US2711953A - Treating nodular iron - Google Patents

Description

June 28, 1955 G. VENNERQOLM Em 2,11

TREATING NODULAR IRON Filed 001;. 9, 1950 G. l/ENNERHOLM R A MAN PATTE/V ATTORNEYS nited States Patent T TREATING NODULAR IRON Gosta Vennerholm, Dearborn, and Royal Arch Van Patten, Garden City, Mich, assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Application October 9, 1950, Serial No. 189,133 claims. C1. 75-53 This application is concerned with the founding industry and more particularly with a method for improving the physical properties of nodular cast iron. This socalled nodular iron has received recent widespread publicity both in the current and patent literature and it is thought to be unnecessary to describe it further other than to state that it may be produced by adding surficient magnesium to an appropriate gray iron melt to produce a magnesium residual of about 0.05% and inoculating the melt just prior to pouring into the mold with any of the many commercially available graphitizing inoculants. This treatment, if properly carried out, will result in an as cast product in which the uncombined carbon is present in the form of spherulites or nodules rather than the flaky form which is characteristic of typical gray iron. The matrix may be either ferritic or pearlitic, depending upon the analysis and casting conditions. As is now well understood in the art, the absence of flaky graphite permits the production of the casting having a much higher tensile strength and ductility than ordinary gray iron.

The production of nodular iron castings particularly in highly irregular shapes has been impeded by the persistent occurrence of a phenomenon referred to in the industry as cope defects. This name has been applied because of the tendency of this defect to occur at the upper portion of the castings. A casting seriously weakened by these cope defects may present to the eye a perfect surface and also appear radiographically sound.

However, when fractured the castings will exhibit a large number of inclusions of unknown composition. While the exact composition of these inclusions is unknown, it is apparent that a large amount of graphite is included in their makeup. In a fracture, these inclusions are disclosed as planes of discontinuity varying in size from those barely visible to the naked eye up to one quarter of an inch in diameter. These graphite laden planes of discontinuity, of course, seriously weaken the castings.

These inclusions have been found particularly troublesome in the casting of crankshafts for internal combustion engines inasmuch as they tend to congregate at the juncture of the pin bearing and check, which is precisely the location of maximum stress concentration at which fatigue cracks tend to develop.

It has been discovered that this phenomenon of cope defects can be substantially eliminated by the application to the molten metal of any of the many fluxes which have been developed for use with magnesium.

Particularly good results have been obtained with boric acid, borax, fused borax, and alkali metal fluoborates, as well as the fluxes which are based upon the double chloride of an alkali metal and magnesium. For a detailed description of commercially available fluxes, reference is made to the Metals Handbook, 1948 edition, page 974.

While the inventors have not completely developed the theory underlying their invention, it is their belief that Patented June 28, 1955 oxidizing gases preferentially oxidize the magnesium content of the magnesium containing iron and that the resultant highly refractory magnesium oxide is responsible for the occurrence of cope defects.

To eliminate these cope defects, the inventors intimately contact the magnesium type of flux with the molten magnesium containing iron. nomical and satisfactory method of applying these magnesium type fluxes to the molten metal is the contacting of the molten metal with a porous refractory body which has been impregnated with the magnesium flux. These flux impregnated refractory bodies may readily be prepared by the immersion of the completed refractory body in molten flux. Conversely the fiuxing metal could be included in the original refractory mix or in the case of water-soluble fluxes, it could be applied by dipping the finished refractory in a strong solution of the flux and drying.

In the application of this process, the inventors have been singularly successful in the production of an internal combustion engine crankshaft having the following composition:

Per cent Carbon 3.50-3.80 Silicon 2.20-3.00 Manganese 0.30-1.00 Phosphorus 0.100 Sulphur 0.017 Magnesium 0.050 Iron Remainder along the line 2-2 in Figure 1.

