JP3308102B2 - Metal strip continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting metal strip.

[0002]

BACKGROUND OF THE INVENTION It is known to cast metal strip by continuous casting in a twin roll casting machine.

[0003] In such a method, the molten metal is guided between a pair of horizontal casting rolls that are cooled and rotated in opposite directions, thereby solidifying a metal shell on the surface of the rotating casting rolls, which then solidifies. Both pass through the roll gap to form a cast metal strip, which is discharged downward from the roll gap. The introduction of the molten metal into the roll gap can be performed by a tundish and a metal feed nozzle located below the tundish and receiving the flow of molten metal from the tundish and directing the roll gap to the roll gap. A molten metal reservoir is formed immediately above. The molten metal reservoir can be defined between side plates or weirs slidably held against the roll ends.

[0004]

Twin roll casting has achieved some success with non-ferrous metals, such as aluminum, which rapidly solidify upon cooling. However, when this technique is applied to the casting of ferrous metallic materials, there are various problems. Problem. 1
One major problem is that ferrous metal materials tend to occlude the very narrow molten metal flow path required for twin roll casting equipment due to solid inclusions during casting.

On the other hand, the use of silicon-manganese for ladle deoxidation of steel has been practiced in the production of ingots in the early days of the Bessemer steelmaking process, and the molten manganese silicate, which is a reactant, and manganese remaining in the molten metal, The equilibrium relationships with silicon and oxygen are known as such.

However, due to the development of steel strip manufacturing technology by slab casting and subsequent cold rolling, silicon /
Manganese deoxidation tends to be generally avoided and it is now believed that aluminum killed (killed deoxidized) steel should be used. That is, in the production of steel by slab casting followed by hot rolling (and often followed by cold rolling), silicon / manganese killed steel is
The concentration of contaminants in the intermediate layers of the cast metal strip results in unacceptably high incidence of stringers (strings).
This is because defects such as generation of burrs occur.

[0007] Silicon / manganese killed steels have generally been considered unsuitable for steel strip production because the tendency for contaminants to form in bands or layers in slab casting is reduced by aluminum killed steels. Therefore, it has been thought that it is necessary to use aluminum killed steel in order to continuously cast a steel strip with a twin roll casting apparatus.

[0008] However, continuous casting of steel strip produces a controlled flow of molten metal at a constant rate along the length of the casting roll to achieve sufficiently rapid and uniform cooling over the casting roll surface. It is very important. For this purpose, it is necessary to cause the molten metal to flow into a very narrow flow passage in the refractory material of the metal supply nozzle under a situation where the narrow flow passage is likely to be blocked by solid contaminants.

[0009] After performing an extensive program of strip casting various grades of steel in continuous strip rolling, we have developed a series of aluminum or partially killed steels with an aluminum balance of more than 0.01%. It has been concluded that, in general, sufficient casting cannot be achieved because solid contaminants clump together and block narrow channels in the metal supply system, forming defects and discontinuities in the resulting strip.

The present invention has been made in view of the above circumstances, and has as its object to provide a metal strip continuous casting method capable of obtaining a good casting result for an iron-based metal material.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a molten metal is introduced from a metal supply nozzle into a molten metal reservoir formed at an upper portion between a pair of parallel casting rolls, and the molten metal is cast downward from a roll gap. In the method of continuously casting a metal strip for delivering a strip, the thickness of the cast metal strip delivered downward from the roll gap is in the range of 1 to 4 mm, and the carbon content, manganese content, and silicon content of the molten metal are Each of carbon is 0.05-0.10% by weight, manganese is 0.50-0.70% by weight, silicon is 0.20-0.30% by weight, and the aluminum content is less than 0.008% by weight. The present invention relates to a metal strip continuous casting method using manganese killed steel.

[0012]

The above problem is solved by reducing the aluminum content to 0.008.
It has been found that this can be overcome by using a silicon / manganese killed steel with a carefully selected range of silicon and manganese content, which tends to produce deoxidized products in the molten state at the casting temperature, while maintaining the weight percent below. Was. Furthermore, it has been found that it is possible to cast strips without the stringers and other defects normally associated with silicon / manganese killed steel. This is because the rapid solidification achieved in the twin roll casting machine avoids the generation of large contaminants, and the twin roll casting method distributes the contaminants evenly throughout the strip instead of concentrating on the central layer. You.

