JPH091209A - Equipment for continuously casting and hot-rolling stainless steel strip and manufacture of stainless steel strip excellent in surface quality - Google Patents

Abstract

PURPOSE: To stably manufacture a hot rolled strip whose surface property and internal crystaline structure are good by arranging plural hot rolling mills and a cooling device on the downstream side of a continuous casting machine for thin slabs and hot-rolling the slab taking the total draft as a specified value. CONSTITUTION: The thin cast slab 2 of less than 3mm in thickness is cast with the continuous casting machine 1. The cast slab 2 is fed to the hot rolling mill 3a of the prestage with pinch rolls 7, 8. The cast slab 2 is rolled at the total draft of >=60% in the temp. region of 900-1200 deg.C with the hot rolling mill 3a of the prestage and hot rolling mill 3b of the poststage. The strip 2s just after hot rolling is slowly cooled at the cooling rate of <=5 deg.C/sec for 5-10sec with a cooling device 5. Next, after cooling the strip down to <=600 deg.C at the cooling rate of >=10 deg.C/sec, the strip is coiled with a coiler 9. By executing hot rolling at the draft of >=60%, the hot rolled strip 2s having fine recrystallized grain size is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mainly obtained by continuously casting Cr--Ni type stainless steel at a high speed (10 to 180 m / min) by, for example, a twin roll type continuous casting machine.
A continuous casting hot rolling equipment for stainless steel strip used for producing a stainless steel strip having a plate thickness of 1 to 3 mm by continuously hot rolling a 10 mm thick stainless thin slab at high temperature and high speed, The present invention relates to a method for producing a stainless steel strip having excellent surface quality using a continuous casting hot rolling facility.

[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 viewpoint of improving productivity by reducing steps, reducing 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 processed by the hot rolling mill 3, the heat treatment furnace 4, the cooling device 5, etc. 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 6 is adopted, and it is also proposed to apply this process to the production of stainless strip.

For example, in Japanese Unexamined Patent Publication No. 61-222611, a thin slab cast by twin-drum type continuous casting is prepared by spraying metal shot particles on a high temperature scale generated by oxidation in the atmosphere at high temperature. It is disclosed that the surface of the shot dimples thus removed is rolled and then smoothed by a hot rolling mill to produce a strip having a predetermined plate thickness.

Further, in Japanese Unexamined Patent Publication No. 2-179343, a hot rolling mill is arranged downstream of a twin-drum type continuous casting machine to carry out light rolling under a light reduction to form a uniform cooling of the surface of the casting drum. It is disclosed that the transfer mark of the formed dimple is erased.

Further, in Japanese Patent Laid-Open No. 2-247049, 1250 to 1100 ° C. is pressed at a cooling rate of 200 ° C./sec or more by pressing a cast piece against a casting drum and contacting this drum.
It is also disclosed that the slab is rapidly cooled to the temperature range of 1 and the hot rolling mill disposed downstream thereof is hot-rolled at a reduction rate of 40% or less to produce a strip having no internal defect of the slab. .

Further, in JP-A-2-133528, hot rolling at a rolling temperature of 900 ° C. or higher and a reduction rate of less than 60% is performed, followed by rapid cooling at a cooling rate of 50 ° C./sec or higher and at 550 ° C. or lower. It is disclosed that a cold rolled steel sheet having good surface quality is produced by winding.

Further, the applicant of the present invention has previously reported that in the invention of Japanese Patent Application No. 7-89825, the gloss after cold rolling,
In order to improve the waviness, a slab cast by a twin-drum type continuous casting machine is installed at a temperature of 1000 by a hot rolling mill arranged downstream.
After rolling at a reduction rate of 10 to 50% in a temperature range of ˜1150 ° C. and giving strain energy, 1050 to 1150 ° C.
It is disclosed that the recrystallized grain size of the strip is made fine by performing a heat treatment for 5 seconds.

[0008] In the above-mentioned prior art, shot dimples generated after removing transfer marks and high temperature oxide scale on the surface of the casting drum, which are generated in the thin slab during casting by a twin-drum type continuous casting machine, are mainly used. It is characterized by smoothing by a hot rolling mill of a stand.

Stainless steel strips are required to have no roping (waviness) and have excellent glossiness, and it is known that it is effective to reduce the crystal grain size in order to meet this demand. Has been. In order to reduce the crystal grain size, hot rolling by a hot rolling machine directly connected to the continuous casting machine is most effective.

However, as described above, heat treatment in a heat treatment furnace after hot rolling leads to a reduction in manufacturing cost, manufacturing range expansion,
There is a problem with productivity. Therefore, from such a viewpoint, hot rolling can be performed in a short time in a hot rolling mill directly connected to a continuous casting machine, and it is possible to promote the refinement of recrystallized grains without using a conventional large-scale heat treatment furnace. desirable.

According to recent experimental data, it has been confirmed that the crystal grain inside the thin slab cannot be refined at a reduction rate of 40% by a single-stand hot rolling mill, and the recent twin-drum type continuous According to the report of the hot rolling mill tested in the casting hot rolling line, the rolling reduction was 3 because of the shape control ability.
The rolling reduction of 0 to 45% is said to be the upper limit. on the other hand,
When rolling with multiple hot rolling mills, contact heat transfer of work rolls and heat loss due to heat loss between stands significantly affect the refinement of crystal grains, so hot rolling with multiple hot rolling mills is carried out. The reality is that it has not been done.

