Molding powder for continuous casting of thin slab

Details Molding powder for continuous casting of thin slab Molding powder for continuous casting of thin slab

2000-03-21

2001-11-13

Mai, Ngoclan (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Solid treating composition for liquid metal or charge

C075S252000

Reexamination Certificate

active

06315809

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mold powder for continuous casting of thin slabs having a slab thickness of 150 mm or less.
RELATED ART
Mold powders for continuous casting of steel generally have Portland cement, synthetic calcium silicate, wollastonite, phosphorus-containing slag, etc., as their principal raw materials, and where required, silica materials may be added, soda ash, fluorite, fluorine compounds, and alkali metal and alkaline earth metal compounds may be added as fusion regulating agents, and carbon powder may be added as a melting speed regulating agent.
Mold powder is added at the surface of the molten steel inside the mold, and performs various functions as it is consumed. Major functions of mold powder include: (1) lubricating the mold and the solidified shell; (2) dissolving and absorbing inclusions; (3) insulation of the molten steel; and (4) controlling the speed of heat transfer. For (1) and (2), it is important to regulate the softening point and viscosity of the mold powder, and it is necessary to adjust the chemical composition of the mold powder accordingly. For (3), powder properties such as melting temperature, bulk specific density, and powder spreading, which can be regulated mainly by carbon powder, are considered to be important. For (4), it is important to regulate the crystallization temperature, etc., and it is necessary to adjust the chemical composition accordingly.
Worldwide technical progress in continuous casting of steel has been remarkable, and development continues. Moreover, Hot Charge Rolling (HC) and Hot Direct Rolling (HD) ratios have been improved and high-speed casting has been actively adopted to conserve energy, demands on mold powders have become stricter, and mold powders have become more diverse.
Thin-slab continuous casting has been developed from conventional continuous slab casting and applied with the objective of lower cost production with less heat transfer. There are still few such casters operating in Japan, but there are many operating widely mainly in the United States, but Europe, etc., as well, numbering several tens of units, and large numbers are being constructed in a large number of other countries.
There are several types of production processes in thin-slab continuous casting, including: (1) compact-strip-production (CSP) by SMS Schloemann-Siemag; (2) in-line-strip-production (ISP) by Mannesmann Demag; (3) Tippins Samsung process (TSP) by Tippins-Samsung; (4) flexible thin-slab rolling by Danieli; (5) continuous thin slab and rolling technique by Voest-Alpine Industrieanlagenbau (VAI); and (6) medium slabs (called medium but belonging to thin slabs from 100 mm) by Sumitomo Heavy Industries.
The main characteristic of the thin-slab continuous casting processes is that cast strips are directly hot rolled immediately, and even coiled. Consequently, finished and semi-finished products can be obtained in a matter of minutes from casting to coiling. In the case of conventional continuous casting of a generic slab, the process involves transferring the cast slab strip to a heating furnace and hot rolling it through a roughing-down mill, but in the case of thin-slab continuous casting, the process has a direct connection to the heating furnace and immediate rolling without roughing down in order to minimize the load on the rolling process. For that reason, thin-slab continuous casting is very-high-speed casting in which the casting speed is 3 or more meters per minute and the mold thickness is reduced.
Conventionally, Portland cement, phosphorus-containing slag, synthetic slag, wollastonite, dicalcium silicate, etc., are used as the principal raw materials for mold powders used in thin-slab continuous casting, carbonates such as Na
2
CO
3
, Li
2
CO
3
, MgCO
3
, CaCO
3
, SrCO
3
, MnCO
3
, and BaCO
3
, as well as NaF, Na
3
AlF
6
, fluorite, MgF
2
, LiF, borax, and spodumene, are used as fusion regulating agents, and carbonaceous raw materials are generally added as melting speed regulating agents.
On the other hand, mold powders employing synthetic calcium silicate as their principal raw material (semi-premelted types), and completely molten mold powders (premelted types) in which mold powder without carbon powder is first fused and pulverized to a suitable grain size, and then carbon powder is added, are also used as in the case of conventional generic slab casters.
Japanese Patent Laid-Open No. HEI 2-165853 discloses a high-speed continuous casting method for steel characterized in that its main components are CaO, SiO
2
, and Al
2
O
3
, the ratio of CaO to SiO
2
(by weight percentage) is within a range of 0.5 to 0.95, it contains one or two or more species of oxides, carbonates, or fluorides of alkali metals, alkaline earth metals, or other metals, also contains carbon powder as a melting speed regulating agent, uses a mold powder whose surface tension at 1250° C. is 290 dyne/cm or more, whose solidifying temperature is 1000° C. or less, and in which a relationship between the viscosity &eegr; (poise) at 1300° C. and the casting speed V (m/min) satisfies a range represented by the expression:
3.5≦&eegr;
V≦
6.0,
and the caster operates at a casting speed V≧1.2 m/min for a cast strip having a width of 600 mm or more. However, according to the preferred embodiments of the laid-open patent application in question, the casting speed is approximately 1.2 to 2.0 m/min, and it is clear this is not intended to be a very-high-speed continuous casting method with a casting speed of 3.0 m/min or more. Moreover, since the viscosity of conventional mold powders is too low for very-high-speed casting in which the casting speed is 3.0 m/min or more, heat transfer from the molten steel and the flow of fused powder between the solidified shell and the mold is not uniform, preventing achievement of stable quality and also preventing the achievement of stable operations. Therefore, the casting method described in the laid-open patent application in question and the very-high-speed continuous casting method of the present invention in which the casting speed would be 3.0 m/min or more are completely different casting methods.
At present, ordinary carbon steels such as ultra-low-carbon steels (carbon content: 100 ppm or less), low-carbon steels (carbon content: 0.02 to 0.07 wt %), medium-carbon steels (carbon content: 0.08 to 0.18 wt %), or high-carbon steels (carbon content: 0.18 wt % or more), and special steels such as stainless steel are being cast by thin-slab continuous casting. The characteristics of thin-slab continuous casting are that it is very-high-speed casting having a casting speed of approximately 3 to 8 m/min, and the mold thickness is reduced, as explained above. In addition, the molds in the casters of SMS, etc., have a special shape. That is because a submerged entry nozzle cannot be inserted since the mold thickness is very thin. For that reason, a portion called a “funnel” into which the submerged entry nozzle is inserted is widened and consequently the mold width is not straight but expands in the middle. For that reason, heat stress arises in the expanded funnel portion of the mold, and in addition, heat transfer is not uniform. Consequently, in the case of thin-slab continuous casting, a major problem has been that heat transfer is not uniform due to very-high-speed casting and surface crack occurs even in steel types such as ultra-low-carbon steel, low-carbon steel, or high-carbon steel in which the occurrence of surface crack is uncommon in conventional continuous slab casting. In the case of thin-slab continuous casting methods by other companies as well, heat transfer is not uniform due to very-high-speed casting and surface crack has similarly been a problem.
Furthermore, because it is very-high-speed casting, the molten surface level within the mold is unstable and varies greatly, and for that reason a problem has been that the powder slag gets into the molten steel at the meniscus, causing extreme deterioration in steel sheet quality.
In conventional contin

Affiliated with

Also associated with

Rating

Molding powder for continuous casting of thin slab does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Molding powder for continuous casting of thin slab, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molding powder for continuous casting of thin slab will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2578480