JPH07314097A - Metal strip continuous casting method - Google Patents

Abstract

(57) [Summary] [Structure] In order to continuously cast a cast metal strip 20, a molten metal is introduced into a roll gap between a pair of parallel casting rolls 16 and a metal supply nozzle 19 disposed above the roll gap. Introduced via a casting roll 1 directly above the roll gap
6 A molten metal reservoir supported on the surface is created, and the cast metal strip 20 is delivered downward from the roll gap.
The metal is a silicon / manganese-killed steel having a manganese content of 0.20% by weight or more, a silicon content of 0.01% or more, and a total aluminum content of the steel of less than 0.01% by weight. . [Effect] Good casting results for ferrous metal materials can be obtained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for continuously casting metal strips.

[0002]

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

In such a method, a molten metal is introduced between a pair of horizontal casting rolls which are cooled and rotated in opposite directions to solidify a metal shell on the surface of the rotating casting rolls. Both pass through the roll gap to form a cast metal strip, which is delivered downward from the roll gap. The introduction of the molten metal into the roll gap can be carried out by a tundish and a metal feed nozzle located below the tundish which directs the molten metal flow from the tundish and directs it into 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 that rapidly solidifies by cooling, but there are various ways to apply this technique to casting of ferrous metal materials. There is a problem. 1
One of the major problems is that iron-based metallic materials are subject to solid inclusions during casting, which tend to block the very thin molten metal flow passages required for twin roll casting equipment.

On the other hand, the use of silicon-manganese for deoxidizing steel ladle was carried out in the production of ingots in the early days of the Bessemer steelmaking process. The equilibrium relationship between silicon and oxygen is known as such.

However, due to the development of steel strip manufacturing technology by slab casting and subsequent cold rolling, silicon / silicon
Manganese deoxidation tends to be generally avoided and it is now believed that aluminum killed steel should be used. That is, in the production of steel by slab casting followed by hot rolling (often followed by cold rolling), silicon / manganese killed steel is
Due to the concentration of contaminants in the middle layer of the cast metal strip, unacceptably high stringer (string)
This is because defects such as ers burr) occur.

[0007] Silicon / manganese killed steels have generally been considered unsuitable for steel strip production because the tendency of band or layer inclusions in slab casting is reduced by aluminum killed steel. Therefore, it has hitherto been considered necessary to use aluminum killed steel for continuous casting of steel strip in twin roll casters.

However, in continuous casting of steel strip, the molten metal flow at a constant velocity along the length of the casting roll is produced by fine control to achieve sufficiently rapid and uniform cooling over the surface of the casting roll. Is very important. For this purpose, it is necessary to cause the molten metal to flow into a very narrow flow path in the refractory material of the metal supply nozzle under the situation that the fine flow path is easily blocked by the solid mixture.

After conducting an extensive program to strip cast various grades of steel in continuous strip rolling, we have found that for aluminum killed steel or partially killed steel with an aluminum balance of 0.01% or more. It was concluded that solid casting could not be adequately performed in general, because solid contaminants became lumps and clog the narrow flow paths in the metal supply system, forming defects and discontinuities in the resulting strip.

In view of the above situation, it is an object of the present invention to provide a metal strip continuous casting method capable of obtaining a good casting result for an iron-based metal material.

[0011]

According to the present invention, molten metal is introduced from a metal supply nozzle into a molten metal reservoir formed in an upper portion between a pair of parallel casting rolls, and the casting metal is downwardly moved from a roll gap. In a continuous metal strip casting method for delivering strips, the molten metal has a manganese content of 0.20% by weight or more, a silicon content of 0.01% or more, and a total aluminum content of less than 0.01% by weight. The present invention relates to a method for continuously casting a metal strip characterized by using silicon / manganese-killed steel.

In this case, the carbon content, the manganese content and the silicon content in the molten metal are 0.02 to 0.15% by weight of carbon, 0.20 to 1.0% by weight of manganese and 0.10 to 10% by weight of silicon, respectively. It may be 0.5% by weight.

Further, the thickness of the cast metal strip fed downward from the roll gap is in the range of 1 to 4 mm, and the carbon content, the manganese content and the silicon content in the molten metal are respectively 0.05 to 0.05 carbon. 0.10% by weight manganese 0.40 to 0.80% by weight silicon 0.10 to 0.30% by weight.

Further, the carbon content, the manganese content, and the silicon content in the molten metal are carbon 0.05 to 0.10% by weight, manganese 0.50 to 0.70% by weight, and silicon 0.20 to 0. It may be 30% by weight, and the aluminum content may be less than 0.008% by weight.

[0015]

The above problem is that the content of silicon and manganese in the carefully selected range, which tends to produce a deoxidized product in a molten state at the casting temperature, while keeping the aluminum content below 0.01% by weight. It was found that the problem can be solved by using the silicon / manganese-killed steel. 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,
The twin roll casting method ensures that the contaminants are evenly distributed throughout the strip rather than being concentrated in the central layer.

