US2988444A - Method and apparatus for treating molten metal - Google Patents

Description

June 13, 1961 F. J. o. HURUM METHOD AND APPARATUS FOR TREATING MOLTEN METAL Filed July :51, 1957 2 Sheets-Sheet 1 INVENTOR F REDR/K JORGE/V ORB/N6 HURUM ATTORNEYS June 13, 1961 F. J. o. HURUM 2,988,444

METHOD AND APPARATUS FOR TREATING MOLTEN METAL Filed July 51, 1957 2 Sheets-Sheet 2 INVENTOR FREDRIK JORGE ORB/N6 HURUM ATTORNEYS ilnited? States Patent 2,988,444 METHOD AND APPARATUS FOR TREATING MOLTEN METAL Fredrik J orgen Ording Hurum, Riis Alle 32, Slemdal, Oslo, Norway Filed July 31, 1957, Ser. No. 675,308 Claims priority, application Sweden May 29, 1952 6 Claims. (Cl. 75-53) This application is a continuation-in-part of my applications Serial No. 322,394, filed November 25, 1952; Serial No. 357,383, filed May 25, 1953, both abandoned; and Serial No. 622,820, filed November 19, 1956.

The present invention relates to a method and apparatus for supplying certain substances to a bath of molten metal. In metallurgy, it often happens that it is desired to supply to a metal bath small quantities of substances necessary for certain purposes, such as desulphuration, deoxidation, removing of phosphorus, refining, incorporation of silicon or carbon, etc., or of substances important in connection with the formation of slag. Often it is very difficult to bring such substances into intimate contact with the metal of the bath. The substances, for example, may have a relatively low density, so that when added they will tend to float upon the surface of the metal bath, as differentiated from substances heavier than the metal bath. Their boiling point may be relatively low so that the substances tend to vaporize immediately after having been added to the metal bath. The substances may be easily oxidizable so that they will become oxidized immediately upon being brought into contact with the bath. Therefore, when adding such substances to a bath of molten metal it is necessary to make provisions that these substances shall be brought rapidly into intimate contact with the metal and come into action in the manner desired.

The present invention comprises a method and apparatus specially adapted for this purpose, whereby the substances in question are submerged into the metal bath under full control.

According to the invention, the substances or substance in question are or is crushed to suitable grain sizes, whereupon the substance or substances in the form of dust, powder, balls or granules are briquetted in any desired manner, using eventually one or more bonding agent or agents, which may be of organic or inorganic origin, or even consist solely of water. Generally the briquets will attain considerable strength upon drying. By the use of certain plastic bonding agents, the briquets may be hardened at very low temperatures.

In the preparation of briquets using bonding agents it is generally advantageous to use different grain sizes in suitable proportions, instead of using a single grain size only.

In the art of powder metallurgy, the use of a bonding agent is not always necessary, as the use of pressure followed by or simultaneously with heating or sintering may give good results.

The briquets are prepared so as to have a certain de gree of porosity, so that gases later formed by decomposition of the bonding agents or by other processes may readily escape through the pores.

The invention primarily comprises a method and apparatus for supplying to a metal bath, substances necessary or desirable for certain reactions, for example, desulphurizing, deoxidation, refining, removing of phosphorus, incorporation of silicon or of carbon, and in which said substances, due to a relatively low density or high power of becoming oxidized, are relatively difficult to bring into intimate contact with the metal bath. The method is characterized in that the substance or substances is or are ground, granulated or in other manner given suitable particle size and shape, and formed into briquets, each of which has an aperture therethrough and has end surfaces enabling a tight fit of each briquet to adjacent briquets, said briquets being thereafter used by threading one or more briquets, of similar or dissimilar quality, upon a rod or wire and pressing the briquets together, so that the briquets will suitably protect the rod or wire against attack from the molten metal, when the unit so formed is immersed in the bath of metal, by suitable means.

According to the invention it is suitable to give the briquets a substantially cylindrical shape with plane end surfaces, which preferably are normal to the axis of the aperture, whereby a suitable number of briquets may be piled upon each other and pressed together to form a compact unit having an aperture therethrough which serves to unite the briquets by the introduction of a rod or wire therethrough and also serves to lead away gases evolved within the briquets during their usage.

The briquets also may be prepared within sleeves of metal, which may facilitate the briqueting operation. These sleeves also may serve as a suitable envelope for the briquets.

Alternatively, the briquets may be prepared by surrounding a metal wire, such as an iron wire, which thus forms the core of the briquet. For use, such a briquet may be welded to an iron rod, adapted to serve as a handle when the briquets are to be immersed into the metal bath.

Reference is made to the drawings, which illustrate an embodiment of the invention.

FIG. 1 is an elevation of the apparatus with a fragmentary vertical section;

FIGS. 2, 3, 4 and 5 are diagrammatic views illustrating what occurs on adding applicants briquets to molten metal.

On FIG. 1 of the drawing the numeral 1 designates a ladle filled with molten metal 2, which may consist either of a pure metal or an alloy. 3 are briquets prepared in accordance with the invention assembled on a wire or rod 4 which has been passed through the apertures of the briquets and tightened by means of a nut 5 provided at the top side of an arm 6 to make a tight fit of each briquet to adjacent briquets so that the briquets will protect the rod or wire against attack from'the molten metal. The arm 6 is adapted to be raised or lowered upon a vertical column 7 by means of a suitable steel wire 8 entrained over pulleys and a hoisting gear 9. The column 7 may be rotatably supported so that the arm 6 may be swung through angles when desired.

