Method and apparatus for continuous casting of metals

Abstract: During continuous casting of metals, a non-moving, vibrating magnetic field is applied to a molten metal in a casting mold to impose only vibration on the molten metal. This continuous casting method can produce a cast slab much less susceptible to flux entrainment, capture of bubbles and non-metal inclusions near the surface of the molten metal, and surface segregation. The magnetic field is preferably produced by arranging electromagnets in an opposing relation on both sides of the mold to lie side by side in the direction of longitudinal width of the mold, and supplying a single-phase AC current to each coil. The single-phase AC current preferably has frequency of 0.10 to 60 Hz. A static magnetic field can be applied intermittently in the direction of thickness of a cast slab. This technique can produce a cast slab substantially free from the flux entrainment and the surface segregation. Preferably, the static magnetic field is intermittently applied under setting of an on-time t1 = 0.10 to 30 seconds and an off-time t0 = 0.10 to 30 seconds. Also, the static magnetic field is preferably applied to the surface of the molten metal.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method and apparatus for effecting flow control of molten steel using a magnetic field during continuous casting of steel. 2. Description of Related Art In continuous casting, an immersion nozzle is often used to pour a molten metal into a casting mold. If the flow speed of the surface molten metal is too high at that time, mold flux on the surface of the molten metal is entrained (or involved) into a body of the molten metal, and if the flow speed of the surface molten metal is too low, the molten metal stagnates and segregates there, thus finally giving rise to surface segregation. For reducing such surface defects, there is known a method of applying a static magnetic field and/or a moving magnetic field (AC moving magnetic field) to the molten metal in the mold for controlling the flow speed of the molten metal. However, the known method has problems as follows. When a static magnetic field is applied to brake a flow of the molten metal (for electromagnetic braking) , segregation tends to occur readily, particularly in a position where the molten metal stagnates. Also, when a moving magnetic field is applied to agitate the molten metal (for electromagnetic agitation) , entrainment of the mold flux (flux entrainment) tends to occur readily in a position where the flow speed of the molten metal is high. To cope with the above problems, several proposals have been made as to the manner of applying a magnetic field. For example, Japanese Unexamined Patent Application Publication No. 9-182941 discloses a method of periodically reversing the direction, in which a molten metal is agitated by a moving magnetic field, to prevent inclusions from diffusing downward from an agitation area. Japanese Unexamined Patent Application Publication No. 8-187563 discloses a method of preventing a breakout by changing the magnitude of a high-frequency electromagnetic force depending on vibration of a casting mold. Japanese Unexamined Patent Application Publication No. 8-267197 discloses a method of preventing inclusion defects by providing a gradient to a change rate of the magnetic flux density in the changeover process of an electromagnetic braking force so as to reduce changes of a molten metal flow. Furthermore, Japanese Unexamined Patent Application Publication No. 8-155605 discloses a method of applying a horizontally moving magnetic field at frequency of 10 - 1000 Hz through conductive layers, each of which has low electrical conductivity and is formed to extend continuously in the direction of transverse width of a casting mold, and imposing a pinching force on a molten metal so that a contact pressure between the casting mold and the molten metal is reduced. However, none of these known methods has succeeded in satisfactorily preventing the occurrence of flux entrainment, because a macro flow of the molten metal is caused due to the moving magnetic field, or because the flow speed of the molten metal is increased in a position where the static magnetic field is small. SUMMARY OF THE INVENTION With the view of breaking through the limits of the related art set forth above, it is an object of the present invention to provide a continuous casting method and apparatus for metals, which can produce a cast slab much less susceptible to flux entrainment, capture of bubbles and non-metal inclusions near the surface of a molten metal, and surface segregation. As a result of conducting intensive studies, the inventors have made the following findings. Aspect A of Invention: Application of Non-moving, Vibrating AC Magnetic Field 1) Molten-metal flow control under application of a static magnetic field is very effective in preventing entrainment of mold flux 3 and occurence of inclusions. However, if the magnetic field is too strong, the flow speed of a molten metal is reduced and surface segregation 5 