Note that in Richards et al., US Pat. No. 3,412,781, 0.0
1 to 0.08% carbon, 0.20 to 0.60% manganese, 0.03 to 0.08% silicon, 0.015%
The following continuous casting method of a steel slab in which the composition of molten steel is adjusted to contain aluminum is disclosed.

Smith US Pat. No. 4,529,441 also has a composition of up to 0.06% carbon, 0.04% sulfur, and 0.15% phosphorus. Disclosed is the addition of silicon in the range of 0.05 to 0.25% to a melt of up to 1.0% manganese and 0.001% or less silicon.

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

[0019]

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

1 to 6 show an embodiment of the present invention.

The twin roll casting machine according to the present invention has a main machine frame 11 which is erected from a factory floor 12. The casting roll carriage 13 supported by the main machine frame 11 is horizontally movable between the assembly station 14 and the casting station 15. Molten metal is supplied from a ladle 17 through 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 the cast metal strip 20 is taken out from the roll outlet. The cast metal strip 20 is sent to the main coiler 21 and then to the second coiler 22.
Adjacent to the casting station 15 the main machine frame 11
A container 23 is attached to the tundish 18
Through the overflow port 24 of the
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 pulling out the emergency plug 25 provided in the tundish 18.

The trolley frame 31 constituting the casting roll trolley 13 is mounted on the rail 33 via the wheel 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 attached to a pair of roll cradle 34 held by the carriage frame 31. The roll cradle 34 is attached to the carriage frame 31 via sliding members 35 and 36 which are engaged with each other, and the hydraulic cylinder devices 37 and 3 are provided.
The distance 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 carriage 13 along the rail 33 is connected between the drive bracket 40 of the casting roll carriage 13 and the main machine frame 11,
The casting roll carriage 13 can be moved from the assembly station 14 to the casting station 15 and vice versa.

The pair of casting rolls 16 are rotated in opposite directions via a roll drive shaft 41 of an electric motor (not shown) and a transmission provided on the carriage frame 31. A series of water cooling passages (not shown) which are formed on the copper peripheral wall of the casting roll 16 and which are spaced apart in the circumferential direction and extend in the longitudinal direction are provided with the water cooling hose 4 via the rotary 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 the casting roll 16 for making a mm wide strip is about 500 mm in diameter and 1300 m in length.
up to m.

The ladle 17 is of conventional construction and is supported by an overhead 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 the stopper rod 46 attached to the ladle 17 by a servo cylinder (not shown), the molten metal can be flowed from the ladle 17 to the tundish 18 through the outlet nozzle 47 and the refractory shroud 48.

The tundish 18 also has a conventional structure, and is in the shape of a wide plate 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 is provided with 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 which are separated in the vertical direction (width direction of the casting roll 16). Tundish 1
8 is a mounting bracket 53 for holding the lower part, which is used to mount the tundish 18 on the trolley frame 31, and the trolley frame 3 has an opening provided in the mounting bracket 53.
The tundish 18 is accurately positioned by receiving the positioning peg 54 of 1.

The metal supply nozzle 19 is made of a refractory material such as alumina graphite and has an elongated shape. The lower part is tapered and is recessed inward and downward. Therefore, the metal supply nozzle 19 is inserted into the gap between the casting rolls 16. it can. Mounting bracket 6
No. 0 is provided to support the metal supply nozzle 19 on the trolley frame 31, and a side flange 55 protruding outward is formed on the upper part of the metal supply nozzle 19 to attach the mounting bracket 6.
Engage 0.

The metal supply nozzle 19 has a series of flow passages (outlet openings 52 and the like) which are horizontally separated from each other and extend substantially vertically. The metal supply nozzle 19 produces an appropriately low-speed molten metal flow in the width direction of the casting roll 16. The molten metal can be sent to the gap of the casting roll 16 without directly contacting the surface of the casting roll 16 where the initial solidification occurs. Alternatively, the metal supply nozzle 19 may be in the form of a single elongated hole, and the low-speed curtain-shaped molten metal may be directly fed into 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 ends of the casting roll 16. Side closure plate 56
When the casting roll carriage 13 is at the casting station 15, the casting roll carriage 13 is held in contact with the step portion 57 between the barrel portion and the shaft end portion of the casting roll 16. The side blocking plate 56 is made of a strong refractory material such as boron nitride, and has an arcuate notch 81 corresponding to the peripheral surface of the casting roll 16 in the lower portion. The plate holder 82 to which the side closing plate 56 is attached 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 on the upper portion of the casting roll 16 is closed during the casting operation.

During the casting operation, the stopper rod 46 is actuated so that molten metal is poured from the ladle 17 into the tundish 18 and, through the metal feed nozzle 19, into the nip of the casting roll 16. The clean (clean, scratch-free) 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 the pivot mounting portion 97 on the main machine frame 11, and after the clean tip is formed, the main cylinder 2 is moved by the hydraulic cylinder device 98.
It can be swung towards 1. 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 inoperative position. Cast metal strip 20 wound directly on the main coiler 21
And is simply suspended from the main machine frame 11. The cast metal strip 20 can later be sent to the second coiler 22 and unloaded from the twin roll caster into a final roll.

