JPS5853354A - Continuous casting method for steel - Google Patents

Abstract

PURPOSE:To obtain superior surface characteristics free from oscillation marks in a method for continuous casting of steel by addition of molding powder to a mold which is open at both ends by applying ultrasonic oscillations and mechanical oscillations with the negative strip time shorter than specific seconds upon said mold. CONSTITUTION:Mold powder 7 is added to a mold 1 which is open at both ends, and steel is cast continuously. Ultrasonic oscillators 10 which are driven by an ultrasonic oscillator 9 are mounted to the mold 1 to apply ultrasonic oscillations to the mold 1. At the same time, mechanical oscillations are applied to the mold 1 by means of a mechanical oscillator 6, then molten metal is cast. The negative strip time by mechanical oscillations is kept at <=0.1sec whereby the oscillation marks produced on the surface of an ingot by the negative strip are eliminated.

Description

[Detailed description of the invention] The present invention relates to a continuous casting method for steel.

Conventionally, 1- When continuously casting steel in a mold with both ends open, vibration is applied to the mold to prevent seizure between the mold and shell and promote lubrication between them. A method was taken. That is, as shown in FIG. 1, in this method, molten steel 4 in a tundish 2 is injected into a mold 1 with both ends open through a submerged nozzle 3, and a slab with a shell 5 formed is poured from the bottom of the mold 1. When gradually pulling out the
Vibration is applied to the mold 1 by a mechanical vibration means 6, thereby preventing seizure between the mold 1 and the shell 5, promoting lubrication, and performing casting.

The mechanical vibration means 6 applies vertical vibrations to the mold 1 several tens to hundreds of times per minute, with an amplitude of several meters to several tens of tens of meters. In this case, in order to apply compressive force to the solidified molten steel, promote the healthy growth of the shell 5, and enable continuous drawing, the negative strip ratio (N, S) expressed by the following formula is set to 60
The amplitude and frequency are selected such that the amplitude is ~80%.

In addition, negatives I = IJ tube ratio refers to the time period when the mold is lowered by vibration in the same direction as the slab pulling direction, and the descending speed is greater than the slab pulling speed, and is the negative strip time. means the time at that time.

However, V: casting speed, A: Width, f: frequency of vibration.

However, the above method has the following problems.

Generally, mold powder 7 is supplied to the surface of the molten steel in the mold 1 for the purpose of lubricating the mold and the shell 5 of the slab and keeping the molten steel in the mold 1 warm.In this case, as shown in FIG. Oscillation marks (striped patterns) 8 are produced on the surface of the slab due to the reciprocating vibration of the mold l. This mark is
This can cause vertical cracks on the surface of slabs and horizontal cracks in slabs at slab straightening points5.Also, when transferring slabs after casting to the next process for treatment, harmful surface defects The distinction becomes difficult to ensure quality.

3- Also, in recent years, 20 KII7. A method has been proposed to apply back and forth ultrasonic vibrations to prevent burning between the mold and the shell. That is, as shown in Figure 3,
In this method, an ultrasonic vibrator driven by an ultrasonic oscillator 9 is attached to the mold l, and this vibrator applies vibration to the mold l. The same numbers in FIG. 2 as in FIG. 1 indicate the same items. The ultrasonic transducer 10 is fixed at a resonance position of the mold 1 at intervals.

However, the above method has the following problems.

■Excessive sliding resistance tends to occur between the mold and the shell surface during unsteady speed casting.

■When the cast piece is a slab or a bloom with a large cross section, the frictional resistance between the shell and the mold tends to become weaker partially due to the deformation of the shell.

(2) High-temperature casting - When ultrasonic vibration is applied to the mold, the shell is thin and easily breaks.

This invention was made to solve the above-mentioned problems, and includes the following steps: 4. In a method of continuously casting steel by adding mold powder to a mold with open ends, ultrasonic vibrations are applied to the mold. together with the negatives in the mold) IJ
Casting is carried out while applying mechanical vibrations with a tube time of 0.1 seconds or less, thereby obtaining slabs with excellent surface properties and no oscillation marks.

An embodiment of the method of the present invention will be described with reference to the drawings.

FIG. 4 is a schematic illustration of one embodiment of the method of the present invention.

In FIG. 4, the same numbers as in FIGS. 1 and 3 indicate the same parts.

