JPS6024449A - Method for estimating internal quality of continuously cast piece - Google Patents

Abstract

PURPOSE:To estimate the internal quality of a cast piece over the entire length thereof in a casting direction without time lag in a non-destructive manner, by measuring the upper and lower average width or short side trapezoidal amount of the cast piece on and after the correcting zone outlet of a curved type continuous casting machine. CONSTITUTION:In a low machine height (H) multi-point correcting curved continuous casting machine (LHCCM) having a fundamental circular arc zone 2, a cast piece bending multi-point correcting zone 3, a horizontal zone 4, a secondary cooling (water pouring) zone 5 and a water pouring completion point 6, a continuously cast piece 7 is cast by using a rectangular mold 1 and the upper and lower average width or short side trapezoidal amount thereof is measured directly after the machine end of LHCCM while an internal crack index is calculated by using the scatter diagram of the average width or short trapezoideal amount and the internal crack index. By this method, the internal quality of the cast piece 7 is estimated without time lag in a non-destructive way.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for non-destructively estimating the internal quality of a round slab cast by a curved continuous casting machine, and particularly to a method for non-destructively estimating the internal quality of a round slab cast by a curved continuous casting machine. The purpose of the present invention is to provide a method for estimating the internal quality of continuously cast slabs, which can be estimated non-destructively and without time lag using a low-cost measuring device.

In a curved continuous casting machine, during the cooling process until the slab is completely solidified, the solidification interface of the slab undergoes (1) bulge lag strain εb % due to static pressure of molten steel (2) straightening strain εu s due to straightening of the slab by bending back. (a) Misroll alignment strain (M) due to roll alignment misalignment acts, and if these individual, combined strains, or total strains ET exceed the internal crack occurrence limit strain εC determined by the physical properties of the pan, internal cracks will occur. In order to prevent the occurrence of defective slabs, casting conditions are set to prevent the occurrence of internal cracks and casting operations are carried out, but sudden changes in the set casting conditions or changes over time occur. For example, internal cracks may occur due to increased strain due to increased changes in roll alignment.For this reason, rolls in a continuous casting machine are generally replaced periodically, and the internal quality of the slab is To confirm this, the cast slabs are inspected for the presence or absence of internal defects and the extent of the defects.

This inspection method involves cutting out a cross-sectional sample of a slab and visually inspecting it directly using an S (sulfur) print or the like. Since this method involves sampling, it is impossible to inspect the entire amount of slabs, and furthermore, the inspection takes more than three hours.

By the way, recently, in order to save energy, the direct connection of the continuous casting machine and rolling equipment in the casting to rolling process, that is, the direct roll method, and the so-called hot charging method, which is hot charging into a heating furnace before rolling, have been implemented. However, in the internal quality inspection method using cross-sectional samples, if an internal quality defect occurs, it takes more than three hours to make a determination, so a large number of rejected products (internal defective slabs and rejected rolled products) are produced during that time. There is a serious problem of manufacturing.

To address this problem, a method has recently been proposed in which internal quality is estimated indirectly on-line using casting conditions and four-way alignment information. In other words, the occurrence of internal defects in slabs is strongly correlated with casting speed, amount of secondary cooling water, roll alignment, etc., and it is possible to control p-ru alignment from p-ru reaction force, roll displacement, etc. The aim is to estimate the internal quality by measuring the strain acting on the slab.

However, since a continuous casting machine is made up of a large number of rolls, it is extremely difficult to estimate the internal quality using the above method because a large number of sensors must be installed to measure roll reaction force and roll displacement. Although it is an expensive internal quality estimation device, it has the disadvantage of high estimation cost.

The present invention has been made in view of the above-mentioned actual situation and the conventional drawbacks, and is capable of estimating the internal quality of a slab being cast in a continuous casting machine over the entire length in the casting direction without any time lag using a non-destructive and low-cost device. The present invention provides a method for estimating the internal quality of continuously cast slabs.

The gist of the present invention is as follows.

