JPH0421713A - Method for correcting steel tapping temperature with reserving heat quantity in ladle - Google Patents

Abstract

PURPOSE:To execute correction of steel taping temp. with reserving heat quantity in a ladle and to suitably control the steel tapping temp. by applying the correction under consideration of lowering of the temp. with heat dissipation of ladle refractory, based on inner temp. of the ladle refractory and distance from the inner wall of ladle to temp. measuring point. CONSTITUTION:With a temp. sensor 2 embedded into the ladle refractory 1, the temp. in the ladle refractory 1 is measured. Further, by using a thickness meter 3, the distance L from inner wall 1A of the ladle to the temp. measuring point 2A of a temp. sensor 2 is measured or estimated. Based on this measured result, the reserving heat quantity in the ladle refractory 1 is estimated. The steel tapping temp. is corrected under consideration of the lowering of temp. with the heat dissipation of the ladle refractory 1 from this reserving heat quantity. By this method, the steel tapping temp. is controlled to the desired temp. range, and unevenness of the molten steel temp. at the time of arriving to continuous casting process is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for correcting tapping temperature based on the amount of heat stored in a ladle.

(Prior art) Generally, in the steelmaking process, molten steel produced in a converter or electric furnace is transferred to a ladle, and after undergoing secondary refining, bubbling, etc., it is passed through a tandem shoe mold. , slabs are manufactured by continuous casting, and during continuous casting, it is important to control the NtiA temperature to a predetermined temperature. If the ladle molten steel temperature during continuous casting is too high, the surface quality of the slab will deteriorate, the risk of breakout will increase, and center segregation, which is an internal defect in the slab, will worsen. Therefore, the casting speed must be lowered, reducing process capacity. On the other hand, if the temperature of the molten steel in the ladle during continuous casting is too low, the alumina and solidified base metal present in the molten steel will adhere to the immersion nozzle, increasing the risk of clogging the runner of the immersion nozzle. do. Therefore, it is necessary to control the temperature of molten steel in the ladle during pouring within an appropriate range, and for this reason, control of the tapping temperature is very important.

Conventionally, when correcting the molten steel, the liquidus temperature determined by the concentration of added elements in molten steel, the natural temperature drop between the ladle and the tanday 221, the temperature drop during bubbling, the temperature drop due to transportation time, and the The method used was to take into consideration factors such as temperature drop due to steel alloy addition during secondary refining, natural temperature drop during tapping, etc.

However, with this method, the cause of the variation in molten steel temperature between converter tapping and continuous casting was not clear, and the estimation accuracy was low. There are methods to avoid operational troubles by heating the cold molten steel by energizing the upper nozzle, etc., and controlling the temperature to the desired range by cooling the molten steel when it is too high, such as the method of adding coating material in a tundish. A method was adopted to do so.

(Case B to be solved by the invention) The method of heating molten steel requires high equipment costs, and
There was a problem that running costs (refractories and electricity) increased.

In addition, the method of cooling molten steel is difficult because the converter blow-off temperature is high, which increases the cost of refractories and alloys, and there are restrictions on the temperature control range. However, since it is difficult to melt more than a certain amount of coating material, there is a problem that the temperature control range is limited.

Furthermore, methods for estimating the temperature drop of molten steel from the converter to continuous casting and correcting the temperature at the time of tapping the converter are disclosed in, for example, JP-A-62-297411 and JP-A-1-246313.
As shown in the publication, a technique has been proposed that focuses on the amount of heat stored in the ladle refractory and improves the accuracy of estimating the amount of temperature drop in molten steel. As mentioned above, in order to estimate the amount of molten steel temperature drop between converter tapping and continuous casting, it is necessary to accurately grasp the amount of heat stored in the ladle refractory. In the investigation conducted by the present inventors, the proportion of heat loss from the ladle refractory out of the total temperature drop of molten steel from the tip of the converter to continuous casting is determined by the amount of heat stored in the ladle refractory at the time of receiving the wire Although there are variations depending on the type of steel and operating conditions, such as the amount of alloy input and the presence or absence of secondary refining, it has been revealed that it accounts for 20 to 60%.

However, as shown in JP-A No. 62-297411, in the case of a method of measuring the inner wall surface temperature of the ladle prior to tapping the steel from the converter, the inner wall surface temperature of the ladle is measured at the end of continuous casting. The amount of heat stored in the ladle (after tapping in the converter,
It is difficult to quantitatively evaluate the amount of temperature drop in molten steel up to continuous casting, and as a result of the inventors' investigation using actual machine operation,
In order to estimate the amount of molten steel temperature drop due to heat removal to the ladle refractories using this method, it is necessary to measure within 2 minutes of the start of ladle receiving, and it is not possible to correct the converter tapping temperature. This was difficult due to time constraints.

In addition, as shown in JP-A-1-246313, when only the internal temperature of the ladle refractory is measured, the period from converter tapping to continuous casting to removal is approximately 2 to 4 hours during normal operation. Ladle maintenance and converter tapping are repeated, but under these conditions, the ladle refractories are in a thermally unsteady state. In all cases of method J using Ta.

