JPH0929395A - Manufacture of stainless steel strip by continuous casting hot rolling and heat treatment furnace therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a stainless steel strip by the continuous casting and hot rolling capable of manufacturing the stainless steel strip capable of refining the re-crystallized grain size and excellent in the surface quality and the inner structure at a low cost when the casting thickness is changed in flying during the continuous casting, and to provide a heat treatment furnace to implement the method. SOLUTION: When the casting slab thickness is reduced in flying the casting arc angle is reduced, and the casting speed is reduced, and the heat treatment length of a heat treatment furnace 7 and the cooling length of a cooling zone are reduced, and the opening between the drums is reduced to achieve the continuous casting, and the heat treatment length and the cooling length are increased to the prescribed length. When the casting slab thickness is increased in flying, the opening between the drums is increased while the heat treatment length of the heat treatment furnace 7 and the cooling length of the cooling zone are reduced with the normal casting arc angle, and the casting speed is reduced to achieve the continuous casting, and the heat treatment length of the heat treatment furnace 7 and the cooling length of the cooling zone are increased to the prescribed values.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to continuous casting of thin stainless steel flakes having a thickness of 1 to 10 mm by a twin-drum type continuous casting machine, which is continuously hot-rolled at a high temperature and a high speed, and a heat treatment,
In order to carry out this method and a method for producing a stainless steel strip by continuous casting hot rolling which is applied when changing the thickness of a thin slab during running when producing a stainless steel strip having a plate thickness of 3 mm or less by cooling. The present invention relates to a heat treatment furnace for continuous casting hot rolling of stainless steel strip.

[0002]

2. Description of the Related Art In recent years, for example, in the field of iron and steel, when manufacturing steel sheets, from the viewpoints of productivity improvement by reduction of steps, reduction of equipment cost and heat intensity, for example, as shown in FIG. The thin cast piece 2 is continuously cast by the drum type continuous casting machine 1, and the thin cast piece is continuously treated by the hot rolling mill 6, the heat treatment furnace 7, the cooling device 9 and the like which are continuously arranged downstream of the continuous caster 1. A strip continuous casting hot rolling process in which the strip is wound on a winder 13 has been proposed, and attempts have been made to apply this process to the production of stainless strip. In such a continuous casting hot rolling process for stainless steel strips, in the case of producing small lots of multi-size (plate thickness) strips, it is possible to change the plate thickness between runs from the viewpoints of improving productivity and reducing production costs. Is preferred.

When the strip thickness is changed between runs, it can be dealt with to some extent by changing the rolling conditions, but it is premised on the production of a stainless strip with stable quality (evaluated by the internal structure, gloss, and degree of roping). Since there is a limit to the case, it may be necessary to change the casting thickness. For example, Japanese Patent Laid-Open No. 60-83756 discloses a method for changing the casting thickness in twin drum type continuous casting. Here, as a configuration for calculating and setting the roll gap and the roll rotation speed from the roll reaction force and the roll rotation speed of the continuous casting machine, there is a control method of performing the change of the plate thickness in a short time and casting at a predetermined plate thickness. It is disclosed.

However, in the above disclosed conventional technology,
In the case of producing stainless steel strips, if the casting thickness is changed during running with a continuous casting machine, the recrystallized grain size often cannot be refined even after the hot rolling and heat treatment steps, and the quality (internal structure, It is difficult to stably manufacture a stainless steel strip that is stable in terms of glossiness and evaluation of roping.

[0005]

SUMMARY OF THE INVENTION The present invention is a twin drum type continuous casting machine for continuously casting thin cast pieces, and the thin cast pieces are continuously arranged downstream of the continuous casting machine. Even if the casting thickness is changed between runs during continuous casting with a cooling device, the recrystallized grain size can be reduced by hot rolling and heat treatment, and stainless steel strip with excellent surface quality and internal structure can be reduced. The present invention provides a method for producing a stainless strip by continuous casting hot rolling which can be produced at low cost, and a heat treatment furnace for continuous casting hot rolling of stainless strip for carrying out this method.

[0006]

Means for Solving the Problems The first invention of the present invention is:
Continuous casting hot rolling that continuously casts thin slabs with twin-drum type continuous casting machine, and continuously processes the thin slabs with a hot rolling mill, heat treatment furnace, cooling device, etc. arranged downstream of the continuous casting machine. In the method for producing a stainless steel strip, when the thickness of the cast plate is reduced during running, the height of the molten metal surface of the molten metal pool formed by the drum and the side dam is set to 2 mm from the normal casting arc angle.
After reducing the casting speed to 0 to 30 degrees and reducing the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone, the opening between the drums is closed while the casting rate and the cooling length of the cooling zone are recovered. The thickness is reduced and continuous casting is performed, and after a certain period of time, the casting arc angle is restored to a normal level and the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are increased to a predetermined length as the casting speed increases. Immediately before the thickness change part of the thin cast piece reaches the hot rolling mill, the rolling reduction of the hot rolling mill is 30%.
Hot-rolling is performed under the above control, and the strip hot-rolled by the hot-rolling mill is heat-treated at a strip temperature of 900 to 1200 ° C. for 5 seconds or more in a heat treatment furnace, and then 500 at a cooling zone.
A method for producing a stainless steel strip by continuous casting hot rolling, which comprises cooling to ˜550 ° C.

