JPH06154957A - Continuous casting method for thin cast billet - Google Patents

Abstract

(57) [Summary] [Purpose] The object is to produce a slab that does not crack on the surface of the slab by the twin roll type continuous casting process. [Structure] When a molten steel mainly containing scrap as a melting raw material is rapidly cooled and solidified by a chill roll to produce a thin-walled slab, a rolling force is reduced according to a hot working reduction index CV calculated from the components of the molten steel. Adjust and cast. [Effect] The roll rolling reduction force is reduced according to the hot working reduction index of the cast slab to reduce the stress and eliminate the crack of the cast slab.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a synchronous continuous casting process, particularly a twin roll type casting process, to produce a thin cast piece from a molten metal containing a scrap component in a molten raw material, such as stainless molten steel or molten steel containing iron as a main component. It relates to a direct manufacturing method.

[0002]

2. Description of the Related Art Synchronous continuous casting method is a thin casting having a wall thickness of about 1 to 10 mm which is close to the final shape directly by cooling and solidifying a molten metal (molten metal) in a pool with a cooling roll. It is a method for producing a slab, and therefore it is extremely important to produce a thin slab having a good surface quality.

However, when performing such casting, a playing card element, such as S, contained in the molten metal poured into the molten metal pool.
When n, S, Bi, Zn, Pb, etc. are mixed, they are segregated in the dendrite inter-wood part during solidification cooling, increasing the crack susceptibility and leading to cracking. Until now, a technique for reducing the occurrence of cracks by reducing the impurity elements S and P in molten steel (JP-A-2-
No. 267225) has been proposed.

[0004]

However, if the technique relating to the regulation of the molten steel components of S and P is applied to synchronous continuous casting among these, it is effective in preventing the cracks on the surface of the slab, but for example scrap is melted. SUS304 as raw material
In the case of steel, depending on the type of scrap, Sn, Pb,
Tramp elements such as Bi, S, and Zn were mixed, and it was not possible to prevent cracking.

An object of the present invention is to provide a method for producing an excellent thin-walled slab that does not cause surface cracking of the slab even if it is a molten raw material containing a playing card element.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors have studied in detail the relationship between the molten metal in the pool and the rolling force of the cooling roll. It was confirmed that there are the following important relationships. That is, the molten steel is poured into a molten steel pool portion composed of a pair of cooling rolls rotating in mutually opposite directions and side dams pressed against both end faces of the cooling roll, and is thinned through a gap portion of the cooling roll. In a method of continuously casting a slab, S, Sn, Pb, Zn B contained in the molten steel
When the hot working reduction index CV value specified by i satisfies the following equation (2), the rolling force of the cooling roll is adjusted according to the following equation (1) to perform casting, whereby surface cracking of the slab is achieved. Was able to be greatly improved.

25 kg / cm ≦ P ≦ 300-2 CVkg / cm (1) 0 weight ppm ≦ CV ≦ 100 weight ppm (2) where CV = 0.21 × weight ppm [S] + 0.03 × weight ppm [Sn] + weight ppm [Pb] + weight ppm [Zn]
+ Weight ppm [Bi] Here, for example, weight ppm [S] means a value in which the S component is expressed in weight ppm, and the cooling roll pressing force (pushing force) P
Indicates the rolling force (kg / cm) per unit length of the cooling roll width.

[0008]

According to the present invention, as described above, the cracks generated on the surface of the slab obtained by the continuous casting method are caused by the decrease in the high temperature strength due to the segregation of the Trump element concentrated in the dendrite inter-wood portion. It was made with recognition. That is, the molten steel produced from a scrap material such as SUS304 steel as a raw material has its concentration significantly changed because the surface is plated or the like depending on the location where the raw material was used as a product. When these molten steels are used as they are to produce thin-walled slabs with a twin-roll type casting machine, Sn, Pb,
Since trump elements such as Bi, S, and Zn are accumulated and the hot workability is significantly deteriorated, if an excessive rolling reduction force is applied, as a result, cracks may occur on the surface of the cast slab.

