JPH06246406A - Method for adjusting overheating degree of molten steel in continuous casting mold - Google Patents

Abstract

PURPOSE:To drastically reduce the unevenness in overheating degree of the molten steel in a mold in continuous casting and to stabilize the quality of a steel slab. CONSTITUTION:In a method for holding the molten steel overheating degree DELTAT mold on the molten steel surface in the mold in the continuous casting to the constant, the molten steel overheating degree DELTAT mold on the molten steel surface in the mold is estimated by the following equation and the estimated molten steel overheating degree DELTAT mold on the molten steel surface in the mold and the preset molten steel overheating degree are compared and by changing the powder brand and automatically changing nozzle dipping depth, the molten steel overheating degree DELTAT mold in the mold in the continuous casting is adjusted. DELTAT mold=A(DELTATt)+B(Vc)+C(EMS)+D(Ph)+E(Nd), Wherein, A-E: coefficients obtd. from regression equation, DELTATt: the molten steel overheating degree in the tundish ( deg.C), Vc: casting velocity (mm/min), EMS: intensity of electromagnetic stirring (A), Ph: calorific heat of exothermic powder (kcal), Nd: nozzle dipping depth (mm).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the superheat degree of molten steel in a continuous casting mold in a continuous casting of steel so as to keep it constant.

[0002]

2. Description of the Related Art Continuous casting of steel is carried out by injecting molten steel from a tundish into a mold having a predetermined cross-sectional shape and dimensions and continuously withdrawing it as a slab from below the mold. In continuous casting of such steel, powder is supplied to the surface of the molten steel in the mold, the powder forms a powder layer, a sintered layer and a molten layer by the heat of the molten steel, and the melted powder and the wall surface in the mold. It flows between the surfaces of the slab and plays a role as a lubricant, and also prevents the molten steel from being oxidized. In continuous casting of the above-mentioned steel, it is important to keep the casting temperature constant in an appropriate region in order to maintain high quality of the slab. Originally, the casting temperature should be the superheat degree ΔTmold of the molten steel on the molten metal surface in the mold (molten steel temperature in the mold-liquidus temperature), but it is impossible to measure the temperature of this part, so the conventional temperature The superheat degree ΔTmold of the molten steel in the mold is estimated by using the superheat degree ΔTt (molten steel temperature in the tundish-liquidus temperature) of the molten steel in the dish.

In the above continuous casting, in order to keep the degree of superheat ΔTmold of the molten steel in the mold constant, the degree of superheat ΔTt of the molten steel in the tundish is controlled to the secondary refining end temperature, and in order to alleviate the variation, the immersion nozzle is used. By changing the depth, measures are taken to keep the superheat degree ΔTmold of the molten steel on the molten metal surface in the mold constant. In the above continuous casting, as shown in FIG. 2, when the superheat degree ΔTmold (° C.) of the molten steel in the mold is low, nolokami defects and mold inner skin tension easily occur, and the superheat degree ΔT of the molten steel in the mold ΔT
When the mold is high, the frequency of breakout due to the remelting of the solidified shell is high, so the superheat degree ΔTmold of the molten steel in the mold has an appropriate control region.