A second aspect of the invention is a hot rolling mill, a heat treatment furnace, a cooling device, etc. in which thin cast pieces are continuously cast by a twin-drum type continuous casting machine and the thin cast pieces are continuously arranged downstream of the continuous casting machine. In the method for producing a stainless steel strip by continuous casting hot rolling for continuous treatment, when increasing the casting plate thickness during running, the level of the molten metal surface of the molten metal pool formed by the drum and the side dam is set to the value of the usual casting arc angle. In addition, while shortening the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone, open the opening between the drums to slow down the casting speed to increase the casting plate thickness and perform continuous casting. The heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are increased to a predetermined length according to the decrease in speed, and the reduction ratio of the hot rolling mill immediately before the sheet thickness change part of the thin cast piece reaches the hot rolling mill. Is controlled by 30% or more to perform hot rolling, and A method for producing a stainless steel strip by continuous casting hot rolling, characterized in that the hot-rolled strip is heat-treated in a heat treatment furnace at a strip temperature of 900 to 1200 ° C. for 5 seconds or more and then cooled to 500 to 550 ° C. in a cooling zone. .

A third invention specifies the characteristics of a heat treatment furnace used when heat treating the strip after hot rolling in the first or second invention, and it is a speed range of a continuous casting hot rolling line. It is characterized by using a heat treatment furnace having a responsiveness of (15 to 180 m / min) and a temperature rising rate of 5 to 20 ° C./sec.

The fourth invention is positioned as an example of a heat treatment furnace having a high suitability for heat-treating a strip after hot rolling when carrying out the first invention or the second invention. A part or all of the transfer rolls are arranged so as to be able to advance and retreat with respect to the strips transferred by the in-furnace transfer rolls, and a direct flame burner is used to directly inject burner flames on both sides of the strips with the strips sandwiched therebetween. It is characterized in that it is arranged as follows. Further, a fifth invention is characterized in that, in the fourth invention, a circulating gas cooling device for circulating a cooling gas is attached to a peripheral surface of a part or all of the in-furnace conveying rolls.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the first aspect of the present invention,
Continuous casting hot rolling that continuously casts thin slabs with twin-drum type continuous casting machine, and continuously processes the thin slabs with a hot rolling mill, heat treatment furnace, cooling device, etc. arranged downstream of the continuous casting machine. In the method of manufacturing a stainless steel strip, the twin drum type continuous casting machine is used to change the casting thickness thinly during running. When the casting plate thickness is thinned, the casting arc angle (as shown in FIG. 3) is temporarily changed. Liquid surface ss of molten steel s around drum 1a
After lowering the casting speed by lowering the angle a between the line a connecting the contact point p with the axis of the drum 1a and the horizontal line b connecting the axis of the pair of drums 1a, 1b to 20 to 30 degrees. By reducing the thickness of the cast plate, the hot rolling mill can reduce the specified rolling reduction (3
0 to 50%) and rolled, heat-treated in a heat treatment furnace at a predetermined temperature (900 to 1200 ° C. for 5 seconds or more), and cooled in a cooling zone to a predetermined cooling rate (20 to 90 ° C. /
In order to cool to 500-550 ° C. in 500 seconds, the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are shortened to a predetermined length to prevent overheat treatment and overcooling, and When the casting thickness becomes thinner and the casting speed becomes faster due to the closing of the opening between them, the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone should be set to a predetermined length to prevent heat treatment shortage and cooling shortage. Thus, even if the casting thickness is changed during running, the fine recrystallized grain size can be reduced to a predetermined grain size.

In the above, when the casting arc angle is 20 degrees or less, continuous casting becomes impossible, and when it is 30 degrees or more, the heat treatment and cooling conditions cannot be optimally controlled and the grain size is sufficiently refined. Not only that, the yield in the transitional period of changing the cast plate thickness decreases. In addition, the change width when changing the cast plate thickness without controlling the casting arc angle is 0.1 to 1.0 mm, and the extension of the heat treatment length and the cooling length in this case is equivalent to 3 to 45%. Is expected.

FIG. 1 shows the cast plate thickness, the cast arc angle, the strip speed, when the cast plate thickness is changed thinly during running in the continuous casting hot rolling using the twin-drum type continuous casting machine as described above. It shows the relationship between the processing furnace length of the heat treatment furnace and the cooling length of the cooling zone. If you want to change the casting thickness thin between runs,
Temporarily reducing the amount of molten steel supplied to lower the level of the molten metal, the casting arc angle can be solidified from the normal level (40 degrees) to a level at which it can be solidified (the angle between the center of the drum and the horizontal axis, which is the range in which the drum and the molten steel surface wet). Is called the casting arc angle, and this angle is 30 degrees or less)
To reduce the casting speed and then close the opening (gap amount) of the casting drum to change the casting thickness, but if the casting thickness is changed, the speed of the strip running in the heat treatment furnace will change. To do. That is, the thicker the cast plate, the slower the strip speed in the heat treatment furnace, and the thinner the cast plate, the faster the strip speed.

