KR100674618B1 - Method for manufacturing high manganese steel strip with twin-roll strip casting apparatus - Google Patents

Abstract

A method for manufacturing a high manganese steel strip by a twin-roll strip caster is provided to manufacture a cast strip of high manganese steel with good surface quality by casting an optimal molten steel composition for manufacturing high manganese steel in a nitrogen atmosphere in the state that the degree of superheat of molten steel is adjusted to 10 to 50 deg.C, thereby minimizing formation of dent defects. In a method for manufacturing a high manganese steel strip(11) by supplying molten high manganese steel(7) between the casting rolls of a twin roll strip caster comprising a pair of casting rolls(5) synchronously rotated oppositely to each other, edge dams(9) installed both ends of the casting rolls, and meniscus shields(13) for sealing the molten steel by blocking the surface of molten steel, a method for manufacturing the high manganese steel strip by the twin-roll strip caster comprises: preparing a composition for the molten steel comprising, by weight percent, 0.1 to 2.0% of C, 10 to 35% of Mn, 0.5 to 4.0% of Al, 0.1% or less of N, the balance of Fe and other inevitable impurities; maintaining a nitrogen gas atmosphere as an atmosphere of the surface of molten steel within the meniscus shields; and controlling the degree of superheat of molten steel to 10 to 50 deg.C.

Description

Method for manufacturing sheet of high manganese steel using twin roll sheet casting machine {Method for manufacturing high Manganese steel strip with twin-Roll strip casting apparatus}

1 is a scanning electron microscope (SEM) photograph showing dent defects occurring on a thin plate surface.

Figure 2 is a schematic diagram of a twin roll type sheet casting machine used to produce a high manganese steel sheet according to an embodiment of the present invention.

Figure 3 is a graph showing the dent index of the high manganese steel sheet manufactured by the embodiments and comparative examples of the present invention.

Description of the main parts of the drawing

1: tundish 3: molten steel supply nozzle

5: casting roll 7: molten steel for manufacturing high manganese steel

9: edge dam 11: sheet

13: meniscus shield 15: rolling mill

The present invention relates to a method for producing a thin plate of high manganese steel, and more particularly to a method for manufacturing a thin plate of high manganese steel having excellent surface quality with minimized surface dent defects using a twin roll type sheet casting machine.

As a steel sheet for automobiles, the base structure is ferrite in consideration of formability, and ultra-low carbon steel which has reduced impurities as much as possible has been used. However, in the case of ultra low carbon steel, it has high drawability but does not have sufficient toughness, and also has a disadvantage of low strength.

Recently, high toughness steel sheet is required to minimize impacts in collision of automobiles as a requirement of steel sheet for automobiles, and high strength steel sheet is required for lightening automobiles. Such high strength and high toughness steel sheet is difficult to achieve in the ultra low carbon steel having a base structure of ferrite, and can be achieved by using a transformation induced plasticity (TRIP) or twin induced plasticity (TWIP) phenomenon in a steel having a base structure of austenite. It is known that it can.

As an austenitic steel sheet having high strength and high toughness, research on austenitic high manganese steel has been actively conducted. For example, according to Korean Patent Laid-Open Publication No. 1995- 0026569, the base steel is composed of steel composed of C: 1.5% or less, Mn: 15.0-35.0%, Al: 0.1-6.0%, balance Fe, and other unavoidable impurities by weight. By this, one or two or more selected from the group consisting of B, Ti, Zr, La, and Ca are added thereto, and high manganese steel having excellent hot workability is disclosed.

On the other hand, the so-called strip casting process of manufacturing a thin plate (casting) using a twin-roll thin plate casting machine directly produces a thin plate almost close to the final product, thereby eliminating the entire reheating and hot rolling process. And as a process that can significantly reduce the manufacturing cost, the research for manufacturing the high manganese steel by a strip casting process is in progress.

However, there are many problems to be solved to produce high quality high manganese steel using the strip casting process. One of these problems is surface deterioration due to surface defects in the manufactured high manganese steel sheets. This degradation in surface quality is determined by the surface cracks, dent defects and the amount of oxide incorporated. Among them, the dent defect (D) is a hemispherical pit having a diameter of 0.5 to 3 mm and a depth of about 0.1 to 1 mm generated on the surface of the thin plate, as shown in the scanning electron microscope (SEM) photograph of FIG. Some of them remain on the surface of the thin plate and remain as surface defects, which acts as a factor of lowering the surface quality of the thin plate.

The technical problem to be achieved by the present invention is a method of manufacturing a high manganese thin plate using a twin roll thin plate casting machine, by optimizing the molten steel composition and casting conditions to minimize the dent defects that may occur on the surface of the thin plate produced excellent surface To prepare a thin plate of high manganese of quality.

