JPS6149749A - Continuous casting method of clad steel billet - Google Patents

Abstract

PURPOSE:To weld the entire surface of a clad steel billet to satisfactory quality without deformation and to improve product yield in continuous casting of the clad steel in which a molten steel is supplied, welded and quickly cooled onto the surface of a continuously moving steel strip by preheating the steel strip in plural stages within a specific heating-up range and holding the temp. thereof for prescribed time after pouring. CONSTITUTION:The continuously moving clad steel strip 6 is preheated stepwise within the temp. range of >=300 deg.C and lower by 200 deg.C than the solidus line temp. of the steel strip in plural heating furnaces 12a-c kept within 400 deg.C heating up temp. to prevent the deformation thereof and to heat uniformly the entire surface and thereafter the strip is fed to a pouring part 2. The entire surface is satisfactorily welded in a heat insulating zone 16 and an air cooling zone 17 after pouring then the strip is subjected to quick cooling 18. The clad steel billet 10 has the defectless weld quality without having the unwelded part and without the deformation and buckling thereof. The product yield is thus improved.

Description

[Detailed Description of the Invention] [Technical Analysis of the Invention] The present invention provides a clad steel slab that can be produced by continuous casting at low cost, with high yield, and with high efficiency. This series concerns the method of making bladders.

[Prior art and its problems]

A first-order method is known as a method for manufacturing clad steel materials.

(1) Rolling method (2) Explosion bonding method (3) Overlay method (4) Casting method rolling method involves overlapping base material and cladding material and welding four circumferences.
This is a method of crimping by hot rolling. However, this method requires a lot of time and effort in pre-rolling, such as polishing the surfaces to be joined, welding the four circumferences, and creating a vacuum between the base material and the laminate to prevent oxidation. Since the sword costs λ, manufacturing costs are high and mass production is difficult.

The explosive bonding method is a method in which a base material, a laminate material, and gunpowder are layered and bonded together using shock waves from an explosion. Although this method has the advantage of being applicable to a wide range of metals, it has an upper limit on the area that can be manufactured, and because it uses expensive gunpowder, the manufacturing cost is extremely high and the explosion noise is loud. There are also environmental issues.

The sensitization method is a method that consists of placing a cladding material on the surface of the base material and depositing and melting it. Although this method has the advantage of being able to form a cladding after forming the base material, it requires a lot of effort in melting, and is not suitable for manufacturing large-area products, resulting in poor productivity. .

In the casting method, a composite steel ingot is prepared by setting the composite material in a mold, injecting molten steel that has been mixed with the base metal into the mold and casting the composite material, and then rolling this composite steel ingot to produce it. This is the way to make a sword. While using this method,
Since it requires a laminate with a thickness of a certain size or more,
The cladding ratio is limited, inclusions are trapped, and the surface of the laminate is squeezed.

There are problems such as the need for countermeasures against In particular, the biggest problem is that the yield is greatly reduced due to melting loss of the laminate material and changes in the cladding ratio due to the metal a during rolling.

As mentioned above, all conventional methods for manufacturing clad steel have low productivity and high manufacturing costs, so the reality is that it is difficult to achieve cost benefits and demand expansion is slow.

Therefore, in recent years, research has been carried out to manufacture clad steel slabs by continuous casting.
No. 58-65549 and JP-A No. 58-65549 disclose a method of producing a clad steel slab by casting while supplying all of the molten steel as a base material to the surface of one cladding material or between a pair of cladding materials 7 )> is disclosed.

FIG. 3 is a schematic explanatory diagram of the conventional method described above. Molten steel 5 as a base material in the ladle 1 is injected into a tundish 2 provided below the ladle 1 through a nozzle 3 provided at the bottom of the ladle 1.

A horizontal molten steel discharge port 4 is provided at the lower part of the tundish 2, and the molten steel 5 as a base material in the tundish 2 is discharged through the horizontal molten steel discharge port 4.

On the other hand, the laminating material steel strip 6 is pulled out horizontally by a driving roll 8 of a reel 7 serving as a dispensing device, and guided below the molten steel discharge port 4 provided horizontally at the bottom of the tundish 2. It moves horizontally along the lower surface of Tanditsh 2. Reference numeral 9 denotes a cooling device provided along the movement path of the cladding material steel strip 6 starting from a position below the molten steel discharge port 4.