is caused due to semi-solidification at the surface of the molten metal. (See Fig. 1) 2) Molten-metal flow control under application of a moving magnetic field is able to prevent the surface segregation 5 and capture of foreign matters (bubbles and non-metal inclusions 4) at the solidification interface. With a resulting increase of the flow speed of the molten metal indicated by 2, however, the entrainment of the mold flux 3 is more likely to occur and an amount of the entrained mold flux 3 is apt to increase. (See Fig. 1) 3) A method of applying an electromagnetic force, which induces only vibration without inducing a macro flow, so as to act upon the molten metal is very effective in preventing the semi-solidification at the surface of the molten metal and the capture of foreign matters at the solidification interface while holding down the flux entrainment. Such an electromagnetic force can be produced by an AC magnetic field which is not moved but only vibrated (hereinafter referred to as a "non-moving, vibrating magnetic field)". Thus, the term "non-moving magnetic field" as used herein connotes magnetic flux alternating in opposite directions, whereas a moving magnetic field connotes a magnetic flux continuing in a single direction. The present invention according to this aspect A has been accomplished based on the above-mentioned findings. More particularly, according to this aspect A of the present invention, there is provided a continuous casting method for metals, as defined in claim 1. Preferred embodiments of the inventive method are defined in the dependent sub-claims 2 to 5. Further according to another aspect of the present invention, there is provided an apparatus as defined in claim 6 and an apparatus as defined in claim 8. Preferred embodiments of the inventive apparatuses are defined in dependent sub-claims 7 and 9, respectively. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view for explaining mechanisms that generate flux entrainment, surface segregation, and capture of foreign matters; Fig. 2 is a schematic view showing a first example of a manner of creating a non-moving, vibrating magnetic field; Fig. 3 is a schematic view showing a second example of the manner of creating the non-moving, vibrating magnetic field; Fig. 4 is a schematic view showing one example of a manner of creating a moving magnetic field; Fig. 5 is a schematic view showing one example of a comb-shaped iron core; Figs. 6A and 6B show one example of an apparatus according to the present invention, wherein Fig. 6A is a schematic sectional plan view and Fig. 6B is a schematic sectional side view; Fig. 7 is a waveform chart showing one example of a magnetic flux density produced under application of an AC magnetic field alone; Fig. 8 is a schematic view for explaining molten steel flows occurring under application of an AC magnetic field alone; Fig. 9 is a waveform chart showing one example of a magnetic flux density produced under application of AC and DC magnetic fields; Fig. 10 is a schematic view for explaining molten steel flows occurring under application of AC and DC magnetic fields; Fig. 11 is a schematic sectional plan view showing interference between a circulating flow and an ejected-and-reversed surfacing flow caused by electromagnetic agitation in a meniscus area (the surface of molten steel) ; In the figures, the following reference numerals designate the following components and features: 1. Immersion nozzle 2. Flow speed of the molten metal 3. Mold flux 4. Non-metal inclusions 5. Surface segregation 6. Casting mold 7. Electromagnet 8. Iron core 9. Coil 10. Longitudinal width vibrating flow 11. Transverse width vibrating flow 12. Bulk current 13. Comb-shaped iron core 14. Comb teeth portion 18. DC supplied coils 19. AC supplied coils 20. Direction of the DC magnetic field 21. Direction of the AC magnetic field 22. Magnetic poles 23. Molten steel 24. Electromagnetic force 25. Molten steel flow 26. Non-directional molten steel flow 27. Circulating flow 28. Ejected-and-reversed surfacing flow 29. Vortex 30. Stagnation 31. Moving AC magnetic field DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Aspect A of Invention: "Application of Non-Moving, Vibrating AC Magnetic Field" With the aspect A of the present invention, a non-moving, vibrating magnetic field is applied to a molten metal in a casting mold under continuous casting to impose only vibration on the molten metal. Because of applying a non-moving magnetic field, a bulk flow (macro flow) of the molten metal is not produced, unlike in the case of applying a moving magnetic field, and therefore flux entrainment does not readily occur. Also, because of applying a vibrating magnetic field, minute vibration of the molten metal is generated in the vicinity of the solidification interface. The generated minute vibration contributes to not only preventing capture of foreign matter (bubbles and non-metal inclusions) by the solidification interface, but also holding down uneven solidification in the vicinity of a meniscus area (the surface of the molten steel) which is