US3125442A - Buctile iron casting - Google Patents

Description

March 17, 1964 A. P. ALEXANDER 3,125,442

DUCTILE IRON CASTING Fig. l 250x Nital Etch Fig. 3 250x Nital Etch P19. 5 250x Nltal Etch Filed Nov. 50, 1956 Fig. 4 250x Nital Etch Fig. 6. 250x Nita]. Etch k i2 do ma 7" 5 if P United States Patent 3,125,442 DUCTHE IRQN CAETHIG Adolph P. Alexander, Memphis, Tenn, assignor to Internationm Harvester Company, a corporation of New Jersey Filed Nov. 30, 1956, Ser. No. 625,28 1 Claim. (Cl. 75-423) This invention relates to a new and novel ferrous alloy which may be made from any base irons that are of hypereutectic composition and can be readily made from extremely low strength high-carbon pig iron directly from the blast furnace. More in particular this invention relates to the production of high physical strength nodular iron in the as-cast condition directly from molten pig iron as tapped from a blast furnace or from molten commercial normal base gray iron of hyper-eutectic composition.

Both pig iron and castings made from a normal gray iron mix possess free carbon in the form of flaked graphite which is more or less uniformly distributed throughout the matrix resulting in a product having low tensile strength. For example, a casting made from a normal gray iron mix generally has a tensile strength ranging from 20,000 to 50,000 pounds per square inch while blast furnace pig iron has a tensile strength usually in the range of 10,000 to 20,000 pounds per square inch.

It is well known that if magnesium in amounts necessary to introduce from 0.04 to 0.5 percent in the casting or alternatively cerium in amounts necessary to introduce 0.05 to about 0.5 percent in the casting, or a combination of these two elements, are added to the molten base gray iron mix, the graphitic carbon will essentially coalesce or agglomerate to form nodules of carbon or graphite substantially spheroidal or spherulitic in shape which nodules are more or less disposed uniformly in the matrix of the casting. However, in the previously known cast irons of the nodular type there are several disadvantages existing both in the resulting products as well as the various known processes for making such castings. First there exists the danger associated with the use of magnesium or cerium because of the explosive characteristics of these elements when they are introduced into the molten iron. Secondly, in all of the previously known processes the iron must be poured into casting within minutes after the nodular-impelling agent or agents are added. This is undesirable because the later poured castings from a given ladle of molten iron are progressively poorer in characteristics than the castings poured earlier thus seriously impairing the control of uniform casting quality. Thirdly, nodular iron castings heretofore known do not retain the nodular graphite characteristics if the iron is re-melted and re-cast without further addition of a nodular impelling agent. This invention contemplates the production of uniform high strength nodular iron castings which overcome the aforementioned disadvantages.

It is therefore a prime object of this invention to provide nodular iron castings in the as-cast condition possessing excellent strength, hardness and elongation properties which may be made from molten pig iron as tapped directly from a blast furnace or from normal molten base irons of hyper-eutectic composition.

It is a further object of this invention to provide nodular iron castings in the as-cast condition according to the preceding object wherein the physical properties of the castings are of uniform quality irrespective of the length of time elapsing between the time when the nodular impelling agent is introduced into the molten metal and the time of pouring the resulting castings.

A further object of this invention is to provide nodular iron castings which may be re-melted and re-cast without the further addition of a nodular impelling agent wherein the re-cast product substantially retains its nodular characteristics.

Another object of this invention is to provide a casting directly from molten pig as tapped from a blast furnace winch casting in the as-cast condition is of a strong nodular iron structure.

A still further object of this invention is to provide nodular iron castings according to the preceding objects by means of a relatively safe process whereby the nodular impelling agent is introduced into the molten iron without violent reaction.

These and other desirable objects inherent in and encompassed by the invention will be more readily understood from the ensuing description, the appended claim and the annexed reproductions of photomicrographs wherein:

FIGURES l and 2 are photomicrographs of polished and etched surfaces illustrating the microstructures enlarged by 250 diameters of typical blast furnace pig iron which heat of iron was used as a base iron for all experimental Work described herein.

FIGURE 3 is a photomicrograph of a polished and etched surface illustrating the microstructure enlarged by 250 diameters of blast furnace iron with 0.024 percent elemental lanthanum plus elemental neodymium.

FIGURE 4 is a photomicrograph of a polished and etched surface illustrating the microstructure enlarged by 250 diameters of blast furnace iron with 0.035 percent elemental lanthanum plus neodymium.

