US2863764A - Coated magnesium iron treatment - Google Patents

Description

COATED MAGNESIUM RON TREATMENT Grant E. Spangler, Philadelphia, Pa., and James W. Estes,

New Brunswick, N. J assignors to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York N Drawing. Application July 23, 1956 Serial No. 599,289

11 Claims. (Cl. 75130) This invention relates to an improved method for producing nodular cast iron and to a new addition agent for use in such method. More particularly, the invention relates to an improved method for injecting a new magnesium-containing treating agent beneath the surface of molten ferrous metal to produce a cast iron With improved properties and characteristics and with its graphitic car-.

bon particularly in nodular or spheroidal form.

It is'common knowledge in the art that cast irons having their uncombined carbon in nodular form may be prepared by introducing certain treating agents into a molten bath, such as cerium and magnesium. But the practice of the prior art processes involves certain difiiculties; and such processes have not proved entirely satisfactory for large scale commercial production. For example, the introduction of magnesium into molten metal is an extremely difiicult operation, primarily because of its relatively low boiling point (1107 C.) and high degree of reactivity. Its introduction into a molten bath in the usual way produces a violent reaction, which makes the operation hazardous. Such violence causes relatively high and unpredictable magnesium losses so that reproducibility of a uniform nodular cast iron with the same composition is virtually impossible.

Numerous attempts have been made to minimize or eliminate these difficulties by alloying elemental magnesium with other substances, for example nickel and copper. But even these magnesium alloys have certain objectionable features. For example, undesirable chilling of the molten iron occurs when large quantities of alloys are added thereto; the alloys are expensive; the properties of the cast iron product may be adversely affected by one or more elements alloyed with magnesium; and some of the alloying substances are not eliminated by remelting so that the scrap may contain intolerable amounts of such materials.

In the copending application of James W. Estes and.

rates Patent C tal magnesium beneath the surface of molten metal, to

Grant E. Spangler, Treating Molten Iron, Serial No;

486,714 (assigned to the assignee of the present application), there is disclosed and claimed an improved method for preparing an ungraded and nodular gray cast iron. In the practice of such method, an inert gas stream is passed into the molten metal beneath its surface. A mixture of finely divided calcium carbide particles and finely divided magnesium particles is fed into this gas stream, the magnesium particles constituting about 5% to 15% by weight of the mixture. In certain instances, however, it has been found desirable to include magnesium in amounts exceeding 15 of the mixture in order to obtain the desired nodular cast iron. In such respect, the process of the copending application does not completely and adequately meet the demands of the cast iron industry. The present invention constitutes a further improvement of the process disclosed in the above-identified copending application. I

The primary object of the present invention is to provide an improved method, adapted for large scale commercial use, for introducing calcium carbide and elemenproduce a nodular cast iron product having improved physical and mechanical properties.

Another object is to provide an improved method for injecting finely divided particles of calcium carbide and magnesium, particularly when the magnesium particles exceed 15% by weight of the total mixture or solids.

A further object of the present invention is to provide an improved method for injecting calcium carbide and relatively large quantities of magnesium into molten metal at normal founding temperatures without any injection failures caused by plugging and similar factors.

A still further object is to provide a novel addition agent particularly adapted to introduce calcium carbide and varying amounts of magnesium into cast iron for treatment thereof, resulting in a cast iron product having its graphite in nodular or spheroidal form.

These and other objects and advantages of the present invention will become more apparent from the following detailed description of the invention.

Broadly stated, the treating agent of the invention is a mixture of finely divided particles of calcium carbide, magnesium chips, and a relatively small quantity of calcium oxide. The calcium oxide is admixed with the magnesium chips prior to mixing with thecalcium carbide. The invention further contemplates an improved process for treating molten ferrous baths, particularly gray cast iron baths, with the novel treating agent to effectively introduce and incorporate magnesium in said baths, to reduce the sulphur content thereof, and to provide gray cast irons having its graphite in nodular form.

In its preferred embodiments, the agent contains about 5% to about 20% magnesium, about 2% to about 10% calcium oxide, and the balance essentially calcium carbide. Very good results are obtained when the amount of calcium oxide is about one-half that of the magnesium.

