US3189443A - Iron founding - Google Patents

Description

June 15, 1965 H. B. LAUDENSLAGER, JR., ETAL 3,

IRON FOUNDING Filed Feb. 6, 1965 FIGJ FIG

INVENTORs Everett W. Hole 8 Harry B. LoudenslugegJr creased over the normal cycle.

United States Patent 3,189,443 IRON FOUNDING Harry B. Laudenslager, In, Jamestown, and Everett W.

Hale, Falconer, N.Y., assignors to Blackstone Corporation, a corporation of New York Filed Feb. 6, 1963, Ser. No. 270,484 8 Claims. (Ci. 75-123) This application is a continuation-in-part of our copending application Serial No. 47,197, filed August 3,

This invention relates to iron founding and particularly to a method of forming malleable iron free of the limitations heretofore placed upon its manufacture.

Malleable iron is a well known form of iron which is formed by annealing white cast iron under certain critical conditions to graphitize the combined carbon and leave the iron as ferrite. In the United States the term malleable iron refers to fernitic material of the blackheart .type (A.S.M. Handbook, 8th ed., p. 366) and it is to this type of iron that this invention is directed. In :the past, manufacturers of malleable iron have been limited in many respects. There are very strict limitations on. chemistry, section size and rate of anneal in conventional blackheart malleable practice. For example, in conventional blackheart malleable practice it is critical that the slow cool through the critical zone (about 1360 F.) should not exceed 7 F. per hour. Similarly, if the section size is too great, carbon is precipitated in the grain boundaries.

We have found that all of these limits are Very materially affected by the addition of pure magnesium to white iron prior to heat treatment in amounts such that there will remain a residual magnesium between about 0.02% to 0.05% in the iron. 7

It has long been known that the addition of magnesium and certain other alloy-s to cast ironjwould result in the formation of a ductile form of iron frequently termed nodular iron. These irons are normally a mixture of pearlite and ferrite in varying proportions and while ductile do not have all of the desirable properties'of a conventional blackheart malleable iron. These ductile irons have, in addition, an entirely different shrink rule which makes it impossible to satisfactorily cast from a conventional blackheart malleable pattern.

We have found that while the normal annealing cycle to convert combined carbon to ferrite and graphite in blackheart malleable iron requires a long time cycle, generally 30 to 120 hours, on a particular section, when made according to our practice takes only an 8 hour cycle to produce substantially identical result. well known that iron in sections larger than 1%"is difficult to cast satisfactorily for malleabilization. In order to overcome this difficulty in larger sections, it has been the practice in the past to add tellurium or a mixture of boron and bismuth. When tellurium or the bismuth mixture are added, the annealing cycle is substantially in- By' our practice, these larger sections may be annealed at a much reduced time cycle over the conventional method with the production of results equal or superior to .those produced by the use of tellurium or the bismuth mixture. In addition, when telluriurn or the bismuth mixture is used, the scrap cannot be generally used as remelt stock. When our practice is followed, the scrap may be used as remelt stock with- .out any difficulties arising therefrom. We have also found Similarly, it is Patented June 15, 1965 that by our practice it is possible to take white iron directly from the electric furnace, air furnace, cupola or whatever source is being used.

We have found that the rather critical limits on carbon and silicon content which conventional malleable practice requires are greatly expan ed as will appear here-after.

These limitations on blackheart malleable practice have long been recognized but no satisfactory solution has heretofore been proposed. Gagnebin, Patent 2,578,794, proposes to add sufficient magnesium and other alloys to cause the carbon nuclei to form into dense spheroids, radiating from the center differing from the blackheart type temper carbon and provides difierent physical characteristics in the resulting iron. Gagnebin points out that his spheroidal graphite is markedly different from blackheart type graphite and provides different physical characteristics in the resulting iron. Iron containing spheroidal graphite is difficult to weld; is diificult to galvanize; has different electr-ical characteristics and different casting characteristics,

shrinking at an entirely different rate than that of conventional blackheart malleable.