FIGURE 5 is a photomicrograph of a polished and etched surface illustrating the microstructure enlarged by 250 diameters of blast furnace iron containing 0.040 percent elemental lanthanum.

FIGURE 6 is a photomicrograph of a polished and etched surface illustrating the microstructure enlarged by 250 diameters of blast furnace iron containing 0.050 percent elemental lanthanum.

This invention relates :to high strength gray irons containing nodular shaped graphite or carbon with a measurable ductility in the as-cast condition and to the use of new improved agents for their production. They may be made from base irons that are hyper-eutectic in composition and can be readily made from extremely low-strength high-carbon molten pig iron as tapped directly from the blast furnace. It beshown that small additions of single elements or combinations of elements can markedly improve the properties of hyper-eutectic gray iron or low sulfur content commercial pig iron.

For purposes herein it will be understood that the fol: lowing well known equation adequately defines certain terms referred to in the description:

P-I-Si 3 where TC represents the percent total carbon present in a gray iron casting, P represents the percent phosphorous present and Si represents the percent silicon present. When CE equals 4.30 the iron is said [to be of eutectic composition; when CE exceeds 4.30 the iron is said to be of hyper-eutectic composition; and when CE is less than 4.30 the iron is said to be of hypo-eutectic composition.

As is well known in the trade, gray irons can have their physical strength characteristics considerably enhanced by changing the shape of the free graphite from a normal flake or leaf-like shape to a compressed nodular or spherulitic shape. When certain agents are added to the molten iron the graphite or oanbon will essentially coalesce or agglomerate to form nodules substantially spheroidal or spherulitic in shape which nodules are more CE=TC+ or less disposed uniformly in the matrix of the resulting casting. Such iron is generally termed nodular and castings made therefrom possess much improved physical strength characteristics as compared with normal gray iron castings having the carbon or graphite in flake form.

Probably the most commonly known agents known to impel the formation of graphite or carbon nodules in molten gray iron are the elements cerium and magnesium including various alloys and compounds thereof. In the production of nodular iron castings the sulfur content of the iron was found to be an important factor. Where magnesium is employed as a nodular impelling agent the sulfur content of the iron may be as high as 0.10 percent whereas in the case of cerium the sulfur content must not exceed 0.03 percent. It is concluded that a requirement of the irons of this invention is that the sulfur content must not exceed 0.03 percent.

We have found that when enough lanthanum is added to molten hyper-eutectic iron containing not more than 0.03 percent sulfur so that the resulting casting contains at least 0.020 percent lanthanum the free carbon or graphite in the iron will coalesce or agglomerate to form nodules instead of the normal flakes. As the amount of lanthanum is increased the number of nodules per unit area also increases and the physical strength properties also increases correspondingly.

I have also found that an alloy of lanthanum and neodymium added to the same base iron yielded castings having a greater number of carbon nodules per unit area having better spherulitic shape than that resulting from the use of lanthanum alone. From this it is reasonable to conclude that neodymium may well be a somewhat stronger nodular impelling agent than lanthanum but because of inability to obtain pure neodym ium this conclusion could not at this time be experimentally confirmed.

The employment of a nodular impelling agent having a boiling temperature above the temperatures used in pouring molten iron is important in that the retention of the agent may be maintained at a constant for indefinite periods of time. The following data taken from recognized published literature illustrates an important point in this invention:

1 Unknown but; presumed to be somewhat above that of lanthanum.

From the above it can be seen that both magnesium and cerium boil well below the melting point of iron. Hence where either magnesium or cerium is used as a nodular impelling agent the molten iron mix must be cast promptly before the magnesium or cerium is expelled through distillation as the pouring temperature for molten iron is usually close to 3000 F. However, in the case of metals of the lanthanum series of elements, lanthanum (and probably neodymium, praseodymium and samarium) it can be seen that the boiling point is well above the pouring temperatures used in casting of molten iron and therefore is not expelled by distillation. Hence, the nodular impelling characteristics of lanthanum (and probably neodymium, praseodymium and samarium) may remain indefinitely in the molten iron resulting in the production of uniform nodular iron castings irrespective of any time limit other than, of course, the iron must be cast prior to cooling down to chill temperature. This is an important feature of this invention for it is evident that unless the sulfur content is increased such castings, sprues and gates may be re-rnelted and re-cast without further addition of a nodular carbon impelling agent and the castings made from such re-melt may retain the nodular iron structure. Furthermore the nodular impelling agents of this invention may be incorporated directly into the molten iron both in pellet form without violent reaction of any kind.