responsible for surface segregation. The non-moving, vibrating magnetic field can be created, by way of example, as shown in Figs. 2 and 3. A number of electromagnets 7, each comprising an iron core 8 and a coil 9 wound around the iron core 8, are arranged on both sides of a casting mold 6 in an opposing relation in the direction of transverse width of the mold to lie side by side in the direction of longitudinal width of the mold, and a single-phase AC current is supplied to each coil 9. Note that numeral 20 in Figs. 2 and 3 denotes a magnetic force line. In a first example shown in Fig. 2, each pair of opposing coils 9, 9 are wound in the same direction (x, x or y, y), and pair of adjacent coils 9, 9 on the same side of the mold are wound in opposite directions (x, y). A single-phase AC current is then supplied to each of the coils 9 thus wound. Therefore, magnetic forces developed between every two electromagnets 7, 7 arranged adj acent to each other on the same side are reversed in direction repeatedly over time. As a result, only vibrating flows 10 in the direction of longitudinal width of the mold are induced in the molten metal and no bulk flows are produced. In a second example shown in Fig. 3, each pair of opposing coils 9, 9 are wound in opposite directions (x, y), and pair of adjacent coils 9, 9 on the same side are wound in the same direction (x, x or y, y). A single-phase AC current is then supplied to each of the coils 9 thus wound. Therefore, magnetic forces developed between every two opposing electromagnets 7, 7 are reversed in direction repeatedly over time. As a result, only vibrating flows 11 in the direction of transverse width of the mold are induced in the molten metal and no bulk flows are produced. On the other hand, a moving magnetic field is created, by way of example, as shown in Fig. 4. A number of electromagnets 7, each comprising an iron core 8 and a coil 9 wound over the iron core 8, are arranged on both sides of a casting mold 6 in an opposing relation in the direction of transverse width of the mold to lie side by side in the direction of longitudinal width of the mold, and a three-phase AC current is supplied to each coil 9. Note that letters u, v and w denote different three phases of the three-phase AC current. The left six coils and right six coils are wound in opposite directions (x, y) . With the moving magnetic field thus created, magnetic forces are produced in a constant direction (i.e., a direction from one end toward the other end of the mold along the longitudinal width thereof) . Accordingly, a bulk current 12 is produced in the molten metal to horizontally circulate along inner walls of the mold 6, and it is difficult to hold down the occurrence of flux entrainment. While the iron cores of the electromagnets are constructed as individual single iron cores separate from each other in Figs. 2 and 3, this aspect of the present invention may also implemented by using a comb-shaped iron core 13 as shown in Fig. 5 having comb teeth portions 14 over which the coils 9 are fitted. This construction is advantageous in that fabrication of the electromagnets is facilitated because the electromagnets can be fabricated by providing one comb-shaped iron core 13 on each side of the casting mold 6 in the direction of transverse width of the mold and fitting the coils 9 over the comb teeth portions 14 in a one-to-one relation. Also, in this aspect of the present invention, the single-phase AC current supplied to the coils 9 preferably has frequency of 0.10 - 60 Hz. Setting the frequency to be not lower than 0.10 Hz makes it possible to increase the skin effect, to concentrate the vibration in the vicinity of the solidification interface, and to enhance the effect of preventing the capture of foreign matter. However, if the frequency exceeds 60 Hz, a vibration urging force is reduced down to a level close to viscosity resistance of the molten metal, whereby vibration of the molten metal is weakened and the effect of preventing the capture of foreign matter is lessened. According to this aspect of the present invention, as described above, casting of a high-quality metal slab can be achieved which is free from surface segregation, contains less foreign matter (bubbles and non-metal inclusions) captured in the cast slab, and suffers from less flux entrainment. The electromagnets are preferably disposed in positions close to the surface of the molten metal, but similar advantages can also be obtained even when the electromagnets are disposed in positions lower than the nozzle ejection hole. EXAMPLES (Tables 1 and 2) About 300 tons of ultra low carbon-and-Al killed steel (having a typical chemical composition listed in Table 1) was smelted using the converter - RH process, and a slab being 1500 - 1700 mm wide and 220 mm thick was cast by pouring the molten killed steel into a casting mold at a rate of 4 - 5 ton/min from an immersion nozzle with a continuous casting machine. In this slab casting step, experiments were conducted by arranging electromagnets in each of the layouts shown in Figs. 2 to 4 