As can be readily seen from the drawings the refractory form comprises a body which is circular as seen in the plan view and in section is isosceles trapezoid. A number of holes are provided in this form. The axes of these holes are parallel to the axis of the body. It is under stood that this body is impregnated or coated with a magnesium type flux. This refractory is incorporated in the mold in such a way that all of the metal which will eventually become a part of the finished casting must pass through the holes in the refractory body. The passage of the molten metal through the relatively large number of holes causes a sufliciently intimate contact between the flux and the molten metal to result in the substantially complete elimination of the cope defects.

While the particular form of refractory shown in the drawings has been found to be highly satisfactory for applying the magnesium type flux to the molten metal, the invention is by no means so limited. A refractory body impregnated or coated with magnesium flux may be incorporated in the mold and located so that the metal entering the mold will flow across the refractory body. Also the ladles or other refractory lined facilities employed in handling the molten magnesium treated metals may be given a wash with molten magnesium flux which will coat and to some extent impregnate them with flux. The use of ladles so treated will result in sufficient contact between the fiux and the molten metal to substantially reduce the occurrence of cope defects. Alternatively an ordinary refractory fire brick may be impregnated with magnesium flux and floated in the molten metal While in the ladle or other handling apparatus.

We claim as our invention:

1. The process of producing nodular iron castings comprising adding to an appropriate melt sufiicient magnesium to produce an as cast nodular structure and contacting this magnesium bearing melt with a refractory A particularly ecosubstance, said refractory substance including a magnesium type flux.

2. The process of producing nodular iron castings comprising adding to an appropriate melt sufficient magnesium to produce an as cast nodular structure and contacting this magnesium bearing melt with a refractory substance, said refractory substance including a flux selected from the group consisting of borax, fused borax, boric acid, alkali metal fluoborates and mixtures comprising magnesium chloride and an alkali metal chloride.

3. The process of producing nodular iron castings comprising adding to an appropriate melt suflicient magnesium to produce an as cast nodular structure and contacting this-magnesium bearing melt with a refractory substance, said refractory substance having been coated with a magnesium type flux.

4.' The process of producing nodular iron castings comprising adding to an appropriate melt suflicient magnesium to produce an as cast nodular structure and contacting this magnesium bearing melt with a refractory substance, said refractory substance having been coated and impregnated with a magnesium type flux.

5. The process of producing nodular iron casting comprising adding to an appropriate melt suflicient magnesium to produce an as cast nodular structure and contacting this magnesium bearing melt with a refractory substance by flowing the molten metal over the refractory substance, said refractory substance carrying a magnesium type flux.

6. The process of producing nodular iron castings comprising adding to an appropriate melt sufiicient magnesium to produce an as cast nodular structure and pouring this magnesium bearing melt through a perforate refractory substance, said refractory substance carrying a magnesium type flux.

7. The process of producing nodular iron casting comprising adding to an appropriate melt sufficient magnesium to produce an as cast nodular structure and pouring this magnesium bearing melt through a perforate refractor y substance, said refractory substance carrying a magnesium type flux and being located in the mold in which the casting is poured.

8. The process of producing nodular iron castings comprising adding to an appropriate melt sufiicient magnesium to produce'an as cast nodular structure and handling this magnesium in refractory vessels the refractory portions of which carry a magnesium type flux.

9. The process of producing nodular iron castings comprising adding to an appropriate melt suflicient magnesium to produce an as cast nodular structure and floating in this melt a refractory substance which carries a magnesium type flux.

10. The process of producing nodular iron castings comprising adding to an appropriate melt sufiicient magnesium to produce an as cast nodular structure and casting this melt in molds, said molds containing a refractory body carrying a magnesium type flux and located so that the melt entering the mold will flow over said body.

No references cited.

Claims (1)

1. 7. THE PROCESS OF PRODUCING NODULAR IRON CASTING COMPRISING ADDING TO AN APPROPRIATE MELT SUFFICIENT MAGNESIUM TO PRODUCE AN AS CAST NODULAR STRUCTURE AND POURING THIS MAGNESIUM BEARING MELT THROUGH A PERFORATE REFRACTORY SUBSTANCE, SAID REFRACTORY SUBSTANCE CARRYING A MAGNESIUM TYPE FLUX AND BEING LOCATED IN THE MOLD IN WHICH THE CASING IS POURED.

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