US3210813A

US3210813A - Method for the production of effervescent-steel ingots

Info

Publication number: US3210813A
Application number: US223018A
Authority: US
Inventors: Boeckers Erich
Original assignee: Niederrheinische Huette AG
Current assignee: Niederrheinische Huette AG
Priority date: 1961-09-15
Filing date: 1962-09-12
Publication date: 1965-10-12
Anticipated expiration: 1982-10-12
Also published as: DE1286526B; LU42211A1; AT244373B; GB989029A

Description

Oct. 12, 1965 E. BOECKERS 3,210,813

METHOD FOR THE PRODUCTION OF EFFERVESGENT-STEEL INGO'IS Filed Sept. 12, 1962 2 Sheets-Sheet 1 5 55 E Q C 8 Q 5 3 C Q Q N 2 Q 0 V Q Q ("/Q) .ZOflIV/ J0 HIS/V17 OJJV/V/WbZ/VUO Inventor Erick Bou m's By @46 6' master" Oct. 12, 1965 E. BOECKERS METHOD FOR THE PRODUCTION OF EFFERVESCENT-STEEL INGOTS Filed Sept. 12, 1962 2 Sheets-Sheet 2 In ven Erik! 0:4 am

United States Patent 3,210,813 METHOD FOR THE PRODUCTION OF EFFERVESCENT-STEEL INGOTS Erich Boeckers, Duisburg, Germany, assignor to Niederrlicinische Hiitte Aktiengesellschaft, Worthstrasse, Duisburg, Germany Filed Sept. 12, 1962, Ser. No. 223,018 Claims priority, application Germany, Sept. 15, 1961, N 20,553 3 Claims. (Cl. 22-215) During the solidification of effervescing steel, whether in a refining or a casting process, carbon reacts with oxygen dissolved in the steel in a boiling reaction with the formation of carbon monoxide. The carbon monoxide rises along the solidification front parallel to the mold walls and produces a current which moves upwardly along the walls and downwardly in the center of the ingot. Nonmetallic substances present when the molten steel is cast tend to remain in the liquid phase and, on account of their low specific gravity, rise and collect at the head of the ingot, forming the so-called ingot foam. However, because a convection current is set up in the mold a portion of the nonmetallic substances tends to be drawn down again into the lower part of the mold before reaching the surface of the steel, and indeed part of the ingot foam itself may also be drawn downwards from the surface. These nonmetallic substances can be retained in the ingot during its final solidification and may later give rise to substantial difficulties in working the steel.

It has been proposed to add, for example, fluorspar, garnite or sand to the ingot foam to avoid these deleterious phenomena, but no satisfactory result has been achieved by this technique. When deoxidizing agents, such as aluminum, silicon or titanium are added, the steel is killed (i.e. converted from a rimming steel to a killed or semi-killed steel), the convection currents in the mold disappear and the steel rapidly solidifies. The resultant deoxidation products are, however, drawn into the steel together with the ingot foam and are retained in it because of the cessation of the currents.

Removal of the ingot foam itself leads to no great im provement, since only a part of the foam can be removed, the remainder being stirred into the steel. The ingot foam cannot be allowed to overflow because steel would also overflow and the ingot would be prevented from shrinking and would crack.

According to the present invention, the molten steel is partially killed in the ladle by the addition of a deoxidising agent, cast into an ingot mold, and currents in the steel in the ingot mold are reduced by physical means. It has been found that by the combination of these measures the contaminated ingot length can be substantially reduced.

The first measure, that of adding a deoxidising agent such as aluminum, silicon or titanium to the liquid steel after it has been poured into the ladle, involves adding sufficient deoxidising agent to reduce considerably the boiling action in the ingot mold, without completely killing the steel. As a result the dangerous suction effect is reduced so that the ingot foam can only be drawn into the ingot in very small quantities. In every case it is necessary to avoid increasing the amount of ingot foam or reducing its temperature, as may occur upon addition of fluorspar or other known powder. Aluminum does not act in this way, since the resultant alumina rises in the ladle as slag. It is therefore particularly satisfactory since it neither increases nor cools the ingot foam.