Conventionally, when it is necessary to refine the crystal grains, a large heat treatment furnace and a cooling device are often installed downstream of the single-stand hot rolling mill following the continuous casting machine. With such an equipment structure, for example, when manufacturing a stainless steel trip with a hot thickness of 1 mm or less,
It is necessary to perform heat treatment at about 1150 ° C. in a long heat treatment furnace. For example, in the case of a thin cast piece having a thickness of less than 3 mm, a long heat treatment furnace is required because the casting speed is high. Installing such a large heat treatment furnace increases the cost of threading work of the slab into the furnace, the variable cost of the fuel consumption per unit of the furnace, the facility cost including the building, and the like. This is not preferable.

[0013]

DISCLOSURE OF THE INVENTION According to the present invention, continuously cast thin stainless steel slabs are hot-rolled by a plurality of hot rolling mills and cooled, and then the strips are pickled and cold rolled, annealed pickled or bright. Continuous casting hot rolling equipment for stainless steel strip that can produce high quality hot rolled strip at low cost when annealed to produce stainless steel strip with excellent surface quality (evaluated by the degree of roping and glossiness) Another object of the present invention is to provide a method for producing a stainless steel strip having excellent surface quality.

[0014]

Means for Solving the Problems The first invention of the present invention is:
Continuous casting of stainless strip characterized in that a plurality of hot rolling machines having a structure capable of hot rolling with a total rolling reduction of 60% or more and a cooling device are arranged downstream of the thin cast continuous casting machine. Hot rolling equipment.

In a second aspect of the present invention, in the first aspect of the present invention, a simple heat-retaining device that can adjust the temperature of the thin slab is disposed between the thin slab continuous casting machine and the hot rolling mill. A continuous casting hot rolling facility for stainless steel strips, which is equipped with a simple annealing device that can prevent the temperature of the strips from dropping downstream.

According to a third aspect of the present invention, in the first or second aspect of the invention, a plurality of hot rolling mills share the posts of the housing stands, and the distance between stands is 3 m or less. Characteristic stainless steel strip continuous casting hot rolling facility.

In a fourth aspect of the present invention, a stainless thin ingot having a plate thickness of less than 3 mm, which is cast by a thin ingot continuous casting machine, is processed by a plurality of hot rolling mills arranged downstream of the stainless ingot, respectively, to 900 to 12 respectively.
Rolling is performed in a temperature range of 00 ° C., hot rolling is performed with a total reduction of 60% or more, and the strip immediately after hot rolling is slowly cooled for 5 to 10 seconds at a cooling rate of 5 ° C./second or less, and then a cooling rate. A stainless steel strip with excellent surface quality, characterized by cooling at 10 ° C / sec or more to a temperature range of 600 ° C or less and winding up, pickling and cold rolling this strip, followed by annealing pickling or bright annealing. Manufacturing method.

A fifth aspect of the present invention is to use a plurality of hot rolling mills to heat a thin stainless steel slab with a plate thickness of 3 mm or more cast by a thin slab continuous casting machine by a simple heat storage device arranged downstream thereof. To 900 ~ 1200 ℃ by each hot rolling mill
In the temperature range of 5 to 10%, hot rolling with a total reduction of 60% or more is performed, and the strip immediately after hot rolling is cooled at a cooling rate of 5 ° C / sec or less by a simple slow cooling device on the downstream side for 5 to 10%.
Slow cooling for 2 seconds, then 600 at a cooling rate of 10 ° C / second or more
It is a method for producing a stainless steel strip having excellent surface quality, which comprises cooling to a temperature range of ℃ or less and winding, pickling and cold rolling the strip, and subsequently performing pickling or bright annealing.

[0019]

According to the present invention, a slab having a thickness of 1 to 10 mm cast by a continuous casting machine is hot-rolled at a total rolling reduction of 60% or more by using a plurality of hot-rolling mills. It is possible to manufacture hot-rolled strips with recrystallized grain size. After pickling, cold rolling, annealing, pickling or bright annealing to stably produce stainless strips with excellent surface quality (evaluated by the degree of roping and gloss). It is possible to Also,
Since it is not necessary to install a large-scale heat treatment furnace as in the past, it is possible to make the installation space of the equipment compact and to significantly reduce the equipment cost and fuel consumption rate, and to significantly reduce the manufacturing cost. It is possible.

The present invention will be described below. In the first aspect of the present invention, a plurality of (preferably two stand) hot rolling mills and cooling devices having a structure capable of rolling with a total rolling reduction of 60% or more are provided downstream of the thin cast continuous casting machine. It is characterized by having.

When the thickness of the stainless thin slab cast by the twin-drum type continuous casting machine is less than 1 to 3 mm, the total thickness of the thin slab is reduced by a plurality of hot rolling mills arranged downstream of the continuous casting machine. Hot rolling with a rolling reduction of 60% or more can be performed and cooled by a cooling device to produce a hot rolled stainless steel strip. Here, when hot rolling is performed by a plurality of hot rolling mills at a total reduction ratio of less than 60%, recrystallization does not proceed sufficiently and a satisfactory cold rolled steel sheet cannot be manufactured.

When hot rolling is performed by a plurality of hot rolling mills, the contact heat transfer of work rolls increases the additional load due to the rolling reduction of the hot rolling mill in the subsequent stage by 20 to 30% compared to the hot rolling mill in the preceding stage. Therefore, since shape control becomes difficult, it is effective to share the reduction ratio of 60 to 90% of the total reduction ratio in the former hot rolling mill.