Generally speaking, the invention comprises establishing a molten bath having a gray cast iron composition, injecting a relatively dense stream of inert gas and a mixture comprising calcium carbide, magnesium, and calcium oxide beneath the surface of the metal, and then promptly casting the iron. Such composition contains more than iron, carbon from 1.7% to 4.5%, and silicon from 1.0% to 3.5%. Other elements conventionally found in cast irons are present, such as sulphur, manganese and phosphorous in usual amounts, and impurities or traces of other elements such as titanium and zirconium. Suitable apparatus for injecting the treating agent include, for example, the screw feeding device shown in Hulme Patent No. 2,577,764; the batch feeder disclosed in the copending United States patent application Serial No. 430,864, now abandoned; or the fluidizer injection device shown in the copendingv United States patent application Serial No. 324,998 (all assigned to the assignee of the present application). All of these apparatus are adapted for feeding a solid-gas stream having an apparent density of about one-quarter to two cubic feet of gas per pound of solids. For purposes of this invention, various inert gases may be used provided they do not enter into any chemical or oxidizing reactionwith the molten metal or treating agent. -Dry nitrogen could be employed, for example, since it is readily available and inexpensive. However, other gases which can be used and are just as efficient as nitrogen are helium, argon and carbon dioxide.

For best results, the treating agent contains about 5% to 20% magnesium and 2% to 10% calcium oxide, 1 The amount of calcium oxide is preferably about one-half that of magand the balance calcium carbide.

nesium. vThe presence of a critical amount of calcium the injection tube. In the initial tests made with'r'es'pect Patented Dec. 9, 1958 to treatment of molten metals With an agent containing magnesium, it was readily apparent that the prevention of tube plugging was a serious problem, independent of the hazards ordinarily involved and independent of the 4 t overcome the static head of molten iron and thus prevent the entrance of metal into the passage through which the mixture is injected. The rate of feeding will vary depending upon the size of the metal container and efficiency of treatment. .It was noted that with treating 5 the typ of injection app 1 1& agents composed of only magnesium and calcium car- The treating agent of this invention is prepared by bide,-incidence of injection failures by reason of tube intimately mixing by any conventional means preferably pluggingincreased-as the magnesium. content of the 0211- about 5 to 20' partsof magnesium powder and about cium carbide-magnesium mixture exceeded and 2 to 10 Parts Of .OXldC, Wh h admixtureis then that evid'ence'of injection failures approached 100% as 10 mixed with about 93 10 70 parts finely-divided calcium the magnesium content of such mixture approached Carbide. The calcium carbide may be a commercial 20%. Although the theoretical. explanation is not fully grade of calcium carbide, quite free of impur ties as understood, it is believeicl'that as the percentage of'magmade in electric arc furnaces, from calcium oxide and nesium increases, the possibilities of contact between the hlgh quality coke. The carbide particles pass through particles of magnesium also increase, and consequently, a ZQ-rnesh screen, and about 90% of the particles are any melting of, magnesium particles where physical conretained on a ZOO-mesh screen. The magnesium partact has been established would cause agglomeration in ticles pass through a mesh Tyler standard screen, and the tube,-and,a plug would result. But when the treating about 90% of the particles Wlll lac retained on a 100- agent includes lime in amounts described above, troublemesh screen Examined under a microscope, these parfree injections of mixtures containing as high as 20% 20 ticles have irregular dg WhKfh are frequently rolled magnesium have been made. When the percentage of up. The uantities of the various components of the calcium oxide is more than about one-half the magnesinovel treating agent used per ton of gray cast iron range um content, the oxide tends in a sense to coat the magbetween 10 and 18 pounds of calcium carbide, between iiesium mechanically and thus prevent intimate reaction A; and 12 pounds of magnesium, and between 4 and 6 of the magnesium with the molten metal, so that the pounds of calcium oxide. In any event, the magnesium amount of graphite appearing in nodular form is sigcontent should not exceed 20% of the total mixture. nificantly reduced. The followingtable includes examples of hypo-eutectic The amount of magnesium injected is preferably about and hyper-eutectic cast iron-s, their compositions, and one to six'pounds of magnesium per ton of iron, and the 9 properties after treatment. The composition of the metal amount of calcium oxide injected is thus preferably about in the molten bath 18- that used to make a conventionalv one-half to three pounds per ton of molten metal. The gray cast iron. In the examples, the iron constitutes more amount of calcium carbide injected will depend upon than 90%, the carbon'from 3.30 to 3.60%, and the silicon the amount of certain undesirable impurities in the molfrom 1.40% to 1.90%. Desulphurizing and benefiting ten iron, such as sulphur and oxygen. The higher the or such as deoxidation, was first effected by the injection of content of such impurities in the untreated molten metal, calcium carbide alone, in a proportional amount of 16 the. greater shouldbe the amount of carbide injected. pounds of carbide per ton of molten metal. With this Since desulphurizati-on is required in most instances, it is first step, the sulfur level of the iron is reduced to less than preferred to inject finely divided calcium carbide be- 0.03%, and the iron is more receptive to the beneficial efneath the surface of the metal toreduce the sulphur 4O fects of magnesium. Immediately.thereafter,.the cast content thereof from a relatvely high level to a relatively irons were treated with a reagent comprising (1) calcium low, level, e.g., to a level of 0.03% or less, and prefercarbide, magnesium, and lime, or (2) calcium carbide, ably to about 0.01%, and thereafter injecting the treating magnesium, lime, and a rare earth oxide. A small agent in an amount suflicient to produce the desired noduamount of a rare earth-oxide (REO) may be incorporated lar cast iron. in some instances, it is also preferred to in the carbide-magnesium-lime mixture to insure a totally inoculate the molten metal with a conventional graphnodular cast iron. The REO contains about cerium itizing agent such as ferrosilicon subsequent to the inoxide, 20% lanthanum oxide, and the balance. consists jection of the agent and prior to casting. of other rare earth substances. In the practice of the For purposes of the present invention, the apparent present invention, the RED is finely divided, being at density of the gas-solid stream at the point of its intro r0 least 20 by 0 mesh size. The tables show the proporduction into the molten metal will range from onetioning of the various constituents of the treating agent, quarter to about two cub ic feet of gas per pound of the compositions and the physical properties of the treated solids. The gas is maintained at a pressure sufficient to metal, when carbide treatment is first effected.

