JPH09225598A - Method of manufacturing hot rolled thin steel sheet - Google Patents

Abstract

(57) Abstract: The present invention allows a plate thickness of 1 m to be passed from a single belt type continuous casting machine through a hot rolling machine without using a heating furnace or the like.
A method for producing a hot-rolled thin steel sheet for directly producing a hot-rolled thin steel sheet of m to 6 mm is provided. In a method for manufacturing a hot-rolled thin steel sheet, a single-belt type continuous casting machine (11) for controlling a slab thickness by changing a ratio (L / Vc) of a solidification length (L) and a casting speed (Vc), and a slab cutter (12).
, A slab edge heater 13, an in-line hot rolling mill 14 of three stages or less, and a thin steel plate winding machine 15 are arranged, and the thickness of the slab is determined to be 2.5t ≦ d ≦ 3.6t, and d
= K × (L / Vc) ^1/2, the value of L / Vc is determined using the formula, casting is performed, and then hot rolling is performed by an in-line hot rolling mill with a reduction ratio of 60% or less. 1-6 mm
Of hot rolled steel sheet. [Effect] By reducing the rolling load, fuel costs and operating costs can be reduced and high productivity can be achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling for directly producing a hot rolled thin steel sheet having a thickness t of 1 mm to 6 mm from a single belt type continuous casting machine through a hot rolling mill without using a heating furnace or the like. The present invention relates to a method for manufacturing a thin steel sheet.

[0002]

2. Description of the Related Art Conventionally, in order to produce a thin steel sheet from a thick slab produced by slab rolling or continuous casting, these slabs are placed in a heating furnace or a soaking furnace and heated again,
Then, this was subjected to a rough rolling mill and a finishing rolling mill to manufacture a hot rolled thin steel sheet having a thickness of about 1 to 6 mm.

However, in recent years, instead of rolling from these thick slabs, the production of thin cast pieces using twin drums, twin belts, or single belts has become popular, and hot rolled thin steel sheets are manufactured from these thin cast pieces. By manufacturing, cost reduction and productivity improvement are achieved.

In order to improve the productivity by casting a thin slab by the above method, the thickness (d) of the slab is reduced to increase the casting speed, and the length from the solidification start point to the solidification completion point, that is, It is achieved by increasing the solidification length (L).

Among the above methods, the twin drum method is
High-speed casting is possible, but in order to improve productivity, the solidification length must be increased, which inevitably results in an increase in the molten metal pool formed between the drums and an excessive size of the side weir, and static pressure. And the leakage from the side weir also becomes a problem.

Further, the twin belt method has a restriction on the size of the injection nozzle into the molten metal pool at the time of pouring the molten metal, and is suitable for a slab thickness of 60 mm or more, but for thin slabs smaller than that. Is not suitable, and there is a problem that the static pressure increases and the supporting mechanism and the like become complicated.

The single-belt type continuous casting method is a horizontal casting method, unlike the conventional vertical type continuous casting method and the twin-roll or twin-belt continuous casting method in which thin steel plates and the like are symmetrical. Therefore, an unreasonable straightening force is not applied to the slab during the solidification process, there is no spatial restriction on the upper part of the moving mold, and there is no increase in the static pressure of molten steel in the casting direction, so the supporting mechanism is simple.

Moreover, there is no breakout or bulging,
Large inclusions float up and are easily removed, and because of unidirectional solidification from below, macrosegregation is light and good quality slabs can be obtained. Further, the single-belt continuous casting method is a casting method capable of achieving high productivity because it is easy to extend the length of the mold in the horizontal direction because there is no molten steel static pressure and high-speed casting is also possible.

[0009]

By the way, in the process of casting the conventional thin cast piece and subsequently rolling and manufacturing the thin steel sheet, the thickness of the cast piece that is cast takes into consideration the thickness of the thin steel sheet as the final product. It was almost constant without. That is, a slab having a thickness of 200 to 300 mm is heated again and heated,
And, this was rolled by a multi-stage finishing rolling mill of 5 to 8 stages to produce a hot rolled thin steel sheet of 1 mm to 6 mm.

