JPH04197565A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To regularize the thickness of powder thermal-spraying layer employing the same powder by adjusting condition of amplitude and number of the oscillation while using sum of positive strip times per 1m of a cast slab according to variation of casting velocity as a parameter. CONSTITUTION:The sum SIGMAtp of the positive strip times per 1m of the cast slab has inversed correlation with the casting velocity. Then, while using the SIGMAtp selected so as to come to the suitable powder consumption according to the variation of the continuous casting velocity as the parameter, by adjusting the oscillating condition of amplitude and number of the oscillation, the SIGMAtp is held within a specified range to maintain a constant thickness of powder thermal-spraying layer.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention involves continuous casting by suspending powder on the surface of molten steel in a mold and continuously injecting molten steel into the mold while vibrating the mold. It is about the method.

2. Prior Art] Generally, in a continuous steel casting method, as shown in FIG. 5, molten steel is poured from a ladle 6 into a tundish 7 and is injected into a mold 1 through an immersion nozzle 8. The solidified shell formed in the mold 1 is solidified while being cooled by a spray nozzle 4 between a group of guide rolls 3 provided next to the bottom of the mold 1, and is drawn out as a slab 2. 5 is a pinch roll, and 9 is a ladle turret. In order to reduce the friction between the mold and the solidified shell and improve lubricity, the molten steel surface (
Hereafter, powder 10 is suspended in the meniscus part,
It is melted with powder 10 and supplied between the mold and the solidified shell. In addition, in order to prevent the slab from sticking to the inner wall of the mold, a device 11 is used that vibrates the mold vertically at a predetermined frequency and amplitude (referred to as an oscillation device). It is important to ensure the thickness of the fused powder layer in the meniscus portion to a certain value or more in order to improve the surface quality of the slab (# and Steel, No. 1, 1970, p. 81-88).

FIG. 6 is a t2 diagram showing an example of the relationship between the thickness of the molten powder layer at the meniscus in the mold and surface defects of the slab. Here, when Powder A is used and plotted with * marks, there is a tendency as shown by the solid line, and in order to improve the surface quality of the slab, it is essential to ensure the thickness of the powder molten layer is above a certain value.・It is essential.

It is known that the thickness of the fused powder layer depends on the amount of powder consumed, as shown in FIG. 7 when the same powder is used. The thickness of the fused layer of powder (mm) is plotted on the vertical axis;
Powder consumption (kg/m2) is plotted on the horizontal axis, and the thickness of the powder molten layer when powder consumption is increased using Powder A is plotted with . Can be seen. Furthermore, when Powder B is used and similarly plotted, a decreasing trend can be seen within the range shown by the dotted line. Therefore, when using the same powder, it is effective to keep the powder consumption constant in order to keep the thickness of the fused powder layer constant.

On the other hand, in a method of continuous casting by vibrating a mold, there is an off-sillation constant frequency operation. FIG. 8 is a diagram showing the relationship between casting speed and powder consumption when the mold is vibrated. In the figure, amplitude = 4 mm, frequency 7Qcpm
The case is plotted with a ◎ mark, and the tendency is shown with a solid line.

In addition, when the amplitude is 4 cm and the frequency is 100 cpm,
The trend is indicated by a dotted line. As is clear from the figure, the powder consumption decreases as the casting speed increases, although the value varies depending on the vibration conditions.

Therefore, in order to keep the thickness of the fused powder layer constant, one measure has been to select the type of powder depending on the casting speed.

[Problem to be solved by the invention 2 However, in the continuous casting method, the casting speed must be changed during casting due to factors such as changing the pot, the temperature of the molten steel in the tundish, and machining with the previous process. Cases occur. In such cases, it is difficult to change the type of powder in the mold depending on the casting speed, and it is difficult to change the thickness of the molten layer of powder even with the same powder depending on the casting speed. Technology is required.

In order to keep the thickness of the fused layer of powder constant using the same powder, it is necessary to keep the powder consumption constant depending on the various casting speeds. On the other hand, it is known that powder consumption is proportional to the positive strip time during oscillation when the same powder is used (Nippon Kokan Giho No. 93
, p18-25.1982). The present invention has been achieved through various studies based on the above findings.

SUMMARY OF THE INVENTION An object of the present invention is to provide a continuous casting method that can maintain a constant thickness of a fused powder layer using the same powder even when the casting speed changes from a steady state to an unsteady state.