In this manner it is possible to join briquets of different materials, whereby different reactions are obtainable.

The topmost briquet 12 consists of refractory material. There may be a plurality of such refractory bricks. In this manner the rod is protected in the slag zone.

For the hoisting gear 9 there may be substituted automatically acting devices, giving full control of time fac tors.

It may also be suitable to make use of two arms 6, placed at an angle to each other, so that one arm may operate above the ladle, when the other :arm is outside thereof for positioning of new briquets.

Above the bath of molten metal is a disc 10 preventing splatter, and a member of chamotte may be substituted for the top briquet 12. In the arm 6 may be provided an outlet 11 for gas evolved by the briquets and flowing upwards through the central aperture.

The invention may be used in connection with other devices than a ladle, for example, in connection with a melting furnace or in a suitable cavity in a tap runner extending from a melting furnace.

High frequency furnaces are suitable for practicing the method, and the latter is also well adapted for desulphurization of pig iron that runs from blast furnaces.

In carrying out the operation two distinctly different submersible bodies are used:

(1) Blocks to be consumed in the melt representing an exact dosage of the reacting materials,

(2) Blocks or bricks not to be consumed in the melt but serving only the purpose of protecting the rod above the reacting materials.

I have found that a successful desulphurization or deoxidation by submerging reactive bodies into the metal bath can only be successfully accomplished with sufficient rapidity to gain industrial importance when resorting to the boil of an easily evaporated metal such as, for instance magnesium, sodium or potassium.

It has been found that this boil is so energetic that no artificial stirring of the bath is required.

I have also found that such submersible bodies should not be sintered or fused since such a method would re sult in the rapid loss of such easily volatilizable metals as magnesium, sodium or potassium, which would then burn away in the atmosphere. I have found that such submersible bodies should be briquetted by use of pressure in order to retain the highly reactive character required for a rapid and effective treatment. The evaporation of the metals may then be relied upon for distintegrating the briquets in the metal bath rather than resorting to the slow method of melting away the submerged slag blocks.

I have also found it necessary to keep such reacting briquets fully submerged in the metal bath during the treatment, as otherwise the briquets will rapidly absorb oxygen and nitrogen from the atmosphere and the evaporated metals will become oxidized or turned into nitrides.

It should not be overlooked in connection with the above that the ferrostatic pressure in the metal bath will strongly oppose the evaporation of such metals as, for instance, magnesium, sodium and potassium, so that the upper briquets will be more rapidly consumed than the lower briquets where the opposing ferrostatic pressure is the highest. This means that the upper briquets would disintegrate more rapidly in the melt than the lower briquets and accordingly the metal rod used for the submersion would bend or melt away so that the lower briquets would float unconsumed to the surface of the metal bath. For that reason I have found it necessary to use refractory bricks or a protective material in the slag line in order to bring the treatment under full control.

FIGS. 2, 3, 4 and 5 clearly bring out how the ferrostatic pressure affects the speed with which the briquets are consumed and how the use of a protective material has been found of essential value to the use of submersible briquets for accomplishing metallurgical reactions below the surface of a bath.

FIGS. 2, 3, 4 and 5 make clear how necessary it is to keep the entire body of briquets well submerged in order to keep the method under control.

FIG. 2 shows how a stack of briquets 4 will be attacked by preference near the surface of the bath 2 where the boil is strongest. The result will be that the rod 4 will melt off in this locality and the reaction will be interrupted as the submerged briquets will rise to the surface. The briquets above the metal will, on the other hand, drop down into the bath and become wasted, as shown in FIG. 3.

FIGS. 4 and 5 show the inventors correct application with all the briquets 3 fully submerged and kept safely in position by means of refractory bricks 12 or spacers above the briquets which also give suflicient protection and rigidity to the rod. The result will be a complete reaction under full control.

Referring to FIGS. 2 and 3, all the bricks 3 are of reactive material. The curved arrows 13 represent the motion of the currents in the bath to produce what I call the syphon effect. This causes a wearing away of the briquets at and adjacent the level of the bath 18, bubbles of vapor 4 and particles of slag being thrown off as at 15. This finally causes a melting away of the rod as at 15, FIG. 3. The unconsumed briquets 16 will float then to the surface of the bath. The wasted briquets 17 will subsequently drop down into the metal and form slag.

FIG. 4 represents the mode of operation when proceeding according to applicants invention. The syphon effect causes erosion of the reactive briquets but below the level of the bath and proceeds in the manner shown in FIG. 5.

The following principles are essential to a successful result:

1) The briquets must be very reactive, in order to make the method sufliciently rapid to be suitable for a ladle or an induction furnace.

(2) The briquets must be entirely consumed in the melt in order to make the reaction complete. Without a complete reaction no control of the treatment can be attained.

(3) The generation or release of a metal vapor or gas is in many cases the essential thing in order to produce an energetic boil in the bath which is instrumental to a rapid reaction.

