US2014238A - White cast iron alloy and method of making the same - Google Patents

Description

. Patented Sept. 10, 1935 UNITED STATES PATENT OFFICE WHITE CAST IRON ALLOY AND METHOD OF'MAKING THE SAME Frank A. Raven, Albany, and Clarence D. Foulke,

Buiialo, N. Y.,

assignors to Industrial Furnace New York No Drawins.

Application January 15, 1932,

Serial No. 586,952

2 Claims. (01. 148-21.?)

This invention relates to alloys of white cast iron, and it has particular reference to a white iron alloy, containing, in addition to the usual ingredients, alloying elements in such propor- 5 tions as to render the iron readily amenable to heat treatment to yield an article having desirable physical properties.

Heretofore it has been the general practice to make white iron castings with carbon and silicon,

lo and manganese and sulphur, in such proportions as. to yield, upon heat treatment, the material known as malleable cast iron. Such material, "as a commercial article, has been made with'a tensile strength of something less, on the aver- 5' age, of 55,000 pounds per square inch, with elongations of the order of twelve to twenty per cent in two inches. Metallurgically, malleable cast iron is composed of free iron or ferrite, interspersed with temper carbon. Aside from the If constituents named above, phosphorus is also usually present, but other impurities have been avoided in general foundry practice.

The factors considered in the making of malle- I able castiron have been, that the carbon must be originally present as combined carbon, .or cementite, that the silicon must not be too'high, lest the criterion of combined carbon be defeated, albeit the silicon should be present in appreciable amounts to facilitate the subsequent breakdown of the cementite, or, in otherwords, to accelerate the annealing or graphitizing action. These matters have led to certain limits and ratios for carbon. and silicon; thus, if the carbon be 2.45 per cent, the silicon may be about 0.84 per cent, andifthe carbon be.2.10 per silicon should be about 1.06 percent.

Likewise, the manganese and sulphur, both of which are knownas' retardants of the annealing process, should not be too high, lest the heat treatment be necessarily extended. Foundry practice, however, impom limits on the sulphur, and the manganese value has been made somebeen foimd that while these two elements,

' other. In practice, sulphur values of about 0.06 I to 0.10 per cent have been tolerated, with the manganese-running to about 0.3 per cent; the

conditions and thetypeofcastingdeslred.

It has more recently been discovered that, if the white iron casting is modified in its composition to contain an available excess of retardant,

cent, the

what more than twice the'sulphur, it havingseparately, exert a retarding. eifect, in proper proportions .conjointly they neutralize each.

exact flgures'varyingrof course, with foundry as, for example, an excess of manganese, to

about say 0.6 to 1.5 per cent, and such castings are subjected to certain heat treating operations,

it' is possible to obtain a commercial metal, differing materially from malleable cast iron in its metallurgical aspect, as well as chemical com- 5 position, and also having greatly. enhanced physical properties. In the practice of this process, it has been observed that the time of heat treatment of the white iron casting, neces: sary to effect the breakdown of the free cementite, may run for an appreciable time, say about twenty-four hours at 1700 F. This length of time may be objectionable for economic 'or commercial reasons. It has also been observed,

moreover, that the castings made by the process referred toare open to the general objection of low corrosion resistance as compared to mallecreased resistance to corrosion, by alloying in the white iron casting a combination of elements, which facilitate the breakdown of free cementite,-and so lessen the time of heat treatment required, but which combination does not, however, effect a like influence on the decomposition ,of combined cementite or ,pearlite. In this connection, it may be explained that the conversion of hard andnon-ductile white iron into a more ductile and strong material is thought to be due to the decomposition of the combined carbon or cementite. This cementite occurs in two conditions, first, as free or massive cementite, which is decomposed above certain temperature ranges, generally called the critical. The

balance of the cementite occurs in the form of pearlite, which is broken down by heat at-temperatures below the critical. Our invention is predicated upon the principle of modifying theus normal white iron composition by the inclusion of elements which do not retard or prevent the actions occurring above the critical, but which do exert such effect on the actions below the critical, so that physical changes may take place so in preference to the chemical change which has been sought heretofore in making malleable cast iron. The invention further involves the principle of utilizing, as the modifying means, ele-' ments'which impart to the coating, in its final iorm, enhanced physical properties and a greater resistance to corrosion.

