US1707529A - marshall - Google Patents

Description

April 2, 1929' 2 L. H. MARSHALL 1,707,529

METALLURGICAL PROCESS AND PRODUCT Filed Jan. 19, 1925 4 Sheets-Sheet 1 0 24 73 .94 we I44 146 1.92 2/6 77'me I'n l/aurs LESLIE h. M/ms/Mu April 2, 1929- w L. H. MARSHALL 1,707,529

METALLURGICAL-PROCESS AND PRODUCT Filed Jan. 19, 1925 4 Sheets-Sheet 2 .932 1/12 TEMPE/PA TUEEFHHR'NHEIT F71 a. 2.

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Patented Apr. 2, 1929.

UNITED STATES maria PATENT OFFICE.

LESLIE H. MARSHALL, OF MANSFIELD, OHIO, Aofa'IGNOB TO THE OHIO BRASS COM- PANY, OF MANSFIELD, OHIO, A CORPORATION OF NEW JERSEY.

METALLUBGICAL PROCEfiS AND ERODUCT.

Application filed January My invention relates to malleableized cast iron, and the manufacture of the same. Malleableized cast iron is the result of changing the combined carbon of a casting into a free or graphitic carbon whereby the original casting, which is very hard and brittle, becomes soft and ductile, easily machined and even bent under satisfactory conditions.

The production of malleableized cast iron may be said to comprise two principal steps-first, that of casting the desired article out of hard or white iron in which the carbon is in a chemically combined condition andsecond, annealing the hard iron casting, that is, subjecting the hard, brittle casting to a proper heat treatment whereby the combined carbon will be converted into a free or graphitic carbon.

The production of malleableized cast iron is an old art, but under the present process or processes for producing malleableizcd cast iron the physical properties are not uniform and reliable and there is no assurance they can be Zinc-coated, as by the hot dipped and Sherardizing processes, etc. without embrittlement.

My invention has particularly to do with the annealing cycle and possesses several advantages, namely; the production of A product which will be uniform as to its physical properties and hence reliable,

A product which for any given composition possesses a relatively high impact value as measured by an impact machine,

A product which can be given a rust proofing coating, (such as hot galvanizing or Sherardizing) under heat without embrittlemcnt of the casting,

A product which can be produced in a shorter time than a product subjected to the present commercial process or processes of annealing,

A product having a uniform distribution of its ingredients and hence homogeneous.

Referring to the drawings:

Figs. 1, 2, and 3, show certain curves employed in describing my invention and in differentiating it from the prior art, as will hereinafter more clearly appear.

Fig. l is a perspective view of a furnace which may be employed in carrying my invention into practice.

Fig. 5 is a section on the line 5 5 of Fig. 41-.

As new carried out, generally the process 19, 1925. Serial No. 3,375.

oi. malleableizmg cast iron consists in producing a casting which consists principally of non, carbon, silicon, phosphorus, sulphur and manganese. The carbon is in a chemithe heating ovens and the quality of the-'- iron produced is liable to be affected with too 1 'h a temperature. The time the iron susgected to a temperature above the critical depends upon the temperature and com position, and the higher the temperature the less the time required. Under this heating all the combined carbon is changed to graphitic carbon with the exception of about .8% which remains as combined. carbon. To still further transform the combined carbon, the temperature of the iron is allowed to drop slowly, possibly at the rate of approximately r0 T o A of approximately 1200 F. to .1800 F. is reached, just below the critical, and during this drop in temperature the graphitization is completed or reaches an equilibrium, that is, all the remaining combined carbon has been transformed into free carbon with the exception of about .1% which remains as a combined carbon and is characteristic of malleableizcd cast iron. After the iron has cooled to 1200" F. or 1300 F. it is allowed to cool to room temperature or until it may be handled, but no consideration is given to th rate of cooling other than it is considered necessary to cool slowly.