Conventionally, when manufacturing a thin plate product from a slab or the like, a reduction ratio of about 2.5 to 10 has been sufficient, but in the current method, the reduction ratio is particularly from a thick slab to a thin hot rolling. 200 when rolled down by steel plate
As described above, the rolling method naturally increases the rolling load and the rolling equipment becomes enormous, and the rolling energy cost also increases, which also causes a cost increase, and thus the productivity is not good.

In view of the above problems, the present invention is to produce a hot-rolled thin steel sheet by a single-belt continuous casting machine by selecting casting conditions and performing casting according to the thickness of the thin sheet product.
Provided is a method for manufacturing a thin steel sheet for reducing the total cost from casting to rolling and improving productivity.

[0012]

The present invention is a method for manufacturing a hot-rolled thin steel sheet, wherein the ratio L / V of the solidification length L and the casting speed Vc is L / V.
A single-belt continuous casting machine that controls the thickness of the slab by changing c, a slab cutter that cuts the slab to the slab length necessary to obtain a thin steel plate with a desired winding length, and an in-line heat Hot rolled sheet steel composed of a cast edge heater that compensates for insufficient temperature at the end of the cast width direction required for hot rolling, an in-line hot rolling machine with three or less stages, and a winder for hot rolled steel sheet Using the manufacturing apparatus, a hot rolled thin steel sheet having a plate thickness t of 1 to 6 mm is
After determining the thickness of the slab by the following formula (1), the following (2)
A method for manufacturing a thin steel sheet, characterized in that the value of L / Vc is determined using a formula, and hot rolling is performed by the inline hot rolling mill with a reduction ratio of 60% or less.

[0013]

(3) 2.5t ≦ d ≦ 3.6t (1)

[0014]

## EQU00004 ## d = k.times. (L / Vc) ^1/2 (2) where t: thickness of hot rolled steel sheet (mm) d: thickness of slab (mm) k: solidification constant (mm・ Min ^-1/2 ) L: Solidification length (m) (length from solidification start point to solidification completion point in single belt casting) Vc: Casting speed

FIG. 2 is a schematic side view showing a process of forming a slab necessary for obtaining a thin steel sheet by a single belt type continuous casting machine. First, a tank installed near the rear weir 3 of the casting machine 1. Inject the molten metal 5 from the dish 2 onto the metal belt 1a,
The rear weir 3 and the side weir 4 maintain a constant molten metal level 5a corresponding to the thickness d of the slab.

The molten metal 5 on the metal belt 1a is cooled by a cooling device to form a solidified shell 6 on the bottom surface from the solidification starting point 6a immediately after pouring, and at the same time, the cooling effect of the side dam 4 also solidifies the molten shell on the side surface. The solidification shell 6 grows while following the running of the metal belt 1a, passes through the solidification length L of a predetermined length, and solidification is completed at the solidification completion point 6b near the tip of the metal belt 1a to obtain the thickness d. The slab 7 is formed.

For the purpose of stabilizing the position of the freezing point 6b, the belt may be tilted upward from the horizontal position so that the freezing point 6b side is slightly inclined within about 3 degrees.

According to the present invention, when producing a hot-rolled thin steel sheet having the above-mentioned sheet thickness t, the single-belt type continuous casting machine 1 is used to cast the slab with a cast piece thickness d so as to satisfy the above equation (1). ,
This is a method for manufacturing a hot-rolled thin steel sheet in which the ingot 7 has a rolling reduction of 60% or less by an in-line hot rolling machine having three or less stages and a sheet thickness of 1 to 6 mm.

