DE905856C - Process for the production of rapid malleable cast iron - Google Patents

Description

Process for the production of high-speed malleable cast iron The invention relates to .auf a process for the production of manganese-containing rapid malleable cast iron with high Strength with great security and an elimination of the tempered carbon in races or almost pure spherulitic crystallization forms.

The process: can be used for, @ sand and chill casting. Malleable cast iron, which in contrast to gray cast iron a more compact precipitation of graphite, namely in the form of so-called tempered carbon nodules, has according to this form of training much more favorable strength properties. The Temperkoh # have knots but still very frayed contours and are sometimes quite loosened up. Takes the temper coal, on the other hand, takes on a typical spherulitic, spherical shape, so occurs ; thus increasing the strength.

Spherulites have occasionally been observed in malleable cast iron. Because of the favorable properties, a number of methods have already been given, according to which such spherulitic crystallization forms of the tempered coal are achieved permit. All the methods that are to be explained in the following have disadvantages, which either hinder their technical usability or an expensive, inconvenient manufacturing process.

The formation of spherulites, which appears as an abnormal crystallization phenomenon are to be understood, occurs in the event of sudden solidification from solutions or (melting a .. During the tempering process, however, it must be expected that the elimination of the Tempering charcoal from the base mass goes slowly in front of you. The relationships in malleable cast iron are not yet fully scientifically understood, but it has. (Appearance, as if germs of a certain shape and structure are decisive here. After the first Process, which Schüz and Stotz in their book »Der Temp-rguß « (1930), p.770, a spherical graphite precipitate can be seen, nothing definite is said about their spherulitic crystallization form, thereby producing "that the sulfur content is high in relation to the manganese steel, but that means an undesirable reduction in the manganese content, which also means is usually already present in the starting iron in an amount that is not considered to be very low can be designated.

H. Morrogh, Birmingham, came to the same conclusion in more recent work, according to which spherical tempered coal is only formed when. if the sulfur content is correspondingly higher than the manganese content, then the sulfur was not completely bound to manganese (Mn S), but that it was wholly or partially in which iron is bound, for. these iron sulfides = ole excretion of tempered carbon in such a way flow "that the temper coal is spherulitic crystalline lined. The analogous uA: usdrtick for spherolithic is called spherolitic in English. So here, too, the favorable influence of manganese on the metallic base mass must be dispensed with, since it must be completely bound as slag due to the, relatively speaking, excessively high sulfur content. According to N iaz Ah mad, according to an older work by P ins 1: from 1925, spherical graphite in malleable cast iron can only be produced if long annealing times at high temperatures are used. However, compliance with this condition is a major disadvantage of the process from an economic point of view. In the case of tempering systems in particular, it is important that they are not stressed too long or too heavily.

Occasional spherulitic graphite precipitation in gray cast iron was in misunderstanding of the formation conditions, it is imprecisely referred to as temper carbon precipitation. One suspected in such graphite spherolitheri, as they are correctly designated for gray cast iron Need to become. Structural constituents that only dissipate to a large extent in addition to the known ones Graphite forms would occur, so these researchers did not even attempt it got awake. is to show ways how this type of precipitation is systematic in gray cast iron could be generated.

H. A. Schwarz has found that spherulites can be produced by an additional quenching treatment prior to the actual tempering. But here, too, this process makes it more expensive, quite apart from the fact that the quenching of cast alloys must cause a high percentage of rejects due to cracking.

In white, European malleable cast iron, which is decarburized by the fresh action of the oxide-containing tempering agent, the shape of the graphite formation, i.e. the spherical or spherulitic shape, does not play the decisive role, although here too, due to the low N-orange content, spherulites can easily arise. According to the invention, a method is now proposed which has the disadvantages of a low manganese content in addition to a correspondingly high one. Sulfur content, a long and high tempering time or, finally, an additional quenching treatment and, in return, enables the tempering carbon to be largely precipitated in spherical, spheroidal crystallization forms. According to the method, a eutectic to hypereutectic cast alloy is desulfurized to the extent that less than o, o / o sulfur is present in any manganese old, with. the Si content is chosen so that, given the wall thickness, the iron turns white or shows slight signs of melsified solidification. Furthermore, it is necessary that the melt experience overheating and that therefore a corresponding undercooling occurs during solidification. The overheating can for example wise easily in an electric oven or in one zlarnm # oven, as it is in some @ empengiBerei.en b E iblich eats to be achieved. Here it is the same- valid whether the sulfur content before or after overheating to less than about. o, oi ° / o. is degraded. Due to: the relatively honed Si4 content, which is selected on the one hand because of the manganese and on the other hand because of the low proportion of sulphidic slag, which in larger quantities would cause a tendency to gray solidification. can succeed. now to shorten the tempering time from days to hours or minutes, for example to qo minutes at 90 °. However, a temperature of less than 20 minutes could be reached without increasing the temperature.

For example, if you choose tempering temperatures that are around 85o to 90 °, the TempeTgut is not stressed too much, and it is mostly it is not necessary to pack it in a tempering medium, it can be put in an annealing furnace finished tempering, which is a significant reduction in price and simplification with the best possible , Formation of the structure, namely with spherulitic temper = coal, represents.

A characteristic sign, which is spherulitic malleable cast iron differs from similar types of iron with normal tempered charcoal is the conspicuous one Property that it does no harm if the Ternperrohsguss does not solidify, but already certain signs of mottled solidification in the form of primarily excreted Graphite occur because in the malleable cast iron produced according to the invention also primarily spherulites are already formed, which therefore do no harm, while otherwise graphite sheets or eutectic graphite appear in fine grainy form, which is a severe reduction the achievable tensile strength or fatigue strength. According to the invention Applying method therefore gives a high level of security with regard to the achievement high strength values. The security is made even more by diie-sphere: olith: ische Tempered carbon formation increased in finer distribution.

In order to use it in practice, it is important to be familiar with the the upper limit, which is higher here, can go without uncomfortable Fluctuations to have to fear in the achievable strength values. With die casting or In the case of centrifugal casting, this has the advantage that the tempering time is reduced so much can be that one is able to compete against gray centrifugal casting without doing so the disadvantage of a eutectic graphite formation, diung to have to accept the z. B. practically always occurs in centrifugal cast sleeves and for wear resistance and running properties is felt to be very disadvantageous, without being completely avoided so far to be able to.

Similarly, high-speed malleable cast iron for piston rings offers one Advantage, since the harmful eutectic graphite can be avoided here too, so that even with ferritic formation of the basic structure with otherwise usual contents high wear resistance is achieved with phosphorus, which is better than with normal cast iron piston rings. In this context it is also important that by the above high-speed malleable cast iron because of the finer spherolithic ones mentioned Form of the tempered carbon precipitation an elastic modulus is achieved, which much higher than with single cast piston ring materials. @It is so that the specified Process is still rich in development opportunities, which have already been pointed out here shall be.

Claims (2)

PATENT CLAIMS: i. Process for the production of high-speed malleable cast iron Strength with a precipitation form of the tempered carbon in pure or almost pure spherulitic crystallization forms, characterized in that a eutectic to hypereutectic coal cast melt with a sulfur content during casting. from less than about o, oi ° / o. highly overheated and, due to the appropriate choice of silicon content or the wall thickness is brought to solidification in such a way that the iron becomes white or shows slight signs of mottled; solidification shows. 2. The method according to claim i, characterized in that the silicon content is significantly higher than in normal malleable cast iron, preferably a multiple, e.g. a to 3010. Cited publications: German Patent No. 766592.