjusting to a necessary alloy component, an input means for inputting a content of lead contained in the molten steel of the refining furnace, an input control unit for determining an amount of manganese to be input according to the lead content input through the input means; And an alloy input machine operated under the control of the input control unit to input a predetermined amount of manganese into the refining furnace.

Description

Refining system of continuous casting material and method thereof {SYSTEM FOR REFINING CONTINUOUS CASTING MATERIALS AND METHOD THEREOF}

The present invention relates to a refining system and method for continuous casting material which can produce high quality steel by increasing the solubility limit of lead (Pb) in steel.

Scrap, together with iron ore and raw coal, is the three primary raw materials for steel, accounting for more than 50% of the cost of electric furnace products.

In steel blast furnaces using iron ore, the use of scrap is increased to increase production and save energy and resources.

In the scrap iron, not only iron (Fe), which is a base material, but also a trace element, which is hardly removed by refining such as Pb, Zn, Cu, Sn, As, and the like, is concentrated.

The circulating elements deteriorate the hot / cold workability of the steel and generate an internal crack of the steel during continuous casting, so a countermeasure is required. In particular, the lead (Pb) of the low melting point (327 ℃) of the circulating element is hardly dissolved in Fe, which is a base material, and may be concentrated at the grain boundary during solidification even at a very small amount of several tens of ppm, thereby causing internal cracks.

The present invention is to provide a refining system and method for continuous casting material which can produce high quality steel by increasing the solid solution limit of lead (Pb) in the circulating elements included in scrap metal.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the particular embodiments that are described. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, There will be.

The refining system of the continuous casting material of the present invention for achieving the above object, the refining furnace for raising the molten steel from the electric furnace or converter in the arc heat and adjusting to the required alloy components; Input means for inputting a content of lead (Pb) contained in the molten steel of the refining furnace; An input control unit for determining an amount of manganese to be input according to the lead content input through the input means; And an alloy input machine which is operated under the control of the input control unit and inputs a predetermined amount of manganese into the refining furnace.

Specifically, the input control unit is characterized in that it determines the amount of manganese (Mn [kg]) to be introduced through the operation as shown in the following formula according to the lead content [Pb amount (ppm)].

Equation

Mn [kg] = 12.3 x log [Pb amount in ppm]-19.7

In addition, the input control unit is characterized in that to control the manganese is not added when the lead content is 40ppm or less.

In the continuous casting material refining method of the present invention for achieving the above object, the content of lead contained in the molten steel of the refining furnace in the refining process of the steelmaking process, the lead content in the detected steel [Pb amount (ppm)] Accordingly, the amount of manganese for increasing the solubility of lead is determined by the above formula, and the determined manganese is introduced into the molten steel of the refining furnace.

As described above, according to the present invention, by increasing the limit of the base metal solid solution of lead by adding manganese to molten steel, it is possible to reduce cracks of steel by Pb without adding a refining equipment (for example, vacuum refining equipment) for removing Pb. Breakouts can be prevented.

1 is a side view showing a continuous casting machine related to the present invention.
FIG. 2 is a conceptual view illustrating the continuous casting machine of FIG. 1 based on the flow of molten steel M. Referring to FIG.
3a and 3b is a view showing the lead concentration of the inner crack and crack surface during lead concentration in steel.
4 is a conceptual diagram illustrating a refining system according to an embodiment of the present invention.
Figure 5 is a graph showing to explain the manganese input amount according to the lead content in the steel according to the present invention.
6A and 6B are diagrams showing whether lead is employed before manganese and after manganese.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements in the figures are denoted by the same reference numerals wherever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a side view showing a continuous casting machine related to the present invention.

Referring to this figure, the continuous casting machine may include a ladle 10 and tundish 20, mold 30, secondary cooling stand 60 and 65, pinch roll 70, and cutter 90 have.

