KR100340385B1 - Metal strip continuous casting method - Google Patents

Abstract

In the present invention, the molten metal is guided to a nip between a pair of parallel casting rolls 16 via a metal discharge nozzle 19, wherein the nozzle 19 is positioned on the nip and rolls directly on top of the nip. Forming a casting pool of molten metal supported on the casting surface of the metal, and the casting roll is rotated to release the solidified metal strip 20 downward from the nip, and the metal has a manganese content of at least 0.20% by weight and a silicon content of Metal strip continuous casting process of silicon / manganese mild mild steel with more than 0.10 wt% and total aluminum content less than 0.01%.

Description

Metal strip continuous casting method

The present invention relates to a method for casting steel strips and is particularly applicable to the production of mild steel strips. Mild steel is defined as carbon steel having a carbon content of about 0.25% by weight or less.

In general, the metal strip is continuously cast in a twin roll casting machine, in which molten metal is drawn between a pair of horizontal casting rolls in which the molten metal is reversely rotated and cooled, whereby the steel sheet solidifies on the moving roll surface. It has been produced in a solidified strip that is joined at the nip of and released downward from the nip between the rolls, where the term "nip" is defined as referring to the point where the rolls are closest to each other. On the other hand, molten metal is poured from the ladle into a smaller vessel, penetrating through the metal ejection nozzles located above the nip, and directed towards the nip between the rolls, which is supported on the casting surface of the roll just above the nip and extends along the length of the nip. Forming a casting pool of metal. The casting pool may be partitioned between a dam or side plate that is secured by sliding engagement with both ends of the rolls to prevent overflow from the two ends of the casting pool.

These twin roll castings are suitable for use in nonferrous metals that quickly solidify by cooling, such as aluminum, but present several problems for use in casting metals such as iron, for example, very little metal flow required in twin roll casting machines, especially for mild steel metals. Solid inclusions are formed that block the passage.

The use of silicon-manganese for ladle deoxidation of steel was used in the production of ingots in early Besmer's steel production, including molten manganese silicate reactants and manganese residues and silicon and oxygen in the molten steel state. Equilibrium ratios are known, but silicon / manganese deoxidation has been avoided and aluminum killed steel has been avoided, except as will be described later in the development of techniques for producing metal strips by plate casting and thus cold rolling. It was considered essential to use it. And in producing steel strips by hot rolling after plate casting and low temperature rolling, silicon / manganese calm steels have other drawbacks due to the high incidence of stringers and the concentration of contents in the middle layer of the strip. To create.

On the other hand, the tendency of the inclusions in the bend or layer to be produced by the plate casting process is reduced by the use of aluminum soothing steels, so silicon / manganese soothing steels were generally considered unsuitable for the manufacture of steel strips. Therefore, although it was previously considered necessary to use aluminum chilled steel to continuously cast steel strips in twin roll casting machines, in the casting of continuous steel strips described above, fine control at a constant speed along the length of the casting rolls is performed. The molten metal must flow through a very small flow path of the refractory material in the metal ejector, as it is very important to create a flow of steel to achieve a sufficiently rapid and uniform cooling of the steel over the casting surface of the roll. In this case, the solid content is separated and tends to block the small flow path described above, which is a serious problem in casting of mild steel having a much higher melting point and viscosity than alloy stainless steel, so that casting becomes difficult.

After extensive strip casting of various grades of steel in a continuous strip roll casting machine, it has been found that aluminum genuine mild steel or partial solid steel with 0.01% or more of aluminum residue generally cannot be cast satisfactorily, which is solid This is because the contents clump together to block elaborate flow passages in the metal ejector, forming defects and discontinuities in the final strip product. These problems, however, include silicon / manganes killed mild steel, which maintains the aluminum content below 0.01% by weight and limits the content of silicon and manganese, which tends to produce liquid deoxidizers at casting temperatures, to a selected range. In addition to being overcome by the use, it has been found that mild steel strips can be produced without the usual defects associated with strings or silicon / manganese soothing steels, which solidify rapidly in twin roll casting machines to prevent the formation of large inclusions. The twin roll casting process is because the contents are evenly distributed throughout the contents rather than concentrated in the central layer.

