US1640674A - Making malleable-iron castings - Google Patents

Description

Patented Aug. 7 '30, 1927.

Q I-r;E1) STATES PATENT OFFICE.

may a" scHwAna'a-pr CLEVELAND, b310,, assieNon '10 NATIONAL MALLEAIBLE AND STEEL GASTINGS commas, or CLEVELAND, x10, a CORPORATION 1- 0111 MAKING mAL Ea sLE-moN cAs'rINes.

He Drawing.

In the manufactureof malleable iron castings it is customary to have silicon present in the'iron before casting so that, in the subsequent mall'eabli'zin *operation, it may assist-the decomposition or breaking up of the cementite in the iron. After casting and while the casting is cooling the presence of too much silicon, however, causesthe precipitation during orjust after freezing of a percentage of the carbon in the flaky form normally found in grey iron castings and renders the castings worthless for conversion-into malleable iron, and owing to this action the amount of silicon present or to be added must be regulated with very great care. I have found thatthe addition of small proportions of 'a graphi'tization acceleratorsuch as zirconium to iron containing aninappreciable percentage of silicon greatly accelerates the annealln cycle of such malleable iron, acting in muc the same way as larger amounts of silicon, but without the deleterious effects of silicon.

In carrying out my. invention Ihave found that iron containing no substantial percentage of silicon and to which is added a small'amount of zirconium (approximately .50% or less of zirconium being sufficient in the annealed casting) may be cast without precipitating the carbon, and when annealed graphitizes as completely and more satisfactorily than malleable iron of'normalanalysis which contains substantially .7 O.80%' of silicon and no zirconium. Suitable larger amounts may be added to Iromote still further ease of annealing; In act,

the limit of the amount of' zirconium which may be added is that which will cause primary precipitation of graphite, and such limit varies with the shape and thickness of the castings. I have found, however, that castings co'ntaining after annealing'ap roximately 20% or less of zirconium grap itize completely and-satisfactorily. Similar additions in properly reduced amount can be made to metal having the silicon content equal to or less than that normally present in malleable'iron. Such additionsgeven in amounts as small as 10% or less, will similarly benefit the metal with respect to, its annealingproperties, resultin in a marked reduction bf the time require for anneal.

The effect of silicon in iron for malleable crease n" th jhpplieatien filed October- 30, 1924. Serial 'llo. 746,876.

castings is to raise the critical point above which carbon is soluble and to lower the solubility of free carbon in solid iron at all temperatures above the critical point just mentioned. Silicon thus acts by decreasing the solubility ofcarbon in the iron and renders graphitiz'ati'on during annealing at a given temperature more rapid and complete, but by reason of its completeness there is danger of prec pitation of carbon" while cooling in the mold, which is ordinarilyknown as primary graphitization. Thus, if substant al amounts of primary graphite are present (for instance, as much as .1 O% or even less) the properties of the annealed casting are so fardeteriorated as to practically destroy its commercial value, Zircomum in the small amounts contemplated, on the. other hand, so far as served, has no appreciable efiect on the critical point of the alloy.

My invention is particularly adapted for use in making malleable castings with comsurface, so that the thickness of the ferrite skin on the castings'formed bysuch e'xpo sureis lessened by the shortening of the time of exposure; As this ferrite skin ismore diflicult to machine than the material underneath, a definite improvement inmachining qualities is thus achieved.

facture of malleable iron'castings in which I have '0b-.

increased strength may be obtained by theaddition of. sum 1 percentages of metals such as chromium, as the zirconium and other metals which-act similarly, such as titanium and u m, have the efl'ect not only of offsettin e -very great and prohibltive ine,t1me required for annealin whicli'jis the. usual result of additions\s1ic as chromium, but also assisting in the graph- 'My invention is also useful inthe manuitization of the casting. The chromium also 1 adds valuable rust and oxidization resisting qualities to the iron. I

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described, or portions thereof but recognize that various modifications are possible within the scope of the invention claimed, it being understood that by the use of the term graphitization accelerator I refer to such elements as assist in the graphitization of the metal during annealing.

"What I claim is:

centage of silicon, which comprises adding a small amount of zirconium as a graphitization accelerator, casting the metal Without precipitating a substantial proportion of the carbon, annealing the casting and thereby precipitating the carbon in the form of small particles.

- 2. The process of making malleable iron castings which comprises adding a small' rcentage of zirconium to the iron, annealmg the casting and thereby effecting graphitization of the casting.

castings which comprises adding a small percentage of zirconium tothe iron and also. a strengthemngeleme'nt, annealing the cast-.

ing and thereby effecting graphitization of the casting, the zirconium overcoming the retarding eifect of the strengthening element upon the annealing operation, andalso assisting in the graphitization of the cast- 1. The process of making malleable, iron castings contalning an lnappreciable per- 5. Theprocess' of making malleable iron castings which contain, in addition to the elements usually present in malleable iron, a strengthening element which retards annealing, adding to such iron while 'molten an' element such as zirconium, titanium or uranium which accelerates annealing, suchelement overcoming the retarding effect of the strengthening element and also assisting in the graphitization of the casting,-

carbon in the form of small particles;

f HARRY ii. SCH ARTZ.

annealing the casting and thereby precipitating the