I have found that the rate of cooling and the temperature from which the iron is cooled af er graphitization is completed is of the utmost importance if an iron having the best prop rties is desired, and to the best of my knowledge, no thought has been given in the past to the last step in the annealing process, nanielycooling after graphitization.

It is well to state here that I have found that each composition of iron possesses its to 12 F. per hour until a temperature own characteristics and these are clearly shown when different grades are subjected to coniparative tests and therefore it is not possible to say that characteristics possessed by one grade of iron will apply to other grades, still in order to clearly disclore my invention I am obliged to refer to definite figures and limits in many cases, but it should not be considered ti at these will apply to all compositions of iron.

in Fig. 1 l have shown a set of curves to represent the four steps employed in the annealing or graphitizinp; of the hard iron and curve A represents the thermal cycles through which the iron passes when annealed in afuruace usually employed by malleable cast iron foundries. One of the usual methods of annealing to place the hard iron castings in an inert packing material such as mill-scale or sand contained in pots or containers which are placed on. the floor of the furnace, which is then brought up to the temperature desired, then held, then dropped slowly to a point below the critical temperature and then the furnace is opened. and the content allowed to cool as it will. A complete cycle of 186 hours shown in curve A and comprises hours to bring the contents up to the preliminary graphitizing temperature of 1650 F. at which tem jierature it hold for hours and then allowed to cool slowly at the rate of substantially (3.8" F. per hour to 1200 F. During this period of slow cooling the graphitizaing will reach a state of equilibrium and the furnace doors are opened and the contents allowed to cool either to room temperature or until the pots may be handled conveniently. As the pots are packed in the furnace qui close and as the mass to cool is large, the castings in the pots farthest from the door cool. much slower than the castings in the pots near the door hence there is not a unifo m rate of cooling. In curve A, Fig. l, the furnaces are shown as drawn at El hours after the doors are opened and if the castings near the door reach room temperature, the cooling will be at a rate of about 50 F. per hour, and if those at the rear of the furnace have cooled to 500 15. their rate of cooling will be much slower, about 30 F. per hour. lZLS stated before, I have found the rate of cooling of the greatest importance, but the rate of heating the castings up to the maximum temperature is unimportant, the time, however, of holding at the maximum temperature and the rate of cooling to the temperature at which the furnace door is opened is important and has been recognized for a long time.

n'lalleableized cast iron made as above described is not uniform in its physical. prop erties and is not of the highest quality for any given composition and it will not always hot-galvanize or lend itself to a heat treatiuuoacl ralucs in per cent of that of the normal commercial iron after the various samples had bee.- machined. to a standard size and her ted to different temperatures from about 100 F. to 1472 F. and quenched in water at 1T5 The normal 1 100% line represents the impact value of the untreated commercial. iron producd according to the usual annealing process. The samples after being heated to the temperatures shown by the points on the curves and quenched .in water 175 F. were tested in an l'lzod impact machine which measured the resiliency in foot pounds and these readings wcr reduced to per cent of the inpact value or the normal or commercial iron.

by these curves is heated to certain temperatures and then quenched that th resiliency will be less than before heating; and cooling and the creat 1 loss in re lieney is through that range of temperature to which the iron would be subjected if hot galvanize-d, approximately 850 F. to 025 ii. The curves also show that if the iron heated to certain other tenuaeratures and quenched that the resiliency is greater tl the normal commercial product and in case of the C iron the resiliency isincreased 50% by heating' to about 1130" l and quenching; and in case of l) iron the resiliency is increased about 15% by heating to about 102:2" ll. and quenching. l: have found that iron heated to a temperature above that/at which the curves cross the normal line and then quenched that such irtn, may be hot galvanized without cmbri 'ement. This disclosure is set forth in my copeuding application Serial No. 633,780, filed A nil E21, 1923 (new ,Fatent l lo. 1,553,907, grai'ited September l have also found that some grades of regularly treated commercial inallcableizcd cast iron may he heat ed up to a tcm above the crossing of impact cur the normal line, but below the critical temperature, and then cooled rapidly, as for in stance, at a rate of about 6 F. of 7 per minute, that such trea ed iron will galvanire without emlnittleuiena. The effect of cooling at such rate on a grade of iron from a temperature of 1250 F. is represented by curve F, Fig. 8, and later referred to herein.