US Patent No. 3,412,781 to Richard et al. Discloses a continuous steel plate casting process wherein the composition of the steel melt contains 0.01% to 0.08% carbon, 0.20% to 0.60% manganese, 0.03% to 0.08% silicon and 0.015%. It is adjusted to contain up to% aluminum, but it is not possible to cast steel of the above components in twin roll strip casting to produce a good quality strip.

Smith's U.S. Pat. No. 4,529,441 discloses a process for casting steel continuously and electrically, up to 0.06% carbon, up to 0.04% sulfur, up to 0.15% phosphorus, up to 1.0% manganese and 0.001% 0.05% to 0.25% of silicon is added to the melt containing the following silicon, in the embodiment disclosed herein the steel is partially aluminum soothing steel, in particular in the first embodiment 0.015% of aluminum, the second embodiment Contains 0.012% aluminum and, in the third embodiment, 0.020% aluminum, the aluminum content being detrimental for continuous strip casting of steel.

Accordingly, the present invention introduces molten metal into a nip between a pair of parallel casting rolls through a metal discharge nozzle, and the nozzle is positioned above the nip and supported on the casting surface of the roll just above the nip. Forming a casting pool of the, the casting roll is rotated to provide a continuous metal strip casting method for releasing the solidified metal strip downward from the nip, the metal is silicon / manganese soothing mild steel content of 0.20 manganese The weight ratio is more than 0.1%, the content of silicon is more than 0.10% by weight, the weight ratio of manganese and silicon is 1.4: 1 to 2.8: 1, the total aluminum content of the steel is less than 0.01% by weight.

The invention also allows molten metal to be introduced into a nip between a pair of parallel casting rolls through a metal release nozzle installed on top of the nip to create a casting pool of molten metal supported on the casting surface of the roll just above the nip. While the casting roll is rotated to provide a method for continuously casting the metal strip to release the solidified metal strip from the nip downwards, the metal is a silicon / manganese calm steel, the carbon and manganese and silicon content And the same range.

Carbon 0.02-0.15% by weight

Manganese 0.20- 1.0wt%

0.10-0.5% by weight of silicone

The total aluminum content of the steel here is 0.01% by weight or less.

In order to optimize the production of steel strips with a thickness of 1 mm to 4 mm, the carbon, manganese and silicon contents are preferably in the following ranges:

Carbon 0.05-0.10 wt%

Manganese 0.40-0.80 wt%

Silicone 0.10-0.30 wt%

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

The casting machine shown in the figure has a periodic frame 11 erected from the bottom 12, the frame 11 is a casting roller carriage 13 capable of horizontal movement between the assembly position 14 and the casting position (15) The carriage 13 supports a pair of parallel casting rollers 16 supplied with molten metal from a ladle 17 through a tundish 18 and a discharge nozzle 19 during a casting operation. The casting roller 16 is water cooled and solidified on the surface of the moving roller to be released into the nip between the rolls so that the solidified strip product 20 is discharged from the roller outlet. Here, the strip product may be fed to the standard coiler 21 and then sequentially transferred to the second coiler 22, and the accumulator 23 is mounted on the machine frame adjacent to the casting position. If the article is subjected to severe deformation or other functional impairment, the emergency plug 25 on one side of the tundish may be removed or the flow of molten metal may be diverted into the accumulator via the outlet tube 24 on the tundish. have.

On the other hand, the roller carriage 13 has a carriage frame 31 mounted by a wheel 32 on the rail 33 extending along a part of the main frame frame 11, and the roller carriage 13 has a rail 33. So that the whole is movable along. The carriage frame 31 supports a pair of roller stands 34 on which the rollers 26 are rotatably mounted, and the roller stands 34 are carried by the complementary slide members 35 and 36 coupled to each other. Mounted on (31) so that the roller stem is moved on the carriage under the influence of the hydraulic cylinder devices 37, 38 to adjust the nip between the casting rollers 16 to form a weak line in the transverse direction of the strip as will be described later. When it is necessary, the roller can move quickly and be spaced apart for a short time. The carriage is movable along the rail 33 as a whole by the operation of the dual action hydraulic piston and the cylinder device 39, and is coupled between the driving bracket 40 of the roller carriage and the main frame to assemble the roller carriage. (14) and casting position 15 or in the reverse direction.