at a level corresponding to the position of the molten steel surface, and supplying a three- or single-phase AC current of various frequencies to a coil of each electromagnet, thereby applying a moving magnetic field or a non-moving, vibrating magnetic field with a magnetic flux density of 0.1 T, or applying no magnetic field. In the experiments, three characteristics, i.e., surface segregation, flux-based surface defects, and a bubble/-inclusion amount, were measured for each condition of applying the magnetic field in accordance with the following procedures. Surface Segregation: After grinding the cast slab, the slab was subjected to etching and the number of segregates per 1 m 2 was counted by visual observation. Flux-based Surface Defects: Surface defects in a coil obtained after cold rolling of the cast slab were visually observed, and after picking a defective sample, the number of defects caused by entrainment of mold flux was counted by analyzing the defects. Bubble/Inclusion Amount: Non-metal inclusions were extracted by the slime extracting process from a portion of the cast slab at a position corresponding to a 1/4 thickness thereof, and the weight of the extracted inclusions was measured (the number of bubbles was measured by slicing a surface layer of the cast slab and counting the number of bubbles observed with a transmitted X ray). The experimental results are listed in Table 2 along with the conditions of applying the magnetic field. Note that evaluation values of the above three items are each represented in terms of an index (numerical value obtained by multiplying a ratio of the measured data to the worst data among all the conditions by 10). As seen from Table 2, in Examples according to this aspect of the present invention in which the non-moving, vibrating magnetic field was applied, the surface segregation, the defects caused by the flux entrainment, and the amount of bubbles and non-metal inclusions could be all remarkably reduced. In Example 1, since the frequency was too low, i.e., 0.05 Hz, a macro flow was partly induced in the molten steel and the flux-based surface defects were increased to some extent. Also, in Example 8, since the frequency was too high, i.e., 65 Hz, the vibration was weakened and the number of bubbles and inclusions was increased to some extent. A description will now be made of a modification of this aspect of the present invention in which a DC magnetic field and an AC magnetic field for producing a non-moving, vibrating magnetic field are applied in superimposed fashion in the direction of transverse width of a casting mold. In Figs. 6A and 6B, coils (DC supplied coils) 18, to which a DC current is supplied to produce DC magnetic fields (equivalent to static magnetic fields), and coils (AC supplied coils) 19, to which an AC current is supplied to produce fixed AC magnetic fields, are wound over a common iron core 8 as shown. Two iron cores 8 are disposed to extend respectively along outer surfaces of long sides of a casting mold 6 such that directions of the magnetic fields (i.e., directions 20 of the DC magnetic fields and directions 21 of the AC magnetic fields) are aligned with the direction of transverse width of the mold, and one or more (six on each of the upper and lower sides in the illustrated apparatus) pairs of magnetic poles 22 are positioned to face each other above and below an ejection port of an immersion nozzle 1. A single- or three-phase AC current is supplied to each of the AC supplied coils 19 which are arranged to lie side by side in the direction of longitudinal width of the casting mold 6. In the magnetic field produced by the single-phase AC current, the phase of a waveform representing an intensity distribution in the direction of longitudinal width of the mold (positions of hills and valleys of the distribution) is not changed over time (that is to say, a wave does not move in the direction of longitudinal width of the mold). On the other hand, the so-called conventionally employed moving magnetic field is produced by arranging AC supplied coils in division to three sets and supplying three-phase AC currents to the three sets of coils with different phases from each other. In a magnetic field thus produced, the phase of a waveform representing an intensity distribution in the direction of longitudinal width of the mold is changed over time. Thus, the fixed AC magnetic field employed in the present invention means an AC magnetic field in which a wave does not move in a certain direction, unlike the conventionally employed moving magnetic field (moving AC magnetic field) . Even with the use of a multi-phase AC current, it is also possible to produce an AC magnetic field, in which a wave does not move in a certain direction, by arranging the coils in a proper layout. As shown in Fig. 8, when a single AC magnetic field providing a magnetic flux density as represented by a waveform shown in Figs. 7, by way of example, is applied by the AC supplied coil 19 in the direction of transverse width of the mold (the direction 21 of the AC magnetic field), an