US2515822A

US2515822A - Gray iron castings

Info

Publication number: US2515822A
Application number: US713397A
Authority: US
Inventors: Lester C Crome
Original assignee: Dayton Malleable Iron Co
Current assignee: Dayton Malleable Iron Co
Priority date: 1946-11-30
Filing date: 1946-11-30
Publication date: 1950-07-18
Anticipated expiration: 1967-07-18

Description

Patented July 18, 1950 2,515,822 4 GRAY IRON CASTINGS Lester C. Crome, West Alexandria, Ohio, assignor I to The Dayton Malleable Iron Company, Dayton, Ohio, a. corporation of Ohio No Drawing.

Application November 30, 1946,

Serial No. 713,397

6 Claims. 1

This invention relates to gray iron castings and to methods of producing the same.

In producing gray cast iron in accordance with practices heretofore in common use, difflculty has been encountered, especially in casting shapes having corners, projections, and the like, because of the tendency of the gray iron to chill in such regions with resulting production of hard corners which presented difiiculties in machining. For example, a particular clutch ring required in large quantities consists of an annular disc havin a number of integral projections extending outward from one face of the disc. The projections normally have rather sharp corners and, when the ring was cast from gray iron in the usual way, these corners often chilled and could not be machined properly because of the hard, brittle and generally nonuniform characteristics of the chilled metal.

Also, ordinary gray iron castings normally contain considerable amounts of free ferrite, e. g., ferrite in addition to that which is present as a constituent of pearlite likewise normally found in gray irons, and this free ferrite has further contributed to machining difficulties because of its tendency to foul the machine tool.

The tendency of the iron to chill can be reduced by using a softer gray iron mix, such as a mix containin an increased amount of silicon or other graphitizing agent, such as lithium, zirconium, aluminum or titanium, and it is the general practice in the industry to adjust the silicon content to produce a casting free of chilled hard corners or edges. While this expedient may be effective in avoiding or minimizing the formation of hard corners, at the same time, it tends to increase the ferrite content of the iron and, as a consequence, lowers materially the Brinell hardness of the product. In the case of many products, such as the clutch ring hereinabove described, however, service specifications require high Brinell hardness values as well as good machineability and this has presented conflicting requirements diflicult of attainment by the previous practices in the art.

Furthermore, the metallic matrix of conventional gray iron usually lacks uniformity of structure even outside the chilled regions and, for this additional reason, does not machine with full satisfaction.

It is accordingly a principal object of the invention to so modify the characteristics and properties of ordinary gray irons as to provide improved gray iron castings exhibiting the qualities of substantial absence of hard chilled regions and resulting improved machineability combined with high Brinell hardness values.

A further object is to provide gray iron castings exhibiting more uniform matrix structures which may be machined more satisfactorily than ordinary gray iron castings.

Another object is to so modify the composition of a conventional gray iron mix as to produce therefrom, after casting the mix in the usual way, a gray iron casting of substantially reduced chill without objectionable sacrifice of hardness.

It is also an object of the invention to provide simple, economical and dependable methods of producing gray iron castings exhibiting such improved characteristics.

Other objects and advantages of the invention will become evident from the following description taken in conjunction with the appended claims.

In producing gray iron castings in accordance with the present invention, the desirable freedom from hard corners is retained and, in addition, the undesirable lowering of hardness normally resulting from an increased silicon content is avoided and a final product is obtained which has the combined advantages of such freedom from hard corners together with a maintained or, if desired, increased hardness as may be desirable in any particular instance.

This is accomplished, in accordance with the invention, by preparing a conventional gray iron mix containin the usual constituents of such a mix including a raphitizing agent, in accordance with the general practice hereinabove referred to, in an amount which normally would produce a casting free of hard corners but exhibiting undesirably low hardness and undesirably high content of ferrite, and then incorporating in the mix, while it is in a molten condition and prior to pouring, a small amount of a modifying or addition agent which has the property of counteracting or off-setting the undesirable effects of the graphitizing agent and stabilizing the eutectoid carbides of the mix during the period in which they would otherwise be subject to decomposition with accompanying production of free ferrite. Addition of such modifying agent inhibits and, it is believed, substantially prevents such decomposition and provides for stabilizing up to substantially the entire matrix in the form of pearlite to produce a casting in which the matrix is more uniform and consists predominantly of the pearlitic eutectoid mixture of ferrite and cementite and contains substantially no free ferrite, thus making it possible to secure a Brinell hardness corresponding to such highly pearlitic matrix formation while still avoiding hard chilled regions. Addition of lesser amounts of modifying agent provides intermediate controlling eifects of the same character.

