DE2034806A1 - Process for melting cast iron - Google Patents

Description

Process for melting cast iron

The ürfindung relates to a method for melting cast iron in the electric furnace and in particular a process for cichmelting of cast iron at high temperatures.

In the case of cast iron in electric furnaces, it is customary to precisely control the temperature to which the melt is heated, because excessive overheating above the solidification temperature of cast iron results in excessive quenching or corrosion in the metal or, alternatively, the formation of it Graphite in the supercooled and interdentritic form leads. This limitation in the melting temperature does not allow full utilization of the most prominent feature of the electric furnace, namely the fact _; that high casting temperatures and an increased metal-thin liquid can be achieved quite effortlessly.

The invention is based on the finding that small proportions Silicon carbide can be added to the iJchrnelae, resulting in a complete elimination of the adverse effects of high overheating temperatures leads.

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The "]] invention" aims to create a process by means of its cast iron to a high GieStemperattir without disadvantageous Effects can be heated.

Another purpose of the original discovery is the manufacture of cast iron oils with a normal Crraphite structure "with high superheating temperatures su enable.

The invention aims to improve the male fluidity a cast iron schiaelae.

Another object of the invention is to create an improved one Melt for nodular cast iron.

Further, the invention aims at reducing the expense in the ¹ temperature control ', the lbeis melting of the cast iron is required.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the AbMldongen. In the pictures there are

1 the structure of a © aßelseas in 1OO-fa © lier magnification dais heated to I43O ° C is Trioräen and the arbitrarily arranged by normal graphite and areas unterkäMten is G-raphits in

2 shows the structure of the same cast iron, magnified 100 times , which has been heated to a temperature of 1540 and. that through undercooled it

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Graphite in the form ⁿ D ⁿ and also characterized by graphite in the form ¹¹ E "in interdentritic form,

Fig. 3 shows the structure of a cast iron 100 times Tfegrößerung which has been heated to 1595 ° C after 0.25 $ silicon carbide has been added, and which is characterized by normal flake graphite and slightly subcooled graphite, but not by interdentritisches undercooled graphite in of the form "B",

4 shows the structure of a cast iron enlarged 100 times, which has been heated to 1650 C after 0.25 / '■ Silicon carbide have been added, and that by normal floeken graphite and by a very small one Characterized tendency to form interdentritic graphites is,

Fig. 5, the hard wedge test with a cast iron, which has been heated in steps of 1430 0 55 ° C on I65O ⁰ C, wherein the 3rhöhung in shell hardness with the increase shown tjberhitzungstemperatur, and

Fig. 6 shows the hard wedge sample with a cast iron which after adding $ 0.25. ' Silicon carbide has been heated from I430 ⁰ G in steps of 55 ⁰ G to 1650 ⁰ C, whereby a practically constant hardness can be seen at all overheating temperatures.

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BATH ORIGINAL

When melting cast iron in an electric furnace is. it's a well-known one Fact that serious changes in the tendency to hardship and occur in the resulting structure as the overheating temperatures increase. This happens in all electric ovens, which are highly overheatable, regardless of the design in which they are intended.

In general, it has been found that the effects of overheating are more pronounced and more rapid in those electric furnaces which have high power consumption and in which the rolling effect in the melt is more pronounced. For example, a very high level of local overheating occurs in the electrostatic furnace in the area of the electrodes, and this has a very pronounced effect on the quality of the melt. When a cast iron melt of certain composition is heated above the melting temperature and ultimately above the normal casting temperature in an electric furnace, the first noticeable change in the properties of the iron is that there is an increase in the shell hardness value of the melt. This is illustrated in Fig. 5, which shows the increase in the hardness value with the increase in the overheating temperature of a gray cast iron .

It is not known why this increase in hardness occurs because in many cases there is actually very little change in chemical composition of the bath. It is often argued that this increased hardness value is the result of coagulation and the floating of silicate masses or slags the melt is what usually has some effect on the nucleation of the cast iron. The removal of these nuclei leads to an increased hardness value.

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Along with this change in the hardness value and quite frequently shows the melt without any significant change in the hardening. t value occurs, an increased tendency to solidify with graphite in the supercooled state with the degree of increase in overheating, Such supercooled graphite may or may not be desirable, and in the manufacture of high strength cast iron it is usually undesirable because of subsequent nucleation or graphitizing additives are not completely removed can that the molten metal before pouring usual ¥ ice can be added.

IjS has also been found that cast iron, which overheats severely is, although it shows an increased fluidity, due to the fact that it is further above the solidification point is heated, but does not show any increase in the thin liquid which is consistent with the degree of overheating. With with the increase in superheating, in particular with certain compositions of the melt, there is often even a slight decrease in the thin liquid.

