JP2000343182A - Manufacturing method of thin belt casting piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a casting piece with a good shape by improving a solidification and clamping condition of both casting piece ends in a method for manufacturing a thin belt casting piece with a twin drum type continuous casting machine. SOLUTION: A stepped part is installed at both ends of a cooling drum in a way that height (h) and width (w) corresponding to the casting thickness (t) will satisfy the formula: h>=0.17t-0.017w-0.34. The clamping load of solidification shells at a drum kiss point is made to be 0.1 kg/mm2 or more so as to clamp the solidification shells of both casting piece ends at the drum kiss point, thereby preventing leakage of the semi-solidified molten steel from the both casting piece ends and bulging of the both casting piece ends. In this case, w is 3 mm or more and h is 1/2 or less of the casting thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin strip slab by a twin-drum continuous casting machine, wherein a slab having a good shape is manufactured by improving the pressure bonding state of a solidified shell at both ends of the slab. It relates to the technology to be performed.

A feature of the casting of a ribbon slab by a twin-drum continuous caster is that a solidified shell formed on the peripheral surface of the drum is pressed at a drum kiss point (minimum gap between the drums). To control the solidification state of the shell based on the "force". Therefore, as a condition for stable casting, it is necessary that such "drum reaction force" is evenly distributed in the drum width direction. However, in general, due to the variation in molten steel temperature occurring in the width direction of the drum and the heat input from the side weirs, the solidification state of the shell changes slightly in the width direction, especially at both ends of the drum, and the crimping state of the shell at the drum kiss point is not good. Easy to be stable.

As an extreme example where the solidification state of the shell at both ends of the drum becomes unstable, for example, Japanese Patent Publication No. Sho 59-1182
No. 49 and Japanese Patent Publication No. 59-118250,
A casting method is described in which unsolidified molten steel is included in the center of the slab at the drum kiss point. As a problem with this method, it is described that unsolidified molten steel leaks from the end of the slab after the shell has passed the drum kiss point, and in order to prevent this, the shells at both ends of the slab at the drum kiss point have been described. A method is described in which both ends of a slab are "closed in a bag-like manner" by forcibly pressing the slab. The feature of this method is to provide stepped parts at both ends of the drum to "close the ends of the slab in the form of a bag",
It is intended to keep the reaction force generated at the stepped portion and the gap between the drums at the stepped portion constant.

However, in the casting in a state in which the unsolidified molten steel is included as described above, no matter how much the state of pressure contact between the shells at both ends of the drum is improved, the molten steel static pressure and the However, due to the force applied to the peripheral surface of the drum, the shells that should have been press-bonded are peeled off from each other, resulting in molten metal leakage and bulging in which the slab swells in the thickness direction. Therefore,
Generally, such a casting method should be avoided, but as described in JP-B-59-118249, the drum gap of the stepped portion at the drum kiss point is always slightly smaller than the thickness of the solidified shell. As described in JP-B-59-118250, the reaction force generated by pressing the shell against the entire width of the drum changes to the drum reaction force during casting, as described in JP-B-59-118250. If casting is performed by pressing to the extent that gives a squeeze, a strong rolling phenomenon occurs at the drum kiss point, the slab is broken, and in some cases, both ends of the slab are broken during casting,
It has been found that both ends of the slab that are strongly pressed are broken into hoops, which hinders stable casting.

On the other hand, when the height of the stepped portion is increased in order to prevent the molten steel from leaking, a large step is formed at both ends of the slab, and after the casting, hot rolling with a draft of 10% or more is performed. If it does, edge cracks may occur in the stepped portion of the slab due to rolling, or the stepped portion may be cut off.

[0006]

In twin-drum continuous casting, side dams are in contact with both end surfaces of the drum for the purpose of sealing molten steel, and these side dams are usually maintained at a temperature higher than the surface temperature of the drum. Further, since the amount of heat removal at both ends of the cooling drum is smaller than that at the center, the heat removal at both ends of the drum is slower than at the center.

