JP2002153949A - Method for continuously casting different kinds of steels - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for continuously casting different kinds of steels with which the yield of molten steel can be improve without charging a separating material into a mold. SOLUTION: A threshold value is arranged in the composition difference between the different kinds of steels, and the separating material is charged between the first and the second molten steels only in the case of exceeding the above threshold value in the composition difference between the first molten steel and the second molten steel differing from mutually the kinds of steels poured into the mold cast mutually before and after times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for continuously casting different types of steel.

[0002]

2. Description of the Related Art When converting from continuous casting of a first molten steel to continuous casting of a second molten steel of a different steel type, a second molten steel of a different steel type is continuously cast into a mold by any conventional method without any means. In the case of injecting by casting, mixed slabs of different steel types are formed at the boundary between the two, and cannot be used for any of the steel types and must be discarded as scrap.
This discarded length reaches 4 to 5 m, which deteriorates the molten steel yield. Therefore, conventionally, as disclosed in, for example, JP-A-51-112431, JP-A-52-30723, and JP-B-57-36059, an isolating material is placed in a mold after the completion of the first molten steel injection. By charging and then injecting the second molten steel, the mixed length of different steel types is reduced. According to this method, for example, in Japanese Patent Publication No. 57-36059, the length of mixing different steel types is reduced to about 50 cm by replacing the tundish and injecting new different steel types.

[0003]

However, from a different point of view, according to the conventional technique, a mixed length of different steel types is inevitably generated even if it is as short as about 50 cm, and the part is discarded. Therefore, there is still room for improvement in the yield of molten steel. In addition, there is a concern that in the continuous casting operation, a step of adding molten material into the mold by interrupting injection of molten steel into the mold is added.

Accordingly, an object of the present invention is to provide a method for continuously casting different types of steel capable of improving molten steel yield without charging a separator into a mold.

[0005]

According to the present invention, a threshold value is provided for the composition difference between different steel types, and the composition difference between the first molten steel and the second molten steel of different steel types injected into a mold immediately before and after is set to the threshold value. A method of continuously casting different types of steel, characterized in that an isolating material is inserted between the first and second molten steels only when the temperature exceeds the limit. The threshold value is preferably determined based on characteristics of a hot-rolled product using a joint portion of a slab as a raw material. This hot-rolled product is preferably an H-section steel.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, when a first molten steel and a second molten steel of different steel types are injected into a mold one after another, a separator is inserted between the first and second molten steels in any case. I was That is, as shown in FIG. 1 (a), it is determined whether or not the first and second molten steels to be injected into the mold one after another are different types of steel. Without casting, the seam (cast slab including the hot water seam) is cut to an appropriate length in the same manner as the non-seam, and processed in a later step to produce a product. On the other hand, in the case of a dissimilar steel type, an isolating material is charged and continuous casting is performed, and the joint portion is cut into, for example, about 50 cm in length to be scrapped.

On the other hand, in the present invention, a threshold value is provided for the composition difference between the different steel types, and the composition difference between the first molten steel and the second molten steel having different steel types, which are injected into the mold successively, exceeds the threshold. Only when is it necessary to insert an isolating material between the first and second molten steels. That is, as shown in FIG. 1 (b), after determining whether or not the first and second molten steels are different types of steel, it is further determined whether or not the composition difference between the two molten steels exceeds a threshold value. Less than)
In the case of (1), continuous casting is carried out without charging an isolating material, and the seam is cut into an appropriate length in the same manner as the non-seam, and processed in a later step to produce a product. On the other hand, if the threshold value is exceeded, a separator is charged and continuous casting is performed, and the joint is cut into pieces of, for example, about 50 cm in length and turned into waste.

[0008] The threshold value is determined by preliminary experiments or the like as an upper limit of a composition difference at which a processed product can be applied as a product when a joint portion of a continuous cast slab of a different steel type is processed in a subsequent process. That is, the components constituting the composition (chemical composition) of molten steel include C, Si, Mn, P, S, Al, Cu, Ni, Mo, Ti,
V, Nb, Ca, REM, etc. Among these, the concentration and concentration distribution of the molten steel composition at the seam portion that becomes the mixed portion of the first and second molten steels were determined from the preliminary experiments and the like. The above components are selected, and a threshold value is determined for the components. When changing the steel type at the time of continuous casting of different steel types, the first
The concentration difference (difference in content) between the molten steel and the second molten steel is obtained, and the magnitude of the difference with the threshold is determined. Then, the length and range of the seam portion where the mixing portion is generated are determined in advance in the combination of the first molten steel and the second molten steel, and the cutting range of the generated seam portion is determined. Estimation of this steel type mixed part is easy, and with the start of injection of the next steel type into the continuous casting mold or tundish, tracking of the continuous cast slab drawn from immediately below the continuous casting mold is performed, and The mixing range can be determined by specifying the steel type mixing portion, specifying the start point of the next steel type injection, and analyzing the components of the continuously cast slab by drill sampling or the like before and after the starting point.

