US2789898A - Method for producing cast iron - Google Patents

Description

m ALL 1d United States Patent t 2,789,898 METHOD FOR PRODUCING CAST IRON' Lester C. Crome, West Alexandria, Ohio, assignor to The Dayton Malleable Iron Company, Dayton, Ohio N Drawing. Application July 31, 1948,

Serial No. 41,907

, 6 Claims. (Cl. 75-130) .This invention relates to cast iron and more particularly to a new iron, and the production thereof, which when cast produces finished cast iron or castings which are markedly d'dferent in characteristics from the cast I in connection with gray iron.

irons as heretofore known such as so-called gray iron,

malleable iron and white iron.

One of the principal, objects of this invention is to provide a molten mix which in the molten state is such that the addition of small quantities of selected materials, as in the ladle before pouring into the mold, will produce the new iron of characteristics widely differing from the long and widely known gray irons, also from the white iron castings long produced to have such characteristics that upon heat treatment or annealing they will become the so-called malleable irons, and also from the malleableized irons which result from annealing or heat treatment of white iron castings.

Another object of the invention is to produce such new 2,789,898 Patented Apr. 23, 1951 of bending, the castings must be produced from constituents which are such and the proportions of which are such, that when the molten iron mix is poured into the mold and allowed to cool the resulting casting will be free from the flake-like graphitic carbon described above The presence of any appreciable quantity of flake-like graphitic carbon in the iron as cast will render a seemingly white iron casting useless for the production of malleable iron, as the graphitic carbon in malleable iron is that which is formed during the heat treatmentv from combined carbon, or iron carbides, and if graphitic carbon is in the casting as removed from the mold the subsequent heat treatment or annealing will not change the inherent characteristics of the casting to give it those characteristics which are essential for so-called maleable iron. Such a casting, free from'graphitic carbon as cast, in fracture appears white or a very silvery gray, and the appearance of the fracture of such a white iron casting is so markedly different from the appearance of the fracture of a gray iron casting, due to the differences in light reflection that the white or silvery gray appearance from such castings has lead to the designation of white iron." Such castings, are so extremely hard with respect to the usual machining operations, etc., that they are produced 7 (except perhaps for some special end use) only because the inherent characteristics are such that upon the proper iron, and castings of desired form directly, as by pouring into the mold with subsequent solidification on cooling, and without the necessity of the expensive annealing whichis required to make white ir-on castings into the usual malleableized castings.

Still another object of the invention is'to provide a method in the production of such molten iron mixes and the forming of castings thereof to produce the new iron product.

Other objects and advantages will be apparent from the following description, and the appended claims.

rso-called gray iron, as castings of finished characteristics when removed from the mold, and malleable iron produced by making castings of a white iron'mix and then subjecting the casting to the long andv expensive annealing treatment have long been known in the iron foundry industry. It has also been long recognized that in the making of gray iron castings the constituents and the relative proportions thereof which are present in the molten iron mix (which may be controlled by determin: ing the proportions which are admixed before melting to form the molten gray iron mix) must be such that when the molten gray iron is pouredinto the mold and is allowed to cool, most of the carbon whichis present inthe mix will separate so that in the finished casting heat treatment or annealing the iron carbides break down and form free carbon; but in such circumstances the characteristics of the casting cause the resulting graphitic carbon to appear as so-called nodules. That is, the

' usual malleable annealing operation causes a breaking it will be in flat or flake-like form, of varying dimensions.

This flat or flake-like graphitic carbon, produced by the presence of the constituents in such proportions that at least-one of them has what is called a graphitizing efiect to separate most of the carbon as the flat or flake-like graphitic carbon, is universally recognized as being characteristicof so-called gray iron castings. 'Such a casting, in fracture, has an irregular surface 'which appears as of a definitely gray color, due in part at least to the effect of the flake graphite with respect to the reflected light, which is characteristic; henceits designation as gray iron.

On the other hand, it is equally well recognized that for the production of malleable iron which has generally greater strength than gray iron and also is ductile and is capable of considerable elongation under tension or down of the iron carbides toform free carbon but not in the form of the flat or flake-like graphite which occurs in gray iron castings. Generally the carbon or graphite as separated from the carbides during anneal of a white iron casting appears as so-called nodules of temper carbon, the carbon after such anneal being separated and distributed as generally spherical or nodular as observed under the microscope or in photomicrographs.

