JP3358137B2 - Method for producing thin slab slab containing Cu and Sn and steel sheet containing Cu and Sn - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin slab slab containing Cu and Sn and a steel sheet containing Cu and Sn which can suppress the occurrence of surface defects caused by Cu and Sn.

[0002]

2. Description of the Related Art In recent years, in the field of steel refining, a large amount of scrap has been used as a raw material for steel, such as automobiles,
There are increasing opportunities to use Cu and Sn-containing scraps for home appliances, cans, and the like. Depending on the type of steel, Cu,
Although Sn may be contained as an active component, in the case of general carbon steel, it is often a component that inhibits required characteristics. When the Cu content is 0.1% or more, small cracks are generated on the surface, and the cracks increase in proportion to the increase in the Cu content. The effect of alloy elements on steel is published by Seibundo. It is also known by the description on page 378.

[0003] Since it is difficult to remove Cu and Sn by refining, when refining such a steel type, scrap containing Cu and Sn and scrap not containing Cu and Sn are mixed. A process of reducing the effects of these components by diluting the Cu and Sn contents has also been performed (“1990 Elliot Sympi”).
sium Proceedings, p. 599).

[0004] In addition, with respect to the above-mentioned phenomenon in the Cu-containing steel, Ni is added in the same weight% as the Cu content during the refining of the Cu-containing steel, and the molten steel of Cu at the time of high-temperature oxidation causing surface flaws is added. It has been proposed to prevent the occurrence of surface cracks by suppressing precipitation on the surface. However, in this method, since expensive and scarce resources are used, Ni is used.
The cost increases, and when Sn is contained in addition to Cu, the effect of preventing surface cracking from being caused by the addition of Ni is not significantly exhibited.

[0005] In this way, the steel obtained by refining is
In general, a slab is cast by continuous casting, rolled, and commercialized. In recent years, however, from the viewpoint of omission of steps and reduction of heat loss, as shown in FIG. The continuous casting in-line hot rolling process of continuously casting the piece c, rough-rolling with the in-line hot rough rolling mill d, and subsequently hot-finish rolling with the hot finishing rolling mill e to produce the steel sheet s is adopted. It has become.

[0006] As described above, when slab slabs are manufactured by refining carbon steel containing Cu and Su and continuously casting them with a curved or vertical bending type continuous casting machine, and in slab cast in-line. In a product obtained by hot working such as when a steel sheet is manufactured by hot rolling, generation of surface flaws is observed even if the Cu content is less than 0.2%. In particular, in the case of bending support and rough rolling of a slab, bending in the Cu embrittlement temperature range and occurrence of surface flaws are remarkable when rolling is performed, and surface flaws are obtained on a steel sheet obtained through a hot finish rolling mill. It is not uncommon.

Recently, high-speed continuous casting methods such as twin drum type continuous casting, twin belt type continuous casting, single belt type continuous casting and other special continuous castings have been developed. Attempts have been made to produce a steel sheet having a thickness of about 1.5 mm by an in-line hot finishing rolling mill by casting and omitting a rough rolling step. Even when the steel sheet is manufactured by hot finish rolling in this way, the surface cracks of the slab caused by Cu and Sn generated when the slab is curved are removed by the hot finish rolling of the steel sheet. Since this leads to the occurrence of a fatal defect, it also hinders the realization of a rolling process in which the rough rolling step is omitted.

[0008]

SUMMARY OF THE INVENTION According to the present invention, Cu is reduced to 0.1.
Thickness 7 containing 0.05 to 0.5% and 0.05% or less of Sn
Continuously cast thin slab slab containing 5mm or less Cu and Sn,
When hot finish rolling is performed without rough rolling, the occurrence of surface flaws on the resulting product can be suppressed inexpensively and efficiently, and the rough rolling step can be omitted. It is intended to provide a manufacturing method.

