US3197306A - Method for treating ferrous metals - Google Patents

Description

3,197,306 METHOD FOR TREATING FERROUS METALS Oliver Osborn and John C. Robertson, Lake Jackson, Te'x., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Aug. 31, 1964, Ser. No. 393,420 10 Claims. (CI. 75-130) Thisapplication is a continuation-in-part of application Serial No. 207,032, filed July 2, 1962, now abandoned.

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

It is known in the art that magnesium over and above that required for desulfurization retained in cast iron 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 5 as the normal flake graphite. The terms nodular iron" or nodularization as used hereinafter refer to iron having spheroidal, i.e. compacted graphite inclusion 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 employ 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. Now, unexpectedly a safe, simple, 'easy to handle composition and process has been found to introduce magnesium into a ferrous based melt.

It is a principal object of the present invention, therefore, to provide a novel process for introducing magnesium 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 desirable residual magnesium content in the treated iron.

It is another object of the present invention to provide an inexpensive composition and process for nodularizing llOl'l.

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 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 processfor nodularizing iron wherein alloying elements are not introduced into the melt as in many conventional magnesium treatments. This instant invention thereby permits (1) the incorporation of large quantities, 70 percent or more, of gates, risers and other scrap into subsequent melts without adversely affecting the properties of the iron, and ,(2) the use of heavier post inoculation treat-' ment which is particularly desirable for thin sectioned casting.

7 3,197,306 Patented July 27, 1965 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 magnesium concentration in cast iron is produced by introducing an addition agent comprised of from about 5 to about 35 and ordinarily from about 10 to about 35 weight percent aluminum and from about 95 to about 65 and ordinarily from about 90 to about 65 weight percent magnesium oxide into a molten iron bath. Preferably 30 weight percent aluminum and about-70 weight percent magnesium oxide is used.

Although the process proceeds satisfactorily with this composition substantially complete nodularization is achieved at markedly reduced reaction times if a member selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof is incorporated into the treatingagent composition. Therefore, ordinarily a composition comprising, on a weight basis from about to about 85 percent magnesium oxide, from about 5 to about 80 percent of a member selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof and from about 5 to about 35 percent particulate aluminum is introduced as the addition agent into a molten grey iron bath maintained at a temperature of from about 2450 to about 3000 F, and preferably at from about 2650 F to about 2850 F.

Preferably this treating agent composition comprises from about 35 to about 60 weight percent magnesium oxide, from about 10 to about weight percent calcium oxide' and from about 15 to about 30 weight percent aluminum. I

The amount of this 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 magnesium metal equivalent per ton of cast iron, ranges from about 0.5 to about 25 pounds magnesium per ton of the ferrous based material. Ordinarily, the composition is added in a concentration of from about 1 to about 7 pounds of magnesium (metal equivalent) per ton of cast iron.

The treatment time employed ranges from about 0.25 to about 20 minutes, ordinarily from about 0.5 to about 8 minutes and preferably the reaction is carried out over a period of from about 0.5 to about 2.5 minutes.

The magnesium oxide and calcium containing materials, as used in the present composition, are finely divided and ordinarily are in powder form. Also, these are substantially anhydrous.

High grade, separate components, e.g., MgO, CaC and CaO can be used. Alternatively, burnt dolomite which contains both CaO and MgO as well as trace amounts of other oxides can be employed. With this latter material additional MgO, as needed, can be added to provide the hereinbefore specified operable quantities of MgO and CaO in the final composition. Other metal oxide generating substances such as magnesium silicate, magnesium hydroxide, calcium hydroxide and naturally occurring oxidic materials such as olivine [(Mg, Fe), SiO and the like can be employed.

The aluminum employedin the present invention is in particulate form. The size or shape of this component is not critical except that the particles must not be of such a massive size that they provide a detrimental high mass to surface area relationship. Powders, pellets, flakes, machine chips, curled cuttings, filing, sawdust, chopped foil and the like particles have been found to be particularly tions and introduced as a particulate mix into the molten ferrous based bath-to be treated by any of a variety of conventional means, e.g., plunging bells, etc., as known to one skilled in the art.

The composition is readily introduced into the bath if first fabricated into briquettes, compacts, pellets, bricks or other suchsimilar shape. By preparing such compacted masses, the amount of active ingredients added to a given mass of molten metal can easily and accurately be controlled. Simple pressure compacting of the ingredients without using binder constituents is preferred in the preparation of the compacts. For certain operations these compacts also may be sintered.

The compacted mass, e.g., in briquette form, conveniently is introduced under the surface of a melt by use of a standard perforated plunging device as employed in many ordinary nodularization techniques. Alternatively, the briquette can define an opening passing therethrough and a predetermined number of briquettes can be placed on astick or rod and this assembly then be plunged into the mass to be treated.