I have discovered, that if, when graphitization has been completed, the castings are removed from the oven and quenched or cooled quickly, the entire heat will be uniform, the physical properties of the individual. castings will be improved over those of the usual commercial castings and the structure will be homogeneous, and they may be galvanized or subjected to heat within the galvanizing range without embrittlement and the time of the annealing process will be reduced by the amount of time allowed for the product to cool under presentoperating conditions.

In Fig. 1 I have shown by the lines B and B the last step of annealing by my process when substituted for the last step as shown by curve A and the reduction shown is about 24c hours. B represents the castings drawn as soon as the graphitization has been completed and quenched in water, and B represents the castings drawn at once and cooled at a rate of about 6 F. to 7 F. per minute.

I find that the purer the hard iron the slower it may be cooled in the last step of the annealing operation, as will be shown later, but I have found that quenching or cooling quickly from about 1200 F. to 1300 F. will for any given composition produce a uniform grade of iron of best qualities and this method applies to all compositions usually employed.

It will be recognized that the A step shown in Fig. 1 can be made as rapid as possible, also the A and A steps may be shortened from that shown so long as at each step the proper amount of graphitizat-ion has been carried out, but whatever the A A and A periods may be, by quenching for the A step the total annealing time may be shortened many hours from. the present process.

In carrying out my process with the ordinary furnace (see Figs. 4 and 5) the pots or containers 1 with the hard iron castings therein would be mounted on trucks 2 and run into the furnace on rails 3 and coupled together if two or more are placed end to end by the couplers 4. The furnace would, of course, be provided with a sand or other seal 5 to prevent the heat from afl'ecting the truck mountings and the rails. The furnace is then brought up to the required temperature by means of powdered coal, gas or oil heat through the ports 6 or by other 1 means, and the time and temperature for the A A and A steps manipulated according to a predetermined standard. hen the A step has been completed the furnace doors are opened and the trucks and castings withdrawn at once and dumped, areferably on a grating conveniently located, which will allow the packing material to sift through and expose the castings to the air and hence quench them more quickly, or the pots may be dumped on to a moving conveyance running through water and quenched or cooled still more rapidly. Fig. 5 is a sectional view of Fig. 4 through the plane 5.

Tests made upon specimens of iron containing:

Silicon 0.94 Sulphur 0.063 Manganese 0.35 Phosphorus 0.236 Carbon i 2.31

and using the Izod type of impact machine which measures the resiliency in foot pounds showed that the above iron when put through the first three steps of annealing and quenched in water when the third step had been completed at about 1250 F. had an impact value of 11.5 foot pounds and when other specimens of the same composition and annealed. at the same time and hence under the same conditions were allowed to cool slowly at t o F. per hour, such specimens showed an impact value of only a l foot pounds. lVhen the first 'samples above were subjected to the galvanizing process and then tested by the Izod machine they showed 13.6 feet pounds and when the slowly cooled samples were galvanized and tested they showed only 1.0 foot pound. From these figures it will be noted that rapid cooling from 1250 F. has produced a malleableized cast iron of 34 times the resiliency of an iron cooled slowly from 1250 F. and after galvanizing the resistance of the quickly cooled specimens was 13.6 times that of the slowly cooled specimens.

I also found that the temperature from which the specimens were cooled or quenched had an effect upon the impact value, as for instance, specimens of the same composition of iron above when treated as above and cooled slowly to 1050 F. and quenched from that temperature the impact value was 7.1 foot pounds and after galvanizing 9.0 foot pounds, and this same iron when cooled slowly to and quenched from 850 F. the impact value was only 1.4 feet pounds and after galvanizing 1.1 foot pounds.