(4) No stirring by artificial or mechanical means is necessary as almost any metallurgical reaction will set up a syphon effect in the bath surrounding the briquets. This syphon effect will greatly exceed that obtained by mechanical stirring.

(5) It is advisable to use a thin steel or metal rod for carrying the briquets and tightening the grip on them. Refractory materials are not suitable for this purpose as they are not tough enough and would break during the handling. Furthermore, the briquets require mechanical means to be forced down into the melt as the upward thrust is often considerable and the boil and movement in the bath frequently violent.

(6) The briquets which are held in or close below the surface of the bath are invariably consumed more rapidly than those which are kept deeply submerged. The boil is more energetic near the surface of the bath where the ferrostatic pressure is only insignificant. Such reactions as involve the liberation of a metal vapor or gases will proceed rapidly near the surface of the bath, while they will be retarded not only by the opposing ferrostatic pressure but also by the atmospheric pressure as the briquets are submerged well below the surface of the melt.

(7) Briquets located at the surface of the bath will usually cause a violent spattering of metal and make the treatment disagreeable.

(8) Pressed briquets can be made reactive. If, on the other hand, sintered or fused blocks are used the reactivity will be so strongly reduced that the method will become useless. A dead slag will then stick to the surface of the briquets and stop the transmission of heat and the reaction will stop. Sintering or fusion means a movement towards stable compounds in the briquets with reduced or insufficient reactivity. Sintering or fusing also involves substantial extra costs.

(9) Such briquets as are at the surface of the bath will pass directly into the slag without reacting with the melt to the desired extent and will become wasted. The briquets should be kept well submerged in order to give a complete reaction and control of the method.

My method, as explained above, makes it possible to carry out metallurgical reactions under full control so rapidly that even a succession of selective reactions may be accomplished in a ladle without undue loss of heat. This is, for instance, the case when using sodium vapor as a first step in desulphurization and magnesium vapor as a second step. To do so conveniently and safely, I have found it useful to avail myself of revolving arms to support the different loads or charges of briquets required, such as previously described, whereby the entire treatment is carried out mechanically by means of a carousel device.

When making an addition of an easily oxidizable metal or element to molten metal having a melting temperature which is higher than the boiling point of said added metal or element, it is an advantage to make such additions as a component of briquets to be submerged into the melt or bath of molten metal in order to prevent the component mentioned from being affected by the atmosphere or the slag.

An easily oxidizable element, such as magnesium, which has a boiling point below the melting point of cast iron, is extremely difficult to add to molten iron or steel in such manner that the action of magnesium becomes safe and effective.

Magnesium has in recent years gained importance in ferrous metallurgy in spite of the fact that it does not form any alloy with iron and is practically insoluble in molten iron and steel. It is, however, a powerful deoxidizer and will destroy dissolved oxides of the iron group and undoubtedly also the finely dispersed silicates and in turn form insoluble magnesium oxides and silicates. Magnesium will also attack sulphides of the heavy metals and form insoluble magnesium sulphides which will rise to the surface of the metal. It will remove to some extent both nitrogen and hydrogen.

The treatment of a molten ferrous metal with magnesium is difiicult, not only because magnesium is insoluble in the metal but also because of its low melting and boiling point. Magnesium will accordingly rapidly become evaporated even at the melting point of cast iron. It is the magnesium vapor which exerts its action on the melt.

Magnesium may be added to iron and steel as a nickel magnesium or copper magnesium alloy, but this practice involves costly and appreciable amounts of copper and nickel and these additions are not always desirable. The amount of magnesium used in these alloys is limited.

Magnesium has also been briquetted with lead or iron turnings in order to make the briquets sufficiently heavy to sink down into the molten metal and react with the bath, but this method involves obvious drawbacks.

The well known inverted cup or hell is now extensively used for plunging the light magnesium scrap or the light magnesium bearing briquets down into the molten cast iron. This method, however, also involves certain drawbacks.

First of all, the magnesium vapor formed under the cup or hell will rapidly attain a high pressure and tend to blow both the cup out of the bath and the briquets out of the cup. For that reason the inverted cup has been perforated with a number of holes through which the vapor may escape and become distributed over a large volume of the metal. The escaping magnesium vapor will, however, follow the path of the least resistance and blow through a few of the upper holes only, where the ferrostatic pressure is the smallest. The effect of the magnesium vapor will accordingly be limited to only a few jets acting on a small proportion of the bath.

In order to improve upon the inverted cup, the use of a pressure seal is now very common. A heavy tight fitting lid in which the inverted cup is suspended, is placed over the ladle the moment the inverted cup is submerged into the metal. This pressure seal will set up a pressure to counteract the violence of the escaping magnesium jets. The drawback of this method is that a special ladle equipment and a crane for the handling are required with the ensuing loss of time and heat.

The inverted cup itself means an additional expense because the magnesium briquets or scrap must be carefully fastened and packed inside the cup to which comes the upkeep of the cup.

would get lost.

When it comes to treating steels, the inverted cup is not very suitable because the temperature of the steel is a high one and will lead to damage or destruction of the cup. Furthermore, the steel will become contaminated with refractory materials or dirt from the cup. The

present invention aims at avoiding the difiiculties connected with the use of the inverted cup for submerging briquets into a molten metal.