：Means and Actions for Solving the Problems In order to achieve the above object, the present invention suspends powder in the meniscus part of the mold and continuously injects molten steel into the mold while vibrating the mold. In the continuous casting method, the vibration conditions of amplitude and frequency are adjusted according to changes in the continuous casting force and casting speed, using the sum of positive strip times per meter of slab (hereinafter referred to as Σtp) as a parameter,
The present invention provides a continuous casting method for steel in which the thickness of the molten layer of the powder is maintained constant.

Σtp according to the present invention will be explained with reference to FIG. In Figure 1, the vertical axis represents the vibration speed of the mold, and the horizontal axis represents time.
The vibration speed of the mold is shown by the sine curve in Figure 1, which is a diagram showing the vibration state of the mold and the casting speed.
The straight line represents the casting speed. Σtp is defined as the total sum per meter of slab during the period when the relative moving speed of the mold is smaller than the casting speed. If this Σtp is too large, the amount of powder consumed will be excessive, leading to cracking and sagging of the slab.

Furthermore, if the size is too small, it is not possible to effectively prevent burn-in. Therefore, it is necessary to select ΣtpE and set it as a parameter so as to obtain an appropriate amount of powder consumption.

In the present invention, as will be described later, since Σtp has an inverse relationship with the casting speed, two amplitude The vibration frequency conditions are adjusted to keep Σtp within a certain range, and the thickness of the molten powder layer to be kept constant.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram showing an example of the relationship between Σtp and powder consumption according to the present invention. Here, A)<Udah was used.

In the method of continuous casting by suspending A powder in the meniscus part of the mold and continuously injecting molten steel into the mold while vibrating the mold, from Fig. 2, the appropriate A powder consumption is 03 to 0. so that it is within the range of .4kg/m2,
The corresponding Σtp is selected in the range of 28 to 38 seconds/m using the large arrow. Figure 3 is a diagram showing the development of n Set the swing 1 conditions. Here, the steady state is defined as casting speed 1 □4ml
As the vibration condition, the amplitude τ is 4 mm, and the frequency is 7 Q cpm. Corresponding to the change in casting speed, Σt, p ranges from 28 to 38 seconds m,゛・,.

Adjust the vibration conditions so that it can be maintained.

FIG. 4 is a diagram showing an operation pattern of casting speed in the case of continuous casting according to the present invention.
Unsteady state from 4m7 minutes! The operation pattern was changed to A-building speed of 1.0 m/min, and then to steady-state BfI steel-making speed of 14 m/min. In response to changes in casting speed, the vibration conditions were adjusted using Σt and p as parameters. Here, the amplitude was kept constant and the frequency was adjusted, resulting in powder consumption of 03~Q, 4 kg, 7 m
The thickness of the molten layer of powder should be within the range of 16-20
I was able to maintain it within a certain range of +am. the result,
As shown in Table 1, even when the casting speed was reduced and an unsteady state was reached, the occurrence of surface defects on the slab could be reduced.

Table 1 [Effects of the Invention 2 According to the present invention, the thickness of the molten layer of the powder can be kept constant even when the casting speed changes from a steady state to an unsteady state during casting using the same powder. Therefore, it is possible to obtain a product with fewer casting surface defects.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing the relationship between the vibration state of the mold and the casting speed according to the present invention, FIG. 2 is a diagram showing an example of the relationship between Σtp and powder consumption according to the present invention, and FIG. Figure 3 is a diagram showing the relationship between casting speed, Σtp, and vibration conditions when using the same powder, Figure 4 is a diagram showing the operational pattern of casting speed in the case of continuous casting according to the present invention, and Figure 5 is a diagram showing the relationship between casting speed and vibration conditions when using the same powder. Figure 6 shows an example of the relationship between the thickness of the molten powder layer at the meniscus in the mold and surface defects (solokami) on the slab surface, and Figure 7 shows the amount of powder consumed for the same amount of powder. FIG. 8 is a diagram showing the relationship between casting speed and the same powder consumption amount. 1. Mold, 2. Slab, 10. Powder, 11. Mold vertical vibration device.

Claims (1)

[Claims] In a continuous casting method in which powder is suspended on the surface of molten steel in a mold and molten steel is continuously injected into the mold while vibrating the mold, the thickness of 1 m of slab is changed according to the change in the casting speed of the continuous casting. A continuous casting method for steel, characterized in that the thickness of the molten layer of powder is maintained constant by adjusting vibration conditions such as amplitude and frequency using the total positive strip time per hit as a parameter.