The molten steel 5 as a base material discharged from the tundish 2 through the molten steel discharge port 4 is supplied onto the surface of the horizontally moving cladding steel strip 6, and is welded to the cladding steel strip 6, and then cooled by the cooling device. 9, the laminated steel strip 6 is cooled from the back side and solidified on the surface of the laminated steel strip 6, thus continuously producing a clad steel slab 10.

However, the above-mentioned method has the following problems.

(1) In order for the laminate steel strip 6 and the molten steel 5 as the base material to be completely welded together, the contact interface between the two needs to be at a certain high temperature (for example, solid phase temperature).

However, the laminating material steel strip 6 is at room temperature.
Even if the steel 5 is supplied, it takes 717 hours for the interface temperature to reach the temperature required for welding. Since it is easy to form, an unwelded portion is created between the cladding material steel strip 6 and the molten steel 5.

(2) The laminated steel strip 6 is exposed to the sudden temperature change that occurs when the molten steel 5 as a base material is supplied, that is, from room temperature 71λ to 700-10
Due to the rapid temperature rise to 00° C., deformation (curvature or curve V) and buckling are likely to occur near the supply position of the molten steel 5.

(3) Clad steel slabs are also susceptible to deformation and buckling during the cooling stage after casting.

The deformation and buckling mentioned in (2) and (3) above are caused by thermal expansion and contraction (thermal strain) due to sudden temperature changes, and by extreme temperature non-uniformity in the thickness direction of the steel strip. This is a major problem that hinders the stable production of clad steel slabs.

[Purpose of the invention]

Therefore, an object of the present invention is to produce high-quality clad steel slabs with a sound welding surface and no deformation or buckling in a stable manner with a high yield when manufacturing clad steel slabs by continuous casting. We are here to provide a complete method for continuous production.

[Summary of the invention]

The method of the present invention involves supplying molten steel as a base material onto the surface of a continuously moving cladding steel strip or between a pair of cladding steel strips, and transferring the molten steel to the cladding steel strip. A clad steel slab is welded to a steel strip, and then the entire surface of the clad steel strip opposite to the molten steel is forcedly cooled to solidify the molten steel welded to the clad steel strip. In a continuous casting method for continuous casting of clad steel slabs, before the molten steel serving as the base material is supplied, the cladding material steel strip is made such that the surface roughness on the side to which the molten steel is supplied is 300℃ sword
The steel strip is preheated to a temperature 200°C lower than the solid state temperature of the laminated steel strip, and the preheating is divided into multiple stages to reduce the temperature increase of the steel strip by one preheating. 40
The process is carried out in stages within 0°C, and then the molten steel as the base material is supplied, and the back side of the laminated steel strip to which the molten steel has been supplied is kept warm with a heat insulator for a predetermined period of time, and then the process is carried out in stages. It has the special feature of forced cooling.

[Structure of the invention]

FIG. 1 shows, as one embodiment of the apparatus used in the method of the present invention, an apparatus for producing a single-sided clad steel slab by supplying all of the molten g4 as a base material onto the surface of one laminated steel strip. FIG. A tundish 2 is provided below the ladle 1, and a horizontal molten steel discharge port 4 is provided at the bottom of the tundish 2. The melt m5 in the tundish 2 is injected into the tundish 2 through the provided nozzle 3 and is discharged through the horizontal molten steel outlet 4.

The laminated steel strip 6 wound into a coil is moved to a drive roll 8.
Accordingly, the payoff reel 7η1 as a payout device
The molten steel is pulled out horizontally from the tundish 2 and guided by rollers 13 to the lower part of the molten steel discharge port 4 provided horizontally at the bottom of the tundish 2.
) and moves along the bottom surface of the tanditsh 2.

Along the movement path of the clad steel strip 6 on the entry side of the tundish 2, there is a straightening roll 11 for completely correcting the shape of the clad steel strip 6, and a first straightening roll 11 for preheating the clad steel strip 6.
Heating furnace 12a, second heating furnace 12b, and third heating furnace 12
c is provided. The first heating furnace 12a, the second heating furnace 12b1, and the third heating furnace 12c are set so that the heating temperature gradually increases in this order, and the third heating furnace 12c, which has the highest temperature, is installed immediately before the kundish 2. It is being It is desirable to maintain an inert gas atmosphere in the heating furnaces 12a, 12b, and 12c to prevent oxidation of the laminated steel strip 6.

