US3540518A - Method for continuously casting aluminum-killed steels - Google Patents

Description

Umted States Patent 11113,540,5 g

[72] Inventor CarlE.0ste1rholtz [56] References Cited Bahiehem, ylvania UNITED STATES PATENTS [211 Q J 2 1967 2,268,279 12/1941 Debenham m1 222/572 [221 d 3,261,896 7/1966 Davieset a1. l06/6lX [451 3,294,386 12/1966 Willenbrock.... 266/43X [731 smlcmmm 3,412,781 11/1968 Richards 164/82X a corporation of Delaware Primary Examiner-Robert D. Baldwin Attorney-A. M. Griffin [54] METHOD FOR CONTINUOUSLY CASTING ZF i E B P STEELS ABSTRACT: A nozzle for continuously casting aluminumo "mugs i killed steels, said nozzle being fabricated from a calcined [52] US. Cl 164/82, dolomite mix, and a method of continuously casting alu- 222/566 minum-killed steels through such a nozzle. The nozzle may be [51] Int. Cl 522d 11/10 standard size and shape and may have a tapered orifice. The [50] Field of Search 222/566, orifice in the nozzle remains substantially free of accretions of alumina.

BACKGROUND OF THE INVENTION One of the problems in the continuous casting of aluminumkilled steels is the plugging of the orifice in the nozzle through which the steel is teemed from the ladle to the tundish or from the tundish to the casting mold. The plugging of the orifice in the nozzle is due to the deposition of alumina on the surface of the orifice. The alumina is formed in the steel during the deoxidation of the steel by aluminum added thereto. Fire-clay or high alumina refractory nozzles, normally used in the continuous casting of aluminum-killed steels, are wetted by the steel thereby causing the alumina in the steel to be deposited on the wet surface of the wall of the orifice. Gradually, the buildup of the alumina becomes so great that it restricts the flow of liquid steel through the orifice in the nozzle. Actual stoppage of the flow of liquid steel may and often does occur. The rate of feed of the liquid steel to the mold and the rate of withdrawal of the semisolid casting from the mold cannot be controlled under these conditions to achieve a maximum throughput of steel.

Prior art attempts to alleviate this problem include the use of refractory nozzles made from zirconia or from materials to which boride is added as well as the addition of nonwetting agents, for example tar or pitch, to standard mixes. Zirconia nozzles or nozzles with boride additions are not as easily wetted as the aforementioned fire-clay or high alumina standard nozzles and alumina deposition should not be as great a problem as in conventional nozzles. However, alumina is still deposited on the surface of the base and plugging still occurs. Nozzles to which nonwetting agents have been added are physically weak and do not withstand normal treatment and handling in the shops. Still other attempts to solve the problem have included changing the geometry of the orifice to forms other than circular. However these attempts have not been completely successful.

SUMMARY OF THE INVENTION Broadly, the invention resides in fabricating a basic refractory nozzle from calcined dolomite, the orifice of which is the desired size and shape, through which the molten aluminumkilled steel may be teemed from the ladle to the tundish or from the tundish to a continuous casting mold without a substantial buildup of alumina on the walls of the nozzle orifice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It has been found that calcined dolomite (CaCO -MgCO may be used to manufacture nozzles through which aluminum-killed steels may be successfully continuously cast from a ladle to a tundish or from a tundish to a continuous casting mold without plugging of the nozzle orifice due to deposition of alumina on the surface of said orifice. The basic refractory material may be calcined by any of the conventional methods to reduce the carbonates, for example CaCO and MgCO contained therein, to lime (CaO) and magnesia MgO), and removing substantially all the moisture therefrom. The calcined dolomite is then formed into a nozzle of the desired size and shape. The orifice, for example, may be circular or square in section and may be tapered. During pouring of the liquid steel, the lime (CaO) in the nozzle combines with the alumina in the steel to form a mixture ofseveral calcium aluminates, for example 3 CaO.Al O CaO.Al O l2 CaO. 7 A1 The calcium aluminates thus formed are liquid below the temperatures of molten steel, for example 2,700F. to 2,900F. and are absorbed and/or diffused'into the matrix (CaO and MgO) of the nozzle. While the exact mechanism of the dispersion is not known, it is suggested that at least a portion of it occurs by capillary action. A major portion, but not all, of the alumina in the liquid steel will be removed therefrom as a calcium aluminate thereby providing a cleaner steel casting. Since the orifice in the basic refractory nozzle is substantially free from plugging, a controlled stream of liquid steel may be fed to the casting mold thereby allowing withdrawal of the semisolid casting at a maximum rate.

Any dolomitic material which comes within the following chemical composition:

CaO 45s0 h4 0--. 35-50 S10 T10 Al2O Iron oxide ;I 4. 0

the remainder incidental impurities, may be used to fabricate the nozzle. However, I prefer to use a nozzle made from calcined dolomite having the following chemical composition:

OaO 56-58 M O 38-41 Si 2 1- 0 A1 0 0. 5 TiO J 0. 5 Iron Oxide 2. 0

Percent CaO 56. 8 MgO 39. 6 SiOr 0. 8 A120 O. 4 TiOz O. 5 Iron oxide 1. 9

was used to pour a heat of steel having the following chemical composition:

. Percent C 058 Mn 35 Si 01 A1 045 The steel was deoxidized by adding 3.5 pounds of aluminum per ton of steel to the ladle. The metal flow at the start of the pour was good with no buildup of Al O at the exit end of the nozzle orifice. Microscopic examination of the reaction products in the nozzle structure showed a major portion of the constituents to be calcium aluminates with some iron oxide present. X-ray diffraction studies of a portion of the nozzle showed that the major constituents were calcium aluminate (l2 CaO.7 Al 0 in a matrix of MgO.

In order to compare a calcined dolomitic nozzle and a zirconia nozzle, an aluminum-killed medium carbon heat of steel was cast using a dual nozzle discharge. The nozzles had tapered orifices having nominal diameters of 'Vainch. The chemical compositions were:

Percent Iron C MgO SiO A1 0 TiO oxide ZI'O:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,540 518 November 17 Carl E. Osterholtz It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the grant (only) insert the following:

I claim:

1. In a method for continuously casting aluminum-killed steel the improvement comprising, teeming the molten steel through a nozzle containing about 45 to 60-percent calcium oxide by weight, about 35 to 50-percent magnesia by weight, not more than 4.0-percent silica plus alumina plus titanium oxide plus iron oxide by weight, the remainder incidental im purities, combining the calcium oxide in said nozzle with th alumina in the steel to form a mixture of calcium aluminates and absorbing said mixture into said nozzle to substantially eliminate alumina buildup on the wall of said nozzle 2. The method of claim 1 in which the nozzle contains about 56 to 58-percent calcium oxide by weight, about 38 to 4l-percent magnesia by weight, not more than 4.0-percent silica plus alumina plus titanium oxide plus iron oxide by weight, the remainder incidental impurities.

Column 4 line 5 "411" should read 41- Signed and sealed this 27th day of April 1971.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLEF Attesting Officer Commissioner of Pat