KR100650560B1 - METHOD FOR CONTROLLING delta;-FERRITE IN TWIN ROLL STRIP CASTING - Google Patents

Abstract

A method for controlling delta-ferrite in twin roll strip casting process, that can selectively control the measured delta-ferrite of the strip to a value desired by customers according to a casting mode and strip use by measuring delta-ferrite of a strip produced during casting, is provided. A method for controlling delta-ferrite in twin roll strip casting process comprises: measuring delta-ferrite of a strip produced during casting; and selectively controlling the measured delta-ferrite of the strip to a preset value depending on a casting mode currently being implemented and uses of the strip. The step of measuring delta-ferrite of the strip comprises the step of measuring delta-ferrite in offline using a strip extracted from edge trimming. The step of measuring delta-ferrite of the strip comprises the step of measuring delta-ferrite in online on a discharge line while proceeding a casting operation. The step of controlling delta-ferrite of the strip comprises the step of injecting Ni into molten steel that is contained in a tundish and is being cast.

Description

Method for controlling delta-ferrite in twin roll sheet casting process {Method for controlling δ-ferrite in twin roll strip casting}

1 is a schematic view showing a general twin roll sheet casting machine.

Figure 2 is a schematic configuration for explaining a delta ferrite control method of a twin-roll thin plate casting process according to an embodiment of the present invention.

Figure 3 is a flow chart showing a delta ferrite control method of a twin roll thin plate casting process according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

101: fixed roll 102: moving roll

103: fixed roll chock

104: moving roll chock

105: load cell 106: roll gap distance measuring device (distance sensor)

107: Tundish 108: Immersion nozzle

109: stopper 110: tundish hole

111: molten steel sump 112: molten steel height detection sensor

113: roll gap 114: cast strip

115: x-ray gauge 116: pinch roll

117: rolling mill (IRM) 118: coiler

119 loop pit 120 edge dam

201: Manual Selection 202: Automatic Selection

203: Ni controller 204: Ar mixing controller

205: N ₂ bubbling controller 206: delta ferrite / speed controller

207: Delta Ferrite / Roll Gap Controller

208: motor speed controller 209: motor

210: roll gap controller 211: automatic selection

212: manual selection

213: Delta Ferrite Meter

The present invention relates to a method for controlling delta ferrite (δ-ferrite) of a twin-roll thin plate casting process. In particular, the delta ferrite of the thin plate produced during casting is measured to selectively delta ferrite of the thin plate according to the casting mode and the use of the thin plate. The present invention relates to a delta ferrite control method of a twin roll sheet metal casting process which can be controlled to a desired value by a consumer.

1 is a configuration diagram schematically showing a general twin roll sheet casting machine.

The main function of the sheet casting process using the twin roll sheet casting machine 10 as shown in FIG. 1 is in a sump 111 between two rolls 101 and 102 rotating in opposite directions.

More specifically, when the molten steel is first supplied from the tundish 107 through the immersion nozzle 108 to the sump 111 between the two rolls 101 and 102, the molten steel is in 0.2 seconds in the leader strip and the two rolls 101 and 102. It solidifies in between and is pressed down.

At this time, the molten steel and the leader strip that solidifies and the sheet which is subsequently solidified following generate a Roll Separation Force (RSF), which is detected by a load cell 105 mounted behind the rolls 101 and 102. .

Here, the sides of the two rolls 101 and 102 are blocked by ceramic side dams to prevent the molten steel from leaking to the sides of the rolls 101 and 102.

On the other hand, the solidification capacity of the molten steel is proportional to the cooling capacity of the casting rolls 101 and 102, and also, the distance between the two rolls 101 and 102, that is, the roll gap, the casting speed (rotational speed) of the rolls 101 and 102, and the sump 111 It is affected by the height of the molten steel. Here, the height of molten steel is measured using the water surface height detection sensor 112.

In general, when molten steel solidifies, it generates a rolling force between the rolls 101 and 102, and the solidification reduction rate is affected by the roll gap 113 and the casting speed, where the roll gap 113 is a roll gap distance measuring device 106. Measure with.

For example, if the roll gap 113 is too large or the casting speed is too fast, the solidification point will be lowered below the center line of the roll nip and the rolling reduction is gradually reduced, which causes the unsolidification of the molten steel and the occurrence of plate breakage. do.

In the opposite case, that is, if the roll gap 113 is too small or the casting speed is too slow, the solidification point will rise up, resulting in a high rolling force.

Roll gap, casting speed, and rolling force are thus representative casting parameters that indicate the solidification of the sheet.

Here, the height control of the molten steel requires high precision and stability, so the height of the molten steel is regarded as maintaining the target value immediately after the start of casting. Therefore, the reduction force can be seen as a result of the correlation between the roll gap and the casting speed.

In view of the characteristics of the thin plate casting process, when the delta ferrite of the thin plate manufactured as described above is measured in the width direction, it can be seen that the delta ferrite is generally higher toward the edge of the thin plate than the center portion of the thin plate.

In addition, a case where the measured DC value of the delta ferrite appears higher than the target value occurs.