It proved, however, very difiicult to make such briquets suitable for this treatment and it was found that the magnesium would usually become vaporized with sudden violence so that the briquets would burst and rise to the surface of the metal where the effect of the magnesium It was found that when magnesium powder or an intermetallic magnesium compound was briquetted with a finely crushed ceramic filler or carrying substance, the magnesium would react with the ceramic filler and form a slag. The briquets would subsequently blow up and the surface of the metal would become covered by a fuming and fusing slag and the effect of the magnesium would be only slight. It was found, however, that burnt magnesium oxide could be used as a filler or moderator with powdered metallic magnesium or any intermetallic magnesium compound and that the briquets would not blow up even if the magnesium would amount to 25% by weight of such briquets.

Briquets of this mixture could be submerged in a molten cast iron or a molten steel and the magnesium would become evaporated at a steady rate lasting for a few minutes, and when this boil had finished the briquets could be removed in their original shape without leaving any slag or dirt in the metal. It was also found that finely crushed coke proved a suitable filler and briquets containing as high as 30% metallic magnesium would not collapse when rapidly and deeply submerged in cast iron.

The reason for this behavior may be contributed to the highly refractory character of burnt magnesium oxide and coke and the fact that they will not react with magnesium and that both substances will accordingly retain their porosity as the magnesium component of the briquets becomes evaporated. It is, however, a remark-able feature that the briquets will not collapse in the melt even after the magnesium has evaporated and this may in turn be explained by the considerable ferrostatic pressure which will hold the briquets together. On the other hand, it was found that small addition of fluxes would close up the pores in these briquets with the result that the mag nesium vapor would no longer be able to escape and the briquets would rapidly blow up.

As will be understood, the briquets consisting of burnt magnesium oxide as a filler will not contaminate a steel with slag inclusions and the magnesium vapor will set up an intense stirring or boil which will atfect the entire bath and remove oxides sulphides and gases and certain other impurities. Coke as a filler will play the same part when dealing with cast iron.

The production of cast iron with spherulitic graphite not only calls for an addition of magnesium but also for an inoculation with a substantial amount of ferrosilicon. The magnesium treatment of cast iron could accordingly not be considered entirely successful unless combined with the treatment of ferrosilicon.

Briquets consisting of ferrosilicon are lighter than cast iron and it is diificult to make them dissolve rapidly and uniformly in the metal. They absorb iron from the metal and form a silicoferrite with a high melting point, and considerable stirring is necessary to bring the silicon into complete solution. It was found, however, that whenever the briquets besides the ferrosilicon also contained some magnesium, the magnesium would become evaporated and set up a pressure sufficient to make the briquets dissolve in the melt so rapidly that briquets of this type could be submerged into a ladle with almost instant effect. Not only would the boil make the dissolution of the silicon rapid and complete, but the action 7 of the magnesium also proved surprisingly effective and the treatment could be shortened and simplified. It made no difference if the magnesium was present in the metallic state as a powder or as a finely crushed silicide or intermetallic compound and both a magnesium silicide, a magnesium calcium silicide and a magnesium ferrosilicon could be used with advantage. It was, however, found to be an advantage touse a ferrosilicon with a high content of silicon whenever the temperature of the cast iron was low. It was found that a very high content of magnesium could be used provided that the briquets were rapidly submerged and ferrosilicon briquets containing even more than Mg could be used without danger.

It is known to use briquets consisting of ferrosilicon and bonded with cement or a ceramic bond such as a clay substance for addition to the cupola furnace. Such briquets are, however, not suitable for the rapid treatment of a cast iron in the ladle where time and temperature impose rigid limits and even a high content of magnesium in such briquets would not olfer any remedy but would only result in the briquets blowing to pieces and wasting the magnesium at the surface of the metal. Briquets consisting of ferrosilicon with magnesium should be briquetted with a very small amount of a plastic bond or an organic compound and they will then dissolve without impairing the inoculation or nuclei formation by undesirable slag inclusions.

Magnesium is usually added to cast iron or blast furnace metal as an alloy, such as nickel-magnesium, coppermagnesium or ferrosilicon-magnesium. These alloys are crushed to lumps of suitable size which may be added to the metal in the ladle or at the spout of the furnace. This method of making the addition, however, is unsatisfactory because the ferrosilicon-magnesium alloy has a low specific gravity and will accordingly float to the surface where the magnesium vapor will become oxidized by the atmosphere or the slag. Such alloys as nickelor copper-magnesium have a specific gravity above that of the ferrosilicon-magnesium alloy and the lumps Will partly submerge in the molten iron. The evaporation of magnesium is, however, so violent that the vapor formed under the lumps will tend to force the lumps to the surface of the melt while the magnesium vapor will escape and its effect on the metal will be strongly reduced.

The present invention aims at overcoming these difficulties by which briquets of the character described containing magnesium as a component are kept submerged in the melt while this metal progressively evaporates.

The success of this method will depend on the briquets being made of such mixtures and definite concentrations that they will act in a secure, progressive and eflective way. The briquets must not only have the necessary solidity and strength, but must also be durable so as to be adapted to storage, and they must stand the stress by suddenly being submerged in a very hot metal bath or melt.