Along the movement path of the cladding material steel strip 6 for a predetermined distance from the exit side of the third heating furnace 12c through the molten steel discharge port 4 of the tundish 2, approaching the back surface of the cladding material steel strip 6, Laminating steel strip 6 preheated by heating furnaces 12a, 12b, 12C
A heat insulating material 14 made of a refractory material is provided to completely prevent heat dissipation from the back of the sword. It will be more effective if the heat insulating material 14 is formed into a heat insulating chamber that covers the entire surface of the laminated steel strip 6, and the inside thereof is filled with an inert gas atmosphere.

15 is on the exit side of the molten steel discharge port 4 of the tanditsh 2,
Molten M5 as a base material is supplied onto the surface of the steel strip 6, and a movable type consisting of an endless belt is disposed on both sides of the steel strip 6 along the moving path. This is the side block.

On the outlet side of the molten steel discharge port 4 of the tundish 2, molten steel 5 as a base material is supplied onto the surface of the molten steel discharge port 4 along the movement path of the cladding materials 5 and 4 strips 6 at regular intervals from the molten steel discharge port 4. It consists of a plurality of upward spray nozzles that spray cooling water to cool the laminated steel strip 6 from its back side blade 1.
First cooling zone 18a, second cooling zone 18b, third cooling zone 18
c is provided.

16 is a molten steel base material provided between the molten steel discharge port 4 of the tundish 2 and the first cooling zone 18a. jt! 4
For a predetermined period of time, the back side of the laminated steel strip 6 supplied with
A heat insulating zone 17 for keeping warm with the heat insulating material 14 is an air cooling zone following the heat insulating zone 16.

The laminating steel strip 6 is pulled out by the drive roll 8 and moved horizontally by the payoff reel 77)-1 213.
The surface is preheated to a predetermined temperature in stages by the first heating furnace 12a, the second heating furnace 12b and the third heating furnace 12c, and then the molten steel outlet 4 of the tundish 2 is heated as a base material onto the surface. Molten g! 45 is supplied to the 5° molten steel 5 and the cladding steel strip 6, the cladding steel strip 6 is supplied to the first heating furnace 18.
a, the second heating furnace 18b, and the third heating furnace 18c preheat to a predetermined temperature in stages, so that complete welding occurs without deformation or buckling.

Next, the clad steel strip 6 to which the molten steel 5 has been welded is supported by the side blocks 15 and moved until at least the short sides have solidified, the back side of which is kept warm in the heat insulating zone 16 for a predetermined period of time, and the back surface is kept warm in the air cooling zone 17. After being weakly cooled, the molten steel 5 is cooled in stages by the first cooling zone 18a, the second cooling zone 18b, and the third cooling zone 18C, solidifying the molten steel 5, and forming the clad steel slab 10.
becomes.

A rolling roll 8 for moving the laminated steel strip 6 is provided at an appropriate position between the payoff reel 7 and the tundish 2 and at an appropriate position downstream of the tundish 2, and is provided at an appropriate position downstream from the tundish 2, and is used to move the payoff reel 7 from the drawer. The laminated steel strip 6 is guided at a predetermined speed through the heating furnaces 12a, 12b, 12c@ to below the molten steel outlet 4 of the tundish 2, and from the molten steel outlet 4 onto the surface of the laminated steel strip 6. The clad steel slab 10 to which molten steel 5 is supplied and welded is moved at a predetermined speed.

In manufacturing clad steel strips using the above-described apparatus, the thickness of the base metal can be controlled by the flow rate of the molten steel 5 discharged from the molten steel outlet 4 of the tundish 2 or the moving speed of the clad steel strip 6. can.

In this invention, the surface temperature of the laminate steel strip immediately before the molten steel is supplied as the base material is 300'C71-, and the hardness of the laminate steel strip is 300'C71-. It is necessary to preheat to a temperature that is 200° C. lower than the phase line temperature.