As a rolling temperature range in each hot rolling mill, 900 to 1200 ° C. is an appropriate range, but when the casting speed of the continuously cast thin slab is slow, the hot rolling from the continuous casting machine is performed. Until reaching the mill, or the heat radiation in the idle section between the former hot rolling mill and the latter hot rolling mill is large, and the hot rolling cannot be performed by lowering the temperature below the temperature range of the hot rolling. If there is such a concern, it is necessary to take measures to maintain the hot rolling temperature in each of the hot rolling mills within the temperature range.

According to a second aspect of the invention, in the first aspect of the invention, a simple heat-retaining device for suppressing a temperature drop of the thin slab is provided between the thin slab continuous casting machine and the hot rolling mill, and a plurality of hot slabs are provided. The hot rolling temperature in the rolling mill is set to an appropriate temperature range of 900 to 1200 ° C, and a simple annealing device for adjusting the temperature drop rate of the strip after hot rolling is provided downstream of the post-stage hot rolling mill. Then, by adjusting the cooling rate, a structure is added so that the strain energy generated by hot rolling can be utilized to reduce the crystal grain size in the recrystallization process.

When the thickness of the slab continuously cast by the continuous casting machine is 3 mm or more, the total rolling reduction is made 60% or more by a plurality of hot rolling mills arranged downstream of the continuous casting machine. However, in order to substitute the effect of refining the recrystallized grain size by the conventional heat treatment furnace, the total rolling reduction must be 60% or more as described above. It is necessary to reduce the rolling reduction of at least 25% or more.

In order to stabilize hot rolling at such a high pressure reduction rate, it is necessary to reduce the rolling load to stabilize the shape of the strip after rolling and suppress meandering. In order to reduce the rolling load, it is first necessary to set the temperature on the inlet side of the former hot rolling mill to 1100 to 1200 ° C. Therefore, between the continuous casting machine and the hot rolling mill at the preceding stage, a heat insulating cover, a heat panel, a simple heat-retaining device consisting of an induction heating device, etc. are arranged, and the thin slab on the inlet side of the preceding hot rolling mill is The temperature is maintained at 1100-1200 ° C. At this time, in order to prevent high-temperature oxidation of the slab, it is desirable that the simple heat-retaining device be capable of controlling the atmosphere so that the oxygen concentration is 0.2% or less.

Since the rolling reduction in the latter hot rolling mill is not so high as in the former hot rolling mill, there is no problem if the temperature of the strip slab on the inlet side can be maintained in the temperature range of 900 to 1100 ° C. . A simple annealing device such as a heat insulating cover or a heat panel for adjusting the temperature lowering speed of the strip after hot rolling is disposed downstream of the hot rolling mill in the latter stage. With this simple slow cooling device, the temperature drop rate of the strip after hot rolling is controlled within 5 ° C./sec and held for 5 to 10 seconds to utilize the strain energy generated by hot rolling to Crystals can be promoted and the structure can be made finer.

According to a third invention, in the first invention or the second invention, a plurality of hot rolling mills share a post of a housing stand, and a stand-to-stand distance is 3 m.
The feature of the present invention is that the drop of the strip temperature between the former hot rolling mill and the latter hot rolling mill is minimized as follows.

When hot-rolled by a plurality of hot-rolling mills, there is a significant temperature drop in the strip during the hot-rolling process in the preceding hot-rolling mill. Therefore, in the hot rolling mill in the latter stage, the rolling load increases and the shape controllability deteriorates, so the rolling reduction is restricted, strain energy cannot be applied, and the grain size of the crystal grain in the recrystallization process is reduced. It adversely affects the miniaturization.

Therefore, it is necessary to suppress the temperature drop of the strip due to the roll contact heat transfer due to the hot rolling and the temperature drop due to the radiant heat transfer of the strip in the idle section between the stands. Heat transfer from roll contact can be suppressed by raising the roll temperature, but this is difficult to achieve because the roll surface becomes rough due to thermal fatigue on the roll surface.

In the present invention, particularly in the case of a thin ingot having a thickness of 3 mm or more and a relatively slow casting speed, radiant heat transfer of the strip in the idle section between the preceding hot rolling mill and the subsequent hot rolling mill is used. The temperature drop can be suppressed.

When a heat insulating cover, an induction heating device, etc. are provided between the stands of the hot rolling mill to prevent the temperature of the strip from dropping, a strip guide, a roll cooling device, and a work roll changing device (not shown). This is not preferable because it interferes with the equipment and increases the equipment cost. Therefore, in the present invention, the housing posts of a plurality of hot rolling mill stands are commonly used in order to shorten the idle running section of the strip between the stands and suppress the temperature drop of the strip. The cross-sectional area of the common housing post is doubled in the front and rear hot rolling mills, and the rigidity of the housing during rolling is made the same as in the case where the housing post is independent.

As for the tension between the stands, an elevating type looper which penetrates a common housing post is arranged to control the speed of the subsequent hot rolling mill. As a result, between the stands of the former hot rolling mill and the latter hot rolling mill (between the roll axes)
It is possible to reduce the temperature drop of the strip by shortening the idling section to 3 m or less.