A particularly effective and simple way to introduce the reactants into the molten iron is to aftix the requisite quantity of the briquettes or blocks to the bottom of a ladle. By this technique, this nodularization promoting agent is already in place prior to the time the molten iron is introduced into the pot. Also, this technique assures that the compacts are positioned at a predetermined spot usually near or in the bottom of the ladle or metal'treatment pot.

The size of the compacts, i.e., briquettes, for example, to be employed in the instant process is not critical. For optimum eificiency of operation, however, ordinarily the compacts are provided so as to have a minimum surface area to volume ratio of about 5. Ordinarily, to increase the effective surface-area, a plurality of members rather than a single large brick or block is employed for a given treatment. However, even with ladles holding as much as 400 pounds or more-iron, one briquette designed to have therequisite surface area/volume ratio, as by multiple perforations or wattle effect, for example, satisfactorily can produce the desired nodularization.

4 The following examples will serve to illustrate further the present invcntion, but are not meant-to limit it thercto.

EXAMPLE I A number of runs were made evaluating the effectiveness of a number of MgO-CaO-Al and MgO-Al mixtures as nodularizing agents for cast iron. For these tests, an induction furnace having a capacity of about 4 pounds of molten iron and equipped with a tilting mechanism was charged with a ferrous based metal having the following nominal composition:

Percent C 3.2-3.5 Si 1.5-1.9 Mn 0.2-0.35 P 0.025-0.03 S 0.0040.008 Fe Balance Power of about 6 kilowatts was applied to the furnace containing 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 over the test period.

A cylindrical briquette of the treating agent composed of a dead burned powdered dolomite (56.5% CaO 42.5% MgO, balance substantially other metal oxides),

a high grade powdered. magnesium oxide and an aluminum powder (about 80 percent passing through a 325 US. Standard mesh sieve) was plunged into the molten metal and maintained therein for a predetermined period of time. After removal of the briquette from the melt, about 12.4 grams of silicon was stirred into the melt as a postinoculant in accordance with standard procedure. The powerto the furnace was then shut off and the treated -metal poured into a' Y -block shell mold' for the purpose Table 1 Treating agent composition, Briquette weight percent by weight Residual Run Treatment Condition Mg in iron, No. temperature, time, percent by Actual, tot. Theo, lb. F. min. wt. Al Mg() 1 C210 gins. per 4 M g per ton lbs. Fe v Fe 19. 91 44. 61 35. 24 7 2, 750 2. o 0. 086 15. 73 35. 24 49. 10 .30 7 2, 650 5 0. (180 15. 73 35. 24 49. 10 15 3. 5 2, 750 2. 5 0. 020 19. 91 44. 61 35. 5O 24 7 2, 650 5 t). 086 19. 91 44. 61 35. 50 12 3. 5 2, 750 2. 5 0.022 23. 36 52. 38 24. 29 20 7 2, 650 5 0. 060 23.36 52. 38 24. 29 1O 3. 5 2, 750 2. 5 0. 027 26. 58 59. 60 13. 82 17. 5 7 2, 750 2. 5 0. 053 26. 58 59. 60 13.82 9' 3. 5 2, 650 2. 5 0.03 30. 0 70. 0 15 2 7 2, 650 5 0. 049

1 Total of MgO in dolomite plus added magnesium oxide. 2 About 90% nodularization of graphite in melt. The resulting nodular iron product can be used in any EXAMPLE 11 application and/or subsequently processed by any of the techniques employedfor ductile iron.

Although the present invention finds particular utility in the nodularization of iron, it also finds application in the desulfurization of steels and other ferrous based melts. In this latter application, ready reaction is achieved in a carbide (CaC about 46 percent powdered MgO and non-violent manner to effectively reduce the sulfur content of such materials.

examples, the following compositions can be employed in the process of the present invention:

- Wt. percent Al machine chips MgO (200 mesh U.S. Std. Sieve) 85 CaO (-200 mesh U.S. Std. Sieve) Al chopped foil 35 MgO powder 5O CaC (325 mesh U.S. Std. Sieve) l5 A1 bandsaw dust 5 MgO powder l5 CaO powder 80 Al rotary filings 30 MgO (325 mesh U.S; Std. Sieve) 65 CaO 100 mesh U.S. Std. Sieve) 5 Al pellets (100 to 200 mesh U.S. Std. Sieve) l5 CaO powder 20 CaC powder 20 MgO powder 45 Al powder (30 to 100 mesh U.S. Std. Sieve) l5 MgO 85 These compositions can be simply admixed and injected as a particulate mass into a molten cast iron or steel bath or can be compacted prior to use.