All these facts make it imperative to control dae degree of overheating exactly, that is permissible at a Gußei8anschmelze. If this does not happen, poor quality metal is produced, which brings with it a poor graphic structure, hard white ribbons, faulty castings and the like.

On the other hand, it has also been found, especially in the case of batches that have a high graphitic carbon content, that heating to a limited extent does not always result in a complete solution of the graphite introduced into the melt.

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BATH ORIGINAL

This is how it works. elaem lelstlu bad graphite structure Such S © tai®Ise produced in the GuS $ fisrsas eiser becomes, where only eia tssgsreiKsües is overhits siallsslg »

In practice aas .geselbsm Is it much more desirable to bring the melt to a teaapeasar & ECE ¹ m "high , which, in turn, is more easily cast in the outside and therefore is generally overheated as much as possible, where equilateral ¥ ί3Ε3 &οΜ; becomes ₉ süe Bilflaag tinterkiihl-

ten graphites ia ÜbeEseEgess eäer äae ^ atsteSa®n üaslseE hard values to avoid in metal "

In connection with the isnterMiiilteE GrapMt. Seüaeißt the situation to be such that untea * kAiMtes graphite In eiaassf 3Sl®kt2? oofenschmelze gans Honasl Is ^- S ₅ iäsS aler das iatss ^ esafeEitische graphite, thus graphite Ia eier F & sm ⁸¹ S ⁰ S öas as © ei οώ © 3? Above a temperature τοη 1520 ⁰ G © afssstreteE sefelat ₅ ssSaailieher is, if namely, sis ssaff esse sasehlie ^ esafls SssaMldnag not ate completely _s * sss

In the making tqe Sagsl ^ agMtgaSelsesa isfs ebe & if noted

ψ been that eic niesbsi ^ ss l ^ steadjest Ia & ®τ i ^ jgssngssetaelze except »

tidy ErwüßBehsEswarfe is., BIa solclass? Mstslgex Eärtewert leads to erMfiifes EtsgslgsapMtsalil sd-S ibssBss'ea iaschaHiscIisn properties designed tmd you saeii Hers3%@3.1mEg © IAES Etigelgra- "" phitgußeiaens high ^ salitSt -ciater Eoasaalsm Sssltsem ύοώ, lcagelgraphitbildendeB. Kitteias, Hssisgielßweisa S @ s © s3liia w & ü. Cerium "

Working ajit a Sslsslzie oiles eisea 3k © 2a © m SErt © w © rt leads to free carbides in the & S _f eier from elaes s © l © h. © ia SeSsnelse Gegos-

and it also results in a low nodular graphite count and a poorer spheroidal graphite shape.

When cerium is used as an additive for the production of spherulitic cast iron is used, a melt with a high hardness value produces extremely stable carbides with the addition of cerium, and these Carbides require excessively long annealing temperatures for the Cast that has been made from such a melt.

Therefore, cast iron must generally be melted in sheet metal furnaces arise, regardless of whether they are for cast iron, the flake graphite contains, or used for GuB containing spheroidal graphite, with a relatively low hardness value for the composition in question the melt. If the development is allowed to have higher hardness values than they are for a particular one Composition bu are expected, metal is poorer Quality, for the reasons already given.

Particularly important is the exercise of an absolute 'in this context is monitoring and limiting the overheating of the material to a "¥ ert, which is in most cases slightly below 1565 ⁰ G, often even on a Vert, not more than 1,540 C is.

The presence of a small ilege of silicon carbide in the Melt from molten cast iron permits the development Much higher overheating temperatures without the harmful Effects of overheating occur.

In jig. 6 shows the hardness value of a cast iron melt, the 0.25 μL silicon carbide in granulate form directly

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BATH ORIGINAL

was added after melting but before hot heating. The overheating of these Sclimelze to temperatures Ms to I65O C did not increase the hardness value compared to the value that was already present at overheating temperatures Ms to 1430 ^0C.

In Fig. 5 the hardness value of the same cast iron is shown, however, to which no additive had been added prior to overheating.

In F%. 1 shows the structure of a cast iron that ^{had been heated to 1450 °} C., in FIG. 2 the structure of the same cast iron that had been heated to 1540 G is shown. Parts of the melt were poured into test bars, the microstructure of which was then tinted. In the case of the cast which had been superheated to 1450 ° C. and which is shown in FIG. 1, the structure consisted of normal randomly arranged flake graphite together with some supercooled graphite, which is typical of such cast iron in the non-inoculated state at such an overheating temperature.

