US3367395A - Method and apparatus for treating molten metals - Google Patents

Description

Feb. 6, 1968 s. KARSAY 3,367,395

METHOD AND APPARATUS FOR TREATING MOLITEN METALS Filed May 12, 1965 2 Shqets-Sheet 1 TUBULAR STEEL POUR/N6 L ADL E INVENTOR S76E45 1 414 25) ATTORNEY Feb. 6, 1968 s. 1. KARSAY METHOD AND APPARATUS FOR TREATING MOLTEN METALS Filed May 12, 1965 2 Sheets-Sheet 2 PRIOR ART PLOUGHSHARE SECTION FIG. 2

PRESENT INVENTION PLOUGHSHARE SECTION FIG. 3

INVENTOR STEPHEN I KARSAY United States Patent 3,367,395 METHOD AND APPARATUS FOR TREATING MOLTEN METALS Stephen I. Karsay, Montreal, Quebec, Canada, assignor to Quebec Iron and Titanium Corporation, New York, N.Y., a corporation of (lanada Filed May 12, 1965, Ser. No. 455,143 Claims. (til. 16457) ABSTRACT OF THE DKSCLUEURE The disclosure relates to a method and apparatus for alloying or inoculating castings. The alloying or inoculating material is generally in the form of a solid bar. This bar is disposed with its lower end engaged against the pouring lip of the ladle. It is mounted for sliding movement constantly to engage against the pouring lip. As molten metal is poured from the ladle, the lower end of the bar is washed by the stream of molten metal and is eroded, so that inoculating or alloying material enters the metal. While the inventions described herein are particularly useful in the production of iron castings, the inoculating and alloying technique and apparatus have more general utility, such as, for example, the addition of a wide variety of reagents or fluxes to molten metals.

This invention relates to a process for making ferrous and nonferrous castings and to apparatus and an article for use in practicing the process.

More particularly, the invention is concerned with a process for alloying or inoculating castings; to an appara tus that is useful in the alloying or inoculation step; and to a form of alloying component or inoculant that is particularly useful for the process of the present invention.

In the production of ductile (nodular) cast irons, for most applications, a carbide-free structure is desirable. Experience has demonstrated that the usual treatment with magnesium, for bringing about a desirable nodular iron structure, must be followed by a post-inoculation, in order to achieve a carbide-free structure. An additional benefit of post inoculation is a refined mierostructure, particularly, smaller and better shaped spheroids of graphite with resultant improvement of mechanical properties. One common technique for post-inoculation consists of adding ferrosilicon containing calcium and aluminum into the stream of molten metal while reladling.

Unfortunately, the efiect of an inoculation disappears or fades within a relatively short time. Many foundries attempt to pour inoculated iron within four to seven minutes after post-inoculation, in order to avoid fading. However, the rate of fading is most rapid during the first two or three minutes following post-inoculation, and while fading continues after that, the rate decreases.

In oculation in the mold has been suggested, to minimize fading effects. Unfortunately, this technique tends to cause inclusions and usually results in an uneven distribution of silicon. Moreover, since the amount of inoculant is very small, mold inoculation at best cannot replace conventional post-inoculation, but can only be an additional measure for eliminating chill.

One object of the present invention is to provide an improved post-inoculation process.

Another object of the invention is to provide practical yet simple apparatus for carrying out the improved postinoculation process of the present invention.

Still another object of the invention is to provide postinoculating material in an improved and practical form, particularly adapted for use in carrying out the process 3,367,395 Patented Feb. 6, 1968 0f the present invention and in the apparatus of the present invention.

A more specific object of the invention is to provide a practical post-inoculation technique that can be used in the production of ductile iron castings that include at least one wall one-half inch or thinner, together with apparatus and a practical form of inoculant material, for practicing the process.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In brief summary of the present invention, the inoculating or alloying material is in the form of a solid bar. This bar is disposed with its lower end engaged against the pouring lip of the ladle. It is mounted for sliding movement under its own Weight, constantly to engage against the pouring lip. As molten metal is poured from the ladle, the lower end of the bar is washed by the stream of molten metal and is eroded, so that inoculating or alloying material enters the metal. While the inventions described herein are particularly useful in the production of iron castings, the inoculating and alloying technique, apparatus and article, have more general utility, such as, for example, the addition of a wide variety of reagents or fluxes to molten metals.

