US2841490A - Method for making improved gray cast iron - Google Patents

Description

United States Patent M METHOD FOR MAKING IMPROVED GRAY CAST IRON William Steven, Rubery, and Roger Maxwell Lamb, Kenilworth, England, assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application February 18, 1953 Serial No. 337,686

Claims priority, application Great Britain February 27, 1952 9 Claims. c1. 7s 1so It is known that the properties of alloyed or unalloyed gray cast iron are much improved if some or all of the graphite is present not as flake but is spheroidal, i. e., is in the form of compact, soft, gray-colored, rounded particles or of conglomerates or groups of such particles, as described in detail in U. S. Patent No. 2,485,760 and British specification No. 630,070. In the invention described in that patent and specification this form of graphite is produced by adding magnesium, usually in the form of an alloy, to the molten iron in such an amount and in such a manner as to render at least 25% of the graphite spheroidal by means of retained magnesium in the iron as cast. It .is alsoknown that cerium metal or mischmetal can be used in hypereutectic iron instead of magnesium, but that cerium metal or mischmetal is ineifective by itself to produce spheroidal graphite in 'hypoeutectic or eutectic gray cast iron.

-As is explained in U. S. Patent No. 2,485,760 and British specification No. 630,070, the advantageous eifect of magnesium can be reduced or even eliminated by very small amounts of certain elements which may be present in the iron. We have now found that the effect of such detrimental elements on the action of magnesium in developing the spheroidal form of graphite in eutectic or hypoeutectic iron can be counteracted by a very small amount of rare earth metal, particularly cerium or lanthanum.

According to this invention, we add to the molten iron not only magnesium in such an amount and in such a manner as to render a predominant proportion of the graphite spheroidal in the iron as cast in the absence of any detrimental element but also a relatively small amount of rare earth metal to counteract the effect of detrimental elements.

As is well known, lanthanum, cerium and other rare earth metals are commonly sold as constituents of mischmetal and it is this, or any material containing appreciable amounts of these elements, which is preferably used.

The eutectic or hypoeutectic irons treated according to the invention are those in which the percentage carbon content is not more than 4.3 minus /3 :(Si-l-P), where Si and P represent the percentage silicon and phosphorus content of the iron.

The rareearth metal is most eflective and therefore the smallest amount of it is required if it is added after the magnesium. In such a case as little as 0.001% rare earth metal by weight of the molten iron will produce a beneficial effect though the amount required depends on the nature and amount of the detrimental element or elements present in the iron. If, therefore, it is suspected that the iron includes any detrimental element or elements .in such an amount as to act strongly in suppressing proi ductionof the spheroidal form of graphite by magnesium,

.all of low sulfur content (0.02%).

2,841,490 Patented July 1, 1958 more than 0.001% rare earth metal should be added. In practice, since the total amount of detrimental elements present generally cannot be determined without inconvenience, the amount of rare earth metal added may advantageously be from 0.005% to 0.02% by weight of the molten iron. This amount, it will be understood, is much less than that of the magnesium added, which :is in general about 0.10% to 0.5% by weight of the molten iron. The magnesium addition will provide a small but efitective amount up to 0.2% or even 0.3% or higher of retained magnesium in the treated cast iron. The amount of mischmetal or rare earth metal is always small in relation to the amount of magnesium, and it is of the essence of this invention that enough magnesium is used and is retained in the iron to render substantially all the graphite spheroidal were the iron free of detrimental elements.

The amount of rare earth metal should not be too great, as not only is there no increase in the proportion of the graphite which is rendered spheroidal when the amount of rare earth metal exceeds an optimum value, but also there is a harmful change in the nature of the spheroidal structure. This optimum figure naturally varies from one cast iron to another. By way of example an iron containing 3.3% lcarbon, 1.8% silicon, 0.02% phosphorus and about 0.15% titanium was treated according to this invention. Titanium is an element which, though harmless in the small amounts in which it is usually present, is detrimental in larger amounts, and it was deliberately added to this iron for experimental purposes. About 90% of the graphite in the magnesium-containing iron as cast was consistently rendered spheroidal by additions of mischmetal ranging from 0.004% to 0.05%, but with greater additions of mischmetal some of the graphite particles became ragged in outline.

if the rare earth metal is added before or with the magnesium (e. g., includedin an alloy with. the magnesium) instead of after the magnesium, more of it is required, as indicated above. If it is added after the magnesium it may be added with an inoculant if, as usual, one is used and the rare earth metal may be either alloyed or mixed with the inoculant.