I have obtained similar variations to the above on other grades or compositions of iron, all tendinn' to show that the rate of cooling and the temperature from which the iron is cooled important and varies with the compos i of the iron, hence it is impossible to give figures which will apply to all compositions of iron.

Along this line the curves shown in Fig. 3 will be of value. The compositions of the commercial iron vary considerably as to phosphorus, silicon and carbon and it will llll'jl! in phosphorus and silicon (and equiv he noted that there is :1 ditlctence in the imparrot \"(Ell'il' queiu-hed value which czuul wnuuz'lly be ill mm on the cutse as; it is too For to the right.

(Tux-ye F shown that the iron it represent: llllh' practicaliy watched 1 maximum i'euilicncy when cooled at not lest-,4 than about 7 F. 1:01 mi z-520 l per hour) from 1350 l und that more rapid cooling does not int-tome the r'er-rilicucy, as mezuluiell hy the liuod machine to 21 grout extent.

Curve it show: that the iron it 1'01)l05' 3?1ir requires :1 cooling rote of least 110 F. PC. minute to upplu' ximete the beet results and to equal thut secured on l? iron when ll. per minute, this iron cooled at about 4 should, tlici-z-tore. he qucucliml in ntcr from. about 1250 .ll. to secure the g t-cute. t exilioncy.

The impacttout the specimens had at tho fit-P52; hot=rn if? JLl 'itlllZHl and show i only the c i: n cooling); miter; on the colupooiti-lme of iron, but :zlwo the fuel 1 (litter-cut compositions only he given cent twmluwnts o1 votes o coolin' hut tl at ,ci'e is a. minimum rote which i, decl'muml W iron o'li int e2" .ulity. The curves 2. so Show that ulv: iii ling the item produced by my lHOPOLa don. not cmloi'i'tle the iron. iron 1" ])l'="i-?(l1ltl hy the curve G is; unueuullv l'lllllt'f'l were on: after cooled o quenched 250 1*. :1 l then emhi'ijtlc when ,gmlmnizcd.

u le rclung tor :1 c: use tor the benefits t ived Jom proper cooling from the final gnzi'plliliizauthuz tenupci'utiare l have come to the concluuhm that at n1e temporzttlwe be.- low the critical tempoimure the impu'f or olhcv li1 :-e lic?\t:-1 are uniiol'z ily dispel: d tln'oug hout the nines. .lif {allowed to cool :-=lo\vl "horn this tempeutui'e, the impurities and other ingredients are given an oppcttunity to route along}: the crystalline boummm thceehy giving it non-holno om: structure which is; wool: at some t and .rc at other, the i'Ps-nlt being; on uiu-clluh c product and one which will not hot uilv'zinim 'uilhouvdun of emhz'it'llemoot; bemoan these #eggeugmt:one :u-e emlullthwl by 'ugr tmeauiment and ofl i- 2m cosy pal to fracture. The a ter the amount of inu nu'ities; the mentor the uniteliahility of the product under ordinary proceasel: of annealing, also the lower the impact *olue.

It on the other hand the iron at slightly below the critical tcmpei'eture is Suddenly quenched or cooled with Sufficient mpidity the impurities and other ingredients Which are uni sully ,lrih: do not have time to scgr gate or collect in grows but are held in u uuihu'mly distributed state when the nun-1s cool. quickly or is quenched and hence w; have a htz-motmneous; mess with the ingredients dish-muted uniformly through out the ei'yotulline grains; thereby giving It uniform and relizih e product of the greatest resilient value WlllCll that grade oi. iron is c mhle of and one which will hot galvanize Without emhrittlement.