In this reduction stage, generally, the maximum limit value of the reduction ratio of the multi-stage hot rolling mill is restricted by the strength of the rolling stand, the heat load factor of the rolls, etc.
%, It is as small as 15 to 20% in the latter stage, and is about 35% on average. Using this average value, the final plate thickness obtained under multi-stage pressure is calculated as follows (here, the entry side plate thickness t ₀ = 1).

[0020]

[Number 5] the first stage out of the side plate thickness _{t 1 = (1-0.35) = 0.65} ...... (3) 2 -stage delivery side thickness ^{_{t 2 = (1-0.35) 2 =}} 0.423 ...... (4) 3rd step Outlet plate thickness t ₃ = (1-0.35) ³ = 0.275 …… (5)

On the other hand, from the viewpoint of the material quality of the hot rolled material, it is said that the total reduction ratio of the strict material is required to be about 60% (final plate thickness 0.4), which means that the total reduction ratio under the two-stage reduction is almost the same. A reduction rate can be secured. However, in the case of strict materials, the total reduction ratio is insufficient, and it is desirable to allow some margin for operating conditions depending on the type of hot-rolled sheet thickness. Occurs.

The slab thickness needs to be 2.5 times or more the thickness of the hot-rolled sheet in order to secure a total reduction of 60%. On the other hand, the upper limit of the slab layer must be 3.6 (the reciprocal of 0.275) times or less than that of the hot-rolled sheet, because the outlet plate thickness under the three-stage reduction is 0.275. From the above reason, the condition of the above formula (1) is derived.

Next, regarding the casting method, it is a feature of the single belt type continuous casting machine that the casting thickness can be varied. In the formula (1), in order that the hot rolled sheet thickness t is in the range of 1 to 6 mm, the cast piece thickness d is in the range of the following formula (6).

[0024]

[Equation 6] 2.5 × 1 = 2.5 mm ≦ d ≦ 3.6 × 6 = 21.6 mm (6)

The relationship between the cast piece thickness d, the length from the solidification start point 6a to the solidification completion point 6b in the case of single belt casting, ie, the solidification length L, and the casting speed Vc is expressed by the following equation (7). .

[0026]

## EQU00007 ## d = k.times. (L / Vc) ^1/2 ... (7)

[0027]

[Equation 8] ∴Vc = L (k / d) ² ………… (8) ∴L = Vc (d / k) ² ………… (9) where k is a solidification constant of 22 to 30 (mm · mi
The value is about n ^−1/2 ).

The solidification length L is the distance from the solidification start point to the completion point, but since the single-belt type continuous casting machine is arranged almost horizontally, the solidification length L is not restricted by the molten steel downward pressure. It can be easily taken long. Here, solidification length L = 1
Considering the case of 5 m and the solidification constant k = 25 mm · min ^−1/2 , the casting speed Vc corresponding to the casting thickness of the equations (8) to (6) is as shown in the following equation (10). .

[0029]

[Equation 9] 20 m / min ≦ Vc ≦ 1500 m / min (10)

The maximum speed of 1500 m / min is not so large that the tension body such as the metal belt 1a of the single belt type continuous casting machine 1 resonates. For example, the number of Shinkansen cables is 4
Resonance does not occur even at 000 m / min. The relationship between the casting thickness, the casting speed, and the casting length when there is no restriction on the maximum speed is shown by the solid line in FIG. However, the maximum speed may be limited due to the restriction of the reduction ratio of the belt drive motor.
If the maximum and minimum ratio of the reduction ratio is 10 times, the casting speed V
c is expressed as in equation (11).

[0031]

[Equation 10] 20 m / min ≦ Vc ≦ 200 m / min (11)

The maximum speed of the equation (11) is 200 m / mi
The slab thickness d corresponding to n is d = 6.8 from the above equation (7).
Therefore, a slab of 2.5 ≦ d ≦ 6.8 (mm) is cast at a maximum casting speed of 200 m / min, and the casting length is changed according to the equation (9), that is, the dotted line shown in FIG. Become.

