US3666449A - Method for the introduction of volatile additives into a melt - Google Patents

Abstract

INTRODUCTION OF VAPORIZABLE ADDITIVES, SUCH AS MAGNESIUM, INTO AN IRON MELT IN WHICH THE VAPORAZATION IS INITIATED BY A TILTING MOVEMENT OF A TREATMENT VESSEL. THE VAPORIZABLE MATERIAL IS CONTAINED IN A SEPARATE CONPARTMENT WHICH CAN BE EXTERNALLY CHARGED AND WHICH, IN ONE POSITION OF THE VESSEL SEGREGATES THE ADDITIVE FROM HTE MELT, BUT ON TILTING THE VESSEL, PERMITS COMMUNICATION WITH THE MELT THROUGH OPENINGS LOCATED A DIFFERENT LEVELS. THE VAPOR BUBBLES FORMED ASCEND THROUGH THE MELT WITH SUCH A SIZE AND IN SUCH A NUMBER THAT AT LEAST A PORTION OF THE BUBBLES ESCAPE FROM THE SURFACE OF THE MELT. THE VAPOR BUBBLES HAVE A GREAT SURFACE AREA TO PROVIDE, FOR EXAMPLE WITH MAGNESIUM, A YIELD OF AT LEAST 30% AND PREFERABLY MORE THAN 40% OF THE ADDITIVE IN THE MELT WHILE THE VELOCITY OF THE ASCENDING VAPOR BUBBLES IS SUCH AS TO PRODUCE A FLUSHING ACTION ON THE MELT RESULTING IN A REDUCTION OF THE REACTION PRODUCTS AND RESIDUAL UNDESIRABLE IMPURITIES IN THE MELT.

Description

A. ALT

May 30, 1972 METHOD FOR THE INTRODUCTION OF VOLATILE ADDITIVES INTO A MELT Filed Jan. 22, 1969 INVENTOR ///7a// 4Z6 f ATTORNEYS United States Patent ice 3,666,449. Patented May 30, 1972 US. Cl. 75-130 B 12 Claims ABSTRACT OF THE DISCLOSURE Introduction of vaporizable additives, such as magnesium, into an iron melt in which the vaporization is initiated by a tilting movement of a treatment vessel. The vaporizable material is contained in a separate compartment which can be externally charged and which, in one position of the vessel segregates the additive from the melt, but on tilting the vessel, permits communication with the melt through openings located at different levels. The vapor bubbles formed ascend through the melt with such a size and in such a number that at least a portion of the bubbles escape from the surface of the melt. The vapor bubbles have a great surface area to provide, for example with magnesium, a yield of at least 30% and preferably more than 40% of the additive in the melt while the velocity of the ascending vapor bubbles is such as to produce a flushing action on the melt resulting in a reduction of the reaction products and residual undesirable impurities in the melt.

BACKGROUND OF THE INVENTION The present invention relates to an improved method for the introduction of volatile or vaporizable additives into a melt, especially magnesium, into an iron-carbon melt, in which the vaporization is initiated by a tilting movement of the treatment vessel whereby the volatile additives are immersed beneath the surface of the melt, and further, wherein the speed of vaporization is retarded by means of a receiving compartment for the additives which are to be vaporized, such receiving compartment being equipped with openings directed into the interior of the treatment vessel and relates further to the use of the same for the production for various materials.

The introduction of magnesium into iron melts is the surest technical and the most economical manner to produce iron-carbon cast materials with spherical graphite. In so doing, magnesium, as well as also other elements of the earth alkaline group and the group of the rare earths, causes, in known manner, a separation of the graphite in spherical form during solidification and/or subsequent heat treatment, and therefore results in improved mechanical properties.

However, the introduction of magnesium is associated with known difiiculties. Its specific weight of 1.74 g./cm. is considerably lower than that of the iron melts. Above all magnesium, with a boiling point of 1107 C. at a generally encountered temperature of the iron melt of 1480" C., develops a vapor pressure of approximately 12 atmospheres. Therefore, in the majority of instances, magnesium is introduced in the form of key alloys or hardeners with a magnesium content of to 30% into the melt which is to be treated, since the vapor pressure is reduced in accordance with the dilution.