As a stable operation method in the above continuous casting, the inflow condition of powder into the mold is measured, and the powder condition in the mold, the molten metal surface position measurement and the powder consumption amount are grasped. A method of controlling the inflow situation of the powder by selecting the powder and changing the input amount, the input time and the operating condition to prevent surface flaws and breakout (Japanese Patent Laid-Open No. Sho 5
7-202952 gazette), the molten steel temperature in the master ladle at the time of carrying out the molten steel treatment process of the previous process is measured, and the molten steel temperature in the master ladle at the start of the master ladle injection is measured from the measured value and the elapsed time until the start of pouring Calculate the temperature of the molten steel in the master pot during the injection of the master pot and the temperature of the molten steel in the master pot at the start of the injection of the master pot, and calculate the elapsed time from the start of casting into the tundish and this tundish. The molten steel temperature in the tundish is calculated from the constant based on the type of the molten steel and the molten steel temperature in the master pot during the injection, and the molten steel temperature in the tundish is measured at least once per charge. The molten steel temperature in the master pot and the molten steel temperature in the tundish are modified, and the molten steel temperature in the tundish or the value of the molten steel temperature in the master pot during injection and the molten steel temperature in the tundish and the tundish start from Seeking molten steel temperature of the mold in the meniscus portion from an elapsed time, a method of secondary cooling control this casting temperature data as the initial value of the slab temperature (JP 59-15
No. 6559), molten steel superheat degree in tundish ΔTt
However, a method of pouring molten metal into a mold under the condition of 20 ° C ≤ ΔTt ≤ 100 ° C and performing a predetermined forging process on the portion before the solidification of the molten steel inside the cast piece drawn from the mold is completed (special (Kaihei 2-155550), the thermal condition of the refractory in the tundish is quantified from the molten steel passing amount of the tundish, and the temperature of the molten steel from the time of tapping to the tundish is taken into consideration. Method of estimating the amount of drop and adjusting the molten steel temperature during tapping to an appropriate range (Japanese Patent Laid-Open No. 4-28)
Many proposals have been made.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent No. 2952 is intended to prevent surface flaws and breakouts due to defective inflow of powder between the mold and the slab, and do not make the superheat degree ΔTmold of the molten steel in the mold constant. Further, the method disclosed in Japanese Patent Laid-Open No. 59-156559 relates to the setting of the pouring temperature which is the basis of the secondary cooling control using the process computer, and does not make the superheat degree ΔTmold of the molten steel in the mold constant. Absent. Further, the method disclosed in Japanese Patent Application Laid-Open No. 2-155550 reduces the center segregation of cast slabs and reduces inclusions, and the degree of superheat ΔTt of molten steel in a tundish is 20.
If the mold is poured under the condition of satisfying the condition of ° C ≤ ΔTt ≤ 100 ° C, the degree of superheat ΔTmold of the molten steel in the mold cannot be made constant. Furthermore, the method disclosed in Japanese Unexamined Patent Publication No. 4-28467 is intended to reduce the variation due to the charge of the molten steel temperature in the tundish, and it is not possible to make the superheat degree ΔTmold of the molten steel in the mold constant.

An object of the present invention is to provide a method for adjusting the degree of superheat of molten steel in a mold in continuous casting, which can keep the degree of superheat ΔTmold of the molten steel in the mold in continuous casting.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to achieve the above object. As a result, as factors affecting the superheat degree ΔTmold of the molten steel in the mold, the superheat degree ΔTt of the molten steel in the tundish, the casting speed Vc, the electromagnetic stirring strength EMS in the mold, the powder brand, and the nozzle immersion depth were considered. Therefore, regarding these five factors, the actual casting conditions and the degree of superheat of molten steel in the mold ΔTmold
According to the regression equation, the superheat degree ΔTmold of the molten steel in the mold that cannot be measured online during the operation is estimated, and based on the estimated superheat degree ΔTmold of the molten steel in the mold, if the powder brand is changed and the nozzle immersion depth is changed, It was found that the superheat degree ΔTmold of the molten steel in the mold can be kept substantially constant, and the present invention was reached.

That is, according to the present invention, in the method of maintaining the molten steel superheat degree ΔT mold on the molten metal surface in the mold in continuous casting constant, the molten steel superheat degree ΔT on the molten metal surface in the mold is
Mold is estimated by the following formula, and the estimated molten steel superheat degree ΔTmold on the molten metal surface in the mold is compared with a preset molten steel superheat degree. If the molten steel superheat degree ΔTmold is out of an appropriate value, the powder brand is changed and the nozzle immersion depth is changed. This is a method for adjusting the degree of superheat of molten steel in a continuous casting mold, which is characterized by automatic change. ΔTmold = A (ΔTt) + B (Vc) + C (EM
S) + D (Ph) + E (Nd) where A to E are coefficients obtained by the regression equation, ΔTt: superheated degree of molten steel in tundish (° C) Vc: casting speed (mm / min) EMS: electromagnetic stirring strength (A) Ph: heating value of heating powder (kcal) Nd: nozzle immersion depth (mm)