An object of the present invention is to provide a method for correcting tapping temperature based on the amount of heat stored in a ladle refractory, which can solve the problems of these conventional methods.

(Means for Solving the Problems) The gist of the present invention is to measure or estimate the internal temperature of a ladle refractory and the distance of a temperature measurement point from the inner wall of the ladle;
The present invention provides a method for correcting the tapping temperature based on the amount of heat stored in the ladle, which is characterized in that based on the results, correction is made in consideration of the temperature drop due to heat extraction from the ladle refractory.

(Function) As a result of various studies to quantitatively understand the amount of heat storage in the ladle refractories, it was found that the temperature of the ladle refractories was It has been found that it is sufficient to know the temperature of one or more points within the range of 5 to 80III11 from the internal point, that is, the inner wall, and the distance of the temperature measurement point from the inner wall of the refractory.

If the measurement point is less than 5IllII from the inner wall, there will be large noise and quantitative information cannot be obtained, and if it is more than 8゜I, the effect on the temperature drop of molten steel between the converter and the ingot making process will be small. Therefore, the necessary fixed information on the amount of heat storage in the ladle refractories cannot be obtained.

In the unsteady heat conduction according to the present invention, in order to quantitatively evaluate the amount of heat storage in the ladle refractory, not only temperature information but also information from the inner wall of the ladle at the temperature measurement point is required. This was revealed as a result of the research conducted by the present inventors.

Taking the energy balance in the thickness direction (-dimension) of the refractory, (1) When the thermophysical properties of the refractory can be assumed to be constant values regardless of temperature T: Temperature (K) t: Time (s) X : Distance (m) C: Specific heat CJ/ (kg-K)) ρ: Density (kg/n?) λ: Thermal conductivity (W/ (m-K)) (2) Temperature of thermophysical property values of refractory When dependence cannot be ignored, λ=λ (T), c=c (T), ρ=ρ (
T), and in either case, the amount of heat stored in the ladle is
In addition to temperature, a term for distance from the inner wall is required.

As a result of the above, it has been difficult to grasp quantitatively in the past, and
The amount of heat stored in the ladle refractories, which was the main cause of variation in the temperature drop of molten steel in the continuous casting process, can be accurately grasped, and this information can be used in calculations to estimate the transition of molten steel temperature from the converter tapping process to the continuous casting process. By estimating the amount of molten steel temperature drop using a model and presenting an appropriate converter blow-off temperature during converter blowing, it has become possible to control the tapping temperature within the desired temperature range.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention,
FIG. 2 is a sectional view illustrating a sensor for measuring the internal temperature of the ladle refractory according to the present invention.

As shown in FIGS. 1 and 2, the present invention provides a measuring sensor 2 and a thickness gauge 3 to measure ladle refractories 1 during converter blowing.
Information necessary for measuring the internal temperature of the temperature measuring point 2A and the distance from the ladle inner wall 14, as well as predicting the converter blow-off temperature,
That is, ladle information, predicted time schedule information, and planned alloy input amount are collected.

In the example, the inner surface temperature of the ladle and the distance from the inner wall were measured 10 minutes before the converter was stopped.

The results are shown in Table 1. Also, according to measurements from the sub-lance during converter blowing, the amount of alloy input for component adjustment after tapping from the converter and before reaching the continuous casting process is 10.8 k
g/Ton and the times predicted from the continuous casting process and the secondary smelting process are shown in Table 2. In this example, the appropriate converter blow-off temperature was calculated using the system shown in FIG. 1 and was 1693°C based on the condition of 0 or more in which no deposits were observed on the ladle. In addition,
Table 3 shows the calculated values and actual measured values of the molten steel temperature after the converter was blown off in this example.

In FIG. 2, 4 is a terminal box, and 5 is a movable cable.

Table 1 Measurement Results Table 2 Operating Conditions (Unit: Minutes) Table 3 Estimated Temperature Drop Value and Actual Measurement 4M (Unit: °C) (Effect of the Invention) With the present invention, the variation (standard deviation) of the molten steel temperature upon arrival at the continuous casting process ) decreased to 8.4℃-'2.1℃, lowering the converter blow-off temperature (average) by 6℃, and reducing quality and operational problems caused by temperature in continuous casting. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view illustrating a sensor for measuring the internal temperature of a ladle refractory according to the present invention. 1: Ladle refractory 2: Temperature sensor 3: Thickness meter 4: Terminal box 5: Movable cable Patent applicant Nippon Steel Corporation

Claims (1)

[Claims] It is characterized by measuring or estimating the internal temperature of the ladle refractory and the distance of the temperature measurement point from the inner wall of the ladle, and making corrections based on the results in consideration of temperature drop due to heat extraction from the ladle refractory. A method for correcting tapping temperature based on the amount of heat stored in the ladle.