electromagnetic force (pinching force) 24 with a magnitude varying periodically acts upon a molten steel 23 and gives rise to a molten steel flow 25. In this case, however, the applied magnetic field is attenuated by an induction current magnetic field generated by mold copper plates, etc. Accordingly, the magnetic flux density produced within the mold is only on the order of about several hundred Gauss, and it is difficult to increase the electromagnetic force 24. On the other hand, as shown in Fig. 10, when an AC and DC superimposed magnetic field providing a magnetic flux density as represented by a waveform shown in Fig. 9, by way of example, is applied by the AC supplied coil 19 and the DC supplied coil 18 in the direction of transverse width of the mold (the direction 21 of the AC magnetic field and the direction 20 of the DC magnetic field) , the magnetic flux density produced within the mold can be increased to a level of several thousands Gauss and the electromagnetic force 24 can also be increased. An AC component of the electromagnetic force (i.e., an electromagnetic pumping force) causes disorder in the molten steel flow 25, whereby movement of heat and material is activated and the Washing effect is also promoted. Since an AC magnetic field is gradually attenuated due to the skin effect as it approaches the interior of a material, the electromagnetic pumping force is relatively large near a widthwise surface a solidified shell, but relatively small near the center of the molten steel in the direction of transverse width of the mold. A DC magnetic field is hardly attenuated across the overall transverse width of the mold. Near the center of the molten steel in the direction of transverse width of the mold, therefore, a DC component of the electromagnetic force (i.e., an electromagnetic braking force) acting to brake the molten steel prevails over the periodically varying component that is attenuated there. As a result, it is possible to attenuate flows branched from an ejected flow to move upward and downward, and at the same time to activate the molten steel flow near the widthwise surface of the solidified shell. In addition, because of employing the fixed AC magnetic field in which a wave does not move in the direction of transverse width of the mold, the molten steel flow in a meniscus area near long walls of the casting mold 6 becomes a non-directional molten steel flow 26 that moves in random directions, as shown in Fig. 6. This prevents generation of a circulating flow 27, shown in Fig. 11, that moves along the periphery of the casting mold 6. Hence, neither vortex 29 nor stagnation 30 is produced due to collision between the circulating flow 27 and an ejected-and-reversed surfacing flow 28 from the immersion nozzle 1, thus resulting in a remarkable reduction of such disadvantages as the entrainment of flux powder with the vortex and the capture of inclusions by the solidified shell in the stagnation. In order to sufficiently develop the above-mentioned effects, the AC and DC superimposed magnetic field is preferably applied from one or more pairs of magnetic poles 22 disposed in an opposing relation above and/or below the ejection port of the immersion nozzle 1, as shown in Fig. 6. Applying the AC and DC superimposed magnetic field above the ejection port of the immersion nozzle 1 can hold down the occurrence of the vortex and stagnation in the meniscus area, and applying it below the ejection port of the immersion nozzle 1 can promote braking against the downward flow from the immersion nozzle 2 and enlarge the range within which the Washing effect exerts. Furthermore, by arranging the magnetic poles in an opposing relation, the magnetic field can be symmetrically applied from both the sides of the casting mold in the direction of transverse width of the mold. Still further, by arranging one or more pairs of the magnetic poles, the molten steel flow is disordered near the widthwise surface of the solidified shell more evenly in the direction of longitudinal width of the mold, and the Washing effect can be developed thoroughly in the direction of longitudinal width of the mold with more ease. From the standpoint of apparatus construction, the AC supplied coils 19 and the DC supplied coil 18 are preferably wound over the same iron core 8, as shown in Fig. 6, for ease in positioning of the applied magnetic fields, aligned application of the AC and DC superimposed magnetic field to the desired positions, and independent adjustment of DC and AC components of the superimposed magnetic field. Additionally, the AC supplied coils 19 are each preferably wound over one of a plurality of magnetic poles 22 which are formed by branching a front end portion of the iron core 8 into the shape of comb teeth, whereas the DC supplied coil 18 may be wound over a root (referred to as a "common pole") in common to the magnetic poles 22 formed side by side in the shape of comb teeth at the front end portion of the iron core 8. Also, in the modification of this aspect of the present invention, the AC magnetic field preferably has