The practice of our invention can perhaps best be understood by reference to the following example:

Example I A white cast iron was prepared having the following composition:

The iron wastreated by the addition of silicon to raise th silicon to 2.5% for the purpose of increasing fluidity deoxidizing and strengthening the ferrite as the iron was poured into the ladle at about 2900 F. on an optical pyrometer. When the ladle was filled to the desired level, a cover was placed over the ladle and because of the high sulfur content calcium carbide was injected into the molten metal below the surface thereof through a hollow carbon tube by means of nitrogen at about 32 psi. This prQ- duced a flow of about 15 pounds of calcium carbide per minute and about 31 c.f.m. of nitrogen through the A orifice of the feed hopper with the end of the carbon tube within 3" of the bottom of the ladle. This practice reduced the sulfur to .O2%. 'If the sulfur content of the iron is low, this calcium carbide treatment may be omitted or the sulfur may be eliminated by the use of additional magnesium. After the completion of the calcium carbide injection, magnesium spheres were injected into the bath through the same carbon tube with an identical nitrogen gas carrier at the rate of about 4 pounds per minute until 0.5% magnesium was injected. The carbon tube was withdrawn, the nitrogen was shut off, the cover raised from the ladle. The magnesium addition was made in the form of magnesium metal spheres in the size rang of 6 to mesh. We have found that it is essential that at least 50% of the magnesium being added be in the form of spheres of 6 to 100 mesh. The balance may be powdered magnesium, fine flaked magnesium, magnesium chips or any other form of finely divided magnesium. The magnesium addition should be as pure metallic magnesium as possible since nickel, copper, chromium, aluminum, etc.

. a 3 I; in substantial quantities very seriously affect the iron by of the annealing cycle. The resulting iron was cast and (permitted to solidify. The resulting white iron casting was then annealed for three hours at 1650 F. and for iive hours at 1300 F. Theresulting malleable casting had properties equal to or exceeding those of a conventional malleable in the same form which would have required a long annealing cycle instead of the 8 hour cycle given the casting of the example. g

'The effect of nickel and copper on malleable iron is illustrated in the Transactions of the American Foundryimens Society, volume 56. This publication shows in .Table 4, appearing on page 413, that the introduction of nickel and copper in excess of 0.5% reduces the percent causing graphitization or by seriously affecting the results elongation of Grade A malleable below the minimum ac- V ceptable for Grade A malleable iron. In our material Percent fCarbon 1 to 4.0 :,;Manganese 0; to 1 iSilicon" 0.5 to 4.5 ZSillfur Up to 0.02 "Phosphorus Up to 0.15 Magnesium 0.02 to 0.05

The balance. iron with usual impurities in ordinary "amounts. We prefer, however, to produce our malleable within the narrower limits of:

The balance iron with usual' impurities in 'ordinary amounts.

jfThe ordinary impurities referred to are those which {are normally found in the foundryas the result of the .;addition of rernelt scrap. .amounts of nickel, chromium, copper, tin, aluminum, boron, calcium and the like in ordinary amounts within They may include small thelimits generally recognized asacceptable in malleable practice. -In no case, however, can the nickel, chromium or copper exceed about 0.5% collectively if a Grade A j malleable is desired.

The effect of section size with relation to our invention is perhaps best illustrated .by the photomicrographs which accompany this application and are identified as follows:

FIGURE 1--a photomicrograph of a malleable iron of I large section size not treated by our invention.

FIGURE 2--a photomicrograph of an identical section of thesame malleable iron containing 0.05% magnesium L according to this invention.

Referring to the figures, it will be noted that the photoi-micrograph of large section size identified as FIGURE 1 .shows a very high percentage of primary graphite precipitated in the grain boundaries, whereas FIGURE 2 shows, the elimination of .this primary type graphite from "the grain boundaries and the formation of ferrite and primary carbides acceptable'in blackheart malleable practice.

Thispractice can be used with any conventional maleral, eliminates the problems which have plagued the malleable iron foundingtechniques.

- the carbon appears as temper carbon in a matrix of ferrite like that of conventional blackheart malleable iron.

' I In our practice, we maintain the iron within the following broad composition limits:

7 Example 1 1 V This'composition was selected :to produce a malleable iron that possesses unusual cold forming propertieswhere- I i by the yield point is lowered and the elongation increased. 7

A White cast iron was prepared having the. same general composition as that of Example 1; Carbon was added-to:

produce a final composition of:

I Percent Carbon 3.75 Silicon 1.61 Manganese .31 Phosphorus .04

The molten mass was treated as in Example I by the injection of calcium carbide followed by pure magnesium spheres. The resulting final alloy-had the above composition with 0.037% magnesium as a residual and only a trace of sulfur. hours atl650 F. followed .by 5 hours at 1 300 F. The resulting casting was fully ferritic and had the following physicals: V

Yield 34,000 .p.s.i.

Tensile 54,000 p.s.i.

Elongation in 2".

Brinell V 131.