However, the use of key alloys or hardeners possesses the drawback that other elements are introduced into the melt to a certain degree in undesirable quantities. Consequently, the possibility of using such key alloys or hardeners is generally limited. The use of such materials necessitates starting with melts of low sulfur content. Melts of low sulfur content can ordinarily only be realized in a basic melting furnace unit or in an acidic melting furnace unit while using a sulfur-poor material charge or by using a special desulfurizing technique. Moreover, the use of key alloys or hardeners is associated with increased costs. Thus, the cost for the same quantity of added magnesium utilizing conventional key alloys or hardeners amounts to about five to twenty times that of using pure magnesium.

Accordingly, a whole series of techniques have become known to the art which are concerned with the introduction of pure magnesium into the iron melts. Thus, at the present time, a small quantity of cast iron with spherical graphite may be produced according to a technique in which pure magnesium is added under a pressure which corresponds to the vapor pressure at the given treatment temperature. Methods are also known to the art wherein pure magnesium is continuously, added in solid, liquid, or gaseous condition, the speed of reaction being controlled by the speed with which the material is added. It has also already been proposed to reduce to an acceptable degree the vigor or intensity of the reaction of magnesium during continuous or one-time addition by mixing the same with suitable inert materials in powdery-or pasty-like condition, by imbuing porous materials with magnesium, by the use of suitable coatings, or by introducing the magnesium into a container having predetermined openings limiting the contact with the melt.

In addition to the conventional methods of adding magnesium to the melt by pouring-over, immersion or introduction with a pipe or similar device, it has also been proposed heretofore to bring about the addition or introduction in such a manner that the magnesium is placed into a tiltable vessel within a specially provided pocket therefor. After filling with iron the magnesium is brought below the surface of the bath by carrying out a tilting movement through about Additionally, a technique has also become known according to which the device provided for the reception of the magnesium is constructed in the form of a compartment which can be externally charged and which is equipped with an opening towards the inside, the size of which is decisive for the heat delivered by convection to the magnesium through the melt and, therefore, for the speed of vaporization. The drawback of this method resides in the fact that the considerable quantity of vapor hinders the continuous flow of heatsupplying melt. Consequently, on the one hand, this causes an irregular reaction process which is associated with violent eruptions and, on the other hand, the dimensioning of the opening towards the lower extreme is limited and thus renders impossible a delay or retardation of the reaction to the desired degree.

According to another known method, the yield is considerably increased due to the arrangement of a number of small openings, whereby the melt does not enter into the chamber or compartment containing the magnesium, rather the heat required for vaporization is delivered by conducting heat through the walls of the chamber. However, with this technique, the flushing effect is practically lost.

SUMMARY OF THE INVENTION Therefore, it is a primary object of this invention to provide a method for the introduction of vaporizable materials to an iron melt which is free from the foregoing 'and other such disadvantages.

It is a further object of this invention to provide techniques for the addition of varoprizable materials, specifically magnesium, wherein the vapor bubbles of the vaporizing additives are permitted to ascend through the 3 melt with a size and speed that there occurs a rather extensive absorption of the vapor by the melt and, additionally, the bubbles cause a flushing action which is efiective to separate the reaction products between the melt and the va or.

EX still further object of this invention is the provision of a method for the addition of other materials such as fluxing agents and carbon to the melt simultaneously with the addition of the vaporizable materials.

The basic objects of the invention are to permit the vapor =bubbles formed by the additives to ascend through the melt with such a size and in such a number that at least a portion of the formed vapor bubbles escape from the surface of the bath with such a large velocity that the ascending bubbles exert a flushing action upon the melt. This results in a reduction of the reaction products and residual undesirable mixtures or impurities in the melt. On the other hand, the size of the vapor bubbles is chosen to be such that there results a sufficiently great reaction surface of the vapor bubbles ascending in the melt whereby there is obtained a favorable yield of the additives introduced into the melt, for instance, a magnesium yield in iron-carbon melts at the usual treatment temperature of at least 30% and preferably above 40%.