In my experiments I employed two novel basic nodular impelling agents in varying amounts. The first nodular impelling agent employed was elemental metallic lanthanum. The second nodular impelling agent employed was an alloy consisting of about 60 percent elemental metallic lanthanum and about 40 percent elemental metallic neodymium. My experiments further indicated that the content of lanthanum in the casting should preferably be in the range of 0.020 and 0.040 percent. Amounts of lanthanum in the casting exceeding 0.040 percent appear to act as a carbide stabilizer and should only be employed where very hard and wear resistant iron castings are desired. Amounts of lanthanum below 0.020 percent in the casting appear to be insufiicient to cause the carbon to coalesce to form the nodular structure in the matrix.

In each of the following specific examples of this invention standard 1 inch thick Y-block test castings illustrated in Military Specification MlLIl7166A (SHIPS) were made and tested for comparison with similar castings made from the untreated base iron.

EXAMPLE 1 A ladle of base iron mix consisting of molten pig iron as tapped directly from a blast furnace was cast and allowed to cool normally. The castings were subsequently tested in the as-cast condition and found to have the properties shown in Table I of this specification and the microstructure of the matrix is shown in FIGURES 1 and 2. This same ladle of molten blast furnace iron was used as a base iron in each of the succeeding examples described below.

EXAMPLE 2 To an aliquot portion of the molten base iron mix described in Example '1 was added sufiicient elemental metallic lanthanum with agitation to obtain uniform mixture to raise the lanthanum content of the resulting iron castings to 0.040 percent. The molten iron mix was then graphitized by inoculation with about 0.40 percent of ferro-silicon containing about 50 percent silicon as a graphit-izing agent and then cast into 1 inch thick Y- bloc castings. The castings were allowed to cool normally and subsequently tested in the as-cast condition. The test results obtained therefrom are shown in Table II Otf this specification and the microstructure of the matrix shown in FIGURE 5.

EXAMPLE 3 To an aliquot portion of the molten base iron mix described in Example 1 was added suflicient elemental metallic lanthanum with agitation to obtain uniform mixture to raise the lanthanum content of the resulting iron castings to 0.050 percent. The molten iron mix was then graphitized by inoculation with about 0.40 percent of ferro-silicon containing about 50 percent silicon as a graphitizing agent and then cast into 1 inch thick Y- block castings. The castings were allowed to cool normally and subsequently tested in the as-cast condition. The test results obtained are shown in Table II of this specification and the microstructure of the matrix is shown in FIGURE 6.

EXAMPLE 4 To an aliquot portion of molten base iron mix described in Example 1 was added sufiicient alloy consisting of about 60 percent elemental metallic lanthanum and about 40 percent elemental metallic meodymium with agitation to obtain uniform mixture to raise the lantha- 1mm content of the resulting iron castings to 0.024 percent. The molten iron mix was then graphitized by inoculation with about 0.40 percent of ferrosilicon containing about 50 percent silicon as a graphitizing agent and then cast into 1 inch thick Y-block castings. The cast ings were allowed to cool normally and subsequently tested in the as-oast condition. The test results obtained are shown in Table III of this specification and the microstructure of the matrix is shown in FIGURE 3.

EXAMPLE 5 To an aliquot portion of molten base iron mix described in Example 1 was added sufiicient alloy consisting of about 60 percent elemental metallic lanthanum and about 40 percent elemental metallic neodymium with agitation to obtain uniform mixture to raise the lanthanum content of the resulting iron castings to 0.035 percent. The molten iron mix was then graphitized by inoculation with about 0.40 percent of ifei'rosilicon containing about 50 percent silicon as a graphitizing agent and then cast into 1 inch thick Y-block castings. 'Ilhe castings were allowed to cool normally and subsequently tested in the as-cast condition. The test results obtained are shown in Table III of this specification and the microstiuoture of the matrix is shown in FIGURE 4.

The test data obtained from castings made in accordance with the above referred to specific examples together with test data obtained from castings made in a similar manner varying in lanthanum content with and without neodymium are shown in Table II and Table III below.

Table I.Base Iron MOLTEN PIG IRON AT BLAST FURNACE Tensile,

T.C Mn S P St BHN 1 psi.

Ultimate 1 See footnote 1, Table III. Table H.Efiect of Elemental Lanthanum Additions Percent Tensile, Tensile, Elonga- Example No. La In BHN 1 psi. p.s.i. tion,

Iron Ultimate Yield Percent 1 See footnote 1, Table III.