The amount of deoxidising agent required is determined by the weight, the composition and the temperature of the melt. To establish the optimum amount of, say, aluminum, that should be added to a given steel a number of test ingots were cast from molten steel to which different p ce amounts of aluminum have been added. The length of ingot which is contaminated was then measured, and is plotted as a percentage of the total length of the ingot against the amount of aluminum added. The correct amount of deoxidising agent is that which produces the smallest contamination. As an example, this procedure was followed for an elfervescing open hearth steel with 0.07% carbon and 0.30 to 0.35% manganese and the results were plotted as shown in FIGURE 1 of the accompanying drawings. It can be seen that the most satisfactory amount of aluminum for this steel is from about 0.25 to 0.33 kg. of aluminum per ton of steel.

Since the steel should solidify in an effervescing state, that is to say while gas is being evolved and currents are produced as described above, the sucking in of the ingot foam cannot be completely suppressed by the use of deoxidising agents. To obtain the purpose of the invention therefore physical means are also used, which influence the composition, constitution, toughness and surface tension of the ingot foam as well as the nature, direction and velocity of the current in the steel in the mold, either individually or together. One method, for example, is to close the top of the mold when casting is ended in such a way that the gases evolved can escape without hindrance while at the same time heat is retained in and reflected back towards the ingot. j

The physical means for reducing the quantity of ingot foam drawn into the steel can take various forms. Some of these are illustrated diagrammatically in FIGURES 2 to 6 of the accompanying drawings, which are all sections through ingot molds.

FIGURE 2 illustrates a mold 1 in which the sides taper upwards. To reduce currents in the mold and reduce the amount of foam drawn into the steel by them, the mold is tilted. Upward currents then meet downward currents in the region 2 and there results a weaker, downwardly directed current. In other words, the symmetry of the currents is destroyed.

In FIGURE 3 the mold 3 widens from its base towards the mouth 4. The upwardly-directed currents are to some extent dissipated by an outward movement in the region of the mouth 4, and hence the downward currents are reduced in strength.

FIGURE 4 illustrates a mold 5 in which a box-like device 6, open at both ends, is suspended. This device may be made of steel and may be suspended by Wires or rods. It will tend to melt in the molten steel, but as it does this only slowly it also has the effect of keeping the ingot foam at the sides of the mold, so that the downwardly-directed currents contain little or no ingot foam.

In FIGURE 5 a mold 7 has a heating device 8. This has the effect of heating the ingot foam and so altering its consistency that it is less readily drawn down into the steel. The foam may be heated by means of a conventional hot top which heats the foam by means of, for example, an exothermically buring composition, a gas burner or an electric arc.

FIGURE 6 illustrates a combination of the physical means of FIGURES 3 and 4. Here the mold 9 widens, while the box 10 is inverted. The result is the same, namely that downward currents are reduced.

In FIGURE 7 a cross-shaped body 12 is immersed in the steel in a mold 11. This has the effect of breaking a single strong downward current into four weaker ones, which can draw little foam down into the steel.

What is claimed is:

1. A method of producing solid effervescent-steel ingots comprising the steps of preparing a heat of molten effervescent steel in a ladle; partially killing the molten steel in said ladle by adding to said heat a deoxidizing agent in an amount sufficient to reduce gaseous evolution from said heat but not sufficient to convert it to completely killed steel; casting the only partially killed molten steel from said ladle into a generally upright ingot mold; cooling the steel within said mold to solidify the ingot while generating ascending gas-entraining currents of steel and gases along the periphery of the mold and descending currents of steel in-a central regionof said mold and forming a layer of team at the top-of the .steel within said mold; and reducing the strength of said descending currents .to limit the contamination of the ingot by .said descending currents, ;the strength of .said .descending currents being reduced by directing ,an ascending current of steel and gases counter to said descending currents over at least a portion .of the central region of .said mold, said ascending current of steel and gases being directed counter to said descending currents .by ,the tilting of .said -mold, during the pouring .of saidmolten-steel therein through an angle to the vertical suflicient to deflect an ascending current from the periphery ,of said mold generally vertically to intercept said descending currents.