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

We claim:

1. A process for treating comprises;

ferrous based melts which 4. The process as defined in claim 3 wherein from about 1 to about 7 pounds of said agent, expressed in pounds of magnesium metal equivalent per ton of metal, is introduced into the molten mass of grey cast iron and maintained in the molten mass for a periodof from about 0.5 to about 2.5 minutes.

5. A process for treating ferrous based melts which comprises;

(l) introducing into a molten mass of a ferrous based metal an addition agent comprising from about 5 to about 35 weight percent aluminum, from about 15 to about 85 weight percent magnesium oxide and from about 80 to about 5 weight percent of a member selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof, and

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

- 6. The process as defined in claim 5 wherein the agent is maintained in said molten mass for a period ranging from. about 0.5 to about 2.5 minutes.

7. A- process for producing grey cast iron containing spheroidal graphite and magnesium which comprises;

(1) introducing into a molten mass of a ferrous based metal an addition agent comprising from about 5 to about 35 weight percent aluminum and from about 95 to about 65 weight percent magnesium oxide, and

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

2 The process as defined in claim 1 wherein the molten mass of ferrous based metal is a grey cast iron andsaid iron is treated with an addition agent comprising from about 10 to about 35 weight percent aluminum and from about 90 to about 65 weight percent magnesium oxide.

and the agent is maintained in said molten mass for a period ranging from about 0.5 to about 2.5 minutes.

3. A process for producing grey cast iron containing spheroidal graphite and magnesium which comprises;

(1) introducing into a molten mass of grey cast iron an addition agent comprising from about 10 to about 35 weight percent aluminum and from about 90 to about 65- weight percent magnesium oxide, the amount of said agent, expressed as pounds of magnesium metal equivalent per ton of iron being from about 0.5 to about 25, and (2) maintaining said agent in said molten mass for a period of time ranging from about 0.25 to about 20 minutes.

(1) introducing into a molten mass of grey cast iron an addition agent comprising from-about 5 to about 35 weight percent aluminum, from about 15 to about 85 weight percent magnesium oxide and from about to about 5 weight percent of a member. selected from the group consisting of calcium oxide, calcium carbide and mixtures thereof, the amount of said agent, expressed as pounds of magnesium metal equivalent per ton of iron being from about 0.5 to about 25, and v (2) maintaining said agent in said mass for a period of time rangingfrom about 0.25 to about 20 minutes.

v8. The process as defined in claim I wherein from about 1. to about 7 pounds of said' agent, expressed as pounds of magnesium metal equivalent per ton of metal, is'introduced into the molten mass of grey cast iron and maintainedin the molten mass vfor a period of from about 0.5 to about 2.5 minutes.

9. The process as defined in claim 7 wherein the molten mass of grey iron is maintained at from'about 2450 to about 3000 F. during the period said agent is maintained in said molten iron.

10. A process for producing grey cast iron containing spheroidal graphite and magnesium which comprises;

(1) introducing into a molten mass of grey cast iron maintained at from about 2650 to about 2850 F. an addition agent comprising on a weight basis from about 15 to about 30 weight percent particulate aluminum, from about 35 to about 60weight percent finely divided magnesium oxide and from about 50 to about 10 percent CaO, the amount of said agent, expressed as pounds of magnesium metal equivalent per ton of iron being from about 0.5 to about 25, (2) maintaining said agent in said mass for a period of time ranging from about 0.5 to about 2.5 minutes, and (3) casting the sd-treated grey iron, thereby.to prepare cast grey iron""oontaining spheroidal graphite and magnesium. v

No references cited.

BENJAMIN HENKIN, Primary Examiner.

iron). A treatment time of about 8 minutes was employed. In this test, about seconds elapsed before the reaction started. Once under way, the reaction continued actively and was still progressing well when the briquette was removed from the melt after about 8 minutes.

The resulting solidified iron product was found upon metallographic examination to contain graphite only in posely doped with iron sulfide to provide a high sulfur content iron (0.037 weight percent sulfur) was employed as the melt.

The results of this study show both excellent desulfurization as well as nodularization of the so-treated metal product.

Table 3 summarizes the process conditions and results of this study.

Table 3 Results (percent by wt.)

Run Treating l\lelt Theo. Treating Treating No. pvllels (to- (grains) (lbs. Mg tcmperatime Sulfur tal grams) per ton Fe) ture F.) (min) Residual Mg in Fe Orig. Final 1 5O 12, O 2 .Z 2, 650 1. 5 0. 037 O. 007 l). 022 2 11, 500 3 "i 2, 700 1. 0 0. 037 U. 010 t). 023 r spheroidal form. Chemical analysis of the iron indicated EXAMPLE V a. magnesium content of about 0.043 percent.