That is, as the base metal; The entire interface between the two can be quickly brought to the high temperature required for welding.Therefore, the molten steel supplied onto the surface of the cladding steel strip will not cool down and a solidified shell will be generated, resulting in a sound welding interface. Clad steel slabs can be stably produced.

If the temperature of the preheated laminated steel strip is less than 300°C, the desired effect cannot be obtained from the above action. On the other hand, if the temperature of the preheated laminate steel strip is 200°C lower than its solidus temperature, the tensile strength of the laminate steel strip will decrease significantly, resulting in deformation or deformation of the laminate steel strip. There is a problem in that the steel strip breaks or the temperature of the steel strip increases too much due to the molten steel supplied to the surface of the steel strip, causing the steel strip to melt or break.

The above-mentioned preheating of the laminated steel strip is performed in stages using multiple heating furnaces, and the temperature rise of the steel strip due to one preheating is as follows:
It is necessary to keep the temperature within 400℃, and the cooling of the laminated steel strip to which the molten steel as the base material has been welded is carried out in stages using multiple cooling zones after keeping the back side of the steel strip warm for a predetermined period of time. Temperature cooling is required.

FIG. 2 is a graph showing an example of the preheating temperature of the cladding steel strip and the cooling temperature of the cladding steel strip to which molten steel has been welded. As shown in the drawing, the laminated steel strip is heated in the first heating furnace 12a.
It is preheated to about 400°C in the second heating furnace 12b, and heated to about 750°C in the second heating furnace 12b.
℃ and heated to about 1100℃ in a third heating furnace 12C.
Preheated to ℃.

The cladding steel strip to which the molten steel has been welded is then
The temperature is maintained at approximately 1400℃, and the temperature is maintained at approximately 1150℃ in air cooling zone 17.
After being slowly cooled to about 850°C in the first cooling zone 18a,
Second cooling zone 18b-1? It is cooled to about 70° C. and then to about 350° C. in the third cooling zone 18C.

When continuously supplied steel strip is heated in a heating furnace, the difference in temperature between the front and rear must be within a certain range before buckling or deformation occurs, depending on the material of the cladding steel strip.

Heating Method 1 Although it differs depending on the method of supporting the laminate steel strip, etc., the strain caused by thermal expansion can be expressed as follows using a simple model equation.

In this equation, X is the distance from the heating start position, Xo is the distance from the heating start position to the position where the steel strip temperature reaches a steady temperature, ε is the strain at distance X, and α is the coefficient of expansion of the clad steel strip. , ΔT is the temperature difference between the laminated steel strip before and after heating.

The above equation is a quadratic function with respect to distance X, and when differentiated with respect to X, it becomes α·ΔT ε'= (2x Xo).

0Z Therefore, the strain ε becomes maximum at x=xo/2. The strain εmax at this time is εmax"α・△T/4 Elastic limit strain εcr k O, 2%, the condition ε that buckling deformation does not occur due to temperature change. r ≥ εmax means that the steel strip is Ordinary carbon @ (α=8.8~14.4X10
In the case of Kl, ΔT≦570. Stainless steel (α=1
1.5 to 20.2X10-6), ΔT≦4
It becomes 00. Therefore, the steel strip temperature increases with one heating process'(
If the temperature is within i-400°C, the laminated steel strip can be preheated without causing any deformation buckling.

Note that the heating furnace can be appropriately selected from gas furnaces, electric resistance furnaces, induction heating furnaces, etc., taking into consideration conditions such as the material of the steel strip and the heating temperature, and these can also be used in combination.

On the other hand, during cooling, if the steel strip to which the molten steel is welded is immediately water-cooled, the mating steel strip and the molten steel as the base material will age 1.
The difference in shrinkage ratio causes strain near the interface, and if the strain is large, the laminate and base material may separate. Furthermore, the steel strip to which the molten steel is welded may be deformed due to nonuniform temperature in the thickness direction during cooling. In order to prevent these, it is effective to perform mild cooling using air cooling or the like, and to cool gradually to an extent that no distortion occurs, similar to when heating. However, even in that case, it is necessary to provide a heat insulating zone near the pouring port to achieve sufficient melting Mk of the laminate material and the base material.