As additional illustrations of the effect of mischmetal in counteracting the detrimental action of titanium, the following examples may be given. A melt was made of iron containing 3.2% carbon, 1.6% silicon, 0.4% manganese, 0.02% sulfur, 0.02% phosphorus: and 0.16% titanium. Two taps were taken from the melt and 1% of a nickel-magnesium alloy containing 15 magnesium was added to each tap. 0.005% mischmetal was added to one tap, and each tap was finally inoculated with 0.5% silicon, added as ferrosilicon containing silicon, and cast into a green-sand mold to give a 2T diameter bar. The bar cast from the metal, to which no mischmetal was added contained 0.07% magnesium and 0.15% titanium, and only about 5% of the graphite in it was spheroidal, the remainder being flake. The bar cast from the metal to which mischmetal had been. added after the magnesium contained 0.067% magnesium and 0.14% titanium and of the graphite in it was spheroidal, the remainder being rounded flake. When mischmetal was added to an iron of substantially the same composition before 1% of the 15% magnesium-nickel alloy, 0.005% mischmetal produced only about 30% spheroidal graphite, and it was not until 0.01% mischmetal was added that 90% of the graphite became spheroidal in the iron as cast.

The irons referred to in the foregoing example were If the rare earth metal is added before or with magnesium to irons of higher sulfur content more rare earth metal must be used than when it is added after the magnesium.

As an example of the effect of mischmetal in counteracting the action of another detrimental element, a melt containing lead Was treated. The molten iron contained 3.36% carbon, 2.05% silicon, 0.027% sulfur, 0.02% phosphorus, less than 0.1% manganese, less than 0.02% titanium and 0.02% lead. The iron was treated with 1% of the magnesium-nickel alloy and inoculated with 0.5% silicon added as ferrosilicon. Without any addition of mischmetal none of the graphite was spheroidal in the iron as cast, due to the markedly interfering effect of the 0.02% lead. When 0.02% mischmetal was added after the magnesium but before the inoculation, 95% of the graphite was spheroidal in the iron as cast.

Indium, thallium, tin, bismuth and antimony are also elements which exert a detrimental elfect on the production of spheroidal graphite, and the use of a rare earth metal according to the invention counteracts the effect of these elements as well.

A particularly convenient way of carrying out the invention compr ses plunging below the surface of the molten iron. while this is at a temperature of from 1370 to 1410" C., a perforated container holding both the magnesium and the rare earth metal. By making the addition in this way the violence of the reaction which normally takes place when elemental magnesium is added vto the molten iron is considerably reduced. If the invention is carried out by plunging the additions into the melt, the magnesium need not be added as an alloy relatively lean in magnesium so long as certain precautions are observed. When. the magnesium is added as such or as a magnesium-rich alloy, that is. an alloy containing at least 80% magnesium. it is preferable to ensure first that the temperature of the molten iron at the time of treatment is between 1370" and 1410 C. and second that the magnesium is in the form of chins not exceeding 0.06 inch in thickness. so that the surface area of the magnesium added is high in relation to its volume. The chips are conveniently in the form of turnings. The temperature is important in that if it is below 1370 C. the plunger tends to become clogged with pasty metal, and if it is above 1410 C. the reaction is violent. The chins are packed in a perforated container which preferably has an open bottom and is tapered towards its bottom. If the ta er is insufiicient to retain the chins, a paper lining. which also serves to prevent them falling through the holes. may be f lded over to fill up the open bottom of the container. The container should be protected from attack b molten iron by coating it with graphite of the ty e used for the facing of dry-sand molds. The coating should be applied before first use of the container and after each use. Magnesium forms alloys with the rare earth metals which can be used in this invention. Alloys of mischmetal and magnesium are brittle in comparison with magnesium metal due to the presence of a brittle grain-boundary constituent and can be broken up more easily to a suitable size.

