JP2668479B2 - Killed steel ingot method - 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 ingoting killed steel, and more particularly to a method for ingoting a concentrated segregation portion on the steel ingot main body side.

[0002]

2. Description of the Related Art When a killed steel such as an aluminum silicon killed steel is manufactured by a normal ingot making method, a feeder frame is generally provided on the upper part of the mold to keep the upper part of the mold warm. That is, the molten steel injected into the mold is cooled and gradually solidifies over time, but solidification shrinkage and macrosegregation that occur during solidification are phenomena that cannot be avoided, and the shrinkage that has occurred in the steel ingot. The pores and macro-segregation significantly reduce the quality of the product, and depending on the degree, the product cannot be used. Therefore, as a countermeasure against these problems, a feeder frame is provided on the upper part of the mold to delay the solidification to facilitate the replenishment of molten steel to the solidification contraction part, and to concentrate the concentrated segregation part inside the final solidification feeder. A method is being taken to ensure the soundness of the mass itself. However, the thick segregation may reach the steel ingot main body side instead of staying in the feeder.Thus, the thick segregation part is cut off according to the quality requirement of the product, but the quality requirement for steel materials becomes stricter. Nowadays, with the increasing diversification, it is inevitable that the yield is reduced due to the increase of the cut amount of the dense segregation portion.

[0003] In general, in order to solve the above-mentioned problems, a method of improving the heat insulating property of the feeder frame by changing the material of the feeder frame to one having a low thermal conductivity or making the feeder frame thicker has been taken. There is. However, even if the heat insulation of the feeder frame is increased, if the amount of feeder is not secured above a certain amount, the feeder will solidify before the steel ingot due to insufficient heat capacity of the feeder, and as a result, the dense segregation Exists up to the ingot body. In other words, there is an appropriate combination of mold size, overall thermal conductivity and thickness of feeder frame, and amount of feeder (molten steel volume of the feeder). There was no standardized index, and appropriate operating conditions were determined by trial and error based on actual steel ingot tests. On the other hand, Japanese Patent Application Laid-Open No. 55-19451 is known as a proposal.

[0004]

Problems to be Solved by the Invention JP-A-55-1945
No. 1 gazette heats or heats the outer circumference of the mold riser part from the lowermost end of the riser to the height above the wall thickness of the mold when making a large steel ingot having a thickness or equivalent diameter of 400 mm or more. By reducing the segregation of the steel ingot head by reducing the amount of cut off of the head, in addition to the normal riser heat retention or heating of the mold outer surface is required and many manpower is required,
In the case of heating, there is a difficulty in work, such as a large heating device needs to be set at the site. Therefore, it is desired to develop an ingot-making method in which the concentrated segregation portion is limited to the feeder portion only with a normal feeder frame and the cut amount is small.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its gist is to provide a method for forming an ingot of killed steel in which a feeder is provided on the upper part of a mold. When the length H ₂ (m) of the short side of the mold at the lower end of the molten metal is smaller than the height H ₁ (m) from the lower end of the feeder to the bottom of the mold H ₂ ² <4.86 × V / A × l / λ + 0. 273 ··· (1) A method for ingot making of killed steel, wherein ingot making is performed while satisfying the condition (1). Where V: volume of molten steel in the feeder section (m ³ ) A: surface area of the feeder frame in contact with the molten steel (m ² ) l: overall thickness of the feeder frame (m) λ: overall thermal conductivity of the feeder frame (kcal / m · hr · ° C). Note that, as described above,
Less than the height H ₁ from the feeder head portion the lower end to the mold bottom is H ₂ is
The reason for this is to identify the mold,
The present invention is made on the assumption of the following conditions. sand
KazuSatoshi, mold short side length H ₂ until the mold bottom from riser portion lower end
If the height is less than H ₁ , the upper heat removal area of the mold is small.
Therefore, the amount of heat removed from the upper part can be ignored. So
Therefore, in the present invention, the above heat removal amount is ignored and the above (1)
It has been determined that the expression is valid. Therefore, if
When H ₂ is larger than H _1, the upper heat removal area of the mold is large.
So that the upper heat removal can be neglected
However, the capacity of the heat retaining agent is limited, and the above equation (1) is not established.
No.