In the present invention, an ultrasonic vibrator 10 driven by an ultrasonic oscillator 9 is attached to a mold 1 to apply ultrasonic vibration to the mold l, and mechanical vibration is applied to the mold 1 by a mechanical vibration device 6. This is a method of performing casting while maintaining the vibration of both of the above.

Especially 1 negative strip time due to mechanical vibration 0
．． The oscillation marks on the surface of the slab due to the negative strip are removed for less than 1 second.

As shown in FIG. 5, the influence of the vibration conditions of the mold on the depth of the oscillation mark varies greatly with the negative strip time (1N) expressed by the following equation.

However, V: casting speed, A: Shaking cloth.

f: frequency of vibration.

That is, as 1N approaches O, the depth of the oscilloscope mark becomes shallower.

Next, the relationship between negative strip time (tN) and negative strip rate (N, S) will be explained.

Figure 6 shows that the casting speed M is 1 m/min and the swing width (A) is G:
4 shows the relationship between the frequency f and tN and N,8 when fighting.

6- tN changes uniquely with frequency and rapidly becomes O at low cycle frequencies. On the other hand, N and S become smaller as the vibration frequency becomes smaller.

Therefore, in order to eliminate oscillation marks, tN
When N and S are set to small values, N and S reach 25% or less, so the conventional range of N and S is not satisfied at all.

It is clear that such mechanical vibration alone causes frequent breakouts and does not allow smooth casting.

Therefore, as described above, this invention applies a combination of ultrasonic vibration and mechanical vibration to the mold, and for mechanical vibration, the negative strip time is set to 0.1 seconds or less to prevent the occurrence of oscillation marks. This was prevented. Applying ultrasonic vibration to the mold prevents seizure between the mold and shell, which tends to occur under conditions of low negative stripping ratio, reduces the sliding resistance between them, and facilitates smooth drawing of the slab. This is for the purpose of achieving this goal.

The ultrasonic vibration applied to the mold has a frequency of 15 to 25 KHz, and an amplitude of -7 = several μm to several tens of μm, taking into account the resonance of the mold material such as copper or steel. Let's discuss an example.

52 ultrasonic vibrators of 60 mmφ were attached to a water-cooled copper mold with a short side of 160 ram, a long side of 800 ram, and a length of 7 BON, and vibrations at a frequency of 22 KHz were applied from an ultrasonic vibration generator with a power of 20 KW. . The horn with the vibrator attached was identified by a screw at the position corresponding to the vibration node on the mold wall. On the other hand, the mechanical vibration of the mold was set at a width of ±4B and a frequency of 40 cpm.

Casting of ordinary carbon steel is carried out in the above mold at a drawing speed of 1 m/nth nth using mold powder.

The oscillation marks and surface properties of the slab thus obtained are shown in Table 1 in comparison with those under pond conditions.

Note that the surface properties in Table 1 were determined based on minute cracks and bite defects that occurred in the slabs.

8-Table 1 As is clear from Table 1, the slabs cast by the method of the present invention do not produce oscillation marks and have excellent surface properties.

As explained above, according to the present invention, extremely useful effects such as being able to produce slabs with excellent surface properties without producing oscillation marks are brought about.

[Brief explanation of drawings]

1 and 3 are schematic explanatory diagrams of a conventional casting method,
FIG. 2 shows the release of the oscillation mark at the 9-gate; FIG. 4 is a schematic illustration of the method of the present invention;
This figure shows the relationship between the negative strip time and the maximum depth of the O/Ration mark, and FIG. 6 shows the relationship between the vibration frequency, the negative strip time tN, and the negative strip ratios N and S. In the drawing. 1.Mold 2.Tandish 3..
・Immersion nozzle 4... Molten steel 5... Shell
6... Mechanical vibrator 7... Mold powder 8... Oscillation 9... Ultrasonic oscillator Mark 10... Ultrasonic vibrator Applicant: Representative of Nippon Koukan Co., Ltd. Keita Tsutsumi (song) -]〇- Figure 5 Figure 3 Figure 6 Vibration vh number (f) (cpm)

Claims (1)

[Claims] A method of continuously casting steel by adding mold powder to a mold with both ends open, in which ultrasonic vibration is applied to the mold, and mechanical vibration is applied to the mold with a negative strip time of 0.1 seconds or less. This is a continuous casting method for steel, which is characterized by producing slabs with no oscillation marks and excellent surface properties.