As an illustration of the plunging method, the following example may be given. A melt was made of iron containing 3.5% carbon, 1.8% silicon, 0.3% manganese, 0.01% sulfur and 0.02% phosphorus. Three samples of this melt were taken and contaminated with 0.12% titanium, 0.018% lead and 0.16% titanium, respectively. The first two melts were treated at 1405 C. by plunging into the body of the melt 0.26% of magnesium metal chips (0.060" thickx A x /2" approximately) mixed with 0.01% of mischmetal. The third sample was treated at 1420" C. by plunging into the body of the melt 0.28%

v of a magnesium alloy which contained 95% magnesium and 5% mischmetal. The alloy was in the form of small, irregular chips of about /a" to A" diameter. All the samples were then inoculated with 0.5% silicon added as ferrosilicon containing 80% silicon and cast into 2-inch Silicon, Manga- Tita- Lead, Magne- Bar Percent nese, nium, Percent slum,

Percent Percent Percent I and In 2.1 0. 40 0.12 0. 096 II and 11a 2.0 0.38 0.018 0.093 III and HM 2. 05 0.39 0.16 0.063

Bars I, II and III contained traces of rare earth metals and almost all their graphite was spheroidal. Bars Ia, Ila and HM had only 15, 0 and 5%, respectively, of their graphite in the spheroidal form.

In the example just given the sulfur content was low. Good results can also be .obtained with irons of higher sulfur content. As an example, an iron containing 0.06%

sulfur and contaminated with titanium was tapped at 1420 C. and two samples were treated and cast into bars IV and V. The first sample (bar IV) was treated with 1% of the 15% magnesium-nickel alloy and then inoculated with 0.5% silicon added as ferrosilicon, whilst the second sample (bar V) was treated by plunging 0.36% of 0.060" thick magnesium chips mixed with 0.01% mischmetal into the molten iron and was then similarly inoculated. The bars contained carbon, silicon, titanium and magnesium as follows:

Bar Percent Percent Percent Percent O Si T1 Mg IV 3. 8 2. 15 0. 11 0. 079 V 3. 3 2. 05 0. 13 0. 115

In bar IV only about 3% of the graphite was spheroidal, whereas in bar V over of the graphite was spheroidal.

It may be noted that the treatment according to the invention may affect the matrix structure of the cast iron. For example, the effects of lead, bismuth and thallium in stabilizing pearlite are counteracted by the addition of rare earth metal. It is to be observed that the present invention is particularly applicable to the treatment of molten gray cast iron baths containing over 0.02% sulfur and containing subversive amounts of detrimental elements which interfere with the effect of magnesium in producing spheroidal graphite. In the treatment of such iron baths, particularly satisfactory results are obtained with very small amounts of rare earth metal by first adding magnesium in amounts which would produce at least 25% of the graphite in a spheroidal form in the grap cast iron if detrimental elements were absent, and thereafter adding about 0.001% to 0.010%, e. g., 0.005% to 0.010%, of a rare earth metal, e. g., cerium and/or lanthanum. These amounts of rare earth metal used in this sequence overcome the subversive efiects of the elements which are detrimental to the effect of magnesium in producing spheroidal graphite and, in the presence of these detrimental elements, increase the proportion of graphite which occurs in the spheroidal form.

As previously noted, the cast iron baths treated in accordance with the present invention are those whlch will produce castings which have a eutectic or hypoeutectic composition. Such baths in general will contain about 1.7% to about 3.9% carbon, preferably about 2.5% to 3.7% carbon, about 1% to about 7% silicon, preferably about 1.5% to 3% silicon, about 0.05% to about 2% manganese, up to about 0.5% phosphorus, up to about 10% nickel, e. g., about 0.05% to about 3% nickel, and

the balance essentially iron. at least about 85% or 87% of the bath and the iron is usually in the alpha form at atmospheric temperatures.