In order to achieve the above technical problem, the present invention, a pair of roll-shaped thin plate including a pair of casting rolls that rotate in synchronization with each other in the opposite direction, the meniscus shield for sealing by blocking the edge dam and the molten steel bath surface installed on both ends of the casting roll In the method for producing a high-manganese steel sheet by supplying molten steel of high manganese steel between the casting rolls of the casting machine, the molten steel in the weight% C: 0.1 to 2.0%, Mn: 10 to 35%, Al: 0.5 to 4.0% , N: 0.1% or less, balance Fe and other unavoidable impurities, the atmosphere of the molten steel bath surface in the meniscus shield nitrogen gas atmosphere, the superheat of the molten steel characterized in that the degree of superheat of 10 ~ 50 degrees Provided is a thin plate manufacturing method of high manganese steel using a casting machine.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the scope of the invention to those skilled in the art will fully convey. Like numbers refer to like elements throughout.

Figure 2 is a schematic diagram of a twin roll type sheet casting machine used to produce a high manganese steel sheet according to an embodiment of the present invention.

Referring to FIG. 2, a twin roll type sheet casting machine is disposed at both ends of a pair of casting rolls 5 and a pair of casting rolls 5 that are cooled by cooling water and rotated in synchronization in opposite directions to each other to prevent outflow of molten steel. An edge dam 9 and a meniscus shield 13 positioned on the casting roll 5 to block the sealing surface of the molten steel 7 to prevent the formation of oxides on the surface of the molten steel are included. The solidified shell solidified on the surface of the casting roll (5) is coalesced at the closest point of the casting roll (5) and cast into a thin plate (11), which is hot rolled and coiled by 10 to 50% during the rolling mill (15). . The casting roll 5 has a cooling water hole provided as a passage of cooling water therein, and is made of a material having good heat transfer such as copper or a copper alloy. In addition, the surface may be coated with a metal such as nickel to improve the wear resistance. In addition, in order to improve solidification of the molten steel, the nickel coating layer may be formed of non-directional roughness, for example, using a process such as shot-blast. In Fig. 2, reference numeral '1' denotes a tundish and reference numeral '3' denotes a molten steel supply nozzle.

According to the present invention, first, the molten steel 7 for manufacturing high manganese steel is injected between the pair of casting rolls 5 rotating in synchronism in opposite directions through the molten steel supply nozzles 3. The injected molten steel 7 is in contact with the casting roll 5 to form a solidified shell and, as the casting roll 5 rotates, is coalesced at the closest point of the casting roll 5 to form a thin plate 11 of high manganese steel. Is cast. The molten steel 7 for manufacturing high manganese steel injected between the casting rolls 3 is melted in a melting furnace as in general steel grades, and then subjected to ladles, followed by temperature adjustment and fine adjustment in a refining facility for secondary refining of the molten steel. Component adjustments were made.

In the present invention, the molten steel (7) for manufacturing high manganese steel is C: 0.1 to 2.0% by weight, Mn: 10 to 35%, Al: 0.5 to 4.0%, N: 0.1% or less, balance Fe and other unavoidable impurities It is made up of. Here, the content value of each component is limited for the following reason. Mn is added in an amount of 10 to 35% by weight in order to stabilize austenite in the microstructure, Al is also added in an amount of 0.5 to 4.0% by weight for the purpose of stabilizing austenite during processing and causing twin transformation. 0.1 to 2.0% by weight is added to improve and maintain the solid-liquid section. In addition, the content of N in the molten steel is added at 0.1% by weight or less in order to prevent the excessive production of nitride.

On the other hand, the dent defect of the thin plate surface is generated while the gas entrained on the casting roll surface during the casting gradually expands in the molten steel and this expansion occurs until the molten steel solidifies to increase the size of the dent defect. Therefore, in order to reduce such dent defects, it is necessary to prevent the incorporation of gas between the casting roll and the molten steel or to prevent the entrained gas from thermal expansion. In general, in order to prevent gas from being mixed between the casting roll and the molten steel, it is preferable not to give roughness to the casting roll surface, but in this case, cracking may occur on the thin plate surface of high manganese steel.

In order to prevent dent defects, it is necessary to prevent the entrained gas from thermal expansion. In order to prevent the mixed gas from expanding, it is necessary to use an atmosphere gas having a solubility with respect to molten steel, that is, nitrogen gas, as the atmosphere gas. When the nitrogen gas is used as the atmosphere gas, the nitrogen gas is dissolved into the molten steel while generating AlN by reacting with Al in the molten steel 7 for manufacturing the high manganese steel. Through this process, the force of expansion of the entrained gas is weakened. Therefore, according to the present invention, during casting of the molten steel 7 for manufacturing high manganese steel having the composition as described above, the casting of the thin plate surface by performing casting with the hot water atmosphere inside the meniscus shield 13 as the nitrogen atmosphere. Dent defects can be reduced.