The casting roller 16 is rotated in the opposite direction from the transmission mounted on the electric motor and the carriage frame 31 via the drive shaft 41 and extends in a series of longitudinal directions and has a water cooling passage formed along the outer circumference. It has one copper outer wall. Cooling water is supplied to the water cooling passage through both ends of the roller from the water supply pipe in the roller drive shaft 41 connected to the water supply hose 42 through the rotary stopper 43, in order to produce a strip having a width of 1300 mm. The diameter of the can usually be up to about 500mm, length up to 1300mm.

Since the ladle 17 is a conventional structure as a whole, it is supported by the yoke 45 on the upper crane and can be discharged in place from the hot metal receiving position, and the ladle is started by a servo cylinder. It is coupled to a possible stopper rod 46 to allow molten metal to flow from the ladle into the tundish 18 through the outlet nozzle 47 and the heat resistant side plate 48.

The tundish 18 is also a conventional structure, having a wide dish-like shape made of a heat-resistant material such as magnesium oxide (MgO), and one side of the tundish receives an outlet tube as described above while receiving molten metal from the ladle. 24) and an emergency plug 25, the other side being provided with a series of longitudinally spaced metal exit openings 52, while the lower part of the tundish is placed on the roller carriage frame 31. While supporting the mounting bracket 53 to be mounted, it has a gap for receiving the indexing pegs 54 on the carriage frame to accurately position the tundish.

And the discharge nozzle 19 is a long body shape made of a heat-resistant material such as alumina graphite, the lower portion is inclined to collect inward and downward to be injected into the nip between the casting roller 16, the discharge nozzle is roller carriage A mounting bracket 60 is supported on the frame, the upper portion of which is shaped like a side flange 55 positioned on the mounting bracket while protruding outward.

The nozzles 19 also have a series of horizontally spaced and vertically starred flow passages to release the metals through the width of the rollers at an appropriately low speed and to directly melt the molten metals on the roller surface where initial solidification occurs. Molten metal may be discharged into the nip between the rollers; alternatively, the nozzle may have a single continuous slot outlet to release the low-speed molten metal hem directly into the nip between the rolls and / or submerged in the pool of molten metal. I can lose it.

The pool is partitioned at both ends of the roller by a pair of side lid plates 56 secured to both ends 57 where the layer of rollers are formed when the roller carriage is in the casting position, and the side lid plates 56 ) Is made of a strong heat resistant material such as, for example, boron nitride, and has scalloped side edges 81 to correspond with the bends of the layered ends 57 of the roller, which side plates By activating the hydraulic cylinder device 83, it can be mounted in the plate holder 82 which is movable in the casting position so that the side plate is engaged with the layered both ends of the casting roller so that the molten metal pool formed on the casting roller during the casting operation is removed. To form a tip lid for.

On the other hand, during the casting operation, the ladle stopper rod 46 is started to flow toward the casting roller as molten metal is poured from the ladle through the metal discharge nozzle into the tundish, and the slender head end of the strip product 20 is moved. The apron table 96 is guided toward the jaw of the coiler 21 by the start of the apron table 96. The apron table 96 is suspended from the pivot mount 97 on the main frame, and the sleek head end. After this is formed, it can be shaken toward the coiler by the actuation of the hydraulic cylinder device 93, while the table 96 can be operated with respect to the upper strip guide flap 99 which is actuated by the piston and the cylinder device 101, The strip product 20 can be partitioned between a pair of vertical side rollers 102. After the head tip is guided to the jaw of the coiler, the coiler is rotated to wind the strip product 20, and the apron table is separated from the strip product directly mounted on the coiler 21 on the machine frame. By simply returning to the suspended non-operational position, the strip product 20 is sequentially released towards the coiler 22 to produce the final coil that is released from the casting machine.

