JPS62176656A - Continuous casting method by solidification under molten metal surface without surface cracking of billet - Google Patents

Abstract

PURPOSE:To improve quality of billet surface by executing reciprocating motion with closely resemblong sine curve in casting direction for integrated type combination mold, making a max. descendent speed of the mold faster than casting speed of the casting billet and making a return-back length, etc. a speci fied value. CONSTITUTION:The integrated type combination mold, which arranges an inter mediate vessel 2 above a water cooling mold 1, and a heat insulating ring 3 at the boundary of the both, executes reciprocating motion with closely resem bling sine curve in the casting direction, and the max. descendent speed of the mold is faster than the casting speed of the casting billet. Further, the casting is executed under condition of which a negative strip time (tN) and the return-back length (lr) satisfy the inequality. In this way, the casting billet having good surface quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a subsurface solidification method in mold vibratory continuous casting.

[Conventional technology]

The minimum dimension of the slab cross section in the continuous casting method is limited by the outer diameter of the immersion nozzle. Therefore, as a method for casting slabs having a diameter smaller than the minimum diameter of the immersion nozzle, a so-called submerged solidification casting method is known, in which a tundish (hereinafter simply referred to as TD) and a mold are directly connected.

An example of the submerged solidification casting method is the Japanese Patent Publication No. 53-3704.
There is a method described in Publication No. 3. In this method, 1. Insert the graphite mold into the TD,
This is a method of casting without vibrating the mold.

In addition, the present applicant uses an integrated combination mold in which an intermediate container is placed above a water-cooled mold and a heat insulating ring is attached to the boundary between the water-cooled mold and the intermediate container as a submerged solidification casting method, and the mold is vibrated. He first applied for a method of casting (patent application filed in 1982)
-159951).

The slab obtained by this submerged solidification casting method is
Powderless casting provides a smooth surface without powder entrainment. However, depending on the vibration conditions of the mold,
Surface cracking of slabs may occur. Surface cracks on the slab occur over the entire circumference of the slab in each cycle, and some have a maximum depth of 2 mm or more, reducing the maintenance yield of the slab.

The generation mechanism of slab surface cracks in this subsurface solidification casting method consists of an initial solidification shell (old shell) generated from the insulating ring side at the boundary between the water-cooled mold and the intermediate vessel, and a crack formed from the old shell side after one cycle of drawing. It is thought that the boundary layer between the new shell and the new shell forms a discontinuous solidification pattern, and this boundary layer between the new and old shells is generated when fusion is poor.

[Problem that the invention seeks to solve]

As a method of subsurface solidification casting to prevent surface cracking, for example, a method can be considered in which the number of cycles for drawing the slab is increased to reduce the time required to form a shell per cycle, thereby making surface cracks shallower. .

However, in order to obtain high cycles while accurately controlling mold vibration, the mechanism of the drawing device becomes complicated, and there are limitations in terms of equipment, making it difficult to prevent surface cracks.

We also conducted casting experiments to find a way to suppress the formation of an initial solidified shell and reduce surface cracks by thinning the insulating ring at the boundary between the water-cooled mold and the intermediate container. However, it was found that by making the heat insulating ring thinner, its mechanical strength decreased and it broke during casting, making stable casting impossible.

Therefore, the actual situation is that a method of preventing surface cracking by submerged solidification continuous casting has not been put to practical use to date.

The present invention provides a technology for producing slabs without surface cracks in a continuous submerged solidification casting method.

[Means for solving problems]

The feature of the present invention is that by creating a region (negative strip region) where the descending speed of the mold is higher than the casting speed of the slab, the initially solidified shell generated is pressed against the casting direction of the slab to fuse the cracks. The aim is to completely prevent the occurrence of

In order to prevent the occurrence of surface cracks, it is necessary to press the new and old shells in the casting direction of the slab within the region where the descending speed of the mold is higher than the casting speed of the slab (negative IJ).
(push time) and amount (push back amount) are required.

Furthermore, if the negative strip time or pushback amount is too large, dents will occur on the surface of the slab, so there is an optimum range under these conditions.

Figure 1 shows the push-back amount (I!P) and negative strip time (tN) affecting surface cracking obtained from casting experiment results.
). As shown in Figure 1, N is thicker than 01m and less than 6.0 long, and 1N is 0.1 sec or more and 0.5
Within the range of sec or less, and! , ≧-10tN+2, it was found that there is a region where almost no surface cracks occur and no dents occur.

The above results can be summarized as follows.