Tllhereloto, in czn'ivinpg out my invention,

litter the product he": eooled to a temper;-

lii'f) at which iplitizution has reached a Stilt, o? in 0'1} llll'JllUlll and all the comu l (nu-hon her been graphitizecl except 0.1% and which. temperature might or 11.1 :1; a no lou'es temperature at which the I lillbtilll'flfi are stil in a homogeneous state oi tribution, or 1 cool z-autliciently rapid twin leh tempo 'atui'es; so as topl'event the '1 mid other ingredients fi'mn segreo woups or other ium-honaogc- U tht-fmgl o tthe moss.

lvlv invention nuty he czl'ried out to admntagc in u conth'iuous tm'nace, kiln in which the pots of hard ii'on castings; are glnccd on a truck and moved into a chamber at 1650" F. or other suitable telnpemtm'e, and v-rhci'e they "will come up to temperature in approximately 5 to 10 hours and they will remain under this l'QlllQGltltlHG- for the neessary time and then moved thing}; to it occond compartment \l'here the temperature is; lower and they will cool slowly at 8 l per homor much taste? as "found practical and until the gmpl.itizetion process has been completed, and then the truck will he: moved 'fozrv-mrd onto a grating and auto matically (lulnpel and the cnetl 's exposed to the llfl'lflfiplllb't'fi and air quenched or they may be thuuped onto a conveyance moving thrz'uug'h WiltQ'z to quench. Using it eontinuous kiln the cycles of time and temperature are shown by curve on Fig.1. 1, and using the some values mid E as for A and A", it will he seen a k. stmnoxiinately 51 hours; is saved in the process. The steps E and E may he shorttmed us; much as the grade of iron and other conditions will per- V iuit in securing: an equilibrium in aphiti- Villllflll ol the iron.

IP01] which has; lucn treated as dewcrihcd from. the gg'i'uphitizztion temperature or other llilfil'fllliltlllfi) derserihecl may be hot galvanized Without einln'ittlement of the iron by applying the galvanizing process as 1s well known, consisting principally in cleaning the castings in dilute hydrochloric, sulphuric acid, etc. then subjecting them to a bath of molten zinc and after shaking the surplus zinc from the castings either cool quickly or quench.

I have found that quenching malleableized iron castings in water from a temperature of approximately 12.50 F. will prevent embrittlement of all compositions of iron of commercial value. Some compositions can be quenched in water from a lower tem perature than 1250 I and will be immune to embrittlement.

All compositions will give a high impact value, when treated herein described, such values depending upon the composition of the iron.

some compositions may be quenched or cooled at a slower rate than others and still be immune from embrittlement.

The greater the impurities the faster the rate of cooling should be and the higher the temperature at which the rapid cooling is initiated (not to exceed the critical temperature).

Apparently when the iron is at a certain temperature the impurities are uniformly dispersed therein and the iron should be cooled or quenched before the impurities have had an opportunity of segregating.

To practice my process it is not necessary to always quench in water, as quenching in air will give the required results if the temperature is sufficiently high and the castings not too large to cool sufficiently rapid, at least this is true of most compositions.

To produce satisfactory results it appears from tests that iron should not be cooled slower than about 360 F. per hour, depending upon the composition, and from a temperature at which the impurities are uniformly disseminated.

If the product is chilled after the impurities have begun to segregate the resulting product will be correspondingly inferior to a product chilled before segregation begins to take place.

Those skilled in the art know that the hard iron can be graphitized by bringing the castings to a temperature just slow the critical temperature, about 1375 F., and holding it there for a protracted period of time, but this is practical only with high silicon iron on account of the time required to bring about the equilibrium. Should this stop be employed, however, then the next step should be to quench from that temperature as described above.

It will also be recognized by those skilled that after the preliminary graphitization above the critical temperature the castings may be cooled as rapidly as oven conditions will permit to a temperature just below the critical temperature and then held at this temperature until the second stage of graph itization has been completed, and if now the castings are chilled, as I have herein described, and before detrimental segregation of the impurities can take place, the beneal results herein described will be secured.

In the appended claims I use the Word quenched, or quenching, to indicate air cooling or liquid cooling; or cooling in a fur- U 7 nace but at a comparatively rapid rate such, for example, as would take place in a comparatively small or experimental furnace as distinguished from a large commercial furnace, or by forcing cold air into the annealing furnace after the graphitization steps have been completed and forcing the hot air out and rapidly drawing off the heat from the castings.