In a fourth invention, a strip continuous casting hot rolling facility selectively combining the first to third inventions is used, and a plate thickness of 3 mm cast by a strip continuous casting machine.
The thin stainless steel slabs of less than 1 are rolled in a temperature range of 900 to 1200 ° C. by a plurality of hot rolling mills arranged downstream thereof, and hot rolling is performed at a total rolling reduction of 60% or more. Temperature decrease rate (cooling rate) after rolling 5 ° C /
Slowly cool for 5-10 seconds at less than 10 seconds, and then cool at 10 ℃
It is characterized in that it is cooled to a temperature range of 600 ° C. or lower at a speed of not less than / sec and wound up, followed by annealing pickling or bright annealing to produce a stainless strip having excellent surface quality.

In the case of stainless steel, when a thin slab having a thickness of less than 3 mm is hot-rolled in a temperature range of less than 900 ° C., the deformation resistance becomes large and the shape control becomes difficult with the increase of rolling load. In addition, metallurgically there is precipitation of Mn and CuS, which may deteriorate the machining characteristics of the strip. Further, when hot rolling is performed at more than 1200 ° C., the recrystallized grain size becomes coarse due to the thermal energy of the slab, which adversely affects the surface quality (roping property, gloss) of the strip after cold rolling.

Further, as described in the prior art, in the coil which is hot rolled at a rolling reduction of less than 60%, the heat treatment is omitted, and the coil is wound at 550 ° C., the grain refinement due to recrystallization does not proceed. However, we cannot manufacture satisfactory hot rolled stainless steel strips. In the present invention, by raising the rolling reduction to 60% or more, the surface quality (evaluated by the degree of roping and the glossiness) of the strip after cold rolling can be significantly improved.

Note that it is necessary to accelerate recrystallization by slow cooling at a temperature decrease rate (cooling rate) of 5 ° C./second or less after hot rolling for 5 to 10 seconds. Subsequently, unless the temperature is cooled to a temperature range of 600 ° C. or lower at a cooling rate of 10 ° C./sec or more, the recrystallized grain size is not refined, and a satisfactory hot-rolled stainless steel strip cannot be manufactured. If the cooling rate is higher than 5 ° C./sec, the temperature is lower than the recrystallization temperature, so that refining does not proceed and a slow cooling section for more than 10 seconds is required, which is not a good measure in terms of equipment cost.

Further, even if the temperature is maintained without cooling at the exit side temperature of the subsequent hot rolling mill, the holding time cannot be shortened compared with the slow cooling time. It is effective to raise the temperature to shorten
A heating furnace is required to raise the temperature above ℃, which is not a good idea in terms of equipment cost. In the case of stainless steel, if the slow cooling is continued at 10 ° C / sec or less after slow cooling, C
r ₂₃ C ₆ (chromium carbide) precipitates to form a Cr-deficient layer, which hinders the corrosion resistance and impairs the gloss of the product. Therefore, at a temperature of 10 ° C / sec or more, preferably 40 ° C / sec or more Cool to below 600 ° C, where precipitation stops.

In the fifth invention, a strip continuous casting hot rolling facility selectively combining the second invention and the third invention is used, and a plate thickness of 3 mm cast by a strip continuous casting machine is used.
The above stainless steel thin slabs are heated by a heat retention device arranged downstream thereof and then introduced to a plurality of hot rolling mills, and each hot rolling mill rolls them in a temperature range of 900 to 1200 ° C. Hot rolling with a rolling reduction of 60% or more,
5 to 10 at a cooling rate of 5 ° C / sec or less due to a downstream heat retention device
It is characterized in that it is slowly cooled for 2 seconds, then cooled to a temperature range of 600 ° C. or lower and wound up, and then subjected to annealing pickling or bright annealing to produce a stainless strip having excellent surface quality.

In the twin-drum type continuous casting machine, when the plate thickness of the slab is 3 mm or more, the inlet temperature of the hot rolling machine is inevitably 1100 ° C. or less. Rolling temperature of 900 ° C. or lower, the reduction rate of 30% or more was applied, and the refinement of the crystal grains did not proceed by recrystallization, and the temperature was raised again to 1100 ° C. in a conventional large-scale heat treatment furnace.
It was confirmed that the crystal grains did not become finer if they could not be held for a second. Therefore, the inlet side temperature of the hot rolling mill in the previous stage should be 11
It is necessary to set the temperature to 00 to 1200 ° C.

Therefore, in the present invention, it is premised that a conventional large-scale heat treatment furnace is not installed, and a slab with a thickness of 3 mm or more cast by a continuous casting machine is treated with a continuous casting machine and a hot rolling mill in the preceding stage. Insulation cover, heat panel, induction heating device and other simple heat-retaining devices are used to keep the heat, and the inlet temperature of the former hot rolling mill is set to 1100 ° C to 200 ° C and the inlet temperature of the subsequent hot rolling mill is set to 900 ° C. To 1100 ° C., hot rolling with a total reduction of 60% or more is performed by the plurality of hot rolling mills, and the strip temperature is set to 850 to 850 seconds for 5 to 10 seconds by a simple heat retaining device arranged downstream of the hot rolling. 1150
6 ° C. and then cooled at a cooling rate of 10 ° C./sec.
After being cooled to 00 ° C. or lower, it is wound, followed by annealing pickling or bright annealing, and cold rolling to produce a stainless steel thin plate having excellent surface quality.