Therefore, one of the most important goals for achieving high quality of sheet metal is to control the delta ferrite value of the manufactured sheet to be lowered below a certain value, and in particular, a control method suitable for the casting situation according to the casting mode and the use of the sheet. Although it is a very important process, currently there is no suitable control method according to the casting situation.

The present invention has been proposed in consideration of the above situation, and a pair capable of selectively controlling the delta ferrite of the sheet to the desired value according to the casting mode and the use of the sheet by measuring the delta ferrite of the sheet produced during casting. An object of the present invention is to provide a method for controlling delta ferrite in a roll type sheet casting process.

The present invention for achieving the above object in the twin-roll thin plate casting process, measuring the delta ferrite of the thin plate produced during casting, and optionally depending on the currently used casting mode or the use of the thin plate delta ferrite It is characterized by controlling to a preset value.

Preferably, the measurement of the delta ferrite of the thin plate can be measured off-line using the thin plate extracted from edge trimming.

Preferably, the measurement of the delta ferrite of the sheet can be measured online in the discharge line during the casting process.

Preferably the control of the delta ferrite of the thin plate may be to inject Ni into the molten steel of the tundish being cast.

Preferably, the control of the delta ferrite of the thin plate, in order to reduce the delta ferrite of the entire thin plate, may be to mix the Ar gas to the sump.

Preferably, the control of the delta ferrite of the thin plate may be N ₂ bubbling through an edge dam when the delta ferrite of the thin plate edge portion is to be reduced.

Preferably, the control of the delta ferrite of the thin plate may be to increase the casting speed by reducing the thickness of the thin plate when the casting mode being executed is the thin plate thickness control.

Preferably, the control of the delta ferrite of the thin plate may be to increase the casting speed to thin the thickness of the thin plate when the casting mode being executed is the thin plate pressing force control.

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

Figure 2 is a schematic diagram for explaining a delta ferrite control method of a twin-roll thin plate casting process according to an embodiment of the present invention.

The delta ferrite control method of the twin roll sheet metal casting process includes an automatic (201, 211) and a manual (202, 212) selector for selecting an automatic mode and a manual mode, a Ni controller (203) for supplying Ni to the tundish (107), and a sump Ar mixing controller 204 for mixing Ar gas to 111, N ₂ bubbling controller 205 for performing N ₂ bubbling, and delta ferrite for controlling the speeds of the two rolls 101 and 102. / Speed controller 206, deltaferrite / rollgap controller 207 for controlling the roll gap of the two rolls 101 and 102, and deltaferrite meter 213 for measuring the deltaferrite of the manufactured sheet.

Here, the motor speed controller 208 is for controlling the rotational speed of the rolls 101 and 102 through the motor 209 according to the setting of the casting process, the delta ferrite / speed controller 206 is a delta ferrite dedicated controller, Calculate the amount of trim of the casting speed according to the ferrite error.

In addition, the roll gap controller 210 is for controlling the cylinders of the rolls 101 and 102 according to the setting of the casting process, the delta ferrite / roll gap controller 207 is a delta ferrite dedicated controller, the trim amount of the lop gap due to the delta ferrite error Calculate

The delta ferrite of the thin plate manufactured by such a structure can be controlled using the following formula.

δ Fe_cal = 3 (Cr + Mo) + 4.5 Si-2.8 Ni-1.4 (Mn + Cu)-84 (C + N)-19.8

Here, each component element is expressed as "% by weight," and if δFe_cal (hereinafter δ_cal) is small, delta ferrite may be reduced. As can be seen from Equation 1 above, for example, Ni and N are added. By adding, it is possible to obtain an effect of reducing delta ferrite.

More specifically, N _i acts in a direction to reduce the overall δ_cal of the thin plate produced. Therefore, when N _i is additionally added to the tundish 107 during casting, it acts in a direction of reducing δ_cal of the thin plate to be manufactured as a whole, which in turn reduces the delta ferrite of the thin plate.

In addition, N acts in the direction of decreasing δ_cal of the edge portion (hereinafter, edge) of the thin plate to be manufactured. Therefore, when N is melted in the molten steel by N ₂ bubbling through the edge dam 120, an effect of reducing the edge δ_cal of the edge of the thin plate can be obtained, which in turn reduces the edge delta ferrite.

On the other hand, another method that can reduce the delta ferrite of the thin plate is a method of adding Ar gas to the sump 111 between the roll 101 and the roll 102, which reduces the heat flux (Heat Flux) Act in the direction. This reduced heat flux acts to improve the state of the sheet edge, which in turn serves to reduce the edge delta ferrite.

In another method, the delta ferrite of the thin plate manufactured can be controlled by adjusting the thickness of the thin plate. The thinner the thin plate is, the shorter the contact time between the rolls 101 and 102 and the molten steel is, This acts in the direction of reducing the lift-off of the sheet edge, and consequently, can improve the state of the sheet edge.

Hereinafter, the method of controlling the delta ferrite of the twin-roll thin plate casting process according to an embodiment of the present invention with reference to FIGS.