The concentration of an easily fusible or volatile component in such briquets must not be higher than can become dispersed in the bath in a progressive and effective way, as a too high concentration may involve that the component melts too rapidly and floats to the surface. If the component is volatile at the temperature of the bath the evaporation may be explosive with undesirable results.

According to the present invention, the method comprises admixing magnesium with a base substance or carrier which must be sufiiciently free from water of crystallization, decomposable hydrates and carbonates that will deprive the briquets of their strength and durability. Such a base substance or carrier should not be liable to be reduced by magnesium, nor should it be liable to destruction from any bonding material. Such base substances, however, must be capable of being finely crushed without great difficulties in order to be mixed with the components when these are pulverized, granulated or produced as a condensate. Such base substances or carriers may either be insoluble in the melt and serve as a filler only, or be soluble as, for example, ferrosilicon, metals or alloys, thus contributing to supply the melt with desired elements or additions.

Burned magnesium oxide or magnesite and coke are materials suitable for production of such base substances for briquets. These materials are easy to pulverize and briquet, and even after long time of storage they are not influenced by atmosphere or by moisture.

Burned magnesium oxide is a suitable material for making briquets with metallic magnesium for deoxidation and desulphurization of steel when such briquets are submerged in the steel bath, because certain steels, such as the stainless ones, are disadvantageously affected by substances containing carbon or carbonates. Such briquets may contain magnesium and burned MgO in the proportion of about 1:4, respective, while in some cases 1:5 or 1:3 is preferred. The content of magnesium in the briquets should be varied Within certain limits, depending on the temperature of the metal to be treated and the size of the briquets. If the temperature is low and the size large, the maximum of magnesium may be allowed such as indicated above. Metallic magnesium as a fine powder is mixed with finely ground burned MgO and eventually bonded with a suitable binder which may be of organic or inorganic origin according to the physical requirements. A great many plastic bonding agents may be used successfully together with small amounts of water or any suitable solvent. Such treated mineral, animal or vegetable oil, known as core-oils, may also be used and preferably mixed with small amounts of water. After pressing of the briquets they are dried and baked and become sufficiently strong to permit transportation and also the sudden heat when submerged into the steel and the tension of the magnesium vapor which will escape from the briquets as a steady boil over a substantial period of time without collapsing. As an inorganic bond for this type of briquet certain salts, such as chlorides of the alkaline earths or of alkali metals may be used in small amounts with a little water. Borax may also be used. When removing hydrogen from steel, I prefer not to use any bonding agent. Metallic magnesium may at will be substituted by such magnesium alloys as silicon-magnesium, ferro-silicon-magnesium and nickelmagnesium, and the amount of the MgO-carrier in the briquet may thus be reduced. The contents of magnesium in such briquets should, however, not exceed 30%, as otherwise the briquet is liable to collapse with an undesirable violence.

It has, in fact, been found that briquets consisting of finely powdered CaO or MgO mixed with metallic magnesium or a magnesium alloy in the powdered state, will not collapse or disintegrate during the submersion even when the content of magnesium is as high as 25% by weight. This behavior of my briquets may be attributed to the fact that the highly refractory oxides of calcium and magnesium will make the briquets retain the full porosity so that the escape of magnesium vapor is not obstructed by slag formations inside the surface of the briquets leading to the bursting of the briquet under the vapor pressure.

It should be pointed out that the magnesium will melt before evaporation and even condense and seal the pores in the briquets so that the vapor formed on or near the surface of the briquets cannot pass through the interior of the briquet and escape through the aperture. Ac cordingly the magnesium vapor formed in the briquet can only escape through the molten metal and create a strong boil.

The magnesium will begin to evaporate from the surface of the briquet and this process will progressively proceed towards the interior so that in the course of a very short time, usually ranging from 1 to 5 minutes, all

9 the magnesium will have. evaporated while the briquets remain undamaged in shape and appearance.

As the magnesium escapes from the indefinite number of pores on the surface of the briquets, a very intimate contact between the magnesium vapor and the metal to be treated is assured.

While burnt lime is available everywhere at a low price, it has the drawback that its purity varies and it also readily absorbs carbon-dioxide and moisture from the air, and accordingly briquets containing burnt lime do not always give fully reliable results.

The same may be said of burnt dolomite which also contains impurities in varying amounts and is exposed to the action of the atmosphere and the hazards of storage.

I prefer to use burnt magnesium oxide or mag-nesite as a carrier or moderator in my briquets containing magnesium. This material is now available at a reasonable price and of a very high purity, such as prepared for the electrolytic production of magnesium. Deadburned magnesium oxide may be stored without harmful effect for long times due to its chemical indifference towards the atmosphere. Such briquets will not crack or disintegrate even when plunged into a steel bath at 1600 C. They will not form any slag and can be removed from the melt without loss of any magnesium oxide.

They have accordingly proved suitable for cleaning steels with magnesium vapor. Such a treatment may be carried out in the ladle with very little loss of temperature, since no heat is required for chemical reactions or the fusion of any slag. I have found that 0.01% magnesium added to a steel by means of these briquets may effect valuable improvements.

Magnesium oxide is a relatively good conductor of heat and for that reason the evaporation of the metallic magnesium is rapid without being violent, and the whole treatment may be carried out in the course of less than minutes.