Continuous casting is a casting method in which a casting or steel ingot is continuously extracted while solidifying molten metal in a mold without a bottom. Continuous casting is used to manufacture simple products such as squares, rectangles, circles, and other simple cross-sections, and slab, bloom and billets, which are mainly for rolling.

The type of continuous casting machine is classified into vertical type, vertical bending type, vertical axis difference bending type, curved type and horizontal type. 1 and 2 illustrate a curved shape.

The tundish 20 is a container that receives the molten metal from the ladle 10 and supplies the molten metal to the mold 30. Ladle 10 is provided in a pair, alternately receives molten steel to supply to the tundish 20. In the tundish 20, the molten metal supply rate is adjusted to the mold 30, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the non-metallic inclusions are separated.

The mold 30 is typically made of water-cooled copper and allows the molten steel to be primary cooled. The mold 30 forms a hollow portion in which molten steel is accommodated as a pair of structurally facing faces are opened. In the case of producing a slab, the mold 30 comprises a pair of barriers and a pair of end walls connecting the barriers. Here, the short wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated to move away from or close to each other to have a certain level of taper. This taper is set to compensate for shrinkage caused by solidification of the molten steel M in the mold 30. The degree of solidification of the molten steel (M) will vary depending on the carbon content, the type of powder (steel cold Vs slow cooling), casting speed and the like depending on the steel type.

The mold 30 has a strong solidification angle or solidifying shell 81, FIG. 2, such that the casting extracted from the mold 30 maintains its shape and does not leak molten metal which is still less solidified. ) Is formed. The water-cooled structure includes a method of using a copper pipe, a method of drilling a water cooling groove in the copper block, and a method of assembling a copper pipe having a water cooling groove.

The mold 30 is oscillated by the oscillator 40 to prevent the molten steel from sticking to the wall of the mold. Lubricants are used to reduce friction between the mold 30 and the casting during oscillation and to prevent burning. Lubricants include splattered flat oil and powder added to the molten metal surface in the mold 30. The powder is added to the molten metal in the mold 30 to become slag, as well as the lubrication of the mold 30 and the casting, as well as the oxidation and nitriding prevention and thermal insulation of the molten metal in the mold 30, and the non-metal inclusions on the surface of the molten metal. It also performs the function of absorption. In order to inject the powder into the mold 30, a powder feeder 50 is installed. The part for discharging the powder of the powder feeder 50 faces the inlet of the mold 30.

The secondary cooling zones 60 and 65 further cool the molten steel that has been primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spray 65 spraying water while maintaining the solidification angle by the support roll 60 so as not to deform. Casting solidification is mostly achieved by the secondary cooling.

The drawing device adopts a multidrive method using a plurality of sets of pinch rolls 70 and the like so that the casting can be taken out without slipping. The pinch roll 70 pulls the solidified tip of the molten steel in the casting direction, thereby allowing the molten steel passing through the mold 30 to continuously move in the casting direction.

The cutter 90 is formed to cut continuously produced castings to a constant size. As the cutter 90, a gas torch, a hydraulic shear, or the like can be employed.

FIG. 2 is a conceptual view illustrating the continuous casting machine of FIG. 1 based on the flow of molten steel M. Referring to FIG.

Referring to this figure, the molten steel (M) is to flow to the tundish 20 in the state accommodated in the ladle (10). For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends to be immersed in the molten steel in the tundish 20 so that the molten steel M is not exposed to air and oxidized and nitrided. The case where molten steel M is exposed to air due to breakage of shroud nozzle 15 is called open casting.

The molten steel M in the tundish 20 flows into the mold 30 by a submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed in the center of the mold 30 so that the flow of molten steel M discharged from both discharge ports of the immersion nozzle 25 can be symmetrical. The start, discharge speed, and stop of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 installed in the tundish 20 corresponding to the immersion nozzle 25. Specifically, the stopper 21 may be vertically moved along the same line as the immersion nozzle 25 to open and close the inlet of the immersion nozzle 25. Control of the flow of the molten steel M through the immersion nozzle 25 may use a slide gate method, which is different from the stopper method. The slide gate controls the discharge flow rate of the molten steel M through the immersion nozzle 25 while the sheet material slides in the horizontal direction in the tundish 20.