' More specifically, we have discovered that ii the composition of the iron be modified by the addition of chromium and copper, the desired results may be obtained.

be noted that, heretofore, chromium has Men recognized as a retardant for the annealing actions, and the eiiect oi chromium, when I present to any appreciable extent, is so marked that its presence is shunned by the white iron manufacturer or founder. Copper, on the other hand, has been stated by some to be a retardant 1 oi the annealing operation, and by others an accelerant, and published reports oi the addition of copper have indicated that it is not emcacious'in increasing the strength oi the heat treated casting. Whatever may be the truth or merits of these several views, we are able to utiline these elements. to advantage, ior we have discovered that, at temperatures oi treatment above the critical, the accelerating eiiect oi copper predominates, so that a shorter time oi heat treatment .may be employed, whereas, at temperatures below the critical, the accelerating eiiect oi cop-- peris sominimiscdas'not tointeriere with the "preierential progress oi the physical actions, desiredinimpartingtothecastingtheenhanced physical properties; We have iurther iound that this combi'nation'oi elements imparts to the ilnal casting an increased resistance to corrosive ae- Inspeakingjustaboveoicoppenitwflhoi course,beunderstoodthatreierenceismadeto thceiiectoithecopperpresentwithotherelements,suchasthe retardants chromium-or manganese. IicopperaloneisemployedJt'appcars that the accelerating influence prevails at temperatnresbothaboveandbelowtheeritimwhile li-chromium alone is used, the retarding eiiect issuchastorenderdiiilcultanyann fl latalL' 'lhe two "specifics, conjointly, however, well attain the object oi accelerating the high temperature reaction, without interiering with the low temperaturechangesdesiredtoobtaintheiinalprodnot herein contemplated.

As exernplaryoitheresultstobeobtained,the

'iollowingdata,derivediromthetestingoisample'barsoiwhitecastirommaybenoted.

'- lilloy A Ohuntaleomposltbn Nod AlloyNm! 2.0) an LIB. LG (ill 0-85 can am 0.07 0.47! 0.!) MIHapproa.)

8amplesoi-each alloyweresubjected aheat treatment at 1700' I". for periods oi time oi 10,15, and 26 hours, theflast time being that which would be used (approximately) in the high temperature heat treatment oi this alloy, ii neither or copper were present, but it the manganesevaluewerehigh,asintheinstant cases. Microscopic examination oi Alloy No. 1 showed that the free cementitewas not broken down inany oi the three heats, thereby showing that, taken alone, or with the a pronoimced retarding effect was obtained with the addition of chromium. 'Alloy No. 2, however,

showed nearly complete breakdown of the mas-.

si've cementite, after heat treatment for only ten hours, thereby showing that the addition of cop- In this connection, it,

a low temperature heat treatmentat 1300 F. for" 1 twenty hours, or that which, with manganese present but chromium and copper absent, could be expeoted'to givea material having aspheroidized structure withanultimatc strength in the neighborhood oi 90,000 pounds. The values 15 obtained were, for Alloy No. 1, ultimate strength 86,100, yield point, 68,300, elongation 3.5 per cent. Theseflguresindicatethat theretardingeiiect oi chromiumwasstill pronounced, sincethe physicalpropertiesarenotasmuchastheyshouldzo be, ii no chromium were present. With Alloy No. 2, the iollowing values were obtained, ultimate, 91,000, yield point 69,600, elongati nine per cent, or about what could be anticipated ii neither chromium or copper were'present; These results 25 7 indicate that the deleterious retardingeilect .oi thechromium,takenaione,hadbeeneliminated, and, also,thattheundueaceeleratingeiiectoi LThemethodoimakinganiron irmn white which comps-mes iorming awhite Q fusion ior 5. length oi time sufllcient to decomposethe massivecementite andtodeveloptem-Tl taining silicon, manganese,

white iron with'an'excess of manganese to make amount of copper. I

the total manganese content between 0.6 and 1.5 per cent, said iron also containing temper carbon 1 derivedfrom cementite but being substantially tree from graphitic carbon andmassive oementlte, said ironiurther containing limited amounts of chromium and copper, the amount of copper being not more than two per cent and the amount of chromium being or the order of one tenth the FRANK A. RAVEN.

CLARENCE D. 10