In the drawings:

FIGURE 1 is a fragmentary schematic diagram showing, in a transverse section in a vertical plane, a pouring ladle that is equipped with apparatus in accordance with one preferred embodiment of the present invention, and showing molten iron being poured from the ladle into the mouth of a mold;

FIGURE 2 is a reproduction of a photograph of a section of a cast ductile iron ploughshare, that was post-inoculated in the conventional way by adding the post-inoculant material into the stream of molten iron while reladling, and that was sectioned along a line perpendicular to the chilled edge of the ploughshare, Nital etched, at a magnification of 250 times; and

FIGURE 3 is a reproduction of a photograph of a section of a ploughshare that was post-inoculated in accordance with one preferred embodiment of the present invention, and that was sectioned along a precisely corresponding line to the section shown in FIGURE 2, perpendicular to the chilled edge, Nital etched, at a magnification of 250 times.

The present invention is particularly concerned with the production of ductile iron castings of the kind in which the casting includes at least one thin wall portion. For the purposes of the present application, a thin wall is considered to be one that has a thickness in the range from about of an inch to about A of an inch. However, by the practice of the present invention and by careful attention to the influence of chemical composition, carbide-free ductile iron castings may be produced with walls that are as thin as the accuracy of molding permits. Such castings might be, for example, hydraulic couplings having vane or wall thicknesses 0n the order of about /3 of an inch; fly wheels having radial arms or webs with a thickness on the order of about /s of an inch; pumpimpellers, having a minimum wall thickness on the order of about of an inch; camera supports of complicated shapes, including tubular sleeves and radially-extending arms, and having a minimum wall thickness on the order of approximately of an inch; and molded for pneumatic tires, having fins that are approximately M of an inch thick. Articles of this general kind are most advantageously produced of ductile iron, which affords several economies and has many inherent advantages. Ductile iron castings with medium or heavy sections do benefit from the present invention in the form of refined microstructure and improved mechanical properties.

In order to explain the invention in greater detail, a description follows of the manufacture of an exemplary casting, in accordance with one preferred embodiment of the invention. The inoculant was prepared in the follow ing manner. Fine particles of calcium-bearing ferrosilicon, containing 85 percent silicon, of a size to pass through a No. 30 US. Standard screen, were mixed with a sodium silicate binder. This mixture was rammed into the bore of a length of soft steel pipe having an internal diameter of A of an inch and a wall thickness of approximately 0.006 inch (0.15 mm.). Several rods made in this way were baked at 500 F. (260 C.) for two hours.

A pouring ladle was then fitted with a supporting yoke including a guide sleeve disposed directly above the pouring lip, for supporting an inoculant rod with one end engaged against the pouring lip, as shown in FIGURE. 1. The ladle had a 150 lb. capacity.

An inoculant rod was mounted in the guide sleeve, and a charge of molten iron was placed in the ladle. The molten iron was then poured into the open mouth of a mold, in the fashion illustrated in FIGURE 1 of the drawings, at a pouring temperature of approximately 2,600 F. (1,427 C.). The mold was selected to form a ploughshare having an edge ranging in thickness from about A in. to about in., which was cast against a chill bar 1 inch wide.

The pouring rate selected was 1.84 lb./sec. (835 grams/sec.), and the pouring time was 7 /2 seconds. The observed rod consumption was at a rate of 0.0024 lb./sec. (1.1 grams/see), resulting in a rate of inoculation of 0.125% ferrosilicon.

The advantages of post-inoculation in accordance with the present invention were quite apparent. First, as the rod was consumed, it fed downwardly, constantly to engage against the pouring lip, under its own weight. The addition of the inoculant therefore required no supervision during pouring, and no complicated driving mechanism. Secondly, the rate of consumption was substantially constant during the entire pouring cycle. It was also observed to remain substantially constant during succeeding pouring cycles. Moreover, inoculation stopped when pouring stopped. Subsequent observations indicated another important advantage, namely, that the rate of consumption of a given inoculant rod or bar depends primarily upon pouring temperature. This is important in the production of castings, of various sizes. Thin castings are usually poured at a higher temperature than more massive castings, and therefore receive a greater amount of inoculant than do the more massive castings which is desirable. In this connection, it is noted that a higher pouring rate does not alter the rate of inoculation although it does increase the rate of rod consumption.

