JP2000280051A - Continuous casting method of steel superior in cleanness property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a billet manufacturing method for manufacture of a steel material superior in surface property while its powder entrainment is small. SOLUTION: When a billet is cast with an usage of a continuous casting equipment, an electromagnetic agitation in the casting die is performed, and a high viscosity powder, the viscosity of which is 3 poises or more, is used so that a steel material having a low powder entrainment and superior cleanness property is continuously cast. In this case, a molten steel flow velocity nearby a meniscus in the casting die is set at 8 cm/sec or faster.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting technique for producing a slab for producing a steel material having excellent cleanliness.

[0002]

2. Description of the Related Art In recent years, ultra-low carbon steels having excellent workability and having a C content of 0.004% or less have been widely used for automobile outer panels and surface-treated steel sheets. As properties required for these ultra-deep drawing materials, not only mechanical properties such as r value and elongation are excellent, but also cleanliness, especially cleanliness of the surface layer which has been conventionally required, There is a demand for improved cleanliness inside a slab, which is a starting point of cracking during processing.

Conventionally, it has been known that the use of high-viscosity powder increases the critical flow rate of powder shaving due to the flow of molten steel in a mold, and reduces the occurrence of defects due to powder entrainment. However, due to the increase in powder viscosity, (1) if the casting conditions such as the mold vibration waveform, stroke, casting speed, etc. are the same, the powder consumption is reduced, the variation in heat removal from the mold is increased, and the slag bearing is increased. (2)
There is a drawback that powder inflow is not uniform and cracks are likely to occur in steel types having high crack susceptibility, and there are various problems in application to actual operation, such as the need to limit the casting speed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a cast piece for producing a steel material having a small powder entrainment and excellent surface properties. It is intended to provide.

[0005]

SUMMARY OF THE INVENTION The present invention is to apply a casting method capable of applying a high-viscosity powder without being restricted by operation. In order to achieve the above object, the present invention has the following constitution. Make a summary. (1) When casting using a continuous casting facility, a high viscous powder having a viscosity of 3 poise or more is used to produce a steel material with less powder entrainment and excellent cleanliness, which is characterized by cleanliness. Excellent steel continuous casting method. (2) The method for continuous casting of steel having excellent cleanliness according to (1), wherein in the casting using the continuous casting facility, electromagnetic stirring in a mold is performed. (3) The method for continuous casting of steel having excellent cleanliness according to (2), wherein the molten steel flow rate (time average) in the vicinity of the meniscus in the mold is 8 cm / sec or more. (4) The method for continuously casting steel with excellent cleanliness according to (1), wherein the molten steel or the continuously cast powder in the mold is heated when casting using the continuous casting facility. It is.

Hereinafter, the present invention will be described in detail.

In the casting method of the present invention, molten steel refined in a steelmaking furnace such as a converter furnace or an electric furnace steelmaking furnace is, if necessary, degassed, powder blown, and agitated by a secondary smelting facility. Perform component adjustment.

[0008] In the casting method of the present invention, when the molten steel melted to a predetermined component is cast by a continuous casting facility, the molten steel is fed from a molten steel container through a refractory injection pipe through a molten steel distribution container such as a tundish. The molten steel is supplied into the water-cooled copper mold by the submerged nozzle. Powdered continuous casting powder as a lubricant is supplied to the molten steel in the mold mechanically or manually. FIG. 4 shows the situation inside the mold. The continuous casting powder 2 supplied into the mold receives heat supply by coming into contact with the molten steel 6 and melts. Generally, the molten steel 6 supplied from the immersion nozzle 1 forms a molten steel flow 7 in a mold as shown in FIG.
Occurs. Since the heat is always removed from the water-cooled copper mold 3, the stagnation part where the flow velocity is small is smaller than the part where the flow velocity is large.
As the molten steel temperature decreases, powder melting is delayed, and as a result, powder supply to the mold and slab interface deteriorates.In the worst case, the powder supply cannot keep up, and the solidified shell of the slab sticks to the mold and the solidified shell is formed. Even torn.

[0009] Then, when the present inventors proceeded with research,
As a fundamental solution, the external force is applied independently of the molten steel discharge flow supplied from the immersion nozzle into the mold, and the molten steel flow is generated to eliminate the portion (stagnation) where the molten steel flow rate is small, It has been found that it is effective to make the temperature distribution in the width direction uniform.