For this reason, the slab discharged from the drum is liable to be in a state of solidification delay at both ends, and when the shells are pressed together at the drum kiss point, the semi-solidified molten steel is extruded toward the end of the slab. Leak out. As a result, chipping or cracking occurs at the end of the slab, or bulging occurs at the end of the slab due to the static pressure of the semi-solidified molten steel after the shell is pressed.

The present invention relates to a method of manufacturing a thin strip slab by a twin-drum continuous caster, wherein a press-bonding state of a solidified shell at both ends of a slab is improved so that shells are pressed together at a drum kiss point. The object of the present invention is to prevent the occurrence of end defects such as chipping and cracking and bulging of the slab end due to leakage of semi-solidified molten steel from the slab end,
Furthermore, when hot rolling is performed subsequent to casting, it is another object of the present invention to prevent occurrence of edge cracks and breaks due to rolling of a stepped portion of a slab.

[0009]

The present invention for solving the above-mentioned problems
Light ribbon slab production method rotates in opposite directions
By twin-drum continuous casting machine with a pair of cooling drums
In the method for producing a ribbon slab, the pair of cooling driers
Height (h) and width according to the casting thickness (t)
(W) is provided with a stepped portion satisfying the following expression (1),
Solidified shells formed on the peripheral surfaces of a pair of cooling drums
0.1 kg / mm at the drum kiss point ^TwoMore crimping negative
It is characterized by crimping under load. h ≧ 0.17t−0.017w−0.34 (1) where w: 3 mm or more h: 1/2 or less of the cast plate thickness

Another method is to produce a strip slab by a twin-drum continuous caster having a pair of cooling drums rotating in opposite directions, and then to reduce the strip slab to a rolling reduction of 10%. In the above method of performing hot rolling, the height (h) corresponding to the casting plate thickness (t) at both ends of the pair of cooling drums is 3 mm or more in width (w) satisfying the following expression (2). A stepped portion is provided, and the solidified shells formed on the peripheral surfaces of the pair of cooling drums are separated by 0.1 k at a drum kiss point.
The crimping is performed under a crimping load of g / mm ² or more. h ≦ 0.08t−0.02 (2) where h: 以下 or less of the cast plate thickness

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a comparison of the state of press-fitting of a shell at a drum kiss point in twin-drum continuous casting. In each figure, 2 is a portion where the shell on the drum peripheral surface solidifies to form a columnar axis crystal, and 3 is a portion where the semi-solidified molten steel solidifies to form an equiaxed crystal. FIG.
Is a case where no stepped portion is provided at both ends of the cooling drums 1 and 1, and the equiaxed crystal 3 in which the semi-solidified molten steel is solidified reaches both ends of the slab to the slab end face. Since the equiaxed crystal 3 is a semi-solidified molten steel at the drum kiss point, the semi-solidified molten steel may leak from the end face of the slab and may cause an end defect.

FIG. 2 shows a case where stepped portions 4 are provided at both ends of the cooling drums 1 and 1. FIG. 3 shows an enlarged portion A surrounded by a broken line in FIG. In FIGS. 2 and 3, the semi-solidified molten steel 3 is closed in a bag-like manner by pressing the shells 2, 2 at both ends 5 of the slab by the stepped portion 4. Can be prevented from leaking.

FIG. 4 shows stepped portions 4 at both ends of the cooling drum in the production of a thin strip by a twin-drum continuous caster.
When the pressure applied between the solidified shells at the drum kiss point is 0.1 kg / mm ² or more, the presence or absence of slab end defects and the height (h) and width of the stepped portion for each casting plate thickness (W) shows the relationship. The drum has a thickness deviation in the width direction of the slab (= central plate thickness−edge 25 mm point plate thickness) of 100.
Taking into account the difference in the amount of thermal expansion between the end and the center of the drum so as to be in the range of ± 50 μm, a concave (drum-shaped) profile larger than this value was given in advance. The height (h) and width (w) of the stepped portion in FIG. 4 are determined by the maximum solid fraction 6 (indicated by the broken line in FIG. 3) of the stepped portion when the shells 2 and 2 shown in FIG. The value at which the solid phase ratio at the center of the plate thickness in the region surrounded by the center is 0.6 or more was obtained by theoretical calculation.
If it is 6 or more, it has been confirmed that no leakage occurs.