[0009]

Means for Solving the Problems The first invention of the present invention is:
When casting a thin slab slab of Cu, Sn-containing steel having a thickness of 75 mm or less containing Cu: 0.05-0.5% and Sn: 0.05% or less by a continuous casting method, a cast casting is provided below the mold. When the slab is curved and carried out, the slab surface temperature at the starting point of the curved support is set to 1050 ° C. or less to suppress the occurrence of slab surface flaws caused by Cu and Sn. And a method for producing a thin slab slab containing Sn, and a second invention provides a method for hot-finish rolling the thin slab slab obtained according to claim 1 to produce a steel sheet at the entry side of the finishing mill. Slab surface temperature of 8
00 ° C. and below ultra 1050 ° C., Cu, which comprises suppressing the occurrence of the steel sheet surface defects due to Sn Cu, S
This is a method for producing an n-containing steel sheet.

[0010]

According to the present invention, Cu is contained in an amount of 0.05 to 0.5.
%, When hot working (continuous casting, hot rolling) Cu, Sn-containing steel containing 0.05% or less of Sn, it is obtained by controlling the temperature at the time of hot working to a predetermined temperature. The generation of surface flaws of the product can be suppressed inexpensively and efficiently, and a high-quality Cu-containing thin slab slab and steel plate can be manufactured.

The present inventors have proposed that Cu is 0.1-0.3%,
When a slab is manufactured by continuously casting a Cu and Sn-containing steel containing 0.05% or less of Sn into a curved type or a vertical bending type, a slab surface crack is generated.
The structure of the slab having cracks was observed. The result is as shown in FIG. 1, and the metal Cu, S
n penetrates into the former austenite grain boundary g to generate a crack h,
Growing. Here, when Sn is contained, Cu is easily melted, and the phenomenon of intrusion into the austenite grain boundary becomes more remarkable than when Sn is not contained. It has been found that this cracking occurs remarkably when the casting radius in the vicinity of the curved support start point of the slab is 10 m or less.

From the above, the melting point of metal Cu in the case of containing Sn was confirmed, and the relationship between the surface temperature of the slab at the starting point of bending support of the slab and the occurrence of surface cracks in the slab was examined with respect to this melting point. Was. The results are as shown in FIG. 2, and it was confirmed that the surface crack generation index can be stably reduced when the temperature of the slab bending support start point is 1050 ° C. or less. However, if the temperature is too low, the slab cannot be curvedly supported at an optimum curvature, so that a smooth casting operation cannot be performed, and it is difficult to hot-roll the slab at an appropriate temperature. Considering these, it is not preferable to set the lower limit of the temperature to about 800 ° C. or less.

In this manner, the occurrence of surface cracks in the slab during casting can be suppressed. However, in the case of hot rolling a slab in which surface cracks caused by Cu are suppressed in this way, processing (rolling) is performed in a temperature range where Cu is remelted.
Therefore, the relationship between the rolling temperature and the occurrence of surface flaws on the steel sheet after rolling was also examined in a hot rolling mill for cast slabs, since cracks might be generated even when the steel sheet was subjected to heat treatment. As a result, as shown in FIG. 3, the slab surface temperature at the entrance side of the hot rolling mill was 1050 ° C.
It was confirmed that the occurrence of surface cracks could be suppressed stably in the following. However, if this temperature is too low, it becomes difficult to hot roll the slab at an appropriate temperature. Considering these facts, it is not preferable to set the lower limit of the slab temperature to about 800 ° C. or less. Hereinafter, the present invention will be described together with examples of the embodiment.

[0014]

EXAMPLE In this example, C was obtained by scouring in a converter.
The molten steel containing u: 0.2% and Sn: 0.05% is continuously cast by a twin belt type continuous casting machine (curved type) to have a thickness of 5%.
This is a case where a thin slab slab of 0 to 75 mm is manufactured, and the thin slab slab is hot-finished and rolled by a hot-finish rolling mill in a continuous casting inline to produce a steel sheet having a thickness of 1.5 mm. .

FIG. 4 is an explanatory view showing an outline of the arrangement of the apparatus in this embodiment. In the figure, 1 is a molten steel pot, 2
Is a molten steel, 3 is a tundish, 4 is an immersion nozzle, 5 is a mold, a pair of belts 6 and 7 having an endless shape and having a cooling structure, and endlessly moving in contact with inner surfaces of both ends of the pair of belts. It is constituted by a pair of moving blocks 8 and 9 having a cooling structure. 10 is a thin slab slab obtained by cooling the molten steel 2 with the mold 5, 11 is a support roll for curving and supporting the thin slab slab, and 12 is a temperature for measuring the temperature at which the thin slab slab starts to bend. It is a temperature measuring device. Reference numeral 13 denotes a heat retaining furnace, 14 denotes an in-line hot finishing rolling mill, 15 denotes a steel sheet obtained by hot rolling, and 16 denotes a thermometer for measuring the temperature of the thin slab slab at the hot rolling mill entry side. ,
Reference numeral 17 denotes a transport roll.

