JP3014256B2 - Continuous casting of thin slabs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-drum continuous caster and a twin-drum continuous caster for producing thin slabs directly from a molten metal of stainless steel, alloy steel, silicon steel, ordinary steel and other metals. It relates to the casting method used.

[0002]

2. Description of the Related Art Thin cast slabs (plate thickness of about 1 to
As a device for producing a molten metal (10 mm), there is known a method in which a molten metal is supplied to the peripheral surface of a rotating cooling drum and solidified by cooling. Such a thin slab continuous caster includes a single-drum continuous caster using one cooling drum and a twin-drum continuous caster using two cooling drums. As for the twin drum type continuous casting machine, as shown in FIG.
A pair of cooling drums 1 rotating in opposite directions are arranged horizontally and opposed to each other so as to be parallel to each other with a predetermined gap therebetween, and a pair of side weirs 2 are crimped to both end surfaces of the cooling drum 1. A pool 3 is defined above the gap between the cooling drums, a molten metal (hereinafter simply referred to as “molten metal”) is poured into the pool 3, and the molten metal is cooled on the outer peripheral surface of the cooling drum 1 to form a solidified shell G. Then, the thin cast piece S is cast by pressing the solidified shell G in the gap between the cooling drums 1.

[0003] The cooling drum of such a continuous casting machine is used to form a solidified shell G on the peripheral surface of the outer cylindrical portion 1A.
The outer cylinder 1A is made of a copper-based material such as copper or a copper alloy having good thermal conductivity, and a cooling medium is circulated on the inner surface of the outer cylinder 1A. In addition, when the copper-based outer cylinder (hereinafter referred to as Cu sleeve) is operated for a long time, a fine crack is generated on the surface thereof. Therefore, a nickel layer is adhered to the peripheral surface of the Cu sleeve by plating or thermal spraying. I have. Further, the surface of the solidified shell formed by the molten metal contacting the peripheral surface of the cooling drum and rapidly quenched is liable to crack due to contraction stress caused by the quenching. In order to prevent the occurrence of cracks, there are cases where a large number of dimples (dents) are provided on the peripheral surface of the cooling drum.

As a conventional cooling drum, a nickel layer having a thickness of 2 mm or more is adhered to a peripheral surface of a Cu sleeve,
A method for preventing the occurrence of unevenness in the thickness of a thin slab due to rapid cooling of a molten metal is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-166962. However, when casting is performed using such a cooling drum, there is a problem that the nickel layer is damaged and the life of the cooling drum is shortened. In particular, when dimples are provided on the peripheral surface of the cooling drum, the dimples are damaged, the life of the cooling drum is remarkably shortened, and fine cracks occur in the cast thin slab.

[0005]

DISCLOSURE OF THE INVENTION The present invention is to prevent the wear of a cooling drum for a continuous casting machine for producing a thin cast piece directly from a molten metal, to prolong the life of the cooling drum and to prevent the thin cast piece from cracking. The task is to prevent it.

[0006]

DISCLOSURE OF THE INVENTION The present inventors have found that a nickel layer adhered to a peripheral surface of a cooling drum of a continuous thin slab caster is easily damaged, and that the nickel layer adhered to the casting drum using the nickel layer-adhered cooling drum. In order to solve these problems, it was effective to adjust the maximum temperature of the cooling drum peripheral surface to a predetermined range in order to solve these problems. In addition, it has been found that it is effective to adjust the heat flux of the cooling drum and the thickness of the nickel layer in order to adjust the temperature of the peripheral surface of the cooling drum. That is, the continuous casting method for thin slabs of the present invention uses
In a method of continuously casting thin slabs using a cooling drum having a sleeve and a nickel layer on the peripheral surface of the Cu sleeve, the surface temperature of the peripheral surface of the cooling drum at a position P not in contact with the solidified shell in FIG. T _NP is detected, and a temperature difference ΔT _N between the maximum surface temperature T _NS of the cooling drum peripheral surface that comes into contact with the solidified shell and the detected surface temperature T _NP is determined in advance.
From the relationship of T _NS −T _NP , T _NS = T _NP + ΔT _N is calculated,
The casting is performed while maintaining the value of T _{NS in} the range of 350 to 450 ° C. In the method of continuously casting the thin slab, the heat flux q (cal /
sec · cm ² ), the thickness t _Ni (mm) of the nickel layer, and the maximum surface temperature T _CS of the Cu sleeve immediately below the peripheral surface in contact with the solidified shell are expressed by the following equation (1). 350 ≦ T _CS + 0.3 × q × t _Ni ≦ 450 Expression (1) In the method for continuously casting the thin cast piece,
A thermocouple is disposed on the Cu sleeve immediately below the interface between the u-sleeve and the nickel layer having a thickness of t _Ni (mm) to detect the maximum temperature T _CS of the surface of the Cu sleeve immediately below the peripheral surface in contact with the solidified shell.
The heat flux q (c) of the cooling drum so that _CS satisfies the expression (1)
al / sec · cm ² ) and nickel plating thickness t _Ni
Is adjusted. 350 ≦ T _CS + 0.3 × q × t _Ni ≦ 450 Equation (1)