[0009]

In the present invention, the molten steel superheat degree ΔTmold at the molten metal in-mold surface is estimated by the above formula, the estimated molten steel superheat degree ΔTmold at the molten metal surface in the mold is compared with the preset molten steel superheat degree, and the molten steel superheat degree ΔTmold is appropriate. If the value deviates, the powder brand is changed and the nozzle immersion depth is automatically changed. Therefore, the molten steel superheat degree ΔTm on the molten metal surface in the mold
It is possible to maintain the old value at an appropriate value, and the variation of the molten steel superheat degree ΔTmold on the molten metal surface in the conventional mold is about 40.
%, And the quality of the cast piece can be stabilized accordingly. The coefficients A to E in the equation for estimating the molten steel superheat ΔTmold on the molten metal surface in the mold differ depending on the individual plant, but may be estimated by obtaining each coefficient by a regression equation in each plant.

In the present invention, among the factors that affect the molten steel superheat degree ΔTmold on the molten metal surface in the mold, the powder brand and the nozzle immersion depth are automatically changed, and the powder brand and the nozzle immersion depth are changed. This is because such effects as the superheated degree of molten steel in the tundish, casting speed, and electromagnetic stirring strength do not have a great influence on the operation directly and can be changed, and the superheated degree of molten steel ΔTmold on the molten metal surface in the mold can be controlled.

[0011]

Example No. 25t capacity with 1-4 strands
In the case of supplying molten steel into the mold from the tundish and continuously casting, the molten steel superheat ΔTmold at the molten metal inside the mold is estimated using the following estimation formula of the molten steel superheat ΔTmold at the molten metal inside the mold obtained by the regression equation. When the molten steel superheat degree ΔTmold on the molten metal surface in the mold was out of the appropriate value, the powder brand was changed and the nozzle immersion depth was automatically changed to perform continuous casting. As a result, the variation of the molten steel superheat degree ΔTmold on the molten metal surface in the mold is shown in FIG.
As shown in, the reduction was about 40% compared to before improvement. ΔTmold = 0.79 (ΔTt) +0.046 (V
c) +0.005 (EMS) +0.074 (Ph)-
0.019 (Nd) However, ΔTt: superheated degree of molten steel in tundish (° C) Vc: pouring speed (mm / min) EMS: electromagnetic stirring strength (A) Ph: heat generation powder calorific value (kcal) Nd: nozzle depth (Mm)

[0012]

As described above, according to the method of the present invention, it is possible to greatly reduce the variation in the molten steel superheat degree ΔTmold in the mold during continuous casting, and to stabilize the quality of the cast piece.

[Brief description of drawings]

FIG. 1 is a graph showing variations in molten steel superheat degree ΔTmold on a molten metal surface in a mold before and after improvement in an example.

FIG. 2 is a graph showing a relationship between a molten steel superheat degree ΔTmold on a molten metal surface in a mold, a slag defect rate, and a breakout frequency.

Claims (1)

[Claims] 1. A method of keeping a molten steel superheat degree ΔTmold on a molten metal surface in a mold in continuous casting constant,
The molten steel superheat degree ΔTmold on the molten metal surface in the mold was estimated by the following equation, and the estimated molten steel superheat degree Δ on the molten metal surface in the mold Δ
A method for adjusting the degree of superheat of molten steel in a continuous casting mold, which comprises comparing Tmold with a preset degree of superheat of molten steel, and automatically changing the powder brand and the immersion depth of the nozzle. ΔTmold = A (ΔTt) + B (Vc) + C (EM
S) + D (Ph) + E (Nd) where A to E are coefficients obtained by the regression equation, ΔTt: superheated degree of molten steel in tundish (° C) Vc: casting speed (mm / min) EMS: electromagnetic stirring strength (A) Ph: heating value of heating powder (kcal) Nd: nozzle immersion depth (mm)