The present invention has to do with the production of a new form of iron in which the finished casting is made from an iron mix which would be generally close in constituents and proportions to the mixes which have 1 long been used in the gray iron foundry industry. By the addition of small quantities of certain other constituents to the molten mix, an iron casting is produced which has free graphitic carbon appearing in the casting but such that there is substantially no flake graphitic carbon of typical gray iron described above formed while the casting is being made. The separated or graphitic carbon is formed into agglomerat'es "of massive form that 'diifer from the flake graphitic carbon of typical gray iron, but some of which agglomerates resemble the nodular carbon in malleableized white iron.

, This invention, therefore, has produced a new cast iron, which in its cast form and without any annealing or other treatment, has free, separated carbon but with the carbon in agglomerates of massive form which interrupt the iron, matrix, which gives the real strength tothe casting, much less than'in the 'case with ordinary gray is much above that of ordinary gray iron castings. and

good grades of malleableized iron castings; As a fair comparison the tensile strength of this new iron is upward of 60,000 lbs. per square inch, whereas the higher grade malleableized castings, have tensile up to about 53,000-55,000 lbs. per square inch, and ordinary gray iron castings have tensile strengths varying widely from under 20,000 lbs. up to 45,000 lbs. per square inch. The iron, however, is not ductile or subject to elongation under tension as is the case with malleableized iron nor has it any substantial capacity for bending, which is true, of course, of malleable iron which can be given a considerable bend without fracture or breaking. In this so-called shock or impact test, a test bar of iron has one end held in a vise, or some other equivalent mechanism, and the other end is struck with a pendulum in a precision machine for such impact testing, in which a free swinging pendulum of given weight and length is elevated to a predetermined height and released. The impact measurement is determined by a scale calibrated to show the foot pounds of energy absorbed to break the test casting. This new iron has a shock or impact test which is far in excess of that of a comparable cross-section gray iron casting. The impact test on a comparable cross-section malleableized white iron casting may be of no import, because of the bending characteristics of malleable iron.

Thus an entirely new iron is made available in cast form, of these characteristics, which gives it great superiority over ordinary gray iron in the respects mentioned, in that it has a high shock or impact test and therefore can withstand shocks or blows in use which Would be completely destructive of gray iron. It also has characteristics incertain respects which are superior to the malleableized white iron casting in that the greater tensile strength as stated above and the impact and transverse strength of the iron permits it to withstand shocks which might cause bending or distortion of a malleableized casting.

In the practicing of the invention it has been found that small proportions of misch metal, when introduced into the molten iron mix having constituents within the range of proportions set out below will result in the production of castings, which when completed and taken from the mold, will have the massive form of graphitic carbon with the various characteristics above referred to. Satisfactory results have been secured by the addition of misch metal to the molten iron mix in the ladle before pouring resulting in the graphitization efiect described whereby the finished casting when taken from the mold has the massive graphitic carbon with none or substantially none of the flake carbon which is normally present and is distinctive of gray iron castings, this massive carbon being present in the new iron when the casting is completed without the long and expensive annealing which is required to change a white iron casting into a so-called malleable casting. V

The misch metal referred to is available commercially, the mixture being generally uniform and a byproduct of the production of thorium, and its commercial composition is approximately within the ranges set out below:

Percent Cerium '-a 45 Lanthanum 25 Neodynium and praseodymium 15 Samarium 10 An iron mix containing constituents within the following percentage ranges:

Percent Carbon 3.0-4.3 Silicon 2.0-4.0 Manganese 0.4-2.0 Phosphorus 0.01-0.4 Sulphur "less than 0.04

has been found to satisfactorily produce this new iron when the misch metal in the proportion of about 0.25%

4 to 0.50% is added to the molten mix in the ladle before pouring.

Although only a small percentage of the misch metal is necessary to be added to the molten iron mix in the ladle to produce castings having the characteristics of this new iron, neverthelessthis represents an appreciable factor of cost. However, this cost is less than the expense of annealing white iron into a malleable iron, and the manufacturing cost of this much superior iron is usually somewhat more than a good grade of gray iron casting and somewhat less than a good malleableized casting.