The molten steel M in the mold 30 starts to solidify from the part in contact with the wall surface of the mold 30. This is because heat is more likely to be lost by the mold 30 in which the periphery is cooled rather than the center of the molten steel M. The rear portion along the casting direction of the strand 80 is formed by the non-solidified molten steel 82 being wrapped around the solidified shell 81 in which the molten steel M is solidified by the method in which the peripheral portion first solidifies.

As the pinch roll 70 (FIG. 1) pulls the tip portion 83 of the fully solidified strand 80, the unsolidified molten steel 82 moves together with the solidified shell 81 in the casting direction. Uncondensed molten steel 82 is cooled by a spray 65 for spraying cooling water in the course of the above movement. This causes the thickness of the unsolidified molten steel 82 to occupy the strand 80 gradually decreases. When the strand 80 reaches a point 85, the strand 80 is filled with the solidification shell 81 in its entire thickness. The solidified strand 80 is cut to a certain size at the cutting point 91 and divided into steel P such as slab.

In the steel produced in this manner, a circulating element that is hardly removed by refining such as Pb, Zn, Cu, Sn, As, etc. is concentrated.

Cyclic elements deteriorate hot / cold workability of steel and generate internal crack of steel during continuous casting, so countermeasures are required but there is no clear management standard.

Among the circulating elements, especially low melting point (327 ° C) of lead (Pb) is hardly dissolved in Fe, which is a base metal, and even at a very small amount of several tens of ppm, it concentrates at the grain boundary during solidification as shown in FIG. 3A and causes internal cracks. Since the solidification shell is torn during casting, the internal molten steel breaks out, which leads to an operation accident. Therefore, it is necessary to remove lead, but it is not completely removed by oxidation refining, a general refining method. It is also possible to volatilize by vacuum refining rather than oxidative refining, but additional vacuum refining equipment investment is required, and environmental problems caused by volatilized lead (Pb) vapor may additionally be caused.

FIG. 3B shows a lead (Pb) enrichment portion of the crack face of FIG. 3A, wherein the oval or circular portion (light portion) is the lead component. Such lead is not employed in the steel, causing internal cracking of the steel.

Therefore, in the present invention, since it is almost impossible to remove Pb by general refining, an alloying element is added to increase the solubility limit in steel of Pb to reduce the grain boundary concentration.

4 is a conceptual diagram illustrating a refining system of a continuous cast material according to an exemplary embodiment of the present invention, and includes a refining furnace 100, an input unit 110, an input control unit 130, and an alloy input machine 150.

The refining furnace (100) ladle furnace heats up the molten steel from the electric furnace or the converter to arc heat and adjusts to the required alloying components.

Input means 110 is configured to input the content of lead (Pb) contained in the molten steel of the refining furnace (100). Here, the content of lead can be known through the component inspection of the molten steel.

The input control unit 130 determines the amount of manganese to be input according to the lead content input through the input means 110, and then controls the amount of manganese introduced through the alloy input machine 150. Here, the input control unit 130 determines the amount of manganese (Mn [kg]) to be introduced through the calculation as shown in Equation 1 according to the lead content [Pb amount (ppm)].

Equation 1
Mn [kg] = 12.3 x log [Pb amount in ppm]-19.7

The alloy input machine 150 is operated under the control of the input control unit 130 to inject a predetermined amount of manganese into the refining furnace 100.