After the hot rolling, the strip temperature is kept at 850 to 950 ° C. for 5 to 10 seconds, then cooled at a cooling rate of 40 ° C./second to 600 ° C. or less, and then re-wound. It is not possible to make the crystal grains and Cr carbide compatible, and a satisfactory hot-rolled stainless steel strip cannot be manufactured.

[0043]

【Example】

(Embodiment 1) The present invention will be described below based on an embodiment shown in FIGS. The embodiment shown in FIG. 1 is a continuous casting hot rolling facility for stainless steel strips that satisfies the first and second aspects of the invention.

Here, a thin slab 2 having a thickness of 1 to less than 1 mm, which is continuously cast by a twin drum type strip continuous casting machine 1 at a casting speed of 50 to 180 m / min, is made downstream by a pinch roll 7 below the casting drum. The pinch roll 8 in front of the front hot rolling mill is used to secure the strip tension on the inlet side of the front hot rolling mill 3a, and the front hot rolling mill 3a 1000 to 12
Hot rolling at a high pressure reduction rate of 40% or more in a temperature range of 00 ° C,
Subsequently, in the subsequent hot rolling mill 3b, hot rolling was performed at a reduction rate of 25% or more necessary for promoting the refinement of the recrystallized structure in the temperature range of 900 to 1100 ° C., and a total of 65% or more. Perform hot rolling at a reduction rate.

Subsequently, the strip 2s after hot rolling is cooled to 600 ° C. at a cooling rate of 10 to 80 ° C./sec by a cooling device 5, and then wound up by a carousel type winder 9 to make a coil 2c of stainless strip. To manufacture. By descaling the surface of the thus-produced stainless steel strip, pickling and cold rolling, and subsequently performing annealing pickling or bright annealing, a stainless steel strip having excellent surface quality can be produced.

Reference numeral 10 in the drawing denotes an atmosphere control cover that has been generally used in the past, and can suppress the temperature drop and oxidation of the thin cast piece 2. A cutting machine 11 is for cutting the strip 2s into a winding length.

FIG. 2 schematically shows an example of the structure of the housing post of the two hot rolling mills 3a and 3b, which is composed of the work roll 3w and the backup roll 3v. Here, by sharing the central housing post 12 of the two hot rolling mills 3a and 3b, two stands 13 are provided.
The distance L between a and 13b is shortened to 3 m or less (the distance is shortened as much as possible), the cast slab 2 is hot-rolled by the pre-stage hot rolling mill 3a, and the hot-rolled strip is the stand 13a. The amount of temperature decrease when running between No. 13 and 13b is minimized.

By doing so, for example, a slab having a thickness of 2 mm is hot-rolled by a former hot rolling mill at a reduction rate of 40%, and the amount of temperature decrease when the strip idles to the latter hot rolling mill is 30. It can be about 50 ° C. In addition, this 2
A simple looper 14 is placed between two stands,
A slight tension control can be implemented.

The embodiment shown in FIG. 3 is a continuous casting hot rolling facility for stainless steel strip which satisfies the second and third aspects of the invention. Here, a slab 2 having a thickness of 3 to less than 10 mm, continuously cast at a casting speed of 20 to 50 mpm by a twin drum type thin slab continuous casting machine 1, is fed downstream by a pinch roll 7 below the casting drum, and the pre-stage heat is applied. The inlet side strip tension of the former hot rolling mill 3a is secured by the pinch roll 8 in front of the hot rolling mill, and 950 to 1050 is applied in the former hot rolling mill 3a.
It is necessary to carry out hot rolling at a high pressure reduction rate of 40% or more in a temperature range of ℃, and subsequently to promote the refinement of the recrystallized structure in a temperature range of 900 to 950 ℃ by a hot rolling mill 3b in the subsequent stage. 25%
The hot rolling is performed at the above reduction rate, and the hot rolling is performed at a reduction rate of 60% or more in total.

Subsequently, the strip 2s after hot rolling is passed through the simple slow cooling device 15 and is heated at 850 to 950 ° C. for 5 to 10 seconds.
The temperature of the strip is maintained for 2 seconds, then cooled to 600 ° C. by a cooling device 5 at a cooling rate of 10 to 80 ° C./second, and then wound by a carousel type winder 9 to manufacture a stainless strip coil. . The stainless steel strip thus produced is pickled and cold-rolled, followed by annealing pickling or bright annealing to produce a stainless steel strip having excellent surface quality.

Reference numeral 16 in the drawing denotes a simple heat retaining device having a heating function such as a heat panel and an induction heating device arranged between the thin cast continuous casting machine 1 and the preceding hot rolling mill 3a. A function of adjusting the temperature of the thin cast piece 2 (strip) on the inlet side of the hot rolling mill 3a and the post-stage hot rolling mill 3b to an appropriate temperature range, and an atmosphere control function for suppressing high temperature oxidation of the thin cast piece 2. It is desirable to use a heat-insulating cover or the like which does not have a heating function but has an excellent temperature drop suppressing function and an oxidation suppressing function.

Since the simple slow cooling device 15 arranged between the rear hot rolling mill 3b and the cooling device 5 is for adjusting the rate of temperature drop, it has a heating function such as a heat panel and an induction heating device and a high temperature. It is preferable that the one having the oxidation suppressing function is provided, but the use of the one having the temperature drop suppressing function and the oxidation suppressing function such as the heat insulating cover has the corresponding effect.