Coke may be used with advantage as a cheap base substance for adding magnesium to cast iron or blast furnace metal, as in these cases the possible carburizing action of the coke would be of no importance.

Metallic magnesium and coke as fine powders may be mixed in the proportion of about 1:4 or I13, and even up to 12%, depending on the temperature and the condition of the melt to be treated. The powders are bonded with the same binders as mentioned for bonding deadburned magnesium oxide. After pressing, the drying and baking follows, after which the briquets have become strong and durable and may be submerged into the melt without suddenly collapsing and will give off the magnesium under a steady boil which may be sustained over a period of time. If the metallic magnesium in this case is substituted by an alloy containing magnesium, the amount of coke may be reduced in the briquets. This is particularly true if silicon-magnesium or ferrosilicon-magnesium are used, because the silicon will absorb iron from the melt and precipitate silico-ferrite which will act as a bond and support the briquet against collapse. Even a small amount of deadburned M'gO will increase the strength of such magnesium-coke briquets.

When magnesium is incorporated in briquets consisting of burnt magnesium oxide (MgO) or coke, these two carriers have almost ideal properties. Their heat-conductivity is good. They are not attacked by magnesium. When briquetted under high pressure both coke and burnt magnesium oxide possess sufiicient cohesion to retain their shape even when the magnesium melts. Accordingly, the molten magnesium will not rise to the surface but will remain lodged or entrapped within the carrier and in this state it will progressively become evaporated. In this manner the evaporation will become governed or controlled by the flow of heat from the ferrous melt surrounding the briquet.

This treatment may be carried out in any ladle and the time required may be in the neighborhood of 5 minutes. The loss of temperature is insignificant because the treatment is rapid and no heat is required for fusing any slag or performing any chemical reactions. As Will be understood, the briquets will not contaminate the metal with any slag inclusions and this is a desirable feature when the metal is subsequently inoculated with ferrosilicon in order to precipitate spherulitic graphite.

Ferrosilicon with varying silicon contents may likewise serve as a base substance in such briquets and this alloy can be briquetted with such components as magnesium, aluminum, nickle-magnesium, copper-magnesium, or with mische metal. Such briquets have the advantage that besides the components mentioned they also add silicon to the melt. By using an alloy with a suitable silicon content, the briquets will dissolve in the metal at a desired rate when giving off the admixed components. In this way the time factor can be controlled which for instance, is of importance by the production of spherulitic graphite cast iron. Such briquets should preferably contain less than 15% magnesium by weight, as otherwise the evaporation of magnesium may become too violent and the briquets may disintegrate or collapse with very undesirable effects instead of dissolving progressively in the melt. Ferrosilicon alloys containing from 20% silicon and upwards to above may be successfully used as a carrier for magnesium and it makes no difference if the magnesium is prealloyed with the ferrosilicon or added in some other form to the briquet, such as metallic magnesium powder or a compound such as magnesium silicide or as an alloy such as nickel-magnesium or copper-magnesium. Such briquets may be bonded with core oils or plastic binders with addition of water or any suitable solvent and when subsequently dried and baked they will possess great strength and will not collapse in the melt but will give off magnesium in a steady boil while the briquets will dissolve in the melt. Ferrosilicon alloys containing less than 20% silicon are difiicult to crush and pulverize and have for that reason been ignored.

The addition of ferrosilicon to a cast iron in the ladle at ordinary temperature requires energetic stirring and considerable time in order to give complete and uniform solution. Ferrosilicon, when submerged in cast iron, will absorb considerable quantities of iron in solid solution and form the compound FeSi with a high melting point. The absorption of further quantities of iron will give silico-ferrite in a pasty condition. The dilfusion of still further iron into the silicoferrite will give a silico-austenite which will finally melt. (F. Hurum: A Study on the Formation of Nodular Graphite, American Foundrymens Society, vol. 62.)

For the above reasons, briquets of ferrosilioon have not proved useful as an addition to cast iron in the ladle.

I have found, however, that briquets when used according to my invention may successfully be used for adding ferrosilicon to a ladle containing cast iron whenever this treatment is combined With the addition of magnesium. Ferrosilicon has, in fact, proved a very satis factory carrier of magnesium. The evaporation of magnesium is in this case more rapid than when using coke or magnesium oxide as a carrier or moderator and it does not appear safe to use more than 15% magnesium in such briquets. Contrary to expectation, the ferrosilicon will dissolve rapidly and completely, even at temperatures as low as 1200 C. This is due to the fact that the magnesium vapor formed in the interior of the porous briquet will exert a pressure on the outer layer consisting of silico-ferrite and silico-austenite in the process of fusion so that this layer will break up and be carried away with the magnesium vapor, thereby exposing the briquet to a progressive and rapid solution. The magnesium treatment thus effected has proved very success- 11 ful for the production of 'spherulitic graphite and the ferrosilicon has vice versa given a very rapid and energetic inoculation under complete freedom of slag inclusions or finely dispersed impurities so harmful to a proper nucleation. This treatment may be accomplished in the course of about 1 minute and the loss of temperature is accordingly insignificant. The required amount of magnesium to produce spherulitic graphite by this treatment may be reduced to less than 0.1% of the weight of the cast iron treated.