Therefore, in order to eliminate cracking of the cast piece, it is necessary to reduce the playing card element as much as possible and to reduce the stress applied to the cast piece as much as possible. According to the present invention, by clarifying the relationship between the hot working reduction index CV obtained from the Trump element and the stress (roll reduction force) applied to the cooling roll as described above, casting is performed by the roll reduction force according to the index CV. Although it is intended to prevent slab cracking, the relationship between the two is shown in FIG.

The index CV is an index obtained by examining the correlation between the tensile strength and the component by statistical means by performing a greeble test by varying the components of the Trump element. As is clear from FIG. 1, the cooling roll rolling force is 3
When it became larger than 00-2CV (kg / cm), many cracks occurred. Further, when it is less than 25 kg / cm, porosity frequently occurs in the central part of the slab, and the workability of the product sheet after cold rolling remarkably deteriorates. Further, when the index CV is larger than 100 ppm by weight, the effect of preventing cracking is small only by controlling the cooling roll rolling force, and many cracks occur.

[0011]

EXAMPLE A molten steel having the components shown in Tables 1 and 2 has a diameter of 12
A slab having a plate thickness of 2.0 to 4.2 mm was manufactured under the casting conditions shown in Table 3 with a cooling roll having a width of 00 mm, a width of 1340 mm and a width of 800 mm. The rolling force P per cooling roll width unit length is 7
0 to 450 kg / cm, and the CV (ppm by weight) determined from the molten steel component was changed to 5.6 to 87.7 ppm by weight.

The obtained slab was pickled and visually evaluated for cracks. The results are shown in Table 2. The crack is the CV (weight by weight) obtained from S, Sn, Pb, Zn, Bi in the molten steel.
ppm), the rolling force P per unit length of roll width is 2
It was found that no phenomenon occurs at all by controlling 5 kg / cm ≦ P ≦ 300-2 CV (kg / cm). For example, No.
87.7 ppm by weight CV at 6, when the roll reduction force P and 160 kg / cm whereas cracks occurred frequently and 1170cm / m ^2, No. 19 CV 85.8 ppm by weight
By setting the roll rolling force P to 120 kg / cm, there was no cracking.

Further, No. 15-No. No. 17 low carbon aluminum killed steel and No. 17 18 ferritic stainless steels,
No. No. 19 Cu-containing stainless steel, No. The slab of Nb-containing ferritic stainless steel of No. 20 had the same result as the austenitic stainless steel, and no difference was observed regardless of the steel type.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

According to the present invention, as described above, it is possible to obtain a thin cast slab having excellent surface properties, and the yield of cold-rolled sheet is remarkably improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an occurrence distribution of cracks restricted by a hot working reduction index of a molten metal component and a roll rolling force.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeo Fukumoto 3434 Shimada, Hikari City, Yamaguchi Prefecture Shin Nippon Steel Co., Ltd.

Claims (2)

[Claims] 1. Molten steel is poured into a molten steel pool portion composed of a pair of cooling rolls rotating in opposite directions and side dams pressed against both end faces of the cooling roll to form a gap between the cooling rolls. In a method of continuously casting thin cast slabs via S, Sn, Pb, Zn contained in the molten steel
A continuous casting method for a thin-walled slab, characterized in that the rolling force P between the cooling rolls is adjusted according to the amount of Bi. 2. The continuous casting method according to claim 1, wherein when the CV in the molten steel satisfies the following formula (2), the rolling force P of the cooling roll is adjusted based on the following formula (1) for casting. 25 kg / cm ≤ P ≤ 300-2 CV kg / cm (1) where P: rolling force per unit length of the cooling roll width (kg /
cm). 0 weight ppm ≤ CV ≤ 100 weight ppm (2) where CV = 0.21 x weight ppm [S] + 0.03 x weight ppm [Sn] + weight ppm [Pb] + weight ppm [Zn]
+ Weight ppm [Bi] Here, for example, weight ppm [S] means a value in which the S component is expressed in weight ppm.