The structure of the housing post 12 of the hot rolling mill used here is the same as that shown in FIG. 2, and the center housing post of the two hot rolling mills 3a and 3b is used. Two stands by sharing 12
The distance L between 3a and 13b is 3 m or less (the distance is shortened as much as possible)
The thin cast piece 2 that has been shortened to the
According to the above, the amount of temperature decrease when the hot-rolled strip is idled between the two stands is minimized.

By doing so, for example, a slab having a thickness of 5 mm is hot-rolled at a reduction rate of 40% by a hot rolling mill in the former stage, and the amount of temperature decrease when the strip idles to the hot rolling mill in the latter stage is 35%. It can be improved by about 60 ° C. Further, since the simple looper 14 is arranged between the two stands, a slight tension control can be performed.

(Embodiment 2) FIG. 4 more specifically shows a temperature control structure example of the stainless strip continuous casting hot rolling equipment shown in FIG. 3 more concretely. The fifth invention is configured to be practicable.

In this embodiment, the thin cast continuous casting machine 1 continuously casts at a casting speed of 20 to 180 mpm and a thickness of 1 to 1.
A strip 2 of 10 mm thin slab 2 is hot-rolled by two hot rolling mills 3a and 3b at a total reduction of 60% or more.
s, and is cooled to manufacture the rolled stainless strip coil 2c.

The stainless steel strip manufactured by this equipment is cold-rolled by pickling and annealed and pickled or bright annealed to be manufactured as a stainless steel strip. The stainless steel strip has no roping and gloss. Good and excellent surface quality can be obtained.

In FIG. 4, 1 is a twin-drum type continuous casting machine for thin slabs, and a hot rolling mill 3 having two stands is provided downstream thereof.
a, 3b are provided. The passage of the thin slab 2 between the thin slab continuous casting machine 1 and the preceding hot rolling mill 3a is surrounded by a heat insulating cover 17 capable of controlling the atmosphere, and the thin slab 2 has a plurality of rows of heat in the passage. A simple heat retention device 16 including a panel 18 and an induction heating device 19 is provided.

As shown in FIG. 5, the heat panel 18 constituting this simple heat retention device 16 is a heat panel (heater) in which a power supply pipe 22 is connected to the wall surface of a refractory brick 21 arranged on the inner surface of the iron skin 20. 23 is attached, and the thin cast piece 2 is disposed so as to face each other with the passage of the thin cast piece 2 interposed therebetween.

Since the induction heating device 19 is a very general device, its explanation is omitted. Further, as shown in FIG. 6, the simple slow cooling device 15 is formed of a heat insulating refractory brick, and includes a heat insulating box 24 having a through space that forms a passage of the strip 2s, and the passage of the strip 2s in the heat insulating box. A plurality of heat panels 18 as shown in FIG.

In the continuous casting hot rolling operation, the temperature conditions in each part are set in advance according to the casting object and casting conditions, and the inlet side thermometer of the former hot rolling mill 3a is set to meet these set conditions. 25 and temperature control (management) in the simple heat retention device 16 and the simple slow cooling device 15 are performed based on the temperature information from the outlet side thermometer 26 of the simple slow cooling device 15 downstream of the post-stage hot rolling mill 3b. Therefore, the inlet side thermometer 25
Simple heat retention device 1 by inputting temperature information from
The temperature control amount of the thin slab 2 (strip) by 6 is calculated, and the simple heat retention device 16 is controlled via the control device 28.

Further, the temperature information from the outlet side thermometer 26 is input to the calculator 29, the temperature adjustment amount by the simple slow cooling device 15 is calculated, and the simple slow cooling device 15 is controlled via the control device 30. . For example, in the case of a thin slab with a thickness of 6 mm or more, since the casting speed is as slow as 6 to 20 m / min, the temperature is lowered by radiative heat transfer until it reaches the hot rolling mill, and the appropriate temperature is set in the hot rolling mill. Hot rolling cannot be performed in the zone.

Therefore, in the present invention, the radiation surface of the thin slab 2 is set to 1150 to 120 by the heat panel of the simple heat retention device 16.
The heat is kept in the temperature range of 0 ° C. and sent to the former hot rolling mill 3a. The temperature of the thin slab 2 on the inlet side of the former hot rolling mill 3a is 11
When the temperature is 50 ° C. or lower, it is 9 in the post-stage hot rolling mill 3b.
Since hot rolling cannot be performed in an appropriate temperature range of 00 ° C to 1200 ° C, in this case, the temperature of the thin slab 2 on the inlet side of the former hot rolling mill 3a is adjusted by the induction heating device of the simple heat retention device 16. Is heated to 50 to 100 ° C.

In the heat insulating cover, the oxygen concentration is set to 0.2% or less in order to suppress high temperature oxidation of the slab and the electric heating element of the simple heat retention device. Further, in the simple slow cooling device 15 downstream of the post-stage hot rolling mill 3b, radiant heat transfer from the strip 2s is suppressed, and the temperature decrease rate of this strip is set to 5%.
C./second or less can be suppressed.

Such a thin cast piece 2 and strip 2
Operation experiment for manufacturing hot rolled stainless steel strip by selecting casting target, casting condition, hot rolling condition, cooling condition, etc. using stainless steel strip continuous casting hot rolling equipment whose temperature can be controlled freely Was carried out. The results are shown in FIGS. 7 to 9 (representative examples are shown) and Table 1.