Figure 3 is a flow chart showing a delta ferrite control method of a twin-roll thin plate casting process according to an embodiment of the present invention.

First, the delta ferrite of the resulting thin plate is measured (step S301), which can be measured offline or online.

That is, the off-line measurement measures the thin plate extracted from the edge trimming through the delta ferrite measuring device 213, or by taking a specimen from a casting coil obtained in advance during continuous casting.

In addition, the online measurement measures the thin plate on the discharge line during the casting process through the delta ferrite meter 213.

Next, it is determined whether the delta ferrite control is in the automatic mode (step S302), and if it is not in the automatic mode, that is, in the manual mode, it is determined whether the delta ferrite of the measured thin plate is higher than a preset value (target value). (Step S303).

Here, when the delta ferrite of the thin plate is lower than the preset value, the separate delta ferrite control is not performed, and the delta ferrite measurement of the thin plate currently being cast is continuously performed for controlling the delta ferrite of the thin plate.

If the delta ferrite of the thin plate is higher than the preset value, Ni is further added to the molten steel of the tundish 107 (step S304).

That is, in order to reduce the overall DC value of the delta ferrite in the thin plate, the Ni controller 203 further injects Ni into the tundish 107.

On the other hand, when the delta ferrite control is in the automatic mode, a method suitable for the present casting situation is determined according to the use of the casting mode or the thin plate (step S305) and selectively performed in the following methods.

First, when it is desired to reduce the delta ferrite of the entire thin plate, Ar gas is mixed (step S306).

That is, in order to reduce the DC value of the entire delta ferrite, the Ar mixing controller 204 mixes Ar gas to the sump 111.

Second, when it is desired to reduce the delta ferrite of the thin plate edge, N ₂ is mixed (step S307).

That is, in order to further reduce the delta ferrite of the specially manufactured thin plate edge, the N ₂ bubbling controller 205 supplies N ₂ through the edge dam 120 to perform N ₂ bubbling.

Third, when the casting mode being executed is thin plate thickness control, the thickness of the thin plate is made thin to increase the casting speed (step S308).

That is, in order to reduce the overall delta ferrite of the thin plate, the roll gap controller 207 increases the casting speed by reducing the thickness of the thin plate by reducing the gap between the rolls 101 and 102 through the roll gap controller 210 connected to the cylinder.

Finally, when the casting mode being executed is thin plate pressing force control, the casting speed is increased to reduce the thickness of the thin plate (step S309).

That is, in order to reduce the overall delta ferrite of the thin plate, the speed controller 206 increases the casting speed by increasing the rotational speed of the motor 209 driving the rolls 101 and 102 through the motor speed controller 207, thereby producing The thickness of the thin plate becomes thinner.

By the control method of such a structure, in view of the conditions in which a thin plate is cast, various methods can be selectively or combined according to each condition.

As described above, the delta ferrite control method of the twin-roll thin plate casting process according to the present invention measures the delta ferrite of the thin plate produced during casting to selectively preset values according to the currently used casting mode and the purpose of the thin plate By controlling, the high delta ferrite normally generated in the twin roll thin plate casting process can be reduced to a certain level and controlled at the same time, and therefore, there is an effect of improving the quality of the produced thin plate.

Claims (8)

In the twin roll sheet metal casting process, The delta ferrite control of the twin-roll sheet metal casting process characterized by measuring the delta ferrite of the thin plate produced during casting, and selectively controlling the delta ferrite of the thin plate to a preset value according to the current casting mode or the purpose of the thin plate. Way. The method of claim 1, The delta ferrite control method of the thin plate delta ferrite, characterized in that the off-line measurement using a thin plate extracted from the edge trimming (edge trimming). The method of claim 1, The delta ferrite control method of the twin-roll thin plate casting process, characterized in that the measurement of the delta ferrite of the thin plate is measured online in the discharge line during the casting process. The method of claim 2, Delta ferrite control of the thin plate is a delta ferrite control method of a twin-roll thin plate casting process, characterized in that the Ni in the molten steel of the casting. The method of claim 3, wherein The control of the delta ferrite of the thin plate is a delta ferrite control method of a twin-roll thin plate casting process, characterized in that, when reducing the delta ferrite of the entire thin plate, Ar gas is mixed to the sump. The method of claim 3, wherein The control of the delta ferrite of the thin plate is a delta ferrite control method of a twin-roll thin plate casting process, characterized in that the bubbling (N ₂ ) through the edge dam, if you want to reduce the delta ferrite of the edge portion of the thin plate. The method of claim 3, wherein The control of the delta ferrite of the thin plate is a delta ferrite control method of the twin-roll thin plate casting process, characterized in that, if the casting mode being executed is the thin plate thickness control, the thickness of the thin plate increases the casting speed by increasing the casting speed. . The method of claim 3, wherein The delta ferrite control of the thin plate delta ferrite is a double-roll thin plate casting process, characterized in that, if the casting mode being executed is a thin plate pressing force control, the delta ferrite is reduced by increasing the casting speed to reduce the thickness of the thin plate. Way.

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