[0007]

The temperature of the nickel plating applied to the peripheral surface of the cooling drum of the continuous cast slab is 450 ° C during casting.
If it exceeds, the amount of wear increases. If the maximum temperature of the nickel plating surface is higher than 450 ° C. and lower than 350 ° C., fine cracks occur in the cast thin slab. Therefore, the present invention prevents the wear of the nickel plating surface and prolongs the life of the cooling drum by casting while maintaining the nickel plating surface maximum temperature, that is, the surface temperature of the cooling drum peripheral surface in the range of 350 to 450 ° C. In addition, it is possible to prevent the occurrence of fine cracks in the cast thin slab.

FIG. 2 shows a twin-drum continuous casting machine in which a nickel plating is applied to a peripheral surface of a Cu sleeve of a cooling drum, dimples having a depth of 40 to 60 μm are provided on the surface of the nickel plating, and the cooling drum is mounted. 3 shows the relationship between the surface temperature of nickel plating during casting, that is, the maximum surface temperature of the cooling drum peripheral surface, and the average depth of dimples in the damaged portion of the cooling drum peripheral surface after casting when stainless steel is cast by using FIG. FIG. 3 shows the relationship between the maximum surface temperature of the peripheral surface of the cooling drum and the amount of fine cracks generated in the cast thin slab when the same casting as in FIG. 2 is performed. In FIG. 2, when the maximum surface temperature of the peripheral surface of the cooling drum during casting exceeds 450 ° C., the damage to the dimples increases, the depth becomes sharply shallow, and the cooling drum reaches the end of its life. In order to extend the life of the cooling drum, it is necessary to perform casting while maintaining the maximum surface temperature of the cooling drum peripheral surface at 450 ° C. or less during casting.

In FIG. 3, when the surface temperature of the peripheral surface of the cooling drum during casting is lower than 350 ° C., the cooling speed of the slab surface is large, and fine cracks are generated due to distortion during cooling. On the other hand, when the temperature exceeds 450 ° C., fine cracks are generated in the damaged portion of the dimple. In order to reduce the amount of fine cracks generated in the thin slab, it is necessary to perform casting while maintaining the maximum surface temperature of the cooling drum peripheral surface in the range of 350 to 450 ° C. during casting. From FIGS. 2 and 3, in order to extend the life of the cooling drum and to prevent the occurrence of microcracks in the thin slab, the maximum surface temperature of the peripheral surface of the cooling drum during casting is set to 350 to 4
It is necessary to maintain the temperature in the range of 50 ° C. for casting.

