US2046912A - Hard cast iron alloy - Google Patents

Description

Patented July 7, 1936 UNITED STATES PATENT OFFICE.

HARD CAST IRON ALLOY No Drawing. Original application January,

1934, Serial No. 707,036. Divided and this application May 24, 1934, Serial No. 727,278

Claims.

The present invention relates to a hard cast metal alloy or mixture, and the objects of the invention are directed to the production of a cast iron alloy of unusual physical properties not heretofore obtained in cast iron or in any ferrous metal mixture or alloy, except at considerable expense and usually accompanied by certain undesirable characteristics such, for example, as

=,extreme brittleness or extreme high melting point. We shall herein refer to our metal as an alloy in the sense of a mixture of metal and other ingredients so combined and integrated that the individual metal and non-metal elements have lost their individual characteristics. So far as our determinations have gone, we believe our new metal is an alloy in the sense stated, but we do not desire to state absolutely that it is in this condition, preferring to state its properties and composition, and herein the term alloy is used to mean either a true alloy or a mixture.

This case represents a divisional application of our case filed under Serial No. 707,036 on January 17, 1934, which matured into Patent No. 2,025,060 dated December 24, 1935.

The principal object of our invention is to provide a relatively inexpensive cast iron alloyas distinguished from steelwhich shall have a melting point sufliciently low to allow it to be readily bonded to other metal by being cast thereon to form a coating affording characteristics not possessed by the metal with which it is combined. One of the most important characteristics in our alloy is its extreme hardness and resistance to wear, and it is this characteristic, perhaps, more than any other, which provides its wide range of usefulness both as a metal for use in articles consisting entirely thereof and ma coating applied :to selected parts of other articles. Before proceeding to describe our invention, it may be noted that hardness and resistance to wear and abrasion are usually associated with steel and particularly certain alloy steels which are expensive to produce, difllcult to use, and

usually-high in melting point. Steel is distinguished from cast iron by the carbon content which in steel ranges from 0.1% to 1.7%, and in cast iron generally runs from about 2% to somewhat above 4%. 'The present invention is, therefore, directed specifically to the production of a cast iron alloy and to one having a carbon content ranging between 2% and about 4%, a silicon contentnot exceeding 2/z%, though preferably lower, and not more than 0.1% of sulphur or phosphorus.

While ordinary cast irons from which we produce our new alloy invariably contain silicon in some amount, we do not wish to be precluded from using a silicon free cast iron, since the presence of silicon is unnecessary to the formation of our alloy or to the unusual characteristics thereof herein described, and is detrimental in amounts over 2 and we prefer to keep the silicon content as low as practicable, say about 1% or preferably less.

Cast iron of the above analysis represents a good standard quality of gray iron which is generally available. Our invention consists, briefly stated, of an alloy of such cast iron with a small amount of a hardening agent capable of combining completely with the iron and the carbon content thereof to produce a cast iron alloy consisting of from about 92% to about 98% of iron, and 2% to 8% total of carbon, the hardening agent, silicon, and other impurities. The specific hardening agent here described as a constituent of our alloy is boron.

Our new alloy may be made by melting cast iron of approximately the analysis stated above and adding thereto boron or a boron-containing material, such as ordinary borax, in an amount hereinafter specified, continuing the heating until the boron is incorporated in the molten mixture and subsequently when in the solid state is combined with the iron and the carbon content thereof. The molten alloy may then be poured directly into molds for the production of the desired castings or into pigs of any desired shape for subsequent melting and use. Since the method of making our new alloy forms no part of the present invention, no further or more detailed description thereof is necessary herein.

The "properties of our improved alloy depend to some extent upon the quantity of the hardening agent employed and its relation to the carbon content, but for most purposes we have found that the unique properties desired can be obtained'in our improved iron alloy with from 0.15% to 4% of boron. An iron alloy containing approximately 3% of carbon, 1% to '1%% of boron, and 1% or less of silicon, will the combined percentage of these two constituents exceeds about 6%, carbon will be precipitated as graphite and the hardness and other desirable qualities of the alloy will be lowered. The same result is produced by increasing the silicon content and the maximum permissible percentage of silicon is approximately 2.5%, though it should usually be kept well below this amount. The total phosphorus and sulphur content should not be over 0.5% and should preferably be kept below this or it may be eliminated, if possible. The phosphorus content should be kept below 0.1% and preferably under 0.05%.

It might be mentioned here that aluminum should be avoided in this alloy as a few percent detrimentally affects the hardness.

A composition for the alloy which we have found to be extremely valuable for general use by reason of the physical properties consists of approximately 1% of the hardening agent, 3% carbon, approximately 1 to 1.5% silicon and approximately iron, with sulphur and phosphorus each not over 0.1%. This alloy is extremely hard and resistant to wear and abrasion, adapting it for many uses where ordinary cast gray iron, or even white iron, can not be satisfactorily used, such, for example, as where used under constant frictional movement with such abrasive material as sand, finely divided metal, or the like. While the hardness is'to some extent dependent upon the percentage of boron in the alloy, from 1% to 1 of boron will produce a metal having a hardness of about 600 or higher as measured on the monotron Brinell scale. By increasing the boron to approximately 1.7%, the hardness is increased to be tween 700 and 800 Brinell, and by higher per centages about 900 Brinell may be reached.

The property of high resistance to wear and abrasion of this alloy is not, of course, identical with hardness, but in comparison with a good grade of cast gray iron, it is approximately five to ten times more resistant to wear when rubbed one against the other. This property to an even greater degree than the hardness adapts the material to wear resistance under extreme conditions.