In the present invention, the heat treatment furnace length in the heat treatment furnace and the cooling length in the cooling zone are changed according to the change in strip speed. That is, the casting speed is reduced by reducing the casting arc angle from the normal level of 40 degrees to the level of 20 to 30 degrees, and the strip speed is reduced by closing the gap between the drums and thinning the casting plate thickness. Increase. In this process, if the length of the treatment furnace in the heat treatment furnace is left unchanged before the thickness of the cast plate is changed, the heat treatment conditions are changed, so that the predetermined heat treatment cannot be performed and the quality is deteriorated. Further, when the cooling length in the cooling zone is left as it is before changing the cast plate thickness, the cooling conditions change, so that predetermined cooling cannot be performed and the quality deteriorates.

Therefore, in the process of reducing the thickness of the cast plate, first, the arc angle of casting is lowered to reduce the length of the processing furnace of the heat treatment furnace and the cooling length of the cooling zone. After that, the casting plate thickness is reduced with the casting arc angle kept constant, and at the same time, the casting speed is increased, and at the same time, the heat treatment length and the cooling length of the cooling zone are restored to the length before the casting plate thickness was changed, and the strip tip Before the heat treatment furnace enters the cooling zone, the treatment furnace length and cooling of the heat treatment furnace are changed to predetermined lengths.
In this way, it is possible to ensure the refinement of the recrystallized grain size even in the process of thinning the cast plate thickness during running.

According to the second aspect of the present invention, when increasing the thickness of the casting plate in a twin-drum type continuous casting machine while running, the level of the molten metal surface of the molten metal pool formed by the drum and the side weir is set to the normal casting arc angle. In addition, while shortening the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone, open the opening between the drums to slow down the casting speed to increase the casting plate thickness and perform continuous casting. The processing furnace length of the heat treatment furnace and the cooling length of the cooling zone are increased to a predetermined length according to the decrease in speed, and the reduction of the hot rolling mill is performed immediately before the thickness change part of the thin cast piece reaches the hot rolling mill. The rate is controlled at 30 to 50% or more to perform hot rolling, and the strip hot rolled by the hot rolling mill is 900 to 1 in the heat treatment furnace.
After heat-treating at a strip temperature of 200 ° C. for 5 seconds or more, it is cooled to 500 to 550 ° C. in a cooling zone. In the above, the change width when changing the cast plate thickness is 0.1-1.0 mm
The reduction of heat treatment length and cooling length in this case is 3 to 45%.
Is preferable.

When the rolling reduction is 30% or less, the gloss of the surface of the product and the roping are not satisfied, so the rolling reduction is 30%.
Above. When the cooling rate is 20 ° C./sec or less, Cr carbide is generated at the grain boundary of the stainless strip and the corrosion resistance is deteriorated. Therefore, the cooling rate is 20 ° C./sec or more.
Also, when the winding temperature is 500 ° C or lower, fine cracks occur on the surface of the chromium-based stainless strip, and
When the temperature is higher than 50 ° C, Cr carbide is generated at the grain boundary of the stainless strip and the corrosion resistance is deteriorated.
It is desirable to wind in a temperature range of 0 to 550 ° C.

FIG. 2 shows the cast plate thickness, the cast arc angle, the strip speed, when the cast plate thickness is changed between running runs in the continuous casting hot rolling using the twin drum type continuous casting machine as described above. It shows the relationship between the processing furnace length of the heat treatment furnace and the cooling length of the cooling zone.

When the cast plate thickness is increased, the casting speed is lowered and the strip speed in the heat treatment furnace is slowed in conjunction with the casting speed.
Although the strip in the heat treatment furnace is overheated, it takes longer than a predetermined heat treatment time for Cr-Ni-based stainless steel, but it is about several tens of seconds, and if it is within 5 minutes, the grain size of recrystallization is Testing has confirmed that there is no concern that growth will affect it.

Therefore, in the process of increasing the thickness of the cast plate, the reduction ratio is kept constant at 30% or more, and the reduction ratio is tracked by 30 according to the change in the plate thickness of the thin cast piece measured by the entrance side plate thickness gauge 14. The roll gap of the rolling mill is controlled so as to be%. On the other hand, in the cooling zone, the strip speed becomes slower, resulting in supercooling at 500 ° C. or less, and as described above, fine cracks occur on the surface of the chromium-based stainless strip, so it is necessary to shorten the cooling length to a predetermined length. is there.
Before the tip of the thickened strip enters the heat treatment furnace and the cooling zone, the treatment furnace length of the heat treatment furnace and the cooling length of the cooling zone are changed to predetermined lengths. In this way, it is possible to ensure the refinement of the recrystallized grain size of the product even in the process of increasing the cast plate thickness during the running.