To demonstrate the invention further, a ladle of 150 lbs. capacity was charged with molten iron that was tapped from a basic cupola, treated with 1.9% ferrosilicon-magnesium alloy, and post-inoculated, during reladling, with an addition of 1.2% ferrosilicon.

Four ploughshare castings were then poured from the ladle, with inoculation at the pouring lip in the manner just described, in accordance with the present invention. The inoculant rod was then removed from the guide sleeve, and four more ploughshare castings were poured.

One of the ploughshares that had been made in accordance with conventional post-inoculation practice, and one ploughshare that had been post-inoculated in accordance with the present invention were sectioned along precisely corresponding lines, perpendicular to their respective chilled edges. Photomicrographs were taken at the chill-sand facing transition line, of each of the two ploughshare sections respectively, in each case at a distance of approximately 0.016 inch (0.4 mm.) from the surface. In each case, the surface was Nital etched, and the magnification was 250 times.

The photomicrograph of the ploughshare that was produced by conventional post-inoculation practice is shown in FIGURE 2. The presence of carbides can easily be observed. A photomicrograph of the section of the ploughshare that was produced in accordance with the postinoculation technique of the present invention is shown in FIGURE 3. As this photomicrograph demonstrates, post-inoculation in accordance with the present invention eliminated all of the carbides. This is particularly remarkable in view of the fact that in each case there was an initial, conventional post-inoculation of 1.2% ferrosilicon. Chemical analyses of castings of both types indicated that there was no detectable change in silicon content. Examination of castings made in accordance with the present invention revealed no trace of inclusions.

Because of the importance of the influence of chemical composition on casting properties, a brief discussion of chemical composition is appropriate. As to the content of carbon and silicon in a molten iron, since a high carbon equivalent is one of the major tools for eliminating carbides, thin ductile iron castings are hypereutectic, that is, the percentage of total carbon, together with 0.31 time the percentage of silicon, is greater than 4.30. It is seldom desirable to increase the silicon content beyond 3.0%. Occasionally, its concentration must be limited to 2.5%. The minimum carbon content, therefore, will range between 3.4 and 3.5%. In the absence of massive sections in the same casting with thin sections, the carbon equivalent for a casting that includes at least one thin wall portion preferably should be in the range from about 4.5 to about 4.6. Accordingly, for the production of. a casting that has a thin wall section, the recommended carbon content is between 3.6 and 3.8%, or even higher if the walls are uniformly thin.

Manganese acts as a carbide promoter and stabilizer in ductile irons. Accordingly, a manganese-free composition is preferred, particularly for castings having a thin Wall section. However, depending upon the balance of the chemical composition and the efficiency of post-inoculation, particularly for massive castings, some manganese, up to approximately 0.5%, may be tolerated.

Nickel, copper and tin promote a pearlitic matrix, without causing the formation of massive eutectic carbides. These elements are therefore desirable alloying agents for the production of castings that must meet high strength requirements or that are exposed to abrasive wear, and that therefore should be fully pearlitic. Moreover, both copper and nickel tend to reduce carbide formation and are therefore particularly beneficial alloying elements for the production of thin ductile iron castings. Both nickel and copper are desirable in the range between 0.5% and about 2.0%, depending upon differences in section size. A preferred tin content is in the vicinity of 0.1%.

For toughness in castings, the phosphorous content is preferably maintained below 0.03%. For light ductile iron castings in general, the phosphorus concentration should be under 0.08% in any case. The need for low sulfur content is well understood. In general, a low sulfur content, preferably 0.03% maximum, together with low retained magnesium, preferably in the range from about 0.02% to about 0.04%, tends to eliminate dross defects and minimizes any carbide-forming tendency. Since both chromium and vanadium tend to promote carbide formation, the level of each should be kept below 0.03%.

Aluminum is frequently added to the melt in the inoculant. In order to avoid the tendency toward pinholing that is associated with the presence of aluminum, the aluminum content of the inoculant should be limited to a maximum of 1.0%, particularly for the production of castings that include a thin section. The tendency toward pinholing is most likely to become apparent when the aluminum content of the ductile iron exceeds 0.02%.