Next, regarding the production amount, the production amount m per strand is expressed by the following equation (12).

[0034]

[Equation 11] However, δ is an infinitesimal symbol, ρ is a slab density, and b is a slab width.

From the d values derived from the equations (6) and (7), d ₁ = 2.5 mm, d ₂ = 6.8 mm, d ₃ = 2
Set to 1.6 mm. As in the case of the description of the casting method, the case where the casting speed Vc has no upper limit and the case where there is an upper limit will be considered separately.

(1) First, when there is no casting speed limitation, the following expression (13) is derived from the expressions (8) and (12).

[0037]

(Equation 12)

When b = 2 m and ρ = 7.8 ton / m ³ , from the above d ₁ , d ₂ , d ₃ and the equation (13), (1
4) Equation is obtained.

[0039]

[Equation 13] m = 51.7 ton / min. = 2230,000 ton / month / strand (14)

(2) Next, the casting speed has an upper limit (Vc _MAX. = 2) _.
00 m / min), the following formula (15) is derived from FIG. 3 and formula (12).

[0041]

[Equation 14]

D ₁ , d ₂ , d ₃ , b = 2 m, ρ =
From the value of 7.8 ton / m ³ and the equation (15), (16)
An expression is obtained.

[0043]

M = 13.42 + 14.74 = 28.16 ton / min. = 1.22 million tons / month / strand ... (16)

In both cases (1) and (2), the monthly production amount per strand is extremely large, which is about 1 of that of the conventional continuous casting machine.
It is equivalent to 0 times, and one strand can cover the total production amount of the largest steel mill, but in actual operation,
Appropriate production adjustments such as equipment maintenance, reduction of casting length L, and adjustment of operating rate are performed. In this way, when manufacturing a hot-rolled thin steel sheet, it is possible to reduce the cost and improve the productivity by directly selecting the casting conditions in the single-belt continuous casting and manufacturing the slab and directly rolling the slab. You can

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an equipment configuration showing an embodiment of a manufacturing apparatus for carrying out the method for manufacturing a hot-rolled thin steel sheet according to the present invention and a processing flow chart thereof.

The production apparatus comprises a single belt type continuous casting machine 11 for controlling the thickness d of the slab by changing the ratio L / Vc between the solidification length L and the casting speed Vc, and a thin winding length desired. A slab cutter 12 that cuts the slab to a slab length necessary to obtain a steel plate, and a slab edge heater that compensates for the temperature shortage of the slab width direction end portion required for in-line hot rolling, and 13, 3
It is composed of an in-line hot rolling mill 14 and a coiling machine 15 for hot-rolled thin steel plate.

The single-belt type continuous casting machine 11 has the same structure as the casting machine 1 described above, and the cast piece thickness d shown in the equation (1) is used.
In order to secure the production amount m shown in the equation (12), (13) or (15), the speed of the metal belt 1a (casting speed Vc) is 20 to 1500 m / min. The molten steel injection amount, the cooling device for the metal belt 1a, and the desired solidification length L that satisfy these equations are secured, and the predetermined casting speed Vc is maintained and 2.5t≤d. The slab 7 corresponding to ≦ 3.6 t is manufactured.

Since the slab cutter 12 is required to cut the traveling slab 7 at a desired length, it is preferable to use a traveling cutting machine.

The present invention intends to reduce the cost and improve the productivity by directly rolling from the casting process without using a heating furnace or the like. However, in the process of casting and solidifying shell formation, Due to the cooling effect of the side surface weir 4, a solidified shell is early formed on the side surface of the slab, and the temperature of the end of the slab drops. The slab edge heater 13 is provided before the rolling process in order to compensate for this drop in the end temperature and maintain a predetermined rolling temperature. The heating means is gas heating, electric heating, high frequency induction heating. Etc. can be used.

