US3414404A - Method for treating ferrous metals - Google Patents

Description

United States Patent 3,414,404 METHOD FOR TREATING FERROUS METALS John C. Robertson, Midland, Mich., and Oliver Osborn, Lake Jackson, Tex., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Feb. 23, 1965, Ser. No. 434,632 7 Claims. (Cl. 75-130) ABSTRACT OF THE DISCLOSURE A process for treating ferrous based melts with thorium which comprises introducing into a melt an addition agent comprised of a thorium halide and a reducing agent for the thorium halide which is capable of reducing the thorium halide to thorium metal while in the molten metal bath.

This invention relates to the treatment of molten ferrous based materials, and more particularly is concerned with a novel process for preparing ductile, i.e. nodular, grey cast iron.

It is known in the art that certain metals, e.g. magnesium, thorium and yttrium, when alloyed with cast iron in low concentrations will cause uncombined carbon present therein to be present in a compacted form, and preferably a spheroidal form. Such cast iron is known as nodular iron and possesses properties different from and improved over that found in grey cast iron where the uncombined carbon is present as the normal flake graphite. The terms nodular iron or nodularization as used hereinafter refer to iron having spheroidal, i.e. compacted graphite inclusions and to the process by which these are formed.

A wide variety of processes and apparatus have been set forth in the art relating to the introduction of magnesium into molten cast iron. Many of these known techniques employed complicated equipment or use compositions whereby undesirable substances are introduced into the molten ferrous bath along with the magnesium. Also, violent, uncontrolled hazardous reactions accompany addition of magnesium into the iron in the employment of a majority of such known processes.

Thorium metal is somewhat more readily introduced into a molten iron melt, but thorium metal is not readily available in large quantities. Further, both thorium and thorium based alloys are costly.

It is the principal object of the present invention, therefore, to provide a novel process for introducing thorium into molten ferrous based melts and for producing nodular iron whereby a rapid, but non-violent reaction is achieved with substantially complete nodularization of the graphite in the iron product along with the establishment of a residual thorium content in the treated iron.

It is another object of the present invention to provide an inexpensive and readily available thorium containing composition and process of its use for nodularizing iron.

It is a further object of the present invention to provide a process suitable for use in nodularizing iron which obviates the need for special plunging equipment to introduce a treating agent under the bath surface and requires no complicated mechanical application equipment.

It is still another object of the present invention to provide a nodularizing composition and process which is safe to use and operate and which obviates the need for covered ladles or other special pressure resistant equipment as are employed in many conventional nodularizing processes.

It is an additional object of the present invention to provide a process for treating molten ferrous materials that does not introduce undesirable constituents, which may alloy with the melt, into the ferrous melt.

It is a further object of the present invention to provide a process for nodularizing iron wherein alloying elements are not introduced into the melt as in many conventional nodularizing treatments. This instant invention thereby permits (1) the incorporation of large quantities, 70 percent or more, of gates, risers and other scrap into subseqeunt melts without adversely affecting the properties of the iron, and (2) the use of a heavier post inoculation treatment which is particularly desirable for thin sectioned castings.

It is also an object of the present invention to provide a novel inexpensive process for introducing thorium into molten ferrous based melts.

It is another object of the present invention to provide a means for nodularizing iron wherein there is substantially no loss of the ferrous-based melt because of spillage, splattering or other violent melt reaction during the treatment.

These and other objects and advantages will become apparent from the detailed description presented hereinafter.

In accordance with the present invention, substantially complete nodularization of graphite and retention of a desirably high thorium alloying metal concentration in ferrous based melts is produced without violence by introducing into a molten ferrous melt an addition agent composition comprised of a thorium halide and a reducing agent for the thorium halide which reducing agent is capable in the molten metal bath of reducing the thorium halide to thorium metal. The addition agent is maintained in the melt for a predetermined period of time,

Ordinarily, the amount of reducing agent in the composition at a minimum is about percent and usually ranges from about 85 to about 125 percent or more and desirably from about to about percent of that required stoichiometrically for reducing the thorium halide to thorium metal.