Although the greatest field of application for the present invention is in the production of thin ductile iron castings with a substantially pearlitic matrix, there is a field of application for the production of such castings with a predominantly or completely ferritic matrix. In order to achieve a ferritic as-cast structure, in thin sections, the carbon content must be lower than that in pearlitic castings, and the three elements manganese, nickel, and copper must be absent. The ferritic structure is achieved by a slow cooling through the critical temperature region of from 1,500" F. to about 1,300 F., and a somewhat increased silicon content as compared to a pearlitic casting. The requirement for silicon increases, to produce a desired ferritic matrix, as the casting section decreases, generally speaking.

In practicing the present invention, a variety of materials may be employed for inoculating gray or ductile irons. Some examples are listed as follows.

TYPICAL COMPOSITIONS FOR INOCULATING RODS Example No.1 No.2 No.3 No.4 No.5

It is known in the art that the act of inoculation is performed by one or a combination of the following four elements: calcium, aluminum, strontium and barium. The inoculating effects of other elements such as carbon (graphite), sodium, potassium, magnesium, zirconium, cerium and other rare earths, beryllium, titanium and oxygen have also been observed. Inoculating rods containing the listed elements in various combinations and amounts can be made.

In addition to the carrying elements listed previously, manganese, chromium, molybdenum, copper and other metals can also be utilized for the manufacture of inoculating rods.

The precise amount of any particular inoculant, that should be used in a particular foundry, is best determined from experience, as has been the case with inoculation techniques employed in the past. The particular characteristics of a molten iron and the melting process are important factors that affect the decision as to the particular inoculant, its chemical composition and the total amount of inoculant, that are most effective.

The rods can be manufactured by a variety of methods, either with or without a steel or other jacket. These methods utilize either the techniques of powder metallurgy of those of pouring either continuously or intermittently. Extrusion or forging techniques can also be employed when producing rods of suitable chemical composition.

In addition to the advantages of the invention previously mentioned, there are the more obvious, but important, advantages of achieving a substantially uniform distribution of the inoculant or alloying element throughout the molten metal and of either completely avoiding or minimizing the fading effect. The present invention is also characterized by flexibility. Thus, the rate of inoculaton is easily varied, within wide limits, since the diameter of the inoculant bar, and the thickness of the sheath in which the inoculant may be enclosed, have an important influence on the rate of addition, as well as the pouring temperature of the molten metal. In addition, the bar can be made up so that its rate of erosion by the molten metal is at any desired rate within a very broad range. For example, instead of preparing the bar in the manner previously described, inoculant grade ferrosilicon can be chillcast into molds that are lined with very thin steel pipes. Bars of this type tend to have a slower erosion rate than those with similar steel jackets, where the inoculant is formed from a particulate mass that is bonded in situ. Similarly, inoculant bars that are formed with nickel or copper bases, that contain a high content of calcium, strontium, or the like, can readily be altered in composition to have dilferent erosion rates.

While the present invention is illustrated through the production of a thin ductile iron casting, ductile iron castings of any section size can be delivered as cast with assurance of quality through the practice of the present invention.

The inoculating effect in gray cast irons fades in time in a fashion similar to that described for ductile irons. The benefits of present invention for gray irons will, again, be increased freedom from carbides, refined microstructure and improved mechanical properties.

Alloying ferrous or non-ferrous metal in accordance with the present invention provides for an even distribution of the alloying elements and at the same time minimizes oxidation losses.

White the invention has been disclosed herein by reference to the details of preferred embodiments thereof, it is to be understood that such disclosure is intended in an illustrative rather than a limiting sense, and it is contemplated that various modifications in the practice of the process, in the construtcion and arrangement of the parts of the apparatus, and in the composition and structure of the bar, will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.

I claim: 1. The method of incorporating an addition reagent in a molten metal, comprising disposing a bar comprising the addition reagent at the pouring lip of a ladle of the molten metal, and

pouring the molten metal from the ladle across the pouring lip and about the bar, theerby eroding the bar to permit the addition reagent to enter the molten metal.

2. The method of incorporating an addition reagent in a molten metal, comprising engaging one end of a bar consisting essentially of the addition reagent under its own weight against the pouring lip of a ladle of the molten metal,

pouring the molten metal from the ladle across the pouring lip and about the bar, thereby eroding the bar to permit the addition reagent to enter the molten metal, and

permitting the bar to move freely under its own weight,

continuously to engage against the lip to make available fresh surfaces of the bar to the flow of molten metal to replace eroded portions of the bar.