.2. A method .of producing ,solid effervescent-steel ingots, comprising the steps of preparing a heat of molten elfervescent steel in a ladle; partially .killing the molten steel insaid ladleby .the addition .to said heat of at least one deoxidizing agent which consists of aluminum; and the casting the .only partially killed molten steel .into a mold tilted initially ,at an .angle to the vertical such that substantially vertical rising .currents .of gases evolved in said steel within said mold during .said casting intercept downwardly directed central currents of steel, thereby weakening said downwardly .directed currents and reducing the entrainment of :nonmetallic substances and part of the ingot foam .from .a .layer thereof formed atop the steel cast in the mold downwardly into a lower part of the ingot where they may be retained during solidification of the steel.

3. A method of producing solid effervescent-steel ingots, comprising the steps of preparing a heat of molten effervescent steel in a ladle; partially killing the molten steel in said ladle by the addition to said heat of an amount ranging between substantially 0.25 and 0.33 kg./ ton of said steel of aluminum; and casting the only partially killed molten steel into a mold tilted at an angle to the vertical such that substantially vertical rising currents of gases evolved in said steel within said mold during said casting intercept downwardly directed central currents of steel, thereby weakening said downwardly directed currents and reducing the entrainment of nonmetallic substances and part of the ingot foam from a layer thereof formed atop the steel cast in the mold downwardy into a lower part of the ingot where they may be retained during solidification of the steel.

References Cited by the Examiner UNITED STATES PATENTS 2,116,630 5/38 Jones 2291 2,480,516 8/49 Stanier et a1 22--216 2,591,517 4/52 Daussan 22216 2,768,892 10/56 Shoenberger 22-215 2,819,503 1/58 Boucek 22215 FOREIGN PATENTS 1,248,643 11/60 France.

695,736 8/ 53 Great Britain.

MARCUS U. LYONS, Primary Examiner.

Claims

1. A METHOD OF PRODUCING SOLID EFFERVESCENT-STEEL INGOTS COMPRISING THE STEPS OF PREPARAING A HEAT OF MOLTEN EFFERVESCENT STEEL IN A LADLE; PARTIALLY KILLING THE MOLTEN STEEL IN SAID LADLE BY ADDING TO SAID HEAT A DEOXIDIZING AGENT IN AN AMOUNT SUFFICIENT TO REDUCE GASEOUS EVOLUTION FROM SAID HEAT BUT NOT SUFFICIENT TO CONVERT IT TO COMPLETELY KILLED STEEL; CASTING THE ONLY PARTIALLY KILLED MOLTEN STEEL FROM SAID LADLE INTO A GENERALLY UPRIGHT INGOT MOLD; COOLING THE STEEL WITHIN SAID MOLD TO SOLIDIFY THE INGOT WHILE GENERATING ASCENDING GAS-ENTRAINING CURRENTS OF STEEL AND GASES ALONG THE PERIPHERY OF THE MOLD AND DESCENDING CURRENTS OF STEEL IN A CENTRAL REGION OF SAID MOLD AND FORMING A LAYER OF FOAM AT THE TOP OF THE STEEL WITHIN SAID MOLD; AND REDUCING THE STRENGTH OF SAID DESCENDING CURRENTS TO LIMIT THE CONTAMINATION OF THE INGOT BY SAID DESCENDING CURRENTS, THE STRENGTH OF SAID DESCENDING CURRENTS BEING REDUCED BY DIRECTING AN ASCENDING CURRENT OF STEEL AND GASES COUNTER TO SAID DESCENDING CURRENTS OVER AT LEAST A PORTION OF THE CENTRAL REGION OF SAID MOLD, SAID ASCENDING CURRENT OF STEEL AND GASES BEING DIRECTED COUNTER TO SAID DESCENDING CURRENTS BY THE TILTING OF SAID MOLD, DURING THE POURING OF SAID MOLTEN STEEL THEREIN THROUGH AN ANGLE TO THE VERTICAL SUFFICIENT TO DEFLECT AN ASCENDING CURRENT FROM THE PERIPHERY OF SAID MOLD GENERALLY VERTICALLY TO INTERCEPT SAID DESCENDING CURRENTS.