Satisfactory results have also been secured by the addition of misch metal alloyed with aluminum to the molten iron mix in the ladle before pouring resulting in the graphitizaton effect described whereby the finished casting as cast has the massive graphitic carbon with none or substantially none of the flake carbon which is normally present in gray iron castings. The use of an alloy consisting of aluminum with substantial quantities of misch metal, has been found thus far to give highly satisfactory results in operation, having in mind the various factors mentioned above. Such an alloy containing approximately 25% misch metal and 75% aluminum gives a new iron casting with the desirable characteristics referred to and with the massive graphitic carbon formed in the iron while the casting is being produced in the mold.

The misch metal aluminum alloy has been found satisfactorily usable within the ranges:

Percent Misch metal 20-40 Aluminum 60-80 and satisfactory results have been secured with the addition of about 0.5% to 0.8% of such alloy depending upon the responsiveness of the iron mix to the new massive precipitation material.

It has also been found that when misch metal is added to the molten metal there is a comparatively short time interval during which sutficient of the misch metal will remain available in the molten metal to have the eifect of controlling to cause the massive agglomerates or aggregates of graphitic carbon to be separated or precipitated in the cooling metal in the mold (or from the high temperature solid solution metal in the mold). Probably due to oxidation, or perhaps reaction of the misch metal with some other materials present, the quantity intro; duced in the molten mix and effective to form the massive graphitic carbon is decreased rather rapidly, the time varying inversely with respect to the temperature of the molten iron in the ladle. In practicable operations producing castings of this new iron, it has been found that the misch metal, in the small percentage ranges specified as effective to produce massive graphitic carbon, will remain as such in sufficient quantity to produce the desired results for a period from about 7 to 13 minutes, after which time the production of the massive gr'aphitic carbon no longer occurs. If the misch metal is introduced into a ladle of molten iron which will be poured under such circumstances that the vitalizing reactions will not be terminated within the short period of pouring, the resulting castings will have the desired characteristics of this new iron.

It has been found, however, that if a longer period than the 7 to 13 minutes referred to is allowed to elapse before the molten iron is all poured into the mold and is in such condition of cooling that the massive graphite is not produced, the adding of small additional quantities of the misch metal described will compensate for so much of the active material of the misch metal as may have been lost through oxidizing, or the like, will restore the effectiveness of this material to produce the new massive graphite iron after the 7 to 13 minutes period stated. The misch metal seems to have a stabilizing effect in the molten iron against graphitic precipitation When the small amounts of the misch metal as referred to above are introduced into the molten iron mix the molten iron should be poured within a period of from about 7 to 13 minutes and unless this is done, it is found that the amount of effective material that is available to cause massive carbon to appear is diminished so that the misch metal is no longer effective to form massive carbon as desired. If the amount of misch metal added the the molten mix is increased too much it not only has a stabilizing effect in the molten iron but also inhibits the breaking down of the carbides after the iron becomes solid which in turn may inhibit the formation of massive carbon.

It has been found however that when additional amounts of misch metal are added into the ladle to prolong the pouring period, the inhibiting effects against the carbides breaking down in the solidified metal can be overcome provided a small percentage of an active graphitizing agent is added along with the misch metal. For example satisfactory results have been secured where the amount of the misch metal which is added is increased after this 7 to 13 minute period by the addition of about .2% on the mix, and at the same time 0.20% of a strong graphitizing agent such as calcium silicide was added, and under these conditions it was possible to increase the time of pouring and at the same time maintaining the stabilizing effect against graphitic precipitation and allowing the carbides to separate and form massive carbon. Not only does the addition of the massive carbon forming metal build up the massive carbon forming characteristics to approximately the original eifectiveness but when added along with a small percentage of the graphitizing agent the period during which this massive carbon forming graphitization will still take place is quite considerably increased, to as much as the 7 to 13 minutes of the original addition which in most cases will be ample for commercial foundry practices. To assure ample time for satisfactory operations over 20 to 26 minutes, however, it may be found desirable to add a second addition of about 0.2% of the misch metal, and a second corresponding addition of about 0.2% of a strong graphitizing agent and a satisfactory casting of the massive carbon containing iron will thus be assured within the maximum time mentioned and without inhibiting the decomposition of the iron carbides.

While the process and product herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise process and product, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A process of producing iron castings of the character described in which the carbon which may form during the casting and cooling thereof is present as free carbon in the form of massive agglomerates and with substantially no separation of flake graphitic carbon which comprises the steps of preparing a molten gray iron mix, adding to said mix before pouring a limited small amount of an alloy of about 25% misch metal and 75% aluminum sufiicient to inhibit the formation of said flake graphitic carbon, pouring said molten mix into a mold and removing the casting from the mold as a finished casting and without subsequent annealing.