In this rolling line, a strict material is used, and the thickness of the slab is still 1 to 6 m from 2.5 t ≦ d ≦ 3.6 t.
In order to obtain a hot-rolled thin steel sheet with a thickness of m, a total reduction rate of about 60% is required, but in view of the results of the examination by the above formulas (3), (4) and (5) Although the total rolling reduction can be secured, a three-stage in-line hot rolling mill 14 is provided in order to allow a margin for operating conditions.

The hot-rolled thin steel sheet 8 which has been rolled by the hot rolling mill 14 and has a predetermined thickness is wound by the winding machine 15.

The apparatus is configured as described above, and after determining the slab according to the above formula (1), the L / Vc value is determined using the formula (2), and an in-line hot rolling mill having three or less stages is used. By hot rolling with a reduction ratio of 60% or less, a hot-rolled thin steel sheet having a desired sheet thickness of 1 to 6 mm can be efficiently manufactured.

[0053]

INDUSTRIAL APPLICABILITY In the present invention, unlike the continuous casting method of twin rolls or twin belts, by applying the continuous casting method of the single belt type, there is no breakout or bulging, and the intervention of large inclusions and macro segregation are also avoided. Light and good quality slabs can be obtained, the solidification length can be long, and high-speed casting is possible, resulting in extremely high productivity.

Further, by changing the solidification length and casting speed of the casting machine to select casting conditions and controlling the thickness and temperature of the slab, the reduction ratio by the hot rolling mill is set to 60% or less to obtain a desired value. It becomes possible to manufacture a hot rolled thin steel sheet of ~ 6 mm, and it is possible to significantly reduce the rolling load and to reduce the fuel cost required for heating by performing direct rolling from casting to rolling. High productivity can be achieved while reducing operating costs.

[Brief description of drawings]

FIG. 1 is a device configuration showing an embodiment of a manufacturing apparatus for carrying out a method for manufacturing a hot-rolled thin steel sheet according to the present invention and a processing flow chart thereof.

FIG. 2 is a schematic side view showing a process of forming a slab by a single belt type continuous casting machine.

FIG. 3 is a drawing showing a relationship between a cast piece thickness, a casting speed, and a casting length in a single belt type continuous casting machine.

[Explanation of symbols]

 1,11 Single-belt continuous casting machine 1a Metal belt 2 Tundish 3 Rear weir 4 Side weir 5 Molten metal 5a Molten metal level 6 Solidification shell 6a Solidification start point 6b Solidification completion point 7 Cast piece 8 Hot rolled thin steel sheet 12 Cast piece cutter 13 Edge heater 14 3-stage hot rolling 15 Winding machine

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area B22D 11/12 B22D 11/12 A 11/126 11/126 K 11/20 11/20 C

Claims (1)

[Claims] 1. A method for producing a hot-rolled thin steel sheet, wherein a single belt type continuous casting machine is used for controlling a thickness of a cast piece by changing a ratio L / Vc between a solidification length L and a casting speed Vc, and a desired winding length. Slab cutter that cuts slabs to the slab length required to obtain the thin steel sheet, a slab edge heater that compensates for insufficient temperature at the end of the slab width direction required for in-line hot rolling, and three stages Using a hot-rolled steel sheet manufacturing apparatus configured by the following in-line hot rolling mill and hot-rolled steel sheet winding machine, a hot-rolled steel sheet having a plate thickness t of 1 to 6 mm was calculated using the following formula 1. After determining the thickness of the cast slab and then determining the value of L / Vc using the following formula 2, hot rolling with a reduction ratio of 60% or less is performed by the inline hot rolling mill. Manufacturing method of thin steel sheet. [Formula 1] 2.5t ≦ d ≦ 3.6t [Formula 2] d = k × (L / Vc) ^{1/2 where} t: thickness of hot-rolled thin steel sheet (mm) d: thickness of slab (mm ) K: Solidification constant (mm · min ^-1/2 ) L: Solidification length (m) (length from solidification start point to solidification completion point in case of single belt casting) Vc: Casting speed