In Fig. 2 the same iron is shown, which has been overheated to a higher temperature, namely to 1540 C. In this case, the structure, which was taken from a test rod, contains a fairly high proportion of int earth tri ti apparent graphite together with normal supercooled graphite. The appearance of the interdentritisehen graphite is typical of cast iron melts, which have been heated to temperatures of 1540 ^0C.

Heating these irons to even higher temperatures leads to an increase in the proportion of interdentritic graphite and also in the appearance of free carbide in the structure.

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BATH ORIGINAL

In Pig. 5 una 4 a similar cast iron is shown, which has been heated to temperatures of 1595 C or I650 ⁰ C. In this "all of the melt was 0.25 immediately after melting f ° granulated silicon carbide added. Vnirden the ropes poured into test bars of the melt showed that the structure in which in I? Ig. Pail 3 shown, in which the heating temperature 1595 ⁰ C, was from normal randomly arranged Flockengr. "- phit together with undercooled graphite consisted in an overheating temperature of I650 ⁰ C was the structure which is shown in 3Fig 4, from normal randomly arranged Plock graphite, only very slight traces. interdentritic supercooled graphite were present.

This clearly shows that silicon carbide prevents the formation of interdental graphite, even at overheating temperatures of up to 1650 ° C. IJenn silicon carbide is not present, these undesirable structures can occur at temperatures from 154O ⁰ O.

The amount of silicon carbide required to carry out the process according to the invention can be up to 1/8% by weight of the melt on the one hand or up to 2% by weight or more of the melt.

usually a smaller amount is preferably added, for example, 0.25 * / '■> the melt, because the sufficient normally complete and is advantageous for reasons of economy. These smaller amounts are also preferred because they do not significantly change the composition of the melt.

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BATH

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As an example, add 0.25% by weight> Silicon carbide in a washing number size of about 1/16 has the following chemical Changes and other changes in the metal on:

A 145O ⁰ CB 1485 ° 0 0 1540 ⁰ CD 1595 ° O E 16_5O ° C

Total carbon 3.18 ρ 3.19 5i 3.14 ii 3.12 * j> - 3.09; ■: silicon 1.72 ρ 1.73 ^c fi 1.73 pounds 1.74 ?> 1.77 ϊ Hangan $ 0.72 S 0.73 # £ 0.73 $ 0.74 o, 73 Ϊ C / 2 (Hechnerisch) 3.59 3.62 3.55 3.70 3.68 C / E (eutectic) 3.75 3.77 3.72 3.55 3.49 Liquidus 2252 2246 2260 2260 2273 Solidus 2085 2084 2085 2080 2085 area 167 162 175 180 188 Cell count 950 950 950 1500 I5OO

Of particular interest here is the relatively constant number of cells, which was found in samples cast from these melts at various superheating temperatures. They little increase in the number of cells at the highest overheating temperatures probably due to a certain dissolution of the silicon carbide in the melt at these temperatures be, and possibly just this solution, is what prevents some of the adverse effects that normally occur when overheating can occur to these temperatures.

While silicon carbide is preferably used in granular form, simply because it is the melt easier to clog, lumps of silicon carbide can just as well be used because the solution of silicon carbide,

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BATH ORIGINAL

which is quite refractory, takes place slowly, and since this If solution starts from the surface of the silicon carbide, it can be quite effective. For this reason, silicon carbide can also be used in Klumpenforci directly from the cold batch in the electric furnace be added. TJs remains throughout the melting process exist and only dissolve in the melt at high superheating temperatures, where it is also needed, to increase the hardness value and the like. to prevent. Preferably However, this silicon carbide is added directly to the melt in relatively small tight spaces, because this makes it possible is to achieve better control of the chemistry of the melt.

Patent claims:

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BAD OBiQiNAU

Claims (6)

Claims 1. Method of melting cast iron at high temperatures sur increase the liquidity while reducing the normally occurring TET subcooling, characterized in that that a batch of castels is melted, the one small one, however effective amount of silicon carbide has been added 2. The method according to claim 1, daduadx characterized in that as small, however effective amount of silicon carbide an amount of 0.125 " up to 2 Ji is added "" based on the weight of iron. J. Method according to. Claim 1, characterized in that an amount in the order of magnitude of $ 0.25, based on the weight of iron, is added as a small but effective amount of silicon carbide. 4. The method according to claim 1, characterized in that, according to the Melting the metal to the metal the silicon carbide is added. 5 · The method according to claim 1, 'characterized in that the cast iron the silicon carbide is added before it melts. 6. The method according to any one of claims 1-5 *, in which a cast iron charge is placed in an electric furnace and the charge is melted, characterized in that the small but effective amount of silicon carbide is added to the charge before it reaches a temperature of 1510 ^° C » 109815/1274