The molten steel is poured into the mold of the continuous casting machine having the above-described structure, and the molten steel is cooled and solidified to have a thickness of 50 to 7 mm.
A 5 mm thin slab slab was cast, and the thin slab slab was hot rolled by a continuous casting in-line hot finishing rolling mill to produce a 1.5 mm thick steel sheet. FIG. 5 shows a change in surface temperature in each step of the cast slab coming out of the mold in this embodiment, together with the case of the conventional example (the example of FIG. 6).

The casting conditions and rolling conditions in this embodiment are as follows. "Casting conditions" Casting steel type: Low carbon steel and the composition of the components are shown in Table 1. Thin slab slab size: thickness 50-75mm, width 1300mm Casting speed: 5m / min Basic casting radius: 10m Curving support starting point: 3500mm position from meniscus "Rolling conditions" Steel plate (product) size: thickness 1.5mm, width 1300mm

In this embodiment of the present invention, when continuously casting a thin slab slab under the above-mentioned casting conditions, the surface temperature of the slab from the mold at the start of curved support of the thin slab slab is set to 1050.
C. or lower, and the surface temperature of the thin slab slab at the entry side of the hot finish rolling mill was set to 1050 ° C. or lower to perform hot finish rolling to produce a steel sheet. The results are shown in Table 2 together with the results of the comparative example and the conventional example outside the scope of the present invention.

[0019]

[Table 1]

[0020]

[Table 2]

As is evident from Table 2, in Examples 1 and 2, which are the scope of the present invention, both the thin slab slab obtained by casting and the steel sheet obtained by hot finish rolling were used.
No surface cracks affecting the quality were found. However, in Example 3, the temperature of the bending support starting point is set to 1
A thin slab slab having no surface cracks was obtained by casting at a temperature of 050 ° C. or lower, and this was obtained by hot rolling the thin slab slab having a hot finish rolling mill at a surface temperature of more than 1050 ° C. Significant cracking that deteriorated the quality was observed in the obtained steel sheet. (Even a thin slab without surface cracks was cracked into a steel sheet obtained by rolling at a temperature higher than 1050 ° C. on the entry side of the hot finishing rolling mill. There is occurrence.)

Further, in Example 4, the surface temperature of the thin slab slab on the side to enter the hot finishing rolling mill was directly cast by setting the temperature at the starting point of the curved support to more than 1050 ° C. and casting the thin slab slab having a surface crack. Hot-rolling at a temperature of 1050 ° C. or lower, the resulting steel sheet was found to have remarkable cracks that deteriorated the quality. Even if the surface temperature on the side is rolled at 1050 ° C. or lower, the steel sheet obtained has cracks.) Further, in Example 5, the surface temperature at the hot finish rolling mill entry side was used as it is with the thin slab slab having a surface crack obtained by casting at a temperature of the bending support starting point of more than 1050 ° C. To 1050
And ℃ than To and hot finish rolling, but in the resulting steel sheet, it will be appreciated that significant cracking to lower the quality was observed.

[0023] Then, in the conventional example 6, a thick slab cast slab, the temperature of the curved support starting point cast in the 1050 ° C. greater than the slab slab with surface cracks as it rough hot rolling machine, the hot finish is obtained by rolled to form a steel plate rolling mill either the temperature of each hot rolling mill entry side is also obtained by the 1050 ° C. ultra <br/>, the resulting steel sheet, cracks were observed . Example 7 shows a case where a thin slab slab without cracks was produced by continuous casting, and re-heating was performed in a separate line in a heating furnace and finish rolling was performed. When rolling was performed at a temperature of not more than ℃, no crack generation was observed.

Example 8 shows a case in which a thin slab slab without cracks was produced by continuous casting, re-heated in a separate line in a heating furnace and finish-rolled. When the temperature was raised to more than 1050 ° C., the occurrence of cracks was observed. Example 9 is a case in which a thin slab slab having a crack is produced by continuous casting, and re-heated in a separate line in a heating furnace and finish-rolled. Even when rolling was performed at 1050 ° C. or less, cracking was observed.