In other words, the invention method is characterized by the fact that the vapor bubbles of the vaporizing additives are permitted to ascend through the melt with such a size and in such a number that, on the one hand, there occurs as extensive as possible absorption or reception of the resulting vapor by the melt and, on the other hand, a favorable flushing action for separating reaction products between the melt and the resulting vapor. During the introduction of the additives into the melt, the same can be simultaneously subjected to a circulatory movement.

As indicated, the invention is also concerned with the provision of an improved tiltable treatment vessel for car rying out the aforesaid inventive process. This tiltable treatment vessel is manifested by the fact that it possesses at least one rigidly-mounted receiving compartment for the additives which compartment can be charged from the outside, that is externally of the vessel. This receiving compartment is arranged at least at 'a portion of the base surface of the interior of the ladle or vessel when the vessel is tilted to its treatment or vertically-extending position. Yet, the interior or inner chamber of the receiving compartment does not communicate with the melt when the vessel is in its filling or horizontally-extending position. Further, the compartment includes a number of openings directed towards the interior of the treatment vessel, which openings are arranged and constructed in such a fashion that the melt passes into the compartment from the treatment vessel through at least some of the openings when the vessel is in its treatment position to vaporize the vaporizable additives with a certain speed and then passes back through at least some of the openings from the compartment into the interior or inner chamber of the treatment vessel.

According to the instant inventive concepts, the techniques hereof may be used for treating cast iron or malleable cast iron melts which have been molten in an acidic process without prior desulfurization, with technically pure magnesium or alloys containing large quantities of magnesium. Further, these techniques may be used for the production of cast iron with a carbon content of 2.5 to 3.8% carbon, as well as for the production of gray cast iron and cast iron with vermicular graphite. I

By virtue of the instant invention, there is simultaneously attained, with an exceptional yield of, for instance, magnesium, such a flushing or agitation effect that the reaction products formed between the melt and the vapor, for instance, magnesium sulfide, are separated from the melt. In contrast, with known techniques wherein the melts are treated with magnesium, the use of melts having a higher starting sulfur content have been excluded due to the formation of undesired inclusions. Consequently, the known treatment of sulfur-rich iron melts, for instance, cast iron or malleable cast iron melts from the acidic cupola furnace cannot be undertaken without previous desulfurization and without harmful products of reaction remaining in the melt. Sulfur-rich starting melts treated according to the inventive method manifest themselves, for instance, by a lower content of sulfur remaining in the melt.

As mentioned, it is advantageous, according to this invention, to equip the receiving compartment or chamber with openings which permit the magnesium vapor bubbles to ascend with such a size or magnitude through the melt that the magnesium yield amounts to at least 30% and preferably, more than 40%.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood, and objects other than those set forth above will become apparent, when consideration is given to the following detailed description thereof. Such description ma'kes reference to the annexed drawing, wherein:

FIG. 1 schematically illustrates an exemplary embodiment of a tiltable treatment vessel according to this invention in its filling or horizontally extending position; and

FIG. 2 depicts the tiltable vessel shown in FIG. 1 in its treatment or vertically extending position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and, more particularly, to FIG. 1, it will be seen that the treatment vessell is lined with refractory material and is filled while in its horizontally extending position with melt 2 to such an extent that the receiving compartment or chamber 3, which can be charged from the outside or externally, remains free, that is to say, does not communicate with the iron melt 2. After opening the stopper or plug 4, the receiving compartment or chamber 3 is charged with the vaporizable additive 5 with the addition of possible further additives, as will be explained hereinafter. By means of the stopper or closure 4, the charging opening of the receiving chamber or compartment 3 is closed and by means of a suitable cover member 6, the charging opening of the vessel 1 is likewise closed. The cover 6 contains an opening of 10 to 50 mm. diameter which is aligned with an opening in the tea can-like pouring spout of the vessel 1 when the cover 6 is in its closed position to vent the vessel.