Therefore, according to the present invention, among the joints generated by the continuous casting of different steel types, those having a composition difference between the first and second molten steels equal to or less than the threshold value are considered as the continuous castings of the cut joints. Since the pieces can be turned to a post-process to be commercialized, the amount of debris can be reduced, that is, the molten steel yield can be improved without the need to insert a separator into the mold. Also, since the mixing of the first and second molten steels can be positively allowed,
Even if the tundish is not replaced, the injection of the next molten steel can be started after the injection of the previous molten steel, so that there is no hindrance to the continuous casting operation.

The threshold value depends on the type of post-process for processing the joint portion. As the post-process, hot rolling using a continuous cast slab as a raw material is preferable. Therefore,
In the present invention, for a hot-rolled product using a seam portion formed by continuous casting of different steel types as a material, the upper limit of the composition difference between the different steel types whose characteristics (dimensions and mechanical properties) satisfy the requirements as a product is set. It is preferable to investigate by preliminary experiments and adopt the result as a threshold. In that case, the seam portion in which the composition difference is equal to or less than the threshold value is hot-rolled and commercialized.
Needless to say, the rolled product from the seam portion and the product from the non-seam portion may be products having different required characteristics. Therefore, the hot rolling conditions (heating temperature, rolling temperature, rolling reduction, etc.) of the joint need not be the same as those of the non-seam part.

In the present invention, the hot rolling as a post-process for treating the seam portion may be any of thick plate rolling, thin plate rolling, strip rolling, and the like.
In the case of plate rolling and sheet rolling, the number of types of products that can be applied to hot-rolled products at the joints is relatively small because the chemical composition range is narrow. In the case of H-shaped rolling, the chemical composition is relatively slow, the range of components is wide, and the applicable types (steel types) are the most. For this reason, in the present invention, it is most preferable that the hot-rolled product at the joint is an H-shaped rolled product (H-shaped steel).

That is, it is preferable that the threshold value be determined based on the characteristics of a hot-rolled product using the joint portion of the slab as a raw material, and in particular, the characteristics of an H-shaped steel which is an H-shaped rolled product.

[0013]

EXAMPLES (Comparative Example) In performing continuous casting of different types of steel using molten steel A and molten steel B, conventionally, injection of molten steel A was stopped and molten steel A was used in accordance with the method described in Japanese Patent Publication No. 57-36059. Evacuate the tundish → Charge cold material (form solidified shell) →
Replacement with the tundish for B molten steel, which had been pre-heated and kept on standby → Injection of B molten steel, the generated seams with a length of about 50 cm were scrapped and scrapped.

(Example) Continuous casting of different steel types was performed using molten steel A and molten steel B having compositions shown in Table 1. The composition of molten steel A
490MPa grade A grade steel (no toughness guaranteed), B molten steel is 490MPa grade B grade steel (with toughness guaranteed), JIS
G3106 Product standard (symbol) is A490 for molten steel A, SM for molten steel B
Corresponds to 490B.

According to JIS G3106, the composition range of SM490A and SM490B is as follows.
%, Si: 0.55 mass% or less, Mn: 1.60 mass% or less,
P: 0.035 mass% or less, S: 0.035 mass% or less,
On the other hand, in SM490B, C: 0.18 mass% or less, Si, Mn, P, S
Since it was in the same range as SM490A, it was determined that the mixed portion could be reused even if the steel type was mixed, and the continuous casting operation was performed by the following method.

[0016]

[Table 1]

First, the molten steel A is cast, and when the remaining molten steel in the tundish at the final stage of the injection of the molten steel A has decreased to a depth of 200 mm, the molten steel B, which is the next molten steel, is injected without changing the tundish. That is, the same tundish used for molten steel A was started and continuous casting was continued.
The mixing part component generated in the mixing part is C: 0.18 mass% or less, which satisfies both SM490A and SM490B, and there is no problem with Si and Mn. The cut slab is used as a material for rolling an H-section steel, which is an H-section steel conforming to the above SM490A standard, without causing scrap and without interrupting continuous casting by charging cold material.
A shaped steel product was obtained.

[0018]

According to the present invention, there is an excellent effect that the yield of molten steel can be improved without charging a separator and without replacing a tundish in a continuous casting operation of different steel types. .

[Brief description of the drawings]

FIG. 1 is a comparative chart of the conventional (a) and the present invention (b).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiromi Fujii 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref.

Claims (3)

[Claims] 1. A threshold value is provided for a composition difference between different steel types, and the first and second molten steels are injected only when the composition difference between the first molten steel and the second molten steel having different steel types, which are injected into a mold one after another, exceeds the threshold value. 2
A continuous casting method for different types of steel, characterized by charging a separator between molten steels. 2. The method according to claim 1, wherein the threshold value is determined based on characteristics of a hot-rolled product using a joint portion of the slab as a raw material. 3. The method according to claim 2, wherein the hot-rolled product is an H-beam.