The present invention mainly uses a twin-drum type continuous casting machine at a casting speed of 15 to 180 m / min and a plate thickness of 1 to 10 mm.
When the present invention is applied in this speed range, the heat treatment furnace has a heating ability to increase the heating rate of the strip to 5 ° C./sec or more. It is necessary to have

Therefore, in the third invention, it is specified to use the heat treatment furnace satisfying such conditions.
In general, the heat treatment furnace has a limit of 1250 ° C. from the viewpoint of ensuring heat resistance strength, and the temperature of the strip introduced into the heat treatment furnace is 900 ° C.
Because of the above, in the heat transfer furnace of the radiative heat transfer type, the heat transfer rate cannot be increased, and the temperature rise and retention of the strip cannot satisfy the responsiveness according to the change of the strip speed due to the change of the cast plate thickness. , Heating rate for strip 5-20
It is difficult to secure the heating ability to be ℃ / second.

In addition, there are two types of combustion type heat treatment furnaces, an induction heating type and a direct flame burner type, and it is possible to secure a heating capacity for raising the temperature rising rate of the strip to 5 to 20 ° C./sec or more. From the viewpoint of equipment cost, the direct fire burner type is most suitable. When using this direct heat burner method heat treatment furnace, the high temperature part of the burner flame is stabilized in the injection distribution to the strip being transported in the furnace, and it is heated uniformly, and it is built into the strip by the transport roll in the furnace. It is necessary to pass the strip in a catenary state while suppressing the occurrence of up defects.

From such a point of view, in the third invention, as the heat treatment furnace used in the present invention, an open flame burner is arranged so as to sandwich the strip to be conveyed, and the burner flame can be directly injected to both sides of the strip. The heating capacity for raising the temperature rising rate to 5 to 20 ° C./second can be easily ensured. Regarding the arrangement of the direct flame burners, they are arranged in a zigzag manner in order to make the high-temperature injection distribution of the burner flame to the strip uniform, and in order to absorb the positional fluctuation of the strip, 5 to 5 in the strip conveying direction.
It is effective to tilt it by 10 degrees.

Further, a part or all of the in-furnace transfer rolls are arranged so as to be able to move forward and backward (elevate) with respect to the strip conveyed by the in-furnace transfer rolls. A dummy sheet that can be retracted to a range where it does not interfere with the strip after being transported is retracted after being transported, so that the chances of buildup occurring are reduced. It is sufficient that the retreat distance is about 250 mm when the distance between the in-furnace conveyance rolls is 4 m and about 600 mm when the distance is 10 m. .

Generally, slip occurs between the strip and the roll on the surface of the roll in the furnace for transporting the strip,
When the surface of the roll is metal, it causes metal structure adhesion at high temperature and builds up (attaches) to the roll side, which causes flaws on the surface of the strip when passing through the surface of the next strip. Cause. Therefore, it is general that a ceramic-based thermal spray coating is formed on the surface of the in-furnace transport roll to prevent the occurrence of adhesion and prevent build-up.

However, in the furnace of the heat treatment furnace used in the present invention, since the temperature of the high temperature strip is raised in a short time, 1200
Since it is exposed to extremely severe temperatures of ℃ or more, conventional ceramic-based thermal spray coatings are easily peeled off and cannot withstand long-term use. Therefore, in the fifth invention, in the third invention, a gas circulation cooling device for injecting a cooling gas to cool the in-furnace transport rolls is attached to a part or all of the in-furnace transport rolls. There is.

The gas used here is the quality of the strip,
Use one that does not impair the heat treatment furnace operation. For example, it is effective to cool the combustion exhaust gas of a heat treatment furnace having a low oxygen concentration to 300 ° C. or less through a cooling device, circulate the exhaust gas, and inject it to the surface of the in-furnace transport roll.

Among the in-furnace transfer rolls, at least the roll used for threading the dummy bar is
It is necessary to prevent meandering of the dummy bar so that the strip can pass through stably. Therefore, it is effective to form a taper portion inclined by 5 to 30 degrees toward the central portion on both sides of the strip conveying region of the in-furnace conveying roll. By doing so, the strip can be transported in the furnace without meandering.

Further, in the case of raising and lowering the in-furnace conveying rolls as described above, it is effective to dispose a movable lid on the furnace wall portion to prevent gas ejection from the inside of the furnace. Further, it is effective to dispose the drive device for the in-furnace transport roll outside the furnace so as not to be exposed to the high temperature atmosphere in the furnace.

[0030]

【Example】

(Embodiment 1) An embodiment of the present invention will be described with reference to FIGS. What is shown here is the case where the present invention is applied in a continuous casting hot rolling process of stainless strip.