According to the study by the present inventors, under the same casting conditions, as the viscosity of the powder increases, the powder consumption tends to decrease as shown in FIG.
When the viscosity exceeds 3 poise, as shown in FIG. 3, the consumed powder amount becomes 0.3 kg / ts which is considered to be appropriate.
(Weight of powder consumed per ton of molten steel).
The appropriate amount of powder consumption varies depending on the steel type composition, casting speed and mold size of the continuous casting equipment,
In order to maintain stable operation, at least 0.2 kg / t
s powder consumption is required.

[0011] Further, the consumed powder was collected just below the mold, and the powder consumption in the slab width direction was examined. As a result, the portion corresponding to the portion where the flow rate of the molten steel in the mold was small (stagnation portion) was found. Has found that the powder consumption is small as can be seen from FIG. Based on this knowledge, by applying external force to the molten steel in the mold by electromagnetic force and applying a flow independent of the discharge flow from the immersion nozzle, the stagnation part of the molten steel in the mold is eliminated, and even if it is highly viscous, it is stable Found that it can be cast. FIG. 2 shows the relationship between the flow rate of molten steel in the vicinity of the meniscus and the powder consumption when the molten steel in the mold was continuously rotated using electromagnetic stirring. As is clear from the figure, by ensuring the average flow velocity of the portion with the lowest molten steel flow velocity at 8 cm / sec or more, a sufficient powder consumption can be stably ensured even with high viscosity. FIG. 2 shows the data when the molten steel in the mold is continuously rotated. The time-averaged molten steel flow velocity near the meniscus is also used in the case of alternating stirring in which the stirring direction is reversed in time and translation stirring in which the stirring steel is flowed in one direction. It was confirmed that similar effects could be expected if they could be secured similarly. In measuring the molten steel flow velocity, a refractory having a strain sensor attached thereto was immersed in the molten steel, and the force received from the molten steel was converted into a flow velocity and used (the molten steel immersion depth of the refractory was 70 m).
m).

On the other hand, it is conceivable to improve the solubility of the powder by adding a third element or by adding a heat-generating substance, which lowers the melting temperature in the powder component in order to ensure powder inflow. However, the addition of the third element or the addition of the exothermic substance generally increases the cost, which is not desirable. Further, since the variation in the temperature distribution in the width direction of the mold is not eliminated, the unevenness in the powder consumption in the width direction is not eliminated, which is not desirable in that good slab properties are obtained.

In the present invention, the electromagnetic stirrer is provided because heat is supplied to the molten steel in the mold independently of the flow of the molten steel inevitably caused by the supply of the molten steel into the mold. Or to supply heat to a part where supply is insufficient and to make it uniform. In the present invention, as a means for promoting heat supply, a molten steel stirring device in a mold has been described as an example, but it is also possible to heat molten steel or continuous cast powder with a heating device and a heater. However, the important thing is
Since it is important to supply heat at the interface between the supplied continuous powder and the molten steel in the mold, heat is supplied from the outside to raise the temperature of the molten steel in the mold or eliminate parts with lower temperatures. Accordingly, it is important to make the temperature of the molten steel in the surface layer of the molten steel in the mold uniform.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments.

[0015]

EXAMPLES In the converter-RH-continuous casting process, the casting method of the present invention was used to produce Ti-added ultra-low carbon steel for automobiles and thick steel for general structures. 300 tons of molten steel
Then, casting was performed by a vertical bending type continuous casting facility equipped with an in-mold electromagnetic stirring device.

In order to produce Ti-added ultra-low carbon steel for automobiles, molten steel 300 ton produced in a converter is adjusted to a predetermined component concentration shown in Table 1 by RH, and a vertical bending type continuous casting facility is prepared. In the conditions shown in Table 2, 2, 3, 4, 8, 15
Using powder having different poise and viscosity, continuous rotation was applied to the molten steel in the mold by an electromagnetic stirrer, and the output was changed to investigate the relationship between the flow rate of molten steel near the meniscus in the stagnation portion and the powder consumption. The casting conditions are those shown in Table 2.

The viscosity at 1300 ° C. was used as the viscosity of the powder. In measuring the viscosity, a rotating cylinder method was used. A sample obtained by decarburizing the powder to be measured at 700 ° C. for 60 minutes was inserted into a graphite crucible, preliminarily melted at 1400 ° C. for 10 to 15 minutes, transferred to an iron crucible, and placed in a vertical tubular furnace (Erema furnace). Dipping the rotor of the mold viscometer into the slag,
After stabilizing at 00 ° C. for 30 minutes, the rotor was rotated and the torque due to viscous resistance was measured to determine the viscosity. The E-type viscometer is calibrated in advance with a standard viscosity liquid.