0.1sec≦1. ≦0.5sec O ■ Otori <72. ≦ 6.0 Otori-l, ≧-
10tN+Madashi tN=60/π1cos-1(V#rsf) (s
ec) 11p = S-sin (πf-tN/60)
v-tN/60 (m)■ = Casting speed (am/
min) S: Vibration stroke (11) f: Vibration cycle (c/min) [Function] Figure 2 shows that when the mold is reciprocated in a sine curve, there is a region where the maximum descending speed of the mold is greater than the casting speed. In the existing mold vibration method, the relationship between mold speed change, slab casting (lowering) speed, mold displacement and slab displacement, relative displacement between slab and mold, and the state of formation of an initial solidified shell at that time are shown. .

a shows the change in mold vibration speed, and b shows the casting (lowering) speed of the slab. In this figure, the diagonally shaded area between ■ and ■ indicates a negative strip area.

Further, C indicates the displacement state of the mold, and d indicates the displacement state of the slab. e indicates the relative displacement between the slab and the mold.

The lower part of FIG. 2 shows the formation of an initial solidified shell. From ■, the initial solidified shell (old shell 11) descends and the mold l rises, and the new shell 12 starts to be formed between the old shell 11 and the heat insulating ring 3. This shows that a crack 13 has occurred at the boundary between the new shell 11 and the new shell 12. Generation of the new shell 12 is completed in (2), and the new shell 12 has the maximum length. Beyond this point, the new shell 12 begins to be pushed back in the negative strip area, and cracks that have occurred on the surface of the slab begin to be fused. l in the figure is the pushback amount. In step (3), the negative strip area is completed and the cracks that have occurred on the surface are fused.

As described above, the feature of this casting method is that there is a region where the descending speed of the mold is higher than the casting speed of the slab, and the amount by which the generated shell is pressed in the casting direction of the slab (ip) and the negative strip time (LH) are controlled. By casting within the range of the method of the present invention, slabs without surface cracks can be obtained.

〔Example〕

Using the example of the equipment shown in Fig. 3, a 30TON slab of 5US304 with a cross section of 150φ can be produced at a rate of 400 to 1,500 times.
Casting was performed using a heating device at a casting speed of 1 min and a cycle of 9.8 to 15 Q c /min so that the molten steel did not solidify in the intermediate vessel. In FIG. 3, 1 is a water-cooled mold, 2 is an intermediate container, 3 is a heat insulating ring, 4 is an immersion nozzle, 5 is a solidified shell, and 6 is a heating device for maintaining the molten steel in the intermediate container in a molten state. The results are shown in Table 1. N119
As shown in Figures 1 to 19, as a result of casting in the area of the present invention, good slabs with no surface cracks were obtained.

The method of the present invention can also be applied to various continuous casting methods as shown in FIGS. 4 and 5. FIG. 4 shows an example of multi-strand casting, and FIG. 5 shows an example of combination with the core casting continuous casting method. In FIG. 5, 7 is a core.

〔Effect of the invention〕

By implementing the present invention in the sub-surface solidification continuous casting method, it is possible to prevent the surface cracks characteristic of conventional sub-surface solidification continuous casting materials, and to produce slabs with good surface quality that can be extruded and rolled without manual work. I was able to get it.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the pushback amount and negative strip time affecting the surface crack depth, and Figure 2 is a diagram showing the relationship between mold displacement and slab displacement, the relative displacement between the slab and mold, and its relationship. FIGS. 3, 4, and 5 are explanatory diagrams showing an example of an apparatus for carrying out the present invention. l: water-cooled mold, 2: intermediate container, 3: heat insulating ring, 4:
Immersion nozzle, 5: solidified shell, 6: heating device, 7: core. Figure 1 Necatif "Strip Time" ~ (SeC) Figure 4

Claims (1)

[Claims] An integrated combination mold is used in which an intermediate container is placed above a water-cooled mold and a heat insulating ring is attached to the boundary between the water-cooled mold and the intermediate container, and the integrated combination mold is approximated to a sine curve. At the same time, the maximum descending speed of the mold is made faster than the casting speed of the slab, and the negative strip time (t_N) and the pushback amount (l_P) are
A subsurface solidification continuous casting method that does not cause surface cracks in slabs, characterized in that casting is performed under conditions that satisfy the following formulas. 0.1sec≦t_N≦0.5sec 0mm<l_P≦6.0mm l_P≧−10t_N+2 However, t_N=60/πf・cos＾−＾1(V/πsf)
sec) l_P=S・sin(πf・t_N/60)−V−t_
N/60 (mm) V: Casting speed (mm/min) S: Vibration stroke (mm) f: Vibration cycle (c/min)