(1) Measure the average amount of trapezoiding on the top and bottom surfaces of the continuously cast slab within the slab bending straightening zone of the curved continuous casting machine or after the exit of the straightening zone, and based on this measurement value, A method for estimating the internal quality of continuously cast slabs, characterized by estimating the internal quality of the slabs.

(2) A method for estimating the internal quality of continuously cast slabs by counting the average amount of dilatation on the upper and lower surfaces of the continuously cast slabs after the outlet of the slab bending straightening zone of a curved continuous casting machine.

The method of the present invention will be explained in detail below.

The present inventors have developed a low machine height (H) multi-point straightening curved continuous casting machine (hereinafter referred to as LHCCM) having a multi-point straightening zone or zone 3 for bending slabs with a small arc radius R, as shown in FIG. As a result of conducting various casting experiments using a rectangular mold l whose horizontal cross-sectional shape is shown in Fig. 2 and performing various analyses, it was found that the average of the upper and lower surfaces of the slab 7 showing the external surface strain of the slab 7, The amount of trapezoidization on the short side and the inside of the slab 4 indicates the horizontal zone, 5 indicates the secondary cooling (water injection) zone r16 indicates the water injection completion point, 8 indicates the meniscus, and the machine end is not shown. Also in Figure 2? , 1o indicates a long side mold piece, and 11 indicates a short side mold piece.

Figures 3 and 4 are obtained from the above experimental measurements and analysis, and show that the average upper and lower sides of nine completely solidified room-temperature slabs cast using LHCCM under the conditions shown in Table 1 and the casting conditions shown in Table 2 have a trapezoidal shape on the short side. This figure shows the relationship between the amount of cracking and the internal cracking index.

Table I LHCCM Condition Table 2 If the casting conditions are used, even if the secondary cooling conditions are changed in the range of 25 to 30, the average temperature of the entire slab cross section at the machine end remains constant. Medium X and short side trapezoidization:
iY is defined as a+bX□,Y=l)-a, where the upper surface is a1 and the lower surface width is b in FIG. 5 showing the cross-sectional shape of the slab 7. Note that C in FIG. 5 is the slab thickness.

It is clear from FIGS. 3 and 4 that in the same casting speed range, the internal cracking index decreases as the average middle X of the upper and lower surfaces increases and as the short side trapezoidization amount Y increases.

Therefore, for example, when casting under the conditions of Table 2 in an LHCCM with the conditions of Table 1, at a specified position after the exit of the multi-point straightening zone 3 in Fig. 1, for example, the running cutting machine in the horizontal zone 4 and behind the end of the machine. Slab 7 at the specified position of the zone up to the deployment position
To estimate the amount of trapezoidization on the short side of the room-temperature slab and the internal quality of the slab with internal cracks, as shown in Fig. 4, Can be done. The reason why the internal quality of a hot slab can be immediately estimated from the room temperature correlation diagram is that the short side trapezoidization iiY is almost equal to #1 at room temperature and at high temperature.

Also, taking advantage of the fact that the average temperature of the entire section at the end of the machine is constant (1280°C), the average middle of the upper and lower surfaces of the high-temperature slab 7 is measured at a position immediately after the end of the machine, and the average middle of this high-temperature slab is The internal quality of the slab is estimated by converting it into the average temperature of the room-temperature slab, and calculating the internal cracking index from the correlation diagram between the average temperature of the room-temperature slab and the internal cracking index (hereinafter referred to as the correlation diagram between the average temperature and internal cracking index) in Figure 3. I can do it with Jin. Conversely, the horizontal axis of the correlation diagram in Figure 3 was converted in advance to the average of the upper and lower surfaces at the temperature of the hot slab at the measurement position in the average of the upper and lower surfaces, and this was calculated from the measured values in the high temperature range. The internal crack index may be calculated from the average of the upper and lower surfaces.

Furthermore, the normal temperature correlation equation and the high temperature correlation equation may be determined from FIGS. 3 and 4, and the index may be calculated from the measured value.