In FIG. 4, the area where no slab end defect occurs is defined by lines 12 to 1 determined for an arbitrary step width (w).
4 is a region having a lower limit. Therefore, from FIG. 4, the condition under which the slab end portion defect does not occur is a condition in which the casting plate thickness (t) and the height (h) and width (w) of the stepped portion satisfy the following expression (1). h ≧ 0.17t−0.017w−0.34 (1) where w: 3 mm or more h: 1/2 or less of the cast plate thickness

At this time, if the pressure applied between the solidified shells at the drum kiss point is less than 0.1 kg / mm ² , the pair of shells is peeled off from the central portion of the plate thickness due to poor press bonding at the point where the drum kiss point is reached. Cannot produce cast slabs with good shape. In order to prevent peeling of the shell and cracking of the stepped portion of the slab, it is necessary to set the pressure bonding load to 0.1 kg / mm ² or more. When the width w of the stepped portion is 3 mm, there is a case where the molten metal leaks or the end of the slab is broken. The height h of the stepped portion is naturally not more than の of the cast plate thickness. In addition, since the concave (drum-shaped) profile imparted to the drum contributes to the height (h) of the stepped portion, if the thickness deviation in the width direction of the slab is smaller than 50 μm, the portion is stepped. It is necessary to add to the height (h) of the part. For example, when the thickness deviation is zero, 1/2 of 50 μm is 25 μm.
(0.025 mm) is added to the height (h) of the stepped portion.

In FIG. 4, it can be seen that in order to produce a slab having a wider range of cast plate thickness with one kind of drum, it is better to increase the step width. However, on the other hand, even when the solidification property at the stepped portion is improved, the quality of the slab may not always be the same in comparison with the width center portion. If the edge is cut off after casting to ensure quality, yield loss will occur. In this case, it is advantageous to reduce the step width.

FIG. 5 shows that in the production of a ribbon slab by a twin-drum continuous casting machine, the above-mentioned concave profile is applied to the drum and stepped portions are provided at both ends, and the solidified shells are pressed together at the drum kiss point. Load 0.1 kg / mm ²
And casting a strip slab as a
The relationship between the occurrence of edge cracks or tearing at the end of the slab in hot rolling and the height (h) of the stepped portion for each casting plate thickness when hot rolling of up to 30% is performed is shown. . The width (w) of the stepped portion is 3 to 15 mm, and the height (h) of the stepped portion is the solid phase in the maximum solid phase ratio portion 6 of the stepped portion (the area surrounded by the broken line in FIG. 3). The value at which the ratio is 0.6 or more is determined by theoretical calculation.

In FIG. 5, the shape of the stepped portion is such that the cast plate thickness (t) and the height (h) of the stepped portion are as follows (1) in order to prevent the occurrence of edge cracks or tearing at the end of the slab. ) Must be satisfied, and the width (w) of the stepped portion must be 3 mm or more. h ≦ 0.08t−0.02 (2) where h: 以下 or less of the cast plate thickness. The reason for limiting the height (h) and width (w) of the stepped portion is as described above. Is the same as Naturally, both defects such as chipping at the end of the slab, such as chipping or cracking and bulging, which occur during casting, and edge cracks or shreds at the end of the slab, which occur during hot rolling following casting. In order to prevent the above, it is necessary to satisfy both the expressions (1) and (2).

[0019]

EXAMPLES Table 1 shows SUS by a twin-drum continuous casting machine.
An example is shown in which 304 stainless steel is cast to produce a thin strip with a width of 1000 mm. No. Reference numeral 8 denotes a conventional example in which a stepped portion is not provided at both ends of the drum, and FIG. 6 shows a cross-sectional shape of an end of the slab. In this case, the semi-solidified molten steel leaks from the end of the slab, and a protrusion 7 and a crack 8 are generated at the end. During the subsequent transportation and hot rolling, the protrusion (high-temperature portion) and the center of the slab (low temperature) Section 9), which caused a severe breakage in operation.