My observations have made it evident that this good result may be attributed to the fact that the magnesium is evaporated before the ferrosilicon is dissolved. If, on the other hand, an easily fusible carrier-alloy had been used, this alloy would have fused and risen to the surface before the evaporation of magnesium had been completed and the effect would have been strongly reduced.

Briquets consisting of magnesium and ferro-silicon should be kept fully submerged in the melt. If the briquets are kept tightly pressed together, they will not explode or break up but will become progressively dissolved in the melt. It is important, however, that they are kept submerged at a constant depth in the molten bath. lf they are allowed to be raised in the melt, the ferrostatic pressure will diminish and the briquets will explode due to the sudden release of magnesium vapor.

Nickel magnesium and copper magnesium alloys containing about 20% magnesium are commonly used today for adding magnesium to cast iron. Such alloys may be readily crushed and pulverized to fine size and briquetted with a suitable bonding agent such as a core oil and pressed to briquets which, after drying and baking, will be strong and durable and may be used successfully as an efficient way of adding magnesium to a melt. It is, however, possible to dispense with important amounts of the expensive nickel if ferrosilicon is added to briquets containing the nickel magnesium alloy with a compensating addition of magnesium as desired.

While in principle metallic magnesium in the state of a powder appears best suited for my magnesium treat ment, it may be advantageous for the purpose of crushing to fine powder and mixing to use an alloy or an intermetallic compound of magnesium such as a magnesium-silicide, calcium-magnesium silicide, the compounds of magnesium with nickel or copper, or such alloys as magnesium-ferrosilicon, magnesium-silicon or magnesium-calcium-silicon. These compounds and alloys are easily crushed to a fine powder suitable for mixing and briquetting. While deadburned magnesium oxide is best suited as a carrier for the treatment of steel, it would be within my invention to use such irreducible substitutes as burnt dolomite and burnt lime.

The following examples will testify to the efiiciency of the method:

1. A pig-iron containing 4.2% C, 0.4% Si, 0.6% Ti and 0.72% V was treated with briquets consisting of 80% millscale ('Fe O and 20% limestone. The treatment lasted only 4 minutes at 14501420 C. and the melt then contained 3.8% C, .05 Si, 01% Ti and 06% VA. valuable vanadium slag containing 10.5% V had been produced and the stoichiometric efficiency of the oxygen in the briquets exceeded 80%. It will be realized that this means a surprisingly high recovery of iron from the millscale. The formation of CO-gas set up a pronounced syphon effect in the bath.

II. -A stainless steel was deoxidized in the ladle by means of briquets containing 70% ferrotitanium (40% Ti) and 30% of a magnesium-ferrosilicon alloy with 10% Mg. The briquets were completely dissolved in the bath inside 40 seconds and the recovery of titanium in the cast metal amounted to 70%. The magnesium vapor released stirred up the bath and ensured uniform results.

III. A cast iron was desulphurized in the ladle by means of briquets releasing magnesium-vapor. The briquets contained 7% Mg. The treatment lasted only 2 hours and 50 minutes at 1420 C. and the sulphur was brought down from .087% to .035%. Only 8.15 kg. of briquets were used to treat 620 kg. of cast iron and the magnesium consumed in relation to sulphur removed was 1.821 by weight.

IV. A stainless chrome nickel molybdenum steel which by experience was very difficult to forge, was treated in the ladle with briquets consisting of one part of magnesium powder to five parts of burnt magnesium oxide, One kilogram of magnesium powder was used for 10,- 000 kg. steel. The briquets were kept submerged near the bottom of the ladle and gave an energetic boil which lasted for about 5 minutes. The briquets could then be removed in apparently an undamaged condition. The ingots could be forged down under the hammer without any breakage or crack-formations. Similar results have been obtained with other alloy steels which have a tendency to crack up during the forging. It is assumed that soluble oxides and finely dispersed silicates are destroyed by this treatment. It is known that nitrogen and hydrogen also to some extent are removed. No harmful slag inclusions were discovered.

V. A pig-iron with very low sulphur content was melted in a low-frequency induction furnace of the coreless type and shortly before casting inoculated with briquets containing 6% magnesium and 70% silicon (as ferrosilicon). The briquets were dissolved in 40 seconds with all the silicon recovered in the metal and the cast metal revealed the desired structure with spherulitic graphite and mechanical properties satisfying the highest requirements. The magnesium consumption amounted to only 0.07% of the weight of the treated cast iron. A basic lining was used in this case.

VI. A synthetic cast iron made from melting steel scrap in an acid lined high frequency induction furnace with coke, was found to contain 0.07% sulphur. After pouring it in the ladle, the metal was first treated with briquets consisting of coke and magnesium (30% Mg in the briquets). This gave an energetic boil which lasted slightly over 4 minutes. This treatment was immediately followed by briquets containing ferrosilicon with magnesium (10% Mg) and these briquets were dissolved in about 45 seconds. The metal was poured and the test bars were found to have the desired mechanical properties while the microscopic examination revealed spherulitic graphite of a highly desirable appearance. The total magnesium consumption in this case was 0.15% based on the weight of the cast iron.

Briquets for the treatment of molten iron and steel may have about the following composition: (1) 25% magnesium and 75% of an alkaline earth oxide; and (2) 30% magnesium and 70% coke; (3) 15% magnesium and ferrosilicon.