Another property of our alloy which greatly facilitates its use, particularly in connection with other materiali. e. where it is applied as a coating-is its low melting point which is below 2050 F. and ranges from 1950 F. to 2000 F. with the analysis given above.

Another property which sharply distinguishes the present alloy from ordinary cast iron is its thermal conductivity which is less than one-fifth the conductivity of ordinary cast gray iron. With a boron content of as low as 0.22% the conductivity is 7.5% B. t. u. per hour per square foot of one foot thickness and runs as low as 4.3% B. t. u. for a boron content of 2.5%.

Another important property of our alloy is its low coefficient of friction which is approximately half that of cast gray iron. Its low coefficient of friction makes it extremely desirable for the uses already referred to, also for such articles as cylinders, pistons, plungers, or other articles moving under pressure against another metal.

The tensile strength of the alloy is approximately 24,000 pounds per square inch which is slightly above the strength of all but the best grades of gray iron. Its modulus of elasticity is about 34,000,000 pounds, or approximately twice that of cast gray iron, and its thermal expansion is 3.12 times 10" per degree Fahrenheit as compared with cast iron, the thermal expansion of which is 539x10 The thermal conductivity has already been stated to be from a third to about a sixth that of gray iron.

From a study of the above properties of our improved alloy, it will be readily apparent that the alloy is sharply distinguished in its physical characteristics from gray iron and ordinary white iron and has certain propertieswhich either approximate or exceed those of expensive steel alloys which, by reason of their melting point, cannot be used for the purposes already referred to and for many other purposes for which our alloy metal is ideally adapted.

Our present alloy provides for the first time a relatively inexpensive cast iron alloy, as distinguished from steel, which has a sufliciently low melting point to allow it to be readily used in the arts as against other materials, which also possesses the extreme hardness and resistance to wear which have heretofore been found only in expensive alloy steels and other alloys of high melting point. We desire to emphasize the fact that our alloy is an alloy of cast iron and not a steel and that totally different properties are secured in this cast iron alloy than can be secured in steels to which the same or different percentages of the present or other hardening agents have been added. We are aware that various hardening agents including boron have been experimented with in attempts to harden or improve steel and in some cases forthe purpose of hardening iron, but without material success because of the failure to recognize the importance of the carbon range and the relationship existing between the total content of carbon and the hardening agent, and the fact that the carbon present in the alloy must be in combined form with the iron and the agent if the improved properties hereinbefore stated are to be secured. The carbon in our alloy being all in combined form yields a metal free from graphitic carbon, and showing a silvery white fracture.

We claim:

1. A hard substantially unmachinable cast ferrous alloy containing: combined carbon ranging from about 2 to 4%, boron ranging from about 0.2 to 3%, silicon in amount not exceeding about 2/z%, sulphur and phosphorus together not exceeding about 0.5%, substantially the balance being iron; the combined carbon and boron content ranging between about 3 and 6%; said alloy as cast characterized by a hardness ranging from about 400 to 900 monotron Brinell, an internal structure substantially free from graphitic car- 5 bon, a silvery white fracture, a melting point below 2050 F., and retaining said characteristics upon successive remeltings and castings.

2. A hard substantially unmachinable cast ferrous alloy containing: combined carbon ranging from about 2 to 4%, boron ranging from about 0.75 to 2/2%, silicon in amount not exceeding about 2 /2%, sulphur and phosphorus together not exceeding about 0.5%, substantially the balance being iron; the combined carbon and boron content ranging between about 3 to 5/2%: said alloy as cast characterized by a hardness ranging from about 500 to 900 monotron Brinell, an internal structure substantially free from graphitic carbon, a silvery white fracture, a melting point below 2050 F., and retaining said characteristics upon successive remeltings and castings.

8. A hard substantially unmachinable cast ferrous alloy containing: combined carbon ranging from about 2 to 3 boron ranging from about 0.75 to 1%%, silicon in amount not exceeding about 2 /z%, sulphur and phosphorus together not exceeding about 0.5%. substantially the balance being iron; the combined carbon and boron content ranging between about 3'to 5Vz%; said alloy as cast characterized by a hardness ranging from about 500 to 900 monotron Brinell, an internal structure substantially free from graphltic carbon, 9. silvery white fracture, a melting point below 2050 F., and retaining said characteristics upon successive remeltings and castings.

4. A hard substantially unmachinable cast ferrous alloy containing: combined carbon ranging from about 2 to 3 /2%, boron ranging from about 1 to 1 A%, silicon in amount not exceeding about 2%, sulphur and phosphorus together not exceeding about 0.51%, substantially the balance being iron; the combined carbon and boron content ranging between about 3 to 5 /2%; said alloy as cast characterized by a hardness ranging from about 600 to 900 monotron Brinell, an internal structure substantially free from g-raphitic carbon, a silvery white tracture, a melting point below 2050 F., and retaining said characteristics upon successive remeltings and castings.

5. A hard substantially unmachinable cast ferrous alloy containing: combined carbon ranging from about 2 to 3'/ boron ranging from about 1 to 1 silicon in amount not exceeding about 1%, sulphur and phosphorus together not exceeding about 0.4%, substantially the balance being iron; the combined carbon and boron content ranging between about 3 to 5 /2%; said, alloy as cast characterized by a hardness ranging from about 600 to 900 monotron Brinell, an internal structure substantially free from graphitic carbon, a silvery white fracture, a melting point below 2050 F., and retaining said characteristics upon successive remeltings and castings.

FREDERICK A. KORMANN. WALTER F. HIRSCH.