[0006]

The present inventors have found that the dense segregated portion (check analysis C / ladle analysis C ≧ 1.2) also exists on the ingot main body side because the feeder portion is located ahead of the ingot main body due to lack of feeder. The reason is that solidification occurs, and as a countermeasure, it was thought that the concentrated segregation part could be concentrated in the riser part by setting the condition that the riser part partially melted until the solidification of the steel ingot body was completed. Therefore, in order to ensure that the above conditions were met, heat balance calculation and ingot segregation investigation were carried out based on the ingot forming conditions of the actual steel ingot. In FIG. 3, 1 is a mold, 2 is a feeder frame, (A) is a feeder section, (B)
Indicates the steel ingot main body, H ₁ is the height from the bottom of the feeder frame to the bottom of the mold (m), H ₂ is the length of the short side of the mold at the bottom of the feeder frame (m), V is the molten steel volume of the feeder ( m ³ ). Here, assuming that the time until the ingot body (B) is completely solidified is t ₁ , t
₁ is obtained by the following equation. t ₁ = (H ₂ / 2k) ² ···

On the other hand, if the time until the solidification of the feeder (A) is completed is t ₂ , then t ₂ = CpρV (T _LL -T _SL ) ÷ {A × (λ / l) × ( T _LL −T)}, and if t ₁ <t ₂ , all the dense segregation is contained inside the riser. Where k: solidification coefficient, Cp: specific heat of molten steel (kca
l / kg ・ ° C) ρ: Specific gravity of molten steel (kg / m ³ ), T _LL : Liquidus temperature (° C) T _SL : Solidus temperature (° C), T: Mold temperature (° C) λ: Filler frame Overall thermal conductivity (kcal / m · hr · ° C), l: Overall thickness of feeder frame (m), A: Surface of feeder frame in contact with molten steel (m ² ).

The condition that t ₁ <t ₂ is H ₂ ² <{(4k ² · Cp · ρ · (T _LL −T _SL ))} × V / A × l / λ + a. : From the actual steel ingot test, H ₂ ² <4.86 × V / A × l / λ + 0.273 ... Next, examples of the present invention will be described together with comparative examples.

[0009]

[Example] Using a feeder frame having the composition and thermal conductivity shown in Table 1, the ingot was cast under the casting conditions shown in Table 2 to make an ingot. Table 3 shows the molten steel components.

[0010]

[Table 1]

[0011]

[Table 2]

[0012]

[Table 3]

The size of the mold used is the mold height 230.
0 mm, short side length (upper 900 mm, lower 670 mm,
Steel ingot unit weight is 24.3t, average long side length (upper 2079mm, lower 2021mm, average 2050)
mm). This ingot is slab-rolled and the thickness is 220 mm ×
The slab was 2100 mm wide and 6740 mm long. A drill fir sample (drill diameter = 5% of slab thickness) was collected from a portion corresponding to the steel ingot axis of the slab by a drill, and the carbon (C) content was examined by chemical analysis. The ratio (C / Co) between the analytical value (C) obtained from the Kirimi fir sample and the analytical value (Co) obtained from the sample collected after the ladle refining is completed.
Was determined as a thick segregated portion, and it was investigated whether or not this portion was inside the feeder. The result is shown in FIG.
As shown in FIG. 2, the thick segregated portion is concentrated inside the feeder in the example of the present invention, whereas the thick segregated portion exists outside the feeder in the comparative example.

Thus, gas was cut to remove the thick segregated portion where C / Co ≧ 1.2. Table 2 also shows the final cutting length and yield after gas cutting. In the case of the present invention, the gas cutting was only for the amount of the riser, but in the case of the comparative example, both were also on the steel ingot main body side. Due to the presence of the dense segregation, the gas cut amount was large and the yield was low.

[0015]

As described in detail above, according to the present invention, since the concentrated segregation portion can be reliably stopped in the feeder when the killed steel is ingot, it is possible to reduce the cut amount in the slab. Is. Also, workability is good.

[Brief description of the drawings]

FIG. 1 is a view showing whether or not a thick segregation portion in the present embodiment remains in a feeder.

FIG. 2 is a view showing a relationship between a distance from a steel ingot top and a thick segregated portion in the present embodiment.

FIG. 3 is an explanatory diagram showing symbols used in a mathematical formula for obtaining a time until completion of solidification of a feeder and a steel ingot main body.

[Explanation of symbols]

1 mold 2 feeder frame (A) feeder part (B) steel ingot main body H ₁ height from bottom of feeder frame to bottom of mold H ₂ short side length of feeder at bottom of feeder frame V molten metal volume of feeder part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiro Takagi 5-3 Tokai-cho, Tokai-shi, Aichi Nippon Steel Corporation Nagoya Steel Works (56) Reference JP-A-56-117866 (JP, A) Kai 57-68246 (JP, A)

Claims (1)

(57) [Claims] 1. A structure of killed steel in which a feeder is provided on the upper part of a mold.
When lumping, the length of the short side of the mold at the lower end of the feederH
₂ (M) is the height from the bottom of the riser to the bottom of the moldH
₁ (M) less thanH ₂ ² <4.86 × V / A × 1 / λ + 0.273 (1)
Ingot making method. Where V: volume of molten steel in the feeder section (m³) A: Surface area of feeder frame in contact with molten steel (m²L: Overall thickness of the feeder frame (m) λ: Overall thermal conductivity of the feeder frame (kcal / m · hr · ° C)