Means for casting while maintaining the surface temperature of the cooling drum peripheral surface in the range of 350 to 450 ° C. during casting include, for example, the surface of the cooling drum peripheral surface at a position P not in contact with the solidified shell as shown in FIG. The temperature T _NP is detected by, for example, an infrared radiation thermometer, and a temperature difference ΔT _N = T _NS − between a previously determined maximum surface temperature T _NS of the cooling drum peripheral surface in contact with the solidified shell and the detected surface temperature T _NP. From the relationship of T _NP , T _NS = T _NP + ΔT _N is obtained, and this value is set to 350 to
Casting is maintained at 450 ° C. As another means for casting while maintaining the maximum surface temperature of the cooling drum peripheral surface in the range of 350 to 450 ° C. during casting, for example, a thermocouple is buried immediately below the interface between the cooling drum and the nickel plating of the Cu sleeve. The maximum surface temperature T _cs of the Cu sleeve is measured, the maximum surface temperature T _NS of the cooling drum peripheral surface is estimated using the following equation (2), and the casting is performed while maintaining this value at 350 to 450 ° C. T _NS = T _cs + α × (q / λ) × (1/10) t _Ni (2) where T _NS ; maximum surface temperature of cooling drum peripheral surface in contact with solidified shell (° C.) T _cs ; Cu just below the peripheral surface of the cooling drum in contact with the solidified shell
Maximum surface temperature of sleeve (° C) t _Ni ; Nickel plating thickness (mm) λ; Nickel plating thermal conductivity (= 0.18 cal / sec)
c · cm · K) The nickel plating thermal conductivity λ changes with temperature, but it is difficult to accurately estimate the average temperature of the nickel plating layer when in contact with the molten metal. The temperature range is about 100 to 450 ° C. (however, the surface).
The intermediate value of the thermal conductivity at each of 0 ° C. and 300 ° C. was adopted. There is no problem because a slight error is corrected by the following correction coefficient (α). q: Nickel plating average heat flux (cal / sec · c
m ² ) α; correction coefficient (= 0.54) Note that this correction coefficient varies depending on the casting arc angle (the contact angle with the molten metal, θ in FIG. 1), but is within the normal casting range of 30.
This is a value adjusted by a two-dimensional unsteady heat transfer analysis so as to be fit at ５０50 deg. When a numerical value is substituted into the equation (2), T _NS = T _cs + 0.3 × q × t _Ni (3) Therefore, the maximum surface temperature T _NS of the cooling drum peripheral surface is 35.
In order to maintain the temperature in the range of 0 to 450 ° C., the heat flux q of the cooling drum and the nickel plating thickness t are set so that the maximum surface temperature T _cs of the Cu sleeve immediately below the peripheral surface in contact with the solidified shell satisfies the expression (1). Adjust _Ni . 350 ≦ T _cs + 0.3 × q × t _Ni ≦ 450 (1) As means for adjusting the heat flux q of the cooling drum, the amount of cooling water supplied to the cooling water channel provided immediately below the Cu sleeve is adjusted. Alternatively, it is preferable to adjust the nickel plating thickness t _Ni . Since nickel has a smaller thermal conductivity than copper, the most effective way to adjust the heat flux q is to adjust the nickel plating thickness t _Ni . A specific method for adjusting the nickel plating thickness t _Ni is that the nickel plating thickness t _Ni satisfies the following expression (1). (350−T _cs ) / (0.3 × q) ≦ t _Ni ≦ (450−T _cs ) / (0.3 × q) (4) where, t _Ni ; nickel plating thickness (mm) T _cs ; Cu immediately below the peripheral surface of the cooling drum in contact with the solidified shell
Sleeve surface maximum temperature (° C) q; Nickel plating average heat flux (cal / sec · cm)
² ) T _cs is measured by a thermocouple buried at the interface between the Cu sleeve of the cooling drum and the nickel plating.

[0011]

Examples Tables 1 and 2 show that the peripheral surface of the Cu sleeve of the cooling drum for the twin-drum type continuous casting machine shown in FIG. 1 was plated with nickel of various thicknesses and then provided with dimples having a depth of 40 to 60 μm. The results of casting a total of about 200 tons of SUS304 stainless steel using a cooling drum are shown.

[0012]

[Table 1]

[0013]

[Table 2]

In Tables 1 and 2, the maximum surface temperature of the peripheral surface of the cooling drum is a value obtained by equation (3). The damage area ratio of the nickel plating surface is the ratio of the area of the damaged portion to the entire peripheral surface of the cooling drum, and the amount of fine cracks generated in the slab is the total length of cracks generated per 1 m ² of the slab surface.

