US2651570A - Manufacture of malleablized white cast iron - Google Patents

Description

Sept 8., 1953 R. w. HEINE 2,651,570

MANUFACTURE oF MALLEABLIZED WHITE cAsT IRON Filed Nv. 19 -1949 S 2.0 t U3 E 10 m g ir Q ALUM/NUM /U//o/V- INVENTOR.

Patented Sept. 8, 1953 umn-:o PATENT Richard `W. Heine,A Madison, Wis., assigner to Wisconsin Alumni Research Foundation, Mad son, Wiss,4 a' corporation of Wisconsin Application November 19, 149, serai No. 128,274

I Claim.l (Cl. 752130)? This invention relates, generally, to the manuj facture of whitev cast iron and it has particular relation to the' control of the annealing of graph# itizedA or malleablized Whitecast iron,` andthe chemical composition and the physical properff ties thereof. l

In thernanuiac'zture -of white cast' iron forl malleable purposes, it has not been normalmelting practice to accomplish deoxidation by ladle or furnace additions` It has been considered-v that the highY siliconcontent of castv iron Iowers the oxygen residual in the iron through the for-` mation of silica or silicatesA to such a value thatdeoxidation by the addition of another material' is unwarranted. ne reason for this is that it had not been realized previously that the xing of the oxygen by a powerful deoxidizer might produce effects of considerable signin-canoe i-n the malleabli-zingprocess when applied to White east' ironsv so treated.

Accordingly, among the objects of this invention are: to determine the time required for the mal-leablizing hea't treatment of white cast iron" so that the same will be accomplished in a minimum of time; to control thel physicalproperties" over a wide range: so aste provide readily those' desired for a particular application; toadd a' deoxi'dizer to the molten iron in ariamount so asv to provide the? minimum til-ne` for heat treatlnent for a given speciii'cation"V of physical characteristic's; to demonstrate how the amounty of deoxidizelrV to he' added can? bei vdei;erinled' for any' iron composition andmelting practice; and? to produceirons'- with lower'= silicon contents; and faster anne`a`iingl characteristics than have here-- tofore` been commercially feasible; n

Other" objects of th-isf invention will inpart-be obvious and in partappear herein'a-"fteriv For a more complete understand-ingof the'na''-' turev and scope of this invention, reference can be had to the followingdetailed description takentogether withv the accompanyingl drawing, ini:-

which:

Figure 1 shows a curve which indicates' the time required for complete first stage graphitization as' ordinates plotted against"-pe1-"centag'fe` a111- minum addition as abscissae'; and',

Figure 2` shows: a curveI which indieates' the ratio of the numbero'f graphite particles' in the untreated ironi to the number `of graphite parti'- cles in the aluminum@ treated iron as ordinates plotted againstA the percentage aluminum' additionas abscissae.

The curves shown Figures l and 2` appl-y to irons from a particular foundry and should be Z considered typical for that foundry'. other simi'- l'ar curves may be developed for the metal produced in another foundry.

the present inven'tion'is employed, the tirrerefduired for the' malleablizing heat treat ment of white cast iron can he' reduced to a I nini-g mur, the nur'nber of graphite nodules developed duringxthj'e heat treatment lnay loe controlled, and desired' physical properties may besobtainedjrang ingl frc'nnI Aheter than grade A to substantially any lesser values that maybe desired. Alsogra Wide variety of pearlitic nialjlea'ble irons may be pr'o-` duced in this way. Thev present invention de-' ponds for its success upon the relating of the oxygen content of the iron and extent of its deoxidation with a powerful' deoXidiZer to` these: variables, and aninit'ially satisfactory melting practice which will produce an iron that Will respond todeoxidiz'ing additionsvv according to the manner' herein described?. Further; this invention shows hov'v to determine whether and when a foundry is; producing an' viron which ifs Basically satisfactory in containing suili'cient` oxygen so thatl it will yrespond to the deox'idiz'ing treatments as setJK forth hereinaft'er. I'liee'xt'ent of deoxid'ation by' ad :itionstonrolten white castiron determines the" timereq-uired "for its annealing'.