Table I Injection Mix (Lbs/Ton) Percent Chemical Analyses Properties Chill sai rnple %agei Depth O30, .REO Mg 030 T. C Si Mn Base S Final S P Mg (LE. U.T.S. B.H.N. Elong. Gz

20 1.0 3.0 1.5 1.00 3.55 2.47. 0.35 0.093 N. R. 0.037 0.023 4. 37 66,900 154 19.5 20 13 1.0 4.0 2.0 1. 00 3.59 2.22 0.34 0.103 N. R. 0.032 0.033 4.33 66,500 152 13.0 22 17 2.4 1.2 1.00 3.41 2.52 0.33 0.035 N. R. 0.042 N. R. 4.25 47,900 150 4.0 36 21 3.0 1.5 1.00 3.44 2.45 0.34 0.093 N. R. 0.042 N. R. 4.26 53,350 152 5.5 24 21 3.0 1.5 1.00 3.55 2.40 0.34 0.096 N.R. 0.035 N. R. 4.35 65,300 159 13.5 23 16 1.0 2.0 1.0 1.00 3.53 2.49 0.72 0.091 N.R. 0.044 N.R. 4.36 60,100 166 4.5 15 20 1.0 3.0 1.5 1.00 3.56 2.45 0.62 0.103 0.006 0. 035 ,N. R. 4.33 76,900 191 7.0 24 62 2.0 12.0 4.0 1. 00 3.54 2.37 0.33 0.107 0.004 0.034 0.033 4.33 91,300 196 9.5 44 15 1.0 1.0 0.5 1.00 3.46 2.54 0.71 0.102 0.012 0.033 0.003 4.31 49,200 143 2.5 22 16 1.0 0.5 1.00 3.51 2.51 0.72 0.090 0.014 0.035 N. R. 4.35 22,300 113 1.0 16 15 1.0 1.0 0.5 1.60 3.63 3.10 0.17 0.103 N. R. 0.047 N.R. 4.73 53,300 144 4.5 7 10.3 0.51 2.05 0.25 1.00 3.30 2.21 0.74 0.103 'N. R. 0.039 N. R. 4.07 ,500 3.0 32 20 1.0 4.0 2.0 1. 00 3.47 2.23 0.76 0.115 N. R- 0.033 N. R. 4.24 92,300 212 5.0 32 20 1.0 4.0 2.0 1.00 3.33 2.15 0. 72 0.103 N. R. 0.075 N. R. 4.09 99,200 232 4.5 '33 15 1.0 1.0 0.5 1.00 3.34 2.14 0.74 0.103 N. R. 0075 N. R. 4.07 59,300 174 2.5 '32 16 1.0 0.5 1. 00 3.34 2.17 0.74 0.101 N. R. 0.021 N. R. 4.10 45,650 135 1.0 13 34 2.0 4.0 4 1. 00 3.01 2.25 0.32 0.106 N. R. 0.032 0.024 4.36 64,700 159 7.5 13 32 2.0 4.0 2 i. 00 3.57 2.46 0.33 0. 039 N. R. 0.035 0.036 4.39 67,200 152 19.5 20 20 1.0 3.0 1.5 1. 00 3.43 2.46 0.34 0.034 N. R. 0.024 0. 032 4.30 70,850 166 14.0 20

I Not requested.