After closing the plug 4 and the cover member 6, the entire treatment vessel 1 can be tilted by a remote controlled drive mechanism (not shown) into the treatmen or vertically extending position depicted in FIG. 2. In the vertically extending position of the treatment vessel 1, the receiving compartment 3 is located below the surface of the melt 2, and the melt passes via the openings 7 and 8 into the interior of the receiving compart-ment 3 where it contacts the additive 5 causing vaporization of the same. The formed vapor escapes in accordance with the lift through the discharge openings 8 arranged at the top of the receiving compartment 3, while the melt 2 continuously flows through the inlet openings 7 arranged at the lower region of the receiving compartment 3. Accordingly, the delivery of the heat in this manner assists and supports the vaporization process which is associated with a considerable take-up of heat. By appropriately dimensioning the cross-section of the openings 7 and 8, it is possible to predetermine the reaction velocity or speed of the pure magnesium 5 located in the receiving compartment 3, without requiring undesired additivematerials. The walls of the compartment 3 are preferably formed of refractory material, preferably clay graphite plates of 10 to 50 mm. thickness. The openings 7 are preferably of a diameter of 20 to 40 mm. and the openings 8 are preferably of a diameter of to 30 mm. with the openings 8 distributed over at least a third of the base surface of the vessel 1 and the entire cross-sectional area of the openings 7 being smaller than the entire cross-sectional area of the openings 8.

By virtue of the arrangement of the openings 7 and 8 of the receiving compartment 3 depicted in the drawing, the inlet openings 7 are subjected to a greater hydrostatic pressure (H than the outlet or discharge openings 8 I-I Due to contact of the molten cast iron with the magnesium, there result vapor bubbles which escape through the discharge openings 8. Consequently, there exists a through-flow of the molten cast iron through the receiving compartment 3, so that there occurs a uniform reaction of the magnesium.

The vapor bubbles escaping through the openings 8 move through the melt 2 towards the top and, in so doing, are intentionally taken up in part by the melt. The melt which is treated in this manner is again emptied through the filling openings by tilting the treatment vessel 1. In order to dampen the reaction of the pure magnesium located in the receiving compartment 3, it is possible to additionally introduce into this compartment cold scrap iron or another cooling agent. Through the arrangement of one or a number of grid-like intermediate floors formed of refractory material in the vessel 1 (not shown), it is possible to still further improve the yield of the additives. In order to obtain an overpressure in the treatment vessel 1, it is possible to appropriately construct the cover member 6.

The mode of operation of the inventive method will now be explained in conjunction with the following examples:

Example 1 A cast iron melt of the following chemical composi tion:

Percent C 3.80 Si 1.80 Mn 0.57 P n 0.07 0.179

Percent S 0.002

Thus, the magnesium yield amounted to 66%. The structure of the cast test pieces after innoculation with 0.5% ferrosilicon consisted of spherical graphite, that is to say, 96% Type VI according to VDG Merkblatt, P 441 and 4% Type V.

Example 2 A malleable cast iron melt of the following chemical composition:

Percent C 2.88 Si a 1.65 Mn 0.27 P 0.08 S 0.163

had added thereto at a temperature of 1510 C., according to the inventive process, 0.28% pure magnesium in the form of bars, or ingots. The amount of iron to be treated amounted to 860 kg. The vaporization of the magnesium lasted 120 seconds. After emptying the treatment vessel into a ladle, the following chemical composition was determined:

Percent S 0.002 Mg 0.056

Thus, the magnesium yield amounted to 63.5%.

Furthermore, it is known for the carburization of iron-carbon melts to add carbon to the surface of the bath of a melt located in an electric induction furnace. However, the degree of carburization with such a technique is dependent to a large extent upon the agitation effect of the magnetic coils and the type of slag cover. With lower input power to the electric furnace, carburization cannot be positively carried out and, moreover, the drawback exists that the carbon content on the order of magnitude of 3.6 to 3.8% C, such as required for the production of cast iron with spherical graphite, is considerably burned off in the electric furnace. Furthermore, it is also known to undertake carburization together with desulfurization in the ladle, whereby the required bath movement, on the one hand, is produced by rotation or centrifuging or, on the other hand, by air-or gas flushing.

These known techniques exhibit the drawback that the treatment times last up to 10 minutes and the carbon yield is low and subjected to certain undesired fluctuations.

