US3336118A - Magnesium alloy for cast iron - Google Patents

Description

United States Patent 3,336,118 MAGNESIUM ALLOY FOR CAST IRON George B. Newitt, Wheaton, IH., assignor to Alloy Metal Products, Inc., Davenport, Iowa, a corporation of Iowa No Drawing. Filed Nov. 9, 1964, Ser. No. 410,001 4 Claims. (Cl. 29-192) ABSTRACT OF DISCLOSURE An improved iron nodularization alloy containing maximally 20% silicon, minimally 15% magnesium, minimally 50% nickel, and the balance iron. Small percentages of the rare earth, cerium, may be added to re place some of the iron as an additional inoculant. As an article of manufacture, the briquette form of the alloy is set forth.

This invention relates to a new alloy useful as an addition agent for the treatment of molten iron prior to casting and to a process for treating cast iron to produce ferrous products with improved properties and characteristics. In particular the invention relates to an alloy which when added to molten cast iron will render the graphite in the iron spheroidal.

It is well known in the art of making cast iron that carbon present as graphite, may be in one of two formsflake or spheroidal. In flake form, the graphite provides weakening discontinuities in the iron crystalline structure resulting in a cast iron of greatly reduced tensile strength, fatigue resistance, toughness and ductility. When graphite is in spheroidal form, however, a more regular iron crystalline structure results eliminating the deleterious effects vf flake graphite.

It is further well known that inoculation of molten cast iron with silicon enhances graphitizing of carbon present in the iron, i.e. prevents carbon from reacting with iron to form carbides which render the iron hard, brittle and difficult to work. Further it is well known that by proper inoculation shrinkage of an iron melt during cooling after casting is minimized.

It is well known that spheroidal graphite is produced in iron by adding magnesium to an iron melt. However, attempts to add magnesium to molten iron results in violent explosions since the boiling point of magnesium is below the temperature of iron melts. In order to successfully introduce magnesium into molten iron, many attempts have been made to alloy magnesium with other materials so that upon addition to molten iron no exp1osive vaporization occurs. U.S. Patent 2,675,308 sets out a comprehensive summary of attempts in the art to use magnesium as an addition agent to produce spheroidal graphite in cast iron. Further, U.S. Patent 2,563,859 describes a special alloy of nickel, magnesium and silicon which when added to molten iron results in a cast iron in which graphite present is in compacted or spheroidal form. The alloy described contains from about 32% to about 50% silicon, about 12% to 20% magnesium, up to about 12% iron, and the balance essentially nickel.

Although such alloy does produce some spheroidal graphite and eliminates the danger of adding elemental magnesium to molten iron baths, there still exists the problem of shrinkage of the batch when molded and cooled and further the production of even more spheroidal graphite rendering the iron accordingly stronger.

It has now been discovered that if there is employed as an inoculation material an alloy of silicon content maximally 20%, nickel content minimally 50%, iron content minimally 15% and the balance magnesium, there is produced cast iron containing residual magnesium of .02% to .05% with a microstructure showing a high quantity of spheroidal graphite, and which exhibits little or no 3,336,118 Patented Aug. 15, 1967 shrinkage while cooling. It is essential that silicon not be present in the alloy more than 20%. In addition, it has been discovered that when employing such alloy, graphite rendered spheroidal by the magnesium remains spheroidal for a longer time while the iron is molten thus permitting a greater length of time to utilize iron in its molten state. Thus, use of my new alloy permits a foundry to use a heavier post inoculation of ferrosilicon which aids in preventing the fading reaction wherein spheroidal graphite reverses to graphite flake.

It has further been found that when using the new alloy material, the resultant cast iron shows high tensile strength, yield point and good elongation properties. Such addition agent further minimizes the amount of inclusions usually found in cast iron and thus improves the matrix of the iron and results in a more uniform distribution of graphite. Such is believed due to the thermodynamics of the oxidation-reduction reactions occurring between iron, carbon, silicon and magnesium.

As stated above, my new alloy permits greater postinoculation of ferrosilicon, i.e. having an alloy with low silicon content means that foundry operators can increase the percentage of after-added ferrosilicon, or post-inoculation, and still insure that the final silicon percentage in the ductile iron castings is in a predetermined desired range. Increasing the percentage of late ferrosilicon addi tion, as opposed to adding large percent-ages of silicon as part of the alloy, greatly improves the graphite dis-tribution, results in better formed spheroids, disperses and reduces carbides to a minimum, reduces internal and external shrinkage, reduces scrap due to cracking of castings, cuts costs of heat treatment due to less carbide formation in the matrix of the ductile iron, aids in the proper pattern shrinkage, decreases the time for fading to start, improves machineability of castings and shows a marked improvement in the tensile, yield and elongation strengths of cast products.

The new alloy addition agent thus provides the proper combination of silicon, magnesium, iron and nickel which greatly aids in propelling the thermodynamics of the interstitial reaction which occur and which are responsible for the formation and orientation of spheroidal graphite. This results in a preferred orientation of graphite in the iron.

