JPH07223049A - Continuous casting method - Google Patents

Abstract

PURPOSE:To obtain a cast slab, in which the recessed part and crack sensitivity are released and the defect is not developed by regulating the relation between carbon content and S content, in the case of continuously casting a medium carbon steel. CONSTITUTION:At the time of continuously casting the carbon steel or the low alloy steel containing at least 0.06-0.20wt.% C and 0.002-0.060wt.% S, the C concn. and the S concn. are adjusted by combining so as to satisfy the following condition. That is, when C<0.12wt.%, 0.12-0.15wt.% and >0.15wt.%, S is made to be >=0.017wt.%, <=0.015wt.% and <=0.037wt.%, respectively. By this method, the cast slab having stable quality can be cast and the product yield is high and the product can be supplied at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing pit dents or slab vertical cracks generated in continuous casting of iron-based materials such as carbon steel and low alloy steel.

[0002]

2. Description of the Related Art In continuous casting of steel, it is general that molten steel is continuously poured into a water-cooled mold and the casting amount is controlled to cast at a predetermined drawing speed.

When performing continuous casting of steel, powder (having CaO and SiO ₂ as main components, Al ₂ O ₃ and Na ₂₎ is placed in a mold.
O, etc.) is added to form a molten state, and the molten state is caused to flow between the mold and the slab for lubrication.

Since molten steel needs to be solidified in the mold, it is also necessary to properly maintain heat removal from the mold as a function of powder.

Therefore, when powder is used, it is generally known that forced vibration of the mold is performed in the casting direction to achieve uniform inflow of the lubricant.

The uniform inflow of powder is necessary in order to uniformly grow a solidified shell.
Since 06 to 0.20 wt% C steel transforms from the δ phase to the γ phase during and after solidification, the solidified shell is likely to be deformed due to the difference in the lattice structure. Occurrence of not only the quality defect but also the operation failure may be accompanied by the one-sided crack. Steel types with this carbon content are called medium carbon steel or hypoperitectic solidified steel.

Conventionally, in order to solve such problems, it has been a common practice to improve the powder, aiming at uniform inflow and slow cooling of mold heat removal.

[0008] As a method of improving the surface defects of the slab with powder, the Iron and Steel Institute of Japan "Materials and Processes"
Vol. 4, No. 4 (1991) P1256-125
7 and similarly P1284 can be exemplified.

[0009] This disclosure reports on prevention of defects in medium carbon steel in which cracks and dents are particularly problematic, and shows that slow cooling with powder is effective.

However, the disclosure merely shows the characteristics of medium carbon steel and the effect of slowly cooling the powder, and does not suggest the importance of the combination of casting components in terms of eradicating casting defects. , Only one aspect of manufacturing technology for manufacturing on an industrial scale.

[0011]

SUMMARY OF THE INVENTION The object of the present invention is to mainly influence the concentration of C and S mainly in the relationship of components that can be easily cast even in the case of steel types such as medium carbon steel which are likely to be accompanied by defects. It is to provide a manufacturing method that can realize the concrete operational index on an industrial scale.

[0012]

The inventors of the present invention have noticed that the allowable range for the steel composition is defined as is clear from the JIS standard, and even a slight allowable range of the medium carbon steel composition is defective. It was found that it had a great influence on the occurrence, and the following conclusions were obtained through repeated experimental studies on the solution of the casting defects of medium carbon steel. That is, the gist of the present invention is

In continuous casting of carbon steel or low alloy steel containing at least 0.06 to 0.20% by weight of C and 0.002 to 0.060% by weight of S, the following conditions are satisfied. A continuous casting method for steel, characterized in that the C concentration and the S concentration are combined and adjusted as described above.

When C <0.12% by weight, S ≧ 0.017% by weight 0.12 ≦ C ≦ 0.15% by weight, S ≦ 0.015% by weight C> 0.15% by weight, S ≦ 0.037% by weight

The following conditions are satisfied in continuous casting of carbon steel or low alloy steel containing at least 0.06 to 0.20% by weight of C and 0.002 to 0.060% by weight of S. A continuous casting method for steel, characterized in that the combination and adjustment are performed so as to satisfy the C concentration and the S concentration.