As is well. known, when gray iron mixes are cooled from a molten to a solid condition, as when such compositions are cast in an ordinary sand mold, they undergo a series of transformations including the formation of eutectoid care bides initially consisting principally of. austenite followed by transformation of the austenite into other eutectoid carbides such as martensite,. pearlite and the like and, finally, in the usual case, with th production of a solid castiron containing a mixture of pearlite, flakes of graphitic carbon, perhaps some free cementite, and substantial amounts of free ferrite. In the present invention, however, the series of decompositions are inhibited in the later stages by stabilizing the pearlitic eutectoid against further decomposition so that, production of free ferrite is substantially avoidedand a matrix consisting essentially of pearlite of highly uniform structure is produced.

In practical effect, agray, iron. casting, of lower chi l and free of hardfcorners is obtained without. lowering the Brinellfihardness and,if desired, the Brinell hardness may in factv be increased substantially while still. avoidingv hard, chilled corners. Notwithstanding. such increased hardness, the castings of th present inventionv may be machined-with considerably greater easeand uniformity because of the absence of free ferrite and the resulting freedom from its usual fouling effect on the machine toolas. well asth'e greater uniformity of thematrix structure itself.

A preferred modifying agent for addition. to the gray iron mix in accordance with the present invention comprises. antimony which may. be added. to the molten mix eitherin th form of an alloy with another metal or in the .formof antimony alone, such as the lumnantimony'available. commercially. only. small amounts. of an-. timony are required to achieve the improved results described anditsbeneficial effects persist through the course of several successive castings and remeltings of the. modified iron mix.

Thus it has. been found that the addition to a usual gray. iron mix, prior to pouring, of av small percentage of the order of 0.05% of antimony based on. the total weightof the iron. mix is sufficient. to bring about the .marked improvements hereinabove described. Larger amounts. of antimony may, be. added if desired, but as, the amount of antimony. is increased. the iron tends to become more.brittle and. it. will usually not befound desirable to .addmore. than about 0.10% of antimony. Smaller amounts also may be added with somewhat decreased effect in the lower ranges andit will. ordinarily be desirable to use. effective amountsfrom 0.01% to 0.05%, about 0.04 to.0.05%. being preferred for-regular foundry practice.

The antimony may be addedmost conveniently by placing the requisite amount of lump antimony in the bottom of.a ladle and then running in the molten iron mix although the antimony also may be added afterithe ladle has been filled, or otherwise, prior. to the actual pouring of the metal.

Gray iron mixtures customarily aretapped at temperatures of 2700-2800 F. and' may cool down to temperatures of from 2400 to 2600 F. in the ladle, depending primarily upon the weight of casting being poured which in turn largely determines the time interval during which the molten iron mix will remain in the ladle. Since metallic antimony boils at 2624" FL, some loss of this material from the molten iron is to be expected and white vapors, believed to be vapors of antimony, have been observed coming off when antimony is placed in the bottom of a ladle hot from a previous pouring or when it is added to a ladle full of molten metal. Because of the difficulty of accurate analysis, no precise determination has been made of the amount of antimony lost'but it is estimated that as much as half may be lost by vaporization when 0.05% is added while considerably less than half the antimony would probably be lost if a smaller amount of the order of 0.01% were added.

It has also been found that such loss of antimony by vaporization may be reduced or, at least, that correspondingly-improved properties in the ironmay be secured with somewhat lesser amounts of antimony 'if it is added in the form of arr-alloy with another suitable non-ferrous metal such ascopper orlead which can be alloyed wit'h antimony and Which does not itself have any substantial deleterious eifect in the iron mix; For example; alloys of 10% antimony with 90 of either lead or copper and 20% antimony with of-either lead or copper will be foundquite suitable for addition to the molten iron in the same way lump'antimony is added as 'hereinabove described. The relative proportions ofthe alloy constituents are not critical insofar as the presentinvention is concerned, the only requisite being that the alloy contain an effective amount of antimony falling generally within the ranges hereinabove indicated. Ordinarily, however, smaller amounts of antimony in the lower portions of the indicated ranges, and perhaps as much as half the amount otherwise required, will be found adequately effective when added in-the form of an alloy, either because less antimony is then lost by evaporation or because of some synergistic efiect-not yetunderstood.

Notwithstanding possible loss of substantial portions of the added antimony by evaporation, its beneficial eifects persistthrough a series-of several castings and remeltings of themix, indicating either that'an effective amount of antimony remains in the mix; as such; or perhaps that the antimonyenters into-chemicalcombination with-some of the other ingredients to produce a new antimony-containing agent stable under casting temperaturesandeffective to produce the desired results.-

Specific: examples of gray-iron compositions modified by the addition; of antimony. in: accord-. ance with'the invention will nowbe set out, the amounts of antimony in each instance indicating the amount actually added to the molten iron mi-x and-not necessarily. the amountpersisting in the finished'cast iron:

Example 1,

Constituent: 7 Percent Silicon 2.90 Sulfur 0.125 Phosphorous 0.130 Manganese 0:60 Carbon 3.45" Antimony 0.05 Iron Balance Example 2 Constituent: Percent Silicon -1 2.60 Sulfur 0.135 Phosphorous a 0.130 Manganese 0.65