It should be noted that in Richards et al US Pat. No. 3,412,781, 0.00.0
1 to 0.08% carbon, 0.20 to 0.60% manganese, 0.03 to 0.08% silicon, 0.015%
A continuous casting method of a steel slab in which the composition of molten steel is adjusted to include aluminum is disclosed.

Also, in US Pat. No. 4,529,441 to Smith, the composition is up to 0.06% carbon, up to 0.04% sulfur, up to 0.15% phosphorus, It is disclosed to add from 0.05 to 0.25% silicon in a melt that is up to 1.0% manganese and up to 0.001% silicon.

However, in the example disclosed in this patent,
It can be seen that the steel is partially killed by aluminum. More specifically, Example 1 uses 0.015% aluminum, Example 2 has 0.012% aluminum, and Example 3 has 0.020% aluminum. Including such amounts of aluminum has been found to be detrimental to continuous strip casting of steel.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 6 show an embodiment of the present invention.

The twin roll casting apparatus according to the present invention has a main machine frame 11 erected from a factory floor 12. A casting roll trolley 13 supported by the main machine frame 11 is horizontally movable between an assembly station 14 and a casting station 15. Molten metal is supplied from a ladle 17 via a tundish 18 and a metal supply nozzle 19 to a pair of parallel casting rolls 16 held by a casting roll carriage 13 during casting. Since the inside of the casting roll 16 is water-cooled, a solidified metal shell is formed on the surface of the moving roll, and a casting metal strip 20 is taken out from the roll outlet. The cast metal strip 20 is sent to a main coiler 21 and then to a second coiler 22.
Main machine frame 11 adjacent to casting station 15
A container 23 is attached to the tundish 18.
Through the overflow 24 of the or the severe deformation of the product, etc.
When there is a serious inconvenience during the casting operation, the molten metal in the tundish 18 can be released to the container 23 by removing the emergency plug 25 provided in the tundish 18.

A bogie frame 31 constituting the casting roll bogie 13 is mounted on a rail 33 via wheels 32,
Since the rail 33 extends along a part of the main machine frame 11, the entire casting roll carriage 13 is movably mounted on the rail 33. The casting roll 16 is rotatably mounted on a pair of roll cradle 34 held by the carriage frame 31. The roll cradle 34 is attached to the bogie frame 31 via sliding members 35 and 36 engaged with each other, and the hydraulic cylinder devices 37 and 3
The spacing between the casting rolls 16 is adjusted by 8 so that the casting rolls 16 can be rapidly moved in opposite directions in a short time when necessary. A double-acting hydraulic piston cylinder device 39 capable of moving the entire casting roll truck 13 along the rail 33 is connected between the drive bracket 40 of the casting roll truck 13 and the main machine frame 11,
The casting roll trolley 13 can be moved from the assembly station 14 to the casting station 15 or vice versa.

The pair of casting rolls 16 are rotated in mutually opposite directions via a roll drive shaft 41 of an electric motor (not shown) and a transmission provided on the bogie frame 31. A series of water-cooling passages (not shown) formed on the copper peripheral wall of the casting roll 16 and extending in the vertical direction while being spaced apart in the circumferential direction are provided with a water-cooling hose 4 through a rotating gland 43.
Cooling water is supplied through a roll end from a water cooling conduit (not shown) in the roll drive shaft 41 to which 2 is connected. 1300
The typical size of a casting roll 16 for making strips of mm width is about 500 mm in diameter and 1300 m in length
m.

The ladle 17 has a conventional configuration, is supported by a ceiling crane (not shown) via a yoke 45, and can be moved from a hot metal receiving station (not shown) to a fixed position. By moving a stopper rod 46 attached to the ladle 17 with a servo cylinder (not shown), the molten metal can flow from the ladle 17 to the tundish 18 via the outlet nozzle 47 and the refractory shroud 48.

The tundish 18 also has a conventional configuration, and is a wide dish made of a refractory material such as magnesium oxide (MgO). One side of the tundish 18 receives the molten metal from the ladle 17 and has the overflow port 24 and the emergency plug 25 described above. The other side of the tundish 18 is provided with a plurality of outlet openings 52 spaced apart in the vertical direction (the width direction of the casting roll 16). Tundish 1
The mounting bracket 53 holding the lower portion 8 is for mounting the tundish 18 to the bogie frame 31, and the bogie frame 3 is provided with an opening provided in the mounting bracket 53.
The tundish 18 is accurately positioned by receiving the first alignment peg 54.

