JPH04237549A - Method for predicting longitudinal crack of continuously cast slab - Google Patents

Abstract

PURPOSE:To predict the development of longitudinal crack of a cast slab in a mold during continuous casting. CONSTITUTION:As the predicting method to the longitudinal crack of cast slab during continuously casting a steel, metal gap measuring elements 2 are embedded in the prescribed pitch P in width direction of inner face 11 in the mold 1 for continuous casting and plural lines in casting direction to measure the gap between the inner face 11 in the mold and surface of the cast slab and detect unevenness in the width direction of the gaps, and the development of longitudinal crack of the cast slab is predicted to control casting condition of change of oscillation, etc.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting longitudinal cracks in continuously cast slabs in continuous steel casting.

0002

2. Description of the Related Art In continuous casting of steel, particularly in continuous casting of medium carbon steel slabs having a carbon content of 0.09 to 0.15% by weight, vertical cracks often occur on the surface of the slab. When the carbon content is 0.09 to 0.15% by weight, peritectic solidification occurs, and the amount of shrinkage during solidification is large. Therefore, a local gap (hereinafter referred to as a gap) is generated between the inner surface of the mold and the surface of the slab, and a non-uniform solidified shell is likely to be generated. As a result, it is thought that cracks occur due to thermal stress.

[0003] Therefore, methods for preventing such vertical cracks include (1) a method of optimizing the viscosity of the powder; (2) a method of optimizing the viscosity of the powder;
Methods have been proposed in which the amount of heat removed from molten steel is reduced by joining a metal with low thermal conductivity to the inner surface of a copper mold plate or by forming grooves.

On the other hand, vertical cracks tend to occur during the first and second charges at the initial stage of casting. Measures to deal with this change over time are desired. Additionally, the occurrence of vertical cracks during casting can only be detected by optical detection on the output side of the pinch roll or by visual inspection during hot maintenance of the slab, and countermeasures must be taken during casting. It is.

Therefore, it cannot be said that the above-mentioned measure (1) can completely prevent the problem due to variations in powder physical properties. With the above-mentioned measure (2), the risk of breakout occurring due to insufficient solidified shell thickness during high-speed casting increases. None of the countermeasures are effective against the change over time that causes vertical cracks to occur in the early stages of casting, and it must be said that these measures are excessive.

Other gap measurement methods include a method of measuring energy from a powder film (iron-to-steel,
83-S161) has been proposed. Since this method also measures directly under the mold, real-time measurement is not possible and there are major problems with durability. Therefore,
It is necessary to detect the occurrence of longitudinal cracks in slabs within the mold and take preventive measures in real time. Currently, information inside the mold includes temperature information from the mold copper plate. Although this information can predict breakouts in slabs, it is not sensitive enough to predict vertical cracks. There is a need for a measure that can be predicted within the mold and linked to preventive measures.

[0007]

[Problems to be Solved by the Invention] The problem to be solved by the present invention is to predict the occurrence of vertical slab cracks in the mold during continuous casting, promptly implement appropriate preventive measures, and prevent the occurrence of longitudinal cracks in slabs. The object of the present invention is to obtain a method for predicting longitudinal cracks in slabs that can minimize the occurrence of cracks.

[0008]

[Means for Solving the Problems] The method for predicting longitudinal cracks in continuously cast slabs of the present invention is a method for predicting vertical cracks in a continuously cast slab in a continuous casting method for steel. A metal gap measuring element is embedded in the row to measure the gap between the inner surface of the mold and the surface of the slab, detect non-uniformity in the width direction of the gap, predict the occurrence of vertical cracks in the slab, change the oscillation, etc. The above problem has been solved by a means characterized by controlling the casting conditions.

[0009]

[Operation] Figure 2 shows the relationship between the occurrence of longitudinal cracks and the widthwise gap distribution. If the deviation in the width direction gap between adjacent measuring elements is 0.2 mm or more, the probability of vertical cracking increases rapidly. Therefore, if the gap exceeds 0.2 mm, a longitudinal crack prediction warning is issued and the oscillation conditions are adjusted. Measures such as changing the casting speed or reducing the casting speed may be taken.

However, since the limit amount of the gap varies depending on the steel type, casting speed, etc., it is necessary to determine various limit amounts in advance depending on the casting conditions.

FIG. 3 shows the relationship between the breakout occurrence rate and the gap amount. When the value of the gap amount becomes 0.05 mm or less, the breakout occurrence rate increases rapidly. Therefore,
When the gap amount becomes 0.05 mm or less, a breakout prediction alarm is issued, and measures to reduce the casting speed may be taken.