Example III 1 Another series of castings were made in the same man ner as Example 11 but to a final analysis of:

Percent Carbon 3.79 Silicon j 1.60 Sulfur 7 Trace Manganese 0.31 Phosphorus 0.04 Magnesium 0.04

After the same anneal cycle as described in Example 11 r a the castings had the following physical properties:

Yield 33,000 psi. Tensile 56,000 p.s.i. Elongation 24% in2". Brinelll 128. Earample' IV Another series of castings were made in the same manner as described in connection with Example I but to a final analysis of: 7

Percent Carbon 2.37 Silicon 2.2 1 Sulfur Trace Manganese 0.32 Phosphorus 0.04

Magnesium 0.43

The castings were annealed at 1650 F. for 2 /2 hours followed by 1300 F. for 4 hours. The physical tests showed the following results using a standard A.S.T.M.

ileable type iron to produce a malleable which is free of {the limitations on section size and on chemistry which j were heretofore placed on malleable practice. The practice of our invention permits a greater freedom in the use of starting materials, a greatly accelerated annealing cycle to form the graphitized malleable structure and, in gen- %unmachined malleable test bar: a

45 ,000 p.s.i.

Yield Tensile 64,000 p.S.i.

Elongation 25.78% in 2".

Brinell Example V A similar high silicon series of castings were made in the same manner as Example IV to the following analysis:

- 'Percent Carbon 2.37 Silicon 4.34 Manganese 0.32 Sulfur Trace Phosphorus 0.032

Magnesium 0.042

The metal was cast and annealed for 3 The physicals were:

The malleable irons made according to our invention may be treated by the conventional practices of the malleable foundry art and give the maximum physical properties under those conditions. Tempering and stress relieving of our malleable may be accomplished by heating to temperatures ranging from 600 F. to 1300 F. depending upon structures and hardness desired. A significant and important factor, however, is that the time period for each of the heat treatment steps may be drastically reduced in the case of our malleable.

Our practice also permits us to make malleable irons having higher and lower carbon and higher silicon contents than any malleable practice heretofore known. The practice of our invention substantially eliminates the hot tear problem upon solidification. This is a very real problem in conventional malleable practice. These factors give us a flexibility of composition and handling previously unknown to the foundry art.

We have found that the malleable iron produced according to our invention has welding characteristics entirely different than conventional malleable iron and iron containing carbon in the form of spheroidal graphite. We have made welds on a material according to our Example I and compared them to welds made on conventional malleable material having the composition:

C 2.15 Si 1.50 S 0.044 Mn 0.24 Mg 0 P 0.049

and with welds on iron containing carbon in spheroidal The weld on the material of this invention showed the carbon remaining in combined form free from flake type graphite, whereas the iron containing graphite in spheroidal form showed flake graphite throughout the weld area. Physical tests of the three welds Without heat treatment or stress relieving showed that the tensile strength of the weld in the malleable iron of our invention was actually higher than that of the surrounding base metal whereas in both the conventional malleable and the iron with spheroidal graphite the tensile strength was much less than that of the surrounding base metal. Like welds on each material were subjected to twisting through 90 at room temperature. The test piece of our invention showed no tearing or cracking whereas both of the other test pieces failed as evidenced by fractures, cracking and surface checking.

While we have illustrated and described certain preferred practices of our invention, it will be understood that this invention may be otherwise embodied within the scope of the following claims.

We claim:

1. The process of producing blackheart type malleable iron substantially free from section criticality comprising the steps of melting a white iron composition substantially free of nickel and copper above the normal residual amounts acceptable in conventional malleable practice and consisting essentially of about 1% to 4% carbon,

about 0.5% to 4.5 silicon, manganese up to about 1%, sulfur up to about 0.02%, phosphorus up to about 0.15%,

and the balance iron with usual impurities in ordinary amounts, adding thereto metallic magnesium at least 50% of which is in the form of spheres of 6 to mesh size in an amount sufiicient to produce a residual magnesium between about 0.02% to 0.05%, casting the resulting molten mass, solidifying the cast and annealing to produce graphitization of carbon and feritization of the iron.

2. The process of producing blackheart type malleable iron substantially free from section criticality comprising the steps of melting an iron composition in which all of the carbon is in the combinedform and which is substan tially free of nickel and copper and consisting essentially of about 2% to 3.5% carbon, about 1.5% to 4% silicon, about 0.2% to 0.8% manganese, up to about 0.02% sulfur, up to about 0.15% phosphorus, and the balance iron with usual impurities in ordinary amounts, adding thereto metallic magnesium at least 50% of which is in the form of spheres of 6 to 100 mesh size in an amount sufficient to produce a residual from about 0.02% to about 0.05%, casting the resulting molten mass, solidifying the cast and annealing to produce graphitization of carbon and ferritization of the iron.