[0016]

[Equation 3] S ≧ 7 [wt% C] ² −0.89 [wt% C]
+0.039

Or

[0018]

[Equation 4] S ≦ 3.89 [wt% C] ² −0.64 [wt% C] +0.031

[0019]

[0020]

The details and effects of the present invention will be described.

The present invention has a carbon content of 0.06 to 0.20.
The reason for limiting the content to molten steel containing 0.002 to 0.060% by weight of S and 0.002 to 0.060% by weight is that the carbon region causes dents and vertical cracks in the slab as described above, and impairs the quality of the slab. This is because the influence is strongest and that the present application is mainly to improve the component region. Of course, it is expected that it will be sufficiently established even if it deviates from the carbon region.

Next, the S concentration is based on the fact that it is the element that exerts the greatest influence in the carbon concentration region and that the effect has been confirmed by the present inventors. It can be expected that the amount of S also holds in a region exceeding this range, like the carbon concentration.

Therefore, in the present invention, the carbon and S concentration regions are limited to more clearly show the effect of the present invention.

When C <0.12% by weight, S ≧ 0.0
The reason for setting the content to 17% by weight was empirically found that, in the carbon region of less than 0.12% by weight, when the amount of S decreases, the vertical cracks in the dents of the cast piece increase.

On the other hand, when C ≧ 0.12% by weight, C <0.
Contrary to the region of 12% by weight, it was found that when the S concentration was high, the number of dents and vertical cracks increased, and it was found that the carbon content was different.

That is, when 0.12 ≦ C ≦ 0.15% by weight, S ≦ 0.015% by weight, and when C> 0.15% by weight, S ≦
A problem occurred when the condition of 0.037% by weight was not satisfied.

Next, in the above classification method, since the relationship between the C amount and the S amount is complicated, the relation between the C amount and the S amount is presented as a mathematical expression as an index that is easier to handle industrially. Shows the relationship of concentration

[0028]

[Equation 5] S ≧ 7 [wt% C] ² −0.89 [wt% C]
+0.039

Or

[0030]

[Equation 6] S ≦ 3.89 [wt% C] ² −0.64 [wt% C] +0.031

The following relationship was sought.

By using the formula relating to the above concentration, it was possible to easily adjust the components in the melting step and completely prevent slab dents and vertical cracks.

Needless to say, it is possible to carry out the operation a little beyond the range of the concentration combination, but this range is desirable because the probability of occurrence of slab dents and vertical cracks increases.

More preferably, in the steel type requiring 0.10% by weight or less of carbon, the carbon content should be as low as possible within the allowable range, and in the specification of 0.10% by weight or more, the melting point should be as high as possible. It is effective to manufacture and minimize the influence of δ / γ transformation.

At this time, it goes without saying that the addition amount of S tends to be higher or lower.

Generally, the amount of S can be controlled in the range of about 0.001 to 0.002% by weight, so that it can be industrially sufficiently manufactured.

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing the relationship between the occurrence rate of cast slab defects (depressions and vertical cracks) and the amounts of carbon and S which are molten steel components. The plots in the figure show the conditions performed in the examples described below.

FIG. 2 shows carbon, S, which prevents the occurrence of slab defects.
It is explanatory drawing which shows the limit area | region of density.

From FIG. 1, it can be seen that the slab dents and cracks have carbon content and S
It can be seen that there is a close relationship between the amounts, and the S concentration that can be prevented differs depending on the amount of carbon.

Therefore, it can be seen that by controlling the S content in accordance with the carbon content, it is possible to manufacture a slab without defects.

From FIG. 2, it is possible to suppress the generation of vertical cracks by controlling the S content when the carbon content is determined from the slab defect prevention limit area divided by carbon and S content. I understand.

[0043]

EXAMPLES The present invention will be described below with reference to specific examples.