Table [IL-Efiecl of Lanthanum Neodymium Alloy Additions Percent Tensile, Tensile, Elonga- Example No. La In BHN 1 p.s.i. p.s.i. tion,

Iron Ultimate Yield Percent 1 Brinell Hardness Number (3000 kilogram load10 mm. ball).

indicates that even small amounts of lanthanum exhibited a tendency to cause the carbon to coalesce or agglomerate into smaller aggregates. At about 0.020 percent the presence of some nodular form of carbon appears in the matrix mixed with short length flake carbon which reflects in a marked improvement in physical strength properties of the castings. As the amount of lanthanum in the casting is increased the number of nodules of carbon in a given area increases proportionately and the amount of carbon in short length flake form decreases rapidly. It will be seen from Table II that when the lanthanum content of the castings exceed about 0.040 the iron becomes more hard without substantial change in tensile strength although the elongation indicates that there exists a measurable ductility in the castings. It appears that lanthanum contents in excess of about 0.040 percent acts as a carbide stabilizer and should be used only when hard wear resistant iron is desired. It should, however, be pointed out that inoculation of the molten iron with a graphitizing agent such as ferro-silicon is not necessary according to this invention. If the molten iron is inoculated with a graphitizing agent it appears that more carbon becomes available to form nodules than that obtained when the graphitizing inoculation is omitted.

Referring to Table III it will be seen that the addition of neodymium alloyed with lanthanum to the molten iron further improves both tensile strength and elongation without substantially effecting the hardness of the resulting castings. Thus, the use of neodymium alloyed with lanthanum in molten base iron will produce ductile castings of high strength superior to that when lanthanum is used alone. As stated previously it would appear from our data shown herein that neodymium without lanthanum may well be a more potent nodular impelling agent than lanthanum. Owing to the commercial unavailability of pure neodymium I was unable to directly confirm the effect of neodymium without the presence of lanthanum. In any event it appears that the effective range of lanthahum content is 0.020 to 0.060 percent. However the lanthanum or neodymium content in no event should exceed 1 percent each.

FIGURES 1 and 2 showing the microstructure of the base iron (pig iron) illustrates the large graphite or carbon flakes in a matrix of coarse pearlite and ferrite which is typical of a low strength hyper-eutectic iron. FIG- URES 5 and 6 show the microstructures of the same base iron of FIGURES 1 and 2 illustrating the effect of the lanthanum addition. Nodules of carbon are formed but are dispersed with short stubby agglomerates of carbon which appear to be in a transition stage approaching nodular form. The castings illustrated in FIGURES 3 and 5 are comparable in both microstructure and physical properties but it should be noted that the irori of FIGURE 3 contains slightly more than half as much lanthanum as the iron shown in FIGURE 5 but the lanthanumneodymium alloy was used in the iron of FIGURE 3 whereas only lanthanum alone was used in FIGURE 5.

Referring now to FIGURE 4 it will be seen that a further increase of the lanthanum-neodymium alloy over that of the iron in FIGURE 3 resulted in an iron wherein the tree carbon is substantially percent in nodular form and the physical strength and elongation properties substantially increased over that of the FIGURE 3 iron.

Summarizing it has now been shown that molten pig iron as tapped directly from a blast furnace may be immediately converted to nodular iron by a simple nonviolent addition of lanthanum or neodymium or a combination of the two elements which iron may be cast into crankshafts for internal combustion engines, gears and the like with uniformity in quality of the castings and without limitation of time elapsing between the addition of the nodular impelling agents of this invention and the casting into the mold. Thus, high quality nodular iron castings may be made as part of a blast furnace operation which tremendously reduces the cost of making 3,1 7 nodular iron castings as compared with the present practice 0f first casting pig iron, then remelting the pig iron in a second furnace, adding a nodular impelling agent of the heretofore known types and casting same within a limited time after the addition of the agent.

Having thus described my invention including several specific examples thereof it can now be seen that the objects of the invention have been fully achieved and it must be understood that changes and modifications might be made which do not depart from the spirit of the invention as disclosed nor from the scope thereof as defined in the appended claim.

What is claimed is:

As an article of manufacture a ductile iron casting containing uncombined carbon substantially in spherulitic nodular form dispersed in the matrix thereof, said iron casting having no sulfur in excess of 0.03 percent by 8 Weight and containing from 0.02 percent to 0.04 percent by weight of elemental lanthanum as a nodular carbon impelling agent, said iron casting being re-meltable and re-cast while retaining said carbon in spherulitic nodular form without further addition of said nodular carbon impelling agent.

References Cited in the file of this patent UNITED STATES PATENTS

Images