(1) FIG. 7 shows a thin cast piece 2 having a thickness of less than 3 mm cast by a twin-drum type thin cast continuous casting machine 1 by hot rolling with two-stand hot rolling mills 3a, 3b and cooling. It shows the temperature history until the device 5 cools and winds it on the winder 6.

A casting speed of 75 to 38 is applied by the thin cast continuous casting machine 1.
The thin cast piece 2 continuously cast at 0 m / min rapidly lowers the temperature by heat transfer by heat radiation, and is hot-rolled at 1200 ° C. at a reduction rate of 40% or more in the former hot rolling mill 3a. Due to the contact heat transfer with the work roll 3w during this rolling, the temperature of the hot-rolled strip is lowered to 1030 ° C. here, and in the post-stage hot rolling mill, it is rolled at 1030 ° C. with a reduction rate of 30%, and the total 70%. % Hot rolling is carried out. This hot-rolled strip was idled in the simple slow-cooling device 15 downstream of the post-stage hot rolling mill 3b for 15 seconds or longer, and then cooled at 40 ° C. /
It was cooled to 550 ° C. at a cooling rate of 2 seconds and wound by a winder. (2) FIG. 8 shows a two-stand hot rolling mill 3a, 3b for a thin cast piece 2 having a thickness of 3 mm or more continuously cast by a twin-drum type thin cast continuous casting machine 1 at a casting speed of 10 to 75 m / min. It shows the temperature history from the thin cast continuous casting machine in the case of hot rolling to hot rolling, cooling and winding.

The thin cast piece 2 continuously cast by the twin-drum type thin cast piece continuous casting machine 1 suppresses the temperature drop of the thin cast piece 2 due to the radiative heat transfer by the simple heat-retaining device 16, and the former hot rolling mill. In the temperature range of 1180 to 1200 ° C. in 3a, the temperature drops due to contact heat transfer with the work roll 3w during the hot rolling at a reduction rate of 40%, and in the temperature range of 950 to 1030 ° C. in the latter stage hot rolling mill, Hot rolling is performed at a rolling reduction of not less than%, and a total of 70% hot rolling is performed.

The temperature of the strip on the outlet side of the post-rolling mill 3b is about 900 to 990 ° C. Therefore, in order to promote the refinement of the crystal grains in the recrystallization of the strip, the strip of the post-stage hot rolling mill 3b is 5 to 1 in the downstream simple annealing device 15
After running for 0 seconds without cooling, it was cooled to 550 ° C. at a cooling rate of 40 ° C./second with a cooling device and then wound up with a winder.

(3) FIG. 9 shows a single-stand hot rolling mill 3 for thin cast pieces 2 having a thickness of 10 mm or less continuously cast by a twin-drum type thin cast continuous casting machine 1 at a casting speed of 10 to 160 m / min. From the thin cast continuous casting machine 1 in the comparative example of the present invention, which was hot-rolled in the conventional heat treatment furnace 4, heat-treated in the conventional heat treatment furnace 4, cooled in the cooling device 5 and wound in the winder 6. It shows the temperature history from rolling to cooling and winding.

In this conventional example, one stand of the hot rolling mill 3 is used.
Hot rolled at a reduction ratio of 40% in the temperature range of 1,080 to 1,180 ° C., and the hot rolled strip is 1100-1.
Heat treatment was carried out by keeping the temperature in the temperature range of 150 ° C. for 10 seconds or more, followed by cooling to a temperature of 550 ° C. or lower and winding. The length of the heat treatment furnace in this conventional example is 5 to 6
At 0 m, the heat treatment time is 5 to 10 seconds.

The strips produced by the above (1) to (3) are subjected to a general pickling cold rolling, annealing pickling or bright annealing step for producing a stainless steel strip, and the surface properties of the obtained stainless strip are In particular, surface waviness (roping) and gloss were investigated. The results are shown in Table 1.

[0073]

[Table 1]

[0074]

[Table 2]

As shown in Table 1, No. 1 is an example of the present invention. In Nos. 1 to 10, hot rolling conditions by a two-stand hot rolling mill and optimum temperature holding conditions after hot rolling,
Combined with the cooling rate control conditions, all of them showed satisfactory surface quality.

On the other hand, the conventional example No. In Nos. 11 to 13, when the furnace length was 5 m and the heat treatment time was less than 10 seconds, which was insufficient, the roping was large and the gloss was poor even if cooling control was performed thereafter. I couldn't get it.

When two hot rolling mills were used, the stainless strips of Comparative Examples manufactured under the conditions outside the scope of the present invention (Nos. 14 to 18) exhibited large roping and gloss. Poor and no satisfactory surface quality was obtained.

As described above, according to the present invention, it is not indispensable to install the conventional type heat treatment, and a simple heat-retaining device and a simple slow-cooling device are used as necessary depending on the manufacturing object, so that good surface quality can be obtained. This makes it possible to manufacture various stainless steel strips, and can significantly reduce equipment costs and heat intensity.

The present invention is not limited to the above-mentioned embodiment, and is not limited to the thin cast continuous casting machine, the hot rolling mill, the simple heat-retaining device, the simple annealing device, the cooling device, the winding machine, and the accessory. apparatus,
Various control structures, specifications of each of these elements, the number of arrangements, operating conditions, etc. are changed within a range that satisfies the above claims 1 to 5 of the present invention, depending on the casting target, casting conditions, and hot rolling conditions. It is a thing. The pickling cold rolling, annealing pickling or bright annealing conditions are not different from those in general industrial operations.