In addition, when the superheating degree of molten steel is high, the solidification time takes longer, and thus the temperature of the mixed gas increases, which accelerates the thermal expansion of the gas and increases the size of the dent defect. It is necessary to lower. However, when the degree of superheat of molten steel is excessively low, molten steel solidifies on the surface of the edge dam 9 made of a ceramic component, and when a solidified product is detached from the edge dam 9 and mixed in a thin plate, it may act as a defect. . Therefore, the degree of superheat of molten steel needs to be above a certain level, that is, above 10 degrees. In addition, in order to prevent the growth of dent defects generated on the thin plate surface, molten steel superheat of less than 50 degrees is required.

Therefore, according to the present invention, while casting the molten steel 7 for manufacturing high manganese steel having the composition as described above, the hot water atmosphere inside the meniscus shield 13 is a nitrogen atmosphere and the molten steel superheat is 10 to 50. By minimizing the occurrence and growth of dent defects on the surface of the thin plate it is possible to manufacture a high manganese thin plate with excellent surface quality.

Experimental Example

In order to determine the surface quality of the high manganese steel sheet produced according to the embodiment of the present invention, the high manganese steel sheet was cast using molten steel 7 for manufacturing the high manganese steel having the above-described composition. Also, for comparison, high manganese steel sheets were cast by varying the atmosphere gas and molten steel superheat.

Table 1 below shows the dent index of the thin plate surface when the high manganese steel sheet was cast by varying the atmospheric gas and molten steel superheat. 3 is a graph showing the results of <Table 1>. The dent index means the area ratio occupied by the dent defect on the surface of the thin plate. In general, when the dent index is within 0.2, the dent index does not act as a surface defect after rolling, indicating that the surface quality of the thin plate is good.

Psalm No. Atmosphere gas Molten steel superheat degree Cast Surface Dent Index Remarks One nitrogen 100 1.688 Bad 2 nitrogen 50 0.196 Good 3 nitrogen 100 0.848 Bad 4 nitrogen 20 0.004 Good 5 nitrogen 80 0.975 Bad 6 argon 100 1.325 Bad 7 argon 120 3.208 Bad 8 argon 80 0.733 Bad

  As shown in Table 1 and Figure 3, as in the embodiment of the present invention when casting the atmosphere gas to nitrogen and molten steel superheat of 50 degrees or less, that is, in the case of specimen 2 and specimen 4 The surface dent index was measured to be 0.196 and 0.004, respectively, to produce a sheet of high manganese steel with very good surface quality. On the other hand, when the specimens according to the comparative example, ie, argon is used as the atmosphere gas (Samples 6, 7, and 8) or the molten steel superheat exceeds 50 degrees (Samples 1, 3 and 5), the surface dent index of the slab It can be seen that more than 0.2 dent defects occurred in comparison with the embodiment of the present invention.

These results indicate that, in order to reduce the occurrence of dent defects, the use of nitrogen can reduce the dent index compared to using argon as the atmosphere gas, and in addition, when the superheat of molten steel is maintained at 50 degrees or less, the dent The occurrence of defects can be minimized.

As described above, according to the present invention, in manufacturing a thin plate of high manganese steel using a twin roll thin plate casting machine, molten steel for manufacturing high manganese steel, which has been formulated with an optimum composition, is used, and the atmosphere of the hot water surface is a nitrogen atmosphere, and the molten steel is overheated. By casting at a degree of 10 to 50 degrees, dent defects on the surface can be minimized, and thin manganese pieces of high manganese steel having good surface quality can be manufactured.

Claims (1)

The molten steel of high manganese steel between the casting rolls of a twin-roll sheet metal casting machine including a pair of casting rolls rotating in synchronism in opposite directions, an edge dam provided at both ends of the casting roll, and a meniscus shield blocking the molten steel surface. In the method of manufacturing a thin plate of high manganese steel by supplying The molten steel is composed of C: 0.1 to 2.0% by weight, Mn: 10 to 35%, Al: 0.5 to 4.0%, N: 0.1% or less, balance Fe and other unavoidable impurities, and the molten steel in the meniscus shield. A hot-manganese steel sheet manufacturing method using a twin-roll thin sheet casting machine, characterized in that the atmosphere of the hot water surface is a nitrogen gas atmosphere, and the superheat degree of molten steel is 10 to 50 degrees.

Images