2. A method of producing new iron castings of the character described having carbon formed during the casting and cooling thereof present as substantially free carbon in the casting as cast and without subsequent annealing which comprises the steps of preparing a molten iron mix, adding to said mix just before pouring a predetermined small percentage of about 0.25% to 0.50% of a reaction material consisting essentially of misch metal effective to inhibit primary graphitization and formation of flake graphitic carbon, pouring said molten mix before exhaustion of said inhibiting eifect to form a casting in which the carbon is present as free carbon and in generally massive agglomerate form.

3. A process for producing iron castings of the character described in which graphitic carbon is present in the as-cast state as agglomerates of massive or nodular form and with substantially no separation of flake-like graphitic carbon, which process comprises the steps of preparing a molten gray iron mix, adding to said mix before pouring a predetermined controlling amount of 0.5% to 0.8% of an alloy comprising about to 40% misch metal and 60% to 80% aluminum, pouring said molten mix into a mold and removing the casting from the mold as a finished casting.

4. A process for producing iron castings of the character described in which graphitic carbon is present in the as-cast state as agglomerates of massive or nodular form and with substantially no separation of flake-like graphitic carbon, which process comprises the steps of preparing a molten gray iron mix, before beginning to pour said mix making a first addition to said mix of a predetermined small graphite controlling amount of an alloy of misch metal and aluminum, beginning to pour said mix to form a casting, approximately seven to thirteen minutes after said first addition and before the pouring of said mix is completed making a second addition of a small modifying amount of said alloy less than said first addition and sufliicient to inhibit precipitation of flake-like graphitic carbon, and completing the pouring of said mix to form a casting having graphitic carbon present as said agglomerates without subsequent annealing.

5. A process for producing iron castings of the character described in which graphitic carbon is present in the as-cast state as agglomerates of massive or nodular form and with substantially no separation of flake-like graphitic carbon, which process comprises the steps of preparing a molten gray iron mix, before beginning to pour said mix making a first addition to said mix of a predetermined small graphite controlling amount of approximately 0.25% to 0.5% misch metal, beginning to pour said mix to form a casting, approximately seven to thirteen minutes after said first addition and before the pouring of said mix is completed making a second addition of a small modifying amount of said misch metal less than said first addition and sufficient to inhibit precipitation of flake-like graphitic carbon, and completing the pouring of said mix to form a casting having graphitic carbon present as said agglomerates without subsequent annealing.

6. The process of producing nodular gray iron castings of the character described having enhanced physical properties and in which substantially all the free carbon is in nodular form and with substantially no separation of fiake graphitic carbon which comprises the steps of preparing a molten gray iron mix, adding to said mix in the ladle just before pouring about 0.5 by weight of misch metal for controlling precipitation of said graphitie carbon into said nodular form, and pouring said molten mix into a mold to form said casting.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,760 Millis et al. Oct. 25, 1949 2,488,511 Morrough Nov. 15, 1949 FOREIGN PATENTS 474,689 Belgium August 1947 OTHER REFERENCES Metals and Alloys, September 1934, pages 188 and 189.

Paper No. 875, Presented at the forty-fourth Annual meeting of The Institute of British Foundrymen, Nottingham, England, June 17 to 20, 1947.

American Foundrymen, April 1948, pages 91 to 106.

Claims (1)

1. 6. THE PROCESS OF PRODUCING NODULAR GRAY IRON CASTINGS OF THE CHARACTER DESCRIBED HAVING ENHANCED PHYSICAL PROPERTIES AND IN WHICH SUBSTANTIALLY ALL THE THE FREE CARBON IS IN NODULAR FORM AND WITH SUBSTANTIALLY NO SEPARATION OF FLAKE GRAPHITIC CARBON WHICH COMPRISES THE STEPS OF PREPARING A MOLTEN GRAY IRON MIX, ADDING TO SAND MIX IN THE LADLE JUST BEFORE POURING ABOUT 0.5% BY WEIGHT OF MISCH METAL FOR CONTROLLING PRECIPITATION OF SAID GRAPHITIC CARBON INTO SAID NODULAR FORM, AND POURING SAID MOLTEN MIX INTO A MOLD TO FORM SAID CASTING.