The above-mentioned upper and lower surface average medium X1 short side trapezoidation amount Y can be measured using various measuring devices.For example, a laser scanning distance needle is used as a measuring sensor of the measuring device for the above-mentioned upper and lower surface average medium X1 short side trapezoidization amount Y. When measuring the distance from a fixed position to the short side of the slab at a predetermined sampling period and calculating the amount of trapezoidization on the short side in the average of the upper and lower surfaces, the distance from the fixed position to the short side of the slab can be calculated using
Measure the distance between the short side 7S surface at the position where d and (d=,) are included from the upper surface 7L and the lower surface 7F and the reference position f (g) and 1()'' and k). - If the fixed distance between g is 1, then the average middle X of the upper and lower surfaces and the amount of trapezoidation on the short side Y
is determined by X=1−. However, Q indicates the slab thickness.

In addition, in FIG. 6, Plo indicates the long side dimension.

By the way, continuously cast slabs are usually subjected to heavy cutting in the next rolling process, but when the cross-sectional shape is trapezoidal, it
When cutting the width, an extra reduction pass must be performed,
There is a disadvantage that energy loss, roll consumption, etc. are significantly increased.In order to prevent these, the rectangular mold 1 of the LHCCM shown in Fig. 1 is replaced with a trapezoidal mold 12 whose horizontal cross-sectional shape is shown in Fig. 7. It is known that the slab has a substantially rectangular cross section.

The dimensions of the trapezoidal mold 12 in FIG. 7 above are H2Lr, L
t, then LM=(L
F+LL)/2 and the short side trapezoidization amount 2=LF-LL.

Application of the method of the present invention in the case of a trapezoidal mold will be explained below. The trapezoidal mold shown in Fig. 7 was adopted for the LHCCM shown in Fig. M1 under the conditions shown in Table 1, and cast under the conditions No. 1 and 2,
A method for determining the internal crack index when measuring the average medium X or short side trapezoidization amount Y of the slab between the LHCCM machine end and the running cutting device will be explained as an example.

In the mold dimension symbols shown in FIGS. 2 and 7,
When using a trapezoidal mold 12 where L=(LL+LF)/2 and using the correlation diagram in FIG.
The average of the upper and lower surfaces of the horizontal axis in the figure is converted into the dimension at the slab temperature at the measurement position. Then, measure the average medium X of the upper and lower surfaces of the slab, and use the above-converted correlation diagram to determine the internal crack index of Chita,
From this, the internal quality of the slab can be estimated, and the fourth
When using the correlation diagram shown in the figure, the correlation diagram is obtained by subtracting the short side trapezoidization amount Y on the horizontal axis of FIG. 4 by the amount (LF LL). Then, the short side trapezoidization MY of the slab is measured, and the internal crack index is determined from the above-converted correlation diagram, and the internal quality of the slab can be estimated from this.

In this way, by measuring the average amount of trapezoidization on the upper and lower surfaces of the slab at a specified position after the outlet of the slab bending straightening zone of the curved continuous casting machine, the internal crack index of the slab is determined. From this, the internal quality of the slab can be estimated.

The above method measures the average upper and lower surfaces or the amount of trapezoidization on the short side of the slab at a predetermined position after the exit of the straightening zone, and determines the average upper and lower surface or the amount of trapezoidization on the short side based on the internal division measurement value. The following describes how the quality of the internal quality can be estimated from the following.

First, Figure 8 shows LHCCM under the conditions of Table 1, and measurements were taken within the multi-point correction zone when casting was performed under the conditions of Table 2 except that the casting speed was 1.4 to 1.7 m/min. The correlation between the short side trapezoidization amount and the meniscus distance is shown by converting the short side trapezoidization amount into cumulative surface strain.

Here, the cumulative surface strain E is expressed as follows.

However, W and 2 (u-v) are equations showing values proportional to the slab thickness and short side trapezoidization amount of the fully solidified slab shown in Fig. 10, respectively, and 2 (rs) is, The slab 7 having the unsolidified phase 7' shown in FIG. 9 at each measurement position shown in the first
L R is the first
This is the basic arc radius of the LHCCM shown in the figure.