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

Silicon and manganese are very useful deoxidizing agents when used in combination and exert a synergistic effect. We have found that twin / roll casters of the type described above can be used to produce cast metal strip 20 with acceptable oxygen levels by using silicon / manganese killed steel. Running a twin roll casting machine, the resulting cast metal strip 20 is fine and
A homogeneously dispersed manganese silicate can be included as a contaminant, which has a fairly high density and a mechanical content of the cast metal strip 20 of even about 100 to 150 ppm oxygen content. Has no significant adverse effect on properties. If it were aluminum killed steel, such an oxygen content would be unacceptable. This is because the aluminate inclusions cluster together to form planar defects in the cast metal strip 20. The silicate contaminants are not dense and, in any event, the agglomeration is limited in the strip casting process to form extremely large contaminants that are detrimental to the mechanical properties of the cast metal strip 20. It Moreover, since the cast metal strip 20 is not widely rolled in the post process,
The contaminants are not stretched.

According to the present invention, since the contents of silicon and manganese are optimally selected, it is possible to hold the deoxidized product in a molten state during the casting operation, and therefore, the tundish 18 and the metal supply nozzle. 19 throttle orifices (flow paths)
Solves the blockage problem in.

The carbon, manganese and silicon content levels selected according to the present invention are such that the solidification process in the complete iron (δ) region is maintained. Ideally, the composition should be chosen to maximize the difference between the liquid and solid phases and maintain a sufficiently soft layer (mushy layer) in the casting. . This is because the cast metal strip 20 thus produced is of a quality that is less susceptible to the detrimental effects of the disturbance of the molten metal reservoir 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 state is not maintained under the extremely rapid cooling condition inside the twin roll casting apparatus, and it is necessary to take measures so as not to cause solidification in the austenite + iron region.

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

If the carbon content is too low, defects called "herring bones" can occur. This defect is essentially a periodic thickness variation that occurs in the width direction (or at an angle to the width direction) of the cast metal strip 20 and causes the solidified metal shell to move to the casting roll 16
It is believed to be related to the behavior of the soft layer when combined at the gap of. 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 thus the force exerted by the cast metal strip 20 on the casting roll 16. And as a result, cast metal strip 20
Affect the thickness of.

We have made extensive runs of twin roll casters of the type described above using various grades of steel. To produce a cast metal strip 20 having a thickness in the range of approximately 1-4 mm, the optimum steel composition is as follows. Carbon 0.05 to 0.10% by weight Manganese 0.50 to 0.70% by weight Silicon 0.20 to 0.30% by weight Aluminum less than 0.008% by weight

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

FIG. 6 shows the results of various trial castings using mild steels having various silicon and manganese contents which were melted in the atmosphere. In this figure, the circles indicate the steels that could be successfully cast to produce good quality cast metal strip 20, while the + indicate steels that consistently had casting problems and strip defects. Trials have shown that the steel with the composition of region A in FIG. 6 produces strip sheeting due to poor deoxidation.

Steels having a manganese content of more than 1.0% by weight and thus entering zone B create casting problems with manganese oxide fume deposits on the casting roll 16.

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

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0042]

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

[Brief description of drawings]

FIG. 1 is a plan view of a twin roll casting machine configured to operate in accordance with the present invention.

2 is a side view of the twin roll casting apparatus shown in FIG. 1. FIG.

FIG. 3 is a view on arrow III-III in FIG. 1.

FIG. 4 is a view taken along the line IV-IV in FIG.

5 is a view taken along the line VV of FIG.

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

[Explanation of Codes] 16 Casting Roll 19 Metal Supply Nozzle 20 Cast Metal Strip

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Alan John Brazzwick Australia New South Wales Jean Bleu Owen Street 16

Claims (4)

[Claims] 1. A continuous strip of metal, 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 delivered downward from a roll gap. In the casting method, use a silicon / manganese-killed steel with a manganese content of 0.20% by weight or more, a silicon content of 0.01% or more, and a total aluminum content of less than 0.01% by weight as the molten metal. A continuous casting method for metal strips, which is characterized in that 2. The content of carbon, the content of manganese and the content of silicon in the molten metal are 0.02 to 0.15% by weight of carbon, 0.20 to 1.0% by weight of manganese and 0.10 to 0. The metal strip continuous casting method according to claim 1, wherein the content is 5% by weight. 3. The thickness of the cast metal strip fed downward from the roll gap is in the range of 1 to 4 mm, and the carbon content, the manganese content and the silicon content in the molten metal are respectively 0.05 to carbon. 0.10 weight% manganese 0.40-0.80 weight% Silicon 0.10-0.30 weight% The metal strip continuous casting method of Claim 1 which is 0.10-0.30 weight%. 4. The carbon content, the manganese content, and the silicon content in the molten metal are carbon 0.05 to 0.10% by weight, manganese 0.50 to 0.70% by weight, and silicon 0.20 to 0. The method for continuous casting of metal strip according to claim 3, wherein the content is 30% by weight and the aluminum content is less than 0.008% by weight.