In carrying out the process contemplated by the present invention, a graphitizing inoculation is almost always required shortly before casting the metal to insure the production of gray or graphitic iron castings. This graphitizing inoculation is accomplished by the late addition of a graphitizing inoculant, e. g., silicon, along with or subsequent to the treatment described hereinbefore. Satisfactory results have been obtained using ferrosilicon, e. g., an iron alloy containing a major proportion up to about 95% silicon, although other metallic silicon-containing agents or alloys and various proprietary alloys commonly used for reducing dendriticism and reducing chill in foundry gray cast irons may be employed.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast iron which comprises establishing a bath of molten gray cast iron containing a small amount of magnesium effective in the absence of detrimental elements to induce the occurrence of spheroidal graphite in castings made from the bath, said iron containing a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium in an amount sufficient substantially to suppress the effect of magnesium in producing spheroidal graphite in castings made from the iron, adding to said bath a small amount up to about 0.05% of a rare earth metal to counteract the suppressive effect of the detrimental elements, inoculating the bath, and casting metal from the thus-treated bath to provide gray cast iron castings containing a substantial proportion of the graphite in a spheroidal form.

2. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast irons containing over 0.02% sulfur and containing a subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of such a molten gray cast iron, introducing into said bath a small amount of magnesium effective in the absence of said detrimental elements to induce the occurrence of the graphite predominantly in the spheroidal form in the iron as cast, thereafter introducing about 0.005% to 0.010% of rare earth metal to counteract the suppressive effect of said detrimental elements, and casting metal from said bath in an inoculated condition to provide gray cast iron castings having a carbon content not more than 4.3 minus /3 (Si-l-P), where Si and P represent the percentage of silicon and phosphorus in the iron, and containing a predominant proportion of the graphite in a spheroidal form.

3. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast irons containing over 0.02% sulfur and containing a subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of such a molten gray cast iron, introducing into said bath a small amount of magnesium effective in the absence of said detrimental elements to induce the occurrence of at least 25% of the graphite in the spheroidal form in the iron The iron content is usually as cast, thereafter introducing about 0.001% to 0.010% of rare earth metal to counteract the suppressive effect of said detrimental elements, and casting metal from said bath in an inoculated condition to provide gray cast iron castings having a carbon content not more than 4.3 minus /3 (Si-l-P) where Si and P represent the percentage of silicon and phosphorus in the iron, and containing a substantial proportion of the graphite in a spheroidal form.

4. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast irons containing a subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of such a molten gray cast iron, introducing into said bath a small amount of magnesium effective in the absence of said detrimental elements to induce the occurrence of thegraphite predominantly in the spheroidal form in the iron as cast and about 0.005% to 0.010% of rare earth metal to counteract the suppressive effect of said detrimental elements, and thereafter casting metal from said bath in an inoculated condition to provide gray cast iron castings having a carbon content not more than 4.3 minus /3 (Si-l-P), where Si and P represent the percentage of silicon and phosphorus in the cast iron, and containing a predominant proportion of the graphite in a spheroidal form.

5. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast irons containing a subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of such a molten gray cast iron, adding to said bath about 0.1% to 0.5% of magnesium effective in the absence of said detrimental elements to induce the occurrence of at least 25% of the graphite in the spheroidal form in the iron as cast and about 0.001% to 0.02% of rare earth metal to counteract the suppressive effect of said detrimental elements, and thereafter casting metal from said bath to provide gray cast iron castings having a'carbon content not more than 4.3 minus /3 (Si+P), where Si and P represent the percentage of silicon and phosphorus in the cast iron, and containing a substantial proportion of the graphite in a spheroidal form. 6. The method for producing spheroidal graphite in cast Iron castings made from molten hypoeutectic and eutectic gray cast irons containing a subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of such a molten gray cast iron, introducing into said bath a small amount of magnesium effective in the absence of said detrimental elements to induce the occurrence of at least 25% of the graphite in the spheroidal form in the iron as cast and a small but effective amount up to about 0.02% of rare earth metal to counteract the suppressive effect of said detrimental elements, and thereafter casting metal from said bath in an inoculated condition to provide gray cast iron castings having a carbon content not more than 4.3 minus /3 (Si-i-P), where Si and P represent the percentage of silicon and phosphorus in the cast iron, and containing a substantial proportion of the graphite in a spheroidal form.

7. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast iron containing a small but subversive amount of a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium suppressive to the effect of magnesium in inducing spheroidal graphite which comprises establishing a bath of such a molten gray cast iron having a temperature of about 1370 to 1410 C.; plunging beneath the surface of saidmolten cast iron metal containing at least about 80% magnesium in an amount sufiicient When introduced into the iron to render a substantial proportion of the graphite spheroidal in the absence of subversive amounts of detrimental elements and rare earth metal in a small amount up to about 0.05% to counteract the suppressive effect of said detrimental elements; and casting metal from the thus-treated bath to provide cast iron castings having a carbon content not more than 4.3 minus /3 (Si-l-P), Where Siand P represent the percentage of silicon and phosphorus in the iron, and containing a substantial proportion of the graphite in a spheroidal form.

8. The method for producing spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast iron which comprises establishing a bath of molten gray cast iron containing a small amount of magnesium effective in the absence of detrimental elements to induce the occurrence of spheroidal graphite in castings made from the bath, said iron containing a detrimental element from the group consisting of indium, thallium, tin, bismuth, antimony, lead and titanium in an amount suflicient substantially to suppress the effect of magnesium in producing spheroidal graphite in castings made from the iron, inoculating said bath With an amount of a graphitizing agent containing a rare earth metal toprovide an addition of rare earth metal of about 0.001% to about 0.02%, and casting metal from said bath in an inoculated condition to provide gray cast iron castings containing a substantial proportion of the graphite in a spheroidal form.

9. The method for producing. spheroidal graphite in cast iron castings made from molten hypoeutectic and eutectic gray cast irons containing subversive amounts of elements detrimental to the effect of magnesium in inducing the occurrence of spheroidal graphite which comprises establishing a bath of said molten gray cast iron containing at least about 85% iron, a subversive amount of at least one detrimental element, a small amount of magnesium effective in the absence of detrimental elements to induce the occurrence of spheroidal graphite, and a small amount up to 0.05% of rare earth metal to counteract said subversive amount of detrimental element, and

casting molten metal from the bath containing magnesium.

and rare earth metal in an inoculated condition to produce a gray cast iron casting containing at least about 85% iron and a substantial portion of the graphite in a spheroidal form in a matrix having iron in the alpha form.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. THE METHOD FOR PRODUCING SPHEROIDAL GRAPHITE IN CAST IRON CASTINGS MADE FROM MOLTEN HYPOEUTECTIC AND EUTECTIC GRAY CAST IRON WHICH COMPRISES ESTABLISHING A BATH OF MOLTEN GRAY CAST IRON CONTAINING A SMALL AMOUNT OF MAGNESIUM EFFECTIVE IN THE ABSENCE OF DETRIMENTAL ELEMENTS TO INDUCE THE OCCURRENCE OF SPHEROIDAL GRAPHITE IN CASTINGS MADE FROM THE BATH, SAID IRON CONTAINING A DETRIMENTAL ELEMENT FROM THE GROUP CONSISTING OF INDIUM, THALLIUM, TIN, BISMUTH, ANTIMONY, LEAD AND TITANIUM IN AN AMOUNT SUFFICIENT SUBSTANTIALLY TO SUPPRESS THE EFFECT OF MAGNESIUM IN PRODUCING SPHEROIDAL GRAPHITE IN CASTINGS MADE FROM THE IRON, ADDING TO SAID BAT A SMALL AMOUNT UP TO ABOUT 0.05% OF A RARE EARTH METAL TO COUNTERACT THE SUPPRESSIVE EFFECT OF THE DETRIMENTAL ELEMENTS, INOCULATING THE BATH, AND CASTING METAL FROM THE THUS-TREATED BATH TO PROVIDE GRAY CAST IRON CASTINGS CONTAINING A SUBSTANTIAL PROPORTION OF THE GRAPHITE IN A SPHEROIDAL FORM.