frequency of 0.01 - 50 Hz. If the frequency is lower than 0.01 Hz, the intensity of a produced electromagnetic force becomes insufficient, and if the frequency exceeds 50 Hz, it is difficult for the molten metal flow to follow changes of the electromagnetic force. In any case, it is difficult to make the molten metal flow disordered satisfactorily near the widthwise surface of the solidified shell. EXAMPLE (Table 3) A strand of low carbon-and-Al killed steel being 1500 mm wide and 220 mm thick was cast by pouring the molten killed steel at a casting rate of 1.8 m/min and 2.5 m/min and an immersion nozzle ejection angle of 15° downward from the horizontal with a continuous casting machine of the vertical bending type. In this casting step, experiments were conducted by employing the apparatus shown in Fig. 6, and applying magnetic fields to a portion of the strand corresponding to the mold position under various conditions of applying the magnetic fields as listed in Table 3. A cast slab was subjected to measurement of a surface defect index determined by inspecting surface defects of a steel plate after being rolled, and a machining crack index determined by inspecting inclusion-based machining cracks caused during pressing of a steel plate. The surface defect index and the machining crack index are each defined as an index that takes a value of 1.0 when electromagnetic flow control is not carried out. In table 3, in each pole to which a moving AC magnetic field was applied, AC supplied coils were arranged in division to three sets so as to provide a moving-magnetic-field pole pitch of 500 mm, and three-phase AC currents were supplied to the three sets of coils with different phases from each other. In each pole to which a fixed AC magnetic field was applied, a single-phase AC current was supplied to each of AC supplied coils wound over the respective magnetic poles, and the phase of a magnetic flux density was set to the same for each magnetic pole. Also, in Table 3, the intensity of the AC magnetic field is represented by an effective value of the magnetic flux density at an inner surface position of a mold copper plate when the AC magnetic field is solely applied, and the intensity of the DC magnetic field is represented by a value of the magnetic flux density at the center of the cast slab in the direction of thickness thereof when the DC magnetic field is solely applied. The pole, in which the intensities of both the AC and DC magnetic fields are not 0 T, represents a pole to which the AC and DC superimposed magnetic field was applied. As shown in Table 3, the conditions 1 to 5 represent Comparative Examples departing from the scope of the present invention, and the condition 6 represents Example falling within the scope of the present invention. Measurement results of the surface defect index and the machining crack index are also listed in Table 3. Note that the measured result is expressed by an average of two values measured for two different casting rate conditions. In the Comparative Examples of Table 3, the DC magnetic field and the moving magnetic field (moving AC magnetic field) were applied solely or in superimposed fashion. When only the DC magnetic field was applied, supply of the molten steel heat was insufficient and a claw-like structure grew in an initially solidified portion. The claw-like structure catches flux powder and increased the surface defect index. When only the moving magnetic field was applied, growth of the claw-like structure could be held down, but the electromagnetic braking force was so small that inclusions intruded into a deeper area of a not-yet-solidified molten steel bath within the cast slab. In addition, a vortex and stagnation were caused in the meniscus area upon collision between the circulating flow along the periphery of the casting mold and the ejected-and-reversed surfacing flow. The intrusion of inclusions into the deeper area of the not-yet-solidified molten steel bath within the cast slab increased the machining crack index. The vortex brought about entrainment of flux powder, and the stagnation promoted the capture of inclusions by the solidified shell. Any of the vortex and the stagnation increased the surface defect index. By superimposing the DC magnetic field on the moving magnetic field, the inclusions could be avoided from intruding into the deeper area of the not-yet-solidified molten steel bath, but the occurrence of vortex and stagnation could not be avoided. Under the best condition 5 among the Comparative Examples in which the moving magnetic field and the DC magnetic field were applied to both upper and lower poles, therefore, the machining crack index was reduced down to 0.1, but the surface defect index still remained as high as 0.2. By contrast, the Example of Table 3 employed the condition 6 in which the fixed AC magnetic field was applied instead of the moving magnetic field employed in the condition 5. Under the condition 6, the electromagnetic pumping force was caused to act upon the widthwise surface of the solidified shell to enhance the Washing