FIG. 4 shows an example of arrangement of hot-rolling equipment for continuous casting of stainless strip to which the present invention is applied. In FIG. 4, 1 is a twin-drum type continuous casting machine, 2 is a continuously cast thin slab, and 3 is an atmosphere cover for suppressing oxidation and temperature drop of the thin slab. A hot rolling mill 6 having a pair of front pinch rolls 5, a work roll 6w, and a backup roll 6b is arranged. 7 is a heat treatment furnace, 8 is a heat treatment furnace outlet side pinch roll, 9 is a cooling zone, 10 is a pinch roll before the cutting machine, 11 is a cutting machine, 12 is a pinch roll before the winder, and 13 is a carousel type winder. is there.

The twin-drum type continuous casting machine 1 has a drum rotation speed (casting speed), a molten metal level, a side weir pressing force,
A well-known control device (not shown) for controlling the opening degree between the drums and the like is connected. Further, a plate thickness gauge 14 is arranged between the pair of rolling mill front pinch rolls 5, and the plate thickness information from this plate thickness gauge is sent to the rolling reduction control device 15, and heat is transmitted via this rolling reduction control device. The rolling control of the inter-roll mill 6 is performed.

Further, the plate thickness information from the plate thickness gauge 14 is sent to the cooling zone controller 17 together with the temperature information from the strip thermometer 16 arranged on the inlet side of the cooling zone 8, and this controller controls the cooling zone. The injection device 18 is controlled to control the cooling conditions in the cooling zone 8. The heat treatment furnace 7 used here can control the heat treatment conditions by following the line speed fluctuation caused by a change in casting thickness.
It is required to have a responsiveness of -20 ° C / sec.

Further, it is necessary to prevent the buildup due to the in-furnace transport rolls and to ensure the quality of the strip. Therefore, a heat treatment furnace having a structure as shown in FIGS. 5 to 7 is used here. This heat treatment furnace 7
As shown in FIGS. 5 and 6, a large number of direct flame heating direct flame burners 19 for directly injecting flames from both sides of the strip 2s being conveyed in the furnace to the furnace wall to directly heat the strip 2s are provided,
In this burner, fuel gas and supporting gas are added to the header pipe 20.
The fuel gas and auxiliary gas supply systems are divided into multiple pieces in the furnace length direction, and the heat treatment length can be changed by opening and closing each supply system to change the heat treatment conditions. . By changing the heat treatment conditions, it is also possible to adjust the amount of fuel gas and auxiliary gas supply to each supply system.

Further, here, five transfer rolls in the furnace are arranged, and as shown in FIGS. 6 (a) and 6 (b), a lift device (hydraulic cylinder) 23 is used to lift and lower, and the dummy sheet 22 is transferred. At times, this dummy sheet is supported and conveyed by all the in-furnace conveying rolls 21s and 21x, and in the strip conveying process, from the viewpoint of suppressing buildup, the in-furnace conveying roll 21x is lowered and retracted so as not to contact the strip 2s. The transport rolls are supported as few as possible, for example, 21 s, and transported by being supported.

This in-furnace transport roll has a taper portion 2 which is inclined 5 to 30 degrees toward the center on both sides of the strip transport region.
1t is formed so that the strip can be prevented from meandering during conveyance, and the driving device 24 is arranged outside the furnace. Further, on the furnace wall portion where the shaft 21o of the transfer roll moves up and down, the movable lid 2 which moves up and down together with the shaft 21o of the transfer roll by the lifting device 23 and slides on the surface of the furnace wall
5 are provided. In the figure, 26 is a seal roll for a heat treatment furnace.

Further, the in-furnace transport rolls 21s and 21x are
Since it is also exposed to a high-temperature burner flame, as shown in FIG. 7, it has a curved surface 29c along the peripheral surface of this in-furnace transport roll 21x, which is close to the peripheral surface of this roll. A cooling pad 29 having a cooling gas injection hole 27 and a discharge hole 28 is provided.

Since the exhaust gas 30 mixed with scale is discharged from the discharge hole 28, there is a risk of damaging the pipeline. Therefore, the scale in the exhaust gas 30 is removed from the scale separation chamber 32.
The exhaust gas 30c separated from the scale is cooled and circulated through the cooling device 31 through which the cooling water 33 flows, and is injected from the injection holes 27 onto the surface of the furnace conveyance roll 21s.

The cooling gas jetted from the cooling pad 29 to the peripheral surface of the transport roll 21s has a temperature of low oxygen concentration from the heat treatment furnace 7 in order to prevent the strip from oxidizing and to have a slight effect on the heat treatment. Is 8
Combustion exhaust gas of 00 to 900 ° C. is used, and this is a cooling device 3
It is cooled to 300 ° C. or lower via 1 and circulated, and jetted from the jet hole 27.

The present invention can be carried out using the continuous casting hot rolling equipment as described above. In the present invention,
When changing the sheet thickness during continuous casting of stainless steel,
In the case of stainless steel, the molten metal surface cast by the twin-drum type continuous casting machine 1 is lowered to a casting arc angle of 20 to 30 degrees to slow the casting speed, and then the opening between the casting drums is closed. By changing the cast plate thickness during running, the rolling reduction of the downstream hot rolling mill is not changed, the effective superheating range is not extended in the heat treatment furnace, and it is 500 ~ in the cooling zone.
Even if the product is cooled to a temperature of 550 ° C. and manufactured, the influence of refining the recrystallized grain size disappears.