No. 5 is a comparative example in which stepped portions are provided at both ends of the drum, and FIG. 7 shows a cross-sectional shape of an end portion of the slab.
In this case, bulging occurred at the end of the slab and cracks 8 occurred in the bulging portion 10 due to insufficient step height. Cut-off width is 20mm to remove cracks
Was needed. Note that when the truncation width is large, scrap may be generated due to insufficient product width.

No. 2 is an example of the present invention in which stepped portions are provided at both ends of the drum, and FIG. 8 shows a cross-sectional shape of an end portion of the slab. In this case, since no defects such as bulging and cracks occurred at the end of the slab, it was unnecessary to cut off the end.

[0022]

[Table 1]

[0023]

According to the present invention, there is provided a method for producing a strip slab using a twin-drum continuous caster.
By improving the pressure bonding state, leakage of semi-solidified molten steel from the slab end when the shells are pressed together at the drum kiss point, chipping and cracking of the slab end, and furthermore, occurrence of bulging at the slab end are prevented. At the same time, the edge of the slab is prevented from cracking and tearing, whereby a slab having a good shape can be stably manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a solidified state of both ends of a slab when a stepped portion is not provided.

FIG. 2 is a cross-sectional view showing a solidified state of both ends of a slab when a stepped portion is provided.

FIG. 3 is an enlarged sectional view showing a portion surrounded by a broken line in FIG. 3;

FIG. 4 is a graph showing a relationship between occurrence of a slab end defect in casting and height and width of a stepped portion for each casting plate thickness.

FIG. 5 is a graph showing the relationship between the occurrence of edge cracks and tearing at the end of a slab and the height of a stepped portion for each casting thickness in hot rolling following casting.

FIG. 6 is a sectional view showing a sectional shape of an end portion of a slab according to a conventional example.

FIG. 7 is a sectional view showing a sectional shape of an end portion of a slab according to a comparative example.

FIG. 8 is a sectional view showing a sectional shape of an end portion of a slab according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 2 ... Solidified shell and columnar crystal at a drum kiss point 3 ... Semi-solid molten steel and equiaxed crystal at a drum kiss point 4 ... Stepped portion at both ends of drum 5 ... Stepped portion at both ends of cast slab 6 ... Step Maximum central solid phase fraction in the region with the slab 7 Projection at the end of the slab 8 Crack at the end of the slab 9 Boundary portion 10 Bulging portion at the end of the slab 12 to 14: Lower limit at which no defective slab end w ... Width of stepped part h ... Height of stepped part

Claims (2)

[Claims] 1. A method for producing a strip slab by a twin-drum continuous caster having a pair of cooling drums rotating in opposite directions to each other, wherein both ends of the pair of cooling drums have a casting plate thickness (t). A stepped portion having a height (h) and a width (w) corresponding to the following formula (1) is provided, and the solidified shells formed on the peripheral surfaces of the pair of cooling drums are separated by 0.1 kg / kg at the drum kiss point. A method for producing a thin strip slab, comprising performing crimping under a crimping load of at least ² mm2. h ≧ 0.17t−0.017w−0.34 (1) where w: 3 mm or more h: 1/2 or less of the cast plate thickness 2. A strip slab is manufactured by a twin-drum continuous caster having a pair of cooling drums rotating in opposite directions, and subsequently the strip slab is hot-rolled with a rolling reduction of 10% or more. The height (h) according to the casting plate thickness (t) is set at both ends of the pair of cooling drums as described in (2) below.
A stepped portion having a width (w) of 3 mm or more that satisfies the formula is provided, and the solidified shells formed on the peripheral surfaces of the pair of cooling drums are pressed against each other at a pressure of 0.1 kg / mm ² or more at the drum kiss point. A method of manufacturing a thin strip slab, comprising crimping underneath. h ≦ 0.08t−0.02 (2) where h: 以下 or less of the cast plate thickness