In or'cleifto practice this invention, curves such asI those shownirr lliguresI 1 and' 2 are drawn for the particular iron composition to be used, theY melting pract ce' e""p'loye' l,k and other variable conditions for agiven foundry, curves the'zainount f, thedeoiiidize to be added may be selected so as to obtain any one' of the following:

1. sporto-'sr annealing sito; n

2. Max'iinni physical properties ,3. intermediate effect or0 characteristic which i'sa coin'proinise between the shortest annea'ling'" tii'ne' and maximum' physical properties.A

In practicingv theDresentinvention various' deoxidizing elements' or' combinations thereof*v can be; employed". For' creampie,v aluminum, zirconilling i'jit'a'ni-11111Ain"a`,g` hesi'mn',l boron, vanadium, calcillin',v or' silicon can. he employed- Combinations of these elements" can be used and; other eleinentsl having' a powerfur afnityfor oxygen in molten white cast' iron* olsooanjsto employed. specifi'- cally a'luii'nurn ran-ging lfrom` .005 to .l5 per cent, titanirnra'ngin'lg from .92' to .25' per cent, or zircon in' ranging from .02 to .30 per centy can be emp oyedf.- n Y For? the fastest annealing characteristics or shone er annealing time, the additiono'f the deoxi'dizi-ngt argent'should'v be suiicient to approach From these` complete deoxidation and still maintain the physical properties above the minimum values which are required. Such additions for this purpose would range from .04 to .15 per cent aluminum, .05 to .25 percent titanium, and from .05 to .30 per cent zirconium or equivalent amounts of other deoxidizing elements or combinations thereof.

It is preferred that the deoxidizing agent be added to the ladle and that the molten metal then be poured into it. The metal so treated should be cast into molds immediately.

The duration and temperature cycle of the heat treatment may be carried out over a broad range along the lines of conventional malleablizing treatment but keeping in mind that the steps employed should be such as to reduce the time required to a minimum. The minimum time for rst stage graphitization may be selected from the curve shown in Figure 1 for a given amount ofaluminum addition. For other deoxidizers a similar set of curves Would be prepared. Heating to the temperature indicated on this curve may be accomplished as rapidly as furnace equipment and casting design permit. Also, the

cooling from the rst stage to the second stage graphitization temperature may be accomplished as rapidly as furnace equipment permits. The second stage graphitization is carried out as rapidly as the silicon content and deoxidizer content will cause it to occur and generally would call for the cooling of the casting from about 1450 degrees F. to about 1200 degrees F. at rates varying from 80 degrees F. per hour down to '7 degrees F. per hour. For example, a complete heat treatment cycle may consist of heating the casting to from 1700 degrees F. to 1750 degrees F. in one to three hours, holding at this temperature range for from one to ten hours, cooling rapidly to 1430 degrees F., and then cooling from this temperature to 1.300 degrees F. at the rate of from 20 degrees F. to 40 degrees F. per hour. The total heat treating time should range from ve to twenty hours or longer.

In practicing this invention it is essential that the amount of the deoxidizing addition required to provide the shortest annealing time and required physical properties be very accurately controlled. If too great an amount of deoxidizer is added, the annealing time is correspondingly reduced but there is an undesired lowering in the physical properties. Accordingly, .an important part of the present invention is to show the exact amount of deoxidizing addition that is required to provide the shortest annealing time for a given set of physical characteristics.

The amount of addition agent which is used is not necessarily the same for each heat or batch of molten iron for the reason that the percentage of oxygen in the molten iron prior to the deoxidation is an uncontrolled variable in the usual foundry practice. The oxygen or degree of oxidation in the molten iron may vary from .005 per cent to .20 per cent and, accordingly, the percentage of deoxidizer addition must be correspondingly varied to a chemically equivaient extent. In order to determine the kdegree of oxidation of the molten metal so as to select correctly the percentage of deoxidizer which must be added, the following test can be conducted on a given batch of molten white cast iron.V If a foundry has an unusually well standardized melting practice, Where the oxygen is well controlled,` this test may not be necessary;

To va series of several small ladles increasing percentages of the deoxidizer are added. For example, aluminum in the percentages .02 per cent, .05 per cent, .08 per cent, .11 per cent, .14 per cent, and .17 per cent, are added to the small ladles. Then molten iron from the heat or batch to be tested is poured into each ladle. From each of these ladles having the different percentage of aluminum addition, a test sprue is poured of such a diameter and length that it may be fractured readily. After the test sprues have cooled and solidified, they are broken transversely and the fractures are examined for mottling. The minimum percentage of deoxidizing addition required to produce mottling in the white cast iron establishesthe maximum percentage of deoxidizer which is required to deoxidize the metal completely. Experience with this test in a particular foundry ultimately will reduce the number of test sprues required until usually only one or two are required to provide the necessary information. While the oxygen is not completely eliminated from an exact scientific standpoint Whenmottling is produced, the amount of oxygen remaining is ineffective. The term complete deoxidation, as used herein, describes that degree of deoxidation which is produced by a deoxidizing addition of aluminum of sufficient magnitude to cause mottling in the test sprue.