Since both longitudinal crack prediction and breakout prediction are determined by the gap amount up to 200 mm below the meniscus, it is sufficient to arrange the measuring coils in two rows in the width direction from the meniscus.

[0013] When the breakout prediction alarm is issued, the casting conditions such as changing the oscillation, changing the powder, and reducing the casting speed are controlled.

The metal gap measuring element used in the method of the present invention is disclosed in, for example, a patent application filed by the present applicant (Japanese Patent Application No. 2-298/1999).
536) may be used. The method for measuring the gap between surfaces of a metal body according to the invention of this patent application is to install a pair of coils on one side of metal bodies disposed facing each other, separated by an appropriate length in a plane parallel to the facing surface of the other metal body. buried,
A low-frequency excitation current is applied to one of these coils to function as a transmitting coil that generates a magnetic field, and the energy of this magnetic field propagates through both metal bodies and the gap between them to reach the other coil. When the induced current is captured, this induced current has a phase delay and a decrease in strength depending on the difference in the propagation path of the magnetic field energy, especially the size of the gap. The dimension of the gap is determined by detecting a phase change and/or intensity change between the induced current and the induced current.

[0015]

[Embodiment] An embodiment of a method for predicting vertical cracks in continuously cast slabs will be described with reference to FIGS. 1 to 4.

As shown in FIG. 1, the inner surface 11 of the continuous casting mold 1 has a predetermined pitch P (for example, 100 mm) in the width direction.
The metal gap measuring elements 2 are embedded in a plurality of rows (two rows in the illustrated example) in the casting direction to measure the gap between the mold inner surface 11 and the slab surface. The non-uniformity of this gap in the width direction is detected, the occurrence of vertical cracks in the slab is predicted, and casting conditions such as changes in oscillation are controlled.

Two rows of elements 2 are provided at a distance d1 (for example, 50 mm) below the position of the meniscus 3, and a distance d2 (for example, 100 mm) further below the position of the meniscus 3.

The installation interval P of the metal gap measuring elements 2 (for example, excitation coils) is preferably about 100 mm in consideration of mutual interference and measurement range. Vertical cracks in slabs occur at the early stage of casting, so (meniscus) is 3 to 200 m.
Up to about m. Therefore, it is preferable to provide a plurality of rows (preferably two rows) of the elements 2 in the width direction.

In a one-point straightening continuous casting machine with a bending radius of 10 m, medium carbon steel (C = 0.10%), 200 mm thick
A slab with a width of 1800 mm was continuously cast at a casting speed of 3.0 m/min. No. In one strand mold, 19 coils for gap measurement according to the method of the present invention were embedded in the width direction at a pitch of 100 mm, and a total of 38 coils were embedded on one side in two rows 50 mm and 150 mm below the meniscus. No. For comparison, a conventional mold was used for the second strand.

FIG. 4 shows the occurrence of vertical cracks during continuous casting under the above conditions. No. by conventional mold. With 2 strands, vertical cracks occurred frequently at the early stage of casting, and the casting length was approximately 60 mm.
There was a tendency to occur up to m. No. 1 using a mold based on the method of the present invention. In the case of 1 strand, the gap amount deviation was 0.2 mm or more at the beginning of casting, and a vertical crack prediction warning was issued, so by changing the oscillation stroke from 6 mm to 5 mm, no vertical cracks occurred. Then, after the casting speed reached a steady state, the stroke was increased to 6 m.
m, but vertical cracks no longer occurred, and casting was continued under normal conditions.

[0021]

According to the present invention, vertical cracking, particularly in the early stages of continuous casting, can be significantly reduced, the maintenance process can be omitted, and the hot charge ratio can be improved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a mold to which the method of the present invention is applied.

FIG. 2 is a graph showing the relationship between gap amount deviation between adjacent coils and longitudinal cracking strength of slab.

FIG. 3 is a graph showing the relationship between gap amount and breakout incidence rate.

FIG. 4 is a graph showing the results of applying the method of the present invention and the conventional method to an actual machine.

[Explanation of symbols]

1 Mold 2 Measurement element 3 Meniscus 11　Inner surface of mold

Claims (1)

[Claims] Claim 1: In a continuous casting method for steel, metal gap measuring elements are embedded in the inner surface of a continuous casting mold at a predetermined pitch in the width direction and in multiple rows in the casting direction, and the metal gap measuring elements are embedded in the inner surface of the continuous casting mold in a plurality of rows in the casting direction. Vertical cracking in continuously cast slabs characterized by measuring the gap between them, detecting non-uniformity in the width direction of the gap, predicting the occurrence of vertical slab cracking, and controlling casting conditions such as changing oscillation. Prediction method.