The main components of the carbon steel used for casting are as shown in Table 1.

The casting conditions are shown below.

In the embodiment, the slab size is 162 mm × 162.
mm continuous casting machine.

The casting speed used was 1.6 m / min.
The range is 3.2 m / min.

The degree of superheat of molten steel is 25 to 25 in the tundish.
It was carried out in the range of 40 ° C.

The powder used for casting has CaO of 41-41.
42% by weight, SiO ₂ 31 to 32% by weight, Al ₂ O _{3 3} to 3.2% by weight, Na ₂ O 10.5 to 11.2% by weight, ZrO ₂ 3.5% by weight and other unavoidable It is a powder made of impurities.

The physical properties of the powder are basic (CaO / Si
O ₂ weight ratio) is 1.32, viscosity is 0.7 poise,
The solidification temperature is 1210 ° C.

FIG. 1 is an explanatory diagram in which an example is plotted in relation to the occurrence of a cast slab defect and the relationship between the carbon content and the S content as molten steel components. Further, the symbols in the figure are indicated by the symbol ◯ when the slab dents and cracks did not occur, and by the symbol ● when the slab dents and cracks occurred.

From FIG. 1, the slab dents and cracks were found to have carbon content and S
It can be seen that there is a close relationship between the amounts, and the S concentration that can prevent dents and cracks differs depending on the amount of carbon.

That is, when the carbon content is 0.12% by weight or less, dents and cracks occur in the low S content area, and conversely, in the carbon content of 0.12% by weight or more, the high S content area is dented. You can see that it breaks easily.

Therefore, it is clear that the amount of S to be satisfied differs depending on the amount of carbon.

FIG. 2 shows carbon, S, which prevents the occurrence of slab defects.
The concentration limit region is shown, and the example is illustrated in the same plot as in FIG.

It can be seen from FIG. 2 that the slab defect occurrence rate is classified according to the combination of carbon and S concentration, and the defect occurrence rate can be suppressed by defining the relationship between the carbon content and the S content.

[0057]

[Table 1]

[0058]

As described above, in order to prevent slab dents and vertical cracks that occur during the casting of carbon steel or alloy steel in the medium carbon region, the relationship between the carbon content and S content of the steel is specified. It was shown concretely that a slab with excellent surface quality can be manufactured by reducing the dent and crack susceptibility.

Therefore, according to the method of the present invention, a slab of stable quality can be cast, the product yield is high, and a cheaper product can be supplied, which can be said to be an industrially extremely useful invention.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the occurrence of cast slab defects and the amounts of carbon and S that are molten steel components.

FIG. 2 is an explanatory view of a limit region showing a relationship between carbon in molten steel and S that can prevent the occurrence of a cast slab defect.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masashi Yoshida 12 Nakamachi, Muroran City Muroran Works, Muroran Works (72) Inventor Takeyuki Sekiya 12 Nakamachi, Muroran-shi Muroran Shin Nippon Steel Co., Ltd. Inside the steelworks

Claims (2)

[Claims] 1. When continuously casting carbon steel or low alloy steel containing at least 0.06 to 0.20% by weight of C and 0.002 to 0.060% by weight of S, the following conditions are required: A continuous casting method for steel, characterized in that the C concentration and the S concentration are combined and adjusted so as to satisfy the above condition. C <0.12 wt%, S ≧ 0.017 wt% 0.12 ≦ C ≦ 0.15 wt%, S ≦ 0.015 wt% C> 0.15 wt%, S ≦ 0.037 weight% 2. The following conditions are required for continuous casting of carbon steel or low alloy steel containing at least 0.06 to 0.20% by weight of C and 0.002 to 0.060% by weight of S. A continuous casting method for steel, which is characterized by combining and adjusting so as to satisfy the C concentration and the S concentration. [Equation 1] S ≧ 7 [wt% C] ² −0.89 [wt% C]
+0.039 or ## EQU2 ## S ≦ 3.89 [wt% C] ² -0.64 [wt% C] +0.031