In the practice of the present invention usually a composition comprising thorium fluoride and a reducing agent such as magnesium, calcium carbide, calcium or a calcium carbide-calcium silicon alloy mixture is employed within the ranges set forth hereinbefore.

Preferably a magnesium-thorium fluoride composition containing about 14 weight percent magnesium and about 86 weight percent thorium fluoride or a calcium carbidethorium fluoride composition containing about 30 weight percent calcium carbide and about 70 weight percent thorium fluoride is employed in the practice of the present invention.

When metal reducing agents, such as magnesium and calcium, for example, which in themselves are known to be graphite nodularizing agents for ferrous melts, are employed in excess of that required stoichiometrically for reduction of the thorium halide to thorium metal, the present invention offers the additional advantage that the thorium metal need not all be employed for the nodularizing treatment. Instead this can serve to counteract detrimental effects of subversive elements such as lead, bismuth, thallium, antimony and titanium which, if present in the melt, have an adverse elfect on nodularization.

The amount of the nodularizing agent to be employed in treating a molten mass of a ferrous based material, e.g. grey iron, by the instant process, expressed as pounds of thorium metal equivalent per ton of cast iron, ranges from about 0.2 to about 50 pounds of the thorium per ton of the ferrous based material. Ordinarily, the composition is added in a concentration of from about 10 to about 30 pounds of the thorium metal equivalent per ton of cast iron.

The treatment time employed ranges from about 0.25 about 20 minutes, ordinarily from about 0.5 to about 8 minutes and preferably the reaction is carried out over a aeriod of from about 1 to about minutes.

Both the thorium halide and reducing agent as used in he present composition, are in particulate form, prefertbly finely divided, and ordinarily are in powder form. \lso, these are substantially anhydrous.

The reactants can be blended by simple mixing operltions and introduced as a particulate mix into the molten errous based bath to be treated by any of a variety of :onventional means, e.g. plunging bells, etc. as known to me skilled in the art.

The composition is readily introduced into the bath if irst fabricated into briquettes, compacts, pellets, bricks or ither such similar shapes. By preparing such compacted nasses, the amount of active ingredients added to a given mass of molten metal can easily and accurately be conrolled. Simple pressure compacting of the ingredients vithout using binder constituents is preferred in the preplration of the compacts. For certain operations these :ompacts also may be sintered.

The campacted mass, e.g. in briquette form, convenently is introduced under the surface of a melt by use of 1. standard perforated plunging device as employed in many ordinary nodularization techniques. Alternatively, he briquette can define an opening or openings passing herethrough and a predetermined number of briquettes :an be placed on a stick or rod and this assembly then be ilunged into the mass to be treated.

A particularly effective and simple way to introduce the 'eactants into the molten iron is to afiix the requisite quanity of the briquettes or blocks to the bottom of the ladle. 3y this technique, this nodularization promoting agent is tlready in place prior to the time the molten iron is introluced into the pot. Also, this technique assures that the :ompacts are positioned at a predetermined spot usually tear or in the bottom of the ladle or metal treatment pot.

The size of the compacts, i.e. briquettes, for example, 0 be employed in the instant process is not critical. For )ptimum efliciency of operation, however, ordinarily the :ornpacts are provided so as to have a minimum surface rrea to volume ratio of about 5. Ordinarily, to increase he effective surface area, a plurality of members rather ban a single large brick or block is employed for a given reatment. However, even with ladles holding as much LS 400 pounds or more iron, one briquette designed to rave the requisite surface area/volume ratio, as by multile perforations or waffle eifect, for example, satisfactorily :an produce the desired nodularization.

The resulting nodular iron product can be used in any .pplication and/or subsequently processed by any of the echniques employed for ductile iron.

Although the present invention finds particular utility n the nodularization of iron, it also finds application in he desulfurization of steels and other ferrous based melts. n this latter application, ready reaction is achieved in a ion-violent manner to effectively reduce the sulfur conent of such materials.

The following examples will serve to illustrate further he present invention, but are not meant to limit it thereto.