No. 1 and No. In No. 2, since the nickel plating was thick, the temperature of the peripheral surface of the cooling drum was too high, the nickel plating was softened, the dimples were crushed, and fine cracks occurred in the thin slab corresponding to that portion. No. 10
However, since the nickel plating was thin, the nickel plating did not soften, but the temperature of the cooling drum peripheral surface was too low, and the cooling rate of the thin slab was increased, so that fine cracks occurred in the thin slab. Also, since the nickel plating is thin, it is difficult to guarantee the accuracy of the plating thickness. No. In Nos. 3 to 11, since the nickel plating thickness or the amount of cooling water was appropriate, the temperature of the cooling drum peripheral surface was appropriately low, and the nickel plating did not soften. Also, most of the fine cracks in the thin slab (10cm /
m ² or less) did not occur.

[0016]

According to the present invention, the peripheral surface of the cooling drum can be prevented from being damaged, the life thereof can be greatly extended, and the surface quality can be greatly improved by eliminating the occurrence of fine cracks in the thin slab. be able to.

[Brief description of the drawings]

FIG. 1 is a front view showing a twin-drum continuous casting machine according to the present invention.

FIG. 2 is a diagram illustrating a relationship between a surface temperature of a cooling drum peripheral surface and an average dimple depth.

FIG. 3 is a diagram showing the relationship between the surface temperature of the peripheral surface of a cooling drum and the amount of micro-cracks generated in thin slabs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 1A ... Outer cylinder part (Cu sleeve) of a cooling drum 2 ... Side dam 3 ... Hot water pool part G ... Solidified shell S ... Thin cast piece P ... Drum surface temperature detection position

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Chihiro Yamaji 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Isao Mizuchi 3434 Shimada, Oaza, Hikari-shi, Yamaguchi Prefecture Inside Nippon Steel Corporation Hikari Works (72) Inventor Kunimasa Sasaki 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd.Hiroshima Works (72) Inventor Keiichi Yamamoto Kan-on, Nishi-ku, Hiroshima 4-6-22 Shinmachi Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory (56) References JP-A-1-166686 (JP, A) JP-A-3-90250 (JP, A) JP-A-2-165649 (JP, A A) JP-A-3-230847 (JP, A)

Claims (3)

(57) [Claims] In a method of continuously casting thin slabs using a cooling drum having a Cu sleeve on an outer cylinder portion and a nickel layer on a peripheral surface of the Cu sleeve, the method includes the steps of: Surface temperature T of cooling drum peripheral surface
_NP is detected, and the maximum surface temperature T _NS of the cooling drum peripheral surface that comes into contact with the solidified shell determined in advance and the detected surface temperature T
_From the relationship of temperature difference ΔT _N = T _NS −T _NP with _NP , T _NS = T _N
Calculates the _NP + [Delta] T _N, the value of this T _NS 350 to 450 ° C.
A continuous casting method for thin cast slabs, wherein the casting is performed while maintaining the thickness in the range described above. 2. A method of continuously casting thin slabs using a cooling drum having a Cu sleeve in an outer cylinder portion and a nickel layer on a peripheral surface of the Cu sleeve, wherein the heat flux q (cal) of the cooling drum is provided. / Sec · cm ² ), thickness of the nickel layer t _Ni (mm) and Cu just below the peripheral surface in contact with the solidified shell
A continuous casting method for a thin cast piece, wherein the maximum surface temperature T _{CS of the} sleeve is in the relationship of the formula (1). 350 ≦ T _CS + 0.3 × q × t _Ni ≦ 450 Equation (1) 3. A method of continuously casting thin slabs using a cooling drum having a Cu sleeve on an outer cylinder portion and a nickel layer on a peripheral surface of the Cu sleeve, wherein the Cu sleeve and a thickness t _Ni (mm ) of the thermocouple is disposed on the Cu sleeve immediately below the interface between the nickel layer, it detects the Cu sleeve surface maximum temperature T _CS immediately below the circumferential surface in contact with the solidified shell, T _CS is (1)
The heat flux q of the cooling drum (cal / se
c · cm ² ) and a nickel plating thickness t _Ni . 350 ≦ T _CS + 0.3 × q × t _Ni ≦ 450 Equation (1)