[0080]

According to the present invention, a slab having a thickness of 1 to 10 mm cast by a continuous casting machine is used by a plurality of hot rolling mills.
By hot rolling at a total reduction of 60% or more,
It is possible to roll hot-rolled strips with good surface properties and internal crystal structure, and after cold rolling, it is possible to stably manufacture stainless steel strips with excellent surface quality (roping property, gloss) by annealing and pickling. is there. In addition, since it is not necessary to install a large-scale heat treatment furnace as in the past, it is possible to make the installation space of the equipment compact and significantly reduce the equipment cost, which can significantly reduce the manufacturing cost. is there.

[Brief description of the drawings]

FIG. 1 is a side conceptual explanatory view showing an arrangement example of a stainless steel strip continuous casting hot rolling facility of the present invention.

FIG. 2 is a side conceptual explanatory view showing a structural example of a hot rolling mill used in the continuous casting hot rolling equipment for stainless steel strips of the present invention.

FIG. 3 is a side view conceptual diagram showing another arrangement example of the stainless strip continuous casting hot rolling equipment of the present invention.

FIG. 4 is a side view conceptual explanatory view showing an example of a temperature control structure of a slab (strip) in the stainless steel strip continuous casting hot rolling facility of the present invention.

FIG. 5 is a sectional conceptual explanatory view showing an example of a simple heat retaining device used in the continuous casting hot rolling equipment for stainless steel strips of the present invention.

FIG. 6 is a sectional conceptual explanatory view showing an example of a simple slow cooling device used in the continuous casting hot rolling equipment for stainless steel strip of the present invention.

FIG. 7 is an explanatory view of temperature history of a cast piece (strip) in the example of the present invention.

FIG. 8 is a temperature history explanatory diagram of a cast piece (strip) according to another embodiment of the present invention.

FIG. 9 is an explanatory view of a temperature history of a cast piece (strip) in a conventional example.

FIG. 10 is a side view conceptual diagram showing an arrangement example of a strip continuous casting hot rolling facility of a conventional example.

[Explanation of symbols]

 1 twin drum type thin cast continuous casting machine 2 thin cast 2s strip 2c strip coil 3 single stand hot rolling mill 3a front hot rolling mill 3b post hot rolling mill 3w work roll 3v backup roll 4 heat treatment furnace 5 cooling device 6 Winding machine 7 Casting drum lower pinch roll 8 Previous hot rolling mill Front pinch roll 9 Carousel type winding machine 10 Atmosphere control cover 11 Cutting machine (shear) 12 Housing post 13a, 13b (Rolling) stand 14 Simple looper 15 Simplified slow cooling device 16 Simplified heat retention device 17 Insulation cover 18 Heat panel 19 Induction heating device 20 Iron crust 21 Refractory brick 22 Power supply pipe 23 Heat panel (heater) 24 Insulation box 25 Inlet thermometer of previous hot rolling mill 26 Simple Output side thermometer of slow cooling device 27 computing unit 28 control unit 29 computing unit 30 control device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B22D 11/06 330 B22D 11/06 330B 11/12 11/12 A C21D 9/52 101 C21D 9 / 52 101

Claims (5)

[Claims] 1. A plurality of hot rolling mills having a structure capable of hot rolling with a total rolling reduction of 60% or more and a cooling device are arranged downstream of a thin cast continuous casting machine. Continuous casting hot rolling equipment for stainless steel strip. 2. A simple heat-retaining device for adjusting the temperature of the thin slab is provided between the thin slab continuous casting machine and the hot rolling mill, and it is possible to prevent the temperature drop of the strip downstream of the hot rolling mill. The continuous casting hot rolling facility for stainless steel strip according to claim 1, further comprising an annealing device. 3. The continuous casting of stainless strip according to claim 1, wherein a plurality of hot rolling mills share the posts of the housing stands, and the distance between the stands is 3 m or less. Hot rolling equipment. 4. A plate thickness of 3 mm cast by a thin cast continuous casting machine.
The thin stainless steel slabs of less than 1 are rolled in a temperature range of 900 to 1200 ° C. respectively by a plurality of hot rolling mills arranged downstream thereof, and hot rolling is performed at a total rolling reduction of 60% or more. The strip just after rolling is slowly cooled at a cooling rate of 5 ° C./sec or less for 5 to 10 seconds, then cooled to a temperature range of 600 ° C. or less at a cooling rate of 10 ° C./sec or more and wound up,
A method for producing a stainless steel strip having excellent surface quality, which comprises subjecting this strip to pickling cold rolling, followed by annealing pickling or bright annealing. 5. A thin cast piece of stainless steel having a plate thickness of 3 mm or more cast by a continuous casting machine for thin cast pieces is heat-retained by a simple heat-retaining device arranged downstream thereof and introduced to a plurality of hot rolling mills. Each is rolled in a temperature range of 900 to 1200 ° C. by a hot rolling mill to perform hot rolling with a total reduction of 60% or more, and the strip immediately after hot rolling is subjected to a simple annealing device downstream.
The cooling rate is set to 5 ° C./second or less and gently cooled for 5 to 10 seconds,
Subsequently, the strip is cooled to a temperature range of 600 ° C. or lower at a cooling rate of 10 ° C./sec or higher and wound up, and the strip is pickled and cold rolled,
Subsequently, an annealing pickling or bright annealing is performed, which is a method for producing a stainless steel strip having excellent surface quality.