Example I.An induction furnace having a capacity of bout 4 pounds of molten iron and equipped with a tilting mechanism was charged with .a ferrous based metal having be following nominal composition:

Power of about 6 kilowatts was applied to the furnace ontaining about 4 pounds of the iron for a period of about one hour. The temperature of the molten mass was read with an optical pyrometer and was held essentially constant at a temperature of about 2750 F. over the test period.

A 28 gram briquette of the present treating agent composed of about 14 weight percent particulate magnesium (about minus 100 mesh US. Standard Series) and 86 iweight percent finely divided thorium fluoride was prepared. This was calculated to give a thorium metal addition equivalent to about 20 pounds thorium per ton of ferrous melt.

The briquette was placed in a perforated graphite plunging bell and plunged into the molten metal and maintained therein for a total period of about 30 seconds. At the end of the 30 second immersion period the plunger was withdrawn from the melt and the power to the furnace cut off. Approximately one minute elapsed while the residue was being removed from the plunging bell. After this treatment the residue from the Mg-ThF, briquette was placed on the surface of the melt and rabbled into the iron by stirring with a graphite rod for a period of about 1 minute. At no time during the reaction period was there violent reaction or any splattering of ferrous metal from the furnace. After the stirring of the briquette into the melt, about 12.4 grams of silicon was stirred into the melt as a post-inoculant in accordance with standard procedure. The treated metal was poured into a shell mold and solidified.

Metallographic examination of the iron produced showed .a completely spheroidal graphite microstructure.

The casting was sampled by drilling and analyzed by emission spectroscopy. This analysis showed a residual magnesium content of only 0.002 percent (too low to produce nodular iron) and a residual thorium content of 0.095 weight percent.

Example IL-Using the same experimental apparatus and procedure as described in Example 1, two 1 /2 inch diameter cylindrical briquettes, of 14 weight percent Mg-86 weight percent ThR, each weighing 28 grams, were made and used for the nodularizing treatment.

The two briquettes had a total thorium equivalent of about 40 pounds thorium metal per ton of iron.

In this treatment, one of the briquettes with a small hole drilled through its center, was mounted on the end of a graphite rod, plunged to the bottom of the bath and held there for about 2 minutes before withdrawal. This operation was then repeated with the second briquette. No fire, obnoxious or toxic fumes or smoke was observed as the briquettes were plunged into the melt. The initial reaction was very active but not violent so as to throw metal from the furnace.

After the plunging treatment, the cast iron was postinoculated with about 12.4 grams of silicon in accordance with standard practice and the melt cast in a Y-block shell mold for the purpose of obtaining four one-fourth inch diameter sample specimens according to the standard ASTM procedure A44560T.

The resulting solidified iron product was found upon metallographic examination to contain graphite only in spheroidal form. Spectrographic analysis of the iron indicated a residual magnesium content of only about 0.0007 weight percent and was about 0.3 weight percent thorium.

Example III.The same compacting techniques were used with a blended powdered mixture of about 30' weight percent calcium carbide and about weight percent thorium fluoride to produce a cylindrical compact weighing about 51.4 grams. This was equivalent to a thorium content of about 30 pounds per ton of ferrous based metal. This when plunged to the bottom of a molten ferrous melt in accordance with the technique described in Example II give active, but non-violent reactivity. After about 45 seconds, the briquette began to disintegrate. A fluid slag resulted which came to the surface of the melt. The treatment period was about 3 minutes. After this period, the melt was post-inoculated with about 20 grams of 85 percent ferrosilicon. The heat was tapped into a shell mold. A specimen was cut from the solidified casting. This, under microscopic examination, showed a completely nodular graphite structure. Spectrographic analysis of the iron showed about 0.12 weight percent thorium residual in the melt.

In a manner similar to that described for the foregoing examples, the following compositions of thorium fluoride and a reducing agent can be employed in the process of the present invention:

Percent (1) ThF (powdered); Mg (atomized pellets minus 100 mesh) 85 (2) ThF (particulate); Calcium carbide, Calcium silicon alloy 120 (3) ThCl Ca (minus mesh) -5 110 (4) ThF CaSi 100 The percents of the reducing agent for these reaction mixtures shown directly hereinbefore are expressed as the percent based upon that required stoichiometrically for reduction of the thorium halide to thorium metal.