The phrase, Percent Late FeSi, refers to the addition of ferrosilicon (75% silicon) as a percentage of the iron being treated. The ferrosilicon was added by reladling, although it may be injected with a carrier gas. The data under the heading Chemical Analyses refers to the analyses of the treated metal with respect to silicon, manganese, and phosphorus; initial and final sulfur contents; the total carbon content and carbon equivalent referred to as T. C. and C. B, respectively; and the retained magnesium content. The Injection Mix data defines the amount of materials injected in terms of pounds of each material per ton of iron. The properties shown include ultimate tensile strength (U. T. S.), Brinell hardness number (B. H. N.), and elongations (Elong.) as percentages in two inches. The chill figure was obtained by casting into a sand mold against a graphite block as a base. The wedge formed was 3 /2 inches high, /8 inch wide at the top and 7 inch at the bottom. The tabulated figures are the depths of the chill from the bottom of the Wedge contacting the block in 32nds of an inch.

In all the examples set forth in the above table, the treating agent includes a small amount of powdered lime (CaO). Ordinarily, the lime was added in fine powdered form to the various mixtures which may be mechanically mixed, for example, by tumbling. Best results, mechanically and metallurgically, were obtained when the powdered lime was added in an amount equal to onehalf the amount of powdered magnesium by weight in the mixture. In no instance did plugging occur in the injection tube when the lime content varied from 25% to 50% of the magnesium content. Further, the use of the lime particles did not adversely affect the carbidemagnesium treatment, as evidenced by the physical properties of the metal treated. For example, the tensile strengths of the cast irons treated in accordance with the process of the present invention range from about 50,000 to 99,000 p. s. i. The addition of lime to the various mixtures permitted the use of 10%-15% magnesium concentration by weight and even to as high as 20% without any occurrence of plugging in the injection tube. It is believed that the lime coats the particles of magnesium powder and the injection tube wall, thus preventing melting or sintering of the particles to the tube or to each other. Optimum flow results were obtained when the lime particles were finer than 100 mesh. The lime used in the examples is a soft light grade of technical calcium oxide which contains considerable quantities of calcium carbonate and calcium hydroxide. The lime used in the examples has the following analyses:

The lime described above has a tendency to adhere to the smooth surfaces of the injection tube, and thus prevent or minimize melting or fusing of the treating particles to the walls of the tube. The lime provides lubricating properties to the addition agent of the invention, that is, to mixtures comprising at least finely-divided calcium carbide and magnesium. The lime also serves to maintain a fiow of solids having a substantially uniform composition of solids, through the entire treating operation.

It will be noted from the examples listed above that the presence of the lime powder in the treating mixture did not adversely affect the properties of the resulting product when the treating mixture comprises (1) calcium carbide, magnesium, and lime, or (2) calcium carbide, magnesium, rare earth oxides, and lime. When the carbide content of the treating agent was maintained constant and the magnesium content was increased, the properties of the as cast product were improved; and when rare earth oxides were added to the mixture, the

properties were improved, as would'be of the prior art.

It will now be appreciated that the instant invention provides a practical method for treating molten iron compositions with addition agents comprising calcium carbide and magnesium in an amount as high as twenty (20) percent by weight. The amount of lime added to the mixture is preferably 20% to 50% of the magnesium. With the use of the novel agent, plugging in the injection tube is virtually eliminated.

It will be understood that the invention is not limited to the specific examples described herein, but may be practiced inother ways without departing from the spirit and scope of the invention as defined in the following claims.

What we claim is:

1. A method of improving the physical properties of an as-cast gray cast iron comprising establishing a molten quantity of gray cast iron containing more than 0.03% sulphur,'injecting into said molten cast iron sufficient calcium carbide so that the quantity of the sulphur is reduced to less than about 0.03% sulphur, injecting a; mixture comprising about 5% to 20% magnesium chips, 2.0% to 10% calcium oxide, and 70% to 93.0% finely divided calcium carbide, said mixture being carried beneath the surface of the molten iron by an inert gas, and the stream of gas and mixture containing from about A to 2 cubic feet of gas per pound of solids injected.

2. A method according to claim 1, in which the amount of calcium oxide in said mixture is about onehalf that of magnesium.

3. A method according to claim 1, in which a finely divided oxide is incorporated in said mixture, and the amount of said last mentioned oxide employed is about 1 to 2 pounds per ton of molten iron.