Carbon 3.40

Antimony 0.04 Iron Balance When prepared in the manner described and cast in the usual way in sand molds, each of the foregoing compositions will produce a high quality gray iron shape having a matrix of highly uniform structure consisting essentially of pearlits and containing substantially no free ferrite, the all-pearlitic matrix and the greatly increased uniformity of matrix structure being readily apparent when prepared surfaces of the castings are examined under a microscope in the manner well understood in the art and compared with similar castings made in the same way but for omission of the antimony. Undesirable chill and hard corners are substantially completely avoided but the Brinell hardness will be substantially higher than would be the case if the antimony were omitted. In utilizing the invention in the casting of the particular clutch ring previously mentioned, the resulting product was found to machine satisfactorily, even at the sharp corners of the upstanding projections, and the Brinell hardness was increased to values ranging from 200 to 235 instead of values ranging from 179 to 200 which normally are obtained with similar gray iron mixes without addition of antimony or similar modifying agents.

While the processes and products herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise processes and products, 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 gray iron casting of such composition, size and configuration as normally .to be substantially free of chilled hard regions difficult to machine satisfactorily and to have a Brinell hardness of the order of 179-200, said casting containing appreciable amounts of carbon in flake form and having a metallic matrix of great uniformity consisting predominately of pearlite to the substantial exclusion of free ferrite and containing as an essential constituent a small amount of antimony of the order of 0.01% to 0.10%, said casting being substantially free of chilled hard regions, and exhibiting a Brinell hardness of the order of 200-235.

2. A gray iron casting containing appreciable amounts of primary graphitic carbon in flake form and in which the metallic matrix consists predominately of pearlite to the substantial exclusion of free ferrite and which contains antimony as an essential constituent in an amount not exceeding about 0.10%.

3. A gray iron casting containing appreciable amounts of carbon in flake form and having a metallic matrix consisting predominately of pearlite to the substantial exclusion of free ferrite and containing as an essential ingredient for such condition an amount of antimony of about 0.01% to 0.05%.

4. A gray iron casting containing appreciable amounts of carbon in flake form and having as an essential constituent a small amount of antimony of the order of 0.01% to 0.10%, said casting in its final form being characterized by having a metallic matrix of great uniformity consisting predominantly of pearlite to the substantial exclusion of free ferrite, said casting having increased hardness compared with the same gray iron mix without antimony.

5. A composition of matter consisting essentially of gray iron cast from a molten mix and having a large preponderance of the carbon in the molten mix separated and distributed through the cast iron as primary graphite in flake form and with the remaining proportions of carbon combined as iron carbide uniformly admixed with ferrite to form essentially all pearlitic iron and containing antimony included in the molten mix and in an amount from 0.01% to 0.1% and less than would inhibit formation of primary graphitic carbon during the cooling of the molten iron mix to normal room temperatures.

6. A composition of matter consisting essentially of gray iron cast from a molten mix to separate a large preponderance of the carbon in the molten mix during transition of the molten mix to the solid state as primary graphite in flake form distributed through the solidified iron and the remainder of the carbon in the cast com position combined as iron carbide and uniformly admixed with ferrite to form essentially all pearlitic iron and containing antimony included in the molten mix and in an amount from 0.01 to 0.1% and less than would inhibit formation of primary graphitic carbon during the cooling of the molten iron mix to normal room temperatures, said solidified iron material having the pearlite distributed essentially uniformly throughout and the composition being substantially free from chilled edges or sections and from non-pearlitic regions.

LESTER C. CROME.

REFERENCES CllED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,973,263 Mitchell et al Sept. 11, 1934 2,253,502 Boegehold Aug. ,26, 1941 2,378,548 Gregg June 19, 1945 FOREIGN PATENTS Number Country Date 142,090 Austria June 11, 1935 809,815 France Mar. 10, 1937

Claims

1. A GRAY IRON CASTING OF SUCH COMPOSITION, SIZE AND CONFIGURATION AS NORMALLY TO BE SUBSTANTIALLY FREE OF CHILLDED HARD REGIONS DIFFICULT TO MACHINE SATISFACTORILY AND TO HAVE A BRINELL HARDNESS OF THE ORDER OF 179-200, SAID CASTING CONTAINING APPRECIABLE AMOUNTS OF CARBON IN FLAKE FORM AND HAVING A METALLIC MATRIX OF GREAT UNIFORMITY CONSISTING PREDOMINATELY OF PEARLITE TO THE SUBSTANTIAL EXCLUSION OF FREE FERRITE AND CONTAINING AS AN ESSENTIAL CONSTITUENT A SMALL AMOUNT OF ANTIMONY OF THE ORDER OF 0.01% TO 0.10%, SAID CASTING BEING SUBSTANTIALLY FREE OF CHILLED HARD REGIONS, AND EXHIBITING A BRINELL HARDNESS OF THE ORDER OF 200-235.