These compositions can be simply admixed and injected as a particulate mass into a molten cast iron, molten steel bath, a molten blast furnace iron or can be compacted prior to use in such ferrous based melts.

Various modifications can be made in the present invention without departing from the spirit and scope thereof for it is underrood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process lor producing grey cast iron containing spheroidal graphite and thorium which comprises:

(at) introducing into a molten mass of grey cast iron an addition agent comprising thorium fluoride and magnesium, the amount of said magnesium being that required stoichio-metrically to reduce said thorium fluoride to thorium metal the amount of said addition agent expressed as pounds of thorium metal equivalent per ton of iron being from about 0.2 to about 50, and

(b) maintaining said agent in said molten mass for a period of time ranging from about 0.5 to about 8 minutes.

2. The process as defined in claim 1 wherein from about 10 to about pounds of said agent, expressed in pounds of thorium metal equivalent per ton of metal, is introduced into the molten mass of grey cast iron and maintained in the molten mass for a period of from about 1 to about 5 minutes.

3. A process for treating ferrous based melts which comprises:

(a) introducing into a molten mass of a ferrous based metal an addition agent comprising thorium fluoride and magnesium, the amount of magnesium in said addition agent being about that required to reduce said thorium fluoride to thorium metal, and

(b) maintaining said agent in said molten mass for a period of time ranging from about 0.25 to about 20 minutes.

4. The process as defined in claim 3 wherein the agent is maintained in said molten mass for a period ranging from about 0.5 to about 8 minutes.

5. A process for producing grey cast iron containing spheroidal graphite and thorium which comprises:

(a) introducing into a molten mass of grey cast iron an addition agent comprising thorium fluoride and calcium carbide, the amount of said calcium carbide being about that required stoichiometrically to reduce said thorium fluoride to thorium metal, the amount of said addition agent expressed as pounds of thorium metal equivalent per ton of iron being from about 10 to about 30', and

(b) maintaining said agent in said mass for a period of time ranging from about 0.5 to about 8 minutes.

6. A process for producing grey cast iron containing spheroidal graphite and thorium which comprises:

(a) introducing into a molten mass of grey cast iron maintained at from about 2600 to about 3000 F. an addition agent comprising on a weight basis from 86 weight percent particulate thorium fluoride and about 14 weight percent particulate magnesium, the amount of said agent, expressed as pounds of thorium metal equivalent per ton of iron being from about 10 to about 30,

(b) maintaining said agent in said mass for a period of time ranging from about 1 to about 5 minutes, and

(c) casting the so-treated grey iron, thereby to prepare cast grey iron containing spheroidal graphite and magnesium.

7. A process for producing grey cast iron containing spheroidal graphite and thorium which comprises:

(a) introducing into a molten mass of grey cast iron maintained at from about 2600 to about 3000 F. an addition agent comprising on a weight basis about weight percent particulate thorium fluoride and about 30 weight percent particulate calcium carbide, the amount of said agent, expressed as pounds of thorium metal equivalent per ton of iron being from about 10 to about 30,

(b) maintaining said agent in said mass for a period of time ranging from about 1 to about 5 minutes, and

(c) casting the so-treated grey iron, thereby to prepare cast grey iron containing spheroidal graphite and thorium.

References Cited UNITED STATES PATENTS 2,734,822 2/1956 Lamb --130 X 2,821,473 1/1958 Moore 75-130 2,980,530 4/1961 Crome 75130 3,065,070 11/1962 Otani 75-58 X FOREIGN PATENTS 882,311 11/l961 Great Britain.

OTHER REFERENCES Eflect of Thorium on Cast Iron, article in The Iron Age; Dec. 31, 1942, p. 41.

L. DEWAYNE RUTLEDGE, Primary Examiner.

H. W. TARRING, Assistant Examiner.