JP2007237279A - Continuous casting mold and continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting mold and a continuous casting method with which the uneven cooling in the width direction of a mold is relaxed and a product surface quality is improved by restraining surface crack and break-out of a cast slab and also, the service life of a mold cooling plate is extended by preventing the development of crack of the cooling plate. <P>SOLUTION: Cooling liquid flowing passage (slit) 12 for cooling plate 10 for continuous casting mold, is inclined to the casting directional axis at position in at least ≥50% of the whole circumference in the mold cross section at the right angle to the casting direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a continuous casting mold and a continuous casting method, and more particularly to a continuous casting mold capable of uniformly cooling molten metal, which is suitable for use in continuous casting of steel, and continuous casting using the same. Regarding the method.

  Since the cooling plate 10 (also referred to as a copper plate) of the casting mold for continuous casting has a large thermal load, generally, in order to prevent thermal distortion during casting, FIG. 1 (front view seen from the cooling water passage side) and FIG. 2 (cross-sectional view taken along line II-II in FIG. 1), the steel backup frame 20 is fixed through stud bolts 22 provided at substantially equal intervals in the vertical and horizontal directions, and a fixing portion by the bolts 22 is avoided. As described above, a plurality of cooling water passages (also referred to as slits) 12 of the copper plate 10 are provided in a straight line parallel to the casting direction (vertical direction in FIG. 1). In the figure, 14 is a temperature measuring hole provided in the copper plate 10, 16 is a mold flux layer, 18 is a solidified shell, and 24 is packing.

  For this reason, although the space | interval of the slit 12 between the stud bolts 22 can be set arbitrarily, the stud bolt 22 is influenced by the diameter of a bolt, Usually, the space | interval of the slit which pinched | interposed the stud bolt part is wider than other parts. It becomes. As a result, in the width direction of the mold, a periodic non-uniform portion of cooling corresponding to the pitch of the stud bolt is formed. In particular, in the stud bolt portion, the density of the slits 12 is reduced and the cooling is weakened. Non-uniformity occurs.

  Also, as shown in FIG. 3 (a), the portion where the molten steel starts to solidify at the molten metal surface position until it exits the mold until the mold cooling slit portion begins to solidify is positioned relative to that slit until it exits the mold. Hardly changes. Such a relationship is the same with respect to a portion where solidification starts at the stud bolt portion and a portion where solidification starts between the cooling slits. That is, the uneven cooling state in the width direction is maintained from the start of solidification to the mold exit side.

  For this reason, cooling is performed to the mold exit side while the cooling is weak at the stud bolt part or the part without the slit that is weaker than the other part, and the cooling is strong at the slit part that is stronger than the other part. Therefore, if solidified steel is used, uneven cooling in the width direction is promoted. As a result, the solidified shell has a strong tendency to form a solidified delay portion linearly in the casting direction at the same position in the width direction. Such a situation is schematically shown in FIG. Thermal strain tends to concentrate on the solidification delay part, and vertical cracks are generated.

  Recently, there is a tendency to further increase the casting speed for the purpose of improving productivity, so that the molten steel flow in the mold can be efficiently controlled by electromagnetic force in order to stabilize the casting and suppress the deterioration of slab quality. In addition, with the aim of suppressing magnetic field attenuation in the mold copper plate, the mold copper plate tends to be thinner than before, and the above-described problems become apparent. These phenomena are prominent in the case of slabs and bloom mold copper plates.

  Therefore, the following problems occur.

  (1) Since solidification of the slab is delayed at the stud bolt portion, vertical cracks and slab buckling (dents) are likely to occur in the slab corresponding to the part. These problems become apparent when high-speed casting is performed, or when casting ultra-low carbon steel or medium carbon steel that tends to solidify unevenly.

  (2) The copper plate temperature in the vicinity of the stud bolt becomes high, and a crack occurs in the copper plate at this portion, and the life of the copper plate is shortened. In addition, water leaking from the cracks may come into contact with the molten metal, causing a steam explosion.

  In order to solve these problems, Patent Documents 1 and 2 propose a method in which the gap between the slits sandwiching the stud bolt portion is twisted only in a portion where there is no stud bolt in the casting direction.

  Non-Patent Document 1 also proposes providing a slit in the horizontal direction.