The metal supply nozzle 19 is made of a refractory material such as alumina graphite in an elongated shape, and has a tapered lower portion and is tapered inward and downward. it can. Mounting bracket 6
Numeral 0 is provided for supporting the metal supply nozzle 19 with the bogie frame 31, and a side flange 55 projecting outward is formed above the metal supply nozzle 19 so that the mounting bracket 6
0 is engaged.

The metal supply nozzle 19 has a series of flow paths (e.g., outlet openings 52) that are horizontally separated and extend substantially up and down, and generate a suitably low-speed molten metal flow in the width direction of the casting roll 16. The molten metal can be sent to the gap between the casting rolls 16 without directly contacting the surface of the casting rolls 16 where the initial solidification occurs. Alternatively, the metal supply nozzle 19 may be in the form of a single slot, and the low-speed curtain-shaped molten metal may be directly sent to the gap between the casting rolls 16. In any case, the metal supply nozzle 19 may be immersed in the molten metal reservoir.

The molten metal reservoir is defined by a pair of side closure plates 56 at the end of the casting roll 16. Side closing plate 56
When the casting roll carriage 13 is at the casting station 15, it is held in contact with a step 57 between the body of the casting roll 16 and the shaft end. The side closing plate 56 is made of a strong refractory material such as boron nitride, and has an arc-shaped notch 81 corresponding to the peripheral surface of the casting roll 16 at the lower portion. The plate holder 82 to which the side closing plate 56 is mounted is movable by the operation of a pair of hydraulic cylinder devices 83 provided in the casting station 15, and the side closing plate 56 is pressed against the step 57 of the casting roll 16. Then, the end of the molten metal reservoir formed above the casting roll 16 during the casting operation is closed.

During the casting operation, the stopper rod 46 is actuated so that molten metal is poured from the ladle 17 to the tundish 18 and through the metal feed nozzle 19 into the gap of the casting roll 16. The clean (ordered, undamaged) tip of the cast metal strip 20 is guided to the jaws of the main coiler 21 by actuation of the apron table 96.
The apron table 96 is suspended from a pivot mounting portion 97 on the main machine frame 11, and after a clean tip is formed, the main coiler 2 is moved by the hydraulic cylinder device 98.
1 can be rocked. The apron table 96 is operated corresponding to the upper strip guide flap 99 operated by the piston cylinder device 101, and the cast metal strip 20 is guided between the pair of vertical side rolls 102. When the tip of the cast metal strip 20 is guided by the jaw of the main coiler 21, the main coiler 21 is rotated to wind up the cast metal strip 20, and the apron table 96 is rotated downward to return to the inactive position. Cast metal strip 20 wound directly on main coiler 21
Away from the main machine frame 11. The cast metal strip 20 can later be sent to a second coiler 22 and carried out of a twin roll casting machine to become the final roll.

Aluminum killed steel (killed deoxidation) is satisfactory because the formation of aluminate when the molten metal passes through the small orifices of the tundish 18 and metal feed nozzle 19 creates a blockage problem. It has been found that cast metal strip 20 cannot be produced.
This prevents even the flow of molten metal into the molten metal reservoir, resulting in the inability to produce cast metal strip 20 or the production of severely defective products.

Silicon and manganese are very useful deoxidizers when used in combination, and exhibit a synergistic effect. We have found that using a silicon / manganese killed steel in a twin roll casting apparatus of the type described above can produce cast metal strips 20 with acceptable oxygen levels. Operating the twin roll casting apparatus, the resulting cast metal strip 20 is fine and
Uniformly dispersed manganese silicate may be included as a contaminant, which contaminates the cast metal strip 20 mechanically, even at fairly high densities and an oxygen content of about 100-150 ppm. Does not have significant adverse effects on properties. With an aluminum killed steel, such an oxygen content would be unacceptable. This is because the aluminate contaminants can condense and form planar defects in the cast metal strip 20. The silicate contaminants do not condense, and in any event, limit the agglomeration in the strip casting process to form extremely large contaminants that are detrimental to the mechanical properties of the cast metal strip 20. You. Moreover, since the cast metal strip 20 is not extensively rolled in the post-process,
Contaminants are not stretched.

According to the present invention, the contents of silicon and manganese are optimally selected, so that the deoxidized product can be kept in a molten state during the casting operation, so that the tundish 18 and the metal supply nozzle can be maintained. 19 throttle orifices (flow paths)
Obstruction problem is solved.