4. A method for the production of nodular cast iron comprising establishing a' molten gray iron composition containing more than iron, carbon from 1.7% to 4.5%, silicon from 1.0% to 3.5%, and sulfur in excess of 0.03%, incorporating into said bath a treating agent containing about 5% to 20% magnesium, about 2.0% to 10% calcium oxide, and about 70% to 93% finely divided calcium carbide, said agent being injected into said molten iron with an inert gas carrier, in the ratio of from about A to 2 cubic feet of gas per pound of solids injected, the amount of calcium carbide employed being in excess of that required to reduce the sulphur content to about 0.01%, and casting said iron composition to form castings characterized by the occurrence of uncombined graphite in predominantly nodular form.

5. A method for the production of nodular cast iron comprising establishing a molten gray iron composition containing more than 0.03% sulfur, injecting into said molten iron sufi'lcient calcium carbide to reduce the sulfur content to less than 0.03%, injecting beneath the surface of said molten metal by means of a carrier gas a treating agent comprising about 5% to 20% magnesium, 2.0% to 10% calcium oxide, and the balance finely divided calcium carbide, inoculating said treated iron with a con ventional graphitizing agent subsequent to injection of said agent and prior to casting, and casting said iron composition promptly to form castings characterized by the presence of uncombined graphite in predominantly nodular form.

6. A homogeneous treating material particularly adapted for introducing magnesium into molten gray cast iron with very little loss, said material containing about 5% to 20% of small chip-like particles of elemental magnesium, about 2% to 10% calcium oxide, and about 70% to 93% calcium carbide, said oxide and carbide particles being in finely divided form.

7. An agent particularly adapted for the production of nodular cast iron, said agent containing about 5% to 20% magnesium, calcium oxide in an amount sufficient to prevent any significant loss of magnesium prior to its expected in view introduction into molten. metal, and the balance substantially calcium carbide, said magnesium particles being of afineness-sufiiciehtato pass; through a '20 mesh screen but which particles will-be retained ona 100 mesh screen, and'said calcium carbideiparticlesbeing ofv a fineness sufiicient to pass throughya 20 mesh screen but which will beretaine'dmnva 200 mesh screen, said magnesitun and calcium oxide particles being thoroughly mixed.

.8. A homogeneous treating material particularly-adapted for continuously injecting magnesium into a molten gray cast iron with very little loss,:said1 material containing about 5% to 20% of small chip-like particles of elemental magnesium, an amount' of calcium oxide; particles equal to about one-half that-ofmagnesium, and thebalance substantially finely divided particles of calcium carbide, said magnesium and calcium oxide'particles being thoroughly mixed.

'9. The treating-material as ,definedin cIaim'Sand being further characterized in containing finely divided rare earth oxide, the amount of said last-named oxide .employed being about 1. to 2 pounds per ton of molten iron treated.

10.*A:,h omogene.ous particulate treating materials-particularlyadapted for introducing magnesium into ,a molten ferrous metal composition, comprising magnesium,

calcium oxide and calcium carbide, the magnesium being present-in anamount up to the calcium oxide being present;in;the amount of abouti2% to 10% and:th balance being substantially calcium carbide.

11. A homogeneous particulate treating material particularly adapted for. introducing magnesium into amolten ferrous 2 metal composition, comprising magnesium, calcium oxide andcalciumcarbide, the magnesium being present.inganpamount upto 20%, the calcium oxide being-presentin an amountequal to about 20% to of the amount of ;magnesium, and the balance being substantially calcium carbide.

Belgium Sept. 30, 1952 Austria Mar. 10, 1954

Claims (1)

1. A METHOD OF IMPROVING THE PHYSICAL PROPERTIES OF AN AS-CAST GRAY CAST IRON COMPRISING ESTABLISHING A MOLTEN QUANTITY OF GRAY CAST IRON CONTAINING MORE THAN 0.03% SULPHUR, INJECTING INTO SAID MOLTEN CAST IRON SUFFICIENT CALCIUM CARBIDE SO THAT THE QUANTITY OF THE SULPHUR IS REDUCED TO LESS THAN ABOUT 0.03% SULPHUR, INJECTING A MIXTURE COMPRISING ABOUT 5% TO 20% MAGNESIUM CHIPS, 2.0% TO 10% CALCIUM OXIDE, AND 70% TO 93.0% FINELY DIVIDED CALCIUM CARBIDE, SAID MIXTURE BEING CARRIED BENEATH THE SURFACE OF THE MOLTEN IRON BY AN INERT GAS, AND THE STREAM OF GAS AND MIXTURE CONTAINING FROM ABOUT 1/4 TO 2 CUBIC FEET OF GAS PER POUND OF SOLIDS INJECTED.