The introduction of magnesium to molten metals and alloys, particularly to iron, nickel and the different types of steel and cast iron, has in recent years gained considerable importance for the reason that magnesium is a powerful deoxidizer and desulphurizer and is able to give a clean metal and remove dissolved gases.

The effect of magnesium as a deoxidizer and cleansing agent is attributed to its ability to destroy dissolved oxides of the iron group and finely dispersed silicates and in turn form insoluble magnesium oxides and magnesium silicates. It is furthermore well known that magnesium attacks the soluble sulphides of the iron group and forms an insoluble magnesium sulphide which will rise to the surface where it can be removed.

It should be borne in mind that magnesium does not form an alloy with iron and is practically insoluble in the molten metal. Magnesium will boil at a temperature below the melting point of cast iron and as the temperature increases the boil wil become so violent that the burning 13 vapor may involve serious hazards and the effect will rapidly get lost. Accordingly, magnesium should be added to the ladle shortly before the metal is poured.

The success of my invention is due to the use of magnesium in such a state that it will become completely evaporated and the use of a carrier which will not consume any magnesium in chemical reactions and which will not contaminate the metal with inclusions. It is also an advantage for the heat economy and efficiency that the carrier will not fuse, although the carrier may dissolve in the metal provided it does not fuse before the magnesium is evaporated.

The method gives full control of the amount of magnesium introduced in that the weight of magnesium and/ or its alloy as incorporated in the briquets is accurately measured and the control of the amount introduced is accordingly assured.

What is claimed is:

1. An apparatus for treating molten metal comprising a plurality of assembled briquets chemically reactive with the molten metal and having end surfaces enabling a tight fit of each briquet to adjacent briquets, means for holding and pressing the briquets together tightly in superposed position with the end surfaces of the briquets having a liquid tight fit of each briquet when the unit so formed is immersed in the molten metal, and a piece of refractory material non-reactive with the metal superposed on the reactive briquets.

2. Method for treating molten metals and alloys of the iron group, comprising forming a porous briquet of a mixture of magnesium in a vaporizable, reduced state, capable of giving off a vapor of metallic magnesium at a pressure exceeding that of the amosphere at the temperature of the molten metal and in a powder-like physical condition and a carrier of powdered magnesium oxide (MgO), submerging the briquet below the surface of the metal bath, proportioning the magnesium and the carrier so that the pressed briquet will release the magnesium as a vapor from the surface of the briquet directly into the molten metal at a pressure exceeding atmospheric, the can'ier having the property of being irreducible by magnesium.

3. An apparatus for treating molten metal comprising a plurality of superposed assembled briquets chemically reactive with the molten metal, the briquets being provided with an aperture therethrough, a rod passing through the apertures, means for tensioning the rod to provide a liquid tight fit of each briquet to an adjacent briquet when the unit so formed is immersed in the molten metal, and a piece of refractory material non-reactive with the metal superposed on the reactive briquets.

4. Method for treating molten metals and alloys of the iron group, comprising forming a porous briquet of a mixture of magnesium in a vaporizable, reduced state, capable of giving off a vapor of metallic magnesium at a pressure exceeding that of the atmosphere at the tem perature of the molten metal and in a powder-like physical condition and a carrier of powdered deadburned magnesium oxide (MgO) in the proportion of about one part of magnesium to four parts of magnesium oxide, submerging the briquet below the surface of the metal bath, proportioning the magnesium and the carrier so that the pressed briquet will release the magnesium as a vapor from the surface of the briquet directly into the molten metal at a pressure exceeding atmospheric, the carrier having the property of being irreducible by magnesium.

5. Method of treating a bath of molten metal comprising forming a column made up of a briquet that is chemically reactive to the molten metal and having superposed thereon a piece of refractory material non-reactive with the molten metal, submerging the column in the molten metal bath with the reactive material briquet at all times below the level of the bath and the refractory briquet in the slag line of the bath, and maintaining the column in this position until the reaction is complete.

6. Method of claim 5, in which the components of the reactive briquet are proportioned so that they will be entirely consumed when the reaction is completed.

References Cited in the file of this patent UNITED STATES PATENTS 1,239,178 Grosvenor Sept. 4, 1917 1,876,732 Neuhauss Sept. 13, 1932 1,916,042 Edgar June 27, 1933 2,179,823 Kemmer Nov. 14, 1939 2,671,019 Du Rostu Mar. 2, 1954 2,675,308 Milis et a1 Apr. 13, 1954 2,726,152 Eash Dec. 6, 1955 FOREIGN PATENTS 521,592 Canada Feb. 7, 1956

Claims (1)

1. AN APPARATUS FOR TREATING MOLTEN METAL COMPRISING A PLURALITY OF ASSEMBLED BRIQUETS CHEMICALLY REACTIVE WITH THE MOLTEN METAL AND HAVING END SURFACES ENABLING A TIGHT FIT OF EACH BRIQUET TO ADJACENT BRIQUETS, MEANS FOR HOLDING AND PRESSING THE BRIQUETS TOGETHER TIGHTLY IN SUPERPOSED POSITION WITH THE END SURFACES OF THE BRIQUETS HAVING A LIQUID TIGHT FIT OF EACH BRIQUET WHEN THE UNIT SO FORMED

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