US2348849A - Cast iron and its manufacture - Google Patents

Description

friction strength and to result Patented May 16, 1944 UNITED STATE PATENT OFFICE -cas'r IRON AND rrs MANUFACTURE 'Leonce Reygagne, Decazeville, France: vested in.

j 1 the Alien Property Custodian new... Application October 2'2, 1941, Serial No. 416,756. In France September 30, 1940 Moldable cast iron such aspr'oduced in accordance with blast-furnace processes, 1. e., in apparatus supplied with coke and a blast of hot air, have a total carbon, content which is generally from 3.50 per cent to 4.00 per cent or even more,

0.60 to 1 per cent being in the form of combined 7 carbon. When a cast-iron oi the above type is examined with a microscope. free carbon is seen as graphite flakes which are generallyvoluminous, of variable. although always relatively large length, and irregularly distributed.

Until recently, these raw cast-irons were satisfactory as regards the requirements of remelting founders: the mechanical stresses imposed on cast-iron castings were very small, as the metal was conside'red as a second rate and imperfect material. But since twenty odd years ago, it has been iound that, contrary to previously admitted theory, it is possible to obtain remelted cast-irons having mechanical characteristics far better than those previously accepted; the considerable improvement in mechanical propertiesis substantially attributable to the realization of particular structures and, to a minor extent, to that of 'a determined chem- I wear and so on).

ical composition. In case of strong cast irons,

so called steel or pearlitic cast-irons, which is the most common type, the required structure admittedly consists in pearlite with free carbon in form of short and thin flakes, as regular as possible in respect of dimensionsand distribu tion: excess ferrite should be prohibited, and the amount of free cementite should be as low as possible. To sum up, according topresent conceptions the material should be given a pearlltic structure, and the strength towards mechanical stresses should be lowered as little as possible by .those components which specifically characterize cast-iron, to wit, free graphite and free cementite. On the contrary the form of the latter components should be such .as to highly increase lathe production of castings free from defects.

It is particularly advisable to remove ferrit'ic stains which are frequently found in. cracked pigs. Asa matter of'fact when such pigs are melted, thecastings produced therefrom exhibitlike stains and manydifnculties are experienced in their employment (lowered mechanical cmms. (ems-56y.

strength, liability to seizing under friction, rapid The remelted, pearlitic, strong cast-irons generally have the following chemical composition:

Total carbon .2.80 to 3.20 per cent Combined carbon 0.7 to 0.9 per cent Silicon. .Widely variable ac- Z cordingtothedlmenslons of the piece and the cool- 7 1 0 ing process sulphur --As little as possible Phosphorus Maximum 0.20 per 7 l cent, preferably 0.12 per cent Various methods are known for producing cast-iron shapes having the required micrographic structural characteristics and hence the required mechanical qualities." Amongst these methods, one of them is more and more preferred by founders by reason of its advantages such as its being easily carried out and the value and regularity of the resultsobtained therefrom. It is the method which consists in melting in a cupola or any other suitable apparatus, charges containing a predetermined proportion of a special fine-grained,iraw cast-iron which has a low carbon content; furthermore they generally contain scraps arising from the manufacture of strong moulded pieces. Therefore experienced founders have regularly required such blastfurnace cast-iron with close grain and a low carbon content. i

Until recently, the said cast-irons could be manufactured only in a few blast-furnaces producing haematite mouldable cast iron and the process differs from the usual process for produca controlled.

ing-mouldable cast-iron in the following respects: A particular manner of working in the blastfurnace, i

The use of suitable charges, Or a combination ofboth.

By reason of the particular operation of th blast-furnace, it is possible to Obtain: 1. A relatively low carbon content, 2.,A araphite the development of which is 3. No structural anomalies. V

I have-now found that the manufacture in the just described conditions may be completed with full success by an after-treatment of cast-iron.

The latter treatment has for an object, in addition, to adjusting, as is always desirable, the proportions of chemical elements (carbon, silicon and so on), to act on the non-metallic inclusions suspended in cast-iron, which according to an approved theory, determine by reason of their manner of production and their distribution in the metal, the shape and dimensions of graphite as well as the structural anomalies above referred to. v

According to this invention, the'after-treatment comprises pouring the metal from the blast-furnace into a mixture of iron or steel shavings and hammer-scales. Any other divided scrap may be substituted for shavings; likewise the'hammer-scales may be replaced by ferrosO- ferric oxide F8304 from other sources. Instead of the said mixture of shavings and hammer-scales, I may also use any other granular or powdery material consisting principally of iron and iron oxides. 1

A portion of the oxygen in the oxides willbum a part of the carbon in the cast-iron, thereby producing C and CO2; another portion, by combining with silicon, will yield an amount of heat larger than necessary for decomposing oxides.