In the appended claims I use the expressions carbon-combining temperature and critical temperature synonymously. By neutral temperature I mean such temperature that if the iron is brought to a temperature below the critical temperature and not less than said neutral temperature, and then cooled, it will not be embrittled, or in danger of embrittlement. These various expressions will be understood when considered in the light o f the above disclosure and also when considered in the light of the disclosure in my copending application Ser. No. (333,789 (now Patent No. 1,553,907).

In the specification of my said application Serial No. 633,789 (now Patent No. 1,553,- 307) and the specification of the present application two processes, among others, are taught. Cne of these two processes includes the following steps ((4) Raising the temperature of the iron in the hard iron condition to a temperature above the critical or carbon-combining temperature,

(2)) Cooling the iron comparatively slowly to a temperature below the carboncombining temperature,

(0) Cooling the iron at a more rapid but still comparatively slow rate as by opening the door of a comparatively large furnace,

((Z) Raising the temperature of the iron to a temperature below the carbon-combining or critical temperature but above the neutral temperature; i. e., a temperature within the safety zone,

(6) Quenching the iron; i. e., plunging it in liquid, cooling in air, or opening the doors of a small experimental furnace.

The other of the two processes referred to includes the following steps:

(a) Raising the temperature of the iron in the hard iron condition to a temperature above the critical or carbon-combining temperature,

(Z2) Cooling the iron comparatively slowly to a temperature below the carboncombining temperature but above the neutral temperature, I

(c) Quenching the iron (i. e., plunging it inliquid, cooling in air, or opening the doors of a small experimental furnace) before its temperature has been allowed to drop be low the neutral temperature.

All of the claims of the said Patent No. 1,553,907, cover the first oi the two processes outlined above; some of the claims of the patent cover that process but not the second process; and others of the claims of the patent cover both processes. in the present applicationthe claims cover the second of the two processes outlined above but not the first.

it claim:

1. The method of producing malleable cast iron com n'ising the steps o'l heating the iron to a tem ierature above the carbon-combining temperature, lowering the temperature of the iron to a temperature below the carbon-combining temperature, and th quenching the iron while its temperature is above and before its tenu nniature has been allowed to drop below that which will, cauee the iron to be in danger of en'ibrittleinent.

2. The method of producing malleable cast iron comprising the steps or heating the iron to a temperature above the Lilil'blllPCUlll bining tei'nperature, lowering the temperature ot the iron to a temperature below the carbon-eombining temperature, and then quenching the iron in liquid while its temperature is above and before its temperature has been allowed to drop below that which will cause the iron to be in danger of embrittlcment.

3. The method of producing malleable cast iron comprising the step of heating the iron to a temperature above the carbonimoneae combining temperature, maintaining the iron at that temperature for a period dependent upon the composition of the iron and the temperature to which it has been raised, and cooling the iron to a tempera ture below the carbon-combining temperature, in accordance with the ordinary American commercial annealing operation, and then quenching the iron while its temperature above and before its temperature has; been allowed to drop below the neutral temperature.

l. The method of producing malleable cast iron comprising the steps of annealing the iron in the hard iron condition by sub jecting the iron to such temperature for such time as to cllange-the combined carbon into free or graphite carbon, then stabilizing the annealed iron by quenching it before its temperature has been allowed to drop below that which will cause the iron to be embrittled.

5. The method of producing rust-proof malleable cast iron which comprises the steps of heating the iron to a temperature above the arbon-conibining temperature, maintaining the iron at that tempearture for a period dependent upon the composition of the iron and the temperature to which it has been raised, and cooling the iron to a temperature below the carbon-combining temperature, in accordance with the ordinary American commercial annealing operation;

quenching the iron while its temperature is above and before its temperature has been allowed to drop below the neutral temperature, and coatingtheiron with a rust-proofing matt-arial with the application of heat.

testimony whereof I allix my signature LESLIE H. MARSHALL.

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