effect, and the electromagnetic braking force was caused to act upon a central portion of the cast slab in the direction of thickness thereof to reduce the flow speeds of the molten steel flows (upward and downward flows branched from the ejected flow) and to promote creation of laminar flows. Furthermore, generation of the circulating flow in the meniscus area could be held down, and the vortex and stagnation were avoided from being produced there. As a result, both the surface defect index and the machining crack index could be reduced down to 0.05 that was not obtained with Comparative Examples. While the present invention has been described above in connection with several preferred embodiments, it is to be expressly understood that those embodiments are solely for illustrating the invention, and are not to be construed in a limiting sense. After reading this disclosure, those skilled in this art will readily envision insubstantial modifications and substitutions of equivalent materials and techniques, and all such modifications and substitutions are considered to fall within the true scope of the appended claims. C Si Mn P S Al Ti 0.0015 0.02 0.08 0.015 0.004 0.04 0.04

Claims: A method of continuously casting metals, comprising applying a non-moving, vibrating magnetic field generated with an AC current of 60 Hz or less to a molten metal in a casting mold to impose only vibration on the molten metal, wherein non-moving magnetic field is defined that a wave representing an intensity distribution in the direction of longitudinal width of the mold thereof does not move in a certain direction. The method according to Claim 1, wherein said non-moving, vibrating magnetic field is produced by arranging electromagnets, each of which comprises an iron core and a coil wound over the iron core, in a facing relation on opposite sides of said mold along a transverse width thereof to lie side by side along a longitudinal width of said mold, and supplying a single-phase AC current to each coil. The method according to Claim 2, wherein said iron core comprises individual single iron cores separate from each other, or a comb-shaped iron core having a comb-teeth portion over which coils are wound. The method according to Claim 1, wherein a DC magnetic field and an AC magnetic field for producing said non-moving, vibrating magnetic field are applied in superimposed fashion along a transverse width of said mold. The method according to Claim 4, wherein the superimposed magnetic field is applied from at least one pair of magnetic poles arranged to face each other above or/and below an ejection port of an immersion nozzle. An apparatus for continuous casting of molten metals, the molten metal being continuously cast using a casting mold, said apparatus comprising: means for applying a non-moving, vibrating magnetic field to the molten metal in said mold to impose only vibration on the molten metal, said non-moving magnetic field is defined that a wave representing an intensity distribution in the direction of longitudinal width of the mold thereof does not move in a certain direction; electromagnets each comprising an iron core and a coil wound over said iron core, said electromagnets being arranged in a facing relation on opposite sides of said mold along a transverse width thereof to lie side by side along a longitudinal width of said mold; and means for supplying a single-phase AC current of 60 Hz or less to each coil. The apparatus according to Claim 6, wherein said iron core comprises individual single iron cores separate from each other, or a comb-shaped iron core having a comb-teeth portion over which the coils are wound. An apparatus for continuous casting of molten metals, the molten metal being continuously cast using a casting mold, said apparatus comprising: a coil supplied with a DC current for producing a DC magnetic field and a coil supplied with an AC current of 60 Hz or less for producing a non-moving, vibrating magnetic field, both said coils being wound over each of common iron cores, said iron cores being arranged around said mold such that a direction of the magnetic fields produced by said coils is aligned with a transverse width of said mold, wherein said non-moving magnetic field is defined that a wave representing an intensity distribution in the direction of longitudinal width of the mold thereof does not move in a certain direction. The apparatus according to Claim 8, wherein magnetic poles of said iron core are arranged in at least one pair to face each other above or/and below an ejection port of an immersion nozzle.

Inventors: BESSHO NAGAYASU, KIRIHARA TADASU, MIKI YUJI, TAKEUCHI SHUJI, YAMANE HIROSHI, BESSHO, NAGAYASU, KIRIHARA, TADASU, MIKI, YUJI, TAKEUCHI, SHUJI, YAMANE, HIROSHI, BESSHO, Nagayasu, Kawasaki Steel Corporation, Kirihara, Tadasu, Kawasaki Steel Corporation, MIKI, Yuji, Kawasaki Steel Corporation, Takeuchi, Shuji, c/o Techn. Res. Labor., Yamane, Hiroshi, Kawasaki Steel Corporation
Applicants: JFE STEEL CORP, JFE STEEL CORPORATION
Application year: 2000
Main classification: B22D11
IPC codes: B22D11