[Embodiments of the invention]

Next, this invention? This will be further explained in detail with reference to Examples.

Stainless clad steel pieces were manufactured using the apparatus shown in FIG. Thickness 5 Deafness 1 Width 1000. =, +lli
The laminating material is 18-8 stainless steel (SUS 304) steel strip, and the base material is ordinary carbon 914 (0.10%
We supplied C-containing steel. The stainless steel strip used as the cladding material was a hot-rolled coil, which was pickled before use.

A stainless steel strip as a laminate is preheated in a heating furnace with an argon + 3% hydrogen atmosphere, and about 40% of the molten steel is placed on its surface.
It was supplied to a thickness of 0+o+. At this time, the stainless steel strip is preheated in three heating furnaces as shown in Fig. 1. h1 The first heating furnace 12a is heated to about 400°C, the second heating furnace 12b is heated to about 750°C, and the third heating furnace is heated to about 750°C. Approximately 1 in furnace 12c
Preheated to 100°C.

Molten fA as a base material was supplied onto the surface of the laminated steel strip preheated to about 1100° C. to a thickness of about 40 mm. The molten steel supply temperature was 1570°C, the casting speed (steel strip movement speed) was 2 m/1ln, the cross-sectional shape of the molten steel supply port was a flat slit, and the direction of the molten steel discharge flow was relative to the laminated steel strip. The angle was set at 25°.

The laminated material steel strip to which the molten steel as a base material has been supplied is kept warm on the back side with a heat insulating material in the heat insulating zone 16 between the molten steel supply position and 50 holes, and then placed in an air cooling zone with a length of 50 holes. 1
After slow cooling in step 7, cooling was performed in stages in the first cooling zone 18a, second cooling zone 18b1, and third cooling zone 18c, in which the amount of cooling water increased in stages.

As a result, clad steel slabs with a sound weld interface,
The product could be manufactured without deformation or buckling.

This invention is not limited to the case where molten steel as a base material is supplied onto the surface of one clad steel strip as described above to produce a single-sided clad steel slab '5r; Of course, this method can also be applied to the case where all of the molten steel is supplied as the base material during the manufacturing process, and a double-sided clad steel slab is produced.

〔Effect of the invention〕

As explained above, according to the method of the present invention, a high-quality clad slab with a healthy welded interface with no unwelded parts at the interface, without deformation or buckling, and with a high yield and stability. It provides an industrially superior effect that can be produced economically.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the apparatus used in the method of the present invention, and FIG. 2 is an example of the preheating temperature of the laminated steel strip and the cooling temperature of the laminated steel strip supplied with molten steel. The graph showing , and Figure 3 are explanatory diagrams showing an example of a conventional device. In the drawing, 1... ladle, 2.
・Tan r it/yu, 3...nozzle, 4・
... Molten steel discharge port, 5... Molten steel, 6...
- Laminated steel strip, 7... Payoff reel, 8...
Drive 0-le, 9...Cooling device, 10...
- Clad steel slab, 11... Straightening roll, 12
a...first heating furnace, 12b...second heating furnace,
12c...Third heating furnace, 13...Roller,
14...Insulating material, 15...Side block, 16
...Insulation and heat retention zone, 17...Air cooling zone, 18
a... first cooling zone, 18b... second cooling zone,
18c...Third cooling zone.

Claims (1)

[Claims] Molten steel as a base material is supplied onto the surface of one cladding steel strip or between a pair of cladding steel strips that move continuously, and the molten steel is transferred to the cladding steel. The clad steel slab is continuously welded to the strip, and then the surface of the clad steel strip opposite to the welded surface of the molten steel is forcedly cooled to solidify the molten steel welded to the clad steel strip. In the continuous casting method of clad steel slabs manufactured in
The steel strip is preheated to a temperature that is 200°C lower than the solidus temperature of the laminated steel strip, and the preheating is divided into multiple stages to reduce the temperature rise of the steel strip due to one preheating by 40°C.
The process is carried out in stages within 0°C, and then the molten steel as the base material is supplied, and the back side of the laminated steel strip to which the molten steel has been supplied is kept warm for a predetermined period of time with a heat insulating material, and then the molten steel is heated in stages. A continuous casting method for clad steel slabs characterized by forced cooling.