Such heat, together with the sensible heat in cast-iron above solidification temperature, will be available to melt ferrous metallic materials or the jet to sprinkle the whole mass or nonmelted metallic materials, finally introducing dry wood poles into the molten mass to stir it as a result of gas evolution.

As an example, in a batch of 7,030 kg. of castiron the original contents of C=3.50 per cent and Si=3.08 per cent (with manganese=0.90 per cent; phosphorus-i-sulphur less than 1.10 per cent) were lowered to C=3.31 per cent and Si=1.98 per cent by adding 205 kg. of shavings and 400 kg. of hammer-scales. Inabatoh of 8,600 kg of cast-iron, the carbon content was brought from 3.27 per cent to 2.97 per cent by adding 790 kg. of shavings. In a batch of 6,920 kg. of castiron, the carbonand silicon content were brought from 3.25 per cent and 4.66 per cent respectively to 3.05 per cent and 3.52 per cent respectively by adding 234 kg. of shavings and 575 kg. of hammer scales- Finally, in a batch of 6,530 kg. of

aiter reduction of any oxides present therein.

Finally a part of the addition is converted into slag together with the oxidation products from cast-iron (MnOz, SiOa and the like). Thus with a properly calculated addition 01a mixture of shavings or iron scrap and hammer scales,the

carbon and silicon contents are lowered and a slag is obtained, the properties of which control the form of graphite of cast-iron. The production of this slag as a result of addition of iron oxide is one or the characteristic features in this invention.

According as the case may be, the respective proportions of iron or steel and iron oxide may vary within broad limits.- I I a The above mentioned additions may be made either in the runner or in a suitable vessel, either stationary or movable, either heated or not, and into which cast-iron is poured. They may be made continuously in the runner or the vessel or in one or more batches.

Where a vessel is used, the addition is foundto be more efiicient. Furthermore, this process enables or checking results by cursory chemical analysis and by means of test-pieces, well known in the art. wherefrom the carbon and silicon content can be ascertained with sufiicient precision. Thus, it is possible to produce a castiron having a predetermined composition, and possessing the advantages of a controlled" structure. It is also possible to produce very homogeneous metal by mechanically stirring for instance by rotating the furnace,- by creating a rotating field with polyphase currents, by a pneumatic process and so on. c I

Good results were secured by placing in a ladle suitably alternating layers ofshavings and hammer-scales, and pouring cast-iron at first at one point to enable cast-iron of running to the bottom of the ladle, then moving the ladle cast-iron, the carbon and silicon content were brought from 3.09 per cent and 3.68 per cent respectively to 2.76 per cent and 2.33 per cent respectively by pouring itupon 310 v kg. or shavings, 905 kg. of hammer-scales and 202 kg. of roasted pyrites.

.When oxygen containing materials are added an exothermic reaction takes place, whereby. the amount of shavings or divided iron scraps'may be increased.

t On the other hand, the carbon and silicon contents may be adjusted and the cast-iron structure may be altered in such a way as to produce a homogeneous structure. f

Theinvention allows of producing new types of cast-irons (more particularly as soon as they leave the blast-furnace) the carbon content of which may vary irom' 3.40 to 2.40 percent and the silicon content may be lowered to 1.5 per cent with a homogeneous structure and no ferrite stains; no similar cast irons have ever'been produced up to this time even in a special iumace'.

" What I claim is: 1

" l. The method 01' refining carbon and silicon in cast-iron which comprises pouring molten' blast-fumace iron into the bottom-oi a ladle containing alternate layers of low carbon iron scrap and hammer-scale and stirring.

2. Themethod of refining molten cast-iron containing more than three per cent each of carbon 'andsilicon which comprises pouring said cast-iron into the bottom of a ladle containin alternate layers oflow carbon iron hammer-scale and stirring.- v

3. The method of refining molten cast iron containing more than three' percent each of carbon and silicon which comprises pouring said cast-iron into the bottom of a ladle containin alternate .layers of low carbon iron scrap and hammer-scale, producing a protective slag by the reaction and stirring the iron to promote 'contact'with the scrap and scalebeneath the scrap and