In operation of the above apparatus, aluminum calm steels do not produce satisfactory strip products due to the disturbances caused by aluminum inclusions when liquid steel passes through the small orifices in tundish 18 and discharge nozzle 19. This would impede the uniform flow of steel towards the casting pool, making it impossible to produce continuous strip products or producing defective products. In addition, silicon and manganese are very effective deoxidizers in the combined state, and they work synergistically, and the silicon / manganese soothing steels used in the above-mentioned strip casting machines can produce steel strips having an acceptable level of oxygen. The strip produced by the operation of this casting machine is precisely and uniformly distributed in the form of manganese silicate, in which the strip does not seriously damage its mechanical properties, even if its density has a moderately high oxygen content of about 100-150 ppm. To be included. The level of oxygen in the aluminum calming steel here is undesirable since the aluminum inclusions can form a planar defect in the strip as the aluminum inclusions dense together, but the silicate inclusions do not form clusters, At any time during the casting operation, the agglomerates not only do not form excessively large inclusions that are detrimental to the mechanical properties of the strip, but also the strips do not spread out extensively so that the inclusions do not stretch like threads.

In addition, the level of silicon and manganese selected in accordance with the present invention can maintain the deoxidizer in the liquid state during the casting operation, thereby eliminating the problem of confined orifices in the tundish and metal distribution nozzle.

In addition, the degree of carbon, manganese and silicon selected according to the present invention is to maintain the solidification process in a complete ferritic (δ), ideally by selecting the composite to maximize the temperature difference between the liquid and solid layer sufficiently soft during casting It is possible to obtain a casting strip of reduced quality that reduces the adverse effects of the casting pool which may be in a rapid solidification process. However, the equilibrium is not maintained under very fast cooling conditions in the strip casting machine, so it is important not to get too close to the austenite plus ferrite part in the equilibrium diagram, so as not to accidentally solidify in the austenitic plus ferrite part. Care must be taken.

On the other hand, increasing the silicon level and reducing the carbon level promotes the formation of δ ferrite during solidification, thereby reducing the tendency to form a rugged strip surface known as "crocodile skin". It is associated with local differences in the cooling rate (and hence the deformation of the microstructure) due to inconsistent contact of the surfaces.

If the carbon content is too low, a defect known as a "herring bone" will occur, which is a change in the periodic thickness that extends across the width of the strip (or at an angle in the width direction of the strip). It is thought to be associated with the characteristics of the soft area such as the coagulation shell is bonded at the nip of the roll, and if the temperature range in which the soft layer is present is too narrow, obstacles in the uneven part of the casting pool are serious for the thickness and viscosity of the soft layer. This may affect the force exerted by the strip on the casting roll, which in turn affects the strip thickness.

The extensive operation of the above-described strip casting machine with various grades of steel has shown that the optimal steel mix for producing steel strips having a thickness in the range of about 1 mm to 4 mm is as follows.

Carbon 0.05-0.10 wt%

Manganese 0.50-0.70 wt%

Silicone 0.20-0.30 wt%

Less than 0.008% by weight of aluminum

The steel here is preferably preheated to 1500 to 1600 degrees Celsius for casting, preferably tundish is preheated to a range of 1000 to 1300 degrees Celsius, and the discharge nozzle is also preheated to 1000 degrees to 1300 degrees Celsius.

Figure 6 shows the results of various test castings using mild steel and atmospheric melting of various silicon and manganese components, in which the dots show the steel cast to be suitable for producing high quality steel strips and the crosshairs show the casting problem. It is indicated that the steel with which the strip bonds were brought about, in the above test, steel having a composite belonging to part A of FIG. 6 would produce strip sheeting due to poor deoxidation.

And the manganese content greater than 1.0% by weight of steel in B area causes casting problems due to MnO smoke waste on the casting rolls, and the steel in C area with silicon content of 0.5% by weight or more results in strips with poor forming characteristics. Will result.

As shown in FIG. 6 above, the positive resultant band determines the best bond line when the weight ratio of manganese and silicon is 2: 1, and the positive resultant band has a weight ratio of 1.4: 1 to 2.8: Corresponding to the range of 1, the ratio within the above range is preferable to solve the problem of casting.

1 is a plan view of a continuous strip casting machine operable according to the present invention,

FIG. 2 is a side view of the strip casting machine shown in FIG.