3. The process of producing blackheart type malleable iron substantially free of section criticality comprising the steps of preparing a white iron composition substantially free of nickel and copper, containing about 1% to about 2.5% carbon about 0.5% to 4.5 silicon, manganese up to about 1%, sulfur up to about 0.02%, phosphorus up to about 0.15 and the balance iron with usual impurities in ordinary amounts, adding thereto metallic magnesium at least 50% of which is in the form of spheres of 6 to 100 mesh size, in an amount suflicient to provide a residual from about 0.02% to 0.05%, casting the resulting molten mass, solidifying the cast and annealing to produce graphitization of the carbon and ferritization of the iron.

4. The process for producing blackheart type malleable iron comprising the steps of melting a white iron composition consisting essentially of about 1% to 4% carbon, about 0.5 to 4.5% silicon, manganese up to about 1%, sulfur up to about 0.02%, phosphorus up to about 0.15%, and the balance iron with usual impurities in ordinary amounts, injecting metallic magnesium into the molten iron composition in the form of spheres having a size range between about 6 to 100 mesh in an amount sufficient to provide a residual magnesium content in the iron of about 0.02% to about 0.05%, casting the resulting molten mass, solidifying the cast and annealing to produce graph itization of carbon and ferritization of the iron.

5. A blackheart type malleable iron consisting essentially of about 1% to 4% carbon, about 0.5% to 4.5% silicon, manganese up to about 1%, sulfur up to about 0.02%, phosphorus up to about 0.15%, magnesium about 0.02% to 0.05 balance iron with usual impurities in ordinary amounts and characterized by substantial freedom from section criticality and hot tearing and by improved weldability.

6. A blackheart type malleable iron consisting essentially of about 2% to 3.5% carbon, about 1.5% to 4% silicon, about 0.2% to 0.8% manganese, up to about 0.02% sulfur, up to about 0.15% phosphorus, about 0.02% to 0.05% magnesium and the balance iron with usual impurities in ordinary amounts and characterized by substantial freedom from section criticality and hot tearing and by improved weldability.

7. A blackheart malleable iron consisting essentially of about 1% to 4% carbon, about 0.5% to 4.5% silicon, manganese up to about 1%, sulfur up to about 0.02%, phosphorus up to about 0.15%, magnesium about 0.02% to 0.05 balance iron with usual impurities in ordinary amounts and in which after annealing the carbon is present in the form of temper carbon in a matrix of ferrite, said iron being characterized by substantial freedom from I lability. V

1 j .,8."A blackheart malleable iron consisting essentially of about 2% to 3.5% carbon, about 1.5% to'4%,si1icon,

about. 0.2% to 0.8% manganese, up .to about 0.02% 5111- i fur, up to about 0.15% phosphorus, about 0.02% to 0.05% magnesium, thebalance iron with usual impurities in ordinary amounts and in which after annealing the V carbon is present inthe form of temper carbon in a matrix .section criticality and hot tearing and by improved weldfreedom from section criticality and'hot tearing; and by improved weldability.

References Cited by the Examiner 3,080,228 3/63 Hale et a1. 75130 3 of ferrite, said iron being characterized 'by substantial DAVID L. RECK, Primary Examiner. V

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No a 3, 189,443 June 15, 1965 Harry B Laudenslager, Jr., et a1 It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 58, for "rang" read range column 4, line 55, for "0,43" read 0.043

Signed and sealed this 28th day of December 1965,,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. THE PROCESS OF PRODUCING BLACKHEART TYPE MALLEABLE IRON SUBSTANTIALLY FREE FROM SECTION CRITICALITY COMPRISING THE STEPS OF MELTING A WHITE IRON COMPOSITION SUBSTANTIALLY FREE OF NICKEL AND COPPER ABOVE THE NORMAL RESIDUAL AMOUNTS ACCEPTABLE IN CONVENTIONAL MALLEABLE PRACTICE AND CONSISTING ESSENTIALLY OF ABOUT 1% TO 4% CARBON, ABOUT 0.5% TO 4.5% SILICON, MANGANESE UP TO ABOUT 1%, SULPHUR UP TO ABOUT 0.02%, PHOSPHORUS UP TO ABOUT 0.15%, AND THE BALANCE IRON WITH USUAL IMPURITIES IN ODINARY AMOUNTS, ADDING THERETO METALLIC MAGNESIUM AT LEAST 50% OF WHICH IS IN THE FORM OF SPHERES OF 6 TO 100 MESH SIZE IN AN AMOUNT SUFFICIENT TO PRODUCE A RESIDUAL MAGNESIUM BETWEEN ABOUT 0.02% TO 0.05%, CASTING THE RESULTING MOLTEN MASS, SOLIDIFYING THE CAST AND ANNEALING TO PRODUCE GRAPHITIZATION OF CARBON AND FERITIZATION OF THE IRON.

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