Example 10 shows a case where a thin slab slab having a crack was produced by continuous casting, and was reheated in a separate heating line in a heating furnace and finish-rolled. When the temperature was raised to more than 1050 ° C., the occurrence of cracks was observed. In the case of a slab cast piece having a thickness of 75 mm or more, it is difficult to obtain a steel sheet having a thickness of 1.5 mm level by hot finish rolling without rough rolling.

As described above, when a thin slab slab having a thickness of 75 mm or less is cast from a steel containing Cu and Sn with a curved or vertical bending continuous casting machine, the thin slab slab having a curved support starting point is used. By setting the temperature to 1050 ° C. or lower, a thin slab cast having good quality without cracking can be stably obtained. When the thin slab slab without cracking obtained in this way is hot-finished and rolled to produce a steel sheet having a thickness of up to 1.5 mm, the thin slab cast on the entry side of the hot finishing rolling mill is required. By setting the temperature of the piece to 1050 ° C. or less, a steel sheet of good quality without cracking can be stably obtained. In the above embodiment, the present invention is employed in the continuous casting in-line hot finish rolling process. However, the present invention is also employed when the continuous casting and hot finish rolling of thin slab slabs are independently performed. Can be.

[0027]

According to the present invention, the content of Cu is set to 0.05 to
When continuously casting thin slab slabs containing Cu and Sn containing 75% or less and containing 0.5% and 0.05% of Sn and having a thickness of 75% or less, and directly hot finishing rolling without rolling during roughing,
The generation of surface flaws in the obtained product can be suppressed inexpensively and efficiently, and a Cu-containing thin slab slab and a steel sheet of good quality can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a solidification structure of a crack-producing slab.

FIG. 2 is an explanatory diagram showing a relationship between a slab surface temperature at a bending support start point and occurrence of a slab crack.

FIG. 3 is an explanatory diagram showing the relationship between the slab temperature and the occurrence of cracks in a steel sheet on the side where a finishing rolling mill enters.

FIG. 4 is a schematic side sectional view showing an example of equipment arrangement in a continuous casting and in-line hot finish rolling process in an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a change with time of a slab surface temperature in a continuous casting and an in-line hot finish rolling process in an example of the present invention.

FIG. 6 is a schematic side sectional explanatory view showing an example of equipment arrangement in a conventional continuous casting and in-line hot rolling process.

[Explanation of symbols]

 1: Molten steel pot 2: Molten steel 3: Tundish 4: Dipping nozzle 5: Mold 6, 7: Belt 8 (9): Moving short side 10: Thin slab cast piece 11: Support roll 12: Temperature measuring device 13: Heat retention Furnace 14: Hot finishing mill 15: Steel plate 16: Temperature measuring device

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-162943 (JP, A) JP-A-6-31393 (JP, A) JP-A-5-185185 (JP, A) JP-A-6-185185 292949 (JP, A) JP-A-7-100593 (JP, A) JP-A-6-328211 (JP, A) JP-A-7-251248 (JP, A) JP-A-7-116703 (JP, A) JP-A-7-246402 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 1/00-11/00 B22D 11/00-11/12 C22C 38/00-38 / 16

Claims (2)

(57) [Claims] 1. Cu: 0.05-0.5%, Sn: 0.
When casting a thin slab of Cu, Sn-containing steel having a thickness of 75 mm or less containing 0.05% or less by a continuous casting method,
When the cast slab is curvedly supported and unloaded under the mold, the slab surface temperature at the starting point of the curved support is set to 10 °.
A method for producing a thin slab cast slab containing Cu and Sn, wherein the slab cast is controlled to 50 ° C. or lower to suppress the occurrence of surface flaws caused by Cu and Sn. 2. When the thin slab slab obtained according to claim 1 is subjected to hot finish rolling to produce a steel sheet, the surface temperature of the slab at the entry side of the finishing rolling mill exceeds 800 ° C.
Is controlled to 50 ° C. or less, Cu, Cu, characterized by suppressing the occurrence of the steel sheet surface flaws caused by Sn, the manufacturing method of the Sn-containing steel sheet.