[0018]

[Table 1]

[0019]

[Table 2]

The flow rate was measured by immersing a refractory with a strain gauge attached in molten steel, and measuring the powder consumption by collecting the powder falling immediately below the mold.

As shown in FIG. 2, although there is a difference depending on the viscosity of the powder, the powder consumption increases due to the improvement in the flow velocity of the molten steel in the stagnation portion, and the flow velocity of the molten steel in the vicinity of the meniscus is increased by electromagnetic stirring. The powder consumption could be increased. As a result, a stable powder consumption can be ensured in the width direction of the mold as shown in FIG. 6 even when the viscosity is high, the powder is prevented from getting into the slab, and the casting for thin steel sheets for automobiles having excellent surface properties is achieved. Pieces can now be cast stably. In addition, as a result of imparting a swirling velocity independently of the molten steel discharge flow from the immersion nozzle to the vicinity of the meniscus by an electromagnetic stirrer, inclusions on the slab surface layer are also reduced, and a slab excellent in cleanliness near the slab surface layer is obtained. I was able to.

FIG. 1 shows the rate of occurrence of flaws attributable to powder in the linear flaws of the cold rolled sheet after the hot rolling and cold rolling steps using the present slab. It can be seen that in the cold-rolled sheet using the cast slab of the present invention, the incidence of linear flaws caused by the continuous casting powder is drastically reduced as compared with the comparative example using the conventional powder.

FIG. 5 shows the relationship between the viscosity of the continuously cast powder used and the formability during processing (the ratio of the number of processed cracks).
It can be seen that the moldability is improved by using a high-viscosity continuous casting powder.

This time, the vertical bending type continuous casting equipment was used, but the same effect can be expected in the curved type and vertical type continuous casting equipment.

Although the present embodiment has been described in connection with the production of a slab for a thin steel sheet for an automobile, the essence of the present technology is to impart non-uniform powder melting by applying molten steel flow. The present invention is effective in producing cast pieces of other steel types such as a thick plate, a steel pipe, and the like, and is not limited at all by the applied steel type.

[0026]

According to the present invention, as described above, according to the present invention, it is possible to produce a good workability thin steel sheet which has good formability and has few linear defects caused by nonmetallic inclusions in steel. Can be provided. Not only can the cold rolled steel sheet be manufactured using the present steel material, but also, after annealing, as an electrogalvanized or alloyed electrogalvanized steel sheet, and further, an original sheet of an organic coated steel sheet can be manufactured. In addition, as long as the conditions for continuous annealing are satisfied, it can be used as a steel material for steel sheets for continuous annealing hot-dip galvanizing and alloyed hot-dip galvanizing. Therefore, since it can be applied to a wide range of applications such as home electric appliances and automobiles, the effect on the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between powder viscosity and powdery defects

FIG. 2 is a diagram showing the relationship between molten steel flow velocity near the meniscus and powder consumption.

FIG. 3 is a diagram showing the relationship between powder viscosity and powder consumption.

FIG. 4 is a schematic view showing a flow of molten steel in a mold.

FIG. 5: Relationship between powder viscosity and ratio of the number of processed cracks generated

FIG. 6: Effect of improving powder inflow by applying electromagnetic stirring

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Continuous casting powder 3 Water-cooled copper mold 4 Part where molten steel flow is large 5 Part where molten steel flow is small 6 Molten steel 7 Molten steel flow

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Aso 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works F-term (reference) 4E004 FB04 GB02 MB14 NA01 NA02 NC01

Claims (4)

[Claims] When casting using a continuous casting facility, a highly viscous powder having a viscosity of 3 poise or more is used to produce a steel material with less powder entrainment and excellent cleanliness. Excellent steel continuous casting method. 2. The method for continuously casting steel with excellent cleanliness according to claim 1, wherein in the casting using the continuous casting equipment, electromagnetic stirring in a mold is performed. 3. The continuous casting method for steel having excellent cleanliness according to claim 2, wherein the molten steel flow rate (time average) in the vicinity of the meniscus in the mold is 8 cm / sec or more. 4. The method for continuously casting steel having excellent cleanliness according to claim 1, wherein the molten steel or the continuously cast powder in the mold is heated when casting using the continuous casting facility.