It will be apparent that this test determines the degree of oxidation of the molten iron prior to any deoxidation treatment. This, in itself, provides for controlling the physical characteristics of the resulting product. The quality of the malleable iron may be improved by using-this test. Y For example, in a foundry Where the melting practice does not introduce su'icient oxygen into the molten metal so that the desired physical characteristics result, the underoxidized character of the molten metal can be determined and the melting practice modified so as to be more oxidizing. Further tests can be made with aluminum as the deoxidizing agent, for example, until the desired physical properties and annealing time are obtained. Thus the test above set forth can be used as a process control by setting up a standard deoxidation specification. For example, the addition of .08 per cent of aluminum could be specified as a minimum for producing the mottling of the iron; this in order to control the physical properties and time of annealing. By specifying a minimum and a maximum per cent of deoxidizer addition necessary to produce the mottling effect, it is possible to control the oxygen content of the molten metal and its annealingY characteristics with respect to the physical properties and annealing time required.

In accordance with this invention, the deoxidizing treatment of the molten metal can be practiced when the extent of oxidation thereof has been determined by the test set forth above. It is preferred to have the molten metal sufficiently oxidized so that a minimum of .08 per cent aluminum is required to produce the mottle inthe test; Thehigher the amount of aluminum required to produce mottle in the test, the greater the deoxidizing treatment may become. While aluminum has been mentioned as being employed in the test to determine the degree of oxidation of the molten iron, it will be understood that the other deoxidizing elements mentioned hereinbefore can be employedV in lieu of aluminum.

. In order to speed up the annealing process and obtain high physical properties such as grade A.

malleable iron, additions up to .05 per cent aluminum orrits chemical equivalent of other deoxidizers may be employed. The amount to use for a given batch on which the test has been run may be found by deducting .10 per cent aluminum, or its equivalent of other deoxidizers from the amount required to produce mottle and then adding the diierence as a deoxidizing addition to the molten iron. Ordinarily the aluminum addition would range from .005 per cent to .05 per cent. Additions of this magnitude are employed to provide the best physical properties after a short annealing treatment. The required annealing treatment has been accomplished in as little as twenty-seven hours in a particular foundry, but this time may be decreased. The normal temperatures of malleablizing heat treatment are satisfactory.

When it is desired to obtain a more rapid annealing than outlined above with intermediate physical properties, for example, the production of grade B malleable iron, additions which are greater by .01 per cent to .04 per cent of aluminum over those specified above for producing grade A malleable iron may be used. Instead of aluminum other deoxidizers in amounts chemically equivalent to aluminum can be used. Better physical properties are obtained when smaller additions are employed while faster annealing is obtained by the use of larger additions.

Where the minimum of annealing time is desired and sub-standard physical properties are acceptable, additions up to the amount of aluminum or equivalent amount of other deoxidizer required to produce mottling may be used. As indicated, better physical properties are obtained using smaller amounts of addition agent While faster annealing is obtained when larger amounts are employed.

Where the machineability of the malleablized white cast iron is the important factor, the deoxidizing treatment can be employed. The larger the amount of the addition agent the better the machineability, as long as this agent functions as a deoxidizer.

Since certain changes can be made in the foregoing process and different steps may be employed in practicing the same, it is intended that all matter shown in the accompanying drawing and described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

What is claimed as new is:

Method of making white iron castings which are subsequently malleablized comprising; melting iron, removing a plurality of samples of the molten iron and adding thereto aluminum in graduated amounts ranging below that necessary to produce mottling to in excess thereof, combining with the molten iron a deoxidizing addition of aluminum equal to said amount required to produce mottlng less 0.10%, and thereafter casting the molten metal.

RICHARD W. HEINE.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,498,128 Sowers June 17, 1924 1,636,657 Schwartz July 19, 1927 2,253,502 Boegehold Aug. 26, 1941 2,253,574 Norbeck Aug. 26, 1941 2,595,567 Creme May 6, 1952 OTHER REFERENCES Cast Iron, pages 98, 99, and 100. Edited by l-Iateld. Published in 1912 by Charles Griiiin and Company, London, England.

Transactions, American Foundrymens Association, vol. 34, page 434. Published in 1934 by the American Foundrymens Association, Chicago, Illinois.

The Foundry, June 1945, pages 100, 101, 246 and 248.

Structure of Cast Irons, page 59, published in 1947 by the American Society for Metals, Cleveland, Ohio.

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