When the thin plate portion reaches the heat treatment furnace, the predetermined heat input by the heat treatment furnace is reduced, so that the effective heat treatment length of the heat treatment furnace can be shortened. Therefore, the heat input can be efficiently reduced.

The cooling zone is tracked by a strip thickness gauge upstream of the hot rolling mill, and the cooling zone required depending on the strip thickness entering the cooling zone, the temperature of the strip on the cooling zone entering side and the speed thereof. The length is calculated and cooled, and the winding temperature is controlled to 500 to 550 ° C.

When changing the plate thickness during continuous casting of stainless steel, by opening the opening between the casting drums to slow down the casting speed and changing the cast plate thickness between runs, In the hot rolling mill 6 on the downstream side, the same rolling reduction (30
˜50%), the furnace temperature heating range (heat treatment length) is extended to a predetermined effective heating length by the heat treatment control device 34 before the thick plate portion reaches the heat treatment furnace 7. The influence of the plate thickness on the refinement of the crystal grain size disappears.

The cooling zone 9 is tracked by the sheet thickness gauge 14 upstream of the hot rolling mill 6 as in the case where the strip thickness is made thin, and the strip 2s enters the cooling zone 9 by the cooling zone controller 17. The required cooling zone length is calculated and cooled according to the thickness and the strip temperature from the plate thermometer 16 on the cooling zone entrance side and its speed, and the winding temperature is controlled to 500 to 550 ° C.

The hot rolling mill 6 comprises a high speed bender and a high speed AG.
C (not shown), a plate thickness gauge 14 is provided on the inlet side, measures the shape of the thin slab 2, and uses the reduction control device 15 to perform high-speed bending (shape control) of the hot rolling mill 6. ), High-speed AG
Feed forward control of C (plate thickness control device) measures the change in plate thickness on the inlet side of the hot rolling mill 6 at the portion where the plate thickness is changed by the drum, and tracks and tracks the shape without breaking the shape in the hot rolling mill. By performing the reduction at a high speed, the yield of the strip 2s in the transitional period of changing plate thickness can be improved.

The heat treatment furnace 7 is an open flame burner type heat treatment furnace, and the line speed fluctuation (± 30
%) So that the amount of heat input to the strip can be controlled by the heat treatment controller 34 according to
The temperature of the strip can be directly changed at a rate of 5 to 20 ° C / sec.

Variations in casting speed and variations in sheet thickness on the hot rolling mill entrance side are measured with a sheet thickness gauge, and the sheet thickness variation points up to the inside of the heat treatment are tracked to change the casting sheet thickness between runs. The heat treatment can be controlled according to the change in the strip 2s speed due to the above, and the recrystallized grain size can be reduced.

On the other hand, the dummy sheet 22 is used for transporting the slab at the start of casting, but when the dummy sheet passes through the heat treatment furnace 7, the temperature rise is suppressed and the dummy sheet and the thin slab 2 are connected. It is possible to achieve a predetermined heat pattern by ensuring the strength of the portion, performing full combustion after the strip enters the heat treatment furnace 7, and performing rapid heating.

Generally, when the strip 2s becomes thicker, the heat treatment time becomes longer and the strip thickness becomes thinner. The heat treatment controller 34 controls the effective heat treatment length of the heat treatment furnace 7 accordingly. In this case, a burner with good responsiveness such as the direct fire burner 19 is more efficient and can achieve energy saving.

Further, the in-furnace roll 21x for conveying the dummy sheet in the heat treatment furnace 7 has a lifting function, so that a part of it can be retracted and the number of strips 2s conveyed in the furnace can be reduced. , It is possible to reduce the chance of buildup. Furthermore, since the exhaust gas from the heat treatment furnace having a low oxygen concentration is circulated through the furnace transfer roll 21s that transfers the strip 2s through the cooling device 31 and is injected from the cooling pad 29 to cool the exhaust gas, the atmosphere inside the furnace is reduced. In-furnace transport roll 21 without damage
It is possible to prevent buildup from occurring in x.
Further, the roll surface temperature can be suppressed to 900 ° C. or lower, the peeling of the ceramic sprayed coating on the surface can be suppressed, and the durability thereof can be improved.

The open flame burner 19 in the heat treatment furnace 7 is
Since the strips 2s are arranged so as to be inclined, the nozzles can be prevented from being damaged by the reflected flame from the strip 2s, and the convective heat transfer effect due to the flow of the burner flame can be improved by about 5%. Since the strip 2s is in the catenary state, the direct flame burner arrangement is set in consideration of this and even if the burner flame moves away from the burner due to the catenary, the heat transfer coefficient can be slightly reduced. Further, by arranging the open flame burners 19 in a zigzag pattern in the strip conveying direction, it is possible to disperse heat spots due to local heat transfer of the open flame burner and suppress temperature unevenness.