It has now been additionally found that is is possible to positively carburize and simultaneously desulfurize and, if desired, regulate the residual magnesium content required for the spherical graphite formation of an ironcarbon melt in a simple manner, if during the performance of the inventive process before and/or during the introduction of magnesium into the iron-carbon melt, carbon is added to the surface of the bath. The carbon is added in the form of conventional carburizing agents, preferably in the form of coke grit or sand or graphite or carbon electrodes.

The above method is especially suitable for the carburization of cast iron, and indeed, specifically for the production of cast iron with spherical graphite.

During the production of cast iron with spherical graphite, it is necessary to reduce the sulfur content of the melt delivered from the acidic adjusted cupola furnace and to increase the carbon content to approximately 3.6 to 3.8% C.

As the treatment vessel there can advantageously be used a converter, as such has previously been described in conjunction with FIGS. 1 and 2.

The carbon for carburization of the melt, after filling of the starting melt, is added to the uncovered bath in the converter which is located in its horizontally extending position. After the subsequent rocking or pivoting of the converter into the vertically extending position, the vaporizing magnesium brings about a pronounced agitation of the bath which promotes carburization. Furthermore, the strongly reducing conditions, the basic slag, and the reduction of the sulfur content, act favorably for carburization. Due to the cooperation of these conditions, it is possible to desulfurize a melt in a single working operation within! approximately 70 seconds to approximately 0.003% final sulfur content, and the carbon content can be increased by approximately 0.6% and the residual magnesium content can be regulated to the amount necessary for cast iron with spherical graphite.

The formation of slag in the receiving compartment and in the openings between this compartment and the treatment vessel can be prevented by the addition of small amounts of fluxing agents, such as NaCl. In so doing, the fluxing agent is added to the pure magnesium ingots, for instance, in a ratio of 0.2 kg. NaCl/ 1000 kg. iron prior to treatment in the receiving compartment.

With this technique, it is, for instance, possible, even with treatment temperatures of 1480 C., and a carbon equivalent of 4.2%, to carburize by 0.7% a treated quantity of 900 kg. within 70 seconds with a carburization degree of 80%.

It should be apparent from the foregoing detailed description that the objects set forth at the outset to the specification have been successfully achieved.

Accordingly, what is claimed is:

1. In the introduction of metallic additives into a metal melt by contacting the additive in solid form with the molten metal in a submerged location in the melt, the improvement comprising providing a reaction zone to contain the solid additive,

said zone having at least one inflow orifice and at least one outflow orifice,

the total cross-sectional area of said at least one inflow orifice being smaller than the total crosssectional area of said at least one outflow orifice, said at least one inflow orifice and said at least one outflow orifice being spaced from each other by a significant distance;

providing a body of molten metal in a melt-confining zone which is vented to the atmosphere;

providing in said reaction zone a quantity of an additive in solid form,

said additive being vaporizable at the temperature of the molten metal in said melt-confining zone and said quantity being adequate to effect an improving effect on said body of molten metal; and positioning said reaction zone, with said reaction zone sealed save for said at least one inflow orifice and said at least one outflow orifice, in a location at the bottom of said melt-confining zone, with said at least one inflow orifice adjacent the bottom of said meltconfining zone and said at least one outflow orifice spaced thereabove,

said reaction zone being located a substantial distance below the surface of said body of molten metal and there being a significant difference between the hydrostatic pressure applied by said body of molten metal at said at least one outflow orifice and the hydrostatic pressure applied by said body of molten metal at said at least one inflow orifice due to the space between said inflow and outflow orifice,

the step of positioning said reaction zone in a location at the bottom of said melt-confining zone causing molten metal to flow into said reaction zone, via said at least one inflow orifice, into direct contact with said additive, whereby said additive is caused to vaporize with the vapors so produced generating pres sure in said reaction zone at least adequate to overcome the hydrostatic head of the molten metal and allow the vapor to escape via said at least one outflow orifice into the molten metal, and such escape of the vapors allowing continued entry of molten metal into said reaction zone via said at least one inflow orifice.

2. The improved method according to claim 1, wherein said molten metal is a cast iron melt having a substantial sulfur content, and

said additive is selected from the group consisting of magnesium alloys.

3. The improved method according to claim 2, wherein said additive is magnesium.

4. The improved method according to claim 3, wherein a minor quantity of a fluxing agent is provided in said reaction zone.