In general, alloy elements that increase the solid solubility of Pb in steel include Mn, S, Cu, and Ni. However, S and Cu, like Pb, are concentrated at grain boundaries and deteriorate steel properties. Transition metals Mn and Ni are good. However, since Ni is more expensive than Mn, Mn is commercially advantageous. Of course, in the embodiment of the present invention has been described as to put Mn in the molten steel, it is natural that Ni may be added to the molten steel depending on the situation. However, when Ni is added, the dose may be different from the dose of Mn.

As shown in the graph of manganese loading according to the lead content of steel in FIG. 5, when Pb content in molten steel is 40 ppm or more (dotted line), Mn alloy iron is added in refining in proportion to the content of Pb to induce negative effects due to grain boundary concentration. Can be reduced. As shown in FIG. 5, since lead does not significantly affect the crack of steel at a lead content of 40 ppm or less, manganese is not added, and only a predetermined amount of manganese is added according to Equation 1 only at a lead content of 40 ppm or more. Do.

In FIG. 5, dots represent various amounts of manganese input according to lead content in molten steel, and show a range in which lead solid solution effects can be increased. Therefore, each dot is shown as a curve graph, and the curve is numerically calculated so that the optimum amount of manganese according to the lead content in steel is functionalized as in Equation 1 above.

6A is a diagram showing whether lead is employed before manganese injection, and FIG. 6B is a diagram showing whether lead is employed after manganese injection as in the present invention.

That is, if manganese (Mn) is not added to molten steel, lead (Pb) is not dissolved in iron (Fe) as a base material, as shown in FIG. 6A, and is concentrated at grain boundaries. If manganese (Mn) is added to molten steel, lead is shown in FIG. 6B. (Pb) is dissolved together with manganese (Mn) in the base iron (Fe) to reduce the operation accidents in which molten steel leaks due to tearing of cracks and solidification shells of the steel generated in the continuous casting process of FIGS. 1 and 2. .

As described above, in the present invention, by adding manganese to molten steel to increase the base metal employment limit of lead, cracking and operation accident of steel by Pb without the addition of a refining facility (for example, vacuum refining facility) for removing Pb. break-out).

The present invention has been described with reference to the preferred embodiments, and those skilled in the art to which the present invention pertains to the detailed description of the present invention and other forms of embodiments within the essential technical scope of the present invention. Could be. Here, the essential technical scope of the present invention is shown in the claims, and all differences within the equivalent range will be construed as being included in the present invention.

10: ladle 15: shroud nozzle
20: tundish 25: immersion nozzle
30: mold 40: mold oscillator
50: powder feeder 51: powder layer
52: liquid fluidized bed 53: lubricating layer
60: support roll 65: spray
70: pinch roll 80: strand
81: solidified shell 82: unsolidified molten steel
83: tip 85: solidification completion point
100: refining furnace 110: input means
130: input control unit 150: alloy input machine

Claims

A refining furnace for heating the molten steel from the electric furnace or the converter to arc heat and adjusting it to the required alloying component;
Input means for inputting a content of lead (Pb) contained in the molten steel of the refining furnace;
An input control unit for determining an amount of manganese (Mn) to be added according to the lead content input through the input means; And
And an alloy injector which is operated under the control of the input control unit to inject a predetermined amount of manganese into the refining furnace.

The method of claim 1,
The injection control unit refining system of the continuous casting material to determine the amount of manganese (Mn [kg]) to be introduced through the calculation according to the following formula according to the lead content [Pb amount (ppm)].
Equation
Mn [kg] = 12.3 x log [Pb amount in ppm]-19.7

The method of claim 1,
The input control unit refining system of the continuous casting material to control the manganese is not added when the lead content is 40ppm or less.

Detecting the amount of lead contained in the molten steel of the refining furnace in the refining process of the steelmaking process;
Determining the amount of manganese for increasing the solubility of lead according to the detected lead content [Pb amount (ppm)] in the steel by the following formula; And
Injecting the determined manganese into the molten steel of the refining furnace; Refining method of a continuous cast material comprising a.
Equation
Mn [kg] = 12.3 x log [Pb amount in ppm]-19.7