Japanese Patent No. 3443109 JP 2005-114133 A I. G. Saucedo et. Al. “Characterization of the Effects of Mold Oscillation on Heat Transfer Rate and Mold Friction during Continuous Casting”, Proceedings of The Sixth International Iron and Steel Congress, 1990, Nagoya, ISIJ, pp325-333

  However, even with the techniques described in Patent Documents 1 and 2, the above problem is not necessarily completely suppressed.

  In addition, the method described in Non-Patent Document 1 has a problem in that bubbles in the cooling water are not easily detached and a temperature distribution is generated in the horizontal direction, resulting in a decrease in mold cooling ability.

  Also, when casting round slabs (round bloom, round billet), due to the characteristics of the shape itself, the slab and bloom mold copper plate structure as described above may be used. Even if it is not low-carbon steel or medium-carbon steel, slab vertical cracks are likely to occur. To solve this problem, mold taper optimization and mold flux improvement (slow cooling) have been implemented, but they are not necessarily complete. It was not suppressed.

  The present invention has been made to solve the above-mentioned conventional problems, and suppresses the slab surface cracks to improve the product surface quality, and prevents the occurrence of cracks in the cooling plate to extend the life of the mold cooling plate. The problem is to extend.

  The present invention is characterized in that the coolant flow path of the cooling plate for the continuous casting mold is inclined with respect to the casting direction axis at a portion of at least 50% or more of the entire circumference of the mold cross section perpendicular to the casting direction. The above-mentioned problem is solved by a continuous casting mold.

  In particular, in the case of slabs and blooms, it is preferable to periodically change the tilt angle of the coolant flow path in the casting direction, and the casting direction cycle of the tilt angle of the coolant flow path is equal to the casting direction stud. It is desirable that the total amplitude is equal to twice the bolt pitch, the total amplitude is one pitch or more of the coolant channel, and the maximum inclination angle between the coolant channel and the casting direction axis is 3 to 85 °. .

  On the other hand, when the mold is a cylinder, it is desirable that all the coolant flow paths are formed in a spiral shape in the casting direction, and the inclination angle formed between the cooling water passage and the casting direction axis is 3 to 85 °.

  According to the present invention, uneven cooling in the mold width direction is mitigated, slab surface cracking and breakout are suppressed, the product surface quality is improved, cracking of the cooling plate is prevented, and the life of the mold cooling plate is increased. Extended.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The front view which looked at the copper plate 10 of 1st Embodiment of this invention from the cooling water channel | path (slit) 12 side is shown in FIG. The cooling water slit 12 is structured to be inclined with respect to the casting direction axis, and the inclination angle is periodically changed in the width direction, that is, a slit shape having a sinusoidal shape. For this reason, between the time when molten steel starts solidification and the time when it exits the mold, the relative positional relationship between the portion E where solidification has started in the cooling slit shown in FIG. It will be. For example, in the portion E where solidification is started at the cooling slit portion, the cooling condition of the solidified shell alternately changes from slit portion → copper plate portion between slits → slit portion → copper plate portion between slits. Moreover, in the part D which starts solidification between stud bolts, the copper plate part between slits → the slit part → the copper plate part between the slits → the stud bolt part → the copper plate part between the slits → the slit part → the copper plate part between the slits → the slit part → Cooling conditions change, such as copper plate part between slits → stud bolt part. That is, since the solidified shell passes through the cooling portion and the non-cooling portion alternately while descending in the mold, the cooling unevenness in the width direction is shown in FIG. A mitigating effect is obtained compared to the comparative example.

  Further, since the slit is not a straight line but a curve, the slit length (the length of the line segment between the entry side and the exit side) in the present invention is longer than that in the prior art. For this reason, the cooling area (slit length × slit width) increases, and an increase in the amount of heat removed from the mold can be expected even with the same amount of water. Therefore, the synergistic effect of suppressing the cooling unevenness in the mold width direction and increasing the cooling capacity, as well as curving the slits, reduce the absolute temperature of the copper plate, suppress the temperature unevenness, and reduce the thermal strain concentration on the copper plate. There is also an effect of drastically reducing the possibility of.

  Such a slit shape needs to be applied at least 50% of the entire circumference of the mold cross-section in an assembled mold such as a slab or bloom. In the case of a slab, vertical cracks on the long side surface are prominent, and the ratio of the long side surface to the entire mold periphery is generally 75% or more in consideration of the size (100 to 300 thickness × 700 to 3000 width). Is preferred. In Bloom, since the difference between the width of the long side and the short side is small, it is preferable to provide an inclined slit on the entire circumference.