EXAMPLE III 7 A series of runs was made evaluating the effectiveness of an Al-CaO-MgO composition as a n'odularizing agent for cast iron. For these tests, an induction furnace having a zircon crucible with a maximum capacity ofabout 30 pounds of molten iron and equipped with a tilting mechanism was charged with a. ferrous based metal having the following nominal composition: weight percent Sorel pig iron, 18 weight percent steel punchings and 2 weight percent of an ferrosilicon. This resulting composition is substantially the same as an ordinary ductile iron.

' The melt was raised to a predetermined temperature and I wafer-shaped pellets, about 0.5 inch diameter by about 0.125 inch thick, of the treating composition consisting of a blend of about 19.65 weight percent aluminum, 19.85

Weight percent magnesium oxide and about 60.5 Weightpercent burnt dolomite introduced therein near the bottom of the melt by means of a graphite plunger apparatus. The plunger was designed so as to distribute magnesium throughout the melt with a minimum of undesirable channeling. The plunger was maintained within the melt for a predetermined period of time. After the treatment period, the plunger was removed and about 0.5 weight percent of 85% ferrosilicon was rabbled into the melt following standard pos t inoculation procedures. The molten iron was cast into a shell mold in the shape of a standard ASTM 11-inch keel block. After the casting had cooled, drillings were taken for analysis of residual magnesium. In all the runs carried out in this series of tests, the reaction rates were active but not violent and there was no evidence of melt splashing or splattering during the treatment.

Table 2 which follows summarizes the treatment conditions employed and the residual magnesium content in the iron product. The results of this study, as evidenced by the residual magnesium content of the product, clearly show that the graphite is in the desirable nodular form.

were poured from this melt.

An approximately 2000-pound 1026 steel heat was melted in an acid, direct arc, electric furnace. This melt had a sulfur analysis of about 0.034%. Approximately 500 pounds of the molten charge was reladled into a zircon-lined ladlccontaining a clay-graphite plunger bell holding about 4.66 pounds of aspirin-sized pellets comprised of about 15.7 weight percent powdered aluminum (about 80 percent passing through a No. 325 U.S. Stand ard Sieve), about 49.1 weight percent powdered CaO and about 35.2 weight percent powdered MgO. -A controlled, steady reaction proceeded as the pellets were contacted by the molten steel. The sulfur analysis of the steel, following the treatment, indicated a residual sulfur of about 0.02%.' This is about a 40 percent reduction from the sulfur originally present in the steel.

EXAMPLE VI Five pounds of about 1.5-inch diameter pellets comprised on a weight basis of about 19.9 percent Al, about 35.5 percent CaO and about 44.6 percent MgO were loaded into a perforated clay graphite plunger bell. The plunger was placed in a ladle and a 400-pound cast iron heat was tapped into the ladle. The plunger was kept in the ladle for about 3.5 minutes during which time a controlled, continuing reaction was observed. There was no violence in the melt and no excessive heat loss. (The heat was tapped at about 2750 F. and eight castings The melt temperature as the last casting was poured was about 2610 F.) The resulting product was found to be fully nodular.

In a second run, /z-inch diameter, aspirin-shaped pellets of the nodularizing composition were placed into the bottom of a preheated, zircon-lined ladle. These became bonded thereto and adhered to the ladle during the melttap.

In a third 400-pound test heat, 5 pounds of '4-inch diameter briquettes, with linch diameter holes drilled through their centers, were slipped onto the end of a rod Table 2 Treating Theo. (lb. Treating Treating Residual Run No. pellets Melt Mg per item pera time Mg in Fe (total (grams) ton Fe) ture F.) (111111.) (percent I grams) by wt.)

EXAMPLE IV and this assembly placed in the ladle prior t tapping.

Duplicate runs were made using the same type and shape of treating agent and process operations as set forth in Example III, except that a Sorcl pig iron pur- These briquettes were of the same composition as those described directly hereinbefore.

In a manner similar to that described for the foregoin UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,197,306 July 27, 1965 Oliver Osborn et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 1, line 44, before "residual" insert high column 2, line 17, before "30" insert about column 3, line 73, strike out "carbide (CaC about 46 percent powdered MgO and" and insert the same after "calcium in line 70 column 4 Signed and sealed this 12th day of July 1966.

(SEAL) Attest: ERNEST w. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. A PROCESS FOR TREATING FERROUS BASED MELTS WHICH COMPRISES; (1) INTRODUCING INTO A MOLTEN MASS OF A FERROUS BASED METAL AN ADDITION AGENT COMPRISING FROM ABOUT 5 TO ABOUT 35 WEIGHT PERCENT ALUMINUM AND FROM ABOUT 95 TO ABOUT 65 WEIGHT PERCENT MAGNESIUM OXIDE, AND (2) MAINTAINING SAID AGENT IN SAID MASS FOR A PERIOD OF TIME RANGING FROM ABOUT 0.25 TO ABOUT 20 MINUTES.