It is thus an object of this invention to provide a new alloy addition agent comprising a magnesium containing material of specific elements in specific proportions, particularly adapted to the treatment of cast iron baths to improve the casting produced therefrom.

Another object of the invention is to provide an improved process for producing cast iron containing spheroi dal graphite which utilizes my new alloy addition agents.

A further object is to provide an inoculation alloy low in silicon content thus producing a cast iron to which high post-inoculation of silicon or ferrosilicon can be elfected without changing the final and overall silicon content.

In particular, the present invention contemplates a magnesium-containing alloy comprising 50% nickel, 20% silicon, 15% magnesium, and 15% iron. Alternatively, the alloy may contain 0.1% to 5% cerium or other rare earth metals. In the latter case, the rare earth metal replaces part of the iron in the alloy.

When employing the :above addition agent, magnesium may be added to molten cast iron baths without danger of explosive reaction. The cast iron resulting from addition of such alloy contains magnesium from .02% to .05% which is known in the art as a proper quantity for producing graphite in spheroidal form.

The additional alloy of the invention may be compounded in any manner known in the art e.g. by melting, or by pelletizing or briquetting powdered metals. The

resultant lumps, granules, pellets or briquettes may be introduced into the ladle of molten iron in varying amounts as required by good foundry practice. The alloy may either be placed in the ladle and the molten iron poured into the ladle or the material may be used in a plunging device which is immersed into a ladle of molten iron.

Magnesium retained in cast iron, as is known in the art, has been found to have a decided effect in whitening or carbide stabilizing which is undesirable in gray iron castings. Accordingly, in the production of magnesium containing gray cast iron, i.e. cast iron wherein substantially no carbodization has occurred it has usually been necessary to inoculate magnesium-containing cast iron baths before casting with a graphitizing material such as silicon or ferrosilicon and to cast the baths in an inoculated condition. It is a feature of the present invention that magnesium introduction and initial silicon inoculation are done simultaneously. This is effected by having silicon included in the alloy material.

Such simultaneous inoculation has two effects. First, the silicon present in the alloy in maximally 20% insures graphitization of carbon present in the iron. Second, the magnesium renders the graphite spheroidal in form. Further, by using initially no more than 20% silicon in the alloy, it has been found that the graphite remains in spheroidal for-m for longer periods while the iron is molten thus permitting a greater post-inoculation of silicon if such is desired.

In a preferred embodiment of the invention, cerium is used in the alloy in 0.1% to 5% by weight. Cerium as well as other rare earth metals, is a well known gettering agent which masks the harmful effects of tramp impurities such as tin or lead. Such impurities, unless masked, cause cracking of the iron and adversely affect welding properties.

In order to more fully understand the invention the following illustrated examples are given.

Example I A cast iron melt was established and the temperature of the bath was adjusted to about 2700 F. to permit successful casting. To the bath was added 1% of an alloy containing magnesium, silicon, 15% iron and 50% nickel. The molten metal was then cast. On cooling, the cast showed substantially no center line shrinkage. The resultant casting contained 0.03% magnesium, and was found to have excellent tensile strength, yield point, and elongation properties. A photomicrograph of a polished surface of the iron showed the graphite to be present in substantially all spheroidal form.

Example II A molten iron bath was prepared as in the Example I. To the bath was added an alloy, being 1% of the molten bath, containing nickel, 20% silicon, 15% magnesium, 14% iron, and 1% cerium. The molten metal was cast. Substantially no center line shrinkage was observed in cooling. The castings were found to contain about .035 magnesium, .and had excellent tensile strength, yield point, and elongation properties.

It is to be understood as hereinbefore stated that the silicon content of the alloy addition agent of this invention must contain at maximum 20% silicon and at minimum 50% nickel. Iron content must not be below 15% unless cerium is used in which event the iron content may be as low as 10%.

I claim:

1. A composition of matter useful as an addition agent for the treatment of cast iron baths to improve the quality of castings made therefrom, consisting essentially of an alloy of 15% magnesium, 20% silicon, 50% nickel and the balance iron.

2. A composition of matter useful as an addition agent for the treatment of cast iron baths to improve the quality of castings made therefrom, as set forth in claim 1 including 0.1% to 5% cerium.

3. As an article of manufacture, a briquette of powdered metals consisting essentially of 15% magnesium, 20% silicon, 50% nickel and the balance iron.

4. As an article of manufacture, a briquette of powdered metals as set forth in claim 3 including 0.1% to 5% cerium.

References Cited UNITED STATES PATENTS 2,675,308 4/1954 Millis et a1. -130 2,690,392 9/1954 Millis et a l. 75130 3,030,205 4/1962 Millis et a1. 75-130 DAVID L. RECK, Primary Examiner.

PAUL WEINSTEIN, Assistant Examiner.

Claims (1)

1. 3. AS AN ARTICLE OF MANUFACTURE, A BRIQUETTE OF POWDERED METALS CONSISTING ESSENTIALLY OF 15% MAGNESIUM, 20% SILICON, 50% NICKEL AND THE BALANCE IRON.

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