  In the case of an assembled mold, as shown in FIG. 5 (a), if the straight line is formed by inclining the slit 12, if there is too much inclination, there is a portion where the length of the slit is different. The water pressure loss also changes, and the uniformity of the flow rate for each slit cannot be maintained, which causes uneven cooling of the entire mold. Therefore, as shown in FIG. 5 (b), it is preferable that the inclination angle is made uniform in the region where the metal to be cast is cooled.

  The inclination of the slit may be periodically changed in the casting direction, and a waveform having substantially the same length, for example, a sine waveform is preferable. However, in the case of a mold for casting a round slab as illustrated in FIG. 6, this is not a limitation, and a straight line with a slanted slit when the mold is deployed, as in the second embodiment shown in FIG. 7. It is preferable to construct the slit in a spiral shape. Of course, as in the case of the assembled mold, since the effect can be exhibited if the cooling part and the non-cooling part are alternately arranged in the casting direction, it is not necessary to have a spiral shape, and a sinusoidal waveform may be used.

  If the angle of inclination of the slit with the casting direction axis is too small, the effect will not be exhibited.On the other hand, if it is too large, it will lead to an increase in pressure loss that causes cooling water to flow. Since there is a concern about the decrease, a maximum of 3 to 85 ° is preferable with respect to the vertical direction.

  Like the sine waveform, the period of periodically changing the inclination angle between the slit and the casting direction axis is such that a cooling water slit can be provided between the stud bolts in the casting direction from the viewpoint of preventing uneven cooling in the casting direction. In addition, it is desirable that the pitch is at least twice the pitch of the stud bolt in the casting direction.

  Moreover, the amplitude which changes the inclination angle which makes a casting direction axis | shaft of a slit periodically like a sine waveform is one or more cooling water slits between the stud bolts of a casting direction from a viewpoint of cooling nonuniformity of a casting direction. It is desirable that the distance between the slits on both sides of the stud bolt is greater than or equal to the distance between the stud bolts.

  From the above, when the slit has a sinusoidal waveform, the casting direction (Z) locus of the slit width center line can be expressed by the following equation.

    y = (Wp / 2) sin (2πft) (1)

  Here, when formula (1) is arranged with t = Z / V and f = 1 / (2Bp / V), formula (2) is obtained.

    y = (Wp / 2) sin [πZ / Bp] (2)

Where y: slit position in the mold width direction
Wp: n times the cooling water slit interval passing between the stud bolts in the casting direction, or n times the cooling water slit interval in other parts

Bp: Casting stud bolt pitch
V: Casting speed
t: time
f: period of sine wave slit

Therefore, the maximum value θmax of the inclination angle formed with the casting direction of the slit is inevitably determined (the maximum value of the differential value of the equation (2)), Bp = 80 to 150 mm, Wp = 20 to 35 mm (n = 1) Then,
θmax = arctan [(dy / dZ) max]
= Arctan (πWp / 2Bp)
= 12 to 38 ° (n = 1), 23 to 50 ° (n = 2), and 32 to 64 ° (n = 3).

  The sinusoidal waveform does not need to be expressed by the same expression over the entire length of the slit, and if Bp changes in the middle of the casting direction, the pitch of the waveform may be changed corresponding to the value. Similarly, the amplitude may be changed for each location as long as the slit interval is changed in the copper plate width direction. For example, in the stud bolt portion, Wp may be given by the sum of the slit interval on both sides of the stud bolt and the other slit interval that is equally spaced. For slit portions that are equally spaced, an integer multiple thereof is optimal.

  The sinusoidal slit can be easily processed by NC processing by computer control.

Using a vertical bending type continuous casting machine, medium carbon steel (C / 0.09 to 0.13, Si / 0.35 to 0.55, Mn / 1.0 to slab size 235 mm thickness x 1600 to 1800 mm width) 1.3, P / 0.015-0.030, S / 0.005-0.020, Al / 0.015-0.040, Nb / 0-0.050, N / 0.0035-0. 0100% by mass) at a casting speed of 1.8 to 2.0 m / min, and the rate of occurrence of vertical cracks in the slab (= crack generation rate of 5 mm or more per slab = number of cracked slabs / total number of slabs ) And the cutting life of the mold copper plate (the number of charges cast before cutting the surface of the copper plate to re-plat the surface due to surface plating wear, peeling, cracks, etc.) are shown in FIG. The present invention is applied only to the long side copper plate, and the short side copper plate has a normal structure. The amount of cooling water was 3500 L / min / surface (long side) in both the comparative example and the present invention example. The cooling water supply pressure at the time of carrying out the present invention increased by 0.5 kg / cm ^{2 at the} maximum from the comparative example, but could be cast without any problem. The cooling slit shape of the copper plate used was shown in FIG. 1 as a comparative example and FIG. 4 as an example of the present invention. The copper plate material was deoxidized copper containing silver chrome, and the copper plate surface plating was a Ni 0.5 mm base with a Cr plating thickness of 30 μm.