The present invention is not limited to the above-mentioned embodiments, and is not limited to the continuous casting machine, the hot rolling mill, the heat treatment furnace, the cooling device, the winding device, the accessory device, the various control structures, and each of these elements. The specifications, the number of arrangements, the operating conditions, etc. may be changed according to the casting target, the casting conditions, the plate thickness changing conditions, the hot rolling conditions, etc. within the range satisfying claims 1 to 5 of the present invention. is there.

The stainless strip obtained in the present invention is manufactured into a product through a pickling cold rolling, an annealing pickling or a bright annealing step. The conditions in these treatment steps are unique to the present invention. There are no conditions, and there is no particular problem under general industrial operating conditions.

(Embodiment 2) Using a twin-drum type continuous casting hot rolling equipment having the construction as shown in Embodiment 1, a Cr-Ni system stainless steel having a plate thickness of 2 to 3 mm (component composition: Cr
When producing a strip of 8% or more, Ni 13% or more, balance Fe), the present invention is applied, and the operation of changing the cast plate thickness is performed during continuous casting (running). The stainless steel strip was commercialized by cold-rolling and annealing and annealing, and its quality was evaluated. The results are shown in Table 1 together with the operating conditions. The pickling cold rolling and annealing pickling conditions are common conditions, and thus the description thereof is omitted.

[0055]

[Table 1]

As shown in Table 1, in the examples of the present invention in which the present invention is adopted and the casting arc angle is reduced to 30 degrees, which is 10 degrees smaller than the normal level, during running, the casting plate thickness is changed thinly. Occurrence was not observed, and the gloss was uniform and sufficiently satisfactory. On the other hand, in the conventional example in which the casting plate thickness was changed thinly during running while keeping the casting arc angle at 40 degrees, the roping was obvious and the glossiness was non-uniform, which was satisfactory. I couldn't get what I could.

In addition, in the examples of the present invention in which the present invention is adopted and the casting arc angle is lowered to 30 degrees, which is 10 degrees smaller than the normal level, during running, the occurrence of roping is recognized in all the examples of the present invention. Moreover, the gloss was uniform and was sufficiently satisfactory. On the other hand, in the conventional example in which the casting plate thickness was changed to be thick between running while keeping the casting arc angle at 40 degrees, which is a normal level, there was obvious roping,
Moreover, the glossiness was non-uniform, and a satisfactory product could not be obtained.

[0058]

According to the present invention, when the plate thickness is changed thinly during running, it is not necessary to extend the furnace length in the transition period of the change of the plate thickness, and the furnace length can be shortened. In addition, the portion where the plate thickness is changed during running does not drop in yield and can be commercialized in the same manner as the stationary portion. In addition, energy saving can be achieved by adopting an open flame burner in the heat treatment furnace. Furthermore, the transfer rolls of the heat treatment furnace can be moved up and down, and when the strips are transferred after the dummy sheet is transferred, some of the transfer rolls can be retracted so that they do not come into contact with the strips. Can be reduced. Further, by circulating and cooling the in-furnace transfer roll of the heat treatment furnace with gas, it is possible to prevent the sprayed coating of ceramics or the like formed on the roll surface from peeling off and prevent build-up defects.

[Brief description of drawings]

FIG. 1 is a casting arc angle according to a change (decrease) in a cast plate thickness in a strip continuous casting hot rolling heat treatment facility of the present invention,
FIG. 4 is a conceptual explanatory diagram of a relationship example between a strip speed, an effective heat treatment length of a heat treatment furnace, and an effective cooling length of a cooling zone.

FIG. 2 is a view showing a casting arc angle according to a change (increase) in a cast plate thickness in a strip continuous casting hot rolling heat treatment facility of the present invention,
FIG. 4 is a conceptual explanatory diagram of a relationship example between a strip speed, an effective heat treatment length of a heat treatment furnace, and an effective cooling length of a cooling zone.

FIG. 3 is a side view conceptual diagram showing a casting arc angle of continuous casting in the strip continuous casting hot rolling heat treatment equipment of the present invention, FIG. 3 (a) shows the lower limit of casting arc angle, and FIG. Indicates the upper limit of the arc angle.

FIG. 4 is a side conceptual illustration showing an arrangement example of strip continuous casting hot rolling heat treatment equipment of the present invention.

FIG. 5 is a side view conceptual diagram showing a structural example of a heat treatment furnace in a strip continuous casting hot rolling heat treatment facility of the present invention.

FIG. 6 is a side conceptual explanatory view showing an example of an elevating structure of in-furnace transport rolls of a heat treatment furnace in a strip continuous casting hot rolling heat treatment facility of the present invention, FIG. And (b) shows the (down) state during strip transport.

FIG. 7 is a side view conceptual diagram showing an example of a circulating gas cooling structure of an in-furnace carrier roll of a heat treatment furnace in a strip continuous casting hot rolling heat treatment facility of the present invention.