3 is a vertical cross-sectional view taken along line 3-3 shown in FIG.

4 is a 4-4 vertical cross-sectional view shown in FIG. 1,

5 is a vertical cross-sectional view taken along line 5-5 shown in FIG. 1;

6 shows the results of test castings using steel of variable constituents.

<Description of the symbols for the main parts of the drawings>

11 --- periodic frame, 12 --- floor,

13 --- casting roller carriage, 14 --- assembly position,

15 --- casting position, 16 --- casting roller,

17 --- ladle, 18 --- tundish,

19 --- discharge nozzle 20 --- solidified strip,

21 --- reference coil, 22 --- second coil,

23 --- storage device, 24 --- outlet pipe,

25 --- emergency plug, 31 --- carriage frame,

32 --- wheel, 33 --- rail,

34 --- roller stand, 35, 36 --- slide element,

37,38,83,98 --- Hydraulic cylinder device, 39,101 --- Cylinder,

40 --- drive bracket, 41 --- drive shaft,

42 --- supply hose, 43 --- rotary stopper,

45 --- yoke, 46 --- stopper rod,

47 --- outlet nozzle, 48 --- side plate,

57 --- stratified leading edge, 81 --- side leading edge,

96 --- apron table, 97 --- pivot mount,

99 --- Guide flaps, 102 --- Side rollers

Claims (9)

Molten metal is introduced into the nip between a pair of parallel casting rolls through a metal discharge nozzle, and the nozzle is disposed above the nip to create a casting pool of molten metal supported on the casting surface of the roll just above this nip. In the method of continuously casting the metal strip to the cast roll is rotated to release the solidified metal strip downward from the nip, the metal is less than 0.25% by weight of carbon, 0.20% by weight of manganese content and silicon content Is 0.10 wt% or more of silicon / manganese mild mild steel, and the weight ratio of manganese and silicon is in the range of 1.4: 1 to 2.8: 1, and the total aluminum content of the metal is less than 0.01 wt%. The method of claim 1, wherein the manganese content of the steel (mild steel) is within the range of 0.20% to 1.0% by weight. The metal strip continuous casting method according to claim 1 or 2, wherein the carbon content of the steel is 0.15% by weight or less. The method of claim 1, wherein the steel has a content of 0.02 to 0.15% by weight of carbon, 0.20 to 1.0% by weight of manganese, and 0.10 to 0.5% by weight of silicon. The method of claim 1, wherein the thickness of the solidified metal strip discharged downward from the nip is within the range of 1mm to 4mm, the steel is 0.05 to 0.10% by weight of carbon and 0.4 to 0.8% by weight of manganese, and 0.10 to 0.30 Metal strip continuous casting method characterized by having a silicon content of weight percent. 6. The metal strip continuous according to claim 5, wherein the steel has 0.05 to 0.10 wt% carbon and 0.50 to 0.70 wt% manganese, 0.20 to 0.30 wt% silicon, and less than 0.008 wt% aluminum. Casting method. Molten metal is introduced into the nip between a pair of parallel casting rolls through a metal ejecting nozzle, the nozzle being positioned on the nip to create a casting pool of molten metal supported on the casting surface of the roll just above the nip. A method of continuously casting a metal strip in which a casting roll is rotated so that the solidified metal strip is discharged downward from the nip, wherein the metal is 0.02-0.15 wt% carbon, 0.20-1.0 wt% manganese, and 0.10-0.5 wt% silicon. A metal strip continuous casting method characterized in that the silicon / manganese calming steel having a content of% and the total aluminum content of the steel is less than 0.01% by weight. The method of claim 7, wherein the solidified metal strip discharged downwardly from the nip has a thickness of 1 mm to 4 mm, wherein the steel is 0.05 to 0.10 wt% carbon, 0.4 to 0.8 wt% manganese, and 0.10 to 0.30 wt% Metal strip continuous casting method characterized in that it has a silicon content of. 9. A continuous as claimed in claim 8 wherein the steel has 0.05 to 0.10 weight percent carbon and 0.50 to 0.70 weight percent manganese, 0.20 to 0.30 weight percent silicon, and less than 0.008 weight percent aluminum content. Casting method.