3. The method of inoculating molten iron comprising disposing a bar of inoculant at the pouring lip of a ladle of the molten iron, and

pouring the molten iron from the ladle across the pouring lip and about the bar, thereby eroding the bar to permit the inoculant to enter the molten iron.

4. The method of inoculating molten iron comprising engaging one end of a bar, that consists essential of an inoculant, under its own weight against the pouring lip of a ladle of molten iron,

pouring the molten iron from the ladle across the pouring lip and about the bar, thereby eroding the bar to permit the inoculant to enter the molten metal, and permitting the bar to move freely under its own weight, continuously to engage against the pouring lip, to make available fresh surfaces of the bar to the flow of molten metal to replace eroded portions of the bar.

5. The method of inoculating molten iron with a calcium-bearing inoculant, comprising forming particulate inoculant material into a bar that will erode upon contact with a flow of molten iron, disposing the bar at the pouring lip of a ladle of molten iron, and

pouring the molten iron from the ladle across the pouring lip and about the bar, directly into a mold, thereby eroding the bar to permit the inoculant to enter the molten metal.

6. The method of forming a ductile iron casting that includes at least 1 thin wall having a thickness between about inch and about A inch, by a post-inoculating technique with a calcium-bearing ferro-silicon inoculant, comprising forming particulate inoculant material into a bar that will erode upon contact with a How of molten iron, engaging one end of the bar under its own weight against the pouring lip of a ladle of molten iron, pouring the molten iron from the ladle across the pouring lip and about the bar, directly into a mold for the casting, thereby eroding the bar to permit the inoculant to enter the molten iron, and

permitting the bar to move freely under its own weight,

continuously to engage against the pouring lip to make available fresh portions of the bar to the flow of molten iron to replace eroded portions of the bar.

7. The method in accordance with claim 1 including the additional step of advancing the bar into the molten metal stream during pouring, to permit erosion to occur throughout the entire pour.

8. A method in accordance with claim 1 wherein the rate of advancement is such that a substantially constant length of the bar is exposed to contact with the molten metal.

9. Apparatus for inoculating molten iron at the pouring lip of a ladle, upon pouring of the molten iron from the ladle into a mold, comprising a bar of inoculant material, and

sleeve means supported from the ladle, slidably supporting the bar, with one of its ends engaged against the pouring lip of the ladle, in position so that at least a portion of the bar at the end is washed by molten iron as it is poured from the ladle, said sleeve means permitting advancement of the bar under its own weight, constantly to engage against the pouring lip. 10. Apparatus for adding a reagent to molten metal at the pouring lip of a ladle, upon pouring of the molten metal from the ladle, comprising a bar of reagent, material, and sleeve means supported from the ladle, slidably supporting the bar, with one of its ends engaged against the pouring lip of the ladle, in position so that at least a portion of the bar at that end is washed by molten metal as it is poured from the ladle, said sleeve means permitting advancement of the bar to engage against the pouring lip.

11. The apparatus of claim 10 wherein the bar comprises a bonded mass of particulate inoculant material.

12. The apparatus of claim 10 wherein the bar comprises a tubular supporting sheath and a mass of particulate inoculant material that is bonded in situ within the sheath.

13. The apparatus in claim 10 wherein the bar is calcium-bearing.

14. The apparatus in claim 10 wherein the bar comprises calcium-bearing ferrosilicon.

15. The apparatus in claim 10 including means foradvancing the bar at such a rate that a substantially constant length of the bar is exposed to contact with the molten metal during the pour to permit erosion to occur continuously throughout the pour.

References Cited UNITED STATES PATENTS 1,184,523 5/1916 Field 16457 2,370,467 2/1945 Hopkins 164-52 2,519,593 8/ 1950 Otfenhauer. 2,595,292 5/1952 Reece. 2,716,602 8/1955 Ensign. 2,819,503 1/1958 Boucek 164-56 2,882,571 4/1959 Easton 164-56 3,305,902 2/1967 Bjorksten 16455 3,108,151 10/1963 Garmy et a1. 3,251,681 5/1966 Wakamatso et al. 266-86 XR I. SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Assistant Examiner.

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