FIG. 8 is a side view conceptual diagram showing an arrangement example of a strip continuous casting hot rolling heat treatment facility in a conventional example.

[Explanation of symbols]

 1 Twin-drum type thin cast continuous casting machine 2 Thin cast 3 Atmosphere control cover 4 Cast drum lower pinch roll 5 Hot rolling mill front pinch roll 6 Hot rolling mill 6w Work roll 6b Backup roll 7 Heat treatment furnace 8 Heat treatment furnace exit Side pinch roll 9 Cooling device 10 Cutting machine front pinch roll 11 Cutting machine 12 Winder front pinch roll 13 Carousel type winding machine 14 Plate thickness gauge 15 Rolling down control device 16 Plate temperature gauge 17 Cooling zone control device 18 Cooling zone injection Device 19 Direct-fire burner 20 Header pipe 21s, 21x Furnace transport roll 21t Tapered part 21o Shaft 22 Dummy sheet 23 Lifting device 24 Drive device 25 Movable lid 26 Seal roll 27 Gas injection hole 28 Gas discharge hole 29 Cooling pad 30, 30c Exhaust gas 31 cooling device 32 separation chamber 33 cooling water 34 heat treatment furnace control device

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B22D 11/12 B22D 11/12 A 11/124 11/124 K 11/20 11/20 A C21D 8/02 9270 -4K C21D 8/02 Z 9/46 9/46 Q 9/56 101 9/56 101A 101G

Claims (5)

[Claims] 1. A continuous casting method in which a thin cast piece is continuously cast by a twin-drum type continuous casting machine, and the thin cast piece is continuously processed by a hot rolling mill, a heat treatment furnace, a cooling device, etc. which are continuously arranged downstream of the continuous casting machine. In the method for producing a stainless steel strip by hot rolling by casting, when reducing the thickness of the cast plate during running, the level of the molten metal surface of the molten metal pool formed by the drum and the side dam is 20 to 30 degrees from the usual casting arc angle. The casting speed is slowed down and the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are shortened, and then the opening between the drums is closed to reduce the casting plate thickness while recovering the casting rate and the cooling length of the cooling zone. Continuous casting, the casting arc angle is restored to a normal level after a certain period of time, and the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are increased to a predetermined length as the casting speed increases. The thickness change part of is hot Immediately before reaching the rolling mill, the rolling reduction of the hot rolling mill is controlled at 30% or more to perform hot rolling, and the strip hot-rolled by the hot rolling mill is heated to 900 in the heat treatment furnace.
A method for manufacturing a stainless steel strip by continuous casting hot rolling, comprising heat-treating at a strip temperature of ~ 1200 ° C for 5 seconds or more and then cooling to 500-550 ° C in a cooling zone. 2. A continuous casting process in which a thin cast piece is continuously cast by a twin-drum type continuous casting machine, and the thin cast piece is continuously processed by a hot rolling mill, a heat treatment furnace, a cooling device, etc. which are continuously arranged downstream of the continuous casting machine. In the method for producing a stainless steel strip by hot rolling by casting, when increasing the thickness of the cast plate during running, heat treatment is performed while maintaining the level of the molten metal surface of the molten metal pool formed by the drum and the side dam at the usual casting arc angle. While shortening the heat treatment length of the furnace and the cooling length of the cooling zone, open the opening between the drums to slow down the casting speed to thicken the casting plate and perform continuous casting, and after a certain period of time, reduce the casting speed. Accordingly, the heat treatment length of the heat treatment furnace and the cooling length of the cooling zone are increased to a predetermined length, and the reduction ratio of the hot rolling mill is 30% or more immediately before the sheet thickness change part of the thin cast piece reaches the hot rolling mill. It was hot-rolled by the hot-rolling mill. Strips in heat treatment furnace 900-1
A method for producing a stainless steel strip by continuous casting hot rolling, which comprises performing heat treatment at a strip temperature of 200 ° C. for 5 seconds or more and then cooling to 500 to 550 ° C. in a cooling zone. 3. A speed range (1) of a continuous casting hot rolling line.
5. The stainless steel strip produced by continuous casting hot rolling according to claim 1 or 2, wherein the heat treatment is performed in a heat treatment furnace having a response rate of 5 to 180 m / min) and a temperature rising rate of 5 to 20 ° C./sec. Manufacturing method. 4. A part or all of the in-furnace transfer rolls is arranged so as to be able to move forward and backward with respect to the strip conveyed by the in-furnace transfer rolls, and an open flame burner is provided with a burner flame with the strips sandwiched therebetween. A heat treatment furnace for continuous casting hot rolling of stainless strip, which is arranged so as to be directly jetted to both sides of the strip. 5. The continuous casting hot rolling of a stainless steel strip according to claim 4, wherein a circulating gas cooling device for circulating a cooling gas is attached to a peripheral surface of a part or all of the in-furnace conveying rolls. Heat treatment furnace.