5. The improved method according to claim 4, wherein said fluxing agent is sodium chloride.

6. The improved method according to claim 1, wherein said reaction zone has a plurality of outflow orifices;

and

said step of positioning said reaction zone is carried out to locate the same adjacent one wall of said meltconfining zone, the transverse extent of said reaction zone being smaller than the transverse extent of said melt-confining zone.

7. The improved method according to claim 1, wherein cold metal compatible with said molten metal is provided in said reaction zone to dampen the reaction of said additive resulting when the molten metal entering via said inflow orifice contacts said additive.

8. The improved method according to claim 1, wherein said molten metal is a cast iron melt having a substantial sulfur content;

said additive is magnesium; and

the method further comprises adding carbon to said molten metal for carburization thereof,

said carbon being present in the melt when the molten metal enters said reaction zone, the vapors escaping from said reaction zone agitating the melt to promote carburization thereof.

9. In the treatment of a metal melt with a solid metallic additive, the improvement comprising placing a quantity of the solid metallic additive in a chamber having at least one inflow orifice and at least one outflow orifice, the chamber being sealed save for said orifices,

the total cross-sectional area of said at least one inflow orifice being smaller than the total crosssectional area of said at least one outflow orifice, the locations of said at least one inflow orifice and said at least one outflow orifice being spaced from each other by a significant distance; and confining a body of the molten metal to be treated in a space which surrounds said chamber in such fashion that said chamber is located at the bottom of the body of molten metal and said at least one outflow orifice is spaced above said at least one inflow orifice, said space being vented to the atmosphere at a point above the surface of the body of molten metal; said solid metallic additive vaporizing at the temperature of said molten metal and the quantity of said additive placed in said chamber being adequate to provide an improving effect on the quantity of said molten metal confined in said space; presence of said body of molten metal in said space, and the fact that said body provides a hydrostatic pressure at the location of said at least one inflow orifice which is greater than the hydrostatic pressure at the location of said at least one outflow orifice, causing molten metal to flow into said chamber via said at least one inflow orifice and into contact with said solid metallic additive,

contact of said molten metal with said additive causing said additive to vaporize, with the resulting vapors generating pressure in said chamber to oppose and thereby regulate the flow of said molten metal into said chamber via said at least one inflow orifice and to cause said vapors to escape via said at least one outflow orifice into said body of molten metal.

10. The improvement according to claim 9, wherein said molten metal is a cast iron melt and said additive is magnesium.

11. The improvement according to claim 9, wherein said space is defined by a vessel which is upright at the time of the flow of molten metal into said chamber,

said chamber is of smaller horizontal extent than is said space and is positioned off-center relative to said space, whereby a portion of said body of molten metal is beside said chamber, and

said at least one outflow orifice is directed generally upwardly and said at least one inflow orifice is directed generally laterally to communicate between the interior of said chamber and said portion of said body of molten metal which is beside said chamber. 12. The improvement according to claim 11, wherein said molten metal is a cast-iron melt having a substantial sulfur content; said additive is pure magnesium metal; and the method further comprises adding carbon to said molten metal for carburization thereof,

said carbon being present in said body of molten metal when molten metal flows into said chamber via said at least one inflow orifice, the magnesium vapor escaping from said chamber agitating said molten metal to promote carburization thereof.

References Cited UNITED STATES PATENTS 2,678,266 5/1954 Ziiferer 75-130 2,754,201 7/ 1956 Zwicker 75-130 2,997,3 86 8 /1961 Feichtinger 75-93 3,295,960 1/1967 Parlee 75-93 10 Robertson 75-130 X Fishell 75-130 B X Klingbeil 75-130 B X Grandpierre 75-130 B Wallace 75-123 Schelleng 75-130 X Kopke 75-130 B X OTHER REFERENCES 10 K. J. Wastschenko and L. Sofroni, Magnesiumbehandeltes Gusseisen, Leipzig, Germany, veb D'eutscher Verlag fiir Grundstotfindustrie, 1960, p. 141-144.

L. DEWAYNE RUTLEDGE, Primary Examiner 15 I. E. LEGRU, Assistant Examiner US. Cl. X.R.

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