The carbon, manganese and silicon content levels selected according to the present invention are such that the solidification process in the full iron (δ) region is maintained. Ideally, the composition should be selected to maximize the difference between the liquid and solid temperatures and maintain a sufficiently soft layer (mushy layer) throughout casting. . This is because the resulting cast metal strip 20 is of a quality that is less susceptible to the detrimental effects of molten metal reservoir disturbances during the rapid solidification process. However, it is important not to get too close to the austenite + iron region in the equilibrium phase diagram. This is because the equilibrium is not maintained under very rapid cooling conditions inside the twin roll casting machine and measures must be taken to prevent accidental solidification in the austenitic + iron region.

Increasing the silicon content and decreasing the carbon content promotes the formation of δ-iron during solidification, resulting in a cast metal strip 20 known as a "crocodile skin" defect. The tendency for unevenness of the surface to be easily formed is reduced. Typically, such defects are associated with local fluctuations in the cooling rate (and the resulting microstructural fluctuations) caused by the solidified metal shell not making solid contact with the surface of the casting roll 16.

If the carbon content is too low, a defect called "herring bone" can occur. This defect is essentially a periodic thickness variation that occurs with respect to the width direction (or at an angle to the width direction) of the cast metal strip 20, and the solidified metal shell forms the casting roll 16.
It is thought to be related to the behavior of the soft layer when it is fitted in the gap. If the temperature range in which the soft layer is present is too narrow, disturbances in the molten metal reservoir meniscus will have a significant effect on the thickness and viscosity of the soft layer, and therefore the force that the cast metal strip 20 exerts on the casting roll 16. To the cast metal strip 20
Affects the thickness of the

We have performed an extensive operation of a twin roll casting apparatus of the type described above, using various grades of steel. To produce a cast metal strip 20 having a thickness in the range of about 1-4 mm, the optimal steel composition is as follows. Carbon 0.05-0.10% by weight Manganese 0.50-0.70% by weight Silicon 0.20-0.30% by weight Aluminum Less than 0.008% by weight

The steel is preferably between 1500 and 160 for casting.
Preheat to a temperature in the range of 0 ° C. Preferably, tundish 18 is preheated to a temperature in the range of 1000-1300 ° C, and metal feed nozzle 19 is also preheated to a temperature in the range of 1000-1300 ° C.

FIG. 6 shows the results of various trial castings using mild steels having various silicon and manganese contents melted in the atmosphere. In this figure, .largecircle. Indicates steel that was successfully cast and produced a good quality cast metal strip 20, while + indicates steel that consistently had casting problems and strip defects. Trials have shown that steel having the composition of region A in FIG. 6 produces strip sheeting due to poor deoxidation.

Steels having a manganese content above 1.0% by weight, and thus entering zone B, create casting problems due to manganese oxide fume deposits on the casting roll 16.

Steels having a silicon content of more than 0.5% by weight and thus entering zone C produce strips with poor forming properties.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention.

[0039]

As described above, according to the continuous casting method of a metal strip of the present invention, an excellent effect that a good casting result can be obtained for an iron-based metal material can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a twin roll casting apparatus configured to operate according to the present invention.

FIG. 2 is a side view of the twin roll casting apparatus shown in FIG.

FIG. 3 is a view taken in the direction of arrows III-III in FIG. 1;

FIG. 4 is a view taken in the direction of arrows IV-IV in FIG. 1;

FIG. 5 is a view taken in the direction of arrows VV in FIG. 1;

FIG. 6 is a diagram showing the results of trial casting using steels with different compositions.

[Explanation of symbols]

 16 Casting roll 19 Metal supply nozzle 20 Cast metal strip

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-71392 (JP, A) JP-A-52-90419 (JP, A) JP-A-56-16616 (JP, A) JP-A-6-716 594 (JP, A) JP-A-5-293506 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/06 330 B22D 11/00 C22C 38/00 301 C22C 38 / 04

Claims (1)

(57) [Claims] 1. A continuous metal strip, wherein molten metal is introduced from a metal supply nozzle into a molten metal reservoir formed at an upper portion between a pair of parallel casting rolls, and the cast metal strip is fed downward from a gap between the rolls. In the casting method, the thickness of the cast metal strip delivered downward from the roll gap is in the range of 1 to 4 mm, and the carbon content, manganese content, and silicon content of the molten metal are each 0.05 to 0 carbon. 0.10% by weight of manganese 0.50 to 0.70% by weight of silicon 0.20 to 0.30% by weight of aluminum and less than 0.008% by weight of silicon / manganese killed steel. A method for continuously casting metal strip.