  As can be seen from FIG. 8, the occurrence rate of vertical cracks was greatly reduced by the present invention, and an increase in the number of times of use of the copper plate was confirmed, indicating that the effect of the present invention was remarkable.

Using a curved continuous caster, a seamless oil well steel pipe material 13% Cr steel with a round billet product size of 170 mmφ was cast at a casting speed of 1.3 to 1.5 m / min, and the rate of occurrence of vertical cracks in the slab (= Crack occurrence rate of 5 mm or more per slab = crack occurrence rate Number of slabs / total number of slabs) and cutting life of the mold copper plate (surface plating due to surface plating wear, delamination, cracks, etc.) FIG. 9 shows the number of charges cast before reworking. The amount of cooling water was 980 L / min for both the comparative example and the inventive example. The cooling water supply pressure at the time of carrying out the present invention increased by 0.2 kg / cm ^{2 at the} maximum compared to the comparative example, but could be cast without any problem. The cooling water slit shape of the copper plate used is shown in FIG. 6 as Comparative Example 1 (no slit, only with a ring-shaped water passage 13), and provided with a vertical slit in Comparative Example 2 as an example of the present invention. It was set to 7. The copper plate material was deoxidized copper containing silver chrome, and the copper plate surface plating was a Ni 0.5 mm base with a Cr plating thickness of 50 μm.

  As can be seen from FIG. 9, according to the present invention, the occurrence rate of vertical cracks and the occurrence rate of breakout (number of generated charges / total number of castings) were greatly reduced, indicating that the effect of the present invention was remarkable.

  The present invention is applicable to continuous casting metal and alloy molds, and is not limited to steel casting, but can also be used for continuous casting of aluminum, copper, brass, etc., and a cooling substrate (a copper alloy in the case of steel). ) Can be applied to all molds having a structure capable of providing a slit structure. Further, the material of the cooling plate is not limited to the copper plate, and the cooling liquid is not limited to water.

Plan view showing a conventional example of a continuous casting mold cooling plate for steel Sectional view along line II-II in FIG. Conceptual diagram of slit structure avoiding stud bolt in comparative example and embodiment of present invention The top view which looked at 1st Embodiment of this invention from the cooling water channel | path side Conceptual diagram showing preferred and unsuitable examples of linear inclined slit structure The figure which shows the comparative example of the mold structure for round billets The figure which shows the casting_mold | template structure for round billets which is 2nd Embodiment of this invention. The figure which shows the example in the mold copper plate for slab compared with the comparative example The figure which shows the example in the mold copper plate for the round billet in comparison with the comparative example

Explanation of symbols

10 ... Cooling plate (copper plate)
12 ... Cooling water passage (slit)
20 ... Backup frame 22 ... Stud bolt

Claims (7)

  Continuous casting characterized in that the coolant flow path of the continuous casting mold cooling plate is inclined with respect to the casting direction axis at a portion of at least 50% or more of the entire circumference of the mold cross section perpendicular to the casting direction. template.   The continuous casting mold according to claim 1, wherein an inclination angle of the coolant flow path is periodically changed in a casting direction.   3. The continuous casting mold according to claim 2, wherein a casting direction period of the inclination angle of the coolant flow path is made to coincide with twice a casting direction stud bolt pitch.   4. The continuous casting mold according to claim 3, wherein the total amplitude of the cyclic change in the casting direction of the coolant flow path inclination angle is 1 pitch or more of the coolant flow path.   The continuous casting mold according to claim 1, wherein a maximum value of an inclination angle formed by the coolant flow path and a casting direction axis is 3 to 85 °.   6. The continuous casting mold according to claim 1, wherein the casting mold is a cylinder, and all the coolant flow paths are formed in a spiral shape in the casting direction.   A continuous casting method using a mold satisfying any one of claims 1 to 6.

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