From Figure 8, the pattern of cumulative surface strain calculated by converting the amount of trapezoidization on the short side of the slab within the straightening zone, that is, the presence or absence of internal cracks depending on the amount of trapezoidization on the short side. It is clear that it is possible to determine the amount of trapezoidization on the short side of the slab within the straightening zone, and if the mold is rectangular, based on Fig. 8,
The presence or absence of internal cracks can be determined. In the case of a single trapezoidal mold, the amount of short side trapezoidization of the trapezoidal mold is also shown in FIG.

(LFI-LLI) is plotted on the vertical axis of FIG. 8, and based on the corrected FIG. 8, the internal quality of the Chita slab can be estimated from the internal crack index.

In the above explanation, the amount of trapezoidization on the short side was measured in the straightening zone, the cumulative surface strain was calculated based on this measurement value, and the internal crack index was estimated from Chita and the internal quality of the slab from this and Figure 8. Both the short side trapezoidization amount and the average medium indicate the external strain of the slab, and as shown in Fig. 11, there is a strong correlation between the two, so the average of the upper and lower surfaces within the multi-point straightening zone is Based on the measured value of the inside, calculate the short side trapezoidization amount from the correlation diagram as shown in Figure 11 based on the average value of the upper and lower surfaces, and further calculate the cumulative surface strain and calculate 8.
From the figure, it is possible to estimate the internal crack index and the internal quality of the slab.

The present invention measures the average medium X or short side trapezoidization amount Y of the upper and lower surfaces of continuously cast slabs, determines the internal crack index of the slab based on this Xl or Y, and estimates the internal quality from this. Therefore, according to the present invention, only a single average width meter or short-side trapezoidal measuring needle is required, and the internal quality of slabs can be estimated stably and without time lag using a low-cost device. This can prevent the production of rejected products.

[Brief explanation of the drawing]

The drawings are all explanatory diagrams of matters related to the present invention.
Figure 2 is an explanatory diagram of the profile of a curved continuous casting machine, Figure 2 is an explanatory diagram of a rectangular mold, and Figure 3.4 is an average of the upper and lower surfaces of a completely solidified room-temperature slab, the amount of trapezoidization on the short side, and the internal cracking index. Fig. 5 is a cross-sectional view of the slab for explaining the amount of average medium and short side trapezoidization on the upper and lower surfaces, and Fig. 6 is for explaining the method for measuring the average medium and short side trapezoidation on the upper and lower surfaces. Figure 7 is an explanatory diagram of a trapezoidal mold, Figure 8 is a diagram of the relationship between the distance of the meniscus and cumulative surface strain, and Figures 9 and 10 are diagrams of the relationship between the short side trapezoidization amount and cumulative surface strain. This is the current state of affairs. FIG. 11 is an explanatory diagram of the correlation between the average width of the gun piece and the amount of short side trapezoidization. 1... Rectangular mold, 2... Basic circular arc zone, 3... Multi-point straightening zone or zone for slab bending, 4... Horizontal zone, 5... Secondary cooling (water injection) zone, 6... ... Water injection completion point, 7... Slab, 8... Meniscus, 9... Long side mold piece, 10... "" 11... Short side mold piece, 12... Trapezoidal mold, 7L...Top surface of the long side of the slab, 7F..."" Bottom surface, 7S...Short side of the slab, 7'...Unsolidified phase of the slab, Y...Amount of trapezoidation on the short side. Agent Patent attorney Masa Aki Sawa Mitsugai 2 name mouth (komo'aQJ 口α) Cane (A) 11pi 1ψ person ψ Sho 7 (M, 41■μmφ saw ψ

Claims (1)

[Scope of Claim] A method for estimating the internal quality of a continuously cast slab, characterized by measuring the amount of trapezoidization and estimating the internal quality of the slab based on this measured value. A method for estimating the internal quality of a continuously cast slab according to claim (1), wherein the internal quality of the continuously cast slab is estimated by determining the internal crack index of the slab based on the measured values of (1) and (1).